Polymer welding using ferromagnetic particles

Details Polymer welding using ferromagnetic particles Polymer welding using ferromagnetic particles

2002-03-28

2004-08-17

Staicovici, Stefan (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Direct application of electrical or wave energy to heat the...

C264S249000, C264S403000, C264S404000, C264S486000, C264S487000, C264S491000, C156S245000, C156S272400, C425S17480R

Reexamination Certificate

active

06776949

ABSTRACT:

BACKGROUND OF THE DISCLOSURE
The disclosure generally relates to bonding techniques and, more particularly, relates to methods and apparatus for bonding polymeric materials.
FIELD OF THE DISCLOSURE
Bonding or welding of two or more polymeric components can be accomplished according to a variety of methods. For example, in the construction of medical devices, such as balloon catheters, or the like, it is known to bring the polymeric components of the catheter into contact with a medium which is at the melting temperature of the polymers. More specifically, the polymeric components can be placed within a heated clam shell, or mold-type of device, which surrounds the polymeric material, and transfers heat from the material of the clam shell to the material of the polymeric component. Alternatively, the polymeric materials can be exposed to a hot air stream which is at a temperature sufficient to melt the polymer. A disadvantage of such systems is the time required to bring the polymer to a molding temperature is so great that the transferred heat tends to dissipate throughout the polymeric material and to any adjoining areas of the device. It is therefore difficult to restrict the area affected by the heat.
According to other techniques, it is known to expose a form of energy to the welding area to heat the polymeric material either by direct absorption by the polymeric material, or indirectly, by adding an energy-absorbing additive through the polymer. For example, with regard to laser welding, it is known to disperse an additive throughout the polymeric material which is adapted to absorb the laser frequency. The polymeric material is heated by the hysteresis losses resulting from the laser frequency absorbing additive. While the polymeric material can be heated quickly according to such a method, and the welding spot can be precisely located by direct placement of the energy-absorbing additive, it is difficult to control the temperature accurately.
In still further systems, it is known to add ferromagnetic materials to the polymeric materials and then expose the combined materials to an electromagnetic field. The polymeric material is thereby heated due to hysteresis losses associated with the vibrating ferromagnetic materials. Moreover, one advantage of such a system over the above-referenced laser welding system, is that temperatures can be more accurately controlled due to the fact that the hysteresis losses will only occur up to the Curie temperature of the ferromagnetic material. By selecting a ferromagnetic material with a Curie temperature equal to a point at which the polymeric materials will bond, it is possible to heat and bond the polymeric materials, without damage to the polymeric materials due to overheating of the material. Moreover, the materials can be heated quickly with such a system.
Additionally, the electromagnetic field can pass through all polymers and therefore heat ferromagnetic material placed on the inside of such structures, therefore enabling heating from the inside out.
While such systems are effective, the addition of the ferromagnetic material to the device being created, has certain inherent drawbacks. For example, the particle size of the ferromagnetic materials currently in use, which are on the order of at least one micron, is such that the particles themselves are often as thick as the walls or individual polymer layers of the devices being created, thereby creating weak spots due to a lack of a chemical connection between the polymer matrix and the ferromagnetic particles. The addition of the ferromagnetic material will also often stiffen the bond site, a disadvantage when the medical device being created must be flexible. A disadvantage of large (i.e., larger than one micron) ferromagnetic particles is the relatively small surface-to-volume ratio in comparison to smaller nano-sized ferromagnetic particles.
SUMMARY OF THE DISCLOSURE
In accordance with one aspect of the disclosure, a method of bonding multiple polymeric elements is provided. The method may comprise the steps of distributing ferromagnetic particles through a molding device, placing multiple polymeric elements into operative association with the molding device, exposing the molding device to an electromagnetic field, and heating any polymeric elements by way of contact with the molding device.
In accordance with another aspect of the disclosure, a method of bonding multiple polymeric elements together is provided. The method may comprise the steps of providing a first polymeric element, providing a second polymeric element, applying a material containing ferromagnetic particles to an outside surface of at least one of the first and second polymeric elements, engaging the first and second polymeric elements with the material containing ferromagnetic particles being placed between the first and second polymeric elements, and exposing the material containing ferromagnetic particles to an electromagnetic field. The exposure causes the material to rise in temperature and thereby fuse the first and second polymeric elements together.
In accordance with another aspect of the disclosure, an apparatus for bonding first and second polymeric elements together is provided. The apparatus may comprise a molding element with a surface complementary to at least one of the first and second polymeric elements, ferromagnetic particles operatively associated with the molding element, and a magnetic field source to subject the molding element to a magnetic field. The molding element surface is adapted to engage at least one of the first and second elements.
These and other aspects and features of the disclosure will become more apparent from the following detailed description, when taken in conjunction with the accompanying drawings.


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