JP5932196B2 - Image forming method and image forming apparatus - Google Patents

Description

The present invention, images forming method, and an image forming apparatus.

  The ink jet recording method has features that noise during recording is low and a high-resolution image can be obtained at high speed by using a highly integrated recording head, and is widely used in various fields.

  Conventionally, an ink containing a pigment (pigment ink) is used as a color material from which a recorded matter having a high image density and excellent fastness is obtained as an ink used in an ink jet recording method. As for the pigment ink, for example, there are proposals relating to black ink containing carbon black and a dispersant, and black ink containing a self-dispersing pigment capable of dispersing the pigment without using a dispersant (Patent Documents 1 to 3). reference).

  In recent years, in offices, schools, stores, etc., various report materials and bulletin materials are generally performed using full-color recorded materials. For this reason, it is required to form not only a high-quality black image but also a high-quality full-color image as an image obtained by the ink jet recording method. When such a full-color image is formed, various kinds of so-called plain paper such as copy paper, report paper, notebook, notepaper, bond paper, continuous slip paper, and the like are used as a recording medium. Furthermore, from the viewpoint of environmental protection and resource protection in recent years, plain paper containing recycled materials has been widely used as a recording medium. For this reason, even when a wide variety of plain papers are used as a recording medium, in order to form a high-quality image, studies have been made from various aspects such as ink composition and physical properties.

  In the ink jet recording method, a full-color image is widely formed by using the pigment ink as described above as a black ink and further combining with other inks, particularly color inks. Specific examples of such color inks include at least one selected from magenta ink, cyan ink, yellow ink, red ink, green ink, and blue ink. At this time, in a general ink set, the characteristics of each ink may be adjusted as follows. That is, the color ink is made to have a relatively high permeability to a recording medium in order to suppress the ink fixing property and the occurrence of bleeding at the boundary between images formed with a plurality of color inks. Further, in order to improve the character quality of the black ink, the penetrability of the black ink into the recording medium is set to be relatively small as compared with the color ink. That is, the surface tension of the black ink is relatively increased, and the surface tension of the color ink is relatively decreased. When an image is formed using an ink set having such black ink and color ink, the following problems may occur. That is, there is a phenomenon in which bleeding occurs at the boundary between an image formed with black ink and an image formed with color ink (bleeding), or a phenomenon in which image quality deteriorates due to non-uniform mixing of black ink and color ink. May occur. In order to suppress the occurrence of bleeding, the first ink and the second ink that reacts with the first ink are used so that the second ink overlaps the region to which the first ink is applied. There is a proposal regarding a recording method to be applied (see Patent Document 4).

In addition, in order to suppress the occurrence of bleeding, when the color ink and the black ink containing the pigment are applied in an overlapping manner, the image density and color tone of the obtained image differ depending on the order of applying the color ink and the black ink. That is, color unevenness may occur. In order to suppress the occurrence of this uneven color, there has been a proposal regarding an ink set and an image recording method in which the black ink contains a pigment and a salt, and the color ink contains a component that destabilizes the dispersion state of the pigment in the black ink. Yes (see Patent Documents 5 and 6).
JP 63-152681 A JP-A 64-6074 JP-A-8-3498 Japanese Patent Laid-Open No. 11-343441 JP 2001-150793 A JP 2001-152059 A

  In recent years, in the ink jet recording method, in order to improve the image quality, a method of recording an image having the same width as the length of the recording head by reciprocating the recording head twice or more in the main scanning direction ( Hereinafter, this is referred to as multi-pass recording). When performing multi-pass printing, even if the number of nozzles that eject one type of ink is increased, or the width at which a plurality of ejection ports that eject one type of ink is arranged in the recording head is increased, There are cases where the recording time cannot be shortened sufficiently. Therefore, in order to shorten the recording time, a method of recording in both the forward and backward directions of the main scanning of the recording head (hereinafter referred to as reciprocal recording), or an image of a unit area in the main recording head of one recording head. A method of recording by scanning (hereinafter referred to as one-pass recording) has been attempted. Recording is performed by combining 1-pass recording and reciprocal recording, that is, by performing 1-pass reciprocal recording, it is not necessary to scan one unit area on the recording medium a plurality of times, thereby greatly reducing the recording time. Can do.

  However, as a result of the study by the present inventors, it has been found that the following problems occur when recording is performed at high speed such as one-pass reciprocal recording. That is, the present inventors have found a problem that bleeding is remarkably generated. Furthermore, when the black ink and the color ink that reacts with the black ink are applied in an overlapping manner as in the inventions described in Patent Documents 5 and 6 in order to suppress the occurrence of bleeding, the color unevenness is remarkably generated. I found a problem. By performing one-pass reciprocal recording, the color unevenness is recorded by superimposing the black ink on the color ink having an image area on which the reactive color ink is superimposed on the black ink. It is particularly noticeable in images that are mixed with image areas. In other words, the inventions described in Patent Documents 5 and 6 are not suitable as a method for forming a high-level high-quality image that has been required in recent years at high speed even when a wide variety of plain paper is used as a recording medium. It is enough.

Accordingly, an object of the present invention, in the case of recording at a high speed as in one-pass reciprocal printing also, it is possible to obtain an image generation of bleeding or color unevenness is suppressed, moreover, that provides high image quality images forming method, and to provide an image forming apparatus.

The above object is achieved by the present invention described below. That is, in the image forming method according to the present invention, a black ink containing a self-dispersing pigment and at least one water-based ink are each ejected from an inkjet recording head and applied to plain paper to form an image. An image forming method comprising: applying the black ink and the water-based ink to the plain paper so as to overlap at least in a part of the plain paper , and bringing the black ink and the water-based ink into contact with each other. The water-based ink contains a reactive component that destabilizes the dispersion state of the self-dispersing pigment and a surfactant, and the surfactant is a surfactant represented by the following general formula (1). agents and a formula (2) at least one selected from surfactants represented by, and the aqueous ink, a surfactant represented by the general formula (1) and before Content of at least one compound selected from surfactants represented by the general formula (2) (wt%) is, based on the total mass of the ink, is 2.0 mass% or more 0.30 wt%, the maximum of the water-based ink according bubble pressure method, and the dynamic surface tension at a lifetime of 30m sec 41 mN / m or more and a dynamic surface tension at a lifetime of 500m sec Ri der below 28 mN / m or more 38 mN / m, the black static surface tension of the ink, with greater than the static surface tension of the water-based ink, characterized in der Rukoto below 30 mN / m or more 60 mN / m.
General formula (1)

(In general formula (1), a, m, and n 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), b, x, and y are each independently an integer of 1 or more, and x + y is an integer of 12 to 21.)

An image forming apparatus according to another embodiment of the present invention applies a black ink containing a self-dispersing pigment and at least one water-based ink to a plain paper by respectively ejecting them from an ink jet recording head. An image forming apparatus for forming an image by applying the black ink and the water-based ink to the plain paper so as to overlap at least in a part of the plain paper. The aqueous ink contains a reactive component that destabilizes the dispersion state of the self-dispersing pigment and a surfactant, and the surfactant is represented by the following general formula (1). is at least one selected from surfactants represented by the surfactant and the general formula (2) is represented, and, in the aqueous ink, surfactants represented by the general formula (1) The content (mass%) of at least one selected from the surfactant and the surfactant represented by the general formula (2) is 0.30 mass% or more and 2.0 mass% or less based on the total mass of the ink. The dynamic surface tension of the water-based ink by the maximum bubble pressure method at a lifetime of 30 milliseconds is 41 mN / m or more, and the dynamic surface tension at a lifetime of 500 milliseconds is from 28 mN / m to 38 mN / m. Ri, static surface tension of said black ink, said with greater than the static surface tension of the aqueous ink, and wherein the der Rukoto below 30 mN / m or more 60 mN / m.
General formula (1)

(In general formula (1), a, m, and n 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), b, x, and y are each independently an integer of 1 or more, and x + y is an integer of 12 to 21.)

According to the present invention, in a case of recording at a high speed as in one-pass reciprocal printing also, it is possible to obtain an image suppressed occurrence of bleeding or color unevenness, moreover, that provides high image quality images A forming method and an image forming apparatus can be provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

  The water-based ink of the present invention is a water-based ink used together with a black ink containing a self-dispersing pigment, wherein the water-based ink contains a reactive component that destabilizes the dispersion state of the self-dispersing pigment, The dynamic surface tension of the water-based ink by a bubble pressure method at a lifetime of 30 milliseconds is 41 mN / m or more, and the dynamic surface tension at a lifetime of 500 milliseconds is from 28 mN / m to 38 mN / m. To do.

  In the present invention, the maximum bubble pressure method used for measuring the dynamic surface tension is as follows. Specifically, this is a method of measuring the maximum pressure required to release bubbles formed at the tip of a probe (thin tube) immersed in the liquid to be measured and determining the surface tension from the maximum pressure. In addition, when the bubble is formed at the tip of the probe in the maximum bubble pressure method, the lifetime is determined from the point when a new bubble surface is formed after the bubble leaves the tip. Time until the radius and the radius of the probe tip portion become equal). The dynamic surface tension in the present invention is a value measured at 25 ° C.

  Hereinafter, in the present invention, a black ink containing a self-dispersing pigment is referred to as a “pigment black ink”. A water-based ink containing a reactive component that destabilizes the dispersion state of the self-dispersing pigment in the pigment black ink is referred to as “reactive ink”. An ink that does not contain a reactive component that destabilizes the dispersion state of the self-dispersing pigment in the pigment black ink is referred to as “non-reactive ink”. The reactive ink and non-reactive ink may be color ink or black ink, but in the present invention, color ink is particularly preferable.

  In the present invention, the method of applying each ink to a recording medium mainly has the following two orders. The reactive ink is first applied to at least a part of the region to which the pigment black ink is applied, and then the pigment black ink is applied to at least a part of the region to which the reactive ink is applied. Alternatively, the pigment black ink is applied first, and then the reactive ink is applied to at least a part of the region where the pigment black ink is applied. These two methods may be combined, and the order in which each ink is applied to the recording medium is not particularly limited.

  At this time, the application amount of each ink is preferably 2/100 to 50/100 with respect to the application amount of the pigment black ink. That is, when the amount of pigment black ink applied is 100, the amount of reactive ink applied is preferably 2 or more and 50 or less. The reason why the applied amount of each ink is preferably in the above range is as follows. This is because if the amount of reactive ink applied is too small relative to the amount of pigment black ink applied, the effects of the present invention may not be sufficiently obtained. Further, if the amount of the reactive ink applied is too much relative to the amount of the pigment black ink applied, a new bleed may occur and the image quality may be lowered.

  In the present invention, even when recording is performed at high speed, such as one-pass reciprocal recording, occurrence of bleeding and color unevenness can be suppressed. That is, in order to suppress the occurrence of bleeding, color unevenness caused by the difference in the order of applying the reactive ink and the pigment black ink can be reduced. The reason why such an effect can be obtained is not clearly clear, but as a result of investigations by the present inventors, it is considered that it is due to the mechanism described below.

[Image formation mechanism when a reactive ink having a dynamic surface tension of 41 mN / m or more at a lifetime of 30 milliseconds is used]
First, the meaning of defining the dynamic surface tension of a reactive ink at a lifetime of 30 milliseconds will be described below. The present inventors have studied the characteristics of reactive inks that can solve the problems of the present invention by using various pigment black inks and reactive inks as inks applicable to the ink jet recording method. . Specifically, studies were made on controlling the dynamic surface tension characteristics of ink at a lifetime of 10 milliseconds, 1000 milliseconds, and the like, which has been attracting attention. However, it has been found that no effect can be obtained in solving the problems of the present invention under any dynamic surface tension conditions that have been attracting attention.

  Therefore, the inventors have returned to the behavior of minute droplets such that the ejection volume per droplet of ink is, for example, 6 picoliters or less, and have created an ideal model as a state that the ink on the recording medium can take. As a result of the investigation, it was found that: That is, the time difference when the pigment black ink and the reactive ink come into contact with each other on the recording medium is about 20 msec to 50 msec, no matter how the configuration of the nozzle in the recording head and the parameters such as the ejection frequency change. It was found that it was an extremely short time. Therefore, as a result of the inventors paying attention within this time, the color unevenness in the recorded matter and the dynamic surface tension of the reactive ink at the lifetime of 30 milliseconds show the strongest correlation, that is, It turns out to be the dominant element. The present inventors consider that the strong correlation between the value of the dynamic surface tension and the color unevenness of the reactive ink at a lifetime of 30 milliseconds means the following. The behavior including the permeability of the reactive ink to the recording medium at the time when 30 msec has passed since the reactive ink was applied to the recording medium controls the balance of reactivity between the reactive ink and the pigment black ink. I think that. This balance of reactivity is considered to determine color unevenness in an image to which these inks are superimposed.

  In the case where an image is formed by using a reactive ink having a dynamic surface tension characteristic at a lifetime of 30 milliseconds as defined in the present invention or a reactive ink not having this characteristic in combination with a pigment black ink, respectively. Consider. In the following discussion, it is assumed that the pigment black ink has a relatively low permeability to the recording medium in order to improve character quality. That is, it is assumed that the (static) surface tension of the pigment black ink is relatively large, and the (static) surface tension of the color ink is relatively small.

  (1) The case where a dynamic surface tension at a lifetime of 30 milliseconds is 41 mN / m or more and a reactive ink containing a reactive component and a pigment black ink are used.

  (1-1) When each ink is applied in the order of pigment black ink and reactive ink.

  First, when a pigment black ink is applied to a recording medium, the pigment black ink covers the recording medium. At this time, since the pigment black ink penetrates into the recording medium relatively slowly, the self-dispersing pigment in the pigment black ink starts to aggregate on the surface of the recording medium. Here, the reactive ink is applied over the pigment black ink. At this time, the pigment black ink having a property of relatively slow penetration into the recording medium comes into contact with the reactive ink in a liquid state on the surface of the recording medium. For this reason, the pigment black ink and the reactive ink are quickly mixed with each other at the interface, and are easily uniformed. Then, due to the action of the reactive component in the reactive ink, the aggregation of the pigment proceeds rapidly and uniformly, and the pigment comes to be uniformly distributed near the surface of the recording medium. As a result, image uniformity and image density can be improved.

  (1-2) When each ink is applied in the order of reactive ink and pigment black ink.

  First, when reactive ink is applied to a recording medium, the reactive ink covers the recording medium. Next, a pigment black ink is applied over the reactive ink. At this time, a reactive ink having a dynamic surface tension of 41 mN / m or more at a lifetime of 30 milliseconds has a high surface tension, so that it does not immediately permeate the recording medium and is in a liquid state on the surface of the recording medium. Existing. In this way, the pigment black ink contacts the reactive ink in a liquid state on the surface of the recording medium. For this reason, the pigment black ink and the reactive ink are quickly mixed with each other at the interface, and are easily uniformed. Then, due to the action of the reactive component in the reactive ink, the aggregation of the pigment proceeds rapidly and uniformly, and the pigment comes to be uniformly distributed near the surface of the recording medium. As a result, image uniformity and image density can be improved.

When recording is performed at high speed, such as one-pass reciprocal recording, the recording of (1-1) and (1-2) is repeated. In this way, an image is formed in which a region where each ink is applied in the order of pigment black ink and reactive ink and a region where each ink is applied in the order of reactive ink and pigment black ink are mixed. Is done. However, by using each ink that satisfies the requirements defined in the present invention , the uniformity of the image and the image density are excellent in both cases (1-1) and (1-2). Unevenness does not occur.

  (2) When the dynamic surface tension at a lifetime of 30 milliseconds is less than 41 mN / m and a reactive ink containing a reactive component and a pigment black ink are used.

  (2-1) When applying each ink in the order of pigment black ink and reactive ink.

  Image uniformity and image density can be improved by the same mechanism as described in (1-1) above.

  (2-2) When each ink is applied in the order of reactive ink and pigment black ink.

  First, when reactive ink is applied to a recording medium, the reactive ink covers the recording medium. Next, a pigment black ink is applied over the reactive ink. At this time, the reactive ink having a dynamic surface tension of less than 41 mN / m at a lifetime of 30 milliseconds has a low surface tension, so that permeation into the recording medium starts before the pigment black ink is applied to the recording medium. For this reason, the ratio of the reactive ink and the pigment black ink that are in contact with each other in a liquid state on the surface of the recording medium is relatively small, and the reactive ink and the pigment black ink are easily mixed non-uniformly at the interface. Further, the aggregation of the pigment due to the action of the reactive component in the reactive ink also proceeds non-uniformly, so that the pigment exists non-uniformly in the vicinity of the surface of the recording medium. At this time, the portion where the agglomerated pigment is thinly present feels whitish. As a result, the image becomes non-uniform and the image density may not be sufficiently obtained.

  When recording is performed at high speed, such as one-pass reciprocal recording, the recording of (2-1) and (2-2) is repeated. In this way, an image is formed in which a region where each ink is applied in the order of pigment black ink and reactive ink and a region where each ink is applied in the order of reactive ink and pigment black ink are mixed. Is done. Therefore, a uniform image and a non-uniform image are alternately formed for each recording pass, resulting in color unevenness.

[Dynamic surface tension at a lifetime of 500 milliseconds]
As described above, in the present invention, the reactive ink contains a reactive component that destabilizes the dispersion state of the self-dispersing pigment, and the reactive ink according to the maximum bubble pressure method operates at a lifetime of 30 milliseconds. It is necessary that the target surface tension is 41 mN / m or more. Furthermore, reactivity ink, and uniformity in the color solid image, in order to prevent the ink escapes the back surface of the recording medium (print-through), the characteristics of dynamic surface tension at a lifetime of 500m seconds as described below It is necessary to have.

  When plain paper or the like is used as the recording medium, it is important that the uniformity of the color solid image is high in order to improve the image quality of the full color image. However, since plain paper often has uneven ink wettability, if plain paper or the like is used as a recording medium, the color material in the color ink may not be present uniformly on the recording medium. . Here, when the ink having the dynamic surface tension characteristics as described above is a reactive color ink, the dynamics of the ink at the time when 30 milliseconds have elapsed since the ink was applied to the recording medium. The surface tension is as high as 41 mN / m or more. For this reason, there is a case where ink does not penetrate into the inside of the recording medium (in the direction of the thickness of the recording medium) and uniformity in a color solid image cannot be obtained. Therefore, as a result of studies by the present inventors, in order to obtain excellent uniformity in a color solid image, the dynamic surface tension of the reactive ink at a lifetime of 500 milliseconds needs to be 38 mN / m or less. I found out.

  Here, the meaning which prescribes | regulates the dynamic surface tension in the lifetime of 500 milliseconds of reactive ink is described below. As a result of the study by the present inventors, it has been found that the uniformity in the color solid image and the surface tension of the reactive ink at a lifetime of 500 milliseconds show the strongest correlation, that is, the dominant factor. . The present inventors consider that the strong correlation between the value of the dynamic surface tension of the reactive ink at a lifetime of 500 milliseconds and the uniformity in the solid color image means the following. . After the reactive ink is applied to the recording medium, the time required to complete the fixing to the recording medium while the colorant is associated or aggregated due to the evaporation of moisture or the like in the ink is approximately It is several hundred milliseconds to 1,000 milliseconds. At this time, it is considered that the dynamic surface tension of the reactive ink at a lifetime of 500 milliseconds greatly affects the speed at which the color material is fixed to the recording medium. The speed at which the coloring material is fixed to the recording medium and the balance of the aggregation of the coloring material are considered to determine the uniformity in the solid color image.

  As described above, when the dynamic surface tension of the reactive ink at a lifetime of 500 milliseconds is 38 mN / m or less, the reactive ink is easily wetted with respect to the recording medium. It is considered that the color material penetrates uniformly and is fixed to the recording medium uniformly. On the other hand, when the dynamic surface tension of the reactive ink at a lifetime of 500 milliseconds exceeds 38 mN / m, the reactive ink remains difficult to wet with respect to the recording medium. It is thought that uniform fixing occurs.

  However, if the dynamic surface tension of the reactive ink at a lifetime of 500 milliseconds is too low, specifically, less than 28 mN / m, the ink permeability to the recording medium becomes too high. As a result, particularly when plain paper is used as the recording medium, the ink easily penetrates into the inside of the recording medium (in the direction of the thickness of the recording medium). May occur. For this reason, the dynamic surface tension of the reactive ink at a lifetime of 500 milliseconds must be 28 mN / m or more.

[Upper limit of dynamic surface tension at a lifetime of 30 milliseconds]
Further, when the dynamic surface tension of the reactive ink at a lifetime of 30 milliseconds is too large, specifically, exceeds 51 mN / m, the time required for the ink to penetrate into the recording medium becomes long. As a result, the ink spreads on the surface of the recording medium, and the quality of characters formed with the reactive ink may deteriorate. For this reason, it is preferable that the dynamic surface tension of the reactive ink at a lifetime of 30 milliseconds is 51 mN / m or less.

<Ink>
Hereinafter , with respect to each ink, the characteristics of the ink and each component constituting the ink will be described.

[Reactive ink]
The reactive ink contains a reactive component that destabilizes the dispersion state of the self-dispersing pigment in the pigment black ink, and further has the following dynamic surface tension characteristics. That is, it is necessary that the dynamic surface tension of the reactive ink at a lifetime of 30 msec is 41 mN / m or more and the dynamic surface tension at a lifetime of 500 msec is 28 mN / m or more and 38 mN / m or less. . As described above, the dynamic surface tension of the reactive ink at a lifetime of 30 milliseconds is preferably 51 mN / m or less.

  In the present invention, destabilizing the dispersion state of the self-dispersing pigment in the pigment black ink is defined as satisfying the following (1) or (2). First, a reactive ink and a pigment black ink are mixed in an equal volume to prepare a mixed ink. At this time, (1) a mode in which aggregation and precipitation of the self-dispersing pigment occurs in the mixed ink, (2) a viscosity A of the reactive ink, a viscosity B of the pigment black ink, and a viscosity C of the mixed ink are C> (( A mode satisfying the relationship of A + B) / 2) × 1.2, and the like. The viscosity is a value measured at room temperature (25 ° C.), and the unit is mPa · s. Specifically, the above aspect (1) or (2) can be, for example, the following (A), (B), (C), or (D).

  (A) A mode in which the self-dispersing pigment in the pigment black ink has an anionic group and the reactive ink has a cationic component as a reactive component. In this case, when the pigment black ink and the reactive ink are mixed, the cationic component in the reactive ink reacts with the anionic group of the self-dispersing pigment in the pigment black ink, and the dispersion state of the pigment becomes unstable. Pigment aggregation and precipitation occur, and the mixed ink thickens.

As the cationic component, for example, a polyvalent metal can be used. A specific means for the ink to contain a polyvalent metal is, for example, that the ink contains a polyvalent metal salt. The polyvalent metal salt exists in the ink by dissociating into a polyvalent metal ion and an anion. In the present invention, the ink is also expressed as containing a polyvalent metal. Specific examples of the polyvalent metal ion include Mg ²⁺ , Ca ²⁺ , Cu ²⁺ , Co ²⁺ , Ni ²⁺ , Fe ²⁺ , La ³⁺ , Nd ³⁺ , Y ³⁺ , and Al ³⁺ . Further, specifically, the anion is preferably, for example, an inorganic acid ion such as NO ₃ ⁻ , SO ₄ ²⁻ or Cl ⁻ or an organic acid ion such as CH ₃ COO ⁻ . In the present invention, among the polyvalent metal ions described above, in view of storage stability of the reactive ink and not dissolving a member that contacts the reactive ink (such as an ink flow path constituting the ink jet recording apparatus). Mg ²⁺ is preferably used. Further, from the viewpoint of solubility, among the above anions, NO ₃ ⁻ , SO ₄ ²⁻ , Cl ⁻ , CH ₃ COO ⁻ are preferably used, and since the solubility in water is excellent, NO ₃ ⁻ , SO ₄ ^2-, _CH 3 COO ^- is particularly preferably used. The content (% by mass) of the polyvalent metal in the reactive ink is preferably 0.01% by mass or more and 10.0% by mass or less based on the total mass of the ink. In the form of the polyvalent metal salt, the content (% by mass) of the polyvalent metal salt in the reactive ink is from 0.1% by mass to 20.0% by mass based on the total mass of the ink. It is preferable that they are 0.2 mass% or more and 15.0 mass% or less.

  (B) A mode in which the self-dispersing pigment in the pigment black ink has a cationic group and the reactive ink has an anionic component as a reactive component. In this case, when the pigment black ink and the reactive ink are mixed, the anionic component in the reactive ink reacts with the cationic group of the self-dispersing pigment, destabilizing the dispersion state of the pigment, Precipitation occurs and the mixed ink thickens.

  (C) A mode in which the self-dispersing pigment in the pigment black ink is stably dispersed at pH 3 to 7, and the pH of the reactive ink is 8 to 11. In this case, when the pigment black ink and the reactive ink are mixed, the pH of the pigment black ink rises, the dispersion state of the pigment becomes unstable, the pigment aggregates and precipitates, and the mixed ink increases in viscosity. .

  (D) A mode in which the self-dispersing pigment in the pigment black ink is stably dispersed at a pH of 7 to 11, and the pH of the reactive ink is 3 to 6. In this case, when the pigment black ink and the reactive ink are mixed, the pH of the pigment black ink is lowered, the dispersion state of the pigment becomes unstable, the aggregation and precipitation of the pigment occurs, and the mixed ink is thickened. .

(Color material)
Even if the reactive ink is an ink not containing a color material or an ink containing a color material, the effect of the present invention can be obtained in any case. When a reactive ink containing a color material is used, the color material of the reactive ink may be appropriately selected and used, whether it is a known one or a newly synthesized one. The content (% by mass) of the color material in the reactive ink is preferably 0.05% by mass or more and 15.0% by mass or less based on the total mass of the ink.

  Below, the color material which can be used for reactive ink is mentioned according to color tone. Of course, the present invention is not limited to these.

[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.

[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.

[Other color materials]
In the present invention, so-called special color inks such as red, green, and blue can be used together with the above-described color tone ink as necessary. Specific examples of color materials that can be used for these inks are given below. Of course, the present invention is not limited to these.
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. 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. 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.

(Surfactant)
The reactive ink 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, fatty acid diethanolamide, acetylene glycol compound, 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]
Fluorosurfactant, silicone surfactant, etc.

  In the present invention, it is necessary that the reactive ink is adjusted to have the dynamic surface tension characteristics described above. In order for the reactive 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. Can be achieved.

  In the present invention, it is particularly preferable to adjust the dynamic surface tension of the reactive ink using a nonionic surfactant, more preferably a polyoxyethylene alkyl ether, among the above surfactants. When such a surfactant is used, the content (% by mass) of the surfactant in the reactive ink is 0.10% by mass to 3.0% by mass based on the total mass of the ink. It is preferable that they are 0.5 mass% or more and 2.0 mass% or less. When the content is less than 0.10% by mass, sufficient wetting with respect to the members constituting the ink flow path of the ink jet recording apparatus cannot be obtained, and the ejection stability may be lowered. On the other hand, if the content exceeds 3.0% by mass, when the water in the ink evaporates in the vicinity of the discharge port of the ink jet recording apparatus, the content of the surfactant becomes too high, and the ink locally In some cases, the viscosity increases, and the ejection stability of the ink decreases.

  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). It is particularly preferred. Since inks containing these surfactants have a large change in dynamic surface tension with respect to a change in lifetime, they are particularly suitable for achieving both suppression of bleeding and color unevenness and high image quality.

  General formula (1)

(In general formula (1), a, m, and n 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), b, x, and y are each independently an integer of 1 or more, and x + y is an integer of 12 to 21.)

  When the surfactant represented by the general formula (1) or the general formula (2) is used, the content (% by mass) is 0.30% by mass or more and 2.0% by mass based on the total mass of the ink. Hereinafter, it is further preferable that the content is 0.75 mass% or more and 1.5 mass% or less. By setting it as the above range, it is possible to achieve both the suppression of bleeding and color unevenness and high image quality, and further to obtain the discharge stability.

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)
If the HLB value is less than 12.0, the hydrophilicity of the surfactant is too low, and therefore the surfactant may not be dissolved in the ink when the ink is stored. On the other hand, if the HLB value is larger than 16.5, the hydrophilicity of the surfactant is too high, and it may be difficult to lower the dynamic surface tension with a lifetime of 500 milliseconds.

(Aqueous medium)
The reactive ink preferably contains an aqueous medium that is a mixed solvent of water and a water-soluble organic compound . The Lee ink, if it is adjusted to have the characteristics of dynamic surface tension of the ink as described above, can be used any of water-soluble organic compound. 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;

  Moreover, it is preferable to use deionized water (ion exchange water) as the water. The water content (% by mass) in the reactive ink is such that the ink has an appropriate viscosity for stably ejecting the ink and the ink at the nozzle tip is prevented from being clogged. It is preferable that it is 50.0 mass% or more and 95.0 mass% or less on the basis of mass.

(Other ingredients)
The reactive ink may contain a moisturizing compound such as urea, a urea derivative, trimethylolpropane, trimethylolethane and the like in addition to the above components in order to maintain the moisturizing property. The content (% by mass) of the moisturizing compound in the reactive ink is 0.1% by mass or more and 20.0% by mass or less, further 3.0% by mass or more and 10.0% by mass based on the total mass of the ink. % Or less is preferable. Furthermore, the reactive ink may contain various compounds as necessary in addition to the above components in order to obtain an ink having a desired physical property value. Specifically, for example, it contains various additives such as a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an anti-reduction agent, an evaporation accelerator, a chelating agent, and a water-soluble polymer. May be.

(Ink physical properties)
In the present invention, the static surface tension of the reactive ink is preferably 20 mN / m or more and 40 mN / m or less, more preferably 25 mN / m or more and 35 mN / m or less.

[Pigment black ink]
(Color material)
In the present invention, the pigment used in the pigment black ink needs to be a self-dispersing pigment. The self-dispersing pigment in the present invention is a pigment having at least one hydrophilic group bonded to the surface of the pigment particle directly or through another atomic group, as will be described in detail later. By using a pigment black ink containing a self-dispersing pigment together with the reactive ink described above, high-level image quality required in recent years, that is, occurrence of bleeding and color unevenness was effectively suppressed. An image can be obtained. The present inventors consider this reason as follows. That is, the pigment black ink containing a self-dispersing pigment causes the aggregation of the pigment to occur more rapidly when it comes into contact with the reactive ink than other pigments such as a resin-dispersed pigment. It is believed that can be obtained more prominently.

  In the present invention, the self-dispersing pigment used in the pigment black ink is particularly preferably self-dispersing carbon black. In addition to the self-dispersing pigment, dyes listed as color materials for reactive ink can be used for the pigment black ink for the purpose of color matching and the like. The content (% by mass) of the self-dispersing pigment in the pigment black 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 based on the total mass of the ink. % Or less is preferable.

〔Carbon black〕
Examples of the pigment used for the pigment black ink include carbon black. For example, furnace black, lamp black, acetylene black, channel black, or the like can be used as the carbon black. Specifically, for example, the following commercially available products can be used. These pigments may be used alone or in combination of two or more. Of course, the present invention is not limited to these.
Ray Van: 7000, 5750, 5250, 5000ULTRA, 3500, 2000, 1500, 1250, 1200, 1190ULTRA-II, 1170, 1255 (above, Colombia). Black Pearls: L, Legal: 400R, 330R, 660R, Mougl: L, Monak: 700, 800, 880, 900, 1000, 1100, 1300, 1400, 2000, Vulcan: XC-72R (above, manufactured by Cabot). Color Black: FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Printex: 35, U, V, 140U, 140V, Special Black: 6, 5, 4A, 4 (above, manufactured by Degussa). No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (above, manufactured by Mitsubishi Chemical).

  Carbon black newly prepared for the present invention can also be used. 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.

(Self-dispersing pigment)
In the present invention, at least one hydrophilic group is bonded to the surface of the pigment particle directly or through another atomic group (—R—) as the carbon black described above (hereinafter sometimes referred to as a pigment). Self-dispersing pigments can be used. Such a self-dispersing pigment is a pigment that can be dispersed in an aqueous medium constituting an ink without using a resin dispersant. Of course, a resin dispersant can be used in combination as required.

Specifically, the hydrophilic group bonded to the surface of the pigment particle is, for example, —COO (M ₁ ), —SO ₃ (M ₁ ), —PO ₃ H (M ₁ ), —PO ₃ (M _{1) 2, - (COO (} M 1)) n and the like. In the formula, “M ₁ ” is a hydrogen atom, an alkali metal, ammonium, or organic ammonium, and n is an integer of 2 or more. Examples of the other atomic group (—R—) include an alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, and a substituted or unsubstituted naphthylene group. Of course, the present invention is not limited to this. Incidentally, the form of the hydrophilic group in the ink may be any form in which a part thereof is dissociated or completely dissociated. In the present invention, in particular, a pigment obtained by a diazo coupling method and having a compound having a structure of the above-mentioned —R— (COOM ₁ ) _n group in part as a surface can be suitably used.

Further, in the -R- bonded to the surface of the pigment particle, - (COOM ₁₎ is a carbon atom adjacent to the carbon atom to which they are attached, - it is preferably bonded to (COOM _1). The n is preferably 2, and the R is preferably C ₆ H ₃ . Note that in -R- bonded to the surface of the pigment particle, - (COOM ₁₎ is a carbon atom adjacent to the carbon atom to which they are attached, - the fact that by combining (COOM _1), Two or more adjacent carbon atoms in R both have a — (COOM ₁ ) group. Specifically, this is to have a structure represented by the following general formula (3). In the present invention, it is preferable to use a self-dispersing pigment in which a group represented by the following formula (1) is bonded to the surface of the pigment particle.

  General formula (3)

Further, in the pigment black ink, it is preferable that the —R— (COOM ₁ ) _n group is bonded to the surface of the pigment particle at a higher density. Specifically, for example, the hydrophilic group density on the surface of the pigment particles is preferably 2.00 μmol / m ² or more. In the present invention, the hydrophilic group density in the pigment particle is greatly affected by the specific surface area of the pigment, the structure of the functional group bonded to the surface of the pigment particle, and the like. Absent. In addition, the upper limit of the hydrophilic group density on the surface of the pigment particles is preferably 4.0 μmol / m ² or less.

Furthermore, in the pigment black ink, when M ₁ is ammonium, it is particularly preferable because better water resistance can be obtained. This is because, when the ink is applied to the recording medium, the ammonium is decomposed, the ammonia is evaporated, and the hydrophilic group bonded to the surface of the pigment particles becomes H type (acid type), and the hydrophilicity is lowered. This is thought to be due to Here, the self-dispersing pigment in which M ₁ is ammonium can be obtained by the following method. For example, for a self-dispersing pigment in which M ₁ is an alkali metal, an ion exchange method is used to replace M ₁ with ammonium, or an acid is added to form H to add ammonium hydroxide. Examples include a method of converting ₁ to ammonium.

(salt)
The pigment black ink preferably contains a salt. Thereby, since aggregation of the pigment on the recording medium is promoted, the effects of the present invention can be stably obtained regardless of the type of the recording medium.

  The form of the salt in the pigment black ink may be in any dissociated state or completely dissociated state. In addition, although salt dissociates and exists in a metal ion and an anion in an ink, in this invention, it expresses that an ink contains salt also in this case.

Specific examples of the salt that can be used in the pigment black ink include, for example, (M ₂ ) NO ₃ , CH ₃ COO (M ₂ ), C ₆ H ₅ COO (M ₂ ), C ₂ H ₄ (COO (M ₂ )) ₂ , C ₆ H ₄ (COO (M ₂ )) ₂ , (M ₂ ) ₂ SO _{4 and the} like. In the above formula, “M ₂ ” is an alkali metal, ammonium, or organic ammonium. Examples of the alkali metal include lithium, sodium, and potassium. Examples of the organic ammonium include acetamido, benzamide, methylamino, butylamino, diethylamino, and phenylamino. Of course, the present invention is not limited to these.

  The salt content in the pigment black ink only needs to be within a range where the effects of the present invention can be sufficiently obtained. Specifically, the salt content (% by mass) is preferably 0.05% by mass or more and 10.0% by mass or less based on the total mass of the ink. When the content is less than 0.05% by mass, the effect of the present invention may not be obtained. When the content is more than 10.0% by mass, the storage stability of the ink may not be obtained.

(Aqueous medium)
The pigment black ink 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 water content (% by mass) in the pigment black ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink.

  The water-soluble organic compound is particularly preferably one having an effect of suppressing ink drying. The content (% by mass) of the water-soluble organic compound in the pigment black ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink. Specifically, for example, the following water-soluble organic compounds can be used. The following water-soluble organic compounds can be used alone or in combination of two or more.

  Alcohols having 1 to 6 carbon atoms such as ethanol, isopropanol, 2-propanol, n-butanol, isobutanol, butanol, pentanol and hexanol. Carboxylic acid amides such as N, N-dimethylformamide or N, N-dimethylacetamide. Ketones such as acetone, methyl ethyl ketone, and 2-methyl-2-hydroxypentan-4-one; Cyclic ethers such as keto alcohol, tetrahydrofuran and dioxane. Polyhydric alcohols such as glycerin, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2- or 1,3-propylene glycol, 1,2- or 1,4-butylene glycol, polyethylene glycol. 1,3-butanediol, 1,2- or 1,5-pentanediol, 1,2- or 1,6-hexanediol, dithioglycol, 2-methyl-1,3-propanediol, 1,2,6 -Polyhydric alcohols such as hexanetriol and trimethylolpropane. 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;

(Other ingredients)
The pigment black ink may contain a moisturizing compound such as urea, urea derivative, trimethylolpropane, trimethylolethane and the like in addition to the above components in order to maintain the moisturizing property. The content (% by mass) of the moisturizing compound in the pigment black ink is 0.1% by mass or more and 20.0% by mass or less, and further 3.0% by mass or more and 10.0% by mass based on the total mass of the ink. % Or less is preferable. In addition to the above components, the pigment black ink is a surfactant, a pH adjuster, an antifoaming agent, an antirust agent, an antiseptic agent, and an antifungal agent, as necessary, in order to obtain an ink having a desired physical property value. Further, additives such as an antioxidant, an anti-reduction agent, an evaporation accelerator and a chelating agent may be contained.

(Ink physical properties)
In the present invention, the static surface tension of the pigment black ink is preferably 30 mN / m or more and 60 mN / m or less, more preferably 35 mN / m or more and 50 mN / m or less.

[Non-reactive ink]
In the present invention, in addition to the reactive ink and the pigment black ink described above, other inks can be used in combination. The other ink in the present invention includes, for example, an ink that does not contain a reactive component such as a polyvalent metal, that is, an ink that does not react with the pigment black ink (non-reactive ink). The coloring material of the non-reactive ink can be a dye or a pigment, and these coloring materials can be appropriately selected and used, whether they are known or newly synthesized. . Specifically, what can be used as the coloring material of the reactive ink can be used. The content (% by mass) of the color material in the non-reactive ink is preferably 0.05% by mass or more and 15.0% by mass or less based on the total mass of the ink. In addition, as the aqueous medium and additive of the non-reactive ink, the same reactive ink and pigment black ink as described above can be used.

<Ink set>
Lee Nkusetto is made of a plurality of inks, at least, and having a reactive ink and pigment black ink described above. The ink set may further include at least one of the non-reactive inks described above and other inks. 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. Or, an ink cartridge formed by accommodating a plurality of inks independently are also state in which is detachably configured for ink-jet recording device are also included in Lee Nkusetto. Anyway, Lee Nkusetto may be composed so that it can be used in combination with at least reactive ink and the pigment black ink is not limited to the above embodiments, there in any form May be.

<Image Forming Method and Image Forming Apparatus>
An image forming method according to the present invention is an image in which a black ink containing a self-dispersing pigment and at least one aqueous ink are each ejected from an inkjet recording head and applied to plain paper to form an image. A method of forming, comprising: applying the black ink and the water-based ink to the plain paper so as to overlap at least part of the region, and bringing the black ink and the water-based ink into contact with each other, wherein the aqueous ink contains a reactive component, and a surfactant destabilizing the dispersion state of the self-dispersing pigment, a polyoxyethylene alkyl ether of the surfactant specified structure, and the aqueous The content (mass%) of the polyoxyethylene alkyl ether having the specific structure in the ink is 0.30 based on the total mass of the ink. And a quantity% to 2.0 wt% or less, of the water-based ink according to the maximum bubble pressure method, and the dynamic surface tension at a lifetime of 30m sec 41 mN / m or more and a dynamic surface tension at a lifetime of 500m sec 28mN / m to 38 mN / m Ri der hereinafter static surface tension of said black ink, with greater than the static surface tension of the water-based ink, characterized in der Rukoto below 30 mN / m or more 60 mN / m .

The image forming apparatus according to the present invention forms an image by ejecting a black ink containing a self-dispersing pigment and at least one water-based ink from a recording head of an ink jet system onto a plain paper. The image forming apparatus includes a means for applying the black ink and the water-based ink to the plain paper so as to overlap at least in a part of the plain paper and bringing the black ink and the water-based ink into contact with each other. The water-based ink contains a reactive component that destabilizes the dispersion state of the self-dispersing pigment, and a surfactant, and the surfactant is a polyoxyethylene alkyl ether having a specific structure , and The content (% by mass) of the polyoxyethylene alkyl ether having the specific structure in the water-based ink is 0. 0% based on the total mass of the ink. 0 is% by mass or more and 2.0 mass% or less, of the water-based ink according to the maximum bubble pressure method, and the dynamic surface tension at a lifetime of 30m sec 41 mN / m or more and a dynamic surface tension at a lifetime of 500m sec 28 mN / m or more 38 mN / m Ri der hereinafter static surface tension of said black ink, with greater than the static surface tension of the aqueous ink, and wherein der Rukoto below 30 mN / m or more 60 mN / m To do.

  As an image forming apparatus suitable for recording using the reactive ink or pigment black ink described above, an ink jet recording apparatus capable of reciprocal recording will be described with reference to FIGS.

  FIG. 1 is a schematic explanatory view showing an example of an ink jet recording apparatus. The chassis 1 is composed of a plurality of plate-like metal members having a predetermined rigidity, and forms a skeleton of the ink jet recording apparatus. The chassis 1 includes a paper feed unit 2 that feeds the recording medium, a transport unit 4 that guides the recording medium to a predetermined recording position and leads to the discharge unit 3, a recording unit that performs predetermined recording on the recording medium, and recovery of the recording unit A recording head recovery unit 5 that operates is incorporated. The recording unit includes a carriage 7 that is supported so as to be able to scan along the carriage shaft 6, a recording head cartridge 10 that is detachably mounted on the carriage 7 via a recording head set lever 8, and a carriage cover that positions the recording head cartridge 10 at a predetermined position. 9 One end of a contact flexible printed cable (hereinafter abbreviated as a contact FPC) 11 is connected to another engaging portion of the carriage 7 with respect to the recording head cartridge 10. The contact portion 15 (see FIG. 2) formed at the end of the contact FPC 11 and the contact portion 15 which is an external signal input terminal provided in the recording head cartridge 10 are in electrical contact to exchange various information. For example, power is supplied to the recording head cartridge 10.

  When forming an image, the carriage 7 places a recording head cartridge 10 incorporating a recording head at a target image forming position, and ejects ink from the recording head based on various information received through the contact portion 15. Then, recording is performed on the recording medium. Specifically, the main scanning in which the carriage 7 scans in the column direction along the carriage shaft 6 and the sub-scan in which the transport unit 4 transports the recording medium in the row direction are alternately repeated while performing recording by the recording head. Then, an image is formed on the recording medium. At this time, an image forming method for forming an image by one main scanning of the recording head with respect to a unit area of the recording medium is one-pass recording, and this one-pass recording is performed in the forward direction and the sub-direction of the main scanning. The image forming method to be performed is one-pass reciprocal recording. An image forming method for forming an image on a unit area of a recording medium by n-time scanning of the recording head is n-pass recording (n is 1 or more). The unit area refers to one pixel, one band, or the like, and the unit area can be set as various areas as necessary. Here, one pixel is one pixel corresponding to the resolution, and one band is an image area formed by one scan of the recording head. In order to obtain the effects of the present invention, it is particularly preferable to configure the image forming method and the image forming apparatus so as to include one-pass reciprocal recording.

FIG. 2 is a schematic explanatory view showing an example of the recording head cartridge 10. Here, a case where three types of color inks and pigment black ink are used will be described as an example. At least one of these three color ink and reactivity ink. The recording head cartridge 10 is similarly set to the ejection port array 14 of the pigment black ink recording head 12 and the color ink recording head 13 based on the recording signal received from the recording apparatus main body through the contact portion 15. Ink is ejected from the outlet row. In the above has been described as three color inks, ink number is not limited to this, also, of which at least one is a color ink if the reactivity ink, the hue of the ink and the number ink It can be set appropriately.

  Examples of the recording head include a bubble jet (registered trademark) type recording head that causes film boiling in the ink by the action of thermal energy and discharges the ink. 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. In the case of the on-demand type, thermal energy is generated by applying to the electrothermal transducer at least one drive signal that gives a rapid temperature rise exceeding nucleate boiling corresponding to the recorded information. This is effective because film boiling occurs on the heat acting surface of the recording head, and as a result, bubbles in the ink corresponding to the drive signals can be formed on a one-to-one basis. Ink is ejected through the ejection port by the growth and contraction of the bubbles. It is more preferable that the drive signal has a pulse shape, since bubbles are grown and contracted immediately and appropriately, and ink ejection with particularly excellent responsiveness can be achieved.

  In addition to the recording head described above, a recording head that ejects ink by the action of mechanical energy may be used. In this case, the recording head includes a nozzle forming substrate having a plurality of nozzles, a piezoelectric material disposed facing the nozzles, a pressure generating element made of a conductive material, and ink filling the periphery of the pressure generating element. Prepare. In this embodiment, the pressure generating element is displaced by the applied voltage, and ink is ejected.

  Furthermore, the ink jet recording apparatus can be used even if the recording head and the ink cartridge are separated, or they are integrated so as not to be separated. The ink cartridge is integrated with the recording head so as to be separable or non-separable and mounted on the carriage, or provided at a fixed portion of the ink jet recording apparatus, and the recording head via an ink supply member such as a tube. The ink may be supplied to the ink. 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 configuration in which an absorber is disposed in the ink storage portion of the ink cartridge, or a configuration having 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. Can be adopted. The ink jet recording apparatus preferably employs a serial recording method as described above, but 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.

  Hereinafter, although it demonstrates more concretely using an Example, a comparative example, and a reference example, this invention is not limited to these, unless the summary is exceeded. In the following description, “%” is based on mass unless otherwise specified.

<Preparation of pigment dispersion>
To a solution obtained by dissolving 5 g of concentrated hydrochloric acid in 5.5 g of water, 1.5 g of 4-amino-1,2-benzenedicarboxylic acid was added while being cooled to 5 ° C. Next, the container containing the solution was placed in an ice bath and the solution was stirred to keep the solution constantly at 10 ° C. or lower, and 1.8 g of sodium nitrite was dissolved in 9 g of water at 5 ° C. The solution was added. The solution was further stirred for 15 minutes, and 6 g of carbon black having a specific surface area of 220 m ² / g and a DBP oil absorption of 105 mL / 100 g was added with stirring. Thereafter, the mixture was further stirred for 15 minutes. The obtained slurry was filtered with a filter paper (trade name: Standard filter paper No. 2; manufactured by Advantech), and then the particles were sufficiently washed with water and dried in an oven at 110 ° C. to prepare self-dispersing carbon black. About the obtained self-dispersion type carbon black, sodium ions were replaced with ammonium ions by an ion exchange method. Further, water was added to the obtained self-dispersing carbon black and dispersed so that the pigment concentration became 10% by mass to prepare a dispersion. By the above method, a pigment dispersion was obtained in a state where self-dispersing carbon black in which —C ₆ H ₃ — (COONH ₄ ) ₂ groups were introduced on the surface of carbon black particles was dispersed in water.

When the ionic group density of the self-dispersing carbon black prepared above was measured, it was 3.1 μmol / m ² . The ionic group density used here was measured by measuring the sodium ion concentration of the self-dispersing carbon black (sodium salt type) prepared above using an ion meter (manufactured by Toa DKK). It was converted into the ionic group density of the dispersed carbon black.

<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 values of m, n, a, and m + n when the structure of the main component of each surfactant and the structure of the surfactant correspond to the general formula (1). In addition, when the general formula (2) is satisfied, the values of x, y, b, and x + y are also shown.

  In Table 1, EMALEX 1610, EMALEX 1615, and EMALEX 1825 are surfactants manufactured by Nippon Emulsion. NIKKOL BT-7 and NIKKOL BT-12 are surfactants manufactured by Nikko Chemicals. Further, acetylenol E100 is a surfactant manufactured by Kawaken Fine Chemicals.

<Preparation of ink>
The components shown in Tables 2 to 5 below were mixed and dissolved or dispersed by sufficiently stirring. Then, the pigment black ink was applied to a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm and the other inks having a pore size of 0.2 μm. Then, pressure filtration was performed to prepare an ink. In Tables 2 to 5, EMALEX 1610, EMALEX 1615, and EMALEX 1825 are surfactants manufactured by Nippon Emulsion. NIKKOL BT-7 and NIKKOL BT-12 are surfactants manufactured by Nikko Chemicals. Further, acetylenol E100 is a surfactant manufactured by Kawaken Fine Chemicals.

<Reactivity of mixed ink of reactive ink or non-reactive ink and pigment black ink>
20 g of pigment black ink and 20 g of reactive ink or non-reactive ink shown in Table 6 below were mixed and sufficiently mixed to prepare a mixed ink, and then the mixed ink was allowed to stand for about 24 hours. Thereafter, the presence or absence of precipitates or aggregates in the mixed ink was visually confirmed to evaluate the reactivity. The evaluation results are shown in Table 6.

  From Table 6, it can be seen that in the combination of the pigment black ink and the reactive ink, the reactive inks R-1 to R-16 are inks that destabilize the dispersion state of the pigment in the pigment black ink. .

<Evaluation>
(Measurement of dynamic surface tension)
For each reactive ink and non-reactive ink obtained above, the dynamic surface tension of the ink at (1) life time 30 msec and (2) 500 msec was measured. For the measurement, an apparatus (Bubble Pressure Tesiometer BP2; manufactured by KRUSS) that measures dynamic surface tension by the maximum bubble pressure method was used. Table 7 shows the evaluation results of the dynamic surface tension.

(Color unevenness in a black solid image)
A solid black image was formed by an image forming method in which other inks were applied in a region to which the pigment black ink was applied using a combination of the front ink and the post ink shown on the left side of Table 8 below. The image forming apparatus used was a modified ink jet recording apparatus BJF850 (manufactured by Canon Inc.) capable of reciprocal recording. As the recording medium, four types of plain papers were used: Canon Extra, Canon Office Multi-Function Applications, EN100, high color plain paper super white paper SW101 (manufactured by Canon Inc.). The respective inks were applied to the recording medium in the order of the first ink and the second ink described in Table 8 below. The image was formed by one-way reciprocal recording. In this case, the amount of ink applied was about 28 ng of pigment black ink and about 4.5 ng of other inks per 1/600 inch square.

  For each of the images obtained using the four types of recording media, the difference between the image density and the color tone of the image formed by the forward recording and the image formed by the backward recording is visually confirmed and evaluated, and the average of these is evaluated. The value was the evaluation result of color unevenness in a black solid image. Furthermore, the evaluation of color unevenness in the black solid images of Examples 1 to 14, Comparative Examples 1 to 7, and Reference Example 1 was relatively evaluated in five stages of A, B, C, D, and E. . That is, the image with the best image density and color tone difference between the image formed by the forward recording and the image formed by the backward recording is A, and the image of the image formed by the forward recording and the image formed by the backward recording Evaluation was performed with E being the inferior state of density or color difference. As a result of the evaluation, it was determined that among the five stages A, B, C, D, and E, A and B are acceptable levels of color unevenness in the black solid image currently required. The evaluation results are shown in Table 8.

(Bleeding resistance)
An image in which a black solid image similar to that formed in the evaluation of the black solid image and a solid image formed with color inks are adjacent to each other was formed. At this time, the following components were mixed into the color ink, dissolved sufficiently by stirring, and then subjected to pressure filtration with a microfilter (manufactured by Fuji Film) having a pore size of 0.2 μm. Reactive ink was used. Components constituting the ink include C.I. I. Acid yellow 23: 3.0 parts, glycerin: 5.0 parts, 1,5-pentanediol: 10.0 parts, diethylene glycol 5.0 parts, acetylenol E100: 1.0 part, and water: 76.0 parts did. The image forming apparatus used was a modified ink jet recording apparatus BJF850 (manufactured by Canon Inc.) capable of reciprocal recording. As the recording medium, four types of plain papers were used: Canon Extra, Canon Office Multi-Function Applications, EN100, high color plain paper super white paper SW101 (manufactured by Canon Inc.). The image was formed by one-pass reciprocal recording. In this case, the amount of ink applied was about 28 ng of pigment black ink and about 14 ng of non-reactive ink per 1/600 inch square.

  For each of the images obtained using the four types of recording media, the blurring at the boundary between the black and color images was visually confirmed and evaluated, and the average value thereof was taken as the bleeding evaluation result. Furthermore, the bleeding resistance of Examples 1 to 14, Comparative Examples 1 to 7, and Reference Example 1 was relatively evaluated in three stages of A, B, and C. That is, the evaluation was made with A having the least blurring and being good and A having the most blurring and having C. As a result of the evaluation, it was determined that A and B were currently acceptable bleeding tolerance levels among the three stages of A, B, and C. The evaluation results are shown in Table 8.

(Uniformity in color solid images)
A solid color image was formed using the ink shown on the right side of Table 8 below. At this time, pigment black ink was not used. The image forming apparatus used was a modified ink jet recording apparatus BJF850 (manufactured by Canon Inc.) capable of reciprocal recording. As the recording medium, four types of plain papers were used: Canon Extra, Canon Office Multi-Function Applications, EN100, high color plain paper super white paper SW101 (manufactured by Canon Inc.). The image was formed by one-pass reciprocal recording. The amount of ink applied at this time was about 14 ng in a 1/600 inch square area.

  For each of the images obtained using the four types of recording media, the uniformity in the color solid image was visually confirmed and evaluated, and the average value thereof was taken as the evaluation result of the uniformity in the color solid image. . Furthermore, the uniformity in the solid color images of Examples 1 to 14, Comparative Examples 1 to 7, and Reference Example 1 was relatively evaluated in four stages of A, B, C, and D. That is, the evaluation was performed with A having the highest uniformity in the color solid image as A and D having the lowest uniformity in the color solid image as D. As a result of the evaluation, it was determined that among the four stages A, B, C, and D, A and B are the acceptable level of uniformity in the solid image of the color that is currently required. The evaluation results are shown in Table 8.

(Color character quality)
Using the ink shown on the right side of Table 8 below, a 12-point Gothic color character was formed. At this time, pigment black ink was not used. The image forming apparatus used was a modified ink jet recording apparatus BJF850 (manufactured by Canon Inc.) capable of reciprocal recording. As the recording medium, four types of plain papers were used: Canon Extra, Canon Office Multi-Function Applications, EN100, high color plain paper super white paper SW101 (manufactured by Canon Inc.). The image was formed by one-pass reciprocal recording. The amount of ink applied at this time was about 18 ng in a 1/600 inch square area.

  For each of the images obtained using the four types of recording media, the color character quality was visually confirmed and evaluated, and the average value thereof was taken as the color character quality evaluation result. Furthermore, the character quality of the color of Examples 1-14, Comparative Examples 1-7, and Reference Example 1 was relatively evaluated in two stages of A and B. That is, the color character quality was highest and good, and the evaluation was evaluated as A, and the color quality that was inferior to A but acceptable was B. The evaluation results are shown in Table 8.

  When the back surface of the portion of the color image formed on the recording medium using the reactive ink (R-16) of Comparative Example 7 was visually confirmed, there was a see-through. On the other hand, no show-through occurred on the back surface of the color image portion formed on the recording medium using reactive ink or non-reactive ink other than the reactive ink (R-16) of Comparative Example 7 above.

It is the schematic which shows an example of an inkjet recording device. FIG. 3 is a schematic diagram illustrating an example of a recording head cartridge.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Chassis 2 Paper feed part 3 Ejection part 4 Conveyance part 5 Recording head recovery | restoration part 6 Carriage shaft 7 Carriage 8 Recording head set lever 9 Carriage cover 10 Recording head cartridge 11 Contact flexible print cable (contact FPC)
12 recording head for pigment black ink 13 recording head for color ink 14 discharge port array 15 contact portion

Claims (5)

An image forming method for forming an image by ejecting a black ink containing a self-dispersing pigment and at least one water-based ink from a recording head of an ink jet system and applying it to plain paper ,
Applying the black ink and the water-based ink to the plain paper so that they overlap at least in a part of the plain paper , and bringing the black ink and the water-based ink into contact with each other;
The water-based ink contains a reactive component that destabilizes the dispersion state of the self-dispersing pigment, and a surfactant,
The surfactant is at least one selected from a surfactant represented by the following general formula (1) and a surfactant represented by the general formula (2) , and in the water-based ink, The content (mass%) of at least one selected from the surfactant represented by the general formula (1) and the surfactant represented by the general formula (2) is 0. 30% by mass or more and 2.0% by mass or less,
General formula (1)

(In general formula (1), a, m, and n 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), b, x, and y are each independently an integer of 1 or more, and x + y is an integer of 12 to 21.)
Maximum of the water-based ink according bubble pressure method, and the dynamic surface tension at a lifetime of 30m sec 41 mN / m or more and a dynamic surface tension at a lifetime of 500m sec Ri Der below 28 mN / m or more 38 mN / m,
The static surface tension of the black ink, the conjunction greater than the static surface tension of the aqueous ink, an image forming method comprising der Rukoto below 30 mN / m or more 60 mN / m.   The image forming method according to claim 1, wherein the dynamic surface tension of the water-based ink by a maximum bubble pressure method at a lifetime of 30 milliseconds is 51 mN / m or less. Wherein the surfactant in the aqueous ink, HLB value by Griffin method, image forming method according to claim 1 or 2 is 12.0 or more 16.5 or less. The reactive component, image forming method according to any one of claims 1 to 3 is a polyvalent metal ion. An image forming apparatus for forming an image by ejecting a black ink containing a self-dispersing pigment and at least one water-based ink from a recording head of an ink jet system and applying the ink to plain paper ,
The black paper and the water-based ink are applied to the plain paper so as to overlap at least in a part of the paper , and the black ink and the water-based ink are brought into contact with each other.
The water-based ink contains a reactive component that destabilizes the dispersion state of the self-dispersing pigment, and a surfactant,
The surfactant is at least one selected from a surfactant represented by the following general formula (1) and a surfactant represented by the general formula (2) , and in the water-based ink, The content (mass%) of at least one selected from the surfactant represented by the general formula (1) and the surfactant represented by the general formula (2) is 0. 30% by mass or more and 2.0% by mass or less,
General formula (1)

(In general formula (1), a, m, and n 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), b, x, and y are each independently an integer of 1 or more, and x + y is an integer of 12 to 21.)
Maximum of the water-based ink according bubble pressure method, and the dynamic surface tension at a lifetime of 30m sec 41 mN / m or more and a dynamic surface tension at a lifetime of 500m sec Ri Der below 28 mN / m or more 38 mN / m,
The static surface tension of the black ink, the conjunction greater than the static surface tension of the aqueous ink, an image forming apparatus according to claim der Rukoto below 30 mN / m or more 60 mN / m.