JP2012051995A - Polyimide film and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyimide film that achieves both transparency and heat resistance by suppressing occurrence of a haze caused by crystallization on imidation and a method for manufacturing the same.SOLUTION: A polyamic acid solution obtained by causing an aromatic diamine to react with an aromatic acid dianhydride in an organic solvent is cast and heated on a support to give a self-supporting gel film having a residual volatile content within the range of 15-45%, which is imidated to give a polyimide film having an exothermic peak temperature at 250°C or higher resulting from crystallization as measured by differential scanning calorimetry (DSC), a YI of at most 23 and a haze of at most 5%.

Description

The present invention relates to a polyimide film having excellent transparency. In particular, by controlling the amount of residual volatile components within an appropriate range, it is possible to suppress the occurrence of haze even in crystalline polyimides that are susceptible to thermal history, and products or members that have high requirements for heat resistance and transparency The present invention relates to a polyimide film that can be suitably used as a material for forming (for example, substitute for display glass).

In recent years, with the rapid progress of displays such as liquid crystal, organic EL, and electronic paper, and electronics such as solar cells and touch panels, devices have been required to be thinner and lighter, and more flexible. . In these devices, various electronic elements such as thin transistors and transparent electrodes are formed on a glass plate. By changing this glass material to a film material, the panel itself becomes flexible, thin and lightweight. Can be achieved. The film material used in this application is required to have heat resistance in the formation process of the electronic element.

  As a general film material excellent in heat resistance, a polyimide film can be mentioned. Polyimide films are widely used in electronic devices and semiconductor applications, such as flexible printed wiring boards, taking advantage of their heat resistance and insulation. However, polyimide films are generally colored yellow and brown, and have a higher coefficient of linear expansion than glass. Therefore, transparency can be improved and a low coefficient of linear expansion can be realized to replace glass. It was a challenge. Attempts to solve these problems have been made in the past, for example, obtained from 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and 2,2′-bis (trifluoromethyl) benzidine. Polyimide is excellent in transparency in addition to heat resistance and linear expansion coefficient, and there have been several reports so far (see, for example, Patent Document 1).

  Depending on the combination of the raw material diamine and acid dianhydride, the polyimide may exhibit crystallinity. A polyimide obtained from the above 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and 2,2'-bis (trifluoromethyl) benzidine also exhibits crystallinity. When crystal grains are formed by crystallization, haze is generated by light scattering depending on the size. Since conventional polyimides are mainly used for molded products and wiring boards, even if haze is generated, there has been no major problem. However, when used as a glass substitute, when haze is generated, the light transmittance is lowered, and thus means for suppressing the generation of haze has been demanded.

JP 2007-46054 A

  This invention is made | formed in view of the above, Comprising: The objective is to provide the polyimide film with which haze was suppressed, and its manufacturing method.

As a result of intensive studies in view of the above problems, the present inventors have found that the haze of the resulting film can be reduced by controlling the amount of residual volatile components during the formation of the polyimide film, and the present invention has been completed. It was.
That is, the present invention has the following configuration.

  1). A polyimide film having an exothermic peak derived from crystallization by differential scanning calorimetry (DSC) at 250 ° C. or more, YI of 23 or less, and haze of 5% or less.

  2). A solution containing polyamic acid obtained by reacting an aromatic diamine and an aromatic dianhydride in an organic solvent is cast and heated on a support to obtain a self-supporting gel film. The polyimide film as described in 1), which is imidized by heating.

  3). 2. The polyimide film as described in 2), wherein the amount of residual volatile components of the gel film obtained by the following formula is in the range of 15 to 45%.

(Formula); (AB) / B × 100 (%)
(A: weight of gel film, B: weight of residue after heating gel film at 350 ° C. for 10 minutes)
4). The polyimide film according to 2) or 3), wherein the maximum temperature during imidization is (exothermic peak temperature derived from crystallization + 50) ° C. or less.

  5). The initial temperature at the time of imidization is (exothermic peak temperature due to crystallization−200) ° C. or higher to (exothermic peak temperature derived from crystallization−80) ° C. or lower, 2) to 4) The polyimide film according to any one of the above.

  6). A polyamic acid solution obtained by reacting an aromatic diamine and an aromatic dianhydride in an organic solvent is cast and heated on a support, and the amount of residual volatile components is in the range of 15 to 45%. The method for producing a polyimide film according to any one of 1) to 5), wherein the gel film is obtained and then imidized.

Generation | occurrence | production of haze is suppressed and the polyimide film obtained by this invention is used suitably for the use as which transparency and heat resistance are calculated | required simultaneously.

  Embodiments of the present invention will be described below.

<Polyamide acid>
The polyimide film according to the present invention is obtained by imidizing a polyamic acid obtained by reacting an aromatic diamine and an aromatic dianhydride in an organic solvent. The polyimide film according to the present invention preferably has a rigid structure as the aromatic diamine component and / or aromatic dianhydride component in order to realize a low linear expansion coefficient. Furthermore, it is preferable to use what has an electron withdrawing group from the point which improves the transparency of the polyimide film obtained. Examples of the electron withdrawing group include halogen and halogenated hydrocarbon. Among them, mention may be made of fluorinated hydrocarbons, in particular methyl trifluoride. It is preferable to use an aromatic diamine component and / or an aromatic acid dianhydride component having these electron-withdrawing groups. Among aromatic diamine components having an electron withdrawing group and / or aromatic dianhydride components, it is preferable to use a component having an electron withdrawing group in the diamine component.

  When a diamine having an electron withdrawing group is used as the aromatic diamine component, the proportion of the diamine having an electron withdrawing group in the aromatic diamine component is 50 to 100% by weight, more preferably 70 to 100% by weight, and particularly the total amount. It is preferable to use an aromatic diamine having an electron-withdrawing group from the viewpoint of improving the transparency of the resulting polyimide.

  Specific examples of suitable raw materials include p-phenylenediamine, 2,2′-bis (trifluoromethyl) benzidine, 2,2-di (3-aminophenyl) -1,1,1,3 as aromatic diamines. , 3,3-hexafluoropropane, 2,2-di (4-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 2- (3-aminophenyl) -2- (4 -Aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [3- (3-aminophenoxy) phenyl] -1,1,1,3,3,3- Hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2′-dimethylbenzidine, 4,4′- And diaminodiphenyl sulfone. .

  Examples of the aromatic dianhydride include pyromellitic dianhydride and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride. These aromatic diamines and aromatic acid dianhydrides may be used alone or in combination of two or more.

  Any known method can be used for producing the polyamic acid. Usually, aromatic dianhydride and aromatic diamine are dissolved in an organic solvent in a substantially equimolar amount, and polymerization of the acid dianhydride and diamine is completed under controlled temperature conditions. Produced by stirring until.

  A conventionally known organic solvent can be used as the solvent for the polyamic acid polymerization, but amides such as N, N-dimethylformamide and N, N-dimethylacetamide are considered in consideration of the solubility of the raw material and the produced polyamic acid. System solvents can be suitably used. N, N-dimethylacetamide is preferred in view of the fact that coloring of the resulting polyimide film can be suppressed.

  Regarding the concentration of the polyamic acid solution at the time of synthesis, a lower concentration is preferable because the amount of the solvent contained in the polyamic acid solution increases and the mixing property with the imidization accelerator is improved. However, if the concentration is too low, it is difficult to produce a thick film. The concentration of the polyamic acid solution is preferably 5 to 30% by weight, and more preferably 10 to 25% by weight.

  Moreover, about the viscosity of a polyamic-acid solution, since the lower one improves a miscibility with an imidation promoter, it is preferable. However, since lowering the viscosity leads to lowering the molecular weight of the polyamic acid, the resulting film may not exhibit the desired mechanical strength. When considering both compatibility and ensuring film strength, the viscosity of the polyamic acid solution is preferably 1000 to 3500 poise, and more preferably 1500 to 3000 poise. On the other hand, the viscosity of the polyamic acid depends on the concentration. If the molecular weight is the same, the lower the concentration, the lower the viscosity. Therefore, the concentration of the polyamic acid may be adjusted so as to obtain a desired viscosity. However, in order to obtain a film having sufficient strength, the weight average molecular weight of the polyamic acid is preferably at least 100,000 or more.

<Imidation accelerator>
As a method of imidizing a polyimide film, a method of imidizing only by heating, a method of imidizing by adding an imidization catalyst, an imidization accelerator composed of an imidization catalyst and a dehydrating agent, and heating imidization The method of doing is mentioned. The method of adding an imidization accelerator has the highest imidization rate, so that productivity is excellent, and the linear expansion coefficient of the obtained film tends to be low. On the other hand, since the reaction rate is high, it is necessary to sufficiently cool the entire reaction system, which is disadvantageous in that it has poor long run properties. Which method is used may be appropriately selected in view of productivity and the like.

  As the imidization catalyst, tertiary amines such as aliphatic tertiary amines, aromatic tertiary amines, and heterocyclic tertiary amines can be suitably used. Among them, it is preferable to use any of β-picoline, imidazole, and 3,5-diethylpyridine from the balance between the catalytic ability and the film colorability.

  Examples of the dehydrating agent include aliphatic acid anhydrides such as acetic anhydride, and aromatic acid anhydrides such as phthalic anhydride. These dehydrating agents are preferably used alone or in combination.

  What is necessary is just to set suitably about the addition amount of an imidation promoter in consideration of the characteristic and production conditions of the film obtained. If the amount of the dehydrating agent and the imidization catalyst is intentionally illustrated, it is preferable that the number of moles of dehydrating agent / number of moles of amide groups in polyamic acid = 10 to 0.01, and the number of moles of amide groups in polyamic acid = 10 to 0. .01 is preferred. More preferably, the number of moles of dehydrating agent / the number of moles of amide groups in the polyamic acid is preferably 5 to 0.5, and the number of moles of amide groups in the imidization catalyst / polyamic acid is preferably 5 to 0.5.

<Film>
The polyimide film of the present invention can be obtained by forming a dope solution obtained by mixing a polyamic acid and an imidization accelerator into a film. A conventionally known apparatus / system can be used as the molding method. As a preferred example, it is possible to use a method in which the dope solution is extruded from a T die or the like onto a support such as a rotating drum or an endless belt. The cast polyamic acid solution is heated on the support to volatilize the solvent, and then imidization proceeds to some extent to obtain a self-supporting raw dry film (referred to as a gel film in this application). A polyimide film can be obtained by peeling off from the support and passing through a heating furnace with both ends in the width direction fixed to complete the removal of the remaining solvent and imidization.

  On the other hand, if you want to obtain a laminate of polyimide film and glass or metal foil, cast and heat the dope solution onto glass or metal foil to form a gel film, and then heat it without peeling off from the substrate. Removal and imidization may be completed. Needless to say, a polyimide film may be produced alone and then thermocompression bonded with glass or metal foil to form a laminate.

  Regardless of which means is used, it is very important to control the amount of residual volatile components of the gel film in order to suppress the haze of the resulting polyimide film. That is, it is necessary to make the amount of residual volatile components of the gel film calculated | required by a following formula into the range of 15 to 45 weight%. The range is preferably 20 to 40% by weight, more preferably 20 to 30% by weight.

(Formula); (AB) / B × 100 (%)
(A: weight of gel film, B: weight of residue after heating the gel film at 350 ° C. for 10 minutes).

  When the residual volatile component amount of the gel film is higher than the above range, it may be difficult to suppress haze of the obtained polyimide film. Conversely, when lower than the said range, the intensity | strength of a gel film falls and it may become difficult to produce a thick film.

The reason why the haze of the polyimide film obtained by controlling the residual volatile component amount of the gel film can be suppressed will be described below.
The polyimide film according to the present invention can be obtained by imidizing the precursor polyamic acid. At the gel film stage, a part of the polyamic acid is imidized, but since the heating temperature is not so high, the solvent remains in a large amount and is partially imidized in an almost amorphous state. By heating at a higher temperature from here, volatile components such as a solvent are removed from the film and imidization proceeds, but a large amount of volatile components such as a solvent remain in the initial stage of heating.

  Therefore, due to the plasticizer effect of these residual volatile components, the apparent crystallization temperature (Tc) is lowered in the step of baking the gel film at a high temperature to completely imidize it, and it is heated at a temperature lower than Tc. Nevertheless, the portion that has been imidized at the stage of the gel film is crystallized. As a result, haze is generated in the obtained polyimide film. By reducing the amount of residual volatile components in the gel film, the plasticizer effect can be suppressed and crystallization during heating can be suppressed, so that haze of the resulting polyimide film can be suppressed.

  In the present invention, a polyimide film having an exothermic peak derived from crystallization at 250 ° C. or more can obtain a polyimide film having a small YI together with haze by setting the amount of residual volatile components in this gel film stage to a specific range. It was something that was found.

  The amount of residual volatile components of the gel film can be controlled by the heating temperature and the heating time during gel film production. If the heating temperature is raised, the amount of residual volatile components can be lowered in a short time, which is preferable in terms of productivity. However, if the temperature is too high, crystallization proceeds at the same time when the gel film is produced, so the resulting polyimide The haze of a film may become high. The heating temperature during gel film production is preferably in the range of 60 to 180 ° C, more preferably in the range of 70 to 160 ° C.

The heating time is preferably in the range of 30 to 1000 seconds, and more preferably in the range of 90 to 800 seconds. Since the amount of residual volatile components varies depending on the thickness of the gel film even under the same heating conditions, it may be adjusted as appropriate within the above range. The heating temperature may be a single temperature, but it is preferable to heat in a plurality of steps because the amount of residual volatile components in the gel film can be easily controlled.
As temperature conditions in that case, when using an apparatus having two heating furnaces, for example, 60-100 ° C and 90-180 ° C, and further, 80-100 ° C and 90-160 ° C are successively increased in temperature. Heating under such a plurality of temperature conditions is preferable because the amount of residual volatile components in the gel film can be easily controlled.

  The polyimide film of the present invention is obtained by further heating the gel film obtained above at a high temperature. Conventionally known devices can be used as the heating device, but in consideration of productivity, it is preferable to use a plurality of heating furnaces or a device provided with a plurality of temperature steps in the heating furnace. At this time, in order to prevent film shrinkage at the time of solvent volatilization, it is preferable to fix the film end with a clip or a pin. However, in the case where polyimide is directly formed on a substrate such as a glass plate or a metal foil, this is not the case because the gel film is in close contact with the substrate and shrinkage is suppressed.

The maximum temperature during heating is preferably (exothermic peak temperature derived from crystallization + 50) ° C. or lower. More preferably, the temperature is (exothermic peak temperature derived from crystallization + 30) ° C. or lower. The lower limit of the maximum temperature is preferably (exothermic peak temperature derived from crystallization−40) ° C. or higher. More preferably, the temperature is (exothermic peak temperature derived from crystallization−20) ° C. or higher.
When higher than the said temperature, crystallization advances during a heating and the haze of the polyimide film obtained may become high. Moreover, when the gel film is suddenly heated at the maximum temperature, crystallization may proceed due to the plasticizer effect of the solvent even if the temperature is not higher than the above temperature. On the other hand, when the temperature is lower than the above temperature, the possibility that the above problem occurs is suppressed because the heating is performed at a temperature lower than the crystallization temperature. However, since the temperature is low, it is difficult to remove residual volatile components. In order to compensate for this, it is necessary to increase the length of the heating furnace or increase the residence time by lowering the line speed, which is problematic in terms of equipment cost and productivity. The heating is preferably performed in a plurality of stages from the low temperature side.

  At this time, lowering the initial heating temperature is preferable because crystallization is less likely to occur, but lowering the initial temperature setting increases the temperature difference from the maximum temperature, so the heating furnace may be lengthened to prevent sudden temperature changes. There are problems in terms of equipment cost and productivity because it is necessary to increase the temperature step by increasing the number of heating furnaces or to increase the residence time by reducing the line speed. In the present application, by appropriately controlling the amount of residual volatile components of the gel film, it is possible to suppress the occurrence of haze even if the initial heating temperature is increased to some extent.

From the above, the initial heating temperature is preferably (exothermic peak temperature derived from crystallization−200) ° C. or higher to (exothermic peak temperature derived from crystallization−80) ° C. or lower, and (derived from crystallization). More preferably, the exothermic peak temperature is −150) ° C. or higher and the exothermic peak temperature derived from crystallization is −100) ° C. or lower.
The heating time may be appropriately set in consideration of the thickness of the film and the temperature setting. However, considering the productivity, the heating time is preferably in the range of 30 to 4000 seconds, and is preferably in the range of 100 to 2000 seconds. Further preferred.

When using a method in which multiple heating furnaces are used or multiple temperature steps are provided in the heating furnace to raise the heating temperature in multiple stages, the heating time is the lowest heating temperature in the initial stage of imidization. Conditioning time: Time of highest temperature condition in imidation = 1: 0.5 to 1: 2.5, more preferably 1: 0.8 to 1: 2.
Regarding the temperature drop after heating, in order to reduce the hysteresis of the obtained film, it is preferable to lower the temperature by providing a heating furnace having a temperature condition lower than the maximum temperature after heating at the highest temperature condition. The temperature and time can be appropriately selected and employed.

  The exothermic peak temperature (crystallization temperature, Tc) derived from the crystallization of the polyimide film is controlled to be 250 ° C. or higher, but is preferably controlled to 280 ° C. or higher, more preferably 300 ° C. or higher. When the Tc of the polyimide film is lower than the above range, the apparent Tc in the gel film state containing the residual volatile component becomes very low. Therefore, even if the residual volatile component amount of the gel film is controlled to be low, the resulting polyimide The haze of the film may not be suppressed. The upper limit of Tc is not particularly limited, but the higher the Tc, the higher the maximum heating temperature. Therefore, imidization at a high temperature in a short time is possible, which is excellent in productivity. Since Tc is derived from the primary structure of polyimide, it can be controlled by changing the combination of aromatic diamine and aromatic dianhydride as raw materials.

  In order to prevent long-time transportability and blocking during winding, inorganic particles may be added to the polyimide film according to the present invention as an anti-blocking material. The material of the inorganic particles is not particularly limited. However, when inorganic particles having a large particle diameter are added, the transmitted light is scattered and the haze of the film is increased. Therefore, the size of the inorganic particles is preferably 100 nm or less.

  The addition amount of the inorganic particles can be appropriately selected in consideration of the haze of the obtained film. Regarding the addition method, it may be added to the polyamic acid solution during the polymerization of the polyamic acid, or may be added to the imidization accelerator during the preparation of the imidization accelerator.

  The polyimide film of the present invention can achieve transparency and heat resistance suitable as a glass substitute material by the above means. Specifically, YI is 23 or less and haze is 5% or less. In order to be suitably used as a film member, YI can be 20 or less, haze can be 3% or less, particularly YI can be 18 or less, and haze can be 2.5% or less.

  Since the polyimide film according to the present invention has high transparency and dimensional stability in addition to the original properties of polyimide such as heat resistance and insulation, fields and products in which these properties are effective, for example, inorganic Film member having thin film or inorganic microstructure on its surface, for example, film for thin film transistor, color filter film, film with transparent electrode, gas barrier film, inorganic glass or organic glass formed from silicon, metal oxide or organic substance It can be applied to films with laminated films.

  These members can be used for films for liquid crystal displays, films for organic EL, films for electronic paper, films for solar cells, films for touch panels, and the like.

EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to these. In addition, the evaluation method of the crystallization temperature, YI, haze, and polyamic acid molecular weight of the polyimide film in an Example and a comparative example is as follows.

<Crystalization temperature>
The crystallization temperature of the film was measured using a differential scanning calorimeter Q200 manufactured by TA Instruments. The measurement was performed using a 10 mg sample in a modulation measurement mode at a temperature range of 0 to 400 ° C. with a temperature amplitude of 1 ° C., a temperature cycle of 60 seconds, and a temperature increase rate of 3 ° C./min. The obtained heat flow was separated into a reversible component and an irreversible component, and the exothermic peak temperature of the irreversible component was defined as the crystallization temperature.

<YI>
The YI of the film was measured using HANDY COLORIMTER NR-3000 manufactured by Nippon Denshoku Industries Co., Ltd. The measurement was performed at five locations by changing the position of an 18 cm square sample, and the average value was taken as the measured value of the film.

<Haze>
The haze of the film was performed using a Nippon Denshoku Industries Co., Ltd. haze meter NDH5000. The measurement was performed at five locations by changing the position of an 18 cm square sample, and the average value was taken as the measured value of the film.

<Polyamic acid molecular weight>
The weight average molecular weight (Mw) of the polyamic acid was measured using a Waters GPC under the following conditions: (column: KD-806M 2 manufactured by Shodex, temperature 60 ° C., detector: RI, flow rate: 1 ml / min, Developing solution: DMF (lithium bromide 0.03 M, phosphoric acid 0.03 M), sample concentration: 0.2 wt%, injection amount: 20 μl, reference substance: polyethylene oxide).

(Synthesis Example 1: Synthesis of polyamic acid solution)
In a reactor maintained at 20 ° C. under a nitrogen atmosphere, 758.5 g of N, N-dimethylacetamide (hereinafter referred to as “DMAc”) was added, and 3,3 ′, 4,4′-biphenyltetracarboxylic acid dihydrate was stirred with stirring. 95.8 g of anhydride (hereinafter referred to as BPDA) was added. While stirring, 83.4 g of 2,2′-bis (trifluoromethyl) benzidine (hereinafter referred to as TFMB) was added.

  Stirring was continued for 2 hours. After visually confirming that there was no undissolved residue, 17.7 g of TFMB was added, and the mixture was further stirred for 1 hour. A solution in which TFMB was dissolved in DMF at a solid content of 7% by weight was prepared separately, and 41.6 g of this solution was gradually added to the reaction system. After completion of the addition, stirring was continued for 40 hours to obtain a polyamic acid solution having a viscosity of 2000 poise and a solid content concentration of 20%. The weight average molecular weight of the polyamic acid was 120,000.

Example 1
To the polyamic acid solution obtained in Synthesis Example 1, an imidization accelerator composed of acetic anhydride / β-picoline / DMAc (weight ratio 10/3/1) was added at a weight ratio of 35% with respect to the polyamic acid solution. The mixture was stirred with a mixer, extruded from a T-die, and cast onto a stainless steel endless belt. After heating this resin film at 150 ° C. × 350 seconds, the self-supporting gel film is peeled off from the endless belt and fixed to the tenter clip, and each of them is carried out at 200 ° C., 250 ° C., 300 ° C., 320 ° C., and 200 ° C. for 35 seconds. Each was dried and imidized to obtain a polyimide film having a thickness of 50 μm. The exothermic peak temperature derived from crystallization of the film was 330 ° C.

(Example 2)
To the polyamic acid solution obtained in Synthesis Example 1, an imidization accelerator composed of acetic anhydride / β-picoline / DMAc (weight ratio 10/3/1) was added at a weight ratio of 35% with respect to the polyamic acid solution. The mixture was stirred with a mixer, extruded from a T-die, and cast on a 125 μm-thick PET film (Lumirror, Toray). After heating the resin film at 80 ° C. for 300 seconds and 150 ° C. for 300 seconds, the self-supporting gel film is peeled off from the PET film and fixed to the tenter clip, and dried and imidized under the same conditions as in Example 1. A polyimide film having a thickness of 50 μm was obtained.

(Example 3)
An imidization accelerator composed of imidazole / DMAc / toluene (weight ratio 1/5/6) was added to the polyamic acid solution obtained in Synthesis Example 1 at a weight ratio of 50% with respect to the polyamic acid solution, and continuously mixed. And then extruded from a T-die and cast on a glass plate having a thickness of 1 mm. After heating this resin film at 80 ° C. × 240 seconds and 140 ° C. × 360 seconds, it is dried and imidized at 200 ° C., 250 ° C., 300 ° C., 320 ° C., and 200 ° C. for 60 seconds each while being in close contact with the glass plate. A laminate of a polyimide film having a thickness of 10 μm and a glass plate was obtained.

(Comparative Example 1)
To the polyamic acid solution obtained in Synthesis Example 1, an imidization accelerator composed of acetic anhydride / β-picoline / DMAc (weight ratio 10/3/1) was added at a weight ratio of 35% with respect to the polyamic acid solution. The mixture was stirred with a mixer, extruded from a T-die, and cast onto a stainless steel endless belt. After heating this resin film at 100 ° C. for 350 seconds, the self-supporting gel film is peeled off from the endless belt and fixed to the tenter clip, dried and imidized under the same conditions as in Example 1, and a polyimide film having a thickness of 50 μm Got.

(Comparative Example 2)
To the polyamic acid solution obtained in Synthesis Example 1, an imidization accelerator composed of imidazole / DMAc (weight ratio 1/11) was added at a weight ratio of 50% with respect to the polyamic acid solution. The product was extruded from a die and cast on a glass plate having a thickness of 1 mm. The resin film was heated at 80 ° C. × 240 seconds, 120 ° C. × 360 seconds, and then dried and imidized under the same conditions as in Example 3 while being in close contact with the glass plate, and a laminate of a 10 μm thick polyimide film and glass plate Got.

(Comparative Example 3)
To the polyamic acid solution obtained in Synthesis Example 1, an imidization accelerator composed of acetic anhydride / β-picoline / DMAc (weight ratio 10/3/1) was added at a weight ratio of 35% with respect to the polyamic acid solution. The mixture was stirred with a mixer, extruded from a T die, and cast on a glass plate having a thickness of 1 mm. The resin film was heated at 80 ° C. for 60 minutes under reduced pressure, and then the self-supporting gel film was peeled off from the glass plate and fixed to the tenter clip, and dried and imidized under the same conditions as in Example 1. However, the film was broken on the way, and a polyimide film could not be obtained.

  The evaluation results of the obtained film are shown in Table 1. By suppressing the amount of residual volatile components of the gel film within an appropriate range, it was possible to suppress YI and haze of the obtained polyimide.

Claims (6)

  A polyimide film having an exothermic peak derived from crystallization by differential scanning calorimetry (DSC) at 250 ° C. or more, YI of 23 or less, and haze of 5% or less.   A solution containing polyamic acid obtained by reacting an aromatic diamine and an aromatic dianhydride in an organic solvent is cast and heated on a support to obtain a self-supporting gel film. The polyimide film according to claim 1, which is imidized by heating. The polyimide film according to claim 2, wherein the residual volatile component amount of the gel film obtained by the following formula is in the range of 15 to 45%.
(Formula); (AB) / B × 100 (%)
(A: weight of gel film, B: weight of residue after heating gel film at 350 ° C. for 10 minutes)   4. The polyimide film according to claim 2, wherein the maximum temperature during imidization is (exothermic peak temperature derived from crystallization + 50) ° C. or less. 5.   The initial temperature at the time of imidation is (exothermic peak temperature due to crystallization-200) ° C. or higher to (exothermic peak temperature derived from crystallization−80) ° C. or lower. The polyimide film according to any one of the above.   A polyamic acid solution obtained by reacting an aromatic diamine and an aromatic dianhydride in an organic solvent is cast and heated on a support, and the amount of residual volatile components is in the range of 15 to 45%. The polyimide film production method according to any one of claims 1 to 5, wherein the polyimide film is imidized after obtaining a conductive gel film.