JP2007118444A - Inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording method capable of controlling the diameters of dots by the surface tension, to smoothly reproduce the gradation by decreasing sticking of the dots under an intermediate tone, hardly generating a pseudo-profile, and recording a natural image hardly generating changes in granularity and in color tone of the image recorded. <P>SOLUTION: In a printing duty, a row of nozzles having the same color, the same density and individually different surface tensions is provided for obtaining a smooth image quality free from granularity, and two inks start impacting on the positions where the two inks merges with each other. Inks having high surface tensions is applied on a recording medium to reduce adhesion of the inks. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet recording apparatus and an ink jet recording method.

  An image display device that expresses an image by forming dots on a display medium such as a print medium or a liquid crystal screen is widely used as an output device of various image devices. Such an image display device can express only the state of whether or not to form dots locally, but it can be achieved by appropriately controlling the dot formation density according to the gradation value of the image. It is possible to express a gradation image.

  A technique called an error diffusion method is widely used as a technique for determining the presence or absence of dot formation for each pixel so that dots are formed at an appropriate density according to the gradation value of the image. In the error diffusion method, an error in gradation expression caused by the formation of a dot in a pixel of interest or the absence of a dot is diffused and stored in undetermined pixels around the pixel of interest. In determining the presence or absence of dot formation for a pixel, this is a method for determining the presence or absence of dot formation so as to eliminate the error diffused from the surrounding pixels. Since the error diffusion method determines whether or not dots are formed so as to eliminate the error in this way, dots can be formed with an appropriate density according to the gradation value of the image, and a high-quality image can be displayed on the image display device. Can be displayed.

  In recent years, image display devices that can actively control gradation values expressed by individual dots have been widely used. For example, the gradation value expressed per single dot can be controlled by making it possible to form various dots of different sizes, or by using different inks when using ink to form dots. be able to. In these image display devices, the generation of errors can be suppressed by controlling the gradation values expressed by individual dots in accordance with the gradation values of the image. Furthermore, if the presence / absence of dot formation is determined using the error diffusion method, the error can be quickly eliminated by forming dots with appropriate gradation values according to the error diffused from the surrounding pixels. Is possible. For this reason, if the error diffusion method is applied to the determination of dot formation in an image display device capable of forming various dots having different gradation values to be expressed, a higher quality image can be displayed.

For example, Patent Document 1 and Patent Document 2 can be cited as conventional examples.
JP 2000-225716 A JP 2004-34475 A

  However, at the halftone print duty, the inks land at positions where the inks stick to each other, which increases the dot diameter and deteriorates the graininess. In addition, even in an ink jet recording apparatus having inks of the same density and different ink volumes, large dots and small dots stick to each other at a halftone print duty, resulting in a blurred image. .

  Therefore, in order to obtain a smooth image quality without graininess, an ink having a high surface tension at a print duty having a nozzle row having different surface tension inks of the same color and the same density and at which the two inks start to land on each other. Is applied to the recording medium, thereby reducing ink sticking.

  In order to achieve the above object, a head having a nozzle capable of forming two or more types of dots having different diameters is provided, and it is determined which dot is to be formed according to the printing conditions and the gradation value of the image data. A printing apparatus capable of printing an image on a print medium by forming dots according to the determination result by the recording head, and for one specific dot that can independently express a predetermined gradation value, from the specific dot In addition, when forming an image using dots with a large diameter in one step, the ink with high surface tension is applied to the recording medium with the ink with a large diameter in one step at the print duty at which the small dots and the large dots start to land. To reduce ink sticking.

  Further, in order to achieve the above object, the surface tension of the print duty which has different surface tension inks in ink colors such as cyan, magenta, black, etc., which are particularly easy to visually recognize, and the two inks start to land on the sticking position. Ink sticking is reduced by applying high ink to the recording medium.

  When the printing duty is higher than these printing duties, by applying ink with low surface tension to prevent white spots and the like to the recording medium, gradation reproduction is smoothed, pseudo contour is hardly generated, and recorded images are printed. It is also possible to record a natural image that hardly changes in graininess and color tone.

  As described above, the dot diameter is controlled by the surface tension, and the gradation reproduction is smoothed by reducing the dot sticking in the halftone, the pseudo contour is not easily generated, the graininess change and the color tone of the recorded image are reduced. It is also possible to record a natural image that hardly changes.

  FIG. 1 is a plan view showing a schematic configuration of an ink jet recording apparatus according to each embodiment of the present invention. A plurality of inkjet recording heads (hereinafter simply referred to as recording heads) 21-1 to 21-4 are mounted on the carriage 20, and each inkjet recording head 21 has a plurality of ink ejection openings for ejecting ink. It is arranged. 21-1, 21-2, 21-3, and 21-4 are recording heads for ejecting black (K), cyan (C), magenta (M), and yellow (Y) inks, respectively. It is. A heating element (electrothermal converter) that generates thermal energy for ink ejection is provided inside the ink ejection opening (liquid path) of the recording head 21. The ink cartridge 22 includes ink jet recording heads 21-1 to 21-4 and ink tanks 22-1 to 22-4 that supply ink to them.

  Control signals and the like to the ink jet recording head 21 are sent via the flexible cable 23. A recording medium 24 such as plain paper, high-quality exclusive paper, OHP sheet, glossy paper, glossy film, postcard or the like is sandwiched between a pair of paper discharge rollers 25 facing each other via a conveyance roller (not shown) to drive the conveyance motor 26. Along with this, it is sent in the arrow direction (sub-scanning direction). The carriage 20 is movably supported by the guide shaft 27 and the linear encoder 28. The carriage 20 reciprocates along the guide shaft 27 in the main scanning direction that intersects (is orthogonal to) the sub-scanning direction along the guide shaft 27 by driving the carriage motor 30 via the driving belt 29. At the time of reciprocal movement, a pulse signal is output from the linear encoder 28, and the position of the carriage 20 can be detected by counting the pulse signal.

  Further, the heating element of the recording head 21 is driven based on the recording signal as the carriage 20 moves, and forms an image by flying and adhering ink droplets onto the recording medium.

  A recovery unit 32 having a cap portion 31 is installed at the home position of the carriage 20 set outside the region in the main scanning direction where the recording operation is performed on the recording medium. When recording is not performed, the carriage 20 is moved to the above-described home position, and the ink discharge port surfaces of the corresponding inkjet recording heads 21 are sealed by the caps 31-1 to 31-4 of the cap unit 31, so that the ink solvent is removed. Prevents clogging due to thickening of ink, sticking or adhesion of foreign matters such as dust due to evaporation.

  Further, the capping function of the cap unit 31 is used for empty ejection in which ink is ejected to the cap unit 31 in a state separated from the ink ejection port in order to eliminate ejection failure and clogging of the ink ejection port with low recording frequency. Then, the pump (not shown) is operated in a state where the cap portion 31 is in operation, and the ink is sucked from the ink discharge port, and is used for recovery of the discharge function of the discharge port that caused the discharge failure. Reference numeral 33 denotes an ink receiving portion that performs preliminary ejection toward the ink receiving portion 33 when each of the ink jet recording heads 21-1 to 21-4 passes above the ink receiving portion 33 immediately before recording. Further, by disposing a wiping member (blade or the like) (not shown) at a position adjacent to the cap portion 31, the ink discharge port forming surface of the recording head 21 can be cleaned.

  Next, FIG. 2 is an explanatory diagram showing an enlarged configuration of the recording head 21 described above. In FIG. 2, the recording head has a large number of ink ejection nozzles n in a direction substantially perpendicular to the recording direction. In this figure, the ink ejection nozzles are symmetrically composed of large and small nozzles in one recording head, and the nozzle arrays may be symmetrically arranged. Also, as shown in FIG. 2, the interval in the sub-scanning direction between adjacent nozzles is referred to as the recording head resolution, nozzle pitch, and nozzle density.

  In addition, this recording head is configured to perform recording corresponding to the width of the nozzle row by ejecting ink while moving the recording head in the direction of the arrow (main scanning direction) in the figure. The (ink discharge operation) can be performed by one or both of the forward and backward movements of the recording head. Furthermore, the same number of recording heads as the number of ink colors used for recording are prepared. For example, when performing full-color recording using three colors of cyan, magenta, and yellow, three recording heads are prepared. When performing monochrome recording using only black ink, one recording head is prepared. Just do it. In the case of recording using large and small inks, a recording head may be prepared for each of large cyan, small cyan, large magenta, small magenta, black, yellow, and the like, and a recording head that discharges special color inks. It is also possible to use.

  FIG. 3 is a block diagram showing an example of the configuration of the control system of the ink jet recording apparatus in each embodiment of the present invention.

  In FIG. 3, 1 is an image data input unit for inputting multi-value image data from an image input device such as a scanner or a digital camera, or multi-value image data stored in a hard disk of a personal computer, and 2 is a setting of various parameters. An operation unit 3 having various keys for instructing the start of recording is a CPU as a control means for controlling various arithmetic processes and control operations described later according to various programs in the storage medium.

  A storage medium 4 stores a control program and an error processing program for controlling the recording apparatus. All recording operations in this embodiment are executed by these programs. As the recording medium 4 for storing the program, a ROM, FD, CD-ROM, HD, memory card, magneto-optical disk, or the like can be used. By 4a, the data input by the large / small sorting table is distributed to small ink data and large ink data. FIG. 4 shows an example of the conversion graph of the large / small sorting table. Here, the solid line corresponds to the small ink data, and the dashed line corresponds to the large ink data. If the value of the 8-bit monochrome data is in the range of 0 to 128, the large ink data is “0” and the small ink data. Is output in the range of "0 to 128". If the value of the single color data is in the range of 128 to 255, the large ink data corresponds to "0 to 255" and the small ink data corresponds to "128 to 0". To output. FIG. 5 shows an example of a conversion graph of a table in which the data sorted according to the size in this embodiment is further sorted into inks having different surface tensions. If the 8-bit monochrome data value is in the range of 0 to 64, the large ink data is "0" and the small ink high surface tension ink data is in the range of "0 to 128". Is set to “0”. Next, if the value of the single color data is in the range of 64 to 128, the data for large ink is “0”, the data for high surface tension ink for small ink is “128 to 0”, and the data for low surface tension ink for small ink is used. “0 to 128”. Further, if the value of the monochromatic data is in the range of 128 to 192, the high surface tension data of the large ink is set to “0 to 255”, and the data of the low surface tension ink of the small ink is set to “128 to 0”. Further, if the value of the monochromatic data is in the range of 192 to 255, the high surface tension data of the large ink is output corresponding to “255 to 0”, and the low surface tension data of the large ink is output corresponding to “0 to 255”. In short, when the input data is low (highlight side), the ink with a small ink volume (small ink) is mainly used. Furthermore, when the input data starts from high surface tension ink, and the input data is halftone Ink is also recorded using a high surface tension ink using a large ink volume (large ink).

  Reference numeral 5 denotes a RAM used as a work area for various programs in the storage medium 4, a temporary save area for error processing, and a work area for image processing. The RAM 5 can also copy various tables in the recording medium 4, change the contents of the tables, and proceed with image processing while referring to the changed tables.

  An image data processing unit 6 processes the recording data. The input multi-valued image data is quantized into N-value recording data for each pixel, and the gradation value “T” indicated by each quantized pixel is obtained. Corresponding ejection pattern data is created. For example, when multi-value image data expressed in 8 bits (256 gradations) is input to the image input unit 1, the recording data processing unit 6 converts the gradation value of the output image data into 25 (= 24 + 1) values. There is a need to. Here, the multi-value error diffusion method is used for the T-value processing of the input gradation image data. However, the image processing method for performing the T-value conversion place is not limited to the multi-value error diffusion method, and the average density storage method. Any halftone processing method such as a dither matrix method can also be used. Further, by repeating the above-described T-value conversion processing for all the pixels based on the density information of the image, a binary drive signal for ejection and non-ejection for each ink nozzle is formed, and further, for each nozzle. A drive signal is formed and recorded. The nozzle information creation means, the prediction means, the correction information creation means, etc. in the present invention are mainly composed of the image processing unit 6 and the CPU 3. It is also possible to control with a printer driver processed in a PC or the like.

  A recording unit 7 ejects ink based on the ejection pattern created by the image data processing unit 6 to form a dot image on a recording medium, and includes an ink cartridge 22 and a carriage 20. Reference numeral 8 denotes a bus line for transmitting address signals, data, control signals, and the like in the apparatus.

  Next, the ink used in this example will be described. Ink jet ink has a surface tension lowered by a nonionic surfactant to improve permeability to a recording medium. The surface tension of the ink can be changed by changing the concentration of the surfactant. In general, when the surface tension is low, the ink has good wettability with the recording medium, so that it easily spreads on the recording medium and penetrates quickly. On the other hand, when the surface tension is high, the wettability of the ink with the recording medium deteriorates, so that the ink hardly spreads on the recording medium, and the permeation is slow. In this example, a commercially available photo black ink for ip8600 (manufactured by Canon Inc.) was used, and two types of inks having different surface tensions were prepared by changing the concentration of acetylene glycol. 0.6 wt% of the low surface tension ink was added and 0.1 wt% of the high surface tension ink was added. The surface tension at that time was about 30 dyn / cm and about 40 dyn / cm, respectively. The surface tension of a general inkjet ink is 30 to 35 dyn / cm in order to improve the permeability of plain paper. The permeation mechanism of the ink into the recording medium is a process in which the ink permeates while spreading on the recording medium after the ink has landed on the recording medium as shown in FIG. 6a. On the other hand, the high surface tension ink penetrates the recording medium almost without spreading after landing on the recording medium as shown in FIG. 6b. The dot diameter after fixing on these two recording media is naturally different, and the low surface tension ink is about 10% larger than the high surface tension.

  Next, a description will be given of when these inks have landed adjacent to each other. Whether or not these inks stick to each other depends on the resolution, ink volume, landing time difference, recording medium, etc. In this embodiment, the resolution is 1200 dpi (about 21 μm) and the ink volume is 2 pl (dot diameter 28 μm). ), The landing time difference was 0.5 msec, and the recording medium was printed on PR101 (manufactured by Canon Inc.). A schematic diagram of recording with low surface tension inks is shown in FIG. 7a. In this embodiment, the ink did not stick immediately after landing, but in the process of ink penetrating into the recording medium, the ink adheres on the recording medium and the final dot shape takes the shape shown in FIG. 8a. On the other hand, FIG. 7b shows a schematic diagram when recording is performed with high surface tension inks. In the process of penetrating immediately after landing, it does not stick on the recording medium, and the final dot shape is as shown in FIG. 8b.

  Thus, since the high surface tension ink is difficult to spread on the recording medium, the dot shape of 2 dots becomes an ideal dot shape. As shown in FIGS. 9 and 10, when a small dot and a large dot having a high surface tension (5 pl (dot diameter 40 μm)) are mixed, an ideal dot shape is obtained by reducing the contact amount. In particular, when a large dot is landed first, and then a small dot is landed adjacently thereafter, the closer the distance is, the more the ink of the small dot is drawn into the large dot due to the pressure gradient, and the original small dot is not retained. Therefore, by reducing the amount of contact between the small dots and the large dots, a dot shape close to the ideal dot shape can be obtained, and the deterioration of the graininess at the print duty at which the large dots and the small dots start to stick together is reduced. In this embodiment, inks having different surface tensions are used for both the small dots and the large dots. However, the present invention is also effective only for the large dots where the dots are easily visually recognized. Even if the ink color is easy to be visually recognized, there is an effect. In this embodiment, the landing time difference is set to 0.5 msec, but the same phenomenon as described above occurs because the previously ejected ink remains on the recording medium up to several tens of msec. In this embodiment, two types of inks having different surface tensions are used, but the number of types is not limited to two, and a plurality of types may be used.

1 is a front view showing an outline of an ink jet recording apparatus according to an embodiment of the present invention. It is a figure which shows the structure of the inkjet head applicable to this invention. It is a block diagram which shows the structural example of the inkjet recording device control system of this invention. It is an example of the conversion graph of a large and small distribution table. It is an example of the conversion graph of the size distribution table used for the present Example. It is the figure which showed the osmosis | permeation behavior by the difference in the surface tension of 1 droplet. It is the figure which showed the osmosis | permeation behavior by the difference in the surface tension of 2 droplets. FIG. 6 is a diagram showing a fixing dot shape depending on a difference in surface tension between two droplets. It is the figure which showed the osmosis | permeation behavior by the difference in the surface tension of a large and small droplet. It is the figure which showed the fixation dot shape by the difference in the surface tension of a large and small droplet.

Claims (3)

  In an ink jet recording apparatus that performs recording by ejecting ink onto a recording medium while moving in the main scanning direction, in order to perform image formation, it has nozzle rows having different surface tension inks of the same color and the same density, and two An ink jet recording method in which an ink having a high surface tension is applied to a recording medium at a print duty at which ink starts to land at a position where the ink sticks.   A head having nozzles capable of forming two or more types of dots with different diameters is provided. After determining which dot is to be formed according to the printing conditions and the tone value of the image data, the recording head determines A printing apparatus capable of forming a corresponding dot and printing an image on a recording medium, and for one specific dot capable of expressing a predetermined gradation value independently, a dot having a one-step diameter larger than the specific dot An ink jet recording method in which an ink having a large one-step diameter and a high surface tension is applied to a recording medium at a print duty at which the dots start to land at a position where the dots stick together when an image is formed.   3. The ink jet recording apparatus according to claim 1, wherein ink having high surface tension is applied to the recording medium at a printing duty having different surface tension inks in ink colors that are easy to visually recognize, and two inks starting to land on the sticking positions. Inkjet recording method.

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