Patent Application
20070142526
Not Applicable
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11252921 | Oct 2005 | US |
| Child | 11680681 | Mar 2007 | US |
