JP2012183798A - Liquid ejection method, liquid ejection device, and image formed material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such the problem that curling after recording can not be sufficiently suppressed due to attachment of a large amount of ink onto plain paper when performing high-speed printing of photograph, graphic or the like onto the plain paper by using, for example, an inkjet recording apparatus for sheet of paper according to the conventional inkjet recording method.SOLUTION: The heater 41 of the liquid ejection device 1 dries a first surface of a paper sheet to have a predetermined difference between a moisture content on the first surface of the paper sheet and a moisture content on the second surface of the paper sheet. Further, an ejector 73 ejects and attaches aqueous liquid to the first surface of the dried paper sheet. Thereby, such an effect that occurrence of back curl just after the recording can be reduced is obtained.

Description

  The present invention relates to a liquid ejection method for ejecting and attaching an aqueous liquid onto a sheet.

  In recent years, an ink jet recording method that forms an image by ejecting ink onto a recording medium has become widespread. In particular, the ink jet recording method for recording by discharging water-based ink onto plain paper has an advantage that a high-quality recorded matter can be easily obtained. Further, along with the widespread use of an ink jet recording apparatus equipped with a line head instead of a serial head, it has become possible to perform high speed printing using an ink jet recording method.

  However, when recording photographs or drawings on plain paper using water-based ink, the amount of ink adhering increases, resulting in a phenomenon that the recorded matter is back curled (the recording medium warps on the side opposite to the recording surface). ). When the recorded material is back-curled, there are problems such as poor conveyance of the recording medium in the ink jet recording apparatus, and difficulty in processing such as packing and binding of the recorded material. In view of this, there has been a demand for an ink jet recording method with little back curl even when recording is performed by discharging aqueous ink onto plain paper.

  In recent years, alcohol is applied to paper prior to recording with ink, and the paper is substantially dried at the recording position, and then an image is formed with ink to suppress curling of the recorded paper. Has been proposed (Patent Document 1). According to this proposed method, the hydroxyl group of the alcohol liquid is bonded to the hydroxyl group present at the bonding point by hydrogen bonding between the cellulose fibers, so that even if water comes later, the water molecule is excluded by the hydrophobic group portion of the alcohol liquid. Since the bonding point between the fibers cannot be reached, it is difficult for the bonding point to move between the fibers in the process of drying the paper, and curling of the paper is suppressed.

  However, with this proposed method, for example, when a photograph or a figure is printed at high speed on plain paper using a single-sheet ink jet recording apparatus, a large amount of ink adheres to the plain paper, thereby preventing back curl after recording. There was a problem that it could not be sufficiently suppressed.

  In order to solve the above-mentioned problem, the invention according to claim 1 is a liquid ejection method for ejecting and adhering an aqueous liquid onto a sheet, wherein the first surface of the sheet is dried and the first surface of the sheet is dried. A drying step for providing a predetermined amount of difference between the moisture content on the surface and the moisture content on the second surface, and a ejection step for ejecting and adhering the aqueous liquid to the first surface of the paper dried in the drying step. And a liquid discharge method characterized by comprising:

  The invention according to claim 2 is the liquid ejection method according to claim 1, wherein in the drying step, the moisture front / back difference represented by the formula (1) is set to 20% or more.

  The invention according to claim 3 is the liquid ejection method according to claim 1 or 2, wherein, in the drying step, the first surface of the sheet is heated and the second surface is cooled. .

  The invention according to claim 4 has a calculation step of calculating a printing rate when discharging the aqueous liquid onto the paper in the discharging step, and based on the printing rate calculated in the calculation step in the drying step. The liquid discharge method according to claim 1, wherein the first surface of the sheet is dried.

  The invention according to claim 5 has a measuring step of measuring the moisture content of the first surface and the moisture content of the second surface of the paper dried in the drying step, and the measuring step includes the measuring step. When the difference between the moisture content of the first surface and the moisture content of the second surface, measured in step 1, is greater than a predetermined value, the aqueous liquid is ejected and adhered to the first surface of the paper. The liquid discharge method according to claim 1, wherein:

  The invention according to claim 6 is characterized in that, in the drying step, the first surface of the paper is dried based on the moisture content measured in the measurement step. It is a liquid discharge method of description.

  The invention according to claim 7 is characterized in that, in the heating step, the first surface of the paper is heated using a heated gas. It is.

  The invention according to claim 8 is characterized in that, in the cooling step, the second surface of the sheet is cooled using a cooled liquid, and the liquid ejection method according to any one of claims 3 to 7 It is.

  The invention according to claim 9 is a liquid ejection device for ejecting and adhering an aqueous liquid to a sheet, wherein the first surface of the sheet is dried, the moisture content of the first surface of the sheet, and the first A drying unit that provides a predetermined amount of difference in moisture content between the two surfaces, and a discharging unit that discharges and adheres the aqueous liquid to the first surface of the paper dried in the drying step. It is a liquid discharge apparatus.

  According to a tenth aspect of the invention, the aqueous liquid is an aqueous ink, and an image is formed by ejecting the aqueous ink onto a sheet by the liquid ejection method according to any one of the first to eighth aspects. Is an image formed product.

  According to the liquid ejection method of the present invention, the first surface of the paper is dried to provide a predetermined amount of difference between the moisture content of the first surface of the paper and the moisture content of the second surface of the paper. Further, an aqueous liquid is discharged and adhered to the first surface of the dried paper. As a result, it is possible to reduce the occurrence of back curl immediately after recording.

It is a schematic block diagram of the liquid discharge apparatus which concerns on one Embodiment of this invention. It is explanatory drawing which shows the correlation with a moisture content and IM-D value. It is a block diagram for demonstrating the control part of the liquid discharge apparatus of one Embodiment of this invention. It is a conceptual diagram which shows a preset temperature management table. It is a conceptual diagram which shows a moisture content calculation formula management table. It is a processing flow figure showing a processing method in a liquid discharge device concerning one embodiment of the present invention.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

<<< Configuration of Liquid Discharge Device >>>
FIG. 1 is a schematic configuration diagram of a liquid ejection apparatus according to an embodiment of the present invention. First, the configuration of the liquid ejection apparatus according to the present embodiment will be described with reference to FIG.

  In the present embodiment, the liquid ejecting apparatus 1 is an apparatus that ejects and attaches an aqueous liquid to a sheet. Here, “ejection” means to eject the liquid to the outside. That is, the ejection includes not only ejecting droplets by a nozzle but also ejecting a mist or foamy liquid by spraying. The “aqueous liquid” means a liquid containing water as a main component of a solvent or a dispersion medium. In the present embodiment, an ink jet recording apparatus as an example of a liquid ejection apparatus that ejects aqueous ink as an example of an aqueous liquid will be described.

  As shown in FIG. 1, the liquid ejection apparatus 1 includes a paper feeding unit 2, a heating unit 3, a cooling unit 4, a measurement unit 5, a transport unit 6, a ejection unit 7, a paper ejection unit 8, an operation unit 9, and A control unit 10 is provided. Hereinafter, the respective components of the liquid ejection apparatus 1 will be described in order.

  The paper feed unit 2 includes a paper feed tray 21, a drawing roller 22, and a paper feed roller 23 in order to supply paper to the transport path in the liquid ejection apparatus 1. The paper feed tray 21 is a tray for storing paper. The paper stored in the paper feed tray 21 is not particularly limited, and examples thereof include plain paper, glossy paper, special paper, and general-purpose printing paper. Of these, plain paper does not have a coating layer containing an inorganic filler, resin, or the like on its surface, and therefore is less stiff than glossy paper, special paper, general-purpose printing paper, and the like. For this reason, plain paper is a paper that easily causes back curl, but the occurrence of back curl can be reduced by using the liquid ejection device of this embodiment. The drawing roller 22 pulls out the sheets stored in the sheet feeding tray 21 one by one. The paper feed roller 23 feeds the paper drawn by the drawing roller 22 to the transport path in the liquid ejecting apparatus 1.

  The heating unit 3 includes a predetermined heating unit 31 as an example of a drying unit in order to dry the sheet by heating the upper surface (first surface) of the sheet fed by the sheet feeding unit 2. The heating unit 31 is a unit that heats the upper surface of the paper by bringing the heated gas or solid into contact with the first surface of the paper. Examples of the heat source of the heating unit 31 include a heating element such as nichrome and a medium such as water and oil. The degree of heating by the heating means 31 is controlled by the control unit 10 based on the set temperature received by the operation panel 9 or the measurement result by the measuring unit 5.

  Specific examples of the heating means 31 include a warm air heater and a heat roller. Of these, the warm air heater heats the heated gas (warm air) in contact with the first surface of the paper. Thereby, the warm air heater can not only vaporize the moisture on the paper surface but also easily remove the moisture vaporized because it is not in contact with the paper. In this case, since the difference between the moisture content of the first surface and the moisture content of the second surface can be increased, the warm air heater is preferably used.

  The cooling unit 4 includes a predetermined cooling unit 41 in order to prevent the second surface of the paper from being dried by cooling the lower surface (second surface) of the paper fed by the paper feeding unit 2. . The cooling means 41 is means for cooling the lower surface of the paper by bringing the cooled gas or solid into contact with the second surface of the paper. For this cooling, a thermoelectric element such as a Peltier element or a liquid such as water or antifreeze is used. The degree of cooling by the cooling means 41 is controlled by the control unit 10 based on the set temperature received by the operation panel 9 or the measurement result by the measuring unit 5.

  Although it does not specifically limit as the cooling means 41, A Peltier device cooling plate, a cooling roller, etc. are mentioned. Among these, a cooling roller that cools (cools) water using cooled water can be cooled while transporting paper. Thereby, the conveyance time is shortened, and the moisture on the second surface of the paper can be suppressed from being vaporized during the conveyance. Therefore, the cooling roller is preferably used.

  In the liquid ejecting apparatus 1 shown in FIG. 1, the heating unit 31 and the cooling unit 41 are provided at the same position on the sheet conveyance path, but the arrangement is not limited thereto. If it is possible to give a predetermined amount of difference between the moisture content on the first surface and the moisture content on the second surface of the paper, one of the heating means 31 and the cooling means 41 is replaced with the paper feed unit 2 and the measurement unit 4. May be arranged on the upstream side on the conveyance path between the two and the other may be arranged on the downstream side.

  In the present embodiment, the amount of water means the amount of water contained in the paper. In this case, the moisture amount is calculated, for example, by dividing the mass of moisture contained in the paper by the sum of the mass of the paper and the mass of moisture contained in the paper. Also, the difference in the predetermined amount of moisture is the amount of moisture on the first surface and the second surface of the paper before recording necessary for the degree of back curl immediately after recording to satisfy a predetermined standard. Means a difference. An example of the difference in moisture content is a moisture front / back difference represented by equation (1). Moreover, as a difference of the predetermined amount of moisture content, it can be 20% or more, for example. The range of the predetermined amount is not limited to this range, and can be set according to the external environment (temperature, humidity, etc.) and the type of paper when ejecting the water-based ink.

  Here, the reason why it is preferable that the moisture front / back difference of the paper before recording is 20% or more will be described. The inventors of the present invention have considered that the cause of back curl immediately after ink jet recording is due to a difference in moisture front and back caused by water-based ink adhering to the first surface of the paper. That is, the present inventors considered that when the water-based ink adheres to the first surface of the paper, the cellulose fibers on the first surface of the paper are loosened due to water wetting, so that the paper curls.

  Therefore, inkjet recording was performed on the first surface using various types of paper, and the moisture content of the paper before and after recording was measured with an infrared moisture meter. As a result, it was confirmed that the back curl at the four corners of the paper was 20 mm or more when the moisture front / back difference represented by the above formula (1) was 20% or more after recording. In addition, the first surface of the paper is dried in advance, and the moisture front / back difference before recording is set to 20% to 70%, so that the first surface is solid with water-based ink (attachment amount 200 mg to 400 mg / A4). Even when the film was formed, the difference between the moisture front and back of the paper immediately after recording was suppressed to less than 20%. That is, even when the amount of water-based ink attached is large, it was confirmed that the back curl can be prevented by setting the moisture front / back difference before recording to 20% to 70%. Note that the moisture content on the surface of the paper measured by an infrared moisture meter under an environmental condition of 23 ° C. and 50% Rh is 8 to 10% of the paper weight, and there is no significant difference depending on the paper. For this reason, it is considered that the above conditions can be applied to various types of paper.

  The measurement unit 5 includes a first moisture meter 51a that measures the moisture content of the first surface of the paper heated by the heating unit 31, and a second moisture meter 51b that measures the moisture content of the second surface of the paper. And. In the present embodiment, the “moisture meter 51” is used when an arbitrary moisture meter is shown among the moisture meters (51a, 51b).

  The moisture meter 51 is preferably a moisture meter 51 that can measure the moisture content of the first surface or the second surface of the paper in real time. Here, the real time means that the time until the paper heated by the heating means 31 or the paper cooled by the cooling means 41 passes through the measuring section 5 and reaches the discharge section 7 on the transport path is within 1 minute. It means the time that can be controlled. When the time to reach the discharge unit 7 exceeds 1 minute, the effect of suppressing the occurrence of curling may be reduced due to moisture absorption of the paper after heating or cooling.

  Although it does not specifically limit as the moisture meter 51 which can measure a moisture content in real time, The moisture meter which measures a moisture content by an infrared system is mentioned. Here, the principle of measuring the moisture content by the infrared method will be described. Water has the property of absorbing a specific wavelength of light (near infrared). The energy of light absorbed by water increases as the amount of water increases. An infrared moisture meter applies this physical phenomenon, and measures the amount of moisture from the reflection intensity (IM-D value) of near infrared rays applied to the substance.

  Typical wavelengths of near infrared rays absorbed by water include 1.2 μm, 1.45 μm, 1.94 μm, and the like. An infrared moisture meter can measure not only near-infrared rays of these wavelengths but also wavelengths adjacent to these wavelengths. Thereby, the S / N (signal-noise) ratio of the reflection intensity can be increased depending on the color and surface state of the substance.

  In addition, the IM-D value may vary depending on the substance even if the water content is the same. For example, plain papers with different surface states and colors may have different IM-D values even with the same moisture content. In this case, create a calibration curve (see Fig. 2) that shows the correlation between the moisture content measured by the absolute dry method and the measured IM-D value for each paper that has been classified according to characteristics such as the surface condition and color. You can calibrate it. Thereby, the moisture content can be obtained by comparing the IM-D value of a certain sheet with the calibration curve of the certain sheet.

  A commercially available product can be used as the moisture meter 51 for measuring the moisture content by the infrared method, and examples include IM-3SCV Model-1000 manufactured by Fuji Work. The sensor head of this moisture meter has heat resistance up to 150 ° C. Moreover, the response at the time of measurement of this moisture meter is 1 second or less. Therefore, it is possible to measure in real time the moisture content of the paper conveyed by this moisture meter.

  The transport unit 6 transports the paper whose moisture content has been measured by the measuring unit 5 to the paper discharge unit 8 via the discharge unit 7 and the transport belt 61, the driving roller 62, the driven roller 63, and the auxiliary roller 64. , 65. The conveyance belt 61 conveys the sheet in the direction of the paper discharge unit 8 on the conveyance path in accordance with the timing of the ink ejection operation of the ejection head 73. The conveyor belt 61 is stretched between the driving roller 62 and the driven roller 63 in a tensioned state, and moves in the conveying direction on the conveying path as the driving roller 62 rotates. The auxiliary rollers 64 and 65 suppress the upper surface of the paper transported on the transport belt 61.

  The ejection unit 7 includes a tank 71, a supply line 72, and an ejection head 73 in order to form an image by ejecting aqueous ink onto the paper conveyed by the conveyance unit 6. The tank 71 is a container that stores water-based ink of each color such as yellow, cyan, magenta, and black. The supply line 72 is a supply unit that supplies the water-based ink stored in the tank 71 to the ejection head 73.

  The discharge head 73 is a discharge unit that discharges by applying stimulation (energy) to the water-based ink supplied by the supply line 72 in order to form an image on a sheet. The energy applied to the ink is not particularly limited, and examples thereof include heat (temperature), pressure, vibration, and light. Of these, heat and pressure are preferably used. These may be used alone or in combination of two or more.

  As the discharge head 73, a known head including a liquid chamber portion, a fluid resistance portion, a diaphragm, a nozzle member, and the like is used. In this case, at least a part of these constituent elements may be formed of a material containing silicone or nickel. The diameter of the nozzle can be, for example, 30 μm or less, preferably 1 to 20 μm. Specific examples of the discharge head 73 include a piezoelectric head, a thermal head, and an electrostatic head. Further, even if the ejection head 73 is a serial head that records by passing a paper in a transport direction different from the scanning direction under the head that scans in a predetermined scanning direction, the paper is placed under the fixed head. May be a line head for recording by passing through. Among these, when a line head is used, since recording can be performed on a sheet in a short time, the time until the recorded matter is conveyed after recording is shortened. In this case, the recorded matter is transported in a state where moisture is not sufficiently vaporized. However, when the liquid ejection method of the present embodiment is used, the occurrence of back curl is reduced, which affects transportation. Hard to give.

  The paper discharge unit 8 includes an auxiliary roller 81, a paper discharge roller 82, and a paper discharge tray 83 for discharging the paper transported by the transport unit 6. The auxiliary roller 81 and the paper discharge roller 82 are devices for discharging the paper on which the image is formed to the paper discharge tray 83. The paper discharge tray is a tray for storing discharged paper.

  The operation unit 9 includes a display operation panel 91 in order to receive an operation input from the user. The display operation panel 91 serves as both a display panel that displays the operating status of the liquid ejection device 1 and notifies the user, and an operation panel that receives an operation input from the user.

  The control unit 10 controls the overall operation of the liquid ejection apparatus 1. For this reason, the control unit 10 includes a storage device such as a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), which will be described later.

<<< Hardware Configuration and Functional Configuration of Control Unit >>>
The hardware configuration and functional configuration of the control unit 10 of the liquid ejection apparatus 1 according to the present embodiment will be described with reference to FIG. FIG. 3 is a block diagram for explaining the control unit 10 of the liquid ejection apparatus 1 of the present embodiment.

  The control unit 10 of the liquid ejection apparatus 1 according to this embodiment includes a CPU 101 that controls the operation of the entire liquid ejection apparatus 1, a ROM 102 that stores a program for the liquid ejection apparatus, a RAM 103 that is used as a work area for the CPU 101, and an IM for each sheet. -Non-volatile memory (NVRAM) 104 that stores data (see FIG. 2) indicating the correlation between the D value and the moisture content and retains the data even while the power of the liquid ejection apparatus 1 is shut off, and various signal processing for image data To perform image processing such as rearrangement, or ASIC (Application Specific Integrated Circuit) 105 that processes input / output signals for controlling the entire liquid ejecting apparatus 1, and transmission / reception of data and signals to / from an external device such as a host computer. I / F (Interface) 106 and I / O (Input / Output) port 107 for inputting the measurement result of the moisture meter 51 A.

  Further, a set temperature management DB (Data Base) configured by a set temperature management table as shown in FIG. 4 is constructed in the storage area of the NVRAM 104 of the control unit 10. In the set temperature management table, the printing rate when the discharge head 73 discharges the water-based ink onto the paper, the set temperature of the heating unit 31, and the set temperature of the cooling unit 41 are managed in association with each other. Note that “<” in FIG. 4 means “below”. Further, “−” in Table 4 means that the temperature need not be set. The set temperature of the heating unit 31 and the set temperature of the cooling unit 41 can be added, deleted, and updated based on the input from the user received by the display operation panel 91.

  When setting the set temperature of the heating means 31 and the set temperature of the cooling means 41, it is preferable to set so that the moisture front / back difference expressed by the above equation (1) of the paper before recording is 20% or more. . The set temperature of the heating unit 31 is preferably 80 ° C. or higher and 300 ° C. or lower. If the set temperature of the heating means 31 is less than 80 ° C., the moisture front / back difference may not be within the above range, and if it exceeds 300 ° C., the paper may deteriorate. In addition, the set temperature of the cooling means 41 is preferably room temperature or lower, for example, 10 ° C. or lower. When the set temperature of the cooling means 31 is higher than room temperature, the moisture front / back difference may not be within the above range.

  In the storage area of the NVRAM 104 of the control unit 10, a water content calculation formula management DB configured by a water content calculation formula management table as shown in FIG. 5 is constructed. In the moisture amount calculation formula management table, a moisture amount calculation formula for calculating the moisture amount is associated and managed for each sheet. The moisture amount calculation formula can be added, deleted, and updated based on the input from the user received by the display operation panel 91.

  Moreover, the control part 10 of the liquid discharge apparatus 1 is implement | achieved by operate | moving by the command from CPU101 according to the program memorize | stored in ROM102, the heating control part 113, the cooling control part 114, the calculation part 115, conveyance A control unit 116 and a discharge control unit 117 are included.

  The heating control unit 113 controls the output of the heating unit 31 according to a command from the CPU 101 according to a program stored in the ROM 102. In this case, the heating control unit 113 controls the output of the heating unit 31 based on the input of the set temperature received by the display / operation panel 91. Further, the heating control unit 113 automatically controls the output of the heating unit 31 based on a printing rate calculated by a later-described discharge control unit 117 and a moisture amount calculated by the measurement unit 5.

  The cooling control unit 114 controls the output of the cooling unit 41 according to a command from the CPU 101 according to a program stored in the ROM 102. In this case, the cooling control unit 114 controls the output of the cooling unit 41 based on the input of the set temperature received by the display operation panel 91. In addition, the cooling control unit 114 automatically controls the output of the cooling unit 41 based on a printing rate calculated by a later-described discharge control unit 117 and a moisture amount calculated by the measurement unit 5.

  The calculation unit 115 calculates the amount of moisture based on the measurement result of the moisture meter 51 in accordance with a command from the CPU 101 according to a program stored in the ROM 102. In this case, the CPU 101 calculates the moisture amount using the measurement result of the moisture meter 51 received by the I / O port 107 and the moisture amount calculation formula acquired from the moisture amount calculation formula management table. Further, the calculation unit 115 calculates the difference between the moisture amount calculated from the measurement result of the moisture meter 51a and the moisture amount calculated from the measurement result of the moisture meter 51b.

  The conveyance control unit 116 is configured to output the drawing roller 22 and the sheet feeding roller 23 of the sheet feeding unit 2, the conveyance motor 66 of the conveyance unit 6, and the sheet discharging unit 8 according to a command from the CPU 101 according to a program stored in the ROM 102. The driving of the paper discharge roller 82 is controlled. In this case, the conveyance control unit 116 performs control to drive the drawing roller 22 and the paper supply roller 23 of the paper supply unit 2, so that the paper stored in the paper supply tray 21 is supplied. Further, when the conveyance control unit 116 performs control to drive the conveyance motor 66, the drive roller 62 rotates in conjunction with the conveyance belt 61 and moves. Thereby, the paper on the conveyance belt 61 is conveyed. Further, when the conveyance control unit 116 performs control to drive the paper discharge roller 82 of the paper discharge unit 8, the paper discharge roller 82 rotates and the paper on the conveyance path is discharged to the paper discharge tray 83.

  The ejection control unit 117 generates a drive waveform for driving and controlling the pressure generating unit of the ejection head 73 according to a command from the CPU 101 according to a program stored in the ROM 102, and performs control for ejecting ink. . In this case, the discharge control unit 117 performs image processing on the print data received by the I / F 106 by the ASIC 105 to create image data. Further, the discharge control unit 117 calculates the ratio (printing rate) of the area of the recording portion to the area of the entire sheet based on the created image data. Further, the ejection control unit 117 creates head drive information based on the image data and outputs it to the ejection head 73.

<<< Water-based ink >>>
Next, the water-based ink used in the liquid ejection method of this embodiment will be described. In the liquid ejection method of the present embodiment, although not particularly limited, it contains an aqueous dispersion of water-insoluble vinyl polymer particles containing a colorant, a water-soluble organic solvent, and water, and contains other components as necessary. A water-based ink is preferably used. Each component of the water-based ink will be described in order.

<Colorant>
As the colorant, a pigment is preferably used from the viewpoint of weather resistance, but a dye may be contained within a range in which the weather resistance is not deteriorated for the purpose of adjusting the color tone. There is no restriction | limiting in particular as a pigment, According to the objective, it selects suitably, For example, the inorganic pigment, organic pigment, etc. for black or color are used. These colorants may be used alone or in combination of two or more.

  The inorganic pigment is produced by a known method such as a contact method, a furnace method, a thermal method, in addition to titanium oxide and iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, and chrome yellow. Carbon black can be used.

  Examples of the organic pigment include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments). , Dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, quinofullerone pigments, etc.), dye chelates (eg basic dye chelates, acid dye chelates), nitro pigments, nitroso pigments, aniline black, etc. . Of these pigments, those having good affinity with water are particularly preferably used.

  Specific examples of pigments that are more preferably used in the above-mentioned pigments include black for carbon black (CI pigment black 7) such as furnace black, lamp black, acetylene black, channel black, or copper, iron. (CI pigment black 11), metals such as titanium oxide, and organic pigments such as aniline black (CI pigment black 1).

  Further, examples of color pigments include C.I. I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104 , 408, 109, 110, 117, 120, 128, 138, 150, 151, 153, 183, C.I. I. Pigment orange 5, 13, 16, 17, 36, 43, 51, C.I. I. Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48: 2, 48: 2 (Permanent Red 2B (Ca)), 48: 3, 48: 4, 49: 1, 52: 2, 53: 1, 57: 1 (Brilliant Carmine 6B), 60: 1, 63: 1, 63: 2, 64: 1, 81, 83, 88, 101 (Bengara), 104, 105, 106, 108 ( Cadmium red), 112, 114, 122 (quinacridone magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 185, 190, 193, 209, 219, C.I. I. Pigment violet 1 (rhodamine lake), 3, 5: 1, 16, 19, 23, 38, C.I. I. Pigment Blue 1, 2, 15, 15: 1, 15: 2, 15: 3 (phthalocyanine blue), 16, 17: 1, 56, 60, 63, C.I. I. Pigment green 1, 4, 7, 8, 10, 17, 18, 36, and the like.

  The content of the pigment in the aqueous ink is preferably 2 to 15% by mass, more preferably 3 to 10% by mass, and still more preferably 5 to 8% by mass in terms of solid content. When the content is less than 2% by mass, the color developability and image density of the recorded matter may be lowered. When the content exceeds 15% by mass, the water-based ink is thickened and the ejection stability is deteriorated. In some cases, it is also not economical.

<Water-insoluble vinyl polymer>
The water-insoluble vinyl polymer is obtained by polymerizing a monomer mixture containing a monomer represented by the general formula (1) (monomer A), a salt-forming group-containing monomer (monomer B), and a hydrophobic monomer (monomer C). It is done. These monomers may be used as a composition by mixing the required amounts of the respective monomers, or monomers other than the monomers A, B and C may be used additionally.

In the general formula (1), R ₁ is preferably a hydrogen atom or a methyl group from the viewpoint of polymerizability. R ₂ is an alkylene group having 2 to 8 carbon atoms or an alkylene group having 2 to 4 carbon atoms in which a hydrogen atom is substituted with a phenyl group, and an ethylene group, propylene group or butylene group having 2 to 4 carbon atoms is preferable. n is an average added mole number, and is a number of 2 to 30, but from the viewpoint of image density and storage stability, a number of 2 to 25 is preferable, a number of 2 to 15 is more preferable, and 2 to 10 is preferable. Numbers are particularly preferred. The n R _{2 s} may be the same or different, and when they are different, either block addition or random addition may be used. R ₃ is a linear or branched alkyl group having 2 to 30 carbon atoms, preferably an alkyl group having 2 to 22 carbon atoms from the viewpoint of high image density and good storage stability, and has 8 to 18 carbon atoms. An alkyl group is more preferable, and an octyl group, 2-ethylhexyl group, decyl group, dodecyl (lauryl) group, tetradodecyl (myristyl) group, hexadecyl (cetyl) group and octadecyl (stearyl) group are particularly preferable.

  As the monomer A, octoxypolyethylene glycol mono (meth) acrylate, octoxypoly (ethylene glycol / propylene glycol) mono (meth) acrylate, octoxypoly (ethylene glycol / butylene glycol) mono (meth) acrylate, lauroxypolyethylene glycol (meth) Examples include acrylate, lauroxy poly (ethylene glycol / propylene glycol) mono (meth) acrylate, stearoxy polyethylene glycol mono (meth) acrylate, stearoxy poly (ethylene glycol / propylene glycol) mono (meth) acrylate, and the like. These can be used alone or in admixture of two or more.

  The monomer A is obtained by a method in which an aliphatic alcohol terminal (—OH) is polymerized with an alkylene oxide, and the polymerized terminal group (—OH) is etherified. Specific examples of commercially available monomer A include Light Acrylate EA-C manufactured by Kyoeisha Chemical Co., Ltd., and 50 POEP-800B, PLE200, and PSE-400 manufactured by NOF Corporation.

  By using the monomer A, a water-based ink having a high image density and excellent storage stability can be obtained. This is presumably because the terminal alkyl group of monomer A tends to remain on the paper surface. Further, by using the monomer A, excellent dispersion stability can be imparted to the water-based ink.

  In addition, since the monomer A exhibits high compatibility with a specific water-soluble organic solvent, when the specific water-soluble organic solvent is contained in the ink, the ink that has reached an equilibrium state due to evaporation of water Even in the residue, dispersion stability can be imparted to the polymer particles.

  The content of the monomer A in the monomer mixture used for polymerizing the water-insoluble vinyl polymer is 3 to 25% by mass, preferably 5 to 20% by mass, from the viewpoint of image density and ink viscosity.

  In this embodiment, the salt-forming group-containing monomer (monomer B) refers to a monomer having a salt-forming group that forms a salt by a neutralization reaction. Examples of the salt-forming group-containing monomer suitably used in the present embodiment include an anionic monomer having an anion-generating group. This anion-generating group generates an anion in water, imparts dispersion stability to the polymer dispersion by electrostatic repulsion, and loses the electrostatic repulsive force due to pH change when aqueous ink adheres to the paper. Promotes pigment fixation. An anionic monomer can be used individually or in mixture of 2 or more types.

  Examples of the anionic monomer include one or more selected from an unsaturated carboxylic acid monomer, an unsaturated sulfonic acid monomer, and an unsaturated phosphoric acid monomer.

  Examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid. These can be used alone or in admixture of two or more.

  Examples of the unsaturated sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylic acid ester, bis- (3-sulfopropyl) -itaconic acid ester, and the like. . These can be used alone or in admixture of two or more.

  Examples of unsaturated phosphoric acid monomers include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxy Examples thereof include ethyl phosphate. These can be used alone or in admixture of two or more.

  Among the anionic monomers, unsaturated carboxylic acid monomers are preferable, and acrylic acid and methacrylic acid are more preferable from the viewpoint of image density and storage stability.

  The content of the monomer B in the monomer mixture used for polymerizing the water-insoluble vinyl polymer is 3 to 25% by mass, preferably 5 to 20% by mass, and more preferably 12 to 12% from the viewpoint of image density and storage stability. 14% by mass. When the content of the monomer B is less than 3% by mass, there are problems such as difficulty in dissolving in the basic substance and difficulty in coating the pigment.

  Examples of the monomer C suitably used in the present embodiment include a monomer represented by the general formula (2), a monomer represented by the general formula (3), and a macromer.

（式中、Ｒ_４は水素原子又はメチル基、Ｒ_５は炭素数１〜２２のアルキル基、炭素数６〜２２のアリール基、アルキルアリール基若しくはアリールアルキル基又は炭素数３〜２２の環式炭化水素基を示す。）

Wherein R ₄ is a hydrogen atom or a methyl group, R ₅ is an alkyl group having 1 to 22 carbon atoms, an aryl group having 6 to 22 carbon atoms, an alkylaryl group or an arylalkyl group, or a cyclic group having 3 to 22 carbon atoms. Indicates a hydrocarbon group.)

（式中、Ｒ_６は水素原子又はメチル基、Ｒ_７は置換基を有しても良いフェニル基、ビフェニル基、又はナフタレン基を示す。）

(In the formula, R ₆ represents a hydrogen atom or a methyl group, and R ₇ represents an optionally substituted phenyl group, biphenyl group, or naphthalene group.)

  These can be used alone or in admixture of two or more. Monomer C preferably contains one or more selected from aromatic ring-containing monomers and macromers from the viewpoint of image density and scratch resistance.

As the monomer having an alkyl group represented by the general formula (2), a monomer in which R ₄ is a methyl group is preferable, and methyl (meth) acrylate, ethyl (meth) acrylate, (iso) propyl (meth) acrylate, (iso Or tertiary) butyl (meth) acrylate, (iso) amyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (iso) octyl (meth) acrylate, (iso) decyl (meth) acrylate, (iso) dodecyl ( Examples include (meth) acrylates in which an ester moiety such as (meth) acrylate, (iso) stearyl (meth) acrylate, and behenyl (meth) acrylate is an alkyl group having 1 to 22 carbon atoms. These can be used in combination of two or more. In addition, (iso or tertiary) and (iso) mean both the case where these groups are present and the case where these groups are not present. When these groups are not present, they indicate normal. (Meth) acrylate means both methacrylate and acrylate. The same applies to the following.

  Examples of the monomer having an aryl group represented by the general formula (2) include benzyl (meth) acrylate and phenoxyethyl (meth) acrylate. These can be used alone or in admixture of two or more.

  The monomer having a cyclic hydrocarbon group represented by the general formula (2) is a monocyclic, bicyclic, or tricyclic or higher polycyclic (meth) acrylate having 3 or more carbon atoms. Specifically, as monocyclic (meth) acrylate having 3 or more carbon atoms, cyclopropyl (meth) acrylate, cyclobutyl (meth) acrylate, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) Examples include acrylate, cyclooctyl (meth) acrylate, cyclononyl (meth) acrylate, and cyclodecyl (meth) acrylate, and examples of bicyclic (meth) acrylate include isobornyl (meth) acrylate and norbornyl (meth) acrylate. Examples of the tricyclic (meth) acrylate include adamantyl (meth) acrylate. Among these, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, and adamantyl (meth) acrylate are preferable from the viewpoint of storage stability. These can be used in combination of two or more.

As the aromatic ring-containing monomer represented by the general formula (3), a monomer in which R ₆ is hydrogen or a methyl group is preferable. From the viewpoint of water resistance, styrene, vinyl naphthalene, α-methyl styrene, vinyl toluene, ethyl vinyl benzene And one or more selected from 4-vinylbiphenyl. Among these, one or more selected from styrene, α-methylstyrene, vinyl toluene, and vinyl naphthalene are more preferable from the viewpoint of image density and scratch resistance.

  Examples of the macromer include a macromer having a polymerizable functional group at one end and having a number average molecular weight of 400 to 500,000, more preferably 600 to 12,000. Specific examples of the macromer include a styrene macromer having a polymerizable functional group at one end, a silicone macromer having a polymerizable functional group at one end, a methyl methacrylate macromer having a polymerizable functional group at one end, Examples thereof include a styrene / acrylonitrile macromer having a polymerizable functional group, a butyl acrylate macromer having a polymerizable functional group at one end, and an isobutyl methacrylate macromer having a polymerizable functional group at one end. In these, since formation of the water-insoluble vinyl polymer particle containing a coloring agent is easy, the styrenic macromer which has a polymerizable functional group in one terminal is preferable.

  Examples of the styrenic macromer having a polymerizable functional group at one end include styrene homopolymers having a polymerizable functional group at one end, and copolymers of styrene having a polymerizable functional group at one end and other monomers. Can be mentioned. Among the styrenic macromers having a polymerizable functional group at one end, a styrenic macromer having an acryloyloxy group or a methacryloyloxy group as a polymerizable functional group at one end is preferable from the viewpoint of dispersibility.

  Examples of commercially available styrenic macromers include AS-6 (S), AN-6 (S), HS-6 (S) manufactured by Toa Gosei Co., Ltd., and the like. The number average molecular weight of the macromer is measured using polystyrene as a standard substance by gel chromatography using 1 mmol / L dodecyldimethylamine-containing chloroform as a solvent.

  The content of the monomer C in the monomer mixture used for polymerizing the water-insoluble vinyl polymer is 50 to 95% by mass, preferably 60 to 85% by mass, from the viewpoint of storage stability and water resistance.

  When an aromatic ring-containing monomer is used as the monomer C, the content of the aromatic ring-containing monomer in the monomer C is preferably 30 to 80% by mass, more preferably 35 to 75% by mass, from the viewpoint of scratch resistance and ink viscosity. %.

  When a macromer is used as the monomer C, the content of the macromer in the monomer C is preferably 3 to 40% by mass, more preferably 5 to 25% by mass, from the viewpoint of water resistance and scratch resistance.

  The water-insoluble vinyl polymer is produced by polymerizing the monomers A, B, and C by a known polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method. Among these polymerization methods, the solution polymerization method is preferable. The solvent used in the solution polymerization method is preferably a polar organic solvent. When the polar organic solvent is miscible with water, it can be used by mixing with water. Examples of the polar organic solvent include aliphatic alcohols having 1 to 3 carbon atoms such as methanol, ethanol and propanol; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate and the like. Among these, methanol, ethanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, or a mixed solution of these with water is preferable. If necessary, toluene may be used.

  In the polymerization, a radical polymerization initiator can be used. As radical polymerization initiators, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), dimethyl-2,2′-azobisbutyrate, 2,2 An azo compound such as' -azobis (2-methylbutyronitrile) and 1,1'-azobis (1-cyclohexanecarbonitrile) is preferred. Moreover, organic peroxides, such as t-butyl peroxy octoate, di-t-butyl peroxide, dibenzoyl oxide, can also be used. The amount of the polymerization initiator is preferably 0.001 to 5 mol, more preferably 0.01 to 2 mol, per mol of the monomer mixture.

  In the polymerization, a polymerization chain transfer agent may be further added. Specific examples of the polymerization chain transfer agent include mercaptans such as octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-tetradecyl mercaptan and 2-mercaptoethanol; xanthogen disulfides such as dimethylxanthogen disulfide and diisopropylxanthogen disulfide. ; Thiuram disulfides such as tetramethylthiuram disulfide and tetrabutylthiuram disulfide; halogenated hydrocarbons such as carbon tetrachloride and ethylene bromide; hydrocarbons such as pentaphenylethane; acrolein, methacrolein, allyl alcohol, 2- Ethylhexyl thioglycolate, terbinolene, α-terpinene, γ-terpinene, dipentene, α-methylstyrene dimer, 9,10-dihydroanthracene, , 4-dihydronaphthalene, indene, 1,4-cyclohexadiene unsaturated cyclic hydrocarbon compounds of a diene and the like; 2,5-unsaturated heterocyclic compounds dihydrofuran like, and the like. These polymerization chain transfer agents can be used alone or in admixture of two or more.

  Since the polymerization conditions of the monomer vary depending on the radical polymerization initiator, the monomer, the type of the solvent, and the like, it cannot be determined unconditionally. Usually, the polymerization temperature is preferably 30 to 100 ° C., more preferably 50 to 85 ° C., and the polymerization time is preferably 2 to 24 hours. The polymerization atmosphere is preferably an inert gas atmosphere such as nitrogen gas.

  After completion of the polymerization reaction, the produced water-insoluble vinyl polymer can be isolated from the reaction solution by a known method such as reprecipitation or solvent distillation. The obtained water-insoluble vinyl polymer can be purified by repeating reprecipitation or removing unreacted monomers by membrane separation, chromatographic methods, extraction methods, and the like.

  The weight average molecular weight of the water-insoluble vinyl polymer is preferably 3,000 to 300,000, more preferably 5,000 to 200,000, from the viewpoint of image density and ejection stability.

<Aqueous dispersion of water-insoluble vinyl polymer particles containing colorant>
As a method of obtaining an aqueous dispersion of water-insoluble vinyl polymer particles containing a pigment as a colorant, the above-mentioned water-insoluble vinyl polymer is dissolved in an organic solvent, and the pigment, water, neutralizing agent, and optionally surface active A method of adding an agent and kneading, then diluting with water as necessary, and distilling off the organic solvent to make an aqueous system is preferred.

  The amount of the pigment in the water-based ink is preferably 20 to 1200 parts by weight, more preferably 50 to 900 parts by weight with respect to 100 parts by weight of the water-insoluble vinyl polymer from the viewpoint of image density and ease of inclusion in the polymer particles. Parts, more preferably 65 to 600 parts by mass.

  As said organic solvent, an alcohol solvent, a ketone solvent, and an ether solvent are preferable, and these hydrophilic organic solvents are more preferable. Examples of the alcohol solvent include isopropanol, n-butanol, tertiary butanol, isobutanol, diacetone alcohol and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of the ether solvent include dibutyl ether, tetrahydrofuran, dioxane and the like. Of these solvents, acetone, methyl ethyl ketone and methyl isobutyl ketone are preferred. The organic solvent may be used in combination with toluene.

  A base is used as the neutralizing agent, and specific examples include tertiary amines such as trimethylamine and triethylamine, ammonia, sodium hydroxide, potassium hydroxide and the like. There is no particular limitation on the degree of neutralization. Usually, it is preferable that the obtained aqueous dispersion has neutral liquidity, for example, pH of 4 to 10.

  Depending on the type of the salt-forming group, the solubility in water at 25 ° C. of the water-insoluble vinyl polymer after neutralizing the salt-forming group with sodium hydroxide or acetic acid is 100%. To 10% by mass or less, preferably 5% by mass or less, more preferably 1% by mass or less.

  In this embodiment, the average particle diameter of the water-insoluble vinyl polymer particles containing the colorant in the aqueous dispersion and in the aqueous ink is preferably 0.01 to 0.00 from the viewpoint of prevention of nozzle clogging and storage stability. The thickness is 50 μm, more preferably 0.02 to 0.30 μm, still more preferably 0.04 to 0.20 μm.

<Water-soluble organic solvent>
Examples of the water-soluble organic solvent include polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, propylene carbonate, Ethylene carbonate is mentioned.

  The water-soluble organic solvent is compatible with the water-insoluble vinyl polymer particles containing the pigment to prevent the pigment from agglomerating even when the ink is evaporated for a long period of time and has excellent storage stability. Is granted. In addition, the water-soluble organic solvent imparts fluidity to the ink by retaining a large amount of moisture even when the ink is left open.

  In this case, by using a water-soluble organic solvent with a high equilibrium water content, even when the ink water evaporates and reaches an equilibrium state, the water-soluble organic solvent retains a large amount of water and the ink has an extremely high viscosity. The rise can be suppressed.

In the present embodiment, the water-soluble organic solvent having a high equilibrium moisture content is a water-soluble organic solvent (water-soluble organic solvent) having an equilibrium moisture content of 30 wt% or more, preferably 40 wt% or more in an environment having a temperature of 23 ° C. and a humidity of 80%. Solvent A) is meant. By using the water-soluble organic solvent A, the water-soluble organic solvent A can retain a large amount of water and prevent an increase in viscosity even when the water content of the ink evaporates and reaches a water balance. Equilibrium water content means that a mixture of water-soluble organic solvent and water is opened to air at a constant temperature and humidity, and the evaporation of water in the solution and the absorption of water in the ink into the ink are in an equilibrium state. Says the amount of water when it becomes. Specifically, the equilibrium water content is determined by using a saturated aqueous solution of potassium chloride, keeping the temperature and humidity in the desiccator at 23 ± 1 ° C. and 80 ± 3%, and weighing 1 g of each water-soluble organic solvent in the desiccator. The petri dish can be stored for a period until the mass change disappears, and can be obtained by the following formula.
Equilibrium water content (%) = {Moisture absorbed in organic solvent / (Amount of organic solvent + Moisture absorbed in organic solvent)} × 100

  The boiling point of the water-soluble organic solvent A is preferably 140 ° C. or higher, more preferably 250 ° C. or higher. If the boiling point of the water-soluble organic solvent A is 140 ° C. or higher, vaporization does not occur in a normal ink use environment, so that it is possible to prevent a decrease in water that can be retained by vaporization of the water-soluble organic solvent.

  From the above points, examples of the water-soluble organic solvent A preferably used in the present embodiment include polyhydric alcohols having an equilibrium water content in an environment of a temperature of 23 ° C. and a humidity of 80% of 30 wt% or more. Specific examples of such water-soluble organic solvent A include 1,2,3-butanetriol (bp175 ° C./33 hPa, 38 wt%), 1,2,4-butanetriol (bp190-191 ° C./24 hPa, 41 wt%). ), Glycerin (bp 290 ° C., 49 wt%), diglycerin (bp 270 ° C./20 hPa, 38 wt%), triethylene glycol (bp 285 ° C., 39 wt%), tetraethylene glycol (bp 324-330 ° C., 37 wt%), diethylene glycol (bp 245) C, 43 wt%), 1,3-butanediol (bp203-204 ° C, 35 wt%) and the like. Of these, glycerin and 1,3-butanediol are particularly preferably used for reasons such as lowering the viscosity when water is contained, and keeping the pigment dispersion stable without aggregation. When the water-soluble organic solvent A is used in an amount of 50 wt% or more of the total amount of the water-soluble organic solvent agent, it is preferable because it is excellent in securing ejection stability and preventing waste ink sticking in a maintenance device of the ink ejection device.

  In this embodiment, in addition to the water-soluble organic solvent A, the water-based ink can be used in combination with a water-soluble organic solvent (water-soluble organic solvent B) having an equilibrium water content of less than 30 wt% at 23 ° C. and 80%. Examples of the water-soluble organic solvent B include polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, propylene carbonate, and carbonic acid. Ethylene, other wetting agents, and the like.

  Specific examples of the polyhydric alcohols of the water-soluble organic solvent B include, for example, dipropylene glycol (bp 232 ° C), 1,5-pentanediol (bp 242 ° C), 3-methyl-1,3-butanediol (bp 203 ° C). ), Propylene glycol (bp 187 ° C.), 2-methyl-2,4-pentanediol (bp 197 ° C.), ethylene glycol (bp 196-198 ° C.), tripropylene glycol (bp 267 ° C.), hexylene glycol (bp 197 ° C.), polyethylene Glycol (viscous liquid to solid), polypropylene glycol (bp 187 ° C), 1,6-hexanediol (bp253-260 ° C), 1,2,6-hexanetriol (bp178 ° C), trimethylolethane (solid, mp199- 201 ° C), trimethylolpropane Solid, MP61 ° C.), and the like.

  Examples of polyhydric alcohol alkyl ethers include ethylene glycol monoethyl ether (bp 135 ° C.), ethylene glycol monobutyl ether (bp 171 ° C.), diethylene glycol monomethyl ether (bp 194 ° C.), diethylene glycol monoethyl ether (bp 197 ° C.), and diethylene glycol monobutyl ether. (Bp 231 ° C.), ethylene glycol mono-2-ethylhexyl ether (bp 229 ° C.), propylene glycol monoethyl ether (bp 132 ° C.) and the like. Examples of polyhydric alcohol aryl ethers include ethylene glycol monophenyl ether (bp 237 ° C.) and ethylene glycol monobenzyl ether.

  Examples of the nitrogen-containing heterocyclic compound include 2-pyrrolidone (bp 250 ° C., mp 25.5 ° C., 47-48 wt%), N-methyl-2-pyrrolidone (bp 202 ° C.), 1,3-dimethyl-2-imidazolide. Non (bp 226 ° C.), ε-caprolactam (bp 270 ° C.), γ-butyrolactone (bp 204-205 ° C.) and the like. Examples of amides include formamide (bp 210 ° C.), N-methylformamide (bp 199-201 ° C.), N, N-dimethylformamide (bp 153 ° C.), N, N-diethylformamide (bp 176-177 ° C.), and the like. It is done. Examples of amines include monoethanolamine (bp 170 ° C), diethanolamine (bp268 ° C), triethanolamine (bp360 ° C), N, N-dimethylmonoethanolamine (bp139 ° C), N-methyldiethanolamine (bp243 ° C). N-methylethanolamine (bp159 ° C.), N-phenylethanolamine (bp282-287 ° C), 3-aminopropyldiethylamine (bp169 ° C) and the like. Examples of the sulfur-containing compounds include dimethyl sulfoxide (bp 139 ° C.), sulfolane (bp 285 ° C.), thiodiglycol (bp 282 ° C.), and the like. Other solid wetting agents are preferably sugars.

Examples of saccharides include monosaccharides, disaccharides, oligosaccharides (including trisaccharides and tetrasaccharides), polysaccharides, and the like. Specific examples include glucose, mannose, fructose, ribose, xylose, arabinose, galactose, maltose, cellobiose, lactose, sucrose, trehalose, maltotriose, and the like. Here, the polysaccharide means a saccharide in a broad sense, and is used to include a substance that exists widely in nature such as α-cyclodextrin and cellulose. Examples of derivatives of these saccharides include saccharide reducing sugars (for example, sugar alcohols (general formula: HOCH ₂ (CHOH) nCH ₂ OH (where n represents an integer of 2 to 5))). Oxidized sugars (for example, aldonic acid, uronic acid, etc.), amino acids, thioic acids, etc. Among them, sugar alcohols are preferred, and specific examples include maltitol, sorbit and the like.

  The mass ratio between the water-insoluble vinyl polymer particles containing the pigment and the water-soluble organic solvent A has a great influence on the stability of ink ejection from the head, and also prevents waste ink sticking in the maintenance device of the ink ejection device. There is an impact. That is, if the water-insoluble vinyl polymer particles containing the pigment have a high solid content, but the blending amount of the water-soluble organic solvent A is small, water evaporation near the ink meniscus of the nozzle may progress and cause ejection failure. The mass ratio of the water-insoluble vinyl polymer particles containing the pigment and the water-soluble organic solvent A is preferably 1: 2 to 1:10, more preferably 1: 3 to 1: 8.

  Further, the ratio of the mass of the water-insoluble vinyl polymer particles containing the pigment and the mass of water that can be maintained when the water-soluble organic solvent A is in equilibrium (temperature 25 ° C., humidity 80%) is preferably 1: 0.2 to 1: 7, more preferably 1: 0.6-1: 4.

  The content of the water-soluble organic solvent in the aqueous ink is preferably 20 to 50% by mass, and more preferably 25 to 45% by mass. When the content is less than 25% by mass, the ejection stability is lowered, and there is a possibility that the waste ink is fixed by the maintenance device. On the other hand, if it exceeds 50% by mass, the drying property on paper is inferior and the character quality on plain paper may be lowered.

<Penetration agent>
In the present embodiment, the water-based ink preferably contains at least one polyol compound having 8 to 11 carbon atoms or glycol ether compound having 8 to 11 carbon atoms as a penetrating agent. Unlike the water-soluble organic solvent, the penetrant has low wettability and can be said to be non-wettable. Here, the non-wetting agent property means having a solubility of between 0.2 and 5.0% by mass in water at 25 ° C. Among these, 2-ethyl-1,3-hexanediol [solubility: 4.2% (25 ° C.)], 2,2,4-trimethyl-1,3-pentanediol [solubility: 2.0% (25 ° C)] is particularly preferably used. These penetrants are preferable in that they have good compatibility with the water-insoluble vinyl polymer obtained by polymerizing the monomers A, B, and C, and do not cause an increase in the viscosity of the ink residue from which water has evaporated.

  As other polyol compounds, as aliphatic diols, for example, 2-ethyl-2-methyl-1,3-propanediol, 3,3-dimethyl-1,2-butanediol, 2,2-diethyl-1, 3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2,4-dimethyl-2,4-pentanediol, 2,5-dimethyl-2,5-hexanediol, 5-hexene- 1,2-diol and the like can be mentioned.

  Other penetrants that can be used in combination are not particularly limited as long as they can be dissolved in ink and adjusted to desired physical properties, and can be appropriately selected according to the purpose. Other penetrants that can be used in combination include, for example, alkyl and aryl ethers of polyhydric alcohols such as diethylene glycol monophenyl ether, ethylene glycol monoallyl ether, propylene glycol monobutyl ether, tetraethylene glycol chlorophenyl ether, and lower alcohols such as ethanol. , Etc.

  The content of the penetrant in the water-based ink is preferably 0.1 to 4.0% by mass. If the content is less than 0.1% by mass, quick drying may not be obtained and a blurred image may be obtained. On the other hand, if the content exceeds 4.0% by mass, the dispersion stability of the colorant is impaired, the nozzles are easily clogged, and the permeability to the paper becomes higher than necessary, resulting in a decrease in image density. And strikethrough may occur.

<Surfactant>
In the present embodiment, the surfactant used in the water-based ink is preferably a surfactant that has low surface tension, low penetrability, and high leveling property without impairing dispersion stability depending on the combination of the colorant and the water-soluble organic solvent. . Examples of such surfactants include anionic surfactants, cationic surfactants, nonionic surfactants, fluorosurfactants, silicone surfactants, and amphoteric surfactants. These surfactants can be used alone or in combination of two or more.

  Anionic surfactants include polyoxyethylene alkyl ether acetates, dialkyl sulfosuccinates, dodecylbenzene sulfonates, laurates, polyoxyethylene alkyl ether sulfate salts, alkyl allyl sulfonates, alkyl naphthalene sulfonates , Alkyl phosphate, alkyl sulfate, alkyl sulfonate, alkyl ether sulfate, alkyl sulfosuccinate, alkyl ester sulfate, alkyl benzene sulfonate, alkyl diphenyl ether disulfonate, alkyl aryl ether phosphate, alkyl aryl Ether sulfate, alkyl aryl ether ester sulfate, olefin sulfonate, alkane olefin sulfonate, polyoxyethylene alkyl ether phosphate, poly Xylethylene alkyl ether sulfate, ether carboxylate, sulfosuccinate, α-sulfo fatty acid ester, fatty acid salt, higher fatty acid and amino acid condensate, naphthenate, and the like. Among these, polyoxyethylene alkyl ether Acetate and dialkyl sulfosuccinate are preferred.

  Nonionic surfactants include, for example, acetylene glycol surfactants, polyoxyethylene alkyl ethers, polyoxypropylene polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene sorbitan fatty acids. Examples include esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, and the like.

  Examples of the cationic surfactant include alkylamine salts, dialkylamine salts, aliphatic amine salts, benzalkonium salts, quaternary ammonium salts, alkylpyridinium salts, imidazolinium salts, sulfonium salts, phosphonium salts, and the like. It is done.

  Examples of amphoteric surfactants include imidazoline derivatives such as imidazolinium betaine, dimethylalkyllauryl betaine, alkylglycine, and alkyldi (aminoethyl) glycine.

  As the fluorine-based surfactant, those having 2 to 16 carbon atoms substituted with fluorine are preferable, and those having 4 to 16 carbon atoms substituted with fluorine are more preferable. If the number of fluorine-substituted carbons is less than 2, the effect of fluorine may not be obtained, and if it exceeds 16, problems such as ink storage stability may occur.

  Examples of fluorosurfactants include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate compounds, perfluoroalkyl ethylene oxide adducts, and perfluoroalkyl ether groups in the side chain. And polyoxyalkylene ether polymer compounds. Among these, a polyoxyalkylene ether polymer compound having a perfluoroalkyl ether group in the side chain has a low foaming property, and is particularly preferable, and a fluorine-based surfactant represented by the following structural formula (4) is more preferable. is there.

ただし、構造式（４）中、ｍは０〜１０の整数を表す。ｎは１〜４０の整数を表す。

However, m represents the integer of 0-10 in Structural formula (4). n represents an integer of 1 to 40.

Examples of the perfluoroalkyl sulfonic acid compound include perfluoroalkyl sulfonic acid, perfluoroalkyl sulfonate, and the like. Examples of the perfluoroalkyl carboxylic acid compound include perfluoroalkyl carboxylic acid and perfluoroalkyl carboxylate. Examples of the perfluoroalkyl phosphate compound include perfluoroalkyl phosphate esters, perfluoroalkyl phosphate salts, and the like. The polyoxyalkylene ether polymer compound having a perfluoroalkyl ether group in the side chain includes a polyoxyalkylene ether polymer having a perfluoroalkyl ether group in the side chain, and a polyoxyalkylene ether polymer having a perfluoroalkyl ether group in the side chain. And a salt of a polyoxyalkylene ether polymer having a perfluoroalkyl ether group in the side chain. As counter ions of salts in these fluorosurfactants, Li, Na, K, NH ₄ , NH ₃ CH ₂ CH ₂ OH, NH ₂ (CH ₂ CH ₂ OH) ₂ , NH (CH ₂ CH ₂ OH) ₃ etc. are mentioned.

  As a fluorine-type surfactant, what was synthesize | combined suitably may be used and a commercial item may be used. Examples of commercially available products include Surflon S-111, S-112, S-113, S-121, S-131, S-132, S-141, S-145, and S-386 (all Asahi Glass Co., Ltd.). Manufactured); Fullrad FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, FC-431 (all manufactured by Sumitomo 3M Limited); Megafac F- 470, F-1405, F-474 (all manufactured by Dainippon Ink & Chemicals, Inc.); Zonyl TBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, FS-300, UR (All manufactured by DuPont); FT-110, FT-250, FT-251, FT-400S, FT-150, FT-400SW (all Made formula company Neos Co., Ltd.), poly Fox PF-151N (manufactured by OMNOVA Solutions Inc.), and the like. Among these, FS-300 manufactured by DuPont, FT-110, FT-250, FT-251 manufactured by Neos Co., Ltd., from the point that the good recording quality, particularly color developability, and leveling property on paper are remarkably improved. FT-400S, FT-150, FT-400SW and Polynova PF-151N manufactured by Omninova are particularly preferred.

  The silicone-based surfactant is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably one that does not decompose even at high pH, such as side chain-modified polydimethylsiloxane, both-end modified polydimethylsiloxane, Examples thereof include one-end-modified polydimethylsiloxane and side-chain both-end-modified polydimethylsiloxane, and polyether-modified silicone surfactants having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modification group are aqueous surfactants. Is particularly preferable since it exhibits good properties.

  The polyether-modified silicone surfactant is not particularly limited and can be appropriately selected according to the purpose. For example, a polyalkylene oxide structure represented by the following structural formula is added to the side chain of the dimethylpolysiloxane in the Si part. Introduced compounds and the like.

ただし、（５）式中、ｍ、ｎ、ａ、及びｂは整数を表す。Ｒ及びＲ’はアルキル基、アルキレン基を表す。

However, in the formula (5), m, n, a, and b represent integers. R and R ′ represent an alkyl group or an alkylene group.

  As the silicone-based surfactant, those appropriately synthesized may be used, or commercially available products may be used. Commercially available products can be easily obtained from, for example, Big Chemie, Shin-Etsu Silicone, Toray Dow Corning Silicone, etc. A commercially available product can be used as the polyether-modified silicone surfactant, and examples thereof include KF-618, KF-642, and KF-643 (all manufactured by Shin-Etsu Chemical Co., Ltd.).

  The content of the surfactant in the aqueous ink is preferably 0.01 to 3.0% by mass, and more preferably 0.5 to 2% by mass. When the content is less than 0.01% by mass, the effect of adding a surfactant may be lost. When the content exceeds 3.0% by mass, the paper penetration becomes higher than necessary, and the image density is reduced. Decrease or strikethrough may occur.

<PH adjuster>
In this embodiment, a highly reliable ink can be obtained by adding a pH adjusting agent as a pigment aggregation preventing agent and adjusting so that the ink pH is not lowered and the pigment is not aggregated or thickened during ink storage. The pH adjuster is not particularly limited as long as it can adjust the pH to 8 to 11 without adversely affecting the aqueous ink, and can be appropriately selected according to the purpose. For example, alcohol amines, alkali Examples thereof include metal element hydroxides, ammonium hydroxides, phosphonium hydroxides, and alkali metal carbonates. When the pH is less than 8 or more than 11, the amount of the ink jet head or the ink supply unit that melts is large, and problems such as ink deterioration, leakage, and ejection failure may occur.

  Examples of alcohol amines include diethanolamine, triethanolamine, 2-amino-2-ethyl-1,3-propanediol, and the like. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of the ammonium hydroxide include ammonium hydroxide, quaternary ammonium hydroxide, quaternary phosphonium hydroxide, and the like. Examples of the alkali metal carbonate include lithium carbonate, sodium carbonate, and potassium carbonate.

<Other ingredients>
Other components are not particularly limited and can be appropriately selected as necessary.For example, known water-dispersible resins, antiseptic / antifungal agents, chelating reagents, rust preventives, antioxidants, ultraviolet absorbers, Examples include oxygen absorbers and light stabilizers.

<Example of ink production>
In this embodiment, the water-based ink is prepared by dispersing or dissolving an aqueous dispersion of water-insoluble vinyl polymer particles containing a pigment, a water-soluble organic solvent, and water, and, if necessary, other components in an aqueous medium. It is manufactured by stirring and mixing as necessary. The dispersion can be performed by, for example, a sand mill, a homogenizer, a ball mill, a paint shaker, an ultrasonic disperser, or the like. The stirring and mixing can be performed with a stirrer using a normal stirring blade, a magnetic stirrer, a high-speed disperser, or the like.

<Ink physical properties>
In the present embodiment, the physical properties of the water-based ink are not particularly limited and can be appropriately selected according to the purpose. For example, the viscosity, surface tension, pH, and the like are preferably in the following ranges.

  The viscosity of the water-based ink at 25 ° C. is preferably 5 to 20 mPa · s. By setting the water-based ink viscosity to 5 mPa · s or more, an effect of improving image density and character quality can be obtained. On the other hand, by suppressing the ink viscosity to 20 mPa · s or less, ejection stability can be ensured. In this embodiment, the viscosity of the ink is a viscosity measured by a cone-plate rotational viscometer according to JIS K7117-2. Here, the viscosity can be measured at 25 ° C. using, for example, a viscometer (RE-80L, RE-550L, manufactured by Toki Sangyo Co., Ltd.).

  The pH of the water-based ink is greater than 7, preferably 8 or more at 25 ° C., more preferably 9 or more. When the pH of the ink is 7 or less, the ejection stability may be reduced due to thickening. When the pH of the water-based ink is increased to 11 or more, the parts used in the liquid ejecting apparatus may be deteriorated.

  The surface tension of the water-based ink is preferably 35 mN / m or less, more preferably 32 mN / m or less at 25 ° C. If the surface tension exceeds 35 mN / m, ink permeation and leveling are unlikely to occur and the drying time may be prolonged.

<<< Operation / Processing of Liquid Discharge Device >>>
Subsequently, a processing method in the liquid ejection method according to the present embodiment will be described with reference to FIG. FIG. 6 is a process flow diagram showing a processing method in the liquid ejection apparatus 1 according to the present embodiment.

  First, the I / F 106 of the liquid ejection apparatus 1 receives print data from an external device such as a host computer (step S1). Next, the ejection control unit 117 performs image processing on the print data received by the I / F 106 by the ASIC 105 to create image data (step S2). Further, the ejection control unit 117 calculates the ratio of the area of the recording portion (printing rate) to the area of the entire sheet based on the created image data (step S3).

  Subsequently, the heating control unit 113 controls the output of the heating unit 31 based on the printing rate calculated by the discharge control unit 117 (step S4). In this case, the heating control unit 113 searches the set temperature management table (see FIG. 4) using the printing rate calculated by the discharge control unit 117 as a search key, and reads the heating means set temperature. Next, the heating control unit 113 transmits the heating unit set temperature read out via the I / O port 107 to the heating unit 31. Thereby, the heating means 31 controls the output based on the heating means set temperature by a known temperature control means such as a thermostat.

  Similarly, the cooling control unit 114 controls the output of the cooling unit 41 based on the printing rate calculated by the discharge control unit 117 (step S4). In this case, the cooling control unit 114 searches the set temperature management table (see FIG. 4) using the printing rate calculated by the discharge control unit 117 as a search key, and reads the cooling unit set temperature. Next, the cooling control unit 114 transmits the cooling unit set temperature read out via the I / O port 107 to the cooling unit 41. Thereby, the cooling means 41 controls the output based on the cooling means set temperature by a known temperature control means such as a thermostat.

  When the output of the heating unit 31 and the output of the cooling unit 41 are controlled to a predetermined temperature, the conveyance control unit 116 performs a drawing roller of the sheet feeding unit 2 according to a command from the CPU 101 according to a program stored in the ROM 102. 22 and control for driving the paper feed roller 23 are performed (step S5). As a result, the sheets stored in the sheet feed tray 21 are pulled out one by one and fed to the transport path.

  When the paper fed by the paper feed roller 23 reaches the heating unit 3 on the transport path, the heating unit 31 heats the first surface of the paper (step S6). In the present embodiment, the set temperature of the heating means 31 is accepted by the display operation panel 91 from the user.

  In the present embodiment, simultaneously with the heating of the first surface of the sheet by the heating unit 31, the cooling unit 41 cools the second surface of the sheet (step S6). In the present embodiment, the set temperature of the cooling means 41 is accepted by the display operation panel 91 from the user.

  When the paper heated by the heating unit 3 reaches the measuring unit 5, the moisture meter 51 measures the moisture content of the first surface and the second surface of the paper (step S7). In this embodiment, an infrared moisture meter is used as each moisture meter 51, and the moisture content on the first surface and the moisture content on the second surface of the paper are simultaneously measured in real time. In this case, the first moisture meter 51a irradiates the first surface of the paper with near infrared rays having a specific wavelength and outputs the reflection intensity (IM-D value). Similarly, the second moisture meter 51b irradiates the second surface of the paper with near infrared light having a specific wavelength and outputs the reflection intensity (IM-D value). Each output IM-D value is transmitted to the I / O port 107 of the control unit 10.

  Subsequently, the calculation unit 115 uses the IM-D value of the moisture meter 51 received by the I / O port 107 and the moisture amount calculation formula obtained from the moisture amount calculation formula management table to obtain the first surface. And the moisture content of the second surface are calculated. Here, the water content calculation formula is acquired based on the type of paper received by the display operation panel 91. Further, the calculation unit 115 calculates a moisture front / back difference indicating the difference between the calculated moisture content of the first surface and the moisture content of the second surface based on the above equation (1).

  The paper whose moisture content has been measured by the measuring unit 5 is transported by the transport belt 61 (step S8). In this case, the conveyance control unit 116 performs control to drive the conveyance motor 66 of the conveyance unit 6 according to a command from the CPU 101 according to a program stored in the ROM 102. As a result, the driving roller 62 rotates in conjunction with it, and the conveying belt 61 moves. Here, the paper on the transport belt 61 is transported on a transport path that reaches the paper discharge section 8 via the discharge section 7.

  After the moisture amount is measured by the measurement unit 5, the discharge control unit 117 determines whether or not the moisture front / back difference calculated by the calculation unit 115 is equal to or greater than a predetermined threshold (step S9). In this case, the predetermined threshold value may be received by the display operation panel 91 or may be predetermined by a program.

  If it is determined in step S9 that the moisture front / back difference is equal to or greater than the predetermined threshold (YES in step S9), the discharge control unit 117 generates a drive waveform for driving and controlling the pressure generating means of the discharge head 73. Control for generating and discharging water-based ink is performed (step S10). In this case, the ejection control unit 17 creates head driving information for driving the head based on the image data created in Step 2 and outputs the head driving information to the ejection head 73. Accordingly, the ejection head 73 ejects ink based on the head drive information in accordance with the timing of conveyance of the sheet by the conveyance belt 61 and forms an image on the first surface of the sheet.

  When the ejection process in step S10 is completed, the paper discharge unit 8 discharges the paper transported by the transport belt 61 (step S11). In this case, the conveyance control unit 116 performs control to drive the paper discharge roller 82 of the paper discharge unit 8 according to a command from the CPU 101 according to a program stored in the ROM 102. As a result, the paper discharge roller 82 rotates, and the paper on the conveyance path is discharged to the paper discharge tray 83 to complete the process.

  If it is determined in step S9 that the moisture front / back difference is less than the predetermined threshold (NO in step S9), the display operation panel 91 displays a predetermined error message (step S12). With this error message, the display / operation panel 91 can notify the user by displaying that a sufficient amount of moisture could not be applied to the paper.

  Subsequently, the paper discharge unit 8 discharges the unrecorded paper transported by the transport unit 6 (step S13). In this case, by switching the conveyance path by a known switching unit, the paper discharge unit 8 discharges a sheet that is not recorded in a paper discharge tray that is different from the paper discharge tray 83 from which the recorded paper is discharged. May be.

  Subsequently, the heating control unit 113 controls the output of the heating means 31 (step S14). In this case, the heating control unit 113 adds a predetermined temperature to the current heating unit set temperature read in step S4, and sets a new heating unit set temperature. Next, the heating control unit 113 transmits the set new heating unit setting temperature to the heating unit 31 via the I / O port 107. Thereby, the heating means 31 can control the output based on the new heating means set temperature by a known temperature control means such as a thermostat.

  Similarly, the cooling control unit 114 controls the output of the cooling means 41 (step S14). In this case, the cooling control unit 114 subtracts a predetermined temperature from the current cooling means set temperature read in step S4, and sets a new cooling means set temperature. Next, the cooling control unit 114 transmits the set new cooling means set temperature to the cooling means 41 via the I / O port 107. Thereby, the cooling means 41 can control the output based on the new cooling means set temperature by a known temperature control means such as a thermostat.

<<< Supplement to the embodiment >>>
In the above-described embodiment, an inkjet recording apparatus that discharges water-based ink has been described as an example of the liquid discharge apparatus 1. However, the present invention is not limited to this. In this case, examples of the liquid discharge device include a coating device that applies a water-based paint to a sheet, a processing device that discharges an aqueous processing liquid, and the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples at all.

<< Production Example 1 >>
In a reaction vessel, 20 parts by mass of methyl ethyl ketone, 0.03 part by mass of a polymerization chain transfer agent (2-mercaptoethanol), and 10% by mass of each monomer (indicated by mass) shown in Table 1 are added and mixed. Then, nitrogen gas replacement was sufficiently performed to obtain a mixed solution.

  On the other hand, the remaining 90% by mass of each monomer (indicated by mass) shown in Table 1 was charged into a dropping funnel, then 0.27 parts by mass of a polymerization chain transfer agent (2-mercaptoethanol), and 60% by mass of methyl ethyl ketone. And 1.2 parts by mass of 2,2′-azobis (2,4-dimethylvaleronitrile) were mixed and mixed, and nitrogen gas substitution was sufficiently performed to obtain a mixed solution.

  Under a nitrogen atmosphere, the mixed solution in the reaction vessel was heated to 75 ° C. while stirring, and the mixed solution in the dropping funnel was gradually dropped into the reaction vessel over 3 hours. After completion of the dropwise addition, the liquid temperature of the mixed solution was maintained at 75 ° C. for 2 hours, and then a solution in which 0.3 part by mass of 2,2′-azobis (2,4-dimethylvaleronitrile) was dissolved in 5 parts by mass of methyl ethyl ketone was prepared. In addition to the mixed solution, the mixture was further aged at 75 ° C. for 2 hours and 85 ° C. for 2 hours to obtain a polymer solution.

  A portion of the resulting polymer solution was isolated by drying at 105 ° C. under reduced pressure for 2 hours and removing the solvent. The weight average molecular weight was measured by gel permeation chromatography using polystyrene as a standard substance and 60 mmol / L phosphoric acid and 50 mmol / L lithium bromide-containing dimethylformamide as a solvent.

The details of each compound shown in Table 1 are as follows.
* Ethoxypolyethylene glycol monomethacrylate: a monomer in which n is 9, R ₁ is a methyl group, R ₂ is an ethylene group, and R ₃ is an ethyl group in the general formula (1) * Methacrylic acid: manufactured by Mitsubishi Gas Chemical Co., Ltd. Product name GE-110 (MAA)
* 2-ethylhexyl methacrylate: Mitsubishi Rayon Co., Ltd., trade name Acryester EH
* Styrene monomer: Nippon Steel Chemical Co., Ltd., trade name styrene monomer * Styrene macromer: Toa Gosei Co., Ltd., trade name AS-6S (styrene macromer), number average molecular weight 6000

<< Preparation of Pigment Dispersion: Adjustment Example 1 >>
To 77 parts of the solution obtained by adjusting the polymer obtained in Production Example 1 to 50% with methyl ethyl ketone, 90 parts of methyl ethyl ketone and a predetermined amount of neutralizing agent (5N aqueous sodium hydroxide solution) were added to neutralize methacrylic acid (neutralization degree 90). After that, 370 parts of ion-exchanged water and 90 parts of carbon black (Nexex 150 manufactured by Degussa) as a colorant were added, mixed with a disperser, and further treated with a disperser (Microfluidizer M-140K, 150 MPa) for 5 passes. .

  To the obtained aqueous dispersion, 100 parts of ion-exchanged water was added and stirred. Then, methyl ethyl ketone was removed at 60 ° C. under reduced pressure, and a part of the water was removed. Diameter: 2.5 cm, filtered through a 25 mL needleless syringe (made by Terumo Corp.) with a volume of 25 ml, and removed coarse particles, and a pigment dispersion having a solid content of 25% (adjustment example) 1) was obtained.

<< Adjustment of water-based ink: Adjustment examples 2 and 3 >>
A water-soluble organic solvent, a penetrating agent, a surfactant, an antifungal agent, an antifoaming agent, a pH adjuster and water shown in Table 2 were mixed and stirred for 1 hour to mix uniformly. A water-dispersible resin was added to this mixed solution and stirred for 1 hour, and a pigment dispersion was added and stirred for 1 hour. This dispersion was subjected to pressure filtration with a polyvinylidene fluoride membrane filter having an average pore size of 5.0 μm to remove coarse particles and dust, thereby preparing ink jet inks of Preparation Examples 2 and 3.

In addition, the unit in Table 2 is mass%. Abbreviations in Table 2 represent the following meanings.
* Self-dispersing pigment dispersion: manufactured by Cabot, CAB-O-JET (R) 300, solid content: 15% by mass
* Fluororesin emulsion: Asahi Glass Co., Ltd., Lumiflon FE4500, solid content 50 mass%, average particle size 136 nm, minimum film-forming temperature (MFT) = 28 ° C.
* Zonyl FS-300: polyoxyethylene perfluoroalkyl ether (manufactured by Dupont, active ingredient 40 mass%)
* Orphine EXP4001: Acetylene glycol surfactant, manufactured by Nissin Chemical Industry Co., Ltd., 80% by mass of active ingredient
* Proxel GXL: Antifungal agent based on 1,2-benzisothiazolin-3-one (Avicia, 20% by mass, containing dipropylene glycol)
* KM-72F: Self-emulsifying silicone defoaming agent (manufactured by Shin-Etsu Silicone Co., Ltd., 100% by mass)

The physical properties of the water-based inks of Preparation Examples 2 and 3 were evaluated by the following evaluation methods. The results are shown in Table 3.
(Solid content concentration)
The total content of pigment and resin (coating resin or water-dispersible resin) in the ink was calculated.
(viscosity)
The viscosity of the ink was measured at 25 ° C. using a viscometer (RE-550L, manufactured by Toki Sangyo Co., Ltd., cone rotor 1 ° 34 ′ × R24). In addition, while measuring the pH of the ink with a pH meter HM-30R (manufactured by TOA-DKK), 1N hydrochloric acid was dropped into the ink to prepare an ink neutralized product adjusted to pH 7, and 25 with a viscometer. The viscosity at 0 ° C. was measured. Further, by the following method, the ink was left in a temperature of 25 ° C. and humidity of 15% environment until there was substantially no change in mass to obtain an ink residue. About this ink residue, the viscosity in 25 degreeC was measured with the said viscometer RE-550L. In Table 3, “<” means “above”.

(Residual viscosity)
2.5 g of the water-based ink was sampled on a 33 mm caliber glass petri dish with a precision upper pan electronic balance capable of measuring up to four decimal places. Next, it is stored in an ESPEC constant temperature and humidity chamber (ModelPL-3KP) at a temperature of 25 ± 0.5 ° C. and a humidity of 15 ± 5%, and each sample is taken out every hour to measure its mass. Storage was continued until the mass change per hour was 1% or less of the total ink mass. The viscosity of 25 ° C. was measured for the obtained ink residue using a RE-550L viscometer (manufactured by Toki Sangyo Co., Ltd.) cone rotor 3 ° × R14.

(Average particle size)
The average particle diameter (D50%) was measured using a particle size distribution measuring device (Nikkiso Co., Ltd., Nanotrac UPA-EX150).

(surface tension)
The surface tension of the ink was measured at 25 ° C. using a fully automatic surface tension meter (CBVP-Z, manufactured by Kyowa Interface Science Co., Ltd.).

(PH)
The pH of the ink was measured at 25 ° C. using a pH meter HM-30R (manufactured by TOA-DKK).

<< Examples 1 to 10, Comparative Examples 1 to 3: Back Curl Evaluation >>
In an environment adjusted to a temperature of 23 ± 0.5 ° C. and 50 ± 5% RH, the ink jet recording apparatus of FIG. 1 (a modified version of IPSiO GX-5000, manufactured by Ricoh Co., Ltd.) as an example of the liquid ejection apparatus 1 is used. The drive voltage of the piezo element was varied so that the discharge amount of the water-based ink in each adjustment example was uniform, and the same amount of water-based ink was attached to the first surface of the paper. For Comparative Example 3, an ink jet recording apparatus (IPSiO GX) in which the heating unit 3 and the cooling unit 4 of the ink jet recording apparatus of FIG. 1 are provided between the transport unit 6 and the paper discharge unit 8 on the paper transport path. -5000 modified product) and set in the same manner as above.

After the setting, the first surface of the paper is heated by the heating means 31 shown in Table 4, the second surface of the paper is cooled by the cooling means 41, and the first surface of the paper is solid on the following recording conditions. An image was formed. In Comparative Examples 1 and 2, no heat treatment was performed. In Table 4, the cooling treatment was not performed in Examples and Comparative Examples where no cooling means was described.
[Recording conditions]
Recording density: 300 × 600 dpi
Recording area: 526.3 cm ² / A4
Ink discharge adhesion amount: 5.6 g / m ²

  In addition, the measurement result of the moisture content of the first surface (heating surface in the case of heating) of the paper by the moisture meter 51a of the ink jet recording apparatus, and the measurement result of the cooling surface (second surface) of the paper by the moisture meter 51b, Table 4 shows the difference between the water content and the front and back calculated by the equation (1) based on the measurement result. As the moisture meter 51, an IM-3SCV Model-1000 manufactured by Fuji Work was used.

表４中の加熱手段３１及び冷却手段４１を以下に示す。
温風ヒータ ：石崎電気製作所製ヒーターガンを用紙全体に温風が当たるように改造したもの。
ヒートローラ：電子写真定着ローラユニットを温度コントロールできるように改造したもの。
冷却板 ：ペルチェ素子を使用した電子クーラー（電装産業株式会社製ＴＫＧ−３１１−１３０）
水冷ローラ ：内部の冷却した冷媒により冷却するローラ。

The heating means 31 and the cooling means 41 in Table 4 are shown below.
Hot air heater: A heater gun manufactured by Ishizaki Electric Co., Ltd., modified so that hot air is applied to the entire paper.
Heat roller: An electrophotographic fixing roller unit modified to allow temperature control.
Cooling plate: Electronic cooler using Peltier element (TKG-311-130 manufactured by Denso Sangyo Co., Ltd.)
Water-cooled roller: A roller that is cooled by the internally cooled refrigerant.

Back curl (back curl when the printing surface is placed on a flat desk) immediately after printing (within 5 seconds after paper discharge from the recording device) and one day with the printing surface facing down on a flat desk The curl height after being allowed to stand was measured under the following measurement conditions. The results are shown in Table 5.
〔Measurement condition〕
The curled surface was placed on a flat desk and placed gently, and the heights of the four corners of A4 size paper were measured with a JIS_1 grade, and the four-point measurement values were averaged. In addition, when the back curl was too large and became a cylinder, the diameter of the cylinder was measured.

Moreover, the measurement result was determined according to the following evaluation criteria.
〔Evaluation criteria〕
◎: Less than 10 mm ○: 10 mm or more and less than 20 mm Δ: 20 mm or more and less than 50 mm ×: Tubular

<< Main effects of the embodiment >>
As described above, according to the first to tenth embodiments, the heating unit 31 heats and dries the first surface of the paper, and the moisture content of the first surface and the moisture content of the second surface is increased. A predetermined amount of difference (difference exceeding 0%) was provided. Further, the water-based ink was ejected and adhered to the first surface of the paper by the ejection head 73. Thereby, generation | occurrence | production of the back curl after attaching water-based ink was able to be suppressed.

  Further, according to Examples 1 to 7, 9, and 10, the back curl of the paper immediately after recording could be further suppressed by setting the moisture front / back difference to 20% or more.

  Further, according to the second to fifth, fifth, seventh, ninth and tenth embodiments, the first surface of the sheet is heated by the heating unit 31, the second surface of the sheet is cooled by the cooling unit 41, and the first sheet A predetermined amount of difference was provided between the moisture content of the surface and the moisture content of the second surface. Further, the water-based ink was ejected and adhered to the first surface of the dried paper by the ejection head 73. As a result, the occurrence of back curl after the water-based ink was adhered could be suppressed.

  Note that the discharge control unit 117 of the ink jet recording apparatus according to the embodiment may calculate the printing rate when discharging the aqueous liquid onto the paper (see Step S3). Accordingly, the heating control unit 113 can control the output of the heating unit 31 based on the printing rate, and can dry the first surface of the paper (see Steps S4 to S6). In this case, when an image such as a character with a low printing rate is formed, the output of the heating means 31 can be set low, so that the energy required for image formation can be reduced.

  In addition, the moisture meter 51 of the ink jet recording apparatus of the embodiment can measure the moisture content on the first side of the dried paper and the moisture content on the second side of the paper (see step S7). As a result, when the difference in the amount of water calculated by the calculation unit 115 is equal to or greater than the threshold value, a drive waveform for driving and controlling the pressure generation unit of the discharge control unit 117 and the discharge head 73 is generated, and ink is discharged. Control may be performed (step S10). In this case, since the water-based ink can be ejected onto the paper whose water content difference is equal to or greater than the threshold value, the occurrence of back curl can be suppressed.

  Moreover, when the difference in the amount of moisture calculated by the calculation unit 115 is less than the threshold value, the heating control unit 113 may control the output of the heating unit 31 (step S14). That is, the liquid ejection apparatus 1 may dry the first surface of the paper based on the moisture amount measured by the moisture meter 51. Thereby, even when an image cannot be formed with the output of the initial setting of the heating unit 41, the heating control unit 113 can automatically control the output.

  In Examples 1 to 5, 9, and 10, the first surface of the paper was heated with a warm air heater. Thereby, compared with the case where other means are used, the difference in moisture content between the front and back can be increased, so that the occurrence of back curl can be easily suppressed.

  In Examples 3 and 7, the second surface of the paper was cooled by a water cooling roller. Thereby, compared with the case where other means are used, the difference in moisture content between the front and back can be increased, so that the occurrence of back curl can be easily suppressed.

DESCRIPTION OF SYMBOLS 1 Liquid discharge apparatus 2 Paper feed part 3 Heating part 4 Cooling part 5 Measuring part 6 Transport part 7 Discharge part 8 Paper discharge part 9 Operation part 10 Control part 21 Paper feed tray 22 Pull-out roller 23 Paper feed roller 31 Heating means 41 Cooling means 51 Moisture Meter 61 Conveying Belt 62 Drive Roller 63 Driven Roller 64 Auxiliary Roller 65 Auxiliary Roller 66 Conveyor Motor 71 Tank 72 Supply Line 73 Discharge Head 81 Auxiliary Roller 82 Discharge Roller 83 Discharge Tray 91 Display Operation Panel 101 CPU
102 ROM
103 RAM
104 NVRAM
105 ASIC
106 I / F
107 I / O Port 113 Heating Control Unit 114 Cooling Control Unit 115 Calculation Unit 116 Transport Control Unit 117 Discharge Control Unit

JP2004-136458

Claims (10)

A liquid ejection method for ejecting and attaching an aqueous liquid to paper,
A drying step of drying the first surface of the paper and providing a predetermined amount of difference in the moisture content of the first surface and the moisture content of the second surface of the paper;
A discharge step of discharging and attaching the aqueous liquid to the first surface of the paper dried in the drying step;
A liquid discharge method comprising: 2. The liquid ejection method according to claim 1, wherein in the drying step, the moisture front / back difference represented by the formula (1) is set to 20% or more.

  3. The liquid ejection method according to claim 1, wherein, in the drying step, the first surface of the paper is heated and the second surface is cooled. A calculating step of calculating a printing rate when discharging the aqueous liquid onto the paper in the discharging step;
4. The liquid ejection method according to claim 1, wherein, in the drying step, the first surface of the sheet is dried based on the printing rate calculated in the calculation step. 5. A measuring step of measuring the moisture content of the first surface and the moisture content of the second surface of the paper dried in the drying step;
In the discharging step, when the difference between the moisture content of the first surface and the moisture content of the second surface measured in the measurement step is larger than a predetermined value, the aqueous liquid is applied to the first surface of the paper. The liquid discharging method according to claim 1, wherein the liquid is discharged and adhered.   6. The liquid ejection method according to claim 1, wherein, in the drying step, the first surface of the sheet is dried based on the moisture amount measured in the measurement step.   The liquid discharging method according to claim 3, wherein, in the heating step, the first surface of the paper is heated using a heated gas.   The liquid discharging method according to claim 3, wherein the second surface of the sheet is cooled using the cooled liquid in the cooling step. A liquid ejection device for ejecting and adhering aqueous liquid to paper,
Drying means for drying the first surface of the paper and providing a predetermined amount of difference between the moisture content of the first surface of the paper and the moisture content of the second surface;
Discharge means for discharging and attaching the aqueous liquid to the first surface of the paper dried in the drying step;
A liquid ejecting apparatus comprising: The aqueous liquid is an aqueous ink,
An image formed article, wherein an image is formed by ejecting water-based ink onto a sheet by the liquid ejection method according to claim 1.

Images