Method for operating a printing device, printing device, and software product

Abstract

The present invention relates to a method for applying an image onto a receiver medium, the image being applied onto a recording medium (15) by depositing a UV-curable ink (17), the ink being irradiated with radiation (10a, 10b), the radiation comprising two types of UV radiation (10a, 10b). The present invention further relates to a printing apparatus and a software product.

Description

[Technical Field]

[0001] The present invention relates to a method for applying an image onto a receiver medium, the image being applied onto the recording medium by depositing a UV-curable ink, the ink being irradiated with radiation, the radiation comprising two types of UV radiation. The present invention further relates to a printing apparatus and a software product. [Background technology]

[0002] Methods for operating a printing device with radiation-curable inks are known in the art and generally involve applying the radiation-curable ink onto a recording medium, for example, by ejecting droplets of the ink using an inkjet printer.

[0003] After the ink has been applied onto the recording medium, the ink is hardened by irradiating the ink with a curing unit configured to emit a suitable radiation source, such as UV radiation, when in operation. The radiation source may be included in the curing unit. The curing unit may be a pagewidth curing unit. An example of a printing apparatus including such a pagewidth curing unit is disclosed in EP 3481640.

[0004] When preparing a printed image, it is desirable for the ink to adhere well to the receiving medium in order to obtain a robust image. However, it is often observed that the ink does not adhere well to the recording medium. This is also referred to as poor adhesion of the ink to the recording medium. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] European Patent Application Publication No. 3481640 Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, a need exists for a printing method that provides prints that have sufficient adhesion to the recording medium.

[0007] It is therefore an object of the present invention to provide a printing method by which a print having sufficient adhesion to a recording medium is prepared. It is a further object of the present invention to provide a printing apparatus by which a print having sufficient adhesion to a recording medium can be prepared. [Means for solving the problem]

[0008] The objects of the present invention are realized by a method for applying an image onto a receiver medium, the method comprising: a) applying a predetermined pattern of UV curable ink onto a recording medium to form an image; b) exposing the UV curable ink to UV radiation, the UV radiation comprising at least two types of UV radiation, a first type of UV radiation having a first wavelength and a second type of UV radiation having a second wavelength, the first wavelength being shorter than the second wavelength; In step b, The ink is first irradiated with a first type of radiation at a first intensity and a second type of radiation at a second intensity, the first intensity being greater than the second intensity.

[0009] The method may be performed using a printing device. The printing device may also be referred to as a printer. The printer may be configured to apply UV curable ink during a printing operation. The UV curable ink may be a UV curable inkjet ink, such as a UV gel ink. Suitable types of radiation curable inkjet inks, including UV curable inkjet inks, are known in the art. Preferably, the printer may be an inkjet printer configured to apply ink onto a recording medium by ejecting droplets of the ink onto the recording medium in a predetermined pattern to form an image.

[0010] The printing apparatus may comprise a print unit configured to, in operation, deposit a predetermined pattern of UV curable ink onto the recording medium, and in step a) of the method according to the invention, the predetermined pattern of UV curable ink is applied onto the recording medium to form an image.

[0011] The print unit may include at least one inkjet printhead configured to eject ink onto the recording medium during operation. The printhead may be, for example, a thermal inkjet printhead or a piezoelectric inkjet printhead. The printer may include multiple inkjet printheads. One type or color of ink may be used to form the image; however, alternatively, multiple types and / or colors of ink may be used. Cyan, magenta, yellow, and black ink may be used to form the image. Additionally, one or more of white ink, brown ink, gray ink, light magenta, light cyan, red, green, orange, and purple ink may be used. Additionally, one or more of a primer composition, an overcoat composition, and a metallic ink may be used. The print unit may be a pagewidth print unit or a scanning print unit. The scanning print unit may be configured to move back and forth in a scanning direction during operation. The scanning direction may be perpendicular to the media transport direction.

[0012] The printing device may further comprise a media support. The media support may be configured to support the recording medium during operation. Optionally, the recording medium may be moved in a media transport direction. The media support may comprise a flat table. Optionally, the media support may comprise an endless belt. The media support may comprise holes for applying underpressure. The application of underpressure may secure the recording medium to the media support.

[0013] Optionally, the printing device may include a media transport unit, which may be configured to, in operation, move the recording medium relative to the printer in a media transport direction.

[0014] The printing apparatus further includes a curing unit. The curing unit is configured to irradiate the recording medium supplied with the UV-curable ink during operation. Irradiating the UV-curable ink can cause a chemical reaction in the UV-curable ink, which can result in curing or pre-curing of the fluid. The curing unit can be a scanning curing unit. Alternatively, the curing unit can be a pagewidth curing unit. The pagewidth array can extend in a first direction, which is substantially perpendicular to a relative recording medium transport direction. The recording medium can move relative to the scanning print unit. The relative movement is achieved by moving at least one of the recording medium and the print unit. The direction of relative movement of the print unit and the recording medium is the relative recording medium transport direction.

[0015] In the method according to the present invention, in step b) the UV curable ink is irradiated with UV radiation; the UV radiation comprises at least two types of UV radiation, the first type of UV radiation having a first wavelength and the second type of UV radiation having a second wavelength, the first wavelength being shorter than the second wavelength.

[0016] UV radiation is electromagnetic radiation. The wavelength of UV radiation ranges from 100 nm to 415 nm. The effect of UV radiation on UV-curable inks may depend on the wavelength of the UV radiation.

[0017] UV-C radiation is UV radiation having a wavelength ranging from about 100 nm to about 280 nm. UV-B radiation is UV radiation having a wavelength ranging from about 280 nm to about 315 nm. UV-A radiation is UV radiation having a wavelength ranging from about 315 nm to about 415 nm. UV-C, UV-B, and / or UV-A radiation may be used in the present invention. The first and second types of radiation may be selected from UV-C, UV-B, and UV-A radiation. Optionally, both the first wavelength and the second wavelength may fall within one of UV-C, UV-B, or UV-A radiation, provided that the first wavelength is shorter than the second wavelength.

[0018] In one embodiment, the intensity of the radiation can be irradiance, which is the energy impinging on a unit horizontal area per unit time and has standard units of Wm. -2 The first type of radiation may have a first irradiance, while the second type of radiation may have a second irradiance.

[0019] In one embodiment, the ink may be first irradiated in a first curing zone. The first curing zone may be an area on the recording medium. The first curing zone is an area where the ink deposited on the recording medium is first irradiated. Upstream of the first curing zone in the media transport direction, the ink deposited on the recording medium may not receive radiation.

[0020] In one embodiment, the first wavelength may have a particular distribution, and the second wavelength may also have a particular distribution, and the wavelength may refer to the wavelength with the highest intensity among all wavelengths in the wavelength distribution.

[0021] In the method according to the invention, in step b, the ink is first irradiated with a first type of radiation at a first intensity and a second type of radiation at a second intensity, the first intensity being greater than the second intensity.

[0022] Surprisingly, it has been found that this can result in improved adhesion of the ink onto the recording medium after curing of said ink.

[0023] In one embodiment, the ink is then irradiated with the first type of radiation at a third intensity and the second type of radiation at a fourth intensity, the fourth intensity being greater than the third intensity.

[0024] The intensities of the first type of UV radiation and the second type of UV radiation can vary over time. First, the intensity of the first type of radiation can be higher than the intensity of the second type of radiation. Second, the intensity of the second type of radiation can be higher than the intensity of the first type of radiation. The second type of radiation has a larger wavelength than the first type of radiation, which can lead to different curing behavior than the first type of radiation. For example, applying a relatively high intensity of the second type of radiation after the initiation of curing can result in improved through-cure of the ink layer. Through-cure is curing within the ink layer.

[0025] In the printing system, the recording medium is moved in a media transport direction during a printing operation, and at a first location, the radiation has a first wavelength distribution, and at a second location, the radiation has a second wavelength distribution. In the first wavelength distribution, the first intensity is greater than the second intensity, and in the second wavelength distribution, the fourth intensity is greater than the third intensity. The first location can be upstream of the second location in the media transport direction. Thus, as the recording medium is moved relative to the curing unit, the recording medium is first irradiated with the first wavelength distribution and then with the second wavelength distribution. This can result in improved through-cure of the ink layer. Improved through-cure can result in improved adhesion of the ink layer.

[0026] In one embodiment, the ink is irradiated with the first type of radiation at a third intensity and the second type of radiation at a fourth intensity in a second curing zone. The second curing zone can be an area on the recording medium. The second curing zone can be a location downstream of the first curing zone in the media transport direction.

[0027] In one embodiment, at the start of irradiation, the intensity of the first type of radiation is increased at a first rate and the intensity of the second type of radiation is increased at a second rate, the first rate being at least three times higher than the second rate.

[0028] First, the intensity of the first type of radiation may be increased at a faster rate than the intensity of the second type of radiation. Thus, early in the curing process, the ink may be subjected to a relatively high dose of the first type of radiation and a relatively low dose of the second type of radiation. This may result in improved adhesion of the ink to the recording medium.

[0029] In a further embodiment, the intensity of the UV radiation may be low at the beginning of the irradiation, which may be increased in later stages of the irradiation.

[0030] In one embodiment, the intensity of the second type of radiation is zero.

[0031] When the ink applied to the recording medium is first exposed to radiation, the radiation may not include the second type of radiation, in which case the curing process may be initiated using the first type of radiation rather than the second type of radiation.

[0032] In one embodiment, the UV-curable ink is a gelling UV-curable ink.

[0033] A particular class of UV-curable inkjet ink compositions is gelled UV-curable inkjet ink compositions. These inks are fluid at elevated temperatures and become solid at lower temperatures, even if not yet cured. These inks are typically jetted at elevated temperatures. Gelled UV-curable inks can become solid or semi-solid when cooled on a recording medium, such as a sheet of paper. As a result, spreading of ink droplets on the recording medium can be reduced and color bleeding can be prevented.

[0034] Gelled UV-curable inkjet inks may be jetted at high temperatures and may undergo a rapid increase in viscosity when jetted onto a recording medium. Due to the increased viscosity, ink droplets jetted onto the recording medium cannot spread much, and therefore, bleeding of color can be prevented even if the ink composition is not immediately cured after being applied to the recording medium. The gelling behavior may be achieved by adding a suitable gelling agent to the UV-curable ink composition.

[0035] When using UV gelling ink, it may be possible to achieve a time interval between applying the ink to the recording medium and irradiating the ink. Therefore, it may be easier to control the timing of the irradiation step. Furthermore, using gelling UV curable ink may allow multiple layers to be applied before the ink is irradiated.

[0036] In one embodiment, the second wavelength is in the range of 375 nm to 415 nm.

[0037] UV radiation in the range of 375 nm to 415 nm can efficiently induce the curing reaction of ink applied to a recording medium. UV radiation in the range of 375 nm to 415 nm can improve the surface curing of ink. Surface curing can be hindered by oxygen inhibition. Therefore, using UV radiation in the range of 375 nm to 415 nm can be advantageous because it can result in a printed image that has undergone sufficient surface curing.

[0038] In one embodiment, the first wavelength is in the range of 100 nm to 315 nm.

[0039] UV radiation having a wavelength in the range of 100 nm to 315 nm is a type of radiation that can efficiently induce polymerization reactions in inks. This type of radiation has high energy compared to types of UV radiation with longer wavelengths. Without wishing to be bound by any theory, it is believed that this type of UV radiation with extremely high energy value can efficiently induce polymerization reactions in inks, thereby leading to satisfactory curing properties.

[0040] In one embodiment, the first wavelength is in the range of 350 nm to 395 nm.

[0041] UV radiation, having a wavelength in the range of 100 nm to 315 nm, is another type of radiation that can efficiently induce polymerization reactions in inks.

[0042] In one embodiment, the difference between the first wavelength and the second wavelength is between 5 nm and 50 nm.

[0043] The wavelength difference can be in the range of 5 nm to 50 nm. If the wavelength difference is less than 5 nanometers, the difference in the curing behavior induced by the two types of radiation may be too small. A wavelength difference between 5 nm and 50 nm can efficiently induce curing of the ink.

[0044] In one embodiment, in step a), the predetermined pattern comprises multiple ink layers.

[0045] A printed image may include multiple layers of ink. The ink may be applied in multiple swaths, with new layers of ink applied over previously applied layers of ink. The layers may integrally form an image. Alternatively, different layers may have different appearances. For example, a background layer may be formed and then an image layer may be formed. The image layer may be applied on top of the background layer, or the background layer may be applied on top of the image layer. The background layer may be formed by a single background color, such as white. The image layer may be formed by multiple different colored inks. Preferably, all ink layers are applied onto the recording medium before the ink is cured. The use of UV gelling inks allows for the application of relatively thick layers onto the recording medium before curing the ink. Thick layers of ink are difficult to cure because radiation must penetrate the thick layer of ink to cure the entire layer, including the ink-recording medium interface, the layer mass, and the ink-air interface. The present invention allows for the efficient curing of the entire ink layer and the creation of prints with sufficient adhesion.

[0046] In one aspect of the present invention, there is provided a printing device, the printing device comprising: At least one print unit for depositing UV-curable ink; · Hardening unit; · Recording medium support for supporting recording media; a control unit configured to control the printing device so that, in operation, it performs the method according to the invention; Equipped with.

[0047] The printer is therefore configured to carry out the method according to the invention.

[0048] In a further aspect of the present invention, there is provided a software product comprising program code on a non-transitory machine-readable medium, the program code, when loaded into a controller of a printing device comprising at least one printing unit for depositing UV curable ink, a curing unit, and a control unit, causing the controller to perform a method according to the present invention.

[0049] The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings, which are provided for purposes of illustration only and are therefore not limiting of the present invention. [Brief explanation of the drawings]

[0050] [Figure 1] 1 is a schematic perspective view of a first example of a printing system according to the present invention in a first printing mode; [Figure 2] FIG. 2 is a schematic perspective view of a second example of a printing system according to the present invention in a second printing mode. [Figure 3] FIG. 3 is a schematic diagram of a control unit of the reproduction system according to FIG. 1 or 2. [Figure 4] FIG. 1 shows a schematic diagram of a first example of a method according to the invention. [Figure 5] FIG. 2 shows a schematic representation of a second example of the method according to the invention. [Figure 6A] FIG. 4 shows a schematic diagram of a third example of the method according to the invention. [Figure 6B] 6B is a diagram illustrating the intensities of the first type of radiation and the second type of radiation at different positions according to the third example shown in FIG. 6A; [Figure 7A] FIG. 4 shows a schematic diagram of a fourth example of the method according to the invention. [Figure 7B] 7B is a diagram illustrating the intensities of the first type of radiation and the second type of radiation at different positions according to the fourth example shown in FIG. 7A. [Figure 8A] FIG. 10 is a schematic diagram of a stiffening array according to a fifth example of the present invention. [Figure 8B] FIG. 10 is a schematic diagram of a pagewide stiffening array according to a sixth embodiment of the present invention. [Figure 9] FIG. 10 shows a schematic diagram of a seventh example of the method according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0051] In the drawings, like reference numbers refer to like elements.

[0052] The present invention will now be described with reference to the accompanying drawings, wherein the same reference numerals are used throughout the several views to identify the same or similar elements.

[0053] Printing System FIG. 1 illustrates a printing apparatus, also known as a printer. The printing apparatus 1 includes a scanning and printing unit 7 for printing on a recording medium 15. The recording medium 15 in FIG. 1 is a relatively rigid substrate, such as a panel. The recording medium 15 is supplied from a media input unit 14, which may be configured to store a plurality of such print media 15 and supply them to the printer 1. The printer 1 includes a media support 4. The printer 1 may further include transport means for receiving and transporting the recording medium 15 along the scanning and printing unit 7. In FIG. 1, the media support is embodied as an endless belt 4. The endless belt is an endless transport belt 4 supported on a plurality of support rollers 3A, 3B, and 3C. At least one of the support rollers 3A, 3B, and 3C is provided with a drive means for moving the belt 4. Thus, the belt 4 is configured to support and transport the recording medium. Furthermore, one or more of the support rollers 3A, 3B, and 3C may be configured to be moved and / or tilted to adjust and control the lateral position of the belt 4. The scanning and printing unit 7 may be provided with a sensor 8, such as a CCD camera, for determining the relative position of the belt 4 and / or the recording medium 15. Data from the sensor 8 may be used to control the position of the belt 4 and / or the recording medium 15. The belt 4 may further be provided with through-holes and a suction box connected to a suction source (not shown) so that negative pressure can be applied to the recording medium 15 through the through-holes of the belt 4. The negative pressure tightly holds the recording medium 15 to the belt 4 and prevents displacement of the recording medium 15 relative to the belt 4. This belt 4 retention allows the recording medium 15 to be transported. It will be understood that other suitable transport means, such as rollers or steppers, may alternatively be applied. The recording medium 15 may be transported in steps and / or continuously. The scanning and printing unit 7 is configured to translate along the first guide beam 6 in a scanning direction, which is perpendicular to the direction in which the print medium is transported by the belt 4.The scanning and printing unit 7 carries a plurality of printheads (not shown) configured to jet a plurality of different marking materials (different color inks, primers, coatings, etc.) onto the recording medium 15. Each marking material for use by the scanning and printing unit 7 is stored in one of a plurality of reservoirs disposed in fluid communication with a respective printhead for the purpose of supplying the marking material to said printhead for printing an image on the recording medium 15.

[0054] The application of marking material, such as radiation-curable ink, from a printing unit occurs according to data provided in each print job. The printing unit may include one or more inkjet printheads. The timing at which droplets of marking material are ejected from the one or more printheads determines their position on the recording medium 15. The timing may be adjusted based on the position of the scanning printing unit 7 along the first guide beam 6. The above-mentioned sensor 8 may be applied thereto to determine the relative position and / or velocity of the scanning printing unit 7 with respect to the recording medium 15. Based on the data from the sensor 8, the timing of the ejection of the marking material may be adjusted.

[0055] As the marking material is ejected, some of the marking material may spill and remain on the nozzle surface of the printhead. Marking material present on the nozzle surface adversely affects the ejection of droplets and the placement of these droplets on the recording medium 15. Therefore, it may be advantageous to remove excess marking material from the nozzle surface. Excess marking material may be removed, for example, by wiping with a wiper and / or by application of a suitable surface anti-wetting property, such as provided by a coating.

[0056] The marking materials may require processing to properly fuse them onto the print media. Therefore, a fuser unit is provided downstream of the scan-print unit 7. The fuser unit can emit radiation to facilitate the marking material fusing process. In the example of FIG. 1, the fuser unit is a pagewidth curing array 10. The pagewidth curing array 10 extends in the main scan direction. The pagewidth curing array does not move in the main scan direction during operation. The pagewidth array can move in the media transport direction, which is perpendicular to the scan direction. In an alternative embodiment (not shown), the fuser unit may be a scan-fusing unit, which moves back and forth in the scan direction during operation.

[0057] The pagewide curing array 10 is configured to emit radiation of a certain frequency that interacts with the marking material, e.g., UV light in the case of UV-curable inks, in operation. Optionally (not shown), the scanning print unit 7 may be provided with an additional fusing unit on the same carriage that holds the printheads. This additional fusing unit may be used to (partially) cure and / or harden the marking material, either independently of the pagewide curing array 10 or in interaction with the pagewide curing array 10.

[0058] After printing and fusing, the recording medium 15 is transported to a receiving unit (not shown), which may include a take-up roller for winding up the recording medium 15, a receiving tray for supporting sheets of recording medium 15, or a rigid media handler similar to the media input unit 14. Optionally, the receiving unit may include processing means for processing the media 8, 9 after printing, for example, post-processing devices such as a coater, folder, cutter, or puncher.

[0059] The printing device 1 further comprises a user interface 11 for receiving and, optionally, manipulating print jobs. The local user interface unit 11 is integrated into the print engine and may comprise a display unit and a control panel. Alternatively, the control panel may be integrated into the display unit, for example in the form of a touchscreen control panel. The local user interface unit 11 is connected to a control unit 12 connected to the printer 1. The control unit 12, for example a computer, comprises a processor adapted to issue commands to the printer 1, for example to control the printing process. The printer 1 may optionally be connected to a network. The connection to the network may be via a cable or wirelessly. The printer 1 may receive print jobs via the network. Furthermore, optionally, the control unit 12 of the printer 1 may be provided with an input port, such as a USB port, so that print jobs may be sent to the printer 1 via this input port.

[0060] Hybrid Printing System The printer 1 in FIG. 1 is a so-called hybrid printer that can handle both flexible and rigid substrates. In FIG. 1, the printer 1 is operating in a first printing mode, and the printer 1 is configured to transport a rigid substrate, such as a recording medium 15. Such rigid printing media 15 can be panels, such as panels for doors or walls, corrugated media, plates made of plastic or metal, and the like. To handle these rigid printing media 15, the printer 1 in FIG. 1 is configured with a substantially linear transport path from the media input device 14, in which the recording medium 15 moves forward along the scanning printing unit 7 at a substantially constant height. The media input unit 14 and receiving unit are positioned at the level of the media support surface of the belt 14. In FIG. 2, a flexible web media 16 is fed into the printer 1. The web media 16 may be, for example, paper, adhesive printing sheets, coated paper, plastic, or a woven fabric. The web media 16 is fed from an input roller 2A and extends across the belt 4 to a take-up roller 2B, where the web media 16 is rewound. Printer 1 is configured to switch between print modes quickly and efficiently.

[0061] control An embodiment of the control unit 12 is presented in more detail in Fig. 3. As shown in Fig. 3, the control unit 12 comprises a central processing unit (CPU) 31, a graphical processor unit (GPU) 32, a random access memory (RAM) 33, a read-only memory (ROM) 34, a network unit 36, an interface unit 37, a hard disk (HD) 35, and an image processing unit 39, such as a raster image processor (RIP). The aforementioned units 31-37 are interconnected through a bus system 38. However, the control unit 12 can also be a distributed control unit.

[0062] The CPU 31 controls the printing system 1 according to a control program stored in the ROM 34 or on the HDD 35 and the local user interface panel 5. The CPU 31 also controls the image processing unit 39 and the GPU 32. The ROM 34 stores programs and data, such as a boot program, a setup program, and various setup data, that are read and executed by the CPU 31. The hard disk 35 is an example of a non-volatile storage unit for storing and saving programs and data that cause the CPU 31 to execute the printing process described later. The hard disk 35 also includes an area for saving data of a print job submitted externally. The programs and data on the HDD 35 are read by the CPU 31 into the RAM 33 as needed. The RAM 33 has an area for temporarily storing programs and data read by the CPU 31 from the ROM 34 and the HDD 35, as well as a work area used by the CPU 31 to execute various processes. The interface unit 37 connects the control unit 12 to client devices, such as the scanning device 19, and the printing system 1. The network unit 36 ​​connects the control unit 12 to a network N and is designed to provide communication with workstations (not shown) and with other devices 19 reachable via the network N. The image processing unit 39 may be implemented as a software component running on the operation system of the control unit 12 or as a firmware program embodied in, for example, a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). The image processing unit 39 has the functionality to read, interpret, and rasterize print job data. The print job data includes image data to be printed (i.e., fonts and graphics describing the content of the document to be printed or written in a page description language, for example), image processing attributes, and print settings.

[0063] FIG. 4 illustrates a schematic diagram of a first example of a method according to the present invention. A print unit 7 is provided that is configured to eject ink droplets 17 onto a receiver medium 15. While only one print unit 7 is depicted in FIG. 4, in practice, multiple printheads, optionally ejecting inks of different colors, may be provided. Each droplet of droplet 17 is in a fluid state when ejected by the print unit 7. To bring the ink into and maintain a fluid state, the print unit 7 may be provided with heating means (not shown). The ink may begin to cool after being ejected from the print unit 7 through a nozzle (not shown). As the ink cools, the ink may undergo a phase change. The receiver medium 15, to which the ink droplets 17 are applied, is moved in a direction Y, which is the recording medium transport direction. For example, when a scanning inkjet process, as shown in FIGS. 1 and 2, is used, the recording medium transport direction is often referred to as the sub-scan direction. After the ink droplets are applied, the droplets continue to cool and may undergo a phase change, resulting in the formation of immobile droplets 18. The stuck droplets 18 are transported together with the receiver medium 15 in the recording medium transport direction Y. This causes the stuck droplets 18 to move directly beneath the first UV radiation source 10a. The first UV radiation source 10a emits a first type of radiation, shown schematically as a radiation beam 22. The radiation emitted by the first source 10a may have a first intensity. The stuck droplets 18 are irradiated by the radiation beam 22 emitted by the first radiation source 10a.

[0064] After the droplets 18 have been irradiated by the first radiation source 10a, the droplets are moved beneath a second UV radiation source 10b, which emits a second type of radiation, shown schematically as a beam of radiation 23. The radiation emitted by the second source 10b may have a second intensity that is lower than the first intensity. The immobilized droplets are further cured by the beam of radiation 23 emitted by the second radiation source 10b. Further curing of the droplets 18 fixes them onto the receiver medium 15, forming a robust image.

[0065] The types of the first UV radiation source 10a and the UV second radiation source 10b may be selected appropriately.

[0066] FIG. 5 shows a schematic diagram of a second example of a method according to the present invention. The third example differs from the first example in the nature of the first and second radiation sources. The radiation source according to the third example is an assembly of a global UV radiation source 10 and a filter. A first filter 10c and a second filter 10d are provided. The first and second filters 10c, 10d may be, for example, optical filters. Each of the filters 10c, 10d absorbs a portion of the radiation emitted by the global UV radiation source 10 and transmits a portion of the UV radiation emitted by the global UV radiation source 10. A portion of the beam of radiation, shown schematically as radiation ray 20, passes through the first filter 10c, and another portion of the beam passes through the second filter 10d. The portion of the beam that passes through the first filter 10c provides a first beam of radiation, shown schematically as radiation ray 22. The radiation in the first beam of radiation has a first wavelength and a first intensity.

[0067] A second filter 10d is provided adjacent to the first filter 10c. A portion of the beam emitted by the overall radiation source 10 that passes through the second filter 10d provides a second beam of radiation, shown schematically as a ray of radiation 23. The radiation of the second beam of radiation has a second wavelength and a second intensity. Thus, the first filter 10c and the second filter 10d each absorb a portion of the radiation emitted by the overall radiation source 10, thereby generating two different beams of radiation, each having a different wavelength. The first filter 10c is provided upstream in the media transport direction compared to the second filter 10d. Thus, ink droplets applied and immobilized on the receiver medium 15 first pass beneath the first filter 10c and are thereby irradiated with the first type of radiation. Subsequently, droplets 18 pass beneath the second filter 10d and are then irradiated with the second type of radiation.

[0068] Therefore, in this embodiment, the first radiation source and the second radiation source are suitably embodied by providing a general radiation source 10 and first and second filters 10c, 10d.

[0069] FIG. 6A illustrates a third example of a method according to the present invention. A first radiation source 10a and a second radiation source 10b are provided. The first radiation beam 22a emitted by the first radiation source 10a diverges; that is, the beam diameter increases with increasing distance from the radiation source 10a. The radiation emitted by the first radiation source 10a is of the first type. The second radiation beam 23a emitted by the second radiation source 10b also diverges. The radiation emitted by the second radiation source 10b is of the second type. The first and second radiation beams 22a and 23a irradiate a receiver medium 15 and droplets 18 deposited thereon. The droplets form an ink layer. As the droplets 18 move in the paper transport direction, they are first irradiated by the first radiation source 10a. Irradiation by the first radiation source 10a begins at point A. In a printing operation, the recording medium 15 and curing units 10a, 10b move relative to each other in direction Y. A location on the recording medium will first pass point A, then point B, then point C, and then point D.

[0070] Figure 6B shows a schematic representation of the intensities of the first and second types of radiation at different positions according to the third example shown in Figure 6A. Point A represents the first curing zone. At point A, the ink is irradiated by the first beam 22a. Thus, the ink receives the first type of radiation but not the second type of radiation. The first type of radiation is increased at a rate r1 at the start of the radiation (point A).

[0071] At point B, the ink is irradiated with both the first type of radiation and the second type of radiation. 1-1 while the intensity of the second type of radiation is I 2-1 At point B, the intensity of the first type of radiation is I 1-1 is the intensity of the second type of radiation I 2-1 Higher than.

[0072] Point C represents the second curing zone. At point C, as at point B, the ink is irradiated with both the first type of radiation and the second type of radiation. At point C, the intensity of the first type of radiation I 1-2 is the intensity of the second type of radiation I 2-2 Higher than.

[0073] Halfway between points C and D, the intensity of the first type of radiation is reduced to zero. At point D, the intensity of the second type of radiation is also zero.

[0074] FIG. 7A schematically illustrates a fourth example of a method according to the present invention. Similar to the example shown in FIG. 7A, a first radiation source 10a and a second radiation source 10b are provided. The first radiation beam 22a emitted by the first radiation source 10a diverges; that is, the beam diameter increases with increasing distance from the radiation source 10a. The radiation emitted by the first radiation source 10a is a first type of radiation. Furthermore, the second radiation beam 23a emitted by the second radiation source 10b also diverges. The radiation emitted by the second radiation source 10b is a second type of radiation. The first and second radiation beams 22a and 23a irradiate a receiving medium and droplets 18 deposited thereon. The droplets form an ink layer. As the droplets 18 move in the paper transport direction, they are first irradiated by the first radiation source 10a. Irradiation by the first and second radiation sources 10a and 10b begins at point A. In a printing operation, the recording medium and the curing unit move relative to each other in direction Y. A location on the recording medium will first pass point A, then point B, then point C, and then point D.

[0075] 7B shows the intensities of the first and second types of radiation at different positions according to the fourth example shown in FIG. 7A. At point A, the ink is irradiated by the first beam 22a and the second beam 23a. Thus, the ink is subjected to the first and second types of radiation. At the start of the radiation (point A), the first type of radiation is increased at a rate r1, while the second first type of radiation is increased at a rate r2, where r1 is higher than r2.

[0076] At point B, the ink is irradiated with both the first type of radiation and the second type of radiation. 1-1 while the intensity of the second type of radiation is I 2-1 At point B, the intensity of the first type of radiation is I 1-1 is the intensity of the second type of radiation I 2-1 Lower than.

[0077] Halfway between points B and C, the intensity of the first type of radiation is reduced to zero. At point C, the intensity of the second type of radiation is also zero.

[0078] 8A is a schematic diagram of a curing array according to a fifth example of the present invention. The page-width curing array 10 includes two radiation-emitting elements: a first radiation-emitting element 10-1 and a second radiation-emitting element 10-2. Optionally, the first and second radiation-emitting elements 10-1, 10-2 may be individually controllable. The first radiation-emitting element 10-1 is configured to emit a first type of radiation during operation. The second radiation-emitting element 10-2 is configured to emit a second type of radiation during operation. The curing array 10 may be positioned such that, during a printing operation, ink deposited on a recording medium is first irradiated with the first type of radiation and subsequently irradiated with the second type of radiation.

[0079] FIG. 8B is a schematic diagram of a pagewide curing array according to a sixth example of the present invention. The pagewide curing array 10 includes a plurality of LED elements 10-1, 10-2, 10-3, ..., 10-48. In the example shown in FIG. 6B, the LED elements 10-1, 10-2, 10-3, ..., 10-48 are arranged in two rows. The first row includes LED elements 10-1 through 10-24, and the second row includes LED elements 10-25 through 10-48. Each of the individual LED elements 10-1, 10-2, 10-3, ..., 10-48 can be switched on or off independently of the other LED elements 10-1, 10-2, 10-3, ..., 10-48. The first row of LED elements 10-1-10-24 are configured, during operation, to emit radiation having a first wavelength, while the second row of LED elements 10-25-10-48 are configured, during operation, to emit radiation having a second wavelength. The curing array 10 may be arranged such that, during a printing operation, ink deposited on a recording medium is first irradiated with the first type of radiation and subsequently irradiated with the second type of radiation.

[0080] FIG. 9 schematically illustrates a seventh example of a method according to the present invention. A print unit 7 is provided configured to eject ink droplets 17 onto a receiver medium 15. The ink is preferably a UV gel ink. While only one print unit 7 is depicted in FIG. 9, in practice, multiple printheads, optionally ejecting inks of different colors, may be provided. Each droplet of the droplets 17 is in a fluid state when ejected by the print unit 7. To bring the ink to and maintain its fluid state, the print unit 7 may be provided with heating means (not shown). The ink may begin to cool after being ejected from the print unit 7 through a nozzle (not shown). The ink may undergo a phase change due to ink cooling. The receiver medium 15, to which the ink droplets 17 are applied, is moved in a direction Y, which is the recording medium transport direction. For example, when a scanning inkjet process as shown in FIGS. 1 and 2 is used, the recording medium transport direction is often referred to as the sub-scan direction. After the ink droplets are applied, the droplets continue to cool and may undergo a phase change, resulting in the formation of immobile droplets 18. The stuck droplets 18 are transported together with the receiving medium 15 in the recording medium transport direction Y, thereby moving the stuck droplets 18 directly below the curing unit 10. The page-width curing array 10 includes two radiation-emitting elements: a first radiation-emitting element 10-1 and a second radiation-emitting element 10-2. The first radiation-emitting element 10-1 emits a first type of radiation, indicated generally by arrow 21. The first type of radiation may have a first intensity. The second radiation-emitting element 10-2 emits a second type of radiation, indicated generally by arrow 22. The second type of radiation may have a second intensity. As the recording medium 15 supplied with the ink droplets 18 and the curing unit move relative to each other in the medium transport direction Y, the ink droplets are first irradiated with the first type of radiation 21 and subsequently with the second type of radiation 22. Optionally, there may be an overlap between the first type of radiation and the second type of radiation. Thus, when ink droplets 18 are first exposed to radiation, they are exposed to a higher intensity of the first type of radiation than the second type of radiation.

[0081] Detailed embodiments of the present invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the present invention, which may be embodied in various forms. Accordingly, the specific structural and functional details disclosed herein should not be construed as limiting, but merely as a basis for the claims and as a representative basis for teaching those skilled in the art to variously utilize the present invention in connection with a substantial and appropriately detailed structure. In particular, features presented and described in separate dependent claims may be applied in combination, and any combination of such claims is hereby disclosed. Furthermore, the terms and phrases used herein are not intended to be limiting; rather, they are intended to provide an understandable description of the present invention. The terms "a" or "an," as used herein, are defined as one or more than one. The term "plurality," as used herein, is defined as two or more than two. The term "another," as used herein, is defined as at least a second or more than a third. The terms "comprise" and / or "have," as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly.

Claims

1. 1. A method for applying an image onto a receiver medium, comprising: a) applying a predetermined pattern of UV curable ink onto a recording medium to form an image; b) exposing the UV curable ink to UV radiation, the UV radiation comprising at least two types of UV radiation, a first type of UV radiation having a first wavelength and a second type of UV radiation having a second wavelength, the first wavelength being shorter than the second wavelength. and in step b, A method in which the ink is first irradiated with a first type of radiation at a first intensity and a second type of radiation at a second intensity, the first intensity being greater than the second intensity.

2. The method of claim 1 , wherein the ink is then irradiated with the first type of radiation at a third intensity and the second type of radiation at a fourth intensity, the fourth intensity being greater than the third intensity.

3. 10. The method of claim 1, wherein at the start of irradiation, the intensity of the first type of radiation is increased at a first rate and the intensity of the second type of radiation is increased at a second rate, the first rate being at least three times higher than the second rate.

4. 2. The method of claim 1, wherein at the start of irradiation, the intensity of the second type of radiation is zero.

5. The method of claim 1 , wherein the UV curable ink is a gelled UV curable ink.

6. The method of claim 1 , wherein the second wavelength is in the range of 375 nm to 415 nm.

7. The method of claim 6 , wherein the first wavelength is in the range of 100 nm to 315 nm.

8. 7. The method of claim 6, wherein the first wavelength is in the range of 350 nm to 395 nm.

9. 9. The method of claim 8, wherein the difference between the first wavelength and the second wavelength is 5 nm to 50 nm.

10. 6. The method of claim 5, wherein in step a), the predetermined pattern comprises multiple ink layers.

11. at least one print unit for depositing a UV curable ink; - a curing unit, a recording medium support for supporting the recording medium; a control unit configured, in operation, to control a printing device to perform the method of claim 1; A printing device comprising:

12. 10. A software product comprising program code on a non-transitory machine-readable medium, the program code, when loaded into a controller of a printing device comprising at least one printing unit for depositing UV curable ink, a curing unit, and a control unit, causing the controller to perform the method of claim 1.

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