JP7630408B2 - Image recording method and image recording device - Google Patents

Description

The present invention relates to an image recording method and an image recording device, and in particular to a technique for recording an image on a recording medium supported on a guide surface.

Inkjet recording devices are known that eject ink from an inkjet head onto a recording medium transported by a transport unit to record an image on the recording medium. The guide surface of the transport unit that supports the recording medium may be provided with multiple projections and recesses depending on the application.

Patent document 1 discloses an inkjet recording device that includes a paper carrying drum that carries and transports paper, which is a recording medium, on its outer circumferential surface, and an ink ejection section that ejects ink toward the paper carried on the paper carrying drum. This paper carrying drum has suction holes on its outer circumferential surface, and when the suction device is operating, a suction force is generated that attracts the paper to the suction holes.

Patent No. 6850429

However, the inkjet recording device described in Patent Document 1 has a problem in that the ease of heat transfer differs between the suction holes on the outer circumferential surface of the paper carrying drum and the areas other than the suction holes, resulting in uneven drying.

The present invention was made in consideration of these circumstances, and aims to provide an image recording method and an image recording device that suppress uneven drying of an image formed on a recording medium supported by a guide surface.

One aspect of an image recording method for achieving the above object is an image recording method comprising a transport step of supporting a recording medium on a guide surface and transporting the recording medium integrally with the guide surface, an image forming step of ejecting liquid from a liquid ejection head onto the transported recording medium to form an image, and a preheating step of preheating the recording medium prior to the image forming step, wherein the temperature of the guide surface in the image forming step is T _G and the temperature of the recording medium is T _P , and the relationship is 0≦T _G -T _P ≦1.2 [° C.]. According to this aspect, it is possible to suppress uneven drying of an image formed on the recording medium supported by the guide surface.

It is preferable that the relationship be 0≦T _G −T _P ≦1.0° C. This can further suppress uneven drying.

It is preferable that the temperature of the recording medium is the temperature of the recording medium at the position where the liquid is applied, and the temperature of the guide surface is the temperature of the guide surface at a position on the recording medium that is the same as the position where the liquid is applied. By having the temperature T _P of the position on the recording medium where the liquid is applied and the temperature T _G of the guide surface at a position that is the same as the position, within the above-mentioned range, the liquid applied to the recording medium dries without moving, and therefore uneven drying of the formed image can be suppressed.

It is preferable to include a treatment liquid application step of applying a treatment liquid to the recording medium prior to the image forming step, a switching step of switching between the presence or absence of the treatment liquid application step, and a treatment liquid drying step of heating the recording medium on which the treatment liquid has been applied when the treatment liquid application step has been performed, the treatment liquid drying step also serving as a preheating step regardless of the presence or absence of the treatment liquid application step. When the treatment liquid is applied, the treatment liquid can suppress drying unevenness, and when the treatment liquid is not applied, the predrying can suppress drying unevenness by setting T _G and T _P in the above ranges.

The guide surface may have at least one of a convex portion and a hole portion. According to this aspect, even if the guide surface has at least one of a convex portion and a hole portion, it is possible to suppress uneven drying. The guide surface may have at least one of a large number of convex portions and holes arranged two-dimensionally.

In the conveying process, it is preferable that the recording medium is supported by using the peripheral surface of a drum rotating around an axis as a guide surface. According to this embodiment, even if the peripheral surface of a drum rotating around an axis is the guide surface, uneven drying can be suppressed.

A liquid drying process may be provided to dry the liquid after the image forming process. According to this aspect, even if the guide surface is heated due to the influence of the liquid drying process, uneven drying can be suppressed.

It is preferable to have a temperature measuring step for measuring the temperature of the recording medium, and the preheating step for preheating the recording medium based on the measured temperature. This makes it possible to control T _G and T _P in the image forming step within the above ranges. The temperature measuring step may measure the temperature of the guide surface.

One aspect of an image recording device for achieving the above object is an image recording device that includes a transport mechanism that supports a recording medium on a guide surface and transports the recording medium integrally with the guide surface, a liquid ejection head that ejects liquid onto the transported recording medium to record an image, and a preheating mechanism that preheats the recording medium before recording the image, where the temperature of the guide surface when recording the image is T _G and the temperature of the recording medium is T _P , the relationship is 0≦T _G -T _P ≦1.2 [° C.]. According to this aspect, it is possible to suppress uneven drying of an image formed on the recording medium supported by the guide surface.

The preheating mechanism preferably includes a fan that supplies dry air to the recording medium. This allows the recording medium to be preheated by the dry air.

The device may be provided with a drying mechanism for drying the ejected liquid. According to this aspect, even if the temperature of the guide surface rises due to the effect of the drying mechanism, uneven drying can be suppressed.

According to the present invention, it is possible to suppress uneven drying of an image formed on a recording medium supported by a guide surface.

FIG. 1 is a schematic diagram showing an example of a guide surface. FIG. 2 is a cross-sectional view of the guide surface and the paper when the paper is supported by the guide surface and ink is applied thereto. FIG. 3 is a top view of the paper. FIG. 4 is a schematic diagram showing an example of a guide surface. FIG. 5 is a cross-sectional view of the guide surface and the paper when the paper is supported by the guide surface and ink is applied thereto. FIG. 6 is a top view of the paper. FIG. 7 is a diagram showing the overall configuration of an inkjet recording apparatus. FIG. 8 is a perspective view showing the configuration of the tip portion of the ink-jet head. FIG. 9 is an enlarged view of a portion of the nozzle surface. FIG. 10 is a plan view of the nozzle surface of the head module. FIG. 11 is a vertical cross-sectional view showing the three-dimensional structure of the ejector. FIG. 12 is a functional block diagram of a control system of the inkjet printing apparatus. FIG. 13 is a graph showing the relationship between the difference between the temperature of the peripheral surface of the image forming drum and the temperature of the paper, and the visibility of drying unevenness.

A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

<Occurrence of uneven drying>
An image recorded (image formed) by an inkjet recording device may have drying unevenness. Drying unevenness is a phenomenon in which light and dark shades appear in an image, including a phenomenon in which a part of an image looks dark, and a phenomenon in which a part of an image looks white and light due to a lack of color. Drying unevenness occurs when the ink that has landed moves on the recording medium.

Conventionally, a treatment liquid is applied to the recording medium in a process prior to ejecting the ink, increasing the viscosity of the ink and suppressing its fluidity. On the other hand, if no treatment liquid is applied, the ink is prone to movement. Below, we will explain the case where no treatment liquid is applied.

Ink migration is likely to occur when the temperature distribution on the recording medium is uneven. When the temperature distribution is uneven, the ink dries easily where the temperature is high and does not dry easily where the temperature is low. In places where the ink dries easily, the ink is concentrated and the surface tension is high. Conversely, in places where the ink is difficult to dry, the ink is not concentrated as much and the surface tension is relatively low. This difference in surface tension causes the ink to move from areas with low surface tension to areas with high surface tension, resulting in uneven drying.

The inventors of this application have discovered that the shape of the guide surface of the transport unit can cause uneven temperature distribution, resulting in uneven drying. For example, if the guide surface is uneven, the unevenness can cause uneven contact with the recording medium, and the degree to which heat is transferred to the recording medium varies depending on the location of contact.

The guide surface of the transport unit, which contacts and supports the recording medium during image formation, may have an uneven shape. FIG. 1 is a schematic diagram showing an example of a guide surface 10 that supports a recording medium. The guide surface 10 shown in FIG. 1 has multiple protrusions 12 and multiple holes 14. The protrusions 12 have a cylindrical shape with a diameter of 1.0 mm and a height of 0.1 mm. The protrusions 12 are arranged two-dimensionally at regular intervals in the vertical direction and in the horizontal direction perpendicular to the vertical direction. The holes 14 are through holes with a diameter of 1.0 mm that penetrate the guide surface 10. The holes 14 are arranged two-dimensionally at regular intervals in the vertical direction and in the horizontal direction.

Figure 2 is a cross-sectional view of the guide surface 10 and paper P when paper P, an example of a recording medium, is supported by the guide surface 10 and ink I is applied, showing the change in surface tension due to the penetration, drying and concentration of the ink. Also, Figure 3 is a top view of the paper P, showing the drying unevenness that occurs when a solid image is formed on the paper P supported by the guide surface 10. A solid image is an image with an ink coverage rate of more than 100%. Here, we consider a case where the temperature of the guide surface 10 is relatively higher than the temperature of the recording medium.

Because the guide surface 10 is made of a material with a relatively high thermal conductivity compared to the surrounding air, heat is easily transferred to the paper P at the points where it comes into contact with the convex portions 12 (positions corresponding to the convex portions 12), and the temperature of the paper P at the points where it comes into contact with the convex portions 12 becomes locally high. Therefore, the temperature of the positions where the paper P comes into contact with the convex portions 12 is relatively high compared to positions where it is not in contact. For this reason, as shown in FIG. 2, the ink I applied to the paper P is dried and concentrated at the positions of the paper P where it comes into contact with the convex portions 12, and the surface tension becomes relatively high compared to positions where it is not in contact. This difference in surface tension causes the ink to move from areas with low surface tension to areas with high surface tension, and the ink is concentrated at the positions of the paper P where it comes into contact with the convex portions 12.

As a result, as shown in Figure 3, drying unevenness occurs, where parts of the image become relatively darker. Note that Figure 3 highlights the darker areas. The darker areas are areas where ink is concentrated. In the example shown in Figure 3, the darker areas occur in correspondence with the positions of the protrusions 12, and each is a circle with a diameter of about 1.0 mm.

The guide surface of the transport unit may have multiple holes. FIG. 4 is a schematic diagram showing an example of a guide surface 20 that supports paper P. The guide surface 20 shown in FIG. 4 has multiple holes 22. The holes 22 are through-holes with a diameter of 0.5 mm that penetrate the guide surface 20. The holes 22 are two-dimensionally arranged at regular intervals in the vertical and horizontal directions.

Figure 5 is a cross-sectional view of the guide surface 20 and paper P when paper P is supported by the guide surface 20 and ink I is applied, showing the change in surface tension due to the penetration, drying and concentration of the ink. Also, Figure 6 is a top view of paper P, showing the uneven drying that occurs when a solid image is formed on paper P supported by the guide surface 20. Here again, we consider a case where the temperature of the guide surface 10 is relatively higher than the temperature of the recording medium.

The holes 22 (air) in the guide surface 20 have a relatively low thermal conductivity compared to the material of the guide surface 20, so heat is not easily transferred to the paper P at the point where it comes into contact with the air in the holes 22 (the position corresponding to the hole 22). Therefore, the temperature of the position of the paper P corresponding to the hole 22 is relatively lower than the position in contact with the guide surface 20. For this reason, as shown in FIG. 5, the ink I applied to the paper P does not dry and concentrate at the position of the paper P corresponding to the hole 22, and the surface tension is relatively small compared to the position in contact with the guide surface 20. Due to this difference in surface tension, the ink moves from the area with low surface tension to the area with high surface tension, and the ink at the position of the paper P corresponding to the hole 22 spreads and decreases.

As a result, as shown in Figure 6, parts of the image are left blank and the density becomes relatively light, resulting in drying unevenness. Note that Figure 6 highlights the areas with low density. Areas with relatively low density are areas with little ink. In the example shown in Figure 6, the areas with relatively low density occur in correspondence with the positions of the holes 22, and are each circular with a diameter of approximately 0.5 mm.

To address the above issues, reducing the thermal conduction from the guide surface to the recording medium and decreasing the ink fluidity is an effective way to improve uneven drying.

Here, two possible measures can be taken to suppress heat conduction: "use a guide surface made of a material with low thermal conductivity" or "reduce the temperature difference between the guide surface and the recording medium as much as possible." However, it is unrealistic to use a material with the same thermal conductivity as air for the guide surface of the transport unit. Therefore, in order to suppress heat conduction from the guide surface to the recording medium, a practical solution is to reduce the temperatures of the guide surface and the recording medium as much as possible. Specifically, this is done by adding a function to control the temperature of the guide surface or the recording medium. Below, an image recording method and an image recording device for controlling the temperature of the recording medium are described.

<Inkjet Recording Apparatus>
[Overall structure]
7 is an overall configuration diagram showing a schematic configuration of the inkjet recording apparatus 100. The inkjet recording apparatus 100 is a sheet-fed printing apparatus (an example of an "image recording apparatus") that prints a color image on a sheet of paper P. The paper P is, for example, ordinary paper such as high-quality copy paper.

As shown in FIG. 7, the inkjet recording device 100 includes a paper feed section 110, a treatment liquid application section 120, a treatment liquid drying section 130, an image forming section 140, an ink drying section 200, and an accumulation section 240.

[Paper feed section]
The paper feed section 110 automatically feeds the paper P one sheet at a time. The paper feed section 110 includes a paper feed device 112, a feeder board 114, and a paper feed drum 116. The paper feed device 112 takes out the paper P set in a stack in a paper feed tray 112A one sheet at a time from the top, and feeds it to the feeder board 114. The feeder board 114 transfers the paper P received from the paper feed device 112 to the paper feed drum 116.

The paper feed drum 116 receives the paper P fed from the feeder board 114 and transfers the received paper P to the treatment liquid application section 120.

[Treatment liquid application section]
The treatment liquid application section 120 applies treatment liquid to the paper P. The treatment liquid is a liquid that has the function of aggregating, insolubilizing, or thickening the color material components in the ink. The treatment liquid application section 120 includes a treatment liquid application drum 122 and a treatment liquid application device 124.

The treatment liquid application drum 122 receives the paper P from the paper feed drum 116 and transfers the received paper P to the treatment liquid drying section 130. The treatment liquid application drum 122 has a gripper 123 on its circumferential surface, and rotates while gripping the leading end of the paper P using the gripper 123, wrapping the paper P around its circumferential surface and transporting it.

The treatment liquid application device 124 applies treatment liquid to the paper P being transported using the treatment liquid application drum 122 (an example of a "treatment liquid application process"). The treatment liquid is applied using a roller.

The inkjet recording device 100 has a mode in which treatment liquid is applied to the paper P and a mode in which treatment liquid is not applied to the paper P. In contrast, the treatment liquid application unit 120 is configured to be able to switch between applying treatment liquid to the paper P and not applying treatment liquid to the paper P. When treatment liquid is not applied to the paper P, the roller that applies treatment liquid is configured to retreat from the transport path of the paper P.

[Treatment liquid drying section]
The treatment liquid drying section 130 (an example of a "pre-heating mechanism") dries the paper P on which the treatment liquid has been applied. The treatment liquid drying section 130 includes a treatment liquid drying drum 132, a hot air blower 134, a hot air blower 135, and a hot air blower 136. The treatment liquid drying drum 132 receives the paper P from the treatment liquid application drum 122, and transfers the received paper P to the image forming section 140. The treatment liquid drying drum 132 includes a gripper 133 on its circumferential surface. The treatment liquid drying drum 132 rotates while gripping the leading end of the paper P using the gripper 133, and transports the paper P.

The hot air blower 134 is installed at a position facing the peripheral surface of the treatment liquid application drum 122. The hot air blower 134 is a non-contact heating means that blows air that has been heated and dried by a heater (not shown) out of an outlet (not shown) by a fan (not shown). The hot air blower 134 blows dry air (hot air) at 30 to 50°C onto the paper P being transported by the treatment liquid application drum 122 to dry the treatment liquid (an example of a "preheating process").

The hot air blower 135 and the hot air blower 136 are each installed inside the treatment liquid drying drum 132. The configuration of the hot air blower 135 and the hot air blower 136 is the same as that of the hot air blower 134. The hot air blower 135 and the hot air blower 136 each blow dry air (hot air) at 30 to 50°C onto the paper P transported using the treatment liquid drying drum 132 to dry the treatment liquid. In this embodiment, the treatment liquid is dried by the hot air blower 134 installed at a position facing the circumferential surface of the treatment liquid application drum 122, and the hot air blower 135 and the hot air blower 136 installed inside the treatment liquid drying drum 132, but the number of hot air blowers and their positions are not particularly limited.

As described below, the treatment liquid drying unit 130 blows dry air onto the paper P regardless of whether treatment liquid is applied to the paper P. The temperature of the dry air may be changed depending on whether treatment liquid is applied.

[Image forming section]
The image forming section 140 includes an image forming drum 142, a head unit 144, and a scanner 190. The image forming drum 142 (an example of a "transport mechanism") is a cylindrical member having a rotation shaft (not shown). The image forming drum 142 receives the paper P from the treatment liquid drying drum 132, and transfers the received paper P to the ink drying section 200 by rotating around the rotation shaft (an example of a "transport process"). A peripheral surface 142A corresponding to the guide surface of the image forming drum 142 is made of SUS (Steel Use Stainless).

The image forming drum 142 has a gripper 143 on its peripheral surface 142A. The image forming drum 142 grips the leading edge of the paper P using the gripper 143 and rotates, winding the paper P around the peripheral surface 142A (an example of a "guide surface"), supporting the back side of the paper P with the peripheral surface 142A and transporting it together with the peripheral surface. The image forming drum 142 has an adsorption mechanism (not shown) that adsorbs the paper P wound around the peripheral surface to the peripheral surface 142A.

Negative pressure is used for adhesion. The image forming drum 142 has a number of suction holes on the peripheral surface 142A (for example, hole portion 14 in FIG. 1), and paper P is attracted to the peripheral surface 142A by suction from the inside through the suction holes. Static electricity may also be used for adhesion. In this case, adhesion is achieved by charging the image forming drum 142.

The image forming drum 142 may have a number of protrusions (e.g., protrusions 12 in FIG. 1) on the peripheral surface 142A to prevent the paper P from wrinkling.

The head unit 144 includes an inkjet head 146C (an example of a "liquid ejection head") that ejects cyan (C) ink (an example of a "liquid"), an inkjet head 146M that ejects magenta (M) ink, an inkjet head 146Y that ejects yellow (Y) ink, and an inkjet head 146K that ejects black (K) ink.

Each of inkjet heads 146C, 146M, 146Y, and 146K is arranged at regular intervals on the transport path of paper P using image forming drum 142.

When ink is ejected from nozzles 162 (see FIG. 10) of inkjet head 146C, inkjet head 146M, inkjet head 146Y, and inkjet head 146K (an example of a "liquid ejection head") toward paper P transported by image forming drum 142, an image is recorded on the surface of paper P (an example of an "image forming process").

Note that, although the configuration shown here uses four colors of ink: cyan, magenta, yellow, and black, the combination of ink colors and the number of colors is not limited to this embodiment, and light inks, dark inks, and special color inks may be added as necessary.

Scanner 190 reads the image recorded on paper P using inkjet head 146C, inkjet head 146M, inkjet head 146Y, and inkjet head 146K.

[Ink drying section]
The ink drying unit 200 (an example of a "drying mechanism") performs a drying process (an example of a "liquid drying step") on the paper P on which an image has been recorded by the image forming unit 140. The ink drying unit 200 includes a chain delivery 210, a paper guide 220, a hot air blower 230, and a paper detection sensor 232.

The chain delivery 210 receives the paper P from the image forming drum 142 and transfers the received paper P to the stacking section 240. The chain delivery 210 has a pair of endless chains 212 that travel along a specified travel path, and grips the leading edge of the paper P using grippers 214 provided on the pair of chains 212 to transport the paper P along the specified transport path. Multiple grippers 214 are provided at regular intervals along the travel direction of the chains 212.

The paper guide 220 is a member that guides the transport of paper P using the chain delivery 210. The paper guide 220 is composed of a first paper guide 222 and a second paper guide 224.

The first paper guide 222 guides the paper P to be transported through the first transport section of the chain delivery 210. The second paper guide 224 guides the paper to be transported through the second transport section following the first transport section.

The hot air blower 230 blows hot air onto the paper P being transported using the chain delivery 210. Note that the hot air from the hot air blower 230 may heat the image forming drum 142, causing the temperature of the peripheral surface 142A to rise.

The paper detection sensor 232 detects the presence or absence of paper P. Examples of the paper detection sensor 232 include a reflective optical sensor or a transmissive optical sensor.

[Stacking section]
The stacking section 240 includes a stacking device 242. The stacking section 240 includes a stacking device 242 that receives the paper P transported from the ink drying section 200 by using the chain delivery 210 and stacks the paper P. The chain delivery 210 releases the paper P at a predetermined stacking position.

The stacking device 242 includes a stacking tray 244. The stacking device 242 receives the paper P released from the chain delivery 210 and stacks the paper P in a bundle on the stacking tray 244.

<Example of inkjet head configuration>
[Overall structure]
The same configuration may be applied to the inkjet head 146C, the inkjet head 146M, the inkjet head 146Y, and the inkjet head 146K. In the following description, the inkjet head 146C will be described as a representative.

Figure 8 is a perspective view showing the configuration of the tip portion of inkjet head 146C. Inkjet head 146C is a line-type liquid ejection head having a nozzle row that can print an image at a specified printing resolution in a single scan across the entire recording area of paper P in the width direction of paper P. Such a liquid ejection head is also called a full-line type liquid ejection head or a page-wide head. The width direction of paper P is a direction perpendicular to the transport direction of paper P and parallel to the surface of paper P.

The tip of the inkjet head 146C has a nozzle surface 148. The nozzle surface 148 has nozzles 162 (see Figure 10) formed therein that eject ink.

The inkjet head 146C has a structure in which multiple head modules 150-i are connected in a row along the longitudinal direction. Note that i is an integer from 1 to n. Note that in the following description, head module 150-i may be referred to as head module 150, with the i representing the head module number omitted.

The head modules 150-i are attached to and integrated with the support frame 152. Each head module 150-i is equipped with a cable 154 for electrical connection.

[Nozzle arrangement]
1 is a partially enlarged view of the nozzle surface 148. The nozzle surface 148-i of the head module 150-i is a parallelogram. Dummy plates 156 are attached to both ends of the support frame 152. The nozzle surface 148 of the inkjet head 146, together with a surface 156A of the dummy plate 156, is rectangular as a whole.

A strip-shaped nozzle arrangement section 158-i is provided in the center of the nozzle surface 148-i of the head module 150-i. The nozzle arrangement section 158-i functions as the actual nozzle surface 148-i. Nozzles 162 are provided in the nozzle arrangement section 158-i. Note that in FIG. 9, the nozzles 162 are not shown individually, but a nozzle row 160 consisting of multiple nozzles is shown.

Figure 10 is a plan view of the nozzle surface 148-i of the head module 150-i. The Y direction in Figure 10 represents the transport direction of the paper P, and the X direction represents the width direction of the paper P. A plurality of nozzles 162 are two-dimensionally arranged on the nozzle surface 148-i of the head module 150-i.

Head module 150-i has a parallelogram shape in plan view, with a long side end face aligned in the V direction at an angle β relative to the width direction of the paper P, and a short side end face aligned in the W direction at an angle α relative to the transport direction of the paper P.

In the head module 150-i, a plurality of nozzles 162 are arranged in a matrix with rows along the V direction and columns along the W direction. The nozzles 162 may be arranged in rows along the width direction of the paper P and in columns that intersect diagonally with the width direction of the paper P.

In the case of inkjet head 146C, the projected nozzle row obtained by projecting each nozzle 162 along the X direction can be considered equivalent to a single nozzle row in which each nozzle 162 is arranged at approximately equal intervals at a nozzle density that achieves the maximum recording resolution in the X direction. Approximately equal intervals means that the nozzles are substantially equal in intervals as droplet ejection points that can be recorded by inkjet recording device 100. For example, the concept of equal intervals also includes cases in which the intervals are slightly different to take into account at least one of manufacturing errors and the movement of droplets on paper P due to landing interference.

The nozzle arrangement of the inkjet head 146 is not limited, and various nozzle arrangements can be adopted. For example, instead of a two-dimensional matrix arrangement, a linear arrangement in one row, a V-shaped nozzle arrangement, and a zigzag arrangement such as a W-shape with V-shaped arrangements as repeating units are also possible.

[Ejector Configuration]
11 is a vertical cross-sectional view showing the three-dimensional structure of the ejector 164. The ejector 164 includes a nozzle 162, a pressure chamber 166 communicating with the nozzle 162, and a piezoelectric element 168. The nozzle 162 communicates with the pressure chamber 166 via a nozzle flow path 170. The pressure chamber 166 communicates with a supply-side common branch flow path 174 via an individual supply path 172.

The diaphragm 176 that constitutes the top surface of the pressure chamber 166 has a conductive layer (not shown) that functions as a common electrode corresponding to the lower electrode of the piezoelectric element 168. The pressure chamber 166, the walls of the other flow path parts, and the diaphragm 176 can be made of silicon.

The material of the diaphragm 176 is not limited to silicon, and it may be made of a non-conductive material such as resin. The diaphragm 176 itself may be made of a metal material such as stainless steel, and may serve as a diaphragm that also serves as a common electrode.

A piezoelectric unimorph actuator is formed by stacking a piezoelectric element 168 on a vibration plate 176. A drive voltage is applied to the individual electrode 178, which is the upper electrode of the piezoelectric element 168, to deform the piezoelectric body 180, deflecting the vibration plate 176 and changing the volume of the pressure chamber 166. The pressure change caused by the change in volume of the pressure chamber 166 acts on the ink, causing it to be ejected from the nozzle 162.

When the piezoelectric element 168 returns to its original state after ink ejection, new ink is filled into the pressure chamber 166 through the individual supply path 172 from the supply-side common branch path 174. The action of filling the pressure chamber 166 with ink is called refilling.

The planar shape of the pressure chamber 166 is not particularly limited, and may be a variety of shapes, such as a rectangle or other polygon, a circle, or an ellipse. A cover plate 182 is provided above the individual electrode 178. The cover plate 182 is a member that maintains the movable space 184 of the piezoelectric element 168 and seals the periphery of the piezoelectric element 168.

A supply side ink chamber (not shown) and a recovery side ink chamber (not shown) are formed above the cover plate 182. The supply side ink chamber is connected to a supply side common main flow path (not shown) via a communication passage (not shown). The recovery side ink chamber is connected to a recovery side common main flow path (not shown) via a communication passage (not shown).

<Control system configuration>
12 is a functional block diagram of a control system of the inkjet recording apparatus 100. The inkjet recording apparatus 100 includes a system controller 250. The system controller 250 is an overall control unit that comprehensively controls each unit of the inkjet recording apparatus 100. The system controller 250 is a calculation unit that performs various calculation processes. The system controller 250 is a memory controller that controls reading and writing of data in memory.

[Communications Department]
The inkjet recording apparatus 100 includes a communication unit 252. The communication unit 252 transmits and receives data to and from a host computer 254 connected via a communication interface (not shown).

[Image memory]
The inkjet recording apparatus 100 includes an image memory 256. The image memory 256 functions as a temporary storage unit for various data including image data. Data is read from and written to the image memory 256 via the system controller 250. Image data acquired from a host computer 254 via a communication unit 252 is stored in the image memory 256.

[Transport control unit]
The inkjet recording apparatus 100 includes a transport control unit 258. The transport control unit 258 controls the operation of the transport unit 109. The transport unit 109 includes the paper feed drum 116, the treatment liquid application drum 122, the image forming drum 142, and the chain delivery 210 shown in FIG.

[Paper feed control unit]
The inkjet recording apparatus 100 includes a paper feed control unit 260. The paper feed control unit 260 operates the paper feed unit 110 in response to a command from a system controller 250.

[Treatment liquid application control unit]
The inkjet recording apparatus 100 includes a treatment liquid application control unit 262. The treatment liquid application control unit 262 controls the operation of the treatment liquid application unit 120 in response to a command from the system controller 250.

The treatment liquid application control unit 262 controls switching between applying and not applying treatment liquid to the paper P by the treatment liquid application unit 120 according to the set mode (an example of a "switching process"). Switching between a mode in which treatment liquid is applied to the paper P and a mode in which treatment liquid is not applied to the paper P may be performed by user input via the operation unit 272, or may be performed by automatically determining the need for treatment liquid by, for example, determining the type of paper P using a sensor (not shown).

[Treatment Liquid Drying Control Unit]
The inkjet recording apparatus 100 includes a treatment liquid drying control unit 264. The treatment liquid drying control unit 264 controls the operation of the treatment liquid drying unit 130 in response to a command from the system controller 250.

[Drawing control section]
The inkjet recording apparatus 100 includes an image formation control section 266. The image formation control section 266 controls the operation of the image forming section 140 in response to a command from the system controller 250.

The image formation control unit 266 includes an image processing unit (not shown). The image processing unit forms dot data from input image data. The image processing unit includes a color separation processing unit (not shown), a color conversion processing unit (not shown), a correction processing unit (not shown), and a halftone processing unit (not shown).

The color separation processing unit performs color separation processing on the input image data. For example, if the input image data is expressed in RGB (Red Green Blue), the input image data is separated into data for each of the colors R, G, and B.

The color conversion processing unit converts the image data for each color separated into R, G, and B into C, M, Y, and K, which correspond to the ink colors.

The correction processing unit performs correction processing on the image data for each color converted to C, M, Y, and K. Examples of correction processing include gamma correction processing, uneven density correction processing, and abnormal recording element correction processing.

The halftone processing unit converts image data expressed in multiple tones, such as 0 to 255, into dot data expressed in binary or multiple values of 3 or more values that are less than the number of tones of the input image data. The halftone processing unit applies predetermined halftone processing rules. Examples of halftone processing rules include the dither method and the error diffusion method.

The image formation control unit 266 includes a waveform generation unit (not shown), a waveform storage unit (not shown), and a drive circuit (not shown). The waveform generation unit generates a waveform of the drive voltage. The waveform storage unit stores the waveform of the drive voltage.

The drive circuit generates a drive voltage having a drive waveform according to the dot data. The drive circuit supplies the drive voltage to inkjet head 146C, inkjet head 146M, inkjet head 146Y, and inkjet head 146K shown in FIG. 7.

That is, the ejection timing and ink ejection amount for each pixel position are determined based on the dot data generated through processing by the image processing unit. A drive voltage according to the ejection timing and ink ejection amount for each pixel position, as well as a control signal that determines the ejection timing for each pixel, are generated. The drive voltage and control signal are supplied to inkjet head 146C, inkjet head 146M, inkjet head 146Y, and inkjet head 146K, and dots are formed on paper P by the ink ejected from inkjet head 146C, inkjet head 146M, inkjet head 146Y, and inkjet head 146K.

[Ink drying control unit]
The inkjet recording apparatus 100 includes an ink drying control unit 268. The ink drying control unit 268 controls the operation of the ink drying unit 200 in response to a command from the system controller 250.

[Integration control section]
The inkjet recording apparatus 100 includes a stacking control unit 270. The stacking control unit 270 controls the operation of the stacking unit 240 in response to a command from the system controller 250. The operation of the stacking unit 240 may include an opening and closing operation of the gripper 214 when stacking the paper P on which an image has been formed in the stacking device 242 shown in FIG.

[Operation section]
The inkjet recording apparatus 100 includes an operation unit 272. The operation unit 272 includes operation members such as an operation button, a keyboard, and a touch panel. The operation unit 272 may include a plurality of types of operation members. Information input using the operation unit 272 is transmitted to the system controller 250. The system controller 250 generates command signals for executing various processes in accordance with the information transmitted from the operation unit 272. The system controller 250 transmits the command signals to a processing unit that performs various processes.

[Display section]
The inkjet recording apparatus 100 includes a display unit 274. The display unit 274 includes a display device (not shown), such as a liquid crystal panel, and a display driver (not shown). The display unit 274 displays various information, such as various setting information of the apparatus and abnormality information, on the display device in response to a command from the system controller 250. The display unit 274 may be a touch panel type display device and may also function as the operation unit 272.

[Parameter storage unit]
The inkjet recording apparatus 100 includes a parameter storage unit 276. The parameter storage unit 276 stores various parameters used in the inkjet recording apparatus 100. The various parameters stored in the parameter storage unit 276 are read out using the system controller 250. The various parameters are set in each unit of the apparatus using the system controller 250.

[Program storage section]
The inkjet recording apparatus 100 includes a program storage unit 278. The program storage unit 278 stores programs used by each unit of the inkjet recording apparatus 100. The various programs stored in the program storage unit 278 are read out via the system controller 250 and executed in each unit of the apparatus.

[Sensor]
The inkjet recording apparatus 100 includes a sensor 280. The sensor 280 includes at least an optical sensor and a pressure sensor. The sensor 280 may include various sensors such as a temperature sensor and a flow rate sensor.

[Hardware configuration of various control units]
Processors are applied to the various control units shown in Fig. 12. The hardware structure of the processor is various processors as shown below. The various processors include a CPU (Central Processing Unit), which is a general-purpose processor that executes software (programs) and acts as various functional units, a GPU (Graphics Processing Unit), which is a processor specialized for image processing, a PLD (Programmable Logic Device), which is a processor whose circuit configuration can be changed after manufacture such as an FPGA (Field Programmable Gate Array), and a dedicated electric circuit, which is a processor having a circuit configuration designed specifically for executing specific processing such as an ASIC (Application Specific Integrated Circuit).

A processing unit may be configured with one of these various processors, or may be configured with two or more processors of the same or different types (for example, multiple FPGAs, or a combination of a CPU and an FPGA, or a combination of a CPU and a GPU). Multiple functional units may also be configured with one processor. As an example of configuring multiple functional units with one processor, first, as represented by a computer such as a client or server, one processor is configured with a combination of one or more CPUs and software, and this processor acts as multiple functional units. Second, as represented by a SoC (System On Chip), there is a form in which a processor is used that realizes the functions of the entire system including multiple functional units with a single IC (Integrated Circuit) chip. In this way, the various functional units are configured using one or more of the above various processors as a hardware structure.

More specifically, the hardware structure of these various processors is an electrical circuit that combines circuit elements such as semiconductor elements.

The processor executes instructions stored in memory (not shown). The memory stores instructions to be executed by the processor. The memory includes RAM (Random Access Memory) and ROM (Read Only Memory), not shown. The processor uses the RAM as a working area, executes software using various programs and parameters, including a research support program, stored in the ROM, and executes various processes by using parameters stored in the ROM, etc.

<Function of Inkjet Recording Apparatus>
The inkjet recording device 100 performs an image recording method in which the paper P is heated by the treatment liquid drying section 130, the preheated paper P is supported by the peripheral surface 142A of the image forming drum 142 and transported integrally with the peripheral surface 142A, and ink is ejected from the inkjet heads 146C, 146M, 146Y, and 146K onto the paper P transported by the image forming drum 142 to form an image. According to this image recording method, the paper P is preheated by the treatment liquid drying section 130, so that the temperature difference between the peripheral surface 142A of the image forming drum 142 and the paper P when an image is formed can be relatively small. Therefore, the heat conduction from the peripheral surface 142A to the paper P can be suppressed to reduce the fluidity of the ink, and therefore uneven drying can be suppressed.

The inkjet recording device 100 also implements an image recording method in which the treatment liquid drying control unit 264 switches between the presence and absence of a treatment liquid application process. When the treatment liquid application process is included, treatment liquid is applied to the paper P in the treatment liquid application unit 120 prior to the image formation process, and the paper P coated with the treatment liquid is heated in the treatment liquid drying unit 130, which also serves as preheating (an example of a "treatment liquid drying process"). When the treatment liquid application process is not included, the treatment liquid drying control unit 264 preheats the paper P in the treatment liquid drying unit 130 (an example of a "preheating process").

According to this image recording method, when the treatment liquid is applied, the treatment liquid can suppress drying unevenness. Furthermore, when the treatment liquid is not applied, the treatment liquid drying unit 130 pre-dries the paper P, suppressing heat conduction from the peripheral surface 142A to the paper P, reducing the fluidity of the ink and suppressing drying unevenness. Furthermore, while adding a new temperature control mechanism for pre-heating is not cost-effective, according to this image recording method, the treatment liquid drying unit 130 also functions as a pre-heating mechanism, thereby reducing costs.

<Relationship between temperature difference on guide surface and paper and visibility of drying unevenness>
It has been confirmed that uneven drying can be reduced by preheating the paper P and relatively reducing the temperature difference between the circumferential surface 142A of the image forming drum 142 and the paper P.

Fig. 13 is a graph showing the relationship between the temperature difference (T _G -T _P ) between the temperature T _G of the peripheral surface 142A of the image forming drum 142 of the inkjet recording apparatus 100 and the temperature T _P of the paper P, and the visibility of drying unevenness. In Fig. 13, the horizontal axis shows the temperature difference (T _G -T _P ), and the vertical axis shows the results of a sensory evaluation of the visibility level of drying unevenness of a solid image formed at each temperature difference.

The temperature T _G of the peripheral surface 142A of the image forming drum 142 and the temperature T _P of the paper P were measured at positions immediately before ink droplets were ejected by the inkjet head 146C, the inkjet head 146M, the inkjet head 146Y, and the inkjet head 146K. Here, the temperature T _G of the peripheral surface 142A of the image forming drum 142 was 26 to 32°C. The temperature of the ink was 30°C.

The results of the sensory evaluation of the visibility of drying unevenness were classified as follows. Classification A or above is the pass mark.

A ⁺⁺ : Very good (no visible drying marks)
A ⁺ : worse than A ⁺⁺ and better than A A: good (drying unevenness is barely visible)
B ⁺ : worse than A and better than B B: poor (drying unevenness is slightly visible)
C ⁺ : worse than B and better than C C: very poor (uneven drying is visible)
The visibility of drying unevenness of a solid image formed at each temperature difference was plotted in the graph of Fig. 13. The straight line shown in Fig. 13 is an approximation straight line derived from each plot point.

As shown in Figure 13, in order to bring the visibility of drying unevenness in a solid image above the pass line, it is preferable that the temperature T _G of the guide surface when the ink lands on the paper P and the temperature T _P of the paper P have a relationship of 0≦T _G -T _P ≦1.2 [°C], and it is even more preferable that they have a relationship of 0≦T _G -T _P ≦1.0 [°C].

The amount of heat required in the treatment liquid drying section 130 varies depending on the type of paper P, such as its material and thickness. It is therefore preferable to provide a reference table that links the type of paper P to the amount of heat (e.g., the temperature of the drying air) and to control the treatment liquid drying section 130 to an amount of heat that corresponds to the type of paper P. The amount of heat required also varies depending on whether treatment liquid is applied. It is therefore preferable to provide a reference table that links the amount of heat to whether treatment liquid is applied and to control the treatment liquid drying section 130 to an amount of heat that corresponds to whether treatment liquid is applied.

＜Other＞
So far, a case has been described in which the temperature of the peripheral surface 142A of the image forming drum 142 is higher than the temperature of the paper P. On the other hand, when the temperature of the paper P is higher than the temperature of the peripheral surface 142A of the image forming drum 142, in order to make the visibility of the drying unevenness of the solid image equal to or higher than the pass line, it is considered that, based on the findings so far, it is preferable to have a relationship of -1.2≦T _G -T _P ≦0 [°C], and it is more preferable to have a relationship of -1.0≦T _G -T _P ≦0 [°C]. Integrating these, in order to make the visibility of the drying unevenness of the solid image equal to or higher than the pass line, it is preferable to have a relationship of |T _G -T _P |≦1.2 [°C], and it is more preferable to have a relationship of |T _G -T _P |≦1.0 [°C].

A temperature sensor (not shown) may be provided to measure the temperature of the paper P transported by the image forming drum, and the treatment liquid drying control unit 264 may measure the temperature of the paper P using the temperature sensor (an example of a "temperature measurement process") and feedback control the treatment liquid drying unit 130 based on the measurement result of the temperature sensor. In this case, the treatment liquid drying control unit 264 may set the temperature of the drying air according to the measurement result of the temperature sensor. A temperature sensor (not shown) may be provided to measure the temperature of the peripheral surface 142A of the image forming drum 142, and the treatment liquid drying control unit 264 may measure the temperature of the peripheral surface 142A using the temperature sensor, and feedback control the treatment liquid drying unit 130 based on the measurement result of the temperature sensor.

In this embodiment, the guide surface that supports the paper P is the peripheral surface 142A of the image forming drum 142, which is a curved surface, but the guide surface is not limited to a curved surface and may be a flat surface, and a flat guide surface may have at least one of a large number of protrusions and a large number of holes.

In this embodiment, the recording medium is a sheet of paper P, but the recording medium is not limited to paper, and various sheet bodies, such as resin sheets, films, and other materials and shapes, can be used.

In this embodiment, the recording medium is preheated to satisfy the relationship 0≦T _G -T _P ≦1.2 [°C], but the relationship 0≦T _G -T _P ≦1.2 [°C] may also be satisfied by adjusting the temperature of the guide surface (e.g., cooling it).

The technical scope of the present invention is not limited to the scope described in the above embodiments. The configurations of each embodiment can be appropriately combined with each other without departing from the spirit of the present invention.

10... guide surface 12... convex portion 14... hole portion 20... guide surface 22... hole portion 100... inkjet recording apparatus 109... transport section 110... paper feed section 112... paper feed device 112A... paper feed tray 114... feeder board 116... paper feed drum 120... treatment liquid application section 122... treatment liquid application drum 123... gripper 124... treatment liquid application device 130... treatment liquid drying section 132... treatment liquid drying drum 133... gripper 134... hot air blower 135... hot air blower 136... hot air blower 140... Image forming section 142...Image forming drum 142A...Circumferential surface 143...Gripper 144...Head unit 146...Inkjet head 146C...Inkjet head 146K...Inkjet head 146M...Inkjet head 146Y...Inkjet head 148...Nozzle surface 148-i...Nozzle surface 150...Head module 150-i...Head module 152...Support frame 154...Cable 156...Dummy plate 156A...Surface 158-i ...Nozzle arrangement section 160...Nozzle row 162...Nozzle 164...Ejector 166...Pressure chamber 168...Piezoelectric element 170...Nozzle flow path 172...Individual supply path 174...Supply side common branch path 176...Vibration plate 178...Individual electrode 180...Piezoelectric body 182...Cover plate 184...Moveable space 190...Scanner 200...Ink drying section 210...Chain delivery 212...Chain 214...Gripper 220...Paper guide 222...First paper guide 224...Second paper guide 230...Hot air Blower 232...paper detection sensor 240...accumulation section 242...accumulation device 244...accumulation tray 250...system controller 252...communication section 254...host computer 256...image memory 258...transport control section 260...paper feed control section 262...treatment liquid application control section 264...treatment liquid drying control section 266...image formation control section 268...ink drying control section 270...accumulation control section 272...operation section 274...display section 276...parameter memory section 278...program storage section 280...sensor

Claims (11)

a conveying step of supporting the recording medium with a guide surface and conveying the recording medium integrally with the guide surface;
an image forming step of forming an image by ejecting liquid from a liquid ejection head onto the conveyed recording medium;
a preheating step of preheating the recording medium before the image forming step;
Equipped with
In the image forming process, the temperature of the guide surface is T _G and the temperature of the recording medium is T _P.
0≦T _G -T _P ≦1.2 [℃]
The image recording method has the following relationship: 0≦T _G -T _P ≦1.0 [℃]
2. The image recording method according to claim 1, wherein the relationship is: the temperature of the recording medium is the temperature of the recording medium at a position where the liquid is applied,
3. The image recording method according to claim 1, wherein the temperature of the guide surface is the temperature of the guide surface at a position on the recording medium that is the same as the position where the liquid is applied. a treatment liquid application step of applying a treatment liquid to the recording medium prior to the image forming step;
A switching step of switching between the presence and absence of the treatment liquid application step;
a treatment liquid drying step of heating the recording medium on which the treatment liquid has been applied when the treatment liquid application step has been performed, the treatment liquid drying step also serving as the preheating step regardless of whether the treatment liquid application step has been performed or not;
The image recording method according to claim 1 , further comprising: The image recording method according to any one of claims 1 to 4, wherein the guide surface has at least one of a convex portion and a hole portion. The image recording method according to any one of claims 1 to 5, wherein the conveying step supports the recording medium using the peripheral surface of a drum that rotates around an axis as the guide surface. The image recording method according to any one of claims 1 to 6, further comprising a liquid drying step of drying the liquid after the image forming step. a temperature measuring step of measuring a temperature of the recording medium,
The image recording method according to claim 1 , wherein the preheating step preheats the recording medium based on the measured temperature. a conveying mechanism that supports the recording medium with a guide surface and conveys the recording medium integrally with the guide surface;
a liquid ejection head that ejects liquid onto the transported recording medium to record an image;
a preheating mechanism for preheating the recording medium before recording the image;
Equipped with
When the image is recorded, the temperature of the guide surface is T _G and the temperature of the recording medium is T _P.
0≦T _G -T _P ≦1.2 [℃]
An image recording device having the above relationship. The image recording device according to claim 9, wherein the preheating mechanism includes a fan that supplies dry air to the recording medium. The image recording device according to claim 9 or 10, further comprising a drying mechanism for drying the ejected liquid.

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