JP6071822B2 - Image forming method - Google Patents

Description

  The present invention relates to an image forming method.

2. Description of the Related Art Conventionally, an image forming method for forming an image on a recording medium by an ink jet method using an ink containing a coloring material, water, and an organic solvent is known.
In such an image forming method, a recording medium on which an image is recorded may be curled. Various studies have been made so far in order to suppress curling of the recording medium.

For example, as an ink jet printer that does not cause curling on recording paper, an ink jet printer is known in which a liquid containing at least water is attached to the back side of a recording medium printing surface by using, for example, an application roller and the same amount or less as the amount of ink required for printing. (For example, refer to Patent Document 1).
Further, as an ink jet recording method in which the recording medium after printing by ink jet does not curl, the wetting time to the recording medium in the Bristow method is 30 ms or more and the absorption coefficient is 1.9 ml / m ² · ms ^1/2 or more. After printing on a recording medium using a certain ink, a liquid containing at least water is attached to the back side of the printing surface of the recording medium in an amount equal to or less than the amount of ink required for printing using, for example, an application roller. An ink jet recording method is known (see, for example, Patent Document 1).
In addition, as an image recording method having excellent curling aptitude, resistance to see-through, and double-sided printing aptitude for various recording media, a step of applying or printing an ink composition on the recording surface of the recording medium, and recording on the recording medium There is known an image recording method having a step of applying or printing a white ink composition containing hollow resin particles, an anti-curl agent, and water on a surface opposite to the surface (see, for example, Patent Document 3). .
In addition, as a liquid ejection device that can reduce the number of ejection data for the anti-curl agent nozzle as much as possible, a first nozzle that ejects a colored liquid onto a medium, and a second nozzle that ejects a colorless liquid onto the medium There is known a liquid ejection apparatus in which the resolution of an image formed using the second nozzle is lower than the resolution of an image formed using the first nozzle (for example, Patent Documents 4 and 5). reference).
Also, as an ink jet recording apparatus that can substantially completely suppress curling of recording paper, a first ink jet recording head that forms an image by ejecting colored ink droplets onto the recording paper, and colorless ink droplets onto the recording paper A second ink jet recording head for forming an image, and print data of an image formed by ejecting the colorless ink droplet is opposite to a surface on which the colorless ink droplet is ejected. There is known an ink jet recording apparatus that is calculated based on print data of an image formed by ejecting the colored ink droplets on a surface (see, for example, Patent Document 6). In Patent Document 6, it is preferable that print data of an image formed by discharging colorless ink droplets is substantially the same as a mirror image of an image formed by discharging colored ink droplets.

Japanese Patent Laid-Open No. 10-151733 JP-A-10-272828 JP 2010-221532 A JP 2008-188877 A JP 2008-188878 A JP 2006-76129 A

  As described above, a technique for suppressing curling of a recording medium by applying a liquid to the surface opposite to the ink application surface of the recording medium is known. This liquid is called an “anti-curl solution”.

Incidentally, in recent years, there has been an increasing demand for speeding up image formation (image recording) by the ink jet method.
However, when applying an anti-curl solution for high-speed image formation, the recording medium conveyance speed is deliberately slow when applying the anti-curl solution in order to provide a sufficient amount of the anti-curl solution to obtain an anti-curl effect. Or it may be necessary to increase the number of ink jet heads for applying the anti-curl solution. For this reason, there is a case where the demand for high-speed image formation cannot be satisfied or the manufacturing cost of the image forming apparatus increases.
Therefore, particularly when performing image formation at high speed, there is a demand for a technique for more effectively suppressing curling of the recording medium with a smaller amount of anti-curl liquid.
In addition, there is a need for a technique for more effectively suppressing the curl from the viewpoint of improving the merchantability of a recording medium on which an image is formed.

Further, according to the study of the present inventors, when the difference in the amount of the organic solvent contained in the ink is large on both sides of the recording medium (specifically, when the difference is 1.5 mL / m ² or more). It was found that the curl of the recording medium becomes more prominent.
Therefore, in this case, it is required to suppress the curl more effectively than in the past.

This invention is made | formed in view of the above, and makes it a subject to achieve the following objectives.
That is, it is an object of the present invention to effectively curl a recording medium even when image formation is performed at high speed and there is a large difference in the amount of organic solvent contained in the ink on both sides of the recording medium. It is an object of the present invention to provide an image forming method that can be suppressed.

Specific means for achieving the object are as follows.
<1> An ink containing a coloring material, water, and an organic solvent is applied to at least one surface of the recording medium by an inkjet method, and the recording medium contains water and an organic solvent, and the content ratio of the coloring material is It has an application step of applying an anti-curl solution that is less than 0.1% by mass by an ink jet method, and the surface of the recording medium having the larger amount of organic solvent contained in the ink is the front surface When the surface with the smaller amount of the organic solvent contained in the ink is the back surface, the application step is a region corresponding to the region where the ink is applied to the front surface of the back surface of the recording medium. At least a part of the anti-curl solution is applied, and the difference in the amount of organic solvent contained in the ink on both sides of the recording medium is expressed as Vi (mL / m ² ). the application amount ^{V-c (mL / m 2} ) The volume average SP value of the organic solvent contained in the ink SP-i ^{(MPa 1/2),} when the volume average SP value of the organic solvent contained in anticurl solution was SP-c ^{(MPa 1/2)} An image forming method satisfying the following formula (1) to the following formula (4).
Formula (1): 1.5 <= V-i
Formula (2): SP-i ≦ SP-c
Formula (3): SP-c * V-c <V-i * SP-i
Formula (4): 0.25 × V−i ≦ V−c

<2> The image forming method according to <1>, wherein the content ratio of the organic solvent in the curl prevention liquid on a mass basis is higher than the content ratio on the mass basis of the organic solvent in the ink.
<3> The image according to <1> or <2>, wherein the content ratio of the organic solvent in the anti-curl solution on a mass basis is 1.2 times or more of the content ratio on the mass basis of the organic solvent in the ink. It is a forming method.
<4> The image forming method according to any one of <1> to <3>, wherein SP-c is 27.0 MPa ^1/2 or more.
<5> The organic solvent in the anti-curl solution is at least one selected from the group consisting of glycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, and tripropylene glycol <1> to <4> The image forming method according to any one of <4>.
<6> The image forming method according to any one of <1> to <5>, wherein the content ratio of the organic solvent in the anti-curl solution is 10% by mass to 80% by mass.
<7> The image forming method according to any one of <1> to <6>, wherein the content ratio of the organic solvent in the ink is 5% by mass to 40% by mass.
<8> The image forming method according to any one of <1> to <7>, wherein Formula (2) is SP-i <SP-c.
<9> The image forming method according to any one of <1> to <8>, wherein the basis weight of the recording medium is 130 g / m ² or less.
<10> The applying step is the image forming method according to any one of <1> to <9>, wherein the ink and the anti-curl liquid are applied to a recording medium conveyed at a conveyance speed of 50 m / min or more.
<11> The application step applies any one of <1> to <10>, in which the anti-curl liquid is applied to the entire area corresponding to the area shape where ink is applied to the front surface of the back surface of the recording medium. The image forming method described in 1. above.

  According to the present invention, even when image formation is performed at high speed, even when the difference in the amount of organic solvent contained in the ink on both sides of the recording medium is large, curling of the recording medium is effectively suppressed. An image forming method that can be used can be provided.

1 is a schematic configuration diagram illustrating an example of an ink jet recording apparatus suitable for an image forming method of the present invention.

Hereinafter, the present invention will be described in more detail.
In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
In addition, in this specification, when referring to the amount of each component in the composition (ink, anti-curl solution), when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, It means the total amount of the plurality of substances present in the composition.
Further, in this specification, the term “process” is not limited to an independent process, and even if it cannot be clearly distinguished from other processes, the term is used as long as the intended purpose of the process is achieved. include.

In the image forming method of the present invention, an ink containing a coloring material, water, and an organic solvent is applied to at least one surface of a recording medium by an ink jet method, and the recording medium contains water and an organic solvent. The surface of the recording medium having a larger amount of the organic solvent contained in the ink, having an application step of applying an anti-curl solution having a material content of less than 0.1% by mass by an inkjet method. When the surface on which the amount of the organic solvent contained in the ink is smaller is the back surface, the applying step is a region where the ink is applied to the front surface of the back surface of the recording medium. The anti-curl solution is applied to at least a part of the region corresponding to, and the difference in the applied amount of the organic solvent contained in the ink on both sides of the recording medium is contained in Vi (mL / m ² ), the anti-curl solution. The amount of organic solvent applied is V- (ML ^{/ m} 2), the volume average of the organic solvent SP value SP-i ^{(MPa 1/2)} contained in the ink, the volume average SP value of the organic solvent contained in the anti-curl liquid SP-c (MPa ^1/2 ), the following formulas (1) to (4) are satisfied.
Formula (1): 1.5 <= V-i
Formula (2): SP-i ≦ SP-c
Formula (3): SP-c * V-c <V-i * SP-i
Formula (4): 0.25 × V−i ≦ V−c

  In the image forming method of the present invention, the ink may be applied to only one side of the recording medium, or may be applied to both sides of the recording medium. Needless to say, when ink is applied to only one side of the recording medium, a colored image is formed only on one side of the recording medium, and when ink is applied to both sides of the recording medium, a colored image is formed on both sides of the recording medium. Is done.

In the present invention, the “surface with a larger amount of the organic solvent contained in the ink” (that is, “front surface”) corresponds to the case where ink is applied to only one surface of the recording medium. One surface (the surface to which ink is applied) is also included.
In the present invention, the “surface with less amount of organic solvent contained in the ink” (that is, “back surface”) is the other surface when ink is applied to only one surface of the recording medium ( Surfaces to which no ink is applied are also included.
Further, “applied amount” in the present invention means an amount applied to the recording medium. The “applied amount” can be rephrased as “coating amount”.
In the present invention, “difference in applied amount” means an absolute value of the difference in applied amount. For example, “the difference in the applied amount is large” means that the absolute value of the difference in the applied amount is large, and “the difference in applied amount is 1.5 mL / m ² or more” means the absolute value of the difference in the applied amount. It means that the value is 1.5 mL / m ² or more.

In general, when an ink containing a coloring material, water, and an organic solvent is applied to only one side of a recording medium, the one side contracts as the applied ink dries, thereby causing curling of the recording medium. There is a case. In this case, the recording medium curls in the direction of the front surface (the surface to which ink has been applied).
Here, “curl in the direction of the front surface” means a shape in which both end portions of the recording medium are located on the front surface side with respect to the central portion of the recording medium (in other words, convex toward the back surface direction). Bend to the shape).

According to the study of the present inventor, when the ink is applied only to one side of the recording medium and the applied amount of the organic solvent contained in the ink is 1.5 mL / m ² or more (that is, the above formula ( When 1) is satisfied, it has been found that curling in the direction of the front surface becomes significant.
Furthermore, when the ink is applied to both sides of the recording medium according to the study of the present inventors, the difference in the applied amount of the organic solvent contained in the ink on both sides is 1.5 mL / m ² or more. It was also found that curling in the direction of the front surface becomes significant (when the above formula (1) is satisfied). The reason for this is that when the difference in the amount of the organic solvent contained in the ink on both sides is 1.5 mL / m ² or more, the ink containing the organic solvent in an amount corresponding to this difference is only on one side. This is probably because the same phenomenon as that given to the case occurs.
Thus, it is considered that the curl of the recording medium is greatly affected by the difference in the amount of the organic solvent applied to the ink on both sides of the recording medium.

In recent years, there has been an increasing demand for speeding up image formation (image recording) by the ink jet method. In order to perform image formation at high speed, it is necessary to increase the conveyance speed of the recording medium when ink is applied.
However, when applying an anti-curl solution for high-speed image formation, the recording medium conveyance speed is deliberately slow when applying the anti-curl solution in order to provide a sufficient amount of the anti-curl solution to obtain an anti-curl effect. Or it may be necessary to increase the number of ink jet heads for applying the anti-curl solution. For this reason, there is a case where the demand for high-speed image formation cannot be satisfied or the cost of the image forming apparatus increases.
Therefore, particularly when performing image formation at high speed, there is a demand for a technique for more effectively suppressing curling of the recording medium with a smaller amount of anti-curl liquid.
In addition, there is a need for a technique for more effectively suppressing the curl from the viewpoint of improving the merchantability of a recording medium on which an image is formed.

Regarding the above-described points, according to the image forming method of the present invention, even when the above formula (1) where the curl of the recording medium is particularly remarkable is satisfied and image formation is performed at high speed, the image is formed. Curling of the recording medium after formation can be effectively suppressed.
Hereinafter, the reason why the above effect is obtained will be described.

<Formula (1): 1.5 ≦ V−i>
Needless to say, the formula (1) indicates that the difference (Vi) in the amount of the organic solvent contained in the ink on both sides of the recording medium is 1.5 mL / m ² or more. .
As described above, it has been found that when this equation (1) is satisfied, the curl of the recording medium becomes particularly significant.

As a result of further investigation, the present inventor has found that the SP value of the organic solvent contained in the ink strongly affects the curling of the recording medium after image formation (hereinafter, also simply referred to as “curling of the recording medium” or “curling”). I found out. Specifically, it has been found that an organic solvent having a larger SP value, that is, an organic solvent having a higher water retention function (hydrophilicity) has a stronger property of curling the recording medium (that is, causing stronger curling by the recording medium).
Based on this finding, it is specified in the present invention that the above formula (2) is satisfied.

<Formula (2): SP-i ≦ SP-c>
The above formula (2) indicates that “the organic solvent contained in the anti-curl solution has the same property of curling the recording medium as the organic solvent contained in the ink or stronger than the organic solvent in the ink. Means.
In other words, the anti-curl solution has a function of promoting curling rather than being alone. In the present invention, the anti-curl liquid is applied to the surface (back surface) of the recording medium where the amount of the organic solvent contained in the ink is smaller. When the anti-curl liquid is applied to the back surface, a force that causes a curl in a direction opposite to the direction of curl generated by the application of ink acts on the recording medium. That is, when the anti-curl liquid is applied to the back surface, it has a function of correcting the curl of the recording medium caused by the application of ink (hereinafter also referred to as “curl correcting function”).
As a result, in the present invention, the curling of the recording medium caused by the ink application is corrected by the anti-curling liquid applied to the back surface, and curling of the recording medium can be suppressed when viewed as the entire image forming method.
And by satisfy | filling said Formula (2), compared with the case where the said Formula (2) is not satisfy | filled, curling of a recording medium can be suppressed with a smaller application amount of curl prevention liquid.

However, the curl correction function works excessively only by satisfying the above formula (2), and actually the curl direction opposite to the curl direction caused by the application of ink (hereinafter also referred to as “reverse curl”). ) May occur. In this case, as a result, there is no change in the curling of the recording medium. Therefore, it cannot be said that the curling of the recording medium is suppressed.
Further, only satisfying the above formula (2) makes the function of the curl correcting function insufficient, and curling of the recording medium may not be suppressed.
That is, in order to suppress curling of the recording medium, it is important to balance the force with which the ink curls the recording medium and the force with which the curl prevention liquid curls the recording medium (curl correcting function).
In view of this balance, it is specified in the present invention that the above formula (3) and the above formula (4) are satisfied.

<Formula (3): SP-c * Vc <Vi * SP-i>
When the above formula (3) is modified, the following formula (3B) is obtained.
Formula (3B): V−c <V−i × (SP−i / SP−c)
That is, Formula (3) (Formula (3B)) defines the upper limit of the applied amount (Vc) of the organic solvent contained in the anti-curl solution.
By satisfying this equation (3), the phenomenon of the occurrence of curling in the opposite direction (reverse curling) is suppressed, and as a result, the curl suppressing effect by the application of the anti-curl solution is effectively exhibited.

In said formula (3), Vc (mL / m < ² >) shows the provision amount of the organic solvent contained in a curl prevention liquid.
Here, “the amount of the organic solvent contained in the anti-curl solution” means that the anti-curl solution is applied to the recording medium (back surface), so that all the organic solvents contained in the anti-curl solution are Means the amount given to

Moreover, in the said Formula (3), Vi (mL / m < ² >) points out the difference of the provision amount of the organic solvent contained in the ink in both surfaces of a recording medium.
Here, “the amount of the organic solvent contained in the ink” means the amount of all the organic solvent contained in the ink applied to one side of the recording medium by applying the ink to one side. means.
The above Vi represents the difference between the two sides of the recording medium in the “amount of the organic solvent contained in the ink”.

<Formula (4): 0.25 × V−i ≦ V−c>
In the present invention, it is specified that the above formula (4) is satisfied in addition to the above formula (2) and the above formula (3).
By satisfying the above formula (4), the curl correcting function of the anti-curl solution works sufficiently, and as a result, curling of the recording medium is suppressed.
When the above formula (4) is not satisfied, the function of the curl correcting function of the anti-curl solution becomes insufficient.

  As described above, according to the image forming method of the present invention, all of the above formulas (2) to (4) are satisfied even when the above formula (1) where the curl of the recording medium is particularly remarkable is satisfied. Thus, curling of the recording medium is effectively suppressed.

In the present invention, the SP value (solubility parameter / unit: MPa ^1/2 ) is a value represented by the square root of the molecular aggregation energy, and is described in RF Fedors, Polymer Engineering Science, 14, p.147-154 (1974). It refers to the value calculated by the described method.

The volume average SP value in the present invention refers to a value defined in accordance with AFM Barton, Chem. Rev., 75, p731 (1975).
Specifically, in the present invention, the volume average SP value (SP-i) of the organic solvent contained in the ink is determined for each organic solvent species (compound) contained in the ink. It was obtained by respectively obtaining the product of the volume fraction of the specific organic solvent species in the solvent type) and the SP value of the specific organic solvent species, and adding the products obtained for each organic solvent species. Points to the value. That is, when only one organic solvent (organic solvent species) is contained in the ink, the volume average SP value is equal to the SP value of the one organic solvent (organic solvent species).
In the present invention, the volume average SP value (SP-c) of the organic solvent contained in the anti-curl solution is included for each organic solvent species (compound) contained in the anti-curl solution. By calculating the product of the volume fraction of the specific organic solvent species in the total organic solvent species) and the SP value of the specific organic solvent species, and adding the products obtained for each organic solvent species together Refers to the value obtained. That is, when only one organic solvent (organic solvent species) is included in the anti-curl solution, the volume average SP value is equal to the SP value of the one organic solvent (organic solvent species).

For example, when the organic solvent in the ink is composed of two organic solvent species (organic solvent species 1 and organic solvent species 2), SP-i is obtained by the following formula (A).
Further, the organic solvent in the ink is composed of two or more organic solvent species (organic solvent species 1, organic solvent species 2,..., And organic solvent species n; where n is an integer of 3 or more). In this case, SP-i is obtained by the following formula (B).
Formula (A): SP-i = φ1δ1 + φ2δ2
Formula (B): SP−i = φ1δ1 + φ2δ2... + Φnδn
[In Formula (A) and Formula (B), φ1 represents the volume fraction of organic solvent species 1 relative to the entire organic solvent, φ2 represents the volume fraction of organic solvent species 2 relative to the entire organic solvent, and φn represents the organic solvent. It represents the volume fraction of organic solvent species n relative to the whole.
In the formula (A) and the formula (B), δ1 represents the SP value of the organic solvent species 1, δ2 represents the SP value of the organic solvent species 2, and δn represents the SP value of the organic solvent species n.
In the formula (B), n represents an integer of 3 or more. ]

In the present invention, the applied amount (mL / m ² ) of the organic solvent contained in the ink is the discharge amount (pL) per dot from the inkjet head, the resolution (dpi; dot per inch), the area ratio [ It is determined based on the area of the image forming area / (the area of the image forming area + the area of the non-image forming area)] and the content ratio of the organic solvent in the ink.
It is calculated | required similarly about the provision amount (mL / m < ² >) of the organic solvent contained in a curl prevention liquid.

In the image forming method (applying step) of the present invention, an anti-curl solution is applied to at least a part of a region corresponding to a region where ink is applied to the front surface of the back surface of the recording medium. That is, in the application step, when viewed from one side (front surface side or back surface side) of the recording medium, an ink application region on the front surface side and an anti-curl solution application region on the back surface side are provided. The ink and the anti-curl liquid are applied so as to have an overlapping portion.
This can reduce the difference in shrinkage between the front surface and the back surface of the recording medium, as compared with the case where the anti-curl solution is applied to the back surface of the recording medium by roller application.
Therefore, the curl suppressing effect by the anti-curl liquid can be effectively obtained regardless of the image formed by applying the ink.
In the application process, ink is applied to the front surface and curling is prevented from occurring on the back surface (specifically, at least a part of the back surface corresponding to the region where ink is applied to the front surface). Any of the liquids may be applied first. Details of the application order of the ink and the anti-curl liquid in the application step will be described later.

In the application step of the present invention, both the ink and the anti-curl liquid are applied based on the image data, and an image of image data (hereinafter also referred to as “image B”) used for applying the anti-curl liquid is recorded. It is preferably at least a part (preferably the whole) of a mirror image of an image of image data (hereinafter also referred to as “image A”) used for applying ink to the front surface of the medium.
That is, it is preferable that at least a part of the image A and the image B have a mirror image relationship.
Here, at least a part of the image A and the image B have a mirror image relationship that the position of at least a part of the image A on the recording medium (the position where ink is applied) and the position of the image B on the recording medium. This means that the position (position where the anti-curl solution is applied) is in a mirror image relationship. Here, it goes without saying that the shapes of characters, figures, patterns, etc. included in at least a part of the image A and the shapes of characters, figures, patterns, etc. included in the image B are in a mirror image relationship.
Therefore, in the present invention, ideally, when viewed from one side of the recording medium, at least a part of the image (image A) formed by the ink formed on the front side of the recording medium and the recording medium are recorded. An anti-curl solution and ink are applied so that the image (image B) formed by the anti-curl solution formed on the back side of the medium overlaps (for example, paragraphs 0039 to 0042 and JP-A-2006-76129 and FIG. 7 and FIG. 8). However, the two do not need to overlap exactly, and deviation within the range of the droplet deposition position accuracy of the image forming apparatus is allowed. Even if this degree of deviation occurs, the effects of the present invention are sufficiently exhibited.

Further, in the image forming method (applying step) of the present invention, the anti-curl liquid is applied only to the region where the ink is not applied among the regions corresponding to the region where the ink is applied to the front surface of the back surface of the recording medium. An aspect to be imparted (hereinafter also referred to as “aspect A”) is also preferable.
In this aspect A, when ink is applied only to the front surface and no ink is applied to the back surface, the entire region corresponding to the region where ink is applied to the front surface of the back surface of the recording medium. Apply an anti-curl solution.

  In the image forming method of the present invention, from the viewpoint of more effectively suppressing curling of the recording medium, an anti-curling liquid is applied to the entire area corresponding to the area where ink is applied to the front surface of the back surface of the recording medium. Is preferably given.

In the present invention, it is preferable that the content ratio of the organic solvent in the anti-curl liquid on a mass basis is higher than the content ratio on the mass basis of the organic solvent in the ink.
In this aspect, the curl correction function of the anti-curl liquid is further enhanced, and therefore the curl suppression effect (effect of correcting curl due to ink application) when viewed as the entire image forming method is further enhanced. Therefore, the amount of anti-curl solution used (amount applied to the recording medium) can be further reduced.

Many of the conventional anti-curl liquids have a configuration in which the color material in the ink is replaced with the same amount of water. For this reason, in many of the conventional anti-curl solutions, the content ratio of the organic solvent in the anti-curl solution based on the mass is equal to the content ratio of the organic solvent in the ink based on the mass.
When many such conventional anti-curling liquids are used, it is necessary to apply the same amount of the anti-curl liquid as the ink in order to suppress the curling by the ink.
On the other hand, in the present invention, when the content ratio of the organic solvent in the anti-curl liquid on a mass basis is higher than the content ratio on the mass basis of the organic solvent in the ink, the anti-curl solution is applied. The amount can be reduced.
For this reason, when it is set as the aspect whose content rate by the mass reference | standard of the organic solvent in an anti-curl liquid is higher than the content rate by the mass reference | standard of the organic solvent in ink, it uses 4 inkjet heads, for example. In the case of ejecting color (for example, four colors of cyan, magenta, yellow, and black), it is possible to eject the anti-curl liquid from only one ink-jet head for anti-curl liquid.

In the present invention, the content ratio of the organic solvent in the anti-curl liquid on a mass basis is preferably 1.2 times or more of the content ratio on the mass basis of the organic solvent in the ink.
That is, it is more preferable that the ratio [the content ratio of the organic solvent in the anti-curl solution based on the mass basis / the content ratio of the organic solvent in the ink based on the mass basis] is 1.2 or more.
When the ratio is 1.2 or more, the curl correction function of the anti-curl liquid is further enhanced, and thus the curl suppression effect (effect of correcting curl due to ink application) is further enhanced when viewed as the entire image forming method. It is done. Therefore, the amount of anti-curl solution used (amount applied to the recording medium) can be further reduced.

The SP-c is preferably 27.0 MPa ^1/2 or more.
In this aspect, the curl correction function of the anti-curl liquid is further enhanced, and therefore the curl suppression effect (effect of correcting curl due to ink application) when viewed as the entire image forming method is further enhanced. Therefore, the amount of anti-curl solution used (amount applied to the recording medium) can be further reduced.
The SP-c is preferably 28.0 MPa ^1/2 or more.
The upper limit of the SP-c is not particularly limited, but the SP-c is preferably 40.0 MPa ^1/2 or less.

The organic solvent in the anti-curl solution is glycerin (41.0), ethylene glycol (36.5), diethylene glycol (30.6), triethylene glycol (27.8), propylene glycol (32.6), And at least one selected from the group consisting of dipropylene glycol (27.1).
Here, the numerical value in parentheses after the compound name is the SP value (unit: MPa ^1/2 ) of the compound.
In this aspect, the curl correction function of the anti-curl liquid is further enhanced, and therefore the curl suppression effect (effect of correcting curl due to ink application) when viewed as the entire image forming method is further enhanced. Therefore, the amount of anti-curl solution used (amount applied to the recording medium) can be further reduced.

The content ratio of the organic solvent in the anti-curl solution (total amount of all organic solvent species) is preferably 10% by mass to 80% by mass, and more preferably 20% by mass to 80% by mass with respect to the total amount of the anti-curl solution.
When the content ratio of the organic solvent in the anti-curl solution is 10% by mass or more, the curl correcting function of the anti-curl solution is further enhanced. The effect of correcting the) is further enhanced. Therefore, the amount of anti-curl solution used (amount applied to the recording medium) can be further reduced.
When the content ratio of the organic solvent in the anti-curl solution is 80% by mass or less, the content ratio of water in the anti-curl solution becomes a more preferable range.

The content ratio of the organic solvent in the ink (total amount of all organic solvent species) is preferably 5% by mass to 40% by mass and more preferably 5% by mass to 30% by mass with respect to the total amount of the ink.
When the content ratio is 40% by mass or less, curling of the recording medium due to application of ink can be further reduced. Therefore, the amount of anti-curl solution used (amount applied to the recording medium) can be further reduced.
When the content ratio is 5% by mass or more, it is advantageous in that the viscosity of the ink is increased to some extent, and thereby the ejection stability of the ink from the inkjet head can be further improved.

Moreover, in this invention, it is preferable that Formula (2) is SP-i <SP-c.
In this aspect, since the organic solvent in the anti-curl solution has a stronger property of curling the recording medium than the organic solvent in the ink, the curl correcting function of the anti-curl solution is further enhanced. Therefore, the amount of anti-curl solution used (amount applied to the recording medium) can be further reduced.

In the present invention, the curl suppressing effect is more effectively exhibited when the basis weight of the recording medium is 130 g / m ² or less.
More specifically, a recording medium having a basis weight of 130 g / m ² or less tends to curl more easily. In the present invention, the curl suppressing effect can be more effectively exhibited by applying the anti-curl liquid to a recording medium having a basis weight that is more easily curled and is 130 g / m ² or less.

Further, in the present invention, the applying step is more effective in suppressing curl when applying ink and an anti-curl solution to a recording medium conveyed at a conveyance speed of 50 m / min or more (that is, in the case of high-speed image formation). Effectively demonstrated.
From the viewpoint of speeding up image formation, it is preferable that the conveyance speed be higher, and the conveyance speed is more preferably 80 m / min or more, more preferably 100 m / min or more, and even more preferably 150 m / min or more.
The upper limit of the transport speed is not particularly limited, but the upper limit is preferably 350 m / min from the viewpoint of stability when transporting the recording medium.

  Next, the application process, the ink, the anti-curl solution, and other processes (such as a drying process) provided as necessary will be described.

<Granting process>
In the image forming method of the present invention, the ink is applied to at least one surface of the recording medium by an ink jet method, and a specific area on the back surface of the recording medium (specifically, ink is applied to the front surface). An application step of applying the anti-curl solution by an inkjet method to at least a part of the region corresponding to the region.
In this step, either ink or anti-curl application may be applied first. This is because the curling of the recording medium is a phenomenon that occurs when the ink applied to the recording medium is dried (including natural drying).
Therefore, in the present invention, the anti-curl solution may be applied before the recording medium is curled, and the application order of the ink and the anti-curl solution is not particularly limited.

Further, as described above, the ink may be applied to only one side of the recording medium or may be applied to both sides of the recording medium.
In any case, in this step, the recording medium is applied with an organic solvent in an amount satisfying the above formula (1) (1.5 ≦ V−i), that is, contained in the ink on both sides of the recording medium. An amount of ink is applied so that the amount difference (V-i) is 1.5 mL / m ² or more.
When the formula (1) is not satisfied, that is, when V-i is less than 1.5 (mL / m ² ), curling due to application of ink hardly occurs. The effect is not demonstrated.
As V-i is larger, curling is more likely to occur. Therefore, 1.7 or more is preferable, 1.8 or more is more preferable, and 2.0 or more is particularly preferable from the viewpoint that the curl suppressing effect due to application of the anti-curl solution is more effectively exhibited. There is no particular limitation on the upper limit of Vi.

As described above, there is no particular limitation on the application order of the ink and the anti-curl liquid in this step.
Examples of the application order in this step include Examples 1 to 4 below as examples when ink is applied to both surfaces, and Examples 5 to 6 below as examples when ink is applied only to one surface. .
Example 1. Application of ink to the front surface → Application of anti-curl liquid to the back surface → Application of ink to the back surface Example 2 2. Ink application to the front side → Ink application to the back side → Application of anti-curl liquid to the back side Application of anti-curl solution to back side → Application of ink to back side → Application of ink to front side Example 4 4. Application of ink to the back side → Application of anti-curling liquid to the back side → Application of ink to the front surface Application of ink to front side → application of anti-curl liquid to back side Example 6 Applying anti-curl solution to the back side → Applying ink to the front side

In this step, the formula (3) (SP−c × V−c <V−i × SP−i) and the formula (4) (0.25 × V−i ≦ V) are applied to the recording medium regardless of the application order. An amount of anti-curl solution that satisfies -c) is applied.
Formula (4) is preferably 0.30 × V−i ≦ V−c, and 0.50 × V−i ≦ V−c from the viewpoint of more effectively using the curl correcting function by the anti-curl solution. It is more preferable that

  In this step, the method for applying the ink and the anti-curl liquid by the inkjet method is not particularly limited, and a known method such as the method described in paragraphs 0023 to 0060 of JP-A-2006-76129 can be used. Can be used.

  Further, the ink application to the recording medium may be an aspect in which only one color ink is applied to one side of the recording medium, or an aspect in which two or more colors of ink are applied to one side of the recording medium. Good.

Hereinafter, the preferable aspect of application | coating of the ink by the inkjet method in this process is demonstrated.
In addition, although description is abbreviate | omitted, it is the same also about the preferable aspect of provision of the anti-curl liquid by the inkjet method in this process.

The ink application by the ink jet method can be performed by discharging the ink composition onto a desired recording medium by supplying energy. As a preferable image forming method of the present invention, the method described in paragraph Nos. 0093 to 0105 of JP-A No. 2003-306623 can be applied.
The ink jet method is not particularly limited, and a known method, for example, a charge control method in which ink is ejected using electrostatic attraction, and a piezoelectric element that generates mechanical distortion by application of voltage is used to supply ink. Piezo ink-jet method to eject, acoustic ink-jet method to change the electrical signal into an acoustic beam, irradiate the ink and eject the ink using the radiation pressure, and thermal to use the pressure generated by heating the ink to form bubbles Any of an ink jet (bubble jet (registered trademark)) system and the like may be used.
The inkjet method uses a method of ejecting a large number of low-density inks called photo inks in a small volume, a method of improving image quality using a plurality of inks having substantially the same hue and different concentrations, and colorless and transparent inks. The method used is included.

  As the ink jet method in the present invention, a piezo ink jet method is suitable. In the piezo ink jet system, the distortion form of the piezoelectric element may be any of a bending mode, a longitudinal mode, and a shear mode. A known technique can be adopted for the configuration of the piezoelectric element and the structure of the piezo head without particular limitation.

There is no particular limitation on the ink jet head (hereinafter also simply referred to as “head”) used in the ink jet method, and it can be appropriately selected according to the purpose.
The inkjet method applicable to the present invention may be a shuttle system in which a short serial head is used to perform recording while scanning the head in the width direction of the recording medium, but corresponds to the entire area of one side of the recording medium. Thus, a mode in which a line system using a line head in which recording elements are arranged is applied is preferable. In the case of the line method, image recording can be performed on the entire surface of the recording medium by scanning the recording medium in a direction orthogonal to the arrangement direction of the recording elements.

  The amount of ink droplets to be ejected is preferably 0.5 to 6 pL (picoliter), more preferably 1 to 5 pL, and still more preferably 2 to 4 pL from the viewpoint of obtaining a high-definition image.

<Ink>
The ink in the present invention contains a color material, water, and an organic solvent.
Hereinafter, components in the ink will be described.

(water)
The ink in the present invention is a water-based ink containing water.
There is no restriction | limiting in particular in the content rate of the water in an ink, It can set suitably in consideration of the content rate of another component.
The content ratio of water is preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 30% by mass or more with respect to the total amount of ink from the viewpoint of ensuring stability and ejection reliability. More preferably, it is 40% by mass or more, and particularly preferably 50% by mass or more.
The upper limit of the content ratio of water varies depending on the content ratios of other components, but can be 90% by mass, for example.

  The water is preferably water from which ionic impurities such as pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, distilled water or ultrapure water are removed as much as possible. Further, when water sterilized by ultraviolet irradiation or addition of hydrogen peroxide is used, it is preferable in terms of preventing generation of mold and bacteria when the pigment dispersion and the ink composition using the same are stored for a long period of time. .

(Organic solvent)
The ink in the present invention contains an organic solvent.
The organic solvent is composed of at least one organic solvent species (compound).
There is no restriction | limiting in particular as an organic solvent seed | species, A well-known thing can be used. In the present invention, the organic solvent species can be appropriately selected so that at least the above formula (2) is satisfied.

Hereinafter, preferred organic solvent species (compounds) are exemplified. In the following examples, the value in parentheses after the compound name is the SP value (unit: MPa ^1/2 ).
Examples of organic solvent species include glycerin (41.0), 1,2,6-hexanetriol (32.9), trimethylolpropane (32.6), ethylene glycol (36.5), propylene glycol (32). .6), diethylene glycol (30.6), triethylene glycol (27.8), tetraethylene glycol (26.1), pentaethylene glycol (25.0), dipropylene glycol (27.1), tripropylene glycol Glycols such as (25.3), 2-butene-1,4-diol (39.0), 2-ethyl-1,3-hexanediol (25.3), 2-methyl-2,4- Pentanediol (26.8), 1,2-octanediol (25.6), 1,2-hexanediol (27.4), 1,2-pen In addition to polyhydric alcohols such as alkanediols such as diol (28.6) and 4-methyl-1,2-pentanediol (27.1), sugars described in paragraph 0116 of JP2011-42150A And sugar alcohols, hyaluronic acids, alkyl alcohols having 1 to 4 carbon atoms, glycol ethers, and the like. These organic solvents can be used by appropriately selecting one kind or two or more kinds. Polyhydric alcohols are also useful as drying inhibitors and wetting agents, and examples include the examples described in paragraph 0117 of JP-A-2011-42150. Moreover, a polyol compound is preferable as a penetrant, and examples of the aliphatic diol include those described in paragraph 0117 of JP2011-42150A.
Examples of the organic solvent species include the organic solvents described in paragraphs 0036 to 0039 of JP2009-190379A, the organic solvent species described in paragraphs 0176 to 0179 of JP2011-46872A, and the like. The organic solvent species described in paragraphs 0063 to 0074 of Kai 2013-18846 are also included.

  Furthermore, as the organic solvent species, an alkylene oxide adduct of glycerin can also be used. As the alkylene oxide adduct of glycerin, a compound represented by the following structural formula (1) is preferable from the viewpoint of ink permeability to the recording medium.

In Structural Formula (I), l, m, and n each independently represent an integer of 1 or more and satisfy l + m + n = 3-15. When the value of l + m + n is 3 or more, the curl suppressing effect is good, and when it is 15 or less, good discharge properties can be maintained. Especially, l + m + n has the preferable range of 3-12, and the range of 3-10 is more preferable. AO in the structural formula (I) represents ethyleneoxy (sometimes abbreviated as EO) and / or propyleneoxy (sometimes abbreviated as PO), and among them, a propyleneoxy group is preferable. Each AO of (AO) ₁ , (AO) _m , and (AO) _n may be the same or different.

  Examples of the compound represented by the structural formula (I) are shown below. However, the present invention is not limited to these.

_{· NC 4 H 9 O (AO} ) 4 -H
(AO = EO or PO (EO: PO = 1: 1), SP value = 20.1)
_{· NC 4 H 9 O (AO} ) 10 -H
(AO = EO or PO (EO: PO = 1: 1), SP value = 18.8)
・ HO (A'O) ₄₀ -H
(A′O = EO or PO (EO: PO = 1: 3), SP value = 18.7)
・ HO (A''O) ₅₅ -H
(A ″ O = EO or PO (EO: PO = 5: 6), SP value = 18.8)
・ HO (PO) ₃ −H (SP value = 24.7)
HO (PO) ₇ -H (SP value = 21.2)
1,2-hexanediol (SP value = 27.4)
In addition, EO and PO represent an ethyleneoxy group and a propyleneoxy group, respectively.

  As the alkylene oxide adduct of glycerin, a commercially available product may be used. For example, as polyoxypropylated glycerin (ether of polypropylene glycol and glycerin), Sannix GP-250 (average molecular weight 250, SP value = 24.6), GP-400 (average molecular weight 400), GP-600 (Average molecular weight 600) [Sanyo Chemical Industries, Ltd.], Rheocon GP-250 (average molecular weight 250), GP-300 (average molecular weight 300, GP-400 (average molecular weight 400), GP-700 (Average molecular weight 700) [above, manufactured by Lion Corporation], polypropylene triol glycol triol type (average molecular weight 300, average molecular weight 700) [above, manufactured by Wako Pure Chemical Industries, Ltd.] and the like.

A pyrrolidone derivative can also be used as the organic solvent species.
As the pyrrolidone derivative, the compounds described in paragraphs 0047 to 0059 of JP2013-18282A are preferable.
Examples of the pyrrolidone derivative include 2-pyrrolidone (25.9), N-methyl-2-pyrrolidone (23.6), N-ethyl-2-pyrrolidone (22.8), N-butyl-2-pyrrolidone ( 21.7), N-vinyl-2-pyrrolidone, 5-methyl-2-pyrrolidone, N-phenyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone and the like. Among these, 2-pyrrolidone, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone are preferable from the viewpoint of improving the abrasion resistance of the image, and 2-pyrrolidone and N-methyl-2-pyrrolidone are more preferable. 2-Pyrrolidone is preferred, and particularly preferred.

In the present invention, the average SP value (SP-i) of the organic solvent in the ink is preferably 27.5 MPa ^1/2 or less from the viewpoint of further reducing the curl itself of the recording medium due to the application of the ink. .
From the same viewpoint, the SP value of the organic solvent species contained in the ink is preferably 27.5 MPa ^1/2 or less.
From the same viewpoint, 70% by mass or more of the organic solvent in the ink is preferably an organic solvent species of 27.5 MPa ^1/2 or less.
Although there is no particular restriction on the lower limit of the SP-i, from the viewpoint of stability of the ink, SP-i is preferably 15.0 MPa ^1/2 or more, 20.0 MPa ^1/2 or more is more preferable.

  The preferred range of the content ratio of the organic solvent in the ink (total amount of all organic solvent species) is as described above.

(Coloring material)
The ink in the present invention contains at least one coloring material.
As the color material, pigments, dyes, and the like are preferable, and among these, pigments are preferable from the viewpoint of fastness (for example, light resistance).

-Pigment-
The pigment is not particularly limited and can be appropriately selected depending on the purpose. For example, the pigment may be either an organic pigment or an inorganic pigment.
Examples of the organic pigment include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Among these, azo pigments and polycyclic pigments are more preferable. Examples of the azo pigments include azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments. Examples of the polycyclic pigment include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments. Examples of the dye chelates include basic dye chelates and acidic dye chelates.
Examples of the inorganic pigment include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Among these, carbon black is particularly preferable. In addition, as said carbon black, what was manufactured by well-known methods, such as a contact method, a furnace method, and a thermal method, is mentioned, for example.

Coloring materials (preferably pigments) may be used singly or in combination of a plurality of types selected from each group or between groups.
The content ratio of the color material (preferably pigment) in the ink is 0.1% by mass to 15% by mass with respect to the total amount of the ink from the viewpoint of color density, granularity, ink stability, and ejection reliability. Preferably, 0.5 mass%-12 mass% are more preferable, and 1 mass%-10 mass% are especially preferable.

As the pigment, a water dispersible pigment can be used.
Regarding specific examples of the water-dispersible pigment, reference can be made to the descriptions in paragraphs 0026 to 0032 of JP2013-18282A.
In addition, as the pigment in the present invention, a resin-coated pigment in which at least a part of the pigment surface is coated with a crosslinked polymer obtained by crosslinking a water-soluble resin with a crosslinking agent can also be used. Regarding the resin-coated pigment, the descriptions in paragraphs 0036 to 0045 and 0090 to 0093 of JP2013-18282A can be appropriately referred to.

-Pigment dispersant-
When the ink in the present invention contains a pigment as a coloring material, it may further contain a pigment dispersant. Thereby, the dispersion | distribution stabilization after dispersion | distribution after the dispersion | distribution of a pigment can be achieved.
As the pigment dispersant, for example, the dispersants described in paragraphs 0033 to 0035 of JP2013-18182A, paragraphs 0057 to 0064 of JP2013-18948A, and the like can be used.
As the pigment dispersant, a polymer dispersant is preferable, and a styrene- (meth) acrylic acid copolymer, a styrene- (meth) acrylic acid- (meth) acrylic acid ester copolymer, a (meth) acrylic acid ester- (meta ) Acrylic acid copolymer, polyethylene glycol (meth) acrylate- (meth) acrylic acid copolymer, styrene-maleic acid copolymer are more preferred, and (meth) acrylic acid ester- (meth) acrylic acid copolymer is more preferred. Further preferred.
Among them, benzyl (meth) acrylate- (meth) acrylic acid-methyl (meth) acrylate terpolymer is particularly preferable.
Here, (meth) acrylic acid refers to acrylic acid or methacrylic acid, and (meth) acrylate refers to acrylate or methacrylate.

The weight average molecular weight of the pigment dispersant is preferably 2,000 to 200,000, more preferably 3,000 to 100,000, still more preferably 5,000 to 80,000, particularly preferably 10,000 to 60,000. 000.
The amount of the pigment dispersant is preferably 10% by mass to 100% by mass, more preferably 20% by mass to 70% by mass, and particularly preferably 40% by mass to 60% by mass with respect to the pigment.

(Surfactant)
The ink in the present invention can contain at least one surfactant.
Thereby, the surface tension of the ink can be adjusted more effectively.
There is no restriction | limiting in particular as surfactant, It can select from well-known surfactant suitably and can be used.
As the surfactant, an acetylene glycol surfactant is preferable.
The acetylene glycol-based surfactant is easy to keep the surface tension and the interfacial tension between the ink jet head member (head nozzle and the like) in contact with the ink and the foaming less likely to occur than other surfactants. For this reason, when the ink contains an acetylene glycol surfactant, the ejection stability of the ink is enhanced. Further, when the ink contains an acetylene glycol surfactant, the wettability and penetrability with respect to the recording medium are improved, and the uneven density and bleeding of the ink are suppressed. This is advantageous for fine image formation.

  Examples of the acetylene glycol surfactant include Surfynol 104, 104E, 104H, 104A, 104BC, 104DPM, 104PA, 104PG-50, 104S, 420, 440, 465, 485, 2520, SE, SE-F, 504, 61, DF37, DF110D, CT111, CT121, CT131, CT136, TG, GA (all above, Air Products and Chemicals. Inc.), Olfin B, Y, P, A, STG, SPC, E1004, E1006, E1008, E1010, PD-001, PD-002W, PD-003, PD-004, EXP. 4001, the same EXP. 4036, EXP. 4051, AF-103, AF-104, AK-02, SK-14, SK-3, AE-3 (all of which are manufactured by Nissin Chemical Industry Co., Ltd.), acetylenol E00, E00P, E40, E100 (all of which are manufactured by Kawaken Fine Chemical Co., Ltd.) and the like.

When the ink in the present invention contains a surfactant, the surfactant contained may be only one type or two or more types.
When the ink of the present invention contains a surfactant, the content can be appropriately selected in consideration of the surface tension of the ink, but is preferably 0.1% by mass to 2% by mass, and more preferably 0.1% by mass to 1%. 0.5% by mass is more preferable, and 0.2% by mass to 1% by mass is particularly preferable.

(Other ingredients)
The ink in the present invention may contain resin particles (polymer particles).
As the resin particles, known resin particles described in paragraphs 0071 to 0077 of JP2013-18282A, paragraphs 0068 to 0103 of JP2013-18948A, and the like can be used.
Furthermore, in addition to the above-described components, the ink according to the present invention may contain additives such as a penetrating solvent, a moisturizer, an antiseptic, an antifungal agent, a pH adjuster, and a chelating agent as necessary. Can be contained. For details of these additives, the description in paragraphs 0067 to 0076 of JP-A-2010-90266 can be appropriately referred to.

Further, the viscosity of the ink in the present invention is not particularly limited, but the viscosity at a liquid temperature of 30 ° C. is preferably 3 mPa · s to 14 mPa · s from the viewpoint of ejection stability from an inkjet head, and 3 mPa · s. 10 mPa · s is more preferable, 3 mPa · s to 8 mPa · s is further preferable, and 4 mPa · s to 7 mPa · s is particularly preferable.
The viscosity of the ink here refers to a value measured under a temperature condition of 30 ° C. using VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD).
The surface tension of the ink of the present invention is not particularly limited, but is preferably 20 mN / m to 40 mN / m, more preferably 30 mN / m to 38 mN / m, and particularly preferably 35 mN / m to 37 mN / m. m.
The surface tension of the ink here refers to a value measured at 25 ° C. by a plate method using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

<Anti-curling solution>
The anti-curl solution in the present invention contains water and an organic solvent, and the content ratio of the coloring material is less than 0.1% by mass with respect to the total amount of the anti-curl solution.
Here, the content ratio of the color material with respect to the total amount of the anti-curl solution being less than 0.1% by mass with respect to the total amount of the anti-curl solution means that the anti-curl solution does not substantially contain the color material. Thereby, the influence on the colored image by the ink can be reduced.

(water)
The anti-curl liquid in the present invention is also an aqueous liquid containing water, like the ink.
There is no restriction | limiting in particular in the content rate of the water in an anti-curl liquid, It can set suitably in consideration of the content rate of another component.
The content ratio of water is preferably 10% by mass or more, and more preferably 20% by mass or more, based on the total amount of the anti-curl solution, from the viewpoint of ensuring stability and ejection reliability.
The upper limit of the content ratio of water varies depending on the content ratios of other components, but can be, for example, 90% by mass, and preferably 80% by mass with respect to the total amount of the anti-curl solution.

(Organic solvent)
The anti-curl solution in the present invention contains an organic solvent (that is, at least one organic solvent species).
There is no restriction | limiting in particular as an organic solvent seed | species, A well-known thing can be used. In the present invention, the organic solvent species can be appropriately selected so that the above formula (2) is satisfied.
As the organic solvent (organic solvent species) in the anti-curl solution, for example, the same organic solvent (organic solvent species) in the ink can be used.

  The preferred volume average SP value (SP-c) of the organic solvent in the anti-curl solution, the preferred range of the organic solvent species contained in the anti-curl solution, and the preferred content ratio of the organic solvent in the anti-curl solution are respectively described above. It is as follows.

(Surfactant)
The anti-curl solution in the present invention can contain at least one surfactant.
The surfactant is not particularly limited and may be appropriately selected from known surfactants, but acetylene glycol surfactants are preferred for the same reason as in the case of ink.
Preferred examples of the acetylene glycol surfactant that can be contained in the anti-curl solution are the same as the preferred examples of the acetylene glycol surfactant that can be contained in the ink.

When the anti-curl solution in the present invention contains a surfactant, the contained surfactant may be only one kind or two or more kinds.
When the anti-curl solution in the present invention contains a surfactant, the content thereof can be appropriately selected in consideration of the surface tension of the anti-curl solution and the like, but is preferably 0.1% by mass to 2% by mass. 1 mass%-1.5 mass% are more preferable, and 0.2 mass%-1 mass% are especially preferable.

(Other ingredients)
The anti-curl solution in the present invention may contain other components other than those described above.
Examples of other components that can be contained in the anti-curl solution include the same components as those that can be contained in the ink described above.
However, from the viewpoint of more effectively expressing the function of the anti-curl solution, the total content ratio of water and the organic solvent in the anti-curl solution is 80% by mass or more based on the total amount of the anti-curl solution. Is preferable, more preferably 90% by mass or more, still more preferably 98% by mass or more, and particularly preferably 99% by mass or more.

<Recording medium>
The recording medium to which the ink and the anti-curl liquid are applied in the applying step is not particularly limited, and may be either plain paper or inkjet special paper.
As described above, when a recording medium having a basis weight of 130 g / m ² or less is used, the curl suppressing effect according to the present invention is more effectively exhibited.

Further, the image forming method of the present invention may have other steps other than the applying step.
Hereinafter, other steps provided as necessary will be described.

<Drying process>
The image forming method of the present invention may further include a drying step of drying the ink and the anti-curl liquid applied to the recording medium.
This aspect is advantageous from the viewpoint of speeding up image formation.

A preferable form of drying in this step is heat drying.
Heating and drying can be performed by known heating means such as a heater, air blowing means using air blowing such as a dryer, or a combination of these.
As a heating method, for example, a method in which heat is applied by a heater or the like from the ink application surface of the recording medium and the opposite side (specifically, for example, warm air is applied to the ink application surface and the opposite of the ink application surface) The surface is heated with a heater drum), the method of applying warm air or hot air to the ink application surface of the recording medium, and the heating method using an infrared heater. As a heating method, you may heat combining these two or more.

  There is no restriction | limiting in particular as temperature at the time of heat drying, What is necessary is just to select the temperature range which can be dried. For example, the recording medium may be heated so that the temperature of the recording medium is 40 to 80 ° C. by air blowing, or may be dried so that the temperature of the recording medium is 40 to 80 ° C. by contacting with a drying drum of 50 to 110 ° C. . These may be used in combination and dried.

<Cooling process>
The image forming method of the present invention may include a cooling step of cooling the recording medium after heating and drying once in the drying step.
As a cooling method, any method may be used as long as it can actively lower the temperature of the recording medium. Examples of the cooling method include a method of passing a recording medium through a cooling zone, a method of applying cold air to the recording medium, and a method of bringing the recording medium into contact with a cooled object.

<Heat fixing process>
The image forming method of the present invention may further include a heat fixing step of heat fixing the ink on the recording medium after the applying step, if necessary.
In the heat fixing step, the image formed by applying the ink is heated and fixed on the recording medium. The image on the recording medium is fixed by the heat fixing process, and the scratch resistance of the image can be further improved.

Heat fixing may be performed under pressure.
When heat fixing is performed under pressure, the pressure during pressing is preferably in the range of 0.1 to 3.0 MPa in terms of surface smoothing.
Further, when the ink contains resin particles, the heating is preferably performed at a temperature equal to or higher than the minimum film-forming temperature (MFT) of the resin particles in the image. By heating to MFT or higher, the resin particles become a film and the image is enhanced.

  The heating method is not particularly limited, but a non-contact drying method such as a method of heating with a heating element such as a nichrome wire heater, a method of supplying warm air or hot air, a method of heating with a halogen lamp, an infrared lamp or the like. Preferably, it can be mentioned. The heating and pressing method is not particularly limited. For example, a method of pressing a hot plate against the image forming surface of a recording medium, a pair of heating and pressing rollers, a pair of heating and pressing belts, or a recording medium Using a heating and pressing device equipped with a heating and pressing belt arranged on the image recording surface side and a holding roller arranged on the opposite side, heat fixing by bringing them into contact, such as a method of passing a pair of rollers, etc. The method of performing is mentioned suitably.

<Cutting process>
The image forming method of the present invention may include a cutting step of cutting a recording medium on which an image is formed. When the image forming method of the present invention includes at least one of a drying step, a cooling step, and a heat fixing step, the cutting step is preferably provided after the at least one step.
For example, when an image is formed with tension applied to the recording medium, the curling of the recording medium often occurs after the recording medium is cut.
Also, when forming an image by applying ink, it is desirable to form an image leaving a margin at the edge of the recording medium from the viewpoint of preventing contamination of the image forming apparatus. When an image is formed with a margin at the end of the recording medium, the margin of the recording medium is often less likely to occur due to the margin. However, when the margin is cut off by cutting after image formation, the recording medium is easily curled.
Due to the above circumstances, when the image forming method of the present invention includes a cutting step, the effect of curling the recording medium is more effectively exhibited.
Cutting in this step can be performed by a normal method using a cutter or the like.

<Image forming apparatus>
The image forming method of the present invention is capable of applying ink to at least one surface of a recording medium based on image data, and provides an anti-curl liquid on the surface having a smaller amount of organic solvent contained in the ink of the recording medium. There is no particular limitation as long as it is an image forming apparatus having a configuration capable of imparting image quality, and publicly known images described in JP 2008-188877 A, JP 2008-188878 A, JP 2006-76129 A, and the like. A forming apparatus (inkjet recording apparatus) can be used.

Hereinafter, an example of an image forming apparatus suitable for the image forming method of the present invention will be described with reference to FIG. 1, but the present invention is not limited to the following example.
FIG. 1 is a schematic configuration diagram conceptually showing an example (ink jet recording apparatus 100) of an image forming apparatus suitable for the image forming method of the present invention.
As shown in FIG. 1, the ink jet recording apparatus 100 is configured so that the first recording medium 10 is sequentially moved along the transport direction (arrow direction in the drawing) of the recording medium 10 that is fed from the paper feeding unit and continuously transported. A first ink discharge portion 22 that discharges ink of each color onto the surface 10A, a first anti-curl liquid discharge head 20 that discharges anti-curl liquid onto the first surface 10A, and ink applied to the first surface 10A And a first drying section 24 that dries at least one of the anti-curl liquid, a second ink ejection section 32 that ejects ink of each color onto a second surface 10B that is the opposite surface of the first surface 10A, and a second ink ejection section 32. A second anti-curl discharge head 30 that discharges the anti-curl liquid onto the surface 10B, and a second drying unit 34 that dries at least one of the ink and the anti-curl liquid applied to the second surface 10B are provided. ing. The recording medium 10 that has passed through the second drying unit 34 is discharged to the discharge unit.

The ink jet recording apparatus 100 is provided with transport rollers 12 and 14 for transporting the recording medium 10.
In the inkjet recording apparatus 100, the first surface 10 </ b> A of the recording medium 10 faces the first ink discharge unit 22 and the first anti-curl liquid discharge head 20 on the upstream side in the transport direction as viewed from the transport rollers 12 and 14. On the downstream side in the transport direction as viewed from the transport rollers 12 and 14 (hereinafter, also simply referred to as “downstream side”), the second surface 10B of the recording medium 10 includes the second ink discharge section 32 and the second anti-curl liquid discharge head. 30.
Thereby, the ink and the anti-curl liquid can be applied to both surfaces of the recording medium 10.
However, the anti-curl liquid is preferably ejected from only one of the first anti-curl liquid ejection head 20 and the second anti-curl liquid ejection head 30. Specifically, it is preferable that the anti-curl liquid is ejected only on the surface where the amount of the organic solvent contained in the ink of the recording medium 10 is smaller.
In addition, the ink does not necessarily have to be ejected from both the first ink ejection unit 22 and the second ink ejection unit 32. When a color image is formed only on one side, ink is ejected from only one of the first ink ejection unit 22 and the second ink ejection unit 32.

Needless to say, the inkjet recording apparatus 100 may be provided with conveyance rollers other than the conveyance rollers 12 and 14.
For example, a long recording medium is used as the recording medium 10. Normally, the recording medium is conveyed in the direction of the arrow in a state where tension is applied to the long recording medium.
As a modification of the ink jet recording apparatus 100, the recording medium 10 may be replaced with a conveyance belt, a recording medium cut in advance may be adsorbed on the conveyance belt, and the recording medium may be conveyed by conveyance of the conveyance belt.

  The first ink discharge section 22 includes ink discharge heads 22K and 22C connected to each of the ink storage sections that store black (K), cyan (C), magenta (M), and yellow (Y) color inks. 22M and 22Y are arranged. Each ink storage unit (not shown) stores ink of each color, and is supplied to each of the ink ejection heads 22K, 22C, 22M, and 22Y as necessary when recording an image.

  The ink ejection heads 22K, 22C, 22M, and 22M eject ink from ejection nozzles that are arranged to face the first surface 10A of the recording paper 10, respectively. Ink ejection is performed based on image data transmitted from a control unit (not shown). Thereby, each color ink is applied on the first surface 10A, and a desired colored image is recorded.

Each of the ink ejection heads 22K, 22C, 22M, and 22Y is a full line head in which a large number of ejection ports (nozzles) are arranged over the maximum recording width (maximum recording width) of an image recorded on the recording medium. It has become.
A full-line head records images on a recording medium at a higher speed than a short shuttle head that performs recording while reciprocally scanning in the width direction of the recording medium (direction perpendicular to the conveying direction on the recording medium conveying surface). Can do.

A first anti-curl discharge head 20 connected to an anti-curl storage unit that stores the anti-curl solution is disposed downstream of the first ink discharge unit 22. An anti-curl liquid storage unit (not shown) stores an anti-curl liquid, and is supplied to the first anti-curl liquid discharge head 20 as necessary.
The first anti-curl discharge head 20 performs recording as needed (particularly when the amount of the organic solvent contained in the ink is larger on the second surface 10B than on the first surface 10A). An anti-curl liquid is discharged from a discharge nozzle disposed opposite to the first surface 10A of the paper 10.

A first drying unit 24 is disposed downstream of the first anti-curl discharge head 20.
Although the configuration of the first drying unit 24 is not illustrated, for example, the second surface 10B is heated while applying warm air to the first surface 10A to which liquid (at least one of ink and anti-curl liquid) is applied. It is configured to be heated by a drum. However, other than this configuration, a configuration in which warm air or hot air is applied to the ink application surface, or a configuration in which heating is performed by an infrared heater may be used.
In the first drying unit 24, the liquid applied to the first surface 10A is dried. Thereby, the liquid is suppressed from adhering to the downstream side of the first drying unit 24 of the inkjet recording apparatus 10.

A second ink ejection unit 32 is disposed on the downstream side of the first drying unit 24.
In the second ink discharge section 32, ink discharge heads 32K, 32C, 32M, and 32M are arranged.
Further, a second anti-curl discharge head 30 is disposed on the downstream side of the second ink discharge portion 32.
The ink discharge heads 32K, 32C, 32M, and 32M and the second anti-curl liquid discharge head 30 are configured for ink discharge except that their discharge surfaces are opposed to the second surface 10B. The configurations of the heads 22K, 22C, 22M, and 22M and the first anti-curl discharge head 20 are the same.

  Here, the ink ejection heads 22K, 22C, 22M, 22Y, 32K, 32C, 32M, and 32Y, and the first anti-curl liquid ejection head 20 and the second anti-curl liquid ejection head 30 are all the same. It has a structure.

A second drying unit 34 is disposed on the downstream side of the second anti-curl discharge head 30.
Although the configuration of the second drying unit 34 is not illustrated, for example, the temperature is applied to the second surface 10B to which the liquid is applied by at least one of the second ink discharge unit 32 and the second anti-curl liquid discharge head 30. The first surface 10A is heated by a heater drum while wind is applied. However, other than this configuration, a configuration in which warm air or hot air is applied to the ink application surface, or a configuration in which heating is performed by an infrared heater may be used.
In the second drying unit 34, the liquid (at least one of ink and anti-curl liquid) applied to the second surface 10B is dried. This suppresses the liquid from adhering to the downstream side of the second drying unit 34 of the inkjet recording apparatus 10.

A discharge unit is provided on the downstream side of the second drying unit 34.
Although not shown, a cutter for cutting the recording medium is usually provided on the downstream side of the discharge unit. The curling of the recording medium often occurs after the cutting of the recording medium.

In the inkjet recording apparatus 100, for example, the first surface 10A has a larger amount of organic solvent contained in the ink than the second surface 10B (ink is applied only to the first surface 10A). In other cases, the anti-curl solution is not ejected from the first anti-curl solution ejection head 20, and the anti-curl solution is ejected only from the second anti-curl solution ejection head 30.
In addition, for example, when the second surface 10B has a larger amount of the organic solvent contained in the ink than the first surface 10A (including the case where the ink is applied only to the second surface 10B). In this case, the anti-curl solution is not discharged from the second anti-curl solution discharge head 30, and the anti-curl solution is discharged only from the first anti-curl solution discharge head 20.
In any case, the curling of the recording medium due to the application of ink to the front surface is corrected by applying the anti-curling liquid to the back surface, and finally the curling of the recording medium is suppressed.

As a modification of the ink jet recording apparatus 100, the first anti-curl discharge head 20 and the second ink discharge unit 32 are omitted, or the second anti-curl discharge head 30 and the first ink discharge. An example in which the part 22 is omitted is given.
When ink is applied only to one side of the recording medium, the same curling suppression effect as that of the inkjet recording apparatus 100 can be obtained even in these modified examples.
Further, by adding a mechanism for transporting the recording medium in the direction opposite to the direction of the arrow and a mechanism for reversing the front and back of the recording medium to the ink jet recording apparatus 100, the recording medium is provided with the first ink ejection unit 22, By allowing the first anti-curl liquid discharge head 20 and the first drying unit 24 to pass twice, the second ink discharge part 32, the second anti-curl liquid discharge head 30, and the second The drying unit 34 can be omitted.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. Unless otherwise specified, “part” and “%” are based on mass.

[Example 1]
<Synthesis of Polymer Dispersant P-1>
According to the following scheme, a polymer dispersant P-1 was synthesized as shown below.

To a 1000 ml three-necked flask equipped with a stirrer and a condenser tube, 88 g of methyl ethyl ketone was added and heated to 72 ° C. in a nitrogen atmosphere. Here, 50 g of methyl ethyl ketone, 0.85 g of dimethyl 2,2′-azobisisobutyrate, 60 g of benzyl methacrylate Then, a solution in which 10 g of methacrylic acid and 30 g of methyl methacrylate were dissolved was dropped over 3 hours. After completion of the dropwise addition, the reaction was further continued for 1 hour, and then a solution of 0.42 g of dimethyl 2,2′-azobisisobutyrate in 2 g of methyl ethyl ketone was added, heated to 78 ° C. and heated for 4 hours. The obtained reaction solution was reprecipitated twice in a large excess amount of hexane, and the precipitated polymer was dried to obtain 96 g of polymer dispersant P-1. In addition, the number of each structural unit of the polymer dispersant P-1 shown above represents a mass ratio.
The composition of the obtained polymer dispersant P-1 was confirmed by ¹ H-NMR. The polymer dispersant P-1 had a weight average molecular weight (Mw) determined by GPC of 44,600. Furthermore, when the acid value was calculated | required by the method as described in JIS specification (JISK0070: 1992), it was 65.2 mgKOH / g.

<Preparation of pigment dispersion>
(Preparation of cyan dispersion)
Pigment Blue 15: 3 (phthalocyanine blu-A220, manufactured by Dainichi Seika Co., Ltd.) which is a cyan pigment, 5 parts of the above polymer dispersant P-1, 42 parts of methyl ethyl ketone, 1N aqueous NaOH solution5. 5 parts and 87.2 parts of ion-exchanged water were mixed and dispersed with a bead mill using 0.1 mmφ zirconia beads for 2 to 6 hours.
After removing methyl ethyl ketone at 55 ° C. under reduced pressure and further removing a part of the water under reduced pressure, using a high-speed centrifugal cooler 7550 (manufactured by Kubota Seisakusho), using a 50 mL centrifuge tube, Centrifugation was performed at 8000 rpm for 30 minutes, and the supernatant liquid other than the precipitate was collected. Thereafter, the pigment concentration was determined from the absorbance spectrum, and a dispersion (cyan dispersion C) of resin-coated pigment particles (pigment coated with a polymer dispersant) having a pigment concentration of 10.2% by mass was obtained.

(Preparation of magenta dispersion)
Preparation of cyan dispersion was the same as the preparation of cyan dispersion except that Pigment Red 122, which is a magenta pigment, was used instead of Pigment Blue 15: 3 (Phthalocyanine-A220, manufactured by Dainichi Seika Co., Ltd.). Thus, a dispersion (magenta dispersion M) of resin-coated pigment particles (pigment coated with a polymer dispersant) was prepared.

(Preparation of yellow dispersion)
Resin-coated pigment was prepared in the same manner as in the preparation of the cyan dispersion, except that Pigment Yellow 74, which is a yellow pigment, was used instead of Pigment Blue 15: 3 (Phthalocyaniburu-A220, manufactured by Dainichi Seika Co., Ltd.). A dispersion (yellow dispersion Y) of particles (pigment coated with polymer dispersant) was prepared.

(Preparation of black dispersion)
In the preparation of the cyan dispersion, carbon black (NIPEX 160-IQ, manufactured by Degussa), which is a black pigment, was used instead of Pigment Blue 15: 3 (Phthalocyanine-A220, manufactured by Dainichi Seika Co., Ltd.) A dispersion (black dispersion K) of resin-coated pigment particles (pigment coated with a polymer dispersant) was prepared in the same manner.

<Preparation of ink and anti-curl solution>
Using each of the pigment dispersions obtained above, the respective components were mixed so as to have the composition of each ink (cyan ink, black ink, magenta ink, and yellow ink) shown in Table 1 below. Cyan ink, black ink, magenta ink, and yellow ink were respectively prepared by filtering with a plastic disposable syringe through a PVDF 5 μm filter (Millex SV, Millipore, diameter 25 mm).
Moreover, each component was mixed so that it might become a composition of the curl prevention liquid shown in following Table 1, and the curl prevention liquid c-1 was obtained.
In Table 1, “Olfin E1010” is a nonionic surfactant (acetylene glycol surfactant) manufactured by Nissin Chemical Industry Co., Ltd.

<Image formation>
Using a remodeling machine of DYMATICS Material Printer DMP-2831 (inkjet printer) manufactured by FUJIFILM Daimatics Co., Ltd., the ink of each color and the anti-curl liquid are sequentially loaded in the cartridge, and the recording medium is conveyed at a conveyance speed of 100 m / The following image formation was carried out while being conveyed at min.
In this image formation, a 10 pL ejection cartridge (DMC-11610) was used as the cartridge. Further, DMP-2831 was modified so that liquid could be supplied to the cartridge from the outside and an image could be formed while the recording medium was conveyed at a conveyance speed of 100 m / min.
As the recording medium, Npi Form NEXT-IJ 70 (basis weight 80.4 to 86.4 g / m ² ) manufactured by Nippon Paper Industries Co., Ltd. was used as an inkjet dedicated paper.
The size of the recording medium was B3 size (515 mm × 364 mm).

The image formation was performed assuming an image in which curling is likely to occur.
Details of image formation were as follows.
A four-color solid image was formed by superimposing and applying four-color inks to a half area of one side (front surface) of the recording medium. No image was formed on the remaining half of the front surface.
At this time, the total applied amount of the four colors of ink on the front surface was 12.28 mL / m ² . Since the content ratio of the organic solvent in the ink is 20% by mass, the above-described Vi (difference in the amount of the organic solvent contained in the ink on both sides) is 2.46 mL / as shown in Table 2 below. the m ^2.
No ink was applied to the back surface (the surface opposite to the surface on which the four-color solid image was formed) of the recording medium (the total amount of ink applied to the back surface was 0 mL / m ² ).
Further, an anti-curl solution was applied to the area corresponding to the four-color solid image on the back surface of the recording medium. In other words, the position where the anti-curl solution is applied to the back surface of the recording medium (image by the anti-curl solution) is a mirror image of a four-color solid image on the front surface of the recording medium.
At this time, the total application amount of the anti-curl solution on the back surface was 6.14 mL / m ² . Since the content ratio of the organic solvent in the anti-curl solution is 37% by mass, the above-described Vc (amount of the organic solvent contained in the anti-curl solution) is 2.27 mL / m as shown in Table 2 below. ² .

<Evaluation of curls>
The recording medium after the image formation was cut into a size of 254 × 127 mm to obtain a curl evaluation sample. At this time, the curl evaluation sample was cut so that the entire area of one side of the curl evaluation sample was a four-color black solid image.
This sample for curl evaluation was left for 24 hours under conditions of a temperature of 25 ° C. and a humidity of 55% RH.
The curl state of the sample for curl evaluation after being left standing was subjected to sensory evaluation according to the following evaluation criteria by five evaluators.
Subsequently, the average score of the evaluation results by the five evaluators was calculated, and the final score was obtained by rounding off the decimal point of the obtained average score.
The final evaluation results are shown in Table 1 below.

-Evaluation criteria-
5: The curl was almost unrecognizable and could be used without any problem.
4: The curl was at a level that could be recognized slightly, and could be used without any problem.
3: A level at which curl can be recognized, but in a practically acceptable range.
2: It was a level at which curl can be recognized and has a quality that hinders practical use.
1: A level at which curl can be clearly recognized, and a quality that impedes practical use.

[Examples 2 to 9, Comparative Examples 1 to 6]
Implemented except that the type of organic solvent in each ink and the content ratio in each ink, and the type of organic solvent in the anti-curl solution and the content ratio in the anti-curl solution were changed as shown in Table 2 below. The same operation as in Example 1 was performed, and the same evaluation as in Example 1 was performed.
The evaluation results are shown in Table 2 below.
In each example, the type of the organic solvent in the ink and the content ratio in the ink were the same among the four colors of ink (this is also the same as in Example 1).

Only in Examples 7 and 8, the total application amount of the anti-curl solution on the back surface was changed. The total application amount of curl preventing liquid in the back side, and 2.50 mL / ^{m 2} in Example 7, was 2.00 mL / ^{m 2} in Example 8.
In Example 9, a mixed solvent of glycerin and GP250 (Sanix GP-250 manufactured by Sanyo Chemical Industries, Ltd.) was used as the organic solvent in the ink.
In Comparative Examples 1 to 3 and 6, no anti-curl solution was used.

[Examples 10 and 11, Comparative Example 7]
In Example 6, the same operation as in Example 6 was performed except that Vc was changed as shown in Table 2 below by changing the application amount of the anti-curl solution, and the same evaluation as in Example 6 was performed. Went.
The evaluation results are shown in Table 2 below.

-Description of Table 2 below-
The numerical value in the Vi column indicates the total amount of organic solvent applied in the four color inks.
-The number in parentheses after the organic solvent name represents the SP value of the organic solvent.
-The unit of SP value (including SP-i and SP-c) is MPa ^1/2 .
-GP250 is Sanyox GP-250 made by Sanyo Chemical Industries.
-SP-i in Example 9 was calculated based on the density of glycerol (1.261 g / cm ³ ) and GP250 (1.088 g / cm ³ ).

As shown in Table 2, in Examples 1 to 11 satisfying the following formulas (1) to (4), curling was remarkably suppressed.
Formula (1): 1.5 <= V-i
Formula (2): SP-i ≦ SP-c
Formula (3): SP-c * V-c <V-i * SP-i
Formula (4): 0.25 × V−i ≦ V−c

In contrast, Comparative Examples 1 to 3 and 6 that did not use the anti-curl solution, Comparative Example 4 that does not satisfy Expression (2), Comparative Example 5 that does not satisfy Expression (3), and Comparison that does not satisfy Expression (4) In Example 7, significant curling occurred.
Among these, in the comparative example 5, since Vc is too large, curl in the direction opposite to the direction of curl due to ink application (reverse curl) occurred.
In Comparative Example 1, when the ink application amount is reduced so that Vi is less than 1.5, curling of the recording medium is hardly recognized.

[Examples 1B to 11B and Comparative Examples 1B to 7B]
As Examples 1B to 11B and Comparative Examples 1B to 7B, Npi Foam NEXT-IJ 70, which is an inkjet-dedicated paper, is used as Npi Foam 70 (basis weight 80.4-86.4 g / m), which is plain paper. Except having changed to ² ), operation similar to Examples 1-11 and Comparative Examples 1-7 was performed, and Example 1-11 and Comparative Examples 1-7 were evaluated. As a result, the curl evaluation was exactly the same as in Examples 1-11 and Comparative Examples 1-7.

[Example 1C, Example 1D, Example 1E]
In Example 1, Npi Form NEXT-IJ 70 was replaced with Npi Form NEXT-IJ 55 (basis weight 63 to 72 g / m ² ) (Example 1C) manufactured by Nippon Paper Industries Co., Ltd., Npi Form NEXT-IJ manufactured by Nippon Paper Industries Co., Ltd. 90 (basis weight 102.7 to 110.7 g / m ² ) (Example 1D), or Npi Foam NEXT-IJ 110 (basis weight 125.9 to 133.9 g / m ² ) manufactured by Nippon Paper Industries Co., Ltd. (Example) The same operation as in Example 1 was performed except that it was changed to 1E), and the same evaluation as in Example 1 was performed.
As a result, the curl suppressing effect was confirmed in any of Example 1C, Example 1D, and Example 1E.
In comparison with Example 1, the curl suppression effect was more effectively exhibited as the basis weight decreased with Example 1E, Example 1D, Example 1, and Example 1C.

DESCRIPTION OF SYMBOLS 10 ... Recording medium 10A ... 1st surface 10B of a recording medium ... 2nd surface 22 of a recording medium ... 1st ink discharge part 20 ... For 1st anti-curl liquid discharge Head 24... First drying section 32... Second ink ejection section 30... Second anti-curl liquid ejection head 34... Second drying sections 22 K, 22 C, 22 M, 22 Y, 32K, 32C, 32M, 32Y ... ink ejection head

Claims (12)

An ink containing a coloring material, water, and an organic solvent is applied to at least one surface of the recording medium by an ink jet method, and the recording medium contains water and an organic solvent, and the content ratio of the coloring material is 0.00. Having an application step of applying an anti-curl solution of less than 1% by mass by an inkjet method;
Of the two surfaces of the recording medium, the surface having the larger amount of organic solvent contained in the ink is the front surface, and the surface having the smaller amount of organic solvent contained in the ink is the back surface. When the application step, the anti-curl liquid is applied to at least a part of the area corresponding to the area where the ink is applied to the front surface of the back surface of the recording medium,
The difference in the applied amount of the organic solvent contained in the ink on both sides of the recording medium is Vi (mL / m ² ), and the applied amount of the organic solvent contained in the anti-curl solution is Vc (mL). / M ² ), the volume average SP value of the organic solvent contained in the ink is SP-i (MPa ^1/2 ), and the volume average SP value of the organic solvent contained in the anti-curl solution is SP-c (MPa). ^1/2 ), an image forming method satisfying the following formula (1) to the following formula (4).
Formula (1): 1.5 <= V-i
Formula (2): SP-i ≦ SP-c
Formula (3): SP-c * V-c <V-i * SP-i
Formula (4): 0.25 × V−i ≦ V−c   The image forming method according to claim 1, wherein a content ratio of the organic solvent in the anti-curl liquid on a mass basis is higher than a content ratio on the mass basis of the organic solvent in the ink.   The content ratio on a mass basis of the organic solvent in the anti-curl solution is 1.2 times or more of a content basis on a mass basis of the organic solvent in the ink. Image forming method. The image forming method according to claim 1, wherein the SP-c is 27.0 MPa ^1/2 or more.   The organic solvent in the anti-curl solution is at least one selected from the group consisting of glycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and dipropylene glycol. 2. The image forming method according to item 1.   The image forming method according to claim 1, wherein a content ratio of the organic solvent in the anti-curl solution is 10% by mass to 80% by mass.   The image forming method according to claim 1, wherein a content ratio of the organic solvent in the ink is 5% by mass to 40% by mass.   The image forming method according to claim 1, wherein the formula (2) is SP−i <SP−c. The image forming method according to claim 1, wherein a basis weight of the recording medium is 130 g / m ² or less.   10. The image forming method according to claim 1, wherein in the applying step, the ink and the anti-curl liquid are applied to the recording medium transported at a transport speed of 50 m / min or more.   The said application | coating process provides the said anti-curl liquid to the whole area | region corresponding to the area | region where the said ink is provided to the front surface among the back surfaces of the said recording medium. The image forming method according to item. The image forming method according to claim 1, wherein the organic solvent contained in the ink is a compound represented by the following structural formula (1).

In Structural Formula (I), l, m, and n each independently represent an integer of 1 or more and satisfy 1 + m + n = 3-15. AO represents at least one of ethyleneoxy and propyleneoxy, and (AO) _l , (AO) _m And (AO) _n Each AO may be the same or different.