Patent Application
20150251420
This invention relates to inkjet printheads, such as thermal bubble-forming inkjet printheads. It is has been developed primarily for minimizing formation of satellite droplets during droplet ejection.
The Applicant has developed a range of Memjet® inkjet printers as described in, for example, WO2011/143700, WO2011/143699 and WO2009/089567, the contents of which are herein incorporated by reference. Memjet® printers employ a stationary pagewidth printhead in combination with a feed mechanism which feeds print media past the printhead in a single pass. Memjet® printers therefore provide much higher printing speeds than conventional scanning inkjet printers.
An inkjet printhead is comprised of a plurality (typically thousands) of individual inkjet nozzle devices, each supplied with ink. Each inkjet nozzle device typically comprises a firing chamber having a nozzle aperture and an actuator for ejecting ink through the nozzle aperture. The design space for inkjet nozzle devices is vast and a plethora of different nozzle devices have been described in the patent literature, including different types of actuators and different device configurations.
Satellite droplets (or ‘satellites’) are a perennial problem in the field of inkjet printheads. When an ink droplet is ejected from a nozzle aperture, there is a tendency for the tail of the droplet to break up into one or more trailing satellite droplets, each having a volume smaller than the main droplet. If ink droplets are ejected perfectly perpendicularly with respect to a nozzle plate of the printhead, then the satellites will tend to land on print media at the same position as the main droplet, causing minimal print artefacts.
However, inkjet nozzle devices usually have an inherent degree of asymmetry, which means that ink droplets may be ejected somewhat skewed from the nozzle plate of the printhead. With skewed droplet ejection, satellite droplets tend to land on print media at a different position than the main droplet and this causes a reduction in print quality.
Hitherto, most attempts to minimize the effects of satellites have focused on compensating for asymmetry in the nozzle device. For example, U.S. Pat. No. 7,780,271, the contents of which are herein incorporated by reference, describes an inkjet nozzle device having a heating element which is offset from the nozzle aperture. The offset compensates for asymmetric bubble formation in the firing chamber and enables non-skewed droplet ejection.
U.S. Pat. No. 8,267,501 (assigned to Eastman Kodak Company) describes inkjet nozzle devices having multi-lobed nozzle apertures. These multi-lobed nozzle apertures are reported to provide advantages, such as straighter trajectory, shorter tails, better accuracy, smaller ink volume, and less satellite effects.
For the sake of completeness, U.S. Pat. No. 5,812,159 (assigned to Eastman Kodak Company) describes inkjet nozzle devices comprising a heating bar extending across the nozzle aperture. The heating bar actuates droplet ejection by lowering the surface tension of an ink meniscus. With a positive ink pressure, this reduction in surface tension at the meniscus enables controlled droplet ejection upon actuation of the heating bar.
It would be desirable to provide an inkjet nozzle device, which minimizes satellite droplet formation and improves print quality.
In accordance with the present invention, there is provided an inkjet nozzle device comprising:
a firing chamber having a nozzle aperture; and
a heating element for generating gas bubbles in the firing chamber so as to eject ink through the nozzle aperture,
wherein a non-heating stabilizing bar extends across the nozzle aperture.
Inkjet nozzle devices according to the present invention exhibit reduced satellite droplet formation compared to inkjet nozzle devices lacking a stabilizing bar. Without wishing to be bound by theory, it is understood by the present inventors that the stabilizing bar provides more consistent venting of gas bubbles via the nozzle aperture. In conventional nozzle apertures, venting of gas bubbles tends to be a chaotic and non-repeatable process, which affects the consistency of droplet formation and results in a greater number of satellites. Experimentally, it has been observed that the stabilizing bar, which obscures part of the nozzle aperture, provides more consistent droplet formation with fewer satellites and improved overall print quality.
Preferably, the stabilizing bar extends parallel with the heating element (otherwise known in the art as a “resistive heating element” or simply “heater”). Preferably, a central longitudinal axis of the stabilizing bar is aligned with a central longitudinal axis of the heating element. Without wishing to be bound by theory, it is understood by the present inventors that, in conventional nozzle apertures, venting occurs preferentially at the parts of the nozzle aperture in line with the heating element. Advantageously, the stabilizing bar obscures this part of the nozzle aperture to provide more consistent and repeatable venting. Therefore, the stabilizing bar aligned with the heating element results in fewer satellites and improved overall print quality.
Preferably, the nozzle aperture comprises a pair of sub-apertures, the sub-apertures being defined symmetrically on either side of the stabilizing bar. Preferably, each sub-aperture is generally D-shaped.
Preferably, the nozzle aperture is symmetrical about a longitudinal axis and a transverse axis of the stabilizing bar. In other words, the nozzle aperture has mirror symmetry about two orthogonal axes.
In some embodiments, the nozzle aperture is circular and the stabilizing bar extends across a diameter of the nozzle aperture. In such embodiments, a width Ws of the stabilizing bar and a diameter d1 of the nozzle aperture may be in a ratio 2<d1/Ws<10, or preferably a ratio 3<d1/Ws<6
In other embodiments, the nozzle aperture is elliptical and the stabilizing bar extends across a major axis of the nozzle aperture. In such embodiments, a width Ws of the stabilizing bar and a minor axis d2 of the nozzle aperture may be in a ratio 2<d2/Ws<10, or preferably a ratio 3<d2/Ws<6.
Typically, the stabilizing bar obscures from 5 to 50%, or 10 to 40% of an area of the nozzle aperture, relative to a nozzle aperture lacking the stabilizing bar.
Preferably, a width Wh of the heating element and a width Ws of the stabilizing bar are in a ratio of 0.1<Ws/Wh<5, or preferably a ratio 0.5<Ws/Wh<1.25. In some embodiments, Ws=Wh. Typically, the heating element and stabilizing bar are aligned with each other, as described above.
Preferably, the stabilizing bar is coplanar with a roof of the firing chamber, the roof having the nozzle aperture defined therein.
Preferably, the stabilizing bar and the roof are comprised of a same material. Thus, nozzle apertures having the stabilizing bar may be readily fabricated by suitably modifying a mask used for etching the nozzle apertures. Therefore, inkjet nozzle devices according to the present invention do not require any extra fabrication steps compared to conventional devices.
The heating element may be bonded to a floor of the firing chamber or suspended within the firing chamber. Inkjet nozzle devices comprising bonded heating elements are ubiquitous in commercially-available thermal inkjet printers and will be well known to the person skilled in the art. By way of example only, the inkjet nozzle device may be as described in U.S. application Ser. No. 61/859,889 filed on 30 Jul. 2013, the contents of which are herein incorporated by reference. Examples of suspended heating elements may be found in, for example, U.S. Pat. No. 6,755,509, the contents of which are herein incorporated by reference.
The present invention further provides an inkjet printhead having a plurality of nozzle apertures, wherein a non-heating stabilizing bar extends across each nozzle aperture. Preferably, the printhead comprises a plurality of inkjet nozzle devices as described herein.
Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:
Referring initially to
Referring now to
Turning to
For the sake of clarity, like reference numerals are used to indicate like features in the prior art inkjet nozzle device 1 and the inkjet nozzle device 100 in
Referring to
By virtue of the stabilizing bar 16 bisecting the nozzle aperture 10, the nozzle aperture comprises a pair of sub-apertures 18A and 18B, which are defined symmetrically on either side of the stabilizing bar. Each of the sub-apertures 18A and 18B is generally D-shaped, having a straight edge defined by one longitudinal edge of the stabilizing bar 16. It will be readily apparent that the nozzle aperture 10 is symmetrical about a longitudinal axis and an orthogonal transverse axis of the stabilizing bar 16.
The relative dimensions of the stabilizing bar 16, the heating element 14 and the nozzle aperture are not particularly limited, and suitable ranges for these dimensions are described hereinabove. For example, as shown in
Although not exemplified in the drawings, this invention contemplates other nozzle aperture shapes aside from circular nozzle apertures. For example, elliptical nozzle apertures having a major axis aligned with a longitudinal axis of the heating element 14 are within the ambit of the present invention. In such embodiments having elliptical nozzle apertures, the stabilizing bar 16 extends along the major axis of the elliptical nozzle aperture so as to be aligned with the heating element 14.
Referring now to
By contrast,
It will, of course, be appreciated that the present invention has been described by way of example only and that modifications of detail may be made within the scope of the invention, which is defined in the accompanying claims.
| Number | Date | Country | |
|---|---|---|---|
| 61947673 | Mar 2014 | US |
