GB2061130A - Polymerisation processes and products - Google Patents

Abstract

Microwave energy is used in the formation and use of resins that are of particular value as electrical insulation resins. In one aspect microwave energy is used to effect curing or bonding of an appropriate material that is present as a coating on metal layers, for instance in a coil, while in another aspect microwave energy is used to effect condensation of monomeric components to form a condensation polymer. Preferably a polyester formed from a dihydroxy compound and a dicarboxylic acid and often a trifunctional compound is formed or cured.

Description

SPECIFICATION Polymerisation processes and products During the last five years, conservation of fuel and energy has become of primary importance to industry Oil, gas and electric power have increased in cost. The availability of oil and gas has periodically become critical, forcing industry to either slow down or stop. Coal is one of the United States' most avail abide fuels, but it lacks the convenience of oil or natural gas. Coal, however, is a viable source for the production of electricity. Hydroelectric and atomic power stations also contribute significantly to the production of electric power. Therefore, it is probable that electric power will be the most dependable course of power for the future.

When compared to gas or oil, electric heat is more expensive and is not preferred when alternatives exist. As shown in Table 1, the cost of heating with electricity is about four times as expensive as natural gas (as of March 1,1979).

TABLE 1 COST TYPE BtulUNlT PER UNIT Btul OF FUEL OF MEASURE (US. Currency) $1.00 Electricity 3413 Btu/k Wh $0.0282/k Wh 121,028 Natural Gas 1000 Btu/Ft.3 0.2250/100 Ft3 444,444 Fuel Oil #2 140000 Btu/Gal. 0.5000/Gal. 280.000 Fuel Oil #6 144000 Btu/Gal. 0.2817/Gal. 511,182 When any form of energy is used to heat air in an oven and, in turn, electrical parts passing through that hot air, the efficiency of heat transfer is quite poor. The key to using electric energy is in the effi cienttransferal of that energy to the parts being heated.

We have now found that microwave energy is of particular value in polymerisation processes and products and that particularly advantageous results are achieved by employing microwave energy as the source of heat needed for effecting condensation, curing or fusion processes.

Microwave technology for home and industrial use has been available for 20 years. Yet industry has been slow to accept and use microwave. Where metals were concerned, it seemed obvious that they would reflect the microwaves and, therefore, would not heat.

Contrary to what would have been expected, it has now been found that when armatures, stators, transformers and coils are placed in a microwave field their temperatures increase at a surprising rate. This enables rapid cure of a varnish or enamel coating.

The microwave curing has been found to be effective whether the metal is in coil form or in a laminate with a dielectric material in between e.g, in a capacitor configuration. Also it is useful for effecting bonding of bondable material.

A process according to a first aspect of the invention is one in which a metal article comprising a plurality of coated metal layers is heated by applying microwave energy to the article and in this process the coating is of a material selected from (a) curable material that is cured by the heating to form a thermosetting resin and (b) a bondable material that is caused by the heating to bond to its adjacent metal surface.

In one method ofthe invention an article comprising a metal part in the form of a coil having a coating, or a metal laminate having a dielectric material between the metal layers as a coating on the metal layers, is heated by application of microwave energy and the coating is of a curable synthetic resin that is cured by the application of microwave energy.

In another method according to the invention an article comprising a coil of bondable wire carrying a bondable coating of thermoplastic polymer is heated by applying microwave energy sufficient to render the polymer bondable.

A process according to a second aspect of the invention is one in which a condensation polymer is prepared by reacting monomeric components while splitting out a volatile material, and the reaction is caused by heating the components by application of microwave energy. This second aspect of the invention is preferably applied to the production of a polymer selected from polyesters (including both polyesters free of imide groups and polyester imides), phenylformaldehyde resins and isocyanate based polyamides.

According to a third aspect of the invention a thermoset polyester is obtained from a polyhydroxyl compound and a polycarboxylic acid and the reaction is conducted using microwave energy. The polyester may be a polyester imide, and the reaction may involve curing of the polyester while present as a coating on layers of metal present in a coil or as laminated layers.

Throughout this specification all parts and percentages are by weight unless otherwise specified.

We now describe the first aspect of the invention and reference may be made to the accompanying drawing which shows how five coil bobbins may be positioned in the cavity of a microwave furnace.

For use in the first aspect of the invention there can be employed as metals, the following; iron, copper, silver, aluminium, nickel, zinc or alloys, e.g.

steel. For electrical purposes there usually is employed copper, aluminium and electric-grade steel.

In the working examples below the microwave oven employed was model SMC 1-33H of Despatch Industries Inc. and described in their catalogue 600-978 on pages 16-17.

For microwave curing, it was found that the gen eral ranges of 900 to 950 megahertz and 2400 to 2500 megahertz were best suited. Based on these findings, equipment was employed which had been set at 2450 megahertz with a variable power supply of 0 to 1 kWh (3.6 x 106 joules). A mode stirrer and turn tablewere included in the oven to direct the microwave field randomly in the cavity.

Microwave energy is traditionally considered to be approximately 30 to 35% efficient. For every kWh of power drawn, only 0.300 to 0.350 kWh (1.08 x 106 to 1.26 > c joules) arrives in the cavity. These estimates were found to be quite accurate. Table 2 shows that the best efficiency is obtained when the demand is high (50%). A recording ammeter, voltmeter, and power-factormeterwere used to determine how many kWh were used at each power setting. At the same time, the number of kWh's delivered to the cavity was accurately determined by measuring the heat rise in a predetermined amount of water. This value divided by the total power coming into the oven determined the efficiency. Contributing to the loss in efficiency was the use of motors for the mode stirrer, turntable, and exhaust fans.

TABLE2 (1) (2) kWhlJoules x 106) In Oven TotalkWh Cavity Cain. % Efficiency %Power (Joules x 106) On Water jj2x 100 Output Drawn Temp. Rise (1) O (Standby) 0.699(2.516) 0(0) 10 0.754(2.7t4) 0.053(0.191) 7.0 20 0.967(3.481) 0.152(0.547) 15.7 30 1.118(4.025) 0.268(0.965) 24.0 40 1.328(4.781) 0.350(1.260) 26.4 50 1.528(5.501) 0.462(1.663) 30.2 60 1.738(6.257) 0.570(2.052) 32.8 70 1.985(7.146) 0.715(2.574) 36.0 80 2.262(8.143) 0.800(2.880) 35.4 90 2.576(9.274) 0.880(3.168) 34.2 100 3.062(11.023) 1.080(3.888) 35.3 It has been found that the secondary efficiency (the conversion of microwave energy to heat in the electrical parts) more than compensates for the initial inefficiency from source to cavity.

This process of the present invention can be used to cure anythermosetting resin on a metal coil or metal laminate with a dielectric material inbetween.

Thus there can be used any of the conventional resins employed for coating metals, e.g., electrical conductors in the form of insulating varnishes and enamels. Thus for example there can be employed curable polyesters from a dihydric alcohol such as ethylene glycol, propylene glycol, neopentyl glycol, 2,2,4,4 - tetramethyl - 1,3- cyclobutanediol, butanediol - 1,4 and a polyhydric alcohol containing at least three hydroxyl groups, e.g., glycerine, tris t2 hydroxyethyl) isocyanurate, trimethylolprnpane, and a polycarboxylic acid, e.g., 4,4' - benzophenone dicarboxylic acid, terephthalic acid, isophthalic acid, the imide dicarboxylic acid prepared from trimellitic anhydride with oxydianiline or methylene dianiline, o - phthalic acid, adipic acid, trimellitic acid, trimesic acid.

There can also be employed otherthermosetting resins such as phenol-formaldehyde, cresol formaldehyde, phenol-furfural, melamine formaldehyde, epoxy resins, e.g., bisphenol A-epichlorhydrin, glycerine-epichlorhydrin, unsatu rated polyesters, e.g., from glycols such as those mentioned above with an unsaturated dicarboxylica cid, e.g., maleic acid, fumaric acid or itaconic acid with or without other polycarboxylic acids, e.g., adipic acid, succinic acid, terephthalic acid, isoph thalic acid, o-phthalic acid and an unsaturated monomer such as styrene, diallyl phthalate, t-butyl styrene, methyl methacrylate, methyl acrylate, vinyl toluene, etc.

Thus there can be used any of the thermosetting resins set forth in Laganis U.S. patent 3,338,743, Meyer U.S. patent 3,342,780, Meyer U.S. patent 3,425,866, Laganis, U.S. patent 3,108,083, Meyer U.S. patent 3,249,578, Sheffer U.S. patent 3,312,573, Jordan U.S. patent 3,296,024, Laganis U.S. patent 4,016,330, Sheffer U.S. patent 3,523,820, Galkiewicz U.S. patent 4,073,826, Laganis U.S. patent 4,105,639, Keating U.S. patent 4,119,758, Laganis U.S. patent 4,133,787, Sheffer U.S. patent 2,982,754, Laganis U.S. patent 3,479,307, Jordan U.S. patent 3,480,589, Laganis U.S. patent 3,498,940, Jordan U.S. patent 3,646,374, Sheffer U.S. patent 2,889,304 and Laganis U.S. patent 4,196,109.

Preferably any polyester resin that is formed is not a Werner complex-type polyester. Thus all the components involved in the reaction are preferably in the final polyester.

The first test used;five small stators weighing approximately 34G grams each. The total copper weight was estimated at about 450 grams. The first set of stators was varnished and cured using a microwave source, while the second set was varnished and cured using electric hot air heating.

Since the same microwave oven was also capable of heating by electric forced hot air, it was used for both sets of stators. In this way there was eliminated many of the uncontrolled variables which would have occurred if a different oven had been used. One noteworthy observations is that, when parts were heated in an electric hot air oven, the iron appeared to heat preferentially compared to the copper coil.

With microwave, however, the opposite was true.

The coil temperature was always hotter than that of the iron. (See Table 3).

Table 3 shows that the microwave cured parts have coil temperatures approximately 25"F (14"C) higher than that ofthe iron. Thus, microwave curing is significantly better because the applied varnish will cure best on the areas adjacent to the coils. This is exactly where the best cure is wanted.

A second point to be considered is that, when heating with electric hot air ovens, the electrical resistance heating rods are energized first. This is followed by heat transfer to the air moving past them. Next, the hot air must heat the walls of the oven and maintain that temperature. The hot air must also heat the incoming parts. Hot air in the venting system (exhaust) is a total loss. Finally, when the oven is not in use, the same number of Btu's are expended per hour. Altogether, from the heating rods to the finally processed parts, many inefficiencies exist in an electric hot air system.

TABLE 3 CYCLE -- Microwave (kWh (Joules)Varies) Time Power Temp.Out("Fl"CI kWh(Joules x 106) (Mim) ) Output Iron Coils Used Comment Preheat 2 60% 180/82 200/93 0.058 - (0.209) Dip 0.5 0% - - 0.006 - (0.022) Drain 5 0% - - 0.058 (0.209) Bake #1 5 70% 240/116 270/132 0.165 Slightly (0.594) tacky Bake #2 5 70% 270/132 300/149 0.165 Tack-free (0.594) coils soft Bake #;3 5 60% 300/149 320/160 0.145 Fully (0.522) cured Totals 22.5 0.597 (2.149) CYCLE -- Electric Heating Oven (Oven Temp. at 325"F (163 C)/Forced Air/3.805 kWh (13.698 x 106 Joules) Avg.) Time Temp. Out(0F10C) kWh (Joules x 106) (Min.) lron Coils Used Comment Preheat 2 125/52 120/49 0.127 (0.457) Dip 0.5 - - 0.032 - (0.115) Drain 5 - - 0.317 (1.141) Bake #1 15 200/93 160/71 0.951 Wet (3.424) Bake #2 15 250/121 220/104 0.951 Wet (3.424) Bake #;3 15 260/127 235/113 0.951 Tacky (3.424) Bake #4 15 275/135 240/116 0.951 Tack-free (3.424) coils soft Bake #5 15 300/149 275/135 0.951 Cured (3.434) Totals 82.5 5.231 (18.832) With microwave, there is no heat transferal by air.

Rather, the microwave which falls on the part is converted efficiently to heat. The oven walls and air do not heat. The amount of air exhausted to the outside can be reduced since it is only necessary to sweep solvent vapors away from the hot unit. Finally, when the oven is not in use, the microwave electronics may be put on "standby" where very little energy is consumed. Obviously, the most dramatic saving is in time. The conventional heating system of forced hot air required 82.5 minutes from beginning to end in order to effect a satisfactory cure, but the microwave cycles totalled only 22.5 minutes. Comparing the bake cycles only, microwave curing required only 15 minutes versus one hour and 15 minutes forthe electric forced hot air system.

An economic comparison of the five stators is shown in Table 4. Certain assumptions were made in order to present values corresponding to natural gas, oil (Fuel #2) and oil (Fuel #6). The values for electric hot air heating were accurately measured.

The number of kWh's used in the electric hot air heating was converted to Btu/kWh (see Table 1).

Then the costs for gas and oil were calculated, assuming the same number of Btu's would be used to heat the oven temperature to the same tempera ture (325 F/163 ) in this case. Table 4 shows the Btu's used for electric (hot air oven), natural gas, and the two oils as equivalent. The electricity used in mic rowave heating has been accurately measured and is shown in both Tables 3 and 4.

TABLE4 ELECTRIC MICROWAVE HEA TING OVEN Weight of the Five Parts 1700 1772g Approx. Wt. of Copper 465g 487g Gauge of Copper in Windings 30 AWG 30 AWG (0.302mm) (0.302 mm) Varnish Used AQUANELt600 AOUANEL" 600 (Water-borne (Water-borne Polyester) Polyester) ECONOMICS (See Fuel Cost Table 1 for Conversion Information.) Btu's Cost to (Joules x 106) Cure 5 Parts Used (US. Currency) Electric (Microwave) 2,038( 2.150) $0.01684 Electric (Heating Oven) 17,853(18.835) 0.14751 Natural Gas (Heating Oven) 17,853(18.835) 0.04017 Oil Fuel #2 (Heating Oven) 17,853(18.835) 0.06376 Oil Fuel #;6* (Heating Oven) 17,853(18.835) 0.03492 * Fuel #6 is generally used in boilers for producing steam or heating a heat-exchange liquid. No attempt has been made to correct this value based on the heat-exchange efficiency.

The comparison of the costs to cure five parts is quite dramatic. The amount of energy consumed (number of Btu's) was significantly less when mic rowave heating was employed. Even the cost saving compared with natural gas is quite significant. The primary factor influencing the low cost is the rela tively short time necessary to cure the varnish on the parts.

Aquane600 is a water borne modified polyester insulating varnish made in accordance with the above identified Laganis Patent 4,196,109. It is a mix ture of an oil modified alkyd resin made from tall oil fatty acids, dipropylene glycol, trimethylol propane, isophthalic acid and trimellitic anhydride and a p-t-butylphenolbisphenol A-salicylic acid formaldehyde resin, hexamethyl ether or hex amethylol melamine (Resimene X-745) and dimethylethanolamine in a mixture of 2-butoxyethanol (butyl Cellosolve) and water and has a viscosity (Gardner-Holdt) of K-M.

In the next experiment two automobile alternator armatures were used. The two parts had a combined weight of 12 pounds (5.4 kilograms). Again a com parison was made between microwave curing and electric forced hot air. (See Table 5).

In order to control the heat rise in the oven, the power input was varied. By increasing the power, a rapid increase in temperature was realized. A reduction in power (e.g., by 10%) could maintain temperature or slow the temperature rise. As can be seen in Table 5, the microwave baking cycle (bakes #1, #2, #3, and #4) totalled only 17 minutes and gave a complete cure, while conventional heating yielded a soft cure even after 6 & minutes in the oven.

The economics forthistrial are presented in Table 6. The cost saving of microwave over natural gas is not as dramatic asthat shown in the first study. The smaller number of Btu's consumed is nonetheless significant.

TABLE 5 CYCLE -- Microwave (kWh (Joules) Varies) Power Time Tem p, Out kWh (Joules 106) (Min.) Power { FI C) Used Comment Preheat 5 70% 120/49 0.165 (0.594) Dip 0.5 0% - 0.006 (0.022) Drain 5 0% - 0.058 (0.209) Bake #1 5 80% 190/88 0.189 Slightly (0.680) tacky Bake #2 5 90% 270/132 0.215 Slightly (0.774) tacky Bake #3 5 90% 310/154 0.215 Tack-free (0.774) soft gel Bake #4 2 90% 320/160 0.086 Cured (0.309) Totals 27.5 0.934 (3.362) CYCLE- EIectnc Heating Oven (Oven Temp. at 325 F (163 C)/Forced Air/3.891 kWH (14.008 x 106 Joules) Avg.) Time Temp.Out kWh rJoules x 106) (Min.) { F/ C) Used Comment Preheat 5 130/54 0.324 (1.166) Dip 0.5 - 0.032 - (0.115) Drain 5 - 0.324 (1.166) Bake #1 30 260/127 1.946 Tacky (7.006) Bake #2 30 295/146 1.946 Tack-free (7.006) soft cure Totals 70.5 4.282 (15.415) TABLE 6 ELECTRIC MICROWAVE HEATING OVEN Weight of the Two Parts 5580 g 5444 9 Rectangular 90 x 150 mils. 90 x 150 mils.

Copper Gauge (2.286 x 3.81 mm) (2.286 x 3.81 mm) Varnish Used AQUANELe 600 AQUANEL 600 (Water-borne (Water-borne Polyester) Polyester) ECONOMICS (See Fuel Cost Table 1 for Conversion Information.) Btu's Cost To (Joules x 106) Cure2Parts Used (U.S. Currency) Electric (Microwave) 3,198( 3.374) $0.0264 Electric (Heating Oven) 14,614(15.418) 0.12075 Natural Gas 1(Heating Oven) 14,614(15.418) 0.03288 Oil Fuel #2 (Heating Oven) 14,614(15.418) 0.05219 Oil Fuel #6* (Heating Oven) 14.614(15.418) 0.02859 * Fuel #6 is generally used in boilers for producing stream or heating a heat-exchange liquid. No attempt has been made to correct this value based on the heat-exchange efficiency.

In the next experiment, one large stator was used as the test piece. It weighed slightly over ten pounds.

Table #7 presents two different conditions for microwave curing, as well as the conventional electric forced hot air system. In Cycle A (microwave), the power was applied slowly over a period of time. In Cycle B, the temperature was increased quickly for a shorter period of time. This modification was made to demonstrate the variations possible when microwave curing is used. In both Cycles A and B, the baking times involved were much shorter than by the conventional method.

This experiment also demonstrates that the thermosetting properties of the varnish are significantly dependent on the temperature. The faster one obtains temperatures above 275 F (135 C), the shorterthe overall cure time. In the parts which took 30 minutes to reach 245-250 F (118-121 C) (see Electric Heating portion of Table 7), only the solvent had been driven off and very little thermosetting had occurred in the polymer. In Cycle B (microwave), the temperature reached 325 F (163 C) after twenty minutes. By that time all solvent had been driven off and chemical crosslinking was well underway.

TABLE 7 CYCLE A - Microwave (kWh (Joules) Varies) Joules kWh Time Power Temp Out x 106) IMin.) Output { FI C) Used Comment Preheat 5 70% 165/74 0.165 - (0.594) Dip 0.5 0% 0.006 - (0.022) Drain 5 0% - 0.058 (0.209) Bake #1 20 70% 240/116 0.0662 Wet (2.383) Bake #;2 15 70% 260/127 0.496 Tacky (1.786) Bake #3 15 80% 300/149 0.566 Tack-free (2.038) Bake #4 5 88% 320/160 0.210 Cured (0.756) Totals 65.6 2.163 (7.787) CYCLE B - Microwave (kWh (JoulesiVaries) Preheat 5 70% 165/74 0.175 (0.630) Dip 0.5 0% - 0.006 - (0.022) Drain 5 0% - 0.058 (0.209Li Bake #1 10 80% 220/104 0.329 Slightly (1.184)) tacky Bake #2 10 90% 325/163 0.423 Tack-free (1.525) Bake & um;;3 3 90% 350/177 0.127 Cured (0.4P Totals 33.5 1.168 (4.2a5) CYCLE- Electric Heating Oven (Oven Temp. at 325"F (163 C)/Forced Air/3.953 kWh (14.231 x 106 Joules) Avg.) kWh (Joules Time Temp.Out x 106) (mien.) /"F/"C) Used Comment Preheat 5 130/54 0.329 (1.184) Dip 0.5 - 0.032 - (0.115) Drain 5 - 0.329 (1.184) Bake #1 30 245/118 1.977 Wet (7.117) Bake #2 30 275/135 1.977 Tacky (7.117) Bake #3 30 290/143 1.977 Tack-free (7.117) (7.117) soft cure Totals 100.5 (23.836) An interesting comparison isthe number of Btu's used in the two microwave cures. Basically, in the first study (Cycle A in Table 7), the optimum condition (power output) was not obtained for the fastest cure. However, conditions such as those shown in Cycle A could be desirable in certain applications.

Cycle A (microwave) cost more than the estimated cost for natural gas, while Cycle B was less expensive than gas. Table 8 shows the economics and energy consumption for each of the trials.

TABLE 8 ELECTRIC MICROWAVE HEATING OVEN Weight of Part 4753 g 4753 g Gauge of Wire 22 AWG (0.643 mm) 22 AWG (0.643 mm) 18-1/2 AWG (1.00 mm) 18-1/2 AWG (1.00 mm) Varnish Used AQUANEL5 600 AQUANEIS 600 (Water-borne (Water-borne Polyester) Polyester) ECONOMICS (See Fuel Cost Table 1 for Conversion Information.) Btu's Cost To (Joules x 106) Cure 5Parts Used (U.S. Currency) Electric (Microwave- 7,382(7.788) $0.06099 Cycle A) Electric (Microwave- 3,986(4.2055) 0.03294 Cycle B) Electric (Heating Oven) 22,597(23.840) 0.18671 Natural Gas (Heating Oven) 22,597(23.840) 0.05084 Oil Fuel #2 (Heating Oven) 22,597(23.840) 0.08070 Oil Fuel #6* (Heating Oven) 22,597(23.840) 0.04421 * Fuel # ;6 is generally used in boilers for producing steam or heating a heat-exchange liquid. No attempt has been made to correct this value based on the heat-exchange efficiency.

Thus, it is clearthat electrical parts may be heated efficiently in a microwave oven. Two other basic tests were conducted to further enhance the understanding of microwave.

First, a solid block of steel was placed in the oven; it had little or no temperature rise. However, there was definitely an increase in temperature when a stator core containing no copper was placed in the oven. The temperature increase (74"F/41"C) was not as high as when copperwindings were present.

While not being limited to any theory one explanation of the reason why microwave curing of ther mosetting synthetic resins on metal coils or laminates is successful is that when a high frequence R-F field impinges on a metallic loop (i.e., be it a plane metallic sheet or a loop of wire), a circulating current is induced which attempts to oppose the applied magnet component of the R-F field. The magnitude of this current will depend on the magnitude of the R-F field and the effective resistance of the metal. For wire coils, the capacitive coupling completes the loop allowing resistive heating of the wire in relation to wire size and number of turns. For laminations, the existence of magnetic versus the copper case explains the heating observed in the laminant structure. The still lower heating observed in a solid block relates to the increased skin effect.

In the second trial, coils wound around plastic bobbins were used. These pieces heated very well.

In this study, wires of four different gauges were used (35,31,30, and 23 AWG/0.160,0.274, 0.302, and 0.643 mm, respectively). For all the runs, the output power was kept constant at 40% (approximately 0.350 kWh (1.26 x 106Joules) in the cavity). All trials were run for a period of one minute. Five bobbins of each wire gauge were placed on the turntable such that each would pass through a different area in the cavity while being rotated.

This is illustrated in the drawing.

In Table 9, Trial ,#1 shows copper weights for fully wound bobbins, while Trial #2 corresponds to copper weights afterseveral turns of the winding had been removed. The column "Temperature After Two Minutes" indicatetlte approximate temperatures after waiting two minutes for the parts to come to equilibrium. (See Ta ble 9).

TABLE9 36AWG (0.160 mm) COPPER TEMPERATURE TEMPERATURE WEIGHT IN RISEOF AFTER EACH COIL (g) EACH("F/"C/ 2MIN. (0F/0C1 TRIAL #r a) 27.6 275/135 200/93 b) 27.4 275/135 200/93 c) 27.3 310/154 200/93 d) 26.7 260/127 200/93 e) 27.3 260/127 200/93 Avg. 27.3 276/136 200/93 31 AWG (0.274 mum) TRIAL #1 a) 39.7 190/88 165/74 b) 40.8 225/107 165/74 c) 41.3 225/107 165/74 d) 41.2 195/91 165/74 e) 39.1 195191 165/74 Avg. 40.4 206/97 165/74 30AWG (0.302 mmJ TRIAL #1 a) 49.7 185185 165/74 b) 49.5 2Q0/93 160/71 c) 49.5 205/96 165t74 d) 50.0 175n9 155/68, e) 49.6, 170/77 155/68 Avg. 497 187/86 160/71 23AWG 60.643mum) TRIAL #1 a) 93.7 135/57 125/52 b) 93.7 140/60 125/52 c) 93.6 135/57 125/52 d) 93.9 145/63 130/54 e) 93.6 140/60 124/52 Avg. 93.7 139/59 126152 36AWG (a 160 mmJ TRIAL #;2 a) 19.4 > 320/160 260/127* b) 19.4 > 320/160 260/127* c) 19.3 > 320/160 260/127* d) 18.3 > 320/160 260/127* e) 19.3 > 120/160 260/127* Avg. 19.1 > 320/160 260/127* 31AWG (a274mm) 36AWG (0.160 mm) COPPER TEMPERA TURE TEMPERA TURE WEIGHT IN RISE OF AFTER EACH COIL (g) EACH ( FI C) 2MIN. ('F/0C) TRIAL #2 a) 21.4 320/160 200/93 b) 21.4 280/138 210/99 c) 21.0 250/121 200/93 d) 23.1 320/160 205/96 e) 21.1 250/121 180/82 Avg. 21.2 2841140 199/93 30AWG {0.302 mum) TRIAL #2 a) 29.7 270/132 200/93 b) 29.5 250/121 200/93 c) 29.5 240/116 200/93 d) 29.9 220/104 190/88 e) 29.6 210/99 190/88 Avg. 29.6 238/114 196/91 23AWG(0.643mml TRIAL #;2 a) 43.7 220/104 180/83 b) 43.7 225/107 175/79 c) 43.6 230/110 180/82 d) 43.9 210/99 180/82 e) 43.4 210/99 170/77 Avg. 43.7 219/104 177/81 * Only run for 30 seconds using 36 AWG due to plastic melting.

Fortrials using approximatelythe same weight of copper, the heat rise is about the same (compare 30 AWG (0.302 mm)/Trial #1 with 23 AWG (0.643 mm/Trial #2). If these values were plotted using the average weight values for the x-axis and the average temperature rise (using either the initial readings or the readings after two minutes) on they-axis, the curve would be near hyperbolic.

In further experiments other classes of insulating varnish were applied to 1" bobbin-wound coils to note the effect of microwave. In all cases the applied liquid varnish advanced to either a cured state or partially cured state after 4 minutes at 40% power (0.350 KWH). The final temperature on the part was in excess of 300"F indicating; 1) all the solvent had been removed -thus allowing the part temperature to exceed 260 F.

2) The part temperature was well within the trad if tionally established cure temperature range.

The individual results are given below: Generic Condition of Varnish Used Classification Temp. Cure ISOLITEC 2991 Unsaturated (uncatalyzed) polyester 300"F Cured ISOLATE6 2991 (Cat. With 1% Unsaturated (TBP) polyester 300"F Cured ISONEL 32E50 Phenolic Mod.

polyester 300"F Cured ISOPOXY6 433-50A Phenolic Mod.

epoxy 300"F Cured Dow DC-997 Silicone 200"F Tacky In the case of the DC-997, this condition of tacky is not unexpected since silicones traditionally require 4 times the time necessary to cure a phenolic-modified polyester.

Isolite 2991 is an unsaturated polyester-reactive unsaturated monomer composition made from a polyester made from dimerized fatty acids (Empol 1018), propylene glycol and maleic anhydride and vinyl toluene as the unsaturated monomer. To this there is added glyceryl tris - (12 - hydroxystearate) as a thixotropic agent and Resimene X-745. The Isolite 2991 has about 60% solids in vinyl toluene as the solvent. There are also present a small amount of hydroquinone and t- butyl catechol as polymeriza tion inhibitors.

It is completely surprising that this resin composi tion cures without a catalyst.

Isoiite 2991 catalyzed with 1% tert butyl peroxide (TBP) is the same as Isolite 2991 except there is added 1% of TBP based on the weight of the resin solution prior to applying the product to the wire.

Isonel 32E5C is a phenolic modified polyester insulating varnish comprising a polyester made from tall oil fatty acid, trimethylolethane, isophthalic acid, soybean oil and glycerine and a phenolic resin made from bisphenol A, P - alkylphenol and formal dehyde dissolved in a mixture of xylene and mineral spirits to give a product having about 50% solids. (It has a viscosity of 190-245 cps at 77% solids in this solvent.) Isopoxy 433-50A is an insulating varnish particularly suited for hermetic application made from a phenolic resin and Epon 1007 (bisphenol A-epichlorhydrin) dissolved in a mixture of n-butanol, monomethyl ether of propylene glycol and xylene having a solids content of about 50% at a viscosity of T-V.

Dow DC-997 is a silicone resin containing insulating varnish.

In another aspect of the present invention there can be prepared bondable wire by the process of the present invention. Bondable wire is wire e.g. copper wire, coated with an enamel, e.g. polyvinyl formal (Formvar) or a polyamide - imide - polyester and overcoated with polyvinyl butyral (Butvar) orother thermoplastic polymer, e.g. a linear polyester such as polyethylene terephthalate (e.g. Dacron). The bondable wire is preformed into a coil and then exposed to microwave energy to heat the product and make the thermoplastic overcoat flow and bond adjacent layers of coil.

In a specific example employing bondable copper wire wherein the copper was coated with Formvar and overcoated with phenolic modified Butvar (p phenylphenolformaldehyde modified polyvinyl butyral) and the wire coil wound on a plastic bobbin was placed in a microwave oven at a power output of 0.268 kWh. At 1 minute in the oven the temperature of the coil was 31 5"F and at 2 minutes the overcoat had softened and bonded strand to strand.

We now describe the second aspect of the invention, in which microwave energy is used for effecting condensation reactions. Unlike the process described in the first aspect of the invention there is no need to have coils or a metal laminate with a dielectric inbetween. The monomers to be condensed are simply placed in a microwavetransparent container and subjected to microwave heating and allowed to condense to the desired degree. The condensation products prepared by the process of the invention can be used in the same manner as condensation polymers made in other manners, e.g.

in preparing electrical insulating varnishes and wire enamels, as coatings for paper, masonry, metal and ceramics, as monolithic articles, as films, sheeting, fabrics, threads, paint ingredients, etc.

There can be prepared both thermoplastic and thermosetting condensation polymers.

Thus there can be prepared thermosetting polyesters, e.g. by condensing ethylene glycol, tris(2 - hyd roxyethyl) isocyanurate and terephthalic acid to form a thermosetting polyester as well as polyesters made from a dihydric alcohol such as ethylene glycol, propylene glycol, neopentyl glycol, 2,2,4,4tetramethyl - 1,3 - cyclobutanediol, butanediol - 1,3 and a polyhydric alcohol containing at least three hydroxyl groups, e.g. glycerine, tris (2 - hydroxyethyl) isocyanurate, trimethylolpropane, pentaerythritol and a polycarboxylic acid, e.g. 4,4' - benzophenone dicarboxylic acid, terephthalic acid, isophthalic acid, adipic acid, trimellitic acid, trimesic acid or the imide dicarboxylic acid prepared from trimellitic an hydride with oxydianiline or methylenedianiline.

Likewise there can be prepared other alkyd resins, e.g. from glycerine and phthalic anhydride and oilmodified alkyd resigns, e.g. from cottonseed oil, glycerine and phthalic an hydride or phenolic resins, e.g., from phenol, p - cresol, m - cresol, o - cresol, p to butyl phenol and formaldehyde orfurfural. Both novolak and resole resins can be prepared.

Likewise there can be prepared resins from tiazines, e.g. melamine or benzoguanamine and formaldehyde, or resins from. urea and formaldehyde.

Likewise there can be prepared nylon, e.g., from hexamethylene diamine or p - phenylene diamine and adipic acid.

Likewise epoxy resins can he prepared, e.g., from bisphenol A or glycerine andepichlorohydrin.

Polyimides can be prepared by condensing methylene dianiline or oxydianiline and trimellitic anhydride. Polyesterimidescan be prepared by condensing ethylene glycol, tris - (2 - hydroxyethyl) isocyanurate or glycerine, terephthalic acid, trimellitic an hydride, methylenedianiline or oxydianiline.

It is not possible to prepare polyethylene terephthalate by reacting two moles of ethylene glycol with one mole of terephthalic acid since after the initial reaction the product appeared to be transparent to microwave energy. However, other thermoplastic resins can be made, e.g. nylon (from hexamethylene diamine and adipic acid).

There can be used microwave heating for example in the range of 900 to 950 megahertz or 2400 to 2500 megahertz. In the following examples there was used 2450 megahertz.

There can be made any of the condensation polymers from the starting monomers set forth in Laganis U.S. patent3,338,743, Meyer U.S. patent 3,342,780, Meyer U.S. patent 3,425,866, Laganis U.S.

patent 3,108,083, Meyer U.S patent 3,249,578, Sheffer U.S. patent 3,312,573, Jordan U.S. patent 3,296,024, Laganis U.S. patent4,016,330, Sheffer U.S. patent 3,523,820, Galkiewicz U.S. patent 4,073,826, Laganis U.S. patent 4,105,639, Keating U.S. patent4,119,758, Laganis U.S. patent 4,133,787, Sheffer U.S. patent 2,982,754, Laganis U.S. patent 3,479,307, Jordan U.S. patent 3,480,589, Laganis U.S. patent 3,498,940, Keating U.S. patent 3,843,587, Sheffer U.S. patent 3,518,230, Zalewski U.S. patent Reissue patent 29,213, Sheffer U.S. patent 3,578,639, Zalewski U.S. patent 3,562,217, Petersen U.S. patent 3,478,127 andSheffer U.S. patent 2,889,304.

In the working examples below the microwave oven employed was model SMC 1-33H of Despatch Industries, Inc. and described in their catalogue 600-978 on pages 16-17. The entire disclosure of the catalogue is hereby incorporated by reference.

Using this oven in the examples at 2450 megahertz the relation of percent output to KWH microwave is given in Table 10.

TABLE 10 Percent Output KWH Microwave 10 .055 20 .268 30 .419 40 .629 50 .829 60 1.039 70 1.286 80 1.563 90 1.877 100 2.363 The general procedure in the working examples was to employ a three-neck flask equipped with a stirrer through the central opening (which was appropriately sealed). One of the other openings was employed for fitting materials into the flask and was closed during the reaction and the other opening was equipped with a fractionating column and condenser with a trap to remove distillates.

The batch was loaded outside the microwave cavity. The ingredients depend on what is to be made.

The loaded flask is placed in the microwave cavity and all necessary attachments are made to ailow stirring, reflux and water removal.

Microwave energy is applied and when the batch is fluid enough stirring is started. Information recorded included: a. Percent output. This is a measure of the total microwave power output of the unit (see Table 10).

The percent output determines how hot (fast) the batch runs and is limited by the efficiency of the fractioning column in returning ethylene glycol and passing water.

b. The Variac setting. This sets percent output.

c. Forward and reflected power. This is a ratio of power actually delivered to the power returned to the microwave generator.

d. Volume of distillate.

e. Percent ethylene glycol in distillate. The percent output should be set to keep the percent ethylene glycol less than five until nearthe end of the reaction.

As the batch proceeds it will be clear, then the rate of distillation will slow down. Check cut viscosities are used to follow the batch to completion. When the batch is complete, the flask attachments are removed, the batch is removed and dumped hot into a pan. When cooled the hard resin is broken up and used to make an enamel. In some cases, four to eight hours can be saved with microwave heating over conventional heating.

When the product is made into a wire enamel, it is made in conventional manner as follows. The base as produced above is dissolved in the solvent mixture. Additives are loaded and the batch is held at 250'Ffortwo hours. The batch is cooled and filtered.

A polyester was prepared using (a) conventional electric mantle heating and (b) microwave heating. The materials employed and heating times are summarised in Table 11.

TABLE 11 ExampleA Examples Method of heating electric mantle microwave Ethylene Glycol 172 9. 170 g.

Tris (2- hydroxyethyl) Isocyanurate 627 g. 621 g.

Terephthalic Acid 715 g. 708 g.

Time to first distillate 30 min. 40 min.

Time to reaction termination 350 min. 290 min.

Total batch cycle time 390 min. 330 min.

Total distillate off batch 156 ml. 154 my.

In Example 1 a total of 20 ml. distilled in the first 65 minutes after distillation began, 50 ml. in the first 125 minutes after distillation began, 117 ml. distilled in the first 185 minutes after distillation began, 150 ml.

distilled in the first 245 minutes after distillation began and 154 ml. distilled in the first 275 minutes after distillation began. Throughout the distillation the ethylene glycol was 3-4% of the distillate.

In Example 1 the percent output was 30% during the entire time of the microwave heating and the Variac setting was 180 throughout. The final product W3S 100% solid.

The products of Example A and Example 1 were made up into wire enamels and applied on the wire tower to No. 18 AWG copper wire at 45 ft/min. The enamel formulations and test results on the wire are given in Table 12.

TABLE 12 Example A Example 1 Base 253 g. 222 9.

CresylicAcid 399 g. 332 9.

Solvesso 150 Aromaticsolvent 1649. 1369.

Heavy Aromatic Naphtha Solvent 70 g. 59 g.

Cresol-formaldehyde resin at 40% solids 63 9. 53 9.

Tetraisopropyl Titanate 13.3 9. 11.2 g.

840 Silicone resin solution (Dow) 0.7 g. 0.6 9.

Wire Test Run No. C-8106 C-9565 Appearance Smooth Smooth Build Polyester, mils 2.3 2.3 Build Polyamideimide Topcoat, mils 0.7 0.6 Mandrel pass after smap 2x lx Heat Shock Mandrel (20% pre-stretch 1/2 hour. 200"C) % pass at 1 x 50 10 % pass at 2x 80 50 % pass at 3x 100 90 % pass at 4x 100 100 A polyester-imide was prepared using (a) conventional electric mantle heating and (b) microwave heating. The materials and heating times are summarized in Table 13.

TABLE 13 Example B Example 2 Method of Heating electric mantle microwave Cresylic Acid 95 g. 305 9.

Ethylene Glycol 46 9. 136 9.

Tris (2- hydroxyethylene) Isocyanurate 179 9. 572 g Trimellitic Anhydride 115 g. 369 g.

Methylene Dianiline 60 g. 190 g.

Terephthalic Acid 131 g. 418 g.

Total Distillate 48 ml. 180 ml.

Reaction Time 720 min. 540 min.

Total Batch Cycle 810 min. 559 min.

The heating protocol in making the product of Example 2 was as follows: Forward/ Total Time Variac % Output Reflected % EG EG Loss 3:20 180 30 .28/.04 3:35 180 30 .35/.04 3:38 180 30 .30/.04 3:39 180 30 .25/.05 3:42 180 30 .28/.05 1 - 3:47 175 25 .20/.03 not determined 3:58 175 25 .18/.02 0.5 - 4:14 175 25 .191.03 4 4:28 175 172 23 .23/.04 4 4:44 172 < 170 25 .25/.02 5.5 52 mi 4:50 - > 175 (no distillation at 170) 4:59 175 22 .18/.02 3.5 54 ml 5:14 175 24 .24/.03 4 58 ml 5:29 175 25 .26/.02 4 62 ml 5:44 175 26 .26/.03 3.5 66 ml 6:00 175 26 .25/.01 4 72 ml 6:15 175 26 .27/.02 4 75 ml 6:30 175 27 .26/.04 3.5 79 ml 6:45 175 27 .25/.01 4 83 ml 7:00 175 27 .26/.02 4 86 ml 7:15 175 27 .25/.01 4 90 ml 7::36 175 26 .24/.02 4 94ml 7:45 175 24 .19/.02 4 97 ml 8:00 175 24 .20/.03 4 100 ml 8:15 175 25 .25/.02 4 102 ml 8:30 175 27 .23/.04 4 104 ml 9:00 175 26 .23/.01 4 110 ml 9:15 175 27 .22/.01 4 113 ml 9:30 175 27 .25/.04 4 116 ml 9:45 175 27 .24/.04 4 120 ml 10:00 175 27 .24/.04 4 124 ml 10:15 175 28 .24/.04 4 128 ml 10:30 175 26 .23/.04 4 132 ml 10:45 175 27 .23/.02 4 136 ml 11:00 175 27 .25/.03 4.5 141 ml 11:15 175 28 .23/04 5.0 145 ml 11:30 175 < 0 270 .24/.04 < 0 4.5 148 ml 11:40 Kettle dismantled from microwave 8:50 170 10 .04/.0 Heat on 9:00 178 20 .1/.01 stirring 9:16 182 30 .25/.04 good stirring 9:27 178 25 .15/03 reflux starts 9: :38 178 25 .16/.03 4.5 150 ml 9:45 178 25 .18/.04 5.0 154 ml 10:00 178 25 .17/.04 5.0 158 ml 10:30 180 30 .23/.02 5.0 164 ml 10:50 178 25 .18/.04 8.0 172 ml 11:00 Distillation stopped 11:00 180 30 .23/.04 11:15 180 30 .24/.04 10 174 ml 11:35 180 30 .25/.04 180 ml The products of Example B and Example 2 were made up into wire enamels and applied on the wire towerto No. 18 AWG copper wire at 45 ft/min. The enamel formulations and test results on the wire are given in Table 14: TABLE 14 Example B Example 2 Base 221 g. 224g.

Cresylic Acid 321 g. 297 g Solvesso 100 186 9. 188 9.

Cresol-formaldehyde resin at40% solids 25.5g. 25 9.

Tetraisopropyl Titanate 8.6 g. 8.5 g.

Blocked Isocyanate (toluene diisocyanate trimer blocked with phenol) 53 g. 56 g.

Dow 840 Silicone Resin 0.6 g. 0.6 g.

From the experiments carried out the difference in time in favor of microwave heating compared to conventional heating appears to be increased when the initial load in the reactor contains more liquid.

Materials which are liquids and capable of reacting with each other should exhibit the highest efficiency when using microwave energy for chemical reactions. It appears that the use of such energy can be used to make in a shorter period of time products that are comparable to those made using conventional heating methods.

The process can comprise, consist essentially of or consist of the steps set forth with the materials set forth.

In preparing polyesters the polyhydric alcohol can be reacted with the free carboxylic acid or an ester forming derivative thereof, e.g. an acyl halide, anhydride or an ester of a monohydric alcohol. Thus, forexample, glycerine can be reacted with phthalic anhydride, phthaloyl chloride or dimethyl phthalate as well as with phthalic acid.

In making polyester-imides, for example, trimellitic anhydride can be prereacted with a diamine, e.g.

oxydianiline or methylenedianiline to form the imide dicarboxylic acid if desired or all of the reactants can be put into the reactor together.

Using the microwave oven described above additional polymerizations were carried out.

A phenol-formaldehyde novolakwas prepared by reaction 940 parts phenol, 9.4 parts oxalic acid, 559 parts of 44% formaldehyde and 30 parts of water at about 30% outputto obtain a novolak melting at 114"C.

An epoxy ester was prepared by condensing 588 parts of Pamolyn 327-B fatty acid, 876 parts of Epon 1004 (bisphenol A-epichlorohydrin) and 35 parts xylene solvent at about 30% output to an esterified epoxy resin.

An unsaturated polyester resin was prepared from 535 parts of dipropylene glycol, 152 parts of propylene glycol, 95 parts maleic anhydride and 718 parts of phthalic an hydride (0.06 parts of hydroquinone was added as an antioxidant. The oven was run at about 20-30% output to give a resin soluble in styrene and having an acid number of 63.8.

An oil modified polyester prepared from 6aO parts of Acintol fatty acid No. 42 parts dipropylene glycol, 402 parts oftrimethylol propane, 408 parts of isophthalic acid and 133 parts of trimellitic anhydride at an oven output of 30% which was decreased near the end of the reaction to 20% to obtain a sol'id resin.

There was employed a mixture of 995 parts of N methyl pyrrolidine, 218 parts of toluene diisocyanate, 144 parts of methylene b is(p henylisocya n-ate), 209 parts of terephthalic acid, 90 parts of isophthalicacid at oven output of 30% which was lowered to 5% as soon as the reaction went vigorously. The product was a solution of the polyamide in N - methyl pyrrolidine. The product was prepared in 165 minutes compared to 325 minutes required using a normal electric heating mantle.

Nylon 6,6 was prepared by reacting 710.9 parts of hexamethylene diamine, 812.7 parts of adipic acid and 50 parts of water at an oven output of 30% which was gradually increased during the reaction to 52% to form a high molecular weight nylon 6,6 polymer.

In the claims the term "at least trifunctional" means that the material has at leastthree groupings that can take part in the condensation reaction. The presence of at leastthree groupings in one of the reactants permits the formation of a thermosetting product. The other reactant or reactants should include at least one which is at least difunctional, i.e.

has at least two groupings that can take part in the reaction.

In the above described third aspect of the invention, appropriate features may be selected from the description above of the first and second aspects of the invention.

Claims (41)

1. A process in which a metal article comprising a plurality of coated metal layers is heated by applying microwave energy to the article and in which the coating is of a material selected from (a) a curable material that is cured by the heating to form a thermosetting resin and (b) a bondable thermoplastic material that is caused by the heating to bond to its adjacent metal surface.

2. A process in which an article comprising a metal part in the form of a coil and a coating, or metal laminate having a dielectric material between the metal layers as a coating on the metal layers, is heated by application of microwave energy, and in which the coating is of a curable synthetic resin and is cured by the application of microwave energy.

3. A process according to claim 1 or claim 2 in which the article comprises a coated metal coil.

4. A process in which an article comprising a coil of bondable wire carrying a bondable coating of thermoplastic polymer is heated by applying microwave energy sufficient to render the polymer bondable.

5. A process according to any of claims 1 to 3 in which the coating is of a synthetic resin which comprises a polyester.

6. A process according to claim 5 in which the polyester is derived from a dihydric alcohol, a trihydric alcohol and a dicarboxyid acid.

7. A process according to claim 6 in which the polyester is derived from (1) ethylene glycol, (2) glycerine or tris(2 - hydroxyethyl) isocyanurate and (3) a dicarboxylic acid comprising terephthalic acid or isophthalic acid.

8. A process according to claim 5 in which the polyester is an oil free polyester.

9. A process according to claim 5 in which the polyester is an ethylenically unsaturated polyester.

10. A process according to claim 9 in which the polyester is dissolved in an ethyienically unsaturated monomer.

11. A process according to claim 10 in which the unsaturated monomer is styrene, butyl styrene, methyl methacrylate, vinyl toluene or diallyl phthalate.

12. A process according to claim 11 in which the monomer is vinyl toluene.

13. A process according to claim 11 in which the monomer is diallyl phthalate.

14. A process according to claim 13 in which the polyester is an oil modified polyester.

15. A process according to claim 14 in which the polyester is a tall oil acid modified polyester.

16. A process according to claim 14 in which the polyester is a soybean oil modified polyester.

17. A process according to any preceding claim wherein the microwave curing is at 900 to 950 or 2400 to 2500 megahertz.

18. A process according to claim 17 in which the curing is at 2400 to 2500 megahertz.

19. A process according to any preceding claim in which the metal is copper.

20. A process according to any preceding claim in which the coating is a thermoplastic polymer and in which the metal article is a coil of copper wire coated with an enamel and top coated with the thermoplastic polymer.

21. A process according to any of claims 1 to 20 substantially as herein described.

22. An article made by a process according to any of claims 1 to 21.

23. A process in which a condensation polymer is made by reacting monomeric components and splitting out a volatile material, and in which the reaction is caused by heating the components by applying microwave energy.

24. A process according to claim 23 in which the condensation polymer is a polyester, a phenol formaldehyde resin, an epoxy resin or an isocyanate based polyamide.

25. A process according to claim 24 in which the condensation polymer is (1) a polyester from ethylene glycol, tris(2 - hydroxyethyl) isocyanurate and terephthalic acid, (2) a polyester - imide from ethylene glycol, tris(2 - hydroxyethyl) isocyanurate, trimellitic anhydride, methylene dianiline and terephthalic acid, (3) a phenolformaldehyde novalak from phenol and formaldehyde, (4) an epoxy resin from fatty acid and bisphenol A - epichlorohydrin, (5) an unsaturated polyester from dipropylene glycol, propylene glycol, maleic an hydride and phthalic anhydride, (6) an oil modified polyester from fatty acids, dipropylene glycol, trimethyol propane, isophthalic acid and trimellitic anhydride or (7) a polyamide from toluene diisocyanate, methylene bis(phenylisocyanate), terephthalic acid and isophthalic acid.

26. A process according to claim 24 in which the condensation polymer is a polyester formed from monomeric components comprising polyhydric alcohol and polycarboxylic acid or ester forming derivatives thereof.

27. A process according to claim 26 in which the monomeric reactants include a dihydric alcohol, a trihydric alcohol and a dicarboxylic acid.

28. A process according to claim 27 in which the reactants comprise (1) ethylene glycol, (2) glycerine ortris(2 - hydroxyethyl) isocyanurate and (3) a dicarboxylic acid comprising terephthalic acid or isophthalic acid.

29. A process according to claim 28 in which the reactants consist essentially of ethylene glycol, tris-(2 - hydroxyethyl) isocyanurate and terephthalic acid.

30. A process according to claim 27 in which the reactants also include either (1) trimellitic anhydride and oxydianiline or methylenedianiline or (2) the imidedicarboxylic formed by reacting trimellitic an hydride with oxydianiline or methylene dianiline.

31. A process according to any of claims 23 to 30 carried out in the presence of an inert solvent.

32. A process according to any of claims 23 to 31 in which the reactants include at least one reactant which is at leasttri-functional and the product is a thermosetting polymer.

33. A process according to any of claims 23 to 31 in which the reactants include at least two which are difunctional and are capable of reacting together to form a thermoplastic polymer and the product is a thermoplastic polymer.

34. A process according to any of claims 23 to 33 in which the microwave energy is at 900 to 950 or 2400 to 2500 megahertz.

35. A process according to claim 34 in which the microwave energy is at 2400 to 2500 megahertz.

36. A process according to claim 23 substantially as herein described.

37. A condensation polymer made by a process according to any of claims 23 to 36.

38. A process of forming a thermoplastic or cured thermosetting polyester obtained from polyhydroxy compounds and polycarboxylic acid and in which the process comprises polymerisation or curing induced by the application of microwave energy.

39. A process according to claim 38 in which the polymer is formed from monomers as listed in any of claims 26 to 30.

40. A process according to claim 38 for the production of a thermosetting polyester comprising applying microwave energy to a coil or laminate of metal layers in which the layers are coated by uncured polyester.

41. A polyester, oran article comprising polyester, made by a process according to any of claims 38 to 40.