JP2013100379A - Polyimide film, laminate using same, and flexible thin-film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyimide film which has a relatively small average linear expansion coefficient, can resist a high-temperature heat treatment and is particularly suitable for a lamination with an inorganic metal and a semiconductor, and a method of manufacturing the same.SOLUTION: The polyimide film is formed by extending and imidizing a self-supporting film obtained from an aromatic tetracarboxylic acid dianhydride and an aromatic diamine. The average linear expansion coefficient (α1) at 50°C to 200°C is a positive value, and the value of the ratio α2/α1 of the average linear expansion coefficient (α1) at 50°C to 200°C and the average linear expansion coefficient (α2) at 350°C to 450°C is 1.4 or less.

Description

  The present invention relates to a polyimide film that can withstand high-temperature heat treatment and is suitable for lamination with inorganic metals and semiconductors, and a method for producing the same. The present invention also relates to a laminate using the polyimide film and a flexible thin film solar cell having high conversion efficiency.

  Polyimide film is a highly harmonious material in mechanical, electrical, thermal and chemical properties, and is mainly used in the electrical / electronic industry and aerospace field as a highly functional polymer material. . In recent years, not only copper wiring but also other inorganic metals and semiconductors are laminated on a polyimide film, and application to compound semiconductor-based flexible thin film solar cells such as amorphous silicon and CIS, flexible TFT substrates, etc. is also progressing. (Patent Documents 1 and 2).

  By the way, in general, the linear expansion coefficient (hereinafter referred to as “CTE”) of a polymer is temperature-dependent and increases as the temperature increases. In particular, when the glass transition temperature is exceeded, molecular mobility increases and CTE generally rises greatly. Also in the polyimide film, for example, if the average linear expansion coefficient at 50 ° C. to 200 ° C. is defined as α1 and the average linear expansion coefficient at 350 ° C. to 450 ° C. is defined as α2, the value of α2 / α1 is generally around 2. there were. In contrast, the CTE of inorganic metals and semiconductors laminated on polyimide is about 4 to 16 ppm, and there is almost no temperature dependence in the temperature range from room temperature to about 500 ° C. That is, the value of α2 / α1 of inorganic metals and semiconductors is approximately 1. For this reason, even if the CTE of polyimide at room temperature to around 200 ° C. is the same as that of an inorganic metal or a semiconductor, CTE mismatch occurs in a high temperature region, and problems such as cracks and warpage due to thermal stress may occur.

  Patent Document 3 proposes a polyimide in which a change in CTE of 350 ° C. or less is reduced. However, also in this polyimide film, the CTE greatly increased in a high temperature range exceeding 350 ° C., and was insufficient for use in a further high temperature range.

  Patent Document 4 discloses 3,3 ′, 4,4′-biphenyltetracarboxylic acid (hereinafter referred to as “s-BPDA”), pyromellitic dianhydride (hereinafter referred to as “PMDA”), paraphenylenediamine (hereinafter referred to as “PMDA”). A coating film having a thickness of 9 to 11 μm has been proposed. However, this coating film is a thin film having a thickness of 11 μm or less, and when the PMDA ratio is 50 mol% or less, the CTE greatly increases when the temperature is further increased. .

JP 2003-179238 A JP 2007-317834 A JP 2006-199740 A Journal of Polymer Science: Part B: Polymer Physics, Vol. 39, 796-810 (2001)

  An object of the present invention is to provide a polyimide film that can withstand high-temperature heat treatment and that is particularly suitable for lamination with inorganic metals and semiconductors, and a method for producing the same. Moreover, it is providing the flexible thin film type solar cell which has the laminated body using the said polyimide film, and high conversion efficiency.

The present inventors have intensively studied the chemical composition, the conditions of the production method, the physical properties of the polyimide film, etc., and completed the invention.
That is, the present invention relates to the following matters.
(1) A polyimide film obtained by stretching and imidizing a self-supporting film obtained from an aromatic tetracarboxylic dianhydride and an aromatic diamine, and having an average coefficient of linear expansion (α1) at 50 ° C. to 200 ° C. A polyimide film having a positive value and a ratio α2 / α1 of 1.4 or less with respect to an average linear expansion coefficient (α2) at 350 ° C. to 450 ° C.
(2) Aromatic tetracarboxylic dianhydride containing at least PMDA as an aromatic tetracarboxylic dianhydride and containing 85 mol% or more of s-BPDA and PMDA, and 85 mol% of PPD as an aromatic diamine Mixing with the aromatic diamine containing above to make a polyimide precursor, by partially imidizing the polyimide precursor to a self-supporting film, stretch the self-supporting film to 1.05 times or more, 2 times or less, The method for producing a polyimide film according to (1), wherein the stretched product is imidized and the film after imidization is annealed.
(3) A laminate obtained by forming a conductive layer on the polyimide film of (1).
(4) A flexible thin film solar cell using the laminate of (3).
(5) A CIS solar cell in which a chalcopyrite compound semiconductor layer is formed on the laminate of (3).

  According to the present invention, it is possible to reduce the ratio of the average linear expansion coefficient (α2 / α1) between the high temperature region and the low temperature region of the polyimide film as compared with the conventional one, and to the linear expansion coefficient of inorganic metals and semiconductors. Since it shows a close value, it is possible to suppress warpage and cracks during lamination with inorganic metals and semiconductors and in subsequent heat treatment steps. For this reason, the polyimide film that can be obtained in the present invention is preferably used as a flexible thin film solar cell that requires high-temperature treatment in the manufacturing process, particularly as a base material for a CIS solar cell or a flexible TFT substrate. Can do.

  The polyimide film of the present invention can be produced as follows. First, an aromatic tetracarboxylic acid component and an aromatic diamine component are reacted to synthesize a polyimide precursor (polyamic acid). Next, this polyimide precursor solution is cast-coated on a support and heated to produce a self-supporting film of the polyimide precursor solution. Next, this self-supporting film is stretched, heated and imidized.

[Polyimide precursor (polyamic acid)]
As a polyimide precursor, what is manufactured from aromatic tetracarboxylic dianhydride and aromatic diamine is preferable. The aromatic tetracarboxylic dianhydride used in the present invention contains at least PMDA. As the aromatic tetracarboxylic dianhydride, PMDA and s-BPDA are preferably the main components. Specifically, the aromatic acid dianhydride preferably contains s-BPDA and PMDA in an amount of 85 mol% or more, and particularly contains PMDA in an amount of 5 mol% to 50 mol% and s-BPDA in an amount of 50 mol% to 95 mol%. Is more preferable from the viewpoint of reducing CTE in a high temperature region and suppressing thermal decomposition at high temperature. Furthermore, other aromatic tetracarboxylic dianhydride components can be used in combination as long as the characteristics of the present invention are not impaired.

  In the present invention, the aromatic tetracarboxylic dianhydride component that can be used in combination with the s-BPDA and PMDA is 2,3 ′, 3,4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4. , 4′-benzophenone tetracarboxylic dianhydride, 2,2 ′, 3,3′-benzophenone tetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2, , 2-bis (2,3-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2 2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) -1,1 1,3,3,3-hexafluoropropane dianhydride and the like.

  As an aromatic diamine, it is preferable to contain PPD as a main component. More specifically, the aromatic diamine preferably contains PPD at 85 mol% or more, and more preferably 95 mol% or more. Furthermore, other diamines can be used in combination as long as the characteristics of the present invention are not impaired. As aromatic diamine components that can be used in combination with PPD, metaphenylenediamine, 2,4-diaminotoluene, 2,6-diaminotoluene, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 3,4′- Diaminodiphenyl ether, 3,3′-dimethyl-4,4′-diaminobiphenyl, 2,2′-dimethyl-4,4′-diaminobiphenyl, 2,2′-bis (trifluoromethyl) -4,4′- Diaminobiphenyl, 4,4′-diaminobenzophenone, 3,3′-diaminobenzophenone, 4,4′-bis (4-aminophenyl) sulfide, 4,4′-diaminodiphenylsulfone, 4,4′-diaminobenzanilide 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) ) Benzene, 1,3-bis (3-aminophenoxy) benzene, 4,4′-bis (4-aminophenoxy) biphenyl, 4,4′-bis (3-aminophenoxy) biphenyl, 2,2-bis ( 4-aminophenoxyphenyl) propane, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 2,2-bis [4- (4-aminophenoxy) Phenyl] hexafluoropropane and the like.

  The synthesis of the polyimide precursor is achieved by random polymerization or block polymerization of approximately equimolar aromatic tetracarboxylic dianhydride and aromatic diamine in an organic solvent. May also be mixed with the reaction conditions was keep two or more polyimide precursors in which either of these two components is excessive, the respective polyimide precursor solution together. At this time, as described above, aromatic tetracarboxylic dianhydride containing at least PMDA as an aromatic tetracarboxylic dianhydride and containing 85 mol% or more of s-BPDA and PMDA, and aromatic diamine It is preferable to mix with an aromatic diamine containing 85 mol% or more of PPD to obtain a polyimide precursor. The polyimide precursor solution thus obtained can be used for the production of the next self-supporting film as it is, or if necessary, by removing the organic solvent or newly adding an organic solvent.

  Examples of the organic solvent for random polymerization or block polymerization and the newly added organic solvent include N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide and the like. It is done. These organic solvents may be used alone or in combination of two or more.

  If necessary, an imidization catalyst, an organic phosphorus-containing compound, inorganic fine particles, and the like may be added to the polyimide precursor solution. Examples of the imidization catalyst include a substituted or unsubstituted nitrogen-containing heterocyclic compound, an N-oxide compound of the nitrogen-containing heterocyclic compound, a substituted or unsubstituted amino acid compound, an aromatic hydrocarbon compound having a hydroxyl group, or an aromatic heterocyclic compound. Cyclic compounds such as 1,2-dimethylimidazole, N-methylimidazole, N-benzyl-2-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 5-methylbenzimidazole and the like. Benzimidazoles such as alkylimidazole and N-benzyl-2-methylimidazole, isoquinoline, 3,5-dimethylpyridine, 3,4-dimethylpyridine, 2,5-dimethylpyridine, 2,4-dimethylpyridine, 4-n- Preferred are substituted pyridines such as propylpyridine It can be used for. The amount of the imidization catalyst used is preferably about 0.01-2 times equivalent, particularly about 0.02-1 times equivalent to the amic acid unit of the polyamic acid. By using an imidization catalyst, the self-supporting film may be easily stretched, or may be effective in suppressing whitening of the film due to crystallization during heating imidization. Moreover, the physical property of the polyimide film obtained, especially elongation and end tear resistance may be improved.

  Examples of the organic phosphorus-containing compounds include monocaproyl phosphate, monooctyl phosphate, monolauryl phosphate, monomyristyl phosphate, monocetyl phosphate, monostearyl phosphate, triethylene glycol monotridecyl Monophosphate of ether, monophosphate of tetraethylene glycol monolauryl ether, monophosphate of diethylene glycol monostearyl ether, dicaproyl phosphate, dioctyl phosphate, dicapryl phosphate, dilauryl phosphate, dimyristyl phosphate, Dicetyl phosphate, distearyl phosphate, diethylene phosphate of tetraethylene glycol mononeopentyl ether, triethyl Diphosphate of glycol mono tridecyl ether, diphosphate of tetraethyleneglycol monolauryl ether, and phosphoric acid esters such as diphosphate esters of diethylene glycol monostearyl ether, amine salts of these phosphates. As amine, ammonia, monomethylamine, monoethylamine, monopropylamine, monobutylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, monoethanolamine, diethanolamine, triethanolamine Etc.

  Inorganic fine particles include fine particle titanium dioxide powder, silicon dioxide (silica) powder, magnesium oxide powder, aluminum oxide (alumina) powder, inorganic oxide powder such as zinc oxide powder, fine particle silicon nitride powder, and titanium nitride powder. Inorganic nitride powder such as silicon carbide powder, inorganic carbide powder such as silicon carbide powder, and inorganic salt powder such as particulate calcium carbonate powder, calcium sulfate powder, and barium sulfate powder. These inorganic fine particles may be used in combination of two or more. In order to uniformly disperse these inorganic fine particles, a means known per se can be applied.

[Self-supporting film]
A method for producing a self-supporting film by partially imidizing the polyimide precursor obtained above will be described. Partial imidization may be performed by any of imidation by heat (thermal imidization), chemical imidization (chemical imidization), or a method in which thermal imidization and chemical imidization are used in combination.

First, the manufacturing method of the self-supporting film by thermal imidation is demonstrated. The self-supporting film of the polyimide precursor solution is prepared by applying an organic solvent solution of the polyimide precursor as described above or a polyimide precursor solution obtained by adding an imidization catalyst, an organic phosphorus-containing compound, inorganic fine particles, and the like on the support. Manufactured by casting and partially imidizing by heating to the extent that it becomes self-supporting. Here, the degree of self-supporting refers to a state where it can be peeled from the support.
The polyimide precursor solution preferably contains about 10 to 30% by mass of the polyimide precursor. Moreover, as a polyimide precursor solution, what the density | concentration of the polyimide after imidation is about 8-25 mass% is preferable. The heating temperature and the heating time can be appropriately determined. For example, the heating may be performed at a temperature of 100 to 180 ° C. for about 3 to 60 minutes.

  As the support, it is preferable to use a smooth base material such as a stainless steel substrate, a stainless steel belt, or a glass plate. The self-supporting film preferably has a loss on heating in the range of 20 to 50% by mass, further a loss on heating in the range of 20 to 50% by mass and an imidization ratio in the range of 8 to 55%, More preferably, it is in the range of 10 to 50% because the mechanical properties of the self-supporting film are sufficient and it is preferable from the viewpoint of stretching.

The heating loss of the self-supporting film is a value obtained from the following formula from the mass W1 of the self-supporting film and the mass W2 of the cured film.
Heat loss (%) = (W1-W2) / W1 × 100
The imidization rate of the above partially imidized self-supporting film is measured by IR (ATR), and the ratio of the vibration band peak area or height between the film and the fully cured product is used to determine the imidization rate. Can be calculated. As the vibration band peak, a symmetric stretching vibration band of an imidecarbonyl group, a benzene ring skeleton stretching vibration band, or the like is used.

  In this invention, you may apply | coat the solution of surface treating agents, such as a coupling agent and a chelating agent, to the single side | surface or both surfaces of the self-supporting film obtained in this way as needed. As surface treatment agents, various coupling agents such as silane coupling agents, borane coupling agents, aluminum coupling agents, aluminum chelating agents, titanate coupling agents, iron coupling agents, copper coupling agents, and chelating agents. Examples thereof include a treatment agent that improves adhesiveness and adhesion of the agent. In particular, as a surface treatment agent, an excellent effect is obtained when a coupling agent such as a silane coupling agent is used.

  Examples of silane coupling agents include epoxy silanes such as γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyldiethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, and vinyltrichloro. Silane, vinyltris (β-methoxyethoxy) silane, vinyltriethoxysilane, vinyltrimethoxysilane and other vinylsilane systems, γ-methacryloxypropyltrimethoxysilane and other acrylic silane systems, N-β- (aminoethyl) -γ- Aminosilanes such as aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercapto Propyltrime Kishishiran, .gamma.-chloropropyl trimethoxy silane and the like. Further, titanate coupling agents include isopropyl triisostearoyl titanate, isopropyl tridecylbenzenesulfonyl titanate, isopropyl tris (dioctylpyrophosphate) titanate, tetraisopropylbis (dioctyl phosphite) titanate, tetra (2,2-diallyloxy) Methyl-1-butyl) bis (di-tridecyl) phosphite titanate, bis (dioctylpyrophosphate) oxyacetate titanate, bis (dioctylpyrophosphate) ethylene titanate, isopropyltrioctanoyl titanate, isopropyltricumylphenyl titanate, etc. .

  As coupling agents, silane coupling agents, especially γ-aminopropyl-triethoxysilane, N-β- (aminoethyl) -γ-aminopropyl-triethoxysilane, N- (aminocarbonyl) -γ-aminopropyl Such as triethoxysilane, N- [β- (phenylamino) -ethyl] -γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, etc. Aminosilane coupling agents are preferred, and among them, N-phenyl-γ-aminopropyltrimethoxysilane is particularly preferred.

  Examples of the solvent for the solution of the surface treatment agent such as a coupling agent and a chelating agent include the same organic solvent as the polyimide precursor solution (the solvent contained in the self-supporting film). The organic solvent is preferably a solvent that is compatible with the polyimide precursor solution, and is preferably the same as the organic solvent of the polyimide precursor solution. The organic solvent may be a mixture of two or more.

  The organic solvent solution of the surface treatment agent such as a coupling agent or a chelating agent has a surface treatment agent content of 0.5% by mass or more, more preferably 1 to 100% by mass, particularly preferably 3 to 60% by mass, What is preferably 5 to 55% by mass is preferable. The water content is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less. The rotational viscosity (solution viscosity measured by a rotational viscometer at a measurement temperature of 25 ° C.) of the organic solvent solution of the surface treatment agent is preferably 0.8 to 50000 centipoise.

  As the organic solvent solution of the surface treatment agent, the surface treatment agent is particularly uniformly dissolved in the amide solvent at a concentration of 0.5% by mass or more, particularly preferably 1 to 60% by mass, and more preferably 3 to 55% by mass. The low viscosity (especially rotational viscosity 0.8-5000 centipoise) is preferable.

The coating amount of the surface treatment agent solution may be appropriately determined, for example, preferably 1 to 50 g / ^{m 2,} more preferably ^{2~30g / m 2, 3~20g / m} 2 is particularly preferred. The amount applied may be the same on both sides or different.

  The surface treatment agent solution can be applied by a known method, for example, gravure coating method, spin coating method, silk screen method, dip coating method, spray coating method, bar coating method, knife coating method, roll coating method. And publicly known coating methods such as blade coating and die coating.

  Next, the manufacturing method of the self-supporting film by chemical imidation is demonstrated. Chemical imidization may be performed according to a known method. For example, a polyimide precursor is synthesized in the same manner as in the case of thermal imidization to prepare a polyamic acid solution that is a polyimide precursor solution. To this is added a dehydrating agent and a catalyst. If necessary, inorganic fine particles as described in thermal imidization may be added to the polyamic acid solution. The solution is cast on a suitable support (for example, a metal belt) to form a film, and the film is heated to 200 ° C. or lower using a heat source such as hot air or infrared rays. A self-supporting film is produced by heating to a temperature, preferably 40-200 ° C., to the extent that it is self-supporting.

  Examples of the dehydrating agent include organic acid anhydrides such as aliphatic acid anhydrides, aromatic acid anhydrides, alicyclic acid anhydrides, heterocyclic acid anhydrides, or a mixture of two or more thereof. Specific examples of the organic acid anhydride include, for example, acetic anhydride, propionic anhydride, butyric anhydride, formic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, benzoic anhydride, picolinic anhydride, and the like. Acetic anhydride is preferred. It is preferable that the usage-amount of a dehydrating agent is 0.5 mol or more with respect to 1 mol of amic acid bonds of the aromatic polyamic acid in a solution.

  The catalyst includes organic tertiary amines such as aliphatic tertiary amines, aromatic tertiary amines, heterocyclic tertiary amines, or mixtures of two or more thereof. Specific examples of the organic tertiary amine include, for example, trimethylamine, triethylamine, dimethylaniline, pyridine, β-picoline, isoquinoline, quinoline and the like, and isoquinoline is preferable. It is preferable that the usage-amount of a catalyst is 0.1 mol or more with respect to 1 mol of amic acid bonds of the aromatic polyamic acid in a solution. In the case of chemical imidization, as in the case of thermal imidization, if necessary, a solution of a surface treatment agent such as a coupling agent or a chelating agent is applied to one side or both sides of the self-supporting film before imidization. It may be applied.

[Stretching of self-supporting film]
The self-supporting film is then stretched. The draw ratio is 1.05 to 2 times, preferably 1.05 to 1.2 times, more preferably 1.1 to 1.2 times. Here, the stretching ratio refers to the ratio of stretching the film, and 1 times means that no active stretching is performed. Stretching is determined from a practical point of view because the value of the ratio (α2 / α1) of the average linear expansion coefficient between the high temperature region and the low temperature region can be reduced as compared with the conventional case. As a specific stretching method, at least one end of the self-supporting film is fixed with a pin tenter, a clip, etc., then introduced into a heating furnace, and stretched in a range of 1.05 to 2 times in a uniaxial direction or a biaxial direction. To do. The stretching may be sequential or simultaneous. The stretching temperature is preferably 100 ° C. to 280 ° C., more preferably 130 ° C. to 250 ° C., from the viewpoint of easy stretching and stretching efficiency.

[Polyimide film]
By heating the stretched product obtained above, it is imidized to obtain a polyimide film. In the heat treatment, it is appropriate to gradually perform imidization of the polymer and evaporation / removal of the solvent at a temperature of about 100 to 550 ° C. for about 0.05 to 5 hours, particularly 0.05 to 3 hours. In particular, this heat treatment is a stepwise primary heat treatment at a relatively low temperature of about 100-170 ° C. for about 0.5-30 minutes, and then at a temperature of 170-220 ° C. for about 0.5-30 minutes. It is preferable to perform the second heat treatment, and then the third heat treatment at a high temperature of 220 to 400 ° C. for about 0.5 to 30 minutes, and further the fourth high temperature heat treatment at a high temperature of 400 to 550 ° C. .

  The polyimide film can be produced by a batch method or a continuous method. In the case of producing by a continuous method, it is possible to use both the first half process of the heating furnace exclusively for stretching or the heating furnace for heating and imidization. When a heating furnace for imidization is used, stretching is performed by fixing both ends of the film in the direction perpendicular to the longitudinal direction of the long solid film, that is, the width direction of the film, using a pin tenter, a clip, or the like. Stretching may be performed by any method of uniaxial stretching, sequential biaxial stretching, or simultaneous biaxial stretching as necessary.

[Annealing treatment]
The obtained polyimide film is annealed. Here, annealing refers to heating the film at a high temperature. As a specific annealing method, it is preferable to heat-treat the polyimide film at 500 ° C. or higher with substantially no stress applied.

  The state where substantially no stress is applied refers to a state where no external force (tension) is applied. For example, both ends of the polyimide film are not fixed. You may use the method of expanding or contracting a fixed end suitably according to the dimensional change of a film. This heat treatment may be performed subsequent to the quaternary heat treatment for imidization described above, or may be performed in a state where substantially no stress is applied at the stage of the quaternary heat treatment. good. The polyimide film obtained after imidization may be cooled and then heated again. In addition, it is preferable to perform the cooling after the heat treatment in a state where no stress is applied. This heat treatment is preferably performed at 500 ° C. or more and 550 ° C. or less, more preferably 500 ° C. or more and 520 ° C. or less for 30 seconds to 10 minutes, more preferably 1 minute to 5 minutes. It is possible to reduce the thermal shrinkage in the high temperature range above the glass transition temperature due to the residual stress, and to obtain a polyimide film that expands and contracts reversibly in the temperature rising process and the temperature falling process substantially up to 450 ° C. Thereby, for example, it is possible to obtain a polyimide film having a small dimensional change rate in a heat treatment at a high temperature of 500 ° C. or more, in particular, small shrinkage of the film when the temperature is lowered.

  When manufacturing a polyimide film by a continuous method, there exists a possibility that it may become an obstacle in terms of the stable production of a film to convey a film above 500 degreeC in the state by which both ends are not actually fixed. In this case, it is possible to create a state in which substantially no stress is applied by reducing the width of the pin tenter or clip that fixes both ends in accordance with the shrinkage of the film.

The polyimide film thus obtained is a polyimide film obtained by stretching and imidizing a self-supporting film obtained from an aromatic tetracarboxylic dianhydride and an aromatic diamine, at 50 ° C to 200 ° C. The average linear expansion coefficient (α1) is a positive value, and the ratio α2 / α1 to the average linear expansion coefficient (α2) at 350 ° C. to 450 ° C. is 1.4 or less. Moreover, the weight decreasing rate after heat processing for 20 minutes at 500 degreeC is 1 mass% or less. Thereby, it can be used also in a high temperature field.
Moreover, the 5% thermogravimetric decrease temperature in air | atmosphere is 600 degreeC or more. Furthermore, the average linear expansion coefficient (α1) at 50 ° C. to 200 ° C. is greater than 0 and 16 ppm / ° C. or less. Further, the shrinkage after heat treatment at 500 ° C. for 20 minutes is 0.3% or less based on the dimensions before heat treatment. Furthermore, although the thickness of a polyimide film is not specifically limited, It is about 12-250 micrometers, Preferably it is about 12-150 micrometers, More preferably, it is about 12-125 micrometers, More preferably, it is about 12-100 micrometers. The aromatic tetracarboxylic dianhydride preferably contains at least PMDA and 85 mol% or more of s-BPDA and PMDA in total, and the aromatic diamine preferably contains 85 mol% or more of PPD.

In the polyimide film obtained in the present invention, CTE hardly increases in the temperature range exceeding the glass transition temperature. It is also possible to make the CTE in the high temperature range smaller than the CTE in the low temperature range by increasing the draw ratio, and it is also possible to obtain a polyimide that expresses negative CTE in the high temperature range by increasing the draw ratio. is there. From this, it is possible to make the value of the ratio (α2 / α1) of the average linear expansion coefficient between the high temperature region and the low temperature region of the polyimide film relatively small compared to the conventional one, and to the linear expansion coefficient of inorganic metals and semiconductors. Since it shows a relatively close value, it is possible to suppress warpage and cracks during lamination with inorganic metals and semiconductors and in subsequent heat treatment steps. In some cases, by making the CTE in the high temperature region smaller than the CTE in the low temperature region, it is possible to reduce the total dimensional change rate up to the high temperature region, and to reduce the total thermal stress in the high temperature treatment process of the laminate. It can be reduced.
A laminate obtained by forming a conductive layer on the polyimide film obtained in the present invention can also be obtained. The conductive layer here refers to a layer that conducts current, and specifically, a metal, a metal oxide, an organic conductor, or the like. The conductive layer is preferably a molybdenum layer from the viewpoints of heat resistance, chemical resistance, thermal conductivity, workability, economy, and the like.
Since the polyimide film and laminate obtained in the present invention have a small weight loss rate at 500 ° C. and can be used in a higher temperature range, the laminate requires a heat treatment at a high temperature in the production process, and It can be suitably used for a flexible TFT substrate or a flexible solar cell using the same. In particular, it can also be suitably used for a CIS solar cell in which a chalcopyrite compound semiconductor layer is formed on a laminate.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

The evaluation method of the physical property of a polyimide film is as follows.
(1) Heat loss measurement method of self-supporting film The self-supporting film was heated in an oven at 480 ° C for 5 minutes. The weight loss after heating was calculated according to the following formula (1), where the original weight was W1 and the weight after heating was W2.
Heat loss (%) = (W1-W2) / W1 × 100 (1)

(2) Imidation rate measuring method of self-supporting film ATR-IR was measured using ZnSe using FT / IR-4100 manufactured by Jasco. 1772 cm ^-1 vicinity of the maximum value of the peak around X1,1517cm ^-1 the maximum value of the peak and the area ratio X1 / X2 of the self-supporting film when formed into a X2, area ratio of I fully imidized is progressed film The imidization ratio of the self-supporting film was calculated according to the following formula (2) using X1 / X2. In the measurement of the self-supporting film, both surfaces of the film were measured, and the average of both surfaces was taken as the imidization rate. The film that had been completely imidized was measured using a film heated at 480 ° C. for 5 minutes. In the film, the cast support side is the A side and the gas side is the B side.
Imidation ratio (%) = (a1 / a2 + b1 / b2) × 50 (2)
However, in Formula (2), the maximum value of the peak near 1772 cm ⁻¹ is X1,
The maximum value of the peak near 1517 cm ⁻¹ is X2,
The area ratio X1 / X2 on the A side of the self-supporting film is a1,
The area ratio X1 / X2 on the B side of the self-supporting film is b1,
The area ratio X1 / X2 on the A side of the film that has been completely imidized is a2,
The area ratio X1 / X2 on the B side of the film that has been completely imidized is defined as b2.

(3) Average linear expansion coefficient of polyimide film For the polyimide film to be measured, the average linear expansion coefficient α1 from the dimensional changes of 50 ° C. to 200 ° C. and 350 ° C. to 450 ° C. in the temperature rising process under the following conditions by TMA. And α2, and the value of the ratio of the average linear expansion coefficients α2 / α1 was calculated. In addition, the dimensional change during the temperature lowering process was also measured, and it was confirmed that the residual stress was removed by overlapping with the dimensional change during the actual temperature rising process at 450 ° C. or lower. Furthermore, the thermal contraction rate after heating at 500 ° C. was determined by comparing the size after cooling to 25 ° C. with the initial size.
Measuring device: TMA / SS6100 manufactured by SII Technology
Measurement mode: tensile mode, load 2g,
Sample length: 15 mm,
Sample width: 4 mm
Temperature rising start temperature: 25 ° C.
Temperature rise end temperature: 500 ° C
Temperature drop end temperature: 25 ° C
Temperature increase / decrease rate: 20 ° C./min,
Measurement atmosphere: nitrogen.

(4) Weight loss rate after heat treatment of polyimide film at 500 ° C. for 20 minutes With respect to the polyimide film to be measured, the temperature was increased from room temperature to 500 ° C. at 50 ° C./min. ₀ was measured. And after hold | maintaining for 20 minutes at 500 degreeC as it was, the weight W of the polyimide film was measured and the weight reduction | decrease rate was calculated | required from following Formula.
Weight reduction rate (%) = (W ₀ −W) / W ₀ × 100

(5) Thermogravimetric analysis Using TGA-50 manufactured by Shimadzu Corporation, the film was heated to 600 ° C. at 10 ° C./min in a nitrogen atmosphere. A 5% weight loss temperature (Td5) was determined from the obtained thermogravimetric weight loss curve. When the weight reduction rate at 600 ° C. was 5% or less, Td5> 600 ° C. was indicated.

[Reference Example 1]
(Preparation of polyamic acid solution)
N, N-dimethylacetamide (273.3 g) was placed in a 500 ml separable flask, and p-phenylenediamine (PPD) (16.532 g, 0.1529 mol) was added thereto and stirred. Further, 4.335 g (0.0199 mol) of pyromellitic dianhydride (PMDA) was added and reacted for 1 hour at room temperature and normal pressure. Next, 39.133 g (0.1330 mol) of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) was added and polymerized at 30 ° C. for 10 hours to obtain a polyamic acid solution ( A polyimide precursor solution) was obtained. The rotational viscosity at 30 ° C. of the obtained polyamic acid solution was 2500 poise. Table 1 shows the molar ratio of each raw material used in the polymerization.

[Example 1]
(Manufacture of polyimide film)
The polyamic acid solution composition obtained by adding monostearyl phosphate triethanolamine salt to the polyamic acid solution obtained in Reference Example 1 at a ratio of 0.25 parts by mass with respect to 100 parts by mass of the polyamic acid and mixing uniformly. I got a thing. This polyamic acid solution composition is cast on glass, heated at 80 ° C. for 2.5 minutes, and then heated at 135 ° C. for 2.5 minutes, and then peeled off from the glass and partially imidized polyamic acid self-supporting film (raw film) ) The imidation rate of the obtained self-supporting film was 18.5%, and the heat loss was 37% by mass.
Next, the self-supporting film was gripped at both ends in one direction, and stretched in the direction gripped in an oven at an atmospheric temperature of 150 ° C. over 1.05 times over 20 seconds. Was pinched and heated from 150 ° C. to 480 ° C. for 16 minutes and imidized to obtain a polyimide film of about 35 μm. Subsequently, the polyimide film was subjected to heat treatment (annealing) at 500 ° C. for 2.5 minutes in a state where stress was not applied by removing the pins holding the four sides. Table 2 shows the measurement results for the obtained polyimide film.

[Examples 2 to 6]
Other than the polyamic acid solution obtained by using the aromatic acid dianhydride and the aromatic diamine in the ratio (mol%) shown in Table 1 in the same procedure as in Reference Example 1, the film was drawn at the draw ratio shown in Table 1. Performed the same operation as Example 1 to obtain a polyimide film. Table 2 shows the measurement results for the obtained polyimide film.

Example 7
In a polyamic acid solution obtained by using the aromatic dianhydride and the aromatic diamine in the ratio (molar ratio) shown in Table 1 in the same procedure as in Reference Example 1, 0.24 against 100 parts by mass of the polyamic acid. Monostearyl phosphate triethanolamine salt was added at a ratio of parts by mass and mixed uniformly to obtain a polyamic acid solution composition. The obtained polyamic acid solution composition was continuously cast from a slit of a T-die mold onto a smooth endless belt-like stainless steel support in a casting / drying furnace, and then 125 ° C. (set temperature), 8 It dried for minutes and obtained the elongate self-supporting film. The imidation ratio was 14.2%, and the heat loss was 40.6% by mass.
The self-supporting film was stretched 1.1 times in the running direction (MD) at an ambient temperature of 135 ° C. Next, both ends in the width direction are gripped and inserted into a continuous heating furnace (curing furnace), and further stretched substantially 1.06 times in the width direction (TD) of the film within the range of 125 ° C. to 270 ° C. Specifically, it was heated to 480 ° C. for 5 minutes to obtain a polyimide film. Subsequently, the polyimide film was heat-treated at 500 ° C. for 2.5 minutes in a heating furnace in a state where no stress was applied to the gripping portions at both ends in the width direction of the film (no stress state). Table 2 shows the measurement results for the obtained polyimide film.

[Comparative Examples 1-7]
Other than the polyamic acid solution obtained by using the aromatic acid dianhydride and the aromatic diamine in the ratio (mol%) shown in Table 1 in the same procedure as in Reference Example 1, the film was drawn at the draw ratio shown in Table 1. Performed the same operation as Example 1 to obtain a polyimide film. In Comparative Examples 5 to 7, no stretching was performed (stretching ratio 1). The measurement results for the obtained polyimide film are shown in Table 1. When PMDA was not included, even when the self-supporting film was stretched, the CTE in the high temperature range was not relatively lowered, and the value of α2 / α1 was 1.4 or more. Further, even when PMDA was included, the CTE in the high temperature range was not relatively lowered unless stretching was performed, and the value of α2 / α1 was 1.4 or more.

[Comparative Examples 8 and 9]
The physical properties of a commercially available polyimide film were measured. Apical (registered trademark) (manufactured by Kaneka Corporation, NPI) and Kapton (registered trademark) (manufactured by Toray DuPont Co., Ltd., EN-C) were used as the polyimide film. The results are shown in Table 2. α1 and α2 indicate both numerical values in the horizontal and vertical directions of the sheet-like polyimide film.

Claims (16)

A polyimide film obtained by stretching and imidizing a self-supporting film obtained from an aromatic tetracarboxylic dianhydride and an aromatic diamine, and having a positive average linear expansion coefficient (α1) at 50 ° C. to 200 ° C. A polyimide film having a ratio α2 / α1 of 1.4 or less with respect to an average linear expansion coefficient (α2) at 350 ° C. to 450 ° C.   The polyimide film according to claim 1, wherein a weight reduction rate after heat treatment at 500 ° C. for 20 minutes is 1% by mass or less.   The polyimide film according to claim 1 or 2, wherein a 5% thermogravimetric temperature reduction temperature in the atmosphere is 600 ° C or higher.   4. The polyimide film according to claim 1, wherein an average linear expansion coefficient (α1) at 50 ° C. to 200 ° C. is greater than 0 and 16 ppm / ° C. or less. 5.   5. The polyimide film according to claim 1, wherein a shrinkage ratio after heat treatment at 500 ° C. for 20 minutes is 0.3% or less based on a dimension before heat treatment.   The polyimide film according to any one of claims 1 to 5, which has a thickness of 12 to 100 µm.   The aromatic tetracarboxylic dianhydride includes at least pyromellitic dianhydride (PMDA), and 85 mol in total of 3,3 ′, 4,4′-biphenyltetracarboxylic acid (s-BPDA) and PMDA. The polyimide film according to claim 1, wherein the aromatic diamine contains 85 mol% or more of paraphenylene diamine (PPD). The aromatic tetracarboxylic dianhydride contains at least PMDA, and the s-BPDA and PMDA together contain 85 mol% or more, and the aromatic tetracarboxylic dianhydride contains 85 mol% or more of PPD as the aromatic diamine. Mixing with aromatic diamine to make polyimide precursor,
Self-supporting film by partially imidizing the polyimide precursor,
Stretching the self-supporting film from 1.05 times to 2 times,
Imidizing the stretched product,
The manufacturing method of the polyimide film of any one of Claim 1 to 7 which anneals the film after the said imidation.   The method for producing a polyimide film according to claim 8, wherein the aromatic tetracarboxylic dianhydride contains PMDA in an amount of 5 mol% to 50 mol% and s-BPDA in an amount of 50 mol% to 95 mol%.   The method for producing a polyimide film according to claim 9, wherein the imidization ratio of the partial imidization is 10 to 50%.   The method for producing a polyimide film according to any one of claims 8 to 10, wherein a temperature at the time of stretching is in a range of 100C to 280C.   The method for producing a polyimide film according to any one of claims 8 to 11, wherein the annealing treatment is a step of heat-treating the polyimide film after imidation at a temperature of 500 ° C or higher in a state where substantially no stress is applied. .   The laminated body formed by forming a conductive layer on the polyimide film of any one of Claim 1 to 7.   The laminate according to claim 13, wherein the conductive layer is a molybdenum layer.   The flexible thin film type solar cell using the laminated body of Claim 13 or 14.   The CIS type solar cell in which the chalcopyrite type compound semiconductor layer was formed on the laminated body of Claim 13 or 14.