Secondary Electrical Insulation Coatings Containing Nanomaterials

Info

Publication number: 20070142526
Type: Application
Filed: Mar 1, 2007
Publication Date: Jun 21, 2007
Applicant: THE P. D. GEORGE COMPANY (St. Louis, MO)
Inventors: Ronald Goetter (Maryville, IL), David Vines (Imperial, MO)
Application Number: 11/680,681

Abstract

Use of the barrier property effect of nanomaterials to improve the electrical insulation resistance and corrosion protection strength properties of electromagnetic devices. The beneficial effects are realized with nanomaterial loadings of 1-20%, and preferably between 1-5%, parts by weight of coating resins. Nanomaterials include, but are not limited to, silica, alumina, zirconia, and antimony pentoxide, which are dispersed either directly into a coating, or pre-dispersed in a carrier appropriate to the solvent of the resin system. The rheology of the resin system is not significantly altered which would otherwise affect processing of the resins for their intended applications.

Description

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending application Ser. No. 11/252,921 which was filed on Oct. 18, 2005, is entitled “Use Of Nanomaterials In Secondary Electrical Insulation Coatings”, and which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND

This invention relates to electromagnetic devices; and, more particularly, to the use of nanomaterials in insulation coatings for these devices.

Organic resin compositions are used as coatings for the mechanical, electrical and environmental-resistance they impart to electromagnetic devices. The coatings provide a mechanical strength, electrical insulation, and environmental protection for improved long-term durability of the devices, as well as increasing the quality of the final product. Some of these beneficial properties can be improved by the addition of inorganic fillers such as silica, calcium carbonate, alumina, etc. However, a problem with the current state of this technology is that the inorganic materials used in the coatings do not always remain suspended in the coatings, resulting in a non-homogeneous mixture. When the coatings are applied to the devices, areas of weakness result that, in turn, can cause failure of a device.

This current state of the art raises several issues related to the handling of the coating, its agitation (to produce homogeneity before application) and its pumping, and concerns about the homogeneity of both the applied liquid and the resulting cured film. Prior approaches employed to address these problems have focused on the use of fumed silica used to increase viscosity and improve suspension of the inorganic materials. But, in some instances, use of these agents produced undesirable results because of rheological changes which occur and cause inconsistencies in the applied coatings.

SUMMARY

The present invention is directed to coatings utilizing the barrier property effect of nanomaterials to improve the electrical insulation resistance and corrosion protection of electromagnetic devices; without the coating having the non-homogeneity problems described above. These beneficial effects are realized with nanomaterial loadings of 1-20%, and preferably between 1-5%, parts by weight to the coating resin. The nanomaterials used include, but are not limited to, silica, alumina, zirconia, and antimony pentoxide. These nanomaterials are dispersed either directly into a coating, or pre-dispersed in a carrier appropriate to the solvent of the resin system being modified. The resulting formulations benefit from the fact that anti-settling agents need not be incorporated in the mixture to keep the inorganic material suspended in the coating. A further benefit is that the rheology of the resin system is not significantly altered which would otherwise affect the processing of the resins in their intended applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph comparing the viscosity of Epoxy-unsaturated polyester copolymer with and without nanomaterials over time;

DETAILED DESCRIPTION

The following detailed description illustrates the invention by way of example and not by way of limitation. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what we presently believe is the best mode of carrying out the invention. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

In accordance with the present invention, barrier property effects of nanomaterials are used to improve the electrical insulation resistance and corrosion protection properties of electromagnetic devices coated with a coating resin incorporating the nanomaterials, while simultaneously avoiding the homogeneity problems previously discussed. To achieve these desired results, inorganic materials in the 1-150 nanometer (nm) range are used in formulating the coating resins applied to the devices. By contrast, the size of inorganic particles in current, state-of-the-art filler systems is on the order of 3000-4500 nm. Suitable chemistries for the coating resin include, but are not limited to, unsaturated polyesters, epoxies, urethanes, waterborne polyesters, epoxy emulsions, organic solvent borne alkyds, acrylated and methacrylated urethanes, acrylated and methacrylated epoxies, acrylated and methacrylated polyols, and acrylated and methacrylated vegetable oils. The desired effects are achieved using nanomaterial loadings of between 1-20% part by weight, and preferably between 1-5% part by weight, of a nanomaterial to the resin. Nanomaterials that can be used include, but are not limited to, silica, alumina, zirconia, and antimony pentoxide. Those skilled in the art will understand that the resulting coatings can be tailored to meet specific performance requirements for a device by the inclusion of an appropriate amount of a nanomaterial or a combination of nanomaterials. One important advantage of the coatings of the present invention is that the rheology of the resin system is not significantly altered; although, in some instances, there is an increase in the viscosity of the resulting mixture. Overall, though, processing of the resins for their intended applications is not materially affected.

With respect to the use of nanomaterials, their small particle size means that a given amount of material is more evenly distributed throughout the resin, creating a more tortuous path which is harder for corrosive agents to penetrate. Further, the particles being in close proximity to each other promotes dissipation of any electrical charge, thereby leading to improved electrical properties of a device in which the coating is incorporated.

The barrier effect resulting from use of the nanomaterials produces significant results in the coatings made in accordance with the invention. For example, the improved electrical and corrosion resistance properties referred to above occur even though lower amounts of inorganic nanomaterials are used in producing a coating than when using other inorganic filler materials. The coatings also have an equal abrasion resistance, even though, again, lower amounts of inorganic nanomaterials are used in the coating. Third, some of the new coatings may have a lower viscosity than current coatings. All of these features serve to provide greater flexibility in processing options for the coating, while achieving desired performance characteristics for the completed device.

During preparation, the nanomaterials are either dispersed directly into a coating resin, or the nanomaterials are pre-dispersed in a carrier appropriate to the solvent of the resin system being modified. A significant advantage of the resulting formulations is that viscosity increasing anti-settling or suspension agents do not need to be added to the resulting mixture to keep the nanomaterial suspended in the mixture. A second advantage is that homogeneity of the coating mixture is achieved and maintained with a minimal amount of agitation of the mixture as compared to that required for conventional coating mixtures having inorganic fillers.

Nanomaterial modified organic coatings are applied using the same processes currently used in the industry. These include, but are not limited to, dip and bake, trickle, vacuum/pressure impregnation, roll through, spray, and vacuum impregnation. In addition, coatings made in accordance with the present invention are cured using currently available methods. Such curing methods include, but are not limited to, gas-fired ovens, resistance heating, infrared radiation heating, chemical catalyzation and ultraviolet (UV) radiation curing. Regardless of the method of application, coatings incorporating a nanomaterial more readily flow into the areas of the electromagnetic device being coated, since the inorganic nanomaterial is of a smaller particle size than the inorganic filler materials used in conventional coatings. Further, with respect to UV curing processes, coatings made in accordance with the present invention have been found to exhibit an improved optical clarity. This facilitates use of UV induced curing processes that cannot now be used because of the presence of organic fillers in current coatings.

The following refers to Tables 1 and 2.

TABLE 1 Standard Filled unsaturated polyester (UPE) System I System II Commercial 70 99 97 Polyester A Silica, 2.9 microns 30 0 0 Nanoalumina, 50 nm 0 1 3

TABLE 2 Standard Waterborne Polyester (WBPE) System III Commercial Waterborne 100 97 Polyester Nanoalumina, 150 nm 0 3

Preparation:

Referring to Table 1, a standard, filled unsaturated polyester (UPE) coating was prepared by dispersing 30 parts by weight (pbw) of silica in 70 pbw of a UPE resin using a high speed dispersion process until the resulting mixture was homogeneous. In addition, two nano-modified UPE samples were prepared. The first, referred to as System I in Table 1, was prepared by adding 1 pbw of a nanomaterial (50 nm nanoalumina) to 99 pbw of the UPE resin and then mixing until a homogenous mixture was achieved. The second, referred to as System II in Table 1, was prepared by adding 3 pbw of the nanomaterial (50 nm nanoalumina) to 97 pbw of the UPE resin and again mixing until a homogeneous mixture was achieved.

Referring to Table 2, a nano-modified waterborne polyester (WBPE) coating, referred to as System III in the Table, was prepared by adding 3 pbw of a nanomaterial (150 nm nanoalumina) to 97 pbw of WBPE and mixing until a homogenous mixture was achieved. Because the polyester is a waterborne polyester, the nanoalumina was predispersed in water. This predispersed nanoalumina/water solution was added to the WBPE material. Stated differently, the nanoalumina was added as a dispersion in water to reach a final concentration of 3%.

Physical properties of the representative formulations are listed in Table 3.

TABLE 3 Standard UPE Standard UPE Filled UPE w/Nanomaterial Inorganic Loading, % 0 30 3 Viscosity, 25° C., Cp 100-200 150-250 150-400 Density, 25° C. 1.09 1.30 1.09

As seen in Table 3, the nanomaterial loaded UPE had a viscosity similar to the standard filled UPE even though it was made using only 10% of the amount of inorganic material used in the standard filled UPE. This gave the nanomaterial loaded UPE of the present invention a density that was about 17% less than the density of the standard filled UPE and about equal to the standard UPE. An unsaturated polyester which uses fumed silica to prevent settling of inorganic fillers has a viscosity of in the range of about 8000 to about 12000 centipoise. As can be seen, the use of the nanomaterial provides for a composition having a viscosity which is substantially less than the viscosity of a polyester resin thickened with fumed silica. Rather, the polyester with nanomaterials has a viscosity that is similar to the viscosity of the standard polyester.

Test results of formulation examples are listed in Table 4 in which corrosion and settling ratings of 1-10 for corrosion are based on 1 being worst, and 10 best.

TABLE 4 Standard System System Filled UPE I II Pulse Endurance, min. 3200 4 >6000 Helical coil bond 23 15 20 strength, lbs Dielectric strength, vpm 3000 3500 4300 Corrosion 6 1 9 Settling 1 9 9

TABLE 5 Standard WBPE System III Pulse Endurance, minutes 28 56 Helical coil bond strength, lbs 12 12 Dielectric strength, vpm 5400 3100 Corrosion 10 10 Settling 10 9

As seen from Tables 4 and 5, the System I and II (nanomaterial loaded) UPE'S had significantly better settling properties—that is, the inorganic material did not settle, but remained substantially suspended in the resin. The System I and II coatings also had higher dielectric strengths; and the System II coating had a substantially higher pulse endurance than the standard filled UPE. The System III similarly had a substantially higher pulse endurance than did the standard WBE.

In another set of tests, concentrated dispersions of nanoalumina (50 nm) and nanosilica (20 nm) in an epoxy unsaturated polyester were prepared by SW mill technique. These were used to make versions of precatalyzed epoxy-unsaturated polyester copolymer at 3% and 5% nanoparticles. Test results comparing the epoxy-unsaturated polyester copolymer without the nanomaterials (standard) with the nanomaterial containing epoxy-unsaturated polyester copolymer are set forth below in Tables 6 and 7. The test data for the “standard” is set forth in both Tables 6 and 7.

TABLE 6 Nanoalumina in epoxy unsaturated polyester Standard Experimental Formula 1 Experimental Formula 2 Epoxy- Epoxy-unsaturated Epoxy-unsaturated unsaturated polyester copolymer polyester copolymer polyester with 3% nanoalumina with 5% nanoalumina copolymer (50 nm) (50 nm) Viscosity 569 634 670 125 C gel 10.1 10.3 9.8 Bond Strength, lbs @ 28.5 29.4 29.8 25° C. Bond Strength, lbs @ 5.4 8.2 8.4 150° C. Dielectric Strength, 4938 4597 1369 volt/mil Film thickness 1 mil 0.8 0.9 Pulse Endurance 500′ >6000′

TABLE 7 Nanosilica in epoxy unsaturated polyester Experimental Experimental Standard Formula 3 Formula 4 Epoxy- Epoxy-unsaturated Epoxy-unsaturated unsaturated polyester copolymer polyester copolymer polyester with 3% nanosilica with 5% nanosilica copolymer (20 nm) (20 nm) Viscosity cP 569 606 623 125 C gel 10.1 9.9′ 10.4′ Bond Strength, 28.5 29.9 32.0 lbs @ 25° C. Bond Strength, 5.4 6.5 6.2 lbs @ 150° C. Dielectric 4938 4967 4694 Strength, volt/mil Film thickness 1 mil 0.8 0.8 Pulse 500′ >6000′ Endurance

The nanoalumina and nanosilica in epoxy unsaturated polyester formulas settled badly, so a lot of work was put into finding different additives to help keep the particles suspended. By using a commercially available dispersing agent, the nanoparticles remained suspended long enough to work with.

Table 8, below, shows data comparing Epoxy-unsaturated polyester copolymer loaded with 5% nanosilica (20 nm) with Epoxy-unsaturated polyester copolymer containing no nanosilica.

TABLE 8 Epoxy unsaturated polyester copolymer with 5% Nanosilica Epoxy-unsaturated polyester copolymer Epoxy-unsaturated without polyester copolymer nanomaterials with 5% nanosilica Specific gravity 1.07 g/cm³ 1.10 g/cm³ Gel time @ 125° C. (minutes) 13.7 11.4 Dielectric Strength, v/mil 1294 1241 Thickness, mils 17 18 Tan Delta @ 155° C., 60 Hz, 0.0130 0.1425 500 V Tan Delta @ 180° C., 60 Hz, 0.0380 0.1425 500 V Accelerated aging @ 50° C., viscosity (cP) @ 25° C. At 0 hours 653 856 At 24 hours 669 879 At 48 hours 694 933 At 72 hours 719 971 At 96 hours 741 1014 At 168 hours 807 1136

As seen from the results tabulated in Table 8, the addition of the nanosilica reduced the gel time for the coating, even at similar coating thicknesses. The Tan Delta ratio (the ratio of the storage modulus to the loss modulus values) at 155° C. and at 180° C. was substantially increased by the addition of the nanosilica. Also, as shown graphically in FIG. 1, the nanosilica loaded epoxy-unsaturated polyester copolymer set substantially faster than the epoxy-unsaturated polyester copolymer without nanomaterials. The equation for the trendline for the two curves is shown on the chart of FIG. 1. As seen, the slope of the nanomaterial loaded resin has a slope of about 1.7 whereas the resin without the nanomaterial has a slope of about 0.9. In fact, after 168 hours, the epoxy-unsaturated polyester copolymer without nanomaterials had not even reached the viscosity of the epoxy-unsaturated polyester copolymer with nanomaterials.

Results for polyester with antimony pentoxide nanoparticles (added as a commercially available 40% dispersion) in a standard unsaturated polyester resin are shown below in Table 9. To make the mixture, a commercially available 40% dispersion of antimony pentoxide in polyester was added to the polyester resin. A sufficient amount of the dispersion was added to the polyester resin to produce the 1%, 3% and 5% by weight mixtures set forth below in Table 9.

TABLE 9 Unsaturated Unsaturated Unsaturated polyester polyester Standard polyester with with with unsaturated 1% antimony 3% antimony 5% antimony polyester pentoxide pentoxide pentoxide Viscosity, cP 200 Not tested 315 427 Pulse 4 Not tested Not tested >6000 Endurance, minutes Helical 20.6 14.7 13.2 12.4 Coil bond strength, lbs

As can be seen from Table 9, as the amount of antimony pentoxide added to the polyester was increased, the viscosity of the mixture increased, the pulse endurance of the mixture increased, and the helical coil bond strength of the mixture decreased. The lower bond strengths that resulted are believed to be due to the fact that the polyester used is saturated and unreactive with the unsaturated polyester used in the tests.

Results for water reducible polyamide imide (PAI) with nanoalumina particles are shown below in Table 10. The coating made from this mixture blistered badly when cured at 200° C. This prevented any testing on cured properties, but did not have any bearing on the properties set forth below in Table 10. It has been suggested that it might be possible to bake the coating at 100° C. to remove the bulk of the water and then cure at 200° C. Water is a by-product of the cure, so blistering is still a possibility.

TABLE 10 Water Water reduced PAI at 20% reduced PAI at 20% nonvolatile material with nonvolatile material 5% nanoalumina Viscosity, cP 233 162 % nonvolatile material 20.1 20.8 Appearance Clear dark brown Milky dark brown liquid liquid

In view of the above, it will be seen that we have provided a nanomaterial containing coating, the properties of which surpass the properties of currently available organic resin coatings. Importantly, the coating composition does not require viscosity increasing anti-settling agents to keep the nanomaterial suspended in the mixture. Further, the inclusion of the nanomaterial in the mixture does not significantly altering the rheology of the coating for use in a particular application.

Claims

1. A coating composition for an electromagnetic device to improve the electrical insulation resistance and corrosion protection properties of the device, the coating composition comprising a substantially homogenous mixture of a commercially available coating resin material and an inorganic nanomaterial; the nanomaterial being added to the resin material by between approximately 1-20% part by weight of the composition.

2. The coating composition of claim 1 in which the nanomaterial is an inorganic material in the range of 1-150 nanometers.

3. The coating composition of claim 2 in which the nanomaterial is chosen from the group consisting of silica, alumina, zirconia, antimony pentoxide and combinations thereof.

4. The coating composition of claim 1 in which the nanomaterial comprises between approximately 1-5% part by weight of the composition.

5. The coating composition of claim 1 in which the resin material is a standard filled unsaturated polyester (UPE) coating material.

6. The coating composition of claim 1 in which the resin material is a water borne polyester (WBPE) coating material.

7. The coating composition of claim 1 in which the nanomaterial is dispersed directly into the resin material.

8. The coating composition of claim 1 in which the nanomaterial is pre-dispersed into a carrier appropriate for the resin material with which the nanomaterial is mixed.

9. The coating composition of claim 1 in which the barrier effect resulting from use of the nanomaterial improves electrical and corrosion resistance properties of the coating using lower amounts of the nanomaterial than a coating produced using a standard inorganic filler material.

10. The coating composition of claim 9 in which the barrier effect resulting from use of the nanomaterial further improves the abrasion resistance of the coating.

11. The coating composition of claim 10 in which the barrier effect resulting from use of the nanomaterial produces a coating having a low viscosity relative to systems where fumed silica is used to prevent settling of fillers, thereby providing flexibility in processing options for the coating.

12. The coating composition of claim 11 in which the coating has a viscosity of less than 1000 centipoise.

13. A coating composition for an electromagnetic device to improve the electrical insulation resistance and corrosion protection properties of the device, the coating composition consisting of a substantially homogenous mixture of a commercially available coating resin material and an inorganic nanomaterial; the nanomaterial being added to the resin material by between approximately 1-20% part by weight of the composition; the nanomaterial being chosen from the group consisting of silica, alumina, zirconia, antimony pentoxide and combinations thereof; and the resin material being chosen from the group consisting of unsaturated polyesters, epoxies, urethanes, waterborne polyesters, epoxy emulsions, organic solvent borne alkyds, acrylated and methacrylated urethanes, acrylated and methacrylated epoxies, acrylated and methacrylated polyols, acrylated and methacrylated vegetable oils, and combinations thereof.

14. The coating composition of claim 13 in which the nanomaterial is an inorganic material in the range of 1-150 nanometers.

15. The coating composition of claim 13 in which the nanomaterial comprises between approximately 1-5% part by weight of the composition.

16. A process for producing a coating composition for an electromagnetic device to improve the electrical insulation resistance and corrosion protection properties of the device; the process comprising:

formulating a coating resin using a commercially available resin material;

adding to the resin material between approximately 1-20% part by weight of a nanomaterial;

mixing the resin material and nanomaterial together until a homogeneous composition is achieved.

17. The process of claim 16 in which between approximately 1-5% part by weight of the nanomaterial is added to the resin material.

18. The process of claim 16 in which the nanomaterial is an inorganic material in the range of 1-150 nanometers.

19. The process of claim 16 wherein the nanomaterial is chosen from the group consisting of silica, alumina, zirconia, antimony pentoxide and combinations thereof.

20. The process of claim 16 in which the resin material is a standard filled unsaturated polyester (UPE) coating material.

21. The process of claim 16 in which the resin material is a water borne polyester (WBPE) coating material.

22. The process of claim 16 wherein the step of adding the nanomaterial to the resin comprises dispersing the nanomaterial directly into the resin.

23. The process of claim 16 wherein the step of adding the nanomaterial to the resin comprises pre-dispersing the nanomaterial into a carrier appropriate for the resin material with which the nanomaterial is mixed and mixing the pre-dispersed nanomaterial with the resin.