JP2007125855A - Image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method which can prevent a color unevenness from occurring when a multi-color image or characters are formed by hitting inks of two colors or more on the same dot by a single path printing. <P>SOLUTION: Fine droplets of inks are discharged from a plurality of discharging ports in response to a recording signal, and are made to adhere to a medium to be recorded to perform a recording. In this case, by using the inks of two colors or more which consist of at least water, a water-soluble organic solvent, a pigment, and a surface active agent, and of which the surface tensions are different, the inks are discharged onto the medium to be recorded by a single path in order from the ink having a higher surface tension. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming method for forming a multicolor image by superposing two or more colors of ink in a single pass.

  The ink jet printer apparatus can form a multicolor image by ejecting two or more colors of ink from a nozzle of an ink ejection head onto a recording medium such as paper or film in the form of minute droplets.

  In this ink jet printer apparatus, as a method of ejecting ink as fine droplets, the ink is ejected using electrostatic attraction by applying a high voltage, a charge control method by applying a high voltage, and a piezoelectric element. There are various systems such as a piezo system that gives mechanical vibration or variation to ink, and a thermal jet system that uses pressure generated by bubbles generated by heating the ink. Ink jet printer apparatuses using these methods can obtain extremely high-definition images.

  Inkjet printers print on various recording media such as paper. For example, document printing in general households, printing for image appreciation, signboard printing in industrial applications such as wide format, color display such as liquid crystal It has been applied to a wide variety of applications such as the production of color filters used in Ink jet printer apparatuses are actively applied to image ornamental printing, and are required to be able to form high-quality images. In addition, it is required for an ink jet printer apparatus as an indispensable element from the viewpoint of image forming efficiency to simultaneously increase the image forming speed. For this reason, an inkjet printer device is required to achieve both high-quality image formation and improvement in image formation speed.

  One method for obtaining high-quality images at a faster image formation speed is that the nozzles that eject ink are arranged in parallel in the width direction of the recording medium, and printing can be performed across the width direction of the recording medium with a single ejection. It has been proposed to use a so-called line-type ink jet printer apparatus (see, for example, Patent Document 1). The line-type inkjet printer apparatus has one or more nozzle lines arranged in parallel in the same direction as the recording medium feeding direction, for example, for each color of yellow, magenta, cyan, and black from the upstream side in the recording medium conveyance direction. Ink discharge heads are provided. In such a line-type inkjet printer, ink is ejected onto a recording medium in the order of yellow, magenta, cyan, and black.

  Since the line-type ink jet printer apparatus ejects ink for each nozzle line, printing can be performed in the width direction of the recording medium at a time, and recording is performed while scanning the ink ejection head in the width direction of the recording medium. High-quality images can be printed at a higher image forming speed than a serial type ink jet printer apparatus. This printing method using a line-type ink jet printer apparatus corresponds to single-pass printing in which a single line is printed by scanning the ink discharge head once in the width direction of the recording medium in the serial ink-jet printer apparatus. In single-pass printing, because one line of printing is performed in one scan, the ink of the next color is immediately discharged before the ink previously discharged on the recording medium is completely dried. Therefore, even in the case of a line type ink jet printer apparatus, the ink of the next color is ejected before the ink previously ejected on the recording medium is completely dried.

  In addition, a serial type inkjet printer apparatus has multi-pass printing as a printing method compared with single-pass printing. In multi-pass printing, when printing across the width direction of the recording medium, the dot interval by one scan is wide, and the next color is printed on the blank area between each dot and the ink ejected earlier in the next scan. A multicolor image is formed by discharging the ink. In the case of multi-pass printing, since the ink of the next color is ejected on the ink previously ejected on the recording medium, the time for the ink ejected first to permeate the recording medium In other words, since there is a time for drying, the occurrence of uneven color due to mixing with the next ejected ink is suppressed.

  On the other hand, since the line-type ink jet printer device uses single-pass printing, it cannot gain ink permeation time into the recording medium as in multi-pass printing, and the previously ejected ink is applied to the recording medium. Since the ink of the next color is ejected one after another before it penetrates sufficiently and is not completely dried, the inks come into contact with each other in a liquid state. In single-pass printing, when ink ejected earlier and ink ejected later contact in liquid state, the ink does not diffuse sufficiently and does not mix evenly. Will occur. In a line type ink jet printer apparatus, color unevenness is likely to occur in a mixed color portion of two or more colors, particularly when a high density image is formed on a recording medium.

  Further, color unevenness is likely to occur particularly in the case of pigment ink using a pigment as a coloring material. Pigment inks are far superior to dye inks in terms of long-term storage of images, but the colorant pigments can be easily laminated on the surface of the recording medium, and the penetration is generally slower than dye inks. They are difficult to mix with each other, and color unevenness is likely to occur in a mixed color portion of two or more colors in the formed image. In particular, when a so-called glossy paper for photographic image quality having a porous layer formed of a hydrophilic binder and fine particles is used as the ink receiving layer, the pore size is small and pigment clogging tends to occur. For this reason, when photographic image quality glossy paper is used, color unevenness occurs most significantly.

  As a method for suppressing the occurrence of such color unevenness, for example, as proposed in Patent Document 2 below, there is a method of defining a change in ink physical properties during a drying process within a specific range. Patent Document 3 proposes controlling the absorption coefficient of ink into a recording medium indicated by the Bristow method.

  The methods proposed in Patent Document 2 and Patent Document 3 are based on the premise that multi-pass printing is performed by a serial printer device, and is performed by single-pass printing by a serial printer device or by a line-type inkjet printer device. The printing cannot sufficiently prevent the occurrence of color unevenness.

JP 2002-36522 A JP 2004-292585 A JP 2002-138232 A

  It is an object of the present invention to provide an image forming method capable of preventing color unevenness when a multicolor image or character is formed by landing two or more inks on the same dot by single pass printing. To do.

  In the image forming method according to the present invention, at least water, a water-soluble organic solvent, and a recording medium are used when recording is performed by ejecting minute droplets of ink from a plurality of ejection openings in accordance with a recording signal and attaching them to a recording medium. Using two or more colors of inks composed of a pigment and a surfactant and having different surface tensions, the inks are ejected in order from the ink with the highest surface tension in a single pass onto the recording medium.

  In the present invention, since the surface tension of the ink ejected first is higher than the surface tension of the ink ejected later, the ink ejected earlier and the ink ejected later are recorded when performing recording in a single pass. Uniform mixing can prevent color unevenness.

  Hereinafter, an ink, an ink cartridge, and a recording method to which the present invention is applied will be described with reference to the drawings. As shown in FIG. 1, the ink is used as ink i when performing multicolor printing on a recording paper P as a recording medium using, for example, an inkjet printer device 1 (hereinafter, referred to as a printer device 1).

  First, prior to the description of the ink i to which the present invention is applied, the line type printer apparatus 1 using the ink i will be described.

  The printer apparatus 1 includes an ink jet printer head cartridge (hereinafter referred to as a head cartridge) 2 that discharges the ink i described above onto the recording paper P, and an apparatus main body 3 to which the head cartridge 2 is mounted. This printer apparatus 1 is a so-called line type printer apparatus in which one or more nozzles serving as ejection openings for the ink i are arranged in a line substantially in the width direction of the recording paper P, that is, in the direction of the arrow W in FIG. The printer apparatus 1 can form multicolor images and characters by ejecting two or more colors of yellow ink (Y), magenta ink (M), and cyan ink (C) onto the same dot. it can. In addition to plain paper, the recording paper P is, for example, commercially available glossy paper or glossy paper for photographic image quality having a porous layer formed of a hydrophilic binder and fine particles as an ink receiving layer.

  The head cartridge 2 ejects the ink i of each color described above with the pressure generated by the pressure generating means using, for example, an electrothermal conversion type, and causes the ink i to land on the main surface of the recording paper P. The head cartridge 2 is mounted with ink tanks 11y, 11m, 11c, and 11k (hereinafter also referred to as ink tanks 11) that serve as ink cartridges containing the inks i of the respective colors. Specifically, as shown in FIGS. 1 and 2, the head cartridge 2 includes an ink tank 11y containing yellow ink (Y), an ink tank 11m containing magenta ink (M), and cyan ink (C ) And an ink tank 11k containing black ink (K) from the back side to the front side of the main body 3 from the front side to the yellow ink tank 11y, magenta ink tank 11m, and cyan ink. The tank 11c and the black ink tank 11k are mounted in this order. The ink tank 11 may be one in which the ink tanks 11y, 11m, 11c, and 11k for each color are integrated and are partitioned for each color.

  The ink tank 11 is formed in a substantially rectangular shape having substantially the same size as that of the recording paper P in the width direction. Specifically, as shown in FIG. 3, each ink tank 11 includes an ink storage unit 12 that stores the ink i, and an ink supply unit that sends the ink i from the ink storage unit 12 to the cartridge body 21 of the head cartridge 2. 13.

  The ink accommodating portion 12 is provided with an external communication hole 14 that is a hole for taking in external air at the center of the upper surface, and an air introduction pipe 15 that extends from the external communication hole 14 toward the inside is provided. The air can be taken into the inside. Thus, in each ink tank 11, when ink i is supplied to the cartridge body 21, air corresponding to the reduced amount of ink i is taken into the ink storage portion 12 through the external communication hole 14.

  The ink supply unit 13 is provided at a substantially central portion below the ink storage unit 12. The ink supply unit 13 is a substantially protruding nozzle that communicates with the ink storage unit 12 and is opened and closed by a valve mechanism (not shown). The ink supply unit 13 is fitted into a connection unit 25 of the head cartridge 2 to be described later, thereby opening the nozzle by a valve mechanism, connecting the ink storage unit 12 and the cartridge main body 21 of the head cartridge 2, and the head cartridge. Ink i can be supplied to the two sides.

  The head cartridge 2 to which the ink tank 11 as described above is mounted has a cartridge body 21 as shown in FIGS. The cartridge main body 21 includes a mounting portion 22 to which the ink tank 11 is mounted, an ink discharge head 23 that discharges ink i, and a head cap 24 that protects the ink discharge head 23.

  The mounting portion 22 to which the ink tank 11 is mounted is formed in a substantially concave shape, and a partition wall 22a that partitions each ink tank 11y, 11m, 11c, 11k is provided on the bottom surface. Each ink tank 11 is attached to each area partitioned by the partition wall 22a.

  A connection part 25 connected to the ink supply part 13 of each of the ink tanks 11y, 11m, 11c, and 11k attached to the attachment part 22 is provided at a substantially longitudinal center of the attachment part 22. The connection portion 25 supplies ink i to the ink discharge head 23 that discharges ink i provided on the bottom surface of the cartridge body 21 from the ink supply portions 13 of the ink tanks 11y, 11m, 11c, and 11k attached to the attachment portion 22. The ink supply path is supplied. The connection unit 25 adjusts the supply of ink i from the ink tanks 11y, 11m, 11c, and 11k to the ink discharge head 23 by a valve mechanism.

  In the head cartridge 2, when the ink tank 11 is attached to the attachment portion 22, the supply ports of the ink supply portions 13 of the ink tanks 11 y, 11 m, 11 c, and 11 k are opened by the valve mechanism. Connected to the connection unit 25. Thereby, in the head cartridge 2, the yellow ink (Y), the magenta ink (M), the cyan ink (C), and the black ink (K) filled in the ink tanks 11y, 11m, 11c, and 11k are supplied to the ink supply unit. Through the 13 supply ports, the air flows into the connection portion 25 and is supplied to the ink discharge head 23.

  The ink discharge head 23 to which the ink i is supplied from the connection portion 25 is disposed along the bottom surface of the cartridge main body 21. In the ink discharge head 23, nozzles 32a, which will be described later, which are discharge ports for discharging the ink i supplied from the connection portion 25 are arranged in line for each color in a substantially line shape in the width direction of the recording paper P, that is, the arrow W direction in FIG. It is installed. That is, the ink discharge head 23 is provided with nozzle lines for each color according to the arrangement of the ink tanks 11 for each color mounted on the cartridge body 21 from the back side to the front side of the apparatus body 3. The ink ejection head 23 ejects ink i for each nozzle line of yellow, magenta, cyan, and black without moving in the width direction of the recording paper P when ejecting ink i.

  As shown in FIG. 4, the ink ejection head 23 is provided with a circuit board 31 provided with an electrothermal change type heating resistor 31 a, a nozzle sheet 32 on which nozzles 32 a are formed, and the circuit board 31 and nozzle sheet 32. And an ink flow path 34 for supplying the ink i supplied from the connection portion 25 to each nozzle 32a. This ink flow path 34 is formed long in the direction in which the nozzles 32a are arranged in parallel, that is, in the direction of arrow W in FIG. As a result, in the ink discharge head 23, the ink i flows from the ink tanks 11y, 11m, 11c, and 11k to the ink flow path 34 via the connection portion 25 of the cartridge main body 21, and the ink flow from the ink flow path 34 to each nozzle 32a. i is supplied.

  The ink discharge head 23 is formed with an ink liquid chamber 35 surrounded by a circuit board 31, a nozzle sheet 32, and a film 33 and in which the heating resistor 31a pressurizes the ink. The ink liquid chamber 35 is connected to the ink flow path 34, and the ink i is supplied from the ink flow path 34.

  In the ink ejection head 23 configured as described above, a pulse current is supplied to the heating resistor 31a selected based on the control signal, for example, at a driving frequency of 9 kHz. As a result, the ink discharge head 23 rapidly heats the heating resistor 31a. When the ink discharge head 23 heats the heating resistor 31a, as shown in FIG. 4A, bubbles b are generated in the ink i in contact with the heating resistor 31a. Then, as shown in FIG. 4B, the ink discharge head 23 pressurizes the ink i while the bubbles b expand, and discharges the pressed ink i from the nozzle 32a in the form of droplets. Further, the ink discharge head 23 returns to the state before discharge again by supplying the ink i to the ink liquid chamber 35 through the ink flow path 34 after discharging the ink i in a droplet state. The ink discharge head 23 repeats the above-described operation based on the control signal.

  A head cap 24 for protecting the ejection surface 23a of the ink ejection head 23 closes the ejection surface 23a of the ink ejection head 23 and protects the ejection surface 23a from drying or the like when printing is finished. Further, the head cap 24 is provided with a cleaning roller 24a for sucking excess ink i adhered to the ejection surface 23a, and the excess ink i adhered to the ejection surface 23a when the ejection surface 23a is opened and closed. And the discharge surface 23a is cleaned.

  As shown in FIG. 1, the head cartridge 2 is attached to the head cartridge attachment portion 41 in the apparatus main body 3 to which the head cartridge 2 is attached. Further, as shown in FIG. 5, the apparatus main body 3 is provided with a paper supply / discharge mechanism 42 for conveying the recording paper P.

  The paper supply / discharge mechanism 42 takes out the recording paper P before printing stacked on the paper supply tray 44 attached to the paper supply port 43 from the paper supply tray 44 and attaches it to the head cartridge mounting unit 41 from the paper supply port 43. Then, the recording paper P is conveyed to a position facing the ejection surface 23a of the head cartridge 2 and printed on the recording paper P, and then the printed recording paper P is discharged from the paper discharge port 45 to the paper discharge tray 46. The recording paper P travels from the back side to the front side of the mounting body 3 on the nozzle surface 23 a of the ink discharge head 23 by the paper supply / discharge mechanism 42. Accordingly, the ink i is landed on the recording paper P in the order of yellow ink (Y), magenta ink (M), cyan ink (C), and black ink (K).

  Further, the apparatus main body 3 is provided with a cap opening / closing mechanism 47 that opens and closes the head cap 24 provided on the ejection surface 23 a side of the head cartridge 2 mounted on the head cartridge mounting portion 41. Further, the head cap opening / closing mechanism 47 moves the head cap 24 to the front side when starting printing, and exposes the ejection surface 23a of the head cartridge 2 to the outside. The head cap opening / closing mechanism 47 moves the head cap 24 to the bottom surface of the head cartridge 2 after printing, closes the ejection surface 23a of the head cartridge 2, and prevents the ejection surface 23a from being exposed to the outside.

  With the above configuration, the printer apparatus 1 is controlled by the control circuit 51 shown in FIG. 6 that controls printing based on print data input from an information processing apparatus provided outside. The control circuit 51 includes a printer drive unit 52 that controls the drive of the paper supply / discharge mechanism 42 and the cap opening / closing mechanism 47 of the apparatus main body 2 described above, a discharge control unit 53 that controls the current supplied to the ink discharge head 23, and the like. An input / output terminal 54 for inputting / outputting signals to / from the information processing device 58, a ROM (Read Only Memory) 55 in which a control program and the like are recorded, and a read control program and the like are temporarily stored and read out as necessary. A random access memory (RAM) 56 and a control unit 57 that controls each unit.

  Based on the control signal from the control unit 57, the printer drive unit 52 drives the drive motor that constitutes the head cap opening / closing mechanism 47 to move the head cap 24 and open / close the ejection surface 23a. To control. Further, the printer driving unit 52 drives the driving motor constituting the paper feeding / discharging mechanism 42 based on the control signal from the control unit 57 to feed the recording paper P from the paper feeding port 43 of the apparatus main body 3 and carry it. The paper supply / discharge mechanism 42 is controlled so that it is transported through the apparatus at a speed of 49.5 mm / sec or more and the recording paper P is discharged from the paper feed tray 44 after printing.

  The discharge control unit 53 selectively supplies a pulse current to the heating resistor 31a based on a control signal from the control unit 57, and drives and controls the heating resistor 31a at a frequency of 9 kHz or more.

  From the input / output terminal 54, print data and printing conditions from the connected information processing device 58 are input, and data to be displayed on the information processing device 58 is output. Here, the information processing apparatus 58 described above is an electronic device such as a personal computer or a PDA (Personal Digital Assistant).

  The ROM 55 is a memory in which a program for each process performed by the control unit 57 is stored. The stored program is loaded into the RAM 56 by the control unit 57. The RAM 56 stores programs read from the ROM 55 by the control unit 57 and various states of the printer device 1.

  The control unit 57 is a CPU (Central Processing Unit), for example, and drives each unit based on a program loaded in the RAM 56 to perform printing according to print data.

  Specifically, first, when the printer unit 1 is instructed to start printing by operating the operation button 3 a provided on the apparatus body 3, the paper supply / discharge mechanism 42 is controlled by a control signal from the control unit 57. Then, the head cap opening / closing mechanism 47 is driven as follows to make it possible to print as shown in FIG.

  The printer apparatus 1 moves the head cap 24 to the front side where the paper feed tray 44 and the paper discharge tray 46 are provided with respect to the head cartridge 2 by the head cap opening / closing mechanism 47. Thereby, in the printer apparatus 1, the nozzle 32a provided on the ejection surface 23a of the ink ejection head 23 is exposed to the outside, and the ink i can be ejected.

  The printer apparatus 1 uses the paper supply / discharge mechanism 42 to pull out the recording paper P from the paper supply tray 44 by means of the paper supply roller 61, and to feed only one recording paper P by a pair of separation rollers 62 a and 62 b that rotate in opposite directions. The recording paper P is fed into the apparatus main body 3 to the reversing roller 63, and the reversing roller 63 reverses the conveying direction to the discharge surface 23 a side, and the recording paper P is conveyed onto a conveying belt 64 provided at a position facing the discharge surface 23 a. The printer apparatus 1 holds the recording paper P conveyed to the conveying belt 64 at a predetermined position by the platen plate 65, and the recording paper P faces the ejection surface 23a. In the printer apparatus 1, the recording paper P is transported by the paper supply / discharge mechanism 42 at a transport speed of 49.5 mm / sec or more.

  Next, in the printer apparatus 1, the ejection control unit 53 is driven by a control signal based on the print data from the control unit 57, and a pulse current is selectively applied to the heating resistor 31 a of the ink ejection head 23 at a frequency of 9 kHz or more. The heating resistor 31a is heated. As shown in FIG. 4, the printer device 1 heats the heating resistor 31a to apply the ink i of each color from the nozzle 32a to the recording paper P conveyed to a position facing the ejection surface 23a. The ink is ejected in the form of droplets to form a multicolor image or character composed of ink dots.

  Specifically, the printer apparatus 1 is provided with nozzle lines in the order of yellow ink (Y), magenta ink (M), cyan ink (C), and black ink (K) from the back side to the front side of the apparatus body 3. Therefore, the ink i is ejected in the order of yellow ink (Y), magenta ink (M), cyan ink (C), and black ink (K) while the recording paper P is running. Specifically, when forming a multicolor image or character on the recording paper P, the yellow ink (Y) located on the upstream side in the transport direction, that is, on the back side of the apparatus body 3 is ejected first, The recording paper P is transported to the front side, and magenta ink (M) located downstream from the yellow ink (Y) is ejected onto the same dot formed by the yellow ink (Y) to red (R). Form. Further, in the printer apparatus 1, cyan ink (C) is ejected onto yellow ink (Y) dots to form green (G), or cyan ink (C) is ejected onto magenta ink (M) dots. Then, blue (B) is formed, or magenta ink (M) and cyan ink (C) are ejected in this order on yellow ink (Y) dots to form black (K).

  Next, the printer device 1 is provided on the paper feed tray 44 side, facing the transport belt 64 of the paper feed / discharge mechanism 42 that rotates the printed recording paper P in the direction of the paper feed tray 44 and the transport belt 64. The recording paper P is sent to the paper feed tray 44 by the paper discharge roller 66 and discharged from the apparatus main body 3.

  This printer apparatus 1 has a nozzle line in which nozzles are arranged in parallel in the width direction of the recording paper P for each color of yellow ink (Y), magenta ink (M), cyan ink (C), and black ink (K). Since the ink i is ejected for each nozzle line, an image can be formed at a higher speed than a serial printer that moves the head in the width direction of the recording paper P. Such a printer apparatus 1 corresponds to single-pass printing in terms of a serial type printer apparatus.

  Furthermore, the printer apparatus 1 can form images and characters at a higher speed because the conveyance speed of the recording paper P is 49.5 mm / sec or more and the driving frequency of the heating resistor 31a is 9 kHz or more. . As a result, in the printer device 1, the discharge interval with the next color ink i is shortened, and when the ink i of two or more colors is mixed, before the ink i discharged first penetrates the recording paper P, Since the ejected ink i is ejected onto the previously ejected ink i, they come into contact with each other in a liquid state on the recording paper P.

  Here, in the printer apparatus 1, the surface tension of the ink i is lowered in accordance with the ejection order of the ink i to be used, that is, the order of yellow ink (Y), magenta ink (M), and cyan ink (C). That is, in the printer apparatus 1, the surface tension of yellow ink (Y) is the highest, the surface tension of magenta ink (M) is the next highest, and the surface tension of cyan ink (C) is the lowest. In the printer 1, since the surface tension of the ink i ejected first is higher than the surface tension of the ink i ejected later, the ink i ejected earlier and the ink i ejected later are uniform. To prevent color unevenness.

  Specifically, the ink i used in the printer apparatus 1 will be described. The ink i contains a pigment as a colorant, a solvent containing water and a water-soluble organic solvent in which the pigment is dispersed or dissolved, and a surfactant that adjusts the surface tension.

  As the pigment, for example, an inorganic pigment or an organic pigment is preferably used. Here, as the inorganic pigment, titanium oxide, iron oxide, carbon black, or the like can be used. Organic pigments include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments), polycyclic pigments (phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo Pigments, isoindolinone pigments, quinofuranone pigments, etc.), nitro pigments, nitroso pigments, aniline black, and the like.

  Examples of pigments used in yellow ink include C.I. I. Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 114, 128, 129, 151, 154 and the like. However, it is not limited to these.

  Examples of pigments used in magenta ink include C.I. I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, 168, 184, 202 and the like. However, it is not limited to these.

  Examples of pigments used for cyan ink include C.I. I. Pigment Blue 1, 2, 3, 15, 15: 3, 15:34, 16, 22, 60, C.I. I. Vat Blue 4, 60 etc. are mentioned. However, it is not limited to these.

  The dispersant is preferably a copolymer including a unit containing an anionic functional group and a unit containing an aromatic ring and / or an alkyl group.

  An anionic dispersant is a state in which units containing an aromatic ring and / or an alkyl group are strongly adsorbed on the surface of an organic pigment, and the electrostatic repulsive force caused by the unit containing an anionic functional group It is presumed that there is an effect of reducing the cohesive strength. Examples of the anionic functional group include a carboxyl group, a sulfone group, and a phosphoric acid group. These functional groups may exist as metal salts such as sodium or ammonium salts.

  Although the molecular weight of an anionic dispersing agent is not specifically limited, It is more preferable that it is the range of 1000 or more and 30000 or less. When the molecular weight of the anionic dispersant is in the range of 1000 or more and 30000 or less, the cohesive force between the organic pigments is reduced by electrostatic repulsion, while the coarse particles are adsorbed and aggregated on a plurality of organic pigment particles. This is to prevent the formation of particles.

  The content of the dispersant in the ink i varies depending on the type of the dispersant, but is generally 0.1% by weight to 20% by weight, preferably 0.1% by weight to 10% by weight with respect to the total weight of the ink i. %.

  In addition to the pigment-dispersant adsorbing type in which the pigment and dispersant are contained in the ink i as described above, the colorant is preferably a carbonyl group, carboxyl group, hydroxyl group, sulfone group. A self-dispersing pigment having a surface hydrophilized by having at least one functional group among sulfonic acid groups and salts thereof can be used.

  Furthermore, as other colorants, microencapsulated pigments produced by known physical mechanical methods or chemical methods are also suitable.

  As the solvent for dispersing or dissolving the pigment, at least water or an aqueous medium composed of a mixed solvent of water and a water-soluble organic solvent can be used, and a mixed solvent of water and a water-soluble organic solvent is preferably used. Ink i has a pigment or a dispersant dispersed or dissolved in these aqueous media. For example, deionized water is preferably used as the water. The content of water in ink i is 50 to 95% by weight based on the total weight of the ink. If the water content is less than 50% by weight with respect to the total amount of ink, the viscosity of the ink i becomes too high, and if it is more than 95% by weight, the viscosity of the ink i becomes too low. In either case, the ejection stability of the ink i may be lowered.

  As the water-soluble organic solvent, those having an effect of preventing the drying property of the ink i are preferable. Examples of the water-soluble organic solvent include alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and dimethyl Amides such as formamide and dimethylacetamide, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diacetone alcohol or keto alcohols, ethers such as tetrahydrofuran and dioxane, polyalkylene glycols such as polyethylene glycol and polypropylene glycol, ethylene glycol , Propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol Polyols, such as coal and diethylene glycol, having 2 to 6 carbon atoms, lower alkyl ether acetates such as polyethylene glycol monomethyl ether acetate, glycerin, ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether Lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl (or ethyl) ether, polyhydric alcohols such as trimethylolpropane and trimethylolethane; N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3- Examples include dimethyl-2-imidazolidinone. These water-soluble organic solvents can be used alone or as a mixture.

  The content of the water-soluble organic solvent in the ink i is 3% by weight to 50% by weight with respect to the total weight of the ink. When the content of the water-soluble organic solvent is less than 3% by weight with respect to the total weight of the ink, the ink i is dried at the nozzle and nozzle clogging is likely to occur. On the other hand, when the content of the water-soluble organic solvent is more than 50% by weight with respect to the total amount of the ink, the ink i is difficult to dry on the recording medium.

  In addition to the pigment, a surfactant dissolved or dispersed in a solvent adjusts the surface tension of the ink i. Examples of the surfactant include various nonionic surfactants, anionic surfactants, and amphoteric surfactants. Among these, nonionic surfactants are particularly preferable because they can adjust the surface tension of the ink i even with a small amount.

  Nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkyl amides and other ethylene oxide addition types, glycerin alkyl esters, sorbitan alkyl esters, sugar alkyl esters, etc. Polyol ester type, polyether type such as polyhydric alcohol alkyl ether, alkanolamide type such as alkanolamine fatty acid amide, and the like can be used.

  Examples of the anionic surfactant include fatty acid sodium, fatty acid potassium, sodium alkyl sulfate, alkyl ethanol triethanolamine, ammonium alkyl sulfate, sodium alkylbenzene sulfonate, sodium alkyl naphthalene sulfonate, sodium dialkyl sulfosuccinate, sodium alkyl diphenyl ether disulfonate, Polyoxyethylene alkyl potassium potassium, polyoxyethylene alkyl ether sodium sulfate, polyoxyethylene alkyl ether sulfate triethanolamine, polyoxyethylene alkyl ether sodium acetate, sodium alkane sulfonate, and the like can be used.

  As the amphoteric surfactant, alkyldimethylcarboxymethylbetaine, alkylamidopropylbetaine, alkylhydroxysulfobetaine, 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, alkyldimethylamine oxide, etc. are used. .

  The content of the surfactant in the ink i is 0.01% by weight to 5.0% by weight, and more preferably 0.1% by weight to 3.0% by weight with respect to the total weight of the ink. This is because if the surfactant content is less than 0.01% by weight, the desired surface tension cannot be adjusted. This is because when the content of the surfactant is more than 5% by weight, the ejection stability may be lowered.

  Further, when the surfactant is added to the ink i, it may be added when preparing a dispersion containing a pigment or the like in a solvent, or may be added when the ink is formed. It is more effective to add.

  Moreover, since it is preferable that the ink i has a characteristic which can be discharged from the nozzle 32a of the ink discharge head 23, from a viewpoint of discharge property, for example, the viscosity is 1 to 15 cPs and the surface tension is 25 dyn / cm or more. In particular, the viscosity is more preferably 1 to 5 cPs and the surface tension is more preferably 25 to 50 dyn / cm. In the ink i, a preferable aqueous medium capable of supporting such characteristics is a mixed solvent composed of water and a water-soluble organic solvent. Among the above-mentioned water-soluble organic solvents, glycerin, trimethylolpropane, thiodiglycol, ethylene glycol, diethylene glycol, isopropyl alcohol, and acetylene alcohol are preferable.

  Further, in the ink i, in addition to the above-described pigments and surfactants, an antifoaming agent, an antiseptic, an antifungal agent, a pH adjuster, an antioxidant, etc. are obtained in order to obtain desired physical properties as required. A commercially available water-soluble dye or the like may be added for the purpose of toning and the like.

  Ink i having the above-described configuration is prepared by adding a predetermined amount of pigment to an aqueous medium containing a predetermined amount of a dispersant, sufficiently stirring, then dispersing using a disperser, centrifugation, etc. After removing the coarse particles, an anionic functional group salt, a predetermined solvent, an additive and the like are added, followed by stirring, mixing, and filtration.

  Any commercially available disperser can be used. Examples of the dispersing machine include colloid mill, flow jet mill, slasher mill, high speed disperser, ball mill, attritor, sand mill, sand grinder, ultra fine mill, Eiger motor mill, dyno mill, pearl mill, agitator mill, cobol mill, 3 A main roll, two rolls, an extruder, a kneader, an optimizer, a microfluidizer, a laboratory homogenizer, an ultrasonic homogenizer, and the like can be used, and these may be used alone or in combination. Alternatively, after mixing a predetermined solvent, a predetermined amount of a dispersant may be added, and then an organic pigment may be added and dispersed using a disperser.

  The ink i having such a configuration has the highest surface tension of the yellow ink (Y) according to the ejection order, that is, the order of the yellow ink (Y), the magenta ink (M), and the cyan ink (C). Adjustment is performed so that the surface tension of the ink (M) is high and the surface tension of the cyan ink (C) is the lowest. The surface tension of the ink i of each color is adjusted by the type or content of the surfactant.

  In the ink i, the surface tension of the ink i ejected first on the recording paper P is made higher than the surface tension of the ink i ejected later, so that the ink i ejected earlier on the recording paper P is ejected later. The ink i is uniformly mixed with each other in the liquid state.

  That is, in the printer device 1 described above, since the surface tension of the yellow ink (Y) discharged first is higher than the surface tension of the magenta ink (M) discharged later, the yellow ink (Y) and the magenta ink (M) is mixed to form a mixed color portion made of red (R) so that the yellow ink (Y) and the magenta ink (M) are uniformly mixed in a liquid state on the recording paper P. Become. As a result, the printer apparatus 1 can form uniform red without color unevenness.

  In the printer apparatus 1, the yellow ink (Y) and the cyan ink (C) are mixed to form a green (G), or the magenta ink (M) and the cyan ink (C) are mixed to form a blue ( Similarly, when forming black (K) by forming B) or mixing yellow ink (Y), magenta ink (M), and cyan ink (C), the ink is discharged first onto the recording paper P. Since the surface tension of the ink i is higher than the surface tension of the ink i to be ejected later, the ink i can be uniformly mixed and a mixed color portion can be formed without color unevenness.

  From the above, since the printer device 1 ejects ink i for each nozzle line of each color, this corresponds to single pass printing, and the conveyance speed of the recording paper P is 49.5 mm / sec or more, and the heating resistor 31a. Since the driving frequency is 9 kHz or more, the surface tension of the ink i ejected first is higher than the surface tension of the ink i ejected later even if the ejection interval with the next color ink i is short. Therefore, the ink i ejected first and the ink i ejected later are uniformly mixed. As a result, the printer apparatus 1 can prevent color unevenness from occurring in the mixed color portion composed of the ink i of two or more colors and can form a uniform mixed color, thereby forming a high-quality multicolor image. Can do.

  In the printer apparatus 1 described above, it has been described that yellow ink (Y), magenta ink (M), cyan ink (C), and blank ink (K) are ejected in this order. However, the color ejection order is limited. If the surface tension of the ink i ejected first on the recording paper P is higher than the surface tension of the ink i ejected later, the same effect can be obtained.

  Further, when forming an image using the printer apparatus 1 as described above, glossy paper and photo quality glossy paper are used. This glossy paper and glossy paper for photographic image quality have a porous layer formed of a hydrophilic binder and fine particles as an ink receiving layer. In the printer apparatus 1, when an image is formed by ejecting ink i onto this glossy paper or glossy paper for photographic image quality, the ink i is glossy paper or photo because the pore size of the porous layer serving as the ink receiving layer is small. The ink i of the next color is ejected before penetrating the glossy paper for image quality. In the printer apparatus 1, since the surface tension of the ink i ejected first is higher than the surface tension of the ink i ejected later, the inks i are uniformly mixed, and even on glossy paper and glossy paper for photographic image quality. Unevenness can be prevented, and a high-quality multicolor image can be formed.

  Although the printer apparatus has been described above as an example of the present invention, the present invention is not limited to this and can be widely applied to other liquid ejection apparatuses. For example, the present invention can be applied to a facsimile, a copier, and the like.

  In the above-described printer apparatus 1, the line type printer apparatus has been described as an example. However, the present invention is not limited to this, and for example, a serial type printer in which the head cartridge moves in the width direction of the recording paper P. Even in the case of single-pass printing in the apparatus, the above-described color unevenness can be prevented.

  Further, the above-described printer device 1 employs an electrothermal conversion method in which the ink i is heated by the heating resistor 31a and the ink i is ejected from the nozzle 32a. However, the present invention is not limited to such a method. Electromechanical conversion systems in which ink i is ejected from a nozzle electromechanically by an electromechanical conversion element such as a piezoelectric element (Japanese Patent Laid-Open Nos. 55-65559, 62-160243, and 2- 270561 gazette) may be adopted.

  In the above-described printer apparatus 1, the ink discharge head 23 that discharges the ink i by heating by the one heating resistor 31 a has been described as an example. However, the present invention is not limited to such a structure. It is also applicable to a printer apparatus having a plurality of pressure generating elements for one nozzle 32a and having discharge means that can control the discharge direction by supplying energy to each pressure generating element at different energy or at different timing. It is.

  Hereinafter, inks to which the present invention is applied will be described with reference to comparative examples and examples.

  First, yellow, magenta, and cyan color dispersions were prepared, and yellow, magenta, and cyan inks were prepared using the pigment dispersion. In the following description, “parts” and “%” are based on weight unless otherwise specified.

<Yellow dispersion>
A yellow dispersion using a yellow pigment is C.I. I. Pigment Yellow 128, 15% styrene-acrylic acid (trade name John Crill 57, manufactured by Johnson Polymer Co., Ltd.) as a dispersant, 3% pure water and 82% pure water, and mixed into a paint shaker (media is zirconia) 1 mm diameter, media filling rate 70%) and coarse particles were removed by a centrifuge.

<Magenta dispersion>
A magenta dispersion using a magenta pigment is C.I. I. Pigment Red 122 (Ciba Specialty Chemicals, trade name DMQ) is 15%, Styrene-acrylic acid (Daiichi Kogyo Seiyaku Co., Ltd., trade name JP91-010) is 5%, and pure water is 80%. Then, they were mixed, dispersed with a paint shaker (media: 1 mm diameter of zirconia, media filling ratio 70%), and coarse particles were removed with a centrifuge.

<Cyan dispersion>
A cyan dispersion using a cyan pigment is C.I. I. Pigment Blue 15: 3 (Ciba Specialty Chemicals, trade name Blue 8700) is 15%, Styrene-maleic acid (Daiichi Kogyo Seiyaku Co., Ltd., trade name KS140) is 3%, and pure water is 82%. Then, they were mixed, dispersed with a paint shaker (media: 1 mm diameter of zirconia, media filling ratio 70%), and coarse particles were removed with a centrifuge.

  Using the yellow dispersion prepared as described above, yellow inks shown in Table 1 were prepared.

  The yellow ink (Y1) shown in Table 1 was produced as follows. In preparing the yellow ink (Y1), 23% of the yellow dispersion, 8.0% of 1,5-pentanediol as the water-soluble organic solvent, and 1.0 of 2-ethyl-1,3-hexanediol were prepared. %, A polyoxyethylene derivative (Emogen A60, manufactured by Kao Corporation) as a surfactant is mixed to 1.0% and pure water to 67.0%, and after sufficient stirring, is again placed in a centrifuge. The coarse particles were removed to prepare a yellow ink (Y1). The surface tension of the obtained yellow ink (Y1) was 44.0 mN / m. For this surface tension, a static surface tension value at 20 ° C. was measured using an automatic surface tension meter CBVP-Z (Wilhelmi method, platinum plate) manufactured by Kyowa Interface Chemical Co., Ltd.

  For yellow ink (Y2) to yellow ink (Y4), yellow dispersion, 1,5-pentanediol, 2-ethyl-1,3-hexanediol, polyoxyethylene derivative, and pure water were mixed in the composition shown in Table 1. It was produced in the same manner as the yellow ink (Y1). The surface tension of the obtained yellow ink (Y2) to yellow ink (Y4) was measured in the same manner as the surface tension of the yellow ink (Y1) and was as shown in Table 1.

  Next, magenta inks shown in Table 2 were prepared using a magenta dispersion.

  The magenta ink (M1) shown in Table 2 was produced as follows. In preparing the magenta ink (M1), 20% of the magenta dispersion, 12.5% of propylene glycol as the water-soluble organic solvent, and polyoxyethylene 2-ethylhexyl ether (ethylene oxide addition mole number 3) as the surfactant ) (Nippon Oil & Fats Co., Ltd. Nonion EH203) was mixed to 0.3% and pure water to 67.2%, and after sufficient stirring, coarse particles were removed again by a centrifuge and magenta Ink (M1) was prepared. The surface tension of the obtained magenta ink (M1) was measured in the same manner as the yellow ink (Y1), and was 40.4 mN / m.

  Magenta ink (M2) uses polyoxyethylene 2-ethylhexyl ether (ethylene oxide addition mole number 3) (Nonion EH203, manufactured by NOF Corporation) as a surfactant, as in magenta ink (M1). It mixed with the composition shown and produced like the magenta ink (M1).

  Magenta ink (M3) and magenta ink (M4) are compositions shown in Table 2 using polyoxyethylene 2-ethylhexyl ether (number of moles of ethylene oxide added 2) (Nonion EH202 manufactured by NOF Corporation) as a surfactant. And were prepared in the same manner as magenta ink (M1).

  Magenta ink (M5) to magenta ink (M7) were used as surfactants with polyoxyethylene n-decyl ether (3 moles added ethylene oxide) (Conion N-30, manufactured by Shin Nippon Rika Co., Ltd.). Were prepared in the same manner as magenta ink (M1).

  Magenta ink (M8) was mixed with the composition shown in Table 2 using polyoxyethylene ethyl hexyl glycol ether (ethylene oxide addition mole number 6) (TGG 11703, manufactured by Kyowa Hakko Co., Ltd.) as a surfactant, and magenta ink (M1). It produced similarly.

  Magenta ink (M9) contains polyoxyethylene 2-ethylhexyl ether (ethylene oxide addition mole number 3) (Nonion EH203 manufactured by NOF Corporation) and polyoxyethylene n-decyl ether (ethylene oxide addition mole number) as surfactants. 10) (Nippon Rika Co., Ltd. Conion N-100) was used, and 2-ethyl-1,3-hexanediol was used as the water-soluble organic solvent in addition to propylene glycol, and the compositions shown in Table 2 were mixed. This was prepared in the same manner as magenta ink (M1).

  The surface tensions of magenta ink (M2) to magenta ink (M9) were measured in the same manner as yellow ink (Y1), and the results are shown in Table 2.

  Next, cyan ink shown in Table 3 below was prepared using the cyan dispersion.

  The cyan ink (C1) shown in Table 3 was produced as follows. When preparing the cyan ink (C1), 15% of the cyan dispersion, 6.0% of 1,3-butanediol as the water-soluble organic solvent, 8.0% of 2-pyrrolidone, and polysiloxane as the surfactant Oxyethylene n-decyl ether (methylene oxide addition mole number 6) (Shin Nippon Rika Co., Ltd., Conion N-60) was mixed to 1.0% and pure water to 70.0%, and sufficiently stirred. Thereafter, the coarse particles were removed again with a centrifugal separator to produce cyan ink (C1). The surface tension of the obtained magenta ink (C1) was measured in the same manner as the yellow ink (Y1), and was 32.7 mN / m.

  Similar to the cyan ink (C1), the cyan ink (C2) and the cyan ink (C3) are polyoxyethylene n-decyl ether (6 moles of ethylene oxide added) as a surfactant (Conion N, manufactured by Shin Nippon Rika Co., Ltd.). -60), and were mixed in the composition shown in Table 3 and produced in the same manner as the cyan ink (C1).

  Cyan ink (C4) was mixed with the composition shown in Table 3 using polyoxyethylene n-decyl ether (ethylene oxide addition mole number 3) (Conion N-30, manufactured by Shin Nippon Chemical Co., Ltd.) as a surfactant. This was prepared in the same manner as cyan ink (C1).

  Cyan ink (C5) was mixed in the composition shown in Table 3 using polyoxyethylene 2-ethylhexyl ether (ethylene oxide addition mole number 2) (Nonion EH202, manufactured by NOF Corporation) as a surfactant. It was produced in the same manner as (C1).

  Cyan ink (C6) was mixed with the composition shown in Table 3 using polyoxyethylene ethyl hexyl glycol ether (ethylene oxide addition mole number 2) (TGG 11702, manufactured by Kyowa Hakko Co., Ltd.) as a surfactant, and cyan ink (C1). It produced similarly.

  Cyan ink (C7) was mixed with the composition shown in Table 3 using polyoxyethylene ethylhexyl glycol ether (ethylene oxide addition mole number 6) (TGG 11703, manufactured by Kyowa Hakko Co., Ltd.) as a surfactant, and cyan ink (C1). It produced similarly.

  Cyan ink (C8) was mixed with the composition shown in Table 3 using polyoxyethylene diethyl pentane glycol ether (ethylene oxide addition mole number 2) (8603-GX, manufactured by Kyowa Hakko Co., Ltd.) as a surfactant. It was produced in the same manner as (C1).

  The surface tensions of cyan ink (C2) to cyan ink (C8) were measured in the same manner as yellow ink (Y1), and were as shown in Table 3.

  Using the yellow inks (Y1) to (Y4), magenta inks (M1) to (M9), and cyan inks (C1) to (C8) produced as described above, the mixed color portion composed of two or three colors For color unevenness, mixed colors were prepared and evaluated using the combinations of inks shown in the examples and comparative examples.

  In Examples 1 to 8 and Comparative Examples 1 to 5, as shown in Table 4 below, yellow ink (Y) and magenta ink (M) were combined when producing mixed colors.

  In Example 1, as shown in Table 4, the discharge order 1 ink that is discharged first on the recording paper is the yellow ink (Y1) having a surface tension of 44.0 mN / m, and the discharge order 2 ink that is discharged next time. The magenta ink (M1) having a surface tension of 40.4 mN / m was set so that the surface tension of the ink in ejection order 1 was higher than that of the ink in ejection order 2.

  In Example 2 to Example 8, as in Example 1, the ink in the ejection order 1 and the ink in the ejection order 2 are set so that the surface tension of the ink in the ejection order 1 is higher than the surface tension in the ejection order 2. Were combined as shown in Table 4.

  In Comparative Example 1, a yellow ink (Y1) having a surface tension of 44.0 mN / m is used as the ink in the discharge order 1, and a magenta ink (M2) having a surface tension of 44.7 mN / m is used as the ink in the discharge order 2. The surface tension of ejection order 2 was made higher than the surface tension of ink of order 1.

  In Comparative Example 2 to Comparative Example 5, as in Comparative Example 1, the ink in the ejection order 1 and the ink in the ejection order 2 are mixed so that the surface tension in the ejection order 2 is higher than the surface tension of the ink in the ejection order 1. The combinations were made as shown in Table 4.

  In Examples 9 to 17 and Comparative Examples 6 to 9, as shown in Table 5 below, yellow ink (Y) and cyan ink (C) were combined when producing mixed colors.

  In Example 9, as shown in Table 5, the ink with ejection order 1 is yellow ink (Y1) with a surface tension of 44.0 mN / m, and the ink with ejection order 2 is cyan with a surface tension of 32.7 mN / m. Ink (C1) was used so that the surface tension of the ink in the ejection order 1 was higher than the surface tension of the ink in the ejection order 2.

  In Examples 10 to 17, as in Example 9, the ejection order 1 ink and the ejection order 2 ink are set so that the surface tension of the ejection order 1 ink is higher than the surface tension of the ejection order 2. Were combined as shown in Table 5.

  In Comparative Example 6, a yellow ink (Y1) having a surface tension of 44.0 mN / m is used as the ink in discharge order 1, and a cyan ink (C6) having a surface tension of 53.2 mN / m is used as the ink in discharge order 2. The surface tension of ejection order 2 was made higher than the surface tension of ink of order 1.

  In Comparative Example 7 to Comparative Example 9, the ink in the ejection order 1 and the ink in the ejection order 2 are combined as shown in Table 5 so that the surface tension in the ejection order 2 is higher than the surface tension of the ink in the ejection order 1. It was.

  In Examples 18 to 22 and Comparative Examples 10 to 17, as shown in Table 6 below, magenta ink (M) and cyan ink (C) were combined when producing mixed colors.

  In Example 18, as shown in Table 6, the ink in the ejection order 1 is magenta ink (M9) with a surface tension of 34.7 mN / m, and the ink in the ejection order 2 is cyan with a surface tension of 32.7 mN / m. Ink (C1) was used so that the surface tension of the ink in the discharge order 1 was higher than the surface tension in the discharge order 2.

  In Examples 19 to 22, as in Example 18, the ink in the ejection order 1 and the ink in the ejection order 2 are set so that the surface tension of the ink in the ejection order 1 is higher than the surface tension in the ejection order 2. Were combined as shown in Table 6.

  In Comparative Example 10, a magenta ink (M9) having a surface tension of 34.7 mN / m was used as the ink in discharge order 1, and a cyan ink (C2) having a surface tension of 35.4 mN / m was used as the ink in discharge order 2. The surface tension of ejection order 2 was made higher than the surface tension of ink of order 1.

  In Comparative Example 11 to Comparative Example 17, as in Comparative Example 10, the ink in the ejection order 1 and the ink in the ejection order 2 are mixed so that the surface tension in the ejection order 2 is higher than the surface tension of the ink in the ejection order 1. The combinations were made as shown in Table 6.

  In Examples 23 to 25 and Comparative Examples 18 to 26, yellow ink (Y), magenta ink (M), and cyan ink (C) are used in producing mixed colors as shown in Table 7 below. And combined.

  In Example 23, the first ink to be ejected in the discharge order 1 is a yellow ink (Y1) having a surface tension of 44.0 mN / m, and the second ink to be ejected in the next order is a surface tension of 43.1 mN / m. Magenta ink (M6), the next discharge order 3 ink to be discharged is cyan ink (C3) having a surface tension of 40.2 mN / m, the discharge order 1 ink has the highest surface tension, and the next discharge order The surface tension of the ink No. 2 was high, and the surface tension of the ink of order 3 was the lowest.

  In Examples 24 to 25, as in Example 23, the surface tension of the ink in the discharge order 1 is the highest, the surface tension of the ink in the discharge order 2 is next high, and the surface tension of the ink in the discharge order 3 is high. As shown in Table 7, the ink in the ejection order 1, the ink in the ejection order 2, and the ink in the ejection order 3 were combined so as to be the lowest.

  In Comparative Example 18, the discharge order 1 ink is cyan ink (C3) having a surface tension of 40.2 mN / m, and the discharge order 2 ink is yellow ink (Y1) having a surface tension of 44.0 mN / m. The ink of order 3 is magenta ink (M6) having a surface tension of 43.1 mN / m, the surface tension of the ink of discharge order 1 is the lowest, the surface tension of the ink of discharge order 3 is low, and the ink of discharge order 2 The surface tension of the ink was maximized.

  In Comparative Examples 19 to 26, as in Comparative Example 18, the surface tension of the ink in the discharge order 1 is the highest, the surface tension of the ink in the discharge order 2 is next high, and the surface tension of the ink in the discharge order 3 is high. In order not to become the lowest, the ink in the ejection order 1, the ink in the ejection order 2, and the ink in the ejection order 3 were combined as shown in Table 7.

  Recording images for evaluation were prepared using the inks of Examples 1 to 25 and Comparative Examples 1 to 26 shown in Tables 4 to 7. The recording image for evaluation is prepared by filling the ink cartridge of the printer device 1 with the ink of each of the examples and the comparative examples, and 600 × 600 dpi on photographic glossy paper (EPP-20A4GP manufactured by Sony Corporation). The head drive frequency was 9 kHz, and printing was performed under the condition that the recording speed was 49.5 mm / sec. Further, when creating a recording image for evaluation, in Examples 1 to 22 and Comparative Examples 1 to 17, the ejection amount of the ink in the ejection order 2 is changed stepwise from 1 to 8. Eight levels of density gradation were obtained. In the example 23 to the example 25 and the comparative example 18 to the comparative example 26, by changing the ejection amount of the ink in the ejection order 2 and the ejection order 3 from 1 to 8 in a stepwise manner, the density gradation property in 8 stages is obtained. Obtained. The amount of droplets for each dot in each gradation is as shown in Table 8.

  In the recording images for evaluation obtained as described above, when no color unevenness occurs in each gradation in Tables 4 to 7, they are indicated by ◯ and are displayed in a high print density region of 7 to 8 gradations. Only when color unevenness is confirmed, it is indicated by Δ, and when color unevenness is confirmed from the intermediate print density region of 5 to 6 gradations, it is indicated by ▲ and low printing of 3 to 4 gradations. When color unevenness is observed in the density area, it is indicated by x, and when color unevenness is observed in the low print density area of 3 to 4 gradations and color repellency is observed in the high print density area , Indicated by xx.

  As shown in Tables 4 to 7, in Examples 1 to 25, color unevenness did not occur in the mixed color part, or color unevenness was confirmed only in the high print density region, and the image quality was good. there were.

  On the other hand, in Comparative Examples 1 to 26, color unevenness is observed in the intermediate print density region of 5 to 6 gradations and the low print density region of 3 to 4 gradations, and in the low print density regions of 3 to 4 gradations. Color unevenness was observed, and color repelling was observed in the high print density region, resulting in a reduction in image quality.

  In Comparative Examples 1 to 17, since the surface tension of the ink in the ejection order 1 is lower than the surface tension of the ink in the ejection order 2, the ink in the ejection order 1 and the ink in the ejection order 2 do not mix evenly. Color unevenness and color repelling occurred in the print density area and the low print density area.

  In Comparative Examples 18 to 26, the surface tension of the ink in the discharge order 1 is the highest, the surface tension of the ink in the discharge order 2 is next high, and the surface tension of the ink in the discharge order 3 is the lowest. Therefore, the inks of the ejection order 1, the ejection order 2, and the ejection order 3 are not mixed uniformly, and color unevenness is observed in the low print density region of 3 to 4 gradations, or the inks of 3 to 4 gradations are observed. Color unevenness was observed in the low print density area, and color repelling occurred in the high print density area.

  In contrast to these comparative examples, in Examples 1 to 22, the surface tension of the ink in the ejection order 1 is higher than the surface tension in the ejection order 2, so that the ink in the ejection order 1 and the ink in the ejection order 2 The ink was uniformly mixed, and color unevenness did not occur in each gradation, or color unevenness occurred only in the high print density region of 7 to 8 gradations.

  In Examples 23 to 25, the surface tension of the ink in the ejection order 1 is the highest, the surface tension of the ink in the ejection order 2 is next high, and the surface tension of the ink in the ejection order 3 is the lowest. For this reason, the inks in the respective ejection orders are mixed uniformly, and color unevenness does not occur in each gradation, or color unevenness occurs only in the high print density region of 7 to 8 gradations. For these reasons, in Examples 1 to 25, a uniform color mixture was obtained in the color mixture part, and a high-quality image was obtained.

It is a perspective view which shows an example of a printer apparatus. FIG. 3 is a perspective view illustrating an example of a head cartridge mounted on the printer device. It is sectional drawing which shows the head cartridge. An example of the ink discharge head provided in the head cartridge is shown. FIG. 4A is a cross-sectional view schematically showing a state where bubbles are generated in the heating resistor, and FIG. It is sectional drawing which shows the discharged state typically. FIG. 2 is a side view illustrating a part of the printer device. 2 is a block diagram schematically showing a control circuit of the printer apparatus. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Inkjet printer apparatus, 2 Head cartridge, 3 Apparatus main body, 11 Ink cartridge, 21 Cartridge main body, 23 Ink ejection head, 31 Circuit board, 31a Heating resistor, 32 Nozzle sheet, 32 Nozzle, 33 Film, 34 Ink flow path, 35 Ink chamber

Claims (6)

In an image forming method of forming an image by ejecting minute droplets of ink from a plurality of ejection openings in accordance with a recording signal and attaching them to a recording medium.
Using two or more colors of ink with different surface tensions, consisting of at least water, a water-soluble organic solvent, a pigment, and a surfactant, and sequentially ejecting the inks with the highest surface tension in a single pass onto the recording medium. An image forming method.   The image forming method according to claim 1, wherein the ink has at least a yellow color, a magenta color, and a cyan color.   The image forming method according to claim 1, wherein the discharge ports are arranged in a line in the width direction of the recording medium. The ink has a yellow color, a magenta color, and a cyan color, and the surface tension is the highest in the yellow color, then the magenta color is the highest, and the cyan color is the lowest,
2. The image forming method according to claim 1, wherein the surface tension is discharged in the order of yellow, magenta, and cyan.   The image forming method according to claim 1, wherein the ink is ejected from the ejection port at a driving frequency of 9 kHz or more, and recording is performed at a recording medium conveyance speed of 49.5 mm / sec or more.   2. The image forming method according to claim 1, wherein the recording medium is a glossy paper having a porous layer formed of a hydrophilic binder and fine particles as an ink receiving layer.

Images