Ink jet recording method

Abstract

To provide an ink jet recording method capable of suppressing dew condensation on a jig surface near an ink jet head when directly performing ink jet recording with aqueous ink on a low-liquid-absorbency recording medium.SOLUTION: There is provided an ink jet recording method for directly performing one-pass ink jet recording on a low-liquid-absorbency recording medium using an ink jet recording apparatus having an ink jet head that discharges an aqueous ink. The ink jet head is at least two series of ink jet heads. In the low-liquid-absorbency recording medium, a difference (T1'-T1) between a temperature T1' at a portion on which the aqueous ink from the most sheet-discharge-side ink jet head in a conveying direction of the low-liquid-absorbency recording medium is deposited and a temperature T1 of a jig surface near the most sheet-discharge-side ink jet head in the conveying direction of the low-liquid-absorbency recording medium is 0°C or more and 4°C or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an inkjet recording method.

Background Art

[0002] The inkjet recording method is a method of ejecting ink droplets from fine nozzles and attaching them to a recording medium to obtain a recording in which characters and images are recorded. This method has many advantages such as being easy and inexpensive to achieve full color, and furthermore, plain paper can be used as the recording medium, and it is non-contact with the recording medium, so it has become very popular. The inkjet recording method can eject both water-based and solvent-based inks, but water-based inks are mainly used from the viewpoints of environmental impact and safety. In recent years, in addition to highly absorbent recording media called plain paper, there has been a demand for compatibility with low absorbent recording media such as coated paper, or non-absorbent recording media such as polyvinyl chloride resin, polypropylene resin, and polyester resin.

[0003] When recording on a low absorbent recording medium with water-based ink by the inkjet recording method, after inkjet recording, in order to evaporate the moisture of the ink on the recording medium early, an operation of raising the temperature of the recording medium above room temperature is used. However, in the operation of raising the temperature of the recording medium above room temperature, dew condensation occurs on the surfaces of the inkjet head and the jig for fixing the inkjet head, which are present in the inkjet apparatus in the vicinity of the recording medium, due to the evaporated moisture. When the dew-condensed moisture drops onto the recording surface of the recording medium, problems such as image bleeding and streaks in the image occur. In Patent Document 1, there is an inkjet recording apparatus having a discharge head that discharges ink to form an image, a discharge medium on which an image is formed by the discharge head, head heating means for heating the discharge head to a temperature T1, and heating means for heating the discharge medium, and at the time of forming the image, control means for adjusting such that the temperature T1 of the discharge head and the temperature T2 after heating of the discharge medium at the position where the image is formed by the discharge head have a relationship of T1 > T2 is provided. An inkjet recording apparatus characterized by this and an inkjet recording method using the apparatus are disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Although Patent Document 1 can suppress condensation on the inkjet head, when performing direct inkjet recording on a low liquid-absorbing recording medium, condensation may occur on the surface of the jig to which the inkjet head is fixed. In addition, nozzle clogging due to evaporation of ink from the nozzle openings of the inkjet head also becomes prominent, and streaks may occur due to the occurrence of non-discharging nozzles. An object of the present invention is to provide an inkjet recording method capable of suppressing condensation on the surface of a jig near an inkjet head when performing direct inkjet recording on a low liquid-absorbing recording medium with aqueous ink.

Means for Solving the Problems

[0006] The inventors have found that in an inkjet recording method of inkjet recording on a low-absorbency recording medium in a one-pass system, by keeping the difference between the temperature of the site where the aqueous ink of the low-absorbency recording medium adheres and the temperature of the surface of a jig near the inkjet head on the side where the low-absorbency recording medium is discharged among a plurality of series of inkjet heads of the inkjet recording apparatus (i.e., the portion where inkjet recording is finally performed on the low-absorbency recording medium) within a certain range, the above problems can be solved. The present invention relates to the following [1]. [1] An inkjet recording method of directly performing inkjet recording on a low-absorbency recording medium in a one-pass system using an inkjet recording apparatus including an inkjet head that discharges aqueous ink, wherein the inkjet head is at least two series of inkjet heads, and the difference (T1'-T1) between the temperature T1' of the site where the aqueous ink adheres from the inkjet head on the most paper discharge side with respect to the conveyance direction of the low-absorbency recording medium in the low-absorbency recording medium and the temperature T1 of the surface of a jig near the inkjet head on the most paper discharge side with respect to the conveyance direction of the low-absorbency recording medium is 0°C or more and 4°C or less. [Advantages of the Invention]

[0007] According to the present invention, there can be provided an inkjet recording method capable of suppressing dew condensation on the surface of a jig near the inkjet head when directly performing inkjet recording of aqueous ink on a low-absorbency recording medium in a one-pass system. Further, according to the present invention, when performing inkjet recording on a low-absorbency recording medium with aqueous ink, it is easy to suppress clogging of nozzles. [Brief Description of the Drawings]

[0008]

Figure 1

[0009] [Inkjet Recording Method] The inkjet recording method of the present invention is an inkjet recording method for directly inkjet recording on a low-liquid-absorbent recording medium by a one-pass system using an inkjet recording apparatus equipped with an inkjet head that ejects a water-based ink, wherein the inkjet head is an inkjet head with at least two lines, and the difference (T1'-T1) between the temperature T1 of the portion of the low-liquid-absorbent recording medium to which the water-based ink adheres from the inkjet head that is closest to the discharge side in the conveyance direction of the low-liquid-absorbent recording medium and the temperature T1 of the surface of a jig near the inkjet head that is closest to the discharge side in the conveyance direction of the low-liquid-absorbent recording medium is 0°C or more and 4°C or less.

[0010] In this specification, "recording" refers to the operation of fixing characters or images on a medium in a state where they can be visually recognized by a human, and this concept includes printing and printed letters, and "recorded matter" refers to the concept of printed matter or printed matter in which characters or images have been fixed in a state where they can be recognized by a human, and is the result obtained upon completion of a recording operation. Note that in the inkjet recording method of the present invention, the operation of applying a liquid that has the effect of increasing the fixation property of ink or enhancing the color development property of color, i.e., a liquid that does not contain a colorant, to a recording medium using an inkjet head does not constitute "recording." Furthermore, "low liquid absorption" means that the amount of water absorption of the recording medium when the recording medium is in contact with pure water for 100 ms is 0 g / m 2 More than 10g / m 2 or less, preferably 0 g / m 2 More than 6g / m 2 The water absorption amount is measured by the method described in the examples. Furthermore, "water-based ink" means that water accounts for the largest proportion of the components constituting the ink on a mass basis.

[0011] The inkjet recording method of the present invention is an inkjet recording method in which inkjet recording is performed directly on a low-liquid-absorbent recording medium by a one-pass method using an inkjet recording apparatus equipped with an inkjet head that ejects a water-based ink. In the inkjet recording method of the present invention, "direct inkjet recording" means a method in which ink ejected from an inkjet head adheres directly to a recording medium to obtain a recorded matter, which is different from a method in which ink is temporarily adhered to an object other than the recording medium and the adhered ink is transferred to the recording medium to obtain a recorded matter. In the inkjet recording method of the present invention, the "one-pass method" means a method in which an inkjet head is fixed to an inkjet recording apparatus and inkjet recording is performed by moving a recording medium. In an inkjet recording apparatus using the one-pass method, the length of the inkjet head in a direction orthogonal to the conveyance direction of the recording medium is equal to or greater than the width of the recording medium. Also, the inkjet heads included in one series may be a single inkjet head or a combination of a plurality of inkjet heads to form an inkjet head group. In the inkjet recording method of the present invention, in the case of a single inkjet head and in the case of a combination of a plurality of inkjet heads to form an inkjet head group, the inkjet head is simply referred to as the "inkjet head". In addition, in the inkjet recording method of the present invention, room temperature means 20°C.

[0012] According to the inkjet recording method of the present invention, there is an effect that dew condensation on the surface of a jig near the inkjet head can be suppressed when performing direct inkjet recording on a low-absorbency recording medium with aqueous ink. The reason is not clear, but it is considered as follows. When directly inkjet recording aqueous ink on the low-absorbency recording medium by the one-pass method, in order to quickly fix the aqueous ink landing on the recording medium, the temperature of the recording medium is raised above room temperature. At this time, as the recorded recording medium advances toward the paper discharge side with respect to the conveyance direction, the amount of aqueous ink ejected onto the recording medium increases, so the moisture evaporated from the ejected aqueous ink exists in large amounts particularly near the inkjet head installed on the side where the recording medium is discharged. In this case, by setting the difference (T1'-T1) between the temperature T1' of the portion of the low-absorbent recording medium where the aqueous ink adheres from the inkjet head closest to the discharge side in the conveyance direction of the low-absorbent recording medium and the temperature T1 of the jig surface near the inkjet head on the discharge side in the conveyance direction of the low-absorbent recording medium to 0°C or higher and 4°C or lower, condensation of moisture on the jig surface near the inkjet head on the discharge side can be suppressed. Furthermore, since the gas atmosphere near the gas-liquid interface of the inkjet head nozzle and the gas atmosphere near the recording medium where the aqueous ink adheres can be made similar in composition, thickening due to evaporation of moisture from the gas-liquid interface of the inkjet head nozzle can be suppressed, and clogging of the inkjet head nozzle can be suppressed. As a result, the inkjet recording method of the present invention can prevent deterioration in the image quality of the resulting recorded product.

[0013] <Low-absorbent recording medium> In the inkjet recording method of the present invention, the low-liquid-absorbent recording medium is preferably a low-liquid-absorbent coated paper or a non-liquid-absorbent resin film, and more preferably a resin film. Preferred examples of coated paper include general-purpose glossy paper and multicolor foam gloss paper. Preferred examples of resin films include polyester film, polyvinyl chloride film, polypropylene film, and polyethylene film. When a resin film is used as the low-liquid-absorbent recording medium, it is more preferred to use a resin film that has been subjected to a surface treatment such as corona treatment, and it is also preferred to use a resin film that has been subjected to one type of stretching treatment selected from the group consisting of uniaxial stretching and biaxial stretching. In the inkjet recording method of the present invention, the low liquid-absorbent recording medium may be in a continuous form wound into a roll, or may be cut into predetermined sizes such as A0 to A6 or B0 to B5.

[0014] <Inkjet recording device> In the present invention, an inkjet recording apparatus includes an inkjet head that discharges aqueous ink, and means an apparatus for directly performing inkjet recording on a low-absorbency recording medium in a one-pass system. Further, in the present invention, the inkjet head is at least two series of inkjet heads.

[0015] (Inkjet head) In the present invention, the "series" of the inkjet head means one group by which the inkjet head is controlled. That is, in the present invention, "at least two series of inkjet heads" means having at least two inkjet heads that are independently controlled of each other. In the present invention, from the viewpoint of recording various characters and images, the inkjet head is preferably three series or more, more preferably four series or more, and from the viewpoint of productivity, preferably six series or less, more preferably five series or less. Further, in the inkjet recording method of the present invention, from the viewpoint of suppressing dew condensation on the surface of the jig near the inkjet head, the inkjet head is more preferably four series.

[0016] <The inkjet head on the most paper discharge side with respect to the conveyance direction of the low-absorbency recording medium> In the inkjet recording method of the present invention, the paper discharge side with respect to the conveyance direction means the downstream side in the conveyance direction of the low-absorbency recording medium. That is, in the inkjet recording method of the present invention, the inkjet head on the most paper discharge side with respect to the conveyance direction of the low-absorbency recording medium means the inkjet head located on the most downstream side in the conveyance direction of the low-absorbency recording medium among at least two series of inkjet heads that the inkjet recording apparatus has. That is, the inkjet head on the most paper discharge side with respect to the conveyance direction of the low-absorbency recording medium is the inkjet head that finally performs inkjet recording on the low-absorbency recording medium. Therefore, the low-absorbency recording medium that has passed through the inkjet head on the most paper discharge side is the one on which the inkjet recording of the present invention is completed.

[0017] <The inkjet head on the sheet feeding side closest to the conveyance direction of the low liquid-absorbing recording medium> In the inkjet recording method of the present invention, the sheet feeding side with respect to the conveyance direction means the upstream side in the conveyance direction of the low liquid-absorbing recording medium. That is, in the inkjet recording method of the present invention, the inkjet head on the sheet feeding side closest to the conveyance direction of the low liquid-absorbing recording medium means the inkjet head located on the most upstream side in the conveyance direction of the low liquid-absorbing recording medium among at least two series of inkjet heads that the inkjet recording apparatus has. That is, the inkjet head on the sheet feeding side closest to the conveyance direction of the low liquid-absorbing recording medium is the inkjet head that first performs inkjet recording on the low liquid-absorbing recording medium. Therefore, when the low liquid-absorbing recording medium passes through the inkjet head on the sheet feeding side closest to the conveyance direction of the low liquid-absorbing recording medium, the inkjet recording method of the present invention is started.

[0018] <Other inkjet heads> In the inkjet recording method of the present invention, the inkjet heads other than the inkjet head on the sheet discharging side closest to the conveyance direction of the low liquid-absorbing recording medium and the inkjet head on the sheet feeding side closest to the conveyance direction of the low liquid-absorbing recording medium are collectively referred to as other inkjet heads. The other inkjet heads are installed in the inkjet recording apparatus between the inkjet head on the sheet discharging side closest to the conveyance direction of the low liquid-absorbing recording medium and the inkjet head on the sheet feeding side closest to the conveyance direction of the low liquid-absorbing recording medium.

[0019] In the inkjet recording method of the present invention, each series of inkjet heads may be filled with aqueous inks of the same hue or aqueous inks of different hues. However, from the viewpoint of recording various characters and images, it is preferable that the aqueous inks of different hues are filled. The number of hues of the aqueous ink is preferably two or more, more preferably three or more, and still more preferably four or more. Furthermore, when there are four or more series of inkjet heads, the hues of the water-based inks filled in the inkjet heads of each series preferably include at least four of the following: cyan, magenta, yellow, and black. That is, in the inkjet recording method of the present invention, the inkjet recording apparatus preferably comprises at least four or more types of ink, more preferably at least four or more types of water-based ink including cyan ink, magenta ink, yellow ink, and black ink, and even more preferably at least four types of water-based ink including cyan ink, magenta ink, yellow ink, and black ink.

[0020] <Temperature T1 of the jig surface closest to the inkjet head on the paper ejection side in the conveyance direction of the low-liquid-absorbent recording medium> In the inkjet recording method of the present invention, the temperature T1 of the surface of the jig nearest to the inkjet head on the discharge side in the transport direction of the low-liquid-absorbent recording medium (hereinafter also referred to as "temperature T1") means the surface temperature of the jig (hereinafter also referred to as "jig J1"), among the jigs of the inkjet device to which the inkjet head is fixed, nearest to the inkjet head on the discharge side in the transport direction of the low-liquid-absorbent recording medium. From the viewpoint of efficiently drying the water-based ink, the temperature T1 is preferably 30°C or higher, more preferably 32°C or higher, even more preferably 34°C or higher, and still more preferably 36°C or higher, and from the viewpoint of suppressing condensation in the inkjet head, the temperature T1 is preferably 50°C or lower, more preferably 48°C or lower, even more preferably 46°C or lower, and still more preferably 44°C or lower.

[0021] (Method for measuring temperature T1) In the inkjet recording method of the present invention, the temperature T1 is preferably measured by a temperature sensor installed on the surface of a jig near the inkjet head, among the jigs to which the inkjet head is fixed. In the inkjet recording method of the present invention, the temperature sensor may be installed in multiple locations. When multiple temperature sensors are installed, the temperature T1 is preferably determined by averaging the values measured by the sensors.

[0022] (Method for adjusting temperature T1) In the inkjet recording method of the present invention, as the method for adjusting the temperature T1, it is preferable to have one or more selected from the method in which the jig J1 is heated by the inkjet head itself and the method in which the jig J1 is heated from outside the inkjet head. It is more preferable to have both the method in which the jig J1 is heated by the inkjet head itself and the method in which the jig J1 is heated from outside the inkjet head. It is even more preferable to have both the method in which the jig J1 is heated by the inkjet head itself and the method in which the jig J1 is heated from the paper discharge side from outside the inkjet head and in the conveyance direction of the low liquid-absorbing recording medium. In the inkjet recording method of the present invention, the method in which the jig J1 is heated by the inkjet head itself includes that the inkjet head generates heat during inkjet recording, and thereby the jig J1 is heated. The specific method of heating the jig J1 from outside the inkjet head to adjust the temperature T1 preferably includes the method of using a planar electric heater. That is, in the inkjet recording method of the present invention, it is preferable that the method for adjusting the temperature T1 has a method of heating the jig (jig J1) near the inkjet head on the most paper discharge side with respect to the conveyance direction of the low liquid-absorbing recording medium by a planar electric heater. It is more preferable to have a method of heating the jig (jig J1) near the inkjet head on the most paper discharge side with respect to the conveyance direction of the low liquid-absorbing recording medium from the paper discharge side by a planar electric heater.

[0023] (Temperature T1' of the site where the aqueous ink adheres from the inkjet head on the most paper discharge side with respect to the conveyance direction of the low liquid-absorbing recording medium in the low liquid-absorbing recording medium) In the inkjet recording method of the present invention, in a low liquid-absorbing recording medium, the temperature T1' (hereinafter, also referred to as "temperature T1'") of the portion where the aqueous ink adheres from the inkjet head on the most paper discharge side with respect to the conveyance direction of the low liquid-absorbing recording medium means the temperature of the portion where the aqueous ink adheres from the inkjet head on the most paper discharge side with respect to the conveyance direction of the low liquid-absorbing recording medium, which is the surface of the front and back surfaces of the low liquid-absorbing recording medium on which the ink coating is formed by the inkjet head. From the viewpoint of efficiently drying the aqueous ink, the temperature T1' is preferably 30°C or higher, more preferably 32°C or higher, still more preferably 34°C or higher, and even more preferably 36°C or higher. And from the viewpoint of suppressing dew condensation on the inkjet head, it is preferably 50°C or lower, more preferably 48°C or lower, still more preferably 46°C or lower, and even more preferably 44°C or lower.

[0024] (Method for measuring temperature T1') In the inkjet recording method of the present invention, the measurement location of the temperature T1' is preferably in the vicinity of the upstream side or the downstream side of the inkjet head on the most paper discharge side with respect to the conveyance direction of the low liquid-absorbing recording medium. Also, the temperature T1' is preferably measured with a contact thermometer. The vicinity of the upstream side of the inkjet head on the most paper discharge side with respect to the conveyance direction of the low liquid-absorbing recording medium means a position upstream from the inkjet head on the most paper discharge side with respect to the conveyance direction of the low liquid-absorbing recording medium, preferably a position separated by 1 cm or more, more preferably 2 cm or more, still more preferably 2.5 cm or more, and preferably a position separated by 10 cm or less, more preferably 5 cm or less, still more preferably 4 cm or less. The vicinity of the downstream side of the inkjet head on the most paper discharge side with respect to the conveyance direction of the low liquid-absorbing recording medium means a position downstream from the inkjet head on the most paper discharge side with respect to the conveyance direction of the low liquid-absorbing recording medium, preferably a position separated by 1 cm or more, more preferably 2 cm or more, still more preferably 2.5 cm or more, and preferably a position separated by 10 cm or less, more preferably 5 cm or less, still more preferably 4 cm or less. Among these, it is more preferable that the numerical value obtained by measuring the temperature of the site where the aqueous ink of the low-absorbency recording medium adheres is defined as temperature T1', in the vicinity of the upstream side of the inkjet head on the most paper discharge side with respect to the conveyance direction of the low-absorbency recording medium. Also, the measurement of temperature T1' may be the average value of the measured values at a plurality of locations.

[0025] (Method for adjusting temperature T1') In the inkjet recording method of the present invention, examples of the method for adjusting temperature T1' include a method of blowing a gas heated to room temperature or higher onto the low-absorbency recording medium, and a method of heating the low-absorbency recording medium with a planar electric heater. Among these, the method of heating the low-absorbency recording medium with a planar electric heater is more preferable. As the method of heating the low-absorbency recording medium with a planar electric heater, a method of heating with a planar electric heater from the side opposite to the surface on which the ink coating film is formed is preferable. It is more preferable to heat the low-absorbency recording medium with a planar electric heater from the side opposite to the surface on which the aqueous ink adheres, on the upstream side from the inkjet head on the most paper discharge side with respect to the conveyance direction of the low-absorbency recording medium. It is more preferable to heat the low-absorbency recording medium with a planar electric heater from the side opposite to the surface on which the aqueous ink adheres, over the entire surface facing each inkjet head of the low-absorbency recording medium. It is still more preferable to heat the low-absorbency recording medium with a planar electric heater from the side opposite to the surface on which the aqueous ink adheres, over the entire surface facing each inkjet head of the low-absorbency recording medium and in the range on the paper feed side from the inkjet head. That is, it is preferable that the inkjet recording method of the present invention has a method of heating the low-absorbency recording medium with a planar electric heater from the side opposite to the surface on which the aqueous ink adheres, as the method for adjusting temperature T1'.

[0026] (Difference between temperature T1' and temperature T1 (T1' - T1)) In the inkjet recording method of the present invention, the difference (T1’ - T1) between the temperature T1’ of the portion where the aqueous ink adheres from the inkjet head on the most paper discharge side with respect to the conveyance direction of the low liquid-absorbing recording medium and the temperature T1 of the surface of the jig near the inkjet head on the most paper discharge side with respect to the conveyance direction of the low liquid-absorbing recording medium is 0°C or more and 4°C or less. In the inkjet recording method of the present invention, from the viewpoint of enhancing the effect of suppressing dew condensation of moisture on the surface of the jig near the inkjet head on the most paper discharge side with respect to the conveyance direction of the low liquid-absorbing recording medium and suppressing dew condensation on the surface of the jig near the inkjet head, the difference (T1’ - T1) is preferably 3°C or less, more preferably 2°C or less, still more preferably 1°C or less, even more preferably 0.5°C or less, and even more preferably 0°C.

[0027] <The temperature T2 of the surface of the jig near the inkjet head on the most paper feed side with respect to the conveyance direction of the low liquid-absorbing recording medium> In the inkjet recording method of the present invention, the temperature T2 (hereinafter, also referred to as “temperature T2”) of the surface of the jig near the inkjet head on the most paper feed side with respect to the conveyance direction of the low liquid-absorbing recording medium means the surface temperature of the jig (hereinafter, also referred to as “jig J2”) near the inkjet head on the most paper feed side with respect to the conveyance direction of the low liquid-absorbing recording medium among the jigs of the inkjet device to which the inkjet head is fixed. In the inkjet recording method of the present invention, the measurement method of the temperature T2 is preferably the same method as the measurement method of the above-described temperature T1. From the viewpoint of efficiently drying the aqueous ink, the temperature T2 is preferably 28°C or more, more preferably 30°C or more, still more preferably 32°C or more, and from the viewpoint of suppressing dew condensation of the inkjet head, it is preferably 50°C or less, more preferably 48°C or less, still more preferably 46°C or less, and even more preferably 44°C or less.

[0028] (Method for adjusting the temperature T2) In the inkjet recording method of the present invention, the method of adjusting the temperature T2 preferably includes at least one method selected from a method in which the jig J2 is heated by the inkjet head itself and a method in which the jig J2 is heated from a source other than the inkjet head, more preferably includes both a method in which the jig J2 is heated by the inkjet head itself and a method in which the jig J2 is heated from a source other than the inkjet head, and even more preferably includes both a method in which the jig J2 is heated by the inkjet head itself and a method in which the jig J2 is heated from the discharge side relative to the transport direction of the low liquid-absorbent recording medium by a source other than the inkjet head. In the inkjet recording method of the present invention, the method in which the jig J2 is heated by the inkjet head itself includes a method in which the inkjet head generates heat during inkjet recording, thereby heating the jig J2. A specific method for heating the jig J2 from a source other than the inkjet head to adjust the temperature T2 preferably includes a method using a planar electric heater. That is, in the inkjet recording method of the present invention, the method of adjusting the temperature T2 preferably includes a method of heating a jig (jig J2) nearest to the inkjet head on the paper feed side in the transport direction of the low liquid-absorbent recording medium using a planar electric heater, and more preferably a method of heating a jig (jig J2) nearest to the inkjet head on the paper feed side in the transport direction of the low liquid-absorbent recording medium from the paper discharge side using a planar electric heater.

[0029] <Difference between temperature T1 and temperature T2 (T1-T2)> In the inkjet recording method of the present invention, the difference (T1 - T2) between the temperature T1 of the surface of the jig near the inkjet head on the most paper discharge side with respect to the conveyance direction of the low liquid-absorbing recording medium and the temperature T2 of the surface of the jig near the inkjet head on the most paper feed side with respect to the conveyance direction of the low liquid-absorbing recording medium is preferably 0 °C or higher, more preferably 2 °C or higher, still more preferably 3 °C or higher, and even more preferably 4 °C or higher, from the viewpoint of suppressing dew condensation of moisture on the surface of the jig near the inkjet head on the most paper feed side with respect to the conveyance direction of the low liquid-absorbing recording medium, and is preferably 10 °C or lower, more preferably 9 °C or lower, still more preferably 8 °C or lower, and even more preferably 7 °C or lower. When the difference (T1 - T2) is within the above range, the components that volatilize during the operation of raising the temperature of the recording medium to room temperature or higher following the inkjet recording are in a large amount on the side where the low liquid-absorbing recording medium is discharged, and it is considered that it becomes difficult for the volatilizing components to reach the vicinity of the inkjet head on the side where the low liquid-absorbing recording medium is fed, so that dew condensation on the surface of the jig near the inkjet head can be suppressed.

[0030] <The temperature T3 of the surface of the jig near the other inkjet head> In the inkjet recording method of the present invention, when the inkjet head has three or more series of inkjet heads, the inkjet recording method of the present invention has other inkjet heads. The other inkjet heads are installed between the inkjet head on the most paper discharge side with respect to the conveyance direction of the low liquid-absorbing recording medium and the inkjet head on the most paper feed side with respect to the conveyance direction of the low liquid-absorbing recording medium in the inkjet recording apparatus. In the inkjet recording method of the present invention, the temperature T3 of the surface of the jig near the other inkjet head is preferably not higher than T1 and not lower than T2. In the inkjet recording method of the present invention, the temperature T3 of the surface of the jig near the other inkjet head (hereinafter, also referred to as "temperature T3") means the surface temperature of the jig near the other inkjet head (hereinafter, also referred to as "jig J3") among the jigs of the inkjet device to which the other inkjet head is fixed. That is, it is preferable that the temperatures T1, T2, and T3 satisfy the following relationship (A). T2 ≦ T3 ≦ T1 (A) When the temperature T3 of the surface of the jig near the other inkjet head is equal to or lower than T1 and equal to or higher than T2, the amount of the component that volatilizes during the operation of raising the temperature of the recording medium to room temperature or higher following the inkjet recording is large on the side where the low-absorbency recording medium is discharged, and it becomes difficult for the volatile component to reach the vicinity of the other inkjet head on the side where the low-absorbency recording medium is fed. Therefore, it is considered that dew condensation on the surface of the jig near the other inkjet head can be suppressed.

[0031] When the inkjet head is an inkjet head of 4 series or more, among the other inkjet heads, the temperature of the surface of the jig (hereinafter, also referred to as "jig J3a") near the inkjet head on the feeding side with respect to the conveyance direction of the low-absorbency recording medium is preferably equal to or lower than the temperature of the surface of the jig (hereinafter, also referred to as "jig J3b") near the inkjet head on the discharging side with respect to the conveyance direction of the low-absorbency recording medium. That is, for example, when the inkjet head is an inkjet head of 4 series, among the other inkjet heads, when the temperature of the surface of the jig near the inkjet head on the feeding side with respect to the conveyance direction of the low-absorbency recording medium is T3a and the temperature of the surface of the jig near the inkjet head on the discharging side with respect to the conveyance direction of the low-absorbency recording medium is T3b, it is preferable that the temperatures T1, T2, T3a, and T3b satisfy the following relationship (B). T2 ≦ T3a ≦ T3b ≦ T1 (B) The method for measuring the temperature T3 of the surface of the jig near the other inkjet head is preferably the same as the method for measuring the temperature T1 or the temperature T2. Also, the method for adjusting the temperature T3 is preferably the same as the method for adjusting the temperature T1 or the temperature T2.

[0032] From the viewpoint of efficiently drying the aqueous ink, the temperature T3 is preferably 28 °C or higher, more preferably 30 °C or higher, still more preferably 32 °C or higher, and from the viewpoint of suppressing dew condensation on the inkjet head, it is preferably 50 °C or lower, more preferably 48 °C or lower, still more preferably 46 °C or lower, and even more preferably 44 °C or lower.

[0033] <Temperature T2' at the site where the aqueous ink adheres from the inkjet head on the sheet feeding side with respect to the conveyance direction of the low-absorbency recording medium in the low-absorbency recording medium> In the inkjet recording method of the present invention, the temperature T2' at the site where the aqueous ink adheres from the inkjet head on the sheet feeding side with respect to the conveyance direction of the low-absorbency recording medium in the low-absorbency recording medium means the temperature at the site where the aqueous ink adheres from the inkjet head on the sheet feeding side with respect to the conveyance direction of the low-absorbency recording medium, on the surface of the front and back surfaces of the low-absorbency recording medium where the ink coating is formed by the inkjet head. From the viewpoint of efficiently drying the aqueous ink, the temperature T2' is preferably 30 °C or higher, more preferably 32 °C or higher, still more preferably 34 °C or higher, and even more preferably 36 °C or higher, and from the viewpoint of suppressing dew condensation on the inkjet head, it is preferably 50 °C or lower, more preferably 48 °C or lower, still more preferably 46 °C or lower, and even more preferably 44 °C or lower. In the inkjet recording method of the present invention, the measurement method and adjustment method of the temperature T2' are preferably the same as the measurement method and adjustment method of the above-described temperature T1'.

[0034] <Difference between the temperature T2' and the temperature T2 (T2' - T2)> In the inkjet recording method of the present invention, in a low liquid-absorbing recording medium, the temperature T2' of the portion where the aqueous ink adheres from the inkjet head on the most paper-feeding side with respect to the conveyance direction of the low liquid-absorbing recording medium, and the temperature T2 of the surface of the jig near the inkjet head on the most paper-feeding side with respect to the conveyance direction of the low liquid-absorbing recording medium, the difference (T2' - T2) is preferably 0°C or more and 4°C or less from the viewpoint of enhancing the effect of suppressing dew condensation of moisture on the surface of the jig near the inkjet head on the most paper-feeding side with respect to the conveyance direction of the low liquid-absorbing recording medium. From the same viewpoint, it is more preferably 3°C or less, still more preferably 2°C or less, even more preferably 1°C or less, even more preferably 0.5°C or less, and even more preferably 0°C.

[0035] <In the low liquid-absorbing recording medium, the temperature T3' of the portion where the aqueous ink adheres from other inkjet heads> In the inkjet recording method of the present invention, the temperature T3' of the portion where the aqueous ink adheres from other inkjet heads in the low liquid-absorbing recording medium means the temperature of the portion where the ink coating film is formed by the inkjet head on the surface of the low liquid-absorbing recording medium, and the aqueous ink from other inkjet heads adheres. From the viewpoint of efficiently drying the aqueous ink, the temperature T3' is preferably 30°C or more, more preferably 32°C or more, still more preferably 34°C or more, and even more preferably 36°C or more. And from the viewpoint of suppressing dew condensation of the inkjet head, it is preferably 50°C or less, more preferably 48°C or less, still more preferably 46°C or less, and even more preferably 44°C or less. Also, for example, when the inkjet head is a 4-series inkjet head, among the portions where the aqueous ink adheres from the other inkjet heads, the temperature of the portion where the aqueous ink adheres from the other inkjet head on the paper-feeding side with respect to the conveyance direction of the low liquid-absorbing recording medium is T3a', and the temperature of the portion where the aqueous ink adheres from the other inkjet head on the paper-discharging side with respect to the conveyance direction of the low liquid-absorbing recording medium is T3b'. In this case, the temperatures T3a' and T3b' are preferably in the same range as the above temperature T3'. In the inkjet recording method of the present invention, the method for measuring and adjusting the temperature T3’ (T3a’ and T3b’) is preferably the same as the method for measuring and adjusting the above-described temperature T1’.

[0036] <The difference between the temperature T3’ and the temperature T3 (T3’ - T3)> In the inkjet recording method of the present invention, regarding the low-absorbency recording medium, the difference (T3’ - T3) between the temperature T3’ of the site where the aqueous ink adheres from other inkjet heads and the temperature T3 of the surface of the jig near the other inkjet heads is preferably 0°C or higher and 4°C or lower from the viewpoint of enhancing the effect of suppressing moisture condensation on the surface of the jig near the other inkjet heads. From the same viewpoint, it is more preferably 3°C or lower, still more preferably 2°C or lower, even more preferably 1°C or lower, even more preferably 0.5°C or lower, and even more preferably 0°C. Also, for example, when the inkjet head is a 4-series inkjet head, the difference (T3a’ - T3a) between the temperature T3a’ and the temperature T3a and the difference (T3b’ - T3b) between the temperature T3b’ and the temperature T3b are preferably in the same range as the above difference (T3’ - T3).

[0037] (Drying process) The inkjet recording method of the present invention may further include a drying process after the completion of the inkjet recording. Specifically, as the drying process, the low-absorbency recording medium on which the inkjet recording has been completed is heated to room temperature or higher and then held in that state to promote the removal of the liquid component mainly composed of water from the ink coating film on the low-absorbency recording medium. In the drying process, from the viewpoint of promoting the removal of the liquid component mainly composed of water in the ink coating film and obtaining a recorded matter at an early stage, the drying temperature is preferably 30°C or higher, more preferably 35°C or higher, and still more preferably 40°C or higher. And from the viewpoint of suppressing the thermal denaturation of the recording medium, it is preferably 160°C or lower, more preferably 120°C or lower, and still more preferably 110°C or lower.

[0038] (Conveying speed of the low-absorbency recording medium) In the inkjet recording method of the present invention, the conveyance speed of the low liquid-absorbing recording medium, that is, the speed at which the low liquid-absorbing recording medium moves from the paper feed side to the paper discharge side in the conveyance direction, is preferably 1 m / min or more, more preferably 5 m / min or more, still more preferably 10 m / min or more, and preferably 100 m / min or less, more preferably 50 m / min or less, still more preferably 40 m / min or less, from the viewpoint of achieving both improvement in the quality of the resulting recording and shortening of the recording time.

[0039] (Temperature of the inkjet head during inkjet recording) In the inkjet recording method of the present invention, the temperature of the inkjet head during inkjet recording is preferably kept constant at room temperature or higher from the viewpoints of stabilizing ink ejection and improving the quality of the resulting recording. That is, the temperature of the inkjet head during inkjet recording is preferably 23°C or higher, more preferably 25°C or higher, still more preferably 30°C or higher, even more preferably 32°C or higher, and preferably 50°C or lower, more preferably 45°C or lower, still more preferably 40°C or lower, even more preferably 38°C or lower. The temperature of the inkjet head during inkjet recording is a different concept from the temperature of the surface of the jig near the inkjet head in the inkjet recording method of the present invention.

[0040] (Temperature of the aqueous ink during inkjet recording) In the inkjet recording method of the present invention, the temperature of the aqueous ink ejected by the inkjet head during inkjet recording is preferably kept constant at room temperature or higher from the viewpoints of stabilizing ink ejection and improving the quality of the resulting recording. That is, the temperature of the aqueous ink supplied to the inkjet head during inkjet recording is preferably 23°C or higher, more preferably 25°C or higher, still more preferably 30°C or higher, even more preferably 32°C or higher, and preferably 50°C or lower, more preferably 45°C or lower, still more preferably 40°C or lower, even more preferably 38°C or lower. The temperature of the water-based ink ejected from the ink-jet head during ink-jet recording is a different concept from the temperature of the surface of the jig in the vicinity of the ink-jet head in the ink-jet recording method of the present invention.

[0041] <Water-based ink> In the ink-jet recording method of the present invention, the water-based ink has the largest proportion of water on a mass basis among the components constituting the ink. The water content in the water-based ink is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, and is preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less.

[0042] (Coloring material) In the present invention, dyes, pigments, and combinations of dyes and pigments can be used as colorants for the water-based ink. However, from the viewpoint of suppressing printing unevenness and improving solid filling, pigments are preferred. The pigment may be either an inorganic pigment or an organic pigment, and lake pigments and fluorescent pigments may also be used. If necessary, these pigments may also be used in combination with extender pigments. Examples of inorganic pigments include carbon black, titanium oxide, iron oxide, metal oxides such as red iron oxide and chromium oxide, and pearlescent pigments. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments. In the case of achromatic inks, achromatic pigments such as white, black, and gray can be used, and in the case of chromatic inks, chromatic organic pigments such as cyan, magenta, yellow, blue, red, orange, and green can all be used. Preferred organic pigments include, for example, C.I. Pigment Blue as a cyan-based pigment; C.I. Pigment Red, C.I. Pigment Orange, and C.I. Pigment Violet as magenta-based pigments; and one or more product numbers selected from the group consisting of C.I. Pigment Yellow as a yellow-based pigment. The pigments can be used singly or in combination of two or more within each color system of cyan, magenta, and yellow. In the inkjet recording method of the present invention, the aqueous ink may not contain a colorant. Specifically, before inkjet recording an aqueous ink containing a colorant, a liquid that does not contain a colorant but is ejected from an inkjet head to enhance the fixing property and color development property of the aqueous ink containing a colorant, so-called a pretreatment liquid, or a liquid that has the same effect and does not contain a colorant and is ejected from an inkjet head subsequent to inkjet recording an aqueous ink containing a colorant, so-called a post-treatment liquid.

[0043] In the inkjet recording method of the present invention, the content of the water-soluble organic solvent in the aqueous ink is preferably 10% by mass or more, more preferably 15% by mass or more, still more preferably 20% by mass or more from the viewpoints of suppressing drying of the ink in the inkjet head nozzle, controlling the behavior of droplets, and suppressing printing unevenness, and from the same viewpoints as above, preferably 40% by mass or less, more preferably 35% by mass or less, still more preferably 30% by mass or less.

[0044] (Surfactant) In the inkjet recording method of the present invention, from the viewpoints of controlling the behavior of droplets by adjusting the air-liquid interface energy of the aqueous ink and suppressing printing unevenness, and improving the solid filling property, it is preferable that the aqueous ink contains a surfactant. Examples of the surfactant include nonionic surfactants, anionic surfactants, and amphoteric surfactants, and nonionic surfactants are preferable. Examples of the nonionic surfactant include acetylene-based surfactants, polyoxyalkylene alkyl ether-based surfactants, polyhydric alcohol-based surfactants, fatty acid alkanolamides, silicone-based surfactants, and fluorine-based surfactants. Among these, as the surfactant, one or more selected from the group consisting of acetylene-based surfactants, polyoxyalkylene alkyl ether-based surfactants, and silicone-based surfactants are preferably mentioned. Among these, it is more preferable to contain one or more selected from acetylene-based surfactants and silicone-based surfactants.

[0045] In the inkjet recording method of the present invention, the aqueous ink may further contain various additives such as a fixing resin, a humectant, a wetting agent, a wetting and penetrating agent, a viscosity modifier, an antifoaming agent, a preservative, a fungicide, and a rust preventive as required. The aqueous ink can be produced by mixing a pigment dispersion, a water-soluble organic solvent, and, if necessary, various additives such as water and a surfactant.

Examples

[0046] In the following Examples, Comparative Examples, and Production Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The measurement methods for each physical property are as follows.

[0047] (1) Water absorption amount of the recording medium at a contact time of 100 ms between the recording medium and pure water Using an automatic scanning liquid absorber (manufactured by Kumagai Riki Kogyo Co., Ltd., KM500win), the transfer amount at a contact time of 100 ms of pure water was measured under the conditions of 23°C and a relative humidity of 50%, and the water absorption amount at 100 ms was used. The measurement conditions are shown below. <Measurement Conditions> 「Spiral Method」 Contact Time (sec): 0.010 - 1.0 Pitch (mm): 7 Length Per Sampling (degree): 86.29 Start Radius (mm): 20 End Radius (mm): 60 Min Contact Time (ms): 10 Max Contact Time (ms): 1000 Sampling Pattern (1 - 50): 50 Number of Sampling Points (>0): 19 「Square Head」 Slit Span (mm): 1 Slit Width (mm): 5

[0048] (2) Measurement of the weight-average molecular weight of the water-insoluble polymer Using a solution prepared by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L respectively as the eluent, by gel permeation chromatography [GPC apparatus (HLC-8120GPC) manufactured by Tosoh Corporation, columns (TSK-GEL, α-M × 2) manufactured by Tosoh Corporation, flow rate: 1 mL / min], using monodisperse polystyrene with a known molecular weight in advance as the standard substance for measurement.

[0049] (3) Measurement of the solid content concentration of the pigment dispersion Weigh 10.0 g of sodium sulfate, which has been constant-weighted in a desiccator, into a 30 ml polypropylene container (φ = 40 mm, height = 30 mm), add approximately 1.0 g of the sample, mix, weigh accurately, maintain at 105 °C for 2 hours to remove the volatile matter, then leave it in the desiccator for 15 minutes and measure the mass. The mass of the sample after removing the volatile matter was taken as the solid content, and divided by the mass of the added sample to obtain the solid content concentration.

[0050] (4) Measurement of the average particle size of the pigment-containing polymer particles Cumulant analysis was performed and measured using a laser particle analysis system “ELS-8000” (manufactured by Otsuka Electronics Co., Ltd.). The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and an integration count of 100 times. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The measurement concentration was 5×10 -3 mass% (in terms of solid content concentration).

[0051] (5) Measurement of the viscosity of the aqueous ink Using an E-type viscometer “TV-25” (manufactured by Toki Sangyo Co., Ltd., standard cone rotor 1°34’×R24, rotation speed 50 rpm), the viscosity was measured at 32°C.

[0052] (6) Static surface tension of the aqueous ink Using a surface tension meter (manufactured by Kyowa Interface Science Co., Ltd., product name: CBVP-Z), a platinum plate was immersed in a cylindrical polyethylene container (diameter 3.6 cm × depth 1.2 cm) containing 5 g of the aqueous ink, and the static surface tension of the aqueous ink was measured at 20°C.

[0053] (7) Measurement of the pH of the aqueous ink Using a desktop pH meter “F-71” (manufactured by Horiba, Ltd.) with a pH electrode “6337-10D” (manufactured by Horiba, Ltd.), the pH of the aqueous ink at 25°C was measured.

[0054] (Manufacture of the aqueous ink) Production Example 1 (Synthesis of a water-insoluble polymer) 16 parts of methacrylic acid (reagent of Fuji Film Wako Pure Chemical Industries, Ltd.), 44 parts of styrene (reagent of Fuji Film Wako Pure Chemical Industries, Ltd.), 30 parts of styrene macromonomer “AS-6S” (manufactured by Toagosei Co., Ltd., number average molecular weight 6,000, solid content 50%), and 25 parts of methoxypolyethylene glycol methacrylate “Blemmer PME-200” (NOF Corporation) were mixed to prepare 115 parts of a monomer mixture. 18 parts of methyl ethyl ketone, 0.03 part of 2-mercaptoethanol as a chain transfer agent, and 10% (11.5 parts) of the monomer mixture were placed in a reaction vessel, mixed, and sufficiently purged with nitrogen gas. On the other hand, the remaining 90% (103.5 parts) of the monomer mixture, 0.27 part of the chain transfer agent, 42 parts of methyl ethyl ketone, and 3 parts of a polymerization initiator 2,2'-azobis(2,4-dimethylvaleronitrile) "V-65" (reagent of FUJIFILM Wako Pure Chemical Corporation) were mixed, and the resulting mixture was placed in a dropping funnel. While stirring the mixed solution in the reaction vessel under a nitrogen atmosphere, the temperature was raised to 75°C, and the mixed solution in the dropping funnel was added dropwise over 3 hours. After 2 hours had elapsed at 75°C from the end of the dropwise addition, a solution prepared by dissolving 3 parts of the polymerization initiator in 5 parts of methyl ethyl ketone was added, and the mixture was further aged at 75°C for 2 hours and at 80°C for 2 hours. Further, 50 parts of methyl ethyl ketone was added to obtain a solution of a water-insoluble polymer (weight average molecular weight: 50,000). The solid content concentration of the water-insoluble polymer solution was 45% by mass.

[0055] Production Example 2 (Production of an aqueous dispersion of polymer particles containing a black pigment) 95.2 parts of the water-insoluble polymer solution obtained in Production Example 1 was diluted with 53.9 parts of methyl ethyl ketone, and 15.0 parts of a 5N aqueous sodium hydroxide solution, 0.5 part of 25% aqueous ammonia, and 341.3 parts of deionized water were added thereto as neutralizing agents. Further, 100 parts of C.I. Pigment Black 7 (P.B.7, manufactured by Cabot Corporation) as a carbon black pigment was added to obtain a pigment mixture. The degree of neutralization was 78.8 mol%. The obtained pigment mixture was mixed for 1 hour at 7000 rpm and 20°C using a dispersing blade. The obtained dispersion was subjected to a dispersion treatment at a pressure of 180 MPa for 15 passes using a microfluidizer "High Pressure Homogenizer M-140K" (manufactured by Microfluidics). The resulting pigment-containing polymer particle dispersion was subjected to vacuum decompression at 60°C to remove methyl ethyl ketone, and then a portion of the water was removed. The resulting dispersion was centrifuged. The liquid layer was filtered through a Minisart syringe filter (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding an aqueous dispersion of pigment-containing polymer particles. The solids concentration was 25% by mass. To 100 parts of the resulting aqueous dispersion of pigment-containing polymer particles, 0.45 parts of trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX321L) and 15.23 parts of deionized water were added, and the mixture was heated at 70°C for 3 hours with stirring to perform a crosslinking treatment. After cooling to room temperature, the liquid layer was filtered through a Minisart syringe filter (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding an aqueous dispersion of black pigment-containing polymer particles (solids concentration: 22.0% by mass). The average particle size of the black pigment-containing polymer particles was 100 nm.

[0056] Manufacturing Examples 3 to 5 In Production Example 2, the black pigment was changed to a cyan pigment (PB15:3, manufactured by DIC Corporation), a magenta pigment (PR150, manufactured by Fuji Colorants Co., Ltd.), or a yellow pigment (PY74, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), and aqueous dispersions of each pigment-containing polymer particle (solid concentration: 22% by mass) were obtained under the conditions shown in Table 1. The compositions and physical properties are shown in Table 1.

[0057] [Table 1]

[0058] Production Example 6 (Production of Black Ink (Bk)) 46.3 parts of an aqueous dispersion of black pigment-containing polymer particles (solid content: 22.0% by mass) obtained in Production Example 2 (pigment amount: 7.0% by mass), 20.0 parts of propylene glycol, 5.0 parts of diethylene glycol mono-isobutyl ether, 0.5 part of a silicone-based surfactant (manufactured by Shin-Etsu Chemical Co., Ltd., product name: SAG-005), and 1.2 parts of an acetylene-based surfactant (manufactured by Nisshin Chemical Industry Co., Ltd., Surfynol 104PG50, active ingredient: 50% by mass) were added, and deionized water was added so that the total amount of the ink became 100 parts to obtain a mixed solution. The obtained mixed solution was filtered through a mini-salt syringe filter (acetyl cellulose-based membrane filter: aperture diameter 5 μm, manufactured by Sartorius) to obtain a black ink (Bk) as an aqueous ink.

[0059] Production Examples 7 to 9 (Production of Cyan Ink (C), Magenta Ink (M), and Yellow Ink (Y)) In Production Example 6, except that the aqueous dispersion of black pigment-containing polymer particles was changed to the aqueous dispersions of cyan, magenta, and yellow pigment-containing polymer particles obtained in Production Examples 3 to 5, cyan ink (C), magenta ink (M), and yellow ink (Y) were obtained as aqueous inks in the same manner as in Production Example 6. The ink compositions and physical properties are shown in Table 2.

[0060]

Table 2

[0061] Example 1 Using the aqueous ink obtained above on corona-treated PET (manufactured by Futamura Chemical Co., Ltd., Taiko polyester film FE2001, water absorption of the recording medium at a contact time of 100 msec between the recording medium and pure water: 0 g / m 2 ), each evaluation was performed using a printing evaluation apparatus with the following settings.

[0062] (Settings of the printing evaluation apparatus) Figure 1 is a schematic diagram of the printing evaluation apparatus used in this example. In an environment with a temperature of 25 ± 1°C and a relative humidity of 30 ± 5%, a one-pass printing evaluation apparatus (manufactured by Trytec Co., Ltd.) equipped with a carriage on which an inkjet head (manufactured by Kyocera Corporation, "KJ4B-HD06MHG-STDV", piezo type) is fixed was filled with aqueous ink. These inkjet heads are provided in the printing evaluation apparatus with black ink, cyan ink, magenta ink, and yellow ink in order from the paper feed side in the conveyance direction of the recording medium. Ink was filled so that the black ink (Bk), cyan ink (C), magenta ink (M), and yellow ink (Y) obtained in Production Examples 6 to 9 were ejected from their respective inkjet heads. The interval between each inkjet head was set to 55 cm. As shown in Fig. 1, planar electric heaters 61 to 64 were respectively installed at portions that do not contact the inkjet heads 41 to 44 of the jigs J2 (51) for fixing the inkjet head 41 of black ink and are on the paper discharge side, portions that do not contact the inkjet heads 42 of the jigs J3a (52) for fixing the inkjet head 42 of cyan ink and are on the paper discharge side, portions that do not contact the inkjet heads 43 of the jigs J3b (53) for fixing the inkjet head 43 of magenta ink and are on the paper discharge side, and portions that do not contact the inkjet heads 44 of the jigs J1 (54) for fixing the inkjet head 44 of yellow ink and are on the paper discharge side. Also, as shown in Fig. 1, planar electric heaters 65 and 66 for heating the recording medium 3 were installed from the surface of the recording medium 3 opposite to the surface facing the inkjet heads. The distance between the planar electric heaters 65 and 66 and the recording medium 3 was set to 0.25 mm, and the distance between the inkjet heads 41 to 44 and the recording medium 3 was set to 1.0 mm.

[0063] The planar electric heaters 61 to 64 were adjusted so that the temperature of the surface of the jig near each inkjet head (the temperature of the jig for fixing each inkjet head) would be as follows. The temperature T2 of the jig J2 near the inkjet head of black ink: 34°C The temperature T3a of the jig J3a near the inkjet head of cyan ink: 36°C Temperature T3b of jig J3b near the magenta inkjet head: 38°C Temperature T1 of the jig J1 near the yellow inkjet head: 40°C The surface temperature of the planar electric heater 65 was set to 40°C, and the surface temperature of the planar electric heater 66 was set to 43°C.

[0064] The conditions for the print evaluation device were set as follows: head voltage 26V, frequency 10kHz, appropriate amount of ejected liquid 3pL, inkjet head temperature 32°C, resolution 600dpi, number of pre-ejection flushings 200, and negative pressure -4.0kPa.

[0065] (Temperature measurement of the jig surface near the inkjet head, evaluation of condensation) A print command was transferred to the print evaluation device, and ink was ejected in the order of black ink (Bk), cyan ink (C), magenta ink (M), and yellow ink (Y), and a nozzle check pattern for each color was printed to confirm that ink was being ejected from all nozzles. A 20 cm wide solid image (each ink was ejected at 100% duty, 400% duty) was then printed in a length of 200 meters. After printing 20 meters, the temperature T1' of the area where the water-based ink was attached was measured with a contact thermometer at position A1 (position indicated by reference numeral 8 in Figure 1), 3 cm away from the inkjet head ejecting the yellow ink (Y) in the direction opposite to the transport direction of the recording medium. The temperature T1' at this time was 40°C. Furthermore, when the temperature of the jig surface near each inkjet head was measured after printing for 20 m, it was found to be the same as the temperature adjusted above. After printing 200 meters, a command to print a nozzle check pattern was immediately transferred, and the temperature of the jig surface of each inkjet head was measured while printing the nozzle check pattern. The temperature was the same as the temperature adjusted above and the temperature at the time when 20 meters had been printed. After printing the nozzle check pattern, the presence or absence of condensation on the surface of the jig J1 near the inkjet head ejecting yellow ink was checked at the condensation check position 100, and evaluated according to the following condensation evaluation criteria. The results are shown in Table 3. <Evaluation criteria for condensation on the surface of the jig near the inkjet head> 1: No water droplets were generated on the surface of jig J1. 2: Water droplets were generated on the surface of the jig J1, but the water droplets did not come into contact with the low liquid-absorbent recording medium. 3: Water droplets formed on the surface of the jig J1, and came into contact with the low-liquid-absorbent recording medium during printing. The condensation criterion is that the smaller the number, the less condensation there is and the better the product is.

[0066] (Method for evaluating the number of nozzle blockages) In evaluating condensation on the surface of the jig near the inkjet head, the number of blocked nozzles (the number of nozzles that were not ejecting) was confirmed from a nozzle check pattern printed after 200 meters of printing was completed. The results are shown in Table 3. The fewer blocked nozzles there were, the better the performance.

[0067] In Example 1, the settings of the print evaluation device were adjusted so that the jig temperature of each inkjet head was set to the conditions shown in Table 3 by adjusting the conditions of the planar electric heater, and the evaluations of Examples 2 to 4 and Comparative Example 1 were carried out in the same manner as in Example 1. The results are shown in Table 3.

[0068] [Table 3]

[0069] Table 3 shows that the inkjet recording methods of Examples 1 to 4, in which the difference between temperature T1' and temperature T1, T1'T1, is 0° C. or more and 4° C. or less, are less likely to cause condensation on the surface of the jig near the inkjet head than the inkjet recording method of Comparative Example 1, in which T1'-T1 is 6° C. Therefore, it is clear that the inkjet recording methods of Examples 1 to 4 can suppress condensation on the surface of the jig near the inkjet head. [Explanation of symbols]

[0070] 1: Print evaluation device 2: Recording medium transport table 3: Recording media 41, 42, 43, 44: Inkjet head 51: Jig J2 for fixing the inkjet head on the paper feed side 52: J3a, a fixture for fixing other inkjet heads 53: J3b, a fixture for fixing other inkjet heads 54: Jig J1 for fixing the inkjet head on the paper ejection side 61, 62, 63, 64, 65, 66: Planar heat transfer heater 71, 72, 73, 74: Temperature sensors 8:Position A1 (temperature T1' measurement position) 9:Position A2 (temperature T2' measurement position) 10:Position A3 (temperature T3a' measurement position) 11:Position A4 (temperature T3b' measurement position) 100:Condensation check position

Claims

1. An inkjet recording method for directly inkjet recording on a low-liquid-absorbent recording medium by a one-pass method using an inkjet recording apparatus equipped with an inkjet head that ejects a water-based ink, comprising: the inkjet head is an inkjet head having at least two lines, the difference (T1'-T1) between the temperature T1' of the portion of the low liquid-absorbent recording medium where the aqueous ink adheres from the inkjet head closest to the paper discharge side in the conveyance direction of the low liquid-absorbent recording medium and the temperature T1 of the surface of a jig near the inkjet head closest to the paper discharge side in the conveyance direction of the low liquid-absorbent recording medium is 0°C or more and 4°C or less.

2. 2. The inkjet recording method according to claim 1, wherein the temperature T1 of the surface of the jig nearest to the inkjet head on the paper discharge side in the conveying direction of the low liquid-absorbent recording medium is 30°C or higher and 50°C or lower.

3. 3. The inkjet recording method according to claim 1, wherein the method for adjusting the temperature T1 of the surface of a jig near the inkjet head closest to the discharge side in the transport direction of the low liquid-absorbent recording medium comprises a method for heating the jig near the inkjet head closest to the discharge side in the transport direction of the low liquid-absorbent recording medium by a planar electric heater.

4. 3. The inkjet recording method according to claim 1, wherein a method for adjusting the temperature T1′ of the low liquid-absorbent recording medium at a portion on the low liquid-absorbent recording medium where the water-based ink adheres from the inkjet head closest to the paper discharge side in the conveyance direction of the low liquid-absorbent recording medium comprises a method for heating the low liquid-absorbent recording medium from a surface opposite to the surface on which the water-based ink adheres, using a planar electric heater.

5. 3. The ink jet recording method according to claim 1, wherein the low liquid-absorbent recording medium is a resin film.

6. 3. The inkjet recording method according to claim 1, wherein the inkjet recording apparatus comprises at least four kinds of water-based inks including cyan ink, magenta ink, yellow ink and black ink.

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