Electric resistance heating devices – Heating devices – Immersion heater details
Reexamination Certificate
1999-03-24
2001-05-15
Walberg, Teresa (Department: 3742)
Electric resistance heating devices
Heating devices
Immersion heater details
C219S216000, C219S544000
Reexamination Certificate
active
06233398
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to electrical resistance heating elements, and more particularly, to polymer-based resistance heating elements for preconditioning print media for better printing resolution.
BACKGROUND OF THE INVENTION
Thermal ink-jet printers are fast and durable and are known to produce high definition color printouts easily and cost effectively. A typical thermal ink-jet printer is disclosed in U.S. Pat. No. 4,728,963, assigned to Hewlett-Packard Company, Palo Alto, Calif.
The '963 patent discloses an inkjet printer employing a plurality of resister elements to expel droplets of ink to a plurality of nozzles. Upon energizing a particular resister element, a droplet of ink is expelled through a process of vaporization through the nozzle toward the print medium, such as paper, fabric or plastic film. The firing of ink droplets can be microprocessor controlled. As the ink cartridge containing the nozzles is moved repeatedly across the width of the medium to be printed, each of the nozzles is caused to eject ink or refrain from ejecting ink according to the instructions provided by the microprocessor. In order to obtain multi-colored printed images, a plurality of ink-jet cartridges are used, each having a chamber holding a different color ink.
Ink-jet printers are known to have two common deficiencies associated with ink saturation into a porous media, such a paper. The first is that the often liquid inks absorb into the cellulosic fibers of the paper, causing them to swell. This generates unacceptably wavy or “cockled” formations in the ordinarily flat paper media. “Paper cockle” can cause a degradation of print quality due to uncontrolled spacing between the pen and paper, and can sometimes cause the paper to come in contact with the print head, which results in a low quality images and print. The second problem is that adjacent colors of colored ink-jet print tend to run or bleed into one another, causing a reduction in resolution and clarity of the final image.
Heating elements have been proposed for drying the ink rapidly after it has been printed. This has helped to reduce smearing, but has only limited effectiveness in reducing paper cockle or ink migration that occurs during printing, and in the first few fractions of a second after printing.
One solution provided by U.S. Pat. Nos. 5,406,321 and 5,633,668, also assigned to Hewlett-Packard Company, and hereby incorporated by reference, includes a preconditioning preheater disposed along the medium path for heating the medium before it reaches the print area. The preheater of the '321 patent includes a thin heating surface, such as a thin flexible film having a large area suspended in air by a support structure. The preheater has very low thermal mass so as to avoid long warmup intervals, and is supported by securing one edge of the preheater film along the print area with spring tensioners for keeping the film taut. The film is designed to assume a curved edge support, while suspending most of the area of the preheater in air.
While thin film heating elements are known to effectively precondition paper for ink-jet printers, such members represent an additional component of a thermal ink-jet heater, adding to its overall cost. Moreover, thin film heating elements can very easily be dislodged or damaged during heavy use, and may unintentionally cause temporary or permanent thermal damage to the often polymeric medium path immediately adjacent to the print area.
Accordingly, there remains a need for a heating element for preconditioning print media which is more cost effective, and which does not present a possible obstacle in the media pathway or cause thermal distortion of polymeric printer components during use.
SUMMARY OF THE INVENTION
This invention provides heating elements and attendant methods, for preheating a printing media for an ink-jet printer. The heating elements of this invention include an electrical resistance heating member for generating resistance heating when electrically activated and an optional fibrous support layer disposed over said electrical resistance heating member. The resistance heating member and fibrous support layer are encapsulated within a polymeric layer which is resistant to thermal deformation and melting at temperatures ranging from 80-150° C.
The heating elements of this invention are cost effective since they can be made to be integral with the media pathway itself, either as part of the overall molded construction of the printer mid-frame assembly, carriage or paper tray, for example, or melt-bonded, cross-linked, or adhered to the surface of the media pathway after the media pathway is molded. The polymeric layer of the heating elements of this invention can be made of the same polymer as the overall housing of the printer, or a temperature-resistant polymer which has the same, or similar coefficient of thermal expansion as the polymer resin of the media pathway so as to avoid warping or thermal deformation of the pathway proximate to the print area. They are designed to provide heating to the media by direct contact, or radiant or convective heating.
The integrally formed heating element of this invention can reduce a number of components in a thermal ink-jet printer, so as to minimize cost of the overall device, while simultaneously eliminating the problems associated with expensive quartz heaters, or flimsy film heaters which normally require tensioning means and careful handling of the media. The heating elements can be “multipurpose” in that they can provide structural support and preconditioning for the media at the same time.
This invention also provides a heating element for preconditioning a printed medium which includes an electrical resistance heating wire forming a serpentine circuit, a first glass mat disposed on a top surface of said resistance heating wire, and a second glass mat support layer located on a bottom surface of said resistance heating wire. The resistance heating wire and first and second glass mat supporting layers are then disposed within a substantially encapsulating, high temperature, polymeric resin, whereby the first and second glass mat supporting layers provide mechanical support for the electric resistance heating wire during the application of the resin, such as by compression molding.
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pat
Arx Theodore Von
Eckman Charles J.
Rutherford James M.
Campbell Thor
Duane Morris & Heckscher LLP
Walberg Teresa
Watlow Polymer Technologies
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