JPH01114096A - Flexible printed wiring board - Google Patents

Abstract

PURPOSE:To satisfy various performance requirements of a flexible printed wiring board simultaneously by a method wherein an electrical insulating layer is made of polyurea resin which is obtained by the reaction between amine system compound of a specific composition and polyisocyanate compound and the like. CONSTITUTION:Amine compound with a composition shown by the formula, aromatic polyamine and polyisocyanate compound are made to react with each other and cured. In the formula, R denotes n-valent polyalkylene, polyalkylene ester or polyalkylene polyester with an average molecular weight not less than 200. (A) denotes oxygen atom or imino group. (n) denotes positive integer 1, 2 or 3 and (m) denotes positive integer 2, 3 or 4. Electrical insulating layer made of polyurea resin obtained like this is used as the material of a substrate or a cover-lay film. As a result, a flexible printed board which has excellent solderability, foldability and adhesiveness and conforms to various high performance requirements of a flexible printed board and can be manufactured with a low cost can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a flexible printed wiring board that has excellent solder resistance, bending durability, attachment properties, and electrical insulation properties.

(Prior Art) In recent years, as demands for higher density, lighter weight, etc. of electronic devices have increased, demand for flexible printed wiring boards has increased.

Conventionally, flexible printed wiring boards have frequently used polyester film, polyimide film, etc. as the base material or coverlay film as an electrical insulating layer, and there are also those using glass epoxy film, fluororesin film, or aramid paper.

(Problem to be Solved by the Invention) However, in flexible printed wiring boards using polyimide film, although the polyimide film has extremely excellent heat resistance, when this film is heat-pressed with metal foil and adhesive, However, the adhesion was not always sufficient and the cost was high.

In addition, the polyester film used has excellent mechanical properties and electrical insulation properties, but has the drawbacks of high heat shrinkage and low heat resistance, and cannot be used at high temperatures during the soldering process. The problem is that it cannot withstand Furthermore, those using glass epoxy film have a serious drawback of being inferior in folding durability, which is a basic property of flexible printed wiring boards. As described above, each of the conventional flexible printed wiring boards has advantages and disadvantages, and no one has been available that simultaneously satisfies various increasingly sophisticated performances.

(Means for Solving the Problems) The present inventors have overcome the drawbacks of conventional flexible printed wiring boards, and have developed a flexible printed wiring board that has excellent solder resistance, folding durability, and adhesion, and is low in cost. As a result of intensive research to manufacture wiring boards, we have discovered that a polyurea resin obtained by using two specific types of polyamine compounds as amine compounds and curing them by reaction in combination with a polyisocyanate compound has excellent solder resistance. It has been discovered that a flexible printed wiring board that exhibits properties such as flexibility and bending durability and uses this as an electrical insulating layer satisfies the above objectives, and based on this knowledge, the present invention has been accomplished.

That is, the present invention is based on the general formula (wherein R represents an n-valent polyalkylene, polyalkylene ether or polyalkylene polyester having an average molecular weight of 200 or more, and A represents an oxygen atom or an imino group. R preferably has an average molecular weight 200 to 5000.However, the polyalkylene may contain an unsaturated bond.Also, 1m represents an integer of 1 to 3, and n represents an integer of 2 to 3.
Represents an integer of 4. ) A flexible printed wiring board characterized in that a polyurea resin obtained by reacting an amine compound represented by the following, an aromatic polyamine, and a polyisocyanate is used as a base material or coverlay for an electrically insulating layer. It is something to do.

The polyurea resin used in the present invention has the general formula (wherein R represents a polyalkylene, polyalkylene ether or polyalkylene polyester having an n-valent average molecular weight of 200 or more, A represents an oxygen atom or an imino group, R preferably has an average molecular weight of 200 to 5000.However, the polyalkylene may contain an unsaturated bond, m is an integer of 1 to 3, and n is 2.
Represents an integer from ~4. ) It is obtained by reacting an amine compound represented by the following formula, an aromatic polyamine, and a polyisocyanate.

The amine compound represented by the general formula (I) used in the production of the polyurea resin used in the present invention has the general formula % () (wherein R, A and n have the same meanings as above). ) A nitro compound obtained by reacting a polyol compound or a terminal amino group-containing polyol compound with n equivalents of 0-lm- or p-nitrobenzoyl chloride or di- or trinitrobenzoyl chloride in the presence of a dehydrochlorination agent. or by reacting the polyol compound represented by the general formula (II) or the terminal amino group-containing polyol compound with n equivalents of isatoic anhydride.

The polyol compound represented by the general formula (■) or the terminal amino group-containing polyol compound used in synthesizing the amine compound represented by the general formula (I) is, for example, a compound obtained by condensing an aliphatic glycol with a dicarboxylic acid. Aliphatic polyester glycols such as polyethylene adipate, polybutylene adipate, and polypropylene adipate obtained by elongating the chain; polypropylene ether glycol and tetramethylene ether glycol obtained by ring-opening polymerization of ethylene oxide, propylene oxide, tetrahydrofuran, etc. Alkylene ether glycols, polyester glycols obtained by ring-opening polymerization of ε-caprolactone, polybutadiene with hydroxyl terminal groups, copolymers of two or more alkylene oxides, and copolymers of two or more glycols and dicarboxylic acids. Long-chain diols such as mixtures of polymers and aromatic glycols, polyester polyols obtained by cocondensation polymerization of polyols such as glycerin and trimethylolpropane, aliphatic glycols, and dicarboxylic acids, or chrycerin and trimethylolpropane. Tris( Examples include 2-hydroxyethyl) isocyanurate.

The synthesis of the amine compound represented by the general formula (I) is disclosed in Japanese Patent Publication No. 60-32641 and Japanese Patent Publication No. 56-135511.
It can be carried out according to the method described in No.

In the present invention, the use of a polyurea resin manufactured using a polyether polyol as a polyol component gives good results in terms of the folding durability required for a flexible printed wiring board.

Examples of the amine compound represented by the general formula (I) include the following.

Polyethylene glycol bis(4-aminobenzoate) Polyethylene glycol bis(2-aminobenzoate) Polyethylene glycol bis(3-aminobenzoate) Polytetramethylene glycol bis(4-aminobenzoate) Polytetramethylene glycol bis(2-aminobenzoate) Polypropylene glycol Bis(4-aminobenzoate) Polypropylene glycol bis(2-aminobenzoate) Poly(oxyethylene-oxypropylene) glycol bis(4-aminobenzoate) Polyoxybutylene glycol bis(4-aminobenzoate) Polytetramethylene glycol bis(3-aminobenzoate) ,5-diaminobenzoate) Polypropylene ether glycerol tris(4-aminobenzoate) Polypropylene ether bentaerythol tetrakis(4-aminobenzoate) Polyoxyethylene bis(4-aminobenzamide) Polyoxypropylene bis(4-aminobenzamide) Polyoxypropylene bis(3,5-aminobenzamide) In these formulas, the terms and numbers are always the average molecular weight of the central alkyl group or the number 'I!l', which is within the range of 200 or more.

The aromatic polyamine used in the polyurea resin used in the present invention may have an arbitrary substituent such as a halogen atom, an alkyl group, a trifluoromethyl group, or an alkoxycarbonyl group introduced into the aromatic nucleus.

Examples of aromatic polyamines include 4.4'-methylenebisaniline, 4.4'-methylenebis(2-chloroaniline), 4.4'-methylenebis(2,3-dichloroaniline) (TCDAM), 4. 4'-methylenebis(2
, 5-dichloroaniline), 4.4”-methylenebis(
2-methylaniline), 4.4”-methylenebis(2-
4.4”-methylenebis(2-isopropylaniline), 4.4′-methylenebis(2,6
-dimethylaniline), 4,4'-methylenebis(2,
6-dichloroaniline).

4.4'-methylenebis(2-ethyl-6-methylaniline), 4.4'-methylenebis(2-rizu)
glow 6-methylaniline), 4,4'-methylenebis(2-chloro-6-nitylaniline).

4.4'-methylenebis(3-chloro-2,6-dinithylaniline), 4.4''-methylenebis(2-trifluoromethylaniline), 4.4'-methylenebis(2-
Diaminodiphenylmethane-based aromatic diamines such as methoxycarbonylaniline), 4,4'-diaminodiphenyl ether, 4,4'-diamino-3,3'-dichlorodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 4,4'-Diamino-3,3'-dichlorodiphenylsulfone, bis(4-aminophenoxyphenyl)sulfone, 1,2-bis(2-aminophenylthio)ethane, bis-[2-(2-aminophenylthio)ethyl] Aromatic diamines containing oxygen or sulfur atoms such as terephthalate, 1,3-propanediol bis(4-
aminobenzoate), 1,4-butanediol bis(
4-aminobenzoate), diethylene glycol bis(4-aminobenzoate), triethylene glycol bis(4-aminobenzoate), 4-chloro-3,5
-Isopropyl diaminobenzoate, 4-chloro-3,5
-Aminobenzoic acid ester aromatic diamine such as isobutyl diaminobenzoate, 2.4-toluenediamine, 2
゜6-Toluenediamine, 3,5-diethyl-2゜4-
Toluenediamine-based aromatic compounds such as toluenediamine, 3,5-diethyl-2゜6-toluenediamine, 3,5-dimethylthio-2,4-toluenediamine, and 3,5-dimethylthio-2,6-)-toluenediamine Diamine, 2
, 2-bis(4-aminophenyl)propane, 2.2-
Bis(4-amino-3-methylphenyl)propane, 2
, 2-bis(4-amino-3-ethylphenyl)propane, 2,2-bis(4-amino-3-isopropylphenyl)propane, 2.2-bis(4-amino-3,5-
dimethylphenyl)propane, 2゜2-bis(4-amino-3,5-diethylphenyl)propane, 2,2-bis(4-amino-3゜5-diisopropylphenyl)propane, 2.2-bis(4 -amino-3-ethyl-5-
Aromatic diamines based on diaminodiphenylpropane such as methylphenyl)propane, 3,3'-diaminobenzophenone, m- or p-phenylenediamine, m- or p-xylylenediamine, etc.
．． 3", 4.4"-tetraaminophenyl ether, 3
, 1'4,4'-tetraaminobiphenyl and other aromatic tetramines. These aromatic polyamines can be used alone or as a mixture.

Examples of the polyisocyanate compounds used in the production of the polyurea resin used in the present invention include hexamethylene diisocyanate (HMDl), 2,2.4-trimethylhexamethylene diisocyanate, 3.6-
Hexamethylene triisocyanate, cyclohexane diisocyanate, dicyclohexylmethane diisocyanate, 2-isocyanate ethyl-2,6-ditucyanatohexanoate, adduct of trimethylolpropane and hexamethylene diisocyanate, 2.4-)-
lylene diisocyanate (2,4-TDI), 2.6-
)-lylene diisocyanate (2,6-TDI) and mixtures of these 2.4-TDI and 2.6-TDI, 2.4
-)- Dimer of lylene diisocyanate, xylylene diisocyanate (XDI), metaxylylene diisocyanate (MXDI), tetramethylxylylene diisocyanate, m-phenylene diisocyanate, 4
, 4'-biphenyl diisocyanate, diphenyl ether-4,4'-diisocyanate, 3,3'-ditoluene-4,4'-diisocyanate (TODI)
, dianisidine diisocyanate (DADI), 4.4
”-diphenylmethane diisocyanate (MDI), 3
．． 3”-dimethyl-4,4′-diphenylmethane diisocyanate, l,5-naphthalene diisocyanate (
NDI), )-rephenylmethane triisocyanate (
TTI) etc. or hexamethylene, 1,6-diisocyanate, 2,2,4-)-limethylhexamethylene-1,4-diisocyanate, 4-isocyanatemethyl-1,8-octamethylene diisocyanate, 1,3
．． Cyclic trimers (isocyanurates) such as tris(6-isocyanatomethyl)isocyanurate, which are synthesized by trimerizing aliphatic polyisocyanates such as 6-hexamethylene triisocyanate by adding a trimerization catalyst according to a known method. Any polyisocyanate used in conventional polyurethane elastomer manufacture can be used. These polyisocyanates can be used alone or as a mixture.

Moreover, reaction products of these polyisocyanates and ordinary polyols, so-called prepolymers, can also be used in this reaction.

In the production of the polyurea resin used in the present invention, the proportion of the aromatic polyamine in the amine component (the amine compound represented by the general formula (I) and the aromatic polyamine) varies depending on the desired physical properties, workability, etc. , usually 5~
It is 50% by weight, preferably 20 to 40% by weight. If the amount of aromatic polyamine is too small, the resulting polyurea resin will have insufficient heat resistance, and if it is too large, the mixed solution of the amine compound represented by the general formula (I) and the aromatic polyamine will have difficulty maintaining its liquid state. Even if it remains liquid, it becomes highly viscous, making handling and molding operations difficult, and polyurea crystals may precipitate in the specially molded product, making it impossible to obtain a uniform resin.

Further, the ratio of the amine compound represented by the general formula CI) and the polyisocyanate containing the amine compound and aromatic polyamine is usually the molar ratio of the amino group (-NH2) to the isocyanate group (-NGO) -NH2/-NC0 The molar ratio is 0.9 to 1.5, preferably 1.0 to 1.3.

In the production of the polyurea resin used in the present invention, a catalyst can be used if necessary. This catalyst is preferably one that dissolves in the mixture of the amine compound represented by the general formula (I) and the aromatic polyamine,
Examples include:

For example, triethylenediamine, triethylamine, tripropylamine, tributylamine, hexamethylenetetramine, N-alkylmorpholine, N-pentamethyldiethylenetriamine, N-hexamethyltriethylenetetramine, N.

N-diethylaniline, N,N-dimethylbenzylamine, N,N-dimethyllaurylamine.

N,N-dimethylpiperidine, N,N'-dimethylpiperazine, N,N,N",N"-tetramethyleneethyldiamine, N,N,N",N'-tetramethylpropyldiamine, N,N,N ',N''-tetramethyl-1,3-
Butanediamine, N.

N,N",N"-tetramethylhexamethylenediamine, N,N,N",N",N"-pentamethyldiethylenetriamine, tris(dimethylaminomethyl)phenol, N,N',N"-)- Lis(dialkylaminoalkyl)hexahydro-5-triazine, 1,8-diaza-bicyclo-5゜4.0-undecene, 1,8-diaza-bicyclo-5,4,O-undecene-methylammonium methosulfate Examples include tertiary amines such as aziridinyl compounds. Other catalysts include organometallic catalysts, such as Lewis acid catalysts, such as tetra-n-butyltin, tri-n-
Organotin compounds, acetylacetone zinc salts, such as butyltin acetate, n-butyltin trichloride, trimethyltin hydroxide, dimethyltin dichlorite, dibutyltin dilaurate, dibutyltin di-2-ethylhexoate, stannath octoate, etc.
Acetylacetone metal salts such as acetylacetone aluminum salt, acetylacetone cobalt salt etc., naphthenate metal salts such as zinc naphthenate, lead naphthenate, lead caprylate, cobalt naphthenate etc., phenylmercury acetate, phenylmercury oleate, mercury octoate,
Organomercury compounds such as mercury natuthanate, organolead compounds such as lead octoate, lead naphthanate, etc.
or basic metal salts of organic borate esters and organic boron compounds, alkali gold Mjl of carboxylic acids having 2 to 12 carbon atoms! (Potassium acetate, potassium propionate, 2-
ethylhexane potassium, sodium benzoate, etc.),
Basic substances such as alkali metal salts of carboxylic acids having 13 or more carbon atoms (sodium oleate, potassium lylphate, etc.), alkali metal salts of weak acids other than carboxylic acids such as sodium ferulate, sodium methoxide, benzyl trimethyl Strong basic substances such as ammonium hydroxide and alkali metal hydroxides.

Chelate compounds such as salicylaldehyde and potassium chelate compounds, or promoters (phenols,
epoxy compounds, alkyl carbonates, etc.). The above catalysts can be used alone or as a mixture. When using a catalyst, the amount used is 0.01 to 5 parts by weight, preferably 0.05 to 5 parts by weight, per 100 parts by weight of the mixture of the amine compound represented by the general formula (I) and the aromatic polyamine.
It is 3 parts by weight.

Furthermore, the polyurea resin used in the present invention includes antioxidants, ultraviolet absorbers, anti-coloring 1L agents, hydrolysis inhibitors, antifungal agents, flame retardants, colorants, extenders, fillers,
A surface treatment agent, a low shrinkage agent, etc. can be included as appropriate depending on the use of the polyurea resin. It is also possible to dilute with a solvent such as alcohols, ketones, DMF, or DMSO.

The curing reaction of the polyurea resin used in the present invention can usually be carried out at room temperature to 200°C in several minutes to several hours.

The method for forming the flexible printed wiring board of the present invention is not particularly limited, but a predetermined solution containing the constituent components of the polyurea resin described above is poured directly onto the metal foil, and the flexible printed wiring board is integrated with the metal foil without using an adhesive. There are two methods: a method of forming a polyurea resin film (referred to as the first method), and a method of first making a polyurea resin film by a conventional method and bonding it to metal foil with an adhesive (referred to as the second method). Can be adopted.

More specifically, in the first method, for example, a predetermined amount of aromatic polyamine is mixed with the amine compound represented by the general formula (I), and after heating to completely dissolve the mixture,
~20 mm 11 g Sufficiently defoamed under reduced pressure and cooled to room temperature. Next, a predetermined amount of polyisocyanate is added to the obtained mixed liquid and mixed thoroughly, followed by defoaming and preliminarily
It is poured onto a metal foil heated to room temperature to 200'C, and heated and pressed with a roll or press at that temperature to harden it. Thereafter, if necessary, heat the laminate at room temperature to 200°C.
By heat-treating it in an oven set at

In the second method, it is preferable to apply an adhesive to a metal foil, dry it, heat press it with a polyurea resin film, and perform post-curing to obtain a flexible printed wiring board.

In addition, in order to improve the adhesion with the adhesive, known surface treatments such as alkali treatment and plasma treatment can also be performed.

In the present invention, when a polyurea resin is used as a coverlay for a flexible wiring board, a polyurea resin film is made in advance, coated with an adhesive, and used in the same form as a normal coverlay film.

The flexible printed wiring board of the present invention includes not only those in which the polyurea resin electrical insulating layer is used as either the base material or the coverlay of the flexible printed wiring board, but also those in which it is used in both.

As the metal foil used in the flexible printed wiring board of the present invention, any material that can be a conductor, such as electrolytic copper foil, rolled copper foil, and aluminum foil, can be used.

Further, in the present invention, paper and fiber-based materials can be used as the reinforcing base material, and organic and inorganic fibers such as polyester, polyamide, and glass fibers, as well as non-woven fabrics and woven fabrics of the above-mentioned fibers, etc. may also be used. These can be used by being impregnated with the above polyurea resin.

(Effects of the invention) In the present invention, the adhesiveness of the polyurea resin film laminated on the metal foil is extremely good, and the formed flexible printed wiring board has excellent hunter resistance and bending resistance, and is low-cost and has good electrical properties and mechanical properties. It has an excellent effect of well-balanced physical properties. In particular, if the flexible printed wiring board of the present invention is produced by forming a polyurea resin film directly on metal foil as described above, it is possible to create a laminate with high adhesive strength (flexible printed wiring board) without using an adhesive. ) can be obtained. Further, in the case of using a method of laminating the metal foil L using an adhesive, it is possible to achieve a high adhesive strength using an ordinary adhesive, which is an extremely excellent practical effect.

(Example) Next, the present invention will be explained in more detail based on examples.

Example 1 4,4' to 70 parts by weight of polytetramethylene glycol bis(P-aminobenzoate) (an amine compound with a molecular weight of 970 in the portion corresponding to R in general formula (I))
- 30 parts by weight of methylenebis(2-chloroaniline) was mixed, heated and dissolved, defoamed, and cooled to room temperature. Next, 48.7 parts by weight of liquid MDI and 6.2 parts by weight of Duranate THA-Zoo (trade name, trimer of HMDI, manufactured by Asahi Kasei Industries, Ltd.) were added to this liquid at room temperature, mixed, defoamed, and preliminarily mixed. It was poured onto the rough surface of an electrolytic copper foil with a thickness of 35 JLm that had been preheated to 100°C, cured under a 100°0140kg/rrf heat press for 1 hour, and then heat-treated in an oven at 180°C for 4 hours. , a wiring board having a thickness of 10 to 10 liters was obtained by integrally molding with copper foil and using no adhesive.

Example 2 Polytetramethylene glycol bis(p-aminobenzoate (the molecular weight of the portion corresponding to R in general formula (I) is 9
To 70 parts by weight of amine compound No. 70), 30 parts by weight of 4,4'-methylenebis(2-chloroaniline) was mixed and dissolved by heating at 80°C, and then this solution was heated to 80°C. Part and Duranate T) (A-1o
.

16.3 parts were added, mixed, and defoamed. Using this liquid, integral molding was performed in the same manner as in Example 1 to obtain a flexible printed wiring board integrally molded with copper foil and having a thickness of 100 to 110 pm without using an adhesive.

Example 3 Aramid nonwoven IIj (30 Bm thick) was used as a reinforcing base material.
Nomex Vapor (trade name, manufactured by DuPont) was impregnated with a polyurea resin solution having the same composition as in Example 2, and then integrally molded with copper foil in the same manner as in Example 1.
A flexible printed wiring board having a thickness of 130 to 140 JLm without using an adhesive was obtained.

Example 4 On the rough surface of an electrolytic copper foil with a thickness of 357 zm, an NBR thermosetting adhesive (trade name: Hybon
An adhesive-coated electrolytic copper foil was prepared by drying at 0 to 130"C for 3 to 5 minutes. Next, a 50Bm thick film having the same resin composition as in Example 2 was applied to the adhesive side of the adhesive-coated electrolytic copper foil. Polyurea resin films were stacked together and heat-pressed at 150°C x 10 minutes to form a laminate sheet, and then heated at 150°C x 60 minutes.
A flexible printed wiring board was obtained by post-curing for several minutes.

Comparative Example 1 On the rough surface of an electrolytic copper foil with a thickness of 35 ILm, reprint adhesive Hibon XA961-2 was applied at approximately 30 g/rn' dry.
An electrolytic copper foil with adhesive was prepared by drying at 100 to 130°C for 3 to 5 minutes. A polyimide film with a thickness of 25 ILm was superimposed on the adhesive side of this adhesive-coated electrolytic copper foil at 150°C.
A laminate sheet was obtained by hot pressing at x10 minutes, and then post-curing was performed at 150° C. for 60 minutes to obtain a flexible printed wiring board.

Comparative Example 2 A polyester film with a thickness of 50 ILm was coated with an adhesive compound (5 parts by weight of the cross-linking agent Dismodur L was added to 100 parts by weight of Hybon 7040, a solvent-based adhesive developed for lamination, mainly composed of saturated polyester resin). The rough surface of the 35 gm electrolytic copper foil was overlaid on the adhesive-coated polyester film, which was coated with 1.5 g/rr1' trial of 1.5 g/rr1' of polyester film and dried at 60°C for 3 minutes.
Lamination was carried out using a hot press at 130''C for 5 minutes to obtain a flexible printed wiring board.

The bending durability and solder heat resistance of the flexible printed wiring boards obtained in Examples 1 to 4 and Comparative Example 1.2 and the adhesive strength, surface resistance, volume resistivity, dielectric constant, and dielectric loss tangent of the polyurea resin film were evaluated. It was measured according to the method shown in Table 1. The results are shown in Table 1.

, / / / /' Example 5 Hibon XA961- on the shiny surface of electrolytic copper foil with a thickness of 35 pm
2 Approximately 30 g/m″ dry applied, 100-130
A polyurea resin film with a resin composition or a thickness of 50 gm similar to that in Example 2 was superimposed on the glossy surface of the electrolytic copper foil with adhesive, which had been dried for 3 to 5 minutes at ℃, and heated and pressed at 150 cm to form a laminate sheet. Thereafter, a post cure was performed at 150° C. for 60 minutes.

The physical properties of the sample thus prepared were measured in the same manner as in Example 1. The results are shown in Table 2.

Table 2 Patent Applicant Ihara Chemical Industry Co., Ltd. Agent Patent Attorney Ii 1) Toshi Mizu・

Claims (1)

[Claims] (1) General formula ▲ Numerical formula, chemical formula, table, etc. ▼ (In the formula, R represents polyalkylene, polyalkylene ether, or polyalkylene polyester with an n-valent average molecular weight of 200 or more, and A represents an oxygen atom or an imino group. However, the polyalkylene may contain an unsaturated bond. Also, m represents an integer of 1 to 3, and n represents 2
Represents an integer from ~4. ) A flexible printed wiring board characterized in that an electrical insulating layer made of a polyurea resin obtained by reacting an amine compound represented by the following formula, an aromatic polyamine, and a polyisocyanate is used as a base material or a coverlay.