JP2013147000A - Printing apparatus and printing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve filling of a lower layer image by an ink for printing an upper layer image.SOLUTION: A printing apparatus using an ink cured by irradiation with light controls the light of first energy to be irradiated per unit area of a main image when a first mode is set in which an auxiliary image is not printed but the main image is printed on a medium. The printing apparatus controls the light of second energy lower than the first energy to be irradiated per unit area of a lower layer image among the auxiliary image and the main image before printing an upper layer image among the auxiliary image and the main image when a second mode is set in which the auxiliary image and the main image are overlapped and printed on the medium.

Description

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

  Examples of the printing apparatus include an ink jet printer (hereinafter referred to as a printer) that prints an image on a medium by ejecting ink droplets from a nozzle provided in a head toward a medium such as paper. Some printers use a photocurable ink that is cured by irradiation with light such as ultraviolet rays (see, for example, Patent Document 1). With such a printer, it is possible to print an image on a medium made of plastic or metal that does not have an ink receiving layer.

JP 2009-208286 A

  Also, some printers that use light curable inks, for example, print a color image superimposed on a white image with white ink. However, if color ink droplets are ejected onto a white image that has been completely cured, the color ink droplets will flow on the white image and the adjacent color ink droplets will be connected or separated. . Then, the filling of the white image with the color ink is worsened, and a large amount of the color ink has to be ejected as compared with the case where the color image is directly printed on the medium.

  Accordingly, an object of the present invention is to improve the filling of the lower layer image (for example, white image) with the ink for printing the upper layer image (for example, color image).

The main invention for solving the above problems is: (A) a first head for printing a main image, which discharges ink that is cured by light irradiation; and (B) an auxiliary image that overlaps the main image. A second head that ejects ink that is cured by irradiation with light; (C) an irradiation unit that emits light; and (D) the auxiliary image is printed without printing the main image. When the first mode for printing on the medium is set, control is performed so that light of the first energy is emitted per unit area of the main image, and the auxiliary image and the main image are overlapped on the medium. When the second mode for printing is set, before printing the upper layer image of the auxiliary image and the main image, per unit area of the lower image of the auxiliary image and the main image, Lower than the first energy And a control unit which light energy is controlled so as to irradiate a printing apparatus characterized by comprising (E).
Other features of the present invention will become apparent from the description of this specification and the accompanying drawings.

1 is a block diagram illustrating an overall configuration of a printer. It is a schematic sectional drawing of a printer. 3A is a diagram illustrating an image printed in the single mode, FIG. 3B is a diagram illustrating an image printed in the front printing mode, and FIG. 3C is a diagram illustrating an image printed in the reverse printing mode. It is. 4A to 4C are diagrams illustrating a printing method of a comparative example. It is a figure explaining the printing method of the surface printing mode of this embodiment. 3 is a flowchart illustrating a printing method according to the first exemplary embodiment. It is a table | surface which shows the evaluation result which changed the ratio of the irradiation energy at the time of front printing and back printing mode with respect to the time of single mode. 10 is a flowchart illustrating a printing method according to the second exemplary embodiment.

=== Summary of disclosure ===
At least the following will become apparent from the description of the present specification and the accompanying drawings.

That is, (A) ink for printing a main image, which discharges ink that is cured by light irradiation, and (B) ink for printing an auxiliary image that overlaps the main image, the light A second head that discharges ink that is cured by irradiation, (C) an irradiation unit that irradiates the light, and (D) a first mode that prints the main image on a medium without printing the auxiliary image. If so, the second mode for controlling the main image to be irradiated with light of the first energy and printing the auxiliary image and the main image on the medium is set. A second energy lower than the first energy per unit area of a lower layer image of the auxiliary image and the main image before printing an upper layer image of the auxiliary image and the main image. The light of A control unit for controlling the a printing apparatus characterized by comprising (E).
According to such a printing apparatus, filling of the lower layer image with the ink for printing the upper layer image can be improved.

In this printing apparatus, the control unit may irradiate the lower layer image in the second mode, rather than the irradiation intensity of the light that the irradiation unit irradiates the main image in the first mode. Decreasing the irradiation intensity of the light.
According to such a printing apparatus, the amount of light irradiated per unit area of the lower layer image in the second mode is higher than the energy (first energy) of light irradiated per unit area of the main image in the first mode. Energy (second energy) can be lowered.

In this printing apparatus, the irradiation unit irradiates the image with the light while relatively moving in a predetermined direction with the medium on which the image is printed, and the control unit is configured to irradiate the irradiation in the first mode. A relative movement speed between the irradiation section and the medium in the second mode is made faster than a relative movement speed between the section and the medium.
According to such a printing apparatus, the amount of light irradiated per unit area of the lower layer image in the second mode is higher than the energy (first energy) of light irradiated per unit area of the main image in the first mode. Energy (second energy) can be lowered.

In this printing apparatus, the second energy is 45% or more and 55% or less of the first energy.
According to such a printing apparatus, it is possible to ensure the peelability of the lower layer image while improving the filling of the lower layer image with the ink for printing the upper layer image.

In addition, there is a first mode in which a main image is printed on a medium without printing the auxiliary image, and a second mode in which the auxiliary image and the main image are superimposed and printed on the medium, and is cured by light irradiation. In the printing method of printing the auxiliary image and the main image with the ink to be used, and when the first mode is set, after printing the main image on the medium, per unit area of the main image, When the second mode is set by irradiating light of the first energy, the lower image of the auxiliary image and the main image is printed on the medium, and per unit area of the lower image, After irradiating light having a second energy lower than the first energy, an upper layer image of the auxiliary image and the main image is printed over the lower layer image, and the upper layer image is irradiated with light. And comprising A printing method characterized and.
According to such a printing method, filling of the lower layer image with the ink for printing the upper layer image can be improved.

=== Printing system ===
The embodiment will be described with reference to an example of a printing system in which a “printing apparatus” is an inkjet printer (hereinafter referred to as a printer) and a printer and a computer are connected.
FIG. 1 is a block diagram illustrating the overall configuration of the printer 1, and FIG. 2 is a schematic cross-sectional view of the printer 1 viewed from a direction that intersects the conveyance direction of the medium S.
The printer 1 of the present embodiment prints an image on a medium S (for example, paper, cloth, plastic film, etc.) using ultraviolet curable ink (photo curable ink) that is cured by irradiating ultraviolet (light). To do. The ultraviolet curable ink (UV ink) is an ink containing an ultraviolet curable resin, and is cured by a photopolymerization reaction occurring in the ultraviolet curable resin when irradiated with ultraviolet rays.

  The computer 60 is communicably connected to the printer 1 and outputs print data for causing the printer 1 to print an image to the printer 1 by a printer driver installed therein. The printer driver is recorded on a recording medium such as a CD-ROM or can be downloaded to the computer 60 via the Internet.

  The controller 10 is a control unit for controlling the printer 1, and includes an interface unit 11, a CPU 12, a memory 13, and a unit control circuit 14. The interface unit 11 transmits and receives data between the computer 60 that is an external device and the printer 1. The CPU 12 is an arithmetic processing device for performing overall control of the printer 1. The memory 13 is for securing an area for storing a program of the CPU 12, a work area, and the like. The CPU 12 controls each unit via the unit control circuit 14 in accordance with a program stored in the memory 13. Further, the detector group 50 monitors the situation in the printer 1, and the controller 10 controls each unit based on the detection result.

  The transport unit 20 is for transporting the medium S in the transport direction, and includes a transport belt 21 and transport rollers 22a and 22b. As the motor (not shown) rotates, the transport rollers 22a and 22b rotate and the transport belt 21 rotates, whereby the medium S on the transport belt 21 is transported downstream in the transport direction. The medium S faces the heads 31 and 32 and the irradiation units 41 and 42 when being conveyed on the conveyance belt 21.

  The head unit 30 is for ejecting UV ink onto the medium S, and has an upstream head 31 positioned on the upstream side in the transport direction and a downstream head 32 positioned on the downstream side in the transport direction. A large number of nozzle openings, which are UV ink ejection openings, are provided on the lower surfaces of the heads 31 and 32, and nozzle arrays are formed for each color of ink to be ejected. Specifically, on the lower surface of each head 31, 32, a nozzle row for ejecting black ink K, a nozzle row for ejecting cyan ink C, a nozzle row for ejecting magenta ink M, a nozzle row for ejecting yellow ink Y, A nozzle row for discharging the white ink W is formed. In each nozzle row, a plurality of nozzle openings are arranged at predetermined intervals in the width direction intersecting the transport direction of the medium S.

  Further, the length of the nozzle row is equal to or longer than the maximum width of the medium S. Accordingly, when the medium S passes under the heads 31 and 32, the heads 31 and 32 eject UV ink toward the medium S, whereby a two-dimensional image is printed on the medium S. The ink discharge method from the nozzle opening may be a piezo method in which ink is discharged from the nozzle opening by applying a voltage to the drive element (piezo element) to expand and contract the ink chamber, or a nozzle using a heating element. A thermal method may be employed in which bubbles are generated inside and ink is ejected from the nozzle openings by the bubbles.

  The irradiation unit 40 is for irradiating the UV ink on the medium S with ultraviolet rays to cure the UV ink, and includes an upstream irradiation unit 41 and a downstream irradiation unit 42. The upstream irradiation unit 41 and the downstream irradiation unit 42 irradiate the medium S moving in the transport direction with ultraviolet rays. Examples of the light source (ultraviolet irradiation source) include a light emitting diode (LED), a metal halide lamp, and a mercury lamp.

  The upstream irradiation unit 41 is disposed at a position downstream of the upstream head 31 in the transport direction and at a position upstream of the downstream head 32 in the transport direction. For this reason, the upstream irradiation unit 41 cures the image printed by the upstream head 31. The downstream irradiation unit 42 is disposed at a position downstream of the downstream head 32 in the transport direction. Therefore, the downstream irradiation unit 42 mainly cures the image printed by the downstream head 32.

The controller 10 adjusts the irradiation intensity (mW / cm ² ) of the ultraviolet rays that the irradiation units 41 and 42 irradiate per unit area by changing the current value input to the light sources of the irradiation units 41 and 42. . In addition, the irradiation energy (mJ / cm ² ) of ultraviolet rays irradiated to the UV ink ejected per unit area of the medium S is the product of the irradiation intensity (mW / cm ² ) of ultraviolet rays and the irradiation time (s). Determined by

=== Print mode ===
3A is a diagram illustrating an image printed in the single mode, FIG. 3B is a diagram illustrating an image printed in the front printing mode, and FIG. 3C is an image printed in the reverse printing mode. It is a figure explaining. The printer 1 of the present embodiment has three types of printing modes, that is, a single mode, a front printing mode, and a back printing mode.

  When the single mode is set (FIG. 3A), the printer 1 uses only four color inks (KCMY) of black, cyan, magenta, and yellow as appropriate, and uses only “color image (corresponding to main image)” as a medium. Print directly on S. The color image includes a monochrome image. In this case, the printer 1 prints a color image with the upstream head 31 and cures the color image with the upstream irradiation unit 41. However, the present invention is not limited thereto, and a color image may be printed by the downstream head 32 and the color image may be cured by the downstream irradiation unit 42, or a color image may be printed using white ink.

  When the front printing mode is set (FIG. 3B), the printer 1 prints a “white image (corresponding to an auxiliary image)” on the medium S using white ink (W), and then A four-color ink (KCMY) is used to print a “color image” superimposed on a white image. Therefore, the image printed in the front printing mode is an image that is visually recognized from the printing surface side, as indicated by an arrow in the drawing. In this case, the printer 1 prints a white image with the upstream head 31 (corresponding to the second head), cures the white image with the upstream irradiation unit 41, and then uses the downstream head 32 (corresponding to the first head). A color image is printed, and the color image is cured by the downstream irradiation unit 42.

  When the reverse printing mode is set (FIG. 3C), the printer 1 prints the “color image” on the medium S first, and prints the “white image” on the color image. Therefore, the image printed in the reverse printing mode is an image that is viewed from the side opposite to the printing surface side via the medium S, as indicated by an arrow in the drawing. Therefore, when the transparent medium S such as a plastic film is used, the back printing mode is performed. In this case, the printer 1 prints a color image with the upstream head 31 (corresponding to the first head), cures the color image with the upstream irradiation unit 41, and then uses the downstream head 32 (corresponding to the second head). A white image is printed, and the white image is cured by the downstream irradiation unit 42.

  As in the front printing mode and the back printing mode, an image with good color development can be printed by printing a white image on the color image as a background of the color image. Further, when the medium S is transparent, it is possible to prevent the opposite side of the color image from being seen through, and the color image can be shielded.

=== Printing Method of Comparative Example ===
4A to 4C are diagrams illustrating a printing method of a comparative example. Here, a case where a color image (so-called solid image) to which color ink is applied without a gap is printed will be described as an example. FIG. 4A is a diagram illustrating a color image printed in the single mode. The UV ink used by the printer 1 has a relatively high viscosity. Therefore, as shown in the left diagram of FIG. 4A, the color ink droplets just after landing on the medium S are in a state of protruding in a granular shape. However, the color ink droplet spreads wet at the position where it has landed on the medium S until the ultraviolet rays are irradiated by the irradiation units 41 and 42. Therefore, in the single mode, as shown in the right diagram of FIG. 4A, the medium S is filled with the color ink without any gap even if the color ink droplets do not discharge so much as the color ink droplets overlap or contact each other. And a solid color image can be printed.

  4B and 4C are diagrams for explaining a color image printed in the front printing mode. In the printing method of the comparative example, when the front printing mode is set, the white image before the color ink is ejected is irradiated with strong ultraviolet rays to completely cure the white image. Thereafter, color ink droplets are ejected onto the completely cured white image.

  In the comparative example shown in FIG. 4B, in order to print a solid color image, the same amount of color ink as in the single mode (FIG. 4A) is ejected. Therefore, as shown in the left diagram of FIG. 4B, the color ink droplets that have just landed on the white image do not overlap or come into contact with neighboring color ink droplets, and are in an independent state. However, as the degree of cure of the lower layer image is higher, the UV ink droplets that have landed thereon do not penetrate the lower layer image and are repelled on the lower layer image, so that the lower image is more likely to flow on the lower layer image. For this reason, as in this comparative example, if the color ink droplets are ejected onto a completely cured white image, the color ink droplets will not appear on the white image before landing on the white image. The color ink droplets in the vicinity are connected or separated from each other. As a result, as shown in the right diagram of FIG. 4B, a gap occurs in the color image, the white image cannot be filled with the color ink, and a solid color image cannot be printed.

  On the other hand, in the comparative example shown in FIG. 4C, in order to print a solid color image, a larger amount of color ink is ejected than in the single mode (FIG. 4A). Therefore, as shown in the left diagram of FIG. 4C, the color ink droplets landed on the white image are in contact with neighboring color ink droplets. In this case, even though the degree of curing of the white image is high and the color ink droplets easily flow on the main image, all the color ink droplets are connected. As a result, as shown in the right diagram of FIG. 4C, the white image can be filled with the color ink without any gap, and a solid color image can be printed.

  That is, when the white image as a lower layer is completely cured, the color ink droplets are bounced and flowed on the white image, and the filling of the white image with the color ink becomes worse. For this reason, even if the same color image is printed, if only the same amount of color ink is ejected as in the single mode (FIG. 4A) (FIG. 4B), the filling of the white image becomes worse.

  On the other hand, by discharging a larger amount of color ink than in the single mode (FIG. 4A) (FIG. 4C), it is possible to ensure that the white image is filled as in the single mode. However, the amount of color ink consumed increases and costs increase. Even when the same color image is printed, different amounts of color ink must be ejected in the single mode and the front printing mode, which complicates printing control. For example, the printer 1 must have a mode for printing two types of color images, or the printer driver must be able to create print data for two types of color images. In addition, since a large amount of color ink is ejected, a sense of thickness is generated in the image and the appearance is deteriorated.

  In FIG. 4, the front printing mode is taken as an example, but the same problem occurs in the back printing mode. That is, before the white ink is ejected, if the underlying color image is completely cured with high-energy ultraviolet rays, the white ink droplets bounce and flow on the color image, and the color image is filled with the white ink. Will get worse. For this reason, a large amount of white ink must be ejected, which increases costs. Also, different amounts of white ink must be ejected between the front printing mode and the back printing mode, which complicates printing control.

  Therefore, the printer 1 of the present embodiment aims to improve the filling of the lower layer image with the ink for printing the upper layer image in the mode in which the color image and the white image are overlaid.

=== Printing Method of this Embodiment (Overview) ===
FIG. 5 is a diagram illustrating a printing method in the front printing mode according to the present embodiment. In the present embodiment, for example, when the front printing mode is set, the white image before the color image is printed is irradiated with ultraviolet rays having relatively weak energy. Then, color ink is ejected onto a semi-cured white image that is not completely cured. In this embodiment, a color image is printed even in the front printing mode with the same amount of color ink as in the single mode (FIG. 4A).

  Compared to the case where it is ejected onto the completely cured lower layer image, the UV ink droplets ejected onto the semi-cured lower layer image penetrates the lower layer image and spreads on the lower layer image. It is difficult to flow on the lower layer image. For this reason, when a color ink droplet is ejected onto a semi-cured white image, the color ink droplet does not flow on the main image and spreads wet on the spot between landing and irradiation with ultraviolet rays. . That is, the adjacent color ink droplets are not connected or separated as in the comparative example (FIG. 4B), and the white image can be thinly covered with the color ink as shown in the right diagram of FIG. Can be printed.

  That is, by setting the white image at the time of discharging the color ink to a semi-cured state, the color ink droplets are wet and spread on the white image, and the filling of the white image with the color ink can be improved. Therefore, the color image is printed as in the case of printing the color image directly on the medium S (as in the single mode) without increasing the discharge amount of the color ink as in the comparative example shown in FIG. 4C. Can do.

  In the printing method of the present embodiment, even when the reverse printing mode is set, the color image before discharging the white ink is irradiated with ultraviolet rays having relatively weak energy. Then, white ink is ejected onto a color image in a semi-cured state that is not completely cured. By doing so, the flow of the white ink droplets on the color image is suppressed, and the white ink droplets spread out on the color image, so that the filling of the color image with the white ink can be improved. Therefore, the consumption of white ink can be suppressed.

In summary, the controller 10 (corresponding to the control unit) of the printer 1 of the present embodiment prints a color image (corresponding to a main image) on the medium S without printing a white image (corresponding to an auxiliary image). When the mode (corresponding to the first mode) is set, light having a relatively high energy (corresponding to the first energy) is irradiated per unit area of the color image so that the color image is completely cured. To control.
On the other hand, when the front printing mode for printing the white image and the color image on the medium S and the back printing mode (corresponding to the second mode) are set, the controller 10 selects the white image and the color image. Control so that light of lower energy (equivalent to second energy) is irradiated per unit area of the lower layer image per unit area so that the lower layer image is not completely cured before printing the upper layer image .

  By doing so, in the single mode, the color image can be completely cured and the color image can be fixed on the medium S. On the other hand, in the front printing mode and the back printing mode, the lower layer image can be in a semi-cured state, and the filling of the lower layer image with ink for printing the upper layer image can be improved. Therefore, it is possible to reduce the consumption of ink for printing the upper layer image, and to reduce the cost. In addition, the thickness of the upper layer image can be reduced, and the feeling of image thickness can be suppressed (t1> t2).

  In addition, the same amount of ink for printing a color image may be used in the single mode (and the reverse printing mode) in which a color image is directly printed on the medium S and in the front printing mode in which a color image is printed on a white image. Print control can be facilitated. Similarly, the amount of ink for printing a white image can be made the same in the front printing mode for printing a white image directly on the medium S and the back printing mode for printing a white image on a color image. Can be easily. For example, the printer driver can create data for printing a color image in the same manner and create data for printing a white image in the same way regardless of the print mode.

=== Example 1: Printing Method ===
FIG. 6 is a flowchart illustrating the printing method according to the first embodiment. In Example 1, the irradiation energy (mJ / cm ² ) of ultraviolet rays irradiated per unit area of the color image in the single mode and the irradiation energy of ultraviolet rays irradiated per unit area of the lower layer image in the front printing / back printing mode ( mJ / cm ² ), the controller 10 controls the irradiation intensity (mW / cm ² ) of the irradiation units 41 and 42.

Hereinafter, a specific flow of the printing method will be described with reference to FIG.
First, when receiving a print job (S001), the controller 10 checks whether the print mode is set to the front print mode or the reverse print mode or the single mode (S002). For example, when the user sets the print mode in the computer 60 in which the printer driver is installed, the controller 10 acquires information about the print mode from the printer driver and confirms the print mode.

When the print mode is set to “single mode” (S002 → N), the controller 10 sets the irradiation intensity of the upstream irradiation unit 41 that irradiates the color image with ultraviolet rays to “I (mW / cm ² )”. Set to. In the single mode, since the downstream head 32 does not print an image, the controller 10 turns off the downstream irradiation unit 42 and sets the ultraviolet irradiation from the downstream irradiation unit 42 (S004).

On the other hand, when the printing mode is set to “front printing mode” or “back printing mode” (S002 → Y), the controller 10 upstream irradiates the lower layer image before the upper layer image is overprinted. The irradiation intensity of the side irradiation unit 41 is set to an irradiation intensity “I / 2 (mW / cm ² )” that is half of the irradiation intensity I (mW / cm ² ) in the single mode. In the front printing / back printing mode, since the upper layer image is printed by the downstream head 32, the controller 10 turns on the downstream irradiation unit 42. The setting, as an upper layer image is completely cured, the irradiation intensity of the downstream-side irradiation unit 42, the same irradiation intensity and the irradiation intensity I (mW / cm ²⁾ alone mode "I (mW / cm ^2)" To do.

  As described above, the controller 10 executes the printing process while controlling each unit (S005). In the first embodiment, the controller 10 controls the transport unit 20 so that the transport speed of the medium S becomes a constant speed “V (cm / s)” regardless of the print mode. That is, the time during which the unit area of the image faces the upstream irradiation unit 41 is made constant, and the time during which the upstream irradiation unit 41 irradiates the unit area of the image with ultraviolet rays is made constant.

As a result, when the single mode is set, the medium S on which the color image is printed is transported under the upstream irradiation unit 41 whose ultraviolet irradiation intensity per unit area is I (mW / cm ² ). It is conveyed at a speed V (cm / s). That is, the upstream irradiation unit 41 and each unit area (cm ² ) of the color image face each other during the time “1 / V (s)”, and the upstream irradiation unit 41 has a unit area (cm ^{2) of the} color image. ) For a period of time 1 / V (s). Therefore, for each unit area of the upstream side irradiation unit 41, the irradiation energy of the ultraviolet rays irradiated per unit area of the color image is “irradiation intensity × irradiation time = I (mW / cm ² ) × 1 / V (s)”. = I / V (mJ / cm ² ) ”.

On the other hand, when the front printing / back printing mode is set, the upstream side irradiation unit 41 whose medium S on which the lower layer image is printed has an ultraviolet irradiation intensity per unit area of I / 2 (mW / cm ² ). Is conveyed at a conveyance speed V (cm / s). Therefore, each unit area (cm ² ) of the upstream irradiation unit 41 and the lower layer image is opposed over time 1 / V (s). Therefore, for each unit area of the upstream side irradiation unit 41, the irradiation energy of the ultraviolet rays irradiated per unit area of the lower layer image is “irradiation intensity × irradiation time = I / 2 (mW / cm ² ) × 1 / V ( s) = I / 2V (mJ / cm ² ) ”.

As described above, in Example 1, the upstream irradiation unit 41 in the front printing / back printing mode is more than the irradiation intensity (I (mW / cm ² )) of the ultraviolet rays that the upstream irradiation unit 41 irradiates the color image in the single mode. The irradiation intensity (I / 2 (mW / cm ² )) of the ultraviolet rays 41 irradiates the lower layer image is weakened (here, half). By doing so, lower the irradiation energy of the UV light irradiated per unit area of the lower layer image in the front printing / back printing mode than the irradiation energy of UV light irradiated per unit area of the color image in the single mode. Can be done (half here).

  In addition, the irradiation intensity of the upstream irradiation unit 41 and the conveyance speed V of the medium S are set so that the irradiation energy of ultraviolet rays applied to the color image in the single mode becomes the irradiation energy recommended by the type of ink. In other words, in the front printing / back printing mode, the irradiation intensity of the upstream irradiation unit 41 and the conveyance speed V of the medium S are set so that half of the recommended irradiation energy is irradiated to the lower layer image.

  Accordingly, in the single mode, the color image can be completely cured. On the other hand, in the front printing / back printing mode, the upper layer image can be printed on the semi-cured lower layer image. Therefore, the flow of ink droplets on the lower layer image is suppressed, and the ink can be spread thinly. Therefore, filling of the lower layer image with the ink for printing the upper layer image can be improved.

  In the present embodiment, the irradiation energy of ultraviolet rays irradiated per unit area of the lower layer image in the front printing / back printing mode is set to half (50%) in the single mode. When the irradiation energy of the ultraviolet light applied to the UV ink is lowered in this way, the degree of curing of the UV ink is lowered and the UV ink is easily peeled off from the medium S. Therefore, in order to prevent the problem of the peelability of the lower layer image from the medium S while lowering the degree of cure of the lower layer image in order to ensure filling with the ink for printing the upper layer image, the ultraviolet ray in the front printing / back printing mode is prevented. The irradiation energy should be determined.

  FIG. 7 is a table showing the evaluation results when the ratio of the irradiation energy in the front printing / back printing mode with respect to the single mode is changed. The irradiation energy of the ultraviolet rays irradiated per unit area of the color image in the single mode is set as the irradiation energy recommended for the UV ink for printing the image. Then, in order to determine the appropriate irradiation energy in the front printing / back printing mode, the ratio of the recommended irradiation energy is changed to 35%, 45%, 55%, 65%, and the lower layer. The image (white image or color image) is cured. Thereafter, the upper layer image is printed on the lower layer image. The irradiation energy for curing the upper layer image is constant, and the irradiation energy recommended for the UV ink for printing the image. The degree of filling and peelability of the lower layer image were evaluated for images printed under the above conditions.

As a result, as shown in FIG. 7, when the lower layer image was cured with 65% irradiation energy in the single mode (recommended irradiation energy), there was no problem of peelability (性), but the upper layer image was printed. The degree of filling of the lower layer image with ink has become lower than the degree of filling desired (×).
When the lower layer image was cured with irradiation energy of 45% and 55% in the single mode, the degree of filling of the lower layer image became the desired degree of filling (（). Moreover, although the peelability was lower than that at the irradiation energy of 65%, the peelability to the extent that no problem occurred was obtained (◯).
When the lower layer image was cured with 35% irradiation energy in the single mode, the degree of filling of the lower layer image became a desired degree of filling (埋). However, the peelability deteriorated to the extent that a problem occurred (x).

  As a result, the ultraviolet irradiation energy (corresponding to the second energy) irradiated per unit area of the lower layer image in the front printing / back printing mode is equivalent to the ultraviolet irradiation energy (corresponding to the second energy) irradiated per unit area of the color image in the single mode ( 45% or more and 55% or less of the first energy). By doing so, when the front printing / back printing mode is set, the lower layer image is sufficiently peelable to prevent problems while ensuring the degree of filling of the lower layer image with the ink for printing the upper layer image. I can do it.

=== Example 2: Printing Method ===
FIG. 8 is a flowchart illustrating a printing method according to the second embodiment. In Example 2, the ultraviolet irradiation energy (mJ / cm ² ) irradiated per unit area of the color image in the single mode and the ultraviolet irradiation energy (per unit area of the lower layer image in the front printing / back printing mode) mJ / cm ² ), the controller 10 controls the transport speed (cm / s) of the medium S that passes under the upstream irradiation unit 41. In other words, according to the printing mode, the time during which the image faces the upstream irradiation unit 41 is controlled, and the time during which the upstream irradiation unit 41 irradiates the image with ultraviolet rays is controlled.

A specific flow of the printing method will be described with reference to the flow of FIG. First, when receiving a print job (S101), the controller 10 confirms the set print mode (S102). When the single mode is set (S102 → N), the controller 10 sets the transport speed of the medium S passing under the upstream irradiation unit 41 to “V (cm / s)” (S104). . On the other hand, when the front printing mode or the back printing mode is set (S102 → Y), the controller 10 sets the transport speed of the medium S passing under the upstream irradiation unit 41 to 2 in the single mode. The double conveyance speed is set to “2 V (cm / s)” (S103). The irradiation intensity of the upstream irradiation unit 41 is set to a constant “I (mW / cm ² )” regardless of the printing mode.

By doing so, when the single mode is set, the medium S on which the color image is printed is below the upstream irradiation unit 41 whose ultraviolet irradiation intensity per unit area is I (mW / cm ² ). , And conveyed at a conveyance speed V (cm / s). Therefore, the upstream side irradiation unit 41 and each unit area (cm ² ) of the color image face each other over time 1 / V (s). Therefore, for each unit area of the upstream side irradiation unit 41, the irradiation energy of the ultraviolet rays irradiated per unit area of the color image is “irradiation intensity × irradiation time = I (mW / cm ² ) × 1 / V (s)”. = I / V (mJ / cm ² ) ”.

On the other hand, when the front printing / back printing mode is set, the medium S on which the lower layer image is printed is below the upstream irradiation unit 41 whose ultraviolet irradiation intensity per unit area is I (mW / cm ² ). Are transported at a transport speed 2 V (cm / s) which is twice that in the single mode. Therefore, each unit area (cm ² ) of the upstream side irradiation unit 41 and the lower layer image is opposed to the half time ½ V (s) in the single mode. Therefore, for each unit area of the upstream side irradiation unit 41, the irradiation energy of the ultraviolet rays irradiated per unit area of the main image is “irradiation intensity × irradiation time = I (mW / cm ² ) × 1/2 V (s)”. = I / 2V (mJ / cm ² ) ”.

  In this way, the controller 10 increases the transport speed 2V of the medium S in the front printing mode and the back printing mode, compared with the transport speed V (corresponding to the relative movement speed) of the medium S in the single mode (here, 2V). Double). By doing so, lower the irradiation energy of the UV light irradiated per unit area of the lower layer image in the front printing / back printing mode than the irradiation energy of UV light irradiated per unit area of the color image in the single mode. Can be done (half here).

  Accordingly, in the single mode, the color image can be completely cured. On the other hand, in the front printing / back printing mode, the upper layer image can be printed on the semi-cured lower layer image. Therefore, the flow of ink droplets on the lower layer image is suppressed, and the ink can be spread thinly. Therefore, filling of the lower layer image with the ink for printing the upper layer image can be improved.

  In general, a certain part of the medium S faces the upstream irradiation unit 41, and at the same time, another part of the medium S faces the heads 31 and 32 or the downstream irradiation unit 42. . That is, the ultraviolet irradiation by the upstream irradiation unit 41 and the printing by the heads 31 and 32 and the ultraviolet irradiation by the downstream irradiation unit 42 are performed simultaneously. Therefore, in the second embodiment in which the conveyance speed of the medium S passing under the upstream irradiation unit 41 is doubled in the front printing / back printing mode compared to the single mode, the single mode is also used for the ink discharge interval from the nozzles. It is good to make it different between the front and back printing modes. Further, the irradiation intensity of the downstream irradiation unit 42 may be made stronger than the irradiation intensity of the upstream irradiation unit 41 so that the lower layer image is completely cured.

=== Modification ===
<Modification 1>
In the above embodiment, the irradiation intensity of the upstream irradiation unit 41 and the conveyance of the medium S are changed in order to change the irradiation energy of the ultraviolet rays applied to the color image in the single mode and the lower layer image in the front printing / back printing mode. Although either one of the speeds is adjusted, the present invention is not limited to this, and both may be adjusted. That is, in the front printing / back printing mode, the irradiation intensity of the upstream irradiation unit 41 may be weakened and the conveyance speed of the medium S may be increased as compared with the single mode.

<Modification 2>
In the surface printing / back printing mode, when the downstream irradiation unit 42 irradiates the upper layer image with ultraviolet rays, part of the ultraviolet rays may pass through the upper layer image and contribute to the curing of the lower layer image. Therefore, the irradiation intensity of the downstream irradiation unit 42 in the front printing / back printing mode may be made stronger than the irradiation intensity of the upstream irradiation unit 41 in the single mode. By doing so, even if the lower layer image is in a semi-cured state in the front printing / back printing mode, the downstream side irradiation unit 42 can increase the degree of curing of the lower layer image.

<Modification 3>
In the above-described embodiment, the printer 1 can perform both the front printing mode and the back printing mode. However, the present invention is not limited to this, and the printer 1 that performs only one of the modes may be used. For example, in the case of the printer 1 that performs only the front printing mode, the upstream head 31 shown in FIG. 2 can eject only the white ink W, and the downstream head 32 can eject only the four-color ink KCMY for printing a color image. do it.

<Modification 4>
In the above-described embodiment, the ink for printing the auxiliary image is white ink, but is not limited thereto. For example, an auxiliary image may be printed with a metallic ink containing a metal pigment or the like in order to print an image having a metallic gloss. Also, an auxiliary image may be printed with other color inks such as yellow, or an auxiliary image in which white color is adjusted by appropriately mixing four inks (KCMY) with white ink may be printed. Further, a single image using white ink or four-color ink (KCMY) may be printed on the same medium S together with an image obtained by superimposing the auxiliary image and the main image.

=== Other Embodiments ===
The above-described embodiments are for facilitating the understanding of the present invention, and are 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. The following embodiments may be used.

<About ink>
In the above embodiment, the case of using an ultraviolet curable ink (UV ink) is taken as an example, but the present invention is not limited to this. For example, the present invention can also be applied when using ink that is cured by irradiation with light such as visible light.

<About the printer>
In the above embodiment, when the medium passes under the fixed head extending over the width of the medium, the head ejects ink onto the medium, thereby generating a two-dimensional image on the medium. Although a printer for printing is taken as an example, the present invention is not limited to this. For example, the operation of ejecting photocurable ink onto the medium while the head moves in the moving direction and the operation of the transport unit transporting the medium in the transport direction are alternately repeated and arranged downstream of the head in the transport direction. A printer that cures the photocurable ink on the medium by the irradiated unit may be used.

<About white>
The term “white” in the present specification is not limited to white in the strict sense that is the surface color of an object that reflects 100% of all wavelengths of visible light. It shall include a color called white. For example, “white” means (1) color measurement mode: spot colorimetry, light source: D50, backing: Black, printing medium: transparent film, using a colorimeter eye-one Pro manufactured by x-rite When the colorimetry is performed, the Lab-based mark is on the a ^* b ^* plane within the circumference of the radius 20 and the inside thereof, and the color is within the hue range represented by L ^* being 70 or more. (2) When the color is measured with the color mode CM2022 manufactured by Minolta in the measurement mode D502 ° field of view, SCF mode, and white background, the label in the Lab system is on the circumference of the radius 20 on the a ^* b ^* plane and inside Or a color within the hue range represented by L ^* of 70 or more, or (3) the color of the ink used as the background of the image as described in JP-A-2004-306591, If it is used, it is not limited to pure white.

1 Printer, 10 Controller, 11 Interface section,
12 CPU, 13 memory, 14 unit control circuit,
20 transport unit, 21 transport belt, 22a transport roller,
22b Transport roller, 30 head unit, 31 upstream head,
32 downstream head, 40 irradiation unit, 41 upstream irradiation section,
42 Downstream irradiation unit, 50 detector groups, 60 computers

Claims (5)

(A) a first head that prints a main image and ejects ink that is cured by light irradiation;
(B) a second head that ejects an ink that prints an auxiliary image that overlaps the main image, the ink being cured by the light irradiation;
(C) an irradiation unit for irradiating the light;
(D) When the first mode in which the main image is printed on a medium without printing the auxiliary image is set, control is performed so that light of the first energy is emitted per unit area of the main image. And
When the second mode in which the auxiliary image and the main image are superimposed and printed on the medium is set, the auxiliary image and the main image are printed before printing the upper layer image of the auxiliary image and the main image. A control unit that controls so that light of the second energy lower than the first energy is irradiated per unit area of the lower layer image of
A printing apparatus comprising (E). The printing apparatus according to claim 1,
The control unit weakens the irradiation intensity of the light that the irradiation unit irradiates the lower layer image in the second mode, rather than the irradiation intensity of the light that the irradiation unit irradiates the main image in the first mode. To
Printing device. The printing apparatus according to claim 1 or 2, wherein
The irradiation unit irradiates the image with the light while relatively moving in a predetermined direction with the medium on which the image is printed,
The control unit increases the relative movement speed of the irradiation unit and the medium in the second mode than the relative movement speed of the irradiation unit and the medium in the first mode.
Printing device. The printing apparatus according to any one of claims 1 to 3, wherein
The second energy is 45% or more and 55% or less of the first energy.
Printing device. Ink that has a first mode in which a main image is printed on a medium without printing the auxiliary image and a second mode in which the auxiliary image and the main image are printed on the medium in an overlapping manner, and is cured by light irradiation A printing method for printing the auxiliary image and the main image by:
When the first mode is set, after printing the main image on the medium, irradiating light of first energy per unit area of the main image;
When the second mode is set, a lower layer image of the auxiliary image and the main image is printed on the medium, and has a second energy lower than the first energy per unit area of the lower layer image. After irradiating with light, printing the upper layer image of the auxiliary image and the main image on the lower layer image, irradiating the upper layer image with light,
A printing method comprising:

Images