WO2022169193A1 - High-thickness multilayer polyimide film and method for producing same - Google Patents

Abstract

The present invention provides: a multilayer polyimide film having a thickness of at least 50 μm, and including at least two polyimide unit films comprising a polyimide core layer and adhesive layers laminated on one or both surfaces of the polyimide core layer, wherein the at least two polyimide unit films are adhered and laminated through the adhesive layers; and a method for producing same.

Description

High-thickness multilayer polyimide film and manufacturing method thereof

The present invention relates to a high-thickness polyimide unit film, a multilayer polyimide film including the same, and a manufacturing method thereof.

Recently, electronic devices are becoming lighter, smaller, thinner, and highly integrated, and as a result, a lot of heat is generated in the electronic devices. Such heat may shorten the life of the product or cause malfunction or malfunction. Accordingly, thermal management of electronic devices is emerging as an important issue.

The graphite sheet has a higher thermal conductivity than a metal sheet such as copper or aluminum, and is attracting attention as a heat dissipation member for electronic devices. In particular, research on a high thickness graphite sheet advantageous in terms of heat capacity compared to a thin graphite sheet (eg, a graphite sheet having a thickness of about 40 μm or less) is being actively conducted.

The graphite sheet may be manufactured by various methods, for example, it may be prepared by carbonizing and graphitizing a polymer film. In particular, the polyimide film is in the spotlight as a polymer film for graphite sheet production due to its excellent mechanical, thermal dimensional stability, chemical stability, and the like.

In order to manufacture a high-thickness graphite sheet, a high-thickness polyimide film (for example, a polyimide film having a thickness of about 100 μm or more) must be prepared in advance. There is a problem in that it is difficult to manufacture a high-thickness polyimide film because it is difficult to uniformly harden the inside and the outside in a conventional method, and separation, bubbles, etc. occur. In addition, in the case of manufacturing a high-thickness polyimide film by bonding two or more polyimide films using an adhesive, layer separation due to heat resistance of the adhesive layer in the process of the polyimide film being subjected to high-temperature heat for carbonization and graphitization There is a problem in that it is impossible to manufacture a high-thickness graphite sheet because graphitization does not proceed in development or in the adhesive layer.

Alternatively, two or more thin graphite sheets can be laminated using a double-sided tape to manufacture a high-thickness graphite sheet, in this case, the double-sided tape interferes with thermal diffusion, thereby reducing the thermal conductivity of the entire laminated graphite sheet. .

[Prior art literature]

[Patent Literature]

(Patent Document 1) Republic of Korea Patent Publication No. 2017-0049912

An object of the present invention is to provide a high thickness polyimide unit film and a multilayer polyimide film including the same.

Another object of the present invention is to provide a method for producing a multilayer polyimide film.

In one embodiment of the present invention for achieving the above object, the slope ratio of the plastic deformation section to the slope of the elastic deformation section (the slope of the plastic deformation section / the slope of the elastic deformation section) is 0.025 or less,

A polyimide film is provided.

(However, the plastic deformation section corresponds to a section from an elongation of 30% to just before fracture in a stress-strain curve of the polyimide film, and the elastic deformation section has a strain of 3% It corresponds to the following section.)

Another embodiment of the present invention includes a polyimide core layer including the polyimide film and an adhesive layer laminated on one or both surfaces of the polyimide core layer,

The adhesive layer includes an imide group,

Thickness of 50 μm or more,

A polyimide unit film is provided.

Another embodiment of the present invention is manufactured by laminating two or more of the polyimide unit films,

A multilayer polyimide film is provided.

Another embodiment of the present invention comprises the steps of: forming two or more polyimide unit films in which an adhesive layer is laminated and integrated on one side or both sides of a polyimide core layer;

laminating the two or more polyimide unit films to be adhered through the adhesive layer; and

Including; thermocompression bonding the laminated two or more polyimide unit films;

The thickness of the polyimide unit film is 50㎛ or more,

A method for manufacturing a multilayer polyimide film is provided.

The present invention has the effect of providing a high thickness polyimide unit film, a multilayer polyimide film including the same, and a manufacturing method thereof.

1 is a stress-strain curve (SS-curve) of a polyimide film according to a manufacturing example of the present invention, and is a graph showing a plastic deformation section and an elastic deformation section.

2 is a schematic diagram of a multilayer polyimide film according to an embodiment of the present invention.

3 is a schematic diagram of a multilayer polyimide film according to an embodiment of the present invention.

4 is a photograph showing the firing results of the polyimide films of Preparation Examples 1 and 2 and Comparative Preparation Example 1 of the present invention.

Hereinafter, embodiments and examples of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily carry out the present invention. However, the present invention may be embodied in many different forms, and is not limited to the embodiments and examples described herein. Throughout this specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

In this specification, the singular expression includes the plural expression unless the context clearly dictates otherwise.

In interpreting the components, it is interpreted as including an error range even if there is no separate explicit description.

In the present specification, in "a to b" representing a numerical range, "to" is defined as ≥a and ≤b.

In the polyimide film according to an aspect of the present invention, the slope ratio of the plastic deformation section to the slope of the elastic deformation section (the slope of the plastic deformation section / the slope of the elastic deformation section) may be 0.025 or less, preferably 0.023 or less. .

The plastic deformation section corresponds to a section from an elongation of 30% to just before fracture in a stress-strain curve (SS-curve) of the polyimide film shown in FIG. 1, and the elastic deformation section is It corresponds to a section in which the strain is 3% or less.

Meanwhile, the ratio of the slope of the plastic deformation section to the slope of the elastic deformation section of the polyimide film (the slope of the plastic deformation section/the slope of the elastic deformation section) of the polyimide film may be 0.01 or more.

In one embodiment, the slope of the plastic deformation section of the polyimide film may be 0.05 GPa or less.

Meanwhile, a slope of the plastic deformation section of the polyimide film may be 0.020 GPa or more. The slope of the plastic deformation section of the polyimide film may be preferably 0.027 GPa or more, more preferably 0.030 GPa or more.

In addition, the slope of the elastic deformation section of the polyimide film may be 2.1 GPa or more. The slope of the elastic deformation section of the polyimide film may be preferably 2.11 GPa or more.

Meanwhile, the slope of the elastic deformation section of the polyimide film may be 3.0 GPa or less.

When the ratio of the plastic deformation section to the slope of the elastic deformation section of the polyimide film and/or the plastic deformation section slope of the polyimide film exceeds or falls below the above range, firing (graphitization) for manufacturing the graphite sheet is easy may not

That is, since the multilayer polyimide film produced by laminating polyimide unit films is very thick, firing (graphitization) is not easy and the manufacture of graphite sheets is difficult, so it is necessary to use a polyimide core layer that is easy to bake there is

In order to facilitate firing, it is necessary to suppress the imidization progress of the polyimide to be used as the core layer, which can be achieved by adjusting the amount of heat in the polyimide production.

In one embodiment, the tensile strength of the polyimide film may be 200 MPa or less, preferably 195 MPa or less.

In addition, the tensile strength of the polyimide film may be 170 MPa or more.

This is because, as a result of adjusting the amount of heat to facilitate firing, the tensile strength of the polyimide film is affected, and the tensile strength is lowered.

The dianhydride monomer for preparing the polyimide film of the present invention is pyromellitic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride , 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 2,3,3',4-biphenyltetracarboxylic dianhydride, 3, 3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, bis( 3,4-dicarboxyphenyl)propane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis( 2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)ethane dianhydride, oxydiphthalic dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, p-phenylene bis(trimellitic monoesteric anhydride), ethylenebis(trimellitic monoesteric anhydride), bisphenol A bis(trimellitic monoesteric anhydride), or a derivative thereof, or a combination thereof, and a diamine As a monomer, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-oxydianiline, 3,4'-oxydianiline, 1,3-bis(4-aminophenoxy) C)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, p-phenylene Diamine, m-phenylenediamine, 4,4'-diaminodiphenylpropane, 4,4'-methylenedianiline, 3,3'-methylenedianiline, benzidine, 3,3'-dichlorobenzidine, 4,4 '-diaminodiphenylsulfide, 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenyl ether, 3,3'-diaminodi Phenyl ether, 3,4'-diaminodiphenyl ether, 1,5-diaminonaphthalene, 4,4'-diaminodiphenyldiethylsilane, 4,4'-diaminodiphenylsilane, 4,4' -diaminodiphenylethylphosphine oxide, 4,4'-diaminodiphenylN-methylamine, 4,4'-diaminodiphenylN-phenylamine, 1,4-diaminobenzene (p-phenyl lendiamine), 1,3-diaminobenzene, 1,2-diaminobenzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, or derivatives thereof, or combinations thereof may be used. can

A polyimide unit film according to another aspect of the present invention includes a polyimide core layer including the polyimide film, and an adhesive layer laminated on one or both surfaces of the polyimide core layer, wherein the adhesive layer is already It contains a group, and the thickness of the polyimide unit film may be 50 μm or more.

For example, the polyimide unit film may have a thickness of 50 μm to 500 μm, for example 100 μm to 300 μm, and for another example 125 μm to 250 μm, but is not limited thereto.

In one embodiment, in the polyimide unit film, a ratio of the thickness of the polyimide core layer to the thickness of the adhesive layer may be 1:0.004 to 1:0.095.

That is, when the polyimide unit film has an adhesive layer laminated on only one surface of the polyimide core layer, a ratio of the thickness of the polyimide core layer to the thickness of the adhesive layer may be 1:0.004 to 1:0.095.

In addition, when the polyimide unit film has adhesive layers laminated on both sides of the polyimide core layer, the ratio of the thickness of the polyimide core layer to the thickness of the adhesive layer (the sum of the thicknesses of the adhesive layers laminated on both sides) is 1 :0.008 to 1:0.19.

In one embodiment, the glass transition temperature (Tg) of the adhesive layer may be 300 ℃ or less, and the polyimide core layer may have a glass transition temperature (Tg) of 350 ℃ or more.

In particular, the polyimide core layer may include a non-thermoplastic polyimide, and the adhesive layer may include a thermoplastic polyimide. Preferably, the polyimide core layer is made of only a non-thermoplastic polyimide, and the adhesive layer is a thermoplastic polyimide. It can be done with only mids.

In one embodiment, the polyimide core layer and the adhesive layer may be formed of a dianhydride monomer and a diamine monomer. For example, the polyimide core layer and the adhesive layer may be prepared by imidizing a polyamic acid formed by reaction of a dianhydride monomer and a diamine monomer. The types of dianhydride and diamine monomers usable for forming the polyimide core layer and the adhesive layer may be the above-described dianhydride monomers and diamine monomers, but are not particularly limited thereto, and are not particularly limited in the field of polyimide film production. Various monomers used as can be used.

For example, the polyimide core layer may be formed by reacting 100 mol% of pyromellitic dianhydride (PMDA) as a dianhydride monomer and 100 mol% of 4,4' oxydianiline (ODA) as a diamine monomer. In addition, in the adhesive layer, 100 mol% of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) as a dianhydride monomer and 100 mol% of 4,4' oxydianiline (ODA) as a diamine monomer are reacted. It can be formed by

For example, pyromellitic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3',4,4'-ratio as the dianhydride monomer for forming the polyimide core layer and the adhesive layer Phenyltetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 2,3,3',4-biphenyltetracarboxylic acid Dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 3,4,9,10-perylenetetracarboxylic acid Dianhydride, bis(3,4-dicarboxyphenyl)propane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)ethane dianhydride, oxydiphthalic dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride , p-phenylenebis(trimellitic monoesteric anhydride), ethylenebis(trimellitic monoesteric anhydride), bisphenol Abis(trimellitic monoesteric anhydride), or a derivative thereof, or a combination thereof As the diamine monomer, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-oxydianiline, 3,4'-oxydianiline, 1,3-bis(4 -Aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, p -phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylpropane, 4,4'-methylenedianiline, 3,3'-methylenedianiline, benzidine, 3,3'-dichlorobenzidine, 4,4'-diaminodiphenylsulfide, 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenyl ether, 3,3'- Diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,5-diaminonaphthalene, 4,4'-diaminodiphenyldiethylsilane, 4,4'-diaminodiphenylsilane, 4 , 4'-diaminodiphenylethyl phosphine oxide, 4,4'-diaminodiphenyl N-methylamine, 4,4'-diaminodiphenyl N-phenylamine, 1,4-diamino benzene (p-phenylenediamine), 1,3-diaminobenzene, 1,2-diaminobenzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, or a derivative thereof, or Combinations of these may be used.

In one embodiment, the non-thermoplastic As a dianhydride monomer for forming the polyimide core layer, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4-biphenyltetracarboxylic dianhydride , oxydiphthalic anhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride or a combination thereof is used, and as a diamine monomer, 4, 4'-oxydianiline, 3,4'-oxydianiline, p-phenylenediamine, m-phenylenediamine, 4,4'-methylenedianiline, 3,3'-methylenedianiline, or a combination thereof In this case, it is possible to form a polyimide layer having excellent orientation, and thus a graphite sheet having excellent thermal conductivity during carbonization and graphitization may be formed, but the present invention is not limited thereto.

In one embodiment, the thermoplastic polyimide As a dianhydride monomer for forming the adhesive layer, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4-biphenyltetracarboxylic dianhydride, 3,3',4,4 '-benzophenonetetracarboxylic dianhydride or a combination thereof is used, and as a diamine monomer, 4,4'-oxydianiline, 3,4'-oxydianiline, 1,3-bis(4-aminophenoxy) is used. benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, or a combination thereof may be used. have.

For example, the polyimide core layer may be formed by reacting 100 mol% of pyromellitic dianhydride (PMDA) as a dianhydride monomer and 100 mol% of 4,4' oxydianiline (ODA) as a diamine monomer. In addition, in the adhesive layer, 100 mol% of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) as a dianhydride monomer and 100 mol% of 4,4' oxydianiline (ODA) as a diamine monomer are reacted. It can be formed by

In one embodiment, any method may be applied to the production of the polyimide unit film, as long as it is a known film lamination method.

For example, a coating method, a bonding sheet method, a co-extrusion method, etc. may be applied. The coating method is a method of manufacturing a polyimide unit film by forming an adhesive layer to a certain thickness on a polyimide core layer prepared by a conventional method, and then drying it.

And, the bonding sheet method is a method of manufacturing a polyimide unit film by simultaneously injecting a polyimide core film and an adhesive layer film (bonding sheet) made in the form of a sheet into a calendaring process.

In addition, the co-extrusion method is a method of manufacturing a polyimide unit film by simultaneously forming an adhesive layer and a polyimide core layer using a co-extrusion die in the step of casting a polyamic acid solution on a metal support layer.

The multilayer polyimide film according to another aspect of the present invention may be manufactured by laminating two or more polyimide unit films.

The thickness of the multilayer polyimide film can be easily controlled by adjusting the thickness (eg, the thickness of the polyimide core layer, the thickness of the adhesive layer) and the number of the laminated polyimide unit film. For example, the multilayer polyimide film may include two or more polyimide unit films (eg, 2, 3, 4, 5, 6, 7, 8, 9) to satisfy a predetermined thickness. 10, 11, 12, 13, 14 or 15 or more), another example 2 to 1,000, another example 2 to 100, another example 2 to 50, for example, 2 to 10 may be stacked to form.

That is, the multilayer polyimide film includes two or more polyimide unit films including a polyimide core layer and an adhesive layer laminated on one or both surfaces of the polyimide core layer, wherein the two or more polyimide unit films may be adhesively laminated through the adhesive layer.

For example, in the case of a thermoplastic polyimide layer, the adhesive layer can be easily adhered by thermocompression bonding or the like, and has excellent adhesive strength.

In one embodiment, the thickness of the multilayer polyimide film may be 100㎛ or more.

For example, the multilayer polyimide film may have a thickness of 100 μm to 20,000 μm, for example 150 μm to 2,000 μm, and for another example 200 μm to 1,000 μm, but is not limited thereto.

In one embodiment, each polyimide unit film included in the multilayer polyimide film may be the same as or different from each other. For example, each polyimide unit film may have the same or different polyimide core layer and/or adhesive layer material (eg, polyimide precursor component, component content), thickness, and the like.

In addition, when the polyimide unit film is laminated on both sides of a polyimide core layer made of non-thermoplastic polyimide to have an adhesive layer including a thermoplastic polyimide layer, the thermoplastic polyimide layer of each adhesive layer may also be the same or different from each other.

In addition, the non-thermoplastic polyimide layer and/or the thermoplastic polyimide layer included in the polyimide unit film may be formed of a single layer or a plurality of layers.

In one embodiment, the thermoplastic polyimide layer included in each polyimide unit film may be of the same material, and in this case, the adhesion between the thermoplastic polyimide layers is more excellent, and the peeling prevention effect during the post-processing process is more excellent. However, the present invention is not limited thereto.

2 schematically shows a multilayer polyimide film 100 according to an embodiment of the present invention. Referring to FIG. 2 , the multilayer polyimide film 100 is a polyimide including polyimide core layers 111 and 121 and adhesive layers 112 and 122 laminated on one surface of the polyimide core layers 111 and 121 . It may include unit films 110 and 120, and optionally a polyimide unit film including a polyimide core layer between the polyimide unit films 110 and 120 and an adhesive layer laminated on both surfaces of the polyimide core layer. (not shown) may further include one or more (eg, 2, 3, 4, 5, 6, 7, 8, 9, or 10 or more).

For example, the multilayer polyimide film may include a polyimide core layer, and two first polyimide unit films including an adhesive layer laminated on one surface of the polyimide core layer, and a polyimide core layer, and the polyimide core layer. at least one second polyimide unit film including an adhesive layer laminated on both sides, wherein the at least one second polyimide unit film is interposed between the two first polyimide unit films, wherein the first polyimide The unit film and the second polyimide unit film may be adhesively laminated through an adhesive layer included in the first polyimide unit film and the second polyimide unit film.

3 schematically shows a multilayer polyimide film 200 according to another embodiment of the present invention. Referring to FIG. 3 , the multilayer polyimide film 200 is polyimide including polyimide core layers 211 and 221 and adhesive layers 212 and 222 laminated on both surfaces of the polyimide core layers 211 and 221 . It may include unit films 210 and 220, and optionally a polyimide unit film (not shown) including a polyimide core layer between the polyimide unit films 210 and 220 and an adhesive layer on both sides of the polyimide core layer. city) may further include one or more (eg, 2, 3, 4, 5, 6, 7, 8, 9 or 10 or more).

In one embodiment, the adhesive force between the laminated polyimide unit films of the multilayer polyimide film may be 0.3 kgf / cm or more, for example, 0.5 kgf / cm or more, for another example, 0.6 kgf / cm or larger.

Meanwhile, the adhesive force between the laminated polyimide unit films of the multilayer polyimide film may be 1.5 kgf/cm or less.

In one embodiment, when the multilayer polyimide film is heated at 600° C. or higher for 1 hour or less, interlayer separation may not occur between the laminated polyimide unit films, for example, interlayer separation may not occur. The heating time may be 50 minutes or less, for example 30 minutes or less.

In addition, the temperature at which the interlayer separation may not occur between the laminated polyimide unit films may be, for example, 650°C or higher, for example, 700°C or higher.

On the other hand, the temperature at which interlayer separation does not occur between the stacked polyimide unit films may be 3,000° C. or less.

In one embodiment, the multilayer polyimide film may be used for manufacturing a graphite sheet.

The multilayer polyimide film has excellent adhesion between the polyimide unit films, so that a high-thickness graphite sheet having excellent thermal conductivity can be manufactured without layer separation at the adhesive interface during carbonization and graphitization of the multilayer polyimide film.

When the multilayer polyimide film is used for manufacturing a graphite sheet, the polyimide unit film may further include an inorganic filler, preferably a sublimable inorganic filler.

Here, the 'sublimable inorganic filler' may mean an inorganic filler that is sublimated by heat during carbonization and/or graphitization processes in the manufacture of graphite sheets. When the polyimide film contains the sublimable inorganic filler, voids are formed in the graphite sheet by the gas generated through sublimation of the sublimable inorganic filler during the manufacture of the graphite sheet, thereby exhausting the sublimation gas generated during the manufacture of the graphite sheet It is possible to obtain a graphite sheet of good quality by smoothly forming the graphite sheet, as well as improve the flexibility of the graphite sheet to ultimately improve the handleability and formability of the graphite sheet. Examples of the sublimable inorganic filler include, but are not limited to, calcium carbonate, dicalcium phosphate, barium sulfate, and the like.

The average particle diameter (D ₅₀ ) of the sublimable inorganic filler may be 0.05 μm to 5.0 μm (eg, 0.1 μm to 4.0 μm), and a good quality graphite sheet can be obtained in the above range, but is not limited thereto.

The content of the sublimable inorganic filler may be 0.001 to 0.5 parts by weight based on 100 parts by weight of the polyimide film, and a good quality graphite sheet may be obtained in the above range, but is not limited thereto.

In one embodiment, in the polyimide unit film, a sublimable inorganic filler may be included in both the polyimide core layer and the adhesive layer. According to another embodiment, the adhesive layer may include the sublimable inorganic filler and the polyimide core layer may not include the sublimable inorganic filler, or vice versa.

A method of manufacturing a multilayer polyimide film according to another aspect of the present invention comprises: forming two or more polyimide unit films in which an adhesive layer is laminated and integrated on one or both surfaces of a polyimide core layer; laminating the two or more polyimide unit films to be adhered through the adhesive layer; and thermocompression bonding the laminated at least two polyimide unit films, wherein the polyimide unit film has a thickness of 50 μm or more, and the polyimide core layer may include the polyimide film. have.

First, a polyimide unit film in which an adhesive layer is laminated and integrated on one or both surfaces of a polyimide core layer can be formed by a known film lamination method.

The polyimide unit film is, for example, prepared by preparing a non-thermoplastic polyimide layer precursor composition as a polyimide core layer, preparing a thermoplastic polyimide layer precursor composition as an adhesive layer, and preparing the non-thermoplastic polyimide layer precursor composition and the thermoplastic polyimide The layer precursor composition may be prepared in the form of a film of two or more layers on a support and dried to form a gel film, and may be prepared by heat-treating the gel film.

The non-thermoplastic polyimide layer precursor composition may be prepared, for example, by mixing a solvent, a diamine monomer, and a dianhydride monomer to form a polyamic acid solution, optionally including a sublimable inorganic filler in the polyamic acid solution; It may further comprise adding a dehydrating agent and/or an imidizing agent. The thermoplastic polyimide layer precursor composition may be prepared, for example, by mixing a solvent, a diamine monomer, and a dianhydride monomer to form a polyamic acid solution, and optionally a sublimable inorganic filler, a dehydrating agent in the polyamic acid solution and/or adding an imidizing agent. See above for diamine monomers, dianhydride monomers and sublimable inorganic fillers.

The solvent is not particularly limited as long as it can dissolve the polyamic acid. For example, the solvent may include an aprotic polar solvent. Examples of the aprotic polar solvent include amide solvents such as N,N'-dimethylformamide (DMF) and N,N'-dimethylacetamide (DMAc), and phenolic solvents such as p-chlorophenol and o-chlorophenol. solvent, N-methyl-pyrrolidone (NMP), gamma butyrolactone (GBL), Diglyme, and the like, and these may be used alone or in combination of two or more. In some cases, the solubility of the polyamic acid may be adjusted by using an auxiliary solvent such as toluene, tetrahydrofuran (THF), acetone, methyl ethyl ketone (MEK), methanol, ethanol, and water.

According to one embodiment, the polyamic acid solution has a solid content, i.e., the weight percentage of the diamine monomer and the dianhydride monomer relative to the total weight of the diamine monomer, the dianhydride monomer and the solvent, for example 5 to 35% by weight, another example For example, it may be 10 to 30% by weight. In the above range, the polyamic acid solution may have a suitable molecular weight and viscosity to form a film, but is not limited thereto.

According to one embodiment, the polyamic acid solution for forming the non-thermoplastic polyimide layer may have a viscosity of 100,000 cP to 500,000 cP at 23°C. In the above range, while the polyamic acid has a predetermined molecular weight, processability may be excellent when forming a polyimide film. Here, 'viscosity' may be measured using a HAAKE Mars viscometer. For example, the viscosity of the polyamic acid solution may be 150,000 cP to 450,000 cP at 23° C., for example, 200,000 cP to 400,000 cP, for another example, 220,000 cP to 350,000 cP, but is not limited thereto.

According to one embodiment, the polyamic acid solution for forming the thermoplastic polyimide layer may have a viscosity of 1,000 cP to 500,000 cP at 23°C. While the polyamic acid has a predetermined molecular weight within the above range, the polyimide film may have excellent processability when forming a film, and thermocompression bonding may be possible under an appropriate temperature and pressure. Here, 'viscosity' may be measured using a HAAKE Mars viscometer. For example, the viscosity of the polyamic acid solution may be 1,000cP to 100,000cP at 23° C., for example, 1,000cP to 50,000cP, for another example, 5,000cP to 50,000cP, but is not limited thereto.

According to one embodiment, the polyamic acid for forming the non-thermoplastic polyimide layer may have a weight average molecular weight of 50,000 g/mol to 500,000 g/mol. It may be advantageous to manufacture a graphite sheet having better thermal conductivity in the above range. Here, the 'weight average molecular weight' may be measured using gel chromatography (GPC) and using polystyrene as a standard sample. For example, the weight average molecular weight of the polyamic acid may be 150,000 g/mol to 500,000 g/mol, for example, 100,000 g/mol to 400,000 g/mol, but is not limited thereto.

According to one embodiment, the polyamic acid for forming the thermoplastic polyimide layer may have a weight average molecular weight of 5,000 g/mol to 500,000 g/mol, but is not limited thereto. It may be advantageous to manufacture a graphite sheet having better thermal conductivity in the above range. Here, the 'weight average molecular weight' may be measured using gel chromatography (GPC) and using polystyrene as a standard sample.

The dehydrating agent promotes a ring closure reaction through dehydration action on polyamic acid, for example, aliphatic acid anhydride, aromatic acid anhydride, N,N'-dialkylcarbodiimide, halogenated lower aliphatic halide, halogenated lower fatty acid anhydride , arylphosphonic acid dihalide, thionyl halide, and the like, and these may be used alone or in combination of two or more. Among these, aliphatic acid anhydrides, such as acetic anhydride, propionic anhydride, and lactic anhydride, can be used individually or in mixture of 2 or more types from a viewpoint of availability and cost. The dehydrating agent may be added in an amount of 0.5 mol to 5 mol (eg, 1 mol to 4 mol) based on 1 mol of the amic acid group in the polyamic acid. However, the present invention is not limited thereto.

The imidizing agent promotes the ring closure reaction with respect to the polyamic acid, and for example, an aliphatic tertiary amine, an aromatic tertiary amine, and a heterocyclic tertiary amine may be used. Among them, a heterocyclic tertiary amine can be used from the viewpoint of reactivity as a catalyst. Examples of the heterocyclic tertiary amine include quinoline, isoquinoline, β-picoline, pyridine, and the like, and these may be used alone or in combination of two or more. The imidizing agent may be added in an amount of 0.05 mol to 3 mol (eg, 0.2 mol to 2 mol) based on 1 mol of the amic acid group in the polyamic acid. It may be advantageous, but is not limited thereto.

Thereafter, the non-thermoplastic polyimide layer precursor composition and the thermoplastic polyimide layer precursor composition may be prepared in the form of two or more layers on a support and dried to form a gel film.

Any known manufacturing method may be applied to the production of a film shape of two or more layers. For example, a coating method, a bonding sheet method, a co-extrusion method, etc. may be applied.

In particular, in the case of manufacturing using co-extrusion, the non-thermoplastic polyimide layer precursor composition and the thermoplastic polyimide layer precursor composition are simultaneously supplied to an extruder having a die for extrusion molding of two or more layers, and the two compositions are supplied from the outlet of the die. can be co-extruded into a film shape of two or more layers and dried to prepare a gel film.

More specifically, the non-thermoplastic polyimide layer precursor composition and the thermoplastic polyimide layer precursor composition are simultaneously supplied to a die for molding with two or more layers, and the two compositions discharged from the die for extrusion molding with two or more layers are continuously applied on a support. After making a film shape, heat drying (for example, 30° C. to 300° C.) to prepare a self-supporting gel film, and after separating the gel film from the support, high temperature (eg, 50° C. to 700° C.) °C), a polyimide film can be obtained. As a die for molding two or more layers, various known structures may be used, and for example, a T die for manufacturing a multilayer film (eg, a feed block T die or a multi-manifold T die) may be used.

According to one embodiment, the non-thermoplastic polyimide layer and the thermoplastic polyimide layer of the polyimide unit film may be in direct contact. Here, 'direct contact' may mean that another layer is not interposed between the non-thermoplastic polyimide layer and the thermoplastic polyimide layer.

A glass plate, an aluminum foil, an endless stainless belt, a stainless drum etc. are mentioned as a support body. Drying is, for example, 30 ℃ to 300 ℃ (eg, 80 ℃ to 200 ℃, for example, 100 ℃ to 180 ℃, another example 100 ℃ to be carried out at a temperature of 150 ℃), but , but is not limited thereto. The drying time may be, for example, 1 minute to 10 minutes, for example 2 minutes to 7 minutes, and for another example 2 minutes to 5 minutes, but is not limited thereto.

In some cases, it may include stretching the gel film in order to control the thickness and size of the finally obtained polyimide unit film and to improve orientation, and stretching is performed in at least one of MD (machine direction) and TD (transverse direction). It can be done in one direction. This stretching process should be performed at a low temperature of less than 50 degrees in order to form a smooth alignment of the polymer. This is because the imidization reaction is accelerated at a temperature of 50°C or higher, and the orientation of the polymer is disturbed.

Thereafter, the gel film may be heat-treated to prepare a polyimide unit film. Most of the amic acid groups remaining in the gel film are imidized by heat treatment of the gel film to obtain a polyimide film. The heat treatment temperature is 50° C. to 700° C., for example 150° C. to 600° C., for example 200° C. to 600° C., for another example 350° C. to 500° C., for another example 400° C. to 450° C. However, the present invention is not limited thereto. The heat treatment time may be, for example, 1 minute to 20 minutes, for example 1 minute to 10 minutes, and for another example 2 minutes to 8 minutes, but is not limited thereto.

Next, two or more polyimide unit films may be laminated so that they can be adhered through an adhesive layer (eg, a thermoplastic polyimide layer). More specifically, each polyimide unit film may be laminated so that the adhesive layers face each other.

Next, the laminated two or more polyimide unit films may be thermocompression-bonded. Thermocompression bonding may be performed, for example, at a pressure of 0.1 MPa to 30 MPa and a temperature of 250° C. to 450° C. for 10 seconds to 150 seconds, but is not limited thereto.

According to one embodiment, the thermoplastic polyimide layers of the polyimide unit film (for example, when two polyimide unit films are included, the thermoplastic polyimide layer of one polyimide unit film and the other one polyimide unit) The thermoplastic polyimide layers of the film) may be in direct contact with each other.

The multilayer polyimide film prepared as described above is adhesively laminated through the adhesive layer by thermocompression bonding two or more polyimide unit films in which an adhesive layer is laminated and integrated on one or both sides of the polyimide core layer, whereby the polyimide unit films are excellent It can be adhered by adhesive force.

Such excellent adhesion can be converted into a high-thickness graphite sheet having excellent thermal conductivity without layer separation at the bonding interface during graphitization and/or when the multilayer polyimide film is carbonized for graphite sheets.

According to another aspect of the present invention, there is provided a graphite sheet prepared from the above-described multilayer polyimide film, or the multilayer polyimide film prepared by the above-described manufacturing method. This graphite sheet is 50 μm or more, for example 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or 200 μm or more, for example 50 μm to 4,000 μm, another example 50 μm. It may have excellent thermal conductivity while having a thickness of about 500 μm.

According to one embodiment, the graphite sheet has a thermal conductivity of 500W/m·K or more (eg, 500W/m·K, 600W/m·K, 700W/m·K, 800W/m·K, 900W/m ·K, 1,000W/m·K, 1,100W/m·K, 1,200W/m·K, 1,300W/m·K, 1,400W/m·K, or 1,500W/m·K or more). For example, the thermal conductivity of the graphite sheet may be 500W/m·K to 2,000W/m·K, for example, 1,000W/m·K to 2,000W/m·K, but is not limited thereto.

The above-mentioned graphite sheet may be manufactured by various methods commonly used in the field of manufacturing the graphite sheet. For example, the graphite sheet may be produced by carbonizing and graphitizing the above-described multilayer polyimide film.

'Carbonization' is a process of thermally decomposing the polymer chain of a polyimide film to form a preliminary graphite sheet including an amorphous carbon body, an amorphous carbon body and/or an amorphous carbon body. For example, the polyimide film is heated under reduced pressure or in an inert gas atmosphere. It may include, but is not limited to, raising and maintaining the temperature over 10 hours to 30 hours from room temperature to a temperature ranging from 1,000°C to 1,500°C, which is the highest temperature under Optionally, pressure may be applied to the polyimide film using a hot press or the like during carbonization for high carbon orientation, and the pressure at this time is, for example, 5 kg/cm ² or more, for example, 15 kg/cm ² or more. , Another example may be 25kg/cm ² or more, but is not limited thereto.

Graphitization is a process of forming a graphite sheet by rearranging the carbon of an amorphous carbon body, an amorphous carbon body, and/or an amorphous carbon body, for example, a preliminary graphite sheet, optionally under an inert gas atmosphere from room temperature to the highest temperature of 2,500 It may include, but is not limited to, raising and maintaining the temperature over 2 to 30 hours to a temperature in the range of ℃ to 3,000 ℃. Optionally, pressure may be applied to the preliminary graphite sheet using a hot press or the like during graphitization for high orientation of carbon, and the pressure at this time is, for example, 100 kg/cm ² or more, for example, 200 kg/cm ² Above, another example may be 300kg/cm ² or more, but is not limited thereto.

Hereinafter, the present invention will be described in more detail by way of examples. However, this is presented as a preferred example of the present invention, and it cannot be construed as limiting the present invention in any sense.

production example

205.0 g of dimethylformamide as a solvent was added to the reactor, and the temperature was adjusted to 20°C. Here, 21.5 g of 4,4' oxydianiline (ODA) was added as a diamine monomer, and then 23.4 g of pyromellitic dianhydride (PMDA) was added as a dianhydride monomer to prepare a polyamic acid solution having a viscosity of 230,000 cP. . Subsequently, in the prepared polyamic acid solution, 39.5 g of acetic anhydride as a dehydrating agent, 4.8 g of β-picoline as an imidizing agent, 0.12 g of dibasic calcium phosphate (average particle diameter (D ₅₀ ): 2.5 μm) as a sublimable inorganic filler, and a solvent As a non-thermoplastic polyimide precursor solution was prepared by mixing 30.4 g of dimethylformamide.

A non-thermoplastic polyimide precursor solution prepared with a film forming apparatus was formed into a film on a SUS plate (100SA, Sandvik Corporation), and dried to prepare a gel film. After separating the prepared gel film from the SUS plate, heat treatment was performed to prepare a polyimide film.

At the time of the heat treatment, the polyimide films of Preparation Examples 1 and 2 and Preparation Comparative Example 1 by adjusting the amount of heat such that the highest temperature during the heat treatment was 510° C. in Preparation Example 1, 520° C. in Preparation Example 2, and 550° C. in Preparation Comparative Example 1 was prepared.

According to ASTM D882 of the polyimide films of Preparation Examples 1 and 2 and Preparation Comparative Example 1, the result of measuring the tensile properties is shown in a stress-strain diagram in which the vertical axis is the tensile strength (MPa) and the horizontal axis is the strain (%). curve), and after measuring the slope of the plastic deformation section and the slope of the elastic deformation section as shown in Table 1 below, the ratio was calculated.

The plastic deformation section corresponds to a section from an elongation of 30% to just before fracture in a stress-strain curve (SS-curve) of the polyimide film shown in FIG. 1, and the elastic deformation section is It corresponds to a section in which the strain is 3% or less.

The slope of each section was derived by calculating the amount of change in tensile strength/change in strain in each section, and at this time, for example, 3% of strain was calculated by changing it to 0.03.

	Plastic deformation section slope (GPa)	Elastic deformation section slope (GPa)	Plastic deformation section slope/ Elastic deformation section slope
Preparation Example 1	0.031	2.194	0.014
Preparation 2	0.048	2.118	0.023
Preparation Comparative Example 1	0.064	2.050	0.032

The polyimide films of Preparation Examples 1 and 2 were within the range of the slope ratio of the plastic deformation section to the slope of the elastic deformation section of the present application (the slope of the plastic deformation section / the slope of the elastic deformation section) and the slope of the plastic deformation section, Manufacturing Comparative Example 1 was out of the range of the slope ratio of the plastic deformation section to the slope of the elastic deformation section of the present application (the slope of the plastic deformation section / the slope of the elastic deformation section) and the slope of the plastic deformation section. The tensile strengths of the polyimide films of Examples 1 and 2 were 180 MPa and 191 Mpa, respectively, which corresponded to 200 MPa or less.

On the other hand, the tensile strength of the polyimide film of Preparation Comparative Example 1 was measured to be about 210 MPa.

After heating the polyimide films of Preparation Examples 1 and 2 and Preparation Comparative Example 1 to 1,200° C. at an average rate of 0.5° C./min under argon gas using an electric furnace, carbonization was carried out by maintaining at the temperature for 3 hours. Again, the temperature was raised to 2,800°C at an average rate of 1.0°C/min under argon gas, and the temperature was maintained at the temperature for 1 hour to proceed with graphitization.

As shown in Figure 4, the polyimide films of Preparation Examples 1 and 2 did not have a problem in graphitization (Figs. 4a and 4b, respectively), but the slope of the plastic deformation section and the slope of the plastic deformation section of the present application / slope of the elastic deformation section It was confirmed that the polyimide film of Preparation Comparative Example 1 outside the range of ? was not easily sintered due to excessive imidization, and was not graphitized properly (FIG. 4c).

Examples and Experimental Examples

Example 1

A non-thermoplastic polyimide precursor solution (used as a polyimide core layer) was prepared in the same manner as in the above-mentioned Preparation Example.

In a separate reactor, 217.5 g of dimethylformamide as a solvent was added, and the temperature was adjusted to 20°C. To this was added 4,4' oxydianiline (ODA) (13.2) g as a diamine monomer, followed by 19.3 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) as a dianhydride monomer was added to prepare a polyamic acid solution having a viscosity of 10,000 cP. Then, in the prepared polyamic acid solution, 23.2 g of acetic anhydride as a dehydrating agent, 3.0 g of β-picoline as an imidizing agent, 0.09 g of dibasic calcium phosphate (average particle diameter (D ₅₀ ): 1.5 μm) as a sublimable inorganic filler, and a solvent 18.6 g of dimethylformamide was mixed to prepare a precursor solution for an adhesive layer (thermoplastic polyimide layer).

A SUS plate (100SA) using a film forming device in which a three-layer extrusion die is installed so that the prepared precursor solution for the non-thermoplastic polyimide layer and the precursor solution for the thermoplastic polyimide layer are laminated and integrated with the thermoplastic polyimide layer on both sides of the non-thermoplastic polyimide layer. , Sandvik), and dried at 130° C. for 3 minutes to prepare a gel film. After separating the prepared gel film from the SUS plate, heat treatment at 420 to 550° C. for 4 minutes to form a thermoplastic polyimide layer/non-thermoplastic polyimide layer/thermoplastic polyimide layer (thickness: 3㎛/46㎛/3㎛) structure A polyimide unit film was prepared.

After laminating 4 prepared polyimide unit films, the multilayer polyimide film having a thickness of 202 μm was prepared by thermocompression bonding at 350° C. for 1 minute while applying a pressure of 20 MPa.

Experimental Example 1

Adhesion between polyimide unit films was measured using the multilayer polyimide film specimen prepared in Example 1. Adhesion was measured by peeling off one side at a speed of 25 mm/min at a 90° angle at a speed of 25 mm/min after preparing a 10 mm wide and 100 mm long specimen.

The average adhesive force between the laminated polyimide unit films was measured to be 0.63 kgf/cm.

Experimental Example 2

The glass transition temperature (Tg) of each of the polyimide core layer and the adhesive layer of the polyimide unit film of Example 1 was measured. For the glass transition temperature, the loss modulus and storage modulus of each layer were obtained using DMA, and the inflection point was measured as the glass transition temperature in their tangent graph.

As a result of the measurement, the glass transition temperature of the polyimide core layer was 395°C, and the glass transition temperature of the adhesive layer was 280°C.

Experimental Example 3

After heating the multilayer polyimide film specimen prepared in Example 1 at 700° C. for 30 minutes in a heating furnace, the separation between the layers was checked by SEM, but the separation between the layers was not confirmed.

Example 2

The multilayer polyimide film of Example 1 was heated to 1,200° C. at a rate of 1° C./min under nitrogen gas using an electric furnace, and then maintained at the temperature for 2 hours to carbonize. Then, after raising the temperature to 2,800 °C at a rate of 20 °C/min under argon gas, and graphitizing by maintaining at the temperature for 1 hour, the graphite having a thickness of 100 µm is passed through between the upper and lower two metal rolls at room temperature. A sheet was prepared.

Experimental Example 4

A specimen was prepared by cutting the graphite sheet of Example 2 into a circular shape having a diameter of 25.4 mm, and after measuring the thermal diffusivity by a laser flash method using a thermal diffusivity measuring instrument (LFA 467, Netsch Co.) for the specimen, the Thermal conductivity was obtained by multiplying the measured value of thermal diffusivity by density and specific heat (theoretical value: 0.85 kJ/kg·K). As a result, it was confirmed that the graphite sheet of Example 2 had excellent thermal conductivity of 1,030 W/m·K.

The embodiment of the manufacturing method of the present invention is only a preferred embodiment that allows those skilled in the art to easily practice the present invention, and is not limited to the above-described embodiment. The scope of the present invention is not limited. Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims. In addition, it will be apparent to those skilled in the art that various substitutions, modifications and changes are possible within the scope of the present invention, and it is apparent that parts easily changeable by those skilled in the art are also included in the scope of the present invention. .

The present invention has the effect of providing a high thickness polyimide unit film, a multilayer polyimide film including the same, and a manufacturing method thereof.

Claims (14)

1. The slope ratio of the plastic deformation section to the slope of the elastic deformation section (the slope of the plastic deformation section / the slope of the elastic deformation section) is 0.025 or less,

   polyimide film.

   (However, the plastic deformation section corresponds to a section from an elongation of 30% to just before fracture in a stress-strain curve of the polyimide film, and the elastic deformation section has a strain of 3% It corresponds to the following section.)
2. According to claim 1,

   The plastic deformation section slope is less than or equal to 0.05 GPa,

   polyimide film.
3. According to claim 1,

   The elastic deformation section slope is 2.1 GPa or more,

   polyimide film.
4. According to claim 1,

   Tensile strength of 200 MPa or less,

   polyimide film.
5. A polyimide core layer comprising the polyimide film of claim 1 and

   An adhesive layer laminated on one or both surfaces of the polyimide core layer,

   The adhesive layer includes an imide group,

   Thickness of 50 μm or more,

   Polyimide unit film.
6. 6. The method of claim 5,

   The thickness ratio of the polyimide core layer and the adhesive layer (thickness of the polyimide core layer: the thickness of the adhesive layer) is 1:0.004 to 1:0.095,

   Polyimide unit film.
7. 6. The method of claim 5

   The glass transition temperature (Tg) of the adhesive layer is 300 ℃ or less,

   The glass transition temperature (Tg) of the polyimide core layer is 350 ° C. or higher,

   The polyimide core layer includes a non-thermoplastic polyimide,

   The adhesive layer comprises a thermoplastic polyimide,

   Polyimide unit film.
8. 6. The method of claim 5,

   The polyimide core layer includes pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4-biphenyltetracarboxylic dianhydride, oxydiphthalic anhydride, dianhydride monomers including bis(3,4-dicarboxyphenyl)sulfone dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride or combinations thereof, and

   4,4'-oxydianiline, 3,4'-oxydianiline, p-phenylenediamine, m-phenylenediamine, 4,4'-methylenedianiline, 3,3'-methylenedianiline or these formed from diamine monomers comprising combinations,

   Polyimide unit film.
9. 6. The method of claim 5,

   The adhesive layer is 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride monomers, including dianhydrides or combinations thereof, and

   4,4'-oxydianiline, 3,4'-oxydianiline, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3- formed from diamine monomers comprising bis(3-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, or combinations thereof;

   Polyimide unit film.
10. Claims 5 to 9, prepared by laminating two or more polyimide unit films of any one of claims

    Multilayer polyimide film.
11. 11. The method of claim 10,

    Adhesion between the laminated polyimide unit films is 0.3 kgf / cm or more,

    Multilayer polyimide film.
12. 11. The method of claim 10,

    When heated above 600℃ for 1 hour or less,

    Interlayer separation does not occur between the laminated polyimide unit films,

    Multilayer polyimide film.
13. 11. The method of claim 10,

    For the manufacture of graphite sheets,

    Multilayer polyimide film.
14. forming two or more polyimide unit films in which an adhesive layer is laminated and integrated on one or both sides of the polyimide core layer;

    laminating the two or more polyimide unit films to be adhered through the adhesive layer; and

    Including; thermocompression bonding the laminated two or more polyimide unit films;

    The thickness of the polyimide unit film is 50 μm or more,

    The polyimide core layer comprises the polyimide film of claim 1,

    A method for producing a multilayer polyimide film.

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