JP2008200855A - Inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet printer which can prevent nozzles from clogging. <P>SOLUTION: A heating unit 4 is arranged on the downstream side in a conveyance direction of an image receiving film by a conveying belt 1 from an inkjet head 3, and heating and evaporating the moisture included in an ink image formed on an image receptor by the inkjet head 3. Curling generated when a plain paper is printed by the inkjet printer can be suppressed accordingly. Also, a part to which the nozzles of the inkjet head 3 are opposed can be prevented from being heated, so that clogging of the nozzles can be prevented from occurring. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an ink jet printer that performs printing by ejecting ink droplets to form an ink image on an intermediate transfer member and then transferring the ink image formed on the intermediate transfer member to a printing medium.

2. Description of the Related Art Conventionally, in an ink jet printer that performs printing by ejecting ink droplets from a nozzle of an ink jet head onto a print medium, for example, when plain paper having no ink receiving layer is used as the print medium, cellulose constituting the print medium There is a possibility that the printing medium curls immediately after printing because the fiber absorbs moisture contained in the ink and swells (discharge curl).
Further, when the moisture contained in the ink evaporates from the state where the cellulose fibers of the printing medium are swollen, there is a possibility that the paper curls in the opposite direction (permanent curl).

Therefore, in order to solve such problems, for example, ink droplets are ejected from the nozzles of an inkjet head to form an ink image on the intermediate transfer member, and at the same time, ink droplets are ejected from the back side of the intermediate transfer member. By heating the portion facing the nozzles to evaporate the water contained in the ink image, and then transferring the ink image in which the water is evaporated to a print medium,
There is one that suppresses the penetration of water into the print medium (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2002-240412

However, in the above conventional ink jet printer, the nozzle of the ink jet head faces the heated intermediate transfer member, so that the ink in the nozzle thickens and dries, and the nozzle is clogged. Ink may not be ejected normally.
The present invention has been made in view of the above-described conventional inkjet printer, and an object thereof is to provide an inkjet printer capable of preventing nozzle clogging.

In order to solve the above problems, the ink jet printer of the present invention discharges ink droplets to form an ink image on an intermediate transfer member, and then transfers the ink image formed on the intermediate transfer member to a printing medium for printing. An ink jet printer that performs transport of the intermediate transfer member, an ink jet head that forms ink images by ejecting ink droplets from nozzles onto the intermediate transfer member transported by the transport belt, and the ink jet A heating unit that is disposed downstream of the head in the transport direction of the intermediate transfer member by the transport belt and that heats and evaporates moisture contained in the ink image formed on the intermediate transfer member by the inkjet head; and Image transfer means for transferring the ink image whose moisture has been evaporated by the heating means to the print medium. The features.

The ink jet head is disposed above the transport belt and forms an ink image on an intermediate transfer member transported by the transport belt by ejecting ink droplets vertically downward from the nozzle. The ink droplets are disposed so as to contact the back surface of the belt on the downstream side in the transport direction of the intermediate transfer body from the ink droplet ejection position by the inkjet head, and are included in the ink image by heating the contact portion of the belt. You may make it evaporate by heating a water | moisture content.
With such a configuration, it is not necessary to heat the portion of the inkjet head facing the nozzle, and it is possible to prevent thickening and drying of the ink in the nozzle and to prevent clogging of the nozzle.

Furthermore, a fixing unit that fixes the ink image transferred to the print medium by the image transfer unit to the print medium may be provided.
Further, a cooling unit that cools the conveyance belt after the transfer operation by the image transfer unit may be provided.
The image forming device may further include a cleaning unit that cleans the conveying belt with a cleaner liquid after the transfer operation by the image transfer unit, and the cooling unit cools the cleaner liquid.
According to such a configuration, the conveyance belt heated by the heating unit can be radiated more reliably, and the temperature of the intermediate transfer member can be kept constant.

In addition, the inkjet heads are a plurality of inkjet heads that are shifted in the conveyance direction of the intermediate transfer member by the conveyance belt, and a plurality of the heating means are provided corresponding to each of the inkjet heads. There may be.
According to such a configuration, when ink is ejected from the ink jet head, the ejected ink is increased before ink is ejected from another ink jet head downstream in the transport direction of the intermediate transfer member by the transport belt. It is possible to form a more appropriate ink image by suppressing the color mixing of the ink.

Further, the plurality of heating means may be configured to perform heating with a larger amount of heat as it is arranged on the downstream side in the transport direction of the intermediate transfer member by the transport belt.
According to such a configuration, it is possible to prevent the ink ejected from the inkjet head on the upstream side in the transport direction of the intermediate transfer member by the transport belt from being repeatedly heated to increase the viscosity of the ink. The difference in viscosity can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<First Embodiment>
<Configuration>
FIG. 1 is a configuration diagram showing a schematic configuration of an inkjet printer for single-sided printing according to the present embodiment. As shown in FIG. 1, the ink jet printer includes a transport belt 1, an image receiving liquid coating unit 2, a plurality of ink jet heads 3, a heating unit 4, a paper feeding unit 5, a transfer roller 6, a paper discharge unit 7, and a cleaner 8. Consists of including.

The conveying belt 1 is wound around a driving roller 9, a driven roller 10, and a tension roller 11, and is rotated by a conveying belt motor (not shown) built in the driving roller 9 to form an image receiving film formed on the conveying belt 1. (Described later) Image receiving liquid coating unit 2 → inkjet head 3
→ heating unit 4 → paper feed unit 5 → transfer roller 6 → paper discharge unit 7 → cleaner 8 in this order,
That is, it is conveyed from the right side to the left side (in the direction of the arrow in the figure).

The image receiving liquid application unit 2 is disposed below the conveyor belt 1 and includes an image receiving liquid container 12, a first application roller 13, and a second application roller 14.
The image receiving liquid container 12 stores the image receiving liquid to be applied to the conveying belt 1, and a good thin film (image receiving film) is formed on the conveying belt 1 by the image receiving liquid so that the stored image receiving liquid is appropriately applied. The temperature of the image receiving liquid is adjusted by the temperature sensor 15 and the heating element 16 so as to be formed.

The image receiving liquid is preferably one that can curl due to paper fibers by absorbing ink moisture. For example, (A) gelatin: 15 parts, preservative: 0.1 part, pure water:
(B) urethane latex: 10 parts, polydiallyldimethylammonium chloride cationic resin: 3 parts, preservative: 0.1 part, pure water: remaining part, (C) polyvinyl Alcohol: 10 parts, Jeritin: 3 parts, Preservative: 0.1 part, Pure water: Remaining part, (D) Polyvinyl alcohol: 10 parts, Polyvinylpyrrolidone: 3 parts, Preservative: 0.1 parts Pure water: What is comprised with the remainder is mentioned.

The first application roller 13 is disposed with its longitudinal direction oriented in the horizontal direction, and the lower part is immersed in the image receiving liquid in the image receiving liquid container 12 so that the image receiving liquid adheres to the outer periphery, and the image receiving liquid attached to the outer periphery The upper part is in contact with the second application roller 14 so as to adhere to the second application roller 14.
The second application roller 14 is arranged in parallel with the first application roller 13, and the lower part is first so that the image receiving liquid adhering to the outer periphery of the first application roller 13 adheres to the outer periphery of the second application roller 14.
The upper part is in contact with the conveying belt 1 so that the image receiving liquid adhering to the outer periphery is thinly and uniformly applied to the conveying belt 1 (so that an image receiving film is formed).

That is, the image receiving liquid stored in the image receiving liquid container 12 is secondly applied by the first application roller 13.
After adhering to the application roller 14, the amount of the image receiving liquid adhering to the second application roller 14 is reduced by applying the adhering image receiving liquid to the conveying belt 1, and the image receiving liquid adhering to the second application roller 14. The image receiving liquid thus thinned is applied to the conveyor belt 1 by the second application roller 14, and the thickness of the image receiving liquid applied to the conveyor belt 1 is further reduced to a thin layer state (image receiving film).

In the present embodiment, the example in which the second application roller 14, that is, one application roller is interposed in the transfer of the image receiving liquid between the first application roller 13 and the conveyor belt 1 is shown. The higher the viscosity, the more application rollers may be interposed.
The inkjet head 3 is disposed above the conveyance belt 1 while being shifted in the conveyance direction of the image receiving film for each color of yellow (Y), magenta (M), cyan (C), and black (K), and is conveyed by the conveyance belt 1. By ejecting a required amount of ink droplets (water-based ink using water as a solvent) vertically downward from a plurality of nozzles formed in a direction intersecting the conveyance direction of the image receiving film at a required portion of the image receiving film, Fine ink dots (ink images) are formed on the image receiving film.

The heating unit 4 is disposed downstream of the inkjet head 3 in the conveyance direction of the image receiving film by the conveyance belt 1 and includes a temperature sensor 17 and a heating element 18.
The temperature sensor 17 is disposed at the end of the driven roller 10 so as not to affect the transfer operation of the ink image formed on the conveyor belt 1, detects the temperature of the driven roller 10, and outputs a signal indicating the detection result. Output to the heating element 18.

The heating element 18 is incorporated in the driven roller 10 so that the temperature of the driven roller 10 becomes constant based on a signal output from the temperature sensor 17, that is, moisture contained in the ink image formed on the image receiving film ( The driven roller 10 is heated to a temperature at which the evaporation of the solvent is promoted (a temperature determined by the properties and viscosity of the image receiving liquid, for example, about 40 to 80 ° C.).
That is, the driven roller 10 incorporating the heat generating unit 4 is located on the back side of the conveying belt 1 on the downstream side in the conveying direction of the image receiving film from the ink droplet ejection position by the inkjet head 3, that is,
It arrange | positions so that the surface opposite to the surface in which an image receiving film is formed may be arrange | positioned, and the water | moisture content contained in an ink image is heated and evaporated by heating the contact part of the conveyance belt 1. FIG.

The paper feeding unit 5 accommodates a plurality of printing media 19 and controls the pickup roller 20 and the paper feed roller in synchronization with the position of the ink image formed on the image receiving film conveyed by the conveying belt 1. The printing medium 19 is fed one by one between 1 and the transfer roller 6.
The transfer roller 6 is an ink image (an ink image in which moisture is evaporated by the heating unit 4).
The printing medium 19 fed from the conveyance belt 1 and the paper feeding unit 5 that conveys the image receiving film on which is formed is pressed between the driven roller 10 and the ink image is transferred to the printing medium 19.

The paper discharge unit 7 acquires and stores the print medium onto which the ink image has been transferred by the transfer roller 6.
The cleaner 8 is disposed below the conveyor belt 1 and includes a cleaner liquid container 21 and a cleaner roller 22.
The cleaner liquid container 21 contains cleaner liquid for cleaning ink, image receiving liquid and the like slightly remaining on the conveyor belt 1.
The cleaner roller 22 is arranged with its longitudinal direction oriented in the horizontal direction, and the lower part is immersed in the cleaner liquid of the cleaner liquid container 21 so that the cleaner liquid adheres to the outer periphery. The upper part is in contact with the conveyor belt 1 so as to scrape off liquid or the like.

<Operation>
Next, the operation of the ink jet printer of the present embodiment will be described based on a specific situation.
First, it is assumed that there is a print command from an external device (not shown) to the inkjet printer. Then, the image receiving film 2 forms an image receiving film on the rotationally driven conveyance belt 1 by the image receiving liquid coating unit 2, an ink image is formed on the image receiving film by the inkjet head 3, and an ink image formed on the image receiving film by the heating unit 4. The water contained in is evaporated.
Next, the printing medium 19 is provided between the conveyance belt 1 and the transfer roller 6 by the paper feeding unit 5.
Is fed by a transfer roller 6, and a printing medium 19 fed from a feeding unit 5 that feeds an image receiving film on which an ink image is formed and a driven roller 10. The ink image is transferred to the print medium 19 and printing is performed.

Finally, the print medium onto which the ink image has been transferred by the transfer roller 6 is acquired and stored by the paper discharge unit 7, and the ink, image receiving liquid, etc. remaining on the conveyor belt 1 are scraped off by the cleaner 8. Thus, the conveyor belt 1 is cleaned.
1 constitutes the conveyor belt described in the claims, and similarly, the image receiving film constitutes the intermediate transfer member, and the inkjet head 3 in FIG. 1 constitutes the inkjet head. One heating unit 4 constitutes a heating means, and the transfer roller in FIG. 1 constitutes an image transfer means.

<Action and effect>
(1) Thus, in the ink jet printer of this embodiment, the heating unit 4 is disposed downstream of the ink jet head 3 in the transport direction of the image receiving film by the transport belt 1, and the ink jet head 3 serves as an image receiver. Since water contained in the formed ink image is heated and evaporated, curling that occurs when plain paper is printed by an ink jet printer can be suppressed, and the nozzle head of the ink jet head 3 is opposed to the portion. Is not heated, and clogging of the nozzle can be prevented.
Incidentally, in the method of drying the entire print medium 19 after printing, a large amount of energy is required for drying the print medium 19, and the energy required for drying increases as the printing speed is increased. The printer becomes larger.

Specifically, when solid printing is performed on the A4 size printing medium 19 and printing is performed with 0.67 (g) ink, if the moisture content in the ink is 75%, the printing medium 19 has a thickness of 0.00. 67 × 07
5 = about 0.5 (g) of water will be included. In order to heat and evaporate all of this water, if the latent heat of vaporization 2404 (J / g) at 40 ° C. is used, the required energy E is 1
202J (E = 2404 × 0.5 = 1202J).
Based on this energy E, the energy per unit time is calculated for each recording speed (ppm) of the print medium 19 as shown in Table 1 below.

(2) Further, an ink jet head 3 is disposed above the transport belt 1, and an ink image is formed on an image receiving film transported by the transport belt 1 by ejecting ink droplets vertically downward from the nozzles. The heating unit 4 is disposed so as to be in contact with the back surface of the transport belt 1 on the downstream side in the transport direction of the image receiving film with respect to the ink droplet ejection position, and the contact portion of the transport belt 1 is heated to remove moisture contained in the ink image. It was heated to evaporate. Therefore, the portion of the inkjet head 3 facing the nozzle does not need to be heated more reliably, and nozzle clogging can be easily prevented.

Second Embodiment
Next, 2nd Embodiment of this invention is described based on drawing.
As shown in FIG. 2, the second embodiment is different from the first embodiment in that a cooler 23 for cooling the conveying belt 1 after the transfer operation by the transfer roller 6 is provided.
The cooler 23 cools the temperature of the cleaner liquid in the cleaner liquid container 21 to a room temperature or lower so that the temperature of the conveyor belt 1 decreases when the conveyor belt 1 is cleaned by the cleaner 8.
Examples of the cooler 23 include an electronic cooler using the Peltier effect, an air cooler that performs air cooling by passing a cleaner liquid through a heat exchanger (radiator), a water-cooled heat exchanger, and a heat pump.
As described above, the cooler 23 of FIG. 2 constitutes the cooling means described in the claims.

<Action and effect>
As described above, in the ink jet printer according to the present embodiment, the cooler 23 that cools the transport belt 1 after the transfer operation by the transfer roller 6 is provided. Therefore, the transport belt 1 heated by the heating unit 4 can be radiated more reliably. The temperature (viscosity) of the image receiving liquid can be kept constant, and the phenomenon that the ink jet head 3 dries due to the heat history in which heat remains on the conveyor belt 1 during continuous printing or the like can be suppressed. In addition, the environment under the ink jet head 3 can be made in a good state, and nozzle clogging can be prevented.
In this embodiment, the conveyor belt 1 is cooled by cooling the cleaner liquid by the cooler 23.
Although an example of indirectly lowering the temperature is shown, it is not limited to this. For example, the conveyor belt 1 may be directly cooled by the cooler 23.

<Third Embodiment>
Next, 3rd Embodiment of this invention is described based on drawing.
As shown in FIG. 3, the third embodiment is different from the first embodiment in that a fixing device 24 for fixing the ink image transferred to the print medium 19 to the print medium 19 is provided.
The fixing device 24 heats and presses the ink image transferred to the print medium 19 to the print medium 19 and permeates and fixes the print image on the print medium 19.
As described above, the fixing device 24 of FIG. 3 constitutes the fixing means described in the claims.

<Action and effect>
As described above, in the ink jet printer of the present embodiment, the fixing device 24 for fixing the ink image transferred to the print medium 19 is provided on the print medium 19. The amount of heating that can transfer the ink image to the printing medium 19 can be suppressed, and the phenomenon that the inkjet head 3 dries due to the heat history in which heat remains on the conveyor belt 1 by continuous printing or the like can be suppressed. It is possible to prevent the nozzles from being clogged by making the environment under the ink jet head 3 good.

<Fourth embodiment>
Next, 4th Embodiment of this invention is described based on drawing.
In the fourth embodiment, as shown in FIG. 4, first to fourth transport rollers 25 _{1 to} 25 ₄ are provided between the inkjet heads 3, and the first to fourth transport rollers 25 _{1 to} 25 ₄ are respectively provided. First
The fourth embodiment is different from the third embodiment in that fourth heating elements 26 _{1 to} 26 ₄ are incorporated.
As shown in FIG. 5, the _first to fourth heating elements 26 _{1 to} 26 ₄ satisfy the condition that the fourth conveyance roller 25 ₄ > the third conveyance roller 25 ₃ > the second conveyance roller 25 ₂ > the first conveyance roller 25 _1. In this way, the first to fourth transport rollers 25 _{1 to} 25 ₄ are sequentially heated. That is, heating is performed with a larger amount of heat as it is arranged on the downstream side in the conveyance direction of the image receiving film by the conveyance belt 1.

<Action and effect>
As described above, in the ink jet printer according to the present embodiment, since the plurality of heating elements 26 _{1 to} 26 ₄ are provided so as to correspond to the respective ink jet heads 3, when the ink is ejected from the ink jet head 3, the transport belt. 1 can increase the viscosity of the ejected ink by several percent before the ink is ejected from the other inkjet head 3 on the downstream side in the conveying direction of the image receiving film, thereby suppressing ink color mixing and more appropriate ink image. Can be formed.
Further, the heating elements 26 ₁ to 26 arranged on the downstream side in the conveying direction of the image receiving film by the conveying belt 1.
26 ₄ more for performing heating with a large amount of heat, is heated repeatedly ink ejected from the inkjet head 3 on the upstream side in the transport direction of the image receiving layer by the conveyor belt 1 it is possible to prevent the viscosity of the ink increases, the ink The difference in viscosity depending on the discharge order can be reduced.

1 is a configuration diagram illustrating a schematic configuration of an inkjet printer according to a first embodiment. It is a block diagram which shows schematic structure of the inkjet printer of 2nd Embodiment. It is a block diagram which shows schematic structure of the inkjet printer of 3rd Embodiment. It is a block diagram which shows schematic structure of the inkjet printer of 4th Embodiment. It is a flowchart which shows operation | movement of an inkjet printer.

Explanation of symbols

1 is a conveying belt, 2 is an image receiving liquid coating unit, 3 is an inkjet head, 4 is a heating unit, 5 is a paper feeding unit, 6 is a transfer roller, 7 is a paper discharge unit, 8 is a cleaner, 9 is a driving roller, and 10 is A driven roller, 11 is a tension roller, 12 is an image receiving liquid container, 13 is a coating roller, 14 is a coating roller, 15 is a temperature sensor, 16 is a heating element, 17 is a temperature sensor, 18 is a heating element, 19 is a printing medium, 20 Is a pick-up roller, 21 is a cleaner liquid container, 22 is a cleaner roller, 23 is a cooler, 24 is a fixing device, 25 _{1 to} 25 ₄ are first to fourth transport rollers, 2
6 _{1-26 4} first to fourth heating element

Claims (7)

An ink jet printer that discharges ink droplets to form an ink image on an intermediate transfer member and then transfers the ink image formed on the intermediate transfer member to a printing medium for printing.
A transport belt that transports the intermediate transfer member; and an inkjet head that forms ink images by ejecting ink droplets from nozzles onto the intermediate transfer member transported by the transport belt;
A heating unit disposed downstream of the inkjet head in the conveyance direction of the intermediate transfer member by the conveyance belt and heating and evaporating moisture contained in an ink image formed on the intermediate transfer member by the inkjet head; An ink-jet printer comprising: an image transfer unit that transfers the ink image, the water of which has been evaporated by the heating unit, to the print medium. The inkjet head is disposed above the transport belt, and forms an ink image on an intermediate transfer member transported by the transport belt by discharging ink droplets vertically downward from the nozzle.
The heating means is disposed so as to be in contact with the back surface of the belt on the downstream side in the transport direction of the intermediate transfer body with respect to the ink droplet ejection position by the ink jet head, and heats the contact portion of the belt to heat the ink. 2. The ink jet printer according to claim 1, wherein moisture contained in the image is heated and evaporated. The inkjet printer according to claim 1, further comprising a fixing unit that fixes the ink image transferred to the print medium by the image transfer unit to the print medium. The inkjet printer according to claim 1, further comprising a cooling unit that cools the conveyance belt after the transfer operation by the image transfer unit. A cleaning means for cleaning the transport belt using a cleaner liquid after the transfer operation by the image transfer means;
The inkjet printer according to claim 4, wherein the cooling unit cools the cleaner liquid. The inkjet heads are a plurality of inkjet heads arranged to be shifted in the conveyance direction of the intermediate transfer member by the conveyance belt;
6. The ink jet printer according to claim 1, wherein a plurality of the heating means are provided corresponding to each of the ink jet heads. The inkjet printer according to claim 6, wherein the plurality of heating units perform heating with a larger amount of heat as they are arranged on the downstream side in the conveyance direction of the intermediate transfer member by the conveyance belt.

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