CN112055724B

CN112055724B - Polyimide film containing bismaleimide resin and carbon black and preparation method thereof

Info

Publication number: CN112055724B
Application number: CN201880093068.5A
Authority: CN
Inventors: 金纪勋; 李吉男; 崔祯烈
Original assignee: Polyimide Advanced Materials Co ltd
Current assignee: Polyimide Advanced Materials Co ltd
Priority date: 2018-05-14
Filing date: 2018-09-28
Publication date: 2023-02-28
Anticipated expiration: 2038-09-28
Also published as: WO2019221342A1; KR20190130365A; CN112055724A; KR102138704B1

Abstract

The present invention provides a polyimide film comprising: a polyimide resin; a bismaleimide resin containing 5 parts by weight or more per 100 parts by weight of the polyimide resin; and carbon black.

Description

Polyimide film containing bismaleimide resin and carbon black and preparation method thereof

Technical Field

The invention relates to a polyimide film containing bismaleimide resin and carbon black and a preparation method thereof.

Background

Polyimide (PI) is a polymer material having thermal stability based on a rigid aromatic skeleton, and has excellent mechanical strength, chemical resistance, weather resistance, and heat resistance based on chemical stability of an imide ring.

In addition, as a high-performance material, polyimide is widely spotlighted because it is useful in microelectronics and optics due to its excellent electrical properties (such as insulation and low dielectric constant).

As an example of the field of microelectronics, a highly integrated circuit included in a portable electronic device and a communication device can be cited. Polyimide may be used as a film that is attached or added to the circuit to provide electrical insulation for the circuit and, at the same time, to protect the circuit from moisture, light sources, impact, and the like.

As the film for protecting the circuit as described above, there may be various examples, but in the case where the composite film has an adhesive layer formed on one side or both sides of the film, it may be referred to as a cover layer (cover) in a narrow sense, and a polyimide film may be preferably used for the cover layer.

Recently, special polyimide films containing carbon black and having a black color tone have been attracting attention as a covering material with emphasis on visual safety, a shielding function, and a light shielding function of a circuit.

In order to produce a polyimide film having a black color tone, a process of mixing and uniformly dispersing carbon black in polyamic acid as a precursor is indispensable. If the carbon black is not uniformly dispersed during this process, problems such as poor shielding effect or surface defects may occur. Essentially, carbon black differs in physical/chemical properties from polyamic acid or polyimide, and is therefore less miscible and/or dispersible in polyimide or polyamic acid.

In addition, the manufacturing process of the circuit may include a drilling (drill) process, an electroplating process, a desmear (desmear) process, a cleaning process, and the like, and the polyimide film may be exposed to an alkaline solution in the above process. At this time, when the polyimide film is slightly decomposed or modified by the alkaline solution, a large amount of carbon black contained in the polyimide film may be dropped.

Therefore, the black tone may be removed from the cover layer while the shielding property is lost, and the surface and the weight and thickness may be reduced due to the falling off of the carbon black, so that the function as the cover layer may be greatly reduced.

Therefore, a technology that can fundamentally solve these problems is urgently required.

Disclosure of Invention

Technical problem to be solved by the invention

The invention aims to provide a polyimide film and a preparation method thereof.

According to an aspect of the present invention, a polyimide film includes bismaleimide resin and carbon black, and is prepared to include the bismaleimide resin in a preferred content and the carbon black in a preferred content.

In this regard, the bismaleimide resin can improve miscibility and/or dispersibility of carbon black in polyamic acid as a precursor of a polyimide film.

In addition, even if the polyimide film is inevitably modified or decomposed by an alkaline solution or the like, the bismaleimide resin can effectively suppress the falling of carbon black.

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

It is therefore the object of the present invention to provide specific embodiments thereof.

Means for solving the problems

In one embodiment, the present invention provides a polyimide film comprising: a polyimide resin; a bismaleimide resin containing 5 parts by weight or more with respect to 100 parts by weight of the polyimide resin; and carbon black.

In one embodiment, the present invention provides a method of preparing the polyimide film.

In one embodiment, the present invention provides a cover layer (cover) including the polyimide film and an electronic device including the cover layer.

Hereinafter, embodiments of the present invention will be described in more detail in the order of "polyimide film" and "method for producing polyimide film" of the present invention.

Before this, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and should be construed as meanings and concepts corresponding to technical ideas of the present invention on the basis of the principle that the concept of a term can be appropriately defined so as to explain the inventor's own invention in the best way.

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 and does not represent all technical ideas of the present invention, and various equivalents and modifications may exist at the time of the present application to be able to replace them.

As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. In this document, the terms "comprising", "including" or "having" are to be understood as meaning the presence of stated features, numbers, steps, components or combinations thereof, which do not preclude the presence or addition of one or more other features or numbers, steps, components or combinations thereof which may be present or added.

It is intended herein that "dianhydride" includes precursors or derivatives thereof, which may not technically be a dianhydride, but nonetheless reacts with a diamine to form a polyamic acid that can be converted back to a polyimide.

It is intended herein that "diamine" includes precursors or derivatives thereof, which may not technically be a diamine, which nevertheless react with the dianhydride to form a polyamic acid that can be converted back to a polyimide.

It will be understood that if an amount, concentration, or other value or parameter given herein is an enumeration of ranges, preferred ranges or preferred upper values and preferred lower values, then regardless of whether ranges are individually disclosed, all ranges that may be formed as any pair of any upper range threshold or preferred value and any lower range threshold or preferred value are specifically disclosed. When a numerical range is disclosed herein, unless otherwise stated, the range is intended to include the endpoints and all integers and fractions within the range. It is intended that the scope of the invention not be limited to the particular values disclosed in defining the range.

Polyimide film

The polyimide film according to the present invention may comprise: a polyimide resin; a bismaleimide resin containing 5 parts by weight or more per 100 parts by weight of the polyimide resin; and carbon black.

Generally, polyimides are susceptible to, e.g., degradation or modification by basic components when exposed to basic environments. In addition, as described above, the polyimide film containing carbon black is not only difficult to produce but also more susceptible to the influence of the alkali component due to the falling off of carbon black. Accordingly, there is a need to improve the "alkali resistance" of polyimide films, particularly polyimide films comprising carbon black.

The alkali resistance refers to a property that a polyimide film is not easily decomposed and/or modified even when exposed to an alkali environment, and since the thickness of the polyimide is reduced in the decomposition and/or modification process, the alkali resistance can be judged based on the thickness reduction.

In connection with this, as one example of evaluating the alkali resistance, there is a method of exposing a polyimide film to an alkali solution and measuring a change in film thickness before and after the exposure. In the present invention, as a method for evaluating the alkali resistance of the polyimide film, the test method (a) is defined as follows. The test method (a) may include: corona treating both surfaces of the polyimide film; a step of preparing a flexible circuit board sample by laminating a polyimide film, an adhesive sheet and a copper foil in this order, then bonding them at a temperature of 160 ℃ for 30 minutes at a pressure of 50kgf, and then cutting them into 4 x 10 cm; and a step of measuring a thickness of a sample of the flexible circuit board by exposing the same sample to a 10% NaOH solution at 50 ℃ for 100 minutes.

The thickness reduction rate according to the test method (a) can be expressed in percentage by calculating the change in thickness of the flexible circuit board sample measured after exposure to the NaOH solution compared to the thickness of the flexible circuit board sample measured before exposure to the NaOH solution. That is, the thickness reduction ratio can be regarded as a quantitative value for alkali resistance.

In the case of a conventional polyimide film containing carbon black, the thickness reduction ratio by the test method (a) may be about 35% to 45%. For reference, a thickness reduction rate of more than 30% can be judged as a degree that it is substantially difficult to commercialize the polyimide film.

On the other hand, the polyimide film of the present invention comprising a bismaleimide resin and carbon black may have a thickness reduction rate of 30% or less, specifically 28% or less, more specifically 26% or less, by the test method (a), and have higher alkali resistance as compared to a conventional polyimide film.

In this regard, the present invention is explained in more detail by "embodiments of the present invention", but it is presumed that the bismaleimide resin is based on being present in the polyimide film in at least one state selected from the following: a first state (A) in which the surface of carbon black is coated; a second state (B) physically bonded to the polymer chain of the polyimide resin; and a third state (C) chemically bonded to the polymer chain of the polyimide resin.

The first state facilitates the miscibility and/or dispersion of carbon black in polyamic acid that is a precursor of the polyimide film. This can advantageously act on the preparative processability of the polyimide containing carbon black.

When the carbon black is not easily miscible and/or dispersible, the following problems may occur. In terms of the preparative processability, when carbon black is not uniformly dispersed but concentrated in a part, there may be a problem that a defect occurs on the surface of the thin film due to the formation of a protrusion in the film forming process. In the alkali resistance, when the carbon black is exposed to an alkali component at a position where the carbon black is concentrated, the carbon black may be largely peeled off due to decomposition or modification of the polyimide resin. In addition, in the case where carbon black is concentrated in a portion, the content of carbon black in the portion other than the portion is relatively low, and therefore there may be a problem that shielding performance is lowered when viewed from the entire polyimide film.

When simply mixed with polyamic acid, carbon black tends to be less dispersible. On the other hand, bismaleimide resins can be readily miscible with polyamic acids. Therefore, the above-described problem can be solved by the first state, which can be considered as the encapsulation of carbon black by bismaleimide resin.

Bismaleimide resins are also known as resins excellent in chemical resistance. The bismaleimide resin dispersed in the polyimide film together with carbon black can greatly inhibit decomposition and/or modification of the polyimide resin due to an alkali component between carbon black and the polyimide resin, based on its inherent excellent chemical resistance.

In addition, the bismaleimide resin has low hygroscopicity, which may help to retard a phenomenon of penetration of an alkali component into the polyimide film or reduce the amount of penetration of the alkali component. Therefore, the first state can minimize the falling of carbon black by, for example, an alkali component, and this can be effectively used to improve the alkali resistance of the polyimide film.

In other words, the bismaleimide resin may mainly act to reduce the moisture absorption rate of the polyimide film and to reduce the moisture absorption rate, thereby contributing to delay and/or suppress permeation of alkali components or the like that can promote decomposition of the polyimide resin, in addition to moisture.

Therefore, the moisture absorption rate of the polyimide film of the present invention may be less than 2%.

In the second state, at least a portion of the bismaleimide resin may be physically entangled with a polymer chain of the polyimide resin. In addition, the bismaleimide resin may hinder penetration of an alkaline component, and may effectively function to improve alkali resistance of the polyimide film.

In the second state, the bismaleimide resin may also serve to fix the carbon black to the polymer chain of the polyimide resin, and therefore, the inclusion of the bismaleimide resin and the expression of the second state due thereto may positively act to minimize the shedding of the carbon black caused by the basic component.

The third state is that at least a part of the bismaleimide resin is chemically bonded to at least a part of a polymer chain of the polyimide resin, and may provide similar advantages to the second state.

Thus, based on the above advantages, the polyimide film of the present invention comprising a bismaleimide resin may have improved alkali resistance, together with carbon black.

However, in spite of the above advantages, it is not preferable to unconditionally contain a large amount of bismaleimide resin.

In particular, the above advantages may be exhibited when the content of the bismaleimide resin is at a certain level, but if it is exceeded, the mechanical properties of the polyimide film may be greatly reduced. That is, it is important to include an appropriate amount of bismaleimide resin in order to make the mechanical properties of the polyimide film compatible with the aforementioned advantages.

Therefore, in the present invention, the bismaleimide resin may be included by 5 to 10 parts by weight with respect to 100 parts by weight of the polyimide resin. This will be explained specifically below, but it is emphasized again that the bismaleimide resin should be selected within a limited range so that the above-described advantages can be exhibited and the mechanical properties of the polyimide film can be brought to a desired level.

The bismaleimide resin that can be used in the present invention is a resin obtained by polymerizing at least one monomer selected from the group consisting of 4,4' -bismaleimidodiphenylmethane, 2, 4-bismaleimidotoluene, 4-methylenediphenylene, 4' -dicyclohexylmethane, and 1,3' -phenylenebismaleimide, but is not limited thereto. However, this is merely an example of the means for carrying out the present invention, and as a matter of course, materials known in the art may be used in consideration of the desired properties and effects.

The carbon black may be included in an amount of 1 to 10 parts by weight, based on 100 parts by weight of the polyimide resin. Within this range, the polyimide film of the present invention containing carbon black may have a light transmittance of 5% or less in the visible light region.

When it is less than the above range, the light transmittance is increased so that the polyimide film may not have a desired level of shielding performance, and when it exceeds the range, a portion of carbon black may be accumulated and defects may occur on the surface of the film. In addition, the presence of excess carbon black may adversely affect the mechanical properties of the polyimide film.

The carbon black may have an average particle diameter of 0.1 to 5 μm.

When the average particle diameter is higher or lower than the range, the same disadvantage as the content of carbon black may occur.

On the other hand, the polyimide resin of the present invention may be derived from polyamic acid. The polyamic acid may be polymerized from a dianhydride monomer and a diamine monomer.

Detailed examples of the dianhydride monomer and the diamine monomer will be described in detail in the following embodiments.

The polyimide resin of the present invention may further comprise a filler for improving physical properties or processability thereof. Detailed examples thereof will be described in detail in the following embodiments.

Preparation method of polyimide film

The method for preparing the polyimide film of the present invention may comprise: a step of preparing a first composition by mixing a first organic solvent, carbon black and a bismaleimide resin; a step of preparing a second composition comprising polyamic acid by mixing and polymerizing a dianhydride monomer and a diamine monomer into a second organic solvent; a step of preparing a precursor composition by mixing the first composition and the second composition; and a step of obtaining a polyimide film by imidizing the precursor composition.

Here, separately performing the step of preparing the first composition may induce the carbon black and the bismaleimide resin in the polyimide film to exist in at least one state selected from the group consisting of: a first state (A) in which the surface of the carbon black is coated; a second state (B) physically bonded to a polymer chain of the polyimide resin; and a third state (C) chemically bonded to the polymer chain of the polyimide resin.

Preferably, the step of preparing the first composition alone may facilitate the bismaleimide resin in the polyimide film to exist in a first state of being coated on the surface of the carbon black.

Meanwhile, the preparation of the first composition may be performed through a milling process. Grinding using, but not limited to, a bead milling (bead milling) method is contemplated. The bead mill can efficiently stir even in the case where the flow rate of the mixture is low, which is advantageous in dispersing the carbon black. It will be appreciated that this is merely an example of how the invention may be put into practice.

As a non-limiting example of the first organic solvent used in the step of preparing the first composition, carbon black may also be dispersed and polyamic acid may be dissolved when mixed with the second composition, and specifically may be an aprotic polar solvent.

Non-limiting examples of the aprotic polar solvent include amide solvents (e.g., N '-Dimethylformamide (DMF) and N, N' -dimethylacetamide (DMAc) and the like, phenolic solvents (e.g., p-chlorophenol and o-chlorophenol and the like), N-methyl-pyrrolidone (NMP), γ -butyrolactone (GBL), and Diglyme (Diglyme), and the like, which may be used alone or in combination of two or more.

The steps for preparing the second composition are described in detail.

Polyamic acids can be prepared by the polymerization of one or more diamine monomers and one or more dianhydride monomers in an organic solvent.

The diamine monomer that can be used in the polymerization of polyamic acid is an aromatic diamine, and can be exemplified as follows.

1) Diamines having a benzene ring in the structure, having a relatively rigid structure, such as 1, 4-diaminobenzene (or p-phenylenediamine, PDA), 1, 3-diaminobenzene, 2, 4-diaminotoluene, 2, 6-diaminotoluene, 3, 5-diaminobenzoic acid (or DABA);

2) <xnotran> , 4,4' - ( , ODA), 3,4' - ,4,4' - ( ), 3,3' - -4,4' - ,2,2 ' - -4,4' - ,2,2 ' - ( ) -4,4' - ,3,3' - -4,4' - ,3,3' - -4,4' - ,3,3', 5,5' - -4,4' - , (4- ) ,4,4' - ,3,3' - ,3,3' - ( o- ), 2,2' - ( ), 3,3' - ,2,2 ' - ,3,3' - ,3,4 ' - ,4,4' - ,3,3' - ,3,4 ' - ,4,4' - ,3,3' - ,3,4 ' - ,4,4' - ,3,3' - ,4,4' - ,3,3' - -4,4' - ,3,3' - -4,4' - , </xnotran> <xnotran> 3,3'- ,3,4' - ,4,4'- ,2,2- (3- ) ,2,2- (4- ) ,2,2- (3- ) -1,1,1,3,3,3,3- ,2,2- (4- ) -1,1,1,3,3,3- ,3,3' - ,3,4 '- ,4,4' - ; </xnotran>

Diamines having three benzene rings in the structure, for example, 1, 3-bis (3-aminophenyl) benzene, 1, 3-bis (4-aminophenyl) benzene, 1, 4-bis (3-aminophenyl) benzene, 1, 4-bis (4-aminophenyl) benzene, 1, 3-bis (4-aminophenoxy) benzene, 1, 4-bis (3-aminophenoxy) benzene (or TPE-Q), 1, 4-bis (4-aminophenoxy) benzene (or TPE-Q), 1, 3-bis (3-aminophenoxy) -4-trifluoromethylbenzene, 3' -diaMino-4- (4-phenyl) phenoxybenzophenone, 3' -diaza Mino-4,4' -di (4-phenylphenoxy) benzophenone, 1, 3-bis (3-aminophenyl) benzene, 1, 3-bis (4-aminophenyl) benzene, 1, 4-bis (4-aminophenyl) benzene, 1, 3-bis (3-aminophenyl) sulfone, 1, 3-bis (3-aminophenyl) benzene, 1, 2-bis [4- (4-aminophenyl) phenyl ] benzene, 1, 2-bis [ 4-aminophenyl ] benzene, 1, 3-bis (4-isopropyl) phenyl ] benzene, 2, 4-isopropyl) benzene, 1, 3-bis [ 4-aminophenyl ] phenyl ] benzene, 4-phenyl ] sulfone, 1, 4-bis [ 4-phenyl ] benzene, 3-bis (4-phenyl) benzene, 4-phenyl) sulfone, etc.;

<xnotran> 4 , ,3,3'- (3- ) ,3,3' - (4- ) ,4,4'- (3- ) ,4,4' - (4- ) , [3- (3- ) ] , [3- (4- ) ] , [4- (3- ) ] , [4- (4- ) ] , [3- (3- ) ] , [3- (4- ) ] , [4- (3- ) ] , [4- (4- ) , [3- (3- ) ] , [3- (4- ) ] , [4- (3- ) ] , [4- (4- ) ] , [3- (3- ) ] , [3- (4- ) ] , [4- (3- ) ] , [4- (4- ) ] , </xnotran> <xnotran> [3- (3- ) ] , [3- (4- ) ] , [4- (3- ) ] , [4- (4- ) ] ,2,2- [3- (3- ) ] ,2,2- [3- (4 ] - ) ] ,2,2- [4- (3- ) ] ,2,2- [4- (4- ) ] (BAPP), 2,2- [3- (3- ) ] -1,1,1,3,3,3- ,2,2- [3- (4- ) ] -1,1,1,3,3,3- ,2,2- [4- (3- ) ] -1,1,1,3 ,3,3- ,2,2- [4- (4- ) ] -1,1,1,1,3,3,3- . </xnotran> These may be used alone or in combination of two or more, as required.

The dianhydride monomer that may be used for the polymerization of the polyamic acid may be an aromatic tetracarboxylic dianhydride.

<xnotran> ( PMDA), 3,3',4,4' - ( s-BPDA), 2,3,3',4' - ( a-BPDA), ( ODPA), -3,4,3',4' - ( DSDA), (3,4- ) ,2,2- (3,4- ) -1,1,1,3,3,3- ,2,3,3 ',4' - ,3,3', </xnotran> 4,4 '-benzophenonetetracarboxylic dianhydride (or BTDA), bis (3, 4-dicarboxyphenyl) methane dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, p-phenylene bis (tertiarymonoacid), p-phenylene bis (tertiarymonoacid anhydride), m-triphenyl-3, 4,3',4 '-tetracarboxylic dianhydride, p-triphenyl-3, 4,3',4 '-tetracarboxylic dianhydride, 1, 3-bis (3, 4-dicarboxyphenoxy) benzene dianhydride, 1, 4-bis (3, 4-dicarboxyphenoxy) biphenyl dianhydride, 2-bis [ (3, 4-dicarboxyphenoxy) phenyl ] propane dione hydride (BPADA), 2,3,6, 7-naphthalenetetracarboxylic dianhydride, 1,4,5, 8-naphthalenetetracarboxylic dianhydride, 4' - (2, 2-hexafluoro and low-isopropylidene) diphthalic dianhydride. These may be used alone or in combination of two or more, as required.

The second organic solvent is not particularly limited as long as it is a solvent that can dissolve the polyamic acid, and may be an aprotic polar solvent as an example.

Non-limiting examples of the aprotic polar solvent include amide solvents (e.g., N '-Dimethylformamide (DMF) and N, N' -dimethylacetamide (DMAc), and the like), phenolic solvents (e.g., p-chlorophenol and o-chlorophenol, and the like), N-methyl-pyrrolidone (NMP), γ -butyrolactone (GBL), and Diglyme (Diglyme), and the like, which may be used alone or in combination of two or more thereof.

According to circumstances, the solubility of the polyamic acid can be adjusted by using an auxiliary solvent such as toluene, tetrahydrofuran, acetone, methyl ethyl ketone, methanol, ethanol, water, and the like.

In one example, the second organic solvent that may be particularly preferably used for preparing the second composition of the present invention may be N, N '-dimethylformamide and N, N' -dimethylacetamide as an amide solvent.

For example, the method of polymerizing the polyamic acid can be listed as follows.

The method (1) is a method in which the whole amount of the diamine monomer is put into an organic solvent, and then polymerization is carried out by adding a dianhydride monomer so as to be substantially equimolar with the diamine monomer.

The method (2) of putting the whole amount of dianhydride monomer into an organic solvent and then carrying out polymerization by adding a diamine monomer so as to be substantially equimolar to the dianhydride monomer.

Method (3) after some components of the diamine monomer are placed in the organic solvent, some components of the dianhydride monomer are mixed in a ratio of about 95 to 105 mol% with respect to the reaction components, then the remaining diamine monomer component is added, the remaining dianhydride monomer component continues to be added, and polymerization is performed by making the diamine monomer and dianhydride monomer substantially equimolar.

Method (4) of putting a dianhydride monomer in an organic solvent, mixing a part of components of a diamine compound in a proportion of 95 to 105 mol% with respect to a reaction component, then adding other dianhydride monomer components, continuing to add the remaining diamine monomer component, and carrying out polymerization by making the diamine monomer and the dianhydride monomer substantially equimolar.

Method (5) after reacting some of the diamine monomer components and some of the dianhydride monomer components in an organic solvent to one of an excess to form a first polymer and reacting some of the diamine monomer components and some of the dianhydride monomer components in another organic solvent to one of an excess to form a second polymer, mixing the first polymer and the second polymer and completing polymerization, at which time, when the diamine monomer component is in excess when forming the first polymer, the dianhydride monomer component is in excess in the second polymer and when the dianhydride monomer component is in excess in the first polymer, the diamine monomer component is in excess in the second polymer, the polymerization is conducted in such a manner that the total of the diamine monomer component and the dianhydride monomer component used in these reactions are substantially equimolar by mixing the first polymer and the second polymer.

However, the method is an example to help implement the present invention, and the scope of the present invention is not limited thereto, and any known method may be used.

The weight average molecular weight of the polyamic acid prepared as described above may be 150000g/mole or more to 1000000g/mole or less, specifically 260000g/mole or more to 700000g/mole or less, more specifically 280000g/mole or more to 500000g/mole or less.

The polyamic acid having such a weight average molecular weight can be preferably used for producing a polyimide film having more excellent heat resistance and mechanical properties.

Generally, the weight average molecular weight of the polyamic acid may be proportional to the viscosity of the precursor composition comprising the polyamic acid and the organic solvent, so that the weight average molecular weight of the polyamic acid may be controlled within the above-mentioned range by adjusting the viscosity.

This is because the viscosity of the precursor composition is proportional to the content of the polyamic acid solids, specifically the total amount of dianhydride monomer and diamine monomer used in the polymerization reaction. However, the weight average molecular weight does not indicate a linear one-dimensional proportional relationship with the viscosity, but is proportional in the form of a logarithmic function.

That is, even if the viscosity is increased to obtain a higher weight average molecular weight polyamic acid, the range within which the weight average molecular weight can be increased is limited, but when the viscosity is too high, a problem in manufacturability may be caused due to an increase in pressure inside the mold, or the like, when the precursor composition is discharged through the mold during the polyimide film formation.

Thus, the second composition of the present invention may comprise 15 to 20 wt% of polyamic acid solids and 80 to 85 wt% of organic solvent, in which case the viscosity may be in the range of 90000cP or more and 300000cP or less, in particular 100000cP or more and 250000cP or less. In such a viscosity range, the weight average molecular weight of the polyamic acid may fall within the above range, and the second composition does not cause a problem in the above film forming process.

On the other hand, a filler may be added during the preparation of polyamic acid to improve various properties of the film, such as slidability, thermal conductivity, electrical conductivity, corona resistance, and loop hardness of the polyimide film derived from the second composition. The filler to be added is not particularly limited, but preferable examples thereof include silica, titanium oxide, alumina, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, mica, dicalcium phosphate, barium sulfate, calcium carbonate and the like.

The average particle diameter of the filler is not particularly limited, and may be determined according to the characteristics of the modified polyimide film and the kind of the filler to be added. In one example, the filler may have an average particle size of 0.05 μm to 100 μm, more particularly 0.1 μm to 75 μm, more preferably 0.1 μm to 50 μm, and particularly 0.1 μm to 25 μm.

If the average particle diameter is less than this range, the modification effect is insignificant, and if the average particle diameter is greater than this range, the filler may impair the surface properties of the polyimide film or may cause a reduction in the mechanical properties of the film.

The amount of the filler to be added is not particularly limited, and may be determined by the properties of the modified polyimide film, the particle diameter of the filler, and the like.

In one example, the filler is added in an amount of 0.01 to 100 parts by weight, preferably 0.01 to 90 parts by weight, and more preferably 0.02 to 80 parts by weight, relative to 100 parts by weight of the precursor composition.

When the addition amount of the filler is less than this range, the modification effect by the filler is hardly exhibited, and when the addition amount of the filler is more than this range, the mechanical properties of the polyimide film may be greatly reduced. The method of adding the filler is not particularly limited, and any known method can be used.

Meanwhile, the imidization of the step of obtaining the polyimide film may include casting the precursor composition on a support and drying to prepare a gel film, and then imidizing the gel film to form the polyimide film.

Specific methods of such imidization include a thermal imidization method, a chemical imidization method, or a complex imidization method using the thermal imidization method and the chemical imidization method in combination, which will be described in more detail by the following non-limiting examples.

< thermal imidization method >

The thermal imidization method is a method of removing a chemical catalyst and causing an imidization reaction by a heat source such as hot air or an infrared dryer, and may include: a step of drying the precursor composition to form a gel film; and a step of heat-treating the gel film to obtain a polyimide film.

Here, a gel film may be understood as having a self-supporting film intermediate at an intermediate stage of the conversion from polyamic acid to polyimide.

The gel film may be formed by casting the precursor composition as 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 drying the precursor composition on the support at a variable temperature ranging from 50 ℃ to 200 ℃, specifically from 80 ℃ to 150 ℃.

This may result in the formation of a gel film by partial curing and/or drying of the precursor composition. Which can then be peeled off from the support to obtain a gel film.

According to circumstances, a process of stretching a gel film may be performed to adjust the thickness and size of a polyimide film obtained in a subsequent heat treatment process and improve orientation, and stretching may be performed in at least one of a machine transport direction (MD) and a Transverse Direction (TD) with respect to the machine Transport Direction (TD).

The gel film thus obtained is fixed to a tenter, and then subjected to a heat treatment at a temperature of 50 ℃ to 500 ℃, in detail at a variable temperature ranging from 150 ℃ to 500 ℃, to remove water, residual solvent and the like remaining in the gel film, and almost all of the amic acid groups are imidized to obtain the polyimide film of the present invention.

According to circumstances, the polyimide film obtained as described above may be heated to a temperature of 400 to 650 ℃ for 5 to 400 seconds to further cure the polyimide film, and may be performed under a predetermined tension 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 amic acid groups by adding a dehydrating agent and/or an imidizing agent to a precursor composition.

Herein, the term "dehydrating agent" means a substance which promotes ring-closure reaction by dehydration of polyamic acid, and may be, as non-limiting examples thereof, aliphatic acid anhydrides, aromatic acid anhydrides, N' -dialkylcarbodiimide, halogenated lower aliphatic, halogenated lower fatty acids, arylphosphonic acid dihalides, thionyl halide, and the like. Among them, in view of easy availability and cost, aliphatic acid anhydrides are preferable, and non-limiting examples thereof may be Acetic Anhydride (AA), propionic anhydride and lactic acid anhydride, which may be used alone or in a mixture of two or more.

The "imidizing agent" is a substance having an action of promoting a ring-closing reaction of polyamic acid, and may be, for example, an imide component such as an aliphatic tertiary amine, an aromatic tertiary amine, or a heterocyclic tertiary amine. Among them, heterocyclic tertiary amines may be preferable in view of reactivity as a catalyst. Non-limiting examples of the heterocyclic tertiary amine include quinoline, isoquinoline, β -methylpyridine (BP), pyridine and the like, which may be used alone or in combination of two or more thereof.

The addition amount of the dehydrating agent is preferably in the range of 0.5 mol to 5 mol, and particularly preferably in the range of 1.0 mol to 4 mol, relative to 1 mol of amic acid groups in polyamic acid. In addition, the addition amount of the imidizing agent is preferably in the range of 0.05 mol to 2 mol, and particularly preferably in the range of 0.2 mol to 1 mol, relative to 1 mol of amic acid groups in the polyamic acid.

When the dehydrating agent and the imidizing agent are less than the above ranges, chemical imidization is insufficient and cracks may be formed in the polyimide film to be produced, and the mechanical strength of the film may be reduced. In addition, when these addition amounts exceed the above ranges, imidization may proceed too quickly, in which case it is difficult to cast in the form of a film or the resulting polyimide film may exhibit brittleness (britle), and thus it is not preferable.

< Complex imidization method >

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

Specifically, the complex 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 heat-treating the gel film.

In the chemical imidization, the kinds and amounts of the dehydrating agent and the imidizing agent may be appropriately selected according to the chemical imidization method.

In forming the gel film, the precursor composition comprising the dehydrating agent and/or the imidizing agent is cast in the form of a film on a support such as a glass plate, an aluminum foil, an endless stainless steel belt, or a stainless steel drum, and then the precursor composition on the support is dried at a variable temperature ranging from 50 ℃ to 180 ℃, specifically from 80 ℃ to 180 ℃. In this process, a chemical conversion agent and/or an imidization agent may be used as a catalyst so that an amic acid group can be quickly converted to an imide group.

The gel film thus obtained is fixed in a tenter, and then subjected to a heat treatment at a temperature of 50 to 500 ℃, particularly at a variable temperature of 150 to 300 ℃ to remove water, residual solvent, and the like remaining in the gel film, and almost all of the amic acid groups can be imidized to obtain the polyimide film of the present invention. In such a heat treatment process, a dehydrating agent and/or an imidizing agent may be used as a catalyst to rapidly convert an amic acid group into an imide group, and a high imidization rate may be achieved.

In some cases, the polyimide film obtained as described above may be heated to a temperature of 400 to 650 ℃ for 5 to 400 seconds to further cure the polyimide film, and may remain in the resulting polyimide film. This can be done at a predetermined tension to relieve the pressure.

Detailed Description

Hereinafter, the operation and effect of the present invention will be described in more detail by specific examples of the present invention. However, these embodiments are given only as an example of the present invention, and the scope of the present invention is not determined thereby.

< example 1>

Preparation examples 1 to 1: preparation of the first composition

As bismaleimide resin, 0.21g of "Compound 200" manufactured by the company Yingchu Germany (Evonik) and 71.45g of carbon black were mixed with 213.42g of DMF, and then put into a bead mill to prepare a first composition.

In this case, the average particle diameter of carbon black was 0.4. Mu.m.

For convenience, the addition amounts of bismaleimide and carbon black were collated in parts by weight with respect to 100 parts by weight of the polyimide resin, and are shown in table 1 below.

Preparation examples 1 to 2: preparation of the second composition

652.00g of DMF was charged to a 1L reactor under a nitrogen atmosphere.

After setting the temperature to 25 ℃, 70.84g of ODA as a diamine monomer was added and stirred for about 30 minutes to confirm the monomer dissolution, and then 77.16g of PMDA was added in divided portions, and the final additive amount was adjusted so that the viscosity was in the range of 200000cP to 300000 cP.

After the addition was completed, the mixture was stirred for 1 hour while maintaining the temperature to prepare a second composition comprising polyamic acid polymerized to have a final viscosity of 250000 cP.

Preparation examples 1 to 3: preparation of polyimide film

25.73g of the second composition prepared in production example 1-2 was mixed with 1.22g of the first composition prepared in production example 1-1, and 1.31g of Isoquinoline (IQ) (dehydrating and imidizing agent), 6.20g of Acetic Anhydride (AA), and 4.44g of DMF were added as catalysts to be uniformly mixed, cast to 70 μm on SUS board (1000SA, sandvik) using a spatula, and dried at a temperature of 100 ℃ to 200 ℃.

Then, the film was peeled off from the SUS plate, fixed to a pin frame, and transferred to a high-temperature tenter.

After heating the film from 200 ℃ to 600 ℃ in a high-temperature tenter, it was cooled at a temperature of 25 ℃ and then separated from the pin frame to prepare a polyimide film having a thickness of about 13 μm.

< example 2> to < example 4>

A polyimide film having a thickness of about 13 μm was prepared by the same method as example 1, except that the addition amounts of carbon black and bismaleimide resin were changed as shown in the following table 1 to prepare the first composition according to preparation examples 1-1.

< comparative example 1>

A polyimide film having a thickness of about 13 μm was prepared by the same method as example 1, except that a bismaleimide resin was added, and except that the amount of carbon black was changed as shown in table 1 to prepare the first composition according to preparation example 1-1.

< comparative example 2> to < comparative example 7>

[ Table 1]

	Carbon black (parts by weight)	Bismaleimide resin (parts by weight)
			Example 1	1	5
Example 2	3	7
			Example 3	5	9
Example 4	7	10
			Comparative example 1	3	0
Comparative example 2	1	1
			Comparative example 3	7	3
Comparative example 4	0.3	1
			Comparative example 5	0.5	0.5
Comparative example 6	12	3
			Comparative example 7	7	15

< experimental example 1: alkali resistance test >

The polyimide films prepared in examples 1 to 4 and comparative examples 1 to 6 were subjected to an alkali resistance test according to the above test method (a), and the thinning rate of each polyimide film was calculated, as shown in table 2 (the first thickness is the thickness before immersion in the NaOH solution, and the second thickness is the thickness after immersion in the NaOH solution).

[ Table 2]

	First thickness (μm)	Second thickness (μm)	Reduction ratio (%)
				Example 1	13	9.1	30
Example 2	12.5	9	28
				Example 3	13.2	9.76	26
Example 4	12.3	9.35	24
				Comparative example 1	13	7.8	40
Comparative example 2	13	7.93	39
				Comparative example 3	13	8.19	37
Comparative example 4	12.5	8	36
				Comparative example 5	13	8.19	37
Comparative example 6	13	8.58	34

As shown in table 2, examples within the scope of the present invention comprising bismaleimide resins exhibit relatively excellent alkali resistance.

On the other hand, comparative example 1 containing no bismaleimide resin showed the lowest alkali resistance, indicating that the inclusion of bismaleimide resin mainly acts to improve the alkali resistance.

In addition, it can be seen that the comparative examples containing a very small amount of bismaleimide resin outside the scope of the present invention are inferior in alkali resistance to the examples.

< experimental example 2: moisture absorption test >

The polyimide films of examples 1 to 4 and comparative examples 1 to 6 were cut into a square shape having a size of 5cm × 5cm according to the astm d570 method to prepare a sample, and after the cut sample was dried in an oven at 50 ℃ for 24 hours or more, the weight was measured, and the weighed sample was immersed in water at 23 ℃ for 24 hours and then weighed again, and the weight difference obtained here was expressed in% to measure the moisture absorption rate, the results of which are shown in the following table 3.

[ Table 3]

The results of test example 2 show that examples containing carbon black and bismaleimide resin within the scope of the present invention show relatively good moisture absorption rate.

On the other hand, comparative example 1, which does not contain bismaleimide resin, has the lowest moisture absorption rate.

On the other hand, it can be seen that at least one of carbon black and bismaleimide resin is not within the scope of the present invention and that the comparative example containing an excessive amount or a small amount is inferior in hygroscopicity.

< experimental example 3: light transmittance test >

The transmittance of the polyimide film in the visible light region was measured using a QualColorQuesetXE model manufactured by hunterli (HunterLab) usa, and the results are shown in table 4 below.

However, the polyimide films of examples 1 to 4 and comparative examples 4 to 6 were tested, which can determine the change in light transmittance according to the content of carbon black according to the cause and effect relationship.

[ Table 4]

As a result of example 3, examples including carbon black within the scope of the present invention show very good moisture absorption rate.

On the other hand, comparative examples 4 to 6 in which the content of carbon black was too small within the scope of the present invention showed significantly high light transmittance.

< experimental example 4: tensile Strength test >

The polyimide films of examples 1 to 4 and comparative example 7 were subjected to a tensile strength test. The tensile strength was measured by the method proposed in korean industrial specification KS 6518. The results are shown in Table 5 below.

[ Table 5]

	Tensile Strength (kgf/cm) ² )
		Example 1	230
Example 2	230
		Example 3	225
Example 4	225
		Comparative example 7	170

As can be seen from the results of experimental example 4, comparative example 7 in which the bismaleimide resin was excessively contained had very poor tensile strength. On the other hand, examples 1 to 4 showed good tensile strength despite containing the bismaleimide resin.

From the above results, it can be seen that the polyimide film of the present invention can be compatible with mechanical properties as well as previous alkali resistance, moisture absorption and light transmittance to a desired level.

The foregoing has been a description of embodiments of the present invention, but those skilled in the art to which the present invention pertains will appreciate that many applications and modifications are possible within the scope of the present invention.

Industrial applicability

The polyimide film according to the present invention has been fully described above to improve alkali resistance by containing a bismaleimide resin with carbon black.

In summary, the bismaleimide-based resin is relatively miscible with polyamic acid, and when coated on carbon black, can be readily miscible with and/or dispersed in polyamic acid.

The bismaleimide resin also has excellent chemical resistance, based on which decomposition and/or modification of the polyimide resin by the alkali component between the carbon black and the polyimide resin can be suppressed.

In addition, based on the bismaleimide resin, it is possible to retard the phenomenon of the penetration of the basic component into the polyimide film or to reduce the amount of the penetration of the basic component based on the hygroscopicity thereof.

According to the production method of the present invention, there is a substantial advantage in that the above polyimide film can be realized.

Claims

1. A polyimide film, comprising:

a polyimide resin;

a bismaleimide resin comprising 5 to 10 parts by weight with respect to 100 parts by weight of the polyimide resin; and

carbon black comprising 1 to 10 parts by weight relative to 100 parts by weight of the polyimide resin,

wherein the carbon black has an average particle diameter of 0.1 to 5 μm,

wherein the bismaleimide resin is present in at least one state selected from the group consisting of:

a first state (A) in which the surface of carbon black is coated;

a second state (B) physically bonded to the polymer chain of the polyimide resin; and

and a third state (C) chemically bonded to the polymer chain of the polyimide resin.

2. The polyimide film according to claim 1, wherein the bismaleimide resin is a resin obtained by polymerizing at least one monomer selected from the group consisting of 4,4' -bismaleimidodiphenylmethane, 2, 4-bismaleimidotoluene, and 1, 3-phenylenebismaleimide.

3. The polyimide film according to claim 1,

the polyimide resin is derived from a polyamic acid,

the polyamic acid is polymerized by a dianhydride monomer and a diamine monomer.

4. The polyimide film according to claim 1, wherein a light transmittance in a visible light region is 5% or less.

5. The polyimide film according to claim 1, wherein the thickness reduction ratio by the test method (a) is 30% or less,

wherein the test method (a) comprises the steps of:

corona treating both surfaces of the polyimide film;

a step of preparing a flexible printed circuit board sample by laminating a polyimide film, an adhesive sheet and a copper foil in this order, then using thermocompression bonding at a temperature of 160 ℃ and a pressure of 50kgf for 30 minutes, and then cutting into 4 x 10 cm; and

a step of exposing the flexible printed circuit board sample to a 10% NaOH solution at 50 ℃ for 100 minutes after measuring the thickness of the flexible printed circuit board sample to measure the thickness.

6. The polyimide film according to claim 1, wherein the moisture absorption rate is less than 2%.

7. The method for preparing a polyimide film according to claim 1, comprising:

a step of preparing a first composition by mixing a first organic solvent, carbon black and a bismaleimide resin;

a step of preparing a second composition comprising polyamic acid by mixing and polymerizing a dianhydride monomer and a diamine monomer into a second organic solvent;

a step of preparing a precursor composition by mixing the first composition and the second composition; and

a step of obtaining a polyimide film by imidizing the precursor composition.

8. The method of claim 7, wherein the step of preparing the first composition is performed by a milling procedure.

9. The method of claim 7, wherein the second composition further comprises at least one filler selected from the group consisting of silica, titania, alumina, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, mica, dicalcium phosphate, barium sulfate, and calcium carbonate.

10. The method according to claim 7, wherein the imidizing step includes a step of casting the precursor composition on a support and drying to prepare a gel film, and then imidizing the gel film to form a polyimide film.

11. A cover layer comprising the polyimide film according to claim 1.

12. An electronic device comprising the cover layer of claim 11.