WO2009008030A1

WO2009008030A1 - Process of producing composite film

Info

Publication number: WO2009008030A1
Application number: PCT/JP2007/000750
Authority: WO
Inventors: Toshihiko Takaki; Kazuyuki Fukuda; Chaobin He; Khine Yi Mya
Original assignee: Mitsui Chemicals, Inc.; Agency For Science, Technology And Research
Priority date: 2007-07-10
Filing date: 2007-07-10
Publication date: 2009-01-15
Also published as: JP2010533213A

Abstract

The process of producing a polyimide-clay mineral composite film includes a step (A) of dissolving a polyimide precursor in a first solvent, a step (B) of dispersing a clay mineral which is not subjected to the organic modification in a second solvent, a step (C) of preparing a mixture solution by admixing the solution obtained by the above step (A) with the dispersion solution obtained by the above step (B), and a step (D) of forming a film by spreading the mixture solution obtained by the above step (C) on a substrate followed by drying the solvents.

Description

PROCESS OF PRODUCING COMPOSITE FILM

Technical Field

[0001] The present invention relates to a process of producing a composite film. Background Art

[0002] Since polyimide is excellent in mechanical strength, thermal properties and electric properties, it has been widely used in the field such as electric and electronics devices as an application for a film, an insulating resin layer of a circuit substrate and the like. From now on, it is expected that polyimide will be widely used in a field in which heat resistance is required, and an excellent polyimide has been developed.

[0003] For example, along with the advancement of miniaturization, high performance and densification of an electronics device using a print circuit board, the use of polyimide film that enables high density mounting of components and elements as a circuit board material is growing. In particular, as an application for an electronic material, it is required to improve the dimensional stability to heat and water and workability by high transparency.

[0004] Conventionally, it has been known that an inorganic substance is added to polyimide in order to improve the thermal properties and mechanical properties of polyimide. However, when an inorganic substance such as a clay mineral, as it is, is added to polyimide, the affinity of the clay mineral to polyimide is low, thus causing problems that the clay mineral was not homogeneously dispersed in polyimide and the characteristics of polyimide was not improved.

[0005] In Japanese Patent Laid-Open Publication No. 2006-57099, there is disclosed the addition of a layered silicate which is increased in affinity with a resin by chemically modifying (organic modification) a thermoplastic resin containing a thermoplastic polyimide in advance.

[0006] However, an organically modified clay mineral contains alkyl ammonium, thereby causing the deterioration of heat resistance and mechanical properties and discoloration.

Consequently, in Japanese Patent Laid-Open Publication No. 2000-302867, in order to solve such problems, there is disclosed a polyimide composite material composed by combining a clay mineral that is not organically modified with a polyimide resin. Patent Citation 1 : Japanese Patent Laid-Open Publication No. 2006-57099. Patent Citation 2: Japanese Patent Laid-Open Publication No. 2000-302867. Disclosure of Invention

[0007] However, when used as a film, the polyimide composite material described in the above Japanese Patent Laid-Open Publication No. 2000-302867 was desired to have improved transparency to properly perform operation, while it was required to be excellent in heat resistance and to have a high elastic modulus at a high temperature and thus there remained a problem of the compatibility in both transparency and elastic modulus.

[0008] An object of the present invention is to provide a process of producing a composite film which is excellent in the compatibility in both transparency and elastic modulus.

[0009] According to the present invention, there is provided a process of producing a composite film, containing:

(A) a step of dissolving a polyimide precursor in a first solvent, (B) a step of dispersing a clay mineral which is not subjected to the organic modification in a second solvent, (C) a step of preparing a mixture solution by admixing the solution obtained by the above step (A) with the dispersion solution obtained by the above step (B), and (D) a step of forming a film by spreading the mixture solution obtained by the above step (C) on a substrate followed by drying the solvents.

[0010] According to the present invention, there is provided a process of producing a composite film which is excellent in the compatibility in both transparency and elastic modulus.

Best Mode for Carrying Out the Invention

[0011] Hereinafter, the present invention will be explained in detail.

[0012] Firstly, a summary of a process of producing a composite film in the present embodiment will be explained.

The process of producing a composite film in the present embodiment contains the following steps:

(A) a step of dissolving a polyimide precursor in a first solvent,

(B) a step of dispersing a clay mineral which is not subjected to the organic modification in a second solvent,

(C) a step of preparing a mixture solution by admixing the solution obtained by the above step (A) with the dispersion solution obtained by the above step (B), and

(D) a step of forming a film by spreading the mixture solution obtained by the above step (C) on a substrate followed by drying the solvents.

[0013] Next, the steps (A) to (D) will be explained in detail.

[0014] (A) Step of dissolving a polyimide precursor in a first solvent

The polyimide precursor is dissolved in the first solvent. The dissolution method is not particularly limited but may be carried out by a publicly -known method. [0015] The first solvent is a solvent that dissolves the polyimide precursor and is mixable with the second solvent. In addition, preferably the functional group contained in the first solvent does not react with the polyimide precursor. As the first solvent, a basic solvent may be used. For example, a tertiary amine is preferable and there may be mentioned pyridine, trialkylamine, beta-picoline, alkylpyperidine and the like. These may be used alone or by mixing two to more kinds.

[0016] (B) Step of dispersing a clay mineral which is not subjected to the organic modification in a second solvent

The organic modification is a treatment to homogeneously disperse clay minerals in the resin by chemically treating a clay mineral to exchange a metal cation contained between layers of a clay mineral with an organic compound to increase the affinity with a resin and thus preventing the clay minerals from coagulating each other in a solution. For example, there is mentioned a treatment in which sodium ions contained in clay minerals are substituted by alkylammonium. The clay minerals not subjected to the organic modification are clay minerals not subjected to such treatment. By so doing, a film that is excellent in heat resistance and elastic modulus may be obtained.

[0017] The second solvent means a solvent that disperses clay minerals not subjected to the organic modification and is soluble with the first solvent. Water may be used as the second solution.

[0018] Dispersion means a state in which the solvent molecules are incorporated between the clay minerals and clay minerals are homogeneously dispersed in a solvent. The dispersion method is not particularly limited, but there may be mentioned, for example, a method of stirring a solution using a magnetic stirrer, mechanical stirrer and ho- mogenizer.

[0019] (C) Step of preparing a mixture solution by admixing the solution obtained by the above step (A) with the dispersion solution obtained by the above step (B)

The mixture solution means a homogeneously mixed solution obtained by admixing the solution obtained in step (A) with the dispersion solution obtained in step (B). The polyimide precursor is maintained in a state in which it is dissolved in the solution and clay minerals are maintained in a state where they are not coagulated and are homogeneously dispersed in the solution. By so doing, clay minerals may be homogeneously dispersed in polyimide.

[0020] In the present embodiment, since the solution obtained in the step (A) and the dispersion solution obtained in the step (B) are separately prepared, the degree of freedom of conditions for the selection of solvents, preparation time and the like is improved and the preparation conditions may be optimized. By so doing, the dispersion stability of the mixture solution may be improved.

The order of the step (A) and the step (B) is not particularly limited. Therefore, the step (B) may be carried out after the step (A) and the step (A) may be carried out after the step (B). In addition, the step (A) and the step (B) may be carried out simul- taneously.

[0021] (D) Step of forming a film by spreading the mixture solution obtained by the above step (C) on a substrate followed by drying the solvents

The film formation method is not particularly limited and may be carried out by a publicly-known method. By spreading the mixture solution on the substrate followed by drying the solvents, a film with a fixed thickness may be obtained. A publicly- known method may be appropriately selected and used depending on the concentration of the mixture solution, type of solvent and the like.

After the step (D), further heat treatment may be carried out. The heating temperature is not particularly limited, but the heat treatment is carried out at a temperature of 100 degrees C to 500 degrees C. A composite film containing polyimide may be obtained by conducting dehydration imidization.

[0022] The type of a substrate is not particularly limited, but there may be mentioned, for example, glass, metal, plastics and the like. In addition, the drying method is not particularly limited, and there may be used a publicly-known method, for example, using air blasting, hot blast, hot nitrogen, far- infrared radiation, high frequency wave and the like.

[0023] In the present invention, as the precursor of polyimide, there may be used a publicly- known polyimide polymer and/or polyamide acid copolymer synthesized by using a diamine compound and an acid dianhydride without any limitation.

[0024] The polyimide precursor preferably contains a polyimide polymer and/or a polyamide acid copolymer synthesized from one or more kinds of diamine compounds and one or more kinds of tetracarboxylic acid dianhydrides.

[0025] In the present invention, as the diamine compound used as a raw material of a polyimide polymer and/or a polyamide acid copolymer, there may be mentioned, for example, 1 ,3-bis(3-aminophenoxy)benzene, 4,4-bis(3-aminophenoxy)biphenyl,

3,3-diaminobenzophenone, p-phenylenediamine, 4,4'-diaminodiphenylether, l,3-bis(3-(3-aminophenoxy)phenoxy)benzene,

1 ,3-bis(3-(4-aminophenoxy)phenoxy)benzene, 5,7-diamino- 1 , 1 ,4,6-tetramethyl indaine, 1 ,3-bis(4-(3-aminophenoxy)phenoxy)benzene, l,3-bis(3-(2-aminophenoxy)phenoxy)benzene, l,3-bis(4-(2-aminophenoxy)phenoxy)benzene, l,3-bis(2-(2-aminophenoxy)phenoxy)benzene, l,3-bis(2-(3-aminophenoxy)phenoxy)benzene, l,3-bis(2-(4-aminophenoxy)phenoxy)benzene, l,4-bis(3-(3-aminophenoxy)phenoxy)benzene, l,4-bis(3-(4-aminophenoxy)phenoxy)benzene, l,4-bis(3-(2-aminophenoxy)phenoxy)benzene, l,4-bis(4-(3-aminophenoxy)phenoxy)benzene,

1 ,4-bis (4- (2-aminophenoxy)phenoxy)benzene,

1 ,4-bis (2- (2-aminophenoxy)phenoxy)benzene, l,4-bis(2-(3-aminophenoxy)phenoxy)benzene,

1 ,4-bis (2- (4-aminophenoxy)phenoxy)benzene, l,2-bis(3-(3-aminophenoxy)phenoxy)benzene, l,2-bis(3-(4-aminophenoxy)phenoxy)benzene, l,2-bis(3-(2-aminophenoxy)phenoxy)benzene,

1 ,2-bis (4- (4-aminophenoxy)phenoxy)benzene, l,2-bis(4-(3-aminophenoxy)phenoxy)benzene,

1 ,2-bis (4- (2-aminophenoxy)phenoxy)benzene,

1 ,2-bis (2- (2-aminophenoxy)phenoxy)benzene, l,2-bis(2-(3-aminophenoxy)phenoxy)benzene,

1 ,2-bis (2- (4-aminophenoxy)phenoxy)benzene, l,3-bis(3-(3-aminophenoxy)phenoxy)-2-methylbenzene, l,3-bis(3-(4-aminophenoxy)phenoxy)-4-methylbenzene, l,3-bis(4-(3-aminophenoxy)phenoxy)-2-ethylbenzene, l,3-bis(3- (2-aminophenoxy )phenoxy ) -5 - sec-butylbenzene,

1 , 3 -bis (4- (3 -aminophenoxy )phenoxy ) -2,5 -dimethylbenzene, l,3-bis(4-(2-amino-6-methylphenoxy)phenoxy)benzene, l,3-bis(2-(2-amino-6-ethylphenoxy)phenoxy)benzene, l,3-bis(2-(3-aminophenoxy)-4-methylphenoxy)benzene, l,3-bis(2-(4-aminophenoxy)-4-tert-butylphenoxy)benzene, l,4-bis(3-(3-aminophenoxy)phenoxy)-2,5-di-tert-butylbenzene, l,4-bis(3-(4-aminophenoxy)phenoxy)-2,3-dimethylbenzene, l,4-bis(3-(2-amino-3-propylphenoxy)phenoxy)benzene, l,2-bis(3-(3-aminophenoxy)phenoxy)-4-methylbenzene, l,2-bis(3-(4-aminophenoxy)phenoxy)-3-n-butylbenzene, l,2-bis(3-(2-amino-3-propylphenoxy)phenoxy)benzene and the like.

One or two or more kinds of these diamine compounds may be used.

In addition, as at least one of the diamine compounds, preferably used is a compound represented by the following general formula (1) [Chem.l]

( D

(in the formula (1), X¹ and X² are each independently selected from the group consisting of a single bond, an oxygen atom, a sulfur atom, a carbonyl group, a sulfonyl group and a hydrocarbon group which may have been substituted with a halogen atom, Ys are each independently selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxyl group, an alkoxy group, a nitro group and a hydrocarbon group which may have been substituted with a halogen atom, and n represents an integer of 0 to 8).

[0027] As at least one of the diamine compounds, preferably used is a compound represented by the following general formula (2) [Chem.2]

[0028] In addition, when two or more kinds of the diamine compounds are used, at least one or more kinds of them are preferably selected from l,3-bis(3-aminophenoxy)benzene, 4,4-bis(3-aminophenoxy)biphenyl, 3,3'-diaminobenzophenone, p-phenylenediamine and 4,4'-diaminophenylether.

[0029] In the present invention, as the acid dianhydride used as a raw material of a polyimide polymer and/or a polyamide acid copolymer, a publicly-known acid dianhydride may be used without any limitation.

[0030] As the acid dianhydride, there may be mentioned, for example, pyromellitic acid dianhydride,

3,3',4,4'-biphenyltetracarboxylic acid dianhydride,

3,3',4,4'-benzophenonetetracarboxylic acid dianhydride,

2,3,3',4'- biphenyltetracarboxylic acid dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, bis(3,4-dicarboxyphenyl)sulfide dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride,

2,2-bis(3,4-dicarboxyphenyl)propane dianhydride,

2,2-bis(3,4-dicarboxyphenyl)- 1,1,1 ,3,3,3-hexafluoropropane dianhydride,

1 ,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride,

1 ,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride,

4,4'-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride,

2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride,

2,3,6,7-naphthalenetetracarboxylic dianhydride,

1 ,4,5,8-naphthalenetetracarboxylic dianhydride, butane- 1 ,2,3,4-tetracarboxylic dianhydride, pentane- 1 ,2,4,5-tetracarboxylic dianhydride, cyclobutanetetracraboxylic acid dianhydride, cyclopentane- 1 ,2,3,4-tetracarboxylic dianhydride, cyclohexane- 1 ,2,4,5-tetracarboxylic dianhydride, cyclohexa-l-ene-2,3,5,6-tetracarboxylic dianhydride, 3-ethylcyclohexa-l-ene-3-(l,2),5,6-tetracarboxylic dianhydride, l-methyl-3-ethylcyclohexane-3-(l,2),5,6-tetracarboxylic dianhydride, l-methyl-3-ethycyclohexa-l-ene-3-(l,2),5,6-tetracarboxylic dianhydride, l-ethylcyclohexane-l-(l,2),3,4-tetracarboxylic dianhydride, 1-propylcyclohexane- l-(2,3),3,4-tetracarboxylic dianhydride, l,3-dipropylcyclohexane-l-(2,3),3-(2,3)-tetracarboxylic dianhydride, dicylohexyl-3,4,3',4'-tetracarboxylic dianhydride, bicyclo[2.2. l]heptane-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]octo-7-ene-2,3,5,6-tetracarboxylic dianhydride and the like.

[0031] Among these, one or two or more kinds of the tetracarboxylic acid dianhydrides may be used. As the tetracarboxylic acid dianhydride, especially preferable are pyromellitic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride. The reaction mole ratio of a diamine compound to a tetracarboxylic acid dianhydride is typically in the range of 0.75 to 1.25.

[0032] In the present invention, any other ingredients may be contained in a polyimide polymer and/or a polyamide acid copolymer depending on the purpose

[0033] As the clay mineral which is not particularly limited, preferable is a layered clay mineral and there may be mentioned serpentine-kaolin group clay minerals such as lizardite, amesite, chrysotile, kaolinite, dickite and halloysite; smectite group clay minerals such as saponite, hectlite, montmorillonite and beidellite; vermiculite group clay minerals such as trioctahedral vermiculite and dioctahedral vermiculite; and mica group clay minerals such as swelling mica, golden mica, illite, white mica and paragonite. Among these clays, especially preferable is smectite group clay minerals or at least one kind selected from the group of swelling mica, vermiculite and halloysite. By so doing, the elastic modulus at a high temperature is improved. Still more preferably, among the smectite group clay minerals, there may be mentioned montmorillonite. The effect on elastic modulus at a high temperature and dimensional stability is increased. One or two or more kinds of these clay minerals may be used.

[0034] The content of a clay mineral is not particularly limited, but is preferably not less than 1 part by weight and more preferably not less than 2.5 parts by weight, based on 100 parts by weight of the total of the composite film. By so doing, the heat resistance and elastic modulus at a high temperature are improved. In addition, the content of the clay mineral is preferably not more than 30 parts by weight and more preferably not more than 20 parts by weight, based on 100 parts by weight of the total of the composite film. By so doing, a material that is excellent in the balance between transparency and elastic modulus at a high temperature, suitable for the operation by visual confirmation, for example, when used for a circuit substrate and the like, and excellent in dimensional stability may be provided.

[0035] The composite film preferably has an elastic modulus of not less than 0.3 GPa. By so doing, the film is excellent in elasticity at a high temperature and is improved in dimensional stability. In addition, the composite film preferably has an elastic modulus of not more than 30 GPa at 450 degrees C. The reduction in the flexibility of the film due to too high an elastic modulus may be prevented.

[0036] When the thickness of the composite film is 20 micrometers, the composite film preferably has a light transmittance of not less than 50 % at a wavelength of 650 nm and more preferably of not less than 53 %. By so doing, the operation by visual confirmation through a composite film will be feasible, thereby further improving the accuracy of the operation. Incidentally, the light transmittance of a film with a thickness of 20 micrometers is calculated by converting the light transmittance determined for a film with a thickness of not less than 15 micrometers and not more than 25 micrometers to those of a composite film with a thickness of 20 micrometers by using the following equation (3). Absorbance (E)=log I₀/I=kCL (3)

For a light of intensity I obtained by passing a monochromatic light of intensity I₀ through a sample having molar concentration C and thickness L, the relationship of the above equation (3) is established. The percentage of I₀ /I represents a light transmittance (%T), log I₀ /I represents an absorbance and k represents a molar absorbance coefficient. Especially when the sample is a dilute solution, the relationship to which the above equation (3) is applied is called the Lambert-Beer Law.

[0037] It has been conventionally difficult to obtain a semiconductor device such as a circuit substrate by using a composite film that is compatible in both a high elastic modulus at a high temperature and a high light transmittance.

[0038] The thickness of the composite film is not particularly limited, but is typically in the range of 5 to 150 micrometers, and preferably, a composite film having a thickness in the range of 8 to 50 micrometers is typically used.

[0039] The composite film has a hygroscopic expansion coefficient of preferably not less than 5 ppm/% RH and not more than 20 ppm/% RH and more preferably of not less than 5 ppm/% RH and not more than 15 ppm/% RH at a relative humidity of 20 to 60 %. By so doing, the deforaiation of the composite film at the time of drying and moisture absorption is unlikely to occur and the dimensional stability of the composite film may be maintained. For example, the composite film may be applied to the miniaturization and densification of a circuit substrate.

[0040] The composite film preferably has a linear expansion coefficient in the range of 10 to 100 ppm/ degree C at a temperature of 380 to 430 degrees C. By so doing, the deformation of the composite film due to the change in temperature is unlikely to occur and the dimensional stability of the composite film may be maintained. For example, in the process of mounting a circuit substrate, the warpage and peeling-off of the composite film due to heating may be prevented.

[0041] The composite film has a water absorption coefficient of preferably not less than 0 % and not more than 2 % and more preferably of not more than 1.5 %. By so doing, the deterioration of electric properties such as dielectric constant due to water absorption may be prevented, thereby improving the dimensional stability.

[0042] Since a composite film is excellent in the compatibility in both transparency and elastic modulus at a high temperature, it may be widely applied in the field such as electric and electronics devices.

For example, it may be used as an insulating resin layer of a circuit substrate, a flexible circuit substrate further containing a metal layer and a chip-on-film substrate (COF substrate). These circuit substrates may be an insulating resin layer using at least one or more layers of the composite film without any limitation.

[0043] A circuit substrate is prepared as follows.

A sheet or film used as an insulating resin layer may be obtained by preparing a mixture solution by admixing a solution (A) in which a polyimide precursor is dissolved in a first solvent with a dispersion solution (B) obtained by dispersing a clay mineral which is not subjected to the organic modification in a second solvent and then spreading the mixture solution on a substrate such as a metal foil or an insulating layer followed by drying the solvents. After the above drying, further heat treatment may be carried out.

The circuit substrate has at least one layer of the insulating resin layer obtained as above and the insulating resin layer may be laminated many times. In addition, other insulating layer and metal layer may be laminated.

[0044] Further, the circuit substrate may be prepared by thermally compressing a metal foil and/or a laminate onto the composite film. Even in this case, further another insulating layer and metal layer may be laminated onto the insulating resin layer containing the composite film.

[0045] The insulating resin layer composed of the composite film may be directly laminated onto the metal layer or prepared onto an adhesion layer. In addition, when the circuit substrate is a multilayer substrate, the insulating resin layer may be used at any layer and further may be used many times. The preferred location of the composite film of the present invention is on a metal foil or on a thermoplastic polyimide layer prepared on the metal foil.

[0046] As the metal used as the metal layer in the flexible circuit substrate, any metal may be used without particular limitation. As a preferable example, there may be mentioned at least one kind of metal selected from the group consisting of copper, nickel, cobalt, chromium, zinc, aluminum and stainless steel as well as an alloy thereof and more preferable are copper and copper alloy, stainless steel, nickel and nickel alloy (including 42 alloy), aluminum and aluminum alloy and the like. Further more preferable are copper and copper alloy.

[0047] There is no limitation on the thickness of the metal layer if the metal layer is formed in a tape shape, and the metal layer has a thickness of preferably not less than 0.1 micrometers and not more than 150 micrometers, more preferably not less than 2 micrometers and not more than 105 micrometers and further more preferably not less than 3 micrometers and not more than 35 micrometers. The thickness may be selected accordingly from the above range, for example, a thin foil is preferably used for the application requiring wiring processing of a fine pattern and a thick foil is preferably used for the wiring requiring rigidity and the large current application.

[0048] The composite film used in the present invention is excellent in transparency, elastic modulus at high temperature and dimensional stability (low thermal expansion coefficient). For this reason, since the circuit substrate has at least one more layers using the composite film as the insulating resin layer, it has a significant effect that the deformation of a substrate is unlikely to occur and problems such as wire disconnection, sinking, peeling and plating penetration will not occur, even when a chip is mounted at a high temperature and pressure.

[0049] When an insulating resin layer containing the composite film of the present invention is used for a chip-on-film substrate which is widely used in the TAB (Tape Automated Bonding) tape processing line, the insulating resin layer is easy in operation and excellent in dimensional stability because it has a high elastic modulus at a temperature near the mounting temperature. The temperature near the mounting temperature is not less than 250 degrees C and not more than 500 degrees C, preferably not less than 300 degrees C and not more than 450 degrees C and more preferably not less than 350 degrees C and not more than 450 degrees C.

[0050] Since the composite film of the present invention is transparent, the metal wiring may be recognized by image through the insulating resin layer using the composite film after the circuit processing as above, thereby enabling the layout when a chip is mounted by an inner lead bonder. [0051] According to the present invention, by the compatibility in both transparency and a high elastic modulus at a high temperature which were not obtained in a molded product composed of a complex of a conventional polyimide and clay minerals, a polyimide-clay mineral complex may be applied to a film and a circuit substrate and the like. In addition, the polyimide-clay mineral complex improves the workability by visual confirmation because of its transparency and prevents the reduction in elasticity due to heating, and, therefore, may be applied to the miniaturization and densification of electric and electronics devices and the like. Mode for the Invention

[0052] Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited at all by these Examples. Incidentally, the abbreviations in Examples mean the folio wings.

DMAc: dimethylacetoamide

NMP: N-methyl-2-pyrrolidone

APB : l,3-bis(3- aminophenoxy )benzene m-BP: 4,4'-(3-aminophenoxy)biphenyl

ODA: 4,4'-oxydianiline(4,4'-diaminodiphenylether)

PPD: p-phenylenediamine

BTDA: 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride

BPDA: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride

PMDA: anhydrous pyromellitic acid

APB-BMI : 1 , 3 -bis (3 -maleimidephenoxy )benzene

Further, each evaluation in Examples was performed as follows. [0053] (Viscoelasticity Measurement: Measurement of Storage modulus at 450 degrees C)

For the evaluation of the elastic modulus, the temperature distribution measurement in a tensile deformation mode was performed by using RSA-II manufactured by Rheometrics Corp. The measurement was made under the condition of a temperature range of 30 to 500 degrees C, a heating rate of 3 degrees C/min, a strain of 0.02 % under the control of auto-strain and a frequency of 1 Hz. In addition, the storage modulus E' was determined at 450 degrees C using a test specimen having a length of 20 mm and a width of 5 mm. [0054] (Thermal Expansion Coefficient Measurement)

The average coefficient of thermal expansion at a temperature in the range of 100 to 250 degrees C and 380 to 430 degrees C was determined by a tensile method in which the extension (shrinkage) of the film was measured by changing the temperature in the range of 50 to 500 degrees C while applying a certain loading to both ends of the film by using a thermomechanical analyzer (TMA-50, manufactured by Shimadzu Cor- poration). [0055] (Light Transmittance Measurement)

The light transmittance at a wavelength of 650 nm was determined by measuring a light transmittance of a film having a thickness shown in Table 1 by using an ultraviolet-visible spectrophotometer (UV-2200, manufactured by Shimadzu Corporation). The light transmittance converted to that of a film with a thickness of 20 micrometers was calculated from the thickness and light transmittance of the film by using the following equation (3).

Absorbance (E)=log I₀/I=kCL (3)

For a light of intensity I obtained by passing a monochromatic light of intensity I₀ through a sample having molar concentration C and thickness L, the percentage of I₀ /I represents a light transmittance (%), log I₀ /I represents an absorbance and k represents a molar absorbance coefficient. [0056] (Confirmation of a dispersion state of clay minerals)

A prepared polyimide/clay composite film was trimmed using a Leica Ultracut UCT ultra-microtome. The resulting microtome thin sections were placed on 200 mesh copper grids and examined the dispersion state of clay minerals by using a transmission electron microscope (TEM) (CM300-FEGTEM, manufactured by Philips Co., Ltd.) at an acceleration voltage of 300 kV. [0057] (Hygroscopic Expansion Coefficient Measurement)

A length of a film was measured by using a thermomechanical analyzer equipped with a humidity control unit (TMA-2200S, manufactured by Shimadzu Corporation) at a relative humidity of 20, 40 and 60 %. A slope of a line, that is, a hygroscopic expansion coefficient (ppm/% RH), was determined by plotting the measured length of films against the relative humidity and by applying linear approximation to the points plotted. [0058] (Water Absorption Measurement)

The water absorption of a film stored for more than 1 week under the atmosphere of a temperature of 23 degrees C and a relative humidity of 50 % was measured at 250 degrees C by using a heating vaporization moisture content measuring device (manufactured by Hiranuma Sangyo Co., Ltd.). [0059] Synthesis Example 1

Into a flask equipped with a stirrer and a nitrogen introduction tube was added 261.0 g of DMAc as a solvent, and then 20.44 g of ODA and 16.12 g of m-BP were added, followed by stirring and dissolving at 20 to 30 degrees C. Then, 30.84 g of PMDA was added and the raw materials adhered to the inside of the flask were washed off with 11.0 g of DMAc. The resulting mixture was heated to 50 to 60 degrees C and stirred for approximately 1 hour and subsequently 0.44 g of PMDA was added and stirred for approximately 4 hours while maintaining the temperature at 60 degrees C to obtain varnish (a). Next, into another flask equipped with a stirrer and nitrogen introduction tube was added 263.0 g of NMP as a solvent and then 19.62 g of PPD was added and dissolved by stirring at 20 to 30 degrees C. Thereafter, 37.0 g of BPDA and 11.06 g of PMDA were added and the raw materials adhered to the inside of the flask were washed off with 10.0 g of NMP. The resulting mixture solution was heated to 50 to 60 degrees C and stirred for approximately 4 hours to obtain varnish (b). Finally, in another flask equipped with a stirrer and a nitrogen introduction tube, varnish (b) and varnish (a) were mixed at a weight ratio of 77:23. The resulting mixture solution was heated to 50 to 60 degrees C and stirred for approximately 4 hours to obtain a polyamic acid solution. The resulting polyamic acid solution had a polyamic acid content of 20 % by weight and an E type viscosity at 25 degrees C of 30000 milli pascal-second. [0060] (Example 1)

The polyamic acid produced in Synthesis Example 1 was reprecipitated in methanol and dissolved in pyridine so that the concentration was 10 % by weight of the polyimide after imidization to obtain a polyamic acid/pyridine solution. This solution was used as a first solution.

In addition to this, a 2 % aqueous dispersion solution was prepared by adding 1.6 g of montmorillonite (Kunipia G, manufactured by Kunimine Industries Co., Ltd.) which is not subjected to the organic modification to 78.4 g of water and stirring at 10,000 rpm for 1 hour by a homogenizer. This resulting solution was diluted 8-fold with water to obtain a 0.25 % dispersion solution, which was used as a second solution. A homogeneous solution was obtained by gradually adding 20.51 g of the second solution to 20 g of the first solution over 30 minutes using a microtube pump to obtain a homogeneous solution. The homogeneous solution was transferred to glass Petri-dishes and dried at room temperature for 1 week under a flow of nitrogen and subsequently thermally treated in an inert oven at 200, 250, 300 and 350 degrees C for 1 hour, respectively, to obtain polyimide-clay mineral composite films with a thickness of 15 to 20 micrometers. When the resulting composite films were observed by TEM, it was confirmed that clay minerals were homogeneously dispersed in units from one to a few layers. In addition, the physical properties of the resulting composite films are shown in Table 1. [0061 ] (Examples 2 and 3)

The composite film was prepared in the same operation as in Example 1 so that the content of clay minerals to polyimide meets the conditions described in Table 1. The physical properties of the resulting composite film are shown in Table 1. [0062] (Examples 4 to 6)

By changing Kunipia G in the second solution of Example 1 to a synthetic smectite (Smecton SA, manufactured by Kunimine Industries Co., Ltd.), the composite films were prepared in the same operation as in Example 1 so that the content of clay minerals to polyimide meets the conditions described in Table 1. The physical properties of the resulting composite films are shown in Table 1. [0063] (Comparative Example 1)

The polyamic acid prepared by the condition of Synthesis Example 1 was applied on a glass substrate so that the dried film thickness is 15 to 21 micrometers and dried by increasing the temperature from 50 to 180 degrees C at a heating rate of 3 degrees C/ min in an inert oven and subsequently imidized to obtain a polyimide film. The physical properties of the resulting polyimide film are shown in Table 1. [0064] (Comparative Example 2)

A solution was prepared by adding NMP to the polyamic acid produced in Synthesis Example 1 so that the weight of the polyimide after imidization is 19 % by weight. This solution was used as a first solution.

In addition to this, a dispersion solution was prepared by adding 1.6 g of montmor- illonite (Kunipia G, manufactured by Kunimine Industries Co., Ltd.) which is not subjected to the organic modification to 78.4 g of NMP and stirring for 1 hour by a magnetic stirrer and subsequently treating for 1 hour by an ultrasonic washer. This dispersion solution was used a second solution. A homogeneous solution was obtained by adding 4.87 g of the second solution to the 20 g of the first solution. The homogeneous solution was applied on a glass substrate and dried by increasing the temperature from 50 degrees C to 200 degrees C at a heating rate of 5 degrees C/min and subsequently thermally treated at 200 degrees C for 5 hours in an inert oven to obtain a composite film with a thickness of 15 micrometers. The resulting composite film was not homogeneous in which montmorillonite was agglomerated. [0065] (Comparative Examples 3 and 4)

The composite films were prepared in the same operation as in Comparative Example 2 so that the content of clay minerals to polyimide meets the conditions described in Table 1. The resulting films were not homogeneous in which montmorillonite was agglomerated. [0066] (Comparative Example 5)

In addition to this, a 2 % dispersion solution was obtained by adding 1.6 g of an organic montmorillonite treated with dimethyldistearylammonium (S-BEN NX, manufactured by Hojun Co., Ltd.) to 78.4 g of NMP and stirring for 1 hour while applying ultrasonic treatment. This dispersion solution was used as a second solution. A ho- mogeneous solution was obtained by adding 4.87 g of the second solution to 20 g of the first solution. The homogeneous solution was applied on a glass substrate and dried by increasing the temperature from 50 degrees C to 200 degrees C at a heating rate of 5 degrees C/min and subsequently thermally treated at 200 degrees C for 5 hours in an inert oven to obtain a composite film with a thickness of 16 micrometers. In addition, the physical properties of the resulting composite film are shown in Table 1. [0067] (Comparative Examples 6 and 7)

The composite films were prepared in the same operation as in Comparative Example 5 so that the content of clay minerals to polyimide meets the conditions described in Table 1. The physical properties of the resulting composite films are shown in Table 1. [0068] (Comparative Example 8)

A solution was prepared by adding NMP to the polyamic acid solution produced in Synthesis Example 1 so that the weight the polyimide after imidization is 10 % by weight. This solution was used as a first solution.

In addition to this, a 2 % aqueous dispersion solution was obtained by adding 1.6 g of a montmorillonite (Kunipia G, manufactured by Kunimine Industries Co., Ltd.) which was not subjected the organic modification to 78.4 g of water and stirring at 10,000 rpm for 1 hour by a homogenizer. To this solution was added 80 g of NMP to obtain a 1 % dispersion solution, which was used as a second solution. A homogeneous solution was obtained by adding 10.53 g of the second solution to 20 g of the first solution. This homogeneous solution was applied on a glass substrate and dried by increasing the temperature from 50 degrees C to 200 degrees C at a heating rate of 5 degrees C/min and subsequently thermally treated in an inert oven at 200, 250, 300 and 350 degrees C for 1 hour, respectively, to obtain a composite film with a thickness of 15 to 20 micrometers. In addition, the physical properties of the resulting composite film are shown in Table 1. [0069] (Comparative Example 9)

The composite film was prepared in the same operation as in Comparative Example 8 so that the content of clay minerals to polyimide meets the conditions described in Table 1. The physical properties of the resulting composite films are shown in Table 1. [0070] (Comparative Example 10)

A solution was prepared by adding NMP to the polyamic acid solution produced in Synthesis Example 1 so that the weight of the polyimide after imidization is 10 % by weight. This solution was used as a first solution.

In addition to this, a 1 % aqueous dispersion solution was prepared by adding 0.8 g of montmorillonite (Kunipia G, produced by Kunimine Industries Co., Ltd.) which is not subjected to the organic modification to 79.2 g of water and stirring at 10,000 rpm for 1 hour by a homogenizer. This dispersion solution was used as a second solution. When 10.53 g of the second solution was gradually added to 20 g of the first solution, brownish yellow precipitates were produced and no homogeneous solution was obtained. [Table 1]

Claims

[1] A process of producing a composite film, wherein said process comprises: a step (A) of dissolving a polyimide precursor in a first solvent, a step (B) of dispersing a clay mineral which is not subjected to the organic modification in a second solvent, a step (C) of preparing a mixture solution by admixing the solution obtained by the above step (A) with the dispersion solution obtained by the above step (B), and a step(D) of forming a film by spreading the mixture solution obtained by the above step (C) on a substrate followed by drying the solvents.

[2] The process of producing a composite film according to claim 1, wherein said first solution is a basic solvent.

[3] The process of producing a composite film according to claim 1 or 2, wherein said second solvent is water.

[4] The process of producing a composite film according to any of claims 1 to 3, wherein said clay mineral is a layered clay mineral.

[5] The process of producing a composite film according to any of claims 1 to 4, wherein said clay mineral is not less than 1 part by weight and not more than 50 parts by weight based on 100 parts by weight of said composite film.

[6] The process of producing a composite film according to claim 4 or 5, wherein said clay mineral contained in said insulating resin layer is smectite group clay minerals or at least one kind selected from the group of swelling mica, vermiculite and halloysite.

[7] The process of producing a composite film according to any of claims 1 to 6, wherein said polyimide precursor is a polyimide precursor containing a polyimide polymer and/or a polyamide acid copolymer synthesized from one or more kinds of diamines and one or more kinds of tetracarboxylic acid anhydrides.

[8] The process of producing a composite film according to any of claims 1 to 7, wherein said polyimide precursor, as at least one diamine compound, is a polyimide precursor produced by using a compound represented by the following general formula (1):

[9] The process of producing a composite film according to any of claims 1 to 7, wherein said polyimide precursor, as at least one diamine compound, is a polyimide precursor produced by using a compound represented by the following general formula (2): [Chem.4]

[10] A process of producing a composite film, wherein the composite film obtained by the process of producing a composite film according to any of claims 1 to 9 is a film used for a circuit substrate.

[H] A process of producing a composite film, wherein the composite film obtained by the process of producing a composite film according to any of claims 1 to 9 is a film used for a flexible circuit substrate.

[12] A process of producing a composite film, wherein the composite film obtained by the process of producing a composite film according to any of claims 1 to 9 is a film used for a chip-on-film substrate.

[13] A process of producing a composite film, wherein the composite film obtained by the process of producing a composite film according to any of claims 1 to 9 has an elastic modulus of not less than 0.3

GPa and not more than 30 GPa at 450 degrees C.

[14] A process of producing a polyimide-clay mineral composite film, wherein the composite film obtained by the process of producing a composite film according to any of claims 1 to 9 has a light transmittance of not less than 50 % at a wavelength of 650 nm when the thickness of the film is 20 micrometers.

[15] A process of producing a composite film, wherein the composite film obtained by the process of producing a composite film according to any of claims 1 to 9 has a hygroscopic expansion coefficient of not less than 5 ppm/% RH and not more than 20 ppm/% RH at a relative humidity of 20 to 60 %.

[16] A process of producing a composite film, wherein the composite film obtained by the process of producing a composite film according to any of claims 1 to 9 has a water absorption of not more than 2 %.