The present invention is directed to novel curable oxaspiro resin compositions and uses thereof in electrical and power apparatus.

BACKGROUND OF THE INVENTION

An important problem encountered in using organic materials as engineering plastics is the high degree of shrinkage found during polymerization of the monomeric materials to the polymers. Shrinkage during curing may cause many problems such as cracking, delamination, poor adhesion in castings, potting and encapsulation applications. This is particularly important in the use of engineering plastics in electrical power apparatus. Another related problem is that in motor and generator coils, where mica is normally used as the dielectric material, resin shrinkage can result in microvoid formation which, in turn, may cause electrical corona and possible delamination of the ground wall insulation from the conductor, thereby impairing the electrical capability and reliability of the equipment. This problem is typical to the internal structure of a generator. An external problem related to shrinkage and degradation of the engineering plastics is that there may be loosening

of the coil windings within the stator slots, which may be caused by shrinkage of the insulating system, which usually includes a resin. The loss of direct contact at the interface between the conductive coating and the iron slot walls produces a combination of abrasion (primarily from vibration) and erosion by capacitive sparking of the slot discharge.

Many conventional materials used in locking the windings into the slot may not be able to cope with the coil vibration. When given any space to vibrate, the hard ther oset resin insulators produce sharp, hammerlike blows that are capable of moving and even destroying the wedgers, spacers and packing materials. The resins currently used in insulation systems in, for example, hydrogenerators, show some degree of shrinkage during polymerization and cure, and also during thermal aging. This shrinkage produces many of the above problems such as void formation, cracking, etc. One attempt to solve this problem has been to apply a conducting elastomeric coating or an elastomeric bead to the coils prior to insertion into the stator slot. However, such elastomeric materials have a tendency to creep under load and may not retain their usefulness for extended periods of time.

It is believed that a primary source of the above problems is due to the shrinkage of the resin as it is polymerized or cured. Shrinkage which occurs while the resin is still in the liquid state does not usually cause any great problem since the viscous liquid resin can still flow and no appreciable stresses are formed. However, as the polymerization proceeds, the resin becomes rigid. Any shrinkage which occurs after rigidification produces tension.

compression and/or shear within a resin and at its interface with the component substrates. Depending upon the cohesive and adhesive strength of the resin vis-a-vis the internal stresses which develop during polymerization or curing, separation at the interface between the resin and the component substrate may occur. This separation may happen immediately upon cure or later, and in either case it leads to degradation of the resin and the aforementioned problems in the electrical power apparatus.

Some of the shrinkage can be controlled or reduced through the use of inert fillers such as quartz, sand or alumina trihydrate. However, the amount of reduction of the shrinkage depends upon the amount of filler used. The resulting increased viscosity of the uncured resin due to the filler additive must be carefully controlled so as not to retard or eliminate the resin flow, which reduces contact with the component substrate.

The work of William J. Bailey in recent years has revealed classes of spiro monomers which expand during polymerization. See, for example. Patent No. 4,387,215. Curable compositions comprising such spiro monomers have been disclosed by Endo, et aj.. in Patent No. 4,368,314.

It is an object of the present invention to provide novel curable compositions and their cured resin products which expand upon curing and which have particularly improved properties for structural and electrical applications in electrical power generating apparatus.

SUMMARY OF THE INVENTION

The present invention provides curable resins comprising 15-35% by weight of oxaspiro monomers selected from the group consisting of 3,9-di- ( norborn- 2 ' -βn-5 • -yl ) - 1 , 5 , 7 , 11- tetraoxaspiro[5.5]undecadecane and 1,5,7,11- tetraoxaspiro[5.5]undecane; 65-85% by weight of an epoxy compound; and a polymerization-initiating amount (preferably 0.5-3.0% by weight) of a cationic polymerization initiator. The resin is cured, preferably at a temperature of about 70-180*C, to produce a cured resin which is characterized by a larger volume than that of the uncured resin. The present invention also provides articles of manufacture comprising these resins which are particularly advantageous as structural or insulating components of electrical power apparatus. Another spiro composition, in which the oxaspiro compound is used in greater than 50% by weight, with an arylated epoxy compound comprises 3,9-di-(methylene)-l,5,7,ll- tetraoxaspiro[5.5]undecane.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to novel curable resins comprising oxaspiro monomers, present in the amount of about 15-35% by weight, selected from the group consisting of 3,9-di-(norborn-2'-en-5*-yl)- l,5,7,ll-tetraoxaspiro[5.5]undecane and 1,5,7,11- tetraoxaspiro[5.5]undecane. Such spiro compounds are disclosed in various papers authored or coauthored by William J. Bailey, including J. Poly. Sci.. Poly. Lett. Ed. 18. pp. 25-27 (1980) ; ACS Svm. Series. Rinσ-Openinσ Polv Int. Symp. _f 59 _r pp. 38-59 (1977); J. Dent. Res.. 58 (5), 1522-1523 (1979); J. Polv. Sci.. Polv. Lett. Ed.. 13, 193-5 (1975); Macromol.

Chem. 176. 2897-903 (1975); Macromol. Chem.. 1977 (11), 3131-5 (1976); Polv. Prep.. ACS. Polv. Chem. Div.. 15. 445-50 (1974), and papers cited therein. The curable resin compositions according to the present invention will also contain from about 65-85% by weight of an epoxy compound, such as p,p'-di-(2,3- epoxy-l-propoxy)- iphenyldimethylmethane (commercially known as Bisphenol A epoxy) , epoxidized styrene and styrene derivatives, 2,3-epoxy cyclopentane- ,7-endomethylene cyclohexane-6-glycidyl ether, diglycidyl ether hexahydrophthalic anhydride, or any other epoxy-containing materials. Arylated epoxy compounds are particularly preferred.

The curable compositions according to the present invention also contain a polymerization-initiating amount (usually about 0.5-3.0% by weight) of a cationic polymerization initiator. Inorganic initiators should be used, particularly a borontrihalide etherates, or a ine complexes, preferably borontrichloride amine complex. Organic acid catalysts should be avoided as curing agents as they may become incorporated in the forming polymers and result in undesired premature termination of the polymer chains or cross-linking.

In one modification, instead of the above-mentioned spiro compounds, the spiro compound 3,9-di-methylene- l,5,7,ll-tetraoxaspiro[5.5]undecane may be utilized, but it must be utilized at about 50% by weight, usually 40-60% of the curable composition in order to achieve the desirable properties according to the present invention. When this spiro compound is utilized, the amount of the epoxy compound may be less than the 65-85% range recited above and may be utilized in the range of 60 to 40% by weight of the total curable resin composition.

It may be desirable to also add to the composition a curing accelerator such as an aromatic amine, tertiary amine or quaternary ammonium salt, imadazole derivative, pyridine derivative, or other chelating compounds. The amount of the curing accelerator will be usually small, usually less than 0.5% by weight of the total composition. The particular preferred curing accelerator to be used in combination with a borontrifluoride etherate initiator is o-phenylene diamine.

The curable compositions according to the present invention are cured by heating. Although the temperature at which the curing is effected is not particularly critical, provided that the temperature is below the temperature at which the organic components will degrade or oxidize, it is preferred that the temperature of curing be carried out in the range of about 70-180', particularly in the range of 80-150*C. The period of time required to complete the curing process will depend upon the temperature of the curing, with the lower the temperature the longer the time required for curing. For this reason the preferred temperature ranges should be utilized since they are convenient for maintaining the flowable properties of the uncured composition during curing and for ensuring that sufficient adhesion is obtained between the cured surface and the substrate with which it is in contact.

The compositions according to the present invention will have a larger volume in the cured state as compared to their uncured state, with a typical degree of expansion being about 1-5% by volume.

The invention will be further illustrated with reference to particular examples for purposes of illustration. These examples, however, are not intended to limit the invention in any way.

EXAMPLE 1

A cationic initiated composition was cured which initially contained 22% by weight 3,9-di-(norborn- 2 en-5 ^/ -yl)-l,5,7, ll-tetraspiro[5.5]undecane (hereinafter referred to as NSOC) , 70% by weight di- glycidyl ether of bisphenol A (hereinafter Bisphenol A epoxy) and 8% by weight borontrifluoride etherate orthophenylene diamine. The composition was heated at 100*C for four and one-quarter hours, then at 150* for one hour. The copolymer product showed on the average of 1-1.6% expansion with respect to the uncured composition.

EXAMP E 2

An uncured resin formulation was formed containing the following: 5.32 parts by weight Bisphenol A epoxy, 0.61 parts by weight orthophenylene diamine, 1.66 parts by weight NSOC and 0.22 parts by weight of a cationic initiator. The glass transition temperature of the cured copolymer is in excess of 150*C. To demonstrate the expansion characteristics of this copolymer, two large motor coil sections were cast to a simulated slot. One coil section was cast in place using a controlled epoxy resin (containing no NSOC) while the other was cast in place using the expanding copolymer resin according to the present invention which contained 21% by weight of NSOC. After cure, the control sample exhibited several cracks and also showed separation from the metal slot. The expanding copolymer sample according to

the present invention did not show any cracks or separation. After further aging of the specimens for six weeks at 150*C the size of the cracks increased in the control sample. However, the expanding copolymer specimen showed only slight separation from the slot wall in one corner of the slot. To determine how firmly the aged specimens were locked into the slots, the load was measured which was required to break them loose and to push them out of the slot. The control resin required a breaking load of 43 pounds per square inch and a pushing load of 29 pounds per square inch. The control resin volume change from uncured to cured state was -4 to -6% (exhibiting a shrinkage) . The copolymer resin according to the present invention required a breaking load of 430 pounds per square inch and a pushing load of 314 pounds per square inch. The volume change from the uncured resin to the cured resin was +1-1.6% (exhibiting an expansion). The same copolymer according to invention was subject to electrical tests. Electrical dissipation values ranged from 0.5-2% at 155'C. Voltage breakdown was tested and shown to be between 350 and 500 volts per mil on a 60 mil thick sample. The specimen was not degassed prior to the cure and thus may have contained small voids which adversely affect the breakdown. It is therefore expected that somewhat higher and more consistent values would be obtained if the sample were degassed.

E? MPI£ ?

A B-staged resin rich mica paper tape was prepared from Macallem mica paper tape #12042 (United Technology) and an expanding resin system containing

the epoxy compound of Example 1 (76.5%), NSOC (21.5%) and boron trichloride amine complex (2%) (XU-213). The mica tape was impregnated with the expanding resin system and B-staged at 150*C for 20 minutes producing a pliable and flexible resin rich tape containing approximately 25% by weight of the expanding resin. The resin loaded tape was manually wrapped, in half-lap manner, and as tightly as possible around an 8" length of 2" x 1/2" copper bar stock. Fourteen layers of resin rich tape were applied to each test bar. Strain gauges were positioned in the center of the bar between the seventh and eighth layers of tape on several test bars. An outer single layer of B-staged glass tape, containing the same expanding resin system, was applied at the protective armor layer. A final layer of 1 mil Teflon tape was applied to the wrapped bar and the bar placed into a forming and sizing mold, between a sheet of 1 mil Mylar film. The bar was then sized to its required dimensions and placed in an oven and cured as per the cure schedule shown in Table 1 (Sample 2) .

Upon removal from the oven the bar was extricated from the mold and the Mylar and Teflon layers removed. A conducting coating was applied to the outer surface of the bar to complete its construction. By the method eight inch bars simulating small sections of a generator coil were formed.

Control test bars also were prepared with the same mica paper tape. These bars were wrapped with dry, unloaded mica paper tape and then were vacuum/pressure impregnated with a conventional VPI resin system used in hydrogenerator coils. The impregnated bars were then sized and cured as done

previously. The dimensions for all of the finished test bars were identical.

The test bars were placed into simulated generator slot fixtures and locked into position with the appropriate side wedges, top wedges and ripple springs to produce the test models. The test models were then thermally aged at 100*C and pertinent properties monitored.

In Table 2 are shown the power factor values at room temperature, 75*C and 100 ^* C under 1 kV and 4 kV. The groundwall insulation systems (1 and 2) containing the expanding resin had power factors comparable to the control VPI resin formulation.

In Table 3 are shown the dielectric constants under the same test conditions. Again, it can be seen that the ground wall insulation containing the expanding polymer was comparable to the conventional VPI/groundwall system.

The change in stresses within the groundwall insulating systems during thermal aging at 100*C are shown in Table 4. After 2000 hours of aging the groundwall insulations containing the expanding resin showed an average of 0.0014% expansion. The standard VPI/groundwall system during the same aging period showed 0.0014% expansion. The standard VPI/groundwall system during the same aging period showed 0.0061% shrinkage. These results confirm that residual unpoly erized expanding monomer is still present in the groundwall insulation after the initial cure, and during thermal aging the residual expanding monomer polymerizes and produces expansion which increases the "locking-in" pressure. On the other hand, the VPI resin shrinks. This results in a

reduced "locking-in" pressure which ultimately causes the coil to loosen within the slot.

TABLE 1

Comparison of Properties Detween (W) VPI Systea and Expanding Polyaer Systeu

Sample Coaposition 70.5X 828 70.0% 828 74% 828 OOX 828 Standard

10.5% NSOC 10.0% NSOC 24% NSOC OX NSOC Bydrogenerator

1.0% XU-213 2.0% XU-213 2% XU-213 IX XU-213 VPI Resin

Power Factor 0.08 0.035 0.025 <0.114 0.045

(Tan δ 0160°C) Diel. Constant 6.7 5.2 4.0 5.0-8.7 6.1

Diel. Strength 425 425 440 425 438 (Volts/Mils)

Vol. Change (X) -0.200 -0.35 40.84 -2.75 -5.27

I

Tensile Strength β,793 6,800 5,106 6,700

(psi) Tensile Modulus 0.51

(psi x 10°) Elongation (X) 1.43 1.30 1.27 0.5

Coef. of Theraal 80 x 10 -6 78 x 10 -6 65 x 10 -6 68 x 10 -6 143 x 10 ^"β Expansion (in./in. C)

Class Transition 124 121 118 136 101 (T _g °C)

Cure Schedule

TABLE 3 Dielectric Constant (e')

Strain Gauge Measurement After 2000 Hours at 100°C

Indicator 0.0003% Expansion 0.0014% Expansion 0.0013% Expansion 0.0014% Expansion 0.0027 Expansion 0.0071% Shrinkage

0.0050% Shrinkage 0.0062% Shrinkage

Microinches/inch - Values taken 100°C test temperature.

There are many other uses of the composition according to the present invention in electrical apparatus which include, but are not limited to, use as a sealing resin for electrical and optical feedthroughs, as a bracing resin for generator coil inturns, as a filler resin for endtums of brushless excitors, as a bonding resin for stator core laminations of motors and generators, as an adhesive bonding resin for leadless chip carriers, as a potting compound for electronic circuitry, pressurized fittings and feedthroughs, as an adhesive bonding resin for metglas wound transformers, and as a groundwall insulating resin for large rotating electrical apparatus.