KR102245672B1 - Method for preparing polyimide film having improved heat resistance - Google Patents

Abstract

The present invention can provide a method for producing a polyimide with improved thermal stability in which shrinkage does not occur even at a high temperature by controlling the amount of acid dianhydride when preparing a polyimide precursor, and a polyimide film manufactured by this method Silver can suppress the occurrence of problems such as cracking of the inorganic film and lifting of the film by inducing residual stress on the substrate during the high temperature heat treatment process.

Description

Manufacturing method of polyimide with improved heat resistance {METHOD FOR PREPARING POLYIMIDE FILM HAVING IMPROVED HEAT RESISTANCE}

The present invention relates to a polyimide having improved heat resistance and a method for producing the same.

Polyimide (PI) is a polymer with relatively low crystallinity or mostly amorphous structure. It is easy to synthesize, can make a thin film, and does not require a crosslinker for curing, as well as its transparency and rigid chain structure. As a polymer material that has excellent heat resistance, chemical resistance, excellent mechanical properties, electrical properties, and dimensional stability, it is widely used in electric and electronic materials such as automobiles, aerospace, flexible circuit boards, liquid crystal alignment films for LCD, adhesives and coatings. have

However, although polyimide is a high-performance polymer material that has high thermal stability, mechanical properties, chemical resistance, and electrical properties, it does not satisfy the colorless and transparent properties, which are the basic requirements for use in the display field, and further lower the coefficient of thermal expansion. There is a task to do. For example, the coefficient of thermal expansion of Kapton sold by DuPont is about 30 ppm/℃, showing a low coefficient of thermal expansion, but this also does not meet the requirements of a plastic substrate. Therefore, many studies are currently being conducted to minimize changes in optical properties and thermal history while maintaining the basic properties of polyimide.

However, in order to be used in the display field, the need to develop polyamideimide for flexible displays having a lower coefficient of thermal expansion, high solubility, transparency, and thermal stability is continuously required.

The problem to be solved by the present invention is to provide a method for producing a polyimide with improved heat resistance.

Another problem to be solved by the present invention is to provide a polyimide film manufactured by the above manufacturing method.

Another problem to be solved by the present invention is to provide a flexible display including the polyimide film.

The present invention in order to solve the above-described technical problem,

A polyimide film having a positive coefficient of thermal expansion is provided when the first temperature is raised from 100°C to 450°C and then cooled from 450°C to 100°C.

In addition, the present invention comprises the steps of polymerizing a polyamic acid by reacting an acid dianhydride of Formula 1 and a diamine of Formula 2 under a polymerization solvent;

Preparing a polyimide precursor composition comprising the polymerized polyamic acid and an organic solvent; And

In the polyimide production method comprising the step of preparing a polyimide film by coating and curing the polyimide precursor composition on a substrate, the acid dianhydride of Formula 1 is reacted with the diamine of Formula 2 in the same amount or in excess It provides a method for producing a polyimide.

[Formula 1]

[Formula 2]

In order to solve another problem of the present invention, a flexible display including the polyimide film is provided.

The present invention can provide a method for producing a polyimide with improved thermal stability in which shrinkage does not occur even at a high temperature by controlling the amount of acid dianhydride when preparing a polyimide precursor, and a polyimide film manufactured by this method Silver can suppress the occurrence of problems such as cracking of the inorganic film and lifting of the film by inducing residual stress on the substrate during the high temperature heat treatment process.

1 is a graph showing the dimensional change according to the temperature change in the first cooling process.
2 is a graph showing the dimensional change according to the temperature change in the second heating process after the first cooling process.

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

In the present specification, all compounds or functional groups may be substituted or unsubstituted unless otherwise specified. Here, the term'substituted' means that at least one hydrogen contained in the compound or functional 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, and a hydroxy group. , It 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.

In addition, unless otherwise specified, the term'combination of these' in the present specification is a single bond, a double bond, a triple bond, an alkylene group having 1 to 10 carbon atoms (e.g., a methylene group (-CH ₂ -), Ethylene group (-CH ₂ CH ₂ -), etc.), a fluoroalkylene group having 1 to 10 carbon atoms (e.g., a fluoromethylene group (-CF ₂ -), a perfluoroethylene group (-CF ₂ CF ₂₎ -), etc.), a hetero atom such as N, O, P, S, or Si, or a functional group containing the same (e.g., an intramolecular carbonyl group (-C=O-), an ether group (-O-), an ester group) (-COO-), -S-, -NH- or a heteroalkylene group including -N=N-, etc.), or two or more functional groups are condensed or linked.

The demand of the flexible display is increasing because of its light and thin characteristics and non-breakable characteristics due to its free structure. In implementing such a flexible display, a polyimide composed of 3,3',4,4'-Biphenyltetracarboxylic dianhydride (BPDA)-PDA (phenylen diamine) having excellent heat resistance has been mainly used.

In general, when the polyimide for a substrate is polymerized, a ratio of diamine as a monomer and diamine among the dianhydrides has been used in an excessive amount. However, polyimide is advantageous in terms of viscosity and molecular weight stability for various defects such as cracking of inorganic film and film lifting by inducing residual stress on the substrate polymerized with an excessive amount of diamine. However, polyimide substrates with an excessive amount of diamine are CTE at high temperatures. It shows the behavior of shrinking, and has a problem that can occur in a high-temperature heat treatment process.

Accordingly, in order to solve the above problems, the present invention is to provide a method of manufacturing a polyimide in which shrinkage does not occur even in a high temperature process.

In order to solve the above problems, the present invention,

A polyimide film having a positive coefficient of thermal expansion is provided when the first temperature is raised from 100°C to 450°C and then cooled from 450°C to 100°C.

The film may have a positive coefficient of thermal expansion when cooled from 400°C to 350°C.

In addition, the film may have a positive coefficient of thermal expansion at 350°C to 450°C when the cooled polyimide film is heated from 100°C to 520°C for the second time.

In addition, the film may have a difference between the coefficient of thermal expansion measured at the time of cooling after the first heating and the coefficient of thermal expansion measured at the time of the second heating from 100°C to 520°C within ±5.0 ppm/°C.

In addition, the film may have a coefficient of thermal expansion of 1 to 10 ppm/°C at 100°C to 300°C when the first temperature is raised.

In addition, the film may have a thermal expansion coefficient of 0.5 to 8 ppm/°C when cooling from 450°C to 100°C after the first heating.

In addition, the film may have a thermal expansion coefficient of 1 to 13 ppm/°C when the second temperature is raised from 100°C to 520°C.

The present invention further comprises the steps of polymerizing a polyamic acid by reacting an acid dianhydride of Formula 1 and a diamine of Formula 2 under a polymerization solvent;

Preparing a polyimide precursor composition comprising the polymerized polyamic acid and an organic solvent; And

In the polyimide production method comprising the step of preparing a polyimide film by coating and curing the polyimide precursor composition on a substrate, the acid dianhydride of Formula 1 is reacted with the diamine of Formula 2 in the same amount or in excess It provides a method for producing a polyimide.

[Formula 1]

[Formula 2]

The present invention provides a polyimide prepared by reacting an acid dianhydride of Formula 1 with a diamine of Formula 2 in the conventional method for producing a flexible polyimide.

In general, efforts have been made to improve the physical properties of the polyimide film, focusing on the stability of the viscosity and molecular weight of the polyimide precursor solution by reacting an excessive amount of diamine in the process of manufacturing the polyimide. In the case of the resulting polyimide, there is a problem that thermal stability such as a coefficient of thermal expansion may occur. Accordingly, the present invention is a polyimide film that has a positive coefficient of thermal expansion even at a high process temperature by adding an excessive amount of acid dianhydride to provide a polyimide having improved thermal stability and improved mechanical properties, that is, a polyimide film that does not cause shrinkage. Can provide.

In the present invention, by adjusting the mixing ratio of the acid dianhydride of Formula 1 and the diamine of Formula 2, the contraction reaction at high temperature can be controlled. More specifically, the present invention is to react an acid dianhydride in the same amount or excess with diamine so that the true thermal expansion coefficient is 0 or more in a temperature range of 350° C. or higher, that is, above the glass transition temperature of the prepared polyimide. It provides a method for producing a polyimide.

In this case, the true coefficient of thermal expansion is the slope value of the curve corresponding to each temperature in the temperature-sample length relationship curve measured using TMA (Thermomechanical Analyzer) to measure the size change due to the expansion and contraction of the sample. Can be defined as

Thermal expansion due to temperature can be quantified by changes in the length of the specimen. Therefore, the coefficient of thermal expansion (CTE) of the sample is defined as the rate of change in the length of the sample according to the temperature change. However, since the degree of thermal expansion of materials used in a wide temperature range may vary depending on temperature, it is sometimes necessary to define a strict thermal expansion coefficient in consideration of measurement conditions.

The coefficient of thermal expansion can be largely divided into two types: the average coefficient of thermal expansion defined in the measurement temperature range (T=T ₂ -T _{1) and the true coefficient of thermal expansion defined at a specific temperature.} Equation 1 is the definition of the average coefficient of thermal expansion. The length change (L) of the specimen in the measurement temperature range (T) is divided _{by the temperature difference (T 2} -T _{1 ).} Therefore, it can be viewed as the average of the deformation of the specimen between the two temperatures. In the present specification, the coefficient of thermal expansion shall refer to the average coefficient of thermal expansion unless otherwise specified.

[Equation 1]

On the other hand, as in Equation 2, the thermal expansion coefficient of a specific temperature rather than the range of temperature is also defined, which is called the true thermal expansion coefficient. The true coefficient of thermal expansion is the thermal expansion at a specific temperature divided by the initial length of the specimen. It can be simply thought of as the differential value of thermal expansion according to temperature.

[Equation 2]

The true coefficient of thermal expansion can be used to examine how the coefficient of thermal expansion of a specimen changes over a wide temperature range.

In the present invention, by adjusting the true coefficient of thermal expansion at a high temperature, specifically, at a temperature of 350° C. or higher to have a positive value of zero or more, the average coefficient of thermal expansion can also be adjusted to have a positive value. Provides.

According to an embodiment, the acid dianhydride of Formula 1 and the diamine of Formula 2 may be adjusted within a molar ratio of 1:1 to 1:0.95, and preferably, 1:0.99 to 1:0.95, or 1: 0.99 To 1: 0.96, or 1:0.99 to 1:0.97, more preferably, it can be reacted in a molar ratio of 1:0.99 to 1:0.98, without causing shrinkage of the specimen at high temperature in the above range, polyimide Other mechanical properties of, for example, cracks and physical properties such as adhesion to the substrate can be maintained. For example, the true coefficient of thermal expansion of the polyimide prepared by the above blending ratio may have a true coefficient of thermal expansion of 350°C or higher, preferably in a temperature range of 350°C to 400°C, that is, the slope of the curve may have a positive value of zero or more. , When the diamine is included in an excessive amount, the true thermal expansion coefficient has a negative value, that is, has a negative slope, so that the specimen may decrease as the temperature increases.

In the present invention, by adjusting the true coefficient of thermal expansion to have a positive value of zero or more, the average coefficient of thermal expansion over the entire temperature range can also be adjusted to have a positive value. The average coefficient of thermal expansion may have a value of 0 to 20 ppm/℃, preferably 0 to 15 ppm/℃, more preferably 0 to 12 ppm/℃, and the diamine of Formula 2 is the formula When it is less than the content of the acid dihydrate of 1, the average coefficient of thermal expansion may have a value of 0 to 5 ppm/°C.

According to one embodiment, even when the acid dianhydride reacts with the diamine at the same mixing ratio, the true coefficient of thermal expansion has a positive value, but according to a more preferred embodiment, it is prepared by reacting in excess compared to the polyimide reacted at the same molar ratio. In the case of polyimide, compared to polyimide prepared with a 1:1 blending ratio, the absolute value may exhibit a lower true coefficient of thermal expansion over the entire temperature range, and even at a temperature range of 350°C or higher, the absolute value may exhibit a lower true coefficient of thermal expansion. .

In addition, in the polyimide according to the present invention, the coefficient of thermal expansion differs between the thermal expansion change occurring in the cooling process after the first heating process and the degree of change when measuring the thermal expansion due to the secondary heating after the cooling process. In general, the degree of change can be large when measuring the thermal expansion caused by an increase in temperature. For example, in the range of 450°C to 100°C, the thermal expansion change due to the cooling process has an average coefficient of thermal expansion of 0 to 10 ppm/°C, preferably 0.5 to 8 ppm/°C, more preferably 1 to It may represent a value of 6 ppm/°C, and when measuring the change in thermal expansion due to heating in the range of 100°C to 520°C in the secondary heating step after the cooling step, the average coefficient of thermal expansion is 0 to 20 ppm/°C. , Preferably 0 to 15 ppm/°C, more preferably 1 to 13 ppm/°C, and may be measured somewhat higher than the coefficient of thermal expansion of the cooling process.

In addition, according to a more preferred example, the present invention may exhibit a lower average coefficient of thermal expansion than when the acid dianhydride is added in an excessive amount compared to the mixing ratio of 1:1. For example, the acid dianhydride and diamine are 1:0.99 to 1 In the case of a polyimide prepared by reacting at a mixing ratio of 1: 0.98, the average coefficient of thermal expansion is 0 to 10 ppm/°C, preferably 0 to 6 ppm/°C, more preferably 0 to 3 ppm/ It may have a value of °C, and the difference in the average coefficient of thermal expansion is within ±10.0 ppm/℃, preferably within ±5.0 ppm/℃, and more preferably within ±2.0 during the second heating process after the cooling process. It may appear as an error range within ppm/°C, which can prove that the reaction of the acid dianhydride in a somewhat excessive amount compared to the diamine may be more stable in the thermal stability of the polyimide.

In the polyimide manufacturing method, in addition to the acid dianhydride of Formula 1 and the diamine of Formula 2, a polyimide polymerized with an acid dianhydride of Formula 3 and a diamine of Formula 4 may be copolymerized or blended and used as needed.

However, in the case of copolymerization, it may be blended and used within a range that does not deviate from the blending ratio, and the acid dianhydride of Formula 1 is 80 molar ratio or more, preferably 90 molar ratio or more, more preferably based on 100 mol of the total content of the acid dianhydride added. Preferably, it should be included in an amount of 95 molar or more, and the diamine of Formula 2 should be included in an amount of 80 molar or more, preferably 90 molar ratio or more, more preferably 95 molar ratio or more, based on 100 mol of the total amount of diamine added. .

[Formula 3]

[Formula 4]

According to the present invention, X may be a tetravalent organic group including an aliphatic ring having 3 to 24 carbon atoms or an aromatic ring having 6 to 30 carbon atoms. rigid), that is, a single ring structure, a structure in which each ring is bonded by a single bond, or a tetravalent organic group including a heterocyclic structure in which each ring is directly linked, for example, the following formula 3a A tetravalent organic group of 3k to 3k may be mentioned, but the present invention is not limited thereto.

At least one hydrogen atom in the tetravalent functional group of Formulas 3a to 3k is an alkyl group having 1 to 10 carbon atoms (e.g., methyl group, ethyl group, propyl group, isopropyl group, t-butyl group, pentyl group, hexyl group, etc.), A fluoroalkyl group having 1 to 10 carbon atoms (e.g., a fluoromethyl group, a perfluoroethyl group, a trifluoromethyl group, etc.), an aryl group having 6 to 12 carbon atoms (e.g., a phenyl group, a 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, preferably a fluoroalkyl group having 1 to 10 carbon atoms.

The Y is each independently a divalent organic group of an aliphatic, alicyclic or aromatic having 6 to 30 carbon atoms having 4 to 30 carbon atoms, or as a combination group thereof, an aliphatic, alicyclic or aromatic divalent organic group is directly connected, or Or it is derived from a diamine containing a structure selected from divalent organic groups connected to each other through a crosslinked structure. For example, the Y may be a monocyclic or polycyclic aromatic having 6 to 30 carbon atoms, a monocyclic or polycyclic alicyclic having 6 to 30 carbon atoms, or a structure in which two or more of these are linked by a single bond, and more specifically , The Y may be an aromatic ring or an aliphatic structure to form 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 is directly linked It may be a divalent organic group including a heterocyclic structure, for example, a divalent organic group represented by the following Formulas 4a to 4k, but is not limited thereto.

At least one hydrogen atom in the divalent functional group of Formulas 4a to 4k is an alkyl group having 1 to 10 carbon atoms (e.g., methyl group, ethyl group, propyl group, isopropyl group, t-butyl group, pentyl group, hexyl group, etc.), A fluoroalkyl group having 1 to 10 carbon atoms (e.g., a fluoromethyl group, a perfluoroethyl group, a trifluoromethyl group, etc.), an aryl group having 6 to 12 carbon atoms (e.g., a phenyl group, a 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, preferably a fluoroalkyl group having 1 to 10 carbon atoms.

As the content of the monomer having an organic group having a rigid structure such as Formulas 3a to 3k or 4a to 4k increases, the heat resistance at high temperature of the polyimide film may increase, and when used with an organic group having a flexible structure It is possible to prepare a polyimide film having improved heat resistance as well as transparency.

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.

The reaction may be carried out under anhydrous conditions, and the polymerization reaction may be carried out at a temperature of -75 to 50°C, preferably 0 to 40°C. It is carried out by adding an acid dianhydride while the diamine-based compound is dissolved in an organic solvent. Among them, the diamine-based compound and the acid dianhydride-based compound are contained in an amount of about 10 to 30% by weight in the polymerization solvent. The molecular weight is adjusted according to the polymerization time and reaction temperature.

In addition, as an organic solvent that can be used in the polymerization reaction, specifically, γ-butyrolactone, 1,3-dimethyl-imidazolidinone, methyl ethyl ketone, cyclohexanone, cyclopentanone, 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 (cellosolve) such as dipropylene glycol diethyl ether and triethylene glycol monoethyl ether; 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 Acetamide (DMAc), N,N-diethylacetamide, dimethylformamide (DMF), diethylformamide (DEF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP) , N-ethylpyrrolidone (NEP), N-vinylpyrrolidone 1,3-dimethyl-2-imidazolidinone, N,N-dimethylmethoxyacetamide, dimethylsulfoxide, pyridine, dimethylsulfone, hexa Methylphosphoamide, tetramethylurea, N-methylcarrolactam, tetrahydrofuran, m-dioxane, P-dioxane, 1,2-dimethoxyethane, bis(2-methoxyethyl) ether, 1, What is selected from the group consisting of 2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)] ether, and mixtures thereof may be used.

More preferably, sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide, formamide solvents such as N,N-dimethylformamide and N,N-diethylformamide, and N,N-dimethylacetamide , N,N-diethylacetamide, and other acetamide solvents, and N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, and other pyrrolidone solvents may be used alone or as a mixture. However, the present invention is not limited thereto, and an aromatic hydrocarbon such as xylene and toluene may be further used, and in order to promote dissolution of the polymer, an alkali metal salt or alkaline earth metal salt of about 50% by weight or less based on the total amount of the solvent may be further added to the solvent. It can also be added.

In the case of synthesizing the polyamic acid or polyimide of the present invention, in order to inactivate an excess polyamino group or acid anhydride group, the molecular end is reacted with a dicarboxylic acid anhydride or a monoamine to further seal the end of the polyimide. Can be added.

A method of manufacturing a polyimide film using the prepared polyimide precursor composition includes applying the polyimide precursor composition to one surface of a substrate and separating from the substrate after imidization and curing processes.

Specifically, the polyimide precursor composition prepared according to the above manufacturing method may be in the form of a solution in which a polyimide precursor is dissolved in the organic solvent, and in the case of having such a form, for example, a polyimide precursor is synthesized in an organic solvent. In one case, the polyimide precursor composition may be obtained by adding the polyimide precursor solution itself or the same solution obtained after polymerization, or may be obtained by diluting the polyimide precursor solution obtained after polymerization with another solvent.

The polyimide precursor composition preferably contains a solid content in an amount such that it has an appropriate viscosity in consideration of fairness such as coatability during the film formation process, and the solid content is 5 to 20% by weight based on the total weight of the polyimide precursor composition. Can be included as. Alternatively, it may be desirable to control the polyimide precursor composition to have a viscosity of 400 to 50,000 cP. The viscosity of the polyimide precursor composition may be less than 400 cP, and if the viscosity of the polyimide precursor composition exceeds 50,000 cP, the fluidity is lowered during the manufacture of a display substrate using the polyimide precursor composition, so that it is not evenly applied during coating, etc. It may cause a problem in the manufacturing process of.

Next, the polyimide precursor composition prepared above may be applied to one surface of a substrate, thermally imidized and cured at a temperature of 80°C to 400°C, and then separated from the substrate to prepare a polyimide film.

At this time, as the substrate, a glass, metal substrate, or plastic substrate may be used without particular limitation. Among these, it has excellent thermal and chemical stability during the imidization and curing process for the polyimide precursor, and curing without a separate release agent treatment. A glass substrate that can be easily separated without damage to the polyimide-based film formed after may be desirable.

In addition, the coating process may be performed according to a conventional coating method, and 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, Spray method, dipping method, brushing method, etc. may be used. Among these, a continuous process is possible, and it may be more preferable to perform a casting method capable of increasing the imidation rate of the polyimide-based resin.

In addition, the polyimide-based solution may be applied on the substrate in a thickness range such that the finally produced polyimide-based film has a suitable thickness for a display substrate.

Specifically, it may be applied in an amount such that it has a thickness of 10 to 30 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 performed according to a conventional method, and specifically, may be performed at a temperature of 140°C or less, or 80°C to 140°C. When the drying process is performed at a temperature of less than 80°C, the drying process is prolonged, and when it exceeds 140°C, imidization proceeds rapidly, making it difficult to form a polyimide-based film having a uniform thickness.

Subsequently, the curing process may be performed by heat treatment at a temperature of 80°C to 400°C. The curing process may be performed by multi-stage heat treatment at various temperatures within the above-described temperature range. In addition, the curing time during the curing process is not particularly limited, and may be performed for 3 to 30 minutes as an example.

In addition, after the curing process, a subsequent heat treatment process may be optionally further performed in order to increase the imidation rate of the polyimide-based resin in the polyimide-based film to form a polyimide-based film having the above-described physical properties.

The subsequent heat treatment process is preferably performed at 200° C. or higher, or 200° C. to 450° C. for 1 minute to 30 minutes. In addition, the subsequent heat treatment process may be performed once or may be performed in multiple stages at least two times. Specifically, it may be carried out in three stages including a first heat treatment at 200 to 220°C, a second heat treatment at 300 to 380°C, and a third heat treatment at 400 to 450°C.

Thereafter, a polyimide-based film may be manufactured by peeling the polyimide-based film formed on the substrate from the substrate according to a conventional method.

The polyimide according to the present invention may have a glass transition temperature of about 360°C or higher. Since it has such excellent heat resistance, the film including the polyimide can maintain excellent heat resistance and mechanical properties even against high temperature heat added during the device manufacturing process.

In addition, the polyimide film can be used as a display substrate, and the occurrence of warpage and deterioration in reliability such as lifting of the coating can be suppressed during the process of manufacturing a device on the display substrate, and as a result, improved characteristics and reliability It is possible to manufacture a device having Accordingly, the polyimide may be particularly usefully used in the manufacture of flexible substrates in electronic devices such as OLED or LCD, electronic paper, and solar cells.

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

<Example 1> BPDA-pPDA (1:1) polyimide polymerization

Dissolve 1 mol of biphenyl dianhydride (BPDA) in 2 kg of dimethylacetamide (DMAc), add 1 mol of para-phenylenediamine (p-PDA), and add 1 kg of dimethylacetamide (DMAc) to polymerize at 25°C for 24 hours. The prepared polyimide precursor solution was prepared.

The prepared polyimide precursor composition was spin-coated on a glass substrate. The glass substrate coated with the polyimide precursor composition was placed in an oven and heated at a rate of 4°C/min, and cured by holding at 120°C for 30 minutes, 200°C for 30 minutes, 350°C for 30 minutes, and 450°C for 60 minutes. The process proceeded. After completion of the curing process, the film formed on the glass substrate was removed to prepare a film.

<Example 2> BPDA-pPDA (1:0.988) polyimide polymerization

Dissolve 1 mol of biphenyl dianhydride (BPDA) in 2 kg of N-methylpyrrolidone (NMP), add 0.988 mol of para-phenylenediamine (p-PDA), and put it in 1 kg of NMP for 24 hours at 25°C. A polyimide precursor solution prepared by polymerization was prepared. The prepared polyimide precursor composition was spin-coated on a glass substrate. The glass substrate coated with the polyimide precursor composition was placed in an oven and heated at a rate of 4°C/min, and cured by holding at 120°C for 30 minutes, 200°C for 30 minutes, 350°C for 30 minutes, and 450°C for 60 minutes. The process proceeded. After completion of the curing process, the film formed on the glass substrate was removed to prepare a film.

<Comparative Example 1> BPDA-pPDA (0.988:1) polyimide polymerization

Dissolve 0.988 mol of biphenyl dianhydride (BPDA) in 2 kg of N-methylpyrrolidone (NMP), add 1 mol of para-phenylenediamine (p-PDA) to 1 kg of NMP, and polymerize at 25°C for 24 hours. The prepared polyimide precursor solution was prepared. The prepared polyimide precursor composition was spin-coated on a glass substrate. The glass substrate coated with the polyimide precursor composition was placed in an oven and heated at a rate of 4°C/min, and cured by holding at 120°C for 30 minutes, 200°C for 30 minutes, 350°C for 30 minutes, and 450°C for 60 minutes. The process proceeded. After completion of the curing process, the film formed on the glass substrate was removed to prepare a film.

<Experimental Example 1> Measurement of thermal expansion change due to cooling

For each of the polyimide-based films prepared in Examples 1 and 2 and Comparative Example 1, a film was prepared in a size of 5 x 20 mm, and then a sample was loaded using an accessory. The length of the film actually measured was the same as 16 mm. Set the film pulling force to 0.02N and proceed with the first heating process at a temperature increase rate of 4°C/min in the temperature range of 100°C to 450°C, and then cool the film at 4°C/min in the temperature range of 450°C to 100°C. The change pattern of thermal expansion when cooled at a rate was measured by TMA (Q400 manufactured by TA).

In the first heating process, the coefficient of thermal expansion in the temperature range of 100° C. to 300° C. was measured as 6 ppm/° C. and 4 ppm/° C. in Examples 1 and 2, respectively.

The dimensional change of the sample according to the temperature change due to the cooling is shown in FIG. 1, and the average coefficient of thermal expansion measured in the temperature range is shown in Table 1 below.

<Experimental Example 2> Measurement of thermal expansion change in the temperature raising process

Each sample cooled in Experimental Example 1 was heated at a heating rate of 5°C/min at 100°C to 520°C, and the change in thermal expansion of the sample was measured by TMA. The dimensional change pattern of the sample according to the temperature change due to the heating is shown in FIG. 2, and the average coefficient of thermal expansion measured in the temperature range is shown in Table 1 below.

division Coefficient of thermal expansion (ppm/℃) Cooling 450℃ ~ 100℃ Heating 100℃~520℃ Example 1 5.8 11.0 Example 2 2.3 2.4 Comparative Example 1 -0.4 -2.9

From the above results, it can be seen that Examples 1 and 2 in which the acid dianhydride was reacted in the same amount or in excess of the diamine showed a generally positive slope in the temperature range of 350° C. or higher in FIGS. It means that the true coefficient of thermal expansion, which means the slope, has a positive value of zero or more. In addition, in Examples 1 and 2, since the true coefficient of thermal expansion having a positive value in the temperature range is indicated, the average coefficient of thermal expansion corresponding to the measured temperature range may indicate a positive value. On the other hand, in the case of polyimide reacted in excess of diamine, the slope of the curve has a negative value in the temperature range of 350°C or higher, which indicates that the true thermal expansion coefficient is negative, that is, the shrinkage of the sample occurs in the temperature range. This can mean, and due to this, the average coefficient of thermal expansion over the entire measurement temperature range exhibits a negative value, and it can be seen from the result values in Table 1 that this aspect may be more pronounced in the heating process after cooling. On the other hand, in Examples 1 and 2, especially Example 2, it can be seen that the difference in the coefficient of thermal expansion is relatively small during the heating process after cooling, which can be an index indicating the excellent heat resistance of the polyimide according to the present invention. .

As described above, a specific part of the present invention has been described in detail, and for those of ordinary skill in the art, it is obvious that this specific technique is only a preferred embodiment, and the scope of the present invention is not limited thereby. something to do. Therefore, it will be said that the practical scope of the present invention is defined by the appended claims and their equivalents.

Claims (8)

Polymerizing polyamic acid by reacting the acid dianhydride of Formula 1 and the diamine of Formula 2 in a molar ratio of 1:0.99 to 1:0.95 under a polymerization solvent;
Preparing a polyimide precursor composition comprising the polymerized polyamic acid and a solvent; And
In the method for producing a polyimide comprising the step of preparing a polyimide film by coating the polyimide precursor composition on a substrate and curing at a maximum curing temperature of 450°C,
The curing includes performing a first heat treatment at 200°C to 220°C, a second heat treatment at 300°C to 380°C, and a third heat treatment at 400°C to 450°C at a heating rate of 4°C/min,
The polyimide film has a positive coefficient of thermal expansion when cooling from 100°C to 450°C at a heating rate of 4°C/min and then cooling from 450°C to 100°C at a cooling rate of 4°C/min. C. Polyimide film manufacturing method:
[Formula 1]

[Formula 2]

.
The method of claim 1,
A method for producing a polyimide film for controlling the thermal expansion coefficient of the resulting polyimide film by controlling the content of the acid dianhydride of Formula 1 and the diamine of Formula 2 in a molar ratio of 1:0.99 to 1:0.98. The method of claim 1,
A method for producing a polyimide film in which the organic solvent included in the polyimide precursor composition is a pyrrolidone-based solvent. The method of claim 1,
The polyimide film is a method of producing a polyimide film having a positive coefficient of thermal expansion when cooled from 400°C to 350°C. The method of claim 1,
The polyimide film is a method of producing a polyimide film having a positive coefficient of thermal expansion at 350°C to 450°C when the cooled polyimide film is heated from 100°C to 520°C for the second time. The method of claim 1,
The polyimide film has a positive coefficient of thermal expansion at 350°C to 450°C when the polyimide film cooled after the first heating is heated from 100°C to 520°C when the second temperature is raised, and the coefficient of thermal expansion measured when cooling after the first heating is 100 A method of producing a polyimide film in which the difference in coefficient of thermal expansion measured at the second temperature increase from ℃ to 520 ℃ is within ±5.0 ppm/℃ The method of claim 1,
The polyimide film is a method of manufacturing a polyimide film having a coefficient of thermal expansion of 1 to 10 ppm/°C at 100°C to 300°C when the first temperature is raised. The method of claim 1,
The polyimide film has a positive coefficient of thermal expansion at 350°C to 450°C when the cooled polyimide film is heated from 100°C to 520°C when the second temperature is raised, while the thermal expansion coefficient at the second temperature increase from 100°C to 520°C. A method for producing a polyimide film of 1 to 13 ppm/°C.

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