JP2010234643A - Inkjet printer and printing method of inkjet system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately draw an image regardless of a tone value of the image in an inkjet printer. <P>SOLUTION: When the image is printed on a printing medium such as high-quality paper in the inkjet printer, if the tone value is at least a minimum tone value (0) and smaller than a tone threshold value (128), a curing time of the ink is made longer to facilitate diffusion on the printing medium, whereby dots of the ink become unnoticeable, enabling drawing of a smooth image. If the tone value is at least the tone threshold value (128) and at most a maximum tone value (255), the curing time of a part of dots of the same kind of ink is shortened, and a ratio of the number of dots of a long curing time in a total number of dots is reduced as the tone value increases. Hence, a density insufficiency in a shadow region can be prevented and a color region can be prevented from being narrow. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an inkjet printer that performs printing by an inkjet method, and an inkjet printing method.

  2. Description of the Related Art Conventionally, an ink jet printing apparatus that performs printing by scanning a discharge mechanism in which a large number of discharge ports for discharging minute droplets of ink are arranged relative to a print medium has been used. In such a printing apparatus, printing is performed on various printing papers such as high-quality paper, coated paper, and ink jet dedicated paper, and various inks such as ultraviolet curable ink, oil-based ink, and water-based ink are used for printing.

  For example, when printing is performed on a printing paper having a relatively large surface fiber gap, such as high-quality paper, an ink that is relatively diffusible on the printing paper, such as an aqueous dye ink, is used. Since the ink penetrates to the deep part of the paper, the ink dots become inconspicuous in the highlight area of the image, and a smooth image can be drawn. In addition, since the film thickness of the ink on the printing paper is reduced, color turbidity due to overlapping of different color dots is reduced in the case of multicolor printing, and the color development of the image is improved.

  Also, when printing on printing paper with relatively small surface fiber gaps such as coated paper or inkjet paper, use ink that is difficult to diffuse on the printing paper, such as aqueous pigment ink. Since ink bleeding is suppressed, a figure or the like can be drawn sharply in an intermediate gradation area of an image.

  In Patent Literature 1 and Patent Literature 2, a first black nozzle group for ejecting a first black ink having a water-soluble dye and a second black ink having a pigment are ejected to a recording head of an ink jet recording apparatus. When the second black nozzle group is provided and the recording paper is a dedicated paper, the first black ink is ejected toward the recording paper. When the recording paper is a plain paper, the first black ink and the first black ink are discharged. A technique for discharging two black inks simultaneously or selectively toward a recording sheet is disclosed.

JP 2000-225719 A JP 2006-168370 A

  By the way, when printing on high-quality paper with water-based dye ink, there is a possibility that the density is insufficient in the shadow area of the image or the color gamut becomes narrow. In addition, when printing is performed on coated paper or inkjet exclusive paper with water-based pigment ink, streak unevenness may occur in the shadow region of the image. In the ink jet recording apparatuses of Patent Document 1 and Patent Document 2, two types of black ink can be ejected, but a solution to the problems such as insufficient density and uneven stripes in the shadow area described above is not shown.

  The present invention has been made in view of the above problems, and an object of the present invention is to perform appropriate drawing regardless of the gradation value of an image in an inkjet printer.

  The invention according to claim 1 is an inkjet printer, comprising: a discharge mechanism that discharges micro droplets of ink from a plurality of first discharge ports and a plurality of second discharge ports toward a print medium; and the print medium. The moving mechanism that moves relative to the ejection mechanism and the ink ejected from the plurality of first ejection ports are cured after the first curing time has elapsed and ejected from the plurality of second ejection ports. A curing unit that cures ink after a second curing time that is different from the first curing time, and a print control unit that renders an image on the print medium by controlling the ejection mechanism and the moving mechanism. And the print control unit controls the discharge mechanism, so that the plurality of first discharge ports and the plurality of second discharge ports are partially included in a range of gradation values that can be expressed on the print medium. Ink is ejected from one side toward the print medium, and the sum of the ink ejection rate from the plurality of first ejection ports and the ink ejection rate from the plurality of second ejection ports as the gradation value increases And the first ink ratio, which is the ratio of the ink discharge rate from the plurality of first discharge ports in the total discharge rate in the part of the range of the gradation value, is gradually increased. Decrease gradually.

  A second aspect of the present invention is the ink jet printer according to the first aspect, wherein the first curing time is longer than the second curing time, and the ejection mechanism is controlled by the print control unit. When the gradation value is not less than 0 and less than a predetermined gradation threshold, the first ink ratio is 100%, and the gradation value is not less than the gradation threshold and not more than the maximum gradation value. The first ink ratio gradually decreases from 100% as the gradation value increases.

  A third aspect of the present invention is the ink jet printer according to the first aspect, wherein the first curing time is shorter than the second curing time, and the ejection mechanism is controlled by the print control unit. When the gradation value is not less than 0 and less than a predetermined gradation threshold, the first ink ratio is 100%, and the gradation value is not less than the gradation threshold and not more than the maximum gradation value. The first ink ratio gradually decreases from 100% as the gradation value increases.

  According to a fourth aspect of the invention, there is provided the inkjet printer according to the third aspect, wherein the discharge mechanism is controlled by the print control unit, so that the vicinity of the maximum gradation value including the maximum gradation value. In the range of gradation values, the total discharge rate is greater than 100%.

  The invention according to claim 5 is the ink jet printer according to claim 2 or 3, wherein the size of dots drawn by the first ink in the ejection mechanism is switched between a small size and a large size. The discharge rate of the first ink is a sum of a discharge rate of a droplet for drawing the small-sized dots and a discharge rate of a droplet for drawing the large-sized dots, and the printing By controlling the ejection mechanism by the control unit, the small occupying the ejection rate of the first ink when the gradation value is less than another gradation threshold value that is 0 or more and less than the gradation threshold value. When the small size ratio indicating the ratio of the discharge rate of droplets for drawing dots of size is 100%, and the gradation value is greater than or equal to the other gradation threshold and less than the gradation threshold, According to the increase of the key value Te, the small size ratio gradually decreases from 100%.

  The invention according to claim 6 is the ink jet printer according to any one of claims 1 to 5, wherein the print control unit compares the pixel value of the image with the threshold value of the threshold value matrix. The discharge rate of the discharge mechanism is controlled.

  A seventh aspect of the present invention is the ink jet printer according to any one of the first to sixth aspects, wherein the curing unit has energy having a first intensity in the ink ejected from the plurality of first ejection ports. A first curing unit that cures by irradiating a wave; and a second curing unit that cures the ink ejected from the plurality of second ejection ports by irradiating an energy wave having a second intensity. The first curing time and the second curing time are different due to the difference between the strength and the second strength.

  The invention according to an eighth aspect is the ink jet printer according to any one of the first to sixth aspects, wherein the plurality of first discharge ports in a relative movement direction of the print medium with respect to the discharge mechanism by the moving mechanism. The first curing time and the second curing time are different because the distance between the first curing time and the curing part is different from the distance between the plurality of second discharge ports and the curing part.

  A ninth aspect of the present invention is the ink jet printer according to any one of the first to eighth aspects, wherein the first discharge is related to a direction perpendicular to a relative movement direction of the print medium to the discharge mechanism by the movement mechanism. The outlets and the second discharge ports are alternately arranged.

  The invention according to claim 10 is an ink jet printing method, in which a) fine droplets of ink are ejected from a plurality of first ejection ports and a plurality of second ejection ports of a ejection mechanism toward a printing medium. And b) drawing the image on the print medium by moving the print medium relative to the ejection mechanism in parallel with the step a), c) the plurality of first The step of curing the ink ejected from the ejection ports after the elapse of the first curing time and curing the ink ejected from the plurality of second ejection ports after the elapse of a second curing time different from the first curing time. And a plurality of first discharge ports and a plurality of second discharge ports in a part of a range of gradation values that can be expressed on the print medium by controlling the discharge mechanism in the step a). Said from both exits Ink is ejected toward the printing medium, and the sum is the sum of the ink ejection rate from the plurality of first ejection ports and the ink ejection rate from the plurality of second ejection ports as the gradation value increases. As the discharge rate gradually increases, the first ink ratio, which is the ratio of the ink discharge rate from the plurality of first discharge ports, to the total discharge rate in the part of the gradation value range, gradually decreases. .

  In the present invention, appropriate drawing can be performed regardless of the gradation value of the image.

It is a figure which shows the inkjet printer which concerns on 1st Embodiment. It is an enlarged view of a discharge part. It is a figure which shows the flow of printing by an inkjet printer. It is a figure which shows a threshold value matrix and an original image abstractly. It is a figure which shows the relationship between the gradation value of a halftone image, and the discharge rate of an ink in the inkjet printer of a comparative example. It is a figure which shows the relationship between the gradation value of a halftone image, and the discharge rate of an ink in the inkjet printer which concerns on 1st Embodiment. FIG. 5 is a diagram illustrating a relationship between a gradation value of a halftone image and an ink discharge rate. FIG. 5 is a diagram illustrating a relationship between a gradation value of a halftone image and an ink discharge rate. FIG. 5 is a diagram illustrating a relationship between a gradation value of a halftone image and an ink discharge rate. FIG. 5 is a diagram illustrating a relationship between a gradation value of a halftone image and an ink discharge rate. It is an enlarged view of the discharge part of the inkjet printer which concerns on 3rd Embodiment. FIG. 5 is a diagram illustrating a relationship between a gradation value of a halftone image and an ink discharge rate. FIG. 5 is a diagram illustrating a relationship between a gradation value of a halftone image and an ink discharge rate. It is an enlarged view of the discharge part of the inkjet printer which concerns on 4th Embodiment. FIG. 5 is a diagram illustrating a relationship between a gradation value of a halftone image and an ink discharge rate. FIG. 5 is a diagram illustrating a relationship between a gradation value of a halftone image and an ink discharge rate.

  FIG. 1 is a diagram showing a configuration of an ink jet printer 1 according to a first embodiment of the present invention. The ink jet printer 1 is a sheet-fed printing apparatus that sequentially performs color printing on a plurality of print media 9 using an ink jet method.

  As shown in FIG. 1, the inkjet printer 1 includes a moving mechanism 2 that moves a plurality of printing media 9 in the (+ Y) direction in FIG. 1, and a minute liquid of ink toward the printing medium 9 that is being transported by the moving mechanism 2. A discharge unit 3 that discharges droplets, a supply unit 51 that supplies the print medium 9 to the moving mechanism 2, a discharge unit 52 that receives the print medium 9 after printing from the transfer mechanism 2, and a print control unit that controls these mechanisms 4 is provided.

  The moving mechanism 2 includes a plurality of stages 21 each for sucking and holding one sheet-like print medium 9 (printing paper in the present embodiment), an annular guide 22 for guiding the plurality of stages 21, and a guide. The belt which moves the belt 21 in the counterclockwise direction in FIG. 1 to move the stage 21 holding the printing medium 9 in the (+ Y) direction below the discharge unit 3 (that is, on the (−Z) side). A drive mechanism (not shown) is provided.

  FIG. 2 is an enlarged view of the discharge unit 3. The ejection unit 3 is disposed on each (+ Y) side of each of the eight ejection heads 31a to 31h and the ejection heads 31a to 31h that eject micro droplets of ink (for example, aqueous dye ink) from a plurality of ejection ports. And curing heads 33a to 33h that irradiate light toward the print medium 9, and a head support portion 35 that supports the ejection heads 31a to 31h and the curing heads 33a to 33h. In other words, the ejection heads 31a to 31h and the curing heads 33a to 33h are alternately arranged in the Y direction in FIG. In FIG. 2, the inside of the head support portion 35 is drawn to facilitate understanding of the drawing (the same applies to FIGS. 11 and 14).

  In the discharge unit 3, the curing heads 33 a to 33 h are each connected to a light source via an optical fiber (not shown), and discharged from the discharge head adjacent to the (−Y) side of each curing head onto the print medium 9. By irradiating the ink with light, the ink dots are dried and cured. The intensity of light applied to the print medium 9 from the curing heads 33a, 33c, 33e, and 33g is higher than the intensity of light applied to the print medium 9 from the curing heads 33b, 33d, 33f, and 33h. Is due to the difference in the output of the light source to which each curing head is connected. The ink on the print medium 9 is heated to about 50 ° C. when irradiated with light from the curing heads 33a, 33c, 33e, and 33g, and irradiated with light from the curing heads 33b, 33d, 33f, and 33h. To about 30 ° C.

  In the discharge section 3, the discharge heads 31a and 31b located on the (−Y) side in FIG. 2 discharge the same type of K (black) ink. The ink dots ejected from the plurality of ejection ports of the ejection head 31a onto the print medium 9 are cured by being heated to about 50 ° C. by the light from the curing head 33a, and the printing medium is ejected from the plurality of ejection ports of the ejection head 31b. The dots of the ink ejected onto 9 are heated to about 30 ° C. by the light from the curing head 33b and cured. The ink on the print medium 9 is not cured at the moment when the light from the curing head is irradiated, but curing is accelerated by the light from the curing head, and the curing is completed after a predetermined time. In the following description, the time from when the ink is ejected onto the print medium 9 until the ink is completely cured is referred to as a curing time.

  In the ink jet printer 1, since the intensity of light applied to the ink on the print medium 9 from the curing head 33a and the curing head 33b is different, the curing time of the ink ejected from the ejection head 31a and the ink ejected from the ejection head 31b are different. And the dot diffusivity indicating the degree of ease of spreading of the fine droplets of ink on the print medium 9 is also different. As described above, since the intensity of the light applied to the ink from the curing head 33a is higher than the intensity of the light applied to the ink from the curing head 33b, the curing time of the ink ejected from the ejection head 31a is the ejection time. The dot diffusibility of the ink discharged from the discharge head 31b onto the print medium 9 is shorter than the curing time of the ink discharged from the head 31b. Lower than sex. In the following description, the curing time of the ink ejected from the ejection head 31a is referred to as “low diffusion curing time”, and the curing time of the ink ejected from the ejection head 31b is referred to as “high diffusion curing time”.

  In the ejection unit 3, the ejection heads 31c and 31d eject the same type of C (cyan) ink, and the dot diffusibility of the ink ejected from the ejection head 31c is the dot diffusivity of the ink ejected from the ejection head 31d. Lower than. The ejection heads 31e and 31f eject the same type of M (magenta) ink, and the dot diffusibility of the ink ejected from the ejection head 31e is lower than the dot diffusivity of the ink ejected from the ejection head 31f. Become. The ejection heads 31g and 31h eject the same type of Y (yellow) ink, and the dot diffusibility of the ink ejected from the ejection head 31g is lower than the dot diffusivity of the ink ejected from the ejection head 31h.

  In the inkjet printer 1, each of the ejection heads 31 a to 31 h of the ejection unit 3 extends over the entire width of the printing medium 9 (that is, the X direction) with respect to the X direction perpendicular to the moving direction (Y direction) of the printing medium 9 by the moving mechanism 2. The print heads 9a to 31h pass through the positions on the print medium 9 only once by the relative movement of the print medium 9 in the (+ Y) direction once. Printing on the medium 9 is completed. That is, the inkjet printer 1 performs printing (so-called one-pass printing) that does not involve reciprocal movement of the print medium 9 in the X direction. In the ejection heads 31a and 31b that eject K ink, the ejection ports of the ejection head 31a and the ejection ports of the ejection head 31b are alternately arranged in the X direction. In other words, the plurality of ejection ports of the ejection head 31a and the plurality of ejection ports of the ejection head 31b are arranged so as to sandwich one ejection port of the other ejection head with respect to the X direction. Similarly, in the two ejection heads that eject ink of each color of C, M, and Y, the ejection ports of one ejection head and the ejection ports of the other ejection head are alternately arranged in the X direction.

  A computer 7 is connected to the ink-jet printer 1 shown in FIG. 1, and the computer 7 receives data of the original image of multi-gradation (that is, continuous gradation) and a threshold value matrix (SPM (Screen Pattern Memory) data) is also sent to the print control unit 4 of the inkjet printer 1. In this embodiment, gradation expression is realized by changing the number of halftone dots of a certain size (one dot (or pixel) or a set of dots joined together) that are irregularly arranged. A threshold matrix for FM (Frequency Modulated) screening is sent to the print control unit 4.

  Next, the flow of image printing by the inkjet printer 1 will be described with reference to FIG. When printing is performed by the inkjet printer 1, first, the print control unit 4 compares the original image data with the threshold value matrix to form a halftone dot (that is, a halftone process is performed). ), Halftone image data used for printing (hereinafter also simply referred to as “halftone image”) is generated (step S11). In the halftone image data, the original image data is separated into K, C, M, and Y colors, and the separated image data is formed into halftone dots using a threshold matrix. Data of halftone dot images of M and Y colors are included.

  When the original image is halftone (that is, when generating a halftone image representing the original image), the original image 70 is divided into a plurality of regions of the same size as shown in FIG. A repetitive area 71 serving as a unit for dotization is set. The screen pattern memory (SPM) of the print control unit 4 has a matrix space (matrix region) that is a storage area corresponding to one repeating area 71, and each address of the matrix space (that is, each pixel of the repeating area 71 is assigned to each pixel). The threshold value matrix 710 is generated by setting the threshold value to the coordinates (pixels) of the corresponding matrix space.

  Conceptually, each repeating area 71 of the original image 70 and the threshold matrix 710 are overlapped, and the gradation value (pixel value) of each pixel in the repeating area 71 is compared with the corresponding threshold in the threshold matrix 710. Thus, it is determined whether or not drawing is performed at the position of the pixel on the printing medium 9 which is a halftone recording medium (that is, whether or not a minute droplet of ink is ejected from each ejection port of the ejection unit 3). Is done. Therefore, if the gradation value of the original image 70 is uniform, drawing is performed on a pixel at an address for which a threshold value smaller than the gradation value is set in the threshold value matrix 710, and is macroscopically uniform. A halftone dot is generated. Actually, since the original image 70 has light and shade (that is, portions having various gradation values), the state of the halftone dot changes in the repeat area 71 according to the light and shade of the original image 70.

  Subsequently, the printing medium 9 shown in FIG. 1 is supplied and held on the stage 21 from the supply unit 51, and the moving mechanism 2, the discharge heads 31 a to 31 h of the discharge unit 3, and the curing head based on the halftone image data. When the print control unit 4 controls 33a to 33h (see FIG. 2), the print medium 9 moves in the (+ Y) direction (step S12), and the ejection heads 31a to 31h are directed toward the moving print medium 9. To K, C, M, and Y inks are ejected to draw an image (step S13). On the print medium 9, the ink ejected from the ejection heads 31a to 31h is cured by the light emitted from the curing heads 33a to 33h (step S14).

  Then, by one relative movement in the (+ Y) direction of the print medium 9 with respect to the discharge unit 3, the discharge heads 31a to 31h pass through each position on the print medium 9 only once, and the drawing of the image is completed. Thereafter, the print medium 9 is collected by the discharge unit 52. In the inkjet printer 1, the above-described printing is sequentially performed on a plurality of print media 9 (the same applies to other embodiments described below).

  Next, regarding the ejection control of the ejection head by the printing control unit 4 performed in step S13, ejection heads 31a and 31b that eject K ink, and curing heads 33a and 33b that cure the K ink (see FIG. 2). I will focus on and explain. The following description is the same for the inks of other colors. In the following description, it is assumed that printing is performed on the print medium 9 in which the gap between the surface fibers is relatively large and the applied ink is relatively easy to spread, such as high-quality paper.

  In the ink jet printer 1, the ejection head 31 a and the ejection head 31 b are ejection mechanisms that eject minute ink droplets toward the printing medium 9. In addition, the curing head 33a and the curing head 33b cure the ink ejected from the plurality of ejection ports of the ejection head 31a after the low diffusion curing time has passed, and the ink ejected from the plurality of ejection ports of the ejection head 31b. The cured portion is cured after the elapse of a high diffusion curing time longer than the low diffusion curing time.

  Then, the ejection mechanism is controlled by the print control unit 4 based on the gradation value of the halftone dot image of K, whereby the ejection rate of the ink from the ejection head 31a and the ink from the ejection head 31b The discharge rate is changed. In the inkjet printer 1, ink is directed toward the printing medium 9 from both the plurality of ejection ports of the ejection head 31 a and the plurality of ejection ports of the ejection head 31 b in a part of the range of gradation values that can be expressed on the printing medium 9. Is discharged. The above-described ink discharge rate is the actual number of ink dots that can be applied from one discharge head to a unit area, with the number of positions defined as positions where ink dots can be applied in the unit area on the print medium 9 as a reference number. This value indicates the ratio of the number of ejected dots to the reference number. When the gradation value is the maximum gradation value, it is normally 100%, and when the gradation value is the minimum gradation value (0). Becomes 0%.

  FIG. 5 shows a halftone dot of K color in an inkjet printer that discharges one type of ink for each color onto a print medium and cures the ink with a single curing head (hereinafter referred to as “comparative example inkjet printer”). It is a figure which shows the relationship between the gradation value of an image, and the discharge rate of the ink in the discharge mechanism which discharges the K ink. In FIG. 5, the horizontal axis indicates the tone value of the halftone image, and the vertical axis indicates the ink ejection rate. In the inkjet printer of the comparative example, as the gradation value increases from 0, which is the minimum gradation value, to 255, which is the maximum gradation value, the discharge rate (region 601 indicated by parallel diagonal lines) is proportional to the gradation value. However, it gradually increases from 0% to 100%.

  FIG. 6 shows the gradation value of the K halftone image and the ink discharge rate in the discharge mechanism (that is, the discharge heads 31a and 31b) for discharging K ink in the inkjet printer 1 according to the present embodiment. It is a figure which shows a relationship. In FIG. 6, the horizontal axis indicates the gradation value of the halftone image, the left vertical axis indicates the ink ejection rate, and the right vertical axis indicates the high diffusion ink ratio described later (FIGS. 9, 12, and FIG. 6). The same applies to 15). In FIG. 6, a region 611 indicated by a broken parallel oblique line indicates an ink discharge rate from the discharge head 31b, and a region 612 indicated by a solid parallel oblique line indicates an ink discharge rate from the discharge head 31a. A straight line 615 indicating the left boundary of the region 611 indicates a total ejection rate that is the sum of the ejection rate of ink from the ejection head 31a and the ejection rate of ink from the ejection head 31b.

  As shown in FIG. 6, in the inkjet printer 1, the gradation values increase from 0, which is the minimum gradation value, to 255, which is the maximum gradation value, by controlling the ejection heads 31 a and 31 b by the print control unit 4. Accordingly, the total discharge rate gradually increases from 0% to 100% while being proportional to the gradation value. Further, when the gradation value is not less than the minimum gradation value (0) and less than a predetermined gradation threshold value (128 in the present embodiment), the ink from the discharge head 31b occupies the total discharge rate (that is, high The ratio of the high diffusion ink, which is the ratio of the discharge rate of the ink cured during the diffusion hardening time, is 100%, and the ink is discharged from only the discharge head 31b of the discharge heads 31a and 31b, and the high diffusion hardening time has elapsed. It hardens later. In FIG. 6, the high diffusion ink ratio is indicated by a line 616. On the other hand, when the gradation value is not less than the gradation threshold (128) and not more than the maximum gradation value (255), ink is ejected from the ejection head 31a in addition to the ejection head 31b, and ejected from the ejection head 31a. The resulting ink is cured after the low diffusion curing time has elapsed. As the gradation value increases from the gradation threshold value (128) to the maximum gradation value (255), the high diffusion ink ratio (that is, the ratio of the number of dots with a long curing time to the total number of dots) is 100%. Gradually decreases from 0 to 0%.

  By the way, in the ink jet printer of the comparative example described above, in printing an image on a printing paper having a relatively large surface fiber gap such as fine paper, the ink ejected from the ejection head is cured after a relatively long curing time has elapsed. (That is, when the dot diffusibility of the ink on the printing paper is increased), the image density is insufficient or the color gamut in the shadow area where the gradation value is close to the maximum gradation value (that is, the high gradation area). May become narrower. In printing an image on the printing paper, when the ink ejected from the ejection head is cured after a relatively short curing time (that is, when the dot diffusibility of the ink on the printing paper is lowered), In the highlight area where the tone value is close to the minimum gradation value (that is, in the low gradation area), the ink dots become conspicuous, and the smoothness of the image may be reduced.

  On the other hand, in the inkjet printer 1 according to the present embodiment, when an image is printed on the printing medium 9 having a relatively large surface fiber gap such as fine paper, the gradation value is as described above. When the minimum gradation value (0) or more and less than the gradation threshold value (128), the high diffusion ink ratio is 100%, and the gradation value is not less than the gradation threshold value (128) and not more than the maximum gradation value (255). In some cases, the percentage of highly diffused ink is gradually reduced from 100% as the gradation threshold increases.

  In this way, in the highlight area (for example, the range where the gradation value is 0 or more and less than 85) of the image to a part of the intermediate gradation area (for example, the range where the gradation value is 85 or more and less than 128), By curing all the dots of the ink ejected above in a high diffusion curing time, the dots of the ink become inconspicuous and a smooth image can be drawn. In addition, ejection is performed on the print medium 9 in a shadow region (for example, a range of gradation values 170 to 255) from a part of the intermediate gradation region (for example, a range of gradation values 128 to 170). Some of the ink dots are cured with a high diffusion hardening time and the remaining dots are hardened with a low diffusion hardening time, and the high diffusion ink ratio is decreased as the gradation value increases, thereby reducing the low diffusion ink ratio ( That is, by increasing the ratio of the ejection rate of ink that is cured in a low diffusion curing time in the total ejection rate), it is possible to prevent insufficient density in the shadow area and to prevent the color gamut from becoming narrower. be able to.

  In the ink jet printer 1, the discharge port of the discharge head 31a and the discharge port of the discharge head 31b are alternately arranged in the X direction, so that the ink cured in the high diffusion curing time and the ink cured in the low diffusion curing time. In the range of gradation values in which drawing is performed with both the ink and the ink (that is, in the range where the gradation value is 128 or more and 255 or less), dots of ink that are cured with a high diffusion curing time, and a low diffusion curing time It is possible to distribute the dots of the ink cured in approximately uniformly. As a result, the uniformity of the image can be improved.

  As described above, the print control unit 4 controls the ejection rates of the ejection heads 31a and 31b by comparing the pixel values of the image with the threshold values of the threshold matrix. For this reason, the ejection head 31a is used by an error diffusion method or the like from a part of the intermediate gradation area where the ink cured in the low diffusion hardening time is used for drawing to the shadow area (the gradation value is 128 or more and 255 or less). , 31b can be improved as compared with the case where the discharge rate is controlled.

  In the inkjet printer 1, printing may be performed on a print medium 9 in which the gap between the surface fibers is relatively small and the applied ink is relatively difficult to spread, such as coated paper or inkjet dedicated paper. When printing is performed on the printing medium 9 such as coated paper, the printing control unit 4 controls the ejection mechanism (ejection heads 31a and 31b) different from the control (see FIG. 6) performed when printing on quality paper or the like. Against. FIG. 7 is a diagram illustrating the relationship between the tone value of the K color halftone image and the ink ejection rate in the ejection mechanism that ejects K ink when printing on coated paper or the like is performed. In FIG. 7, the horizontal axis indicates the tone value of the halftone image, the left vertical axis indicates the ink ejection rate, and the right vertical axis indicates the low diffusion ink ratio described later (FIGS. 8, 10, and FIG. The same applies to 13).

  When printing on coated paper or the like, unlike printing on high-quality paper or the like, drawing of a part of the highlight area and intermediate gradation area of the image (that is, the gradation value is in the range of 0 to less than 128) However, it is performed only with the ink cured in the low diffusion curing time ejected from the ejection head 31a.

  In FIG. 7, a region 621 indicated by a solid parallel oblique line indicates a discharge rate of the ink that is discharged from the discharge head 31a and is cured in a low diffusion hardening time, and a region 622 indicated by a broken parallel oblique line is the discharge head 31b. The discharge rate of the ink hardened | cured in the high diffusion hardening time discharged from is shown. A straight line 625 indicating the left boundary of the region 621 indicates a total discharge rate that is the sum of the discharge rate of the ink cured in the low diffusion hardening time and the discharge rate of the ink cured in the high diffusion hardening time. A line 626 indicates a low diffusion ink ratio, which is a ratio of the discharge rate of the ink cured in the low diffusion hardening time in the total discharge rate.

  As shown in FIG. 7, when printing on coated paper or the like is performed in the inkjet printer 1, the gradation values are the minimum gradation values by controlling the ejection heads 31 a and 31 b by the print control unit 4. As the maximum gradation value increases from 0 to 255, the total discharge rate gradually increases from 0% to 100% in proportion to the gradation value. Further, when the gradation value is not less than the minimum gradation value (0) and less than the gradation threshold value (128), the low diffusion ink ratio is set to 100%, and ink is ejected from only the ejection head 31a among the ejection heads 31a and 31b. It is discharged and hardens after the low diffusion hardening time has elapsed. On the other hand, when the gradation value is not less than the gradation threshold value (128) and not more than the maximum gradation value (255), ink that is cured in a low diffusion hardening time is ejected from the ejection head 31a and the ejection head 31b. Ink that is cured in a high diffusion curing time is discharged. As the gradation value increases from the gradation threshold value (128) to the maximum gradation value (255), the low diffusion ink ratio gradually decreases from 100% to 50%.

  By the way, in the ink jet printer of the comparative example described above, in printing an image on a printing paper having a relatively large surface fiber gap such as coated paper, the ink ejected from the ejection head is cured after a relatively long curing time. (That is, when the dot diffusibility of the ink on the printing paper is increased), the ink may be blurred in the highlight area or the intermediate gradation area, and the gradation value is close to the maximum gradation value. There is also a possibility that the image density is insufficient in the shadow area (that is, the high gradation area). On the other hand, in printing an image on the printing paper, when the ink ejected from the ejection head is cured after a relatively short curing time (that is, when the dot diffusibility of the ink on the printing paper is lowered), the image There is a risk of uneven stripes in the shadow area.

  On the other hand, in the inkjet printer 1 according to the present embodiment, when an image is printed on the printing medium 9 having a relatively small surface fiber gap such as coated paper, the gradation value is as described above. The ratio of the low diffusion ink when the minimum gradation value (0) or more and less than the gradation threshold (128) (that is, the ratio of the ejection ratio of the ink cured in the low diffusion curing time to the total ejection ratio) is 100. %, And the gradation value is not less than the gradation threshold (128) and not more than the maximum gradation value (255), the low diffusion ink ratio is gradually decreased from 100% as the gradation threshold is increased.

  In this way, drawing is performed using only the ink that is cured in the low diffusion hardening time in the part of the intermediate gradation area from the highlight area of the image (the gradation value is in the range of 0 to less than 128). In addition, it is possible to draw a figure or the like sharply while suppressing ink bleeding. In addition, ink that is cured with a low diffusion curing time and ink that is cured with a high diffusion curing time in a part to a shadow region (a gradation value range of 128 or more and 255 or less) of an intermediate gradation region of an image As the gradation value increases, the ratio of the ink ejection rate cured in the low diffusion curing time decreases to the total ejection rate, and the ink ejection rate cured in the low diffusion curing time decreases. By increasing the ratio, it is possible to suppress the occurrence of streaks in the shadow area.

  In the inkjet printer 1, when printing on a printing medium 9 such as coated paper is performed, when the image density in the shadow area is further increased, control slightly different from the above-described control (see FIG. 7) For the heads 31a, 31b). FIG. 8 is a diagram showing the relationship between the tone value of the halftone image relating to the control and the ink ejection rate in the ejection mechanism.

  In FIG. 8, a region 631 indicated by solid parallel oblique lines indicates the discharge rate of ink that is cured from the discharge head 31a during the low diffusion hardening time, and a region 632 indicated by broken parallel oblique lines is the discharge head 31b. The discharge rate of the ink hardened | cured in the high diffusion hardening time discharged from is shown. A line 635 indicating the left boundary of the region 631 represents a total discharge rate that is the sum of the discharge rate of the ink cured in the low diffusion hardening time and the discharge rate of the ink cured in the high diffusion hardening time. A line 636 indicates a low diffusion ink ratio, which is a ratio of the total ejection rate of the ink cured in the low diffusion curing time.

  In the control shown in FIG. 8, in the shadow area of the image, as in the control shown in FIG. 7, the ink cured from the ejection heads 31 a and 31 b onto the print medium 9 in the low diffusion curing time and the high diffusion curing time. Curing ink is ejected, and ink droplets are ejected from the ejection head 31b onto some of the plurality of dots of ink from the head 31a applied on the print medium 9, and a high diffusion curing time has elapsed. It hardens later (so-called overcoating is performed). For this reason, the increase rate of the total discharge rate in the shadow area (that is, the increase amount of the total discharge rate in a predetermined range of gradation values) increases, and the level near the maximum gradation value including the maximum gradation value (255). In the range of the adjustment value, the total discharge rate becomes larger than 100%. In the present embodiment, the total discharge rate at the maximum gradation value is 120%.

  In the range where the gradation value is not less than the gradation threshold value (128) and not more than the maximum gradation value (255), the gradation value increases from the gradation threshold value to the maximum gradation value as in the control shown in FIG. Accordingly, the low diffusion ink ratio gradually decreases from 100%. However, in the control shown in FIG. 8, the reduction ratio of the low diffusion ink ratio is shown in the gradation value range near the maximum gradation value including the maximum gradation value. This is smaller than the control shown in FIG.

  In the control shown in FIG. 8, as in the control shown in FIG. 7, curing is performed in a low diffusion hardening time from a highlight area of the image to a part of the intermediate gradation area (a gradation value is in the range of 0 to less than 128). By drawing using only the ink to be drawn, it is possible to draw a figure or the like sharply while suppressing ink bleeding. In addition, ink that is cured with a low diffusion curing time and ink that is cured with a high diffusion curing time in a part to a shadow region (a gradation value range of 128 or more and 255 or less) of an intermediate gradation region of an image As the gradation value increases, the ratio of the ejection rate in the total ejection rate of the ink cured in the low diffusion curing time decreases and the ejection rate of the ink cured in the high diffusion curing time By increasing the ratio, it is possible to suppress the occurrence of streaks in the shadow area.

  Further, in the control shown in FIG. 8, in particular, ink droplets are ejected from the ejection head 31b onto the ink dots from the head 31a applied on the print medium 9 in the shadow region, and include the maximum gradation value. By making the total discharge rate larger than 100% in the gradation value range near the maximum gradation value, the density of the image in the shadow area can be increased compared to the control shown in FIG.

  In the inkjet printer 1 according to the first embodiment, the control of the ejection unit 3 by the print control unit 4 is changed corresponding to the type of the print medium 9, and one type of ink ejected in the highlight region is highly diffused. It is switched between ink that is cured at cure time and ink that is cured at low diffusion cure time. Here, the curing time of the ink ejected in the highlight region (that is, the high diffusion curing time for printing on high-quality paper and the like, and the low diffusion curing time for printing on coated paper or the like) is defined as “first curing time” and first curing. The other curing time, which is different from the time, is referred to as “second curing time”, and the ejection port that ejects ink cured at the first curing time and ink cured at the second curing time is referred to as “first ejection port”. ”And“ second discharge port ”, in the inkjet printer 1, ink is supplied from the plurality of first discharge ports and the plurality of second discharge ports in a part of the range of gradation values that can be expressed on the print medium 9. Is controlled such that the first ink ratio, which is the ratio of the discharge ratio of the ink that is cured in the first curing time to the total discharge ratio, gradually decreases as the gradation value increases.

  Thereby, on the printing medium 9, a dot with low dot diffusibility and a dot with high dot diffusibility can be mixed by the ratio suitable for each gradation value. As a result, appropriate drawing can be performed regardless of the gradation value of the image. Further, by changing the ratio of the discharge rate of the ink cured in the high diffusion curing time and the ink cured in the low diffusion curing time in the total discharge rate according to the type of the print medium 9, the print medium is changed. Appropriate drawing according to the nine types can be performed.

  In the inkjet printer 1, the first curing time is longer than the second curing time when printing on fine paper or the like, and the first curing time is shorter than the second curing time when printing on coated paper or the like. The difference between these curing times is the intensity (hereinafter referred to as “first”) of light emitted from the curing head (hereinafter referred to as “first curing portion”) to the ink ejected from the plurality of first ejection ports. Intensity ”) and the intensity of light emitted from the curing head (hereinafter referred to as“ second curing portion ”) to the ink ejected from the plurality of second ejection ports (hereinafter referred to as“ second intensity ”). ").) Is different.

  Next, an ink jet printer according to a second embodiment of the present invention will be described. The ink jet printer according to the second embodiment has the same structure as that of the ink jet printer 1 shown in FIGS. 1 and 2, and the same reference numerals are given to corresponding configurations in the following description. In the ink jet printer according to the second embodiment, the size of the small droplets of the ejected ink is large and small in each of the eight ejection heads 31a to 31h of the ejection unit 3 under the control of the print control unit 4. Can be switched between. Alternatively, a plurality of micro droplets having the same size are continuously discharged from one discharge port toward the same position on the print medium 9, and the number of the plurality of micro droplets is large and small. It is possible to switch between them. Thereby, the size of the dot drawn by the ink ejected from each of the ejection heads 31a to 31h can be switched between the small size and the large size. Hereinafter, the ejection control of the ejection head by the print control unit 4 will be described by paying attention to the ejection heads 31a and 31b that eject K ink. The following description is the same for the inks of other colors.

  FIG. 9 is a diagram showing the relationship between the gradation value of the halftone image and the ink ejection rate in the ejection mechanism when printing is performed on the printing medium 9 such as fine paper. In the control shown in FIG. 9, the size of the micro droplets of the ink that is cured in the high diffusion curing time is switched between two types of large and small. In FIG. 9, the region 641 indicated by the alternate long and short dashed lines is the discharge rate of the liquid droplets for drawing small-sized dots out of the discharge rate of the ink cured from the discharge head 31 a during the high diffusion hardening time. The area 642 to which the two-dot chain line parallel diagonal lines are attached is a discharge rate of a droplet for drawing a large-sized dot out of the discharge rate of ink that is cured from the discharge head 31a during a high diffusion hardening time. Indicates. Therefore, the total of the region 641 and the region 642, which is the sum of the discharge rate of the droplets for drawing small-sized dots and the discharge rate of the droplets for drawing large-sized dots, is cured in the high diffusion hardening time. This is the ink discharge rate.

  In addition, a region 643 indicated by solid parallel oblique lines has a discharge rate of ink (in this embodiment, a droplet for drawing a large-sized dot) that is cured in a low diffusion curing time that is ejected from the ejection head 31b. Show. A straight line 645 indicating the left boundary of the region 641 indicates a total discharge rate that is the sum of the discharge rate of the ink cured in the high diffusion hardening time and the discharge rate of the ink cured in the low diffusion hardening time, A line 646 indicates a high diffusion ink ratio, which is a ratio of the discharge ratio of the ink cured in the high diffusion curing time to the total ejection ratio, and a line 647 indicates that the ink cured in the high diffusion curing time. A small size ratio, which is a ratio of a discharge ratio of a droplet for drawing a small size dot in the discharge ratio, is shown (see the right vertical axis in FIG. 9).

  As shown in FIG. 9, in the ink jet printer according to the second embodiment, the discharge heads 31a and 31b (see FIG. 2) are controlled by the print control unit 4 (see FIG. 1), so that the gradation value is changed. As the minimum gradation value (0) increases to the maximum gradation value (255), the total discharge rate gradually increases from 0% to 100% in proportion to the gradation value. When the gradation value is not less than the minimum gradation value (0) and less than a predetermined gradation threshold value (170 in the present embodiment), the total discharge rate of the ink that is cured in the high diffusion curing time is obtained. The ratio of the highly diffusing ink, which is the occupying ratio, is 100%, and ink is ejected only from the ejection head 31b of the ejection heads 31a and 31b.

  In the gradation value range in which only ink cured in the high diffusion curing time is ejected (that is, the highlight area and intermediate gradation area where the gradation value is 0 or more and less than 170), the gradation value is the minimum gradation. The ratio of the small size is 100% when the value is less than another gradation threshold value (85 in the present embodiment) that is greater than or equal to the value and less than the gradation threshold value (170). Only the droplets to be drawn are ejected. In the following description, in order to distinguish two gradation threshold values, the larger gradation threshold value (170) is referred to as “first gradation threshold value”, and the smaller gradation threshold value (85) is referred to as “second floor”. This is called “tone threshold”. When the gradation value is greater than or equal to the second gradation threshold value and less than the first gradation threshold value, the small size ratio gradually decreases from 100% as the gradation threshold value increases, and small size dots are drawn from the ejection head 31b. A droplet and a droplet for drawing a large-sized dot are ejected.

  On the other hand, when the gradation value is not less than the first gradation threshold value (170) and not more than the maximum gradation value (255), the ink that is cured from the ejection head 31b in a high diffusion curing time (small size and large size). Droplets each drawing a size dot) are ejected, and ink that is cured in a low diffusion curing time is ejected from the ejection head 31a. As the gradation value increases from the first gradation threshold value (170) to the maximum gradation value (255), the high diffusion ink ratio gradually decreases from 100% to 0%.

  In the ink jet printer according to the second embodiment, when printing is performed on the printing medium 9 such as high-quality paper, from the highlight area of the image to the intermediate gradation area (the gradation value is in the range of 0 to less than 170). By performing drawing using only the ink that is cured in the high diffusion curing time, as in the first embodiment, the ink dots become inconspicuous and a smooth image can be drawn. Also, in the shadow area of the image (the gradation value is in the range of 170 to 255), drawing is performed with both the ink cured in the high diffusion curing time and the ink cured in the low diffusion curing time. By decreasing the ratio of the discharge rate of the ink cured in the high diffusion curing time in the total discharge rate as the tone value increases, and increasing the ratio of the ink discharge rate cured in the low diffusion curing time, It is possible to prevent insufficient density in the shadow area and to prevent the color gamut from becoming narrow.

  In the ink jet printer according to the second embodiment, in particular, drawing is performed only with ink that is cured in a high diffusion hardening time from the highlight area to the intermediate gradation area (the gradation value is in the range of 0 to less than 170). In the highlight area (the gradation value is in the range of 0 to less than 85), drawing is performed only with a droplet for drawing a small dot, and the intermediate gradation area (the gradation value is in the range of 85 to less than 170). In the range), when drawing with droplets for drawing small and large dots respectively, gradation change is gradually reduced by gradually decreasing the small size ratio as the gradation value increases. And the occurrence of tone jump can be suppressed.

  In the ink jet printer according to the second embodiment, printing on coated paper or the like is also performed as in the first embodiment. FIG. 10 is a diagram illustrating the relationship between the gradation value of the K halftone image and the ink ejection rate in the ejection mechanism that ejects K ink when printing on the print medium 9 such as coated paper is performed. It is. When printing is performed on the printing medium 9 such as coated paper, the highlight area and the halftone area of the image are drawn only by the ink that is cured in the low diffusion curing time ejected from the ejection head 31a. This is done, and the size of the small ink droplet is switched between two types, large and small.

  In FIG. 10, a region 651 indicated by solid parallel diagonal lines indicates a discharge rate of a droplet for drawing a small-sized dot out of the discharge rate of the ink cured from the discharge head 31a in the low diffusion hardening time. A region 652 indicated by a thick solid line with parallel diagonal lines indicates a discharge rate of a liquid droplet for drawing a large-sized dot out of a discharge rate of ink that is discharged from the discharge head 31a and is cured in a low diffusion hardening time. . Therefore, the total of the region 651 and the region 652 that is the sum of the discharge rate of the droplet for drawing small-sized dots and the discharge rate of the droplet for drawing large-sized dots is cured in the low diffusion hardening time. This is the ink discharge rate.

  In addition, a region 653 indicated by broken parallel oblique lines indicates a discharge rate of ink (in this embodiment, a droplet for drawing a large-sized dot) that is hardened in a high diffusion hardening time discharged from the discharge head 31a. Show. A straight line 655 indicating the left boundary of the region 651 indicates a total discharge rate that is the sum of the discharge rate of the ink cured in the low diffusion hardening time and the discharge rate of the ink cured in the high diffusion hardening time, A line 656 indicates a low diffusion ink ratio that is a ratio of a discharge ratio of ink cured at a low diffusion hardening time to a total discharge rate, and a line 657 indicates the ink cured at a low diffusion hardening time. A small size ratio, which is a ratio of a discharge ratio of a droplet for drawing a small size dot in the discharge ratio, is shown (see the right vertical axis in FIG. 10).

  As shown in FIG. 10, in the ink jet printer according to the second embodiment, the discharge values 31a and 31b (see FIG. 2) are controlled by the print control unit 4 (see FIG. 1), so that the gradation value is changed. As the minimum gradation value (0) increases to the maximum gradation value (255), the total discharge rate gradually increases from 0% to 100% in proportion to the gradation value. When the gradation value is not less than the minimum gradation value (0) and less than the first gradation threshold (170), the low diffusion that is the ratio of the discharge rate of the ink cured in the low diffusion curing time to the total discharge rate The ink ratio is 100%, and ink is ejected from only the ejection head 31a of the ejection heads 31a and 31b.

  In the gradation value range in which only ink cured in the low diffusion curing time is ejected (that is, the highlight area and the intermediate gradation area where the gradation value is 0 or more and 170 or less), the gradation value is the minimum gradation. When the value is greater than or equal to the value and less than the second gradation threshold (85), the small size ratio is set to 100%, and only the liquid droplets for drawing the small size dots are ejected from the ejection head 31a. When the gradation value is greater than or equal to the second gradation threshold value and less than the first gradation threshold value (170), the small size ratio gradually decreases from 100% as the gradation threshold value increases, and the small size is discharged from the ejection head 31a. A droplet for drawing a dot and a droplet for drawing a large-sized dot are discharged.

  On the other hand, when the gradation value is not less than the first gradation threshold value (170) and not more than the maximum gradation value (255), the ink (small size and large size) that is cured from the ejection head 31a in a low diffusion curing time. Droplets for drawing the respective dots) and ink that is cured in a high diffusion hardening time is ejected from the ejection head 31b. As the gradation value increases from the first gradation threshold value (170) to the maximum gradation value (255), the low diffusion ink ratio gradually decreases from 100%.

  In the ink jet printer according to the second embodiment, when printing is performed on the printing medium 9 such as coated paper, the intermediate gradation area (the gradation value is in the range of 0 to less than 170) from the highlight area of the image. By performing the drawing using only the ink cured in the low diffusion hardening time, it is possible to draw the figure or the like sharply while suppressing the bleeding of the ink as in the first embodiment. Also, in the shadow area of the image (the gradation value is in the range of 170 to 255), drawing is performed with both the ink cured in the low diffusion curing time and the ink cured in the high diffusion curing time. By decreasing the ratio of the discharge rate of the ink cured at the low diffusion curing time to the total discharge rate according to the increase in the tone value and increasing the ratio of the ink discharge rate cured at the high diffusion curing time, Generation of streak unevenness in the shadow region can be suppressed.

  In the inkjet printer according to the second embodiment, in particular, drawing is performed only with ink that is cured in a low diffusion hardening time from the highlight region to the intermediate gradation region (the gradation value is in the range of 0 to less than 170). When drawing, draw only with a droplet that draws a small dot in the highlight area, and draw with a droplet that draws a small size dot and a large size dot in a part of the intermediate gradation area. When performing, by gradually decreasing the small size ratio as the gradation value increases, the gradation change can be expressed more smoothly and the occurrence of tone jump can be suppressed.

  Next, an ink jet printer according to a third embodiment of the present invention will be described. FIG. 11 is an enlarged view of the ejection unit 3a of the ink jet printer according to the third embodiment. The ejection unit 3a is arranged on the (+ Y) side of each of the twelve ejection heads 31 that eject micro droplets of ink from a plurality of ejection ports, and emits light toward the print medium 9. And 12 heads 35 for supporting the ejection head 31 and the curing head 33 are provided. The other configuration of the ink jet printer according to the third embodiment is the same as that of the ink jet printer 1 shown in FIG. 1, and the same reference numerals are given to the corresponding configurations in the following description.

  In the ejection unit 3a, the three ejection heads 31 from the (−Y) side in FIG. 11 eject the same type of K ink, and irradiate the print medium 9 from the three curing heads 33 from the (−Y) side. The intensity of the emitted light becomes weaker from the (−Y) side toward the (+ Y) side. Therefore, the curing time of the ink ejected from each of the three ejection heads 31 from the (−Y) side becomes longer from the (−Y) side to the (+ Y) side, and the dot diffusibility on the print medium 9 is high. Become. In the following description, the curing time of the ink ejected from the central ejection head 31 among the three ejection heads 31 that eject the same type of ink is referred to as “medium diffusive curing time”. In the ejection unit 3a, the dot diffusibility of the ink ejected from the three adjacent ejection heads 31 on the print medium 9 is also from the (−Y) side for the other three colors (C, M, Y). It becomes higher toward the (+ Y) side.

  FIG. 12 is a diagram showing the relationship between the gradation value of the halftone image and the ink ejection rate of the three ejection heads 31 that eject the same color ink when printing on the printing medium 9 such as fine paper is performed. . In FIG. 12, a region 661 indicated by a broken parallel oblique line indicates the ejection rate of the ink that is cured in the high diffusion curing time, and an area 662 indicated by the alternate long and short dashed parallel line is the ink that is cured in the medium diffusive curing time. A region 663 indicated by a solid parallel oblique line indicates a discharge rate of ink that is cured in a low diffusion hardening time. A straight line 665 indicating the left boundary of the region 661 is cured at an ejection rate of ink cured at a high diffusion curing time, an ejection rate of ink cured at an intermediate diffusion curing time, and a low diffusion curing time. The total discharge rate that is the sum of the ink discharge rates is shown, and a line 666 shows the high diffusion ink ratio that is the ratio of the ink discharge rate cured in the high diffusion curing time to the total discharge rate.

  As shown in FIG. 12, in the ink jet printer according to the third embodiment, the three ejection heads 31 are controlled by the print control unit 4 (see FIG. 1), so that the gradation value is the minimum gradation value ( The total discharge rate gradually increases from 0% to 100% in proportion to the gradation value as it increases from 0) to the maximum gradation value (255). When the gradation value is not less than the minimum gradation value (0) and less than the second gradation threshold value (85), the high diffusion that is the ratio of the discharge rate of the ink cured in the high diffusion curing time to the total discharge rate The ink ratio is set to 100%. In addition, when the gradation value is equal to or greater than the second gradation threshold (85) and less than the first gradation threshold (170), the ink is cured with a high diffusion curing time and the ink is cured with a medium diffusion curing time. Ink is discharged and ink that is cured in a low diffusion curing time is not ejected, and when the gradation value is not less than the first gradation threshold (170) and not more than the maximum gradation value (255), a high diffusion curing time, Ink that is cured in a diffusive curing time and a low diffusion curing time is discharged. In the range where the gradation value is not less than the second gradation threshold and not more than the maximum gradation value, the high diffusion ink ratio gradually decreases as the gradation value increases.

  In the ink jet printer according to the third embodiment, when drawing on the printing medium 9 such as high-quality paper, the drawing is performed using only the ink cured in the high diffusion hardening time in the highlight region of the image. As a result, the ink dots become inconspicuous and a smooth image can be drawn. Also, ink that is drawn with an ink that is cured with a high diffusion curing time and an ink that is cured with a medium diffusion curing time in an intermediate gradation region, and is cured with a high diffusion curing time as the gradation value increases. By reducing the ratio of the discharge rate to the total discharge rate, a figure or the like can be drawn sharply. Furthermore, in the shadow region, drawing is performed with ink that is cured at a high diffusion curing time, a medium diffusion curing time, and a low diffusion curing time, respectively, and the ink that is cured at a low diffusion curing time as the gradation value increases. By increasing the ratio of the discharge rate to the total discharge rate, it is possible to prevent insufficient density in the shadow area and to prevent the color gamut from becoming narrow. In an ink jet printer, drawing is performed by changing the dot diffusivity of the same type of ink into three types, thereby making it possible to more smoothly express changes in gradation and to suppress the occurrence of tone jumps.

  FIG. 13 is a diagram showing the relationship between the gradation value of the halftone image and the ink ejection rate of the three ejection heads 31 that eject the same color ink when printing on the printing medium 9 such as coated paper is performed. . In FIG. 13, a region 671 indicated by a solid parallel oblique line indicates the discharge rate of ink cured in a low diffusion hardening time, and a region 672 indicated by an alternate long and short dash line is indicated by an ink cured by a medium diffusive curing time. A region 673 indicated by a broken parallel oblique line indicates a discharge rate of ink that is cured in a high diffusion curing time. A straight line 675 indicating the left boundary of the region 671 indicates the total discharge rate, and a line 676 indicates the low diffusion ink ratio.

  As shown in FIG. 13, in the inkjet printer according to the third embodiment, the three ejection heads 31 are controlled by the print control unit 4 (see FIG. 1), so that the gradation value is the minimum gradation value ( The total discharge rate gradually increases from 0% to 100% in proportion to the gradation value as it increases from 0) to the maximum gradation value (255). When the gradation value is not less than the minimum gradation value (0) and less than the second gradation threshold value (85), the low diffusion ink ratio is set to 100%. In addition, when the gradation value is equal to or greater than the second gradation threshold (85) and less than the first gradation threshold (170), the ink is cured with a low diffusion curing time and the ink is cured with a medium diffusion curing time. Ink is discharged and ink that is cured in a high diffusion curing time is not ejected, and when the gradation value is not less than the first gradation threshold (170) and not more than the maximum gradation value (255), the low diffusion curing time, Ink that is cured in each of the diffusive curing time and the high diffusion curing time is discharged. In the range where the gradation value is not less than the second gradation threshold value and not more than the maximum gradation value, the low diffusion ink ratio gradually decreases as the gradation value increases.

  In the ink jet printer according to the third embodiment, the ink bleeding can be suppressed by performing drawing using only the ink cured in the low diffusion hardening time in the highlight region of the image. Also, ink that is drawn with an ink that is cured with a low diffusion curing time and an ink that is cured with a medium diffusive curing time in an intermediate gradation region, and is cured with a low diffusion curing time as the gradation value increases. By reducing the ratio of the discharge rate to the total discharge rate, a smooth image can be drawn. Furthermore, in the shadow area, drawing is performed with ink that is cured at a low diffusion curing time, a medium diffusion curing time, and a high diffusion curing time, respectively, and the discharge of the highly diffusible ink occupies the total discharge rate as the gradation value increases. By increasing the rate ratio, the occurrence of streak unevenness in the shadow region can be suppressed. Inkjet printers can render gradation changes more smoothly by drawing with three different dot diffusivities of the same type of ink, similar to printing on high-quality paper. Can be suppressed.

  Next, an ink jet printer according to a fourth embodiment of the present invention will be described. FIG. 14 is an enlarged view of the ejection unit 3b of the ink jet printer according to the fourth embodiment. The ejection unit 3b includes eight ejection heads 31a to 31h each ejecting micro droplets of ink from a plurality of ejection ports, and the (+ Y) side of two adjacent ejection heads that eject the same color and the same type of ink. And curing heads 33a, 33c, 33e, and 33g that cure the ink ejected from each of the two ejection heads by irradiating light toward the print medium 9, and support these ejection heads and the curing head. A head support 35 is provided. Other configurations of the ink jet printer according to the fourth embodiment are the same as those of the ink jet printer 1 shown in FIG. 1, and the same reference numerals are given to the corresponding configurations in the following description.

  When attention is paid to the ejection heads 31a and 31b and the curing head 33a that cures the ink from the ejection heads 31a and 31b shown in FIG. 14, the Y direction between the ejection head 31a and the curing head 33a (that is, the printing medium 9). The distance in the relative movement direction with respect to the discharge unit 3 is larger than the distance in the Y direction between the discharge head 31b and the curing head 33a. In the present embodiment, the distance between the ejection head 31a and the curing head 33a is greater than 10 cm, and the distance between the ejection head 31b and the curing head 33a is less than 10 cm. As a result, the curing time of the ink ejected from the ejection head 31a is longer than the curing time of the ink ejected from the ejection head 31b, and the dot diffusibility of the ink from the ejection head 31a on the print medium 9 is reduced by the ejection head 31b. It becomes higher than the dot diffusibility on the printing medium 9 of the ink from. That is, the ink ejected from the ejection head 31a is cured in a high diffusion curing time, and the ink ejected from the ejection head 31b is cured in a low diffusion curing time.

  In the inkjet printer according to the fourth embodiment, as in the first embodiment, when printing is performed on the print medium 9 such as fine paper, the control shown in FIG. Only ink that is cured with a high diffusion hardening time in the range from the tone value to less than the tone threshold is ejected, and in the range where the tone value is greater than the tone threshold and less than the maximum tone value, high diffusion is achieved as the tone value increases By performing the control of gradually decreasing the ink ratio, the ink dots become inconspicuous in the highlight area of the image, and a smooth image can be drawn. In addition, it is possible to prevent insufficient density in the shadow area and to prevent the color gamut from becoming narrow.

  On the other hand, when printing on the printing medium 9 such as coated paper, the control shown in FIGS. 7 and 8 (that is, the low diffusion hardening time in the range where the gradation value is not less than the minimum gradation value and less than the gradation threshold value). By ejecting only the ink to be cured, and controlling the gradation ratio to gradually decrease the low diffusion ink ratio as the gradation value increases in the range where the gradation value is not less than the gradation threshold value and not more than the maximum gradation value, In a part of the intermediate gradation area from the light area, it is possible to draw a figure or the like sharply by suppressing ink bleeding and to suppress the occurrence of streak unevenness in the shadow area.

  Further, in the inkjet printer according to the fourth embodiment, as in the second embodiment, the size of the dots drawn by the ink ejected from each of the ejection heads 31a to 31h is small and large. May be switchable between. In this case, the discharge control shown in FIGS. 9 and 10 is performed, so that the gradation change can be expressed more smoothly in the printed image, and the occurrence of tone jump can be suppressed. Furthermore, as in the third embodiment, the same color and the same type of ink are ejected from the adjacent three ejection heads, and the distances in the Y direction between the three ejection heads and the curing head are made different. It is also possible to suppress the occurrence of tone jump by curing the ink at a high diffusion curing time, a medium diffusion curing time, and a low diffusion curing time.

  As described above, in the inkjet printer 1 according to the first embodiment, the first cured portion is irradiated with light having the first intensity with respect to the ink ejected from the plurality of first ejection ports, and the plurality of first ejections are performed. It is the curing time of the ink ejected from the plurality of first ejection ports by irradiating the ink ejected from the second ejection ports with light having a second intensity different from the first intensity from the second curing unit. The first curing time is different from the second curing time, which is the curing time of the ink ejected from the plurality of second ejection ports.

  On the other hand, in the inkjet printer according to the fourth embodiment, the distance between the plurality of first discharge ports and the curing unit (that is, the curing head) in the Y direction, and the plurality of second discharge ports and the curing unit. The first curing time and the second curing time are made different from each other by making the distance between them different. In these ink jet printers, the first curing time and the second curing time can be easily made different with a simple structure. As a result, the dot diffusibility of the ink ejected from the plurality of first ejection ports and the dot diffusivity of the ink ejected from the plurality of second ejection ports can be easily made different.

  As mentioned above, although embodiment of this invention has been described, this invention is not limited to the said embodiment, A various change is possible.

  In the inkjet printer 1 according to the first embodiment, for example, the curing head 33a and the curing head 33b are connected to the same light source, and the distance in the Z direction between the curing head 33a and the print medium 9 is set as the curing head. By making the distance smaller than the distance in the Z direction between 33b and the print medium 9, the intensity of the light irradiated from the curing head 33a to the print medium 9 becomes the intensity of the light irradiated from the curing head 33b to the print medium 9. May be higher.

  In the inkjet printer 1, it is not always necessary to cure the ink by irradiating the ink discharged onto the print medium 9 with light and drying it. For example, the dots of ultraviolet curable ink applied on the print medium The film may be cured by irradiating with ultraviolet rays. In this case, by varying the intensity of the ultraviolet rays applied to the ink, the dot diffusibility can be easily varied by varying the ink curing time. In addition, the dot diffusibility of the ink on the print medium 9 may be easily changed by irradiating the ink with an energy wave (for example, an electron beam) other than light or ultraviolet light and changing the intensity of the energy wave.

  In the inkjet printer 1, when printing is performed on a printing medium 9 such as fine paper, the gradation value increases from the gradation threshold value (128) to the maximum gradation value (255) as shown in FIG. Accordingly, the control by the print control unit 4 may be performed so that the high diffusion ink ratio (line 686) gradually decreases from 100% to a ratio larger than 0%.

  In the control shown in FIGS. 6 and 7, the total discharge rate does not necessarily increase gradually in proportion to the increase in gradation value. For example, as shown in FIG. 16, the total discharge rate increases as the gradation value increases. Even when the rate (line 695) gradually increases and the increase rate of the total discharge rate (that is, the increase amount of the total discharge rate in a predetermined range of gradation values) is also gradually increased (or gradually decreased). Good.

  In the control shown in FIG. 8, it is not always necessary to eject the high diffusible ink droplets on the low diffusible ink dots applied on the print medium 9, and the Y direction of the curing head 33 a and the curing head 33 b. The ink droplets of the low diffusibility ink may be ejected onto the dots of the high diffusibility ink applied on the print medium 9 after the positions of the above are reversed.

  The threshold value matrix to be compared with the original image data in step S11 is to change the size of regularly arranged halftone dots (more precisely, a cluster which is a set of dots (or pixels) joined together). It may be for AM (Amplitude Modulated) screening in which gradation expression is realized. If the image quality in the shadow area or the like falls within the allowable range, the halftone image data may be generated by an error diffusion method or the like without using a threshold matrix.

  In an ink jet printer, the ink used for drawing is not limited to water-based dye ink, and for example, oil-based pigment ink, oil-based dye ink, water-based pigment ink, ultraviolet curable ink, and the like may be used as appropriate.

  In the ink jet printer according to the above embodiment, the arrangement order of the discharge heads of the respective colors in the discharge unit may be changed as appropriate. For example, Y, M, C, K from the (−Y) side to the (+ Y) side. The heads that discharge the inks of the respective colors may be arranged. Further, the width in the X direction of each ejection head of the ejection unit is made smaller than the width in the X direction of the print medium 9, and the reciprocation of the ejection unit in the X direction and the movement of the print medium 9 in the (+ Y) direction are performed. Printing on the print medium 9 may be performed by performing in parallel. The moving mechanism 2 does not necessarily need to be a mechanism that moves the print medium 9, and may be a mechanism that moves the print medium 9 relative to the discharge unit by moving the discharge unit, for example.

  In the above-described ink jet printer, the discharge head that discharges the C, M, and Y inks from the discharge unit 3 may be omitted and used as a monochrome printer. For example, printing may be performed on a so-called web that is continuous paper. In an inkjet printer, it is not always necessary to perform printing on a sheet-like print medium 9 such as paper or film, and printing may be performed on a thin plate-like print medium or other various print media.

DESCRIPTION OF SYMBOLS 1 Inkjet printer 2 Moving mechanism 3, 3a, 3b Discharge part 4 Print control part 9 Print medium 31, 31a-31h Discharge head 33, 33a-33h Curing head 70 Original image 710 Threshold matrix S11-S14 Step

Claims (10)

An inkjet printer,
An ejection mechanism for ejecting micro droplets of ink from a plurality of first ejection ports and a plurality of second ejection ports toward a print medium;
A moving mechanism for moving the print medium relative to the discharge mechanism;
The ink ejected from the plurality of first ejection ports is cured after the first curing time has elapsed, and the ink ejected from the plurality of second ejection ports has a second curing time different from the first curing time. A cured portion to be cured after elapse,
A print control unit for drawing an image on the print medium by controlling the ejection mechanism and the moving mechanism;
With
By controlling the discharge mechanism by the print control unit, a part of the range of gradation values that can be expressed on the print medium is obtained from both the plurality of first discharge ports and the plurality of second discharge ports. Ink is ejected toward the print medium, and is the sum of the ink ejection rate from the plurality of first ejection ports and the ink ejection rate from the plurality of second ejection ports as the gradation value increases. As the total discharge rate gradually increases, the first ink ratio, which is the ratio of the discharge rate of ink from the plurality of first discharge ports to the total discharge rate in the part of the range of the gradation value, gradually decreases. An ink jet printer characterized by the above. The inkjet printer according to claim 1,
The first curing time is longer than the second curing time;
By controlling the ejection mechanism by the print control unit, when the gradation value is 0 or more and less than a predetermined gradation threshold, the first ink ratio is set to 100%, and the gradation value is An ink jet printer characterized in that the first ink ratio gradually decreases from 100% as the gradation value increases when the gradation value is equal to or greater than a gradation threshold value and equal to or less than a maximum gradation value. The inkjet printer according to claim 1,
The first curing time is shorter than the second curing time;
By controlling the ejection mechanism by the print control unit, when the gradation value is 0 or more and less than a predetermined gradation threshold, the first ink ratio is set to 100%, and the gradation value is An ink jet printer characterized in that the first ink ratio gradually decreases from 100% as the gradation value increases when the gradation value is equal to or greater than a gradation threshold value and equal to or less than a maximum gradation value. The inkjet printer according to claim 3,
By controlling the ejection mechanism by the print control unit, the total ejection rate becomes larger than 100% in a range of gradation values in the vicinity of the maximum gradation value including the maximum gradation value. Inkjet printer. An ink jet printer according to claim 2 or 3,
The size of dots drawn by the first ink in the ejection mechanism can be switched between a small size and a large size,
The discharge rate of the first ink is a sum of a discharge rate of a droplet that draws the small-sized dots and a discharge rate of a droplet that draws the large-sized dots,
By controlling the ejection mechanism by the print control unit, it occupies the ejection rate of the first ink when the gradation value is 0 or more and less than another gradation threshold value less than the gradation threshold value. When the small size ratio indicating the ratio of the discharge rate of the droplet for drawing the small size dots is 100%, and the gradation value is not less than the other gradation threshold and less than the gradation threshold, The ink jet printer, wherein the small size ratio gradually decreases from 100% as the gradation value increases. An inkjet printer according to any one of claims 1 to 5,
The ink jet printer according to claim 1, wherein the print control unit controls a discharge rate of the discharge mechanism by comparing a pixel value of the image with a threshold value of a threshold value matrix. An ink jet printer according to any one of claims 1 to 6,
The cured portion is
A first curing unit that cures the ink ejected from the plurality of first ejection ports by irradiating an energy wave of a first intensity;
A second curing unit that cures the ink ejected from the plurality of second ejection ports by irradiating an energy wave of a second intensity;
With
The ink jet printer according to claim 1, wherein the first curing time and the second curing time are different due to the difference between the first strength and the second strength. An ink jet printer according to any one of claims 1 to 6,
In the relative movement direction of the print medium with respect to the discharge mechanism by the moving mechanism, the distance between the plurality of first discharge ports and the curing unit, and between the plurality of second discharge ports and the curing unit. The inkjet printer, wherein the first curing time and the second curing time are different due to a difference in distance. The ink jet printer according to any one of claims 1 to 8,
An ink jet printer, wherein first ejection ports and second ejection ports are alternately arranged in a direction perpendicular to a relative movement direction of the print medium with respect to the ejection mechanism by the moving mechanism. An inkjet printing method,
a) discharging fine ink droplets from a plurality of first discharge ports and a plurality of second discharge ports of the discharge mechanism toward a print medium;
b) drawing an image on the print medium by moving the print medium relative to the ejection mechanism in parallel with the step a);
c) Second ink curing the ink ejected from the plurality of first ejection ports after the first curing time has elapsed, and the ink ejected from the plurality of second ejection ports different from the first curing time. A step of curing after a lapse of time;
With
By controlling the discharge mechanism in the step a), a part of a range of gradation values that can be expressed on the print medium is from both the plurality of first discharge ports and the plurality of second discharge ports. Ink is ejected toward the print medium, and is the sum of the ink ejection rate from the plurality of first ejection ports and the ink ejection rate from the plurality of second ejection ports as the gradation value increases. As the total discharge rate gradually increases, the first ink ratio, which is the ratio of the discharge rate of ink from the plurality of first discharge ports to the total discharge rate in the part of the range of the gradation value, gradually decreases. A printing method characterized by:

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