JP5241110B2 - Aqueous ink, ink jet recording method, ink cartridge, recording unit, and ink jet recording apparatus - Google Patents

Description

  The present invention relates to an aqueous ink containing a pigment dispersed with a resin, and further relates to an ink jet recording method, an ink cartridge, a recording unit, and an ink jet recording apparatus using the ink.

  It is well known to use a water-based ink (pigment ink) containing a pigment as a coloring material in order to improve the light resistance, gas resistance, and water resistance of an image obtained by the ink jet recording method. . Recently, since the type of pigment affects the light resistance and gas resistance of the resulting image, it relates to selecting a pigment that can provide excellent light resistance and gas resistance and using it in a pigment ink. There is a proposal (see Patent Document 1).

  However, compared with ink containing a dye as a coloring material (dye ink), the pigment ink has a problem that clogging is likely to occur in the nozzle tip and in the ink flow path due to the evaporation of moisture from the discharge port. . In response to such problems, there are many proposals relating to devising the type of water-soluble organic solvent used in the ink and defining the characteristics of the pigment or the resin (dispersant) in which the pigment is dispersed (see Patent Documents 2 and 3) ).

JP 2004-217765 A JP-A-9-194780 JP 2003-147243 A

  The present inventors have studied as follows for the purpose of providing a pigment ink having excellent reliability (storage stability and ejection stability) and excellent image quality (fixing property and marker resistance). went. That is, a plurality of inks each containing various resin-dispersed pigments (pigments dispersed by a resin) having different pigment surface treatments were prepared as colorants. And reliability was evaluated by discharging these inks using an inkjet recording device. In this study, a thermal ink jet recording apparatus that discharges ink by the action of thermal energy was used. As a result, it was found that some of the evaluated inks did not provide ejection characteristics (frequency response, stable ejection volume, ejection speed, etc.). In particular, as described later, this tendency is observed in an ink containing a resin-dispersed pigment in which a pigment having a hydrophilicity δm in the range of 21.5 to 23.5 is dispersed with a resin. I found it.

  Furthermore, the present inventors are not due to the clogging that occurs in the discharge port (orifice), which has been conventionally known, but is due to a new phenomenon described below. It was confirmed. In other words, when ink is ejected continuously from the recording head, deposits adhere to the ink flow path and in the vicinity of the ejection port, and the ink flow path is blocked, which makes it impossible to obtain sufficient ejection stability. I found out that

  Accordingly, an object of the present invention is to provide an ink that can provide good ejection stability when used in an ink jet recording method that ejects ink by the action of thermal energy, even though the ink contains a pigment dispersed with a resin. There is to do. Another object of the present invention is to perform a predetermined recovery operation so that ink is normally ejected from the recording head even after the ink cartridge containing the ink is mounted on the recording head and left for a long period of time. An object of the present invention is to provide an ink that is excellent in reliability. Furthermore, another object of the present invention is to provide an ink jet recording method, an ink cartridge, a recording unit, and an ink jet recording apparatus using the ink.

The above object is achieved by the present invention described below. That is, the ink of the present invention is a water-based ink containing a pigment, a resin for dispersing the pigment, and a water-soluble organic solvent used in an inkjet recording method in which the ink is ejected from a recording head by the action of thermal energy. Wherein the pigment is C.I. I. A Pigment Violet 23, a resin for dispersing the pigment, its a weight average molecular weight of 2,000 to 5,000, the content in the ink of the previous SL-soluble organic solvent, the total mass of the ink as a reference state, and are 5.0 mass% or more 17.5% by mass or less, and the water-soluble organic solvent, characterized in that the weight average molecular weight including more than 1,000 polyethylene glycol.

Further , the ink according to another aspect of the present invention further has an absorption property of the ink having a maximum absorption wavelength in a range of wavelengths of 530 nm to 540 nm and a wavelength of 550 nm to 570 nm, respectively, and the wavelength of 530 nm to 540 nm. The relationship between the absorbance (A) at the maximum absorption wavelength in the range of 5 and the absorbance (B) at the maximum absorption wavelength in the range of 550 nm to 570 nm satisfies the following formula (1). It is characterized by.

  An ink jet recording method according to another embodiment of the present invention is characterized in that any one of the above inks is used in an ink jet recording method in which ink is ejected by the action of thermal energy to perform recording on a recording medium.

  In addition, an ink cartridge according to another embodiment of the present invention is characterized in that an ink cartridge provided with an ink storage portion for storing ink is one of the above inks.

  According to another embodiment of the present invention, there is provided a recording unit comprising: an ink storage portion that stores ink; and a recording head that discharges ink by the action of thermal energy. The ink is any one of the above-described inks.

  An ink jet recording apparatus according to another embodiment of the present invention is housed in an ink jet recording apparatus that includes an ink containing portion that contains ink and a recording head that ejects ink by the action of thermal energy. The ink is any one of the inks described above.

  According to the present invention, although it is an aqueous pigment ink containing a pigment dispersed with a resin (hereinafter also referred to as an ink), it has good ejection stability when used for inkjet recording in which ink is ejected by the action of thermal energy. Ink can be obtained. In addition, even after an ink cartridge containing such ink is attached to the recording head and left for a long period of time, the ink can be normally ejected from the recording head by performing a predetermined recovery operation, which is excellent in reliability. Ink can be provided. Furthermore, it is possible to provide an ink jet recording method, an ink cartridge, a recording unit, and an ink jet recording apparatus using the ink that can stably form an image.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments. In the course of studying the problems described above, the present inventors firstly, the hydrophilicity δm of the pigment, and deposits generated in the ink flow path and in the vicinity of the ejection port of the thermal type ink jet recording apparatus And found that there is a large correlation between That is, when ink containing a resin-dispersed pigment in which a pigment having a hydrophilicity δm in the range of 21.5 or more and 23.5 or less is dispersed with a resin is continuously ejected, It was found that deposits were particularly prominent in the vicinity of the exit. Accordingly, the present inventors have obtained a reliable ejection characteristic even when a resin-dispersed pigment in which a pigment having the above surface characteristics (hydrophilicity δm) is dispersed with a resin is used. Further studies were conducted for the purpose of providing ink with high properties.

[Background of the invention]
(Existence of issues)
First, the background to the present invention will be described in detail. The present inventors have provided a resin that can stably give an image that can satisfy higher light resistance, gas resistance, water resistance, scratch resistance and the like as compared with conventional inkjet inks. A study was conducted for the purpose of providing a water-based ink containing a dispersed pigment. As a result, an ink containing a resin-dispersed pigment in which a pigment having a hydrophilicity δm in the range of 21.5 or more and 23.5 or less was dispersed with a resin was continuously ejected using a thermal ink jet recording apparatus. In some cases, it has been found that the following undesirable phenomenon occurs. That is, in this case, in particular, it was confirmed that deposits adhered in the ink flow path and in the vicinity of the discharge ports, and the deposit stability was lowered by the deposits. Therefore, as a result of pursuing the cause of such a phenomenon, the present inventors have noticeably caused the following phenomenon when the resin-dispersed pigment as described above is combined with a thermal ink jet recording method. I came to the conclusion that it would happen.

(Mechanism of deposit formation)
FIG. 1 is a schematic diagram illustrating a mechanism of deposit generation in the vicinity of an ejection port when a thermal ink jet recording apparatus is used. In FIG. 1, (a) shows a state in which film-like bubbles 6 are generated on the heater 1. Also, (b) to (h) are respectively (b) about 1 μsec, (c) about 2.5 μsec, (d) about 3 μsec, (e) about 4 μm from the state of (a). (F) After about 4.5 microseconds, (g) About 6 microseconds, (h) About 9 microseconds after a second. In addition, the part which gave the horizontal direction hatching in (a)-(h) of FIG. 1 shows an orifice plate or a flow-path wall.

  First, as shown in FIG. 1A, bubbles 6 are generated inside the ink flow path 2 on the heater 1 in accordance with the energization of the heater 1 based on a recording signal or the like. At this time, the temperature of the ink in the vicinity of the heater 1 rises to about 200 ° C. In the ink whose temperature has risen, the dispersion of the pigment dispersion occurs, causing phenomena such as desorption of the dispersant (resin) from the pigment and fragmentation of the pigment. As a result, the pigment whose dispersion state has become unstable exists in a mixed state in the ink. At this time, dispersion failure occurs when the adsorption power of the resin to the pigment is particularly weak, or when the amount of resin necessary to maintain a stable dispersion state of the pigment is not adsorbed on the pigment. And many pigments in which the dispersion state of a pigment is inadequate will be in the following states. That is, phenomena such as resin desorption from pigments, pigment fragmentation, and changes to a state in which the resin is dissolved in the ink occur rapidly and excessively, resulting in an unstable dispersion state. There will be many pigments.

  Thereafter, as shown in FIGS. 1B and 1C, the volume of the bubble 6 rapidly expands in about 2.5 μsec. Along with this, the ink whose temperature has risen is cooled. As the temperature of the ink decreases, the pigment in which the dispersion state becomes unstable cannot maintain the dispersion state, and the aggregation of the pigment occurs, so that the pigment deposited in the ink appears. Some of the pigment agglomerates 4 thus deposited are ejected in a state of being contained in the ink droplets 5 from the ejection ports 3, but remain in the ink flow path 2 and flow. Some stick to the road wall. As described above, it is considered that the aggregate 4 deposited in the ink accumulates on the flow path wall by repeating the ink ejection shown in FIGS.

  The present inventors are prone to dispersion failure of pigments in ink containing resin-dispersed pigments in which pigments having a hydrophilicity δm of 21.5 or more and 23.5 or less are dispersed with resin, and the generated deposits are stable in ejection. The reason why the problem of reducing the property is likely to occur is estimated as follows. First, it is considered that the largest cause of such inks that the deposits are specifically attached in the ink flow path and in the vicinity of the discharge ports more than other pigment inks is that the resin adsorption force to the pigment is weak. ing. That is, since a pigment having a hydrophilicity degree δm of 21.5 or more has a relatively high hydrophilicity, a resin functioning as a dispersant is easily detached from the pigment surface. For this reason, when the ink is ejected from the recording head by the action of thermal energy as described above, dispersion destruction due to heat easily and rapidly proceeds. As a result, it is estimated that deposits are generated in the ink flow path and in the vicinity of the ejection openings.

  In contrast to the above, the present inventors use an ink containing a resin-dispersed pigment in which a pigment having a hydrophilicity greater than 23.5 is dispersed with a resin, to the inside of the ink flow path and the vicinity of the discharge port. It was confirmed that the adhesion of the deposit was suppressed. As described above, when an ink containing a resin-dispersed pigment having a hydrophilicity greater than 23.5 is used, the reason why the adhesion of the deposit is reduced is not clear. I guess. That is, even when a pigment having a hydrophilicity greater than 23.5 is dispersed with a resin, the state in which the resin is hardly adsorbed on the pigment surface remains unchanged. However, the hydrophilicity δm of the pigment greatly increases the hydrophilicity of the pigment itself at the boundary of 23.5. Therefore, even if the dispersion of the pigment dispersion progresses due to heat at the time of ejection, the generated dispersion destruction is also high. It is possible to keep water solubility. As a result, when using an ink containing a resin-dispersed pigment having a hydrophilicity greater than 23.5, the generated dispersion destruction product is discharged out of the ink flow path together with the ink without being deposited, and the ink flow It is considered that the deposit hardly adheres in the passage and in the vicinity of the discharge port.

[Solution]
In view of the above, the present inventors have found that even when using a resin-dispersed pigment in which a pigment having a hydrophilicity δm of 21.5 or more and 23.5 or less is dispersed with a resin, the dispersion failure is caused by heat during ejection. The purpose of this study was to provide an ink capable of suppressing the above as much as possible. As a result, the inventors have found that there are two types of methods for solving the above-described problems, and have reached the present invention. Below, two types of methods that can solve the above-described problems of the present invention will be described.

(First method)
A first method for solving the problems of the present invention is to use a water-soluble organic solvent in an ink containing a resin-dispersed pigment in which a pigment having a hydrophilicity δm of 21.5 or more and 23.5 or less is dispersed with a resin. This is a method for optimizing the content (mass%) of. Specifically, the content of the water-soluble organic solvent in the ink is adjusted to be 5.0% by mass or more and 17.5% by mass or less based on the total mass of the ink. According to the first method, deposits in the ink flow path and in the vicinity of the ejection ports can be effectively reduced regardless of the type of the water-soluble organic solvent. The ink according to the first embodiment of the present invention configured by the first method is hereinafter referred to as “first ink”.

  As a result of the study by the present inventors, the following was found about the influence of the content of the water-soluble organic solvent in the ink. First, as the content of the water-soluble organic solvent in the ink increases, the affinity between the aqueous medium in the ink and the hydrophobic portion of the resin that functions as a dispersant increases. That is, it has been found that as the content of the water-soluble organic solvent increases, the adsorptive power of the resin with respect to the pigment tends to be relatively small. In addition, highly hydrophilic pigments having a hydrophilicity δm of 21.5 or more are inherently weak in the adsorptive power between the pigment surface and the hydrophobic part of the resin. Therefore, the pigment is compared with other pigments. Thus, it was found that the ink is particularly susceptible to the influence of the water-soluble organic solvent in the ink.

  As a result of further studies by the present inventors, the following has been found. That is, even when a highly hydrophilic resin-dispersed pigment having a hydrophilicity δm of 21.5 or more and 23.5 or less is used, the content of the water-soluble organic solvent in the ink is set within a specific range. The present inventors have found that the dispersion failure of the pigment dispersion can be suppressed. Specifically, when the content of the water-soluble organic solvent in the ink is 17.5% by mass or less based on the total mass of the ink, it is compared with the affinity between the aqueous medium and the hydrophobic part of the resin. The affinity between the hydrophobic part of the pigment surface and the hydrophobic part of the resin is higher. For this reason, it is presumed that by optimizing the content of the water-soluble organic solvent in the ink, it is possible to suppress the dispersion breakage of the pigment dispersion due to heat during ejection.

  Further, as a result of further studies by the present inventors, it has been found that the content of the water-soluble organic solvent needs to be 5.0% by mass or more based on the total mass of the ink. When the content of the water-soluble organic solvent is less than 5.0% by mass, the generation of deposits is suppressed, but the moisture retention is poor, and precipitation of pigments accompanying evaporation of water near the discharge port, This is because ejection failure due to clogging may occur. The content of the water-soluble organic solvent in the ink is 2.5 times or more and 17.0 times or less based on the content of the pigment in the ink (content of the water-soluble organic solvent / content of the pigment) ( (Mass ratio).

(Second method)
A second method for solving the problems of the present invention is a pigment having a hydrophilicity δm of 21.5 or more and 23.5 or less. I. When using the pigment violet 23, the light absorption characteristics of the ink are optimized by adjusting the dispersion state. According to the second method, deposits in the ink flow path and in the vicinity of the ejection ports can be effectively reduced regardless of the type of water-soluble organic solvent used in the ink. The ink according to the second aspect of the present invention configured by the second method is hereinafter referred to as “second ink”.

  As an example of a pigment having a hydrophilicity δm of 21.5 or more and 23.5 or less, the present inventors have described C.I. I. Pigment Violet 23 was selected, and an investigation was conducted for the purpose of obtaining an ink excellent in storage stability, ejection stability, color developability and the like using such a pigment. Specifically, C.I. I. Several types of pigment dispersions with different pigment violet 23 dispersion conditions were prepared and examined. As a result, it was found that the light absorption characteristics of the pigment dispersion are greatly related to the ejection characteristics and the color developability.

  C. I. The relationship between the light absorption characteristics, the dispersion conditions, and the discharge characteristics in the pigment violet 23 will be described below. As shown in FIG. I. The liquid containing the pigment dispersion of Pigment Violet 23 has a maximum absorption wavelength in each of three wavelength regions of wavelengths of 530 nm to 540 nm, 550 nm to 570 nm, and 620 nm to 630 nm.

  As a result of the study by the present inventors, it has been found that the ratio of absorbance at these three maximum absorption wavelengths changes regularly to some extent when the dispersion conditions for preparing the pigment dispersion are changed. Specifically, pigment dispersions with different dispersion conditions were prepared and examined by changing the type of dispersion machine, dispersion time and peripheral speed, and further the bead diameter and bead type. And the following fact was understood by measuring the light absorption characteristic of these pigment dispersions, respectively.

  That is, it was found that when the dispersion conditions are strict, the ratio of absorbance at the above three maximum absorption wavelengths tends to change as follows. First, the ratio [(B) / (A)] of the absorbance (B) at the maximum absorption wavelength in the range of 550 nm to 570 nm with respect to the absorbance (A) at the maximum absorption wavelength in the range of 530 nm to 540 nm. Tended to be bigger. Further, the ratio [(C) / (A)] of the absorbance (C) at the maximum absorption wavelength in the range of 620 nm to 630 nm to the absorbance (A) at the maximum absorption wavelength in the range of 530 nm to 540 nm. Tended to be bigger.

前記［（Ｂ）／（Ａ）］の値が、上記範囲を満たさないインクを連続して吐出する場合に、インク流路内及び吐出口近傍に堆積物が付着する理由は定かではないが、本発明者らは、以下のように推測している。 Next, the present inventors have a plurality of C.I. I. About the pigment dispersion of Pigment Violet 23, a plurality of inks were prepared by adding a water-soluble organic solvent generally used for inkjet ink and water. Then, these inks are mounted on a thermal ink jet recording apparatus, and the ink is continuously discharged, and details about the relationship between the deposits adhering to the inside of the ink flow path and the vicinity of the discharge port described above. The examination was done. As a result, when the ratio of the absorbance (A) and the absorbance (B) does not satisfy the condition of the following formula (1), a large amount of deposits adhere in the ink flow path and in the vicinity of the ejection port, thereby causing ejection stability. It was found that a decrease in

When the value of [(B) / (A)] continuously discharges ink that does not satisfy the above range, the reason why deposits adhere in the ink flow path and in the vicinity of the discharge port is not clear, The present inventors presume as follows.

[When the value of [(B) / (A)] is smaller than 0.93]
C. value of (B) / (A) smaller than 0.93 I. The liquid (aqueous ink) containing the pigment violet 23 pigment dispersion is in an insufficiently dispersed state. That is, in the liquid containing such a pigment dispersion, there are many coarse particles having cracks on the surface. The greater the proportion of pigment present in the state of coarse particles, the smaller the specific surface area of the pigment, and the smaller the amount of resin (dispersant) adsorbed on the pigment surface. Further, in the liquid containing the pigment dispersion, the resin repeatedly absorbs and desorbs the pigment, that is, the resin adsorbs on the pigment or the resin separates from the pigment and dissolves in the liquid. It is thought that it repeats. As described above, the degree of hydrophilicity δm is 21.5 or more and 23.5 or less. I. Since the pigment violet 23 has a high hydrophilicity of the pigment, desorption of the resin occurs easily, but it is considered that adsorption of the resin hardly occurs. For this reason, C.I. I. It is considered that the pigment in the liquid containing the pigment dispersion of Pigment Violet 23 exists in a state where the resin is not sufficiently adsorbed on the pigment surface. The inventors of the present invention have found that when the value of [(B) / (A)] is smaller than 0.93, the amount of deposits in the ink flow path and in the vicinity of the ejection ports greatly increases. Make sure you do. The reason for this is that when the value of [(B) / (A)] is smaller than 0.93, the resin is not sufficiently adsorbed on the pigment surface. It is presumed that this is due to the rapid progress of the dispersion failure due to the temperature rise caused by the heat of the steel.

[When the value of [(B) / (A)] is greater than 0.97]
A value of [(B) / (A)] greater than 0.97; I. In the liquid (aqueous ink) containing the pigment dispersion of Pigment Violet 23, the pigment is in an overdispersed state. That is, there are many pigments in a very finely pulverized state in a liquid containing such a pigment dispersion. The larger the ratio of the pigment having a small particle diameter, the larger the specific surface area of the pigment. Therefore, it is difficult to maintain a stable dispersion state unless the content of the resin (dispersant) for dispersing the pigment is increased. It may become. However, in the case of ink jet ink, the content of resin in the ink is limited in consideration of reliability. Moreover, since the surface energy of a pigment becomes high, so that the particle diameter of a pigment becomes small, pigments will aggregate easily. Furthermore, as described above, the degree of hydrophilicity δm is 21.5 or more and 23.5 or less. I. Since the pigment violet 23 has a high hydrophilicity of the pigment, it is considered that the resin adsorption hardly occurs. For the above reasons, C.I. I. On the surface of the particles of the pigment violet 23, the proportion of the resin that should function as a dispersant is reduced. For this reason, it may be difficult to maintain a stable dispersed state even with slight environmental changes. As a result, when ink containing such a pigment dispersion is ejected using a thermal type ink jet recording apparatus, deposits are generated in the ink flow path and in the vicinity of the ejection port by the mechanism described above. Conceivable.

  As a result of further studies by the present inventors, when the value of [(B) / (A)] is larger than 0.97 as a boundary, deposits in the ink flow path and in the vicinity of the ejection port Was found to increase in particular. This is because there are many pigment dispersions where it is difficult to maintain a stable dispersion state even if the environmental change is slightly greater than 0.97 (B) / (A). Therefore, it is presumed that the dispersion failure due to the temperature rise due to the heat at the time of discharge proceeds rapidly. Furthermore, a pigment having a high surface energy tends to generate deposits at various portions in the flow path from the ink cartridge that houses the ink to the recording head that ejects the ink. And it thinks that the adhesion | attachment of the reaggregation of the pigment centering on the said deposit | attachment is accelerated | stimulated notably.

  In addition, as long as the present inventors examined, C.I. I. It was found that the value of [(B) / (A)] described above in the liquid containing the pigment violet 23 pigment dispersion was greater than 0.97. The reason for this is not clear, but the present inventors presume as follows. C. I. As the value of [(B) / (A)] in the liquid containing the pigment dispersion of Pigment Violet 23 increases, the color developability improves. On the other hand, the deposits generated in the ink flow path and in the vicinity of the ejection openings as described above, and the ejection characteristics deteriorated due to such deposits, are specifically generated only when ink is ejected using a thermal ink jet recording apparatus. It can be said that this is a problem to be solved. That is, commercially available C.I. I. With regard to Pigment Violet 23, no consideration is given to the ejection characteristics, and the value of [(B) / (A)] is considered to be greater than 0.97 for the purpose of further improving the color developability. It is done. As described above, such commercially available C.I. I. Even in the case of using Pigment Violet 23, an ink containing a pigment dispersion having a range of [(B) / (A)] defined by the present invention can be obtained by appropriately determining the pigment dispersion conditions. Can be obtained.

As described above, what is greatly involved in the generation of deposits is the absorbance (A) at the maximum absorption wavelength in the wavelength range of 530 to 540 nm and the absorbance (B) at the maximum absorption wavelength in the wavelength range of 550 to 570 nm. Ratio [(B) / (A)]. Further, as previously mentioned, C.I. I. The liquid containing the pigment dispersion of Pigment Violet 23 has a maximum absorption wavelength in a wavelength range of 620 nm to 630 nm in addition to the above two ranges (absorbance (C)). The ratio of absorbance at these three maximum absorption wavelengths changes regularly to some extent by changing the dispersion conditions when preparing the pigment dispersion. Accordingly, the inventors of the present invention believe that the absorbance (C) at the maximum absorption wavelength in the wavelength range of 620 nm to 630 nm also has a considerable influence on the color developability and the generation of deposits in the ink flow path and in the vicinity of the ejection port. I thought and examined it further. As a result, the liquid containing the pigment dispersion satisfying the condition of the formula (1) and further satisfying the condition of the following formula (2) is compared with the pigment dispersion satisfying only the condition of the formula (1). It has been found that the generation of deposits in the ink flow path and in the vicinity of the ejection port can be more effectively suppressed.

  Further, according to the study by the present inventors, the maximum absorption wavelength that gives the above absorbances (A), (B), and (C) exists within the following wavelength range, so that It was also found that the generation of deposits near the discharge port can be suppressed particularly effectively. That is, the range in which the absorbance (A) is from 533.0 nm to 535.0 nm, the absorbance (B) is from 562.0 nm to 562.5 nm, and the absorbance (C) is from 624.5 nm to 625.0 nm. It is preferable that it exists in each. In addition, by appropriately determining the pigment dispersion conditions in the same manner as described above, the wavelengths at which the maximum absorption wavelengths giving the respective absorbances (A), (B), and (C) are present are within the above-described ranges. An ink containing a pigment dispersion can be obtained.

(Hydrophilicity of pigment δm)
Here, a method for calculating the hydrophilicity δm of the pigment will be described. The hydrophilicity δm of the pigment in the present invention is a value calculated according to the acetone titration method described below described in “Coloring Materials” [62 [8], 524-528 (1989)]. First, 0.1 g of pigment is added to a beaker containing a stirrer and 50 ml of ion-exchanged water, and gently stirred to such an extent that no vortex is produced. Here, acetone is added dropwise with stirring using a burette. A drop amount of acetone required for the floating pigment to get wet and settle is A. Using the value of A, the hydrophilicity δm of the pigment is calculated from the following formula (3). In addition, the value of 23.43 and 9.75 in following formula (3) is SP value (solubility parameter) of water and acetone which are described in the said literature.

  In the case of measuring the hydrophilicity of a pigment in an ink, that is, a pigment dispersed in a resin (hereinafter referred to as a pigment dispersion), it can be calculated by the same method as described above. However, in the case of a pigment dispersion, it is necessary to measure in a state where the resin adsorbed on the pigment surface is desorbed.

  Here, there are various means for removing the resin from the pigment. Specifically, the following methods can be considered. Examples thereof include a method of salting out or coagulating ink having a pigment dispersion. First, the organic group of the resin is analyzed by a conventional method. For example, when the organic group of the resin contains an anionic group, an acid such as hydrochloric acid or sulfuric acid is added to the ink, and when the organic group contains a cationic group, an alkali such as sodium hydroxide is added. . In this way, the pigment and resin in the ink can be precipitated by salting out. Alternatively, the pigment and the resin in the ink can be precipitated by coagulation by adding an excessive amount of alcohol to the ink. Furthermore, as a method for precipitating the pigment in the ink, the pigment can be effectively taken out by a combination of salting out and coagulation, centrifugation, or the like.

  The precipitate containing the pigment thus obtained is collected by filtration or the like, the solid content is thoroughly washed with pure water, and the solid containing the pigment is dried overnight in an oven at a temperature of 60 ° C. To do. Then, the dried product containing the obtained pigment is washed with a good solvent of the resin adsorbed on the pigment (a water-soluble organic solvent capable of easily dissolving the resin). In addition, although it is necessary to select a good solvent according to the kind of resin, tetrahydrofuran and chloroform can be used, for example. And after repeating the washing | cleaning operation | work with the good solvent of the dried solid substance containing a pigment about 3 times, in order to remove the remaining water and water-soluble organic solvent, a vacuum degree of several hundred Pa or less is used using a vacuum dryer. And drying at a temperature of 60 ° C. for about 3 hours. By such a method, only the pigment can be taken out from the ink.

<Water-based ink>
The first ink of the present invention is characterized by first comprising a pigment having a hydrophilicity δm in the range of 21.5 to 23.5. Furthermore, in the first method described above, the content (% by mass) of the water-soluble organic solvent in the ink needs to be 5.0% by mass or more and 17.5% by mass or less based on the total mass of the ink. It is. In the second method described above, C.I. I. Pigment Violet 23 is used, but it is necessary to adjust the dispersion state of the pigment so that the second ink has a specific absorption wavelength. Note that C.I. I. As described above, Pigment Violet 23 has a pigment hydrophilicity δm of 21.5 or more and 23.5 or less. The first and second inks of the present invention may have the same configuration as the conventional pigment ink except for the above. Below, each component which comprises the ink of this invention is demonstrated.

(Pigment)
Specific examples of commercially available pigments having a hydrophilicity δm in the range of 21.5 to 23.5 used in the present invention include the following. For example, Novoperm Yellow H2G (product name: manufactured by Clariant), B8700 (product name: manufactured by Ciba Specialty Chemicals), Hostaper Violet RL SP (product name: manufactured by Clariant), Monak 880 (product name: manufactured by Cabot) and the like can be mentioned. . C. I. In terms of numbers, Novoperperm Yellow H2G is C.I. I. Pigment Yellow 120. Hosterperm Violet RL SP is a C.I. that can be used particularly suitably for the first and second inks of the present invention. I. Pigment Violet 23. In the first ink of the present invention, as long as the hydrophilicity δm of the pigment is in the range of 21.5 or more and 23.5 or less, the pigment is not limited to the pigments listed above, but any of the pigments listed below. May be used. In addition, in the first and second inks of the present invention, the following pigments can be used in combination in addition to the specific pigment described above.

〔Carbon black〕
As the carbon black, any carbon black such as furnace black, lamp black, acetylene black and channel black can be used. Specifically, commercially available products as listed below can be used.

  Ray Van: 7000, 5750, 5250, 5000 ULTRA, 3500, 2000, 1500, 1250, 1200, 1190 ULTRA-II, 1170, 1255 (above Colombia). Black Pearls L, Legal: 400R, 330R, 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 (Mitsubishi Chemical).

  Carbon black newly prepared for the present invention can also 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.

[Organic pigments]
In addition to carbon black, various organic pigments can be used. Specific examples of the organic pigment include the following. 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 pigment. Condensed azo pigment. Thioindigo pigment. Diketopyrrolopyrrole pigment. 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.

The organic pigment that can be used in the present invention is C.I. I. For example, the following can be cited.
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 and the like. In addition, 180, 184, 192, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240, 254, 255, 272, and the like.
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.

  In the present invention, the content (% by mass) of the pigment in the ink is 0.1% by mass or more and 15.0% by mass or less, more preferably 1.0% by mass or more and 10.0% by mass, based on the total mass of the ink. % Or less, and particularly preferably 1.0% by mass or more and 3.0% by mass or less. If the pigment content is less than 0.1% by mass, a sufficient optical density may not be obtained. If it exceeds 15.0% by mass, the sticking resistance may be lowered.

(Pigment dispersion method)
As the pigment constituting the first and second inks of the present invention, a resin dispersion type pigment (resin dispersion type pigment) dispersed using a polymer dispersant is used. As the dispersant used for the resin-dispersed pigment, it is preferable to use a dispersant that can stably disperse the pigment in an aqueous medium by the action of a hydrophilic group, particularly an anionic group. As specific dispersants, for example, the following can be used. Styrene-acrylic acid copolymer, styrene-acrylic acid-alkyl acrylate copolymer, styrene-maleic acid copolymer, styrene-maleic acid-alkyl acrylate copolymer. Styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid half ester copolymer. Vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer, styrene-maleic anhydride-maleic acid half ester copolymer, benzyl methacrylate-methacrylic acid copolymer, and the like. Or the salt of these copolymers.

  Moreover, it is preferable that the form of resin used as a dispersing agent is a block polymer. The reason is as follows. In the block polymer, hydrophilic units and hydrophobic units are regularly arranged in the molecular structure. On the other hand, in the random polymer, hydrophobic units and hydrophilic units are irregularly arranged in the molecular structure. For this reason, the block polymer has a hydrophobic unit that is easily adsorbed to the pigment locally to some extent in the resin structure as compared with the random polymer. Due to the difference in the form of the resin, the block polymer is less likely to be detached from the pigment than the random polymer, and the generation of deposits in the ink flow path and in the vicinity of the ejection port can be more effectively reduced. it can. The block polymers that can be used in the present invention include the following. Examples include an AB block type in which hydrophobic monomer units (referred to as A blocks) and ionic hydrophilic monomer units (referred to as B blocks) are localized. Or the ABC block type which added the nonionic hydrophilic monomer unit (it calls a C block) further is mentioned. Of course, the present invention is not limited to this.

  The above-described dispersant preferably has a weight average molecular weight of 1,000 or more and 30,000 or less. In the present invention, the weight average molecular weight of the dispersant is particularly preferably 1,500 to 6,000, and more preferably 2,000 to 5,000. Here, the use of a resin having a weight average molecular weight of 2,000 or more and 5,000 or less as a dispersant is very rare in ordinary pigment inks for inkjet. However, in the present invention, it is particularly preferable to use a resin having such a low weight average molecular weight for the reasons described below. As described above, a pigment having a hydrophilicity δm in the range of 21.5 or more and 23.5 or less has a property that the resin adsorbed to the pigment is easily detached. At this time, even if the resin is desorbed from the pigment, since the resin having a small weight average molecular weight is used, the resin present in the ink can be adsorbed again relatively easily at the site where the resin is desorbed from the pigment. it can. That is, because the weight average molecular weight of the dispersant is small, it is difficult to be affected by the steric hindrance of the resin already adsorbed, and the above-described resin re-adsorption tends to occur. As a result, a stable dispersed state can be maintained, and the generation of deposits in the ink flow path and in the vicinity of the ejection ports can be further suppressed. However, if the weight average molecular weight of the dispersant is too small, the dispersion state of the pigment becomes unstable, and the generation of deposits in the ink flow path and in the vicinity of the discharge ports may not be suppressed. Therefore, in the present invention, it is most preferable to use a resin having a weight average molecular weight in the range of 2,000 to 5,000 as the dispersant.

  Further, the resin content in the ink is preferably 30.0% or more and 90.0% or less based on the pigment content in the ink (resin content / pigment content). When the resin content in the ink is less than 30.0% based on the pigment content (ie, resin / pigment), it may be difficult to maintain the dispersion stability of the pigment over a long period of time. is there. Further, even when the resin content in the ink is greater than 90.0% based on the pigment content, the effect on dispersion stability and deposit generation may not be further improved. . Rather, the viscosity of the ink increases, and when the ink is ejected from the recording head, it causes ejection failure due to the resin adhering to the face surface (the surface having the ejection port for ejecting ink). , Reliability may be reduced.

  The resin content (% by mass) in the ink is 0.5% by mass to 3.0% by mass, and more preferably 0.9% by mass to 1.8% by mass, based on the total mass of the ink. Preferably there is. If the content of the resin in the ink is 0.9% by mass or more and 1.8% by mass or less as described above, the ejection stability does not decrease, and the dispersion stability is excellent over a long period of time. This is because the sex is obtained.

(Aqueous medium)
For the ink, it is preferable to use water or an aqueous medium containing water and a water-soluble organic solvent. In the first ink of the present invention, the content (% by mass) of the water-soluble organic solvent in the ink is set to 5.0% by mass or more and 17.5% by mass or less based on the total mass of the ink. is necessary. In the second ink of the present invention, the content (% by mass) of the water-soluble organic solvent in the ink is 3.0% by mass to 50.0% by mass, and further 4.0% by mass to 20. It is preferably 0% by mass or less, particularly preferably 5.0% by mass or more and 17.5% by mass or less.

  As the water-soluble organic solvent, for example, the following can be used. Alkanols having 1 to 4 carbon atoms such as ethanol, isopropanol, n-butanol, isobutanol, secondary butanol and tertiary butanol. Carboxylic acid amides such as N, N-dimethylformamide or N, N-dimethylacetamide. Ketones or ketoalcohols such as acetone, methyl ethyl ketone, 2-methyl-2-hydroxypentan-4-one; Cyclic ethers such as tetrahydrofuran and dioxane. Glycerin. Glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2- or 1,3-propylene glycol, 1,2- or 1,4-butylene glycol, polyethylene glycol, and thiodiglycol; 1,3-butanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 2-methyl-1,3-propanediol, 1,2,6-hexanetriol, etc. Alcoholic alcohols. Alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or ethyl) ether, triethylene glycol monoethyl (or butyl) ether. Heterocycles such as 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N-methylmorpholine. Sulfur-containing compounds such as dimethyl sulfoxide. These water-soluble organic solvents can be used alone or in combination of two or more.

  In the present invention, among the above water-soluble organic solvents, it is preferable to use glycerin, ethylene glycol, diethylene glycol, polyethylene glycol, or 2-pyrrolidone. Further, when a resin having a weight average molecular weight of 1,500 to 6,000, more preferably 2,000 to 5,000 is used as a pigment dispersant, the average molecular weight is 1,000 as a water-soluble organic solvent. It is particularly preferable to use the above polyethylene glycol. This is because an ink containing a resin having a weight average molecular weight as described above and a polyethylene glycol having an average molecular weight of 1,000 or more has particularly good ejection stability when ejected continuously for a long period of time. In addition, it is preferable that the upper limit of the average molecular weight of polyethylene glycol is 1,500 or less.

  Moreover, it is preferable to use deionized water. The content (% by mass) of water in the ink is 50.0% by mass or more and 95.0% by mass or less, and further 78.5% by mass or more and 91.0% by mass or less based on the total mass of the ink. Is preferred. Furthermore, in the case of the first ink of the present invention, it is particularly preferable that the content (% by mass) of water in the ink is 78.5% by mass or more and 91.0% by mass or less. When the water content is 78.5% by mass or more, the content of water in the ink is relatively large, while the content of components other than water, such as water-soluble organic solvents and surfactants, is high. Relatively small. As a result, the components such as the water-soluble organic solvent and the surfactant described above can suppress the action of weakening the adsorptive power between the pigment and the resin, and the generation of deposits can be more effectively suppressed.

(Other additives)
In addition to the components described above, the ink of the present invention may further contain various additives as necessary. For example, solid humectants such as urea and urea derivatives, trimethylolethane, and trimethylolpropane can be used. Furthermore, a surfactant, an antifoaming agent, a preservative, an antifungal agent, and the like can be used to obtain an ink having desired physical properties. However, if the ink contains a surfactant having a high orientation rate to the pigment, the surfactant is likely to be selectively oriented at the location where the resin is detached from the pigment. As a result, a stable dispersed state cannot be maintained, and the ejection stability may decrease. Therefore, in the present invention, in order to obtain ejection stability, when a surfactant is used, the surfactant having a critical micelle concentration of an aqueous solution containing only the surfactant is 28 dyn / cm (mN / m) or more. It is preferable to select and use. At this time, the content (% by mass) of the surfactant in the ink is preferably 0.7% by mass or more and 1.0% by mass or less based on the total mass of the ink.

<Inkjet recording method>
The first and second inks of the present invention are preferably used in an ink jet recording method for recording on a recording medium by discharging ink by an ink jet recording method. Ink jet recording methods include a method of ejecting ink by applying mechanical energy to the ink, and a method of ejecting ink by applying thermal energy to the ink. The first and second inks of the present invention can obtain a remarkable effect particularly when used in an ink jet recording method using thermal energy.

<Ink cartridge>
The ink cartridge of the present invention is characterized in that it is provided with an ink storage portion that stores the first or second ink of the present invention.

<Recording unit>
The recording unit of the present invention includes an ink storage unit that stores the first or second ink of the present invention, and a recording head that discharges these inks. In particular, when the recording head is a recording unit that ejects ink by applying thermal energy to the ink, a remarkable effect can be obtained.

<Inkjet recording apparatus>
An ink jet recording apparatus according to the present invention includes an ink storage portion that stores the first or second ink of the present invention, and a recording head that discharges the ink. In particular, a remarkable effect can be obtained when the recording head is an ink jet recording apparatus that discharges ink by applying thermal energy to the ink.

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

  FIG. 2 is a perspective view of the ink jet recording apparatus. 3 and 4 are diagrams for explaining the internal mechanism of the ink jet recording apparatus. FIG. 3 is a perspective view from the upper right part, and FIG. 4 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 are sent to a nip portion including a paper feeding roller M2080 and a separation roller M2041 in a paper feeding unit including a paper feeding tray M2060 (FIGS. 3 and 4). reference). The recording medium is separated at the nip portion, and only the uppermost recording medium is conveyed. The recording medium sent to the conveyance unit is guided by the pinch roller holder M3000 and the paper guide flapper M3030, and is sent to the roller pair of the conveyance roller M3060 and the pinch roller M3070. A roller pair composed of a conveyance roller M3060 and a 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 (see FIGS. 3 and 4 above).

  When forming an image, the carriage unit has a recording head H1001 (see FIG. 5) disposed at a target image forming position, and ink is ejected onto the recording medium in accordance with a signal from the electric substrate E0014 (see FIG. 3). The The detailed configuration of the recording head H1001 will be described later. The main scanning in which the carriage M4000 (see FIG. 3) scans in the column direction while recording is performed by the recording head H1001, and the sub-scan in which the transport roller M3060 (see FIGS. 3 and 4) transports the recording medium in the row direction alternately. By repeating the above, an image is formed on the recording medium.

  Finally, the recording medium is sandwiched by the nip between the first paper discharge roller M3110 and the spur M3120 at the paper discharge unit (see FIG. 4), conveyed, and discharged to the paper discharge tray M3160 (see FIG. 2).

  The cleaning unit cleans the recording head H1001. When the pump M5000 (see FIG. 3) is operated in a state where the cap M5010 (see FIG. 3) is in close contact with the ejection port of the recording head H1001, the cleaning unit sucks ink or the like from the recording head H1001. Further, if the ink remaining in the cap M5010 is sucked with the cap M5010 opened, ink sticking and other harmful effects do not occur.

(Configuration of recording head)
The configuration of the head cartridge H1000 will be described (see FIG. 5). 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. The head cartridge H1000 is detachably mounted on the carriage M4000 (see FIG. 3).

  FIG. 5 is a diagram showing how the ink cartridge H1900 is mounted on the head cartridge H1000. The ink jet recording apparatus forms an image with, for example, yellow, magenta, cyan, black, red, green, and blue inks. Therefore, the ink cartridge H1900 is also prepared for seven colors independently. In the above, the ink of the present invention is used as at least one kind of ink. As shown in FIG. 5, each ink cartridge is attachable to and 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 (see FIG. 3).

  FIG. 6 is an exploded perspective view of the head cartridge H1000. The head cartridge H1000 includes a recording element substrate, a plate, an electric wiring substrate H1300, a tank holder H1500, a flow path forming member H1600, a filter H1700, a seal rubber H1800, and the like. The recording element substrate is composed of a first recording element substrate H1100 and a second recording element substrate H1101, and the plate is composed of a first plate H1200 and a second plate H1400.

  The first recording element substrate H1100 and the second recording element substrate H1101 are Si substrates, and a plurality of recording elements (nozzles) for ejecting ink are formed on one side thereof by a photolithography technique. An electric wiring such as Al for supplying electric power to each recording element is formed by a film forming technique, and a plurality of ink flow paths corresponding to individual recording elements are also formed by a photolithography technique. Further, an ink supply port for supplying ink to the plurality of ink flow paths is formed to open on the back surface.

  FIG. 7 is an enlarged front view illustrating the configuration of the first recording element substrate H1100 and the second recording element substrate H1101. H2000 to H2600 are printing element rows (hereinafter also referred to as nozzle rows) for supplying different inks. On the first recording element substrate H1100, nozzle rows for three colors, a nozzle row H2000 for yellow ink, a nozzle row H2100 for magenta ink, and a nozzle row H2200 for cyan ink, are formed. On the second recording element substrate H1101, nozzle rows for four colors, a red ink nozzle row H2300, a black ink nozzle row H2400, a green ink nozzle row H2500, and a blue ink nozzle row H2600, are formed. Yes.

Each nozzle row is composed of 768 nozzles arranged at an interval of 1,200 dpi (dot / inch; reference value) in the conveyance direction of the recording medium, and ejects about 2 picoliters of ink. The opening area at each discharge port is set to about 100 μm ² .

  Hereinafter, a description will be given with reference to FIGS. 5 and 6. The first recording element substrate H1100 and the second recording element substrate H1101 are bonded and fixed to the first plate H1200. Here, an ink supply port H1201 for supplying ink to the first recording element substrate H1100 and the second recording element substrate H1101 is formed. Further, a second plate H1400 having an opening is bonded and fixed to the first plate H1200. The second plate H1400 holds the electrical wiring substrate H1300 so that the electrical wiring substrate H1300 is electrically connected to the first recording element substrate H1100 and the second recording element substrate H1101.

  The electrical wiring substrate H1300 applies an electrical signal for ejecting ink from each nozzle formed on the first recording element substrate H1100 and the second recording element substrate H1101. The electric wiring board H1300 is arranged on the electric wiring corresponding to the first recording element substrate H1100 and the second recording element substrate H1101, and an external part for receiving an electric signal from the ink jet recording apparatus. And a signal input terminal H1301. The external signal input terminal H1301 is positioned and fixed on the back side of the tank holder H1500.

  In the tank holder H1500 that holds the ink cartridge H1900, a flow path forming member H1600 is fixed by, for example, ultrasonic welding to form an ink flow path H1501 that communicates from the ink cartridge H1900 to the first plate H1200. A filter H1700 is provided at the ink cartridge side end of the ink flow path H1501 that engages with the ink cartridge H1900, and can prevent dust from entering from the outside. Further, a seal rubber H1800 is attached to the engaging portion with the ink cartridge H1900 so that the ink can be prevented from evaporating from the engaging portion.

  Furthermore, as described above, the head cartridge H1000 is configured by bonding the tank holder portion and the recording head portion H1001 by bonding or the like. The tank holder portion includes a tank holder H1500, a flow path forming member H1600, a filter H1700, and a seal rubber H1800. The recording head portion H1001 includes a first recording element substrate H1100, a second recording element substrate H1101, a first plate H1200, an electric wiring substrate H1300, and a second plate H1400.

  Here, as an embodiment of the recording head, a thermal ink jet recording head that performs recording using an electrothermal transducer (recording element) that generates thermal energy for causing ink to cause film boiling in accordance with an electrical signal. Said. About this typical structure and principle, for example, what is performed using the basic principle disclosed in US Pat. Nos. 4,723,129 and 4,740,796 is preferable. . This method can be applied to both a so-called on-demand type and a continuous type.

  The thermal ink jet method is particularly effective when applied to an on-demand type. In the case of the on-demand type, at least one drive that applies a rapid temperature rise exceeding nucleate boiling corresponding to the recording information to the electrothermal transducer disposed corresponding to the liquid flow path holding the ink Apply a signal. As a result, thermal energy is generated in the electrothermal transducer, and film boiling occurs in the ink. As a result, bubbles in the ink corresponding to the drive signal on a one-to-one basis can be formed. At least one droplet is formed by ejecting ink through the ejection port by the growth and contraction of the bubbles. It is more preferable that the driving signal has a pulse shape, since the bubble grows and contracts immediately and appropriately, so that ink discharge with particularly excellent response can be achieved.

  The ink of the present invention is not limited to the thermal ink jet method, and can be preferably used in an ink jet recording apparatus using mechanical energy as described below. An ink jet recording apparatus having such a configuration includes a nozzle forming substrate having a plurality of nozzles, a pressure generating element made of a piezoelectric material and a conductive material disposed to face the nozzles, and ink filling the periphery of the pressure generating element. Become. Then, the pressure generating element is displaced by the applied voltage, and ink is ejected from the nozzle.

  As described above, the ink jet recording apparatus is not limited to one in which the recording head and the ink cartridge are separated from each other. Further, the ink cartridge is integrated with the recording head so as to be separable or non-separable and mounted on the carriage, and is provided at a fixed portion of the ink jet recording apparatus, and recording is performed via an ink supply member such as a tube. An ink may be supplied to the head. Further, when the ink cartridge is provided with a configuration for applying a preferable negative pressure to the recording head, the following configuration can be adopted. That is, a mode in which an absorber is disposed in the ink storage portion of the ink cartridge, or a mode in which a flexible ink storage bag and a spring portion that applies a biasing force in the direction of expanding the inner volume of the flexible ink storage bag are provided. It can be. The ink jet recording apparatus may take the form of a line printer in which recording elements are aligned over a range corresponding to the entire width of the recording medium, in addition to the serial type recording method described above.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. The present invention is not limited to these unless it exceeds the gist. In the following description, “parts” and “%” are based on mass unless otherwise specified.

<Preparation of pigment dispersion>
Each pigment dispersion was prepared according to the following procedure and composition. Table 1 shows the acid value and weight average molecular weight of the resin used for the preparation of each pigment dispersion, the type of resin (block polymer or random polymer), and the dispersion conditions (dispersion time and peripheral speed) for preparing the pigment dispersion. , And the content [%] of the pigment and resin in each pigment dispersion.

In addition, all the pigments used for the preparation of the pigment dispersions 1 to 18 were C.I. I. Pigment Violet 23 (product name: Hostaperm Violet RL SP; manufactured by Clariant). The hydrophilicity δm of this pigment was measured as follows. First, 0.1 g of the above pigment was added to a beaker containing a stirring bar and 50 ml of ion-exchanged water, and gently stirred to such an extent that vortexing was not possible. Here, acetone was added dropwise with stirring using a burette. The dripping amount A of acetone required for the floating pigment to get wet and settle was 6.3 [mL]. And from the following formula (3), the hydrophilicity δm of the pigment was calculated to be 21.9. In addition, 23.43 and 9.75 in following formula (3) are SP values (solubility parameter) of water and acetone.

(Preparation of pigment dispersion 1)
A pigment solution 1 was prepared by mixing 10 parts of the pigment, 9 parts of a dispersant, and 81 parts of ion-exchanged water. The dispersant was obtained by neutralizing an AB block polymer having an acid value of 250 and a weight average molecular weight of 6,000, synthesized by a conventional method using benzyl methacrylate and methacrylic acid as raw materials, with an aqueous potassium hydroxide solution. Resin A was used. This pigment solution 1 was charged into a circulation type bead mill, filled with 85 parts of 0.3 mm zirconia beads, and dispersed. At this time, pigment dispersion 1 was prepared with the dispersion time and peripheral speed shown in Table 1 respectively. Thereafter, coarse particles were removed by centrifugation. Furthermore, the pigment dispersion 1 having a pigment content (solid content) of 10% by mass and a resin A content of 9% by mass by pressure filtration with a micro filter having a pore size of 3.0 μm (manufactured by Fuji Film). Was prepared.

(Preparation of pigment dispersion 2)
The pigment content (solid content) is 10% by mass and the content of the resin A is 9% by mass in the same manner as the pigment dispersion 1 except that the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. Pigment dispersion 2 was prepared.

(Preparation of pigment dispersion 3)
The pigment content (solid content) is 10% by mass and the content of the resin A is 9% by mass in the same manner as the pigment dispersion 1 except that the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. Pigment dispersion 3 was prepared.

(Preparation of pigment dispersion 4)
The pigment content (solid content) is 10% by mass and the content of the resin A is 9% by mass in the same manner as the pigment dispersion 1 except that the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. Pigment dispersion 4 was prepared.

(Preparation of pigment dispersion 5)
A pigment solution 2 was prepared by mixing 10 parts of the pigment, 9 parts of a dispersant, and 81 parts of ion-exchanged water. The dispersant was obtained by neutralizing an AB type block polymer having an acid value of 250 and a weight average molecular weight of 1,500, which was synthesized by a conventional method using benzyl methacrylate and methacrylic acid as raw materials, with an aqueous potassium hydroxide solution. Resin B was used. The pigment content (solid content) is 10% in the same manner as in the pigment dispersion 1 except that the pigment solution 2 is used instead of the pigment solution 1 and the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. %, And pigment dispersion 5 having a resin B content of 9% by mass was prepared.

(Preparation of pigment dispersion 6)
A pigment solution 3 was prepared by mixing 10 parts of the pigment, 9 parts of a dispersant, and 81 parts of ion-exchanged water. The dispersant was obtained by neutralizing an AB type block polymer having an acid value of 250 and a weight average molecular weight of 2,000, synthesized by a conventional method using benzyl methacrylate and methacrylic acid as raw materials, with an aqueous potassium hydroxide solution. Resin C was used. The pigment content (solid content) is 10% in the same manner as the pigment dispersion 1 except that the pigment solution 3 is used instead of the pigment solution 1 and the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. %, And pigment dispersion 6 having a resin C content of 9% by mass was prepared.

(Preparation of pigment dispersion 7)
A pigment solution 4 was prepared by mixing 10 parts of the pigment, 9 parts of a dispersant, and 81 parts of ion-exchanged water. The dispersant was obtained by neutralizing an AB type block polymer having an acid value of 250 and a weight average molecular weight of 5,000, synthesized by a conventional method using benzyl methacrylate and methacrylic acid as raw materials, with an aqueous potassium hydroxide solution. Resin D was used. The pigment content (solid content) is 10% in the same manner as in the pigment dispersion 1 except that the pigment solution 4 is used instead of the pigment solution 1 and the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. %, And pigment dispersion 7 having a resin D content of 9% by mass was prepared.

(Preparation of pigment dispersion 8)
The pigment content (solid content) is 10% by mass and the content of the resin A is 9% by mass in the same manner as the pigment dispersion 1 except that the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. A pigment dispersion 8 was prepared.

(Preparation of pigment dispersion 9)
The pigment content (solid content) is 10% by mass and the content of the resin A is 9% by mass in the same manner as the pigment dispersion 1 except that the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. A pigment dispersion 9 was prepared.

(Preparation of pigment dispersion 10)
The pigment content (solid content) is 10% by mass and the content of the resin A is 9% by mass in the same manner as the pigment dispersion 1 except that the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. A pigment dispersion 10 was prepared.

(Preparation of pigment dispersion 11)
The pigment content (solid content) is 10% by mass and the content of the resin A is 9% by mass in the same manner as the pigment dispersion 1 except that the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. Pigment dispersion 11 was prepared.

(Preparation of pigment dispersion 12)
The pigment content (solid content) is the same as that of the pigment dispersion 1 except that the pigment solution 4 is used in place of the pigment solution 1 and the dispersion time and peripheral speed are set to the values shown in Table 1, respectively. A pigment dispersion 12 having 10% by mass and a resin D content of 9% by mass was prepared.

(Preparation of pigment dispersion 13)
A pigment solution 5 was prepared by mixing 10 parts of the pigment, 9 parts of a dispersant, and 81 parts of ion-exchanged water. The dispersant was obtained by neutralizing an AB type block polymer having an acid value of 250 and a weight average molecular weight of 2,000, synthesized by a conventional method using benzyl methacrylate and methacrylic acid as raw materials, with an aqueous potassium hydroxide solution. Resin E was used. The pigment content (solid content) is 10% in the same manner as the pigment dispersion 1 except that the pigment solution 5 is used instead of the pigment solution 1 and the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. %, And a pigment dispersion 13 having a resin E content of 9% by mass was prepared.

(Preparation of pigment dispersion 14)
A pigment solution 6 was prepared by mixing 10 parts of the pigment, 9 parts of a dispersant, and 81 parts of ion-exchanged water. The dispersant was obtained by neutralizing an AB type block polymer having an acid value of 250 and a weight average molecular weight of 1,500, which was synthesized by a conventional method using benzyl methacrylate and methacrylic acid as raw materials, with an aqueous potassium hydroxide solution. Resin F was used. The pigment content (solid content) is 10% in the same manner as in the pigment dispersion 1 except that the pigment solution 6 is used instead of the pigment solution 1 and the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. %, And a pigment dispersion 14 having a resin F content of 9% by mass was prepared.

(Preparation of pigment dispersion 15)
A pigment solution 7 was prepared by mixing 10 parts of the pigment, 2 parts of a dispersant, and 88 parts of ion-exchanged water. The resin A was used as the dispersant. The pigment content (solid content) is 10% in the same manner as the pigment dispersion 1 except that the pigment solution 7 is used instead of the pigment solution 1 and the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. %, And a pigment dispersion 15 having a resin A content of 2% by mass was prepared.

(Preparation of pigment dispersion 16)
A pigment solution 8 was prepared by mixing 10 parts of the pigment, 2 parts of a dispersant, and 88 parts of ion-exchanged water. The resin D was used as the dispersant. The pigment content (solid content) is 10% in the same manner as the pigment dispersion 1 except that the pigment solution 8 is used instead of the pigment solution 1 and the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. %, And a pigment dispersion 16 having a resin D content of 2 mass% was prepared.

(Preparation of pigment dispersion 17)
A pigment solution 9 was prepared by mixing 10 parts of the pigment, 9 parts of a dispersant, and 81 parts of ion-exchanged water. The dispersant G is a resin G obtained by neutralizing a random polymer having an acid value of 250 and a weight average molecular weight of 6,000, synthesized by a conventional method using benzyl methacrylate and methacrylic acid as raw materials, with an aqueous potassium hydroxide solution. Was used. The pigment content (solid content) is 10% in the same manner as in the pigment dispersion 1 except that the pigment solution 9 is used instead of the pigment solution 1 and the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. %, And a pigment dispersion 17 having a resin G content of 9% by mass was prepared.

(Preparation of pigment dispersion 18)
A pigment solution 10 was prepared by mixing 10 parts of the pigment, 9 parts of a dispersant, and 81 parts of ion-exchanged water. The dispersant is a resin H obtained by neutralizing a random polymer having an acid value of 250 and a weight average molecular weight of 5,000, synthesized by a conventional method using benzyl methacrylate and methacrylic acid as raw materials, with an aqueous potassium hydroxide solution. Was used. The pigment content (solid content) is 10% in the same manner as the pigment dispersion 1 except that the pigment solution 10 is used instead of the pigment solution 1 and the dispersion time and the peripheral speed are set to the values shown in Table 1, respectively. %, And a pigment dispersion 18 having a resin H content of 9% by mass was prepared.

<First method>
(Preparation of the first ink according to the first method)
Each component shown in the upper part of the following Table 2 and Table 3 was mixed and sufficiently stirred, and then pressure filtered with a micro filter (manufactured by Fuji Film) having a pore size of 1.0 μm to prepare inks 1 to 18. In Tables 2 and 3, in order to clarify the configuration of each ink, the content of each of the pigment, resin, water, and water-soluble organic solvent in the ink, and the resin content / The pigment content value and the water-soluble organic solvent content / pigment content value are also shown. Here, the content of the water-soluble organic solvent does not include the content of the surfactant.

(Evaluation of ink according to the first method)
(1) Continuous ejection stability Each ink obtained above was filled in an ink cartridge and mounted on an inkjet recording apparatus PIXUS990i (manufactured by Canon) that ejects ink by the action of thermal energy. Thereafter, 400 solid images of 19 cm × 26 cm were recorded on an A4 size PPC paper office planner (manufactured by Canon). At this time, the nozzle check pattern of PIXUS990i was recorded after the 200th and 400th sheets were recorded. The obtained nozzle check pattern was visually observed to evaluate continuous discharge stability. The evaluation criteria for continuous discharge stability are as follows. The evaluation results are shown in Table 4.

A: The nozzle check pattern is not disturbed and can be recorded normally.
B: There is a slight disturbance in the nozzle check pattern, but there is no non-ejection.
C: No ejection or disturbance is clearly confirmed in the nozzle check pattern, and normal recording cannot be performed.

(2) Deposits Each ink obtained above was filled in an ink cartridge and mounted on an ink jet recording apparatus PIXUS990i (manufactured by Canon) that discharges ink by the action of thermal energy. Thereafter, 400 solid images of 19 cm × 26 cm were recorded on an A4 size PPC paper office planner (manufactured by Canon). At this time, after recording the 200th sheet and the 400th sheet, the recording head was removed from the ink jet recording apparatus, and the inside of the nozzle was observed with an optical microscope to check for the presence of deposits. Further, 50 arbitrary nozzles are selected before recording and after recording of the 200th and 400th sheets, 40,000 inks are ejected from each nozzle, and the mass per one ink droplet before and after the ejection is determined. It was determined as follows. First, the change in the mass of the ink cartridge before and after 40,000 ejections was measured, and the mass per ink droplet was measured from the number of all ejected ink droplets. Then, the change rate of the mass per drop of ink before recording and on the 200th and 400th sheets was obtained and evaluated using this. The evaluation criteria for deposits are as follows. The evaluation results are shown in Table 4.

A: There is almost no deposit.
B: It was confirmed that a small amount of deposit was present on the nozzle wall, but the rate of change in mass per drop of ink is the same as before recording and 200th recording, or before recording and 400th recording. In comparison, it was less than 5.0%.
C: It is confirmed that deposits exist entirely in the nozzles, and the rate of change in mass per drop of ink is the same as before recording and 200th recording, or before recording and 400th recording. Compared to the time, it was 5.0% or more.

(3) Fixing recovery property Each ink obtained above was filled in an ink cartridge and mounted on an ink jet recording apparatus PIXUS990i (manufactured by Canon) that discharges ink by the action of thermal energy. Thereafter, 400 solid images of 19 cm × 26 cm were recorded on an A4 size PPC paper office planner (manufactured by Canon). Thereafter, the ink cartridge was left mounted for 2 weeks in an environment of a room temperature of 35 ° C. and a humidity of 10% with the ink cartridge mounted on the ink jet recording apparatus. Then, after performing a recovery operation appropriately, a nozzle check pattern of PIXUS990i was recorded. The obtained nozzle check pattern was visually observed, and the state of recording with the ink ejected from each nozzle was confirmed to evaluate the fixing recoverability. The evaluation criteria for fixing recovery are as follows. The evaluation results are shown in Table 4.

A: By performing manual suction within two times, all nozzles are recovered to be able to discharge without problems.
B: All nozzles ejected by performing manual suction three times or more, but the nozzle check pattern was slightly disturbed in some nozzles.
C: There are some nozzles that do not discharge even when manual suction is performed five times or more.

As can be seen from Table 4, the evaluation results of the deposits of Example 3 and Reference Example 4 were the same. However, when the amount of deposit generated after 400 solid images of 19 cm × 26 cm were recorded was compared, the amount of deposit generated in Reference Example 4 was small. On the other hand, Example 3 was more excellent in fixing recovery than Reference Example 4. Further, the amount of deposits generated after recording 400 sheets in Reference Examples 10 and 11 was slightly larger than in the other examples. Moreover, the evaluation results of the continuous discharge stability in Reference Examples 9 and 10 were the same as the evaluation results of the continuous discharge stability in examples other than Examples 3 and 6 and Reference Example 15. However, since the condition of the face surface after the test was relatively wet, the degree of twisting of the nozzle check pattern was slightly inferior. Furthermore, the inks of Reference Examples 11 and 12 (inks 11 and 12) were put in Teflon (registered trademark) containers, sealed, and stored in an oven kept at a temperature of 60 ° C. for 1 month. The particle size before and after storage was measured using a particle size measuring device ELS8000 (manufactured by Otsuka Electronics), and the change rate of the particle size of each ink was measured. As a result, the change rate of the particle size of Reference Example 12 was smaller than the change rate of the particle size of Reference Example 11. As can be seen from Table 4, the evaluation results of deposits and adhesion recovery are particularly excellent in Examples 3 and 6 and Reference Example 16, and there is almost no deposit even in the 400th sheet, and the adhesion recovery is excellent. It was.

<Second method>
(Preparation of the second ink according to the second method)
Each component shown in the upper part of the following Tables 5 and 6 was mixed and sufficiently stirred, and then pressure filtered through a micro filter (manufactured by Fuji Film) having a pore size of 1.0 μm to prepare inks 19 to 38. In Tables 5 and 6, in order to clarify the constitution of each ink, the content of each of the pigment, resin, water, and water-soluble organic solvent in the ink, and the resin content / The value of the pigment content is also shown. Here, the content of the water-soluble organic solvent does not include the content of the surfactant.

(Measurement of absorbance)
About the diluted ink obtained by diluting each ink obtained above with ion-exchange water 1,500 times (mass times), using a spectrophotometer (trade name: U-3300, manufactured by Hitachi, Ltd.), Absorbance was measured in the range of 400 nm to 700 nm. The measurement results are shown in Table 7. As can be seen from Table 7, inks 19 to 34 are inks of examples satisfying the requirements defined by the second method of the present invention. Inks 35 to 38 are inks of comparative examples.

(Evaluation of the second ink according to the second method)
Each ink obtained above was evaluated in the same manner as described above for continuous ejection stability, deposits, and adhesion recovery. The evaluation results are shown in Table 8.

As can be seen from Table 8, in Reference Examples 22 and 23, Example 24 and Reference Examples 28-31 , deposits were hardly generated and the results were very good. In particular, in Example 24 (ink 26), the rate of change in mass per drop of ink was 1% or less before and after the recording of 400 19 cm × 26 cm solid images. This can be said to be better than about 2.7% in Reference Example 22 (ink 24) and about 2.2% in Reference Examples 23 and 29 (inks 25 and 31). Moreover, the evaluation results of the deposits after recording 400 sheets in Reference Examples 17 to 21 and after recording 200 sheets in Comparative Examples 3 and 5 were all B. However, the amount of deposits after recording 400 sheets in Reference Examples 17 to 21 was clearly smaller than the amount of deposits after recording 200 sheets in Comparative Examples 3 and 5. In addition, the evaluation result of the continuous discharge stability of Reference Example 29 is A, and the deterioration of the discharge stability due to the deposit was hardly observed. However, compared with the other examples in which the continuous ejection stability is A, the state of the face surface after the completion of the test of Reference Example 29 was relatively wet, so that the degree of deflection of the nozzle check pattern was slightly inferior. It was. Further, the inks of Reference Examples 27 and 28 (inks 29 and 30) were put in Teflon (registered trademark) containers, sealed, and stored in an oven kept at a temperature of 60 ° C. for one month. The particle size before and after storage was measured using a particle size measuring device ELS8000 (manufactured by Otsuka Electronics), and the change rate of the particle size of each ink was measured. As a result, the change rate of the particle size of Reference Example 28 was smaller than the change rate of the particle size of Reference Example 27. Furthermore, the inks of Reference Examples 30 and 31 (inks 32 and 33) were put in Teflon (registered trademark) containers, sealed, and stored in an oven maintained at a temperature of 60 ° C. for 1 month. The particle size before and after storage was measured using a particle size measuring device ELS8000 (manufactured by Otsuka Electronics), and the change rate of the particle size of each ink was measured. As a result, the change rate of the particle diameter of Reference Example 31 was smaller than that of Reference Example 30.

It is a schematic diagram which shows the mechanism of deposit generation. 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. It is a disassembled perspective view of a head cartridge. FIG. 6 is a front view showing a recording element substrate in the head cartridge. C. I. It is a graph which shows an example of the absorption spectrum of pigment violet 23.

Explanation of symbols

1: Heater 2: Ink flow path 3: Ejection port 4: Aggregate 5: Ink droplet 6: Bubble M2041: Separation roller M2060: Paper feed tray M2080: Paper feed roller M3000: Pinch roller holder M3030: Paper guide flapper M3040: Platen M3060: conveying roller M3070: pinch roller M3110: paper discharge roller M3120: spur M3160: paper discharge tray M4000: carriage M5000: pump M5010: cap E0002: LF motor E0014: electric substrate H1000: head cartridge H1001: print head H1100: first Recording element substrate H1101: second recording element substrate H1200: first plate H1201: ink supply port H1300: electrical wiring substrate H1301: external signal input terminal H1400: second plate H 500: Tank holder H1501: Ink channel H1600: Channel forming member H1700: Filter H1800: Seal rubber H1900: Ink cartridge H2000: Yellow nozzle column H2100: Magenta nozzle column H2200: Cyan nozzle column H2300: Red nozzle column H2400: Black nozzle column H2500: Green nozzle row H2600: Blue nozzle row

Claims (9)

A water-based ink comprising a pigment, a resin for dispersing the pigment, and a water-soluble organic solvent, which is used in an ink jet recording method for discharging ink from a recording head by the action of thermal energy,
The pigment is C.I. I. Pigment violet 23,
The resin for dispersing the pigment has a weight average molecular weight of 2,000 or more and 5,000 or less ,
Content in the ink of the previous SL-soluble organic solvent, based on the total mass of the ink state, and are 17.5 wt% to 5.0 wt% or more,
The water-soluble organic solvent contains polyethylene glycol having a weight average molecular weight of 1,000 or more .   The water-based ink according to claim 1, wherein the resin is a block polymer. The water-soluble organic solvent include glycerin, ethylene glycol, diethylene glycol,及 Beauty, aqueous ink according to claim 1 or 2 comprising at least one member selected from the group consisting of 2-pyrrolidone. Furthermore, the light absorption characteristics of the ink each have a maximum absorption wavelength in a wavelength range of 530 nm to 540 nm and a wavelength range of 550 nm to 570 nm.
The relationship between the absorbance (A) at the maximum absorption wavelength in the range of 530 nm to 540 nm and the absorbance (B) at the maximum absorption wavelength in the range of 550 nm to 570 nm is the condition of the following formula (1): the aqueous ink according to any one of claims 1 to 3 satisfies the.

The light absorption characteristics of the ink further have a maximum absorption wavelength in a wavelength range of 530 nm to 540 nm and a wavelength range of 620 nm to 630 nm,
The relationship between the absorbance (A) at the maximum absorption wavelength in the range of 530 nm to 540 nm and the absorbance (C) at the maximum absorption wavelength in the range of 620 nm to 630 nm satisfies the condition of the following formula (2). The aqueous ink according to claim 4, which is filled.

6. An ink jet recording method for recording on a recording medium by discharging ink by the action of thermal energy, wherein the ink is the water-based ink according to any one of claims 1 to 5. . An ink cartridge comprising an ink container for containing ink, wherein the ink is the water-based ink according to any one of claims 1 to 5 . The water-based ink according to any one of claims 1 to 5 , wherein the ink is a recording unit including an ink storage portion that stores ink and a recording head for discharging ink by the action of thermal energy. A recording unit characterized by being. The water-based ink according to any one of claims 1 to 5 , wherein the ink is an ink jet recording apparatus including an ink containing portion for containing ink and a recording head for discharging ink by the action of thermal energy. An ink jet recording apparatus characterized by the above.

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