JP2020186390A - Display device, polyimide film for display device, polyimide film and polyimide precursor - Google Patents

Abstract

To provide a polyimide film having all of a low thermal expansion coefficient, heat resistance, transparency and strength of a form and suitable to be used as a support substrate that forms an organic EL device, and a display device using the film and a method for manufacturing the display device.SOLUTION: A display device and a method for manufacturing the display device, and a polyimide film for the display device are provided, which are characterized in that: the display device is obtained through steps of flow-casting a polyimide precursor or a polyimide solution on an inorganic substrate and heat-treating to form a polyimide film, mounting a display element on the polyimide film, and stripping the polyimide film with the display element from the inorganic substrate; and the polyimide film has a glass transition temperature of 300°C or higher, a 5%-thermal decomposition temperature of 530°C or higher, a complete light transmittance of 80% or more when the film thickness is 30 μm or less, a coefficient of thermal expansion of 40 ppm/K or less, and a tearing spreading resistance of 1.3 mN/μm or more.SELECTED DRAWING: None

Description

The present invention relates to a polyimide film used as a supporting base material for forming a display device, a display device using the polyimide film, and the like.

Organic EL devices used for various display applications, such as large displays such as televisions and small displays such as mobile phones, personal computers, and smartphones, are generally thin film transistors (hereinafter referred to as TFTs) on a glass substrate which is a supporting base material. Is formed, and an electrode, a light emitting layer, and an electrode are sequentially formed on the electrode, and these are hermetically sealed with a glass substrate, a multilayer thin film transistor, or the like. The structure of the organic EL device includes a bottom emission structure that extracts light from the glass substrate side that is the support base material and a top emission structure that extracts light from the side opposite to the glass substrate that is the support base material. Has been done. Further, since the structure allows external light to pass through as it is, a transparent structure has been proposed in which an electronic element such as a TFT can be seen through from the outside. Both can be realized by selecting transparent electrodes and substrate materials.

In addition, by replacing the supporting base material of such an organic EL device with a resin, it can be made thinner, lighter, and more flexible, and the use of the organic EL device can be further expanded. However, resins are generally inferior in dimensional stability, transparency, heat resistance, moisture resistance, film strength, etc. to glass, and therefore various studies have been conducted.

For example, Patent Document 1 relates to a polyimide useful as a plastic substrate for a flexible display and an invention relating to a precursor thereof. A polyimide obtained by casting a polyimide precursor solution having a specific structure on an inorganic substrate, drying and imidizing the polyimide. It discloses a laminate composed of a film and an inorganic substrate, and reports that it has high light transmittance and low outgas. However, since the coefficient of thermal expansion (CTE) of the polyimide obtained here exceeds 40 ppm / K, the difference from the coefficient of thermal expansion of the glass substrate is large, so that the organic EL substrate is warped and after the device is formed. It becomes difficult to obtain an organic EL device having excellent shape stability due to peeling and cracking.

Further, Patent Document 2 relates to an invention relating to a polyimide precursor resin composition for forming a flexible device substrate such as a display device and a light receiving device manufactured by peeling from a carrier substrate, and has a glass transition temperature of 300 ° C. or higher and 20 ppm / K. It is stated that it shows the following coefficient of thermal expansion. However, there is a problem that the heat treatment time is as long as 1 hour or more and the productivity is low.

Further, Patent Document 3 has a glass film having a thickness of 20 to 200 μm and a polyimide resin layer, and the polyimide resin layer has a coefficient of thermal expansion of 10 ppm / K or less and a light transmittance of 80% at a wavelength of 500 nm. It is described to provide the above transparent flexible laminate. This transparent flexible laminate is also excellent in heat resistance and gas barrier properties, and can be suitably used for a flexible substrate in a display device and a transparent substrate in a solar cell. However, a resin substrate is formed on a support substrate such as an organic EL flexible display display device and an organic EL illumination display device, a display element is mounted on the resin substrate, and then the resin substrate is peeled off together with the display element. Those having a manufacturing process require the strength of the resin substrate in particular, and it is considered that further improvement is necessary in order to apply the resin substrate to these applications.

In addition to the above, attempts have been made to reduce the weight by using a flexible resin for the support base material. For example, in Patent Document 4, a polyimide having high transparency and excellent low coefficient of thermal expansion is applied to the support base material. An organic EL device has been proposed. However, the polyimide films described in these have a large coefficient of thermal expansion and a large amount of outgas, and there is a concern about device contamination in the process.

By the way, the organic EL device has a weak resistance to moisture, and the characteristics of the EL element which is a light emitting layer are deteriorated by the moisture. Therefore, when a resin is used as the supporting base material, a resin having a low hygroscopicity is preferred in order to prevent the intrusion of water and oxygen into the organic EL device. In general, an inorganic material typified by silicon oxide or silicon nitride is used as the organic EL substrate, and the coefficient of thermal expansion (CTE) of these materials is usually 0 to 10 ppm / K. On the other hand, since transparent polyimide generally has a CTE of about 60 ppm / K, if a transparent polyimide is simply applied to a supporting base material of an organic EL device, it may warp, crack, or peel off due to thermal stress. Problems such as

Further, in order to form a TFT required for display applications, an annealing step of generally reaching about 400 ° C. is required. There was no particular problem when a glass substrate was used as the support base material, but when a resin was used as the support base material, it was necessary to have heat resistance and dimensional stability with respect to the heat treatment temperature of the TFT. Become. Incidentally, the organic EL device for lighting may not require a TFT, but the resistance value of the transparent electrode is lowered by raising the film formation temperature of the transparent electrode adjacent to the supporting base material, and the power consumption of the organic EL device is reduced. Similarly, the support base material is required to have heat resistance even in the case of lighting applications because it can be reduced. As such a transparent electrode, a metal oxide such as ITO is generally used, and since these CTEs are 0 to 10 ppm / K, the same degree is required in order to avoid the problem of cracks and peeling. A resin having the CTE of is required.

Further, in order to perform color display on the organic EL display device, materials capable of emitting the three primary colors of red (R) green (G) blue (B) are vapor-deposited for each color using a shadow mask. However, this method has a problem that it is very difficult to manufacture a shadow mask and it is expensive. In addition, it is difficult to increase the definition and size of the shadow mask in manufacturing. To solve these problems, an organic EL display device that displays a color by combining a white light emitting organic EL with a color filter has been proposed. However, in order to form a color filter, heat treatment of a resist that reaches 230 ° C. or higher is required. It is generally necessary, and in particular, in order to reduce the outgas from the resist, heat treatment at 300 ° C. or higher is preferable. When such high-temperature heat treatment is performed, if the thermal expansion coefficient and the humidity expansion coefficient of the TFT substrate and the color filter substrate are inconsistent, the dimensional change of each substrate differs due to the change of temperature and humidity. This causes problems such as warpage of the display device and peeling between the substrates. Therefore, when a resin is used as a supporting base material for a color filter, it is necessary to have heat resistance at the heat treatment temperature of the resist and dimensional stability equivalent to that of the TFT substrate. These problems can be solved by using the same material for the supporting base material of the TFT and the supporting base material of the color filter.

Further, since the polyimide film is generally colored yellowish brown, there is a problem that it is difficult to find it with the naked eye or with a visual inspection apparatus when a minute foreign substance is mixed in the polyimide film. In particular, it is extremely difficult to find foreign substances such as rust on metals that are similar in color to polyimide. If foreign matter is present in the polyimide film, defects in the gas barrier layer formed on the surface thereof, short circuits between electrodes, and the like occur, which causes defects. In this regard, by using a transparent polyimide film, it becomes easier to find foreign substances and it can contribute to the prevention of a decrease in yield. Therefore, as a function of the display device, the supporting base material does not require transparency. It is also useful to use a transparent polyimide film as a supporting base material in a display device such as the above. Incidentally, the transmittance of glass in the visible light region is generally about 90%, and when a resin is used as a supporting base material, it is necessary to bring it as close as possible to this. Since the wavelength of light emitted from the light emitting layer of the organic EL is mainly 440 nm to 780 nm, the average transmittance in this wavelength region is at least 80% or more for the supporting base material used in the organic EL device. Desired. In addition, it is desirable that the resin itself forming the supporting base material also has moisture resistance.

In addition, when the film is peeled off from the inorganic substrate, mechanical properties such as mechanical strength and elongation of the film are required to be above a certain level. In particular, if the tear propagation resistance is small, the film will break when peeled off. There's a problem. Therefore, a film used as a supporting base material is required to have high tear propagation resistance.

In this regard, various methods for peeling the film from the inorganic substrate have been proposed (Patent Documents 5 and 6), but attention is paid to the fact that not only the process is complicated and costly, but also the breakage of the film is suppressed. It has not been. Further, Patent Document 7 is a display device provided with a gas barrier layer on a supporting base material made of a polyimide film, wherein the polyimide film has a transmittance of 80% or more in a wavelength region of 440 nm to 780 nm and a coefficient of thermal expansion. Discloses a display device characterized in that the coefficient of thermal expansion is 15 ppm / K or less and the difference in coefficient of thermal expansion from the gas barrier layer is 10 ppm / K or less. It is thin, lightweight, flexible, has no problems of cracking or peeling due to thermal stress, has excellent dimensional stability, prevents defects in the manufacturing process, and has a long life and a good element. It can show its characteristics. However, in the manufacturing process of the display device, for example, when the polyimide film is peeled off from the inorganic substrate, attention has not been paid to suppressing the breakage of the polyimide film, and the yield improvement in the manufacturing process has been further improved. Improvement is desired.

Considering the above points, when replacing the supporting substrate for the display device from the glass substrate to the resin substrate, it is necessary to satisfy at least low CTE, heat resistance, transparency, and high tear propagation resistance at the same time. There was no resin substrate that could satisfy all of these requirements.

Japanese Unexamined Patent Publication No. 2012-40836 JP-A-2010-202729 Japanese Unexamined Patent Publication No. 2013-163304 WO 2013/146460 Pamphlet Japanese Unexamined Patent Publication No. 2011-65173 Japanese Patent Application No. 2011-142168 WO 2013/191180 Pamphlet

Therefore, as a result of diligent research to solve the above problems, the present inventors have surprisingly used a polyimide film made of polyimide containing a predetermined repeating structural unit, and further, the structural unit of the polyimide film. By specifying the ratio, it was found that a polyimide film capable of simultaneously satisfying low CTE, heat resistance, transparency, and high tear propagation resistance and a display device provided with the polyimide film can be obtained, and the present invention has been completed.

Therefore, an object of the present invention has low CTE, heat resistance, low moisture absorption, strength and transparency, which are suitable as supporting base materials for forming display devices such as organic EL displays, organic EL lighting, electronic papers and touch panels. The purpose is to provide a polyimide film.

Another object of the present invention is to provide a display device using the polyimide film as a supporting base material. Since the resin substrate of the display device of the present invention is not easily damaged in the manufacturing process, it is not easily torn in the device forming step and then the peeling step from the inorganic substrate, and the productivity is high.

That is, in the present invention, a polyimide film is formed by casting a polyimide precursor or a solution of polyimide on an inorganic substrate and performing heat treatment, and further, a display element is mounted on the polyimide film, and the display element is mounted on the polyimide film. A display device obtained by peeling off the polyimide film together with the display element. Total light transmission at a film thickness of 300 ° C. or higher, 5% thermal decomposition temperature of 530 ° C. or higher, and 30 μm or lower of the polyimide film. The present invention relates to a display device characterized in that the rate is 80% or more, the thermal expansion coefficient is 40 ppm / K or less, and the tear propagation resistance is 1.3 mN / μm or more.

Further, in the display device, it is preferable that the polyimide component constituting the polyimide film is composed of structural units represented by the following formulas (1) and (2).

当該式（１）及び（２）において、Ｘは単結合または−Ｃ−もしくは−Ｏ−を含む置換基である。ただし、ｍ／（ｍ＋ｎ）＝０．１１〜０．４０ である。

In the formulas (1) and (2), X is a single bond or a substituent containing -C- or -O-. However, m / (m + n) = 0.11 to 0.40.

Further, in the display device, it is preferable that X is a single bond or a divalent substituent represented by the following formulas (3), (4) or (5).

Further, in the display device, the hygroscopicity of the polyimide film is preferably 0.8 wt% or less.

Further, the display device is preferably a touch panel.

Further, in the present invention, a polyimide film is formed by casting a polyimide precursor or a solution of polyimide on an inorganic substrate and performing heat treatment, and further, a display element is mounted on the polyimide film, and the display element is mounted on the polyimide film. A polyimide film for a display device obtained by peeling off the polyimide film together with a display element, wherein the glass transition temperature of the polyimide film is 300 ° C. or higher and the 5% thermal decomposition temperature is 530 ° C. or higher and the film thickness is 30 μm or lower. The present invention relates to a polyimide film for a display device, characterized in that the total light transmittance is 80% or more, the thermal expansion coefficient is 40 ppm / K or less, and the tear propagation resistance is 1.3 mN / μm or more.

ここで、当該式（１）及び（２）において、Ｘは単結合または下記式（４）で表される置換基である。ただし、ｍ／（ｍ＋ｎ）＝０．１１〜０．４０である。

Further, the present invention relates to a polyimide and a polyimide precursor, which have a weight average molecular weight of 100,000 to 400,000 and are composed of structural units represented by the following formulas (1) and (2).

Here, in the formulas (1) and (2), X is a single bond or a substituent represented by the following formula (4). However, m / (m + n) = 0.11 to 0.40.

The polyimide film of the present invention has low thermal expansion, high transmittance in the visible region and excellent transparency, excellent dimensional stability, high heat resistance, low moisture absorption rate, and high strength. High and productive. Therefore, it can be suitably used as a supporting base material for display devices such as organic EL displays, organic EL lighting, electronic paper, and touch panels.
In addition, the display device of the present invention is highly productive because the resin substrate is not easily damaged during the manufacturing process.

Hereinafter, the present invention will be further described.
In the display device of the present invention, a polyimide film is formed by casting a polyimide precursor or a solution of polyimide on an inorganic substrate and performing heat treatment, and further, a display element is mounted on the polyimide film, and the inorganic substrate is mounted. This is a display device obtained by peeling the polyimide film together with the display element, and the total light beam at a film thickness of 300 ° C. or higher, 5% thermal decomposition temperature of 530 ° C. or higher, and 30 μm or lower of the polyimide film. The permeability is 80% or more, the thermal expansion coefficient is 40 ppm / K or less, and the tear propagation resistance is 2.0 mN / μm or more.

A polyimide film is produced by polymerizing a raw material diamine and an acid anhydride in the presence of a solvent to prepare a solution of a polyimide precursor, then casting the solution on an inorganic substrate and imidizing it by heat treatment. Can be done. Alternatively, it can be produced by casting a polyimide solution on an inorganic substrate and imidizing it by heat treatment.
The molecular weight of the polyimide film can be mainly controlled by changing the molar ratio of the raw material diamine and the acid anhydride, but the molar ratio is usually 1: 1. If necessary, it can be adjusted from 0.985 to 1.025. The range of the molecular weight Mw (weight average molecular weight) is preferably 80,000 or more. Further, it is more preferable to adjust the range from 80,000 to 400,000. More preferably, it is adjusted to more than 100,000 and 400,000 or less, and even more preferably, it is adjusted to the range of 120,000 to 400,000 or less. Here, the molecular weight Mw is a polystyrene-equivalent molecular weight measured and calculated by GPC (Gel Permeation Chromatography).

In the polyimide precursor solution, first, diamine is dissolved in an organic solvent, and then acid dianhydride is added to the solution to produce polyamic acid, which is a polyimide precursor. Examples of the organic solvent include dimethylacetamide, dimethylformamide, n-methylpyrrolidinone, 2-butanone, diglime, xylene, butyrolactone, triethylene glycol dimethyl ether and the like, and these may be used alone or in combination of two or more. it can.

When the obtained polyimide precursor solution is cast on an inorganic substrate, the viscosity of the solution is preferably in the range of 500 to 70,000 cps by adjusting the concentration and molecular weight of the polyimide precursor. More preferably, it is 2000 to 20000 cps.

Further, the surface of the substrate or the substrate to be coated with the resin solution may be appropriately surface-treated and then cast. In the above, it is appropriate that the drying condition is 150 ° C. or lower for 2 to 10 minutes, and the heat treatment for imidization is performed at a temperature of about 130 to 360 ° C. for about 2 to 60 minutes. A known method can be used as the casting method, but a spin coating method or a coater method is preferable.

The subsequent imidization step by heat treatment can be performed by using thermal imidization by heat dehydration or chemical imidization by reacting the polyimide precursor with a dehydrating agent and a catalyst. In the case of thermal imidization, the heating temperature is preferably 90 to 360 ° C. On the other hand, in the case of chemical imidization, the heating temperature is preferably 50 to 250 ° C. When the polyimide solution is cast on the inorganic substrate and the polyimide film is formed by heat treatment, the temperature may be such that the solvent in the solution is volatilized, preferably 100 to 250 ° C.

As the inorganic substrate, known substrates can be used without limitation, but glass, SUS, and aluminum are preferable, and glass is more preferable because of smoothness, high heat resistance, and low dimensional change rate.

By the above heat treatment, a polyimide film having a total light transmittance of 80% or more at a film thickness of 30 μm or less (in the present invention, it means a transmittance in a wavelength region of 380 nm to 780 nm) can be obtained on an inorganic substrate. In particular, the heating time (hereinafter referred to as high temperature holding time) in the high temperature heating temperature range from a temperature 20 ° C. lower than the maximum heating temperature (maximum ultimate temperature) at the time of temperature rise in the above heat treatment to the maximum ultimate temperature is set to 60 minutes or less. It is preferable to do so. If this high temperature holding time exceeds 60 minutes, the production efficiency of the process may deteriorate, and the transparency of the polyimide film may decrease due to coloring or the like. In order to maintain transparency, it is better that the high temperature holding time is short, but if the time is too short, the effect of the heat treatment may not be sufficiently obtained. The optimum high temperature holding time varies depending on the heating method, the heat capacity of the base material, the thickness of the polyimide film, and the like, but is preferably 0.5 minutes or more and 120 minutes or less. More preferably, it is 0.5 minutes or more and 60 minutes or less.

Further, the polyimide film obtained by the above heat treatment has a total light transmittance of 80% or more at a film thickness of 30 μm or less, a glass transition temperature of 300 ° C. or more, a 5% thermal decomposition temperature of 530 ° C. or more, and thermal expansion. The coefficient is 40 ppm / K or less and the tear propagation resistance is 1.3 mN / μm or more.
When the total light transmittance is less than 80%, when an organic EL element is used as the display element, the light emitted from the light emitting layer of the organic EL (wavelength is mainly 380 nm to 780 nm) sufficiently transmits the polyimide film. do not do. Therefore, for example, in the case of a bottom emission structure, it is not possible to sufficiently extract light emitted from the light emitting layer. More preferably, the total light transmittance is 85% or more. Further, when a transparent conductive film for a touch panel is used as a display element, the total light transmittance is 85% or more for the reason of ensuring sufficient visibility.
The thickness of the polyimide film is not limited as long as the total light transmittance at a film thickness of 30 μm or less is 80% or more, but the film thickness is preferably 5 to 30 μm, more preferably 10 to 20 μm.

The glass transition temperature of the polyimide film is 300 ° C. or higher. It is preferably 330 ° C. or higher, and more preferably 350 ° C. or higher. If the crow transition temperature is less than 300 ° C., the polyimide film may be deformed by the heat when the display element is mounted.

The 5% thermal decomposition temperature (Td5%) of the polyimide film is 530 ° C. or higher. If the temperature is lower than 530 ° C., the polyimide film may be partially decomposed due to the heat generated when the display element such as the TFT or the transparent conductive film is mounted. More preferably, the weight loss rate at 530 ° C. is 3% or less.

Further, as described above, the coefficient of thermal expansion of the polyimide film is 40 ppm / K or less, preferably between −10 ppm / K and 40 ppm / K. If it is less than -10 ppm / K, or if it exceeds 40 ppm / K, problems such as warping, cracking, and peeling of the display device occur due to thermal stress when the display element is mounted. Sometimes. More preferably, it is 0 ppm / K to 30 ppm / K.

The tear propagation resistance of the polyimide film is 1.3 mN / μm or more. If it is less than 1.3 mN / μm, for example, the polyimide film may be broken in a step of mounting a display element on the polyimide film and peeling the polyimide film from the inorganic substrate. A more preferable range is 1.5 mN / μm or more. A more preferable range is 2.0 mN / μm or more.

Further, in the organic EL device and the touch panel device, low hygroscopicity of the supporting base material is preferred in order to prevent the adsorption of water into the device. Therefore, the polyimide film preferably has a hygroscopicity of 0.8 wt% or less. More preferably, it is 0.6 wt% or less. Further, when the moisture absorption rate is 0.8 wt% or less, the reliability of the display device is improved without swelling and foaming when the TFT is mounted or when the transparent conductive film is laminated.

Further, in the polyimide film satisfying the above-mentioned performance, it is preferable that the polyimide component constituting the polyimide film is composed of the structural units represented by the above formulas (1) and (2).

In the above formula (2), X is a single bond or a substituent containing -C- or -O-. However, m / (m + n) = 0.11 to 0.40. It is more preferably 0.12 to 0.40, and even more preferably 0.15 to 0.40.
Here, examples of the substituent containing −C− include −CO−, −C (CF ₃ ) ₂₋ , and −C (CH ₃ ) ₂₋ . More preferably, it is a substituent represented by the above formula (3) or (5).
Substituents containing -O- include, for example, -O-Ph-O-, -O-Ph-Ph-O-, -O-, -O-Ph-C (CF ₃ ) ₂ -Ph-O. -Is mentioned. Here, Ph is a phenylene group. More preferably, it is a substituent represented by the above formula (3) or (4).

Here, the structural unit of the above formula (1) mainly improves properties such as low thermal expansion and high heat resistance, and the structural unit of the above formula (2) improves high transparency and tear propagation resistance. It is effective for. Therefore, when m / (m + n) is smaller than 0.11, the coefficient of thermal expansion is large, the glass transition temperature is low, and the process of mounting the TFT tends to be unbearable. More preferably, it is 0.20 or more. On the other hand, if it exceeds 0.40, the tear propagation becomes low, and for example, the polyimide film tends to break easily in a step of mounting a display element on the polyimide film and peeling the polyimide film from the inorganic substrate. In addition, transparency tends to decrease.

In order to obtain a high molecular weight resin, in the present invention, the molar ratio of acid anhydride to diamine is preferably adjusted in the range of 0.985 to 1.025, more preferably in the range of 1.00 to 1.020. Is. More preferably, it is 1.002 to 1.015. At other molar ratios, the molecular weight is low and the tear propagation resistance is low.

In addition, inorganic fine particles such as silica, alumina, boron nitride, and aluminum nitride may be added to the polyimide film for the purpose of improving slipperiness and thermal conductivity.

Further, the polyimide film may be made of a plurality of layers of polyimide. In the case of a single layer, it is preferable to have a thickness of 3 μm to 50 μm. On the other hand, in the case of a plurality of layers, the main polyimide layer may be a polyimide film having the above-mentioned thickness. Here, the main polyimide layer refers to the polyimide layer in which the thickness occupies the largest ratio among the plurality of polyimide layers, and the thickness thereof is preferably 3 μm to 50 μm, more preferably 4 μm to 30 μm. is there.

After the heat treatment is completed, the display element is mounted on the polyimide film. Here, the type of display element is not particularly limited, but includes components of a liquid crystal display device, an organic EL display device, a display device such as electronic paper, and a display device such as a color filter. In addition, the display device includes an organic EL lighting device, a touch panel device, a conductive film on which ITO and the like are laminated, a gas barrier film that prevents permeation of moisture, oxygen, and the like, and components of a flexible circuit board. Various functional devices used are also included. That is, the display element referred to in the present invention includes not only components such as a liquid crystal display device, an organic EL display device, and a color filter, but also an organic EL lighting device, a touch panel device, an electrode layer or a light emitting layer of the organic EL display device, and the like. It also includes one type or a combination of two or more types such as a gas barrier film, an adhesive film, a thin film transistor (TFT), a wiring layer of a liquid crystal display device, or a transparent conductive layer.

Examples of the method for forming the display element include a display element (for example, in the case of an organic EL display device, a barrier layer, a TFT, an ITO, an organic EL light emitting layer, and a color filter layer, and in the case of a touch panel, transparent conductivity. The formation conditions are appropriately set according to the electrode layer such as a film or a metal mesh.) Generally, after forming a metal or the like on a polyimide film, a predetermined shape is required. It can be obtained by using a known method such as patterning or heat treatment. That is, the means for forming these display elements is not particularly limited, and for example, sputtering, vapor deposition, CVD, printing, exposure, immersion, etc. are appropriately selected, and if necessary, in a vacuum chamber or the like. You may want to perform these process processes in. The inorganic substrate and the polyimide film may be separated immediately after the display element is formed through various process treatments, and may be integrated with the inorganic substrate for a certain period of time, for example, immediately before being used as a display device. It may be separated and removed.

After mounting the display element, the polyimide film is peeled off from the inorganic substrate together with the display element. When the polyimide film is peeled from the inorganic substrate, if the polyimide film is stretched, the retardation becomes large. Therefore, a method of peeling so that the stress applied to the polyimide film at the time of peeling is reduced is preferable.

In order to prevent the polyimide film from stretching, another layer is formed on the inorganic substrate, a polyimide is formed on the inorganic substrate, a display element is mounted on the layer, and then the polyimide film is applied to the other layer and the display element. A method of peeling the film together and dispersing the stress required for the peeling in the other layer is preferable. This is especially effective when the polyimide film is thin. In this case, the polyimide film of the present invention is regarded as including the other layers. Examples of the method for forming the other layer include bonding, coating, and vapor deposition of a resin film or metal foil with an adhesive.

Further, other known methods can be applied as a method for facilitating the peeling of the polyimide film from the base material and preventing stretching. For example, in Japanese Patent Application Laid-Open No. 2007-512568, a yellow film such as polyimide is formed on glass, then a thin film electronic element is formed on the yellow film, and then the bottom surface of the yellow film is irradiated with UV laser light through the glass. Discloses that it is possible to peel off the glass and the yellow film. According to this method, since the polyimide film is separated from the glass by UV laser light, no stress is generated at the time of peeling, which is one of the preferable methods for the peeling process of the present invention. However, unlike the yellow film, transparent plastic does not absorb UV laser light, so it is also disclosed that an absorption / release layer such as amorphous silicon needs to be provided under the film in advance.

Further, Japanese Patent Application Laid-Open No. 2012-511173 discloses that a laser having a spectrum within a spectrum of 300 to 410 nm is used for peeling the glass and the polyimide film by irradiation with UV laser light. Incidentally, as a peeling method, a method of irradiating a laser from the glass side to separate the resin base material having a display portion from the glass, a method of applying a peeling layer to a glass substrate to form the resin base material, and then polyimide on the peeling layer. A method of peeling the polyimide film layer from the peeling layer after the resin is applied and the manufacturing process of the organic EL display device is completed, the coupling agent treatment on the surface of the inorganic layer is performed, and then the pattern of this coupling agent is subjected to UV irradiation or the like. Examples thereof include a method of forming a laminate having a good adhesive portion and an easy peeling portion having different peel strengths by performing a chemical treatment treatment, and then peeling the laminate.

Since the wavelength of light emitted from the light emitting layer of the organic EL device is mainly 440 nm to 780 nm, the average transmittance in this wavelength region of the supporting base material used in the organic EL device is at least 80% or more. Is required. On the other hand, when the glass and the polyimide film are peeled by the irradiation of the UV laser light described above, if the transmittance at the wavelength of the UV laser light is high, it is necessary to provide an absorption / peeling layer under the film. This reduces productivity. In order to perform peeling without providing an absorption / peeling layer, the polyimide film itself needs to sufficiently absorb laser light, and the transmittance of the polyimide film at 400 nm is preferably 60% or less, and further. It is preferably 40% or less.

Further, in order to prevent moisture and oxygen from entering the organic EL device and the touch panel device, a gas barrier layer may be formed on the polyimide film. In this case, the polyimide film of the present invention is regarded as including the gas barrier layer. It may be formed on a single polyimide film, or may be formed on a laminate of a base material such as glass or metal foil and a polyimide film. A known gas barrier layer can be used, but as a gas barrier layer having a barrier property against oxygen, water vapor, etc., silicon oxide, aluminum oxide, silicon carbide, silicon carbide oxide, silicon carbide, silicon nitride, silicon nitride, etc. An inorganic oxide film is preferably exemplified, and a film may be composed of only one kind of composition, or a film in which two or more kinds of compositions are confused may be selected.

Hereinafter, the contents of the present invention will be described in more detail based on Examples and the like, but the present invention is not limited to the scope of these Examples.

First, abbreviations for monomers and solvents for synthesizing polyimide, methods for measuring various physical properties in Examples, and their conditions are shown below.

TFMB: 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl PMDA: pyromellitic dianhydride DMAc: N, N-dimethylacetamide 6FDA: 2,2'-bis (3,4--) Dicarboxyphenyl) Hexafluoropropane dianhydride ODPA: 4,4'-oxydiphthalic acid dianhydride BPADA: 2,2'-bis (4- (3,4-dicarboxyphenoxy) propanoic dianhydride)
BPDA: 3,3', 4,4'-biphenyltetracarboxylic dianhydride m-TB: 2,2'-dimethylbenzidine TPE-R: 1,3-bis (4-aminophenoxy) benzene support substrate: Glass substrate (made by Corning, 0.7 mm thick)
Solvent: Dimethylacetamide (DMAc)

[Coefficient of thermal expansion (CTE)]
A polyimide film with a size of 3 mm x 15 mm was subjected to a constant temperature rise rate (20 ° C / min) from 30 ° C to 280 ° C while applying a load of 5.0 g using a thermomechanical analysis (TMA) device TMA100 manufactured by SEIKO. The temperature was raised, then lowered to 30 ° C, and a tensile test was performed in this temperature range, and the coefficient of thermal expansion (ppm / K) was measured from the amount of elongation of the polyimide film with respect to the temperature change from 250 ° C to 100 ° C. ..

[Tear propagation resistance]
A test piece of a polyimide film (63.5 mm × 50 mm) was prepared, a notch having a length of 12.7 mm was made in the test piece, and the measurement was performed at room temperature using a light load tear tester manufactured by Toyo Seiki. The measured tear propagation resistance value was expressed as a resistance value (mN / μm) per unit thickness.

[Glass transition temperature Tg]
Motion when a polyimide film (10 mm x 22.6 mm) is heated from 20 ° C to 500 ° C at 5 ° C / min with a dynamic viscoelasticity measurement (DMA) device RSA3 manufactured by TA Instruments Japan. The viscoelasticity was measured, and the glass transition temperature Tg (tan δ maximum value) was determined.

[Light transmittance]
The average value of the light transmittance of the polyimide film (50 mm × 50 mm) from 440 nm to 780 nm was determined with a U4000 spectrophotometer.

[Total light transmittance]
The total light transmittance of a polyimide film (5 cm square) was measured using HAZE METER NDH-5000 manufactured by Nippon Denshoku Kogyo.

[Pyrolysis temperature (Td5%)]
Measure the weight change when a polyimide film weighing 10 to 20 mg is heated from 30 ° C. to 550 ° C. at a constant speed with a thermogravimetric analysis (TG) device TG / DTA6200 manufactured by SEIKO in a nitrogen atmosphere. The temperature when the weight loss rate was 5% was defined as the thermal decomposition temperature. When the weight loss rate did not reach 5% in the above temperature range, an arbitrary temperature of 530 ° C. or higher and the weight loss rate at that temperature were described.

[Hygroscopicity]
The polyimide film (4 cm × 20 cm) was dried at 120 ° C. for 2 hours and then allowed to stand in a constant temperature and humidity chamber at 23 ° C./50% RH for 24 hours, and the weight change before and after that was calculated by the following formula.
Moisture absorption rate (%) = [(weight after moisture absorption-weight after drying) / weight after drying] x 100

[Peelability]
If the polyimide film could be peeled off from the support substrate without breaking or tearing, it was judged as ◯. In addition, if the peeling process caused breakage or tearing and the peeling became impossible, it was judged as x.

[Humidity expansion coefficient (CHE)]
Prior to coating, the polyamic acid solution was added DMAc to adjust its viscosity to about 10000 cP. Then, it is applied on a copper foil having a thickness of 18 μm using an applicator so that the film thickness after drying is about 10 μm, dried at 50 to 130 ° C. for 2 to 60 minutes, and then further from 130 ° C. to 360 ° C. Was heat-treated for 30 minutes to form a polyimide layer on the copper foil to obtain a laminate. This laminate was cut into a size of 25 cm × 25 cm, an etching resist layer was provided on the copper foil side, and this was formed in a pattern in which 16 points having a diameter of 1 mm were arranged at 10 cm intervals on four sides of a square having a side of 30 cm. The exposed portion of the etching resist opening was etched to obtain a polyimide film for CHE measurement having 16 remaining copper foil points. After drying this film at 120 ° C. for 2 hours, the film was allowed to stand in the environments of 23 ° C./30% RH, 23 ° C./50% RH and 23 ° C./70% for 24 hours, respectively, and between the copper foil dots in each environment. CHE (ppm /% RH) was determined from the dimensional change of. The dimensional change was measured by a two-dimensional length measuring machine.

[warp]
A laminate of copper foil and polyimide film was cut out to a size of 10 cm × 10 cm, placed on a flat place, and the state of warpage of the laminate was judged. The warp of less than 1 mm was evaluated as ◯, the warp of 1 mm or more and less than 3 mm was evaluated as Δ, and the warp of 5 mm or more was evaluated as x.

[Weight average molecular weight Mw]
The weight average molecular weight Mw was measured and calculated by a GPC device (TOSOH HLC-8220 GPC manufactured by Tosoh Corporation). The column used was Tskgel GMHHR-M x 2 from Tosoh. The standard sample is polystyrene and the detector type is RI. As the solvent, a DMAc-based developing solvent was used.

[Synthesis Example 1]
(Polyamic acid A)
TFMB25.907 was dissolved in 200 g of DMAc of solvent under a nitrogen stream with stirring in a 500 ml separable flask. Then, 14.0 g of PMDA and 5.019 g of ODPA were added to this solution. The molar ratio of acid anhydride to diamine was set to 1.005. Then, 55 g of DMAc was added so that the solid content was 15 wt%. Then, the solution was stirred at room temperature for 5 hours to carry out a polymerization reaction and kept for 24 hours. A viscous colorless polyamic acid solution was obtained, and it was confirmed that a polyamic acid A having a high degree of polymerization was produced. The weight composition of the monomer in polyamic acid A is shown in Table 1.

[Synthesis Examples 2 to 16]
(Polyamic acids B to P)
Polyamic acids B to P according to Synthesis Examples 2 to 16 were obtained in the same manner as in Synthesis Example 1 except that the compositions shown in Tables 1 to 3 were used. The Mw of polyamic acid E was 211,596. The Mw of polyamic acid N was 195,170.

[Example 1]
DMAc was added to the polyamic acid A solution obtained above, and the mixture was diluted to a viscosity of 5000 cP. It is applied on a glass substrate with a thickness of 0.5 mm and 10 mm square using an applicator so that the film thickness after heat treatment is about 25 μm, and the temperature is raised from 90 ° C. to 360 ° C. over 30 minutes on the glass substrate. Polyimide was formed to obtain a laminate A. Next, the polyimide film was peeled off from the glass substrate to obtain a colorless polyimide film A. Table 4 shows the results of various evaluations of the obtained polyimide film A and the laminate A.
The evaluation of the coefficient of thermal expansion (CHE) and the warpage was performed according to the procedures described in the above-mentioned [coefficient of thermal expansion (CHE)] and [warp], respectively. The evaluation results are shown in Table 4.

[Examples 4, 6 and 7, and Reference Examples 2, 3 and 5]
Examples 4, 6 and 7 and the laminates B to G according to Reference Examples 2, 3 and 5 in the same manner as in Example 1 except that polyamic acids B to G were used instead of polyamic acid A. Polyamide films B to G were produced. The evaluation results are also shown in Table 4.

[Reference Examples 8, 9, 11]
Lamination according to Reference Example 8 in the same manner as in Example 1 except that polyamic acid C, E or N was used instead of polyamic acid A and was applied so that the film thickness after heat treatment was about 10 μm. A body C-2 and a polyimide film C-2, a laminate E-2 and a polyimide E-2 according to Reference Example 9, and a laminate N and a polyimide film N according to Reference Example 11 were produced. The evaluation results are also shown in Tables 4 and 6, respectively.

[Reference example 12]
The laminate O and the polyimide film O according to Reference Example 12 were applied in the same manner as in Example 1 except that polyamic acid O was used instead of polyamic acid A and the film was applied so that the film thickness after heat treatment was about 8 μm. Was produced. The evaluation results are also shown in Table 6.

[Example 10]
In the same manner as in Example 1, a laminated body A was obtained, and a color filter layer was further formed on the polyimide surface of the laminated body A. Subsequently, the polyimide on which the color filter layer was formed was peeled off from the glass to obtain a color filter substrate using the polyimide film A as the flexible substrate. In the manufacturing process of the color filter substrate, the warp of the laminated body was less than 1 mm. Moreover, the polyimide could be peeled off from the glass cleanly. In addition, no damage was observed in the flexible substrate in the obtained color filter substrate.

[Comparative Examples 1 to 6]
Laminates HM and polyimide films HM according to Comparative Examples 1 to 6 were prepared by the same method as in Example 1 except that polyamic acids HM were used instead of polyamic acid A. The evaluation results are shown in Table 5.

[Comparative Examples 7 to 8]
The laminate P and the laminate P according to Comparative Example 7 were applied in the same manner as in Example 1 except that polyamic acid P or I was used instead of polyamic acid A and the film was applied so that the film thickness after heat treatment was about 10 μm. Polyimide film P and the laminate I-2 and polyimide film I-2 according to Comparative Example 8 were produced. The evaluation results are shown in Table 6.

※重量減少率が５％に達しなかった。なお、カッコ内の数値は、表に記載の温度における重量減少率を表す。

* Weight reduction rate did not reach 5%. The numerical value in parentheses represents the weight loss rate at the temperature shown in the table.

※重量減少率が５％に達しなかった。なお、カッコ内の数値は、表に記載の温度における重量減少率を表す。

* Weight reduction rate did not reach 5%. The numerical value in parentheses represents the weight loss rate at the temperature shown in the table.

As shown in Tables 4 and 6, the polyimide films according to Examples 1, 4, 6 and 7 and Reference Examples 2, 3, 5, 8, 9, 11 and 12 satisfying the conditions of the present invention have heat resistance. The film was durable and could be peeled off from the support substrate cleanly, with excellent transparency and small warpage. Therefore, such a polyimide film can be suitably used as a supporting base material for forming a display device such as an organic EL display, an organic EL lighting, and an electronic paper.
On the other hand, as shown in Tables 5 and 6, the polyimide films according to Comparative Examples 1 to 8 that do not satisfy the conditions of the present invention have a large coefficient of thermal expansion, the laminated body with glass has a large warp, and the film is brittle. Therefore, it could not be peeled off from the glass substrate cleanly, and it was not suitable as a polyimide film for forming a display device.

Claims (5)

A display device in which a display element is mounted on a polyimide film, and the total light transmittance at a film thickness of the polyimide film having a glass transition temperature of 300 ° C. or higher and a 5% thermal decomposition temperature of 530 ° C. or higher and 30 μm or lower. 80% or more, coefficient of thermal expansion of 40 ppm / K or less, tear propagation resistance of 1.3 mN / μm or more, moisture absorption rate of 0.6 wt% or less, and the polyimide component constituting the polyimide film has a weight average molecular weight of 100,000. A display device having a size of ~ 400,000 and comprising structural units represented by the following formulas (1) and (2).

In the formulas (1) and (2), X is a single bond or a substituent represented by the following formula (4). However, m / (m + n) = 0.11 to 0.40.

The display device according to claim 1, wherein the display device is a touch panel. A polyimide film for a display device in which a display element is mounted on a polyimide film, the polyimide film having a glass transition temperature of 300 ° C. or higher and a 5% thermal decomposition temperature of 530 ° C. or higher and a film thickness of 30 μm or lower. The total light transmittance is 80% or more, the thermal expansion coefficient is 40 ppm / K or less, the tear propagation resistance is 1.3 mN / μm or more, the moisture absorption rate is 0.6 wt% or less, and the polyimide component constituting the polyimide film is weight. A polyimide film for a display device having an average molecular weight of 100,000 to 400,000 and comprising structural units represented by the following formulas (1) and (2).

In the formulas (1) and (2), X is a single bond or a substituent represented by the following formula (4). However, m / (m + n) = 0.11 to 0.40.

A polyimide having a weight average molecular weight of 100,000 to 400,000 and comprising structural units represented by the following formulas (1) and (2).

In the formulas (1) and (2), X is a single bond or a substituent represented by the following formula (4). However, m / (m + n) = 0.11 to 0.40.

A polyimide precursor having a weight average molecular weight of 100,000 to 400,000 and consisting of structural units represented by the following formulas (1) and (2).

In the formulas (1) and (2), X is a single bond or a substituent represented by the following formula (4). However, m / (m + n) = 0.11 to 0.40.