KR20150108812A - Polyamic acid solution - Google Patents

Abstract

The present invention relates to a polyamic acid solution and a display device and, more specifically, to a polyamic acid solution which can be used for a base layer or a protective layer of a display device, and to a display device including a film formed by the imidization of the polyamic acid solution. The polyamic acid solution has excellent thermal properties such as a low rate of thermal expansion and a high pyrolysis temperature, and can thus be applied to a base layer or a protective layer of the display device.

Description

Polyamic acid solution < RTI ID = 0.0 >

The present invention relates to a polyamic acid solution and a method for producing the same, and more particularly, to a polyamic acid solution which can be used as a substrate layer or a protective layer of various display devices.

Digital convergence, which is a convergence or combination of computer, communication, and information appliances, is rapidly proceeding, as it is entering the ubiquitous era where information can be accessed anytime and anywhere. Accordingly, the importance of a display serving as an interface between an electronic information device and a human is increasing. In addition, demands for high brightness and high definition image information are becoming stronger while having a high resolution, and a large-size liquid crystal display, a plasma display, and an organic light emitting diode (OLED) have.

In recent years, a flexible display that can be bent or bent into one of the next generation displays for the purpose of carrying is attracting attention. In order to enable such a bending or bending type display, a substrate of a new material having flexibility in place of the existing glass substrate is required.

The currently developed flexible display type is developed in the same way as LCD, OLED, EPD based on passive or active type driving device. These are driven by a passive or active driving device on a flexible polymer substrate to drive the display, and more and more attention is being paid to the active type of pixel implementation rather than passive type. Particularly, the active flexible display forms a unit element of a display by structuring a gate, an insulating film, a source and a drain on a polymer material substrate and finally attaching an electrode and a display element. However, most of the manufacturing processes are performed at a high temperature in order to manufacture the above-mentioned active type display device. Therefore, if a polymer substrate material having no heat resistance is used, the dimensions of the polymer material substrate tends to be deformed, Alignment of the pattern is not matched, or the surface characteristics of the polymer substrate are changed, which poses a problem in use as a display substrate.

Therefore, various high heat-resistant plastic materials for flexible displays have been developed. Representative heat-resistant plastic materials include polyethylene naphthalate (PEN), polyether sulfone (PES) polycarbonate (PC) Also, since the glass transition temperature (Tg) is less than 300 ° C and the coefficient of thermal expansion (Tg) is 20 to 60 ppm / ° C, the dimensional stability is not good at 300 ° C or higher. There is a possibility of adversely affecting display quality (John Scheirs and Timothy E. Long, Modern Polyesters: Chemistry and Technology of Polyesters and Copolyesters, 2004); And Sumilite 占 FS-1300, Sumitomo Bakelite Catalog).

In addition, when the plastic film of the above material is used, there is no supporting force. Therefore, a display device should be manufactured by adhering on a metal foil or a glass plate. In this case, the adhesion between the plastic film and the metal foil or the glass plate is further adhered There is a drawback in that the smoothness of the adhesion may not be satisfactory.

In consideration of this point, Applicant has filed a patent application for a polyamic acid solution which has a low thermal expansion coefficient and is excellent in stiffness and elastic modulus and can be applied as a substrate layer or a protective layer of a display device (Korean Patent Laid-Open Publication No. 10-2010-0080301 number). However, the thermal expansion rate is not sufficiently low and the dimensional stability at a high temperature is not satisfied.

Disclosed is a polymer material for a flexible display which is excellent in dimensional stability even at a high temperature of 500 ° C or higher. The polymer material can be used for a substrate layer or a protective layer of a display device having excellent heat resistance and a low thermal expansion coefficient.

In addition, the polyamic acid to be provided in the present invention is provided in the form of a liquid, and if it is provided in the form of a film, there is no supporting force for maintaining the shape of the film itself. Therefore, a display device should be manufactured by adhering on a metal foil or a glass plate. There is a disadvantage in that the polymer film and the metal foil or the glass plate are further adhered to and peeled from each other, and if the adhesion is not smooth, there is a problem in smoothness. The current display device fabrication process is a high temperature process with a process temperature of 450 ° C. However, when the adhesive is bonded to the metal foil or the glass plate, the adhesive does not exist at the high temperature, so that the above method is not suitable for the actual process.

Accordingly, the polyamic acid to be provided in the present invention may be provided in liquid form rather than in the form of a film, and may be applied to a pretreated ceramic support or a glass plate (or any other support, of course) and dried to form an imidized film This is to facilitate the process for maintaining the shape and manufacturing the display device on the pretreated ceramic support or a glass plate or the like (although it may be any other support, of course).

The present invention also provides a manufacturing method for commercialization of a plastic material having a high thermal decomposition temperature and a low thermal expansion rate.

The manufacturing method for commercialization refers to a manufacturing method in a scale applicable to an actual display device manufacturing process, not a production on a laboratory scale. In the present invention, a scale of 50 L (solution basis) is used, 5 L (solution basis) or more.

For commercialization, foreign matters such as polyamic acid manufacturing process should also be specialized. The reason for this is that the presence of the foreign substance in the display device manufacturing process acts as a cause of the failure or defect of the fabrication, which greatly affects the production yield.

As a first preferred embodiment, the present invention is a reaction product of an aromatic dianhydride and an aromatic diamine as a first preferred embodiment, and has a thermal expansion coefficient at a temperature range of 50 to 450 DEG C of 5 ppm / DEG C or less , And a pyrolysis temperature defined by a temperature at which the weight consumption rate reaches 1% in pyrolysis measurement by a thermogravimetric analyzer is at least 500 ° C. The base layer or the polyamic acid solution for forming the protective layer is provided.

The polyamic acid solution according to this embodiment may have a viscosity of 50 to 5000 poise.

In this embodiment, the reaction product between the aromatic rings, -O-, -CO-, -NHCO-, -S-, -SO 2 -, -CO-O-, -CH 2 - and -C (CH ₃₎ It is desirable that the reaction product of a hard aromatic diaanhydride containing no ₂ - chain and a hard aromatic diamine is used.

In a specific embodiment, the reaction product is a reaction product of para-phenylenediamine as the aromatic diamine, pyromellitic anhydride as the aromatic dianhydride and biphenyl tetracarboxylic acid anhydride, and in a preferred embodiment the reaction product Contains up to 40 mol% of biphenyltetracarboxylic anhydride in aromatic dianhydride.

In one embodiment of the present invention, the reaction product involves commercial considerations in which the production scale is at least 5 L per polymerization.

In one embodiment of the present invention, the reaction product is prepared by adding the required amount of the reaction solvent to the aromatic dianhydride and the aromatic diamine in the powder form, And a showering process in which the raw material in the form of a powder is washed out and dissolved in a solution.

In addition, the reaction product may be obtained by including a step of raising the temperature of the reactor to about 40 to 80 DEG C after the showering step and stirring.

Additionally or alternatively, the reaction product may be obtained by blowing an inert gas into the bottom of the reactor during the dissolution process after the feedstock is charged.

An embodiment of the present invention provides a polyimide coating layer formed from a polyamic acid solution obtained from the above embodiments.

In one exemplary embodiment of the present invention, there is provided a display device comprising such a polyimide coating layer as a protective layer or a display device comprising such a polyimide coating layer as a base layer.

Hereinafter, the present invention will be described in more detail.

The present invention is a reaction product of an aromatic dianhydride and an aromatic diamine as a preferred embodiment and has a thermal expansion coefficient of 5 ppm / ° C or less and a pyrolysis temperature of 50 to 450 ° C Thereby providing a polyamic acid solution having a temperature of 500 ° C or higher. Here, the pyrolysis temperature is defined as the temperature at which the weight consumption rate reaches 1% at the time of pyrolysis measurement by a thermogravimetric analyzer, that is, Td 1%.

The thermal expansion rate and the thermal decomposition temperature within the above-mentioned temperature range can be controlled by changing the thermal environment experienced during the manufacturing process of the display device when the imidized film imidized after the polyamic acid solution is applied as the substrate layer or the protective layer of the display device And the dimensional stability and pyrolysis stability at high temperature are taken into consideration.

In the display device, the substrate layer is repeatedly exposed to a high-temperature environment during the manufacturing process of the display device. In this case, the smaller the thermal expansion, the more advantageous to manufacture the display device, and in order to easily design the manufacturing process, .

That is, when the thermal expansion of the polymer material is larger than the thermal expansion of the ceramic substrate and the driving element in the process of manufacturing the electrode and the driving element, the circuit operation becomes impossible and the display device is warped and misalignment with the driving element It is preferable that the polyamic acid solution has a coefficient of thermal expansion of 5 ppm / 占 폚 or less measured at 50 to 450 占 폚 when an imidized film is formed. In addition, if a polymer material generates volatile organic compounds by pyrolysis while undergoing a high-temperature process, the production process itself may become impossible due to contamination of production facilities. Therefore, it is possible to fabricate a device at a high temperature only by using a polymer material having a high pyrolysis temperature, which is based on pyrolysis temperature, especially a small amount of weight reduction.

If a large amount of foreign matters exist in the polymer material itself, circuit operation during the display device manufacturing process may become impossible, and even if the operation is possible, the foreign matter may be defective and may be caused by defective display.

Therefore, the polymer material itself must be accompanied by a special composition, conditions and process that can reduce or eliminate foreign matter during the manufacturing process.

In order to provide such a polyamic acid solution, the polyamic acid solution may be obtained from the polymerization of a dianhydride and a diamine monomer (hereinafter, a hard monomer) in which there is no flexible chain between aromatic rings. The term "hard monomer" specifically refers to an aromatic ring having between -O-, -CO-, -NHCO-, -S-, -SO ₂ -, -CO-O-, -CH ₂ -, -C ₃ ) a ₂ -chain, that is, a monomer without a soft chain.

For example, as the dianhydride, there may be used 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (1,2,4,5 -benzenetetracarboxylic dianhydride (PMDA), and the like. Examples of the diamine include para-phenylene diamine (pPDA), 2- (4-aminophenyl) -5-aminobenzoxazole , And more preferably p-phenylenediamine.

In general, the diamine and dianhydride may be used in a molar ratio of 1: 0.9 to 0.9: 1. If the molar ratio of the monomers is within the range of the molar ratio of the monomers to satisfy the above-described object, one dianhydride and one diamine may be used respectively, More than one species may be used, one or more diamines may be used, two or more diamines may be used, and one or more dianhydrides may be used. Particularly in terms of lowering the thermal expansion coefficient and increasing the thermal decomposition temperature, it is preferred that the biphenyltetracarboxylic acid dianhydride is contained in an amount of up to 40 mol% in the aromatic dianhydride.

When the polyamic acid solution, which is a precursor of polyimide, is polymerized, the polyamic acid solution can be prepared by dissolving and reacting the dianhydride component and the diamine component in an equimolar amount in an organic solvent.

The reaction conditions are not particularly limited, but the reaction temperature is preferably -20 to 80 占 폚, and the reaction time is preferably 2 to 48 hours. It is more preferable that the reaction atmosphere is an inert atmosphere such as argon or nitrogen.

The organic solvent for the polymerization reaction of the polyamic acid solution is not particularly limited as long as it is a solvent dissolving the polyamic acid. As the known reaction solvent, there may be used, for example, m-cresol, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethylsulfoxide (DMSO) One or more polar solvents are used. In addition, a low boiling point solution such as tetrahydrofuran (THF), chloroform or a low-absorbency solvent such as? -Butyrolactone may be used.

In order to obtain the molecular weight and viscosity of the appropriate polyamic acid solution, the organic solvent is preferably 50 to 95% by weight, more preferably 70 to 90% by weight, based on the total amount of the polyamic acid solution, Is more preferable.

The polyimide resin prepared by imidizing the polyamic acid solution thus prepared preferably has a glass transition temperature of 300 ° C or higher in consideration of thermal stability.

That is, the polyimide-based polymer is a well-known high-temperature-resistant material exhibiting a high Tg and a low coefficient of thermal expansion, so that TFTs and the like can be manufactured at a temperature of 400 ° C. or more. Therefore, if a polyamic acid solution is applied and cured, It can be easily fixed on a support and therefore can maintain flatness easily, and as a result, it can be a very advantageous material for realizing a flexible display.

In the case of the present invention in which a filler is added to a polyamic acid solution for the purpose of improving various characteristics such as a surface property and a thermal conductivity of the polyimide coating layer when the polyimide coating layer is formed using the polyamic acid solution, It may act as a defect in the final display, which may lead to defective displays or a reduction in yield. Therefore, the present invention is limited to not adding any filler.

Even if the filler is not added as described above, foreign matter may be generated or invaded during the production process of the polyamic acid. Therefore, the foreign matter may be filtered through a solution.

The filtering process can be used in ordinary processes and is not particularly limited. However, the pore size of the filter must be 10 μm or less, preferably 1 μm or less.

As a method for producing an imidized film from a polyamic acid solution, a method in which a flexible display manufacturing process is simulated can be used, and a method in which a polyamic acid solution is uniformly applied to a substrate and imidized. That is, in the display device manufacturing process, a method of applying a barium polyamic acid solution as a substrate layer, in which an electrode and a display portion are sequentially stacked on the upper surface of a substrate layer, is coated with a polyamic acid solution on a separate support Imidization is carried out to prepare an imidized film, a display element laminating process is performed on the imide film in accordance with a conventional method, and finally the support is peeled off. In this case, the film-shaped plastic material may be advantageous in that the flatness of the base layer can be enhanced as compared with the case where the substrate is applied.

If there is a film type, a support and an additional adhesive layer should be present. However, since there is no adhesive layer usable at the high temperature of the present display device process, the method of applying the polyamic acid solution to the support proposed in the present invention will be the only method.

The polyamic acid solution may be coated on a component stacked on a display device to imidize the polyimide coating layer as a protective layer.

In this case, the viscosity of the polyamic acid solution may preferably be in the range of 50 to 5,000 poise in consideration of the coating workability and coating uniformity.

This viscosity can be determined by the coating method and the required imide film thickness.

The present invention also provides a method of producing scales capable of polymerizing more than 5 L (solution basis) in a batch type at a time, which can be commercialized.

Such large scales (> 5L) require special methods in reactors and reaction methods, unlike at laboratory scales below. The most significant difference is the dissolution of raw materials in powder form. In a large-scale reactor, the dissolution of the raw material is not desirable due to the limit of the stirring ability. Accordingly, the present invention also provides a solution to such a problem.

In the present invention, the required amount of the reaction solvent is initially supplied only when a certain amount is excluded, not all of the initial amount is supplied. In order to smoothly and reliably dissolve the solution after the introduction of all the powdered raw materials, the raw materials in the form of unsalted powder remaining on the wall of the reactor and the agitator are washed out and dissolved in the solution by using each powder type of the raw materials. This process is called a showering process. After each showering step, the temperature of the reactor is raised to about 40 to 80 DEG C by an additional method and stirred. Also, in the case of a large-scale reactor for commercialization as in the present invention, there is a high possibility that an undissolved product exists in the lowest portion of the reactor due to the limitation of the stirring performance thereof. Therefore, an inert gas such as argon or nitrogen is blown into the bottom of the reactor by an additional method It is added into the solution in the reactor together with the bubbles to add the lowermost stirring performance of the reactor which is a blind spot of the stirring performance. This is called bubbling process.

At this time, the amount of the inert gas may be varied depending on the type of the inlet valve and the viscosity of the solution.

The dissolving method such as the temperature raising of the reactor, the showering process, and the inert gas bubbling process may be performed according to the dissolution state of the solution, or may be carried out by one or more methods or all of them.

However, it is advantageous to use all the dissolving methods such as reactor temperature elevation, showering process and inert gas bubble input.

The polyamic acid solution thus obtained has 30 or fewer foreign particles of 0.5 탆 or more based on 40 g of the solution, and has few foreign matters. Here, the foreign objects are visually measured objects through an optical microscope (magnification: about 50 to 500 times).

The polyimide coating layer can be formed by coating and imidizing the polyamic acid solution. Examples of the imidation method applicable to the formation of the imide film include a thermal imidation method, a chemical imidation method, a thermal imidation method, Can be applied in combination with other methods. In the chemical imidation method, a dehydrating agent represented by an acid anhydride such as acetic anhydride or the like and a imidation catalyst represented by isoquinoline, β-picoline, or tertiary amines such as pyridine are added to the polyamic acid solution to imidize the imidation. When the thermal imidation method or the thermal imidation method and the chemical imidization method are used in combination, the heating conditions of the polyamic acid solution may be varied depending on the type of the polyamic acid solution, the required imide film thickness, and the like.

When a thermal imidization method and a chemical imidization method are used in combination, an example of the imidized film formation method will be described in more detail. The dehydrating agent and the imidization catalyst are put into a polyamic acid solution, cast on a separate support, Deg.] C, preferably 100 to 180 [deg.] C, activating the dehydrating agent and the imidization catalyst, partially curing and drying, and then heating at 200 to 400 [deg.] C for 1 to 120 minutes to obtain an imidized film.

Display element parts and the like may be sequentially laminated on the imide film as described above. Alternatively, a solution in which a dehydrating agent and an imidation catalyst are put in a polyamic acid solution may be coated on a display element part and an imidized film may be formed It can be applied as a protective layer.

As described above, by applying the polyamic acid solution to the display element, a display element having excellent thermal stability and appropriate flexibility and mechanical strength can be provided.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited to the following Examples.

≪ Example 1 >

N, N-dimethylacetamide (DMAc) (39,000 g) was charged into a 50 L reactor equipped with a stirrer, a nitrogen injection device, a differential injection device, a temperature controller, a condenser and a filtering system, And 2,013.55 g (18.62 mol) of p-PDA [para-Phenylene Diamine] is injected using a differential injection device. This was followed by stirring and dissolution to maintain the solution at 25 占 폚. Then, 1,000 g of N, N-dimethylacetamide (DMAc) was used to wash off the undissolved p-PDA remaining on the reactor wall surface and the stirrer and dissolve in the solution. At this time, the temperature of the reactor is raised to 40 to 80 ° C and stirred for smooth and reliable dissolution of the solution. In addition, in the case of a large-scale reactor for commercialization such as the present invention as an additional method, there is a high possibility that an undissolved matter exists in the lowest portion of the reactor due to the limit of the stirring performance thereof. Therefore, an inert gas such as argon or nitrogen is blown into the bottom of the reactor It is added into the solution in the reactor together with the bubbles to add the lowermost stirring performance of the reactor which is a blind spot of the stirring performance.

After confirming the complete dissolution of the p-PDA, the temperature of the reactor was adjusted to 25 ° C and 1,627.06 g (5.53 mol) of BPDA [3,3 ', 4,4'-Biphenyltetracarboxylic Dianhydride] . This was followed by stirring and dissolution to maintain the solution at 25 占 폚. Then, 2,000 g of N, N-dimethylacetamide (DMAc) is used to wash off the un-dissolved BPDA remaining on the reactor wall surface and the agitator, etc., and dissolve in the solution. The temperature of the reactor is raised to about 40 to 80 DEG C and stirred. In addition, an inert gas such as argon or nitrogen is blown into the bottom of the reactor so as to be injected into the solution in the reactor together with the bubbles.

After confirming the complete dissolution of BPDA, the temperature of the reactor is adjusted to 25 ° C. and 2,814.52 g (12.90 mol) of PMDA [Pyromellitic Dianhydride] is introduced into the reactor using a differential powder injector. At this time, the amount of the PMDA may be supplied at once or may be divided into 2 to 5 times at a predetermined time interval (10 minutes to 3 hours).

* It is recommended to inject about 99 wt% of the final charge first, and after a certain period of time (30 min to 1 hour), test the degree of reaction or degree of polymerization indirectly through the viscosity etc., and then add the amount of step by step of 0.5 wt% Is advantageous.

By using N, N-dimethylacetamide (DMAc) for each charging step, undissolved PMDA remaining on the wall of the reactor and the stirrer is washed away and dissolved in the solution. The amount of N, N-dimethylacetamide (DMAc) required in each step of the showering process is 1,500 g, since the step of PMDA corresponds to 2 to 5 times in this showering process.

The temperature of the reactor is raised to about 40 to 80 DEG C and stirred. In addition, an inert gas such as argon or nitrogen is blown into the bottom of the reactor so as to be injected into the solution in the reactor together with the bubbles.

Finally, the polymerized solution is filtered through a filter having a pore size of 1 mu m to remove impurities. The filter type, material and shape of the filtering process are not particularly limited.

Thereafter, the solution was stirred for 24 hours to obtain a polyamic acid solution having a viscosity of 100 poise (Mw = 110,000). The viscosity of the polyamic acid solution was measured using a Brookfield viscometer.

In order to simulate and evaluate the use as a substrate layer or a protective layer for a flexible display, the obtained polyamic acid solution was defoamed in vacuo, cooled to room temperature, cast on a stainless steel plate to a thickness of 60 to 100 탆 and dried in hot air at 150 캜 for 10 minutes Thereafter, the temperature was raised to 450 占 폚, and the mixture was heated for 30 minutes, then slowly cooled and separated from the support to obtain a polyimide film having a thickness of 10 to 15 占 퐉.

≪ Example 2 >

The composition was changed to 3,288.28 g (15.07 mol) of PMDA [Pyromellitic Dianhydride] and 1,108.88 g (3.77 mol) of BPDA [3,3 ', 4,4'-Biphenyltetracarboxylic Dianhydride] in the same manner as in Example 1 above.

≪ Example 3 >

(17.35 mol) of PMDA [Pyromellitic Dianhydride] and 567.08 g (1.93 mol) of BPDA [3,3 ', 4,4'-Biphenyltetracarboxylic Dianhydride] in the same manner as in Example 1 above.

<Example 4>

Filtering was performed twice in the same manner as in Example 1, except that the filter was the same specification.

&Lt; Example 5 >

Filtering was performed in the same manner as in Example 1 except that the filter size was changed to a filter having a specification of 0.5 mu m.

&Lt; Example 6 >

The same procedure as in Example 1 was carried out except that 2,360.98 g (10.82 mol) of PMDA [Pyromellitic Dianhydride] and 2,123.14 g (7.22 mol) of BPDA [3,3 ', 4,4'-Biphenyltetracarboxylic Dianhydride] were changed.

&Lt; Reference Example 1 &

N, N-dimethylacetamide (DMAc) (39,000 g) was charged into a 50 L reactor equipped with a stirrer, a nitrogen injection device, a differential injection device, a temperature controller, a condenser and a filtering system, And 2,013.55 g (18.62 mol) of p-PDA [para-Phenylene Diamine] is injected using a differential injection device. This was followed by stirring and dissolution to maintain the solution at 25 占 폚. Then, 1,000 g of N, N-dimethylacetamide (DMAc) is used to wash off undissolved p-PDA remaining in the reactor wall and stirrer, etc. and dissolve in the solution. At this time, the temperature of the reactor is raised to 40 to 80 ° C and stirred for smooth and reliable dissolution of the solution. In addition, in the case of a large-scale reactor for commercialization such as the present invention as an additional method, there is a high possibility that an undissolved matter exists in the lowest portion of the reactor due to the limit of the stirring performance thereof. Therefore, an inert gas such as argon or nitrogen is blown into the bottom of the reactor It is added into the solution in the reactor together with the bubbles to add the lowermost stirring performance of the reactor which is a blind spot of the stirring performance.

After confirming the complete dissolution of the p-PDA, the temperature of the reactor was adjusted to 25 ° C and 2,598.48 g (8.83 mol) of BPDA [3,3 ', 4,4'-Biphenyltetracarboxylic Dianhydride] . This was followed by stirring and dissolution to maintain the solution at 25 占 폚. Then, 2,000 g of N, N-dimethylacetamide (DMAc) is used to wash off the un-dissolved BPDA remaining on the reactor wall surface and the agitator, etc., and dissolve in the solution. The temperature of the reactor is raised to about 40 to 80 DEG C and stirred. In addition, an inert gas such as argon or nitrogen is blown into the bottom of the reactor so as to be injected into the solution in the reactor together with the bubbles.

After the complete dissolution of BPDA was confirmed, the temperature of the reactor was adjusted to 25 ° C and 1,926.38 g (8.83 mol) of PMDA [Pyromellitic Dianhydride] was added using a differential powder injector. At this time, the amount of the PMDA may be supplied at once or may be divided into 2 to 5 times at a predetermined time interval (10 minutes to 3 hours).

It is recommended to inject about 99 wt% of the final charge first, and after a certain period of time (30 minutes to 1 hour), test the degree of reaction or degree of polymerization indirectly through the viscosity, etc., and then add the remaining amount by 0.5 wt% The method is advantageous.

By using N, N-dimethylacetamide (DMAc) for each charging step, undissolved PMDA remaining on the wall of the reactor and the stirrer is washed away and dissolved in the solution. The amount of N, N-dimethylacetamide (DMAc) required in each step of the showering process is 1,500 g, since the step of PMDA corresponds to 2 to 5 times in this showering process.

The temperature of the reactor is raised to about 40 to 80 DEG C and stirred. In addition, an inert gas such as argon or nitrogen is blown into the bottom of the reactor so as to be injected into the solution in the reactor together with the bubbles.

Finally, the polymerized solution is filtered through a filter having a pore size of 1 mu m to remove impurities.

The filter type, material and shape of the filtering process are not particularly limited.

Thereafter, the solution was stirred for 24 hours to obtain a polyamic acid solution having a viscosity of 100 poise (Mw = 110,000). The viscosity of the polyamic acid solution was measured using a Brookfield viscometer.

In order to simulate and evaluate the use as a substrate layer or a protective layer for a flexible display, the obtained polyamic acid solution was defoamed in vacuo, cooled to room temperature, cast on a stainless steel plate to a thickness of 60 to 100 탆 and dried in hot air at 150 캜 for 10 minutes Thereafter, the temperature was raised to 450 占 폚, and the mixture was heated for 30 minutes, then slowly cooled and separated from the support to obtain a polyimide film having a thickness of 10 to 15 占 퐉.

<Reference Example 2>

The same procedure as in Reference Example 1 was carried out except that the composition was changed to 1,509.57 g (6.92 mol) of PMDA [Pyromellitic Dianhydride] and 3,054.38 g (10.38 mol) of BPDA [3,3 ', 4,4'-Biphenyltetracarboxylic Dianhydride].

<Reference Example 3>

(5.09 mol) of PMDA [Pyromellitic Dianhydride] and 3,491.99 g (11.87 mol) of BPDA [3,3 ', 4,4'-Biphenyltetracarboxylic Dianhydride] in the same manner as in Reference Example 1,

<Reference Example 4>

The same procedure as in Reference Example 1 was carried out except that 725.11 g (3.32 mol) of PMDA [Pyromellitic Dianhydride] and 3,912.39 g (13.30 mol) of BPDA [3,3 ', 4,4'-Biphenyltetracarboxylic Dianhydride] were changed.

<Reference Example 5>

The same procedure as in Reference Example 1 was carried out except that 355.57 g (1.63 mol) of PMDA [Pyromellitic Dianhydride] and 4,316.59 g (14.67 mol) of BPDA [3,3 ', 4,4'-Biphenyltetracarboxylic Dianhydride] were changed.

<Reference Example 6>

The same as Example 1, but no filtering was performed.

<Reference Example 7>

Filtering was performed in the same manner as in Example 1 except that the filter size was changed to a filter having a specification of 3 mu m.

<Reference Example 8>

The same procedure as in Example 1 was carried out except that 4,194.12 g (18.62 mol) of APAB [2- (4-aminophenyl) -5-aminobenzoxazole] was used instead of p-PDA [para-phenylene diamine].

<Reference Example 9>

The same procedure as in Example 1 was carried out except that 2,013.55 g (18.62 mol) of ODA [3,3-Oxydianilne] was used instead of p-PDA [para-Phenylene Diamine]

<Reference Example 10>

The procedure of Example 1 was the same as that of Example 1 except that the showering step was not performed after the feedstock was charged.

<Reference Example 11>

The same procedure as in Example 1 was performed except that the inert gas bubbling process was not performed during the dissolution process after the feedstock was charged.

(1) Coefficient of Thermal Expansion

Prior to the measurement of the thermal expansion rate, the sample was annealed at 450 占 폚 for 10 minutes. The thermal expansion rate was measured by cutting a part of the polyimide coating layer into a width of 4 mm × a length of 24 mm and measuring the coefficient of thermal expansion using a TA mechanical thermo-mechanical analyzer. The sample was placed on a support and subjected to a force of 50 mN, and then the thermal expansion rate was measured by heating at 50 DEG C to 450 DEG C in a nitrogen atmosphere at a heating rate of 5 DEG C / min. The coefficient of thermal expansion ranges from 50 ° C to 450 ° C to the first decimal place and is expressed in [° C / ppm].

(2) Pyrolysis temperature

The pyrolysis temperature was measured using a TGA measuring apparatus of Perkin Elmer. The imide film was finely cut into a size of 3 mm x 3 mm, placed on a pre-treated and weighed fan, heat-treated at 110 ° C for 30 minutes, cooled to room temperature and then heated to 600 ° C at a rate of 5 ° C per minute to measure weight loss . The pyrolysis temperature was calculated by setting the weight consumption rate to 1% of the weight of the imide membrane loaded first.

(3) Foreign body

For the foreign material analysis, 40 g of the manufactured product (the amount used in the manufacture of the display of the size of 370 mm * 470 mm) is diluted with NMP [N-methyl-2-pyrrolidone] (40 g of product + 360 g of solvent = 400 g in total).

400 g of the diluted solution was added with a vacuum and filtered with a 0.5 탆 filter. The above filter is dried in an oven at about 80 캜. However, at this time, the sealing should be performed as much as possible so as to prevent further inflow of foreign matter. The dried filter is counted by using an optical microscope or the like.

division Composition (molar ratio%) Filtering Thermal expansion rate
[ppm /] Pyrolysis temperature
[] thickness
[] bow
[ea] Dianhydride Diamine PMDA BPDA p-PDA APAB ROOM Example 1 70 30 100 0 0 1, 1 time 0.98 525 12 21 Example 2 80 20 100 0 0 1, 1 time 1.58 533 12 24 Example 3 90 10 100 0 0 1, 1 time -2.50 535 10 17 Example 4 70 30 100 0 0 1, 2 times 0.98 525 11 9 Example 5 70 30 100 0 0 0.5, 1 time 0.98 525 12 5 Example 6 60 40 100 0 0 1, 1 time 2.54 522 11 20 Reference Example 1 50 50 100 0 0 1, 1 time 6.35 520 11 18 Reference Example 2 40 60 100 0 0 1, 1 time 13.6 515 10 21 Reference Example 3 30 70 100 0 0 1, 1 time 16.69 513 11 10 Reference Example 4 20 80 100 0 0 1, 1 time 17.68 505 11 27 Reference Example 5 10 90 100 0 0 1, 1 time 17.73 495 11 13 Reference Example 6 70 30 100 0 0 X 0.98 525 12 More than 50 Reference Example 7 70 30 100 0 0 3, 1 time 0.98 525 12 More than 50 Reference Example 8 70 30 0 100 0 1, 1 time 9.88 540 11 25 Reference Example 9 70 30 0 0 100 1, 1 time 50.33 525 12 19 Reference Example 10 70 30 100 0 0 Showering process X
Polymerization X (less than 50 poise) Reference Example 11 70 30 100 0 0 Inert gas bubble process X
Polymerization X (less than 50 poise)

As a result of the physical property evaluation, the polyamic acid solution according to the embodiment of the present invention had no problem in imidation and coating. The polyimide coating layer obtained from the polyamic acid solution according to Examples 1 to 6 has a thermal expansion coefficient of 5 ppm / ° C or less and a pyrolysis temperature of 500 ° C or higher at a temperature range of 50 to 450 ° C, It can be expected that it does not induce the substance.

It is expected that the polyimide coating layer according to Examples 1 to 6 has not more than 30 foreign particles, thereby causing no deterioration of the display properties of the display or occurrence of defects during the display production.

On the other hand, the polyimide coating layer formed of the polyamic acid solution according to Reference Examples 1 to 5 and Reference Examples 8 to 9 is satisfactory in thermal decomposition temperature but has a thermal expansion rate exceeding 5 ppm / It can be understood that it is less optimal when used for forming the base layer or the protective layer of the substrate.

The polyimide coating layer according to Reference Examples 6 to 7 has a number of foreign particles of more than 30, which is very likely to cause poor display properties or defects in the display manufacturing process, It can be seen that it is less optimal when used.

Therefore, the polyamic acid solution can be applied to a substrate layer or a protective layer for a display device requiring flexibility, and the polyamic acid solution according to the embodiments is particularly optimal.

In addition, since the polyimide coating layer formed of the polyamic acid solution does not require the use of an adhesive for the supporting plate (metal foil, glass plate, etc.) used for fixing, it can be seen that the additional process for bonding does not occur and the process can be simplified.

In addition, when the display device is manufactured by applying the polyamic acid solution according to the embodiment, the display device manufacturing process can be easily designed since the temperature is not significantly affected.

Claims (9)

A reaction product of an aromatic dianhydride and an aromatic diamine,
Is defined as the temperature at which the thermal expansion coefficient at a temperature range of 50 to 450 ° C is 5 ppm / ° C or less in the formation of the imide film and the weight consumption rate at the time of pyrolysis measurement reaches 1% A thermal decomposition temperature of 500 ° C or higher,
A polyamic acid solution for forming a substrate layer or a protective layer of a display element.
The method of claim 1 wherein the reaction product is -O- in the aromatic ring, -CO-, -NHCO-, -S-, -SO 2 -, -CO-O-, -CH 2 - and -C (CH ₃ ) Polyamic acid solution for forming a base layer or a protective layer of a display element which is a reaction product of a hard aromatic diallyl high hydride containing no ₂ - chain and a hard aromatic diamine.
3. The process according to claim 1 or 2, wherein the reaction product is a reaction product of para-phenylenediamine as an aromatic diamine, pyromellitic dianhydride as an aromatic dianhydride and biphenyl tetracarboxylic dianhydride, A polyamic acid solution for forming a substrate layer or a protective layer of a display element.
4. The polyamic acid solution for forming a base layer or protective layer of a display element according to claim 3, wherein the reaction product comprises biphenyltetracarboxylic dianhydride in a maximum of 40 mol% in aromatic dianhydride.
The polyamic acid solution for forming a base layer or a protective layer of a display element according to claim 1, having a viscosity of 50 to 5000 poise.
The polyamic acid solution for forming a base layer or protective layer of a display element according to claim 1, wherein the reaction product has a production scale of 5 L or more at the time of polymerization.
A polyimide coating layer formed from the polyamic acid solution of claim 1.
A display device comprising the polyimide coating layer of claim 7 as a protective layer.
A display element comprising the polyimide coating layer of claim 7 as a substrate layer.