JP2001151929A - Method for manufacturing porous polyimide film and film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a film having a porous layer in the central part thereof and dense layers on the both surfaces in a simple operation. SOLUTION: The method for manufacturing a porous polyimide film having dense layers on the both surfaces thereof and the central part comprising a porous layer comprises imidization by a heat treatment of a film-like composition (C) comprising a homogeneous solution (A) of a polyimide precursor and a poor solvent of the polyimide precursor, the poor solvent (B) having a boiling point or a thermal decomposition temperature higher than or equal to the imidization initiation temperature of the polyimide precursor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a porous polyimide film having a dense layer on both surfaces and a porous layer in the center, and more particularly to a low dielectric constant film useful in the electronic field. .

[0002]

2. Description of the Related Art Hitherto, a porous polyimide membrane having excellent heat resistance, chemical resistance and mechanical strength has been known for high performance gas separation. As described in JP-A-49-45152, for example, a polyamic acid obtained by a polymerization reaction between an aromatic tetracarboxylic dianhydride and an aromatic diamine is used as the porous polyimide membrane for gas separation. Is cast onto a liquid thin film, and the thin film is precipitated while being imidized in a non-solvent by a method for producing an aromatic polyimide gas separation membrane.

Further, a solution of a polyamic acid obtained by a polycondensation reaction between a tetracarboxylic dianhydride and an aromatic diamine is prepared, a liquid thin film is formed with the solution of the polyamic acid, and the thin film is mixed with a non-solvent. And finally obtained by a method for producing a semipermeable membrane of the polyamic acid.
Furthermore, while partially forming imidation while forming a thin film with a solution of polyamic acid, the thin film is deposited in a non-solvent, and finally, the semipermeable membrane of polyamic acid-imide is heated to complete imidization. There is known a method for producing a semipermeable membrane of polyimide by using the method. Further, a method is known in which a liquid thin film of a polyamic acid is precipitated in an imidizing agent-containing non-solvent while being imidized, and the obtained imide film is heated.
Then, a method is known in which a polyamic acid dissolved in a solvent is cast into a film and then brought into contact with a non-solvent to induce phase separation and precipitation of the polyamic acid.

[0004] The polyimide porous membrane produced by these methods has a dense layer formed on one surface and a porous layer formed on the other surface in contact with a non-solvent. Express the ability. However, such a polyimide porous film cannot be said to be suitable as a low dielectric constant film in which a coating type adhesive is used because the porous layer on one side has a porous structure.

On the other hand, as a low dielectric constant polymer film,
Japanese Patent Application Laid-Open No. Hei 9-100363 discloses a low dielectric constant plastic insulating film composed of a low dielectric constant foamed resin film and a laminate. As a specific example, a foam body in which both surfaces are bonded with a non-porous film is described. That is, it is considered that a flat film without firing is suitable for the surface layer.

[0006]

However, the above-mentioned production method requires two kinds of base materials, that is, a laminate of a low dielectric constant foamed resin film and a non-porous film, and an adhesive. The heat resistance of the dielectric plastic insulating film is reduced, and a step of laminating two types of base materials is required. An object of the present invention is to provide a method for producing a film having a porous layer at the center of the film and a dense layer on both surfaces by a simple operation.
Another object of the present invention is to provide a porous film and a low dielectric constant film having a porous layer at the center of the film and a dense layer on both surfaces obtained by a simple operation.

[0007]

The present invention provides a film composition (C) comprising a homogeneous solution (A) of a polyimide precursor and a poor solvent (B) of the polyimide precursor, wherein the poor solvent is Has a boiling point or a thermal decomposition point at a temperature higher than or equal to the imidation start temperature of the polyimide precursor, and heat-treats the film-like composition to imidize the film, characterized in that a dense layer is formed on both surfaces of the film. And a film central portion relates to a method for producing a porous polyimide film comprising a porous layer. The present invention also relates to a single-layer or multi-layer porous film containing, as a constituent element, the porous polyimide film obtained by the above-mentioned production method. The present invention also relates to a low-dielectric-constant film made of a porous polyimide obtained by the above production method.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be listed below. 1) The method for producing a porous polyimide film described above, wherein the homogeneous solution (A) of the polyimide precursor comprises 0.3 to 60% by weight of the polyimide precursor and 99.7 to 40% by weight of a good solvent. 2) The film-form composition (C) is prepared by adding 100 parts by weight of the homogeneous solution (A) of the polyimide precursor to the poor solvent (B) 10 to 10 parts by weight.
The above method for producing a porous polyimide film, which is obtained by adding 40 parts by weight to form a uniform mixed solution and casting the mixed solution on a substrate.

3) The film composition (C) is prepared by casting a homogeneous solution (A) of a polyimide precursor on a substrate to form a solution film, and immersing the solution film in a coagulation bath of a poor solvent (B). The method for producing a porous polyimide film as described above, which is obtained by removing a film-like material from a coagulation bath by depositing the film-like material. 4) Production of the above porous polyimide film in which the poor solvent (B) is removed from the film-like composition (C) by vaporization or thermal decomposition during a step in which the polyimide precursor is heat-treated and imidization proceeds. Law.

5) A film obtained by subjecting the film composition (C) to heat treatment and imidization has a total thickness of 5 to 150 μm and a dense layer having a thickness of 10 nm or more on each side. And the sum of the thicknesses of the dense layers on both sides of the film is not more than about 50% of the total thickness of the film. 6) A low dielectric constant film according to the above manufacturing method, which is used as an insulating material in a metal layer-insulating material laminate including an insulating material and a metal layer as essential constituent materials.

The polyimide precursor in the present invention is a polyamic acid obtained by polymerizing a monomer of a tetracarboxylic acid component and a diamine component, preferably a monomer belonging to an aromatic compound, or a partially imidized polyamic acid. By heat treatment and thermal imidization or chemical imidization, the ring can be closed to obtain a polyimide resin. The polyimide resin is a heat-resistant polymer having an imidization ratio of about 50% or more, which will be described later.

A tetracarboxylic acid component and an aromatic diamine component are dissolved and polymerized in an approximately equimolar amount in an organic solvent, preferably with a logarithmic viscosity (30 ° C., concentration; 0.5 g / 100 mL).
A polyimide precursor which is a polyamic acid having an NMP of 0.3 or more, especially 0.5 to 7 is produced. When the polymerization is carried out at a temperature of about 80 ° C. or higher, a polyimide precursor which is partially closed and imidized is produced.

The organic solvent for producing the above polyimide precursor includes parachlorophenol, N-methyl-2-pyrrolidone (NMP), pyridine, N, N-dimethylacetamide (DMAc), N, N -Dimethylformamide, dimethylsulfoxide, tetramethylurea,
Phenol, cresol and the like.

The above-mentioned tetracarboxylic acid component includes:
3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (hereinafter sometimes abbreviated as s-BPDA),
Biphenyltetracarboxylic dianhydride such as 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride (hereinafter sometimes abbreviated as a-BPDA) is preferable,
2,3,3 ', 4'- or 3,3', 4,4'-biphenyltetracarboxylic acid, or 2,3,3 ', 4'-
Alternatively, a salt of 3,3 ′, 4,4′-biphenyltetracarboxylic acid or an esterified derivative thereof may be used.
The biphenyltetracarboxylic acid component may be a mixture of the above biphenyltetracarboxylic acids.

The above-mentioned tetracarboxylic acid component includes pyromellitic acid, 3,3 ', 4,4' as tetracarboxylic acid in addition to the above-mentioned biphenyltetracarboxylic acids.
-Benzophenonetetracarboxylic acid, 2,2-bis (3,4-dicarboxyphenyl) propane, bis (3,4-dicarboxyphenyl) sulfone, bis (3,4-dicarboxyphenyl) ether, bis ( Tetracarboxylic acids such as (3,4-dicarboxyphenyl) thioether, butanetetracarboxylic acid, or acid anhydrides, salts or esterified derivatives thereof may be used. %, Particularly preferably 5 mol% or less.

As the aromatic diamine, for example,
Following formula _{H 2 N-Bz (R 1} ) m - [A- (R 2) n Bz] l -NH 2 ( where in the general formula, Bz is a benzene ring,
R ₁ or R ₂ is a substituent such as hydrogen, lower alkyl, lower alkoxy, etc., and A is independently a direct bond, O, S, C
A divalent group such as O, SO ₂ , SO, CH ₂ , C (CH ₃ ) ₂ , 1 is an integer of 0 or 1-2, and m or n is 1 to
4 is an integer. The aromatic diamine compound represented by the formula (1) is preferred.

Specific compounds of the aromatic diamine represented by the above formula include 4,4'-diaminodiphenyl ether (hereinafter sometimes abbreviated as DADE), 3,3
3'-dimethyl-4,4'-diaminodiphenyl ether, 3,3'-diethoxy-4,4'-diaminodiphenyl ether, para-phenylenediamine (PPD) and the like. Also, a mixture of the above compounds may be used. Alternatively, the aromatic diamine may be diaminopyridine, and specific examples include 2,6-diaminopyridine, 3,6-diaminopyridine, 2,5-diaminopyridine, and 3,4-diaminopyridine. No.

In the present invention, the film-like composition (C) comprising the homogeneous solution (A) of the polyimide precursor and the poor solvent (B) of the polyimide precursor is heat-treated to imidize it. The homogeneous solution (A) of the polyimide precursor in the present invention comprises the above-mentioned polyimide precursor and a good solvent. Homogeneous solution of this polyimide precursor (A)
May be used as it is, or may be obtained by separating and obtaining or concentrating a polyimide precursor, mixing with a good solvent and dissolving.

Examples of good solvents for the polyimide precursor include parachlorophenol, N-methyl-2-pyrrolidone (NMP), pyridine, N, N-dimethylacetamide (DMAc), N, N-dimethylformamide, Dimethyl sulfoxide, tetramethyl urea and the like can be mentioned.

A homogeneous solution of the above polyimide precursor (A)
Is preferably 0.3 to 60% by weight, especially 1 to 30% by weight of the polyimide precursor and a good solvent 9 for the polyimide precursor.
It is a solution consisting of 9.7 to 40% by weight, especially 99 to 70% by weight. When the proportion of the polyimide precursor is less than 0.3% by weight, the mechanical strength of the film becomes small, and when the proportion of the polyimide precursor is more than 60% by weight, it becomes difficult to obtain a uniform solution, which is not preferable. The homogeneous solution (A) of the polyimide precursor preferably has a solution viscosity of 10 to 10,000 poise, particularly 40 to 3000 poise. If the solution viscosity of the homogeneous solution (A) of the polyimide precursor is less than 10 poise, the strength of the obtained porous film is decreased, and if it is more than 10,000 poise, it is difficult to cast the film into a film. Absent.

The poor solvent (B) for the polyimide precursor has a boiling point or a thermal decomposition temperature at a temperature higher than or equal to the imidation start temperature of the polyimide precursor (generally, about 170 ° C.). Solvent is used. Such a solvent may be a solvent that does not dissolve the polyimide precursor at all. Here, the temperature equivalent to the imidization start temperature means a temperature of about 10 to 20 ° C. before and after 170 ° C. Further, the poor solvent (B) is preferably a solvent that is compatible with a good solvent of the polyimide precursor. The poor solvent (B) is a non-solvent of a polyimide precursor having a boiling point or a thermal decomposition point at a temperature lower than the imidization start temperature, for example, water, methanol, ethanol or the like in an amount of 50% by volume or less. Can be included in proportions.

In particular, as the poor solvent (B), a poor solvent having a higher boiling point than the good solvent of the polyimide precursor constituting the homogeneous solution (A) of the polyimide precursor is preferable. Specifically, a poor solvent having a boiling point or a thermal decomposition point of 150 to 500 ° C., more preferably a boiling point or a thermal decomposition point of 17 to
It is a poor solvent of 0 to 300 ° C.

As the poor solvent (B) for the polyimide precursor, one which is removed from the film-like composition (C) by vaporization or thermal decomposition during the step of heat imidization of the polyimide precursor proceeds Is desirable. During the step in which the poor solvent (B) undergoes thermal imidization,
If not removed from the film-like composition (C), the resulting porous film is not preferred in the field of electronic materials.

The poor solvent (B) which satisfies the above conditions includes a linear primary alcohol having 7 or more carbon atoms, a secondary alcohol having 7 or more carbon atoms, a branched alcohol, and a cyclic alcohol. Alcohol, alicyclic alcohol, aromatic alcohol, and other high-boiling alcohols. Specifically, for example, n-heptanol (boiling point 176.3)
° C), n-octanol (bp 1793 ° C), n-nonal (boiling point 203 ° C), n-decanol (boiling point 231)
° C), n-undecanol (boiling point 243 ° C), 2-octanol (boiling point 179 ° C), 2-ethylhexanol (boiling point 184.7 ° C), 2,6-dimethyl-4-heptanol ( Boiling point 178 ° C), 3,5,5-trimethyl-1
-Hexanol (boiling point 194 ° C), tetrahydrofurfuryl alcohol (boiling point 178 ° C), α-terpineol (boiling point 219 ° C), furfuryl alcohol (boiling point 170
° C) and benzyl alcohol (boiling point: 205.8 ° C). In particular, n-decanol can be suitably used.

In the ether system as the poor solvent (B), methyl anisole (boiling point 171 ° -177 ° C.), ethylbenzyl ether (boiling point 186 ° C.), diisoamyl ether (boiling point 173.2 ° C.), 1,8-cineole (boiling point 176.4 ° C), phenetole (boiling point 170.3 ° C)
° C) and butylphenyl ether (boiling point: 210.2 ° C).

Furthermore, polyhydric alcohols and their derivatives as poor solvents (B) include ethylene glycol (boiling point 197 ° C.) and dipropylene glycol (boiling point 231.
8 ° C.), dipropylene glycol monoethyl ether (bp 198 ° C.), dipropylene glycol monobutyl ether (boiling point 231 ° C.), triethylene glycol dimethyl ether (boiling point 216 ° C.), trimethylene glycol (boiling point 213 ° C), hexylene glycol (boiling point 2
13 ° C.). In particular, ethylene glycol and the like can be suitably used.

In the present invention, the film composition (C) comprising the above-mentioned homogeneous solution (A) of the polyimide precursor and the poor solvent (B) of the polyimide precursor is subjected to heat treatment. In order to obtain the film composition (C), the following two methods can be used.

As the first method, 10 to 40 parts by weight, particularly 15 to 30 parts by weight, of the poor solvent (B) is added to 100 parts by weight of the homogeneous solution (A) of the polyimide precursor, and the mixture is uniformly mixed. A film composition (C) can be obtained by forming a solution and casting the mixed solution on a substrate. In the above method, if the amount of the poor solvent (B) is less than 10 parts by weight based on 100 parts by weight of the homogeneous solution (A), the effect of adding the poor solvent is small, and the amount of the poor solvent (B) is less than 40 parts by weight. If the amount is large, it is difficult to form a uniform mixed solution, so the above ratio is preferable. Each of the good solvent and the poor solvent (B) in the homogeneous solution (A) may be used alone or in combination of two or more.

As a second method, the above-mentioned homogeneous solution (A) of the polyimide precursor is cast on a substrate to form a solution film, and then this solution film is immersed in a coagulation bath comprising a poor solvent (B). Thus, a film-like material containing the poor solvent (B) is precipitated, and the film-like material is taken out of the coagulation bath to obtain a film-like composition (C).

As a method for obtaining the film composition (C) containing the poor solvent (B) according to the present invention, any of the above two methods may be used, but the film composition obtained by either method may be used. By heat-treating (C) in a state containing the poor solvent (B) and imidizing it, it is possible to form a porous polyimide film in which the central portion of the film is a porous layer and both surface portions of the film are dense layers. it can.

In the above two methods, a dope consisting of a mixed solution of a homogeneous solution (A) of a polyimide precursor and a poor solvent (B) or a dope consisting of a homogeneous solution (A) of a polyimide precursor is cast on a substrate. Examples of the method include a method of coating using a spray method or a doctor blade method,
Suitable examples include a method in which the polyimide precursor solution is cast on a substrate such as glass or a movable belt, and a method in which the polyimide precursor solution is extruded from a T-die. The dope solution for casting may contain a surfactant, a flame retardant, a coloring agent, or a reinforcing material such as glass fiber, silicon-based fiber, or inorganic powder. These additives and reinforcing materials may be added to the homogeneous solution (A) of the above-mentioned polyimide precursor, or a dope for casting may be used.
May be added to the solution.

In the present invention, the film composition (C) obtained as described above is dried by heating. This heat treatment is heated immediately after casting on a film,
It is preferable to proceed to the drying and imidation steps at a temperature at which imidization occurs. At this time, since the film-like composition (C) tends to separate from the substrate at the very beginning of the heat treatment step, it is preferable to fix the film separated from the substrate using a pin, a chuck or a pinch roll. .
The imidation of this film by heat treatment is preferably performed in the air, preferably at 280 to 500 ° C. for about 5 to 90 minutes. Also, the imidization can be performed by thermal imidization or chemical imidization.

The above chemical imidization is carried out by using an aliphatic acid anhydride,
The reaction is carried out using an aromatic acid anhydride as a dehydrating agent and using a tertiary amine such as triethylamine as a catalyst. Further, as disclosed in JP-A-4-339835, imidal, benzimidazole, or a substituted derivative thereof may be used.

[0034] The multilayer polyimide porous film can be produced by suitably laminating the film-like composition (C), followed by heat treatment and imidization treatment. .

The porous polyimide film thus produced has heat resistance of 200 ° C. or more, and preferably has a thickness (total thickness) of 5 to 150 μm and a tensile strength of 200 to 1
000 kgf / cm ² , the thickness of the dense layer is 10 nm or more on each side, the total thickness of the dense layer is about 50% or less of the thickness of the entire film, and the porosity is 30 to
85%, especially 40-70%, the average pore size of the porous layer is 0.
It is about 0.01 to 5 μm, especially about 0.05 to 1 μm. If the thickness of the entire film is less than 5 μm, the mechanical strength of the film is poor, and if it is more than 150 μm, the flexibility is poor.
On the other hand, if the thickness of the dense layer is smaller than 10 nm on each side, it is not preferable because defects easily occur in the surface dense layer. On the other hand, if the total thickness of the dense layer is about 50% or more of the thickness of the entire film, the portion of the porous layer is too small, and the effect of the porous film, for example, the effect of a low dielectric constant, is not preferable.

The porous polyimide film of the present invention is a low dielectric constant film. The dielectric constant of the porous polyimide film of the present invention will depend on the porosity, 25 ° C., 10 ³ Hz
Under the conditions described above, the dielectric constant of the bulk polyimide film is 3.
It is 1.3 to 2.8 while it is 2 to 3.4.

The porous polyimide film obtained by the present invention may be used alone or in combination of two or more layers. By combining two or more layers, it can be used for reinforcement or for thick objects depending on the application. Further, it may be used in combination with another material, another polymer film, fiber, or inorganic substance.

When mounting the porous polyimide film of the present invention, it is also possible to use a single layer or a plurality of layers of the porous polyimide film, and a new dense polyimide film to be laminated on the porous polyimide film. It is. Further, for example, the porous polyimide film of the present invention can be laminated on an organic, inorganic or metal substrate such as a polyimide film, a silicon substrate, a glass substrate, a carbon substrate, or an aluminum substrate via a heat-resistant adhesive.

On one or both sides of the porous polyimide film of the present invention, a heat-resistant film-like adhesive layer such as thermoplastic polyimide or polyimide siloxane-epoxy resin is laminated, and an aromatic polyimide, A laminate can be obtained by providing a protective film made of a resin film such as an aromatic polyester, polyethylene, polypropylene, or polybutene-1. This laminate prevents dust from adhering and facilitates transportation, peels off the protective film at the time of use, and is a conductive metal foil for electronic circuits known per se such as electrolytic copper foil, rolled copper foil, and rolled aluminum foil. And a circuit board can be easily obtained.

Further, a heat-resistant adhesive solution is applied to one or both sides of the porous polyimide film of the present invention, dried, and then a conductive metal foil for an electronic circuit is laminated thereon to obtain a laminate. it can.

Further, the porous polyimide film of the present invention and an inorganic substrate such as a silicon substrate, a glass substrate or a carbon substrate, or a metal substrate such as an aluminum substrate may be used.
The laminate is sandwiched between heat-resistant adhesive layers, and then heat-pressed. Then, the other surface of the porous polyimide film, which is the porous insulating material of the laminate, and the conductive metal foil are heated with the heat-resistant adhesive layer. The laminate can be obtained by pressure bonding. Furthermore, an inorganic, organic or metal substrate such as a silicon substrate is bonded to one surface of the porous polyimide film of the present invention via a heat-resistant adhesive, and the other surface is directly or via a heat-resistant adhesive. A laminate provided with a metal layer may be used. In this case, as the conductive metal layer for the circuit, a metal known per se such as copper, nickel, chromium, or aluminum is used in various combinations of vapor deposition (vacuum vapor deposition or sputtering) and plating (electroless plating, electroplating). Conductive metal layer may be formed. In addition,
Depending on the environment, the porous polyimide film of the present invention may be used after removing moisture contained in the pores or polyimide by heating and drying.

[0042]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. In each of the following examples, the following physical properties of the porous film were measured and evaluated.

Tensile strength Measured according to JIS K7127. Using a Tensilon universal testing machine (manufactured by Toyo Boldwin Co., Ltd.), the measurement was performed at a tensile speed of 10 mm / min. Porosity The thickness and weight of the porous film cut into a predetermined size were measured, and the porosity was determined from the basis weight by the following formula. In the formula, S is the area of the porous film, d is the film thickness, W is the measured weight, D is the density of the polyimide, and the density of the polyimide was 1.34 g / m ³ . Porosity (%) = 100−100 × (W / D) / (S ×
d)

Thickness and Ratio of Dense Layer The cross section of the porous film was cut out, and the thickness of the dense layer and the total thickness of the film were measured with a scanning microscope to determine the ratio of the dense layer. Heat shrinkage A sample with a scale marked on a predetermined length
After leaving still in an oven set at 5 ° C. for 8 hours, the dimensions after removal were measured. The heat shrinkage ratio follows the following equation. L _{1 in the} following equation
Means the film dimensions after removal from the oven;
₀ means the initial film size. Heat shrinkage (%) = [1− (L ₁ / L ₀ )] × 100

Piercing Strength A sample was fixed to a circular holder having a diameter of 11.28 mm and an area of 1 cm ² , and a tip having a tip shape of 0.5R and a diameter of 1 mmΦ.
The dollar was lowered at a speed of 2 mm / sec and pierced, and the penetration load was measured. The dielectric constant was measured at a frequency of 1000 Hz according to JIS-C-6481.

Example 1 s-BPDA was used as a tetracarboxylic acid component and DADE was used as a diamine component.
NMP (bp 202 ° C.) so that the molar ratio of DE is 0.994 and the total weight of the monomer components is 18% by weight.
And polymerized at 40 ° C. for 6 hours to obtain a homogeneous solution (A) of a polyimide precursor.

A homogeneous solution of the above-mentioned polyimide precursor (A)
N-decanol (bp 231 ° C.) as a poor solvent (B)
Is added, the polyimide precursor is about 15% by weight, NM
A dope solution containing 68% by weight of P and 17% by weight of n-decanol was prepared.

The above dope solution was cast on a glass plate so as to have a thickness of about 150 μm, and dried at about 80 ° C. In a state where the polyimide precursor film (polyimide precursor gel) peeled off from the glass plate at the beginning of drying is fixed to a pin tenter, heat treatment is performed at 300 ° C. for 40 minutes in the air to obtain a porous polyimide film. Was.

Observation of the cross section of the obtained porous polyimide film with a scanning microscope showed that both surface layers were dense layers and had continuous fine pores in the center in the cross section direction. The measurement results of the tensile strength, film thickness, porosity, surface morphology, dense layer thickness, central morphology, heat shrinkage, and piercing strength of this porous polyimide film are shown below.

Evaluation results Tensile strength 460 kgf / cm ² Film thickness 85 μm Porosity 65% Surface morphology Dense layer Dense layer thickness 2.1 μm (both sides) Central part porosity Layer heat shrinkage 0.3% Puncture strength 385 gf

Example 2 As a poor solvent (B) added to a homogeneous solution (A) of a polyimide precursor, ethylene glycol was used in place of n-decanol.
(Bp 197.8 ° C.) to prepare a dope solution containing about 10% by weight of the polyimide precursor, 48% by weight of NMP, and 42% by weight of ethylene glycol. Was carried out in the same manner as in Example 1 except that a porous polyimide film was obtained. The structure and tensile strength of the obtained porous polyimide film obtained by observing the cross section of the film with a scanning microscope were the same as those obtained in Example 1. The measurement results of the film thickness, porosity, surface morphology, dense layer thickness, central morphology, heat shrinkage, and piercing strength are shown below.

Evaluation result Film thickness 83 μm Porosity 52% Surface morphology Dense layer Dense layer thickness 3.0 μm (both sides) Central part form Porous layer Heat shrinkage 0.3% Puncture strength 408 gf

Example 3 As a poor solvent (B), ethylene glycol (bp 197.
(8 ° C.), a homogeneous solution (A) of the polyimide precursor is spread upstream of the glass plate to form a solution film, which is immersed together with the glass plate in a coagulation bath of ethylene glycol to precipitate a film. The deposited film was taken out of the coagulation bath, fixed with a pin tenter, and immediately
Heating for 0 minutes and imidization yielded a porous polyimide film. The structure and tensile strength of the obtained porous polyimide film obtained by observing the cross section of the film with a scanning microscope were the same as those obtained in Example 1. The measurement results of the film thickness, the porosity, the surface shape, the shape of the dense layer at the center of the thickness, the heat shrinkage, and the piercing strength are shown below.

Evaluation Results Thickness 84 μm Porosity 49% Surface Morphology Dense Layer Dense Layer Thickness 1.8 μm (both sides) Central Morphology Porous Layer Heat Shrinkage 0.3% Puncture Strength 410 gf

Comparative Examples 1-2 Ethanol (bp 78.3 ° C.) was used in place of n-decanol as the poor solvent (B) (Comparative Example 1), or methanol (bp 64.1 ° C.) ) Was performed in the same manner as in Example 1 except that) was used. The resulting polyimide film is
According to the scanning microscope observation of the film cross section, each of the films was a film having only a dense layer without a porous layer.

Example 4 A homogeneous solution (A) of a polyimide precursor obtained by using PPD instead of DADE as the diamine component was used, and the heating temperature (maximum temperature) was changed to 425 ° C. And a porous polyimide film was obtained. The evaluation result of this porous polyimide film is equivalent to that of Example 1.

Example 5 The porous polyimide films obtained in Examples 1 to 4 were evaluated as insulating materials. All exhibited good characteristics. The dielectric constant of the porous polyimide film obtained in Example 1 measured at 23 ° C. and 1000 Hz was 2.1, and the loss factor was 0.004.

Comparative Example 3 Evaluation was made using a commercially available nonporous polyimide film having a thickness of 25 μm. At 23 ° C. and 1000 Hz, the dielectric constant was 3.2, the loss coefficient was 0.004, and the dielectric constant was insufficient.

[0059]

According to the present invention, a porous polyimide film comprising a polyimide having excellent heat resistance, chemical resistance and mechanical strength, having both surface layers being dense layers and having continuous fine pores in the center in the cross-sectional direction of the film. Can be manufactured.

Continued on front page F-term (reference) 4F071 AA60 AC05 AC06 AF37 AH12 BB02 BC01 BC02 BC12 4F074 AA74 AD04 CB43 CB45 CC04W CC29Y CC29Z DA02 DA08 DA19 DA20 DA22 DA23 DA24 DA47 DA54 4J043 PA02 PC015 PC115 RA35 SA06 TA14 UA UA 012 UA UB122 UB152 UB292 UB302 UB401 UB402 VA021 VA022 VA062 YA06

Claims (9)

[Claims] 1. A homogeneous solution (A) of a polyimide precursor,
A film composition (C) comprising a poor solvent (B) of the polyimide precursor, wherein the poor solvent has a boiling point or a thermal decomposition point at a temperature higher than or equal to the imidation start temperature of the polyimide precursor. A method for producing a porous polyimide film comprising a dense layer on both surfaces of a film and a porous layer at the center of the film, wherein the film-like composition is subjected to a heat treatment to imidize the film. 2. A homogeneous solution (A) of a polyimide precursor,
0.3 to 60% by weight of polyimide precursor and 99.7 of good solvent
2. The method for producing a porous polyimide film according to claim 1, comprising from about 40% by weight to about 40% by weight. 3. A film-form composition (C) is obtained by adding 10 to 40 parts by weight of a poor solvent (B) to 100 parts by weight of a homogeneous solution (A) of a polyimide precursor to form a uniform mixed solution.
2. The method for producing a porous polyimide film according to claim 1, obtained by casting the mixed solution on a substrate. 4. A film composition (C) is prepared by casting a uniform solution (A) of a polyimide precursor on a substrate to form a solution film, and dipping the solution film in a coagulation bath of a poor solvent (B). 2. The method for producing a porous polyimide film according to claim 1, wherein the film-like substance is precipitated by removing the film-like substance from a coagulation bath. 5. The method according to claim 1, wherein the poor solvent (B) is removed from the film-like composition (C) by vaporization or thermal decomposition during a step in which the polyimide precursor is heated and imidization proceeds. Manufacturing method of porous polyimide film. 6. A film obtained by subjecting the film-like composition (C) to heat treatment and imidization has a total thickness of 5 to 150 μm and a thickness of the dense layer of 1% on each side.
0 nm or more, and the sum of the thicknesses of the dense layers on both sides of the film is about 50% or less of the total thickness of the film.
2. The method for producing a porous polyimide film according to 1. 7. A single-layer or multi-layer porous film containing the porous polyimide film obtained by the production method according to claim 1 as a constituent element. 8. A low dielectric constant film comprising a porous polyimide obtained by the production method according to claim 1. 9. The low dielectric constant film according to claim 8, which is used as an insulating material in a metal layer-insulating material laminate including an insulating material and a metal layer as essential constituent materials.