CN111315806A

CN111315806A - Ultrathin black polyimide film and preparation method thereof

Info

Publication number: CN111315806A
Application number: CN201880072480.9A
Authority: CN
Inventors: 林铉才; 李吉男; 金纪勋
Original assignee: SKCKolon PI Co Ltd
Current assignee: Polyimide Advanced Materials Co ltd
Priority date: 2017-11-10
Filing date: 2018-10-16
Publication date: 2020-06-19
Anticipated expiration: 2038-10-16
Also published as: WO2019093669A2; CN111315806B; KR101906394B1; WO2019093669A3

Abstract

The present invention provides a method for preparing an ultra-thin black polyimide film obtained by mixing and imidizing two or more different polyamic acids, the method comprising: a step (a) of polymerizing a first polyamic acid having excellent rigidity from a first dianhydride and a first diamine; a step (b) of polymerizing a second polyamic acid having excellent chemical resistance from an End-Capping Agent, a second dianhydride, and a second diamine; a step (c) of preparing carbon black having an average particle diameter of 0.1 to 5 μm using a grinder and preparing a black crude liquid containing the carbon black; a step (d) of preparing a mixed solution by mixing the second polyamic acid and the black crude liquid; and (e) mixing and dispersing the mixed solution in the first polyamic acid, and then forming a film on a support and imidizing the film by heat treatment.

Description

Ultrathin black polyimide film and preparation method thereof

Technical Field

The invention relates to an ultrathin black polyimide film and a preparation method thereof.

Background

Generally, a Polyimide (PI) resin refers to a high temperature resistant resin prepared by solution-polymerizing an aromatic acid dianhydride with an aromatic diamine or an aromatic diisocyanate to prepare a polyamic acid derivative, followed by dehydration by ring closure at high temperature and by imidization.

The polyimide resin is generally polymerized from an aromatic acid dianhydride, such as pyromellitic dianhydride (PMDA) or biphenyltetracarboxylic dianhydride (BPDA), and an aromatic diamine component, such as Oxydianiline (ODA), p-phenylenediamine (p-PDA), m-phenylenediamine (m-PDA), Methylenedianiline (MDA), bisaminophenylhexafluoropropane (HFDA).

Polyimide resins are insoluble and infusible, super heat-resistant resins and have excellent properties such as thermal oxidation resistance, heat resistance, radiation resistance, low-temperature properties, chemical resistance and the like, and thus are widely used for heat-resistant high-tech materials such as automobile materials, aviation materials, spacecraft materials and the like, and electronic materials such as insulating coating agents, insulating films, semiconductors, electrode protective films of TFT-LCDs and the like.

Recently, as a cover film (cover), it is widely used for portable electronic devices and communication devices.

The cover film is used for protecting electronic components such as lead frames of printed circuit boards and semiconductor integrated circuits, and physical properties such as thinning and ultra-thinning are required, and recently, optical properties such as safety, portability, visual effect, and concealment of the electronic components or mounted components are also required.

On the other hand, when a polyimide film is used as a coverlay film for a printed circuit board, the manufacturing process of the printed circuit board includes a drilling (drill) process, an electroplating process, a desmear (desmear) process, a cleaning process, and the like, through which the coverlay film composed of the polyimide film is inevitably exposed to an alkaline solution.

However, it is well known that polyimides are generally very susceptible to alkali, for example, being decomposed or undergoing denaturation or the like upon exposure to an alkaline environment.

Therefore, there is a problem that when a polyimide film is used as a coverlay film, it is inevitably exposed to alkali, thereby decomposing or denaturing the polyimide, making the thickness of the film thin or changing the physical properties, and thus its function as a coverlay film is deteriorated and the reliability of products manufactured using it is remarkably lowered.

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

Disclosure of Invention

Technical problem to be solved by the invention

The present invention is made to solve the above-described problems of the prior art and the problems required in the related art.

The present inventors have conducted intensive studies and various experiments, as described hereinafter, by including a step of mixing a mixed solution in which a second polyamic acid and a black crude liquid are mixed in a first polyamic acid to perform imidization, thereby providing an ultra-thin black polyimide film having a thickness of 8 μ or less, but having excellent optical properties such as gloss, transmittance, mechanical stability, and alkali resistance.

In the step of polymerizing the second polyamic acid, the storage stability of the mixed solution containing the second polyamic acid and the black crude liquid can be improved by adding an end-capping agent.

This can improve reliability of physical properties of the polyimide film without being affected by the storage time of the raw material.

Means for solving the problems

In order to achieve the object, the present invention provides a method for preparing an ultra-thin black polyimide film obtained by mixing and imidizing two or more different polyamic acids, the method comprising: a step (a) of polymerizing a first polyamic acid having excellent rigidity from a first dianhydride and a first diamine; a step (b) of polymerizing a second polyamic acid having excellent chemical resistance from an End-Capping Agent, a second dianhydride, and a second diamine; a step (c) of preparing carbon black having an average particle diameter of 0.1 to 5 μm using a grinder and preparing a black crude liquid containing the carbon black; a step (d) of preparing a mixed solution by mixing the second polyamic acid and the black crude liquid; and (e) mixing and dispersing the mixed solution in the first polyamic acid, and then forming a film on a support and imidizing the film by heat treatment.

Specifically, the first polyamic acid and the second polyamic acid may form a first polyimide chain and a second polyimide chain, respectively, through an imidization step.

Also, the first polyamic acid and the second polyamic acid may form a structure in which at least a part of the first polyimide chain and the second polyimide chain is crosslinked through an imidization step.

The film may comprise, relative to the total weight of the polyimide film: 80 to 93 weight percent of a first polyimide chain having excellent rigidity; 2 to 15 weight percent of a second polyimide chain having excellent chemical resistance; and 3 to 10 weight percent of carbon black having an average particle diameter of 0.1 to 5 μm, the alkali resistance index evaluated based on the thickness of the polyimide film may be 70% or more, and the thickness of the film may be 8.0 μm or less.

The first dianhydride and the second dianhydride may be each independently one or more selected from the group consisting of pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), oxydiphthalic anhydride (ODPA), and benzophenonetetracarboxylic dianhydride (BTDA), and the first diamine and the second diamine may be each independently one or more selected from the group consisting of 1, 4-phenylenediamine (PPD), 4 '-Oxydianiline (ODA), 3,4' -oxydianiline, 2-bis [4'- (4-aminophenoxy) phenyl ] propane (BAPP), 4' -Methylenedianiline (MDA), and 1, 3-bis (4-aminophenoxy) benzene (TPE-R).

Specifically, the first dianhydride may not include a flexible dianhydride, or the first dianhydride may include less than 10 mol% of a flexible dianhydride with respect to the total amount of dianhydride monomers constituting the first polyamic acid, and the first diamine may not include a flexible diamine, or the first diamine may include less than 80 mol% of a flexible diamine with respect to the total amount of diamine monomers constituting the first polyamic acid, and the flexible dianhydride and the flexible diamine may respectively include two or more benzene rings in a molecular structure.

And the second dianhydride may include 80 mol% or more of a flexible dianhydride with respect to the total amount of dianhydride monomers constituting the second polyamic acid, and the second diamine may include 80 mol% or more of a flexible diamine with respect to the total amount of diamine monomers constituting the second polyamic acid, and the flexible dianhydride and the flexible diamine may respectively include two or more benzene rings in a molecular structure.

In a more specific example, the flexible dianhydride may be one or more selected from the group consisting of biphenyl tetracarboxylic dianhydride (BPDA), Oxydiphthalic Dianhydride (ODPA), and Benzophenone Tetracarboxylic Dianhydride (BTDA).

The flexible diamine may be one or more selected from the group consisting of 4,4 '-Oxydianiline (ODA), 3,4' -oxydianiline, 2-bis [4'- (4-aminophenoxy) phenyl ] propane (BAPP), 4' -Methylenedianiline (MDA), and 1, 3-bis (4-aminophenoxy) benzene (TPE-R).

On the other hand, when the solid content is 15%, the polymerization viscosity of the second polyamic acid may be 100000 to 150000 cps, the concentration of the mixed solution may be 2 to 10 weight%, and the viscosity may be 50 to 1000 cps.

The content of the end-capping agent may be 0.05 to 1 weight percent with respect to the solid content of the second polyamic acid.

Specifically, the capping agent may be one or more selected from the group consisting of Phthalic Anhydride (PA), Maleic Anhydride (MA), and Glutaric Anhydride (GA).

Also, the present invention may provide an ultra-thin black polyimide film prepared by the preparation method.

The present invention also provides an ultra-thin black polyimide film obtained by mixing and imidizing two or more different polyamic acids, including, based on the total weight of the polyimide film: 80 to 93 weight percent of a first polyimide chain having excellent rigidity; 3 to 15 weight percent of a second polyamide chain having excellent chemical resistance; and 3 to 10% by weight of carbon black having an average particle diameter of 0.1 to 5 μm, the alkali resistance index being 70% or more as evaluated based on the thickness of the polyimide film.

The film may have a thickness of 3 to 7.5 μm, a light transmittance of 10% or less in a visible light region, and a glossiness of 10 to 50%.

Also, the present invention may provide a coverlay (coverlay) including the ultra-thin black polyimide film, and may provide an electronic device including the coverlay.

Drawings

Fig. 1 is a photograph of the outer surface of FCCL prepared using the ultra-thin black polyimide film of comparative example 1 after exposure to alkali.

Fig. 2 is a photograph of the outer surface of FCCL prepared using the ultra-thin black polyimide film of example 1 after exposure to alkali.

Detailed Description

According to the method for preparing an ultra-thin black polyimide film of the present invention, a polyimide film obtained by mixing and imidizing two or more different polyamic acids may include: a step of polymerizing a first polyamic acid having excellent rigidity from a first dianhydride and a first diamine; a step of polymerizing a second polyamic acid having excellent chemical resistance from an end-capping agent, a second dianhydride, and a second diamine; a step of preparing carbon black having an average particle diameter of 0.1 to 5 μm using a grinder and preparing a black crude liquid containing the carbon black; a step of preparing a mixed liquid by mixing the second polyamic acid and the black crude liquid; and a step of mixing and dispersing the mixed solution in the first polyamic acid, then forming a film on a support, and performing imidization by heat treatment.

Also, the first polyamic acid and the second polyamic acid may form a first polyimide chain and a second polyimide chain, respectively, through an imidization step.

Specifically, the first polyamic acid and the second polyamic acid may form a structure in which at least a part of the first polyimide chain and the second polyimide chain is cross-linked through an imidization step.

That is, the present invention includes a step of imidizing by mixing after polymerizing 1 polyamic acid having superior rigidity and a second polyamic acid having superior chemical resistance, respectively, so that a first polyimide chain having superior rigidity and a second polyimide chain having superior chemical resistance can be maintained in a polyimide film, whereby the polyimide film can increase chemical resistance to a level corresponding to the second polyimide chain while maintaining mechanical rigidity at a level corresponding to the first polyimide chain.

Polyimide polymerized with a low-flexibility monomer has excellent mechanical rigidity, but its chemical resistance is relatively low; while polyimide polymerized with highly flexible monomers has excellent chemical resistance, its mechanical rigidity is relatively low.

In order to simultaneously secure mechanical rigidity and chemical resistance of the polyimide film, the polyamic acid is polymerized by mixing a low-flexibility monomer and a high-flexibility monomer, and when the polyimide film is thus prepared, only a polyimide film having moderate mechanical rigidity and moderate chemical resistance can be obtained, and a polyimide film having excellent mechanical rigidity and chemical resistance as in the present invention cannot be obtained.

That is, the preparation method according to the present invention maintains the properties of each polyimide chain even after the imidization step, compared to the preparation method of polymerizing a polyamic acid solution by simply mixing monomers having different properties, and thus has an advantage that the mechanical properties and the chemical properties of the prepared film can be simultaneously satisfied.

In the step of polymerizing the first polyamic acid or the second polyamic acid, an aprotic polar solvent (aprotic polar solvent) is generally used as the amide-based solvent.

For example, N '-Dimethylformamide (DMF), N' -Dimethylacetamide (DMF), N-methyl-pyrrolidone (NMP), and the like can be used alone or in combination of 2 or more, as necessary.

The dianhydride and the diamine may be added in the form of powder (powder), block (bump) or solution, and are preferably added in the form of solution in order to adjust the polymerization viscosity while the reaction is carried out by adding the dianhydride and the diamine in the form of powder in the initial stage of the reaction.

For example, the dianhydride and the diamine are added in powder form to react with each other, and then the dianhydride is added in solution form to react until the viscosity of the first polyamic acid or the second polyamic acid reaches a predetermined range.

On the other hand, the catalyst may be further added to a mixed solution of the first polyamic acid, the second polyamic acid, and carbon black, and then applied to a support.

In this case, a dehydration catalyst composed of an anhydrous acid such as acetic anhydride and a tertiary amine such as isoquinoline, β -methylpyridine, pyridine and the like may be used as the catalyst, and may be used in the form of an anhydrous acid/amine mixture or an anhydrous acid/amine/solvent mixture.

The amount of the anhydrous acid to be added may be calculated from the molar ratio of the o-carboxyamide functional groups (o-carboxyamide functional groups) in the first polyamic acid solution and the second polyamic acid solution, and may be 1.0 mol to 5.0 mol, and the amount of the tertiary amine to be added may be calculated from the molar ratio of the o-carboxyamide groups in the polyamic acid solution, and specifically, may be 0.2 mol to 3.0 mol.

And, in the step of gelling by heat-treating the polyamic acid solution applied to the support, the gelling temperature condition may be 100 to 250 ℃.

The carrier may use a glass plate, an aluminum foil, a circulating stainless steel belt, a stainless steel tub, or the like.

The treatment time required for gelation may be 5 to 30 minutes, but is not limited thereto, and may vary depending on the gelation temperature, the kind of support, the coating amount of the polyamic acid solution, and the mixing conditions of the catalyst.

After separating the gel film from the support, heat treatment is performed to complete drying and imidization.

The heat treatment temperature may be 100 to 500 deg.c and the heat treatment time may be 1 to 30 minutes. When the gel film is heat-treated, it can be heat-treated while being fixed on a fixable supporter such as a pin-type frame or a clip-type.

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 process conditions such as the discharge amount, rate, pressure, and the like when applying (discharging) polyamic acid to a support.

In particular, it is required to minimize the shock when the polyamic acid solution is discharged from a T-Die (T-Die) to an Endless Belt (end Belt) and landed in a film form, and for this reason, when the discharged film is formed, it may be generally used at a pressure lower than that used in the preparation of the polyimide film, for example, 10mmH₂O to 40mmH₂Air (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 formulas, for example, the amount discharged from the T-die may be 150 kg/hr to 300 kg/hr, and the velocity of the endless belt may be 15mpm to 25 mpm.

[ formula ]

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

On a laboratory level, a polyimide film of an ultra-thin thickness can be obtained by adjusting the casting thickness, but in a mass production process, when the range is satisfied, an ultra-thin thickness of 8 μ or less can be achieved.

Also, when the heat treatment is performed by using a dryer or the like after being fixed to the pin-type frame, in order to prevent the film from being cracked during the heat treatment, the heat treatment may be performed at a temperature lower than the maximum heat treatment temperature standard of 50 ℃ to 150 ℃ in the case of preparing a yellow polyimide film of the same thickness.

The imidized film can be formed into a thin film by cooling treatment at a temperature of 20 to 30 ℃.

On the other hand, the film prepared by the method for preparing an ultra-thin black polyimide film may include, relative to the total weight of the polyimide film: 80 to 93 weight percent of a first polyimide chain having excellent rigidity; 2 to 15 weight percent of a second polyimide chain having excellent chemical resistance; and 3 to 10 weight percent of carbon black having an average particle diameter of 0.1 to 5 μm, the alkali resistance index evaluated with the thickness of the polyimide film as a standard being 70% or more, and the thickness of the film being 8.0 μ or less.

That is, the film prepared by the method of preparing an ultra-thin black polyimide film of the present invention includes a small amount of the second polyimide chain having excellent chemical resistance of 3 to 15 weight percent, so that it is possible to maintain physical properties of high mechanical rigidity, high insulation, etc. corresponding to the level of the first polyimide chain at a desired level, and also to improve chemical resistance to a level corresponding to the second polyimide chain, in detail, to improve alkali resistance index.

When the content of the second polyimide chain is less than 2 weight percent, it is difficult to achieve desired chemical resistance, and on the contrary, when the content of the second polyimide chain is more than 15 weight percent, mechanical rigidity and thermal properties of the prepared film may be lowered, thus being undesirable.

As described above, in general, polyimide is susceptible to alkali, for example, being decomposed or denatured when exposed to an alkaline environment.

The alkali resistance refers to a property that the polyimide film is not easily decomposed or denatured even when exposed to an alkali environment.

As an index for evaluating the alkali resistance, a method of measuring a change in thickness of a polyimide film before and after exposure to a NaOH solution and a desmear solution after the exposure to the film can be used.

The method of evaluating the alkali resistance index (evaluation method (a)) is as follows.

After the double-sided corona treatment of the polyimide film, a flexible circuit board (FCCL) sample was prepared by applying a Hot Press (Hot Press) at a pressure of 50kgf and a temperature of 160 ℃ for 30 minutes for bonding in a structure of the polyimide film, an adhesive sheet (adhesive), and a copper foil.

FCCL cut to 4 x 10cm was exposed to 10% NaOH solution for 3 minutes at 55 ℃ and to desmear solution (10% NaMnO) at 55 ℃₄+ 4% NaOH) was repeated twice after 5 minutes and the thickness of the film was measured, the thickness before exposure and the degree of change in thickness after exposure being expressed as a percentage compared to the thickness before exposure to the NaOH solution and the desmearing solution.

The ultra-thin black polyimide film prepared according to the preparation method of the present invention may have a structure in which a polyimide chain having excellent rigidity and at least a portion of a polyimide chain having excellent chemical resistance are simultaneously cross-linked, and thus has excellent advantages not only in mechanical properties but also in chemical properties such as alkali resistance.

Also, with this structure, even if the first polyimide chain having relatively low chemical resistance is decomposed due to exposure to alkali, the second polyimide having excellent chemical resistance supports the entire film, so that the degree of external deformation such as thickness of the polyimide film can be significantly reduced.

On the other hand, the first dianhydride and the second dianhydride may each independently be one or more selected from the group consisting of pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), oxydiphthalic anhydride (ODPA), and benzophenonetetracarboxylic dianhydride (BTDA).

The first diamine and the second diamine may be each independently at least one selected from the group consisting of 1, 4-phenylenediamine (PPD), 4 '-Oxydianiline (ODA), 3,4' -oxydianiline, 2-bis [4'- (4-aminophenoxy) phenyl ] propane (BAPP), 4' -Methylenedianiline (MDA), and 1, 3-bis (4-aminophenoxy) benzene (TPE-R).

Specifically, the first dianhydride may not include a flexible dianhydride, or the first dianhydride may include less than 10 mole percent of a flexible dianhydride with respect to the total amount of dianhydride monomers constituting the first polyamic acid, the first diamine may not include a flexible diamine, or the first diamine may include less than 80 mole percent of a flexible diamine with respect to the total amount of diamine monomers constituting the first polyamic acid, and the flexible dianhydride and the flexible diamine may each include two or more benzene rings in a molecular structure.

Specifically, the first dianhydride may not include a flexible dianhydride, or the first dianhydride may include less than 5 mole percent of a flexible dianhydride with respect to the total amount of dianhydride monomers constituting the first polyamic acid, the first diamine may not include a flexible diamine, or the first diamine may include less than 75 mole percent of a flexible diamine with respect to the total amount of diamine monomers constituting the first polyamic acid.

More specifically, the first dianhydride may not comprise a flexible dianhydride, or the first dianhydride may comprise less than 3 mole percent of a flexible dianhydride relative to the total amount of dianhydride monomers comprising the first polyamic acid; the first diamine may not include a flexible diamine, or may include less than 70 mol% of a flexible diamine with respect to the total amount of diamine monomers constituting the first polyamic acid.

In this case, when the first dianhydride constituting the first polyamic acid contains the flexible dianhydride in the above-described range or the first diamine constituting the first polyamic acid contains the flexible diamine in the above-described range with respect to the diamine monomer, the mechanical rigidity is rather lowered, which is not preferable.

On the other hand, the second dianhydride comprises 80 mole percent or more of flexible dianhydride relative to the total amount of dianhydride monomers constituting the second polyamic acid, the second diamine comprises 80 mole percent or more of flexible diamine relative to the total amount of diamine monomers constituting the second polyamic acid, and the flexible dianhydride and the flexible diamine may respectively comprise two or more benzene rings in a molecular structure.

Specifically, the second dianhydride includes the flexible dianhydride in an amount of 90 mol% or more with respect to the total amount of dianhydride monomers constituting the second polyamic acid, and the second diamine may include the flexible diamine in an amount of 90 mol% or more with respect to the total amount of diamine monomers constituting the second polyamic acid.

More specifically, the second dianhydride comprises 95 mole percent or more of a flexible dianhydride with respect to the total amount of dianhydride monomers constituting the second polyamic acid, and the second diamine may comprise 95 mole percent or more of a flexible diamine with respect to the total amount of diamine monomers constituting the second polyamic acid.

At this time, when the second dianhydride constituting the second polyamic acid contains the flexible dianhydride in an amount less than the range with respect to the total amount of dianhydride monomers, or the second diamine constituting the second polyamic acid contains the flexible diamine in an amount less than the range with respect to the total amount of diamine monomers, a desired degree of chemical resistance cannot be achieved, and thus it is not preferable.

In one specific example, the flexible dianhydride is not particularly limited as long as it is a structure including two or more benzene rings in a molecular structure, and for example, the flexible dianhydride may be one or more selected from the group consisting of biphenyl tetracarboxylic dianhydride (BPDA), Oxydiphthalic Dianhydride (ODPA), and Benzophenone Tetracarboxylic Dianhydride (BTDA), and more particularly, the flexible dianhydride may be BPDA, but is not limited thereto.

In another specific example, the flexible diamine is not particularly limited as long as it is a structure including two or more benzene rings in a molecular structure, and for example, the flexible diamine may be one or more selected from the group consisting of 4,4 '-Oxydianiline (ODA), 3,4' -oxydianiline, 2-bis [4'- (4-aminophenoxy) phenyl ] propane (BAPP), 4' -Methylenedianiline (MDA), and 1, 3-bis (4-aminophenoxy) benzene (TPE-R), and more particularly, the flexible diamine may be ODA, but is not limited thereto.

On the other hand, in the usual case, the second polyamic acid may contain amine groups at the terminal, which may collide with the linking sites of other compounds or be hydrolyzed, thereby reducing the molecular weight of the polymer chain and eventually may greatly change the viscosity of the second polyamic acid solution.

Similarly, even in the process of mixing the first polyamic acid and the mixed solution before the imidization step, the end of the first polyamic acid and the end of the second polyamic acid are polymerized so that the chain length may become excessively long.

Thus, the viscosity of the polyamic acid solution may be excessively increased due to the increase in the molecular weight of the polyamic acid, and thus there may be a problem in that the reliability of the imidization process designed based on a predetermined viscosity range may be lowered.

In contrast, the preparation method according to the present invention includes a step of adding an end-capping agent in the polymerization step of the second polyamic acid, thereby having advantages that since the amine terminal is capped, the viscosity change as described above can be minimized, the mixed solution is easily stored, and the viscosity change is minimized at normal temperature, resulting in excellent process stability.

Specifically, the second polyamic acid may have a 30-day viscosity retention at normal temperature of 80% or more.

At this time, the content of the capping agent may be 0.05 to 1 weight percent with respect to the weight of the second polyamic acid, and the capping agent may be one or more selected from the group consisting of Phthalic Anhydride (PA), Maleic Anhydride (MA), and Glutaric Anhydride (GA), and specifically may be PA.

On the other hand, as described above, the method for preparing an ultra-thin black polyimide film according to the present invention includes a step of mixing carbon black, which may have an average particle diameter of 0.1 μm to 5 μm, to realize a black color of the film and maintain low glossiness, so that an ultra-thin black polyimide film having a thickness of 8 μm or less can be realized.

In this case, the carbon black may be mixed with the second polyamic acid as a solution-like black crude liquid dispersed in a solvent, and the polar solvent may be one or more selected from the group consisting of N, N '-dimethylformamide, N' -dimethylacetamide, and N-methyl-pyrrolidone as the protic polar solvent.

In general, in a method for preparing a polyimide film, carbon black is subjected to a grinding process together with a dispersant for improving dispersibility, and then subjected to a step of mixing with polyamic acid, and if the dispersibility of carbon black is low, there may occur problems that the surface area of a part of the film prepared is widened and carbon particles are unevenly dropped when exposed to an alkaline environment.

In contrast, in the present invention, the dispersibility of carbon black in the mixed liquid is primarily improved by the step of first mixing the carbon black in the form of a black crude liquid with the second polyamic acid to prepare the mixed liquid, and then mixing the mixed liquid with the first polyamic acid, so that the dispersibility of carbon black as described above can be further improved.

Specifically, when the solid content is 15%, the polymerization viscosity of the second polyamic acid may be 100000 to 150000 cps, the concentration of the mixed solution of the black crude liquid and the second polyamic acid may be 2 to 10 weight%, and the viscosity may be 50 to 1000 cps.

When the polymerization viscosity or the viscosity of the mixed solution exceeds the above range, the second polyamic acid takes a long time in the mixing process, and thus the workability is lowered, and when it is less than the above range, the dispersibility of the carbon black may be lowered.

When the dispersibility of carbon black is improved, there is an advantage in that the hiding property of the polyimide film is improved and the mechanical physical properties of the film are prevented from being lowered.

Also, the present invention can provide an ultra-thin black polyimide film prepared by the preparation method.

As described above, the thickness of the ultra-thin black polyimide film according to an embodiment of the present invention may be 7.5 μ or less, and specifically, may be 3 μm to 7.5 μ, and more specifically, may be 5 μm to 7.5 μ.

Also, the film may have a light transmittance of 10% or less or 9.7% or less in a visible light region to provide a light-shielding function, and the glossiness may be 10% to 50% or 15% to 50%, and the lower these values are more preferable.

When the film is applied to a cover film, an insulating film, a semiconductor, or the like, not only can the product be thinned, but also the aesthetic property can be improved, and the internal shape and charged parts can be blocked, which is useful for safety.

And, the Coefficient of Thermal Expansion (CTE) of the film in the length (MD) direction and the width (TD) direction may be 10 ppm/DEG C to 20 ppm/DEG C.

The film may comprise, relative to the total weight of the polyimide film: a first polyimide chain having 80 to 93 weight percent and having excellent rigidity; a second polyimide chain having 2 to 15 weight percent and having excellent chemical resistance; and carbon black having 3 to 10 weight percent and an average particle diameter of 0.1 to 5 μm.

Hereinafter, the present invention will be described in more detail by way of specific examples and comparative examples. The following examples are intended to more specifically illustrate the present invention, but the present invention is not limited to the following examples.

< example 1>

Preparation examples 1 to 1: polymerization of the first Polyamic acid

As a first polyamic acid solution polymerization process, 407.5g of dimethylformamide was added as a solvent in a 1L reactor under a nitrogen atmosphere.

After setting the temperature to 25 ℃, 35.1g of ODA and 6.3g of PPD were added as diamine monomers and stirred for about 30 minutes, and after confirming that the monomers were dissolved, 51.0g of PMDA was added in portions, and finally, the final addition amount was adjusted to be added so that the viscosity was 250000 cps to 300000 cps.

After the addition was complete, the temperature was maintained while stirring for 1 hour to polymerize a first polyamic acid solution containing less than 10% flexible dianhydride with a final viscosity of 260000 centipoise and less than 80 mole percent flexible diamines.

Preparation examples 1 to 2: polymerization of second polyamic acid

As a polymerization process of the second polyamic acid, 425g of dimethylformamide was added in a 1L reactor under a nitrogen atmosphere.

After setting the temperature to 25 ℃, 30.4g of ODA was added as a diamine monomer and stirred for about 30 minutes, and after confirming the dissolution of the monomer, 44.6g of BPDA was added in portions and a small amount was added so that the final viscosity became 100000 to 150000 cps, and 0.135g of PA was added as an end-capping agent.

After the addition was complete, the temperature was maintained while stirring for 1 hour to polymerize a second polyamic acid comprising a flexible dianhydride with a final viscosity of 120000 centipoise and 80 mole percent or more of a flexible diamine and comprising 0.18 weight percent solids of capping agent.

Preparation example 2-1: preparation of a mixture of the Black crude liquid and the second polyamic acid

After 10g of carbon black was mixed with 89.1g of DMF and 0.1g of dispersant BYK-1162, a black crude liquid having an average particle diameter of 1.2 μm was prepared using a grinder.

20g of the second polyamic acid solution prepared in the preparation example 1-2 and 46g of the black crude liquid were mixed with 34g of DMF to prepare a mixed solution containing 3% of the second polyamic acid and 4.6% of carbon black.

Preparation example 3-1: preparation of ultrathin black polyimide film

20g of the mixed solution prepared in the preparation example 2-1 was mixed with 100g of the first polyamic acid solution prepared in the preparation example 1-1, 4.76g of Isoquinoline (IQ), 26.36g of Acetic Anhydride (AA), and 18.87g of DMF were added as catalysts, followed by uniform mixing, casting to 70 μm on SUS plate (100SA, Sandvik) using a doctor blade, and further drying at a temperature ranging from 100 ℃ to 200 ℃.

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

The film was heated from 200 to 600 c on a high temperature tenter, cooled at 25 c, and then separated from the pin frame, thereby preparing an ultra-thin black polyimide film of 7.5 μ. thickness comprising 81.6 weight percent of the first polyimide chains, 3 weight percent of the second polyimide chains, and 5 weight percent of carbon black, relative to the total weight of the polyimide film.

< example 2>

An ultra-thin black polyimide film having a thickness of 7.5 μ. was prepared in the same manner as in example 1, except that 100g of the first polyamic acid solution prepared in preparation example 1-1 was used, and 20g of a mixed solution in which 33.3g of the second polyamic acid solution prepared in preparation example 1-2, 47g of the 10% black crude liquid, and 19.3g of DMF were mixed was used, so that 90 wt% of the first polyimide chain, 5 wt% of the second polyimide chain, and 5 wt% of carbon black were included, relative to the total weight of the polyimide film.

< example 3>

An ultra-thin black polyimide film having a thickness of 7.5 μ. was prepared in the same manner as in example 1, except that 100g of the first polyamic acid solution prepared in preparation example 1-1 was used, and 40g of a mixed solution in which 35.6g of the second polyamic acid solution prepared in preparation example 1-2, 24.5g of the 10% black crude liquid, and 39.8g of DMF were mixed was used, so that the first polyimide chain was included in an amount of 85 weight percent, the second polyimide chain was included in an amount of 10 weight percent, and carbon black was included in an amount of 5 weight percent, based on the total weight of the polyimide film.

< example 4>

An ultra-thin black polyimide film having a thickness of 7.5 μ. was prepared in the same manner as in example 1, except that 100g of the first polyamic acid solution prepared in preparation example 1-1 was used, and 40g of a mixed solution in which 56.7g of the second polyamic acid solution prepared in preparation example 1-2, 26g of the 10% black crude liquid, and 17.3g of DMF were mixed was used, so that 80 weight percent of the first polyimide chain, 15 weight percent of the second polyimide chain, and 5 weight percent of carbon black were included, relative to the total weight of the polyimide film.

< example 5>

A second polyamic acid solution containing a capping agent at a solids content of 0.18 wt% was prepared in the manner described in preparation examples 1-2.

< comparative example 1>

An ultra-thin black polyimide film of 7.5 μ. thickness was prepared in the same manner as in example 1, except that 100g of the first polyamic acid solution prepared in the preparation example 1-1 was used without using the second polyamic acid solution so as to include 95 weight percent of the first polyimide chain and 5 weight percent of carbon black, relative to the total weight of the polyimide film.

< comparative example 2>

An ultra-thin black polyimide film having a thickness of 7.5 μ. was prepared in the same manner as in example 1, except that 100g of the first polyamic acid solution prepared in preparation example 1-1 was used, and 50g of a mixed solution in which 64.3g of the second polyamic acid solution prepared in preparation example 1-2, 22.5g of the 10% black crude liquid, and 13.2g of DMF were mixed was used, so that 75 wt% of the first polyimide chain, 20 wt% of the second polyimide chain, and 5 wt% of carbon black were included, relative to the total weight of the polyimide film.

< comparative example 3>

An ultra-thin black polyimide film having a thickness of 7.5 μm was prepared in the same manner as in example 1, except that 100g of the first polyamic acid solution prepared in preparation example 1-1 was used, and 84g of the black crude liquid mixed with 64.3g of the second polyamic acid solution prepared in preparation example 1-2, 22.5g of the 10% black crude liquid, and 13.2g of DMF was used, so that 65 weight percent of the first polyimide chain, 30 weight percent of the second polyimide chain, and 5 weight percent of carbon black were included, relative to the total weight of the polyimide film.

< comparative example 4>

An ultra-thin black polyimide film of 7.5 μ. thickness was prepared in the same manner as in example 1, except that 27.2g of ODA and 2.6g of PPD were added as a diamine monomer, and 5.2g of PMDA and 27.2g of BPDA were added as dianhydride monomers in the preparation example 1-1 such that the flexible dianhydride and the flexible diamine were included in the first polyamic acid solution by 80 mol% or more.

< comparative example 5>

An ultra-thin black polyimide film of 7.5 μ. thickness was prepared in the same manner as in example 1, except that 21.1g of ODA and 7.6g of PPD were added as a diamine monomer, and 31.0g of BPDA and 15.3g of PMDA were added as dianhydride monomers in the preparation examples 1-2, so that less than 80 mole percent of flexible dianhydride and flexible diamine were contained in the second polyamic acid solution.

< comparative example 6>

A second polyamic acid solution was prepared in the same manner as in example 5, except that no end-capping agent was used in the preparation example 2-1.

< comparative example 7>

A second polyamic acid solution was prepared in the same manner as in example 5, except that 0.05g of PA as a terminal-blocking agent was added to the preparation examples 1 to 2 so that the terminal-blocking agent was contained in the second polyamic acid solution at 0.07 weight percent based on the solid content.

Experimental example 1: gloss evaluation

For the ultra-thin black polyimide films respectively prepared in < examples 1> to < example 4> and < comparative examples 1> to < comparative example 3>, measured by the ASTM D523 method at an angle of 60 ° using a gloss measuring apparatus (model: E406L, manufacturer; Elcometer), the results thereof are shown in the following table 1.

Experimental example 2: transmittance evaluation

For the ultra-thin black polyimide films respectively prepared in < example 1> to < example 4> and < comparative example 1> to < comparative example 4>, the transmittance was measured in the visible light region by the ASTM D1003 method using a transmittance measuring apparatus (model: ColorQuesetXE, manufacturer: HunterLab), and the results thereof are shown in the following table 1.

TABLE 1

Experimental example 3: evaluation of tensile Properties

For the ultra-thin black polyimide films respectively prepared in < example 1> to < example 4> and < comparative example 1> to < comparative example 4>, tensile properties, i.e., tensile strength, elongation, and elastic modulus, were measured according to ASTM D882, and the results thereof are shown in table 2 below.

TABLE 2

As shown in tables 1 and 2, it was confirmed that in the case of the ultra-thin black polyimide films of examples 1 to 4, although physical properties such as gloss, transmittance, tensile property, etc. were not reduced as compared with comparative example 1 not including the second polyimide chain although the range of 3 to 15 weight% of the second polyimide chain imidized with the flexible dianhydride and the flexible diamine was included, in the case of comparative examples 2 to 3 not including the content of the second polyimide chain exceeding the content according to the present invention, the physical properties as described above were reduced as compared with example 1.

In addition, it was confirmed that in comparative example 4 in which 80 mol% or more of the flexible dianhydride and the flexible diamine were contained in the first polyamic acid solution, the physical properties such as gloss, transmittance, and tensile property were reduced as compared with example 1.

Experimental example 4: evaluation of alkali resistance index

In < examples 1> to < example 4>, < comparative examples 1> to < comparative example 3> and < comparative example 5>, after double-sided corona treatment was performed on polyimide films of respectively prepared ultra-thin blacks, FCCL samples were prepared by bonding through the black polyimide film, an adhesive sheet (adhesive) and a copper foil structure using a Hot Press (Hot Press) at a pressure of 50kgf and a temperature of 160 ℃ for 30 minutes.

FCCL, cut to 4 x 10cm, was exposed to a 10% NaOH solution for 3 minutes at 55 deg.C and to a desmutting solution (10% NaMnO) at 55 deg.C₄+ 4% NaOH) was repeated twice after 5 minutes, and the thickness of the film was measured, and the degree of change in the thickness after exposure, compared to the thickness before exposure to the NaOH solution and the desmearing solution, was expressed as a percentage in table 3 below.

TABLE 3

As shown in table 3, it was confirmed that in the case of the ultra-thin black polyimide films of examples 1 to 4, the alkali resistance index was 70% or more, and when the second polyimide chain was prepared so as to contain a small amount of the second polyimide chain, the content thereof was in the range according to the present invention, i.e., in the range of 3 to 15 weight%, chemical resistance was remarkably superior as compared to comparative example 1 not containing the second polyimide chain.

Also, it was confirmed that in the case of comparative examples 2 and 3 in which the content of the second polyimide chain exceeded the content range according to the present invention, the alkali resistance index was 85% or more, and excellent chemical resistance was exhibited, but as in the foregoing tables 1 and 2, in the case of the ultra-thin black polyimide films of comparative examples 2 and 3, physical properties were degraded compared to example 1.

Also, it was confirmed that in the case of comparative example 5 in which less than 80 mole percent of the flexible dianhydride and the flexible diamine were contained in the second polyamic acid solution, the chemical resistance was inferior compared to example 1.

On the other hand, fig. 1 shows a photograph of an outer surface of an FCCL prepared by using the ultra-thin black polyimide film of comparative example 1 after being exposed to alkali, and fig. 2 shows a photograph of an outer surface of an FCCL prepared by using the ultra-thin black polyimide film of example 1 after being exposed to alkali.

Referring to fig. 1 and 2, the surface of the FCCL according to comparative example 1 was damaged more than the surface of the FCCL prepared in example 1 having improved chemical resistance.

Experimental example 5: evaluation of storage stability

For the second polyamic acid solution prepared in < example 5> and the second polyamic acid solutions prepared in < comparative example 6> and < comparative example 7>, the change with time of the viscosity for 30 days was measured using a brookfield viscometer at normal temperature, the viscosity of the second polyamic acid solution measured initially was compared with the amount of retention of the viscosity for 30 days of storage, respectively, and shown in table 4 below.

As shown in table 5, it was confirmed that the second polyamic acid of example 5, to which the end-capping agent was added in the polymerization step, was superior in stability to the second polyamic acid of comparative example 6, to which the end-capping agent was not used in the polymerization step, and comparative example 7, to which the end-capping agent was added in a content range smaller than that of the present application.

The foregoing has been with reference to embodiments of the present invention, but numerous applications and modifications within the scope of the present invention may be made by those skilled in the art to which the present invention pertains, based on the foregoing.

As described above, the method for preparing an ultra-thin black polyimide film according to the present invention is a method for preparing an ultra-thin black polyimide film having a thickness of 8 μ or more, by which the ultra-thin black polyimide film prepared maintains low glossiness and has low light transmittance in a visible light region.

Further, the storage stability of the mixed liquid containing the second polyamic acid and the black crude liquid is improved, and the reliability of the physical properties of the polyimide film can be improved without being affected by the storage time of the raw material.

Further, the polyimide film according to the present invention is excellent in mechanical stability and alkali resistance, and thus has excellent mechanical and chemical resistance, and can be effectively used in ultra-thin devices, cover films, insulating films, semiconductor devices, and the like.

Claims

1. A method for preparing an ultrathin black polyimide film, which is to mix more than two different polyamic acids and carry out imidization to obtain the polyimide film, comprises the following steps:

a step (a) of polymerizing a first polyamic acid having excellent rigidity from a first dianhydride and a first diamine;

a step (b) of polymerizing a second polyamic acid having excellent chemical resistance from a capping agent, a second dianhydride, and a second diamine;

a step (c) of preparing carbon black having an average particle diameter of 0.1 to 5 μm using a grinder and preparing a black crude liquid containing the carbon black;

a step (d) of preparing a mixed solution by mixing the second polyamic acid and the black crude liquid; and

and (e) mixing and dispersing the mixed solution in the first polyamic acid, and then forming a film on a support and imidizing the film by heat treatment.

2. The method of claim 1, wherein the first polyamic acid and the second polyamic acid form a first polyimide chain and a second polyimide chain, respectively, through an imidization step.

3. The method of preparing an ultra-thin black polyimide film according to claim 2, wherein the first polyamic acid and the second polyamic acid form a structure in which at least a portion of the first polyimide chains and the second polyimide chains are cross-linked through an imidization step.

4. The method for preparing an ultra-thin black polyimide film according to claim 1,

relative to the total weight of the polyimide film, the polyimide film comprises the following components:

80 to 93 weight percent of a first polyimide chain having excellent rigidity;

2 to 15 weight percent of a second polyimide chain having excellent chemical resistance; and

3 to 10% by weight of carbon black having an average particle diameter of 0.1 to 5 μm,

the alkali resistance index evaluated by taking the thickness of the polyimide film as a reference is more than 70 percent,

the thickness of the polyimide film is 8.0 μm or less.

5. The method for preparing an ultra-thin black polyimide film according to claim 1,

the first dianhydride and the second dianhydride are each independently at least one selected from the group consisting of pyromellitic dianhydride, biphenyl tetracarboxylic dianhydride, oxydiphthalic anhydride, and benzophenone tetracarboxylic dianhydride,

the first diamine and the second diamine are each independently at least one selected from the group consisting of 1, 4-phenylenediamine, 4 '-oxydianiline, 3,4' -oxydianiline, 2-bis [4'- (4-aminophenoxy) phenyl ] propane, 4' -methylenedianiline, and 1, 3-bis (4-aminophenoxy) benzene.

6. The method for preparing an ultra-thin black polyimide film according to claim 1,

the first dianhydride does not comprise a flexible dianhydride, or the first dianhydride comprises less than 10 mole percent of a flexible dianhydride relative to the total amount of dianhydride monomers comprising the first polyamic acid;

the first diamine does not include a flexible diamine, or includes less than 80 mole percent of a flexible diamine with respect to the total amount of diamine monomers constituting the first polyamic acid,

the flexible dianhydride and the flexible diamine respectively contain more than two benzene rings in the molecular structure.

7. The method for preparing an ultra-thin black polyimide film according to claim 1,

the second dianhydride comprises more than 80 mole percent of flexible dianhydride relative to the total amount of dianhydride monomers constituting a second polyamic acid,

the second diamine contains 80 mol% or more of a flexible diamine based on the total amount of diamine-based monomers constituting the second polyamic acid,

the flexible dianhydride and the flexible diamine respectively comprise more than two benzene rings in molecular structures.

8. The method for preparing an ultra-thin black polyimide film according to claim 6 or 7,

the flexible dianhydride is one or more selected from the group consisting of biphenyl tetracarboxylic dianhydride, oxydiphthalic anhydride and benzophenone tetracarboxylic dianhydride.

9. The method for preparing an ultra-thin black polyimide film according to claim 6 or 7,

the flexible diamine is one or more selected from the group consisting of 4,4 '-oxydianiline, 3,4' -oxydianiline, 2-bis [4'- (4-aminophenoxy) phenyl ] propane, 4' -methylenedianiline and 1, 3-bis (4-aminophenoxy) benzene.

10. The method of preparing an ultra-thin black polyimide film according to claim 1, wherein the polymerization viscosity of the second polyamic acid is 100000 cps to 150000 cps when the solid content is 15%.

11. The method of preparing an ultra-thin black polyimide film according to claim 1, wherein the second polyamic acid has a viscosity retention of 80% or more at room temperature for 30 days.

12. The method of claim 1, wherein the mixed solution has a concentration of 2 to 10 wt% and a viscosity of 50 to 1000 cp.

13. The method of preparing an ultra-thin black polyimide film according to claim 1, wherein the capping agent is contained in an amount of 0.05 to 1 wt% with respect to the solid content of the second polyamic acid.

14. The method of preparing an ultra-thin black polyimide film according to claim 1, wherein the capping agent is one or more selected from the group consisting of phthalic anhydride, maleic anhydride, and glutaric anhydride.

15. An ultra-thin black polyimide film prepared by the method of claim 1.

16. An ultra-thin black polyimide film obtained by mixing and imidizing two or more different polyamic acids,

80 to 93 weight percent of a first polyimide chain having excellent rigidity;

3 to 15 weight percent of a second polyimide chain having excellent chemical resistance; and

the alkali resistance index evaluated based on the thickness of the polyimide film is 70% or more.

17. The ultra-thin black polyimide film of claim 16, wherein the polyimide film has a thickness of 3 to 7.5 μ ι η.

18. The ultra-thin black polyimide film of claim 16, wherein the polyimide film has a light transmittance of 10% or less and a glossiness of 10 to 50% in a visible light region.

19. A coverlay film comprising the ultra-thin black polyimide film of claim 16.

20. An electronic device comprising the cover film according to claim 19.