Recording method

Abstract

Provided is a recording method realizing good fixability of ink to a low-permeability medium having low ink permeability, and good high-speed printing stability. This recording method comprises a recording step of discharging, from a nozzle (34A) of a printing head (34), an inkjet ink containing water and a water dispersion resin dispersed in water with the water as a dispersion medium. The storage elastic modulus of the inkjet ink at 1000 Hz is less than 0.5 Pa. The percentage by weight of the water dispersion resin with respect to the total amount of the ink is 3 wt% or more. The viscosity of the inkjet ink is in the range between 3.5 mPa·s and 12 mPa·s (both inclusive). The printing head (34) has a piezoelectric element (91) that is driven in accordance with a discharge signal to cause the nozzle (34A) to discharge the inkjet ink. In the recording step, the piezoelectric element (91) repeats discharge of the inkjet ink at a drive frequency of 60 kHz or higher.

Description

Recording method

[0001] The present disclosure relates to an ink containing water and a water-dispersed resin, and a recording method of discharging the ink from nozzles of a head.

[0002] In recent years, the demand for water-based inks with less environmental load, such as the inkjet recording ink described in Patent Document 1, has been increasing. The inkjet recording ink of Patent Document 1 contains a water-dispersed resin dispersed with water as a dispersion medium in order to firmly fix the ink on a low-permeability medium with low ink permeability.

[0003] Japanese Patent Application Laid-Open No. 2023-127117

[0004] On the other hand, when a water-dispersed resin is contained in the ink, there is a problem that it is difficult to stably discharge the ink from the nozzles at high speed. In the inkjet recording ink of Patent Document 1, high-speed printing stability is not considered.

[0005] An object of the present disclosure is to provide a recording method having good ink fixing property and high-speed printing stability with respect to a low-permeability medium having low ink permeability.

[0006] (1) The present disclosure relates to a recording method. The recording method includes a recording step of discharging an inkjet ink containing water and a water-dispersed resin dispersed with water as a dispersion medium from nozzles of a print head. The storage elastic modulus of the inkjet ink at 1000 Hz is less than 0.5 Pa. The weight percentage of the water-dispersed resin with respect to the total amount of the ink is 3% by weight or more. The viscosity of the inkjet ink is within the range of 3.5 mPa·s or more and 12 mPa·s or less. The print head has a piezoelectric element that is driven in response to a discharge signal and discharges the inkjet ink from the nozzles. In the recording step, the piezoelectric element repeats discharging the inkjet ink at a driving frequency of 60 kHz or more.

[0007] Inkjet ink adheres firmly to low-penetration media with low ink permeability. In high-speed printing where the piezoelectric element repeatedly ejects inkjet ink at a driving frequency of 60.0 kHz or higher, inkjet ink is stably ejected from the nozzle. As a result, the adhesion of inkjet ink to low-penetration media and the stability of high-speed printing are excellent.

[0008] (2) The difference between the viscosity of the inkjet ink measured by a vibratory viscometer with the oscillator frequency set to 100 Hz and the viscosity of the inkjet ink measured by a vibratory viscometer with the oscillator frequency set to 1000 Hz may be 0.3 mPa·s or less.

[0009] Even with a 900Hz difference in the oscillator frequencies, the difference in viscosity is small. Therefore, when ink is ejected from the nozzle, the time it takes for the ink column to completely break off from the nozzle tends to be consistent. Consequently, high-speed printing stability is improved.

[0010] (3) The water-dispersible resin may further contain resin fine particles that disperse in the water to form an emulsion.

[0011] The adhesion of inkjet inks to low-penetration media is improved.

[0012] (4) The water-dispersible resin may include a resin-dispersed pigment which comprises a pigment and a pigment-dispersing resin which disperses the pigment in the water.

[0013] The adhesion of inkjet inks to low-penetration media is improved.

[0014] (5) The weight percentage of the above-mentioned water-dispersible resin relative to the total amount of ink may be 15% by weight or less.

[0015] High-speed printing stability is further improved.

[0016] (6) In the recording step described above, the inkjet ink may be ejected from the nozzle into a low-penetration medium in which the amount of water absorbed from the start of contact in the Bristow method up to 15 msec is 10 mL / m2 or less.

[0017] Inkjet inks adhere well to low-penetration media.

[0018] (7) The low-penetration medium may be any of coated paper, plastic film, synthetic paper, or coated cardboard.

[0019] It offers good inkjet ink adhesion to coated paper, plastic film, synthetic paper, and coated cardboard.

[0020] (8) After the recording step, the process may further include a heating step in which the low-penetration medium, the inkjet ink adhering to the low-penetration medium, or the low-penetration medium and the inkjet ink adhering to the low-penetration medium are heated to a temperature at least 20°C higher than the glass transition temperature of the water-dispersible resin.

[0021] The adhesion of inkjet inks to low-penetration media is improved.

[0022] (9) In the recording step described above, the inkjet ink may be heated so that its viscosity is within the range of 3.5 mPa·s to 12 mPa·s before being ejected from the nozzle.

[0023] High-speed printing stability is improved.

[0024] According to this disclosure, the ink fixation and high-speed printing stability are good for low-penetration media with low ink permeability.

[0025] Figure 1 is a perspective view of the printing apparatus 10. Figure 2 is a schematic diagram showing the internal configuration of the printing apparatus 10. Figure 3 is a close-up view of the vicinity including the nozzle 34A. Figure 4 is a block diagram of the controller 74. Figure 5 is a schematic diagram showing the internal configuration of a modified printing apparatus 10.

[0026] Preferred embodiments of the present disclosure are described below. It goes without saying that these embodiments are only one embodiment of the present disclosure, and the embodiments can be modified without altering the gist of the present disclosure.

[0027] Embodiments of the present disclosure will be described below with reference to the drawings as appropriate. It should be noted that the embodiments described below are merely examples of the present disclosure, and the embodiments of the present disclosure can be modified as appropriate without altering the gist of the disclosure. In the following description, the vertical direction is defined based on the state in which the printing device 10 is installed for use, as shown in Figure 1. The front-to-back direction is defined with the direction in which the discharge port 13 of the printing device 10 opens being forward. The left-to-right direction is defined when viewing the printing device 10 from the front. The front-to-back direction, the vertical direction, and the left-to-right direction are orthogonal to each other.

[0028] [External Configuration of Printing Device 10] As shown in Figure 1, the printing device 10 comprises a housing 20, a panel unit 21, a cover 22, a paper feed tray 23, and a paper output tray 24. The panel unit 21 is held in the housing 20. The panel unit 21 is equipped with a touch panel and a number of operation switches. The panel unit 21 accepts user input.

[0029] The paper feed tray 23 is located at the bottom of the housing 20. The paper feed tray 23 accommodates multiple sheets 6. The multiple sheets 6 are recording media cut to predetermined dimensions. The paper feed tray 23 may also accommodate rolls of paper on which the sheets are wound. The output tray 24 is located at the bottom of the housing 20, above the paper feed tray 23. The cover 22 is located on the right side of the front of the housing 20. The cover 22 is rotatable relative to the housing 20. When the cover 22 is opened, the ink storage tank 70 is accessible.

[0030] In this embodiment, only one tank 70 is shown. The tank 70 is not limited to storing a single color of ink, such as black. For example, the tank 70 may further have a storage chamber for yellow, a storage chamber for cyan, and a storage chamber for magenta.

[0031] [Internal Configuration of Printing Device 10] As shown in Figure 2, the housing 20 houses the printing engine 50. The printing engine 50 mainly consists of a paper feed roller 25, a transport roller 26, a rotary encoder 96, an ejection roller 27, a platen 28, a print head 34, and a heater 35. The paper feed roller 25 is capable of contacting the sheet 6 placed on the paper feed tray 23. The paper feed roller 25 is held by a frame located inside the housing 20. The paper feed roller 25 is rotated by a feeding motor 102 shown in Figure 4.

[0032] The rotating paper feed roller 25 feeds the sheet 6 into the transport path 37. The transport path 37 is a space partitioned by guide members located inside the housing 20. In Figure 2, the transport path 37 curves and extends from the rear end of the paper feed tray 23 to a position above the paper feed tray 23. From the position above the paper feed tray 23, the transport path 37 extends forward.

[0033] The transport roller 26 is located downstream of the paper feed tray 23 in the direction of sheet 6 transport. The transport roller 26, together with the driven roller 29, forms a roller pair. The transport roller 26 is rotated by the transport motor 101 shown in Figure 4. The transport roller 26 and the driven roller 29 transport the sheet 6 that has been fed into the transport path 37 by the paper feed roller 25 while gripping it.

[0034] The rotary encoder 96 has an encoder disk 97 and an optical sensor 98. The encoder disk 97 is fixed to the rotation axis of the transport roller 26. The encoder disk 97 is coaxial with the transport roller 26. The encoder disk 97 rotates together with the transport roller 26. Multiple indices of two types with different transmittances are arranged alternately around the entire circumference of the encoder disk 97.

[0035] The optical sensor 98 is capable of optically reading two types of indices on the encoder disk 97. By reading the two types of indices on the rotating encoder disk 97, the optical sensor 98 outputs two types of signals in pulse form. The output signals from the optical sensor 98 are received by the controller 74, which will be described later, and the rotation speed of the transport roller 26 is determined.

[0036] The discharge roller 27 is located downstream of the transport roller 26 in the transport direction of the sheet 6. The discharge roller 27, together with the driven roller 36, forms a roller pair. The discharge roller 27 is rotated by the transport motor 101 shown in Figure 4. The discharge roller 27 and the driven roller 36 transport the sheet 6 while gripping it and discharge it into the paper output tray 24.

[0037] The platen 28 is located between the conveying roller 26 and the discharge roller 27 in the front-rear direction. In other words, the platen 28 is located downstream of the conveying roller 26 and upstream of the discharge roller 27 in the conveying direction of the sheet 6. The upper surface of the platen 28 is a support surface that supports the sheet 6. An opening that generates suction pressure is located on the upper surface of the platen 28. The suction pressure generated on the upper surface of the platen 28 causes the sheet 6 to come into close contact with the upper surface of the platen 28.

[0038] The print head 34 is located between the transport roller 26 and the discharge roller 27 in the front-rear direction. The print head 34 is located above the platen 28. The print head 34 faces the platen 28 in the vertical direction. The print head 34 is a so-called serial head. However, the print head 34 may also be a so-called line head.

[0039] As shown in Figures 2 and 3, the print head 34 has an ink channel 90. Ink flows through the ink channel 90. The ink channel 90 is connected to a tube 31. The ink channel 90 communicates with a tank 70 through the tube 31. As a result, ink in the tank 70 is supplied to the print head 34 through the tube 31.

[0040] The print head 34 has a common channel 12A and a plurality of individual channels 12B. The plurality of individual channels 12B branch off from the common channel 12A. The plurality of individual channels 12B include a nozzle 34A and a pressure chamber 12P. The nozzle 34A opens downward on the lower surface of the print head 34. The pressure chamber 12P communicates with the nozzle 34A. The upper end of the pressure chamber 12P is defined by a diaphragm 14.

[0041] The print head 34 has a plurality of piezoelectric elements 91 and a head substrate 92. The plurality of piezoelectric elements 91 are fixed to the upper surface of the diaphragm 14. The plurality of piezoelectric elements 91 are in a thin film shape. The plurality of piezoelectric elements 91 can be independently deformed according to the potential.

[0042] As shown in FIGS. 3 and 4, the head substrate 92 has a driver IC 92A. The driver IC 92A is electrically connected to the plurality of piezoelectric elements 91. The driver IC 92A applies a voltage to the plurality of piezoelectric elements 91 according to the ejection signal from the controller 74. As a result, the plurality of piezoelectric elements 91 are driven to deform together with the diaphragm 14, and the volume of the pressure chamber 12P decreases. As a result, ink is ejected from the plurality of nozzles 34A.

[0043] The voltage applied to the plurality of piezoelectric elements 91 is supplied from a power supply circuit (not shown). The voltage applied to the plurality of piezoelectric elements 91 is a voltage that periodically changes at 60 kHz or more. As a result, the plurality of piezoelectric elements 91 repeat the ejection of ink from the plurality of nozzles 34A at a driving frequency of 60 kHz or more. Preferably, the plurality of piezoelectric elements 91 repeat the ejection of ink within a range of 60 kHz or more and 62.5 kHz or less. Thereby, even when the sheet 6 is conveyed at high speed, printing is possible. That is, high-speed printing is possible.

[0044] When the conveyance speed of the sheet 6 is, for example, when the sheet 6 is A4 size, it is 100 sheets / min or more. Preferably, the conveyance speed of the sheet 6 is, for example, within a range of 100 sheets / min or more and 120 sheets / min or less. When the roll paper is housed in the paper feed tray 23, the conveyance speed of the sheet drawn out from the roll paper is preferably, for example, within a range of 75 m / min or more and 100 m / min or less.

[0045] As shown in FIG. 2, the heater 35 is located in front of the print head 34 in the front-rear direction. In other words, the heater 35 is located downstream of the print head 34 in the conveyance direction of the sheet 6. The heater 35 is located above the conveyance path 37. The heater 35 is a so-called halogen heater. Specifically, the heater 35 has a halogen lamp 40, a reflector 41, and a housing 42.

[0046] The halogen lamp 40 is located in the internal space of the housing 42. The halogen lamp 40 has an elongated cylindrical shape in the left-right direction. The halogen lamp 40 is a heating element that emits infrared rays. The housing 42 has a substantially rectangular parallelepiped shape and is open downward. An opening 43 is located in the lower wall of the housing 42.

[0047] The reflector 41 is located in the internal space of the housing 42. The reflector 41 is located above the halogen lamp 40. The reflector 41 is a metal plate coated with a ceramic film or the like. The reflector 41 is curved in an arc shape centered around the vicinity of the opening 43. Note that instead of the reflector 41, a halogen lamp 40 coated with a ceramic film or the like may be used. Heat from the halogen lamp 40 and the reflector 41 is radiated to the outside through the opening 43.

[0048] The heater 35 heats both the sheet 6 passing below the opening 43 and the ink adhered to the sheet 6. When the ink is heated, the resin fine particles undergo glass transition. The glass-transitioned resin fine particles are cured as the sheet 6 passing below the heater 35 cools. Thereby, the ink is fixed to the sheet 6.

[0049] The sheet 6 is a low-permeability medium with low ink permeability. Specifically, the sheet 6 has a water absorption of 10 mL / m2 or less from the contact start to 15 msec in the Bristol method. For example, examples of the sheet 6 include coated paper, plastic film, synthetic paper, and coated cardboard.

[0050] A controller 74 is disposed in the internal space of the housing 20. As shown in FIG. 4, the controller 74 includes a CPU 131, a ROM 132, a RAM 133, an EEPROM 134, and an ASIC 135. The CPU 131, the ROM 132, the RAM 133, and the EEPROM 134 are connected to the ASIC 135 via a bus 137 so as to be capable of data communication. The CPU 131 executes a program stored in the ROM 132.

[0051] The ASIC 135 controls the operation of the printing device 10 by performing specific functions that have been set. Specifically, the ASIC 135 transmits an ejection signal to the driver IC 92A. The driver IC 92A applies a voltage corresponding to the ejection signal to a plurality of piezoelectric elements 91. The ASIC 135 allows power to be supplied to the heater 35 so that the heater 35 reaches a predetermined temperature. The ASIC 135 cuts off the power supply to the heater 35.

[0052] The ASIC 135 controls the rotation of the transport motor 101 so that the transport speed of the sheets 6 is, for example, 100 sheets / min or more. This transport speed control is achieved, for example, by controlling the rotation of the transport rollers 26 based on the signal from the rotary encoder 96.

[0053] [Ink Composition] The details of the ink stored in tank 70 are described below. The ink is an example of an inkjet ink. The ink is an aqueous ink containing a resin-dispersed pigment, resin fine particles, an organic solvent, and water.

[0054] Resin-dispersed pigments include a pigment and a pigment-dispersing resin for dispersing the pigment in water. Resin-dispersed pigments are not particularly limited. For example, resin-dispersed pigments include carbon black, inorganic pigments, and organic pigments. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black.

[0055] Examples of inorganic pigments include titanium dioxide, iron oxide-based inorganic pigments, and carbon black-based inorganic pigments. Examples of organic pigments include azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments. Examples of organic pigments include polycyclic pigments such as phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments. Examples of organic pigments include dye lake pigments such as basic dye-type lake pigments and acid dye-type lake pigments. Examples of organic pigments include nitro pigments, nitroso pigments, and aniline black daylight fluorescent pigments.

[0056] Other resin-dispersed pigments include, for example, C.I. Pigment Black 1, 6 and 7; C.I. Pigment Yellow 1, 2, 3, 12, 13, 14, 15, 16, 17, 55, 73, 74, 75, 78, 83, 93, 94, 95, 97, 98, 114, 128, 129, 138, 150, 151, 154, 180, 185 and 194; C.I. Pigment Orange 31 and 43; C.I. Examples include Pigment Red 2, 3, 5, 6, 7, 12, 15, 16, 48, 48:1, 48:3, 53:1, 57, 57:1, 112, 122, 123, 139, 144, 146, 149, 150, 166, 168, 175, 176, 177, 178, 184, 185, 190, 202, 209, 221, 222, 224, 238 and 254; C.I. Pigment Violet 19 and 196; C.I. Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 16, 22 and 60; C.I. Pigment Green 7 and 36; and solid solutions of these pigments. Furthermore, the ink may contain other pigments and dyes in addition to the resin-dispersed pigment. The resin-dispersed pigment is an example of a water-dispersible resin.

[0057] The content of resin-dispersed pigment in the total amount of water-based ink is not particularly limited. The content of resin-dispersed pigment in the total amount of water-based ink is appropriately determined, for example, by the desired optical density or saturation. Preferably, the content of resin-dispersed pigment is in the range of 0.1% by weight or more and 20% by weight or less. More preferably, the content of resin-dispersed pigment is in the range of 0.3% by weight or more and 15% by weight or less. Particularly preferably, the content of resin-dispersed pigment is in the range of 0.5% by weight or more and 10% by weight or less. One type of resin-dispersed pigment may be used alone, or two or more types may be used in combination.

[0058] The resin microparticles can be, for example, those containing at least one of methacrylic acid and acrylic acid as monomers. Commercially available resin microparticles may also be used. The resin microparticles may further contain, for example, styrene, vinyl chloride, etc., as monomers. The resin microparticles may also be, for example, contained in a resin emulsion. A resin emulsion is composed of, for example, resin microparticles and a dispersion medium such as water. The resin microparticles are not dissolved in the dispersion medium but are dispersed within a specific particle size range. In other words, a resin emulsion is an emulsion state in which resin microparticles are dispersed in a dispersion medium.

[0059] Examples of resin fine particles contained in the resin emulsion include acrylic acid resins, maleic acid ester resins, vinyl acetate resins, carbonate-type resins, polycarbonate-type resins, styrene-type resins, ethylene-type resins, polyethylene-type resins, propylene-type resins, polypropylene-type resins, urethane-type resins, polyurethane-type resins, polyester-type resins, and copolymer resins of the above resins.

[0060] The glass transition temperature of the resin fine particles is preferably in the range of 33°C to 112°C. It is 33°C or higher. Hereafter, the glass transition temperature will be denoted as Tg. The Tg of the resin fine particles is more preferably in the range of 33°C to 95°C. The Tg of the resin fine particles is particularly preferably in the range of 40°C to 80°C. Using resin fine particles with a Tg of 33°C or higher yields an ink with excellent fixation properties on sheet 6.

[0061] As the resin emulsion, for example, a commercially available product may be used. For example, a commercially available product is "Hyros-X (registered trademark) KE-1062" (Tg: 112°C) manufactured by Seikoh PMC Co., Ltd. ), "Hyros-X (registered trademark) QE-1042" (Tg: 69°C); "Movinyl (registered trademark) 6969D" (Tg: 71°C), "Movinyl (registered trademark) 5450" (Tg: 53°C), "Movinyl (registered trademark) DM774" (Tg: 33°C), "Movinyl (registered trademark) 6899D" (Tg: 49°C), "Movinyl (registered trademark) 6800D" (Tg: 80°C), "Movinyl (registered trademark) 702" (Tg: -19°C), "Movinyl (registered trademark) 7525" (Tg: -16°C), "Movinyl (registered trademark) LDM7522" (Tg: -15°C), "Movinyl (registered trademark) LDM7010" (Tg: -22°C), "Movinyl (registered trademark) 461" (Tg: -48°C) ), "Movinyl (registered trademark) 462" (Tg: -48°C), "Movinyl (registered trademark) 490" (Tg: -53°C), "Movinyl (registered trademark) 987B" (Tg: -2°C), "Movinyl (registered trademark) S-71" (Tg: -53°C), "Movinyl (registered trademark) 718A" (Tg: -6°C), "Movinyl (registered trademark) 730L" (Tg: -13°C), "Movinyl (registered trademark) 7320" (Tg: -20°C), "Movinyl (registered trademark) 7400" (Tg: -41°C), "Movinyl (registered trademark) 7420" (Tg: -26°C), "Movinyl (registered trademark) 6730" (Tg: -2°C), "Movinyl (registered trademark) 6775" (Tg: 5°C), "Movinyl (registered trademark) 7502" (Tg: -35°C), "Movinyl (registered trademark) VDM7410" (Tg: -4°C), "Movinyl (registered trademark) 6960" (Tg: -23°C), "Movinyl (registered trademark) 727" (Tg: 5°C)"Movinyl (registered trademark) 742A" (Tg: 45°C), "Movinyl (registered trademark) 743N" (Tg: 37°C), "Movinyl (registered trademark) 745" (Tg: 21°C), "Movinyl (registered trademark) 1711" (Tg: 30°C), "Movinyl (registered trademark) 6520" (Tg: 41°C), "Movinyl (registered trademark) 6530" (Tg: 30°C), "Movinyl (registered trademark) 7180" (Tg: 53°C), "Movinyl (registered trademark) 7470" (Tg: 42°C), "Movinyl (registered trademark) 7720" (Tg: 4°C), "Movinyl (registered trademark) 7820" (Tg: 4°C), "Movinyl (registered trademark) DM772" (Tg: 6°C), "Movinyl (registered trademark) DM77 4" (Tg: 13°C), "Movinyl (registered trademark) LDM7156" (Tg: 37°C), "Movinyl (registered trademark) LDM7520" (Tg: 4°C), "Movinyl (registered trademark) 7980" (Tg: 55°C), "Movinyl (registered trademark) 735" (Tg: 14°C), "Movinyl (registered trademark) 742A" (Tg: 39°C), "Movinyl (registered trademark) 747" (Tg: 42°C), "Movinyl (registered trademark) LDM7582" (Tg: 26°C), "Movinyl (registered trademark) 710A" (Tg: 9°C), "Movinyl (registered trademark) 731A" (Tg: 0°C), "Movinyl (registered trademark) 749E" (Tg: 25°C), "Movinyl (registered trademark) 752" (Tg: 15°C), "Movinyl (registered trademark) 880" (Tg: 3°C), "Movinyl (registered trademark) 940" (Tg: 3°C), "Movinyl (registered trademark) 1752" (Tg: 16°C), "Movinyl (registered trademark) 1760" (Tg: 7°C), "Movinyl (registered trademark) 6720" (Tg: 34°C), "Movinyl (registered trademark) DM60" (Tg: 3°C), "Movinyl (registered trademark) 975N" (Tg: 27°C), "Movinyl (registered trademark) 972" (Tg: 101°C)); "Superflex® 126" (Tg: 72°C), "Superflex® 150" (Tg: 40°C), "Superflex® 300" (Tg: -42°C), "Superflex® 420" (Tg: -10°C), "Superflex® 420NS" (Tg: -10°C), "Superflex® 460" (Tg: -21°C), "Superflex® 460S" (Tg: -28°C), "Superflex® 470" (Tg: -31°C), "Superflex® 500M" (Tg: -39°C), "Superflex® 650" (Tg: -17°C), "Superflex® 740" (Tg: -34°C), "Superflex® E-2000" (Tg: -38°C), "Superflex® E-4800" (Tg: -65°C), "Superflex® 150HS" (Tg: 32°C), "Superflex® 170" (Tg: 75°C), "Superflex® 210" (Tg: 41°C), "Superflex® 620" (Tg: 43°C), "Superflex® 820" (Tg: 46°C), "Superflex® 830HS" (Tg: 68°C), "Superflex® 860" (Tg: 36°C), "Superflex® 870" (Tg: 78°C), "Superflex® 130" (Tg: 101°C); "Saibinol® EK-61" (Tg: 24°C), "Saibinol® EK-1920" manufactured by Saiden Chemical Co., Ltd. Tg: 40℃); Sanyo Chemical Industries, Ltd.'s "U-Coat UX-300" (Tg: -25℃), "U-Coat UX-310" (Tg: -25℃), "U-Coat UX-340" (Tg: -50℃), "Permarine UA-150" (Tg: -70℃), "Permarine UA-200" (Tg: -35℃), "Permarine UA-350" (Tg: -30℃), "Permarine UA-368" (Tg: -20℃),"U-Coat UWS-145" (Tg: -45°C), "Euprene UXA-307" (Tg: -45°C); Mitsui Chemicals, Inc.'s "Takelac® WS-6021" (Tg: -60°C), "Takelac® W-6110" (Tg: -20°C), "Takelac® W-5030" (Tg: 85°C), "Takelac® W-5661" (Tg: 70°C), "Takelac® W-6010" (Tg: 90°C), "Takerack (registered trademark) W-6020" (Tg: 90℃), "Takerack (registered trademark) W-6061" (Tg: 25℃), "Takerack (registered trademark) W-635" (Tg: 70℃), "Takerack (registered trademark) WS-5984" (Tg: 70℃), "Takerack (registered trademark) W-405" (Tg: 135℃), "Takerack (registered trademark) W-605" (Tg: 100℃), "Takerack (registered trademark) WS-4000" (Tg: 136℃), "Takerack (registered trademark) WS-4022" (Tg: 115℃), "Takerack (registered trademark) WS-5000" (Tg: 6 Examples include "Takelac® WS-5100" (Tg: 120°C), "Joncryl 74-A" (Tg: -16°C), "Joncryl 77" (Tg: 21°C), "Joncryl 80" (Tg: -30°C), "Joncryl 82" (Tg: -10°C), "Joncryl 89" (Tg: 98°C), "Joncryl 98" (Tg: 1°C), "Joncryl 537" (Tg: 44°C), "Joncryl 538-A" (Tg: 64°C), "Joncryl 585" (Tg: -20°C), and "Joncryl 617-A" (Tg: 7°C) manufactured by BASF Co., Ltd. Resin fine particles are an example of water-dispersible resins.

[0062] The content of resin fine particles in the total amount of water-based ink is not particularly limited. Preferably, the content of resin fine particles in the total amount of water-based ink is in the range of 0.1% by weight or more and 30% by weight or less. More preferably, the content of resin fine particles is in the range of 0.5% by weight or more and 20% by weight or less. Particularly preferably, the content of resin fine particles is in the range of 2.5% by weight or more and 14.5% by weight or less. One type of resin fine particle may be used alone, or two or more types may be used in combination. Note that the content of resin fine particles does not include resin-dispersed pigment and water.

[0063] Furthermore, the total content of resin fine particles and resin-dispersed pigments in the total amount of water-based ink is 3% by weight or more. Preferably, the total content of resin fine particles and resin-dispersed pigments in the total amount of water-based ink is within the range of 3% by weight or more and 15% by weight or less.

[0064] The organic solvent prevents the ink from drying out at the nozzle tip of the print head 34, for example. Examples of organic solvents include propylene glycol, glycerin, triethylene glycol, butylene glycol, dipropylene glycol, tripropylene glycol, thiodiglycol, trimethylolpropane, trimethylolethane, polyethylene glycol, and polypropylene glycol. One type of organic solvent may be used alone, or two or more types may be used in combination.

[0065] The content of organic solvents in the total amount of water-based ink is, for example, within the range of 30% by weight or more and 60% by weight or less.

[0066] The ink may further contain a penetrant to adjust the drying speed on the sheet 6. Examples of penetrants include glycol ethers. Examples of glycol ethers include ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol-n-propyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol-n-propyl ether, diethylene glycol-n-butyl ether, diethylene glycol-n-hexyl ether, triethylene glycol methyl ether, triethylene glycol ethyl ether, triethylene glycol-n-propyl ether, triethylene glycol-n-butyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol-n-propyl ether, propylene glycol-n-butyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol-n-propyl ether, dipropylene glycol-n-butyl ether, tripropylene glycol methyl ether, tripropylene glycol ethyl ether, tripropylene glycol-n-propyl ether, and tripropylene glycol-n-butyl ether. Penetrating agents may be used individually or in combination of two or more types.

[0067] The amount of penetrant in the total amount of aqueous ink is preferably in the range of 0% to 20% by weight. More preferably, the amount of penetrant is in the range of 0% to 15% by weight. Particularly preferably, the amount of penetrant is in the range of 1% to 3% by weight.

[0068] The water is preferably deionized water, pure water, or ultrapure water. The water content in the total amount of aqueous ink is preferably in the range of 10% to 90% by weight. More preferably, the water content is in the range of 20% to 80% by weight. The water content may be, for example, the remainder of the other components.

[0069] The ink may further contain conventionally known additives as needed. Examples of additives include surfactants, pH adjusters, viscosity modifiers, surface tension modifiers, and antifungal agents. Examples of viscosity modifiers include polyvinyl alcohol, cellulose, and water-soluble resins. The ink can be prepared by uniformly mixing the ink components using conventionally known methods and removing insoluble materials with a filter or the like.

[0070] The viscosity of the ink is within the range of 3.5 mPa·s to 12 mPa·s. The viscosity of the ink is measured, for example, by a vibratory viscometer. Preferably, the difference between the viscosity measured under measurement condition 1 and the viscosity measured under measurement condition 2 is 0.3 mPa·s or less. Measurement condition 1 is when the frequency of the vibratory viscometer's oscillator is 100 Hz. Measurement condition 2 is when the frequency of the vibratory viscometer's oscillator is 1000 Hz.

[0071] The storage modulus of the ink measured under a measurement condition of 1000 Hz is less than 0.5 Pa. "Storage modulus" reflects the elastic properties of a material and represents its resistance to deformation. The storage modulus of ink can be measured, for example, using a piezoelectric high-frequency rheometer such as the "TriPAV" manufactured by Trijet Limited.

[0072] Because the ink's storage modulus is less than 0.5 Pa, the time it takes for the ink column to break off from the nozzle 34A after the ink is ejected is shortened. In other words, even if the ink is ejected many times in a short period of time, the ink is ejected smoothly, improving high-speed printing stability.

[0073] Next, a recording method using the printing device 10 will be described. In this recording method, the following steps are performed sequentially: preparation, transport, recording, heating, and paper discharge.

[0074] In the preparation process, the heater 35 is turned on. Specifically, the controller 74 allows power to be supplied to the heater 35 so that it reaches a predetermined temperature. The predetermined temperature is, for example, 20°C or more higher than the Tg of the resin fine particles. The predetermined temperature is, for example, 90°C.

[0075] In the transport process, the sheets 6 contained in the paper feed tray 23 are transported to the print head 34. Specifically, the controller 74 rotates the feeding motor 102 and the transport motor 101 by a predetermined amount of rotation. This transports the sheets 6 from the paper feed tray 23 to the print head 34. The sheets 6 transported to the print head 34 are supported on the upper surface of the platen 28.

[0076] In the recording process, the controller 74 transports the sheet 6 in the transport direction while ejecting ink from multiple nozzles 34A of the print head 34 toward the sheet 6. Specifically, when the sheet 6 is A4 size, the controller 74 controls the rotation of the transport motor 101 so that the transport speed of the sheet 6 is 100 sheets / min or more. At the same time, the controller 74 transmits an ejection signal to the driver IC 92A. The driver IC 92A applies a voltage that changes periodically at 60 kHz or higher to multiple piezoelectric elements 91 from a power supply circuit (not shown). As a result, the multiple piezoelectric elements 91 repeatedly eject ink from multiple nozzles 34A at a drive frequency of 60 kHz or higher. Consequently, ink is recorded on the sheet 6 supported on the upper surface of the platen 28.

[0077] During the heating process, the sheet 6 passes beneath the heater 35. Specifically, the controller 74 continues to rotate the transport motor 101. As a result, the sheet 6 is heated by the heater 35 as it passes beneath it. Simultaneously, the resin particles of the ink on the sheet 6 soften due to the heat of the heater 35, and the evaporation of moisture from the ink is promoted. Subsequently, the resin particles solidify through natural cooling. As a result, even if the sheet 6 is a low-penetration medium, the ink adheres firmly to the sheet 6.

[0078] In the paper discharge process, the controller 74 continues the rotation of the transport motor 101 for a predetermined amount of time, and then stops the rotation of the transport motor 101. As a result, the sheet 6 is discharged into the paper discharge tray 24.

[0079] [Effects of the Embodiment] In the above embodiment, even if the sheet 6 is a low-penetration medium with low ink permeability, the ink adheres firmly to the sheet 6. In high-speed printing, where the piezoelectric element 91 repeatedly ejects ink at a driving frequency of 60.0 kHz or higher, ink is stably ejected from multiple nozzles 34A. As a result, the ink adhesion to the sheet 6 and the high-speed printing stability are good.

[0080] In the above embodiment, the viscosity of the ink is such that the difference between the viscosity measured under condition 1 and the viscosity measured under condition 2 is 0.3 mPa·s or less. Under condition 1, the frequency of the vibrating viscometer's oscillator is 100 Hz. Under condition 2, the frequency of the vibrating viscometer's oscillator is 1000 Hz. Thus, even with a difference of 900 Hz in oscillator frequency, the difference in viscosity is small. Therefore, when the ink is ejected from the nozzle, the time it takes for the ink column to completely break off from the nozzle tends to be constant. Consequently, high-speed printing stability is good.

[0081] In the above embodiment, the ink contains resin fine particles that disperse in water to form an emulsion. Therefore, the ink adheres well to the sheet 6.

[0082] In the above embodiment, the ink comprises a pigment and a resin-dispersed pigment containing a pigment-dispersing resin that disperses the pigment in water. Therefore, the ink has high adhesion to the sheet 6.

[0083] In the above embodiment, the total content of resin fine particles and resin-dispersed pigment in the total amount of aqueous ink is 15% by weight or less. Therefore, high-speed printing stability is good.

[0084] In the above embodiment, during the recording process, ink is ejected onto the sheet 6 from multiple nozzles 34A of the print head 34. The sheet 6 has a water absorption capacity of 10 mL / m2 or less from the start of contact in the Bristow method up to 15 msec. Therefore, even if the sheet 6 is a low-penetration medium with low ink permeability, the ink adheres well to the sheet 6.

[0085] In the above embodiment, the sheet 6 is made of coated paper, plastic film, synthetic paper, or coated cardboard. Therefore, the ink adheres well to plastic film, synthetic paper, and coated cardboard.

[0086] In the above embodiment, during the heating process, the sheet 6 and the ink on the sheet 6 are heated by the heater 35 to a temperature at least 20°C higher than the Tg of the resin fine particles. As a result, the ink adheres well to the sheet 6.

[0087] [Modification] In the above embodiment, the viscosity of the ink is such that the difference between the viscosity measured under condition 1 and the viscosity measured under condition 2 is 0.3 mPa·s or less. Condition 1 is when the frequency of the vibrating viscometer's oscillator is 100 Hz. Condition 2 is when the frequency of the vibrating viscometer's oscillator is 1000 Hz. However, the difference between the viscosity measured under condition 1 and the viscosity measured under condition 2 may be greater than 0.3 mPa·s.

[0088] In the above embodiment, the ink contains resin fine particles, but the resin fine particles may be omitted.

[0089] In the above embodiment, the sheet 6 has a water absorption rate of 10 mL / m² or less from the start of contact in the Bristow method to 15 msec. However, the sheet 6 may have a water absorption rate of more than 10 mL / m² from the start of contact in the Bristow method to 15 msec.

[0090] In the above embodiment, the sheet 6 is cut to a predetermined size. However, the sheet 6 may be drawn from a roll wound in a cylindrical shape. The sheet 6 may also be of the fanfold type. The sheet 6 may also be glossy paper, matte paper, cardboard, or corrugated cardboard. The sheet 6 may also be tack paper, which is a combination of adhesive and release paper.

[0091] In the above embodiment, during the heating step, the sheet 6 and the ink on the sheet 6 are heated by the heater 35 to a temperature at least 20°C higher than the Tg of the resin fine particles. However, during the heating step, the sheet 6 and the ink on the sheet 6 do not necessarily have to be heated by the heater 35 to a temperature at least 20°C higher than the Tg of the resin fine particles.

[0092] In the above embodiment, during the heating process, the heater 35 heated both the sheet 6 passing below the opening 43 and the ink adhering to the sheet 6. However, during the heating process, it is sufficient if only one of the sheet 6 and the ink adhering to the sheet 6 is heated.

[0093] In the above embodiment, the viscosity of the ink stored in the tank 70 is in the range of 3.5 mPa·s to 12 mPa·s. However, the viscosity of the ink may be higher than 12 mPa·s. In this case, during the recording process, for example, ink whose viscosity has been heated to the range of 3.5 mPa·s to 12 mPa·s may be discharged from a plurality of nozzles 34A.

[0094] In this case, for example, as shown in Figure 5, the ink stored in the tank 70 may be heated by the heater 75. The heater 75 is fixed to the inner surface of the tank 70. In this case, the heater 35 may be omitted.

[0095] Examples 1 to 5 and Comparative Examples 1 to 10 of this disclosure are shown below. The storage modulus, viscosity, and viscosity difference of the inks in Examples 1 to 5 and Comparative Examples 1 to 10 were measured by the following methods.

[0096] (Measurement Method of Storage Modulus) The storage modulus was measured using a TriPAV piezoelectric high-frequency rheometer manufactured by Trijet Limited. Specifically, 100 μL of ink was dropped between two plates in an atmosphere of 25°C, and the dropped ink was sandwiched between the two plates. The gap between the two plates when the ink was sandwiched was 15 μm. Next, one of the plates was vibrated at 1000 Hz using a piezo actuator with a lock-in amplifier. Then, the piezoelectric excitation of the lower plate and the overall response were detected by a passive piezoelectric sensor. Finally, the storage modulus was calculated by analyzing the change in response amplitude and phase when ink was dropped and when ink was not dropped.

[0097] (Method for measuring ink viscosity) The viscosity of the inks in Examples 1 to 5 and Comparative Examples 1 to 10 was measured using a vibrating viscometer set to measurement condition 1. Measurement condition 1 is an atmosphere of 25°C and a vibrator frequency of 100 Hz.

[0098] (Method for measuring the viscosity difference of inks) The viscosity of the inks of Examples 1 to 5 and Comparative Examples 1 to 10 was measured using a vibrating viscometer set to measurement condition 2. Measurement condition 2 was an atmosphere of 25°C and a vibrator frequency of 1000 Hz. The viscosity difference of the inks was calculated by subtracting the viscosity measured by the vibrating viscometer set to measurement condition 2 from the viscosity measured by the vibrating viscometer set to measurement condition 1.

[0099] (Example 1) The ink contains 9.5% by weight of resin fine particles and 0.5% by weight of resin-dispersed pigment as a water-dispersible resin. Takelac WS-5000 (Tg: 65°C) manufactured by Mitsui Chemicals, Inc. was used as the resin fine particles. The ink contains 30.0% by weight of glycerin as an organic solvent. The ink contains 1.0% by weight of a surfactant. The ink contains ultrapure water as the remainder. The storage modulus of the ink is less than 0.1 Pa. The viscosity of the ink is 4.1 mPa·s. The viscosity difference of the ink is 0.3 mPa·s. The resin fine particles contained in Takelac WS-5000 were blended to be 9.5% by weight of the total amount of ink. The 0.5% by weight of resin-dispersed pigment was obtained by the following method 1. A mixture was obtained by adding pure water to 20% by mass of pigment (carbon black) and 7% by mass of sodium hydroxide neutralized styrene-acrylic acid copolymer (acid value 175 mg KOH / g, molecular weight 10000) to make a total of 100% by mass and stirring. This mixture was placed in a wet sand mill packed with 0.3 mm diameter zirconia beads and dispersed for 6 hours. After that, the zirconia beads were removed with a separator and the mixture was filtered through a 3.0 μm pore size cellulose acetate filter to obtain pigment dispersion A. The pigment dispersion A was then formulated so that the resin-dispersed pigment contained in pigment dispersion A was 0.5% by weight of the total ink amount. Styrene-acrylic acid copolymer is a water-soluble polymer commonly used as a dispersant for pigments.

[0100] (Example 2) The ink contains 7.0% by weight of resin fine particles and 3.0% by weight of resin-dispersed pigment as a water-dispersible resin. As the resin fine particles, Joncryl 537 (Tg: 44°C) manufactured by BASF Co., Ltd. was used. The ink contains 45.0% by weight of glycerin as an organic solvent. The ink contains 1.0% by weight of a surfactant. The ink contains ultrapure water as the remainder. The storage modulus of the ink is less than 0.1 Pa. The viscosity of the ink is 11.8 mPa·s. The viscosity difference of the ink is 0.3 mPa·s. The resin fine particles contained in Joncryl 537 were blended to be 7.0% by weight of the total ink amount. In addition, the resin-dispersed pigment contained in pigment dispersion A obtained by Method 1 above was blended to be 3.0% by weight of the total ink amount.

[0101] (Example 3) The ink does not contain resin fine particles as a water-dispersible resin. The ink contains 10.0% by weight of resin-dispersed pigment as a water-dispersible resin. The ink contains 30.0% by weight of glycerin as an organic solvent. The ink contains 1.0% by weight of surfactant. The ink contains ultrapure water as the remainder. The storage modulus of the ink is less than 0.1 Pa. The viscosity of the ink is 10.6 mPa·s. The viscosity difference of the ink is 0.2 mPa·s. The resin-dispersed pigment contained in pigment dispersion A obtained by Method 1 above was formulated to be 10.0% by weight of the total amount of ink.

[0102] (Example 4) The ink contains 14.5% by weight of resin fine particles and 0.5% by weight of resin-dispersed pigment as a water-dispersible resin. As the resin fine particles, "Movinyl® 6969D" (Tg: 71℃) manufactured by Japan Coating Resin Co., Ltd. was used. The ink contains 40.0% by weight of glycerin as an organic solvent. The ink contains 1.0% by weight of a surfactant. The ink contains ultrapure water as the remainder. The storage modulus of the ink is 0.4 Pa. The viscosity of the ink is 9.5 mPa·s. The viscosity difference of the ink is 0.3 mPa·s. The resin fine particles contained in Movinyl 6969D were blended to be 14.5% by weight of the total amount of ink. In addition, the resin-dispersed pigment contained in pigment dispersion A obtained by Method 1 above was blended to be 0.5% by weight of the total amount of ink.

[0103] (Example 5) The ink contains 2.5% by weight of resin fine particles and 0.5% by weight of resin-dispersed pigment as a water-dispersible resin. As the resin fine particles, "Movinyl® 6969D" (Tg: 71℃) manufactured by Japan Coating Resin Co., Ltd. was used. The ink contains 50.0% by weight of glycerin as an organic solvent. The ink contains 1.0% by weight of a surfactant. The ink contains ultrapure water as the remainder. The storage modulus of the ink is less than 0.1 Pa. The viscosity of the ink is 9.9 mPa·s. The viscosity difference of the ink is 0.1 mPa·s. The resin fine particles contained in Movinyl 6969D were blended to be 2.5% by weight of the total amount of ink. In addition, the resin-dispersed pigment contained in pigment dispersion A obtained by Method 1 above was blended to be 0.5% by weight of the total amount of ink.

[0104] (Comparative Example 1) The ink does not contain resin fine particles as a water-dispersible resin. The ink contains 0.5% by weight of resin-dispersed pigment as a water-dispersible resin. The ink contains 59.5% by weight of glycerin as an organic solvent. The ink contains 1.0% by weight of surfactant. The ink contains ultrapure water as the remainder. The storage modulus of the ink is less than 0.1 Pa. The viscosity of the ink is 9.9 mPa·s. The viscosity difference of the ink is 0.1 mPa·s. This was obtained by formulating the pigment dispersion A obtained by Method 1 above so that the resin-dispersed pigment contained in it is 0.5% by weight of the total amount of ink.

[0105] (Comparative Example 2) Comparative Example 2 differs from Comparative Example 1 in that it contains 9.5% by weight of resin fine particles as a water-dispersible resin and 30.0% by weight of glycerin as an organic solvent. The content of other ink components is the same as in Comparative Example 1. Takelac® W-6110 (Tg: -20℃) manufactured by Mitsui Chemicals, Inc. was used as the resin fine particles. The storage modulus of the ink is 0.9 Pa. The viscosity of the ink is 5.2 mPa·s. The viscosity difference of the ink is 0.5 mPa·s. The resin fine particles contained in Takelac W-6110 were blended to be 9.5% by weight of the total amount of ink. In addition, the resin-dispersed pigment contained in pigment dispersion A obtained by the above method 1 was blended to be 0.5% by weight of the total amount of ink.

[0106] (Comparative Example 3) Comparative Example 3 differs from Comparative Example 2 in that the resin fine particles were obtained by the following method 2. The content of the ink components is the same as in Comparative Example 2. The resin fine particles were obtained by reacting glycols with polyisocyanate. During the above synthesis, the acid value of the resin fine particles was controlled by adjusting the mixing ratio of each composition and functional groups such as carboxyl groups and amino groups. The acid value of the resin fine particles was measured according to JIS K2501 and was found to be 48 mgKOH / g. The Tg of the resin fine particles is 70°C. The resin fine particles obtained by the above method 2 were blended to be 9.5% by weight of the total amount of ink. The storage modulus of the ink is 1.0 Pa. The viscosity of the ink is 7.5 mPa·s. The viscosity difference of the ink is 0.4 mPa·s.

[0107] (Comparative Example 4) Comparative Example 4 differs from Comparative Example 2 in that Takelac® W-6061 (Tg: 25°C) manufactured by Mitsui Chemicals, Inc. was used as the resin fine particles. The content of the ink components is the same as in Comparative Example 2. The storage modulus of the ink is 2.1 Pa. The viscosity of the ink is 7.3 mPa·s. The viscosity difference of the ink is 0.8 mPa·s. The resin fine particles contained in Takelac W-6061 were blended to be 9.5% by weight of the total amount of ink. In addition, the resin dispersed pigment contained in pigment dispersion A obtained by the above method 1 was blended to be 0.5% by weight of the total amount of ink.

[0108] (Comparative Example 5) Comparative Example 5 differs from Comparative Example 2 in that "Movinyl® 6775" (Tg: 5℃) manufactured by Japan Coating Resin Co., Ltd. was used as the resin fine particles. The ink component content is the same as in Comparative Example 2. The storage modulus of the ink is 5.6 Pa. The viscosity of the ink is 13.0 mPa·s. The viscosity difference of the ink is 3.0 mPa·s. The resin fine particles contained in Movinyl 6775 were blended to be 9.5% by weight of the total amount of ink. In addition, the resin dispersed pigment contained in pigment dispersion A obtained by Method 1 above was blended to be 0.5% by weight of the total amount of ink.

[0109] (Comparative Example 6) Comparative Example 6 differs from Comparative Example 2 in that "Takelac® W-5030" (Tg: 85°C) was used as the resin fine particles. The content of the ink components is the same as in Comparative Example 2. The storage modulus of the ink is less than 0.1 Pa. The viscosity of the ink is 2.8 mPa·s. The viscosity difference of the ink is 0.1 mPa·s. The resin fine particles contained in Takelac W-5030 were blended to be 9.5% by weight of the total amount of ink. In addition, the resin dispersed pigment contained in pigment dispersion A obtained by the above method 1 was blended to be 0.5% by weight of the total amount of ink.

[0110] (Comparative Example 7) Comparative Example 7 differs from Comparative Example 2 in that it uses "Movinyl® 6969D" (Tg: 71°C) manufactured by Japan Coating Resin Co., Ltd. as the resin fine particles. Comparative Example 7 also differs from Comparative Example 2 in that it contains 53.0% by weight of glycerin as the organic solvent. The content of other ink components is the same as in Comparative Example 2. The storage modulus of the ink is less than 0.1 Pa. The viscosity difference of the ink is 0.2 mPa·s. The viscosity of the ink is 14.7 mPa·s. The resin fine particles contained in Movinyl 6969D were blended to be 9.5% by weight of the total amount of ink. Furthermore, the resin dispersed pigment contained in pigment dispersion A obtained by the above method 1 was blended to be 0.5% by weight of the total amount of ink.

[0111] (Comparative Example 8) Comparative Example 8 differs from Comparative Example 2 in that it contains 1.5% by weight of resin fine particles as a water-dispersible resin. Comparative Example 8 differs from Comparative Example 2 in that "Movinyl® 6969D" (Tg: 71°C) manufactured by Japan Coating Resin Co., Ltd. was used as the resin fine particles. Comparative Example 8 differs from Comparative Example 2 in that it contains 50.0% by weight of glycerin as an organic solvent. The content of other ink components is the same as in Comparative Example 2. The storage modulus of the ink is less than 0.1 Pa. The viscosity of the ink is 6.2 mPa·s. The viscosity difference of the ink is 0.2 mPa·s. The resin fine particles contained in Movinyl 6969D were blended to be 1.5% by weight of the total amount of ink. In addition, the resin-dispersed pigment contained in pigment dispersion A obtained by the above method 1 was blended to be 0.5% by weight of the total amount of ink.

[0112] (Comparative Example 9) Comparative Example 9 differs from Comparative Example 2 in that it contains 15.5% by weight of resin fine particles as a water-dispersible resin. Comparative Example 9 differs from Comparative Example 2 in that "Movinyl® 6969D" (Tg: 71°C) manufactured by Japan Coating Resin Co., Ltd. was used as the resin fine particles. Comparative Example 9 differs from Comparative Example 2 in that it contains 40.0% by weight of glycerin as an organic solvent. The content of other ink components is the same as in Comparative Example 2. The storage modulus of the ink is 0.6. The viscosity of the ink is 10.5 mPa·s. The viscosity difference of the ink is 0.3 mPa·s. The resin fine particles contained in Movinyl 6969D were blended to be 15.5% by weight of the total amount of ink. In addition, the resin-dispersed pigment contained in pigment dispersion A obtained by the above method 1 was blended to be 0.5% by weight of the total amount of ink.

[0113] (Comparative Example 10) Comparative Example 10 differs from Comparative Example 2 in that it does not contain resin fine particles as a water-dispersible resin and contains 10.0% by weight of resin-dispersed pigment as a water-dispersible resin. Comparative Example 10 also differs from Comparative Example 2 in that the resin-dispersed pigment was obtained by the following method 3. The content of other ink components is the same as in Comparative Example 2. The storage modulus of the ink is 0.7 Pa. The viscosity of the ink is 6.9 mPa·s. The viscosity difference of the ink is 0.8 mPa·s. The 10.0% by weight of resin-dispersed pigment was obtained by the following method 3. 20% by mass of pigment (C.I. Pigment Blue 15:3) and 7% by mass of sodium hydroxide neutralized styrene-acrylic acid copolymer (acid value 50 mg KOH / g, molecular weight 10000) were mixed with pure water to make a total of 100% by mass, and the mixture was stirred to obtain a mixture. This mixture was placed in a wet sand mill filled with 0.3 mm diameter zirconia beads and dispersed for 6 hours. Afterward, the zirconia beads were removed using a separator, and the mixture was filtered through a 3.0 μm pore size cellulose acetate filter to obtain pigment dispersion B. The resin-dispersed pigment in pigment dispersion B was then formulated to be 10.0% by weight of the total ink volume. Note that styrene-acrylic acid copolymer is a water-soluble polymer commonly used as a pigment dispersant.

[0114] The high-speed printing stability and fixation of Examples 1 to 5 and Comparative Examples 1 to 10 were tested using the following method.

[0115] [High-Speed ​​Printing Stability Test] High-speed printing stability was evaluated according to the following criteria. Pinch-off refers to the state where, when ink is continuously ejected from the nozzle, the previous ejection is completed when the next ejection begins. Ejection completion means that when the ink is ejected from the nozzle, the ink column has completely detached from the nozzle. In other words, ejection completion means that pinch-off has occurred. A: Pinch-off occurs even when the piezoelectric element repeatedly ejects ink from the nozzle at a driving frequency of 62.5 kHz. B: Pinch-off occurs when the piezoelectric element repeatedly ejects ink from the nozzle at a driving frequency of 60.0 kHz. C: Pinch-off does not occur even when the piezoelectric element repeatedly ejects ink from the nozzle at a driving frequency of 60.0 kHz.

[0116] The process of liquid droplets being ejected from the nozzle was captured using a strobe light, and by visually examining the frame-by-frame images captured using the strobe, it was determined whether or not pinch-off was being used.

[0117] [Fixage Test] A drawdown was performed on a 10 cm x 10 cm square sheet to achieve an ink adhesion rate of 1 mg / cm². The adhesion rate was controlled by adjusting the thickness of the drawdown. The sheet used was Art Coat Paper Tack manufactured by Oji Tack Co., Ltd. Afterwards, the sheet was placed in a constant-temperature dryer and dried at 100°C for 30 seconds. A DX402 low-temperature dryer manufactured by Yamato Scientific Co., Ltd. was used.

[0118] Abrasion tests were conducted on inks dried in a low-temperature dryer using a Japan Society for the Promotion of Science (JSPS) type friction fastness tester. The JSPS type friction fastness tester used was the AB-301 manufactured by Tester Sangyo Co., Ltd. In the abrasion test, the ink on the sheet was rubbed 10 times back and forth with a cloth under a load of 200g. The adhesion was visually evaluated according to the following evaluation criteria: A: The area of ​​ink abrasion is 10% or less. B: The area of ​​ink abrasion is greater than 10% and 50% or less. C: The area of ​​ink abrasion is greater than 50% and 80% or less. D: The area of ​​ink abrasion is greater than 80%.

[0119]

[0120] [High-Speed ​​Printing Stability Evaluation] As shown in Table 1, Examples 1 to 5 all received a rating of "B" or higher, while Comparative Examples 2 to 5, 9, and 10 all received a rating of "C". The storage modulus of the inks in Examples 1 to 5 was 0.4 Pa or less, while the storage modulus of the inks in Comparative Examples 2 to 5, 9, and 10 were all 0.6 Pa or higher. Thus, it is thought that the storage modulus of the inks in Comparative Examples 2 to 5, 9, and 10 was higher than that of Examples 1 to 5. From this, it can be seen that if the storage modulus of the ink is less than 0.5 Pa, high-speed printing stability is good.

[0121] Furthermore, comparing Examples 1 to 3 and 5 with Example 4 and Comparative Example 9, it can be seen that the lower the storage modulus, the better the high-speed printing stability. In other words, it is thought that the lower the storage modulus, the shorter the time it takes for the ink column to completely break off from the nozzle when the ink is ejected from the nozzle. From this, it can be inferred that if the storage modulus of the ink is less than 0.5 Pa, high-speed printing stability will be good even if the piezoelectric element repeatedly ejects ink from the nozzle at a driving frequency of 60.0 kHz or higher.

[0122] Furthermore, while the viscosity difference of the inks in Examples 1 to 5 was 0.3 mPa·s or less, the viscosity difference of the inks in Comparative Examples 2 to 5 and 10 was 0.4 mPa·s or more. From this, it can be seen that high-speed printing stability is improved when the viscosity difference of the inks is 0.3 mPa·s or less.

[0123] On the other hand, the storage modulus of Comparative Examples 6 and 7 was low, both less than 0.1 Pa. However, Comparative Examples 6 and 7 both received a "C" rating. This is likely because the viscosity of the ink in Comparative Example 6 was 2.8 mPa·s, which was lower than the viscosity of the inks in Examples 1 to 5. The lower the viscosity of the ink, the easier it is for the ink meniscus to follow the ink column when it breaks apart. As a result, Comparative Example 6 received a "C" rating, which is likely because the time it took for the ink column to completely break apart from the nozzle after the ink was ejected increased.

[0124] On the other hand, the reason why Comparative Example 7 received a "C" rating is likely because the viscosity of the ink in Comparative Example 7 was 14.7 mPa·s, which was higher than the viscosity of the inks in Examples 1 to 5. In other words, it is thought that the time it took for the ink column to completely break off from the nozzle when the ink was ejected was longer. From the above, it can be seen that high-speed printing stability improves when the viscosity of the ink is within the range of 3.5 mPa·s to 12 mPa·s.

[0125] Examples 1 to 5 all received a rating of "B" or higher, which was better than Comparative Example 9. This is likely because, in Examples 1 to 5, the total content of resin fine particles and resin-dispersed pigment as the water-dispersible resin was low, at 15.0% by weight or less. On the other hand, in Comparative Example 9, the total content of resin fine particles and resin-dispersed pigment as the water-dispersible resin was high, at 16.0% by weight. From this, it can be seen that if the total content of resin fine particles and resin-dispersed pigment as the water-dispersible resin is 15.0% by weight or less, the high-speed printing stability will improve.

[0126] Example 4 received a rating of "B," which is worse than Examples 1 through 3 and 5. This is likely because the storage modulus of the ink in Example 4 was 0.4 Pa, which is higher than that of Examples 1 through 3 and 5. Furthermore, in Example 4, the total content of resin fine particles and resin-dispersed pigment as water-dispersible resin was 15.0% by weight. Therefore, it is also possible that the higher content of water-dispersible resin in Example 4 compared to Examples 1 through 3 and 5 contributed to the lower rating.

[0127] Furthermore, comparing Examples 1 to 3 with Example 4 and Comparative Example 9, it can be seen that the storage modulus of the ink tends to increase as the water-dispersible resin content increases. From this, it can be seen that high-speed printing stability improves when the water-dispersible resin content is 15.0% by weight or less. On the other hand, the water-dispersible resin content of Example 1 was the same as that of Comparative Examples 2 to 4. However, the storage modulus of Example 1 was lower than that of Comparative Examples 2 to 4. This is thought to be because different types of resin microparticles were used as the water-dispersible resin. From this, it can be seen that it is important to select resin microparticles so that the storage modulus of the ink is less than 0.5 Pa.

[0128] [Evaluation of Fixation] As shown in Table 1, all of Examples 1 to 5 received a rating of "B" or higher, while Comparative Examples 1 and 8 both received a rating of "C" or lower. This is thought to be because in Examples 1 to 5, the total content of resin fine particles and resin-dispersed pigments as the water-dispersible resin was high, at 3.0% by weight or more. On the other hand, in Comparative Examples 1 and 8, the total content of resin fine particles and resin-dispersed pigments as the water-dispersible resin was low, at 2.0% by weight or less. From this, it can be seen that if the total content of resin fine particles and resin-dispersed pigments as the water-dispersible resin is 3.0% by weight or more, the fixation will be good.

[0129] Examples 3 and 5 received worse evaluations than Examples 1, 2, and 5. This is likely because the resin microparticle content in Examples 3 and 5 was lower than that in Examples 1, 2, and 5.

[0130] 34...Print head 34A...Nozzle 91...Piezoelectric element

Claims

1. A recording method comprising a recording step of ejecting an inkjet ink containing water and a water-dispersible resin dispersed in water as a dispersion medium from the nozzles of a print head, wherein the storage modulus of the inkjet ink at 1000 Hz is less than 0.5 Pa, the weight percentage of the water-dispersible resin relative to the total amount of ink is 3% by weight or more, the viscosity of the inkjet ink is in the range of 3.5 mPa·s to 12 mPa·s, the print head has a piezoelectric element that is driven in accordance with an ejection signal and ejects the inkjet ink from the nozzles, and in the recording step, the piezoelectric element repeatedly ejects the inkjet ink at a driving frequency of 60 kHz or higher.

2. The recording method according to claim 1, wherein the difference between the viscosity of the inkjet ink measured by a vibratory viscometer with a vibrator frequency set to 100 Hz and the viscosity of the inkjet ink measured by a vibratory viscometer with a vibrator frequency set to 1000 Hz is 0.3 mPa·s or less.

3. The recording method according to claim 1, further comprising resin fine particles that disperse in the water to form an emulsion.

4. The recording method according to claim 3, wherein the above-mentioned water-dispersible resin comprises a resin-dispersed pigment comprising a pigment and a pigment-dispersing resin for dispersing the pigment in the water.

5. The recording method according to claim 1, wherein the weight percentage of the above-mentioned water-dispersible resin relative to the total amount of ink is 15% by weight or less.

6. The recording method according to claim 5, wherein, in the recording step described above, the inkjet ink is ejected from the nozzle into a low-penetration medium in which the amount of water absorbed from the start of contact in the Bristow method to 15 msec is 10 mL / m2 or less.

7. The recording method according to claim 6, wherein the low-penetration medium is one of coated paper, plastic film, synthetic paper, or coated cardboard.

8. The recording method according to claim 6, further comprising a heating step of heating the low-penetration medium, the inkjet ink adhering to the low-penetration medium, or the low-penetration medium and the inkjet ink adhering to the low-penetration medium at a temperature 20°C or higher than the glass transition temperature of the water-dispersible resin, after the recording step described above.

9. The recording method according to claim 8, wherein, in the recording step described above, the inkjet ink is heated so that the viscosity of the inkjet ink becomes within the range of 3.5 mPa·s to 12 mPa·s, and the inkjet ink is discharged from the nozzle.

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