Patent Application
20170282555
The invention relates to a jetting method of a liquid wherein the jetting viscosity, i.e. the viscosity at the jetting temperature, is at least 20 mPa·s and wherein the architecture of a valvejet printhead and especially a nozzle in the valvejet printhead is adapted to jet reliable the liquid with a good performance.
Thermal printheads are cheap and disposable and restricted to water based inks (integrated with ink supply). They have been used (for a few decades) in the office (SOHO—printers from HP™, Canon™, Epson™, . . . ) and more recently in commercial/transactional printing such as HP™ T300 and T400. The use of water based resin inks in thermal printheads for the wide format graphics (Sign & Display) market was demonstrated by HP™ on the exhibition drupa 2008.
Piezoelectric printheads are more expensive, require a separate ink supply and are capable to deal with a broad range of ink chemistries (hot melt, water, oil, solvent and UV curable inks). They are also used in commercial/transactional printing in combination with water based inks and to a lesser extent oil based inks. Web fed presses for transactional printing from Océ™, Miyakoshi™, Impika™, Dainippon Screen™ and sheet fed inkjet presses from Fuji™, Landa™ and Screen™ use piezo printheads from Kyocera™, Panasonic™ or Dimatix™ in combination with water based dye or water based pigment inks.
The solvent, UV curable and water based resin inks in piezo printheads are used in the wide format graphics market for applications such as industrial print and sign & display).
Through-flow piezoelectric printheads are predominantly used in the ceramics market with oil based inks. The dominant printhead in the market is Xaar™ 1001. This through-flow piezoelectric printhead is also used in inkjet label presses from Durst™, SPGPrints™, FFEI™ and EFI™ (with UV IJ inks). Toshiba Tec™ through flow printheads are used by Riso Kagaku Corporation™ for IJ office printers with oil based inks.
Typically the jetting viscosity of the state of the art for jettable liquids is from 3 mPa·s to 15 mPa·s. None of the inkjet inks used in the field described above, such as commercial/transactional inkjet printing or wide format inkjet printing have a jetting viscosity larger than 15 mPa·s.
There is a need to improve the performance and cost of the current low viscosity inkjet inks for several applications. An increase of jetting ink viscosity could allow to improve the adhesion on several ink receivers such as textiles or glasses, due to a larger choice in raw materials. This formulation latitude of the jettable liquid allows, for example, to include oligomers and/or polymers and/or pigments in a higher amount. This results in a wider accessible receiver range; reduced odour and migration and improved cure speed for UV curable jettable liquids; environmental, health and safety benefits (EH&S); physical properties benefits; reduced raw material costs and/or reduced ink consumption for higher pigment loads.
Another benefit of higher pigment load for a white UV curable inkjet ink with a jetting viscosity at least 20 mPa·s is the higher opaqueness of the jetted ink layer. In addition, a higher pigment load in an UV curable colour inkjet ink with a jetting viscosity at least 20 mPa·s, allows to reduce the ink layer thickness resulting in improved stretchability and flexibility.
Previous work on higher viscous inks in standard printheads exhibited serious difficulties. The main problem was the formation of satellites and mist particles due to an increased tail length of an inkjet droplet jetted at higher jetting viscosity. An increase of a few mPa·s from 6 mPa·s to 12 mPa·s was sufficient to generate many satellites and mist particles per ink droplet.
Also in literature examples of the increase in tail length and satellite formation with increased jetting viscosity in standard printheads has been disclosed. In Figure 4.7 of “WIJSMAN, HERMAN. Structure and fluid-dynamics in piezo inkjet printheads. Thesis University Twente. 2008”, the pinch-off-time of the tail was measured as a function of ink viscosity and surface tension. Higher viscosity and lower surface tension gave rise to an increase in pinch-off-time which negatively influences the jetting performance. As a higher surface tension of the ink would also reduce the adhesion on a wide range of ink receivers, it should be clear that further improvement of jetting performance is still required.
In order to overcome the problems described above, preferred embodiments of the present invention have been realised by a high viscosity jetting method, as defined below and a valvejet printhead suitable for a high viscosity jetting method, as also defined below.
It was surprisingly found that good performance and reliability for jettable liquids with a jetting viscosity of at least 20 mPa·s could be achieved by modification of the valvejet printhead architecture, more specifically the geometry of a nozzle (500) in the valvejet printhead.
In the high viscosity jetting method according to a preferred embodiment of the present invention, a liquid is jetted by a valvejet printhead through a nozzle (500); wherein a section of a nozzle (Ns) has a shape (S) comprising an outer edge (OE) with a minimum covering circle (C); wherein the maximum distance (D) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) is greater or equal than the minimum distance (d) from the outer edge (OE) to the centre (c) from the minimum covering circle (C) times 1.2; and wherein the jetting viscosity of the liquid is from 20 mPa·s, gave a better jetting performance than a outer edge (OE) similar to a circle, as in the state-of-the-art. Probably the differences between the maximum distance (D) and minimum distance (d) guides the liquid while jetting to optimal jetting performance such as drop forming and less or no satellite forming by having smaller pinch-off-times and/or tail length of jetted liquid. In a preferred embodiment the jetting viscosity is from 20 mPa·s to 3,000 mPa·s and in a more preferred embodiment the jetting viscosity is from 25 mPa·s to 1,000 mPa·s and in a most preferred embodiment the jetting viscosity is from 30 mPa·s to 500 mPa·s.
In a preferred embodiment the liquid is jetted by a valvejet printhead through a nozzle (500); wherein a section of a nozzle (Ns) has a shape (S) comprising an outer edge (OE) with a minimum covering circle (C); wherein the maximum distance (D) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) is greater or equal than the minimum distance (d) from the outer edge (OE) to the centre (c) from the minimum covering circle (C) times the square root of two; and wherein the jetting viscosity of the liquid is from 20 mPa·s, gave a better jetting performance than a outer edge (OE) similar to a circle, as in the state-of-the-art. Probably the differences between the maximum distance (D) and minimum distance (d) guides the liquid while jetting to optimal jetting performance such as drop forming and less or no satellite forming by having smaller pinch-off-times and/or tail length of jetted liquid. In a preferred embodiment the jetting viscosity is from 20 mPa·s to 3,000 mPa·s and in a more preferred embodiment the jetting viscosity is from 25 mPa·s to 1,000 mPa·s.
The present invention overcomes in particular the problem of spray and elongated tail of the jetted liquid without introducing a reduction in print speed or fine ink channel architecture optimizations. In mathematical terms the distances (D,d) in the embodiment meet the following equation:
D>d×1.2
In a preferred embodiment the maximum distance (D) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) is greater than the minimum distance (d) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) times the square root of three; and in a more preferred embodiment the maximum distance (D) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) is greater than the minimum distance (d) from the outer edge (OE) to the centre (c) from the minimum covering circle (C) times the square root of four; and in the most preferred embodiment the maximum distance (D) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) is greater than the minimum distance (d) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) times the square root of five.
In a preferred embodiment the maximum distance (D) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) is smaller than the minimum distance (d) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) times 150; and in a more preferred embodiment the maximum distance (D) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) is smaller than the minimum distance (d) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) times 100; and in a most preferred embodiment the maximum distance (D) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) is smaller than the minimum distance (d) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) times 50.
In a preferred embodiment the maximum distance (D) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) is between 5 μm and 0.50 mm. The area of the shape (S) of the nozzle is preferably between 50 μm2 and 1 mm2.
It was found that symmetry of the shape is important to have a good jetting performance, the shape (S) comprises preferably a set of axes of symmetry through the centre (c) of the minimum covering circle (C), more preferably comprises one or more axes of symmetry through the centre (c) of the minimum covering circle (C) and most preferably comprises two or more axes of symmetry through the centre (c) of the minimum covering circle (C). The symmetry of the shape minimizes disturbing effects in the flow of the liquid which results in a good jetting performance.
To achieve symmetry, the shape (S) with the outer edge (OE) is preferably similar to a shape defined by the formula:
This formula is a generalization of the superellipse and was first proposed by Johan Gielis. Johan Gielis suggested that this formula, also called the superformula of Gielis, can be used to describe many complex shapes and curves that are found in nature wherein symmetry is evident. The formula was further popularized by Piet Hein, a Danish mathematician.
Further advantages and preferred embodiments of the present invention will become apparent from the following description.
In a preferred embodiment of the present invention, the method comprises a step of recirculating the high viscosity liquid through the valvejet printhead. The advantage to recirculate the high viscosity liquids in the valvejet printhead is that the liquid is in motion so less inertia is involved resulting in a better jettability of the high viscosity liquid.
The liquid is in a preferred embodiment an UV curable inkjet ink, a water based pigment ink or a water based resin inkjet ink, more preferably a solventless UV curable inkjet ink. A solventless UV curable inkjet ink requires less printer maintenance versus a liquid such as a solvent inkjet ink. Generally also a wider range of ink receivers can be addressed by an UV curable inkjet ink. If the liquid is an UV curable inkjet ink, the high viscosity jetting method preferably comprises a step of solidifying the jetted liquid on the receiver (200) by a UV radiation means.
In a preferred embodiment, an axis of symmetry from the set of axes of symmetry is parallel or perpendicular to the direction of the nozzle row. In an inkjet printing system the direction of the nozzle row is mostly parallel to the print direction, such as in a wide-format inkjet printer. It was surprisingly found that the axis of symmetry of this preferred embodiment influences the drop placement in the print direction in the advantage of better print quality. A possible reason is that the axes of symmetry parallel or perpendicular to the direction of the nozzle row influences favourable the dot accuracy in slow scan direction or fast scan direction of the inkjet printer which results in a better print quality.
Recirculation of a high viscosity liquid in a valvejet printhead avoids sedimentations, for example of pigment particles, in the valvejet printhead (e.g. in the liquid channels or manifolds (102)). Sedimentation may cause obstructions in the ink flow thereby negatively influencing the jetting performances. The recirculation of a liquid results also in less inertia of the liquid. In a preferred embodiment the recirculation of the high viscosity liquid occurs in a valvejet printhead, also called through-flow valvejet printhead, wherein the high viscosity liquid is recirculated in a continuous flow through a liquid transport channel where the pressure to the liquid is applied by a droplet forming means and wherein the liquid transport channel is in contact with the nozzle plate (
A printhead is a means for jetting a liquid on a receiver (200) through a nozzle (500). The nozzle (500) may be comprised in a nozzle plate (150) which is attached to the printhead. A set of liquid channels, comprised in the printhead, corresponds to a nozzle (500) of the printhead which means that the liquid in the set of liquid channels can leave the corresponding nozzle (500) in the jetting method. The liquid is preferably an ink, more preferably an UV curable inkjet ink or water based inkjet ink, such as a water based resin inkjet ink. The liquid used to jet by a printhead is also called a jettable liquid. A high viscosity jetting method with UV curable inkjet ink is called a high viscosity UV curable jetting method. A high viscosity jetting method with water based inkjet ink is called a high viscosity water base jetting method.
The high viscosity jetting method of the embodiment may be performed by an inkjet printing system. The way to incorporate printheads into an inkjet printing system is well-known to the skilled person.
A printhead may be any type of printhead such as a valvejet printhead, piezoelectric printhead, thermal printhead, a continuous printhead type, electrostatic drop on demand printhead type or acoustic drop on demand printhead type or a page-wide printhead array, also called a page-wide inkjet array.
A printhead comprises a set of master inlets (101) to provide the printhead with a liquid from a set of external liquid feeding units (300). Preferably the printhead comprises a set of master outlets (111) to perform a recirculation of the liquid through the printhead. The recirculation may be done before the droplet forming means but it is more preferred that the recirculation is done in the printhead itself, so called through-flow printheads. The continuous flow of the liquid in a through-flow printheads removes air bubbles and agglomerated particles from the liquid channels of the printhead, thereby avoiding blocked nozzles that prevent jetting of the liquid. The continuous flow prevents sedimentation and ensures a consistent jetting temperature and jetting viscosity. It also facilitates auto-recovery of blocked nozzles which minimizes liquid and receiver (200) wastage.
The number of master inlets in the set of master inlets is preferably from 1 to 12 master inlets, more preferably from 1 to 6 master inlets and most preferably from 1 to 4 master inlets. The set of liquid channels that corresponds to the nozzle (500) are replenished via one or more master inlets of the set of master inlets.
In a preferred embodiment prior to the replenishing of a set of liquid channels, a set of liquids is mixed to a jettable liquid that replenishes the set of liquid channels. The mixing to a jettable liquid is preferably performed by a mixing means, also called a mixer, preferably comprised in the printhead wherein the mixing means is attached to the set of master inlets and the set of liquid channels. The mixing means may comprise a stirring device in a liquid container, such as a manifold (102) in the printhead, wherein the set of liquids are mixed by a mixer. The mixing to a jettable liquid also means the dilution of liquids to a jettable liquid. The late mixing of a set of liquids for jettable liquid has the benefit that sedimentation can be avoided for jettable liquids of limited dispersion stability.
The liquid leaves the liquid channels by a droplet forming means (103), through the nozzle (500) that corresponds to the liquid channels. The droplet forming means (103) are comprised in the printhead. The droplet forming means (103) are activating the liquid channels to move the liquid out the printhead through the nozzle (500) that corresponds to the liquid channels.
The valvejet printhead is suitable for jetting a liquid having a jetting viscosity of 20 mPa·s to 3000 mPa·s. A preferred printhead is suitable for jetting a liquid having a jetting viscosity of 20 mPa·s to 200 mPa·s and a more preferred printhead is suitable for jetting a liquid having a jetting viscosity of 30 mPa·s to 150 mPa·s.
The maximum drop size in a print head is preferably lower than 50 pL, more preferably lower than 30 pL and most preferably lower than 15 pL.
Preferred valvejet printheads have a nozzle diameter between 45 and 600 μm. The valvejet printheads comprising a plurality of micro valves, allow for a resolution of 15 to 150 dpi that is preferred for having high productivity while not comprising image quality. A valvejet printhead is also called coil package of micro valves or a dispensing module of micro valves. The way to incorporate valvejet printheads into an inkjet printing device is well-known to the skilled person. For example, US 2012105522 (MATTHEWS RESOURCES INC) discloses a valvejet printer including a solenoid coil and a plunger rod having a magnetically susceptible shank. Suitable commercial valvejet printheads are chromoJET™ 200, 400 and 800 from Zimmer, Printos™ P16 from VideoJet and the coil packages of micro valve SMLD 300's from Fritz Gyger™. A nozzle plate of a valvejet printhead is often called a faceplate and is preferably made from stainless steel.
The droplet forming means (103) of a valvejet printhead controls each micro valve in the valvejet printhead by actuating electromagnetically to close or to open the micro valve so that the medium flows through the liquid channel. Valvejet printheads preferably have a maximum dispensing frequency up to 3000 Hz.
In a preferred embodiment the valvejet printhead the minimum drop size of one single droplet, also called minimal dispensing volume, is from 1 nL (=nanoliter) to 500 μL (=microliter), in a more preferred embodiment the minimum drop size is from 10 nL to 50 μL, in a most preferred embodiment the minimum drop size is from 10 nL to 300 μL. By using multiple single droplets, higher drop sizes may be achieved.
In a preferred embodiment the valvejet printhead has a native print resolution from 10 DPI to 300 DPI, in a more preferred embodiment the valvejet printhead has a native print resolution from 20 DPI to 200 DPI and in a most preferred embodiment the valvejet printhead has a native print resolution from 50 DPI to 200 DPI.
In a preferred embodiment with the valvejet printhead the jetting viscosity is from 20 mPa·s to 3000 mPa·s more preferably from 25 mPa·s to 1000 mPa·s and most preferably from 30 mPa·s to 500 mPa·s.
In a preferred embodiment with the valvejet printhead the jetting temperature is from 10° C. to 100° C. more preferably from 20° C. to 60° C. and most preferably from 25° C. to 50° C.
The high viscosity jetting method is preferably performed by an inkjet printing system. The way to incorporate printheads into an inkjet printing system is well-known to the skilled person. More information about inkjet printing systems is disclosed in STEPHEN F. POND. Inkjet technology and Product development strategies. United States of America: Torrey Pines Research, 2000, ISBN 0970086008.
An inkjet printing system, such as an inkjet printer, is a marking device that is using a printhead or a printhead assembly with one or more printheads, which jets ink on a receiver (200). A pattern that is marked by jetting of the inkjet printing system on a receiver (200) is preferably an image. The pattern may be achromatic or chromatic colour.
A preferred embodiment of the inkjet printing system is that the inkjet printing system is an inkjet printer and more preferably a wide-format inkjet printer. Wide-format inkjet printers are generally accepted to be any inkjet printer with a print width over 17 inch. Digital printers with a print width over the 100 inch are generally called super-wide printers or grand format printers. Wide-format printers are mostly used to print banners, posters, textiles and general signage and in some cases may be more economical than short-run methods such as screen printing. Wide format printers generally use a roll of substrate rather than individual sheets of substrate but today also wide format printers exist with a printing table whereon substrate is loaded.
A printing table in the inkjet printing system may move under a printhead or a gantry may move a printhead over the printing table. These so called flat-table digital printers most often are used for the printing of planar substrates, ridged substrates and sheets of flexible substrates. They may incorporate IR-dryers or UV-dryers to prevent prints from sticking to each other as they are produced. An example of a wide-format printer and more specific a flat-table digital printer is disclosed in EP1881903 B (AGFA GRAPHICS NV).
The high viscosity jetting method may be comprised in a single pass printing method. In a single pass printing method the inkjet printheads usually remain stationary and the substrate surface is transported once under the one or more inkjet printheads. In a single pass printing method the method may be performed by using page wide inkjet printheads or multiple staggered inkjet printheads which cover the entire width of the receiver (200). An example of a single pass printing method is disclosed in EP 2633998 A (AGFA GRAPHICS NV).
The inkjet printing system may mark a broad range of substrates such as folding carton, acrylic plates, honeycomb board, corrugated board, foam, medium density fibreboard, solid board, rigid paper board, fluted core board, plastics, aluminium composite material, foam board, corrugated plastic, carpet, textile, thin aluminium, paper, rubber, adhesives, vinyl, veneer, varnish blankets, wood, flexographic plates, metal based plates, fibreglass, transparency foils, adhesive PVC sheets and others.
Preferably the inkjet printing system comprises one or more printheads jetting UV curable ink to mark a substrate and a UV source, as dryer system, to cure the inks after marking. Spreading of a UV curable inkjet ink on a substrate may be controlled by a partial curing or “pin curing” treatment wherein the ink droplet is “pinned”, i.e. immobilized whereafter no further spreading occurs. For example, WO 2004/002746 (INCA) discloses an inkjet printing method of printing an area of a substrate in a plurality of passes using curable ink, the method comprising depositing a first pass of ink on the area; partially curing ink deposited in the first pass; depositing a second pass of ink on the area; and fully curing the ink on the area.
A preferred configuration of UV source is a mercury vapour lamp. Within a quartz glass tube containing e.g. charged mercury, energy is added, and the mercury is vaporized and ionized. As a result of the vaporization and ionization, the high-energy free-for-all of mercury atoms, ions, and free electrons results in excited states of many of the mercury atoms and ions. As they settle back down to their ground state, radiation is emitted. By controlling the pressure that exists in the lamp, the wavelength of the radiation that is emitted can be somewhat accurately controlled, the goal being of course to ensure that much of the radiation that is emitted falls in the ultraviolet portion of the spectrum, and at wavelengths that will be effective for UV curable ink curing. Another preferred UV source is an UV-Light Emitting Diode, also called an UV-LED.
The inkjet printing system that performs the embodiment may be used to create a structure through a sequential layering process by jetting sequential layers, also called additive manufacturing or 3D inkjet printing. So the high viscosity jetting method of the embodiment is preferably comprised in a 3D inkjet printing method. The objects that may be manufactured additively by the embodiment of the inkjet printing system can be used anywhere throughout the product life cycle, from pre-production (i.e. rapid prototyping) to full-scale production (i.e. rapid manufacturing), in addition to tooling applications and post-production customization. Preferably the object jetted in additive layers by the inkjet printing system is a flexographic printing plate. An example of such a flexographic printing plate manufactured by an inkjet printing system is disclosed in EP2465678 B (AGFA GRAPHICS NV).
The inkjet printing system that performs the embodiment may be used to create relief, such as topographic structures on an object, by jetting a sequential set of layers, e.g. for manufacturing an embossing plate. An example of such relief printing is disclosed in US 20100221504 (JOERG BAUER). So the high viscosity jetting method of the embodiment is preferably comprised in a relief inkjet printing method. Jetting with liquids at a jetting viscosity of at least 20 mPa·s allows to add high molecular weight chemical compounds for a better result in relief inkjet printing, such as the harness of the relief for a embossing plate or flexographic plate.
The inkjet printing system of the embodiment may be used to create printing plates used for computer-to-plate (CTP) systems in which a proprietary liquid is jetted onto a metal base to create an imaged plate from the digital record. So the high viscosity jetting method of the embodiment is preferably comprised in an inkjet computer-to-plate manufacturing method. These plates require no processing or post-baking and can be used immediately after the ink-jet imaging is complete. Another advantage is that platesetters with an inkjet printing system is less expensive than laser or thermal equipment normally used in computer-to-plate (CTP) systems. Preferably the object that may be jetted by the embodiment of the inkjet printing system is a lithographic printing plate. An example of such a lithographic printing plate manufactured by an inkjet printing system is disclosed EP1179422 B (AGFA GRAPHICS NV). Jetting with liquids at a jetting viscosity of at least 20 mPa·s allows to add high molecular weight chemical compounds for a better result in inkjet computer-to-plate method such as the offset ink accepting capability.
Preferably the inkjet printing system is a textile inkjet printing system, performing a textile inkjet printing method. In industrial textile inkjet printing systems, printing on multiple textiles simultaneously is an advantage for producing printed textiles in an economical manner. So the high viscosity jetting method of the embodiment is preferably comprised in a textile printing method by using a printhead. Jetting with liquids at a jetting viscosity of at least 20 mPa·s allows to add high molecular weight chemical compounds for a better result in textile inkjet printing method such as flexibility of the jetted liquid after drying on a textile.
Preferably the inkjet printing system is a ceramic inkjet printing system, performing a ceramic inkjet printing method. In ceramic inkjet printing systems printing on multiple ceramics simultaneously is an advantage for producing printed ceramics in an economical manner. So the high viscosity jetting method of the embodiment is preferably comprised in a printing method on ceramics by using a printhead. Jetting with liquids at a jetting viscosity of at least 20 mPa·s allows to add high molecular weight chemical compounds, such as sub-micron glass particles and inorganic pigments for a better result in ceramic inkjet printing method.
Preferably the inkjet printing system is a glass inkjet printing system, performing a glass inkjet printing method. In glass inkjet printing systems printing on multiple glasses simultaneous is an advantage for producing printed glasses in an economical manner. So the high viscosity jetting method of the embodiment is preferably comprised in a printing method on glass by using a printhead.
Preferably the inkjet printing system is a decoration inkjet printing system, performing a decoration inkjet printing method, to create digital printed wallpaper, laminate, digital printed objects such as flat workpieces, bottles, butter boats or crowns of bottles.
Preferably the inkjet printing system is comprised in an electronic circuit manufacturing system and the high viscosity jetting method of the embodiment is comprised in an electronic circuit manufacturing method wherein the liquid is a inkjet liquid with conductive particles, often generally called conductive inkjet liquid.
The embodiment is preferably performed by an industrial inkjet printing system such as a textile inkjet printing system, ceramic inkjet printing system, glass inkjet printing system, decoration inkjet printing system.
The embodiment of the high viscosity jetting method is preferably comprised in an industrial inkjet printing method such as a textile inkjet printing method, a ceramic inkjet printing method, a glass inkjet printing method, a decoration inkjet printing method.
A nozzle (500) is an orifice in a nozzle plate (150) of a valvejet printhead through which a liquid is jetted on a receiver (200).
The length of a nozzle is the distance between the entrance of the nozzle and the exit of the nozzle. If the nozzle (500) is comprised in a nozzle plate (150), the length of the nozzle is defined by the thickness of the nozzle plate.
The flow path of the liquid is from the entrance of the nozzle to the exit of the nozzle. Typically the distance between the receiver (200) and the exit of the nozzle, also called the printhead gap, is between 100 μm and 10000 μm.
A section of a nozzle is the intersection of the nozzle and a plane parallel to the plane wherein the outlet of the nozzle is located.
A sub-nozzle (550) of a nozzle is the part of the nozzle between two different sections of the nozzle wherein the section nearest to the entrance of the nozzle is called the inlet of the sub-nozzle (550) and the section nearest to the exit of the nozzle is called the outlet of the sub-nozzle (550).
The inlet of a nozzle is the intersection of the nozzle and the plane wherein the backside of the nozzle plate is comprised so the inlet of the nozzle is facing a set of liquid channels. The inlet of the nozzle is thus a section of the nozzle.
The outlet of a nozzle is the intersection of the nozzle and the plane wherein the front side of the nozzle plate is comprised so the outlet of the nozzle is facing the receiver (200) of the jetted liquid. The outlet of the nozzle is thus a section of the nozzle.
The shape of the inlet of a sub-nozzle (550) in the embodiment is preferably similar with the shape of the outlet of a sub-nozzle (550). To avoid a high resistance in the nozzle (500) for the jettable liquid such similarity is preferred for a better jetting performance. Two shapes are similar if one can be transformed into the other by a uniform scaling, together with a sequence of rotation, translations and/or reflections. Two edges, such as outer edges of a shape, are similar if one can be transformed into the other by a uniform scaling, together with a sequence of rotation, translations and/or reflections.
In a preferred embodiment wherein the nozzle (500) is comprised in a nozzle plate, the axis between the centres of the minimum covering circle (C) from the outer edges from the inlet and outlet of sub-nozzle (550) is perpendicular to the nozzle plate (150). It was found that symmetries in a sub-nozzle (550) give better jetting performance.
The maximum diameter of the minimum covering circle (C) from the outlet of sub-nozzle (550) is preferably from 10 μm to 100 μm, more preferably from 15 μm to 45 μm, and most preferably from 20 μm to 40 μm.
The minimum distance (d) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) is preferably from 0.001 μm to 75 μm.
A two-dimensional shape is the form of a two-dimensional object which has an external boundary which is defined by its outer edge (OE). A two-dimensional shape is also called a shape if it is clear that the two-dimensional shape lies in a plane.
Two shapes are similar if one can be transformed into the other by a uniform scaling, together with a sequence of rotations, translations and/or reflections.
In a preferred embodiment the outer edge (OE) from the shape in the embodiment comprises a set of axes of symmetry. Preferably one of the set of axes of symmetry is parallel or perpendicular to the plane wherein the nozzle plate (150) lies. It is found that symmetry of a section in the nozzle (500) is a big advantage, for example with less disturbance in the liquid flow (175), for jetting performance which is the case when the outer edge (OE) from the shape comprises a set of axes of symmetry. An axis of symmetry in a two-dimensional shape is also called a mirror line in the two-dimensional shape.
A minimum point on an edge, such as an outer edge (OE), is a point on the edge wherein the distance from that point to the centre of the minimum covering circle (C) of the edge is the minimum distance in view from all points on the edge to the centre of the minimum covering circle (C) of the edge.
A maximum point on an edge, such as an outer edge (OE), is a point on the edge wherein the distance from that point to the centre of the minimum covering circle (C) of the edge is the maximum distance in view from all points on the edge to the centre of the minimum covering circle (C) of the edge.
The amount of minimum points on the outer edge (OE) is preferably from 1 to 12, more preferably from 1 to 6 and most preferably from 1 to 4 minimum points on the outer edge (OE). The amount of minimum points on the outer edge (OE) is preferable a multiplier of two with a minimum of two minimum points on the outer edge (OE).
The amount of maximum points on the outer edge (OE) is preferably from 1 to 12, more preferably from 1 to 6 and most preferably from 1 to 4 maximum points on the outer edge (OE). The amount of maximum points on the outer edge (OE) is preferable a multiplier of two with a minimum of two maximum points on the outer edge (OE).
In a preferred embodiment the outer edge (OE) of the shape is an ellipse wherein the transverse diameter is larger than the conjugate diameter of the ellipse. The transverse diameter is the largest distance between two points on the ellipse and the conjugate diameter is the smallest distance between two points on the ellipse.
In a preferred embodiment the outer edge (OE) of the shape is a rectangle.
In a preferred embodiment the outer edge (OE) of the shape is an epicycloid with k cusps and where k is an integer number, more preferably the shape is an epicycloid with 1, 2, 3, 4 or five cusps. An epicycloid is a plane curve produced by tracing the path of a chosen point of a circle—called an epicycle—which rolls without slipping around a fixed circle (
wherein k defines the amounts of cusps so k is a positive integer and k is more than zero). An epicycloid with one cusp is called a cardioid, one with two cusps is called a nephroid and one with five cusps is called a ranunculoid. It is found that symmetry of a section in the nozzle (500) is a big advantage for jetting performance which is the case in epicycloids. The symmetry of such epicycloids minimizes the disturbing effects in the liquid flow (175) which results in better dot forming. The outside boundary of an epiclyoid defines the shape of the epicycloid which in a preferred embodiment is similar to the shape (S) of the section of a nozzle (Ns) in the embodiment.
In a more preferred embodiment the outer edge (OE) from the shape is similar to a superellipse, defined by the following formula, defined in Cartesian coordinates (II):
Superellipses with a equal to b are also known as Lamé curves or Lamé ovals, and the case a=b with r=4 is sometimes known as the squircle. By analogy, the superellipse with a not equal to b and r=4 might be termed the rectellipse. It is found that symmetry of a section in the nozzle (500) is a big advantage for jetting performance which is the case in superellipses.
In a most preferred embodiment the outer edge (OE) from the shape is similar to the generalisation of the superellipse, proposed by Johan Gielis, defined by the following formula, defined in polar coordinates (III):
wherein the parameter m and the use of polar coordinates gives rise outer edges and/or inner edges with m-fold rotational symmetry. The formula is also called the ‘superformula’ (
It is found that symmetry of a section in the nozzle (500) is a big advantage for jetting performance which is the case in the ‘superformula’ of Johan Gielis. Symmetry in the shape results in minimized disturbing effects of the liquid flow (175).
In a preferred embodiment the outer edge (OE) of the shape is a rounded rectangle, rectellipse, semicircle, a stadium, oval. A stadium is a two-dimensional geometric shape constructed of a rectangle with semicircles at a pair of opposite sides. More information about rectellipse is disclosed in Fernandez Guasti, M. “Analytic Geometry of Some Rectilinear Figures.” Int. J. Educ. Sci. Technol. 23, 895-901, 1992. A semicircle is a one-dimensional locus of points that forms half of a circle.
In a preferred embodiment the outer edge (OE) of the shape from a section of a nozzle (Ns) has a set of corners such as in a square or rectangle. It was surprisingly found that in this preferred embodiment, the jetting performance, for example by smaller pinch-off-times, was increased. Probably the liquid flow in the nozzle of this preferred embodiment is delayed in a corner of the set of corners so the supplying of the liquid to the centre of the nozzle is reduced and the tail length is smaller. The corner has preferably an internal angle (thus inside the outer edge (OE) smaller than 160 degrees, more preferably smaller than 120 degrees.
A covering circle describes a circle wherein all of a given set of points are contained in the interior of the circle or on the circle. The minimum covering circle (C) is the covering circle for a given set of points with the smallest radius.
Like any circle, a covering circle is defined by its centre in which the distance between the centre and each point on the circle is equal. The distance between the centre and a point on the circle is called the radius. A circle is a simple closed curve which divides the plane, wherein the circle is comprised, into two regions: an interior and an exterior.
Finding the minimum covering circle (C) of a given set of points is called minimum covering circle (C) problem, also called the smallest-circle problem.
More information how to solve the minimum covering circle (C) problem can be found in MEGIDDO, NIMROD. Linear-time algorithms for linear programming in R3 and related problems. SIAM Journal on Computing. 1983, vol. 12, no. 4, p. 759-776.
A simple randomized algorithm to solve the minimum covering circle (C) problem can be found in WELZL, EMO. Smallest enclosing disks (balls and ellipsoids). New Results and New Trends in Computer Science (H. Maurer, Ed.), Lecture Notes in Computer Science 555. 1991, p. 359-370.
The minimum covering circle (C) of the outer edge (OE) of a shape is the minimum covering circle (C) from all points on this outer edge (OE) from the shape. This means also that all points of the shape and in the shape are contained in the interior of minimum covering circle (C) or on the minimum covering circle (C).
From each point of the outer edge (OE) of the shape, the distance between the point and the centre of the minimum covering circle (C) can be calculated and thus also the minimum and maximum distance from the outer edge (OE) from the shape to the centre of the minimum covering circle (C) of the outer edge (OE) of the shape can be determined.
In a preferred embodiment, the liquid is an ink, such as an inkjet ink, and in a more preferred embodiment the inkjet ink is an aqueous curable inkjet ink, and in a most preferred embodiment the inkjet ink is an UV curable inkjet ink.
A preferred aqueous curable inkjet ink includes an aqueous medium and polymer nanoparticles charged with a polymerizable compound. The polymerizable compound is preferably selected from the group consisting of a monomer, an oligomer, a polymerizable photoinitiator, and a polymerizable co-initiator.
An inkjet ink may be a colourless inkjet ink and be used, for example, as a primer to improve adhesion or as a varnish to obtain the desired gloss. However, preferably the inkjet ink includes at least one colorant, more preferably a colour pigment.
The inkjet ink may be a cyan, magenta, yellow, black, red, green, blue, orange or a spot color inkjet ink, preferable a corporate spot color inkjet ink such as red colour inkjet ink of Coca-Cola™ and the blue colour inkjet inks of VISA™ or KLM™.
In a preferred embodiment the liquid is an inkjet ink comprising metallic particles or comprising inorganic particles such as a white inkjet ink.
The jetting viscosity is measured by measuring the viscosity of the liquid at the jetting temperature.
The jetting viscosity may be measured with various types of viscometers such as a Brookfield DV-II+ viscometer at jetting temperature and at 12 rotations per minute (RPM) using a CPE 40 spindle which corresponds to a shear rate of 90 s−1 or with the HAAKE Rotovisco 1 Rheometer with sensor C60/1 Ti at a shear rate of 1000 s−1
In a preferred embodiment the jetting viscosity is from 20 mPa·s to 200 mPa·s more preferably from 25 mPa·s to 100 mPa·s and most preferably from 30 mPa·s to 70 mPa·s.
The jetting temperature may be measured with various types of thermometers.
The jetting temperature of jetted liquid is measured at the exit of a nozzle in the printhead while jetting or it may be measured by measuring the temperature of the liquid in the liquid channels or nozzle while jetting through the nozzle.
In a preferred embodiment the jetting temperature is from 10° C. to 100° C. more preferably from 20° C. to 60° C. and most preferably from 30° C. to 50° C.
The nozzles in the examples have all a length of 70 μm. The contact angle inside the nozzles is 60 degrees for all examples and the contact angle of the front side of the nozzle plate is for all examples 110 degrees.
For Nozzle 1 the shape is a circle which is the current state of the art. For Nozzle 2 the shape is an ellipse, for Nozzle 3 the shape is a composition of two circles, for Nozzle 4 the shape is a circle with 4 protrusions, for Nozzle 5 the shape is a square. By comparing Nozzle 1, the current state of the art, with the Nozzle 2, Nozzle 3, Nozzle 4 and Nozzle 5, which meets the embodiment of the invention, the pinch-off-time of the jetted liquid was determined for jettable liquids having a jetting viscosity of 10 mPa·s (Liquid 1), 20 mPa·s (Liquid 2), 30 mPa·s (Liquid 3), and 50 mPa·s (Liquid 4). Liquid 1 with a jetting viscosity of 10 mPa·s represents the current state of the art when used with Nozzle 1.
To distinguish the jetting performance such as minimal number of satellites, the pinch-off-time in μs was determined. The smaller the pinch-off-time of the jetted liquid, the better the jetting performance. Also in some comparisons the tail length in μm was determined. The smaller the tail length of the jetted liquid, the better the jetting performance such as minimal number of satellites.
Nozzle 1: The shape of all sections in the nozzle was a circle with a radius of 17.197 μm. The area of the shape was 929.12 μm2 and the volume was 65038.4 μm3. The maximum distance (D) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) was 17.197 μm and the minimum distance (d) from the outer edge (OE) to the centre (c) from the minimum covering circle (C) was 17.197 μm so the maximum distance D was not greater than the minimum distance (d) times 1.2.
Nozzle 2: The shape of all sections in the nozzle was an ellipse with as conjugate diameter 2×12.16 μm and with as transverse diameter 2×24.321 μm. The area of the shape was 929.12 μm2 and the volume was 65202.83 μm3. The maximum distance (D) from the outer edge (OE) to the centre (c) of the minimum covering circle (C) was 24.321 μm and the minimum distance (d) from the outer edge (OE) to the centre (c) from the minimum covering circle (C) was 12.16 μm so the maximum distance D was greater than the minimum distance (d) times square root of two. Nozzle 21: The shape of all sections in the nozzle was an ellipse with a conjugate diameter 2×9.928 μm and with as transverse diameter 2×29.789 μm.
Nozzle 3 was similar as illustrated in
Nozzle 4 was similar as illustrated in
Nozzle 5: The shape of all sections in the nozzle was a square where each side was 30.48 μm. The area of the shape was 929.12 μm2 and the volume was 65040 μm3. Nozzle 51: The shape of all sections in the nozzle was a rectangle with a width of 43.108 μm and length 21.554 μm. Nozzle 52: The shape of all sections in the nozzle was a rectangle with a width of 52.796 μm and length 17.598 μm.
The four jettable liquids (Liquid 1, Liquid 2, Liquid 3, Liquid 4) had a surface tension of 32 mN/m and a density of 1000 kg/m3.
The pressure at the inlet of the nozzle was changed in the examples depending on the shape of the nozzle so that the drop velocity at 500 μm nozzle distance was 6 m/s.
In the following table (Table 1) the pressure at the inlet of the nozzle in bar was determined for each nozzle example with a liquid of 50 mPa·s (Liquid 4) so the drop velocity at 500 μm nozzle distance was 6 m/s.:
A nozzle distance is a distance of a jetted liquid droplet from the nozzle plate in the direction of the receiver.
In the following table (Table 2) the time in μs of the drop reaching a certain nozzle distance is shown for different nozzle distances in μm using a liquid of 50 mPa·s (Liquid 4) and a pressure at the inlet of the nozzle as defined in Table 1:
The speed in m/s at a certain nozzle distance in μm can be found in the following table (Table 3) for each nozzle example with a liquid of 50 mPa·s (Liquid 4) and the pressure at the inlet of the nozzle as defined in Table 1:
In the following table (Table 4) the result of the nozzle geometry examples for the pinch-off-time in μs for each nozzle example with a liquid of 50 mPa·s (Liquid 4) and the pressure at the inlet of the nozzle as defined in Table 1. The pinch-off-time is smaller for Nozzle 2, Nozzle 3, Nozzle 4 and Nozzle 5 versus the nozzle geometry of the state of the art when using a high viscosity jetting method:
The following table (Table 5) is the result of the comparison of state of the art nozzle geometry (Nozzle 1) and elliptical nozzle geometry (Nozzle 2) wherein the different liquids (Liquid 1, Liquid 2, Liquid 3, Liquid 4) are examined versus the pinch-off-time in μs. The smaller the pinch-off-time, better the jetting performance, such as minimal amount of satellites what is the case for Nozzle 2.
The following table (Table 6) is the result of the comparison of state of the art nozzle geometry (Nozzle 1) and elliptical nozzle geometry (Nozzle 2) wherein the different liquids (Liquid 1, Liquid 2, Liquid 3, Liquid 4) are examined versus the tail length in μm. Smaller the tail length of the jetted liquid, better the jetting performance such as minimal amount of satellites what is the case for Nozzle 2.
The following table (Table 7) is the result of the comparison of the state of the art nozzle geometry (Nozzle 1) versus rectangular nozzle geometry (RECT) with different aspect ratio's between width and height (Nozzle 5, Nozzle 51 and Nozzle 52) and the comparison of the state of the art nozzle geometry (Nozzle 1) versus elliptical nozzle geometry (ELLIPSE) with different aspect ratio's between the conjugate and transverse diameter (Nozzle 2, Nozzle 21) by using a liquid of 50 mPa·s (Liquid 4). The Table 7 includes the pressure at the inlet of the nozzle in bar so the drop velocity at 500 μm nozzle distance was 6 m/s, the pinch-off-time in μs and the tail length of the jetted liquid. Smaller the tail length of the jetted liquid, better the jetting performance such as minimal amount of satellites what is the case for Nozzle 2, Nozzle 21, Nozzle 5, Nozzle 51, Nozzle 52.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14186638.4 | Sep 2014 | EP | regional |
This application is a 371 National Stage Application of PCT/EP2015/071611, filed Sep. 21, 2015. This application claims the benefit of European Application No. 14186638.4, filed Sep. 26, 2014, which is incorporated by reference herein in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/071611 | 9/21/2015 | WO | 00 |
