Image forming device

Abstract

To inhibit smudges in a recording medium.SOLUTION: An image formation device according to one embodiment of the invention includes: a first liquid application part which applies liquid to a first surface of a recording medium; a second liquid application part which applies the liquid to a second surface of the recording medium in which the liquid is applied to the first surface by the first liquid application part; a transport part which transports the recording medium, in which the liquid is applied to the second surface by the second liquid application part, in a transport direction; and a heating part which heats the recording medium transported by the transport part. The transport part contacts with the first surface of the recording medium to transport the recording medium. The heating part heats the recording medium at different temperatures between an upstream side and a downstream side of the recording medium in the transport direction.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] 2. Description of the Related Art Conventionally, in an inkjet type image forming apparatus, a configuration is known in which, after ink is applied to a recording medium, the ink applied to the recording medium is heated and dried.

[0003] Furthermore, as the above-mentioned image forming apparatus, a configuration has been disclosed which includes an information acquisition means for acquiring information on the amount of ink droplets ejected onto the surface of the recording medium in order to prevent cockling of the heated recording medium, a first drying means for drying the recording medium before recording an image, and a drive condition determination means for determining the drive conditions of the first drying means based on the information on the amount of ink droplets ejected acquired by the information acquisition means (see, for example, Patent Document 1). Summary of the Invention [Problem to be solved by the invention]

[0004] However, when forming images on both sides of a recording medium using the image forming apparatus, an image is formed by applying a liquid such as ink to a first side such as the front side of the recording medium, and then an image is formed by applying a liquid to a second side such as the back side of the recording medium. Then, while the first side is brought into contact with a transport roller or the like and the recording medium is transported, the ink applied to the second side is heated and dried. In this case, with the configuration of Patent Document 1, there is a concern that the liquid applied to the first side will adhere to the transport roller when drying the second side, and the recording medium that subsequently comes into contact with the transport roller will be contaminated.

[0005] An object of the present invention is to suppress contamination of a recording medium. [Means for solving the problem]

[0006] An image forming apparatus according to one aspect of the present invention includes a first liquid application unit that applies liquid to a first surface of a recording medium, and a second liquid application unit that applies liquid to a second surface of the recording medium on which liquid has been applied by the first liquid application unit; A conveying roller is included. a transport section that transports the recording medium, on which liquid has been applied by the second liquid application section, in a transport direction, and a heating section that heats the recording medium transported by the transport section, the heating unit includes a first heating unit that is disposed inside the transport roller and heats the recording medium transported in contact with an outer circumferential surface of the transport roller from the inside, and a plurality of second heating units that are disposed opposite the outer circumferential surface of the transport roller along a transport direction of the recording medium by the transport roller and heats the recording medium transported in contact with the outer circumferential surface of the transport roller from the outside, The conveying unit conveys the recording medium while contacting the first surface of the recording medium, and the heating unit heats the recording medium at different temperatures on the upstream side and the downstream side in the conveying direction of the recording medium. The outer circumferential surface of the conveying roller is provided with a plurality of recesses. . Effect of the Invention

[0007] According to the present invention, contamination of the recording medium can be suppressed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of an overall configuration. [Diagram 2] FIG. 2 is a diagram illustrating an example of the configuration of a drying unit. [Diagram 3] FIG. 11 is a diagram illustrating an example of the overall configuration of a second embodiment. [Figure 4] FIG. 11 is a diagram illustrating an example of temperature control at a first location. [Diagram 5] FIG. 11 is a diagram illustrating an example of temperature control at a second location. [Figure 6] FIG. 13 is a diagram showing an example of the relationship between the amount of ink and variable elements in the maximum amount of heat per unit time. [Figure 7] FIG. 13 is a diagram showing an example of the relationship between the maximum heat quantity and the drying heat quantity. [Figure 8] FIG. 13 is a diagram illustrating an example of the overall process. [Figure 9] FIG. 13 is a diagram illustrating an example of the configuration of an image forming apparatus according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The optimum and minimum mode for carrying out the invention will be described below with reference to the drawings. Note that in the drawings, when the same reference numerals are used, it indicates that the configuration is the same, and duplicated explanations will be omitted. Also, the specific examples shown in the drawings are merely examples, and the configuration may further include configurations other than those shown in the drawings.

[0010] First Embodiment <Overall configuration example> Fig. 1 is a diagram showing an example of the overall configuration. Hereinafter, the direction in which a sheet of paper 1, an example of a recording medium, is transported is referred to as the "X direction." The direction perpendicular to the X direction, i.e., the direction of gravity, is referred to as the "Z direction." Furthermore, the direction perpendicular to the X direction is referred to as the "Y direction."

[0011] In the following description, the first surface of both surfaces is referred to as the "front surface." Meanwhile, the second surface opposite the first surface is referred to as the "rear surface."

[0012] For example, as shown in the figure, the image forming apparatus 100 ejects droplets of ink or the like to form an image on a sheet of paper 1. In the following, an example in which the image forming unit is a head 2 will be described.

[0013] The image forming apparatus 100 forms an image on both sides by, for example, ejecting ink from the head 2. Specifically, the image forming apparatus 100 first forms an image on the front side by ejecting ink onto the front side (hereinafter referred to as "front side ink 3b"). Next, if the paper 1 is turned over, for example, an image can be formed on the back side of the paper 1 by ejecting ink onto the back side (hereinafter referred to as "back side ink 3a") as shown in the figure.

[0014] Here, the paper 1 is an example of a recording medium, the front side of the paper 1 is an example of a first side, the back side of the paper 1 is an example of a second side, and ink is an example of a liquid.

[0015] The paper 1 is conveyed by, for example, conveying rollers 7. That is, when the conveying rollers 7 rotate, the paper 1 moves in the direction in which the conveying rollers 7 rotate. In this manner, the conveying rollers 7 are rotated by an actuator such as a motor, whereby the conveying rollers 7 convey the paper 1. In this example, the conveying rollers 7 convey the paper 1 to the drying rollers 6, for example, after image formation is performed by the head 2.

[0016] The drying roller 6 dries the paper 1. For example, the drying section made up of the drying roller 6 and the like has the following configuration.

[0017] <Example of drying section> Fig. 2 is a diagram showing a configuration example of the drying unit. For example, as shown in Fig. 2(A), the drying roller 6 includes a roller 8 for conveying the paper 1 and a heater 5 for heating that is provided inside the roller 8.

[0018] It is desirable that roller 8 contains a material with high thermal conductivity, such as metal. Like transport roller 7, roller 8 is a mechanism for transporting paper 1. Specifically, as shown in FIG. 1, roller 8 comes into contact with paper 1 to transport and heat paper 1. In other words, the surface of roller 8 transfers heat from heater 5 to paper 1, and is therefore also a heating surface. Therefore, roller 8 is desirably made of a material that easily transfers heat from heater 5.

[0019] The heater 5 is disposed, for example, inside the drying roller 6 and concentrically with respect to the axis of the roller 8 as shown in the drawing.

[0020] As shown in the figure, the drying section desirably includes a dryer 4 in addition to the drying roller 6. In this manner, if the drying section is configured to dry the paper 1 by blowing hot air or the like in addition to the drying roller 6, higher heat can be applied to the paper 1, and the paper can be dried more quickly.

[0021] The number of dryers 4 may be multiple as shown in the figure, or may be one.

[0022] For example, the dryer 4 is a hot air heater or an IR (infrared) heater. In this way, it is preferable that the dryer 4 is a device that can dry the paper 1 without contacting the paper 1. When drying can be performed in this manner without contact, the paper 1 or the dryer 4 is less likely to become dirty than when drying is performed in contact.

[0023] 2B is an enlarged view showing an example of the heating surface. For example, the heating surface has through holes 9, which are an example of recesses. With the through holes 9, the area of ​​contact with the paper 1 can be reduced. This reduces the possibility of the heating surface becoming dirty.

[0024] The through holes 9 are formed by a process such as punching.

[0025] When the heating surface becomes dirty, the dirt adhering to the heating surface may be transferred to the recording medium on which the next image is formed. Therefore, when the heating surface is dirty, the dirt may stain the recording medium. Therefore, by reducing the dirt on the heating surface, the dirt on the recording medium can be reduced.

[0026] The recess may have a shape other than that shown in the figure. That is, the recess is not limited to a through hole. The recess may have any mechanism that can reduce the contact area between the heating surface and the recording medium. Therefore, the recess may be a non-through hole that does not penetrate. In addition, the recess may not be round. That is, the recess may be a predetermined shape such as a rectangle, an ellipse, a star, or a combination of these.

[0027] The heating surface may have a protrusion. For example, the protrusion may be formed by raising a part of the heating surface, or by arranging a metal member or the like on the heating surface. In this way, the protrusion may be any mechanism that reduces the contact area between the heating surface and the paper 1.

[0028] <Second embodiment> 3 is a diagram showing an example of the overall configuration of the second embodiment. In the following, the same components as those in the first embodiment are given the same reference numerals and the description thereof will be omitted.

[0029] The second embodiment differs from the first embodiment in that the heater and dryer are controlled so that the temperature distribution varies depending on the position.

[0030] For example, the heater, dryer, etc. are controlled so that the following temperature distribution is obtained at the position where the paper 1 contacts the drying roller 6 the earliest (hereinafter referred to as the "first position P1") and at the position where the paper 1 contacts the drying roller 6 the latest (hereinafter referred to as the "second position P2").

[0031] The first location P1 may be located upstream of the second location P2. In other words, the first location P1 is upstream, while the second location P2 may be located downstream of the first location P1.

[0032] 1 will be referred to as the "first dryer 41," the "second dryer 42," the "third dryer 43," and the "fourth dryer 44" in that order from the upstream on the path along which the paper 1 is transported. The dryer used at the first location P1 will be referred to as the first dryer 41, and the dryer used at the second location P2 will be referred to as the fourth dryer 44.

[0033] The heater 5 is composed of a plurality of heaters. That is, the heater 5 is configured so that it can be controlled so that different parts have different temperatures.

[0034] <Example of temperature control at the first location> 4 is a diagram showing an example of temperature control at the first location. For example, the heater 5 is controlled so that the temperature at which the heating surface used at the first location P1 is heated becomes a first heating temperature T51. Meanwhile, the first dryer 41 is controlled so that the temperature at which the paper 1 is dried at the first location P1 becomes a first back surface temperature T41. The first back surface temperature T41 is the temperature of the hot air blowing against the back surface of the paper 1.

[0035] Heating by the heater 5 increases the first heating temperature T51. When the first heating temperature T51 increases, the temperature of the heating surface of the drying roller 6 that is used for heating at the first location P1 (hereinafter referred to as the "first location heating surface temperature T61") increases. Such a first location heating surface temperature T61 becomes the temperature at which the surface of the paper 1 is heated. This example is an example of temperature control in which the first location heating surface temperature T61 is set to converge to the first convergence temperature TC1.

[0036] <Example of temperature control at the second location> For example, while the temperature at the first location P1 is controlled as described above, the temperature at the second location P2 is controlled as follows.

[0037] 5 is a diagram showing an example of temperature control at the second location. As in the first location, for example, the heater 5 is controlled so that the temperature at which the heating surface used at the second location P2 is heated is a second heating temperature T52. Meanwhile, the fourth dryer 44 is controlled so that the temperature at which the paper 1 is dried at the second location P2 is a second back surface temperature T44. The second back surface temperature T44 is the temperature of the hot air blowing against the back surface of the paper 1.

[0038] Heating by the heater 5 increases the second heating temperature T52. When the second heating temperature T52 increases, the temperature of the heating surface of the drying roller 6 that is used for heating at the second location P2 (hereinafter referred to as the "second location heating surface temperature T62") increases. Such second location heating surface temperature T62 becomes the temperature at which the surface of the paper 1 is heated. This example is an example of temperature control that is set so that the second location heating surface temperature T62 converges to the second convergence temperature TC2.

[0039] As described above, it is desirable to set the second convergence temperature TC2 to be higher than the first convergence temperature TC1. In other words, it is desirable to control the temperature so that the second location P2, which is downstream, is dried at a higher temperature than the first location P1, which is upstream.

[0040] Ink is often drier downstream than upstream. Therefore, it is desirable to perform drying at a lower temperature upstream, such as at the first location P1, than downstream. For example, upstream, an image may not be sufficiently dried and may be so-called semi-dried. In this way, if a high-temperature heating surface is applied to an image that is not sufficiently dried, ink and the like are likely to adhere to the image and the image may become dirty. On the other hand, if the temperature is lowered, the amount of dirt can be reduced. Therefore, it is desirable to perform drying upstream at a relatively low temperature, such as the first convergence temperature TC1.

[0041] On the other hand, downstream such as at the second location P2, the image is often drier than upstream because the paper 1 is dried to a certain extent upstream. Therefore, it is desirable to dry the paper 1 at a higher temperature downstream than upstream. In this way, drying at a higher temperature downstream can reduce the number of cases where the image is insufficiently dried.

[0042] In order to dry the upstream and downstream at different temperatures, for example, different heaters can be used upstream and downstream. Furthermore, if different metals are used for the heating surface upstream and downstream, or if the heating surface upstream and downstream are insulated to some extent, it is possible to control the temperature to different values ​​even with one heater. As described above, as long as the configuration allows different temperatures to be set upstream and downstream, the arrangement of the heating surface and the device is not limited to the configuration shown in the figure.

[0043] In order to make the upstream and downstream temperatures different, for example, the following configuration is desirable.

[0044] 3, the heater 5 is desirably disposed eccentrically with respect to the center CR (hereinafter simply referred to as "center CR") of the drying roller 6. For example, as shown in the figure, the heater 5 is desirably disposed eccentrically so that the heater 5 is closer to the surface of the drying roller 6 than the center CR toward the downstream.

[0045] In this way, when the heater 5 is disposed eccentrically, the distance from the heater 5 to the surface of the drying roller 6 (hereinafter simply referred to as "distance") can be set to be different depending on the position on the path along which the paper 1 is transported. Specifically, the distance at the first point P1 is set to be a "first distance DS1." It is desirable that the heater 5 is disposed eccentrically so that the distance becomes a second distance DS2, a third distance DS3, and a fourth distance DS4 as it progresses downstream from the first point P1.

[0046] That is, it is desirable that the distance between the surface of the heating surface and the heater 5 is closer toward the downstream, such that "first distance DS1>second distance DS2>third distance DS3>fourth distance DS4".

[0047] The longer the distance, the harder it is for the heat source to be transmitted, so the temperature tends to drop as the distance increases. Therefore, it is desirable to adjust the distance to be closer downstream by using an eccentric arrangement or other method, so that drying can be performed at a higher temperature downstream.

[0048] Furthermore, it is preferable that the distance between the dryer and the recording medium at each position (hereinafter referred to as "dryer distance") is set to be different depending on the position. For example, at the first position P1, the dryer distance between the first dryer 41 and the recording medium is set to "first dryer distance DSM1." It is preferable that each dryer is disposed so that the dryer distance becomes a second dryer distance DSM2, a third dryer distance DSM3, and a fourth dryer distance DSM4 as it moves downstream from the first position P1.

[0049] If the dryer is far away, it is difficult for the hot air to reach the dryer, so the temperature tends to drop as the distance increases. Therefore, it is desirable to adjust the ventilation distance so that the downstream areas are closer, so that the downstream areas are dried at a higher temperature.

[0050] In addition, in order to dry at different temperatures upstream and downstream, it is not limited to making the distance or the dryer distance different between the upstream and downstream as described above. For example, it is also possible to vary the strength of the heating by the heater so that the temperature is different between the upstream and downstream.

[0051] It is also preferable to set the following temperatures:

[0052] As shown in FIG. 4 and FIG. 5, a first set temperature TX, a second set temperature TY, and a third set temperature TZ are preferably set.

[0053] The first set temperature TX is desirably the highest temperature among the temperatures at which transfer does not occur even when ink in a semi-dried state or the like comes into contact with the drying roller 6.

[0054] The second set temperature TY is desirably a temperature at which the ink can be dried, that is, the second set temperature TY is a temperature at which the ink is sufficiently solidified (a margin may be set), or the like.

[0055] The third set temperature TZ is preferably a temperature that is approximately the melting point of additives such as wax added to the ink. In other words, at a temperature below the third set temperature TZ, the ink that has completed drying does not melt even when it comes into contact with the drying roller 6, and therefore the ink is less likely to be transferred to the paper 1. On the other hand, at a temperature above the third set temperature TZ, the tack of the ink is likely to increase, and the ink becomes sticky and more likely to be transferred.

[0056] 4, for example, it is desirable to control the temperature of the first convergence temperature TC1, i.e., the heating surface, at the first location P1 to be equal to or lower than the first set temperature TX. In this way, when the temperature of the heating surface is controlled to be equal to or lower than the first set temperature TX, even if a recording medium in a semi-dried state comes into contact with the heating surface, transfer is unlikely to occur, and therefore contamination of the heating surface can be reduced.

[0057] Similarly, the first heating temperature T51 is desirably controlled so as to converge to a temperature equal to or lower than the first set temperature TX.

[0058] However, in a state where the drying roller 6 has not yet warmed up sufficiently (for example, during the first preheating period TM1 in the figure), the first heating temperature T51 may be a high temperature that exceeds the first set temperature TX, etc. In other words, even if the first heating temperature T51 rises suddenly as in the first preheating period TM1, the first heating surface temperature T61, which is the temperature of the drying roller 6, often does not experience a similar temperature rise. Therefore, until the first heating surface temperature T61 is raised to a certain temperature, the first heating temperature T51 may be a high temperature that exceeds the first set temperature TX, etc., as in the first preheating period TM1.

[0059] The first preheating period TM1 is set in advance based on the material used for the drying roller 6, the time required for the temperature to converge, temperature characteristics, etc. Therefore, the first preheating period TM1 may be set to be longer than the period shown in the figure, for example.

[0060] Moreover, it is preferable that the first heating temperature T51 does not exceed the third set temperature TZ even during the first pre-heating period TM1.

[0061] Then, in a state in which the first heating surface temperature T61 has converged, it is desirable to control the first heating temperature T51 so that it converges to the first set temperature TX or lower.

[0062] Similarly, the first back surface temperature T41 may be a high temperature exceeding the third set temperature TZ, etc., as in the second preheating period TM2, when the drying roller 6 is not yet sufficiently warmed up. On the other hand, it is preferable that the first back surface temperature T41 is temperature controlled so as to converge to a temperature exceeding the second set temperature TY when the first heating surface temperature T61 has converged.

[0063] In addition, the first set temperature TX, the second set temperature TY, and the third set temperature TZ often differ depending on the type of droplets, the amount of droplets, etc. Therefore, the appropriate temperature for each set temperature is determined in advance by experiment, etc.

[0064] Moreover, at the second location P2, it is preferable that temperature control is performed as shown in FIG. 5 based on the first set temperature TX, the second set temperature TY, and the third set temperature TZ similar to those at the first location P1.

[0065] Specifically, first, the second heating temperature T52 is desirably controlled to be equal to or higher than the first set temperature TX and not to exceed the third set temperature TZ when the second location heating surface temperature T62 has converged. Also, similar to the temperature control at the first location P1, the second heating temperature T52 may be a high temperature exceeding the second set temperature TY, such as during the third preheating period TM3, when the drying roller 6 is not yet sufficiently warmed up.

[0066] The second location heating surface temperature T62 is desirably set so that the convergence temperature is equal to or lower than the third set temperature TZ. Furthermore, the second location heating surface temperature T62 may be set so that the convergence temperature is greater than the second set temperature TY. However, when the temperature at which the second location heating surface temperature T62 converges is set to a temperature greater than the second set temperature TY, it is desirably set when it is expected that the ink at the second location P2 is in a state of drying to some extent.

[0067] The second back surface temperature T44 is preferably controlled to be equal to or higher than the second set temperature TY when the second heating surface temperature T62 has converged. When the drying roller 6 is not yet sufficiently warmed up, the second back surface temperature T44 may be high and exceed the third set temperature TZ, as in the fourth preheating period TM4.

[0068] By carrying out the above-mentioned temperature control, the heating surface is prevented from becoming dirty, and therefore the recording medium can be less likely to become dirty.

[0069] In addition, if the material constituting the drying roller 6 has a small heat capacity, the drying roller 6 tends to heat up easily. Therefore, it may be difficult to create a difference in temperature between the first position P1 and the second position P2 as shown above. Therefore, in order to create a difference in temperature at each position, a cooling mechanism for cooling the drying roller 6 may be provided between the first position P1 and the second position P2. With such a configuration having a cooling mechanism, a temperature gradient can be created between the first position P1 and the second position P2. In other words, a temperature distribution can be created in the drying roller 6.

[0070] <Third embodiment> The third embodiment differs from the second embodiment in that the amount of heat required to dry the ink and the drying capacity of the dryer are calculated and compared as follows. In the following, the same components are denoted by the same reference numerals, and duplicated explanations will be omitted.

[0071] In the following explanation, the heat quantity at the drying capacity when the heater is set to the highest temperature among the temperatures that can be set, is referred to as the "maximum heat quantity" and is expressed as "Qo" (unit system is "J" (Joules)). Note that the maximum heat quantity "Qo" is calculated in advance for each printing speed.

[0072] In the following explanation, the amount of heat used to dry the ink and make it less likely to be transferred to other objects is referred to as the "drying heat amount" and is expressed in "Qi" (units are "J" (Joules)).

[0073] Hereinafter, a case will be described as an example in which the first amount of heat is the maximum amount of heat "Qo" and the second amount of heat is the drying amount of heat "Qi".

[0074] The maximum heat quantity "Qo" is calculated, for example, according to the following formula (1). Qo = Ch × ρ × Vi × Δt (1) In the above formula (1), "Ch" is the specific heat of the ink (hereinafter, simply referred to as "specific heat" and the unit system is "J / kg·°C" (Joules / kilogram·degrees)). "ρ" is the density of the ink (hereinafter, simply referred to as "density" and the unit system is "kg / L" (kilograms / liters). "Vi" is the total amount of ink calculated from the data of the image to be formed (hereinafter, simply referred to as "ink amount" and the unit system is "L" (liters)). "Δt" is the rise in temperature caused by drying when passing through a drying location such as the first location P1 (hereinafter, simply referred to as "rise in temperature" and the unit system is "°C" (degrees). "t" is the time it takes to pass through a drying location such as the first location P1 (hereinafter, simply referred to as "passing time" and the unit system is "seconds"). Note that the recording medium is in contact with the heating surface at the drying location, and the passing time "t" corresponds to the time the recording medium is in contact with the heating surface at the drying location. The same applies below.

[0075] The rise in temperature "Δt" is calculated as the difference between the final ink temperature at the drying point and the initial ink temperature at the drying point. The transit time "t" is calculated as "X÷V÷60=t" where the printing speed is "V" (units are "mpm" (meters per minute)) and the length of the drying point is "X" (units are "m" (meters)).

[0076] Then, based on the above formula (1), the maximum heat quantity per unit time "ΔQo" (unit system is "W" (watts)) is calculated, for example, as shown in the following formula (2). ΔQo = Ch × ρ × Vi × Δt / t (2) To specify the ink amount "Vi", for example, the color gradation is set to "10%" to "100%", and the ink amount corresponding to each gradation is stored in advance in stages. In this way, the ink amount is specified, for example, on a pixel-by-pixel basis, based on the color gradation indicated by the image data.

[0077] For example, when the printing speed "V" is any of "V1," "V2," and "V3," the ink amount "Vi" and the variable element "Δt / t" for the maximum heat quantity per unit time have the following relationship:

[0078] FIG. 6 is a diagram showing an example of the relationship between the ink amount and the variable element at the maximum heat amount per unit time. In the diagram, the horizontal axis indicates the ink amount "Vi", while the vertical axis indicates the variable element "Δt / t" at the maximum heat amount per unit time. As shown in the diagram, three types of printing speed "V" are shown: "V1", "V2", and "V3".

[0079] When the printing speed "V" increases, the time that the recording medium contacts the heated surface at the drying point decreases. Therefore, when the printing speed "V" increases, the increase width "Δt" tends to decrease.

[0080] Droplets of ink or the like dry when the moisture or organic solvent contained in the droplets evaporates. Therefore, in order to dry the ink and make it difficult for the ink to be transferred to another object, at least the amount of heat required to raise the temperature to a temperature at which the moisture or organic solvent contained in the droplets evaporates and the amount of heat required to vaporize the ink are applied to the ink.

[0081] That is, the amount of drying heat per unit time "ΔQi" (unit system is "W" (watts)) is calculated, for example, as shown in the following formula (3). ΔQi = ρ × Vi × {Ck + Δt' × Ch} / t (3) In the above formula (3), "Ck" is the amount of heat required to vaporize ink per unit of material (hereinafter referred to as "heat of vaporization" in units of kJ / kg (kilojoules / kilogram)). Also, "ρ", "Vi", "Ch", and "t" are the same as in the above formula (1).

[0082] "Δt'" is the temperature difference from the initial temperature of the ink to the temperature at which the water or organic solvent contained in the ink evaporates (hereinafter referred to simply as "temperature difference" in units of "°C" (degrees)).

[0083] The above formula (3), i.e., the amount of heat for drying per unit time "ΔQi", may be converted into water as shown in the following formula (4).

[0084] Water often has a higher heat of vaporization and specific heat than other types of solvents, etc. Therefore, if the heat amount is calculated using water, it is possible to easily calculate the heat amount required to sufficiently dry the entire ink, even if multiple other types of solvents, etc. are included. ΔQi = ρ × Vi × (x / xw) ×{Ckw + Δt' × Chw} / t (4) In the above formula (3), "x" is the mass of the ink (units are "g" (grams)). Additionally, "xw" is the amount of water contained in the ink (units are "g" (grams)). Furthermore, "Ckw" is the heat of vaporization of water (units are "kJ / kg" (kilojoules / kilogram)). Furthermore, "Chw" is the specific heat of water (units are "J / kg·℃" (joules / kilogram·degrees)).

[0085] Then, based on the calculated maximum heat quantity "Qo" and the drying heat quantity "Qi", it is desirable to make a comparison and judgment, for example, as follows.

[0086] 7 is a diagram showing an example of the relationship between the maximum heat quantity and the drying heat quantity. In the diagram, the horizontal axis represents the ink amount "Vi", while the vertical axis represents the heat quantity.

[0087] The maximum heat quantity "Qo" is, for example, a value calculated by the above formula (1).

[0088] The drying heat quantity "Qi" is, for example, the value calculated by the above formula (3) multiplied by the transit time "t".

[0089] Then, based on the point where the maximum heat quantity "Qo" and the drying heat quantity "Qi" intersect (hereinafter, the intersection point "Vi" is referred to as the "threshold value Th"), the image forming apparatus determines whether or not to perform drying at different temperatures upstream and downstream. In other words, at the threshold value Th, the maximum heat quantity "Qo" and the drying heat quantity "Qi" are the same.

[0090] When the maximum heat quantity "Qo"≦the drying heat quantity "Qi" (on the right side of the threshold value Th in the figure), the image forming apparatus determines that drying will be performed at different temperatures upstream and downstream. On the other hand, when the maximum heat quantity "Qo">the drying heat quantity "Qi" (on the left side of the threshold value Th in the figure), the image forming apparatus determines that drying will not be performed at different temperatures upstream and downstream.

[0091] When drying is performed at different temperatures upstream and downstream, for example, the image forming apparatus controls the temperature so that a higher temperature is used downstream.

[0092] When the maximum heat quantity "Qo" > the drying heat quantity "Qi", i.e. when the amount of ink is small, the ink is often dried sufficiently by drying on the heating surface without having to use different temperatures upstream and downstream. Therefore, by comparing the maximum heat quantity "Qo", which is an example of the first heat quantity, with the drying heat quantity "Qi", which is an example of the second heat quantity, if the second heat quantity is equal to or greater than the first heat quantity, it is desirable to control the temperature so that drying is performed at different temperatures upstream and downstream.

[0093] In this way, the first heat amount and the second heat amount calculated based on the ink amount etc. are compared, and if drying using the heated surface is found to be sufficient based on the drying capacity, drying is performed using the heated surface rather than using different temperatures upstream and downstream. In this way, the start-up time for different temperatures upstream and downstream can be shortened.

[0094] On the other hand, if the second heat quantity is smaller than the first heat quantity, drying at only one location may not be sufficient. In such a case, the temperature is controlled so that drying is performed at different temperatures upstream and downstream.

[0095] For example, the image forming apparatus controls the temperature so that the temperature is higher toward the downstream for drying. By controlling the temperature in this manner, the heating surface is prevented from becoming dirty, and therefore the recording medium can be less likely to become dirty.

[0096] <Overall processing example> FIG. 8 is a diagram illustrating an example of the overall process.

[0097] In step S1, the image forming apparatus determines the amount of ink droplets to be used in the image based on the image. Specifically, the image forming apparatus inputs data indicating the image to be formed, and determines the amount of ink to be used in the image based on the data.

[0098] In step S2, the image forming apparatus calculates a first heat quantity.

[0099] In step S3, the image forming apparatus calculates a second amount of heat.

[0100] In step S4, the image forming apparatus judges whether the first amount of heat is equal to or greater than the second amount of heat. If the result of this comparison indicates that the first amount of heat is equal to or greater than the second amount of heat (YES in step S4), the image forming apparatus proceeds to step S5. On the other hand, if the first amount of heat is not equal to or greater than the second amount of heat (NO in step S4), the image forming apparatus proceeds to step S6.

[0101] In step S5, the image forming apparatus performs drying using different temperatures for the upstream and downstream.

[0102] In step S6, the image forming apparatus performs drying using the same temperature upstream and downstream.

[0103] As described above, the image forming apparatus compares the first amount of heat with the second amount of heat, and switches between whether or not to perform drying using different temperatures upstream and downstream.

[0104] <Third embodiment> Next, the configuration of an image forming apparatus according to a third embodiment will be described with reference to Fig. 9. Note that the same components as those described in the first and second embodiments are given the same reference numerals, and duplicated descriptions will be omitted as appropriate.

[0105] 9 is a diagram showing an example of the configuration of an image forming apparatus 100a according to the third embodiment. As shown in FIG. 9, the image forming apparatus 100a includes a front-side head 2′, a dryer 4′, a transport drum 6′, a transport roller 7′, and a turntable 50.

[0106] The front surface head 2' is an example of a first liquid application unit that applies ink to the front surface of the paper 1. The front surface head 2' applies ink to the front surface of the paper 1 by ejecting ink and causing the ejected ink to land on the surface of the paper 1. Front surface ink 3b shown in FIG. 9 represents ink applied to the front surface of the paper 1.

[0107] The transport drum 6' transports the paper 1 in the transport direction 10 by rotating with its outer circumferential surface in contact with the back surface of the paper 1. The transport roller 7' is disposed downstream of the transport drum 6' in the transport direction 10, and transports the paper 1 in the transport direction 10 by rotating with its outer circumferential surface in contact with the back surface of the paper 1.

[0108] Similar to the dryer 4, the dryer 4' includes four hot air heaters. The four hot air heaters are provided at different positions along the conveying direction 10 so as to face the paper 1 conveyed by the conveying drum 6'. A distance DS' represents the distance between the dryer 4' and the outer circumferential surface of the conveying drum 6'.

[0109] The dryer 4' heats the paper 1 by supplying hot air from four hot air heaters to the paper 1 being transported, and dries the ink applied to the surface of the paper 1. The dried ink is fixed to the surface of the paper 1. P1' indicates a location on the upstream side of the transport drum 6', and P2' indicates a location on the downstream side of the transport drum 6'.

[0110] Dryer 4' is a general term for four hot air heaters. However, the number of hot air heaters included in dryer 4' is not limited to four and may be increased or decreased. Also, it is not limited to hot air heaters, and dryer 4' may include other heating means such as IR heaters, or may include a combination of multiple types of heating means.

[0111] The turntable 50 is an example of a changing unit that changes the orientation of the paper 1 so that the back surface of the paper 1, on whose front surface the ink has been applied by the front-surface head 2', faces the head 2. The turntable 50 is provided downstream of the transport rollers 7' in the transport direction 10. The turntable 50 changes the orientation of the paper 1 so that the front and back surfaces of the paper 1 are inverted, thereby enabling the back surface of the paper 1 to face the head 2 at the position where the head 2 is provided.

[0112] After ink is applied to the front surface by the front head 2', the paper 1 is heated by a dryer 4' to dry the ink, and then the paper 1 is turned over by a turntable 50 and transported to the position of the head 2 with the back surface facing the head 2.

[0113] The head 2 is an example of a second liquid application section that applies ink to the rear surface of the transported paper 1. The head 2 applies ink to the rear surface of the paper 1 by causing the ejected ink to land on the rear surface of the paper 1. Rear surface ink 3a shown in FIG. 9 represents the ink applied to the rear surface of the paper 1.

[0114] The drying roller 6 is an example of a transport section that transports the paper 1, on whose back surface the ink has been applied by the head 2, in the transport direction 10. The drying roller 6 contacts the front surface of the paper 1 to transport the paper 1. More specifically, the drying roller 6 transports the paper 1 with its outer circumferential surface 61 in contact with the front surface of the paper 1, i.e., the surface to which the front surface ink 3b has been applied.

[0115] The drying roller 6 has a built-in heater 5. The heater 5 is an example of a heating section that heats the paper 1 transported by the drying roller 6. The heater 5 heats the paper 1 in contact with the outer circumferential surface of the drying roller 6, thereby drying the ink applied to the back surface of the paper 1. P1 indicates a first location on the upstream side of the drying roller 6, and P2 indicates a second location on the downstream side of the drying roller 6.

[0116] Each of the first dryer 41, the second dryer 42, the third dryer 43, and the fourth dryer 44 is an example of a heating unit that heats the paper 1 transported by the drying roller 6. The first dryer 41, the second dryer 42, the third dryer 43, and the fourth dryer 44 each include a hot air heater, and are provided at different positions along the transport direction 10 so as to face the paper 1 transported by the transport drum 6'. The first dryer 41, the second dryer 42, the third dryer 43, and the fourth dryer 44 supply hot air from the four hot air heaters to the transported paper 1, thereby heating the paper 1 and drying the ink applied to the back surface of the paper 1. The dried ink is fixed to the back surface of the paper 1.

[0117] The number of the first dryer 41, the second dryer 42, the third dryer 43, and the fourth dryer 44 is not limited to four and may be increased or decreased. Furthermore, the first dryer 41, the second dryer 42, the third dryer 43, and the fourth dryer 44 are not limited to those including a hot air heater and may include other heating means such as an IR heater, or may include a combination of multiple types of heating means.

[0118] In the present embodiment, the first dryer 41, the second dryer 42, the third dryer 43, and the fourth dryer 44, and the heater 5 are exemplified as the configuration of the heating section, but are not limited thereto. The heating section may be configured by either the dryers such as the first dryer 41, the second dryer 42, the third dryer 43, and the fourth dryer 44, or the heater 5.

[0119] Here, when the paper 1 is heated by the first dryer 41, the second dryer 42, the third dryer 43, and the fourth dryer 44, or the heater 5, the surface ink 3b applied to the surface of the paper 1 may be remelted by the heat. If the remelted surface ink 3b adheres to the outer peripheral surface 61 of the drying roller 6, there is a concern that the surface ink 3b adhered to the outer peripheral surface 61 of the drying roller 6 will be transferred to the surface of the paper 1 that is subsequently transported, i.e., the surface that comes into contact with the outer peripheral surface 61 of the drying roller 6, and the paper 1 will be contaminated.

[0120] In particular, on the upstream side of the paper 1 in contact with the outer peripheral surface 61 of the drying roller 6, the transport distance after drying by heating in the dryer 4' is shorter than on the downstream side, and the fixation of the surface ink 3b to the paper 1 is low, making it more likely to become contaminated by re-melting. Note that the fixation of the surface ink 3b to the paper 1 refers to the fixing strength and stability of the surface ink 3b to the paper 1.

[0121] In contrast to the above, in this embodiment, the first dryer 41, the second dryer 42, the third dryer 43, and the fourth dryer 44, as well as the heater 5, heat the paper 1 at different temperatures on the upstream and downstream sides in the transport direction of the paper 1.

[0122] For example, a first dryer distance DSM1 between the first dryer 41 arranged on the upstream side in the conveying direction 10 and the outer circumferential surface 61 of the drying roller 6 is longer than a second dryer distance DSM2 between the second dryer 42 arranged on the downstream side and the outer circumferential surface 61 of the drying roller 6. Due to the longer distance, the first dryer 41 can heat at a lower heating temperature than the second dryer 42.

[0123] Similarly, a second dryer distance DSM2 between the second dryer 42 and the outer peripheral surface 61 of the drying roller 6 is longer than a third dryer distance DSM3 between the third dryer 43 disposed downstream and the outer peripheral surface 61 of the drying roller 6. Due to the longer distance, the second dryer 42 can be heated at a lower heating temperature than the third dryer 43.

[0124] In addition, a third dryer distance DSM3 between the third dryer 43 and the outer peripheral surface 61 of the drying roller 6 is longer than a fourth dryer distance DSM4 between the fourth dryer 44 disposed downstream and the outer peripheral surface 61 of the drying roller 6. Due to the longer distance, the third dryer 43 can be heated at a lower heating temperature than the fourth dryer 44.

[0125] In addition, a first distance DS1 between the heater 5 at the position where the first dryer 41 is disposed and the outer peripheral surface 61 of the drying roller 6 is longer than a second distance DS2 between the heater 5 at the position where the second dryer 42 is disposed and the outer peripheral surface 61 of the drying roller 6. Since the distance is longer, the heater 5 can heat at a lower heating temperature at the position where the first dryer 41 is disposed compared to the position where the second dryer 42 is disposed.

[0126] Similarly, the second distance DS2 between the heater 5 at the position where the second dryer 42 is disposed and the outer circumferential surface 61 of the drying roller 6 is longer than the third distance DS3 between the heater 5 at the position where the third dryer 43 is disposed and the outer circumferential surface 61 of the drying roller 6. Since the distance is longer, the heater 5 can heat at a lower heating temperature at the position where the second dryer 42 is disposed compared to the position where the third dryer 43 is disposed.

[0127] In addition, a third distance DS3 between the heater 5 at the position where the third dryer 43 is disposed and the outer circumferential surface 61 of the drying roller 6 is longer than a fourth distance DS4 between the heater 5 at the position where the fourth dryer 44 is disposed and the outer circumferential surface 61 of the drying roller 6. Since the distance is longer, the heater 5 can heat at a lower heating temperature at the position where the third dryer 43 is disposed compared to the position where the fourth dryer 44 is disposed.

[0128] In this way, the paper 1 in contact with the outer circumferential surface 61 of the drying roller 6 can be heated at a lower heating temperature toward the upstream side, where the transport distance after drying by the dryer 4' is shorter. As a result, the risk of the front surface ink 3b remelting can be reduced, and contamination of the paper 1 can be suppressed.

[0129] On the other hand, in order to reduce the risk of the front ink 3b remelting, it is also possible to lower the heating temperatures of the first dryer 41, the second dryer 42, the third dryer 43, the fourth dryer 44, and the heater 5 overall to a degree that does not cause remelting. However, since the heating temperature is generally lowered in this method, in order to sufficiently dry the front ink 3b and the back ink 3a, it is necessary to lower the conveying speed of the paper 1 to extend the heating time, or to extend the conveying distance after drying by heating with the dryer 4'. As a result, there is a concern that the productivity, which is the efficiency with which the image forming apparatus 100a forms images, will decrease, and the image forming apparatus 100a will become larger.

[0130] In contrast, in this embodiment, the heating temperatures of the first dryer 41, the second dryer 42, the third dryer 43, and the fourth dryer 44, and the heater 5 are higher on the downstream side than on the upstream side.

[0131] In this way, the front surface ink 3b and the back surface ink 3a can be sufficiently dried without slowing down the transport speed of the paper 1 to lengthen the heating time or lengthening the transport distance after drying by heating with the dryer 4'. As a result, it is possible to suppress a decrease in productivity of the image forming apparatus 100a while suppressing contamination of the paper 1. In addition, it is possible to suppress an increase in size of the image forming apparatus 100a while suppressing contamination of the paper 1.

[0132] Furthermore, this embodiment has a turntable 50 (changing unit) that changes the orientation of the paper 1 so that the back surface of the paper 1, to which the front surface ink 3b has been applied by the front surface head 2', faces the head 2. The front surface head 2' faces the front surface of the paper 1 and applies the front surface ink 3b, and the head 2 faces the back surface of the paper 1 and applies the back surface ink 3a, and the turntable 50 is provided between the front surface head 2' and the head 2.

[0133] This configuration can reduce the time and effort required to reset the paper 1 in the image forming apparatus 100a in order to form images on both the front and back sides of the paper 1, thereby improving the productivity of the image forming apparatus 100a. Thus, contamination of the paper 1 can be suppressed while improving the productivity of the image forming apparatus 100a.

[0134] <About recording media> The type of recording medium is not limited to paper. That is, the recording medium may be made of a material other than paper. That is, the recording medium may be made of a material to which a liquid can be attached even temporarily, including, for example, paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, ceramics, etc. Therefore, the type of recording medium may be, for example, a film product, a cloth product for clothing, wallpaper, or a building material such as flooring, or a material used in leather products, etc.

[0135] Furthermore, the recording medium is not limited to cut paper, but may be roll paper or the like.

[0136] <Other embodiments> The nozzle head and the head driving device may be integrated into one device.

[0137] Each device does not have to be a single device. That is, each device may be a combination of multiple devices. Note that the configuration may further include devices other than those shown in the drawings.

[0138] All or part of each process according to the present invention may be implemented by a program written in a computer language for causing a computer to execute the control method. That is, the program is a computer program for causing a computer, such as a droplet ejection device, an image forming device, a droplet ejection system, or an image forming system, to execute each process.

[0139] Therefore, when the control method is executed based on the program, the arithmetic unit and the control unit of the computer perform arithmetic and control based on the program to execute each process, and the storage device of the computer stores data used in the process based on the program to execute each process.

[0140] The program may be distributed in a form recorded on a computer-readable recording medium. The recording medium may be a magnetic tape, a flash memory, an optical disk, a magneto-optical disk, a magnetic disk, or the like. The program may be distributed through a telecommunications line.

[0141] The embodiment of the present invention may be realized by a droplet ejection system or an image forming system having a plurality of information processing devices. The droplet ejection system or the image forming system may execute each process and data storage in a redundant, distributed, parallel, virtualized, or combination of these.

[0142] Although one example of the embodiment has been described above, the present invention is not limited to the above embodiment, and various modifications and improvements are possible within the scope of the present invention. [Explanation of symbols]

[0143] 1 Paper 2 Head (an example of a second liquid application unit) 2' Front surface head (an example of a first liquid application unit) 3a Backside ink 3b Surface Ink 4, 4' dryer 5 Heater (an example of a heating unit) 6 Drying roller (an example of a conveying section) 6' Transport drum 7 Transport roller 8. Lola 9 Through holes 41 First dryer (an example of a heating section) 42 Second dryer (an example of a heating section) 43 Third dryer (an example of a heating section) 44 Fourth dryer (an example of a heating section) 50 Turntable (Example of changeable part) 100, 100a Image forming apparatus CR-centered DS1 1st Distance DS2 Second distance DS3 3rd distance DS4 4th distance DSM1 1st dryer distance DSM2 2nd dryer distance DSM3 3rd dryer distance DSM4 4th dryer distance P1 1st Place P2 2nd Place T41 1st backside temperature T44 2nd backside temperature T51 1st heating temperature T52 2nd heating temperature T61 First heating surface temperature T62 Second heating surface temperature TC1 First convergence temperature TC2 Second convergence temperature Th Threshold TM1 First preheating period TM2 Second preheating period TM3 Third pre-heating period TM4 4th preheating period TX 1st set temperature TY 2nd set temperature TZ 3rd set temperature [Prior art documents] [Patent documents]

[0144] [Patent Document 1] JP 2009-241309 A

Claims

1. a first liquid application unit that applies liquid to a first surface of a recording medium; a second liquid application unit that applies liquid to a second surface of the recording medium on which liquid has been applied by the first liquid application unit; a conveying section including a conveying roller, which conveys in a conveying direction the recording medium on which the liquid has been applied by the second liquid application section; a heating unit that heats the recording medium transported by the transport unit, The heating unit includes: a first heating section disposed inside the transport roller and configured to heat the recording medium from the inside while the recording medium is transported in contact with an outer circumferential surface of the transport roller; a plurality of second heating sections each arranged to face the outer circumferential surface of the transport roller along a transport direction of the recording medium by the transport roller and configured to heat the recording medium from the outside as the recording medium is transported in contact with the outer circumferential surface of the transport roller; the transport unit contacts the first surface of the recording medium and transports the recording medium; the heating unit heats the recording medium at different temperatures on the upstream side and the downstream side in a transport direction of the recording medium, In the image forming apparatus, a plurality of recesses are provided on the outer circumferential surface of the transport roller.

2. The image forming apparatus according to claim 1 , wherein a heating temperature by the heating section is higher on the downstream side than on the upstream side.

3. a change unit that changes the orientation of the recording medium so that the second surface of the recording medium, on which liquid has been applied by the first liquid application unit, faces the second liquid application unit; the first liquid application unit applies the liquid to the first surface of the recording medium, the second liquid application unit applies the liquid to the second surface of the recording medium in a direction opposite to the second surface of the recording medium; The image forming apparatus according to claim 1 , wherein the change unit is provided between the first liquid deposition unit and the second liquid deposition unit.

Images