Printing method using liquid drop generator

Abstract

A method of printing a halftone image by a liquid droplet generator (100) having a liquid deposit having the highest density at a first location in a manifold of the generator and having two inlets, and; wherein the portion is determined by using a printing mask (1000) having a width and a height for displacing the liquid precipitate to a second position in the manifold, the printing mask (1000) dividing the plurality of nozzles in at least three consecutive zones between the first inlet (516) and the second inlet (517) within a selected printing period, the at least three consecutive zones comprise at least the following zones for printing the determined portion: a first zone (1001) at the first inlet (516), where the print mask (1000) determines the nozzles in the first zone (1001) for N1% of the portion; and a second zone (1002) intermediate the first inlet (516) and the second inlet (517), where the print mask (1000) determines the nozzles in the second zone (1002) for N2% of the portion; and a third zone (1003) at the second inlet (517), where the print mask (1000) determines nozzles in the third zone (1003) for N3% of the portion; wherein the gt is 100gt; = N1gt; n2gt; n3gt, N3gt; = 0.

Description

Technical Field

[0001] The present invention relates to image formation by a liquid droplet generator, wherein image quality problems due to liquid settling in a manifold of the liquid droplet generator are avoided. Background Art

[0002] Image formation is the process of printing a digital image onto a medium, for example by ejecting droplets of a liquid or another type of printing fluid onto the medium, such as paper, plastic, a substrate for 3D printing.

[0003] Such image formation is commonly used in devices such as printers (e.g., inkjet printers), but is also used in fax machines, copiers, plotters, multifunction peripherals, etc. At the heart of a typical jetting device or image forming device is one or more liquid droplet generators (also called "print heads") having nozzles that expel liquid droplets, a mechanism for moving the liquid droplet generators and / or the medium relative to each other, and a controller that controls how the liquid is expelled from the individual nozzles of the liquid droplet generators onto the medium in the form of pixels.

[0004] A typical liquid droplet generator includes a plurality of nozzles aligned in one or more rows (referred to as "nozzle rows") along a discharge surface of the liquid droplet generator. Each nozzle is part of a "jet channel," which includes a nozzle, a pressure chamber, and an actuator, such as a piezoelectric actuator. The liquid droplet generator also includes a drive circuit that controls when each individual jet channel is activated based on image data. To eject from a jet channel, the drive circuit provides a jet pulse to the actuator, which causes the actuator to deform the wall of the pressure chamber. The deformation of the pressure chamber generates a pressure wave within the pressure chamber that ejects a drop of a printing fluid (e.g., liquid) out of the nozzle.

[0005] Drop-on-demand (DoD) printing is moving towards higher productivity and quality, which requires small droplet sizes to be ejected at high jetting frequencies. The print quality provided by a liquid droplet generator depends on ejection or jetting characteristics, such as droplet velocity, droplet mass (or volume / diameter), jetting direction, etc. Unfortunately, liquid precipitation inside the liquid droplet generator, especially in the manifold, negatively affects the jetting characteristics and therefore negatively affects the image quality, especially when the liquid droplet generator has a manifold with two inlets on both sides of the manifold. Liquid precipitation in the manifold occurs when, for example, the liquid droplet generator filled with liquid is not used for a long time. Such a liquid droplet generator is described in EP3536508A1 (RICOH). It has been found that the problem of liquid precipitation in the manifold of such a type of head leads to faulty nozzles and unequal densities between droplets of the nozzles, which leads to a troublesome density distribution of the liquid droplet generator.

[0006] The problem of liquid precipitation leads to frequent maintenance of the liquid droplet generator using a so-called "flushing" or "cleaning" liquid for unclogging the nozzle and cleaning the nozzle plate of the liquid droplet generator. For example, EP 2157163A (TOYO INK) discloses a maintenance liquid for an inkjet printer, which contains at least one of ethylene glycol ethers and ethylene glycol esters and 45 to 10 mg / L of dissolved oxygen. EP 1621348A (TOSHIBATEC) discloses a cleaning solution for cleaning a cationic UV curable inkjet inkjet print head, which contains not less than 50 parts by weight of a polymerizable compound selected from at least two polymerizable compounds included in the ink and having the lowest viscosity among the at least two polymerizable compounds, or not less than 50 parts by weight of a polymerizable compound having a viscosity of 30 mPa·s or less at normal temperature.

[0007] During the investigations it was found that the liquid flow rate drops due to the collision of the liquid from the first inlet and the second inlet in the middle of the manifold (the so-called dead zone). Now, if the liquid droplet generator is not used for a while, a liquid deposit is formed at the bottom of the manifold (= it is the side closest to the nozzle). But when the manifold is (re)filled via the first inlet and the second inlet, the liquid deposit in the manifold accumulates at the dead zone. The liquid deposit has a higher (volume mass) density here than the liquid at other locations in the manifold. It was found that during printing, faulty nozzles appear in nozzles close to the dead zone and / or large printing density differences appear at nozzles close to the dead zone. Therefore, the operator has to maintain the liquid droplet generator by flushing and / or cleaning, or the expensive liquid droplet generator has to be replaced, so the production time is reduced. Therefore, there is a need for an efficient printing method for a liquid droplet generator that has not been used for a while and has liquid deposits in the manifold, without the need for expensive time costs for maintenance procedures. Summary of the invention

[0008] It has been found that when using a liquid droplet generator (100) having a manifold with two inlets at both sides of the manifold, the above problems can be overcome by a method of printing a halftone image, wherein the determined portion of the halftone image is printed by a plurality of nozzles of the liquid droplet generator arranged in one or more rows, wherein the liquid droplet generator has a liquid deposit having a highest (bulk mass) density at a first location in a manifold of the liquid droplet generator, and wherein the manifold: - having a first inlet (516) and a second inlet (517) for filling the manifold with liquid; - extending parallel to the plurality of nozzles between the first inlet (516) and the second inlet (517); and - configured to provide a liquid path for liquid to a plurality of nozzles; wherein the portion is determined by using a print mask (1000) having a width and a height for displacing the liquid deposit to a second position in the manifold, the print mask (1000) dividing the plurality of nozzles into at least three continuous zones between the first inlet (516) and the second inlet (517) during a selected printing period, the at least three continuous zones including at least the following zones for printing the determined portion: - a first zone (1001) at a first inlet (516), wherein the print mask (1000) determines that the nozzles in the first zone (1001) are used to print N1% of the portion; and - a second zone (1002) intermediate the first inlet (516) and the second inlet (517), wherein the print mask (1000) determines that the nozzles in the second zone (1002) are used to print N2% of the portion; and - a third zone (1003) at the second inlet (517), wherein the print mask (1000) determines that the nozzles in the third zone (1003) are used to print N3% of the portion; Where 100>=N1>N2>N3>=0. The manifold is preferably filled simultaneously via the first inlet and the second inlet.

[0009] By shifting the liquid deposition nozzle, faults and (printing) density distribution caused by liquid deposition in the manifold are solved, thereby eliminating the need for periodic maintenance (e.g., cleaning, flushing, etc.) of the liquid droplet generator and extending the life of the liquid droplet generator.

[0010] Further advantages and embodiments of the invention will become apparent from the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 2 Yes Figure 1 2 is a cross-sectional view of a liquid droplet generator (100) in an illustrative embodiment shown in FIG. Through this cross-sectional view, elements of a (supply) manifold (314) are visible. Manifold 314 is formed by an elongated body (316) of body (302) extending between ends (317, 318) (in Figure 2314). The manifold (314) is further formed by a first inlet (516) and a second inlet (517) (517) which fluidly couple the supply port (330) to said opposite ends (317, 318) of the elongated body (316). Thus, in this embodiment, printing fluid is supplied to the elongated body (316) at the opposite ends (317, 318). The elongated body (316) is a conduit for the flow of printing fluid. The bottom portion of the elongated body (316), and therefore the manifold, is open to the jet channels connected to the nozzles in the nozzle row (304). Thus, the elongated body (316) is the portion of the (supply) manifold (314) that delivers printing fluid to the jet channels.

[0012] Figure 3 The nozzle row (304) of a liquid droplet generator (100) with 15 nozzles (illustrated as circles) is shown as an example. The selection of nozzles for ejection is determined by a (repeatable) print mask (1000) for two-pass printing, wherein the print mask (1000) has a width of 7 and a height of 15, and the nozzle row is divided into three consecutive zones (1001, 1002, 1003). The "1" in the print mask (1000) is used for the first pass; the "2" in the print mask (1000) is used for the second pass. Obviously, in the first pass, the nozzles in the first zone (1001) should be used more than the nozzles in the second zone (1002), and even more than the nozzles in the third zone (1003). DETAILED DESCRIPTION

[0013] Liquid droplet generator

[0014] The liquid droplet generator (100) in this embodiment and the preferred embodiment has one or more rows of nozzles for ejecting droplets of liquid, also known as a drop-on-demand inkjet printhead. Preferably, the droplet ejection is performed by using the piezoelectric effect. Such printheads are now dominant in home and office inkjet printing systems, but also in industrial applications for printing or digital manufacturing. Several actuation mechanisms are possible, such as a push mode actuator or a squeeze mode actuator.

[0015] The liquid droplet generator (100) in this embodiment has a basic manifold extending parallel to the nozzle row; and is configured to provide a liquid path for liquid to a plurality of nozzles. The liquid is provided by a first inlet (516) and a second inlet (517), each connected to the manifold at two sides of the manifold. Preferably, no outlet is provided, as is known in refluxing liquid droplet generators. The flow rate of the liquid at the two inlets determines the liquid flow rate in the manifold. Preferably, the flow rate in the first inlet (516) and the second inlet (517) is the same.

[0016] The liquid droplet generator (100) may have a main liquid inlet, which is divided into the first inlet (516) and the second inlet (517). Then, a liquid supply is connected to the main liquid inlet, and liquid from the liquid supply is further supplied to the liquid droplet generator (100) via the first inlet (516) and the second inlet (517).

[0017] As already described, around the middle of such a manifold (the so-called dead zone), the liquid flow rate drops due to the collision of the liquids from the first inlet and the second inlet. Due to the dead zone, the liquid deposits in the manifold accumulate at a high density at the dead zone, whereby during printing, a malfunctioning nozzle occurs in the nozzles near the dead zone and / or a large density difference occurs at the nozzles near the dead zone.

[0018] However, by using the printing mask (1000) according to the present embodiment and the preferred embodiment, the liquid deposits in the manifold can be displaced, whereby the liquid droplet generator (100) can be directly used for printing without necessary maintenance, so that the operator can directly start the production of printed products.

[0019] The liquid drop generator is part of a multi-pass inkjet printer, where a halftone image is printed in multiple passes and the part is jetted in a single pass. The print mask (1000) then defines the jetting of the nozzles in each pass.

[0020] In a preferred embodiment, the determined portion of the halftone image is additionally printed by a further plurality of nozzles of a liquid droplet generator (100) arranged in one or more rows, wherein the liquid droplet generator (100) has a liquid deposit with the highest density at a third position in another manifold, and wherein the another manifold: - having a third inlet and a fourth inlet for filling the further manifold with liquid; and - extends parallel to the further plurality of nozzles between the third inlet and the fourth inlet; and - configured to provide another liquid path for liquid to another plurality of nozzles; and wherein a complementary print mask to the print mask (1000) is additionally used to define the portion for displacing liquid deposition of liquid in another manifold to a fourth position. Printing System

[0021] The liquid droplet generator (100) is preferably part of a printing system such as an inkjet printer. The printing system is preferably used for printing on a flat ink receiving medium, but may also be a three-dimensional printing system.

[0022] In a printing system, an image is formed by one or more of the liquid drop generators capable of printing one ink or multiple inks.

[0023] The printing system is preferably configured to move the liquid droplet generator (100) for printing portions of an image, such as a multi-pass inkjet printing system. The multi-pass inkjet printing method is described in the Jeti Tauro manufactured by AGFA NV. TM It is used in, has a maximum printable width of 254 cm, and it can accommodate rigid media with a length of up to 400 cm, for example.

[0024] The printing system may also be a hybrid printing device in which conventional printing technology and liquid droplet technology are combined in the printing system.

[0025] The idea of ​​displacement of liquid deposits in the manifold was tested by printing a large right triangle with base and height with white ink after a period of no printing. The height was oriented parallel to the nozzle row (and printing direction) and the base was oriented parallel to the scanning direction of the liquid drop generator. By adjusting the base / height of the monochrome triangle and / or mirroring the triangle, displacement of liquid deposits in the manifold can be detected. Printing Mask

[0026] The use of print masks is well known in the art of printing using liquid jet technology, primarily in multi-pass inkjet printing technology. The print mask is stored in a memory of the printing system, such as in a hardware or software printer driver, and controls the signals applied to the liquid drop generator (100). The actual implementation of the print mask in hardware or software format is considered to be within the skill of a person having knowledge of the inkjet printer field when such skill is applied according to the teachings herein.

[0027] The printing mask (1000) in this embodiment has a width and a height, i.e., a so-called two-dimensional printing mask (1000). The width and the height are greater than 1.

[0028] The number of contiguous zones may be 3, 4, 5, 6, 7, 8, 9 or 10 or equal to the width of the print mask (1000) or the number of nozzles.

[0029] Preferably, the print mask (1000) represents a blue noise halftone gradient from the nearest nozzle of the plurality of nozzles at the first inlet (516) to the nearest nozzle of the plurality of nozzles at the second inlet (517) and from dark to light, respectively.

[0030] In a preferred embodiment, the print mask (1000) divides the plurality of nozzles into other continuous areas between the first inlet (516) and the second inlet (517) in another selected printing period after the selected printing period, and the other continuous area at least includes the following areas for printing the determined portion: - a fourth zone at the first inlet (516), wherein the print mask (1000) determines that N4% of the portion is printed using nozzles in the fourth zone; and - a fifth zone intermediate the first inlet (516) and the second inlet (517), wherein the print mask (1000) determines N5% of the portion to be printed using the nozzles in the fifth zone; and - a sixth zone at the second inlet (517), wherein the print mask (1000) determines that N6% of the portion is printed using nozzles in the sixth zone; Among them, 0>=N4>N5>N6>=100.

[0031] In a preferred embodiment, the portion is determined by using a print mask (1000) which divides the plurality of nozzles into a continuous region between the first inlet (516) and the second inlet (517) during a determined printing period, the continuous region comprising at least: - a first zone (1001) at the first inlet (516), wherein the print mask (1000) determines that 100% to 80% of the determined portion is printed by nozzles in the first zone (1001); - a second zone (1002) in the middle of the first inlet (516) and the second inlet (517), wherein the print mask (1000) determines that 70% to 30% of the determined portion is printed by nozzles in the second zone (1002) for printing the determined portion; - a third zone (1003) at the second inlet (517), wherein the print mask (1000) determines that 20% to 0% of the determined portion is printed by nozzles in the third zone (1003) for printing the determined portion, and More preferably, for another determined printing period after the determined printing period, the plurality of nozzles in the (other) continuous region between the first inlet (516) and the second inlet (517) at least comprises: - a fourth zone at the first inlet (516), wherein the print mask (1000) determines that 20% to 0% of the determined portion is printed by nozzles in the fourth zone for printing the determined portion; - a fifth zone at the middle of the first inlet (516) and the second inlet (517), wherein the print mask (1000) determines that 70% to 30% of the determined portion is printed by nozzles in the fifth zone for printing the determined portion; - a sixth zone at the second inlet (517), wherein the print mask (1000) determines that 100% to 80% of the portion is printed by nozzles in the sixth zone for printing the determined portion. liquid

[0032] The liquid is preferably an ink, but it may also be a varnish, a primer, a coating, a cleaning liquid, a top protection coating, a pre-treatment liquid, a post-treatment liquid.

[0033] Liquid sediments lead to clogging of the liquid droplet generator (100) and poor storage stability of the liquid. They are mainly some particles of the liquid, which have a specific gravity between the particles and the liquid medium.

[0034] The liquid is preferably Pigmented inkjet inks , because the use of color pigments provides higher light stability to the decorative laminated panel than dyes. It can be a pigmented aqueous inkjet ink or a UV curable inkjet ink. The pigment is mainly present in the liquid precipitate.

[0035] Aqueous inkjet inks preferably comprise at least a colour pigment and water, more preferably completed with one or more organic solvents such as a wetting agent and a dispersant if the colour pigment is not a self-dispersible colour pigment.

[0036] The UV curable inkjet ink preferably comprises at least a color pigment, a polymer dispersant, a photoinitiator and a polymerizable compound, such as a monomer or an oligomer.

[0037] Preferably, the liquid Jetting viscosity Between 2mPa·s and 50mPa·s, and the liquid Injection temperature Between 20°C and 85°C. Jetting viscosity is measured by measuring the viscosity of the liquid at the jetting temperature. Jetting viscosity can be measured using various types of viscometers such as a Brookfield DV-II+ viscometer at the jetting temperature and a temperature corresponding to 90s -1The shear rate was measured at 12 rpm (rpm) using a CPE 40 rotor or at 1000 s using a HAAKE Rotovisco 1 rheometer with sensor C60 / 1Ti. -1 In a preferred embodiment, the jetting viscosity is from 10 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 can be measured using various types of thermometers. The jetting temperature of the jetted liquid is measured at the outlet of the nozzle in the liquid droplet generator (100) during jetting, or can be measured by measuring the temperature of the liquid in the liquid channel or nozzle when 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.

[0038] The liquid preferably has a pigment with an average particle size greater than 100 nm, more preferably 200 nm, or has a pigment in an amount greater than 16 wt% based on the total weight of the liquid. Such liquids are known to have problems with liquid sedimentation in the manifold of the liquid droplet generator (100). The pigment is preferably an inorganic pigment, and most preferably a white pigment as a colorant. Determination of numerical mean particle size This is best performed by photon correlation spectroscopy using a 4 mW HeNe laser at a wavelength of 633 nm on a diluted sample of the pigmented inkjet ink. A suitable particle size analyzer used is the Malvern Spectroscopy available from Goffin-Meyvis TM nano-S. For example, a sample can be prepared by adding a drop of ink to a cuvette containing 1.5 mL of ethyl acetate and mixing until a homogenous sample is obtained. The measured particle size is the average of 3 consecutive measurements consisting of 6 runs of 20 seconds.

[0039] White pigment Preferably, the pigment particles have a numerical average size greater than 180 nm in order to have a strong opacity. Suitable white pigments are given in Table 2 of

[0116] of WO 2008 / 074548 (AGFA GRAPHICS). White pigments are preferably pigments having a refractive index greater than 1.60. White pigments can be used alone or in combination. Preferably, titanium dioxide is used as the pigment having a refractive index greater than 1.60. Suitable titanium dioxide pigments are those disclosed in

[0117] and

[0118] of WO 2008 / 074548 (AGFA GRAPHICS).

[0040] If the liquid is based on a UV-curable pigmented inkjet ink, the liquid has to be cured by ultraviolet radiation. UV curing Chemical deviceIt can be arranged in combination with a liquid droplet generator (100), traveling therewith, so that the UV curable inkjet ink is exposed to curing radiation very shortly after it has been ejected. This method of curing is called "UV-pinning" and helps to provide high image quality, such as high definition. When the UV dose in UV-pinning is insufficient to obtain complete curing, UV-pinning is usually followed by a final UV curing step. As long as part of the emitted light can be absorbed by the photoinitiator or photoinitiator system, any UV light source can be used as a radiation source, such as high-pressure or low-pressure mercury lamps, cold cathode tubes, black light lamps, UV LEDs, UV lasers and flash lamps. Among them, the preferred source is a source that exhibits a relatively long wavelength UV contribution, which has a dominant wavelength of 300-400nm. In particular, a UV-A light source is preferred because it reduces the accompanying light scattering, resulting in more efficient internal curing. Preferably, UV LEDs are used for UV curing and especially UV pinning. In a particularly preferred embodiment, UV LEDs with an emission wavelength higher than 370nm are used for UV curing. In contrast to, for example, mercury bulbs, UV LEDs have a long life and an almost constant UV dose until the end of life. To facilitate curing, the inkjet printer may include one or more oxygen depletion units. The oxygen depletion unit places a nitrogen blanket or other relatively inert gas (e.g., CO2) with an adjustable position and an adjustable inert gas concentration to reduce the oxygen concentration in the curing environment. The residual oxygen level can be maintained as low as 200 ppm, but generally in the range of 200 ppm to 1200 ppm.

Claims

1. A method for printing a halftone image, wherein: The determined portion of the halftone image is printed by a plurality of nozzles of a liquid droplet generator (100) arranged in one or more rows, wherein the liquid droplet generator (100) has a liquid deposit with the highest density at a first location in a manifold of the liquid droplet generator (100), and wherein the manifold - having a first inlet (516) and a second inlet (517) for filling the manifold with liquid; - extending parallel to the plurality of nozzles between the first inlet (516) and the second inlet (517); and - configured to provide a liquid path for said liquid to said plurality of nozzles; wherein the portion is determined by using a print mask (1000) having a width and a height for displacing the liquid deposit to a second position in the manifold, the print mask (1000) dividing the plurality of nozzles into at least three consecutive zones between the first inlet (516) and the second inlet (517) during a selected printing period, the at least three consecutive zones comprising at least the following zones of the portion determined for printing: - a first zone (1001) at said first inlet (516), wherein said print mask (1000) determines that said nozzles of said first zone (1001) are used to print N1% of said portion; and - a second zone (1002) intermediate the first inlet (516) and the second inlet (517), wherein the print mask (1000) determines that the nozzles of the second zone (1002) are used to print N2% of the portion; and - a third zone (1003) at the second inlet (517), wherein the print mask (1000) determines that the nozzles of the third zone (1003) are used to print N3% of the portion; Among them, 100>=N1>N2>N3>=0.

2. The method according to claim 1, wherein: The print mask (1000) represents a blue noise halftone gradient from the nearest nozzle of the plurality of nozzles at the first inlet (516) to the nearest nozzle of the plurality of nozzles at the second inlet (517) and from dark to light, respectively.

3. The method according to the preceding claim, wherein: The printing mask (1000) divides the plurality of nozzles into a continuous area between the first inlet (516) and the second inlet (517) in another selected printing period after the selected printing period, wherein the continuous area at least includes the following areas for printing the determined portion: - a fourth zone at the first inlet (516), wherein the print mask (1000) determines that the nozzles in the fourth zone are used to print the portion, N4% of the portion; and - a fifth zone intermediate the first inlet (516) and the second inlet (517), wherein the print mask (1000) determines that the nozzles in the fifth zone are used to print the portion, N5% of the portion; and - a sixth zone at said second inlet (517), wherein said print mask (1000) determines said nozzles in said sixth zone for printing said portion, N6% of said portion; Among them, 0>=N4>N5>N6>=100.

4. A method according to any one of the preceding claims, wherein: The drop generator is part of a multi-pass inkjet printer, wherein the halftone image is printed in multiple passes and the parts are jetted in a single pass.

5. A method according to any one of the preceding claims, wherein: The first inlet (516) and the second inlet (517) fill the manifold at the same flow rate.

6. A method according to any one of the preceding claims, wherein: The determined portion of the halftone image is additionally printed by a further plurality of nozzles of the liquid droplet generator (100) arranged in one or more rows, wherein the liquid droplet generator (100) has a liquid deposit with the highest density at a third location in another manifold, and wherein the another manifold: - having a third inlet and a fourth inlet for filling said further manifold with said liquid; and - extends parallel to said further plurality of nozzles between said third inlet and said fourth inlet; and - configured to provide another liquid path for said liquid to said further plurality of nozzles; and wherein a complementary print mask (1000) of said print mask (1000) is additionally used to define said portion for displacing said liquid deposit of said liquid in said further manifold to a fourth position.

7. A method according to any one of the preceding claims, wherein: The jetting viscosity of the liquid is between 2 mPa·s and 50 mPa·s, and the jetting temperature of the liquid is between 20°C and 85°C.

8. The method according to claim 7, wherein: The liquid has a pigment having an average particle size greater than 150 nm or has the pigment in an amount greater than 16% by weight, based on the total weight of the liquid.

9. A method according to claim 8 or any one of the preceding claims, wherein: The pigment is an inorganic pigment.

10. The method according to claim 9, wherein: The inorganic pigment is a white pigment as a colorant.

Images