JP2017025204A - Polyimide film, and method for producing polyimide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyimide film having high peelability from base material and capable of preventing the occurrence of a poor appearance, and a method of producing the same.SOLUTION: The polyimide film comprises polyimide and at least one selected from the group consisting of γ butyrolactone and N, N-dimethyl acetamide, and has a yellowness of 10 or less. When a mass ratio of the γ butyrolactone is G(ppm) and a mass ratio of the N, N-dimethyl acetamide is D(ppm), the polyimide film satisfies 30≤G+D≤10000.SELECTED DRAWING: None

Description

  The present invention relates to a polyimide film and a method for producing a polyimide film.

  Conventionally, glass has been used as a base material for various display members such as solar cells and displays. However, glass has a drawback that it is easy to break and is heavy, and has not yet had a sufficient material for thinning and lightening the display and making it flexible in recent years. Therefore, a polyimide film has been studied as a transparent member of a flexible device that replaces glass (see, for example, Patent Documents 1 and 2).

US Pat. No. 8,207,256 JP 2008-163309 A

  However, conventional polyimide-based films are not sufficiently peelable from the base material and may have poor appearance.

  This invention is made | formed in view of the said subject, and it aims at providing the polyimide-type film which can implement | achieve a favorable external appearance defect with high peelability from a base material, and its manufacturing method.

The polyimide film according to the present invention includes a polyimide polymer,
It contains at least one selected from the group consisting of γ-butyrolactone and N, N-dimethylacetamide, and has a yellowness of 10 or less. When the mass ratio of γ-butyrolactone is G (ppm) and the mass ratio of N, N-dimethylacetamide is D (ppm), 30 ≦ G + D ≦ 10000 is satisfied.

  Here, the film preferably has a haze of 1 or less.

  The film preferably has a total light transmittance of 85% or more.

The method for producing a polyimide film according to the present invention includes:
(A) applying at least one of γ-butyrolactone and N, N-dimethylacetamide and a liquid containing a polyimide polymer to a substrate;
(B) drying the applied liquid to form a film.
When the mass ratio of γ-butyrolactone in the film is G (ppm) and the mass ratio of N, N-dimethylacetamide is D (ppm), the film after the step (b) is 30 ≦ G + D ≦ 10000. Meet.

  ADVANTAGE OF THE INVENTION According to this invention, the polyimide-type film which has high peelability from a base material and can implement | achieve a favorable external appearance, and its manufacturing method are provided.

(Polyimide film)
The polyimide film includes at least one selected from the group consisting of a polyimide polymer and γ-butyrolactone and N, N-dimethylacetamide.
In this specification, the polyimide polymer means a polymer containing at least one repeating structural unit represented by the formula (PI), the formula (a), the formula (a ′) or the formula (b).

G in the formula (PI) represents a tetravalent organic group, and A represents a divalent organic group. G ² in the formula (a) represents a trivalent organic group, and A ² represents a divalent organic group. G ³ in the formula (a ′) represents a tetravalent organic group, and A ³ represents a divalent organic group. G ⁴ and A ⁴ in the formula (b) each represent a divalent organic group.

  Examples of G in the formula (PI) include a tetravalent organic group selected from the group consisting of an acyclic aliphatic group, a cyclic aliphatic group, and an aromatic group. From the viewpoint of the transparency and flexibility of the resin film 10, G is preferably a cyclic aliphatic group or an aromatic group. Examples of the aromatic group include a monocyclic aromatic group, a condensed polycyclic aromatic group, and a non-condensed polycyclic aromatic group in which aromatic groups are connected to each other directly or through a bonding group. From the viewpoint of transparency of the resin film and suppression of coloring, G is a cyclic aliphatic group, a cyclic aliphatic group having a fluorine-based substituent, a monocyclic aromatic group having a fluorine-based substituent, or a fluorine-based substitution. It is preferably a condensed polycyclic aromatic group having a group or a non-condensed polycyclic aromatic group having a fluorine-based substituent.

  In this specification, the fluorine-based substituent means a group containing a fluorine atom. The fluorine-based substituent is preferably a fluoro group (fluorine atom, -F) and a perfluoroalkyl group, more preferably a fluoro group and a trifluoromethyl group.

More specifically, G represents, for example, a saturated or unsaturated cycloalkyl group, a saturated or unsaturated heterocycloalkyl group, an aryl group, a heteroaryl group, an arylalkyl group, an alkylaryl group, a heteroalkylaryl group, and , Selected from groups having any two of these groups (which may be the same), which are connected to each other directly or by a linking group. As the linking group, —O—, an alkylene group having 1 to 10 carbon atoms, —SO ₂ —, —CO— or —CO—NR— (wherein R represents a methyl group, an ethyl group, a propyl group, etc. 3 represents an alkyl group or a hydrogen atom).

  The carbon number of G is usually 2 to 32, preferably 4 to 15, more preferably 5 to 10, and further preferably 6 to 8. When G is a cycloaliphatic group or an aromatic group, some of the carbon atoms may be replaced with heteroatoms. Heteroatoms include O, N, or S.

Specific examples of G include groups represented by the following formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), or formula (26). It is done. * In the formula indicates a bond. Z in Formula (26) is a single bond, —O—, —CH ₂ —, —C (CH ₃ ) ₂ —, —Ar—O—Ar—, —Ar—CH ₂ —Ar—, —Ar—. C _{(CH 3)} represents a 2 -Ar- or _-Ar-SO 2 -Ar-. Ar represents an aryl group having 6 to 20 carbon atoms, and examples thereof include a phenylene group. At least one of the hydrogen atoms of these groups may be substituted with a fluorine-based substituent.

  A in the formula (PI) may be a divalent organic group selected from the group consisting of an acyclic aliphatic group, a cyclic aliphatic group, and an aromatic group. The divalent organic group represented by A is preferably a cyclic aliphatic group or an aromatic group. Examples of the aromatic group include a monocyclic aromatic group, a condensed polycyclic aromatic group, and a non-condensed polycyclic aromatic group having two or more aromatic rings and connected to each other directly or by a bonding group. Groups. From the viewpoint of transparency of the resin film and suppression of coloring, it is preferable that a fluorine-based substituent is introduced into at least a part of A.

More specifically, A represents, for example, a saturated or unsaturated cycloalkyl group, a saturated or unsaturated heterocycloalkyl group, an aryl group, a heteroaryl group, an arylalkyl group, an alkylaryl group, a heteroalkylaryl group, and , Selected from groups having any two of these groups (which may be the same), which are connected to each other directly or by a linking group. Examples of the hetero atom include O, N, or S, and examples of the bonding group include —O—, an alkylene group having 1 to 10 carbon atoms, —SO ₂ —, —CO—, or —CO—NR— (R represents methyl. Group, an alkyl group having 1 to 3 carbon atoms such as an ethyl group or a propyl group, or a hydrogen atom).

  Carbon number of the bivalent organic group represented by A is 2-40 normally, Preferably it is 5-32, More preferably, it is 12-28, More preferably, it is 24-27.

Specific examples of A include groups represented by the following formula (30), formula (31), formula (32), formula (33), or formula (34). * In the formula indicates a bond. Z ^{1 to} Z ³ are each independently a single bond, —O—, —CH ₂ —, —C (CH ₃ ) ₂ —, —SO ₂ —, —CO— or —CO—NR— (R is Represents a C 1-3 alkyl group such as a methyl group, an ethyl group, or a propyl group, or a hydrogen atom. In the following groups, Z ¹ and Z ² , and Z ² and Z ³ are each preferably in the meta position or the para position with respect to each ring. Further, it is preferable that Z ¹ and the single bond at the end, Z ² and the single bond at the end, and Z ³ and the single bond at the end are in the meta position or the para position. In one example, Z ¹ and Z ³ are —O— and Z ² is —CH ₂ —, —C (CH ₃ ) ₂ — or —SO ₂ —. One or two or more hydrogen atoms of these groups may be substituted with a fluorine-based substituent.

  In at least one of A and G, at least one hydrogen atom is substituted with at least one functional group selected from the group consisting of a fluorine-based substituent, a hydroxyl group, a sulfone group, an alkyl group having 1 to 10 carbon atoms, and the like. May be. In addition, when A and G are each a cyclic aliphatic group or an aromatic group, it is preferable that at least one of A and G has a fluorine-based substituent, and both A and G have a fluorine-based substituent. It is more preferable.

G ² in formula (a) can be selected from the same groups as G in formula (PI) except that it is a trivalent group. For example, G ² may be a group in which any one of the four bonds in the groups represented by Formula (20) to Formula (26) exemplified as specific examples of G is replaced with a hydrogen atom. . A ² in formula (a) can be selected from the same groups as A in formula (PI).

G ³ in formula (a ′) can be selected from the same groups as G in formula (PI). A ³ in formula (a ′) can be selected from the same groups as A in formula (PI).

G ⁴ in formula (b) can be selected from the same groups as G in formula (PI) except that it is a divalent group. For example, G ⁴ may be a group in which any two of the four bonds in the groups represented by formulas (20) to (26) exemplified as specific examples of G are replaced with hydrogen atoms. . A ⁴ in formula (b) can be selected from the same groups as A in formula (PI).

  The polyimide polymer contained in the resin film 10 is composed of a diamine and a tetracarboxylic acid compound (including tetracarboxylic acid compound analogs such as an acid chloride compound and tetracarboxylic dianhydride) or a tricarboxylic acid compound (acid chloride compound). And a condensed polymer obtained by polycondensation with at least one of tricarboxylic acid compound analogs such as tricarboxylic acid anhydride). Further, dicarboxylic acid compounds (including analogs such as acid chloride compounds) may be polycondensed. The repeating structural unit represented by the formula (PI) or the formula (a ′) is usually derived from a diamine and a tetracarboxylic acid compound. The repeating structural unit represented by the formula (a) is usually derived from diamines and tricarboxylic acid compounds. The repeating structural unit of the formula (b) is usually derived from diamines and dicarboxylic acid compounds.

  Examples of the tetracarboxylic acid compound include aromatic tetracarboxylic acid compounds, alicyclic tetracarboxylic acid compounds, and acyclic aliphatic tetracarboxylic acid compounds. Two or more of these may be used in combination. The tetracarboxylic acid compound is preferably tetracarboxylic dianhydride. Examples of tetracarboxylic dianhydrides include aromatic tetracarboxylic dianhydrides, alicyclic tetracarboxylic dianhydrides, and acyclic aliphatic tetracarboxylic dianhydrides.

  From the viewpoint of solubility in a solvent, transparency when the resin film 10 is formed, and flexibility, the tetracarboxylic acid compound is preferably an alicyclic tetracarboxylic compound, an aromatic tetracarboxylic acid compound, or the like. From the viewpoint of transparency of the resin film and suppression of coloring, the tetracarboxylic acid compound is preferably an alicyclic tetracarboxylic acid compound having a fluorine-based substituent and an aromatic tetracarboxylic acid compound having a fluorine-based substituent. More preferably, it is an alicyclic tetracarboxylic acid compound.

  Examples of the tricarboxylic acid compounds include aromatic tricarboxylic acids, alicyclic tricarboxylic acids, acyclic aliphatic tricarboxylic acids, and related acid chloride compounds, acid anhydrides, and the like. The tricarboxylic acid compounds are preferably aromatic tricarboxylic acids, alicyclic tricarboxylic acids, acyclic aliphatic tricarboxylic acids, and related acid chloride compounds. Two or more tricarboxylic acid compounds may be used in combination.

  From the viewpoint of solubility in a solvent, transparency when the resin film 10 is formed, and flexibility, the tricarboxylic acid compound is preferably an alicyclic tricarboxylic acid compound and an aromatic tricarboxylic acid compound. From the viewpoint of transparency of the resin film and suppression of coloring, the tricarboxylic acid compound is preferably an alicyclic tricarboxylic acid compound having a fluorine-based substituent and an aromatic tricarboxylic acid compound having a fluorine-based substituent.

  Examples of the dicarboxylic acid compounds include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, acyclic aliphatic dicarboxylic acids, and related acid chloride compounds, acid anhydrides, and the like. The dicarboxylic acid compounds are preferably aromatic dicarboxylic acids, alicyclic dicarboxylic acids, acyclic aliphatic dicarboxylic acids, and related acid chloride compounds. Two or more dicarboxylic acid compounds may be used in combination.

  From the viewpoints of solubility in a solvent, transparency when the resin film 10 is formed, and flexibility, the dicarboxylic acid compound is preferably an alicyclic dicarboxylic acid compound and an aromatic dicarboxylic acid compound. From the viewpoint of transparency of the resin film and suppression of coloring, the dicarboxylic acid compound is more preferably an alicyclic dicarboxylic acid compound having a fluorine-based substituent and an aromatic dicarboxylic acid compound having a fluorine-based substituent.

  Examples of diamines include aromatic diamines, alicyclic diamines, and aliphatic diamines. Two or more diamines may be used in combination. From the viewpoints of solubility in a solvent, transparency when the resin film 10 is formed, and flexibility, the diamine is preferably an alicyclic diamine and an aromatic diamine having a fluorine-based substituent.

  The polyimide-based polymer may be a copolymer including a plurality of different types of the above repeating units. The weight average molecular weight of the polyimide polymer is usually 10,000 to 500,000. The weight average molecular weight of the polyimide polymer is preferably 50,000 to 500,000, more preferably 70,000 to 400,000. The weight average molecular weight is a standard polystyrene equivalent molecular weight measured by GPC. The higher the weight average molecular weight of the polyimide polymer, the easier it is to obtain higher flexibility, but if the weight average molecular weight of the polyimide polymer is too large, the viscosity of the varnish tends to increase and the workability tends to decrease. There is.

  The polyimide-based polymer may contain a halogen atom such as a fluorine atom that can be introduced by the above-described fluorine-based substituent. When the polyimide polymer contains a halogen atom, the elastic modulus of the resin film can be improved and the yellowness can be reduced. Thereby, it can suppress that a crack, wrinkles, etc. generate | occur | produce in a resin film, and can improve the transparency of a resin film. A halogen atom is preferably a fluorine atom. The content of halogen atoms in the polyimide polymer is preferably 1% by mass to 40% by mass, more preferably 1% by mass to 30% by mass, based on the mass of the polyimide polymer.

The resin film 10 may contain 1 type, or 2 or more types of ultraviolet absorbers. The ultraviolet absorber can be appropriately selected from those usually used as an ultraviolet absorber in the field of resin materials. The ultraviolet absorber may contain a compound that absorbs light having a wavelength of 400 nm or less. Examples of the ultraviolet absorber that can be appropriately combined with the polyimide polymer include at least one compound selected from the group consisting of benzophenone compounds, salicylate compounds, benzotriazole compounds, and triazine compounds. .
In the present specification, the “system compound” refers to a derivative of the compound to which the “system compound” is attached. For example, a “benzophenone compound” refers to a compound having benzophenone as a host skeleton and a substituent bonded to benzophenone.

  The amount of the ultraviolet absorber is usually 1% by mass or more, preferably 2% by mass or more, more preferably 3% by mass or more, and usually 10% by mass or less with respect to the total mass of the resin film. , Preferably it is 8 mass% or less, More preferably, it is 6 mass% or less. By including the ultraviolet absorber in these amounts, the weather resistance of the resin film 10 can be particularly effectively enhanced.

(Residual solvent)
The polyimide film has a mass ratio of γ-butyrolactone (hereinafter sometimes referred to as GBL) as G (ppm) and a mass ratio of N, N-dimethylacetamide (hereinafter sometimes referred to as DMAC) as D ( ppm), 30 ≦ G + D ≦ 10000 is satisfied.
Preferably, 100 ≦ G + D and G + D ≦ 8000. Either one of G and D may be zero.

  In addition, although a polyimide-type film can also contain other organic solvents, such as a dimethylformamide (DMF) and a dimethylsulfoxide (DMSO), it is preferable that these total mass ratios are 30 ppm or less.

(Inorganic particles)
The polyimide film can further contain inorganic particles from the viewpoint of increasing the strength. Examples of inorganic particles include particles containing silicon atoms, and examples of particles containing silicon atoms include silica particles. Other examples of inorganic particles include titania particles, alumina particles, zirconia particles, and the like.

  The average primary particle diameter of the inorganic particles is usually 10 nm to 100 nm, and preferably 20 nm to 80 nm. The reason why the average primary particle size of the inorganic particles is preferably within the above range is that the transparency of the film is improved when the average primary particle size is 100 nm or less, and the film has an average primary particle size of 10 nm or more. It is because the intensity | strength of improves. In addition, when the average primary particle diameter of the silica particles is 10 nm or more, the cohesive force of the silica particles is weakened, so that the handling tends to be easy. The measurement of the primary particle diameter can be an average value of 10 points of the fixed direction diameter by a transmission electron microscope (TEM).

  In the polyimide film, the mixing ratio of the polyimide and the inorganic particles is preferably 1: 9 to 10: 0, more preferably 3: 7 to 10: 0, more preferably 3: 7 to mass ratio. 8: 2 is more preferable, and 3: 7 to 7: 3 is even more preferable. When the compounding ratio of polyimide and inorganic particles is within the above range, transparency and mechanical strength tend to be improved.

  The inorganic particles may be bonded by molecules having a siloxane bond (—SiOSi—).

  The polyimide film may further contain other components as long as transparency and flexibility are not impaired. Examples of other components include antioxidants, mold release agents, stabilizers, bluing agents, flame retardants, lubricants, thickeners, and leveling agents.

  The polyimide film may also contain an organic silicon compound such as a quaternary alkoxysilane such as tetraethyl orthosilicate (TEOS) or a silsesquioxane derivative.

  Components other than the polyimide, the inorganic material, and the solvent are preferably more than 0% and 20% by mass or less, more preferably more than 0% and 10% by mass or less based on the mass of the resin film 10.

  Although the thickness of a polyimide-type film is suitably adjusted according to a use, it is 10 micrometers-500 micrometers normally, it is preferable that they are 15 micrometers-200 micrometers, and it is more preferable that they are 20 micrometers-100 micrometers.

The polyimide film preferably has a total light transmittance of 85% or more based on JIS K 7136: 2000, more preferably 90% or more.
In addition, the polyimide film has a haze based on JIS K 7136: 2000 of preferably 2 or less, more preferably 1 or less, and even more preferably 0.9 or less.
Further, this polyimide film has a yellowness YI based on JIS K 7373: 2006 of 10 or less, preferably 5 or less.
A haze of 2 or less means that the film is substantially transparent, and a YI of 10 or less means that the film is substantially colorless.

  Such a polyimide film is easy to peel from the film-forming substrate, and as a result, has an excellent appearance. The reason why the peelability from the substrate is easy is not clear, but the following reasons are conceivable. When G + D exceeds 10,000, the solvent with high wettability with respect to the film-forming substrate still remains, or the adhesiveness with the film-forming substrate is high, and the peelability becomes unstable. There is a tendency that appearance defects such as fold marks accompanying separation failure are likely to occur. On the other hand, when G + D is less than 30, the adhesiveness with the film-forming substrate tends to increase again, and it is considered that peeling becomes difficult.

(Production method)
Next, the manufacturing method of the polyimide-type film of this embodiment is demonstrated.
Using a known synthesis method such as polyimide, the polymerized solvent-soluble polyimide polymer is dissolved in a solvent to prepare a polyimide polymer varnish. Any polyimide-based polymer may be used as long as it is a solvent-soluble polyimide-based polymer.

  The solvent contains at least γ-butyrolactone and / or N, N-dimethylacetamide as described above. When the solvent is a mixture of γ-butyrolactone and N, N-dimethylacetamide, these ratios are arbitrary. The solvent may include other organic solvents such as DMF and DMSO, but the mass ratio of γ-butyrolactone and N, N-dimethylacetamide in the total solvent is preferably 80% or more, and 90% or more. It is preferable.

  The polyimide varnish can contain water in addition to the above solvent. Content of water is 0.1-20 mass parts normally with respect to 100 mass parts of solid content in a varnish.

  The polyimide varnish can further contain the above-described inorganic particles. When the polyimide varnish contains inorganic particles, the varnish preferably contains water.

When the polyimide varnish contains inorganic particles, the varnish may contain a metal alkoxide such as alkoxysilane in order to improve solution stability. A preferred metal alkoxide is an alkoxysilane having an amino group. Alkoxysilane contributes to bond formation between inorganic particles.
The addition amount of a metal alkoxide is 0.1-10 mass parts normally with respect to 100 mass parts of inorganic particles, and it is preferable that it is 0.5-5 mass parts.

  Further additives may be added to the polyimide varnish. Examples of the additives include antioxidants, mold release agents, stabilizers, bluing agents, flame retardants, lubricants, thickeners, and leveling. An agent or the like may be added.

  Next, the varnish is applied onto a substrate such as a PET film, a SUS belt, and a glass plate by a known roll-to-roll or batch method to form a coating film. Next, the coating film is dried to remove the solvent, thereby forming a polyimide film. Thereafter, the film is peeled off from the substrate.

In particular, in this embodiment, the film is dried so that the film before peeling satisfies 30 ≦ G + D ≦ 10000.
The solvent can be dried at a temperature of 50 ° C. to 350 ° C. by appropriately evaporating the solvent in an inert atmosphere or under reduced pressure. Adjustment of G + D is adjustment of drying temperature, drying time, drying atmosphere pressure, adjustment of solvent composition, for example, adjustment of mixing ratio of γ-butyrolactone and N, N-dimethylacetamide, concentration of water, etc., molecular structure of polyimide It can be appropriately performed depending on selection.

(Use)
Since such a polyimide film is excellent in peelability from the substrate, the appearance is improved and can be suitably used as a component of a flexible display. For example, it can be used as a front plate (window film) for protecting the surface of a flexible display.
Moreover, it can also be set as the laminated body which added various functional layers, such as an ultraviolet absorption layer, a hard-coat layer, an adhesion layer, a hue adjustment layer, a refractive index adjustment layer, to this polyimide film.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to a following example.

Example 1
In a polymerization tank substituted with nitrogen, a compound represented by formula (1), a compound represented by formula (2), a compound represented by formula (3), a solvent (γ-butyrolactone and dimethylacetamide) and 1.5 g of a catalyst. Was charged. The amount charged was 75.0 g of the compound represented by formula (1), 36.5 g of the compound represented by formula (2), 76.4 g of the compound represented by formula (3), 438.4 g of γ-butyrolactone, dimethyl Acetamide was 313.1 g. The molar ratio of the compound represented by Formula (2) and the compound represented by Formula (3 is 3: 7, the sum of the compound represented by Formula (2) and the compound represented by Formula (3) and the formula The molar ratio with the compound represented by (1) was 1.00: 1.02.

  After stirring the mixture in the polymerization tank and dissolving the raw materials in the solvent, the temperature of the mixture was raised to 100 ° C., and then the temperature was raised to 200 ° C. and kept warm for 4 hours to polymerize the polyimide. During this heating, water in the liquid was removed. Then, the polyimide was obtained by refinement | purification and drying.

  Next, a polyimide γ-butyrolactone solution adjusted to a concentration of 20% by mass, a solution in which silica particles having a solid content concentration of 30% by mass are dispersed in γ-butyrolactone, a dimethylacetamide solution of an alkoxysilane having an amino group, and water are mixed. And stirred for 30 minutes.

  Here, the mass ratio of silica and polyimide is 60:40, the amount of alkoxysilane having an amino group is 1.67 parts relative to 100 parts by mass of silica and polyimide, and water is 100 parts by mass of silica and polyimide. The amount was 10 parts by mass.

  The mixed solution was applied to a glass substrate, heated at 50 ° C. for 30 minutes, 140 ° C. for 10 minutes, and 210 ° C. for 1 hour to dry the solvent to form a polyimide film. Thereafter, the film was peeled from the glass substrate to obtain a transparent polyimide film having a thickness of 75 μm.

(Example 2)
The same procedure as in Example 1 was performed except that polyimide was synthesized using 1,2,4,5-cyclohexanetetracarboxylic acid instead of the compound represented by formula (1).

(Example 3)
Example 1 was repeated except that “Neoprim” manufactured by Mitsubishi Gas Chemical Company was used as the polyimide.

Example 4
The same procedure as in Example 1 was conducted except that “Neoprim” manufactured by Mitsubishi Gas Chemical Co., Ltd. was used and the drying conditions were 210 ° C. for 20 minutes.

(Comparative Example 1)
The drying conditions of Example 1 were the same as Example 1 except that the drying time was shortened.

(Comparative Example 2)
Example 4 was the same as Example 4 except that the drying temperature was 300 ° C. for 3 hours.

(Residual amount of solvent in the film)
The film was pulverized using a freeze pulverizer (Model JFC-300, manufactured by Nippon Analytical Industrial Co., Ltd.) for 5 minutes and then for 10 minutes. About 200 mg of the pulverized film was extracted with a high-speed solvent extraction apparatus (ASE-200 manufactured by Dionex) at a temperature of 140 ° C., a pressure of 1000 psi, a time of 10 minutes, N 2 purge of 100 s, and 2-propanol (IPA). Nitrogen was blown over the extract to evaporate IPA, and 0.2 mL of acetone was added. The obtained acetone solution was analyzed under the conditions of the following gas chromatograph, and the solvent amounts of GBL (retention time 2.9 minutes) and DMAc (retention time 3.3 minutes) were calculated by the absolute calibration curve method.
Equipment: Gas chromatograph (Agilent gas chromatograph 6890N type)
Inlet temperature: 280 ° C
Injection volume: 1μL
Oven temperature: Hold at 50 ° C. for 1 minute, then heat up to 350 ° C. at a rate of temperature increase of 20 ° C./minute, and hold at 350 ° C. for 5 minutes.
Carrier gas: He 1.0ml / min
Column: SGE BPX5 (0.25mmφ × 30m thickness 0.25μm)
Split ratio: 50: 1
Detector: Hydrogen flame ionization type detector Detector temperature: 355 ° C

(Evaluation of peelability)
The peelability when peeling the dried film from the substrate was evaluated as follows.
The film was peeled from the substrate at a peeling angle of 90 ° with respect to the surface of the substrate. The case where peeling was possible with a stable peel strength and peel speed was marked with ◯, the case where the peel strength or peel speed was unstable was marked with Δ, and the case where the peel strength and peel speed were unstable were marked with x.

(Appearance evaluation)
The appearance of each film after peeling was evaluated as follows. When a film with good appearance without peeling failure is obtained, ◯ is given, and when a film with poor peeling or poor appearance is obtained, △ is given, and peeling failure such as a crease or tear occurs in a part of the film at the time of peeling. In the case, it was set as x.

(Evaluation of YI)
The yellowness (Yellow Index: YI) of the films of Examples and Comparative Examples was measured with an ultraviolet-visible near-infrared spectrophotometer V-670 manufactured by JASCO Corporation based on JIS K 7373: 2006. After measuring the background in the absence of a sample, the film was set on a sample holder, the transmittance for light of 300 nm to 800 nm was measured, and tristimulus values (X, Y, Z) were obtained. YI was calculated based on the following formula.
YI = 100 × (1.28X−1.06Z) / Y

(Evaluation of Haze)
The Haze (%) of the film was measured by a fully automatic direct reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd. according to JIS K 7136: 2000.

(Evaluation of total light transmittance Tr)
The total light transmittance of the film was measured by a fully automatic direct reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd. according to JIS K 7136: 2000. These results are shown in Table 1.

Claims (5)

Polyimide polymer,
and at least one selected from the group consisting of γ-butyrolactone and N, N-dimethylacetamide,
Yellowness is 10 or less,
A polyimide film satisfying 30 ≦ G + D ≦ 10000, where G (ppm) is the mass proportion of γ-butyrolactone and D (ppm) is the mass proportion of N, N-dimethylacetamide.   The polyimide film according to claim 1, wherein the haze is 2 or less.   The polyimide film according to claim 1 or 2, wherein the total light transmittance is 85% or more. (A) applying at least one selected from the group consisting of γ-butyrolactone and N, N-dimethylacetamide, and a liquid containing a polyimide polymer to a substrate;
(B) drying the applied liquid to form a film;
A method for producing a polyimide film comprising:
When the mass proportion of γ-butyrolactone in the film is G (ppm) and the mass proportion of N, N-dimethylacetamide is D (ppm), the film after the step (b) satisfies 30 ≦ G + D ≦ 10000. A method for producing a polyimide film.   Furthermore, the manufacturing method of the polyimide-type film of Claim 4 provided with the process of peeling a film from a base material (c).