CN112399984B

CN112399984B - Polyimide film containing clay particles and carbon black and preparation method thereof

Info

Publication number: CN112399984B
Application number: CN201880095601.1A
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: 2018-07-18
Filing date: 2018-09-28
Publication date: 2023-08-04
Anticipated expiration: 2038-09-28
Also published as: KR102153506B1; CN112399984A; WO2020017692A1; KR20200009362A

Abstract

The present invention provides a polyimide film comprising: polyimide resin; flat clay (clay) particles; and carbon black, the clay particles being dispersed into the film to form a plurality of barrier layers, at least a portion of the carbon black being located between the barrier layers.

Description

Polyimide film containing clay particles and carbon black and preparation method thereof

Technical Field

The invention relates to a polyimide film containing clay particles and carbon black and a preparation method thereof.

Background

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

Furthermore, polyimide has been attracting attention as a highly functional material, which can be used in microelectronics and optical fields based on insulating properties, excellent electrical properties such as low permittivity, and the like.

As an example of the microelectronic field, there is a high-integrated circuit including a portable electronic device and a communication device. The electrical insulation can be provided to the circuit by attaching or adding polyimide to the circuit, and at the same time can be used as a film to protect the circuit from moisture, light sources, impact, etc.

As described above, as a film for protecting a circuit, various examples are possible, but for a composite film in which an adhesive layer is formed on one or both sides of the film, it may be called a cover film (cover) in a narrow sense, and preferably, a polyimide film may be used in the cover film.

Recently, with importance attached to visual safety, shielding function and light shielding function of a circuit, a special polyimide film containing carbon black and having a black tone has been attracting attention as a cover film material.

However, 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 in the above processes, the polyimide film may be exposed to an alkaline solution.

At this time, when the polyimide film is slightly decomposed or denatured by the alkaline solution, the carbon black contained therein may be largely exfoliated.

Therefore, with the removal of the black tone in the cover film, the shielding property may disappear, and the reduction in surface, weight, and thickness may be caused by the shedding of the carbon black particles, so that the function as the cover film may be greatly reduced.

Therefore, a technology capable of fundamentally solving 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 is prepared in such a manner as to contain clay particles and carbon black.

In this respect, even if unavoidable deformation or decomposition of the polyimide film is caused by an alkaline solution or the like, clay particles contained in the polyimide film of the present invention can effectively act to suppress the shedding of carbon black.

In another aspect, clay particles may help to delay the penetration of alkaline components into polyimide films, or reduce the penetration of alkaline components.

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

In this regard, the present invention essentially aims to provide specific embodiments thereof.

Means for solving the technical problems

In one embodiment, the present invention provides a polyimide film comprising: polyimide resin; flat clay (clay) particles; and carbon black, the clay particles being dispersed into the film to form a plurality of barrier layers, at least a portion of the carbon black being located between the barrier layers.

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

In one embodiment, the invention provides a cover film (coverlay) comprising the polyimide film and an electronic device comprising the cover film.

Embodiments of the present invention are described in further detail below in the order of "polyimide film" and "method for producing polyimide film" of the present invention.

Before this, the terms or words used herein and in the scope of the invention claimed should not be construed as limited to general or dictionary meanings, but interpreted as meanings and concepts conforming to the technical spirit of the present invention on the basis of the principle that the inventor can properly define terms in order to explain his invention in the best manner.

Therefore, it should be understood that the structure of the embodiments described herein is only one embodiment among the preferred embodiments of the present invention and does not represent all technical spirit of the present invention, so various equivalent substitutions and modifications may be made for the present application.

As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. It will be understood that the terms "comprises," "comprising," "includes," "including" or "having," etc., when used herein, are intended to specify the presence of stated features, integers, steps, components, or groups thereof, but do not preclude the presence or addition of one or more other features or integers, steps, components, or groups thereof.

Herein, "dianhydride" is intended to include precursors or derivatives thereof, which may not be dianhydrides in the art, but nevertheless react with diamines to form polyamic acids which can be reconverted to polyimides.

"diamine" is herein intended to include precursors or derivatives thereof, which may not be diamines in the art, but nevertheless react with dianhydrides to form polyamic acids which can be reconverted to polyimides.

When an amount, concentration, or other value or parameter is given as either a range, preferred range, or an enumeration of upper preferable and lower preferable, whether or not the range is individually disclosed, it is to be understood that all ranges which may be formed by any pair of any upper range limit or preferred and any lower range limit or preferred are specifically disclosed. Where a range of values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. The scope of the invention is intended to be limited not to the particular values mentioned when defining the scope.

Polyimide film

The polyimide film is characterized by comprising: polyimide resin; flat clay (clay) particles; and carbon black, the clay particles being dispersed into the film to form a plurality of barrier layers, at least a portion of the carbon black being located between the barrier layers.

Such a polyimide film will be described in detail below, but clay particles have the effect of minimizing permeation of an alkaline solution and suppressing unavoidable denaturation due to the alkaline solution and shedding of carbon black.

As described above, polyimide is generally susceptible to alkaline components, e.g., being decomposed or denatured, when exposed to alkaline environments.

In addition, the polyimide film containing carbon black is not only difficult to prepare, but also, as described above, it can be said that the carbon black is more susceptible to the alkaline component due to the falling off of the carbon black.

The falling off of the carbon black may also cause the light transmittance of the polyimide film containing the carbon black to decrease.

Therefore, there is a need for improving polyimide films, and in particular for improving the 'alkali resistance' of polyimide films containing carbon black.

By alkali resistance is meant a property that the polyimide film is not easily decomposed and/or denatured even when exposed to an alkaline environment, and since the thickness of the polyimide film is reduced upon the decomposition and/or denaturation, alkali resistance can be judged based on the reduction in thickness.

In this regard, as an example of evaluation of alkali resistance, a method of exposing a polyimide film to an alkali solution and measuring a change in film thickness before and after exposure can be exemplified.

The evaluation method (a) is used in the present invention as an evaluation for alkali resistance of a polyimide film.

The evaluation method (a) may include: corona treating the two sides of the polyimide film; a step of preparing a flexible circuit board sample by sequentially laminating a polyimide film, an adhesive sheet, and a copper foil, bonding the laminated polyimide film, adhesive sheet, and copper foil by hot pressing at a temperature of 160 ℃ and a pressure of 50kgf for 30 minutes, and cutting the laminated polyimide film, adhesive sheet, and copper foil into 4 x 10cm pieces; and measuring the thickness of the flexible circuit board sample after exposing the same sample to 10% naoh solution at 50 ℃ for 100 minutes.

The thickness reduction rate of evaluation method (a) can be calculated as a percentage after exposure by calculating the thickness change after exposure compared to the thickness of the flexible circuit board sample measured before exposure to NaOH solution, and expressed as an alkali resistance index.

That is, the alkali resistance index calculated by the thickness reduction rate can be regarded as a quantitative value for alkali resistance.

The alkali resistance index after the above evaluation method (a) can be expressed as about 60% or less for a conventional polyimide film, and in particular, as about 50% or less for an ultrathin film polyimide film having a film thickness of 8 μm or less.

In contrast, for the polyimide film of the present invention containing clay particles and carbon black, since the alkali resistance index of the evaluation method (a) may be 60% or more, specifically 65% or more, there is improved alkali resistance compared to conventional polyimide films.

On the other hand, the clay particles according to the present invention are clay minerals of a layered structure laminated by oxide layers having negative charges, and may be natural clay or synthetic clay particles having a thickness of about 1nm to 100nm, a length of a long axis of 1 μm to 10 μm, and an aspect ratio of about 1 to 1000.

In a specific example, the clay particles may be negatively charged phyllosilicates (phyllosilicides) consisting of nano-sized aluminum silicate or magnesium silicate layers, or sodium ions (Na ⁺ ) Or potassium ion (K) ⁺ ) Potassium or sodium phyllosilicate.

In a more specific example, the phyllosilicate may be chosen from montmorillonite (montm orillonite), hectorite (hectorite), saponite (saponite), beidellite (beidellite)

One or more selected from the group consisting of anhydrite (nontronite), vermiculite (vermicolite), volkonskoite (volkonskoite), sauconite (sauconite), fluorohectorite (fluorohectorite), magadiite (magadite), kaolinite (kaolinite), and halloysite (halloysite), but not limited thereto.

Further, the phyllosilicate, sodium phyllosilicate, and potassium phyllosilicate can be used as (modified) clay treated with quaternary ammonium ions, and such clay particles have hydrophobicity, whereby the phenomenon that an alkaline component permeates into the inside of a polyimide film can be delayed, or the permeation amount of the alkaline component can be reduced, and according to the structure provided inside the polyimide film, even if unavoidable denaturation or decomposition in the polyimide film is caused by an alkaline solution or the like, the falling off of carbon black can be effectively suppressed.

Regarding the above, although it will be more specifically demonstrated by the 'detailed description', in summary, it is estimated that clay particles exist in a polyimide film in at least one state selected from the following states.

In a specific example, the clay particles form a plurality of barrier layers in at least one state selected from the group consisting of:

(a) A first state in which the long axes of the clay particles are at an angle of 0 DEG to 45 DEG to the machine direction (machine direction, MD) of the polyimide film; and

(b) In the second state, the long axes of the clay particles are at an angle of 0 DEG to 45 DEG with respect to the transverse direction (transverse direction, TD) of the polyimide film.

In a more specific example, the first state may be a structure in which long axes of clay particles are parallel with respect to an MD direction of the polyimide film to form a plurality of barrier layers, and the second state may be a structure in which long axes of clay particles are parallel with respect to a TD direction of the polyimide film to form a plurality of barrier layers.

In yet another specific example, the clay particles form a plurality of barrier layers in at least one state selected from the group consisting of:

(a) In a third state, clay particles are arranged on the surface of the polyimide film;

(b) In a fourth state, clay particles are arranged adjacent to the surface of the polyimide film; and

(C) And in a fifth state, clay particles are arranged inside the polyimide film.

As described above, when the polyimide film is slightly decomposed or denatured by the alkaline solution, the carbon black contained in the polyimide film is largely exfoliated, and particularly, the alkaline solution continues to permeate into the site where decomposition or denaturation proceeds from the surface to continuously decompose or denature, so that a problem of continuous exfoliation of the carbon black contained in the polyimide film may occur.

In contrast, the polyimide film of the present invention can form a barrier layer in a third state in which clay particles are disposed on the surface of the polyimide film, and the clay particles having hydrophobicity can inhibit permeation of an alkaline solution from the surface of the polyimide film.

Further, the barrier layer can be formed in a fourth state in which clay particles are disposed adjacent to the surface of the polyimide film and a fifth state in which clay particles are disposed inside the polyimide film, and even if the polyimide film is decomposed or denatured by permeation of an alkaline solution, the phenomenon that carbon black located between the plurality of barrier layers formed of flat clay particles falls off from the polyimide film can be suppressed due to their structures.

Therefore, it is possible to delay the penetration of the alkaline solution into the polyimide film based on the hydrophobicity and the structure of the flat clay particles, or to solve the problem of massive shedding of carbon black even if the alkaline solution is penetrated, and to effectively act on the improvement of the alkali resistance of the polyimide film.

As such, the polyimide film of the present invention containing carbon black and clay particles may have improved alkali resistance based on the clay particles present in the first to fifth states as described above.

However, despite the advantages described above, it is not preferable to conditionally contain a large amount of clay particles.

Specifically, when the content of the clay particles is at a prescribed level, the above-described advantages can be exhibited, but if the content exceeds this level, there is a possibility that the physical properties of the polyimide film are drastically deteriorated, and the advantages due to the clay particles are not significantly increased.

According to circumstances, the clay particles present in excess beyond the scope of the present invention may deteriorate physical properties, and structural defects such as pinholes, cracks, etc. of the polyimide film due to mutual aggregation may make the alkaline solution or the like penetrate better, and at this time, alkali resistance may be reduced instead.

In the present invention, it is important that the physical properties of the polyimide film and the above-mentioned advantages are combined by containing an appropriate amount of clay particles.

In this regard, in the present invention, the polyimide resin may be contained in an amount of 85 to 94.5 wt%, the clay particles in an amount of 2 to 5 wt%, and the carbon black in an amount of 5 to 10 wt%, with respect to the total weight of the polyimide film.

The average particle diameter of the carbon black may be 0.1 μm to 5 μm, and although the content of the carbon black may be selected to exhibit a desired barrier property in the polyimide film, excessive addition of the carbon black may deteriorate the physical properties of the polyimide film and may cause surface defects due to mutual coagulation, so that it is not preferable.

Also, when the content of carbon black is less than the range, the polyimide film cannot have a desired degree of shielding property due to an increase in light transmittance.

In another aspect, the polyimide resins of the present invention may be derived from polyimide acids. The polyimide acid may be polymerized from dianhydride monomers and diamine monomers.

The diamine monomer is an aromatic diamine, and can be classified as follows for example.

1) Diamines having one benzene ring in the structure, diamines having a relatively hard 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), etc.;

2) Diamines having two benzene rings in the structure, for example, diaminodiphenyl ether such as 4,4' -diaminodiphenyl ether (or oxydianiline, ODA), 3,4' -diaminodiphenyl ether and the like, 4,4' -diaminodiphenylmethane (methylenediamine), 3' -dimethyl-4, 4' -diaminobiphenyl, 2' -dimethyl-4, 4' -diaminobiphenyl 2,2' -bis (trifluoromethyl) -4,4' -diaminobiphenyl, 3' -dimethyl-4, 4' -diaminodiphenylmethane, 3' -dicarboxy-4, 4' -diaminodiphenylmethane, 3',5,5' -tetramethyl-4, 4' -diaminodiphenylmethane, bis (4-aminophenyl) sulfide, 4' -diaminobenzanilide, 3' -dichlorobenzidine, 3' -dimethylbenzidine (or o-toluidine), and 2,2' -dimethylbenzidine (or m-toluidine), 3' -dimethoxybenzidine, 2' -dimethoxybenzidine, 3' -diaminodiphenyl ether, 3,4' -diaminodiphenyl ether 2,2' -dimethylbenzidine (or m-toluidine), 3' -dimethoxybenzidine 2,2' -dimethoxy benzidine, 3' -diaminodiphenyl ether, 3,4' -diaminodiphenyl ether, 3,3 '-diamino-4, 4' -dimethoxybenzophenone, 3 '-diaminodiphenylmethane, 3,4' -diaminodiphenylmethane, 4 '-diaminodiphenylmethane, 2-bis (3-aminophenyl) propane, 2-bis (4-aminophenyl) propane 2, 2-bis (3-aminophenyl) -1, 3-hexafluoropropane 2, 2-bis (4-aminophenyl) -1, 3-hexafluoropropane 3,3' -diaminodiphenyl sulfoxide, 3,4 '-diaminodiphenyl sulfoxide, 4' -diaminodiphenyl sulfoxide, and the like;

3) 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-trifluoromethylphenyl, 3' -diamino-4- (4-phenyl) phenoxybenzophenone, 3' -diamino-4, 4' -bis (4-phenylphenoxy) benzophenone, 1, 3-bis (3-aminophenyl sulfide) benzene, 1, 3-bis (4-aminophenyl sulfide) benzene, 1, 3-bis (3-aminophenyl sulfone) benzene, 1, 3-bis (4-aminophenyl) benzene, 1, 4-aminophenyl sulfone, 1-bis [ 1, 3-aminophenyl ] isopropyl ] benzene, 1, 3-bis [ 4-aminophenyl ] phenyl ] isopropyl ] benzene 1, 4-bis [2- (4-aminophenyl) isopropyl ] benzene;

4) Diamines having four benzene rings in the structure, for example, 3 '-bis (3-aminophenoxy) biphenyl, 3' -bis (4-aminophenoxy) biphenyl, 4 '-bis (3-aminophenoxy) biphenyl, 4' -bis (4-aminophenoxy) biphenyl, bis [3- (3-aminophenoxy) phenyl ] ether, bis [3- (4-aminophenoxy) phenyl ] ether, bis [4- (4-aminophenoxy) phenyl ] ether, bis [3- (3-aminophenoxy) phenyl ] ketone, bis [3- (4-aminophenoxy) phenyl ] ketone, bis [4- (3-aminophenoxy) phenyl ] ketone, bis [4- (4-aminophenoxy) phenyl ] ketone, bis [3- (3-aminophenoxy) phenyl ] sulfide, bis [3- (4-aminophenoxy) phenyl ] sulfide, bis [4- (4-aminophenoxy) phenyl ] sulfide, bis [3- (3-aminophenoxy) phenyl ] sulfone, bis [3- (4-aminophenoxy) phenyl ] sulfone, bis [4- (4-aminophenoxy) phenyl ] sulfone, bis [3- (3-aminophenoxy) phenyl ] methane, bis [3- (4-aminophenoxy) phenyl ] methane, bis [4- (3-aminophenoxy) phenyl ] methane, bis [4- (4-aminophenoxy) phenyl ] methane, 2-bis [3- (3-aminophenoxy) phenyl ] propane, 2-bis [3- (4-aminophenoxy) phenyl ] propane, 2-bis [4- (3-aminophenoxy) phenyl ] propane, 2, 2-bis [4- (4-aminophenoxy) phenyl ] propane (BAPP), 2-bis [3- (3-aminophenoxy) phenyl ] -1, 3-hexafluoropropane, 2, 2-bis [3- (4-aminophenoxy) phenyl ] -1, 3-hexafluoropropane, 2, 2-bis [3- (4-aminophenoxy) phenyl ] -1, 3-hexafluoropropane. These may be used alone or in combination of two or more kinds thereof, as required.

The dianhydride monomer may be an aromatic tetracarboxylic dianhydride.

The aromatic tetracarboxylic dianhydride may be, for example, pyromellitic dianhydride (or PMDA), 3',4' -biphenyl tetracarboxylic dianhydride (or s-BPDA), 2, 3',4' -biphenyl tetracarboxylic dianhydride (or a-BPDA), oxydiphthalic dianhydride (or ODPA), diphenylsulfone-3, 4,3',4' -tetracarboxylic dianhydride (or DSDA), bis (3, 4-dicarboxyphenyl) sulfide dianhydride, 2-bis (3, 4-dicarboxyphenyl) -1, 3-hexafluoropropane dianhydride, 2, 3',4' -benzophenone tetracarboxylic dianhydride, 3',4,4' -benzophenone tetracarboxylic dianhydride (or BTDA), bis (3, 4-dicarboxyphenyl) methane dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, p-phenylene bis (trimellitate monoanhydride), p-biphenylene bis (trimellitate monoanhydride), 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 dianhydride, 2,3,6, 7-naphthalene tetracarboxylic dianhydride, 1,4,5, 8-naphthalene tetracarboxylic dianhydride, 4,4' - (2, 2-hexafluoroisopropylidene) diphthalic dianhydride. These may be used alone or in combination of two or more kinds thereof, as required.

Preparation method of polyimide film

The preparation method of the polyimide film in the invention can comprise the following steps: a step (a) of polymerizing a polyimide acid from at least one dianhydride monomer and at least one diamine monomer; a step (b) of preparing a first composition comprising clay particles and a first organic solvent; step (c) of preparing a second composition comprising carbon black and a second organic solvent; a step (d) of mixing the first composition and the second composition into the polyimide acid to prepare a polyimide precursor composition; and (e) forming a film of the polyimide precursor composition on a support and performing a heat treatment to imidize the polyimide precursor composition.

The method for preparing the polyimide acid solution in the invention can be, for example:

(1) A method of polymerizing by adding the entire amount of diamine monomer to a solvent, and then adding dianhydride monomer so as to be substantially equimolar to the diamine monomer;

(2) A method of polymerizing by adding the entire amount of dianhydride monomer to a solvent, and then adding a diamine monomer so as to be substantially equimolar to the dianhydride monomer;

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

(4) A method in which a dianhydride monomer is added to a solvent, a part of components in a diamine compound are 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 so that the diamine monomer and the dianhydride monomer are substantially equimolar to each other to polymerize;

(5) In one solvent, a part of the diamine monomer component and a part of the dianhydride monomer component are reacted so that any one is in excess to form a first composition, in the other solvent, after a part of the diamine monomer component and a part of the dianhydride monomer component are reacted so that any one is in excess to form a second composition, the first and second compositions are mixed and polymerization is completed, and in this case, as the method, there may be exemplified a method in which when the diamine monomer component is in excess when the first composition is formed, the second composition contains an excess of the dianhydride monomer component, and when the first composition contains an excess of the dianhydride monomer component, the second composition is mixed so that all of the diamine monomer component and the dianhydride monomer component used in these reactions are substantially equimolar to polymerize.

The organic solvent is not particularly limited as long as it is a solvent capable of dissolving the polyimide acid, but may be an aprotic polar solvent (aprotic polar solvent) as an example.

As a non-limiting example of the aprotic polar solvent, an amide solvent such as N, N '-Dimethylformamide (DMF) and N, N' -dimethylacetamide (DMAc), a p-chlorophenol, an o-chlorophenol-based solvent, N-methyl-pyrrolidone (NMP), γ -butyrolactone (GBL), and methyl ether (Diglyme) may be cited, and two or more kinds may be used alone or in combination.

According to circumstances, an auxiliary solvent such as toluene, tetrahydrofuran, acetone, methyl ethyl ketone, methanol, ethanol, and water may be used to adjust the solubility of the polyamic acid.

In one example, the organic solvent that may be particularly preferred for use in the preparation of the polyimide precursor composition of the present invention may be N, N '-dimethylformamide and N, N' -dimethylacetamide as the amide solvent.

Of course, the polymerization method is not limited to the above-described examples, and any known method may be used.

The dianhydride monomer may be appropriately selected from the above examples, and in particular, may further include at least one selected from the group consisting of pyromellitic dianhydride (PMDA), 3',4' -biphenyl tetracarboxylic dianhydride (s-BPDA), and 2, 3',4' -biphenyl tetracarboxylic dianhydride (a-BPDA).

The diamine monomer may be appropriately selected from the above examples, and specifically, at least one selected from the group consisting of 1, 4-diaminobenzene (PPD), 1, 3-diaminobenzene (MPD), 2, 4-diaminotoluene, 2, 6-diaminotoluene, and 3, 5-diaminobenzoic acid (DABA) may be preferably used.

The polyimide acid thus prepared may have a weight average molecular weight of from 150000g/mole to 1000000g/mole, specifically from 260000g/mole to 700000g/mole, more specifically from 280000g/mole to 500000 g/mole.

Polyimide acids having such weight average molecular weights can be preferably used in the preparation of polyimide films having excellent heat resistance and physical properties.

In general, the weight average molecular weight of the polyimide acid may be proportional to the viscosity of the precursor composition including the polyimide acid and the organic solvent, and the weight average molecular weight of the polyimide acid may be controlled within the range by adjusting the viscosity.

This is because the viscosity of the precursor composition is proportional to the content of the polyimide acid solid component, specifically, to the total amount of the dianhydride monomer and the diamine monomer used in the polymerization reaction.

However, the weight average molecular weight does not show a one-dimensional linear proportional relationship with respect to viscosity, but is proportional in a logarithmic function.

That is, in order to obtain a polyimide acid having a higher weight average molecular weight, the range of the weight average molecular weight that can be increased is limited even if the viscosity is increased, whereas if the viscosity is too high, there may be a problem in manufacturability due to a pressure rise or the like in the inside of the die when the precursor composition is discharged through the die in the film forming process of the polyimide film.

In this regard, the polyimide acid of the present invention may contain 15 to 20% by weight of polyimide acid solids and 80 to 85% by weight of an organic solvent, and the viscosity may be 90000cP or more and 300000cP or less, and may be 100000cP or more and 250000cP in particular.

Within this viscosity range, the weight average molecular weight of the polyimide acid may fall within the range, and does not cause the aforementioned problems in the film forming process.

On the other hand, in the preparation of the polyimide acid, a filler may be added to achieve the object of improving various properties of a polyimide film derived from the polyimide acid, such as slidability, thermal conductivity, electrical conductivity, corona resistance, coil hardness, and the like.

The filler to be added is not particularly limited, but preferable examples thereof include silica, titanium oxide, aluminum oxide, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, mica, dicalcium phosphate, barium sulfate and calcium carbonate.

The average particle diameter of the filler is not particularly limited, and may be determined according to the characteristics of the polyimide film to be modified and the kind of filler to be added.

In one example, the filler may have an average particle size of 0.05 μm to 100 μm, specifically 0.1 μm to 75 μm, more specifically 0.1 μm to 50 μm, and particularly 0.1 μm to 25 μm.

When the average particle diameter is smaller than this range, the modifying effect is very small, and when larger than this range, the filler may greatly impair the surface properties of the polyimide film or may cause a decrease in physical properties.

The amount of filler to be added is not particularly limited, and may be determined based on the polyimide film characteristics, filler particle diameter, and the like, which need to be modified.

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, more preferably 0.02 to 80 parts by weight, relative to 100 parts by weight of the precursor composition.

When the filler addition amount is less than this range, the modifying effect due to the filler is hardly exhibited, and when it is more than this range, the physical properties of the polyimide film may be greatly lowered. The method of adding the filler is not particularly limited, and any known method can be used.

The step of preparing the first composition or the second composition may be performed by a grinding process.

For the grinding, a bead grinding (bead milling) method may be considered without limitation. Bead milling is also effective at stirring at low flow rates of the mixture, and is advantageous in dispersing clay particles or carbon black.

However, it should be understood that this is merely helpful in practicing the present invention.

As a non-limiting example of the first organic solvent or the second organic solvent that can be used in the step of preparing the first composition or the second composition, a solvent that can disperse clay particles or carbon black and can dissolve polyimide acid after mixing, specifically, the aforementioned aprotic polar solvent can be cited.

In the step of preparing the first composition or the second composition, according to circumstances, a dispersant may be further added, and 0.5 parts by weight or more and 2 parts by weight or less of the dispersant may be added based on 100 parts by weight of the clay particles or the carbon black, and for this kind, a surfactant, a synthetic polymer or a natural polymer may be used as long as it can be dissolved in the first organic solvent or the second organic solvent.

In addition, DISPERBYK-2155, which is commercially available from Pick Germany (BYK), may also be used.

When the addition amount of the dispersant exceeds the range, it is possible to reduce mechanical properties such as corona resistance, heat resistance and the like of the polyimide film, and when it is less than the range, it is difficult to promote carbon black dispersion.

In another aspect, the imidizing in the step of obtaining a polyimide film may include a step of imidizing the gel film to form a polyimide film after casting the precursor composition to a support and drying to prepare the gel film.

As a specific method of such imidization, there may be exemplified a thermal imidization method, a chemical imidization method, or a composite imidization method using the thermal imidization method and the chemical imidization method in combination, and these methods are more specifically described by the following non-limiting examples.

Thermal imidization process

The thermal imidization method is a method of initiating imidization reaction by a heat source such as hot air or an infrared dryer other than a chemical catalyst, 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.

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

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

Partial curing and/or drying may occur in the precursor composition, which may form a gel film. Thereafter, the gel film was peeled from the carrier.

The thickness and size of the polyimide film obtained in the subsequent heat treatment process may be adjusted according to circumstances, and the gel film may be stretched to improve orientation, wherein the stretching process may be performed in at least one of a Machine Direction (MD) and a Transverse Direction (TD) with respect to the machine direction.

After the thus obtained gel film is fixed in a tenter, heat treatment is performed at a variable temperature ranging from 50 ℃ to 500 ℃, specifically from 150 ℃ to 500 ℃ to remove water, residual solvent, and the like remaining in the gel film, and imidization is performed on almost all the amide acid groups remaining, whereby the polyimide film of the present invention can be obtained.

According to circumstances, the polyimide film obtained in the above manner may be heated and processed for 5 seconds to 400 seconds at a temperature of 400 ℃ to 650 ℃ to further cure the polyimide film, and in order to alleviate internal stress that may remain in the obtained polyimide film, the step may also be performed under a predetermined tension.

Chemical imidization process

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

The "dehydrating agent" means a substance that promotes a ring-closure reaction by dehydration of polyamic acid, and as non-limiting examples thereof, aliphatic acid anhydrides, aromatic acid anhydrides, N' -dialkylcarbodiimides, halogenated lower aliphatic acid anhydrides, dihalogenated aryl phosphine, halogenated sulfinyl groups, and the like can be cited.

Among them, aliphatic acid anhydride is preferable in terms of easy purchase and cost, and Acetic Anhydride (AA), propionic anhydride and lactic anhydride may be exemplified by non-limiting examples thereof, and these may be used alone or in combination of two or more.

The "imidizing agent" means a substance having an effect of promoting a ring-closure reaction with respect to the polyamic acid, and may be an imine component, for example, an aliphatic tertiary amine, an aromatic tertiary amine, a heterocyclic tertiary amine, or the like.

Among them, heterocyclic tertiary amines may be preferable from the viewpoint of reactivity of the catalyst. As non-limiting examples of the heterocyclic tertiary amine, quinoline, isoquinoline, β -picoline, pyridine, and the like can be cited, 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 mol to 5 mol, particularly preferably in the range of 1.0 mol to 4 mol, relative to 1 mol of the amide groups 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, based on 1 mole of the amide groups in the polyamic acid.

If the dehydrating agent and the imidizing agent are less than the ranges, chemical imidization may be insufficient, resulting in formation of cracks in the prepared polyimide film, and the mechanical strength of the film may be lowered. And if the amount of them added is more than the range, imidization proceeds too fast, at which time it may be difficult to cast in a film form, or the polyimide film produced exhibits brittleness (brittle), and thus is not preferable.

Composite imidization method

In combination with the chemical imidization method described above, a composite imidization method in which a thermal imidization method is additionally performed may be used in the preparation of the polyimide film.

Specifically, the composite imidization method may include: a step of adding a dehydrating agent and/or an imidizing agent to the precursor composition at a low temperature; and a step of a thermal imidization method, wherein the precursor composition is dried to form a gel film, and the gel film is subjected to a thermal treatment.

In the step of performing the chemical imidization method, the types and the addition amounts of the dehydrating agent and the imidizing agent may be appropriately selected according to the description of the chemical imidization method.

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, a circulating (endless) stainless steel belt or a stainless steel tub, and then the precursor composition on the support is dried at a variable temperature ranging from 50 to 200 ℃, specifically, from 80 to 150 ℃. In these processes, chemical conversion agents and/or imidizing agents act as catalysts, allowing the amide groups to be rapidly converted to imide groups.

After the thus obtained gel film is fixed in a tenter, heat treatment is performed at a variable temperature ranging from 50 ℃ to 500 ℃, specifically from 150 ℃ to 300 ℃ to remove water, catalyst, residual solvent, etc. remaining in the gel film, and imidization is performed on almost all amide acid groups remaining, whereby the polyimide film of the present invention can be obtained.

In the heat treatment as described above, the dehydrating agent and/or the imidizing agent also serve as a catalyst, and an amide group can be rapidly converted into an imide group, so that a high imidization rate can be achieved.

According to circumstances, the polyimide film obtained in the manner described above may be heated and processed for 5 seconds to 400 seconds at a temperature of 400 ℃ to 650 ℃ to further cure the polyimide film, and in order to alleviate internal stress that may remain in the obtained polyimide film, the step may also be performed under a predetermined tension.

On the other hand, in the present invention, in order to realize an ultra-thin film of 8 μm or less, it is necessary to control the process conditions such as the ejection amount, the speed, and the pressure when applying (ejecting) the polyimide acid to the carrier.

Specifically, when it is desired to minimize vibration at the time of discharging the polyamic acid solution from the T-Die to the endless belt (end belt) and landing in the form of a film, for this reason, when forming a discharged film, it is possible to apply a pressure lower than that used at the time of producing a conventional polyimide film, for example, at 10mmH ₂ O to 40mmH ₂ Air (air) is supplied under pressure of O.

At this time, the amount discharged from the T-die and the velocity of the endless belt may satisfy the following formula, for example, the amount discharged from the T-die may be 150 kg/hour to 300 kg/hour, and the velocity of the endless belt may be 15mpm to 25mpm.

Equation 1:

the amount of discharge from the T-die/the time of discharge from the T-die=specific gravity of film (T-die cross-sectional area)/(velocity of endless belt)

On the laboratory level, an ultrathin polyimide film can be obtained by adjusting the casting thickness, however, in the mass production process, when the range is satisfied, an ultrathin thickness of 8 μm or less can be achieved.

Specifically, the polyimide film according to the present invention may have a thickness of 7.5 μm or less, specifically, 3 μm to 7.5 μm, more specifically, 5 μm to 7.5 μm.

Also, when the heat treatment is performed by using a dryer or the like after being fixed to the pin frame, in order to prevent the film from being broken in the heat treatment process, the heat treatment may be performed at a temperature of 50 to 150 ℃ lower based on the highest heat treatment temperature when the yellow polyimide film of the same thickness is prepared.

In addition, the imidized film may be thinned by cooling treatment at a temperature of 20 ℃ to 30 ℃.

Detailed Description

Hereinafter, the operation and effect of the invention will be further described by means of specific examples of the invention. However, such embodiments are presented as examples of the invention only and are not intended to limit the scope of the invention as claimed thereby.

Example 1

Preparation example 1: polymerization of polyamic acid

As a polymerization process of the polyimide acid solution, 425g of Dimethylformamide (DMF) was added as a solvent in a 500mL reactor under a nitrogen atmosphere.

After setting the temperature to 25 ℃, 35.90g of 4,4' -diaminodiphenyl ether (ODA) was added as a diamine monomer, and stirred for about 30 minutes, after confirming that the monomer was dissolved, 39.10g of pyromellitic dianhydride (PMDA) was added as a dianhydride monomer, and finally, the final addition amount was adjusted and then added so that the final viscosity was 250000 cps to 280000 cps.

After the addition was completed, the temperature was maintained while stirring for 1 hour to polymerize the polyamic acid solution so that the final viscosity was 280000 centipoise.

Preparation example 2: preparation of the first composition

In the form of a first organic solvent100g of the agent of N, N' -Dimethylformamide (DMF) was mixed with 10g of montmorillonite (Cloisite) as clay particlesTo prepare a first composition.

Preparation example 3: preparation of the second composition

After mixing 10g of carbon black and 0.1g of BYK-430 dispersant in 100g of DMF as a second organic solvent, a second composition containing carbon black having an average particle size of 0.4 μm was prepared using a mill.

Preparation example 4: preparation of polyimide film

After mixing 6.55g of the first composition prepared in preparation example 2, 2.81g of the second composition prepared in preparation example 3, and adding 4.76g of Isoquinoline (IQ), 26.36g of Acetic Anhydride (AA), and 18.87g of DMF as catalysts to 50g of the polyimide acid solution prepared in preparation example 1, they were uniformly mixed, cast on a stainless steel (SUS) plate (100 SA, manufactured by Sandvik corporation, sweden) to 70 μm using a doctor blade, and then dried at a temperature ranging from 100 to 200 ℃.

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

After heating the film from 200 ℃ to 600 ℃ on a high temperature tenter, cooling at 25 ℃ and then separating from the pin frame, a polyimide film of 7.5 μm thickness was prepared which contained 7 wt% of carbon black and 3 wt% of clay particles with respect to the total weight of the polyimide film.

Examples 2 to 4

A polyimide film having a thickness of about 7.5 μm was produced by the same method as in example 1, except that the contents of carbon black and clay particles were changed to those shown in table 1 below.

Comparative example 1

A polyimide film having a thickness of about 7.5 μm was prepared by the same method as in example 1, except that clay particles were not added.

Comparative examples 2 to 9

TABLE 1

Experimental example 1: alkali resistance index evaluation

For the polyimide films prepared in examples 1 to 4, comparative examples 1 to 9, respectively, the thickness change rate was measured according to the foregoing evaluation method (a), and the results thereof are shown in table 2 below.

Experimental example 2: transmittance evaluation

For the polyimide films prepared in examples 1 to 4, comparative examples 1 to 9, respectively, transmittance was measured in the visible light region by the ASTM D1003 method of the american society for testing and materials using a transmittance measuring apparatus (model: colorQuesetXE, manufacturer: hunterLab, usa), the results of which are shown in table 2 below.

Experimental example 3: tensile property evaluation

For the polyimide films prepared in examples 1 to 4, comparative examples 1 to 9, respectively, tensile properties were measured by the method provided in KS6518 of korean industrial standard, and the results thereof are shown in table 2 below.

TABLE 2

	Alkali resistance index (%)	Transmittance (%)	Tensile Property (MPa)
				Example 1	62	0.14	225
Example 2	67	0.11	235
				Example 3	63	0.07	230
Example 4	67	0.05	235
				Comparative example 1	54	0.12	210
Comparative example 2	67	0.01	150
				Comparative example 3	56	0.09	215
Comparative example 4	59	65.0	220
				Comparative example 5	63	20.0	200
Comparative example 6	62	7.0	195
				Comparative example 7	56	0.0	160
Comparative example 8	49	0.0	145
				Comparative example 9	40	0.0	125

Referring to the table 2, for examples containing clay particles and carbon black in the scope of the present invention, it was confirmed that alkali resistance indexes were 60% or more and that the shedding of carbon black due to alkaline solution was relatively small.

That is, it was confirmed that the polyimide film of the example was high in alkali resistance.

In addition, it was confirmed that the transmittance was 0.5% or less and the tensile property was 225MPa or more, which satisfies the physical properties of polyimide films that can be used as a desired shielding property.

In contrast, it was confirmed that the alkali resistance index was not excellent for comparative example 1 containing no clay particles and comparative example 3 containing clay particles less than the scope of the present invention, and that the measured tensile properties were lower than those of comparative example 2 containing clay particles in excess.

In addition, comparative examples 4 and 5 containing clay particles or carbon black less than the range of the present invention have very high transmittance and thus cannot be used as polyimide films requiring shielding performance.

In contrast, it was confirmed that any one of physical properties of alkali resistance index, transmittance or tensile properties was significantly lowered for comparative examples 6 to 9 containing clay particles or carbon black in excess of the range of the present invention.

Although the present invention has been described in detail with reference to the embodiments thereof, a person of ordinary skill in the art to which the present invention pertains can make various applications and modifications within the scope of the present invention based on the above.

Industrial applicability

In the above, it has been fully explained that the polyimide film according to the present invention contains clay particles and carbon black, so that alkali resistance can be improved.

In summary, since the polyimide film containing clay particles is excellent in chemical resistance, the decomposition and/or denaturation of the polyimide resin due to the alkaline component can be suppressed between the carbon black and the polyimide resin based on this.

Furthermore, the clay particles may delay the penetration of the alkaline component into the polyimide film based on the hygroscopicity thereof, or may reduce the penetration amount of the alkaline component.

The preparation method according to the present invention has a substantial advantage in that the aforementioned polyimide film can be realized.

Claims

1. A polyimide film, comprising, relative to the total weight of the polyimide film:

85 to 94.5% by weight of a polyimide resin;

2 to 5% by weight of flat clay particles; and

5 to 10% by weight of carbon black,

wherein the total weight of each component is 100 wt%,

the clay particles are dispersed into the film to form a plurality of barrier layers,

at least a portion of the carbon black is located between the barrier layers,

the polyimide film has an alkali resistance index of 60% or more as evaluated by taking the thickness as a reference,

wherein the polyimide film has a light transmittance of 0.5% or less in the visible light region and a tensile strength of 225MPa or more.

2. The polyimide film according to claim 1, wherein,

the clay particles form a plurality of barrier layers in at least one state selected from the group consisting of:

(a) A first state in which the long axes of the clay particles are at an angle of 0 DEG to 45 DEG with respect to the machine direction of the polyimide film; and

(b) In the second state, the long axes of the clay particles are at an angle of 0 DEG to 45 DEG with respect to the transverse direction of the polyimide film.

3. The polyimide film according to claim 2, wherein the first state is a state in which long axes of clay particles are parallel with respect to a machine direction of the polyimide film to form a plurality of barrier layers.

4. The polyimide film according to claim 2, wherein the second state is a state in which long axes of clay particles are parallel with respect to a lateral direction of the polyimide film to form a plurality of barrier layers.

5. The polyimide film according to claim 1, wherein,

6. The polyimide film according to claim 1, wherein the clay particles are at least one selected from the group consisting of phyllosilicates, phyllosilicates filled with sodium ions between layers, phyllosilicates filled with potassium ions between layers, and clay treated with quaternary ammonium ions.

7. The polyimide film according to claim 6, wherein the phyllosilicate is at least one selected from the group consisting of montmorillonite, hectorite, saponite, beidellite, anhydrite, vermiculite, volkonskoite, sauconite, fluorohectorite, magadite, kaolinite, and halloysite.

8. The polyimide film according to claim 1, wherein,

the polyimide resin is derived from a polyimide acid,

the polyimide acid is an acid polymerized from at least one dianhydride monomer and at least one diamine monomer.

9. The polyimide film according to claim 8, wherein the dianhydride monomer is selected from the group consisting of pyromellitic dianhydride, 3',4' -biphenyl tetracarboxylic dianhydride, 2, 3',4' -biphenyltetracarboxylic dianhydride, oxydiphthalic dianhydride, diphenyl sulfone-3, 4,3',4' -tetracarboxylic dianhydride, bis (3, 4-dicarboxyphenyl) sulfide dianhydride, 2-bis (3, 4-dicarboxyphenyl) -1, 3-hexafluoropropane dianhydride, 2, 3',4' -benzophenone tetracarboxylic dianhydride, 3',4' -benzophenone tetracarboxylic dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, p-phenylene bis (trimellitate monoanhydride), p-biphenylene bis (trimellitate monoanhydride), m-triphenyl-3, 4,3', at least one of the group consisting of 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 dianhydride, 2,3,6, 7-naphthalene tetracarboxylic dianhydride, 1,4,5, 8-naphthalene tetracarboxylic dianhydride, 4' - (2, 2-hexafluoroisopropylidene) diphthalic dianhydride.

10. The polyimide film according to claim 8, wherein, the diamine monomer is selected from the group consisting of diaminodiphenyl ether including 1, 4-diaminobenzene, 1, 3-diaminobenzene, 2, 4-diaminotoluene, 2, 6-diaminotoluene, 3, 5-diaminobenzoic acid, 4 '-diaminodiphenyl ether, 3,4' -diaminodiphenyl ether, 4 '-diaminodiphenyl methane, and 3,3' -dimethyl-4, 4 '-diaminobiphenyl, 2' -bis (trifluoromethyl) -4,4 '-diaminobiphenyl, 3' -dimethyl-4, 4 '-diaminodiphenylmethane, 3' -dicarboxy-4, 4 '-diaminodiphenylmethane, 3', at least one selected from the group consisting of 5,5 '-tetramethyl-4, 4' -diaminodiphenylmethane, bis (4-aminophenyl) sulfide, 4 '-diaminobenzanilide, 3' -dichlorobenzidine, 3 '-dimethylbenzidine and 2,2' -dimethylbenzidine.

11. The polyimide film according to claim 1, wherein the carbon black has an average particle diameter of 0.1 μm to 5 μm.

12. The polyimide film according to claim 1, wherein the polyimide film has a thickness of 2 μm to 8 μm.

13. A method for producing a polyimide film, which is used for producing the polyimide film according to claim 1, characterized by comprising:

Step (a) of polymerizing a polyimide acid from at least one dianhydride monomer and at least one diamine monomer;

a step (b) of preparing a first composition comprising clay particles and a first organic solvent;

step (c) of preparing a second composition comprising carbon black and a second organic solvent;

a step (d) of mixing the first composition and the second composition into the polyimide acid to prepare a polyimide precursor composition; and

and (e) forming a film and heat-treating the polyimide precursor composition on a carrier to imidize.

14. A cover film comprising the polyimide film according to claim 1.

15. An electronic device comprising the cover film according to claim 14.