JP7630264B2 - Manufacturing method of LCP extrusion film - Google Patents

Description

The present invention relates to a method for producing an LCP extrusion film, etc.

Conventionally, varnish-impregnated composite materials have been known as insulating materials for circuit boards, which are made by impregnating glass cloth with a varnish containing a thermosetting resin such as epoxy resin, an inorganic filler, a solvent, etc., and then hot-press molding. However, this manufacturing method has poor process tolerance during manufacturing, and is inferior in productivity, for example, in terms of the resin flow during varnish impregnation and the hardening property during hot-press molding. In addition, thermosetting resins are prone to absorbing moisture, and the dimensions change as a result of this moisture absorption, so the dimensional accuracy (heated dimensional accuracy) of the resulting varnish-impregnated composite material is inferior.

On the other hand, liquid crystal polymers (LCPs) are polymers that exhibit liquid crystallinity in a molten or solution state. In particular, thermotropic liquid crystal polymers that exhibit liquid crystallinity in a molten state can be extruded and have excellent properties such as high gas barrier properties, high film strength, high heat resistance, high insulation, low water absorption, and low dielectric properties in the high frequency range. For this reason, films using thermoplastic liquid crystal polymers are being considered for practical use in gas barrier film materials, electronic materials, and electrical insulating materials.

However, when single-layer extrusion molding was actually performed, it was found that due to the high degree of liquid crystal orientation of the thermoplastic liquid crystal polymer, it was difficult to obtain a thermoplastic liquid crystal polymer film with high industrial utility, i.e., a thermoplastic liquid crystal polymer film with excellent thickness accuracy and good appearance and surface flatness.

For example, Patent Document 1 discloses that a three-layer coextrusion die is used instead of a single-layer extrusion die, and a wholly aromatic polyester-based thermotropic liquid crystal polymer is coextruded as an intermediate layer with a polyolefin resin or polycarbonate resin as both outer layers to form a three-layer laminate film in which the intermediate layer is a thermoplastic liquid crystal polymer layer and both outer layers are thermoplastic resin layers, and the thermoplastic resin layers of both outer layers are peeled off to remove the intermediate layer as a film, thereby obtaining a thermoplastic liquid crystal polymer film with excellent thickness accuracy and good appearance and surface flatness.

For example, Patent Document 2 discloses that the strength in the TD (transverse direction) direction relative to the MD (machine direction) direction in the thermoplastic liquid crystal polymer film described in Patent Document 1 is not practically tolerable, and that by using a feedblock type three-layer coextrusion die instead of a multi-manifold type coextrusion die, the anisotropy of the strength in the TD and MD (machine direction) directions of the resulting thermoplastic liquid crystal polymer film is alleviated.

Japanese Unexamined Patent Publication No. 63-31729 Japanese Unexamined Patent Publication No. 2-178016

Insulating materials for circuit boards using liquid crystal polymers have been attracting attention in recent years as insulating materials for circuit boards such as flexible printed circuit boards (FPCs), flexible printed circuit board laminates, and fiber-reinforced flexible laminates in the upcoming 5th generation mobile communication systems (5G) and millimeter wave radars due to their excellent high frequency characteristics and low dielectric constant.

The techniques described in Patent Documents 1 and 2 above are said to be capable of producing a thermoplastic liquid crystal polymer film with excellent thickness accuracy, good appearance, and good surface flatness. However, in reality, although peeling of the skin layer and peeling of fibrillated fibers caused by the thermoplastic liquid crystal polymer being highly molecular oriented on the film surface can be suppressed, the thermoplastic liquid crystal polymer films described in Patent Documents 1 and 2 still have a high molecular orientation of the thermoplastic liquid crystal polymer as a whole film, and are not practical to use as an insulating material for circuit boards.

The present invention has been made in consideration of the above problems. The object of the present invention is to provide a new method for producing an extruded LCP film that can significantly reduce the high orientation of thermoplastic liquid crystal polymers, which was difficult to avoid in conventional extrusion molding.

The inventors of the present invention have conducted extensive research into various extrusion molding methods for single-layer and multilayer films to solve the above problems, and have discovered that a specific two-kind, three-layer co-extrusion molding method can significantly reduce the high orientation of thermoplastic liquid crystal polymers, which was difficult to avoid in conventional extrusion molding, and have thus completed the present invention.

That is, the present invention provides various specific embodiments as shown below.
(1) (1) A method for producing an LCP extruded film, comprising the steps of: preparing a resin composition A for a first surface layer containing a thermoplastic resin; preparing a resin composition B for a central layer containing a thermoplastic liquid crystal polymer; and preparing a resin composition C for a second surface layer containing a thermoplastic resin; co-extruding the resin compositions A, B, and C from a two-kind three-layer extruder under conditions of a shear stress of 40 kPa or less and a drawdown ratio of 3.5 or less to form a two-kind three-layer film having at least the first surface layer, the central layer, and the second surface layer in this order; and removing the first and second surface layers from the two-kind three-layer film to obtain an LCP extruded film having a thickness of 15 μm or more and 300 μm or less.

(2) The method for producing an LCP extruded film according to (1), which obtains an LCP extruded film in which the hardness H1 at a depth of 1 μm located 1 μm in the thickness direction from the film surface and the hardness H2 at the center of the thickness, measured by nanoindentation on a film cross section parallel to the MD direction, satisfy -10.0≦100×(H2-H1)/H1≦0.0, and the linear expansion coefficients in the MD direction and TD direction at 23 to 200°C, measured by the TMA method according to JIS K7197, are within the range of -30 to 55 ppm/K.

(3) The method for producing an LCP extruded film according to (1) or (2), wherein the thermoplastic liquid crystal polymer contains a (wholly) aromatic polyester resin.
(4) The method for producing an LCP extruded film according to any one of (1) to (3), wherein the thermoplastic resin comprises one selected from the group consisting of polyolefin resins, acrylic resins, polyamide resins, acrylonitrile-butadiene-styrene copolymers, polystyrene, polyvinyl chloride, polybutylene terephthalate, polyethylene terephthalate, polycarbonate, polyether ether ketone, and polyphenyl sulfide.

(5) The method for producing an LCP extruded film according to any one of (1) to (4), wherein the resin composition B further contains an inorganic filler.
(6) The method for producing an LCP extruded film according to any one of (1) to (5), in which the resin composition A, the resin composition B, and the resin composition C are co-extruded from a T-die.
(7) The method for producing an extruded LCP film according to any one of (1) to (6), which produces an extruded LCP film having a linear expansion coefficient in the TD direction of 55 ppm/K or less.

(8) The method for producing an extruded LCP film according to any one of (1) to (7), further comprising heating and pressurizing the extruded LCP film obtained under conditions of 200 to 360° C.
(9) The method for producing an LCP extruded film according to any one of (1) to (8), wherein the extruded LCP film has no tape-peelable skin layer on the film surface in an adhesion test by a cross-cut method in accordance with JIS K5600-5-6.

According to one aspect of the present invention, it is possible to provide a novel method for producing an extruded LCP film that can significantly reduce the high orientation of thermoplastic liquid crystal polymers, which was difficult to avoid in conventional extrusion molding.

FIG. 1 is a schematic perspective view showing an embodiment of an LCP extruded film. FIG. 1 is a diagram showing a calculation method for hardness measurement by a nanoindentation method. FIG. 1 is a schematic cross-sectional view showing an embodiment of an LCP extruded film. FIG. 2 is a conceptual diagram showing the principle of calculating the degree of orientation based on the area ratio of the orientation peak. FIG. 1 illustrates a melt co-extrusion process for an embodiment of an LCP extruded film. FIG. 1 illustrates a melt co-extrusion process for an embodiment of an LCP extruded film. FIG. 1 illustrates a melt co-extrusion process for an embodiment of an LCP extruded film.

The following describes in detail the embodiments of the present invention with reference to the drawings. Unless otherwise specified, the positional relationships, such as up, down, left, and right, are based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of the drawings are not limited to those shown. However, the following embodiments are merely examples for explaining the present invention, and the present invention is not limited to these. In other words, the present invention can be implemented with any modifications within the scope of the gist of the invention. In this specification, for example, the expression of a numerical range such as "1 to 100" includes both the lower limit "1" and the upper limit "100". The same applies to the expression of other numerical ranges.

(LCP extrusion film)
1 is a schematic cross-sectional view showing a main portion of an extruded LCP film 100 of this embodiment. The extruded LCP film 100 of this embodiment is formed by extruding a thermoplastic liquid crystal polymer into a film having a thickness of 15 μm to 300 μm.

As mentioned above, in the conventional LCP extrusion film, the thermoplastic liquid crystal polymer had an extreme molecular orientation on the film surface, such as peeling of the skin layer and peeling of the fibrillated fibers. This is presumably because the thermoplastic liquid crystal polymer is subjected to shear stress from the side of the device during extrusion, resulting in high orientation of the thermoplastic liquid crystal polymer on the surface of the extrusion molded body. It was confirmed that the extreme molecular orientation of the thermoplastic liquid crystal polymer on the film surface was alleviated by the improvements in Patent Documents 1 and 2, but at the same time, the inventors' findings revealed that it was not possible to realize a material that could withstand the required performance as an insulating material for circuit boards by only controlling the molecular orientation of the thermoplastic liquid crystal polymer on the film surface.

The LCP extruded film 100 of this embodiment is different from the conventional technology in that the molecular orientation and internal strain of the thermoplastic liquid crystal polymer are relaxed not only on the film surface but also inside the film. That is, the LCP extruded film 100 of this embodiment is characterized in that the hardness H1 at a depth of 1 μm located 1 μm from the film surface in the thickness direction and the hardness H2 at the center point of the thickness, measured by the nanoindentation method on the film cross section parallel to the MD direction, satisfy -10.0≦100×(H2−H1)/H1≦0.0, and the linear expansion coefficient in the MD direction and TD direction at 23 to 200° C., measured by the TMA method according to JIS K7197, is within the range of -30 to 55 ppm/K. This will be described in more detail below.

As the LCP extruded film 100, an extruded film such as a T-die extruded film is preferably used. As the LCP extruded film 100, a thermoplastic liquid crystal polymer layer that is the middle layer (core layer) of a three-layer co-extruded film having a laminated structure in which a thermoplastic resin layer, a thermoplastic liquid crystal polymer layer, and a thermoplastic resin layer are arranged at least in this order is also preferably used. In this case, by removing the thermoplastic resin layers of both outer layers of the three-layer co-extruded film, it can be used as a single-layer thermoplastic liquid crystal polymer film (LCP extruded film 100). Extruded films of thermoplastic liquid crystal polymers can be produced at low cost and with uniform quality compared to woven fabrics or nonwoven fabrics made of thermoplastic liquid crystal polymer fibers.

The thermoplastic liquid crystal polymer contained in the LCP extruded film 100 may be any known one in the industry, and the type is not particularly limited. Liquid crystal polymers are polymers that form an optically anisotropic molten phase, and representative examples include thermotropic liquid crystal compounds. The properties of the anisotropic molten phase can be confirmed by known methods such as a polarization inspection method using crossed polarizers. More specifically, the anisotropic molten phase can be confirmed by using a Leitz polarizing microscope to observe a sample placed on a Leitz hot stage at a magnification of 40 times under a nitrogen atmosphere.

Specific examples of thermoplastic liquid crystal polymers include, but are not limited to, those obtained by polycondensation of monomers such as aromatic or aliphatic dihydroxy compounds, aromatic or aliphatic dicarboxylic acids, aromatic hydroxycarboxylic acids, aromatic diamines, aromatic hydroxyamines, and aromatic aminocarboxylic acids. The thermoplastic liquid crystal polymer is preferably a copolymer. Specific examples include, but are not limited to, aromatic polyamide resins obtained by polycondensation of monomers such as aromatic hydroxycarboxylic acids, aromatic diamines, and aromatic hydroxyamines; (all) aromatic polyester resins obtained by polycondensation of monomers such as aromatic diols, aromatic carboxylic acids, and aromatic hydroxycarboxylic acids; and the like. These can be used alone or in any combination and ratio of two or more.

Thermoplastic liquid crystal polymers are generally classified into types I, II, III, etc., from the viewpoint of heat distortion temperature (TDUL). The LCP extruded film 100 of this embodiment can be suitably used with any type of thermoplastic liquid crystal polymer, and may be appropriately selected depending on the application. For example, in electronic circuit board applications requiring application to lead-free solder at about 230 to 260°C, a highly heat-resistant type I thermoplastic liquid crystal polymer with a TDUL of about 250 to 350°C and a relatively heat-resistant type II thermoplastic liquid crystal polymer with a TDUL of about 240 to 250°C are suitably used.

Among these, (fully) aromatic polyester resins that exhibit thermotropic liquid crystal-like properties and have a melting point of 250°C or higher, preferably 280°C to 380°C, are preferably used. As such (fully) aromatic polyester resins, for example, (fully) aromatic polyester resins that are synthesized from monomers such as aromatic diols, aromatic carboxylic acids, and hydroxycarboxylic acids and that exhibit liquid crystallinity when melted are known. Representative examples include polycondensates of ethylene terephthalate and parahydroxybenzoic acid, polycondensates of phenol and phthalic acid and parahydroxybenzoic acid, and polycondensates of 2,6-hydroxynaphthoic acid and parahydroxybenzoic acid, but are not limited to these. The (fully) aromatic polyester resins can be used alone or in any combination and ratio of two or more. Depending on the required performance, a wholly aromatic polyester resin that has a relatively high melting point or high heat distortion temperature and is highly heat resistant can be used, or an aromatic polyester resin that has a relatively low melting point or low heat distortion temperature and is excellent in moldability can be used.

A preferred embodiment is a (fully) aromatic polyester resin having a basic structure of 6-hydroxy-2-naphthoic acid and its derivatives (hereinafter, sometimes simply referred to as "monomer component A") and at least one monomer component (hereinafter, sometimes simply referred to as "monomer component B") selected from the group consisting of parahydroxybenzoic acid, terephthalic acid, isophthalic acid, 6-naphthalenedicarboxylic acid, 4,4'-biphenol, bisphenol A, hydroquinone, 4,4-dihydroxybiphenol, ethylene terephthalate, and derivatives thereof. In the molten state, such (fully) aromatic polyester resins form an anisotropic molten phase in which the linear chains of molecules are regularly aligned, and typically exhibit thermotropic liquid crystal-like properties, and have excellent basic performance in terms of mechanical properties, electrical properties, high frequency properties, heat resistance, moisture absorption, etc.

In addition, the (all) aromatic polyester resin of the above-mentioned preferred embodiment can have any configuration as long as it has monomer component A and monomer component B as essential units. For example, it may have two or more types of monomer component A, or it may have three or more types of monomer component A. In addition, the (all) aromatic polyester resin of the above-mentioned preferred embodiment may contain other monomer components (hereinafter, simply referred to as "monomer component C") other than monomer component A and monomer component B. That is, the (all) aromatic polyester resin of the above-mentioned preferred embodiment may be a two-component or more polycondensate consisting of only monomer component A and monomer component B, or a three-component or more polycondensate consisting of monomer component A, monomer component B, and monomer component C. Examples of other monomer components include those other than the above-mentioned monomer component A and monomer component B, specifically aromatic or aliphatic dihydroxy compounds and derivatives thereof; aromatic or aliphatic dicarboxylic acids and derivatives thereof; aromatic hydroxycarboxylic acids and derivatives thereof; aromatic diamines, aromatic hydroxyamines, or aromatic aminocarboxylic acids and derivatives thereof; and the like, but are not particularly limited thereto. The other monomer components can be used alone or in any combination and ratio of two or more.

In this specification, the term "derivative" refers to a monomer component having a modification group such as a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom), an alkyl group having 1 to 5 carbon atoms (e.g., a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an s-butyl group, a t-butyl group, etc.), an aryl group such as a phenyl group, a hydroxyl group, an alkoxy group having 1 to 5 carbon atoms (e.g., a methoxy group, an ethoxy group, etc.), a carbonyl group, or -O-, -S-, _-CH2- , etc. introduced into a part of the monomer component (hereinafter, this may be referred to as a "monomer component having a substituent"). Here, the "derivative" may be an ester-forming monomer such as an acylation product, an ester derivative, or an acid halide of the monomer components A and B which may have the above-mentioned modifying group.

Particularly preferred embodiments include binary polycondensates of parahydroxybenzoic acid and its derivatives with 6-hydroxy-2-naphthoic acid and its derivatives; ternary or higher polycondensates of parahydroxybenzoic acid and its derivatives with 6-hydroxy-2-naphthoic acid and its derivatives and monomer component C; and polycondensates of parahydroxybenzoic acid and its derivatives with 6-hydroxy-2-naphthoic acid and its derivatives and terephthalic acid, isophthalic acid, 6-naphthalenedicarboxylic acid, 4,4'-biphenol, bisphenol A, hydroquinone, 4,4-dihydroxybiphenol. terephthalic acid, 6-hydroxy-2-naphthoic acid, terephthalic acid, isophthalic acid, 6-naphthalenedicarboxylic acid, 4,4'-biphenol, bisphenol A, hydroquinone, 4,4-dihydroxybiphenol, ethylene terephthalate, and derivatives thereof; and quaternary or higher polycondensates consisting of one or more monomer components C and one or more selected from the group consisting of parahydroxybenzoic acid and its derivatives, 6-hydroxy-2-naphthoic acid and its derivatives, terephthalic acid, isophthalic acid, 6-naphthalenedicarboxylic acid, 4,4'-biphenol, bisphenol A, hydroquinone, 4,4-dihydroxybiphenol, ethylene terephthalate, and derivatives thereof. These can be obtained as having a relatively low melting point compared to, for example, homopolymers of parahydroxybenzoic acid, and therefore, thermoplastic liquid crystal polymers using these have excellent moldability when thermocompressed to an adherend.

From the viewpoint of lowering the melting point of the (all) aromatic polyester resin, improving the moldability during thermocompression bonding of the LCP extruded film 100 to an adherend, or obtaining high peel strength when the LCP extruded film 100 is thermocompression bonded to a metal foil, the molar ratio of the monomer component A to the (all) aromatic polyester resin is preferably 10 mol% or more and 90 mol% or less, more preferably 30 mol% or more and 85 mol% or less, and even more preferably 50 mol% or more and 80 mol% or less. Similarly, the molar ratio of the monomer component B to the (all) aromatic polyester resin is preferably 10 mol% or more and 90 mol% or less, more preferably 15 mol% or more and 70 mol% or less, and even more preferably 20 mol% or more and 50 mol% or less. In addition, the content of the monomer component C that may be contained in the (all) aromatic polyester resin is preferably 10 mol% or less, more preferably 8 mol% or less, even more preferably 5 mol% or less, and particularly preferably 3 mol% or less, in terms of molar ratio.

The (fully) aromatic polyester resin can be synthesized by any known method, and is not particularly limited. Known polycondensation methods that form ester bonds using the above-mentioned monomer components, such as melt polymerization, melt acidolysis, and slurry polymerization, can be used. When applying these polymerization methods, an acylation or acetylation step may be carried out according to the usual method.

The LCP extruded film 100 may further contain an inorganic filler. By containing an inorganic filler, an LCP extruded film 100 with a reduced linear expansion coefficient can be realized, and specifically, an LCP extruded film 100 with reduced anisotropy of the linear expansion coefficient in the MD direction, TD direction, and ZD direction (Z-axis direction; film thickness direction) can be easily obtained. Such an LCP extruded film 100 is particularly useful in rigid substrate applications requiring multi-layer lamination, for example.

Inorganic fillers known in the industry can be used, and the type is not particularly limited. For example, kaolin, calcined kaolin, calcined clay, uncalcined clay, silica (e.g., natural silica, fused silica, amorphous silica, hollow silica, wet silica, synthetic silica, aerosil, etc.), aluminum compounds (e.g., boehmite, aluminum hydroxide, alumina, hydrotalcite, aluminum borate, aluminum nitride, etc.), magnesium compounds (e.g., magnesium aluminometasilicate, magnesium carbonate, magnesium oxide, magnesium hydroxide, etc.), calcium compounds (e.g., calcium carbonate, calcium hydroxide, calcium sulfate, calcium sulfite, calcium borate, etc.), molybdenum compounds (e.g., molybdenum oxide, zinc molybdate, etc.), talc (e.g., natural talc, calcined talc, etc.), mica, titanium oxide, zinc oxide, zirconium oxide, barium sulfate, zinc borate, barium metaborate, sodium borate, boron nitride, aggregated boron nitride, silicon nitride, carbon nitride, strontium titanate, barium titanate, stannates such as zinc stannate, etc., but are not particularly limited thereto. These can be used alone or in combination of two or more. Among these, silica is preferred from the viewpoint of dielectric properties, etc.

The inorganic filler used here may be one that has been subjected to a surface treatment known in the art. The surface treatment can improve moisture resistance, adhesive strength, dispersibility, etc. Examples of surface treatment agents include, but are not limited to, silane coupling agents, titanate coupling agents, sulfonic acid esters, carboxylic acid esters, and phosphate esters.

The median diameter (d50) of the inorganic filler can be set appropriately depending on the required performance, and is not particularly limited. From the viewpoints of kneadability and handleability during preparation, the effect of reducing the linear expansion coefficient, etc., the d50 of the inorganic filler is preferably 0.01 μm or more and 50 μm or less, more preferably 0.03 μm or more and 50 μm or less, and even more preferably 0.1 μm or more and 50 μm or less. In this specification, the median diameter (d50) of the inorganic filler means a value measured on a volume basis by the laser diffraction/scattering method using a laser diffraction/scattering type particle size distribution measuring device (LA-500 manufactured by Horiba, Ltd.).

The content of the inorganic filler is not particularly limited and can be appropriately set according to the required performance, taking into consideration the balance of the composition with other essential and optional components. From the viewpoints of kneadability and handleability during preparation, the effect of reducing the linear expansion coefficient, etc., the content of the inorganic filler is preferably 1% by mass or more and 45% by mass or less in total, more preferably 3% by mass or more and 40% by mass or less in total, and even more preferably 5% by mass or more and 35% by mass or less in total, calculated as solid content relative to the total amount of the LCP extruded film 100.

The LCP extrusion film 100 may contain resin components other than the above-mentioned thermoplastic liquid crystal polymer (hereinafter, simply referred to as "other resin components"), such as thermosetting resins and thermoplastic resins, within a range that does not excessively impair the effects of the present invention. In addition, the LCP extrusion film 100 may contain additives known in the art, such as release improvers such as higher fatty acids having 10 to 25 carbon atoms, higher fatty acid esters, higher fatty acid amides, higher fatty acid metal salts, polysiloxanes, and fluororesins; colorants such as dyes and pigments; organic fillers; antioxidants; heat stabilizers; light stabilizers; ultraviolet absorbers; flame retardants; antistatic agents; surfactants; rust inhibitors; defoamers; fluorescent agents, etc., within a range that does not excessively impair the effects of the present invention. Each of these additives can be used alone or in combination of two or more. These additives can be included in the molten resin composition prepared when molding the LCP extrusion film 100. The content of these resin components and additives is not particularly limited, but from the viewpoint of moldability and thermal stability, it is preferably 0.01 to 10% by mass each, more preferably 0.1 to 7% by mass each, and even more preferably 0.5 to 5% by mass each, based on the total amount of the LCP extruded film 100.

The thickness of the LCP extrusion film 100 can be set appropriately according to requirements and is not particularly limited. Considering the ease of handling and productivity during extrusion molding, the thickness is preferably 15 μm or more and 300 μm or less, more preferably 18 μm or more and 250 μm or less, and even more preferably 20 μm or more and 200 μm or less.

In order to alleviate molecular orientation and internal distortion of the thermoplastic liquid crystal polymer not only on the film surface but also inside the film, the LCP extruded film 100 of this embodiment is adjusted so that the hardness H1 at a depth of 1 μm located 1 μm in the thickness direction from the film surface and the hardness H2 at the center point of the thickness, measured by nanoindentation method on a film cross section parallel to the MD direction, satisfy the relationship shown below.
Preferably, −10.0≦100×(H2−H1)/H1≦0.0.
More preferably, −7.5≦100×(H2−H1)/H1≦0.0.
More preferably, −5.0≦100×(H2−H1)/H1≦0.0.
The relationship represented by the above formula, i.e., the relationship between the hardness H1 at a depth of 1 μm and the hardness H2 at the center point of the thickness, indicates the orientation of the thermoplastic liquid crystal polymer in the film, and the lower the absolute value, the more isotropic the orientation in the MD and TD directions.

Here, the hardness H1 at a depth of 1 μm located 1 μm from the film surface in the thickness direction in the film cross section parallel to the MD direction (a position 1 μm from one film surface in the thickness direction in the plan view of the film cross section) is an index indicating the molecular orientation and internal strain of the thermoplastic liquid crystal polymer near the film surface of the LCP extrusion film 100. The hardness H1 at the depth of 1 μm tends to be larger as the orientation of the thermoplastic liquid crystal polymer is lower, and tends to be smaller as the orientation of the thermoplastic liquid crystal polymer is higher. The hardness H1 at the depth of 1 μm is preferably 0.250 GPa or more, more preferably 0.255 GPa or more. On the other hand, the hardness H2 at the thickness center point (a position equidistant from one film surface and the other film surface in the plan view of the film cross section) in the film cross section parallel to the MD direction is an index indicating the molecular orientation and internal strain of the thermoplastic liquid crystal polymer inside the film of the LCP extrusion film 100. The hardness H2 at the thickness center point tends to be larger as the orientation of the thermoplastic liquid crystal polymer is lower, and tends to be smaller as the orientation of the thermoplastic liquid crystal polymer is higher. The hardness H2 at the thickness center point is preferably 0.240 GPa or more, more preferably 0.245 GPa or more. The method for producing the film cross section parallel to the MD direction of the LCP extruded film 100 is not particularly limited, but from the viewpoint of ensuring objectivity between the measurement data, the LCP extruded film 100 is ion beam processed under freezing conditions to produce a smooth film cross section parallel to the MD direction.

In this specification, the hardness measurement by the nanoindentation method is performed by using a diamond Berkovich type indenter at an indentation depth hmax = 0.05 μm to measure the hardness H1 at a point 1 μm from the film surface and the hardness H2 at the thickness center point on a film cross section parallel to the MD direction of the LCP extruded film 100. As shown in Figure 2, the hardness H1 and hardness H2 are calculated from the following formula based on the maximum load Pmax and the contact projected area A (the area where the indenter contacts the film cross section).
Hardness (GPa) = Pmax/A

On the other hand, in the LCP extrusion film 100 of the present embodiment, not only the molecular orientation of the thermoplastic liquid crystal polymer represented by the above-mentioned degree of orientation, but also the molecular orientation of the thermoplastic liquid crystal polymer represented by the linear expansion coefficient in the MD direction and the TD direction is sufficiently reduced. As mentioned above, in the LCP extrusion film described in Patent Documents 1 and 2 of the prior art, the molecular orientation of the thermoplastic liquid crystal polymer is slightly relaxed by being protected by the thermoplastic resin layers of both outer layers during three-layer coextrusion, and this can be seen to relax the anisotropy of the strength in the MD direction and the TD direction of the obtained thermoplastic liquid crystal polymer film. However, in reality, the LCP extrusion film described in Patent Documents 1 and 2 has a stable linear expansion coefficient in the MD direction of about -20 ppm/K, while the linear expansion coefficient in the TD direction exceeds 55 ppm, and sometimes reaches about 100 ppm/K. As is clear from this, it is easily understood that the molecular orientation of the thermoplastic liquid crystal polymer still remains large in the LCP extrusion film described in Patent Documents 1 and 2 of the prior art, or that internal distortion, etc. remains large in the film as a whole. Therefore, the molecular orientation and internal strain of the thermoplastic liquid crystal polymer in the entire LCP extruded film 100 must be controlled by combining the hardness and linear expansion coefficient measured by the nanoindentation method described above.

The linear expansion coefficient (CTE, α2, 23-200°C) of the LCP extruded film 100 in the MD and TD directions of this embodiment is in the range of -30 to 55 ppm/K. The LCP extruded film 100 with a linear expansion coefficient in this range is in a state in which internal distortion, etc. is sufficiently reduced. From the viewpoint of improving adhesion to metal foil, the linear expansion coefficient (CTE, α2, 23-200°C) in the MD direction of the LCP extruded film 100 in this embodiment is preferably in the range of -30 to 10 ppm/K, more preferably in the range of -25 to 5 ppm/K, and even more preferably in the range of -20 to 0 ppm/K. Furthermore, the coefficient of linear expansion in the TD direction (CTE, α2, 23 to 200°C) of the LCP extruded film 100 of this embodiment is preferably in the range of 0 to 55 ppm/K, more preferably in the range of 0 to 50 ppm/K, and even more preferably in the range of 0 to 45 ppm/K, from the viewpoint of improving adhesion to the metal foil.

In this specification, the linear expansion coefficient is measured by the TMA method according to JIS K7197, and the average linear expansion coefficient means the average value of the linear expansion coefficients from 23 to 200°C measured by the same method. The linear expansion coefficient measured here means the value when the LCP extruded film 100 is heated at a heating rate of 5°C/min (1st heating), cooled to the measurement environment temperature (23°C) (1st cooling), and then heated a second time at a heating rate of 5°C/min (2nd heating) in order to see the value after the thermal history is eliminated. Other detailed measurement conditions are in accordance with the conditions described in the examples described later.

In addition, from the viewpoint of alleviating molecular orientation and internal distortion of the thermoplastic liquid crystal polymer not only on the film surface but also inside the film, it is desirable that the orientation degree α1 including the exposed film surface S1 and the orientation degree α2 including the film surface S2 located at a depth of 5 μm from the film surface S1 and exposed by etching the film surface S1 in the thickness direction of the film surface S1 satisfy the relationship shown below.
Preferably, −4.0≦[(α2−α1)/α1]×100≦0.0.
More preferably, −3.0≦[(α2−α1)/α1]×100≦0.0.
More preferably, −2.0≦[(α2−α1)/α1]×100≦0.0.

Here, as shown in FIG. 3, the film surface S1 is the outermost surface of the LCP extrusion film 100 of this embodiment, and is the exposed surface exposed toward the outside. The orientation degree (orientation degree α1) including the film surface S1 is preferably 39.0% or less, more preferably 38.5% or less, and even more preferably 38.0% or less. On the other hand, the film surface S2 is a surface that is newly exposed by etching the film surface S1 of the LCP extrusion film 100 of this embodiment in the thickness direction, and is represented by a dashed line in FIG. 3 as a virtual surface located at a depth of 5 μm from the film surface S1. The orientation degree (orientation degree α2) including this film surface S2 is preferably 37.7% or less, more preferably 37.5% or less, and even more preferably 37.3% or less. In addition, the depth at which the film surface S2 is located does not need to be strictly 5 μm from the film surface S1, taking into account dissolution errors during etching, etc., and may be 5.0 μm or more from the film surface S1. In addition, the etching conditions for preparing the film surface S2 are not particularly limited, but in order to ensure objectivity between the measurement data, they should follow the conditions described in the examples below.

In this specification, the orientation degrees α1, α2 (%) including the film surfaces S1, S2 of the LCP extruded film 100 refer to values calculated from the following formula based on the area ratio of the orientation peak in the diffraction intensity distribution curve obtained by performing X-ray diffraction measurement by a transmission method using an X-ray diffraction device. Generally, in the case of a measurement object with a low orientation degree (%), a broad diffraction peak with a low peak intensity is observed in the X-ray diffraction measurement, so that a calculation method based on the half-width of the orientation peak cannot guarantee high measurement accuracy. Therefore, in this specification, the orientation degrees α1, α2 (%) including the film surfaces S1, S2 are calculated using a calculation method based on the area ratio of the orientation peak, rather than the half-width of the orientation peak. Specifically, as shown in FIG. 4 and Equation 1, the calculation method based on the area proportion of the orientation peak involves measuring the peak intensity (orientation component) by 2θ/θ scanning, and measuring the intensity in the azimuth direction from 0° to 360° by β scanning to obtain the intensity distribution in the azimuth direction (base intensity (isotropic component)). The orientation degree (%) is calculated as the percentage of the area occupied by the orientation component excluding the area of the base isotropic component to the total area (area of the orientation component + area of the isotropic component).

On the other hand, the dielectric properties of the LCP extruded film 100 of the present embodiment can be appropriately set according to the desired performance, and are not particularly limited. From the viewpoint of obtaining higher dielectric properties, the relative dielectric constant _εr (36 GHz) is preferably 3.0 to 3.7, more preferably 3.0 to 3.5. Similarly, the dielectric loss tangent tanδ (36 GHz) is preferably 0.0010 to 0.0050, more preferably 0.0010 to 0.0045. In this specification, the relative dielectric constant _εr and the dielectric loss tangent tanδ refer to values at 36 GHz measured by a cavity resonator contact method in accordance with JIS K6471. Other detailed measurement conditions are in accordance with the conditions described in the examples described later.

(Method of manufacturing LCP extrusion film)
The LCP extruded film 100 of this embodiment can be obtained by extruding a resin composition containing the above-mentioned thermoplastic liquid crystal polymer and optional components such as inorganic fillers and other resin components as necessary to a predetermined thickness. The extrusion method can be any known method, and the type is not particularly limited. For example, the T-die method or the inflation method; for example, the multi-manifold coextrusion method or the feed block coextrusion method; for example, the multi-layer coextrusion method such as the two-layer coextrusion method or the three-layer coextrusion method; can be applied in any combination.

Among these, from the viewpoint of ease of control of the molecular orientation of the thermoplastic liquid crystal polymer on the film surface (film surface S1) and inside the film (film surface S2), a preferred embodiment is a method in which the above-mentioned resin composition is extruded from a T-die by an extrusion molding method using a T-die (hereinafter, sometimes simply referred to as the "T-die extrusion method") to form a film, and then, as necessary, a cooling treatment, a pressure bonding treatment, a pressurized heating treatment, etc. are performed to obtain a predetermined LCP extrusion film 100. Specifically, a resin composition A for the first surface layer containing a thermoplastic resin, a resin composition B for the center layer containing a thermoplastic liquid crystal polymer, and a resin composition C for the second surface layer containing a thermoplastic resin are each prepared, and these are co-extruded from the co-extrusion die of the extruder to extrude a three-layered co-extrusion molten product, and the LCP extrusion film 100 is formed as a thermoplastic liquid crystal polymer layer of the intermediate layer. According to such co-extrusion molding, the molecular orientation of the thermoplastic liquid crystal polymer in the thermoplastic liquid crystal polymer layer of the intermediate layer is relaxed by being protected by the thermoplastic resin layers of both outer layers. A preferred embodiment of the method for producing the LCP extruded film 100 of this embodiment is described in detail below.

5 to 7 are diagrams showing a preferred embodiment of the manufacturing method of the LCP extrusion film 100 of the present embodiment described above. Here, the above-mentioned resin composition B containing the above-mentioned thermoplastic liquid crystal polymer and optional components such as inorganic filler and other resin components as necessary is melt-extruded into a film shape from a T-die of an extruder. At this time, resin compositions A and C containing thermoplastic resins are co-extruded on both sides of the above-mentioned film-shaped melt extrusion product to produce a co-extrusion melt (three-layer laminated film) of a predetermined thickness having a first outer layer (peeling layer) containing a thermoplastic resin, an intermediate layer (LCP layer) containing a thermoplastic liquid crystal polymer, and a second outer layer (peeling layer) containing a thermoplastic resin. This co-extrusion melt is drawn out by a take-up roll and sent to a cooling roll and a pressure-bonding roll. Thereafter, the first outer layer and the second outer layer are peeled off from the intermediate layer, and the thermoplastic resin layers of both outer layers and the thermoplastic liquid crystal polymer layer (LCP extrusion film 100) of the intermediate layer are wound up on a take-up roll, respectively.

The preparation of the resin composition B containing the thermoplastic liquid crystal polymer may be carried out according to a conventional method, and is not particularly limited. The above-mentioned components may be manufactured and processed by known methods, such as kneading, melt kneading, granulation, extrusion molding, pressing, or injection molding. When melt kneading, kneading devices such as commonly used single-screw or twin-screw extruders and various kneaders may be used. When supplying each component to these melt kneading devices, the liquid crystal polymer, other resin components, inorganic fillers, additives, etc. may be dry-blended in advance using a mixing device such as a tumbler or Henschel mixer. When melt kneading, the cylinder setting temperature of the kneading device may be appropriately set, and is not particularly limited, but is generally preferably in the range of from the melting point of the liquid crystal polymer to 360°C, and more preferably from the melting point of the liquid crystal polymer +10°C to 360°C.

The resin compositions A and C containing thermoplastic resins may be prepared according to conventional methods and are not particularly limited. Examples of thermoplastic resins include polyolefin resins such as polyethylene, polypropylene, polymethylpentene, and ethylene-α-olefin copolymers, acrylic resins such as PMMA, polyamide resins, acrylonitrile-butadiene-styrene copolymers (ABS resins), polystyrene (PS), polyvinyl chloride, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polycarbonate (PC), polyether ether ketone (PEEK), and polyphenyl sulfide (PPS), but are not particularly limited to these. When the resin is coextruded into a melt, it functions effectively as a release layer, whether it is a polar resin such as polycarbonate or a non-polar resin such as polymethylpentene. These thermoplastic resins may be blended with optional components such as other resin components and inorganic fillers that may be contained in the above-mentioned LCP extruded film 100. The resin composition A and the resin composition C may have the same resin composition or different resin compositions, and may contain the same thermoplastic resin or different thermoplastic resins. The resin compositions A and C containing thermoplastic resins can be manufactured and processed by known methods such as kneading, melt kneading, granulation, extrusion molding, pressing, or injection molding. When melt kneading, kneading devices such as commonly used single-screw or twin-screw extruders and various kneaders can be used. When supplying each component to these melt kneading devices, the thermoplastic resin, other resin components, inorganic fillers, additives, etc. may be dry-blended in advance using a mixing device such as a tumbler or Henschel mixer. When melt kneading, the cylinder setting temperature of the kneading device may be set appropriately below a temperature at which the thermoplastic resin does not deteriorate due to thermal decomposition, but is not particularly limited, and is generally preferably above the melting point of the thermoplastic resin, and more preferably above the melting point of the thermoplastic resin + 10°C.

The conditions for co-extrusion are not particularly limited and may be set appropriately depending on the type and composition of the resin composition used, the desired performance of the target extruded film, etc. For example, the set temperature of the cylinder of the extruder is not particularly limited and may be set appropriately depending on the type and composition of the resin composition used, the desired performance of the target extruded film, etc., but is preferably 230 to 360°C, more preferably 280 to 350°C.

Similarly, the die width (mm) of the T-die can be set appropriately depending on the type and composition of the resin composition used, the desired performance of the target extruded film, etc., and is not particularly limited, but is generally preferably 200 to 2000 mm, and more preferably 400 to 1500 mm.

Furthermore, for example, the lip opening (mm) of the T-die can also be set appropriately depending on the type and composition of the resin composition used, the desired performance of the target extruded film, etc., and is not particularly limited, but is generally preferably 0.1 to 3.0 (mm), and more preferably 0.2 to 2.0 (mm).

Similarly, the shear rate (sec ^-1 ) of the lip wall of a T-die may be appropriately set depending on the type and composition of the resin composition used, the desired performance of the intended extruded film, etc., and is not particularly limited, but is generally preferably 100 to 1500 (sec ^-1 ), and more preferably 150 to 1000 (sec ^-1 ).

Similarly, the total extrusion rate (mm ³ /sec) of the resin composition from the T-die can be appropriately set depending on the type and composition of the resin composition used, the desired performance of the target extruded film, etc., and is not particularly limited; however, it is generally preferably 500 to 15,000 (mm ³ /sec), and more preferably 1,500 to 10,000 (mm ³ /sec).

The melt viscosity (Pa·sec) of the thermoplastic liquid crystal polymer may be set appropriately according to the type and composition of the resin composition used, the desired performance of the target extruded film, etc., and is not particularly limited, but is generally preferably 10 to 300 (Pa·sec), and more preferably 20 to 250 (Pa·sec). The melt viscosity (Pa·sec) of the thermoplastic liquid crystal polymer refers to the value measured in accordance with JIS K7199 using a Capilograph 1D (manufactured by Toyo Seiki Seisakusho Co., Ltd.) under the conditions of a cylinder length of 10.00 mm, a cylinder diameter of 1.00 mm, and a barrel diameter of 9.55 mm under the conditions during the production of the LCP extruded film 100 (die temperature and shear rate of the lip wall).

Similarly, the take-up speed (mm/sec) of the co-extruded film can be set appropriately depending on the type and composition of the resin composition used, the desired performance of the target extruded film, etc., and is not particularly limited, but is generally preferably 15 to 1000 (mm/sec), and more preferably 20 to 500 (mm/sec).

Here, from the viewpoint of reducing the molecular orientation of the thermoplastic liquid crystal polymer in the MD direction during co-extrusion, it is desirable that the shear stress (kPa) during co-extrusion is low. If the shear stress during co-extrusion is large, the thermoplastic liquid crystal polymer is likely to be highly oriented in the MD direction and internal strain is likely to remain, and if the shear stress during co-extrusion is small, the molecular orientation of the thermoplastic liquid crystal polymer is likely to be reduced both on the film surface and inside the film, and internal strain is likely to remain. The shear stress (kPa) during co-extrusion is a value represented by the product of the shear rate (sec ^-1 ) of the lip wall surface and the melt viscosity (Pa.sec) of the thermoplastic liquid crystal polymer, and the shear rate is a value calculated based on the total discharge amount of the resin composition during co-extrusion, the die width, and the lip opening. Therefore, the shear stress during co-extrusion can be controlled by adjusting each of these values. Specifically, the shear stress during co-extrusion is preferably 40 kPa or less, more preferably 38 kPa or less, and even more preferably 36 kPa or less. The lower limit is not particularly limited, but is preferably 5 kPa or more, more preferably 10 kPa or more, taking into consideration productivity and the like.

In addition, from the viewpoint of reducing the molecular orientation of the thermoplastic liquid crystal polymer in the MD direction during coextrusion, it is desirable that the drawdown ratio during coextrusion is low. If the drawdown ratio during coextrusion is large, the thermoplastic liquid crystal polymer is likely to be highly oriented in the MD direction and internal strain is likely to remain, and if the drawdown ratio during coextrusion is small, the molecular orientation of the thermoplastic liquid crystal polymer is likely to be reduced both on the film surface and inside the film, and internal strain is unlikely to remain. The drawdown ratio is a value expressed by the take-up speed (mm/sec)/flow rate of the thermoplastic liquid crystal polymer (mm/sec), and the flow rate of the thermoplastic liquid crystal polymer is a value calculated based on the total discharge amount of the resin composition during coextrusion, the die width, and the lip opening. Therefore, the drawdown ratio during coextrusion can be controlled by adjusting each of these values. Specifically, the drawdown ratio during coextrusion is preferably 3.5 or less, more preferably 3.3 or less, and even more preferably 3.1 or less. The lower limit is not particularly limited, but taking into consideration productivity, etc., it is preferably 1.0 or more, and more preferably 1.2 or more.

The thickness of the resulting LCP extrusion film 100 can be set appropriately according to requirements and is not particularly limited. Considering the ease of handling and productivity during extrusion molding, the thickness is preferably 15 μm or more and 300 μm or less, more preferably 18 μm or more and 250 μm or less, and even more preferably 20 μm or more and 200 μm or less.

The melting point (melting temperature) of the resulting LCP extrusion film 100 is not particularly limited, but from the viewpoint of the heat resistance and processability of the film, the melting point (melting temperature) is preferably 200 to 400°C, and from the viewpoint of improving the thermal compression bonding to metal foil in particular, the melting point (melting temperature) is preferably 250 to 360°C, more preferably 260 to 355°C, even more preferably 270 to 350°C, and particularly preferably 275 to 345°C. In this specification, the melting point of the LCP extruded film 100 refers to the melting peak temperature in differential scanning calorimetry (DSC) when the extruded film is heated (1st heating) at a temperature rise rate of 20°C/min in the temperature range of 30 to 400°C using a DSC8500 (manufactured by PerkinElmer) to see the value after removing the thermal history, cooled (1st cooling) at a temperature drop rate of 50°C/min, and then heated a second time (2nd heating) at a temperature rise rate of 20°C/min. In addition, the other conditions are as described in the examples below.

The extrusion-molded LCP extrusion film 100 can be used as is, but if necessary, a pressurizing and heating process can be carried out to further reduce the molecular orientation of the thermoplastic liquid crystal polymer or further release the internal strain.

The heat and pressure treatment may be performed using a method known in the art, such as contact heat treatment or non-contact heat treatment, and the type is not particularly limited. For example, heat setting may be performed using known equipment such as a non-contact heater, oven, blower, heat roll, cooling roll, heat press, double belt heat press, etc. At this time, if necessary, a release film or porous film known in the art may be arranged on the surface of the LCP extrusion film 100 and heat treatment may be performed. In addition, when performing this heat treatment, from the viewpoint of controlling the orientation, a heat and pressure molding method is preferably used in which a release film or porous film is arranged on the front and back of the LCP extrusion film 100 and is thermocompressed while being sandwiched between the endless belt pair of the double belt press machine, and then the release film or porous film is removed. The heat and pressure molding method may be performed by referring to, for example, JP-A-2010-221694. The processing temperature when the LCP extrusion film 100 using the above resin composition is thermocompressed between the pair of endless belts of a double belt press is preferably at a temperature higher than the melting point of the liquid crystal polymer and lower than a temperature 70°C higher than the melting point, more preferably at a temperature higher than +5°C higher than the melting point and lower than a temperature 60°C higher than the melting point, and even more preferably at a temperature higher than +10°C higher than the melting point and lower than a temperature 50°C higher than the melting point. The thermocompression bonding conditions at this time can be appropriately set according to the desired performance and are not particularly limited, but are preferably performed under conditions of a surface pressure of 0.5 to 10 MPa and a heating temperature of 250 to 430°C, more preferably under conditions of a surface pressure of 0.6 to 8 MPa and a heating temperature of 260 to 400°C, and even more preferably under conditions of a surface pressure of 0.7 to 6 MPa and a heating temperature of 270 to 370°C. On the other hand, when a non-contact heater or oven is used, it is preferable to perform the thermocompression bonding under conditions of, for example, 200 to 320°C for 1 to 20 hours.

The LCP extrusion film 100 of this embodiment significantly reduces the high orientation of the thermoplastic liquid crystal polymer, which was difficult to avoid in conventional extrusion molding, and can be used as a material for circuit boards such as electronic circuit boards and multilayer boards. In addition, the LCP extrusion film 100 of this embodiment has excellent dielectric properties in the high frequency range, is easy to manufacture, and has excellent productivity, making it a particularly useful material as an insulating material for flexible printed circuit boards (FPCs) in fifth-generation mobile communication systems (5G) and millimeter-wave radars.

The following examples and comparative examples will explain the characteristics of the present invention in more detail, but the present invention is not limited by these. In other words, 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 the present invention. In addition, the various manufacturing conditions and evaluation result values in the following examples are meant as preferred upper or lower limits in the implementation of the present invention, and the preferred numerical range may be a range defined by a combination of the above-mentioned upper or lower limits and the values of the following examples or the values of the examples.

[Melt Viscosity]
The melt viscosity [Pa·sec] of each LCP extruded film was measured under the following conditions.
Measuring equipment: Capillograph 1D (manufactured by Toyo Seiki Seisakusho)
Equipment used: Cylinder length 10.00mm, cylinder diameter 1.00mm, barrel diameter 9.55mm
Measurement conditions: temperature [°C] and shear rate [sec ^-1 ] during extrusion of each LCP extruded film

[Hardness measurement by nanoindentation method]
The hardness H1 at a depth of 1 μm and the hardness H2 at the center of the thickness of each LCP extruded film were measured by a nanoindenter method in accordance with ISO 14577.
Measuring equipment: Nanoindenter Hysitron TI 950 TriboIndenter (manufactured by Bruker)
Indenter used: Diamond Berkovich type indenter Measurement conditions: Indentation depth hmax 0.05 μm
Measurement method Load-unload test The measurement surface of each LCP extruded film was a smooth cross section of the film parallel to the MD direction of each LCP extruded film, and such a smooth cross section of the film was prepared by cutting each LCP extruded film using ion beam processing under freezing conditions.

[Linear expansion coefficient]
The linear expansion coefficient of each LCP extruded film was measured by the TMA method in accordance with JIS K7197.
Measuring equipment: TMA 4000SE (NETZSCH)
Measurement method: Tensile mode Measurement conditions: Sample size 25 mm x 4 mm x thickness 50 μm
Chuck distance: 20mm
Temperature range: 23 to 200°C (2nd RUN)
Heating rate: 5°C/min
Atmosphere: Nitrogen (flow rate 50 ml/min)
Test load: 5gf
*The value from the 2nd run was used to see the value after eliminating the heat history.

[Orientation degree]
Using an X-ray diffraction device Smartlab (manufactured by Rigaku Corporation), X-ray diffraction measurements were performed on each LCP extrusion film including the film surface S1 or film surface S2 by the transmission method, and the orientation degree was measured. Here, a Cu sealed tube was used as the X-ray source, and X-ray diffraction measurements (2θ/θ scan, β scan) were performed by the parallel beam optical system and the transmission method, and first, it was confirmed that there was a peak top at 2θ = 19.5 ° in the 2θ/θ scan. Next, the intensity distribution in the azimuthal direction was obtained by measuring the intensity from 0 ° to 360 ° in the azimuthal direction for the diffraction peak at 2θ = 19.5 in the β scan. The orientation degree was calculated from the above formula based on the area ratio of the orientation peak from the base intensity (isotropic component) and peak intensity (orientation component) of the obtained β profile.
The film surface S2 of each LCP extruded film was conditioned by immersing each LCP extruded film in a 70% aqueous solution of monoethylamine (manufactured by Daicel Corporation) for 168 hours in a 23°C, 50% RH environment, etching both surfaces of each LCP extruded film to a depth of 5 μm, washing with running water for 5 minutes, washing with distilled water, drying at 80°C for 1 hour, and cooling in a 23°C, 50% RH environment for 24 hours.

[Tape peeling test]
The film surface of each LCP extrusion film was subjected to an adhesion test by a cross-cut method according to JIS K5600-5-6 to confirm the presence or absence of a skin layer. At this time, Nichiban Co., Ltd.'s Cellotape (registered trademark) with a width of 24 mm and a length of 50 mm was used, and if the tape did not peel off into the grid after peeling, it was judged as "no skin layer" and if peeling occurred, it was judged as "skin layer present."
○ No skin layer × Skin layer

(Examples 1 to 3)
A type II thermoplastic liquid crystal polymer (a copolymer of 74 mol% p-hydroxybenzoic acid and 26 mol% 6-hydroxy-2-naphthoic acid, with a melt viscosity of 80 Pa·sec at a temperature of 300°C and a shear rate of 500 sec- ¹ ) was used as the central layer, and polycarbonate PC (Teijin Ltd. Panlite L-1225L) was used as the surface layers on both sides of the central layer, and the resins were co-extruded at 300°C by a T-die casting method from a two-type three-layer extruder equipped with a T-die with a die width of 600 mm and a lip opening of 0.2 to 1.0 mm under the molding conditions shown in Table 1, to form a two-type three-layer film with a central layer of 50 μm. The polycarbonate films of both surface layers were peeled off from the molded two-type three-layer film on a winding line, and the LCP extrusion films of Examples 1 to 3 having a melting point of 280°C and a thickness of 50 μm were obtained, respectively.

(Comparative Example 1)
Using a type II thermoplastic liquid crystal polymer (a copolymer having a monomer composition of 74 mol% p-hydroxybenzoic acid and 26 mol% 6-hydroxy-2-naphthoic acid, the melt viscosity at a temperature of 300°C and a shear rate of 500 sec ^-1 was 80 Pa·sec), the liquid crystal polymer was extruded at 300°C by a T-die casting method from a single-layer extruder equipped with a T-die having a die width of 600 mm and a lip opening of 0.3 mm under the molding conditions shown in Table 1, to obtain an LCP extruded film of Comparative Example 1 having a melting point of 280°C and a thickness of 50 μm.

(Comparative Examples 2 to 4)
Except for changing the molding conditions as shown in Table 1, the same method as in Example 1 was used to obtain LCP extruded films of Comparative Examples 2 to 4 each having a melting point of 280° C. and a thickness of 50 μm.

(Examples 4 to 6)
Except for using a type I thermoplastic liquid crystal polymer (a copolymer having a monomer composition of 79 mol% p-hydroxybenzoic acid, 20 mol% 6-hydroxy-2-naphthoic acid, and 1 mol% terephthalic acid, with a melt viscosity of 70 Pa·sec at a temperature of 330°C and a shear rate of 500 sec- ¹ ) in the central layer instead of the type II thermoplastic liquid crystal polymer, and co-extruding each resin at 330°C, the same method as in Example 1 was used to obtain LCP extruded films of Examples 4 to 6 having a melting point of 315°C and a thickness of 50 μm.

(Comparative Example 5)
An LCP extruded film of Comparative Example 2 having a melting point of 315°C and a thickness of 50 μm was obtained in the same manner as in Comparative Example 1, except that a type I thermoplastic liquid crystal polymer (a copolymer having a monomer composition of 79 mol% p-hydroxybenzoic acid, 20 mol% 6-hydroxy-2-naphthoic acid, and 1 mol% terephthalic acid, with a melt viscosity of 70 Pa· ^sec at a temperature of 330°C and a shear rate of 500 sec-1) was used instead of the type II thermoplastic liquid crystal polymer, and the liquid crystal polymer was extruded at 330°C.

(Comparative Examples 6 to 8)
Except for changing the molding conditions as shown in Table 2, the same method as in Example 4 was used to obtain LCP extruded films of Comparative Examples 6 to 8 each having a melting point of 315° C. and a thickness of 50 μm.

(Examples 7 to 9)
Except for using polymethylpentene PMP (TPX MX004 manufactured by Mitsui Chemicals, Inc.) instead of polycarbonate on both surface layers, the same method as in Example 1 was used to obtain LCP extruded films of Examples 7 to 9 having a melting point of 280° C. and a thickness of 50 μm.

(Comparative Examples 9 to 11)
Except for changing the molding conditions as shown in Table 3, the same method as in Example 7 was used to obtain LCP extruded films of Comparative Examples 9 to 11 each having a melting point of 280° C. and a thickness of 50 μm.

Table 4 shows the measurement results.

The LCP extrusion film of the present invention can be widely and effectively used in applications such as electronic circuit boards, multilayer boards, high heat dissipation boards, flexible printed wiring boards, antenna boards, optoelectronic hybrid boards, and IC packages. In particular, since it is suitable for ultra-fine processing and highly reliable, it can be widely and effectively used as an insulating material for flexible printed wiring boards (FPCs) in fifth-generation mobile communication systems (5G) and millimeter-wave radars, as well as metal foil-clad laminates.

100 . . . LCP extrusion film 100a . . . Surface 100b . . . Surface H1 . . . Hardness at 1 μm depth point H2 . . . Hardness at thickness center point S1 . . . Film surface S2 . . . Film surface at 5 μm depth

Claims (9)

A step of preparing a resin composition A for a first surface layer containing a thermoplastic resin, a resin composition B for a central layer containing a thermoplastic liquid crystal polymer, and a resin composition C for a second surface layer containing a thermoplastic resin;
A process of co-extruding the resin composition A, the resin composition B, and the resin composition C from a two-kind three-layer extruder under conditions of a shear stress of 40 kPa or less and a drawdown ratio of 3.5 or less to form a two-kind three-layer film having at least the first surface layer, the central layer, and the second surface layer in this order; and removing the first and second surface layers from the two-kind three-layer film to obtain an LCP extruded film having a thickness of 15 μm or more and 300 μm or less.
Method for producing LCP extruded film. 2. The method for producing an LCP extruded film according to claim 1, wherein the hardness H1 at a depth of 1 μm located 1 μm from the film surface in the thickness direction and the hardness H2 at the center point of the thickness, measured by nanoindentation on a film cross section parallel to the MD direction, satisfy -10.0≦100×(H2−H1)/H1≦0.0, and the linear expansion coefficients in the MD direction and TD direction at 23 to 200° C., measured by the TMA method in accordance with JIS K7197, are within the ranges of -30 to 55 ppm/K. The method for producing an extruded LCP film according to claim 1 or 2, wherein the thermoplastic liquid crystal polymer comprises a (wholly) aromatic polyester resin. The method for producing an LCP extrusion film according to any one of claims 1 to 3, wherein the thermoplastic resin comprises one selected from the group consisting of polyolefin resins, acrylic resins, polyamide resins, acrylonitrile-butadiene-styrene copolymers, polystyrene, polyvinyl chloride, polybutylene terephthalate, polyethylene terephthalate, polycarbonate, polyether ether ketone, and polyphenyl sulfide. The method for producing an LCP extruded film according to any one of claims 1 to 4, wherein the resin composition B further contains an inorganic filler. The method for producing an LCP extruded film according to any one of claims 1 to 5, wherein the resin composition A, the resin composition B, and the resin composition C are co-extruded from a T-die. The method for producing an extruded LCP film according to any one of claims 1 to 6, wherein the extruded LCP film has a linear expansion coefficient in the TD direction of 55 ppm/K or less. The method for producing an extruded LCP film according to any one of claims 1 to 7, further comprising heating and pressurizing the extruded LCP film obtained under conditions of 200 to 360°C. The method for producing an LCP extruded film according to any one of claims 1 to 8, wherein the LCP extruded film does not have a tape-peelable skin layer on the film surface in an adhesion test by a cross-cut method according to JIS K5600-5-6.