Konica Minolta’s silicon MEMS printhead

EP 2 716 461 A1
Inkjet head and inkjet drawing device provided with same
Konica Minolta, Inc.

This patent application seeks to overcome two problems. When designing a high density printhead with multiple rows of nozzles it is difficult to provide electrical connections to actuators as the wiring must pass between other chambers. In addition the electrical contacts and piezo actuators may be sensitive to moisture.

April-14aHere a section through the printhead is shown. At the bottom is a silicon nozzle plate 11 and a spacer layer 12 made from glass. Next is a silicon on insulator (SOI) substrate, with layer 13 forming the chambers and thin layer 14 forming the diaphragm. Thin film piezo actuators 31 are formed on the diaphragm layer. At the top of the printhead is the wiring substrate layer 21 which is also silicon. On the surface of the wiring substrate are the wiring

Connections between the external exible circuit board 25 with driver chips 24 and the actuators. The printhead assembly is connected to the wiring substrate layer 21 by a resin adhesive layer 30. This is patterned to provide cavities for the actuators and the ink channels. above the printhead is ink manifold 40.

April-14bOn the left the structure is shown in more detail. The wiring on the substrate 21 is more visible. Connections are made from the upper surface to the lower surface with vias. Both top and bottom surfaces of the wiring substrate are protected by films 26 and 28. As the wiring substrate only has ink passages through it, almost the whole surface is available for wiring tracks to the multiple actuator rows.

On top of the piezo actuator is a gold bump 16. At the corresponding point on the wiring substrate is a solder bump 29. Heating the printhead to above the solder melting point of 139C makes the connection. the printhead and wiring substrates are fixed together by the resin adhesive layer 30 in the presence of dry nitrogen. This results in the actuators being encapsulated in a dry inert environment, preventing both the electrical connections and actuators from deterioration in the presence of moisture.

Identifying missing nozzles

US 2014/0085369 A1
Method of identifying defective nozzles in an inkjet printhead 
Zamtec Ltd

Patents previously led by silverbrook Research are now led and held by Zamtec Ltd, also known as Memjet IP holdings Ltd. The Memjet page array printhead has over 70,000 nozzles and it is important to be able to detect any nozzle failures so that any necessary corrections can be made.

Mar-14a The conventional way to carry out the detection of missing nozzles is to print a line of drops 101 from the nozzles. if a nozzle isn’t working then a blank space 104 is left. The spacing between nozzles 103 that are simultaneously printing is determined by the resolution of the scanning system that will evaluate the image. In addition spaces 102 are left between the ends of one array of nozzles and the next to discriminate between the line segments printed by different groups of nozzles.

There are several problems with this method. The pattern is very low density, with most of the printed test area empty, and is therefore inefficient. in addition the nozzles are being driven in an unrealistic way which may result in some artefacts not being recorded. For instance poor nozzle refill rates may only be apparent when adjacent nozzles are also generating drops, which will never occur with this test pattern. Also misdirected jets may lead to misinterpretation as to which nozzle’s behaviour is defective.

The solution is to use a more complex test pattern where the pixel pattern generated is encoded and then later decoded. A Hadamard matrix is used for this purpose. This is a square matrix with entries only either 1 and -1, and where the sum of each row or column (except for the first ones) is zero.

Mar-14b
Above an example pattern is shown. The nozzles across the array are divided into a number of cells. In addition a secondary scheme known as a Maximal length sequence or M-sequence is used. The values of these are shown above the pixels; 4 rows of pixels are shown. Note that every pixel sequence for a nozzle prints two drops, so the duty cycle is 50%.

Mar-14c
Here a section of a sequence is shown. After printing the image is scanned and analysed. If a nozzle isn’t working then no pixels are printed, as with the 4th nozzle from the left. If a nozzle is firing intermittently, such as nozzle 8 from the left, then this will also be detected.

Large drop volumes from Xaar printhead

WO 2014/023981 A1
Droplet deposition apparatus and method for depositing droplets of fluid
Xaar Technology Limited

The Xaar face shooter architecture with through flow ink circulation has been very successfully commercialised in the 1001 printhead. This patent application discusses some improvements, in particular using a different shaped nozzle to allow larger drops to be generated on the same nozzle pitch.

Feb-14In the Xaar design the piezo walls 3 move to reduce the channel volume 2 to create pressure waves to generate drops. The ink is continuously circulated through the channels, as shown by the arrows, at a rate around an order of magnitude greater than the flow through the nozzles at maximum drop frequency. Attempts to elongate the nozzle in the flow direction were found to allow more efficient removal of debris from the vicinity of the orifice. In addition the effciency of drop ejection increased due to the acoustic wave being present at the orifice for longer.

However, the directional accuracy of drops deteriorated in the direction of the elongation when the nozzle was made elliptical. Experiments showed that the benefits of elongation could be retained just by elongating the inlet side. If the outlet (orifice) was circular, or up to an aspect ratio of 1.2, then the directionality of drops was similar in all directions.

Feb-14bBy increasing the nozzle area through elongation then the drop volume ejected increased as shown in the table on the left. Larger drop volumes are desirable for some applications, such as printing of ceramic tiles, one of the main applications for the 1001 printhead.

Digital binder printing for décor applications

US 2014/0028772 A1 Digital binder printing
WO 2014/017972 A1 Digital binder printing
Floor Iptech AB

These patent applications describe a method of printing decorative boards and in particular flooring. The inventor is also CEO of Välinge, a leading R&D company in the flooring industry, and both companies are based in Viken, Sweden.

There have been several proposals to print onto laminated board or flooring using ink jet. Traditional printing is only cost efficient in very long runs. However the cost of ink jet printing laminate flooring is around €1/m2 assuming the cost of the ink jet ink used is €100/litre. This is 10 times the cost of ink for conventional printing. In addition ink jet inks are limited by viscosity and therefore the solids contents that can be used.

Jan-14

The solution is to use ink jet heads to form a wet image on the substrate, then apply a powder of resin and pigment, and vacuum off excess powder from the non-image areas. The ink jet head 32 jets a liquid on to the substrate 2 to form the desired image 11 of the rst colour. The liquid can be just water, as long as it remains wet enough for the next step. The substrate typically has a top coating of a thermosetting resin, preferably a melamine formaldehyde.

Next the powder is applied by scattering unit 27, consisting of an embossed drum and an oscillating brush. The powder is a mix of the first colour pigment and melamine formaldehyde. Where the image is wet the binder melts. This ‘image’ is then cured and dried by UV lamp 23. The powder in the non-image areas that was just scattered on the substrate surface is then removed by the vacuum unit 28. The powder that is removed is returned to the feed hopper for the scattering unit.

Other colours can be printed in exactly the same way until the image is complete. The board is then subjected to 40 bar pressure and 160C to cure and form a hard wear-resistant surface.

The cost of the powder reduces the cost of printing to around €0.2 m2, one fifth that of direct printing with ink jet.

Decorating glass with functional coating of metal

US 2013/0323477 A1
Method for manufacturing a decorated glass sheet
AGC Glass Europe 

This patent presents a process for producing decorated glass with a functional coating of a metal or metal oxide to give properties such as low-emissivity, solar protection (reduction of heat exchange) or electric conductivity or physical protection and enhanced toughness.  The process may be applied to the production of a number of articles such as shelves, kitchen appliance doors and refrigerated counters, table tops, partitions, lighting, shop windows and automotive glass.  Dimensioning of the glass is not necessary at the outset of the process, so several parts can be produced simultaneously: the glass can thus be cut to size at the end of the process.  Both PLF (full width: 6000 mm x 3210 mm) and DLF (half width: 3210 mm x 2250/2200 mm) sheet may be processed.  The glass is first decorated by a printing process such as ink jet printing and after drying, is coated by a magnetron cathodic sputtering process to give the desired functionality.

The enamel-based decorative inks consist of vitreous substances such as silica, feldspar, kaolin and metal oxides.  Such inks are available from Dip-Tech Digital Printing Technologies Ltd.  The drying process after printing must remove the vast majority of the ink solvent so that outgassing does not occur during the subsequent vapour deposition coating process.  Inks mainly have a boiling point below 300C, and drying time is related to the thickness of the glass (40 to 90 seconds per mm thickness of glass).  A drying time of 320 seconds at 150C is typically adequate.

The functional coating is subsequently applied by a magnetron cathodic sputtering process.  This is a form of ionised vapour deposition in which films are deposited from atoms and ions in precise ratios.  Specific ionic compositions will thus determine the functionality of the coating.  An example coating is a low-emissivity, solar shield, which may also be electrically conductive and can be based on one or more doped oxides such as tin-doped indium oxide or aluminium or gallium-doped zinc oxide.  Low emissivity or solar shield coatings may also be based on a silver layer with a dielectric layer on either side of it.  Following deposition of the functional coating, the coated glass is fired at 670 to 700C in a sintering or fritting process, during which toughening of the glass may occur and the glass may be bent in order to shape it.

While the image is designed to be viewed through the glass with the functional coating behind it, in some instances it is helpful to deposit a base or barrier layer (up to 30 nm thickness) of silicon oxide for example, prior to printing the decorative image.  This will enhance adhesion of the image and will also prevent migration of silver through the enamel-based decoration.  Alternatively, the ink formulation itself may contain elements that prevent such diffusion of silver.

Thermal inkjet head with improved jet straightness

US 2013/0293638 A1
Fluid ejection device having firing chamber with mesa
Hewlett-Packard Development Company, L.P.

There have been several thermal ink jet printhead designs in the past that have attempted to improve jet straightness.  As drops are formed, the bulk of the ink moves rapidly to the substrate.  Some of the ink is contained in the tail, which breaks off.  Often the tail will fragment into fine drops which either slowly follow the main drop to the substrate or fall back on the nozzle plate.  In addition erratic tail break-off can lead to mis-directed drops.

The proposed solution is to redesign the heater chamber floor with a central column or mesa and a circular heater.  The silicon substrate is etched to form a circular pit 230 around a central column 250.  The heater 205 is formed on the outer wall of the pit.  The heater, electrodes 208 and the exposed surface of the substrate are coated with an insulator, which also increases the robustness of the structure.

The column is centrally positioned under the nozzle.  It is thought that the tail then breaks more centrally than otherwise.   In addition, because the heater is not at the centre of the chamber, it is far less likely to be damaged by the collapsing bubble.  Therefore the overcoat layer, which has a protective function as well as being an insulator, can be reduced in thickness and therefore increase the efficiency of the device.

Hewlett-Packard’s nano-colourant dispersion

US 2013/0284050 A1
Colorant dispersion for an ink
Hewlett-Packard Development Company L.P.

Ink jet inks usually contain organic colorants, as these materials when chosen correctly show strong absorption, low density and in the case of pigments are usually available at particle sizes suitable for incorporation into ink jet inks.  Inorganic pigments are used in speciality ink jet inks when the inherent stability to heat and UV is required – tile printing would be one example. However the range of available inorganic pigments is narrow and the colour of such materials tends to be dull.

This patent focuses on a nano-dispersion of Fe3O4 (iron(II,III)oxide) with a particle size of around 30 nm, which at this particle size has a burnt red colour unsuitable for black text printing.  When manufactured at a large particle size, iron(II,III) oxide is used as a black pigment (C.I pigment black 11).

The example takes an ~8 wt% Fe3O4 suspension in water synthesised by a basic precipitation process and adds Silquest A1230 (a reactive alkyleneoxide dispersant, 50 wt% on pigment) and citric acid (10 wt% on pigment).  This mixture was then bead milled to give a dark red dispersion with an average particle size of ~30 nm.  To this dispersion was then added 5 wt% gallic acid (3,4,5-trihydroxybenzoic acid) and it was heated to 60C for one hour, during which the colour changed from dark red to black.  This black dispersion was then made into a basic ink jet ink by dilution with water and 2-pyrolidone as humectant and successfully ink jet printed to give sharp text that was significantly more black than the pale yellow comparative ink produced without the gallic acid heating step.

From the examples it seems that although the heating step significantly improves the colour of the inorganic pigment, the intensity and neutrality is not quite the same as a comparative carbon black ink made to the same formulation.  However, scratch resistance and gloss were significantly better than the carbon black ink.

UV stability is unfortunately not mentioned, as it would be interesting to see if the pigment would revert to its former dark red colour.  If not this could be an interesting approach to the production of small particle size black pigments for extreme ink jet applications.

Inside Landa’s Nanography process

WO 2013/132418 A2
Digital printing process
Landa Corporation Limited

This patent application describes the complete process and makes the basic claims for the overall process.  The first drawing is a schematic and is not to scale.  Multiple array printheads 300 print an image on to a heated intermediate substrate belt 130 which rotates clockwise around rollers 104 and 106.  The image dries partly due to the heated belt but with additional heating from above (not shown).  The printheads can be moved backwards from the belt to maintenance and capping stations.

Sheets are fed from a conventional offset press sheet feeder 506 and are transported through the machine by a series of gripper drums.  Drums 502 and 504 bring the substrate into contact with the image on the belt, transfer being enabled by pressure from back-up rollers 140 and 142.  After the first side of the sheet has been printed at the first impression, it is passed by a further gripper drum to the perfecting cylinder 524.  The perfecting cylinder has a circumference twice that of the other drums.  The grippers are timed so that as the trailing edge passes drum 526 the grippers grab the rear edge.  At the second impression stage the back side of the sheet is then printed.  In this way the single imaging engine can be used to print duplex.  To do this the images for Sep13-2
each side of the sheet are formed alternately and mirror-imaged so that after transfer they are correctly orientated.

After transfer to the sheet, the ink is dry enough to be handled by the gripper drums and the output stacker 508.  No further curing or drying of the image is required.

Other configurations are possible, and in fact a simplex web press was shown at Drupa 2012.  There is just one impression cylinder and pressure roller pair 502 and 140.  To ensure none of the web substrate is wasted, it’s fed intermittently past the impression cylinder to close up any gaps between the images on the transfer belt.  As the web drive has considerable momentum, the intermediate feed is achieved by using dancer rollers 554 and 556.

Going back to the duplex sheet-fed press, the figure below shows the intermediate substrate or blanket support system with the blanket and front support removed.   The roller 104 serves to pull the belt past the printheads at a constant speed, while roller 106 is also driven but is adjusted to keep the belt in a state of constant tension across the top run.  Roller 104 is mounted in pillow blocks so that it can be moved to allow for belt stretch.  Pressure rollers 140 and 142 are mounted inside the support, press against the blanket at the transfer points to the substrate, and can be raised and lowered.

Sep13-3
The blanket runs in contact with thermally conductive support plates 130.  The junctions between these plates are deliberately staggered to prevent the creation of a line along the belt.  Heater elements 132 under the plates supply the heat to the belt along the upper run.

Not shown is a fan system to create a negative air pressure within the blanket support box.  This helps keep the blanket in contact with the heated plates, and also keeps the bottom run of the blanket from contacting the impression cylinders when the pressure rollers are withdrawn.

Each of the sides of the blanket support has a track 180 which engages in features fixed to the sides of the blanket.  This serves two purposes.  Firstly it enables the blanket to be threaded through the machine by entering it into the guides.  Although the blanket could be made as an endless belt, it is more economical to make it as a sheet and join the ends within the machine.  Secondly it steers the belt past the printheads and maintains tension across the belt.

Sep13-4
To the left is a top view of belt 210.  Alongside each side are features 270.  These can be one half of a zip fastener that has been sewn to the edges of the blanket.  The projections 270 are contained within the channel of track 280.  Roller bearings 282 can be used to reduce the friction.  As the belt is heated the components must be capable of withstanding up to 250C.  Suitable materials for the projections include a polyamide reinforced with molybdenum disulphide.  The guides are used to stabilise and tension the belt as it passes the printheads to ensure accurate image formation, but can be omitted through the drying station and in other places where the belt is slack.

Sep13-5
The blanket is formed into a continuous belt using a zip or hooks and loops fastener.  This may be supplemented by adhesive or tape.  It is important that the seam is the same thickness as the belt itself, otherwise there will be speed variations when the seam passes over the driven rollers.

Details of the ink can be found in Directions September/October 2013 page 17, and materials and structure of the blanket in the media reviews in this issue of Direction on page 22.  The surface of the blanket has a thin upper release layer that is hydrophobic, such as a silicone material.  This is formed on a reinforcement layer, such as a fabric.

A pre-treatment liquid can be applied to the blanket by a roller mounted opposite tension roller 106.  This coats the blanket with a thin dilute film of charged polymer to modify the surface properties.  By the time the blanket reaches the printheads the film is completely dry.

The purpose of this chemical treatment is to counteract the surface tension of the aqueous ink when it contacts the hydrophobic release layer of the blanket.  Without the pre-treatment the drops would flatten on the blanket surface on impact, and then surface tension forces would restore the ink into drops or beads.  With the pre-treatment the negatively charged polymer particles in the ink drop adjacent to the surface are attracted by the positively charged pre-treatment film.  This “freezes” the drop after impact so that beading does not occur.  The effect is very short-lived but long enough for the water to be dried out of the image without the drops coalescing, beading or otherwise disrupting the image.

The blanket is heated from below to around 150C.  In addition, after the print station external air blowers pass hot air over the image to further aid drying.  The polymers in the ink remain tacky at this temperature, aiding the transfer process.

There are many claimed advantages to this process.  First of all, it uses aqueous-based inks which are environmentally friendly, and compared to UV-curable inks use relatively low-cost materials.

The freezing of the ink drops on the blanket enables very thin image layers to be produced, typically 500-800 nm.  This means the image takes up the surface features of the substrate, so that an image on a glossy surface will be glossy, and matt on a matt surface, matching the non-image areas.

When the drops are flattened on impact with the blanket and then frozen they retain the shape formed on impact, hopefully circular.  There is no irregular bleed that is sometimes encountered with direct ink jet printing.  In addition inter-colour bleed is also reduced.

The transferred thin film is less likely to split compared to thicker films, reducing the chances of ink being retained on the blanket and thus requiring cleaning.

Optically clear nano-particle ink from Hewlett Packard

US 2013/0222496 A1
Optically clear fluid composition
Hewlett-Packard Development Company, L.P.

Uniform gloss on paper substrates requires a transparent ink to raise the gloss level of the chosen media to the same level of the coloured components of the ink.  If such an ink is to be used then there is a good argument for printing it over the full printed image.  This helps to improve mechanical properties, such as scratch and rub resistance, and potentially introduces other benefits such as UV absorption, therefore increasing the stability of the printed image.

This patent discusses a clear ink jet ink designed to be printed over the full image to equalise gloss, improve mechanical properties and absorb UV, without increasing the overall haze of the printed image.

The novelty of the patent is to use metal oxide nano-particles with a particle size below 140 nm.  This small particle size is necessary for transparency of these materials.  The patent suggests that it is also beneficial if the metal oxide average particle size is similar to that of the colorant pigment particles, in order to stack efficiently and therefore minimise coating roughness and haze.  Such nano-particulate materials also show benefits with respect to stability and printhead performance.

Additionally, these metal oxide dispersions should be compatible with the printed inks in order to prevent aggregation of these nano-particles which might increase haze.  Generally, such metal oxide dispersions are electrostatically stabilised and can be formulated to be stable at a pH of 8-10, the range for ink series such as HP 38 and HP 70.  Specifically the pH of the metal oxide dispersion should be within 0.5 pH units of the coloured inks.

The specific metal oxide particles used should be transparent to visible light and have a refractive index greater than 1.65.  Zinc and aluminium oxide work well for this technology, whereas silica (with a refractive index of 1.45) does not, as it apparently gives hazy coatings.

Exemplified coating formulations contain around 2 wt% of a polyurethane binder, 2 wt% (dry solids) of the metal oxide particles, 10 wt% of humectants (1,2-hexanediol, 2-pyrolidone or similar), ~0.5 wt% surfactants and biocides, with the remainder water.  The mechanical properties of such coatings were compared to a silver halide print, giving equal or better scratch resistance and very low haze levels.

Hewlett Packard’s microwave-curable media coating

WO 2013/062510 A1
Inkjet recording medium, and method of using the same
Hewlett-Packard Development Company, L.P.

Over the years, much effort has been put into improving the image stability and gloss of photo prints.  Here, ink passes through a porous top coating which is subsequently made to be non-porous, so providing both image protection in the form of wet and dry rub resistance along with good levels of gloss and image distinctness.

The substrate can be any typical medium such as paper, olefin coated paper or polymer film.  It is first coated with an ink receiving coating that will absorb fluid from the ink.  This is a typical porous coating and primarily consists of a porous pigment and a binder.

Protection is given to the image by the particulate-based reactive coating applied above the porous coating.  This is in itself porous to the ink and so the ink will pass through it and be absorbed in the ink receiving coating.  After printing, barrier properties are created by exposure to microwave radiation which will cause cross-linking of some of the particles and coalescence of others.  This is shown in the figure in which ink (26) is shown absorbed in the ink absorbing layer (14), having almost entirely passed through the protective coating (16).

Jun13aJun13b

The coating is applied as a latex in which both reactive and non reactive particles are dispersed.  Suitable reactive polymers include those with epoxy functionality, and those with fatty acid, alkoxy-silane, acetoacetoxy, hydroxyl, amine or carboxyl functional groups.  Self cross-linking polymers can be used or a cross-linking agent can be included.  The uncured particles (0.2 to 10 µm) should have good mechanical stability (Youngs Modulus 600 to 3000 MPa) at a temperature below 110C.

A polar microwave radiation cure promoter may also be included.  This acts to strengthen the dipole relaxation effect in which particles turn or rotate with some lag as the dipole direction changes at high frequency.  Heat is also generated which is helpful to both the curing and coalescence processes.  Suitable agents are calcium acetate monohydrate, calcium propionate and calcium propionate hydrate.  Exposure to microwaves also induces coalescence of the non reactive polymer particles which are generally hydrophobic polymers such as PTFE or hydrocarbon waxes.  It appears that much or all of the coalescence and cure processes will take place at temperatures exceeding 110C.

These media appear to be suitable for most types of aqueous, solvent or latex ink and can be applied using more or less any mode of ink jet.  Microwave exposure can be carried out either in-line or off-line at a frequency of 0.3 to 300 GHz.  Exposure time should be from around 10 seconds to 4 minutes, although the longer times would seem impractical.