RU2337932C1 - Ink, method of jet printing, printing unit, ink cartridge and printing device for jet printing - Google Patents

Abstract

FIELD: polygraphic industry.

SUBSTANCE: invention is attributed to ink for jet printing. Ink for jet printing is described which ink includes coloring substance with formula (I), or its salt, (I)

where: M - hydrogen atom, alkaline metal, alkali-earth metal or cation or ammonium ion of organic amine; n - integer 1 or 2, and water-soluble organic solvent, selected from the group including ethylene glycol, diethylene glycol, 2-pyrrolidone, 1,5-pentanediol, 1,6-hexanediol and ethylene-carbamide, in the quantity of 50 wt % or more relative to content of all organic solvents in the ink. Suggested yellow ink has enhanced humidity resistance and color hue stability due to lowered migration.

EFFECT: obtaining ink with enhanced humidity resistance and color hue stability.

7 dwg, 10 tbl, 21 ex

Description

FIELD OF THE INVENTION

The present invention relates to inkjet inks having good dyeing property, good moisture resistance and high reliability, an inkjet printing method, a printing unit, an ink cartridge and an inkjet printing apparatus.

State of the art

The inkjet printing method is a printing method involving applying a droplet of ink to any of the print media, such as plain paper and glossy media, to form an image and quickly found wide application due to lower costs and increased print speed. Due to the rapid proliferation of digital cameras and movie cameras, as well as improving the quality of the image obtained by this method, he has found application as a method of obtaining a photographic image comparable to that obtained using silver halide.

In recent years, image quality has improved, despite the marginal reduction in ink drop size and the improvement in color gamut provided for with the introduction of multicolor inks. Meanwhile, the need for a coloring material and ink has increased, therefore, requirements have been tightened, for example, to such properties in the context of coloring and reliability, as adhesion and stability of ejection.

Compared to a photograph obtained with silver halide, the inkjet printing method poses problems, for example, in the sense of image retention stability of the finished printed product. Generally speaking, a printed product obtained by the inkjet printing method is inferior in image retention stability to a photograph obtained with silver halide and causes a problem in that the coloring material on the printed product is prone to deterioration, which causes a change in color tone and discoloration of the image when the printed product is exposed to light, humidity, heat, ambient gas present in the air, etc. for a long period of time. To solve this problem, a large number of technical solutions have been proposed.

Generally speaking, the ink jet method involves the use of ink, each of which has a shade of yellow, bright red, cyan, black, and the like. flowers. Until now, it was believed that among these inks, yellow inks should be improved in light fastness, water resistance, moisture resistance, etc. To improve these properties, it is proposed, for example, to use a coloring material having a specific structure, for example, the direct dye in yellow (CI) direct dye 173 (CI Direct Yellow 173) or the direct dye presented in the dye guide yellow under number 86 (CI Direct Yellow 86) (see, for example, documents JP-A 02-233781 and JP-A 04-233975). The use of such a coloring material as mentioned above demonstrates significant increases in light fastness, water resistance and moisture resistance, but color tone, staining property, reliability, etc. are not at satisfactory levels.

It is also proposed to use the 132 yellow direct dye in the dye reference book (CI Direct Yellow 132) as any of the materials, such as yellow ink and a coloring material, for an ink set (see, for example, JP-A 11- 29729 and JP-A 2001-288391). Although this coloring material has often been used to produce inkjet inks due to its proper coloring property, this coloring material causes a problem in that it has extremely poor moisture resistance.

It is also proposed the use of a coloring material having a specific structure to increase moisture resistance (see, for example, JP-A 11-217529), as well as the use of an ink set of several colors to increase moisture resistance (see, for example, JP-A 11- 180028).

In each of the proposals described, an attempt was made to increase the moisture resistance, but depending only on the structure of the coloring material. In other words, neither the proposal to increase moisture resistance by means of a coloring material having a specific structure, nor the proposal to increase moisture resistance by means of a set of inks of several colors cannot prevent migration, i.e. image quality deterioration due to a change in color tone in an environment such as an environment with high temperature and high humidity.

Also proposed is the synthesis of a new coloring material having moisture resistance, light resistance, water resistance, as well as giving a shade and sharpness suitable for inkjet printing (see, for example, JP-A 2003-321627). However, even when such a coloring material is used, it is not possible to achieve the level of moisture resistance required in some cases when implementing the modern ink jet printing method.

Summary of the invention

An object of the present invention is to increase the moisture resistance, which is the most important factor in a coloring material having a yellow tint, as well as to obtain yellow ink, excellent both in dyeing property and in moisture resistance.

The coloring material used in conventional yellow inkjet inks is prone to decrease moisture resistance, and said coloring material is prone to deteriorate the coloring property when this coloring material has adequate moisture resistance. Generally speaking, a coloring material having a large molecular weight is difficult to move in the recording medium when the coloring material comes into contact with excess moisture after this coloring material has settled on the printed information medium. As a result, moisture resistance can be improved. Meanwhile, a coloring material having a high molecular weight has a structure in which a large part that is not involved in dyeing is large, which reduces the dyeing efficiency in terms of unit weight. Therefore, when using a coloring material having a high molecular weight and proper moisture resistance, the coloring property should be satisfactory. In other words, it is necessary to achieve compatibility between the coloring property and moisture resistance in the ink containing the yellow coloring material in order to increase the image retention stability of the inkjet printed product to a level characteristic of a photograph obtained with silver halide or a higher level.

Extensive research has been conducted to discover the mechanism by which the color tone of a printed product changes due to migration, and to prevent migration itself. In particular, studies were conducted to find a specific ink composition, in the presence of which a change in its color tone due to migration is detected in the printed product obtained with these inks. As a result, it was found that the occurrence of migration depends mainly on the presence or absence of a particular water-soluble organic solvent. That is, it is proved that migration occurs when a water-soluble organic solvent remaining in the printed product absorbs moisture in air present in an environment with high temperature and high humidity.

The present invention was created on the basis of the above research results, attention was paid to the image formed on the print medium, the difference between the ink component before the image formation and the component of the water-soluble organic solvent remaining in the print medium after image formation, and the corresponding properties of the water-soluble organic solvent in Ink. As a result, a mechanism was discovered in the presence of which a change in the color tone due to migration occurs due to the difference in the properties of the water-soluble organic solvent remaining in the printed product. Then it was concluded that the change in color tone due to migration depends on the total amount of water-soluble organic solvent remaining in the printed product, and on the property according to which the water-soluble organic solvent essentially contains water molecules. Extensive research has been conducted in connection with this feature, completing the creation of the present invention.

As described above, it was found that migration is caused by the interaction between the moisture resistance of the coloring material and a water-soluble organic solvent.

Therefore, the main objective of the present invention is to provide a new method of suppressing changes in color tone due to migration, paying attention to the amount of water-soluble organic solvent present in the printed product.

Another objective of the present invention is the development of inks that are excellent in moisture resistance and properties such as intermittent ejection stability, as ink for inkjet printing.

Another objective of the present invention is the development of inks that are excellent in moisture resistance, stability of intermittent ejection, image density and color tone.

These problems are solved using the present invention, described below. That is, in accordance with one aspect of the present invention, there is provided an inkjet ink containing at least a coloring material, and water-soluble organic solvents, the ink is characterized in that they satisfy the following conditions (A) and (B):

(A) the color contrast ΔE, the judgment of which is made by the judgment of the properties of the dyeing material, is 9 or less, said judgment method comprising steps (1) to (3): in which

1) applying a modeling ink containing a coloring material, water and a water-soluble organic solvent having an evaporation rate X (wt.%) Lower than the evaporation rate of water and a moisture absorption coefficient (wt.%), Which is 20 or more and satisfactory the ratio of Y≥2.8X + 10, and the application of transparent ink obtained by replacing only the coloring material of the modeling ink with water, in such an amount that the number of modeling ink is less than the number of transparent ink;

2) keeping the printed product obtained in step (1) in an environment at a temperature of 25 ° C and a humidity of 60% for 48 hours, followed by keeping this printed product in an environment at a temperature of 30 ° C and a humidity of 80% for 168 hours;

3) a judgment on color contrast (ΔE), represented by the following expression (1), between the printed product before aging for 168 hours and the printed product after aging for 168 hours:

ΔЕ = √ ((L ₁ -L ₂ ) ² + (a ₁ -a ₂ ) ² + (b ₁ -b ₂ ) ² ) (one)

where: L ₁ , a ₁ and b ₁ represent the parameters L, a and b of the Lab calorimetric system after aging for 48 hours and before aging for 168 hours, respectively; L ₂ , a ₂ and b ₂ represent the parameters L, a and b of the Lab calorimetric system after aging for 168 hours;

(B) the content of a water-soluble organic solvent in which the evaporation rate X (wt.%) And the moisture absorption coefficient Y (wt.%) Satisfy the ratio given by the following expression (2), in all water-soluble solvents in the ink is 50 wt.% Or more :

Y < 2.8X + 10 (2)

where: X represents the rate of evaporation, Y represents the coefficient of moisture absorption.

In another aspect of the present invention, there is provided an inkjet printing method, characterized in that it comprises the step of ejecting the above ink using the ink jet printing method.

In accordance with yet another aspect of the present invention, there is provided an ink cartridge, characterized in that it includes an ink storage part for inkjet printing.

In accordance with another aspect of the present invention, there is provided a printing unit, characterized in that it includes a part for storing ink for inkjet printing and a printhead for ejecting this ink.

In accordance with another aspect of the present invention, there is provided an inkjet printing apparatus, characterized in that it includes a part for storing inkjet ink and a printhead for ejecting this ink.

In accordance with the present invention, yellow inkjet inks can be developed that meet the dyeing property requirements of an inkjet ink and have high moisture resistance even when letters are printed by ink on various recording media, and also an inkjet printing method, a printing unit, an ink cartridge and an inkjet printing device, each of which provides for the use of said ink.

Brief Description of the Drawings

The invention is further explained in the description of the preferred embodiments with reference to the accompanying drawings, in which:

FIG. 1 shows a diagram of the relationship between the evaporation rate and the moisture absorption coefficient according to the invention;

FIG. 2 is a general view of a printing apparatus according to the invention;

FIG. 3 is a general view of the mechanical part of a printing apparatus according to the invention;

FIG. 4 is a sectional view of a printing apparatus according to the invention;

FIG. 5 is a general view of a device in which an ink tank is mounted on a cartridge of a head according to the invention;

FIG. 6 is a perspective view of a device with a spatial separation of parts of a head cartridge according to the invention;

FIG. 7 is a front view illustrating a substrate with printing elements on a head cartridge.

Description of preferred embodiments of the invention

In the present invention, when the compound is a salt, the salt dissociates to form ions in the ink, and this condition is conveniently characterized by the expression “contains salt”.

Ink

It was determined that migration is the result of the interaction between the moisture resistance of the coloring material and the water-soluble organic solvent. Below will be a detailed description of the component that is part of the ink, corresponding to the present invention.

Coloring material

Inkjet ink (sometimes referred to simply as “ink” hereinafter) corresponding to the present invention should contain a coloring material having a color contrast (ΔE), which is judged by a judgment method on the properties of the coloring material of 9 or less.

The method of judging the properties of the coloring material

A method for judging the properties of a coloring material in the present invention includes steps (1) to (3). Below we will give a more detailed description of these stages with their division into the following stages (a) - (g).

(a) Obtaining modeling ink and transparent ink

Modeling ink is obtained containing a coloring material, water and a water-soluble organic solvent having an evaporation rate X (wt.%) Lower than the evaporation rate of water and a moisture absorption coefficient (wt.%) Y of 20 or more, and satisfying the ratio Y≥2.8X + 10 or, preferably, Y> 2.8X + 10 (the technical meaning of the ratio Y≥2.8X + 10 will be explained below), and transparent ink obtained by replacing only the coloring material in the above composition with water. With this composition, the ink is in conditions under which migration does not occur. It is important that this composition meets the above conditions, because the purpose of this composition is to make judgments about the properties (especially moisture resistance) of the coloring material.

The evaporation rate X (wt.%) In the present invention is determined as follows: 5 g of a water-soluble organic solvent are placed in a cuvette having an outer diameter of 31 mm and a height of 15 mm; leave this cuvette to stand motionless in an environment having a temperature of 60 ° C and a humidity of 10% for 192 hours; once again measure the mass of the water-soluble organic solvent and determine the evaporation rate based on the decreased mass of the water-soluble organic solvent. The moisture absorption coefficient Y (wt.%) Is determined as follows: 5 g of a water-soluble organic solvent are placed in a cuvette having an outer diameter of 31 mm and a height of 15 mm; leave this cuvette to stand motionless in an environment having a temperature of 30 ° C and a humidity of 80% for 192 hours; once again measure the mass of the water-soluble organic solvent and determine the coefficient of moisture absorption, based on the increased mass of the water-soluble organic solvent.

Modeling ink was prepared in accordance with the following composition, which used glycerol and urea as water-soluble organic solvents, Acetylenol E-100 (manufactured by Kawaken Fine Chemicals Co., Ltd.) as a surfactant and presented in the direct dye guide yellow dye number 132 (CI Direct Yellow 132) as a coloring material. Table 1 shows the evaporation rate X (wt.%) For each of such substances as glycerin and urea, as well as the evaporation rate X (wt.%) For water (pure water). The following table 1 demonstrates that each of such substances as glycerin and urea corresponds to a water-soluble organic solvent having an evaporation rate lower than the evaporation rate of water and a moisture absorption coefficient of 20 wt.% Or more.

Table 1 Composition (wt.%) Evaporation Rate (wt.%) The coefficient of moisture absorption (wt.%) Glycerol 10.0 0,0 66.9 Urea 10.0 0.1 86.0 Acetylenol
E-100 1,0 - - Cidirect
Yellow 132 3.0 - - Pure water 76.0 100.0 -

(b) Creating an image for evaluation

Modeling ink and transparent ink thus obtained were superimposed on each other to obtain an image for evaluation. Although this image may have an arbitrary ink usage ratio when printing, overlapping modeling ink and transparent ink on top of each other is important. The reason for this, given the state of the printed product in a real environment, is that printing is generally rarely done with any one type of ink. In other words, we can say that migration occurs in the presence of several inks. Therefore, it is important to create an image for evaluation by superimposing modeling ink and transparent ink on top of each other in order to reproduce this situation. In addition, the amount of applied modeling ink is preferably less than the amount of transparent ink. The reason is that when an image for evaluation is created by applying modeling ink and transparent ink on top of each other under the conditions described above, the amount of water-soluble organic solvent applied - relative to the coloring material - on the recording medium increases, resulting in the occurrence of migration more likely. This approach allows us to establish a clearer difference in some property (in particular, moisture resistance) between the coloring materials, so that it becomes possible to more clearly evaluate the properties (in particular, moisture resistance) of the target coloring material. In the present invention, the simulating ink described above and the transparent ink described above were used, and the range of utilization of each of them was varied from 5% to 100% in 5% increments to create an evaluation image in which the modeling ink and the transparent ink were superposed .

In the present invention, the assessment of properties, in particular the moisture resistance of the coloring material, does not require a specific printing device or print medium. To the extent that the printing device is capable of applying ink to the recording medium, and the recording medium can absorb ink, there are no restrictions on the shapes of the printing device or recording medium. A specific example of such a printing apparatus includes a printing apparatus including an ink storing part for storing ink and a print head for ejecting ink.

(c) Creating an image for evaluation in the initial standard state

Measures are taken to promote the evaporation of both the water-soluble organic solvent and the water present in the evaluation image created in the manner described above. The image for evaluation is left in an environment having a temperature of T ₁ ° C and a humidity of _H1% for a certain period of time to take measures to promote vaporization and the water-soluble organic solvent and water present in the image for evaluation. As a result, you can create an image for evaluation in the initial standard state. In order to take measures that promote the evaporation of both the water-soluble organic solvent and the water present in the image for evaluation, it is important to reduce the absolute water content characteristic of the environment in which the image for evaluation is located.

Although it is important to leave an image for evaluation in an environment having a temperature of T ₁ ° C and a humidity of H ₁ % for a certain period of time, this period can be arbitrary. In particular, this period is preferably such that the evaporation of both the water-soluble organic solvent and the water from the inside of the image for evaluation is reduced, and the mass of the image for evaluation becomes constant. For example, the inventors proved that the evaporation of both a water-soluble organic solvent and water from within the image for evaluation reaches essentially equilibrium in 48 hours, and the mass of the image for evaluation becomes constant in the environment, having a temperature of T ₁ = 25 ° C and humidity H ₁ = 60%, and these temperatures and humidity are selected based on the state of the printed product in the environment.

When the image for evaluation is left for a period of less than 48 hours, the evaporation of both the water-soluble organic solvent and the water does not reach equilibrium, and therefore it is expected that either the water-soluble organic solvent or the water will remain in the image for evaluation. As a result, the initial standard state does not stabilize and it is likely that the state of occurrence of migration will change and the accuracy of the judgment on moisture resistance will decrease. When an image for evaluation is left for a period of more than 48 hours, the initial standard state may stabilize, but it can be expected that additional measures will have to be taken to promote the evaporation of both the water-soluble organic solvent and the water. As a result, the amount of the water-soluble organic solvent remaining in the image for evaluation is reduced, in which it can be expected that the water-soluble organic solvent will cause migration, and the amount of the water-soluble organic solvent capable of absorbing moisture is reduced. Therefore, the occurrence of migration becomes unlikely. For the above reasons, the image for evaluation is preferably left in the environment having a temperature of T ₁ = 25 ° C and a humidity of _H1 = 60% for 48 hours. Under the above conditions, it is expected that it will be possible to realize the evaporation of both a water-soluble organic solvent and water while maintaining the state of the printed product in a real environment. It should be noted that the absolute content of water present in the environment having a temperature of T ₁ = 25 ° C and a humidity of H ₁ = 60% is about 13.8 g / m ³ .

(d) Measure the color tone of the image for evaluation in the initial standard state

Measure the color tone (La ^* b ^* values in the color space standardized by CIE (CIE) - International Commission on Lighting (La ^* b ^* CIE values)) of the image obtained in the above manner for evaluation in the initial standard state. This measurement is intended to numerically determine the color tone of the image for evaluation in the initial standard state, maintained over a period of time. In the present invention, the color tone of the image for evaluation in the initial standard state was measured by a spectrophotometer (Spectrolino (trademark), manufactured by Gretag Macbeth).

(e) Creating an image for evaluation after acceleration test

The image for evaluation in the initial standard state, created in the aforementioned manner, is left in an environment (with high temperature and high humidity) having a temperature of T ₂ ° C and a humidity of H ₂ %, to cause migration to occur at an increasing speed, thereby creating an image for evaluation after an acceleration test. Temperature and humidity during acceleration are arbitrary provided that T ₁ <T ₂ and H ₁ <H ₂ . That is, it is important to increase the absolute content of water present in the environment by setting a higher temperature and higher humidity. In general, it is believed that migration occurs when a water-soluble organic solvent present in a printed product absorbs moisture. Accordingly, it is important to take measures that promote migration by increasing the absolute content of water present in the environment in which the image for evaluation is located. In particular, the temperature T ₂ ° C is preferably 30 ° C or more, and the humidity H ₂ % is preferably 80% or more, and therefore it is possible to increase the absolute content of water present in the environment in which the image for evaluation is located. In the present invention, in view of the conditions in which the printing apparatus and the printing product are in a real environment, the temperature T ₂ ° C and humidity H ₂ % are set to 30 ° C and 80%, respectively. As a result, a condition is reproduced under which migration in the printed product may occur when the user is using the printing device. It should be noted that the absolute content of water present in the environment, having a temperature of 30 ° C and a humidity of 80%, is about 24.3 g / m ³ .

The period of time during which the image for evaluation is maintained in an environment (with high temperature and high humidity) having a temperature of T ₂ ° C and humidity H ₂ % is set chronologically following the measurement of the color tone of the image for evaluation. In particular, a change in the color tone of the image is recorded for evaluation from the initial standard state, and the point at which the rate of change is reduced is preferably set to the appropriate period of time during which the image for evaluation in the initial standard state is kept in the environment (with high temperature and high humidity) having a temperature of T ₂ ° C and a humidity of H ₂ %. In a more preferred embodiment, the point at which almost no change is observed in the color tone is set corresponding to a suitable period of time during which the image for evaluation in the initial standard state is maintained in the environment (high temperature and high humidity), having a temperature T ₂ ° C and humidity H ₂ %. For example, the rate of change in color tone will decrease in an environment having a temperature of T ₂ = 30 ° C and humidity H ₂ = 80% for 96 hours, and a change in color tone will hardly be observed at around 168 hours. Therefore, to assess migration, it is important that the image for assessment in the initial standard state remains in an environment (with high temperature and high humidity) having a temperature of T ₂ ° C and a humidity of H ₂ %, for 96 hours or more. In a more preferred embodiment, the image for evaluation in the initial standard state is kept in an environment (with high temperature and high humidity) having a temperature of T ₂ ° C and a humidity of H ₂ %, for 168 hours or more, since the color tone changes in In this case, it has an almost constant value, so that it allows one to more accurately evaluate the difference in a certain property (in particular, moisture resistance) between the coloring materials. For the above reasons, it is preferable to maintain the image for evaluation in an environment having a temperature of T ₂ = 30 ° C and a humidity of H ₂ = 80% for 168 hours.

(e) Image Measurement for Evaluation after Acceleration Test

The color tone (La ^* b ^* MCO values) of the image obtained in the above manner is measured for evaluation after the acceleration test. This measurement is intended to quantify the color tone of an image for evaluation after an acceleration test. In the present invention, the hue of the image for evaluation after the acceleration test was measured by a spectrophotometer (Spectrolino (trade name), manufactured by Gretag Macbeth) in the same manner as in the above step (g).

(g) Calculation of color contrast (ΔE)

The color contrast (ΔE) was calculated based on the following expression (1), based on the color tone (La ^* b ^* MCO values) of the image for evaluation in the initial standard state, measured in the above step (g), and the color tone (La ^* b values ^* CIE) images for evaluation after the acceleration test and measuring said image in the above step (e).

The values La ^* b ^{* of the} image for evaluation in the initial standard state, located in the color space of the parameters La ^* b ^* CIE, are (L ₁ , a ₁ , b ₁ ).

The values of La ^* b ^* images for evaluation after testing for acceleration, located in the color space of the parameters La ^* b ^* MCO, are (L ₂ , a ₂ , b ₂ ).

ΔЕ = √ ((L ₁ -L ₂ ) ² + (a ₁ -a ₂ ) ² + (b ₁ -b ₂ ) ² ). (one)

The color contrast (ΔE) calculated based on the expression (1) represents the magnitude of the color tone change. Therefore, the greater the color contrast (ΔE), the greater the change in color tone. In other words, greater color contrast (ΔE) means that there is a tendency for migration to occur, so that the degree of migration can be numerically represented by color contrast (ΔE).

The following procedure is essential in the present invention. The properties (in particular, the moisture resistance) of each coloring material are evaluated by means of the above-described method of judging the properties of the coloring material, the color contrasts (ΔE) -ΔE1, ΔE2, ... are calculated in the corresponding images for evaluation created by the corresponding coloring materials, and coloring material having a color contrast (ΔE), which is the maximum of the calculated digital contrasts and is 9 or less.

A coloring material represented by the general formula (I)

Another embodiment of the present invention is characterized in that a coloring material having a color contrast (ΔE) of 9 or less, which is judged by a judgment method on the properties of the coloring material, is a compound of general formula (I) or a salt thereof.

General formula (I)

where: M independently represents a hydrogen atom, an alkali metal, alkaline earth metal or an organic amine cation or ammonium ion; index n is independently an integer 1 or 2.

Specific examples of the coloring material represented by the general formula (I) include compounds having the structures shown in the following table 2. Of course, the present invention is not limited to them. For convenience, the substitution position of the sulfone group is shown in Table 2 by ring A or ring B, as shown in the following general formula (II). The substitution position of the sulfone group is that which is defined in the following general formula (II).

General formula (II)

where: M independently represents a hydrogen atom, an alkali metal, alkaline earth metal or an organic amine cation or ammonium ion; index n is independently an integer 1 or 2.

table 2 Deputy position Ring a Ring B Possible connection one 2 four 2 four four 3 2 4.6 four 4.6 four

A preferred specific example of a coloring material represented by general formula (I) includes a possible compound 1 as set forth below. Of course, the present invention is not limited to them.

Possible connection 1

A coloring material other than a coloring material represented by the general formula (I)

To further increase the density of the image, to obtain a more preferred color tone for other purposes, the present invention preferably uses coloring materials of two or more types. Particularly preferred as such coloring materials are the coloring material represented by the general formula (I) and the direct dye yellow No. 132 (C.I. Direct Yellow 132) presented in the dye guide. Accordingly, another embodiment of the present invention is characterized in that C.I. Direct Yellow 132 is used as a coloring material in addition to the coloring material represented by general formula (I).

The content of the coloring material

The content of the ink coloring material of the inkjet printing according to the present invention is preferably in the range of 1.0 wt.% Одерж content 4 4.0 wt.% With respect to the total ink weight. When the content of the coloring material is less than 1.0 wt.%, In some cases it is not possible to obtain the effects of the present invention that are satisfactory in the context of the coloring property and moisture resistance. When the content of the coloring material exceeds 4.0 wt.%, Reliability may decrease - in the context of the stability of intermittent ejection and other properties of inkjet printing.

In addition, the content of the coloring material represented by the general formula (I) is preferably 10 wt.% Or more with respect to the total content of all coloring materials in the ink in order to satisfactorily obtain the effects of the present invention. When the colorant materials are used in conjunction with the direct dye yellow in the dye reference number 132 (C.I. Direct Yellow 132), its content is preferably 10 wt.% Or more relative to the total content of all the coloring materials in the ink. In addition, the ratio of the content of the coloring material represented by the general formula (I) to the content of C.I. Direct Yellow 132 (the content of the coloring material represented by the general formula (I): C.I. Direct Yellow 132 content) is in the range of mass ratios from 0.5: 5 to 2: 5. An excessively low content of the coloring material represented by the general formula (I) makes it difficult to obtain a satisfactory effect of the present invention, while an excessively large content of the coloring material represented by the general formula (I) tends to decrease the image density.

A method of testing a coloring material

Possible compound 1, which is an example of a coloring material used in the present invention, can be tested using each of the following methods (1) to (3), each of which involves the use of high-performance liquid chromatography (HPLC):

(1) determination of peak duration;

(2) determination of the maximum absorption wavelength at the peak according to (1);

(3) mass / charge definition, M / Z (pos., Neg.), At the peak according to (1).

Analysis conditions for high performance liquid chromatography are given below. An ink solution diluted 1000 times with pure water is analyzed by high resolution liquid chromatography under the following conditions to measure the duration of the main peak and the maximum absorption wavelength at the peak.

Column: symmetric, model C18, 2.1 mm × 150 mm

Column temperature: 40 ° C

Flow rate: 0.2 ml / min

Photodiode Array (PDA): 210 nm to 700 nm

The state of the mobile phase and gradient: table 3

Table 3 0-5 min 5-40 min 40-45 min A Water 85% 85%> 0% 0% To methanol 10% 10%> 95% 95% C An aqueous solution of sodium acetate concentration of 0.2 mol / l 5% 5% 5%

In addition, the following are the conditions for the analysis of the mass spectrum. The mass spectrum at the resulting peak is measured under the following conditions, and for each positive and negative value, the most pronounced M / Z ratio is changed.

Ionization method

Electrospray ionization (IEMR)

Capillary stress 3.5 kV Desolvating gas 300 ° C Ion source temperature 120 ° C Detector for positive values: 40 V, 200-1500 atomic mass units (amu) / 0.9 sec for negative values: 40 V, 200-1500 amu / 0.9 sec

Table 4 shows the duration, maximum absorption wavelength, M / Z (pos.) And M / Z (neg.), For example, for each of possible compounds 1 and C.I. Direct Yellow 132 described above. When the coloring material has the parameter values indicated in Table 4, this coloring material can be defined as being a coloring material that can be used in the present invention.

Table 4 Duration (min) Maximum Absorption Wavelength (nm) M / z Position Negatives. Possible connection 1 31-32 390-410 938-939 468-469 C.I.Direct
Yellow 132 33-34 390-410 640-641 319-320

Water soluble organic solvent

The water-soluble organic solvents used in the present invention should be such that the content of the water-soluble organic solvent in which the evaporation rate X (wt.%) And the moisture absorption coefficient Y (wt.%) Satisfy the ratio represented by the following equation (2) with respect to the total content of water-soluble organic solvents in the ink, which is 50 wt.% or more.

Migration is thought to occur when the water-soluble organic solvent present in the printed product absorbs moisture. Therefore, migration can be suppressed by introducing into the ink one or another amount of a water-soluble organic solvent that easily evaporates and has a low coefficient of moisture absorption. However, inks containing only a water-soluble organic solvent that readily vaporizes and has a low moisture absorption coefficient tend to cause problems in the context of adhesion at the tip of the nozzle, stability of intermittent ejection, and the like. In the present invention, ink with suppressed migration, suppressed adhesion at the end of the nozzle and, for example, excellent stability of interrupted ejection can be obtained when the water-soluble organic solvent has the above composition.

Y < 2.8X + 10 (2)

where: X represents the rate of evaporation, Y represents the coefficient of moisture absorption.

The evaporation rate X (wt.%) In the present invention is determined as follows: 5 g of a water-soluble organic solvent are placed in a cuvette having an outer diameter of 31 mm and a height of 15 mm; leave this cuvette to stand motionless in an environment having a temperature of 60 ° C and a humidity of 10% for 192 hours; once again measure the mass of the water-soluble organic solvent and determine the evaporation rate based on the decreased mass of the water-soluble organic solvent. The moisture absorption coefficient Y (wt.%) Is determined as follows: 5 g of a water-soluble organic solvent are placed in a cuvette having an outer diameter of 31 mm and a height of 15 mm; leave this cuvette to stand motionless in an environment having a temperature of 30 ° C and a humidity of 80% for 192 hours; once again measure the mass of the water-soluble organic solvent and determine the coefficient of moisture absorption, based on the increased mass of the water-soluble organic solvent.

In FIG. 1 is a diagram of the relationship between the evaporation rate and the moisture absorption coefficient of each water-soluble organic solvent calculated by the above method. The terms Gly, DEG, PEG, 2P, 15PD, 16HD, 126HT, Urea, and EtUrea represent glycerin, diethylene glycol, polyethylene glycol, 2-pyrrolidone, 1,5-pentanediol, 1,6-hexanediol, 1,2,6-hexanetriol, urea and ethylene urea, respectively.

Ink was prepared containing each of the aforementioned water-soluble organic solvents, and the following experiment was performed. Modeling inks were obtained that contained 3% by weight of the direct dye yellow dye reference number 132 (CI Direct Yellow 132), 20% by weight of each organic solvent, and 0.5% by weight Acetylenol EH (trade name, manufactured by Kawaken Fine Chemicals Co., Ltd.) as a surfactant, and the rest was water. Separately from the modeling ink, transparent ink was obtained, replacing the coloring material with water. The utilization coefficient of each of the modeling ink and transparent ink was varied from 0 to 100% to create a printed product having an image formed on it in which modeling ink and transparent ink were superimposed. PIXUS 950I (a trademark manufactured by CANON Inc.) was used as an inkjet printer, and premium photo paper (SP-101, manufactured by CANON Inc.) was used as a recording medium.

The resulting printed product was kept in an environment (with normal temperature and normal humidity) having a temperature of 25 ° C and a humidity of 60% for 48 hours to cause evaporation of the water-soluble organic solvent and water from the print medium. The color tone (La ^* b ^* MCO values) after being kept for 48 hours in an environment having a temperature of 25 ° C. and a humidity of 60% was measured using a spectrophotometer (trademark Spectrorino, manufactured by Gretag Macbeth) to determine the La values ^* b ^* . After that, the resulting printed product was kept in an environment (with high temperature and high humidity) having a temperature of 30 ° C and a humidity of 80% for 168 hours to cause the migration of a water-soluble organic solvent. The color tone (La ^* b ^* MCO values) after keeping for 168 hours in an environment having a temperature of 30 ° C and a humidity of 80% was measured using the same spectrophotometer as described above to determine the La ^* b ^* values after migration of a water soluble organic solvent. Based on the results obtained, the maximum color contrast (ΔE) was determined. We can say that the greater the color contrast (ΔE), the greater the change in color tone in an environment with high temperature and high humidity and the lower the moisture resistance.

The experimental results described above and the relationship between the evaporation rate and the moisture absorption coefficient of each water-soluble organic solvent showed that there is a correlation between the evaporation rate and the moisture absorption coefficient.

Migration is associated with a deterioration in image quality due to a change in color tone, for example, in an environment with high temperature and high humidity. Therefore, the lower the color contrast caused by the environment, the better the migratory ability of the water-soluble organic solvent. A water-soluble organic solvent having the proper migratory ability, i.e. proper moisture resistance, is characterized by the fact that this solvent easily evaporates and absorbs moisture heavily. In other words, a water-soluble organic solvent with enhanced migration ability exhibits less color contrast (ΔE).

ΔЕ < 5.5

ΔE> 5.5

In general, an image having a color contrast (ΔE) of 5.5 or less is preferable because a change in color tone due to migration does not occur even in an environment with high temperature and high humidity. In contrast, an image having a color contrast (ΔE) of more than 5.5 shows a noticeable change in color tone due to migration in an environment with high temperature and high humidity, resulting in poor print quality. Expression (2) obtained by finding the relationship between the migration of each water-soluble organic solvent and the moisture absorption coefficient of this solvent based on the above criterion. That is, in FIG. 1 shows that the water-soluble organic solvent to the right of the line Y = 2.8X + 10 has a color contrast (ΔE) of 5.5 or less.

Generally speaking, to increase moisture resistance, you can use a water-soluble organic solvent having a low solubility for the coloring material ("bad" solvent). However, none of the coloring materials used in the present invention has demonstrated a relationship between migration and the solubility of the coloring material in a water-soluble organic solvent. That is, it is not the solubility of the coloring material in the water-soluble organic solvent, but the evaporation rate and the moisture absorption coefficient of the water-soluble organic solvent in the ink that are dominant in improving the moisture resistance of the coloring material used in the present invention.

Specific examples of a water-soluble organic solvent satisfying the dependence represented by expression (2) include ethylene glycol, diethylene glycol, 2-pyrrolidone, 1,5-pentanediol, 1,6-hexanediol, ethylene urea, N-methyl-2-pyrrolidone, butyl carbitol and isopropyl alcohol. Of these water-soluble organic solvents, ethylene glycol, diethylene glycol, 2-pyrrolidone, 1,5-pentanediol, 1,6-hexanediol and ethylene urea are preferred, and ethylene urea is particularly preferred. In particular, ethylene urea, diethylene glycol and 2-pyrrolidone are preferably used in combination to improve inkjet printing properties such as reliability. You can use a water-soluble organic solvent, different from those described above, to the extent that this solvent satisfies the dependence represented by the expression (2).

A water-soluble organic solvent that does not satisfy the dependence represented by the expression (2), such as glycerin, urea or polyethylene glycol, can be used in the inks of the present invention to the extent that this water-soluble organic solvent has an effect without prejudice to the tasks and effects of the present invention. At the same time, the content of a water-soluble organic solvent satisfying the dependence represented by the expression (2) with respect to the total content of water-soluble organic solvents in the ink should be 50 wt.% Or more in order to satisfactorily obtain the effects of the present invention. The content of a water-soluble organic solvent satisfying the dependence represented by expression (2) with respect to the total content of water-soluble organic solvents in the ink is preferably 65 wt.% Or more, since the effects of the present invention are clearly expressed.

In the present invention, the content of a water-soluble organic solvent satisfying the dependence represented by expression (2) with respect to the total content of water-soluble organic solvents in the ink is 50 wt.% Or more. When the content of the water-soluble organic solvent satisfying the dependence represented by the expression (2) is too low, it is not possible to obtain a significant effect of the present invention.

Meanwhile, the total content of all water-soluble organic solvents in the ink is preferably in the range of 10 wt.% < Content < 50 wt.% Or less with respect to the total weight of the ink. When the total content of all water-soluble organic solvents in the ink is less than 10 wt.% Or exceeds 50 wt.%, Inkjet printing properties such as reliability can be degraded.

Additives, etc.

Inks according to the present invention can use substances in the form of solid particles that retain moisture, such as urea and a urea derivative, if necessary.

In addition, additives such as a surfactant, a pH adjuster, a corrosion inhibitor, an antiseptic, an antifungal agent, an antioxidant, a reduction inhibitor, an evaporation accelerator, a chelating agent and a water-soluble polymer can be added to the ink of the present invention.

Print Media

Any print medium may be used to form images by ink according to the present invention, since printing is carried out by applying ink to this print medium.

The present invention is applicable to a recording medium in which a coloring material, such as a paint or a pigment, is absorbed into a small particle forming a porous structure in an ink-absorbing layer, and an image is formed of at least this small particle with a coloring material absorbed therein. moreover, the present invention is suitable specifically for the case when the method of creating an ink jet. Such an ink jet recording medium is preferably a so-called absorbing type medium in which ink is absorbed by a gap formed in the ink-absorbing base layer.

The ink-absorbing layer of the absorbing type is made in the form of a porous layer consisting mainly of small particles and containing a binder and any other additive, if any. Specific examples of fines include inorganic pigments such as silica, clay, talc, calcium carbonate, kaolin, alumina (eg, alumina or aluminum hydroxide), kieselguhr, titanium oxide, hydrotalcite and zinc oxide; and organic pigments, such as urea-formalin polymer, ethylene-based polymer and styrene-based polymer. One or more types of such particles may be used. Examples of a binder that is suitable for use include a water soluble polymer and latex. Examples of an available binder include polyvinyl alcohol or its denatured product; starch or its denatured product; gelatin or its denatured product; gum arabic; cellulose derivatives such as carboxymethyl cellulose, hydroxymethyl cellulose and hydroxypropyl methyl cellulose; latexes based on vinyl copolymers, such as latex based on an elastomeric butadiene-styrene copolymer (SBR), latex based on an elastomeric butadiene-nitrile copolymer (NBR), latex based on a methyl methacrylate-butadiene copolymer, latex based on a polymer with a functionally modified group and a copolymer of ethylene and vinyl acetate; polyvinylpyrrolidone, maleic anhydride or a copolymer thereof; and an acrylic acid ester copolymer. If necessary, two or more types of such binders can be used. In addition, an additive can be used, and examples of such an additive that can be used if necessary include a dispersant, thickener, pH adjuster, lubricant, flow denaturing agent, surfactant, antifoam, release agent, fluorescent brightener, ultraviolet light absorber and antioxidant .

In particular, the present invention preferably uses a recording medium having an ink absorbent layer formed thereon, consisting mainly of small particles having an average particle size of 1 μm or less. Particularly preferred examples of fine particles include fine silica particles and fine alumina particles. Preferred fine particles of silica are small particles of silica, of which colloidal silica is a typical representative. Colloidal silica, which itself is purchased on the market, in particular, is as described in JP 2803134 or JP 2881847. Preferred fine particles of alumina are fine particles of aluminum hydroxide, and the like. Aluminum hydroxide represented by the following general formula can be cited as one example of such small particles of aluminum hydroxide.

AlO _3-n (OH) _2n · mH ₂ O

where: n is an integer equal to 1, 2 or 3, and m is a value from 0 to 10, in the preferred embodiment, from 0 to 5, but provided that m and n cannot be equal to 0 at the same time. The number m can be integer or fractional, because the mH ₂ O term also represents an aqueous phase that can desorb and does not participate in the formation of a crystal lattice with mH ₂ O in many cases. In addition, heating of this type of material can cause m to reach 0.

Aluminum hydroxide can be obtained by a well-known method, such as the hydrolysis of aluminum alkoxide or sodium aluminate, described in US 4242271 or US 4202870, or a method involving the addition of an aqueous solution of sodium sulfate, aluminum chloride and the like. in an aqueous solution of sodium aluminate, etc. to effect neutralization as described in JP-B57-44605.

The recording medium preferably has a basis for supporting the ink absorbing layer described above. Any base can be used without any particular limitation, since its ink-absorbing layer can be formed from the above-described porous fine particles, and this base provides rigidity, so that this base can be transported by a transport mechanism of an inkjet printer and the like. Specific examples of the base include a paper base formed from a pulp type feedstock, consisting mainly of natural cellulose fibers; a plastic base consisting of a material such as polyester (e.g. polyethylene terephthalate), cellulose triacetate, polycarbonate, polyvinyl chloride, polypropylene or polyimide; resin coated paper (e.g., RC paper) having on one side of the paper base a layer of polyolefin resin coating with the addition of white pigment or the like.

Ink kit

The ink according to the present invention can preferably also be used in combination with any other ink to provide an ink kit. In the sense in which the term "ink set" is used in this description, it refers to the state in which the ink according to the present invention is used in combination with any other ink, such as cyan ink, bright red ink, yellow ink or black ink . There are no restrictions on other inks that can be used in combination with the inks of the present invention to provide an ink set. The use of the term "ink set" in the present invention also extends to the case of sharing several ink containers, as well as to the case of using an ink tank, which itself has several ink containers, made as a single unit with each other. The use of the term "ink set" also extends to the product, which is made as a single unit of ink and a print head.

Inkjet printing method

The ink of the present invention is conveniently used, in particular, in an inkjet printing method involving ejecting ink by creating an ink jet. Examples of the inkjet printing method include a printing method comprising applying mechanical energy to the ink for ejecting ink, and a printing method comprising applying thermal energy to the ink to eject ink. In particular, a printing method involving the use of thermal energy is preferred for use in the present invention.

Ink cartridge

An example of an ink cartridge suitable for printing by ink of the present invention includes an ink cartridge including an ink storage portion.

Printing block

An example of a printing unit suitable for printing by ink in accordance with the present invention includes a printing unit including an ink storage portion and a print head. In particular, an example of a printing unit can be given in which the print head applies thermal energy corresponding to the print signal to the ink to form an ink droplet by means of said energy.

Inkjet printing device

An example of a printing apparatus suitable for printing by ink in accordance with the present invention includes a printing apparatus in which thermal energy corresponding to a printing signal is applied to the ink in a chamber of a print head having an ink storage portion to form an ink droplet by this energy.

Below will be described the conditional composition corresponding to the example of the mechanical part of the device for inkjet printing. The case of the printing device consists of a sheet feeding part, a transporting part sheet, a carriage part, a sheet releasing part and a cleaning part, as well as an external closing part intended to protect said parts and providing each of their mechanisms with the ability to fulfill its intended role. Below will be described the basic principles of operation of each of these parts.

In FIG. 2 shows a general view of a printing apparatus. In FIG. 3 and 4 are images illustrating the internal mechanism of the housing of the printing device, respectively. In FIG. 3 is a general view from above and to the right, and in FIG. 4 is a cross-sectional view of a printing apparatus.

When a sheet of paper is fed into the printing device, a gap consisting of a sheet feeding roller M2080 and a separating roller M2041 in a sheet feeding part including a sheet feeding tray M2060 is loaded with only a predetermined number of sheets of printed information medium. The printed information carriers arranged in this way are separated in the gap, and only the top sheet of the printed information carrier is transported. The recording medium sent to the sheet transporting part is guided by the pressure roller holder M3000 and the paper folding guide stop M3030 and sent to a pair of rollers consisting of the conveyor roller M3060 and the pressure roller M3070. A pair of rollers, consisting of a transport roller M3060 and a pressure roller M3070, rotate under the action of driving the left front electric motor E0002, and this rotation causes the transportation of the print medium on the paper support roller M3040.

In the carriage part, when an image is formed on the recording medium, the print head H1001 (Fig. 5) is located in the image forming position, and ink is ejected onto the information medium in accordance with a signal from the electrical substrate E0014. Details of the composition of the print head H1001 will be described below. When the print head H001 performs printing, the main print scan, in which the M4000 carriage scans in the column direction, and the auxiliary scan, in which the storage medium is transported in the row direction by the conveyor roller M3060, are repeated in alternating order, as a result of which an image is formed on the storage medium.

And finally, the information carrier on which the image is formed is in the gap between the first sheet-releasing roller M3110 and the spur 3120 in the sheet-release position, transported and released to the sheet-feeding tray M3160.

In the cleaning part, when the M5000 pump is able to operate in a state where the M5010 cover is brought into tight contact with the ink ejection hole of the print head H1001 in order to clean the print head H1001 before and after printing, unnecessary ink is sucked, etc. from the print head H1001. The ink remaining in the cover of the M5010 is sucked in with the cover open, as a result of which neither sticking of the remaining ink nor the subsequent harmful effect of this occurs.

Printhead

The following describes the cartridge H1000 print head. The printhead cartridge H1000 includes a printhead H1001, means for installing ink tanks H1900 and means for supplying ink from ink tanks H1900 to the printhead, and is mounted on the M4000 carriage so that it can be connected to and disconnected from it .

In FIG. Figure 5 shows how the H1900 ink tanks are mounted on the H1000 carriage. The printing apparatus forms an image by means of yellow, bright red, cyan, black, pale red, pale blue and green ink, so that the ink tanks H1900 are independently prepared for seven colors. Inks in accordance with the present invention are used as at least one of the mentioned inks. In addition, as shown in the drawing, each ink tank is detachably mounted to the head cartridge H1000. H1900 ink tanks can be disconnected when the H1000 printhead cartridge is installed on the M4000 carriage.

In FIG. 6 is a perspective view of the spatial separation of parts of the head cartridge H1000. The head cartridge H1000 includes a first substrate H1100 with printing elements, a second substrate H1101 with printing elements, a first plate H1200, a second plate H1400, a substrate H1300 with electrical wiring, a holder H1500 for containers, an element H1600 forming flow channels, an H1700 filter and a rubber seal H1800 .

Each of the first substrate H1100 with printing elements and the second substrate H1101 with printing elements is a silicon substrate having a plurality of printing elements (nozzles) for ejecting ink and formed on one surface by photolithography. An electrical wiring made of aluminum or the like for supplying power to each printing element is formed by a film forming method, and numerous ink flow channels corresponding to the individual printing elements are also formed by photolithography. In addition, the ink supply channels for supplying ink to the plural ink flow channels are formed so that they open on the rear surface.

In FIG. 7 is an enlarged front view for explaining the composition of each of the first substrate H1100 with printing elements and the second substrate H1101 with printing elements. Positions H2000-H2600 denote sequences of printing elements (which may also be referred to as nozzle sequences in the following text) corresponding to different ink colors. The first substrate H1100 with printing elements has a sequence of nozzles for three colors: a sequence of H2000 nozzles into which yellow ink is supplied; a sequence of H2100 nozzles into which bright red ink is supplied; and a sequence of H2200 nozzles into which blue ink is supplied. The second printing element substrate H1101 has nozzle sequences for four colors: a nozzle sequence H2300 into which pale blue ink is supplied; a sequence of H2400 nozzles into which black ink is supplied; an H2500 nozzle sequence into which orange ink is supplied; and a 2600 nozzle sequence into which pale red ink is supplied.

Each nozzle sequence consists of 768 nozzles spaced at 1200 dpi (dpi, reference value) in the direction of transport of the print medium, and each nozzle emits 2 picoliters (pl) of ink. The area of the hole in each ejection hole of the nozzle is set equal to approximately 100 μm ² . The first substrate H1100 with printing elements and the second substrate H1101 with printing elements are connected and bonded to a first plate H1200 having openings H1201 made thereon for supplying ink to a first substrate H1100 with printing elements and a second substrate H1101 with printing elements.

The second plate H1400 having openings is also connected and bonded to the first plate H1200. The second plate H1400 supports the wiring substrate H1300 in such a way that the wiring substrate H1300, the first substrate H1100 with printing elements and the second substrate H1101 with printing elements are electrically connected.

The wiring substrate H1300 provides an electrical signal forcing each of the nozzles formed on the first substrate H1100 with the printing elements and the second substrate H1101 with the printing elements to eject ink. The wiring substrate H1300 has an electrical wiring connected to each of the first substrate H1100 with printed elements and the second substrate H1101 with printed elements, and an input terminal H1301 for an external signal, which is located at the end of the wiring to receive an electrical signal from the housing of the printing device. The input terminal H1301 for an external signal is mounted on the rear side of the surface of the holder H1500 containers and bonded to the aforementioned side.

By the way, the H1600 element forming the flow channels is fastened, for example, by means of ultrasonic welding with an H1500 container holder to support H1900 ink tanks. As a result of this, a flow channel H1501 is formed, passing from the ink tanks H1900 to the first plate H1200.

The H1700 filter is located at the end of the ink flow channel H1501, which communicates with the ink tanks H1900, so that the H1700 filter prevents dust from entering from the outside. On the part where the flow channel H1501 communicates with the ink tanks H1900, a rubber seal H1800 is installed to prevent the ink from evaporating from the said part.

In addition, as described above, the head cartridge H1000 is formed by joining by welding or a similar method to connect the container holder part formed by the container holder H1500, the flow channel forming member H1600, the filter H1700 and the rubber seal H1800, and the print head portion H1001 formed by the first a substrate H1100 with printing elements, a second substrate H1101 with printing elements, a first plate H1200, a substrate H1300 with electrical wiring and a second plate H1400.

In the foregoing description, as an embodiment of the print head, a print head is provided corresponding to the Bubble Jet system, which prints by means of an electrothermal converter (printing element) for generating thermal energy, causing the film to boil ink depending on the electrical signal.

The characteristic structure and principle of the bubble jet method specific to the aforementioned system is preferably based on the basic principle described in US Pat. Nos. 4,723,129 and 4,740,796. This principle is applicable to on-demand and continuous supply. It is effective, in particular, with regard to supply on demand, for the following reason. At least one excitation signal, which corresponds to print information and causes a sudden increase in temperature to a value higher than the bubble boiling point, is supplied to an electrothermal converter located in accordance with the path along which the sheet or liquid passes and on which the liquid (ink) is held , and thereby causes the generation of thermal energy by an electrothermal converter. After that, the surface of the print head exposed to heat causes film boiling. As a result, it is possible to form an air bubble in a liquid (ink) in a one-to-one correspondence with an excitation signal. The growth and contraction of the air bubble causes the ejection of liquid (ink) through the ejection hole, resulting in at least one drop. The preferred excitation signal is a pulsed signal, because it is capable of immediately and adequately causing the growth and contraction of an air bubble, whereby it is possible to eject liquid (ink) to achieve excellent responsiveness.

An example of a second embodiment of an inkjet printing apparatus that uses mechanical energy, includes an on-demand inkjet printhead including a nozzle-forming substrate having multiple nozzles; a pressure generating element located opposite the nozzles and consisting of a piezoelectric material and an electrically conductive material; and ink filling the space surrounding the pressure generating element, while the pressure generating element is moved by the applied voltage, which causes the droplet of ink to eject from the nozzle.

We also note that the device for inkjet printing does not have to be the same as the above device, in which the head and ink tank are separate elements, but can be the one in which the head and ink tank are made as a whole, so that they turn out to be inseparable. The ink tank may be separate from the head or inseparable, integral with the head mounted on the carriage, or may be installed in the fixed part of the device for supplying ink to the print head by means of an ink supplying element such as a tube. When the ink tank has a structure for applying a preferred negative pressure to the print head, absorbent means may be located in the ink storage part, or the ink tank may have a flexible ink container and a spring portion for applying a driving force to expand the internal volume of the container . In the printing apparatus, the above sequential printing method may be borrowed, or it may be in the form of a progressive printing apparatus obtained by aligning the printing elements in a range corresponding to the full width of the recording medium.

Examples

The following is a more detailed description of the invention by way of examples and comparative examples. However, within the spirit of the present invention, it is not limited to the following examples. Unless otherwise indicated, the term "part" of each ink component in the examples and comparative examples is a "mass part".

Obtaining coloring material

The interaction of diazotized 4-nitro-4'-aminostilbene-2,2-disulfonic acid and 3-aminonaphthalene-1-sulfonic acid was ensured. The resulting product was placed in triazole, and the triazole nitro group was reduced to the amino group by the usual known method for the preparation of aminostilbentriazole. Aminostilbenbenzene was dissolved in water and sodium nitrite and hydrochloric acid were added drop by drop to this solution to conduct diazotization. The resulting product was added dropwise to an aqueous solution of the compound represented by the following compound (1), and the whole was reacted with subsequent dialysis with sodium chloride. The compound was diazotized with an aqueous solution of sodium nitrite and converted to triazole by adding an aqueous solution of 6-aminonaphthalene-2-sulfonic acid. Triazole was dialyzed with sodium chloride to obtain the coloring material represented by the following possible compound 1.

Compound (1)

Possible connection 1

Judging the properties (moisture resistance) of the coloring material

The properties (moisture resistance) of the possible compound 1 obtained in the aforementioned manner and the corresponding coloring materials shown in the following table 5 were judged by a judgment method on the properties of the coloring material according to the present invention.

Getting modeling ink and transparent ink

Modeling inks containing each coloring material were prepared according to the following formulation.

Each coloring material 3.0 parts Glycerol 9.0 parts Urea 9.0 parts Acetylenol E100 1.0 part (manufactured by Kawaken Fine Chemicals Co., Ltd.) Water Rest

Then, transparent ink was obtained, replacing the coloring material in the above composition with water.

Water had an evaporation rate X (wt.%) Of 100 wt.%. Glycerin and urea, used as water-soluble organic solvents in the above composition, have evaporation rates X (wt.%) Of 0 wt.% And 0.1 wt.%, Respectively. In addition, glycerin has a moisture absorption coefficient Y (wt.%) Of 66.9 wt.%, And urea has a moisture absorption coefficient Y (wt.%) Of 86.0 wt.%. Therefore, both glycerin and urea correspond to a water-soluble organic solvent having an evaporation rate lower than the evaporation rate of water and a moisture absorption coefficient of 20 wt.% Or more.

Create an image to evaluate and calculate color contrast

The utilization of the modeling ink was varied from 0% to 100% in increments of 5% to create an image for evaluation having a graded overlay pattern. To create an image for evaluation, we used an inkjet printer (PIXUS 950I trademark, manufactured by CANON Inc.) and a print medium (SP-101, manufactured by CANON Inc.). The resulting printed product was kept in an environment having a temperature of 25 ° C and a humidity of 60% for 48 hours, and then the color tone of the plot of the graduated overlay chart was measured using a spectrophotometer (Spectrorino (trademark), manufactured by Gretag Macbeth). The printed product was additionally kept in an environment having a temperature of 30 ° C and a humidity of 80% for 168 hours, and then the color tone of the plot of the graded overlay pattern was measured in the manner described above using the above-described spectrophotometer. The color contrast (ΔE) in the image for evaluation was calculated based on the following expression (1), based on the color tone of the image for evaluation after exposure to an environment having a temperature of 25 ° C and a humidity of 60%, for 48 hours, and color image tones for evaluation after exposure to an environment having a temperature of 30 ° C and a humidity of 80% for 168 hours.

Situated in the color space La ^* b ^* parameters of the CIE values of La ^* b ^* image for evaluation after standing in an environment having a temperature of 25 ° C and humidity 60% (i.e., in the initial standard state) for 48 hours make up (L ₁ , a ₁ , b ₁ ).

Are parameters of the color space La ^* b ^* values of the CIE La ^* b ^* image for evaluation after standing in an environment having a temperature of 30 ° C and humidity 80% (i.e. after acceleration test) for 168 hours in E make up (L ₂ , a ₂ , b ₂ ).

ΔЕ = √ ((L ₁ -L ₂ ) ² + (a ₁ -a ₂ ) ² + (b ₁ -b ₂ ) ² ). (one)

The maximum color contrast (ΔE) was calculated from the color contrasts in the respective images for evaluation, calculated on the basis of expression (1). The results are shown in table 5.

Table 5 Coloring material E _max Possible connection 1 7.5 C.I. Food yellow 3 10,4

Ink

Ink A-G according to examples and ink HK according to comparative examples were obtained by using possible compound 1, obtained as described above, and presented in the manual on dyes (CI) food yellow color (Food Yellow) under number 3 (CI Food Yellow 3) in accordance with the recipe indicated in table 6.

Table 6 Ink A B C D E F G H I J K Possible connection 1 3.0 4,5 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 C.I. Food Yellow 3 3.0 Ethylene glycol 4.0 11,2 Diethylene glycol 9.2 9.2 9.2 5.2 5,0 9.2 9.2 9.2 10.0 2-pyrrolidone 5,0 5,0 5,0 2.0 5,0 9,4 6.0 5,0 5,0 Ethylene urea 5 5 2 2 5,0 1,5-pentanediol 5,0 N-methyl-2-pyrrolidone 4.0 Butylcarbitol 2.0 Isopropyl alcohol 3.0 Urea 9.0 5,0 10.0 Glycerol 9.0 7.0 9.0 8.0 8.0 10.0 10.0 8.0 5,0 9.0 5.5 Polyethylene glycol (* 1) 5,0 5,0 Acetylenol E100 (* 2) 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Surfynol 104PG50 (* 3) 0.1 Non-ionized water 67.9 68,4 67.9 69.9 69.9 76.1 67.5 58.9 77.9 67.9 60.6 (* 1) Molecular mass of 200
(* 2) Adduct of ethylene oxide and acetylene glycol (surfactant) (manufactured by Kawaken Fine Chemicals Co., Ltd.)
(* 3) Surfactant, manufactured by Nissin Chemical Industry Co., Ltd.

Print Rating

Received transparent ink AK by replacing with water each of the coloring materials in the recipe obtained in the above manner, ink A-G according to the examples and ink HK according to comparative examples. An inkjet printer (brand PIXUS 950I, manufactured by CANON Inc.) was used for evaluation.

(1) Moisture resistance of ink

The range of utilization of each ink according to the examples and comparative examples was varied from 0% to 100% in increments of 5% to create an image for evaluation having a graded overlay pattern. The combination of ink and transparent ink was a combination of ink A and transparent ink A, a combination of ink B and transparent ink B, and the like. A glossy print medium (SP-101, manufactured by CANON Inc.) was used as a print medium. The resulting printed product was kept in an environment having a temperature of 25 ° C and a humidity of 60% for 48 hours, and then the color tone of the plot of the graduated overlay chart was measured using a spectrophotometer (Spectrorino (trademark), manufactured by Gretag Macbeth). The printed product was additionally kept in an environment having a temperature of 30 ° C and a humidity of 80% for 168 hours, and then the color tone of the plot of the graded overlay pattern was measured in the manner described above using the above-described spectrophotometer. The color contrast (ΔE) in each image for evaluation was calculated based on the following expression (1), based on the color tone of the image for evaluation after exposure to an environment having a temperature of 25 ° C and a humidity of 60% for 48 hours, and the color tone of the image for evaluation after exposure to an environment having a temperature of 30 ° C and a humidity of 80% for 168 hours.

Situated in the color space La ^* b ^* parameters of the CIE values of La ^* b ^* image for evaluation after standing in an environment having a temperature of 25 ° C and humidity 60% (i.e., in the initial standard state) for 48 hours make up (L ₁ , a ₁ , b ₁ ).

Are parameters of the color space La ^* b ^* values of the CIE La ^* b ^* image for evaluation after standing in an environment having a temperature of 30 ° C and humidity 80% (i.e. after acceleration test) for 168 hours in E make up (L ₂ , a ₂ , b ₂ ).

ΔЕ = √ ((L ₁ -L ₂ ) ² + (a ₁ -a ₂ ) ² + (b ₁ -b ₂ ) ² ). (one)

The maximum color contrast (ΔE) was calculated from the color contrasts in the respective images for evaluation calculated on the basis of expression (1), and each ink was evaluated for moisture resistance based on the following criteria. The results are shown in table 7.

BUT 4.0 ≥ ΔЕ AT 5.5 ≥ ΔЕ> 4.0 FROM 7.0 ≥ ΔE> 5.5 D ΔE> 7.0

(2) Stability of intermittent ejection

The ink jet printer on which the ink cartridge is installed, having a supply of each of the ink according to the examples and comparative examples, was kept in an environment having a temperature of 15 ° C. and a humidity of 10% for one day. After that, they printed on high-quality specialized paper (trademark HR-101, manufactured by CANNON Inc.) in an environment with a temperature of 15 ° C and a humidity of 10%, using ink consumed with a utilization rate of 50%. Then, printing was again carried out in the same manner as described above, after a certain time interval after the above-described printing, and a time interval was measured after which a noticeable lack of slippage was observed at the early printing stage. Intermittent ejection stability was evaluated by the measured time based on the following criteria. The results are shown in table 7.

A Pause for 5 seconds or more B Pause for 3 seconds or more, but less than 5 seconds C Pause less than 3 seconds

Table 7 Example Comparative example one 2 3 four 5 6 7 one 2 3 four  Yellow ink A B C D E F G H I J K X [wt.%] (* 4) 28,2 26.2 28,2 26.2 26.2 20,0 28.6 32,2 19.0 28,2 30.5 Y [wt.%] (* 5) 19.2 19.2 19.2 13,2 13,2 10.0 18.6 15,2 9.0 19.2 15.0 Z [%] (* 6) 68.1 73.3 68.1 50,4 50,4 50,0 65.0 47.2 47.4 68.1 49.2 Moisture resistance A A A B B B A C C D C Intermittent ejection stability A B B A B B B A A A B (* 4) The total content of water-soluble organic solvents (wt.%)
(* 5) Content (wt.%) Of a water-soluble organic solvent satisfying the expression (2)
(* 6) Ratio (%) of the content of a water-soluble organic solvent satisfying expression (2) to the total content of water-soluble organic solvents

As can be seen from the above table 7, when comparing examples 1-7 with comparative examples 1, 2 and 4, it turns out that excellent moisture resistance is obtained when possible compound 1 is used, having a component of 9 or less color contrast (ΔЕ), which is rendered by a judgment method on the properties of the coloring material, and the content of the water-soluble organic solvent satisfying the dependence represented by the expression (2) with respect to the total water content -soluble organic solvents in the ink is 50 wt.% or more. When comparing examples 1, 2, 3 and 7 with examples 4, 5 and 6, it turns out that excellent moisture resistance is also obtained when the content of a water-soluble organic solvent satisfying the dependence represented by expression (2) with respect to the total content of water-soluble organic solvents in ink is 65 wt.% or more. When comparing example 1 with example 3, it turns out that proper moisture resistance and excellent intermittent ejection stability are obtained when ethylene urea is introduced as a water-soluble organic solvent satisfying the dependence represented by expression (2). When comparing example 4 with example 5, it turns out that proper moisture resistance and excellent intermittent ejection stability are obtained when diethylene glycol, 2-pyrrolidone and ethylene urea are introduced as a water-soluble organic solvent satisfying the dependence represented by expression (2).

Judging the moisture resistance of the coloring material

The moisture resistance of each of the various coloring materials was judged by the following method. Next will be described a specific example of a method of making judgments about moisture resistance.

Getting modeling ink and transparent ink

For specificity, we note that the modeling ink was obtained in accordance with the following composition by using glycerol and urea as water-soluble organic solvents, Acetylenol E100 (manufactured by Kawaken Fine Chemicals Co., Ltd.) as a surfactant and presented in the reference for yellow direct dye dyes under the number 132 (CI Direct Yellow 132) as a coloring material.

Glycerol 10 wt.% Urea 10 wt.% Acetylenol E100 (manufactured by Kawaken Fine Chemicals Co., Ltd.) 1.0 wt.% C.I. Direct yellow 132 3.0 wt.% Water Rest

Then, transparent ink was obtained separately from the modeling ink, replacing part of the coloring material of the modeling ink with water.

Water had an evaporation rate of 100%. Meanwhile, glycerin and urea, used as water-soluble organic solvents in the above composition, have evaporation rates X (wt.%) Of 0 wt.% And 0.1 wt.%, Respectively. In addition, glycerin has a moisture absorption coefficient Y (wt.%) Of 66.9 wt.%, And urea has a moisture absorption coefficient Y (wt.%) Of 86.0 wt.%. Therefore, both glycerin and urea correspond to a water-soluble organic solvent having an evaporation rate X (wt.%) Lower than the evaporation rate of water and a moisture absorption coefficient (wt.%) Of 20 wt.% Or more.

Printing with Modeling Ink and Transparent Ink

To create an image for evaluation, we used a PIXUS 950I inkjet printer (trademark, manufactured by CANON Inc.) and a recording medium (trademark SP-101, manufactured by CANON Inc.). An image that corresponded to a total ink utilization rate of 80%, and in which the aforementioned modeling inks were used, the utilization rate of which at printing was 10%, and the aforementioned transparent ink, the utilization rate of which at printing was 70%, was printed in an environment having a temperature of 25 ° C and a humidity of 60%.

Printed product aging

The printed product was kept in an environment having a temperature of 25 ° C. and a humidity of 60% for 48 hours. After that, the Lab MCO values for the image were measured using a spectrophotometer (Spectrolino trademark, manufactured by Gretag Macbeth) and the Lab = (L ₁ , a ₁ , b ₁ ) values were determined in the color space of the La ^* b ^* MCO parameters in the initial standard state. At this point, L ₁ = 3.6, a ₁ = -7.5, and b ₁ = 36.8.

After that, the resulting printed product was kept in an environment having a temperature of 30 ° C and a humidity of 80% for 168 hours, and then the Lab CIE values for the image were measured using a spectrophotometer (trademark Spectrolino, manufactured by Gretag Macbeth) and the values determined Lab = (L ₂ , a ₂ , b ₂ ) in the color space of the parameters La ^* b ^* MCO in the initial standard state. At this point, L ₁ = 93.5, a ₁ = -9.6, and b ₁ = 45.0. The results confirmed the following expression:

ΔЕ = √ ((L ₁ -L ₂ ) ² + (a ₁ -a ₂ ) ² + (b ₁ -b ₂ ) ² ) = 8.5.

The color contrast (ΔE) between any other coloring material before exposure to an environment having a temperature of 30 ° C. and a humidity of 80% and the coloring material after exposure to the same environment is shown in the following table 8.

Table 8 Coloring material The maximum value of ΔE obtained by the method of making judgments about moisture resistance Yellow coloring
material Y1 7.5 Direct yellow 132 8.5 Direct yellow 142 8.0 Direct yellow 86 5,0 Direct yellow 173 4.8 Acid yellow 23 9.7

Ink

The L-U ink according to the examples and the V-Y ink according to the comparative examples were obtained by using the possible compound 1 obtained in the manner described above and the corresponding coloring materials in accordance with the formulation shown in table 9.

Table 9 Ink L M N O P Q R S T U V W X Y  Possible connection 1 0.5 1,0 0.5 0.5 0.5 0.5 0.5 0.5 0.5 3.0 0.5 0.5 0.5 0.5 Cidirect
Yellow 132 2,5 3.0 2,5 2,5 2,5 2,5 2,5 2,5 2,5 2,5 Cidirect
Yellow 142 3.0 Cidirect
Yellow 86 3.0 Cidirect
Yellow 173 0.5 Ciacid
Yellow 23 2,5 Ethylene glycol 4.2 11,2 3.0 10.0 Diethylene glycol 9.2 9.2 9.2 5,0 5,0 9.2 9.2 9.2 9.2 9.2 2-pyrrolidone 5,0 5,0 5,0 2.0 5,0 9,4 5,0 5,0 5,0 5,0 5,0 5,0 Urea ethylene 5,0 5,0 3.0 3.0 5,0 5,0 5,0 5,0  1,5-pentanediol 5,0 N-methyl-2-pyrrolidone 4.0 Butylcarbitol 2.0 Isopropyl alcohol 3.0 Urea 5,0 10.0 5,0 10.0 Glycerol 9.0 7.0 9.0 12.0 12.0 10.0 10.0 9.0 9.0 9.0 13.0 5,0 9.0 5.5 Polyethylene Glycol (* 1) Syrfynol
104PG50 (* 3) 0.1 Non-ionized water 67.9 68.9 67.9 69.9 69.9 76.1 67.5 67.4 67.4 62,4 65.1 77.9 67.9 65.6 (* 1) Molecular mass of 200
(* 2) Adduct of ethylene oxide and acetylene glycol (surfactant) (manufactured by Kawaken Fine Chemicals Co., Ltd.)
(* 3) Surfactant, manufactured by Nissin Chemical Industry Co., Ltd.

Print Rating

Received transparent L-Y ink by replacing each of the coloring materials with water in the formulation of the above-obtained L-U ink according to the examples and V-Y ink according to the comparative examples. An inkjet printer (brand PIXUS 950I, manufactured by CANON Inc.) was used for evaluation.

(1) Moisture resistance of ink

The range of utilization of each ink according to the examples and comparative examples was varied from 0% to 100% in increments of 5% to create an image for evaluation having a graded overlay pattern. The combination of ink and transparent ink was a combination of ink L and transparent ink L, a combination of ink M and transparent ink M, and the like. A glossy print medium (SP-101, manufactured by CANON Inc.) was used as a print medium. The resulting printed product was kept in an environment having a temperature of 25 ° C. and a humidity of 60% for 48 hours, and then the color tone of the graded plot portion was measured using a spectrophotometer (trademark Spectrorino, manufactured by Gretag Macbeth). The printed product was additionally kept in an environment having a temperature of 30 ° C and a humidity of 80% for 168 hours, and then the color tone of the plot of the graded overlay pattern was measured in the manner described above using the above-described spectrophotometer. The color contrast (ΔE) in each image for evaluation was calculated based on the following expression (1), based on the color tone of the image for evaluation after exposure to an environment having a temperature of 25 ° C and a humidity of 60% for 48 hours, and the color tone of the image for evaluation after exposure to an environment having a temperature of 30 ° C and a humidity of 80% for 168 hours.

Situated in the color space La ^* b ^* parameters of the CIE values of La ^* b ^* image for evaluation after standing in an environment having a temperature of 25 ° C and humidity 60% (i.e., in the initial standard state) for 48 hours make up (L ₁ , a ₁ , b ₁ ).

Are parameters of the color space La ^* b ^* values of the CIE La ^* b ^* image for evaluation after standing in an environment having a temperature of 30 ° C and humidity 80% (i.e. after acceleration test) for 168 hours in E make up (L ₂ , a ₂ , b ₂ ).

ΔЕ = √ ((L ₁ -L ₂ ) ² + (a ₁ -a ₂ ) ² + (b ₁ -b ₂ ) ² ). (one)

The maximum color contrast (ΔE) was calculated from the color contrasts in the respective images for evaluation calculated on the basis of expression (1), and each ink was evaluated for moisture resistance based on the following criteria. The results are shown in table 9.

BUT 4.0 ≥ ΔЕ AT 5.5 ≥ ΔЕ> 4.0 FROM 7.0 ≥ ΔE> 5.5 D ΔE> 7.0

(2) Stability of intermittent ejection

The ink jet printer on which the ink cartridge is installed, having a supply of each of the ink according to the examples and comparative examples, was kept in an environment having a temperature of 15 ° C. and a humidity of 10% for one day. After that, they printed on high-quality specialized paper (trademark HR-101, manufactured by CANNON Inc.) in an environment with a temperature of 15 ° C and a humidity of 10%, using ink consumed with a utilization rate of 50%. Then, printing was again carried out in the same manner as described above, after a certain time interval after the above-described printing, and a time interval was measured after which a noticeable lack of slippage was observed at the early printing stage. Intermittent ejection stability was evaluated by the measured time based on the following criteria. The results are shown in table 9.

BUT Pause for 5 seconds or more AT Pause for 3 seconds or more, but less than 5 seconds FROM Pause less than 3 seconds

(3) Image Density

Each of the inks according to the examples and comparative examples was used for printing with a utilization rate of 100%, thereby obtaining a printed product. A glossy print medium (trademark SP-101, manufactured by CANNON Inc.) was used as a print medium. The resulting printed product was dried for 24 hours. The optical density of the printed product was measured using a spectrophotometer (trademark Spectrolino, manufactured by Gretag Macbeth) and the image density was estimated based on the following criteria.

BUT Optical density greater than 1.85 AT The optical density is from 1.75 or more to 1.85 or less FROM Optical density less than 1.75

(4) Hue

Each of the inks according to the examples and comparative examples was used for printing with a utilization rate of 100%, thereby obtaining a printed product. A glossy print medium (trademark SP-101, manufactured by CANNON Inc.) was used as a print medium. The resulting printed product was dried for 24 hours. The saturation (C) of the color and the angle (h) of the hue of the portion of the printed product were measured using a spectrophotometer (trademark Spectrolino, manufactured by Gretag Macbeth). The color saturation (C) was calculated based on the following expression (3), based on the values of a ^* b ^* located in the color space of the parameters La ^* b ^* MCO. Color saturation and hue angle were evaluated based on the following criteria. The results are shown in table 10.

Saturation (C) of color

BUT C is 105 or more AT C is from 95 or more to 105 or less

Hue (h)

BUT h is from 85 or more to 90 or less AT h is from 83 or more to 85 or less, or is from 90 or more to 92 or less FROM h less than 83 or greater than 92.

Table 10 Example Comparative example 8 9 10 eleven 12 13 fourteen fifteen 16 17 5 6 7 8 Ink L M N O P Q R S T U V W X Y X [wt.%] (* 4) 28,2 26.2 28,2 26.2 26.2 20,0 28.6 28,2 28,2 33,2 31,0 19.0 28,2 30.5 Y [wt.%] (* 5) 19.2 19.2 19.2 14.2 14.2 10.0 18.6 19.2 19.2 19.2 8.0 9.0 19.2 15.0 Z [%] (* 6) 68.1 73.3 68.1 54,2 54,2 50,0 65.0 68.1 68.1 57.8 25.8 47.4 68.1 49.2 Moisture resistance A A A B B B A B A B D C C C Intermittent ejection stability A B B A B B B B B B A A B B Image density A A A A A A A B A B A A C A Saturation (C) of color A A A A A A A A A B A A A BUT Hue (h) A A A A A A A B C B A A B A (* 4) The total content of water-soluble organic solvents (wt.%)
(* 5) Content (wt.%) Of a water-soluble organic solvent satisfying the expression (2)
(* 6) Ratio (%) of the content of a water-soluble organic solvent satisfying expression (2) to the total content of water-soluble organic solvents

As can be seen from the above table 10 when comparing examples 8-17 with comparative examples 5, 6 and 8, excellent moisture resistance is obtained when the content of a water-soluble organic solvent satisfying the dependence represented by expression (2) with respect to the total content of water-soluble organic solvents in the ink is 50 wt.% or more. When comparing examples 8, 9, 10 and 14 with examples 11, 12 and 13, which stipulate the use of the same coloring material, it turns out that excellent moisture resistance is also obtained when the content of a water-soluble organic solvent satisfying the dependence represented by expression (2), in relation to the total content of water-soluble organic solvents in the ink is 65 wt.% or more. Comparing examples 9-14 with examples 15-17 in terms of image density and color tone, it is found that excellent moisture resistance, excellent intermittent ejection stability, excellent image density and excellent color tone are obtained when a combination of possible compound 1 is used as a water-soluble organic solvent and presented in the reference for dyes direct yellow dye at number 132 (CI Direct Yellow 132). When comparing example 8 with example 10, it turns out that proper moisture resistance and excellent intermittent ejection stability are obtained when ethylene urea is introduced as a water-soluble organic solvent satisfying the dependence represented by expression (2). Comparing example 11 with example 12, it turns out that proper moisture resistance and excellent intermittent ejection stability are obtained when any of compounds such as diethylene glycol, 2-pyrrolidone and ethylene urea.

This application claims the priority of Japanese patent applications No. 2004-196446, filed July 2, 2004, 2004-196449, filed July 2, 2004, and 2005-193806, filed July 1, 2005, all of which are mentioned here for reference.

Claims (8)

1. Inkjet ink containing at least a dye and a water-soluble organic solvent, characterized in that the dye contains a compound represented by the following general formula (I)

or its salt, where M independently represents a hydrogen atom, an alkali metal, an alkaline earth metal, or an organic amine cation or ammonium ion; index n is independently an integer 1 or 2, wherein the water-soluble organic solvent contains at least one water-soluble organic solvent selected from the group consisting of ethylene glycol, diethylene glycol, 2-pyrrolidone, 1,5-pentanediol, 1,6-hexanediol and ethylene urea, and a total content of at least at least one water-soluble organic solvent is 50 wt.% or more with respect to the content of all water-soluble organic solvents in the ink. 2. Ink for inkjet printing according to claim 1, characterized in that it further comprises a direct yellow dye in the reference book for dyes at number 132 as a coloring matter. 3. Inkjet ink according to claim 1, characterized in that the content of water-soluble organic solvent is 65 wt.% Or more relative to the content of all water-soluble organic solvents in the ink. 4. Inkjet ink according to claim 1, characterized in that the water-soluble organic solvent contains diethylene glycol, 2-pyrrolidone or ethylene urea. 5. An inkjet printing method comprising an ink ejection operation of an inkjet method, characterized in that the ink contains inkjet ink according to claim 1. 6. An ink cartridge comprising an ink storage unit, characterized in that the ink contains inkjet ink according to claim 1. 7. A printing unit comprising an ink storage unit and a printhead for ejecting ink, characterized in that the ink contains inkjet ink according to claim 1. 8. An inkjet printing device comprising an ink storage unit and a printhead for ejecting ink, characterized in that the ink contains inkjet ink according to claim 1.

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