High Temperature Adhesive Overcoat For Magnet Wire

Abstract

An electrical conductor is coated with a high temperature thermosetting wire enamel base coat and overcoat of an aromatic thermoplastic polysulfone adhesive to form a composite insulated electrical conductor.

Description

BACKGROUND OF THE INVENTION

This invention relates to high temperature adhesive magnet wire insulation. In particular, this invention relates to magnet wire overcoat solutions of modest cost containing thermoplastic linear aromatic polysulfone resins, that will meet class 155.degree. C-180.degree. C requirements as a baked overcoat film, and as such, exhibit a superior combination of adhesive qualities, heat shock resistance, and thermal stability in air, together with satisfactory properties as regards flexibility, abrasion resistance, and the like.

There is a need for replacing the costly varnishing operation required to bond magnet wire turns in coils of electrical equipment so that they are rigid and remain in place. There is also a need for a resinous adhesive having higher operational temperatures than the presently used epoxy-urethane, polyvinyl formal and polyvinyl butyral adhesives used to overcoat electrical equipment coils.

We have found that polysulfone resin based overcoats in particular can solve present problems and fulfill the need for a high temperature magnet wire adhesive.

Polysulfones were introduced to the market in 1965 as a novel type of linear aryl polymer consisting of phenylene units linked by isopropylidene, ether and sulfone groups. This material, having high deflection temperatures under load and high tensile strength, was found suitable for use as housings for engineering, electrical and domestic appliances where heat and/or creep resistance were important requirements. Applications also encompassed use as electronic parts including connectors, integrated circuit carriers and other molded components. They have also been suggested as possible adhesives, impregnating resins, wire coatings and electrical insulating materials where severe and corrosive ambient conditions are found (British Pat. No. 1,060,546) and high temperature base coat extruded wire insulation (R. K. Waton, 1968-1969 Modern Plastics Encyclopedia, p. 286).

In terms of its chemical makeup, polysulfone has the repeating structure shown below: ##SPC1##

The most distinctive feature of the backbone chain is the diphenylene sulfone group: ##SPC2##

This group imparts excellent thermal and oxidation resistance. Flexibility in the backbone of the polymer to impart toughness is contributed by the ether linkage and augmented by the isopropylidene link. Such aryl polymers can be prepared via the nucleophilic aromatic substitution reaction shown below, where n is the monomer number: ##SPC3##

Evaluating our high temperature, composite, base enamel-adhesive overcoated wire involved numerous tests. These will be described briefly below and their significance indicated.

In the Quick-Elongation Test, a piece of our coated wire, 12 inches in length, with an S-bend at its midpoint, was placed between a stationary and movable chuck, and elongated rapidly to break the wire at a point about 1 inch from either fastener. This test measures flexibility of the insulation and indicates the degree of coating adhesion. It is also used as a control test to determine if the insulation is underbaked or overbaked.

In the Elongation +1X Test, one end of a length of our coated wire was mounted in a stationary chuck and the other end mounted in a movable chuck. The wire was elongated a fixed percentage until flaws appeared in the insulation. The maximum elongation, in percent, that the insulation will remain flawless and free of imperfections after being wrapped on a 1X mandrel is considered the degree of flexibility of the insulation. This test measures the ductility of an insulation film on a conductor and indicates the degree to which a wire can be elongated and remain free of cracks, faults, and other imperfections. This simulates the stretching and stress to which a wire is subjected when passing over small radii pulleys, guides, and on coil forms as it is being wound into finished coils.

In the G.E. Repeated Scrape Abrasion Test, abrasion of our wire coating was accomplished by moving a 16-mil diameter, No. 11 needle, back and forth a distance of three-eighths inch at a right angle to the wire by a motor and eccentric shaft mechanism. The number of cycles required to cause the needle to break through the insulation is the GESA value.

In the Westinghouse Scrape Test, a 12 inch length of our coated wire was pulled under a 9-mil diameter weighted steel piano wire at right angles to the piano wire for a distance of 3 inches on each of four sides (90.degree. apart). The weight required to scrape off one-half the insulation on the conductor is considered the scrape value.

In the Emerson Scrape Test, our coated wire was drawn at 60 ft./min. under and at a right angle to a weighted 51-mil diameter needle, which was repeatedly placed on and off the moving wire by a cam action assembly. The weight required to scrape through to the conductor 8 out of 10 times is the reported single scrape value.

These scrape tests measure the resistance of the insulation to scrape and abrasion, and the degree of adhesion of the film to the base metal or the cohesion between coating layers. These properties are indications of the ability of the enamel base coat and overcoat films to withstand coil winding abuses.

In the Heat Shock Test, a length of our coated wire was wrapped on a 1X mandrel 20 times to form a coil. Each test sample was placed in an oven at a specified temperature. The highest temperature at which the stressed coils withstood visual breaks or failure occurring in the insulation after being heated for 1 hour and cooled to room temperature is considered the heat shock value. Visual observation was made under a microscope at approximately 23X magnification. This test indicates the ability of the insulated wire to withstand heat while in a stressed conditions as encountered in wound magnet wire coils.

Another test is the Thermal Life Test. This is a test measuring the expected thermal-class rating of varnished or unvarnished magnet wires in electrical equipment and is based on the theory of electrical-insulation deterioration treated as a chemical-rate phenomenon. The test procedure used was that described in IEEE No. 57. Data for our insulated wire is reported in terms of hours-to-failure at a given temperature.

Values for the results of all these tests on our composite insulated wire is reported hereinafter in Table 1.

BRIEF SUMMARY OF THE INVENTION

It has been found that novel high temperature resinous solutions, based on thermoplastic linear aromatic polysulfone resins having melting points (point where the resin begins to soften, i.e., transition point) above about 180.degree. C, can be made compatible with high temperature wire enamel base coat films, such as polyester-amide-imide enamels. These polysulfone resins maintain the same melting point characteristics after being applied as an adhesive coating. Polysulfone adhesive coatings having melting (transition) points below about 180.degree. C will not give the high temperature characteristics necessary for high temperature coil class 155.degree. C-180.degree. C requirements.

Polysulfone, dissolved in a suitable solvent such as dimethylacetamide makes an excellent coil wire adhesive overcoat solution that we have successfully coated over enameled wire. This adhesive-enamel coated wire was wound into a magnet wire coil and the turns of the magnet wire were fused together to a rigid form by resistance heating and also by heating in a high temperature atmosphere between about 200.degree. and 260.degree. C. We found that we could apply the base coat enamel, followed by a coating of the polysulfone adhesive solution in one continuous operation, rather than having to coat the two components at different temperatures in two different operations. This is a tremendous advantage in manufacturing operations and is due to the similar coating and curing characteristics of the base enamel and adhesive overcoat. The combination of a wire conductor with a base coat enamel and adhesive overcoat, with subsequent coil winding and heat treatment to cause the adhesive to bond the coils together, results in a rigid coil having a thermal life rating of about 180.degree. C.

The use of our adhesive overcoat eliminates subsequent varnishing and additional baking operations usually associated with bonding the loose magnet wire turns in a coil into a rigid coil. It also results in better heat transfer through the coil and in motor stator slots containing coils because heavy sections of varnish are eliminated and there is greater space for air circulation.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention reference may be had to the exemplary embodiments shown in the accompanying drawings, in which:

FIG. 1 shows a fragmentary isometric view of a conductor with a thermosetting insulating enamel base coat and a polysulfone high temperature adhesive overcoat;

FIG. 2A shows a three dimensional view of a magnet wire transformer coil, the wound conductors of which may be fused together with the polysulfone adhesive of this invention;

FIG. 2B shows a sectional view of the coil of FIG. 2A wherein the conductors are bonded to each other by polysulfone adhesive;

FIG. 3 shows a fragmentary view of a motor stator slot containing coils; and

FIG. 4 shows a flow diagram of a method for producing the composite insulated wire of this invention and coils made therefrom.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The novel high temperature wire adhesive of this invention comprises resinous solutions of aromatic polysulfone resins. These are used for overcoating specific high temperature wire enamel films as shown in FIG. 1.

The polysulfone resin can be made by the condensation of bisphenol with activated aromatic dihalides. In one method of making this resin, 51.36 grams (0.225 mole) of high purity bisphenol A, [2,2-bis (4-hydroxyphenyl) propane], 115 grams of dimethyl sulfoxide and 330 grams of chlorobenzene are added to a reaction vessel and heated to about 70.degree. C. Air is displaced from the system by flushing with nitrogen and 0.45 moles of 50 percent aqueous sodium hydroxide is added, resulting in two liquid phases: one chlorobenzene and the other a disodium salt dissolved in aqueous dimethyl sulfoxide. The system is brought to reflux using a fractionating column. Water is removed and the chlorobenzene that codistills is continuously returned until the temperature reaches 140.degree. C, at which point the disodium salt of bisphenol A appears as a precipitate.

A 50 percent solution of 64.61 grams (0.225 mole) of 4,4'-dichlorodiphenyl sulfone in dry chlorobenzene maintained at 110.degree. C is then added over a 10-minute period, the excess solvent being allowed to distill at a rate sufficient to hold the material temperature at about 160.degree. C. When all the sulfone has been added, polymerization is continued until the desired degree of polymerization is reached: ##SPC4##

where n is the monomer number.

The viscous polymer is then cooled and diluted with about 700 grams of chlorobenzene. The by-product sodium chloride is removed by vacuum filtration and the solution is coagulated in three or four volumes of ethanol. The resulting material is dried in a vacuum oven. The yield is about 90 percent of theory. Further details of preparation can be found in an article by R. H. Johnsen et al. in the Journal of Polymer Science, Part A-1, Vol. 5, pp. 2375-2395 (1967).

This linear aromatic polysulfone resin is a thermoplastic, has a melting point of about 187.degree. C and a deflection temperature of about 174.degree. C at 264 psi. (ASTM method D648). Thermal stability is provided by the high strength bonds of the diphenylene sulfone group. This group is an aromatic entity, and capable of a high degree of resonance. A strongly resonant structure produces bonds that are stronger than otherwise possible. Therefore, large amounts of incident energy in the form of heat can be dissipated without chain scission or crosslinking taking place.

Other polysulfones that are useful as the resin component of high temperature magnet wire adhesive enamel solutions would include [(4,4'-diphenoxy)-4,4'-diphenylsulfonyl] -4,4'-diphenoxydiphenyl sulfone: ##SPC5##

polysulfone (polyarylether)

where the monomer number n is about 3. This linear aromatic polysulfone is a thermoplastic, has a melting point of about 227.degree. C and can be prepared by reacting the potassium salt of 4-hydroxy-4'-phenoxydiphenyl sulfone with 4,4'-difluorodiphenyl sulfone for about 4 hours at between 135.degree. C and 155.degree. C. Further details of preparation can be found in an article by W. F. Hale et al. in the Journal of Polymer Science, Part A-1, Vol. 5, pp. 2403-2405 (1967).

Other linear aromatic polysulfone thermoplastic resins suitable for adhesive overcoats of our invention can be made by Friedel-Crafts polycondensation of dinuclear aromatic sulfonyl chlorides and aromatic hydrocarbons: ##SPC6##

where the monomer number n = 20 -- 500; and ##SPC7##

where the monomer number n = 45 -- 1,000.

In the above reaction, the sulfone group has a deactivating effect on the aromatic ring to which it is attached or becomes attached during polymerization. With proper temperature control the deactivating effect prevents more than monosulfonation in any one aromatic ring. Chain branching or crosslinking is thus avoided. The synthesis requires only small quantities of ferric chloride catalyst (about 0.1 to 1.0 mole percent depending upon the solvent, at reaction-temperature from 80.degree. to 250.degree. C). The solvents that are preferred as a reaction medium include acetylene tetrachloride and dimethyl sulfone.

These linear polyarylsulfones contain no aliphatic carbon-carbon bonds and have melting points of about 250.degree. C and deflection temperatures as high as 370.degree. C at 264 psi. For a detailed description and synthesis of these two polymers, reference may be made to French Pat. No. 1,453,031 and British Pat. No. 1,060,546. The value of n (repeating monomer number) in the formula for these two polymers is such that the inherent viscosity (.eta. inherent) = (1n. .eta. relative)/C = 0.2-2.0. The relative viscosity (.eta. relative) is determined by dividing the flow time in a capillary viscometer of a dilute solution of the polymer by the flow time for the pure solvent. The concentration (C) is 1.0 gram of polymer per 100 ml of solution and the measurements are made at 25.degree. C in dimethyl-formamide solution.

These linear aromatic polysulfone thermoplastic resins are used in solution and cured to form adhesive films over specific high temperature thermosetting wire enamels. The high temperature wire enamels which form the base coating on the wire conductor and with which these adhesive solutions are compatible in terms of curing temperature and curing characteristics include polyester amide-imide, polyester imide, polyester, polyamide-imide and polyimide resinous enamels. Of these, the preferred enamel is the polyester amide-imide, which is described in U.S. Ser. No. 730,833, now U.S. Pat. No. 3,555,113, filed on May 21, 1968 and assigned to the assignee of this invention. Polyester imide resins are described in British Pat. Nos. 973,377 and 996,649; polyamideimide resins are described in U.S. Pat. No. 3,179,635; polyimide resins are described in U.S. Pat. Nos. 3,179,630, 3,179,631, 3,179,632 3,242,128 and British Pat. No. 941,158 and polyester resins are described in Brydson, Plastics Materials, D. Van Nostrand Publishing Co., pp. 431-450 (1966). Reference can be made to the aforementioned book and patents for the detailed synthesis of these classes of resins. A specific example for their preparation will, however, be given below.

Generally, the polyester imides can be prepared by reaction of a polyester with a diimidodicarboxylic acid. In a conventional manner, a polyester is produced from 388 grams of dimethyl terephthalate, 112 grams of ethylene glycol and 75 grams of glycerine, reacted at a temperature between 180.degree. and 215.degree. C. This terephthalate resin is reacted at the same temperature with 137 grams of a diimidodicarboxylic acid precipitate that is a reaction product prepared by (1) adding 0.3 moles of 4,4' diamino-diphenylmethane to a solution of 0.6 moles of trimellitic acid anhydride dissolved in 500 grams of a commercial cresol at 150.degree. C and (2) stirring the mixture at 140.degree. C for 6 hours and cooling to form a precipitate which is filtered and washed. When the diimidodicarboxylic acid precipitation has been completely taken up by the terephthalate resin, 1.8 grams of cadmium acetate are added. Condensation is continued for 3 hours at 215.degree. C and finally under vacuum. The resin obtained is dissolved in 450 grams of commercial cresol and a solution of 9 grams of butyl titanate in 27 grams of cresol is added. This is diluted with a mixture of 2 parts of solvent naphtha and 1 part of cresol to give a wire enamel solution, suitable for coating copper wire, having a solids content of about 37 percent.

Polyamide-imides can generally be prepared by reacting 35 grams of m-amino-benzoyl-p-aminoanilide in 206 grams of dimethylacetamide with 32 grams of pyromellitic dianhydride, added to the solution over a 5-minute period to form a soluble polymeric intermediate suitable as a wire enamel solution for coating copper or other type conductors.

Polyimides can be prepared by dissolving 209.7 grams of 4,4'-diaminodiphenyl ether in 739.5 grams of N,N-dimethylacetamide and 1,479.0 grams N-methyl-2-pyrrlidone at 25.degree. C. To this solution 221.7 grams of pyromellitic anhydride is added with rapid agitation to give a polyamic acid solution having a polymer content of about 16.5 percent by weight. To this solution is added 0.01 gram moles of formic acid per 100 grams of polyamic acid. This solution is suitable as a wire enamel solution for coating copper wire. Curing of the applied enamel solution at elevated oven temperatures converts the polymeric solution to baked polyimide enamel film.

In a wire-enamel formulation and in the adhesive overcoat solutions of this invention, the selection of an appropriate solvent is important. Although benzene and its homologs, toluene and xylene are relatively inexpensive, so that there is a considerable incentive to use them for modest cost formulations, these solvents tend to lack the aggressive solvent power that is required to dissolve some of the resins heretofore described. Some more expensive and aggressive solvents, such as phenol, o-cresol, m-cresol, p-cresol, and the isomeric mixture of cresols (monomethyl phenols) referred to as "cresylic acid" have been found useful.

Particularly useful solvents for polysulfone solid resins are dimethylacetamide, acetylene tetrachloride, nitrobenzene, dimethyl sulfone, N-methylpyrrolidone, and especially cresylics and mixtures thereof with xylene, "Solvesso 100" and "Solvesso 150" described hereinafter.

A suitable solvent may be used alone in the wire-enamel and adhesive overcoat solution formulations, but in most circumstances it is desirable to reduce the cost of the formulations by using a substantial portion, up to 60 weight percent, of a diluent. These are compounds or mixtures of compounds, that although not themselves of such great solvent power as to be useful alone, will serve satisfactorily to extend and tend to liquify the formulation being made. The chief requirement is that the diluent have a suitable boiling temperature range (about 125.degree. to 200.degree. C) and be substantially unreactive with the desired chemical reactions to be effected. Various aliphatic and carbocyclic hydrocarbons, esters, aldehydes, alcohols, etc., are suitable. Good results have been obtained with the use of a hydrocarbon fraction of aromatic nature boiling at 161.degree.-177.degree. C. under 1 atmosphere of pressure, such as that sold commercially under the name "Solvesso 100," or the similar cut boiling at 187.degree.-211.degree. C, sold commercially under the name "Solvesso 150."

The particular advantage in our invention is of course the application of our high temperature adhesive solutions over the enumerated high temperature wire enamel base coat films, on round, flat metal foil or rectangular conductors. The cured base-adhesive coated conductors may then be wound in a plurality of turns as magnet wire in a coil, such as that shown for example in FIG. 2A, and then fused together.

The manner of using wire-enamel formulations is one known to those skilled in the art. A wire or conductor is coated with enamel solution by dipping, spraying, or other suitable means. For example, in one preferred method a die is used to wipe off excess liquid after passing the wire through the base coat solution, to produce on the conductor or wire a build (increase in diameter of the insulated wire due to the insulation addition) of suitable thickness. The build is usually about 0.001 to 0.005 inch with successive coatings, each generally followed by heating in an oven or vertical tower to cure the enamel composition. This can be done in suitable continuously operating equipment, for example a 15-20 foot enameling tower, having an entrance temperature of about 100.degree. C and an exit temperature on the order of 430.degree. C, with a temperature of about 380.degree. C three-fourths of the way through the tower. A line speed of preferably about 15 to 40 feet per minute can be used, depending on the characteristics of the wire-enamel formulation.

In the method of applying our adhesive overcoat solution, we additionally overcoat the enamel film with a 0.0,001 to 0.0,050 inch build of the adhesive film, preferably, as part of a continuous operation of coating the wire conductor. This adhesive overcoat solution may be cured in the enameling tower and the wire may be wound into a plurality of magnet wire turns and bonded or fused together as shown in FIG. 2B, a cross sectional illustration of the coil of FIG. 2A, by subjecting the conductor to a high current or heating the coil unit in a high temperature atmosphere.

Other applications besides magnet wire transformer coils include use in electric motor stator slots as shown in FIG. 3. The wire conductors 30, base coated with a high-temperature wire enamel 31 and an aromatic polysulfone adhesive overcoat 32 may be wound in the coil retaining slots 34 between the teeth 35 of the main magnetic core 36 of the stator of a dynamoelectric machine such as a motor. The polysulfone adhesive overcoat may then be fused together at coil winding contact points 37. Also shown are slot liners 38 which may be formed of paper, asbestos or other suitable material. The irregular interstices or air spaces 39 between adjacent insulated conductors can also be seen.

The fusion temperature of the adhesive coated wire may range between about 200.degree. and 260.degree. C but preferably between 210.degree. and 235.degree. C. Fusion temperatures above 260.degree. C shorten the life of the base coat enamel without contributing to bonding strength of the adhesive overcoat and temperatures below 200.degree. C will not give adequate bond strength for coil applications.

The polysulfone adhesive coating thickness should be in the range of about 0.1 to 5 mils build (0.0,001 to 0.005 inches of film added to the diameter of the wire) for wire sizes No. 42 A.W.G. to No. 4 A.W.G. (0.0,025 inch diameter to 0.204 inch diameter). Under 0.1 mils build for No. 42 A.W.G. wire and under 2.0 mils build for No. 4 A.W.G. wire and the coil windings will not adhere with sufficient bond strength during the adhesive fusing step.

FIG. 4 illustrates a process for making our composite high temperature enamel base coat-polysulfone adhesive overcoat insulated conductor and fused magnet wire coils made therefrom. A flat, rectangular or round, copper, aluminum, silver or other type conductor may be annealed, after which it is passed through an enamel applicator containing the aforedescribed high temperature, base coat wire enamel solutions. Dies may be used to wipe off the excess enamel from the conductor after it passes through the applicator to achieve a coating of the desired thickness. The base coated wire is then passed through an enameling tower or oven, which may be from about 10 to 40 feet long, at a desired uniform speed of between 2 to 600 ft/min depending on the wire diameter. The oven or tower will have a temperature gradient from about 100.degree. C at the entrance to about 380.degree. C three-fourths of the way through, to about 430.degree. C near the exit end. The conductor enters the oven with the applied solution coating and exits having a cured film build thereon. After at least one pass through the base coat enamel applicator and oven, the base coated conductor is passed through an applicator containing an adhesive overcoat solution that is compatible with the base coat resinous film. The conductor is then, in a continuous operation, passed through the oven heretofore described (about 2 to 600 ft/min with a temperature gradient from about 100.degree. C to 430.degree. C). The number of passes (shown as 2,2', 3 and 4 in FIG. 4) may vary widely depending on the desired final build of base coat and adhesive overcoat. The wire may then be stored and used for various applications or used as magnet wire when wound into a coil and the magnet wire turns fused together at between about 200.degree. and 260.degree. C. The fusion temperatures for whatever application must be between about 200.degree. and 260.degree. C to insure good bonding of the thermoplastic polysulfone adhesive overcoat of adjacent conductors.

EXAMPLE 1

A polyester amide-imide resin enamel base coat solution at about 30 percent solids, prepared in accordance with the aforementioned patent application was coated on No. 18 A.W.G. (0.040 inch dia.) round copper wire and cured in an electrically heated vertical wire enameling tower 18 feet high. The bottom half of the tower was maintained at between about 100.degree. and 340.degree. C and the top half was maintained at between about 340.degree. and 430.degree. C. The wire coating speed was about 25 feet per minute. The enamel solution was metered onto the wire by means of passing the wire through an enamel solution pan and then using the conventional dog box die coating method to give a 0.5 mil (0.005 inch) build or coating for each pass through the pan and die, i.e., the diameter of the wire was increased by 0.5 mils for each pass. After five successive passes through the enamel solution pan, dog box dies of increasing size, and the enameling tower, a high temperature thermoset base enamel film build of about 2.5 mils was obtained.

From a second pan, our polysulfone enamel solution, at about 30 percent solids, was metered onto the base coated wire prior to the sixth pass of the wire through the same enameling tower at the same temperature in a continuous operation, by means of another dog box die to give a 1.0 mil build or coating of high temperature thermoplastic adhesive overcoat. The total composite adhesive insulating film build on the conductor was 3.5 mils thick. We found no need to use separate enameling towers or different curing temperatures with the adhesive overcoat, saving both time and expense.

The thermosetting polyester amide-imide wire enamel base coat solution was prepared from a blend of (1) a polyester amide-imide of trimellitic anhydride, ethylene glycol and metaphenylenediamine, (2) a polyester of dimethylterephthalate, tris(2-hydroxyethyl) isocyanurate and ethyleneglycol, (3) an ester-urethane-isocyanate compound prepared from dimethylterephthalate, tris(2-hydroxyethyl) isocranurate and tolylene diisocyanurate and a small amount of phenolformaldehyde resin and tetraisopropyltitanate in a solution of cresylic acid to give about 30 percent solids content and a viscosity of 8.0 poises at 25.degree. C.

The thermoplastic linear aromatic polysulfone resin can be prepared from 2,2-bis(4-hydroxyphenyl) propane (bis-phenol A) and 4,4'-dichlorodiphenylsulfone as previously described. It is sold commercially as Union Carbide Corp. P1700 Natural 11 grade Bakelite polysulfone extrusion and molding compound. This polysulfone is of low molecular weight polysulfone and has the formula: ##SPC8##

where the monomer number n has an average of about 50-65.

The P1700 resin pellets were first dried in an oven for 16 hours at 135.degree. C to remove any residual moisture. Thirty grams of the dried P1700 polysulfone was added to 46 grams of "Solvesso 100" and 23 grams of cresylic acid to make approximately a 30 percent solids solution. This was then roller-milled for about 16 hours at room temperature until all the polysulfone resin was in solution at which time it was ready for use as an adhesive overcoat enamel solution having a viscosity of 8.0 poises at 25.degree. C.

The base coat-adhesive coated wire described above was then wound into a magnet wire coil for an electrical apparatus and heated in an oven for 6 hours at 250.degree. C and then cooled. The thermoplastic polysulfone adhesive overcoat softened during heating and after cooling fused the coil wires together to form a rigid coil, solidly bonded together without undue amounts of resinous adhesive.

The coated wire described above was also wound into standard bond strength test coils and fused in an oven at 225.degree. C. These coils were then heat aged at 175.degree. C and 200.degree. C for 120 days with excellent bond strength results when tested at 150.degree. C. Here the number of pounds applied to break the bond of a long coil the ends of which rested on a support was recorded. Polyvinyl butryal and epoxy adhesives could not withstand the temperatures used in these tests.

EXAMPLE 2

A coated wire was prepared using the same method and equipment of Example 1 with a final 2.5 mil enamel film build of the same polyester amide-imide used in Example 1 overcoated by a 1.0 mil adhesive film build of polysulfone. The polysulfone was a higher molecular weight polysulfone than used in Example 1, however, having the formula (I), as shown heretofore in the specification, where the monomer number n had an average of about 65-80. This polysulfone is sold commercially as Union Carbide Corp. 3500 grade Bakelite polysulfone extrusion and molding compound. It was similarly dissolved as in Example 1, in "Solvesso 100" and cresylic acid to make approximately a 30 percent solids solution. The amide-imide-ester solution was also prepared as in Example 1.

EXAMPLE 3

A coated wire was prepared using the same method and equipment of Example 1 with a final 2.5 mil enamel film build of the same polyester amide-imide used in Example 1. The polyester amide-imide solution was prepared as in Example 1. No polysulfone overcoat adhesive was used however.

A variety of tests hithertofore described were run on the coated wires of the Examples. The results of those tests are tabulated below in Table 1. --------------------------------------------------------------------------- TABLE I

Enamel Ex. 1 Ex. 2 Ex. 3 __________________________________________________________________________ Coating Speed 25 25 25 Build (mils):basecoat + 2.5+1.0 2.5+1.0 2.5 overcoat (overcoat) overcoat Quick Elongation Test OK OK OK Elongation + 1X Test (%) greater greater 25 than 35 than 35 G.E. Repeated Scrape 19-20 17-20 22-25 Abrasion Test (700 gr. load) (cycles) Westinghouse Scrape Test (oz) 65 65 45 Emerson Scrape Test (lbs) 40 (wire 40 (wire 32 broke broke) Heat Shock - 1X Test at 225.degree. C OK OK OK 250.degree. C OK OK failed slightly 275.degree. C OK OK failed moderately Thermal Life Test (hrs) at 225.degree. C 100% OK 100% OK 100% OK after after after 2352 2352 2352 250.degree. C 1368 1872 1620 275.degree. C 449 449 245 __________________________________________________________________________

as can be seen from this data, our combination of high temperature base enamels and high temperature adhesive overcoats meet 155.degree. C-180.degree. C requirements easily. They exhibit superior thermal life and heat shock properties than a wire having the same base coat but no high temperature adhesive overcoat. Our composite wire is flexible, resistant to abrasion, and with thin overcoat films, it will fuse easily in a coil configuration to form solid bonded coils without an excess of resin, thus allowing excellent heat transfer through the bonded coil. Such a composite wire coil eliminates varnishing operations and allows long range operational temperatures as high as 190.degree. C.

The adhesive overcoat can be used on the enumerated high temperature base coat enameled round and rectangular metal (copper, silver, aluminum, etc.) conductors or on flat metal foil conductors in all motors, dry and liquid filled type transformers, TV yoke coils and other electrical equipment where turns of wire or foil or two parallel conductors need to be bonded to form a rigid structure.

Claims

We claim as our invention:

1. An adhesive coated, high temperature insulated electrical conductor comprising in combination, a metal conductor, a base coat of a cured solid high temperature thermosetting resin selected from the group consisting of polyester amide-imide, polyester, polyamide-imide and polyimide deposited on the conductor, and an overcoat, between 0.0,001 and 0.005 inch thick, of solid thermoplastic adhesive consisting essentially of linear aromatic polysulfone resin having a melting point between 180.degree. C and 260.degree. C deposited over said base coat.

2. The insulated conductor of claim 1 wherein the polysulfone is selected from the group consisting of polysulfones having the formulas: ##SPC9##

3. The insulated conductor of claim 1 wherein the polysulfone has the formula: ##SPC10##

and the thermosetting resin is polyester amide-imide resin.

4. A transformer coil having a plurality of turns of the insulated conductor of claim 3.

5. A method of making a magnet wire coil for an electrical apparatus comprising the steps of:

1. depositing a base coat of high temperature thermosetting resin selected from the group consisting of polyester amide-imide, polyester imide, polyester, polyamide-imide and polyimide in a solution on a conductor;

2. passing the coated conductor through an oven having a temperature between about 100.degree. C and 430.degree. C, at a uniform speed, to form a solid film;

3. depositing an adhesive overcoat of aromatic thermoplastic polysulfone resin, having a melting point between 280.degree. C and 260.degree. C, in solution on the base coated conductor; followed by

4. repeating step (2) to continuously form a base coated conductor having an overcoat between 0.0,001 and 0.005 inch thick of adhesive; followed by

5. winding the composite coated conductor into a coil having a plurality of adjacent contacting conductor turns; and finally

6. heating the composite coated coil between about 200.degree. to 260.degree. C to fuse the thermoplastic polysulfone overcoats of adjacent conductor turns together.

6. The method of claim 5 wherein the oven of step (2) has a temperature gradient of between about 100.degree. C at the entrance and about 430.degree. C near the exit.

7. The method of claim 7 wherein the heating in step (6) is resistance heating.

8. The method of claim 6 wherein the polysulfone is selected from the group consisting of polysulfones having the formulas: ##SPC11##

9. The method of claim 6 wherein the polysulfone has the formula: ##SPC12##

and the thermosetting resin is polyester amide-imide resin.