Image forming method, image forming device, and image forming system

Abstract

This image forming method comprises: an image forming step for forming an image by applying an ink containing water, resin particles, and an organic solvent to a recording surface of a recording medium to form an ink film; a drying step for drying the ink film formed on the recording surface; and an accumulation step for accumulating the recording medium having the dried ink film, wherein expression (1) or (2) is satisfied, where X [MPa1 / 2] is the SP value of the organic solvent in the ink, Y [µg / cm2] is the residual amount of the organic solvent remaining on the recording surface during the accumulation of the recording medium in the accumulation step, Tg [°C] is the glass transition temperature of the resin particles, and Tc [°C] is the film surface temperature of the ink film on the recording surface during the accumulation. (1): 0≤X×Y≤4000 (2): 4000＜X×Y≤6000, and Tg－Tc≥10

Description

Image forming method, image forming apparatus, and image forming system

[0001] The present disclosure relates to an image forming method, an image forming apparatus, and an image forming system.

[0002] In an image forming apparatus, such as an inkjet printer using aqueous ink, a printing method is known in which multiple sheets of paper are printed in succession and then stacked in a stacking device. In this method, an image is formed by applying ink to one or both recording surfaces of the paper to form an ink film. Known inks include water-based inks (sometimes called aqueous inks) that contain water as the primary solvent. In such a printing apparatus, the sticky ink film can cause blocking, where overlapping sheets of paper stick to each other in the stacking device.

[0003] Japanese Patent Application Laid-Open No. 2012-135984 proposes an image forming apparatus equipped with a cooling device that cools the heated and dried ink film in order to suppress the occurrence of such blocking.

[0004] However, even after drying and cooling, blocking still occurred in some cases.

[0005] The present disclosure has been made in consideration of the above circumstances, and aims to provide an image forming method, an image forming apparatus, and an image forming system that can more reliably suppress the occurrence of blocking when recording media are stacked.

[0006] The image forming method of the present disclosure includes an image forming step of forming an image by applying an ink containing water, resin particles, and an organic solvent to a recording surface of a recording medium to form an ink film, a drying step of drying the ink film formed on the recording surface, and a collecting step of collecting the recording medium on which the ink film has dried, wherein the SP value of the organic solvent of the ink is X [MPa １／２ ], and the amount of residual organic solvent remaining on the recording surface when the recording medium is accumulated in the accumulation process is Y [μg / cm ２], the glass transition temperature of the resin particles is Tg [°C], and the surface temperature of the ink film during accumulation is Tc [°C], the image forming method satisfies the following formula (1) or formula (2): 0≦X×Y≦4000 (1) 4000<X×Y≦6000 and Tg−Tc≧10 (2)

[0007] When formula (1) is satisfied, it is preferable to satisfy the following formula (1-1): 1500≦X×Y≦4000 (1-1)

[0008] When formula (1) is satisfied, it is more preferable to satisfy the following formula (1-2): 2500≦X×Y≦4000 (1-2)

[0009] When formula (1) is satisfied, it is preferable that the following formula (3) be further satisfied: Tg - Tc ≥ 10 (3)

[0010] When formula (1) or formula (2) is satisfied, it is more preferable that the following formula (3-1) is further satisfied: Tg - Tc ≥ 40 (3-1)

[0011] When formula (1) or formula (2) is satisfied, it is particularly preferable that the following formula (3-2) be further satisfied: Tg - Tc ≥ 60 (3-2)

[0012] In the image forming method of the present disclosure, the glass transition temperature Tg of the resin particles is preferably −5° C. or higher and 150° C. or lower.

[0013] In the image forming method of the present disclosure, the ink preferably contains wax.

[0014] In the image forming method of the present disclosure, the image forming process and the drying process may be performed sequentially on the first and second recording surfaces, which are the front and back surfaces of the recording medium. In this case, the recording surface during accumulation is the second recording surface. In this case, when the film surface temperature of the second recording surface during accumulation is Tc and the film surface temperature of the first recording surface is Tc1 [°C], it is preferable that the following formula (4) is satisfied: Tg - Tc ≧ 40, and Tc - Tc1 ≧ 20 (4)

[0015] In the image forming method of the present disclosure, the SP value X preferably satisfies 18≦X≦28, and more preferably satisfies 20≦X≦23.

[0016] The image forming apparatus of the present disclosure includes an image forming unit that forms an image by applying ink to a recording surface of a recording medium to form an ink film, a drying unit that dries the ink film formed on the recording surface, and a collecting device that collects the recording medium on which the ink film has been formed and dried, wherein the image forming unit applies ink containing water, resin particles, and an organic solvent, and the SP value of the organic solvent of the ink is X [MPa １／２ ], and the amount of residual organic solvent remaining on the recording surface when the recording medium is accumulated in the accumulation device is Y [μg / cm ２ ], the glass transition temperature of the resin particles is Tg [°C], and the film surface temperature of the ink film on the recording surface during accumulation is Tc [°C], the image forming apparatus satisfies the following formula (1) or formula (2): 0≦X×Y≦4000 (1) 4000<X×Y≦6000 and Tg−Tc≧10 (2)

[0017] The image forming apparatus of the present disclosure preferably includes a processor that controls the drying unit, and the processor is configured to control the drying unit under drying conditions that satisfy formula (1) or formula (2).

[0018] The drying unit preferably includes a heating and drying section that heats and dries the ink film.

[0019] The drying unit preferably includes a cooling section for cooling the ink film that has been heated and dried.

[0020] The image forming system of the present disclosure is an image forming system including ink and an image forming apparatus, wherein the ink contains water, resin particles, and an organic solvent, and the image forming apparatus includes an image forming unit that forms an image by applying ink to a recording surface of a recording medium to form an ink film, a drying unit that dries the ink film formed on the recording surface, a transport mechanism that is a transport unit arranged downstream of the drying unit and includes a contact-type transport unit that transports the recording medium by bringing a contact member into contact with the recording surface of the recording medium transported downstream from the drying unit, and a collecting device that collects the recording medium on which the ink film has been formed and dried, and wherein the SP value of the organic solvent is X [MPa １／２ ], and the amount of residual organic solvent remaining on the recording surface when the recording medium is accumulated in the accumulation device is Y [μg / cm ２ ], the glass transition temperature of the resin particles is Tg [°C], and the film surface temperature of the ink film on the recording surface during accumulation is Tc [°C], the image forming system satisfies the following formula (1) or formula (2): 0≦X×Y≦4000 (1) 4000<X×Y≦6000, and Tg−Tc≧10 (2).

[0021] According to the image forming method, image forming apparatus, or image forming system of the present disclosure, it is possible to more reliably prevent blocking from occurring when recording media are stacked.

[0022] 1 is a schematic configuration diagram of an inkjet printing apparatus according to an embodiment.

[0023] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this specification, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.

[0024] In the present disclosure, the amount of each component in a composition means the total amount of the components in the composition unless otherwise specified, when the composition contains multiple substances corresponding to each component. In the present disclosure, a combination of two or more preferred aspects is a more preferred aspect. In the present disclosure, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0025] In this disclosure, unless otherwise specified, "upstream side" means the upstream side in the transport direction of the recording medium, and "downstream side" means the downstream side in the transport direction of the recording medium, unless otherwise specified.

[0026] [Image Forming Method] The image forming method of the present disclosure includes an image forming process, a drying process, and a collecting process. In addition, there is a preparation process as a stage preceding the image forming process. The preparation process is a process of preparing ink containing water, resin particles, and an organic solvent. Details of the ink will be described later. The image forming process is a process of forming an image by applying ink to the recording surface of a recording medium to form an ink film. The drying process is a process of drying the ink film formed on the recording surface. The collecting process is a process of collecting the recording medium with the dried ink film. Details of each process will be described later.

[0027] In the image forming method of the present disclosure, the SP value of the organic solvent of the ink is X [MPa １／２ ], and the amount of residual organic solvent remaining on the recording surface when the recording medium is accumulated in the accumulation process is Y [μg / cm ２ ], the glass transition temperature of the resin particles is Tg [°C], and the film surface temperature of the ink film on the recording surface during accumulation is Tc [°C], the image forming method satisfies the following formula (1) or formula (2): 0≦X×Y≦4000 (1) 4000<X×Y≦6000 and Tg−Tc≧10 (2)

[0028] In the image forming method disclosed herein, the recording medium is a sheet-like recording medium that can be stacked and stored. Recording media include those referred to by various terms, such as paper, recording paper, printing paper, printing media, print media, print-receiving media, image-forming media, image-receiving media, image-receiving media, and ejection-receiving media. When stacked, the recording media are stacked with the recording surface on which the last image was formed facing up. That is, the recording media are stacked without the recording surface on which the last image was formed contacting the previously stacked recording media, and the next recording medium is stacked on top of that recording surface. The "recording surface on which the last image was formed" refers to the surface on which an image is formed in the case of single-sided printing (described below), and to the recording surface on which a second image is formed in the case of double-sided printing (described below).

[0029] According to the image forming method of the present disclosure, the occurrence of blocking during accumulation of recording media can be more reliably suppressed than in the past.

[0030] The lower the amount of residual solvent in the ink film, the more the resin in the ink film hardens, and the less adhesive it becomes. Furthermore, if the SP value of the organic solvent is small, it becomes hydrophobic, which tends to harden the resin in the ink film and suppress blocking. Therefore, it is preferable for the organic solvent to be somewhat hydrophobic. On the other hand, if the organic solvent is too hydrophobic, moisture evaporates too quickly during rapid drying, and in the case of high-density images, cracks may occur in the image due to thermal shrinkage before a continuous film is formed, which may lead to a decrease in density, etc.

[0031] When the above formula (1) is satisfied, the amount of residual solvent is sufficiently small, so that stickiness can be suppressed and the occurrence of blocking during accumulation can be suppressed.

[0032] In the image forming method of the present disclosure, when the above formula (1) is satisfied, the product X×Y of X and Y is preferably 1500 or more, and more preferably 2500 or more. That is, it is preferable to satisfy the following formula (1-1), and it is more preferable to satisfy the following formula (1-2): 1500≦X×Y≦4000 (1-1) 2500≦X×Y≦4000 (1-2)

[0033] When drying is performed rapidly in the drying step, the lower the SP value of the organic solvent, the less likely cracks will occur in the ink film. Therefore, by satisfying the above formula (1-1), and more preferably the above formula (1-2), it is possible to suppress both the occurrence of blocking and cracks.

[0034] When formula (1), formula (1-1), or formula (1-2) is satisfied, the blocking suppression effect is obtained without being largely dependent on the ink film surface temperature Tc during accumulation. However, when formula (1), preferably formula (1-1), and more preferably formula (1-2) is satisfied, it is preferable to further satisfy the following formula (3): Tg - Tc ≧ 10 (3)

[0035] It is more preferable that the following formula (3-1) is satisfied, and it is even more preferable that the following formula (3-2) is satisfied: Tg - Tc ≧ 40 (3-1) Tg - Tc ≧ 60 (3-2) The upper limit of Tg - Tc is, for example, Tg - 20, and practically, it is 100°C or less.

[0036] On the other hand, when the above formula (2) of 4000<X×Y≦6000 is satisfied, the amount of residual solvent in the ink film is relatively large, and the ink film is therefore more likely to become sticky than when formula (1) is satisfied. However, if the relationship between the glass transition temperature Tg of the resin in the ink film and the surface temperature Tc of the ink film during accumulation also satisfies Tg−Tc≧10, it is possible to suppress stickiness.

[0037] In the image forming method of the present disclosure, even when the above formula (2) is satisfied, it is preferable to satisfy the above formula (3-1), and it is more preferable to satisfy the above formula (3-2).

[0038] The greater the difference between Tg and Tc, the more effectively the ink film surface can be prevented from becoming sticky, and as a result, the more effectively the ink can be prevented from blocking during accumulation.

[0039] The glass transition temperature Tg of the resin particles is preferably −5° C. or higher and 150° C. or lower, more preferably 60° C. or higher, even more preferably 70° C. or higher, and particularly preferably 90° C. or higher. When the Tg is 150° C. or lower, good abrasion resistance can be obtained. Furthermore, when the Tg is −5° C. or higher, stickiness of the ink film can be suppressed and cracking of the image (ink film) can be suppressed.

[0040] The image forming method disclosed herein can be applied both to forming an image on only one side of a recording medium (single-sided printing) and to forming an image on both the first recording surface and the second recording surface, which are the front and back sides of the recording medium (double-sided printing).

[0041] When forming images on the front and back surfaces of a recording medium, the image forming process and drying process described above can be performed sequentially on the first and second recording surfaces. In this case, the recording surface that becomes the top surface (the surface that does not come into contact with the previously stacked recording medium) during stacking is the second recording surface.

[0042] When images are formed on both sides, the film surface temperature of the second recording surface of the stacked recording media during stacking is the above-mentioned film surface temperature Tc. Here, when the film surface temperature of the first recording surface during stacking is Tc1 [°C], it is preferable to satisfy the following formula (4): Tg - Tc ≧ 40, and Tc - Tc1 ≧ 20 (4)

[0043] When recording media with images formed on both sides are stacked, the second recording side of the first recording media stacked is in contact with the first recording side of the next recording media stacked. By satisfying the above formula (4), that is, by sufficiently cooling the film surface temperature of the first recording side, it is possible to suppress the fusion of the ink film surfaces, and when images are formed on both sides, it is possible to achieve a high effect of suppressing the occurrence of blocking.

[0044] (SP Value) The SP (Solubility Parameter) value is a value (solubility parameter) expressed as the square root of the molecular cohesive energy, and is a value calculated by the method described in R. F. Fedors, Polymer Engineering Science, 14, pp. 147-154 (1974). In the present disclosure, the "SP value" is defined as MPa １／２It means the SP value in units.

[0045] The organic solvent in the ink may be a single organic solvent, or may contain multiple organic solvents. When multiple organic solvents are contained, the SP value of the organic solvent in the ink means the weighted average value of the individual organic solvents. The weighted average SP value is calculated using the following formula (A): In formula (A), the SP value of the i-th organic solvent (i is an integer of 1 or more) contained in the ink is substituted for Si, and the mass fraction of the i-th organic solvent in all the organic solvents contained in the ink is substituted for Wi. X = ΣSiWi / ΣWi (A)

[0046] For example, if the organic solvent in the ink has an SP value X of 20 MPa, １／２ Solvent 1 (10 mass%) and SP value X of 25 MPa １／２ Solvent 2 (20 mass%) and SP value X of 30 MPa １／２ The SP value of the organic solvent in the ink containing solvent 3 (70% by mass) is calculated by the following formula: X (MPa １／２ ) = (20 MPa １／２ ×10+25MPa １／２ ×20+30MPa １／２ ×70) / (10+20+70) =28MPa １／２

[0047] The SP value X [MPa １／２ ] is preferably 18 or more and 28 or less, and more preferably 20 or more and 23 or less.

[0048] Specific organic solvents and their SP values ​​are listed below. The values ​​in parentheses represent the SP values. Propylene glycol (27.6 MPa) １／２ ) Ethylene glycol (30.3 MPa １／２ ) Diethylene glycol (30.6 MPa １／２ ) Triethylene glycol (27.8 MPa １／２ ) Tripropylene glycol (24.7 MPa １／２ ) 2-methyl-1,3-butanediol (28.4 MPa １／２ ) 1,2-pentanediol (25.0 MPa １／２) 1,5-pentanediol (29.0 MPa １／２ ) 1,2-hexanediol (24.1 MPa １／２ ) 1,6-hexanediol (27.7 MPa １／２ ) Glycerin (33.5 MPa １／２ ) Methanol (28.2 MPa １／２ ) Isopropyl alcohol (23.7 MPa １／２ ) Triethanolamine (32.4 MPa １／２ ) Ethylene glycol (30.3 MPa １／２ ) Dipropylene glycol (27.1 MPa １／２ ) Tripropylene glycol (24.7 MPa １／２ ) Ethylene glycol monoethyl ether (23.5 MPa １／２ ) Ethylene glycol monopropyl ether (22.7 MPa １／２ ) Ethylene glycol monobutyl ether (22.1 MPa １／２ ) Diethylene glycol monomethyl ether (23.0 MPa １／２ ) Diethylene glycol monoethyl ether (22.4 MPa １／２ ) Diethylene glycol monopropyl ether (21.9 MPa １／２ ) Diethylene glycol monobutyl ether (21.5 MPa １／２ ) Triethylene glycol monomethyl ether (22.1 MPa １／２ ) Triethylene glycol monoethyl ether (21.7 MPa １／２ ) Triethylene glycol monobutyl ether (21.1 MPa １／２ ) Propylene glycol monomethyl ether (23.1 MPa １／２ ) Propylene glycol monoethyl ether (22.3 MPa １／２ ) Propylene glycol monopropyl ether (21.8 MPa １／２ ) Propylene glycol monobutyl ether (21.4 MPa １／２ ) Dipropylene glycol monomethyl ether (21.3 MPa １／２ ) Dipropylene glycol monopropyl ether (20.7 MPa１／２ ) Dipropylene glycol monobutyl ether (20.5 MPa １／２ ) Dipropylene glycol t-butyl ether (20.0 MPa １／２ ) Tripropylene glycol monomethyl ether (20.4 MPa １／２ ) Diethylene glycol monohexyl ether (20.9 MPa １／２ ) Ethylene glycol mono-2-ethylhexyl ether (20.5 MPa １／２ ) Diethylene glycol mono-2-ethylhexyl ether (20.3 MPa １／２ )

[0049] (Residual Solvent Amount) In the present disclosure, the residual solvent amount Y of the organic solvent remaining on the recording surface is a value measured by forming an image under the following conditions. In an image forming apparatus for carrying out the target image forming method, a full-area image (solid image) is formed on the recording surface of a recording medium having a size of 585 mm x 750 mm, which corresponds to a paper size B2. At this time, the ink is blue with a 100% concentration, and the ink application amount is 12.3 g / m ２ A blue solid image is formed using the same method. Immediately after the solid image is formed and the recording medium is transported to the accumulation position, it is removed and four 1.5 cm x 0.8 cm samples are cut from the center of the recording medium (i.e., the center of the image). This sample is placed in a vial, and 0.5 mL each of methanol and THF (tetrahydrofuran) is added to the vial, which is then capped and extracted over one day. The amount of residual solvent in the resulting extract is quantified using gas chromatography.

[0050] (Glass Transition Temperature) In this specification, the glass transition temperature (Tg) refers to the measured Tg obtained by actual measurement. The measured Tg is measured under normal measurement conditions using a differential scanning calorimeter, for example, a differential scanning calorimeter manufactured by SII NanoTechnology Inc. (product name "EXSTAR6220"). However, when measurement is difficult due to decomposition of the material, etc., the calculated Tgk (absolute temperature [K]) calculated using the following formula is converted to Celsius temperature [°C] and used as the glass transition temperature Tg. The calculated Tgk is a value calculated using the following formula (B): 1 / Tgk = Σ(Xi / Tgi) ... (B) Here, the polymer to be calculated is assumed to be a copolymer of n types of monomer components, i = 1 to n. Xi is the mass fraction of the i-th monomer (ΣXi = 1), and Tgi is the glass transition temperature (absolute temperature) of a homopolymer of the i-th monomer. Here, Σ is the sum from i = 1 to n. The glass transition temperature (Tgi) of the homopolymer of each monomer is taken from Polymer Handbook (3rd Edition) (by J. Brandrup and EH Immergut, Wiley-Interscience, 1989).

[0051] (Film surface temperature) The ink film surface temperature is a value measured using a radiation thermometer (for example, FT-H20 manufactured by Keyence Corporation). The ink film surface temperature Tc during accumulation is a value measured using a radiation thermometer placed directly above the recording media in the accumulation device where the recording media are accumulated. Furthermore, when images are formed on both sides of a recording medium, the film surface temperature Tc1 of the first recording surface of the recording medium is a value measured using a radiation thermometer placed diagonally below the accumulation device immediately before accumulation.

[0052] Each step of the image forming method of the present disclosure will be described below.

[0053] [Preparation Step] In the preparation step, an ink containing water, resin particles, and an organic solvent (hereinafter also referred to as "specific ink") is prepared. The ink preparation step may be a step of simply preparing a specific ink that has been prepared in advance, or may be a step of preparing the specific ink.

[0054] The specific ink contains water, that is, it is a so-called water-based ink. The specific ink is prepared by containing, as the organic solvent in the ink, an organic solvent having an SP value X that satisfies the above formula (1) or (2).

[0055] A specific example of the specific ink is an inkjet ink described in WO 2023 / 047767 that contains water, a pigment, resin particles, and an organic solvent, has a pH of 7.2 to 11, and satisfies the following inequality (X): ORPi - [285 - 59 x (pHi - 6.2)] ≧ 0 Inequality (X) In inequality (X), ORPi represents the oxidation-reduction potential of the inkjet ink in units of V, measured under apparatus conditions such that the oxidation-reduction potential of water at a pH of 6.2 is 310 mV, and pHi represents the pH of the inkjet ink. It is preferable that the specific ink contains wax.

[0056] [Image Forming Process] In the image forming process, an image is formed by applying ink to the recording surface of a recording medium to form an ink film. The ink is applied by an inkjet method.

[0057] The application of ink by the inkjet method means that the ink is applied to the recording surface by ejecting the ink from an inkjet head. There are no particular limitations on the method of ejecting the specific ink from the inkjet head.

[0058] [Drying Step] In the drying step, the ink film formed on the recording surface is dried. Specifically, this is a step of drying the ink film by heat drying, but a cooling step may be included after the heat drying step.

[0059] The heat drying method is not particularly limited, and examples thereof include infrared (IR) drying, hot air blowing (i.e., hot air drying, such as a hair dryer), and heat drying using a heating device (such as a heater, hot plate, heating drum, or heating furnace). The heat drying method may be a combination of two or more of these methods. Heat drying can be performed by heating the ink film from at least one of the front and back surfaces of the recording medium.

[0060] The heating temperature in the heat drying of the ink film is preferably 35° C. or higher, more preferably 40° C. or higher, even more preferably 50° C. or higher, and even more preferably 60° C. or higher. There is no particular upper limit to the heating temperature, but 100° C. is preferred, and 90° C. is more preferred.

[0061] The heating time for heating and drying the ink film is not particularly limited, but is preferably 1 to 180 seconds, more preferably 1 to 120 seconds, and even more preferably 1 to 60 seconds.

[0062] As a means for cooling after heat drying, there may be mentioned a blowing means for blowing air at room temperature of about 20° C. or cooled air below 20° C. onto the recording medium.

[0063] In the drying step, the heat drying or the heat drying and cooling step is carried out under the condition that the amount of remaining solvent Y at the time of accumulation satisfies the formula (1) or the formula (2) in relation to the SP value X of the organic solvent contained in the specific ink.

[0064] [Stacking Process] In the stacking process, the recording media with dried ink films are stacked. Multiple recording media with images formed on them are stacked in a stacking device. The next recording media with an image formed on it is stacked on top of the recording surface (the surface with the ink film formed on it) of the previously stacked recording media.

[0065] If the ink film is sticky, blocking, in which recording media stick to each other, occurs during this accumulation process. However, in the present disclosure, an image forming method that satisfies the above formula (1) or (2) is carried out, and therefore the occurrence of blocking can be suppressed.

[0066] The image forming method of the present disclosure may include other steps in addition to the steps described above.

[0067] 1 is a schematic diagram of an inkjet printing apparatus 1 according to an embodiment of the image forming apparatus of the present disclosure. The inkjet printing apparatus 1 is an image forming apparatus according to an embodiment of the present disclosure that is used in the image forming method of the present disclosure.

[0068] The inkjet printing device 1 is an inkjet color digital printing device that forms a desired image on a sheet of paper P. The inkjet printing device 1 is capable of single-sided printing, in which an image is formed on only one side of the paper P, and double-sided printing, in which an image is formed on both sides of the paper P. The paper P is an example of a recording medium of the technology disclosed herein.

[0069] 1, the inkjet printing apparatus 1 includes a transport mechanism 10, a paper feeder 20, an image forming unit 40, a drying unit 50, and a stacking device 70. In this example, the drying unit 50 includes a heat drying section 52 and a cooling section 54. Although not shown in FIG. 1, the inkjet printing apparatus 1 also includes a processor that controls each section.

[0070] The transport mechanism 10 has a transport path 12 along which the paper P is transported. In Fig. 1, the direction in which the paper P is transported is indicated by a dashed arrow. The image forming unit 40 and the drying unit 50 are arranged on the transport path 12. The paper P is transported along the transport path 12 to various units, where it is subjected to various processes.

[0071] The transport path 12 includes a main transport path 13, a supply path 14 that supplies paper P to the main transport path 13, a discharge path 15 that discharges paper from the main transport path 13, and a return transport path 16 that branches off from the main transport path 13 and the discharge path 15. The return transport path 16 constitutes a path that returns paper P that has passed through the main transport path 13 back to the main transport path 13 for double-sided printing.

[0072] The supply path 14 supplies paper P from the paper feed device 20 to the main transport path 13. One end of the supply path 14 is disposed on the paper feed device 20 side, and the other end is connected to the main transport path 13. Paper P is supplied from the paper feed device 20 to one end of the supply path 14, transported along the supply path 14, and supplied from the other end of the supply path 14 to the main transport path 13.

[0073] The discharge path 15 transports the paper P from the main transport path 13 to the stacking device 70. One end of the discharge path 15 is connected to the main transport path 13, and the other end is connected to the stacking device 70. The paper P is discharged from the main transport path 13 to one end of the discharge path 15, transported along the discharge path 15, and discharged from the other end of the discharge path 15 to the stacking device 70.

[0074] The return transport path 16 has a starting end connected to the ending end of the main transport path 13 and an ending end connected to the starting end of the main transport path 13, forming a circular path together with the main transport path 13. The return transport path 16 returns the paper P that has passed through the main transport path 13 and has an image formed on its first recording surface by the image forming unit 40 to the image forming unit 40, allowing an image to be formed on its second recording surface.

[0075] The return transport path 16 is provided with a switchback section 17 that reverses the traveling direction of the paper P. The switchback section 17 temporarily pulls out the paper P from the return transport path 16 to reverse the traveling direction of the paper P. That is, the leading edge of the paper P in the traveling direction when it was transported on the return transport path 16 before being pulled into the switchback section 17 becomes the trailing edge in the traveling direction after it is returned from the switchback section 17 to the return transport path 16. By passing through this switchback section 17, the front and back of the paper P that is supplied again from the return transport path 16 to the main transport path 13 is reversed.

[0076] The transport mechanism 10 includes a plurality of transport members (not shown) arranged along the transport path 12. The plurality of transport members include a transport drum, a belt conveyor, a pair of transport rollers, a chain gripper, and a transport guide. The transport mechanism 10 also includes a drive unit (not shown) such as a motor (not shown) as a power source and a motor drive circuit (not shown). The paper P is transported along the transport path 12 by these elements that make up the transport mechanism 10.

[0077] The paper feed device 20 includes a paper feed tray on which a stack of multiple sheets of paper P is placed. There are no particular limitations on the type of paper P, but it is possible to use, for example, printing paper that is primarily made of cellulose, such as high-quality paper, coated paper, and art paper.

[0078] The paper feeder 20 takes out the sheets P from the stack set therein one by one in order from the top, and supplies them to the supply path 14 of the transport path 12 .

[0079] The image forming unit 40 performs an image forming process on the recording surface of the paper P. The image forming unit 40 forms an image by forming an ink film on the recording surface of the paper P. The image forming unit 40 includes an inkjet head (not shown). The inkjet head may be a single head or multiple heads. For example, the image forming unit 40 may include an inkjet head that ejects cyan ink droplets, an inkjet head that ejects magenta ink droplets, an inkjet head that ejects yellow ink droplets, and an inkjet head that ejects black ink droplets. The inkjet heads are supplied with ink from ink tanks (not shown) that serve as ink supply sources for the corresponding colors via piping (not shown). This ink contains water, resin particles, and an organic solvent, and corresponds to the specific ink previously prepared in the preparation process.

[0080] Droplets of ink are ejected from the inkjet head toward the transported paper P, and the ejected droplets adhere to the paper P, thereby forming an image on the paper P. That is, in the image forming unit 40, an image is formed by applying ink to the recording surface of the paper P to form an ink film on the recording surface.

[0081] The drying unit 50 carries out a drying process for drying the ink film formed on the recording surface of the paper P. In the drying unit 50, the heating and drying section 52 carries out the heating and drying process, and the cooling section 54 carries out the cooling process.

[0082] The heat drying section 52 is provided with, for example, a belt conveyor equipped with a heating belt that also serves as part of the transport mechanism 10. The belt conveyor transports the paper P while adsorbing it from the back side and heating it by contact heating. The heat drying section 52 may also include a heater disposed opposite the transport surface of the heating belt. Examples of heaters that can be used include convection heating means such as a hot air blower, radiant heating means such as an infrared (IR) lamp, an ultraviolet (UV) lamp, or a microwave generator, and a superheated steam generator.

[0083] The cooling unit 54 cools the ink film that has been heated and dried by the heating and drying unit 52. As an example, the cooling unit 54 includes a blower (not shown) that blows room temperature air or air that is cooler than room temperature. The blower is disposed opposite the recording surface (i.e., the ink film surface) of the paper P. The blower's blowing temperature and output are adjustable. The cooling means included in the cooling unit 54 may be a contact cooling mechanism that cools the paper P by contacting the side opposite the recording surface, instead of a blower that cools the paper P without contacting the paper P, or both.

[0084] The stacking device 70 stacks the sheets P on which images have been formed. The stacking device 70 receives the sheets P discharged from the discharge path 15 of the transport path 12, and stacks the sheets P on a stacking tray (not shown).

[0085] The inkjet printing device 1 is capable of single-sided printing and double-sided printing, and is configured to be able to selectively switch between a single-sided printing mode and a double-sided printing mode. Depending on which mode is selected, the transport path is switched, and the paper P is transported along the transport path appropriate for each mode.

[0086] In the single-sided printing mode, the paper P is transported along a path that passes through the supply path 14, the main transport path 13, and the discharge path 15. More specifically, the paper P fed from the paper feeder 20 to the supply path 14 is transported to the main transport path 13, where an image forming process by the image forming unit 40 and a drying process by the drying unit 50 are sequentially performed. Thereafter, the paper P with an image printed on its first recording side is transported to the discharge path 15 and discharged to the stacking device 70.

[0087] In the double-sided printing mode, the paper P is transported along a path that passes through the supply path 14, the main transport path 13, the return transport path 16, the main transport path 13, and the discharge path 15 in this order. Specifically, the paper P fed from the paper feed device 20 to the supply path 14 is transported to the main transport path 13, where an image formation process and a drying process are sequentially performed on the first recording side of the paper P. The paper P is then transported from the main transport path 13 to the return transport path 16, where it is inverted to its front and rear ends by passing through the switchback unit 17, and the paper P with its front and rear ends inverted is transported along the return transport path 16. The paper P is returned to the main transport path 13 along the return transport path 16. When the paper P is returned to the main transport path 13, it is inverted so that the second recording side of the paper P becomes the image formation side. In the main transport path 13, an image formation process and a drying process are sequentially performed on the second recording side. Then, the paper P with images printed on both sides is transported from the main transport path 13 to the discharge path 15 and discharged to the stacking device 70.

[0088] The processor includes a CPU (Central Processing Unit). The processor functions as a processing unit and / or a control unit that performs various processes by executing instructions of a program stored in the storage device. The processor comprehensively controls the conveying mechanism 10, the paper feeder 20, the image forming unit 40, the drying unit 50, and the stacking device 70.

[0089] A storage device is a non-transitory storage medium and a tangible computer-readable medium. The storage device includes a memory, which is a main storage device, and a storage, which is an auxiliary storage device. The storage device may be, for example, a semiconductor memory, a hard disk drive (HDD), a solid state drive (SSD), or a combination of these. Part or all of the storage area of ​​the storage device may be included in the processor.

[0090] The storage device stores various parameters used by the inkjet printing apparatus 1 and programs used by each unit of the inkjet printing apparatus 1. The storage device also functions as a temporary storage unit for various data including image data.

[0091] The various parameters stored in the storage device are read out via the processor and set in each part of the device, and the various programs stored in the storage device are read out via the processor and executed in each part of the device.

[0092] The processor calculates the SP value of the organic solvent in the ink by X [MPa １／２ ], and the amount of residual organic solvent remaining on the recording surface when the recording medium is accumulated in the accumulation process is Y [μg / cm ２ ], the glass transition temperature of the resin particles is Tg [°C], and the surface temperature of the ink film during accumulation is Tc [°C], the ink is controlled so that each part satisfies the following formula (1) or (2): 0≦X×Y≦4000 (1) 4000<X×Y≦6000 and Tg−Tc≧10 (2)

[0093] For example, conditions such as the conveying speed, heating and drying, and cooling required to satisfy the above formula (1) or (2) are determined in advance according to the type of ink and the type of paper, and a lookup table is stored in a storage device. The processor may be configured to refer to the lookup table based on information about the ink and paper during printing, and control each section under conditions according to that information.

[0094] The hardware structure of the processor can be any of the following types of processors: The various types of processors include a CPU, which is a general-purpose processor that executes software (programs) and functions as various processing units, as well as dedicated electrical circuits such as a PLD (Programmable Logic Device) that can change its circuit configuration after manufacture, such as an FPGA (Field-Programmable Gate Array), and an ASIC (Application Specific Integrated Circuit), which is a processor with a circuit configuration designed specifically for executing specific processing.

[0095] The above-described processing may be performed by one of these various processors, or by a combination of two or more processors of the same or different types (e.g., a plurality of FPGAs, or a combination of a CPU and an FPGA). Furthermore, a plurality of processing units may be configured by a single processor. An example of configuring a plurality of processing units by a single processor is a system-on-chip (SOC), in which a processor is used to realize the functions of an entire system including a plurality of processing units on a single IC (Integrated Circuit) chip.

[0096] Furthermore, more specifically, the hardware structure of these processors can be an electric circuit that combines circuit elements such as semiconductor elements.

[0097] The image forming system of the present disclosure includes, for example, the inkjet printing device 1, which is the image forming device described above, and a specific ink.

[0098] The inkjet printing apparatus 1 may further include a pretreatment liquid application unit and a pretreatment liquid drying unit upstream of the image forming unit 40. The pretreatment liquid application unit applies the pretreatment liquid to the recording surface of the recording medium before ink is applied. The pretreatment liquid drying unit dries the pretreatment liquid applied to the recording surface. Here, the pretreatment liquid is a liquid called a "precoat," "preconditioner," "undercoat liquid," or "treatment agent," and has the function of aggregating, insolubilizing, or thickening the colorant components in the ink. Thus, when the pretreatment liquid application step is included, "forming an image by applying ink to the recording surface of the recording medium to form an ink film" means applying ink onto a coating of the pretreatment liquid provided on the recording surface of the recording medium.

[0099] Examples of the present disclosure will be described below, but the present disclosure is not limited to the following examples.

[0100] A plurality of types of ink were prepared, and an image forming process using any of the inks, a drying process under different drying conditions, and an accumulation process were carried out, and tests were carried out to evaluate blocking, image cracking, and abrasion resistance.

[0101] "Ink Preparation" <Preparation of Resin Particles C01> An aqueous dispersion of resin particles C01 having a glass transition temperature Tg of 97°C was prepared as follows. Water (250 g), 12-methacrylamidodecanoic acid (6.7 g), potassium bicarbonate (0.17 g), and isopropanol (20 g) were charged into a three-neck flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, and the temperature was raised to 85°C under a nitrogen stream. To this was added a mixed solution consisting of 4,4'-azobis(4-cyanovaleric acid) (radical polymerization initiator, product name "V-501", Fujifilm Wako Pure Chemical Industries, Ltd.) (0.11 g), potassium bicarbonate (0.08 g), and water (9 g), and the mixture was stirred for 10 minutes. Next, a monomer solution consisting of styrene (14 g), benzyl methacrylate (14 g), methyl methacrylate (48 g), butyl methacrylate (3.3 g), and hydroxylethyl methacrylate (14 g) was added dropwise to the three-neck flask at a constant rate so that the addition was completed within 3 hours. Furthermore, a mixed solution consisting of V-501 (0.06 g), potassium bicarbonate (0.04 g), and water (6 g) was added in two portions: immediately after the start of the addition of the monomer solution and 1.5 hours after the start of the addition of the monomer solution. After the addition of the monomer solution was completed, the mixture was stirred for 1 hour. Subsequently, a mixed solution consisting of V-501 (0.06 g), potassium bicarbonate (0.04 g), and water (6 g) was added to the resulting reaction mixture, and the mixture was stirred for an additional 3 hours. The resulting reaction mixture was filtered through a 50 μm mesh to obtain an aqueous dispersion of resin particles C01.

[0102] <Preparation of Resin Particles C02> An aqueous dispersion of resin particles C02 of a methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (27 / 63 / 10) having a glass transition temperature Tg of 155°C was prepared as follows. 293 g of methyl ethyl ketone was charged into a 2-liter three-neck flask (hereinafter also referred to as the "reaction vessel") equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, and the temperature was raised to 80°C. Next, while maintaining the temperature inside the reaction vessel at 80°C, a mixed solution consisting of 60.0 g of methyl methacrylate (manufactured by Mitsubishi Gas Chemical Company, Inc.), 160.4 g of isobornyl methacrylate (manufactured by Kyoeisha Chemical Co., Ltd.), 25.5 g of methacrylic acid (manufactured by Mitsubishi Gas Chemical Company, Inc.), 48 g of methyl ethyl ketone, and 1.25 g of "V-601" (a polymerization initiator manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise at a constant rate so that the addition was completed within 2 hours. After completion of the dropwise addition, (1) a solution containing 0.60 g of "V-601" and 5.0 g of methyl ethyl ketone was added and stirred for another 2 hours. Then, step (1) was repeated four times, and a solution containing 0.60 g of "V-601" and 5.0 g of methyl ethyl ketone was added and stirred for 3 hours. As a result, a polymer solution containing a methyl methacrylate / isobornyl methacrylate / methacrylic acid (= 27 / 63 / 10 [mass ratio]) copolymer was obtained. Next, 588.2 g of the polymer solution was weighed into a reaction vessel, and 165 g of isopropanol and 120.8 ml of a 1 mol / L aqueous sodium hydroxide (NaOH) solution were added, and the temperature in the reaction vessel was raised to 80 ° C. Next, 718.0 g of distilled water was added dropwise to the reaction vessel at a rate of 20 ml / min, and aqueous dispersion was performed. The temperature in the reaction vessel was then maintained at 80°C for 2 hours, 85°C for 2 hours, and 90°C for 2 hours under atmospheric pressure, and then the pressure in the reaction vessel was reduced, and a total of 913.7 g of isopropanol, methyl ethyl ketone, and distilled water was distilled off. In this way, an aqueous dispersion (emulsion) of resin particles C02 with a solid content concentration of 23.2 mass% was obtained.

[0103] <Preparation of Resin Particles C03> An aqueous dispersion of resin particles C03 made of a methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (35 / 55 / 10) having a glass transition temperature Tg of 150°C was prepared as follows. 293 g of methyl ethyl ketone was charged into a 2-liter three-neck flask (hereinafter also referred to as the "reaction vessel") equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, and the temperature was raised to 80°C. Next, while maintaining the temperature inside the reaction vessel at 80°C, a mixed solution consisting of 90.0 g of methyl methacrylate (manufactured by Mitsubishi Gas Chemical Company, Inc.), 139.4 g of isobornyl methacrylate (manufactured by Kyoeisha Chemical Co., Ltd.), 25.5 g of methacrylic acid (manufactured by Mitsubishi Gas Chemical Company, Inc.), 48 g of methyl ethyl ketone, and 1.25 g of "V-601" (a polymerization initiator manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise at a constant rate so that the addition was completed within 2 hours. After completion of the dropwise addition, (1) a solution containing 0.60 g of "V-601" and 5.0 g of methyl ethyl ketone was added and stirred for another 2 hours. Then, step (1) was repeated four times, and a solution containing 0.60 g of "V-601" and 5.0 g of methyl ethyl ketone was added and stirred for 3 hours. As a result, a polymer solution containing a methyl methacrylate / isobornyl methacrylate / methacrylic acid (= 35 / 55 / 10 [mass ratio]) copolymer was obtained. Next, 588.2 g of the polymer solution was weighed into a reaction vessel, and 165 g of isopropanol and 120.8 ml of a 1 mol / L aqueous sodium hydroxide (NaOH) solution were added, and the temperature in the reaction vessel was raised to 80 ° C. Next, 718.0 g of distilled water was added dropwise to the reaction vessel at a rate of 20 ml / min, and aqueous dispersion was performed. The temperature in the reaction vessel was then maintained at 80°C for 2 hours, 85°C for 2 hours, and 90°C for 2 hours under atmospheric pressure, and then the pressure in the reaction vessel was reduced, and a total of 913.7 g of isopropanol, methyl ethyl ketone, and distilled water was distilled off. In this way, an aqueous dispersion (emulsion) of resin particles C03 with a solid content concentration of 23.2 mass% was obtained.

[0104] In addition, commercially available resin particles with different glass transition temperatures Tg were prepared as the resin particles. The correspondence between the glass transition temperature Tg for each test and the resin particles in the ink used is as shown in Table 1 below.

[0105] The glass transition temperature Tg of each resin particle is a value measured under normal measurement conditions using a differential scanning calorimeter (product name "EXSTAR6220") manufactured by SII NanoTechnology Inc.

[0106] <Preparation of Pigment Dispersion> Projet Cyan APD1000 (manufactured by FUJIFILM Imaging Colorants, cyan pigment dispersion, pigment concentration in pigment dispersion: 14.1% by mass) was prepared.

[0107] <Ink Preparation> The effective ingredients of the ink described below were mixed with water, and coarse particles were removed from the resulting mixture to obtain an ink. The total amount of the effective ingredients of the ink and the amount of water was 100 parts by mass. Ion-exchanged water was used as the water.

[0108] (Inks of Test Examples Nos. 78 to 80) Table 2 shows the active ingredient A of the inks used in Test Examples Nos. 78 to 80.

[0109] In the above active ingredient A, the organic solvent is propylene glycol (PG), and the SP value is 27.6 MPa. １／２ The glass transition temperature Tg of the resin particles is 97°C, and the melting point Tm of the wax is 83°C. The Tg, Tm, and SP value X for each test are summarized in Tables 4 and 5 below. Below, the formulation of active ingredient A of the ink is used as the standard, and differences between the active ingredients of the inks used in other tests will be mainly explained.

[0110] Test Examples No. 1 to No. 77 do not contain wax as an active ingredient. In Tables 4 and 5 below, the notation "-" in the wax column means that wax is not contained. When wax is not contained, the total amount of organic solvent was adjusted to 21.9 parts by mass. The inks used in each test were as follows.

[0111] (Inks of Test Examples 1 to 14 and 101 to 106) The inks were prepared so that the active ingredient A did not contain wax and the total amount of organic solvent was 21.9 parts by mass. The active ingredient of the inks of Test Examples 1 to 14 is referred to as active ingredient B.

[0112] (Inks of Test Examples Nos. 15 to 18) The same procedures were followed as above, except that in the active ingredient B of the ink, the resin particles were changed to resin particles C02 having a glass transition temperature Tg of 155°C.

[0113] (Inks of Test Examples Nos. 19 to 22) The same procedures were followed except that in the active ingredient B of the ink, the resin particles were changed to resin particles C03 having a glass transition temperature Tg of 150°C.

[0114] (Inks of Test Examples No. 23 to 26) The inks were the same as those in Test Examples No. 23 to 26, except that the resin particles in the active ingredient B of the ink were changed to Neocryl A-614, an acrylic resin particle manufactured by Kusumoto Chemicals Co., Ltd., with a glass transition temperature Tg of 74°C and a solids concentration of 32%.

[0115] (Inks of Test Examples No. 27 to 30) The inks were the same as those in Test Examples No. 27 to 30, except that the resin particles in the active ingredient B of the ink were changed to Neocryl A-6092, an acrylic resin particle manufactured by DSM, having a glass transition temperature Tg of 56°C and a solids concentration of 43%.

[0116] (Inks of Test Examples No. 31 to 34) The inks were the same as those tested, except that the resin particles in the active ingredient B of the ink were changed to Movinyl 6820 acrylic resin particles manufactured by Japan Coating Resins Co., Ltd., with a glass transition temperature Tg of 35°C and a solids concentration of 51%.

[0117] (Inks of Test Examples No. 35 to 38) The inks were the same as those tested, except that in the active ingredient B of the ink, the resin particles were changed to Movinyl SA-200 acrylic resin particles manufactured by Japan Coating Resins Co., Ltd., with a glass transition temperature Tg of -6°C and a solids concentration of 40%.

[0118] (Ink of Test Example No. 39) The ink was prepared in the same manner as in Test Example No. 39, except that the resin particles in the active ingredient B of the ink were changed to Hi-Loss PE-1126 acrylic resin particles manufactured by Seiko PMC Co., Ltd., with a glass transition temperature Tg of -12°C and a solids concentration of 41.5%.

[0119] (Test Example Nos. 40 to 45, 69 Ink) In the active ingredient B of the ink, the organic solvent is used at a PGSP value of 24.7 MPa. １／２ The same procedure was followed except that tripropylene glycol (TPG) was used.

[0120] (Test Example Nos. 46 to 51, 74 Ink) In the active ingredient B of the ink, the organic solvent was replaced with PG, and the SP value was 21.5 MPa. １／２ The same procedure was followed except that diethylene glycol monobutyl ether (DEGmBE) was used instead.

[0121] (Test Example Nos. 52 to 57 Ink) In the active ingredient B of the ink, the organic solvent was replaced with PG, and the SP value was 20.4 MPa. １／２ The same procedure was followed except that tripropylene glycol monomethyl ether (TPGmME) was used instead.

[0122] (Test Example Nos. 58 to 63 Ink) In the active ingredient B of the ink, the organic solvent was replaced with PG, and the SP value was 33.5 MPa. １／２ The same procedure was followed except that glycerin was used.

[0123] (Test Example No. 64 Ink) In the active ingredient B of the ink, the organic solvent was replaced with PG, and the SP value was 33.5 MPa. １／２ The same procedure was followed except that the resin particles were changed to resin particles C03 having a glass transition temperature Tg of 150°C.

[0124] (Ink of Test Example No. 65) In the active ingredient B of the ink, the organic solvent was replaced with PG, and the SP value was 33.5 MPa. １／２ The same procedure was followed except that the resin particles were changed to styrene / acrylic resin particles Neocryl A-633 manufactured by Kusumoto Chemicals Co., Ltd., having a glass transition temperature Tg of 63°C and a solids concentration of 42%.

[0125] (Ink of Test Example No. 66) In the active ingredient B of the ink, the organic solvent was replaced with PG, and the SP value was 33.5 MPa. １／２ The same procedure was followed except that the resin particles were changed to glycerin, and the resin particles were changed to Movinyl 6820 acrylic resin particles manufactured by Japan Coating Resins Co., Ltd., having a glass transition temperature Tg of 35°C and a solids concentration of 51%.

[0126] (Ink of Test Example No. 67) In the active ingredient B of the ink, the organic solvent was replaced with PG, and the SP value was 33.5 MPa. １／２The same procedure was followed except that the resin particles were changed to glycerin, and the resin particles were changed to Movinyl SA-200 acrylic resin particles manufactured by Japan Coating Resins Co., Ltd., with a glass transition temperature Tg of -6°C and a solids concentration of 40%.

[0127] (Ink of Test Example No. 68) In the active ingredient B of the ink, the organic solvent was replaced with PG, and the SP value was 24.7 MPa. １／２ The same procedure was followed except that the resin particles were changed to tripropylene glycol (TPG) having a glass transition temperature Tg of 150°C and the resin particles were changed to resin particles C03 having a glass transition temperature Tg of 150°C.

[0128] (Ink of Test Example No. 70) In the active ingredient B of the ink, the organic solvent was replaced with PG, and the SP value was 24.7 MPa. １／２ The same procedure was followed except that the resin particles were changed to Neocryl A-633, a styrene / acrylic resin particle manufactured by Kusumoto Chemicals Co., Ltd., having a glass transition temperature Tg of 63°C and a solids concentration of 42%.

[0129] (Ink of Test Example No. 71) In the active ingredient B of the ink, the organic solvent was replaced with PG, and the SP value was 24.7 MPa. １／２ The same procedure was followed except that the resin particles were changed to Movinyl 6820 acrylic resin particles manufactured by Japan Coating Resins Co., Ltd., with a glass transition temperature Tg of 35°C and a solids concentration of 51%.

[0130] (Ink of Test Example No. 72) In the active ingredient B of the ink, the organic solvent was replaced with PG, and the SP value was 24.7 MPa. １／２ The same procedure was followed except that the resin particles were changed to tripropylene glycol (TPG), and the resin particles were changed to Movinyl SA-200 acrylic resin particles manufactured by Japan Coating Resins Co., Ltd., having a glass transition temperature Tg of -6°C and a solids concentration of 40.

[0131] (Ink of Test Example No. 73) In the active ingredient B of the ink, the organic solvent was replaced with PG, and the SP value was 21.5 MPa. １／２The same procedure was followed except that the resin particles were changed to diethylene glycol monobutyl ether (DEGmBE) having a glass transition temperature Tg of 150°C and the resin particles were changed to resin particles C03 having a glass transition temperature Tg of 150°C.

[0132] (Ink of Test Example No. 75) In the active ingredient B of the ink, the organic solvent was replaced with PG, and the SP value was 21.5 MPa. １／２ The same procedure was followed except that the resin particles were changed to diethylene glycol monobutyl ether (DEGmBE), and the resin particles were changed to Neocryl A-633, a styrene / acrylic resin particle manufactured by Kusumoto Chemicals Co., Ltd., having a glass transition temperature Tg of 63°C and a solids concentration of 42%.

[0133] (Ink of Test Example No. 76) In the active ingredient B of the ink, the organic solvent PG was replaced with an ink having an SP value of 21.5 MPa. １／２ The same procedure was followed except that the resin particles were changed to diethylene glycol monobutyl ether (DEGmBE) and the resin particles were changed to Movinyl 6820 acrylic resin particles manufactured by Japan Coating Resins Co., Ltd., having a glass transition temperature Tg of 35°C and a solids concentration of 51%.

[0134] (Ink of Test Example No. 77) In the active ingredient B of the ink, the organic solvent was replaced with PG, and the SP value was 21.5 MPa. １／２ The same procedure was followed except that the resin particles were changed to diethylene glycol monobutyl ether (DEGmBE) having a glass transition temperature Tg of -6°C and a solids concentration of 40% by weight, respectively, and the resin particles were changed to Movinyl SA-200 acrylic resin particles manufactured by Japan Coating Resins Co., Ltd.

[0135] (Inks of Test Examples No. 81 to 83) The same procedures were followed as in Test Examples No. 81 to 83, except that in the active ingredient A of the ink, the wax was changed to Hitec E6314 (manufactured by Toho Chemical Industry Co., Ltd., an aqueous dispersion of wax particles made of polyethylene wax) having a melting point Tm of 137°C.

[0136] (Inks of Test Examples No. 84 to 86) The inks were the same as in Test Example Nos. 84 to 86, except that in the active ingredient A of the ink, the resin particles were changed to resin particles C03 having a glass transition temperature Tg of 150°C, and the wax was changed to Hitec E6314 (manufactured by Toho Chemical Industry Co., Ltd., an aqueous dispersion of wax particles made of polyethylene wax) having a melting point Tm of 137°C.

[0137] (Ink of Test Example No. 87) The ink was prepared in the same manner as in Test Example No. 87, except that the organic solvent in the active ingredient A of the ink was replaced with a single solvent of PG by a mixture of multiple solvents shown in Table 3 below. The organic solvents were adjusted so that the total mass of the organic solvents was 21.9 parts. The weighted average SP value of the organic solvents was 24.7 MPa. １／２ It was.

[0138] <Image Forming Method> Using the inkjet printing device 1 shown in FIG. 1, printing was performed on paper using the above-mentioned ink for each test. That is, images were formed on paper as a recording medium. Single-sided or double-sided printing was performed depending on the evaluation items described below. Bon Ivory 310 gsm paper was used. The amount of ink applied by the inkjet method in the image forming unit was 4.8 pL / pixel. The drying method in the heating and drying unit 52 was blowing hot air and heating the paper by suction. The cooling method in the cooling unit 54 was blowing air.

[0139] [Drying Process] In Test Examples 1 to 87, heating and cooling were performed under conditions that resulted in the drying temperature Td (°C) and film surface temperature Tc (°C) during accumulation shown in Tables 4 and 5. In Test Examples 101 to 106, heating and cooling were performed under conditions that resulted in the drying temperature Td (°C), film surface temperature Tc (°C) on the second recording surface during accumulation, and film surface temperature Tc1 (°C) on the first recording surface during accumulation shown in Table 6. Here, the drying temperature Td is the film surface temperature of the ink film immediately after heating and drying in the heating and drying section 52. The film surface temperature Tc during accumulation is the film surface temperature of the ink film formed on the recording surface that becomes the upper surface during accumulation after double-sided printing. The film surface temperature Tc during accumulation is the film surface temperature of the ink film on the first recording surface during single-sided printing, and is the film surface temperature of the ink film on the second recording surface during double-sided printing. The first recording surface film temperature Tc1 during accumulation is the film surface temperature of the ink film formed on the first recording surface, which becomes the lower surface during accumulation after double-sided printing.

[0140] The drying temperature Td, film surface temperature Tc, and film surface temperature Tc1 were measured using a radiation thermometer (FT-H20 manufactured by Keyence Corporation). As shown in FIG. 1, radiation thermometers S1 to S3 were placed inside the inkjet printing apparatus 1 to measure the temperatures. The drying temperature Td was detected by the radiation thermometer S1 installed near the outlet from the heat drying section 52. The film surface temperature Tc was detected by the radiation thermometer S2 installed directly above the position where the paper P was accumulated in the accumulation device 70. The film surface temperature Tc1 was detected by the radiation thermometer S3 installed diagonally below the accumulation device 70.

[0141] <Test Examples No. 1 to 87> Using the ink prepared for each test example, printing was performed according to the image forming method described above under conditions where Td and Tc were as shown in Table 4 or Table 5, and the following evaluations were performed. For example, in Test Example No. 1, printing was performed under conditions where Td = 65°C and Tc = 44°C. The evaluation results for each evaluation are shown in Tables 4 and 5.

[0142] [Double-sided blocking] 300 sheets of paper were continuously printed with a predetermined image on both sides and stacked, and the stacked sheets were left for one day, after which the blocking state was visually evaluated. The predetermined images were a vertical stripe image printed on the first recording surface and a horizontal stripe image printed on the second recording surface. Evaluation was based on the following criteria. AA, A, B, and C are practically acceptable ranges. AA: No blocking occurred on any of the 300 sheets. A: There were some areas of slight localized blocking among the 300 sheets, but the total number was 10 or less. B: Slight localized blocking occurred after 250 sheets counted from the top. C: Blocking occurred in a partial area of ​​the paper after 200 sheets counted from the top. D: Blocking occurred over the entire paper even within 200 sheets counted from the top.

[0143] [Image cracks] A predetermined image (surface printing: 4C solid image) was printed, and the state of the image surface (ink film surface) was visually evaluated according to the following criteria. Here, a "4C solid image" is an image printed with the maximum amount of ink, mainly K, using four colors (K, C, M, Y). A: No cracks occurred B: Visible when observed with a magnifying glass, but almost invisible to the naked eye C: Cracks in the image were visible in part of the image

[0144] [Abrasion Resistance] A predetermined image (here, a 4C solid image) was printed on 10 sheets, and the abrasion resistance of the 10th sheet was evaluated. The image surface was rubbed back and forth five times with a paperweight wrapped around matte paper (OK Topcoat Matte 104) manufactured by Oji Paper Co., Ltd. The rubbed area of ​​the paperweight was 10.5 cm. ２ The load per unit area is 76 g / cm ２ The image surface after rubbing with the paperweight was visually inspected and evaluated according to the following criteria. A and B are practically acceptable ranges. A: No rubbing B: Change in gloss C: Scratches visible

[0145] The inks, drying process conditions, and evaluation results for Test Nos. 1 to 87 are shown in Tables 4 and 5. In the remarks columns of Tables 4 and 5, "Ex." and "Com." refer to Examples and Comparative Examples, respectively (the same applies to Table 6).

[0146]

[0147] The relationship between X×Y and Tg−Tc and the blocking suppression effect was compiled from Tables 4 and 5 to obtain the map shown in Table 6.

[0148]

[0149] As shown in Table 6, when 0≦X×Y≦4000 is satisfied, the blocking evaluation is C or higher regardless of Tg−Tc, and it has been found that a blocking suppression effect can be obtained. Furthermore, when 4000<X×Y≦6000, and Tg−Tc is 10 or higher, it has been found that the blocking evaluation is C or higher, and a blocking suppression effect can be obtained. That is, it has been found that the examples (Ex.) of the present disclosure that satisfy formula (1) or formula (2) have a blocking evaluation of at least C or higher, and an improved suppression effect can be obtained. 0≦X×Y≦4000 (1) 4000<X×Y≦6000 and Tg−Tc≧10 (2) On the other hand, the comparative example (Com.) that does not satisfy either formula (1) or formula (2) has a blocking evaluation of D, and is therefore not suitable for practical use.

[0150] Furthermore, from a comparison of Test Examples Nos. 47 to 51 or Test Examples Nos. 53 to 57, it was found that satisfying Formula (1-1) allows the blocking evaluation to be C or higher and the crack evaluation to be B or higher, thereby enabling both blocking and crack suppression. Furthermore, it was found that satisfying Formula (1-2) allows the blocking evaluation to be C or higher and the crack evaluation to be A or higher, thereby enabling both blocking and crack suppression to be achieved at a high level. 1500≦X×Y≦4000 (1-1) 2500≦X×Y≦4000 (1-2)

[0151] Furthermore, comparison of Test Examples Nos. 4, 8, and 9, or comparison of Test Examples Nos. 6, 10, and 14, etc., revealed that when formula (1), formula (1-1), or formula (1-2) is satisfied, the larger the Tg-Tc value, the higher the blocking suppression effect. Specifically, when formula (1), formula (1-1), or formula (1-2) is satisfied, if formula (3) is satisfied, a blocking evaluation of C or higher is obtained, if formula (3-1) is satisfied, a rating of B or higher is obtained, and if formula (3-2) is satisfied, a rating of A or higher is obtained. Tg-Tc≧10 (3) Tg-Tc≧40 (3-1) Tg-Tc≧60 (3-2)

[0152] Similarly, comparison of Test Examples 3, 7, and 11 revealed that even when formula (2) was satisfied, the larger the Tg-Tc value, the higher the blocking suppression effect. Specifically, when formula (2) was satisfied, if formula (3-1) was also satisfied, a rating of B or higher was obtained, and if formula (3-2) was satisfied, a rating of A or higher was obtained.

[0153] It is noted from Tables 4 and 5 that a glass transition temperature Tg of 150° C. or lower gave a rating of B or higher for abrasion resistance, and it was found that a glass transition temperature Tg of 150° C. or lower is preferred. From the viewpoint of improving the inhibition of blocking and cracking, the glass transition temperature Tg is preferably 5° C. or higher, and more preferably 60° C. or higher.

[0154] Furthermore, as shown in Test Examples Nos. 78 to 87, when the ink contained wax, very good rub resistance was obtained.

[0155] <Tests 101 to 106> Tests were conducted to examine the difference Tc-Tc1 between the film surface temperature Tc1 of the first recording surface and the film surface temperature Tc of the second recording surface during accumulation, and the blocking suppression effect after double-sided printing. Double-sided printing was performed under different Tc-Tc1 conditions, and the blocking suppression effect was evaluated. Specifically, tests were conducted to evaluate the above-mentioned [Double-sided blocking]. The inks, drying process conditions, and evaluation results for Tests No. 101 to 106 are shown in Table 7.

[0156]

[0157] As shown in Table 7, Test Examples 101 and 102, which satisfied Tg - Tc ≥ 40 and Tc - Tc1 ≥ 20 during double-sided printing, exhibited a higher blocking suppression effect than Test Examples 103 to 106. It is believed that the first recording surface was sufficiently cooled and solidified, which effectively suppressed fusion of the ink film surfaces.

[0158] The following supplementary notes are further disclosed regarding the above embodiment. <Supplementary Note 1> The method includes a preparation step of preparing ink containing water, resin particles, and an organic solvent, an image formation step of forming an image by applying the ink to a recording surface of a recording medium to form an ink film, a drying step of drying the ink film formed on the recording surface, and a collection step of collecting the recording medium on which the ink film has dried, wherein the SP value of the organic solvent in the ink is X [MPa １／２ ], and the amount of residual organic solvent remaining on the recording surface when the recording medium is accumulated in the accumulation process is Y [μg / cm ２], the glass transition temperature of the resin particles is Tg [°C], and the film surface temperature of the ink film during accumulation is Tc [°C], the image forming method satisfies the following formula (1) or (2): 0≦X×Y≦4000 (1) 4000<X×Y≦6000 and Tg−Tc≧10 (2) <Appendix 2> The image forming method according to Appendix 1, which, when formula (1) is satisfied, satisfies the following formula (1-1): 1500≦X×Y≦4000 (1-1) <Appendix 3> The image forming method according to Appendix 1, which, when formula (1) is satisfied, satisfies the following formula (1-2): 2500≦X×Y≦4000 (1-2) <Appendix 4> The image forming method according to any one of Appendices 1 to 3, which, when formula (1) is satisfied, further satisfies the following formula (3): Tg - Tc ≧ 10 (3) <Appendix 5> The image forming method according to any one of Appendices 1 to 3, wherein when formula (1) or formula (2) is satisfied, the following formula (3-1) is further satisfied: Tg - Tc ≧ 40 (3-1) <Appendix 6> The image forming method according to any one of Appendices 1 to 3, wherein when formula (1) or formula (2) is satisfied, the following formula (3-2) is further satisfied: Tg - Tc ≧ 60 (3-2) <Appendix 7> The image forming method according to any one of Appendices 1 to 6, wherein the glass transition temperature Tg of the resin particles is −5° C. or higher and 150° C. or lower. <Appendix 8> The image forming method according to any one of Appendices 1 to 7, wherein the ink contains wax. <Supplementary Note 9> The image forming method according to any one of Supplementary Notes 1 to 8, wherein an image forming process and a drying process are sequentially performed on a first recording surface and a second recording surface, which are the front and back surfaces of the recording medium, and the recording surface during accumulation is the second recording surface. <Supplementary Note 10> The image forming method according to Supplementary Note 9, wherein the following formula (4) is satisfied when the film surface temperature of the second recording surface during accumulation is Tc and the film surface temperature of the first recording surface is Tc1 [°C].Tg-Tc≧40, and Tc-Tc1≧20 (4) <Supplementary Note 11> An image forming apparatus is provided with an image forming unit that forms an image by applying ink to the recording surface of a recording medium to form an ink film, a drying unit that dries the ink film formed on the recording surface, and a collecting device that collects the recording medium on which the ink film has been formed and dried, wherein the image forming unit applies ink containing water, resin particles, and an organic solvent, and the SP value of the organic solvent of the ink is X [MPa. １／２ ], and the amount of residual organic solvent remaining on the recording surface when the recording medium is accumulated in the accumulation device is Y [μg / cm ２ ], the glass transition temperature of the resin particles is Tg [°C], and the film surface temperature of the ink film on the recording surface during accumulation is Tc [°C], the following formula (1) or formula (2) is satisfied: 0≦X×Y≦4000 (1) 4000<X×Y≦6000 and Tg−Tc≧10 (2) <Appendix 12> The image forming apparatus according to Appendix 11, which includes a processor that controls a drying unit, and the processor controls the drying unit under drying conditions that satisfy formula (1) or formula (2). <Appendix 13> The image forming apparatus according to Appendix 11, wherein the drying unit includes a heat drying section that heats and dries the ink film. <Appendix 14> The image forming apparatus according to Appendix 13, wherein the drying unit includes a cooling section that cools the heated and dried ink film. <Supplementary Note 15> An image forming system including ink and an image forming apparatus, wherein the ink contains water, resin particles, and an organic solvent, and the image forming apparatus includes an image forming unit that forms an image by applying the ink to a recording surface of a recording medium to form an ink film, a drying unit that dries the ink film formed on the recording surface, and a collecting device that collects the recording medium on which the ink film has been formed and dried, and wherein the SP value of the organic solvent is X [MPa １／２ ], and the amount of residual organic solvent remaining on the recording surface when the recording medium is accumulated in the accumulation device is Y [μg / cm ２], the glass transition temperature of the resin particles is Tg [°C], and the film surface temperature of the ink film on the recording surface during accumulation is Tc [°C], the image forming system satisfies the following formula (1) or formula (2): 0≦X×Y≦4000 (1) 4000<X×Y≦6000 and Tg−Tc≧10 (2).

[0159] The disclosure of Japanese Patent Application No. 2024-135399, filed on August 14, 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. An image forming process for forming an image by applying ink containing water, resin particles, and an organic solvent to a recording surface of a recording medium to form an ink film; a drying process for drying the ink film formed on the recording surface; and a collecting process for collecting the recording medium on which the ink film has been dried, wherein the SP value of the organic solvent in the ink is X [MPa １／２ ], and the amount of the organic solvent remaining on the recording surface when the recording medium is collected in the collecting step is Y [μg / cm ２ ], the glass transition temperature of the resin particles is Tg [°C], and the film surface temperature of the ink film during the accumulation is Tc [°C], the following formula (1) or formula (2) is satisfied: 0≦X×Y≦4000 (1) 4000<X×Y≦6000 and Tg−Tc≧10 (2) 2. The image forming method according to claim 1, wherein when the formula (1) is satisfied, the following formula (1-1) is satisfied: 1500≦X×Y≦4000 (1-1) 3. The image forming method according to claim 1, wherein when the formula (1) is satisfied, the following formula (1-2) is satisfied: 2500≦X×Y≦4000 (1-2) 4. The image forming method according to any one of claims 1 to 3, wherein when the formula (1) is satisfied, the following formula (3) is further satisfied: Tg - Tc ≥ 10 (3) 5. The image forming method according to any one of claims 1 to 3, wherein when the formula (1) or the formula (2) is satisfied, the following formula (3-1) is further satisfied: Tg - Tc ≧ 40 (3-1) 6. The image forming method according to any one of claims 1 to 3, wherein when the formula (1) or the formula (2) is satisfied, the following formula (3-2) is further satisfied: Tg - Tc ≧ 60 (3-2) 7. The image forming method according to any one of claims 1 to 3, wherein the glass transition temperature Tg of the resin particles is -5°C or higher and 150°C or lower.

8. The image forming method according to any one of claims 1 to 3, wherein the ink contains a wax.

9. An image forming method according to any one of claims 1 to 3, wherein the image forming process and the drying process are carried out sequentially on a first recording surface and a second recording surface, which are the front and back surfaces of the recording medium, and the recording surface at the time of accumulation is the second recording surface.

10. The image forming method according to claim 9, wherein, when the film surface temperature of the second recording surface during the accumulation is Tc and the film surface temperature of the first recording surface is Tc1 [°C], the following formula (4) is satisfied: Tg-Tc≧40 and Tc-Tc1≧20 (4) 11. The image forming method according to any one of claims 1 to 3, wherein the SP value X satisfies 18≦X≦28.

12. The image forming method according to any one of claims 1 to 3, wherein the SP value X satisfies 20≦X≦23.

13. A recording medium for recording an image, comprising: an image forming unit that applies ink to a recording surface of a recording medium to form an ink film; a drying unit that dries the ink film formed on the recording surface; and a collecting device that collects the recording medium on which the ink film has been formed and dried, wherein the image forming unit applies ink containing water, resin particles, and an organic solvent, and the SP value of the organic solvent in the ink is X [MPa １／２ ], and the amount of the organic solvent remaining on the recording surface when the recording medium is accumulated in the accumulation device is Y [μg / cm ２ ], the glass transition temperature of the resin particles is Tg [°C], and the film surface temperature of the ink film on the recording surface during the accumulation is Tc [°C], the image forming apparatus satisfies the following formula (1) or formula (2): 0≦X×Y≦4000 (1) 4000<X×Y≦6000 and Tg−Tc≧10 (2) 14. The image forming apparatus according to claim 13, further comprising a processor that controls the drying unit, wherein the processor controls the drying unit under drying conditions that satisfy the formula (1) or the formula (2).

15. The image forming apparatus according to claim 13, wherein the drying unit includes a heating and drying section that heats and dries the ink film.

16. The image forming apparatus according to claim 15, wherein the drying unit is provided with a cooling section that cools the ink film that has been heated and dried.

17. An image forming system including ink and an image forming device, wherein the ink contains water, resin particles, and an organic solvent, and the image forming device comprises an image forming unit that forms an image by applying the ink to a recording surface of a recording medium to form an ink film, a drying unit that dries the ink film formed on the recording surface, and a collecting device that collects the recording medium on which the ink film has been formed and dried, and wherein the SP value of the organic solvent is X [MPa １／２ ], and the amount of the organic solvent remaining on the recording surface when the recording medium is accumulated in the accumulation device is Y [μg / cm ２ ], the glass transition temperature of the resin particles is Tg [°C], and the film surface temperature of the ink film on the recording surface during the accumulation is Tc [°C], the image forming system satisfies the following formula (1) or formula (2): 0≦X×Y≦4000 (1) 4000<X×Y≦6000 and Tg−Tc≧10 (2).

Images