Diimidodicarboxylic Acids

The following examples A - M relate to the production of imide group-containing starting materials for the production of ester imide resins according to the present invention. The scope of the invention is, of course, not meant to be limited to these specific examples.

115 g (0.6 mols) of trimellitic acid anhydride are introduced into 500 g of a technical cresol mixture at a temperature of 150.degree. C. When all of the trimellitic acid anhydride has been dissolved, 60 g (0.3 mol) of 4,4'-diaminodiphenyl methane are added thereto. This mixture is stirred for 6 hours at 140.degree. C.

Upon cooling a yellowish, finely crystalline precipitate forms which is filtered off and washed several times with alcohol and ether.

The obtained product does not melt at temperatures up to 360.degree. C.

24.8 g (0.1 mol) of 4,4'-diaminodiphenyl sulfone and 38.4 g (0.2 mol) of trimellitic acid anhydride are stirred into 500 g of technical cresol mixture to form a slurry, and this slurry is heated for 4 hours at 175.degree. C. After cooling there is obtained a white, crystalline precipitate which is washed as described in Example A.

The product does not melt at temperatures up to 360.degree. C.

32.4 g (0.3 mol) of p-phenylenediamine and 115.2 g (0.6 mol) of trimellitic acid anhydride are heated with 1200 g of technical cresol mixture for 4 hours at 180.degree. C. After cooling the mixture is filtered and the green crystals constituting the obtained reaction product are washed as described in Example A.

The product does not melt at temperatures up to 360.degree. C.

23.2 g (0.2 mol) of hexamethylenediamine and 76.8 g (0.4 mol) of trimellitic acid anhydride are heated for 3 hours at 190.degree. C. in 400 g of a technical cresol mixture. After cooling and filtering the obtained white crystals are washed with alcohol and ether.

The melting point of the product is 301.degree. C.

20 g (0.1 mol) of 4,4'-diaminodiphenyl ether and 38.4 g (0.2 mol) of trimellitic acid anhydride are heated for 4 hours at 200.degree. C. and 500 g of technical cresol mixture, whereby a portion of the cresol is distilled off. After cooling and filtering the obtained brown crystals are washed with alcohol and ether.

The product does not melt at below 360.degree. C.

334 g (2.44 mol) of p-aminobenzoic acid are dissolved in 1700 cc of warm technical cresol mixture. This solution is added to a warm solution of 446 g (2.44 mol) of trimellitic acid anhydride in 1300 c of technical cresol. These combined solutions are then heated to refluxing for 1 hour. After cooling and filtering the very finely granular white powder is washed with alcohol and ether.

The product does not melt at below 360.degree. C.

Titration of the acid in dimethyl formamide with water free sodium methylate solution with cresol red as indicated gives an equivalent weight of 153 (calculated value 155.5).

75 g (1 mol) of glycocol and 500 cc of technical cresol are heated to 100.degree. C. To the obtained suspension is added in small portions 109 g (0.5 mol) of pyromellitic acid anhydride. The mixture is then further heated to 200.degree. C., whereby water distills off. After cooling the finely crystalline residue is filtered off and washed with methylene chloride. After recrystallization from 1,4-dioxane the product which is obtained is in the form of yellowish-white crystals and does not melt up to temperatures of 320.degree. C.

334 g (2.44 mol) of p-aminobenzoic acid is dissolved under warming in 1300 cc of technical cresol mixture and the solution is added to a hot solution of 266 g (1.22 mol) of pyromellitic acid dianhydride in 800 cc of cresol. The mixture is heated for 5 hours at 190.degree. C., whereby 50 cc of water distilled off. The precipitated white precipitate is filtered off after cooling and washed with methanol and water.

75 g (1 mol) of glycocol are mixed with 200 g of technical cresol to form a slurry and 192 g (1 mol) of trimellitic acid anhydride are added to the suspension warmed to a temperature of 100.degree. C. Upon heating of the mixture water distills off and at 200.degree. C. a clear solution is obtained from which a yellowish precipitate falls upon cooling.

The obtained suspension is stirred with a large amount of acetone and the insoluble portion is separated by filtration.

The obtained yellowish white crystalline powder melts at 275.degree. C.

218 g (1 mol) of pyromellitic acid anhydride are dissolved in 400 cc of dimethyl formamide at 80.degree. C. under nitrogen atmosphere. Monoethanolamine is slowly added dropwise to this solution at the same temperature in an amount of 122 g (2 mol). The dimethyl formamide is subsequently distilled off under vacuum at a temperature between 100 and 120.degree. C. The dirty white residue is recrystallized with the addition of activated carbon from 1,4-dioxane, whereby finely yellowish-white crystals having a melting point of 271.degree. C. are obtained.

218 g (1 mol) of pyromellitic acid dianhydride and 150 g (2 mol) of 3-aminopropanol are mixed with each other as described in Example H. The obtained crude product is recrystallized from ethylene glycol monomethyl ether with the addition of activated carbon. The obtained white crystalline powder melts at 234.degree. C.

192 g (1 mol) of trimellitic acid anhydride are dissolved under nitrogen atmosphere at 100.degree. C. in dimethyl formamide and there is added dropwise to the solution at 60.degree. C. 61 g (1.0 mol) of monoethnolamine. The solvent is subsequently distilled off under vacuum at temperatures of 100 - 130.degree. C. The yellowish-white residue is recrystallized two times from dioxane with the addition of activated carbon, and the compound melts at 197.degree. C.

Instead of producing the imide group-containing compounds as described in the previous examples, to isolate the same and then to use them as starting compounds for the production of the ester imide resins according to the present invention, it is also possible, as indicated previously, to produce the imide group-containing compounds during the synthesis of the ester imide resins and to directly react the same with the polyester reactants. Essentially the same type of ester imide resins are obtained if the imide group-containing compounds are not first separately produced and isolated, but instead the compounds (a) and (b) are permitted to react in the apparatus used for the production of the ester imide resin and then directly permitted to react with the other starting materials used in the production of the ester imide resin.

The point of time at which the compounds (a) and (b) are brought to reaction is not essential. In many cases it is preferable to first produce the imide group-containing compounds by reacting (a) and (b) and then to use the resulting compound in the further production of the ester imide resin by adding this compound to the esterification reactants. It is also possible, however, to first esterify the imide group-free starting substances with each other, then to add the reaction product of compounds (a) and (b) thereto and to react these together and subsequently to cause the resulting imide group-containing compound to react with the already formed polyester resin. On the other hand it is also possible and sometimes advantageous to mix the compounds (a) and (b) with the other starting materials used for the production of the ester imide resins together and then to react all of the components together.

The following examples are given to illustrate the production and working up of the ester imide resins of the present invention. The scope of the invention is not, however, meant to be limited to the specific details of these examples.

A polyester is produced in known manner from 388 g of dimethyl terephthalate, 112 g of ethylene glycol and 75 g of glycerin and this polyester is mixed in two portions with 137 g of the reaction product of Example A at a temperature of 180 - 215.degree. C. After the diimidedicarboxylic acid (reaction product as Example A) has been completely taken up in the terephthalic acid resin, 1.8 g of cadmium acetate is added thereto. The reaction mixture is subsequently further condensed for 3 hours at 215.degree. C., finally under vacuum. The thus obtained resin is dissolved in 450 g of technical cresol whole still hot and this solution is reaccted with a solution of 9 g of butyl titanate in 27 g of cresol.

The resulting lacquer is then diluted with a mixture of 2 parts of solvent naphtha and 1 part pf cresol to a solid body content of 37% and the resulting lacquer has a viscosity according to DIN 53 211 with a 4 mm nozzle at 20.degree. C. of 156 seconds. (The expression "DIN" stands for Deutsche Industrienormalien which is the German Industrial Standards.).

Copper wire of 1 mm diameter is lacquered in a continuous process with this wire lacquer in accordance with the following technical data: Horizontal wire lacquering oven of 3.50 meters length, oven temperature 470.degree. C., coating apparatus of rollers and felt, 6 coats, drawing speed of 4 m/min., coating thickness (= increase of diameter of the wire) 0.05 mm.

The testing of the lacquer insulation gives the following values:

After 24 hours of ageing at 180.degree. C. the lacquer elongation amounts to 34%. The insulation is and remains solid upon winding about its own diamter under a tension load of 0.6 kp/mm.sup.2 (kp = kilopond).

A polyester is produced in known manner from 388 g of dimethyl terephthalate, 112 g of ethylene glycol and 75 g of glycerin, and mixed with 204 g of the reaction product of Example A at a temperture of 180 - 215.degree. C., in two portions. After the diimidodicarboxylic acid (of Example A) is completely taken up in the terephthalate resin, 1.0 g of cadmium acetate is added thereto and the reaction mixture is further condensed for 3 hours at 215.degree. C., finally under vacuum. The obtained resin is dissolved in 450 g of technical cresol while still hot, and mixed with a solution of 9 g of butyl titanate in 27 g of cresol.

This lacquer is diluted to a solid body content of 34% and a viscosity of 120 seconds as described in Example 1, and copper wire is lacquered therewith.

The testing of the lacquer insulation gives the following values:

After 16 hours of ageing at 200.degree. C. the elongation of the lacquer is 22%. The insulation remains solid upon winding about 4 times its own diameter under a tension load of 6 kp/mm.sup.2.

A polyester is produced in known manner from 388 g of dimethyl terephthalate, 112 g of ethylene glyceol and 75 g of glycerin, and mixed with 273 g of the reaction product of Example A, added thereto in two portions at a temperture of 180 - 215.degree. C. Subsequently the reaction product is worked up as described in Example 1, the obtained lacquer is diluted to a solid body content of 27% and the viscosity of 55 seconds, and copper wire is lacquered therewith.

The testing of the insulation of the lacquer gives the following values:

After 24 hours of ageing at 180.degree. C. the elongation of the lacquer amounts to 30%. The insulation remains solid upon winding about its own diameter under a tension load of 0.6 kp/mm.sup.2.

A polyester produced in known manner from 388 g of dimethyl terephthalate, 112 g of ethylene glycol and 75 g of gylcerin has 80 g of technical cresol added thereto and the mixture is heated to 80.degree. C. 144 g of trimellitic acid anhydride and 74 g of 4,4'-diaminodiphenyl methane is then added to the resin melt and the temperature is slowly increased to 215.degree. C. At 140.degree. C. the resin melt becomes turbid and highly viscous, obviously due to the formation and separation of the diimidodicarboxylic acid of Example A.

Upon further temperature increase the reaction mixture slowly becomes thinly liquid again and the precipitated diimidodicarboxylic acid is gradually taken up by the resin melt. After the resin melt reaches a temperature of 215.degree. C. it becomes clear, then 1 g of cadmium acetate is added thereto and the cresol is distilled off under vacuum at 155.degree. C. The reaction mixture is further condensed finally for an additional 3 hours at 215.degree. C. The obtained resin is further worked up according to Example 1 to a lacquer of 34% solid body content and the viscosity of 108 seconds, and a copper wire is then enameled therewith.

The testing of the lacquer insulation gives the following values:

After 16 hours storage at 200.degree. C. the elongation of the lacquer amounts to 23%. The insulation is solid upon winding about 4 times its own diameter under a tension load of 6 kp/mm.sup.2.

388 g of dimethyl terephthalate, 112 g of ethylene glycol, 75 g of glycerin, 150 g of technical cresol mixture, 144 g of trimellitic acid anhydride and 74 g of 4,4'-diaminodiphenyl methane are melted together with the addition of 1 g of cerium naphthenate and stirred while heating. At about 130.degree. C. the separation of the diimidodicarboxylic acid described in Example 1 starts. Upon further slow temperature increases methanol and water distill off. Upon reaching a temperature of 215.degree. C. the temperature is maintained for 3 hours and the resulting resin melt becomes clear. 1 g of cadmium acetate is added thereto, the cresol is distilled off under vacuum at a temperature of 175.degree. C., and finally condensation is continued for an additional 3 hours at 225.degree. C.

The obtained resin is worked up as described in Example 1 to a lacquer of 34% solid body content and a viscosity of 120 seconds, and copper wire is enameled therewith.

The testing of the lacquer insulation gives the following values:

After 16 hours of ageing at 200.degree. C. the lacquer elongation amounts to 21%. The insulation remains solid upon winding about 4 times its own diameter under a tension load of 6 kp/mm.sup.2.

144 g of trimellitic acid anhydride, 74 g of 4,4'-diaminodiphenyl methane, and 500 g of technical cresol are heated under vigorous stirring, whereby the resulting suspension at 150.degree. C. becomes highly viscous. Upon further temperature increase to 195.degree. C. 27 cc of water distills off. Subsequently 200 cc of cresol distills off at 120.degree. C. under vacuum.

To the suspension of diimidodicarboxylic acid resulting therefrom is added 388g of dimethyl terephthalate, 112 g of ethylene glycol and 75 g of glycerin along with 1 g of cerium naphthenate. The mixture is heated, whereupon methanol and water distill off. The temperature is then increased to 215.degree. C. and maintained at this temperature until the resin melt becomes clear. After the addition of 1 g of cadmium acetate the remaining cresol is distilled off under vacuum at 170.degree. C. and the resin melt is further condensed an additional 3 hours at 215.degree. C.

The remaining resin is further worked up as described in Example 1 to a lacquer of 34% solid body content and a viscosity of 112 seconds, and copper wire is lacquered therewith.

The testing of the lacquer insulation gives the following values:

After 16 hours of ageing at 200.degree. C. the lacquer elongation amounts to 24%.

The insulation remains solid upon winding about 4 times its own diameter under a tension load of 6 kp/mm.sup.2.

A polyester produced in known manner from 353 g of dimethyl terephthalate, 153 g of ethylene glycol and 88 g gylcerin is heated to 80.degree. C. with the addition of 52 g of cresol. After the further addition of 200 g of trimellitic acid anhydride and 103 g of 4,4'-diaminodiphenylmethane the reaction mixture is further heated, whereby at a temperature of 140.degree. C. the diimidodicarboxylic acid of Example A separates. After further temperature increase esterification occurs at 215.degree. C., until the resin becomes clear. After the addition of 350 g of technical cresol the mixture is cooled to 80.degree. C.

Thereupon 299 g of trimellitic acid anhydride and 154 g of 4,4'-diaminodiphenylmethane are again added and the mixture is further esterified at 215.degree. C. until a clear resin melt is obtained. The obtained product is dissolved in 1100 g of cresol and 600 g of solvent naphtha and the mixture of 20 g of butyl titanate and 60 g of cresol are added to this solution.

This solution is diluted to a solid body content of 27% and a viscosity of 123 seconds as described in Example 1 and copper wire is lacquered therewith.

The testing of the lacquer insulation gives the following values:

After 16 hours of ageing at 200.degree. C. the lacquer elongation amounts to 20%. The insulation remains solid upon winding about 4 times its own diameter under a tension lead of 6 kp/mm.sup.2.

218 g of diimidodicarboxylic acid produced according to Example A, 13 g of trimellitic acid anhydride, 31 g of ethylene glycol, 12 g of glycerin and 1 g of tin (II) oxalate in 500 g of technical cresol for 8 hours at 185.degree. C. 225 g of cresol are then distilled off and the residue is heated for an additional 8 hours at 200.degree. C. The obtained resin solution is diluted to a lacquer of 27% solid body content and the viscosity of 120 seconds as described in Example 1 and copper wire is lacquered therewith.

The testing of the lacquer insulation gives the following vaues:

After 16 hours of ageing at 200.degree. C. the lacquer elongation amounts to 27%. The insulation remains solid upon winding about 4 times its own diameter under a tension load of 6 kp/mm.sup.2.

546 g of diimidodicarboxylic acid of Example A, 43.5 g of ethylene glycol and 43.5 g of glycerin, as well as 2 g of tin (II) oxalate and 2 g of antimony (III) oxide are heated in 1000 g of o-cresol for 8 hours at 185.degree. C., whereby the reaction water is distilled off. Subseqently 740 g of cresol are distilled off and the residue is heated for 6 hours at 200.degree. C. The obtained resin solution is diluted as described in Example 1 to a lacquer of 29% solid body content and a viscosity of 123 seconds, and copper wire is lacquered therewith.

The testing of the lacquer insulation gives the following values:

After 16 hours of ageing at 200.degree. C. the lacquer elongation amounts to 33%. The insulation is solid upon winding about 4 times its own diameter under a tension lead of 6 kp/mm.sup.2.

The procedure followed is as described in Example 2 with the exception that instead of 204 g of the diimidodicarboxylic acid of Example A, there is used 171 g of the diimidodicarboxylic acid of Example D. The obtained lacquer has a solid body content of 34% and a viscosity of 110 seconds. Copper wire is lacquered therewith.

The testing of the lacquer insulation gives the following values:

After 16 hours of ageing at 200.degree. C. the lacquer elongation amounts to 23%. The insulation remains solid upon winding about 4 times its own diameter under a tension load of 6 kp/mm.sup.2.

A polyester is produced from 364 g of dimethyl terephthalate, 112 of ethylene glycol and 75 of glycerin and further worked up as described in Example 1, with the exception that instead of 137 g of the diimidodicarboxylic acid (of Example A) there is used 156 g of the reaction product of Example F. The obtained lacquer has a solid body content of 26% and a viscosity of 130 seconds and is used for the lacquering of wire as described in Example 1.

The testing of the lacquer insulation gives the following values:

After 24 hours of ageing at 180.degree. C. the lacquer elongation amounts to 32%. The insulation remains solid upon winding about its own diameter under a tension load of 0.6 kp/mm.sup.2.

A polyester is produced in known manner from 388 g of dimethyl terephthalate, 112 g of ethylene glycol and 75 g of glycerin are further worked up as described in Example 1. However, instead of the 137 g of diimidodicarboxylic acid of Example A there is used 125 g of the reaction product of Example G. The obtained lacquer has a solid body content of 33% and a viscosity of 111 seconds and copper wire is lacquered therewith as described in Example 1.

The testing of the lacquer insulation gives the following values:

After 16 hours of ageing at 200.degree. C. the insulation remains solid upon winding about 4 times its own diameter under a tension load of 6 kp/mm.sup.2.

218 g of dimethyl terephthalate, 28 g of ethylene glycol, 46 g of glycerin and 102 g of the reaction product of Example K, with the addition of 1 g of cerium naphthemate and 0.4 g of cadmium acetate, are esterified for 12 hours. During this period the temperature is gradually increased from 160.degree. C. to 240.degree. C. As a result the methanol bound to the dimethyl terephthalate distills off. After the end of the reaction the resin is dissolved in a mixture of 285 g of technical cresol and 185 g of solvent naphtha and stirred with 23 g of a 15% solution of butyl titanate in a cresol-solvent naphtha mixture.

The obtained lacquer of 30% solid content and a viscosity of 92 seconds is used for the lacquering of copper wire as in Example 1.

The testing of the lacquer insulation gives the following values:

After 24 hours of ageing at 180.degree. C. the lacquer elongation amounts to 31%. The insulation is solid upon winding about its own diameter under a tension load of 0.6 kp/mm.sup.2.

218 g of dimethyl terephthalate, 28 g of ethylene glycol, 46 g of glycerin and 111 g of the reaction product of Example L, with the addition of 1 g of the cerium naphthenate and 0.4 g of cadmium acetate are mixed with each other and reacted as described in Example 12. The obtained lacquer of 26% solid body content and a viscosity of 130 second is used for the lacquering of copper wire as described in Example 1.

The testing of the lacquer insulation gives the following values:

After 16 hours of ageing at 200.degree. C. the lacquer elongation amounts to 22%. The insulation is solid upon winding about 4 times its own diameter under a tension load of 6 kp/mm.sup.2.

A polyester is produced from 300 g of dimethyl terephthalate, 64 g of ethylene glycol and 63 g of glycerin under the addition of 65 g of technical cresol, and 248 g of the reaction product of Example M are added at 125.degree. C. The temperature of 190 - 220.degree. C. is used for esterification until an acid number of less than 10 is obtained. The reaction mass is subsequently further condensed an additional 90 minutes at 190 - 230.degree. C. with the distillation off of cresol under vacuum.

The resulting resin melt is mixed while still hot with 450 g of technical cresol and there is subsequently added a mixture of 11 g of butyl titanate, 17 g of cresol and 17 g of solvent naphtha and thereafter it is diluted with a mixture of equal parts of cresol and solvent naphtha to a solid body content of 25% and a viscosity of 111 seconds.

A copper wire of 1 mm diameter is lacquered with this lacquer as described in Example 1.

The testing of the lacquer insulation gives the following values:

40 g of monoethanolamine are added dropwise to a mixture of 192 g of trimellitic acid anhydride and 500 g of technical cresol at a temperature of 20.degree. C. under stirring, and then 450 g of cresol are again distilled off at 130.degree. C. under vacuum. 65 g of ethylene glycol are then added and the mixture is esterified at a temperature of 160 - 200.degree. C. with a distillation off of water until the reaction product has an acid number of 3. Subsequently during a two hour time period an additional 50 g of distillate are distilled off under vacuum at a temperature of 210.degree. C.

The residue is dissolved hot in a mixture of 450 g of cresol and 150 g of solvent naphtha and the thus obtained solution has a solid body content of 27% and a viscosity of 135 seconds.

Copper wire of 1 mm diameter is lacquered with this solution using a horizontal lacquering oven of 2.5 m length and an oven temperature of 500.degree. C. The drawing speed amounts to 2.3 m/min. Six coatings are applied, whereupon a diameter increase of the wire of 0.045 mm is obtained.

The testing of the lacquer insulation gives the following values:

After 16 hours of ageing at 200.degree. C. the insulation is solid upon winding about 4 times its own diameter under a tension load of 6 kp/mm.sup.2.

116 g of trimellitic acid anhydride and 65 g of pyromellitic acid dianhydride are dissolved in 200 g of dimethyl formamide at a temperature of 100.degree. C. and 43 g of monomethanolamine are added dropwise under stirring to the solution of 60.degree. C. 185 g of dimethyl formamide are subsequently distilled off under vacuum at 140.degree. C. After the addition of 56 g of ethylene glycol the reaction mixture is esterified 7 hours at a temperature from 170.degree. C. gradually increasing to 220.degree. C. whereby an additional 20 g of distillate are obtained.

The obtained resin is dissolved hot in a mixture of 380 g of technical cresol mixture and 130 g of solvent naphtha. The obtained lacquer has a solid body content of 38% and a viscosity of 149 seconds and is used for the lacquering of copper wire as described in Example 16.

The testing of the lacquer insulation gives the following values:

192 g of trimellitic acid anhydride are dissolved in 200 g of dimethyl formamide at 90.degree. C. and 30 g of 4,4'-diaminodiphenylmethane are added in small portions to the solution at 60.degree. C., whereby a light yellowish precipitate gradually precipitates. 28 g of monoethanolamine are subsequently added dropwise and 170 g of dimethyl formamide are again distilled off under vacuum at a temperature of 140.degree. C. The residue is esterified with 64 g of ethylene glycol for 6 hours, whereby the temperature during this time is gradually increased, 170.degree. C, to 220.degree. C. 25 g of distillate are thus obtained, and upon a subsequent vacuum treatment for 90 minutes at 220.degree. C. an additional 25 g of distillate are obtained.

The residue is dissolved still hot in a mixture of 425 g of technical cresol and 175 g of solvent naphtha the obtained lacquer has a solid body content of 33% and a viscosity of 118 seconds and is used for the lacquering of copper wires described in Example 16.

The testing of the lacquer insulation gives the following values:

A mixture of 192 g of trimellitic acid anhydride and 200 g of dimethyl formamide are heated to 100.degree. C. under stirring, whereby a clear solution results. 34 g of monoethanolamine are added thereto at 80.degree. C. dropwise and subsequently the dimethyl formamide is distilled off at 100 - 150.degree. C. under vacuum. 52 g of neopentyl glycol and 53 g of ethylene glycol are then added thereto and the temperature is increased gradually and evenly from 180.degree. C. during a time period of 9 hours to 220.degree. C. with a separation of 30 g of distillate, the esterification being carried out until an acid number of 6 is obtained. The reaction mixture is then further condensed for 2 hours at 220.degree. C. under vacuum.

The obtained resin is dissolved hot in a mixture of 500 g of technical cresol and 250 g of solvent naphtha. The lacquer has a solid body content of 28% and a viscosity of 135 seconds. The lacquer is used for the lacquering of copper wire as described in Example 16.

In accordance with the method described in Example 16 a resin is produced of the following starting components: 192 g of trimellitic acid, 37 g of ethylene glycol, 18 g of glycerin and 43 g of monoethanolamine. The obtained brown resin is dissolved hot in a mixture of 290 g of cresol and 90 g of solvent naphtha and the mixture is then diluted with a mixture of equal parts of cresol and solvent naphtha to a solid body content of 27% and a viscosity of 119 seconds. This lacquer is then used for the lacquering of copper wire as described in Example 16.

The testing of the lacquer insulation gives the following values:

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptation should and are intended to be comprehended within the meaning and range of equivalence of the following claims.