JP5932199B2 - Ink set, ink jet recording method, ink cartridge, recording unit, ink jet recording method, and water-based ink - Google Patents

Description

  The present invention relates to an aqueous ink, an ink set, an ink jet recording method, an ink cartridge, a recording unit, and an ink jet recording method.

  In recent years, it has been demanded to improve the image quality of an image formed on a recording medium, particularly plain paper, by an ink jet recording method, specifically, the gradation and color uniformity of an image. For example, the gradation can be improved by reducing the area per dot formed by ink on the recording medium. Conversely, if the area per dot is large, multiple dots are more likely to be connected. Therefore, even if the amount of ink applied per unit area is increased or decreased, the area that the ink covers the surface of the recording medium is strictly controlled. You may not be able to. In addition, since a plurality of dots are easily connected, ink bleeding on the recording medium is likely to occur.

  In order to solve such a problem, there is a proposal for suppressing ink bleeding on a recording medium by increasing the static surface tension (so-called “surface tension”) of the ink. For example, there is a proposal for suppressing bleeding by setting the surface tension of ink at 20 ° C. to 45 mN / m or more (see Patent Document 1). In addition, there is a proposal for suppressing bleeding by setting the ink surface tension to 40 mN / m or more (see Patent Document 2).

  In addition, as a technique for controlling ink bleeding or penetration into a recording medium, proposals have been made focusing on the dynamic surface tension of the ink. For example, bleeding is suppressed by setting the surface tension at a bubble cycle T (second / bubble) ≦ 0.2 to 40 mN / m or more, and the surface tension at a bubble cycle T (second / bubble)> 1 is set to less than 50 mN / m. There is a proposal for improving discharge reliability by doing (see Patent Document 3).

  In addition, there is a proposal relating to improving the ejection reliability by setting the ink dry viscosity to 100 mPa · s or less and defining the characteristics of dynamic surface tension in a specific lifetime (see Patent Document 4). Specifically, bleeding is suppressed by setting the dynamic surface tension at a lifetime of 10 milliseconds to 45 mN / m or more, and quick drying is improved by setting the dynamic surface tension at a lifetime of 1000 ms to 35 mN / m or less. It is described.

Further, as a technique for controlling bleeding and penetration between different colors on plain paper, a proposal has been made focusing on the relationship between dynamic surface tensions of a plurality of inks constituting an ink set (see Patent Document 5). . That is, in an ink set composed of black, yellow, magenta, and cyan inks, the dynamic surface of each ink at the same lifetime within a temperature range of 25 ° C. and a lifetime of 30 milliseconds to 1000 milliseconds according to the maximum bubble pressure method. The tension is defined as follows. (1) Yellow ink is more than black ink. (2) The difference between yellow ink and black ink is 5 mN / m or less. (3) The difference between yellow ink and magenta ink and the difference between yellow ink and cyan ink are both 3 mN / m or more. (4) Magenta ink and cyan ink are lower than black ink. According to these regulations, it is described that mixing is prevented at the boundary between different colors on plain paper.
JP 63-213581 A JP 2004-83621 A JP-A-9-296139 Japanese Patent Laid-Open No. 2003-231838 JP 2006-63322 A

  However, as in the inventions described in Patent Document 1 and Patent Document 2 mentioned above, it is not possible to suppress bleeding by simply increasing the static surface tension of the ink, or the surface of the recording medium is uniformly wetted. Inability to do so may reduce the color uniformity in the image. In addition, when the static surface tension of the ink is increased, the permeability of the ink into the recording medium is reduced. Therefore, it takes a long time until the ink has completely penetrated into the recording medium, and ink transfer may occur. is there.

  In the inventions described in Patent Documents 3 to 5 mentioned above, an attempt is made to control bleeding and penetration by paying attention to a change in the dynamic surface tension of the ink. However, as a result of the study by the present inventors, in the definition of the dynamic surface tension described in Patent Documents 3 to 5, when plain paper or the like is used as a recording medium, gradation is maintained while maintaining color uniformity in an image. It was not possible to improve the sex. That is, when plain paper or the like is used as the recording medium, the lateral spread of the ink (gradation) and color uniformity (uniform wetting of the ink on the surface of the recording medium) are appropriately controlled. There was no ink that could form ideal dots.

  Therefore, when using plain paper or the like as the recording medium, the present inventors appropriately control the dynamic surface tension of the ink so that the behavior from when the ink is applied to the recording medium until the permeation ends is obtained. Attention was paid to an ink that can solve the above-mentioned problems. As a result, it has been found that, even when using plain paper or the like as a recording medium, a new problem arises when using an ink set containing the ink, even if the ink provides an excellent image. Specifically, when an image is formed on a recording medium having an ink receiving layer using an ink set containing the ink, bleeding that does not occur on a recording medium such as plain paper is in an unexpectedly remarkable state. I found it to happen.

  Accordingly, a first object of the present invention is to provide an ink set that can suppress bleeding in a recording medium or the like having an ink receiving layer in an ink set containing ink with controlled dynamic surface tension. A second object of the present invention is to provide a recording medium having an ink receiving layer in an ink set containing an aqueous ink capable of improving gradation while maintaining color uniformity when using plain paper or the like as a recording medium. It is an object of the present invention to provide an ink set that can suppress bleeding in the ink. 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 method using the water-based ink constituting the ink set. Another object of the present invention is to provide an aqueous ink for use in an ink set capable of suppressing bleeding in a recording medium having an ink receiving layer.

The above object is achieved by the present invention described below. That is, the ink set according to this onset Ming, while being composed of only a plurality of aqueous inks containing a dye, an ink set used for recording on a recording medium having an ink-receiving layer, said ink set Comprises a first aqueous ink containing at least a dye and a surfactant, the surfactant in the first aqueous ink is a polyoxyethylene alkyl ether, and a first aqueous ink The content (% by mass) of the surfactant in the ink is 0.30% by mass or more and 1.5% by mass or less based on the total mass of the ink, and the first aqueous ink has the following (1 ) To (3), the lightness of the first water-based ink and at least one water-based ink other than the first water-based ink included in the ink set is relatively high. Dynamic surface tension gamma _a at a lifetime of 500m seconds have ink A (mN / m), the dynamic surface tension gamma _b at a lifetime of 500m sec lightness is relatively low ink B is (mN / m), -5 ≦ (γ _a −γ _b ) ≦ 3 is satisfied. (1) The dynamic surface tension at a lifetime of 50 milliseconds is 42 mN / m or more and less than 49 mN / m. (2) The dynamic surface tension at a lifetime of 500 milliseconds is 28 mN / m or more and 38 mN / m or less. (3) The difference between the dynamic surface tension at a lifetime of 50 milliseconds and the dynamic surface tension at a lifetime of 500 milliseconds is 7 mN / m or more.

The ink set according to another embodiment of the present invention, an ink set used to carry out while being composed of only three or more kinds of water-based ink you containing a dye, a recording medium having an ink-receiving layer The ink set includes at least a first aqueous ink containing a dye and a surfactant, and the surfactant in the first aqueous ink is a polyoxyethylene alkyl ether. In addition, the content (% by mass) of the surfactant in the first aqueous ink is 0.30% by mass or more and 1.5% by mass or less based on the total mass of the ink, and the first aqueous ink is used. The ink satisfies the following conditions (1) to (3), and lightness is relatively high among two types of water-based inks arbitrarily selected from at least three types of water-based inks constituting the ink set. Dynamic surface tension gamma _a at a lifetime of 500m sec link A (mN / m), the dynamic surface tension gamma _b at a lifetime of 500m sec lightness is relatively low ink B is (mN / m), the ink set In all combinations in which any two types of water-based inks are selected from at least three types of water-based inks constituting the above, a relationship of −5 ≦ (γ _a −γ _b ) ≦ 3 is established. (1) The dynamic surface tension at a lifetime of 50 milliseconds is 42 mN / m or more and less than 49 mN / m. (2) The dynamic surface tension at a lifetime of 500 milliseconds is 28 mN / m or more and 38 mN / m or less. (3) The difference between the dynamic surface tension at a lifetime of 50 milliseconds and the dynamic surface tension at a lifetime of 500 milliseconds is 7 mN / m or more.

  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 a water-based ink constituting the ink set.

  An ink cartridge according to another embodiment of the present invention is an ink cartridge having an ink containing portion for containing ink, wherein the ink contained in the ink containing portion is a water-based ink constituting the ink set. It is characterized by being.

  According to another aspect of the present invention, there is provided a recording unit including an ink storage portion that stores ink and a recording head that discharges ink, wherein the ink stored in the ink storage portion is It is the water-based ink which comprises this ink set.

  An ink jet recording apparatus according to another embodiment of the present invention is an ink jet recording apparatus that includes an ink storage portion that stores ink and a recording head that discharges ink, and the ink stored in the ink storage portion. A water-based ink constituting the ink set.

  ADVANTAGE OF THE INVENTION According to this invention, the ink set which can suppress bleeding in the recording medium etc. which have an ink receiving layer in the ink set containing the ink by which dynamic surface tension was controlled can be provided. In addition, according to the present invention, when plain paper or the like is used as a recording medium, bleeding in a recording medium or the like having an ink receiving layer is achieved in an ink set including an aqueous ink that can improve gradation while maintaining color uniformity. An ink set that can be suppressed can be provided. In addition, according to the present invention, it is possible to provide an ink jet recording method, an ink cartridge, a recording unit, and an ink jet recording method using the water-based ink constituting the ink set. In addition, according to the present invention, it is possible to provide an aqueous ink for use in an ink set that can suppress bleeding in a recording medium or the like having an ink receiving layer.

  Hereinafter, the present invention will be described in more detail with reference to the best mode for carrying out the invention. In the following description, the water-based ink may be referred to as “ink”, and the first water-based ink may be referred to as “first ink”. In addition, bleeding in the present invention refers to unintentional blurring that occurs at the boundary between these images when images formed using a plurality of dye-containing inks are adjacent to each other. It is.

  First, the maximum bubble pressure method used for measuring the dynamic surface tension in the present invention will be described. The maximum bubble pressure method is a method of measuring the maximum pressure required to release bubbles formed at the tip of a probe (capillary tube) immersed in the liquid to be measured, and determining the dynamic surface tension from this maximum pressure. It is. In the maximum bubble pressure method, the lifetime is the time when a bubble is formed at the tip of the probe, from the point when a new bubble surface is formed after the bubble is separated from the tip. This is the time until the radius of curvature equals the radius of the probe tip. The dynamic surface tension in the present invention is a value measured at 25 ° C.

  First, the first problem of the present invention, that is, bleeding that occurs remarkably when an image is formed on a recording medium or the like having an ink receiving layer using an ink set containing ink with controlled dynamic surface tension. The suppression will be described below. In order to examine the bleeding, the present inventors prepared various inks having different characteristics in which the dynamic surface tension changes, and studied using these inks. As a result, depending on the characteristics of the dynamic surface tension of the ink, it was found that when an image is formed on a recording medium having an ink receiving layer using an ink set containing the ink, remarkable bleeding occurs. Specifically, in an ink set including an ink in which the dynamic surface tension greatly changes such that the difference in dynamic surface tension between the lifetime of 50 milliseconds and the lifetime of 500 milliseconds is 7 mN / m or more, it is remarkable as expected. It has been found that bleeding occurs in this state.

  Conventionally, it is generally known that the static surface tensions of a plurality of inks are made uniform in order to make the permeability to a recording medium uniform, and in fact, this can suppress bleeding. However, when an ink whose dynamic surface tension changes greatly and an ink having a uniform static surface tension are used as an ink set, bleeding occurs significantly when an image is formed on a recording medium having an ink receiving layer. Accordingly, the present inventors have examined the reason why bleeding occurs particularly remarkably in a recording medium having an ink receiving layer.

  First, consider the mechanism by which bleeding occurs. Since plain paper has many relatively large voids, ink is applied to wet the surface of the plain paper, so that the ink is taken into the voids and the movement of the ink is restricted to some extent. For this reason, when plain paper or the like is used as the recording medium, the influence of the physical property relationship of the plurality of inks on the bleeding is limited. That is, when plain paper or the like is used as a recording medium, in an ink set composed of a plurality of inks, the wettability between each ink and plain paper and the degree of bleeding in each ink can be appropriately determined. It is a very important factor to suppress bleeding.

  On the other hand, a recording medium having an ink receiving layer has very small voids, and the voids exist as pores. Therefore, penetration of ink into the recording medium having an ink receiving layer occurs due to capillary action. For this reason, the phenomenon is greatly different from the case of using plain paper or the like as a recording medium.

  The inventors of the present invention have studied the behavior from when ink is applied to the recording medium until it permeates when a recording medium having an ink receiving layer is used. As described above, the penetration of the ink into the recording medium having the ink receiving layer occurs by capillary action. In general, it is known that the capillary force is proportional to the surface tension of the liquid when the liquid has sufficient wettability with respect to the wall surface of the capillary. Therefore, in order to suppress the bleeding that occurs remarkably when using a recording medium having an ink receiving layer, the static surface tensions of a plurality of inks constituting the ink set can be aligned as in the conventional knowledge. It will be good. However, in an ink set including an ink whose dynamic surface tension greatly changes, as described above, bleeding occurs in an unexpectedly remarkable state, and thus it is understood that this model is not applicable.

  The present inventors considered this phenomenon as follows. When the ink penetrates into the gap of the recording medium having the ink receiving layer, the ink moves at the place where the gas-liquid interface of the ink and the wall surface of the gap of the recording medium come into contact, that is, where the capillary force is developed. It is always updated while you are. For this reason, it is considered that the surface tension that expresses the capillary force may correspond to the dynamic surface tension in a certain lifetime rather than the static surface tension. Under such a hypothesis, the present inventors use various ink sets including inks having different characteristics in which the dynamic surface tension changes, and the ink moves through the voids of the recording medium having the ink receiving layer. The lifetime of dynamic surface tension affecting the capillary force during the period was investigated. As a result, it was found that the dynamic surface tension at the lifetime of 500 milliseconds is more dominant than the static surface tension of the ink. More specifically, in two types of inks, ink flows from an ink having a low dynamic surface tension at a lifetime of 500 milliseconds toward an ink having a high dynamic surface tension at a lifetime of 500 milliseconds, and bleeding occurs. I found out that

  That is, when a plurality of inks come into contact with each other in a state where the penetration into the recording medium having the ink receiving layer has not ended, the following phenomenon occurs. Specifically, penetrable, ie, ink with a relatively high dynamic surface tension at a lifetime of 500 milliseconds, “draws” ink with a low permeability, ie, a relatively low dynamic surface tension at a lifetime of 500 milliseconds. "This happens. In this way, bleeding occurs.

  For this reason, in order to suppress bleeding, it is ideal to make the dynamic surface tensions of the two types of inks equal in the lifetime of 500 milliseconds. However, when the difference in dynamic surface tension between the two inks at a lifetime of 500 milliseconds is very small, it is considered that bleeding that is substantially visible can be prevented.

Therefore, the present inventors examined the relationship between the threshold value of the difference in dynamic surface tension and the degree of bleeding at a lifetime of 500 milliseconds using various ink sets. As a result, it was found that in order to suppress bleeding that can be substantially visually confirmed, the difference in dynamic surface tension between the two inks at a lifetime of 500 milliseconds should be 3 mN / m or less. Furthermore, when the present inventors examined, the relationship of the tint between inks is also related to the occurrence of bleeding, and among the three attributes of color (hue, lightness, saturation) that quantitatively represent the tint. , It was found that brightness was greatly related. Specifically, the dynamic surface tension γ _a (mN / m) of the ink A having a relatively high lightness at a lifetime of 500 milliseconds, and the dynamic surface tension γ of the ink B having a relatively low lightness at a lifetime of 500 milliseconds. _b (mN / m). At this time, it was found that bleeding can be suppressed when the γ _a (mN / m) and the γ _b (mN / m) satisfy the condition of −5 ≦ (γ _a −γ _b ) ≦ 3. In the present invention, −3 ≦ (γ _a −γ _b ) ≦ 3 is more preferable, and it is particularly preferable that −3 <(γ _a −γ _b ) <3.

  This means that the threshold value of the difference in dynamic surface tension at the lifetime of 500 milliseconds of the two inks that can suppress bleeding differs depending on the relative relationship between the lightnesses of the two inks. This is because bleeding that occurs when ink having a relatively high lightness flows toward ink having a relatively low lightness is difficult to visually recognize, so the difference in dynamic surface tension at a lifetime of 500 milliseconds is somewhat large. This is because it is acceptable. On the other hand, since bleeding that occurs when an ink having a relatively low brightness flows toward an ink having a relatively high brightness is easily recognized visually, there is a difference in dynamic surface tension at a lifetime of 500 milliseconds. This is because it is necessary to control to be small.

  In the present invention, the lightness measurement needs to be performed with the same recording medium and recording duty for each ink constituting the ink set. As the recording medium, any recording medium having an ink receiving layer that can be applied to a normal ink jet recording apparatus can be used. Then, using each ink constituting the ink set, a solid image with a uniform ink application amount is formed on the recording medium, and a color value is measured with a spectrophotometer or the like to obtain a brightness value. Can do. When forming the solid image, it is preferable that the amount of ink applied is sufficient to cover the entire surface of the recording medium. In the present invention, for example, PR-101 (manufactured by Canon) can be used as a recording medium having an ink receiving layer. The color measurement can be performed using, for example, a spectrophotometer (trade name: Spectrolino; manufactured by Gretag Macbeth). Further, the amount of ink applied is preferably about 10 ng of ink applied per pixel at a resolution of 600 ppi, for example. Of course, the present invention is not limited to these recording media, spectrophotometers, and ink application amounts.

  The inventors of the present invention have examined the conditions defined for suppressing bleeding in the present invention. Specifically, among the plurality of inks constituting the ink set, the relative relationship of lightness and the dynamic surface tension at the lifetime of 500 milliseconds defined in the two types of inks A and B are used. Regarding the relative relationship, the following was confirmed. That is, as long as the conditions stipulated by the present invention are satisfied, the amount of ink applied per unit area of each of ink A and ink B, the order of applying ink A and ink B to the recording medium, and the number of recording passes It was confirmed that the bleeding performance was independent.

In the case where the application amounts of the two types of inks are greatly different, for example, when the application amount of the ink B having a relatively low lightness is smaller than the application amount of the ink A having a relatively high lightness, the inks A and The lightness relationship between the images formed with the ink B may be reversed. However, although the ink corresponding to the ink A and the ink B is determined from the lightness relationship in each image formed under the predetermined condition, the lightness relationship is reversed depending on the amount of applied ink. In such a case, bleeding that can be visually confirmed does not occur. This is because the amount of ink applied on one side is sufficiently small, and the time until the penetration of the ink into the recording medium is sufficiently short, so that bleeding is not likely to occur in the first place. Therefore, if the condition of −5 ≦ (γ _a −γ _b ) ≦ 3 is satisfied, it can be said that unacceptable bleeding does not occur.

  As described above, the relationship between dynamic surface tension and lightness at a lifetime of 500 milliseconds between a plurality of inks is dominant with respect to the occurrence of bleeding, so the relationship between the hue and saturation of a plurality of inks is not considered. May be. That is, the relationship between the dynamic surface tension and the lightness at a lifetime of 500 milliseconds between a plurality of inks defined in the present invention to suppress bleeding can be similarly applied to various inks. That is, in addition to the cyan, magenta, and yellow inks used in normal ink jet recording systems, the present invention also applies to black, red, green, blue, light cyan, light magenta, and gray inks. Rules can be applied. Furthermore, the provisions of the present invention can be applied to clear ink and the like used to improve the glossiness and fastness of an image. Examples for each of these inks are not listed here, but are encompassed by the present invention. In the present invention, it is more preferable that the ink A described above is a magenta ink and the ink B is a cyan ink. Of course, the present invention is not limited to this.

To summarize what has been described so far, the ink set according to the first embodiment of the present invention has the following configuration. That is, in an ink set having a plurality of inks containing dyes, at least the difference between the dynamic surface tension at a lifetime of 50 milliseconds and the dynamic surface tension at a lifetime of 500 milliseconds is 7 mN / m or more (hereinafter, “ First ink ”). Of the first ink and at least one kind of ink other than the first water-based ink included in the ink set, ink A having a relatively high brightness and ink having a relatively low brightness are used. Ink B. In this case, the dynamic surface tension gamma _a at a lifetime of 500m seconds of the ink A (mN / m), the dynamic surface tension gamma _b at a lifetime of 500m seconds of the ink B is (mN / m), -5 ≦ ( It is necessary to satisfy the relationship of γ _a −γ _b ) ≦ 3.

  The present inventors further examined the first problem of the present invention. As a result, the problem of bleeding when using the first ink in which the difference between the dynamic surface tension at a lifetime of 50 milliseconds and the dynamic surface tension at a lifetime of 500 milliseconds is 7 mN / m or more is the brightness of the ink. It came to the conclusion that it can be technically summarized as a point.

That is, the ink according to another embodiment of the present invention has the following configuration. That is, the ink is used for an ink set having a plurality of inks containing a dye, and the difference between the dynamic surface tension at a lifetime of 50 milliseconds and the dynamic surface tension at a lifetime of 500 milliseconds is 7 mN / m or more. It is the 1st ink to contain. Of the first ink and at least one kind of ink other than the first water-based ink included in the ink set, ink A having a relatively high brightness and ink having a relatively low brightness are used. Ink B. In this case, the dynamic surface tension gamma _a at a lifetime of 500m seconds of the ink A (mN / m), the dynamic surface tension gamma _b at a lifetime of 500m seconds of the ink B is (mN / m), -5 ≦ ( It is necessary to satisfy the relationship of γ _a −γ _b ) ≦ 3.

  Next, the second problem of the present invention, that is, the suppression of bleeding and the improvement of gradation while maintaining color uniformity when plain paper or the like is used as a recording medium will be described below. To do.

  One of the technical ideas for solving the second problem includes the following. In order to improve the gradation of the image by controlling the area per dot to be appropriate, the ink spread immediately after the ink is applied to the recording medium is suppressed, and further the ink spread is suppressed. In this case, the ink is quickly allowed to penetrate into the recording medium. Another technical idea for solving the second problem is to provide sufficient ink wettability with respect to voids existing between fibers constituting the recording medium in order to improve color uniformity in an image. It is to grant.

  The inventors of the present invention have made the following studies on the state of ink spreading on the recording medium. First, various inks having different characteristics in which dynamic surface tension changes depending on the lifetime were prepared, and 1-dot ruled lines were recorded on recording media such as various plain papers using these inks. Then, the relationship between the line width of the ruled line and the dynamic surface tension and static surface tension of the ink from the lifetime of 10 milliseconds to the lifetime of 5000 milliseconds was examined. As a result, it was found that the correlation between the line width of the ruled line and the dynamic surface tension at an ink lifetime of 50 milliseconds was the largest in all types of recording media examined. Further, it has been found that this correlation decreases continuously as the life time increases away from the front and rear of the life time of 50 milliseconds. From this, the present inventors can define the line width of the ruled line, that is, the state where the ink spreads on the recording medium, by examining the dynamic surface tension at an ink lifetime of 50 milliseconds. Obtained knowledge. In the above examination, the line width of the ruled line was measured after the recording was left overnight after recording.

  Based on this, the present inventors further studied paying attention to the characteristics of the dynamic surface tension at an ink lifetime of 50 milliseconds. Specifically, inks with various dynamic surface tensions with a lifetime of 50 milliseconds were prepared, and images were formed using these inks. The relationship of dynamic surface tension at a lifetime of 50 milliseconds was examined. As a result, it was found that if the dynamic surface tension of the ink with a lifetime of 50 milliseconds is set to 42 mN / m or more, excessive spreading of the ink on the recording medium can be suppressed.

  The present inventors consider the reason why a high correlation is observed between the state in which the ink spreads on the recording medium and the dynamic surface tension with a lifetime of 50 milliseconds as follows. That is, at the time of 50 milliseconds after the ink is applied to the recording medium, at least a part of the ink permeates the area near the surface of the recording medium, and this area forms one of the inks formed on the recording medium. This is considered to be an important factor that determines the dot area. In addition, since the dynamic surface tension value of the ink changes after the ink is applied to the recording medium, the contact angle between the ink and the recording medium also changes. It is considered to be an element that determines the area of Further, in the ink immediately after being applied on the recording medium, the evaporation of moisture or the like in the ink occurs relatively much as compared with the ink that has permeated in the thickness direction of the recording medium. It is considered that the amount of ink penetrating in the direction of the thickness of the recording medium also depends on the dynamic surface tension at a lifetime of 50 milliseconds, which also determines the area of one dot formed by the ink on the recording medium. It is considered to be another important factor.

  However, if the ink keeps a high surface tension for a long time, the ink does not penetrate in the thickness direction of the recording medium, and as a result, the ink spreads on the surface of the recording medium and the gradation is deteriorated. There is a case. As a result of investigations by the present inventors, it has been found that the following can be performed in order to suppress a decrease in gradation. First, by increasing the dynamic surface tension at an ink lifetime of 50 milliseconds, excessive spreading of the ink on the recording medium is suppressed. Thereafter, ink dynamic surface tension is rapidly lowered to promote ink permeation in the thickness direction of the recording medium, thereby further suppressing ink spreading on the surface of the recording medium. By doing so, the area per dot formed by the ink on the recording medium can be made appropriate. As a result of the study by the present inventors, in order to cause such a phenomenon, specifically, it is understood that the dynamic surface tension of the ink should be lowered by 7 or more during the lifetime of 50 milliseconds to 500 milliseconds. It was.

  As a result, the inventors of the present invention have a dynamic surface tension of 42 mN / m or more at a lifetime of 50 milliseconds, and a difference in dynamic surface tension between a lifetime of 50 milliseconds and a lifetime of 500 milliseconds is 7 mN / m or more. It has been found that certain inks provide excellent image gradation. Further, the difference in dynamic surface tension between the lifetime of 50 milliseconds and the lifetime of 500 milliseconds is 10 mN / m or more, so that the gradation can be particularly improved.

  When plain paper or the like is used as a recording medium, it is necessary to uniformly fix the dye in the ink to the recording medium in order to improve the color uniformity. Note that the uniformly fixed state is not a state in which the dye in the ink is taken in and localized in a relatively large gap existing in the recording medium, such as plain paper, but the ink in the fibers constituting the recording medium. This means that the dye is uniformly dyed. In order to uniformly fix the dye in the ink, it is necessary for the ink to express wetness with respect to pores such as voids between fibers. When the present inventors have examined the physical properties necessary for the ink to have wettability with respect to the pores, it is necessary to appropriately determine the dynamic surface tension at an ink lifetime of 500 milliseconds. I understood. Specifically, it has been found that the dynamic surface tension of the ink at a lifetime of 500 milliseconds must be 38 mN / m or less. That is, the present inventors require that the ink has the dynamic surface tension characteristics described below in order to improve both the color uniformity and the gradation. I got the knowledge. That is, the dynamic surface tension at a lifetime of 50 msec is 42 mN / m or more, the difference between the dynamic surface tensions at a lifetime of 50 msec and 500 msec is 7 mN / m or more, and the dynamic surface tension at a lifetime of 500 msec. The ink is preferably 38 mN / m or less.

  Note that if the dynamic surface tension of the ink at a lifetime of 50 milliseconds is 49 mN / m or more, even if the degree of subsequent decrease in the dynamic surface tension is large, the ink permeates in the thickness direction of the recording medium. Also, priority is given to spreading of the ink on the surface of the recording medium. For this reason, the area per dot becomes large, and there is a case where gradation is not obtained. For this reason, it is preferable that the dynamic surface tension of the ink at a lifetime of 50 milliseconds is 42 mN / m or more and less than 49 mN / m.

  If the dynamic surface tension of the ink at a lifetime of 500 milliseconds is too low, specifically less than 28 mN / m, the penetration of the ink into the recording medium has priority over the wetting of the gaps between the fibers. As a result, the ink easily penetrates into the inside of the recording medium (in the direction of the thickness of the recording medium), so that the ink may escape to the back surface of the recording medium, that is, the back-through may occur. Therefore, the dynamic surface tension of the ink at a lifetime of 500 milliseconds is preferably 28 mN / m or more and 38 mN / m or less. In the present invention, it is particularly preferable that the dynamic surface tension of the ink at a lifetime of 500 milliseconds is not less than 32 mN / m and not more than 38 mN / m.

  Further, the difference in dynamic surface tension between the lifetimes of 50 milliseconds and 500 milliseconds is that the penetration of the ink into the recording medium is promoted after the region where the ink penetrates into the recording medium is determined to some extent at the lifetime of 50 milliseconds. Is preferably increased. However, as described above, the dynamic surface tension of the ink at a lifetime of 500 milliseconds needs to be 28 mN / m or more. For this reason, the difference in dynamic surface tension between the lifetime of 50 milliseconds and the lifetime of 500 milliseconds should be equal to or less than the value of the dynamic surface tension at the lifetime of 50 milliseconds (mN / m) −28 (mN / m). Is preferred. Furthermore, the difference in dynamic surface tension between the lifetime of 50 milliseconds and the lifetime of 500 milliseconds is more preferably less than 21 mN / m.

  From the above, when plain paper or the like is used as a recording medium, the ink (hereinafter referred to as “first ink”) that can improve gradation while maintaining color uniformity is the following (1). ) To (3) must be satisfied. (1) The dynamic surface tension at a lifetime of 50 milliseconds is 42 mN / m or more and less than 49 mN / m. (2) The dynamic surface tension at a lifetime of 500 milliseconds is 28 mN / m or more and 38 mN / m or less. (3) The difference between the dynamic surface tension at a lifetime of 50 milliseconds and the dynamic surface tension at a lifetime of 500 milliseconds is 7 mN / m or more.

To summarize what has been described so far, the ink set according to the second embodiment of the present invention has the following configuration. That is, an ink set having a plurality of inks containing dyes includes at least the first ink that satisfies the conditions (1) to (3) described above. Of the first ink and at least one kind of ink other than the first water-based ink included in the ink set, ink A having a relatively high brightness and ink having a relatively low brightness are used. Ink B. In this case, the dynamic surface tension gamma _a at a lifetime of 500m seconds of the ink A (mN / m), the dynamic surface tension gamma _b at a lifetime of 500m seconds of the ink B is (mN / m), -5 ≦ ( It is necessary to satisfy the relationship of γ _a −γ _b ) ≦ 3.

Furthermore, the ink set according to the third embodiment of the present invention has the following configuration. That is, an ink set having at least three kinds of inks containing dyes has at least the first ink that satisfies the conditions (1) to (3) described above. Of the two inks arbitrarily selected from at least three inks constituting the ink set, the ink having a relatively high brightness is referred to as ink A, and the ink having a relatively low brightness is referred to as ink B. Further, the dynamic surface tension of the ink A at a lifetime of 500 msec is γ _a (mN / m), and the dynamic surface tension of the ink B at a lifetime of 500 msec is γ _b (mN / m). At this time, it is necessary that a relationship of −5 ≦ (γ _a −γ _b ) ≦ 3 is satisfied in all combinations in which any two types of ink are selected from at least three types of ink constituting the ink set.

In the ink set according to the third embodiment, −5 ≦ (γ _a −γ _b ) ≦ 3 in all combinations in which any two types of inks are selected from at least three types of ink constituting the ink set. It is necessary that this relationship holds. At this time, some combinations of the two types of inks do not need to include the first ink. In this case, in the combination not including the first ink, the occurrence of bleeding can be suppressed by aligning the static surface tension as in the conventional ink set. However, in the present invention, even in a combination that does not include the first ink, the dynamic surface tension at the lifetime of 500 milliseconds satisfies the above relationship in order to align the ink permeability to the recording medium with higher accuracy. Is preferred.

  The ink set of the present invention described above has a plurality of inks containing dyes, and has at least the first ink described above.

  The ink set in the present invention is an ink cartridge that is integrally configured by combining a state of an ink cartridge that independently accommodates a plurality of inks and a plurality of ink accommodating portions that respectively accommodate a plurality of inks. State. The ink cartridge may further have a configuration in which a recording head is integrally formed. Alternatively, the ink set of the present invention also includes a state in which the ink cartridges that individually contain the plurality of inks are configured to be detachable from the ink jet recording apparatus. In any case, the ink set of the present invention only needs to be configured so that at least the first ink and the ink containing the other dye can be used in combination. There may be any form.

  The ink set of the present invention may include an ink containing a pigment in addition to an ink containing a dye. In general, an ink containing a pigment is not used when recording on a recording medium having an ink receiving layer, and therefore may not have the dynamic surface tension characteristics described above. .

<Ink>
In the first embodiment of the present invention, the first ink needs to be adjusted to have the dynamic surface tension characteristics described above. In the second and third embodiments of the present invention, the first ink is adjusted to have the dynamic surface tension characteristics (1) to (3) described above. is necessary. Further, in the present invention, the ink A and the ink B are determined from the plurality of inks constituting the ink set as described above so that these inks have the dynamic surface tension characteristics described above. It is necessary to be adjusted to. Other than that, the configuration may be the same as that of the conventional ink. Below, each component which comprises the ink of this invention is demonstrated.

(Surfactant)
Each ink constituting the ink set of the present invention preferably contains a surfactant as a penetrating agent. It is necessary that the blended ink is adjusted to have the dynamic surface tension change described above. As such a surfactant, for example, the following can be used. The surfactants listed below can be used alone or in combination of two or more.

[Nonionic surfactant]
Polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyethylene alkylphenyl ether, polyoxyethylene / polyoxypropylene block copolymer, and the like. Fatty acid diethanolamide, acetylene glycol ethylene oxide adduct, acetylene glycol surfactant, and the like.

[Anionic surfactant]
Polyoxyethylene alkyl ether sulfate, polyoxyethylene alkyl ether sulfonate, polyoxyethylene alkyl phenyl ether sulfate, polyoxyethylene alkyl phenyl ether sulfonate, and the like. Alpha sulfo fatty acid ester salts, alkylbenzene sulfonates, alkylphenol sulfonates, alkylnaphthalene sulfonates, alkyltetralin sulfonates, dialkylsulfosuccinates and the like.

[Cationic surfactant]
Alkyltrimethylammonium salt, dialkyldimethylammonium chloride and the like.

[Amphoteric surfactant]
Alkyl carboxybetaines and the like.

[Other surfactants]
Fluorine compounds, silicone compounds, etc.

  In the first embodiment of the present invention, the first ink needs to be adjusted to have the dynamic surface tension characteristics described above. In the second and third embodiments of the present invention, the first ink is adjusted to have the dynamic surface tension characteristics (1) to (3) described above. is necessary. In order for the first ink to have the dynamic surface tension characteristics described above, the dynamic surface tension of the ink is adjusted using one or more of the surfactants listed above. It can be achieved by adjusting.

  In the present invention, it is particularly preferable to adjust the dynamic surface tension of the first ink by using an ethylene oxide adduct of polyoxyethylene alkyl ether or acetylene glycol among the above surfactants.

  In the present invention, the polyoxyethylene alkyl ether is at least one selected from a surfactant represented by the following general formula (1) and a surfactant represented by the general formula (2). Is particularly preferred. The ink containing such a surfactant is particularly suitable for achieving both gradation and color uniformity when using plain paper or the like as a recording medium because the change in dynamic surface tension with respect to the change in lifetime is large. It is.

  General formula (1)

(In general formula (1), m, n and a are each independently an integer of 1 or more, and m + n is an integer of 14 to 20.)

  General formula (2)

(In general formula (2), x, y, and b are each independently an integer of 1 or more, and x + y is an integer of 15 to 21.)

Furthermore, in this invention, it is especially preferable that HLB value by the Griffin method of said surfactant is 12.0 or more and 16.5 or less. Here, the Griffin method is a method of calculating the HLB value using the following formula (1) based on the formula weight and molecular weight of the hydrophilic group of the surfactant.
HLB = 20 × (formula weight of hydrophilic group of surfactant) / (molecular weight of surfactant) (1)
When the HLB is less than 12.0, the hydrophilicity of the surfactant is too low, and thus the surfactant may not be dissolved in the ink when the ink is stored. On the other hand, if the HLB is greater than 16.5, the hydrophilicity of the surfactant is too high, and it may be difficult to lower the dynamic surface tension at a lifetime of 500 milliseconds.

  The content (mass%) of the surfactant in the first ink is 0.30 mass% or more and 2.0 mass% or less, further 0.30 mass% or more and 1.5 or less, based on the total mass of the ink. It is preferable that it is below mass%. If the content is less than 0.30% by mass, ink may not be sufficiently wetted with respect to the members constituting the ink flow path of the ink jet recording apparatus, and the ejection stability may be lowered. On the other hand, when the content exceeds 2.0% by mass, the content of the surfactant becomes too high when the water content in the ink evaporates near the discharge port of the recording head, and the viscosity of the ink is locally increased. May increase, and the ink ejection stability may decrease. Furthermore, in order to obtain an excellent image quality when using plain paper or the like as the recording medium, the lower limit of the content (% by mass) of the surfactant in the first ink is 0. 0 based on the total mass of the ink. It is preferably 30% by mass or more, and more preferably 0.75% by mass or more. When the content is less than 0.30% by mass, sufficient ink wettability with respect to plain paper may not be obtained, and color uniformity may deteriorate. By setting the surfactant content in the ink within the above range, both excellent ejection stability and excellent image quality, especially excellent color uniformity, when using plain paper as the recording medium can do.

  Further, the content (mass%) of the surfactant in the ink other than the first ink constituting the ink set is 0.10 mass% or more and 2.0 mass% or less based on the total mass of the ink. It is preferable that it is 0.30 mass% or more and 1.5 mass% or less. Of course, the range varies depending on the structure of the surfactant and the HLB value, and is not limited to the above range.

  Further, in the present invention, the ink A and the ink B are determined as described above, and these inks are adjusted so as to have the dynamic surface tension characteristics at the lifetime of 500 milliseconds as described above. It is necessary. In order for these ink A and ink B to have the dynamic surface tension characteristics described above, the dynamic surface tension is set using one or more of the surfactants listed above. It can be done by adjusting. The surfactant content (mass%) in these ink A and ink B is 0.10 mass% or more and 2.0 mass on the basis of the total mass of the ink, as described above, from the viewpoint of ejection stability. % Or less, more preferably 0.30 mass% or more and 1.5 mass% or less.

(Aqueous medium)
Each ink constituting the ink set of the present invention preferably contains an aqueous medium that is a mixed solvent of water and a water-soluble organic compound. It is preferable to use deionized water (ion exchange water) as the water. The content (% by mass) of water in the ink is determined so that the ink has an appropriate viscosity for stably discharging the ink, and in order to obtain an ink in which clogging at the nozzle tip is suppressed, As a reference, it is preferably 30.0% by mass or more and 90.0% by mass or less.

  As the water-soluble organic compound, any water-soluble organic compound can be used as long as the ink of the present invention is adjusted to have the dynamic surface tension characteristics described above. The content (% by mass) of the water-soluble organic compound in the ink is 1.0% by mass or more and 50.0% by mass or less, and further 3.0% by mass or more and 40.0% by mass or less based on the total mass of the ink. It is preferable that Specifically, for example, the following water-soluble organic compounds can be used.

  Alcohols having 1 to 6 carbon atoms such as ethanol, isopropanol, 2-propanol, n-butanol, isobutanol, pentanol and hexanol. Carboxylic acid amides such as N, N-dimethylformamide and 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. Alkylene 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; Glycerin, 1,3-butanediol, 1,2- or 1,5-pentanediol, 1,2- or 1,6-hexanediol, 2-methyl-1,3-propanediol, 1,2,6- Polyhydric alcohols such as hexanetriol. Alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or ethyl) ether, and 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 and thiodiglycol;

  Among these, it is particularly preferable to use a water-soluble organic compound having high permeability in order to appropriately adjust the surface tension of the aqueous medium. Specifically, it is particularly preferable to use alcohols such as ethanol, 2-propanol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, and 1,6-hexanediol.

  In the first embodiment of the present invention, the first ink needs to be adjusted to have the dynamic surface tension characteristics described above. In the second and third embodiments of the present invention, the first ink is adjusted to have the dynamic surface tension characteristics (1) to (3) described above. is necessary. In order for the first ink to have the dynamic surface tension characteristics described above, the dynamic surface tension is adjusted using one or more of the water-soluble organic compounds listed above. Can also be achieved. Furthermore, in order to obtain particularly excellent gradation when using plain paper or the like as the recording medium, the static surface tension of the aqueous medium in the first ink is 45 mN / m or more and 57 mN / m or less. Is preferred. The “aqueous medium in the ink” in the present invention means an aqueous medium excluding the coloring material and the surfactant in the ink, that is, water and a water-soluble organic compound. When the static surface tension of the aqueous medium is higher than 57 mN / m or less than 45 mN / m, the gradation property is improved when a recording medium having a relatively large surface energy unevenness is used. You may not get enough. When the static surface tension of the aqueous medium is higher than 57 mN / m, among the high and low surface energy portions present in the vicinity of the ink-applied portion of the recording medium, toward the high surface energy portion. Ink tends to flow selectively. As a result, feathering is likely to occur, and the variation in area per dot increases, so that sufficient gradation may not be obtained. On the other hand, if the static surface tension of the aqueous medium is less than 45 mN / m, the surface tension of the aqueous medium in the ink is lower than that in the vicinity of the portion to which the ink is applied in the recording medium. Spreading may occur, and as a result, gradation may be deteriorated.

  In the present invention, the ink A and the ink B are determined from the plurality of inks constituting the ink set as described above, and these inks have the dynamic surface tension at the lifetime of 500 milliseconds as described above. It is necessary to be adjusted to have the following characteristics. In order for these inks A and B to have the dynamic surface tension characteristics described above, dynamic surface tension is used by using one or more of the water-soluble organic compounds listed above. It can also be achieved by adjusting.

(Color material)
The color material used for each ink constituting the ink set of the present invention is a dye. The content (% by mass) of the dye 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. Is preferred.

  The dye is not particularly limited as long as it is a dye that can be used as a coloring material for general inkjet inks. For example, any of direct dyes, acid dyes, reactive dyes, and basic dyes may be used. be able to. In the following, the dyes that can be used in the present invention by color tone are indicated by color index numbers, for example. Even those not described in the color index can be used as long as they are water-soluble dyes.

[Yellow color material]
C. I. Direct yellow: 8, 11, 12, 27, 28, 33, 39, 44, 50, 58, 85, 86, 87, 88, 89, 98, 100, 110, 132, 173, etc. C. I. Acid Yellow: 1, 3, 7, 11, 17, 23, 25, 29, 36, 38, 40, 42, 44, 76, 98, 99, etc.

[Magenta color material]
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, 229, 230, etc. C. I. Acid Red: 6, 8, 9, 13, 14, 18, 26, 27, 32, 35, 42, 51, 52, 80, 83, 87, 89, 92, 106, 114, 115, 133, 134, 145 158, 198, 249, 265, 289, etc. C. I. Food Red: 87, 92, 94, etc. C. I. Direct violet: 107 etc.

[Cyan color material]
C. I. Direct blue: 1, 15, 22, 25, 41, 76, 77, 80, 86, 90, 98, 106, 108, 120, 158, 163, 168, 199, 226, 307, etc. C. I. Acid Blue: 1, 7, 9, 15, 22, 23, 25, 29, 40, 43, 59, 62, 74, 78, 80, 90, 100, 102, 104, 112, 117, 127, 138, 158 161, 203, 204, 221, 244, etc.

[Orange color material]
C. I. Acid orange: 7, 8, 10, 12, 24, 33, 56, 67, 74, 88, 94, 116, 142, etc. C. I. Acid Red: 111, 114, 266, 374, etc. C. I. Direct orange: 26, 29, 34, 39, 57, 102, 118, etc. C. I. Food orange: 3 mag. C. I. Reactive orange: 1, 4, 5, 7, 12, 13, 14, 15, 16, 20, 29, 30, 84, 107, etc. C. I. Disperse orange: 1, 3, 11, 13, 20, 25, 29, 30, 31, 32, 47, 55, 56, etc.

[Green color material]
C. I. Acid Green: 1, 3, 5, 6, 9, 12, 15, 16, 19, 21, 25, 28, 81, 84, etc. C. I. Direct green: 26, 59, 67 etc. C. I. Food green: 3 etc. C. I. Reactive green: 5, 6, 12, 19, 21 etc. C. I. Disperse Green: 6, 9 etc.

[Blue color material]
C. I. Acid blue: 62, 80, 83, 90, 104, 112, 113, 142, 203, 204, 221, 244, etc. C. I. Reactive blue: 49 mag. C. I. Acid violet: 17, 19, 48, 49, 54, 129, etc. C. I. Direct violet: 9, 35, 47, 51, 66, 93, 95, 99 etc. C. I. Reactive violet: 1, 2, 4, 5, 6, 8, 9, 22, 34, 36, etc. C. I. Disperse violet: 1, 4, 8, 23, 26, 28, 31, 33, 35, 38, 48, 56, etc.

[Black color material]
C. I. Direct black: 17, 19, 22, 31, 32, 51, 62, 71, 74, 112, 113, 154, 168, 195, etc. C. I. Acid Black: 2, 48, 51, 52, 110, 115, 156, etc. C. I. Food black: 1, 2, etc.

[Brown color material]
C. I. Reactive Brown 1, 2, 7, 8, 9, 11, 17, 18, 21, 31, 32, 33, 46, 47, etc.

(Other ingredients)
Each ink constituting the ink set of the present invention contains an organic compound that is solid at room temperature such as trimethylolethane and trimethylolpropane, and a nitrogen-containing compound such as urea and ethyleneurea, as necessary, in addition to the above components. May be. Furthermore, in order to make the ink of the present invention an ink having a desired physical property value, in addition to the above components, a pH adjuster, a rust inhibitor, a preservative, a fungicide, an antioxidant, a reduction inhibitor, an evaporation accelerator You may contain various additives, such as an agent and a chelating agent.

<Inkjet recording method>
The ink of the present invention is particularly preferably used in an ink jet recording method in which ink is ejected by an ink jet recording method and recording is performed on a recording medium. As the ink jet recording method, there are a method of ejecting ink by applying mechanical energy to the ink, a method of ejecting ink by applying thermal energy to the ink, and the like. In particular, the ink of the present invention can provide a remarkable effect when used in an ink jet recording method using thermal energy.

<Ink cartridge>
The ink cartridge of the present invention is characterized by including an ink storage portion that stores the ink of the present invention.

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

  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 performing paper feeding, first, a predetermined number of recording media are fed 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. 2 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 places the recording head H1001 (see FIG. 5) 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 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, the ink sticking and other problems 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, light magenta, light cyan, and green ink. Accordingly, the ink cartridge H1900 is also prepared for seven colors independently. 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 with the head cartridge H1000 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 cartridge 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. 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 printing 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 light cyan ink nozzle row H2300, a black ink nozzle row H2400, a green ink nozzle row H2500, and a light magenta ink nozzle row H2600, are formed. Has been.

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 approximately 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 a 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 cartridge holder H1500.

  A flow path forming member H1600 is fixed to the cartridge holder H1500 that holds the ink cartridge H1900, for example, by ultrasonic welding, and forms 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 ink can be prevented from evaporating from the engaging portion.

  Further, the head cartridge H1000 is configured by bonding the cartridge holder portion and the recording head portion H1001 by bonding or the like. The cartridge holder portion includes a cartridge 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.

  The ink jet recording apparatus is not limited to one in which the recording head and the ink cartridge are separated from each other, and may be one in which they are integrated so as not to be separated. Further, the ink cartridge is integrated with the recording head so as to be separable or non-separable and is mounted on the carriage, or 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 exerts a biasing force in the direction of expanding the inner volume of the flexible ink storage bag are provided. It can be. Further, 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 recording method.

EXAMPLES Next, although an Example , a comparative example, and a reference example are given and this invention is demonstrated more concretely, this invention is not limited by the following Example , unless the summary is exceeded. In the text, “parts” and “%” are based on mass unless otherwise specified.

<HLB value and structure of surfactant>
The HLB value of the surfactant was determined. Specifically, the HLB value was calculated using the Griffin method (the following formula (1)) for the main component of each surfactant. The results are shown in Table 1.
HLB = 20 × (formula weight of hydrophilic group of surfactant) / (molecular weight of surfactant) (1)
Table 1 shows the structure of the main component of each surfactant, and when the structure of the surfactant corresponds to the general formula (1) or the general formula (2), m, n, a, and The values of m + n or x, y, b, and x + y are also shown. In Table 1, EMALEX 1615 is a surfactant manufactured by Nippon Emulsion, and acetylenol E100 is a surfactant manufactured by Kawaken Fine Chemical. Also, Emalmin CO-50 and Emalmin NL90 are surfactants manufactured by Sanyo Chemical Industries, and NIKKOL BT-7 is a surfactant of Nikko Chemicals.

<Preparation of ink>
The components shown in Tables 2 to 4 were mixed and sufficiently stirred, and then pressure filtered with a micro filter (made by Pole) having a pore size of 0.2 μm to obtain cyan ink (C1 to C5) and magenta ink (M1). To M8) and yellow inks (Y1 to Y3) were prepared. In Tables 2 to 4, EMALEX 1615 is a surfactant manufactured by Japan Emulsion, and acetylenol E100 is a surfactant manufactured by Kawaken Fine Chemical. Also, Emalmin CO-50 and Emalmin NL90 are surfactants manufactured by Sanyo Chemical Industries, and NIKKOL BT-7 is a surfactant of Nikko Chemicals.

<Evaluation>
(Measurement of dynamic surface tension)
For each of the inks obtained above, the dynamic surface tension of the ink at (1) life time of 50 ms and (2) 500 ms was measured. Further, the difference Δγ [(1)-(2)] in dynamic surface tension between (1) and (2) was obtained. For the measurement, an apparatus (Bubble Pressure Tensiometer BP2; manufactured by KRUSS) that measures the dynamic surface tension by the maximum bubble pressure method was used. The dynamic surface tension was measured at 25 ° C. Table 5 shows the evaluation results of the dynamic surface tension.

(Measurement of brightness)
Each ink obtained above was filled in an ink cartridge, and mounted on a modified ink jet recording apparatus iP3100 (manufactured by Canon) that discharges ink from the recording head by the action of thermal energy. Thereafter, recording was performed on a recording medium (PR-101; manufactured by Canon) so that the applied amount of ink per pixel at a resolution of 600 ppi was 10 ng. The brightness of the obtained image was measured with Spectrolino (manufactured by Gretag Macbeth) under conditions of a light source D65 and a visual field of 2 degrees. Table 5 shows the brightness measurement results.

As is clear from Tables 2 to 5, the ink corresponding to the first ink in the present invention is each of C1 , C2 , M2, and Y1. An image formed using these inks corresponding to the first ink on a plain paper with a recording duty of 100% was excellent in color uniformity. The recording apparatus used at this time is an inkjet recording apparatus iP3100 (manufactured by Canon), and the recording medium is a PPC paper office planner (manufactured by Canon).

(Bleeding in an ink set having two types of ink)
Each of the inks C1 to C5, M1 to M8, and Y1 to Y3 obtained above was used in a combination of two types of inks shown in Table 6 below to form an ink set. As shown in Table 6, among the two types of inks that make up the ink set, ink with relatively high brightness was designated as ink A, and ink with relatively low brightness was designated as ink B. Table 6, the brightness of the ink A and ink B, and ink the dynamic surface tension gamma _a at a lifetime of 500m sec A, ink the dynamic surface tension gamma _b at a lifetime of 500m sec B, and these differences ( The value of _[ gamma] _{a- [} gamma] _b ) was shown.

  An ink jet recording apparatus iP3100 (manufactured by Canon Inc.), in which an ink cartridge is filled with a plurality of inks constituting an ink set, and ink is ejected from a recording head by the action of thermal energy, is mounted on a modified one. Thereafter, the image shown in FIG. 1 was formed in four passes on a recording medium (PR-101; manufactured by Canon). The obtained recorded matter was visually confirmed to evaluate bleeding. The evaluation criteria for bleeding are as follows. The evaluation results are shown in Table 6.

A: No bleeding throughout the image B: Mild bleeding in part of the image, but at an acceptable level C: Bleeding throughout the image

As is apparent from Table 6, Examples 1 to 3, 5, 6, 8 to 11, 13 to 15, 17, 18 and Reference Examples in which the value of γ _a -γ _b is -3 or more and 3 or less In 20-22, there was no bleeding over the whole image, and it was an excellent level. In Examples 4, 7, 12, 16, and 19 in which the value of γ _a -γ _b is -5 or more and less than -3, although there is bleeding in a part of the image, the degree of bleeding is mild and acceptable. It was possible level. On the other hand, in Comparative Examples 1 to 4 in which the value of γ _a -γ _b is more than 3 or less than 5, there was bleeding throughout the image, which was an unacceptable level.

  Focusing on M8, C1, and Y1 among the inks, M8 has a dynamic surface tension of 41 mN / m at 500 msec, and C1 and Y1 both have a dynamic surface tension of 37 mN / m at 500 msec. In the combination of M8 and C1 (Comparative Example 2), there was bleeding throughout the image, which was an undesirable level. On the other hand, in the combination of M8 and Y1 (Example 16), although there was slight bleeding in a part of the image, it was an acceptable level. In the combination of M8 and C1 and the combination of M8 and Y1, the absolute value of the difference in dynamic surface tension at 500 msec between the inks is all equal to 4, but the degree of bleeding that occurs due to the brightness relationship between the inks. There was a difference.

The relationship between the value of γ _a -γ _b and the bleeding in the combination of the two types of ink depends on the type and content of the penetrant (surfactant and / or water-soluble organic compound) used in the ink. I did not.

(Bleeding in an ink set having three types of ink)
Each of the inks C1, C2, M1, M2, M4, and Y1 to Y3 obtained as described above was used in combination of three kinds of inks shown in Table 7 below to form an ink set. As shown in Table 7, for all combinations (three ways) of selecting two types of ink from the three types of ink that make up the ink set, ink A having a relatively high lightness was used, and the lightness was relative. The lower ink was designated as Ink B. Table 7, the lightness of the ink A and ink B, and ink the dynamic surface tension gamma _a at a lifetime of 500m sec A, ink the dynamic surface tension gamma _b at a lifetime of 500m sec B, and these differences ( The value of _[ gamma] _{a- [} gamma] _b ) was shown.

  A modified ink jet recording apparatus iP3100 (manufactured by Canon) that fills ink cartridges with ink A and ink B among a plurality of inks constituting an ink set and discharges ink from the recording head by the action of thermal energy. equipped. Thereafter, the image shown in FIG. 1 was formed in four passes on a recording medium (PR-101; manufactured by Canon). Each recorded matter obtained by all combinations (three ways) of selecting two types of inks from the three types of inks constituting the ink set was visually confirmed, and bleeding was evaluated. The evaluation criteria for bleeding are as follows. Table 7 shows the evaluation results.

A: No bleeding throughout the image B: Mild bleeding in part of the image, but at an acceptable level C: Bleeding throughout the image

  In addition, by visually checking each recorded matter obtained by all combinations (three ways) of selecting two types of ink from the three types of inks constituting the ink set, comprehensive evaluation of bleeding in each ink set Went. The criteria for comprehensive evaluation of bleeding are as follows. Table 7 shows the evaluation results.

A: There is no bleeding throughout the image in any combination of inks. B: Depending on the combination of inks, there is slight bleeding in a part of the image, but this is an acceptable level. C: Depending on the combination of inks, the image There is bleeding throughout

As is clear from Table 7, the same evaluation as in the case of the ink set having the above two types of ink may be performed for all combinations of the two types of ink selected from the ink set having the three types of ink. . In all combinations of the two inks constituting the ink set, in Examples 23 and 24 in which the value of γ _a -γ _b is -3 or more and 3 or less, there is no bleeding over the entire image, and the level is excellent. It was. Further, of the three types of inks constituting the ink set, Example 25 including a combination of two types of inks in which the value of γ _a -γ _b is -4 had the following bleeding performance. That is, in the combination of two types of ink with a value of γ _a -γ _b of −4, there is a slight bleeding in a part of the image, but this is an acceptable level, and in the combination of the other two types of ink, There was no bleeding throughout. In Example 25, bleeding was generally at an acceptable level. On the other hand, in Reference Example 1 including a combination of two types of inks in which the value of γ _a -γ _b is 6 among the three types of inks constituting the ink set, bleeding occurs over the entire image in the combination. The level was unacceptable.

It is a model figure of the image formed in order to evaluate bleeding. 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.

Explanation of symbols

1 Area of solid image formed by applying 15 ng of ink A per pixel at a resolution of 600 ppi and 15 ng of ink B per pixel at a resolution of 600 ppi 2 Applying ink A per pixel at a resolution of 600 ppi Solid image area formed with an amount of 20 ng 3 Solid image area formed with 20 ng of ink B applied per pixel at a resolution of 600 ppi 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 output tray M4000 Carriage M5000 Pong M5010 Cap E0002 LF motor E0014 Electric substrate H1000 Head cartridge H1001 Recording head H1100 First recording element substrate H1101 Second recording element substrate H1200 First plate H1201 Ink supply port H1300 Electric wiring substrate H1301 External signal input terminal H1400 Second Plate H1500 cartridge holder H1501 ink flow path H1600 flow path forming member H1700 filter H1800 seal rubber H1900 ink cartridge H2000 yellow nozzle row H2100 magenta nozzle row H2200 cyan nozzle row H2300 light cyan nozzle row H2400 black nozzle row H2500 green nozzle row H2600 light magenta nozzle Column

Claims (12)

An ink set that is composed of only a plurality of water-based inks containing a dye and is used for recording on a recording medium having an ink receiving layer ,
The ink set comprises at least a first aqueous ink containing a dye and a surfactant;
The surfactant in the first aqueous ink is polyoxyethylene alkyl ether, and the content (% by mass) of the surfactant in the first aqueous ink is based on the total mass of the ink. , 0.30 mass% or more and 1.5 mass% or less,
The first water-based ink satisfies the following conditions (1) to (3):
Of the first water-based ink and at least one water-based ink other than the first water-based ink included in the ink set, the dynamic surface tension γ of the ink A having a relatively high lightness at a lifetime of 500 milliseconds. _a (mN / m), the dynamic surface tension γ _b (mN / m) of the ink B having a relatively low lightness at a lifetime of 500 milliseconds satisfies the relationship −5 ≦ (γ _a −γ _b ) ≦ 3. An ink set characterized by that.
(1) Dynamic surface tension at a lifetime of 50 msec is 42 mN / m or more and less than 49 mN / m (2) Dynamic surface tension at a lifetime of 500 msec is 28 mN / m or more and 38 mN / m or less (3) Life time 50 m Difference in dynamic surface tension in seconds and dynamic surface tension in lifetime 500 msec is 7 mN / m or more While being composed of only three or more kinds of water-based ink you containing a dye, an ink set used for recording on a recording medium having an ink-receiving layer,
The ink set comprises at least a first aqueous ink containing a dye and a surfactant;
The surfactant in the first aqueous ink is polyoxyethylene alkyl ether, and the content (% by mass) of the surfactant in the first aqueous ink is based on the total mass of the ink. , 0.30 mass% or more and 1.5 mass% or less,
The first water-based ink satisfies the following conditions (1) to (3):
Dynamic surface tension γ _a (mN / m) at _a lifetime of 500 msec of ink A having a relatively high lightness among two water-based inks arbitrarily selected from at least three water-based inks constituting the ink set The dynamic surface tension γ _b (mN / m) of the ink B having a relatively low lightness at a lifetime of 500 milliseconds selects any two water-based inks from at least three water-based inks constituting the ink set. An ink set characterized in that a relationship of −5 ≦ (γ _a −γ _b ) ≦ 3 is established in all combinations.
(1) Dynamic surface tension at a lifetime of 50 msec is 42 mN / m or more and less than 49 mN / m (2) Dynamic surface tension at a lifetime of 500 msec is 28 mN / m or more and 38 mN / m or less (3) Life time 50 m Difference in dynamic surface tension in seconds and dynamic surface tension in lifetime 500 msec is 7 mN / m or more The ink set according to claim 1 or 2 , wherein the water-based ink other than the first water-based ink constituting the ink set contains a surfactant. The content (mass%) of the surfactant in the aqueous ink other than the first aqueous ink constituting the ink set is 0.10 mass% or more and 2.0 mass% or less based on the total mass of the ink. The ink set according to claim 3 . The polyoxyethylene alkyl ether is at least one selected from a surfactant represented by the following general formula (1) and a surfactant represented by the following general formula (2). The ink set according to item 1.
General formula (1)

(In general formula (1), m, n and a are each independently an integer of 1 or more, and m + n is an integer of 14 to 20.)
General formula (2)

(In general formula (2), x, y, and b are each independently an integer of 1 or more, and x + y is an integer of 15 to 21.) The ink set according to any one of claims 3 to 5 , wherein the surfactant has an HLB value by a Griffin method of 12.0 or more and 16.5 or less. The ink set, an ink set according to any one of claims 1 to 6 which is for inkjet. 8. An ink jet recording method for discharging ink by an ink jet method, wherein the ink is a water-based ink constituting the ink set according to any one of claims 1 to 7 . The inkjet recording method according to claim 8 , wherein the inkjet method is an inkjet recording method in which ink is ejected from a recording head by the action of thermal energy. 8. An ink cartridge comprising an ink containing part for containing ink, wherein the ink contained in the ink containing part is a water-based ink constituting the ink set according to any one of claims 1 to 7. Ink cartridge. The ink set according to any one of claims 1 to 7 , wherein the ink stored in the ink storage portion is a recording unit including an ink storage portion that stores ink and a recording head that discharges ink. A recording unit comprising a water-based ink constituting the recording unit. The ink set according to any one of claims 1 to 7 , wherein the ink stored in the ink storage portion is an ink jet recording apparatus including an ink storage portion that stores ink and a recording head that discharges ink. An ink jet recording apparatus, characterized in that the ink is a water-based ink.