Ink-jet ink, method for ink-jet recording, ink cartridge and ink-jet recording apparatus

The present invention relates to inkjet inks, inkjet recording methods, ink cartridges, and inkjet recording devices.

The inkjet recording method is a method of recording images, characters, etc. by flying minute droplets of ink and adhering them to a recording medium (paper, etc.) based on various operating principles. It has features such as ease, high flexibility of recording patterns, and no need for development and fixing, and is rapidly becoming widespread in various applications. Furthermore, in recent years, full-color inkjet recording technology has been developed, and it is possible to form multicolor images that are comparable to multicolor printing by plate making and printing by color photography, and the number of copies to be created is small. In some cases, printed matter can be obtained at a lower cost than ordinary multicolor printing or printing. Against this background, improvements have been made to inkjet recording devices and recording methods in response to demands for improving recording characteristics such as high-speed, high-definition, and full-color recording. Since image forming devices such as printers to which the inkjet recording method is applied are used in various usage environments, recording stability is also important, and improvement of image durability is also required as a characteristic of ink.

Various recording media such as plain paper, coated paper, glossy paper, transparencies, and back print films are commercially available for the inkjet recording method, but low-priced plain paper is used for business use in general offices. Often. However, when plain paper is used as the recording medium, it is necessary to alleviate and suppress the curl (warp, curl) phenomenon that occurs when a large amount of ink is applied to the recording medium while satisfying the above-mentioned characteristics. Occurs. This curl phenomenon is largely due to the addition of water. That is, it is known that the curl phenomenon occurs remarkably when the area to which water is applied is large and when the amount of water applied is large. When inkjet recording is performed on plain paper, it is important to alleviate and suppress curl (curl after printing) caused by drying and evaporation of water after printing as well as curl during printing.

Inkjet-printed printed matter (prints) is used for various purposes, but curled paper does not maintain flatness and causes various problems such as stacking and curling when filing. In addition, trial printing of presentation manuscripts such as slides and OHP may be performed using inexpensive plain paper, and at that time, if figures, photographs, and backgrounds are printed in secondary colors (blue, etc.), The paper is often warped and difficult to handle.

Conventionally, several methods have been proposed as methods for alleviating and suppressing curl. For example, an inkjet ink containing a solid substance having four or more hydroxyl groups in its molecular structure and being soluble in water or an aqueous organic solvent has been proposed (see, for example, Patent Document 1). Further, inks containing sugars, sugar alcohols, and specific amide compounds have been proposed as curl inhibitors (see, for example, Patent Documents 2 to 5). Further, an ink containing a combination of a specially specified polyhydric alcohol and glycerin has been proposed (see, for example, Patent Document 6). Further, inks containing a solvent, a polymer binder, a medium dye, a water-soluble curl-preventing compound, a water-soluble degluing compound, a light-resistant compound, an antifoaming agent and the like have been proposed (see, for example, Patent Document 7).<patcit num="1"><text>Japanese Unexamined Patent Publication No. 4-332775</text></patcit><patcit num="2"><text>Japanese Patent Application Laid-Open No. 6-157955</text></patcit><patcit num="3"><text>Japanese Unexamined Patent Publication No. 6-240189</text></patcit><patcit num="4"><text>Japanese Unexamined Patent Publication No. 9-16539</text></patcit><patcit num="5"><text>Japanese Unexamined Patent Publication No. 9-176538</text></patcit><patcit num="6"><text>Japanese Unexamined Patent Publication No. 10-130550</text></patcit><patcit num="7"><text>Japanese Unexamined Patent Publication No. 2000-19826</text></patcit>

<p> Curling can be suppressed to some extent by incorporating a conventional curl-preventing compound in the ink. However, the speed of inkjet recording is further increasing, and ejection stability and reliability during high-speed printing are important. Therefore, after obtaining various physical properties such as stability, permeability, and viscosity of the ink itself, further, basic characteristics as an ink for inkjet recording, particularly inkjet ejection stability, more specifically, an inkjet recording head. Curls are alleviated and suppressed while maintaining a high level of clogging resistance and start-up properties (ink re-ejection from nozzles that temporarily suspend (stop or pause) ink ejection) of the ejection port (nozzle). Is important.</p><p> Therefore, an object of the present invention is to secure the ejection stability (startup property) such that the ejection stability after leaving the head, which is required for the conventional inkjet ink, and the ejection stability (startup property) such that the printed portion of the print is not disturbed or blurred at the start of printing. At the same time, it is an object of the present invention to provide an inkjet ink, an inkjet recording method, an ink cartridge, and an inkjet recording apparatus capable of alleviating and suppressing curl.</p><p> Another object of the present invention is to sufficiently relax and suppress curl, and to make printed matter produced using plain paper easier to handle.</p>

<p> The above object is achieved by the following invention.</p><p> That is, the inkjet ink of the present invention is an inkjet ink containing at least water, a colorant, a water-soluble organic compound 1 and a water-soluble organic compound 2, and the content X (mass%) of the water-soluble organic compound 1 is Is 10% by mass or more based on the total mass of the ink for inkjet, and the content X (mass%) of the water-soluble organic compound 1 and the content Y (% by mass) of the water-soluble organic compound 2 with respect to the total mass of the ink for inkjet. Mass%) is characterized by satisfying the relationship of the following equations (I) and (II). (I) 0 &lt;Y / X 0.9 (II) X + Y 15% by mass Water-soluble organic compound 1: Moisture retention in an environment with a temperature of 23 ° C and a humidity of 45%, and a temperature of 30 ° C and a humidity of 80. A water-retaining, water-soluble organic compound with a water retention difference of 36% or less in an environment of%. Water-soluble organic compound 2: A water-soluble organic compound other than a colorant and a water-soluble organic compound 1.</p><p> In particular, it is preferable that the content Y (mass%) of the water-soluble organic compound 2 is Y &lt;15% by mass, and the difference in water retention capacity is 40% or more.</p><p> Another embodiment of the inkjet ink of the present invention is an inkjet ink containing at least water and a colorant, and further comprises water-soluble organic compound 1-1, water-soluble organic compound 1-2, and water-soluble. The content X of the water-soluble organic compound 1-1 with respect to the total mass of the ink jet ink containing the organic compound 2-1.₁(Mass%), content X of the water-soluble organic compound 1-2 with respect to the total mass of the inkjet ink₂(% by Mass) and the content of the water-soluble organic compound 2 with respect to the total mass of the inkjet ink Y₁(Mass%) is characterized in that it satisfies the relationship of the following equations (1) to (3). (1) 0.1 (X₂+ Y₁) / X₁2.5 (2) X₁+ X₂ 10 mass% (3) X₂+ Y₁ 3% by mass Water-soluble organic compound 1-1: The difference between the water retention capacity in an environment with a temperature of 23 ° C and humidity of 45% and the water retention capacity in an environment with a temperature of 30 ° C and humidity of 80% is 36% or less. A water-soluble polyhydric alcohol or a water-soluble amide compound having a molecular weight Mw in the range of 100 Mw 1000. Water-soluble organic compound 1-2: The difference between the water retention capacity in an environment with a temperature of 23 ° C and a humidity of 45% and the water retention capacity in an environment with a temperature of 30 ° C and a humidity of 80% is 36% or less. A water-soluble alkanediol having a molecular weight Mw in the range of 100 Mw 150 and further having -OH groups at both ends of the main chain. Water-soluble organic compounds 2-1: Water-soluble organic compounds other than colorants, water-soluble organic solvents 1-1, and water-soluble organic solvents 1-2.</p><p> In particular, the content Y of the water-soluble organic compound 2-1₁(Mass%) is Y₁It is preferably &lt;15% by mass, and the difference in water retention capacity is 40% or more.</p><p> Further, the inkjet recording method of the present invention is characterized in that the ink for inkjet is applied to a recording medium by an inkjet head to form an image.</p><p> Further, the ink cartridge of the present invention is characterized by containing the ink for inkjet.</p><p> Further, the inkjet recording apparatus of the present invention is characterized in that the above-mentioned inkjet ink is mounted.</p>

<p> According to the present invention, with respect to the inkjet recording method on plain paper, curling can be sufficiently suppressed, and in particular, printed matter on plain paper can be easily handled. Another object of the present invention is to provide an ink capable of obtaining ink ejection stability and a recording method using the ink in inkjet recording. Further, an ink capable of obtaining good image characteristics and a recording method using the ink are provided.</p>

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments.

[Mechanism of curl]

The present invention has been made for the purpose of suppressing curl of the recording medium after the ink for inkjet (hereinafter referred to as "ink") is applied to the recording medium by the inkjet recording method.

The mechanism by which curling occurs after printing on a recording medium is as follows. Cellulose fibers are made by a paper machine so that they are lined up in the direction in which the paper flows (so to speak, they are forcibly oriented). Since the degree of expansion of cellulose fibers due to moisture differs greatly between the vertical direction and the horizontal direction, the size change of the paper that occurs when moisture is applied differs between the horizontal grain and the vertical grain of the paper. Therefore, when moisture is applied to the paper, the lateral direction of the cellulose fibers of the paper swells, and the direction perpendicular to the flow direction of the machine (often the vertical grain of the paper) when the paper is made (the horizontal grain of the paper). The length of the paper increases. Therefore, if the amount of ink applied during printing, that is, the amount of water applied is large, curling occurs on the opposite side of the surface to which water is applied, that is, negative curl occurs. However, when the water once absorbed by the cellulose fibers gradually evaporates, the cellulose fibers start to re-shrink and the paper shrinks again. Along with this, the paper becomes shorter than the length before it was moistened. Therefore, the paper gradually curls on the moistened surface, that is, causes a plus curl. This is because the moisture given by printing once enters between the fibers and the hydrogen bonds between the fibers, and as the moisture moves due to evaporation or the like, the tension applied at the beginning is loosened, so that the printed portion shrinks. It is thought that it occurs by doing so. This plus curl becomes a problem when inkjet recording is performed on a recording medium such as plain paper.

The present inventors have observed in detail the plus curl phenomenon that occurs when printing is performed by the inkjet recording method. As a result, it was found that when the inkjet ink is applied to the paper, the plus curl phenomenon progresses continuously for a long period of time, unlike the case where the water is simply applied to the paper.

At present, organic compounds such as glycerin and urea contained in many inkjet inks greatly contribute to the reliability of inkjet inks, especially ejection stability. On the other hand, it is considered that these organic compounds are a factor for continuously advancing the plus curl phenomenon.

[Water-retaining water-soluble organic compound]

Since the curl after applying the liquid medium containing water to the paper is considered to have some correlation with the evaporation of the water imparted to the paper, the present inventors consider that the curl is water-soluble, which is usually used for inkjet inks. The following detailed studies were conducted on the water retention capacity of sex organic compounds.

First, 20% by mass aqueous solutions of various water-soluble organic compounds were prepared, 10 g each of them was precisely weighed in a glass petri dish, and left in an environment with a temperature of 23 ° C and a humidity of 45%. At the same time, pure water containing no water-soluble organic compound was also left in the same manner. As the water evaporates, the amount of solution in the petri dish decreases, and the mass eventually becomes constant. Since all of the pure water has evaporated at this point in the pure water-only chalet left at the same time, what remains in the chalet containing the water-soluble organic compound is the water-soluble organic compound and its substance. The water retention capacity of each water-soluble organic compound was calculated by the following formula.

<maths num="1"><img file="JP2005298813A_D0001.tif" /></maths>

Next, move the above petri dish to an environment with a temperature of 30 ° C and a humidity of 80%, wait for equilibrium to be reached in the same manner, measure the residual weight in this environment, and determine the water retention capacity according to the above formula. It was. Furthermore, the same petri dish was moved to an environment with a temperature of 23 ° C and a humidity of 45% again, the residual weight was measured, and the water retention capacity was determined in the same manner. The results obtained are shown in Fig. 1. Furthermore, Fig. 2 shows the difference in water retention capacity under both environments.

The present inventors considered that there is some correlation between the difference in water retention capacity under the above-mentioned environment and the curl generation of plain paper. Therefore, when the aqueous solution containing the water-soluble organic compound examined above was applied to plain paper and the occurrence of curl was investigated, the water retention capacity in an environment with a temperature of 23 ° C and a humidity of 45% and a temperature of 30 ° C were determined. It was discovered that the water-soluble organic compound 1 having a water retention difference of 36% or less in an environment of 80% humidity significantly suppresses curling. Therefore, an ink containing a coloring material, an additive, and these water-soluble organic compounds was further prepared and inkjet recording was performed, and the occurrence of curl was observed. As a result, it was confirmed that curling did not occur even after several days had passed at room temperature after printing.

The water-retaining water-soluble organic compound in the present invention is a water-soluble organic compound having a water retention capacity of 5% or more in an environment of a temperature of 23 ° C. and a humidity of 45%.

However, if an ink composed of a water-soluble organic compound containing only the water-soluble organic compound 1 is mounted on an inkjet recording device in a state of being mounted on an inkjet recording head that ejects droplets from a nozzle and left for a long period of time, the nozzle is clogged. Due to such factors, the ejection stability deteriorates, and the writing portion at the start of printing is disturbed in a low temperature and low humidity environment.

Therefore, the present inventors have proceeded with further studies with the aim of ensuring the same level of ejection stability as conventional inkjet inks while suppressing curling to a certain level or more. As a result, in addition to the water-soluble organic compound 1 described above, the ink for inkjet contains water-soluble organic compounds other than the water-soluble organic compound 1, more specifically, water retention in an environment having a temperature of 23 ° C and a humidity of 45%. Contains water-soluble organic compound 2 in which the difference between force and water retention capacity in an environment with a temperature of 30 ° C and humidity of 80% is greater than 36% at a ratio satisfying the conditions of the following formulas (I) and (II). It was found that the above problem can be solved by making it. (I) 0 &lt;Y / X 0.9 (II) X + Y 15% by mass (X: Content of water-soluble organic compound 1 with respect to total mass of inkjet ink (mass%), Y: With respect to total mass of inkjet ink Content of water-soluble organic compound 2 (mass%)) Furthermore, according to the study of the present invention, when the amount of ink applied is large, specifically 3.0 g / m.²In addition to the above conditions, it was found that the content X (mass%) of the water-soluble organic compound 1 needs to be 10% by mass or more based on the total mass of the inkjet ink in such cases. ..

Further, the water-soluble organic compound 1 is preferably a polyhydric alcohol having an amide bond or a polyhydric alcohol having a sulfone group.

The water-soluble organic compound usually used in inkjet inks corresponds to the water-soluble organic compound 2 in the present invention. The water-soluble organic compound 2 has a large difference in water retention capacity, and easily releases water in the process of drying the recording medium to which water is applied, which increases the shrinkage of cellulose fibers. Many of the water-soluble organic compounds 2 have a small molecular weight of 100 or less and easily move with water in a recording medium, so that they do not easily stay on the cellulose fibers. Therefore, the water-soluble organic compound 2 gradually migrates in the recording medium and promotes curling. Therefore, when a large amount of ink containing the water-soluble organic compound 2, which is a water-soluble organic compound usually used in inkjet inks, is applied to plain paper, the curl becomes considerably large.

As a result of the studies by the present inventors, even if the inkjet ink contains the water-soluble organic compound 2 having the property of advancing curl, the water-soluble organic compound 1 is further contained and the water-soluble organic compound is further contained. By setting the ratio Y / X of the content of 1 and the content of the water-soluble organic compound 2 to 0 &lt;Y / X 0.9 as shown in the formula (I), curling can be effectively suppressed and the discharge is stable. It was found that the sex was also good.

Furthermore, the present inventors have found that the total content X + Y (mass%) of the water-soluble organic compound 1 and the water-soluble organic compound 2 needs to be X + Y 15% by mass. The reason for this is that when ink is applied to the paper, the total content of water-soluble organic compounds in the inkjet ink is increased, especially in order to suppress the evaporation of water in the short term and the shrinkage of the paper due to migration. This is because it is necessary to reduce the amount of water. In addition to this, it is estimated that the total amount of the water-retaining water-soluble organic compound, that is, the water-soluble organic compound 1 and the water-soluble organic compound 2 must be 15% by mass or more in order to prevent the ink applied to the paper from evaporating. There is.

It is more preferable that the X + Y satisfies the relationship of X + Y 20% by mass, and more preferably the relationship of X + Y 25% by mass is satisfied. When the present inventors prepared an ink in which the total content X + Y (mass%) of the water-soluble organic compound 1 and the water-soluble organic compound 2 was increased and observed the curl state, the X + Y was large. Then, it was found that the curl generated in a short period after printing can be effectively suppressed. In particular, when the X + Y is X + Y 25% by mass, the curl generated in a short time after printing is very effectively improved.

Further, the water content is preferably 77% by mass or less, more preferably 71% by mass or less, based on the total mass of the inkjet ink.

Further, the content Y (mass%) in the water-soluble organic compound 2 with respect to the total mass of the inkjet ink is preferably Y &lt;15% by mass. The reason for this is presumed as follows. As described above, since the water-soluble organic compound 2 has a property of advancing curl, the larger the content in the ink, the more likely the curl is to occur. Therefore, even if the ink for inkjet contains a large amount of the water-soluble organic compound 1, the water-soluble organic compound 2 migrates the water-soluble organic compound 1 and reduces the curl suppressing effect of the water-soluble organic compound 1. This is because it will be stored. Further, it is preferable that the difference in water retention capacity of the water-soluble organic compound 2 is 40% or more.

By the way, also by another embodiment of the present invention shown below, good ejection stability is achieved while effectively suppressing post-print curl on a recording medium, particularly plain paper.

The present inventors further studied using the water-soluble organic compound 1 and the water-soluble organic compound 2. As a result, by containing one or more of the water-soluble organic compound 1-1 and the water-soluble organic compound 1-2, which are specific water-soluble organic compounds among the water-soluble organic compounds 1, in the ink jet ink, as described above. We found that the problem could be solved effectively. That is, each of the water-soluble organic compound 1-1, the water-soluble organic compound 1-2, and the water-soluble organic compound 2-1 is contained, and the content X of the water-soluble organic compound with respect to the total mass of the ink jet ink.₁(Mass%), X₂(Mass%), and Y₁It was found that the above problem can be solved by containing (mass%) in a ratio satisfying the following conditions. (1) 0.1 (X₂+ Y₁) / X₁2.5 (2) 10% by mass X₁+ X₂(3) 3 mass% X₂+ Y₁(X₁: Content (mass%) of water-soluble organic compound 1-1 with respect to the total mass of inkjet ink, X₂: Content of water-soluble organic compound 1-2 (mass%) with respect to the total mass of inkjet ink, Y₁: Content of water-soluble organic compound 2-1 with respect to the total mass of the ink for inkjet (mass%)) The actions of the water-soluble organic compound 1-1 and the water-soluble organic compound 1-2 in this embodiment will be described below.

The difference between the water-soluble organic compound 1-1 in an environment with a temperature of 23 ° C and a humidity of 45% and the water-retaining power in an environment with a temperature of 30 ° C and a humidity of 80% is 36% or less. , A water-soluble polyhydric alcohol or a water-soluble amide compound having a molecular weight Mw in the range of 100 Mw 1000.

Since the water-soluble organic compound 1-1 has a large molecular size, it does not easily enter between the cellulose fibers and has little effect on curls generated in a relatively short time after printing. However, once it enters the cellulose fibers, it is not effective. Hard to cause migration. This is because it has an appropriate water-retaining power, it is difficult to hold water more than necessary, and it has a plurality of, at least three or more hydrogen-bonding sites in the molecule, and has a high affinity with cellulose fibers. Conceivable.

For example, 3 or more -OH groups like triols, 2 or more -OH groups and carbonyl groups like saccharides, 2 like N, N'-bis- (2-hydroxyethyl) -urea The above -OH groups and amide bonds, two or more -OH groups and sulfone groups such as bishydroxyethyl sulfone, and two or more -OH groups and at least three or more ether bond groups such as tetraethylene glycol. have. Furthermore, it is considered that multiple factors such as a large molecular size and difficulty in migrating with water are working effectively.

On the other hand, for example, diethylene glycol has a molecular weight of 100 or more, has two -OH groups at both ends of the molecule, and has one ether bond in the molecule, but the curl suppressing effect is small. This is probably because the hydrophilicity (hydrogen bondability) of one ether bond alone is lower than that of one -OH group, and the molecule becomes bent due to the interaction between the ether bond and water in an aqueous solution, resulting in a molecular size. Is considered to be smaller. Therefore, it is considered that at least three ether bonds are required in order to exert the curl-suppressing effect on the diol having an ether bond in the molecule.

The difference between the water-soluble organic compound 1-2 in the environment of temperature 23 ° C and humidity 45% and the water retention capacity in the environment of temperature 30 ° C and humidity 80% is 36% or less. , The molecular weight Mw is in the range of 100 Mw 150, and further, it is a water-soluble alkanediol having -OH groups at both ends of the main chain.

The action of the water-soluble organic compound 1-2 is to suppress curl generated in a relatively short time after printing (several hours after printing). However, although the water-soluble organic compound 1-2 effectively suppresses the curl phenomenon that occurs in a relatively short time after printing, it causes curl that occurs in a longer time region (5, 6 hours to several weeks). On the other hand, the effect is small. The reason for this is that since the water-soluble organic compound 1-2 is an alkanediol having a molecular weight of 100 to 150 or less and having -OH groups at both ends of the main chain, it does not have a hydrophilic bond such as an ether bond in the molecule and the molecule bends. This is probably because the molecular size is relatively large. In addition, the structure inside the molecule is lipophilic, and the end of the molecule is hydrophilic, so it has a surface-active property, and it is considered that it is easy to get wet with cellulose fibers quickly. In addition, since it has an appropriate molecular size, it easily penetrates between cellulose fibers, and it is considered that curls generated in a short time can be suppressed. However, since there are few -OH groups that have an affinity for cellulose fibers, it is considered that migration may occur over a long period of time.

By using the water-soluble organic compound 1-1 and the water-soluble organic compound 1-2 in combination, the present inventors can print curls from a short time after printing, rather than containing these water-soluble organic compounds alone. It was found that it has the effect of suppressing for a long time. The reason for this is that the structures of the water-soluble organic compound 1-1 and the water-soluble organic compound 1-2 are similar, so that they are miscible, and the water-soluble organic compound 1-1 is effective together with the water-soluble organic compound 1-2. Since it can penetrate into the cellulose fibers, it is considered that curling can be suppressed from a short time to a long period after printing.

The present inventors particularly when the total content when the water-soluble organic compound 1-1 and the water-soluble organic compound 1-2 are used in combination is less than 25% by mass with respect to the total mass of the inkjet ink, or when water is used. It has been found that curl can be effectively improved in a short time even when the content is more than 71% by mass with respect to the total mass of the inkjet ink. In particular, under the above conditions, the difference in curl phenomenon that occurs in a relatively short time after printing is remarkable between the ink containing the water-soluble organic compound 1-2 and the ink not containing the water-soluble organic compound 1-2.

As described above, the inkjet ink containing the water-soluble organic compound 1-1 and the water-soluble organic compound 1-2 can effectively suppress curl. However, in order to satisfy the ejection stability of the inkjet ink, it is necessary to use the water-soluble organic compound 2-1 in combination.

Here, the water-soluble organic compound 2-1 is a water-soluble organic compound other than the colorant, the water-soluble organic solvent 1-1, and the water-soluble organic solvent 1-2. More specifically, it is a water-soluble organic compound in which the difference between the water retention capacity in an environment with a temperature of 23 ° C and a humidity of 45% and the water retention capacity in an environment with a temperature of 30 ° C and a humidity of 80% is greater than 36%. is there.

The reason for this can be inferred as follows. As described above, the water-soluble organic compound 1-2 has surface-active properties and is less miscible with the colorant. Therefore, the water-soluble organic compound 1-2 has a higher concentration than other components in the inkjet nozzle. It exists in the vicinity. Therefore, evaporation of water near the nozzle is suppressed. By using this in combination with a water-soluble organic compound 2-1 that has good miscibility with a colorant and has a high water retention capacity, an increase in viscosity inside the nozzle is suppressed and discharge stability is improved.

As a result of the studies by the present inventors, even if the ink for inkjet contains the water-soluble organic compound 2-1 having the property of advancing curl, the above-mentioned water-soluble organic compound 1-1 and the water-soluble organic compound 1 are further contained. The ratio of the contents of -2 and the contents of water-soluble organic compound 1-1, water-soluble organic compound 1-2, and water-soluble organic compound 2 (X)₂+ Y₁) / X₁Is shown by Eq. (1), 0.1 (X)₂+ Y₁) / X₁It was found that by setting 2.5, curling can be continuously suppressed from a short time after printing to a long period of time, and the ejection stability is also improved.

Furthermore, according to the study of the present inventions, when the amount of ink applied is large, specifically 3.0 g /^m2In addition to the above conditions, the total content of the water-soluble organic compound 1-1 and the water-soluble organic compound 1-2 X₁+ X₂(Mass) is X₁+ X₂It was found that 10% by mass, which needs to be.

Furthermore, according to the study of the present inventor, in order to improve the discharge stability, in addition to the above conditions, the total content X of the water-soluble organic compound 1-2 and the water-soluble organic compound 2-1₂+ Y₁But X₂+ Y₁It was found that 3% by mass, which needs to be.

Further, the water content is preferably 77% by mass or less, more preferably 71% by mass or less, based on the total mass of the inkjet ink.

Further, the content Y in the water-soluble organic compound 2-1 with respect to the total mass of the inkjet ink.₁(Mass%) is Y₁&lt;15% by mass is preferable. The reason for this is presumed as follows. As described above, since the water-soluble organic compound 2-1 has a property of advancing curl, the larger the content in the ink, the more likely the curl is to occur. Therefore, even if the ink for inkjet contains a large amount of the water-soluble organic compound 1-1 and the water-soluble organic compound 1-2, the water-soluble organic compound 2-1 is the water-soluble organic compound 1-1 and the water-soluble organic compound. This is because 1-2 is migrated and the curl suppressing effect of the water-soluble organic compound 1-1 and the water-soluble organic compound 1-2 is reduced. Further, it is preferable that the difference in water retention capacity of the water-soluble organic compound 2-1 is 40% or more.

Further, in addition to the above equations (1) to (3), it is preferable that one or more selected from the following conditions (A) to (F) is satisfied. (A) X₁, X₂And Y₁However, the following equation is further satisfied. 0.2 (X₂+ Y₁) / X₁2.0, X₁+ X₂ 13 mass% and X₁+ X₂+ Y₁ 15 mass% (B) X₁, X₂And Y₁However, the following equation is further satisfied. 0.2 (X₂+ Y₁) / X₁1.5 (C) X₁, X₂And Y₁However, the following equation is further satisfied. 0.2 (X₂+ Y₁) / X1 1.5, 0 mass% &lt;Y₁11% by mass and X₁+ X₂+ Y₁ 20 mass% (D) X₁, X₂And Y₁However, the following equation is further satisfied. 0.2 (X₂+ Y₁) / X₁1.5 and X₁+ X₂+ Y₁ 25 mass% (E) X₁, X₂And Y₁However, the following equation is further satisfied. 0.2 (X₂+ Y₁) / X₁1.0, X₁+ X₂ 13 mass% and X₁+ X₂+ Y₁ 20 mass% (F) X₁, X₂And Y₁However, the following equation is further satisfied. 0 &lt;Y₁/ (X₁+ X₂) 0.9 [Inkjet ink]

The components and the like constituting the inkjet ink according to the present invention will be described in detail.

(Water-Retaining Water-Soluble Organic Compound) Specific examples of the water-soluble organic compound 1 or the water-soluble organic compound 1-1, the water-soluble organic compound 1-2, the water-soluble organic compound 2 or the water-soluble organic compound 2-1 below. Is shown.

-Specific example of water-soluble organic compound 1 Ethylene oxide denaturation (ethylene oxide addition number 6 to 30) Glycerin triacrylic acid ester, dipentaerythritol. Ethylene oxide modification (ethylene oxide addition number 8-40) Water-soluble organic compound having a polyethylene glycol skeleton such as acrylic acid ester and having a hydrophilic binding group other than -OH group-Water-soluble organic compound 1 or water-soluble organic compound 1 Specific example of -1 Polyethylene with an average molecular weight of 200 (main component tetraethylene glycol), 300 (main component hexaethylene glycol), 400 (main component nonaethylene glycol), 600 (main component tridecaethylene glycol), 1000 (main component docosaethylene glycol) Polyhydric alcohol compounds of trihydric or higher such as glycol, 1,2,6-hexanetriol, trimethylolpropane, trimethylolethane, pentaerythritol, diglycerin, glucose, sorbitol, bishydroxyethyl sulphon, N, N'-bis A polyhydric alcohol compound having a carbonyl group such as-(2-hydroxyethyl) -urea and tetra- (2-hydroxyethyl) -phenyldiamide, a sulfone group, and a hydrogen-bonding group such as an amide group. Of these, polyethylene glycol having an average molecular weight of 200, 1,2,6-hexanetriol, trimethylolpropane, bishydroxyethyl sulphon, and N, N'-bis- (2-hydroxyethyl) -urea are particularly preferable.

Specific Examples of Water-Soluble Organic Compound 1 or Water-Soluble Organic Compound 1-2 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 3-methyl-1,5-pentanediol, 2- Alkanes having -OH groups at both ends of the carbon main chain, which may have substituents such as amino-2-methyl-1,3-propanediol and 2-amino-2-ethyl-1,3-propanediol. Diol. Of these, 1,6-hexanediol is particularly preferable. -Specific examples of water-soluble organic compound 2 or water-soluble organic compound 2-1 A water-soluble organic compound having a hydrophilic group having a small number of carbon atoms such as urea, ethylene glycol, 2-pyrrolidone, ethylene urea, glycerin, and diethylene glycol. Of these, urea, 2-pyrrolidone, ethylene urea, and glycerin are particularly preferable.

In the present invention, it is preferable that at least one of the water-soluble organic compound 1 or the water-soluble organic compound 1-1 is a water-soluble organic compound having an amide bond in the molecule. Of these, N, N'-bis- (2-hydroxyethyl) -urea is most preferable. The reason for this is that N, N'-bis- (2-hydroxyethyl) -urea has the ability to prevent molecular association, and therefore, in the present invention, it is essential to use it in combination with other water-soluble organic compounds. Prevents association of each water-soluble organic compound. In particular, in the case of ink used in an inkjet recording method, it is possible to more easily bring out performances such as clogging prevention and dye solubility, effectively suppress curling, and greatly improve ejection stability and reliability. In particular, when N, N'-bis- (2-hydroxyethyl) -urea or bishydroxyethyl sulphon is used as the water-soluble organic compound 1 or the water-soluble organic compound 1-1, the number of carbon atoms is 5. It is preferable to use the above diols or triols in combination. Among the diols or triols having 5 or more carbon atoms, 1,6-hexanediol and 1,2,6-hexanetriol are particularly preferable. When these are used in combination, the performance of preventing the association of molecules described above can be exhibited more efficiently, and a particularly excellent curl suppressing effect and discharge stability can be obtained.

In general, those classified as water-soluble organic compounds 1 often have high viscosities when added to ink, and curl improves when the amount added is increased, but there is a problem in start-up property among ejection stability. There was something. In order to improve this problem, it is preferable that at least one of the water-soluble organic compound 1 or the water-soluble organic compound 1-1 is a water-soluble organic compound having a sulfone bond in the molecule. Of these, bishydroxyethyl sulphon is most preferable. The reason for this is that bishydroxyethyl sulphon, when used in combination with other components, makes it difficult for solvation of these other components with water and reduces the viscosity. In particular, in the case of the ink used in the inkjet recording method, it is effective in improving the start-up property of the ejection stability.

Further, water-soluble organic compounds such as urea and ethylene urea are preferable because they have a small molecular weight and the viscosity does not easily increase even if the added amount is increased. A water-soluble organic compound such as urea or ethylene urea can be used as a water-retaining water-soluble organic compound in the present invention by further using it in combination with a water-soluble organic solvent or a water-soluble compound such as a dye. The measurement result (difference depending on the environment) of the water retention capacity of ethylene urea in FIG. 1 is the data when the measurement was performed using the dye together with the dye.

The molecular weight of the water-soluble organic compound having a molecular weight distribution, such as the polyhydric alcohol having an amide bond and polyethylene glycol, was an average molecular weight determined by any of the following. (1) JIS Handbook Chemical Analysis According to K0118 and K0123, mass spectrometric measurement, gas chromatography mass spectrometry (GC-MS) method, and liquid chromatography mass spectrometry (LC-MS method) were performed to measure the molecular weight. (2) For polyethylene glycol having a molecular weight distribution, the average molecular weight was calculated from the size exclusion chromatography method (GPC method) according to JIS Handbook Chemical Analysis K0124 and used as the molecular weight. Further, for the water-soluble organic compound having a molecular weight distribution other than polyethylene glycol, the weight average molecular weight in terms of polyethylene glycol was obtained and used as the molecular weight. (3) The structure of the water-soluble organic compound was specified by NMR method, infrared analysis method, elemental analysis method, etc., and the molecular weight was determined.

(Colorant) Examples of the colorant used in the inkjet ink of the present invention include water-soluble dyes and pigments. The colorant may be used alone or in combination of two or more.

(Dye) Examples of the dye used in the present invention include anionic water-soluble dyes having hues such as black, cyan, magenta, and yellow. The anionic water-soluble dye is not particularly limited as long as it is an acid dye, a direct dye, or a reactive dye listed in the Color Index (COLOR INDEX). Further, even if the dye is not described in the color index, there is no particular limitation as long as it has an anionic group, for example, a sulfone group. These dyes are used in the range of 1 to 10% by mass, preferably 1 to 5% by mass, based on the total mass of the inkjet ink. In addition, dyes other than the above can also be used. Specifically, a dye having a carboxyl group can be mentioned as a solubilizing group. Of these, dyes that show a solubility dependence on pH are preferable. These dyes can be used in the ink in the range of 1 to 10% by mass, preferably 1 to 7% by mass.

When the dye is indicated by the color index (CI) number, the following can be exemplified. Of course, it is not limited to the following. CI Direct Yellow: 8, 11, 12, 27, 28, 33, 39, 44, 50, 58, 85, 86, 87, 88, 98, 100, 110 C.I. Direct Red: 2, 4, 9, 11 , 20, 23, 24, 31, 39, 46, 62, 75, 79, 80, 83, 89, 95, 197, 201, 218, 220, 224, 225, 226, 227, 228, 230 C.I. Direct Blue: 1, 15, 22, 25, 41, 76, 77, 80, 86, 90, 98, 106, 108, 120, 158, 163, 168, 199, 226 C.I. Acid Yellow: 1, 3, 7 , 11, 17, 23, 25, 29, 36, 38, 40, 42, 44, 76, 98, 99 C.I. Acid Red: 6, 8, 9, 13, 14, 18, 26, 27, 32, 35, 42, 51, 52, 80, 83, 87, 89, 92, 94, 106, 114, 115, 133, 134, 145, 158, 198, 249, 265, 289 C.I. Acid Blue: 1, 7 , 9, 15, 22, 23, 25, 29, 40, 43, 59, 62, 74, 78, 80, 90, 100, 102, 104, 117, 127, 138, 158, 161 C.I. Direct Black: 17, 19, 22, 31, 32, 51, 62, 71, 74, 112, 113, 154, 168 C.I. Acid Black: 2, 48, 51, 52, 110, 115, 156 C.I. Reactive Black : 1, 8, 12, 13 C.I. Food Black: 1, 2 (Pigment) Next, the pigment used in the present invention includes, for example, carbon black and organic pigment. These pigments are used in the range of 1 to 20% by mass, preferably 2 to 12% by mass, based on the total mass of the inkjet ink.

-Carbon black Specific examples of carbon black are carbon black pigments such as furnace black, lamp black, acetylene black, and channel black. For example, Raven 7000, Raven 5750, Ravan 5250, Ravan 5000, Ravan 3500, and Ravan 2000. , Rayvan 1500, Rayvan 1250, Rayvan 1200, Rayvan 1190 ULTRA-II, Rayvan 1170, Rayvan 1255 (manufactured by Colombia), Black Pearls L, Regal 400R, Legal 330R, Legal 660R, Mogul ) L, Monarch 700, Monarch 800, Monac 880, Monac 900, Monac 1000, Monac 1100, Monac 1300, Monarch 1400, Valcan XC-72R (manufactured by Cabot), Color Black (Color) Black) FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U , Printex 140V, Special Black 6, Special Black 5, Special Black 4A, Special Black 4 (manufactured by Degussa), No.25, No.33, No.40, No.47, No.52 , No.900, No.2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical Corporation), etc. can be used. Of course, the present invention is not limited to these, and conventionally known carbon black can be used. Further, magnetic fine particles such as magnetite and ferrite, titanium black and the like may be used as the black pigment.

Organic pigment Specific examples of organic pigments include insoluble azo pigments such as toluidine red, toluidine maroon, hanza ero, benzine ero, and pyrazolone red, soluble azo pigments such as litol red, heliobordeaux, pigment scarlet, and permanent red 2B, alizarin, and indantron. Derivatives from building dyes such as thioindigo maroon, phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green, quinacridone pigments such as quinacridone red and quinacridone magenta, perylene pigments such as perylene red and perylene curlet, isoindolinone yellow, Isoindolinone pigments such as isoindolinone orange, imidazolone pigments such as benzimidazolone yellow, benzimidazolone orange, benzimidazolone red, pyranthron pigments such as pyranthron red and pyranthron orange, thioindigo pigments, condensation Examples of other pigments such as azo pigments, thioindigo pigments, flavanthron eros, acylamide eros, quinophthalone eros, nickel azo eros, copper azomethine eros, perinone oranges, anthron oranges, dianthraquinonyl reds, dioxazine violet, etc. it can.

Further, when the organic pigment is indicated by the color index (CI) number, the following can be exemplified. Of course, conventionally known organic pigments can be used other than the following. CI Pigment Yellow: 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 109, 110, 117, 120, 125, 128, 137, 138, 147, 148, 151, 153, 154, 166, 168 C.I. Pigment Orange: 16, 36, 43, 51, 55, 59, 61 C.I. Pigment Red: 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175, 176, 177, 180, 192, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240C.I. Pigment Violet: 19, 23, 29, 30, 37, 40, 50C .I. Pigment Blue: 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64 C.I. Pigment Green: 7, 36 C.I. Pigment Brown: 23, 25, 26 Dispersant When the above-mentioned carbon black or organic pigment is used, it is preferable to use a dispersant in combination. As the dispersant, those capable of stably dispersing the above pigment in an aqueous medium by the action of an anionic group are preferably used. Specific examples of the dispersant include, for example, a styrene-acrylic acid copolymer, a styrene-acrylic acid-alkyl ester copolymer, a styrene-maleic acid copolymer, and a styrene-maleic acid-alkyl ester copolymer. , Styrene-methacrylic acid copolymer, styrene-methacrylic acid-alkyl ester copolymer, styrene-maleic acid half ester copolymer, vinylnaphthalene-acrylic acid copolymer, vinylnaphthalene-maleic acid copolymer, Styrene-maleic anhydride-maleic acid half ester copolymers, salts thereof and the like are included. Further, these dispersants preferably have a weight average molecular weight in the range of 1,000 to 30,000, and particularly preferably in the range of 3,000 to 15,000.

-As a self-dispersing pigment, a pigment that can be dispersed in an aqueous medium without a dispersant by binding an ionic group (anionic group) to the pigment surface, a so-called self-dispersing pigment, can also be used. Examples of such pigments include self-dispersing carbon black. Examples of the self-dispersing carbon black include anionic carbon black in which an anionic group is bonded to the surface of the carbon black.

-Anionic carbon black Anionic carbon black is applied to the surface of carbon black, for example, -COOM, -SO.₃M, -PO₃HM, -PO₃M₂The one in which at least one anionic group selected from the above is bonded is mentioned. In the above formula, M represents a hydrogen atom, an alkali metal, ammonium or organic ammonium. Of these, especially -COOM and -SO₃Carbon black, in which M is bonded to the surface of carbon black and charged anionicly, has good dispersibility in ink and can be particularly preferably used in the present invention.

By the way, among those represented by "M" in the above hydrophilic groups, specific examples of alkali metals include, for example, Li, Na, K, Rb and Cs, and specific examples of organic ammonium include, for example. Examples thereof include methylammonium, dimethylammonium, trimethylammonium, ethylammonium, diethylammonium, triethylammonium, methanolammonium, dimethanolammonium, and trimethanolammonium.

The ink of the present invention containing self-dispersing carbon black in which M is ammonium or organic ammonium can further improve the water resistance of the recorded image, and can be particularly preferably used in this respect. It is considered that this is due to the effect of decomposition of ammonium and evaporation of ammonia when the ink is applied onto the recording medium. Here, the self-dispersing carbon black in which M is ammonium is, for example, a method of substituting self-dispersing carbon black in which M is an alkali metal with ammonium by an ion exchange method, or an H-type by adding an acid. Then, a method of adding ammonium hydroxide to convert M to ammonium can be mentioned.

Examples of the method for producing anionic carbon black include a method in which carbon black is oxidized with sodium hypochlorite, and the -COONa group can be chemically bonded to the surface of the carbon black by this method.

By the way, various hydrophilic groups as described above may be directly bonded to the surface of carbon black. Alternatively, another atomic group may be interposed between the carbon black surface and the hydrophilic group, and the hydrophilic group may be indirectly bonded to the carbon black surface. Specific examples of other atomic groups here include, for example, a linear or branched alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, and a substituted or unsubstituted naphthylene group. Here, examples of the substituent of the phenylene group and the naphthylene group include a linear or branched alkyl group having 1 to 6 carbon atoms. Specific examples of combinations of hydrophilic groups with other atomic groups include, for example, -C.₂H₄COOM, -Ph-SO₃Examples include M, -Ph-COOM, etc. (where Ph represents a phenylene group).

By the way, in the present invention, two or more of the above-mentioned self-dispersing carbon blacks may be appropriately selected as the color material of the ink. The amount of self-dispersing carbon black added to the ink is preferably in the range of 0.1% by mass or more and 15% by mass or less, particularly 1% by mass and 10% by mass or less, based on the total mass of the ink. Within this range, the self-dispersing carbon black can maintain a sufficient dispersed state in the ink. Further, for the purpose of adjusting the color tone of the ink, a dye may be added as a coloring material in addition to the self-dispersing carbon black.

-Colored fine particles / microencapsulated pigments In addition to the above-mentioned colored materials, pigments microencapsulated with a polymer or the like, colored fine particles in which the periphery of resin particles is coated with a colored material, or the like can also be used. Originally, the microcapsules have dispersibility in an aqueous medium, but in order to improve the dispersion stability, a dispersant as described above may be further coexisted in the ink. When the colored fine particles are used as a coloring material, it is preferable to use the above-mentioned anionic dispersant or the like.

(Aqueous medium) In the present invention, water or a mixed solvent of water and a water-soluble organic solvent can be appropriately used as long as the effects of adding these can be obtained and the objective effects of the present invention are not impaired. Specific examples of water-soluble organic solvents include alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol; dimethyl. Amidos such as formamide and dimethylacetamide; ketone or ketoalcohols such as acetone and diacetone alcohols; ethers such as tetrahydrofuran and dioxane; polyalkylene glycols such as: ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, Alkylene glycols containing 2 to 6 carbon atoms with alkylene groups such as thiodiglycol, hexylene glycol, diethylene glycol; glycerin; ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl Lower alkyl ethers of polyhydric alcohols such as (or ethyl) ethers; N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like. The above water-soluble organic solvent can be used alone or as a mixture. Further, it is preferable to use deionized water (ion-exchanged water) as the water.

(Other components) In addition to the above components, a moisturizer may be added to the inkjet ink according to the present invention as needed, as well as a viscosity regulator and a pH adjuster in order to have desired physical property values. Agents, surfactants, defoamers, preservatives, fungicides, antioxidants, etc. may be added as long as the effects can be obtained and the objective effects of the present invention are not impaired. ..

(Physical characteristics) The preferable range of the physical characteristics of the inkjet ink according to the present invention is around 25 ° C, the pH is 3 to 12, preferably 7 to 10, and the surface tension is 10 to 60 dyn / cm, preferably 10 to 40 dyn. It is / cm and has a viscosity of 1 to 30 cps, preferably 1 to 5 cps.

[Inkjet recording device]

By using the inkjet ink of the present invention described above, it is possible to relax and suppress curl and obtain recording characteristics excellent in ejection stability when performing inkjet recording on a recording medium. The inkjet recording apparatus of the present invention is provided with an ink accommodating portion containing the ink, a recording unit provided with a head portion for ejecting the ink, and an ink accommodating portion containing the ink. It is an inkjet recording apparatus including the ink cartridges provided.

A recording device suitable for recording using the ink for inkjet of the present invention applies thermal or mechanical energy corresponding to a recording signal to the ink in the room of a recording head having an ink accommodating portion in which the ink is accommodating. Examples thereof include a device that gives and generates ink droplets by the energy.

FIG. 3 shows an example of an inkjet recording device incorporating this head. In FIG. 3, reference numeral 61 denotes a blade as a wiping member, one end of which is held by the blade holding member to become a fixed end and form a cantilever. The blade 61 is arranged at a position adjacent to the recording area by the recording head, and in the case of the example shown in FIG. 3, is held in a protruding form in the movement path of the recording head. Reference numeral 62 denotes a cap, which is arranged at a home position adjacent to the blade 61, and has a configuration in which the recording head moves in a direction perpendicular to the moving direction of the recording head to come into contact with the discharge surface for capping. Further, 63 in FIG. 3 is an ink absorber provided adjacent to the blade 61, and like the blade 61, is held in a protruding form in the movement path of the recording head.

The blade 61, the cap 62, and the absorber 63 form a discharge recovery unit 64, and the blade 61 and the absorber 63 remove water, dust, dust, and the like from the ink ejection port surface. Reference numeral 65 denotes a recording head having a discharge energy generating means and ejecting ink to a recording material facing the discharge port surface on which the discharge port is arranged to perform recording. 66 is a recording head 65 equipped with a recording head 65. It is a carriage for moving. The carriage 66 is slidably engaged with the guide shaft 67, and a part of the carriage 66 is connected to a belt 69 driven by a motor 68. As a result, the carriage 66 can be moved along the guide shaft 67, and the recording head 65 can move the recording area and the adjacent area thereof.

Reference numeral 51 denotes a paper feed unit for inserting the material to be recorded, and 52 is a paper feed roller driven by a motor (not shown). With these configurations, the material to be recorded is fed to a position facing the discharge port surface of the recording head, and as the recording progresses, the paper is discharged to the paper ejection portion in which the paper ejection roller 53 is arranged.

In the above configuration, when the recording head 65 returns to the home position at the end of recording or the like, the cap 62 of the head recovery unit 64 is retracted from the moving path of the recording head 65, but the blade 61 protrudes into the moving path. As a result, the discharge port surface of the recording head 65 is wiped. When the cap 62 comes into contact with the discharge surface of the recording head 65 for capping, the cap 62 moves so as to protrude into the moving path of the recording head.

When the recording head 65 moves from the home position to the recording start position, the cap 62 and the blade 61 are in the same positions as the above-mentioned wiping positions. As a result, the discharge port surface of the recording head 65 is wiped even in this movement. The above-mentioned movement of the recording head to the home position is performed not only at the end of recording or recovery of discharge, but also at a predetermined interval while the recording head moves the recording area for recording to the home position adjacent to the recording area. Then, along with this movement, the above wiping is performed.

FIG. 4 is a cross-sectional view showing an example of an ink cartridge 45 in which an ink supply member, for example, ink supplied via a tube is housed in the head. Here, reference numeral 40 denotes an ink accommodating portion for storing supply ink, for example, an ink bag, and a rubber stopper 42 is provided at the tip thereof. By inserting a needle (not shown) into the stopper 42, the ink in the ink bag 40 can be supplied to the head. Reference numeral 44 denotes an ink absorber that receives waste ink.

The inkjet recording apparatus used in the present invention is not limited to the one in which the head and the ink cartridge are separated as described above, and the one in which they are integrated as shown in FIG. 5 is also preferably used. In FIG. 5, reference numeral 70 denotes a recording unit, in which an ink accommodating portion containing ink, for example, an ink absorber is accommodating, and the ink in the ink absorber has a head portion having a plurality of orifices. It is configured to be ejected as ink droplets from 71. Reference numeral 72 denotes an atmospheric communication port for communicating the inside of the recording unit with the atmosphere. This recording unit 70 is used in place of the recording head 65 shown in FIG. 3, and is detachable from the carriage 66.

FIG. 6 shows an example of an inkjet cartridge that can be mounted on the above-mentioned inkjet recording device. The cartridge 1012 in this example is a serial type, and its main part is composed of an inkjet recording head 100 and a liquid tank 1001 for storing a liquid such as ink. The inkjet recording head 100 is formed with a large number of discharge ports 832 for discharging liquid, and liquid such as ink is sent from the liquid tank 1001 to a common liquid chamber of the liquid discharge head 100 via a liquid supply passage (not shown). It is supposed to be guided. The cartridge 1012 shown in FIG. 6 has an inkjet recording head 100 and a liquid tank 1001 integrally formed so that liquid can be replenished in the liquid tank 1001 as needed. The liquid discharge head A structure in which the liquid tank 1001 is interchangeably connected to the 100 may be adopted.

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

[Examples 1 to 10, Comparative Examples 1 to 4, Reference Example 1]

(Ink preparation) Each component was mixed according to Table 1 below, and after sufficient stirring, pressure filtration was performed with a membrane filter having a pore size of 0.2 μm to prepare inks 1 to 10, comparative inks 1 to 4, and reference ink 1. .. The reference ink 1 is an ink containing only the water-soluble organic compound 1. Table 2 shows the data of X and Y, as well as X + Y and Y / X.

<tables num="1"><img file="JP2005298813A_D0002.tif" /></tables>

<tables num="2"><img file="JP2005298813A_D0003.tif" /></tables>

(Evaluation of Curl) The obtained ink was applied to a recording medium using an inkjet recording apparatus having an on-demand multi-recording head that ejects the ink by applying thermal energy corresponding to the recording signal to the ink. The inkjet recording device used has the configuration shown in Fig. 3, has a discharge rate of 2.8 pL per dot, a recording density of 2400 x 1200 dpi, and is driven by a device with a drive frequency of 10 kHz. Was used to print so that the print duty was 100%. For printing, 2-pass printing was performed in which the print area was scanned twice. A4 size PPC paper (manufactured by Canon) was used as the recording medium. These recording conditions are the same throughout the examples, comparative examples, and reference examples.

-Curl evaluation method After leaving the printed matter for 1 hour, 1 day, 4 days, and 7 days in an environment with a temperature of 24 ° C and a humidity of 50%, the curl amount was measured over time. The distance from the tip of the curled paper to the ground plane of the paper was measured with a ruler, with + (plus curl) when the printed paper was curled in the concave direction and- (minus curl) when it was curled in the convex direction. .. The curl judgment criteria are as follows. The evaluation results are shown in Table 3. The curl judgment criteria are as follows.

AA: Within ± 10 mm A: Greater than ± 10 mm, within ± 25 mm B: Greater than ± 25 mm, within ± 40 mm C: The tip of the paper is curled inward D: The tip of the paper is curled up inside the paper (Evaluation of ejection stability) The obtained ink is applied to a recording medium using an inkjet recording device having an on-demand multi-recording head that ejects the ink by applying thermal energy corresponding to the recording signal to the ink. did. The inkjet recording device used has the configuration shown in Fig. 3, has a discharge rate of 2.8 pL per dot, a recording density of 2400 x 1200 dpi, and is driven by a device with a drive frequency of 10 kHz. Was used to print so that the print duty was 100%. For printing, 2-pass printing was performed in which the print area was scanned twice. A4 size PPC paper (manufactured by Canon) was used as the recording medium. These recording conditions are the same throughout the examples, comparative examples, and reference examples.

-Ejection stability 1 (Ejection stability after leaving the head) Evaluation method As an evaluation of ink ejection stability, the above ink was set on the head and left for 1 month to see if problems such as nozzle clogging occur. It was printed later and it was confirmed that the image was not distorted or blurred. The criteria for discharge stability 1 (discharge stability after leaving the head) are as follows. The evaluation results are shown in Table 3.

A: No blur B: Slightly blurry, but practically no problem Level C: Blurred, image problem level D: Non-ejection Discharge stability 2 (Startup characteristics) Evaluation method Ink As an evaluation of discharge stability, it was confirmed at the start of printing whether or not the printed part was disturbed or blurred in environment 1: normal temperature and normal humidity, and environment 2: temperature 15 ° C and humidity 10%. The criteria for discharge stability 2 (startup characteristics) are as follows. The evaluation results are shown in Table 3.

A: No blur B: No blur and the image is slightly distorted, but there is virtually no problem Level C: The exported part is blurred and there is a problem with the image Level D: The exported part is greatly blurred

<tables num="3"><img file="JP2005298813A_D0004.tif" /></tables>

[Examples 1 to 10, Comparative Examples 1 to 4, Reference Example 1]

(Preparation of ink) Each component was mixed according to Table 4 below, and after sufficient stirring, pressure filtration was performed with a membrane filter having a pore size of 0.2 μm to prepare inks 11 to 19 and comparative inks 5 and 5. Also, in Table 5, X₁, X₂, Y, and X₁+ X₂, X₂+ Y₁, X₁+ X₂+ Y₁, Y / X, (X₂+ Y) / X₁The data of is shown.

<tables num="4"><img file="JP2005298813A_D0005.tif" /></tables>

<tables num="5"><img file="JP2005298813A_D0006.tif" /></tables>

(Evaluation of curl) The curl evaluation method is the same as above. The evaluation results are shown in Table 6.

(Evaluation of discharge stability) The discharge stability 1 (discharge stability after leaving the head) evaluation method and the discharge stability 2 (startup characteristic) evaluation method are the same as described above. The evaluation results are shown in Table 6.

<tables num="6"><img file="JP2005298813A_D0007.tif" /></tables>

<figref num="1">It is a figure which shows the measurement result of the water retention capacity of various water-soluble organic compounds.</figref><figref num="2">It is a figure which shows the difference of the water retention capacity under two specific environments.</figref><figref num="3">It is a perspective view which shows an example of the inkjet recording apparatus.</figref><figref num="4">It is a vertical sectional view of an ink cartridge.</figref><figref num="5">It is a perspective view of a recording unit.</figref><figref num="6">It is a schematic perspective view which shows an example of the inkjet cartridge provided with the liquid discharge head.</figref>

Code description

40: Ink storage unit 42: Plug 45: Ink cartridge 44: Ink absorber 51: Paper feed unit 52: Paper feed roller 53: Paper discharge roller 61: Blade 62: Cap 63: Ink absorber 64: Discharge recovery unit 65: Discharge energy generating means 66: Carriage 67: Guide shaft 68: Motor 69: Belt 70: Recording unit 71: Head 72: Atmospheric communication port 100: Inkjet recording head 832: Discharge port 1001: Liquid tank 1012: Cartridge