JP2009148904A - Image forming method and image forming apparatus - Google Patents

Abstract

A glossy image that does not feel uncomfortable with offset printing is realized while ensuring image strength.
A step of ejecting colored ink on a recording medium, a step of ejecting transparent UV ink so as to overlap the color ink deposited on the recording medium, and UV for the transparent UV ink And a step of irradiating with light, and the layer thickness of the transparent UV ink after being irradiated with the UV light is 5 μm or less. .
[Selection] Figure 1

Description

  The present invention relates to an image forming method and an image forming apparatus, and more particularly to an image forming method and an image forming method in which a transparent UV ink is deposited so as to overlap the color ink on a recording medium after the color ink is deposited on the recording medium. Relates to the device.

  In general, an ink jet recording apparatus includes an ink jet head in which a large number of nozzles are formed, and forms an image on a recording medium by ejecting ink droplets from the nozzles toward the recording medium. It is widely used because of its excellent performance, low running cost, and the ability to record high-quality images on a wide variety of recording media.

  2. Description of the Related Art Conventionally, in order to fix an image on a recording medium, there is a method in which a recording medium on which an image is formed is sandwiched between a pressure roller and a heating roller and then heat-pressure-fixed after ink ejection is performed by an inkjet head. An applied inkjet recording apparatus is known (see, for example, Patent Document 1).

  However, in the case of such a method, there is a problem that an image cannot be fixed uniformly on a large-sized recording medium. There is also a problem that it cannot be stably fixed on thick paper or embossed paper. In addition, when a thermoplastic resin latex is included in the ink for hot-pressure fixing, the dischargeability of the ink jet head is deteriorated, and the bulk of the ink aggregate is increased. New problems such as the need for energy also arise.

On the other hand, in Patent Document 2, a print head having a plurality of nozzles, a UV ink head for ejecting transparent UV ink, and an ultraviolet irradiation device for solidifying the transparent UV ink are arranged in the print medium feeding direction. A printing method is disclosed in which the printing ink ejected from the printing head onto the printing medium is wrapped with the transparent UV ink ejected from the UV ink head, and then the UV irradiation is performed by the ultraviolet irradiation device to solidify the transparent UV ink. ing.
Japanese Patent No. 2860123 JP 2004-249617 A

  However, in the invention described in Patent Document 2, although the strength of the image can be ensured, the transparent UV ink is ejected thickly (the thickness of the transparent UV ink is 10 to 30 μm), so that the glossy image as if it was varnished. Thus, there is a problem that an image different from the glossiness of offset printing is obtained. In other words, with the conventional technology, it is impossible to realize a glossy image that does not feel uncomfortable with offset printing while ensuring image strength.

  The present invention has been made in view of such circumstances, and provides an image forming method and an image forming apparatus capable of realizing a glossy image that does not feel uncomfortable with offset printing while ensuring image strength. Objective.

  In order to achieve the above object, an image forming method according to the present invention includes a step of depositing colored ink on a recording medium and a step of depositing a transparent UV ink so as to overlap the colored ink deposited on the recording medium. And a step of irradiating the transparent UV ink with UV light, wherein the layer thickness of the transparent UV ink after being irradiated with the UV light is 5 μm or less.

  According to the present invention, when the transparent UV ink is deposited so as to overlap the color ink on the recording medium, the transparent UV ink is applied so that the layer thickness of the transparent UV ink after irradiation with UV light is 5 μm or less. By ejecting droplets, a thin film layer (transparent UV coat layer) made of transparent UV ink can be formed on the recording medium. As a result, it is possible to realize a glossy image that does not feel uncomfortable with offset printing while ensuring image strength.

  In the present invention, an embodiment using a transparent UV ink diluted with a solvent is preferable. For example, the aspect using the transparent UV ink diluted with the volatile solvent and the aspect using the transparent UV ink diluted with water are mentioned. Even when the amount of droplets of the transparent UV ink is large, a thin film layer (transparent UV coat layer) made of the transparent UV ink can be obtained.

  In the present invention, the layer thickness of the transparent UV ink after irradiation with UV light is preferably 3 μm or less, more preferably 1 to 3 μm.

  In the present invention, it is preferable that the permeation suppression process is performed on the surface of the recording medium before the transparent UV ink is deposited on the recording medium. Particularly, it is suitable when the transparent UV ink is diluted with a solvent, and the penetration of the transparent UV ink into the recording medium can be suppressed. As the permeation suppression treatment, a method of spraying a thermoplastic resin latex solution on the surface of the recording medium or a method of applying a thermoplastic resin latex solution to the surface of the recording medium is suitable.

  In the present invention, it is preferable that a step of drying the transparent UV ink deposited on the recording medium is included between the step of ejecting the transparent UV ink and the step of irradiating the UV light. Particularly, it is suitable when the transparent UV ink is diluted with a solvent, and after the transparent UV ink is sufficiently wet and spread on the recording medium, it can be cured after removing the solvent of the transparent UV ink.

  Further, in the present invention, a mode in which transparent UV ink is ejected in a zigzag pattern on the recording medium is preferable, and the droplet ejection density of the transparent UV ink is higher than the recording medium transport direction (sub-scanning direction). It is more preferable that the direction perpendicular to the conveying direction (main scanning direction) is higher. A uniform thin film layer (transparent UV coat layer) made of a transparent UV ink can be obtained without generating a gap on the recording medium.

  In the present invention, an embodiment in which water-based ink is used as the color ink is preferable. Further, before the color ink is ejected onto the recording medium, at least the position at which the color ink is ejected is used. The aspect which provides the process liquid containing the component which aggregates a coloring material is more preferable. In this case, high-speed recording and high image quality can be realized by the two-liquid aggregation reaction between the color ink and the processing liquid. In this case, the color ink preferably contains a humectant that is compatible with the transparent UV ink.

  In the present invention, the color ink is preferably a solvent-based ink. Energy for drying the color ink (solvent ink) can be reduced. Further, it is possible to prevent the recording medium from curling.

  In the present invention, the color ink is preferably a wax ink. It is not necessary to dry the color ink (wax ink), and the curling of the recording medium can be prevented.

  In the present invention, the color ink is preferably oil-based ink. Curling of the recording medium can be prevented.

  In the present invention, the transparent UV ink preferably contains a cationic monomer. In this case, even if UV light is not continuously irradiated, once UV light is irradiated, the polymerization reaction proceeds, which is desirable.

  Further, in the present invention, it is preferable to have a transparent UV ink droplet ejection amount table corresponding to the image density and control the transparent UV ink droplet ejection amount in accordance with the image density. Specifically, there is a mode in which a droplet ejection amount table of transparent UV ink corresponding to halftone of the image is provided and the droplet ejection amount of transparent UV ink is controlled according to the halftone of image. For example, by increasing the droplet ejection amount of the transparent UV ink (that is, increasing the layer thickness of the transparent UV ink) as the image density (image halftone) increases, an image with a glossiness similar to that of offset printing can be obtained. Can be obtained. On the other hand, by reducing the amount of droplets of transparent UV ink as the image density (image halftone) increases (that is, by reducing the layer thickness of the transparent UV ink), the rub resistance of isolated dots can be improved. Can do.

  In order to achieve the above object, an image forming apparatus according to the present invention overlaps color ink droplet ejection means for ejecting color ink onto a recording medium and color ink ejected onto the recording medium. Transparent UV ink droplet ejecting means for depositing transparent UV ink on the surface, UV light irradiation means for irradiating the transparent UV ink with UV light, and layer thickness of the transparent UV ink after the UV light is irradiated Control means for controlling the amount of droplets of the transparent UV ink ejected by the transparent UV ink droplet ejecting means so that the thickness is 5 μm or less.

  According to the present invention, when the transparent UV ink is deposited so as to overlap the color ink on the recording medium, the transparent UV ink is applied so that the layer thickness of the transparent UV ink after irradiation with UV light is 5 μm or less. By ejecting droplets, a thin film layer (transparent UV coat layer) made of transparent UV ink can be formed on the recording medium. As a result, it is possible to realize a glossy image that does not feel uncomfortable with offset printing while ensuring image strength.

  In the present invention, the layer thickness of the transparent UV ink after irradiation with UV light is preferably 3 μm or less, more preferably 1 to 3 μm.

  According to the present invention, when the transparent UV ink is deposited so as to overlap the color ink on the recording medium, the transparent UV ink is applied so that the layer thickness of the transparent UV ink after irradiation with UV light is 5 μm or less. By ejecting droplets, a thin film layer (transparent UV coat layer) made of transparent UV ink can be formed on the recording medium. As a result, it is possible to realize a glossy image that does not feel uncomfortable with offset printing while ensuring image strength.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic view showing an image forming method according to the present invention. As shown in FIG. 1, the image forming method according to the present invention includes a droplet ejection step (FIG. 1A) of ejecting color ink 12 onto a recording medium 14 by the color ink droplet ejection unit 10, and transparent UV ink. The step of ejecting the transparent UV ink 18 so as to overlap the color ink 12 on the recording medium 14 by the droplet ejecting means 16 (FIG. 1B), and the color ink 12 on the recording medium 14 by the UV light irradiation means 20 A step of irradiating the transparent UV ink 18 ejected so as to overlap with UV light (ultraviolet light) (FIG. 1C), and the layer thickness (t ) Within a range of 5 μm or less, preferably 3 μm or less, more preferably 1 to 3 μm (FIG. 1D).

  According to the evaluation experiment conducted by the present inventor, the layer thickness of the transparent UV ink 18 after UV light irradiation satisfies the above range, thereby ensuring the image strength and providing a gloss that is not uncomfortable with offset printing. A feeling image can be realized. Below, this evaluation experiment is demonstrated.

[Evaluation experiment]
First, the experimental method of this evaluation experiment will be described.

  In this evaluation experiment, before the color ink was ejected onto the recording medium (art paper), a 5% phosphoric acid aqueous solution was used as the treatment liquid (coloring material aggregating liquid) on the image forming area (ink ejection area) on the recording medium. Was granted. Specifically, the treatment liquid is applied onto the recording medium by ejecting the treatment liquid from an inkjet head. It is also possible to apply a method of applying the treatment liquid onto the recording medium using an application roller. Subsequently, the treatment liquid applied on the recording medium was completely dried by a heater to form a solid aggregation treatment agent layer (a thin film layer in which the treatment liquid was dried) on the recording medium.

  Next, colored ink (water-based ink) was ejected onto the recording medium. In this evaluation experiment, a color ink having a composition of cyan pigment: 4% by mass, glycerin: 20% by mass, diethylene glycol: 10% by mass, and orphine: 1% by mass was used.

  As the ink droplet ejection conditions, the thickness of the ink droplets deposited on the recording medium is 10 μm (however, the ink droplets land on the recording medium and have a stable thickness), and the droplet ejection density. Was 100% (that is, a solid image was formed).

  Next, transparent UV ink was ejected so as to overlap the color ink on the recording medium. In this evaluation experiment, a transparent UV ink having a composition of acrylate monomer: 83.9% by mass, initiator: 15% by mass, and surfactant: 0.1% by mass was used.

  As the droplet ejection conditions for the transparent UV ink, the droplet ejection amount and droplet ejection density of the transparent UV ink were adjusted as necessary so that the layer thickness of the transparent UV ink after irradiation with UV light became a desired value.

  Both the color ink and the transparent UV ink were ejected using an inkjet head having the same configuration. This inkjet head has a droplet ejection density of 600 dpi in both the main scanning direction (direction perpendicular to the recording medium conveyance direction) and the sub-scanning direction (recording medium conveyance direction).

  Next, the transparent UV ink ejected so as to overlap the color ink on the recording medium was irradiated with UV light to cure the transparent UV ink, thereby completing the image forming process.

  After completion of the image forming process, the image formed on the recording medium was evaluated from two viewpoints of glossiness and abrasion resistance. These evaluation criteria are shown below.

[Glossy]
○: Glossiness and no discomfort in offset printing △: Glossiness and discomfort in offset printing are small (reflection image is reflected)
X: Glossy and uncomfortable feeling of offset printing is large (reflection image is reflected large, varnish coat)
[Abrasion resistance]
○: No color material adheres to art paper when the image surface is rubbed with art paper. Δ: Little color material adheres to art paper when the image surface is rubbed with art paper. Table 1 shows the results of this evaluation experiment in which the color material adheres much to the art paper when the surface of the image is rubbed.

  Under the condition that the transparent UV ink layer thickness is less than 1 μm, the layer thickness of the transparent UV ink is smaller than the surface roughness of the recording medium, and the surface of the recording medium is partially exposed. It is not preferable.

  In addition, the same result as above was obtained when color ink containing a magenta pigment was used.

  From the above, the results shown in Table 2 can be derived.

  As can be seen from Table 2, as the thickness of the transparent UV ink increases, the glossiness changes from an offset printing tone to a varnish coating tone (the reflection image is greatly reflected). Therefore, from the viewpoint of glossiness and abrasion resistance, the layer thickness of the transparent UV ink is desirably 5 μm or less, preferably 3 μm or less, more preferably 1 to 3 μm.

  Next, Table 3 shows the result of measuring the layer thickness of the transparent UV ink when the droplet ejection conditions of the transparent UV ink are appropriately changed.

    In Table 3, “resolution in the main scanning direction” and “resolution in the sub-scanning direction” indicate the resolution of the inkjet head that ejects transparent UV ink. The color ink was also ejected at the same resolution as the transparent UV ink. The “droplet amount” represents the droplet ejection amount (discharge amount) of the transparent UV ink ejected from the nozzles of the inkjet head. The “dot diameter” is the dot diameter of the transparent UV ink that is deposited so as to overlap the color ink on the recording medium, and the “expansion rate” in the parenthesis follows the true droplet. The ratio of the dot diameter to the droplet diameter when converted is shown. In this case, transparent UV ink is used so that the spreading rate is 2 in any case. The “solid film thickness” represents the layer thickness of the transparent UV ink after UV light irradiation.

  As can be seen from Table 3, when the spreading rate of the transparent UV ink is 2, the layer thickness of the transparent UV ink after UV light irradiation is reduced to 5 μm or less by setting the droplet amount of the transparent UV ink to 6 pl or less. can do. In particular, in the above case, the droplet amount of the transparent UV ink is preferably 1 pl or less, and the layer thickness of the transparent UV ink after UV light irradiation can be 3 μm or less. As a result, it is possible to realize a glossy image that does not feel uncomfortable with offset printing while ensuring image strength.

  Next, Table 4 shows the results of measuring the layer thickness of the transparent UV ink when the spreading ratio of the transparent UV ink is 2.5. The spreading rate of the transparent UV ink was set to 2.5 by changing the amount of the surfactant contained in the transparent UV ink.

  As can be seen from Table 4, when the spreading rate of the transparent UV ink is 2.5, the layer thickness of the transparent UV ink after UV light irradiation is 5 μm by setting the droplet amount of the transparent UV ink to 12 pl or less. It can be: In particular, in the above case, the droplet amount of the transparent UV ink is preferably 3 pl or less, and the layer thickness of the transparent UV ink after UV light irradiation can be 3 μm or less. As a result, it is possible to realize a glossy image that does not feel uncomfortable with offset printing while ensuring image strength.

  Next, Table 5 shows the results of measuring the layer thickness of the transparent UV ink when the transparent UV ink has a spreading ratio of 2.0 and the transparent UV ink is diluted with a volatile solvent.

  In Table 5, “dilution rate” represents the dilution rate of the volatile solvent with respect to the transparent UV ink. Moreover, methanol was used as a volatile solvent.

  As can be seen from Table 5, even when the spreading ratio of the transparent UV ink is 2.0, the layer thickness of the transparent UV ink after UV light irradiation is reduced to 3 μm or less by diluting the transparent UV ink with a volatile solvent. be able to.

  Instead of the volatile solvent, a transparent UV ink diluted with water may be used. In this case, it is possible to obtain the same effect as when using a transparent UV ink diluted with a volatile solvent.

  Thus, in the present invention, it is preferable to use a transparent UV ink diluted with a volatile solvent or a solvent such as water, and a thin film layer (transparent) made of transparent UV ink even when the amount of droplets is large (for example, 12 pl). UV coat layer) can be obtained. As a result, it is possible to realize a glossy image that does not feel uncomfortable with offset printing while ensuring image strength.

  In the case of using a transparent UV ink diluted with a solvent, if a permeable recording medium is used, the solvent penetrates into the recording medium and uncured transparent UV ink remains. It is preferable to perform a suppression process. That is, a permeation inhibitor may be applied to the recording medium before applying the transparent UV ink to the recording medium. Examples of the permeation suppression treatment include an aspect in which a thermoplastic resin latex solution is ejected using an inkjet head, and an aspect in which a thermoplastic resin latex is applied using an application means such as an application roller.

  In the case of using a transparent UV ink diluted with a solvent, the layer thickness (film thickness) obtained by removing the solvent from the transparent UV ink deposited so as to overlap the color ink on the recording medium is 5 μm or less, preferably The transparent UV ink may be diluted with a solvent and ejected so as to satisfy the condition of 3 μm or less, more preferably 1 to 3 μm or less.

  In the case of using a transparent UV ink diluted with a solvent, it is preferable that a transparent UV ink drying step is performed between the transparent UV ink droplet ejection step and the UV light irradiation step. In other words, a drying unit is provided between an inkjet head that ejects transparent UV ink and a UV lamp that performs UV light irradiation, and UV light irradiation is applied to the transparent UV ink deposited so as to overlap the color ink on the recording medium. Before the above is performed, the transparent UV ink is dried and then irradiated with UV light. Thus, after the transparent UV ink is sufficiently wet and spread on the recording medium, the transparent UV ink can be cured after removing the solvent of the transparent UV ink. As a result, a thin film layer (transparent UV coat layer) made of transparent UV ink can be obtained.

FIG. 2 is a diagram showing an arrangement state of dots formed by the transparent UV ink. In FIG. 2 and FIG. 3 to be described later, as an example, a case where the transparent UV ink is ejected at a droplet ejection rate of 100% as in the case of forming a solid image on the recording medium is shown. It is not limited. FIG. 2A shows a case where dots 30 made of transparent UV ink have a constant dot pitch P ₁ , P ₁ in the main scanning direction (direction orthogonal to the recording medium conveyance direction) and sub-scanning direction (recording medium conveyance direction), respectively. ₂ represents a so-called square lattice-like dot arrangement arranged at equal intervals. On the other hand, FIG. 2B shows one dot row among the dot rows 32 and 32 adjacent in the main scanning direction when the dot row arranged in the sub-scanning direction in FIG. the shifted in the sub-scanning direction phase by half (i.e., 1/2 of the sub-scanning direction of the dot pitch _{P 2 (= P 2/2} )) phase-shifted in the sub-scanning direction by), a so-called staggered dot arrangement It is a representation. 2A and 2B, the dot pitch P ₁ in the main scanning direction is 28.2 μm, the dot pitch P _{2 in the} sub-scanning direction is 42.4 μm, and the dot diameter D of the dots 30 is 45 μm.

  As shown in FIG. 2A, in the case where dots 30 made of transparent UV ink are ejected in a square lattice pattern, if the spreading rate of the transparent UV ink is small and the dot diameter D of the dot 30 is small, reference numeral 34 is obtained. In some cases, gaps are generated between the dots as indicated by the positions, and the transparent UV ink cannot be thinned uniformly.

  On the other hand, as shown in FIG. 2B, when the dots 30 made of transparent UV ink are ejected in a staggered manner, the dot diameter D of the dots 30 (that is, the spreading rate of the transparent UV ink) is as shown in FIG. ), No gap is generated between the dots. In other words, compared to the case where dots are ejected in a square lattice pattern, the case where dots are ejected in a staggered pattern is less likely to cause a gap between the dots, and is suitable for uniformly thinning the transparent UV ink. Dot arrangement.

  Therefore, in the present invention, a mode in which transparent UV ink is ejected in a staggered manner on a recording medium is preferred. Specifically, a staggered dot arrangement can be realized by appropriately changing the nozzle arrangement and the droplet ejection timing of an inkjet head that ejects transparent UV ink. As a result, the transparent UV ink can be uniformly thinned.

FIG. 3 is a diagram showing a staggered dot arrangement. 3 (a) is a dot pitch _{P 1} in the main scanning direction shows the case the sub-scanning direction is larger than the dot pitch _{P 2 (i.e.,} P _{1> P} 2). On the other hand, FIG. 3B shows a case where the dot pitch P ₁ ′ in the main scanning direction is smaller than the dot pitch P ₂ ′ in the sub-scanning direction (that is, P ₁ ′ <P ₂ ′). 3A and 3B show the dot pitch in the main scanning direction and the dot pitch in the sub scanning direction interchanged (that is, P ₁ = P ₂ ′ and P ₂ = P ₁ ′). Is established). Specifically, the dot pitch P _{1 in the} main scanning direction shown in FIG. 3A and the dot pitch P ₂ ′ in the sub-scanning direction shown in FIG. 3B are 42.4 μm, and FIG. The dot pitch P _{2 in the} sub-scanning direction shown and the dot pitch P ₁ ′ in the main scanning direction shown in FIG. 3B are 28.2 μm. Further, the dot diameter D of the dot 30 shown in FIGS. 3A and 3B is 45 μm.

In the case where the dot 30 formed of a transparent UV ink is ejected in a zigzag manner, as shown in FIG. 3 (a), the dot pitch P ₁ in the main scanning direction and sub-scanning direction is larger than the dot pitch P ₂ (i.e. , P ₁ > P ₂ ), a gap is generated between the dots as indicated by the reference numeral 36, and the transparent UV ink may not be thinned uniformly.

  On the other hand, as shown in FIG. 3B, when the dot pitch P1 ′ in the main scanning direction is smaller than the dot pitch P2 ′ in the sub-scanning direction (that is, P1 ′ <P2 ′), the dot diameter D of the dot 30 (that is, P1 ′ <P2 ′). Even when the spreading rate of the transparent UV ink is the same as that in FIG. 3A, no gap is generated between the dots. In other words, when dots 30 made of transparent UV ink are ejected in a zigzag pattern, dots are ejected so that the dot pitch in the sub-scanning direction is larger than the dot pitch in the main scanning direction. It is a dot arrangement suitable for thinning the transparent UV ink uniformly, with no gap between them.

  Therefore, in the present invention, when transparent UV ink is ejected in a staggered pattern on a recording medium, there is an aspect in which droplets are ejected such that the dot pitch in the sub-scanning direction is larger than the dot pitch in the main scanning direction. preferable. As a result, the transparent UV ink can be thinned more uniformly.

  In the present invention, the image intensity and the glossiness of the image can be designed independently of the color ink. In other words, the color intensity can be controlled by changing the layer thickness (droplet ejection amount) of the transparent UV ink. As the ink, various inks such as water-based ink, solvent-based ink, wax ink, and oil-based ink can be used.

  When the color ink is a water-based ink, an embodiment in which image formation is performed using a two-liquid aggregation reaction with a processing liquid (color material aggregation liquid) is preferable, and high-speed recording and high image quality are possible. In this case, the water-based ink desirably contains a humectant that is compatible with the transparent UV ink.

  When the color ink is a solvent-based ink, the color ink is easily dried, so that the required drying energy can be reduced. Further, it is possible to prevent image deterioration and curling of the recording medium due to the solvent. As a result, a high quality image can be obtained.

  When the color ink is a wax ink, it is not necessary to dry the color ink, and curling of the recording medium can be prevented.

  When the color ink is oil-based ink, curling of the recording medium can be prevented.

  As a preferred embodiment of the present invention, a cationic monomer is preferably used as the monomer of the transparent UV ink. When a cationic monomer is used as the monomer, unlike when a radical monomer is used, the polymerization proceeds even if UV light is not irradiated after the start of the reaction. In addition, the cationic monomer has an advantage of high safety even in an uncured state.

  In the present invention, it is preferable to have a transparent UV ink droplet ejection amount table corresponding to the image density and control the transparent UV ink droplet ejection amount in accordance with the image density. By controlling the droplet ejection amount of the transparent UV ink in accordance with the image density, an image with a desired glossiness can be obtained.

  FIG. 4 is a diagram showing an example of a droplet ejection amount table of transparent UV ink corresponding to the image density. In FIG. 4 and FIG. 5 described later, the horizontal axis represents the halftone of the image, and the vertical axis represents the layer thickness of the transparent UV ink after UV light irradiation. In the droplet ejection amount table shown in FIG. 4, the layer thickness of the transparent UV ink increases as the dot% of the image increases. That is, the higher the image density, the greater the amount of transparent UV ink deposited. For example, the layer thickness of the transparent UV ink may be increased at a certain ratio with respect to the halftone% of the image as indicated by a straight line indicated by reference numeral 40, or the halftone of the image is indicated by curves indicated by reference numerals 42 and 44. The ratio of increasing the layer thickness of the transparent UV ink may be changed according to%. Although not shown, the layer thickness of the transparent UV ink may be increased stepwise. Using such a droplet ejection amount table, the layer thickness of the transparent UV ink is increased as the dot% of the image is increased, that is, the droplet ejection amount of the transparent UV ink is increased as the image density is increased. The glossiness of the density part can be increased.

  In general, in the case of offset printing, the higher the halftone (ie, image density) of an image, the higher the glossiness of the image. Therefore, by controlling the droplet ejection amount of the transparent UV ink according to the droplet ejection amount table as shown in FIG. 4, it is possible to realize an image having the same glossiness as that of offset printing.

  FIG. 5 is a diagram showing another example of the transparent UV ink droplet ejection amount table corresponding to the image density. In the droplet ejection amount table shown in FIG. 5, the layer thickness of the transparent UV ink decreases as the halftone percentage of the image increases. That is, the higher the image density is, the smaller the amount of the transparent UV ink deposited is. For example, the layer thickness of the transparent UV ink may be decreased at a fixed rate with respect to the halftone% of the image as indicated by a straight line indicated by reference numeral 50, or the halftone of the image as indicated by curves indicated by reference numerals 52 and 54. The ratio of decreasing the layer thickness of the transparent UV ink may be changed according to%. Although not shown, the layer thickness of the transparent UV ink may be decreased stepwise. By using such a droplet ejection amount table, the layer thickness of the transparent UV ink is reduced as the halftone ratio of the image is increased, that is, the droplet ejection amount of the transparent UV ink is decreased as the image density is increased. It is possible to increase the rub resistance of isolated dots in the density portion.

[Device configuration example]
FIG. 6 is a schematic configuration diagram showing an example of an image forming apparatus to which the image forming method according to the present invention is applied.

  An image forming apparatus 100 shown in FIG. 6 is a single-sided machine that can print only on one side of a recording medium 114. The image forming apparatus 100 includes a paper feeding unit 102 that supplies a recording medium 114, a permeation suppression processing unit 104 that performs permeation suppression processing on the recording medium 114, and a processing liquid application unit that applies a processing liquid to the recording medium 114. 106, a printing unit (image forming unit) 108 for forming an image by applying color ink to the recording medium 114, a transparent UV ink applying unit 110 for applying transparent UV ink to the recording medium 114, and an image are formed. The paper discharge unit 112 mainly conveys and discharges the recording medium 114.

  The paper feed unit 102 is provided with a paper feed stand 120 on which the recording media 114 are stacked. A feeder board 122 is connected in front of the paper feed tray 120 (left side in FIG. 6), and the recording media 114 stacked on the paper feed tray 120 are sent to the feeder board 122 one by one from the top. The recording medium 114 sent to the feeder board 122 is fed to the surface (circumferential surface) of the pressure drum 126a of the permeation suppression processing unit 104 via the transfer drum 124a.

  In the permeation suppression processing unit 104, a sheet preheating unit 128 and a permeation suppression agent head 130 are arranged at positions facing the surface of the pressure drum 126a in order from the upstream side in the rotation direction of the pressure drum 126a (counterclockwise direction in FIG. 6). , And a permeation inhibitor drying unit 132 are provided.

  The paper preheating unit 128 and the permeation suppression agent drying unit 132 are each provided with a heater capable of controlling the temperature within a predetermined range. When the recording medium 114 held on the pressure drum 126a passes through a position facing the paper preheating unit 128 and the permeation suppression agent drying unit 132, it is heated by the heaters of these units.

  The permeation suppressor head 130 ejects a permeation suppressant onto the recording medium 114 held by the impression cylinder 126a, and each ink head 140C, 140M, 140Y, 140K, 140R of the print unit 108, which will be described later. The same configuration as 140G and 140B is applied.

  In this example, an inkjet head is applied as means for performing the permeation suppression process on the surface of the recording medium 114, but the means for performing the permeation suppression process is not particularly limited to this example. For example, various methods such as a spray method and a coating method can be applied.

  In this example, a thermoplastic resin latex solution is suitably used as the penetration inhibitor. Of course, the penetration inhibitor is not limited to the thermoplastic resin latex solution, and for example, tabular grains (mica and the like), water repellent (fluorine coating agent) and the like can be applied.

  Subsequent to the permeation suppression processing unit 104, a processing liquid application unit 106 is provided. A transfer drum 124b is provided between the pressure drum 126a of the permeation suppression processing unit 104 and the pressure drum 126b of the treatment liquid application unit 106 so as to be in contact with them. As a result, the recording medium 114 held on the pressure drum 126a of the permeation suppression processing unit 104 is transferred to the pressure drum 126b of the processing liquid application unit 106 via the transfer drum 124b after the permeation suppression processing is performed.

  In the treatment liquid application unit 106, a sheet preheating unit 134, a treatment liquid head 136, a position facing the surface of the pressure drum 126 b in order from the upstream side in the rotation direction of the pressure drum 126 b (counterclockwise direction in FIG. 6), And a treatment liquid drying unit 138 are provided.

  Regarding each part of the processing liquid application unit 106 (paper preheating unit 134, processing liquid head 136, and processing liquid drying unit 138), the paper preheating unit 128, the permeation suppression agent head 130, and the permeation suppression of the permeation suppression processing unit 104 described above. Since the same configuration as that of the agent drying unit 132 is applied, description thereof is omitted here. Of course, a configuration different from that of the permeation suppression processing unit 104 can be applied.

  The treatment liquid used in this example is the color contained in the ink ejected from the ink heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B disposed in the printing unit 108 at the subsequent stage toward the recording medium 114. It is an acidic liquid having an action of aggregating the material.

  The heating temperature of the heater of the processing liquid drying unit 138 is such that the processing liquid applied to the surface of the recording medium 114 is dried by the discharge operation of the processing liquid head 136 disposed on the upstream side in the rotation direction of the pressure drum 126b, and the recording medium is dried. The temperature is set such that a solid or semi-solid aggregation treatment agent layer (a thin film layer obtained by drying the treatment liquid) is formed on 114.

  The “solid or semi-solid flocculating agent layer” as used herein refers to one having a moisture content in the range of 0 to 70% as defined below.

  As in this example, it is preferable that the recording medium 114 is preheated by the heater of the paper preheating unit 134 before the treatment liquid is applied onto the recording medium 114. In this case, the heating energy required for drying the treatment liquid can be kept low, and energy saving can be achieved.

  A printing unit 108 is provided following the treatment liquid application unit 106. A transfer drum 124c is provided between the pressure drum 126b of the treatment liquid application unit 106 and the pressure drum 126c of the printing unit 108 so as to be in contact with them. As a result, the recording medium 114 held on the pressure drum 126b of the treatment liquid application unit 106 is applied with the treatment liquid to form a solid or semi-solid aggregating treatment agent layer, and then via the transfer cylinder 124c. The pressure is transferred to the impression cylinder 126 c of the printing unit 108.

  In the printing unit 108, ink heads respectively corresponding to the seven colors of CMYKRGB at positions facing the surface of the pressure drum 126c in order from the upstream side with respect to the rotation direction (counterclockwise direction in FIG. 6) of the pressure drum 126c. 140C, 140M, 140Y, 140K, 140R, 140G, 140B and solvent drying units 142a, 142b are provided, respectively.

  As each of the ink heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B, an ink jet recording head (ink jet head) is applied in the same manner as the permeation suppression agent head 130 and the treatment liquid head 136 described above. That is, each of the ink heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B ejects the corresponding color ink droplets toward the recording medium 114 held by the pressure drum 126c.

  Each of the ink heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B has a length corresponding to the maximum width of the image forming area in the recording medium 114 held by the impression cylinder 126c, and the ink ejection surface thereof Is a full-line head in which a plurality of nozzles for ink ejection (not shown in FIG. 6, indicated by reference numeral 161 in FIG. 7) are arranged over the entire width of the image forming area. The ink heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B are fixedly installed so as to extend in a direction orthogonal to the rotation direction of the impression cylinder 126c (conveying direction of the recording medium 114).

  According to the configuration in which a full line head having a nozzle row covering the entire width of the image forming area of the recording medium 114 is provided for each ink color, the recording medium 114 and each ink in the transport direction (sub-scanning direction) of the recording medium 114 The primary image is recorded in the image forming area of the recording medium 114 by performing the operation of relatively moving the heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B once (that is, by one sub-scan). can do. As a result, printing can be performed at a higher speed than when a serial (shuttle) type head that reciprocates in the direction (main scanning direction) orthogonal to the conveyance direction (sub-scanning direction) of the recording medium 114 is applied. Can be improved.

  In this example, the configuration of seven colors of CMYKRGB is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink, dark ink, and special color ink are added as necessary. May be. For example, it is possible to add an ink head that discharges light-colored ink such as light cyan and light magenta, and the arrangement order of the color heads is not particularly limited.

  The solvent drying units 142a and 142b are configured to include a heater capable of controlling the temperature within a predetermined range, similar to the paper preheating units 128 and 134, the permeation suppression agent drying unit 132, and the treatment liquid drying unit 138 described above. As will be described later, when ink droplets are ejected onto the solid or semi-solid aggregation processing agent layer formed on the recording medium 114, an ink aggregate (coloring material aggregate) is formed on the recording medium 114. ) And the ink solvent separated from the color material spreads, and a liquid layer in which the aggregating agent is dissolved is formed. In this way, the solvent component (liquid component) remaining on the recording medium 114 causes not only curling of the recording medium 114 but also image degradation. Therefore, in this example, the corresponding color inks are ejected onto the recording medium 114 from the ink heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B, and then heated by the heaters of the solvent drying units 142a and 142b. To evaporate the solvent component and dry.

  Subsequent to the printing unit 108, a transparent UV ink application unit 110 is provided. A transfer drum 124d is provided between the pressure drum 126c of the printing unit 108 and the pressure drum 126d of the transparent UV ink applying unit 110 so as to be in contact therewith. Accordingly, the recording medium 114 held on the pressure drum 126c of the printing unit 108 is delivered to the pressure drum 126d of the transparent UV ink application unit 110 via the transfer drum 124d after each color ink is applied.

  In the transparent UV ink applying unit 110, printing is performed to read the printing result by the printing unit 108 at a position facing the surface of the impression cylinder 126d in order from the upstream side in the rotation direction of the impression cylinder 126d (counterclockwise direction in FIG. 6). A detection unit 144, a transparent UV ink head 146, and first UV lamps 148a and 148b are provided.

  The print detection unit 144 includes an image sensor (line sensor or the like) for imaging a printing result of the printing unit 108 (droplet ejection results of the ink heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B). It functions as means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the image sensor.

  The transparent UV ink head 146 has the same configuration as the ink heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B of the printing unit 108, and the ink heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B are applied. Thus, the transparent UV ink is ejected so as to overlap the color ink ejected on the recording medium 114. Of course, it is also possible to apply a configuration different from each of the ink heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B of the printing unit 108.

  The first UV lamps 148 a and 148 b are transparent on the recording medium 114 when the recording medium 114 passes a position facing the first UV lamp 148 after the transparent UV ink is deposited on the recording medium 114. The UV ink is irradiated with UV light (ultraviolet light) to cure the transparent UV ink.

  In this example, the layer thickness of the transparent UV ink after UV light irradiation is 5 μm or less (preferably 3 μm or less, more preferably 1 to 3 μm) by a transparent UV ink droplet ejection amount control unit 180a (see FIG. 9) described later. Thus, the amount of droplets ejected from the nozzles of the transparent UV ink head 146 (the amount of droplets ejected by the transparent UV ink) is controlled. In FIG. 6, “layer thickness of transparent UV ink after UV light irradiation” is the layer thickness of transparent UV ink after UV light is irradiated by a second UV lamp 156 described later. That is, when a plurality of UV lamps are provided, the layer thickness of the transparent UV ink after the UV light irradiation is performed by the UV lamp on the most downstream side in the recording medium conveyance direction.

  A paper discharge unit 112 is provided following the transparent UV ink application unit 110. The paper discharge unit 112 includes a paper discharge drum 150 that receives the recording medium 114 on which the transparent UV ink is ejected, a paper discharge tray 152 on which the recording medium 114 is loaded, and a sprocket provided on the paper discharge drum 150. A paper discharge chain 154 provided with a plurality of paper discharge grippers is provided between a sprocket provided above the paper board 152.

  Between these sprockets, a second UV lamp 156 is provided inside the paper discharge chain 154. The second UV lamp 156 is used until the recording medium 114 transferred from the pressure drum 126d of the transparent UV ink applying unit 110 to the paper discharge drum 150 is conveyed to the paper discharge tray 152 by the paper discharge chain 154. The transparent UV ink on the recording medium 114 is irradiated with UV light (ultraviolet light) to cure the transparent UV ink.

  Next, the structure of the ink heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B arranged in the printing unit 108 will be described in detail. Since the structures of the ink heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B are common, the ink heads (hereinafter, simply referred to as “heads”) may be represented by reference numeral 160 below. .)

  7A is a perspective plan view showing an example of the structure of the head 160, FIG. 7B is an enlarged view of a part thereof, and FIG. 7C is a plan view showing another example of the structure of the head 160. FIG. FIG. 8 is a cross-sectional view (a cross-sectional view taken along line 8-8 in FIGS. 7A and 7B) showing a three-dimensional configuration of the ink chamber unit.

  In order to increase the dot pitch formed on the recording medium 114, it is necessary to increase the nozzle pitch in the head 160. As shown in FIGS. 7A and 7B, the head 160 of this example includes a plurality of ink chamber units 163 including nozzles 161 serving as ink droplet ejection holes, pressure chambers 162 corresponding to the nozzles 161, and the like. Are arranged in a staggered matrix (two-dimensionally) so that the projection is substantially performed so as to be aligned along the head longitudinal direction (main scanning direction orthogonal to the recording medium conveyance direction). High density of nozzle spacing (projection nozzle pitch) is achieved.

  The form in which one or more nozzle rows are configured over a length corresponding to the entire width of the recording medium 114 in a direction substantially orthogonal to the conveyance direction of the recording medium 114 is not limited to this example. For example, instead of the configuration of FIG. 7A, as shown in FIG. 7C, short head blocks 160 ′ in which a plurality of nozzles 161 are two-dimensionally arranged are arranged in a staggered manner and joined together. A line head having a nozzle row having a length corresponding to the entire width of the recording medium 114 may be configured. Although not shown, a line head may be configured by arranging short heads in a line.

  The pressure chamber 162 provided corresponding to each nozzle 161 has a substantially square planar shape, and the nozzle 161 and the supply port 164 are provided at both corners on the diagonal line. Each pressure chamber 162 communicates with a common flow path 165 through a supply port 164. The common flow path 165 communicates with an ink supply tank (not shown) as an ink supply source, and the ink supplied from the ink supply tank is distributed and supplied to each pressure chamber 162 via the common flow path 165.

  A piezoelectric element 168 having an individual electrode 167 is joined to a diaphragm 166 that constitutes the top surface of the pressure chamber 162 and also serves as a common electrode, and the piezoelectric element 168 is applied by applying a drive voltage to the individual electrode 167. Deformation causes ink to be ejected from the nozzle 161. When ink is ejected, new ink is supplied from the common channel 165 to the pressure chamber 162 through the supply port 164.

  In this example, the piezoelectric element 168 is applied as an ejection force generation unit for ink ejected from the nozzles 161 provided in the head 160. However, a heater is provided in the pressure chamber 162, and the pressure of film boiling caused by heating of the heater is used. It is also possible to apply a thermal method that ejects ink.

  As shown in FIG. 7B, the ink chamber units 163 having such a structure are arranged in a fixed manner along a row direction along the main scanning direction and an oblique column direction having a constant angle θ that is not orthogonal to the main scanning direction. By arranging a large number of patterns in a lattice pattern, the high-density nozzle head of this example is realized.

  That is, with the structure in which a plurality of ink chamber units 163 are arranged at a constant pitch d along the direction of an angle θ with respect to the main scanning direction, the pitch P of the nozzles projected in the main scanning direction is d × cos θ. Thus, in the main scanning direction, each nozzle 161 can be handled equivalently as a linear array with a constant pitch P. With such a configuration, it is possible to realize a high-density nozzle configuration in which 2400 nozzle rows are projected per inch (2400 nozzles / inch) so as to be aligned in the main scanning direction.

  In the implementation of the present invention, the nozzle arrangement structure is not limited to the illustrated example, and various nozzle arrangement structures such as an arrangement structure having one nozzle row in the sub-scanning direction can be applied.

  Further, the application range of the present invention is not limited to a printing method using a line-type head, and a short head that is less than the length in the width direction (main scanning direction) of the recording medium 114 is scanned in the width direction of the recording medium 114. Printing in the width direction is performed, and when printing in one width direction is completed, the recording medium 114 is moved by a predetermined amount in a direction (sub-scanning direction) perpendicular to the width direction of the recording medium 114, and the recording medium 114 in the next printing area is moved. A serial method may be applied in which printing in the width direction is performed and printing is performed over the entire printing area of the recording medium 114 by repeating this operation.

  FIG. 9 is a principal block diagram showing the system configuration of the image forming apparatus 100. The image forming apparatus 100 includes a communication interface 170, a system controller 172, a memory 174, a motor driver 176, a heater driver 178, a print control unit 180, an image buffer memory 182, a head driver 184, and the like.

  The communication interface 170 is an interface unit that receives image data sent from the host computer 186. As the communication interface 170, a serial interface such as USB (Universal Serial Bus), IEEE 1394, Ethernet (registered trademark), a wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted. Image data sent from the host computer 186 is taken into the image forming apparatus 100 via the communication interface 170 and temporarily stored in the memory 174.

  The memory 174 is a storage unit that temporarily stores an image input via the communication interface 170, and data is read and written through the system controller 172. The memory 174 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 172 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire image forming apparatus 100 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 172 controls the communication interface 170, the memory 174, the motor driver 176, the heater driver 178, and the like, performs communication control with the host computer 186, read / write control of the memory 174, etc. A control signal for controlling the motor 188 and the heater 189 is generated.

  The memory 174 stores programs executed by the CPU of the system controller 172 and various data necessary for control. Note that the memory 174 may be a non-rewritable storage means, or may be a rewritable storage means such as an EEPROM. The memory 174 is used as a temporary storage area for image data, and is also used as a program development area and a calculation work area for the CPU.

  Various control programs are stored in the program storage unit 190, and the control programs are read and executed in accordance with instructions from the system controller 172. The program storage unit 190 may use a semiconductor memory such as a ROM or an EEPROM, or may use a magnetic disk or the like. An external interface may be provided and a memory card or PC card may be used. Of course, you may provide several recording media among these recording media. The program storage unit 190 may also be used as a recording unit (not shown) for operating parameters.

  The motor driver 176 is a driver that drives the motor 188 in accordance with an instruction from the system controller 172. In FIG. 9, a motor (actuator) arranged at each part in the apparatus is represented by reference numeral 188. For example, the motor 188 shown in FIG. 9 includes motors that drive the pressure drums 126a to 126d, the transfer drums 124a to 124d, and the paper discharge drum 150 shown in FIG.

  The heater driver 178 is a driver that drives the heater 189 in accordance with an instruction from the system controller 172. In FIG. 9, a plurality of heaters provided in the image forming apparatus 100 are represented by reference numeral 189. For example, the heater 189 shown in FIG. 9 includes the paper preheating units 128 and 134, the permeation suppression agent drying unit 132, the treatment liquid drying unit 138, the solvent drying units 142a and 142b shown in FIG.

  The UV light irradiation control unit 179 performs irradiation control of the UV light irradiation means 191. In FIG. 9, a plurality of UV light irradiation means provided in the image forming apparatus is represented by reference numeral 191. For example, the UV light irradiation means 191 shown in FIG. 9 includes the first UV lamps 148a and 148b and the second UV lamp 156 shown in FIG. The optimum irradiation time, irradiation interval, and irradiation intensity of each UV lamp 148a, 148b, and 156 are obtained in advance for each type of recording medium 114 and transparent UV ink, and are converted into a data table and stored in a predetermined memory (for example, memory 174), when the information of the recording medium 114 and the information of the ink used are acquired, the irradiation time, irradiation interval, and irradiation intensity of each of the UV lamps 148a, 148b, and 156 are controlled with reference to the memory.

  As described above, the image forming apparatus 100 of this example includes the plurality of UV lamps 148a, 148b, and 156. By controlling the irradiation time, irradiation interval, and irradiation intensity of each of the UV lamps 148a, 148b, and 156, the glossiness (surface shape) of the image can be controlled, and images with different glossiness can be realized. For example, the first UV lamps 148a and 148b increase the viscosity of the transparent UV ink in the vicinity of the interface with the recording medium 114 to suppress the penetration of the transparent UV ink into the recording medium 114, and are transparent by the second UV lamp 156. The UV ink can be cured from the inside to the surface. Instead of (or with these controls) controlling the irradiation time, irradiation interval, and irradiation intensity of each UV lamp 148a, 148b, 156, the speed at which the recording medium 114 is conveyed may be controlled. The positions of the UV lamps 148a, 148b, and 156 may be changed. In addition, a drying unit is added between the first UV lamps 148a and 148b and the second UV lamp 156, and after the transparent UV ink is deposited, the recording medium is recorded by the first UV lamps 148a and 148b. The transparent UV ink may be cured by the second UV lamp 156 after removing the solvent in the transparent UV ink by the drying unit while suppressing the permeation of the transparent UV ink to 114.

  The print control unit 180 has a signal processing function for performing various processes and corrections for generating a print control signal from the image data in the memory 174 in accordance with the control of the system controller 172. The generated print data This is a control unit that supplies (dot data) to the head driver 184. Necessary signal processing is performed in the print control unit 180, and the ejection droplet amount (droplet ejection amount) and ejection timing of the head 192 are controlled via the head driver 184 based on the image data. Thereby, a desired dot size and dot arrangement are realized. In FIG. 9, a plurality of heads (inkjet heads) provided in the image forming apparatus 100 are represented by reference numeral 192. For example, the head 192 shown in FIG. 9 includes the penetration inhibitor head 130, the treatment liquid head 136, the ink heads 140C, 140M, 140Y, 140K, 140R, 140G, 140B, and the transparent UV ink head 146 shown in FIG. Yes.

  The print control unit 180 is provided with a transparent UV ink droplet ejection amount control unit 180a that controls the droplet ejection amount of the transparent UV ink head 146 shown in FIG. In the transparent UV ink droplet ejection amount control unit 180a, the layer thickness of the transparent UV ink deposited so as to overlap the color ink on the recording medium 114 is 5 μm or less (preferably 3 μm or less, more preferably 1 to 3 μm). As described above, the droplet ejection amount of the transparent UV ink head 146 is controlled via the head driver 184.

  The print control unit 180 is provided with an image buffer memory 182, and image data, parameters, and other data are temporarily stored in the image buffer memory 182 when image data is processed in the print control unit 180. Also possible is an aspect in which the print controller 180 and the system controller 172 are integrated and configured with one processor.

  The head driver 184 generates a drive signal to be applied to the piezoelectric element 168 of the head 192 based on the image data given from the print control unit 180, and applies the drive signal to the piezoelectric element 168 to drive the piezoelectric element 168. Including a driving circuit. The head driver 184 shown in FIG. 9 may include a feedback control system for keeping the driving conditions of the head 192 constant.

  As described with reference to FIG. 6, the print detection unit 144 is a block including a line sensor. The print detection unit 144 reads an image printed on the recording medium 114, performs necessary signal processing, and the like to perform a print status (whether ejection is performed, droplet ejection). And the detection result is provided to the print control unit 180. The print control unit 180 performs various corrections on the head 192 based on information obtained from the print detection unit 144 as necessary.

  The operation of the image forming apparatus 100 configured as described above will be described.

  The recording medium 114 is sent out from the paper supply stand 120 of the paper supply unit 102 to the feeder board 122. The recording medium 114 is held on the pressure drum 126a of the permeation suppression processing unit 104 via the transfer drum 124a, preheated by the paper preheating unit 128, and the permeation suppression agent is ejected by the permeation suppression agent head 130. Thereafter, the recording medium 114 held on the impression cylinder 126a is heated by the permeation suppression agent drying unit 132, and the solvent component (liquid component) of the permeation suppression agent is evaporated and dried.

  The recording medium 114 thus subjected to the permeation suppression process is transferred from the pressure drum 126a of the permeation suppression processing unit 104 to the pressure drum 126b of the treatment liquid application unit 106 via the transfer cylinder 124b. The recording medium 114 held on the impression cylinder 126 b is preheated by the paper preheating unit 134 and the processing liquid is ejected by the processing liquid head 136. Thereafter, the recording medium 114 held on the pressure drum 126b is heated by the treatment liquid drying unit 138, and the solvent component (liquid component) of the treatment liquid is evaporated and dried. Thereby, a solid or semi-solid aggregation treatment agent layer is formed on the recording medium 114.

  The recording medium 114 to which the treatment liquid has been applied to form a solid or semi-solid aggregation processing agent layer is transferred from the impression cylinder 126b of the treatment liquid application section 106 to the impression cylinder 126c of the printing section 108 via the transfer cylinder 124c. Is passed on. Corresponding color inks are ejected from the respective ink heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B on the recording medium 114 held on the impression cylinder 126b in accordance with the input image data.

  When the ink droplet lands on the aggregation treatment agent layer, the contact surface between the ink droplet and the aggregation treatment agent layer lands in a predetermined area due to the balance between the flight energy and the surface energy. The aggregation reaction starts immediately after the ink droplets land on the aggregation treatment agent, but the aggregation reaction starts from the contact surface between the ink droplets and the aggregation treatment agent layer. The agglomeration reaction occurs only in the vicinity of the contact surface, and the color material in the ink is agglomerated in a state where the adhesive force is obtained with a predetermined contact area at the time of ink landing, so that the color material movement is suppressed.

  Even if other ink droplets land adjacent to this ink droplet, the color material of the ink that has landed first is already agglomerated, so the color materials do not mix with the ink that landed later, Bleed is suppressed. Note that after the color material is aggregated, the separated ink solvent spreads, and a liquid layer in which the aggregation treatment agent is dissolved is formed on the recording medium 114.

  The recording medium 114 held on the impression cylinder 126c is heated by the solvent drying units 142a and 142b, and the solvent component (liquid component) separated from the ink aggregates on the recording medium 114 is evaporated and dried. As a result, curling of the recording medium 114 can be prevented and image quality deterioration due to the solvent component can be suppressed.

  The recording medium 114 to which the color ink is applied by the printing unit 108 is transferred from the impression cylinder 126c of the printing unit 108 to the impression cylinder 126d of the transparent UV ink application unit 110 via the transfer cylinder 124d. The recording medium 114 held on the impression cylinder 126d is subjected to the transparent UV ink so that the transparent UV ink head 146 overlaps the color ink on the recording medium 114 after the printing result of the printing unit 108 is read by the printing detection unit 144. Dropped.

  Subsequently, when the recording medium 114 held on the impression cylinder 126d passes through the position facing the first UV lamps 148a and 148b, the UV light is transparent on the recording medium 114 by the first UV lamps 148a and 148b. Irradiated to UV ink. Thereby, the transparent UV ink on the recording medium 114 has a high viscosity at the interface with the recording medium 114, and the penetration of the transparent UV ink into the recording medium 114 is suppressed.

  Further, after that, the recording medium 114 is transferred from the pressure drum 126 d to the paper discharge drum 150 and passes through a position facing the second UV lamp 156 when being conveyed to the paper discharge tray 152 by the paper discharge chain 154. At this time, the UV light is applied to the transparent UV ink on the recording medium 114 by the second UV lamp 156. As a result, the transparent UV ink on the recording medium 114 is cured from the surface to the inside.

  When the transparent UV ink is applied on the recording medium 114 in the transparent UV ink application unit 110, the layer thickness of the transparent UV ink after UV light irradiation is controlled by the transparent UV ink droplet ejection amount control unit 180a shown in FIG. The droplet ejection amount of the transparent UV ink head 146 is controlled so as to be 5 μm or less (preferably 3 μm or less, more preferably 1 to 3 μm). Therefore, a thin film layer (transparent UV coat layer) made of transparent UV ink is formed so as to cover the color ink on the recording medium 114 by the UV light irradiation by the first UV lamps 148a and 148b and the second UV lamp 156. A glossy image similar to offset printing is realized on the recording medium 114.

  The recording medium 114 on which the image has been formed in this manner is transported above the paper discharge table 152 by the paper discharge chain 154 and stacked on the paper discharge table 152.

  According to the image forming apparatus 100 configured as described above, after the color ink is deposited on the recording medium 114, the layer thickness of the transparent UV ink deposited so as to overlap the color ink on the recording medium 114 is the same. The transparent UV ink is ejected so as to be 5 μm or less (preferably 3 μm or less, more preferably 1 to 3 μm), and then the UV light is cured to cure the transparent UV ink. There is no need to fix by heat and pressure after droplet ejection, and a large-size recording medium can be fixed uniformly. Further, it is possible to stably fix an image even on thick paper or embossed paper.

  Further, since it is not necessary to fix by heat and pressure, the content of solid components such as thermoplastic resin latex in the color ink can be reduced, and the ejection reliability of the inkjet head can be improved. Further, since the volume of the ink aggregate is reduced, the solvent component (liquid component) on the recording medium can be efficiently removed.

  FIG. 10 is a schematic configuration diagram showing another example of an image forming apparatus to which the image forming method according to the present invention is applied. In FIG. 10, members that are the same as or similar to those in FIG.

  An image forming apparatus 200 shown in FIG. 10 is a double-sided machine that can print on both sides of a recording medium 114. The image forming apparatus 200 includes a sheet feeding unit 102, a first permeation suppression processing unit 104A, and a first process in order from the upstream side in the conveyance direction of the recording medium 114 (the direction from right to left in FIG. 10). Liquid applying unit 106A, first printing unit 108A, first transparent UV ink applying unit 110A, reversing unit 202 for reversing the recording surface (image forming surface) of recording medium 114, and second permeation suppression A processing unit 104B, a second processing liquid application unit 106B, a second printing unit 108B, a second transparent UV ink application unit 110B, and a paper discharge unit 112 are provided. That is, it corresponds to a configuration in which the permeation suppression processing unit 104, the treatment liquid application unit 106, the printing unit 108, and the transparent UV ink application unit 110 of the image forming apparatus 100 illustrated in FIG. It is.

  In the image forming apparatus 200 of this example, first, as in the image forming apparatus 100 shown in FIG. 6, the first permeation suppression process is performed on one surface of the recording medium 114 fed from the paper feeding unit 102. 104A, first treatment liquid application unit 106A, first printing unit 108A, and first transparent UV ink application unit 110A, permeation suppression processing, treatment liquid droplet ejection, color ink droplet ejection, transparent UV ink The droplets are sequentially ejected.

  After an image is formed on one surface of the recording medium 114 in this way, the recording medium 114 is transferred from the impression cylinder 126d of the first transparent UV ink application unit 110A to the reversal cylinder 204 via the transfer cylinder 206. When recording is performed, the recording medium 114 is reversed. Note that since a known mechanism may be applied as the reversing mechanism of the recording medium 114, a detailed description thereof will be omitted. Further, a second UV lamp 156 is provided at a position facing the surface of the reversing cylinder 204, and on the recording medium 114 together with the first UV lamps 148a and 148b of the first transparent UV ink application unit 110A. It plays the role of curing the transparent UV ink applied to the.

  The inverted recording medium 114 is transferred from the reversing cylinder 204 via the transfer cylinder 208 to the impression cylinder 126a of the second permeation suppression processing unit 104B. Then, with respect to the other surface of the recording medium 114, the second permeation suppression processing unit 104B, the second treatment liquid application unit 106B, the second printing unit 108B, and the second transparent UV ink application unit 110B are used. A permeation suppression process, a droplet of a treatment liquid, a droplet of colored ink, a droplet of transparent UV ink, and the like are sequentially performed.

  After the images are formed on both sides of the recording medium 114 in this way, the recording medium 114 is conveyed above the paper discharge table 152 by the paper discharge chain 154 and stacked on the paper discharge table 152.

[Application example]
The above-described image forming apparatuses 100 and 200 can also be used as a selective varnish coater. Although not shown, the image forming area on the recording medium 114 is provided with means for designating a varnished area (or a non-varnished area), and the layer thickness of the transparent UV ink is provided in the non-varnished area. The transparent UV ink is ejected so that the thickness of the transparent UV ink is 5 μm or less (preferably 3 μm or less, more preferably 1 to 3 μm). The transparent UV ink is ejected so as to be larger than the layer thickness of the UV ink (for example, larger than 5 μm). Specifically, a mode in which the droplet ejection amount (or the number of droplet ejection) of the transparent UV ink is made different between the region designated by varnish and the region not designated by varnish.

  Alternatively, the treatment liquid may be ejected onto the area designated by varnish. Since the wettability of the transparent UV ink is different between the image portion (the surface on which the color ink has been ejected and dried) and the non-image portion (the paper surface), the glossiness may be different between the image portion and the non-image portion. By applying the treatment liquid to the varnish designated area (image portion and non-image portion), the wettability of the surface on which the transparent UV ink is dropped can be made constant, and a uniform glossy feeling can be obtained. As the treatment liquid, an acidic liquid for aggregating ink, a thermoplastic resin latex solution, or the like is applicable.

  The image forming method and the image forming apparatus of the present invention have been described in detail above. However, the present invention is not limited to the above examples, and various improvements and modifications are made without departing from the gist of the present invention. Of course it is also good.

Schematic diagram showing an image forming method according to the present invention The figure which showed the arrangement state of the dot which consists of transparent UV ink The figure which showed the arrangement state of the dot which consists of transparent UV ink The figure which showed an example of the droplet amount table of transparent UV ink corresponding to the density of an image The figure which showed the other example of the droplet amount table of transparent UV ink corresponding to the density of an image 1 is a schematic configuration diagram showing an example of an image forming apparatus to which an image forming method according to the present invention is applied. Plane perspective view showing a configuration example of an ink head Sectional view along line 8-8 in FIG. FIG. 6 is a principal block diagram showing the system configuration of the image forming apparatus shown in FIG. Schematic configuration diagram showing another example of an image forming apparatus to which the image forming method according to the present invention is applied.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Color ink droplet ejection means, 12 ... Color ink, 14 ... Recording medium, 16 ... Transparent UV ink droplet ejection means, 18 ... Transparent UV ink, 20 ... UV light irradiation means, 100 ... Image forming apparatus, 102 ... Paper feed , 104 ... Permeation suppression processing unit, 106 ... Treatment liquid application unit, 108 ... Printing unit, 110 ... Transparent UV ink application unit, 112 ... Paper discharge unit, 114 ... Recording medium, 124a-124d ... Transfer cylinder, 126a-126d ... Impression cylinder, 128 ... Paper preheating unit, 130 ... Penetration inhibitor head, 132 ... Penetration inhibitor drying unit, 134 ... Paper preheating unit, 136 ... Processing liquid head, 138 ... Processing liquid drying unit, 140C, 140M, 140Y, 140K, 140R, 140G, 140B ... ink head, 142a, 142b ... solvent drying unit, 144 ... print detector, 146 ... transparent UV Nkuheddo, 148a, 148b ... first UV lamp, 150 ... delivery cylinder, 156 ... second UV lamp 200 ... image recording apparatus, 202 ... reversing unit, 204 ... reversing cylinder, 206, 208 ... transfer cylinder

Claims (16)

A step of ejecting colored ink on a recording medium;
A step of depositing a transparent UV ink so as to overlap the color ink deposited on the recording medium;
Irradiating the transparent UV ink with UV light,
An image forming method, wherein the layer thickness of the transparent UV ink after being irradiated with the UV light is 5 μm or less.   The image forming method according to claim 1, wherein the layer thickness of the transparent UV ink after being irradiated with the UV light is 3 μm or less.   2. The image forming method according to claim 1, wherein the layer thickness of the transparent UV ink after being irradiated with the UV light is 1 to 3 μm.   The image forming method according to claim 1, wherein the transparent UV ink is diluted with a solvent.   The image forming method according to claim 4, wherein a permeation suppression process is performed on the surface of the recording medium before the transparent UV ink is deposited on the recording medium.   5. The method according to claim 4, further comprising a step of drying the transparent UV ink deposited on the recording medium between the step of ejecting the transparent UV ink and the step of irradiating the UV light. The image forming method according to claim 5.   The image forming method according to claim 1, wherein the transparent UV ink is ejected onto the recording medium in a zigzag manner.   The image forming method according to claim 7, wherein the droplet ejection density of the transparent UV ink is higher in a direction orthogonal to the recording medium conveyance direction than in the recording medium conveyance direction.   The image forming method according to claim 1, wherein the color ink is a water-based ink.   Before the color ink is ejected onto the recording medium, a treatment liquid containing a component that aggregates the color material of the color ink is applied to at least a position where the color ink is ejected. The image forming method according to claim 9.   The image forming method according to claim 9, wherein the color ink includes a humectant that is compatible with the transparent UV ink.   The image forming method according to claim 1, wherein the color ink is a solvent-based ink.   The image forming method according to claim 1, wherein the transparent UV ink contains a cationic monomer.   14. The transparent UV ink droplet ejection amount table corresponding to the image density is provided, and the transparent UV ink droplet ejection amount is controlled in accordance with the image density. 2. The image forming method according to item 1.   The image forming method according to claim 14, further comprising: a droplet ejection amount table of transparent UV ink corresponding to halftone of the image, and controlling the droplet ejection amount of the transparent UV ink according to the halftone of image. Color ink droplet ejection means for ejecting color ink onto a recording medium;
Transparent UV ink droplet ejection means for depositing transparent UV ink so as to overlap the color ink droplets deposited on the recording medium;
UV light irradiation means for irradiating the transparent UV ink with UV light;
Control means for controlling the droplet ejection amount of the transparent UV ink by the transparent UV ink droplet ejection means so that the layer thickness of the transparent UV ink after irradiation with the UV light is 5 μm or less;
An image forming apparatus comprising:

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