Patent Grant
9630421
The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2015-031856 filed in Japan on Feb. 20, 2015.
1. Field of the Invention
The present invention relates generally to an image forming apparatus, an image forming method, and a non-transitory computer-readable medium computer-readable recording media.
2. Description of the Related Art
Decorated plates have conventionally been used as interior parts for vehicles such as automobiles and exterior parts for electrical appliances. Generally, interior parts for vehicles and exterior parts for electrical appliances include a base material made of resin and a print layer printed on the base material with ink or the like. In some type of interior parts for vehicles and exterior parts for electrical appliances, the print layer is configured as a light blocking layer.
The above-described interior parts for vehicles and exterior parts for electrical appliances may be manufactured by, for example, printing a light blocking layer (solid opacifying image portion) on a substrate made of resin such as polycarbonate by screen printing. Screen printing is a printing method of making a screen (stencil) where a print image is drawn from print data and applying solvent-based ink, thermal-curing ink, or the like to a substrate through the screen. Screen printing allows printing a light blocking layer in a single printing operation. Because the light blocking layer is required to exhibit a transmission density that prevents light transmission, it is generally necessary to form a thick film in a single printing operation. However, the thickness of a film that can be formed by screen printing is approximately up to 20 to 30 μm. Furthermore, because screen printing is single-color printing, it is necessary to print a plurality of layers using ink of different colors to form a decorative design or the like. This can increase man hours and time taken for processing and undesirably reduce productivity.
Meanwhile, printing techniques include, aside from screen printing, digital printing techniques such as laser-printer electrophotography, thermal transfer printing, and inkjet printing. The digital printing techniques allow directly drawing on a resin substrate without making a screen from print data and therefore are more suitable for small lots. Inkjet printing, which is one of the digital printing techniques, is a technique of performing printing by ejecting ink droplets from electronically-controlled recording head nozzles. Inkjet printing can print an image of a high resolution (i.e., image of high image quality) inexpensively as compared with screen printing by forming a thick film of multiple layers by repeating printing.
Japanese Laid-open Patent Application No. 2012-192721 (Patent Document 1) discloses a method for manufacturing a printed work (which may be a vehicle interior part or an electrical-appliance exterior part), in which a light blocking layer is formed by inkjet printing. The method for manufacturing a printed work disclosed in Patent Document 1 forms a light blocking layer and a light-blocking correction layer by repeatedly performing a step of ejecting droplets of radiation curing ink for forming the light blocking layer and a step of hardening the droplets of the radiation curing ink by irradiating the droplets with radiation.
However, the method for manufacturing a printed work (which may be a vehicle interior part or an electrical-appliance exterior part) disclosed in Patent Document 1 is disadvantageous in that, because multiple layers of a design film exhibiting fine image quality (high image quality) are printed to be laminated on one another, forming the multilayer film is undesirably time consuming and reduces productivity.
Meanwhile, to increase image quality with a conventional inkjet printing technique, it is desired to perform unidirectional printing. Accordingly, forming a multilayer thick film by repeating unidirectional printing is undesirably time consuming and reduces productivity.
Therefore, it is desirable to provide an image forming apparatus, an image forming method, and a non-transitory computer-readable medium capable of reducing the time taken to form an image made of multiple layers while maintaining fine image quality.
It is an object of the present invention to at least partially solve the problems in the conventional technology.
According to an aspect of the present invention, there is provided an image forming apparatus including: a carriage configured to scan in a direction perpendicular to a conveying direction of a recording medium with an ejection head and an emitter unit mounted on the carriage, the ejection head being configured to eject ink droplets that harden when exposed to active energy line onto the recording medium to form an image, the emitter unit being configured to emit the active energy line that cures the ink droplets landed on the recording medium; and an image forming controller configured to control ejection of the ink droplets from the ejection head and scan of the carriage, the image forming controller forming an ink droplet film of an uppermost layer of the image, the image being made of multiple layers of ink droplet films, with finer image quality than an ink droplet film of each lower layer other than the uppermost layer, and forming the ink droplet film of the each lower layer other than the uppermost layer with coarser image quality than the uppermost layer and in a shorter length of time than a length of time taken to form the uppermost layer.
According to another aspect of the present invention, there is provided an image forming method performed by an image forming apparatus including a carriage configured to scan in a direction perpendicular to a conveying direction of a recording medium with an ejection head and an emitter unit mounted on the carriage, the ejection head being configured to eject ink droplets that harden when exposed to active energy line onto the recording medium to form an image, the emitter unit being configured to emit the active energy line that cures the ink droplets landed on the recording medium, and an image forming controller configured to control ejection of the ink droplets from the ejection head and scan of the carriage, the image forming method including: forming an ink droplet film of an uppermost layer of an image made of multiple layers of ink droplet films by performing at least one of controls of forming the ink droplet film by unidirectional scan of the carriage, increasing the number of scans to a value higher than that for forming an ink droplet film of each lower layer other than the uppermost layer, increasing resolution of the image to a value higher than that of the ink droplet film of the each lower layer other than the uppermost layer, changing a landing order of the ink droplets to be ejected from the ejection heads, and reducing an ink droplet volume to be ejected from the ejection head to a value smaller than that of the ink droplet film of the each lower layer other than the uppermost layer; and forming the ink droplet film of the each lower layer other than the uppermost layer by bidirectional scan of the carriage.
According to still another aspect of the present invention, there is provided a non-transitory computer-readable medium including computer readable program codes, performed by an image forming apparatus, the image forming apparatus including a carriage configured to scan in a direction perpendicular to a conveying direction of a recording medium with an ejection head and an emitter unit mounted on the carriage, the ejection head being configured to eject ink droplets that harden when exposed to active energy line onto the recording medium to form an image, the emitter unit being configured to emit the active energy line that cures the ink droplets landed on the recording medium, and an image forming controller configured to control ejection of the ink droplets from the ejection head and scan of the carriage, the program codes when executed causing the image forming apparatus to execute: forming an ink droplet film of an uppermost layer of an image made of multiple layers of ink droplet films by performing at least one of controls of: forming the ink droplet film by unidirectional scan of the carriage, increasing the number of scans to a value higher than that for forming an ink droplet film of each lower layer other than the uppermost layer, increasing resolution of the image to a value higher than that of the ink droplet film of the each lower layer other than the uppermost layer, changing a landing order of the ink droplets to be ejected from the ejection heads, and reducing an ink droplet volume to be ejected from the ejection head to a value smaller than that of the ink droplet film of the each lower layer other than the uppermost layer; and forming the ink droplet film of the each lower layer other than the uppermost layer by bidirectional scan of the carriage.
The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.
Exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings. Although an inkjet recording apparatus is described as an example of an image forming apparatus in the embodiment discussed below, applications are not limited thereto. Aspects of the present invention are applicable to any image forming apparatus. Furthermore, aspects of the present invention are applicable, rather than only to inkjet recording apparatuses, to any image forming apparatus configured to form an image by ejecting ink droplets onto a recording medium.
The inkjet recording apparatus as an example of the image forming apparatus according to the present embodiment includes a head unit for ejecting ink of six colors, which are black (Bk), cyan (Cy), magenta (Ma), yellow (Ye), clear (Cl), and white (Wh), and forms an image by causing the head unit to reciprocate in a direction perpendicular to a recording-medium conveying direction.
The emitter unit 13 emits active energy line that cures ink droplets landed on the recording medium 10. Examples of the active energy line include visible light, UV light, infrared light, X rays, α rays, β rays, and γ rays. Among them, UV light is most favorable because of its fast reaction rate and because energy generator is relatively inexpensive. Emission energy is preferably equal to or higher than 100 mJ/cm2 and more preferably equal to or higher than 200 mJ/cm2. Hereinafter, description is given by way of example, in which active energy line is UV light.
The emitter unit 13A, which is active energy line emitting means, emits, for example, UV light of a wavelength that cures ink droplets ejected from the head unit 12. The emitter unit 13A is arranged downstream of the head unit 12 in the forward direction 21.
The emitter unit 13B, which is active energy line emitting means, emits, for example, UV light of a wavelength that cures ink droplets ejected from the head unit 12. The emitter unit 13B is arranged downstream of the head unit 12 in the backward direction 22.
Although the emitter units 13A and 13B are arranged at opposite ends of the head unit 12 in the example illustrated in
A light source of the emitter unit 13 may have an emission spectrum of a UV range such as the UV-A range, the UV-B range, or the UV-C range. Examples of the light source include a high-pressure mercury lamp, a metal halide lamp, an electrodeless UV lamp, a UV laser, a xenon lamp, an LED (light-emitting diode) lamp, and a germicidal lamp. Alternatively, an LED irradiation device, which exhibits favorable light emission efficiency at a peak wavelength and provides high irradiance by narrowing down light-emission wavelength to a specific narrow wavelength range and which is low in power consumption and has a long usable life, may be used. Meanwhile, while typical electrode lamps have peak irradiance of a few W/cm2 at 365 nm, LED irradiation devices (which may be a 395-nm LED or a 405-nm LED) have peak irradiance of more than ten W/cm2, which is several times larger than that of the typical electrode lamps. Thus, while an electrode lamp has an emission spectrum of a wide wavelength range, an LED irradiation device has a narrow emission spectrum about its center wavelength.
A lamp used as the light source of the emitter unit 13 is preferably selected based on a photo-polymerization initiator in ink composition and preferably has a peak emission wavelength that matches absorption characteristics of the photo-polymerization initiator. For example, if reaction of the photo-polymerization initiator in the ink composition peaks at a wavelength of 365 nm, it is preferable to select, for example, a metal halide lamp exhibiting high output in a wavelength range of 300 to 450 nm. If reaction of the photo-polymerization initiator in the ink composition peaks at a wavelength of 240 nm, it is preferable to select a high-pressure mercury lamp or the like, for example.
An image partially having desired image quality can be obtained by controlling energy-emission conditions (such as a light emission wavelength, leveling time, and energy-emission intensity) of the emitter unit 13.
The conveyance stage 15 is arranged below a moving range of the carriage 11. The recording medium 10 is placed on the conveyance stage 15. The recording medium 10 placed on the conveyance stage 15 is conveyed on the conveyance stage 15 to a position below the head unit 12, which is an image forming part, where an image is formed on the recording medium 10. More specifically, a desired image can be formed on the recording medium 10 by ejecting, from the head unit 12, UV-curing ink droplets onto the recording medium 10 while moving the carriage 11.
Meanwhile, use of active energy line curing ink in forming an image on the recording medium 10 increases available choices of a material of the recording medium 10 as compared with typical aqueous ink, and makes it possible to form an image even on an impermeable recording medium made of, for example, a plastic material (e.g., polypropylene or polyethylene). In short, forming an image with active energy line curing ink advantageously provides a wider choice of the recording medium 10. Hereinafter, it is assumed that the recording medium 10 is an impermeable recording medium. Hereinafter, a recording medium may sometimes be referred to as “base material”.
A configuration of the head unit 12 mounted on the carriage 11 is described below with reference to
As illustrated in
The ejection heads 101 to 112 may eject ink droplets of, for example, six colors of black (Bk), cyan (Cy), magenta (Ma), yellow (Ye), clear (Cl), and white (Wh). Referring to the example illustrated in
Each of the heads 101 to 112 includes a set of four nozzle rows providing a resolution of 600 dpi (dots per inch), where each row providing a resolution of 150 dpi. For example, black ink is ejected from four nozzle rows of each of the heads 101 and 102. Accordingly, a head print width corresponding to two heads (four nozzle rows) is provided by a single scan of the carriage 11 in the direction perpendicular to the carriage moving direction. The same is true for the other colors.
Note that the number of colors is not limited to six, but may alternatively be four colors of black, cyan, magenta, and yellow, or still another number.
Scan directions of the carriage 11 and images are described below with reference to
As illustrated in
Put another way, while the layout distance between the heads 101 and 102 for black (Bk) and the emitter unit 13A is long, the layout distance between the heads 101 and 102 for black (Bk) and the emitter unit 13B is short. For this reason, in a situation where the scan speed of the carriage 11 in the forward direction 21 and that in the backward direction 22 are equal, the length of time between when ink droplets ejected from the nozzles of the heads 101 and 102 land on the recording medium 10 and when the ink droplets are irradiated with UV light in the forward direction 21 is long, but the same in the backward direction 22 is short.
Because of the above-described reason, a difference occurs in the length of time between when ink droplets ejected from the nozzles of the heads 101 and 102 land on the recording medium 10 and when the ink droplets are irradiated with UV light, which causes leveling of the ink droplets to vary between the forward direction 21 and the backward direction 22 to thereby cause image quality of a final image to undesirably have unevenness (banding). The same is true for the heads for the other colors.
As illustrated in
In view of the above circumstances, the present embodiment is configured to perform unidirectional printing in a printing process for an uppermost layer regardless of a printing process for a layer(s) lower than the uppermost layer, so that a favorable image can be obtained as a final printed image. Even if unevenness (banding) occurs in image quality of an image by performing bidirectional printing in a lower layer as illustrated in
A functional configuration of the image forming apparatus 100 according to the present embodiment is described below with reference to
As illustrated in
The CPU 121, the ROM 122, the RAM 123, the recording head driver 124, the main-scanning driver 125, the sub-scanning driver 126, and the control FPGA 130 are mounted on a main-control circuit board 120. The head unit 12, the emitter unit 13, and the encoder sensor 14 are mounted on the carriage 11.
The CPU 121 performs overall control of the image forming apparatus 100. For example, the CPU 121 executes various control program instructions stored in the ROM 122 while using the RAM 123 as a work area, thereby outputting control commands for controlling various operations of the image forming apparatus 100.
The recording head driver 124, the main-scanning driver 125, and the sub-scanning driver 126 are drivers for driving the head unit 12, the main-scanning motor 16, and the sub-scanning motor 17, respectively.
The control FPGA 130 controls various operations of the image forming apparatus 100 in cooperation with the CPU 121. The control FPGA 130 may include, for example, a CPU controller 131, a memory controller 132, an image forming controller 133, and a sensor controller 134 as functional elements.
The CPU controller 131 communicates with the CPU 121 to pass various types of information acquired by the control FPGA 130 to the CPU 121 and receives control commands output from the CPU 121.
The memory controller 132 performs memory control for the CPU 121 accessing the ROM 122 and the RAM 123.
The image forming controller 133 includes an ink ejection controller 141, a motor controller 142, and an emitter controller 143.
The image forming controller 133 is described below. The image forming controller 133 controls ejection of ink droplets from the ejection heads and scan of the carriage 11.
The image forming controller 133 forms an image made of multiple layers of ink droplet films as follows. The image forming controller 133 forms an ink droplet film of an uppermost layer 33 with finer image quality than an ink droplet film of each lower layer other than the uppermost layer 33, and forms the ink droplet film of the each lower layer other than the uppermost layer 33 with coarser image quality than the uppermost layer 33 and in a shorter length of time than a length of time taken to form the ink droplet film of the uppermost layer 33.
The image forming controller 133 may form the ink droplet film of the uppermost layer 33 by performing at least one of the following control actions: forming the ink droplet film by unidirectional scan of the carriage 11, increasing the number of scans to a value higher than that for forming the ink droplet film of the each lower layer other than the uppermost layer 33, increasing resolution of the image to a value higher than that of the ink droplet film of the each lower layer other than the uppermost layer 33, changing the landing order of the ink droplets to be ejected from the ejection heads, and reducing an ink droplet volume to be ejected from the ejection heads to a value smaller than that of the ink droplet film of the each lower layer other than the uppermost layer 33. The control action, to be performed by the image forming controller 133, of changing the landing order of the ink droplets is, more specifically, a control action of randomly changing a placement order of the ink droplets to be ejected with reference to the scan direction of the carriage 11.
The image forming controller 133 may also perform a control action of forming the ink droplet film of the each lower layer other than the uppermost layer 33 by bidirectional scan of the carriage 11.
The image forming controller 133 may perform any one of a control action of forming the ink droplet film of the each lower layer other than the uppermost layer 33 by changing the landing order of the ink droplets to be ejected from the ejection heads and a control action of forming the same by setting the landing order of the ink droplets according to the scan direction of the carriage 11.
The image forming controller 133 may perform a control action of reducing the size of the ink droplets to be ejected from the ejection heads to form the ink droplet film of the uppermost layer 33 to a size smaller than the size of the ink droplets forming the ink droplet film of the each lower layer other than the uppermost layer 33.
The image forming controller 133 may perform a control action of, even if the number of layers of the ink droplet films making up the image varies, adjusting a total of ink droplet volumes to be ejected to form all the layers to a fixed value.
Assume that an image is made of multiple layers of ink droplet films including a lowermost layer 31, one or more intermediate layers 32 (hereinafter, sometimes simply referred to as the “intermediate layer 32”), and the uppermost layer 33. The image forming controller 133 sets the size of the ink droplets to be ejected from the ejection heads to form an ink droplet film of the lowermost layer 31 contacting the recording medium 10 to a first size, that of ink droplets forming the one or more intermediate layers 32 to a second size, and that of ink droplets forming the uppermost layer 33 to a third size. The second size is substantially equal to or smaller than the first size. The third size is smaller than the second size.
The ink ejection controller 141 controls operation of the recording head driver 124 in accordance with a control command fed from the CPU 121, thereby controlling ejection timing, ejection volume, and the like of ink droplets to be ejected from the head unit 12, which is driven by the recording head driver 124.
The motor controller 142 controls the main-scanning motor 16, which is driven by the main-scanning driver 125, by controlling operation of the main-scanning driver 125 in accordance with a control command fed from the CPU 121, thereby controlling traveling in the main-scanning direction of the carriage 11. The motor controller 142 also controls the sub-scanning motor 17, which is driven by the sub-scanning driver 126, by controlling operation of the sub-scanning driver 126 in accordance with a control command fed from the CPU 121, thereby controlling move in the sub-scanning direction of the recording medium 10 on the conveyance stage 15.
The emitter controller 143 controls the energy-emission conditions (such as a light emission wavelength, leveling time, and energy-emission intensity) of the emitter unit 13 by controlling operation of the emitter unit 13 in accordance with a control command fed from the CPU 121, thereby controlling emission of active energy line that cures ink droplets landed on the recording medium 10.
The emitter controller 143 controls operation of the emitter unit 13, thereby performing a control action of causing the emitter unit 13 to emit active energy line in the following manner. That is, when forming an ink droplet film of the lowermost layer 31 contacting the recording medium 10, a length of time between landing of ink droplets on the recording medium 10 and irradiation of the ink droplets with active energy line is set to a value longer than that for forming an ink droplet film of each upper layer other than the lowermost layer 31, and when forming an ink droplet film of the uppermost layer 33, a length of time between landing of ink droplets on an ink droplet film of an immediately-precedingly-formed lower layer and irradiation of the ink droplets with active energy line is set to a value substantially equal to or shorter than that for forming the lower layer.
The emitter controller 143 performs a control action of causing the emitter unit 13 to emit active energy line in the following manner. That is, when forming the ink droplet film of the lowermost layer 31 contacting the recording medium 10, the length of time between landing of the ink droplets on the recording medium 10 and irradiation of the ink droplets with active energy line is set to a value longer than that for forming an ink droplet film of each of the one or more intermediate layers 32, and when forming the ink droplet film of the uppermost layer 33, a length of time between landing of the ink droplets on an ink droplet film of an immediately-precedingly-formed one of the intermediate layers 32 and irradiation of the ink droplets with active energy line is set to a value substantially equal to or shorter than that for forming an ink droplet film of the intermediate layer 32.
The sensor controller 134 performs processing on a sensor signal such as an encoder value output from the encoder sensor 14.
The elements described above are an example of control functions implemented by the control FPGA 130. Various control functions other than those described above may further be implemented by the control FPGA 130. The image forming apparatus 100 may be configured such that all or a part of the control functions is implemented in program instructions to be executed by the CPU 121 or other general-purpose CPU(s). The image forming apparatus 100 may be configured such that a part of the control functions is implemented by another FPGA than the control FPGA 130 or dedicated hardware such as an ASIC (application specific integrated circuit).
The head unit 12 is driven by the recording head driver 124, operation of which is controlled by the CPU 121 and the control FPGA 130, to form an image by ejecting ink droplets onto the recording medium 10 on the conveyance stage 15.
The emitter unit 13 forms an image by causing the light source to emit light in accordance with a control signal output from the emitter controller 143 to irradiate ink droplets landed on the recording medium 10 with active energy line that cures the ink droplets, thereby hardening the ink droplets.
The emitter unit 13 is controlled by the emitter controller 143 so as to, when forming the ink droplet film of the lowermost layer 31 contacting the recording medium 10, set the length of time between landing of the ink droplets on the recording medium 10 and irradiation of the ink droplets with active energy line longer than that for forming the ink droplet film of the each upper layer other than the lowermost layer 31 and, when forming the ink droplet film of the uppermost layer 33, set the length of time between landing of ink droplets on the ink droplet film of the immediately-precedingly-formed lower layer and irradiation of the ink droplets with active energy line substantially equal to or shorter than that for forming the ink droplet film of the lower layer.
The emitter unit 13 is controlled by the emitter controller 143 so as to, when forming the ink droplet film of the lowermost layer 31 contacting the recording medium 10, set the length of time between landing of the ink droplets on the recording medium 10 and irradiation of the ink droplets with active energy line longer than that for forming the ink droplet film of each of the one or more intermediate layers 32 and, when forming the ink droplet film of the uppermost layer 33, set the length of time between landing of the ink droplets on the ink droplet film of the immediately-precedingly-formed one of the intermediate layers 32 and irradiation of the ink droplets with active energy line substantially equal to or shorter than that for forming the ink droplet film of the intermediate layer 32.
The encoder sensor 14 acquires an encoder value by detecting a marker on an encoder sheet (not shown) and outputs the encoder value to the control FPGA 130. The encoder value is sent from the control FPGA 130 to the CPU 121, where the encoder value is used in calculation of a position, velocity, and the like of the carriage 11, for example. The CPU 121 generates a control command for controlling the main-scanning motor 16 from the position and the velocity of the carriage 11 calculated from the encoder value and outputs the control command.
An image, made of multiple layers of ink droplet films, formed by the image forming apparatus 100 according to the present embodiment is described below with reference to
As illustrated in
Referring to the example image illustrated in
When forming the ink droplet film of the lowermost layer 31 using black (Bk) ink, for example, the UV curing ink is ejected onto the recording medium 10 from the heads 101 and 102 during when (i.e., during forward traveling of) the carriage 11 is moved in the forward direction 21 to form an image. While the carriage 11 is moved in the forward direction 21, UV light that cures the UV curing ink is emitted from the emitter unit 13A concurrently with image formation. A similar process is performed for the backward direction 22; however, in the backward direction 22, UV light is emitted from the emitter unit 13B. Because the ink droplet film of the lowermost layer 31 is the layer directly contacting the recording medium 10, it is necessary to cause the ink droplet film to adhere to the recording medium 10 so as not to be peeled off therefrom. For this purpose, the control action of setting the length of time between landing of the ink droplets on the recording medium 10 and irradiation of the ink droplets with UV light (active energy line) long may preferably be performed so that the ink droplets harden after sufficiently leveled. More specifically, because the layout distance from the heads 101 and 102 to the emitter unit 13A differs from that to the emitter unit 13B as described earlier, the control action of causing the length of time between landing of the ink droplets on the recording medium 10 and irradiation of the ink droplets with UV light (active energy line) to vary between the forward direction 21 and the backward direction 22 may preferably be performed. Furthermore, for the lowermost layer 31, the control action of setting an ink droplet volume to be ejected from the heads 101 and 102 large, thereby increasing the ink droplet size may preferably be performed. The control action of forming the lowermost layer 31 by bidirectional printing may preferably be performed. Thus, the control actions of increasing the ink droplet size and performing bidirectional printing may preferably be performed to increase print speed, thereby increasing productivity.
When forming an ink droplet film of the intermediate layer 32, because an adherend of the ink droplet film is the ink droplet film of the lowermost layer 31, it is unnecessary to wait until ink droplets are sufficiently leveled. For this reason, for the intermediate layer 32, it is preferable to cause the emitter unit 13 to irradiate the ink droplets with UV light before the ink droplets are sufficiently leveled by setting the length of time between landing of the ink droplets on the ink droplet film of the lowermost layer 31 and irradiation of the ink droplets with UV light (active energy line) shorter than that of the lowermost layer 31. In other words, for the intermediate layer 32, the control action of causing the emitter unit 13 to irradiate the ink droplets with UV light while the ink droplets are still standing may preferably be performed. As in the case of the lowermost layer 31 described above, the control action of causing the length of time between landing of the ink droplets on the recording medium 10 and irradiation of the ink droplets with UV light (active energy line) to vary between the forward direction 21 and the backward direction 22 may preferably be performed. The control action of setting the ink droplet volume to be ejected from the heads 101 and 102 large, thereby increasing the ink droplet size may preferably be performed. In other words, the control action of making the ink droplet volume to be substantially equal to that of the lowermost layer 31 may preferably be performed. The control action of forming the intermediate layer 32 by bidirectional printing may preferably be performed. Thus, the control actions of increasing the ink droplet size and performing bidirectional printing may preferably be performed to increase print speed, thereby increasing productivity.
It is desirable to form the uppermost layer 33 so as to provide favorable image quality to a final image. For this purpose, the image formation process for the uppermost layer 33 is preferably controlled to perform unidirectional printing. When forming the ink droplet film of the uppermost layer 33, because an adherend of the ink droplet film is an ink droplet film of the intermediate layer 32, it is unnecessary to wait until the ink droplets are sufficiently leveled. For this reason, for the uppermost layer 33, the control action of setting the length of time between landing of the ink droplets on the ink droplet film of the intermediate layer 32 and irradiation of the ink droplets with UV light (active energy line) to a value substantially equal to or shorter than that for the intermediate layer 32 may preferably be performed so that the emitter unit 13 irradiates the ink droplets with UV light before the ink droplets are sufficiently leveled. In other words, for the uppermost layer 33, the control action of causing the emitter unit 13 to irradiate the ink droplets with UV light while the ink droplets are still standing may preferably be performed. The control action of setting the ink droplet volume to be ejected from the heads 101 and 102 small, thereby reducing the ink droplet size may preferably be performed. In other words, the control action of making the ink droplet volume to be smaller than that of the lowermost layer 31 and the intermediate layer 32 may preferably be performed. In the example illustrated in
As described above with reference to
In the present embodiment, each of the image formation processes for the respective layers may preferably perform at least any one of the following control actions (1) to (5):
When active energy line (UV) curing ink is employed as the ink droplets to be ejected, each of the image formation processes may preferably further perform at least any one of the following control actions (6) and (7):
The present embodiment enables changing properties of coating of a final image as desired by performing at least any one of the control actions (1) to (5) described above and, furthermore, performing at least any one of the control actions (6) and (7). The control actions (1) to (7) may be combined as desired.
The scan direction (i.e., the scan direction of the carriage 11) control may be performed by, for example, selecting, by a user, unidirectional printing or bidirectional printing using software to be configured before printing. For example, forming an image of a fixed resolution by bidirectional printing increases print speed (i.e., increases productivity) as compared with forming the same by unidirectional printing. However, bidirectional printing can disadvantageously cause, for example, color difference between the forward and backward directions due to landing position accuracy of ink droplets and the like to occur, resulting in spread of the ink droplets and degradation in image quality. However, even if degradation in image quality occurs in an ink droplet film of a lower layer other than the uppermost layer 33, because another ink droplet film is formed as an upper layer in the next step, the degradation does not affect image quality of a final image. Thus, by forming each lower layer other than the uppermost layer 33 by bidirectional printing and forming the uppermost layer 33 by unidirectional printing, the time taken to form an image made of multiple layers of films can be reduced while maintaining fine image quality. In short, productivity can be increased while maintaining fine image quality.
The landing order control of the ink droplets to be ejected from the ejection heads may be performed by, for example, changing an ejection-order mask to be used depending on a function of each layer. Ejection-order masks used in the present embodiment and images each formed with landed ink droplets using one of the ejection-order masks are described with reference to
The number-of-scan control may be performed by, for example, performing printing with the nozzle rows of the head unit 12 divided into parts. The number-of-scan control according to the present embodiment is described below with reference to
As illustrated in
Thus, by controlling the image formation processes on a per-layer basis even when the layers to be formed are identical in resolution by, for example, setting the number of scans for forming the ink droplet film of the uppermost layer 33, which directly affects image quality of a finished image, large and setting the number of scans for the ink droplet film of each lower layer other than the uppermost layer 33 small, necessary functions that vary on the per-layer basis can be obtained.
The control of the ink droplet volume to be ejected from the ejection heads (i.e., control of the size of the landing ink droplets) may be performed by, for example, reducing the size of the ink droplets to be ejected from the ejection heads to form the ink droplet film of the uppermost layer 33 to a size smaller than the size of the ink droplets for forming the ink droplet film of the each lower layer other than the uppermost layer 33. In other words, a control action of, when forming the ink droplet film of the uppermost layer 33, reducing the ink droplet volume to be ejected from the ejection heads to a value smaller than the ink droplet volume for forming the ink droplet film of the each lower layer other than the uppermost layer 33 may preferably be performed.
The control of the ink droplet volume to be ejected from the ejection heads of the present embodiment is described below with reference to
Other form than that described above of the control of the ink droplet volume is described below with reference to
In each of the examples illustrated in
In each of the examples illustrated in
In the example illustrated in
As described above, when forming an image made of multiple layers having a fixed film thickness by adjusting the total of the ink droplet volumes (the total ink droplet volume) forming all the layers of the image to a fixed value, if the number of the layers is fixed, functions of the ink droplet films of the respective layers and productivity can be controlled by controlling a combination of the ink droplet volumes. If the number of the layers varies, functions of the ink droplet films of the respective layers and productivity can be controlled by controlling the combination of the ink droplet volumes and a combination of scan directions. Note that the numbers of layers and the combinations of the ink droplet volumes of the respective layers described above with reference to
The timing control for emission of active energy line (UV light) may be performed by performing a control action of, for example, when forming an ink droplet film of the lowermost layer 31 contacting the recording medium 10, setting the length of time between landing of the ink droplets on the recording medium 10 and irradiation of the ink droplets with active energy line (UV light) longer than that for forming an ink droplet film of each upper layer other than the lowermost layer 31, and when forming the ink droplet film of the uppermost layer 33, setting the length of time between landing of the ink droplets on an ink droplet film of an immediately-precedingly-formed lower layer (which is the lowermost layer 31 or the intermediate layer 32) and irradiation of the ink droplets with active energy line (UV light) substantially equal to or shorter than that for forming the ink droplet film of the lower layer.
Thus, in the present embodiment, adherence of the ink droplets landed on the recording medium (base material) 10 to form the lowermost layer 31, which is directly adhered to the recording medium 10, is increased by causing the ink droplets to be sufficiently leveled. The leveling of the landed ink droplets may be controlled by, in the case of the image forming apparatus 100 using UV-curing ink, for example, controlling a parameter for the length of time between landing of the ink droplets on the recording medium (base material) 10 and irradiation of the ink droplets with UV light (active energy line). When the length of time between landing of ink droplets on the recording medium (base material) 10 and irradiation of the ink droplets with UV light (active energy line) is short, the landed ink droplets harden while the ink droplets are still standing (i.e., insufficiently leveled). When the length of time is long, the landed ink droplets horizontally spread (i.e., sufficiently leveled) and harden after being sufficiently leveled. In the present embodiment, leveling time for forming the ink droplet film of the lowermost layer 31 is set long, thereby increasing adherence of the lowermost layer 31 to the recording medium (base material) 10. Meanwhile, when the leveling time is set long, image quality of an image is degraded by wet spreading of landed ink droplets. For this reason, when forming the ink droplet film of the uppermost layer 33, which is desired to have fine image quality, the leveling time is preferably set short.
Such timing control for emission of active energy line (UV light) as that described above is desired when the material of the recording medium 10, on which the ink droplet film of the lowermost layer 31 is to be formed, is plastic (such as polypropylene or polyethylene). There is no functional group on the surface of a plastic material. Accordingly, when forming an image on a plastic material, the need of increasing adherence to an ink droplet film arises. Generally, many plastic materials contain a substance(s) promoting adhesion. However, there can be a case where a plastic material contains a catalyst(s) derived from a product. The catalyst(s) can be dispersed in a boundary between the base material (plastic material) 10 and the ink droplet film and weaken the adherence. Conventionally, a countermeasure such as cleaning the surface of the plastic material with solvent has been taken. However, this countermeasure makes it considerably difficult to configure an image forming procedure so as to be performed on-line. For this reason, as described above, adherence of ink droplets landed on the base material 10 is increased by causing the ink droplets to be sufficiently leveled by means of the timing control for emission of active energy line (UV light).
Meanwhile, light emission wavelength (nm), energy-emission intensity (peak irradiance) (mW/cm2), and integral radiant exposure (mJ/cm2) of UV light that cures the UV curing ink affects adherence between the ink and the base material 10, adherence between ink layers, and properties of a film to be formed. More specifically, film strength, gloss level, and film surface appearance are controllable by adjusting the energy-emission conditions of the UV light. It is desired that the energy-emission conditions be determined carefully and precisely because image quality of a final image depends on the energy-emission conditions. Under the circumstances, the emitter unit 13 of the present embodiment illustrated in
When ink droplets of a same composition are used, properties of films obtained by hardening the ink droplets vary depending on the output power control. Accordingly, not only mechanical and electrical controls of the emitter unit 13 but also the timing control for irradiation of ink droplets ejected from the ejection heads with UV light to form an image are key factors that determine image quality. By, each time one of the layers is printed, changing the energy-emission conditions such as the peak irradiance (mW/cm2) and the integral radiant exposure (mJ/cm2) to those appropriate for a role of the layer, optimum UV light emission can be performed. For example, a same integral radiant exposure (mJ/cm2) can be obtained by using either a control condition of emitting intense light (mJ/cm2) for a short period of time or a control condition of emitting weak light (mJ/cm2) for a long period of time. However, if a certain integral radiant exposure is desired, it is necessary to take productivity into account because some control condition may involve the need of changing the conveyance velocity of the recording medium 10.
An image formation process for forming an image made of a single layer is simple. However, when an image formation process of stacking another one, two, or more layers is required to provide image quality of a certain film transmission density by inkjet printing, it is necessary to form a thick film with dots (ink droplets). Accordingly, it is required to stack a same image(s) on a finished lower image. In this case, an adherend of the lowermost layer 31 is the surface of the recording medium 10, while an adherend of each of formed upper layers other than the lowermost layer 31 is an ink layer. Because the adherend varies between layers in this manner, even if images of the respective layers are formed through a same image formation process, properties of ink droplet films undesirably vary. For example, when forming a film of three layers, the three layers are respectively desired to have the following specifications:
the first layer: required to have adherence to the base material (recording medium) 10,
the second layer: required to have adherence to the lower ink droplet film (the first layer), and
the third layer: required to be an image of high image quality.
Thus, each of the layers is desired to meet a corresponding one of the above specifications.
By controlling the image formation processes on a per-layer basis by combining the image resolution control and the process-linear-velocity control in addition to the above-described scan direction control, the number-of-scan control, the resolution control, the landing order control of ink droplets to be ejected from the ejection heads (i.e., control of the ejection-order masks), the control of the ink droplet volume to be ejected by means of drive waveform control of the ejection heads (i.e., control of the size of landing ink droplets), and the timing control for emission of active energy line (UV light), properties of coating of a final image can be controlled as desired.
Guidelines for the above-described control of the image formation processes may include the following:
Operations to be performed by the image forming apparatus 100 according to the present embodiment are described below.
The image forming controller 133 sets the thickness of films making up an image and the number of layers making up the films (S1). Thereafter, the image forming controller 133 sets control conditions for an image forming process (S2). The image forming controller 133 sets, to the control conditions, at least any one of the following control actions: forming the ink droplet film of the uppermost layer 33 by unidirectional scan of the carriage 11, forming the same with the number of scans increased to a value higher than that for forming an ink droplet film of each lower layer other than the uppermost layer 33, forming the same with resolution of the image increased to a value higher than that for forming the ink droplet film of the each lower layer other than the uppermost layer 33, forming the same with the landing order of the ink droplets to be ejected from the ejection heads changed, and forming the same with an ink droplet volume to be ejected from the ejection heads reduced. The image forming controller 133 sets image formation processes in detail in accordance with the thus-set one or more control conditions (S3). Thereafter, the image forming controller 133 forms ink droplet films of the respective layers by controlling the ink ejection controller 141, the motor controller 142, and the emitter controller 143 in accordance with the thus-set image formation processes, thereby forming an image (S4).
By performing the above-described operations, the image forming apparatus 100 can reduce the time taken to form an image made of multiple layers of ink droplet films while maintaining fine image quality.
Thus, the image forming apparatus 100 of the present embodiment forms the ink droplet film of the uppermost layer 33 by performing at least any one of the following control actions: forming the ink droplet film by unidirectional scan of the carriage 11, increasing the number of scans to a value higher than that for forming the ink droplet film of each lower layer other than the uppermost layer 33, increasing resolution of the image to a value higher than that of the ink droplet film of the each lower layer other than the uppermost layer 33, changing the landing order of the ink droplets to be ejected from the ejection heads, and reducing an ink droplet volume to be ejected from the ejection heads to a value smaller than that for forming the ink droplet film of the each lower layer other than the uppermost layer 33, and forms the ink droplet film of the each lower layer other than the uppermost layer 33 by bidirectional scan of the carriage 11, thereby advantageously achieving reduction in the time taken to form an image made of multiple layers while maintaining fine image quality.
The program instructions to be executed by the above-described image forming apparatus 100 of the present embodiment may be configured to be provided as being recorded in a non-transitory computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, a digital versatile disk (DVD), or a universal serial bus (USB) memory as an installable file or an executable file. The program instructions may alternatively be configured so as to be provided or distributed via a network such as the Internet. The program instructions may alternatively be configured so as to be provided as being installed in a ROM or the like in advance.
Note that the configuration of the image forming apparatus 100 of the present embodiment is only an example and there are various configuration examples varying depending on use and purpose.
According to an aspect of the present invention, the time taken to form an image made of multiple layers can be reduced while maintaining fine image quality.
Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
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