JP2008001800A - Ink set, inkjet recording method, recording unit and inkjet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink set capable of compatibilizing the reliability of ejection stability, storage stability, etc., and the suppression of new color mixing phenomenon. <P>SOLUTION: The ink set contains a plurality of inks, each of the inks is filled in an ink cartridge having an essentially closeable ink holder, the specific gravity difference between the first ink having the highest specific gravity and the second ink having the lowest specific gravity among the inks constituting the ink set is ≥0.020, and the second ink is irreversibly diffused in the first ink when the first ink is brought into contact with the second ink. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink set, an ink jet recording method, a recording unit, an ink jet recording apparatus, and an ink that are contained in an ink cartridge having an ink containing portion in which a plurality of inks constituting the ink set are substantially sealed. .

  In an ink jet recording apparatus, it is required to stably supply ink from an ink cartridge to a recording head so as not to cause a decrease in recording performance due to ink leakage from the recording head or excessive ink supply.

Conventionally, in order to stably supply ink, it has been studied to adjust the pressure of the ink container in the ink cartridge by various methods. For example, there is a proposal regarding a method for preventing ink head pressure from being applied to a recording head (see Patent Document 1). In addition, there is a proposal related to holding ink by using a porous member as a negative pressure generating member in an ink container in an ink cartridge (see Patent Documents 2 to 4). Furthermore, there is a proposal regarding the use of a pressure plate or a spring member as the negative pressure generating member (see Patent Documents 5 and 6).
JP 2002-234183 A JP 63-118260 A Japanese Patent Laid-Open No. 02-522 Japanese Patent Application Laid-Open No. 07-060984 JP 2003-191489 A JP 2003-251821 A

  The present inventors have examined the use of an ink cartridge having the following ink container as an ink cartridge suitable for containing an ink containing a pigment as a coloring material (pigment ink). That is, studies were made to use an ink cartridge that does not have a porous ink holding member as an ink cartridge having an ink storage portion that stores the pigment ink. Such an ink cartridge can suppress the sedimentation of the pigment, and it is considered that the remaining amount of ink in the ink cartridge after the ink is used up can be reduced as much as possible. Further, as an ink jet recording apparatus, an investigation was made using an ink jet recording apparatus capable of mounting a plurality of ink cartridges as described above.

  When the ink jet recording apparatus is not performing recording, the present inventors suck and discharge unnecessary ink or the like from the discharge port by generating a negative pressure with a suction pump communicating with a cap that covers the discharge port of the recording head. A so-called cleaning operation was performed. Thereafter, when the ink was ejected again from the recording head, it was found that the following problems occurred. That is, it has been found that among a plurality of inks sucked and discharged by the same cap, another ink enters a specific ink flow path (hereinafter referred to as a color mixing phenomenon).

  When the present inventors confirmed the above phenomenon for the first time, this color mixing phenomenon was considered to be caused by the same mechanism as the color mixing phenomenon known so far as described below. That is, ink adhering to the surface of the recording head or ink existing in the cap (hereinafter referred to as ink residue) enters the ink flow path due to the capillary force of the ink flow path or the like. As a result, it was considered that other inks entered the vicinity of the discharge port of the ink flow path.

  Therefore, the present inventors performed an operation (hereinafter referred to as preliminary ejection) for ejecting ink into the cap before the start of recording, which is normally performed as a general technique for avoiding the above phenomenon. However, even if the number of ink droplets to be preliminarily ejected (preliminary ejection number) is significantly increased as compared with the number of preliminary ejection sufficient for solving the normal color mixing phenomenon, the color mixing phenomenon has not been solved.

  Therefore, the present inventors repeatedly performed the cleaning operation several times for the purpose of discharging all the ink in the ink flow path where the color mixing phenomenon occurred. However, even if the number of cleaning operations is increased, the mixed color phenomenon is not eliminated, but the mixed color phenomenon is worsened.

  Based on the above results, the present inventors have studied in detail about the color mixing phenomenon and found the following. In other words, the color mixing phenomenon this time is not a color mixing phenomenon in the vicinity of the ink flow channel communicating with each discharge port in the vicinity of the discharge port of the ink flow channel or the common liquid chamber that has been confirmed in the past. It was found that this was a new color mixing phenomenon where other inks entered the interior of the. The common liquid chamber is a common liquid chamber that communicates in common with a plurality of ink flow paths that respectively communicate with a plurality of ejection ports that eject ink in the recording head. In addition, the inside of the ink flow path in the present invention refers to the ink flow path and the common liquid chamber of the recording head, and further the entire ink supply path for supplying ink from the ink container of the ink cartridge to the common liquid chamber. That is.

  Further, when the above-mentioned color mixing phenomenon occurred, after performing the cleaning operation, the ink jet recording apparatus was left for a while without discharging ink from the discharge port. Thereafter, when recording is performed again, the ink that should be ejected from the ejection port is ejected at the beginning. However, when recording is continued for a while in this state, it has been found that a new phenomenon, which has not been confirmed so far, occurs that suddenly ink that is not to be ejected from the ejection port is ejected. . It was found that the ink that is not the ink to be ejected from the ejection port is the other ink that has entered the inside of the ink flow path described above. Furthermore, after the cleaning operation was performed, the longer the time during which recording was not performed, the more the other ink that entered the specific ink flow path entered the inside of the ink flow path. In such a state, it was found that the level of the color mixing phenomenon that can be solved by slightly increasing the number of preliminary discharges is far exceeded.

  Accordingly, an object of the present invention is to provide an ink set capable of satisfying both reliability such as ejection stability and storage stability and suppression of a new color mixing phenomenon as described above.

  Another object of the present invention is to provide an ink jet recording method, a recording unit, and an ink jet recording apparatus using the ink set described above.

  The above object is achieved by the present invention described below. That is, the ink set according to the present invention is an ink set having a plurality of inks, and each of the plurality of inks is accommodated in an ink cartridge having an ink accommodating portion that is substantially sealed, and the ink Among the inks constituting the set, the difference in specific gravity between the first ink having the highest specific gravity and the second ink having the lowest specific gravity is 0.020 or more, and the first ink and the second ink are The second ink diffuses irreversibly into the first ink when brought into contact with each other.

  An ink jet recording method according to another embodiment of the present invention is characterized in that, in the ink jet recording method in which ink is ejected by an ink jet method, the ink is an ink constituting the ink set having the above-described configuration.

  According to another embodiment of the present invention, there is provided a recording unit comprising an ink storage portion for storing ink and a recording head for discharging ink, wherein the ink comprises an ink set having the above-described configuration. It is the ink which comprises.

  An ink jet recording apparatus according to another embodiment of the present invention is an ink jet recording apparatus having an ink containing portion for containing ink and a recording head for discharging ink, wherein the ink is an ink having the above-described configuration. It is the ink which comprises a set, It is characterized by the above-mentioned.

  According to the present invention, even when an ink cartridge in which the ink containing portion is substantially sealed is used, reliability such as ejection stability and storage stability, and the occurrence of color mixing phenomenon can be suppressed. Can be provided. In addition, according to another embodiment of the present invention, an ink jet recording method, a recording unit, and an ink jet recording apparatus using the ink set described above can be provided.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments. In the present invention, the specific gravity of ink, water-soluble organic solvent, coloring material, etc. was measured at 25 ° C. using a floating hydrometer (trade name: standard hydrometer; manufactured by Tech Jam). The viscosity of the ink was measured at 25 ° C. using a RE80L viscometer (manufactured by Toki Sangyo). The surface tension of the ink was measured at 25 ° C. using an automatic surface tension meter CBVP-Z (manufactured by Kyowa Interface Science).

  The present inventors have made various studies in order to elucidate the mechanism by which the above-described color mixing phenomenon that has not occurred in the past. First, an examination was made as to under what conditions the color mixing phenomenon occurred, and it was found that the color mixing phenomenon occurred remarkably when the following conditions were met. That is, (1) The difference in specific gravity of at least two types of inks adjacent to each other among the plurality of inks mounted on the ink jet recording apparatus is 0.020 or more. (2) The at least two types of ink are respectively stored in an ink cartridge in which an ink storage portion for storing the ink is substantially sealed. When the above two conditions (1) and (2) are met, the ink having a small specific gravity enters the ink flow path for discharging the ink having the largest specific gravity. As a result, it has been found that a color mixing phenomenon (hereinafter referred to as a first color mixing phenomenon) occurs inside the ink flow path, which is the subject of the present invention.

  In the present invention, “substantially sealed ink containing portion” means that a portion where the ink containing portion is in contact with the atmosphere can be substantially absent during the cleaning operation. Specifically, this means that the portion where the ink container and the atmosphere are in contact is only the ink supply port. More specifically, the ink container has the following configuration. The ink jet recording apparatus is configured to cover the ejection port of the recording head with a cap in order to prevent ink drying and the like, and the cap communicates with the waste ink absorber through a tube. Then, when performing a cleaning operation of the ink jet recording apparatus, the discharge port of the recording head and the cap abut. Although the tube communicating with the cap communicates with the waste ink absorber, the inside of the tube is filled with ink during the cleaning operation. For this reason, the ink containing portion where the ink containing portion and the atmosphere are in contact with each other is only the ink supply port is substantially sealed. The cap is configured to perform a cleaning operation, that is, suction, by capping a plurality of ejection port arrays together with one cap.

  When the above conditions (1) and (2) are met, the cause of the first color mixing phenomenon is not clear, but the present inventors presume the cause as follows. An ink cartridge using a pressure plate or a spring member as a negative pressure generating member communicates with the atmosphere through only the ink supply port. While a cleaning operation is being performed in an ink jet recording apparatus equipped with such an ink cartridge, the ink container is substantially sealed. On the other hand, after the cleaning operation is completed, the ink containing portion is again opened.

  In the ink cartridge having such a configuration, the negative pressure fluctuation (hereinafter referred to as ripple) in the ink flow path of the recording head is configured so that the ink storage portion is always in contact with the atmosphere, for example, in addition to the ink supply port, the atmosphere communication It becomes larger than an ink cartridge having a mouth. Specifically, the ripple of an ink cartridge having an air communication port in addition to the ink supply port is about 10 mmHg. On the other hand, the ripple of the ink cartridge having the ink containing portion that is substantially sealed is about 20 mmHg to 30 mmHg. The inventors of the present invention have one of the main causes of the first color mixing phenomenon that the force of drawing the ink residue into the ink flow path rapidly increases due to the large ripple. I guess.

  As a result of the study by the present inventors, among the plurality of ink cartridges mounted on the ink jet recording apparatus, when there is an ink cartridge in which the remaining amount of ink in the ink cartridge is extremely small compared to other ink cartridges, the following It was found that this phenomenon occurred. In other words, it was found that the ink flow path of the recording head that communicates with the ink cartridge with a small amount of remaining ink has a larger ripple before and after the cleaning operation than the ink flow path of the recording head that communicates with other ink cartridges. . As a result, it was confirmed that the ink residue was selectively drawn into the ink flow path communicating with the ink cartridge with a small ink remaining amount.

  Next, the relationship between the difference in specific gravity of the plurality of inks and the first color mixing phenomenon, which is the greatest feature of the present invention, will be described. As described above, when an ink cartridge in which the ink containing portion is substantially sealed is used, a phenomenon that ink residue enters the inside of the ink flow path significantly occurs. At this time, when an ink residue having a specific gravity smaller than the specific gravity of the ink originally present in the ink flow path is drawn into the ink flow path, the following phenomenon occurs in the ink flow path. Get up.

  When the first color mixing phenomenon occurs, conventionally known color mixing phenomenon (hereinafter referred to as the first color mixing phenomenon) in the vicinity of the ink flow paths communicating with the individual discharge openings in the vicinity of the discharge openings of the ink flow paths or in the common liquid chamber. (Referred to as a color mixing phenomenon 2), ink residue exists even inside the ink flow path. However, in the first color mixing phenomenon and the second color mixing phenomenon, the ink residue existing state in the ink flow path immediately after the cleaning operation is considered to be almost the same. That is, when the first color mixing phenomenon occurs, the ink residue is distributed over a wider range in the ink flow path. However, in both the first color mixing phenomenon and the second color mixing phenomenon, the state where the ink residue is present in the ink flow path is the same.

  However, when the first color mixing phenomenon occurs, when the influence of the fluid movement caused by the ripple starts to decrease, the fluid movement caused by the difference in specific gravity among the plurality of inks becomes dominant. That is, ink having a large specific gravity originally present in the ink flow path moves to the vicinity of the ejection opening of the ink flow path. The ink having a small specific gravity among the ink residues drawn into the ink flow path moves to the ink supply path for supplying ink from the ink storage portion of the ink cartridge to the common liquid chamber. In this way, a color material density distribution exists inside the ink flow path. As a result, after performing the cleaning operation, if the ink jet recording apparatus is left for a while without discharging ink from the discharge port, and then recording is performed again, the ink to be discharged from the discharge port is discharged at first. . However, when recording is continued for a while in this state, it has been confirmed so far that ink that should not be ejected from the ejection port, that is, ink drawn into the ink flow path, is ejected. It is assumed that a phenomenon that did not occur has occurred. Therefore, as apparent from what has been described so far, the first color mixing phenomenon is completely different from the conventionally known second color mixing phenomenon.

  Furthermore, when the present inventor uses an ink containing a pigment as a color material (pigment ink) as compared with an ink containing a dye as a color material (dye ink), the above first color mixing phenomenon is more remarkable. Confirmed to get up. Although the reason for this is not clear, the present inventors presume the reason as follows. That is, pigments, particularly resin-dispersed pigments to be described later, have a large difference in specific gravity between color materials, that is, pigments and pigment dispersions themselves, compared to dyes. For this reason, when pigment ink is used, movement of the color material due to the difference in specific gravity among the plurality of color materials occurs in addition to the movement of fluid due to the difference in specific gravity among the plurality of inks inside the ink flow path. Therefore, it is considered that the first color mixing phenomenon occurs more remarkably. The difference in specific gravity among the plurality of inks decreases with the passage of time, but the difference in specific gravity of the color material does not decrease with the passage of time. Therefore, as long as the fluidity of the liquid is not lost inside the ink flow path, the color material is always moved due to the difference in specific gravity of the color material. The longer the time during which no recording is performed after the cleaning operation, the more the color material in the ink residue that has entered the ink flow path enters the ink flow path. I guess it is also caused by

  As a result of studies conducted by the present inventors in order to suppress the first color mixing phenomenon described above, the above-described problem is solved by setting the characteristics between a plurality of inks constituting the ink set as follows. I found out that I can do it. That is, when an ink cartridge in which the ink storage portion is substantially sealed is used as an ink cartridge that stores a plurality of inks constituting the ink set, the following configuration must be satisfied. It has been found that the first color mixing phenomenon can be suppressed by making the difference in specific gravity between the first ink having the highest specific gravity and the second ink having the lowest specific gravity among the plurality of inks less than 0.020.

  However, in pigment ink, it is difficult to eliminate the difference in specific gravity of each ink as much as possible. For example, the specific gravity of the ink can be adjusted by appropriately determining the type and content of the components constituting the ink. In addition, in the case of a pigment ink in which a pigment is dispersed in an aqueous medium using a resin as a dispersant, the specific gravity of the ink can be adjusted by appropriately determining the type of resin and the content of the resin. it can. However, the state of the surface, the particle size, and the like vary depending on the type of pigment. For this reason, when using an ink containing a pigment as a coloring material, it is necessary to optimize the type and content of the dispersant and the water-soluble organic solvent according to the characteristics of the pigment. Furthermore, in consideration of reliability such as pigment dispersion stability and ink ejection stability, the types and contents of each component constituting the ink are limited to some extent. Accordingly, it has been found that it is difficult to make the specific gravity of all inks constituting the ink set the same value. Specifically, it has been found that it is very difficult to make the difference in specific gravity of all inks constituting the ink set less than 0.020.

  Therefore, the present inventors find a method of suppressing the first color mixing phenomenon by reducing the number of preliminary ejections as much as possible when the difference in specific gravity among the plurality of inks constituting the ink set is 0.020 or more. For this purpose, the following examination was conducted.

  In general, when two kinds of liquid come into contact with each other, the state of diffusion can be divided into the following two patterns. Hereinafter, a description will be given with reference to FIG. 6 which is a schematic diagram showing the behavior when the first ink and the second ink come into contact with each other. First, in the first pattern, as shown in FIG. 6A, one liquid spreads unilaterally into the other liquid. Next, as shown in FIG. 6B, the second pattern mixes at the boundary portion where these liquids come into contact with each other because the liquids try to diffuse into the other liquid. At this time, when these two kinds of liquids are inks, the ink is in a state where the ink is smeared at the boundary portion where the inks contact. There are various factors that cause the phenomenon of the two patterns as described above. For example, there are a case where two kinds of liquids having different surface tensions are brought into contact with each other, a case where two kinds of liquids having substantially the same surface tension are brought into contact with each other, and the like. At this time, when two kinds of liquids having different surface mass forces are brought into contact with each other, the result is as shown in FIG. 6A, and when two kinds of liquids having substantially the same surface tension are brought into contact with each other, as shown in FIG. 6B. Become. The above phenomenon is confirmed by, for example, observing the behavior when the first ink and the second ink are dropped in equal amounts (mass ratio) onto a petri dish and the inks are brought into contact with each other. Can do.

  Therefore, the present inventors have studied to suppress the first color mixing phenomenon using the above phenomenon. That is, the ink set is configured so that the surface tension of the first ink having the largest specific gravity among the plurality of inks constituting the ink set is smaller than the surface tension of the second ink having the smallest specific gravity. In this way, the investigation was performed in anticipation that the ink residue is pulled in the direction of the ink flow path for discharging the first ink. As a result, it has been found that the first color mixing phenomenon can be suppressed with a smaller number of preliminary ejections than in the case where the surface tension of the ink is not set to the above-described relationship.

  As a result of investigations by the present inventors based on the above-described findings, it has been found that the following configuration must be satisfied. That is, as an ink cartridge that stores a plurality of inks constituting the ink set, an ink cartridge in which the ink storage portion is substantially sealed is used, and the ink set is further set so that the plurality of inks have the following relationship. Constitute. That is, among the plurality of inks, it is necessary to make the surface tension of the first ink having the highest specific gravity smaller than the surface tension of the second ink having the lowest specific gravity. With this configuration, it can be seen that reliability such as ejection stability and storage stability can be obtained at a high level, and the first color mixing phenomenon can be suppressed with the smallest number of preliminary ejections. It came to.

  Note that “irreversibly diffusing” in the present invention means that one liquid diffuses only into the other liquid when the two liquids come into contact as shown in FIG. 6A. To do.

  According to the study by the present inventors, the surface tension of the second ink is increased by 3 mN / m or more than the surface tension of the liquid in which the first ink and the second ink are mixed in equal amounts (mass ratio). Thus, it has been found that the first color mixing phenomenon can be more effectively suppressed.

  It has also been found that the first color mixing phenomenon can be more effectively suppressed by setting the specific gravity of the first ink and the specific gravity of the second ink to 1.030 or more, respectively. When the specific gravity of each of the first ink and the second ink is less than 1.030, when the ink residue is drawn into the ink flow path, the liquid caused by a large ripple before and after the cleaning operation. Increases speed of movement. As a result, the ink residue drawn into the ink flow path easily moves to the inside of the ink flow path. For this reason, the second color mixing phenomenon may be worse than when the specific gravity of the first ink and the specific gravity of the second ink are 1.030 or more, respectively, and it is necessary to increase the number of preliminary ejections. May occur. In consideration of reliability such as ink ejection stability and anti-sticking property, the specific gravity of the first ink and the specific gravity of the second ink are each preferably 1.100 or less. Furthermore, it is particularly preferable that the specific gravity of the first ink and the specific gravity of the second ink are 1.030 or more and 1.100 or less, respectively. Further, it is particularly preferable that the specific gravity of all inks constituting the ink set is 1.030 or more and 1.100 or less, respectively.

  Furthermore, among the water-soluble organic solvents contained in the first ink and the second ink, the water-soluble organic solvent having the smallest specific gravity is used as the first water-soluble organic solvent. At this time, the difference in specific gravity between the first water-soluble organic solvent and the first color material is preferably 0.049 or less. This is because the movement of the color material can be suppressed when the ink jet recording apparatus is left for a long time in a state where a plurality of inks are present in the ink flow path.

  Further, it is preferable that the flow path resistance of the recording head that discharges the first ink is larger than the flow path resistance of the recording head that discharges the second ink. In this way, when performing the cleaning operation, the volume of the ink that is sucked and discharged from the discharge port is larger than the volume of the ink that is sucked and discharged from the discharge port. Can be reduced. As a result, the ripple of the recording head that discharges the first ink is smaller than the ripple of the recording head that discharges the second ink, and the ink residue is drawn into the ink flow path that discharges the first ink. This can be suppressed. Furthermore, since the movement of the fluid due to the ripple can be suppressed inside the ink flow path for discharging the first ink, the movement of the fluid due to the difference in specific gravity among the plurality of inks can be suppressed. As a result, it is considered that the effect of suppressing the first color mixing phenomenon can be obtained remarkably.

  There are various methods for adjusting the flow path resistance of the recording head. In the present invention, the flow path resistance of the recording head can be appropriately adjusted by adjusting the viscosity of the ink. Specifically, by making the viscosity of the first ink larger than the viscosity of the second ink, the flow path resistance of the recording head that discharges the first ink is reduced, and the flow resistance of the recording head that discharges the second ink is reduced. It can be larger than the channel resistance. The difference in viscosity between the first ink and the second ink varies slightly depending on the configuration of the ink flow path. Specifically, the viscosity of the first ink is different from the viscosity of the second ink. It is preferable to increase it by 10% or more, more preferably 15% or more. However, in consideration of reliability such as ink ejection stability and storage stability, the viscosity of the first ink and the second ink is preferably 2.0 mPa · s or more and 4.5 mPa · s or less, respectively. . Moreover, it is particularly preferable that the viscosity of all the inks constituting the ink set is 2.0 mPa · s or more and 4.5 mPa · s or less, respectively.

<Ink>
Hereinafter, each component constituting the ink will be described.

(Aqueous medium)
For the ink constituting the ink set, it is preferable to use an aqueous medium containing water and a water-soluble organic solvent. The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink. The water content (% by mass) in the ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink.

  Specifically, for example, the following water-soluble organic solvents can be used. C1-C6 alkyl alcohols, such as methanol, ethanol, propanol, propanediol, butanol, butanediol, pentanol, pentanediol, hexanol, hexanediol, and the like. Amides such as dimethylformamide and dimethylacetamide. Ketones or ketoalcohols such as acetone and diacetone alcohol. Ethers such as tetrahydrofuran and dioxane. Polyalkylene glycols having an average molecular weight of 200, 300, 400, 600 and 1,000 such as polyethylene glycol and polypropylene glycol. Alkylene glycols having an alkylene group having 2 to 6 carbon atoms such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, and diethylene glycol; Lower alkyl ether acetates such as polyethylene glycol monomethyl ether acetate. Glycerin. Lower alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether. N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like. Among these, it is particularly preferable to use 1,2-hexanediol, 1,5-pentanediol, ethylene glycol, diethylene glycol, glycerin, or 2-pyrrolidone. The water is preferably deionized water (ion exchange water).

(Coloring material)
Any colorant can be used as long as it is used for conventional inks. Specifically, a dye having an anionic group or a pigment can be used. For the pigment, use a resin dispersion type pigment (resin dispersion type pigment) that disperses the pigment using a dispersant, or a self dispersion type pigment (self dispersion type pigment) in which a hydrophilic group is introduced on the surface of the pigment particles. Can do. Also, pigments (resin-bonded self-dispersing pigments) in which organic groups containing a polymer are chemically bonded to the surface of pigment particles, microcapsule types that enhance the dispersibility of pigments and can be dispersed without using dispersants, etc. Pigments and the like can also be used.

[dye]
Any dye may be used as long as it is an acid dye, a direct dye, or a reactive dye described in the color index. Even dyes not described in the color index can be used. In the present invention, it is particularly preferable to use a dye having an anionic group, for example, a carboxyl group or a sulfonic acid group. The content (% by mass) of the dye in the ink is 1.0% by mass or more and 10.0% by mass or less, more preferably 1.0% by mass or more and 5.0% by mass or less, based on the total mass of the ink. preferable.

  When the dye is indicated by a color index (CI) number, for example, the following can be used. C. I. Direct yellow: 8, 11, 12, 27, 28, 33, 39, 44, 50, 58, 85, 86, 87, 88, 98, 100, 110, etc. 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, etc. C. I. Direct blue: 1, 15, 22, 25, 41, 76, 77, 80, 86, 90, 98, 106, 108, 120, 158, 163, 168, 199, 226, etc. C. I. Acid Yellow: 1, 3, 7, 11, 17, 23, 25, 29, 36, 38, 40, 42, 44, 76, 98, 99, etc. 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, etc. 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 etc.

[Pigment]
As the pigment, carbon black or an organic pigment is preferably used. The pigment content (% by mass) in the ink is 0.1% by mass or more and 15.0% by mass or less, and further 1.0% by mass or more and 10.0% by mass or less based on the total mass of the ink. preferable.

  The black ink preferably uses carbon black such as furnace black, lamp black, acetylene black, channel black, or the like as a pigment. Specifically, for example, the following commercially available products can be used. Ray Van: 7000, 5750, 5250, 5000ULTRA, 3500, 2000, 1500, 1250, 1200, 1190ULTRA-II, 1170, 1255 (above, Colombia). Black Pearls L, Legal: 330R, 400R, 660R, Mogul L, Monak: 700, 800, 880, 900, 1000, 1100, 1300, 1400, 2000, Vulcan XC-72R (above, manufactured by Cabot). Color Black: FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Printex: 35, U, V, 140U, 140V, Special Black: 6, 5, 4A, 4 (above, manufactured by Degussa). No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (above, manufactured by Mitsubishi Chemical). Carbon black newly prepared for the present invention can also be used. Of course, the present invention is not limited to these, and any conventional carbon black can be used. Further, the material is not limited to carbon black, and magnetic fine particles such as magnetite and ferrite, titanium black, and the like may be used as a pigment.

  Specifically, for example, the following can be used as the organic pigment. Water-insoluble azo pigments such as toluidine red, toluidine maroon, Hansa yellow, benzidine yellow and pyrazolone red. Water-soluble azo pigments such as Ritolol Red, Helio Bordeaux, Pigment Scarlet, and Permanent Red 2B. Derivatives from vat dyes such as alizarin, indanthrone and 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 scarlet. Isoindolinone pigments such as isoindolinone yellow and isoindolinone orange. Imidazolone pigments such as benzimidazolone yellow, benzimidazolone orange, and benzimidazolone red. Pilanthrone pigments such as pyranthrone red and pyranthrone orange. Indigo pigments, condensed azo pigments, thioindigo pigments, diketopyrrolopyrrole pigments. Flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo yellow, copper azomethine yellow, perinone orange, anthrone orange, dianthraquinonyl red, dioxazine violet, etc. Of course, the present invention is not limited to these.

  Moreover, when an organic pigment is shown by a color index (CI) number, the following can be used, for example. C. I. Pigment Yellow: 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 97, 109, 110, 117, 120, 125, 128, 137, 138, 147, 148, 150, 151, 153 154, 166, 168, 180, 185, etc. C. I. Pigment Orange: 16, 36, 43, 51, 55, 59, 61, 71, etc. C. I. Pigment Red: 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175, 176, 177, 180, 192, etc. 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240, 254, 255, 272, etc. C. I. Pigment violet: 19, 23, 29, 30, 37, 40, 50, and the like. C. I. Pigment Blue: 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64, and the like. C. I. Pigment Green: 7, 36 etc. C. I. Pigment Brown: 23, 25, 26, etc. Of course, the present invention is not limited to these.

[Dispersant]
As the dispersant for dispersing the pigment as described above in the aqueous medium, any resin having water solubility can be used. Of these, those having a weight average molecular weight of 1,000 to 30,000, more preferably 3,000 to 15,000 are preferred. The content (% by mass) of the dispersant in the ink is preferably 0.1% by mass or more and 5.0% by mass or less based on the total mass of the ink.

  Specifically, for example, the following can be used as the dispersant. Monomers of styrene, vinyl naphthalene, aliphatic alcohol esters of α, β-ethylenically unsaturated carboxylic acids, acrylic acid, maleic acid, itaconic acid, fumaric acid, vinyl acetate, vinyl pyrrolidone, acrylamide, or derivatives thereof A polymer. In addition, it is preferable that at least one monomer constituting the polymer is a hydrophilic monomer, and a block copolymer, a random copolymer, a graft copolymer, or a salt thereof may be used. good. Alternatively, natural resins such as rosin, shellac and starch can be used. These resins are preferably soluble in an aqueous solution in which a base is dissolved, that is, an alkali-soluble type.

(Surfactant)
In order to adjust the surface tension of the ink constituting the ink set, it is preferable to use a surfactant such as an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant. Specifically, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenols, acetylene glycol compounds, acetylene glycol ethylene oxide adducts, and the like can be used.

(Other ingredients)
In addition to the above-described components, the ink constituting the ink set may contain a moisturizing solid content such as urea, urea derivatives, trimethylolpropane, and trimethylolethane in order to maintain the moisturizing property. The content (% by mass) of the moisturizing solid content in the ink is 0.1% by mass or more and 20.0% by mass or less, further 3.0% by mass or more and 10.0% by mass or less based on the total mass of the ink. It is preferable to do.

  In addition to the above-described components, the ink constituting the ink set includes a pH adjuster, a rust inhibitor, a preservative, an antifungal agent, an antioxidant, an anti-reduction agent, and an evaporation accelerator as necessary. Various additives may be contained.

<Ink set>
The ink set according to the present invention may take any of the following forms as long as a plurality of inks are used in combination. For example, there is an ink set composed of an ink cartridge or an ink cartridge with a recording head having a structure in which ink storage portions for storing cyan, magenta, yellow, and black inks are integrated. In addition, an ink set composed of an ink cartridge or an ink cartridge with a recording head having a structure in which an ink storage portion for storing cyan, magenta, and yellow inks is integrated. Further, there is an ink set in which the individual ink cartridges for storing the ink as described above are detachable from the ink jet recording apparatus. In any case, the present invention regulates the characteristics of the ink relative to other inks used in combination in an ink jet recording apparatus or as an ink cartridge, and is not limited to the above-described form. Any modification may be used.

<Ink cartridge>
Examples of the ink cartridge suitable for performing recording using the ink constituting the ink set according to the present invention include an ink cartridge provided with an ink containing portion for containing these inks. The configuration of the ink cartridge will be described below.

  FIG. 5 is an exploded perspective view of the ink cartridge. In FIG. 5, the ink cartridge 100 includes a case member composed of a casing 1 and a lid member 2, and a convex sheet 3 bonded to the casing 1 and having a folded portion, thereby forming an ink containing portion. A pressure plate 4 and a compression coil spring 5 that applies the pressure plate 4 to the convex sheet side are provided in the ink containing portion. Thus, by biasing the convex sheet 3 outward, a negative pressure is generated in the ink containing portion. An ink supply port 6 that contacts an ink flow path to a recording head (not shown) is provided on one side of the housing 1. The housing 1 constitutes a container for containing ink as described above. The convex sheet 3 is welded to the outer periphery of the housing 1. A lid member 2 is attached to the opening of the housing 1 to protect the convex sheet 3 that is convex outward.

  In the above description, an example of an ink cartridge having an ink bag structure in which an ink container is loaded with a spring or the like, which is considered to cause the problem of the present invention most significantly, has been described. However, even if the ink storage portion is an ink cartridge having a porous member as an ink absorber, when the amount of ink supplied per unit time from the ink supply port to the recording head is large compared to a conventional ink cartridge, It can be said that the subject of this invention arises. Of course, the effect of the present invention can be obtained even when an ink cartridge having a porous member as an ink absorber as described above is used.

<Recording unit>
A recording unit suitable for performing recording using the ink constituting the ink set according to the present invention includes a recording unit including an ink storage portion for storing these inks and a recording head. In the present invention, it is particularly preferable to use a recording unit that ejects ink from the recording head by the action of thermal energy.

<Inkjet recording apparatus>
An ink jet recording apparatus suitable for performing recording using the ink constituting the ink set according to the present invention is an ink jet recording apparatus including an ink storage portion for storing these inks and a recording head for discharging the ink. Apparatus. In the present invention, it is particularly preferable to use an ink jet recording apparatus that ejects ink from the recording head by the action of thermal energy.

  Below, the structure of the mechanism part of an inkjet recording device is demonstrated. The ink jet recording apparatus includes a paper feed unit, a paper transport unit, a carriage unit, a paper discharge unit, a cleaning unit, and an exterior unit that protects these parts and imparts design properties from the role of each mechanism. The outline of these will be described below.

  FIG. 1 is a perspective view of the ink jet recording apparatus. 2 and 3 are diagrams for explaining the internal mechanism of the ink jet recording apparatus. FIG. 2 is a perspective view from the upper right portion, and FIG. 3 is a side sectional view of the ink jet recording apparatus. is there.

  When paper feeding is performed, first, a predetermined number of recording media in the paper feeding unit including the paper feeding tray M2060 is sent to a nip part including a paper feeding roller M2080 and a separation roller M2041. This recording medium is separated at the nip portion, and only the uppermost recording medium is conveyed. The recording medium sent to the paper transport unit is guided by the pinch roller holder M3000 and the paper guide flapper M3030, and is sent to the roller pair of the transport roller M3060 and the pinch roller M3070. The pair of rollers formed by the conveying roller M3060 and the pinch roller M3070 is rotated by driving of the LF motor E0002, and the recording medium is conveyed on the platen M3040 by this rotation.

  When an image is formed on a recording medium, the carriage unit places a recording head H1001 (FIG. 4) at a target image forming position, and ejects ink onto the recording medium in accordance with a signal from the electric substrate E0014. The detailed configuration of the recording head H1001 will be described later. A configuration in which an image is formed on a recording medium by alternately repeating main scanning in which the carriage M4000 scans in the column direction while recording is performed by the recording head H1001 and sub-scanning in which the recording medium is conveyed in the row direction by the conveyance roller M3060. It has become. Then, the recording medium on which the image is formed is sandwiched by the nip between the first paper discharge roller M3110 and the spur M3120 at the paper discharge unit, conveyed, and discharged to the paper discharge tray M3160.

  In the cleaning unit, when the pump M5000 is operated with the cap M5010 in close contact with the ink discharge port of the recording head H1001 in order to clean the recording head H1001, unnecessary ink or the like is sucked from the recording head H1001. Further, by sucking the ink remaining in the cap M5010 with the cap M5010 opened, consideration is given to preventing the sticking by unnecessary ink and the subsequent adverse effects.

<Configuration of recording head>
The configuration of the head cartridge H1000 will be described. FIG. 4 is a diagram showing how the ink cartridge H1900 is mounted on the head cartridge H1000. The head cartridge H1000 has a recording head H1001, means for mounting the ink cartridge H1900, and means for supplying ink from the ink cartridge H1900 to the recording head, and is detachably mounted on the carriage M4000.

  The ink jet recording apparatus forms an image using each ink such as yellow, magenta, cyan, black, light magenta, light cyan, and green. Accordingly, the ink cartridge H1900 is also prepared for seven colors independently. As shown in FIG. 7, each ink cartridge is detachable from the head cartridge H1000. The ink cartridge H1900 can be attached and detached while the head cartridge H1000 is mounted on the carriage M4000.

  Next, the present invention will be described more specifically with reference to examples and comparative examples. The present invention is not limited by the following examples unless it exceeds the gist. In the text, “parts” and “%” are based on mass unless otherwise specified.

[Preparation of pigment dispersions 1 and 2]
Pigment dispersions 1 and 2 were prepared by the following procedure. In the following description, the specific gravity of the color material is the specific gravity of the liquid in which all components other than the color material (pigment dispersion containing a pigment and a dispersant) and water in the ink are replaced with water. The specific gravity was measured at 25 ° C. using a floating hydrometer (trade name: standard hydrometer; manufactured by Tech Jam).

(Preparation of Pigment Dispersion Liquid 1 Containing CI Pigment Red 122)
8 parts of a pigment (CI Pigment Red 122), 2.8 parts of a dispersant, and 89.2 parts of ion-exchanged water were mixed and dispersed for 3 hours using a batch type vertical sand mill. Thereafter, coarse particles were removed by centrifugation. Furthermore, pressure filtration was performed with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm to obtain a pigment dispersion having a pigment concentration of 8 mass%. The dispersing agent contains poly (benzyl methacrylate-co-acrylic acid) (composition (molar ratio) 70:30) having an acid value of 200 and a weight average molecular weight of 12,000 in a 10% by mass aqueous potassium hydroxide solution. The resin obtained by summing was used.

  Pigment dispersion 1 was prepared by adjusting the pigment dispersion obtained above using ion-exchanged water so that the pigment concentration was 4%. The specific gravity of Pigment Dispersion Liquid 1 was measured and found to be 1.017.

(Preparation of Pigment Dispersion Liquid 2 Containing CI Pigment Green 7)
8 parts of a pigment (CI Pigment Green 7), 4.8 parts of a dispersant, and 87.2 parts of ion-exchanged water were mixed and dispersed for 3 hours using a batch type vertical sand mill. Thereafter, coarse particles were removed by centrifugation. Furthermore, pressure filtration was performed with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm to obtain a pigment dispersion having a pigment concentration of 8% by mass. As the dispersant, a resin obtained by neutralizing an AB type block polymer of benzyl methacrylate and methacrylic acid having an acid value of 250 and a weight average molecular weight of 5000 with a 10% by mass aqueous potassium hydroxide solution was used.

  Pigment dispersion 2 was prepared by adjusting the pigment dispersion obtained above using ion-exchanged water so that the pigment concentration was 4% by mass. It was 1.039 when the specific gravity of the pigment dispersion liquid 2 was measured.

[Preparation of ink]
The components shown in Table 1 below were mixed and sufficiently stirred, and then pressure filtration was performed with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare inks 1 to 14. Table 1 shows specific gravity values, viscosity values, surface tension values, and color material specific gravity values for each ink. The specific gravity was measured at 25 ° C. using a floating hydrometer (trade name: standard hydrometer; manufactured by Tech Jam). The viscosity was measured at 25 ° C. using a RE80L viscometer (manufactured by Toki Sangyo). The surface tension was measured at 25 ° C. using an automatic surface tension meter CBVP-Z (manufactured by Kyowa Interface Science).

[Specific gravity of water-soluble organic solvent]
Table 2 below shows the specific gravity of each water-soluble organic solvent used in preparing the ink. The specific gravity was measured at 25 ° C. using a floating hydrometer (trade name: standard hydrometer; manufactured by Tech Jam).

[Preparation of ink set]
The ink sets obtained above were used in the combinations shown in Table 3 below to obtain ink sets of Examples 1 to 3, Comparative Examples 1 and 2, and Reference Examples 1 and 2. Ink cartridges having the configuration shown in FIG. 5 were filled with the ink constituting each ink set. Here, the ink cartridge having the configuration shown in FIG. 5 has an ink containing portion that is substantially hermetically sealed, that is, has an ink containing portion in which only the ink supply port is in contact with the atmosphere. . The filling amount of each ink when filling each ink cartridge is as follows with respect to the maximum filling amount that can be filled in the ink cartridge. The first ink has a half filling amount relative to the maximum filling amount of the ink cartridge, and the second ink has a maximum filling amount of the ink cartridge. By making the filling amount of each ink constituting the ink set as described above, a difference is generated in the ripple of the recording head that discharges each ink. Table 3 collectively shows various values of each ink constituting the ink set. The surface tension in the liquid in which the first ink and the second ink are mixed is the specific gravity in the liquid in which the first ink and the second ink are mixed in equal amounts (mass ratio).

[Evaluation of ink contact behavior]
0.3 g each of the first ink and the second ink constituting the ink set was dropped on the petri dish, and the inks were brought into contact with each other. The behavior at this time was visually observed and evaluated. The evaluation criteria of the behavior at the time of ink contact are as follows. The evaluation results are shown in Table 4.

(Evaluation standards for ink contact behavior)
A: The second ink diffused irreversibly with respect to the first ink.
B: The first ink diffused irreversibly with respect to the second ink.
C: There was no irreversible diffusion to any one of the inks, and they were slightly mixed on the boundary.

[Evaluation of color mixture]
Two types of ink cartridges respectively filled with each ink constituting the ink set were mounted on a modified ink jet recording apparatus (trade name: PIXUS990i; manufactured by Canon) that ejects ink from a recording head by the action of thermal energy. The ink jet recording apparatus performs recording in one pass and one direction. The number of ejection ports of the recording head is 768 per color, the width of the ejection port array is 0.64 inches, and the ejection volume per ink drop is about 2 pl. The ink cartridge containing the first ink is mounted on the ink jet recording apparatus so that the ink cartridge containing the second ink is in the yellow position and the ink cartridge containing the second ink is in the magenta position. The discharge ports were adjacent. In the ink jet recording apparatus, the yellow and magenta ejection port arrays are capped with a single cap to perform a cleaning operation. Professional photo paper PR-101 (trade name; manufactured by Canon Inc.) was used as the recording medium.

  A recorded matter recorded by using the first ink and the second ink on the recording medium so that a 4 cm × 27 cm solid image (100% duty) formed by the respective inks is adjacent to the recording medium. A sheet was produced. Then, after performing the cleaning operation once, the recording was stopped for 10 minutes. Thereafter, preliminary ejection of 16,000 drops per ejection port was performed in the cap. Thereafter, one recorded matter similar to the above was prepared again, and the state of color mixture of the solid image in the obtained recorded matter was confirmed.

  When color mixing was confirmed in the image, the cleaning operation was performed once again, and then the recording was stopped for 10 minutes. Then, after performing preliminary ejection of 2,000 drops per ejection port in the cap, one printed matter similar to the above is produced again, and the mixed color state of the solid image in the obtained recorded matter is confirmed. did.

  In the recorded matter obtained above, when color mixing was confirmed in the image, the following operation was repeated until no color mixing was confirmed in the solid image. That is, in the same manner as described above except that the number of preliminary discharges per discharge port is increased by 2,000 drops each time the above process is repeated, the cleaning operation, the recording stop for 10 minutes, the preliminary discharge of a predetermined number of ink drops, The process of producing one recorded matter was repeated.

  Further, except that the recording stop time after performing the cleaning operation is set to 30 minutes and 60 minutes, respectively, in the same manner as described above, two recorded materials are produced, the cleaning operation, the recording stop for a predetermined time, and the recorded material. The process of producing one sheet was repeated twice.

  In any case, it was confirmed that no color mixing occurred in the solid image in the second recorded material prepared before the cleaning operation.

  In the solid image, evaluation was performed by counting the number of preliminary ejections until no color mixing was confirmed in the area where the recording was performed in the initial stage and in the vicinity thereof. The evaluation criteria for color mixing are as follows. The evaluation results are shown in Table 4.

(Evaluation criteria for color mixing)
A: When the number of preliminary discharges per discharge port was more than 16,000 drops and less than 18,000 drops, color mixing was not confirmed.
B: Color mixture was not confirmed when the number of preliminary discharges per discharge port was more than 18,000 drops and 20,000 drops or less.
C: Color mixing was not confirmed when the number of preliminary discharges per discharge port was more than 20,000 drops and 22,000 drops or less.
D: Color mixing was not confirmed when the number of preliminary discharges per discharge port was more than 22,000 drops and less than 24,000 drops.
E: Color mixing was confirmed even when the number of preliminary discharges per discharge port was more than 24,000 drops.

[Evaluation of ejection stability]
Two types of ink cartridges respectively filled with each ink constituting the ink set were mounted on a modified ink jet recording apparatus (trade name: PIXUS990i; manufactured by Canon) that ejects ink from a recording head by the action of thermal energy. The ink jet recording apparatus performs recording in one direction in one pass, the number of nozzles of the recording head is 768 nozzles per color, the nozzle width is 0.64 inches, and the ejection volume per ink drop is about 2 pl. is there. The ink cartridge containing the first ink is mounted on the ink jet recording apparatus so that the ink cartridge containing the second ink is in the yellow position and the ink cartridge containing the second ink is in the magenta position. The discharge ports were adjacent. In the ink jet recording apparatus, the yellow and magenta ejection port arrays are capped with a single cap to perform a cleaning operation. As a recording medium, an office planner (trade name; manufactured by Canon Inc.) was used. A recorded matter recorded by using the first ink and the second ink on the recording medium so that a 4 cm × 27 cm solid image (100% duty) formed by the respective inks is adjacent to the recording medium. 1,000 sheets were produced. Then, the state of the obtained recorded matter was visually confirmed and evaluated. Evaluation criteria for ejection stability are as follows. The evaluation results are shown in Table 4.

(Evaluation criteria for ejection stability)
A: There is no unevenness such as streaks on all 1,000 printed materials, and there is no problem in ejection stability.
B: Although there is a recorded matter in which some streaks are observed, it is at a level where there is no problem in actual use.

[Evaluation of storage stability]
After measuring the viscosity of each ink constituting the ink set and the particle diameter of the pigment, each ink was put in a shot bottle and sealed. The shot bottle was stored in an oven at 60 ° C. for 1 month. Thereafter, the shot bottle was taken out of the oven, and the viscosity of the ink and the particle size of the pigment were measured. Evaluation was made by comparing the viscosity of the ink and the particle size of the pigment before and after storage at 60 ° C. The evaluation criteria for storage stability are as follows. The evaluation results are shown in Table 4.

(Evaluation criteria for storage stability)
A: Viscosity and particle size hardly change before and after storage at 60 ° C.
B: Before and after storage at 60 ° C., increases in viscosity and particle size are observed, but there is no problem in actual use.

It is a perspective view of an inkjet recording device. It is a perspective view of the mechanism part of an inkjet recording device. It is sectional drawing of an inkjet recording device. FIG. 6 is a perspective view illustrating a state where an ink cartridge is mounted on the head cartridge. 2 is an exploded perspective view of an ink cartridge. FIG. It is a schematic diagram which shows the behavior when the 1st ink and the 2nd ink contact.

Explanation of symbols

M2041 Separation roller M2060 Paper feed tray M2080 Paper feed roller M3000 Pinch roller holder M3030 Paper guide flapper M3040 Platen M3060 Transport roller M3070 Pinch roller M3110 Paper discharge roller M3120 Spur M3160 Paper discharge tray M4000F Carriage M5000 Pump M500P Head cartridge H1001 Recording head H1900 Ink cartridge 1 Housing 2 Lid member 3 Convex sheet 4 Pressure plate 5 Compression coil spring 100 Ink cartridge Z1000 First ink Z1001 Second ink Z1002 The first ink and the second ink are mixed. Liquid

Claims (8)

An ink set having a plurality of inks,
Each of the plurality of inks is contained in an ink cartridge having an ink containing portion that is substantially sealed.
The difference in specific gravity between the first ink having the largest specific gravity and the second ink having the smallest specific gravity among the inks constituting the ink set is 0.020 or more,
An ink set, wherein the second ink diffuses irreversibly into the first ink when the first ink and the second ink are brought into contact with each other. An ink set having a plurality of inks,
Each of the plurality of inks is contained in an ink cartridge having an ink containing portion that is substantially sealed.
Among the inks constituting the ink set, the difference in specific gravity between the first ink having a relatively large specific gravity and the second ink having a relatively small specific gravity is 0.020 or more,
An ink set, wherein the surface tension of the first ink is smaller than the surface tension of the second ink.   The ink set according to claim 2, wherein the surface tension of the second ink is 3 mN / m or more larger than the surface tension of a liquid in which the first ink and the second ink are mixed in an equal amount (mass ratio). .   Among the color materials contained in the first ink and the second ink, the first color material having the largest specific gravity, and the water-soluble organic solvent contained in the first ink and the second ink The ink set according to any one of claims 1 to 3, wherein a difference in specific gravity in the first water-soluble organic solvent having the smallest specific gravity is 0.049 or less.   The ink set according to any one of claims 1 to 4, wherein the viscosity of the first ink is larger than the viscosity of the second ink.   The inkjet recording method which discharges an ink by an inkjet system, The said ink is the ink which comprises the ink set of any one of Claims 1-5, The inkjet recording method characterized by the above-mentioned.   In the recording unit provided with the ink storage part which stores ink, and the recording head for discharging ink, the said ink is the ink which comprises the ink set of any one of Claims 1-5. A recording unit characterized by that.   An ink jet recording apparatus comprising an ink containing portion for containing ink and a recording head for ejecting ink, wherein the ink is an ink constituting the ink set according to any one of claims 1 to 5. An ink jet recording apparatus, comprising:

Images