JP5966427B2 - Printing apparatus and printing method - Google Patents

Description

  The present invention relates to a printing apparatus and a printing method.

  2. Description of the Related Art Printing apparatuses that perform printing using a liquid (for example, UV ink) that is cured by irradiation with light (a type of electromagnetic wave, for example, ultraviolet (UV)) are known. In such a printing apparatus, after a liquid is ejected from the nozzle of the head onto the medium, the dots formed on the medium are irradiated with light. By doing so, the dots are cured and fixed to the medium, so that it is possible to perform good printing even on a medium that hardly absorbs liquid (for example, see Patent Document 1).

JP 2000-158793 A

  A general UV ink contains a photopolymerization initiator (hereinafter also referred to as an initiator) as a catalyst. Then, when the UV ink is irradiated with UV, the initiator is activated, whereby polymerization of components such as monomers contained in the UV ink is started, and the ink is cured and fixed on the medium. This initiator has a slightly yellowish color, and is decolored by irradiating UV with energy of a predetermined size or more to change to a transparent color. On the contrary, a yellowish color remains at the UV irradiation amount of energy of a predetermined magnitude or less.

  In printing using ordinary UV ink, the ink is often cured by a UV irradiation amount of energy of a predetermined size or less. Therefore, the printed image may appear slightly yellowish. In particular, this yellow tint is conspicuous when printing is performed using a transparent UV ink that does not contain a pigment component. For example, transparent UV ink may be applied thickly on the image surface as an image glossiness adjustment or image coating material, so that the yellow color tends to be noticeable, and the image quality of the printed image appears to deteriorate. For this reason, it is difficult to print an image with good image quality by printing using transparent UV ink.

  An object of the present invention is to provide a printing apparatus capable of printing an image with good image quality using a transparent UV ink.

The main invention for achieving the above object is (A) a liquid discharge part for discharging a liquid containing a catalyst having a yellow component, which is a transparent liquid that is cured by irradiation with light, and (B ) includes an irradiation portion that irradiates the light, and a bleaching unit for irradiating the transparent liquid which is cured, the light decolorizing yellow component of the catalyst by being irradiated with (C) the light, The integrated energy of the light irradiated by the decoloring unit is a printing apparatus that is larger than the integrated energy of the light irradiated by the irradiation unit and larger than 1000 mJ / cm 2 .

  Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

1 is a block diagram illustrating an overall configuration of a printer. FIG. 2 is a schematic side view illustrating a configuration of the printer 1. FIG. 2 is a diagram for explaining the arrangement of a plurality of short heads on the lower surface of the yellow head and the arrangement of nozzles of the short heads. 2 is a cross-sectional view showing a structure of a yellow head 21. FIG. It is a figure explaining how a color image looks when a clear image is formed on a color image. It is a figure showing the relationship between UV irradiation amount and the change of the color of clear UV ink. It is a figure which shows an example of the table showing the relationship between the discharge amount of clear ink, and UV irradiation energy required for yellowing cancellation. It is a flowchart showing the flow of the printing operation in 1st Embodiment. 2 is a schematic side view illustrating a configuration of a printer 2. FIG. 10A to 10C are diagrams illustrating the operation of the decoloring process of the second embodiment.

  At least the following matters will become clear from the description of the present specification and the accompanying drawings.

(A) a transparent liquid that is cured by receiving light irradiation, the liquid discharging section discharging a liquid containing a catalyst having a yellow component, and (B) an irradiation section that irradiates the light; C) a decoloring unit that irradiates the transparent liquid cured by irradiating the light with light that decolorizes the yellow component of the catalyst, and (D) the number of times the light is irradiated by the decoloring unit. And a control unit that controls the printing apparatus.
According to such a printing apparatus, it is possible to print an image with good image quality using a transparent UV ink.

In this printing apparatus, the control unit emits light for decolorizing the yellow component of the catalyst according to the amount of the transparent liquid ejected from the liquid ejection unit to a predetermined area on the medium. It is desirable to determine the irradiation amount and change the number of times the light is irradiated from the decoloring unit based on the determined irradiation amount of the light.
According to such a printing apparatus, the UV irradiation energy necessary for eliminating the yellowing is accurately calculated for each discharge amount of the clear ink, and the UV irradiation is performed, so that waste of energy required for the UV irradiation is suppressed. It is possible to eliminate yellowing with high accuracy.

In this printing apparatus, the control unit decolorizes the amount of the transparent liquid ejected to a predetermined area on the medium and the yellow component of the transparent liquid ejected to the predetermined area. Therefore, it is desirable to have a table showing the relationship between the irradiation amount of light necessary for this purpose.
According to such a printing apparatus, the load on the control unit for calculating the irradiation energy of the bleaching UV can be reduced, and high-quality image printing can be performed more efficiently.

In this printing apparatus, the decoloring unit includes a plurality of light sources that emit light that decolorizes the yellow component of the catalyst, and the control unit is configured to discharge the transparent liquid that is discharged to a predetermined region on the medium. A predetermined number of light sources are selected from among the plurality of light sources based on the irradiation amount of light for decolorizing the yellow component of the catalyst determined according to the amount of the selected light sources. It is desirable to control the number of times the light is irradiated by irradiating the light respectively.
According to such a printing apparatus, since the image forming process and the decoloring process are performed as a series of printing operations while the medium is conveyed from the upstream side to the downstream side, the printing time can be extended and the printing process can be performed. High-quality images can be printed without degrading efficiency.

The printing apparatus includes a transport unit that transports the medium in a transport direction or a direction opposite to the transport direction, and the control unit controls the amount of the transparent liquid that is ejected to a predetermined region on the medium. Based on the irradiation amount of light for decoloring the yellow component of the catalyst determined accordingly, the light transported when the medium transported in the transport direction passes through the region facing the decoloring unit. After the irradiation, the number of times the light is irradiated by repeating irradiation of the light when the medium transported in the direction opposite to the transport direction passes through the region facing the decoloring unit. It is desirable to control.
According to such a printing apparatus, since the number of installed decolorizing UV light sources can be reduced, the cost of the printing apparatus can be kept low, and the configuration of the apparatus can be made compact.

In such a printing apparatus, a liquid that is cured by being irradiated with light and is cured by being irradiated with light by the liquid ejecting unit on an image formed by a liquid containing a color material. It is desirable that the transparent liquid is discharged.
According to such a printing apparatus, even when a clear image is formed on a color image for gloss adjustment or surface protection, deterioration of the image quality of the color image when the clear image is seen is less noticeable. .

  Further, (A) a transparent liquid that is cured by receiving light irradiation, the liquid containing a catalyst having a yellow component is discharged; (B) the light irradiation; and (C And irradiating the transparent liquid cured by irradiation with light with light that decolorizes the yellow component of the catalyst while controlling the number of irradiations. Become.

=== First Embodiment ===
<Basic configuration of printing apparatus>
As a form of a printing apparatus for carrying out the invention, an ink jet printer (printer 1) will be described as an example. The printer 1 is an image forming apparatus capable of forming (printing) an image on a medium by discharging a liquid (for example, ink) onto the medium such as paper, cloth, or a transparent film sheet. The liquid used for printing in the present embodiment is an ultraviolet curable ink (hereinafter also referred to as UV ink) that is cured by being irradiated with light (electromagnetic waves) such as ultraviolet light (hereinafter also referred to as UV). Details of the UV ink will be described later.

  The configuration of the printer 1 according to the first embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a block diagram illustrating the overall configuration of the printer 1. FIG. 2 is a schematic side view showing the configuration of the printer 1.

  As shown in FIG. 1, the printer 1 is communicably connected to a computer 110 that is an external control device. A printer driver is installed in the computer 110. The printer driver is a program for displaying a user interface on the display device of the computer 110 and converting image data output from the application program into print data. This printer driver is recorded on a recording medium (computer-readable recording medium) such as a flexible disk FD or a CD-ROM. Also, the printer driver can be downloaded to the computer 110 via the Internet. In addition, this program is comprised from the code | cord | chord for implement | achieving various functions.

  In order for the computer 110 to print an image on the printer 1, the print data converted from the image data according to the image to be printed is transmitted to the printer 1. The print data is data in a format that can be interpreted by the printer 1 and includes various command data and pixel data. The command data is data for instructing the printer 1 to execute a specific operation. This command data includes, for example, data such as command data indicating the transport amount of the printing medium. The pixel data is data related to pixels of an image to be printed.

  Here, a pixel is a unit element constituting an image, and an image is formed by arranging these pixels two-dimensionally. Pixel data in the print data is data (for example, gradation values) related to dots formed on a medium (for example, film S). The pixel data is composed of 2-bit data for each pixel. This 2-bit pixel data can represent one pixel in four gradations.

  The printer 1 includes a transport unit 10, a head unit 20, an irradiation unit 30, a decoloring unit 40, a detector group 50, and a controller 60 (see FIG. 1). The controller 60 controls each unit such as the transport unit 10 and the head unit 20 based on print data received from the computer 110 which is an external device, and prints an image on a medium. The situation in the printer 1 is monitored by the detector group 50, and the detector group 50 outputs the detection result to the controller 60. The controller 60 controls each unit based on the detection result output from the detector group 50.

<Transport unit 10>
The transport unit 10 is a medium transport unit that transports a medium (for example, a film S) in a predetermined direction (hereinafter also referred to as a transport direction). This conveyance unit 10 has the upstream conveyance roller 12A and the downstream conveyance roller 12B, and the conveyance drum 13 which conveys the elongate film S wound by roll shape on a surrounding surface (refer FIG. 2).

  When a transport motor (not shown) rotates, the upstream transport roller 12A and the downstream transport roller 12B rotate, and the transport drum 13 rotates. The film S along the peripheral surface of the transport drum 13 and pressed and supported by the upstream transport roller 12A and the downstream transport roller 12B is transported in the clockwise direction of FIG. 2 as the transport drum 13 rotates. That is, in the present embodiment, the conveyance direction of the medium is the rotation direction of the conveyance drum 13 (the direction of the circumferential surface of the drum). The medium transport speed (the rotational speed of the transport drum 13) by the transport unit 10 is controlled by the controller 60 so as to be a predetermined speed (almost constant speed).

  Outside the transport drum 13, a head unit 20, an irradiation unit 30, and a decoloring unit 40 are provided between the upstream transport roller 12 </ b> A and the downstream transport roller 12 </ b> B so as to face the peripheral surface of the transport drum. The film S transported by the rotation of the transport drum 13 is transported downstream in the transport direction while being printed in a printable region (region facing the head unit 20). That is, when the transport drum 13 transports the film S, the film S moves in the transport direction with respect to the head unit 20. The film S being transported is electrostatically attracted or vacuum attracted to the transport drum 13.

<Head unit 20>
The head unit 20 is a liquid ejection unit that ejects a liquid (UV ink in the present embodiment) onto the film S, and includes a plurality of heads (21 to 25) for each color of ink. The head unit 20 discharges UV ink onto the film S being conveyed, thereby forming UV ink dots on the film S and printing an image on the film S. The printer 1 of the present embodiment is a line printer, and the head unit 20 can form dots for the width of the film S at a time.

  In this embodiment, as shown in FIG. 2, the yellow head 21 that discharges yellow (Y) ink and the magenta (M) ink is discharged from the upstream side to the downstream side along the transport direction of the film S. There are provided color ink heads for each color, including a magenta head 22, a cyan head 23 for ejecting cyan (C) ink, and a black head 24 for ejecting black (K) ink. An image (color image) is formed by discharging each color ink of YMCK from these color ink heads. In addition to YMCK, a head that discharges UV ink of other colors such as white (W) may be provided, and an image may be printed using five or more colors of UV ink.

  On the downstream side of the black head 24 in the transport direction, a clear head 25 that discharges colorless and transparent clear (CL) ink is provided so as to face the peripheral surface of the transport drum 13. The clear ink (CL) is an ink used for adjusting the glossiness of a printed image, protecting the surface of the image, improving the color developability of the color ink, and generally contains or does not contain a color material or a pigment. Is a small amount of transparent ink. In the present embodiment, a clear image is formed by applying clear ink on the color image formed by the color ink heads (21 to 24), and the glossiness of the color image is adjusted.

In each head (21 to 25) of the head unit 20, a plurality of short heads are arranged in a staggered pattern along the width direction of the film S. FIG. 3 is a diagram for explaining the arrangement of a plurality of short heads on the lower surface of the yellow head 21 and the arrangement of the nozzles of the short heads. As shown in FIG. 3, the yellow head 21 is composed of three short heads 21A, 21B, and 21C. In each short head, a plurality of nozzles Nz are arranged at regular intervals (nozzle pitch) along the width direction of the film S. In the figure, the state in which the nozzles Nz are arranged in each head is indicated by two lines. By discharging yellow ink (Y) from the plurality of nozzles Nz, a plurality of yellow ink dots arranged in the width direction of the film S can be formed. Note that the number of short heads constituting one head is arbitrary, and four or more short heads may be used.
The other heads (22 to 25) other than the yellow head 21 have basically the same structure.

  A specific structure of each head (the above-described short head) will be described using the yellow head 21 as an example. FIG. 4 is a cross-sectional view showing the structure of the short head of the yellow head 21. The yellow head 21 includes a case 211, a flow path unit 212, and a piezo element group PZT. The case 211 houses the piezo element group PZT, and the flow path unit 212 is joined to the lower surface of the case 211. The flow path unit 212 includes a flow path forming plate 212a, an elastic plate 212b, and a nozzle plate 212c. In the flow path forming plate 212a, a groove portion that becomes the pressure chamber 212d, a through hole that becomes the nozzle communication port 212e, a through hole that becomes the common ink chamber 212f, and a groove portion that becomes the ink supply path 212g are formed. The elastic plate 212b has an island portion 212h to which the tip of the piezo element PZT is joined. An elastic region is formed by an elastic film 212i around the island portion 212h. The ink stored in the ink cartridge is supplied to the pressure chamber 212d corresponding to each nozzle Nz via the common ink chamber 212f. The nozzle plate 212c is a plate on which the nozzles Nz are formed. Heads other than yellow (short heads) basically have the same structure.

<Irradiation unit 30>
The irradiation unit 30 is an irradiation unit that irradiates light (UV) toward the ink landed on the film S. The UV ink dots formed on the film S are cured by receiving UV irradiation from the irradiation unit 30. In the printer 1, the irradiation unit 30 includes provisional curing irradiation units 31 to 34 that perform UV irradiation for temporary curing of UV ink, and a main curing irradiation unit 35 that performs UV irradiation for main curing. Two-stage curing is performed. Here, “temporary curing” is to cure the surface portion of the dots in order to suppress the flow of UV ink (dot spread) that has landed on the medium, or to prevent ink bleeding between dots. . Further, “main curing” is for completely curing the UV ink. Normally, the UV energy (UV irradiation amount) irradiated in “main curing” is larger than the UV energy (irradiation amount) irradiated in “temporary curing”.

The temporary curing irradiation units 31 to 34 are provided on the downstream side in the transport direction of the color ink heads 21 to 24, respectively (see FIG. 2), and temporarily cure the color ink dots formed by the upstream color ink heads. Irradiate UV to temporarily cure the dots. The temporary curing irradiation units 31 to 34 are each formed longer than the width of the film S to be printed. Further, a light emitting diode (LED) is used as a light source. The LED can easily change the irradiation energy by controlling the magnitude of the input current. The irradiation intensity of UV for temporary curing is, for example, about 10 to 100 mJ / cm ² .

The main curing irradiation unit 35 is provided on the downstream side in the transport direction of the clear head 25 (see FIG. 2), and is formed by the color image formed by the color ink heads 21 to 24 on the upstream side and the clear head 25. The clear image is irradiated with UV for main curing. As a result, the color image printed on the medium (film S) and the clear image (UV ink dots) formed on the color image are fully cured. The main curing irradiation section 35 is formed longer than the width of the film S to be printed. Further, an LED or a lamp (metal halide lamp, mercury lamp, etc.) is used as a light source. The irradiation intensity of UV for main curing is, for example, about 1000 mJ / cm ² .

  A temporary curing irradiation unit (not shown) for temporarily curing the clear ink dots may be provided between the clear head 25 and the main curing irradiation unit 35.

<Decolorization unit 40>
The decoloring unit 40 is a decoloring unit that decolorizes the yellow component of the catalyst contained in the clear (CL) UV ink by irradiating the clear image after the main curing with UV. Details of the catalyst and decolorization contained in the UV ink will be described later.

  The decoloring unit 40 includes a decolorizing irradiation unit 41 including first to n-th n decoloring light sources. For example, in FIG. 2, the decolorizing irradiation unit 41 includes five decoloring light sources. The number of decoloring light sources installed is the amount of UV irradiation by each decoloring light source and the amount of clear ink ejected by the clear head 25 during image printing (maximum clear ink amount that can be ejected per unit area). Is determined in consideration of As each decolorization light source, an optimal light source is selected according to the irradiation intensity (irradiation energy) of UV necessary for decolorization. For example, the above-described LED or lamp is used.

<Detector group 50>
The detector group 50 is for monitoring the status of the printer 1. The detector group 50 includes a rotary encoder, an optical sensor, and the like (all not shown). The rotary encoder detects the rotation amount of the transport rollers 12A and 12B or the transport drum 13. The optical sensor detects the leading end position of the film S (position of the printing end portion on the downstream side in the transport direction), the rear end position (position of the printing end portion on the upstream side in the transport direction), and the like according to the situation.

<Controller 60>
The controller 60 is a control unit for controlling the printer 1. The controller 60 includes an interface unit 61, a CPU 62, a memory 63, and a unit control circuit 64.

  The interface unit 61 transmits and receives data between the computer 110 that is an external device and the printer 1. The CPU 62 is an arithmetic processing device for performing overall control of the printer 1. The memory 63 is for securing an area for storing a program of the CPU 62, a work area, and the like, and is configured by a storage element such as a RAM or an EEPROM. The CPU 62 controls each unit such as the transport unit 10 and the decoloring unit 40 via the unit control circuit 64 in accordance with a program stored in the memory 63.

<Overview of printing operation>
An operation for printing an image using the printer 1 will be briefly described. When the printer 1 of the present embodiment starts printing, the medium is previously pressed along the circumferential surface of the transport drum 13 and supported by the upstream transport roller 12A and the downstream transport roller 12B.

  When the print data is received from the computer 110, the controller 60 rotates the transport drum 13 at a constant speed to transport the medium, while intermittently passing the UV ink while the medium passes through the area facing the head unit 20. Discharge to form dots. That is, the dot formation process and the medium transport process are performed simultaneously. As a result, a dot row composed of a plurality of UV ink dots along the medium width direction is formed on the medium, and an image is formed by arranging a plurality of dot rows in the transport direction. Then, the formed dot row is irradiated with the UV for temporary curing from the irradiation unit for temporary curing of the irradiation unit 30, respectively, and the color ink dots of each color are temporarily cured.

  Although details will be described later, in this embodiment, after a color image is formed with color ink dots (YMCK), a clear image with clear ink dots (CL) is formed on the color image. Thereafter, UV for main curing is irradiated from the main curing irradiation unit 35 to the color image and the clear image, and the ink dots are finally cured, whereby the ink dots are fixed on the medium, and the image is printed.

=== About printing using UV ink ===
<Composition of UV ink>
First, the UV ink used for printing will be described. The UV ink is an ink containing an ultraviolet curable resin, and is cured by undergoing a photopolymerization reaction in the ultraviolet curable resin when irradiated with UV. The UV ink used in this embodiment contains a polymerizable compound, a catalyst such as a photopolymerization initiator, and other additives.

  A polymerizable compound is a compound capable of undergoing a polymerization reaction when irradiated with light. Specific examples of the polymerizable compound include various (meth) acrylate monomers, various (meth) acrylate oligomers, various vinyl monomers, various vinyl ether monomers, and the like.

  A photopolymerization initiator (hereinafter also referred to as an initiator) is a catalyst having a function of efficiently initiating polymerization of a polymerizable compound when irradiated with light. When the UV ink is irradiated with UV, the initiator is activated to form a reaction start point. Then, the reaction start point activates double bonds such as oligomers, the oligomers are bonded to each other, and finally the ink is changed from liquid to solid by polymerizing in a network.

  Further, the UV ink may contain additives such as a color material (pigment, dye, etc.), a solvent, a surfactant, a polymerization inhibitor, and a polymerization accelerator.

<About yellowing by clear UV ink>
Since the initiator contained in the UV ink usually has a yellow component, the UV ink often has a slightly yellowish color. In the color (YMCK) UV ink, the yellow color of the initiator is not noticeable because the color material contained is dark. On the other hand, a clear (CL) UV ink that does not contain a coloring material may cause problems during printing because the yellow component of the initiator tends to be noticeable and the color is not completely colorless and transparent.

  FIG. 5 is a diagram illustrating how a color image looks when a clear image is formed on the color image. The figure shows a case where a clear image is formed on a color image (shaded portion) formed on a medium as viewed from the side. The figure on the left is when the clear image is thinly formed (clear image thickness = h1), and the figure on the right is when the clear image is thick (clear image thickness = h2 (h1 <h2). ) And). A plurality of black circles shown in the clear image represents an initiator (catalyst) contained in the clear UV ink.

  When adjusting the glossiness of an image using clear UV ink, if the clear image is thinly formed, the amount of clear ink ejected per unit area is small, so it is included in the unit area. The amount of initiator is reduced (left side of FIG. 5). In this case, since the yellow component of the initiator is small, yellowing of the image is not noticeable.

  On the other hand, when printing an image having a high glossiness, the amount of clear ink ejected per unit area increases in order to form a clear image thick. In this case, the amount of the initiator contained in the unit area is also increased (the diagram on the right side of FIG. 5). That is, the yellow component becomes dark and yellowing tends to be noticeable. Therefore, the color image formed under the clear image looks strongly yellow when viewed through the clear image. As a result, the entire image is recognized as yellowish, and the image quality seems to deteriorate. In this specification, such a phenomenon that an image looks yellow with clear ink is called “yellowing” of the image.

<Method of eliminating yellowing>
As a method of eliminating yellowing of an image, there is a method of forming a thin clear image as shown in the left side of FIG. That is, the yellow component can be made inconspicuous by reducing the amount of clear ink ejected per unit area and making the clear image layer thin. However, in order to adjust the glossiness of the image and protect the surface of the image, the clear image is often formed to have a certain thickness during actual printing. Therefore, it is difficult to make the yellowing of the image inconspicuous by forming a thin clear image.

As another method of eliminating the yellowing of the image, there is a method of irradiating the clear image with UV with an energy of a predetermined size or more to change the yellow component of the initiator transparently. The yellow component contained in the initiator gradually changes its color by receiving UV irradiation, and finally changes to a color almost transparent. That is, decolorization is performed according to the amount of UV irradiated. However, in order to decolorize the yellow component of the initiator to a color that is nearly transparent, an energy larger than the UV irradiation energy (for example, about 1000 mJ / cm ² ) irradiated during the main curing is required.

  FIG. 6 shows a relationship between the UV irradiation amount and the color change of the clear UV ink. The vertical axis in FIG. 6 represents the b * value of the L * a * b * color system, and the horizontal axis represents the a * value. Therefore, the yellow component becomes stronger toward the upper side of the graph, and the blue component becomes stronger toward the lower side. Further, the red component becomes stronger toward the right side of the graph, and the green component becomes stronger toward the left side.

In FIG. 6, first, a clear image is formed by ejecting clear UV ink uniformly onto a medium with an ejection amount per unit area of 21.8 ng. Then, UV for main curing is irradiated from the irradiation unit 35 for main curing, and the clear image is finally cured. Subsequently, the clear image after the main curing is subjected to UV irradiation a plurality of times with a predetermined amount of energy (for example, 250 mJ / cm ² ), and the clear layer is color-measured for each number of irradiations. Measure the value. The measured data is plotted with white circles in the graph. That is, each white circle in the graph represents the color of the clear image corresponding to the total number of UV irradiations. Thereby, the amount of change in the color of the clear ink according to the number of times of UV irradiation (that is, the UV integrated irradiation amount) can be known.

  A white square plot in the graph represents a value obtained by measuring the color of the medium itself. In FIG. 6, the b * value of the medium is −5.7, which indicates that the medium has originally bluish color.

  The clear image after the main curing becomes b * = − 1.8 by the first UV irradiation. In this state, the yellow component is stronger than the b * value (= −5.7) of the medium itself. The b * value gradually decreases with the number of subsequent UV irradiations, and converges to a substantially constant value (b * ≈−5.8) by about 15 UV irradiations. At this time, if the difference between the b * value of the medium itself and the b * value of the clear image is Δb, | Δb | = 0.1, and the color difference between the two becomes very small. That is, the yellow component of the clear image is almost decolored and the yellowing is eliminated.

Here, when a dose of UV irradiation energy 250 mJ / cm ^2, the cumulative energy of 15 times by UV irradiation is ^{15 × 250 = 3750mJ / cm 2} . That is, in the example of FIG. 6, it can be understood that yellowing of the clear image can be eliminated by performing UV irradiation with energy of 3750 mJ / cm ² (integrated energy amount). This energy amount is considered to vary depending on the thickness of the clear image and the amount of the initiator (yellow component) contained in the UV ink, so that the printing condition (for example, the clear ink discharged per unit area) Experiments are performed for each amount and type of clear ink. Then, the energy necessary for eliminating yellowing may be stored in a storage medium such as the memory 63 in a table for each condition. FIG. 7 shows the amount of clear ink ejected to a predetermined area on the medium (representing the thickness of the clear image to be formed) and the UV irradiation energy necessary for decolorizing the yellow component of the clear ink. An example of the table showing the relationship is shown. By determining the UV irradiation amount based on such a table, it becomes easy to eliminate yellowing with high accuracy.

=== Printing Operation of the First Embodiment ===
An operation when printing an image using the printer 1 will be specifically described.

  FIG. 8 is a flowchart showing the flow of the printing operation in the first embodiment. In the first embodiment, an image is printed through steps S101 to S104.

  First, a color image is printed (S101). In color image printing, each color ink (YMCK) is ejected onto the medium conveyed at a constant speed by the conveyance unit 10 using the color ink heads 21 to 24, thereby forming color ink dots on the medium. Form. The formed color ink dots are temporarily cured by sequentially irradiating the UV for temporary curing using the temporary curing irradiation units 31 to 34 disposed on the downstream sides of the color ink heads 21 to 24, respectively. As a result, a color image made of each color ink is printed on the medium.

  After the color image is formed, the clear image is printed by discharging clear ink (CL) from the clear head 25 onto the color image (S102). As described above, when a clear image is formed for adjusting the glossiness of a printed image, the glossiness may be adjusted by the user's selection. For example, high gloss, medium gloss, low gloss, and matte gloss levels can be selected, and the user selects a desired gloss level via a user interface (not shown) at the start of printing. The controller 60 adjusts the amount of clear ink ejected for each predetermined area in accordance with the selected glossiness, and ejects clear ink from the clear head 25 to print a clear image. If the discharge amount of the clear ink in a region where the high gloss mode is selected is Xng, the discharge amount of the clear ink is adjusted to 0.6 Xng in the medium gloss mode, 0.3 Xng in the low gloss mode, and the like. Note that after the clear image is printed, the temporary curing UV may be irradiated to temporarily cure the clear ink dots.

  After the color image and the clear image are formed, the main curing UV is irradiated by the main curing irradiation unit 35 to perform the main curing of the image (ink dots) (S103). As a result, the image is fixed on the medium. However, at this stage, the printed image is yellowed due to the yellow component of the initiator contained in the clear ink (see FIG. 5).

  In order to eliminate yellowing, the yellow component of the image is decolored by irradiating UV from the decoloring unit 40 (S104). The controller 60 determines the number of times of UV irradiation according to the amount of clear ink ejected to a predetermined area on the medium, and sequentially uses light sources selected from n light sources provided in the decoloring unit 40. UV irradiation is performed.

  First, the amount of clear ink ejected to a predetermined area is calculated based on the glossiness set in S102. Note that the discharge amount of the clear ink may not be uniform depending on the location, for example, the clear ink is partially discharged. In such a case, the maximum value of the clear ink amount ejected for each predetermined region or the average value of the ejected clear ink amount is used. Then, the data of UV irradiation energy required for decoloring obtained by the above-described experiment is referred to, and UV irradiation energy Es (UV irradiation energy required for decoloring) corresponding to the discharge amount of the clear ink is determined. At this time, a table (for example, the table of FIG. 7) in which the data of the UV irradiation energy Es corresponding to the discharge amount of the clear ink is prepared in advance, and the UV irradiation energy Es may be determined based on the table. Since the processing in the CPU 62 is reduced by using the data table, printing can be performed more efficiently.

  The total UV irradiation energy using the first light source to the m-th light source (however, m ≦ n) among the n light sources provided in the decoloring irradiation unit 41 is used to be Es or more. The number of light sources (m) is determined, and UV irradiation is performed using the m light sources. That is, the number of times of UV irradiation is controlled by adjusting the number of light sources that perform UV irradiation.

Note that the bleaching unit 40 irradiates the bleaching UV continuously from the m light sources used for a predetermined time to the medium conveyed at a constant speed. Therefore, the total amount of UV irradiation energy (mJ / cm ² ) can be accurately calculated by adjusting the irradiation time and the number of light sources used.
Thereby, the yellow component of a clear image can be decolored and the yellowing of an image can be eliminated.

<Modification>
As described with reference to FIG. 6, the degree of yellowing changes according to the integrated UV irradiation amount. Therefore, the degree of yellowing elimination (degree of decolorization) may be set.

  For example, when the image may appear yellow depending on the use of the print image, the degree of decolorization is set to be small, and the number of times of UV irradiation in the decolorization step (S104) is reduced (the integrated UV irradiation energy is reduced). To do). The setting of the degree of decolorization is performed by the controller 60 changing the magnitude of the UV irradiation energy Es required for decoloration, for example, by the user selecting it via a user interface or the like. Thereby, it becomes possible to reduce the energy consumption of UV irradiation in a decoloring process.

  Also, yellowing is particularly problematic in printing using clear ink when there is a large color difference between the area where the clear ink is ejected and the surrounding area. For example, when clear ink is ejected only in a partial area on the medium, yellowing is particularly easily recognized in the partial area. On the other hand, when clear ink is ejected to all areas on the medium, yellowing occurs uniformly over the entire image, and it may be difficult to recognize yellowing. Therefore, the degree of decolorization may be changed according to the size (discharge range) of the clear ink discharge area. For example, when the clear ink is ejected only in a part of the area, decolorization is performed by the method described in the first embodiment, and when the clear ink is ejected over the entire area of the medium, By reducing the irradiation amount or omitting the decoloring step itself, the energy consumption of UV irradiation can be reduced.

<Effects of First Embodiment>
In the first embodiment, a clear (CL) UV ink is applied on a color image, and then UV is irradiated to fully cure the ink dots to form a clear image. Since the formed clear image appears yellowish due to the yellow component of the catalyst contained in the UV ink, the image quality appears to deteriorate. Thus, the yellow component of the clear image is decolored by irradiating the image with a predetermined number of UVs using a decoloring unit. As a result, yellowing that occurs when an image is printed using clear UV ink can be made inconspicuous, and an image with good image quality can be printed.

  Furthermore, by controlling to perform UV irradiation an appropriate number of times according to the discharge amount of the clear ink (that is, the thickness of the clear image), waste of energy can be suppressed and yellowing can be accurately eliminated. Also, since the image forming process and the decoloring process are performed as a series of printing operations while the printing medium is conveyed from the upstream side to the downstream side, the printing time is prolonged and the efficiency of the printing process is deteriorated. And high-quality images can be printed.

=== Second Embodiment ===
In the second embodiment, the decoloring unit 40 prints an image using the printer 2 having only one decoloring light source. In this embodiment, since the clear image is decolored using one decoloring light source, the number of times of UV irradiation is adjusted by controlling the operation of the transport unit 10.

<Configuration of Printer 2>
FIG. 9 is a schematic side view showing the configuration of the printer 2. The basic configuration of the printer 2 is substantially the same as that of the printer 1 described above, but is different from the printer 1 in that the decoloring unit 40 includes a decoloring irradiation unit 42 having a single decoloring light source. In the printer 2, the rotation directions of the transport rollers 12 </ b> A and 12 </ b> B and the transport drum 13 of the transport unit 10 can be freely changed. That is, the conveyance direction of the medium can be changed. In the following description, the clockwise conveyance in FIG. 9 is referred to as “forward direction”, and the counterclockwise conveyance is referred to as “reverse direction”.

<Printing Operation of Second Embodiment>
An operation when printing an image using the printer 2 will be described. The basic flow of the printing operation is the same as in the first embodiment. That is, after passing through a color image printing process, a clear image printing process, and an ink dot main curing process, a decoloring process is performed (see FIG. 8). In the second embodiment, the operation in the decoloring step is different from that in the first embodiment.

(Operation of decoloring process)
FIGS. 10A to 10C are diagrams for explaining the operation of the decoloring process of the second embodiment. For convenience of explanation, in FIG. 10, the conveyance of the medium by the conveyance drum 13 is described as conveyance in the linear direction.

(FIG. 10A)
The medium on which the color image and the clear image (image A) are formed is transported in the forward direction by the transport drum 13 at a constant speed. Then, when the image A passes through the region facing the decoloring unit 40 (the lower part of the decoloring unit 40 in FIG. 10A), it receives UV irradiation from the light source (decoloring irradiation unit 42) provided in the decoloring unit 40. Part of the yellow component of the initiator contained in the UV ink is decolorized. This operation is the first UV irradiation. The conveyance of the medium (forward conveyance) is continued until the image A passes through the region facing the decoloring unit 40, and the first UV irradiation is completed.

(FIG. 10B)
After the first UV irradiation is completed, the controller 60 switches the rotation direction of the transport drum 13 and transports the medium in the reverse direction. As a result, the image A passes through the region facing the decoloring unit 40 again. At this time, UV irradiation is again performed from the decoloring irradiation unit 42, and a part of the yellow component is further decolorized. This operation is the second UV irradiation. The conveyance of the medium in the reverse direction is continued until the image A passes through the region facing the decoloring unit 40, and the second UV irradiation is completed.

(FIG. 10C)
After the second UV irradiation is completed, the controller 60 switches the rotation direction of the transport drum 13 again and transports the medium in the forward direction. Then, when the image A passes through the region facing the decoloring unit 40, UV is irradiated from the decoloring irradiation unit 42, and a part of the yellow component is further decolored (third UV irradiation).

  These operations are repeated a predetermined number of times, and the UV is irradiated until the accumulated energy of UV irradiated to the image A becomes greater than or equal to the UV irradiation energy Es required for decolorization. As a result, the yellow component of the clear image is almost decolorized and the yellowing is eliminated. The process of calculating the UV irradiation energy Es according to the discharge amount of the clear ink and determining the number of times of UV irradiation based on the calculated value is substantially the same as the operation described in the first embodiment. That is, the number of times of UV irradiation capable of obtaining energy equal to or higher than the UV irradiation energy Es is calculated based on the amount of energy by one UV irradiation.

  The above-described printing operation has been described for the case where the decoloring unit 40 has one light source (printer 2). However, the printing operation can also be applied to the case where the decoloring unit 40 has a plurality of light sources.

<Effects of Second Embodiment>
In the second embodiment, the yellow component of the clear image is decolored by irradiating an image formed with UV ink a predetermined number of times using a decoloring unit. At this time, by controlling the number of times of UV irradiation while switching the medium conveyance direction, the integrated irradiation amount of UV irradiated on the clear image is adjusted, and therefore, decolorization can be performed with high accuracy.

  Since the number of light sources of the decoloring unit can be reduced, the cost of the printing apparatus can be kept low, and the configuration of the apparatus can be made compact.

=== Other Embodiments ===
Although a printer or the like as one embodiment has been described, the above embodiment is for facilitating the understanding of the present invention, and is not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<About printing devices>
In the above-described embodiment, the printing apparatus that discharges ink while transporting the medium by rotating the transport drum has been described. However, the present invention is not limited to this. For example, a printing apparatus of a type that performs printing while transporting a medium in a plane, or a serial type printing apparatus that mounts a head unit on a carriage and performs printing while moving the carriage may be used.

<About the head unit 20>
In the above-described embodiment, an example of printing an image using four color inks of YMCK and clear (CL) ink has been described. However, the present invention is not limited to this. For example, printing may be performed using inks of other colors such as light cyan (LC), light magenta (LM), and white (W).

  The arrangement of the color ink heads in the head unit 20 is arranged in the order of YMCK from the upstream side in the transport direction, but is not limited to this. For example, the order of the arrangement of the yellow head (Y) and the magenta head (M) may be switched, or two black heads (K) are arranged. It is good also as a different structure from a head.

<About piezo elements>
In each of the above-described embodiments, the piezo element PZT is exemplified as an element that performs an operation for discharging a liquid. However, other elements may be used. For example, a heating element or an electrostatic actuator may be used.

<About the printer driver>
In each of the embodiments described above, the printer driver processing is performed by the computer 110 (PC). However, the printer driver may be installed in the controller 60 and the printer driver processing may be performed by the printer itself.

1 printer,
10 transport unit, 12A upstream transport roller, 12B downstream transport roller,
13 Conveying drum,
20 head units, 21 yellow heads,
211 case, 212 flow path unit, 212a flow path forming plate, 212b elastic plate,
212c nozzle plate, 212d pressure chamber, 212e nozzle communication port,
212f common ink chamber, 212g ink supply path, 212h island part,
212i elastic membrane,
22 magenta head, 23 cyan head, 24 black head,
25 Clearhead,
30 irradiation units, 31-34 provisional curing irradiation units, 35 curing curing units,
40 Decoloring unit, 41 Decolorizing irradiation unit, 42 Decoloring irradiation unit,
50 detector groups,
60 controller, 61 interface, 62 CPU, 63 memory,
64 unit control circuit,
110 computers,
S film

Claims (7)

(A) a liquid discharge part that is a transparent liquid that is cured by being irradiated with light, and that discharges a liquid containing a catalyst having a yellow component;
(B) an irradiation unit for irradiating the light;
(C) a decoloring unit that irradiates the transparent liquid cured by irradiating the light with light that decolorizes the yellow component of the catalyst ;
Equipped with a,
A printing apparatus in which an integrated energy of light irradiated by the decoloring unit is larger than an integrated energy of light irradiated by the irradiation unit and larger than 1000 mJ / cm 2 . The printing apparatus according to claim 1,
A controller for controlling the number of times the light is emitted by the decoloring unit;
The controller is
In accordance with the amount of the transparent liquid discharged from the liquid discharge unit to a predetermined area on the medium, determine an integrated energy of light for decolorizing the yellow component of the catalyst,
The printing apparatus, wherein the number of times the light is emitted from the decoloring unit is changed based on the determined integrated energy of the light. The printing apparatus according to claim 2,
The controller is
An amount of the transparent liquid discharged to a predetermined area on the medium;
A printing apparatus, comprising: a table representing a relationship between an accumulated energy of light necessary for decoloring a yellow component of the transparent liquid ejected to the predetermined region. The printing apparatus according to claim 2 or 3,
The decolorization unit has a plurality of light sources that emit light that decolorizes the yellow component of the catalyst,
The controller is
Based on the accumulated energy of light for decolorizing the yellow component of the catalyst, determined according to the amount of the transparent liquid discharged to a predetermined area on the medium,
By selecting a predetermined number of light sources from among the plurality of light sources and irradiating the light from each of the selected predetermined number of light sources,
A printing apparatus that controls the number of times the light is irradiated. (A) a liquid discharge part that is a transparent liquid that is cured by being irradiated with light, and that discharges a liquid containing a catalyst having a yellow component;
(B) an irradiation unit for irradiating the light;
(C) a decoloring unit that irradiates the transparent liquid cured by irradiating the light with light that decolorizes the yellow component of the catalyst;
(D) a control unit that controls the number of times the light is emitted by the decoloring unit;
(E) a conveying unit for conveying the conveying direction or conveying direction opposite to the medium body,
With
The controller is
In accordance with the amount of the transparent liquid discharged from the liquid discharge unit to a predetermined area on the medium, determine an integrated energy of light for decolorizing the yellow component of the catalyst,
Based on the determined integrated energy of the light, change the number of times light is emitted from the decoloring unit,
Based on the accumulated energy of light for decolorizing the yellow component of the catalyst, determined according to the amount of the transparent liquid discharged to a predetermined area on the medium,
The medium transported in the transport direction is irradiated with the light when passing through a region facing the decoloring unit, and then the medium transported in a direction opposite to the transport direction faces the decoloring unit. By irradiating the light as it passes through the region,
A printing apparatus that controls the number of times the light is irradiated. The printing apparatus according to any one of claims 1 to 5,
On an image formed by a liquid that is cured by receiving light and contains a coloring material,
The printing apparatus, wherein the transparent liquid that is cured by being irradiated with light is discharged by the liquid discharge unit. (A) discharging a liquid containing a catalyst having a yellow component, which is a transparent liquid that is cured by irradiation with light;
(B) irradiating the light from the irradiation unit ;
(C) irradiating the transparent liquid cured by being irradiated with light from a decoloring unit with light that decolorizes the yellow component of the catalyst;
Have
A printing method in which an integrated energy of light irradiated by the decoloring unit is larger than an integrated energy of light irradiated by the irradiating unit and larger than 1000 mJ / cm ² .

Images