The present invention relates to an insulating composition, and more particularly to a high temperature resistant insulating composition. The present invention also relates to an insulating wire containing the high temperature resistant insulating composition, and a magnetic element having the insulating wire.
Nowadays, magnetic elements such as inductors and transformers are widely used in power supply apparatuses or many electronic devices to generate induced magnetic fluxes. Generally, a magnetic element includes a coil and a magnetic core. The magnetic core is made of soft magnetic material for example. A common soft magnetic material for producing the magnetic core of the magnetic element is Fe magnetic powder. A process for fabricating a magnetic element (e.g. an inductor) by using Fe magnetic powder will be illustrated in more details as follows. First of all, a conductive wire is provided. Then, the conductive wire is coated with an insulating layer and shaped as a coil. The insulating layer is made of for example polyimide, polyester, polyesterimide or polyamideimide. Such insulating layer could usually withstand a temperature lower than 240° C. The coil is then buried in Fe magnetic powder. The coil and the Fe magnetic powder are compacted in a mold, thereby producing a magnetic element.
Since no high-temperature treatment (e.g. above 400° C.) is used after the magnetic element is formed by compacting and the conductive wire is coated with the ordinary insulating material to form the coil, the convention process for fabricating the magnetic element is very simple and cost-effective. The magnetic element produced by the convention process, however, has larger magnetic loss and poor electromagnetic properties. Therefore, the magnetic element fabricated by this convention process is usually used in the low-end electronic products.
For improving the electromagnetic properties of the magnetic element, another process for fabricating the magnetic element uses other magnetic powder core, take Fe-based magnetic powder core for example, such as FeAlSi magnetic powder core, FeNi magnetic powder core, FeNiMo magnetic powder core, FeSi magnetic powder core, FeSiCr magnetic powder core, FeNiZn magnetic powder core or FeMnZn magnetic powder core. The process for fabricating the magnetic element by using the Fe-based magnetic powder core usually needs a high temperature annealing/sintering procedure at a temperature usually above 400° C. The coil coated with the ordinary insulating material fails to withstand such high-temperature treatment.
A process for fabricating the magnetic element by using the Fe-based magnetic powder core will be illustrated in more details as follows. First of all, Fe-based magnetic powder (e.g. FeAlSi magnetic powder) is compacted under a compacting pressure in a mold. Next, the compacted Fe-based magnetic powder core is subject to an annealing procedure at for example 650° C., thereby producing a magnetic core. Afterwards, the coil coated with the ordinary insulating material is wound around the magnetic core, thereby producing the magnetic element. Although the magnetic element fabricated by this process has good electromagnetic properties, this fabricating process is more complicated, has low throughput, and is not excellently suitable for mass production. In addition, the magnetic element has less space utilization and thus fails to be applied in high power density electronic product.
An object of the present invention provides a high temperature resistant insulating composition including an organic polymer and an inorganic binder. The high temperature resistant insulating composition has flexibility and toughness at a low temperature between −60° C. to about 200° C., for example the room temperature. After a high temperature treatment above 400° C. is performed, the residual of the high temperature resistant insulating composition still possesses high strength and insulating property.
Another object of the present invention provides an insulating wire including a conductive wire and an insulating coating layer sheathing around said conductive wire, in which the insulating coating layer is made of the high temperature resistant insulating composition of the present invention.
A further object of the present invention provides a magnetic element including a magnetic body and a coil wound by the insulating wire. The coil could be directly buried within the magnetic powder core that withstands high temperature annealing/sintering procedure, the process for fabricating magnetic elements according to the present invention has increased throughput, and is suitable for mass production.
In accordance with an aspect of the present invention, there is provided a high temperature resistant insulating composition. The high temperature resistant insulating composition includes an organic polymer and an inorganic binder. The inorganic binder is ranged between 10% and 90% by weight of the high temperature resistant insulating composition. The high temperature resistant insulating composition still possesses strength and insulating property after a high temperature treatment.
In accordance with another aspect of the present invention, there is provided an insulating wire. The insulating wire includes a conductive wire and an insulating coating layer. The insulating coating layer is sheathed around the conductive wire and made of a high temperature resistant insulating composition. The high temperature resistant insulating composition includes an organic polymer and an inorganic binder ranged between 10% and 90% by weight of the high temperature resistant insulating composition. The high temperature resistant insulating composition after a high temperature treatment still possesses strength and insulating property.
In accordance with a further aspect of the present invention, there is provided a magnetic element. The magnetic element includes a magnetic body and an insulating wire. The insulating wire is wound into a coil and at least partially accommodated within the magnetic body. The insulating wire includes a conductive wire and an insulating coating layer. The insulating coating layer is sheathed around the conductive wire and made of a high temperature resistant insulating composition. The high temperature resistant insulating composition includes an organic polymer and an inorganic binder ranged between 10% and 90% by weight of the high temperature resistant insulating composition. The high temperature resistant insulating composition after a high temperature treatment still possesses strength and insulating property.
The above contents of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which:
The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.
The present invention relates to a high temperature resistant insulating composition for use in an insulating coating layer of an insulating conductive wire. The high temperature resistant insulating composition comprises an organic polymer and an inorganic binder. The content of the inorganic binder is ranged between 10% and 90% by weight. The high temperature resistant insulating composition has flexibility and toughness at a low temperature between −60° C. to about 200° C., for example the room temperature. After a high temperature treatment between 400° C. and 1000° C. is performed, the residual of the high temperature resistant insulating composition still possesses high strength and insulating property. An example of the organic polymer includes but is not limited to organic silicon resin, polyimide, polyester, polyesterimide, polyamideimide, or a combination thereof. An example of the inorganic binder includes but is not limited to low melting glass powder, low melting glass powder coated ceramic granule/fiber, a mixture of glass and ceramic, a mixture of boric anhydride and aluminum oxide, or a combination thereof.
Before the high temperature treatment is performed, the particles of the inorganic binder are distributed in the organic polymer. The particles of the inorganic binder may be contacted with or separated from each other, but no strong linkage is created between adjacent particles of the inorganic binder. Meanwhile, the flexibility and strength of the high temperature resistant insulating composition is dependent on the properties of the organic polymer. After the high temperature treatment is performed at a predetermined temperature, the property of the organic polymer is somewhat degraded. For example, some organic polymer (e.g. polyvinyl alcohol) is decomposed, oxidized or vaporized. Due to the high temperature treatment, some linkages will be formed between the particles of the inorganic binder and between the inorganic binder and the high temperature residual of the organic polymer.
Moreover, since the volume resistivity of the high temperature residual of the organic polymer is higher than 1MΩmeter, the high temperature resistant insulating composition after the high temperature treatment still possesses sufficient strength and insulating property. In some cases, during the high temperature annealing procedure, the inorganic binder (e.g. low melting glass) will be transformed into liquid state. So, the tiny cracks between the residuals of the organic polymer after the high temperature treatment will be repaired. As a result, after the temperature is reduced, the high temperature resistant insulating composition still possesses strength and insulating property.
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Hereinafter, the present invention will be described in more detail through the following examples.
In this example, an organic silicon resin 0E6630 (commercially available from DowCorning) is selected as the organic polymer, and glass powder (e.g. glass powder used as seal material in ceramic packages) having a softening point of about 450° C. and particle size of about 10 μm is selected as the inorganic binder, wherein the content of the glass powder is ranged between 10% and 90% by weight. After the insulating composition is uniformly coated on a surface of a conductive wire, the insulating composition is baked and cured to form an insulating coating layer. The cured insulating coating layer is sintered at 650° C. for a certain period. The experiment result shows that the sintered product has sufficient strength and possesses insulating property. The volume resistivity is higher than 1MΩmeter. Moreover, if the content of the glass powder is above 40% by weight, the strength is higher than FeAlSi magnetic powder core.
In this example, polyimide is selected as the organic polymer, and glass powder having a softening point of about 450° C. and particle size of about 10 μm is selected as the inorganic binder, wherein the content of the glass powder is ranged between 10% and 90% by weight. After the insulating composition is uniformly coated on a surface of a conductive wire, the insulating composition is baked and cured to form an insulating coating layer. The cured insulating coating layer is sintered at 600° C. for a certain period. The experiment result shows that the sintered product has sufficient strength and possesses insulating property. The volume resistivity is higher than 1MΩmeter.
In this example, an organic silicon resin 0E6630 (commercially available from DowCorning) is selected as the organic polymer, and glass powder having a softening point of about 450° C. and particle size of about 10 μm is selected as the inorganic binder. In this example, the ratio of the organic polymer to the inorganic binder is 10/10, 10/7, 10/6 and 10/4 in order to formulate different concentration of insulating composition. After each insulating composition is uniformly coated on a surface of a conductive wire (e.g. a copper wire), the insulating composition is baked and cured to form an insulating coating layer having a thickness of about 30 μm. Each insulating wire is wound into a coil and accommodated within the FeAlSi magnetic powder, and compacted under a compacting pressure of 20 ton/cm2. A high temperature annealing/sintering procedure at 650° C. is performed to produce a magnetic element (e.g. an inductor). In comparison to the conventional iron powder core inductor having the similar size and inductance, the magnetic element produced in this example has enhanced efficiency (especially light load efficiency) when applied to a point of load (POL) DC-to-DC converter. The testing results demonstrate that each turn of the coil can withstand a voltage value greater than 12V.
If there is a large difference between the thermal expansion coefficient (CTE) of the conductive wire (e.g. a copper wire) and the thermal expansion coefficient (CTE) of the insulating coating layer, some cracks are possibly generated on the insulating coating layer during the cooling procedure after the high temperature annealing/sintering procedure. For avoiding such problems, the contents and types of the organic polymer and the inorganic binder should be elaborated selected or adjusted in order to adjust the thermal expansion coefficient (CTE) of the insulating coating layer to be ranged between the conductive wire (e.g. a copper wire) and the magnetic material (e.g. 5˜17 10−6). Alternatively, by selecting a low melting or softening glass, the softening/sintering point of the inorganic binder could be reduced to about 300° C.
Since the magnetic element (e.g. an inductor) could withstand a voltage value greater than 12V, the micro cracks of the magnetic element are acceptable because air is sufficient to provide isolative effect. On the other hand, for withstanding a relatively higher voltage (e.g. 600V), the problems of causing cracks on the insulating coating layer need to be solved. In some embodiments, the voltage between adjacent turns of coil could be reduced by changing the winding mechanism.
During the coil and the magnetic powder are compacted in the process of fabricating the magnetic element, the semi-finished product is possibly broken because the coil and the magnetic powder core has different coefficient of elastic recovery. The addition of some organic binder into the magnetic powder core could solve this problem.
During the process of fabricating the magnetic element, the magnetic powder is possibly filled between adjacent turns of the coil, and thus the inductance of the magnetic element is reduced. For solving this problem, the coil could be immersed into the high temperature resistant insulating composition and then cured. As such, the gaps between adjacent turns of the coil are completely sealed and the magnetic powder fails to penetrate into the gaps.
In a case that the magnetic element is subject to the annealing/sintering process in a reduced atmosphere, the conductive wire 2 (e.g. a copper wire) becomes brittle because the oxygen content of the conductive wire 2 is too high. For example, when a reduced gas (e.g. hydrogen gas) reacts with cuprous oxide dissolved in copper, water vapor are generated. If the pressure of the water vapor is too high, some cracks are possibly generated on the conductive wire, and thus the strength and the conductivity of the conductive wire is deteriorated. For solving this problem, the oxygen content of the copper wire is preferably lower than 200 ppm. When conductive wire is made of other metallic material, the oxygen content should also be taken into consideration.
From the above description, the high temperature resistant insulating composition of the present invention comprises an organic polymer and an inorganic binder. The high temperature resistant insulating composition has flexibility and toughness at a low temperature. After a high temperature treatment, the high temperature residual of the organic polymer still has sufficient strength and insulating property. The high temperature resistant insulating composition of the present invention is suitable for fabricating a high-performance winding embedded magnetic element. When the high temperature resistant insulating composition is coated on a surface of the conductive wire, an insulating wire is formed. With the insulating wire, a coil can be made. Since the coil could be directly buried within the magnetic powder core that withstands high temperature annealing/sintering procedure, the electromagnetic properties of the magnetic element are enhanced. In addition, the process for fabricating magnetic elements according to the present invention has increased throughput, and is suitable for mass production. Since the magnetic element has increased space utilization, the magnetic element of the present invention can be applied to high power density electronic product.
While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.
Number | Date | Country | Kind |
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098111575 | Apr 2009 | TW | national |