阅读说明：本技术 包含氟树脂的黑色聚酰亚胺薄膜及其制备方法 (Black polyimide film containing fluororesin and preparation method thereof ) 是由 金纪勋 李吉男 林铉才 于 2018-09-27 设计创作，主要内容包括：本发明提供一种聚酰亚胺薄膜,相对于聚酰亚胺薄膜总重量,所述聚酰亚胺薄膜包含：75重量％至95重量％的聚酰亚胺树脂、2重量％至15重量％的氟树脂以及3重量％至10重量％的平均粒径为0.1μm至5μm的炭黑,所述氟树脂在其分子结构中包含氧,所述聚酰亚胺薄膜的厚度为8.0μm以下,以聚酰亚胺薄膜的厚度为基准来评估的耐碱性指数为70％以上。(The present invention provides a polyimide film comprising, relative to the total weight of the polyimide film: 75 to 95% by weight of a polyimide resin, 2 to 15% by weight of a fluororesin containing oxygen in its molecular structure, and 3 to 10% by weight of carbon black having an average particle diameter of 0.1 to 5 μm, the polyimide film having a thickness of 8.0 μm or less and an alkali resistance index of 70% or more as evaluated based on the thickness of the polyimide film.)

1. A polyimide film characterized by comprising a polyimide film,

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

75 to 95 weight percent of a polyimide resin;

2 to 15% by weight of a fluororesin; and

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

the fluororesin contains oxygen in its molecular structure,

the thickness of the polyimide film is 8.0 μm or less, and the alkali resistance index evaluated based on the thickness of the polyimide film is 70% or more.

2. The polyimide film according to claim 1, wherein the thickness of the polyimide film is 3 μm to 7.5 μm.

3. The polyimide film according to claim 1, wherein the polyimide film has a light transmittance of 10% or less in a visible light region.

4. The polyimide film according to claim 1, wherein the fluororesin is a copolymer derived from a monomer composition comprising tetrafluoroethylene and a compound represented by the following formula (1),

formula (1): CF (compact flash)₂＝CF(OR^f)，

In the formula (1), R^fIs C₁-C₆A perfluoroalkyl group.

5. The polyimide film according to claim 4, wherein R is represented by the formula (1)^fIs C₁-C₃A perfluoroalkyl group.

6. The polyimide film according to claim 4, wherein the fluororesin is a perfluoroalkoxy resin.

7. The polyimide film according to claim 4, wherein the fluororesin contains tetrafluoroethylene and a compound represented by formula (1) in a molar ratio of 96:4 to 97: 3.

8. The polyimide film according to claim 1, wherein the fluororesin is chemically bonded to the carbon black to form a matrix structure.

9. The polyimide film according to claim 8, wherein the fluororesin is chemically bonded to the carbon black to form a matrix structure by interaction with an oxygen-containing functional group in a molecular structure.

10. The polyimide film according to claim 9, wherein the oxygen-containing functional group is a perfluoroalkyl ether group.

11. A method for producing a polyimide film according to claim 1, comprising:

step (a) of polymerizing polyamic acid from dianhydride and diamine;

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

a step (c) of preparing a second composition comprising carbon black having an average particle diameter of 0.1 to 5 μm and a second organic solvent;

a step (d) of mixing the first composition and the second composition to produce a third composition; and

and (e) mixing the polyamic acid with the third composition, forming a film on a support, and performing heat treatment to perform imidization.

12. The method for producing a polyimide film according to claim 11, wherein 10 to 30 wt% of a fluororesin is contained with respect to the total weight of the first composition.

13. The method of preparing a polyimide film according to claim 11, wherein in the step (d), a fluororesin is chemically bonded to carbon black to form a matrix structure by mixing the first composition and the second composition.

14. The method for producing a polyimide film according to claim 11,

the first organic solvent and the second organic solvent are the same or different from each other,

comprises one or more selected from the group consisting of N, N '-dimethylformamide, N' -dimethylacetamide, N-methyl-pyrrolidone, gamma-butyrolactone, and diglyme.

15. A coverlay film comprising the polyimide film according to claim 1.

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

Technical Field

The present invention relates to a black polyimide film comprising a fluororesin and a method for preparing the same.

Background

Generally, a Polyimide (PI) resin refers to a high temperature resistant resin prepared by solution-polymerizing an aromatic dianhydride and 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 dianhydride, such as pyromellitic dianhydride (PMDA) or biphenyltetracarboxylic dianhydride (BPDA), and an aromatic diamine component, such as 4,4 '-Oxydianiline (ODA), 3,4' -oxydianiline, p-phenylenediamine (p-PDA), m-phenylenediamine (m-PDA), Methylenedianiline (MDA), bisaminophenylhexafluoropropane (HFDA), and the like.

Polyimide resins are insoluble and infusible, super heat-resistant resins and have excellent characteristics such as thermal oxidation resistance, heat resistance, radiation resistance, low-temperature characteristics, 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 protection films of TFT-L CD and the like.

In the case of electronic materials, a protective film that is attached to circuits included in portable electronic devices and communication devices to impart insulating properties and protect the circuits from moisture, light sources, impact, and the like can be exemplified. In a narrow sense, the film for protecting the circuit as described above may be referred to as a coverlay film (coverlay).

On the other hand, circuits are being miniaturized, thinned, and also developed in a bendable form, so that a cover film is required to be both a thin film which is thinner and also to have ductility, and recently, concealment of parts mounted on the circuits is required.

Therefore, a black film containing carbon black particles, which can impart a black color tone and hiding properties to a polyimide film having a film shape and flexibility, has been attracting attention.

However, the manufacturing process of the circuit may include a drilling (drill) process, an electroplating process, a desmearing (desmear) process, a cleaning process, and the like, and the polyimide film may be exposed to an alkaline solution in the above process.

At this time, when the polyimide film is slightly decomposed or denatured by the alkaline solution, the carbon black particles contained therein may drop in a large amount.

Therefore, the black tone and hiding property may be reduced in the cover film, and the thickness may be reduced due to falling 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 highly required.

Disclosure of Invention

Technical problem

An object of the present invention is to provide a black polyimide film, specifically, a black polyimide film comprising, relative to the total weight of the polyimide film: 75 to 95% by weight of a polyimide resin, 2 to 15% by weight of a fluororesin having an average particle diameter of 0.1 to 5 μm, and 3 to 10% by weight of carbon black having an average particle diameter of 0.1 to 5 μm, the fluororesin including oxygen in its molecular structure, whereby a polyimide film having a thickness of 8 μm or less but excellent optical properties such as gloss, transmittance, mechanical stability, and alkali resistance can be provided.

Technical scheme

To achieve the object, the present invention provides a polyimide film comprising, relative to the total weight of the polyimide film: 75 to 95% by weight of a polyimide resin, 2 to 15% by weight of a fluororesin containing oxygen (O) in its molecular structure and having a thickness of 8.0 μm or less and an alkali resistance index of 70% or more evaluated on the basis of the thickness of the polyimide film, and 3 to 10% by weight of carbon black having an average particle diameter of 0.1 μm to 5 μm.

The polyimide film according to the present invention has a thickness of 8 μm or less, but has excellent optical properties such as gloss and transmittance, mechanical stability, and alkali resistance, so that it can be preferably used as a cover film in portable electronic devices and communication devices.

Embodiments of the present invention will be described in detail below in the order of "polyimide film" and "method for producing polyimide film" according to the present invention.

Before this, terms or words used herein and in the scope of the claimed invention should not be construed as being 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 appropriately define the concept of terms in order to explain his invention in the best way.

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

As used herein, the singular forms "a", "an" and "the" include plural forms unless the context clearly dictates otherwise. It will be understood that, in this document, the terms "comprising", "including", "having" or "with", etc., are intended to specify the presence of stated features, steps, structural elements, or combinations thereof, and do not preclude the presence or addition of one or more other features or numbers, steps, structural elements, or combinations thereof.

Polyimide film

As described above, the polyimide film according to the present invention is characterized by comprising, relative to the total weight of the polyimide film: 75 to 95 weight percent of a polyimide resin; 2 to 15% by weight of a fluororesin; and 3 to 10% by weight of carbon black having an average particle diameter of 0.1 to 5 μm, the fluororesin containing oxygen in its molecular structure, having a thickness of 8.0 μm or less, and having an alkali resistance index of 70% or more as evaluated based on the thickness of the polyimide film.

At this time, when the particle diameter or the content of the carbon black particles is less than the above range, it is difficult to secure a desired concealing property, so that it is not preferable.

In contrast, when the particle diameter or the content of the carbon black particles is more than the above range, dispersibility may become low when mixed with polyamic acid during the production process, and appearance defects may be generated due to protrusion of the filler from the surface of the film, so that it is not preferable.

On the other hand, as described above, polyimide is susceptible to the influence of alkaline components, such as being decomposed or undergoing denaturation, when exposed to an alkaline environment.

The alkali resistance refers to a property of a polyimide film that is not easily decomposed or denatured even when the polyimide film is exposed to an alkali environment, and since the polyimide film is reduced in thickness when decomposed or denatured, the "alkali resistance index" can be determined based on the reduction rate of the thickness.

Specifically, as an index for evaluating alkali resistance, the following method can be utilized: after exposing the polyimide film to the NaOH solution and the desmear solution, the thickness change of the film before and after exposure was measured.

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

After the polyimide film was subjected to double-sided corona treatment, the polyimide film, an adhesive sheet (adhesive), and a copper foil were sequentially stacked, and were subjected to hot pressing and bonding at 160 ℃ for 30 minutes at a pressure of 50kgf using a hot press (HotPress), thereby preparing a flexible circuit board sample.

At a temperature of 55 deg.C, allowing to cutFlexible circuit boards cut to 4 ＊ 10cm were exposed to a 10% NaOH solution for 3 minutes and exposed to a desmear solution (10% NaMnO) at 55 deg.C₄+ 4% NaOH) was repeated twice after 5 minutes and the thickness of the film was measured, representing the degree of change in thickness before exposure and after exposure in percent compared to the thickness before exposure to the NaOH solution and the desmearing solution.

In the case of a conventional polyimide film, the alkali resistance index by the above-mentioned evaluation method (a) may be about 70% or less, and particularly, in the case of an ultrathin polyimide film having a film thickness of 8 μm or less, the alkali resistance index by the above-mentioned evaluation method (a) may be about 60% or less.

In contrast, in the case of the polyimide film according to the present invention, a fluororesin having excellent chemical resistance, which is chemically bonded with carbon black particles to form a matrix structure as described below, is included, so that even if an ultrathin polyimide film having a thickness of 8 μm or less is prepared, an excellent effect of an excellent alkali resistance index of 70% or more is obtained.

In a specific example, the fluororesin may be a copolymer derived from a monomer composition comprising Tetrafluoroethylene (TFE) and a compound represented by the following formula (1),

formula (1): CF (compact flash)₂＝CF(OR^f)，

In the formula (1), R^fIs C₁-C₆A perfluoroalkyl group.

The compound represented by formula (1) may be, for example, perfluoromethyl vinyl ether (PMVE), perfluoroethyl vinyl ether (PEVE), and perfluoropropyl vinyl ether (PPVE), specifically, R in formula (1)^fCan be C₁-C₃A perfluoroalkyl group, more specifically, the compound represented by formula (1) may be perfluoropropyl vinyl ether (PPVE).

The fluororesin may be obtained by, for example, polymerizing tetrafluoroethylene and the compound represented by the chemical formula (1).

At this time, the fluororesin may have a tetrafluoroethylene: specifically, the compound represented by formula (1) may have a molar percentage of 96:10 to 97:1, and specifically may have a tetrafluoroethylene: the compound represented by formula (1) may be 96:4 to 97:3 in a mole percentage, and more specifically, the fluororesin may be a Perfluoroalkoxy (PFA) resin.

On the other hand, the fluororesin may be chemically bonded to the carbon black to form a matrix structure.

Specifically, the fluororesin may be chemically bonded to the carbon black to form a matrix structure through interaction with an oxygen-containing functional group in the molecular structure.

In this case, the oxygen-containing functional group may be a perfluoroalkyl ether group.

That is, in the case of the polyimide film of the present invention, unlike conventional fluororesins, which include a fluororesin not containing oxygen in the molecular structure, such as Polytetrafluoroethylene (PTFE) or fluorinated (fluorinated) ethylene propylene copolymer (FEP), the perfluoroalkyl ether groups may be chemically bonded to carbon black to form a matrix structure.

Specifically, the fluorine resin containing oxygen in the molecular structure, specifically PFA, has physical properties of particles, such as strength, elongation, and modulus (modulus) more than 10% higher than that of PTFE, in an organic solvent mixed with carbon black, since PFA is chemically bonded to carbon black to form a matrix structure, thereby suppressing aggregation of carbon black particles and improving dispersibility.

Therefore, when the polyimide film is slightly decomposed or denatured by the alkaline solution, the problem of dropping a large amount of carbon black particles is also solved.

Preparation method of polyimide film

The invention provides a preparation method of a polyimide film, which comprises the following steps: step (a) of polymerizing polyamic acid from dianhydride and diamine; a step (b) of preparing a first composition comprising a fluororesin and a first organic solvent; a step (c) of preparing a second composition comprising carbon black having an average particle diameter of 0.1 to 5 μm and a second organic solvent; a step (d) of mixing the first composition and the second composition to prepare a third composition; and (e) mixing the polyamic acid with the third composition, forming a film on a support, and performing heat treatment to perform imidization.

In a specific example, the first composition may include 10 to 30 wt% of the fluororesin, with respect to the total weight of the first composition.

When the addition amount of the fluororesin is less than the range, the absolute amount of the fluororesin to be chemically bonded becomes insufficient for each carbon black particle, and there is a possibility that the bonding between the carbon black and the fluororesin particles is insufficient, so that it is not preferable.

In contrast, when the amount of the fluororesin is more than the range, the content of the fluororesin contained in the polyimide film produced becomes excessively high, possibly resulting in a decrease in the physical properties of the polyimide film, and thus it is not preferable.

On the other hand, in the step (d), the fluororesin and the carbon black may be chemically bonded to form a matrix structure by mixing the first composition and the second composition.

That is, unlike the method including a step of simply preparing a polyimide film by mixing carbon black and a fluororesin in a polyamic acid, in the preparation method according to the present invention, a step of preparing a first composition and a second composition, respectively, and mixing the first composition and the second composition to prepare a third composition is included, so that carbon black and fluororesin may be chemically bonded to form a matrix structure.

On the other hand, the polyimide film of the present invention is obtained from a polyamic acid solution as a precursor of polyimide.

Specifically, the polyamic acid solution may be derived from a dianhydride monomer comprising: pyromellitic dianhydride, 2,3,6, 7-naphthalene tetracarboxylic dianhydride, 3,3',4,4' -biphenyl tetracarboxylic dianhydride, 1,2,5, 6-naphthalene tetracarboxylic dianhydride, 2',3,3' -biphenyl tetracarboxylic dianhydride, 3,3',4,4' -benzophenone tetracarboxylic dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 3,4,9, 10-tetracarboxylic dianhydride, bis (3, 4-dicarboxyphenyl) propane dianhydride, 1-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1-bis (3, 4-dicarboxyphenyl) ethane dianhydride, bis (2, 3-dicarboxyphenyl) methane dianhydride, bis (3, 4-dicarboxyphenyl) ethane dianhydride, oxydiphthalic dianhydride, bis (3, 4-dicarboxyphenyl) sulfone dianhydride, p-phenylene bis (trimellitate monoanhydride), ethylene bis (trimellitate monoanhydride), and bisphenol A bis (trimellitate monoanhydride) and their analogs, which may be used alone or in admixture in any proportion.

In addition, the diamine monomer comprises: 4,4 '-oxydianiline, p-phenylenediamine, 4' -diaminodiphenylpropane, 4 '-diaminodiphenylmethane, benzidine, 3' -dichlorobenzidine, 4 '-diaminodiphenyl sulfide, 3' -diaminodiphenylsulfone, 4 '-diaminodiphenylether (4,4' -oxydianiline), 3 '-diaminodiphenylether (3,3' -oxydianiline), 3,4 '-diaminodiphenylether (3,4' -oxydianiline), 1, 5-diaminonaphthalene, 4 '-diaminodiphenyldiethylsilane, 4' -diaminodiphenylsilane, 4 '-diaminodiphenylethylphosphine oxide, 4' -diaminodiphenylethylphosphine oxide, and, 4,4 '-diaminodiphenyl-N-methylamine, 4' -diaminodiphenyl-N-aniline, 1, 4-diaminobenzene (p-phenylenediamine), 1, 3-diaminobenzene, 1, 2-diaminobenzene, and the like, which may be used alone or in a mixture in any ratio.

On the other hand, the polyamic acid solution is prepared by the following method: mixing an aromatic diamine monomer and an aromatic dianhydride monomer in a monomer compound so as to have substantially equimolar amounts, dissolving the monomer mixture in an organic solution, mixing and stirring the mixed solution at a controlled temperature until the aromatic dianhydride monomer and the aromatic diamine monomer are polymerized.

The solid content of the polyamic acid solution is generally a concentration of 5 to 35% by weight, preferably 10 to 30% by weight.

At this concentration range, the polyamic acid solution obtains the appropriate molecular weight and solution viscosity.

The solvent used for synthesizing the polyamic acid solution is not particularly limited, and any solvent can be used as long as it can dissolve the polyamic acid, but an amide solvent is preferable.

Specifically, the solvent may be an organic polar solvent, specifically, an aprotic polar solvent (aproticpolar solvent), and for example, one or more selected from the group consisting of N, N '-Dimethylformamide (DMF), N' -dimethylacetamide (DMAc), N-methyl-pyrrolidone (NMP), γ -butyrolactone (GB L), and Diglyme (Diglyme), but is not limited thereto, and may be used alone or in combination of two or more thereof, as required.

In one example, preferably, N-dimethylformamide and N, N-dimethylacetamide, among others, can be used as the solvent.

On the other hand, the carbon black may be controlled in particle diameter using a bead mill, and these milling processes appropriately mix and disperse a filler of carbon black or the like having a relatively low dispersion degree of particle diameter with the polyamic acid solution, so that the light transmittance of the polyimide film thus prepared remains uniform as a whole, thereby finally further reducing the light transmittance.

In addition, in order to improve the dispersibility of the carbon black and stabilize the dispersed state, a dispersant, a thickener, or the like may be used together with the first organic solvent within a range that does not affect the physical properties of the film.

In this case, the first organic solvent is not particularly limited as long as it can dissolve the polyamic acid while dispersing the carbon black particles.

In addition, the second organic solvent may be the same as or different from the first organic solvent.

Specifically, the first organic solvent and the second organic solvent may be organic polar solvents, more specifically, aprotic polar solvents (aprotic polar solvents), and for example, one or more selected from the group consisting of N, N '-Dimethylformamide (DMF), N' -dimethylacetamide (DMAc), N-methyl-pyrrolidone (NMP), γ -butyrolactone (GB L), and Diglyme (Diglyme), but is not limited thereto, and may be used alone or in combination of two or more thereof, as needed.

On the other hand, in the preparation step of the polyimide film, a catalyst may be further added to the polyamic acid solution, the third composition, and then applied to the support.

As the catalyst, 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 can be used, and can 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 can be calculated from the molar ratio of the o-carboxyamide functional group in the polyamic acid solution, and may be 1.0 mol to 5.0 mol, and the amount of the tertiary amine to be added can be calculated from the molar ratio of the o-carboxyamide functional group in the polyamic acid solution, specifically, may be 0.2 mol to 3.0 mol.

In addition, in the step of gelling by heat-treating the polyamic acid solution coated on the support, the gelling temperature condition may be 100 to 250 ℃.

As the carrier, a glass plate, an aluminum foil, a circulating stainless steel belt, a stainless steel drum, or the like can be used.

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 type of support, the coating amount of the polyamic acid solution, and the mixing conditions of the catalyst.

After the gelled film is separated 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. The gelled film may be fixed on a fixable supporter, for example, a pin-type frame or a clip-type supporter, when being heat-treated, to be heat-treated.

On the other hand, in order to realize an ultra-thin film of 8 μm or less, the process conditions such as the discharge amount, rate, pressure, etc. should be controlled when the polyamic acid is applied (discharged) to the support in the present invention.

Specifically, the polyamic acid solution should be discharged from a T-Die (T-Die) to an endless belt (end belt) and minimize vibration upon landing in the form of a film, and for this reason, when the discharged film is formed, it may be possible to use a pressure lower than that used when a conventional polyimide film is produced, for example, at 10mmH₂O to40mmH₂Air (air) is supplied under pressure of O.

At this time, the amount of discharge from the T die and the velocity of the endless belt may satisfy the following formula, for example, the amount of discharge 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 was ＊ specific gravity of the film (cross-sectional area of the T die) ＊ (speed of the endless belt)

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

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.

And, when heat treatment is performed by using a drier or the like after fixing to the pin type frame, in order to prevent the film from being cracked in the heat treatment process, the heat treatment may be performed at a temperature of 50 to 150 c lower than the highest heat treatment temperature standard in preparing a yellow polyimide film of the same thickness.

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

The polyimide film prepared as described above may have a light transmittance of 10% or less, or 9.7% or less in the visible light region in order to provide a light shielding function, the lower the light transmittance, the better.

The present invention may also provide a coverlay (coverlay) comprising the polyimide film, and an electronic device comprising the coverlay.

The polyimide film is applied to a cover film, an insulating film, a semiconductor, and the like, not only to further thin a product but also to improve aesthetic characteristics, and to shield the internal shape and the charging parts from the external appearance to be advantageous for safety.

Drawings

Fig. 1 is a Scanning Electron Microscope (SEM) picture taken after exposing the outer surface of a flexible circuit board prepared using the polyimide film of comparative example 1 to an alkaline environment.

Fig. 2 is an enlarged picture of fig. 1.

Fig. 3 is an SEM picture taken after exposing the outer surface of the flexible circuit board prepared using the polyimide film of example 1 to an alkaline environment.

Fig. 4 is an enlarged view of fig. 3.

Detailed Description

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

< example 1>

Preparation example 1: polymerization of Polyamic acid

As a polyamic acid solution polymerization process, 407.5g of Dimethylformamide (DMF) as a solvent was added in a 500m L reactor under a nitrogen atmosphere.

After the temperature was set to 25 ℃, 35.90g of 4,4' -oxydianiline was added as a diamine monomer and stirred for about 30 minutes, and after confirming the dissolution of the monomers, 35.90g of pyromellitic dianhydride was added as a dianhydride monomer and after adjusting the final addition amount, the final viscosity was adjusted to 250000 to 280000 million centipoise.

After the addition was complete, the temperature was maintained while stirring for 1 hour to polymerize the amic acid solution with a final viscosity of 280000 million centipoise.

Preparation example 2: preparation of composition comprising fluororesin and carbon black

After 70g of DMF as the first organic solvent was mixed with 30g of PFA resin as the fluororesin, a first composition having a solid content of 30% was prepared.

After 89g of DMF as the second organic solvent was mixed with 10g of carbon black and 1g of dispersant BYK-430, a second composition comprising carbon black having an average particle size of 0.5 μm was prepared using a grinder.

After mixing 100g of the first composition with 100g of the second composition, a third composition was prepared.

Preparation example 3: preparation of polyimide film

30g of the obtained polyamic acid solution prepared in preparation example 1 was mixed with 5g of the third composition prepared in preparation example 2, 4.76g of Isoquinoline (IQ), 26.36g of Acetic Anhydride (AA), and 18.87g of DMF were added as catalysts, and then, the mixture was uniformly mixed, cast on a stainless steel (SUS) plate (100SA, available from Sandvik, Sweden) to 70 μm using a doctor blade, and further, dried 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.

After heating the film from 200 to 600 c on a high-temperature tenter, it was cooled at 25 c and then separated from the pin frame, thereby preparing a polyimide film having a thickness of 7.5 μm, which contained 90 wt% of polyimide resin, 5 wt% of carbon black and 5 wt% of PFA resin, relative to the total weight of the polyimide film.

< example 2>

A polyimide film having a thickness of 7.5 μm was prepared by the same method as example 1, except that the contents of the polyimide resin, the fluororesin and the carbon black were changed to the contents as listed in table 1.

< example 3>

A polyimide film having a thickness of 7.5 μm was prepared by the same method as example 1, except that the contents of the polyimide resin, the fluororesin and the carbon black were changed to the contents as listed in table 1.

< example 4>

A polyimide film having a thickness of 7.5 μm was prepared by the same method as example 1, except that the particle diameter of the carbon black was changed to the particle diameter as listed in table 1.

< example 5>

A polyimide film having a thickness of 7.5 μm was prepared by the same method as example 1, except that the particle diameter of the carbon black was changed to the particle diameter as listed in table 1.

< comparative example 1>

A polyimide film having a thickness of 7.5 μm was prepared by the same method as example 1, except that the first composition was not mixed in preparation example 2, and the contents of the polyimide resin and carbon black were changed to the contents as listed in table 1.

< comparative example 2>

A polyimide film having a thickness of 7.5 μm was prepared by the same method as example 1, except that the contents of the polyimide resin, the fluororesin and the carbon black were changed to the contents as listed in table 1.

< comparative example 3>

A polyimide film having a thickness of 7.5 μm was prepared by the same method as example 1, except that the contents of the polyimide resin, the fluororesin and the carbon black were changed to the contents as listed in table 1.

< comparative example 4>

A polyimide film having a thickness of 7.5 μm was prepared by the same method as example 1, except that the particle diameter of the carbon black was changed to the particle diameter as listed in table 1.

< comparative example 5>

A polyimide film having a thickness of 7.5 μm was prepared by the same method as example 1, except that the particle diameter of the carbon black was changed to the particle diameter as listed in table 1.

< comparative example 6>

A polyimide film having a thickness of 7.5 μm was prepared by the same method as example 1, except that the fluororesin was changed to the fluororesin as listed in table 1.

< comparative example 7>

A polyimide film having a thickness of 7.5 μm was prepared by the same method as example 1, except that the fluororesin was changed to the fluororesin as listed in table 1.

< comparative example 8>

Preparation example 4: preparation of polyimide film

30g of the polyamic acid solution prepared in preparation example 1 was mixed with 1.5g of carbon black having an average particle diameter of 0.5 μm and 1.5g of PFA resin, 4.76g of Isoquinoline (IQ), 26.36g of Acetic Anhydride (AA) and 18.87g of DMF were added as catalysts, and then, the mixture was uniformly mixed, cast on an SUS plate (100SA, available from Sandvik, Sweden) to 70 μm using a doctor blade, and further, dried 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.

After 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, an ultra-thin black polyimide film having a thickness of 7.5 μm, comprising 90 wt% of a polyimide resin, 5 wt% of carbon black, and 5 wt% of a PFA resin, relative to the total weight of the polyimide film, was prepared.

TABLE 1

＊ in the case of comparative example 8, instead of production examples 1 to 3, polyimide films were produced according to production example 1 and production example 4.

Experimental example 1: evaluation of alkali resistance index

After double-sided corona treatment of the polyimide films respectively prepared in < examples 1> to < example 5> and < comparative examples 1> to < comparative example 8>, the polyimide film, the adhesive sheet (adhesive), and the copper foil were sequentially laminated, and were thermocompressed and bonded at 160 ℃ for 30 minutes at a pressure of 50kgf using a thermocompression press (HotPress), thereby preparing test samples.

Test specimens cut to 4 x 10cm were exposed to a 10% NaOH solution for 5 minutes at a temperature of 55 ℃ and to a desmear solution (10% NaMnO) at a temperature of 55 ℃₄+ 4% NaOH) 5 pointsThe washing process was repeated twice after a minute and the thickness of the film was measured, and the thickness before exposure and the degree of change in thickness after exposure were expressed as a percentage compared to the thickness before exposure to the NaOH solution and the desmear solution, and are listed in table 2.

TABLE 2

Referring to table 2, in the case of the polyimide films of examples 1 to 5, the fluororesin having a alkali resistance index in the range of 3 to 15% by weight was very excellent as 70% or more, but in contrast to this, in the case of comparative example 1 not including the fluororesin and comparative example 2 having a content of the fluororesin less than the content range of the present invention, it was confirmed that the alkali resistance was not more than 70% as compared with examples 1 to 5.

In the case of comparative example 3 in which the content of the fluororesin was larger than the content range of the present invention, it was confirmed that the alkali resistance was significantly excellent since the alkali resistance index was 85% or more, but as shown in the evaluation of the physical properties in tables 3 and 4 below, in the case of the polyimide film of comparative example 3, it was confirmed that the physical properties were lower than those of example 1.

Experimental example 2: evaluation of light transmittance

For the polyimide films respectively prepared in < example 1> to < example 5> and < comparative example 1> to < comparative example 8>, the transmittance was measured in the visible light region by the ASTM D1003 method using a transmittance measuring apparatus (model: ColorQuesetXE, manufacturer: Hunter (Hunter L ab) corporation), and the results thereof are shown in table 3 below.

And, for the polyimide films respectively prepared in < example 1> to < example 5> and < comparative example 1> to < comparative example 8>, as in the above described experimental example 1, after being exposed to an alkaline environment, the transmittance was measured in the visible light region by the ASTM D1003 method using a transmittance measuring apparatus (model: ColorQuesetXE, manufacturer: Hunter (Hunter L ab) usa), and the results thereof are shown in the following table 3.

TABLE 3

Experimental example 3: evaluation of tensile Properties

For the polyimide films respectively prepared in < example 1> to < example 5> and < comparative example 1> to < comparative example 8>, tensile properties, i.e., tensile strength, elongation, and elastic modulus were measured according to the specifications of ASTM D882, and the results thereof are shown in table 4 below.

Also, as for the polyimide films respectively prepared in < example 1> to < example 5> and < comparative example 1> to < comparative example 8>, after being exposed to an alkaline environment as in the experimental example 1, tensile properties, i.e., tensile strength, elongation and elastic modulus, were measured according to astm d882, and the results thereof are shown in the following table 4.

TABLE 4

Referring to table 3 and table 4, in the case of the polyimide films of examples 1 to 5, it can be confirmed that even though PFA is contained in a range of 3 to 15 wt% as a fluororesin, physical properties such as light transmittance, tensile properties, etc. are not reduced as compared with comparative example 1 containing no fluororesin, and in the case of comparative example 3 containing a content of fluororesin greater than the content range according to the present invention, it can be confirmed that the physical properties as described above are reduced as compared with example 1.

Also, in the case of comparative example 3 in which the particle diameter of the carbon black is larger than the range according to the present invention and in the case of comparative example 4 in which the particle diameter of the carbon black is smaller than the range according to the present invention, it was confirmed that at least one of the physical properties such as gloss, transmittance, tensile property, or the like is lowered.

In particular, it can be confirmed that the polyimide films of examples 1 to 5 are more excellent than those of comparative examples 1 to 8 in terms of physical properties such as light transmittance, tensile properties, and the like evaluated after exposing the polyimide films to an alkaline environment.

On the other hand, fig. 1 shows a Scanning Electron Microscope (SEM) picture taken after exposing the outer surface of a test sample prepared using the polyimide film of comparative example 1 to an alkaline environment, fig. 2 shows an enlarged picture of a portion of fig. 1, fig. 3 shows an SEM picture taken after exposing the outer surface of a test sample prepared using the polyimide film of example 1 to an alkaline environment, and fig. 4 shows an enlarged picture of a portion of fig. 3.

Referring to these pictures, in the case of the surface of the test sample prepared from comparative example 1, it can be confirmed that the carbon black particles fall from the surface so that the copper foil layer is exposed, and in contrast, in the case of the surface of the test sample prepared from example 1, in which the alkali resistance has been improved, it can be confirmed that the fall of the carbon black particles has been minimized.

Although the present invention has been described in detail with reference to the embodiments thereof, those skilled in the art can make various applications and modifications within the scope of the present invention based on the above-described matters.

Industrial availability

As described above, the polyimide film according to the present invention has low light transmittance in the visible light region.

Further, the polyimide film is excellent not only in mechanical stability but also in alkali resistance, and therefore can be effectively used in a cover film and an electronic device including the cover film.