JP2010208299A - Image forming method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method and an image forming apparatus suppressing creases formed in fixing by suppressing cockling formed on a recording medium. <P>SOLUTION: The image forming method and apparatus has a plotting process for forming an image on the recording medium 114 using aqueous ink, a drying process for drying the aqueous ink on the recording medium 114, and a fixing process for fixing by pressurizing the aqueous ink formed on the recording medium 114. The recording medium 114 is dried so that a dimensional change to the moisture content of 1 g/m<SP>2</SP>is 0.1% or less and that the difference of moisture content between an image section and a non-image section of the recording medium 114 immediately before the fixing process is 3.0 g/m<SP>2</SP>or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming method and an image forming apparatus, and more particularly to an image forming method and an image forming apparatus capable of suppressing the occurrence of wrinkles during fixing.

  An ink jet recording apparatus is an apparatus that forms an image by continuously ejecting ink onto a recording medium. Since the apparatus configuration is simple and an image can be recorded with good image quality, the home for personal use is used. In addition to printers, it is also widely used as office printers and printers for business use. In particular, in business applications, higher processing speed and higher image quality are demanded.

  When ink jet recording is performed on a paper medium using water-based ink, paper deformation (curl or cockling) due to the interaction between water in the ink and paper fibers becomes a problem. Paper has the property that when water is applied, the fibers swell and expand, and when dried, the fibers shrink and shrink. When ink is applied uniformly to the entire surface of the recording medium, curling is likely to occur due to uniform expansion or contraction of the paper surface. The curl can be suppressed to some extent by a known paper drying technique and correction after printing (a reverse tension is applied to the recording medium and a weight is applied from above after paper discharge).

  Cockling is a more serious problem. When an image area and a non-image area are present on the recording medium, the image area greatly expands due to the influence of water in the ink, so that distortion occurs between the image area and the non-image area. There is a problem that the recording medium is lifted or uneven.

  Further, in order to ensure sufficient film strength after printing, it is necessary to fix the ink by nipping the image portion with a heat roller or the like after drawing with ink. However, when cockling has occurred in the recording medium, there has been a problem that wrinkles are generated by crushing the convex portion of the cockling during nip with the heat roller. Since wrinkles once formed on the recording medium exist even after the ink is dried, the printing quality is greatly reduced.

  In order to solve such a problem, for example, in the following Patent Documents 1 to 3, for the purpose of suppressing the occurrence of cockling, the recording medium is forcibly dried after ink application to evaporate water, thereby causing cockling. A technique for suppressing the above is disclosed. Further, Patent Document 4 discloses that when converting the density of the input image data into the droplet ejection ink amount, the cockling is suppressed by performing density conversion control so that the ink amount does not exceed a predetermined value. ing. Patent Documents 5 and 6 disclose a technique for reducing cockling by reducing stretchability between the image portion and the non-image portion by applying a colorless ink mainly composed of water to the non-image portion with an inkjet head. Has been.

JP 2006-212787 A Japanese Patent Application Laid-Open No. 11-198362 JP 2007-160839 A JP 2002-67357 A JP 2004-58308 A JP 2005-212371 A

  However, by performing forced drying as described in Patent Documents 1 to 3, it is possible to suppress the elongation of the image portion, but in the non-image portion, the moisture initially held by the recording medium evaporates. As a result, shrinkage occurred, and cockling could not be sufficiently suppressed. Further, in Patent Document 4, since the upper limit of the amount of ink ejected is set, the color reproduction range is inevitably narrowed, which hinders high-quality printing. In Patent Documents 5 and 6, a head for ejecting colorless ink is further required, which is disadvantageous in terms of apparatus cost. In addition, since the total amount of water to be ejected increases, there is a problem in terms of cost, such as the addition of a drying step and the increase in power consumption.

  The present invention has been made in view of such circumstances, and provides an image forming method and an image forming apparatus capable of suppressing the generation of wrinkles formed during fixing by suppressing cockling. Objective.

According to a first aspect of the present invention, in order to achieve the above object, a drawing step of forming an image on a recording medium using a water-based ink, a drying step of drying the water-based ink on the recording medium, and the recording medium A fixing step of pressing and fixing the image formed thereon, and the recording medium has a dimensional change of 0.1% or less with respect to a moisture amount of 1 g / m ² , and the recording medium immediately before the fixing step Provided is an image forming method characterized in that drying is performed so that a difference in water content between an image portion and a non-image portion of a recording medium is 3.0 g / m ² or less.

According to the first aspect, since the recording medium having a small dimensional change with respect to the moisture content is used as the recording medium, the dimensional change can be suppressed even if a difference in the moisture content occurs between the image portion and the non-image portion. Then, by reducing the difference in water content between the image area and the non-image area immediately before the fixing process to 3.0 g / m ² or less, the difference in the amount of expansion / contraction between the image area and the non-image area is reduced and distortion is reduced. Therefore, cockling can be suppressed. By suppressing cockling, no convex portion is formed on the recording medium, so that an image can be formed without generating wrinkles caused by crushing the convex portion.

  A second aspect of the present invention according to the first aspect is characterized in that the drawing step is droplet ejection by single-pass ink jet using a line head having the width of the recording medium.

  According to the second aspect of the present invention, since the image is formed by droplet ejection by a single-pass ink jet using a line head having a recording medium width as the drawing process, cockling can be more effectively reduced. As another method, for example, in the shuttle scan method, the drawing time is generally long and the time until the recording medium is dried is long, so that the permeation of the ink solvent and the swelling of the paper fiber progress during that time. It is difficult to suppress the degree of cockling as compared with the single pass method. However, in the single pass method, since the time from drawing to drying can be completed in a relatively short time, the penetration of the ink solvent into the recording medium can be suppressed, and cockling can be reduced. By reducing cockling, the occurrence of convex portions of the recording medium can be suppressed, and the generation of wrinkles generated on the recording medium during the fixing process can be suppressed.

A third aspect of the present invention provides the method according to the first or second aspect, wherein the water-based ink is applied to the recording medium such that a water amount per unit area of the recording medium is 7.0 g / m ² or more. Features.

In the present invention, the difference in water content between the image area and the non-image area of the recording medium immediately before the fixing process can be reduced to 3.0 g / m ² or less by the drying process. This is particularly effective because it can be suppressed even under conditions where cockling is likely to occur at a water content of 7.0 g / m ² or more.

  A processing liquid according to any one of the first to third aspects, wherein the processing liquid containing a component that reacts with pigments and resin particles in the water-based ink is applied to the recording medium before the drawing step. It has the provision process, It is characterized by the above-mentioned.

  According to the fourth aspect, since the treatment liquid is applied to the recording medium, it is possible to form a void structure in the ink layer by aggregating the pigment and the resin particles in the aqueous ink. Accordingly, a capillary force acts on the ink solvent, the penetration into the recording medium can be delayed, and the ink solvent can be dried in the drying step, so that cockling can be prevented.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the time from the drawing process to the start of the fixing process is within 8 seconds.

  By setting the time from the drawing process to the fixing process within the above range, drying can be performed before the ink solvent penetrates into the recording medium, and the amount of the ink solvent contained in the recording medium can be suppressed. . Accordingly, the interaction between the recording medium and the ink solvent can be minimized, cockling can be reduced, and wrinkles during fixing can be suppressed.

  A sixth aspect of the present invention is the method according to any one of the first to fifth aspects, wherein the drying step is performed by supplying dry air to the recording medium, and the dry air has a relative humidity at 23 ° C. of 40% RH or more. It is characterized by that.

According to claim 6, in the drying step, drying is performed using drying air, and the residual air amount of the image portion and the non-image portion is set by setting the relative humidity at a temperature of 23 ° C. to 40% RH or more. Can be reduced to 3.0 g / m ² or less, and cockling can be improved. If the drying air has a relative humidity of less than 40% RH at a temperature of 23 ° C., drying of the non-image area also proceeds, so the difference in the residual water amount between the image area and the non-image area is 3.0 g / m ² or less. It becomes difficult to make.

  A seventh aspect of the present invention is characterized in that, in the sixth aspect, the dry air has a relative humidity at 23 ° C. of 90% RH or less.

According to the seventh aspect, since the relative humidity at 23 ° C. of the drying air is 90% RH or less, the drying of the image portion can be promoted, so that the difference in the residual water amount between the image portion and the non-image portion is 3. It can be reduced to 0 g / m ² or less, and cockling can be improved. If the relative humidity at 23 ° C. of the drying air exceeds 90% RH, the drying of the image area does not proceed, and it becomes difficult to make the difference in the residual water amount between the image area and the non-image area 3.0 g / m ² or less. .

  An eighth aspect is characterized in that, in the sixth or seventh aspect, the temperature of the drying air is 50 ° C. or higher.

According to the eighth aspect, since the drying of the image portion can be promoted by setting the temperature of the drying air to 50 ° C. or more, the difference in the residual water amount between the image portion and the non-image portion is 3.0 g / m ² or less. The cockling can be improved.

  A ninth aspect of the present invention is characterized in that, in any one of the first to eighth aspects, the water-based ink contains a water-soluble organic solvent having an SP value of 27.2 or less.

  The damage (expansion and shrinkage) that the ink causes to the recording medium (paper fiber) is caused by the water in the ink. Therefore, a highly hydrophilic (high SP value) water-soluble organic solvent also interacts with the recording medium. , Damage the recording medium. According to the ninth aspect, the SP value of the water-soluble organic solvent contained in the ink is lowered, thereby reducing the hydrophilicity of the water-soluble organic solvent and reducing the interaction with the recording medium, thereby reducing damage. And cockling can be improved.

According to a tenth aspect of the present invention, in order to achieve the above object, a drawing means for forming an image on a recording medium using a water-based ink, a drying means for drying the water-based ink on the recording medium, and the recording medium Fixing means for pressing and fixing the image formed thereon, and the recording medium has a dimensional change of 0.1% or less with respect to a moisture amount of 1 g / m ² , and the recording medium at the time of the fixing means There is provided an image forming apparatus comprising a control means for controlling the drying means so that the difference in water content between the image portion and the non-image portion is 3.0 g / m ² or less.

  A tenth aspect is obtained by developing the image forming method according to the first aspect as an image forming apparatus. According to the tenth aspect, the same effect as the first aspect can be obtained.

  According to the image forming method and the image forming apparatus of the present invention, the difference in moisture content between the image area and the non-image area is reduced by drying, and a recording medium having a small dimensional change with respect to the moisture content is used as the recording medium. Cockling of the recording medium after drying can be suppressed. Therefore, generation of fixing wrinkles formed at the time of fixing can be suppressed.

1 is a schematic configuration diagram of an ink jet recording apparatus according to the present invention. It is a plane sectional view showing an example of composition of a head. It is sectional drawing which shows the three-dimensional structure of an ink chamber unit. It is a principal part block diagram which shows the system configuration | structure of the inkjet recording device shown in FIG. It is a figure explaining the expansion-contraction rate measuring method of a recording medium. It is a table | surface figure which shows the result of the test example 1 of an Example. It is a table | surface figure which shows the result of the test example 2 of an Example. It is a table | surface figure which shows the result of the test example 3 of an Example. It is a table | surface figure which shows the result of the test example 4 of an Example. It is a table | surface figure which shows the result of the test example 5 of an Example. It is a table | surface figure which shows the result of the test example 6 of an Example.

  Hereinafter, preferred embodiments of an image forming method and an image forming apparatus of the present invention will be described with reference to the accompanying drawings.

[Overall configuration of inkjet recording apparatus]
An ink jet recording apparatus will be described as a preferred embodiment of an image forming apparatus that can be used in the image forming method of the present invention. Note that the present invention is not limited to the ink jet recording apparatus. Further, the image is not limited to the drum conveyance method, and an image can be formed by a belt conveyance method.

  The inkjet recording apparatus 100 is configured as an on-demand printing machine that records an image using a sheet of printing paper, and mainly performs a predetermined process on the recording medium 114 and a paper feeding unit 102 that feeds the recording medium 114. A treatment liquid applying unit 106 for applying a liquid, a drawing unit 108 for ejecting colored ink onto the recording medium 114, a fixing unit 110 for fixing an image formed on the recording medium 114, and a recording medium on which the image is formed And a paper discharge unit 112 that conveys and discharges 114. In FIG. 1, each inkjet head 140 of the drawing unit 108 corresponds to a drawing unit, each ink drying unit 142 corresponds to a drying unit, the fixing unit 110 corresponds to a fixing unit, and the paper discharge unit 112 corresponds to a paper discharge unit.

<Paper Feeder>
The paper supply unit 102 is provided with a paper supply magazine 120, in which the recording media 114 in the form of sheets are stacked and stored. A feeder board 122 is connected to the paper feed magazine 120, and the recording media 114 accommodated in the paper feed magazine 120 are sent to the feeder board 122 one by one in order from the top. The recording medium 114 sent to the feeder board 122 is transferred to the pressure drum 126a of the treatment liquid applying unit 106 via the transfer drum 124a.

<Processing liquid application part>
In the treatment liquid application unit 106, a paper preheating unit 134, a treatment liquid application unit 136, and a treatment liquid drying unit 138 are sequentially arranged along the outer peripheral surface of the pressure drum 126a.

  The impression cylinder 126a is formed in a drum shape and is driven to rotate by a motor (not shown). A gripper (not shown) is provided on the outer peripheral surface of the pressure drum 126a, and the recording medium 114 is conveyed while the leading end is gripped by the gripper. A large number of suction ports (not shown) are formed on the outer peripheral surface of the pressure drum 126a, and air is sucked from the suction holes toward the inside. The recording medium 114 is conveyed while being sucked and held in this suction hole.

  The paper preheating unit 134 includes a hot air blower, and blows hot air controlled at a predetermined temperature toward the outer peripheral surface of the impression cylinder 126a. When the recording medium 114 rotated and conveyed by the impression cylinder 126a passes under the sheet preheating unit 134, the recording medium 114 is preheated by blowing hot air onto the surface thereof.

  The treatment liquid application unit 136 applies a treatment liquid having a constant thickness to the surface of the recording medium 114 (image forming surface) that is rotated and conveyed by the impression cylinder 126a, having a function of aggregating the color material in the ink. The treatment liquid application unit 136 includes an inkjet head (line head) having the same configuration as each inkjet head of the drawing unit 108, and is directed toward the recording medium 114 that is rotated and conveyed from the inkjet head by the impression cylinder 126a. Then, the processing liquid is discharged, and the processing liquid is applied to the surface of the recording medium 114 with a certain thickness.

  In addition, the application | coating method of a process liquid is not limited to this, For example, it can also be set as the structure provided with a spray system, a coating system, etc.

  The treatment liquid drying unit 138 includes a hot air blower, and blows hot air controlled to a predetermined temperature toward the outer peripheral surface of the impression cylinder 126a. When the recording medium 114 rotated and conveyed by the impression cylinder 126a passes under the processing liquid drying unit 138, hot air is blown onto the surface of the recording medium 114, and the processing liquid sprayed onto the surface is dried.

  According to the processing liquid application unit 106 configured as described above, the recording medium 114 transferred from the feeder board 122 of the paper supply unit 102 to the impression cylinder 126a via the transfer cylinder 124a is rotated by the impression cylinder 126a. By being conveyed, first, it passes under the paper preheating unit 134. Then, during the passage, hot air is blown from the paper preheating unit 134 to be preheated. Next, the preheated recording medium 114 passes under the treatment liquid application unit 136, and the treatment liquid is applied to the surface from the treatment liquid application unit 136 at a constant thickness during the passage. The recording medium 114 to which the processing liquid is applied finally passes through the processing liquid drying unit 138, and hot air is blown from the processing liquid drying unit 138 when the recording medium 114 passes through the recording medium 114, so that the processing liquid applied to the surface is dried. As a result, an aggregation treatment agent layer is formed on the surface of the recording medium 114.

  By applying the treatment liquid in this way, it is possible to agglomerate the pigment and resin particles in the ink applied at the next drawing section to form a void structure in the ink layer. Therefore, a capillary force acts on the ink solvent, the penetration into the recording medium can be delayed, and cockling can be prevented.

  The recording medium 114 on which the aggregation treatment agent layer is formed on the surface by the treatment liquid application unit 106 is transferred to the pressure drum 126b of the drawing unit 108 via the transfer drum 124b.

  In addition, in FIG. 1, although demonstrated with the structure provided with the process liquid provision part 106, it is also possible to set it as the structure which does not include a process liquid provision part.

<Drawing part>
The drawing unit 108 includes a pressure drum 126b, and an inkjet head 140C that discharges cyan (C) ink droplets and a magenta (M) ink droplet along the outer peripheral surface of the pressure drum 126b. Inkjet head 140M that ejects yellow (Y) ink droplets, inkjet head 140K that ejects black (K) ink droplets, and red (R) ink droplets An inkjet head 140R, an inkjet head 140G that ejects green (G) ink droplets, an inkjet head 140B that ejects blue (B) ink droplets, and ink drying units 142a and 142b are sequentially arranged. .

  In the present invention, the configuration of the inkjet head is not particularly limited, but a particularly preferable effect can be obtained in a single pass system using a line head having a recording medium width. In the shuttle scan system that performs interleaved recording, the drawing time is generally long, and it takes a long time to dry the recording medium. Accordingly, the penetration of the ink solvent and the swelling of the paper fibers proceed during that time, and the degree of cockling is deteriorated. In the single pass method, from drawing to drying can be made relatively shorter than the shuttle scan method, so that the penetration of the ink solvent into the paper fiber can be suppressed, and the cockling can be suppressed more effectively. be able to.

  The pressure drum 126b is formed in a drum shape like the pressure drum 126a of the treatment liquid application unit 106, and is driven to rotate by a motor (not shown). A gripper (not shown) is provided on the outer peripheral surface of the pressure drum 126b, and the recording medium 114 is conveyed while the leading end is gripped by the gripper. In addition, a large number of suction ports (not shown) are formed on the outer peripheral surface of the pressure drum 126b, and air is sucked inward from the suction holes. The recording medium 114 is conveyed while being sucked and held in this suction hole.

  Each of the inkjet heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B is composed of a line head corresponding to the sheet width (in this example, half-size chrysanthemum), and its ink discharge surface is the outer periphery of the impression cylinder 126b. It is arranged to face the surface. The nozzle rows formed on the ink discharge surface are arranged in a direction orthogonal to the rotation direction of the impression cylinder 126b (= conveyance direction of the recording medium 114).

  When the recording medium 114 rotated and conveyed by the impression cylinder 126b passes under each of the inkjet heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B, ink is spread over the entire region in the width direction (direction perpendicular to the conveying direction). Thus, an image is formed over the entire image forming area by one transport (sub-scan).

The water content of the water-based ink applied to the recording medium is preferably 7.0 g / m ² or more. This is particularly effective because the difference in the amount of moisture between the image portion and the non-image portion, such as when the amount of moisture is set to the above range or more, can be suppressed even under conditions where cockling easily occurs.

  The configuration of the inkjet heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B and the configuration of the ink supply mechanism will be described in detail later.

  Each of the ink drying units 142a and 142b includes a hot air blower, and blows hot air controlled at a predetermined temperature toward the outer peripheral surface of the impression cylinder 126b. When the recording medium 114 rotated and conveyed by the impression cylinder 126b passes under the ink drying units 142a and 142b, hot air is blown onto the surface of the recording medium 114, so that the ink ejected on the surface is dried.

  According to the drawing unit 108 configured as described above, the recording medium 114 transferred from the pressure drum 126a of the treatment liquid applying unit 106 to the pressure drum 126b via the transfer drum 124b is rotationally conveyed to the pressure drum 126b. By doing so, it passes under each inkjet head 140C, 140M, 140Y, 140K, 140R, 140G, 140B. Then, during the passage, ink of each color is ejected from each of the inkjet heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B, and an image is formed on the surface. The recording medium 114 on which the image is formed passes under the ink drying units 142a and 142b, and hot air is blown to the surface from the ink drying units 142a and 142b when the recording medium 114 passes through the recording medium 114, thereby drying the ink ejected on the surface. .

The drying is preferably performed so that the difference in the residual water amount between the image portion and the non-image portion of the recording medium 114 immediately before the next fixing step is 3.0 g / m ² or less. By setting the difference in the residual water amount to 3.0 g / m ² or less, the difference in expansion / contraction amount between the image portion and the non-image portion of the recording medium 114 can be reduced. The ring can be improved. Therefore, the occurrence of fixing wrinkles can be suppressed. The difference in the amount of residual water is preferably 2.2 g / m ² or less.

  In order to make the difference in the remaining water amount between the image portion and the non-image portion within the above range, the relative humidity at 23 ° C. of the drying air blown from the drying units 142a and 142b is preferably 40% RH or more, and is set to 50% RH. It is more preferable. Since the image portion contains a large amount of water, the relative humidity near the surface of the recording medium 114 is substantially 100%. However, since the non-image area does not contain moisture, the relative humidity on the surface is low. Therefore, when the relative humidity of the drying air is low, it is advantageous for drying the image portion, but the non-image portion is also dried, so the difference in the remaining water amount cannot be reduced. Since the drying of the non-image area can be delayed by increasing the relative humidity of the drying air, the difference between the image area and the non-image area can be reduced.

  Since the drying air is heated in the dryer and blown to the recording medium 114, the relative humidity of the drying air is reduced by the heating. Even if the relative humidity at 23 ° C. is increased to 90% RH, the drying performance of the image portion can be ensured. However, when the relative humidity exceeds 95% RH, the drying amount of the image portion decreases and the residual water amount of the image portion increases. This is not preferable because the difference from the non-image portion becomes large and cockling occurs.

  In this example, an image is formed using seven colors of CMYKRGB, but the combination of ink colors and the number of colors used is not limited to this. Light ink, dark ink, and special color ink may be added as necessary. For example, it is possible to add a head for ejecting light ink such as light cyan and light magenta. Further, it may be configured by only four colors of CMYK.

  The recording medium 114 having an image formed on the surface by the drawing unit 108 is transferred to the pressure drum 126c of the fixing unit 110 via the transfer drum 124c.

<Fixing part>
The fixing unit 110 is provided with a pressure drum 126c, and an image reading unit 144 and heating rollers 148a and 148b are provided in order from the upstream side in the rotation direction along the outer peripheral surface of the pressure drum 126c.

  The pressure drum 126c is formed in a drum shape like the pressure drum 126a of the treatment liquid application unit 106, and is driven to rotate by a motor (not shown). A gripper (not shown) is provided on the outer peripheral surface of the impression cylinder 126c, and the recording medium 114 is conveyed while the leading end is gripped by the gripper.

  The image reading unit 144 includes an image sensor (line sensor or the like) that images the surface of the recording medium 114 that is rotated and conveyed by the impression cylinder 126c. The image read by the image reading unit 144 is used for detecting clogging of the nozzles of each inkjet head in the drawing unit 108 and other ejection defects.

  The heating rollers 148a and 148b are controlled to a predetermined temperature and are in pressure contact with the outer peripheral surface of the impression cylinder 126c. The recording medium 114 rotated and conveyed by the impression cylinder 126c is heated and pressurized with the impression cylinder 126c when passing through the heating rollers 148a and 148b, whereby an image formed on the surface of the recording medium 114 is formed. It is fixed.

  The heating temperature of the heating rollers 148a and 148b is preferably set according to the glass transition temperature of the resin particles contained in the processing liquid or ink.

  According to the fixing unit 110 configured as described above, the recording medium 114 transferred from the pressure drum 126b of the drawing unit 108 to the pressure drum 126c via the transfer drum 124c is rotated and conveyed by the pressure drum 126c. As a result, the image passes under the image reading unit 144, and an image formed on the surface is read as necessary at the time of the passage. Thereafter, the recording medium 114 is heated and pressed by the heating rollers 148a and 148b, whereby the image formed on the surface is fixed.

  The time from when the image is formed by the drawing unit to when the image is fixed by the fixing unit is preferably within 8 seconds, and more preferably within 5 seconds. By setting the time from the drawing unit to the fixing unit within 8 seconds, drying can be performed before the ink solvent penetrates into the recording medium, and the amount of the ink solvent contained in the recording medium can be suppressed. . Accordingly, the interaction between the recording medium and the ink solvent can be minimized, cockling can be reduced, and wrinkles during fixing can be suppressed. For example, in FIG. 1, the time from when the image is formed by the drawing unit and when the image is fixed by the fixing unit is determined by the heating roller 148 b after ink droplets are ejected from the inkjet head 140 to the recording medium 114. Time until heating and pressurization is started. In the present invention, the difference in water content before fixing is set to a predetermined value or less, thereby reducing cockling and suppressing generation of fixing wrinkles.

  The recording medium 114 on which the image is fixed by the fixing unit 110 is delivered to the conveyor 154 of the paper discharge unit 112.

<Output section>
The paper discharge unit 112 includes a conveyor 154 that conveys the recording medium 114 and a paper discharge magazine 152 that collects the recording medium 114 conveyed by the conveyor 154.

  The recording medium 114 on which the image is fixed by the fixing unit 110 is transferred from the impression cylinder 126 c of the fixing unit 110 to the conveyor 154 and is conveyed to the paper discharge magazine 152 by the conveyor 154.

  The paper discharge magazine 152 receives the recording medium 114 conveyed by the conveyor 154 and collects it in a state of being stacked inside.

(Inkjet head structure)
Next, the structure of each inkjet head will be described. Since the structures of the inkjet heads 140C, 140M, 140Y, 140K, 140R, 140G, and 140B corresponding to the respective colors are the same, the inkjet head (hereinafter simply referred to as “head”) is denoted by reference numeral 200 below. Say).

  2A is a plan perspective view showing a structural example of the head 200, FIG. 2B is an enlarged view of a part thereof, and FIG. 2C is a plan view showing another structural example of the head 200. FIG. FIG. 3 is a cross-sectional view (a cross-sectional view taken along line XX in FIGS. 2A and 2B) showing a three-dimensional configuration of the ink chamber unit.

  In order to increase the dot pitch formed on the recording medium 114, it is necessary to increase the nozzle pitch in the head 200. As shown in FIGS. 2A and 2B, the head 200 of this example includes a plurality of ink chamber units (recording elements) including nozzles 202 serving as ink discharge ports, pressure chambers 204 corresponding to the respective nozzles 202, and the like. It has a structure in which droplet discharge elements 208 as units are arranged in a zigzag matrix (two-dimensionally), and thereby, the head longitudinal direction (direction perpendicular to the conveyance direction of the recording medium 114; main scanning direction) ) To achieve a high density of substantial nozzle intervals (projection nozzle pitch) projected so as to line up along the line.

  The configuration in which one or more nozzle rows are configured over a length corresponding to the entire width of the recording medium 114 in a direction (main scanning direction) substantially orthogonal to the conveyance direction (sub-scanning direction) of the recording medium 114 is not limited to this example. For example, instead of the configuration of FIG. 2A, as shown in FIG. 2C, short head blocks 200 ′ in which a plurality of nozzles 202 are two-dimensionally arranged are arranged in a staggered manner and connected. The line head having a nozzle row having a length corresponding to the entire width of the recording medium 114 as a whole may be configured by increasing the length. Although not shown, a line head may be configured by arranging short heads in a line.

  The pressure chamber 204 provided corresponding to each nozzle 202 has a substantially square planar shape, the nozzle 202 is provided at one of the diagonal corners, and the supply port 206 is provided at the other. ing. Note that the shape of the pressure chamber 204 is not limited to this example, and the planar shape may have various forms such as a quadrangle (rhombus, rectangle, etc.), a pentagon, a hexagon, other polygons, a circle, and an ellipse.

  Each pressure chamber 204 communicates with the common flow path 210 via the supply port 206. The common flow path 210 communicates with an ink tank (not shown) serving as an ink supply source, and ink supplied from the ink tank is supplied to each pressure chamber 204 via the common flow path 210.

  A piezoelectric element 216 having individual electrodes 214 is joined to a diaphragm 212 that constitutes a part of the pressure chamber 204 (the top surface in FIG. 3) and also serves as a common electrode. By applying a driving voltage to the individual electrode 214, the piezoelectric element 216 is deformed to change the volume of the pressure chamber 204, and ink is ejected from the nozzle 202 due to the pressure change accompanying this. When the piezoelectric element 216 returns to its original state after ink ejection, new ink is refilled into the pressure chamber 204 from the common flow path 210 through the supply port 206.

  In this example, the piezoelectric element 216 is applied as a means for generating ink ejection force to be ejected from the nozzle 202 provided in the head 200. However, a heater is provided in the pressure chamber 204, and the pressure of film boiling caused by heating of the heater is used. It is also possible to apply a thermal method that ejects ink.

  As shown in FIG. 2B, the ink chamber units 208 having such a structure are arranged in a fixed manner along a row direction along the main scanning direction and an oblique column direction having a constant angle θ that is not orthogonal to the main scanning direction. By arranging a large number of patterns in a lattice pattern, the high-density nozzle head of this example is realized.

  That is, with the structure in which a plurality of ink chamber units 208 are arranged at a constant pitch d along the direction of an angle θ with respect to the main scanning direction, the pitch P of the nozzles projected so as to be aligned in the main scanning direction is d × cos θ. Thus, in the main scanning direction, each nozzle 202 can be handled equivalently as a linear array with a constant pitch P. With such a configuration, it is possible to realize a high-density nozzle configuration in which 2400 nozzle rows are projected per inch (2400 nozzles / inch) so as to be aligned in the main scanning direction.

  In the implementation of the present invention, the nozzle arrangement structure is not limited to the illustrated example, and various nozzle arrangement structures such as an arrangement structure having one nozzle row in the sub-scanning direction can be applied.

  Further, the application range of the present invention is not limited to a printing method using a line-type head, and a short head that is less than the length in the width direction (main scanning direction) of the recording medium 114 is scanned in the width direction of the recording medium 114. Printing in the width direction is performed, and when printing in one width direction is completed, the recording medium 114 is moved by a predetermined amount in a direction (sub-scanning direction) perpendicular to the width direction of the recording medium 114, and the recording medium 114 in the next printing area is moved. A serial method may be applied in which printing in the width direction is performed and printing is performed over the entire printing area of the recording medium 114 by repeating this operation.

(Description of control system)
FIG. 4 is a block diagram illustrating a schematic configuration of a control system of the inkjet recording apparatus 100.

  As shown in the figure, the inkjet recording apparatus 100 includes a system controller 300, a communication unit 302, an image memory 304, a paper feed control unit 306, a treatment liquid application control unit 308, an ink droplet ejection control unit 310, a fixing control unit 312, A paper discharge control unit 314, an operation unit 316, a display unit 318, and the like are provided.

  The system controller 300 functions as a control unit that controls each unit of the inkjet recording apparatus 100 and also functions as a calculation unit that performs various calculation processes. The system controller 300 includes a CPU, a ROM, a RAM, and the like, and operates according to a predetermined control program. The ROM stores a control program executed by the system controller 300 and various data necessary for control.

  The communication unit 302 includes a required communication interface, and transmits / receives data to / from the host computer 320 connected to the communication interface.

  The image memory 304 functions as a temporary storage unit for various data including image data, and data is read and written through the system controller 300. Image data captured from the host computer 320 via the communication unit 302 is stored in the image memory 304.

  The paper feed control unit 306 controls driving of each unit constituting the paper feed unit 102 in accordance with a command from the system controller 300.

  The processing liquid application control unit 308 controls the driving of each unit constituting the processing liquid application unit 106 in accordance with a command from the system controller 300.

  The ink droplet ejection control unit 310 controls driving of each unit constituting the drawing unit 108 in accordance with an instruction from the system controller 300.

  The fixing control unit 312 controls driving of each unit constituting the fixing unit 110 in accordance with an instruction from the system controller 300.

  The paper discharge control unit 314 controls driving of each unit constituting the paper discharge unit 112 in accordance with an instruction from the system controller 300.

  The operation unit 316 includes necessary operation means (for example, operation buttons, a keyboard, a touch panel, etc.), and outputs operation information input from the operation means to the system controller 300. The system controller 300 executes various processes according to the operation information input from the operation unit 316.

  The display unit 318 includes a required display device (for example, an LCD panel or the like), and displays required information on the display device in accordance with an instruction from the system controller 300.

  As described above, the image data to be recorded on the recording medium 114 is taken into the inkjet recording apparatus 100 from the host computer 320 via the communication unit 302 and stored in the image memory 304. The system controller 300 performs necessary signal processing on the image data stored in the image memory 304 to generate dot data, and controls the driving of each ink head of the drawing unit 108 according to the generated dot data, thereby An image represented by the image data is recorded on the recording medium 114.

  The dot data is generally generated by performing color conversion processing and halftone processing on image data. The color conversion process is a process of converting image data expressed in RGB (for example, RGB 8-bit image data) into color data for each color of ink used in the inkjet recording apparatus 100 (in this example, color data of KCMYRGB). It is. The halftone process is a process of converting the color data of each color generated by the color conversion process into dot data of each color (in this example, KCMYRGB dot data) by a process such as error diffusion.

  The system controller 300 performs color conversion processing and halftone processing on the image data to generate dot data for each color of CMYKRGB. The image represented by the image data is recorded on the recording medium 114 by controlling the driving of the corresponding ink head according to the generated dot data of each color.

[recoding media]
The recording medium used in the present invention is not particularly limited as long as the dimensional change (stretching property) per 1 g / m ^{2 of} water content satisfies the range of 0.10% or less. On the other hand, particularly favorable results can be obtained. The dimensional change of the recording medium is preferably 0.08% or less. Since the coated paper for printing has a slow penetration of the ink solvent, it can be dried while suppressing the penetration of the ink solvent into the recording medium. Therefore, cockling due to a difference in the amount of water generated between the image portion and the non-image portion can be suppressed, and thus generation of wrinkles during fixing can be suppressed. When the sheet expansion / contraction ratio exceeds 0.10%, the difference in expansion / contraction amount between the image portion and the non-image portion is reduced even if the difference in water amount between the image portion and the non-image portion is 3.0 g / m ² or less. Therefore, the recording medium is uneven, and the protrusions are crushed during fixing, thereby causing wrinkles.

  Examples of the support that can be suitably used for coated paper include: chemical pulp such as LBKP and NBKP; mechanical pulp such as GP, PGW, RMP, TMP, CTMP, CMP, and CGP; wood pulp such as waste paper pulp such as DIP And a pigment as a main component, and one or more kinds of additives such as a binder, a sizing agent, a fixing agent, a yield improver, a cationizing agent, and a paper strength enhancer are mixed together to produce a long net paper machine, circular net paper machine. Base paper manufactured using various machines such as a machine, twin-wire paper machine, base paper provided with size press or anchor coat layer using starch, polyvinyl alcohol, etc., or of these size press or anchor coat layer Examples thereof include coated paper such as art paper, coated paper, cast coated paper and the like, on which a coating layer is provided.

The basis weight of the support is usually about 40 to 300 g / m ² , but is not particularly limited. The coated paper used in the present invention is coated with a coating layer on the support as described above. The coating layer is composed of a coating composition mainly composed of a pigment and a binder, and is coated on at least one layer on the support.

  As the pigment, a white pigment can be preferably used. Examples of such white pigments include light calcium carbonate, heavy calcium carbonate, magnesium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, Inorganic pigments such as diatomaceous earth, calcium silicate, magnesium silicate, synthetic amorphous silica, colloidal silica, alumina, colloidal alumina, pseudoboehmite, aluminum hydroxide, lithopone, zeolite, hydrous halloysite, magnesium hydroxide; styrene plastic pigments, Examples thereof include organic pigments such as acrylic plastic pigment, polyethylene, microcapsule, urea resin, melamine resin.

  Examples of the binder include starch derivatives such as oxidized starch, etherified starch, and phosphate esterified starch; cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose; casein, gelatin, soybean protein, polyvinyl alcohol or derivatives thereof; various saponification degrees Polyvinyl alcohol or various derivatives thereof such as silanol-modified products, carboxylated products, and cationized products thereof; conjugated diene copolymer latexes such as polyvinylpyrrolidone, maleic anhydride resin, styrene-butadiene copolymer, and methyl methacrylate-butadiene copolymer Acrylic polymer latex such as polymer or copolymer of acrylic acid ester and methacrylic acid ester; vinyl polymer latex such as ethylene vinyl acetate copolymer; Functional group-modified polymer latex with functional group-containing monomers such as xy groups; water-based adhesives such as thermosetting synthetic resins such as melamine resins and urea resins; acrylics such as polymethyl methacrylate; acid esters; Polymer or copolymer resin; Synthetic resin adhesives such as polyurethane resin, unsaturated polyester resin, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral, alkyd resin, and the like.

 The blending ratio of the pigment and binder in the coating layer is 3 to 70 parts by weight, preferably 5 to 50 parts by weight, based on 100 parts by weight of the pigment. When the blending ratio of the binder with respect to 100 parts by weight of the pigment is less than 3 parts by weight, the coating strength of the ink receiving layer made of such a coating composition may be insufficient. On the other hand, when the blending ratio exceeds 70 parts by weight, the absorption of the high boiling point solvent becomes extremely slow.

  Further, the coating layer includes, for example, a dye fixing agent, a pigment dispersant, a thickener, a fluidity improver, an antifoaming agent, a foam suppressor, a release agent, a foaming agent, a penetrating agent, a coloring dye, a coloring pigment, Various additives such as a fluorescent whitening agent, an ultraviolet absorber, an antioxidant, an antiseptic, an antibacterial agent, a water resistant agent, a wet paper strength enhancer, and a dry paper strength enhancer can be appropriately blended.

The coating amount of the ink receiving layer varies depending on the required gloss, ink absorbency, type of support, etc., and cannot be generally stated, but is usually 1 g / m ² or more. Further, the ink receiving layer may be applied by dividing a certain coating amount into two portions. When coating is performed in two steps in this way, the gloss is improved as compared with the case where the same coating amount is applied once.

  Coating of the coating layer is performed by using various devices such as various blade coaters, roll coaters, air knife coaters, bar coaters, rod blade coaters, curtain coaters, short dwell coaters, and size presses on-machine or off-machine. be able to. Further, after the coating layer is coated, the ink receiving layer may be flattened using a calendar device such as a machine calendar, a TG calendar, or a soft calendar.

In addition, the number of coat layers can be appropriately determined as necessary. Coated paper is classified as art paper, high-quality coated paper, medium-quality coated paper, high-quality lightweight coated paper, medium-weight lightweight coated paper, and fine-coated printing paper according to the coating layer coating amount. The amount is about 40 g / m ² on both sides of art paper, about 20 g / m ² on both sides of high-quality coated paper and medium-quality coated paper, and about 15 g / m ^{2 on} both sides of high-quality lightweight coated paper and medium-weight lightweight coated paper. The industrial printing paper is 12 g / m ² or less on both sides. In addition, there are gloss paper and matte paper according to the gloss of the paper in each classification. Examples of gloss-based art paper include Tohoku Art (Mitsubishi Paper Co., Ltd.) and mat-type art paper (Oji Paper Co., Ltd.). Examples of glossy high-quality coated paper include OK Top Coat (manufactured by Oji Paper Co., Ltd.), Aurora Coat (manufactured by Nippon Paper Industries Co., Ltd.), and Recycle Coat T-6 (manufactured by Nippon Paper Industries Co., Ltd.). (Manufactured by Nippon Paper Industries Co., Ltd.), New V mat (manufactured by Mitsubishi Paper Industries Co., Ltd.), recycle mat T-6 (manufactured by Nippon Paper Industries Co., Ltd.) and the like. Examples of the fine coated printing paper include Aurora L (manufactured by Nippon Paper Industries Co., Ltd.), Kinmari Hi-L (manufactured by Hokuetsu Paper Industries Co., Ltd.) and the like.

[Water-based ink]
Hereinafter, the water-based ink that can be used in the present invention will be described in detail. The aqueous ink includes at least a resin dispersant (A), a pigment (B) dispersed by the resin dispersant (A), self-dispersing polymer fine particles (C), and an aqueous liquid medium (D). Yes.

<Resin dispersant (A)>
The resin dispersant (A) is used as a dispersant for the pigment (B) in the aqueous liquid medium (D), and any resin that can disperse the pigment (B) may be used. The structure of the resin dispersant (A) preferably has a hydrophobic structural unit (a) and a hydrophilic structural unit (b). If necessary, the resin dispersant (A) can include a structural unit (c) different from the hydrophobic structural unit (a) and the hydrophilic structural unit (b).

  The composition of the hydrophilic structural unit (b) and the hydrophobic structural unit (a) depends on the degree of hydrophilicity and hydrophobicity of each, but the hydrophobic structural unit (a) is the entire resin dispersant (A). It is preferable to contain more than 80 mass% with respect to the mass of, and 85 mass% or more is more preferable. That is, the hydrophilic structural unit (b) needs to be 15% by mass or less, and when the hydrophilic structural unit (b) is more than 15% by mass, the aqueous liquid medium alone does not contribute to the dispersion of the pigment. The component dissolved in (D) increases, which deteriorates various properties such as the dispersibility of the pigment (B), and causes the discharge properties of the inkjet recording ink to deteriorate.

<Pigment (B)>
Pigment (B) is a colored substance that is almost insoluble in water and organic solvents as described on page 518 of the 3rd edition of the Chemical Dictionary, April 1, 1994 (edited by Michinori Oki et al.). In the present invention, organic pigments and inorganic pigments can be used.

  In the present invention, the “pigment (B) dispersed by the resin dispersant (A)” means a pigment dispersed and held by the resin dispersant (A), and the resin dispersed in the aqueous liquid medium (D). The pigment is preferably used as a pigment dispersed and held using the agent (A). The aqueous liquid medium (D) may or may not contain a dispersant.

  In the present invention, the pigment (B) dispersed by the resin dispersant (A) is not particularly limited as long as it is a pigment dispersed and held by the resin dispersant (A). From the viewpoint of ejection stability, a microencapsulated pigment produced by a phase inversion method is more preferable.

  A preferred example of the pigment (B) contained in the present invention is a microencapsulated pigment. The microencapsulated pigment is a pigment in which the pigment is coated with the resin dispersant (A).

  The resin of the microencapsulated pigment needs to use the resin dispersant (A), and is a polymer having self-dispersibility or solubility in water and an anionic group (acidic). It is preferable to use the compound for a resin other than the resin dispersant (A).

  The upper pigments may be used alone or in combination of two or more selected.

  The content of the pigment (B) in the aqueous ink in the present invention is preferably 1 to 10% by mass, more preferably 2 to 8% by mass, and 2 to 6% by mass from the viewpoint of dispersion stability and concentration of the aqueous ink. % Is particularly preferred.

<Ratio of pigment (B) to resin dispersant (A)>
The weight ratio of the pigment (B) and the resin dispersant (A) is preferably 100: 25 to 100: 140, and more preferably 100: 25 to 100: 50. When the resin dispersant is 100: 25 or more, the dispersion stability and the abrasion resistance tend to be improved. When the resin dispersant is 100: 140 or less, the dispersion stability tends to be improved.

<Self-dispersing polymer fine particles [resin particles] (C)>
The water-based ink contains at least one kind of self-dispersing polymer fine particles. The self-dispersing polymer fine particles in the present invention are water-insoluble which can be dispersed in an aqueous medium by a functional group (particularly an acidic group or a salt thereof) of the pr resin itself in the absence of other surfactant. It refers to fine particles of a water-insoluble polymer which is a polymer and does not contain a free emulsifier.

  Here, the dispersed state refers to both an emulsified state (emulsion) in which a water-insoluble polymer is dispersed in an aqueous medium and a dispersed state (suspension) in which a water-insoluble polymer is dispersed in an aqueous medium in a solid state. It includes the state of.

  The self-dispersing polymer fine particles of the present invention can be suitably contained in, for example, an aqueous ink composition, and can be used alone or in combination of two or more.

<Aqueous liquid medium (D)>
In the inkjet recording water-based ink, the aqueous liquid medium (D) represents a mixture of water and a water-soluble organic solvent. Water-soluble organic solvents (hereinafter also referred to as “water-soluble organic solvents”) are used for the purpose of drying inhibitors, wetting agents or penetration enhancers.

  In the ink, a water-soluble solvent is used for the purpose of an anti-drying agent, a wetting agent or a penetration accelerator. In particular, when used as an aqueous ink composition of an ink jet recording system, a water-soluble organic solvent is preferably used for the purpose of a drying inhibitor, a wetting agent, or a penetration accelerator.

  Anti-drying agents and wetting agents are used for the purpose of preventing clogging due to drying of the ink-jet ink at the nozzles, and the anti-drying agents and wetting agents are water-soluble organic compounds having a vapor pressure lower than that of water. A solvent is preferred.

  In the present invention, a water-soluble organic solvent having a low SP value is preferably used, and a water-soluble organic solvent having an SP value of 27.2 or less is preferably used in order to reduce damage to the paper fiber by the solvent in the ink. More preferably, it is more preferable to use a water-soluble organic solvent of 20.5 or less. By using an organic solvent having a low SP value, penetration into the recording medium can be suppressed, damage such as swelling and shrinkage can be reduced, and cockling can be improved.

  The aqueous liquid medium (D) preferably contains a compound represented by the following structural formula (1). Here, the “water-soluble organic solvent” and the “compound represented by the structural formula (1)” may be the same or different.

  The solubility parameter (SP value) of the water-soluble solvent referred to in the present invention is a value represented by the square root of the molecular cohesive energy. F. It can be calculated by the method described in Fedors, Polymer Engineering Science, 14, p147 (1967), and this numerical value is adopted in the present invention.

In the structural formula (1), l, m, and n are each independently an integer of 1 or more and represent 1 + m + n = 3-15. Among the above, l + m + n is preferably 3 to 12, and more preferably 3 to 10. In the structural formula (1), AO represents ethyleneoxy and / or propyleneoxy, and among them, a propyleneoxy group is preferable. Each AO of (AO) ₁ , (AO) _m , and (AO) _n may be the same or different.

  Hereinafter, examples of compounds are shown together with SP values (in parentheses).

Diethylene glycol monoethyl ether (22.4)
Diethylene glycol monobutyl ether (21.5)
Triethylene glycol monobutyl ether (21.1)
Dipropylene glycol monomethyl ether (21.3)
Dipropylene glycol (27.2)

_{· NC 4 H 9 O (AO} ) 4 -H ( in AO = EO or PO, the ratio of EO: PO = 1: 1) (20.1)
_{· NC 4 H 9 O (AO} ) 10 -H ( in AO = EO or PO, the ratio of EO: PO = 1: 1) (18.8)
HO (A′O) ₄₀ −H (A′O = EO or PO, the ratio is EO: PO = 1: 3) (18.7)
HO (A ″ O) ₅₅ −H (A ″ O = EO or PO, the ratio is EO: PO = 5: 6) (18.8)
HO (PO) ₃ -H (24.7)
・ HO (PO) _7- H (21.2)
・ 1,2-Hexanediol (27.4)
In the present invention, EO and PO represent an ethyleneoxy group and a propyleneoxy group.

  The proportion (content) of the compound of the structural formula (1) in the aqueous liquid medium is preferably 10% or more, more preferably 30% or more, and further preferably 50% or more. Even if the value is high, no problem arises.

  The water-soluble organic solvent used in the present invention may be used alone or in combination of two or more.

  The content of the water-soluble organic solvent is preferably 1% by mass or more and 60% by mass or less, more preferably 5% by mass or more and 40% by mass or less, from the viewpoint of ensuring stability and ejection reliability in the entire ink composition. 10 mass% or more and 30 mass% or less are used especially preferably.

  The amount of water used in the present invention is not particularly limited, but is preferably 10% by mass or more and 99% by mass or less from the viewpoint of ensuring stability and ejection reliability in the entire ink composition. Is 30 mass% or more and 80 mass% or less, More preferably, it is 50 mass% or more and 70 mass% or less.

<Surfactant>
It is preferable to add a surfactant to the water-based ink. As the surfactant, a compound having a structure having both a hydrophilic part and a hydrophobic part in the molecule can be used effectively. Anionic surfactant, cationic surfactant, amphoteric surfactant, nonionic surfactant Any of the surfactants can be used. Furthermore, the above-mentioned polymer substance (polymer dispersing agent) can also be used as a surfactant.

<Other ingredients>
The water-based ink used in the present invention may contain other additives. Other additives include, for example, ultraviolet absorbers, anti-fading agents, anti-mold agents, pH adjusters, rust inhibitors, antioxidants, emulsion stabilizers, preservatives, antifoaming agents, viscosity modifiers, and dispersion stabilizers. Known additives such as agents and chelating agents are included.

[Treatment solution]
The aqueous treatment liquid contains at least one fixing agent that fixes components in the aqueous ink. The immobilizing agent can immobilize (aggregate) ink by contacting with ink on paper. For example, when the treatment liquid is applied and ink is deposited and brought into contact with the fixing agent on the paper, the components in the ink can be aggregated and fixed on the paper.

  Since it is desirable that the fixing agent can fix (aggregate) the water-based ink, it is preferable that the fixing agent is a material that easily dissolves in the water-based ink when it comes into contact with the water-based ink. A valent metal salt is more preferable, and an acidic substance having high water solubility is more preferable. Further, from the viewpoint of fixing the entire ink by reacting with the aqueous ink, an acidic substance having a valence of 2 or more is particularly preferable. Cationic compounds can also be used.

  Here, the aggregation reaction of the water-based ink can be achieved by reducing the dispersion stability of particles dispersed in the water-based ink (colorant (for example, pigment), resin particles, etc.) and increasing the viscosity of the entire ink. it can. For example, by reducing the surface charge of particles such as pigments and resin particles in inks that are stabilized by weakly acidic functional groups such as carboxyl groups by reacting with acidic substances with lower pKa, the dispersion stability is lowered. can do. Therefore, it is preferable that the acidic substance as a fixing agent contained in the treatment liquid has a low pKa, high solubility, and a valence of 2 or more, and a functional group that stabilizes the dispersion of particles in the ink ( For example, a divalent or trivalent acidic substance having a high buffering capacity in a pH range lower than the pKa of the carboxyl group) is more preferable.

  The content of the fixing agent for fixing the aqueous ink in the aqueous treatment liquid is preferably 1 to 40% by mass, more preferably 5 to 30% by mass, and still more preferably 10 to 25% by mass. is there.

  The aqueous treatment liquid in the present invention can generally contain a water-soluble organic solvent in addition to the fixing agent, and can be constituted by using various other additives in the same manner as the water-based ink. An organic solvent may be used independently and may use 2 or more types together. Moreover, it is preferable that 1-50 mass% of organic solvents are contained in a process liquid.

  Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited thereto.

<Adjustment of treatment liquid>
Each component was mixed so that it might become the following composition, and the process liquid was adjusted.
-Malonic acid: 10% by mass
・ Diethylene glycol monoethyl ether: 20% by mass
・ Orphine E1010 (manufactured by Nissin Chemical Industry): 1% by mass
・ Ion-exchanged water: remaining <Ink adjustment>
Each component was mixed so as to have the following composition to prepare an ink.
Pigment 1: 4% by mass
-Dispersant polymer 1: 2% by mass
・ Resin emulsion: 8% by mass
・ Water-soluble organic solvent: 15% by mass
・ Orphine E1010 (manufactured by Nissin Chemical Industry): 1% by mass
-Ion-exchanged water: remainder The above components are as follows.

Pigment 1: Chromophthal Jet Magenta DMQ (PR-122) manufactured by Ciba Specialty Chemicals
Dispersant polymer 1: benzyl methacrylate / methyl methacrylate / methacrylic acid = 60/30/10 (mass ratio)
Resin emulsion: methyl methacrylate / phenoxyethyl acrylate / acrylic acid = 66/29/5 (mass ratio) glass transition temperature = 65 ° C.
Further, as the water-soluble organic solvents, solvents having different SP values shown in the following table are used. : Used as inks 1-7.

<Recording medium>
The recording medium is shown in Table 2 below.

(Paper expansion / contraction measurement method)
The expansion / contraction rate of each paper shown in Table 2 was measured by the following method.
1. The paper is cut into a size of 15 m × 4 cm. The cutting is performed so that the paper grain (the direction of the paper fiber) is along the short direction (the direction in which the paper is easily expanded and contracted is the longitudinal direction).
2. As shown in FIG. 5, black circles having a diameter of about 2 mm are entered with oil-based magic as stretch length measurement markers at the positions of both ends of the paper.
3. Humidity is adjusted for one day in an environment with a temperature of 23 ° C. and a humidity of 50%.
4). The distance between two markers is measured using a length measuring microscope system (measured value is X1). The paper is sandwiched between two transparent glass plates (larger than the paper size) and placed on the stage of the measuring microscope. As the length measuring microscope system, NEXIV VMR (manufactured by Nikon Corporation) equipped with an imaging and image recognition system and an XY stage system is used.
5). Using a paper transport stage and an inkjet head, pure water is applied to the entire surface of the paper at a coating amount of 1 g / m ² . Here, for the pure water application, an application roller or the like may be used.
6). Immediately after applying pure water, the paper is sandwiched and held between two glass plates. (To prevent moisture evaporation)
7). The paper sandwiched between the glass plates is placed on the stage of the measuring microscope, and the distance between the markers is measured (measured value is X2).
8). The sheet expansion / contraction rate is calculated by (X2-X1) / X1.

<Image forming method>
An image was formed using the ink jet recording apparatus shown in FIG. The conditions of the apparatus are as shown below.
-Paper feeding speed: 500 mm / s
Treatment liquid application: Uniform application on the image surface at an application amount of 1.5 g / m ^{2 with} a coating roller. Treatment liquid drying: Drying for 1 second with a back heater at 40 ° C. and warm air at 70 ° C. : Drawing a predetermined image at a resolution of 1200 dpi and a discharge volume of 4.5 pL and ink drying: heating the back surface of the recording medium at a predetermined pressure drum temperature shown in Table 3 and blowing warm air at a predetermined temperature to generate a pressure drum 126c Ink drying: ink fixing: roller temperature; 70 ° C., roller nip pressure; 0.30 MPa, nip passing time; heat roller at 20 ms (with a predetermined rubber hardness and thickness on a hollow aluminum roller having a diameter of 40 mm) Fixing with silicon rubber)

<Evaluation>
Evaluation of fixing wrinkles was performed by the following method.

  Printing was performed under predetermined printing conditions using A3 size paper. The printed sample was visually observed to evaluate the degree of wrinkles according to the following criteria.

◎ ・ ・ ・ No wrinkles are seen ○ ・ ・ ・ Wrinkles are slightly visible when the sample is observed carefully, but they are almost unnoticeable △ ・ ・ ・ Slight wrinkles are generated, but practically acceptable × ・ ・ ・ Wrinkle is strongly generated and is not allowed. The moisture content contained in the printing paper is obtained by punching out the measurement portion of the paper in a size of 3 cm × 3 cm, and a trace moisture measurement system CA-200 (Co., Ltd.). (Mitsubishi Chemical Analytech). The measured moisture content [g] was divided by the punched area to calculate the moisture content [g / m ² ] per unit area. Further, the residual water amount was a value obtained by subtracting the water amount retained by the paper before printing from the water amount remaining after the ink was deposited and dried. The amount of water retained by the paper was separately measured using unused paper.

<Result>
Residual water amount (Test Example 1), recording medium (Test Example 2), presence or absence of treatment liquid (Test Example 3), time from drawing to fixing (Test Example 4), relative humidity of dry air (Test Example 5), water solubility Each of the SP values (Test Example 6) of the hydrophilic organic solvent was changed to evaluate the fixing wrinkles. The results are shown in FIGS.

With respect to Test Example 1 in which the remaining water amount was changed, an image in which fixing wrinkles of the recording medium are suppressed can be formed by setting the difference in the remaining water amount between the image portion and the non-image portion to 3.0 g / m ² or less. did it. Moreover, fixing wrinkles could be suppressed as the difference in residual water amount became smaller. This is because cockling can be suppressed by reducing the amount of residual water between the image area and the non-image area, so that the recording medium at the time of fixing can be a flat recording medium with few convex portions. Therefore, an image can be formed without being crushed by the heat roller and generating wrinkles. On the contrary, cockling occurred in Comparative Examples 1 and ^{2 in} which the difference in the residual water amount exceeded 3.0 g / m ² , and fixing wrinkles could not be suppressed.

In Test Example 2 in which the recording medium was changed, Examples 1 and 6 to 10 using the recording medium having a stretching ratio of 0.10% when water of 1 g / m ² was applied suppressed fixing wrinkles. However, Comparative Examples 3 to 6 using recording media exceeding 0.10% could not be suppressed.

Similarly to Test Example 1 in which the treatment liquid was applied, similarly to Test Example 1 in which the treatment liquid was not applied, in Examples 11 to 15 in which the residual water amount was 3.0 g / m ² or less, fixing wrinkles could be suppressed. In Comparative Examples 7 and 8 exceeding 3.0 g / m ² , it was not suppressed.

  For Test Example 4 in which the time from the drawing process to the fixing process was changed, the shorter the time, the drying can be performed before the solvent in the ink penetrates the recording medium. There was a tendency to reduce fixing wrinkles. In Test Example 4, adjustment was performed by changing the temperature of the impression cylinder so that the difference in the residual water amount after the drying step became equal.

In Test Example 5 in which the relative humidity of the drying air is changed, Comparative Examples 9 and 10 having a low relative humidity at 23 ° C. of the drying air cause the drying of the non-image portion to proceed simultaneously with the drying of the image portion. The difference in the amount of water could not be reduced and exceeded 3.0 g / m ² . On the other hand, in Comparative Example 11 where the relative humidity is as high as 95% RH, the difference in the residual water amount cannot be reduced because the drying of the image portion does not proceed, and the residual water amount exceeds 3.0 g / m ² . Fixing wrinkles occurred.

  In Test Example 6 in which the SP value of the water-soluble organic solvent was changed, fixing wrinkles could be suppressed in Examples 11 and 27 to 32 using any water-soluble organic solvent, but a solvent having a low SP value was used. By using it, fixing wrinkles could be further suppressed.

  DESCRIPTION OF SYMBOLS 100 ... Inkjet recording apparatus, 102 ... Paper feed part, 106 ... Processing liquid provision part, 108 ... Drawing part, 110 ... Fixing part, 112 ... Paper discharge part, 114 ... Recording medium, 124a-124c ... Transfer cylinder, 126a-126c ... Impression cylinder, 134 ... Paper preheating unit, 136 ... Processing liquid head, 138 ... Processing liquid drying unit, 140C, 140M, 140Y, 140K, 140R, 140G, 140B ... Ink head, 142a, 142b ... Solvent drying unit, 144 ... Image reading unit, 148a, 148b ... heating roller, 150 ... discharge cylinder, 152 ... discharge magazine, 154 ... conveyor

Claims (10)

A drawing step of forming an image on a recording medium using water-based ink;
A drying step of drying the water-based ink on the recording medium;
A fixing step of pressing and fixing the image formed on the recording medium,
The recording medium has a dimensional change with respect to a moisture content of 1 g / m ² of 0.1% or less,
An image forming method, wherein drying is performed so that a difference in water content between an image portion and a non-image portion of the recording medium immediately before the fixing step is 3.0 g / m ² or less.   The image forming method according to claim 1, wherein the drawing step is a single-pass ink jet droplet using a line head having a width of the recording medium. The amount of the water-based ink applied to the recording medium is such that the amount of water per unit area of the recording medium is 7.0 g / m ² or more. Image forming method.   4. The method according to claim 1, further comprising a treatment liquid application step of applying a treatment liquid containing a component that reacts with the pigment and the resin particles in the water-based ink onto the recording medium before the drawing step. The image forming method according to claim 1.   5. The image forming method according to claim 1, wherein the time from the drawing process to the start of the fixing process is within 8 seconds.   6. The drying process according to claim 1, wherein the drying step is performed by supplying a drying air to the recording medium, and the drying air has a relative humidity at 23 ° C. of 40% RH or more. The image forming method described.   The image forming method according to claim 6, wherein the dry air has a relative humidity at 23 ° C. of 90% RH or less.   The image forming method according to claim 6, wherein the temperature of the drying air is 50 ° C. or higher.   The image forming method according to claim 1, wherein the water-based ink contains a water-soluble organic solvent having an SP value of 27.2 or less. Drawing means for forming an image on a recording medium using water-based ink;
Drying means for drying the water-based ink on the recording medium;
Fixing means that presses and fixes an image formed on the recording medium, and the recording medium has a dimensional change of 0.1% or less with respect to a moisture amount of 1 g / m ² ;
An image forming apparatus comprising: a control unit that controls the drying unit so that a difference in water content between the image portion and the non-image portion of the recording medium at the time of the fixing unit is 3.0 g / m ² or less. .

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