JP7203994B2 - Liquid crystal polymer film and manufacturing method thereof, flexible copper-clad laminate, and flexible printed circuit board - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to liquid crystal polymer films and methods of manufacturing the same, flexible copper clad laminates, and flexible printed circuit boards.

In recent years, the frequency used in communication equipment tends to be very high. In order to suppress transmission loss in a high frequency band, it is required to lower the dielectric constant and dielectric loss tangent of insulating materials used for circuit boards.

Conventionally, polyimide has been widely used as an insulating material for circuit boards, but attention has been focused on liquid crystal polymers that have high heat resistance, low water absorption, and low loss in high frequency bands.

For example, in JP-A-2003-340918, after stretching a laminate of a resin film made of a liquid crystal polymer or a polymer alloy containing a liquid crystal polymer and a fluororesin porous film, the porous fluororesin film is peeled off. A liquid crystal polymer film obtained has a melting point of 335° C. or more and a surface roughness Ra of 0.1 μm or less in both the MD and TD directions.

In Japanese Unexamined Patent Application Publication No. 2003-340918, a liquid crystal polymer is melted and extruded into a film to obtain a raw material film, and then a fluororesin porous film is laminated on both sides of the raw material film to produce a laminated film. Thereafter, the laminated film is stretched under a temperature condition equal to or higher than the melting temperature of the liquid crystal polymer, and the fluororesin porous film is peeled off to produce a liquid crystal polymer film. Since the raw material film is obtained by melting the liquid crystal polymer and extruding it into a film shape, the liquid crystal polymer molecules are aligned in the melting direction. Therefore, it is considered that it is easy to tear in the melting direction. In the manufacturing method described in Japanese Patent Application Laid-Open No. 2003-340918, the raw material film is stretched at a temperature condition equal to or higher than the melting temperature of the liquid crystal polymer, thereby relaxing the orientation of the liquid crystal polymer and ensuring toughness. Conceivable. However, in the production method described in JP-A-2003-340918, since the fluororesin porous film is laminated on both sides of the raw material film, the surface layer of the raw material film that is in contact with the fluororesin porous film does not relax the orientation. is insufficient. Therefore, the surface layer of the manufactured liquid crystal polymer film has fragile portions where the liquid crystal polymer molecules are oriented. When such a liquid crystal polymer film is used for a flexible printed circuit board or the like, cohesive peeling may occur inside the film due to stress concentration, thermal strain, etc. when the circuit board is bent.

The present disclosure has been made in view of such circumstances, and according to embodiments of the present invention, the occurrence of cohesive peeling is suppressed, and the liquid crystal polymer film has a low dielectric constant and dielectric loss tangent, a method for producing the same, and , flexible copper clad laminates and flexible printed circuit boards using liquid crystal polymer films are provided.

The present disclosure includes the following aspects.
<1> Contains a liquid crystal polymer, has a polarized Raman spectral dichroic ratio of 0.7 to 1.3 on the surface and in the interior, has voids in the interior, has a surface roughness Ra of 20 nm to 200 nm, and has an average void A liquid crystal polymer film having a void diameter of 0.1 μm to 8.0 μm.
<2> The liquid crystal polymer film according to <1>, which has a peel adhesive strength of 0.5 N/mm or more in a 180° peel test.
<3> The liquid crystal polymer film according to <1> or <2>, which has a porosity of 25% to 50%.
<4> The liquid crystal polymer film according to any one of <1> to <3>, which has a thickness of 5 μm to 50 μm.
<5> The liquid crystal polymer film according to any one of <1> to <4>, wherein the voids are independent voids.
<6> The liquid crystal polymer film according to any one of <1> to <5>, which is used for a flexible printed circuit board.
<7> A flexible copper clad laminate comprising the liquid crystal polymer film according to any one of <1> to <6> and a copper foil disposed on at least one surface of the liquid crystal polymer film.
<8> A flexible printed circuit board formed by processing the copper foil in the flexible copper-clad laminate according to <7>.
<9> A step of preparing a thermally decomposable polymer solution containing a thermally decomposable polymer, a radical scavenger, and a solvent, and dispersing a liquid crystal polymer in the prepared thermally decomposable polymer solution to prepare a dispersion. a step of coating the prepared dispersion on a support to form a coating film; and a step of heat-treating the coating film in an inert gas atmosphere to melt the thermally decomposable polymer and the liquid crystal polymer. 1. A method of producing a liquid crystal polymer film comprising, in this order, a step of heat-treating the coating film in an air atmosphere to form voids inside the coating film.

According to the present disclosure, the occurrence of cohesive peeling is suppressed, and a liquid crystal polymer film having a low dielectric constant and dielectric loss tangent, a method for producing the same, and a flexible copper-clad laminate and a flexible printed circuit board using the liquid crystal polymer film are provided. can do.

The liquid crystal polymer film and method for producing the same, as well as the flexible copper-clad laminate and the flexible printed circuit board of the present disclosure will be described in detail below.

In this specification, the numerical range indicated using "to" means a range including the numerical values before and after "to" as the minimum and maximum values, respectively.
In the numerical ranges described stepwise in this specification, the upper limit or lower limit described in a certain numerical range may be replaced with the upper limit or lower limit of another numerical range described stepwise. Moreover, in the numerical ranges described in this specification, the upper limit or lower limit described in a certain numerical range may be replaced with the values shown in the examples.

As used herein, the amount of each component in the composition refers to the total amount of the multiple substances present in the composition when there are multiple substances corresponding to each component in the composition, unless otherwise specified. means
In the present specification, a combination of two or more preferred aspects is a more preferred aspect.
In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. be

<Liquid crystal polymer film>
The liquid crystal polymer film of the present disclosure contains a liquid crystal polymer, has a polarized Raman spectral dichroic ratio of 0.7 to 1.3 on the surface and inside, has voids inside, and has a surface roughness Ra of 20 nm to 200 nm. The average pore diameter of the pores is 0.1 μm to 8.0 μm.

Conventionally, a liquid crystal polymer is melted and extruded into a film to obtain a raw material film, and then a fluororesin porous film is laminated on both sides of the raw material film to produce a laminated film. A manufacturing method is known in which a liquid crystal polymer film is manufactured by stretching under temperature conditions and peeling off a fluororesin porous film (Japanese Unexamined Patent Application Publication No. 2003-340918). Since the raw material film is obtained by melting the liquid crystal polymer and extruding it into a film shape, the liquid crystal polymer molecules are aligned in the melting direction. Therefore, it is considered that it is easy to tear in the melting direction. In the manufacturing method described in Japanese Patent Application Laid-Open No. 2003-340918, the raw material film is stretched at a temperature condition equal to or higher than the melting temperature of the liquid crystal polymer, thereby relaxing the orientation of the liquid crystal polymer and ensuring toughness. Conceivable. However, in the production method described in JP-A-2003-340918, since the fluororesin porous film is laminated on both sides of the raw material film, the surface layer of the raw material film that is in contact with the fluororesin porous film does not relax the orientation. is insufficient. Therefore, the surface layer of the manufactured liquid crystal polymer film has fragile portions where the liquid crystal polymer molecules are oriented. When such a liquid crystal polymer film is used for a flexible printed circuit board or the like, cohesive peeling may occur inside the film.

In addition, conventionally, polyimide is widely used as an insulating material for circuit boards, and a method of making a polyimide film porous is known in order to lower the dielectric constant and the dielectric loss tangent. The liquid crystal polymer film described in Japanese Patent Application Laid-Open No. 2003-340918 is not porous and is considered to have a high dielectric constant and dielectric loss tangent. In addition, even if the liquid crystal polymer film described in JP-A-2003-340918 is made porous, the surface layer has fragile portions where the liquid crystal polymer molecules are oriented, so cohesion and peeling are more likely to occur. It is considered to be.

On the other hand, the liquid crystal polymer film of the present disclosure has a polarized Raman spectral dichroic ratio of 0.7 to 1.3 on the surface and inside, so the liquid crystal polymer molecules are entangled on the surface and inside, and cohesion and detachment occurs. Hard to generate, high peel strength.

In general, a liquid crystal polymer film has a lower dielectric constant and dielectric loss tangent than a polyimide film. Since the liquid crystal polymer film of the present disclosure has voids inside and has an average void diameter of 0.1 μm to 8.0 μm, the dielectric constant and dielectric loss tangent are lower. Therefore, when the liquid crystal polymer film of the present disclosure is used for a circuit board, it is possible to suppress transmission loss in a high frequency band.

Furthermore, in a high frequency band, the phenomenon (skin effect) in which the current concentrates on the conductor surface increases, but the liquid crystal polymer film of the present disclosure has a small surface roughness Ra of 20 nm to 200 nm. When used for a circuit board, transmission loss can be suppressed.

[Liquid crystal polymer]
A liquid crystal polymer film of the present disclosure comprises a liquid crystal polymer. In the present disclosure, the type of liquid crystal polymer is not particularly limited, and commonly known liquid crystal polymers can be used.
The liquid crystal polymer is preferably a polycondensate of parahydroxybenzoic acid and other monomers. Examples of liquid crystal polymers include polycondensates of ethylene terephthalate and parahydroxybenzoic acid, polycondensates of 6-hydroxy-2-naphthalenecarboxylic acid and parahydroxybenzoic acid, and 4,4-dihydroxybiphenol and terephthalate. A polycondensation product of an acid and parahydroxybenzoic acid can be mentioned.

The liquid crystal polymer film of the present disclosure may contain other components in addition to the liquid crystal polymer film. Other ingredients include, for example, plasticizers, degradation accelerators, glass fibers and hollow silica.

[Polarized Raman Spectral Dichroic Ratio]
The liquid crystal polymer film of the present disclosure has a polarized Raman spectral dichroic ratio of 0.7 to 1.3, preferably 0.9 to 1.1 on the surface and in the interior. A polarized Raman spectral dichroic ratio of 0.7 to 1.3 indicates that the liquid crystal polymer molecules are randomly oriented. In the present disclosure, the liquid crystalline polymer molecules are randomly oriented in any part of the film due to the polarized Raman spectral dichroic ratio of 0.7 to 1.3 on the surface and in the interior. That is, since the liquid crystal polymer molecules are entangled with each other in the entire film, the occurrence of peeling inside the film due to external force (cohesive peeling) is suppressed.

The polarized Raman spectroscopic dichroic ratio can be calculated by the following method using, for example, a microscopic laser Raman spectrometer (product name “NRS-3300”, manufactured by JASCO Corporation).

Since the liquid crystal polymer has an aromatic ring, the vertical and horizontal peak intensities of the C—C stretching peak (around 1615 cm ⁻¹ ) derived from the aromatic ring are measured. The polarized Raman spectral dichroic ratio is represented by an intensity ratio (vertical peak intensity/horizontal peak intensity). The polarized Raman spectroscopic dichroic ratio at the surface is calculated as an average value of peak intensities measured on two main surfaces of the liquid crystal polymer film. The internal polarized Raman spectral dichroic ratio is calculated by cutting the liquid crystal polymer film in the thickness direction, measuring the peak intensity at three points in the center of the thickness direction of the cut surface, and calculating the average value at the three points. .

[Gap]
The liquid crystal polymer film of the present disclosure has internal voids. The shape of the void is not particularly limited, but the cross section is preferably circular or elliptical.

The porosity is preferably 15% to 50%, more preferably 25% to 50%, still more preferably 40% to 50%. When the porosity is 25% or more, the dielectric constant and dielectric loss tangent become lower. On the other hand, when the porosity is 50% or less, a film having sufficient self-supporting properties can be obtained.

The porosity is calculated, for example, by the following formula.
Porosity (%) = {1-(Specific gravity of liquid crystal polymer film having voids/Specific gravity of liquid crystal polymer film having no voids)} x 100
A voided liquid crystal polymer film is the liquid crystal polymer film of the present disclosure. As the void-free liquid crystal polymer film, it is possible to use a liquid crystal polymer film having no internal voids produced by a conventional manufacturing method.
The specific gravity is measured using an electronic hydrometer, for example, the product name "EW-300SG" manufactured by Alpha Mirage.

The average pore diameter is 0.1 μm to 8.0 μm, preferably 0.5 μm to 5.0 μm, more preferably 1.0 μm to 2.0 μm. When the average void diameter is 0.1 μm or more, the dielectric constant and dielectric loss tangent are low. In addition, in order to make the average pore diameter 0.1 μm or more, a high-output ultrasonic dispersing device is not required, and ordinary dispersing conditions can be used, which is preferable from the viewpoint of manufacturing cost. On the other hand, when the average void diameter is 8.0 μm or less, the strength of the liquid crystal polymer film is high, and cohesive peeling is less likely to occur inside the film.

The average void diameter is calculated by the following method, for example, using a scanning electron microscope (SEM). First, a small piece of a liquid crystal polymer film is embedded in an epoxy resin, and a cross-sectional slice is cut out using a microtome (product name “RM2265”, manufactured by Leica). Using a scanning electron microscope (model "S-4800", manufactured by Hitachi High-Technologies Corporation, observation magnification: 5000 times, acceleration voltage: 2.0 kV), SEM images of the cut surface are observed at three different locations. do. From among the voids present in each observation area, 10 voids are selected in descending order of size, and the equivalent circle diameters are measured. From the 30 data obtained by the measurement, 10 data are selected in descending order of equivalent circle diameter, and the average value is taken as the average pore diameter.

In the present disclosure, the voids are preferably independent voids. "The voids are independent voids" means that the voids existing inside the liquid crystal polymer film are not connected to each other, the voids exist independently, and the voids are connected to the outside of the liquid crystal polymer film. It means not connected. Therefore, if the voids are independent, it is possible to suppress the intrusion of air, water, etc. into the inside of the liquid crystal polymer film. Whether or not the voids are independent voids can be determined, for example, by the following method.

First, 10 judgment samples each having a length of 25 mm and a width of 25 mm are cut out from the liquid crystal polymer film. The length, width and thickness of 10 samples for judgment are measured accurately, and the volume V1 is calculated. Next, 10 samples for determination are placed in a dry density meter (product name: "Accupic II 1340", manufactured by Shimadzu Corporation) to measure the volume V2. V1/V2 is calculated, and when V1/V2 is 0.98 or more, the sample for determination is determined to have independent voids. In addition, when V1/V2 is 0.98 or more in all of the 10 determination samples, the liquid crystal polymer film is determined to have independent voids.

[Surface roughness]
The liquid crystal polymer film of the present disclosure has a surface roughness Ra of 20 nm to 200 nm. When the liquid crystal polymer film is used for the circuit board, the liquid crystal polymer film and the copper foil are laminated together. When the surface roughness Ra is 20 nm to 200 nm, the surface unevenness of the bonding surface between the liquid crystal polymer film and the copper foil is reduced. When the frequency of the transmission signal is high, the phenomenon that the current concentrates on the surface of the conductor (skin effect) increases.

The surface roughness Ra is measured according to JIS B 0601:2013 (corresponding to ISO 4287:1997). Specifically, it can be measured using a white interferometer (product name “VertScan (registered trademark) 2.0”, manufactured by Ryoka System Co., Ltd.). In addition, Ra means arithmetic mean roughness.

The liquid crystal polymer film of the present disclosure has internal voids and a surface roughness Ra of 20 nm to 200 nm. That is, the liquid crystal polymer film of the present disclosure preferably does not have unevenness derived from voids on its surface.

[Thickness]
The liquid crystal polymer film of the present disclosure preferably has a thickness of 5 μm to 50 μm, more preferably 10 μm to 25 μm. Since it is as thin as 5 μm to 50 μm and has voids inside, it can be applied to various uses requiring a low dielectric constant and a low dielectric loss tangent.

The thickness can be measured using an adhesive film thickness gauge, for example, an electronic micrometer (product name “KG3001A”, manufactured by Anritsu Corporation).

[Peel adhesion strength in 180° peel test]
The liquid crystal polymer film of the present disclosure preferably has a peel adhesive strength of 0.5 N/mm or more in a 180° peel test. When the peel adhesive strength is 0.5 N/mm or more, when combined with other layers to form a laminate, there is no peeling, and the practicality is high. Although the upper limit of the peel adhesive strength is not particularly limited, it is, for example, 5.0 N/mm. Peel adhesion strength is measured, for example, by the following peel test.

A liquid crystal polymer film is cut into a size of 10 mm wide by 80 mm long. Using a double-sided adhesive tape (product name: Scotch (registered trademark) SPS12, manufactured by 3M) having the same width as the cut liquid crystal polymer film, the cut liquid crystal polymer film is fixed to a 2 mm thick stainless steel plate. According to the width of the liquid crystal polymer film, a single-sided adhesive tape (product name: Scotch (registered trademark) DUCTTP18, manufactured by 3M) with a width of 10 mm and a length of 120 mm was adhered to the cut liquid crystal polymer film, and the tensile speed was 50 mm/min. Measure the 180° peel adhesive strength (N/mm) under the conditions of

More preferably, the liquid crystal polymer film of the present disclosure has a peel adhesive strength of 0.5 N/mm or more, and is peeled at the interface between the liquid crystal polymer film and the single-sided adhesive tape after the peel test. When such a liquid crystal polymer film is processed into a circuit board or the like, cohesive peeling is less likely to occur inside the film. In addition, even if peeling occurs inside the liquid crystal polymer film after the peeling test, the liquid crystal polymer film of the present disclosure can be processed into a circuit board or the like as long as the peel adhesive strength is 0.5 N / mm or more. , cohesive detachment is less likely to occur inside the film.

[Method for producing liquid crystal polymer film]
The method for producing a liquid crystal polymer film of the present disclosure comprises the steps of preparing a thermally decomposable polymer solution containing a thermally decomposable polymer, a radical scavenger, and a solvent, and adding a liquid crystal polymer to the prepared thermally decomposable polymer solution. a step of dispersing to prepare a dispersion; a step of coating the prepared dispersion on a support to form a coating film; and a step of melting the liquid crystal polymer, and a step of heat-treating the coating film in an air atmosphere to form voids inside the coating film.

-Step of preparing thermally decomposable polymer solution-
In the method for producing a liquid crystal polymer film of the present disclosure, first, a thermally decomposable polymer solution containing a thermally decomposable polymer, a radical scavenger, and a solvent is prepared.

(thermally decomposable polymer)
A thermally decomposable polymer is a polymer that has the property of being decomposed by heat. The thermally decomposable polymer is preferably a polymer having the property of decomposing at a temperature of 150°C to 350°C. Further, it is more preferable that the thermally decomposable polymer is decomposed into monomers at a temperature of 150° C. to 350° C., and the decomposed monomers are removed by evaporation.

The thermally decomposable polymer preferably contains a partial structure that is likely to be decomposed or cut in the molecular chain. Examples of thermally decomposable polymers include polymers containing vinyl-based monomers such as styrene monomers and (meth)acrylic acid esters as constitutional units, and polymers having polyoxyalkylene chains. A polymer containing a vinyl monomer as a structural unit may be a homopolymer or a copolymer. Polymers having polyoxyalkylene chains include, for example, polyethylene glycol and polypropylene glycol. Among them, a polymer containing a (meth)acrylic acid ester as a structural unit is preferable, a polymer containing a (meth)acrylic acid alkyl ester as a structural unit is more preferable, and a (meth)acrylic having 1 to 4 carbon atoms is more preferable. It is a polymer containing an acid alkyl ester as a structural unit, and particularly preferably polymethyl methacrylate.

Thermally decomposable polymers may be commercially available. Commercially available products include, for example, methacrylic resin (product name "Techpolymer" IBM-2, Sekisui Plastics Co., Ltd.), and crosslinked polymethyl methacrylate (product name "Techpolymer" MBX series, Sekisui Plastics Co., Ltd. made).

The weight average molecular weight of the thermally decomposable polymer is preferably 3,000 to 1,000,000, more preferably 5,000 to 100,000, from the viewpoint of appropriately controlling the average pore size of the pores in the liquid crystal polymer film. A weight average molecular weight is the value measured using a gel permeation chromatography (GPC). Specifically, as GPC, Tosoh's product name "HLC-8020GPC" is used, and as a column, Tosoh's product name "TSKgel, SuperMultipore HZ-H" (4.6 mm ID × 15 cm) is used. THF (tetrahydrofuran) is used as the eluent. The measurement is performed with a sample concentration of 0.45% by mass, a flow rate of 0.35 ml/min, a sample injection amount of 10 μl, a measurement temperature of 40° C., and an RI detector. For the calibration curve, as a standard sample, the product name "TSK standard polystyrene" manufactured by Tosoh Corporation: "F-40", "F-20", "F-4", "F-1", "A-5000", Eight samples of "A-2500", "A-1000" and "n-propylbenzene" are used.

The thermally decomposable polymer may be used singly or in combination of two or more.

The content of the thermally decomposable polymer is preferably 10% by mass to 25% by mass with respect to the total mass of the dispersion described later.

(radical scavenger)
The radical scavenger has the role of scavenging radicals so that the thermally decomposable polymer is not decomposed by radicals at a stage prior to "the step of forming voids inside the coating film".

Examples of radical scavengers include, but are not limited to, phenolic radical scavengers and hindered amine radical scavengers.

Phenolic radical scavengers include, for example, 2,6-di-tert-butyl-p-cresol, 2,6-diphenyl-4-octadecyloxyphenol, stearyl (3,5-di-tert-butyl-4 -hydroxyphenyl)-propionate, distearyl (3,5-di-tert-butyl-4-hydroxybenzyl)phosphonate, thiodiethylene glycol bis[(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1 ,6-hexamethylenebis[(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,6-hexamethylenebis[(3,5-di-tert-butyl-4-hydroxyphenyl)propionate acid amide], 4,4′-thiobis(6-tert-butyl-m-cresol), 2,2′-methylenebis(4-methyl-6-tert-butylphenol), 2,2′-methylenebis(4-ethyl -6-tert-butylphenol), bis [3,3-bis (4-hydroxy-3-tert-butylphenyl) butyric acid] glycol ester, 4,4'-butylidene bis (6-tert-butyl-m- cresol), 2,2′-ethylidenebis(4,6-di-tert-butylphenol), 2,2′-ethylidenebis(4-sec-butyl-6-tert-butylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl)butane, bis[2-tert-butyl 4-methyl-6-(2-hydroxy-3-tert-butyl 5-methylbenzyl)phenyl]terephthalate, 1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl) isocyanurate, 1,3,5-tris(3,5-di-tert-butyl 4-hydroxy benzyl) isocyanurate, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene, 1,3,5-tris[(3,5 -di-tert-butyl 4-hydroxyphenyl)propionyloxyethyl] isocyanurate, tetrakis [methylene-3-(3',5'-di-tert-butyl 4'-hydroxyphenyl) propionate] methane, 2-tert- Butyl 4-methyl-6-(2-acryloyloxy-3-tert-butyl 5-methylbenzyl)phenol, 3,9-bi Su[1,1-dimethyl-2-{(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy}ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane , triethylene glycol bis[(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate] and 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4 ,6-di-tert-pentylphenyl acrylate.

Examples of hindered amine radical scavengers include 2,2,6,6-tetramethyl-4-piperidyl benzoate, N-(2,2,6,6-tetramethyl-4-piperidyl) dodecylsuccinimide, 1 -[(3,5-di-tert-butyl 4-hydroxyphenyl)propionyloxyethyl]-2,2,6,6-tetramethyl-4-piperidyl-(3,5-di-tert-butyl 4-hydroxy phenyl) propionate, bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, bis (1,2,2 ,6,6-pentamethyl-4-piperidyl)-2-butyl-2-(3,5-di-tert-butyl 4-hydroxybenzyl)malonate, N,N'-bis(2,2,6,6- Tetramethyl-4-piperidyl)hexamethylenediamine, Tetra(2,2,6,6-tetramethyl-4-piperidyl)butanetetracarboxylate, Tetra(1,2,2,6,6-pentamethyl-4-piperidyl) ) butane tetracarboxylate, bis(2,2,6,6-tetramethyl-4-piperidyl)・di(tridecyl)butane tetracarboxylate, bis(1,2,2,6,6-pentamethyl-4-piperidyl )・di(tridecyl)butane tetracarboxylate, 3,9-bis[1,1-dimethyl-2-{tris(2,2,6,6-tetramethyl-4-piperidyloxycarbonyloxy)butylcarbonyloxy} ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane, 3,9-bis[1,1-dimethyl-2-{tris(1,2,2,6,6-pentamethyl- 4-piperidyloxycarbonyloxy)butylcarbonyloxy}ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane, 1,5,8,12-tetrakis[4,6-bis{N- (2,2,6,6-tetramethyl-4-piperidyl)butylamino}-1,3,5-triazin-2-yl]-1,5,8,12-tetraazadodecane, 1-(2- hydroxyethyl)-2,2,6,6-tetramethyl-4-piperidinol/dimethyl succinate condensate, 2-tert-octylamino-4,6-dichloro-s-triazine/N,N'-bis(2 ,2,6,6-tetramethyl-4-piperidyl)hexamethylenediamine condensate, and N,N'-bi and su(2,2,6,6-tetramethyl-4-piperidyl)hexamethylenediamine/dibromoethane condensates.

A commercial item may be sufficient as a radical scavenger. Commercially available products include, for example, 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate (product name: SUMILIZER (registered trademark) ) GS”, manufactured by Sumitomo Chemical Co., Ltd.).

In the thermally decomposable polymer solution, the ratio of the content of the radical scavenger to the content of the thermally decomposable polymer is preferably 0.01 to 0.1, more preferably 0.03 to 0.06. .

The radical scavenger may be used singly or in combination of two or more.

(solvent)
The solvent is not particularly limited as long as it can dissolve the thermally decomposable polymer and the radical scavenger. Solvents include, for example, methyl ethyl ketone, methyl isobutyl ketone, methyl acetate, ethyl acetate, butyl acetate, cyclohexanone, and cyclopentanone.

A solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

The content of the solvent is preferably 30% by mass to 80% by mass with respect to the total mass of the dispersion to be described later.

The thermally decomposable polymer solution may contain other components in addition to the thermally decomposable polymer, radical scavenger and solvent. Other ingredients include, for example, plasticizers, antioxidants, surfactants and leveling agents.

The method for preparing the thermally decomposable polymer solution is not particularly limited, and each component may be added in order, or each component may be added simultaneously.

-Step of preparing a dispersion-
A method for producing a liquid crystal polymer film of the present disclosure includes a step of dispersing a liquid crystal polymer in a prepared thermally decomposable polymer solution to prepare a dispersion.

As the liquid crystal polymer, those described above can be used. Therefore, the detailed description of the liquid crystal polymer is omitted.

In the dispersion, the ratio of the content of the liquid crystal polymer to the content of the thermally decomposable polymer is preferably 0.8 to 5, more preferably 0.9, from the viewpoint of lowering the dielectric constant and dielectric loss tangent. to 3, more preferably 1 to 1.5.

A method for dispersing the liquid crystal polymer in the thermally decomposable polymer solution is not particularly limited, and a known method can be used. Dispersion is performed, for example, using a known dispersing device such as an ultrasonic homogenizer or a high-pressure homogenizer.

-Step of forming coating film-
A method for producing a liquid crystal polymer film of the present disclosure includes a step of applying the prepared dispersion onto a support to form a coating film.

The coating method is not particularly limited, and a known coating method can be used. The dispersion is applied using a coating device such as an applicator, spray coater, bar coater, dip coater, spin coater, doctor blade, or the like. Among them, it is preferable to use an applicator as the coating device from the viewpoint of easy adjustment of the film thickness.

The type of support is not particularly limited, and examples thereof include glass, resin, and metal. The support preferably has a surface treatment layer formed on its surface so that it can be easily peeled off in a later step. The surface treatment layer preferably contains a fluororesin.

When the dispersion is applied to the support and then dried, the solvent in the dispersion is removed and a coating film is formed on the support. Drying is preferably drying using heating means. When a heating means is used, the heating temperature is preferably 60°C to 120°C.

The thickness of the coating film is preferably 5 μm to 50 μm, more preferably 10 μm to 25 μm.

-Step of melting thermally decomposable polymer and liquid crystal polymer-
A method for producing a liquid crystal polymer film of the present disclosure includes a step of heat-treating a coating film in an inert gas atmosphere to melt a thermally decomposable polymer and a liquid crystal polymer.

The term "inactive gas atmosphere" refers to an environment in which the content of inert gas is 90% or more. Examples of inert gases include nitrogen and argon, with nitrogen being preferred.

In an inert gas atmosphere, the oxygen concentration is preferably 300 ppm or less, more preferably 150 ppm or less.

In this step, decomposition of the thermally decomposable polymer can be suppressed by heat-treating the coating film in an inert gas atmosphere.

A heating device used when heat-treating the coating film is not particularly limited, and a known heating device can be used. Examples of the heat treatment method include a method of blowing hot air onto the coating film, and a method of irradiating the coating film with infrared rays using a far-infrared heater or a near-infrared heater. Among them, from the viewpoint of performing the heat treatment efficiently, the method of applying the heat treatment is preferably a method of irradiating the coating film with infrared rays.

The heating temperature is preferably 280°C to 400°C, more preferably 325°C to 375°C. The heating time is preferably 3 to 10 minutes, more preferably 5 to 8 minutes.

When the coating film is heat-treated in an inert gas atmosphere, the thermally decomposable polymer and the liquid crystal polymer are melted and changed into an energetically stable phase state. Since the interfacial tension of the liquid crystal polymer is higher than that of the thermally decomposable polymer, the following phase states occur when the thermally decomposable polymer and the liquid crystal polymer are melted. That is, the thermally decomposable polymer is unevenly distributed as a thin film at the interface with the support and the interface with air, and exists as a dispersed phase dispersed in the liquid crystal polymer phase inside the coating film. Further, the liquid crystal polymer exists as a continuous phase inside the coating film.

The heat treatment is preferably performed while applying ultrasonic vibration to the support on which the coating film is formed. Ultrasonic vibration is performed at a frequency of 10 kHz to 30 kHz and an output of 500 W to 1000 W, for example. By heat-treating the coating film while applying ultrasonic vibrations, the thermally decomposable polymer and the liquid crystal polymer easily change into an energetically stable phase state.

After the heat treatment, it is preferable to naturally cool to room temperature. In the present disclosure, normal temperature indicates a temperature range of 20°C to 30°C.

- A process of forming a void inside the coating film -
A method for producing a liquid crystal polymer film of the present disclosure includes a step of heat-treating a coating film in an air atmosphere to form voids inside the coating film.

A heating device used when heat-treating the coating film is not particularly limited, and a known heating device can be used. Examples of the heat treatment method include a method of blowing hot air onto the coating film, and a method of irradiating the coating film with infrared rays using a far-infrared heater or a near-infrared heater. Among them, from the viewpoint of performing the heat treatment efficiently, the method of applying the heat treatment is preferably a method of irradiating the coating film with infrared rays.

The heating temperature is preferably a temperature at which the thermally decomposable polymer is decomposed into monomers and the decomposed monomers are evaporated and removed. The heating temperature is, for example, 150.degree. C. to 350.degree. The heating time is preferably 5 to 20 minutes, more preferably 10 to 15 minutes.

After the heat treatment, it is preferable to naturally cool to room temperature.

As described above, in the step preceding this step (the step of melting the thermally decomposable polymer and the liquid crystal polymer), the thermally decomposable polymer is unevenly distributed as a thin film at the interface with the support and the interface with the air, and the coating film exists as a dispersed phase dispersed in the liquid crystal polymer phase. In this step, when the coating film is heat-treated under atmospheric pressure, the thermally decomposable polymer is decomposed and voids are formed in the portions where the thermally decomposable polymer was present. That is, the thin film at the interface with the support and the interface with the air, and the dispersed phase inside the coating film become voids due to the heat treatment. As a result, independent voids are formed inside the coating film, and unevenness resulting from the voids is not formed on the surface of the coating film. A coating film having voids formed therein is the liquid crystal polymer film of the present disclosure.

In the method for producing a liquid crystal polymer film of the present disclosure, the coating film is peeled off from the support before the step of forming the void inside the coating film or after the step of forming the void inside the coating film. , it is preferred to remove the support. From the viewpoint of efficiently forming voids inside the coating film, after the step of melting the thermally decomposable polymer and the liquid crystal polymer and before the step of forming voids inside the coating film, the coating film is removed from the support. is more preferable.

-Other processes-
In addition, the method for producing a liquid crystal polymer film of the present disclosure preferably further includes, as a step other than the above, a step of hot-pressing at least one surface of the coating film in which voids are formed.

Hot pressing is performed, for example, using a hot press at a temperature of 200° C. to 400° C. and a pressure of 0.2 MPa to 1.0 MPa. The surface roughness Ra can be reduced by performing a hot press on the coating film having voids formed therein.

[Use]
The liquid crystal polymer films of the present disclosure are preferably used in flexible printed circuit boards. Since the liquid crystal polymer film of the present disclosure has a low dielectric constant and a low dielectric loss tangent, it is useful because it can suppress transmission loss in a high frequency band. In addition, the liquid crystal polymer film of the present disclosure is suitable for manufacturing flexible printed circuit boards because cohesion and peeling due to processing is suppressed.

<Flexible copper-clad laminate>
A flexible copper clad laminate of the present disclosure includes the liquid crystal polymer film and a copper foil disposed on at least one surface of the liquid crystal polymer film.

The flexible copper-clad laminate of the present disclosure can be produced by forming an adhesive layer on one or both sides of a liquid crystal polymer film and laminating the liquid crystal polymer film and copper foil via the adhesive layer. A known adhesive can be used as the adhesive constituting the adhesive layer.

The copper foil may be a rolled copper foil formed by a rolling method or an electrolytic copper foil formed by an electrolytic method, but the rolled copper foil is preferable from the viewpoint of bending resistance.

Although the thickness of the copper foil is not particularly limited, it is preferably 3 μm to 15 μm, more preferably 5 μm to 10 μm. The copper foil may be a carrier-attached copper foil that is detachably formed on a support (carrier). A known carrier can be used. Although the thickness of the carrier is not particularly limited, it is preferably 10 μm to 100 μm, more preferably 18 μm to 50 μm.

<Flexible printed circuit board>
The flexible printed circuit board of the present disclosure is formed by processing the copper foil in the flexible copper-clad laminate. Specifically, the flexible printed circuit board of the present disclosure is preferably manufactured by etching the copper foil of the flexible copper-clad laminate to form a desired circuit pattern.

EXAMPLES Hereinafter, the present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to the following examples as long as the gist thereof is not exceeded.

(Example 1)
Pellets of the liquid crystal polymer were placed in a cryogenic crusher (product name “JFC-2000”, manufactured by Nippon Analytical Industry Co., Ltd.) and crushed under conditions of 1400 reciprocating motions/min for 20 minutes. As a result of measurement using a particle size distribution analyzer (product name “LMS-3000” manufactured by Seishin Enterprise Co., Ltd.), the average particle size was 58 μm.
A thermally decomposable polymer solution was prepared by dissolving a thermally decomposable polymer and a radical scavenger in a solvent. A coating liquid 2 was prepared by dispersing the pulverized liquid crystal polymer in the prepared thermally decomposable polymer solution for 10 minutes using an ultrasonic disperser (product name: "UH-600S", manufactured by SMTE). Content of each component is as follows.

・ Liquid crystal polymer: (product name “Laperos (registered trademark) LCP grade: A950RX”, manufactured by Polyplastics) ... 75 parts by mass ・ Thermally decomposable polymer: methacrylic resin (product name “Techpolymer” grade IBM- 2", manufactured by Sekisui Plastics Co., Ltd.) ... 25 parts by mass Radical scavenger: 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di -tert-pentylphenyl acrylate (product name "SUMILIZER (registered trademark) GS", manufactured by Sumitomo Chemical Co., Ltd.) ... 1 part by mass Solvent: methyl ethyl ketone ... 100 parts by mass

Next, the coating liquid 2 was applied to the fluorine-coated glass plate using an applicator. After that, the glass plate coated with the coating liquid 2 was placed in a drying box at 80° C. to remove the solvent. A glass having a coating film of 100 mm×100 mm size with a thickness of 25 μm was obtained.

Subsequently, the glass having the coating film was placed on a stage in a heating device equipped with a near-infrared heater. From the stage, the glass having the coating film was heated with a near-infrared heater in a nitrogen atmosphere while applying ultrasonic vibrations at a frequency of 20 kHz and an output of 800 W, and the surface temperature of the coating film was kept at 350° C. for 5 minutes. After naturally cooling to room temperature, the coating film was peeled off from the glass plate. Both ends of the peeled coating film were sandwiched with clips, and while floating in the air, the coating film was heated in the same heating apparatus under an air atmosphere with a near-infrared heater, and the surface temperature of the coating film was kept at 250° C. for 10 minutes. After naturally cooling to room temperature, the clipped portion was removed to obtain a liquid crystal polymer film having a thickness of 80 mm×80 mm and a thickness of 25 μm.

Coating liquid 1 and coating liquids 3 to 5 were prepared in the same manner as coating liquid 2 by changing the content of each component contained in coating liquid 2 to the content (unit: parts by mass) shown in Table 1.

(Example 2)
A liquid crystal polymer film was prepared in the same manner as in Example 1, except that coating liquid 2 was changed to coating liquid 3.

(Example 3)
A liquid crystal polymer film was prepared in the same manner as in Example 1, except that coating liquid 2 was changed to coating liquid 4.

(Example 4)
A liquid crystal polymer film was produced in the same manner as in Example 1, except that the output of ultrasonic vibration was changed from 800W to 400W.

(Example 5)
In Example 3, except that after forming a void inside the coating film, heat pressing was performed on both sides of the coating film at a temperature of 300 ° C. and a pressure of 0.5 MPa for 3 minutes. A liquid crystal polymer film was produced in a similar manner.

(Comparative example 1)
A liquid crystal polymer film was produced in the same manner as in Example 1, except that the coating liquid 2 was changed to the coating liquid 1.

(Comparative example 2)
A liquid crystal polymer film was prepared in the same manner as in Example 1, except that the coating liquid 2 was changed to the coating liquid 5.

(Comparative Example 3)
A liquid crystal polymer film was produced in the same manner as in Example 1, except that ultrasonic vibration was not performed.

(Comparative Example 4)
A liquid crystal polymer film having a thickness of 25 μm was produced according to the method described in JP-A-2003-340918. Specifically, a liquid crystal polymer was melted and extruded through a T-die to obtain a raw material film with a thickness of 125 μm. A laminate film (product name: "C-Porous", manufactured by Chukoh Kasei Kogyo Co., Ltd.) was laminated on both sides of the raw material film. The laminate was biaxially stretched under conditions of 350° C., a draw ratio of 1.25 times in the MD direction, and 4.0 times in the TD direction. The MD direction is the extrusion direction of the molten liquid crystal polymer, and the TD direction is the direction at 90° to the MD direction.

The liquid crystal polymer films of Examples and Comparative Examples were measured for void ratio, average void diameter, surface roughness Ra, polarized Raman spectral dichroic ratio on the surface and inside, dielectric constant, and dielectric loss tangent. In addition, a peel test was conducted to measure the peel adhesive strength and observe the peeled portions. Furthermore, it was determined whether or not the voids formed inside were independent voids. Table 2 shows the measurement results. The measurement method is as follows. In Comparative Example 2, no measurement was performed because a liquid crystal polymer film could not be produced.

<Porosity>
The porosity was calculated using the following formula.
Porosity (%) = {1-(Specific gravity of liquid crystal polymer film produced/Specific gravity of liquid crystal polymer film in which voids are not formed)} × 100
The specific gravity was measured using an electronic hydrometer (product name “EW-300SG”, manufactured by Alpha Mirage).
The liquid crystal polymer film produced in Comparative Example 4 was used for the "liquid crystal polymer film without voids" in the formula.

<Average pore diameter>
A small piece of the produced liquid crystal polymer film was embedded in an epoxy resin and cut in the thickness direction using a microtome (product name “RM2265”, manufactured by Leica) to obtain a cross section. Using a scanning electron microscope (model "S-4800", manufactured by Hitachi High-Technologies Corporation, observation magnification: 5000 times, acceleration voltage: 2.0 kV), SEM images of the cut surface are observed at three different locations. bottom. From the voids present in each observation area, 10 voids were selected in descending order of size, and the equivalent circle diameter was measured. From the 30 data obtained by the measurement, 10 data were selected in descending order of equivalent circle diameter, and the average value thereof was adopted as the average pore diameter.

<Surface roughness Ra>
The surface roughness Ra was measured according to JIS B 0601:2013 (corresponding to ISO 4287:1997). The surface roughness of the produced liquid crystal polymer film was measured at three points using a white interferometer (product name: 'VertScan (registered trademark) 2.0', manufactured by Ryoka System Co., Ltd.). The average value of each measured surface roughness was adopted as the surface roughness.

<Dichroic ratio of polarized Raman spectroscopy>
Focusing on the C-C stretching peak (near 1615 cm ^-1 ) derived from the aromatic ring of the liquid crystal polymer, the intensity ratio at this peak (intensity in the direction of 90 ° with respect to the application direction / intensity in the application direction) is used to measure the degree of orientation. was evaluated as the parameter shown. In addition, in the case of Comparative Example 4, the strength ratio was calculated as "strength in the direction at 90° to the MD direction/strength in the MD direction". Hereinafter, in the case of Comparative Example 4, "coating direction" is read as "MD direction".
Specifically, on both surfaces of the prepared liquid crystal polymer film, using a microscopic laser Raman spectrometer (product name “NRS-3300”, manufactured by JASCO Corporation), the film coating direction and 90 ° with respect to the coating direction The peak intensity (intensity near 1615 cm ⁻¹ ) was measured by polarized Raman measurement with respect to the direction. From the peak intensity, an intensity ratio (intensity in the direction 90° to the application direction/intensity in the application direction) was calculated and adopted as the "dichroic ratio of polarized Raman spectroscopy on the surface". A small piece of the liquid crystal polymer film thus prepared was embedded in an epoxy resin and cut parallel to the application direction using a microtome (product name “RM2265”, manufactured by Leica) to obtain a cross-sectional slice. In the central portion of the cross section in the thickness direction, in the same manner as described above, the peak intensity in two directions (thickness direction and application direction) is measured to calculate the intensity ratio (strength in the thickness direction / intensity in the application direction), It was adopted as "the dichroic ratio of polarized Raman spectroscopy in the interior".

<Relative permittivity and dielectric loss tangent>
The dielectric constant and dielectric loss tangent of the produced liquid crystal polymer film at 10 GHz were measured by the cavity resonator perturbation method using a dielectric constant measurement device (model number: CP-531, manufactured by Kanto Denshi Applied Development Co., Ltd.) using a cavity resonator. It was measured. When the dielectric constant was 2.5 or less and the dielectric loss tangent was 0.0015 or less, there was no problem in practical use, and it was determined as "acceptable level".

<Peeling test>
The prepared liquid crystal polymer film was cut into a size of 10 mm width×80 mm length. A double-sided adhesive tape (product name: Scotch (registered trademark) SPS12, manufactured by 3M) having the same width as the cut liquid crystal polymer film was used to fix the cut liquid crystal polymer film to a stainless steel plate having a thickness of 2 mm. According to the width of the liquid crystal polymer film, a single-sided adhesive tape (product name: Scotch (registered trademark) DUCTTP18, manufactured by 3M) with a width of 10 mm and a length of 120 mm was adhered to the cut liquid crystal polymer film, and the tensile speed was 50 mm/min. 180° peel adhesive strength (N/mm) was measured under the conditions of
In addition, the peeled portions of the liquid crystal polymer film after the peeling test were observed. When peeling occurred at the interface between the liquid crystal polymer film and the single-sided adhesive tape, in Table 2, the peeled portion was described as "film surface". On the other hand, when peeling occurred inside the liquid crystal polymer film, the peeling location was described as "inside the film" in Table 2. Delamination occurring inside the film means cohesive delamination.

<Determination of independent voids>
From the prepared liquid crystal polymer film, 10 sheets of samples for judgment having a length of 25 mm and a width of 25 mm were cut out. The length, width and thickness of 10 judgment samples were measured accurately, and the volume V1 was calculated. Next, 10 judgment samples were placed in a dry density meter (product name: "Accupic II 1340", manufactured by Shimadzu Corporation) to measure the volume V2. V1/V2 was calculated, and when V1/V2 was 0.98 or more, the sample for determination was determined to have independent voids. In addition, when V1/V2 was 0.98 or more in all of the 10 judgment samples, it was judged that the produced liquid crystal polymer film had independent voids.
It was found that the liquid crystal polymer films of Examples 1 to 5 and Comparative Examples 1 and 3 all had V1/V2 of 0.99 or more and had independent voids inside.

As shown in Table 2, the liquid crystal polymer films of Examples 1 to 5 contain liquid crystal polymers, have a polarized Raman spectral dichroic ratio of 0.7 to 1.3 on the surface and inside, and have voids inside. Since the surface roughness Ra is 20 nm to 200 nm and the average void diameter of the voids is 0.1 μm to 8.0 μm, cohesive peeling does not occur in the peeling test, and the relative permittivity and dielectric loss tangent are found to be low.

On the other hand, it was found that in Comparative Example 1, the surface roughness Ra exceeded 200 nm, and the dielectric constant and dielectric loss tangent were low.

In Comparative Example 3, since the average void diameter was larger than the film thickness, cohesive peeling occurred in the peeling test, and it was found that the dielectric constant and the dielectric loss tangent were high.

In Comparative Example 4, since the polarized Raman spectral dichroic ratio on the surface is as low as less than 0.7 and there is no void inside, cohesive peeling occurs in the peeling test, and the relative permittivity and dielectric loss tangent was found to be high.

As described above, the liquid crystal polymer film of the present disclosure contains a liquid crystal polymer, has a polarized Raman spectral dichroic ratio of 0.7 to 1.3 on the surface and inside, has voids inside, and has a surface roughness Ra of 20 nm. 200 nm, and the average void diameter of the voids is 0.1 μm to 8.0 μm, cohesive peeling is suppressed, and the dielectric constant and dielectric loss tangent are low. In addition, a flexible printed circuit board using the liquid crystal polymer film of the present disclosure and the flexible copper-clad laminate of the present disclosure has a smaller transmission loss in a high frequency band than conventional ones.

The disclosure of Japanese Patent Application No. 2019-174421 filed on September 25, 2019 is incorporated herein by reference in its entirety. In addition, all publications, patent applications and technical standards mentioned herein are to the same extent as if each individual publication, patent application and technical standard were specifically and individually noted to be incorporated by reference. , incorporated herein by reference.

Claims (8)

It contains a liquid crystal polymer, has a polarized Raman spectral dichroic ratio of 0.7 to 1.3 on the surface and inside, and has a void inside,
The surface roughness Ra is 20 nm to 200 nm,
The liquid crystal polymer film, wherein the average void diameter of the voids is 0.1 μm to 8.0 μm. 2. The liquid crystal polymer film according to claim 1, which has a peel adhesion strength of 0.5 N/mm or more in a 180[deg.] peel test. 3. The liquid crystal polymer film according to claim 1, wherein the porosity is 25% to 50%. The liquid crystal polymer film according to any one of claims 1 to 3, having a thickness of 5 µm to 50 µm. The liquid crystal polymer film according to any one of claims 1 to 4, wherein the voids are independent voids. 6. The liquid crystal polymer film according to any one of claims 1 to 5, which is used for a flexible printed circuit board. A flexible copper clad laminate comprising the liquid crystal polymer film according to any one of claims 1 to 6 and a copper foil disposed on at least one surface of the liquid crystal polymer film. A flexible printed circuit board formed by processing the copper foil in the flexible copper clad laminate according to claim 7.