JP2008238788A - Laminated polyimide film, its manufacturing process, and flexible circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain polyimide film which can acquire extremely large peeling strength by increasing no water suction rate in case of gluing to metallic foil through an adhesive. <P>SOLUTION: In laminated polyimide film composed by laminating two or more layers of the polyimide film, the polyimide of at least one uppermost surface layer of the laminating polyimide film is a characteristic composed of polyimide obtained by thermally and/or chemically imide deriving a polyamic acid synthesized from aromatic diamine containing carboxy-4,4'-diaminodiphenylether of a ratio of 1 to 100 mol.%, and aromatic tetracarboxylate dianhydride or its derivative. This laminating polyimide film has water absorption rate of 3.0 wt.% or less and small dimensional change, and, further, peeling strength in case of pressure bonding through the metallic foil and the adhesive is high such as 10N/cm or more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laminated polyimide film, a method for producing the same, and a flexible circuit board using the laminated polyimide film. More specifically, a laminated polyimide film capable of obtaining extremely high peel strength when bonded to a metal foil via an adhesive without increasing water absorption, a method for producing the laminated polyimide film, and the same The present invention relates to a flexible circuit board.

  Polyimide usually refers to a polymer having a cyclic imide bond in the main chain, and aromatic polyimide has a rigid molecular structure due to conjugation of an aromatic ring and a strong bonding force between molecular chains due to a highly polar imide bond. High heat resistance, mechanical properties and chemical resistance. As a general synthesis method currently used industrially, diamine and tetracarboxylic dianhydride are polymerized in an equimolar amount to obtain a polyamic acid which is a polyimide precursor, and the solution is dried. A desired film or coating is formed and imidized using heat or a catalyst. Polyimides thus obtained are widely used for structural materials such as bearings of copying machines and automobile tire wheels after being molded, and as films for flexible printed circuit boards and insulation coating materials for electric wires.

  Above all, it is an indispensable material in the field of rapidly growing electronics, and as a base film for flexible circuit boards laminated with metal foil such as copper foil via an adhesive, it has excellent effects as a material with high insulation and heat resistance. Demonstrating. However, the polyimide film is required to have high peel strength with the metal foil in forming a high-density circuit. This is not always sufficient. There is a problem in that it may peel off and lack long-term reliability. In order to remedy this drawback, various electrical, physical or chemical treatments have been attempted on polyimide films. However, these treatments have a problem that a lot of reagents, time, and labor are required for the treatment steps. .

  That is, as a method for modifying the adhesive strength of the polyimide film, for example, a method of plasma-treating the film surface (see, for example, Patent Document 1) is known. In this case, the film surface is treated with an alkali. There is a problem that the number of processes increases because the post-plasma treatment is performed.

  Also known is a metal foil-clad laminate (see, for example, Patent Document 2) in which a silane coupling agent is applied to at least one or both of a polyimide film, a thermoplastic polyimide adhesive layer, and a metal foil. ing. However, in this case, the number of steps for applying the silane coupling agent is increased, and care must be taken in adjusting the pH of the silane coupling agent (because cyclic molecules are generated by intramolecular hydrogen bonding at low pH). On the other hand, it is considered that the interaction with the resin is weakened due to the bending structure at a high pH), but there is a problem that the adhesive strength is reduced.

  Furthermore, a polyimide film containing a titanium compound and excellent in adhesiveness (for example, see Patent Document 3) is also known. This method is intended to add titanium atoms to a polyimide film by applying a solution of an organic titanium compound or immersing a film in the solution. However, it is very difficult to add titanium atoms uniformly. There is a problem that quality control is difficult even though the adhesive force is partially improved.

  Furthermore, a solvent-soluble thermoplastic polyimide having excellent adhesion (see, for example, Patent Document 4) is also known, but in this case, when heated in the manufacturing process due to thermoplasticity, the polyimide film substrate is It had the disadvantage of sinking.

In addition to the above-mentioned peel strength, the polyimide film is required to have dimensional stability associated with higher functionality of the electronic component, and therefore it is preferable that the water absorption is low. This is because dimensional stability can be maintained by minimizing changes in size and shape due to water absorption. However, in order to sufficiently improve the peel strength, it is necessary to improve the affinity with the adhesive film, but such affinity is usually a hydrophilic group such as a hydroxyl group or a carboxyl group. In addition, the water absorption tends to increase as the peel strength increases (thus, the dimensional stability tends to decrease), and it is difficult to say that a film that satisfies both at the same time has not yet been completed.
Japanese Patent Laid-Open No. 8-12779 JP 7-137196 A JP-A-11-71474 JP 2003-27014 A

  This invention is made | formed as a result of examining as a subject the solution of the problem in the prior art mentioned above, and the place made into the objective increases a water absorption, when adhere | attaching with metal foil through an adhesive agent. The object is to obtain a polyimide film that can exhibit extremely high peel strength without any problems.

  Another object of the present invention is that the treatment for improving the peel strength of the polyimide film does not require many reagents, time, labor, etc., and is suitable for mass production, low cost and high quality and high peel. The purpose is to establish a method for producing a strength polyimide film.

  Furthermore, an object of the present invention is to provide a flexible circuit board that is thin, light and flexible using the polyimide film, and that achieves both miniaturization and multi-functionality.

（ただし、式中のｍ、ｎは０を含む４以下の整数であり、（ｍ＋ｎ）は１以上の整数である） As a result of intensive studies to achieve the above object, the present inventors have made a polyimide film a laminate of two or more layers, and the polyimide film present in at least one of the outermost surface layers is represented by the following general formula (I) A polyamic synthesized from an aromatic diamine containing carboxy-4,4'-diaminodiphenyl ether represented by 1 to 100 mol% and an aromatic tetracarboxylic dianhydride or a derivative thereof It has been found that the above object can be effectively achieved by comprising a polyimide obtained by imidizing an acid thermally and / or chemically, and has led to the present invention.

(However, m and n in the formula are integers of 4 or less including 0, and (m + n) is an integer of 1 or more.)

  In addition, the laminated polyimide film of the present invention includes an aromatic diamine containing carboxy-4,4′-diaminodiphenyl ether represented by the formula (I) at a ratio of 1 to 100 mol%, and an aromatic tetracarboxylic acid diester. It is characterized by being obtained by applying a polyamic acid synthesized from an anhydride or a derivative thereof to one or both sides of a polyimide film and imidizing it thermally and / or chemically.

Furthermore, it is preferable that the carboxy-4,4′-diaminodiphenyl ether is 3,3′-dicarboxy-4,4′-diaminodiphenyl ether represented by the following general formula (II).

（ただし、式中のＲ₁は、下記一般式で示される基のいずれかであり、

式中のＲ₂は、下記一般式で示される基のいずれかであり、

また、式中のＸ：Ｙのモル比は１：９９〜１００：０である。） The gist is that the polyimide of at least one outermost surface layer of the laminated polyimide film has a structural unit represented by the following general formulas (III) and (IV).

(However, R ₁ in the formula is _one of the groups represented by the following general formula,

R ₂ in the formula is any of the groups represented by the following general formula:

Moreover, the molar ratio of X: Y in the formula is 1:99 to 100: 0. )

  When the laminated polyimide film having the above structure is thermocompression bonded to a metal foil via an adhesive, the surface layer polyimide in contact with the adhesive may be composed of a polyimide having the characteristic structural unit. This is a condition for effectively achieving the object of the invention.

In addition, when thermocompression bonding with a copper foil via an adhesive, the peel strength measured by the following method is 10 N / cm or more, and the water absorption is 3.0 wt% or less. It is mentioned as preferable conditions.
(Peel strength: using Lailax R (registered trademark of DuPont) LF-0100, which is an adhesive film, a laminated polyimide film and a copper foil (thickness 35 μm, BAC-13-T manufactured by Japan Energy Co., Ltd.), 180 The strength obtained by heat-pressing for 60 minutes at a temperature of 4.4 × 10 ⁷ Pa and peeling off the obtained adhesive by the method described in JIS C5016-1994 is defined as the peel strength.
Water absorption rate: After immersing the laminated polyimide film in distilled water for 48 hours, the surface moisture was wiped off, and when heated from room temperature to 200 ° C. at a heating rate of 10 ° C./min. The weight reduction rate between 200 ° C. is the water absorption rate. )

  Further, as one of the methods for producing the laminated polyimide film of the present invention, an aromatic diamine containing the above carboxy-4,4′-diaminodiphenyl ether in a proportion of 1 to 100 mol% and an aromatic tetracarboxylic dianhydride It is preferable to apply a polyamic acid synthesized from a product or a derivative thereof to at least one surface of a polyimide film or a polyamic acid film and imidize it thermally and / or chemically.

  The flexible circuit board of the present invention is characterized in that a metal foil is pressure-bonded to a surface layer made of polyimide having the characteristic structure of the laminated polyimide film via an adhesive.

  Since the laminated polyimide film of the present invention has a polyimide having a novel polyamic acid as a precursor in its surface layer, the peel strength when pressed onto a metal foil via an adhesive is as high as 10 N / cm or more, and A water absorption is also 3.0 wt% or less, and when used as a base film for flexible circuit boards, dimensional stability and peel strength can be maintained for a long time.

  In addition, the process for improving the peel strength of polyimide film does not require a lot of reagents, time, and labor, and is suitable for mass production, providing a method for producing high quality, high peel strength polyimide at low cost. It is possible to provide a flexible circuit board that is thin, light and flexible using the laminated polyimide film, and that achieves both miniaturization and multi-functionality.

（ただし、式中のｍ、ｎは０を含む４以下の整数であり、（ｍ＋ｎ）は１以上の整数である） Hereinafter, the present invention will be specifically described in detail.
The laminated polyimide film of the present invention is characterized in that a polyimide present in at least one outermost surface layer (hereinafter sometimes referred to as “surface layer polyimide”) is obtained using a polyamic acid having a specific structure as a precursor. As is well known, the polyamic acid is obtained by reacting an aromatic diamine and an aromatic tetracarboxylic dianhydride or a derivative thereof in an approximately equimolar amount. In the present invention, the aromatic diamine is represented by the following formula (I). It is an essential condition to contain carboxy-4,4′-diaminodiphenyl ether represented by: This is because when the aromatic diamine is not contained, the obtained polyimide film does not exhibit the intended peel strength. Conventional representative polyimides used 4,4′-diaminodiphenyl ether as an aromatic diamine. Since this compound has two amino groups involved in the bond, no substituent remains on the aromatic ring after polymer formation, and the carboxy-4 of the present invention having a free carboxy group in the adhesive force with the adhesive film, 4'-diaminodiphenyl ether is superior. In addition, the outermost surface layer is a layer located on the outermost side of the polyimide film laminated in two or more layers, and means a surface layer used for adhesion to the metal foil through an adhesive. When stacking laminated polyimide films, adhesives, and metal foils, both outermost surface layers of the laminated polyimide film are used for adhesion to the adhesive, and therefore both outermost surface layers are both polyamic acids having the specific structure described above. It is necessary to be a polyimide obtained using as a precursor.

(However, m and n in the formula are integers of 4 or less including 0, and (m + n) is an integer of 1 or more.)

  The polyamic acid having a specific structure which is a precursor of the surface layer polyimide of the laminated polyimide film of the present invention will be described. As described above, the polyamic acid is synthesized from an aromatic diamine and an aromatic tetracarboxylic dianhydride or a derivative thereof. A polyamic acid having a specific structure uses carboxy-4,4′-diaminodiphenyl ether as an aromatic diamine, and the amount of the polyamic acid varies depending on other acid dianhydrides to be combined and cannot be uniquely determined. In this case, it is important that the amount be in the range of 1 to 100 mol%, preferably 5 to 100 mol%. The mol% in this case refers to the proportion of carboxy-4,4'-diaminodiphenyl ether when the total aromatic diamine is 100 mol%. This is because when the addition amount is less than the above range, it is difficult to obtain the intended peel strength.

The number of substituents of the carboxyl group of the carboxy-4,4′-diaminodiphenyl ether is one or more and may be polysubstituted. When the number of substituents is more than 3, it is desirable to use a relatively small amount as compared with the case of 2 substituents. This carboxy group improves the adhesive strength, but at the same time, it also hydrophilizes the polyimide film, so that an increase in water absorption may affect the dimensional stability. Furthermore, the substitution position of the carboxyl group is an arbitrary position, and specific examples thereof include 2,6′-dicarboxy-4,4′-diaminodiphenyl ether, 3,3′-dicarboxy-4,4′-diaminodiphenyl ether. And 2,3′-dicarboxy-4,4′-diaminodiphenyl ether. However, it is preferable to use 3,3′-dicarboxy-4,4′-diaminodiphenyl ether (the following formula (II)) from the viewpoint of simplicity in terms of synthesis.

  For the synthesis of the polyamic acid having the specific structure, in addition to the carboxy-4,4′-diaminodiphenyl ether, one or more of the following aromatic diamines (hereinafter sometimes referred to as “other aromatic diamines”) are appropriately combined. Can be used. Specifically, paraphenylenediamine, metaphenylenediamine, benzidine, paraxylylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diamino Diphenylsulfone, 3,3′-dimethyl-4,4′-diaminodiphenylmethane, 1,5-diaminonaphthalene, 3,3′-dimethoxybenzidine, 1,4-bis (3methyl-5aminophenyl) benzene, 3, 3'carboxy-4,4'-diaminodiphenylmethane, 2,6'-dicarboxy-4,4'-diaminobiphenyl, 3,3'-dicarboxy-4,4'-diaminobiphenyl and their amide-forming derivatives Is mentioned. Of these, 4,4'-diaminodiphenyl ether, which is easily available and used for typical polyimides, is particularly preferred. This is because the structure is similar to the carboxy-4,4′-diaminodiphenyl ether, and both react evenly in the synthesis of the polyamic acid, and the carboxy-4,4′-diamino is randomly added to the polyamic acid molecular chain. This is because the diphenyl ether units are dispersed, and a uniform adhesive strength after being formed into a film can be obtained.

  Further, when 3,3′carboxy-4,4′-diaminodiphenylmethane is used, it can be used for controlling the Young's modulus of the polyimide film. The amount used is preferably in the range of 1 to 10 mol%. The Young's modulus is a value obtained from the slope of the initial rising portion in a tension-strain curve obtained at a tensile speed of 100 mm / min with a Tensilon type tensile tester manufactured by ORIENREC at room temperature according to JISK7113. . The Young's modulus needs to be not less than 2.5 Gpa and not more than 7 Gpa. If it is less than 2.5 Gpa, handling properties are impaired, and if it is greater than 7 Gpa, flexibility is impaired.

  Furthermore, when 2,6′-dicarboxy-4,4′-diaminobiphenyl and / or 3,3′-dicarboxy-4,4′-diaminobiphenyl is used, the effect of improving the peel strength of the polyimide film is obtained. is there.

  The number of moles of the other aromatic diamines used is such that the total number of moles of carboxy-4,4′-diaminodiphenyl ether is substantially equal to the number of moles of aromatic tetracarboxylic acid in the polyamic acid synthesis system. Can be added. This is because polyamic acid is an alternating polymer of aromatic diamine and aromatic tetracarboxylic acid, and is based on equimolar reaction.

  An aromatic tetracarboxylic dianhydride or a derivative thereof, which is another component of the polyamic acid having a specific structure, will be described. Specific examples of the aromatic tetracarboxylic dianhydride or its derivative include pyromellitic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 2,3 ′, 3,4′-biphenyltetracarboxylic acid. Acid 3,3 ′, 4,4′-benzophenone tetracarboxylic acid, 2,3,6,7-naphthalenedicarboxylic acid, 2,2-bis (3,4-dicarboxyphenyl) ether, pyridine-2,3 , 5,6-tetracarboxylic acid and their amide-forming derivatives. In the production of polyamic acid, acid anhydrides of these aromatic tetracarboxylic acids are preferably used. The aromatic tetracarboxylic acid anhydrides may be used in combination of two or more. Among these, pyromellitic dianhydride is particularly preferable from the viewpoint of easy acquisition and the results used for typical polyimides.

  The aromatic tetracarboxylic acids and aromatic diamines constituting the polyamic acid having the specific structure are polymerized in such a ratio that the respective mole numbers are substantially equal, and one of them is within the range of 10 mol%. It is preferable to mix | blend excessively with respect to the other, and it is more preferable to mix | blend excessively with respect to the other within the range of 5 mol%. This is because the excessively blended component will remain as an unreacted monomer later, but the smaller component is almost completely utilized for polymerization, so that the remaining component can be easily removed in the subsequent film formation process. . It is preferable to select other aromatic diamines as the component to be added in excess. In particular, 4,4′-diaminodiphenyl ether as other aromatic diamines is industrially produced in large quantities, and is advantageous in terms of cost, availability, and ease of removal of residual components. It is.

  Next, polymerization of a polyamic acid having a specific structure which is a precursor of the surface layer polyimide of the present invention will be described. In the polymerization reaction, it is preferable to use an organic solvent that dissolves each component of the reaction system. The solvent is desirably substantially non-reactive with all reaction components and the polyamic acid product. Specific examples of such solvents include sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide, and N, N-dimethyl. Formamide solvents such as formamide, N, N-diethylformamide, acetamide solvents such as N, N-dimethylacetamide, N, N-diethylacetamide, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, etc. List pyrrolidone solvents, phenol solvents such as phenol, o-, m-, or p-cresol, xylenol, halogenated phenol, and catechol, or aprotic polar solvents such as hexamethylphosphoramide and γ-butyrolactone. These can be used alone or as a mixture It is desirable to use Te, but further xylene, the use of aromatic hydrocarbons such as toluene are also possible. Of these, N, N-dimethylformamide and N, N-dimethylacetamide are preferable in terms of operability and cost in the polymerization reaction and the subsequent film forming step.

  The amount of the organic solvent used is preferably 5 to 40% by weight, more preferably 10 to 30% by weight as reaction components (aromatic tetracarboxylic acids and aromatic diamines). This is because the molecular weight of the resulting polyamic acid can be optimally controlled by setting this concentration. As a reaction procedure for obtaining a polyamic acid solution in the present invention, an aromatic diamine is added and dissolved in an organic solvent, and then a solution prepared by dissolving an aromatic tetracarboxylic dianhydride separately prepared in an organic solvent is added. Method or a method of adding an aromatic tetracarboxylic dianhydride in an organic solvent and dissolving it, and then adding a solution prepared by dissolving a separately prepared aromatic diamine in an organic solvent, and adding components to be added later as solids Any method can be used. At this time, as for the addition amount of aromatic tetracarboxylic dianhydride and aromatic diamine, one can add many as above-mentioned, or can also be made substantially equimolar. In a normal polymerization reaction, an aromatic diamine such as carboxy-4,4′-diaminodiphenyl ether is dissolved in the solvent, and a solution in which an aromatic tetracarboxylic dianhydride is dissolved in the solvent is added thereto. Is adopted.

  The polymerization reaction is preferably allowed to proceed continuously for 10 minutes to 30 hours in a temperature range of 0 to 80 ° C. while slowly stirring and / or mixing in an inert atmosphere according to the addition method. The polymerization reaction may be divided or the temperature may be increased or decreased. When several kinds of aromatic tetracarboxylic acids and / or aromatic diamines are used, the block polymer can be produced by alternately adding a solution in which each monomer is dissolved. Furthermore, vacuum degassing during the polymerization reaction is an effective method for producing a high-quality polyamic acid solution because oxygen and the like that inhibit the progress of the polymerization reaction are removed and the solution is made uniform.

  In addition, a small amount of end-capping agent such as aniline, 4-aminobiphenyl, 2-naphthylamine, phthalic anhydride, 3,4-diphenyl ether dicarboxylic acid anhydride, 1,8-naphthalene is added to aromatic diamines before the polymerization reaction. Control of polymerization reaction such as adjustment of molecular weight is performed by adding dicarboxylic acid anhydride etc. in the range of 1-10 mol% with respect to the total number of moles of aromatic diamines and aromatic tetracarboxylic dianhydrides. May be.

  Next, the laminated polyimide film of the present invention and the production method thereof will be described. The surface layer polyimide of the laminated polyimide film of the present invention can be obtained by imidizing a film having the specific structure polyamic acid as a precursor. Aromatic polyimide has a rigid molecular structure due to conjugation of aromatic rings and a strong bonding force between molecular chains due to highly polar imide bonds, so it generally does not have thermoplasticity, and it does not react with solvents. Since it is sparingly soluble, the precursor polyamic acid is used for molding. The solution of the polyamic acid having a specific structure may be prepared by directly using the solution of the polymerization reaction system, or once purifying the polyamic acid to remove the unreacted monomer and re-dissolving it in a solvent for film formation. You can also. The viscosity of the polyamic acid solution for film formation of the present invention is preferably in the range of 10 to 2000 Pa · s, more preferably in the range of 100 to 1000 Pa · s as measured by a Brookfield viscometer, for stable liquid feeding. This is because a viscosity in this range forms a uniform film thickness when forming a film, and an appropriate spread when a solution is applied can be obtained. The polyamic acid having a specific structure in the solution may be partially imidized.

  The laminated polyimide film of the present invention comprises (1) laminating a polyamic acid solution having a specific structure for forming the surface layer polyimide on a polyimide film or polyamic acid film not containing this, or (2) a surface layer first. After a film containing polyimide or a polyamic acid having a specific structure is formed, a polyamic acid film not containing the polyamic acid having the specific structure is laminated thereon. As a method of laminating, there is a co-extrusion method in which lamination is performed during extrusion inside a die from a lamination block, or a method in which lamination is performed after extrusion.

  For example, in the case of laminating the laminated polyimide film having a two-layer structure by the method (1), first, a polyamic acid solution that is a precursor of a polyimide film (hereinafter referred to as “polyimide substrate”) is first heated to a heating drum (belt). ) And then the organic solvent is dried with hot air of 70 ° C to 120 ° C. The polyimide substrate has a solvent content of 40% or less and is finally imidized by a treatment such as heating, but after laminating a polyamic acid solution having a specific structure, the whole may be imidized simultaneously. . When laminating a specific polyamic acid after the polyimide substrate is completely imidized, the polyimide substrate is not dissolved by the solvent when casting the polyamic acid solution later. Convenient. On the other hand, when a specific polyamic acid is laminated with the polyamic acid remaining in the polyimide substrate, the polyimide substrate and the surface layer polyimide are simultaneously imidized, so the bond between the layers of the laminate is stronger. Can be.

  A polyamic acid solution having a specific structure is further cast on the polyimide substrate obtained as described above, and the organic solvent is removed with hot air in the same manner. The laminated film having the two-layer structure thus formed is peeled off from the heating drum, the end is fixed, and then gradually heated at a temperature of 200 ° C. to 500 ° C., preferably 200 ° C. to 400 ° C. It is preferable to obtain a laminated polyimide film by performing heat treatment for ˜5 hours, preferably 2-3 hours. This is because dehydration and cyclization (imidization) can be advanced by heating, and at the same time, residual monomers and solvents can be removed. In the drying process after casting, the laminated film needs to have a solvent content of 5% or more and 40% or less before peeling from the heating drum. This is because if the solvent is contained more than this, wrinkles or the like may occur on the surface of the film during the peeling operation. Moreover, it is because peelability will worsen when there is too little solvent content.

  In addition, if the polyamic acid has a flat surface such as glass, metal, polymer film, and the polyamic acid is cast thereon, it can support the cast polyamic acid instead of the heating drum. Can also be used.

  Imidization may be performed by any of the chemical ring closure method using a dehydrating agent and a catalyst, or the ring closure method using both in addition to the heating method. Examples of the dehydrating agent used in the chemical ring closure method include aliphatic acid anhydrides such as acetic anhydride and acid anhydrides such as phthalic anhydride, and these are preferably used alone or in combination. The concentration range of the dehydrating agent is preferably 200 to 400 mol% with respect to the imide group. This is because the concentration of the component that does not contribute to the reaction only increases even if the concentration is higher than the above, and the sufficient effect is not exhibited if the concentration is lower than the above. Examples of the catalyst include heterocyclic tertiary amines such as pyridine, picoline and quinoline, aliphatic tertiary amines such as triethylamine, and aromatic tertiary amines such as N, N-dimethylaniline. These are preferably used alone or in combination. These catalyst addition amounts cannot be determined unconditionally depending on the catalyst used. For example, when β-picoline is used, it is used in a concentration range of 200 to 400 mol% with respect to the imide group. In addition, the physical property of a film can be improved more by heat-processing at 300 to 500 degreeC after completing imidation in the case of a chemical ring closure method.

  Prior to the casting, a tin (II) salt or a tin (IV) salt can be added to the polyamic acid solution so as to be 0.02 to 10% by weight. This is because further improvement in adhesion can be expected.

  On the other hand, as a method of applying a polyamic acid having a specific structure to a polyamic acid film or a polyimide film, “all coatings” (published December 10, 1999) or “Plastic coating technology overview” ( Roller coater, gravure coater, as described in the Materials Technology Research Association, Plastic Coating Technology Overview Editorial Committee, pp. 299-312, published by Industrial Technology Service Center Co., Ltd., August 3, 1989) There are knife coater, blade coater, knife coater, air doctor coater, screen coating, spray coating, vacuum coating, spin coater, impregnation coating and the like.

（ただし、式中のＲ₁は、下記一般式で示される基のいずれかであり、

式中のＲ₂は、下記一般式で示される基のいずれかであり、

また、式中のＸ：Ｙのモル比は１：９９〜１００：０である。） The polyimide of the surface layer thus obtained is characterized by having structural units represented by the following formulas (III) and (IV). In particular, the polyimide having a carboxy-4,4′-diaminodiphenyl ether unit represented by the formula (III) exhibits excellent properties in peel strength. The structural ratio of the structural unit X of the formula (III) and the structural unit Y of the formula (IV) is such that the peel strength has a desired strength when X: Y is in the range of 1:99 to 100: 0, and the dimensions described later. Although it is set on the basis that the linear expansion coefficient does not affect the stability, the constituent ratio is preferably 3:97 to 50:50, more preferably 5:95 to 20:80. Even if the structural unit of the formula (III) is relatively small, that is, sufficient peel strength can be obtained only by using a polyimide having a precursor of polyamic acid added with a small amount of carboxy-4,4′-diaminodiphenyl ether as an aromatic diamine. Because it can be obtained.

(However, R ₁ in the formula is _one of the groups represented by the following general formula,

R ₂ in the formula is any of the groups represented by the following general formula:

Moreover, the molar ratio of X: Y in the formula is 1:99 to 100: 0. )

  When the polyimide of the surface layer of the present invention is formed on both surfaces of the laminated polyimide film, the polyimide of both surface layers may be made of the same material or may be made of separate materials. The advantage of using the same material is that it only requires one type of polyamic acid with a specific structure to be manufactured, which is cost effective. The advantage of using a different material is that different adhesive films are used. Therefore, the peel strength can be adjusted according to the metal foil.

Here, the peel strength as used in the present invention refers to a laminate polyimide film and a copper foil (thickness 35 μm, BAC-made by Japan Energy Co., Ltd.) using Piralux R (registered trademark of DuPont) LF-0100 which is an adhesive film. 13-T) is the strength when the adhesive obtained by thermocompression bonding at 180 ° C. and 4.4 × 10 ⁷ Pa for 60 minutes is peeled off by the method described in JIS C5016-1994. .

  The peel strength can be further improved by subjecting the polyimide film to electrical treatment such as plasma treatment and corona treatment, physical treatment, and chemical treatment as necessary. However, in this invention, the value measured by the said method in the state which does not perform the said treatment at all is defined as peeling strength. This value is because the peel strength inherently possessed by the polyimide film is accurately reproduced.

  The peel strength of the polyimide film of the present invention is 10 N / cm or more, preferably 13 N / cm or more. A peel strength of less than 10 N / cm is not preferable because the metal foil layer may peel off when used as a flexible circuit board.

  Moreover, a low water absorption is mentioned as a characteristic of the polyimide film of this invention. The water absorption referred to in the present invention means that the laminated polyimide film was soaked in distilled water for 48 hours, and then the surface moisture was wiped off and heated from room temperature to 200 ° C. at a heating rate of 10 ° C./min by heating weight loss analysis. In this case, the weight reduction rate between 50 ° C. and 200 ° C. is defined as the water absorption rate. The smaller the water absorption rate, the better. On the other hand, when the water absorption rate is larger than 3.0 wt%, the polyimide film changes its dimensions due to water absorption when exposed to a high humidity environment, and in extreme cases it is flexible. Warpage may occur during use as a circuit board.

  The total thickness of the laminated polyimide film of the present invention is preferably 3 to 250 μm. That is, when the thickness is less than 3 μm, it is difficult to maintain the shape, and when it exceeds 250 μm, the flexibility is insufficient, so that it is difficult to apply to flexible circuit board applications. In this, the thickness of a polyimide base | substrate is 50 to 80% of the thickness of the whole lamination polyimide film, and surface layer polyimide is 25% to 10% of the thickness of the whole lamination polyimide film per side. When both surfaces of the laminated polyimide film are formed of the surface layer polyimide of the present invention, the thicknesses of the both surfaces may be the same or different. The laminated polyimide film of the present invention has the advantage that it can be adjusted to a preferred thickness by appropriately preparing the surface layer polyimide with respect to the polyimide substrate. In the present invention, only the surface layer used for adhesion may be made of polyimide having a specific polyamic acid as a precursor. Thereby, compared with the conventional polyimide film, peel strength is improved. The laminated polyimide film can be either stretched or unstretched. Furthermore, it is also possible to contain 10% by weight or less of an inorganic or organic additive for the purpose of improving processability.

  The laminated polyimide film of the present invention thus obtained has a water absorption of 3.0 wt% or less, excellent dimensional stability, and a high peel strength of 10 N / cm or more when pressed onto a metal foil via an adhesive. It is extremely useful as a base film for flexible circuit boards.

  The flexible circuit board of the present invention can be obtained by using the above laminated polyimide film as a base film and crimping a metal foil to this through an adhesive, but the adhesive used here is acrylic or polyimide. Although not particularly limited, Pyrarax R (registered trademark of DuPont), which is an adhesive film, can be suitably used.

  The metal foil that is thermocompression bonded to the laminated polyimide film of the present invention via an adhesive is preferably a copper foil, but other metal foils such as aluminum may be used.

  The flexible circuit board of the present invention thus obtained exhibits the performance of maintaining high peel strength over the long term and excellent dimensional stability.

The effects of the present invention will be described more specifically by the following examples. In addition, each physical property value in an Example is the value measured with the following method.
[Peel strength]
Using a Lailax R (registered trademark of DuPont) LF-0100, which is an adhesive film, a laminated polyimide film and a copper foil (thickness 35 μm, BAC-13-T manufactured by Japan Energy Co., Ltd.) at 180 ° C. The strength at which the pressure-sensitive adhesive was peeled off by the method described in JIS C5016-1994 is determined as the peel strength at 60 × 4 ⁷ Pa for 60 minutes.

[Water absorption rate]
After immersing the laminated polyimide film in distilled water for 48 hours, the moisture on the surface was wiped off, and when heated from room temperature to 200 ° C. at a rate of temperature increase of 10 ° C./min. The rate of weight loss between them is the water absorption rate. In addition, the sample shape of the laminated polyimide film used here is about 40 to 70 μm in thickness, 100 mm in length, and 5 mm in width.

[Example 1]
In a 300 ml separable flask equipped with a DC stirrer, 2.20 g (7.6 mmol) of 3,3′-dicarboxy-4,4′-diaminodiphenyl ether and 17.58 g (88 mmol) of 4,4′-diaminodiphenyl ether, N, N′-dimethylacetamide (149.62 g) was added, and the mixture was stirred at room temperature under a nitrogen atmosphere. Further, after 30 minutes to 1 hour, 20.19 g (93 mmol) of pyromellitic dianhydride was added in several portions in a solid (powder) state. After stirring for 1 hour, 12.36 g of an N, N′-dimethylacetamide solution (6 wt%) of pyromellitic dianhydride was added dropwise over 30 minutes, and the mixture was further stirred for 1 hour.

  100.00 g of the obtained polyamic acid solution was degassed for 5 minutes using a hybrid mixer manufactured by Keyence Corporation. A part of this polyamic acid mixture was placed on Kapton R200H (registered trademark of DuPont) having a thickness of 50 μm, and a uniform film was formed using an applicator. This was heated at 100 ° C. for 1 hour, then fixed to a metal frame, and heat-treated at 200 ° C. for 30 minutes, 300 ° C. for 30 minutes, and 400 ° C. for 5 minutes to obtain a laminated polyimide film having a thickness of 63 μm. The results of measuring the peel strength of the obtained laminated polyimide film are shown in Table 1.

[Example 2]
In a 300 ml separable flask equipped with a DC stirrer, 4.07 g (14 mmol) of 3,3′-dicarboxy-4,4′-diaminodiphenyl ether and 16.01 g (80 mmol) of 4,4′-diaminodiphenyl ether, N, 149.75 g of N′-dimethylacetamide was added and stirred at room temperature under a nitrogen atmosphere. Further, 19.91 g (91 mmol) of pyromellitic dianhydride was added in several portions over 30 minutes to 1 hour. After stirring for 1 hour, 11.75 g of a pyromellitic dianhydride N, N′-dimethylacetamide solution (6 wt%) was added dropwise over 30 minutes, followed by further stirring for 1 hour.

  The obtained polyamic acid was used in the same manner as in Example 1 to obtain a laminated polyimide film having a thickness of 61 μm. The results of measuring the peel strength of the obtained laminated polyimide film are shown in Table 1.

[Example 3]
In a 300 ml separable flask equipped with a DC stirrer, 6.64 g (23 mmol) of 3,3′-dicarboxy-4,4′-diaminodiphenyl ether and 13.85 g (69 mmol) of 4,4′-diaminodiphenyl ether, N, N'-dimethylacetamide 149.94g was put, and it stirred at room temperature under nitrogen atmosphere. Further, 19.51 g (89 mmol) of pyromellitic dianhydride was added in several portions over 30 minutes to 1 hour. After stirring for 1 hour, 10.45 g of an N, N′-dimethylacetamide solution (6 wt%) of pyromellitic dianhydride was added dropwise over 30 minutes, and the mixture was further stirred for 1 hour.

  The obtained polyamic acid was used in the same manner as in Example 1 to obtain a laminated polyimide film having a thickness of 64 μm. The results of measuring the peel strength of the obtained laminated polyimide film are shown in Table 1.

[Comparative Example 1]
In a 500 ml separable flask equipped with a DC stirrer, 38.48 g (190 mmol) of 4,4′-diaminodiphenyl ether and 320.00 g of N, N′-dimethylacetamide were placed and stirred at room temperature under a nitrogen atmosphere. Further, after 30 minutes to 1 hour, 40.27 g (185 mmol) of pyromellitic dianhydride was added in several portions. After stirring for 1 hour, 22.01 g of a pyromellitic dianhydride N, N′-dimethylacetamide solution (6 wt%) was added dropwise over 30 minutes, followed by further stirring for 1 hour.

  It stirred for 5 minutes using 100.00 g of obtained polyamic acids and the hybrid mixer by Keyence Corporation. A part of this polyamic acid mixture was taken on a polyester film, and a uniform film was formed using an applicator. This was heated at 100 ° C. for 1 hour and peeled off from the polyester film to obtain a self-holding polyamic acid film. The obtained film was heat-treated at 200 ° C. for 30 minutes, 300 ° C. for 30 minutes, and 400 ° C. for 5 minutes to obtain a 46 μm thick polyimide film. The results of measuring the peel strength of the obtained polyimide film are shown in Table 1.

[Comparative Example 2]
In a 300 ml separable flask equipped with a DC stirrer, 2.20 g (7.6 mmol) of 3,3′-dicarboxy-4,4′-diaminodiphenyl ether and 17.58 g (88 mmol) of 4,4′-diaminodiphenyl ether, N, N′-dimethylacetamide (149.62 g) was added, and the mixture was stirred at room temperature under a nitrogen atmosphere. Further, after 30 minutes to 1 hour, 20.19 g (93 mmol) of pyromellitic dianhydride was added in several portions. After stirring for 1 hour, 12.36 g of an N, N′-dimethylacetamide solution (6 wt%) of pyromellitic dianhydride was added dropwise over 30 minutes, and the mixture was further stirred for 1 hour.

  A polyimide film having a thickness of 52 μm was obtained using the obtained polyamic acid in the same manner as in Comparative Example 1. The results of measuring the peel strength of the obtained polyimide film are shown in Table 1.

[Comparative Example 3]
In a 300 ml separable flask equipped with a DC stirrer, 4.07 g (14 mmol) of 3,3′-dicarboxy-4,4′-diaminodiphenyl ether and 16.01 g (80 mmol) of 4,4′-diaminodiphenyl ether, N, 149.75 g of N′-dimethylacetamide was added and stirred at room temperature under a nitrogen atmosphere. Further, 19.91 g (91 mmol) of pyromellitic dianhydride was added in several portions over 30 minutes to 1 hour. After stirring for 1 hour, 11.75 g of a pyromellitic dianhydride N, N′-dimethylacetamide solution (6 wt%) was added dropwise over 30 minutes, followed by further stirring for 1 hour.

  A polyimide film was obtained from the obtained polyamic acid using the same method as in Comparative Example 1. The results of measuring the peel strength of the obtained polyimide film are shown in Table 1.

[Comparative Example 4]
In a 300 ml separable flask equipped with a DC stirrer, 6.64 g (23 mmol) of 3,3′-dicarboxy-4,4′-diaminodiphenyl ether and 13.85 g (69 mmol) of 4,4′-diaminodiphenyl ether, N, N'-dimethylacetamide 149.94g was put, and it stirred at room temperature under nitrogen atmosphere. Further, 19.51 g (89 mmol) of pyromellitic dianhydride was added in several portions over 30 minutes to 1 hour. After stirring for 1 hour, 10.45 g of an N, N′-dimethylacetamide solution (6 wt%) of pyromellitic dianhydride was added dropwise over 30 minutes, and the mixture was further stirred for 1 hour.

  Using the obtained polyamic acid in the same manner as in Comparative Example 1, a polyimide film having a thickness of 42 μm was obtained. The results of measuring the peel strength of the obtained polyimide film are shown in Table 1.

  As is clear from the results in Table 1, the laminated polyimide films of the present invention (Examples 1 to 3) are significantly improved in adhesion without increasing the water absorption rate compared to the polyimide films of Comparative Examples 1 to 4. It can be seen that Therefore, it is possible to provide a flexible circuit board having dimensional stability even under an extremely high humidity environment.

  As described above, the laminated polyimide film according to the present invention exhibits a peel strength of 10 N / cm or more when the water absorption is controlled to 3.0 wt% or less and bonded to the metal foil through an adhesive. A film can be obtained and can be used as a base film for a flexible circuit board having excellent long-term reliability.

  In addition, according to the present invention, it is not necessary to use a lot of reagents, time, labor and the like for the treatment for controlling the water absorption rate and improving the peel strength with the metal foil, and suitable for mass production, at low cost, and Since a high-quality, high peel strength polyimide film can be produced, the contribution to this field is high.

Claims (8)

It is a laminated polyimide film formed by laminating two or more polyimide films, and the polyimide of at least one outermost layer of the laminated polyimide film is represented by the following general formula (I): carboxy-4,4′- By thermally and / or chemically imidizing a polyamic acid synthesized from an aromatic diamine containing 1 to 100 mol% of diaminodiphenyl ether and an aromatic tetracarboxylic dianhydride or a derivative thereof. A laminated polyimide film comprising the resulting polyimide.

(However, m and n in the formula are integers of 4 or less including 0, and (m + n) is an integer of 1 or more.)   It is synthesized from an aromatic diamine containing 1 to 100 mol% of carboxy-4,4′-diaminodiphenyl ether represented by the formula (I) and an aromatic tetracarboxylic dianhydride or a derivative thereof. A laminated polyimide film obtained by applying polyamic acid to one or both sides of a polyimide film and thermally and / or chemically imidizing it. The carboxy-4,4'-diaminodiphenyl ether is 3,3'-dicarboxy-4,4'-diaminodiphenyl ether represented by the following general formula (II): 2. The laminated polyimide film according to 2.

The polyimide of at least one outermost surface layer of the laminated polyimide film has a structural unit represented by the following general formulas (III) and (IV), according to any one of claims 1 to 3. Laminated polyimide film.

(However, R ₁ in the formula is _one of the groups represented by the following general formula,

R ₂ in the formula is any of the groups represented by the following general formula:

Moreover, the molar ratio of X: Y in the formula is 1:99 to 100: 0. ) The laminated polyimide film according to any one of claims 1 to 4, wherein a peel strength measured by the following method is 10 N / cm or more when thermocompression bonded with a copper foil through an adhesive. .
(Peel strength: using Lailax R (registered trademark of DuPont) LF-0100, which is an adhesive film, a laminated polyimide film and a copper foil (thickness 35 μm, BAC-13-T manufactured by Japan Energy Co., Ltd.), 180 The strength obtained by thermocompression bonding at a temperature of 4.4 × 10 ⁷ Pa at 60 ° C. for 60 minutes and peeling off the obtained adhesive by the method described in JIS C5016-1994 is taken as the peel strength) The laminated polyimide film according to any one of claims 1 to 5, wherein the water absorption measured by the following method is 3.0 wt% or less.
(Water absorption: after immersing the laminated polyimide film in distilled water for 48 hours, wiping the surface moisture, and heating at a rate of temperature increase of 10 ° C./min from room temperature to 200 ° C. by heating weight loss analysis; The weight reduction rate between 1 to 200 ° C. is the water absorption rate.)   A polyamic synthesized from an aromatic diamine containing carboxy-4,4′-diaminodiphenyl ether represented by the formula (I) in a proportion of 1 to 100 mol% and an aromatic tetracarboxylic dianhydride or a derivative thereof. A method for producing a laminated polyimide film, comprising applying an acid to at least one surface of a polyimide film or a polyamic acid film and imidizing it thermally and / or chemically.   A flexible circuit board obtained by pressure-bonding a metal foil to the laminated polyimide film according to any one of claims 1 to 6 via an adhesive.