CN113166446B

CN113166446B - Polyimide film with low dielectric constant and low hygroscopicity and preparation method thereof

Info

Publication number: CN113166446B
Application number: CN201980076632.7A
Authority: CN
Inventors: 白承烈; 李吉男; 崔祯烈
Original assignee: Polyimide Advanced Materials Co ltd
Current assignee: Polyimide Advanced Materials Co ltd
Priority date: 2018-11-20
Filing date: 2019-10-30
Publication date: 2023-07-07
Anticipated expiration: 2039-10-30
Also published as: KR20200058881A; KR102164463B1; CN113166446A; WO2020105888A1

Abstract

The invention relates to a preparation method of a polyimide film, which comprises the following steps: a step (a) of preparing a first polyamic acid by polymerizing an aromatic dianhydride monomer and an aromatic diamine monomer in a first organic solvent; a step (b) of preparing a second polyamic acid by polymerizing a dianhydride monomer and a diamine monomer, at least one of which is an aliphatic dianhydride monomer or an aliphatic diamine monomer, in a second organic solvent; a step (c) of preparing a third polyamic acid by copolymerizing the first polyamic acid and the second polyamic acid in a third organic solvent; step (d) of preparing a precursor composition comprising a third polyamic acid; and (e) imidizing the precursor composition after film formation on a support.

Description

Polyimide film with low dielectric constant and low hygroscopicity and preparation method thereof

Technical Field

The present invention relates to a polyimide film having a low dielectric constant and a low hygroscopicity, and a method for producing the same.

Background

In recent years, advanced information transmission technology is introduced to network these electronic devices and high performance and high functions of computers and communication devices are rapidly developing, and as a part thereof, with an increase in the amount of information transmission to communication apparatuses constituting these electronic devices or networks, high-frequency signals for speeding up processing and transmission technology are underway.

In the past, high-frequency signals of 1MHz or more have been mainly used for limited wireless communication such as airplane or satellite communication, but recently, also used in electronic devices such as cellular phones and wireless LANs, high-speed transmission electronic devices capable of high-speed communication using high-frequency signals of 10GHz or more have been actively developed due to demands for higher calculation speeds and communication speeds.

In order to realize such high-frequency high-speed communication, it is necessary to overcome the problem of signal delay or transmission loss occurring in elements of electronic equipment (e.g., circuit boards for high-speed transmission) mounted in a communication apparatus. Specifically, the signal delay (RC delay) is expressed as a product of capacitance (C) between metal lines and wiring resistance (R), which increases in proportion to the square root of the dielectric constant of an insulator, and according to recent trends of miniaturization and high integration of electronic devices, there is a problem such as further delay of the entire signal transmission due to propagation delay (propagation delay) or crosstalk noise (crosstalk noise). In addition, the transmission loss is divided into conductor loss and dielectric loss, which are proportional to the dielectric constant and dielectric loss tangent of the insulator, and increase with an increase in frequency.

That is, the high frequency characteristics of the electronic device for high-speed transmission are closely related to the dielectric characteristics of the insulating layer in particular. Therefore, the use of an insulating material having a very low dielectric constant is indispensable for high-frequency high-speed communication. Heretofore, a substrate using a fluororesin (PTFE) has been called a resin having excellent high-frequency characteristics among polymer materials, and this substrate was standardized in 1975 in the military specification and standard (Military Specifications and Standards, MILs) and used for aerospace, space and military applications. However, PTFE is a thermoplastic resin having a glass transition temperature close to room temperature, and therefore lacks thermal dimensional stability, and is poor in mechanical strength and thermal conductivity, and requires special plating pretreatment, and has problems in moldability (high temperature of 350 ℃ or higher) and workability.

Therefore, in recent years, the possibility of using polyimide resins for high-speed transmission electronic devices is being studied.

In general, a polyimide resin refers to a high heat resistant resin prepared by solution polymerization of aromatic dianhydride with aromatic diamine or aromatic diisocyanate to prepare a polyamic acid derivative, and then by ring dehydration at high temperature. Since it has very excellent chemical stability and an imide ring of a strong aromatic skeleton, it is a high molecular material having the highest heat resistance, chemical resistance, electrical insulation, chemical resistance and weather resistance among organic materials, and in particular, since the dielectric constant is relatively stable in all frequency ranges and has the advantage of high dielectric breakdown voltage, it has been attracting attention as an insulating material for high-speed communication electronic devices.

However, since polyimide itself has a high moisture absorption rate due to the nature of the material, there is a limit to the representation of a low dielectric constant in spite of the excellent physical properties as described above, and in order to overcome this problem, in recent years, high performance of polyimide has been actively studied, particularly low dielectric constant and low dielectric loss tangent as electrical characteristics corresponding to high frequencies.

For example, in order to lower the dielectric constant of polyimide resins, there have been proposed a polyimide composition of a fluorine-containing resin and a method for producing the same, in which an aromatic polyimide obtained from an aromatic tetracarboxylic acid component aromatic diamine component containing biphenyltetracarboxylic acid as a main component is uniformly dissolved in a soluble organic polar solvent in the presence of a surfactant compound having fluorine atoms in a fluorine-containing resin powder, and a polyimide containing a fluorine-containing surfactant or the like is added, and the dielectric constant or dielectric loss tangent can be lowered to some extent due to the action of the fluorine-containing resin, but the fluorine-containing surfactant or dispersant generally increases the dielectric constant and dielectric loss tangent, and it is difficult to sufficiently improve the electrical properties.

On the other hand, in order to lower the dielectric constant, a technique of simultaneously containing an aromatic polyimide and an aliphatic polyimide in a polyimide film molecule has been proposed, however, in the conventional polyimide production method, there is a limitation in simultaneously achieving excellent mechanical properties and thermal properties such as based on an aromatic main chain and physical properties such as low hygroscopicity based on an aliphatic main chain due to their structural characteristics when distinguishing the characteristics of the aromatic polyimide and the aliphatic polyimide.

In addition, although the aromatic monomer constituting the aromatic polyimide and the aliphatic monomer constituting the aliphatic polyimide have different reaction characteristics with respect to the solvent, they often are not used alone, and thus cause problems in the process.

Accordingly, there is a need to develop a method for producing a polyimide film capable of exhibiting a low dielectric constant return at a high frequency band (e.g., 10GHz or more) while maintaining excellent mechanical and thermal properties of polyimide, and a polyimide film produced by the production method.

Disclosure of Invention

Technical problem to be solved by the invention

The present invention is directed to a polyimide film exhibiting low dielectric constant and low hygroscopicity while maintaining excellent mechanical and thermal properties of polyimide, and a method for preparing the same.

According to an aspect of the present invention, a polyimide film preparation method is prepared by the steps of: a step of preparing a first polyamic acid by polymerizing an aromatic dianhydride monomer and an aromatic diamine monomer in a first organic solvent; and a step of preparing a second polyamic acid by polymerizing a dianhydride monomer and a diamine monomer in a second organic solvent, wherein at least one of the dianhydride monomer and the diamine monomer is an aliphatic dianhydride monomer or an aliphatic diamine monomer.

In this respect, the production method can provide a production method of a polyimide film which can effectively act to suppress the dielectric constant and hygroscopicity of a polyimide film and from which a polyimide film can be produced while achieving excellent mechanical properties, thermal characteristics and low hygroscopicity.

Finally, according to an aspect of the present invention, the problems of the prior art can be solved.

Therefore, it is a practical object of the invention to provide particular embodiments thereof.

Means for solving the technical problems

The present invention provides a method for preparing a polyimide film, comprising: a step (a) of preparing a first polyamic acid by polymerizing an aromatic dianhydride monomer and an aromatic diamine monomer in a first organic solvent; a step (b) of preparing a second polyamic acid by polymerizing a dianhydride monomer and a diamine monomer in a second organic solvent, wherein at least one of the dianhydride monomer and the diamine monomer is an aliphatic dianhydride monomer or an aliphatic diamine monomer; a step (c) of preparing a third polyamic acid by copolymerizing the first polyamic acid and the second polyamic acid in a third organic solvent; step (d) of preparing a precursor composition comprising a third polyamic acid; and (e) imidizing the precursor composition after film formation on a support.

The present invention also provides a polyimide film comprising a polyimide copolymer prepared by imidizing a polyamic acid copolymer, the polyimide copolymer comprising a first unit block which is a structure in which a first polyamic acid prepared by polymerization of an aromatic dianhydride monomer and an aromatic diamine monomer is imidized, and a second unit block which is a structure in which a second polyamic acid prepared by polymerization of a dianhydride monomer and a diamine monomer is imidized, and at least one of the dianhydride monomer and the diamine monomer is an aliphatic dianhydride monomer or an aliphatic diamine monomer.

The present invention can also provide an electronic device for high-speed transmission including the polyimide film.

ADVANTAGEOUS EFFECTS OF INVENTION

In the method for producing a polyimide film of the present invention, in order to effectively exhibit excellent characteristics possessed by each monomer, the method is divided into the following steps: a step of preparing a first polyamic acid by polymerizing an aromatic dianhydride monomer and an aromatic diamine monomer in a first organic solvent; and a step of preparing a second polyamic acid by polymerizing a dianhydride monomer and a diamine monomer in a second organic solvent, wherein at least one of the dianhydride monomer and the diamine monomer is an aliphatic dianhydride monomer or an aliphatic diamine monomer, whereby the polyimide film prepared can achieve low hygroscopicity while maintaining excellent mechanical properties and thermal properties.

In addition, the polyimide film according to the present invention has a dielectric constant of 3.2 or less at 10GHz, a moisture absorption rate of 1.5 wt% or less, a tensile strength of 4.2GPa or more, and a glass transition temperature (Tg) of 310 ℃ or more, and thus an electronic device for high-speed transmission including the polyimide film can realize high-speed communication at a high frequency of 10 GHz.

Detailed Description

Hereinafter, details for realizing the same are described in the present specification.

Before this, the terms or words used in the present specification and claims should not be construed as limited to general or dictionary meanings, and the inventors should appropriately interpret the concept of the terms so as to explain their invention in the best mode, and should be construed as meanings and concepts consistent with the technical spirit of the invention based on definable principles.

Therefore, it should be understood that the configuration of the embodiment described herein is only one of the most preferred embodiments of the present invention, does not represent the entire technical spirit of the present invention, and various equivalents and modifications may exist instead of them at the time of the present application.

In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise. It should be understood that in this specification the terms "comprises," "comprising," or "having" are intended to specify the presence of stated features, integers, steps, elements, or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.

As used herein, "dianhydride" is intended to include precursors or derivatives thereof which may not be technically dianhydride, but will still react with diamine to form a polyamic acid, and the polyamic acid may be converted back to polyimide.

"diamine" as used herein is intended to include precursors or derivatives thereof which may not be diamine in the art, but will still react with dianhydride to form a polyamic acid which again can be converted back to polyimide.

If an amount, concentration, or other value or parameter given herein is a range, preferred range, or an enumeration of preferred upper and lower limits, then any upper limit of any pair, whether ranges are separately disclosed or it is to be understood that all ranges formed by the preferred value and any lower limit or preferred value are specifically disclosed.

When numerical ranges are referred to herein, unless otherwise indicated, the ranges are intended to include the endpoints and all integers and fractions within the range.

It is intended that the scope of the invention is not limited to the specific values recited when defining a range.

< method for producing polyimide film >

The polyimide film preparation method according to the present invention comprises the steps of: a step (a) of preparing a first polyamic acid by polymerizing an aromatic dianhydride monomer and an aromatic diamine monomer in a first organic solvent; a step (b) of preparing a second polyamic acid by polymerizing a dianhydride monomer and a diamine monomer in a second organic solvent, wherein at least one of the dianhydride monomer and the diamine monomer is an aliphatic dianhydride monomer or an aliphatic diamine monomer; a step (c) of preparing a third polyamic acid by copolymerizing the first polyamic acid and the second polyamic acid in a third organic solvent; step (d) of preparing a precursor composition comprising a third polyamic acid; and (e) imidizing the precursor composition after film formation on a support.

In a specific example, the aromatic dianhydride monomer contains at least one selected from the group consisting of pyromellitic dianhydride (PMDA), biphenyl tetracarboxylic dianhydride (BPDA), oxydiphthalic anhydride (ODPA) and Benzophenone Tetracarboxylic Dianhydride (BTDA), and these may be used alone or in combination of two or more as needed.

In addition, the aromatic diamine monomer contains at least one selected from the group consisting of 4-phenylenediamine (PPD), 4' -Oxydiphenylamine (ODA), 3,4' -oxydiphenylamine, 4' -Methylenediphenylamine (MDA) and 1, 3-bis (4-aminophenoxy) benzene (TPE-R), and these may be used alone or in combination of two or more as needed.

The polyimide chain formed by imidizing the first polyamic acid, which is prepared by polymerizing an aromatic dianhydride monomer and an aromatic diamine monomer, may contain the structure derived from an aromatic monomer.

This will be described in more detail later, but the polyimide film according to the present invention can exhibit excellent mechanical and thermal properties as it is due to such an aromatic unit structure.

In another specific example, the aliphatic dianhydride monomer may include at least one selected from the group consisting of 1,2,4, 5-cyclohexane tetracarboxylic dianhydride (HPMDA), 2-bis [4- (3, 4 dicarboxyphenoxy) phenyl ] propane dianhydride (BPADA), bicyclo [2, 2] oct-7-ene-2,3,5, 6-tetracarboxylic dianhydride (BOCA), and cyclobutane-1, 2,3, 4-tetracarboxylic dianhydride (CBDA).

In addition, for example, the aliphatic diamine monomer may comprise Cyclohexanediamine (CHD), 2-bis [ (4-aminophenoxy) phenyl ] propane (BAPP), 2-bis [4- (4-aminophenoxyphenyl) ] Hexafluoropropane (HFBAPP), 4 '-Methylenedicyclohexylamine (MCA), 4' -methylenebis (2-methylcyclohexylamine) (MMCA), 1, 3-adamantanediamine (DAA), 3 '-diamino-1, 1' -diamantane (DADA), isophoronediamine, at least one of the group consisting of 4,4 '-diaminodicyclohexylmethane (4, 4' -diaminodicyclohexylmethane), 3 '-dimethyl-4, 4' -diaminodicyclohexylmethane (3, 3 '-dimethyl-4, 4' -diaminodicyclohexylmethane) and 3,3', 5' -tetramethyl-4, 4 '-diaminodicyclohexylmethane (3, 3',5 '-tetramethyl-4, 4' -diaminodicyclohexylmethane), and specifically, cyclohexanediamine (CHDA) may be used.

More specifically, the Cyclohexanediamine (CHDA) may be, for example, at least one selected from the group consisting of 1, 2-cyclohexanediamine (1, 2-cyclohexanediamine), 1, 3-cyclohexanediamine (1, 3-cyclohexanediamine), 1, 4-cyclohexanediamine, N '-dimethyl-1, 2-cyclohexanediamine (N, N' -dimethyl-1, 2-cyclohexanediamine), 4-methyl-1, 3-cyclohexanediamine (4-methyl-1, 3-cyclohexanediamine), (1 r,2 r) -N, N '-tetramethyl-1, 2-cyclohexanediamine ((1 r,2 r) -N, N' -tetramethyl-1, 2-cyclohexanediamine), and N, N '-dipropylcyclohexamethylenediamine (N, N' -dipropylcyclohexamethylenediamine).

The polyimide chain formed by imidizing the second polyamic acid, which is prepared by polymerizing an aliphatic dianhydride monomer or an aliphatic diamine monomer, may contain a structure derived from an aliphatic monomer.

The structure derived from the aliphatic monomer may be appropriately selected to have non-polarity, and a non-limiting example of the structure derived from the aliphatic monomer may be-CH ₃ 、-CF ₃ Chain aliphatic hydrocarbon groups and cyclic aliphatic hydrocarbon groups.

This will be described in more detail later, but the structure derived from such aliphatic monomer shows non-polarity, so that the polyimide film according to the present invention can show low hygroscopicity. On the other hand, since the structure derived from the aliphatic monomer is contained in the second polyamic acid, the proportion of the amide group that causes an increase in hygroscopicity can be relatively reduced, so that the moisture absorption rate of the polyimide film thus produced can be effectively reduced.

However, in order to reduce the moisture absorption rate as described above, it may be effective to increase the content of the structure derived from the aliphatic dianhydride monomer or the aliphatic diamine monomer, but as the structure derived from such aliphatic monomer increases, the polyimide film thus produced has a problem of deterioration in mechanical properties, and it is difficult to achieve a desired glass transition temperature level.

In addition, as in the conventional method for producing polyamic acid, for example, when polyamic acid is produced by adding an aromatic dianhydride monomer, an aromatic diamine monomer, an aliphatic dianhydride monomer, and an aliphatic diamine monomer at the same time, in the polyimide chain thus produced, a structure derived from an aromatic monomer capable of exhibiting excellent mechanical properties and thermal properties and a structure derived from an aliphatic monomer capable of exhibiting low moisture absorption rate are not generated, and thus there is a possibility that polyimide films exhibiting these physical properties at the same time cannot be produced.

On the other hand, in the case of the production method according to the present invention, in order to efficiently express the excellent properties of the respective monomers, the following steps are divided: a step of preparing a first polyamic acid by polymerizing an aromatic dianhydride monomer and an aromatic diamine monomer in a first organic solvent; and a step of preparing a second polyamic acid by polymerizing a dianhydride monomer and a diamine monomer in a second organic solvent, wherein at least one of the dianhydride monomer and the diamine monomer is an aliphatic dianhydride monomer or an aliphatic diamine monomer, whereby the film prepared can achieve low hygroscopicity while maintaining low mechanical properties and thermal properties.

In one specific example, the weight average molecular weight of the first and second polyamic acids can be 6000g/mole to 60000g/mole, specifically 7000g/mole to 20000g/mole, and more specifically 10000g/mole to 15000g/mole, and more specifically 12000g/mole to 15000g/mole.

When the weight average molecular weights of the first and second polyamic acids exceed the above-described range, the disadvantages of the structure derived from an aromatic monomer, for example, the disadvantages of high dielectric constant and high hygroscopicity, in the polyimide chain prepared therefrom, and the disadvantages of the structure derived from an aliphatic monomer, for example, the deterioration of mechanical properties and thermal properties, may be highlighted, and thus are not preferable.

In contrast, if the weight average molecular weights of the first and second polyamic acids are less than the above range, the conventional production method for producing polyamic acids as if the monomers were added, cannot simultaneously exhibit excellent mechanical and thermal properties of the structure derived from aromatic monomers of the polyimide chain produced therefrom, and low dielectric constant and low moisture absorption of the structure derived from aliphatic monomers, and thus are not preferable.

That is, the present invention is technically characterized in that, after polymerizing a first polyamic acid and a second polyamic acid to have predetermined molecular weights so as to highlight excellent properties of each structure derived from an aromatic monomer and each structure derived from an aliphatic monomer and so that no disadvantages occur, the first polyamic acid and the second polyamic acid are then polymerized to prepare a third polyamic acid and imidized thereto, thereby preparing a polyimide film.

In this case, the weight average molecular weight of the third polyamic acid may be 100000g/mole or more. More specifically, the weight average molecular weight of the third polyamic acid may be 100000g/mole to 200000g/mole.

When the weight average molecular weight of the third polyamic acid exceeds the above-mentioned range, an increase in viscosity of the precursor composition comprising the third polyamic acid is unavoidable because, in the preparation of the polyimide film, when the precursor composition is moved through a pipe, a higher pressure must be applied due to friction with the pipe, and thus the processing cost may be increased and the processing performance may be lowered. In addition, the higher the viscosity, the more time and cost may be required for the mixing process.

Further, the film forming process itself may not be performed due to the excessively high viscosity, and even if the film forming process may be performed, physical properties of the polyimide film prepared therefrom may be deteriorated, which is not preferable.

In contrast, when the weight average molecular weight of the third polyamic acid is less than the range, the effect of the present invention, which highlights the excellent physical properties of the first and second polyamic acids, cannot be exhibited.

Meanwhile, the first polyamic acid and the second polyamic acid can be prepared by mixing the first polyamic acid and the second polyamic acid at 8:2 to 6:4, in particular 7:3 to 6:4 to prepare a third polyamic acid.

At this time, when the molar ratio of the first polyamic acid and the second polyamic acid exceeds the above-described range, the content of the structure derived from the aliphatic monomer contained in the polyimide chain is relatively very low, and thus it may be difficult to exhibit low dielectric constant and low moisture absorption characteristics.

In contrast, when the molar ratio of the first polyamic acid to the second polyamic acid is smaller than the above range, the content of the structure derived from the aliphatic monomer contained in the polyimide chain prepared therefrom is too high, and thus the mechanical properties and thermal properties of the polyimide film may be deteriorated.

For example, the production of polyamic acid in the present invention has the following method:

(1) A method comprising placing the total amount of diamine monomer in a solvent, and then adding dianhydride monomer in a substantially equimolar manner to the diamine monomer to polymerize;

(2) A method comprising adding the total amount of the dianhydride monomer to a solvent, and then adding the diamine monomer in a substantially equimolar manner to the dianhydride monomer to polymerize the diamine monomer;

(3) After adding some components of the diamine monomer to the solvent, mixing some components of the dianhydride monomer in a proportion of about 95 to 105 mole% with respect to the reaction components, then adding the remaining diamine monomer components, and then the remaining dianhydride is a polymerization method in which the diamine monomer and the dianhydride monomer are substantially equimolar by adding the monomer components;

(4) A method in which a dianhydride monomer is added to a solvent, a part of components of a diamine compound is mixed at a ratio of 95 to 105 mol% with respect to the reaction components, then other dianhydride monomer components are added, and then the remaining diamine monomer components are added to polymerize the diamine monomer and the dianhydride monomer to substantially equimolar;

(5) As a method of forming the first composition by reacting some of the diamine monomer components and some of the dianhydride monomer components in a solvent so that any one is excessive, forming the second composition by reacting some of the diamine monomer components and some of the dianhydride monomer components in another solvent so that any one is excessive, then mixing the first and second compositions, and completing the polymerization, at this time, when the diamine monomer components are excessive in forming the first composition, the dianhydride monomer components are excessive in the second composition, when the dianhydride monomer components are excessive in the first composition, the diamine monomer components are excessive in the second composition, and a method of mixing the first and second compositions so that the total diamine monomer components and dianhydride monomer components used in these reactions are substantially equimolar post-polymerized.

The polymerization method may be applied to the polymerization of the first polyamic acid, the polymerization of the second polyamic acid, and the polymerization of the third polyamic acid, respectively.

The polymerization method is not limited to the above examples, and of course, any known method may be used.

Meanwhile, the first to third solvents used in the present invention are not particularly limited as long as they are organic solvents capable of dissolving the polyamic acid, but as an example, aprotic polar solvents (aprotic polar solvent) may be used.

As non-limiting examples of the aprotic polar solvent, an amide solvent (e.g., N '-Dimethylformamide (DMF), N' -dimethylacetamide (DMAc), etc.), a phenol-based solvent (e.g., p-chlorophenol, o-chlorophenol, etc.), N-methylpyrrolidone (NMP), γ -butyrolactone (GBL), and Diglyme (Diglyme), which may be used alone or in combination of two or more.

In some cases, the solubility of the polyamic acid can be controlled by using an auxiliary solvent such as toluene, tetrahydrofuran, acetone, methyl ethyl ketone, methanol, ethanol, and water.

In one example, the organic solvent which may be particularly preferably used for the first organic solvent and the third organic solvent may be an amide solvent N, N '-dimethylformamide and N, N' -dimethylacetamide.

In another example, the organic solvent that may be particularly preferably used for the second organic solvent may be N-methyl-pyrrolidone (NMP).

Meanwhile, a filler may be added to the "precursor composition preparation process" to improve various properties of the film, such as slidability, thermal conductivity, electrical conductivity, corona resistance, and ring hardness. The filler to be added is not particularly limited, and preferable examples include silica, titanium oxide, aluminum oxide, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, and mica.

The particle diameter of the filler is not particularly limited, and may be determined according to the nature of the film to be modified and the type of filler to be added. The average particle diameter is usually 0.05 to 20. Mu.m, preferably 0.1 to 10. Mu.m, more preferably 0.1 to 5. Mu.m, particularly preferably 0.1 to 3. Mu.m.

When the particle diameter is smaller than this range, the modifying effect is less likely to occur, whereas when it exceeds this range, the surface properties may be significantly impaired, or the mechanical properties may be significantly deteriorated.

The amount of filler to be added is not particularly limited, and may be determined according to the film properties to be modified, the particle diameter of the filler, and the like. In general, the filler is added in an amount of 0.01 to 10 parts by weight, preferably 0.01 to 5 parts by weight, more preferably 0.02 to 1 part by weight, relative to 100 parts by weight of the polyimide resin.

If the amount of the filler is less than this range, the modifying effect of the filler is hardly exhibited, and if it exceeds this range, the mechanical properties of the film may be significantly impaired. The method of adding the filler is not particularly limited, and a known method can be used.

As a method for preparing a polyimide film by imidizing the precursor composition prepared as described above, conventionally known methods may be used.

Examples of specific methods of such imidization include a thermal imidization method, a chemical imidization method, or a composite imidization method using a combination of a thermal imidization method and a chemical imidization method, which are described in more detail by way of the following non-limiting examples.

< thermal imidization method >

The thermal imidization method is a method of excluding a chemical catalyst and initiating imidization reaction by a heat source such as hot air or an infrared dryer, and may include: a process of drying the precursor composition to form a gel film; and the heat treatment of the gel film may include a process of obtaining a polyimide film.

Among them, a gel film can be understood as a film intermediate having self-supporting properties in an intermediate step of conversion from polyamic acid to polyimide.

In forming the gel film, the precursor composition is cast in a film form on a support such as a glass plate, aluminum foil, endless stainless steel belt or stainless steel drum, and then the precursor composition on the support may be dried at a variable temperature in the range of 50 to 200 ℃, specifically 80 to 150 ℃.

Thus, a gel film may be formed by partial curing and/or drying of the precursor composition, and the formed gel film may be peeled off from the support to obtain a gel film.

In some cases, a process of stretching the gel film may be performed to control the thickness and size of the polyimide film obtained during the subsequent heat treatment and improve orientation, and stretching may be performed in at least one of a Machine Direction (MD) and a Transverse Direction (TD) with respect to the machine direction.

The gel film thus obtained is fixed on a tenter, and then heat-treated at a variable temperature of 50 ℃ to 500 ℃, specifically 150 ℃ to 500 ℃, to remove water, residual solvent, and the like remaining in the gel film, and by imidizing almost all the amide groups, the polyimide film of the present invention can be obtained.

In some cases, the polyimide film obtained as described above may be heated to a temperature of 300 ℃ to 600 ℃ for 5 seconds to 400 seconds to further harden the polyimide film, and may be performed under a predetermined tension in order to relieve internal stress that may remain in the resulting polyimide film.

< chemical imidization method >

The chemical imidization method is a method of promoting imidization of an amide acid group by adding a dehydrating agent and/or an imidizing agent to a precursor composition.

Among them, the "dehydrating agent" refers to a substance that promotes cyclization reaction by dehydration of polyamic acid, and as non-limiting examples thereof, aliphatic acid anhydride, aromatic acid anhydride, N' -dialkylcarbodiimide, lower halogenated aliphatic, lower halogenated acid anhydride, arylphosphonic acid dihalide, thionyl halide, and the like can be cited. Among them, aliphatic acid anhydrides are preferable from the viewpoints of availability and cost, and non-limiting examples include Acetic Anhydride (AA), propionic anhydride and lactic anhydride, which may be used alone or in combination of two or more.

The "imide reagent" is a substance having an effect of promoting a ring-closure reaction with the polyamic acid, and includes an imine component such as an aliphatic tertiary amine, an aromatic tertiary amine, and a heterocyclic tertiary amine. Among them, heterocyclic tertiary amines are preferable from the viewpoint of reactivity as a catalyst. Non-limiting examples of the heterocyclic tertiary amine include quinoline, isoquinoline, β -picoline (BP), pyridine, and the like, and these may be used alone or in combination of two or more.

The amount of the dehydrating agent to be added is preferably in the range of 0.5 to 5 moles, particularly preferably in the range of 1.0 to 4 moles, relative to 1 mole of the amide acid group in the polyamic acid. The amount of the imidizing agent to be added is preferably in the range of 0.05 to 2 moles, particularly preferably in the range of 0.2 to 1 mole, relative to 1 mole of the amic acid group in the polyamic acid.

When the dehydrating agent and the imidizing agent are less than the above ranges, chemical imidization is insufficient, cracks may be formed in the polyimide film to be produced, and the mechanical strength of the film may also be lowered. In addition, if these addition amounts exceed the above-mentioned ranges, imidization may proceed too quickly, and in this case, it is difficult to cast in the form of a film, or the prepared polyimide film may exhibit brittleness (brittle), which is not preferable.

< method of Complex imidization >

In combination with the above chemical imidization method, a composite imidization method in which a thermal imidization method is further performed may be used to produce a polyimide film.

Specifically, the composite imidization method may include: a chemical imidization process of adding a dehydrating agent and/or an imidizing agent to the precursor composition at a low temperature; and a thermal imidization process of drying the precursor composition to form a gel film, and subjecting the gel film to a heat treatment.

When the chemical imidization process is performed, the types and amounts of the dehydrating agent and the imidizing agent may be appropriately selected as described in the chemical imidization process.

In the process of forming the gel film, a precursor composition containing a dehydrating agent and/or an imidizing agent is cast in the form of a film on a support such as a glass plate, an aluminum foil, an endless (endless) stainless steel belt or a stainless steel drum, and then on a support. The precursor composition is dried at variable temperatures of 50 ℃ to 180 ℃, in particular 80 ℃ to 180 ℃. In this process, the chemical conversion agent and/or imidizing agent may act as a catalyst to rapidly convert the amide acid groups to imide groups.

The gel film thus obtained is fixed to a tenter, and then heat-treated at a variable temperature of 50 ℃ to 700 ℃, specifically 150 ℃ to 600 ℃, to remove water, catalyst, residual solvent, etc. remaining in the gel film, and the polyimide film of the present invention can be obtained by imidizing a large part of the amide groups remaining. In such a heat treatment process, the dehydrating agent and/or the imidizing agent act as a catalyst so that the amide acid groups can be rapidly converted into imide groups, thereby achieving a high imidization rate.

In some cases, the polyimide film obtained as described above may be heated to a temperature of 400 to 500 ℃ for 5 to 400 seconds to further harden the polyimide film, and may also be performed under a predetermined tension in order to relieve internal stress that may remain in the obtained polyimide film.

The polyimide film according to the present invention is a polyimide film comprising a polyimide copolymer prepared by imidizing a polyamic acid copolymer, the polyimide copolymer comprising a first unit block which is a structure in which a first polyamic acid prepared by polymerization of an aromatic dianhydride monomer and an aromatic diamine monomer is imidized, and a second unit block which is a structure in which a second polyamic acid prepared by polymerization of a dianhydride monomer and a diamine monomer is imidized, and at least one of the dianhydride monomer and the diamine monomer is an aliphatic dianhydride monomer or an aliphatic diamine monomer.

In one specific example, the weight average molecular weight of the first unit block and the second unit block may be 6000g/mole to 60000g/mole, specifically 7000g/mole to 20000g/mole, and more specifically 10000g/mole to 15000g/mole, and more specifically 12000g/mole to 15000g/mole.

In general, the weight average molecular weights of the first unit block and the second unit block in the polyimide resin state have very similar values to those of the first polyamic acid and the second polyamic acid described above, and depending on the range of their weight average molecular weights, the above-described problem may occur.

In addition, the polyimide copolymer may have a weight average molecular weight of 100000g/mole or more, and the molar ratio of the first unit block to the second unit block may be 8:2 to 6:4, and more particularly possibly 7:3 to 6:4.

the weight average molecular weight of the polyimide copolymer may have a value similar to that of the third polyamic acid described above, and the molar ratio of the first unit block and the second unit block may also have a very similar value to that of the first polyamic acid and the second polyamic acid, and thus depending on their weight average molecular weight or the range of the molar ratio, the above-described problem may occur.

In one specific example, the first unit block and the second unit block may be represented by the following formulas 1 and 2, respectively.

Formula 1:

wherein n is an integer of 20 to 150.

Formula 2:

wherein m is an integer of 20 to 150.

Meanwhile, the structure derived from the aliphatic dianhydride monomer or the aliphatic diamine monomer contained in the second unit block may be 10 to 30 wt% with respect to the total weight of the polyimide copolymer.

When the content of the structure derived from the aliphatic dianhydride monomer or the aliphatic diamine monomer exceeds the above range, it is difficult to exhibit excellent mechanical properties and thermal properties of the polyimide film, and when it is below this range, it is difficult to achieve a desired level of dielectric constant and hygroscopicity, which is also not preferable.

On the other hand, at 10GHz, the polyimide film according to the present invention may have (a) a dielectric constant of 3.2 or less, (b) a moisture absorption rate of 1.5% by weight or less, (c) a tensile strength of 4.2GPa or more, and (d) a glass transition temperature (Tg) of 310 ℃ or more.

In this regard, in the case of the polyimide film of the present invention satisfying the conditions of the dielectric constant (a) and the moisture absorption rate (b) described above, it is possible to be used as an insulating film used in high-reliability electronic devices, and even when used as an electric signal transmission circuit that transmits signals at a high frequency of 10GHz or more, it is possible to minimize signal delay and transmission loss based on excellent insulation stability.

In addition, in the case of the polyimide film of the present invention satisfying the conditions of the tensile strength (c) and the glass transition temperature (d) described above, excellent mechanical properties and thermal properties can be exhibited.

Hereinafter, these four conditions will be described in detail.

< dielectric constant >

As is well known, the dielectric constant (permitticity) is an indicator dielectric (or insulator), that is, as an important characteristic value representing the electrical performance of a non-conductor, the dielectric constant does not represent the electrical characteristics of a direct current, but directly relates to the characteristics of an alternating current, in particular to alternating electromagnetic waves.

In an insulator (e.g., polyimide film), the + -moment components, which are typically scattered in random directions, are aligned with the variation of the flow of the externally applied electromagnetic field. That is, by changing the moment component according to the changing direction of the electromagnetic field, the electromagnetic wave can be propagated therein while being nonconductive.

In response to such a change in the external electromagnetic field, the degree to which the moment within the material reacts sensitively can be expressed as the dielectric constant, while a high dielectric constant means that the electric energy can be transmitted well, so that the lower the dielectric constant of an insulator such as a polyimide film is, the better.

That is, although the dielectric constant of the conventional polyimide film is higher than a level sufficient to maintain sufficient insulation for high frequency communication, as one example, the dielectric constant of the polyimide film according to the present invention may be 3.2 or less, preferably 3.0 or less, and the lower limit value thereof may be at least 2.2 or more. It can be seen that this represents an ideal dielectric constant as an insulator, considering that the engineering properties of polyimide films are at the highest level.

On the other hand, it can be seen that even if all conductors are separated from each other, there is always capacitive coupling (capacitive coupling) by an electric field between them, so even if layers of the multilayer substrate are electrically separated from each other, this is simply an open circuit (open circuit), but in reality, a capacitor of a certain value is connected between them.

At this time, the capacitor has a characteristic that the higher the frequency of the both-end current or voltage, the lower the impedance, and this value can be expressed as the following equation.

-impedance=1/(2 pi f C), where f is frequency and c=capacitance.

-c=e x S/d, where e is the dielectric constant, S is the area of the conductor and d is the distance.

In general, at a level where both conductors are visible and operable with bare hands, no matter how close they are, the capacitance value (farad) between them is difficult to separate from a pico (pico) cell, and in a typical PCB, as well, C between layers is small, insulation between layers can be maintained even if a circuit operates at a predetermined high frequency, and in the case of a GIGA cell, for example, in the case of a high-speed transmission electronic device operating at a high frequency of 10GHz or more, insulation is difficult to maintain because impedance becomes very low due to the high frequency value, and therefore, in selecting an insulator, a material of low dielectric constant (i.e., a material of low dielectric constant) should be used to minimize electrostatic coupling and capacitance (i.e., impedance).

Thus, the polyimide film according to the present invention exhibits a relatively low dielectric constant as described above by including a structure derived from an aliphatic monomer in a polyimide chain derived from the second polyamic acid. In particular, structures derived from aliphatic monomers have lower specific gravity, molecular density, polarity, and the possibility of forming charge transfer complexes than structures derived from aromatic monomers, and thus the dielectric constant can be reduced.

Therefore, the polyimide film of the present invention has an advantage of easy insulation maintenance even in high-speed transmission electronic devices operating at frequencies of the GIGA unit, for example, at frequencies of 10GHz or more.

< moisture absorption Rate >

The moisture absorption rate is a ratio indicating the amount of moisture absorbed by the material. It is generally known that when the moisture absorption rate is high, the dielectric constant increases, the dielectric constant of water in the solid state is 100 or more, the dielectric constant in the liquid state is about 80, and the dielectric constant in gaseous water vapor is 1.0059.

Therefore, water in a vapor state in the polyimide film does not substantially affect the dielectric constant of the polyimide film, but when water is absorbed into the polyimide film in a liquid state, the dielectric constant may drastically increase. That is, even if the amount of moisture absorption is small, the dielectric constant of the polyimide film may rapidly change, and the dielectric constant significantly increases.

Therefore, it can be seen that low moisture absorption is an essential characteristic for using a polyimide film as an insulating film.

It is expected that the polyimide film according to the present invention is due to the inclusion of-CH which exhibits non-polarity in the molecular structure ₃ 、-CF ₃ Polyimide chains of at least one of a chain aliphatic hydrocarbon group or a cyclic aliphatic hydrocarbon group.

< tensile Strength >

In the present invention, tensile strength refers to resistance to deformation until the film reaches a break when a load is applied to the film. The strength includes compressive strength, bending strength, torsional strength, tensile strength, etc., depending on the loading method, and these strengths have a predetermined relationship with the tensile strength, and thus can be used as a standard of film strength having tensile strength.

The tensile strength unit is expressed in GPa, is the maximum load that the test piece receives in a tensile test, and can be used as an index indicating the mechanical properties of the polyimide film.

< glass transition temperature >

In the present invention, the glass transition temperature can be obtained by the storage elastic modulus and the loss elastic modulus measured by a dynamic viscoelasticity measuring Device (DMA). Specifically, the calculated loss elastic modulus divided by the peak (top peak) where the storage elastic modulus is tan δ can be calculated as the glass transition temperature.

A higher glass transition temperature is preferable because it means heat resistance of the polyimide film. However, in the polyimide film, it is difficult for the highest glass transition temperature and low dielectric constant to coexist, and it is predicted that the strong heat resistance of the polyimide film is due to the chemical stability of the imide group, but since the imide group shows polarity, it is relatively easy to absorb moisture.

Specifically, the polyimide film according to the present invention may have a glass transition temperature of 220 ℃ or higher, specifically 230 ℃ or higher, and more specifically 310 ℃ or higher.

As described above, the polyimide film according to the present invention satisfies all of the four conditions described above, exhibits excellent mechanical and thermal properties, and at the same time, ensures insulation stability also at high frequencies, and can minimize signal delay and transmission loss.

The present invention also provides an electronic device for high-speed transmission including the polyimide film.

The electronic device for high-speed transmission may be an electronic device that transmits signals at a high frequency of at least 2GHz, specifically at least 5GHz, more specifically at least 10 GHz.

The electronic device may be, for example, a communication circuit for a portable terminal, a communication circuit for a computer, or a communication circuit for aerospace, but is not limited thereto.

Hereinafter, the operation and effect of the present invention will be described in more detail by specific examples of the present invention. However, these examples are presented only as examples of the present invention, and thus the scope of the present invention cannot be determined.

Preparation example 1:preparation of first polyamic acid solution

After nitrogen was injected into a 500ml reactor equipped with a stirrer and a nitrogen-injecting/discharging tube, 415g of DMF was added, and the temperature of the reactor was set to 30 ℃, followed by adding 60.63g of BPDA as an aromatic diamine monomer and 22.84g of PPD as an aromatic dianhydride monomer to confirm that it had been completely dissolved. After heating the mixture to a temperature of 40 ℃ under a nitrogen atmosphere and continuing stirring for 120 minutes, a first polyamic acid solution having a solid content of 17% by weight and a viscosity of 2000cP at 23 ℃ was prepared.

At this time, the weight average molecular weight of the first polyamic acid was 15000g/mole as measured by GPC (Tosoh preparation, HLC-8220 GPC).

Preparation example 2: preparation of a second polyamic acid solution

After nitrogen was injected into a 500ml reactor equipped with a stirrer and a nitrogen-injecting/discharging tube, 415g of NMP was added, and the temperature of the reactor was set to 30℃and then 54.56g of HPDA as an aliphatic dianhydride monomer and 28.69g of CHDA as an aliphatic diamine monomer were added to confirm that it was completely dissolved. After heating the temperature to 40 ℃ under a nitrogen atmosphere and continuing to stir for 120 minutes, a second polyamic acid solution was prepared having a solid content of 17% by weight and a viscosity of 2000cP at 23 ℃.

At this time, the weight average molecular weight of the second polyamic acid was 15000g/mole as measured by GPC (Tosoh preparation, HLC-8220 GPC).

Preparation example 3:preparation of the third polyamic acid solution

Nitrogen gas was injected into a 1000ml reactor equipped with a stirrer and a nitrogen injection/discharge tube while setting the temperature of the reactor to 30 ℃, 349.03g of the first polyamic acid solution of production example 1, 149.51g of the second polyamic acid solution of production example 2, and 1.27g of PMDA were heated to 40 ℃ under a nitrogen atmosphere, and stirring was continued for 120 minutes, and then a third polyamic acid solution having a solid content of 17% by weight and a viscosity of 200000cP was produced.

At this time, the weight average molecular weight of the third polyamic acid measured by GPC (Tosoh preparation, HLC-8220 GPC) was 100000g/mole, and the molar ratio between the first polyamic acid and the second polyamic acid was 7:3.

comparative preparation 1: preparation of polyamic acid solution

After nitrogen was injected into a 500ml reactor equipped with a stirrer and a nitrogen injection/discharge tube, 415g of NMP was added, the temperature of the reactor was set to 30℃and then 44.87g of BPDA as an aromatic dianhydride monomer and 18.02g of PPD as an aromatic diamine monomer were added, and 14.51g of HPDA as an aliphatic dianhydride monomer and 7.46g of CHDA as an aliphatic diamine monomer were added to confirm complete dissolution. After heating the added mixture to a temperature of 40 ℃ under a nitrogen atmosphere and continuing stirring for 120 minutes, a polyamic acid solution having a solid content of 17% by weight and a viscosity of 200000cP at 23 ℃ was prepared.

At this time, the weight average molecular weight of the polyamic acid was 100000g/mole as measured by GPC (Tosoh preparation, HLC-8220 GPC).

Comparative preparation 2: preparation of mixed polyamic acid solution

Into a 500ml reactor equipped with a stirrer and a nitrogen injection/discharge tube, nitrogen was injected, 415g of NMP was added, and the reactor temperature was set to 30℃and then 60.50g of BPDA as an aromatic dianhydride monomer and 24.37g of PPD as an aromatic diamine monomer were added to confirm complete dissolution. After heating the mixture to a temperature of 40 ℃ under a nitrogen atmosphere and continuing stirring for 120 minutes, a first polyamic acid solution having a solid content of 17% by weight and a viscosity of 200000cP at 23 ℃ was prepared.

At this time, the weight average molecular weight of the first polyamic acid was 100000g/mole as measured by GPC (Tosoh preparation, HLC-8220 GPC).

Subsequently, 415g of DMF was added while nitrogen was injected into a 500ml reactor equipped with a stirrer and a nitrogen injection/discharge tube, the temperature of the reactor was set to 30℃and then 56.15g of HPDA as an aliphatic dianhydride monomer and 28.69g of CHDA as an aliphatic diamine monomer were added to confirm complete dissolution. After heating the mixture to a temperature of 40 ℃ under a nitrogen atmosphere and continuing stirring for 120 minutes, a second polyamic acid solution having a solid content of 17% by weight and a viscosity of 200000cP at 23 ℃ was prepared.

Next, a mixed polyamic acid solution is prepared by mixing the first polyamic acid solution and the second polyamic acid solution prepared above.

Example 1:preparation of polyimide film

40g of the third polyamic acid solution prepared in preparation example 3 was used as a precursor composition, and bubbles were removed from the precursor composition by high-speed rotation at 1500rpm or more. Thereafter, the defoamed polyimide precursor composition was applied onto a glass substrate using a spin coater. Then, the gel film was dried under a nitrogen atmosphere and at a temperature of 120 ℃ for 30 minutes, heated to 450 ℃ at a rate of 2 ℃/min, heat-treated at a temperature of 450 ℃ for 60 minutes, and cooled to 30 ℃ at a rate of 2 ℃/min, thereby obtaining a polyimide film. After that, the polyimide film was peeled off from the glass substrate by immersing in distilled water.

The polyimide film prepared had a molar ratio of the first unit block comprising the first polyimide resin to the second unit block comprising the second polyimide resin of 7:3, and the thickness is 15 μm. The thickness of the prepared polyimide film was measured using an Anritsu film thickness meter (Electric Film thickness tester).

Example 2

Polyimide films were prepared in the same manner as in example 1, except that the weight average molecular weights of the first polyamic acid and the second polyamic acid in preparation examples 1 and 2 were changed as shown in table 1 below.

Example 3

Example 4

A polyimide film was produced in the same manner as in example 1, except that the weight average molecular weight of the third polyamic acid in production example 3 was changed as shown in table 1 below.

Example 5

A polyimide film was produced in the same manner as in example 1, except that the input amounts of the first polyamic acid and the second polyamic acid were adjusted so that the molar ratio between the first unit block and the second unit block in production example 3 was as shown in table 1 below.

Example 6

Example 7

Comparative example 1

Comparative example 2

Comparative example 3

Comparative example 4

40g of the polyamic acid solution prepared in comparative preparation example 1 was used as a precursor composition, and bubbles were removed by rotating the precursor composition at a high speed of 1500rpm or more. Thereafter, the defoamed polyimide precursor composition was applied onto a glass substrate using a spin coater. Then, the gel film was dried under a nitrogen atmosphere and at a temperature of 120 ℃ for 30 minutes, heated to 450 ℃ at a rate of 2 ℃/min, heat-treated at 450 ℃ for 60 minutes, and cooled to 30 ℃ at a rate of 2 ℃/min, thereby obtaining a polyimide film. After that, the polyimide film was peeled off from the glass substrate by immersing in (dipping) distilled water.

The polyimide film prepared had a molar ratio of the first unit block comprising the first polyimide resin to the second unit block comprising the second polyimide resin of 7:3, and the thickness is 15 μm.

Comparative example 5

40g of the mixed polyamic acid solution prepared in comparative preparation example 2 was used as a precursor composition, and bubbles were removed by rotating the precursor composition at a high speed of 1500rpm or more. Thereafter, the defoamed polyimide precursor composition was applied onto a glass substrate using a spin coater. Then, the gel film was dried under a nitrogen atmosphere and at a temperature of 120 ℃ for 30 minutes, heated to 450 ℃ at a rate of 2 ℃/min, heat-treated at 450 ℃ for 60 minutes, and cooled to 30 ℃ at a rate of 2 ℃/min, thereby obtaining a polyimide film. After that, the polyimide film was peeled off from the glass substrate by immersing in (dipping) distilled water.

TABLE 1

< experimental example 1> evaluation of moisture absorption rate and dielectric constant for the polyimide films prepared in examples 1 to 7 and comparative examples 1 to 5, respectively, moisture absorption rate and dielectric constant were measured in the following manner, and the measurement results are shown in table 2 below.

(1) Moisture absorption rate measurement

The polyimide film was cut into 5cm x 5cm squares according to astm d570 method to prepare samples, and the dried samples were dried in an oven at 50 ℃ for more than 24 hours and then weighed. After immersing in water at 23℃for 24 hours, the weight was measured again, and the weight difference obtained here was expressed in% to measure the moisture absorption rate.

(2) Dielectric constant measurement

The dielectric constant at 10GHz was measured using an SPDR instrument from Keysight.

TABLE 2

<Experimental example 2>Evaluation of tensile Strength and glass transition temperature

For each of the polyimide films prepared in examples 1 to 7 and comparative examples 1 to 5, the tensile strength and glass transition temperature were measured in the following manner, and the results thereof are shown in table 3 below.

(1) Tensile Strength measurement

Tensile strength was measured by the method proposed in KS 6518.

(2) Glass transition temperature measurement

The glass transition temperature (Tg) was determined by using DMA to obtain the loss modulus and storage modulus of each film, and the inflection points of these films were measured as the glass transition temperature.

TABLE 3 Table 3

Referring to tables 2 and 3, it was confirmed that the hygroscopicity and the dielectric constant were low and the heat resistance and mechanical properties were excellent in the case of satisfying the embodiments within the scope of the present invention. On the other hand, in the case where the comparative example is not within the scope of the present invention, it can be determined that it does not satisfy at least one of hygroscopicity, dielectric constant, heat resistance, and mechanical properties. While the invention has been described above with reference to the embodiments thereof, it is within the scope of the invention that those skilled in the art will be able to make various applications and modifications within the scope of the invention.

Industrial applicability

According to the method for producing a polyimide film of the present invention, in order to effectively exhibit excellent characteristics, the method is divided into the following steps: a step of preparing a first polyamic acid by polymerizing an aromatic dianhydride monomer and an aromatic diamine monomer in a first organic solvent; and a step of preparing a second polyamic acid by polymerizing a dianhydride monomer and a diamine monomer in a second organic solvent, wherein at least one of the dianhydride monomer and the diamine monomer is an aliphatic dianhydride monomer or an aliphatic diamine monomer, whereby the film prepared can achieve low hygroscopicity while maintaining low mechanical properties and thermal properties.

Claims

1. A method for producing a polyimide film, comprising:

a step (a) of preparing a first polyamic acid by polymerizing an aromatic dianhydride monomer and an aromatic diamine monomer in a first organic solvent;

A step (b) of preparing a second polyamic acid by polymerizing a dianhydride monomer and a diamine monomer, at least one of which is an aliphatic dianhydride monomer or an aliphatic diamine monomer, in a second organic solvent;

a step (c) of preparing a third polyamic acid by copolymerizing the first polyamic acid and the second polyamic acid in a third organic solvent;

step (d) of preparing a precursor composition comprising a third polyamic acid; and

step (e) of imidizing the precursor composition after film formation on a support,

wherein, by using 8:2 to 6:4 to produce a third polyamic acid.

2. The method for producing a polyimide film according to claim 1, wherein the weight average molecular weight of the first and second polyamic acids is 6000g/mole to 60000g/mole.

3. The method for producing a polyimide film according to claim 1, wherein the weight average molecular weight of the third polyamic acid is 100000g/mole or more.

4. The method for producing a polyimide film according to claim 1, wherein,

the aromatic dianhydride monomer comprises at least one selected from the group consisting of pyromellitic dianhydride, biphenyl tetracarboxylic dianhydride, oxydiphthalic anhydride and benzophenone tetracarboxylic dianhydride,

The aliphatic dianhydride monomer contains at least one selected from the group consisting of 1,2,4, 5-cyclohexane tetracarboxylic dianhydride, 2-bis [4- (3, 4-dicarboxyphenoxy) phenyl ] propane dianhydride, bicyclo [2, 2] oct-7-ene-2, 3,5, 6-tetracarboxylic dianhydride, and cyclobutane-1, 2,3, 4-tetracarboxylic dianhydride.

5. The method for producing a polyimide film according to claim 1, wherein,

the aromatic diamine monomer comprises at least one selected from the group consisting of 1, 4-phenylenediamine, 4' -oxydiphenylamine, 3,4' -oxydiphenylamine, 4' -methylenediphenylamine and 1, 3-bis (4-aminophenoxy) benzene,

the aliphatic diamine monomer includes at least one selected from the group consisting of cyclohexanediamine, 1, 4-cyclohexanedi (methylamine), 2-bis [ (4-aminophenoxy) phenyl ] propane, 2-bis [4- (4-aminophenoxyphenyl) ] hexafluoropropane, 4 '-methylenedicyclohexylamine, 4' -methylenebis (2-methylcyclohexylamine), 1, 3-adamantanediamine, and 3,3 '-diamino-1, 1' -diamantane.

6. The method for producing a polyimide film according to claim 1, wherein the first to third organic solvents comprise at least one selected from the group consisting of N, N '-dimethylformamide, N' -dimethylacetamide, N-methylpyrrolidone, γ -butyrolactone, and diglyme.

7. A polyimide film comprising a polyimide copolymer prepared by imidizing a polyamic acid copolymer, wherein,

the polyimide copolymer comprises a first unit block and a second unit block,

the first unit block is a structure in which a first polyamic acid prepared by polymerization of an aromatic dianhydride monomer and an aromatic diamine monomer is imidized,

the second unit block is a structure in which a second polyamic acid prepared by polymerization of a dianhydride monomer and a diamine monomer is imidized, and at least one of the dianhydride monomer and the diamine monomer is an aliphatic dianhydride monomer or an aliphatic diamine monomer,

wherein the molar ratio of the first unit block to the second unit block is 8:2 to 6:4.

8. the polyimide film according to claim 7, wherein the first and second unit blocks have a weight average molecular weight of 6000g/mole to 60000g/mole.

9. The polyimide film according to claim 7, wherein the polyimide copolymer has a weight average molecular weight of 100000g/mole or more.

10. The polyimide film according to claim 7, wherein,

the first and second unit blocks are represented by the following formulas 1 and 2,

Formula 1:

wherein n is an integer of 20 to 150,

formula 2:

wherein m is an integer of 20 to 150.

11. The polyimide film according to claim 7, wherein the structure derived from an aliphatic dianhydride monomer or an aliphatic diamine monomer contained in the second unit block is 10 to 30% by weight relative to the total weight of the polyimide copolymer.

12. The polyimide film according to claim 7, wherein the polyimide film has a dielectric constant of 3.2 or less, a moisture absorption of 1.5 wt% or less, a tensile strength of 4.2Gpa or more, and a glass transition temperature of 310 ℃ or more.

13. An electronic device for high-speed transmission comprising the polyimide film according to claim 7.