PRINT METHOD

Abstract

The present invention relates to a print method. In the print method, a first layer of ink is deposited and cured before a second layer is applied. The present invention further relates to a software product. The present invention also relates to an inkjet printing apparatus.

Claims

1. A method for applying an image onto a recording medium, the method comprising the steps of: a) applying a first layer of a radiation-curable ink onto a recording medium; b) curing the first layer; c) applying at least a second layer of radiation-curable ink on top of the first cured layer, wherein the coverage of the first layer is 1.0 g/m.sup.2 or less, and wherein the first layer of ink is applied onto the recording medium by applying a first ink from an ink set and wherein the second layer is applied by applying at least the first ink from the ink set.

2. The method for applying an image onto a recording medium according to claim 1, wherein a time interval between applying the first layer of ink and curing the first layer of ink is in the range of 3 - 10 s.

3. The method for applying an image onto a recording medium according to claim 1, wherein the ink comprises a gelling agent.

4. The method for applying an image onto a recording medium according to claim 1, wherein the second layer is applied by applying at least a second ink from the ink set.

5. The method for applying an image onto a recording medium according to claim 1, wherein the first ink is an ink composition comprising a white colorant or wherein the first ink is an ink composition not comprising a colorant.

6. The method for applying an image onto a recording medium according to claim 1, wherein the first layer of ink is applied by a first ink ejecting unit and the second layer of ink is applied by a second ink ejecting unit, the first ink ejecting unit being positioned upstream, in the direction of medium transport, with respect to the second ink ejecting unit.

7. The method for applying an image onto a recording medium according to claim 1, the method further comprising the step of: d. Curing the second layer.

8. A software product comprising program code on a non-transitory machine-readable medium, wherein the program code, when loaded into a controller of a printer with jetting devices for ejecting a radiation-curable ink, causes the controller to perform a method according to claim 1.

9. An ink-jet printing apparatus, the ink-jet printing apparatus comprising: a) a jetting device for ejecting a radiation-curable ink onto a recording medium; b) a curing unit; and c) a controller configured to control the ink-jet printer to perform a method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] These and further features and advantages of the present invention are explained hereinafter with reference to the accompanying drawings showing non-limiting embodiments and wherein:

[0041] FIG. 1A shows a schematic representation of an inkjet printing system according to a first embodiment of the invention.

[0042] FIG. 1B shows a schematic representation of an inkjet print head.

[0043] FIG. 1C shows a schematic representation of an inkjet printing system according to a second embodiment of the invention.

[0044] In the drawings, same reference numerals refer to same elements.

DETAILED DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1A shows an ink jet printing assembly 3. The inkjet printing assembly 3 comprises supporting means for supporting an image receiving medium 2. The supporting means are shown in FIG. 1A as a flat surface 1, but alternatively, the supporting means may be a platen, for example a rotatable drum that is rotatable around an axis. The supporting means may be optionally provided with suction holes for holding the image receiving medium in a fixed position with respect to the supporting means. The ink jet printing assembly 3 comprises print heads 4a - 4e, mounted on a scanning print carriage 5. The scanning print carriage 5 is guided by suitable guiding means 6 to move in reciprocation in the main scanning direction X. Each print head 4a - 4e comprises an orifice surface 9, which orifice surface 9 is provided with at least one orifice 8, as is shown in FIG. 1B. The print heads 4a - 4e are configured to eject droplets of marking material onto the image receiving medium 2.

[0046] The image receiving medium 2 may be a medium in web or in sheet form and may be composed of e.g. paper, cardboard, label stock, coated paper, plastic or textile. Alternatively, the image receiving medium 2 may also be an intermediate member, endless or not. Examples of endless members, which may be moved cyclically, are a belt or a drum. The image receiving medium 2 is moved in the sub-scanning direction Y over the flat surface 1 along four print heads 4a - 4e provided with a fluid marking material.

[0047] The image receiving medium 2, as depicted in FIG. 1A is locally heated or cooled in the temperature control region 2a. In the temperature control region 2A, temperature control means (not shown), such as heating and/or cooling means may be provided to control the temperature of the receiving medium 2. Optionally, the temperature control means may be integrated in the supporting means for supporting an image receiving medium 2. The temperature control means may be electrical temperature control means. The temperature control means may use a cooling and/or heating liquid to control the temperature of the image receiving medium 2. The temperature control means may further comprise a sensor (not shown) for monitoring the temperature of the image receiving medium 2.

[0048] A scanning print carriage 5 carries the five print heads 4a - 4e and may be moved in reciprocation in the main scanning direction X parallel to the platen 1, such as to enable scanning of the image receiving medium 2 in the main scanning direction X. Only five print heads 4a - 4e are depicted for demonstrating the invention. In practice an arbitrary number of print heads may be employed. In any case, at least one print head 4a - 4e per color of marking material is placed on the scanning print carriage 5. For example, for a black-and-white printer, at least one print head 4a - 4e, usually containing black marking material is present. Alternatively, a black-and-white printer may comprise a white marking material, which is to be applied on a black image-receiving medium 2. For a full-color printer, containing multiple colors, at least one print head 4a - 4e for each of the colors, usually black, cyan, magenta and yellow and a further color, such as white, is present. Often, in a full-color printer, black marking material is used more frequently in comparison to differently colored marking material. Therefore, more print heads 4a - 4e containing black marking material may be provided on the scanning print carriage 5 compared to print heads 4a - 4e containing marking material in any of the other colors. Alternatively, the print head 4a - 4e containing black marking material may be larger than any of the print heads 4a - 4e, containing a differently colored marking material.

[0049] The carriage 5 is guided by guiding means 6. These guiding means 6 may be a rod as depicted in FIG. 1A. Although only one rod 6 is depicted in FIG. 1A, a plurality of rods may be used to guide the carriage 5 carrying the print heads 4. The rod may be driven by suitable driving means (not shown). Alternatively, the carriage 5 may be guided by other guiding means, such as an arm being able to move the carriage 5. Another alternative is to move the image receiving material 2 in the main scanning direction X.

[0050] Each print head 4a - 4e comprises an orifice surface 9 having at least one orifice 8, in fluid communication with a pressure chamber containing fluid marking material provided in the print head 4a - 4e. On the orifice surface 9, a number of orifices 8 are arranged in a single linear array parallel to the sub-scanning direction Y, as is shown in FIG. 1B. Alternatively, the nozzles may be arranged in the main scanning direction X. Eight orifices 8 per print head 4a - 4e are depicted in FIG. 1B, however obviously in a practical embodiment several hundreds of orifices 8 may be provided per print head 4a - 4e, optionally arranged in multiple arrays.

[0051] As depicted in FIG. 1A, four print heads 4a - 4d are placed parallel to each other. The four print heads 4a - 4d are print heads configured to eject a colored ink during printing operation, for example, a cyan ink, a magenta ink, a yellow ink and a black ink. The print heads 4a - 4d may be placed such that corresponding orifices 8 of the respective print heads 4a - 4d are positioned in-line in the main scanning direction X. This means that a line of image dots in the main scanning direction X may be formed by selectively activating up to four orifices 8, each of them being part of a different print head 4a - 4d. This parallel positioning of the print heads 4a - 4d with corresponding in-line placement of the orifices 8 is advantageous to increase productivity and/or improve print quality. Alternatively multiple print heads 4a - 4d may be placed on the print carriage adjacent to each other such that the orifices 8 of the respective print heads 4a - 4d are positioned in a staggered configuration instead of in-line. For instance, this may be done to increase the print resolution or to enlarge the effective print area, which may be addressed in a single scan in the main scanning direction X. The image dots are formed by ejecting droplets of marking material from the orifices 8. Further, a fifth print head 4e is provided. This fifth print head 4e is positioned upstream in the sub scanning direction Y with regard to the other print heads 4a-4d. The fifth print head 4e may be configured to apply the first layer of ink onto the recording medium before the second layer is applied onto the recording medium.

[0052] In an alternative embodiment (not shown), the print heads 4a-4e may be placed in parallel. In this embodiment, the activator composition and the ink composition may be applied onto the image receiving material 2.

[0053] The print head carriage 5 is provided with a curing lamp 11c for curing the first layer of ink before the second layer of ink is applied. In the embodiment shown in FIGS. 1, a separate curing lamp is provided. However, in an alternative embodiment (not shown), no curing lamp may be provided adjacent to the fifth print head 4e and the radiation may be provided in an alternative way. For example, a mirror may be provided that is configured to in operation reflect radiation emitted by curing means 11a, 11b.

[0054] The ink jet printing assembly 3 may further comprise curing means 11a, 11b. As shown in FIG. 1A, a scanning print carriage 12 carries the two curing means 11a, 11b and may be moved in reciprocation in the main scanning direction X parallel to the platen 1, such as to enable scanning of the image receiving medium 2 in the main scanning direction X. Alternatively, more than two curing means may be applied. It is also possible to apply page-wide curing means. If page-wide curing means are provided, then it may not be necessary to move the curing means in reciprocation in the main scanning direction X. The first curing means 11a may emit a first beam of UV radiation, the first beam having a first intensity. The first curing means 11a may be configured to provide the radiation for the pre-curing step. The second curing means 11b may emit a second beam of radiation, the second beam of radiation having a second intensity. The second curing means 11b may be configured to provide the radiation for the post-curing step.

[0055] The carriage 12 is guided by guiding means 7. These guiding means 7 may be a rod as depicted in FIG. 1A. Although only one rod 7 is depicted in FIG. 1A, a plurality of rods may be used to guide the carriage 12 carrying the print heads 11. The rod 7 may be driven by suitable driving means (not shown). Alternatively, the carriage 12 may be guided by other guiding means, such as an arm being able to move the carriage 12.

[0056] The curing means may be energy sources, such as actinic radiation sources, accelerated particle sources or heaters. Examples of actinic radiation sources are UV radiation sources or visible light sources. UV radiation sources are preferred, because they are particularly suited to cure UV curable inks by inducing a polymerization reaction in such inks. Examples of suitable sources of such radiation are lamps, such as mercury lamps, xenon lamps, carbon arc lamps, tungsten filaments lamps, light emitting diodes (LED’s) and lasers. In the embodiment shown in FIG. 1A, the first curing means 11a and the second curing means 11b are positioned parallel to one another in the sub scanning direction Y. The first curing means 11a and the second curing means 11b may be the same type of energy source or may be different type of energy source. For example, when the first and second curing means 11a, 11b, respectively both emit actinic radiation, the wavelength of the radiated emitted by the two respective curing means 11a, 11b may differ or may be the same. The first and second curing means are depicted as distinct devices. However, alternatively, only one source of UV radiation emitting a spectrum of radiation may be used, together with at least two distinct filters. Each filter may absorb a part of the spectrum, thereby providing two beams of radiation, each one having intensity different from the other.

[0057] The flat surface 1, the temperature control means, the carriage 5, the print heads 4a -4d, the carriage 12 and the first and second curing means 11a, 11b are controlled by suitable controlling means 10.

[0058] FIG. 1C shows an ink jet printing assembly 3 similar to the inkjet assembly shown in FIG. 1A. The ink jet printing assembly comprises four print heads 4a - 4d that are placed parallel to each other. The four print heads 4a - 4d are print heads configured to eject a colored ink during printing operation, for example, a cyan ink, a magenta ink, a yellow ink and a black ink. The print head carriage 5 is further provided with two first curing lamps 11d, 11e. The first curing lamps are placed adjacent to the print heads 4a-4e. In printing operation, the print head carriage 5 moves in reciprocation in scanning direction X and ink deposited by the print heads may be cured before a subsequent layer of ink is deposited.

[0059] The first curing lamps may optionally comprise a plurality of individual controllable radiation emitting elements. The power of the radiation emitting elements may be individually controlled, thereby controlling the intensity and optionally wavelength of the radiation emitted by the individual radiation emitting elements.

[0060] The nozzles 8 of the print heads 4a-4d may be divided in subsections. At least one of the print heads 4a-4d may comprise at least two subsections of nozzles 8. A first subsection may be positioned upstream in the media transport direction Y with respect to the second subsections of nozzles. The first subsection of nozzles may be configured to in printing operation apply the first layer of ink onto the recording medium. The second subsection of nozzles may be configured to in printing operation apply the second layer of ink and optionally further layers of ink onto the recording medium. The individual radiation emitting units may be controlled such that the first layer of ink applied onto the recording medium may be irradiated differently than the second layer. The subsequent layer of ink may not be irradiated with radiation by the first curing elements 11d, 11e. Alternatively, the second and optionally subsequent layer of ink may be irradiated with a smaller dose of radiation (“pinned”) than the first layer of ink by the first curing elements 11d, 11e.

EXPERIMENTS AND EXAMPLES

Materials

[0061] UVgel 460 inks -commercially available for use with the Colorado 1650 printer- were obtained from Canon. The chemicals were used as received. As recording medium, Lexan® was used. Lexan® is a polycarbonate rigid material and was obtained from Sabic.

Methods

Printing

[0062] Prints were made using a Canon Colorado 1650 printer. The Colorado 1650 printer was operated in the glossy mode, unless stated otherwise.

Adhesion Measurements

[0063] Adhesion was tested using a crosshatch test according to ASTM D3359. The tested samples were allocated a number in the range 0-5, wherein 0 corresponds to bad adhesion and 5 corresponds to excellent adhesion.

Comparison Experiments

Examples and Comparative Examples

Printing Example 1

[0064] A square of black ink having a size of 10 cm × 10 cm was printed by applying 0.5 g/m.sup.2 of yellow ink onto the recording medium as a first layer. The first layer was cured before applying additional layers on top of the first layer.

[0065] After curing the first layer, the recording medium was moved in the reverse medium transport direction until the cured first layer and a second layer was applied onto the cured first layer by applying a square of black ink, having a size of 10 cm × 10 cm by applying 22 g/m.sup.2 of black ink onto the recording medium. The ink was cured afterwards, resulting in printing example Ex1. The adhesion of printing example Ex 1 was determined.

Printing Example 2

[0066] Printing example 2 was prepared and analyzed similarly to printing example 1 (Ex1), but the second layer was applied by applying 17 g/m.sup.2 onto the recording medium. The printing example 2 is referred to as example Ex2.

Comparative Printing Example 1

[0067] A square of black ink, having a size of 10 cm × 10 cm was printed by applying 22 g/m.sup.2 of black ink onto the recording medium. The ink was cured afterwards, resulting in comparative printing example CE1.

[0068] The adhesion of comparative printing example CE1 was determined.

Comparative Printing Example 2

[0069] Comparative printing example 2 was prepared and analyzed similarly to comparative printing example 1 (CE1), only 17 g/m.sup.2 of ink, instead of 22 g/m.sup.2 of ink, was applied onto the recording medium. The printing example 2 is referred to as example CE2.

TABLE-US-00001 comparison printing experiments Printing Experiments Adhesion Printing Example Ex1 5 Printing Example Ex2 5 Comparative Printing Example CE1 1 Comparative Printing Example CE2 2

[0070] Printing examples Ex1 and Ex2, which are printing examples according to the present invention, show excellent adhesion. The adhesion of comparative printing examples CE1 and CE2, which are printing examples not according to the present invention, show poor adhesion.

[0071] From the experimental data, it can be concluded that the adhesion was improved by printing and curing a first layer having a coverage of 0.5 g/m.sup.2, before applying further layers of ink.

[0072] Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually 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 are herewith disclosed. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the 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. The terms including and/or having, 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.