Patent Application
20150273849
The present disclosure relates generally to methods and devices useful for inkjet print heads, including integrated inductive heating elements and methods of manufacturing of the same.
Inkjet print heads are manufactured using stacked metal plates or stacks of metal and plastic layers. In the case of solid inkjet print heads, the print heads are kept close to a phase change temperature of a solid ink using, for example, adhesively mounted resistance heaters. Injection molding of polymers using overmolding can be used to make inkjet print heads that include integrated resistance heaters at lower cost and with higher part-to-part uniformity than using stacks of metal or metal and plastic plates. However, injection molded inkjet print heads can present thermal challenges since plastic has low thermal conductivity.
Embodiments described herein are directed to methods and assemblies used in ink jet printing. Some embodiments are directed to an assembly for an ink jet print head that includes an ink flow path configured to allow passage of a phase-change ink. One or more inductive heating elements may be configured to heat the ink. Relatively uniform heating throughout the volume of a molded part, such as an inkjet print head, can be achieved by using inductive heating elements. In one aspect, a molded plastic part, such as an inkjet print head, is disclosed that includes a polymeric ink-carrying portion. The ink-carrying portion is capable of inductive heating response. The inductive heating response may be the result of including conductive particles in the ink-carrying portion. Additionally, the print head includes a plurality of inductor coils molded into a polymeric inductive heating portion. The print head further includes a source of alternating current configured to supply current to at least one of the plurality of inductor coils.
A method is disclosed that includes energizing at least one of a plurality of inductor coils arranged in an ink jet print head, the energizing causing inductive heating of an ink-carrying portion of the print head. The method further includes flowing ink through the ink-carrying portion, wherein the inductive heating of the ink-carrying portion maintains a temperature of the ink above a melting temperature.
Finally, a method of making a print head is disclosed that includes forming an ink-carrying portion of a print head that is responsive to inductive heating. The method further includes arranging a plurality of inductor coils in proximity to the ink-carrying portion so that the inductor coils, when energized, induce heat in the ink-carrying portion.
The above summary is not intended to describe each disclosed embodiment or every implementation of the present disclosure. A more complete understanding will become apparent and appreciated by referring to the following detailed description and claims in conjunction with the accompanying drawings.
Throughout the specification reference is made to the appended drawings, where like reference numerals designate like elements, and wherein:
The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.
In the following description, reference is made to the accompanying set of drawings that form a part of the description hereof and in which are shown by way of illustration of several specific embodiments. It is to be understood that other embodiments are contemplated and may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense.
Ink jet printers operate by ejecting small droplets of liquid ink onto print media according to a predetermined pattern. In some implementations, the ink is ejected directly on a final print media, such as paper. In some implementations, the ink is ejected on an intermediate print media, e.g. a print drum, and is then transferred from the intermediate print media to the final print media. Some ink jet printers use cartridges of liquid ink to supply the ink jets. Solid ink printers have the capability of using phase-change ink that is solid at room temperature and is melted before being jetted onto the print media surface. Inks that are solid at room temperature advantageously allow the ink to be transported and loaded into the ink jet printer in solid form, without the packaging or cartridges typically used for liquid inks. In some implementations, the solid ink is melted in a page-width print head which jets the molten ink in a page-width pattern onto an intermediate drum. The pattern on the intermediate drum is transferred onto paper through a pressure nip.
The term phase-change (or solid) inkjet printing refers to image-forming processes and/or image-forming devices that employ inks that are presented in a solid, often wax-like, form. The solid inks can be melted into a liquid form or phase between an ink loading portion of an ink storage (reservoir) and supply device and an ejection-type ink delivery print head. The ejection-type ink delivery print head may dispense the ink presented to it in a melted/liquid form or phase onto a heated intermediate transfer structure such as an intermediate transfer drum, or directly onto a substrate of an image receiving medium, which may also have been preliminarily heated to better accept the melted ink.
Phase-change inkjet printers can melt the solid ink to a liquid at an outlet end of the ink storage and supply device before the ink is fed to the complex plumbing of an inkjet print head. The ink then, in its heated/liquid form or phase, can be jetted from the nozzles using a piezoelectric actuated print head, sometimes referred to as a “jetstack.” The print head can be used to deliver the ink, in its heated/liquid form or phase, to a heated surface of the intermediate transfer apparatus for further transfer to a substrate of image receiving medium, or directly to the substrate where the ink cools to form a sometimes significantly raised printed image on the substrate.
Embodiments described herein are directed to an inkjet print head that includes an inductive ink heater arranged to heat ink in the print head. The inductive ink heater comprises an ink carrying portion and a inductive heating portion proximate to the ink carrying portion. The ink carrying portion includes materials capable of an electromagnetic inductive heating response. The materials in the ink-carrying portion that are responsive to the electromagnetic induction are inductively heated by one or more inductive heating elements, e.g., inductor coils, embedded in the inductive heating portion. The inductive heating response in the ink-carrying portion may be configured to heat the ink by a specified temperature uniformity in the ink-carrying portion. Uniform heating within a specified tolerance across and/or through the ink-carrying portion of the inkjet print head may be achieved by controlling the inductive heating. The print head may further include a source alternating current (AC) coupled to supply current to at least one of the plurality of inductive heating elements.
The inkjet print head may include one or more ink pressure chambers coupled to, or in fluid communication with, one or more ink inlets, via which ink is introduced into the inkjet print head from one or more ink sources, and one or more ink ejection outlets, for example, apertures, orifices or nozzles, via which ink is ejected as a stream of ink droplets to be deposited on a substrate. A typical inkjet printer includes a plurality of print heads with a plurality of ink pressure chambers with each of the plurality of ink pressure chambers being in fluid communication with one or more of the apertures/orifices. Each aperture/orifice may be in fluid communication with a respective ink pressure chamber by way of the ink passage.
In some examples, the print head uses piezoelectric transducers (PZTs) for ink droplet ejection, although other methods of ink droplet ejection. Activation of the PZT 375 causes a pumping action that alternatively draws ink into the ink jet body 365 and expels the ink through ink jet outlet 370 and aperture 380. In this example, as the ink moves through the finger manifold 340, the inductive heating features 398, 399 heat the ink and to maintain the ink carrying portion 398 at a specified temperature and/or specified temperature uniformity as the ink passes through the finger manifold 330.
In some embodiments, each inductive heating portion is configured so that the magnetic field generated by the inductive heating portion is stronger at an ink-carrying portion nearest to the inductive heating portion when compared to a channel wall disposed at an opposite side of the ink flow path. The channel wall disposed at the opposing side may also include an ink-carrying portion capable of inductive response. For example, with reference to
When heating portions of the injection molded inkjet print head, it can be difficult to control the heat flux introduced to and permeating the solid wax ink in a jetstack. In the solid ink heating/melting process, the ability to heat the ink to a specified temperature within a specified time accelerates the heating process in a controlled manner. Furthermore, uniform heating of the inkjet print head to within a specified tolerance helps provide consistent inkjet drop size and consistent velocity when the ink is jetted from the print head.
Some embodiments use an inductive heating portion comprising a plurality of small inductor coils co-molded into the inductive heating portion of the print head to achieve more precise heating. Example embodiments include inkjet print heads that have an injection-molded, polymeric induction heating features including the ink-carrying portion capable of an inductive response and a plurality of inductor coils molded into an inductive heating portion of the print head. The inductor coils are configured to generate a magnetic field when energized by an alternating current (AC) and induce heat in the ink-carrying portion. The ink-carrying portion comprises conductive particles and/or filler material that is capable of an inductive response. In some implementations, particles and/or filler may be semiconductive, however, both conductive and semiconductive particles/filler are collectively referred to herein using the term “conductive” with the understanding that the particles and/or filler may be conductive, semiconductive, or a combination of conductive and semiconductive. The inductor coils are configured to be connected to a source that supplies AC to at least one of the plurality of inductor coils. In some embodiments, there may be multiple sources of AC, e.g., each of the inductor coils may be configured to be respectively coupled to one of the AC sources or groups of the inductor coils may be configured to be coupled to one of the AC sources. When energized, the inductor coils produce a magnetic field that can interact with the conductive particles and/or filler within the flux lines of the magnetic field, the magnetic field producing eddy currents in the particles/filler that induce heat in the particles and/or filler. As referred to herein induction responsive particles comprise discrete conductive particles or regions disposed in a binder (which may or may not be inductively responsive), e.g., a polymeric binder. An inductively responsive filler material comprises a homogeneous portion of inductively responsive material.
In
When energized, the inductor coils are configured to generate a magnetic field that induces eddy currents that subsequently heat the conductive particles. At least one of the plurality of inductor coils can be energized by a source of high frequency, low amperage alternating current, e.g., 20 MHz, 0.5 A and 20 kV, supplied by a source not illustrated in
The conductive particles may have any shape and size that is capable of responding to the magnetic field generated by the inductor coils when they are energized. In some embodiments the particles may include flakes that have a thickness up to 0.005 inches, and length and width dimensions between about 0.01 inches and about one inch, depending on the particle size needed to achieve the specified spatial temperature uniformity. More specifically, the particles and/or filler may include flakes that have a thickness no more than 0.001 inches, with the largest dimension not larger than about 0.5 inches. The conductive particles and/or filler may also include filaments that have a size (length) selected to reduce the possibility of having continuous circuits form in the mixture. The filaments may have a diameter of no more than 0.01 inches and a length of no more than two inches, for example. More specifically, the filaments may have a diameter of no more than 0.005 inches and a length of no more than one inch. The conductive particles and/or filler may also be a combination of flakes, filaments or some other type of particle or filler. In some embodiments, the particles and/or filler can be selected to have specified electrical and thermal properties. For example the particles and/or filler material may be selected to have electrical conductivity and thermal conductivity within specified ranges. In some implementations, the particles include a first group of particles that have electrical conductivity within a specified range and a second group of particles that have thermal conductivity within a specified range. Similarly, the filler may include a first material that provides electrical conductivity within a specified range and a second material that provides thermal conductivity within a specified range. The combination of both electrically conductive and thermally conductive particles and/or filler materials can be employed to achieve a target temperature uniformity of the ink carrying portion, for example. In some implementations, ferric particles and/or filler provide the electromagnetically inductive response and copper particles and/or filler enhance the thermal spreading.
The coils 701, 702 may be electrically connected to each other and/or the AC source 710 in any convenient configuration. For example, the coils 701, 702 may be connected in series or parallel or in any combination of series and parallel connections. The frequency provided by the AC source 710 may be at least 1 MHz, and more specifically may be between 20 MHz and 100 MHz. In some embodiments, the AC source 710 operates at a voltage of at least 10 kV, less than 1 A, and at least 1 MHz. More specifically, the AC source 710 operates at a voltage greater than 20 kV, about 0.5 A and between about 20 MHz and 100 MHz.
In some embodiments, the AC current to groups of inductor coils or to each inductor coil individually can be independently controlled. For example, in some configurations, each of the individual coils or groups of coils may be connected to a dedicated controllable AC source. In some configurations the coils or groups of coils can be independently energized using controllable switches or solenoids that electrically connect and disconnect the coils to an AC source.
n. In some embodiments, the desired heat distribution or temperature profile includes maintaining the temperature uniformity across the regions 831, 832, 833 to within about ±5° C., ±1° C., ±0.5° C., or even about ±0.25° C., for example.
The electrical signals from the temperature sensors 851, 852, 853 provide temperature feedback signals for the controller 811. Based on the temperature feedback signals, the controller selectively couples one or more of the groups of coils 841, 842, 843 to the AC source 825. By selecting the groups of coils 841, 842, 843 that are energized based on the temperature feedback signals, the controller can maintain the temperature uniformity across the regions 831, 832, 833 to within a specified tolerance range. For example, based on the temperature feedback signals, at a first point in time all the coil groups 841, 842, 843 may be connected through the switches 861, 862, 863 to the AC source 825; at a second point in time only one of the coil groups may be connected to the AC source 825; at a third point in time none of the coil groups is connected to the AC source 825.
Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range.
Particular materials and dimensions thereof recited in the disclosed examples, as well as other conditions and details, should not be construed to unduly limit this disclosure. Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as representative forms of implementing the claims.
