CN112585195B

CN112585195B - Polyimide film having improved alkali resistance and method for preparing the same

Info

Publication number: CN112585195B
Application number: CN201880096720.9A
Authority: CN
Inventors: 金纪勋; 李吉男; 崔祯烈
Original assignee: Polyimide Advanced Materials Co ltd
Current assignee: Polyimide Advanced Materials Co ltd
Priority date: 2018-08-22
Filing date: 2018-09-28
Publication date: 2023-03-28
Anticipated expiration: 2038-09-28
Also published as: CN112585195A; KR20200022146A; WO2020040347A1; KR102153507B1

Abstract

The present invention provides a polyimide film, wherein the polyimide film is prepared by imidizing a precursor composition comprising: a first polyamic acid obtained by polymerizing a first dianhydride and a first diamine having two or less benzene rings; a second polyamic acid obtained by polymerizing a second dianhydride and a second diamine containing three or more benzene rings; and carbon black; wherein the degree of crystallinity is 65% or more, the light transmittance is 0.09 or less, and the alkali resistance index evaluated based on the thickness of the polyimide film before and after exposure to an alkali component is 70% or more, and the thickness is 8.0 μm or less.

Description

Polyimide film having improved alkali resistance and method for preparing the same

Technical Field

The present invention relates to a polyimide film having improved alkali resistance and a method for preparing the same.

Background

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

Furthermore, polyimide is attracting attention as a highly functional material that can be used in the fields of microelectronics and optics based on excellent electrical characteristics such as insulation properties and low dielectric constant.

Examples of the microelectronics field include highly integrated circuits and the like included in portable electronic devices and communication devices. Electrical insulation is provided to the circuit by attaching or adding polyimide to the circuit, while at the same time serving as a film that protects the circuit from moisture, light sources, impact, etc.

As described above, although various examples of the film for protecting the circuit are possible, a composite film having an adhesive layer formed on one surface or both surfaces of the film may be called a coverlay (coverlay) in a narrow sense, and a polyimide film may be preferably used for the coverlay.

In recent years, with importance placed on visual safety, a shielding function, and a light shielding function of a circuit, a special polyimide film containing carbon black and having a black color tone has been attracting attention as a cover film material.

In order to prepare a polyimide film having a black color tone, a process of mixing and uniformly dispersing carbon black in the precursor polyamic acid is necessary. In this process, if the carbon black is not uniformly dispersed, problems such as a reduction in shielding function and surface defects may occur. In essence, carbon black has physical/chemical properties different from those of polyamic acid or polyimide, and thus is not easily mixed and/or dispersed in polyimide or polyamic acid.

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

Therefore, the shielding property is lost with the removal of black tone from the cover film, and not only surface defects are caused by the removal of carbon black, but also reduction in weight and thickness is accompanied, and thus the function may be greatly reduced due to the covering.

Therefore, a technology capable of fundamentally solving these problems is urgently required.

Disclosure of Invention

Problems to be solved by the invention

According to an aspect of the present invention, although a polyimide film prepared using a first polyamic acid and a second polyamic acid having different characteristics from each other, and using carbon black has an ultra-thin film form of 8 μm or less, it may have very excellent shielding properties and improved resistance to basic components (hereinafter, referred to as "alkali resistance"), while satisfying predetermined mechanical properties required therefor.

According to another aspect of the present invention, when a polyimide film is prepared by preparing a mixed solution including a second polyamic acid and carbon black and mixing it with a first polyamic acid, the dispersibility of carbon black is improved, and a high-quality polyimide film can be obtained.

The problems of the prior art are solved according to these aspects, and it is an object of the present invention to provide specific embodiments thereof.

Means for solving the problems

In one embodiment, the present invention provides a method for preparing a polyimide film by imidizing a precursor composition comprising: a first polyamic acid obtained by polymerizing a first dianhydride and a first diamine having two or less benzene rings; a second polyamic acid obtained by polymerizing a second dianhydride and a second diamine having three or more benzene rings; and carbon black.

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

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

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

By "dianhydride" herein is meant to include precursors or derivatives thereof which may not technically be a dianhydride but which still react with the diamine to form a polyamic acid and which polyamic acid can be converted back to polyimide.

Herein "diamine" is meant to include precursors or derivatives thereof which may not technically be a diamine but which will still react with the dianhydride to form a polyamic acid and which can convert the acid back to polyimide.

When an amount, concentration, or other value or parameter is recited herein as either a range, preferred range or a preferred upper limit and a preferred lower limit, whether or not the range is separately disclosed, it is understood that any pair of any upper range limit or preferred value and any lower range limit or preferred value specifically discloses all ranges that can be formed. When a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. The scope of the present invention is not intended to be limited to the specific values recited when defining a range.

Polyimide film

The polyimide film according to the present invention is prepared by imidizing a precursor composition,

the precursor composition comprises:

a first polyamic acid obtained by polymerizing a first dianhydride and a first diamine having two or less benzene rings;

a second polyamic acid obtained by polymerizing a second dianhydride and a second diamine containing three or more benzene rings; and

carbon black;

wherein the degree of crystallinity is 65% or more, the light transmittance is 0.09 or less, and the alkali resistance index evaluated based on the thickness of the polyimide film before and after exposure to an alkali component is 70% or more, and the thickness is 8.0 μm or less.

In a specific example, the first polyamic acid forms first polyimide chains through imidization, and the second polyamic acid forms second polyimide chains through imidization.

In some aspects, at least a portion of the first and second polyimide chains are cross-linked to each other by imidization.

The first polyamic acid may be a material having a relatively rigid structure in a molecular structure. Thus, the first polyimide chain derived from the first polyamic acid may have a relatively rigid structure.

Such first polyimide chains can contribute to a predetermined mechanical strength of the polyimide film, and in particular, a tensile strength and/or modulus that are inevitably required for the polyimide film.

The second polyamic acid may be a material having a relatively flexible structure in a molecular structure, and may be a material having a relatively high crystallinity and excellent chemical resistance. Therefore, the second polyamideimide chain derived from the second polyamic acid may have both higher crystallinity and excellent chemical resistance.

It is to be noted that, as each of these chains functions complementarily, the polyimide film of the present invention may also have mechanical properties corresponding to the level of the first polyimide chain, and may also have predetermined crystallinity (65% or more) and chemical resistance inherent to the second polyimide chain, which are difficult to be achieved only with the first polyimide chain, in the form of a film of 8 μm or less.

Generally, since polymer crystals scatter or absorb light, the higher the crystallinity, the lower the light transmittance of the film, and the polyimide film of the present invention may have a lower light transmittance relative to a conventional polyimide film having a low crystallinity of less than 65%. This can play a very advantageous role in polyimide films containing carbon black, which require shielding, light shielding, and the like.

Based on the foregoing features, the polyimide film of the present invention may have the following physical properties.

The polymer has a crystallinity of 70% or more in a thin film state,

the tensile strength was 200kgf/cm ³ In the above-mentioned manner,

the modulus is more than 3GPa,

the light transmittance is less than 0.07 percent,

evaluated based on the thickness of the polyimide film before and after exposure to the alkali component, and has an alkali resistance index of 75% or more.

In a particular example, the first polyamic acid can have a viscosity of 50000 to 300000 cps measured at a temperature of 23 ℃ when the solid content is less than 15 wt%, and the second polyamic acid can have a viscosity of 5000 to 30000 cps measured at a temperature of 23 ℃ when the solid content is 15 wt%.

When the viscosity of the first polyamic acid is less than 50000 cps, heat resistance and physical properties of the polyimide film may be greatly reduced. When the viscosity of the first polyamic acid exceeds 300000 cps, there may be a problem in terms of a film manufacturing process. In particular, since the precursor composition has a high viscosity, problems may occur during film formation of the film, and further it may be difficult to prepare a thin film of 8 μm or less.

When the viscosity of the second polyamidoic acid is less than 5000 cps, it may be insufficient to form a second polyamideimide chain. This is not preferable in terms of improving the alkali resistance of the polyimide film. When the viscosity of the second polyamic acid exceeds 30000 cps, since dispersibility of carbon black in the precursor composition may be reduced, it is not preferable from the viewpoint of processability in producing a polyimide film.

On the other hand, when exposed to an alkaline environment, polyimide is susceptible to alkaline components such as decomposition or modification. When the polyimide film containing carbon black is decomposed or modified by an alkaline component, the carbon black is largely peeled off, resulting in a more serious reduction in thickness.

In recent years, in order to cope with miniaturization of electronic devices, an ultra-thin polyimide film having a very thin thickness of, for example, 8 μm or less is required. However, the peeling of carbon black in the ultra-thin polyimide film is more severe than that of the conventional polyimide film having a thickness of 10 μm or more. This is because even if the same absolute amount of carbon black is removed in the conventional polyimide film and the ultrathin film polyimide film, the ratio of carbon black to be peeled off is much higher than that of the entire polyimide film in the ultrathin film type. Also, since the alkali component permeates from the surface, relatively more carbon black can be removed under the same conditions in the case of an ultra-thin polyimide film at a close distance from the surface.

Therefore, in particular, an ultrathin film imide film containing carbon black and having a thickness of 8 μm or less is required to have improved "alkali resistance".

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

In connection with this, one example for evaluating the alkali resistance is a method of measuring a change in film thickness before and after exposure after exposing a polyimide film to an alkali solution, and in the present invention, a test method (a) comprising the following steps is used:

carrying out corona treatment on two sides of the polyimide film;

laminating a polyimide film, an adhesive sheet and a copper foil in sequence, adhering the laminated polyimide film, the adhesive sheet and the copper foil for 30 minutes at the temperature of 160 ℃ by using a hot press under the pressure of 50kgf, and cutting the laminated polyimide film into 4 cm and 10 cm to prepare a flexible circuit board sample and measure the thickness (first thickness);

exposing the flexible circuit board cut 4 cm 10 cm to 10-percent NaOH solution at a temperature of 55 deg.C for 3 minutes, and to a decontamination solution at a temperature of 55 deg.C (10% NaMnO) ₄ +4% naoh) 5 minutes, the washing was repeated twice, and the thickness of the film (second thickness) was measured; and

the degree of change in the second thickness with respect to the first thickness ((first thickness-second thickness)/first thickness x 100) is expressed in percentage.

For a conventional polyimide film, if subjected to the above test method (a), the alkali resistance index may be indicated to be about 50% to 60%.

On the other hand, according to the test method (a), the polyimide film of the present invention may have a alkali resistance index of at least 70% or more, specifically 75% or more, particularly 80% or more. This is a significantly improved alkali resistance compared to conventional polyimide films.

As will be demonstrated in more detail above by the "details for carrying out the invention", however, in summary, since the second polyimide chain derived from the second polyamic acid has relatively strong resistance to the alkali component, not only the penetration of the alkali component into the polyimide film can be prevented, but also the second polyimide chain can maintain the skeleton of the polyimide film to some extent even if the first polyimide chain is decomposed. Therefore, according to this, the frequency of the soot shedding phenomenon can be remarkably reduced.

However, despite the above advantages, it is not preferable to unconditionally include the second polyimide chain in the polyimide film.

Specifically, this is because the previous advantages can be exhibited when the content of the second polyimide chain in the polyimide film is at a certain level, but if it exceeds this range, the advantage of alkali resistance cannot be enhanced or improved, and the tensile strength and/or modulus of the polyimide film is drastically reduced.

This phenomenon may be more pronounced in ultra-thin film type films of 8.0 μm or less. That is, it is important that the polyimide film contains an appropriate amount of the first polyimide chains and the second polyimide chains to ensure physical properties and alkali resistance.

In this regard, the polyimide film of the present invention may include 80 to 92% by weight of the first polyimide chain, 3 to 10% by weight of the second polyimide chain, and 5 to 10% by weight of carbon black having an average particle diameter of 0.1 to 5 μm, relative to the total weight thereof, wherein the thickness of the film may be 7.5 μm or less.

More specifically, the polyimide film of the present invention may include 83 to 92% by weight of the first polyimide chains and 5 to 7% by weight of the second polyimide chains, relative to the total weight thereof.

In one particular example, the first dianhydride is pyromellitic dianhydride (or PMDA),

the second dianhydride may be 3,3',4,4' -biphenyltetracarboxylic dianhydride (or s-BPDA) and/or 2,3,3',4' -biphenyltetracarboxylic dianhydride (or a-BPDA).

The first diamine may be at least one selected from the group consisting of:

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

2) Diamines having two benzene rings in the structure: <xnotran> ' - ( , ODA), ' - , ' - ( ), ' - - ' - , ' - - ' - , ' - ( ) - ' - , ' - - ' - , ' - - ' - , ', ' - - ' - , (4- ) , ' - , ' - , ' - ( o- ), ' - ( m- ), ' - , ' - , ' - , ' - , ' - , ' - , ' - , ' - , ' - , ' - , ' - , ' - , ' - , ' - - ' - , ' - - ' - , </xnotran> 3,3 '-diaminodiphenylmethane, 3,4' -diaminodiphenylmethane, 4,4 '-diaminodiphenylmethane, 2,2-bis (3-aminophenyl) propane, 2,2-bis (4-aminophenyl) propane, 2,2-bis (3-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 2,2-bis (4-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 3,3' -diaminodiphenyl sulfoxide, 3,4 '-diaminodiphenyl sulfoxide, 4,4' -diaminodiphenyl sulfoxide.

The second diamine can be 1,3-bis (4-aminophenoxy) benzene (TPE-R) and/or 1,4-bis (3-aminophenoxy) benzene (TPE-Q).

The first diamine and the first dianhydride have a rigid molecular structure, and a predetermined level of heat resistance, tensile strength, and modulus required in the polyimide film can be achieved by the second polyimide chain formed by combining them.

The TPE-based diamine, which is a monomer containing three benzene rings, is a monomer having excellent chemical resistance and may play a major role in increasing the crystallinity of a polymer.

The BPDA-based dianhydride contains two benzene rings, is a relatively flexible monomer in a molecular structure, and has excellent chemical resistance.

Therefore, the second polyimide chain formed by their combination can achieve excellent chemical resistance.

Preparation method of polyimide film

The method for preparing the polyimide film of the present invention may comprise:

polymerizing first polyamic acid by first dianhydride and first diamine;

polymerizing a second polyamic acid from a second dianhydride and a second diamine;

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;

mixing the second polyamic acid and the black crude liquid to prepare a mixed liquid;

mixing the mixed solution in the first polyamic acid to prepare a precursor composition; and

the precursor composition is imidized to obtain a polyimide film.

Generally, carbon black is not easily dispersed when simply mixed with polyamic acid, but tends to aggregate. In contrast, a first polyamic acid and a second polyamic acid having similar chemistries can be mixed relatively easily.

In this regard, in the production method of the present invention, preliminary dispersion of the carbon black can be easily caused by mixing the carbon black in the form of the black crude liquid with the second polyamic acid having a relatively low viscosity.

Thereafter, if the mixed liquid is mixed with the first polyamic acid, since the second polyamic acid is easily mixed with the first polyamic acid, the dispersed carbon black can be quickly mixed and/or dispersed into the entire first polyamic acid together with the second polyamic acid. The above may be a major advantage of the preparation process according to the invention.

In a specific example, an organic solvent may be utilized in the preparation of the first polyamic acid, the second polyamic acid, and the black crude liquid.

As a non-limiting example of an organic solvent that can be used at these steps, an aprotic polar solvent (aprotic polar solvent) may be mentioned.

Non-limiting examples of the aprotic polar solvent include amide solvents such as N, N '-Dimethylformamide (DMF) and N, N' -dimethylacetamide (DMAc), p-chlorophenol and o-chlorophenol solvents, N-methyl-pyrrolidone (NMP), γ -butyrolactone (GBL), and dimethyl ether (Diglyme), and two or more of these solvents can be used alone or in combination.

The method of polymerizing the first polyamic acid and the second polyamic acid may, for example, be:

(1) A method of performing polymerization by adding all of the diamine monomer to the organic solvent and then adding the dianhydride monomer so as to be substantially equimolar to the diamine monomer;

(2) A method of performing polymerization by adding the whole dianhydride monomer to an organic solvent and then adding a diamine monomer so as to be substantially equimolar to the dianhydride monomer;

(3) A method in which a part of the diamine monomer is added to an organic solvent, and then a part of the dianhydride monomer is mixed at a molar ratio of about 95 to 105 mol% with respect to the reaction components, and then the remaining diamine monomer component is added, and the remaining dianhydride monomer component is continuously added, and polymerization is performed by making the diamine monomer and the dianhydride monomer substantially equimolar;

(4) A method in which a dianhydride monomer is added to an organic solvent, a part of the diamine compound is mixed at a molar ratio of 95 to 105 mol% with respect to the reaction components, and then another dianhydride monomer component is added, and the remaining diamine monomer component is continuously added, thereby polymerizing a diamine monomer and a dianhydride monomer in substantially equimolar amounts;

(5) As a method of reacting a part of the diamine monomer component and a part of the dianhydride monomer component in one organic solvent so that either one component is excessive to form the first polymer, and reacting a part of the diamine monomer component and a part of the dianhydride monomer component in another organic solvent so that either one component is excessive to form the second polymer, after mixing the first and second polymers and completing the polymerization, there can be cited a method of polymerizing by mixing the first and second polymers so that the whole diamine monomer component used in these reactions is substantially equimolar to the dianhydride monomer component when the diamine monomer component is excessive in forming the first polymer, the dianhydride monomer component is excessive in the second polymer, and when the dianhydride monomer component is excessive in the first polymer, the diamine monomer component is excessive in the second polymer.

However, the method is an example for facilitating the implementation of the present invention, and the scope of the present invention is not limited thereto, and of course, any known method may be used.

On the other hand, a filler may be added to improve various characteristics of the polyimide film derived from the precursor composition, such as contact properties, thermal conductivity, electrical conductivity, corona resistance, and loop hardness, when preparing the first polyamic acid, the second polyamic acid, and/or the black crude liquid. The filler to be added is not particularly limited, but as preferable examples, silica, titanium oxide, alumina, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, mica, dicalcium phosphate, barium sulfate and calcium carbonate may be cited.

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

When the average particle diameter is less than this range, the modification effect is insignificant, and when it is more than this range, the filler may significantly impair the surface characteristics of the polyimide film or degrade the mechanical characteristics of the film.

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

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

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

In addition, the obtaining of the polyimide film may include: after the precursor composition is film-formed on a support and dried to prepare a gel film, the gel film is imidized to form a polyimide film.

Specific examples of such imidization include a thermal imidization method, a chemical imidization method, and a composite imidization method using both the thermal imidization method and the chemical imidization method, and these methods are more specifically described by the following non-limiting examples.

< thermal imidization method >

The thermal imidization method is a method of causing an imidization reaction by a hot air or a heat source such as an infrared dryer in addition to a chemical catalyst, and may include:

drying the precursor composition to form a gel film; and

and carrying out heat treatment on the gel film to obtain the polyimide film.

Among these, the gel film is understood to be a film intermediate having a self-supporting property in an intermediate step of converting polyamic acid into polyimide.

The gel film may be formed by casting the precursor composition in the form of a film on a support such as a glass plate, an aluminum foil, a circulating (end) stainless steel belt or a stainless steel drum, and then drying the precursor composition on the support at a variable temperature ranging from 50 ℃ to 200 ℃, particularly from 80 ℃ to 150 ℃.

Thus, a gel film may be formed by partial curing and/or drying of the precursor composition. Then, a gel film can be obtained by peeling from the support.

The process of stretching the gel film may be performed as the case may be, to adjust the thickness and size of the polyimide film obtained during the heat treatment and to improve the orientation, and the stretching may be performed in at least one direction of a machine transporting direction (MD) and a Transverse Direction (TD) with respect to the machine transporting direction.

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

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

< chemical imidization method >

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

The "dehydrating agent" means a material which promotes the ring-closure reaction by the dehydration action with respect to the polyamic acid, and as non-limiting examples thereof, aliphatic acid anhydrides, aromatic acid anhydrides, N' -dialkylcarbodiimides, halogenated lower aliphatic acid anhydrides, dihalogenated aryl phosphines, and halogenated sulfinyl groups, etc. can be mentioned. Among them, from the viewpoint of convenience and cost, aliphatic acid anhydrides are preferable, and non-limiting examples thereof include Acetic Anhydride (AA), propionic anhydride, and lactic anhydride, and these may be used alone or in combination of two or more.

The "imidizing agent" means a material having an effect of promoting a ring-closing reaction with respect to the polyamic acid, and may be an imine component such as an aliphatic tertiary amine, an aromatic tertiary amine, or a heterocyclic tertiary amine. Among them, from the viewpoint of reactivity as a catalyst, a heterocyclic tertiary amine may be preferable. As non-limiting examples of the heterocyclic tertiary amine, quinoline, isoquinoline, β -picoline, pyridine and the like can be cited, and these may be used alone or in combination of two or more.

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

If the amount of the dehydrating agent and the imidizing agent is less than the above range, chemical imidization is insufficient, resulting in the formation of cracks in the polyimide film to be produced and the mechanical strength of the film being lowered. In addition, if these addition amounts exceed the ranges, imidization excessively rapidly proceeds, and at this time, it may be difficult to cast or prepare a polyimide film in the form of a film, which exhibits brittleness (brittle).

< Complex imidization Process >

As for the chemical imidization method, a composite imidization method in which thermal imidization is further performed can be used to prepare a polyimide film.

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

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

In forming the gel film, the precursor composition containing the dehydrating agent and/or the imidizing agent is cast in the form of a film on a support such as a glass plate, an aluminum foil, a circulating (end) stainless steel belt or a stainless steel tub, and then the precursor composition on the support is dried at 50 to 200 ℃, particularly at a variable temperature in the range of 80 to 200 ℃. In these processes, a chemical conversion agent and/or an imidizing agent is used as a catalyst so that amide groups can be quickly converted into imide groups.

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

After the gel film thus obtained is set in a tenter, heat treatment is performed at a variable temperature ranging from 50 ℃ to 600 ℃, specifically from 150 ℃ to 600 ℃ to remove water, catalyst, residual solvent, and the like remaining in the gel film, and almost all of the remaining amic acid groups are imidized, whereby the polyimide film of the present invention can be obtained. Even during such heat treatment, the dehydrating agent and/or the imidizing agent can serve as a catalyst to rapidly convert the amic acid groups into imide groups, so that a high imidization rate can be achieved.

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

Detailed Description

Hereinafter, the action and effect of the invention will be further described by way of specific examples of the invention. However, such embodiments are presented only as examples of the present invention, and the scope of the claims of the present invention is not thereby determined.

< example 1>

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

During the polymerization as the first polyamic acid solution, 407.5g of DMF as a solvent was charged into a 1L reactor under a nitrogen atmosphere.

After setting the temperature to 25 ℃, 13.26g of ODA and 21.48g of PPD as diamine monomers were added, and after confirming the monomer dissolution by stirring for about 30 minutes, 57.76g of PMDA was added in portions, and finally, the final input amount was adjusted and added so that the viscosity was changed from 250000 cps to 300000 cps.

After the addition was complete, the mixture was stirred for 1 hour while maintaining the temperature to obtain a first polyamic acid solution having a final viscosity of 260000 cps.

Preparation examples 1 to 2: polymerization of second polyamic acid

During the polymerization as the second polyamic acid solution, 425g of DMF as a solvent was charged under a nitrogen atmosphere into a 2L reactor.

After setting the temperature to 25 ℃, 37.38g of TPE-R as diamine monomer was added and after confirming monomer dissolution by stirring for about 30 minutes, 37.62g of s-BPDA was added in portions, with small amounts added in portions to change the final viscosity from 5000 cps to 30000 cps.

After the addition was completed, the temperature was maintained while stirring for 2 hours to obtain a second amic acid solution with a final viscosity of 5500 cps.

Preparation examples 1 to 3: preparation of a mixture of the Black crude liquid and the second polyamic acid

After 30g of carbon black was mixed with 70g of DMF and 0.1g of dispersant BYK-1162, a black crude liquid having an average particle diameter of 0.5 μm was prepared using a grinder.

24.5g of the second polyamic acid solution prepared in the preparation example 1-2 and 32g of the black crude liquid were mixed with 43.5g of DMF to prepare a mixed solution.

Preparation examples 1 to 4: preparation of ultrathin black polyimide film

40.5g of the first polyamic acid solution prepared in preparation example 1-1 was mixed with 13.3g of the mixed solution prepared in preparation example 1-3, after adding 3.47g of Isoquinoline (IQ), 16.47g of anhydrous Acetic Acid (AA), and 5.89g of DMF as catalysts, uniformly mixed, cast to 70 μm on SUS plate (100SA, sandvik) using a doctor blade, and 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.

The film was heated from 200 ℃ to 600 ℃ in a high-temperature tenter, cooled to 25 ℃, and separated from the pin frame to prepare a polyimide film having a thickness of 7.5 μm, which contained about 86 wt% of the first polyimide chain, 5 wt% of the second polyimide chain, and 9 wt% of carbon black, relative to the total weight of the polyimide film.

< example 2>

A polyimide film having a thickness of 7.5 μm was prepared in the same manner as in example 1, except that the addition amounts of the first polyamic acid solution and the second polyamic acid solution were respectively adjusted so that the polyimide film included about 88 wt% of the first polyimide chain and 3 wt% of the second polyimide chain, relative to the total weight of the polyimide film.

< example 3>

A polyimide film having a thickness of 7.5 μm was prepared in the same manner as in example 1, except that the addition amounts of the first polyamic acid solution and the second polyamic acid solution were respectively adjusted so that the polyimide film included the first polyimide chain in an amount of about 84 wt% and the second polyimide chain in an amount of 7 wt% based on the total weight of the polyimide film.

< example 4>

A polyimide film having a thickness of 7.5 μm was prepared in the same manner as in example 1, except that the addition amounts of the first polyamic acid solution, the second polyamic acid solution, and carbon black were respectively adjusted so that the polyimide film included about 92 wt% of the first polyimide chain, 3 wt% of the second polyimide chain, and 5 wt% of carbon black, relative to the total weight of the polyimide film.

< comparative example 1>

A polyimide film having a thickness of 7.5 μm was prepared in the same manner as in example 1, except that preparation examples 1 to 2 were omitted, preparation of the mixed solution was omitted in preparation examples 1 to 3, and the addition amount was adjusted in preparation examples 1 to 4 to directly mix the black crude solution in the first polyamic acid so as to include about 91 wt% of the first polyimide chain and 9 wt% of carbon black.

< comparative example 2>

A polyimide film having a thickness of 7.5 μm was prepared in the same manner as in example 1, except that the addition amounts of the first polyamic acid solution and the second polyamic acid solution were respectively adjusted so that the polyimide film included about 90 wt% of the first polyimide chain and 1 wt% of the second polyimide chain, relative to the total weight of the polyimide film.

< comparative example 3>

A polyimide film having a thickness of 7.5 μm was prepared in the same manner as in example 1, except that the amounts of the first polyamic acid solution and the second polyamic acid solution were respectively adjusted so that the polyimide film included about 80 wt% of the first polyimide chain and 11 wt% of the second polyimide chain, relative to the total weight of the polyimide film.

< comparative example 4>

A polyimide film having a thickness of 7.5 μm was prepared in the same manner as in example 1, except that preparation examples 1 to 3 were omitted, and the amounts of the first polyamic acid solution and the second polyamic acid solution were respectively adjusted so that the polyimide film included about 95 wt% of the first polyimide chain and 5 wt% of the second polyimide chain, relative to the total weight of the polyimide film.

< comparative example 5>

A polyimide film having a thickness of 7.5 μm was prepared in the same manner as in example 1, except that the amounts of the first polyamic acid solution, the second polyamic acid solution, and carbon black were adjusted so that the polyimide film included about 92 wt% of the first polyimide chain, 5 wt% of the second polyimide chain, and 3 wt% of carbon black, based on the total weight of the polyimide film.

< comparative example 6>

A polyimide film having a thickness of 7.5 μm was prepared in the same manner as in example 1, except that the amounts of the first polyamic acid solution, the second polyamic acid solution, and carbon black were respectively adjusted so that the polyimide film included about 80 wt% of the first polyimide chain, 5 wt% of the second polyimide chain, and 15 wt% of carbon black, based on the total weight of the polyimide film.

< comparative example 7>

A polyimide film having a thickness of 7.5 μm and including about 86 wt% of the first polyimide chain, 5 wt% of the second polyimide chain, and 9 wt% of carbon black, relative to the total weight of the polyimide film, was prepared in the same manner as in example 1, except that preparation examples 1 to 2 were changed as follows to prepare the second polyamic acid:

as a polymerization process of the second polyamic acid solution, 425g of DMF as a solvent was charged under a nitrogen atmosphere into a 2L reactor. After setting the temperature to 25 ℃, 30.51g of ODA as diamine monomer was added and stirred for about 30 minutes, confirming monomer dissolution, 43.49g of s-BPDA was added in portions, small amounts were added in portions to bring the final viscosity from 5000 centipoise to 30000 centipoise. After the addition was completed, the temperature was maintained while stirring for 1 hour, so that a second amic acid solution was obtained with a final viscosity of 5500 cps.

< comparative example 8>

A polyimide film having a thickness of 7.5 μm was prepared in the same manner as in example 1, except that the second polyamic acid solution described in comparative example 7 was used, and the amounts of the first polyamic acid solution and the second polyamic acid solution were adjusted so that the polyimide film included about 88 wt% of the first polyimide chain and about 3 wt% of the second polyimide chain, respectively, based on the total weight of the polyimide film.

< comparative example 9>

A polyimide film having a thickness of 7.5 μm was prepared in the same manner as in example 1, except that the second polyamic acid solution described in comparative example 7 was used, and the amounts of the first polyamic acid solution and the second polyamic acid solution were adjusted so that the polyimide film included the first polyimide chain in an amount of about 84 wt% and the second polyimide chain in an amount of 7 wt% based on the total weight of the polyimide film.

< experimental examples: evaluation of physical Properties of polyimide film >

For the polyimide films prepared in examples 1 to 4 and comparative examples 1 to 9, respectively, alkali resistance, light transmittance, tensile strength, modulus, and crystallinity were measured in the following manner, and the results are shown in table 1.

1) Alkali resistance test

The alkali resistance index was measured by the test method (a).

2) Light transmittance test

The light transmittance was measured in the visible light region by the ASTM D1003 method using a light transmittance measuring apparatus (model: colorQuesetXE, manufacturer: hunterLab).

3) Tensile strength

Tensile strength was measured according to the method disclosed in KS 6518.

4) Modulus of elasticity

The modulus was measured using the Instron5564 model, with the method disclosed in astm d 882.

5) Degree of crystallinity

The crystallinity was measured by XRD (X-Ray Diffraction) analysis. Generally, with respect to an amorphous polymer material, a peak occupying a wide region appears, however, when a polymer chain includes a crystalline portion, a partially sharp diffraction peak and a wide region may appear at the same time. Wherein crystallinity can be measured by comparing the intensity and relative area of the two peaks.

TABLE 1

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* First polyamic acid: second polyamic acid: weight ratio of carbon black

* Second PAA = second polyamidic acid

As shown in table 1, it can be seen that examples 1 to 4 exhibited relatively high crystallinity, light transmittance of 0.09 or less, had very excellent shielding, light-shielding functions, and had excellent alkali resistance. Furthermore, examples 1 to 4 show relatively good physical properties such as tensile strength and modulus.

On the other hand, comparative example 1, which does not include the second polyimide chain, shows very poor alkali resistance and extremely low crystallinity of about 0, and thus does not show excellent performance in terms of shielding and light shielding properties even when carbon black is included because of relatively high light transmittance. From this, it is understood that the inclusion or non-inclusion of the second polyimide chain according to the present invention mainly contributes to improvement of alkali resistance and shielding and light-shielding properties.

Comparative example 2 is outside the scope of the present invention, and shows a low base resistance due to the inclusion of a small amount of the second polyimide chain.

Comparative example 3 contains an excessive amount of the second polyimide chain outside the range of the present invention, but it was confirmed that the tensile strength and modulus were remarkably decreased. From these results, it is understood that it is important to include the first polyimide chain and the second polyimide chain within the scope of the present invention.

In comparative examples 4 to 6, it can be seen that the inclusion of carbon black is preferable within the scope of the present invention in terms of achieving low light transmittance, and particularly, although comparative example 6 includes a second polyimide chain, the alkali resistance is decreased due to the inclusion of an excessive amount of carbon black.

Comparative examples 7 to 9 realized a second polyimide chain using a monomer different from the monomer disclosed in the present invention. These comparative examples are compared with examples 1 to 3, and it can be seen that the results of the examples are more excellent when the same content of the second polyimide chain is contained. Further, it can be seen that the crystallinity of comparative examples 7 to 9 is lower than that of examples, and the shielding and light shielding properties are not improved as compared with examples.

Although the foregoing has been described with reference to embodiments of the invention, various applications and modifications may be made by those skilled in the art within the scope of the present invention based on the foregoing.

Industrial applicability

The polyimide film according to the present invention includes a first polyimide chain, a second polyimide chain, and carbon black. Since the properties of each polyimide chain work complementarily and have high crystallinity and low light transmittance, such polyimide films can have desired levels of mechanical properties and alkali resistance that are difficult to be compatible with each other.

In particular, the polyimide film of the present invention has a thickness of 8 μm or less, but has excellent alkali resistance, and thus can significantly suppress the falling off of carbon black even when exposed to an alkali component.

The preparation method according to the present invention is advantageous in that it comprises a method of easily dispersing carbon black.

Specifically, in the preparation method of the present invention, the carbon black in the form of a black crude liquid is mixed with the second polyamic acid having a relatively low viscosity so as to easily initiate the preliminary dispersion of the carbon black, and then the mixed liquid is mixed with the first polyamic acid, and then the dispersed carbon black can be rapidly mixed and/or dispersed in the entire first polyamic acid together with the second polyamic acid as the second polyamic acid is easily mixed with the first polyamic acid.

Claims

1. A polyimide film, wherein,

is prepared by imidizing a precursor composition,

the precursor composition comprises:

carbon black;

wherein the first polyamic acid is imidized to form a first polyimide chain,

the second polyamic acid forms a second imide chain by imidization,

wherein the polyimide film comprises, relative to the total weight of the polyimide film: 80 to 92% by weight of first polyimide chains, 3 to 10% by weight of second polyimide chains, and 5 to 10% by weight of carbon black,

2. The polyimide film according to claim 1,

at least a part of the first polyimide chains and the second polyimide chains are cross-linked to each other by imidization.

3. The polyimide film according to claim 1,

the first polyamic acid has a viscosity of 50000 to 300000 cps measured at a temperature of 23 ℃ at a solid content of 15% by weight,

the second polyamic acid has a viscosity of 5000 to 30000 centipoise measured at a temperature of 23 ℃ at a solid content of 15 wt.%.

4. The polyimide film according to claim 1,

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

wherein the thickness of the film is 7.5 μm or less.

5. The polyimide film according to claim 4,

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

83 to 92% by weight of first polyimide chains,

5 to 7% by weight of second polyamide chains.

6. The polyimide film according to claim 1,

the first dianhydride is pyromellitic dianhydride,

the second dianhydride is 3,3',4,4' -biphenyl tetracarboxylic dianhydride and/or 2,3,3',4' -biphenyl tetracarboxylic dianhydride.

7. The polyimide film according to claim 1,

the first diamine is at least one selected from the group consisting of:

1) Diamine having one benzene ring: 1,4-diaminobenzene, 1,3-diaminobenzene, 2,4-diaminotoluene, 2,6-diaminotoluene, 3,5-diaminobenzoic acid; and

2) Diamines having two benzene rings: <xnotran> '- ,' - , '- ,' - - '- ,' - - '- ,' - ( ) - '- ,' - - '- ,' - - '- ,', '- -' - , (4- ) , '- ,' - , '- ,' - , '- ,' - , '- ,' - , '- ,' - , '- ,' - , '- ,' - , '- ,' - , '- ,' - - '- ,' - - '- ,' - , '- ,' - , - (3- ) , </xnotran> 2,2-bis (4-aminophenyl) propane, 2,2-bis (3-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 2,2-bis (4-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 3,3' -diaminodiphenyl sulfoxide, 3,4' -diaminodiphenyl sulfoxide, 4,4' -diaminodiphenyl sulfoxide.

8. The polyimide film according to claim 1,

the second diamine is 1,3-bis (4-aminophenoxy) benzene and/or 1,4-bis (3-aminophenoxy) benzene.

9. The polyimide film according to claim 1,

the light transmittance is 0.07 or less, and the alkali resistance index evaluated based on the thickness of the polyimide film before and after exposure to an alkali component is 75% or more.

10. The polyimide film according to claim 1,

the polymer has a crystallinity of 70% or more in a thin film state,

a tensile strength of 200kgf/cm ³ In the above-mentioned manner,

the modulus is 3GPa or more.

11. A production method for producing the polyimide film according to claim 1, wherein,

the method comprises the following steps:

polymerizing first polyamic acid by first dianhydride and first diamine;

the precursor composition is imidized to obtain a polyimide film.

12. The method for preparing a polyimide film according to claim 11,

the obtained polyimide film comprises the following components: after the precursor composition is film-formed on a support and dried to prepare a gel film, the gel film is imidized to form a polyimide film.

13. A coverlay comprising the polyimide film of claim 1.

14. An electronic device comprising the coverfilm of claim 13.