GB2075999A - Improved Polyamide Acid Polymer Coating Composition and Bondable Substrate - Google Patents

Abstract

A polyamide acid polymer is partially imidized to an imidization level of greater than 6% up to 70%. A coating medium comprises the partially imidized polymer in a phenolic based aromatic solvent. A bondable coating on a substrate such as magnet wire comprises a coating of the coating medium with the polymer partially cured and imidized to a level of not more than 90%. The coating of the partially imidized polyamide acid polymer can be applied over a base coat enamel, such as a polyesterimide, and partially cured to a bondable "B- stage" or fully cured to form a polyimide coating.

Description

SPECIFICATION Improved Polyamide Acid Polymer Coating Composition and Bondable Substrate The present invention relates to an improved polyamide acid polymer enamel composition. More specifically, the invention relates to an improved enamel, finding particular, but not necessarily exclusive, utility for forming improved wire insulation coatings for magnet wire. The invention further relates to substrates coated with the improved enamel composition and having self-bondable properties.

Polyamide acid polymers for coating substrates, and particularly for coating wire to form magnet wire, are well known in the art. Such coating compositions are disclosed, for example, in U.S. Pat. No.

3,652,500, issued March 28, 1 972, to M. A. Peterson for Process for Producing Polyamide Coating Materials by Endcapping, and in U.S. Pat. No. 3,663,510, issued May 1 6, 1972, to M. A. Peterson for Process For Producing Polyamide Coating Materials. Where appropriate, the disclosure of these patents is incorporated herein and made a part hereof by reference. For further disclosures of polyamide acid polymer compositions and polyimides produced therefrom, reference is also made to U.S. Pat. No. 3,507,756, issued April 21, 1970, to F. F. Holub and M. A. Peterson for Method For Electrocoating a Polyamide Acid; U.S. Pat. No.3,179,614, issued April 1965, to W. M.Edwards for Polyamide Acids, Compositions Thereof, and Process for Their Preparation; U.S. Pat. No. 3,179,634, issued April 20, 1965, to W. M. Edwards for Aromatic Polyimides and the Process for Preparing Them; and U.S. Pat. No. 3,190,856, issued June 22, 1965, to E. Lavin et al., for Polyamides from Benzophenonetetracarboxylic Acids and a Primary Diamine.

In the prior art, a cdating medium containing a high molecular weight polyamide acid is prepared and applied to a substrate, such as wire, and heat cured to provide an electrical insulating polyimide coating thereon. The polyamide acid coating compositions have conventionally been prepared in an organic solvent and, in some instances, the polyamide acid is rendered water soluble by the addition of ammonia or an amine base to form a water soluble polyamide acid salt. The composition is then diluted with water to form an aqueous based coating composition. See, for example, U.S. Pat. No. 3,891,601, issued June 24, 1975 to Marvin A. Peterson et al. for Process for Producing Water Soluble Polyamide Resins.

Polyamide acid polymers such as disclosed in the above patents to Peterson are highly effective for producing stable, electrical grade, insulation coatings on wire and other core materials or substrates to produce magnet wire and other electrically insulated products. Such polyamide acid polymer materials may be applied directly to a substrate such as a lamina or wire, or may be applied as an overcoat on a previously coated substrate. A wide variety of base coats are available including polyesters, polyester amides, polyester amide imides, polyester imides, polyamide imides, polyimides and others.

Adhesive varnishes and coatings have long been known in the art to be useful for providing self bonding laminae and magnet wire. Self-bonding magnet wire, for example, can be wound into coils, which are then heated either externally or by internal resistance, to cause the bonding coating to fuse or thermally set to form rigid bonded coil structures. Laminates can be similarly formed. Among such self-bonding adhesive coating materials are certain polysulfones as disclosed in U.S. Pat. No.

3,676,814, issued July 11, 1 972; vinyls such as polyvinyl chloride or polyvinyl acetate as disclosed in U.S. Pat. No. 3,574,015, issued April 6, 1971; polyethylene, as disclosed in U.S. Pat. No. 3,974,016, issued August 10, 1 976; polyvinyl acetals such as polyvinyl butyral as disclosed in U.S. Pat. No.

3,51 6,858, issued June 23, 1970, U.S. Pat. No. 3,300,843, issued January 31, 1967, and U.S. Pat.

No. 3,456,338, issued July 22, 1969; and polyurethanes as disclosed in U.S. Pat. No. 3,916,403, as well as a wide variety of other bondable resins.

In the preparation of magnet wire, insulation coatings are conventionally applied to strands of wire in commercial wire towers such as disclosed in U.S. Pat. No. 3,183,604, issued May 18, 1965, and U.S. Pat. No. 3,183,605, issued May 18, 1965. In the wire towers, the wire is passed through an enamel applicator and receives a coating of resin and solvent in liquid form. The wire then passes through a vertical oven or furnace in which the solvent is removed and the coating cured on the wire.

Multiple passes can be provided to increase the coating thickness. As pointed out in the wire tower patents, care must be taken in the application and cure of the enamel coating to prevent the formation of blisters and other imperfections in the enamel coating.

In accordance with the foregoing and as more particularly described hereinafter, the present invention invoives preparing a polyamide acid enamel solution, including viscosity adjustments and end capping, in the manner described in U.S. Patents, 3,663,510 and 3,652,500. The polyamide acid solution, while still in the reactor, is partially imidized by heating to approximately 700C for about 7 to 8 hours to provide a partial imidization in the range of between 30% and not more than 70%.The partially imidized polyamide acid solution is then further diluted with solvents and diluents, principally of the cresylic and aromatic hydrocarbon type, to provide a finished wire enamel product having approximately 17% solids by weight and a viscosity of between 500 and 800 cps, suitable for use in conventional wire tower wire coating apparatus.

The improved wire enamel is then utilized in a wire tower and may be run at high speeds to produce blister free, scrape resistant wire enamel coatings. By carefully adjusting the wire tower conditions, the enamel coating can further be cured to a "B-stage" or bondable stage in which the wire may be bonded by heating the wire after it has been wound into coils or other shapes or structures. The bondable wire meets the conventional magnet wire specifications required for handling, shipping, storage and use in high speed winding machines conventionally utilized in the art. The bendable wire coating is produced in the wire tower by lowering the temperature of the wire tower ovens approximately 500C as hereinafter described in more detail.

During coil winding operations and the curing of the bondable wire, the bondable coils, during heating, may be subjected to a surge of electrical energy in order to press the coils and bond the turns tightly together.

Figure 1 is a schematic flow diagram illustrating a process for producing a wire enamel embodying the present invention.

Figure 2 is a diagram illustrating imidization levels in the enamel composition embodying the present invention and self-bonding enamel coating produced therefrom.

The polyamide acid polymer coating composition embodying the present invention is characterized by the fact that the polyamide acid polymer is partially imidized to a significant level prior to application of the polymer as a coating on a substrate. The partially imidized polyamide acid polymer is dissolved in a phenolic or cresylic based aromatic solvent, and may further include, as a stabilizing agent, a volatile primary, secondary or tertiary amine or ammonia or ammonium hydroxide, in a quantity sufficient to form a salt with free carboxylic radicals.

The polyamide acid polymer is formed substantially as described in U.S. Pat. 3,652,500, issued March 28, 1972, to M. A. Peterson for Process for Producing Polyamide Coating Materials by Endcapping, and in U.S. Pat. 3,663,510, issued May 16, 1972, to M. A. Peterson for Process for Producing Polyamide Coating Materials. With particular reference to these patents, and utilizing as reactants the dianhydride 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), and the diamine methylene dianiline (MDA), in a phenolic-cresylic solvent, a polyamide acid polymer is prepared and produced as described. While the BTDA and MDA are preferred reactants, other dianhydrides and diamines may be utilized, as described more specifically herein.

As diagrammaticaily illustrated in Figure 1, in the reaction process, BTDA is added to a reactor together with a phenolic solvent. The reaction temperature is maintained at approximately 450C- 500C and MDA is added to the reactor over a short period of time with stirring. In the initial reaction, two moles of BTDA are provided for one mole of MDA. The result is a clear solution, to which is added a further mole of MDA or other appropriate diamine. The reactor contents are maintained at a maximum temperature of about 400C., with stirring, for a period of about 30 minutes. The resulting product is a polyorthoamic acid solution. A small amount of BTDA is added to adjust the inherent viscosity and, thus, the molecular weight, as described in Patent 3,663,510.The polymer is then endcapped with MDA, generally ten percent on a molar basis of the BTDA employed in back addition to provide amine terminals, as described in U.S. Pat. 3,652,500. The product is a polyorthoamic acid polymer solution of the desired molecular weight and having an imidization level of between zero and about two percent.

Following the preparation of the polyorthoamic acid polymer solution, and while holding the solution in the reactor, the reactor temperature is raised to above 700C and held for approximately seven and one half hours to provide an imidization level of greater than about thirty percent and less than about seventy percent. The partially imidized product is then cooled to a temperature less than 500C, that is a maximum temperature of about 450C, and additional solvents and diluents are added to produce a finished, partially imidized, polyorthoamic acid coating composition, having approximately 17% solids by weight and a viscosity at 30 C of between 500 and 800 cps. This composition is the desired coating composition suitable for application as a film to substrates or as an enamel on wire products to produce magnet wire. For most applications, the range of solids will vary from about 10% to about 25% by weight.

A wide variety of tetracarboxylic compounds are useful in accordance with this invention. Such compounds include both acids and acid anhydrides and have the general formula

wherein R is (a) a tetravalent radical with each carboxyl group of a pair being attached to a different adjacent carbon atom, examples of which are: 1,2,3,4-butane tetracarboxylic dianhydride 1 ,2,3,4-cyclopentane tetracarboxylic dianhydride; (b) a tetravalent radical containing at least one ring of six carbon atoms and having benzenoid unsaturation, each carboxyl group of a pair being attached to a different adjacent carbon atom, examples of which are:: pyromellitic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, benzene-1 ,2,3,4-tetracarboxylic dianhydride, 2,6-dichloronaphthalene 1 ,4,5,8-tetracarboxylic dianhydride, 2,7-dichloronaphthalene 1 ,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene 1 ,4,5,8-tetracarboxylic dianhydride, naphtha lene- 1 ,4,5,8-tetracarboxylic dianhydride, naphthalene-1 ,2,4,5-tetracarboxylic dianhydride, 3,3',4,4'-diphenyltetracarboxylic dianhydride, 1 ,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-diphenyltetracarboxylic dianhydride, 3,4,9,1 0-phenylenetetraca rboxylic dia nhydride.

(c) a tetravalent radical containing two or more benzene rings joined by a chemically inert, thermally stable moiety selected from the group consisting of an alkylene chain having from 1 to 3 carbon atoms, an alkyl ester, a sulfone and oxygen, each of the carboxyl groups of a pair being attached to different adjacent carbon atoms of a single separate ring, example of which are:: 4,4'-(2-acetoxy- 1 ,3-glyceryl) bis-anhydro trimellitate, 3,3',4,4'-benzophenonetetracarbyxylic dianhydride, bis(3,4-dicarboxyphenyl) sulfone dianhydride, bis(2,3-dicarboxyphenyl) methane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, bis(3,4-dicarboxyphenyl) ether dianhydride, 2,2-bis(2,3-dicarboxyphenyl) propane dianhydride, 1 ,1-bis(2,3-dicarboxyphenyl) ethane dianhydride, 1 ,1-bis(3,4-dicarboxyphenyl) ethane dianhydride, bisphenol A-phthalic dianhydride; The useful acid anhydrides have the general formula:

wherein R is (a) a trivalent radical with each carboxyl group of the pair being attached to a different adjacent carbon atom, an example of which is:: 1,2,3 propanecarboxylic monoanhydride; (b) a trivalent radical containing at least one ring of six carbon atoms and having benzenoid unsaturation, each carboxyl group of the anhydride pair being attached to a different adjacent carbon atom, examples of which are: trimellitic anhydride hemimellitic anhydride trimesic anhydride 3,4,3'(or 3,4,4', etc.)-diphenyltricarboxylic anhydride 3,4,3'(or 3,4,4' etc)-tricarboxydiphenyl ether anhydride 3,4,3' (or 3,4,4' etc)-tricarboxydiphenyl methane anhydride 3,4,3' (or 3,4,4' etc.)-tricarboxydiphenyl sulfide anhydride 3,4,3' (or 3,4,4' etc.)-tricarboxydiphenyl sulphone anhydride 3,4,3' (or 3,4,4' etc.)-tricarboxydiphenyl ketone anhydride 3,4,3' (or 3,4,4' etc.)-tricarboxydiphenyl propane anhydride radicals having the general formula::

wherein R represents a methylene group, an oxygen atom, a sulfur atom, a SO2 group, a group or a

group.

Where suitable, the acids, esters, halides, or mono-anhydrides of the foregoing may be utilized.

Likewise, various mixtures of the foregoing may be found useful.

The organic diamines that are useful in accordance with this invention are those having the formula: H2N-R'-NH2 wherein R' is a divalent radical selected from the class consisting of

wherein R"' and R"" are an alkyl or an aryl group having 1 to 6 carbon atoms, n is an integer of from 1 to 4 and m has a value of 0, 1 or more and

wherein R" is selected from the group consisting of carbon in an alkylene chain having 1-3 carbon atoms, oxygen, silicon, phosphorous, sulfur, and nitrogen in

wherein R"' and R"" are as aboveefined and x is an integer of at least 0. Specific diamines which are suitable for use in the present invention are: meta-phenylene diamine, para-phenylene diamine, 4A'-diaminodiphenyl propane, 4,4'-diamino-diphenyl methane, benzidine, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-diamino-diphenyl ether, 2,6-diamino-pyridine, bis-(4-amino-phenyl)diethyl silane, bis-(4-amino-phenyl)phosphine oxide, bis-(4-amino-phenyl)-N-methylamine, 1,5-diamino naphthalene, 3,3'-dimethyl4A'-diamino-biphenyl, 3,3'-dimethoxy benzidine, m-xylylene diamine, p-xylylene diamine, 1 ,3-bis-delta-aminobutyltetramethyl disiloxane, 1 ,3-bis-gamma-aminopropyltetraphenyl disiloxane, and mixtures thereof. Other diamines are known, such as listed in U.S. Patent No. 3,428,486.

While a variety of solvents may be utilized, it has been found that the phenols, cresols and xylenols are particularly suitable. In general, the solvents useful in this invention are the organic solvents whose functional groups do not react with either of the reactants (the diamines or the dianhydrides) to any appreciable extent. Besides being inert to the system and preferably, being a solvent for the polyamide acid, the organic solvent must be a solvent for at least one of the reactants, and preferably for both of the reactants. The organic solvent is an organic liquid other than either reactant or homologs of the reactants, that is a solvent for at least one reactant, and contains functional groups, the functional groups being groups other than monofunctional primary and secondary amino groups and other than the monofunctional dicarboxylanhydro groups.Such solvents include dimethysulfoxide, N-methyl-2-pyrrolidone, the normally liquid organic solvents of the N,Ndimethylmethoxyacetamide group, N-methylcaprolactam, tetramethylene urea, pyridine, dimethylsulfone, hexamethylphosphoramide, tetramethylenesulfone, formamide, N-methylformamide, butyrolactane, and N-acetyl-2-pyrrolidone. The solvents can be used alone, as mixtures, or in combination with diluents such as benzene, toluene, xylene, dioxane, cyclohexane, or benzonitrile, and aromatic hydrocarbons such as SC-100, a blend of aromatic hydrocarbons having a distillation range of 1 55-1 730C at 760 mm Hg, and SC-150, a blend of aromatic hydrocarbons having a distillation range of 188-2100C at 760 mm Hg. Minor amounts of n-butanol and water or isopropyl alcohol may also be added.

In order to stabilize the polymer solution and thereby increase the shelf-life thereof, volatile salt forming bases may be added to the solution in order to form salts with the free acid radicals. These bases may include ammonia (NH3), ammonium hydroxide (NH4OH), ammonium carbonate [(NH4)2CO3], and volatile primary, secondary and tertiary aliphatic amines such as methylamine, ethylamine, secondary butylamine, isopropyl amine, dimethylamine, dibutylamine, triethanolamine, triethylamine, diethanolamine, and the like.

The stabilizer forms a water soluble salt by reaction with the free carboxylic acid radicals in the partially imidized polyamide acid polymer. The result of the stabilization is such that the shelf life of the solution is quadrupled, thereby increasing the effective utility of the composition. Further, the magnet wire manufacturing process control conditions are stabilized with respect to time, thereby essentially simplifying the manufacturing operation. Because the composition is water soluble after stabilization, general clean-up around the dies and applicator is facilitated, as is the clean-up of material which the operator may get on his skin. The clean-up is simplified, too, in that valuable and flammable organic solvents are not required for the clean-up.

It has been further determined that a coating of the composition embodying the present invention on a substrate such as magnet wire can be cured to a bondable state or "B-stage" in order to provide a self-bondable wire. This can be accomplished by lowering the curing temperatures in the applicator, such as a wire tower, to provide an under-cure or "B-stage" cure, so that the polymer is not fully cured, but only cured to an acid-amide-imide stage, leaving sufficient acid and amide radicals to provide for a final crosslinking and bond. In conventional wire towers, it has been observed that by lowering the temperature of the tower ovens about 500C, while maintaining the wire speed, bondable or "B-stage" enamels can be produced. It has been observed that the bondable enamel coated substrate, such as bondable magnet wire, is stable, flexible, and scrape-resistant.The bondable wire can be stored without seizing or bonding on the spool. The bondable enamel coating is sufficiently flexible and scrape resistant so that when the bondable wire is utilized, it can be readily wound into coils using high-speed winding machines. The scrape resistance or repeated scrape abrasion characteristics of the bondable enamel wire produced as herein described is between about 25 and about 50 strokes as determined utilizing a 700 g weight, which for the fully cured enamel the scrape resistance, using a 700 g weight, is between 70 and 100 strokes.

Following winding, the adjacent coil turns can be bonded to each other by the application of heat.

Heat can be applied externally by placing wound coils in an oven, or heat can be applied internally by means of a current passed through the coils resulting in an increase in coil temperature. During the bonding process, the final remaining molecules of water are split out as the coating composition becomes fully imidized.

Bondable wire in its preferred form is produced by applying an electrical grade enamel undercoat, such as a polyesterimide undercoat, to the base wire in approximately four passes or coatings. The partially imidized enamel composition embodying the present invention is then applied over the polyesterimide undercoat in approximately two passes or coating operations, and cured to the bondable or "B-stage". Generally speaking, it is desirable that the undercoat comprise approximately two-thirds of the thickness of the total enamel coating.

The high temperature wire enamels which may be utilized to form the base coating on the wire conductor include polyester, polyesterimide, polyimide, polyamideimide, and polyesteramideimide enamels. Of these, the preferred high temperature base enamel undercoat is a polyesterimide enamel which is commercially available from numerous sources. Such polyesterimide enamels are disclosed in British Pat. 973,377, and British Pat. 996,649, U.S. Pat. 3,426,098 and U.S. Pat. 4,145,334, among others. Polyester enamels are disclosed in U.S. Pat 2,936,296. Polyimide enamels are disclosed in U.S. Pat. 3,652,500, U.S. Pat 3,663,510, U.S. Pat. 3,1 79,614 and U.S. Pat. 3,179,634.

Polyamideimide enamels are disclosed in U.S. Pat. 3,179,635. Polyesteramideimide enamels are disclosed in U.S. Pat. 3,555,113.

The base coat, such as a polyesterimide enamel is applied to the wire substrate in a conventional wire tower coating apparatus as described above. Where the base coat is to be provided with a bondable overcoat as herein described, a base coat of approximately two-thirds of the thickness of the total coating is desirably utilized. This can be accomplished, for example, by applying the base coat in four passes in a conventional wire tower in lieu of the more usual six passes. The bondable overcoat is then applied to the previously base coated wire in similar wire tower apparatus, utilizing two passes in order to provide two coats. Illustratively, the base coat is provided in a total build or thickness of about 1 mil on the diameter in four passes, while the overcoat is provided in a total thickness of about .5 mil on the diameter in two passes.

Referring to Figure 2, there is illustrated diagrammatically the various stages of polymer formation in the production of wire enamels and bondable coatings produced therefrom, embodying the present invention. In this diagrammatic illustration, the level of imidization is plotted against product stage. Initially, the polymer synthesis in the reaction kettle produces a solvent solution of a polyamide acid having an imidization level of from about 2 to about 6% (Polymer I). While in the reaction kettle, the polyamide acid polymer is heated for a sufficient period of time with the removal of water to produce an imidization level of between 30% and 70%, and the polymer solution is subsequently diluted with solvents and diluents to produce an enamel composition suitable for use in a wire tower (Polymer II).In the wire tower, the wire enamel is applied to a wire and cured to a bondable stage, but without fully imidizing (Polymer lit). The bondable wire is then wound into coils which are subsequently heated to fully imidize and cure the coating to produce the desired electrical grade coating (Polymer IV). Alternatively, of course, the bondable stage could be eliminated and the polymer fully cured directly to the Polymer IV stage in the wire tower.

Coils formed from the bondable magnet wire herein described, may be pressed and bonded substantially simultaneously utilizing resistance heating of the bondable coating together with a surge of electrical energy in the coils in order to press the coils into the slots of a rotor or stator being formed.

The use of a surge of electrical energy for pressing coils tightly together is disclosed in U.S. Patent 3,456,338, issued July 22, 1969, to D. W. Morhman et al., for Method for Changing the Configuration of and for Bonding Electrical Coils of Inductive Devices. The diclosure of the Mohrman et al. patent is incorporated herein by reference. Briefly, the coil is formed from the bondable wire and the wire is then heated by internal resistance upon the application of an electrical current thereto. The temperature of the coil is raised to that required for bonding of the enamel. When the bonding temperature is reached, a surge of electrical energy is applied to the coil which presses the coil turns tightly together while the enamel is in a bondable state.The coil is immediately cooled by subjecting it to air blasts or other coolant in order to set or harden the coil. Upon release of the electrical surge, the coil remains tightly bonded together. Where appropriate, further heat treatment of the coil to complete the bonding may be appropriate, such as heating in an oven in addition to the electrical heating.

The circuitry for the pulsing of the winding is compatible with that for the resistance heat bonding operation. It is estimated that it would take only approximately one-tenth of a second to discharge, that is pulse the winding, and something less than another tenth of a second to operate the necessary relays. The resistance heating cycle would, in effect, be interupted only during the discharge and transfer time of the relays which is estimated at one tenth to two tenths of second. This would only be a fraction of the time required for resistance bonding, approximately five seconds to reach the bonding temperature, followed by a ten second hold at the bonding temperature of about 2200C. to 2300 C.

Examples The following examples illustrate the present invention and its advantages over prior practices.

For a more comprehensive description of the various physical tests referred to, reference should be made to U.S. Patent 4,004,062.

Example 1 To a reactor equipped with a heating mantle, stirrer, nitrogen atmosphere, entry port, thermometer well, and provisions for cooling, was charged 1 6.73 kg phenol, preheated to 45-500C, followed by 4.21 kg (13.07 mole) 3,3',4,4'-benzophenonetetracarboxylic dianhydride (B) of approximately 99.5% purity and predried 10 hrs. at 1 500C. To the reactor was then charged 1.295 kg (6.54 mole) 4,4'-diaminodiphenyl methane (M), of approximately 99.8% purity, over a period of one min. with stirring, resulting in the formation of a clear solution of a "BMB" polymer building block, which is essentially a diamide diacid dianhyride. To the reactor was then charged, with stirring, 1.295 kg (6.54 mole) 4,4'-diaminodiphenylmethane (M) over a period of two to three min.The temperature was allowed to rise to 650C, and stirring was continued for thirty min. The polyorthoamic acid thus formed was a clear solution and had an 171nh=0.44 dl/g as determined at 0.5 g/dl in N-methyl-2pyrrolidone at 37.80C (100"F), and an imidization level of 46% calculated from a determination of free carboxylic acid groups by titration with tetrabutylammonium hydroxide using thymol blue indicator, on a sample size of 0.5 g in 120 g pyridine. The contents of the reactor were cooled to 40450C.A back addition of "B" was then made to the reactor to adjust the inherent viscosity (llInh) to 0.81 dl/g as described in U.S. Pat 3,663,510. The stirring continued for 30 minutes with the temperature maintained at 40--450C. An end capping of "B" terminals was effected by the addition of about 10% of "M" on a molar basis of the moles of "B" employed in the molecular weight adjustment from TlInh=O.44tO 11ính= .81 dl/g, as described in U.S. Pat. 3,652,500. The rlinh following end capping was at 0.78 dí/g (Polymer I).At this point the temperature of the reactor was allowed to rise to about 65-700C and was held at that level for a period of about 7.5 hrs., after which the level of imidization of the polyorthoamic acid was 47% as calculated from the carboxylic acid content as determined by potentiometric titration of the polymer using 1.0 M tetrabutylammonium hydroxide in methanol diluted to 1.0 N with an 85/15 mixture of toluene/methanol. The partially imidized polymer solution (Polymer II) was diluted by charging to the reactor a mixture comprised of 4.24 kg SC-100 solvent, 0.840 kg SC-1 50 solvent, and 12.19 kg of a blend of phenol, cresol and xylenol such that the resulting overall solvent composition was as follows, by weight %: 58.9% phenol 20.2% o-cresoi 5.4% m,p-cresol 0.7% xylenol 12.4% SC-100 2.4% SC-150.

There resulted a clear polymer enamel having a viscosity of 968 cps at 300C, a surface tension of 35.8 dynes/cm, and a solids level of 15.6%.

This enamel was used to coat .0571 inch aluminum wire, in a conventional wire tower, using six consecutive passes and dies with diameter openings of two at .061, two at .062 and two at .063 inch, and with the appropriate intermittent cure per pass, for a wire speed range of 30 to 40 ft/min. The fully cured polyimide (Polymer IV) presented a smooth concentric film. It exhibited excellent mechanical and physical properties. The resulting .0571 aluminum magnet wire passed a flexibility test involving a combination of 15% elongation plus winding on twice its diameter.

When the wire was quickly elongated by a snap action to the break point, the film pull back was less than the diameter of the wire. In a mandrel adhesion test, using a mandrel twice the diameter of the wire, five pulls were required before catastrophic failure occurred. In a needle adhesion test, there were no failures in three separate test pulls over a 1X diameter needle at a six pound load. In a heat shock test, which involved coil examination following 1/2 hour exposure at 2400C of coils of the wire wound at 1X, 2X and 3X diameter, there were no observed cracks. The film also exhibited excellent electrical properties, having a twisted pair dielectric strength of 8000 to 10,000 volts. The aluminum magnet wire was rated 20,000 hrs. at 2500C in the ASTM 2307 (IEEE 57) test.

The wire enamel was also employed to coat .0403 inch copper using standard six pass die setup resulting in a 2.7-3.0 mii build. The copper magnet wire exhibited excellent mechanical and physical properties including 25% and 1X flexibility. The copper magnet wire was rated 20,000 hrs. at 2400C in the ASTM 2307 (IEEE 57) test.

Example 2a An ammoniated water soluble polyorthoamic acid polymer prepared from 3,3',4,4'benzophenonetetracarboxylic dianhydride (B) and 4,4'-diaminodiphenyl methane (M) as per Example 1 but in N-methyl-2-pyrrolidone with n butanol and water as the diluents and with 17,no=0.78 dl/g as per U.S. Pat. 3,652,500, with the polymer at 0--2% imidization, was used as a wire enamel in the same wire tower with the same number of passes, die setup and wire speed as in Example 1. There resulted severe blistering of the wire in the 30--40 ft/min speed range for aluminum.Only when the number of passes were increased, the die opening decreased, and the wire speed decreased, could reasonably smooth wire be made at approximately the same solids level of the enamel with and 2.7-3.0 mii enamel build on the wire.

Example 2b A polyorthoamic acid polymer prepared from pyromellitic dianhydride and 4,4'-diaminodiphenyl ether in N-methyl-2-pyrrolidone, with SC-100 hydrocarbon diluent, with Inh=0.70 dl/g, and with the polymer at 02% imidization, was used as a wire enamel in the same tower with the same number of passes, die setup and wire speed as in Example 1. There resulted severe blistering of the wire in the 3040 ft./min. speed range. Only when the number of passes were increased, the die openings decreased and the speed decreased could reasonably smooth wire be made at approximately the same solids of the enamel with 2.7-3.0 mil enamel build on the wire.

Example 2c Polymer I of Example 1, at 56% imidization, was diluted with the let-down solvent mixture recited in Example 1. When this enamel was employed at the same tower with the same number of passes, die set up and wire speed as in Example 1, there resulted severe blistering of the film on the wire in the 30 3O0 ft/min. speed range. Only when the number of passes were increased, the die openings decreased, and the speed decreased could reasonably smooth wire be made at approximately the same solids of the enamel and with a 2.7-3.0 mil enamel build on the wire.

Example 3 The Polymer I to Polymer II sequence of Example 1 was duplicated in preparation, except that the 7Bond=0.75 dl/g and the level of imidization was 38%. The resulting Polymer II was diluted by charging to the reactor a mixture of 42.4 g SC-100, 8.4 g SC-1 50 and 121.9 g of a blend of phenol, cresol and xylenol such that the resulting overall solvent composition was as follows by weight%: 51.3% phenol 11.8% o-cresol 4.3% m,p-cresol 7.9% 2,6-xylenol 3.2% 2,4-and 2,5-xylenol 4.6% 3,5-xylenol 1.1% 3,4-xylenol 0.8% post xylenols 12.5% SC-100 2.5% SC-150.

There resulted a clear solution having a viscosity of 1030 cps at 3O0C, a surface tension of 36.0 dynes/cm, and a solids level of 15.8%. This enamel was employed to coat rectangular aluminum and copper wire using Turk's head and modified Turk's head dies (Pittsfield dies) in the 7-11 ft./min.

speed range on 0.225x0.105 inch aluminum wire. Four passes were employed to achieve a 2.3-2.6 mil build on the flats and edges. In another wire tower run, six passes were employed to achieve a 5.66.0 mil build on the flats and edges of .225x.105 copper. The fully cured film (Polymer IV) thus obtained was smooth and exhibited excellent mechanical and electrical properties on both conductors.

Flexibility was tested and found to pass 2X at 10% elongation on the aluminum and 4X at 5% elongation on the copper magnet wire. The rectangular aluminum and copper magnet wire passed the heat shock test of 1/2 hr. at 2400C for a 4X coil. The coating was found to be uniform with no "dogboning", or excess build on the corners, a not uncommon problem found for polyimide wire enamels using the standard N-methyl-2-pyrrolidone solvent systems, such as described in Example 2a.

Example 4 Polymer I of Example 3, at about 56% imidization, was diluted with the let-down solventdiluent mixture recited in Example 3. When this enamel was employed on the same rectangular aluminum wire at the same tower with the same number of passes and die setup as in Example 3, there resulted severe blistering of the film on the wire in the same 7-11 ft./min. speed range.

Example 5a To the reactor of Example 1 was charged 48.9 kg phenol preheated to 45-500C, followed by 10.53 kg (32.70 mole) BTDA (B) of approximately 99.5% purity, predried 10 hrs. at 1 500C. This was followed by the addition of 3.23 kg (16.31 mole) MDA (M) over a period of one min. with stirring. To the clear solution of BMB polymer building block in the reactor was charged, with stirring, 3.24 kg (16.36 mole) MDA over a period of three to four min. The temperature was allowed to rise to 680C., and stirring was continued for an additional thirty minutes.The polyorthoamic acid was a clear solution and had an x1inh=0.48 dl/g. The inherant viscosity (171nh) was adjusted to 0.80 dI/g with BTDA and encapped to a final 11ins of 0.77 dl/g with MDA as described in Example 1. The temperature of the reactor was increased to 68-720C and held for a period of 8 hrs., after which the level of imidization of the polyorthoamic acid (Polymer II) was determined to be at 51%. Polymer II was diluted by charging to the reactor a mixture comprised of 4.48 kg cresol, 1.40 kg phenol, 9.95 kg SC-100,4.97 kg n-butanol and 13.3 kg water. The resulting overall solvent composition was as follows by weight %: 60.6% phenol 5.4%cresol 12.0% SC-100 6.0% n BuOH 16.0% water.

There resulted a clear solution having a viscosity of 450 cps at 300 C, a surface tension of 39.0 dynes/cm, and a solids level of 15.9%. The enamel was employed to coat .0571 inch aluminum wire using process conditions as described in Example 1. The fully cured polyimide film (Polymer IV) was a smooth concentric film exhibiting excellent mechanical, physical and electrical properties not unlike those cited in Example 1.

Example 5b The Polymer il preparation of Example 5a was duplicated with the exception that the 48.9 kg initial charge of phenol to the reactor was replaced with a mixture of 42.9 kg phenol plus 6.0 kg cresol.

The polymer was prepared at llinh at 0.78 dl/g and imidized as per Example 5a to 54%. The let-down solvent-diluent was a mixture comprised of 2.96 kg cresol, 6.2 kg phenol, 1 9.9 kg SC-100 and 4.98 kg of n-butanol. The resulting overall solvent composition was as follows by weight %: 59.2% phenol 10.8% cresol 24.0% SC-100 6.0% n BuOH.

There resulted a clear solution having a viscosity of 856 cps at 300C, a surface tension of 36.3 dynes/cm, and a solids level of 1 5.8% The enamel was employed to coat .0571 inch copper and aluminum conductor using production conditions as described in Example 1. The fully cured polyimide film (Polymer IV) was a smooth, concentric film on both conductors and exhibited excellent mechanical, physical and electrical properties approximately equivalent to those cited in Example 1.

Example 6 To a reactor equipped with a heating mantle, stirrer, nitrogen atmosphere, entry port, thermometer well and provisions for cooling, was charged 167.3 g phenol, preheated to 45--500C, followed by 42.10 g (.1307 mole) 3,3'.4.4'-benzophenonetetracarboxylic dianhydride (BTDA or "B") at approximately 99.5% purity, predried 10 hrs. at 1 500C. To the reactor was then charged 7.07 g (.0654 mole) 1,3-diaminobenzene (DAB or A) over a period of one min. with stirring resulting in formation of a clear solution of BAB polymer building block. To the reactor was then charged with stirring 7.07 g (.0654 mole) 1,3-diaminobenzene (A) over a period of two-three min. The temperature was allowed to rise to 650C. Stirring was continued for thirty min.The polyorthoamic acid was a clear solution and had an x7ính=0.38 dl/g, as determined at 0.5 g/dl in N-methyl-2-pyrrolidone at 37.80C (1000F), and a 4 5% imidization level. The contents of the reactor were cooled to 40 "50C. A back addition of "B" was then made to the reactor to adjust the ?7inh to 0.77 dl/g (U.S. Pat. 3,663,510). The stirring was continued for 30 minutes with the temperature maintained at 40--450C. An end capping of "B" terminals was effected by the addition of about 10% of "A" on a molar basis of the moles of "B" employed in the molecular weight adjustment from x1ính= 38 to 11inh=0.77 dl/g (U.S. Pat. 3,652,500).

The 71ins following end capping was at 0.75 dl/g (Polymer I). At this point the temperature of the reactor was allowed to rise to 65-700C, and was maintained for a period of six hours, after which the level of imidization of the polyorthoamic acid (Polymer II) was determined to be at 51%. The Polymer II was diluted by charging to the reactor a mixture comprised of 42.4 g SC-1 00, 8.4 g SC-150, and 121.9 g of a blend of phenol, cresol and xylenol such that the resulting overall solvent composition was approximately equivalent to that recited in Example 1.

The resulting enamel was a clear solution having a viscosity of 370 cps at 300C, a surface tension of 35.4 dynes/cm and a solids level of 13.3%. The enamel was employed to coat .0571 inch copper and aluminum conductor. The fully curred polyimide film (Polymer IV) was smooth and concentric on both conductors and exhibited excellent mechanical, physical and electrical properties approximately equivalent to those recited in Example 1.

Example 7 To a reactor equipped with a heating mantle, stirrer, nitrogen atmosphere, entry port, thermometer well and provisions for cooling, was charged 167.3 g phenol preheated to 45-500C followed by 42.10 g (.1307 mole) 3,3',4,4'-benzophenonetetracarboxylic dianhydride (B) at approximately 99.5% purity, predried 10 hrs at 1 500C. To the reactor was then charged 13.08 g (.0654 mole) 4,4'-diaminodiphenyl ether (0) over a period of one min., with stirring, resulting in the formation of a clear solution of a BOB polymer building block. To the reactor was then charged, with stirring, 1 3:08 g (.0654 mile) 4,4'-diaminodiphenyl ether (0) over a period of two to three min. The temperature was allowed to rise to 650C, and stirring was continued for thirty min.The polyorthoamic acid was a clear solution and had an w7inh=0.39 dl/g as determined at 0.5 g/dl in N-methyl-2pyrrolidone at 37.80C (1000F), and a 67% imidization level. The contents of the reactor were cooled to 40-450C. A back addition of "B" was then made to the reactor to adjust the rlinh to 0.78 dí/g (U.S. Pat. 3,663,510). The stirring was continued for 30 minutes, with the temperature maintainec at 40-450C. An end capping of "B" terminals was effected by the addition of about 10% of "O" on a molar basis of the moles of "B" employed in the molecular weight adjustment from 71ins=0.39 to w7nh=0.78 dl/g (U.S. Pat. 3,652,500).The ?7inh following end capping was at 0.76 dI/g (Polymer I). At this point the temperature of the reactor was allowed to rise to 65-700C and held for a period of 5.5 hrs. after which the level of imidization of the polyorthoamic acid (Polymer II) was determined to be 40%. Polymer II was diluted by charging to the reactor a mixture comprised of 42.4 g SC-100, 8.42 SC-1 50, and 121.9 g of a blend of phenol, cresol and xylenol such that the resulting overall solvent composition was approximately equivalent to that recited in Example 1.

There resulted a clear solution having a viscosity of 820 cps at 300C, a surface tension of 35.4 dynes/cm, and a solids level of 15.8%. The enamel was employed to coat .0571 inch copper and aluminum conductor. The fully cured polyimide film (Polymer IV) exhibited excellent mechanical, physical and electrical properties on both conductors.

Example 8 To a reactor equipped with a heating mantle, stirrer, nitrogen atmosphere, entry port, thermometer well and provisions for cooling, was charged 1 67.3 g phenol preheated to 45-500C, followed by 63.0 g (.1307 mole) 4,4'-(2-acetoxy-1 ,3-glyceryl) bis-anhydro trimellitate (AGBT or T). To the reactor was then charged 12.95 g (.0654 mole) 4,4'-diaminodiphenyl methane (M) over a period of one min. with stirring resulting in formation of a clear solution of TMT polymer building block. To the reactor was then charged, with stirring, 12.95 g (.0654 moie) 4,4'diaminodiphenylmethane (M) over a period of two to three min. The temperature was allowed to rise to 650C., and stirring was continued for thirty min.The polyorthoamic acid was a clear solution and had an 7inh=0.34 dl/g as determined at 0.5 g/dl in N-methyl-2-pyrrolidone at 37.80C (1 000F) and a 56% imidization level. The contents of the reactor were cooled to 40-450C. A back addition of "T" was then made to the reactor to adjust the 17lnh to 0.80 dl/g (U.S. Pat. 3,663,510). The stirring was continued for 30 minutes with the temperature maintained at 40--450C. An end capping of "T" terminals was effected by the addition of about 10% of "M" on a molar basis of the moles of "T" employed in the molecular weight adjustment from 17ính=0.34 to x7nh=0.80 dI/g (U.S. Pat. 3,652,500). The llInh following end capping was determined to be 0.78 dl/g (Polymer I). At this point, the temperature of the reactor was allowed to rise to 65-700C and was held for a period of 7.5 hrs., after which the level of imidization of the polyorthoamic acid (Polymer II) was determined to be at 37%.Polymer II was diluted by charging to the reactor a mixture comprised of 42.4 g SC-1 00, 8.4 g SC-150, and 121.0 g of a blend of phenol, cresol and xylenol, such that the resulting overall solvent composition was approximately equivalent to that re cited in Example 1.

The resulting enamel was a clear solution having a viscosity of 1400 cps at 300C, a surface tension of 36.8 dynes/cm and a solids level of 1 9.3%. The enamel was employed to coat .0571 inch copper and aluminum wire. The fully cured polyimide film (Polymer IV) exhibited excellent mechanical, physical and electrical properties approximately equivalent to those recited in Example 1.

Example 9 To a reactor equipped with a heating mantle, stirrer, nitrogen atmosphere, entry port, thermometer well and provisions for cooling, was charged 1 67.3 g phenol, preheated to 45-500C, followed by 28.52 g (.1307 mole) pyromellitic dianhydride. To the reactor was then charged 13.08 g (.0654 mole) 4,4'-diaminodiphenyl ether (0), over a period of one min., with stirring, resulting in the formation of a clear solution of "POP" polymer building block. To the reactor was then charged, with a stirring, 13.08 g (.0654 mole) 4,4'-diaminodiphenyl ether (0) over a period of two to three min. The temperature was allowed to rise to 650C., and stirring was continued for thirty min.The polyorthoamic acid was a clear solution and had an 77lah=0.40 dl/g as determined at 0.5 g/dl, in N-methyl-2pyrrolidone, at 37.80C (1 000 F), and a 5 to 6% imidization level. The contents of the reactor were cooled to 40--450C. A back addition of "P" was then made to the reactor to adjust the tenth to 0.84 dl/g (U.S. Pat. 3,663,510). The stirring was continued for 30 minutes with the temperature maintained at 40--45 OC. An end capping of "P" terminals was effected by the addition of about 10% of "O" on a molar basis of the moles of "P" employed in the molecular weight adjustment from 111nh=0.40 to x71nh=0.84 dl/g (U.S. Pat. 3,652,500).The llInh following end capping was at 0.81 dl/g (Polymer I). At this point the temperature of the reactor was allowed to rise to 65-700C and was maintained for a period of 5.0 hrs., after which the level of imidization of the polyorthoamic acid (Polymer II) was determined to be at 30%. Polymer II was diluted by charging to the reactor a mixture cornpnsed of 42.4 g SC-100, 8.4 g SC-1 50, and 121.9 g of a blend of phenol, cresol and xylenol, such that the resulting overall solvent composition was approximately equivalent to that cited in Example 1.

There resulted a clear solution having a viscosity of 540 cps at 300C, a surface tension of 35.6 dynes/cm, and a solids level of 13.0%. The enamel was employed to coat .0571 inch copper and aluminum conductor. The fully cured polyimide film (Polymer IV) exhibited excellent mechanical, physical and electrical properties on both conductors.

Example 10 A conventional, commercially available polyesterimide wire enamel, "lmidex" from General Electric Co., was employed to coat an .0427 copper conductor, using four consecutive dies, in a conventional wire enamelling tower and with the appropriate intermittent cure per pass, such that there resulted a fully cured, two-third of normal insulation build of polyesterimide enamel as compared to the conventional build of enamel for magnet wire to be utilized in the manufacture of hermetic motors.This four-pass or four-layered base coated magnet wire was then overcoated with two additional layers of a "B-stage" polyimide prepolymer magnet wire insulation by using Polymer II of Example 1 in the solvent system cited in Example 1, at viscosity of 968 cps at 300C, surface tension of 35.8 dynes/cm and a solids level of 1 5.6% as cited in Example 1, and partially curing to form a selfbondable polymer overcoating. The "B-stage" bondable overcoat insulation amounted to about onethird of the total normal insulation build for hermetic motors. This "B-stage" bondable enamel is illustrated in Figure 2 as Polymer Ill.In order to produce the bondable "B-stage" polymer enamel, the wire tower temperature profile is adjusted downward by approximately 500C in the top zone of the tower as compared to the temperature required to achieve a fully cured polyimide enamel from the same tower under otherwise identical process conditions, including normal die openings and wire speeds. The resulting one-third "B-stage" bondable polymer enamel top coat with the underlying fully cured two-third polyesterimide base coat enamel resulted in a bondable magnet wire insulation system suitable for bonding at a later time with the aid of heat and controlled pressure. The resulting bondable magnet wire exhibited excellent mechanical, physical and electrical properties. This "B-stage" bondable magnet wire passed a flexibility test involving a combination of 25% elongation plus winding on its diameter.This was unexpected for a "B-stage" bondable polyimide prepolymen All other electrical and mechanical properties required of a hermetic magnet wire were met, including Du Pont refrigerant Freon 22, difluoromonochloro methane, extractables below 0.5% in NEMA test MW-7255.1. The bondable wire also passed the needle adhesion and mandrel adhesion tests described in Example 1. The bondable magnet wire also had excellent shelf life as exhibited by showing no degradation in these properties after one year of shelf life. The bondable enamel overcoated/polyesterimide base coated wire was formed into a helical coil by winding on a one-fourth inch diameter mandrel such that a one and one-half inch length of coil was formed.This coil was then bonded in minutes with aid of a fixture, a preheated 440 g weight positioned axially on top of the coil, and a forced-air oven set at a temperature of 2300 C. Bond strengths of the coil, in pounds force to break were determined with the aid of an Instron machine, and measured at 26 at 250C, 3.2 at 1 800C and 2.5 at 2500C.

Example 11 The bondable magnet wire produced in Example 10 as one-third bondable top coat and two-third fully cured polyesterimide base coat, was wound into helical coils by winding on a one-fourth inch diameter mandrel such that a coil three inches in length was obtained. This coil was then bonded in about ten seconds at 2300C using DC resistance heating of the coil for about five seconds to achieve the temperature of 2300C. The coil was positioned with the aid of a fixture and subjected to axial pressure of 440 g force. Bond strengths for the bonded coil in air at 250C, 1 800C and 2500C were found to average 62.3, 4.9 and 2.3 pounds respectively.Bond strengths of helical coils prepared in the same way were measured in a Freon 22 atmosphere at 130 psia and at temperatures of 230C and 1000C, following immersion exposure for a time period that assured the magnet wire insulating film was saturated with Freon 22 as it would be under normal operation of a hermetic motor in a refrigeration compressor. In this test, the coils were aged in Freon 22 for 10 days at 1 700C and 250 psia. Bond strengths of the coil were found to be an order of magnitude better than those found for conventional materials of construction in the realm of bonding varnishes for hermetic motors. Bond strengths in Freon 22 at 130 psi and at 230C and 1000C, were found to average 51.6 and 46.6 pounds respectively.These values in Freon 22 were found to be an order of magnitude better than when treated with present commercial varnishes such as Du Pont Cavalite varnish, on standard hermetic polyesterimide magnet wire, which in a control test, were found to be 5.2 and 3.4 pounds measured in Freon 22 at 130 psia at 230C and 1000C, respectively.

Example 12 The partially imidized polymer enamel (Polymer II) of Example 1, in the solvent system recited in Example 1, at a solids level of 1 5.6%, was used to coat .0427 inch copper wire, using four consecutive dies in a conventional wire enamelling tower, and with an intermittent cure per pass such that there resulted a fully cured polyimide, of two-thirds of the normal insulation build for hermetic motors. This four-pass or four-layered magnet wire was then overcoated with two additional layers bondable "Bstage" polyimide magnet wire insulation by using the same partially imidized polymer enamel and curing to the "B-stage".In order to achieve the "B-stage" the wire tower temperature profile was adjusted downwardly by approximately 500C in the top zone of the tower as compared to the temperature required to achieve the above four-pass fully cured polyimide enamel, the other processing conditions, including normal die openings and wire speed being unchanged. The resulting one-third "B-stage" bondable top coat with the fully cured two-third polyimide base coat magnet wire resulted in a bondable magnet wire insulation system suitable for bonding at a later time with the aid of heat and controlled pressure. The resulting bondable magnet wire exhibited excellent mechanical, physical and electrical properties. The "B-stage" bondable magnet wire passed the flexibility test of 25% elongation plus winding on its diameter. This was unexpected for a "B-stage" bondable polyimide prepolymer.All other electrical and mechanical properties required of a hermetic magnet wire were met, including Freon 22 extractables below 0.5% in the NEMA Test MW-72C-55.1. The bondable wire also passed the needle adhesion and mandrel adhesion tests described in Example 1. The bondable magnet wire also had excellent shelf life as exhibited by showing no degradation in these properties after one year of shelf life. The bondable magnet wire was formed into a helical coil by winding on a one-fourth inch diameter mandrel such that a one and one-half inch length of coil was formed. This coil was then bonded in minutes with the aid of a fixture, a preheated 440 g weight positioned axially on the top of the coil, and a forced-air oven set at 2300C.Bond strengths of the coil in pounds force to break were measured with the aid of an Instron machine and found to be 28 at 25 OC, 3.0 at 1 800C, and 2.5 at 2500C.

Example 13 The bondable magnet wire produced in Example 12 was wound into helical-coils by winding on a one-fourth inch diameter mandrel such that a coil three inches in length was obtained. The coils were then bonded in about ten seconds at 2300C using DC resistance heating of the coil for about five seconds to achieve a temperature of 2300C. The coils were positioned with the aid of a fixture and subjected to an axial pressure of 440 g. Bond strengths for the bonded coils in air at 250C, 1 800C and 2500C were approximately equivalent to the values recited in Example 12. Bond strengths in Freon 22 at 130 psia at 230C and 1000C were approximately equivalent to the values recited in Example 11 for coils bonded with the same bondable topcoat but using a polyesterimide base coat.

Example 14 A sufficient quantity of the bondable polyesterimide base coat magnet wire described in Example 11 was prepared to enable the winding of standard hermetic stators. The bondable wire, when used in high speed winding equipment, wound equivalently to standard non-bondable hermetic magnet wire.

With the aid of a DC resistance heating unit and a mold for the end turns, the mold pressure and resistance heating were applied in a heating cycle comprised of 5 sec. for the stator windings to rise from room temperature to 2300C, a hold at 2300C for 10 sec., and removal from the mold in an additional 5 sec. There resulted a bonded stator unit which performed in simulated hermetic motor operational tests of the stator equivalent to a conventional hermetic motor stator employing the conventional tie cord and a varnish treatment.

Example 15 A sufficient quantity of bondable magnet wire as described in Example 13 was prepared to enable the winding of standard hermetic stators. The bondable wire wound comparably to standard hermetic magnet wire. With the aid of a DC resistance heating unit and a mold for the end turn, the mold pressure and resistance heating were applied in a heating cycle comprised of 5 sec. for the windings to rise from room temperature to 2400 C, a hold at 2400C for 10 sec., and removal from the mold in additional 5 sec. There resulted a bonded stator unit which performed in simulated operational tests of the stator equivalent to a conventional hermetic motor stator employing the conventional tie cord and a varnish treatment.

Claims (21)

Claims

1. A partially imidized polyamide acid polymer having an imidization level greater than 6%, but not more than 70%.

2. A coating medium comprising a partially imidized polyamide acid polymer in a solvent.

3. A coating medium comprising a partially imidized polyamide acid polymer in a phenolic based aromatic solvent.

4. A coating medium comprising a polyamide acid polymer having an imidization level greater than 6%, but not more than 70% in a phenolic based aromatic solvent.

5. A coating medium comprising a partially imidized polyamide acid polymer in a phenolic based aromatic solvent and having a solids content between about 10% and about 25% by weight.

6. A composition comprising a solution of a polyamide acid of the general formula

wherein one or both X radicals are hydrogen or carboxyl atoms and groups; wherein the e denotes isomerism so that in any recurring unit within the polymeric structure the groups to which the arrows point may exist as shown or in an interchanged position; wherein R is an organic tetravalent radical containing at least two carbon atoms and no more than two carbonyl groups of each polyamide acid unit are attached to any one carbon atom; wherein R' is a divalent radical containing at least two carbon atoms; the amide groups of adjacent polyamide acid units are attached to separate carbon atoms of said divalent radicals; wherein n is an integer sufficient to provide a polyamide acid having an inherent viscosity of from 0.7 to 0.9 dl/g at 0% to 6% imidization as measured at 0.5 g/dl in N-methyl2-pyrrolidone at 37.80C.; and wherein said polyamide acid is partially imidized to more than 6% but not more than 70% imidization; in a phenolic based aromatic solvent.

7. A coating medium comprising a partially imidized polyamide acid polymer in a phenolic based aromatic solvent, the imidization of said polymer being sufficient to preclude blister formation during curing of said polymer, but less than an amount which would preclude curing of a coating of said polymer on a substrate.

8. A coating medium comprising a partially imidized polyamide acid polymer in a solvent and wherein said polymer is imidized to a level greater than the level of imidization required to prevent blistering of said coating medium during curing thereof, but less than the amount of imidization which would preclude curing of a coating of said polymer on a substrate.

9. A bondable magnet wire comprising a metallic wire substrate, and a self-bondable coating on said wire, characterized in that said self-bondable coating comprises a partially cured polyamide acid polymer.

10. A bondable magnet wire comprising a metallic wire substrate, and a self-bondable coating on said wire, characterized in that said bondable coating comprises a partially cured polyamide acid polymer, and self-bondable at between about 2200C. to about 2500C. to form a bond having a strength of between about 30 and about 60 Ibs. at a temperature of between about 200C and about 1200C.

11. A bondable magnetic wire comprising a metallic wire substrate, and a self-bondable coating on said wire, characterized in that said bondable coating comprises a partially cured polyamide acid polymer comprising the reaction product of equal molar proportions of 3,3',4,4'benzophenonetetracarboxylic dianhydride and 4,4'-methylenedianiline in a phenolic based aromatic solvent and cured on the magnet wire to form a heat bondable coating having an imidization level sufficient to provide a stable, windable magnet wire.

12. A bondable magnet wire comprising a metallic wire substrate, an electrical grade enamel coating on said substrate, and a self-bondable coating on said enamel coated wire, characterized in that said self-bondable coating comprises a partially cured polyamide acid polymer.

13. A bondable magnet wire comprising a metallic wire substrate, an electrical grade enamel coating on said substrate, and a self-bondable coating on said enamel coated wire, characterized in that said bondable coating comprises a partially cured polyamide acid polymer, and self-bondable at between about 2200C to about 2500C to form a bond having a strength of between about 2 and about 65 pounds of force at temperatures between about250C and about 2500C.

14. A bondable magnet wire comprising a metallic wire substrate, an electrical grade enamel coating on said substrate, and a self-bondable coating on said enamel coated wire, characterized in that said bondable coating comprises a partially cured polyamide acid polymer comprising the reaction product of equal molar proportions of 3,3',4,4'-benzophenonetetracarboxylic dianhydride and 4,4'methylenedianiline in a phenol solvent and cured on the magnet wire to form a heat bondable coating having an imidization level sufficient to provide a stable, windable, bondable magnet wire.

1 5. A coating composition as defined in any of claims 2, 3, 4, 5, 6, 7 or 8 including a stabilizer selected from the group consisting of ammonia, ammonium hydroxide, ammonium carbonate, and volatile primary, secondary and tertiary aliphatic amines.

1 6. A substrate having a coating thereon of the polyamide acid polymer defined in claim 1.

1 7. A substrate having a coating thereon produced by heat curing a coating thereon of the coating medium defined in claims 2, 3, 4, 5, 6, 7 or 8.

18. A bonded coil of magnet wire produced by heat curing of coil of bondable magnet wire as defined in claims 9,10,11,12, 13 or 14.

19. A bonded coil of magnet wire produced by heat curing a coil of bondable magnet wire as defined in claims 9, 10, 11, 12, 13 or 14 while pressing the turns of the coil together with a surge of electric current.

20. A bondable magnet wire as defined in claims 12, 1 3 or 14 wherein said electrical grade enamel coating is selected from the group consisting of polyester, polyesterimide, polyimide, polyamideimide, and polyesteramideimide enamels.

21. A bondable magnet wire as defined in claim 14 wherein said electrical grade enamel is a polyesterimide.