Patent Grant
11884066
The present application is based on, and claims priority from JP Application Serial Number 2020-198139, filed Nov. 30, 2020, the disclosure of which is hereby incorporated by reference herein in its entirety.
The present disclosure relates to technology for recording an image by curing, using light irradiation, a photocurable ink discharged onto a recording medium.
When a recording medium is supported by a support body, and an image is recorded by curing, using light irradiation, a photocurable ink discharged onto the recording medium, the temperature of the recording medium and the support body increases due to the reaction heat.
The greater the change in the temperature of the recording medium and a drum of the support body, the greater a color difference becomes. This is because, when the temperature of the support body or the recording medium is high, fluidity of the ink after landing is high, and therefore, wet-spreading of the ink occurs more easily and the color becomes darker. Further, when the temperature of the support body and the recording medium is low, the fluidity of the ink after landing is low, and therefore, wet-spreading of the ink occurs less easily and the color becomes lighter.
For this reason, in International Patent Publication WO2016/182037, it is disclosed that the temperature of a transport surface of a transport drum is caused to be a predetermined temperature (45° C.) by heating means or cooling means before printing, and printing is started thereafter, and when a surface temperature of the recording medium is acquired during printing and the temperature has become higher than an upper limit temperature (50° C.), the printing is stopped and the transport drum is cooled.
As a result of diligent experimentation by the present inventors, it was found that the temperature change of the recording medium and the support body (the transport drum) caused by the photocurable ink varies depending on an ejection amount of the ink for each of images to be printed (hereinafter, referred to as a print duty), and a temperature difference between an image of a low print duty and an image of a high print duty is 10° C. or more. Further, it was found that when the print duty is constant, the temperature of the recording medium and the support body is stable at a constant saturation temperature corresponding to the print duty.
Therefore, as described in International Patent Publication WO2016/182037, even when the temperature of the transport surface of the transport drum is caused to be the predetermined temperature (45° C.) by the heating means or the cooling means before the printing, and the printing is started thereafter, if the print duty is different, the saturation temperature of the recording medium and of the support body will differ. As a result, a color difference corresponding to the print duty occurs between the start of the printing and after saturation.
The present disclosure reduces a color difference between a start of printing and after saturation.
In an aspect of the present disclosure, a printing apparatus is configured to include a transport unit configured to transport a recording medium, a support unit configured to support the recording medium transported by the transport unit, a discharge unit located at a position facing the support unit, and configured to discharge photocurable ink onto the recording medium supported by the support unit, to form an image, a light irradiation unit configured to, downstream of the discharge unit on a transport path of the recording medium, irradiate, with light, the photocurable ink discharged onto the recording medium to cure the photocurable ink, a temperature adjustment unit configured to perform at least one of cooling or heating of the support portion, a storage unit configured to store at least one of a relationship between a print duty and a preliminary heating temperature, or a relationship formula expressing the relationship between the print duty and the preliminary heating temperature, and a control unit. The control unit acquires the print duty of the image to be printed, and adjusts the temperature adjustment unit based on the acquired print duty and the relationship or the relationship formula stored in the storage unit, to cause the support unit to be the preliminary heating temperature.
In the above-described configuration, the storage unit stores at least one of 1: the relationship between the print duty and the preliminary heating temperature, and 2: the relationship formula expressing the relationship between the print duty and the preliminary heating temperature. Then, the control unit acquires the print duty of the image to be printed, and adjusts the temperature adjustment unit based on the acquired print duty and the relationship or the relationship formula stored in the storage unit, to cause the support unit to be the preliminary heating temperature.
In this way, according to the aspect of the present disclosure, by acquiring the print duty of the image to be printed and starting printing after the preliminary heating temperature set in accordance with the acquired print duty has been reached, a color difference corresponding to the print duty does not occur even at the time of starting printing and after saturation.
An embodiment of the present disclosure will be described below with reference to the accompanying drawings.
The feeding unit 2 includes the feeding shaft 20 around which the end of the sheet S is wound, and a driven roller 21 on which the sheet S drawn out from the feeding shaft 20 is wound. The feeding shaft 20 supports the sheet S by winding the end of the sheet S around the feeding shaft 20 with the front surface of the sheet S facing outward. Then, when the feeding shaft 20 rotates in the clockwise direction in
While supporting the sheet S fed out from the feeding unit 2 using a platen drum 30, the process unit 3 performs processing as appropriate, using each of functional units 51, 52, 61, 62, and 63 that are disposed along the outer circumferential surface of the platen drum 30, thus recording the image on the sheet S. In this process unit 3, a front driving roller 31 and a rear driving roller 32 are provided on both sides of the platen drum 30, and the sheet S transported from the front driving roller 31 to the rear driving roller 32 is supported by the platen drum 30 and is subjected to the image recording.
The platen drum 30 is a cylindrical drum supported so as to be able to rotate freely, and winds the sheet S transported from the front driving roller 31 to the rear driving roller 32 from the back surface side. In other words, the sheet S transported from the front driving roller 31 to the rear driving roller 32 is supported by the outer circumferential surface of the rotary drum 30. In this way, the front driving roller 31, the rear driving roller 32, and intermediate driven rollers 21, 33, 34, and 41 correspond to a transport unit that transports the recording medium. Further, the platen drum 30 corresponds to a support unit that supports the recording medium transported by the transport unit.
Then, in the process unit 3, in order to record a color image on the front surface of the sheet S supported by the platen drum 30, a plurality of the recording heads 51 corresponding to mutually different colors are provided. Specifically, four of the recording heads 51 corresponding to yellow, cyan, magenta, and black are aligned in this color order in a transport direction Ds. Each of the recording heads 51 faces the front surface of the sheet S wound on the platen drum 30 with a predetermined clearance therebetween, and discharges an ink of the corresponding color using an ink-jet method. Then, as a result of each of the recording heads 51 discharging the ink onto the sheet S transported in the transport direction Ds, the color image is formed on the front surface of the sheet S.
In this way, each of the recording heads 51 is located at a position facing the support unit, and corresponds to a discharge unit configured to discharge photocurable ink onto the recording medium supported by the support unit, to form the image.
As the ink, an ultraviolet (UV) ink (photocurable ink) that is cured by being irradiated with ultraviolet rays (light) is used. Here, in order to cure and fix the ink to the sheet S, the UV lamps 61 and 62 (a light irradiation unit) are provided in the process unit 3. Note that this ink curing is performed in two stages of provisional curing and final curing. The UV lamps 61 for the provisional curing are disposed in each of intervals between the plurality of recording heads 51. In other words, the UV lamps 61 are used for curing (provisional curing of) the ink to a degree such that the ink does not lose its shape, by irradiating the ink with relatively weak ultraviolet rays, and are not used for completely curing the ink. On the other hand, the UV lamp 62 for the final curing is provided downstream of the plurality of recording heads 61 in the transport direction Ds. In other words, the UV lamp 62 is used for completely curing (final curing of) the ink, by irradiating the ink with ultraviolet rays stronger than the ultraviolet rays of the UV lamps 61. In this way, the color image formed by the plurality of recording heads 51 can be fixed to the front surface of the sheet S by performing the provisional curing and the final curing.
As described above, the UV lamps 61 and the UV lamp 62 correspond to the light irradiation unit that irradiates the light onto and cures the photocurable ink discharged onto the recording medium, further downstream than the discharge unit on the transport path of the recording medium.
Note that the provisional curing and the final curing are performed in this example, but the curing is not necessarily performed in the two stages.
In general, when the photocurable ink is irradiated with the ultraviolet rays, reaction heat is generated. Thus, a site of the sheet S (the recording medium) at which the ink is adhered generates heat, and as a result of that heat being transferred to the platen drum 30, the temperature of the platen drum 30 increases. In this case, strictly speaking, a temperature difference occurs between the sheet S and the platen drum 30, but in this example, processing is performed on the assumption that the temperature of both the sheet S and the platen drum 30 is roughly the same.
In this way, in the present disclosure, the temperature is considered to be that of the recording medium or the support unit, without particularly distinguishing between the two.
A plurality of fans F1 and F2 are provided as a cooling mechanism for suppressing the temperature increase caused by the generated heat, and cooling the platen drum 30. Each of the fans F1 and F2 can be turned on and off individually, and a cooling intensity can be changed in a stepwise manner depending on a number of the fans that are operated.
On the other hand, a plurality of heaters H1 and H2 are provided as a heating mechanism for heating the platen drum 30 before the start of printing to a predetermined printing start temperature. Each of the heaters H1 and H2 can be turned on and off individually, and a heating intensity can be changed in a stepwise manner depending on a number of the heaters H1 and H2.
In this way, each of the fans F1 and F2 and the heaters H1 and H2 corresponds to a temperature adjustment unit capable of performing cooling or heating with respect to the support unit. In this embodiment, cooling and heating are performed, but a configuration can be adopted in which cooling alone or heating alone is performed. Further, the intensity is changed by turning the plurality of heaters and fans individually on and off, but the intensity may be adjusted by changing a conducted electric current value in a stepwise manner or continuously in a non-stepwise manner.
Further, in this embodiment, the plurality of heaters H1 and H2 are provided as the heating mechanism for heating the platen drum 30 before the start of printing to the predetermined printing start temperature, but the plurality of heaters H1 and H2 need not necessarily be provided. In this case, in order to heat the platen drum 30 before the start of printing to the predetermined printing start temperature, the photocurable ink may be discharged onto the recording medium, and the generating of the reaction heat at the same time as curing the ink by irradiating this ink with the ultraviolet rays using the UV lamps 61 may be continued until the temperature of the platen drum 30 becomes the predetermined printing start temperature.
The recording head 52 is provided downstream of the UV lamp 62 in the transport direction Ds. The recording head 52 faces the front surface of the sheet S wound on the platen drum 30 with a predetermined clearance therebetween, and discharges a transparent UV ink onto the front surface of the sheet S, using an ink-jet method. In other words, the transparent ink is further discharged onto the color image formed by the recording heads 51 of the four colors. Further, the UV lamp 63 is provided downstream of the recording head 52 in the transport direction Ds. This UV lamp 63 is used for completely curing (final curing of) the transparent ink discharged by the recording head 52, by irradiating the transparent ink with strong ultraviolet rays. In this way, the transparent ink can be fixed to the front surface of the sheet S.
As described above, the sheet S is supported by being wound around the platen drum 30. The sheet S wound around a winding portion Ra of the outer circumferential surface of the platen drum 30 in this manner is irradiated with the ultraviolet rays, to cure the UV ink that has landed on the front surface of the sheet S. Then, in the process unit 3, in order to suppress an increase in the temperature of the UV ink at that time, the platen drum 30 is cooled by the fans F1 and F2 to cause the heat generated by the UV ink to escape to the platen drum 30. Furthermore, when the temperature of the platen drum 30 is lower than the saturation temperature at the start of the printing, the platen drum 30 is heated by the heaters H1 and H2 to increase the temperature of the platen drum 30.
Next, an electrical configuration for controlling the printer 1 will be described.
Furthermore, as an interface with an operator, the host computer 10 is provided with a monitor 130 configured by a liquid crystal display and the like, and an operation unit 140 configured by a keyboard, a mouse, and the like. In addition to an image to be printed, a menu screen is displayed on the monitor 130. Therefore, by operating the operation unit 140 while viewing the monitor 130, the operator can open a printing setting screen from the menu screen, and can set various printing conditions, such as a type of the printing medium, a size of the printing medium, a printing quality, and the like. Note that various modifications are possible in the specific configuration of the interface with the operator. For example, a touch panel type display may be used as the monitor 130, and the operation unit 140 may be configured by the touch panel of the monitor 130.
On the other hand, the printer 1 is provided with a printer control unit 200 that controls each of the units of the printer 1 in accordance with commands from the host computer 10. Then, the recording heads, the UV lamps, and each of the device units of the sheet transport system are controlled by the printer control unit 200. Details of the control by the printer control unit 200 for each of the device units are as follows. The printer control unit 200 is provided with a memory MR as a storage unit. Note that the printer control unit 200 corresponds to a control unit of the present disclosure.
The printer control unit 200 has a function of controlling the transport of the sheet S described above in detail with reference to
As described above, the wet-spreading of the ink varies depending on the temperature of the printing medium or the support body, and this variation affects the image quality. Thus, when the temperature difference between the temperature at the start of the printing and the saturation temperature is large, the difference in image quality will also increase. Therefore, if a magnitude of the difference in image quality is to be kept within a certain range, for example, a color difference ΔE is to be less than 1.0 degrees, which is not likely to be perceived by the human eye, it is necessary to keep the temperature difference between the temperature at the start of printing and the saturation temperature within a certain range.
When the print duty differs, the saturation temperature differs in each case. The temperature at the start of the printing for which the difference between the image quality at each of the saturation temperatures and the image quality at the start of the printing results in the color difference ΔE being in the range of less than 1.0 degrees can be determined via experimentation, and in
When the color difference ΔE is less than 1.0 degrees, the difference is not likely to be perceived by the human eye. This means that, in a single print job, changes in the image quality between a printed material and another printed material at any timing cannot be visually perceived. In other words, a user will perceive the printed materials as being substantially uniform.
In the example shown in
Further, while the saturation temperature and the preliminary heating temperature are experimentally determined when the print duty is high (75%), when the print duty is medium (50%), and when the print duty is low (30%), the saturation temperature and the preliminary heating temperature are determined by performing an interpolation calculation when the print duty does not match one of these print duties. Interpolation calculation formulas are too numerous to mention, but may be an interpolation calculation formula that obtains an average value as a simple proportional gradient, or an arithmetic formula representing a curve that is obtained by calculating that curve smoothly connecting three points.
Further, instead of performing the calculation every time the printing is performed, the calculation may be performed in advance in 1% increments and stored in a table. The storing in the table corresponds to storing a relationship, and the representing the arithmetic formula corresponds to storing a relationship formula.
Since the higher the print duty is, the higher the saturation temperature becomes, basically, when it is assumed that a first temperature corresponds to the preliminary heating temperature when the print duty is a first duty value, it can be said that when the print duty is a second duty value that is higher than when the print duty is the first duty value, a second temperature that is higher than the first temperature corresponds to the preliminary heating value.
The saturation temperature described above represents the temperature at which the temperature increase of the support unit becomes saturated, when the processing for curing the photocurable ink is performed continuously by irradiating the recording medium on which the image has been printed, with the light from the light irradiation unit. When the difference in changes in the image quality is considered as a change of color of the image, causing the color change ΔE to be within a certain range corresponds to starting the printing when the temperature is within a certain temperature range from the saturation temperature, and thus, the preliminary heating temperature is set to be a temperature different by a first temperature difference from the saturation temperature at which the temperature increase of the support unit becomes saturated. Here, when the saturation temperature is set to the first temperature, this can be referred to as being the temperature different from the saturation temperature by the first temperature difference, and when the saturation temperature is set to the second temperature, this can be referred to as being the temperature different from the saturation temperature by a second temperature difference.
In the example shown in
In other experimentation results, when the saturation temperature was high, a degree of increase in the saturation temperature and a degree of change in the image quality were not in a proportional relationship, and the degree of change in the image quality was gradual when the saturation temperature increased. In other words, in a region where the saturation temperature was high, the first temperature difference when the saturation temperature was low was lower than the second temperature difference when the saturation temperature was higher. In other words, the second temperature difference was higher than the first temperature difference.
As described above, when the color difference ΔE between the image printed at the saturation temperature and the image printed at the preliminary heating temperature that is separated from this saturation temperature by the first temperature difference is less than 1.0 degrees, it is assumed that a typical person cannot visually perceive this color difference.
Furthermore, a configuration may be adopted in which the user can set a fluctuation range of the image quality that can be permitted using the user interface, and when the user reduces the fluctuation range of the image quality, the values of the first temperature difference and the second temperature difference may be set to be smaller than when the fluctuation range is set to be larger.
Next, operations of this embodiment having the configuration described above will be described.
The printer control unit 200 performs image selection at step S100. This corresponds to image printing from the user. When the user instructs the printing, the printer control unit 200 recognizes the print image and performs the image selection. Subsequently, at step S105, the printer control unit 200 allocates the selected image in the recording medium. Normally, the printing can be started at this stage, but in the present disclosure, at step S110, the printer control unit 200 calculates an average print duty within a specified range. Since the print duty varies depending on a section, the average print duty is calculated within a predetermined range. The amount of heat generated by the photocurable ink is considered to be proportional to the total amount of ink ejected.
More specifically, for the amount of heat generated, the amount of heat generated can be calculated for each of the ink colors and reflected. For example, in the case of ink colors for which a large amount of heat is generated, the average print duty may be corrected to be larger.
Furthermore, as illustrated in
Subsequently, at step S115, the printer control unit 200 refers to a table using the average print duty as an input, and determines the saturation temperature and the drum preliminary heating temperature. In this embodiment, the saturation temperature and the drum preliminary heating temperature for the print duty are stored as the table, and thus the printer control unit 200 refers to the table using the average print duty as the input, to determine the saturation temperature and drum preliminary heating temperature.
At step S120, the printer control unit 200 investigates the current drum temperature based on a measurement result of the temperature sensor TS. Subsequently, at step S125, the drum is heated or cooled until it reaches, of the saturation temperature and the drum preliminary heating temperature, the temperature for which the difference with the current drum temperature is smaller.
A description will be made with reference to the example shown in
Assuming that the average print duty calculated by the printer control unit 200 at step S110 is 50%, the saturation temperature determined at step S115 is 38 degrees, and the preliminary heating temperature set based on this is 33 degrees. Then, it is assumed that the temperature of the platen drum 30 obtained at step S120 is 25 degrees.
From the information indicating that the current drum temperature is 25 degrees, the saturation temperature is 38 degrees, and the preliminary heating temperature is 33 degrees, the printer control unit 200 can determine that the current drum temperature is closer to the preliminary heating temperature than to the saturation temperature, and furthermore, starts the heating of the platen drum 30 using the heaters H1 and H2 until the current drum temperature reaches the preliminary heating temperature.
The printer control unit 200 stands by until the current drum temperature reaches the preliminary heating temperature, and, once the current drum temperature reaches the preliminary heating temperature, starts the printing at step S130. Note that feedback control is performed in this embodiment, but a method that does not utilize the measurement result of the temperature sensor TS, that is, a method using a simple feed-forward control, is also possible.
On the other hand, a case is also assumed in which the print jobs are continuous, and at this time, a previous print job has an average print duty that is high at 75% and a latter print job has an average print duty that is low at 30%.
In this case, at a time point at which the latter print job is started, the current drum temperature of the platen drum 30 is the saturation temperature of 41 degrees obtained when the average print duty is 75%. At this time, at step S125, from the information indicating that the current drum temperature is 41 degrees, the saturation temperature is 38 degrees, and the preliminary heating temperature is 33 degrees, the printer control unit 200 can determine that the current drum temperature is closer to the saturation temperature than to the preliminary heating temperature, and, furthermore, starts the cooling of the platen drum 30 using the fans F1 and F2 until the current drum temperature reaches the saturation temperature.
Then, once the printer control unit 200 has performed the cooling until the current drum temperature reaches the saturation temperature, the printer control unit 200 starts the printing at step S130.
In this embodiment, when the cooling is necessary, the printer control unit 200 cools the temperature to the saturation temperature and stands by, and when the heating is necessary, the printer control unit 200 stands by until the temperature reaches the preliminary heating temperature that is lower than the saturation temperature. However, a configuration may be adopted in which, even when the cooling is necessary, a preliminary (cooling) temperature is set at which the printing may be started before reaching the saturation temperature, the printing is started before the platen drum 30 reaches the saturation temperature, and the printing is performed while gradually lowering the temperature to the saturation temperature.
In the flowchart illustrated in
As described above, the printer including the printer control unit 200 can be understood to be a printing apparatus of the disclosure, but it goes without saying that each step of the processing that is performed in a chronological manner by the printer control unit 200, as illustrated in
In other words, the printer 1 according to this embodiment can be said to perform processes including:
Note that it goes without saying that the present disclosure is not limited to the examples described above. To a person skilled in the art, it goes without saying that the following is disclosed as an example of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-198139 | Nov 2020 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20130265359 | Sugaya | Oct 2013 | A1 |
| 20150266325 | Mizutani | Sep 2015 | A1 |
| Number | Date | Country |
|---|---|---|
| 2016-182037 | Nov 2016 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20220169015 A1 | Jun 2022 | US |
