Printing method using a droplet generator

Abstract

A method of printing a halftone image with a droplet generator (100), the droplet generator (100) having a liquid deposit with the highest density at a first location in a generator manifold and having two inlets, a portion is determined to move the liquid deposit to a second location in the manifold by using a print mask (1000) having a width and height that separates the plurality of nozzles between the first inlet (516) and the second inlet (517) into at least three consecutive zones for a selected printing time, the at least three consecutive zones being determined by printing the determined portion in a first zone (1001) at the first inlet (516). a second zone (1002) in the middle of the first inlet (516) and the second inlet (517), wherein the printmask (1000) determines that the nozzles in the second zone (1002) are to be used for N2% of the portion; and a third zone (1003) at the second inlet (517), wherein the printmask (1000) determines that the nozzles in the third zone (1003) are to be used for N3% of the portion, where 100>=N1>N2>N3>=0.

Description

[Technical Field]

[0001] The present invention relates to imaging with a droplet generator, and avoids image quality problems caused by liquid-sedimentation in the droplet generator manifold. [Background technology]

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

[0003] Such imaging is widely used in devices such as printers (e.g., inkjet printers), as well as facsimile machines, copiers, plotters, multifunction peripherals, etc. The core of a typical ejection or imaging device is one or more droplet generators (also known as "printheads") having nozzles that eject droplets, mechanisms for moving the droplet generators and / or the media relative to each other, and a controller that controls how the individual nozzles of the droplet generators eject fluid onto the media in the form of pixels.

[0004] A typical drop generator includes multiple nozzles arranged in one or more rows (called "nozzle rows") along the ejection surface of the drop generator. Each nozzle is part of an "ejection channel," which includes the nozzle, a pressure chamber, and an actuator (e.g., a piezoelectric actuator). The drop generator also includes drive circuitry that controls when each individual ejection channel fires based on image data. To eject from an ejection channel, the drive circuitry provides ejection pulses to the actuator, which causes the actuator to deform the walls of the pressure chamber. The deformation of the pressure chamber creates a pressure wave within the pressure chamber that expels droplets of printing fluid (e.g., liquid) from the nozzle.

[0005] Drop-on-demand (DoD) printing is trending toward higher productivity and quality, which requires the ejection of smaller droplets at higher ejection frequencies. The print quality achieved by a droplet generator depends on its ejection or jetting characteristics, such as droplet velocity, droplet mass (or volume / diameter), and jetting direction. Unfortunately, liquid sedimentation inside the droplet generator, particularly in the manifold, negatively impacts the jetting characteristics and therefore image quality, especially when the droplet generator has a manifold with two inlets on either side of the manifold. Liquid sedimentation in the manifold occurs, for example, when the droplet generator is filled with liquid and not used for an extended period of time. Such a droplet generator is described in Patent Document 1 (RICOH). It has been shown that liquid sedimentation problems in the manifold of such a head can lead to nozzle malfunctions and density imbalances between droplets in the nozzles, resulting in an undesirable density profile of the droplet generator.

[0006] The problem of liquid sediment leads to frequent maintenance of droplet generators, using so-called "flushing" or "cleaning" liquids to unclog nozzles and clean the nozzle plates of the droplet generators. For example, Patent Document 2 (TOYO INK) discloses a maintenance liquid for inkjet printers containing at least one of glycol ethers and glycol esters and 45 to 10 mg / L of dissolved oxygen. Patent Document 3 (TOSHIBA TEC) discloses a cleaning solution for cleaning inkjet printer heads for cationic UV-curable inkjet inks, which contains 50 parts by weight or more of a polymerizable compound selected from at least two polymerizable compounds contained in the ink, the polymerizable compound having the lowest viscosity of the at least two polymerizable compounds, or 50 parts by weight or more of a polymerizable compound having a viscosity of 30 mPa.s or less at normal temperatures.

[0007] Research has shown that in the center of the manifold (the so-called dead zone), the liquid flow sinks due to the impingement of the liquid from the first and second inlets. In this situation, if the droplet generator is not used for a certain period of time, a liquid sediment forms at the bottom of the manifold (i.e., the side closest to the nozzle). However, when the manifold is (re)filled through the first and second inlets, the liquid sediment in the manifold accumulates in the dead zone. The liquid sediment here has a higher (volume mass) density than the liquid present elsewhere in the manifold. During printing, nozzles near the dead zone have been found to experience nozzle failure and / or large print density differences. This requires operators to maintain the droplet generator by flushing and / or cleaning, or to replace the expensive droplet generator, resulting in reduced production time. Therefore, there is a need for an efficient printing method for droplet generators that have not been used for a certain period of time and have liquid sediment in the manifold, without incurring expensive time-consuming maintenance procedures. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] European Patent Application Publication No. 3536508 [Patent Document 2] European Patent Application Publication No. 2157163 [Patent Document 3] European Patent Application Publication No. 1621348 Summary of the Invention

[0009] It has now been discovered that the above problems encountered while using a droplet generator (100) having a manifold with two inlets on either side of the manifold can be overcome by a method for printing a halftone image, wherein determined portions of the halftone image are printed by a plurality of nozzles of the droplet generator arranged in one or more rows; The droplet generator has a liquid sediment having a highest (volume mass) density at a first location in a manifold of the droplet generator, the manifold comprising: - having a first inlet (516) and a second inlet (517) for filling the manifold with liquid, - extending parallel to the nozzles between the first inlet (516) and the second inlet (517); - configured to provide a liquid path for the liquid to a plurality of nozzles; The portion is determined to move the liquid deposit to a second location in the manifold by using a print mask (1000) having a width and height that separates the plurality of nozzles between the first inlet (516) and the second inlet (517) into at least three consecutive zones for a selected printing time, the at least three consecutive zones being: a first zone (1001) at the first inlet (516), wherein a print mask (1000) determines that nozzles in the first zone (1001) are to be used for printing N1% of said portion; a second zone (1002) in the middle of the first inlet (516) and the second inlet (517), the print mask (1000) determining that the nozzles in the second zone (1002) are to be used for printing N2% of said portion; a third zone (1003) at the second inlet (517), wherein the print mask (1000) determines that the nozzles in the third zone (1003) are to be used for printing N3% of said portion; At least 100>=N1>N2>N3>=0. The manifold is preferably filled simultaneously through the first inlet and the second inlet.

[0010] The displacement of the liquid sediment eliminates nozzle defects and (printing) density profiles caused by liquid sediment in the manifold, thereby eliminating the need for maintenance (e.g., cleaning, flushing, etc.) of the droplet generator and extending the life of the droplet generator.

[0011] Further advantages and embodiments of the present invention will become apparent from the following description. [Brief explanation of the drawings]

[0012] [Figure 2] 1 is a cross-sectional view of the droplet generator 100 in the exemplary embodiment shown in FIG. 1 . Elements of the (supply) manifold 314 are visible through this cross-sectional view. The manifold 314 is formed by an extension 316 of the body 302 extending (from left to right in FIG. 2 ) between ends 317, 318. The manifold 314 is also formed by a first inlet 516 and a second inlet 517, 517 that fluidly connect a supply port 330 to the opposing ends 317, 318 of the extension 316. Thus, in this embodiment, printing fluid is supplied to the extension 316 at the opposing ends 317, 318. The extension 316 is a conduit for the flow of printing fluid. The bottom of the elongated body (316), and thus the manifold, opens to the ejection channels connected to the nozzles in the nozzle array (304). The elongated body (316) is therefore part of the (supply) manifold (314) that delivers printing fluid to the ejection channels. [Figure 3]One embodiment shows a nozzle array (304) of a droplet generator (100) having 15 nozzles (shown as circles). The selection of nozzles for ejection is determined by a two-pass (repeatable) printmask (1000) having a width of 7 and a height of 15, with the nozzle array divided into three consecutive zones (1001, 1002, 1003). A "1" in the printmask (1000) is used for the first pass, and a "2" in the printmask (1000) is used for the second pass. It is clear that first-pass nozzles in the first zone (1001) are used more than nozzles in the second zone (1002), which are used even more than nozzles in the third zone (1003). DETAILED DESCRIPTION OF THE INVENTION

[0013] Droplet generator The droplet generator (100) in this and preferred embodiments has one or more nozzle arrays for ejecting droplets of liquid, also known as a drop-on-demand printhead. Preferably, the droplet ejection is achieved using the piezoelectric effect. Such printheads are now common in home and office inkjet printing systems, as well as in industrial applications for both printmaking and digital manufacturing. Several actuation mechanisms are possible, including push-mode or squeeze-mode actuators.

[0014] The droplet generator (100) in this embodiment has an integral manifold extending parallel to the nozzle array, configured to provide a liquid path for the liquid to supply a plurality of nozzles. The liquid is supplied by a first inlet (516) and a second inlet (517), which are connected to the manifold on either side of the manifold. Preferably, no outlets are provided, as is known in reflow droplet generators. The liquid flow rate at both inlets determines the liquid flow in the manifold. Preferably, the flow rates at the first inlet (516) and the second inlet (517) are the same.

[0015] The droplet generator (100) may have a main liquid inlet that splits into the first inlet (516) and the second inlet (517), where a liquid supply is connected to the main liquid inlet from which further liquid is supplied to the droplet generator (100) via the first and second inlets (516, 517).

[0016] As previously mentioned, the fluid flow sinks around the center of such a manifold (the so-called dead zone) due to the collision of fluid from the first inlet and the second inlet, and the dead zone causes fluid sediment in the manifold to accumulate at high densities in the dead zone, which can cause nozzle failures and / or large density differences in nozzles near the dead zone during printing.

[0017] However, by using the print mask (1000) according to this and the preferred embodiments, the liquid sediment in the manifold can be displaced, thereby allowing the droplet generator (100) to be immediately used for printing without requiring maintenance, thereby allowing the operator to immediately begin producing printed articles.

[0018] The droplet generator is part of a multi-pass inkjet printer, where the halftone image is printed in multiple passes, with portions being ejected in a single pass, and where a printmask (1000) defines the nozzle firings in each pass.

[0019] In a preferred embodiment, the determined portion of the halftone image is additionally printed by one or more additional rows of nozzles of the droplet generator (100); The droplet generator (100) has the liquid sediment with the highest density at a third location in another manifold, the other manifold comprising: - a third inlet and a fourth inlet for filling the other manifold with liquid; extending parallel to the other plurality of nozzles between the third inlet and the fourth inlet; another liquid path for the liquid configured to supply another plurality of nozzles; A complementary printmask of printmask (1000) is additionally used to determine the portion of the liquid deposit in the other manifold that will move to a fourth location.

[0020] Printing System The droplet generator (100) is preferably part of a printing system, such as an inkjet printer, which is preferably for printing onto flat ink-receiving media, but can also be a three-dimensional printing system.

[0021] In a printing system, an image is formed by one or more of such drop generators capable of printing one ink or multiple inks.

[0022] The printing system is preferably configured to move the droplet generator (100) towards the portion of the image to be printed (such as a multi-pass inkjet printing system). A multi-pass inkjet printing method is used in the Jeti Tauro™ manufactured by AGFA NV, which has a maximum printable width of 254 cm and can accommodate rigid media up to 400 cm in length, for example.

[0023] The printing system may also be a hybrid printing device in which conventional printing technology and droplet technology are combined in the printing system.

[0024] We tested the idea of ​​shifting liquid deposits in the manifold after a period of no printing by printing a large right-angled triangle in white ink with a base and height. The height is oriented parallel to the nozzle row (and printing direction) and the base is oriented parallel to the scan direction of the droplet generator. By adjusting the base / height of a single colored triangle and / or by mirroring the triangle, it is possible to detect the shifting of liquid deposits in the manifold.

[0025] Printed mask The use of printmasks is well known in the art of printing using liquid ejection techniques, primarily in multi-pass inkjet printing. Printmasks are stored in the memory of the printing system, for example, in a hardware or software printer driver, and control signals applied to the droplet generators (100). The actual implementation of printmasks, either in hardware or software form, is considered to be within the skill of one with knowledge of the inkjet printer art, as applied in light of the teachings herein.

[0026] The print mask (1000) in this embodiment has a width and a height, and is a so-called two-dimensional print mask (1000). The width and height are greater than one.

[0027] The number of contiguous zones can be 3, 4, 5, 6, 7, 8, 9, or 10, or equal to the width of the printmask (1000) or the number of nozzles.

[0028] Preferably, the print mask (1000) represents a dark-to-light blue noise halftone gradient from the nozzle of the plurality of nozzles closest to the first inlet (516) to the nozzle of the plurality of nozzles closest to the second inlet (517).

[0029] In a preferred embodiment, the print mask (1000) divides the plurality of nozzles into another continuous zone between the first inlet (516) and the second inlet (517) for another selected printing time after the selected printing time, the other continuous zone being for printing a determined portion of: a fourth zone at the first inlet (516), where the print mask (1000) determines that the nozzles in the fourth zone are to be used for printing N4% of said portion; a fifth zone in the middle of the first inlet (516) and the second inlet (517), the print mask (1000) determining that the nozzles in the fifth zone are to be used for printing N5% of said portion; a sixth zone at the second inlet (517), where the print mask (1000) determines that the nozzles in the sixth zone are to be used for printing N6% of the portion; At least 0>=N4>N5>N6>=100.

[0030] In a preferred embodiment, the portion is determined by using a print mask (1000) that separates the plurality of nozzles into contiguous zones between the first and second inlets (516, 517) over a determined printing time, the contiguous zones comprising: a first zone (1001) at the first inlet (516), wherein the print mask (1000) determines that 100% to 80% of the determined portion is to be printed by the nozzles in the first zone (1001); a second zone (1002) in the middle of the first inlet and the second inlet (516, 517), where the print mask (1000) determines that the nozzles in the second zone (1002) are used to print 70% to 30% of the determined portion; a third zone (1003) at the second inlet (517), wherein the print mask (1000) determines that the nozzles in the third zone (1003) are to be used for printing a determined portion between 20% and 0%; At least The print mask (1000) more preferably divides the plurality of nozzles into (another) continuous zone between the first inlet and the second inlet (516, 517) for another determined printing time after the determined printing time has elapsed, the (another) continuous zone comprising: a fourth zone at the first inlet (516), where the print mask (1000) determines that the nozzles in the fourth zone are used to print between 20% and 0% of the determined portion; a fifth zone in the middle of the first inlet and the second inlet (516, 517), the print mask (1000) determining that the nozzles in the fifth zone are used to print 70% to 30% of the determined portion; - a sixth zone at the second inlet (517), where the print mask (1000) determines that the nozzles in the sixth zone are used to print 100% to 80% of the determined portion; At least includes.

[0031] liquid The liquid is preferably an ink, but can also be a varnish, a primer, a coating, a cleaning liquid, a surface protective coating, a pre-treatment liquid, or a post-treatment liquid.

[0032] Liquid sediment can cause clogging of the droplet generator 100 and poor storage stability of the liquid. Liquid sediment is primarily a few particles of the liquid, with a specific gravity between that of the particles and the liquid medium.

[0033] Since the use of color pigments provides the decorative laminate panel with greater light stability than dyes, the liquid is preferably Pigmented inkjet ink The liquid can be a pigmented water-based inkjet ink or a UV-curable inkjet ink, and the pigment is primarily found in the liquid sediment.

[0034] The aqueous inkjet ink preferably comprises at least a color pigment and water, and more preferably is completed by adding one or more organic solvents (such as a water retention agent) and a dispersant (if the color pigment is not a self-dispersing color pigment).

[0035] The UV curable inkjet ink preferably comprises at least a color pigment, a polymeric dispersant, a photoinitiator, and a polymerizable compound (such as a monomer or oligomer).

[0036] Preferably, liquid Ejection viscosity is 2mPa.s to 50mpA.s, and the liquid Ejection temperature The temperature is 20℃ to 85℃. Jetting viscosity is measured by measuring the viscosity of the liquid at the jetting temperature. -1 The viscosity is measured using various types of viscometers (such as a Brookfield DV-II+ viscometer) at 12 revolutions per minute (RPM) at the jetting temperature using a CPE40 spindle corresponding to a shear rate of 1000 s -1The jetting viscosity can be measured using a HAAKE Rotovisco 1 rheometer equipped with a sensor C60 / 1 Ti at a shear rate of 1000 kJ / min. In a preferred embodiment, the jetting viscosity is between 10 mPa·s and 200 mPa·s, more preferably between 25 mPa·s and 100 mPa·s, and most preferably between 30 mPa·s and 70 mPa·s. The jetting temperature can be measured using various types of thermometers. The jetting temperature of the jetted liquid can be measured at the outlet of the nozzle in the droplet generating device (100) during jetting, or by measuring the temperature of the liquid in the liquid channel or nozzle during jetting through the nozzle. In a preferred embodiment, the jetting temperature is between 10°C and 100°C, more preferably between 20°C and 60°C, and most preferably between 30°C and 50°C.

[0037] The liquid preferably has a pigment with an average particle size of more than 100 nm, more preferably more than 200 nm, or has a pigment amount of more than 16 wt %, based on the total weight of the liquid. Such types of liquids are known to have problems with liquid sedimentation in the manifold of the droplet generator (100). The pigment is preferably an inorganic pigment, most preferably a white pigment as the colorant. Determination of number average particle size is best performed by photon correlation spectroscopy at a wavelength of 633 nm using a 4 mW HeNe laser on diluted samples of pigmented inkjet ink. A suitable particle size analyzer used is the Malvern™ nano-S, available from Goffin-Meyvis. Samples can be prepared, for example, by adding one drop of ink to a cuvette containing 1.5 mL of ethyl acetate and mixing until a homogeneous sample is obtained. The measured particle size is the average of three consecutive measurements consisting of six 20-second runs.

[0038] White pigmentPreferably, the white pigment has a number-average pigment particle size of more than 180 nm so as to have a strong opacifying ability. Suitable white pigments are given in Table 2 of paragraph

[0116] of WO2008 / 074548 (AGFA GRAPHICS). The white pigment is preferably a pigment having a refractive index of more than 1.60. The white pigments may be used alone or in combination. Preferably, titanium dioxide is used as the pigment having a refractive index of more than 1.60. Suitable titanium dioxide pigments are those disclosed in paragraphs

[0117] and

[0118] of WO2008 / 074548 (AGFA GRAPHICS).

[0039] If the liquid is a UV curable based pigmented inkjet ink, the liquid needs to be cured by ultraviolet radiation. UV curing deviceThe UV-curable inkjet ink can be exposed to curing radiation immediately after ejection by a droplet generator (100). This curing method, called "UV pinning," is useful for achieving high image quality (e.g., high sharpness). If the UV dose during UV pinning is insufficient to achieve complete curing, a final UV curing step is often performed after UV pinning. Any UV source can be used as the radiation source (e.g., high- or low-pressure mercury lamps, cold cathode fluorescent lamps, black lights, UV LEDs, UV lasers, and flashlights) as long as a portion of the emitted light can be absorbed by the photoinitiator or photoinitiation system. Among these, preferred sources are those that exhibit a relatively long-wavelength UV contribution with a dominant wavelength of 300 to 400 nm. Specifically, UV-A light sources are preferred because of the associated reduced light scattering, which improves the efficiency of internal curing. UV curing, particularly UV pinning, is preferably performed using a UV LED. In a particularly preferred embodiment, UV curing is performed using a UV LED with an emission wavelength of greater than 370 nm. UV LEDs have a long lifespan and, in contrast to, for example, mercury bulbs, have a nearly constant UV dose over their lifespan. To facilitate curing, inkjet printers can include one or more oxygen reduction units. The oxygen reduction units reduce the oxygen concentration in the curing environment by providing an atmosphere of nitrogen or other relatively inert gas (e.g., CO2) at an adjustable location with an adjustable inert gas concentration. Residual oxygen levels can be maintained as low as 200 ppm, but are generally in the range of 200 ppm to 1200 ppm.

Claims

1. 1. A method for printing a halftone image, comprising: printing a determined portion of said halftone image by a plurality of nozzles of a droplet generator (100) arranged in one or more rows; The droplet generator (100) has a liquid sediment having a highest density at a first location in a manifold of the droplet generator (100), the manifold comprising: - has a first inlet (516) and a second inlet (517) for filling said manifold with liquid, - extending parallel to said plurality of nozzles between said first inlet (516) and said second inlet (517); - a liquid path for said liquid configured to supply said plurality of nozzles; the portion is determined so that the liquid deposit moves to a second location in the manifold by using a print mask (1000) having a width and height that separates the plurality of nozzles between the first inlet (516) and the second inlet (517) into at least three consecutive zones for a selected printing time, the at least three consecutive zones being arranged to print the determined portion; a first zone (1001) at said first inlet (516), said first zone (1001) being determined by said print mask (1000) to use nozzles of said first zone (1001) for printing N1% of said portion; a second zone (1002) in the middle of the first inlet (516) and the second inlet (517), the second zone (1002) being determined by the print mask (1000) to use the nozzles of the second zone (1002) for printing N2% of the portion; a third zone (1003) at said second inlet (517), said third zone (1003) being determined by said print mask (1000) to use nozzles of said third zone (1003) for printing N3% of said portion; At least The method, wherein 100>=N1>N2>N3>=0.

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

3. the print mask (1000) divides the plurality of nozzles into contiguous zones between the first inlet (516) and the second inlet (517) for another selected printing time after the selected printing time has elapsed, the contiguous zones being configured to print a determined portion; a fourth zone at said first inlet (516), said fourth zone being determined by said print mask (1000) to use nozzles in said fourth zone for printing N4% of said portion; a fifth zone in the middle of said first inlet (516) and said second inlet (517), said fifth zone being determined by said print mask (1000) to use nozzles in said fifth zone for printing N5% of said portion; a sixth zone at said second inlet (517), said sixth zone being determined by said print mask (1000) to use nozzles in said sixth zone for printing N6% of said portion; At least 10. The method of the preceding claims, wherein 0>=N4>N5>N6>=100.

4. 10. A method according to any preceding claim, wherein the droplet generator is part of a multi-pass inkjet printer, and wherein the halftone image is printed in multiple passes, and wherein the portions are jetted in a single pass.

5. 10. The method of any preceding claim, wherein the first inlet (516) and the second inlet (517) fill the manifold at the same flow rate.

6. the determined portion of the halftone image is additionally printed by one or more additional rows of nozzles of the droplet generator (100); The droplet generator (100) has a liquid sediment with the highest density at a third location in another manifold, the other manifold comprising: - a third inlet and a fourth inlet for filling said other manifold with said liquid; extending parallel to the other plurality of nozzles between the third inlet and the fourth inlet, - another liquid path for said liquid is configured to supply said other plurality of nozzles; 10. A method according to any preceding claim, wherein a complementary print mask (1000) of the print mask (1000) is additionally used to determine the portion of the liquid in the other manifold such that the liquid sediment moves to a fourth position.

7. 10. A method according to any preceding claim, wherein the jetting viscosity of the liquid is from 2 mPa.s to 50 mpA.s and the jetting temperature of the liquid is from 20°C to 85°C.

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

9. The method of claim 8 wherein the pigment is an inorganic pigment.

10. The method of claim 9, wherein the inorganic pigment is a white pigment as a colorant.

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