Printing apparatus, method for generating print data, and apparatus for generating print data

Abstract

This allows for better image transfer using hot melt resin powder. [Solution] A printing method for drawing an image on a transfer medium (50) by transferring an image printed on the transfer medium to the transfer medium, the method comprising a printing stage in which an image is printed on the transfer medium (50) by a printing unit (14) which is a printing device, a hot melt resin application stage in which hot melt resin powder is applied to the transfer medium (50), and a transfer stage in which the image is transferred from the transfer medium (50) to the transfer medium, the printing unit (14) comprising a colored ink head that ejects colored ink and a clear ink head that ejects clear ink, and during the printing stage, clear ink is further ejected from the clear ink head onto at least a portion of the area on the transfer medium (50) onto which the colored ink is ejected from the colored ink head.

Description

Technical Field

[0001] The present invention relates to a printing method, a printing system, and a printing apparatus.

Background Art

[0002] Conventionally, a method of performing transfer printing using a hot melt layer formed of resin powder has been known. In this method, for example, an image is printed on a transfer medium (such as a transfer sheet) having a release layer formed on its surface, and further, with a hot melt layer formed on the entire surface of the transfer medium, the transfer medium and the transfer target medium are overlapped and heated and pressurized to transfer the image from the transfer medium to the transfer target medium. In this case, for example, a film or the like having a receiving layer formed thereon is used as the transfer medium, an image is printed on the transfer medium using color ink, and a white ink layer is formed on the image using white ink. Then, powder (powder) of a hot melt resin is adhered onto the white ink layer on the transfer medium, and pressure bonding is performed with a heat press machine to execute image transfer. Conventionally, a method of forming a hot melt layer in accordance with an image without forming a hot melt layer on the entire surface of the transfer medium is also known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a layer of white ink is formed on top of an image printed with color ink, the image can be properly represented on the transfer medium even if the background color of the transfer medium is dark. However, in this case, the white ink layer, which is formed over an area larger than the image, is also transferred to the transfer medium, potentially transferring unnecessary parts of the original image, such as margins, and impairing the design and texture. In contrast, by forming a hot melt layer that matches the image, as in the method disclosed in Patent Document 1, only the parts necessary for representing the image can be transferred from the transfer medium to the transfer medium. Furthermore, in this case, by using a fabric with a light color (pale color) such as white or beige as the transfer medium, it becomes possible to utilize the background color and material of the transfer medium and improve the design and texture.

[0005] However, the method disclosed in Patent Document 1 uses a transfer sheet as the transfer medium that is non-water-repellent but maintains sufficient ink impermeability to retain the adhesion of the powder until the image is formed and the powder is sprinkled on. Furthermore, a resin powder of a predetermined grade with small particle size is used as the powder. However, in this case, the conditions for the usable transfer medium and powder are limited, which could lead to a significant increase in printing costs and a significant decrease in the freedom of printing conditions.

[0006] Furthermore, the inventors of this invention conducted various experiments and found that when an image is transferred without using a white ink layer, the quality of the image transferred to the transfer medium may decrease. Therefore, there has been a desire for a more appropriate method of image transfer. Accordingly, the present invention aims to provide a printing method, a printing system, and a printing apparatus that can solve the above problems. [Means for solving the problem]

[0007] The inventors of this application have diligently researched methods for transferring images more appropriately, such as methods that allow for more appropriate image transfer without forming a layer of white ink, even when using general color inks and transfer media used for transfer. In this research, they found that when a layer of white ink is not formed, the transferability decreases in the low-tone range, which expresses lighter colors in the image, compared to the high-tone range, which expresses darker colors, resulting in unintended transfer unevenness. They also found that the reason for this is that in the low-tone range, the amount of color ink decreases, resulting in a decrease in the amount of hot-melt resin adhering to that area, and thus the image cannot be completely transferred. In this case, the reduced transferability of the image in that area results in, for example, areas on the transfer medium where color should be present but are not. As a result, transfer unevenness occurs.

[0008] In response to this, the inventors of the present invention considered using clear ink in addition to color ink, which is less likely to affect the color of the image. With this configuration, for example, in the low-gradation range of the image where the amount of color ink used is small, the amount of hot melt resin that adheres can be appropriately prevented by further dispensing clear ink onto the transfer medium. Furthermore, this can appropriately prevent the deterioration of the image quality after transfer due to, for example, the occurrence of transfer unevenness.

[0009] Furthermore, the inventors of this application, through further diligent research, discovered the features necessary to obtain such effects, leading to the present invention. To solve the above problems, the present invention provides a printing method for drawing an image on a transfer medium by transferring an image printed on a transfer medium to a transfer medium, comprising: a printing step of printing the image on the transfer medium using an inkjet printing apparatus; a hot melt resin attachment step of attaching hot melt resin powder, which is a powder containing a resin that softens when heated, to the transfer medium on which the image is printed; and a transfer step of transferring the image from the transfer medium to the transfer medium by heating the transfer medium to which the hot melt resin powder is attached, and attaching a hot melt resin portion, which is a resin portion formed when the hot melt resin powder softens when heated, to the transfer medium, wherein the printing apparatus comprises a colored ink head, which is an inkjet head that ejects colored ink, which is an ink containing a colorant that shows a color, and a clear ink head, which is an inkjet head that ejects clear ink, which is a colorless and translucent ink, and in the printing step, the clear ink is further ejected from the clear ink head to at least a part of the area on the transfer medium from which the colored ink is ejected from the colored ink head.

[0010] With this configuration, by using clear ink in addition to colored ink when printing onto the transfer medium by the printing device, it is possible to appropriately eject inks other than colored ink onto the transfer medium while appropriately suppressing the influence of the color of the image printed on the transfer medium. Furthermore, by ejecting clear ink at positions where the amount of colored ink ejected is low, for example, the total amount of ink ejected onto the transfer medium can be increased compared to when only colored ink is used. In this case, by increasing the total amount of ink, for example, the hot melt resin powder can be properly adhered to the transfer medium. Furthermore, this makes it possible to appropriately prevent transfer unevenness, etc., caused by insufficient hot melt resin powder during the transfer of an image from the transfer medium to the transfer medium. Therefore, with this configuration, for example, image transfer using hot melt resin powder can be performed more appropriately.

[0011] In this configuration, during the printing stage, for example, printing is performed on the transfer medium using colored ink and clear ink, without using white ink. In this configuration, for example, a known transfer film can be suitably used as the transfer medium. As a known transfer film, for example, a transfer film for DTF (Direct to Film) transfer can be suitably used. Alternatively, a medium other than film (for example, paper) may be used as the transfer medium. As the medium to be transferred, for example, a cloth medium can be suitably used. As a colored ink, for example, a known color ink (for example, a known ink for textile printing) can be suitably used. As a known color ink, for example, an ink containing pigment as a colorant (for example, an aqueous pigment ink) can be suitably used.

[0012] In the transfer stage, for example, an image is transferred from the transfer medium to the transfer medium by moving at least a portion of the colorant attached to the transfer medium together with at least a portion of the hot melt resin portion to the transfer medium. In this case, using clear ink can be used to increase the transfer rate of the colorant. More specifically, for example, if the area on the transfer medium where colored ink is ejected from the colored ink head is defined as the image representation area, and the area where the amount of colored ink ejected per unit area is less than a preset standard amount is defined as the low-ink area, and the proportion of colorant that moves from the transfer medium to the transfer medium in the transfer stage is defined as the transfer rate, then in the printing stage, by ejecting clear ink to at least a portion of the low-ink area within the image representation area using a printing device, the transfer rate in at least a portion of the low-ink area can be increased compared to when clear ink is not ejected. With this configuration, for example, the occurrence of transfer unevenness can be appropriately prevented, and the image can be transferred appropriately. Also, in this case, for example, the area that expresses low-gradation colors in the image may become the low-ink area. Furthermore, in this case, focusing on the low-ink area, for example, by ejecting clear ink to at least a portion of the low-ink area during the printing stage, the amount of hot-melt resin powder that adheres to the hot-melt resin adhesion stage relative to the position where the clear ink was ejected can be increased compared to the case where no clear ink was ejected. With this configuration, for example, the transfer rate in the low-ink area can be appropriately increased. In addition, this can appropriately prevent the occurrence of transfer unevenness, for example.

[0013] Furthermore, in this configuration, in areas where a sufficiently large amount of colored ink is ejected, it is possible to attach a sufficient amount of hot melt resin powder without using clear ink. Therefore, the amount of clear ink ejected to each position on the transfer medium may be varied, for example, according to the amount of colored ink ejected to each position. More specifically, for example, if we define the area within the image representation region where the amount of colored ink ejected per unit area is greater than a predetermined amount greater than the above standard amount as the non-low-volume ink region, and define the amount of clear ink ejected per unit area to each position on the transfer medium as the clear ejection amount, then in the printing stage, it is conceivable to vary the clear ejection amount according to the amount of colored ink ejected per unit area so that the clear ejection amount in the low-volume ink region is greater than the clear ejection amount in the non-low-volume ink region. With this configuration, for example, it is possible to appropriately eject clear ink to the necessary areas while suppressing the amount of clear ink used. In this case, by reducing the clear ejection amount in the non-low-volume ink region, it is also possible to prevent, for example, the total amount of ink ejected to the same position from becoming excessively large.

[0014] Furthermore, if the total amount of ink ejected at the same location becomes large, problems such as bleeding of colored ink may become more likely. For this reason, it is possible to set the amount of clear ink ejected to zero in areas where a large amount of colored ink is ejected. More specifically, in this case, for example, clear ink would not be ejected at locations where the amount of colored ink ejected per unit area during the printing stage exceeds a preset upper limit. With this configuration, it is possible to more effectively prevent the total amount of ink ejected at the same location from becoming excessively large.

[0015] Furthermore, in this configuration, the printing device ejects colored ink and clear ink from the colored ink head and the clear ink head to ejection positions set according to the print resolution, for example. In this case, for example, it is conceivable to eject the clear ink so that an area including multiple ejection positions is continuously covered with colored ink and clear ink. More specifically, if we define an ejection position from which colored ink is ejected from the colored ink head as a colored ejection position, and define an isolated ejection position as a colored ejection position where the adjacent ejection position is not a colored ejection position, then the small ink area can be considered, for example, as an area including an isolated ejection position. Then, during the printing stage, for example, clear ink is ejected from the clear ink head to at least some of the isolated ejection positions in the small ink area, or to ejection positions around said isolated ejection positions, so that at least near said isolated ejection positions, an area including multiple ejection positions including the isolated ejection position is connected by colored ink and clear ink, and printing is performed on the transfer medium. With this configuration, for example, the total amount of ink dispensed near isolated ejection positions in the small ink area can be appropriately increased compared to when clear ink is not used. Furthermore, this allows for more appropriate adhesion of hot melt resin powder to the area near isolated ejection positions.

[0016] Furthermore, in this configuration, the transfer medium could be, for example, a medium having an ink-receiving layer formed thereon that absorbs ink. With this configuration, for example, bleeding of colored ink can be appropriately prevented. Also, in this case, during the printing stage, it is preferable to have the printing device print so that, for example, the colored ink lands on each position of the transfer medium before the clear ink. With this configuration, for example, bleeding can be prevented more appropriately. Also, in this configuration, by using clear ink, for example, graininess can be reduced. More specifically, the colored ink and the clear ink could each be, for example, inks that contain a solvent and are fixed to the transfer medium when the solvent evaporates. Furthermore, regarding the size of the ink dots formed when the colored ink spreads on the transfer medium after impact, if we define the size of the dots formed when both colored ink and clear ink are ejected at the same ejection position as the size when clear ink is used, and the size of the dots formed when only colored ink is ejected at the ejection position as the size when clear ink is not used, then during the printing stage, for example, in the small ink area, clear ink can be ejected at least a portion of the ejection position where colored ink is ejected, such that the size when clear ink is used is larger than the size when clear ink is not used. With this configuration, for example, the size of the ink dots formed by the colored ink can be appropriately widened. In addition, this can appropriately reduce graininess, for example.

[0017] Furthermore, in this configuration, as the colored ink, for example, an ink containing a binder resin, which is a resin fixed to the transfer medium together with the colorant, can be suitably used. In this case, as the clear ink, for example, an ink containing the same resin as the binder resin can be considered. With this configuration, for example, a clear ink with properties similar to those of the colored ink can be appropriately used. In this case, it can be considered that the ink containing the same resin as the binder resin will remain in a state where hot melt resin powder adheres more easily for a longer period of time compared to an ink that does not contain resin. Therefore, by using a clear ink containing resin, for example, hot melt resin powder can be adhered more reliably to the position where the clear ink is dispensed. In addition, as the clear ink, for example, an ink that does not contain the same resin as the binder resin in the colored ink can be considered. Even with this configuration, by using a clear ink, for example, the time it takes for the ink to dry to a state where hot melt resin powder is less likely to adhere to the position where the clear ink is dispensed can be extended. Furthermore, this allows for appropriate adhesion of hot melt resin powder to the position where the clear ink is dispensed, even when using a clear ink that does not contain resin.

[0018] Furthermore, regarding the clear ink dots formed on the transfer medium by ejecting clear ink onto the transfer medium, it can be considered preferable, for example, for the ink dots to be flattened and spread out, in order to make it easier for the hot melt resin powder to adhere to them. In this case, for example, an adjustment step could be performed to adjust the spread of the clear ink dots formed on the transfer medium during the printing stage. With this configuration, for example, the size of the clear ink dots can be appropriately adjusted. In this case, during the adjustment step, for example, it can be determined whether the spread of the clear ink dots is insufficient based on the result of printing an image onto the transfer medium by the printing device under a preset first printing condition. If it is determined that the spread of the dots is insufficient, for example, a second printing condition, which is different from the first printing condition and results in a larger spread of the clear ink dots, is selected as the printing condition for the printing device to perform printing during the printing stage. With this configuration, for example, the hot melt resin powder can be adhered more appropriately to the position where the clear ink was ejected.

[0019] Furthermore, the present invention may also utilize a printing system or printing apparatus having the same characteristics as described above. In these cases as well, for example, the same effects as described above can be obtained. [Effects of the Invention]

[0020] According to the present invention, for example, image transfer using hot melt resin powder can be performed more appropriately. [Brief explanation of the drawing]

[0021] [Figure 1] This figure illustrates a printing system 10 according to one embodiment of the present invention. Figure 1(a) shows an example of the configuration of the printing system 10. Figure 1(b) shows an example of the configuration of the printing unit 14 in the printing system 10. [Figure 2]This is a diagram for further detailed description of the plurality of inkjet heads 202 included in the head unit 102. FIGS. 2(a) to (c) show an example of the configuration of the head unit 102. [Figure 3] This is a flowchart showing an example of an operation executed in the printing system 10 in this example. [Figure 4] This is a diagram for explaining reasons for using clear ink and the like in this example. FIG. 4(a) shows an example of a printing method for the transfer medium 50 by a conventional method. FIG. 4(b) shows an example of a printing method for the transfer medium 50 by a method different from the method shown in FIG. 4(a). FIG. 4(c) shows an example of a printing method for the transfer medium 50 in this example. [Figure 5] This is a diagram for explaining an image to be printed on the transfer medium 50. FIG. 5(a) shows an example of an image to be printed on the transfer medium 50. FIG. 5(b) shows an example of the state of dots of color ink constituting the image. [Figure 6] This is a diagram showing an example of ejection positions for ejecting color ink and clear ink. FIGS. 6(a) to (c) show examples of ways of selecting ejection positions for ejecting clear ink. [Figure 7] This is a flowchart showing an example of an operation for generating print data in the print data preparation unit 12. [Figure 8] This is a diagram for explaining an experiment conducted by the inventor of the present application. FIG. 8(a) shows the composition of the clear ink used in the experiment. FIGS. 8(b) and (c) show the results of the experiment.

Embodiments for Carrying Out the Invention

[0022] Hereinafter, embodiments according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining a printing system 10 according to an embodiment of the present invention. FIG. 1(a) shows an example of the configuration of the printing system 10. FIG. 1(b) shows an example of the configuration of the printing unit 14 in the printing system 10. Except for the points to be described below, the printing system 10 may have the same or similar or similar features as a known printing system 10.

[0023] The printing system 10 is a system that draws an image on a transfer medium (object to be transferred) by transferring an image printed on a transfer medium 50 to the transfer medium. The system uses hot melt resin powder (hot melt powder), which is a powder containing resin that softens when heated, to transfer the image from the transfer medium 50 to the transfer medium. In this example, the transfer medium is a cloth medium such as fabric (for example, various fabrics). The transfer medium may be a cloth medium that has been processed into a predetermined product, such as a T-shirt. Furthermore, as the transfer medium 50, for example, a known transfer medium used for transferring to a cloth transfer medium can be suitably used. More specifically, as the transfer medium 50, for example, a transfer film for transfer using the DTF method (Direct to Film method) can be suitably used. Furthermore, as such a transfer film, for example, PET film can be used. Furthermore, as the transfer medium 50, a medium other than film (for example, a paper medium) can be used.

[0024] Furthermore, known resin powders for transfer can be suitably used as the hot melt resin powder. More specifically, known hot melt resin powders used for transferring fabrics to a transfer medium can be suitably used as the hot melt resin powder. Suitable hot melt resin powders include, for example, powders containing urethane, acrylic, polyester, polyamide, or mixtures thereof. The hot melt resin powder can also be considered, for example, a thermoplastic resin powder. The hot melt resin powder can also be considered, for example, a hot melt adhesive powder for transfer printing. The hot melt adhesive powder can be considered, for example, a powder of an adhesive that is solid at room temperature and mainly composed of a thermoplastic polymer. The hot melt adhesive powder can also be considered, for example, a powder of a solid adhesive that does not contain water or organic solvents. Such a hot melt adhesive powder can include, for example, a powder of a multi-component adhesive.

[0025] Furthermore, in order to perform the transfer using the transfer medium, transfer medium 50, and hot melt resin powder as described above, the printing system 10 in this example comprises a print data preparation unit 12, a printing unit 14, a powder application unit 16, and a thermal transfer unit 18. The print data preparation unit 12 is configured to prepare print data for controlling the operation of the printing unit 14, and generates print data to be supplied to the printing unit 14 based on image data indicating the image to be printed on the transfer medium 50 by the printing unit 14. For example, the print data preparation unit 12 could be a computer that controls the operation of the printing unit 14 according to a predetermined program. In this example, the print data preparation unit 12 generates print data by performing halftone processing on the image data in accordance with the configuration of the printing unit 14. The print data preparation unit 12 then controls the operation of the printing unit 14 by supplying the print data to the printing unit 14, causing the printing unit 14 to perform the printing operation. The operation of generating print data in the print data preparation unit 12 will be explained in more detail later.

[0026] The printing unit 14 is configured to correspond to the printing device in the printing system 10, and performs inkjet printing on the transfer medium 50 based on the printing data supplied from the printing data preparation unit 12. In this example, the printing unit 14 is a serial inkjet printer, and performs printing by causing the inkjet head to perform a main scanning operation in which ink is ejected while moving relative to the object to be printed in a preset main scanning direction (Y direction in the figure). The printing unit 14 also includes, for example, a head unit 102, a platen 104, a Y-bar unit 106, a main scanning drive unit 108, a sub-scanning drive unit 110, and a control unit 120, as shown in Figure 1(b).

[0027] The head unit 102 is a part having multiple inkjet heads, which eject ink toward the transfer medium 50. In this example, the head unit 102 has multiple inkjet heads for color inks that eject color inks of different colors from each other, and an inkjet head for clear ink that ejects clear ink. In this case, each color ink is an example of a colored ink that contains a colorant that indicates a color. Each of the multiple inkjet heads for color inks is an example of a colored ink head. The inkjet head for clear ink is an example of a clear ink head. In this example, the clear ink can be considered as, for example, a colorless and translucent ink. In this case, the fact that the clear ink is colorless can be considered as, for example, intentionally not having a predetermined color. Intentionally not having a predetermined color can be considered as, for example, intentionally not adding a colorant. In addition, the fact that the clear ink is colorless and translucent can be considered as, for example, being in a transparent state that does not substantially absorb light of a specific color in the visible light region. Regarding the principle of not substantially absorbing light of a specific color, this can be considered, for example, as not substantially absorbing light of a specific color in the visible light range within an acceptable range depending on the quality required for printing. More specifically, as a clear ink, for example, it is conceivable to use an ink from which the colorants have been removed from a color ink. In this case, in addition to the colorants, it is conceivable to further remove substances used in relation to the colorants from the color ink. For example, if a dispersant (pigment dispersant) is used in a color ink to disperse colorants such as pigments in the ink solvent, then an ink with a composition obtained by removing the colorants and dispersant from the color ink can be suitably used as a clear ink. Furthermore, as for clear ink, for example, it can be considered to be the same or similar transparent ink as the clear ink conventionally used in the field of inkjet printing. However, in the field of textile printing, which involves printing on fabric, as in this example, there is usually no reason to use clear ink.Therefore, the clear ink used in this example can be considered as an extension of the use of clear ink in inkjet printing other than textile printing, applied to the field of textile printing. The configuration of the print head 102 will be explained in more detail later.

[0028] The platen 104 is a table-shaped member that supports the transfer medium 50 facing the head unit 102. The Y-bar unit 106 is a member that extends in the main scanning direction at a position facing the platen 104 with the transfer medium 50 in between, and guides the movement of the head unit 102 in the main scanning direction during main scanning by holding the head unit 102 on the surface facing the transfer medium 50 in a state that allows movement in the main scanning direction. The main scanning drive unit 108 is a drive unit that causes the multiple inkjet heads in the head unit 102 to perform the main scanning operation. In this example, the main scanning drive unit 108 moves the head unit 102 along the Y-bar unit 106 in accordance with the control of the control unit 120, and ejects ink from each inkjet head in the head unit 102. The sub-scanning drive unit 110 is a drive unit that causes the multiple inkjet heads in the head unit 102 to perform the sub-scanning operation. The sub-scanning operation can be thought of as, for example, an operation in which the printer moves relative to the transfer medium 50 in a sub-scanning direction (the X direction in the figure) that is perpendicular to the main scanning direction. In this example, the sub-scanning drive unit 110 moves the head unit 102 in the sub-scanning direction relative to the transfer medium 50 between main scanning operations, thereby causing multiple inkjet heads in the head unit 102 to perform the sub-scanning operation. The control unit 120 is a part that includes, for example, the CPU of the printing unit 14, and controls the operation of each part of the printing unit 14 based on the printing data supplied from the printing data preparation unit 12, thereby controlling the printing operation on the transfer medium 50. As a result, the printing unit 14 prints the image indicated by the image data onto the transfer medium 50.

[0029] Furthermore, in the printing system 10 of this example, the printing unit 14 applies hot melt resin powder to the transfer medium 50 on which the image has been printed, and the powder application unit 16 applies hot melt resin powder to the transfer medium 50 on which the image has been printed. The powder application unit 16 can be considered, for example, as a configuration for attaching hot melt resin powder to the transfer medium 50 on which the image has been printed. In this example, the powder application unit 16 performs preheating by heating the transfer medium 50, to a predetermined temperature, before transfer. After the hot melt resin powder has been attached to the transfer medium 50, the thermal transfer unit 18 transfers the image from the transfer medium 50 to the transfer medium. In this example, the thermal transfer unit 18 is an example of a transfer unit. The thermal transfer unit 18 can be considered, for example, as a device that transfers an image from the transfer medium 50 to the transfer medium by heating and pressurizing the transfer medium 50 and the transfer medium while they are stacked together. The operation of heating and pressurizing the transfer medium 50 and the transfer medium while they are stacked together can be considered, for example, as an operation of placing the transfer medium 50 on the transfer medium and pressing it into place. Furthermore, a known heat press machine or the like can be suitably used as the heat transfer unit 18. According to this example, for example, an image printed on the transfer medium 50 can be appropriately transferred to the transfer medium. The image transfer operation performed in the printing system 10 will be described in more detail later.

[0030] In the printing system 10, the print data preparation unit 12, the printing unit 14, the powder application unit 16, and the thermal transfer unit 18 can each be considered as functional components of the printing system 10. In this case, for example, a device that includes the configuration for realizing the function of the printing unit 14 can be considered an example of a printing apparatus. Furthermore, when considering the configuration of the printing system 10 as an apparatus, multiple functional components may be realized in a single apparatus. For example, the print data preparation unit 12 and the printing unit 14 may be realized in a single apparatus. In this configuration, for example, the operation of generating print data from image data and the operation of executing printing can be performed in a single apparatus. Also, the printing unit 14 and the powder application unit 16 may be realized in a single apparatus. In this configuration, for example, the operation from printing to preheating can be performed in a single apparatus. Furthermore, it is also conceivable that the entire printing system 10 may be composed of a single apparatus. Moreover, depending on the configuration of the printing system 10, for example, any of the functional components shown in Figure 1(a) may be composed of multiple apparatuses. For example, the powder application unit 16 could be composed of a device for attaching hot melt resin powder to the transfer medium 50 and a device for preheating. In any configuration, it is preferable that the printing operation on the transfer medium 50 in the printing unit 14, the operation of attaching hot melt resin powder to the transfer medium 50 in the powder application unit 16, and the preheating operation performed in the powder application unit 16 be performed by a series of devices. In this case, performing multiple operations by a series of devices can be considered, for example, by performing multiple operations in succession without the user having to carry the transfer medium 50.

[0031] Next, the configuration of the head unit 102 in the printing unit 14 will be explained in more detail. Figure 2 is a diagram that further explains the multiple inkjet heads 202 that the head unit 102 has. Figures 2(a) to (c) are diagrams that show examples of the configuration of the head unit 102 and show examples of the arrangement of the multiple inkjet heads 202 that the head unit 102 has. As indicated by the reference numerals 202y, m, c, k, and t in the diagram to distinguish them, in this example the head unit 102 has multiple inkjet heads 202y, m, c, k, and t, each ejecting ink of a different color from each other. In addition, although not shown in the diagram, the head unit 102 further has, for example, a carriage that holds these inkjet heads 202.

[0032] Furthermore, among these inkjet heads 202, each of the multiple inkjet heads 202y, m, c, and k (hereinafter referred to as inkjet heads 202y-k) is an inkjet head that ejects color ink, and each ejects a different colored ink. More specifically, inkjet head 202y ejects yellow (Y) ink. Inkjet head 202m ejects magenta (M) ink. Inkjet head 202c ejects cyan (C) ink. Inkjet head 202k ejects black (K) ink. In this case, each of the YMCK inks is an example of the process color inks, which are the basic colors used for color representation in subtractive color mixing.

[0033] For each of the YMCK inks ejected from the respective inkjet heads 202y~k, known color inks can be used, for example. Suitable known color inks include, for example, inks used for textile printing, such as those used for printing onto fabric by transfer. Suitable textile inks include, for example, inks containing pigment as a colorant. More specifically, in this example, each of the YMCK inks is an ink that is fixed to the transfer medium 50 by the evaporation of the solvent, and includes a pigment, a dispersant, a binder resin, and a solvent. In this case, the pigment is an example of a colorant. The dispersant is a substance used to disperse the pigment in the solvent. The binder resin is a resin used to fix the pigment to the transfer medium 50. The binder resin can also be considered, for example, as a resin that is fixed to the transfer medium 50 together with the colorant in a colored ink. The solvent is a liquid that dissolves or disperses other components in the ink. Water or other aqueous solvents can be suitably used as the solvent. Alternatively, other solvents (organic solvents) may be used as the solvent for the ink. More specifically, in this example, the YMCK inks used in the inkjet heads 202y~k are aqueous pigment inks for textile printing used for transfer to a transfer medium such as fabric. In this case, known aqueous pigment inks can be suitably used.

[0034] The inkjet head 202t is an inkjet head that ejects clear ink. In this example, the clear ink is colorless and translucent because it does not contain colorants such as pigments. More specifically, as the clear ink, for example, an ink with a composition obtained by removing the pigments and dispersants from each color of YMCK ink can be suitably used. In this case, the clear ink can also be considered as, for example, an ink that fixes to the transfer medium 50 when the solvent evaporates. Furthermore, the clear ink can be considered to contain the same resin as the binder resin in each color of YMCK ink. With this configuration, for example, a clear ink with properties similar to each color of YMCK ink can be appropriately used. Alternatively, as the clear ink, for example, an ink that does not contain the same resin as the binder resin in each color of YMCK ink may be used.

[0035] In the head unit 102, the inkjet heads 202y to k are, for example, aligned in the sub-scanning direction and then aligned in the main scanning direction. In this case, the position of the inkjet head 202t in the sub-scanning direction may be different from that of the inkjet heads 202y to k, as shown in Figure 2(a), or it may be the same as that of the inkjet heads 202y to k, as shown in Figures 2(b) and (c). More specifically, in the example shown in Figure 2(a), the inkjet head 202t is located on one side in the sub-scanning direction relative to the arrangement of the inkjet heads 202y to k. In the example shown in Figure 2(b), the inkjet head 202t is located on one side in the main scanning direction relative to the arrangement of the inkjet heads 202y to k. Furthermore, the number of inkjet heads 202t in the head unit 102 may be multiple, as shown in Figure 2(c). In the example shown in Figure 2(c), each of the multiple inkjet heads 202t is positioned on one side and the other side in the main scanning direction relative to the arrangement of inkjet heads 202y to k. Furthermore, the arrangement of inkjet heads 202y to k and t in the head unit 102 may differ from that shown in Figures 2(a) to (c). For example, some of the inkjet heads 202y to k may be positioned differently from the other inkjet heads 202 in the sub-scanning direction.

[0036] In this example, the transfer medium could be, for example, a transfer film having an ink-receiving layer (accepting layer) that absorbs ink. The ink-receiving layer can be thought of as a layer that prevents ink bleeding by absorbing the ink before it spreads excessively on the transfer medium. By using such a transfer medium, it is possible to appropriately prevent, for example, the bleeding of color ink. Furthermore, in this case, in order to more appropriately prevent the bleeding of color ink, it is preferable to print in the printing section 14 (see Figure 1) such that the color ink lands before the clear ink at each position on the transfer medium. Regarding the color ink landing before the clear ink, for example, when a color ink of one color and clear ink are ejected at the same position, it can be thought of as the color ink of that color landing before the clear ink. Also, as explained above, a medium other than film, such as paper, may be used as the transfer medium. In this case as well, by using a transfer medium having an accepting layer, it is possible to appropriately prevent, for example, the bleeding of ink and to properly print on the transfer medium.

[0037] Furthermore, in this case, with the head unit 102 configured as shown in Figure 2(a), it is conceivable to position the inkjet head 202t downstream of the inkjet heads 202y~k in the transport direction of the transfer medium. The transport direction of the transfer medium can be considered, for example, the direction in which the transfer medium moves relative to the head unit 102. Also, when using the head unit 102 configured as shown in Figure 2(b), it is conceivable to position the inkjet head 202t behind the inkjet heads 202y~k in the direction of relative movement of the head unit 102 with respect to the transfer medium during the main scanning operation. Furthermore, when using the head unit 102 configured as shown in Figure 2(b), it is conceivable to set the direction of relative movement with respect to the transfer medium during the main scanning operation to bidirectional, in one direction and the other, and eject clear ink from the inkjet head 202t only during the main scanning operation in one direction. Furthermore, when using the head unit 102 with the configuration shown in Figure 2(c), for example, the direction of relative movement with respect to the transfer medium during the main scanning operation can be set to bidirectional, and clear ink can be ejected from the inkjet head 202t which is on the rear side of the inkjet heads 202y~k during the main scanning operation in each direction of movement. Depending on the quality required for printing, for example, clear ink may be deposited at each position on the transfer medium before the color ink. In this case, for example, the head unit 102 with the configuration shown in Figure 2(b) can be used, and the direction of relative movement with respect to the transfer medium during the main scanning operation can be set to bidirectional, and clear ink can be ejected from the inkjet head 202t during movement in both directions.

[0038] Next, we will explain in more detail the image transfer operation performed in the printing system 10. Figure 3 is a flowchart showing an example of the operation performed in the printing system 10 in this example. As explained above, in the printing system 10 of this example, the printing unit 14 transfers the image printed on the transfer medium to the transfer medium. In this case, first, the print data preparation unit 12 generates print data to be supplied to the printing unit 14 based on image data indicating the image to be printed on the transfer medium (S102). The operation of generating print data in the print data preparation unit 12 will be explained in more detail later. In this case, the printing unit 14 prints the image on the transfer medium based on the print data supplied from the print data preparation unit 12 (S104). In this example, the operation in step S104 is an example of the operation at the printing stage. In step S104, the printing unit 14 ejects color ink from the inkjet heads 202y~k in the head unit 102 to at least a part of the transfer medium. Then, clear ink is further ejected from the inkjet head 202t to at least a portion of the area on the transfer medium where color ink is ejected from any of the inkjet heads 202y to k. The reason for using clear ink in this example and how the clear ink is ejected will be explained in more detail later.

[0039] Furthermore, after printing on the transfer medium by the printing unit 14, the powder application unit 16 applies hot melt resin powder to the transfer medium on which the image is printed (S106). In this example, the operation in step S106 is an example of the operation in the hot melt resin application stage. In step S106, the application of hot melt resin powder to the transfer medium by the powder application unit 16 can be performed in the same or similar manner as, for example, the application of hot melt resin powder in a known transfer operation using hot melt resin powder. More specifically, the application of hot melt resin powder to the transfer medium can be performed automatically by a device, for example. In this case, the powder application unit 16 has, for example, a powder ejection unit that ejects hot melt resin powder toward the transfer medium. Alternatively, the application of hot melt resin powder to the transfer medium can be performed manually by the user (operator). In this case, the powder application unit 16 allows the user to perform the operation of applying hot melt resin powder to the transfer medium by, for example, holding the transfer medium on which the image is printed in a predetermined state.

[0040] In this example, the hot melt resin powder applied to the transfer medium adheres to the transfer medium by adhering to the ink on the transfer medium. Therefore, on the transfer medium, the hot melt resin powder adheres only to the positions where ink is ejected by the printing unit 14 in step S104. In this case, the hot melt resin powder in positions on the transfer medium where ink is not ejected is removed from the transfer medium, for example, before preheating is performed in the next step, using the same or similar methods as known. The removal of the hot melt resin powder may be performed automatically by the device or manually by the user.

[0041] Furthermore, in the powder application unit 16, after applying hot melt resin powder to the transfer medium and removing any excess hot melt resin powder, preheating is performed on the transfer medium (S108). In this case, it is conceivable to heat the transfer medium until it reaches a temperature at which the hot melt resin powder melts. With this configuration, for example, the hot melt resin powder can be properly fixed to the transfer medium. Fixation of the hot melt resin powder to the transfer medium can be considered, for example, as the hot melt resin powder being fixed to the transfer medium in a state where it can later be transferred to the transfer medium. Preheating can also be considered, for example, as an operation to heat the transfer medium to a predetermined temperature to make the hot melt resin powder tacky. The preheating performed in step S108 can also be performed in the same way as or in the same manner as known methods. More specifically, in step S108, for example, it is conceivable to heat the transfer medium so that the temperature of the hot melt resin powder is about 130°C (for example, about 120-150°C) and maintain that state for about 5 minutes (for example, about 1-10 minutes).

[0042] Furthermore, after preheating, the heat transfer unit 18 performs a transfer (heat transfer) from the transfer medium to the transfer medium (S110). In this example, the operation in step S110 is an example of the operation in the transfer stage. In step S110, the heat transfer unit 18 heats and pressurizes the transfer medium and the transfer medium while they are stacked on top of each other, thereby adhering the hot melt resin portion, which is a resin portion formed by the softening of hot melt resin powder by heating, to the transfer medium. The hot melt resin portion can be thought of as, for example, a resin portion composed of hot melt resin powder that has become tacky by heating. The hot melt resin portion may also be, for example, a resin formed by the integration of softened hot melt resin powder. In this example, in step S110, the colorant that expresses the color in the image printed on the transfer medium is adhered to the transfer medium together with at least a part of the hot melt resin portion, and the image is transferred from the transfer medium to the transfer medium. Such an operation can be considered, for example, as an operation to transfer an image from one transfer medium to another by moving at least a portion of the colorant attached to the transfer medium together with at least a portion of the hot melt resin portion to the transfer medium. The transfer performed in step S110 can also be carried out in the same way as, for example, known methods. More specifically, in step S110, the hot melt resin portion is attached to the transfer medium by heating at a temperature higher than the preheating temperature in step S108 while applying pressure. In this case, for example, the transfer medium and the transfer medium can be heated so that the temperature of the hot melt resin portion is about 140°C (for example, about 100 to 180°C). Furthermore, the heating and pressurizing time in step S110 can be made shorter than the heating time in the preheating in step S108. For example, the heating and pressurizing time in step S110 can be made about 5 seconds (for example, about 1 to 30 seconds).

[0043] After transferring the image from the transfer medium to the transfer target medium in step S110, the transfer medium is peeled off the transfer target medium (S112). In this case, the transfer target medium on which the image has been transferred can be considered as the output product (printed material) of the printing system 10. The peeling off of the transfer medium in step S112 can also be carried out in the same way as, for example, known methods. Furthermore, in this example, a transfer medium having a release layer formed on its surface can be suitably used. With this configuration, for example, the peeling off of the transfer medium in step S112 can be carried out easily and appropriately.

[0044] Through the above operations, the printing system 10 can appropriately produce printed output. Furthermore, in this case, by using clear ink in addition to color ink when printing to the transfer medium, it is possible to improve transferability and reduce transfer unevenness, and to reduce graininess, for example.Therefore, the reasons for using clear ink in this example and the method of ejecting the clear ink will be explained in more detail below.

[0045] Figure 4 is a diagram explaining the reasons for using clear ink in this example, and shows an example of how to print on the transfer medium 50 in this example compared with conventional methods. Figure 4(a) shows an example of how to print on the transfer medium 50 in a conventional method. Figure 4(b) shows an example of how to print on the transfer medium 50 using a method different from that shown in Figure 4(a). Figure 4(c) shows an example of how to print on the transfer medium 50 in this example.

[0046] As explained above, in this example, it is conceivable to use a transfer medium 50 on which an ink receiving layer 54 is formed. Furthermore, such a transfer medium 50 can also be suitably used in conventional methods. In this case, the transfer medium 50 has a base portion 52 and an ink receiving layer 54, as shown in Figures 4(a) to 4(c). The base portion 52 is the substructure of the transfer medium 50. The ink receiving layer 54 is a layer for absorbing ink and is formed on the surface of the base portion 52. The ink receiving layer 54 can be considered, for example, as constituting a part of the base portion 52. In this case, the base portion 52 can also be considered as constituting the entire transfer medium 50. In this example, the printing unit 14 (see Figure 1) in the printing system 10 performs printing on the transfer medium 50 by ejecting ink onto the ink receiving layer 54 on the transfer medium 50, thereby forming an ink layer on the transfer medium 50. In addition, in the conventional configuration, printing is performed on the transfer medium 50 by forming a layer of ink on the transfer medium 50 using a printing device corresponding to the printing unit 14.

[0047] Furthermore, in the conventional method shown in Figure 4(a), for example, a printing apparatus having an inkjet head for color ink and an inkjet head for white ink is used, with a different configuration from the printing unit 14 in this example, to form a color ink layer 302 and a white ink layer 304 on the printing area 300 on the surface of the transfer medium 50. In this case, the color ink layer 302 is a layer of ink formed with color ink. The white ink layer 304 is a layer of ink formed with white ink. The white ink layer 304 can be considered, for example, a layer that hides the background color of the transfer medium after transfer and functions as a background in the subtractive color mixing method. The printing area 300 can be considered, for example, an area where color ink is ejected from the inkjet head. In this case, for example, as shown in the figure, the color ink layer 302 is formed on the transfer medium 50, and then the white ink layer 304 is formed on top of it so as to cover the entire color ink layer 302. The white ink layer 304 is formed, for example, to completely fill the printing area 300 with a predetermined density.

[0048] In this case, after forming a color ink layer 302 and a white ink layer 304 on the transfer medium 50, hot melt resin powder, shown as resin powder 352 in the figure, is attached to the white ink layer 304, as shown in the lower part of Figure 4(a). After attaching the resin powder 352, the transfer medium 50 and the transfer medium are placed on top of each other, and the image is transferred from the transfer medium 50 to the transfer medium by heating and pressurizing. When printing and transferring in this manner, the amount of ink at each position of the printing area 300 is sufficiently large because a solid white ink layer 304 is formed. Therefore, the resin powder 352 can be properly attached to the printing area 300 on the transfer medium 50. Furthermore, this allows for proper attachment of the resin powder 352 and high-quality image transfer, even when transferring images that include low-gradation areas where the amount of ink in the color ink layer 302 is small. Furthermore, in this case, after the image is transferred, the white ink layer 304 becomes a lower layer than the color ink layer 302 on the transfer medium and functions as a background for the color ink layer 302. Therefore, even when using a dark-colored fabric or the like as the transfer medium, the image can be properly represented on the transfer medium.

[0049] However, in this case, the portion corresponding to the white ink layer 304 is also transferred to the transfer medium in addition to the original image, which may impair the design and texture. For example, when using light-colored fabrics such as white or beige as the transfer medium, or when expressing a design that takes advantage of the color and texture of the fabric used as the transfer medium (for example, when using off-white fabric), it may be undesirable to form the white ink layer 304. Also, when using light-colored fabrics such as white as the transfer medium, the base color of the transfer medium after transfer becomes a light-reflective color, so color expression using the subtractive color mixing method can be performed appropriately even without forming the white ink layer 304. In such cases, it is also conceivable to transfer the image without forming the white ink layer 304, as shown in Figure 4(b). In this case, a color ink layer 302 is formed on the printing area 300 of the transfer medium 50 using a printing device having an inkjet head for color inks. Then, resin powder 352 is directly attached on top of the color ink layer 302. Furthermore, after applying the resin powder 352, the transfer medium 50 and the transfer medium are placed on top of each other, and the image is transferred from the transfer medium 50 to the transfer medium by heating and pressurizing. In this way, the image can also be transferred from the transfer medium 50 to the transfer medium. However, depending on the state of the image drawn on the transfer medium 50, the transfer rate may decrease in some parts of the image, resulting in unintended uneven transfer.

[0050] More specifically, the color ink layer 302 is formed by ejecting color inks of each color according to the image drawn on the transfer medium 50. In this case, the amount of ink ejected will differ depending on the position in the printing area 300. For example, in the low-gradation range that expresses lighter colors in the image, the amount of ink will be less compared to the high-gradation range that expresses darker colors. As a result, differences in how the resin powder 352 adheres will easily occur depending on the position in the printing area 300. In this case, for example, in the low-gradation range where the amount of ink is less, the amount of resin powder 352 adhering will be less, which may reduce the transferability. As a result, uneven transfer may occur. Furthermore, reduced transferability may result in poor expression of low gradations. In this regard, for example, in the method shown in Figure 4(a), a solid white ink layer 304 is formed on top of the color ink layer 302, so even if there are differences in the amount of color ink ejected at each position, differences in transferability can be appropriately prevented. However, in the method shown in Figure 4(b), the absence of a white ink layer 304 makes transfer unevenness more likely, as described above.

[0051] In contrast, in this example, by using clear ink in addition to color ink, the occurrence of transfer unevenness is prevented without forming a white ink layer 304. In this case, in the printing section 14, as shown in Figure 4(c), for example, an image layer 306, which is a layer of ink formed by the color ink and clear ink, is formed on the printing area 300 of the transfer medium 50 using color ink and clear ink. Then, without forming a white ink layer 304, etc., the resin powder 352 is directly attached to the image layer 306. Furthermore, after attaching the resin powder 352, the transfer medium 50 and the transfer medium are placed on top of each other, and the image is transferred from the transfer medium 50 to the transfer medium by heating and pressurizing.

[0052] Thus, in this example, by using clear ink in addition to color ink when printing onto the transfer medium 50 by the printing unit 14, it is possible to appropriately eject inks other than color ink onto the transfer medium 50 while appropriately suppressing the influence of the color of the image printed on the transfer medium 50. In this way, for example, even in positions in the printing area 300 where the amount of color ink is small, such as in the low-gradation range, clear ink can be ejected, increasing the total amount of ink ejected onto the transfer medium 50 compared to when only color ink is used. Furthermore, by increasing the total amount of ink, for example, the resin powder 352 can be appropriately adhered to the transfer medium 50. In addition, this makes it possible to appropriately prevent, for example, a decrease in transferability due to insufficient resin powder 352 or the occurrence of transfer unevenness when transferring an image from the transfer medium 50 to the transfer medium. Therefore, according to this example, for example, image transfer using resin powder 352 can be performed more appropriately without forming a white ink layer 304. Also, in this case, unlike white ink containing white pigment, etc., clear ink can be used while suppressing the impact on design aesthetics. Furthermore, since clear ink becomes less noticeable on the transfer medium after transfer, it becomes possible to select and use it only in necessary areas, for example. Therefore, as shown in this example, it becomes possible to perform transfers of higher quality while appropriately preventing damage to the design and texture.

[0053] Furthermore, in this example, by using clear ink in addition to color ink, it becomes possible to reduce, for example, the graininess after transfer. More specifically, when printing using an inkjet method on a transfer medium 50 having an ink receiving layer 54, as in this example, it can be considered that the ink will not spread easily on the transfer medium 50 after landing. As a result, it is possible that graininess will be more likely to occur, for example, especially in the low-gradation range. Moreover, when performing transfer by attaching resin powder 352, it can be considered that the amount of resin powder 352 that adheres depends on the amount of ink (printed amount) ejected at that position. Therefore, for example, when transferring an image using the method shown in Figure 4(b), the amount of resin powder 352 that adheres will be small in the low-gradation range where the printed amount is small, and the transferability will decrease, making the graininess more noticeable on the transfer medium after transfer.

[0054] In contrast, in this example, by using clear ink in addition to color ink, the color ink on the transfer medium 50 can be made to spread more easily compared to the case where only color ink is used. Furthermore, this makes it possible to increase the size of the ink dots formed on the transfer medium 50 by the color ink, thereby reducing the appearance of graininess. In this case, as mentioned above, the use of clear ink can also appropriately prevent a decrease in transferability in the low-gradation range. Therefore, for example, it is possible to more appropriately prevent graininess from becoming noticeable on the transfer medium after transfer. In this case, it is preferable that the printing unit 14 ejects the color ink and clear ink such that the clear ink lands on each position where the color ink is ejected on the transfer medium 50 before the color ink is completely dry. With this configuration, for example, a state in which the color ink spreads easily on the transfer medium 50 can be more appropriately achieved.

[0055] Furthermore, as can be understood from the above explanation, in this example, it is particularly preferable to eject clear ink to positions in the low-gradation range of the image. Therefore, the following will explain in more detail an example of how to eject clear ink. Figures 5 and 6 are diagrams illustrating an example of how to eject clear ink in this example. Figure 5 is a diagram illustrating an image to be printed on the transfer medium 50. Figure 5(a) shows an example of an image to be printed on the transfer medium 50. Figure 5(b) shows an example of the state of the dots of the color inks that make up the image.

[0056] As in this example, when printing (color printing) is performed using multiple color inks by the printing unit 14 (see Figure 1), the amount of each color ink ejected to each position on the transfer medium 50 changes according to the color to be expressed at that position. In this case, for example, the gradation can be considered to change depending on the position of the image. The printing unit 14 then prints an image having, for example, a high-gradation section 312, a medium-gradation section 314, and a low-gradation section 316 onto the transfer medium 50. More specifically, Figure 5(a) shows an example of an image to be printed when printing is performed on multiple printing areas 300a to c by the printing unit 14. In this case, printing area 300a is a printing area that includes a high-gradation section 312, a medium-gradation section 314, and a low-gradation section 316. Printing area 300b is a printing area consisting only of a low-gradation section 316. Printing area 300c is a printing area consisting only of a high-gradation section 312. Furthermore, in this example, each of the printing areas 300a to c is an example of an image representation area in which color ink is ejected from one of the inkjet heads 202y to k (see Figure 2) on the transfer medium 50.

[0057] In this case, the high-gradation section 312 can be considered, for example, as a part of the image that expresses colors with a gradation higher than a predetermined first standard. In this case, the fact that the image's gradation is higher than the first standard can be considered, for example, as the gradation of a color corresponding to any of the color inks (any of the YMCK colors) being higher than the first standard. The medium-gradation section 314 can be considered, for example, as a part of the image other than the high-gradation section 312 and the low-gradation section 316. The low-gradation section 316 can be considered, for example, as a part of the image that expresses colors with a gradation lower than a predetermined second standard that is lower than the first standard. In this case, the fact that the image's gradation is higher than the second standard can be considered, for example, as the gradation of all the colors in the color inks (all the YMCK colors) being lower than the second standard. The high-gradation section 312 can also be considered, for example, as a part that expresses colors in a predetermined high-gradation range. The high-gradation section 312 can also be considered, for example, as a region of the image that expresses dark or rich colors. Furthermore, the low-gradation section 316 can be considered, for example, as a region that expresses colors in a predetermined low-gradation range. The low-gradation section 316 can also be considered, for example, as a part of an image that expresses light or bright colors.

[0058] Furthermore, when printing using an inkjet method, as in the printing section 14 of this example, gradation is expressed by changing the density of ink dots formed per unit area. In this case, in the high-gradation section 312, for example, as shown on the left side of Figure 5(b), many dots 402 are formed densely. In the low-gradation section 316, for example, as shown on the right side of Figure 5(b), fewer dots 402 are formed sparsely compared to the high-gradation section 312. In Figure 5(b), the intersections of the vertical and horizontal dashed lines indicate the ink ejection positions set according to the printing resolution. In this case, the high-gradation section 312, the medium-gradation section 314, and the low-gradation section 316 in the image can also be considered in relation to the amount of color ink ejected per unit area. More specifically, in this case, the high-gradation section 312 can be considered, for example, as a region where the amount of color ink ejected per unit area is increased. Furthermore, the low-gradation section 316 can be considered, for example, as a region that reduces the amount of color ink ejected per unit area.

[0059] In this example, the low-gradation section 316 is an example of a low-ink area, which is a region where the amount of color ink ejected per unit area is less than a preset standard amount. The high-gradation section 312 is an example of a non-low-ink area, which is at least a part of a region that does not fall under the low-ink area. The non-low-ink area can be considered, for example, as a region in each of the printing areas 300a to c where the amount of color ink ejected per unit area is greater than a predetermined amount. In this example, this predetermined amount can be considered to be larger than the standard amount mentioned above for the low-ink area. Depending on the configuration of the printing section 14, for example, the combined portion of the high-gradation section 312 and the medium-gradation section 314 can also be considered an example of a non-low-ink area. In this case, the predetermined amount mentioned above for the non-low-ink area can be considered to be the same amount as the standard amount mentioned above for the low-ink area.

[0060] Furthermore, as explained above, in this example, the printing unit 14 uses clear ink in addition to color ink to print on the transfer medium 50. In this case, the clear ink is ejected to at least a portion of the low-gradation areas 316 in the image. In this case, it is conceivable that the color ink and clear ink be ejected at ejection positions set on the transfer medium 50 according to the printing resolution, for example, as shown in Figure 6.

[0061] Figure 6 shows examples of ejection positions for color ink and clear ink, focusing on some of the multiple ejection positions in the low-gradation section 316 (see Figure 5) to show examples of ejection positions for color ink and clear ink. Figures 6(a) to (c) show examples of how to select an ejection position for clear ink, showing various examples of how to eject clear ink to positions in the low-gradation section 316 where color ink dots 402 are discretely formed. Positions where color ink dots 402 are discretely formed can be considered, for example, as shown in the upper left of each of Figures 6(a) to (c), where multiple color ink dots 402 are formed with spaces in between. In this case, it can be considered that the multiple dots 402 are spread out to a size that does not touch each other. In this case, for example, if clear ink is not used, the amount of ink per unit area will decrease, and the transferability may decrease.

[0062] In contrast, in this example, as explained above, the amount of ink per unit area is increased by further using clear ink. When considering how to eject the clear ink, if we consider increasing the total amount of ink ejected near each ejection position, the simplest approach is to eject a predetermined amount of clear ink to all ejection positions, as shown in the lower left of Figure 6(a). In this case, the lower left figure shows the arrangement of ink dots 404 formed by clear ink at the same positions as the multiple ejection positions shown in the upper left. Also, in the case shown in Figure 6(a), the clear ink dots 404 are formed at all ejection positions that are spaced according to the print resolution. In this case, when the color ink dots 402 and the clear ink dots 404 are combined, as shown on the right side of the figure, clear ink dots 404 are formed at both the positions where color ink dots 402 are present and the positions where color ink dots 402 are not present. With this configuration, for example, in the low-gradation range where the amount of color ink is small, clear ink is added to compensate for the amount of ink. Therefore, with this configuration, for example, the total amount of ink dispensed near each ejection position can be appropriately increased.

[0063] However, depending on the required print quality, it may be preferable to dispense clear ink at only some of the ejection positions rather than at all of them. More specifically, for example, if dispensing clear ink at all ejection positions results in an excessive amount of ink per unit area, it may be possible to reduce the number of positions at which clear ink is dispensed to match the preferred upper limit of ink volume. In this case, for example, as shown in Figures 6(b) and (c), clear ink dots 404 may be formed at only some of the ejection positions.

[0064] More specifically, in the example shown in Figure 6(b), as shown in the lower left of the figure, clear ink dots 404 are formed only at ejection positions where color ink dots 402 are not formed. In this case, when the color ink dots 402 and clear ink dots 404 are combined, as shown on the right side of the figure, either color ink dots 402 or clear ink dots 404 will be formed at each ejection position. Even with this configuration, for example, in the low-gradation range where the amount of color ink is small, clear ink is added to compensate for the amount of ink. Therefore, even with this configuration, for example, the total amount of ink ejected near each ejection position can be appropriately increased.

[0065] Furthermore, the ejection position for clear ink does not necessarily have to precisely match the ejection position for color ink. More specifically, when printing with an inkjet method, the ejection position for color ink is determined, for example, by halftone processing. In this case, even if the tonal range expressed is the same, the ejection positions for color ink are not necessarily the same. Also, in this example, if clear ink is ejected at only some ejection positions, the ejection position for clear ink can also be determined by a predetermined process, such as halftone processing. In this case, the ejection position for clear ink will also be determined by the result of the process. In such cases, the relationship between the ejection position for color ink and the ejection position for clear ink does not need to be strictly determined to a predetermined relationship, but rather can be determined, for example, by the relationship between the tonal range of the image before halftone processing, or the relationship between the amount of ink ejected per unit area. In this case, as shown in Figure 6(c), for example, at some of the ejection positions where the color ink dots 402 are formed, both the color ink dots 402 and the clear ink dots 404 will be formed, while at other ejection positions, only the color ink dots 402 will be formed, without the clear ink dots 404. Furthermore, at some of the ejection positions where the color ink dots 402 are not formed, the clear ink dots 404 will be formed. Even with this configuration, it can be considered as if the amount of ink is being supplemented by adding clear ink to the low-gradation range where the amount of color ink is small. Therefore, even with this configuration, for example, the total amount of ink ejected near each ejection position can be appropriately increased.

[0066] Furthermore, the method for selecting the ejection position for the clear ink is not limited to the method described above; other methods may be used. For example, based on the results of the halftone process, the ejection position where the color ink dot 402 is formed may be confirmed, and the ejection position where the dot 404 is formed may be determined accordingly. In this case, it is conceivable to form the clear ink dot 404 at the ejection position where the color ink dot 402 is formed, such as an ejection position adjacent to the ejection position where the color ink dot 402 is formed. In this case, the clear ink dot 404 may also be formed at the ejection position where the color ink dot 402 is formed.

[0067] Furthermore, as can be understood from the above explanation, in this example, the adhesion of the hot melt resin powder is enhanced by dispensing clear ink in areas of the printing area of ​​the transfer medium 50 where the amount of color ink dispensed is small. In this case, in areas where the amount of color ink dispensed is sufficiently large, it is possible to adhere a sufficient amount of hot melt resin powder without using clear ink. Also, for example, if the total amount of ink, including both color ink and clear ink, dispensed per unit area becomes too large, problems such as bleeding of the color ink are more likely to occur. For this reason, the amount of clear ink dispensed at each position on the transfer medium 50 may be varied, for example, according to the amount of color ink dispensed at each position.

[0068] More specifically, if we define the amount of clear ink ejected per unit area at each position of the transfer medium 50 as the clear ink ejection amount, then it is conceivable to have different clear ink ejection amounts in the printing area between the high-gradation section 312 (see Figure 5), where the amount of color ink ejected per unit area is greater, and the low-gradation section 316, where the amount of color ink ejected per unit area is less. In this case, for example, the clear ink ejection amount in the low-gradation section 316 can be made greater than the clear ink ejection amount in the high-gradation section 312, so that the clear ink ejection amount varies according to the amount of color ink ejected per unit area. With this configuration, for example, it is possible to appropriately eject clear ink to the necessary locations while suppressing the amount of clear ink used. Furthermore, by reducing the clear ink ejection amount in the high-gradation section 312, it is possible to prevent, for example, the total amount of ink ejected at the same position from becoming excessively large.

[0069] Regarding the clear ink discharge amount, for example, it may be different for the medium gradation section 314 and the low gradation section 316. In this case, for example, the clear ink discharge amount in the low gradation section 316 may be greater than the clear ink discharge amount in the medium gradation section 314, and the clear ink discharge amount may be different depending on the amount of color ink discharged per unit area. Also, regarding the clear ink discharge amount, for example, it may be different for the high gradation section 312 and the medium gradation section 314. In this case, for example, the clear ink discharge amount in the medium gradation section 314 may be greater than the clear ink discharge amount in the high gradation section 312, and the clear ink discharge amount may be different depending on the amount of color ink discharged per unit area. Furthermore, for example, in areas where a large amount of color ink is discharged, such as the high gradation section 312, the clear ink discharge amount may be set to zero. In this case, for example, clear ink is not discharged at positions where the amount of color ink discharged per unit area exceeds a preset upper limit. This configuration allows for a more effective prevention of situations where, for example, the total amount of ink ejected at the same location becomes excessively large.

[0070] Furthermore, as explained above, in this example, by using clear ink, for example, the adhesion of the hot melt resin powder in the low-gradation section 316 is enhanced. In this case, it can be considered that by using clear ink, for example, the transfer rate of the pigment, which is a colorant, is increased. In this case, if the transfer rate is defined as the proportion of the colorant that moves from the transfer medium 50 to the transfer medium during transfer, then by ejecting clear ink to at least a part of the low-gradation section 316 during printing in the printing section 14, it can be considered that, for example, the transfer rate in at least a part of the low-gradation section 316 is increased compared to when clear ink is not ejected. Also, in this case, focusing on the low-gradation section 316, for example, by ejecting clear ink to at least a part of the low-gradation section 316 by the printing section 14, it can be considered that the amount of hot melt resin powder that adheres to the powder application section 16 (see Figure 1) at the position where the clear ink was ejected is greater than when clear ink is not ejected.

[0071] As explained above, when printing using an inkjet method, the ejection position of the color ink is determined, for example, by halftone processing. In the printing system 10 of this example, the print data preparation unit 12 (see Figure 1) generates print data by performing halftone processing on the image data. In this case, it is conceivable that the ejection position of the clear ink is also determined in the series of operations performed by the print data preparation unit 12 to generate the print data. In this case, the print data preparation unit 12 generates the print data by the operation shown in Figure 7, for example.

[0072] Figure 7 is a flowchart illustrating an example of the operation of generating print data in the print data preparation unit 12. As explained above, in this example, the print data preparation unit 12 generates print data to be supplied to the print unit 14 based on image data that shows the image to be printed on the transfer medium 50 in the print unit 14. In this operation, first, image data is input to the print data preparation unit 12 (S202). As image data, for example, it is conceivable to use general known color image data that shows a color image. Furthermore, as such image data, for example, an RGB image that shows a color image with red (R), green (G), and blue (B) as primary colors can be suitably used. Regarding the input of image data, for example, it is conceivable to input it to the print data preparation unit 12 from outside the print data preparation unit 12 via a network or storage media. Furthermore, as the color image shown by the image data, it is conceivable to use an image that shows each of the basic colors (primary colors) of color representation in three or more gradations. More specifically, as the color image data, for example, an image that represents each of the basic RGB colors with 8 bits or more of gradation can be suitably used.

[0073] Furthermore, after the image data is input, the print data preparation unit 12 performs preprocessing on the image data in accordance with the halftone processing to be performed later (S204). This preprocessing may include, for example, resolution conversion processing, color conversion processing, and color separation processing. In this case, resolution processing is, for example, a process that changes the resolution of the image to match the resolution of the print to be performed in the print unit 14. Color conversion processing is, for example, a process that converts the color of the image to match the color of the ink used in the print unit 14. In color conversion processing, for example, the image shown in the print data may be converted into an image that expresses the colors in the YMCK color system according to the YMCK inks used for printing. Color separation processing can be, for example, a process that separates the image to be processed into images for each color of ink used in the print unit 14. The print data preparation unit 12 then performs color separation processing on the image after the resolution change processing and color conversion processing have been performed, generating multiple grayscale images, each corresponding to one of the YMCK colors. In this case, the grayscale images corresponding to each YMCK color can be thought of as indicating, for example, the amount of ink of that color ejected at each position in the image. As for the grayscale images corresponding to each YMCK color, for example, it is conceivable to generate grayscale images with 8 bits or more of gradation.

[0074] Furthermore, in this example, after performing the above preprocessing, the print data preparation unit 12 generates a clear image, which is an image used to determine the ejection position for ejecting clear ink (S206). In this case, the clear image can be considered, for example, an image on which the ejection position of clear ink is determined by subsequent halftone processing. For example, a grayscale image can be generated as the clear image. In this case, the clear image can be considered, for example, to indicate the amount of clear ink to be ejected for each position in the image. For example, an image with the same number of gradations as the grayscale images corresponding to each color of YMCK generated in the color separation process can be generated as the clear image. More specifically, in this example, the print data preparation unit 12 calculates the total amount of color ink to be ejected for each position in the image based on the grayscale images corresponding to each color of YMCK generated in the color separation process. Then, based on this total amount, the value (gradation) of each pixel in the clear image is determined. With this configuration, for example, the amount of clear ink ejected can be appropriately changed according to the amount of color ink ejected for each position in the image during printing by the printing unit 14.

[0075] Furthermore, after generating the clear ink image, the print data preparation unit 12 performs halftone processing on the grayscale images corresponding to each YMCK color and the clear ink image (S208). Halftone processing can be thought of as, for example, a process to reduce the number of gradations of the image to match the configuration of the print unit 14. Halftone processing can also be thought of as, for example, a process (RIP processing) to generate a raster image that specifies the ejection position for the ink of the color corresponding to the grayscale image. In this example, the print data preparation unit 12 generates a raster image that specifies the ejection position for the ink of the color corresponding to each YMCK color by performing halftone processing on the grayscale images corresponding to each YMCK color. The print data preparation unit 12 also generates a raster image that specifies the ejection position for the clear ink by performing halftone processing on the clear ink image. The print data preparation unit 12 supplies the data including these raster images to the print unit 14 as print data. With this configuration, for example, print data specifying the ejection positions for each color ink and clear ink can be appropriately supplied to the print unit 14.

[0076] Here, regarding the operation of the print data preparation unit 12, it can be performed in the same way as or in the same manner as known operations for generating print data, except for the points described above. Furthermore, of the operations of the print data preparation unit 12 described above, operations other than those related to the clear image can be performed in the same way as, for example, known operations for generating print data. Also, as described above, in this example, the print data preparation unit 12 performs a color separation process based on the image data input to the print data preparation unit 12 to generate grayscale images corresponding to each color of YMCK. Then, it generates a clear image based on the grayscale images corresponding to each color of YMCK generated by the color separation process. In this case, it can be considered that the clear image is also generated based on the image data input to the print data preparation unit 12, for example. Furthermore, in this case, regarding the operation of the print data preparation unit 12, it can be considered that, for example, the ejection position of the clear ink is automatically determined based on image data that does not directly specify the ejection position of the clear ink. Furthermore, regarding the operation of the print data preparation unit 12, it can be considered that, for example, the amount of clear ink to be ejected at each position of the image is determined according to the gradation of the image shown by the image data. Furthermore, in a modified operation of the print data preparation unit 12, instead of generating a clear image in the print data preparation unit 12, data indicating the clear image may be supplied to the print data preparation unit 12 along with the image data. In this case, it is also conceivable that data directly indicating the ejection position of the clear ink may be supplied to the print data preparation unit 12 instead of a clear image.

[0077] Next, we will explain the experiments conducted by the inventors of this application in relation to the configuration described above. As explained above, when printing is performed on a transfer medium using only color ink, it is conceivable that the transferability from the transfer medium to the transfer target medium will decrease in the low-gradation range (low-gradation areas). In this case, it is conceivable that graininess will become more noticeable in the low-gradation range of the image after transfer to the transfer target medium. In contrast, in this example, the transferability of the image is improved and graininess is reduced (improved) by supplementing the total amount of ink (liquid volume) with clear ink. Furthermore, the inventors of this application have actually conducted experiments to confirm that graininess is reduced by using clear ink.

[0078] Figure 8 illustrates an experiment conducted by the inventor of the present invention. Figure 8(a) shows the composition of the clear ink used in the experiment. Figures 8(b) and (c) show the results of the experiment. In this experiment, a known aqueous pigment ink was used as the color ink. For the convenience of the experiment, only black ink, which shows the granularity most clearly, was used as the color ink. Two types of clear inks, shown as ink A and ink B in the figure, were used. In this case, ink A can be considered, for example, as an ink from which the pigment, which is the coloring agent, has been removed from the color ink. Ink B can be considered, for example, as an ink from which the pigment, which is the coloring agent, and the resin (resin emulsion) corresponding to the binder resin have been removed from the color ink. In this case, inks A and B can be considered to be substantially transparent inks. Furthermore, ink A can be considered, for example, as an ink that is transparent and contains resin.

[0079] In this experiment, as shown in Figure 8(b), the amount of color ink and clear ink dispensed per unit area was varied, and the granularity of the transferred material was checked. The observed granularity was then quantified using a limit sample. In the table shown in Figure 8(b), the upper table shows the experimental results when using ink A. The lower table shows the experimental results when using ink B. In the table, the numerical values ​​0 to 200 corresponding to ink A or ink B indicate the amount of clear ink (ink A or ink B) dispensed per unit area (printed amount). The numerical values ​​0 to 200 corresponding to color ink (black) indicate the amount of color ink dispensed per unit area. In this numerical value, 0 indicates that the corresponding ink is not dispensed. The amount of ink dispensed per unit area increases proportionally to the numerical value. The granularity was evaluated using a 5-point scale from 1 to 5. In this case, the state where the graininess is most noticeable corresponds to a numerical value of 1, and the state where the graininess is least noticeable corresponds to a numerical value of 5.

[0080] As can be seen from the table in the diagram, if clear ink is not dispensed, a small amount of colored ink dispensed will make the graininess more noticeable. Conversely, if the amount of colored ink dispensed is small, increasing the amount of clear ink dispensed can reduce the graininess. Furthermore, whether ink A or ink B is used as the clear ink, the graininess can be reduced. Moreover, when comparing ink A and ink B, ink B reduces the graininess with a smaller amount of dispensed ink. This can be attributed in part to the fact that ink A does not contain resin, making it more prone to drying compared to ink B. More specifically, hot melt resin powder can be considered to adhere easily to inks containing liquid components even before they are completely dry. Therefore, when using ink B, which dries easily, it is often necessary to dispense a larger amount compared to ink A. Also, in ink B, the resin can be considered to maintain its tackiness even when it is partially dry. Therefore, in this respect as well, ink B can be considered to reduce the graininess with a smaller amount of dispensed ink.

[0081] Furthermore, the results shown in Figure 8(b) indicate that, regardless of whether ink A or ink B is used, the graininess can be sufficiently reduced when the total amount of ink discharged, combining the amount of color ink and the amount of clear ink, exceeds a certain amount. This also suggests that, for example, in areas where the amount of color ink discharged is sufficiently large, graininess will not occur even without discharging clear ink. Therefore, the results of this experiment also indicate that it is preferable to vary the amount of clear ink discharged in accordance with the amount of color ink discharged.

[0082] Furthermore, as explained above, in this example, it is possible to prevent transfer unevenness by using clear ink. And, regarding transfer unevenness, as explained above regarding graininess, it was possible to appropriately prevent it regardless of whether ink A or ink B was used as the clear ink. More specifically, the results of the evaluation regarding transfer unevenness when using ink A are shown in the table in Figure 8(c). In the table in Figure 8(c), the amount of color ink and clear ink are shown as the ejection amount (print amount) per unit area. In each cell in the table, the total ink ejection amount, which is the sum of the amount of color ink and the amount of clear ink, is shown as the total print amount per unit area. In this table, the area enclosed by a thick solid line indicates the area where no problematic transfer unevenness occurred. This area can be considered, for example, as the area where transfer unevenness is eliminated by the ejection of clear ink. Furthermore, within the upper left of the area enclosed by the thick solid line, the area enclosed by the dashed lines on the top and left sides and the thick solid lines on the bottom and right sides is an area where only minor transfer irregularities occurred. This area can be considered, for example, as an area where transfer irregularities are significantly reduced by the ejection of clear ink. From the results shown in Figure 8(c), it can be confirmed that, when using ink A, the transferability is improved by using clear ink in addition to the color ink. Moreover, in this case, it can be confirmed that transfer irregularities can be prevented by using clear ink, especially in the low-gradation range where transfer irregularities occur if clear ink is not used.

[0083] In the above experiment, the ejection of color ink and clear ink (ink A or ink B) was performed by ejecting the color ink to each position on the transfer medium, and then ejecting the clear ink to the same position before the color ink at that position was completely dry. In this case, it can be considered that the conditions for ejecting the color ink and clear ink onto the transfer medium simultaneously were met. Although not shown in the diagram, an experiment corresponding to the table in Figure 8(c) was also performed for ink B. This experiment confirmed that the transferability of ink B is improved by using clear ink in addition to color ink, and that transfer unevenness can be prevented by using clear ink in the low-gradation range where transfer unevenness occurs without clear ink.

[0084] Next, we will provide supplementary explanations regarding the configuration described above. As explained above, in this example, a textile printing ink containing a pigment as a coloring agent (textile pigment ink) can be suitably used as the color ink. In this case, for example, an ink with a composition obtained by removing the coloring agent (pigment) and dispersant from the color ink can be suitably used as the clear ink. In this regard, if the ink properties (liquid properties) of the color ink and clear ink used simultaneously in the printing unit 14 differ significantly, differences will occur in how the inks aggregate and separate on the transfer medium, which may cause a decrease in print quality (poor print quality). In contrast, when using a clear ink as described above, it is possible to appropriately prevent a large difference in properties between the color ink and the clear ink. Furthermore, this makes it possible to perform high-quality printing more appropriately.

[0085] Furthermore, as explained above, in this case, it is conceivable to use a color ink containing a binder resin and a clear ink containing the same resin as the binder resin in the color ink. In this case, by including the same resin as the binder resin, it can be assumed that the clear ink will remain in a state where hot melt resin powder adheres more easily for a longer period of time compared to, for example, a clear ink without resin. Therefore, by using a clear ink containing resin, it is possible to more reliably adhere hot melt resin powder to the position where the clear ink is dispensed. Also, as can be understood from the experimental results explained above using Figure 8, it is also possible to use, for example, an ink without resin as the clear ink. In this case as well, by using a clear ink, it is possible to extend the time until the ink dries to a state where hot melt resin powder does not adhere easily to the position where the clear ink is dispensed. Furthermore, this allows for proper adhesion of hot melt resin powder to the position where the clear ink is dispensed, even when using a clear ink without resin. Regarding the difference in composition between the color ink and the clear ink, the reduction in volume resulting from removing some components (colorants, etc.) from the color ink in the clear ink can be adjusted by appropriately changing the amount of solvent. Furthermore, it is conceivable to use a different resin for the clear ink than the binder resin used in the color ink.

[0086] Furthermore, as explained above, in this example, by using clear ink in addition to color ink, it is possible to make the ink dots of the color ink more prone to wetting and spreading, and to increase the size of the dots. In this regard, the wetting and spreading of the color ink due to the ejection of the clear ink can be considered as, for example, bleeding between the clear ink and the color ink. Moreover, this bleeding can be considered to be different from, for example, inter-color bleeding that occurs between different color inks, and does not degrade the print quality. Furthermore, the bleeding between the clear ink and the color ink can be considered to reduce the graininess in the low-gradation range by, for example, lowering the color density and widening the dot diameter compared to when the color ink is used alone.

[0087] Here, to reduce the graininess, it might seem that using so-called light-colored inks would suffice. In this case, for example, in addition to the YMCK inks of normal color intensity, light-colored inks with reduced pigment concentration could be used. However, when printing for the same purpose as in this example, if light-colored inks are used to reduce graininess, it would be necessary to use light-colored inks for at least the three MCK colors. As a result, it would be necessary to increase the number of inkjet heads in the print unit 14 (see Figure 1) by at least three, leading to problems such as pressure on the ink slots and an increase in the size of the print unit 102. Furthermore, even if light-colored inks are used, in the extremely low-gradation range where the gradation of the image is particularly low, the hot-melt resin powder may not adhere well, potentially causing transfer unevenness. In contrast, in this example, instead of using light-colored inks corresponding to specific ink colors, colorless clear inks are used, making it possible to reduce graininess while suppressing the increase in the number of inkjet heads. Furthermore, in this case, it becomes possible to eject the necessary amount of ink even in the very low gradation range, thereby appropriately preventing issues such as uneven transfer.

[0088] Furthermore, in this example, the reduction of graininess by using clear ink can be considered to be related to the fact that, for example, as described above, the size of the color ink dots when using clear ink can be made larger compared to the size of the color ink dots when clear ink is not used. Also, in this regard, in this example, it can be considered that both color ink and clear ink are ejected at least some of the ejection positions. In this case, regarding the size of the color ink dots formed when the color ink spreads on the transfer medium after impact, if we define the size of the dots formed when both color ink and clear ink are ejected at the same ejection position as the size when clear ink is used, and the size of the dots formed when only color ink is ejected at the ejection position as the size when clear ink is not used, then in the printing unit 14, for example, at least some of the ejection positions that eject color ink in the low-gradation areas of the image, it can be considered that clear ink is ejected in such a way that the size when clear ink is used is larger than the size when clear ink is not used. With this configuration, for example, the size of the ink dots formed by the color ink can be appropriately increased. In addition, this can appropriately reduce graininess.

[0089] Furthermore, as described above, in this example, by using clear ink on the low-gradation areas of the image, the hot melt resin powder is adhered more appropriately. In this regard, for example, if color ink is used instead of clear ink, it can be considered that the hot melt resin powder will be particularly less likely to adhere to isolated ink dots where no other ink dots are formed around them. Therefore, in this example, it is preferable to discharge the clear ink to, for example, the discharge position of an isolated color ink dot or a discharge position in the vicinity thereof, thereby increasing the total amount of ink near the discharge position of the isolated color ink dot. More specifically, in this example, the printing unit 14 discharges color ink and clear ink from the inkjet heads for color ink and clear ink to discharge positions set according to the printing resolution. In this case, it is conceivable that the printing unit 14 discharges the clear ink so that an area including multiple discharge positions is continuously covered with color ink and clear ink. The continuous coverage of a range including multiple ejection positions by colored ink and clear ink can be considered, for example, as a sequence of multiple ink dots in contact with each other on the transfer medium forming a range including multiple ejection positions.

[0090] Furthermore, in this case, if we define the ejection position from which color ink is ejected from the inkjet head for color ink as a colored ejection position, and define a colored ejection position where the adjacent ejection position is not a colored ejection position as an isolated ejection position, then the low-tone areas in the image can be considered, for example, as regions including the isolated ejection positions. In this case, the operation of the printing unit 14 can be considered as ejecting clear ink from the inkjet head for clear ink to at least some of the isolated ejection positions in the low-tone areas, or to ejection positions around those isolated ejection positions. Also, in this case, by ejecting clear ink in this way, the printing unit 14 prints on the transfer medium such that, for example, at least near the isolated ejection position, a range including multiple ejection positions including the isolated ejection position is connected by the color ink and the clear ink. With this configuration, for example, the total amount of ink ejected near the isolated ejection position in the low-tone area can be appropriately increased compared to when clear ink is not used. In addition, this allows for more appropriate adhesion of hot melt resin powder to the area near the isolated ejection position. Furthermore, in this case, the operation of ejecting clear ink from the inkjet head for clear ink to ejection positions surrounding the isolated ejection position in the printing unit 14 can be considered as, for example, an operation of ejecting clear ink from the inkjet head for clear ink to at least a portion of the ejection positions where color ink is not ejected. Also, in this case, for example, by ejecting clear ink to ejection positions between different isolated ejection positions, it is possible to connect the dots of multiple color inks located at different isolated ejection positions with dots of clear ink. With this configuration, for example, the hot melt resin powder can be attached more appropriately to the vicinity of the isolated ejection position.

[0091] As explained above, when performing transfer using hot melt resin powder, it has been conventional practice to use white ink in addition to color ink. However, the use and application of the clear ink in this example differ in several respects from the use and application of white ink in conventional configurations. More specifically, when performing color printing using an inkjet method, if a layer of white ink is formed by layering it with a layer of color ink, the white ink layer functions as a background that reflects light in subtractive color mixing (color reproduction). Also, when performing transfer using hot melt resin powder, the white ink layer plays a significant role as an opacity layer that hides the background color of the transfer medium to which the image is transferred. Furthermore, due to these characteristics of the white ink layer, it is usually formed in an area that includes the entire image drawn with color ink.

[0092] In contrast, the clear ink used in this example is a translucent ink, so even if a layer of clear ink is formed, it does not typically function as a background layer that reflects light or as a layer that hides the base color of the transfer medium. Furthermore, as can be understood from the above explanation, in this example, the purpose of using clear ink can be achieved even if it is dispensed only onto a portion of the image drawn with color ink. Also, unlike when a layer of white ink that functions as an opacity layer is formed, when using clear ink as in this example, the inks used other than the color ink do not stand out excessively on the transfer medium. Therefore, according to this example, as explained above, when using white or light-colored (pale-colored) fabrics as the transfer medium, high-quality printing that takes advantage of the texture of the transfer medium can be appropriately performed. Furthermore, in this case, at least in these respects, the use and method of using clear ink in this example differ from the use and method of using white ink in conventional configurations.

[0093] Furthermore, as explained above, in this example, the amount of clear ink discharged to each position on the transfer medium may vary, for example, depending on the amount of color ink discharged to each position. In this case, if the amount of color ink discharged (printed amount) to the area containing each pixel on the transfer medium is less than or equal to a predetermined amount (X%), clear ink may be discharged to that area to compensate for the insufficient amount of ink (liquid). In this case, if the amount of ink deposited per unit area exceeds the predetermined printed amount (liquid), bleeding is likely to occur, or excessive hot melt resin powder may adhere, leaving traces of the hot melt resin powder on the transfer medium. Therefore, the total amount of color ink and clear ink discharged (printed amount) to the area containing each pixel on the transfer medium should not exceed other predetermined amounts (Y%) (Y>X). In contrast, when using white ink, if the amount of white ink dispensed to each position on the transfer medium is varied as described above, it is conceivable that white ink may land in dots between the color inks. As a result, it is conceivable that the colors in some areas of the printed image may appear blurred. In particular, if white ink is dispensed further into the low-tone areas of the image, some of the color ink dots may be covered with white ink, causing the colors in the lighter low-tone areas to become even lighter, making it impossible to print in the intended color. Therefore, in this respect as well, the use and application of the clear ink in this example differs from the use and application of white ink in conventional configurations.

[0094] Furthermore, regarding the clear ink dots formed on the transfer medium by the printing unit 14 ejecting clear ink, it can be considered preferable for the ink dots to be flattened and spread out in order to make them more easily adhered to by the hot melt resin powder. In this case, it is also possible to adjust the way the clear ink dots spread out during the operations performed by the printing system 10. With this configuration, for example, the size of the clear ink dots can be appropriately adjusted. In this case, the operation to adjust the way the clear ink dots spread out can be considered, for example, as an adjustment step operation to adjust the way the clear ink dots formed on the transfer medium by the printing unit 14 spread out. The adjustment step can be considered, for example, as a step to adjust the flattening of the ink dots (leveling adjustment). The operation of the adjustment step can also be considered, for example, as a leveling step operation to flatten the ink dots. The adjustment in the adjustment step can be considered, for example, to be performed before the stage in which the printing unit 14 prints on the transfer medium (printing step). Alternatively, for example, the operation of the adjustment step may be performed after printing on the transfer medium by the printing unit 14, if necessary.

[0095] Furthermore, when performing adjustment operations to adjust the spread of ink dots, for example, the printing unit 14 prints an image onto the transfer medium using a pre-set first printing condition. Based on the result of this printing, it is determined whether, for example, the spread of the clear ink dots (dot gain) is insufficient. If it is determined that the dot spread is insufficient, a second condition different from the first printing condition is selected as the printing condition for the printing unit 14 to perform printing during the printing stage. In this case, as the second condition, a condition that increases the spread of the clear ink dots is selected. With this configuration, it is possible to appropriately determine whether it is necessary to change the printing conditions to flatten the ink dots further, and to appropriately change the printing conditions as needed. Furthermore, this allows for more appropriate flattening of the clear ink dots in the subsequent printing operation on the transfer medium performed by the printing unit 14. Furthermore, it is possible to more appropriately adhere the hot melt resin powder to the position where the clear ink was ejected in the subsequent operation.

[0096] In this case, during the adjustment phase, the second printing condition could be, for example, a printing condition that slows down the printing speed compared to the first printing condition. The printing condition that slows down the printing speed could be, for example, a condition that increases the number of printing passes. In this case, the number of passes could be, for example, the number of main scanning operations performed on the same position of the print target. Furthermore, increasing the number of passes could be considered as a reduction in the relative movement of the inkjet head during a single sub-scanning operation, thereby slowing down the transport speed of the media. In this case, the printing speed in the first printing condition could be, for example, the normal printing speed (standard printing speed) of the printing unit 14. And in this case, the printing speed in the second printing condition could be, for example, a printing speed slower than the normal printing speed. Also, during the adjustment phase, selecting the second printing condition could be considered as, for example, selecting a printing speed slower than a specific printing speed corresponding to the printing speed in the first printing condition.

[0097] Furthermore, in order to increase the spread of the clear ink dots, one could, for example, increase the size of the droplets (ink droplets) ejected from the inkjet head, thereby adjusting the specific surface area. Alternatively, one could adjust the spread of the dots by changing the waveform of the drive signal (drive waveform) that drives the ejection of droplets from the inkjet head. For this reason, the second printing conditions may differ from the first printing conditions, for example, from these perspectives.

[0098] Furthermore, if a printing unit 14 is used that uses a heater to heat the material during printing, the printing conditions may be changed by changing the heating temperature of the heater. For example, if an ink that fixes to the transfer medium as a clear ink is used, it is conceivable to use a heater to heat the transfer medium. In this case, for example, by lowering the heating temperature of the heater in the second printing condition to a lower temperature than in the first printing condition, the drying speed of the ink can be slowed down, and the spread of the clear ink dots can be made larger. Also, in this case, for example, if a printing unit 14 is used that prints while transporting the medium, it is conceivable to make the above adjustments to the heating temperature of an after-heater, which is a heater located downstream of the inkjet head in the transport direction. Furthermore, if an after-heater is used in the printing unit 14, for example, the after-heater may be divided into multiple regions (for example, 2 to 3 regions) and the temperature may be adjusted. In this case, the multiple regions may be, for example, a region closer to the inkjet head in the transport direction and a region further away from the inkjet head. Furthermore, in this case, the heating temperature of the afterheater can be individually changed for each region. With this configuration, for example, the way the ink dots spread can be adjusted in more detail. Also, as the heater in the printing section 14, for example, a heater that heats the inkjet head can be used. In this case, by changing the heating temperature of this heater, for example, the viscosity of the ink before ejection can be changed. In addition, by making the heating temperature in the second printing condition higher than the heating temperature in the first printing condition, for example, the viscosity of the ejected ink can be reduced, making the ink spread more easily on the transfer medium. [Industrial applicability]

[0099] The present invention can be suitably used, for example, in printing methods. [Explanation of Symbols]

[0100] 10...Printing system, 102...Head unit, 104...Platen, 106...Y-bar unit, 108...Main scanning drive unit, 110...Sub-scanning drive unit, 12...Print data preparation unit, 120...Control unit, 14...Printing unit, 16...Powder application unit, 18...Thermal transfer unit, 202...Inkjet head, 300...Printing area, 302...Color ink layer, 304...White ink layer, 306...Image layer, 312...High gradation unit, 314...Medium gradation unit, 316...Low gradation unit, 352...Resin powder, 402...Dot, 404...Dot, 50...Transfer medium, 52...Base unit, 54...Ink receiving layer

Claims

1. A printing apparatus for printing an image to be transferred to a transfer medium onto a transfer medium using an inkjet method, A first inkjet head that ejects colored ink, A second inkjet head that ejects colorless clear ink, The system comprises a control unit that controls the ink ejection of the first inkjet head and the second inkjet head, A printing apparatus characterized in that, for the region on the transfer medium on which the colored ink is ejected, an upper limit of the amount of ink per unit area is set in advance, and when ejecting the clear ink, the amount of clear ink ejected is controlled according to the amount of colored ink printed.

2. The printing apparatus according to claim 1, characterized in that the control unit causes the second inkjet head to eject the clear ink so that the clear ink lands at each position in the transfer medium where the colored ink and the clear ink are ejected, before the colored ink is completely dry.

3. The printing apparatus according to claim 1, characterized in that printing is performed on the transfer medium such that hot melt resin powder, which is a powder containing a resin that softens when heated, adheres to the printed image.

4. A method for generating print data to be supplied to a printing apparatus for printing an image to be transferred to a transfer medium using an inkjet method, The print data is generated based on the image data showing the aforementioned image. The printing data is data that causes the printing device to eject colored ink and colorless clear ink, and a maximum value for the amount of ink per unit area is set in advance for the area on the transfer medium where the colored ink is ejected, and the amount of clear ink ejected is controlled according to the amount of colored ink printed when the clear ink is ejected.

5. A method for generating print data to be supplied to a printing apparatus that prints an image onto a medium using an inkjet method, The print data is generated based on the image data showing the aforementioned image. The aforementioned printing data is data that causes the printing apparatus to eject a colored ink containing a colored pigment and a clear ink which is a colorless ink, wherein the clear ink is ejected to at least a portion of the area on the medium where the colored ink is ejected, and the amount of the clear ink ejected is varied according to the amount of colored ink ejected per unit area of ​​the area. The region in the aforementioned medium where the colored ink is ejected is defined as the image representation region. If a region in which the amount of colored ink ejected per unit area is less than a predetermined standard amount is defined as a low-ink region, As the aforementioned print data, By setting a discharge position for dispensing the clear ink for at least a portion of the small amount of ink area within the image representation area, A method for generating print data, characterized by generating data that increases the transfer rate in at least a portion of the small ink area compared to the case where the clear ink is not ejected.

6. Within the aforementioned image representation area, the area where the amount of colored ink ejected per unit area is greater than a predetermined amount that is greater than the standard amount is defined as the non-small amount ink area. If the amount of clear ink dispensed per unit area at each position of the medium is defined as the clear ink discharge amount, As the aforementioned print data, The method for generating print data according to claim 5, characterized in that data is generated to vary the amount of clear ink ejected per unit area, such that the amount of clear ink ejected in the small amount of ink region is greater than the amount of clear ink ejected in the non-small amount of ink region.

7. As the aforementioned print data, The method for generating print data according to claim 6, characterized in that data is generated not to discharge the clear ink at positions where the amount of the colored ink discharged per unit area exceeds a preset upper limit.

8. A method for generating print data to be supplied to a printing apparatus that prints an image onto a medium using an inkjet method, The print data is generated based on the image data showing the aforementioned image. The aforementioned printing data is data that causes the printing apparatus to eject a colored ink containing a colored pigment and a clear ink which is a colorless ink, wherein the clear ink is ejected to at least a portion of the area on the medium where the colored ink is ejected, and the amount of the clear ink ejected is varied according to the amount of colored ink ejected per unit area of ​​the area. A clear image generation process that generates a clear image, which is an image used to determine the ejection position for ejecting the clear ink, Discharge position determination process, which determines the discharge position of the clear ink by performing halftone processing on the clear image; Perform In the aforementioned clear image generation process, The total amount of the colored ink dispensed at each position in the aforementioned image is calculated. A method for generating print data, characterized by determining the value of each pixel in the clear image based on the total amount.

9. A print data generation device that generates print data to be supplied to a printing device for printing an image to be transferred to a transfer medium by an inkjet method, The print data is generated based on the image data showing the aforementioned image. The printing data generation device is characterized in that the printing data is data that causes the printing device to eject colored ink and colorless clear ink, and an upper limit value for the amount of ink per unit area is set in advance for the area on the transfer medium on which the colored ink is ejected, and the amount of clear ink ejected is controlled according to the amount of colored ink printed when the clear ink is ejected.

Images