DE1769660A1 - Polyimide compounds and metallic objects coated with them - Google Patents

Description

Minnesota Mining and Manufacturing Company,
Saint Paul, Minnesota 55 101, V.St.A.

Polyimide compositions and metallic objects coated therewith

Coating or layering of polymers with metal is known and is a common form of application of polymers with good dielectric properties, e.g. for insulation of electrical conductors, resistors and the like. Metal-polymer composite films are particularly used in the area of electrical switchboards, which use a sheet of copper

009836/214

a dielectric layer is coated, and the Composite film for the production of electrical circuits (circuits) is required, for example. after the known method in which the unnecessary parts are removed and the conductive parts remain behind in a predetermined pattern on the surface of the composite film.

Polyimide coatings on copper for insulation are in the UbA patents 3 179 614, 3 179 634, 3,190,856 and others. Even if for the purposes disclosed in these patents that simply covering or overlaying polyimic and electrically conductive surfaces was satisfactory, The simple layer structures, e.g. made of copper and polyimide, have certain disadvantages that they have for electrical Make control panels or other critical uses less suitable than desirable is.

The one problem with these combinations is the poor adhesive strength of the polymer on the Metal so that the insulating layers are easily removed from The metallic ladders can be withdrawn · Another difficulty is the movement of the conductor on the layer during or after the etching, through which the geometry of the components of the etched

009836/214 control panel

Switchboard is modified in relation to the template according to which it is manufactured and the Alignment of the components of several switchboards in superimposed constructions prevented will"

The masses that are used to coat metal sheets have been used with polyimide films, solutions of polyamic acids in suitable therefor have been heretofore Solvents such as those described in US Pat. No. 3,179,634. With these solutions the sheets were coated, the solvent removed and e.g. "hardening caused by heating"

This invention relates to composite polymer-metal films (composites) are in particular thin metal sheets coated with polyimide polymers or are overlaid, these polymers an addition of amide-modified polyimide polymers contain"

The present invention eliminates this Disadvantages of the prior art by proposing a mass that is a mixture of polyamic acids and amide-modified polyamic acids in usual Solvents contains · When these compounds are applied to the surface, the solvent removed; is and they are hardened, they create

layered 009836 / 2U8

layered composite foils in which the polymeric film adheres very firmly to the metal, and indeed substantially more solid than a PiIm, in which either polyamic acid or amide-modified polyamic acid alone have been used as the film former. The coating compositions can be conveniently referred to as "varnishes" are and are often referred to below as

In one respect, this invention proposes a composition for use as a lacquer or enamel Preparation of dielectric films or coatings, whereby the adhesive strength of the polyimide films on the Metals has been significantly improved In another aspect, the invention proposes metal sheets, -wires or electrical switchboards with improved properties. In another regard it concerns the invention provides certain highly flexible, modified polyimide-metal bundle bodies in which the adhesive strength of the polymer layer on the metal is far greater than that of the previously available ones. The other objects of the invention will become apparent from the description below.

Amide-modified polyamic acids and polyimides of the type used in the compositions of the invention used are described in U.S. Patent 3,320,202 · These polymers are, if

hardened

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are cured, characterized as linear polymeric amide-modified polyimides · They exhibit in the PolymerSkelett amide bonds and become expedient prepared as it is "described in this patent specification, namely by reaction of an aromatic carboxylic acid anhydride, e.g. trimellitic acid anhydride, with aromatic diamines »During The reaction produces an intermediate polyamic acid or a polyamic acid partially converted to imide or an iminolactone polymer, these intermediates in certain solvents, such as dimethylformamide, dimethylacetamide and similar are soluble · The intermediate stages of the polymer are obtained by heating or by chemical Dehydration curable to the polyamide-imide form.

Even after partial hardening or conversion to the imide, the amic acid level retains that of the amide-modified Polymers their solubility in suitable solvents, and some of them can Imide-converted polymers of this type can be used as the coating compositions of this invention. While in some cases the technically available solutions of amic acid polymers are few in number or contain no terminal imide groups at all, it is to be assumed that usually at least

009836/2148

about 15 % of the nitrogen atoms are in the form of imide groups; at a Imidgruppengehalt of 35 i "or slightly more good results are obtained when they are used as base materials for the present invention.

The polyimides used in the invention are of the type described in the United States patents 3,179,634 and 3,179,633. These polymers have an intermediate polyamic acid level which is soluble in certain solvents, and these solvents are useful for manufacture used for coatings or for other manufacturing purposes polyamic acids of this type, which are used for this purpose and the intermediates in the manufacture of these polyimides are described in more detail in U.S. Patent 3,179,614. These polyamic acids are also commonly hardened by heating, although chemical hardening methods are also known

The compositions of the invention are essentially a mixture of the selected polyamic acid having such a proportion described above amide-modified polyamic acid, the adhesive strength effected, namely up to about 90 percent by "- #, in a solvent which is volatile enough to ^w drying "of the mixture 009836/214 ·

to effect a mixture by evaporating the solvent * Additives such as pigments, surfactants can be added to this solution and similar.

The preferred blends contain 10-85 "fc amide-modified / polyamic acid; but even proportions of less than 5 # of added amici-modified polyamic acid cause a remarkable improvement in the bond strength of the polyimide to the metal.

Gear is commonly used in the manufacture of layered polymer-metal composite films of these Invention of a metallic surface, ζ · Β. a copper wire or sheet with a thickness of 0.0125 ~ 0.250mm or more, cleaned first to remove greasy pite from the surface. The surface can then optionally be roughened, e.g. by etching with a chemical etching solution, the solution and each etching residue removed and the sheet dried will. The prepared metal sheet is then coated with a varnish composition of the invention, e.g. Apply with a brush or with a knife or through Spray on · It becomes a practically uniform coating aimed at the entire surface, usually as a moist film that after drying and hardening a surface film from 0.0037 to 0.125 mm thick

divided into . 009836/2148

represents · The thickness of the wet film is influenced by various factors, ΖβΒ. of the Concentration of the pesticides in the solution from which Viscosity of the polymer etc. can change can easily be determined and compensated for by empirical methods.

The thickness of the wet film coating is determined by the thickness of the polyimide layer that is desired * Bas solvent from the damp Film is removed by evaporation, e.g. under reduced pressure, and the film is no longer sticky when it still contains about 40 to 60% by weight of the solvent. At this point the film can be cured by heating, with the remaining solvent evaporates

The intermediate intermediates of the polymer Coatings are preferably hardened by heating, and then they are converted into modified polyimides or transferred into a dielectric layer of the composite film obtained. For the purposes In this invention, it is desirable that the final polyimide not be at least self-supporting e.g. if the metal is removed by etching. A thickness of about 0.0037 to 0.125 mm is preferred in the dry, hardened state.

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The composite films made in accordance with this invention are very "pliable and strong," and that Polymer adheres firmly to the metal »If the excess metal is removed, e.g. by etching, the remaining films are pliable and strong, and the remaining metal is still firmly adhered Shrinkage during etching is relatively small.

Instead of having a dielectric layer of a polyimide on just one side of the metallic To apply underlay to form a composite film, the polyimide layer on both sides of the metallic Layer can be applied, e.g. after etching, in order to obtain a printed circuit diagram

When comparing with simple polyimide films or amide-modified polyimide films that are directly Are formed on the surface of the cleaned copper, the coatings, which are adhered by the technique of the present invention, two to more than ten times as firmly on the metallic Surface. In attempting to separate the layers from one another, at least one generally became partial Destruction of the polymer layer causes, in some cases the metallic base was damaged or destroyed, e.g. if soft metal such as copper was used

It

009836 / 2U8 ""

Any metallic surface can be coated with the dimensions of the invention, and these advantageous results can be achieved. Metal sheets or foils which have proven particularly suitable for the purposes of the invention, for example for the manufacture of electrical switchboards, cables and similar objects are copper, silver and nickel-chromium Legiffung as Nichrome · (Nichrome is the trade designation for a high-melting alloy 60 fi nickel, 25 # iron and 15 fo chromium, or 80 fi nickel and 20 ^c:> contains chromium and is used for electrical resistances ») However, other metals, such as iron, aluminum and the like, can also be coated with these compounds.

The peel strength of layered structures, made in accordance with this invention can be determined by the following procedure: Die Components for the production of a printed circuit diagram are provided with a reserve that is based on printed in the usual way (e.g. silk-raster process) and then etched so that Copper strips 0.8 mm wide are left behind. To After removing the reserve, the composite film is placed in an / Instron experimental device in such a way that

009836/2141

the copper strip from the polyimide film under one Is peeled off at an angle of 180 °, the separation speed being 5 cm / min. * The results are measured in g / cm, the values obtained in this Pall being multiplied by 12.5 «Experiments with various materials have shown a peel strength up to 2520 g / cm on this Ways could be measured; above 2320 g / cm the copper fails

Although the laminations of this invention have been described in terms of their use as flexible switchboards, they are not limited to this, as the process for producing firmly adhering, abrasion-resistant insulating coatings, for example for copper wires, tapes and the like, as well as for heat-resistant coatings, can be et for resistors and heating elements, as well as for heating panels and the like angewer ^third

The following examples in which all parts are parts by weight unless otherwise noted is intended to explain the invention and its novel embodiments in more detail »These examples are not intended to limit the scope of the invention in any way.

example 1 009836 / 2U8

example 1

Commercially available copper foil based on electrolytic Ways was made was coated as follows:

A polyamide-imide polymer, the monomeric components of which were trimellitic anhydride and methylenedianiline (ρ, ρ'-diaminodiphenylmethane), was dissolved in dimethylacetamide so that 15% by weight of pesticides were present. The total viscosity of the solution was about 50 cp. at 23 ° C., the polymer is ^{commercially available under the name "Amoco w} AI type".

A polyamic acid solution was prepared in dimethyl acetamide from a mixture of equimolar proportions of pyromellitic dianhydride and 4 »4'-diaminodiphenyl ether. The polymerization was carried out until the intrinsic viscosity of the polymer was 1.64 at 25 ° G (concentration 0.5 g per 100 ml , Solvent dimethylacetamide) · To facilitate distribution, 0.25 > of a superplasticizer was added to this solution, which consisted of a silicone liquid (commercially available under the name "Union Carbide L-520") · The final pesticide content of this solution was 15 fio Zur Production of exemplary masses and

009836/2148 layer structure

Sehichtgebilde this invention were proportions of polyamic acid solution and the amide-modified polyamic acid solution were mixed to provide mixtures formed in which the proportions of the ami;. Ddmodifizierten polyamic acid 20 MS 95 wt -ψ represent the solids present. This and samples of non-vermisehten solutions were applied to the dull side (commercial name ⁿ Treatment A ", ie · black, oxidized surface) of the copper foil with the aid of a stripping device applied, said wet PiImüberzug 0.3 thus prepared mm thick _e was the Samples of the film coated in this way were placed in a compressed air oven and heated to 315 ° O, left at 315 ° for 15 minutes, and the polymer was thus cured to the polyimide form «

After removal from the furnace it was found that the cured Yerbund foils consisted of a clear, firm and tough film about 0.025 mm thick "which adhered to the copper surface" (The uncoated surface of the copper is due to & ± e oxidation during the This dark residue could be removed from the surface by dipping the composite film into a commercially available ammonium persulphate solution for about 15 seconds, for example.

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To

1 7 6 y 6 6 U

M 2433

After cleaning, the copper composite film is washed with water and dried can optionally be further treated to the copper surface during storage Keep bright and clean «Sodium pyrophosphate is commonly used for this purpose and light oil, inhibitors etc. in suitable aqueous or non-aqueous solvents »

Each of these Yerbund films produced in this way was examined to determine the peel strength. The results were as follows:

Table I.

$> amide-modified polyamic acid in the paint

0 20 40 50 60 70 ÖO 85 90 95 100

Peel strength (lbs / inch) (g / cm) width

0.31 55.4 1.90 339 1 »93 345 2.55 455 3.15 562 3.32 593 2.71 484 2.39 426 0.66 118 0.39 70 0.75 134

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BAD ORIGINAL One

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176S660

Another series of tests, which was carried out with proportions of additional amide-modified polyamic acid including proportions below 20 $ , showed a remarkable improvement in adhesive strength down to 5%, the graph of the values obtained showing that the adhesive strength at 5 ° f was about is twice as large as the value of the adhesive strength that is obtained if no polyamide-modified polyamic acid is used »

Significantly higher values of bond strength were obtained than those summarized in Table I, and depend to some extent on the preparation of the copper surface. Values of more than 535 g / cm with 10 ° ^C. addition and up to 1785 g / cm with 65 % addition were measured; in any case, the effect increases rapidly as soon as the added proportions increase to 10 fi .

ils behind remain fixed flexible, self-supporting, clear amber lilme mm from about 0.0254 strength if one etches away the copper foil from such composite films with iron (II) chloride containing 10 ° / o amide modfcfizierte polyimide films. Standard tests showed that they have excellent electrical properties, namely a dielectric constant K in the range of 3 »53 - 3» 57

Ü09836 / 21A8 bad

at

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at -40 ° to 250 ° C at 100 hertz and from 3.47 3.51 at 100 kilohertz; a distribution factor D _x in the range of 0.20-0.55 x 10 " ² at 100 hertz and 0.22-0.44 x 10" ² at 100 kilohertz.

Example 2

Other types of amide-imide polymers can be used in the compositions of the invention. A copper sheet was coated as in Example 1 with a compound in which the amide-modified polyamic acid solution used is a solution of 16.5% solids in dimethylacetamide of an amide-imide copolymer of pyromellitic acid dipanhydride and 3,4'-diaminobenzanilide _and equal proportions of this The solution and the polyamic acid solution from Example 1 are mixed thoroughly and a moist coating about 0.254 mm thick is applied to the copper using a scraper. The composite film is dried, cured and cleaned according to Example 1. The polyimide layer of the composite film adhered firmly to the copper

Example 3

Wires or sheets made of nichrome can be coated as follows. A smooth sheet of metal

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~ ¹⁷ -

Liichrome (80 $ nickel - 20 ° J> Ghrom alloy) 0.254 mm thick is cleaned by immersing the poly in a 45% bis (II) chloride solution for 20 seconds, immediately afterwards washed with water and dried with warm air A mixture of equal parts of a solution of amide-modified polyimide, which was formed from trimellitic anhydride and methylenedianiline, in dimethylacetamide, the solids content of the solution was 15 fo , and a solution of a polyamic acid in dimethylacetamide, which is made from a mixture of pyromellitic dianhydride and 4 _S 4'-diaminodiphenyl ether, as used in Example 1, is then applied to the surface of the Niekel chromium alloy with the aid of a stripping device, the thickness of the moist film being 0.175 mm. The composite film is then cured according to Example 1. It is not necessary to clean the cured composite film.) The thickness of the polyimide film of the cured composite film is about 0.0125 mm.

The obtained polyimide film is firmly adhered the sheet of nickel-chromium alloy · wires or sheets of silver can be plated in the same way will.

Example 4 009836/2148

Example 4

Composite foils of copper foil and dielectric polyimide layered one above the other, in which the polyimide film contains about 65 fo amide-modified polyimide, are produced according to Example 1. Several plates of such composite foils are layered one on top of the other. The layering can be done either with the plates produced or after an electrical circuit has been created in the desired shape by coating the copper surface with a photosensitive reserve according to the known method, the reserve is irradiated with actinic light through a photographic negative, which is to generating patterns, the unexposed portions of the reserve are removed, the copper is etched away from the exposed portions of the dielectric film, and the remainder of the reserve is removed. The polyimide films are self-supporting, strong and flexible where the copper is removed.

The overlay is carried out according to the following procedure * The dielectric side of the film at least one of the plates is coated with a thin coating by means of a stripping device pressure sensitive adhesive in 40 # solution

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- ¹⁹ -. " _N - M 2433

I / D ■) O OU

Mistake. The adhesive used is Das described in USA Letters Patent 3,307,690 Solvent is released from the adhesive layer on the PiIm removed the sides of the film from two plates by heating to about 80 ° c for 5 minutes, one of which is coated with adhesive, are then connected to one another between two clamping rollers. The one roller which consists of metal is heated to a surface temperature of about 150 ° G; the other roller made of silicone rubber is not heated »The rollers are pressed together with moderate pressure and the rolling speed is about 15 cm / min.

The resulting sandwich construction was firm and free of bubbles _e The layers were separated at the splices with great difficulty.

game 5

There were prepared as described in Example 1, a long strip of a "composite film of an electrolytic copper foil (basis weight of 28.35 g /) and a dielectric layer of polyimide, said PoIyimidschicht about 65 ° / o amide-modif iziertes polyimide contained prepared. These Composite film was v / ie follows a strip cable that contains several wires

held, 009836 / 2U8

held, processed:

Three strips of pressure-sensitive plastic adhesive tape, each 1.25 cm wide (e.g. of the type used for electrical insulation) on the cleaned copper side of the composite foil applied that the strips at a distance of 3.2 mm from. the edge and from each other parallel to the Run edge. In this way, three 1.25 cm wide conductors were placed on a 5 cm wide strip of the

Wk composite foils formed · This arrangement was made into a

brought bubbly etching solution of the following composition:

(MH ₄ J ₂ S ₂ O ₈ 2 kg

H ₂ O 8 liters

conc. H ₂ SO. 100 ml

aqueous 10 $ HgGlp solution 20 drops

Just 30 minutes of immersion in the caustic bath was all Copper that was not under the tape ™ was completely etched away · The plastic tape was then

removed and the composite foil, the copper strips carried on an independent PiIm, was placed in the bubbly etching solution for three minutes, then under Washed under running water and dried

etching 009836/2148

- ■ 21 -

Etching roughened and resembled the rough surface of the slektrolytic copper foil. After drying, the remaining copper strips and the surface of the fertaüMie were coated with a Qwiwh made of ani «modified polyamic acid and polyamic acid solution in the same way as in the production of the original composite foil, so that a continuous dielectric coating is formed in which the copper strips are embedded. The coating was dried and cured for the time and temperature given in Example 1.

The cable strip produced in this way was underneath examined under the microscope and found to be free of delamination or blisters found. The second coating of the polyimide adhered to both the first electrical Polyimide layer as well as on the copper strips very strong · The composite film produced in this way was very strong flexible and strong, and there was continuous insulation © over the conductors

Other dielectric materials can also be used to cover such conductors which form cables as described above. After that, the copper tires. manufactured as a conductor, as described above, e.g. a surface or a strip of irradiated polyethylene can be cut in such a way that

daaa 009836/2148 "

that ifber the entire surface of the dielectric modified polyimide film, it is sufficient, and so the composite film over layers _e Bas irradiated polyethylene was 100 parts less of density polyethylene (commercially available under the designation "DYIH ^M), 10 parts of synthetic rubber ⁽¹¹ GRS-1011") , Q, 15 parts of an antioxidant (eg "Akroflex 0") and 2 (Beilen activated carbon ("Garboloc Ir. 2"), was exposed to a sol fraction of 0.34 and had a film thickness of 0.175 mm. The polyethylene was placed on the surface of the composite film so that it touched the copper and the film surface. A Carver press was used to compress the polyethylene and the composite film holding the copper conductors together for 5 minutes at a temperature of about 150 C and a pressure of about 105 The press was cooled and the layer structure was removed The polyethylene was firmly bound to the composite film without air inclusions, and the polyethylene part of the Sohi The structure could only be peeled off with difficulty.

In the same way, instead of the polyethylene, a film of the thermoplastic copolymer of polytetrafluoroethylene and hexafluoropropylene ("Teflon FEP ^W ) was used. The film was 0.05 mm thick

and

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and "-the assembly was pressed at about 310 ° δ and 2.1 kg / cm ^{2 for} 5 minutes. After cooling, the laminate was removed and it was found that the polymeric resin was present on both the copper and the vacancies firmly adhered to the dielectric modified polyimide base.

(If necessary, the solution of the basis can be used or the polyamic acid intermediate pigments or other additives can be incorporated, e.g. to color them for encryption purposes or around the dielectric or other properties of the modified To change polyimide coatings.

Example 6

Following the procedure of Example 1

a solution of the copolymer from bis (4-amino phenyl} ·

3
ether and; 2.493 ^ 4 · '-Benzophenon-tetracarboxylic acid anhydride instead of "" e of the copolymers of bis (4-amino phenyl) ether and pyromellitic acid dianhydride used, similar results are obtained; This shows that the polyamide-modified polyamic acid polymer improves the adhesive strength of the polyimide on the metal in general.

009836/2 Vk 8 claims

Claims (1)

Patent claims: Main claim I. Composition of metal and polyimide, which consists of a metal layer and a dielectric insulating layer made of polyimide polymer consists, characterized in that the polyimide polymer has such a proportion of amide-modified Polyimide contains, the adhesive strength "causes, namely up to about 90 wt .- ^, and that the polymeric part of this terbund film forms a firm, flexible, adhesive, dielectric material, which is self-supporting when the metal is chemically removed. 1 »composite film according to claim I, characterized in that the proportion of the amide-modified 009836/2148 polyimides Polyimides is about 10 to 85 weight per cent. 2. The composite film according to claim I, characterized in that the metal is copper, silver or is a Kickel-Öhrom alloy. 3 · composite film according to claim 1, characterized in that the polyimide is a poly-bis (4 · - ami, nophenyl) ether-pyromellitimide is " 4 «. Composite film according to claim 1, characterized in that the amide-modified polyimide is a copolymer of trimellitic anhydride and methylenedianiline. 5. The composite film according to claim I, characterized in that the metal is copper or a The Hickel-Ohrom alloy and the polyimide are poly-bis- (4-aminophenyl) -ether-pyromellitimide is. 6 · composite film according to claim 1, characterized in that two or more metal-polymer composite films are glued together in a certain relationship on top of each other » 0 09836/2148 Main claim II 1769860 ^M2433 Main claim II. Dielectrically conductive Metal composite foil which can be etched so that at least one electrical switching element is formed thereon and which is composed of a thin, electrically conductive metal foil and a layered over it. polymeric Polyimiduberzug forming a -dielektrische layer on this film, "is characterized in that the polyimide Polyaerisat containing such a proportion of amide-modified Polyinid, the adhesive strength effected, namely Ibis about 90 fo _t that the polymeric dielectric coating this composite foil carries and that it adheres firmly to the rest of the metal when certain parts of this metal layer are removed by etching, 7 o composite film according to claim II, characterized in that the conductive metallic base is copper and the polyimide is poly-bis (4-aminophenyl) -ether-pyromellitimide. 8. composite film according to claim II, characterized characterized in that the amide-modified polyimide an Oopolymerisat from Irimellitäureanhy <M.d and lendianiline is. 9. Composite film 009836 / 2U8 17B966Q- 9 · composite film according to claim II, characterized marked that the conductive metallic base Copper, silver or a nickel-ohrom alloy is ο Main claim III. Dielectrically insulated, electrical conductor which carries at least one elongated metallic conductor on a base which consists of polymeric dielectric material and contains a polyimide polymer, characterized in that the polyimide polymer contains such a proportion of amide-modified polyimide, the adhesive strength effected, namely that takes place up to about 90 Grewv- and the isolation of this metallic conductor optionally substituted by one second from the first different dielectric, wherein the polymeric $ rope this electrical conductor a solid, flexible, self-supporting, dielectric coating forms, festauf the adheres to the metal. 10 · Ladder according to claim III, characterized in that the polyimide component of the base a poly-bis (4-aminophenyl) -ether-pyromellitimide is that the amide-modified polyimide is a Gopoly-Rnerisat from trimellitic anhydride and methylenedianiline and that the metal is copper. 0 0.9.8 36/2148 · . ϊλ? .. 176S660 ^M2433 11. The conductor of claim III, characterized in that the second polymeric dielectric a polytetrafluoroethylene hexafluoropropylene polymer is. 12. Head according to claim III, characterized in that the second polymeric dielectric consists of a polyimide polymer " 13. Head according to claim III, characterized in that the second polymeric dielectric Polyethylene is β Main claim IV »Hasse containing polyamic acid polymer for coating metallic foundations which form firmly adhering dielectric coatings thereon, characterized in that a solution of a mixture of curable polyamic acid in a volatile solvent contains such a proportion of amide-modified polyamic acid that causes adhesive strength , namely up to about 90% by weight, based on the total Fentstoffhalt _β 14 »Hasse according to claim IV, thereby characterized in that the proportion of amide-modified P) 1; ^: amidic acid was about 10 to 85 wt .- $ 4 009836 / 2U8 BATH - 29 - M 2433 1 7 6 b ö b 0 15 »mass according to claim IY, thereby characterized in that the solvent is bioethylacetamide is. 16ο mass according to claim IV, characterized characterized in that the polyamic acid is poly (4-aminophenyl) -ether-pyromellitamide is. 17c mass according to claim IV, characterized characterized in that the polyamic acid is poly-Ms- (4-aminophenyl) -ether-pyromellitamide and that the amide-modified polyamic acid is an oopolymedsat from irimellitic anhydride and methylenedianiline is. 18e mass according to claim IV, characterized characterized in that the polyamic acid poly-Ms- (4-aminophenyl) ether-pyromellit amide, and that the amide-modified polyamic acid is a copolymer from trimellitic anhydride and methylenedianiline is. 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