JP7077047B2 - Inkjet recording method - Google Patents

Description

The present invention relates to an inkjet recording method.

According to the inkjet recording method, an image can be recorded on various recording media. Then, in order to record a better image, various recording methods according to the recording medium have been proposed. Further, in recent years, in order to improve the fastness of a recorded image, an inkjet recording method using an ink containing a pigment as a coloring material has been proposed. In particular, images recorded on plain paper with black ink are often texts and charts, and in such cases, it is strongly required to be able to record black images having excellent optical density and sharpness.

Further, it is required to record a high-quality image at a higher speed by so-called "one-pass recording" in which a water-based ink containing a pigment is applied to a unit area of a recording medium in one scan and recorded. In such a recording method, inks having different hues may be applied to adjacent regions at once. When inks with different hues are applied to adjacent regions at once, the phenomenon that inks with different hues come into contact with each other before the pigment is fixed to the recording medium (fixed state) due to penetration or drying of the inks. Is likely to occur. When this phenomenon occurs more prominently, inks having different hues are mixed in the recording medium, and the pigment is fixed in a place different from the originally intended place, that is, a so-called "bleeding phenomenon" is likely to occur, and the image is liable to occur. There was a problem that the dignity deteriorated. Further, it is known that if the permeability of the ink is increased in order to suppress the bleeding phenomenon, the optical density of the recorded image tends to decrease.

Various techniques have been proposed so far in order to solve such problems. For example, an inkjet recording method capable of suppressing bleeding using a plurality of dye inks whose permeability to a recording medium and recording density are controlled in a predetermined relationship has been proposed (Patent Document 1). Further, there has been proposed a water-based ink containing polyoxyethylene alkyl ether, having a dynamic surface tension controlled within a predetermined range, having a high image density, and having improved fixability (Patent Document 2).

Japanese Unexamined Patent Publication No. 09-193529 Japanese Unexamined Patent Publication No. 2007-162006

However, in the recording method proposed in Patent Document 1, an ink containing a dye as a coloring material is used, but whether or not bleeding is suppressed when an ink containing a pigment is used has not been investigated at all. It is unknown. Further, Patent Document 2 does not mention whether or not bleeding is suppressed. Furthermore, it was found that there is room for improvement in the optical density and sharpness of images recorded with black ink.

Therefore, an object of the present invention is to provide an inkjet recording method capable of recording an image in which bleeding is suppressed and a black image having high optical density and excellent sharpness on plain paper by one-pass recording. Further, an object of the present invention is to record an image in which bleeding is suppressed and a black image having high optical density and excellent sharpness on plain paper, and black having high optical density and excellent glossiness. It is an object of the present invention to provide an inkjet recording method capable of recording an image on glossy paper.

That is, according to the present invention, there is an inkjet recording method in which an ink set composed of a plurality of water-based inks containing a pigment is used and an image is recorded in a unit area of plain paper in one scan. , Black ink including the first black ink and the second black ink, cyan ink, magenta ink, and yellow ink, and the dynamic surface tension of the first black ink in 50 msec is 45 mN / m or more. The dynamic surface tensions of the second black ink, the cyan ink, the magenta ink, and the yellow ink at 10 msec or less are 40 mN / m or less, respectively, and 10 m of the cyan ink, the magenta ink, and the yellow ink. The difference in dynamic surface tension in seconds is within 3 mN / m in all combinations, and the first black ink has a carboxylic acid group and a phosphonic acid on the surface of carbon black particles having a DBP oil absorption of 100 mL / 100 g or more. At least one of the cyan ink, the magenta ink, and the yellow ink is contained in the self-dispersing pigment to which at least one of the groups is bonded directly or via another atomic group, and the black ink is applied at least one of the cyan ink, the magenta ink, and the yellow ink. Only the second black ink is applied to the boundary region with the ink application portion, or the first black ink and the second black ink are applied, and 10 m of the black ink applied to the boundary area. The difference between the dynamic surface tension in seconds and the dynamic surface tension of the cyan ink, the magenta ink, and the yellow ink in 10 msec is set to be within 3 mN / m, and the black ink is applied to the black ink. Only the first black ink is applied to the non-boundary region other than the boundary region, or the first black ink and the second black ink are applied to the non-boundary region, and the black ink applied to the non-boundary region. An ink-ink recording method characterized in that the dynamic surface tension in 50 msec is 45 mN / m or more and the width of the boundary region is 40 μm or more and 130 μm or less (hereinafter, also referred to as “first ink-ink recording method”). Note) is provided.

Further, according to the present invention, there is an inkjet recording method for recording an image on plain paper or glossy paper using an ink set composed of a plurality of water-based inks containing a pigment, wherein the ink set is the first black. It is composed of black ink including ink and a second black ink, cyan ink, magenta ink, and yellow ink, and the dynamic surface tension of the first black ink in 50 msec is 45 mN / m or more, and the second black. The dynamic surface tension of the ink, the cyan ink, the magenta ink, and the yellow ink at 10 msec or less is 40 mN / m or less, respectively, and the dynamic of the cyan ink, the magenta ink, and the yellow ink at 10 msec. The difference in surface tension is within 3 mN / m in any combination, and the first black ink has at least one of a carboxylic acid group and a phosphonic acid group on the surface of carbon black particles having a DBP oil absorption of 100 mL / 100 g or more. The second black ink contains a self-dispersing pigment bonded directly or via another atomic group, and the second black ink is a resin-dispersed ink in which carbon black having a DBP oil absorption of 100 mL / 100 g or less is dispersed with a resin dispersant. The cyan ink, the magenta ink, and the yellow ink contain a resin dispersion pigment, and when an image is recorded in a unit area of plain paper in one scan, the black ink is applied to the black ink. , The second black ink is applied only to the boundary region between the cyan ink, the magenta ink, and at least one of the yellow inks, or the first black ink and the second black ink are applied. The difference between the dynamic surface tension of the black ink applied to the boundary region at 10 msec and the dynamic surface tension of the cyan ink, the magenta ink, and the yellow ink at 10 msec while applying the black ink. , Both are set to 3 mN / m or less, and only the first black ink is applied to the non-boundary region other than the boundary region among the application points of the black ink, or the first black ink and the second black ink are applied. The dynamic surface tension of the black ink applied to the non-boundary region in 50 msec while applying the black ink is 45 mN / m or more, and the width of the boundary region is 40 μm or more and 130 μm or less. When recording an image on the surface, the black ink is applied. An inkjet recording method (hereinafter, also referred to as “second inkjet recording method”), characterized in that only the second black ink is applied to the portion, is provided.

According to the present invention, it is possible to provide an inkjet recording method capable of recording an image in which bleeding is suppressed and a black image having high optical density and excellent sharpness on plain paper by one-pass recording. Further, according to the present invention, an image in which bleeding is suppressed and a black image having high optical density and excellent sharpness can be recorded on plain paper, and black having high optical density and excellent glossiness. It is possible to provide an inkjet recording method capable of recording an image on glossy paper.

It is sectional drawing which shows an example of the ink cartridge schematically. It is a figure which shows typically an example of the inkjet recording apparatus used in the inkjet recording method of this invention, (a) is the perspective view of the main part of the inkjet recording apparatus, (b) is the perspective view of a head cartridge. It is a schematic diagram explaining the area to apply ink in a recording medium.

<Inkjet recording method>
Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions and exists in the ink, but for convenience, it is expressed as "containing a salt". Further, the water-based ink for inkjet may be simply referred to as "ink". The physical characteristic values are values at room temperature (25 ° C.) unless otherwise specified.

In the present invention, the maximum bubble pressure method adopted for measuring the dynamic surface tension is the maximum pressure required to release the bubbles extruded from the tip of the probe (thin tube) immersed in the liquid to be measured. Is a method of determining the surface tension. The life time is the maximum foam pressure (radius of curvature of the bubble and the tip of the probe) after the new surface is formed after the bubble is separated when the bubble is formed from the tip of the probe in the maximum foam pressure measurement. It means the time until (when the radii of are equal). The measurement temperature is 25 ° C.

The present inventors have studied the recording method proposed in Patent Document 1 using a water-based ink containing a pigment as a coloring material. Specifically, black ink having high permeability, black ink having low permeability, and yellow ink having high permeability were prepared. The permeability of the ink was adjusted by changing the content of the surfactant. As the surfactant, an ethylene oxide adduct of acetylene glycol (trade name "acetylenoll E100", manufactured by Kawaken Fine Chemicals Co., Ltd.) was used. The content of the surfactant in the black ink and the yellow ink having high permeability was 0.5% by mass, and the content of the surfactant in the black ink having low permeability was 0.3% by mass.

Then, when the image was recorded by the recording method proposed in Patent Document 1, it was found that bleeding occurred remarkably. Further investigation revealed that bleeding was suppressed only when an ink set containing ink having higher permeability as the brightness was lower was used and the ink was applied to the recording medium in order from the ink having the lowest brightness. While the recording method proposed in Patent Document 1 uses an ink containing a dye, it is presumed that such a phenomenon occurred because the ink containing a pigment was used in the study conducted by the present inventors. .. In Patent Document 1, the Rf value of the dye is focused on as an index showing the affinity with the cellulose fibers constituting the plain paper. A dye having a high Rf value has a low affinity for cellulose fibers, and therefore easily spreads on a recording medium. It is said that bleeding is likely to occur with a combination of dyes having similar Rf values, and bleeding is suppressed by using a dye having a lower Rf value as the ink has a lower lightness.

When a water-based ink using a pigment as a coloring material is prepared, a so-called resin-dispersed pigment using a water-soluble resin as a dispersant for dispersing the pigment, or an ionic group bonded to the particle surface of the pigment. So-called self-dispersing pigments are commonly used. Since such a pigment has an affinity with cellulose fibers (corresponding to the Rf value of the dye in Patent Document 1), it is considered that bleeding is likely to occur. The pigment in the ink is not dissolved in water, and the resin-dispersed pigment and the self-dispersed pigment interact with the cellulose fibers. That is, it is presumed that the difference in interaction based on the difference in the molecule of the pigment itself is unlikely to occur, and as a result, the affinity with the cellulose fiber is similar. If so, it can be said that it is difficult to apply the recording method proposed in Patent Document 1 to a water-based ink containing a pigment as a coloring material.

It was also found that bleeding was suppressed by using an ink set containing ink having higher permeability as the brightness was lower and applying the ink to the recording medium in order from the ink having the lowest brightness. However, in the case of the serial inkjet recording method in which the recording head scans and records an image, the order of applying ink is reversed in the forward direction and the backward direction of the recording head, which is a big limitation as a recording method.

Next, the present inventors examined a method for suppressing bleeding when an image is recorded with a water-based ink containing a pigment as a coloring material. As a result, it has been found that it is necessary to prepare the ink by paying attention to the surface tension in units of time from the contact between different inks applied to the recording medium to the completion of permeation into the recording medium. More specifically, it is necessary to use a plurality of inks having a dynamic surface tension of 40 mN / m or less in 10 msec and a difference in dynamic surface tension of 3 mN / m or less in any combination. I found.

When observing the behavior of the ink after being applied to the recording medium with a high-speed camera, in the case of so-called one-pass recording in which an image of a unit area is recorded in one scan, different inks come into contact with each other immediately after being applied to the recording medium. You can see that. It was also found that the time required to complete the penetration of the ink into the recording medium varies depending on the type of ink or plain paper, but it takes about 10 msec to 50 msec. Bleeding between different inks occurs by mixing before the penetration into the recording medium is complete, so mixing after penetration can be ignored. That is, in order to suppress bleeding, it is sufficient to suppress the mixing of the inks in the time from the contact of the inks to the completion of penetration into the recording medium.

When various inks were combined and examined, two methods, "tension" and "diffusion", were used to suppress the mixing of the inks in the time from the contact between the inks to the completion of penetration into the recording medium. It turned out that it was necessary to consider the phenomenon.

When droplets of two types of ink are applied to a recording medium so as to be in contact with each other, one ink is instantly drawn into the other ink depending on the combination of inks. Upon closer examination, it was found that such "pull-in" occurs when the difference in dynamic surface tension in a very short time is large. If there is a difference in surface tension when the droplets come into contact with each other, the tension of the ink having the higher surface tension (the force to draw in the ink having the lower surface tension) is stronger. In order to suppress the above-mentioned "pull-in", it is necessary to minimize the difference in surface tension between the inks. Since the inks come into contact with each other almost at the same time as the ink applied to the recording medium forms a new surface, it is necessary to consider the dynamic surface tension in a very short time.

Further, since the types of pigments used are different between inks having different hues, it is practically impossible to suppress diffusion itself. In addition, the mixing of inks due to diffusion is gentler than that of "pull-in" due to tension. Therefore, the present inventors have considered that it is possible to suppress the mixing of inks by shortening the mixing time by diffusion as much as possible, instead of suppressing the diffusion. That is, we examined how to accelerate the penetration into the recording medium as much as possible.

As a result of observing the relationship between the type of ink and the penetration rate with a high-speed camera, it was found that there is a correlation between the dynamic surface tension and the penetration rate in a very short time. Decreasing the dynamic surface tension in a very short time accelerates penetration and saturates at some point. Specifically, in the case of an ink having a dynamic surface tension of more than 40 mN / m in 10 msec, the higher the dynamic surface tension, the slower the penetration, and from the time it is applied to the recording medium until the penetration is completed, it is about. It was found that it took about 10 msec to 50 msec. On the other hand, it was found that in the case of an ink having a dynamic surface tension of 40 mN / m or less in 10 msec, the permeation rate is almost constant, and it takes about 10 msec from the time when the ink is applied to the recording medium until the permeation is completed. ..

Such a tendency was observed without a large difference within the range of the amount of ink droplets applied (1 ng to 100 ng) in the general inkjet recording method. In addition, various types of plain paper were confirmed, but no significant difference was observed due to the difference in the type of plain paper. It is considered that the following process is performed until the ink applied to the recording medium permeates the recording medium. First, after the ink is wetted on the surface of the recording medium, it penetrates into the recording medium by the capillary force, and the penetration is completed. In order to wet the surface of the recording medium with the ink, it is necessary to set the surface tension of the ink low according to the surface energy of the recording medium. Plain paper is usually controlled to be hydrophobic by being internally added or coated with a sizing agent in order to suppress water penetration and ink bleeding. Therefore, the surface energy of plain paper is almost the same, and the condition required to generate wetting of a material with such surface energy in a short time is that the dynamic surface tension in 10 msec is 40 mN / m or less. It is thought to be to do. Further, it is considered that the penetration into the recording medium by the capillary force is sufficiently faster than the time when the ink is wetted. Therefore, it is presumed that the amount of ink applied does not significantly affect the time required to complete the penetration.

Next, the present inventors examined the conditions for suppressing the tension using an ink having a dynamic surface tension of 40 mN / m or less at 10 msec. It was speculated that it is necessary to consider the dynamic surface tension in a very short time because a new surface is formed by the ink droplets applied to the recording medium and the inks come into contact with each other immediately after the life time becomes zero. .. However, it was found that the condition for suppressing the tension can be specified by the dynamic surface tension at the life time of 10 msec by using the maximum foam pressure method which is a simple method. Specifically, it was found that it is necessary to use a plurality of inks having a difference in dynamic surface tension of 3 mN / m or less in 10 msec. It takes approximately 10 msec to complete the penetration of the ink applied to the recording medium. By aligning the changes in surface tension during this 10 msec between the inks, the tension can be effectively suppressed.

As described above, it was found that bleeding is suppressed by using an ink set containing ink having higher permeability as the brightness is lower and applying the ink to the recording medium in order from the ink having the lowest brightness. However, such a phenomenon merely gains time for the ink having low lightness to get wet with the recording medium by first applying the ink having high permeability and low lightness to the recording medium. For example, assuming that the application interval is gradually shortened and the high-brightness ink is applied before the previously applied low-brightness ink gets wet, it is expected that bleeding is likely to occur. That is, since the penetrability of the low-brightness ink is higher, the surface tension of the low-brightness ink is lower, and the low-brightness ink is drawn into the high-brightness ink. In fact, it was confirmed that when the ink application interval was shortened (for example, when the ink application interval was shortened from 8 msec to 2 msec), bleeding was likely to occur.

Next, we examined a method for recording a black image with improved optical density and sharpness. The "black image" in the present invention means an image in which RGB data is R = 0, G = 0, and B = 0. Such black images are recorded using only black ink (not using color ink). First, with reference to the description in Patent Document 2, the relationship between the dynamic surface tension of the ink containing the pigment and the optical density and sharpness of the black image was examined. As a result, the following was found. When an ink having a high dynamic surface tension at 50 msec was used, the optical density and sharpness of the black image were improved. Specifically, in order to record a black image having high optical density and excellent sharpness, it is necessary to use black ink having a dynamic surface tension of 45 mN / m or more, preferably 49 mN / m or more in 50 msec. I understood it.

As described above, the ink having a dynamic surface tension of more than 40 mN / m in 10 msec takes a long time from being applied to the recording medium until the penetration is completed. It is considered that this is because it takes a long time for the ink to get wet on the surface of the recording medium. Here, if the dynamic surface tension at 50 msec is 45 mN / m or more, the dynamic surface tension at 10 msec is also 45 mN / m or more. That is, when the dynamic surface tension at 50 msec is 45 mN / m or more, the ink stays on the surface of the recording medium for a long time. Then, while the ink remains on the surface of the recording medium, the viscosity of the ink increases due to evaporation of water, and the state of the ink changes such as the association and aggregation of the coloring materials, so that the coloring material is effectively applied to the surface of the recording medium. It is considered that the optical density of the black image is increased.

Further, it is known that plain paper has a distribution of surface energy due to the distribution of density of cellulose fibers and the distribution of sizing agents. Here, assuming that various inks are applied to a recording medium having a distribution in surface energy, the following cases will be considered separately. (1) When applying an ink with a surface tension sufficiently lower than the surface energy of plain paper; (2) When applying an ink with a surface tension close to the surface energy of plain paper; and (3) When applying an ink with a surface tension close to the surface energy of plain paper; When applying ink with a surface tension sufficiently higher than that, we considered.

In the case of (1), the ink is quickly wetted on the surface of the plain paper. In addition, since the contact angle becomes small, the ink wets and spreads on the surface of plain paper and is fixed to large circular dots. In the case of (2), in the place where the surface energy of the plain paper is high, the ink is quickly wetted and the contact angle becomes small. On the other hand, in places where the surface energy of plain paper is low, it takes time for the ink to get wet, and the contact angle becomes large. As a result, non-uniformly shaped dots are formed that spread toward places where the surface energy is high. In the case of (3), it takes time for the ink to get wet on the surface of the plain paper, and the contact angle becomes large. As a result, the ink is difficult to spread and is fixed to small circular dots. Then, when these three types of ink were used, a thick ruled line, a ruled line that was not thick but had bleeding, and a ruled line that was narrow and had high sharpness were recorded. From the above, the above-mentioned "surface tension sufficiently higher than the surface energy of plain paper" corresponds to "45 mN / m or more", and the sharpness of the black image recorded by the "dynamic surface tension in 50 msec" is achieved. The degree is considered to be determined.

Next, the present inventors prepared two types of black ink (Bk ink), cyan ink (C ink), magenta ink (M ink), and yellow ink (Y ink). The two types of Bk inks are the first black ink (Bk1 ink) having a dynamic surface tension (γ ₅₀ ) of 45 mN / m or more at 50 msec and the dynamic surface tension (γ ₁₀ ) at 40 mN / m at 10 msec. The following second black ink (Bk2 ink) was prepared. Further, the dynamic surface tension (γ ₁₀ ) of C ink, M ink, and Y ink at 10 msec was set to 40 mN / m or less. Further, the difference in γ ₁₀ between Bk2 ink, C ink, M ink, and Y ink was set to be within 3 mN / m in any combination. Then, a method of recording a full-color image using these five types of ink was examined.

When only Bk1 ink was used, it was possible to record a black image having high optical density and good sharpness. Moreover, when a full-color image was recorded using Bk2 ink, C ink, M ink, and Y ink, the degree of bleeding was slight between all colors, but the optical density and sharpness of the black image decreased. Next, full-color images were recorded using all five inks. Specifically, as shown in FIG. 3, among the Bk ink application points, the boundary area 3 with at least one of the C ink, M ink, and Y ink application points (color recording area 2). Applied only Bk2 ink. Further, only Bk1 ink was applied to the region other than the boundary region 3 (non-boundary region 4). In FIG. 3, reference numeral 1 indicates a non-recording area to which none of the inks is applied. As a result, it was found that the image recorded by applying the Bk1 ink and the Bk2 ink adjacently to each other became whitish and whitish. Specifically, it was confirmed that the image recorded with the Bk1 ink applied in the vicinity of the portion to which the Bk2 ink was applied becomes cloudy and whitish. Hereinafter, such a phenomenon is referred to as "white haze".

Since the hues of both the Bk1 ink and the Bk2 ink are black, bleeding is not visible, and it is predicted that mutual interference cannot be visually recognized even when these inks are applied adjacently. However, it has been found that when Bk1 ink and Bk2 ink having significantly different dynamic surface tension values are applied adjacent to each other, another problem such as white haze occurs in the recorded image.

When Bk1 ink and Bk2 ink having significantly different dynamic surface tensions are applied adjacent to each other, the Bk2 ink is drawn into the Bk1 ink. However, since the inks are of the same color, it is not possible to visually recognize the drawing (movement) of the inks. Since the γ ₅₀ of the Bk1 ink is 45 mN / m or more, it takes time for the surface of the plain paper to get wet, whereas the γ ₁₀ of the Bk2 ink is 40 mN / m or less, so that the plain paper is not wet. Wetting on the surface occurs in a short time. Therefore, the penetration of the Bk2 ink starts before the penetration of the Bk1 ink starts.

At the stage when the penetration of the Bk2 ink starts, the Bk1 ink and the Bk2 ink are already in contact with each other. Therefore, when the penetration of the Bk2 ink starts, the Bk1 ink existing in the vicinity of the Bk2 ink is pulled and penetrates into the application portion of the Bk2 ink. As a result, the amount of Bk1 ink applied in the vicinity of the Bk2 ink application portion is reduced, and the amount of the coloring material in the Bk ink fixed on the recording medium is also reduced, resulting in a cloudy whitish image. It will be recorded.

Therefore, the present inventors have investigated a method for suppressing the penetration of the Bk2 ink before the penetration of the Bk1 ink starts and the Bk1 ink applied in the vicinity of the application portion of the Bk2 ink being suppressed from being pulled. That is, it was speculated that if the viscosity of the Bk1 ink after being applied to the recording medium could be increased more quickly due to the evaporation of water, it would be possible to suppress the image from becoming muddy and whitish. Specifically, the types of coloring materials and additives used for Bk1 ink were examined. As a result, it was found that the viscosity increase of the Bk1 ink due to the evaporation of water can be accelerated by containing the self-dispersing pigment shown below.
[Self-dispersing pigment]: A self-dispersing pigment in which at least one of a carboxylic acid group and a phosphonic acid group is bonded directly to the surface of carbon black particles having a DBP oil absorption of 100 mL / 100 g or more or via another atomic group.

A self-dispersing pigment in which at least one of a carboxylic acid group and a phosphonic acid group is bonded to the surface of carbon black particles directly or via other atomic groups has a concentration of a salt or a water-soluble organic solvent having a low specific dielectric constant due to water evaporation. When it increases, it begins to aggregate. This is thought to increase the viscosity of the ink. Further, it is considered that carbon black having a relatively large amount of DBP oil absorption tends to aggregate and can further accelerate the increase in viscosity. It has been found that by using the Bk1 ink containing such an autocovariant pigment, it is possible to record an image in which the generation of white haze is suppressed. Further, it was found that by further containing the specific salt shown below, the increase in the viscosity of the Bk1 ink due to the evaporation of water can be further accelerated, so that an image in which the white haze is suppressed more effectively can be recorded.
[Salt]: At least one cation selected from the group consisting of alkali metal ions, ammonium ions, and organic ammonium ions, and ^Cl- , _Br- , I- ^{, ClO-} , ClO ^{2- ,} ClO _3- ^, ClO ₄ ^- , NO _2- ^, NO _3- , SO ₄ ^2- , CO ₃ ^2- , HCO _3- ^, HCOO- ^, ( ^COO- ) ² , COOH ( ^COO- ), CH ₃ ^COO- , C ₂ H _{4 (} COO) ^- ) ₂ , C ₆ H ₅ COO- ^, C ₆ H ₄ ( ^COO- ) ₂ , PO ₄ ^3- , HPO ₄ ^2- , and H ₂ PO ₄ ^- with at least one anion selected from the group. Salt composed of bonds

The wider the width of the boundary region to which the Bk2 ink is applied, the more the bleeding could be suppressed. However, if the width of the boundary region is too wide, bleeding is suppressed, but the difference in optical density between the black image recorded with Bk1 ink and the boundary region with Bk2 ink becomes easily visible, and the image becomes easier to see. It was found that white haze occurred in the area. As a result of recording and examining various full-color images, when the width of the boundary region is 40 μm or more and 130 μm or less, bleeding can be effectively suppressed, the difference in optical density of the black image becomes inconspicuous, and the uniformity of the image is improved. I understood it.

Only Bk2 ink may be applied to the above boundary region, or Bk1 ink and Bk2 ink may be applied. However, it is necessary that the difference between the γ ₁₀ of the Bk ink applied to the boundary region and the γ ₁₀ of the C ink, the M ink, and the Y ink is within 3 mN / m. Here, "γ ₁₀ of Bk ink applied to the boundary region" means “γ ₁₀ of Bk2 ink” when only Bk2 ink is applied to the boundary region. Further, when the Bk1 ink and the Bk2 ink are applied to the boundary region, it means "γ ₁₀ of the ink obtained by mixing the Bk1 ink and the Bk2 ink in the same ratio as the applied ratio".

The order in which the inks are applied is not particularly limited, and bleeding can be suppressed regardless of the order in which the inks are applied. For example, even when C ink, M ink, and Y ink are applied after Bk1 ink is applied, and Bk2 ink is further applied to the adjacent portion, bleeding can be suppressed. In the above case, the C ink, the M ink, and the Y ink are drawn into the Bk1 ink and move, but the high-brightness ink is drawn into the low-brightness Bk1 ink, so that it is difficult to see. Then, in the case of recording in one pass, Bk2 ink having a smaller value of γ ₁₀ is applied before the Bk1 ink flows toward the C ink, the M ink, and the Y ink, so that bleeding is suppressed. It is thought that.

Only the Bk1 ink may be applied to the region other than the boundary region, that is, the non-boundary region, or the Bk1 ink and the Bk2 ink may be applied. However, it is necessary that the γ ₅₀ of the Bk ink applied to the non-boundary region is 45 mN / m or more. Here, "γ ₅₀ of Bk ink applied to the non-boundary region" means "γ ₅₀ of Bk1 ink" when only Bk1 ink is applied to the non-boundary region. Further, when the Bk1 ink and the Bk2 ink are applied to the non-boundary region, it means "γ ₅₀ of the ink obtained by mixing the Bk1 ink and the Bk2 ink in the same ratio as the applied ratio".

The Bk2 ink, the C ink, the M ink, and the Y ink may all contain a self-dispersion pigment or may contain a resin dispersion pigment. However, when considering recording an image not only on plain paper but also on glossy paper, the Bk2 ink, C ink, M ink, and Y ink need to contain a resin-dispersed pigment dispersed with a resin dispersant. There is. Further, the Bk2 ink needs to contain a resin-dispersed pigment in which carbon black having a DBP oil absorption of 100 mL / 100 g or less is dispersed with a resin dispersant. When recording an image on glossy paper, only Bk2 ink is applied to the Bk ink application portion, and Bk1 ink is not applied (Bk1 ink is not used). The Bk1 ink contains a self-dispersing pigment using carbon black having a DBP oil absorption of 100 mL / 100 g or more. Therefore, when the Bk1 ink is applied to the glossy paper, a black image in which the glossiness is lost is recorded.

<Water-based ink>
In the inkjet recording method of the present invention, an image is recorded using an ink set composed of a plurality of water-based inks containing a pigment. Hereinafter, the components contained in the water-based ink constituting the ink set used in the inkjet recording method of the present invention, the physical characteristics of the water-based ink, and the like will be described in detail.

(Pigment)
The ink contains a pigment as a coloring material. The Bk1 ink used in the first inkjet recording method contains carbon black as a pigment. The Bk2 ink used in the first inkjet recording method can contain carbon black as a pigment. Further, both the Bk1 ink and the Bk2 ink used in the second inkjet recording method contain carbon black as a pigment.

Organic pigments such as phthalocyanine pigments, quinacridone pigments, and azo pigments can be used as the C ink, the M ink, and the Y ink, respectively. Examples of the organic pigment used for C ink include C.I. I. Pigment Blue 15 can be mentioned. Examples of the organic pigment used for M ink include C.I. I. Pigment Red 122, C.I. I. Pigment Violet 19, a solid solution of quinacridone pigment, and the like. Examples of the organic pigment used for Y ink include C.I. I. Pigment Yellow 74, C.I. I. Pigment Yellow 128, C.I. I. Pigment Yellow 155 and the like can be mentioned.

The pigment contained in the Bk1 ink is a self-dispersing pigment in which at least one of a carboxylic acid group and a phosphonic acid group is directly bonded to the surface of carbon black particles or via another atomic group. The pigment contained in the Bk2 ink used in the second inkjet recording method is a resin-dispersed pigment in which carbon black is dispersed with a resin dispersant. The pigments contained in the C ink, M ink, and Y ink used in the second inkjet recording method are all resin-dispersed pigments. The method for dispersing the pigment contained in the C ink, M ink, and Y ink used in the first inkjet recording method is not particularly limited, and may be either a self-dispersion pigment or a resin-dispersed pigment. The resin-dispersed pigment includes a resin-dispersed pigment in which the pigment is dispersed with a resin dispersant, a microcapsule-type pigment in which the particle surface of the pigment is coated with a resin, and an organic group containing a polymer on the particle surface of the pigment. Includes resin-bound pigments bound to.

The amount of DBP oil absorbed by carbon black can be measured by a method compliant with JIS K6221 or a method compliant with ASTMD 2414. These methods are methods in which dibutyl phthalate is dropped onto 100 g of carbon black under stirring, and the amount of dibutyl phthalate dropped at the time when the torque is maximized is measured. The amount of DBP oil absorbed by the carbon black used in the first black ink is 100 mL / 100 g or more, and more preferably 120 mL / 100 g or more. The DBP oil absorption of carbon black used in the first black ink is preferably 200 mL / 100 g or less, and more preferably 150 mL / 100 g or less. The DBP oil absorption of carbon black used in the second ink is preferably 10 mL / 100 g or more and 100 mL / 100 g or less, and more preferably 30 mL / 100 g or more and 70 mL / 100 g or less.

The self-dispersing pigment is an anionic group bonded directly to the particle surface of the pigment or via another atomic group (-R-). By using such a self-dispersing pigment, it is not necessary to add a dispersant for dispersing the pigment in the ink, or the amount of the dispersant added can be reduced.

The anionic group may be in a partially dissociated state or in a completely dissociated state in the ink. Examples of the anionic group include a carboxylic acid group and a phosphonic acid group. Examples of the counter ion of the anionic group include cations such as hydrogen atom, alkali metal, ammonium, and organic ammonium. Further, the anionic group may be bonded to the particle surface of the pigment via another atomic group (-R-). Examples of the other atomic group (-R-) include an alkylene group, an arylene group, an amide group, a sulfonyl group, an imino group, a carbonyl group, an ester group, an ether group, and a group combining these groups.

The resin-dispersed pigment is a pigment dispersed with a resin dispersant. As the resin dispersant, it is preferable to use an acrylic resin having a hydrophilic unit and a hydrophobic unit as constituent units, preferably a water-soluble acrylic resin. The "water-soluble resin" in the present invention means a resin that does not form particles whose particle size can be measured when neutralized with an acid value and an equivalent amount of alkali and measured by a dynamic light scattering method. do. Hereinafter, each unit constituting the acrylic resin will be described. The "(meth) acrylic" in the present invention means acrylic or methacrylic.

The hydrophilic unit is formed by polymerizing a monomer having a hydrophilic group such as an acid group or a hydroxy group. Examples of the monomer having a hydrophilic group include an acidic monomer having a carboxylic acid group such as (meth) acrylic acid, itaconic acid, maleic acid and fumaric acid; and ethyl (meth) acrylic acid-2-phosphonate. Acidic monomers with phosphonic acid groups; Anionic monomers such as anhydrides and salts of these acidic monomers; -2-hydroxyethyl (meth) acrylate, -3-hydroxypropyl (meth) acrylate. Monomers having a hydroxy group such as; Monomers having an ethylene oxide group such as methoxy (mono, di, tri, poly) ethylene glycol (meth) acrylate and the like can be mentioned. Examples of the cation constituting the salt of the anionic monomer include lithium ion, sodium ion, potassium ion, ammonium ion, and organic ammonium ion.

The hydrophobic unit is formed by polymerizing a hydrophobic monomer having no hydrophilic group such as an acid group or a hydroxy group. Examples of the hydrophobic monomer include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth) acrylate; ethyl (meth) acrylate, methyl (meth) acrylate, and (iso) propyl (meth). Examples thereof include monomers having an aliphatic group such as acrylate, (n-, iso-, t-) butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate.

(salt)
The first black ink preferably contains a predetermined salt. "Salt" means a compound in which a cation and an anion are ionically bonded. By containing the salt in the first black ink, it is possible to further accelerate the increase in the viscosity of the Bk1 ink due to the evaporation of water, so that it is possible to record an image in which white haze is more effectively suppressed. The salt content (% by mass) in the first black ink is preferably 0.20% by mass or more and 0.50% by mass or less based on the total mass of the ink. The salt may be contained in each ink other than the first black ink, but it is preferable not to contain the salt.

The salt contained in the first black ink is preferably a compound formed by binding one or more cations and one or more anions so as to neutralize the electric charge. The cation is at least one selected from the group consisting of alkali metal ions, ammonium ions, and organic ammonium ions. The anions are ^Cl- , ^Br- , I- ^{, ClO-} , ClO ^{2- ,} ClO _3- ^, ClO _4- , NO ^{2- ,} NO _3- ^, SO _{4 2-} , CO ₃ ^{2- ,} HCO _{3- ,} HCOO. ^- , ( ^COO- ) ₂ , COOH ( ^COO- ), CH ₃ COO- ^, C ₂ H ₄ ( ^COO- ) ₂ , C ₆ H ₅ COO- ^, C ₆ H ₄ ( ^COO- ) ₂ , PO ₄ ^3- , HPO ₄ ^2- , ^and H ₂ PO _4- at least one selected from the group.

Examples of the alkali metal ion include lithium ion, sodium ion, potassium ion and the like. Examples of the organic ammonium ion include alkylamines having 1 or more and 3 or less carbon atoms such as methylamine and ethylamine; and alkanolamines having 1 to 4 or less carbon atoms such as monoethanolamine, diethanolamine and triethanolamine; Can be mentioned. Of these, alkali metal ions are preferable, and potassium ions are particularly preferable.

As a salt formed by binding a cation and an anion, for example, when a monovalent cation is represented as (M ₂ ), (M ₂ ) Cl, (M ₂ ) Br, (M ₂ ) I, (M) ₂ ) ClO, (M ₂ ) ClO ₂ , (M ₂ ) ClO ₃ , (M ₂ ) ClO ₄ , (M ₂ ) NO ₂ , (M ₂ ) NO ₃ , (M ₂ ) ₂ SO ₄ , (M ₂ ) ) ₂ CO ₃ , (M ₂ ) HCO ₃ , HCOO (M ₂ ), (COO (M ₂ )) ₂ , COOH (COO (M ₂ )), CH ₃ COO (M ₂ ), C ₂ H ₄ (COO) (M ₂ )) ₂ , C ₆ H ₅ COO (M ₂ ), C ₆ H ₄ (COO (M ₂ )) ₂ , (M ₂ ) ₃ PO ₄ , (M ₂ ) ₂ HPO ₄ , (M ₂ ) H ₂ PO ₄ can be mentioned. Of these, potassium chloride, sodium acetate, sodium benzoate, potassium benzoate, ammonium benzoate, trisodium citrate, potassium phthalate, ammonium phthalate and the like are preferable.

(Aqueous medium)
The ink can contain an aqueous medium which is a mixed solvent of water and a water-soluble organic solvent. As the water, it is preferable to use deionized water or ion-exchanged water. The ink is a water-based ink containing at least water as a water-based medium. The content (% by mass) of water in the ink is preferably 40.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. As the water-soluble organic solvent, any one that can be used for ink for inkjet such as alcohols, glycols, glycol ethers, and nitrogen-containing compounds can be used, and one or more of them may be contained. Can be done. The water-soluble organic solvent preferably has a vapor pressure at 25 ° C. lower than that of water. The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink, and is preferably 15.0% by mass or more and 30.0% by mass. It is more preferably mass% or less.

(Other ingredients)
In addition to the above components, the ink may contain an organic compound that is solid at room temperature, such as trimethylolethane, trimethylolpropane, or a nitrogen-containing compound such as urea or ethylene urea, if necessary. In addition to the above components, various additions such as resins, pH regulators, defoamers, rust inhibitors, preservatives, fungicides, antioxidants, antioxidants, and evaporation promoters are added as needed. The agent may be contained in the ink.

The ink can contain a surfactant. Examples of the type of surfactant include known anionic surfactants, nonionic surfactants, and cationic surfactants. Among them, a nonionic surfactant can be preferably used.

(Physical characteristics of ink)
The dynamic surface tension (γ ₁₀ ) at a lifetime of 10 msec or the dynamic surface tension (γ ₅₀ ) at a lifetime of 50 msec, measured under the condition of 25 ° C. by the maximum foam pressure method, was adjusted to a predetermined value. Use ink. The dynamic surface tension of the ink can be adjusted, for example, by appropriately adjusting the type and content of the surfactant and the water-soluble organic solvent.

The dynamic surface tension of the first black ink at a life time of 10 msec is preferably 50 mN / m or more and 65 mN / m or less, and more preferably 50 mN / m or more and 60 mN / m or less. The dynamic surface tension of the second black, cyan, magenta, and yellow inks at a life time of 10 msec is 40 mN / m or less, preferably 25 mN / m or more, and 30 mN / m or more and 40 mN /. It is more preferably m or less.

The dynamic surface tension of the first black ink at a life time of 50 msec is preferably 45 mN / m or more, preferably 60 mN / m or less, and more preferably 49 mN / m or more and 60 mN / m or less. The dynamic surface tension of the second black, cyan, magenta, and yellow inks at a life time of 50 msec is preferably 25 mN / m or more and 42 mN / m or less, and 30 mN / m or more and 40 mN / m or less. It is more preferable to have.

<Ink cartridge>
The ink cartridge includes ink and an ink accommodating portion for accommodating the ink. The ink contained in the ink accommodating portion is the ink described above. FIG. 1 is a cross-sectional view schematically showing an embodiment of an ink cartridge. As shown in FIG. 1, the bottom surface of the ink cartridge is provided with an ink supply port 12 for supplying ink to the recording head. The inside of the ink cartridge is an ink accommodating portion for accommodating ink. The ink accommodating portion is composed of an ink accommodating chamber 14 and an absorber accommodating chamber 16, and these are communicated with each other through a communication port 18. Further, the absorber accommodating chamber 16 communicates with the ink supply port 12. The ink storage chamber 14 contains the liquid ink 20, and the absorber storage chamber 16 contains the absorbers 22 and 24 that hold the ink in an impregnated state. The ink accommodating portion may not have an ink accommodating chamber for accommodating liquid ink, and may have a form in which the entire amount of ink accommodated is held by an absorber. Further, the ink accommodating portion may have no absorber and may accommodate the entire amount of ink in a liquid state. Further, the ink cartridge may be in the form of having an ink accommodating portion and a recording head.

<Inkjet recording device>
In the inkjet recording method of the present invention, for example, a plurality of inks described above, which constitute an ink set, are ejected from an inkjet recording head to record an image on a recording medium. Examples of the method of ejecting ink include a method of applying mechanical energy to the ink and a method of applying thermal energy to the ink. In the present invention, it is particularly preferable to adopt a method of applying heat energy to the ink to eject the ink. Other than using the plurality of inks described above and applying these inks to a predetermined area to record an image, the steps of the inkjet recording method may be known.

FIG. 2 is a diagram schematically showing an example of an inkjet recording device used in the inkjet recording method of the present invention, (a) is a perspective view of a main part of the inkjet recording device, and (b) is a perspective view of a head cartridge. Is. The inkjet recording apparatus is provided with a transport means (not shown) for transporting the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40, and is configured to set the ink cartridge 42. Ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32 while the head cartridge 36 is conveyed along the carriage shaft 34 in the main scanning direction. Then, the recording medium 32 is conveyed in the sub-scanning direction by the conveying means (not shown), so that the image is recorded on the recording medium 32. Here, an inkjet recording device equipped with a serial type recording head has been described as an example, but a line type recording head in which the ejection port rows are arranged over the entire area covering the width of the recording medium is mounted. An inkjet recording device may be used.

Any recording medium may be used as a recording medium for recording an image by the inkjet recording method of the present invention. Plain paper is a recording medium having no coat layer, and cellulose constituting the recording medium is present on the surface thereof. When recording an image on plain paper, the recording speed is important, so ink is applied to the unit area in one-pass recording performed in one relative scan between the recording head and plain paper. Further, the glossy paper is a recording medium having a coat layer, and an ink receiving layer exhibiting gloss is formed on the surface thereof. The range of "gloss" may be as long as a glossy feeling can be visually felt. For example, it is preferable to use glossy paper having a glossiness of 20 ° glossiness (JIS K5600) of 20 or more. When recording an image on glossy paper, the application of ink to the unit area is performed by one-pass recording performed in one relative scan between the recording head and glossy paper, and multi-pass performed in multiple relative scans between the recording head and glossy paper. It may be any of the records. However, since it is usually important that the image to be recorded on glossy paper has high definition, multipath recording is preferable.

The method of relative scanning between the recording head and the recording medium can be determined by the configuration of the recording head (serial method or line method). Since both one-pass recording and multi-pass recording are possible, it is preferable to use a recording device equipped with a serial recording head. The unit area can be arbitrarily set from one pixel, one band (when a serial type recording head is used, an area that can be recorded by one main scan of the recording head) and the like.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded. In addition, regarding the amount of components, those described as "part" and "%" are based on mass unless otherwise specified.

<Synthesis of resin>
Each of the monomers (unit: part) shown in Table 1 was copolymerized according to a conventional method to synthesize water-soluble resins 1 to 3, respectively. After neutralizing the acidic groups in the resin with an aqueous solution of potassium hydroxide so that the neutralization rate becomes 100%, ion-exchanged water is further added to increase the content of the resin (solid content) to 20.0. An aqueous solution of 1 to 3 resins was obtained. The precipitate obtained by adding hydrochloric acid to the aqueous solution of the resin and precipitating it was vacuum dried at 40 ° C. overnight to obtain a resin. A solution prepared by dissolving the obtained resin in tetrahydrofuran was used as a measurement sample, and the acid value of the resin was measured using an automatic potential difference titrator (trade name "AT-510", manufactured by Kyoto Denshi Kogyo). As the titration solution, potassium hydroxide methanol titration solution was used. The results are shown in Table 1. In addition, the weight average molecular weight of the obtained resin in terms of polystyrene was measured by gel permeation chromatography (GPC). The results are shown in Table 1. The meanings of the abbreviations for the monomers in Table 1 are shown below.
-St: Styrene-BzMA: Benzyl methacrylate-MMA: Methyl methacrylate-BA: Butyl acrylate-AA: Acrylic acid

<Preparation of pigment dispersion>
(Pigment dispersions 1 to 6, 13, 17, 19, and 21)
Using a Silverson mixer, 20.0 g of a pigment of the type shown in Table 2, a treatment agent, and 200 mL of pure water were mixed under room temperature conditions at 6,000 rpm for 30 minutes to obtain a mixture. Potassium nitrite (isomoles with the treatment agent) dissolved in a small amount of water was slowly added to the obtained mixture and mixed. By this mixing, the temperature of the mixture reached 60 ° C., and the reaction was carried out in this state for 1 hour. The pH of the mixture was adjusted to 10 using an aqueous potassium hydroxide solution. After 30 minutes, 20 mL of pure water was added and diafiltration was performed using a spectrum membrane to prepare an autocovariant pigment. Water was added to the prepared self-dispersion pigments to prepare pigment dispersions 1 to 6, 13, 17, 19, and 21 having a pigment content of 10.0%. The types of treatment agents in Table 2 are shown below.
-Treatment agent 1: 4-aminophthalic acid-Treatment agent 2: ((4-Aminobenzoylamino) -methane-1,1-diyl) potassium bisphosphonate-Treatment agent 3: p-aminobenzoic acid-Treatment agent 4: 4 -Aminobenzene sulfonic acid

(Pigment dispersions 7-12, 14-16, 18, and 20)
20.0 parts of the pigments shown in Table 2, 30.0 parts of an aqueous solution of a resin (resin dispersant) (resin (solid content) content: 20.0%), and 50.0 parts of ion-exchanged water are mixed. Then, the dispersion was obtained by dispersing for 10 hours using a batch type vertical sand mill. The obtained dispersion was centrifuged to remove coarse particles, and then pressure-filtered with a microfilter (manufactured by Fujifilm) having a pore size of 3.0 μm to prepare a dispersion. An appropriate amount of ion-exchanged water was added to the prepared dispersion to prepare pigment dispersions 7 to 12, 14 to 16, 18, and 20.

<Ink preparation>
Each component (unit:%) shown in the upper part of Table 3-1, 3-2, 4-1, 4-2, 5 and 6 is mixed, sufficiently stirred, and then a microfilter with a pore size of 3.0 μm (Fujifilm). Each ink was prepared by pressure filtration. "Acetylenol E100" in Tables 3-1, 3-2, 4-1, 4-2, 5 and 6 is a trade name of a surfactant manufactured by Kawaken Fine Chemicals, and "Emar 20SC" is manufactured by Kao. It is a trade name of the surfactant of. Using a dynamic tensiometer (trade name "BUBBLE PRESSURE TENSIOMETER BP-2", manufactured by KRUSS), the dynamic surface tensions γ ₁₀ and γ ₅₀ of the ink prepared by the maximum foam pressure method were measured under the condition of 25 ° C. .. The results are shown in Tables 3-1, 3-2, 4-1 and 4-2, 5 and 6.

<Evaluation>
Images were recorded using an inkjet recording device (a modified version of the product name "PIXUS Pro9500" (manufactured by Canon)) equipped with a recording head that ejects liquid by the action of heat energy. Each of the prepared inks was filled in the ink cartridge. Then, the first black (Bk1) ink was set in the yellow position, and the second black (Bk2) ink was set in the magenta position. Further, the yellow (Y) ink was set in the green position, the magenta (M) ink was set in the red position, and the cyan (C) ink was set in the cyan position. In this embodiment, 1/1200 inch x 1/1200 inch is defined as "1 pixel", and the condition for imparting 4.5 ng ± 10% to a unit area of 1 pixel is defined as "recording duty 100%". do.

Table 7 shows the combinations of the inks constituting the ink set and the width of the boundary area. Table 7 shows the combination and ratio (Bk2 / (Bk1 + Bk2)) of the black ink applied to the boundary region, and the dynamic surface tension (γ ₁₀ ) of the black ink having such a ratio in 10 msec. Further, Table 7 shows the combination and ratio (Bk1 / (Bk1 + Bk2)) of the black ink applied to the non-boundary region, and the dynamic surface tension (γ ₅₀ ) of the black ink in such ratio at 50 msec.

In this example, in the evaluation criteria of each item shown below, "A" and "B" were set as preferable levels, and "C" was set as an unacceptable level.

(1) Evaluation using plain paper One scan starting from the home position of the recording head, or (ii) the opposite side of the home position of the recording head, for the image corresponding to the arrangement width of the discharge port of the recording head. Recording was performed by one-pass bidirectional recording, which was recorded in one scan starting from. Further, the black ink application portion (black image) was divided into a boundary region and a non-boundary region, and Bk1 ink and Bk2 ink were arbitrarily used to record an image in each region. From the original full-color image, the application points of cyan, magenta, yellow, and black inks are determined pixel by pixel. After that, an image of binary information with / without applying cyan, magenta, and yellow ink was recorded for each pixel, and an image was created in which the boundary of the image was expanded by an arbitrary width. .. Next, an image was created by subtracting an image in which the cyan, magenta, and yellow ink application points were integrated from the expanded image, and the overlapped portion of the created image and the black ink application location was extracted. .. Then, the boundary region between the cyan, magenta, and yellow ink-applied portions and the black ink-applied portion was determined. The width to be expanded corresponds to the width of the boundary area to be set.

(Optical density of black image)
Three types of recording media (plain paper) were prepared: the product name "PB PAPER" (manufactured by Canon), the product name "Canon Extra" (manufactured by Canon), and the product name "BUSINESS MULTIPURPOSE 4200 PAPER" (manufactured by Xerox). A solid black image (recording duty 100%) of 1 inch × 1 inch was recorded on the prepared recording medium in one pass. One day later, using a spectrophotometer (trade name "Spectrolino", manufactured by Gretag Macbeth), the optical density of the solid image recorded under the conditions of a light source: D50 and a field of view: 2 ° was measured. From the average value and the minimum value of the optical density of the solid image recorded on the three types of recording media, the optical density of the black image was evaluated according to the evaluation criteria shown below. The results are shown in Table 8.
A: The average value was 1.4 or more, and the minimum value was 1.3 or more.
B: The average value was 1.4 or more, and the minimum value was 1.2 or more and less than 1.3.
C: The average value was less than 1.4.

(Sharpness of black image)
Three types of recording media (plain paper) were prepared: the product name "PB PAPER" (manufactured by Canon), the product name "Canon Extra" (manufactured by Canon), and the product name "BUSINESS MULTIPURPOSE 4200 PAPER" (manufactured by Xerox). Six points of black Gothic characters were recorded in one pass on the prepared recording medium. The recorded characters were observed one day later, and the sharpness of the black image was evaluated according to the evaluation criteria shown below. The results are shown in Table 8.
A: There was no bleeding in the characters on any of the three recording media.
B: There was bleeding in the characters on the recording medium of only one type.
C: Characters were bleeding on two or more types of recording media.

(Bleed resistance near the boundary area)
Three types of recording media (plain paper) were prepared: the product name "PB PAPER" (manufactured by Canon), the product name "Canon Extra" (manufactured by Canon), and the product name "BUSINESS MULTIPURPOSE 4200 PAPER" (manufactured by Xerox). Cyan, magenta, yellow, and black backgrounds (recording duty 100%) and 6-point cyan, magenta, yellow, and black Gothic characters (recording duty 100%) are placed on the prepared recording medium in one pass. Recorded. The combination in which the background part and the characters have the same color is omitted. The recorded image was observed one day later, and the bleeding resistance was evaluated according to the evaluation criteria shown below. The results are shown in Table 8.
A: There was no bleeding in the characters in any of the three types of recording media and in any combination of colors.
B: In the recording medium of only one kind, there was bleeding in the characters in any combination of colors.
C: In two or more types of recording media, there was bleeding in characters in any combination of colors.

(White haze near the boundary area)
Three types of recording media (plain paper) were prepared: the product name "PB PAPER" (manufactured by Canon), the product name "Canon Extra" (manufactured by Canon), and the product name "BUSINESS MULTIPURPOSE 4200 PAPER" (manufactured by Xerox). Cyan, magenta, and yellow backgrounds (recording duty 100%) and 12-point black Gothic characters (recording duty 100%) were recorded on the prepared recording medium in one pass. The recorded image was observed one day later, and the state of the white haze in the character area adjacent to the color background portion was evaluated according to the evaluation criteria shown below. The results are shown in Table 8.
A: In all three types of recording media, the optical density in the character region was uniform.
B: In the recording medium of only one kind, there was a place where the optical density was low in the character area.
C: In two or more types of recording media, there was a place where the optical density was low in the character area.

Regarding the evaluation of bleeding resistance, in Comparative Example 9, in addition to the combination of black and cyan and the combination of black and magenta, the combination of cyan and yellow and the combination of magenta and yellow had bleeding of characters. On the other hand, except for Comparative Example 9, there was no bleeding in the characters in each combination of cyan, magenta, and yellow.

(2) Evaluation using glossy paper An image corresponding to the arrangement width of the discharge port of the recording head is started from (i) scanning starting from the home position of the recording head and (ii) starting from the opposite side of the home position of the recording head. Scanning was performed alternately, and recording was performed by 8-pass bidirectional recording, which was recorded by a total of 8 scans. In addition, only Bk2 ink was applied to the black ink application portion for recording.

(Optical density of black image)
The product name "Canon Photo Paper Gloss Gold" (manufactured by Canon) was prepared as a recording medium (glossy paper, 20 ° gloss = 39). The 20 ° glossiness was measured according to JIS K5600 using a haze meter (trade name "Microhaze Plus", manufactured by Big Gardner). A 1-inch x 1-inch black solid image (recording duty 100%) was recorded on the prepared recording medium in 8 passes. One day later, using a spectrophotometer (trade name "Spectrolino", manufactured by Gretag Macbeth), the optical density of the solid image recorded under the conditions of light source: D50 and field of view: 2 ° was measured, and according to the evaluation criteria shown below. The optical density of the black image was evaluated. The results are shown in Table 9.
A: The optical density was 2.0 or more.
B: The optical density was 1.8 or more and less than 2.0.
C: The optical density was less than 1.8.

(Glossiness of each color image)
The product name "Canon Photo Paper Gloss Gold" (made by Canon) was prepared as a recording medium (glossy paper). Solid images (recording duty 100%) of 1 inch × 1 inch black, cyan, magenta, and yellow were recorded on the prepared recording medium in 8 passes. The recorded solid image was observed one day later, and the glossiness was evaluated according to the evaluation criteria shown below. The results are shown in Table 9.
A: The solid image of any color had a glossy feeling.
C: The solid image of any color did not have a glossy feeling and was matte.

1: Non-recording area 2: Color recording area 3: Boundary area 4: Non-boundary area

Claims (9)

It is an inkjet recording method that records an image in a unit area of plain paper in one scan using an ink set composed of a plurality of water-based inks containing pigments.
The ink set is composed of black ink containing a first black ink and a second black ink, cyan ink, magenta ink, and yellow ink.
The dynamic surface tension of the first black ink at 50 msec is 45 mN / m or more.
The dynamic surface tensions of the second black ink, the cyan ink, the magenta ink, and the yellow ink in 10 msec are 40 mN / m or less, respectively.
The difference in dynamic surface tension between the cyan ink, the magenta ink, and the yellow ink at 10 msec is within 3 mN / m in any combination.
The first black ink contains a self-dispersing pigment in which at least one of a carboxylic acid group and a phosphonic acid group is directly bonded or via another atomic group on the surface of carbon black particles having a DBP oil absorption of 100 mL / 100 g or more. death,
Of the black ink application points, only the second black ink is applied to the boundary region between the cyan ink, the magenta ink, and at least one of the yellow ink application points, or the black ink is applied. The dynamic surface tension of the black ink applied to the boundary region together with the first black ink and the second black ink in 10 msec, and the cyan ink, the magenta ink, and the yellow ink in 10 msec. The difference from the dynamic surface tension shall be within 3 mN / m in each case.
Of the black ink application points, only the first black ink is applied to the non-boundary area other than the boundary area, or the first black ink and the second black ink are applied, and the non-black ink is applied. The dynamic surface tension of the black ink applied to the boundary region in 50 msec is set to 45 mN / m or more, and the dynamic surface tension is set to 45 mN / m or more.
An inkjet recording method characterized in that the width of the boundary region is 40 μm or more and 130 μm or less. The inkjet recording method according to claim 1, wherein the cyan ink, the magenta ink, and the yellow ink contain a resin-dispersed pigment in which the cyan ink, the magenta ink, and the yellow ink are dispersed with a resin dispersant. An inkjet recording method for recording an image on plain paper or glossy paper using an ink set composed of a plurality of water-based inks containing pigments.
The ink set is composed of black ink containing a first black ink and a second black ink, cyan ink, magenta ink, and yellow ink.
The dynamic surface tension of the first black ink at 50 msec is 45 mN / m or more.
The dynamic surface tensions of the second black ink, the cyan ink, the magenta ink, and the yellow ink in 10 msec are 40 mN / m or less, respectively.
The difference in dynamic surface tension between the cyan ink, the magenta ink, and the yellow ink at 10 msec is within 3 mN / m in any combination.
The first black ink contains a self-dispersing pigment in which at least one of a carboxylic acid group and a phosphonic acid group is directly bonded or via another atomic group on the surface of carbon black particles having a DBP oil absorption of 100 mL / 100 g or more. death,
The second black ink contains a resin-dispersed pigment in which carbon black having a DBP oil absorption of 100 mL / 100 g or less is dispersed with a resin dispersant.
The cyan ink, the magenta ink, and the yellow ink contain a resin-dispersed pigment.
When recording an image on the plain paper, the image is recorded in the unit area of the plain paper in one scan.
Of the black ink application points, only the second black ink is applied to the boundary region between the cyan ink, the magenta ink, and at least one of the yellow ink application points, or the black ink is applied. The dynamic surface tension of the black ink applied to the boundary region together with the first black ink and the second black ink in 10 msec, and the cyan ink, the magenta ink, and the yellow ink in 10 msec. The difference from the dynamic surface tension shall be within 3 mN / m in each case.
Of the black ink application points, only the first black ink is applied to the non-boundary area other than the boundary area, or the first black ink and the second black ink are applied, and the non-black ink is applied. The dynamic surface tension of the black ink applied to the boundary region in 50 msec is set to 45 mN / m or more, and the dynamic surface tension is set to 45 mN / m or more.
The width of the boundary region shall be 40 μm or more and 130 μm or less.
When recording an image on the glossy paper,
An inkjet recording method characterized in that only the second black ink is applied to a portion to which the black ink is applied. The inkjet recording method according to claim 3, wherein when the image is recorded on the glossy paper, the image is recorded in the unit area of the glossy paper by a plurality of scans. An inkjet recording method for recording an image on plain paper or glossy paper using an ink set composed of a plurality of water-based inks containing pigments.
The ink set is composed of black ink containing a first black ink and a second black ink, cyan ink, magenta ink, and yellow ink.
The dynamic surface tension of the first black ink at 50 msec is 45 mN / m or more.
The dynamic surface tensions of the second black ink, the cyan ink, the magenta ink, and the yellow ink in 10 msec are 40 mN / m or less, respectively.
The difference in dynamic surface tension between the cyan ink, the magenta ink, and the yellow ink at 10 msec is within 3 mN / m in any combination.
The first black ink contains a self-dispersing pigment in which at least one of a carboxylic acid group and a phosphonic acid group is directly bonded or via another atomic group on the surface of carbon black particles having a DBP oil absorption of 100 mL / 100 g or more. death,
The second black ink contains a resin-dispersed pigment in which carbon black having a DBP oil absorption of 100 mL / 100 g or less is dispersed with a resin dispersant.
The cyan ink, the magenta ink, and the yellow ink contain a resin-dispersed pigment.
When recording an image on the plain paper, the image is recorded in the unit area of the plain paper in one scan.
Of the black ink application points, only the second black ink is applied to the boundary region between the cyan ink, the magenta ink, and at least one of the yellow ink application points, or the black ink is applied. The dynamic surface tension of the black ink applied to the boundary region together with the first black ink and the second black ink in 10 msec, and the cyan ink, the magenta ink, and the yellow ink in 10 msec. The difference from the dynamic surface tension shall be within 3 mN / m in each case.
Of the black ink application points, only the first black ink is applied to the non-boundary area other than the boundary area, or the first black ink and the second black ink are applied, and the non-black ink is applied. The dynamic surface tension of the black ink applied to the boundary region in 50 msec is set to 45 mN / m or more, and the dynamic surface tension is set to 45 mN / m or more.
The width of the boundary region shall be 40 μm or more and 130 μm or less.
When recording an image on the glossy paper, the image is recorded in the unit area of the glossy paper by a plurality of scans.
An inkjet recording method characterized in that only the second black ink is applied to a portion to which the black ink is applied. The inkjet recording method according to any one of claims 1 to 5 , wherein the dynamic surface tension of the first black ink in 50 msec is 49 mN / m or more. The inkjet recording method according to any one of claims 1 to 6, wherein the dynamic surface tension of the black ink applied to the non-boundary region in 50 msec is 49 mN / m or more. The first black ink further comprises at least one cation selected from the group consisting of alkali metal ions, ammonium ions, and organic ammonium ions, and Cl ⁻ , Br ⁻ , I ⁻ , ClO ⁻ , ClO _2- , ^and ClO. _3- ^, ClO _4- , NO ^{2- ,} NO _3- ^, SO _{4 2-} , CO ₃ ^2- , HCO _3- ^, HCOO- ^, ( ^COO- ) ² , COOH ( _COO- ⁾ , CH ₃ COO- ^, C ₂ H ₄ ( ^COO- ) ₂ , C ₆ H ₅ COO- ^, C ₆ H ₄ ( ^COO- ) ₂ , PO ₄ ^3- , HPO ₄ ^2- , and H ₂ PO ₄ ^- at least 1 selected from the group. The inkjet recording method according to any one of claims 1 to 7 , which contains a salt composed of a seed anion and a bond thereof. The inkjet recording method according to any one of claims 1 to 8 , wherein an image is recorded using a recording device equipped with a serial recording head.

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