INKJET RECORDING METHOD AND INKJET RECORDING DEVICE

Abstract

 The present invention addresses the problem of providing an inkjet recording method and an inkjet recording device which can form an image with good glossiness and little ink bleeding. This inkjet recording method forms an image by applying an ink that includes a coloring material and a processing liquid that includes a coagulant, onto a recording medium surface with a liquid droplet ejection means, the method being characterized in that, in a region where the application amount of the ink is equal to or greater than a reference value, the application amount of the processing liquid is controlled so that the application amount of the processing liquid decreases in a region as the application amount of the ink is high, and, in an image contour peripheral region, the application amount of the processing liquid is controlled so as to increase the application amount of the processing liquid.

Description

Technical Field

[0001] The present invention relates to an inkjet recording method and an inkjet recording device. More specifically, the present invention relates to an inkjet recording method capable of forming an image with good glossiness and less ink bleeding.

Background Art

[0002] In the inkjet recording method, it is known that the image quality deteriorates due to liquid gathering phenomenon of the ink in which the ink droplets coalesce on the recording medium, and color bleeding in which bleeding occurs between different colors. As a solution to these problems, a two-liquid inkjet recording method has been disclosed in which a processing liquid for aggregating the coloring material in the ink is applied separately from the ink from the inkjet head (it may be simply called as a "head"), and the ink is well fixed on the recording medium (see, for example, Patent Document 1).

[0003] However, in the two-liquid type inkjet recording method, while it is possible to prevent ink bleeding, if the amount of the processing liquid applied is not appropriately controlled, the ink will aggregate excessively, resulting in producing a problem of poor image glossiness.

[0004] As a method for controlling the application amount of the processing liquid, there has been disclosed means for varying the amount of the processing liquid to be applied that is ejected from a head according to the amount of the ink applied (see, for example, Patent Documents 2 and 3). These techniques are mainly aimed at suppressing curling and cockling of paper, which is a recording medium, and are not sufficient as a means to achieve both prevention of ink bleeding and maintenance of image glossiness.

Citation Lists

Patent Literatures

[0005] 

Patent Document 1: JP-A 8-52867

Patent Document 2: JP-A 2002-321349

Patent Document 3: Japanese Patent No. 4742637

Summary of Invention

Technical Problem

[0006] The present invention has been made in view of the above problems and circumstances, and an object thereof is to provide an inkjet recording method and an inkjet recording device capable of forming an image with good glossiness and less ink bleeding.

Solution of Problem

[0007] In order to solve the above problems, the present inventors investigated the causes of the above problems, and found that, in a high-density region, the processing liquid is applied so that the amount of the processing liquid applied decreases as the amount of the ink applied to the unit region increases. By controlling the amount and controlling the application amount of the processing liquid so that the application amount of the processing liquid is added in the peripheral region of the image contour, an image with good glossiness and less ink bleeding is formed. The inventors have found that it is possible to provide an inkjet recording method that can achieve the present invention. That is, the above problems related to the present invention are solved by the following means.

1. An inkjet recording method for forming an image comprising a step of applying an ink containing a coloring material and a processing liquid containing an aggregating agent onto a surface of a recording medium with a liquid droplet ejection means,

wherein in a region where an application amount of the ink is equal to or greater than a reference value, an application amount of the processing liquid is controlled so that the application amount of the processing liquid decreases as the amount of application of the ink is high in the unit region; and

in an image contour peripheral region, the application amount of the processing liquid is controlled so as to increase the application amount of the processing liquid.

2. The inkjet recording method according to item 1, wherein the reference value is a value that is 50% of a maximum value of the application amount of the ink.

3. The inkjet recording method according to item 1 or 2, wherein in the region where the application amount of the ink is equal to or less than the reference value among the regions to which the ink is applied, the application amount of the processing liquid is controlled so that the application amount of the processing liquid increases as the amount of application of the ink is high in the unit region.

4. The inkjet recording method according to any one of items 1 to 3, wherein the inkjet recording method is a multi-pass method.

5. The inkjet recording method according to any one of items 1 to 4, wherein the recording medium is an absorptive recording medium; and when the reference value is A and the application amount of the processing liquid in the region where the application amount of the ink is the reference value is B, the application amount of the processing liquid is controlled so that a value of a ratio B/A is in the range of 0.14 to 0.50.

6. The inkjet recording method according to any one of items 1 to 4, wherein the recording medium is a non-absorptive recording medium; when the reference value is A, and the application amount of the processing liquid in the region where the application amount of the ink is the reference value is B, the application amount of the processing liquid is controlled so that a value of a ratio B/A is in the range of 0.14 to 0.30.

7. The inkjet recording method according to any one of items 1 to 6, when a maximum value of the application amount of the ink is C, and the application amount of the processing liquid in the region where the applied amount of the ink is a maximum value is D, the application amount of the processing liquid is controlled so that a value of a ratio D/C is in the range of 0.01 to 0.1.

8. The inkjet recording method according to any one of items 1 to 7, when a plurality of types of ink are applied, the application amount of the processing liquid to be changed according to the application amount of the ink for each unit region is determined for each type of ink.

9. An inkjet recording device for forming an image by applying an ink containing a coloring material and a processing liquid containing an aggregating agent onto a surface of a recording medium with a liquid droplet ejection means,

wherein in a region where an application amount of the ink is equal to or greater than a reference value, an application amount of the processing liquid is controlled so that the application amount of the processing liquid decreases as the amount of application of the ink is high in the unit region; and

in an image contour peripheral region, the application amount of the processing liquid is controlled so as to increase the application amount of the processing liquid.

Advantageous Effects of Invention

[0008] According to the above means of the present invention, it is possible to provide an inkjet recording method and an inkjet recording device capable of forming an image with good glossiness and less ink bleeding.

[0009] Although the expression mechanism or action mechanism of the effects of the present invention has not been clarified, it is speculated as follows.

[0010] The present invention is characterized by controlling the amount of processing liquid applied in the regions in which the amount of applied ink is equal to or greater than a reference value (high-density regions), so that the application amount of the processing liquid decreases as the amount of application of the ink is high in the unit region. This prevents the ink from aggregating too much, and maintains the glossiness of the image. However, simply reducing the amount of the processing liquid applied to regions where a large amount of ink is applied will reduce the effect of preventing bleeding. In the present invention, in addition to simply reducing the application amount of the processing liquid in the region where the application amount of ink is large, the ink bleeding is effectively prevented by controlling the amount of the processing liquid applied so that the amount of the processing liquid applied is increased in the peripheral region of the boundary (also referred to as "image contour") where the difference in image density is large. As a result, it is possible to prevent the ink from aggregating too much and to compensate for the effect of preventing bleeding.

[0011] It is considered possible to provide an inkjet recording method capable of forming an image with good glossiness and less ink bleeding due to these expression mechanisms or action mechanisms.

Brief Description of Drawings

[0012] 

[FIG. 1] This is a diagram schematically showing an example of a main part of a two-liquid type inkjet recording device to which the present invention can be applied;

[FIG. 2] This is a diagram schematically showing how the device shown in FIG. 1 applies an ink and a processing liquid from liquid droplet ejection means onto the surface of a recording medium;

[FIG. 3] This is a graph showing an example of the relationship between the amount of the ink applied and the amount of the processing liquid applied in a high-density region.

[FIG. 4] This is a graph 1 showing an example of the relationship between the amount of the ink applied and the amount of the processing liquid applied in a low-density region;

[FIG. 5] This is a graph 2 showing an example of the relationship between the amount of the ink applied and the amount of the processing liquid applied in a low-density region;

[FIG. 6] This is a graph 3 showing an example of the relationship between the amount of the ink applied and the amount of the processing liquid applied in a low-density region;

[FIG. 7] This is a diagram schematically showing the region around the image contour;

[FIG. 8] This is a graph showing the relationship between the amount of the ink applied and the amount of the processing liquid applied when the processing liquid application amount control type in the example is Type 1;

[FIG.9] This is a graph showing the relationship between the amount of the ink applied and the amount of the processing liquid applied when the processing liquid application amount control type in the example is Type 2;

[FIG. 10] This is a graph showing the relationship between the ink application amount and the processing liquid application amount when the processing liquid application amount control type in the example is Type 3;

[FIG. 11] This is a graph showing the relationship between the ink application amount and the processing liquid application amount when the processing liquid application amount control type in the example is Type 4;

[FIG. 12] This is a Document image data 1 in an Example;

[FIG. 13] This is a Document image data 2 in an Example; and

[FIG. 14] This is a Document image data 3 in an Example.

Description of the Embodiments

[0013] The inkjet recording method of the present invention (hereinafter also simply referred to as "recording method") comprises a step of applying an ink containing a coloring material and a processing liquid containing an aggregating agent onto the surface of a recording medium by a liquid droplet ejection means. In the inkjet recording method for forming an image, in regions where the amount of applied ink is equal to or greater than a reference value, the application amount of the processing liquid is controlled so that the application amount of the processing liquid decreases as the amount of application of the ink is high in the unit region, and the application amount of the processing liquid is controlled so that the application amount of the processing liquid is increased in the image contour peripheral region. This feature is a technical feature common to or corresponding to the following embodiments.

[0014] As an embodiment of the recording method of the present invention, the reference value is preferably a value that is 50% of the maximum value of the applied amount of the ink. It is preferable from the viewpoint of balance between the range in which the amount of the treatment liquid to be applied is controlled as the high-density region and the range in which the amount of the treatment liquid to be applied is controlled as the low-density region.

[0015] As an embodiment of the recording method of the present invention, in the region to which the ink application amount is equal to or less than the reference value among the regions to which the ink is applied, from the viewpoint of preventing ink bleeding in low-density regions, it is preferable to control the application amount of the processing liquid so that the application amount of the processing liquid increases as the application amount of the ink is high in the unit region.

[0016] A preferred embodiment of the recording method of the present invention is a multi-pass method. By using the multi-pass method in combination with the method of controlling the amount of the processing liquid according to the present invention, it is possible to form a high-definition image in addition to good glossiness and less ink bleeding.

[0017] As an embodiment of the recording method of the present invention, when the recording medium is an absorptive recording medium, the reference value is A, and when the application amount of the processing liquid in the region where the application amount of the ink is the reference value is B, the processing liquid is controlled so that the value of the ratio B/A is in the range of 0.14 to 0.50. It is preferable in that the image quality in the solid region of the primary color is improved.

[0018] As an embodiment of the recording method of the present invention, when the recording medium is a non-absorptive recording medium, the reference value is A, and when the application amount of the processing liquid in a region where the application amount of the ink is the reference value is B, the application amount of the processing liquid is controlled so that the value of the ratio B/A is in the range of 0.14 to 0.30. It is preferable in that the image quality in the solid region of the primary color is improved.

[0019] As an embodiment of the recording method of the present invention, when the maximum value of the applied ink amount is C and the applied amount of the processing liquid in the region where the applied amount of ink is the maximum value is D, from the viewpoint of exhibiting the effect of the present invention, it is preferable to control the amount of the processing liquid to be applied so that the value of the ratio D/C is in the range of 0.01 to 0.1. When the value of the ratio D/C is 0.01 or more, the ink may be minimally aggregated, and when the value of the ratio D/C is 0.1 or less, gloss reduction due to excessive aggregation is prevented.

[0020] As an embodiment of the recording method of the present invention, when applying a plurality of types of ink, the application amount of the processing liquid to be changed according to the application amount of the ink for each unit region is determined for each type of ink. It is preferable in that the application amount of the processing liquid may be adjusted according to the easiness of aggregation of various inks.

[0021] The inkjet recording device of the present invention (hereinafter also simply referred to as "recording device") applies an ink containing a coloring material and a processing liquid containing an aggregating agent onto the surface of a recording medium by means of a liquid droplet ejection means to form an image. In the region where the application amount of the ink is equal to or greater than the reference value, the application amount of the processing liquid is controlled so that the application amount of the processing liquid decreases as the amount of application of the ink is high in the unit region. Further, the application amount of the processing liquid is controlled so as to increase the application amount of the processing liquid in the image contour peripheral region.

[0022] Hereinafter, the present invention, its components, and the forms and modes for carrying out the present invention will be described. In the present application, "to" is used to mean that the numerical values before and after "to" are included as the lower limit and the upper limit.

(1) Outline of the inkjet recording method of the present invention

[0023] The inkjet recording method of the present invention is an inkjet recording method in which an image is formed by applying an ink containing a coloring material and a processing liquid containing an aggregating agent onto the surface of a recording medium by means of a liquid droplet ejection means. In the region where the amount of the ink applied is equal to or greater than the reference value, the application amount of the processing liquid is controlled so that the application amount of the processing liquid decreases as the application amount of the ink is high in the unit region, and further, the application amount of the processing liquid is controlled so as to increase the application amount of the processing liquid in the image contour peripheral region.

[0024] In the recording method of the present invention, first, the amount of ink to be applied is determined for each unit region. The application amount of the processing liquid is determined so as to change the application amount of the processing liquid for each unit region according to the application amount of the ink. In addition to this, the application amount of the processing liquid to be added to the image contour peripheral region is determined.

[0025] "In a region where the amount of the applied ink is equal to or greater than a reference value, controlling the amount of the processing liquid applied so that the amount of the applied processing liquid is reduced so that the application amount of the processing liquid decreases as the amount of application of the ink is high in the unit area" means that in a high-density region, it defines how the amount of the processing liquid to be applied is changed according to the amount of the ink to be applied.

[0026] The "applied amount" refers to the amount to be applied to a certain unit region, and is the total amount of liquid droplets for each dot in the unit region. The unit of application amount may be expressed in g/m².

[0027] The "reference value" refers to the amount of the applied ink that serves as a reference for dividing the region to which the ink is applied into a high-density region and a low-density region. In the present invention, a region in which the amount of the ink applied is equal to or greater than the reference value is referred to as a "high-density region," and a region to which the ink is applied in an amount equal to or less than the reference value is referred to as a "low-density region." A region where the amount of the applied ink is the reference value is called a "reference value region", and the reference value region is included as part of both the high-density region and the low-density region for the sake of convenience.

[0028] The reference value may be arbitrarily set according to the image to be formed. In the present invention, the application amount of the processing liquid is controlled in each of the high-density region and the low-density region divided by an arbitrarily set reference value.

[0029] The "image contour peripheral region" refers to a region that exists with a certain width on both sides of the image contour as a starting point. The distances from the image contour, which is the starting point, to both ends in the width direction of the image contour peripheral region are substantially the same.

[0030] The "image contour" refers to a boundary with large difference in image density. Image contours may be detected using commercially available image processing software and various methods (Sobel method, Laplacian of Gaussian method, and Canny method). Note that the outer periphery of the region to which the ink is applied, and the image contour do not necessarily match.

(2) Example of recording method and recording device

[0031] The inkjet recording method of the present invention is a so-called two-liquid recording method in which an image is formed by applying an ink and a processing liquid onto the surface of a recording medium by a liquid droplet ejection means.

[0032] FIG. 1 schematically shows an example of a main part of a two-liquid type inkjet recording device to which the present invention may be applied. FIG. 2 schematically shows an example of how the device shown in FIG. 1 applies the ink and the processing liquid from the liquid droplet ejection means onto the surface of the recording medium.

[0033] In the following, the recording method and recording device of the present invention will be described with reference to FIG. 1 and FIG. 2 using a multi-pass method (also referred to as a "scan method") as an example. However, the recording method and recording device of the present invention are not limited to this. It is also applicable to a single-pass method (also referred to as a "line method"), which will be described later.

[0034] In the recording method using the recording device shown in FIG. 1, as shown in FIG. 2, the liquid droplet ejection means 20 ejects each color ink In (yellow ink Y, magenta ink M, cyan ink C, black ink K) and the processing liquid Pr onto the recording medium Me in the scanning direction X (hereinafter, an image is formed by moving in the "X direction".) In the recording device shown in FIG. 1, the recording medium Me is transported by transport means (not shown) in a direction Y perpendicular to the scanning direction X (hereinafter also referred to as "transport direction Y" or "Y direction"). An image may be formed on substantially the entire surface (image forming surface) of the recording medium Me by being sequentially conveyed.

[0035] The liquid droplet ejection means 20 includes a processing liquid head 1Pr, a yellow ink head 1Y, a magenta ink head 1M, a cyan ink head 1C, and a black ink head 1K (hereinafter collectively referred to as "head unit 1"). and a carriage 22 for arranging and holding the head unit 1 along the scanning direction X.

[0036] A surface (nozzle surface) of each head facing the surface of the recording medium Me is provided with a plurality of nozzles 21 arranged along a transport direction Y perpendicular to the scanning direction X. A fine liquid droplet is ejected from these nozzles 21 by appropriately applying pressure to the nozzles 21. The liquid droplet ejecting means 20 is supported such that the nozzle surface of the head unit 1 is separated from the surface of the recording medium Me by a predetermined distance in a direction perpendicular to the surface (height direction).

[0037] The liquid droplet ejection means 20 is scanned in the scanning direction X by the scanning unit 30. The scanning unit 30 has, for example, a rail that supports the carriage 22 in a state in which the nozzle surface is separated from the surface of the recording medium Me by the above-mentioned predetermined distance in the height direction so as to make the carriage 22 movable.

[0038] The entire print region P shown in FIG. 1 is a range in which an image may be formed on the recording medium Me by scanning the liquid droplet ejection means 20 in the X direction and conveying the recording medium Me in the Y direction. Let the length of the entire print region P in the X direction be the print region width PW, and let the length in the Y direction be the print region length PL.

[0039] When the liquid droplet ejection means 20 moves once in the scanning direction X, the ink In and the processing liquid Pr are applied in a region having a width W in a direction Y perpendicular to the scanning direction X of the head unit 1 with respect to the printing region width PW of the entire printing region P. In the multi-pass recording method as shown in FIG. 1, the operation of applying the ink In and the processing liquid Pr to the recording medium Me by moving the liquid droplet ejection means 20 once in the scanning direction X is performed in one printing pass, and a plurality of printing passes are performed on the same region to finally form a desired image on the recording medium Me.

[0040] Here, in the recording device, the control unit determines whether or not the ink In is applied and the amount of application of the ink In for each unit region according to the image data of the document. Further, the presence or absence of the application amount of the processing liquid Pr and the application amount thereof are determined for each unit region according to this, and the liquid droplet ejection means applies the ink In and the processing liquid Pr to the surface of the recording medium Me based on this determination. An image is formed, thereby forming an image.

[0041] Whether or not the ink In is to be applied to each unit region and the amount of the ink to be applied is determined by a known method according to the image data of the document. For example, in the case of an image of a document on a personal computer, the arrangement of pixels to which the ink In is applied in the entire print region P, and the amount of application are determined based on the image data that has undergone halftone processing.

[0042] The presence or absence of the application amount of the processing liquid Pr for each unit region and the determination of the application amount are performed according to the control method of the present invention, for example, by a program introduced into the control unit.

[0043] Although image formation on the recording medium Me may be completed in one printing pass, in the case of forming an image with a high resolution (dpi), the image may be decomposed, and a plurality of printing passes may be performed to form an image on the recording medium Me.

[0044] The number of printing passes is determined by a program preset in the control unit corresponding to the document image. Depending on the document image, the number of printing passes is approximately 2 to 4 times.

[0045] The size of the unit region in which the image is formed (hereinafter also referred to as "unit region U") is appropriately selected within the range in which the effects of the present invention may be exhibited. Specifically, the unit region U may be one pixel. It is preferable that the unit region U has four or more pixels as one unit because the effects of the present invention are easily realized. Further, the unit region U is 4 pixels composed of 2 pixels vertically by 2 pixels horizontally, 16 pixels composed of 4 pixels vertically x 4 pixels horizontally, and 36 pixels composed of 6 pixels vertically x 6 pixels horizontally is more preferable.

[0046] In FIG. 1, the region to which the ink In and the processing liquid Pr are applied by one movement of the liquid droplet ejection means 20 is a region obtained by multiplying the printing region width PW in the scanning direction X by the width W of the head unit 1 in the direction Y perpendicular to the scanning direction X (hereinafter also referred to as "the width W of the head unit 1").

[0047] The total print region P is a collection of the print regions A. The number of print regions A constituting the total print region P is indicated by a value obtained by dividing the print region length PL by the width W of the head unit 1. For example, in the case of the recording medium Me shown in FIG. 1, the total printing region P has six print regions A, and the print regions A1, A1, A2, A3, A4, A5, and A6 are arranged in order to form the entire print region P.

[0048] In FIG. 1, in the entire print region P, images are already formed in the print regions A1, A2 and A3. An image is being formed by the liquid droplet ejection means 20 in the print region A4, and images are sequentially formed in the print regions A5 and A6 after the image formation in the print region A4 is completed. In FIG. 1, Im indicates an ink application region.

[0049] The recording method of the present invention uses, for example, the recording device shown in FIG. 1. In this recording method, an image is formed by applying the ink In and the processing liquid Pr to the surface of the recording medium Me by means of the liquid droplet ejection means 20 and allowing them to coalesce as described above. FIG. 1 and FIG. 2 show a mode in which the processing liquid Pr is applied onto the surface of the recording medium Me before the ink In is applied, but in the recording method of the present invention, the processing liquid Pr may be applied after the ink In. For example, the processing liquid Pr may be applied after applying the ink In by arranging the processing liquid head 1Pr after the ink heads 1Y, 1M, 1C, and 1K.

[0050] The method of each head is not particularly limited, and may be either an on-demand method or a continuous method. Examples of on-demand heads include electro-mechanical conversion types including singlecavity, double-cavity, bender, piston, shear-mode, and shared-wall, as well as electric-heat conversion types including thermal inkjet and bubble-jet ("Bubble Jet" is a trademark of Canon Inc.)

[0051] Among the heads described above, a head using a piezoelectric element as an electro-mechanical conversion element used in an electro-mechanical conversion system (also referred to as a "piezo type inkjet head") is preferable.

[0052] The amounts of the ink In and the processing liquid Pr to be applied may be appropriately adjusted by adjusting the liquid amount per liquid droplet ejected from the nozzles 21 in each head, and it is also easy to make the two amounts different. The ejection mechanism of the ink In or the processing liquid Pr in the head will be described later in the recording device. The amount of the ink In and the processing liquid Pr ejected from the nozzle 21 per liquid droplet (drop amount per dot) may be adjusted within a range of approximately 2 to 40 pL.

[0053] Also, the landing time of the ink In ejected from the nozzles 21 in the head is preferably 1.0 seconds or less, more preferably 0.6 seconds or less. Similarly, the landing time of the processing liquid Pr discharged from the nozzle 21 is preferably 1.0 seconds or less, more preferably 0.6 seconds or less. Note that the landing time of the ink In and the processing liquid Pr corresponds to the time from when the ink In and the processing liquid Pr are ejected from the nozzles 21 to when they are united on the recording medium Me. That is, the time from when the ink In and the processing liquid Pr are discharged to when they are combined is preferably 1.0 seconds or less, and more preferably 0.6 seconds or less. Further, the moving speed of the liquid droplet ejection means 20 having the head unit 1 is preferably 300 to 800 mm/sec.

[0054] So far, the recording method and recording device of the present invention have been described using the multi-pass method as an example with reference to FIG. 1 and FIG. 2. As described above, the recording method and recording device of the present invention may also be applied to the single-pass method.

[0055] In the case of the single-pass method, the liquid droplet ejection means 20 has a length equal to or greater than the print region width PW of the entire print region P with respect to the recording medium Me, and the processing liquid head 1Pr and the ink heads 1Y, 1M, 1C, 1K are arranged in order along the transport direction Y so as to be parallel to the print region width PW. The processing liquid head 1Pr may be arranged before or after the ink heads 1Y, 1M, 1C, and 1K.

[0056] In the single-pass liquid droplet ejection means, one head unit 1 having a print region width PW or more may be used, or a plurality of head units 1 may be combined so as to have a print region width PW or more.

[0057] In addition, a plurality of head units 1 may be arranged side by side so that the nozzles 21 of each head are staggered, and the resolution of the liquid droplet ejection means may be increased for these heads as a whole. Further, a plurality of such liquid droplet ejection means may be arranged in parallel along the transport direction Y of the recording medium.

(3) Control of application amount of processing liquid in high-density region

[0058] In the present invention, the "high-density region" refers to a region where the amount of the ink applied is equal to or greater than the reference value. As described above, the "reference value region", which refers to the region where the amount of the applied ink is the reference value, is included as part of both the high-density region and the low-density region for the sake of convenience.

[0059] The recording method of the present invention is characterized by controlling the amount of the processing liquid applied in a high-density region so that the amount of the processing liquid applied decreases as the amount of the applied ink is high in a unit region. This prevents the ink from aggregating too much, and maintains the glossiness of the image.

[0060] In addition, when the amount of both the ink and the processing liquid applied is large, the coffee ring phenomenon causes unevenness in which the density of the coloring material is partially high at the edges of the coffee ring. If the application amount of the processing liquid is controlled so that the application amount of the processing liquid decreases as the amount of application of the ink increases in the unit region, the coffee ring phenomenon is less likely to occur, and the occurrence of unevenness may be suppressed.

[0061] For example, if the maximum amount of the ink applied is 100%, and the reference value is set to a value that is 50% of the maximum amount of the ink applied, a region within a range of 50% to 100% of the maximum applied amount of the ink is regarded as a high-density region, and in the high-density region, the greater the amount of the applied ink, the smaller the applied amount of the processing liquid. Thus, the application amount of the processing liquid is controlled.

[0062] Here, the "maximum value of the ink applied" refers to the amount of the ink applied to a unit region in which the amount of the ink applied is the largest in the image to be formed. For example, when using the subtractive color mixing method in which two types of the inks from yellow ink, magenta ink, and cyan ink are dropped at the same place to form secondary color dots of red, green, and blue, the amount of the applied ink in the region where the density gradation is maximum among the regions having only the secondary color (also referred to as "solid secondary color region") is the "maximum value of applied amount of ink".

[0063] The smaller the reference value is set, the wider the range for controlling the amount of the processing liquid applied as a high-density region. As the value is set larger, the range in which the application amount of the processing liquid is controlled becomes wider as the low-density region. In the present invention, the reference value may be set arbitrarily within the range of the applied amount of the ink. From the viewpoint of the balance of the range to be controlled, the value is preferably in the range of 30 to 70%, more preferably in the range of 50 to 70%, with respect to the maximum value of the applied amount of the ink. A value of 50% is even more preferred.

[0064] When applying multiple types of ink, in order to adjust the amount of the processing liquid to be applied according to the ease with which various inks aggregate, it is preferred that the amount of application of the processing liquid to be changed according to the amount of application of the ink to each unit region is determined for each type of ink. Note that when a plurality of types of ink are applied, the application amount of the processing liquid is the sum of the application amounts of the processing liquid determined for each type of ink.

[0065] The application amount of the processing liquid in the reference value region may be adjusted as appropriate. When the amount of the applied ink that serves as the reference value is A, and the amount of the processing liquid applied in the reference value region is B, the value of the ratio B/A is preferably in the range of 0.14 to 0.50 when the recording medium is an absorptive recording medium, and is preferably in the range of 0.14 to 0.30 when the recording medium is a non-absorptive recording medium. The difference between an absorptive recording medium and a non-absorptive recording medium is as described below. As a result, the image quality is improved in the region to which only one type of ink is applied (also referred to as "primary color solid region").

[0066] In addition, the application amount of the processing liquid in the region where the application amount of the ink is the maximum value (hereinafter also referred to as "maximum value region") may also be adjusted as appropriate. The value of the ratio D/C is preferably in the range of 0.01 to 0.1, where C is the maximum value of the applied amount of the ink and D is the applied amount of the processing liquid in the maximum value region. When the value of the ratio D/C is 0.01 or more, the ink may be minimally aggregated, and when the value of the ratio D/C is 0.1 or less, gloss reduction due to excessive aggregation is prevented.

[0067] FIG. 3 shows an example of the relationship between the amount of the ink applied and the amount of the processing liquid applied in the high-density region, taking as an example a case where the reference value is set to a value that is 50% of the maximum value of the applied amount of the ink.

[0068] In the graph of FIG. 3, the reference value A is 6.5 g/m², the processing liquid application amount B in the reference value region is 1.3 g/m², the maximum ink application amount C is 13 g/m², the application amount D of the processing liquid in the maximum value region is 0.39 g/m², and in the high-density region, the relationship between the amount of the applied ink and the amount of the applied processing liquid is shown when the applied amount of the processing liquid is controlled so that the applied amount of the processing liquid decreases as the amount of applied ink increases in a unit region. In this case the ratio B/A is 0.2 and the ratio D/C is 0.03. It should be noted that the application amount of the processing liquid shown in this graph does not include the additional application amount for edge processing, which will be described later.

(4) Control of application amount of processing liquid in low-density region

[0069] In the present invention, the term "low-density region" refers to a region to which the ink is applied in an amount equal to or less than a reference value. As described above, the "reference value region", which refers to the region where the amount of the applied ink is the reference value, is included as part of both the high-density region and the low-density region for the sake of convenience.

[0070] In the recording method of the present invention, the method of controlling the application amount of the processing liquid in the low-density region is not particularly limited. From the viewpoint of preventing ink bleeding in low-density regions, as shown in FIG. 4, it is preferable to control the application amount of the processing liquid so that the application amount of the processing liquid increases in the unit region where the application amount of the ink is large in the low-density region. Especially in the case of the multi-pass method, by controlling the application amount of the processing liquid in the low-density region by the control method shown in FIG. 4, it is possible to effectively prevent ink bleeding in the low-density region.

[0071] In addition, as shown in FIG. 5, it is also possible to control the application amount of the processing liquid so that the application amount of the processing liquid is constant in the low-density region. For example, in the case of the single-pass method, since the ink for the entire image is applied at once, the control method shown in FIG. 5 may effectively prevent the ink from bleeding in the low-density region.

[0072] Also, depending on the printing method and other conditions, as shown in FIG. 6, it is also possible to control the amount of application of the processing liquid so that the amount of application of the processing liquid increases as the amount of application of the ink increases in the unit region.

[0073] Similarly to the control in the high-density region, when applying a plurality of types of ink in the low-density region, the application amount of the processing liquid to be changed according to the application amount of the ink for each unit region is determined for each ink type.

(5) Control of application amount of processing liquid in image contour peripheral region (edge processing)

[0074] The recording method of the present invention is characterized by controlling the application amount of the processing liquid so as to increase the application amount of the processing liquid in the peripheral region of the image contour. The processing liquid is additionally added to the application amount of the processing liquid which is changed in the high-density region and the low-density region. As a result, it is possible to effectively prevent the ink from bleeding. In the present invention, adding the amount of processing liquid applied to the peripheral region of the image contour is hereinafter also referred to as "edge processing".

[0075] In the present invention, as described above, the "image contour peripheral region" refers to a region that exists with a certain width on both sides of the image contour as a starting point. The distances from the image contour, which is the starting point, to both ends in the width direction of the image contour peripheral region are substantially the same.

[0076] "Image contour" refers to a boundary with a large difference in image density, as described above. Image contours may be detected using commercially available image processing software and various methods (Sobel method, Laplacian of Gaussian method, and Canny method). For example, when Photoshop (registered trademark) is used, image contours may be detected by applying the "contour tracing" of the "expression method" with an appropriate threshold level set. Note that the outer circumference of the region to which an ink is applied, and the image contour do not necessarily match.

[0077] FIG. 7 is a diagram schematically showing an image contour peripheral region. Starting from the image contour G indicated by the dashed line, the image contour peripheral region S is a region having a certain width on both sides thereof. The distances from the image contour G, which is the starting point, to both ends in the width direction of the image contour peripheral region S are substantially the same. Although the width Sw of the image contour peripheral region S may be set arbitrarily, it is preferably in the range of 60 to 300 µm, more preferably in the range of 100 to 250 µm, from the viewpoint of preventing bleeding.

[0078] In the region around the image contour, ink bleeding is likely to occur. By controlling the application amount of the processing liquid so as to add the application amount of the processing liquid to the region, ink bleeding may be efficiently prevented.

[0079] Furthermore, by performing the edge processing, coagulate-fixation of the ink will be faster, so the coffee ring phenomenon is less likely to occur. As a result, combined with the effect of suppressing the coffee ring phenomenon in high-density regions, the recording method of the present invention may form an image with less unevenness.

[0080] The processing liquid to be added in the image contour peripheral region is dropped at the same position as the ink is dropped in the image contour peripheral region, forming the same dots. The amount of the processing liquid to be dropped is preferably in the range of 10 to 50% of the amount of ink to be dropped per dot.

[0081] The application amount of the processing liquid added to the image contour peripheral region is the sum of the application amounts of the processing liquid for each unit region within the image contour peripheral region. The amount of the processing liquid applied to each unit region is the sum of the amount of the processing liquid dropped for each dot in the unit region. Therefore, it is preferable that the amount of the processing liquid added to the peripheral region of the image contour is in the range of 10 to 50% of the amount of the applied ink in the peripheral region of the image contour.

(6) Ink

[0082] The ink according to the present invention contains at least a coloring material. Moreover, the ink according to the present invention preferably contains a resin, a water-soluble solvent and water in addition to the coloring material.

<Coloring material>

[0083] The coloring material contained in the ink according to the present invention is preferably a pigment. As the pigment, for example, an anionic dispersed pigment, an anionic self-dispersing pigment, or a pigment dispersed with an anionic polymer dispersant may be used. In particular, it is preferable to disperse the pigment with an anionic polymeric dispersant.

[0084] As the pigment, conventionally known pigments may be used without particular limitation. For example, organic pigments such as insoluble pigments and lake pigments, and inorganic pigments such as titanium oxide may be preferably used.

[0085] In titanium oxide, for which it is generally difficult to ensure ink discharge stability and adhesion (adhesion between ink and recording medium), the present invention makes it possible to prevent bleeding and improve adhesion.

[0086] Titanium oxide has three crystal forms: anatase, rutile, and brookite. General-purpose forms may be roughly divided into anatase and rutile. Although not particularly limited, the rutile type having a high refractive index and high hiding power is preferable. Specific examples include the TR series of Fuji Titanium Industry Co., Ltd., the JR series of Tayca Co., Ltd., and TIPAQUE of Ishihara Sangyo Co., Ltd.

[0087] Preferred examples of the insoluble pigment include, but are not limited to, azo, azomethine, methine, diphenylmethane, triphenylmethane, quinacridone, anthraquinone, perylene, indigo, quinophthalone, isoindolinone, isoindoline, azine, oxazine, thiazine, dioxazines, thiazoles, phthalocyanines, and diketopyrrolopyrroles.

[0088] Specific organic pigments that may be preferably used include the following pigments.

[0089] Examples of the pigment for magenta or red include C.I. Pigment Red 2, C.I. Pigment Red 3, C.I. Pigment Red 5, C.I. Pigment Red 6, C.I. Pigment Red 7, C.I. Pigment Red 15, C.I. Pigment Red 16, C.I. Pigment Red 48:1, C.I. Pigment Red 53:1, C.I. Pigment Red 57:1, C.I. Pigment Red 122, C.I. Pigment Red 123, C.I. Pigment Red 139, C.I. Pigment Red 144, C.I. Pigment Red 149, C.I. Pigment Red 166, C.I. Pigment Red 177, C.I. Pigment Red 178, C.I. Pigment Red 202, C.I. Pigment Red 222, and C.I. Pigment Violet 19.

[0090] Examples of the pigment for orange or yellow, include C.I. Pigment Orange 31, C.I. Pigment Orange 43, C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. Pigment Yellow 15, C.I. Pigment Yellow 15:3, C.I. Pigment Yellow 17, C.I. Pigment Yellow 74, C.I. Pigment Yellow 93, C.I. Pigment Yellow 128, C.I. Pigment Yellow 94, C.I. Pigment Yellow 138, and C.I. Pigment Yellow 155. Especially in the balance between color tone and light resistance, C.I. Pigment Yellow 155 is preferred.

[0091] Examples of the pigment for green or cyan include C.I. Pigment Blue 15, C.I. Pigment Blue 15:2, C.I. Pigment Blue 15:3, C.I. Pigment Blue 16, C.I. Pigment Blue 60, and C.I. Pigment Green 7.

[0092] Examples of the pigment for black include C.I. Pigment Black 1, C.I. Pigment Black 6, and C.I. Pigment Black 7.

<Resin>

[0093] The resin used in the ink according to the present invention is preferably fine resin particles, particularly preferably water-insoluble fine resin particles. The water-insoluble resin microparticles used in the present invention are water-insoluble resin microparticles that may accept the ink and exhibit solubility or affinity for the ink.

[0094] Water-insoluble resin fine particles are originally water-insoluble, but have a form in which the resin is dispersed in an aqueous medium as microscopic particles. It is a resin or a water-insoluble resin capable of selfemulsification that forms a stable aqueous dispersion by itself without using an emulsifier or a dispersion stabilizer by introducing a hydrophilic functional group into the molecule. These resins are usually used in a state of being emulsified and dispersed in water or a water/alcohol mixed solvent.

[0095] The fine resin particles used in the ink are preferably polyester-based resin fine particles, polyurethane-based resin fine particles, polyacrylic-based resin fine particles, or composite resin particles of polyurethane-based resin and polyacrylic-based resin. Further, it is preferable that the fine resin particles used in the ink are anionic.

[0096] The fine resin particles used in the ink preferably contain an acid structure, and even if the amount of surfactant added is small, they may be dispersed in water, improving the water resistance of the ink layer. This is called a self-emulsifying type, which means that the urethane-based resin may be dispersed and stabilized in water only with molecular ionic properties without using a surfactant. Examples of the acid structure include acid groups such as a carboxy group (-COOH) and a sulfonic acid group (-SO₃H). The acid structure may be present in the side chain of the resin, or may be present at the end.

[0097] A part or all of the acid structure is preferably neutralized. By neutralizing the acid structure, the water dispersibility of the resin may be improved. Examples of the neutralizing agent that neutralizes the acid structure are preferably organic amines, and organic amines such as trimethylamine, triethylamine, tripropylamine, tributylamine, N-methyldiethanolamine and triethanolamine are preferably used.

[0098] Commercial products may be used as resin fine particles used in the ink. Examples of the commercially available fine resin particles are listed below for each type of resin.

[0099] Commercially available polyester resin fine particles include Pesresin A-110F, A-520, A-613D, A-615GE, A-640, A-645GH, A-647GEX made by Takamatsu Oil & Fat Co., Ltd., and Elitel KA-5034, KA-5071S, KA-1449, KA-0134, KA-3556, KA-6137, KZA-6034, KT-8803, KT-8701, KT-9204, KT-8904, KT-0507, and KT-9511 made by Unitika Ltd.

[0100] Commercially available urethane-based resin fine particles include NeoRez R-967, R-600, and R-9671 made by Kusumoto Kasei Co., Ltd., and W-6061, W-5661, and WS-4000 made by Mitsui Chemicals Inc.

[0101] Commercially available acrylic resin fine particles include NeoCryl A-1127 made by Kusumoto Kasei Co., Ltd., Movinyl 6899D, 6969D, 6800, 6810 made by Japan Coating Resin Corporation, and TOCRYL W-7146, W-7150, W-7152 made by Toyochem Co., Ltd.

[0102] The content of the fine resin particles in the ink is not particularly limited, but is preferably in the range of 2 to 10 mass%, more preferably in the range of 2 to 5 mass%.

<Water-soluble solvent>

[0103] Examples of the water-soluble solvent contained in the ink include alcohols, polyhydric alcohols, amines, amides, glycol ethers, and 1,2-alkanediols having 4 or more carbon atoms.

[0104] Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, t-butanol, 3-methoxy-1-butanol, 3-methoxy -3-methylbutanol, 1-octanol, 2-octanol, n-nonyl alcohol, tridecyl alcohol, n-undecyl alcohol, stearyl alcohol, oleyl alcohol, and benzyl alcohol.

[0105] Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol having 5 or more ethylene oxide groups, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol having 4 or more propylene oxide groups, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, and thiodiglycol.

[0106] Examples of the amine include ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, and tetramethylpropylenediamine.

[0107] Examples of the amide include formamide, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0108] Examples of the glycol ether include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether.

[0109] Examples of the 1,2-alkanediols having 4 or more carbon atoms include 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, and 1,2-heptanediol.

[0110] Particularly preferably used water-soluble solvents are polyhydric alcohols, which may suitably suppress bleeding during high-speed printing. Specifically, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, and tripropylene glycol are preferred.

[0111] The ink may contain one or a combination of two or more selected from these water-soluble solvents.

[0112] The content of the water-soluble solvent in the ink is not particularly limited, but is preferably in the range of 10 to 60 mass%.

<Water>

[0113] The water contained in the ink according to the present invention is not particularly limited, and may be ion-exchanged water, distilled water, or pure water. The water content in the ink is not particularly limited, but is preferably in the range of 45 to 80 mass%.

<Polymer dispersant>

[0114] The polymer dispersant used to disperse the pigment is not particularly limited, but a polymer dispersant having an anionic group is preferable, and one having a molecular weight in the range of 5,000 to 200,000 may be suitably used.

[0115] Examples of the polymer dispersant include a block copolymer having a structure derived from two or more monomers selected from styrene, styrene derivatives, vinylnaphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, a random copolymer and a salt thereof, polyoxyalkylenes, and polyoxyalkylene alkyl ethers may be mentioned.

[0116] The polymer dispersant preferably has an acryloyl group, and is preferably added after being neutralized with a neutralizing agent (neutralizing base). Although the neutralizing base is not particularly limited, it is preferably an organic base such as ammonia, monoethanolamine, diethanolamine, N-methyldiethanolamine, triethanolamine or morpholine. In particular, when the pigment is titanium oxide, the titanium oxide is preferably dispersed with a polymer dispersant having an acryloyl group.

[0117] A commercially available product may be used as a polymer dispersant. Examples of the commercially available polymer dispersant include Joncryl 819 made by BASF.

[0118] The amount of polymer dispersant added is preferably in the range of 10 to 100 mass%, more preferably in the range of 10 to 40 mass%, based on the pigment.

[0119] The pigment is particularly preferably in the form of a so-called capsule pigment, in which the pigment is coated with the polymer dispersant. As a method for coating the pigment with the polymer dispersant, various known methods can be used. For example, a phase inversion emulsification method, an acid precipitation method, and a method of dispersing a pigment with a polymerizable surfactant, supplying a monomer thereto, and coating while polymerizing the pigment may be preferably exemplified.

[0120] As a particularly preferred method, a water-insoluble resin is dissolved in an organic solvent such as methyl ethyl ketone, and after partially or completely neutralizing the acidic groups in the resin with a base, a pigment and ion-exchanged water are added and dispersed. After that, the organic solvent is removed, and if necessary, water is added for preparation.

[0121] The average particle size of the dispersed pigment in the ink is preferably 50 nm or more and less than 200 nm. Thereby, the dispersion stability of the pigment may be improved, and the storage stability of the ink may be improved. Particle size measurement of pigments may be obtained by commercially available particle size measuring instruments using dynamic light scattering method, and electrophoresis method, but measurement by dynamic light scattering method is simple and may accurately measure the particle size region.

[0122] The pigment may be used by dispersing it with a dispersing machine together with a dispersant and other additives necessary for various desired purposes.

[0123] As a disperser, conventionally known ball mills, sand mills, line mills, and high pressure homogenizers may be used. Among them, it is preferable to disperse the pigment by a sand mill because the particle size distribution becomes sharp. The material of the beads used for sand mill dispersion is not particularly limited, but zirconia or zircon is preferable from the viewpoint of preventing the generation of bead fragments and contamination with ionic components. Furthermore, the bead diameter is preferably in the range of 0.3 to 3 mm.

[0124] The content of the pigment in the ink is not particularly limited, but the content of titanium oxide is preferably in the range of 7 to 18 mass%, and the content of the organic pigment is preferably in the range of 0.5 to 7 mass%.

<Surfactant>

[0125] The ink preferably contains a surfactant. As a result, it is possible to improve the ink ejection stability and to control the spread (dot diameter) of liquid droplets that have landed on the recording medium.

[0126] The surfactant that may be used in the ink according to the present invention may be used without any particular limitation. When the other component of the ink contains an anionic compound, the ionic nature of the surfactant is preferably of the anionic, nonionic or betaine type.

[0127] In the present invention, preferably used are fluorine-based or silicone-based surfactants with high ability to reduce static surface tension, anionic surfactants such as dioctyl sulfosuccinate with high dynamic surface tension reduction ability, relatively low molecular weight polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, acetylene glycols, Pluronic surfactants (Pluronic is a registered trademark) and nonionic surfactants such as sorbitan derivatives. It is also preferable to use a fluorine-based or silicone-based surfactant in combination with a surfactant having a high dynamic surface tension-reducing ability.

[0128] By adding a silicone-based or fluorine-based surfactant as a surfactant, it is possible to suppress ink contamination (beading) on non-absorptive recording media and obtain high-quality images.

[0129] The above silicone-based surfactant is preferably a polyether-modified polysiloxane compound. Examples thereof include KF-351A and KF-642 made by Shin-Etsu Chemical Co., Ltd., BYK345, BYK347 and BYK348 made by BYK-Chemie, and Tegowet 260 made by Evonik.

[0130] The above-mentioned fluorine-based surfactant means one in which some or all of the hydrogen atoms bonded to the carbon atoms in the hydrophobic groups of ordinary surfactants are replaced with fluorine. Among these, those having a perfluoroalkyl group in the molecule are preferred.

[0131] Among the fluorine-based surfactants mentioned above, certain types are available from Dainippon Ink and Chemicals under the trade name of Megafac F, from Asahi Glass Co. under the trade name of Surflon, from 3M Company under the trade name Fluorad FC, from Imperial Chemical Industry under the trade name of Zonyls, and from Farbewerke Hoechst under the trade name Licowet VPF, respectively.

[0132] The content of the surfactant in the ink is not particularly limited, but is preferably in the range of 0.1 to 5.0 mass%.

<Other additives>

[0133] The ink according to the present invention may contain various known additives according to the purpose of improving ejection stability, compatibility with print heads and ink cartridges, storage stability, image storage stability, and other various properties.

[0134] In the ink used in the present invention, in addition to those described above, depending on the purpose of improving ejection stability, compatibility with print heads and ink cartridges, storage stability, image storage stability, and other various performances, various known additives such as polysaccharides, viscosity modifiers, resistivity modifiers, film-forming agents, UV absorbers, antioxidants, anti-fading agents, anti-mold agents, and anti-rust agents are appropriately selected and used.

[0135] For example, oil droplet fine particles such as silicone oil, liquid paraffin, dioctyl phthalate, and tricresyl phosphate; UV absorbers described in JP-A 57-74193, JP-A 57-87988, JP-A-62 261476; anti-fading agents described in JP-A 57-74192, JP-A 57-87989, JP-A 60-72785, JP-A-61 146591, JP-A 1-95091, JP-A 3-13376; and fluorescent whitening agents described in JP-A 59-42993, JP-A 59-52689, JP-A 62-280069, JP-A 61-242871, and JP-A 4-219266 may be mentioned.

<Physical properties of ink>

[0136] The viscosity of the ink according to the present invention is preferably in the range of 1 to 40 mPa·s, more preferably 2 to 10 mPa·s, at a temperature of 25 °C.

[0137] The viscosity of the ink may be measured with a rotary viscometer. Unless otherwise specified, the viscosity herein is the viscosity at a temperature of 25 °C.

[0138] The static surface tension of the ink according to the present invention is preferably higher than the static surface tension of the processing liquid at a temperature of 25 °C. Also, the static surface tension of the ink is preferably in the range of 25 to 33 mN/m, more preferably in the range of 25 to 29 mN/m at a temperature of 25 °C. The static surface tension of the ink may be measured with a surface tensiometer that applies the platinum plate method (Wilhelmy method). Unless otherwise specified, static surface tension herein is the static surface tension at a temperature of 25 °C.

(7) Processing liquid

[0139] The processing liquid according to the present invention contains at least an aggregating agent. Moreover, the processing liquid according to the present invention preferably contains a water-soluble solvent and water in addition to the aggregating agent.

[0140] It is preferable that the processing liquid does not contain resin fine particles. Since the processing liquid does not contain fine resin particles, the processing liquid hardly dries and does not thicken on the nozzle surface of the head, and the ejection property of the inkjet is improved.

<Aggregating agent>

[0141] When the processing liquid according to the present invention incorporates a material that produces aggregates, that is, incorporates an aggregating agent, in combining with the ink containing a coloring material, the interaction with the ink is increased, and an effect of fixing the dot of the ink is produced. The aggregating agent may be selected according to the type of coloring material contained in the ink.

[0142] The aggregating agent is preferably a soluble cationic polymer with thermal decomposition property, or an organic acid or a polyvalent metal salt, and is more preferably a soluble cationic polymer or a polyvalent metal salt.

[0143] The soluble cationic polymer and polyvalent metal salt may aggregate by the anionic components (usually coloring materials, or pigments) in the above ink by salting out. Organic acids may aggregate the anionic components in the above ink by pH fluctuations.

[0144] When organic acids are used, pH generally becomes an acidic region. Therefore, the resin such as the adhesive used in the inkjet head may be degraded, and the inkjet head resistance may be inferior. Polyvalent metal salts have a pH value from neutral region to a weak alkali. By appropriately selecting the part number for the soluble cationic polymer, the pH may be adjusted to the neutral range. Therefore, since the above issues may be solved, it is more preferable that the agent is a soluble cationic polymer or a polyvalent metal salt.

[0145] Examples of the soluble cationic polymer contained in the processing liquid as aggregating agents include polyallylamine, polyvinylamine, polyethyleneimine, and polydiallyldimethylammonium chloride. Examples of the commercially available soluble cationic polymer include KHE100L and FPA100L made by Senka Co., Ltd., and PAS-92A, PAS-M-1A and PAS-21CL made by Nittobo Medical.

[0146] The organic acid contained in the processing liquid as an aggregating agent is capable of aggregating the coloring material contained in the ink, and preferably has a first dissociation constant in the range of 3.5 or less, preferably in the range of 1.5 to 3.5. Within this range, the liquid is further prevented from gathering in the low-density region, and ink mixing (beading) in the high-density region is improved.

[0147] In addition, by using an organic acid, it is easy to maintain the storage stability of the processing liquid, and blocking is less likely to occur after the processing liquid is applied and dried. From the above viewpoint, formic acid, acetic acid, propionic acid, isobutyric acid, oxalic acid, fumaric acid, malic acid, citric acid, malonic acid, succinic acid, maleic acid, benzoic acid, 2-pyrrolidone-5-carboxylic acid, lactic acid, acrylic compounds having a carboxy group, including acids and derivatives thereof, methacrylic acid and derivatives thereof, acrylamide and derivatives thereof, sulfonic acid derivatives, and phosphoric acid derivatives are preferred organic acids contained in the aggregating agent.

[0148] Examples of the polyvalent metal salt contained in the processing liquid as aggregating agents include water-soluble salts such as calcium salts, magnesium salts, aluminum salts and zinc salts. Compounds that form salts with polyvalent metals include hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, phosphoric acid, thiocyanic acid, organic carboxylic acids, and organic sulfonic acids. Examples of the organic carboxylic acid include acetic acid, oxalic acid, lactic acid, fumaric acid, fumaric acid, citric acid, salicylic acid, and benzoic acid.

[0149] The aggregating agent is preferably contained in the range of 5 mass% or less with respect to the processing liquid, and it is more preferable to contain in the range of 1 to 4 mass% to effectively aggregate anionic components in the ink from the viewpoint of balancing image quality and hot water resistance.

[0150] Also, when the aggregating agent is an organic acid, the content of the organic acid may be an amount that adjusts the pH of the processing liquid to be less than the first dissociation constant of the organic acid. Bleeding during high-speed printing may be effectively suppressed by containing the organic acid in the processing liquid in such an amount that the pH of the processing liquid becomes less than the first dissociation constant of the organic acid.

[0151] The content of the aggregating agent in the processing liquid may be measured by a known method. For example, the content may be measured by ICP emission spectrometry when the aggregating agent is a polyvalent metal salt, and by high performance liquid chromatography (HPLC) when the aggregating agent is an acid.

<Water-soluble solvent>

[0152] In addition to water, a water-soluble solvent may be contained as a solvent for the processing liquid according to the present invention. As the water-soluble solvent, the same water-soluble solvents as exemplified for the above inks may be used. Although the content of the water-soluble solvent in the processing liquid is not particularly limited, it is preferably in the range of 10 to 50 mass%.

<Water>

[0153] The water contained in the processing liquid according to the present invention is not particularly limited, and may be ion-exchanged water, distilled water, or pure water. The content of water in the processing liquid is not particularly limited, but is preferably in the range of 45 to 80 mass%.

<Surfactant>

[0154] The processing liquid according to the present invention may contain a surfactant. As the surfactant, the same surfactants as exemplified for the above ink may be used. Although the content of the surfactant in the processing liquid is not particularly limited, it is preferably in the range of 0.05 to 3 mass%.

<Other additives>

[0155] The processing liquid may appropriately contain other components such as a cross-linking agent, an antifungal agent, and a bactericide within a range that does not impair the effects of the present invention.

[0156] Furthermore, the followings may be included. For example, the UV absorber described in JP-A 57-74193, JP-A 57-87988, JP-A 62-261476; anti-fading agents described in JP-A 57-74192, JP-A 57-87989, JP-A 60-72785, JP-A 61-146591, JP-A 1-95091 and JP-A 3-13376; various anionic, cationic or nonionic surfactants; and various known additives including fluorescent brightening agents, antifoaming agents, lubricants such as diethylene glycol, preservatives, thickeners, and antistatic agents described in JP-A 59-42993, JP-A 59-52689, JP-A 62-280069, JP-A 61-242871 and JP-A-4-219266 may also be incorporated.

<Physical properties of processing liquid>

[0157] The viscosity of the processing liquid according to the present invention is preferably in the range of 1 to 40 mPa·s, more preferably in the range of 1 to 10 mPa·s, at a temperature of 25 °C. The viscosity of the processing liquid may be measured with a rotary viscometer. Unless otherwise specified, the viscosity in this specification is the viscosity at a temperature of 25 °C.

[0158] The static surface tension of the processing liquid according to the present invention is preferably smaller than the static surface tension of the ink at a temperature of 25 °C. Also, the static surface tension of the processing liquid is preferably in the range of 22 to 30 mN/m, more preferably in the range of 22 to 26 mN/m at a temperature of25 °C. As a result, the ink may be aggregated while enlarging the dot diameter. The static surface tension of the processing liquid may be measured with a surface tensiometer that applies the platinum plate method (Wilhelmy method). Unless otherwise specified, static surface tension herein is the static surface tension at a temperature of 25 °C.

[0159] The dynamic surface tension of the processing liquid according to the present invention is preferably 40 mN/m or less, when the temperature is 25 °C, and the lifetime is 50 ms. It is more preferable to be 36 mN/m or less, and more preferably in the range of 25 to 35 mN/m.
The dynamic surface tension of the processing liquid may be measured using a dynamic surface tensiometer according to the maximum bubble pressure method. For the dynamic surface tension meter, for example, Dynamic Surface Tension Meter BP-D4 type made by Kyowa Interface Science Co., Ltd. may be used. Unless otherwise specified, the dynamic surface tension in this specification is the dynamic surface tension at a temperature of 25 °C, and a lifetime of 50 ms.

(8) Recording medium

[0160] The recording medium that may be used in the present invention is not particularly limited, and may be a non-absorptive recording medium or an absorptive recording medium.

[0161] In the present invention, when measured by the Bristow method described in J. TAPPI paper pulp test method no. 51 "Test method for liquid absorption of paper or paperboard", a recording medium having a water absorption amount of 0.3 g/m² or less from the start of contact to 30 msec^1/2 is called a non-absorptive recording medium, and a recording medium that absorbs more than 0.3 g/m² is called an absorptive recording medium.

<Non-absorptive recording medium>

[0162] A known plastic film may be used as an example of a non-absorptive recording medium. Specific examples include polyester films such as polyethylene terephthalate, polyethylene films, polypropylene films, polyamide films such as nylon, polystyrene films, polyvinyl chloride films, polycarbonate films, polyacrylonitrile films, and biodegradable films such as polylactic acid films may be mentioned. In addition, in order to impart gas barrier properties, moisture resistance, and fragrance retention properties, a film coated with polyvinylidene chloride on one or both sides thereof, or a film deposited with a metal oxide may also be preferably used. The non-water-absorptive film may be preferably used whether it is an unstretched film or a stretched film.

[0163] In addition to these, non-water-absorptive recording media include recording media made of inorganic compounds such as metals and glass.

[0164] It may also be suitably used as a packaging material for retort food, in which a thermosetting resin is provided as a coating layer on a metal recording medium. The packaging material for retort food blocks air, moisture, and light and seals the food inside. It is composed of a film that is laminated with a thermoplastic resin layer and an aluminum foil layer that seals.

[0165] Non-water-absorptive recording media further include leather substrates. Leather used for printing is generally cowhide. Cowhides are usually tanned with chromium compounds to add durability. Generally, tanned leather is coated with acrylic or urethane white pigment paint to form a recording medium.

<Absorptive recording medium>

[0166] Absorptive recording media include plain paper (for example, copy paper, plain printing paper), coated paper, art paper, inkjet paper, inkjet glossy paper, cardboard, wallpaper, and wood.

<Thickness of recording medium>

[0167] In the present invention, the thickness of the recording medium is appropriately selected according to the type of recording medium. When the recording medium is a plastic film, the thickness of the recording medium is preferably 10 to 120 µm, more preferably 12 to 60 µm. When the recording medium is a metal recording medium, the thickness of the recording medium is preferably in the range of 0.05 to 0.5 mm, more preferably 0.1 to 0.3 mm. When the recording medium is a leather substrate, the thickness of the recording medium is preferably in the range of 1 to 5 mm, more preferably 1 to 3 mm. If the recording medium is an absorptive recording medium, the thickness of the recording medium is preferably in the range of 50 to 500 µm.

Examples

[0168] Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these. In addition, although "parts" or "%" is used in the examples, it indicates "parts by mass" or "mass%" unless otherwise specified.

<Preparation of ink>

[0169] A cyan ink was prepared by mixing materials in the amounts shown in Table 1. A yellow ink, a magenta ink and a black ink were prepared in the same manner by using the materials and amounts as shown in Table I except that the pigments were changed to Pigment Yellow 155, a 1:1 (mass ratio) mixture of Pigment Red 202 and Pigment Violet 19, and Pigment Black 7, respectively.

[0170] Table I also shows the physical properties of the prepared cyan ink. The physical properties of yellow ink, magenta ink and black ink were the same as those of the cyan ink shown in Table 1.

[0171] The viscosity was measured at a temperature of 25 °C using a rotary viscometer. The static surface tension was measured at a temperature of 25 °C using a surface tension meter to which the platinum plate method (Wilhelmy method) was applied.

Table I

Material	Pigment	Pigment Blue 15:3	5 Mass%
	Polymer dispersant	Joncryl 819 (BASF)	2 Mass%
	Neutralizing agent	N-Methyldiethanolamine	0.4 Mass%
	Resin fine particles	NeoCry) A-1127 (Kusumoto Kasei)	5 Mass%
	Water-soluble solvent	Propylene glycol	30 Mass%
	Surfactant	KF-351A (Shin-EtsuChemical Co. , Ltd.)	0.5 Mass%
	Ion-exchanged water		Remaining amount
Physical property	Viscosity		5. 12mPa ▪ s
	Static surface tension	-	28. 7mN/m

<Preparation of processing liquid>

[0172] A processing liquid was prepared by mixing materials in the amounts shown in Table II. The physical properties of the prepared processing liquid are also shown in Table II.

[0173] The viscosity was measured at a temperature of 25 °C using a rotary viscometer. The static surface tension was measured at a temperature of 25 °C using a surface tension meter to which the platinum plate method (Wilhelmy method) was applied. The dynamic surface tension was measured by the maximum bubble pressure method using a dynamic surface tensiometer at a temperature of 25 °C and a lifetime of 50 ms.

Table II

Material	Polyvalent metal salt	Calcium acetate	3 Mass%
	Water-soluble solvent	Propylene glycol	30 Mass%
	Surfactant	Tegowet 260 (Evonik)	1 Mass%
	Ion-exchanged water	-	Remaining amount
Physical property	Viscosity	-	5. 09mPa ▪ s
	Static surface tension	-	25. 5mN/m
	Dynamic surface tension		32. 1mN/m

<Image formation>

[0174] Using the ink and the processing liquid prepared above, recording method Nos. 1 to 35 shown in Tables III and IV were used. Each image based on the document image data 1 to 3 shown in FIGs. 8 to 10 was formed on the surface of the recording medium.

[0175] Each of document image data 1 to 3 has a solid yellow region y, a solid magenta region m, a solid cyan region c, a solid black region k, a solid red region r, a solid green region g, and a solid blue region b.

[0176] The yellow solid region y, the magenta solid region m, the cyan solid region c, and the black solid region k, which are the primary color solid regions, are formed by giving only a yellow ink, a magenta ink, a cyan ink, and a black ink, respectively.

[0177] The red solid region r, the green solid region g, and the blue solid region b, which are the secondary color solid regions, were each formed by applying two types of ink in an overlapping manner. The red solid region r was formed by superimposing yellow ink and magenta ink. A green solid region g was formed by superimposing yellow ink and cyan ink. The blue solid region b was formed by superimposing magenta ink and cyan ink.

[0178] The document image data 1 is an image data of a density gradation chart composed of solid regions of the respective colors. In any recording method, the maximum value of the ink application amount in the image based on the document image data 1 was set to 13.0 g/m². The region where the ink application amount is the maximum value of 13.0 g/m² is the region where the density gradation is maximum among the secondary color solid regions r, g, and b.

[0179] The document image data 2 is composed of solid regions of each color, and is an image data in which regions where the solid regions of each color are adjacent to each other and characters (4pt, 6pt, 8pt) are drawn. In any recording method, the amount of the ink applied to the image based on the document image data 2 is 6.5 g/m² in the primary color solid regions y, m, c, and k, and in the secondary color solid regions r, g, b, it is 13.0 g/m².

[0180] The document image data 3 is an image data in which the solid regions of the respective colors are drawn individually. In any recording method, the amount of the ink applied to an image based on the document image data 3 is 6.5 g/m² in the primary color solid regions y, m, c, and k, and in the secondary color solid regions r, g, b, it is 13.0 g/m².

[0181] As the recording medium, a polyester film (made by Futamura Chemical Co., Ltd., FE2001, thickness 50 µm, indicated as "PET" in the table) was used as a non-absorptive recording medium, and coated paper (OK Top, 100 µm thick, made by Oji Paper Co., Ltd.) was used as an absorptive recording medium.

[0182] The printing method was a single-pass method or a multi-pass method. In the case of the single-pass method, it is indicated as "single" in the table. In the case of the multi-path method, "multi" is indicated in the table.

[0183] In the case of the single-pass method, an independently driven inkjet head module (resolution: 1200 dpi, ejection volume: 3 pL droplets) made by Konica Minolta was used as the recording device. The moving speed of the head was 500 mm/sec.

[0184] In the case of the multi-pass method, the recording device is equipped with an independently driven ink jet head (resolution: 360 dpi, ejection volume: 7 pL of small droplets, 15 pL of medium droplets, 23 pL of large droplets) made by Konica Minolta, Inc. as shown in FIG. 1. The independently driven inkjet head corresponds to the droplet ejection means 20 in FIG. 1. The moving speed of the head was 500 mm/sec, and the number of printing passes was 4 times.

[0185] "Processing liquid application amount control type" in the table refers to the control type of the relationship between the amount of the ink applied and the amount of the treatment liquid applied. It is one of Types 1 to 4 shown in FIG. 11 to FIG. 14. Type 1 and Type 2 relate to the present invention, and Type 3 and Type 4 are comparative examples.

[0186] In the case of Type 1, in the high-density region, the application amount of the processing liquid was controlled so that the application amount of the processing liquid decreased as the amount of application of the ink increased in the unit region. In addition, in the low-density region, the application amount of the processing liquid is controlled so that the application amount of the processing liquid increases in the unit region where the application amount of the ink is large.

[0187] In the case of Type 2, in the high-density region, the application amount of the processing liquid was controlled so that the application amount of the processing liquid decreased as the amount of application of the ink increased in the unit region. In addition, in the low-density region, the application amount of the processing liquid was controlled so that the application amount of the processing liquid was constant.

[0188] In the case of Type 3, the application amount of the processing liquid was controlled so that the application amount of the processing liquid increased in all the regions to which the ink was applied, the unit region to which the application amount of the ink was greater. Although the reference value is set to 50% of the maximum value, it is for convenience, and there is no difference in control of the amount of the processing liquid applied between the high-density region and the low-density.

[0189] In the case of Type 4, the application amount of the processing liquid was controlled so that the application amount of the processing liquid was constant in all regions where the ink was applied. Although the reference value is set to 50% of the maximum value, it is for convenience, and there is no difference in control of the amount of processing liquid applied between the high-density region and the low-density region.

[0190] The reference values shown in Tables III and IV are values when the maximum amount of ink applied is 100%. Since the maximum value of the ink application amount for each formed image is 13.0 g/m², for example, when the reference value is 6.5 g/m², the description in the table is 50%.

[0191] In the table, "A" is the reference value, "B" is the applied amount of the processing liquid in the region where the applied amount of the ink is the reference value, "C" indicates the maximum applied amount of the ink, and "D" indicates the applied amount of the processing liquid in the region where the applied amount of the ink is the maximum value.

[0192] As the edge processing, the processing liquid is dropped at the same position as the position where the ink is dropped in the image contour peripheral region, with a dropping amount of 30% of the ink dropping amount (maximum ink amount 100%). The image contour peripheral region is defined as a region with a width Sw of 200 µm shown in FIG. 7, starting from the image contour detected from the original image data using Photoshop (registered trademark). The distance from the image contour, which is the starting point, to both ends in the width direction of the image contour peripheral region is 100 µm. Detection of image contours in Photoshop (registered trademark) was performed by applying the "contour tracing" of the "expression method" with the threshold level set to 35.

<Evaluation method>

[0193] The images formed by each recording method were evaluated by the following methods.

(Bleeding)

[0194] Regarding the images formed based on the document image data 1 and 2, the regions where the solid regions of each color are adjacent to each other and the state of bleeding in the cutout characters were visually confirmed and evaluated according to the following criteria.

"Circle": No bleeding is observed.

"Triangle": Slight bleeding is observed.

"Cross mark": Bleeding is observed.

(Gloss)

[0195] Regarding the image formed based on the document image data 3, the glossiness was measured in the solid region of the primary color yellow and the solid region of the secondary color red, and evaluated according to the following criteria. Glossiness was measured at an angle of 60 degree using a gloss meter (PG-IIM made by Nippon Denshoku Industries Co., Ltd.).

"Double circle": Glossiness is 35 or more.

"Circle": Glossiness is 25 or more and less than 35.

"Cross mark": Glossiness is less than 25.

(Gloss difference)

[0196] From the above-measured glossiness of the solid region of yellow, which is the primary color, and glossiness of the solid region of red, which is the secondary color, the difference in each glossiness was calculated and evaluated according to the following criteria.

"Circle": Difference in glossiness is 6 or less.

"Cross mark": Difference in glossiness is greater than 6.

[0197] (Reflection density)

[0198] For the image formed based on the document image data 3, the reflection density of the solid region of yellow, which is the primary color, was measured and evaluated according to the following criteria. The reflection density was measured using a fluorescence spectrodensitometer (FD-7 made by Konica Minolta, Inc.) under a D50 light source.

"Double circle": Reflection density is 1.5 or more.

"Circle": Reflection density is 1.3 or more and less than 1.5.

"Cross mark": Reflection density is less than 1.3.

[0199] (Dryness)

[0200] An image formed based on document image data 1 was dried in an oven at 80 °C for 1 minute, then rubbed with a finger to check the dryness, and evaluated according to the following criteria.

"Double circle": No peeling with finger rubbing

"Circle": Partially peeled off by finger rubbing

"Cross mark": Distinctly peeled off by finger rubbing

[0201] Tables III and IV show the evaluation results of the images formed by each recording method.

[0202] From the evaluation results shown in Tables III and IV, it can be seen that the recording method of the present invention may form images with good glossiness and less ink bleeding.

Industrial Applicability

[0203] The present invention may be used for an inkjet recording method and an inkjet recording device capable of forming an image with good glossiness and less ink bleeding.

Reference Signs List

[0204] 

1:

Head unit

1C, 1M, 1Y, 1K, 1Pr:

Head

20:

Liquid droplet ejection means

21:

Nozzle

22:

Carriage

30:

Scanning unit

W:

Width of head unit

A1 to A6:

Print region

P:

Total print region

PL:

Print region length

PW:

Print region width

Me:

Recording medium

Im:

Ink application region

G:

Image contour

S:

Image contour peripheral region

Sw:

Width of image contour peripheral region

C, M, Y, K, In:

Ink

Pr:

Processing liquid

Claims

1. An inkjet recording method for forming an image comprising a step of applying an ink containing a coloring material and a processing liquid containing an aggregating agent onto a surface of a recording medium with a liquid droplet ejection means,

wherein in a region where an application amount of the ink is equal to or greater than a reference value, an application amount of the processing liquid is controlled so that the application amount of the processing liquid decreases as the amount of application of the ink is high in the unit region; and

in an image contour peripheral region, the application amount of the processing liquid is controlled so as to increase the application amount of the processing liquid.

2. The inkjet recording method according to claim 1, wherein the reference value is a value that is 50% of a maximum value of the application amount of the ink.

3. The inkjet recording method according to claim 1 or 2, wherein in the region where the application amount of the ink is equal to or less than the reference value among the regions to which the ink is applied, the application amount of the processing liquid is controlled so that the application amount of the processing liquid increases as the amount of application of the ink is high in the unit region.

4. The inkjet recording method according to any one of claims 1 to 3, wherein the inkjet recording method is a multi-pass method.

5. The inkjet recording method according to any one of claims 1 to 4, wherein the recording medium is an absorptive recording medium; and when the reference value is A and the application amount of the processing liquid in the region where the application amount of the ink is the reference value is B, the application amount of the processing liquid is controlled so that a value of a ratio B/A is in the range of 0.14 to 0.50.

6. The inkjet recording method according to any one of claims 1 to 4, wherein the recording medium is a non-absorptive recording medium; when the reference value is A, and the application amount of the processing liquid in the region where the application amount of the ink is the reference value is B, the application amount of the processing liquid is controlled so that a value of a ratio B/A is in the range of 0.14 to 0.30.

7. The inkjet recording method according to any one of claims 1 to 6, when a maximum value of the application amount of the ink is C, and the application amount of the processing liquid in the region where the applied amount of the ink is a maximum value is D, the application amount of the processing liquid is controlled so that a value of a ratio D/C is in the range of 0.01 to 0.1.

8. The inkjet recording method according to any one of claims 1 to 7, when a plurality of types of ink are applied, the application amount of the processing liquid to be changed according to the application amount of the ink for each unit region is determined for each type of ink.

9. An inkjet recording device for forming an image by applying an ink containing a coloring material and a processing liquid containing an aggregating agent onto a surface of a recording medium with a liquid droplet ejection means,

wherein in a region where an application amount of the ink is equal to or greater than a reference value, an application amount of the processing liquid is controlled so that the application amount of the processing liquid decreases as the amount of application of the ink is high in the unit region; and

in an image contour peripheral region, the application amount of the processing liquid is controlled so as to increase the application amount of the processing liquid.

Drawing