KR102276094B1 - An evaluating method for electrical surface charge density of polymer film, polyimide film with improved surface charge density and flexible device using same - Google Patents

Abstract

The present invention provides a method for more accurately evaluating the surface insulation properties of a polymer film, and also provides a polyimide film having a saturation electrification voltage of 1.25 kV and a half-life exceeding 116 seconds as a flexible substrate using the method By doing so, it is possible to provide a flexible device with improved surface insulation properties.

Description

A method for evaluating the surface charge density of a polymer film, a polyimide film with improved surface charge density, and a flexible device using the same

The present invention relates to a method for evaluating the surface charge density of a polymer film, and to a polyimide film having improved surface charge density characteristics, in particular, to a polyimide film for flexible substrates having improved surface charge accumulation and outflow characteristics.

Recently, in the display field, weight reduction and miniaturization of products are becoming important, and in the case of the currently used glass substrate, it is heavy, brittle, and has limitations in that continuous processing is difficult. Therefore, a plastic substrate having the advantage of being light, flexible, and continuous processing is possible by replacing the glass substrate. Research is being actively conducted to apply it to mobile phones, notebook computers, and PDA's.

In particular, polyimide (PI) resin is easy to synthesize, can make a thin film, and has the advantage of being applicable to high-temperature processes. Recently, due to the light weight and precision of electronic products, it is used as an integrated material in semiconductor materials such as LCD and PDP. It is widely applied, and many studies are being conducted to use PI for a flexible display board having light and flexible properties.

A polyimide (PI) film is produced by filming the polyimide resin. In general, the polyimide resin is obtained by solution polymerization of an aromatic dianhydride and an aromatic diamine to prepare a polyamic acid derivative solution, which is then used on a silicon wafer or glass. It is manufactured by coating on the back and curing by heat treatment.

The problem to be solved by the present invention is to provide a new method for evaluating the surface insulating properties of a polymer film.

Another object to be solved by the present invention is to provide a polyimide film having improved surface charge accumulation and outflow properties.

Another problem to be solved by the present invention is to provide a flexible device using the polyimide film as a substrate.

The problem to be solved by the present invention is to provide a new method for evaluating the surface insulating properties of a polymer film.

Another object to be solved by the present invention is to provide a polyimide film having improved surface charge accumulation and outflow properties.

Another problem to be solved by the present invention is to provide a flexible device using the polyimide film as a substrate.

The present invention measures the saturation electrification voltage and half-life of polyimide by a charge-discharge method using corona discharge to confirm the surface charge accumulation and leakage characteristics, and the measured saturation-charge voltage exceeds 1.25 kV, and the half-life time By providing the polyimide film exceeding 116 seconds as a flexible substrate, it is possible to provide a flexible device with improved charge accumulation and outflow characteristics due to an electric field generated during driving of the TFT element.

1 is a view showing the charging discharge measurement principle according to the present invention.
2 is a diagram illustrating the charging and discharging characteristics due to corona discharge according to the difference in the surface resistance of the film.
3 is a graph showing the change in saturation charging voltage and the half-life of polyimide films of Examples and Comparative Examples with time.
4 is a schematic diagram of charge alignment by an electric potential by device driving and a diagram explaining the TFT characteristic variation as an electric field.

Since the present invention can apply various transformations and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing the present invention, if it is determined that a detailed description of a related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted.

All compounds or organic groups in the present specification may be substituted or unsubstituted unless otherwise specified. Here, 'substituted' means that at least one hydrogen contained in the compound or organic group is a halogen atom, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group, a cycloalkyl group having 3 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, or a hydroxyl group. , means substituted with a substituent selected from the group consisting of an alkoxy group having 1 to 10 carbon atoms, a carboxylic acid group, an aldehyde group, an epoxy group, a cyano group, a nitro group, an amino group, a sulfonic acid group, and derivatives thereof.

Currently, in the display industry, a display device is manufactured using a plastic substrate instead of a glass substrate in order to reduce the weight and thickness of the substrate. In particular, a display device in which an OLED element is grafted onto a plastic substrate has an advantage that it can be bent or folded.

However, in making a flexible display device using such a plastic, problems such as a restored afterimage that did not occur when using a glass substrate are suggested. In addition, in the case of a glass substrate, it not only has high heat resistance and thermal conductivity compared to a plastic substrate, but also has high electrical insulation.

Electrical insulation of polymer materials, which are plastic substrate materials, is due to the molecular structure of the polymer material, the complexity of the solid composition, and the presence of impurities to be mixed during manufacturing, resulting in surface charge accumulation due to the formation of carriers in the polymer, and low surface charge accumulation. Due to the phenomenon, an image sticking may be caused by the characteristic change of the TFT device due to the electric field of the device.

Therefore, in order to use a plastic material such as polyimide as a substrate material for a flexible display, research and development for improving the surface charge accumulation and leakage characteristics of the material is required.

In order to solve this conventional problem, the present invention can evaluate the surface charge characteristics of a polymer film with improved surface charge characteristics due to an electric field generated in driving a TFT device as a flexible display substrate material replacing a glass substrate. to provide a new way to

The present invention has developed a method capable of more clearly and precisely evaluating the accumulation and leakage of surface charges of a polymer film, and through this, it is an object to provide a polyimide film with improved surface charge accumulation and leakage characteristics.

In the case of a polymer substrate material, due to the molecular structure of the polymer material and the presence of impurities mixed in during manufacture, a surface charge accumulation phenomenon occurs due to the formation of a carrier in the polymer and an applied electric field. The leakage current may be generated and affect the electrical characteristics of the TFT device. The present invention minimizes the effect of such leakage current by increasing the surface charge density due to surface charge accumulation, thereby enabling stable driving of the TFT device.

According to the present invention, a method for evaluating surface charge accumulation and leakage characteristics,

a) applying a predetermined DC voltage in the form of corona discharge to the surface of a polymer film to be evaluated for surface charge accumulation, thereby accumulating a static charge and detecting a voltage value due to the static charge;

b) obtaining a voltage value when the detected voltage value reaches a saturation value and does not change any more as a saturation voltage value and stopping the application of the corona discharge;

c) obtaining a half-life by continuously detecting the potential value of the film in which the corona discharge application is stopped, and measuring the time at which the detected potential value with respect to the saturation voltage becomes 50%; and

d) determining the surface properties of the polymer film based on whether the measured saturation voltage and half-life are equal to or greater than a predetermined value.

According to the present invention, it is possible to measure the electrostatic properties of the sample by using the characteristics that the saturation electrification voltage and the half-life increase as the electrical insulation of the polymer film increases.

In this case, the half-life means the time at which the saturation voltage becomes 1/2 of the saturation voltage after the power is cut off, and this can be used as an index indicating the static attenuation characteristics of the sample. For example, the static damping characteristic may be defined as being slower as the saturation charging voltage is larger and the half-life time is longer, and a material having a slow static damping characteristic may exhibit higher surface insulation properties.

In general, the insulating properties of the polyimide film can be expressed as a surface resistance value measured by a high resistance meter. However, the surface resistance value of the film measured by such a high-resistance meter is 10 ¹⁴ Ω, and there is almost no difference in most polyimide substrates even with a difference in the polymer structure, so it is difficult to distinguish or an error range may appear very large.

The present invention measures the charge accumulation and outflow characteristics on the surface of a polyimide film by means of a charging and discharging method by corona discharge, thereby measuring the surface insulation characteristics between polyimide films, which were difficult to discriminate with conventional high-resistance measuring instruments. can be more precisely classified, and by using this, it is possible to provide a polyimide film more suitable for a substrate for a flexible display.

According to the present invention, the measurement of the saturation voltage and the half-life time can be measured using a charge-discharge measuring instrument. According to an embodiment, the DC voltage during charging by the corona discharge may be 5 to 20 kV, for example, by applying a DC voltage of 8 to 15 kv or 8 to 12 kV or about 10 kV, corona discharge may be generated.

When a DC voltage is applied to the polyimide film in the form of corona discharge, as shown in FIG. 1 , the detected voltage value reaches a saturation value where there is no further change at a specific voltage. At this time, the voltage is cut off. This saturation voltage is called "saturation versus voltage". After the voltage is cut off, the potential attenuation state of the film is continuously detected. In this case, a time point at which the detected potential becomes 1/2 of the saturation versus voltage is defined as a "half-life".

The longer the half-life, the slower the attenuation of the static charge accumulated in the polyimide film during charging, which may mean that the polyimide film has high insulating properties.

2 is a diagram showing the principle of the charging discharge method by corona discharge according to the present invention. Referring to the figure of FIG. 2 , in the case of a polyimide film having a high saturation charging voltage, the static charge accumulation increases during charging, so that the static charge attenuation after charging is delayed, and thus the half-life is increased.

On the other hand, in the case of a polyimide film having a low resistance surface, the static charge is attenuated during charging, and thus the static charge is rapidly attenuated after charging, thereby reducing the half-life.

Therefore, according to the present invention, by confirming the electrostatic characteristics using the electrostatic discharge characteristics, the insulating characteristics of the film can be measured more clearly, and a polyimide film with high insulating properties can be manufactured using this.

The polyimide film according to the present invention may have a thickness of 5 to 20 μm, and the saturation charging voltage measured by the above-described method may exceed 1.25 kV, and the half-life time may exceed the dissolution time. According to a preferred embodiment, the saturation versus voltage may be 1.3 kV or more and the half-life time may be 120 seconds or more.

The polyimide film according to the present invention can be prepared from a polyimide precursor containing at least one diamine and at least one tetracarboxylic dianhydride as polymerization components.

According to an embodiment, the polyimide precursor may include a repeating structure of Formula 1 formed by reacting BPDA (biphenyl dianhydride) as tetracarboxylic dianhydride and PDA (phenylenediamine) as diamine. and, preferably, 80 to 100 mol% of the repeating structure of Formula 1 may be included in the total polyimide precursor.

[Formula 1]

According to an embodiment, the polyimide film may further include an end-blocking agent or an additive for surface charge accumulation.

Examples of the endcapsulant include maleic anhydride, and may be added in an amount of 1 to 10 moles, preferably 1 to 5 moles, based on 100 moles of the total diamine.

In addition, the additive may be a diisocyanate-based additive, for example, may be selected from Methylenediphenyl 4.4'-Diisocyanate and 1,4-Phenylene Diisocyanate.

According to one embodiment, the polyimide precursor composition may include a diisocyanate-based additive in an amount of 0.3 to 4 wt%, preferably 0.5 to 2 wt%, based on the total weight of the polyimide precursor composition.

The polyimide film according to the present invention can increase the surface charge density through the cross-linked structure.

According to an embodiment, when a polyimide film is prepared by adding a maleic anhydride endcapper such as maleic anhydride, crosslinks may be formed between polyimide molecules as shown in Scheme 1 below, which It is possible to increase the surface charge density.

[Scheme 1]

According to another embodiment, the polyimide precursor composition may further include an additive including a diisocyanate structure, and the diisocyanate structure is cross-linked between polyimide molecules as shown in Scheme 2 below. By forming , it can increase the surface charge density of the polyimide film.

[Scheme 2]

According to one embodiment, an additive including a diisocyanate structure is further added together with Scheme 1, which is a case of manufacturing a polyimide film by adding a maleic anhydride endcapper such as maleic anhydride. By performing the reaction of Scheme 2 together, the polyimide intermolecular crosslinks according to Schemes 1 and 2 can be mixed to form, which can more effectively increase the surface charge accumulation of the polyimide.

According to an embodiment, in the preparation of the polyimide precursor, at least one tetracarboxylic dianhydride may be further included together with BPDA.

For example, as the tetracarboxylic dianhydride, an intramolecular aromatic, cycloaliphatic, or aliphatic tetravalent organic group, or a combination group thereof, in which aliphatic, alicyclic or aromatic structures are connected to each other through a crosslinked structure. A tetracarboxylic dianhydride containing an organic group may be used. Preferably, it may include an acid dianhydride having a monocyclic or polycyclic aromatic, monocyclic or polycyclic alicyclic, or a structure in which two or more of these are linked by a single bond or a functional group. Or, a tetracarboxylic acid containing a tetravalent organic group having a rigid structure such as a single or fused heterocyclic ring structure, or a structure connected by a single bond, in which a ring structure such as aromatic or alicyclic is single or fused. may contain dianhydrides.

For example, the tetracarboxylic dianhydride may include a tetravalent organic group having a structure represented by the following Chemical Formulas 2a to 2e:

[Formula 2a]

[Formula 2b]

[Formula 2c]

[Formula 2d]

[Formula 2e]

In Formulas 2a to 2e, R ₁₁ to R ₁₇ are each independently a halogen atom selected from -F, -Cl, -Br and -I, a hydroxyl group (-OH), a thiol group (-SH), and nitro group (-NO ₂ ), a cyano group, an alkyl group having 1 to 10 carbon atoms, halogenoalkoxy having 1 to 4 carbon atoms, halogenoalkyl having 1 to 10 carbon atoms, and an aryl group having 6 to 20 carbon atoms.

a1 is an integer from 0 to 2, a2 is an integer from 0 to 4, a3 is an integer from 0 to 8, a4 and a5 are each independently an integer from 0 to 3, a6 and a9 are each independently an integer from 0 to 3 , and a7 and a8 may each independently be an integer of 0 to 7,

A11 and A12 are each independently a single bond, -O-, -CR ₁₈ R ₁₉ -, -C(=O)-, -C(=O)NH-, -S-, -SO ₂ -, phenylene group and combinations thereof, wherein R ₁₈ and R ₁₉ are each independently selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, and a fluoroalkyl group having 1 to 10 carbon atoms. can

Alternatively, the tetracarboxylic dianhydride may include a tetravalent organic group selected from the group consisting of the following Chemical Formulas 3a to 3n.

At least one hydrogen atom in the tetravalent organic group of Formulas 3a to 3n is a halogen atom selected from -F, -Cl, -Br and -I, a hydroxyl group (-OH), a thiol group (-SH), a nitro group ( -NO ₂ ), a cyano group, an alkyl group having 1 to 10 carbon atoms, halogenoalkoxy having 1 to 4 carbon atoms, halogenoalkyl having 1 to 10 carbon atoms, and an aryl group having 6 to 20 carbon atoms. For example, the halogen atom may be fluoro (-F), and the halogenoalkyl group is a fluoroalkyl group having 1 to 10 carbon atoms including a fluoro atom, and is a fluoromethyl group, perfluoroethyl group, trifluoro It may be selected from a romethyl group, etc., and the alkyl group may be selected from a methyl group, an ethyl group, a propyl group, an isopropyl group, a t-butyl group, a pentyl group, and a hexyl group, and the aryl group may be selected from a phenyl group and a naphthalenyl group. and, more preferably, a substituent including a fluoro atom such as a fluoro atom and a fluoroalkyl group.

Alternatively, the tetracarboxylic dianhydride has an aromatic ring or an aliphatic structure in which each ring structure is rigid, that is, a single ring structure, a structure in which each ring is bonded by a single bond, or each ring is It may include a tetravalent organic group including a directly connected heterocyclic structure, for example, may include a tetravalent organic group selected from the following Chemical Formulas 4a to 4k.

At least one hydrogen atom in the tetravalent organic group of Formulas 4a to 4k is an alkyl group having 1 to 10 carbon atoms (eg, a methyl group, an ethyl group, a propyl group, an isopropyl group, a t-butyl group, a pentyl group, a hexyl group, etc.); A fluoroalkyl group having 1 to 10 carbon atoms (eg, fluoromethyl group, perfluoroethyl group, trifluoromethyl group, etc.), an aryl group having 6 to 12 carbon atoms (eg, phenyl group, naphthalenyl group, etc.); It may be substituted with a substituent selected from the group consisting of a sulfonic acid group and a carboxylic acid group, and may preferably be substituted with a fluoroalkyl group having 1 to 10 carbon atoms.

According to one embodiment, in the preparation of the polyimide precursor, one or more diamines may be further included together with the PDA.

As the diamine, a monocyclic or polycyclic aromatic divalent organic group having 6 to 24 carbon atoms, a monocyclic or polycyclic alicyclic divalent organic group having 6 to 18 carbon atoms, or a structure in which two or more of these are linked by a single bond or a functional group may contain a diamine containing a divalent organic group structure selected from a divalent organic group comprising a, or a heterocyclic ring structure in which a ring structure compound such as an aromatic or alicyclic compound is singly or fused; Or it may be one selected from a divalent organic group having a rigid structure such as a structure connected by a single bond.

For example, the diamine may include a divalent organic group selected from the following Chemical Formulas 5a to 5e.

[Formula 5a]

[Formula 5b]

[Formula 5c]

[Formula 5d]

[Formula 5e]

In Formulas 5a to 5e,

R ₂₁ to R ₂₇ are each independently a halogen atom selected from -F, -Cl, -Br and -I, a hydroxyl group (-OH), a thiol group (-SH), a nitro group (-NO ₂ ), cya It may be selected from the group consisting of a no group, an alkyl group having 1 to 10 carbon atoms, halogenoalkoxy having 1 to 4 carbon atoms, halogenoalkyl having 1 to 10 carbon atoms, and an aryl group having 6 to 20 carbon atoms,

In addition, A21 and A22 are each independently a single bond, -O-, -CR'R"- (in this case, R' and R" are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms (eg, a methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, tert-butyl group, pentyl group, etc.) and a haloalkyl group having 1 to 10 carbon atoms (eg, trifluoromethyl group, etc.) , -C(=O)-, -C(=O)O-, -C(=O)NH-, -S-, -SO-, -SO2-, -O[CH2CH2O]y-(y is 1 to 44), -NH(C=O)NH-, -NH(C=O)O-, monocyclic or polycyclic cycloalkylene group having 6 to 18 carbon atoms (eg, cyclohexylene group, etc.) ), a monocyclic or polycyclic arylene group having 6 to 18 carbon atoms (eg, a phenylene group, a naphthalene group, a fluorenylene group, etc.), and combinations thereof,

b1 is an integer from 0 to 4, b2 is an integer from 0 to 6, b3 is an integer from 0 to 3, b4 and b5 are each independently an integer from 0 to 4, b7 and b8 are each independently from 0 to an integer of 9, and b6 and b9 are each independently an integer of 0 to 3.

Alternatively, the diamine may include a divalent organic group selected from the group consisting of the following Chemical Formulas 6a to 6p.

At least one hydrogen atom in the divalent organic group of Formulas 6a to 6p is a halogen atom selected from -F, -Cl, -Br and -I, a hydroxyl group (-OH), a thiol group (-SH), a nitro group ( -NO2), a cyano group, an alkyl group having 1 to 10 carbon atoms, halogenoalkoxy having 1 to 4 carbon atoms, halogenoalkyl having 1 to 10 carbon atoms, and an aryl group having 6 to 20 carbon atoms. For example, the halogen atom may be fluoro (-F), and the halogenoalkyl group is a fluoroalkyl group having 1 to 10 carbon atoms including a fluoro atom, and is a fluoromethyl group, perfluoroethyl group, trifluoro It may be selected from a methyl group, and the alkyl group may be selected from a methyl group, an ethyl group, a propyl group, an isopropyl group, a t-butyl group, a pentyl group, and a hexyl group, and the aryl group may be selected from a phenyl group and a naphthalenyl group. may be one, and more preferably a substituent including a fluoro atom such as a fluoro atom and a fluoroalkyl group.

Alternatively, the diamine may include a divalent organic group in which an aromatic ring or an aliphatic structure forms a rigid chain structure, for example, a single ring structure, a structure in which each ring is bonded by a single bond, or Each ring may include a divalent organic group structure including a directly fused heterocyclic ring structure, for example, one including a divalent organic group structure selected from the following Chemical Formulas 7a to 7k However, the present invention is not limited thereto.

At least one hydrogen atom in the divalent organic group of Formulas 7a to 7k is an alkyl group having 1 to 10 carbon atoms (eg, a methyl group, an ethyl group, a propyl group, an isopropyl group, a t-butyl group, a pentyl group, a hexyl group, etc.); A fluoroalkyl group having 1 to 10 carbon atoms (eg, fluoromethyl group, perfluoroethyl group, trifluoromethyl group, etc.), an aryl group having 6 to 12 carbon atoms (eg, phenyl group, naphthalenyl group, etc.); It may be substituted with a substituent selected from the group consisting of a sulfonic acid group and a carboxylic acid group, and may preferably be substituted with a fluoroalkyl group having 1 to 10 carbon atoms.

As the content of the monomer having an organic group having a rigid structure as in Chemical Formulas 4a to 4k or 7a to 7k increases, the heat resistance at high temperature of the polyimide film may increase, and when used with an organic group having a flexible structure A polyimide film with improved heat resistance as well as transparency can be prepared.

The polymerization reaction of the acid dianhydride and the diamine-based compound may be carried out according to a conventional polymerization method of polyimide or a precursor thereof, such as solution polymerization.

Examples of the organic solvent that can be used in the polymerization of the polyamic acid include gamma-butyrolactone, 1,3-dimethyl-2-imidazolidinone, methyl ethyl ketone, cyclohexanone, cyclopentanone, and 4-hydroxy-4 ketones such as -methyl-2-pentanone; aromatic hydrocarbons such as toluene, xylene, and tetramethylbenzene; Ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether , glycol ethers such as dipropylene glycol diethyl ether and triethylene glycol monoethyl ether (Cellosolve); Ethyl acetate, butyl acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, dipropylene glycol monomethyl ether acetate, ethanol, propanol, ethylene glycol, propylene glycol, carbitol, dimethyl Propionamide (dimethylpropionamide, DMPA), diethylpropionamide (DEPA), dimethylacetamide (DMAc), N,N-diethylacetamide, dimethylformamide (DMF), diethylformamide (DEF), N -Methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), N,N-dimethylmethoxyacetamide, dimethylsulfoxide, pyridine, dimethylsulfone, hexamethylphosphoramide, tetramethylurea, N- Methylcaprolactam, tetrahydrofuran, m-dioxane, P-dioxane, 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane , bis[2-(2-methoxyethoxy)]ether, Equamide M100, Equamide B100, and the like, may be used alone or a mixture of two or more thereof.

Preferably, sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide; formamide solvents such as N,N-dimethylformamide and N,N-diethylformamide; N,N-dimethylacetamide; Acetamide solvents such as N,N-diethylacetamide, and pyrrolidone solvents such as N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and N-vinyl-2-pyrrolidone may be used alone or as a mixture, but is not limited thereto.

In addition, aromatic hydrocarbons such as xylene and toluene may be further used, and in order to promote dissolution of the polymer, about 50 wt% or less of an alkali metal salt or alkaline earth metal salt may be further added to the solvent based on the total amount of the solvent.

In addition, in the case of synthesizing polyamic acid or polyimide, in order to inactivate excess polyamino groups or acid anhydride groups, a terminal blocker for sealing the ends of the polyimide by reacting the molecular ends with dicarboxylic acid anhydrides or monoamines is further added can do.

The method of reacting the tetracarboxylic dianhydride with diamine may be carried out according to a conventional polyimide precursor polymerization method such as solution polymerization. Specifically, it can be prepared by dissolving diamine in an organic solvent, and then adding tetracarboxylic dianhydride to the resulting mixed solution for polymerization.

The polymerization reaction may be carried out under an inert gas or nitrogen stream, and may be carried out under anhydrous conditions.

In addition, the reaction temperature during the polymerization reaction may be carried out at -20 to 80 ℃, preferably 0 to 80 ℃. When the reaction temperature is too high, the reactivity may increase and the molecular weight may increase, and the viscosity of the precursor composition may increase, which may be disadvantageous in terms of the process.

It is preferable to include the solid content in the polyamic acid solution prepared according to the above-described manufacturing method in an amount such that the composition has an appropriate viscosity in consideration of fairness such as applicability during the film forming process.

The polyimide precursor composition containing the polyamic acid may be in the form of a solution dissolved in an organic solvent, and in the case of having such a form, for example, when the polyimide precursor is synthesized in an organic solvent, the solution is the obtained reaction solution that It may be itself, or what diluted this reaction solution with another solvent may be sufficient. Moreover, when a polyimide precursor is obtained as solid powder, what was made to melt|dissolve this in an organic solvent and was made into a solution may be sufficient.

According to one embodiment, the content of the composition may be adjusted by adding an organic solvent so that the total content of the polyimide precursor is 8 to 25 wt%, preferably 10 to 25 wt%, more preferably 10 to 20 wt% % or less.

Alternatively, the polyimide precursor composition may be adjusted to have a viscosity of 1,500 cP or more, and the viscosity of the polyimide precursor composition is 10,000 cP or less, preferably 4,000 cP or less, more preferably 2,000 cP or less. It is desirable to control When the viscosity of the polyimide precursor composition exceeds 10,000 cP, the efficiency of defoaming during processing of the polyimide film is lowered, so that not only the efficiency in the process but also the surface roughness of the prepared film is poor due to the generation of bubbles, resulting in electrical, optical, and mechanical properties. may be lowered.

Then, a polyimide film can be prepared by imidizing the polyimide precursor obtained as a result of the polymerization reaction.

According to an embodiment, applying the polyimide film composition on a substrate; and

A polyimide film may be manufactured through the step of heat-treating the applied polyimide film composition.

At this time, as the substrate, glass, metal substrate, or plastic substrate, etc. may be used without any particular limitation. Among them, the polyimide precursor has excellent thermal and chemical stability during imidization and curing processes, and is cured without a separate release agent treatment. A glass substrate that can be easily separated without damage to the polyimide-based film formed afterward may be desirable.

In addition, the coating process may be carried out according to a conventional coating method, specifically, a spin coating method, a bar coating method, a roll coating method, an air-knife method, a gravure method, a reverse roll method, a kiss roll method, a doctor blade method, A spray method, a dipping method, or a brushing method may be used. Among them, a continuous process is possible, and it may be more preferable to be carried out by a casting method that can increase the imidization rate of polyimide.

In addition, the polyimide precursor composition may be applied on the substrate in a thickness range such that the finally manufactured polyimide film has a thickness suitable for a display substrate.

Specifically, it may be applied in an amount such that it has a thickness of 5 to 20 μm or 6 to 16 μm. After the polyimide precursor composition is applied, a drying process for removing the solvent present in the polyimide precursor composition may be optionally further performed prior to the curing process.

The drying process may be carried out according to a conventional method, and specifically may be carried out at a temperature of 140 °C or less, or 80 °C to 140 °C. If the temperature at which the drying process is performed is less than 80° C., the drying process is lengthened, and if it exceeds 140° C., imidization proceeds rapidly, making it difficult to form a polyimide film having a uniform thickness.

Then, the polyimide precursor composition applied to the substrate is heat-treated in an IR oven, a hot air oven or a hot plate, at this time, the heat treatment temperature may be in the range of 300 to 500 ℃, preferably 320 to 480 ℃, the temperature Within the range, it may proceed as a single-step or multi-step heat treatment. The heat treatment process may be carried out for 20 minutes to 70 minutes, preferably for about 20 minutes to 60 minutes.

The polyimide film according to the present invention provides a polyimide film having a saturated charging voltage of more than 1.25 kV and a half-life exceeding 116 seconds, measured using a charging and discharging method using corona discharge, thereby significantly improving insulation properties. A flexible substrate may be provided.

The polyimide film according to the present invention may be particularly usefully used in the manufacture of flexible devices in electronic devices such as OLED or LCD, electronic paper, and solar cells, and in particular, may be usefully used as a substrate of the flexible device.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

<Comparative Example 1> Polyimide polymerization of BPDA-pPDA (98:100)

After filling 100 g of organic solvent NMP (N-methyl-2-pyrrolidone) in a stirrer through which a nitrogen stream flows, p-PDA (para-phenylenediamine) 6.873 g (63.560 mmol) while maintaining the reactor temperature at 25 ° C. was dissolved. 18.327 g (62.289 mmol) of s-BPDA (3,3',4,4'-biphenylcarboxylic acid dianhydride) and 54.8 g of NMP were added to the p-PDA solution at the same temperature and stirred while dissolving for a certain period of time. A polyimide precursor was prepared.

The polyimide precursor solution was prepared by adding the organic solvent to the polyimide precursor prepared from the reaction so that the solid content concentration was 14.0 wt%.

<Example 1> Polyimide polymerization of BPDA-pPDA/MA (98:100:4)

After filling 100 g of organic solvent NMP (N-methyl-2-pyrrolidone) in a stirrer through which a nitrogen stream flows, p-PDA (para-phenylenediamine) 6.806 g (61.679 mmol) while maintaining the reactor temperature at 25 ° C. was dissolved. 18.147 g (61.679 mmol) of s-BPDA (3,3',4,4'-biphenylcarboxylic acid dianhydride) and 54.8 g of NMP were added to the p-PDA solution at the same temperature and stirred while dissolving for a certain period of time. Polyamic acid was polymerized. Thereafter, 0.247 g (2.517 mmol) of MA (maleic anhydride) was added to the polyamic acid solution and stirred for 4 hours to prepare a polyimide precursor.

A polyimide precursor solution was prepared by adding the organic solvent so that the solid content concentration of the polyimide precursor prepared from the above reaction was 14.0 wt%.

<Example 2> Polyimide polymerization of BPDA-pPDA/MA (98:100:2)

After filling 100 g of organic solvent NMP (N-methyl-2-pyrrolidone) in a stirrer through which a nitrogen stream flows, and maintaining the reactor temperature at 25 ° C., p-PDA (para-phenylenediamine) 6.840 g (61.982 mmol) was dissolved. 18.236 g (61.982 mmol) of s-BPDA (3,3',4,4'-biphenylcarboxylic acid dianhydride) and 54.8 g of NMP were added to the p-PDA solution at the same temperature and stirred while dissolving for a certain period of time. Polyamic acid was polymerized. Then, 0.124 g (1.265 mmol) of MA (maleic anhydride) was added to the polyamic acid solution and stirred for 4 hours to prepare a polyimide precursor.

A polyimide precursor solution was prepared by adding the organic solvent so that the solid content concentration of the polyimide precursor prepared from the above reaction was 14.0 wt%.

<Example 3> Polyimide polymerization of BPDA-pPDA (98:100)/0.5 wt% Methylenediphenyl 4,4'-Diisocyanate crosslinking additive

After filling 100 g of organic solvent NMP (N-methyl-2-pyrrolidone) in a stirrer through which a nitrogen stream flows, p-PDA (para-phenylenediamine) 6.873 g (63.560 mmol) while maintaining the reactor temperature at 25 ° C. was dissolved. 18.327 g (62.289 mmol) of s-BPDA (3,3',4,4'-biphenylcarboxylic acid dianhydride) and 54.8 g of NMP were added to the p-PDA solution at the same temperature and stirred while dissolving for a certain period of time. A polyimide precursor was prepared.

After adding the organic solvent so that the solid content concentration of the polyimide precursor prepared from the reaction is 14.0 wt%, 0.126 g (0.5 wt%) of a Methylenediphenyl 4,4'-Diisocyanate crosslinking additive was added to the polyimide precursor solution 8 A final polyimide precursor solution was prepared by stirring for a period of time.

<Example 4> Polyimide polymerization of BPDA-pPDA (98:100)/1.0 wt% Methylenediphenyl 4,4'-Diisocyanate crosslinking additive

After filling 100 g of organic solvent NMP (N-methyl-2-pyrrolidone) in a stirrer through which a nitrogen stream flows, p-PDA (para-phenylenediamine) 6.873 g (63.560 mmol) while maintaining the reactor temperature at 25 ° C. was dissolved. 18.327 g (62.289 mmol) of s-BPDA (3,3',4,4'-biphenylcarboxylic acid dianhydride) and 54.8 g of NMP were added to the p-PDA solution at the same temperature and stirred while dissolving for a certain period of time. A polyimide precursor was prepared.

After adding the organic solvent so that the solid content concentration of the polyimide precursor prepared from the reaction is 14.0 wt%, 0.254 g (1.0 wt%) of a Methylenediphenyl 4,4'-Diisocyanate crosslinking additive was added to the polyimide precursor solution 8 A final polyimide precursor solution was prepared by stirring for a period of time.

<Example 5> Polyimide polymerization of BPDA-pPDA (98:100)/2 wt% Methylenediphenyl 4,4'-Diisocyanate crosslinking additive

After filling 100 g of organic solvent NMP (N-methyl-2-pyrrolidone) in a stirrer through which a nitrogen stream flows, p-PDA (para-phenylenediamine) 6.873 g (63.560 mmol) while maintaining the reactor temperature at 25 ° C. was dissolved. 18.327 g (62.289 mmol) of s-BPDA (3,3',4,4'-biphenylcarboxylic acid dianhydride) and 54.8 g of NMP were added to the p-PDA solution at the same temperature and stirred while dissolving for a certain period of time. A polyimide precursor was prepared.

After adding the organic solvent so that the solid content concentration of the polyimide precursor prepared from the reaction is 14.0 wt%, 0.514 g (2 wt%) of a Methylenediphenyl 4,4'-Diisocyanate crosslinking additive was added to the polyimide precursor solution 8 A final polyimide precursor solution was prepared by stirring for a period of time.

<Example 6> BPDA-pPDA(98:100)/0.5 wt% 1,4-Phenylene Diisocyanate Crosslinking additive Polyimide polymerization

After filling 100 g of organic solvent NMP (N-methyl-2-pyrrolidone) in a stirrer through which a nitrogen stream flows, p-PDA (para-phenylenediamine) 6.873 g (63.560 mmol) while maintaining the reactor temperature at 25 ° C. was dissolved. 18.327 g (62.289 mmol) of s-BPDA (3,3',4,4'-biphenylcarboxylic acid dianhydride) and 54.8 g of NMP were added to the p-PDA solution at the same temperature and stirred while dissolving for a certain period of time. A polyimide precursor was prepared.

After adding the organic solvent so that the solid content concentration of the polyimide precursor prepared from the above reaction becomes 14.0 wt %, 0.126 g (0.5 wt %) of 1,4-Phenylene Diisocyanate crosslinking additive was added to the polyimide precursor solution for 8 hours. A final polyimide precursor solution was prepared by stirring for a while.

<Example 7> BPDA-pPDA (98:100)/1.0 wt% 1,4-Phenylene Diisocyanate Crosslinking additive Polyimide polymerization

After filling 100 g of organic solvent NMP (N-methyl-2-pyrrolidone) in a stirrer through which a nitrogen stream flows, p-PDA (para-phenylenediamine) 6.873 g (63.560 mmol) while maintaining the reactor temperature at 25 ° C. was dissolved. 18.327 g (62.289 mmol) of s-BPDA (3,3',4,4'-biphenylcarboxylic acid dianhydride) and 54.8 g of NMP were added to the p-PDA solution at the same temperature and stirred while dissolving for a certain period of time. A polyimide precursor was prepared.

After adding the organic solvent so that the solid content concentration of the polyimide precursor prepared from the above reaction is 14.0 wt%, 0.254 g (1.0 wt%) of 1,4-Phenylene Diisocyanate crosslinking additive was added to the polyimide precursor solution for 8 hours A final polyimide precursor solution was prepared by stirring for a while.

<Example 8> BPDA-pPDA(98:100)/2 wt% 1,4-Phenylene Diisocyanate Crosslinking additive Polyimide polymerization

After filling 100 g of organic solvent NMP (N-methyl-2-pyrrolidone) in a stirrer through which a nitrogen stream flows, p-PDA (para-phenylenediamine) 6.873 g (63.560 mmol) while maintaining the reactor temperature at 25 ° C. was dissolved. 18.327 g (62.289 mmol) of s-BPDA (3,3',4,4'-biphenylcarboxylic acid dianhydride) and 54.8 g of NMP were added to the p-PDA solution at the same temperature and stirred while dissolving for a certain period of time. A polyimide precursor was prepared.

After adding the organic solvent so that the solid content concentration of the polyimide precursor prepared from the above reaction becomes 14.0 wt%, 0.514 g (2 wt%) of a 1,4-Phenylene Diisocyanate crosslinking additive was added to the polyimide precursor solution for 8 hours A final polyimide precursor solution was prepared by stirring for a while.

<Example 9> Polyimide polymerization of BPDA-pPDA/MA (98:100:4)/2 wt% Methylenediphenyl 4,4'-Diisocyanate crosslinking additive

After filling 100 g of organic solvent NMP (N-methyl-2-pyrrolidone) in a stirrer through which a nitrogen stream flows, p-PDA (para-phenylenediamine) 6.806 g (61.679 mmol) while maintaining the reactor temperature at 25 ° C. was dissolved. 18.147 g (61.679 mmol) of s-BPDA (3,3',4,4'-biphenylcarboxylic acid dianhydride) and 54.8 g of NMP were added to the p-PDA solution at the same temperature and stirred while dissolving for a certain period of time. Polyamic acid was polymerized. Thereafter, 0.247 g (2.517 mmol) of MA (maleic anhydride) was added to the polyamic acid solution and stirred for 4 hours to prepare a polyimide precursor.

After adding the organic solvent so that the solid content concentration of the polyimide precursor prepared from the reaction is 14.0 wt%, 0.514 g (2 wt%) of a Methylenediphenyl 4,4'-Diisocyanate crosslinking additive was added to the polyimide precursor solution 8 A final polyimide precursor solution was prepared by stirring for a period of time.

<Example 10> BPDA-pPDA/MA (98:100:4)/2 wt% 1,4-Phenylene Diisocyanate Crosslinking additive Polyimide polymerization

After filling 100 g of organic solvent NMP (N-methyl-2-pyrrolidone) in a stirrer through which a nitrogen stream flows, p-PDA (para-phenylenediamine) 6.806 g (61.679 mmol) while maintaining the reactor temperature at 25 ° C. was dissolved. 18.147 g (61.679 mmol) of s-BPDA (3,3',4,4'-biphenylcarboxylic acid dianhydride) and 54.8 g of NMP were added to the p-PDA solution at the same temperature and stirred while dissolving for a certain period of time. Polyamic acid was polymerized. Thereafter, 0.247 g (2.517 mmol) of MA (maleic anhydride) was added to the polyamic acid solution and stirred for 4 hours to prepare a polyimide precursor.

After adding the organic solvent so that the solid content concentration of the polyimide precursor prepared from the above reaction becomes 14.0 wt%, 0.514 g (2 wt%) of a 1,4-Phenylene Diisocyanate crosslinking additive was added to the polyimide precursor solution for 8 hours A final polyimide precursor solution was prepared by stirring for a while.

<Experimental Example 1> Measurement of saturation versus voltage and half-life

The polyimide precursor solutions prepared in Examples 1 to 10 and Comparative Example 1 were spin-coated on a glass substrate. The glass substrate coated with the polyimide precursor solution was placed in an oven and heated at a rate of 6° C./min, and the curing process was performed by maintaining at 120° C. for 10 minutes and at 460° C. for 55 minutes. After completion of the curing process, the glass substrate was soaked in water to remove the film formed on the glass substrate and dried in an oven at 100° C. to prepare a polyimide film having a thickness of 6 μm.

For the saturation voltage and half-life measurements, the H-0110 Honestmeter of SHISHIDO ELECTROSTATIC was used in accordance with the JIS L 1094 standard measurement method at a measurement temperature of 25°C and a humidity of 40-50%.

The applied voltage to each of the prepared polyimide films was 10 kV, the distance from the tip of the precipitation electrode of the applying unit to the surface of the rotating disk was 20 mm, and the distance from the electrode plate of the power receiving unit to the surface of the rotating disk was adjusted to 15 mm. The applied voltage of 10 kV was started while rotating the rotating disc, and the application was finished after 100 seconds, and the time until the charged voltage was reduced to half while rotating the rotating disc in that state was measured. The half-life was obtained by measuring the time from when the high voltage was cut off when the value of the potential decreased by 50% of the value of the saturation versus voltage. The measured saturation voltage and half-life are shown in Table 1 below.

Sample thickness
(μm) applied voltage
(kV) saturation voltage
(kV) Half-life voltage arrival time (sec) Thermal properties Td_1%
(℃) Comparative Example 1
BPDA-PDA 6 10 1.25 116 571 Example 1 6 10 1.48 170 570 Example 2 6 10 1.38 165 571 Example 3 6 10 1.30 125 571 Example 4 6 10 1.42 146 570 Example 5 6 10 1.50 173 570 Example 6 6 10 1.31 127 571 Example 7 6 10 1.46 150 571 Example 8 6 10 1.55 182 570 Example 9 6 10 1.59 194 570 Example 10 6 10 1.63 199 570

In Table 1, it can be seen that the saturation versus voltage of Example is larger than that of Comparative Example 1, and the time to reach the half-life voltage is also long. From this, it can be seen that the polyimide film according to the present invention has a larger surface charge accumulation and less charge leakage than the polyimide film of Comparative Example 1.

In addition, the polyimide film of the embodiment according to the present invention uses a terminal blocker such as MA or a crosslinking additive such as Methylenediphenyl 4,4'-Diisocyanate and 1,4-Phenylene Diisocyanate in the BPDA-pPDA backbone, despite the use of surface charge It can be seen that not only the accumulation and leakage characteristics are excellent, but also the heat resistance hardly deteriorates. That is, the present invention can provide a polyimide film with significantly improved charge accumulation and outflow characteristics on the polyimide surface through a polymer structure design that forms a cross-linked structure, as well as a thermal decomposition temperature (Td_1%) at a temperature of 570°C or higher , it is possible to provide a stable and robust polyimide film even in a low temperature polysilicone (LTPS) process of 450° C. or higher for manufacturing a TFT device.

Accordingly, the present invention can provide a polyimide film having a high saturation voltage value and a long half-life, and by using the polyimide film for a flexible substrate, a flexible display device having improved surface insulation properties can be provided.

As described above in detail a specific part of the content of the present invention, for those of ordinary skill in the art, it is clear that this specific description is only a preferred embodiment, and the scope of the present invention is not limited thereby. something to do. Accordingly, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (14)

a) detecting a voltage value due to static charge while accumulating static charge by applying a predetermined DC voltage in the form of corona discharge to the surface of a polymer film to be evaluated for surface charge accumulation and leakage characteristics;
b) obtaining a voltage value when the detected voltage value reaches a saturation value and does not change any more as a saturation voltage value and stopping the application of the corona discharge;
c) obtaining a half-life by continuously detecting the potential value of the film in which the corona discharge application is stopped, and measuring the time at which the detected potential value with respect to the saturation voltage becomes 50%; and
d) the saturation charging voltage measured by the method for evaluating electrical insulation of a polymer film, comprising the step of determining the surface charge accumulation and leakage characteristics of the polymer film based on whether the measured saturation charging voltage and the half-life are equal to or greater than a predetermined value is 1.38 A polyimide film having a kV or more and a half-life of 146 seconds or more,
It is prepared from a polyamic acid containing a repeating structure of Formula 1,
[Formula 1]

The polyamic acid is prepared from a polyimide precursor composition including an acid dianhydride and a diamine, and the polyimide precursor composition contains maleic anhydride in a molar ratio of 2 to 10 with respect to 100 moles of total diamine or a diisocyanate-based additive as a polyimide precursor. A polyimide film comprising 1 to 2% by weight based on the total weight of the composition. According to claim 1,
The DC voltage applied for the corona discharge is 5kV to 10kV, the polyimide film. delete delete delete According to claim 1,
The polyimide film is a polyimide film having a thickness of 5 to 20 μm. delete delete delete According to claim 1,
The diisocyanate-based additive is a polyimide film selected from Methylenediphenyl 4.4'-Diisocyanate and 1,4-Phenylene Diisocyanate. delete delete delete A flexible device comprising the polyimide film according to any one of claims 1, 2, 6 and 10 as a substrate.

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