The present invention relates to an industrial printhead particularly in the form of a configuration of piezoactuated flow channel depositors to form an array that can be used industrially as a reliable high resolution digital printhead for high viscosity fluids.
Piezoactuated needles are known to be useful for the deposition of fluids based on the mechanism described in PCT/HU1999/000015. However, the industrial application of the technology requires that a number of operational characteristics of the system are improved to ensure consistent operation and achieve the resolution required for many applications with a wide range of fluids, including high viscosity fluids.
In this patent we describe a printhead design that overcomes the industrial limitations of the invention described in PCT/HU1999/000015 including the following main elements:
We describe the invention of an industrial printhead configuration that overcomes the limitations of the configuration described in PCT/HU1999/000015 to generate a novel and industrially applicable embodiment of piezo actuated flow channel deposition principle.
An aspect of the invention provides an industrial printhead comprising an array of piezoactuated flow channel dispensers enclosed in a chamber with a multi-orifice plate allowing fluid exit.
Configuration of piezoactuated flow channel depositors to form an array that can be used industrially as a reliable high resolution digital printhead for high viscosity fluids. In order to implement piezoactuated flow channels depositors for reliable industrial use at a suitable resolution for coding and marking and with a wide range of fluids, including high viscosity, several limitations were overcome with the disclosed printhead design that achieve the following improvements: i) Minimising clogging of the dispenser orifices; ii) Increasing the achievable resolution to >5 dpi; iii) Dispensing high viscosity fluids>1000 cposie.
Another aspect of the invention provides a tapered dispenser flow channel wherein the cross section at the inlet is circular with a diameter of >10 mm and tapers to a circular outlet of diameter 5 mm.
Another aspect of the invention provides a locally controlled temperature flow channel tip for control of liquid deposition.
The printhead design described includes an array of flow channels entering a gas-filled chamber that encapsulates the flow channel orifices and acts to manage the fluids that exit the flow channel such that they can be deposited onto a substrate more reliably, at higher resolution and using higher viscosity fluids than an array of flow channels alone.
The chamber design is at the core of this invention and comprises a gas filled headspace, an array of secondary orifices and a means to insert the flow channels into the chamber. A key element of the invention is the geometry of the chamber and the position of the flow channels relative to the chamber nozzle plate orifices and internal structures to direct gas flow in the chamber.
In addition, we describe improvements to the flow channels themselves to enhance performance compared to the flow channels described in (previous patent).
Since surface tension is a function of temperature and generally decreases with increasing temperature, the temperature at which the high shear droplet formation process occurs is found to be important. In this invention we describe a design in which the temperature of the tip of the needle is locally controlled in order to provide localised control of the surface tension of the liquid without changing the liquid bulk temperature.
The bulk temperature of the fluid can be controlled, however for many materials it is not desirable to use elevated temperatures due to materials stability.
This invention is also capable of delivering localised heating such that thermal evaporation may occur alongside high shear droplet formation to create an additional process for droplet formation at the orifice.
A fourth example defines a piezo pulse pattern to remove excess fluid from the nozzle tip. A high amplitude pulse (xx Hz, yy V) that causes the material build-up at the nozzle tip to be removed.
A sixth example defines flow channels with perpendicular piezoactuators to control deposition width. Flow channels actuated by a multiplicity of piezoactuators attached to the needle, in the preferred embodiment there are two piezoactuators attached perpendicular to the flow channel, enabling control of the flow channel perpendicular to the direction of the substrate onto which fluids are being deposited.
This enables several elements of resolution control to be achieved: fixed offsets perpendicular to the substrate travel direction of individual nozzles in an array; oscillation perpendicular to the substrate travel direction.
This invention refers to non-circular cross sections, which enable mechanical control of the piezo-actuator excitation such that off-axis movement is minimised. We refer in this invention specifically to oval, square, triangular section flow channels and variations therein, which are intrinsically stiffer in off axis directions than a circular cross section of comparable wall thickness.
Known in the art is a single piezo-actuated flow channel with constant cross sectional area. However, the fluids that can be transported by this design are limited in viscosity by the overall flow resistance of the channel, which is determined by the cross-sectional geometry required at the outlet for the piezo actuation liquid deposition process to occur. It is known that the channel is filled via capillary flow and that the pressure required is inversely proportional to channel diameter to the third power. Hence it is desirable to reduce the channels flow resistance to enable high viscosity liquids to be transported by capillary flow.
This design is based on the concept that the flow channel is tapered to allow both reduced flow resistance and maintain the required outlet geometry for piezo-actuated liquid deposition to occur. It is known that an outlet geometry with a larger cross sectional area does not enable piezo actuated liquid deposition.
A further embodiment of this concept utilises a constriction of the orifice cross section itself to minimise area of the meniscus, such that statistical variation of the meniscus geometry is minimised.
A tenth example defines a rifled flow channel to reduce resistance to flow in the channel.
Number | Date | Country | Kind |
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1607165.6 | Apr 2016 | GB | national |
Filing Document | Filing Date | Country | Kind |
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PCT/GB2017/051145 | 4/25/2017 | WO | 00 |