Image forming apparatus

The image forming apparatus comprises: an ink ejection device which ejects a droplet of ink toward a recording medium, the ink including a solvent and a coloring material dissolved or dispersed in the solvent; a treatment liquid deposition device which deposits a treatment liquid on the recording medium, the treatment liquid separating the coloring material from the solvent on the recording medium; a solvent absorbing device which absorbs the solvent on the recording medium; a solvent evaporating device which causes the solvent on the recording medium to evaporate; and a solvent removal selection device which selects one removal way of a first removal way where the solvent on the recording medium is removed by absorbing the solvent using the solvent absorbing device and then causing the solvent to evaporate using the solvent evaporating device, and a second removal way where the solvent on the recording medium is removed by causing the solvent to evaporate using the solvent evaporating device without using the solvent absorbing device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus which forms images on a recording medium by ejecting droplets of ink onto the recording medium.

2. Description of the Related Art

The inkjet type image forming apparatus forms images on a recording medium by ejecting droplets of ink from nozzles toward the recording medium, such as a sheet of paper, while relatively moving the recording medium and an ink droplet ejection head having an arrangement of a plurality of nozzles (apertures).

In recent years, improvements in image quality have been sought in image forming apparatuses by increasing the density of the nozzles of the apparatuses. Generally, the ink used in the image forming apparatus of this kind contains a large volume of liquid solvent, such as water, organic solvent, or the like.

If the recording medium is a permeable medium in which the ink permeates the interior of the medium, then unless the solvent component in the ink deposited on the recording medium is not sufficiently removed, so-called “bleeding” can arise as the ink permeates the recording medium. The bleeding includes problems such as that the dot size becomes larger than the prescribed diameter, the boundary regions of the dots become blurred, the spreading of the dots becomes uneven, or the outline of each dot does not become smooth.

If the recording medium is a non-permeable medium in which the ink becomes fixed principally on the surface of the medium, then unless the solvent component in the ink deposited on the recording medium is not sufficiently removed, it is not possible to stably fix the coloring material component in the ink on the surface of the recording medium.

Therefore, various types of image forming apparatuses have been proposed which seek to remove liquid solvent from the ink deposited onto the recording medium.

Japanese Patent Application Publication No. 10-86353 (seeFIG. 9in particular) discloses an image forming apparatus in which a heating device or halogen heater for heating the recording medium is disposed below a platen which opposes an ink droplet ejection head, in such a manner that the recording medium can be heated by means of the single halogen heater, before the image recording, during the image recording, and after the image recording.

Japanese Patent Application Publication No. 2001-179959 (see, in particular, FIG. 1 and paragraphs 0012 and 0013) discloses an image forming apparatus having a roller disposed after an ink droplet ejection head in the conveyance direction of the recording medium. The roller is constituted by a solvent absorbing medium that absorbs liquid solvent in the ink deposited on the recording medium, and a separating member having separating properties that any of the coloring material in the ink hardly adheres to the separating member.

However, if the solvent component on the recording medium is to be removed by heating the recording medium, then even supposing that the recording medium is heated before, during, and after the image recording, a long amount of time is still required from the deposition of the ink on the recording medium until complete drying of the recording medium, and the amount of power consumption required for heating of this kind is constantly high.

On the other hand, if it is sought to absorb the solvent component on the recording medium by means of a roller, then the roller inevitably makes contact with the coloring material and the like. Hence, a surplus external pressure is applied to the coloring material component that is to be fixed onto the recording medium, thereby causing disturbance of the image on the recording medium.

In the method described in Japanese Patent Application Publication No. 2001-179959, especially if the recording medium is a non-permeable medium, the coloring material is repelled by the separating member of the roller in a state where the coloring material is not yet fixed on the recording medium, and hence the image is disturbed. If the separation properties of the separating member in the roller are incomplete, or if a roller having an external surface made of a solvent absorbing member without a separating member of this kind is used, then the coloring material may adhere to the roller when it is sought to sufficiently remove the solvent component, and the image is ultimately disturbed.

SUMMARY OF THE INVENTION

The present invention has been contrived in view of the foregoing circumstances, an object thereof being to provide an image forming apparatus that is capable of preventing or reducing the deterioration of image quality, in such a manner that an excessive external force is not applied to coloring material component of ink deposited on a recording medium while removing the solvent component of the ink.

In order to attain the aforementioned object, the present invention is directed to an image forming apparatus, comprising: an ink ejection device which ejects a droplet of ink toward a recording medium, the ink including a solvent and a coloring material dissolved or dispersed in the solvent; a treatment liquid deposition device which deposits a treatment liquid on the recording medium, the treatment liquid separating the coloring material from the solvent on the recording medium; a solvent absorbing device which absorbs the solvent on the recording medium; a solvent evaporating device which causes the solvent on the recording medium to evaporate; and a solvent removal selection device which selects one removal way of a first removal way where the solvent on the recording medium is removed by absorbing the solvent using the solvent absorbing device and then causing the solvent to evaporate using the solvent evaporating device, and a second removal way where the solvent on the recording medium is removed by causing the solvent to evaporate using the solvent evaporating device without using the solvent absorbing device.

Here, the types of ink include a dye-based ink in which a coloring material is dissolved in liquid solvent in a molecular state (or an ion state), a pigment-based ink in which a coloring material is dispersed in liquid solvent in a state of very fine lumps, and the like.

Furthermore, the treatment liquid can be, specifically, a liquid that acts so that the coloring material contained in the ink gets out of the state of dissolution or dispersion in the liquid solvent and changes to a state of separation from the solvent. Examples of the treatment liquid include: a treatment liquid which separates the coloring material in the ink from the solvent by causing the coloring material to separate or aggregate by reaction between the treatment liquid and the coloring material; a treatment liquid having an effect of promoting the separation between the coloring material and the solvent, without reacting directly with the coloring material; a treatment liquid which separates the coloring material in the ink from the solvent by generating a semi-solid substance (e.g., gel) containing the coloring material; and the like.

Preferably, the treatment liquid deposition device deposits the treatment liquid on the recording medium by ejecting a droplet of the treatment liquid toward the recording medium.

Alternatively, it is also preferable that the treatment liquid deposition device deposits the treatment liquid on the recording medium by applying the treatment liquid to the recording medium.

By adopting these compositions, it is possible to swiftly perform initial solvent removal by means of the solvent absorbing device and then to perform final solvent removal without contacting the recording medium by means of the solvent evaporating device. It is also possible to perform the solvent removal by means of evaporation by the solvent evaporating device only, without performing the absorption by the solvent absorption device. Therefore, excessive external force is not applied to the coloring material component of the ink deposited on the recording medium, and it is possible to reduce or prevent deterioration of the image quality.

Preferably, the image forming apparatus further comprises: a calculation device which calculates at least one of volume of the ink to be deposited on the recording medium and volume of the treatment liquid to be deposited on the recording medium, according to data of an image to be formed on the recording medium, wherein the solvent removal selection device selects the one removal way according to the at least one of the volume of the ink and the volume of the treatment liquid calculated by the calculation device.

By means of this composition, in image forming conditions where a variety of image data are inputted, then if the liquid volume is high in accordance with the data of the image that is actually to be formed, it is possible to swiftly perform the initial solvent removal by means of the solvent absorbing device, and to then perform the final solvent removal without contacting the recording medium by means of the solvent evaporating device. In contrast, if the liquid volume is small, then it is possible to change the solvent removal method so that only the solvent removal by means of evaporation by the solvent evaporating device is performed and the absorption by the solvent absorption device is not performed. Consequently, it is possible to prevent excessive external pressure from being applied to the coloring material component of the ink that is deposited on the recording medium in accordance with the various image data, and hence deterioration of the image quality can be reduced or prevented.

Preferably, the solvent removal selection device selects the one removal way according to permeation speed of the ink into the recording medium.

By means of this composition, depending on the permeation speed of the ink, it is possible to switch between performing initial solvent removal swiftly to a level where the coloring material component is unaffected by means of the solvent absorbing device followed by the final solvent removal without contacting the recording medium by means of the solvent evaporating device, and performing the solvent removal by means of only the evaporation by the solvent evaporating device without performing the absorption by the solvent absorption device. Consequently, it is possible to prevent excessive external pressure from being applied to the coloring material component of the ink deposited on the recording medium in accordance with the various image data, and hence deterioration of the image quality can be reduced or prevented.

Preferably, the image forming apparatus further comprises: a medium information input device to which identification information on the recording medium is inputted; and a storage device which stores relation information for each type of recording medium, the relation information indicating relation between the identification information on the recording medium and information indicating degree of permeation of the ink into the recording medium, wherein the solvent removal selection device selects the one removal way according to the identification information inputted to the medium information input device and the relation information stored in the storage device.

By means of this composition, in image forming conditions where a plurality of types of recording media are handled, depending on the recording medium on which the image is actually to be formed, it is possible to switch between performing the initial solvent removal swiftly to a level where the coloring material component is unaffected by means of the solvent absorbing device followed by the final solvent removal without contacting the recording medium by means of the solvent evaporating device, and performing the solvent removal by means of only the evaporation by the solvent evaporating device without performing absorption by the solvent absorption device. Consequently, it is possible to prevent excessive external pressure from being applied to the coloring material component of the ink deposited on the recording medium in accordance with various types of recording media, and hence deterioration of the image quality can be reduced or prevented.

Preferably, the solvent absorbing device is a roller which has an outer circumferential surface made of a material absorbing liquid and is rotatably disposed on a conveyance path along which the recording medium is conveyed; and the solvent removal selection device controls contact and separation between the outer circumferential surface of the roller and the recording medium conveyed along the conveyance path.

By means of this composition, it is possible to perform the initial solvent removal swiftly by the rotation of the roller, in cases where the solvent absorption is required. Furthermore, it is possible to achieve a composition in which the apparatus can be switched between performing and not performing the solvent absorption, by means of a simple mechanism that relatively moves the recording medium conveyed along the conveyance path and the outer circumferential surface of the roller towards each other, or away from each other.

According to the present invention, it is possible to perform final solvent removal by solvent evaporation without making contact with a recording medium, after swiftly performing initial solvent removal by solvent absorption, only in cases where it is necessary. Therefore, application of excessive external pressure to a coloring material component of ink deposited on the recording medium can be prevented, and deterioration in image quality can be reliably reduced or prevented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

General Composition of Image Forming Apparatus

FIG. 1is a block diagram showing the general composition of the image forming apparatus according to an embodiment of the present invention.

InFIG. 1, the image forming apparatus10comprises: an ink droplet ejection head12; a treatment liquid droplet ejection head (treatment liquid deposition device)16; a solvent absorbing unit18; a solvent evaporating unit19; a conveyance unit26; a main control unit110; an image data input unit111; a memory112; a recording medium ID input unit113; an ink ID input unit114; a permeation determination unit115; a deposition amount calculation unit116; a conveyance control unit126; an ink droplet ejection control unit120; a treatment liquid droplet ejection control unit160; and a solvent removal selection unit210.

The ink droplet ejection head12ejects droplets of ink toward the recording medium, such as a sheet of paper.

As the ink, there are a dye-based ink in which a coloring material is dissolved in liquid solvent in a molecular state (or an ion state), a pigment-based ink in which a coloring material is dispersed in liquid solvent in a state of very fine lumps, and the like. In other words, the coloring materials contained in the ink may be materials which are dissolved in liquid solvent in the molecular state (or in an ion state), or materials which are dispersed in liquid solvent in the state of very fine lumps.

The treatment liquid droplet ejection head16ejects droplets of treatment liquid toward the recording medium.

The treatment liquid acts so that the coloring material contained in the ink gets out of the state of dissolution or dispersion in the liquid solvent and changes to a state of separation from the solvent. Examples of the treatment liquid include: a treatment liquid which separates the coloring material in the ink from the solvent by causing the coloring material to separate or aggregate by reaction between the treatment liquid and the coloring material; a treatment liquid having an effect of promoting the separation between the coloring material and the solvent, without reacting directly with the coloring material; a treatment liquid which separates the coloring material in the ink from the solvent by generating a semi-solid substance (e.g., gel) containing the coloring material; and the like. Hereinafter, the term “insolubilize” designates the action by which the coloring material in the ink is made to leave the state of dissolution or dispersal in the liquid solvent, by means of the above-described direct or indirect action of the treatment liquid to the coloring material in the ink.

The conveyance unit26conveys the recording medium along a prescribed conveyance path. In the present embodiment, the conveyance unit26includes a conveyance belt on which the recording medium is mounted by attraction, and a motor (conveyance belt drive motor) which drives the conveyance belt.

The main control unit110manages the units of the image forming apparatus10in accordance with a prescribed program.

The image data input unit111is inputted with image data from a host computer300. In the present embodiment, more specifically, the image data is received from the host computer300by means of a wired communication interface, such as a universal serial bus (USB), IEEE 1394, or an Ethernet, or by means of a wireless communication interface. In the present embodiment, the image data input mode is not limited to the case where the image data is inputted by means of communications with the host computer300. For example, it is also possible to input the image data by reading in the image data from a removable media, such as a memory card or optical disk.

The memory112stores a program for image formation processing, various information required in order to execute this program, image data inputted from the host computer300, and the like.

In the present embodiment, the memory112stores reference information for determining the degree of permeation of the ink into the recording medium (determination reference information). There are various types of the determination reference information, and those various types of determination reference information are described later.

The recording medium ID input unit113is inputted with a recording medium ID (recording medium identification information), which identifies the type of the recording medium. In the present embodiment, more specifically, the recording medium ID is read in from a recording medium accommodating unit (not shown) accommodating a recording medium. The recording medium accommodating unit can be attached to and detached from the image forming apparatus10. For example, there are an input mode in which the recording medium ID recorded in a barcode is read in, an input mode in which the recording medium ID is read in by radio communications from an IC tag (also called an “RFID”: radio frequency identification), and the like. It is also possible to read in the recording medium ID from the recording medium itself. Moreover, it is possible to input information by communications with the host computer300. Furthermore, it is also possible to input information by the user operation.

The ink ID input unit114is inputted with an ink ID (ink identification information), which identifies the type of the ink. In the present embodiment, more specifically, the ink ID is read in from an ink cartridge (not shown) accommodating the ink. The ink cartridge can be attached to and detached from the image forming apparatus10. For example, there is an input mode in which the ink ID recorded in a barcode is read in, an input mode in which the ink ID is read in by radio communications from an IC tag, and the like. Moreover, it is possible to input information by communications with the host computer300. Furthermore, it is also possible to input information by the user operation.

The permeation determination unit115determines the degree of permeation of the ink into the recording medium. There are various types of determination modes described later.

The deposition amount calculation unit116calculates the amount of ink to be deposited on the recording medium by the ink droplet ejection head12, and the amount of treatment liquid to be deposited on the recording medium by the treatment liquid droplet ejection head16, according to the image data inputted to the image data input unit111. If the image data inputted to the image data input unit111is edited in the image forming apparatus10, then the deposition amount is calculated according to the edited image data (i.e., the image data relating to the image formation).

The conveyance control unit126controls the conveyance unit26. More specifically, the conveyance control unit126controls the attraction of the recording medium by the conveyance belt forming the conveyance unit26, the driving the conveyance belt, and the like. Moreover, the conveyance control unit126changes contact duration per unit area between the recording medium and the solvent absorbing unit18, by changing the conveyance speed of the recording medium.

The ink droplet ejection control unit120controls the droplet ejection of the ink to the recording medium by the ink droplet ejection head12, according to the image data relating to image formation.

The treatment liquid droplet ejection control unit160controls the droplet ejection of the treatment liquid to the recording medium by the treatment liquid droplet ejection head16, according to the image data relating to image formation.

The solvent absorbing unit18directly absorbs the liquid on the recording medium on which the treatment liquid and ink have been deposited. The liquid removed from the recording medium by the absorption is chiefly the solvent that has been separated from the coloring material in the ink on the recording medium by the action of the treatment liquid. If the treatment liquid is remaining on the recording medium, then the treatment liquid on the recording medium is also absorbed.

The solvent evaporating unit19causes the liquid on the recording medium to evaporate, without making contact with the recording medium. The liquid removed from the recording medium by the evaporation is chiefly the solvent that has been separated from the coloring material in the ink on the recording medium by the action of the treatment liquid. If the treatment liquid is remaining on the recording medium, then the treatment liquid on the recording medium is also caused to evaporate.

The solvent removal selection unit210selects whether to remove the solvent on the recording medium by causing the solvent to be absorbed by the solvent absorbing unit18and to then evaporate by the solvent evaporating unit19, or by causing the solvent to evaporate using the solvent evaporating unit19without using the solvent absorbing unit18.

For example, if the amount of the solvent evaporated by the solvent evaporating unit19is half of the maximum droplet deposition amount Dmax, that is to say Dmax/2, and the droplet deposition amount is equal to this maximum droplet deposition amount Dmax, then the removal of one half (Dmax/2) of the solvent is swiftly achieved by means of the absorption of the solvent by the solvent absorbing unit18, and the removal of the remaining half (Dmax/2) of the solvent is achieved by evaporation of the solvent by the solvent evaporating unit19without making contact with the recording medium.

Moreover, the solvent removal selection unit210is capable of changing the interval (clearance) between the recording medium and the solvent absorbing unit18. Furthermore, the solvent removal selection unit210also has a function for controlling the contact pressure of the solvent absorbing unit18with respect to the recording medium.

In the present embodiment, a microprocessor functions as the whole or part of the main control unit110, the permeation determination unit115, the deposition amount calculation unit116, the ink droplet ejection control unit120, the conveyance control unit126, and the treatment liquid droplet ejection control unit160.

FIG. 2is a schematic drawing showing an example of the mechanical structure of the principal parts of the image forming apparatus10according to the present embodiment.

InFIG. 2, the recording medium20is attracted by a conveyance belt43, which forms a portion of the conveyance unit26inFIG. 1, and is conveyed in the direction of the arrow A inFIG. 2(the conveyance direction). In the conveyance path along which the recording medium20is conveyed while being attracted to the conveyance belt43, the treatment liquid droplet ejection head16is disposed on the upstream side with respect to the ink droplet ejection head12(i.e., before the ink droplet ejection head12). On the other hand, the solvent absorbing unit18or a porous roller is disposed on the downstream side with respect to the ink droplet ejection head12(i.e., after the ink droplet ejection head12). Moreover, the solvent evaporating unit19or a halogen heater is disposed on the downstream side with respect to the porous roller18(i.e., after the porous roller18).

Although not shown inFIG. 2, the ink droplet ejection head12includes a plurality of heads of colors, such as black (K), cyan (C), magenta (M), yellow (Y), and the like.

The porous roller18is a rotatable body, having a structure in which a layer of a porous member72absorbing liquid is formed on the outer circumference of a metal member70forming the inner portion of the rotatable body.

The porous roller18is designed in such a manner that the outer circumferential surface thereof (the surface of the porous member71) can be moved away from or moved toward the conveyance surface of the conveyance belt43, by raising or lowering the porous roller18in the direction of the arrow B inFIG. 2(separating/approaching direction).

The porous roller18absorbs liquid on the recording medium20while rotating in the direction of the arrow C inFIG. 2(the direction of rotation) in a state that the porous roller18is disposed near the conveyance belt43. In this case, the porous roller18makes contact with at least the solvent on the recording medium20and absorbs that solvent.

It is possible that the solvent on the recording medium20is absorbed through the porous roller18making no actual contact with the recording medium20, while a slight gap is formed between the recording medium20and the bottommost part of the porous roller18by accurately controlling the movement of the porous roller18toward and away from the conveyance belt43.

Below, in order to simplify the description, the term “making contact with” the recording medium20designates the state where the porous roller18makes contact with the solvent deposited on the recording medium20even if the porous roller18does not make actual contact with the recording medium20itself, in addition to the state where the porous roller18makes actual contact with the recording paper20itself.

In the present embodiment, the solvent absorbing device is not limited in particular to the porous roller, but an absorbing member made of a material capable of swiftly removing the liquid on the recording medium, without applying significant pressure to the coloring material on the recording medium, is used as the solvent absorbing device.

Furthermore, in the present embodiment, the mode of evaporating the solvent is not limited in particular to the mode in which the solvent is evaporated by heating with the halogen heater19, and it is possible to use any device that evaporates the solvent without making contact with the recording medium. For example, it is possible to cause the liquid on the recording medium20to evaporate by applying an air flow to the image-forming-surface of the recording medium20.

Structure of Droplet Ejection Head

Next, an example of the structure of the ink droplet ejection head12and the treatment liquid droplet ejection head16is described with reference toFIGS. 3 and 4.

Below, a case where the ink droplet ejection head12and the treatment liquid droplet ejection head16have a common structure is described, as an example. The ink droplet ejection head12and the treatment liquid droplet ejection head16are denoted here with reference numeral50, which represents both of the droplet ejection heads12and16.

FIG. 3is a plan view perspective diagram showing an example of the structure of the droplet ejection head50, andFIG. 4is a cross-sectional view along line4-4inFIG. 3.

In order to increase the density of the dots formed by ejecting the droplets of ink onto the recording medium20, it is necessary to form the nozzles to a high density in the droplet ejection head50.

As shown inFIG. 3, the droplet ejection head50according to the present embodiment has a structure in which a plurality of liquid droplet ejection elements53are disposed two-dimensionally in the form of a staggered matrix. The effective nozzle interval (the projected nozzle pitch) as projected in the lengthwise direction of the droplet ejection head50(the direction substantially perpendicular to the conveyance direction of the recording medium) is thereby reduced (high nozzle density is achieved). Each liquid droplet ejection elements53includes a nozzle51forming a liquid droplet ejection port, a pressure chamber52corresponding to the nozzle51, a supply port54, and the like.

As shown inFIG. 4, each pressure chamber52is connected to a common flow passage55via the supply port54. The common flow passage55is connected to a tank (not shown) which forms a supply source of the ink (or treatment liquid), and the ink (or treatment liquid) supplied from this tank is distributed to the respective pressure chambers52via the common flow passage55inFIG. 4. An actuator58provided with an individual electrode57is joined to a pressure plate (common electrode)56which forms the upper face of the pressure chamber52. The actuator58, which includes a piezoelectric element for example, is deformed when a drive voltage is applied to the individual electrode57and the common electrode56to change the volume of the pressure chamber52, and the ink (or treatment liquid) is caused to be ejected from the nozzle51by the pressure change in accordance therewith. After the ejection, new ink (or new treatment liquid) is supplied to the pressure chamber52from the common flow channel55via the supply port54.

Although the case where structure of the treatment liquid droplet ejection head16is the same as the structure of the ink droplet ejection head12is described above, the present invention is not particularly limited to the case where the treatment liquid droplet ejection head16has the same structure as the ink droplet ejection head12. The treatment liquid droplet ejection head16may have different structures from that of the ink droplet ejection head12.

Structure of Solvent Absorbing Unit

Next, structural examples of the solvent absorbing unit having the porous roller18, and the parts associated with the solvent absorbing unit, are described below with reference toFIGS. 5 and 6.

FIG. 5is an oblique diagram showing the porous roller18in a state where it has been selected that the absorption of the liquid solvent on the recording medium20is to be performed.FIG. 6is an oblique diagram showing the porous roller18in a state where it has been selected that the absorption of the liquid solvent on the recording medium20is not to be performed.

The porous roller18is supported by elevating devices214through an axis183, in such a manner that the axial direction thereof is perpendicular to the conveyance direction of the recording medium20. Each of the elevating devices214includes a rack211, a pinion212, and a rotational motor213. The elevating devices214convert the rotational actions of the pinions212, which are driven by the motors213, into the linear movements of the racks211, thereby causing the outer circumferential surface of the porous roller18, which is made of a porous member, to separate from or make contact with the recording medium20on the conveyance belt43. The elevating devices214including the racks211, the pinions212and the motors213compose a part of the solvent removal selection unit210shown inFIG. 1.

Moreover, roller supporting sections185to rotatably support the porous roller18have bearing sections184, which rotatably support the rotating axis183of the porous roller18. When the porous roller18is lowered by the elevating device214to the contact position, where the porous roller18makes contact with the recording medium20, then the porous roller18is stably supported by the roller supporting sections185because the bottom faces of the roller supporting sections185make contact with the upper faces of seats186.

More specifically, as shown inFIG. 5, when the pinions212are rotated in the direction of the arrows Pd inFIG. 5by the drive of the motors213, then these rotational movements are converted into linear movements, the racks211move linearly in the direction of the arrows Rd (downward direction) inFIG. 5, the porous roller18moves in the direction of the arrow Bd inFIG. 5(downward direction) by means of the rotating axis183, and the bottommost part of the outer circumferential surface of the porous roller18moves toward the recording medium20. The porous roller18moves in the direction of the arrow Bd inFIG. 5, until the bottom faces of the roller supporting sections185abut against the upper faces of the seats186, and the roller supporting sections185rotatably support the porous roller18through the bearing sections184and the rotating axis183. The porous roller18rotates in the direction of the arrow C inFIG. 5while absorbing the solvent on the recording medium20, which is attracted on the conveyance belt43and conveyed in the direction of the arrow A inFIG. 5. The recording medium20where the solvent has been absorbed to a certain degree by the porous roller18is conveyed to a position for performing solvent evaporation, while the recording medium20is still attracted to the conveyance belt43.

On the other hand, as shown inFIG. 6, when the pinions212are rotated in the direction of the arrows Pu inFIG. 6by the drive of the motors214, then these rotational movements are converted into linear movements, the racks211move linearly in the direction of the arrows Ru (upward direction) inFIG. 6, the porous roller18moves in the direction of the arrow Bu inFIG. 6(upward direction) by means of the rotating axis183, and the bottommost part of the outer circumferential surface of the porous roller18moves away from the recording medium20. In other words, the porous roller18is set in a non-absorbing position where it does not absorb the solvent on the recording medium20. Furthermore, when the porous roller18moves in the direction of the arrow Bu inFIG. 6, the contact between the bottom faces of the roller supporting sections185and the upper faces of the seats186is released. Since the external circumferential surface of the porous roller18is separated from the recording medium20conveyed on the conveyance belt43in the direction of the arrow A inFIG. 6, then the recording medium20is conveyed to a position for performing the solvent evaporation while the recording medium20is still attracted on the conveyance belt43, without performing the solvent absorption by the porous roller18.

The motors213are driven under the control of the main control unit110shown inFIG. 1. The porous roller18is in contact with or separated from the recording medium20attracted on the conveyance belt43in accordance with the driving of the motors213. If the solvent absorption is to be performed by the porous roller18, then as shown inFIG. 5, the porous roller18is set in the state in which the outer circumferential surface of the porous roller18is placed in contact with the recording medium20. On the other hand, if the solvent absorption is not to be performed by the porous roller18, then as shown inFIG. 6, the porous roller18is set in the state where the outer circumferential surface thereof is separated from the recording medium20.

By controlling the driving of the motors213, it is possible to change the clearance between the porous roller18and the recording medium20, and it is also possible to cause the porous roller18to press against the recording medium20, thereby changing the contact pressure therebetween.

Structure of Solvent Evaporating Unit

Next, a structural example of the solvent evaporating unit including the halogen heater19is described below with reference toFIG. 7.

FIG. 7is an oblique perspective diagram showing the halogen heater19in a state where the liquid solvent on the recording medium20is being evaporated. InFIG. 7, the halogen heater19includes a plurality of halogen lamps191(191a,191b,191c,191dand191e), which generate heat, and a reflection plate192, which reflects the heat generated by the halogen lamps191toward the recording medium20. Each halogen lamp191is longer in the lengthwise direction than the width of the recording medium20(the length of the recording medium in the main scanning direction), and is disposed in such a manner that its lengthwise direction is substantially perpendicular to the conveyance direction of the recording medium20(sub-scanning direction). The recording medium20is conveyed by the conveyance belt43in a state where the recording medium20opposes the plurality of halogen lamps191and the reflection plate192, while the recording medium20is heated uniformly and efficiently by the plurality of halogen lamps191with the reflection plate192. In this way, the liquid on the recording medium20is evaporated evenly and sufficiently.

Concrete Example of Insolubilization

Concrete examples of insolubilization are described below with reference toFIGS. 8A through 10.

FIGS. 8A to 8Fare schematic drawings showing one example of a mode where the treatment liquid and the ink are deposited on the recording medium20, and the coloring material of the ink does not permeate the interior of the recording medium20.

Firstly, as shown inFIG. 8A, when an observation point201on the recording medium20reaches a position in the conveyance path at which a droplet of the treatment liquid is to be deposited (treatment liquid droplet deposition position), then a droplet90of the treatment liquid is ejected and deposited onto the recording medium20, and the treatment liquid droplet90is deposited on the observation point201of the recording medium20as shown inFIG. 8B.

Next, as shown inFIG. 8C, when the observation point201on the recording medium20arrives at a position on the conveyance path where a droplet of the ink is to be deposited (ink droplet deposition position), then a droplet92of the ink is ejected toward the recording medium20. Since the droplet90of the treatment liquid has already been deposited on the observation point201of the recording medium20, the ink droplet92newly deposited onto the recording medium20and the treatment liquid droplet90react with each other. Then, as shown inFIG. 8D, the coloring material97and the solvent99in the ink separate almost completely into two parts.

If the porous roller18is set in the absorbing position as shown inFIG. 5, then a portion of the solvent99on the recording medium20is absorbed by the outer circumferential surface of the porous roller18as shown inFIG. 8E.

Furthermore, when the recording medium20is conveyed while facing the halogen heater19as shown inFIG. 7, then the solvent99on the recording medium20is heated and evaporated by the halogen heater19as shown inFIG. 8F. The coloring material97thereby becomes fixed onto the surface of the recording medium20.

On the other hand, if the porous roller18is set in the non-absorbing position as shown inFIG. 6, then the solvent absorption is not performed by the porous roller18, and only the solvent evaporation by the halogen heater19is performed.

FIGS. 9A to 9Fare schematic drawings showing a further example of a mode where the treatment liquid and the ink are deposited on the recording medium20, and the coloring material of the ink permeates the interior of the recording medium20.

Firstly, as shown inFIG. 9A, a droplet90of the treatment liquid is ejected toward the observation point201of the recording medium20, and as shown inFIG. 9B, the treatment liquid droplet90is deposited on the observation point201of the recording medium20. Then, as shown inFIG. 9C, a droplet92of the ink is ejected toward the observation point201of the recording medium20, and the treatment liquid droplet90and the ink droplet92react with each other on the recording medium20, causing the coloring material97and the solvent99in the ink to separate into two parts as shown inFIG. 9D. Simultaneously with the start of the separation, the coloring material97starts to permeate the recording medium20.

If the porous roller18is set in the absorbing position as shown inFIG. 5, then a portion of the solvent99on the recording medium20is absorbed by the outer circumferential surface of the porous roller18as shown inFIG. 9E. After that, the solvent99on the recording medium20is heated and evaporated by the halogen heater19, as shown inFIG. 9F. The coloring material97thereby becomes fixed on the surface and in the interior of the recording medium20.

On the other hand, if the porous roller18is set in the non-absorbing position as shown inFIG. 6, then the solvent absorption is not performed by the porous roller18, and only the solvent evaporation by the halogen heater19is performed.

Next, a detailed example of a case where the coloring material in the ink is insolubilized by a two liquid (anionic/cationic) reaction between the ink and the treatment liquid is described below with reference toFIG. 10.

In the example shown inFIG. 10, a mixture droplet94A composed of the treatment liquid droplet90and the ink droplet92deposited on the recording medium20changes to a mixture droplet94B containing coloring material aggregate96which is charged negatively, due to the two-liquid reaction. Thereupon, the coloring material aggregate96in the mixture droplet94B settles down, and the mixture droplet94B changes to a mixture droplet94C in which a coloring material layer97formed by the coloring material aggregate96is separated from a solvent layer99formed by the solvent98.

On the other hand, the conveyance belt43is charged to the opposite polarity to the coloring material aggregate96(in other words, the conveyance belt43is positively charged) by a voltage applying device100through a drive roller41on which the conveyance belt43is wound (seeFIGS. 14 to 16). By charging the conveyance belt43to the opposite polarity to the coloring material aggregate96, an electrostatic attraction acts in such a manner that the coloring material aggregate96is drawn toward the conveyance belt43, and therefore, the downward settling of the coloring material aggregate96can be accelerated and the coloring material96and the solvent98can be reliably separated.

It is also possible to control the electrical properties of a metal member70K of the porous roller to control the solvent absorption by a porous member72K. Thus, the mixture droplet94C changes to a mixture droplet94D from which the solvent is absorbed by porous member72K as shown inFIG. 10.

Determination of Requirement for Solvent Absorption

Examples of the determination of whether the solvent absorption on the recording medium20is to be performed or not are described below.

A first mode of the determination of the requirement of the solvent absorption is described below, principally with reference toFIG. 11. A first determination reference information table1121shown inFIG. 11includes a recording medium ID1130identifying the type of recording medium, and permeation speed information1151indicating whether recording medium is permeable or non-permeable, for each type of recording medium. The first determination reference information table1121is previously stored in the memory112. Here, “permeable” and “non-permeable” are classified as follows. Namely, any recording medium where the permeation speed of a prescribed ink per prescribed surface area of the recording medium is equal to or lower than a prescribed threshold value, is classified as “non-permeable”. On the other hand, any recording medium having a permeation speed exceeding this threshold value is classified as “permeable”. In other words, any recording medium in which the permeation duration of the prescribed ink per the prescribed surface area of the recording medium is greater than a prescribed threshold value, is designated as a “non-permeable” medium, and any recording medium having a permeation duration equal to or less than this threshold value is designated as a “permeable” medium. For example, when a droplet of 2 pl of aqueous solution having the surface tension of 30 mN/m and the viscosity of 3 cP is deposited on a recording medium, the recording medium that has the permeation duration of more than 100 ms, is classified as a “non-permeable” medium, and the recording medium that has the permeation duration of100ms or less is classified as a “permeable” medium.

In the first determination reference information table1121, the recording medium ID1130(“P001”, “C001”, and the like) and the permeation speed information1151(“non-permeable” or “permeable”) are previously recorded for each of a plurality of recording media. For example, special inkjet papers (printing papers), special OHP sheets for copying machines, and the like, are classified as the non-permeable media, whereas special copying machine paper (copy paper), special inkjet OHP sheets, and the like, are classified as the permeable media. The permeation speed information1151corresponding to the recording medium ID inputted to the recording medium ID input unit113is read out from the memory112. For example, in the case of a “non-permeable” recording medium, the total droplet deposition volume of the treatment liquid and the ink is compared with a prescribed threshold value (e.g., 1.5 ml for a surface area equivalent to A4 paper size). If the total droplet deposition volume exceeds the threshold value, then it is determined that the solvent absorption is to be performed. If the total droplet deposition volume is equal to or less than the threshold value, then it is determined that the solvent absorption is not to be performed. On the other hand, in the case of a “permeable” recording medium, it is determined that the solvent absorption is not to be performed, regardless of the total droplet deposition volume.

The determination between the permeable and non-permeable media may be made before the start of print (image formation). For example, it is possible to make the determination when the type of recording medium on which printing is to be performed is inputted.

A second mode of the determination of the requirement of the solvent absorption is described below, principally with reference toFIG. 12. A second determination reference information table1122shown inFIG. 12includes a recording medium ID1130identifying the type of recording medium, an ink ID1140identifying the type of ink, and a permeation duration1152, for each combination of the recording medium ID1130and the ink ID1140. The second determination reference information table1122is previously stored in the memory112. The permeation duration1152is the permeation duration when a prescribed quantity of ink is deposited onto the recording medium (this permeation duration corresponds to the reciprocal of the permeation speed). The recording medium ID1130, ink ID1140, and permeation duration1152are previously registered in the second determination reference information table1122, with respect to each of-the combinations of the recording media and the inks. The permeation duration1152corresponding to the combination of the recording medium and the ink indicated by the recording medium ID inputted to the recording medium ID input unit113and the ink ID inputted to the ink ID input unit114is read out from the memory112. For example, if the read permeation duration exceeds a prescribed threshold value, then the medium is determined to be “non-permeable”, and it is then determined whether the solvent absorption is required or not by determining the total amount of the treatment liquid and the ink deposited on the recording medium. On the other hand, if the read permeation duration is equal to or less than the prescribed threshold value, then the medium is determined to be “permeable”, and it is determined that the solvent absorption is not to be performed.

The mode of determining the requirement for the solvent absorption is not limited to these modes. For example, it is also possible to previously store the surface tension and the viscosity in the memory112with respect to each type of various inks, as well as to previously store a determination reference value for the surface tension and a determination reference value for the viscosity in order to determine “permeable” or “non-permeable” for each type of recording media. Before actually forming an image, the surface tension and the viscosity of the ink corresponding to the ink ID inputted to the ink ID input unit114are read out from the memory112, and the surface tension determination reference value and the viscosity determination reference value corresponding to the recording medium ID inputted to the recording medium ID input unit113are read out from the memory112. The surface tension and the viscosity of the ink that is actually to be used are compared with the determination reference values for the recording medium that is actually to be used, and it is determined whether the solvent absorption is required or not.

In image forming conditions where the combination of the recording medium and the ink is fixed, it is possible to determine the requirement for the solvent absorption according to only the total amount of the treatment liquid and the ink deposited on the recording medium.

For example, at least one of the amount of the ink deposited per unit surface area of the recording medium by the ink droplet ejection head12, and the amount of the treatment liquid deposited per unit surface area of the recording medium by the treatment liquid droplet ejection head16, is calculated according to the image data relating to the image formation. If the calculated amount exceeds a prescribed threshold value, then it is determined that the solvent absorption is to be carried out. If the calculated amount is equal to or less than the threshold value, then it is determined that the solvent absorption is not to be carried out.

Whole Sequence of Image Forming Process

FIG. 13is a flowchart showing the sequence of one example of an image forming process in the inkjet recording apparatus10according to the present embodiment. The respective steps of this image forming process are executed under the management of the main control unit110, in accordance with a prescribed program.

The ink ID is previously read in by the ink ID input unit114(S2), and the recording medium ID is previously read in by the recording medium ID input unit113(S4).

When image data is inputted from the host computer300to the image forming apparatus10(S6), then the deposition volume of the ink to be deposited on the recording medium by the ejection of ink droplets, and the deposition volume of the treatment liquid to be deposited on the recording medium by the ejection of treatment liquid droplets are calculated on the basis of this image data (S8).

The coloring material in the ink is actually to be fixed to the recording medium20, and it is hence possible to calculate only the amount of the solvent in the ink, rather than calculating the ink deposition volume for the whole of the ink,.

Although the aforementioned description relates to an example where both the ink deposition volume and the treatment liquid deposition volume are calculated, there are, in fact, also cases where only the ink deposition volume or only the treatment liquid deposition value is calculated. For example, if the amount of the treatment liquid remaining on the recording medium after the insolubilization of the ink is so small as to be negligible with respect to the volume of the ink solvent, then it is possible to calculate the ink deposition volume (or solvent volume) only. Furthermore, if the amount of the ink solvent is negligible with respect to the amount of the treatment liquid remaining on the recording medium after the insolubilization of the ink, then it is also possible to calculate only the deposition volume of the treatment liquid.

Next, the recording medium20is relatively moved with respect to the treatment liquid droplet ejection head16while droplets of the treatment liquid are ejected toward the recording medium20by the treatment liquid droplet ejection head16(S10), and the recording medium20is relatively moved with respect to the ink droplet ejection head12while droplets of the ink are ejected toward the recording medium20by the ink droplet ejection head12(S12).

A determination is made regarding whether the liquid (mainly, ink solvent) deposited on the recording medium20is absorbed by means of the porous roller18or not (the determination of the requirement of the solvent absorption) (S14).

More specifically, firstly, it is determined whether the permeation speed of the ink into the recording medium is greater than a prescribed threshold value (permeation speed threshold value) or not (S141). In other words, it is determined whether the recording medium is a non-permeable medium (namely, a medium having the permeation speed equal to or lower than the prescribed threshold value) or a permeable medium (namely, a medium having the permeation speed that is greater than the prescribed threshold value). Secondly, it is determined whether the total amount of the droplet deposition of the ink and the treatment liquid onto the recording medium is greater than a prescribed threshold value (droplet deposition threshold value) or not (S142).

Although the above description relates to a case where both the droplet deposition volume of the ink and the droplet deposition volume of the treatment liquid are taken for consideration for performing the above-mentioned determination, there are also cases where either one of the ink droplet deposition volume and the treatment liquid droplet deposition volume is taken for consideration for performing the determination.

If, as a result of the determination of the requirement of the solvent absorption (S14), it is determined that the recording medium is the non-permeable medium (the medium having the permeation speed equal to or lower than the threshold value), and that the droplet deposition volume is greater than the prescribed threshold value, then the porous roller18used for the solvent absorption is lowered and set in the absorbing position as shown inFIG. 5in such a manner that the liquid (mainly, the ink solvent) on the recording medium is absorbed by the porous roller18(S16). On the other hand, if the recording medium is the permeable medium (the medium having the permeation speed greater than the threshold value), or if the recording medium is a non-permeable medium but the droplet deposition volume is equal to or less than the prescribed threshold value, then the porous roller18for the solvent absorption is raised and set in the non-absorbing position as shown inFIG. 6in such a manner that the solvent absorption is not performed by the porous roller18(S18).

Next, as shown inFIG. 7, the liquid (mainly, the ink solvent) on the recording medium20is caused to evaporate by heating the recording medium20by means of the halogen heater19(S20).

It is determined whether image formation has been completed or a further image formation operation is to be performed (S22). If a further image formation operation is to be performed, then it is determined whether the same image is to be formed again or not (S24).

If it is determined in the step S24that the same image is to be formed again, then the input of image data (S6) and the calculation of the deposition volume (S8) are not necessary, and the steps of the droplet ejection of the treatment liquid (S10), the droplet ejection of the ink (S12), and the determination of the requirement of the solvent absorption (S14) are carried out. If it is determined that the solvent absorption is required, then the solvent absorption by the porous roller18(S16) and the solvent evaporation by the halogen heater19(S22) are carried out. On the other hand, if it is determined that the solvent absorption is not required, then the solvent absorption by the porous roller18is not carried out (S18), and only the solvent evaporation by the halogen heater19is performed (S22).

If it is determined in the step S24that a different image is to be formed, then input of new image data (S6) and calculation of the droplet deposition volume based on this new image data (S8) are carried out, whereupon the steps of the droplet ejection of the treatment liquid (S10), the droplet ejection of the ink (S12), and the determination of the requirement of the solvent absorption (S14) are performed. If it is determined that the solvent absorption is required, then the solvent absorption by the porous roller18(S16) and the solvent evaporation by the halogen heater19(S22) are carried out. On the other hand, if it is determined that the solvent absorption is not required, then the solvent absorption by the porous roller18is not carried out (S18), and only the solvent evaporation by the halogen heater19is performed (S22).

The example inFIG. 13shows a case where the solvent removal selection device controls only whether the porous roller18is used or not by moving the porous roller18toward or away from the recording medium20. However, it is also possible to adjust the clearance between the porous roller18and the recording medium20when the porous roller18is to be used. More specifically, in the step of lowering the position of the porous roller18(S16), the vertical position of the porous roller18is adjusted by the elevating devices214in such a manner that the clearance between the outer circumferential surface of the porous roller18and the recording medium20is adjusted on the basis of at least one of the permeation speed of the ink into the recording medium20, and the droplet deposition volume of the ink. Moreover, it is also possible to press the porous roller18against the recording medium20(and it is further possible to control the pressure of the porous roller18against the recording medium20), according to requirements.

Although the conveyance speed of the recording medium is not changed in the example shown inFIG. 13, it is also possible to change the conveyance speed of the recording medium20by the conveyance belt43in such a manner that the contact duration per unit surface area between the recording medium20and the outer circumferential surface of the porous roller18is adjusted on the basis of the degree of permeation of the ink into the recording medium20and the ink droplet deposition volume on the recording medium20.

Although the case where the solvent is absorbed by the single porous roller18is described above, it is also possible to select the porous roller18that is to be used for the solvent absorption, from among a plurality of types of the porous rollers18having different pore diameters and/or materials of the porous members.

Other Embodiments

In order to facilitate understanding of the embodiment of the present invention, the image forming apparatus is described above with reference to the case where droplets of one color of ink (for example, black ink) are ejected toward the recording medium20. However, in order to form a color image on the recording medium20, it is necessary to eject droplets of a plurality of colors of the ink toward the recording medium20.

FIG. 14shows the principal parts of the image forming apparatus10which is capable of ejecting droplets of the inks of four colors, yellow (Y), cyan (C), magenta (M) and black (K) toward the recording medium20, and is composed in such a manner that droplets of the treatment liquid are ejected for each of the inks of the colors Y, C, M, and K.

InFIG. 14, treatment liquid droplet ejection heads16K,16M,16C and16Y are disposed respectively before ink droplet ejection heads12K,12M,12C and12Y InFIG. 14, porous rollers18K,18M,18C, and18Y are disposed respectively after the ink droplet ejection heads12K,12M,12C, and12Y. The recording medium on the conveyance belt43driven by the drive rollers41and42is successively conveyed to a droplet deposition position of the first treatment liquid droplet ejection head16K, a droplet deposition position of the first ink droplet ejection head12K, an absorption position of the first porous roller18K, a droplet deposition position of the second treatment liquid droplet ejection head16M, a droplet deposition position of the second ink droplet ejection head12M, an absorption position of the second porous roller18M, a droplet deposition position of the third treatment liquid16C, a droplet deposition position of the third ink droplet ejection head12C, an absorption position of the third porous roller18C, a droplet deposition position of the fourth treatment liquid droplet ejection head16Y, a droplet deposition position of the fourth ink droplet ejection head12Y, an absorption position of the fourth porous roller18Y, and an evaporation position of the halogen heater19.

FIG. 15shows the principal parts of the image forming apparatus10which is capable of ejecting droplets of the inks of four colors, Y, C, M and K, toward the recording medium20, and is composed in such a manner that droplets of the treatment liquid are ejected toward the recording medium20in one operation before ejecting droplets of the inks of the colors Y, C, M and K.

InFIG. 15, a single treatment liquid droplet ejection head16is disposed before the ink droplet ejection head12K for black (K) ink in terms of the conveyance direction of the recording medium20(on the right-hand side inFIG. 15). Furthermore, a single porous roller18is disposed after the ink droplet ejection head12Y for yellow (Y) ink in terms of the conveyance direction of the recording medium20(the left-hand side inFIG. 15). The recording medium on the conveyance belt43driven by the drive rollers41and42is successively conveyed to a droplet deposition position of the treatment liquid droplet ejection head16, a droplet deposition position of the first ink droplet ejection head12K, a droplet deposition position of the second ink droplet ejection head12M, a droplet deposition position of the third ink droplet ejection head12C, a droplet deposition position of the fourth ink droplet ejection head12Y, an absorption position of the porous roller18, and an evaporation position of the halogen heater19.

FIG. 16shows the principal parts for image formation by the image forming apparatus10which is capable of ejecting droplets of the inks of four colors, Y, C, M and K toward the recording medium20, and applies the treatment liquid to the recording medium20before ejecting droplets of the inks of the colors Y, C, M and K.

InFIG. 16, a single treatment liquid application roller16′ is disposed before the ink droplet ejection head12K for black (K) ink in terms of the conveyance direction of the recording medium20(on the right-hand side inFIG. 16). Furthermore, a single porous roller18is disposed after the ink droplet ejection head12Y for yellow (Y) ink in terms of the conveyance direction of the recording medium20(the left-hand side inFIG. 16). The recording medium on the conveyance belt43driven by the drive rollers41and42is successively conveyed to an application position of the treatment liquid application roller16′, a droplet deposition position of the first ink droplet ejection head12K, a droplet deposition position of the second ink droplet ejection head12M, a droplet deposition position of the third ink droplet ejection head12C, a droplet deposition position of the fourth ink droplet ejection head12Y, an absorption position of the porous roller18, and an evaporation position of the halogen heater19.

In the embodiment shown inFIG. 16, the amount of the treatment liquid applied to the recording medium20by the treatment liquid application roller16′ corresponds to the deposition amount of the treatment liquid on the recording medium20.

In the embodiments shown inFIGS. 14 and 15, by controlling the treatment liquid deposition volume according to the ink droplet deposition pattern, it is possible to reduce the consumption of the treatment liquid. On the other hand, in the embodiment shown inFIG. 16, it is possible to apply to the recording medium, the treatment liquid having a high viscosity that is difficult to eject in the form of droplets from the treatment liquid droplet ejection head.

As described above, the initial solvent removal is swiftly performed by the porous roller18according to the permeation speed of the recording medium and/or the droplet deposition volume, whereupon the final solvent removal is performed without making contact with the recording medium, by the halogen heater19, and furthermore, it is also possible to perform the solvent removal by means of the evaporation by the halogen heater19alone, without performing solvent absorption by the porous roller18. Therefore, the solvent can be swiftly removed from the recording medium to a degree where there is little or no effect on the coloring material component of the ink adhering to the recording medium.

For example, if both the solvent absorption and the solvent evaporation are performed, then approximately one half of the maximum deposition amount Dmax of the liquid droplets is removed by the solvent evaporation, and the solvent absorption is performed before this solvent evaporation according to requirements.

The maximum deposition amount Dmax is the maximum value of the deposition amount of the ink and the treatment liquid when the ink droplets are ejected toward a region of a prescribed surface area. In general, the maximum deposition amount Dmax is equal to the deposition amount in a case where an intermediate color of two colors from among C, M, and Y is to be formed on the whole surface of the region of a prescribed surface area. For example, if the ink droplets are to be ejected onto the whole surface of an area equivalent to A4 size (210 mm×297 mm), the amount of the treatment liquid is 1.0 ml and the total amount of the two color inks is 2.0 ml (1 ml of each color), then the total deposition volume is 3.0 ml. In the case of light colors or a single color, the droplet deposition volume is smaller than in the case of two colors. If three colors are to be mutually superimposed, then black ink is actually used, and hence the total deposition volume generally becomes less than 3.0 ml.

Therefore, the solvent evaporating unit19used in the present embodiment has a capacity to evaporate 1.5 ml of the liquid, which is one half of the 3.0 ml of the maximum deposition volume in a region equivalent to A4. Since the heat of vaporization of water is approximately 2.3 J/ml, then the heat quantity required to evaporate the 1.5 ml of the liquid is around 3.5 J, and it is preferable that a heat source having the heating capacity exceeding this is used.

In this case, if the recording medium is a non-permeable medium and the droplet deposition volume exceeds 1.5 ml in an area equivalent to A4 size, then the solvent removal selection unit210selects performing the solvent removal by both the solvent absorbing unit18and the solvent evaporating unit19. On the other hand, if the recording medium is a non-permeable medium and the droplet deposition volume is 1.5 ml or less, then the solvent removal selection unit210selects performing the solvent removal by means of the solvent evaporating unit19only, without using the solvent absorbing unit18. Furthermore, if the recording medium is permeable, then the solvent removal selection unit210implements solvent removal by means of the solvent evaporating unit19only, regardless of the droplet deposition volume.

In the above-described embodiments, it is possible to use, as the treatment liquid, an aqueous solution, for example, containing at least the following substances:

Sharol DC-902P, manufactured by Dai-Ichi1 to 20 wt %; andKogyo Seiyaku Co., Ltd.:Olfine E1010, manufactured by Nissin0.1 to 10 wt %.Chemical Industry Co., Ltd.(as a surface-active agent):
The following substances can be added to this aqueous solution:

On the other hand, it is possible to use, as an ink containing a coloring material, an aqueous solution, for example, containing at least the following substances:

an anionic dye compound having the structure1 to 30 wt %; andshown in FIG. 17A, 17B or 17C, for example:Olfine E1010, manufactured by Nissin Chemical0.1 to 10 wt %.Industry Co., Ltd. (as a surface-active agent):
The following substances can be added to this aqueous solution: