RU2424386C2 - Water-based ink, method of jet application of ink, ink cartridge, unit for ink application, jet device for ink application and method of images formation - Google Patents

Abstract

FIELD: printing industry.

SUBSTANCE: ink that contains water, water-insoluble colour and multiple water-soluble organic dissolvents is applied onto a carrier. Specified dissolvents contain a good solvent for the specified colour (A) and a poor solvent for the specified colour (B) with the ratio of A to B, equal from 10:5 to 7:9. The water-soluble organic dissolvent that has maximum value Ka, identified by Bristow method, among all water-soluble organic dissolvents in the ink, relates to poor dissolvents.

EFFECT: high extent of surface coating and high density of OD image even with small quantity of ink.

3 cl, 16 dwg, 11 tbl, 16 ex

Description

State of the art

FIELD OF THE INVENTION

The present invention relates to a water-based paint, which contains a water-insoluble coloring material. More specifically, the present invention relates to a water-based ink, which is preferably used in a printing method and a printing device using an inkjet printing system, and, in addition, in an inkjet image forming method.

State of the art

It is known that a paint containing a water-insoluble coloring material, such as a pigment (pigment paint), can provide images that are excellent in properties such as water resistance or light fastness. In recent years, various technologies have been proposed to improve the optical density of an image formed with such ink. For example, a method is proposed for further improving the image density using a paint containing self-dispersing carbon black and a certain salt (refer, for example, to publication of patent 1). A technology for forming a high-quality image is also proposed in which an ink jet ink composition comprising a pigment, polymer particles, a water-soluble organic solvent and water is applied to a printing medium using an aqueous solution containing a multivalent metal to cause a reaction between the ink composition and the multivalent metal in an aqueous solution (see, for example, unexamined application for publication of Japanese patent No. 2000-63719). In these technologies, the existing pigment dispersed in the ink is forced to agglomerate on the surface of the printing medium in order to prevent the penetration of the pigment into the printing medium, whereby a higher density image can be obtained than with conventional pigment ink.

However, as a result of intensive research, the authors of the present invention found that when in the above technologies, the pigment particles agglomerate on a printing medium, the surface area of the printing medium to be coated with the coloring material using a predetermined number of ink droplets (the so-called area coefficient) , tends to be insufficient. This means that the above technologies require more ink to obtain the same image density compared to conventional pigment inks, in which the pigment is dispersed using a polymer dispersant or the like. This point requires further improvement. Although there is a way to obtain a large area coefficient using small droplets of ink by increasing the permeability of the ink in the printing medium, ink with increased permeability diffuses not only on the surface of the printing medium, but also inside it, resulting in insufficient image density.

The authors of the present invention studied both the advantages and disadvantages of conventional inks and analyzed the characteristics of images formed using such inks. They found that when the ink contains a larger amount of coloring material, problems arise that the coloring material remains on the surface of the printing medium in a higher amount, visually heterogeneous raster dots form, or the coloring material is not used efficiently, but is wasted on loss in a print medium. The inventors have found that images that are superior to conventional images can be obtained by solving at least one of the technical problems below. The present invention solves at least one of the following problems.

1. When a pigment, which is in a state of dispersion, in the ink is forced to agglomerate on the surface of the printing medium, the surface area of the printing medium that the ink can cover with a drop of ink of a predetermined volume (the so-called area coefficient) may be insufficient. In this case, the amount of ink required to obtain the same image density increases.

2. When the permeability of the ink increases, the ink is distributed not only on the surface of the printing medium, but also penetrates in the direction along the thickness of the printing medium. Accordingly, the coloring material cannot be distributed at a high density near the surface of the printing medium, and a high image density cannot be obtained.

Thus, it is an object of the present invention to provide a water-based ink that provides sufficient area even with a small drop of pigment ink (large area coefficient), can provide an image having a high OD (image density), and has long-term storage stability.

Another objective of the present invention is to provide an inkjet printing method using the above ink to form a high resolution, high OD image using a small amount of ink.

Another objective of the present invention is to provide an ink cartridge, a printing unit, and an inkjet device, which are preferably used in the above printing methods.

In addition, another object of the present invention is to provide an image forming method in which color mixing (spreading) is effectively prevented at the boundary between the black ink region and the color ink region without causing the ink to blur when the color image in which the different colors are adjacent to each other another, printed on plain paper.

The technical concept of the present invention can be formulated as follows: a water-based paint that contains water, many different water-soluble organic solvents and a water-insoluble coloring material, where the above water-soluble organic solvents are a good solvent and a poor solvent for a water-insoluble coloring material to be used , and when the Ka values of the above water-soluble organic solvents are determined with Using the Bristow method, the aforementioned poor solvent has the highest Ka value and diffuses along the surface of the printing medium in the form of a substantially regular circle before the good solvent diffuses, thereby agglomerating the above water-insoluble coloring material during diffusion. Due to this structure, the water-based ink of the present invention has the advantage that it does not have to contain a large amount of a coloring material that diffuses and is consumed in the form of losses in the printing medium, without contributing to image density, as is the case in modern prior art. In addition, the image can be formed in perfect condition, that is, most of the coloring material does not localize on the surface of the printing medium, and at the same time, the coloring material does not reach the back of the printing medium, thereby making it possible to print on both sides . As a result, a high density image is uniformly formed on the surface of the printing medium.

The best way to implement the invention

The above objectives are achieved using the present invention, discussed below. In other words, a water-based paint in accordance with one aspect of the present invention contains water, a variety of different water-soluble organic solvents and a water-insoluble coloring material, where the above water-soluble organic solvents consist of a good solvent for the above water-insoluble coloring material and a poor solvent for the above water-insoluble coloring material, and when the total amount (% wt.) of good solvents in the paint is denoted as A, and the total amount (% wt.) of bad solvents in the paint is denoted as B, the ratio of A to B ranges from 10: 5 to 10:30, in both cases the extreme values are included in these ranges, and when the Ka values of the above water-soluble organic solvents determined using the Bristow method and the obtained values are compared with each other, the water-soluble organic solvent having the highest Ka value is a poor solvent.

In addition, the water-based paint in accordance with another aspect of the present invention contains water, a variety of different water-soluble organic solvents and a water-insoluble coloring material, where the above water-soluble organic solvents consist of a good solvent for the above water-insoluble coloring material and a poor solvent for the specified above water-insoluble coloring material, and when the Ka values of the above water-soluble organic solvents are determined using the Bristow method and the obtained values are compared with each other, the water-soluble organic solvent having the highest Ka value is a poor solvent, this is additionally characterized by the fact that the state of connection of this water-based paint with plain paper is determined as follows: when the paint drip onto plain paper using a needle, with a needle diameter of 28 G (inner diameter 0.18 mm and outer diameter 0.36 mm) located 4 mm above the surface of the plain boom and, and it is fixed on the surface, the measured value of the diameter of the raster dot of the paint obtained immediately after the collision of the paint with plain paper, indicated by dI, the measured value of the largest diameter of the spread of paint after fixing the paint on plain paper, indicated by dS, and the measured value of the largest diameter of the spread of water-insoluble dyeing material in the paint after fixing the paint on plain paper, denoted by dC, satisfy the ratio below (formula 1):

dC <dI <dS (Formula 1)

and the penetration depth of the water-insoluble coloring material in plain paper is less than 30 μm after the ink is printed by inkjet printing and fixed on plain paper.

In addition, in another aspect of the present invention, there is provided an ink jet printing method, which is characterized by the step of ejecting a water-based ink having the above structure using an ink jet printing method.

In addition, in another aspect of the present invention, there are provided: an ink cartridge for storing a water-based ink having the above structure; a printing unit comprising a unit for storing water-based inks having the above structure and an ink jet head for ejecting ink; and an inkjet printing apparatus comprising a unit for storing water-based ink having the above structure, and an inkjet head for ejecting ink.

In addition, in another preferred aspect of the present invention, there is provided a method of forming an image by inkjet printing on plain paper using black ink and at least one water-based color ink, characterized in that the water-based ink having the above a structure is used as black ink, and when an image in which an image formed with black ink and an image formed with colored ink are formed next to m with each other, the image is formed by scanning to apply black ink to the area of the black image, and then scanning to apply color paint to the area in which the black image has already been formed.

In addition, in another aspect of the present invention, there is provided a water-based paint that contains water, a variety of different water-soluble organic solvents and a water-insoluble coloring material, wherein the above water-soluble organic solvents consist of a good solvent for the above water-insoluble coloring material and a poor solvent for said above water-insoluble coloring material, and when the highest Ka value of the above water-soluble organically x solvents are determined using the Bristow method, the water-soluble organic solvent having the highest Ka value is a poor solvent, and a poor solvent penetrates the printing medium before it makes a good solvent, so that it agglomerates the above water-insoluble coloring material in good solvent on the surface of the print medium.

(Effect of the invention)

In accordance with the present invention, there is provided a water-based paint, which is a pigmented paint that has a sufficiently large area coefficient even with a small number of drops of paint and creates an image with a high OD (image density). In addition, in accordance with the present invention, when using such ink, there are provided: an inkjet printing method for forming a high-resolution image with a high OD even based on a small additional amount of ink; ink cartridge, preferably used for the above printing method; print unit; and inkjet printing apparatus. In addition, in accordance with the present invention, there is provided an image forming method in which color mixing (spreading) is effectively prevented at the boundary between the black ink region and the color ink region without causing the ink to blur when a color image is formed on plain paper in which various colors are next to each other.

Brief Description of the Drawings

Figure 1 is a longitudinal section of the head of the device for inkjet printing.

Figure 2 is a longitudinal section of the head of the device for inkjet printing.

Figure 3 is a General perspective view for a head consisting of several heads, as shown in figure 1.

FIG. 4 is a perspective perspective view showing an example of an inkjet apparatus.

Figure 5 is a longitudinal section of a paint cartridge.

6 is a perspective perspective view showing an example of a printing unit.

7 is a view showing an example of a structure of a print head.

Fig. 8 is an example of a printhead used in the present invention.

Fig.9 is another example of a printhead used in the present invention.

Figure 10 is another example of a printhead used in the present invention.

11 is another example of a printhead used in the present invention;

12 is another example of a printhead used in the present invention.

13 is another example of a printhead used in the present invention.

Figa, 14B, 14C and 14D schematically illustrate the state when a drop of ink of the present invention falls on the surface of the printing medium.

15 schematically illustrates the difference between the drops of ink from the examples and comparative examples after fixing the ink on plain paper.

Fig is a schematic view showing the difference in the distributions of the coloring material in the depth direction after fixing the paints on plain paper from a specific example and comparative example.

Description of Preferred Embodiments

The present invention will now be described in detail below with reference to preferred embodiments. First, the poor solvent and good solvent used in the present description are described. Detailed definitions will be given below, but as a first approximation, a water-soluble organic solvent that causes a stable dispersion of a water-insoluble coloring material in it is called a good solvent, and a water-soluble organic solvent that causes an unstable dispersion in it of a water-insoluble coloring material is called a poor solvent, regardless of the method of dispersing water coloring material. The authors of the present invention paid attention to water-soluble organic solvents contained in a water-based paint together with a water-insoluble coloring material, and classified them into good solvents having a high ability to dissolve or disperse a water-insoluble coloring material, and poor solvents having poor dissolution or dispersibility coloring material. The present invention is characterized in that the water-based paint is designed in such a way that the relationship between the poor solvent and the good solvent in the paint is established in a certain range. By adapting such a structure, an image can be obtained with reduced ink spreading and spreading even on plain paper, for which there are various problems when forming an image using conventional water-based ink. The present invention provides a paint having a significantly larger area coefficient (forms a large area with a small number of paint droplets) and capable of forming an image with a high OD. In addition, the use of such ink makes it possible to print at high speed, reduce the size of the printing device and reduce costs, including consumables, and, in addition, it implements images with excellent strength and higher print density. Having discovered remarkable effects, such as the formation of high quality images, the authors completed the present invention.

The reason why such advantages can be obtained using the present invention is not well understood, but the authors of the present invention reason as follows. As a rule, when an image is formed using water-based ink on printing paper such as plain paper, it is necessary to produce a coloring material that is effectively held on paper to realize high print density and print quality. As a method for accomplishing this task, there is a method of attaching a reaction solution to a printing medium, and then attaching pigment ink to a printing paper so as to obtain excellent print density and print quality. There is also a method of using a special dispersant to achieve both storage stability and high print density. However, in accordance with the studies of the authors of the present invention, obtaining sufficient print density using these methods is still difficult. In particular, it is impossible to obtain a sufficiently large area coefficient using a small drop of ink, as well as obtaining a high print density.

The water-based paint of the present invention contains at least water, a water-insoluble coloring material and a variety of different water-soluble organic solvents. The above water-soluble organic solvents include a good solvent for the above water-insoluble coloring material and a poor solvent for the above water-insoluble coloring material. When a water-based paint is in a liquid state, where water, a water-insoluble coloring material and water-insoluble organic solvents, including both a good solvent and a poor solvent for a water-insoluble coloring material, are mixed in a certain respect, storage stability of a water-insoluble coloring material such as pigment.

When such a water-based ink of the present invention is printed on a printing medium, and in particular on plain paper, exceptionally excellent print density and print quality can be obtained. The reason is supposed to be the following: as shown in FIG. 14A, when a drop of ink 1301 of the present invention is applied to a printing medium 1300, such as plain paper, the ratio of the components of water, water-insoluble ink and good solvent and poor solvent to water-insoluble ink the material contained in the ink changes after the ink reaches the print medium. That is, as shown in FIGS. 14A and 14B, after a drop of ink 1301 hits the surface 1300 of the printing medium, when the ink is fixed on the printing medium, the poor solvent 1307 having a high Ka value diffuses first upon water evaporation among the water-soluble ones organic solvents in the area near the surface of the printing medium in the form of an almost regular circle, and then a good solvent with a low Ka value diffuses, so that a ink dot is formed.

Fig.14B-14D schematically depict the state of the ink after it enters the medium 1300 for printing, and until it is fixed on it. If in this case scattering of ink raster points is considered, the concentration of poor solvent should be high at the periphery of the raster dot 1302, where the ink and paper are in contact than at the center of the raster dot 1303. As a result, when the raster dot of the ink diffuses along the surface of the printing medium in the form of a substantially regular circle, the concentration of poor solvent 1307 increases sharply, the water-insoluble ink material becomes unstable, so that the ink material agglomerates or destroys the dispersion state. As a result, forming a border that is essentially a regular circle on the surface of the paper (see FIG. 14B), the water-insoluble ink material 1304 remains close to the surface of the printing medium 1300, and a roller of water-insoluble ink material is formed at the periphery of the raster dot. Thus, it is believed that the raster dot of the water-insoluble coloring material is formed in the form of a regular circle and that the raster dot is immobilized on paper in this state (see FIG. 14C). At this point, the formation of a raster dot using a water-insoluble coloring material is completed, but the water-soluble organic solvents and the water contained in the paint still diffuse and are distributed in radial form. In other words, even after the formation of a raster dot using a water-insoluble coloring material, water and water-soluble organic solvents diffuse along the surface of the printing medium. Subsequently, the water-soluble organic solvents evaporate or penetrate the printing medium in the center 1303, where the concentration of a good solvent is high, and the water-insoluble coloring material also precipitates in this region, so that a raster dot 1305 for image formation is obtained (see FIGS. 14A-14D) . The color image formed using the above method has a sufficiently large area coefficient even from a small number of ink droplets and has a high print density. In addition, since the generation of ink smearing is significantly reduced, a high quality image can be obtained.

For the mechanism discussed above, a good solvent and a poor solvent used in the present invention are determined from the condition that it can favorably maintain the dispersed state of the water-insoluble coloring material or not. In other words, a good solvent or a poor solvent is determined depending on their interaction with a water-insoluble coloring material or its dispersant. Accordingly, when a good solvent and a poor solvent are chosen to produce the paint of the present invention, it is preferable to observe the dispersed state or stability of the water-insoluble coloring material to be used with the solvent so as to select good and bad solvents based on the observation results. The inventors of the present invention have conducted various studies regarding the criteria for selecting good and bad solvents that will provide the effects provided by the present invention based on the relationship with the effects of the present invention. A solution containing approximately 50% of the mass. the solvent to be determined and the water-insoluble coloring material to be used in the paint is kept in a dispersed state at 60 ° C for 48 hours. The particle size in the above solution is compared with the particle size of another pigment dispersion solution containing the same pigment, but a small amount of a defined solvent or not containing it at all. If the particle size of the test solution becomes larger, the solvent is defined as being a poor solvent, and if it is almost the same or smaller, then as a good solvent. The inventors of the present invention have found that the above definitions are extremely consistent with the effects of the present invention.

More specifically, whether the solvent is a good solvent or a poor solvent for a particular water-insoluble coloring material is determined as follows. First, two solutions of the dispersion of water-insoluble coloring material A and B are prepared:

A: a dispersion solution of a water-insoluble coloring material containing 50% of the mass. water-soluble organic solvent to be determined, 5% of the mass. water-insoluble coloring material or in the amount of water-insoluble coloring material and substances for its dispersion, and 45% of the mass. water; and

B: a solution of an aqueous dispersion containing a total of 5% of the mass. water-insoluble coloring material and a substance for dispersing it, but without a water-soluble organic solvent.

Subsequently, the above dispersion solution A was stored at 60 ° C. for 48 hours, and then cooled to ambient temperature. The particle size of the dispersion solution A is measured using a particle size analyzer for concentrated solutions (product name: FPAR-1000; manufactured by Otsuka Electronics Co., Ltd.). Similarly, the particle size of the above solution B of an aqueous dispersion is measured using the above particle size analyzer for concentrated solutions. After that, the particle size values of the above dispersion solution A and the aqueous dispersion solution B are denoted as the particle size (A) and particle size (B), respectively, and using these values, it is determined whether the solvent is a good solvent or a poor solvent according to the definitions described below. And a paint having a structure of the present invention is prepared using a good solvent and a poor solvent so determined to confirm that the excellent effects described above are obtained. Regarding the criteria for a good solvent and a poor solvent, when the particle size (A) is larger than the particle size (B), as defined above, the water-soluble organic solvent is called a poor solvent. When the particle size (A) is the same or smaller than the particle size (B), the water-soluble organic solvent is called a good solvent.

The water-based paint of the present invention may have the same composition as a conventional water-based paint containing a water-insoluble coloring material, with the exception that the water-soluble organic solvents have the above specific features. In other words, the first feature of the water-based paint of the present invention is that it contains water, a plurality of water-soluble organic solvents and a water-insoluble coloring material, where the water-soluble organic solvents include at least one good solvent and at least at least , one bad solvent, which are determined by the determination method described above, and when the Ka values of these water-soluble organic solvents are determined by the method Ristow and the obtained values are compared with each other, water-soluble organic solvent having a largest value Ka, is a poor solvent. As a result, the dispersion stability of a water-insoluble coloring material in the ink becomes extremely excellent, and at the same time, it has a sufficiently large area coefficient even for a small drop of ink and shows a high print density when printed on a printing medium, in particular on plain paper, making image formation possible with exceptionally excellent print quality.

The following explains the determination of Ka using the Bristow method. This value is used as the index of the permeability of the ink in the print medium.

In the case of liquid paint, as an example, if the permeability of the paint is denoted by V, i.e. the amount of ink per 1 m ² , then the amount of ink penetrating the printing medium V (ml / m ² = μm), after a certain time t, after the ejection of a drop of ink, is represented by the following Bristow formula:

V = Vr + Ka (t-tw) ^1/2 .

In this case, immediately after applying a drop of ink to the surface of the printing medium, almost all the ink is adsorbed by non-uniform parts on the surface of the printing medium (in large portions on the surface of the printing medium), and the ink hardly penetrates into the inside of the printing medium. The time when ink almost does not penetrate into the interior of the printing medium is referred to as contact time (tw), and the amount of ink adsorbed by the non-uniform parts on the printing medium during contact time is referred to as Vr. When the time elapsed after the ink is attached exceeds the contact time, the amount of ink penetrated into the printing medium increases with an additional time exceeding the contact time, that is, by an amount that is proportional to (t-tw) ^1/2 . Ka is the proportionality constant of this increase in quantity, and it shows a value corresponding to the penetration rate. The Ka value can be measured using the Bristow method using a dynamic fluid permeability research facility (for example, product name: Dynamic Permeability Tester S; manufactured by Toyo Seiki Seisaku-sho, Ltd.), or the like.

In addition, when the total amount (% wt.) Of the good solvent in the water-based paint of the present invention is indicated as A, and the total amount (% wt.) Of the bad solvent in the paint of the present invention is indicated as B, the water-based paint of the present invention is selected as so that the ratio of A to B [total amount (% wt.) of good solvent in the paint to the total amount (% wt.) of bad solvent in the paint] is set between 10: 5 or more and 10:30 or less. It should be noted that the term “total amount” is used here to mean that when, for example, there are many good solvents, all good solvents are included. In addition, the expression "the ratio of A to B is between 10: 5 or more and 10:30 or less" is used here to mean that when A is 10, B is between 5 and 30, and both extreme values are included in this range.

In addition, in another aspect of the present invention, there is provided a water-based paint comprising water, a variety of different water-soluble organic solvents, and a water-insoluble coloring material, wherein the above water-soluble organic solvents consist of a good solvent for the above water-insoluble coloring material and a poor solvent for the above water-insoluble coloring material, and when the Ka values of the above water-soluble organic solvents are determined tsya using the Bristow method and the obtained values are compared with each other, water-soluble organic solvent having a largest value Ka, is a poor solvent, and wherein, furthermore, paint adhesion behavior with respect to the plain paper is as described below.

It has been found that when the water-based paint of the present invention having the above structure is fixed on plain paper, it exhibits a behavior that is different from ordinary paint. This behavior enables the ink to have a sufficiently large area coefficient even with a small number of ink droplets and to achieve image formation with high OD (reflection density). In addition, when a color image in which areas of different colors are adjacent to each other is printed on plain paper, an effect of preventing ink blooming can be achieved. In other words, whether the ink of the present invention provides the above remarkable effects or not, can be determined by measuring the behavior of the ink when the ink is fixed on plain paper in accordance with the following method.

To measure the behavior of water-based paints in relation to plain paper, firstly, a needle with a diameter of 28 G (inner diameter 0.18 mm and outer diameter 0.36 mm) is used, and the tip of the needle is located at a height of 4 mm from the surface plain paper and then paint is dripped from this height. Then the paint is fixed on the surface of the paper. At this time, the diameter of the raster dot of the ink is measured immediately after the ink hits the plain paper, and the measured value is denoted as dI, and the largest diameter of the ink distribution after the ink is fixed on the plain paper, and the measured value is denoted as dS. The largest diameter of the water-insoluble coloring material in the ink is also measured after the ink is fixed on plain paper and the measured value is denoted as dC. In the case of the water-based paint of the present invention, the above obtained measurement values are in the ratio dC <dI <dS (formula 1). In addition to this, the penetration depth of the water-insoluble coloring material in plain paper is less than 30 μm after the ink is printed and fixed on plain paper by inkjet printing.

The above formula 1 means that the largest diameter dC of the spread of the water-insoluble coloring material in the ink depicted in FIG. 14C is smaller than the diameter dI of the raster dot of the ink measured immediately after the ink, which is shown in FIG. 14B, and the largest diameter dS the spread of ink after fixing the ink on the printing medium shown in fig.14D, is greater than dI.

Given the structure of the water-based ink of the present invention, the above inequality means that, after applying a drop of ink to the printing medium, due to the poor solvent with a high Ka value, the coloring material diffuses and is fixed near the surface of the printing medium in a substantially regular form circle, and that water and water-soluble organic solvents contained in the ink additionally diffuse radially near the surface of the printing medium, and that water-insoluble The carrier material is first immobilized, and then water and water-soluble organic solvents diffuse into the printing medium. In addition, the fact that the penetration depth of the water-insoluble ink after fixing the ink on the printing medium is less than 30 μm means that when the water-insoluble ink is applied to the printing medium, it effectively covers the surface of the printing medium.

In contrast, when the behavior of conventional water-based inks with respect to plain paper is measured in the same way, the largest diameter dC of the spread of water-insoluble coloring material in the ink after fixing the ink on plain paper becomes larger than the diameter dI of the ink raster point measured immediately after hitting paint on plain paper, and their relationship is expressed as dI <dC <dS. In addition, the boundary between the region of the water-insoluble coloring material and the region of water and the water-soluble organic solvents distributed around it becomes less distinct than the boundary for the water-based paint of the present invention. This shows that for ordinary ink, when water and water-soluble organic solvents diffuse in the printing medium after ink has been spilled onto plain paper, water-insoluble ink is also distributed with them, thereby the ink cannot effectively cover the surface of the paper. In addition, it also shows that since the border of the coloring material is not a regular circle, printing also becomes fuzzy. In addition, even if between dC, dI and the largest diameter dS of the ink distribution after fixing the ink on the printing medium, the ratio dC <dI <dS may occur if the penetration depth of the water-insoluble coloring material after fixing the ink is 30 μm or more, the water-insoluble coloring material not only diffuses near the surface of the paper, but also penetrates in the depth direction of the paper. This case also demonstrates that the coloring material does not effectively cover the paper.

In the present invention, dI, dS and dC, as defined above, are measured in accordance with the following methods.

First, a small amount of a water-soluble dye is added to the paint, which is soluble in the water-soluble organic solvents contained in the paint to be measured and has a hue different from the color of the water-insoluble coloring material that is a component of the paint, and using the paint thus obtained the largest ink distribution diameter dS after fixing the ink on plain paper can be measured by visual observation. In other words, by adding a small amount of a water-soluble dye that is soluble in the water-soluble organic solvents contained in the paint to be measured, and having a shade different from the shade of the water-insoluble coloring material that is a component of the paint, the distribution conditions of water and water-soluble organic solvents, which diffuse in plain paper after fixing the water-insoluble coloring material in the ink, can be confirmed by visual observation, due to the presence of the above water-soluble dye added to the paint.

The diameter dI of the ink dot of the ink immediately after the ink drop hits the plain paper is measured using Face CONTACT-ANGLEMETER CA-P, manufactured by Kyowa Interface Science Co., Ltd. More specifically, using a needle with a diameter of 28 G (inner diameter 0.18 mm and outer diameter 0.36 mm), the tip of the needle is placed at a height of 4 mm from the surface of plain paper, then paint is dripped from this height onto plain paper, and after dripping the diameter of the droplet of paint is read from the scale of the measuring angle of wetting, thereby measuring the value of dI. That is, the above recorded values represent the diameter of the raster dot of the ink dI immediately after the ink touches the plain paper.

The largest diameter dS of the spread of ink after fixing the ink on plain paper and the largest diameter dC of the spread of water-insoluble coloring material in the ink after fixing the ink on plain paper is measured as follows. The raster dot of the ink that has fallen on plain paper under the conditions described above is left for 6 hours or more, and after stabilization of the ink drop, the size of the raster dot of the ink is measured. The largest ink distribution diameter dS after fixing the ink on plain paper is obtained by measuring the largest linear distribution size of the shade of a water-soluble dye having a shade different from the shade of the water-insoluble coloring material contained in the ink. After that, the largest diameter dC of the distribution of the water-insoluble coloring material in the ink is obtained after fixing the ink on plain paper by measuring the largest linear distribution size having a hue of the water-insoluble coloring material contained in the paint.

In addition, the penetration depth of the water-insoluble coloring material after fixing the ink on plain paper is obtained by transversely cutting the printing area of plain paper after printing using an inkjet printer, and then observing the cross section through a microscope.

So that the raster dot of the paint has such a shape that the total amount (% by mass) of good solvent (s) in the paint is indicated by A and the total amount (% by mass) of bad solvent (s) in the paint is indicated by B, the ratio of A to B [total (% wt.) good solvent (s) in the paint: the total amount (% wt.) of bad solvent (s) in the paint] is preferably in the range between 10: 5 or more and 10:30 or less, more preferably in the range between 10: 5 or more and 10:10 or less, and especially before respectfully, between 10: 6 or more and 10:10 or less.

The water-based paint of the present invention is characterized in that when the Ka values of many different types of water-soluble organic solvents contained in the paint are determined using the Bristow method and the obtained values are compared with each other, the water-soluble organic solvent having the highest Ka value is bad solvent. In addition, in accordance with the studies of the authors of the present invention, to achieve further improvement in the quality of the printed image, the ink is preferably selected so that the Ka value becomes less than 1.5 (ml / m ² / ms ^1/2 ), more preferably 0.2 ( ml / m ² / ms ^1/2 ) or more, but less than 1.5 (ml / m ² / ms ^1/2 ). In other words, if the ink is prepared so that it has a Ka value of less than 1.5 (ml / m ² / ms ^1/2 ), the separation of solid products and liquid occurs at an early stage of the process, when the ink penetrates the printing medium, that a high quality image can be obtained with very little blurry ink. At the same time, by setting the Ka value of the ink to 0.2 (ml / m ² / ms ^1/2 ) or more, a more preferable fixing property can be obtained.

It is noted that the Ka value determined by the Bristow method of the present invention is measured using plain paper [for example, PB paper used for an electrophotographic copy machine, a sheet printer (laser printer) or an inkjet printer manufactured by Canon Inc ., or PPC paper used for an electrophotographic copy machine]. The measurement environment is organized under the assumption of a typical office environment, such as a temperature between 20 ° C and 25 ° C and a humidity between 40% and 60%.

Incidentally, when an image is formed using both black and color inks on plain paper, if the water-based ink of the present invention is used as a black ink, as described above, it is believed that the agglomeration or destruction of the dispersion of the coloring material constituting the black paint is faster than with other paints. In the image forming method of the present invention, the water-based ink of the present invention is used as black ink, and the image formation using the color ink is carried out after the image formation with the black ink, and more preferably, a sweep is applied for applying the black ink, and after the implementation of at least some part of one scan carry out a scan for attaching colored paint. By adapting this method, even when the black ink comes into contact with the color ink, mixing of colors or spreading of the colors between the black ink and the color ink on the paper does not occur, thereby achieving an excellent anti-spread effect in printing. In other words, in accordance with the present invention, the excellent effects described above can be achieved by only imaging with each ink from black and color inks at a certain time interval, replacing a multi-pass multi-scan printing method that requires a long printing time, or a method using systems with different regeneration for black and color inks, which lead to an increase in the size of the devices.

In addition, when the water-based ink of the present invention is used, since the coloring material contained in the ink is effectively held in the printing medium, for the reasons described above, it becomes possible to carry out high density printing with less ink ejected (drop volume), than for ordinary paint. In addition, since printing can be done with less ink, effects such as reducing the cost of image formation or achieving a shorter curing time than conventional ink can be obtained.

The water-based paint of the present invention is characterized in that the water-soluble organic solvents contained in the paint have a composition as described above with respect to the water-insoluble coloring material to be used. In addition to such a composition, the water-based paint of the present invention may have the same composition as a conventional water-based paint. Each component constituting the paint of the present invention will be described below. First, an aqueous medium dispersing a water-insoluble coloring material will be described.

<Aquatic environment>

The water-based paint of the present invention contains a mixture of solvents from water and water-soluble organic solvents. Water soluble organic solvents may be selected from the substances listed below. In the present invention, when water-soluble organic solvents are selected, it is first determined whether the solvent is a good solvent or a poor solvent with respect to the water-insoluble coloring material to be used, and then, based on the determination results, water-soluble organic solvents are selected so that they contain at least both a good solvent and a bad solvent, and that the content of each water soluble organic solvent finds I was within the limits defined in the present invention, and then mix them properly so as to prepare the paint.

Specific examples of such water-soluble organic solvents may include: alkyl alcohols containing from 1 to 4 carbon atoms, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol or tert-butyl alcohol butyl alcohol; amides such as dimethylformamide or dimethylacetamide; ketones or ketone alcohols such as acetone or diacetone alcohol; ethers, such as tetrahydrofuran or dioxane; polyalkylene glycols such as polyethylene glycol or polypropylene glycol; alkylene glycols in which the alkylene group contains from 2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol or diethylene glycol; lower alkyl ether acetate, such as polyethylene glycol monomethyl ether acetate; glycerol; lower alkyl polyhydric ethers, such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, or triethylene glycol monomethyl (or ethyl) ether; N-methyl-2-pyrrolidone, 2-pyrrolidone and 1,3-dimethyl-2-imidazolidinone. In addition, deionized water is preferably used as water.

The content of water-soluble organic solvents in the water-based paint of the present invention is not limited in any way. Preferably it is in the range from 3% of the mass. up to 50% of the mass. in relation to the total weight of the paint. The water content in the paint is preferably in the range from 50% of the mass. up to 95% of the mass. in relation to the total weight of the paint.

In a preferred embodiment of the present invention, the type and content of water-soluble organic solvents constituting the water-based paint are selected so that when the total amount (% by weight) of good solvent (s) in the paint is indicated by A, and the total amount (% by weight. ) bad solvent (s) in the paint is denoted by B, the ratio of A to B is in the range from 10: 5 to 10:30, and both extreme values are included in these limits, preferably in the range from 10: 5 or more to 10:10 or less and more preferably in the range of 10: 6 or more to 10:10 or less.

In accordance with the detailed studies of the inventors of the present invention, when the ratio of the good solvent (s) contained in the water-based ink is higher than the above limits, it becomes difficult to obtain a high density print, although it is excellent in storage stability. In contrast, when the ratio of the good solvent (s) contained in the water-based ink is less than the above limit, sufficient storage stability may not be obtained, although a high print density can be obtained. In contrast to these cases, when the ratio of the good solvent (s) and the poor solvent (s) in the water-soluble organic solvents contained in the ink is set as above, both ink stability during storage and high print density can be obtained. In addition, in the present invention, as stated above, when the type of water-soluble organic solvents contained in the paint is determined in accordance with the Ka value determined using the Bristow method, which is an index showing the permeability of each water-soluble organic solvent in the medium for printing, can be obtained water-based ink, which has a sufficiently large area coefficient even with a small amount of ink droplets, and you can achieve a high density n print. Such impacts have not been achieved to date.

The stability of the paint during storage, as a rule, means the stability of the paint in a state without evaporation of water. High print density is realized through the phenomenon of pigment agglomeration, which occurs when the solvent is distributed on the paper during the formation of a raster dot of the ink when ink enters the paper.

In addition to the effects described above, such as the realization of both storage stability and high print density, the combined use of a good solvent and a poor solvent in the ink leads to the effect of preventing, to a certain extent, pigment agglomeration when water evaporates from the ink. More specifically, when droplets of ink are attached to the nozzle exit of the print head, the density of the coloring material in the ink increases due to the evaporation of the ink. At this point, the combined presence of a good solvent and a poor solvent in the paint can to some extent prevent the pigment from agglomerating under the action of a good solvent. Thus, when a good solvent is contained in the ink, pigment agglomeration at the nozzle exit of the print head is prevented, and for this reason, it can also be expected that the reliability of the print head regeneration operation will increase.

<Water-insoluble coloring material>

The water-insoluble coloring material constituting the water-based paint of the present invention will now be described. Regardless of the dispersion system, the water-insoluble coloring material constituting the water-based paint of the present invention can be a pigment dispersed with a dispersant based on a resin or a surfactant (a pigment dispersed with a resin, a pigment dispersed with a surface active substance), or a coloring material dispersible without the use of a dispersant, and the like, due to the high dispersibility of the coloring material itself, such as an icro-encapsulated pigment, a self-dispersing pigment having hydrophilic groups attached to the surface of the pigment particles, and a modified pigment in which the polymer organic groups are chemically bonded on the surface of the pigment particles (self-dispersing, polymer binding pigment). Of course, these dispersed pigments of various types can be used in combination. The content of the water-insoluble coloring material is from 0.1% to 15% by weight, and more preferably from 1% to 10% by weight, with respect to the total weight of the paint. These pigments used in the present invention will be described below.

[Pigment]

The pigments used for the water-based paint of the present invention are not particularly limited, and any of the following pigments may be used.

Carbon black is preferred as the pigment used for black ink. Examples of such carbon black may include furnace black, lamp black, acetylene black and gas duct black. More specifically, commercially available products can be used as described below: Raven 7000, Raven 5750, Raven 5250, Raven 5000 ULTRA, Raven 3500, Raven 2000, Raven 1500, Raven 1250, Raven 1200, Raven 1190 ULTRA-II, Raven 1170 and Raven 1255 (all manufactured by Colombia Co., Ltd.), Black Pearls L, Regal 400R, Regal 330R, Regal 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, Monarch 2000 and Valcan XC-72R (all produced by Cabot Corp.), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170 , Printex 35, Printex U, Printex V, Printex 140U, Printex 140V, Special Black 6, Special Black 5, Special Black 4A and Special Black 4 (all manufactured by Degussa Corp.), No. 25, No. 33, No. 40, No. 47, No. 52, No. 900, No. 2300, MCF-88, MA600, MA7, MA8 and MA100 (all manufactured by Mitsubishi Chemical Corp.). In addition, carbon black newly produced for the present invention may also be used. However, the present invention is not limited to this, but any commonly known carbon black can be used. Furthermore, such a black pigment is not limited to carbon black, but magnetic particles such as magnetite or ferrite or titanium black can also be used as such black pigment.

Specific examples of organic pigment may include insoluble azo pigments such as Toluidine Red, Toluidine Maroon, Hansa Yellow, Benzidine Yellow or Pyrazolone Red, soluble azo pigments such as Lithol Red, Helio Bordeaux, Pigment Scarlet or Permanent Red 2B, vat dye derivatives, derivatives such as alizarin, indantrone or thioindigo maroon, phthalocyanine pigments such as phthalocyanine blue or phthalocyanine green, quinacridone pigments such as quinacridone red or quinacridone purple, perylene pigments such as perylene red or bright red perylene, isoindolinone pigments, such as isoindolinone yellow or isoindolinone orange, imidazolone pigments, such as benzimidazolone yellow, benzimidazolone orange or benzimidazolone red, pyrantron pigments, such as pyrantron red pigmented pigment, pigmentron red, or based on thioindigo, diketopyrrolopyrrole pigments, flavanthron yellow, acylamide yellow, chinophthalone yellow, nickel-azo yellow, and of copper methine yellow, perinone orange, anthrone orange, diantrahinonilovy red and dioxazine violet. Of course, organic pigments are not limited to this, but other organic pigments can also be used.

In addition, when organic pigments that can be used in the present invention are indicated by a color index value (CI), examples of such CI values may include a yellow pigment with CI No. 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 97, 109, 110, 117, 120, 125, 128, 137, 138, 147, 148, 150, 151, 153, 154, 166, 168, 180 and 185, orange pigment with CI No. 16, 36, 43, 51, 55, 59, 61 and 71, red pigment with CI No. 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175, 176, 177, 180, 192, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240, 254, 255 and 272, purple pigment with CI No. 19, 23, 29, 30, 37, 40 and 50, blue pigment with CI No. 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60 and 64, green first pigment C. I. №№7 and Pigment Brown 36 and with C. I. №№23, 25 and 26.

[Pigment dispersible with resin]

As stated above, a pigment dispersible with a resin, that is, a pigment dispersible by using a dispersant, can be used as the water-insoluble coloring material contained in the water-based paint of the present invention. In this case, a compound is required to disperse each of the hydrophobic pigments listed above. As such compounds, so-called dispersants may be used, including surfactants and resin-based dispersants or the like. Such dispersants or surfactants are not particularly limited, but, inter alia, anionic compounds or nonionic compounds can preferably be used. Examples of such an anionic compound may include a fatty acid salt, alkyl sulfate, alkyl benzene sulfonate, alkyl naphthalene sulfonate, dialkyl sulfosuccinate, alkyl phosphate, naphthalene sulfonate condensates with formalin, alkyl polyoxyethylene sulfate and their substituted derivatives. Examples of such a non-ionic compound may include polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkylamine, glyceric fatty acid ester, hydroxyethylene ethylene oxide block copolymer and their substituted derivatives. Examples of a resin-based dispersant may include a block copolymer, a random copolymer, a grafted copolymer and their salts, which are composed of at least two monomers (at least one of them is a hydrophilic monomer) selected from the group consisting of styrene and its derivatives, vinylnaphthalene and its derivatives, fatty alcohol esters of α, β-ethylene unsaturated carboxylic acid, acrylic acid and its derivatives, maleic acid and its derivatives, itaconic acid and its derivatives, fumaric acid slots and its derivatives, and vinyl acetate, vinyl alcohol, vinyl pyrrolidone, acrylamide and their derivatives.

[Microencapsulated pigment]

As stated above, the water-insoluble coloring material can be coated with an organic microencapsulation polymer so as to obtain a microencapsulated pigment that can be used as the water-insoluble coloring material for the water-based ink of the present invention. Examples of such a method for coating a water-insoluble coloring material with organic microencapsulation polymers may include a chemical production method, a physical production method, a physicochemical production method, and a mechanical production method. Specific examples of such methods may include an interfacial polymerization method, an in situ polymerization method, a method of applying a curing coating by immersion in a liquid, a method of coacervation (phase separation), a method of drying by immersion in a liquid, a method of cooling a dispersion melt, an air suspension coating method, spray drying method, acid deposition method and phase reversal emulsification method.

Examples of the organic polymer used as the material for the microcapsules may include polyamide, polyurethane, polyester, polyurea, epoxy resin, polycarbonate, urea resin, melamine resin, phenolic resin, polysaccharide, gelatin, gum arabic, dextran, casein, casein natural rubber, carboxypolymethylene, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, cellulose, ethyl cellulose, methyl cellulose, nitrocellulose, hydroxyethyl cellulose, cellulose acetate PS, polyethylene, polystyrene, polymer or copolymer of (meth) acrylic acid, polymer or copolymer of (meth) acrylic acid ester, copolymer of (meth) acrylic acid-ester of (meth) acrylic acid, styrene- (meth) acrylic acid copolymer, styrene-maleic acid copolymer, sodium alginate, fatty acid, paraffin, beeswax, Chinese wax, beef tallow, carnauba wax and albumin.

Among these, organic polymers having an anionic group such as a carboxylic acid group or a sulfonic acid group can be used. In addition, examples of a non-ionic organic polymer may include polyvinyl alcohol, polyethylene glycol monomethacrylate, polypropylene glycol monomethacrylate, methoxypolyethylene glycol monomethacrylate, their (co) polymers, and cationic polymers with 2-oxazoline ring opening. Among them, the fully ketonized polyvinyl alcohol product is particularly preferred since it has a low solubility in water and is readily soluble in hot water, but poorly soluble in cold water.

When a phase separation method or an acid deposition method is selected as the microencapsulation method, anionic organic polymers can be used as an organic polymer to form microcapsules. In the phase separation method, a composite or complex consisting of an anionic organic polymer having the ability to self-disperse or dissolve in water and a coloring material such as a self-dispersing organic pigment or carbon black, or a mixture consisting of a coloring material, is used as an organic phase solvent. such as a self-dispersing organic pigment or carbon black, a curing agent and an anionic organic polymer. The phase separation method includes adding water to the above organic solvent phase or adding said organic solvent phase to water in order to self-disperse microencapsulation (phase separation emulsification). In the above phase separation method, water-soluble organic solvents or additives to be used for the paint may be added to the phase of the organic solvent. Considering that a dispersion solution for a paint can be produced directly, it is particularly preferable to mix the liquid medium for the paint into an organic solvent phase.

On the other hand, in the acid deposition method, an aqueous cake is obtained by the steps of: neutralizing part or all of the anionic groups of an organic polymer containing anionic groups, using a basic compound and kneading the polymer together with a coloring material such as self-dispersing organic pigment or carbon black, in the aquatic environment; and adjusting the pH of the mixture to neutral or acidic with an acid compound such that the organic polymer containing the anionic group precipitates by adhering to the pigment. The resulting water-containing pellet is microencapsulated by neutralizing all or part of the anionic groups with the main compound. Using this method, an anionic microencapsulated pigment, which is finely divided and includes a large number of pigments, can be obtained.

Examples of the solvent used in the above microencapsulation may include alkyl alcohols such as methanol, ethanol, propanol or butanol; aromatic hydrocarbons such as benzene, toluene or xylene; esters such as methyl acetate, ethyl acetate or butyl acetate; chlorinated hydrocarbons such as chloroform or ethylene dichloride; ketones such as acetone or methyl isobutyl ketone; ethers, such as tetrahydrofuran or dioxane; and cellosolves such as methyl cellosolve or butyl cellosolve. In addition, the microcapsules obtained by the method described above are subjected to centrifugal separation or filtration to separate them from the solvent, then they are mixed with water or the necessary solvents, and the mixture is mixed and then dispersed again to obtain a microencapsulated pigment of interest . The average particle size of the microencapsulated pigment obtained using the above method is preferably in the range between 50 nm and 180 nm.

[Self-dispersing pigment]

As stated above, as a water-insoluble coloring material contained in the water-based paint of the present invention, a self-dispersing pigment capable of dispersing without a dispersant can be used. As the self-dispersing pigment indicated above, there is a pigment in which hydrophilic groups chemically bind to the surface of the pigment particles either directly or through another group of atoms. For example, pigments may preferably be used in which the hydrophilic group introduced onto the surface of the pigment particle is a group selected from the group consisting of —COOM1, —SO ₃ M1 and —PO ₃ H (M1) ₂ (where M1 is a group selected from the group consisting of a hydrogen atom, an alkali metal, ammonium and an organic ammonium compound). The above other atomic group, which may be a group selected from the group consisting of an alkylene group containing 1-12 carbon atoms, a substituted or unsubstituted phenylene group and a substituted or unsubstituted naphthylene group, can also be preferably used. In addition to this, self-dispersing pigments obtained by the following surface oxidation methods can also preferably be used: a method for oxidizing carbon black with sodium hypochlorite; a method for oxidizing carbon black using ozonation of water; and a method comprising exposing the carbon black to ozonation and then exposing it to wet oxidation with an oxidizing agent so as to modify the surface of the carbon black.

[Self-dispersing pigment with bound polymer]

As stated above, as a water-insoluble coloring material contained in the water-based paint of the present invention, a polymer-type self-dispersing pigment capable of dispersing without the use of dispersants can be used. Such a self-dispersing, polymer-free pigment that does not use a dispersant is preferably a reaction product between functional groups that are chemically bonded to the surface of the pigment, either directly or through another group of atoms, and a copolymer of an ionic monomer and a hydrophobic monomer. In other words, when a self-dispersing polymer-binding pigment having such a structure is used, the copolymerization ratio between the ionic monomer and the hydrophobic monomer, i.e. the starting materials for the copolymer intended to modify the surface of the pigment can be changed accordingly, thereby making it possible to properly control the hydrophilicity of the modified pigment. Accordingly, a self-dispersing polymer binding pigment with the above structure is preferred. In addition, the type of ionic monomer and hydrophobic monomer to be used can be selected appropriately, or their combination can be changed appropriately so that various properties can be imparted to the surface of the pigment. Also from this point of view, the aforementioned self-dispersing polymer binding pigment is preferred.

(Functional group)

The functional group contained in the aforementioned self-dispersing polymer-binding pigment chemically binds to the surface of the pigment, directly or through another group of atoms. The functional group forms an organic group by reaction with the copolymer described below. The type of functional group is selected here in combination with the functional group of the copolymer. Taking into account the fact that the pigment is dispersed in an aqueous medium, the reaction between the functional group and the copolymer preferably forms a bond that does not hydrolyze, such as a reaction causing the formation of an amide bond. An amino group is used as a functional group, the copolymer has a carboxyl group, so that the copolymer can be introduced onto the surface of the pigment particle via an amide bond. In another case, a carboxyl group is used as a functional group, and the copolymer carries an amino group, so that the copolymer can be introduced onto the surface of the pigment particle via an amide bond.

In this case, a functional group that chemically binds to the surface of the pigment can directly bind to it or can bind to it through another group of atoms. However, when a copolymer with a relatively high molecular weight is introduced onto the pigment surface to prevent steric repulsion between the copolymers, it is preferable to introduce a functional group onto the pigment surface through another group of atoms. The other group of atoms here is not limited in any way, as long as it is a multivalent element or organic group. From the point of view of controlling the distance of the functional group from the surface of the pigment, for the reasons described above, it is preferable to use, for example, a divalent organic residue. Examples of such a divalent organic residue may include an alkylene group and an arylene group (phenylene group).

More specifically, in the examples described below, for example, the pigment is reacted with aminophenyl (-sulfoethyl) sulfone to introduce a phenyl (2-sulfoethyl) sulfonic group onto the surface of the pigment. Thereafter, the pentaethylene hexamine amino group is reacted with a phenyl (2-sulfoethyl) sulfonic group so as to introduce the amino group as a functional group. In this case, the amino group chemically binds to the surface of the pigment through a group of atoms containing a phenyl (2-sulfoethyl) group.

(Copolymer for self-dispersing polymer-binding pigment)

An anionic copolymer having anionic properties or a cationic copolymer having cationic properties is preferably used as the copolymer described above consisting of an ionic monomer and a hydrophobic monomer.

Examples of the above anionic copolymer may include a copolymer consisting of a hydrophobic monomer and an anionic monomer, and a salt thereof. Typical hydrophobic monomers used in the above copolymerization may include, but are not limited to, methacrylic acid alkyl esters such as styrene, vinylnaphthalene or methyl methacrylate, acrylic acid alkyl esters such as phenyl methacrylate, benzyl methacrylate, 2-ethoxyethyl methacrylate, methacrylonitrile, 2-trimethylsiloxyethyl methacrylate, glycidyl methacrylate, p-tolyl methacrylate, sorbyl methacrylate or methyl acrylate, phenyl acrylate, benzyl acrylate, acrylonitrile, 2-trimethylsiloxyethyl acryl atm, glycidyl acrylate, p-tolilakrilat and sorbilakrilat.

Examples of the anionic monomer used in the above copolymerization may include, but are not limited to, acrylic acid, methacrylic acid, and maleic acid.

In one embodiment of the copolymer used in the present invention, the anionic copolymer consisting of an anionic monomer and a hydrophobic monomer consists of at least two monomers, which include any monomer selected from the hydrophobic monomers listed above and at least at least one monomer selected from the above anionic monomers. This copolymer includes a block copolymer, a random copolymer, a grafted copolymer and their salts.

The acid number of the anionic copolymer is preferably between 100 and 500. In addition, an anionic copolymer is preferably used, where the dispersion of acid numbers is 20% or less of the average acid number. By setting the acid number of the copolymer within the above ranges, it is possible to effectively reduce the problem that the hydrophilicity of the pigment surface is so high that the water and solvents contained in the ink remain on the pigment surface after printing, thereby causing a slow manifestation of the marker stability of the ink after printing on print medium. In addition, it is also possible to effectively reduce another problem, namely that the excessively low hydrophilicity of the surface of the pigment prevents stable dispersion of the pigment in the paint.

Examples of the above salts may include alkali metal salts such as sodium, lithium or potassium, ammonium salts, alkylamine salts and alkanolamine salts. These salts can be used, as needed, alone or in combination of several types.

Further, in another embodiment of the copolymer used in the present invention, a cationic copolymer consisting of a cationic monomer and a hydrophobic monomer will be described. Examples of such a cationic copolymer may include copolymers consisting of hydrophobic monomers and cationic monomers listed below, or their salts. As hydrophobic monomers, the monomers listed above can be used.

Examples of the cationic monomer used herein may include allyl amine, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, tertiary butylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropylmethacrylamide, N-vinylacrylamidazole,

Examples of the cationic copolymer may include a block copolymer, a random copolymer and a grafted copolymer, which consist of at least two monomers, including a hydrophobic monomer and a cationic monomer selected from the above monomers, and their salts. In particular, cationic copolymers having an amine number in the range of between 100 and 500 are preferred. In addition, the dispersion of amine numbers is preferably 20% or less of the average amine number. The amine number is designated as the amount of mg KOH, which is equivalent to hydrochloric acid, necessary to neutralize 1 g of the sample. Examples of the above salts may include acetic acid, hydrochloric acid, and nitric acid. These salts can be used, as needed, individually or in combination of several types.

The weight average molecular weight (MW) of the anionic or cationic copolymer described above is preferably in the range between 1000 and 20,000, and more preferably in the range between 3,000 and 20,000. In addition, such copolymers are preferably used where the polydispersity Mw / Mn (weight average molecular weight Mw / number average molecular weight Mn) of the cationic copolymer segment is 3 or less. The content of such a cationic copolymer in the paint is preferably in the range of 5% by weight. up to 40% of the mass. in relation to the total mass of pigment particles in which the surface is modified by means of a copolymer. As for the polydispersity of the copolymer, when the polydispersity is large, this leads to a wide distribution of the molecular masses of the copolymer, and the indicated properties of the copolymer, which are based on the molecular weight, are hardly expressed. Accordingly, the molecular weight distribution of the copolymer is preferably uniform.

Next, taking carbon black as an example, a method for modifying a pigment by chemically bonding an organic group on the surface of a pigment particle is described. The methods are not in any way especially limited, and any commonly used method can be used here, provided that the methods include introducing functional groups onto the surface of a pigment particle, bonding a copolymer consisting of an ionic monomer and a hydrophobic monomer to these functional groups, so that the copolymer is chemically bonded to the surface of the pigment particle. For example, the following methods may be used.

A method can be used that includes introducing polyethyleneimine or a similar polymer onto the surface of a pigment particle, for example carbon black, and bonding a copolymer consisting of an ionic monomer and a hydrophobic monomer and having an amino group with its final functional group through a reaction involving diazonium, or a method of binding a copolymer having an amino group and a carboxyl group in its molecule, on the surface of a pigment, such as carbon black, by a reaction involving diazonium. In addition to these methods, the most typical example is described in International Patent Application WO 01/51566 A1.

In the methods described above, where the anionic copolymer chemically binds to the surface, for example, carbon black particles, the following 3 steps are carried out:

the first step of attaching the aminophenyl (2-sulfoethyl) sulfonic group (APSES) to carbon black through a reaction involving diazonium;

a second step of attaching polyethyleneimine or pentaethylenehexamine (PEHA) to the above carbon black treated with APSES; and

the third step is the binding of a copolymer consisting of a hydrophobic monomer and an ionic monomer having a carboxyl group on the surface of the particle.

In the above second step, the phenyl (2-sulfoethyl) sulfone group chemically bonded on the surface of the carbon black via the first step interacts with the APSES amino group so that the amino group is introduced onto the surface of the carbon black as a functional group that is chemically bonded to it. In the third step, for example, a portion of the carboxyl group contained in the portion of the ionic monomer of the copolymer interacts with the amino group to form an amide bond, so that the copolymer is introduced onto the surface of the carbon black by an atomic group containing a phenyl (2-sulfoethyl) group as the APSES residue and PEHA residue.

In addition, in the method described above, where the cationic copolymer is chemically bonded, for example, to the surface of a carbon black particle, the method includes the following two steps:

the first step of attaching the aminophenyl (2-sulfoethyl) sulfonic group (APSES) to carbon black by a reaction involving diazonium; and

the second step is the binding of a copolymer consisting of a hydrophobic monomer and a cationic monomer to the surface of the particle. Through the above first step, a sulfonic group is introduced onto the surface of the carbon black as a functional group chemically bonded to it. After that, using the above-mentioned second stage, for example, a part of the amino group contained in the part of the ionic monomer of the copolymer is reacted with a sulfone group (nucleophilic substitution), so that the copolymer is introduced onto the surface of carbon black by means of a group of atoms containing a phenyl (2-sulfoethyl) group , as the remainder of APSES.

[Water-soluble self-dispersing pigment with resin adsorption]

As indicated above, a resin dispersible pigment, a microencapsulated pigment, a self-dispersing pigment, and a self-dispersing polymer-binding pigment can be used as the water-insoluble coloring material contained in the water-based paint of the present invention. In addition to these pigments, a pigment obtained by adding a water-soluble resin to the pigment can also be used. Such a water-soluble pigment containing a resin will be described below.

Resin adsorption water-soluble self-dispersing pigments obtained by adding a water-soluble resin to the self-dispersing pigments listed above can also be used in the present invention.

Such water-soluble self-dispersing pigments with resin adsorption can be obtained by adding a water-soluble resin to the self-dispersing pigment described above and mixing, and obtaining a mixture. Preferred examples of a water-soluble self-dispersing resin adsorption pigment are described below.

A pigment where a hydrophilic group chemically binds to the surface of a pigment particle, directly or through another group of atoms, is an example of self-dispersing pigments used for water-soluble self-dispersing pigments attached to a resin that can be used in the present invention. For example, pigments may preferably be used in which the hydrophilic group introduced onto the surface of the pigment particle is a group selected from the group consisting of —COOM1, —SO ₃ M1 and —PO ₃ H (M1) ₂ (where M1 is a group selected from the group consisting of a hydrogen atom, an alkali metal, ammonium and an organic ammonium compound). The above other group of atoms may also be preferably used, which may be a group selected from the group consisting of an alkylene group containing 1-12 carbon atoms, a substituted or unsubstituted phenylene group and a substituted or unsubstituted naphthylene group.

In addition to this, self-dispersing pigments obtained by the following surface oxidation methods can also preferably be used: a method for oxidizing carbon black with sodium hypochlorite; a method for oxidizing carbon black using ozonation of water; and a method including exposing the carbon black to ozonation and then exposing it to wet oxidation with an oxidizing agent so as to modify the surface of the carbon black. Soluble in alkaline media, the polymers are preferably adsorbed with respect to the self-dispersing pigments used to produce the water-soluble self-dispersing pigment with resin adsorption. If the surface of the self-dispersing pigment is maximally modified by the carboxylation described above or the like, the adsorption of the polymer soluble in the alkaline medium onto the pigment particles becomes substantially zero. In contrast, if the surface modification is too small, the effects of the modification are unlikely to be obtained. Accordingly, as an indicator of the degree of surface modification, surface modification is carried out in such a way that the content of carboxyl groups on the surface is set between 0.1 and 0.5 mmol / g.

Examples of a water-soluble resin that can be used to produce a water-soluble self-dispersible adsorption pigment for the resin used in the present invention may include a copolymer consisting of a hydrophobic monomer and an anionic monomer, a copolymer consisting of a hydrophobic monomer, a nonionic monomer and an anionic monomer, and salts. Examples of the characteristic hydrophobic monomer used herein may include, but are not limited to, methacrylic acid alkyl esters such as styrene, vinylnaphthalene or methyl methacrylate, acrylic acid alkyl esters such as phenyl methacrylate, benzyl methacrylate, 2-ethoxyethyl methacrylate, methacrylonitol 2-trimethylsiloxyethyl methacrylate, glycidyl methacrylate, p-tolyl methacrylate, sorbyl methacrylate or methyl acrylate, phenyl acrylate, benzyl acrylate, acrylonitrile, 2-trimethylsiloxyethyl acrylate, glycidyl acryl m, n and tolilakrilat sorbilakrilat. Examples of the non-ionic monomer may include, but are not limited to, hydroxyethyl (meth) acrylate, polyethylene glycol (meth) acrylate, alkoxypolyethylene glycol (meth) acrylate, and silicone macromer. Examples of the anionic monomer used herein may include, but are not limited to, acrylic acid, methacrylic acid, and maleic acid. The copolymer here includes a block copolymer, a random copolymer, a grafted copolymer and their salts.

The acid number of the anionic copolymer used here is preferably between 100 and 500. In addition, an anionic copolymer is preferably used, where the dispersion of acid numbers is 20% or less of the average acid number. Examples of the above salts may include alkali metal salts such as sodium, lithium or potassium, ammonium salts, alkylamine salts and alkanolamine salts. These salts can be used, as needed, individually or in combination of several types. The weighted average molecular weight (MW) of the anionic copolymer described above is preferably in the range between 1000 and 20,000, and more preferably in the range between 3,000 and 20,000.

The term “adsorption between a pigment and a water-soluble resin” is used in the present invention to refer to adsorption caused by Van der Waals forces or intermolecular forces. As a means for effecting adsorption, conventional mixing of the pigment and the alkaline soluble polymer is sufficient, but a dispersing device can be used that applies high shear when the pigment adsorbes the alkaline soluble polymer. In order to determine the degree of adsorption of an alkaline soluble polymer on a self-dispersing pigment, an assessment using surface tension is desirable. For example, surface tension is measured by the gradual addition of a water-soluble resin to 1% of the mass. self-dispersing pigment (the amount of polymer soluble in alkaline media depending on γ in a system containing 1% by mass of self-dispersing pigment: graph A), and surface tension is measured for aqueous solutions of a water-soluble resin at various concentrations (amount of water-soluble resin depending on γ: graph B) By comparing graph A with graph B to determine the difference in concentrations of the water-soluble resin at which a certain surface tension is obtained, an approximate amount of the water-soluble resin adsorbed on the pigment can be determined.

<Other components>

To maintain moisture, the water-based paint of the present invention may contain solid moisture-containing products, such as urea, urea derivatives, trimethylolpropane or trimethylolethane, as paint components other than the components described above. Typically, the content of solid moisture-holding products, such as urea, urea derivatives or trimethylolpropane, in the paint is preferably in the range between 0.1% of the mass. and 20.0% of the mass., and more preferably, in the range between 3.0% of the mass. and 10.0% of the mass. in relation to the total weight of the paint.

In addition to this, in addition to the above components, the paint of the present invention may also contain, if necessary, various additives, such as a surfactant, a pH adjusting buffer, an anticorrosive agent, an antiseptic agent, a fungicide, an antioxidant, an anti-reducing agent, an agent evaporation aid or chelating agent.

Preferred examples of the surfactant used in the present invention may include compounds having any of the following formulas (1) to (4).

Formula 1)

(where R is an alkyl group and n is an integer).

Formula (2)

(where R is an alkyl group and n is an integer).

Formula (3)

(where R represents a hydrogen atom or an alkyl group, and each of m and n represents an integer).

Formula (4)

(where each of m and n is an integer).

<< Image forming method using the above paint >>

The image forming method of the present invention is an inkjet printing method for printing on plain paper using black ink and at least one water-based color ink. The method is characterized in that water-based paint having the structure described above is used as black ink, and in that when an image is formed which consists of an image formed from black ink, next to an image formed from colored ink, the image is formed by sweeps for applying black ink, and then sweeps for applying color paint in the area in which the image is formed.

<Colored inks used with black ink>

Next, color inks used with the black ink of the present invention will be described. Any known water-based inks used in inkjet printing can be used in the image forming method of the present invention. Coloring materials for coloring inks may include water-soluble dyes, and in particular, water-soluble dyes having an anionic group as a solubilizing group are preferred. The color of the color ink used in the present invention may suitably be selected from the group consisting of cyan, magenta , yellow, red, green, blue, and orange.

Water-soluble dyes having an anionic group used in the present invention are not limited in any way, provided that they are water-soluble acid dyes, direct dyes, or chemically active dyes described by the color index. In addition, although it is not a dye described using the color index, if the dye has an anionic group, such as a sulfonic group, it is available. These dyes are used in the range between 1% of the mass. and 10% of the mass., and preferably, in the range between 1% of the mass. and 5% by weight, based on the total weight of the paint.

Specific examples of such a dye are as follows.

C. I. direct yellow: 8, 11, 12, 27, 28, 33, 39, 44, 50, 58, 85, 86, 87, 88, 98, 100, 110.

CI straight red: 2, 4, 9, 11, 20, 23, 24, 31, 39, 46, 62, 75, 79, 80, 83, 89, 95, 197, 201, 218, 220, 224, 225, 226, 227, 228, 230.

C. I. direct blue: 1, 15, 22, 25, 41, 76, 77, 80, 86, 90, 98, 106, 108, 120, 158, 163, 168, 199, 226.

C. I. acid yellow: 1, 3, 7, 11, 17, 23, 25, 29, 36, 38, 40, 42, 44, 76, 98, 99.

CI Acid Red: 6, 8, 9, 13, 14, 18, 26, 27, 32, 35, 42, 51, 52, 80, 83, 87, 89, 92, 94, 106, 114, 115, 133, 134, 145, 158, 198, 249, 265, 289.

CI Acid Blue: 1, 7, 9, 15, 22, 23, 25, 29, 40, 43, 59, 62, 74, 78, 80, 90, 100, 102, 104, 117, 127, 138, 158, 161.

In addition to the dyes listed above, paragraphs 1-3, discussed below, can also be used as coloring materials for the color inks used in the present invention. These coloring materials are preferred since most of these coloring materials exhibit excellent water resistance when applied to a printing medium.

1. Dyes having a carboxyl group as a solubilizing group.

2. Oil soluble dyes.

3. Pigments.

Oil-soluble dyes are not in any way limited, as long as they are described using the color index. In addition, it may be a new dye that is not described using the color index, without any specific restrictions. Specific examples are described below. These dyes are used in the range between 1% of the mass. and 10% of the mass., and more preferably, in the range between 1% of the mass. and 5% by weight, based on the total weight of the paint.

C. I. solvent blue: 33, 38, 42, 45, 53, 65, 67, 70, 104, 114, 115, 135.

C. I. red solvent: 25, 31, 86, 92, 97, 118, 132, 160, 186, 187, 219.

C. I. yellow solvent: 1, 49, 62, 74, 79, 82, 83, 89, 90, 120, 121, 151, 153, 154.

When a pigment is used as a coloring material for the color ink used in the present invention, the pigment is used between 1% of the mass. and 20% of the mass., and more preferably, in the range between 2% of the mass. and 12% of the mass. in relation to the total weight of the paint. Colored organic pigments that can be used in the present invention are as follows.

Examples of the pigment used for yellow paint may include CI Pigment Yellow 1, CI Pigment Yellow 2, CI Pigment Yellow 3, CI Pigment Yellow 13, CI Pigment Yellow 16, CI Pigment Yellow 74, CI Pigment Yellow 83 and CI Pigment Yellow 128.

Examples of the pigment used for magenta can include CI Pigment Red 5, CI Pigment Red 7, CI Pigment Red 12, CI Pigment Red 48 (Ca), CI Pigment Red 48 (Mn), CI Pigment Red 57 (Ca) , CI Pigment Red 112 and CI Pigment Red 122.

Examples of the pigment used for blue paint may include CI Pigment Blue 1, CI Pigment Blue 2, CI Pigment Blue 3, CI Pigment Blue 15: 3, CI Pigment Blue 16, CI Pigment Blue 22, CI Pigment Blue 4 and CI Vat Blue 6.

However, the pigments used in the present invention are not limited to this. In addition to the above pigments, of course, a pigment newly produced for the present invention can also be used.

Furthermore, when a pigment is used, any type of dispersant can be used with it to disperse the pigment in the paint, provided that it is a water-soluble resin. A dispersant having a weight average molecular weight between 1000 and 30000 is preferred, and a dispersant having a weight average molecular weight between 3000 and 15000 is more preferred. Specific examples of such a dispersant may include a block copolymer, a random copolymer, a grafted copolymer and its salts, which consist of at least two monomers (at least one of them is a hydrophilic monomer) selected from the group consisting of styrene and its derivatives, vinylnaphthalene and its derivatives, fatty alcohol esters of α, β-ethylene unsaturated carboxylic acid, acrylic acid and its derivatives, maleic acid and its derivatives, itaconic acid and its derivatives, fumaric acid and e derivatives, vinyl acetate, vinylpyrrolidone, acrylamide and their derivatives. In addition, natural resins such as rosin, shellac or starch may also be preferably used. These resins are soluble in an aqueous solution in which the bases are dissolved, and they are resins soluble in alkaline media. Such a water-soluble resin used as a dispersant for a pigment is preferably contained in the paint in the range between 0.1% of the mass. and 5% of the mass. in relation to the total weight of the paint.

The aqueous medium, preferably used for the color ink used in the present invention, is water or a mixed solvent of water and a water-soluble organic solvent. Such water is usually not water containing various ions, but preferably, it is ion-exchanged water (deionized water). Examples of a water-soluble organic solvent used by mixing with water may include: alkyl alcohols containing from 1 to 4 carbon atoms, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec- butyl alcohol or tert-butyl alcohol; amides such as dimethylformamide or dimethylacetamide; ketones or ketone alcohols such as acetone or diacetone alcohol; ethers, such as tetrahydrofuran or dioxane; polyalkylene glycols such as polyethylene glycol or polypropylene glycol; alkylene glycols in which alkylene groups contain from 2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol or diethylene glycol; glycerol; polyhydric alcohol lower alkyl ethers such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether or triethylene glycol monomethyl (or ethyl) ether; N-methyl-2-pyrrolidone, 2-pyrrolidone and 1,3-dimethyl-2-imidazolidinone. Among them, many water-soluble organic solvents, polyhydric alcohols, such as diethyl alcohol, and lower alkyl ethers of polyhydric alcohols, such as triethylene glycol monomethyl (or ethyl) ether, are preferred.

The water-soluble organic solvent described above is contained in a color paint, typically in the range of 3% by weight. up to 50 wt. -%, and preferably in the range from 3% of the mass. up to 40% of the mass. in relation to the total weight of the paint. In addition, the water used here is contained in the paint in the range from 10% of the mass. up to 90% of the mass., and preferably in the range from 30% of the mass. up to 80% of the mass. in relation to the total weight of the paint. In addition, so that the color ink used in the present invention has the desired numerical values of the required physical properties, it may contain, if necessary, various additives, such as a surfactant, anti-foaming agent or antiseptic agent, as well as the above components.

The black and color inks used in the present invention containing the components described above preferably have good release from the inkjet head. Accordingly, from the point of view of release from the inkjet head, the above inks preferably have properties such as a viscosity of 1 to 15 MPa / s and a surface tension of 25 mN / m or more, and more preferably properties such as a viscosity of 1 up to 5 mPa / s and surface tension from 25 to 50 mN / m. In the case of the combined use of black ink and color ink, the surface tension of the color ink is preferably lower than that of black ink. More specifically, the surface tension of the black ink is between 35 and 50 mN / m, and the surface tension of the color ink is between 25 and 35 mN / m.

<Image Forming Method>

The image forming method of the present invention will be described using the following specific examples. The image forming method of the present invention is characterized in that it uses the water-based ink of the present invention having the above structure as black ink, and to form an image in which an image formed with black ink and an image formed with with the help of color paint, they are nearby, with this, the first scan for attaching black paint, and then the scan for attaching color paint, in the area in which the black image is already formed ovano. Specific tools will be described below.

Fig. 8 shows an example of a print head that is used for the image forming method of the present invention. As shown in FIG. 8, the print head has an outlet line for ejecting black ink (Bk) and an outlet line for ejecting each of the three color inks, cyan (C), magenta (M), and yellow (Y). When a color image is formed by the image forming method of the present invention, it is preferable to use a print head in which the line of holes for ejecting black ink and the line of holes for ejecting color inks do not overlap along the sub-scan direction (paper input). Accordingly, to form an image using the print head shown in Fig. 8, for example, when only a black image is formed, the entire portion of the black line of holes is used, and when a color image is formed using both black and color inks, it is preferable to use parts of the black line of the holes shown in Fig. 8, and parts b of the line of holes for C, M, and Y. The case of forming an image consisting of both black ink and color inks will be described below more in detail using Fig. 8.

In Fig. 8, first, using a portion of the line of holes for releasing black ink, the print head expands in a horizontal direction (main scanning direction), so that a black image is formed on a printing medium, such as plain paper, by single-pass printing. Then, the printing medium moves in the vertical direction (sub-scan direction) shown in Fig. 8, a distance a. In the next step, by using part b of each line of color ink holes, a color image is formed by single-pass printing, in the forward direction, in an area in which a black image is formed using the holes of part a. At this time, the openings for releasing black ink in part a simultaneously form another black image in the next region. Repeating this operation, an image is formed consisting of both black ink and color paints.

Fig. 9 shows another example of a print head that is used for the image forming method of the present invention. As in the case of FIG. 8, in FIG. 9, holes for black ink in part a are also used to form a black image, and part b corresponding to the entire portion of each of the line of holes for releasing color inks is used for C, M and Y, and thus, an image consisting of both black ink and color inks is formed in the same manner as described for FIG.

Figure 10 depicts another example of a print head that can be used in the image forming method of the present invention. As in the case of FIG. 8, in FIG. 10, part a of the openings for releasing black ink is also used to form a black image, and part b corresponding to all openings for each color ink C, M and Y is used to form a color image, and Thus, an image is formed consisting of both black ink and color paints.

In the print head of FIG. 10, part a of the line of holes for releasing black ink and part b of lines of holes for releasing color inks are separated by a distance corresponding to the distance a ′ of one paper transfer step, as shown in FIG. 10. Accordingly, a printhead with such a structure generates a time difference that corresponds to the time required for one reciprocating scan to print, from the moment when a black image is formed to the moment when a color image is formed. Accordingly, it can be said that the print head shown in FIG. 10 has a structure more advantageous than that of the print head shown in FIG. 9 from the point of view of spreading between black ink and color inks.

11 depicts another example of a print head that is used in the image forming method of the present invention. As shown in the drawing, this print head is configured in such a way that the outlet lines for both black ink and color inks are on the same line in the paper input direction. In this case, also, a color image is formed after the black image is formed, in accordance with the input of paper.

12 shows another example of a print head that is used in the image forming method of the present invention. The printhead shown in FIG. 12 is configured so that for each color ink, two lines of outlets are provided, i.e. cyan (C1, C2), magenta (M1, M2) and yellow (Y1, Y2), with symmetrical location in the main direction of the scan, so that the order in which color paints get on the paper becomes the same both when scanning forwards and when scanning backwards. As a result, it becomes possible to print in two directions, even if an image is formed consisting of both black ink and color inks. In this case, using the black ink portion a, a black image is first formed in a forward direction from the main scanning direction of the print head. After that, the printing medium is transferred to a distance a. After that, using part b of the line of holes for releasing color inks, the head forms a color image by single-pass printing during backward scanning, in the main direction of the scan, in the area where the black image is formed by holes in part a. At this time, part of the holes for the black ink forms another black image in the next area. When repeating this operation, an image is formed consisting of both black ink and color paints.

The bi-directional print head shown in FIG. 12 can also be configured so that both black nozzles and color nozzles are arranged to create a single scan interval between black image formation and color image formation, as described above, which was would be more beneficial when acting against spreading (see FIG. 13). The image forming method of the present invention is described above, but the shapes of the print head used for the method of the present invention are not limited to those shown in Figs.

[Printing method, print unit, cartridge and printing device]

Next will be described an example of an inkjet device, preferably used in the present invention. First of all, FIGS. 1 and 2 show an example of a head structure, which is the main part of an inkjet printing apparatus using thermal energy. FIG. 1 is a sectional view of a head 13 along a paint channel, and FIG. 2 is a sectional view along a line AB of FIG. 1. The head 13 is formed by connecting glass, ceramic, silicon or plastic and the like, in which at least one path 14 for the flow of paint is provided, with a heat generating element 15 (not limited to that shown in the drawings). The heat generating element 15 consists of a protective film 16 made of silicon oxide, silicon nitride, silicon carbide or the like, aluminum electrodes 17-1 and 17-2 made of aluminum, gold, an aluminum-copper alloy, or or the like, a heat generating layer 18 forming a resistance made of HfB ₂ , TaN, TaAl, and the like, a heat storage layer 19 made of thermally oxidized silicon, oxidized aluminum, and the like, and a substrate 20 made of silicon aluminum, aluminum nitride The line and the like, which is excellent at heat release.

When applying an electrical signal in the form of a pulse to the electrodes 17-1 and 17-2 in the region depicted as "n", heat is rapidly generated with the formation of a bubble in the paint 21 in contact with this region. The meniscus 23 of the ink is ejected by the pressure of the bubble thus created, and is ejected from the opening 22 onto the print medium 25 (e.g. paper) in the form of a drop of ink 24, attaching to the print medium 25. FIG. 3 schematically illustrates a print head having a series of nozzles similar to that shown in FIG. This head is obtained by adhering a glass plate 27 having a series of flow paths 26 with a heat generating head 28 similar to that shown in FIG.

Figure 4 illustrates an example inkjet printing apparatus into which such a head is included, as described above. In figure 4, the knife 61 is a doctor blade, one of the edges of which is a fixed edge, supported by an element that holds the knife on the tray. The knife 61 is provided in a position close to the region in which the print head 65 operates, and, in this aspect, is held in such a shape that it protrudes in the path of the print head 65. Number 62 means a cap for the ejection opening of the print head 65, and a cap, installed in the initial position next to the knife 61, moves in a direction perpendicular to the direction of movement of the print head 65, and closes the hole for ejecting ink when it touches it. Number 63 means a paint absorber provided near the knife 61, which is supported along the path of the print head 65 in a protruding manner, like the knife 61. The above knife 61, cap 62 and ink absorber 63 constitute an ejection extraction unit 64, and the knife 61 and an ink absorber 63 serves to remove moisture and dust at the ink ejection opening.

Number 65 means the print head. The head comprises means for generating energy for ejecting ink, and implements printing by ejecting ink in the direction of the printing medium, opposite the ink ejection opening. Number 66 means a support carriage for the print head 65, designed to move it. The carriage 66 is slidably engaged with the circular guide 67, and the carriage part 66 is connected to a belt 69 (not shown) driven by the drive 68. Thus, the carriage 66 can move along the circular guide of the shaft 67, and the print head 65 can move in the print area and in the area next to it.

The number 51 means a portion of the print medium for inserting the print medium, and the number 52 means a paper feed roller driven by a drive not shown. With this arrangement, the printing medium is introduced into the opposite position of the ink ejection hole of the print head 65 and transferred to the paper exit section provided with a paper exit roller 53 as the printing proceeds. In the device for printing images in accordance with this aspect of the present invention, the print head is moved forward and backward along a direction perpendicular to the direction of transfer of the print medium, and on the path both forward and backward, the head can be applied to the print medium at least one paint from black paint and color paint. Processing data for printing can be carried out using conventional technology associated with printing in two directions.

At the above arrangement, when the print head returns to its original position after printing, the cap 62 of the ejection extracting unit 64 moves backward from the print head moving path, but the knife 61 protrudes from the moving path. As a result, the ink release holes of the print head 65 are cleaned. As a result, the exit section of the print head 65 is also cleaned during this movement. The aforementioned movement of the print head 65 to its initial position occurs not only when printing is completed, or to eject, but also when the print head 65 moves to the printable area for printing, that is, it moves to its original position next to it with the printable area at predetermined time intervals during printing, so as to clean the cut of the ejection port with this movement.

Figure 5 depicts one example of an ink cartridge for storing ink for introducing ink into the print head by means of an ink introducing element, such as a tube. In the drawing, number 40 means the element constituting the ink cartridge 45, an ink storage part, such as an ink bag, the tip of which is provided with a rubber stopper 42. Ink in the ink bag 40 can be inserted into the print head by inserting a needle (not shown) into cork 42. Number 44 means a paint absorber to receive excess paint. In the case of a part for storing paint, its surface in contact with the paint is preferably made of a polyolefin, in particular polyethylene.

The inkjet devices used in the present invention are not limited to such a device as described above, in which a head and ink cartridge are provided separately. For this reason, a device can also be preferably used in which these elements are formed as a unit, as shown in FIG. 6. 6, number 70 means a printing unit including a part for storing ink containing ink, for example, an ink absorption element therein. The paint contained in the ink absorption member is ejected as a drop of paint from the head 71 having a plurality of openings. As the material for the ink absorbing element, polyurethane can preferably be used. Number 72 indicates an air passage for communicating the interior of the printing unit 70 with the atmosphere. This print unit 70 may be used in place of the print head 65 shown in FIG. 4 and removably mounted on the carriage 66.

An example configuration of a printhead using mechanical energy is an inkjet printhead, comprising: a nozzle-forming substrate having a plurality of nozzles, a pressure generating element consisting of a piezoelectric material and an electricity conducting material located opposite the nozzles, and a peripheral ink a portion of the pressure generating element in which the pressure generating element is displaced by applying a voltage so as to eject drops of cr lift of the nozzle.

7, a path 80 for the flow of paint is made of a photosensitive resin; hole plate 81 is made of metal such as stainless steel and nickel; an ejection hole 85 is formed by making a hole in the hole plate 81 by means of an electric or stamping process; the vibration plate 82 is made of a metal film, such as stainless steel, nickel and titanium, and a film of highly elastic resin; and the piezoelectric element 83 is made of a dielectric material such as barium titanate and PZT (ceramic based on lead titanate and zirconate). The print head of the above system works as follows: when a pulse voltage is applied to the piezoelectric element 83, an elastic voltage is created whose energy deforms the vibration plate connected to the piezoelectric element 83, applying a vertical pressure gradient to the ink along the ink flow path 80, and a drop of ink (not shown) is released from the hole 85 of the plate 81 with holes for printing. Such a printhead is included in a printing apparatus similar to that shown in FIG. 4. The detailed action of the details of the printing apparatus may be the same as discussed above. 7 depicts an example of the structure of the print head, which is the main part of the printing device.

The head consists of a paint channel 80 connected to a paint chamber (not shown), a plate 81 with holes for ejecting the desired amount of paint droplets, a diaphragm 82 for directly applying pressure to the paint, a piezoelectric element 83 that connects to the diaphragm 82 and moves under the action of the signal of the electronics, and the substrate 84 to support and fix the plate 81 with holes, the diaphragm 82, or the like.

7, the ink channel 80 is made of a photosensitive resin or the like, and the release assembly 85 is formed by a hole plate 81 made of metal, such as stainless steel or nickel, by drilling or the like, for example, by electric processing or stamping . The diaphragm 82 is made of a metal film, such as stainless steel, nickel or titanium, and a film of highly elastic resin. The piezoelectric element 83 is made of a dielectric material such as barium titanate or PZT. A printhead with the above structure delivers a voltage pulse to the piezoelectric element 83, giving it the opportunity to generate a deforming mechanical stress. Then, the generated energy deforms the diaphragm connected to the piezoelectric element 83, thereby creating a vertical pressure gradient in the ink contained in the ink channel 80, so that droplets of paint (not shown) are ejected from the outlet 85 in the hole plate 81 so that to print. This print head is part of an inkjet printing apparatus similar to that shown in FIG. 4 and is used. The specific operations of the inkjet device are the same as described above.

Examples

The present invention will be described more specifically with reference to the following examples and comparative examples. However, the present invention is not limited by the following examples, provided that it is within the scope of the present invention. It should be noted that "part" and "%" are given in the present description in relation to the mass, unless otherwise indicated.

(Preparation of pigment dispersion solution 1)

Ten parts of carbon black having a specific surface area of 210 m ² / g and oil absorption of DBP (dibutyl phthalate) 74 ml / 100 g, 20 parts of 10% styrene-acrylic acid copolymer (acid number: 200, weighted average molecular weight: 10000) are mixed in water neutralized with sodium hydroxide; and 70 parts of ion-exchanged water. The mixture was dispersed for 1 hour using a sand eraser. After that, large particles are removed by centrifugal separation, and the supernatant is subjected to pressure filtration using a micron filter with a pore size of 3.0 μm (manufactured by Fuji Photo Film Co., Ltd.), to obtain a resin dispersion solution 1 dispersed. The resulting pigment dispersion solution 1 has a solids content of 10%, a pH of 10.0, and an average particle size of 120 nm.

(Preparation of pigment dispersion solution 2)

Carbon black (10 g) having a specific surface area of 230 m ² / g and an oil absorption of DBP of 70 ml / 100 g, 3.41 g of p-amino-N-benzoic acid and 72 g of water are completely mixed and added dropwise to them 1.62 g of nitric acid and stirred at 70 ° C. After a few minutes, a solution of 1.07 g of sodium nitrite in 5 g of water was added to the mixture, followed by further stirring for 1 hour. The resulting suspension was filtered using a Toyo No. 2 filter (manufactured by Advantis), and the pigment particles were washed completely with water and then dried in an oven at 90 ° C. After that, water is added to this pigment to obtain an aqueous pigment solution with a pigment concentration of 10%. The pigment dispersion solution 2 thus obtained contains an anionically charged self-dispersing carbon black having a hydrophilic group bonded to the surfaces of the pigment particles via a phenyl group.

The density of the ion groups of the self-dispersing carbon black thus obtained, measured by the following method, is 1.3 μmol / m ² . The concentration of sodium ions is measured using an ion concentration meter (produced by DKK) and the resulting value is converted to the density of ion groups. Using the method described above, a pigment dispersion solution 2 is obtained in which self-dispersing carbon is obtained by introducing a —C ₆ H ₄ —COONa group onto the surface of carbon black.

(Preparation of pigment dispersion solution 3)

Carbon black (500 g) having a specific surface area of 220 m ² / g and an absorption of DBP oil of 112 ml / 100 g, 45 g of aminophenyl (2-sulfoethyl) sulfone (APSES) and 900 g of distilled water was placed in a reactor and, while maintaining temperature at 55 ° C, the mixture is stirred at 300 rpm for 20 minutes. After that, 40 g of 25% sodium nitrite are added dropwise to the mixture over 15 minutes, and then 50 g of distilled water is added to it. After that, maintaining the temperature at 60 ° C, carry out the reaction for 2 hours. After this, the reaction product is taken, diluting at the same time with distilled water to a solids content of 15%. After that, separation is carried out in a centrifuge and a cleaning treatment to remove impurities. In the dispersion solution thus obtained, the functional groups of the above APSES are bonded to carbon black. This dispersion solution is called A1.

Subsequently, to determine the molar amount of functional groups associated with carbon black in the dispersion solution A1, Na ions are measured in the dispersion solution using a probe-type sodium electrode. The resulting value is converted to the number of groups per particle of carbon black in order to obtain a molar amount of functional groups associated with carbon black. Thereafter, the previously prepared solution A1 of the dispersion with a solids content of 15% is added dropwise to the solution of pentaethylene hexamine (PEHA). During this process, the PEHA solution was stirred vigorously while maintaining it at room temperature, and dispersion solution A1 was added dropwise thereto over 1 hour. During this process, a PEHA concentration of 1 to 10 times the previously determined molar amount of Na ions is determined, and an amount of PEHA solution equal to the amount of dispersion solution A1 is set. After that, the resulting mixture is stirred for 18-48 hours, and then carry out a cleaning treatment to eliminate impurities. Finally, a carbon black dispersion was obtained to which pentaethylene hexamine (PEHA) was added at a solids content of 10%. This dispersion solution is called B1.

After that, a resin solution of a styrene-acrylic acid copolymer resin is prepared by weighing 190 g of a styrene-acrylic acid resin having a weight average molecular weight of 8000, an acid number of 140 and a polydispersity of Mw / Mn (weight average molecular weight Mw / number average molecular weight Mn) 1.5, which add 1800 g of distilled water and NaOH, necessary to neutralize the resin, and mix. Then, with stirring, a styrene-acrylic acid resin, 500 g, of the previously prepared dispersion solution B1 with a solids content of 10% is added dropwise to the above aqueous solution. After that, a mixture of B1 and an aqueous solution of styrene-acrylic acid resin is transferred to a Pyrex evaporator cup (trade name), and then heated at 150 ° C for 15 hours to evaporate. The dried material obtained after evaporation is cooled to room temperature.

After that, using a dispersing device, the dried material obtained after evaporation is dispersed in distilled water, setting the pH to 9.0 with NaOH. While stirring, 1.0 M NaOH was added to the solution to adjust the pH of the solution to 10-11. Pigment dispersion solution 3 is obtained after salting out and purifying the above solution and removing large particles. The pigment dispersion solution 3 has a solids content of 10%, a pH of 10.1 and an average particle size of 130 nm. The following is a synthesis scheme for a self-dispersing pigment with polymer bonding in which the organic group is chemically bonded to the surface of a carbon black particle contained in the above pigment dispersion solution 3.

Modified Pigment Synthesis Scheme

[Method for determining whether the water-soluble organic solvent used is a good solvent or a poor solvent]

To determine whether the water-soluble organic solvent used is a good solvent or a poor solvent for the pigment or for the pigment and dispersant contained in the above pigment dispersion solution, the following experiment is carried out. First, using each of the above solutions 1-3 of a pigment dispersion with a solids content of 10%, a test dispersion solution is prepared to determine a good or bad solvent with the following composition.

(Mixing ratio for the dispersion solution in order to determine a good or bad solvent)

 Each pigment dispersion solution with a solids content of 10%: 50 parts.

 Each water soluble organic solvent described in table 1: 50 parts.

(Definition)

10 g of the test solution prepared above for determining a good or bad organic solvent are placed in a sample jar equipped with a transparent glass lid. After the jar is covered with a glass lid, the solution is mixed well and left to stand in the oven at 60 ° C for 48 hours. After that, the dispersion solution is taken out of the furnace to be used as a sample for measurements. The particle size of the water-insoluble coloring material contained in the solution is measured using a particle size analyzer in concentrated solutions (product name: FPAR-1000; manufactured by Otsuka Electronics). The obtained value is designated as the particle size of the undiluted solution (particle size measured without diluting the solution) for the dispersion solution used to determine if the organic solvent is a good solvent or a poor solvent after storage at 60 ° C for 48 hours. Separately, pigment reference dispersions are prepared in the same way as the preparation of the test dispersion solutions, except that the water-soluble organic solvent is replaced with the same amount of water. The particle size of the water-insoluble coloring material in the undiluted reference solution is measured by using a particle size analyzer in concentrated solutions, but without storing the solution when heated. The obtained particle size of the undiluted test solution is compared with the particle size of the standard dispersion solution. When the first particle size is larger than the last, the available solvent is defined as a poor solvent. In contrast, when the first particle size is equal to or smaller than the last, it is defined as a good solvent.

[Method for measuring the Ka value for each water soluble organic solvent]

First, to facilitate the measurement of the Ka value for each water-soluble organic solvent, a solution of 0.5% dye in water of the following composition is prepared.

 Water soluble dye C. I. direct blue 199 0.5 parts  Pure water 99.5 pieces

Then, using the above 0.5% dye solution, prepare colored aqueous solutions, respectively, containing 20% water-soluble organic solvents, for measurements, with the following composition:

 The above 0.5% aqueous dye solution 80 pieces  Each of the water soluble organic solvents described in table 1 20 pieces

Using the prepared, colored aqueous solution containing 20% water-soluble organic solvent, the Ka value is determined using the Bristow method using Dynamic Permeability Tester S (product name), manufactured by Toyo Seiki Seisaku-sho, Ltd.

<< Definition and determination results >>

Table 1 shows the results obtained by determining whether or not each of the above water-soluble organic solvents suitable for paint is a good solvent or a poor solvent for each of pigment dispersion solutions 1-3, and the results of measuring the Ka value for each 20% aqueous a solution containing a water-soluble organic solvent. In table 1, "polyethylene glycol derivative" means a derivative of the following structure having a molecular weight of approximately 1000:

where each of n and m represents a number ranging from 5 to 20.

Table 1 The results of determining whether each water soluble organic solvent is a good solvent or a poor solvent or not, and Ka values Water soluble organic solvent Water-insoluble coloring material Ka value for 20% aqueous solution Pigment Dispersion 1 Pigment Dispersion 2 Pigment Dispersion 3 Glycerol O O O 0.13 Ethylene glycol O O O 0.09 Diethylene glycol X X X 0.14 Trimethylolpropane O O O 0.19 Polyethylene glycol 600 X X X 0.17 Polyethylene glycol derivative X X X 0.18 2-pyrrolidone X O X 0.19

In the table, O: good solvent, X: poor solvent

<Examples 1-5>

The water-soluble organic solvents described above, the pigment dispersion solutions 1-3 and the components described in Table 2 are mixed and mixed completely to dissolve or disperse. After that, the resulting mixture was subjected to pressure filtration using a microfilter with a pore size of 3.0 μm (manufactured by Fuji Photo Film Co., Ltd.) in order to prepare the paints of examples 1-5. Paints are prepared in such a way that when the total amount (% wt.) Of good solvent in the paint is indicated as A and the total amount (% wt.) Of bad solvent in the paint is indicated as B, the ratio of A to B is between 10: 5 or more and 10:30 or less, and when the Ka values of a plurality of water-soluble organic solvents are determined using the Bristow method and the obtained values are compared with each other, the water-soluble organic solvent having the highest Ka value is a poor solvent.

table 2 The composition of the paints of examples 1-5 Composition (% wt.) Project 1 Project 2 Project 3 Project 4 Ex.5 Water-insoluble coloring material Pigment Dispersion 1 fifty - - - - Pigment Dispersion 2 - fifty - fifty - Pigment Dispersion 3 - - fifty - fifty Water soluble organic solvent Good solvent Glycerol 5 5 5 7 5 Ethylene glycol 5 - - - - Trimethylolpropane - - - - - Bad solvent Diethylene glycol - - 5 3 3 Polyethylene glycol 600 10 fifteen 10 6 - Polyethylene glycol derivative - - - - 10 Surface-active substance The product of the addition of acetylene glycol and EO (*) 0.1 0.1 0.1 0.1 0.1 Pure water 29.9 29.9 29.9 33.9 31.9 (*) Product Name: Acetylenol EH, manufactured by Kawaken Fine Chemicals Co., Ltd.

<Checking the paint of example 4>

Assuming that the composition of the above-obtained ink of Example 4 is unknown, it is determined whether or not the ink is an object of the present invention using the following method. Using this verification method, even if the paint composition is unknown, it can be easily confirmed whether the paint is an object of the present invention or not.

The type and amount of organic solvents contained in the paint can be identified using, for example, GC / MS (product name: TRACE DSQ, manufactured by ThermoQuest). More specifically, for example, a sample obtained by diluting 1 g of the paint of Example 4 with methanol is analyzed using the above GC / MS. As a result, the presence of glycerol, diethylene glycol and polyethylene glycol 600 in the sample is confirmed first of all. It is then necessary to determine if these three types of solvents are good solvents or bad solvents. In the above method for determining whether a solvent is a good solvent or a poor solvent, a dispersion solution is prepared in which a water-insoluble coloring material is dispersed in a solvent and water. However, to prepare such a dispersion solution from the paint, it is necessary to remove the water-insoluble coloring material or dispersant from the paint. However, in this case, the water-insoluble coloring material or dispersant could be damaged during the extraction process.

Thus, the authors of the present invention conducted various studies to find a method that involves the direct use of the paint of Example 4 to determine whether the solvent contained therein is a good solvent or a poor solvent, and provides determination results that are consistent with the results the method of determination described above. As a result, the inventors of the present invention have found that the following verification method is preferred. First, the following three types of paint dilutions are prepared by adding each of the above three types of water-soluble organic solvents, which are to be determined, in equal amounts, to 100 parts of the paint of Example 4, and are determined using these solutions. In other words, 3 types of paint dilutions are prepared with the compositions shown in table 3 (shown in table 3 as examples of checks 1-3), each of which contains approximately 50% of the mass. a water-soluble organic solvent, as a target for determination. After that, these solutions are left to stand at 60 ° C for 48 hours, and the particle sizes of the water-insoluble coloring materials contained in them are then measured using a particle size analyzer in concentrated solutions (product name: FPAR-1000; manufactured by Otsuka Electronics Co., Ltd.). On the other hand, paint that is not stored during heating is also measured in terms of the particle size of the water-insoluble coloring material contained therein. The determination of a good solvent or a bad solvent is carried out in accordance with the criteria that the measured particle size after storage during heating is compared with each other, with the value for paint without storage, and when the first particle size is larger than the last particle size, this is defined as a poor solvent, and when the first particle size is equal to or smaller than the last particle size, this is defined as a good solvent. In Table 3 below, the viscosity (cP) of the solvents used is also shown as a measurement condition for the particle size in undiluted solution. Viscosity is measured with a type E viscometer (VISCONIC type ED, manufactured by Tokyo Keiki Co., Ltd.)

Table 3 The composition of the test samples to determine a good solvent or a bad solvent in relation to the solvents used for the paint of example 4 Paint of Example 4 The composition of the studied examples [parts] one 2 3 Paint of Example 4 - one hundred one hundred one hundred Glycerol - one hundred - - Diethylene glycol - - one hundred - Polyethylene glycol 600 - - - one hundred Viscosity [cP] 2,3 10.1 8.7 33.9

Table 4 shows the particle size of the pigment in the undiluted paint of Example 4 without storage and the particle size of the pigment of each undiluted solution from Examples 1-3 after storage when heated at 60 ° C. for 48 hours, which are measured as described above. Comparing the measured values, it is determined that when the measured particle size values in each of the test examples are larger than that of the paint of Example 4, this is determined to be a poor solvent, and when the measured particle size in each of the test examples is equal to or smaller than paint of example 4, it is defined as a good solvent.

Table 4 The results of studies of solvents contained in the paint of example 4 Sample for measurements Particle size in undiluted solution [nm] Definition Test Example 1 (after storage upon heating) 71.2 O Test Example 2 (after storage upon heating) 167.8 X Test Example 3 (after storage upon heating) 160.7 X The paint of example 4 (without storage) 71.9 -

Storage conditions when heated: 60 ° C, 41 hours.

O: good solvent; X: poor solvent.

As shown in table 4, the results of the method for determining a good solvent or bad solvent using test samples obtained by diluting the prepared paint can confirm that glycerin (used in test example 1) is good solvent and diethylene glycol (used in test example 2) and polyethylene glycol 600 (used in test example 3) are poor solvents, as well as using the determination method shown in table 1, that is, using the above two Different types of determination methods produce the same results. Accordingly, it is confirmed that the method of using real paint to determine whether the solvent used therein is a good solvent or a poor solvent for the coloring material contained therein is effective. For this reason, the above method for determining whether the solvent used is a good solvent or a poor solvent, using a sample obtained by diluting the paint, can also be effectively used in the present invention.

<Comparative Examples 1-17>

(Preparation of paints)

The water-soluble organic solvents described above, the pigment dispersion solutions 1-3, and the components shown in Tables 5-1 to 5-3 are mixed. The resulting mixture was completely mixed to dissolve or disperse, and then it was subjected to pressure filtration using a microfilter with a pore size of 3.0 μm (manufactured by Fuji Photo Film Co., Ltd.) in order to obtain paints of comparative examples 1-17.

Table 5-1 The composition of the paints of comparative examples 1-6 The composition of the paints of comparative examples (% wt.) one 2 3 four 5 6 Water-insoluble coloring material Pigment Dispersion 1 fifty fifty fifty - - - Pigment Dispersion 2 - - - fifty fifty fifty Pigment Dispersion 3 - - - - - - Water soluble organic solvent Good solvent Glycerol 5 - 5 5 - 5 Ethylene glycol - - 5 - - 5 Trimethylolpropane 7 - 5 7 - 5 Bad solvent Diethylene glycol - - - - - - Polyethylene glycol 600 10 fifteen - 10 fifteen - Polyethylene glycol derivative - - - - - - Surface-active substance The product of the addition of acetylene glycol and EO (*) 0.1 0.1 0.1 0.1 0.1 0.1 Pure water 27.9 34.9 34.9 27.9 34.9 34.9 (*) Product Name: Acetylenol EH, manufactured by Kawaken Fine Chemicals Co., Ltd.

Table 5-2 The composition of the paints of comparative examples 7-12 The composition of the paints of comparative examples (% wt.) 7 8 9 10 eleven 12 Water-insoluble coloring material Pigment Dispersion 1 - - - - fifty - Pigment Dispersion 2 - - - - - fifty Pigment Dispersion 3 fifty fifty fifty fifty - - Water soluble organic solvent Good solvent Glycerol 5 - 5 - 3 3 Ethylene glycol - - 5 - - - Trimethylolpropane 7 - 5 - - - Bad solvent Diethylene glycol - - - - - - Polyethylene glycol 600 10 fifteen - - - - Polyethylene glycol derivative - - - - fifteen fifteen Surface-active substance The product of the addition of acetylene glycol and EO (*) 0.1 0.1 0.1 0.1 0.1 0.1 Pure water 27.9 34.9 34.9 39.9 31.9 31.9 (*) Product Name: Acetylenol EH, manufactured by Kawaken Fine Chemicals Co., Ltd.

Table 5-3 The composition of the paints of comparative examples 13-17 The composition of the paints of comparative examples (% wt.) 13 fourteen fifteen 16 17 Water-insoluble coloring material Pigment Dispersion 1 - fifty - - - Pigment Dispersion 2 - - fifty - fifty Pigment Dispersion 3 fifty - - fifty - Water soluble organic solvent Good solvent Glycerol 3 5 5 5 fifteen Ethylene glycol - 8 8 8 - Trimethylolpropane - - - - - Bad solvent Diethylene glycol - - - - - Polyethylene glycol 600 - 5 5 5 - Polyethylene glycol derivative fifteen - - - - Surface-active substance The product of the addition of acetylene glycol and EO (*) 0.1 0.1 0.1 0.1 0.1 Pure water 31.9 31.9 31.9 31.9 34.9 (*) Product Name: Acetylenol EH, manufactured by Kawaken Fine Chemicals Co., Ltd.

<Evaluation of image properties>

The inks of Examples 1-5 and Comparative Examples 1-17 are evaluated in terms of the properties described below using a modified BJS-700 inkjet device (manufactured by Canon Inc.) having a multi-channel pulse head that applies thermal energy to the ink in response to a print signal in order to throw away ink. The obtained evaluation results for the examples are shown in table 6, and the results for comparative examples are shown in table 7.

1. Print Density

Using the above inks and the above ink jet apparatus, characters occupying a solid area of 2 cm x 2 cm are printed on plain A-E copy paper described below. On the day after printing, the print density of the solid portion of 2 cm × 2 cm is measured. The printer driver mode is the default mode. The default mode settings are shown below. The amount of ink ejected onto one raster dot of the ink is within 30 ng ± 10%.

• Paper Type: Plain paper.

• Print quality: standard.

• Setting colors: automatic.

The print density resulting from the above measurement is evaluated in accordance with the following criteria.

O: The average print density for 5 types of paper is 1.4 or higher, and the print density for paper with the lowest print density is 1.25 or higher.

Δ: The average print density for 5 types of paper is 1.4 or higher, and the print density for paper with the lowest print density is less than 1.25.

X: The average print density for 5 types of paper is less than 1.4.

The above print study uses the following types of paper for copier:

A: NSK PPC paper, manufactured by Canon Inc.,

B: PPC NDK paper, manufactured by Canon Inc.,

C: PPC 4024 paper, manufactured by Fuji Xerox Co., Ltd.,

D: PPC Prober Bond paper, manufactured by Fox River Paper Co., and

E: Canon PPC paper manufactured by Die Neusiedler AG.

2. Print density when printing with a small amount of ink

The print density with less ink is measured in the same manner as above, except that the ejected amount of ink per raster dot is set within 24 ng ± 10%. After that, the obtained print density is evaluated in accordance with the same criteria as above.

<Storage Stability Assessment>

Each of the colors of examples 1-5 and comparative examples 1-17 is placed in a thick-walled container, and the container is sealed. Then the container is placed in an oven at 60 ° C. After two weeks, the container is removed, and then the condition of the paint is observed. Storage stability is evaluated in accordance with the criteria described below. The evaluation results obtained for the paints of the examples are shown in table 6, and the results for the paints of the comparative examples are shown in table 7.

O: The coloring materials contained in the paint disperse stably and uniformly.

X: The paint becomes gel, or its top becomes transparent, or it visibly thickens.

Table 6 Assessment of examples Print density Storage stability Normal paint discharge Low ink Example 1 O O O Example 2 O O O Example 3 O O O Example 4 O O O Example 5 O O O

Table 7 Comparative Examples Evaluation Results Print density Storage stability Normal paint discharge Low ink Comparative Example 1 X X O Reference Example 2 O A X Reference Example 3 X X O Reference Example 4 X X O Reference Example 5 O A O Reference Example 6 X X O Reference Example 7 X X O Reference Example 8 O A X Reference Example 9 X X O

Reference Example 10 O A X Reference Example 11 O A X Reference Example 12 O A O Reference Example 13 ABOUT A X Reference Example 14 X X O Reference Example 15 X X O Reference Example 16 X X O Reference Example 17 X X O

<Measurement of ink on plain paper>

(Preparation of example paints and comparative examples for measuring ink on paper)

A pigment dispersion solution 2 was used and mixed with the components shown in table 8. The mixture was completely mixed to dissolve or disperse and was filtered under pressure using a microfilter with a pore size of 3.0 μm (manufactured by Fuji Photo Film Co., Ltd.) in order to obtain each of the colors of example 6 and comparative examples 18-20. When preparing these inks, a water-soluble CI direct blue 199 dye is used to measure the ink on paper to visually observe the ink distribution after it has been fixed on the printing medium. The surface tension of each of these inks is also shown in Table 8. The surface tension is measured using a CBVP tension meter -A3 manufactured by Kyowa Interface Science Co., Ltd. at a measuring temperature of 25.0 ± 0.5 ° C using a 10 mm x 24 mm platinum plate.

Table 8 The composition of the paints of the example and comparative examples for measuring ink on paper Composition (% wt.) Ex.6 Comp. pr 18 Comp. pr. 19 Comp. pr. 20 Water-insoluble coloring material Pigment Dispersion 1 - - - - Pigment Dispersion 2 fifty fifty fifty fifty Pigment Dispersion 3 - - - - Water soluble organic solvent Good solvent Glycerol 7.5 - fifteen - Ethylene glycol - - - - Trimethylolpropane - - - 7.5 Bad solvent Diethylene glycol - - - - Polyethylene glycol 600 7.5 fifteen - 7.5 Polyethylene glycol derivative - - - - Surface-active substance The product of the addition of acetylene glycol and EO (*) 0.1 0.1 0.1 0.1 Water soluble dye C. I. direct blue 199 0.5 0.5 0.5 0.5 Pure water 34,4 34,4 34,4 34,4 Surface tension (mN / m) 39.5 39.6 39,4 40.1 (*) Product Name: Acetylenol EH, manufactured by Kawake Fine Chemicals Co., Ltd.

<Measurement of the diameter of the raster point>

When the diameter of the raster dot of the ink obtained immediately after the ink hit the plain paper is denoted by dI, the largest diameter of the ink distribution after the ink is fixed on the paper is denoted by dS, the largest diameter of the water-insoluble ink material in the raster point after the ink is fixed on the paper is denoted by dC, and the penetration depth of the water-insoluble coloring material into the paper after drying of the ink is represented by the penetration depth, dI, dS, dC values and the penetration depth from are measured using the following methods. First, the diameter dI of the ink raster point is measured immediately after the ink raster dot hits the plain paper using Face CONTACT-ANGLEMETER CA-P manufactured by Kyowa Interface Science Co., Ltd. Using a needle having a needle diameter of 28 G (inner diameter 0.18 mm and outer diameter 0.36 mm), the tip of the needle is placed at a height of 4 mm from the surface of plain paper, then paint is dripped from this height onto plain paper, and after dripping, the diameter the raster dot of the paint is read on the scale of the wetting angle meter. The above recorded value is used as the diameter dI of the raster dot of the ink immediately after ink enters the plain paper. The plain paper used in this study is PB-Paper (NSK paper), manufactured by Canon Inc.

The largest diameter dS of the ink distribution after fixing the ink on the printing medium and the largest diameter dC of the water-insoluble coloring material in the ink after fixing the ink on the printing medium is measured by dropping a raster dot on the plain paper under the conditions described above and leaving it for 6 hours or more and by measuring the corresponding largest linear dimensions after stabilization of the raster dot of the paint. The largest diameter dS of the ink dot point after fixing the ink on the printing medium is obtained by measuring the largest linear distribution of the blue color of the water-soluble dye C. I. direct blue 199, which was added to the ink. The largest diameter dC of a water-insoluble coloring material in the ink after fixing the ink on the printing medium is obtained by measuring the largest linear spreading size of the black color cast of the pigment contained in the ink. In addition, when the largest spreading diameter dC of the water-insoluble coloring material in the paint is measured, a raster dot shape for the black pigment is also observed.

<Measurement of the penetration depth of water-insoluble coloring material>

To measure the penetration depth of the water-insoluble coloring material, the water-soluble dye C. I. direct blue 199 in each of the inks from the above Example 6 and Comparative Examples 18-20 is replaced with water. The paints thus obtained are then filtered under the same conditions in order to prepare new paints. Using these inks, they print on PB-Paper (NSK paper), manufactured by Canon Inc., under the same conditions as the above print density estimate, using a modified BJS-700 inkjet device (manufactured by Canon Inc.) having a pulse head for multi-channel printing, which applies thermal energy to the ink in response to the print signal in order to eject the ink. After printing is completed and ink is fixed, the print area is cut from the back using a blade, and a cross section is observed under a microscope. The thickness (depth) of the distribution of water-insoluble coloring material in the context of paper is measured. Based on the measurement results obtained, the evaluation is carried out in accordance with the evaluation criteria described below. The obtained evaluation results and the measured values of the largest diameter dC are shown in table 9.

[Criteria for evaluation]

(Ratios of raster point diameters)

O: satisfies the relation dC <dI <dS.

X: does not satisfy the relation dC <dI <dS.

(The shape of the raster point of a water-insoluble coloring material)

1: Visual observation, looking at the paper from above

O: The shape of the raster dot of the water-insoluble coloring material is a regular circle, and its edge is sharp.

X: The shape of the raster dot of the water-insoluble coloring material is not a regular circle, and its edges are blurred.

2: Visual observation, looking at the paper from the side

O: The raster dot of water-insoluble ink is present almost at the level of the surface of the paper.

X: The raster dot of the water-insoluble coloring material protrudes clearly above the surface of the paper.

(Depth of penetration of water-insoluble coloring material)

O: less than 30 microns.

X: 30 μm or more.

Table 9 Measurement of ink on paper and the largest diameter of the spread of the coloring material Etc. 6 Comp. pr 18 Comp. pr. 19 Comp. pr. 20 The ratio of the diameters of the raster points O O X O The shape of the raster point of a water-insoluble coloring material 1. Observation from above O O X O 2. Side observation O X O O Depth of penetration of water-insoluble coloring material O O X X The largest diameter dC [mm] of the distribution of water-insoluble coloring material 3.04 2.84 3.75 2.96

15 schematically depicts a top view of raster points formed for the above measurement. Fig is a schematic micrograph used to measure the thickness (depth) of the spread of water-insoluble coloring material in the cross section of the paper. As shown in FIG. 15 and table 9, when the paints of Example 6 and Comparative Example 18 are used, the water-insoluble coloring material forms a raster dot in the form of a regular circle. In the case of comparative example 18, however, a water-insoluble coloring material protrudes above the surface of the paper, and thus, the surface of the paper is coated with an excess amount of water-insoluble coloring material.

Therefore, when the ink of Example 6 is compared with the ink of Comparative Example 18, the ink material is effectively held close to the surface of the paper. On the other hand, when the paint of comparative example 19 is used, a water-insoluble coloring material forms a raster dot with a non-uniform distribution. In addition, water-insoluble coloring material is distributed not only on the surface of the paper, but also in the depth direction of the paper, causing loss of coloring material. In addition, when the paint of comparative example 20 is used, as shown in FIG. 15, the water-insoluble coloring material forms a raster dot in the form of a regular circle. However, as can be seen from the section of the printing section shown in Fig. 16, which is printed using the BJS-700 inkjet printing device (manufactured by Canon Inc.), the coloring material is distributed not only on the surface of the paper, but also in the depth direction of the paper . Thus, it is confirmed that in this case, the coloring material is used inefficiently.

As can be seen from the values of the largest diameter dC of the distribution of the water-insoluble coloring material shown in Table 9, the paint of Example 6, containing both a poor solvent and a good solvent, with an appropriate ratio, has a distribution of a larger water-insoluble coloring material than the paint of comparative example 18 containing only bad solvent. This fact also confirms that the pigment ink of the present invention has a sufficiently large area coefficient even for a small drop of ink and forms an image having a high OD (reflection density). In addition, surfactant-free paints are prepared by replacing the product of the addition of acetylene glycol and EO used as a surfactant with water in the respective paint compositions of example 6 and comparative example 18. These paints are measured by the diameter of the raster the point and depth of penetration of a water-insoluble coloring material under the same conditions for measuring ink on plain paper carried out with the inks of Example 6 and Comparative Example 18. As a result, although surfactant-free paints require a longer fixing time after contact with paper than surfactant-containing paints, a paint containing both a poor solvent and a good solvent, with an appropriate ratio, achieves a distribution of water-insoluble coloring material larger than paint containing only a poor solvent, provided that the ratio is the same as for paints containing a surfactant.

[Study on color mixing (spreading) of the image]

<Examples 7-16>

The above described inks of Examples 1-5 are used as black inks in combination with color inks to form images. The color inks used here (three colors: cyan, magenta, and yellow) are prepared as follows.

(Cooking blue paint)

The components below are mixed and completely mixed so that they dissolve, and then the mixture is filtered under pressure using a 0.2 μm microfilter (manufactured by Fuji Photo Film Co., Ltd.) in order to prepare a blue the paint.

DBL (direct blue) 199 3.5 parts Glycerol 7.5 parts Diethylene glycol 7.5 parts Acetylenol E-100 1.0 part Pure water 80.5 parts

(Cooking purple paint)

Purple paint is prepared from the following components in the same way as for blue paint.

AR (acid red) 289 2.5 parts Glycerol 7.5 parts Diethylene glycol 7.5 parts Acetylenol E-100 1.0 part Pure water 81.5 parts

(Cooking yellow paint)

Yellow paint is prepared from the following components in the same manner as described above.

DY (direct yellow) 86 2.5 parts Glycerol 7.5 parts Diethylene glycol 7.5 parts Acetylenol E-100 1.0 part Pure water 81.5 parts

<Rating>

The black inks of examples 1-5 and the color inks prepared above are used in combination, as shown in table 10 below, and are printed by using these inks and an ink jet printing apparatus having a multi-channel pulse head shown in FIGS. 9 or 10, which applies thermal energy to the ink in response to a print signal in order to eject the ink. After that, the seal is evaluated. The obtained evaluation results are shown in table 11.

Table 10 Types of black ink and printheads used to evaluate print Head structure Black paint Example 7 Fig.9 Example 1 Example 8 Fig.9 Example 2 Example 9 Fig.9 Example 3 Example 10 Fig.9 Example 4 Example 11 Fig.9 Example 5 Example 12 Figure 10 Example 1 Example 13 Figure 10 Example 2 Example 14 Figure 10 Example 3 Example 15 Figure 10 Example 4 Example 16 Figure 10 Example 5

(Spreading Properties)

Solid areas are formed by printing with black ink and each of the color inks (yellow, magenta and cyan), so that the areas are next to each other by the printing method shown in FIGS. 9 and 10. The degree of spreading on the border between the black ink and color paint is visually observed and evaluated in accordance with the criteria described below. The plain paper used here is PB-Paper (NSK paper), manufactured by Canon Inc. The evaluation results are shown in table 11.

AA: Spreading cannot be observed visually.

A: Spreading is barely observed.

B: Spreading is observed, but the level, in fact, does not cause problems.

C: Spreading is such that the borders of the colors are fuzzy.

Table 11 Evaluation Results Resistance to spreading Example 7 A Example 8 A Example 9 A Example 10 A Example 11 A Example 12 AA Example 13 AA Example 14 AA Example 15 AA Example 16 AA

Industrial application

The water-based ink of the present invention is a pigment ink that has a sufficiently large area coefficient, even for a small drop of ink, and reaches an image with a high OD (reflection density). In addition, using the ink of the present invention, there is also provided an inkjet printing method for forming a high quality image with a high OD even for a small amount of ink applied, an ink cartridge, preferably used for the above printing method, a printing unit and an ink jet printing apparatus. In addition, an image forming method is also provided in which color mixing (spreading) at the boundary between the black ink region and the color ink region is effectively prevented without causing the ink to blur when a color image in which different colors are next to each other is printed on plain paper.

Claims (3)

1. The method of inkjet printing, which includes at least the stage of applying a water-based ink to the recording medium by the method of ejecting ink jets, and this ink contains water, many water-soluble organic solvents and a water-insoluble coloring matter,
where the composition of the specified many different water-soluble organic solvents includes at least one good solvent for the specified water-insoluble coloring matter and several bad solvents for the specified water-insoluble coloring matter, and the total amount of A (wt.%) good solvent in the paint and the total amount of B (wt. .%) of poor solvents in the paint are in the ratio A: B from 10: 5 to 7: 9, in both cases inclusive,
wherein said at least one good water-soluble organic solvent is selected from the group consisting of glycerol and ethylene glycol, and at least one of said several poor solvents is selected from the group consisting of diethylene glycol, polyethylene glycol and 2-pyrrolidone,
where said water-insoluble colorant is selected from the group consisting of a pigment dispersed with a resin; microencapsulated pigment; a self-dispersing pigment having hydrophilic groups attached to the surface of the pigment particles through other groups or atoms; and self-dispersible polymer-binding pigment, and
where said recording medium is a plain paper, and
where water-soluble organic solvents include a poor solvent having a Ka value determined using the Bristow method, which is the highest of the Ka values for all water-soluble organic solvents present in the paint. 2. The inkjet printing method according to claim 1, wherein said water-insoluble coloring matter is carbon black. 3. The inkjet printing method according to claim 1 or 2, wherein said hydrophilic pigment groups are selected from the group consisting of —COOM1, —SO ₃ M1, and —PO ₃ H (M1) ₂ , where M1 is a group selected from the group, consisting of a hydrogen atom, an alkali metal, ammonium and an organic ammonium compound.

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