JP2007297513A - Ink set and image formation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink set and an image formation method, capable of forming high quality images excellent in color balance and color development of not only monochrome but also compound color, even in reciprocating printing or low-pass printing by inkjet printing method. <P>SOLUTION: The ink set comprises combination of a reaction liquid containing multivalent metal and two or more water-base inks containing at least yellow ink, wherein the water-base ink contains at least a pigment dispersed by an anionic material or a pigment having an anionic group on the surface thereof, and reactivity of the yellow ink with the reaction liquid is higher than that of a water-base ink other than the yellow ink with the reaction liquid. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink set in which a reaction liquid and two or more water-based inks including at least a yellow ink are combined, and an image forming method using the same. More specifically, the present invention relates to a writing instrument such as a water-based ballpoint pen, a fountain pen, a water-based sign pen, an ink set suitable for an inkjet printer, and an image forming method using the ink set.

  Ink-jet recording, which is characterized by being capable of printing high-resolution, high-quality images at high speed with an inexpensive device, causes droplets of an ink composition (hereinafter referred to as ink) to fly to a recording medium such as paper. This is a printing method in which printing is performed by adhering. However, since the ink used in the ink jet recording method is an aqueous liquid, ink droplets that have landed on the recording medium penetrate into the recording medium, resulting in unclear outlines or boundaries between adjacent different colors. There was a problem that bleeding (so-called color bleeding) occurred.

  In order to solve this problem, as disclosed in Patent Document 1, after a solution of a polyvalent metal salt is newly applied to a recording medium, an ink containing at least one dye having a carboxyl group is applied. An image forming method has been proposed. That is, in this case, an insoluble material is formed when the reaction liquid containing the polyvalent metal ion and the dye in the ink come into contact with each other on the recording medium. As a result, the following effects are obtained. That is, with the configuration as described above, the ambiguity of the contour portion of the image is improved, color bleeding does not occur, and the occurrence of show-through is suppressed (hereinafter referred to as “show-through resistance”). A quality image can be obtained.

  In addition, by using a combination of a black ink that thickens or aggregates due to the action of a salt and a color ink containing the salt, a technology that provides a high-quality color image with high image density and no color bleeding. Means are also disclosed (see Patent Document 2). That is, in this technique, it is possible to obtain a good image by printing two liquids, that is, the first liquid containing salt and the ink. As proposals using two liquids, there are various proposals of Patent Documents 3 and 4.

JP-A-5-202328 JP-A-6-106735 JP-A-3-240557 JP-A-3-240558

  The inventors of the present invention have made various studies on the ink set using the polyvalent metal ions as described above. As a result, when a pigment is used as the colorant in the ink, the ambiguity of the outline is improved, the occurrence of color bleeding is suppressed, and furthermore, it is possible to form a high-quality image with excellent resistance to see-through. On the other hand, it came to recognize the new problem as described below.

  The polyvalent metal ion in the reaction solution destroys the dispersion of the pigment in the ink, and has the effect of improving the ambiguity of the outline and preventing color bleeding. However, there is a problem that the color balance that is reproduced is lost when image recording is performed by the following method, which is performed for the purpose of shortening the printing time, using a reaction liquid containing polyvalent metal ions. Occurs. For example, a method of printing in both forward and backward directions of main scanning (hereinafter referred to as “reciprocal printing”), and a method of low pass printing that completes an image having the same width as the length of the recording head in one main scanning. This is a case where the image recording is performed. More specifically, when a mixed color image such as a blue, red, or green secondary color image or a gray image is formed with an ink set of cyan, magenta, and yellow, the reproduced color balance may be lost. is there. This phenomenon is more prominently detected when an ink set is used in which a plurality of water-based inks used have different reactivities to the reaction liquids used in combination.

  Accordingly, an object of the present invention is to form a high-quality image excellent in color balance and color development not only in a single color but also in a mixed color even when reciprocal printing or low-pass printing is performed by an inkjet recording method. It is an object of the present invention to provide an ink set and an image forming method.

  In the course of studying to solve the above-described problems of the prior art, the present inventors can configure as follows when a plurality of inks having the above characteristics and a reaction liquid are used in combination. I found it effective. In other words, in the combination of a plurality of inks and a reaction liquid constituting an ink set, the reactivity of the reaction liquid and the yellow ink is made higher than the reactivity of the inks of other colors and the reaction liquid, so that a mixed color is obtained. It is possible to form a high-quality image having excellent balance and color developability.

  The present invention has been completed based on this finding. That is, the above object is achieved by the present invention described below. The ink set of the present invention is an ink set in which a reaction liquid containing a polyvalent metal and two or more aqueous inks including at least a yellow ink are combined, and the aqueous ink is dispersed at least by an anionic substance. And the reactivity of the yellow ink and the reaction liquid is higher than the reactivity of the aqueous ink other than the yellow ink and the reaction liquid. It is characterized by that. According to such an ink set, even when reciprocal printing or low-pass printing is performed by an inkjet recording method, it is possible to form a high-quality image that is excellent not only in a single color but also in a mixed color balance and color developability. It becomes.

  The image forming method of the present invention includes (i) a step of applying an aqueous ink constituting the ink set to the recording medium by an ink jet recording method; and (ii) a reaction liquid constituting the ink set. The step (ii) is performed prior to the step (i), and the aqueous ink and the reaction liquid are in contact with each other on the recording medium. It is characterized by that. An image formed by such an image forming method is obtained by securing a color material in a recording medium so that image loss is eliminated, and the contour portion of the image is clear.

Moreover, the following are mentioned as a preferable form of this invention. In the above configuration, a 400-fold diluted aqueous solution of the reaction solution and a 5-fold diluted aqueous solution of any of the aqueous inks constituting the ink set were mixed at a mixing ratio of 50: 1, and after 15 minutes, filtered through a 1.0 μm filter. The absorbance at the maximum visible wavelength in the subsequent visible region (wavelength 550 nm when carbon black is used as a pigment) is taken as (A), and the maximum absorption wavelength in the visible region of a 255-fold diluted aqueous solution of the water-based ink (carbon black as a pigment) In the case of using an ink set, an ink set characterized by satisfying the condition of the following formula (1) in any water-based ink constituting the ink set when the absorbance at a wavelength of 550 nm is (B). .
(A) / (B) <0.8 Formula (1)

Further, in the above configuration, an 800-fold diluted aqueous solution of the reaction liquid and a 5-fold diluted aqueous solution of any of the water-based inks constituting the ink set are mixed at a mixing ratio of 50: 1, and after 15 minutes, a 1.0 μm filter is used. The absorbance at the maximum absorption wavelength in the visible region after filtration (when carbon black is used as a pigment, the wavelength is 550 nm) is (C), and the maximum absorption wavelength in the visible region of a 255-fold diluted aqueous solution of the water-based ink (as pigment) When carbon black is used, an ink set characterized by satisfying the condition of the following formula (2) in any water-based ink constituting the ink set when the absorbance at a wavelength of 550 nm is (B): Can be mentioned.
(C) / (B)> 0.3 ... Formula (2)

  According to the present invention, it is possible to achieve formation of an image that is substantially uniform on a recording medium and that has achieved scratch resistance. Further, according to the present invention, it is possible to obtain a high-quality image in which the ambiguity of the contour portion of the image is improved and no color bleeding occurs.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. The present invention has a novel configuration in which the reactivity between the reaction liquid and the yellow ink is higher than the reactivity between the inks of other colors and the reaction liquid, so that it is excellent in color balance and color development even in a mixed color image. This makes it possible to form a high-quality image.

  The reason why the above-described effect is manifested by combining the combination of the water-based ink and the reaction liquid constituting the ink set as described above is that the present inventors show that the reaction liquid and the water-based ink are on the paper surface (on the recording medium). In this case, it is assumed that the following state occurs. When image formation is performed with a water-based ink on a recording medium to which a reaction liquid is applied, the distribution state of aggregates generated on the recording medium differs depending on the ink used. That is, when the reactivity between the reaction liquid and the water-based ink is high, aggregates are formed near the surface of the recording medium. On the other hand, when the reactivity between the reaction liquid and the water-based ink is low, all the color materials in the ink do not react in the vicinity of the surface of the recording medium, so an aggregate having a wide width in the depth direction is formed. Even when a mixed color image is formed, the distribution state of aggregates differs depending on the reactivity of each ink as in the case of a single color image, so that the color materials of each color are uniformly mixed and aggregates are formed at the same position on the recording medium. It cannot be formed. The difference in the aggregation state on each monochrome recording medium forming the mixed color causes the color balance to be lost. The effect of the reactivity with the reaction liquid on the color balance varies depending on the color of the ink, and yellow ink with high lightness is easily affected, especially when the aggregate of the color material sinks into the recording medium due to its low reactivity. In addition, the color balance of the mixed color image tends to be lost. For this reason, in a combination of a plurality of water-based inks and reaction liquids, the color balance at the time of color mixing is improved by relatively increasing the reactivity between yellow ink, which is the most commonly used water-based ink, and the reaction liquid. Believes that it has improved significantly.

  Next, each component constituting the ink set of the present invention will be described, and the present invention will be described in more detail. The ink set of the present invention is a combination of a reaction liquid containing a polyvalent metal and two or more water-based inks including at least a yellow ink. Furthermore, the water-based ink contains at least a pigment dispersed with an anionic substance or a pigment having an anionic group on the surface. In addition to the basic structure as described above, the ink set of the present invention is characterized in that the reactivity between the yellow ink and the reaction liquid is higher than the reactivity between the aqueous ink other than the yellow ink and the reaction liquid. To do. First, the reactivity between the reaction liquid and the water-based ink will be described, and then each component will be described in detail.

[Reactivity of reaction liquid and water-based ink]
The reactivity of the reaction liquid and the water-based ink constituting the ink set of the present invention is preferably controlled so as to satisfy the following condition [1] or [2]. In particular, a structure controlled so as to satisfy both the conditions [1] and [2] is preferable. These will be described in detail. In addition, the measurement of the light absorbency in the following can be measured with a general self-recording spectrophotometer.

[1] A 400-fold diluted aqueous solution of the reaction liquid and a 5-fold diluted aqueous solution of any of the aqueous inks constituting the ink set were mixed at a mixing ratio of 50: 1, and after 15 minutes, filtered through a 1.0 μm filter, Prepare samples for measurement. The absorbance at the maximum absorption wavelength in the visible region measured for the obtained sample is defined as (A). For example, when carbon black is used as the pigment, the maximum absorption wavelength is 550 nm. The composition of the sample for measurement prepared as described above is a 255-fold diluted aqueous solution of the aqueous ink containing the reaction liquid. Furthermore, as another sample for measurement, the aqueous ink is diluted with water to prepare a 255-fold diluted aqueous solution of the aqueous ink that does not contain the reaction liquid. With respect to the obtained 255-fold diluted aqueous solution, the absorbance at the maximum absorption wavelength in the visible region measured in the same manner as described above is defined as (B). When designing the reaction liquid and the plurality of water-based inks constituting the ink set of the present invention, the relationship between the absorbances (A) and (B) measured as described above constitutes the ink set. In any water-based ink, it is preferable to satisfy the following requirements.
(A) / (B) <0.8

[2] An 800-fold diluted aqueous solution of the reaction liquid and a 5-fold diluted aqueous solution of any of the aqueous inks constituting the ink set were mixed at a mixing ratio of 50: 1, and after 15 minutes, filtered through a 1.0 μm filter, Prepare samples for measurement. The absorbance at the maximum absorption wavelength in the visible region measured for the obtained sample is defined as (C). The composition of the measurement sample prepared as described above is a 255-fold diluted aqueous solution of aqueous ink containing a smaller amount of the reaction liquid than the measurement sample used in measuring the absorbance (A) described above. Become. Further, the relationship between the absorbance (C) obtained above and the absorbance (B) at the maximum absorption wavelength in the visible region of the aqueous ink 255-fold diluted aqueous solution described above is obtained. In any water-based ink constituting the ink set, it is preferable to design the ink set so that the relationship between (C) and (B) satisfies the following requirements.
(C) / (B)> 0.3

  That is, in (1) above, when (A) / (B) is 0.8 or more, the reactivity between the reaction liquid and the ink is insufficient, so that a sufficient image density cannot be obtained, When characters are printed, bleeding may occur. In [2] above, when (C) / (B) is 0.3 or less, aggregates of coloring materials may be localized on the surface of the recording medium. As a result, the scratch resistance is lowered, and there are cases where bad effects such as image smearing during double-sided recording occur.

[Components of water-based ink]
The water-based ink used in the present invention contains at least a pigment dispersed with an anionic substance or a pigment having an anionic group on the surface. Examples of the anionic substance include the following anionic polymer dispersions: Agents.

<Anionic polymer dispersant>
As a polymer dispersant, a polymer or copolymer of monomer components having a radical polymerizable unsaturated bond such as an acrylic resin or a styrene / acrylic resin can be generally used and the functional design of the dispersant can be easily performed. Coalescence is preferably used. Examples of the material for forming such a polymer dispersant include the following monomers.

Examples of the radically polymerizable monomer include the following. For example, acrylic esters such as methyl acrylate, ethyl acrylate, isopropyl acrylate, acrylate-n-propyl, acrylate-n-butyl, acrylate-t-butyl, benzyl acrylate, and the like;
Methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, methacrylate-n-propyl, methacrylate-n-butyl, isobutyl methacrylate, tert-butyl methacrylate, tridecyl methacrylate, benzyl methacrylate, etc. ;
Styrenic monomers such as styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-tert-butylstyrene, and the like;
Itaconic acid esters such as benzyl itaconate;
Maleate esters such as dimethyl maleate;
Fumarate esters such as dimethyl fumarate;
Examples include acrylonitrile, methacrylonitrile, vinyl acetate and the like.

A suitable component for forming the anionic polymer dispersant includes an anionic component that reacts with the polyvalent metal salt contained in the reaction solution. Specifically, it is preferable to use a monomer having an anionic group as described below as a copolymerization component. Examples of the monomer having an anionic group include monomers having a carboxyl group such as acrylic acid, methacrylic acid, crotonic acid, methacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, fumaric acid, and salts thereof;
Monomers having a sulfonic acid group such as styrene sulfonic acid, sulfonic acid-2-propylacrylamide, acrylic acid-2-ethyl sulfonate, ethyl methacrylic acid-2-ethyl sulfonate, butylacrylamide sulfonic acid and the like; and salts thereof;
And monomers having a phosphonic acid group such as ethyl methacrylate-2-phosphonate and ethyl acrylate-2-phosphonate. Among these, it is particularly preferable to use acrylic acid and methacrylic acid.

  As the polymer dispersant composed of the above components, those having an acid value in the range of 100 to 350 are preferable. When the acid value is less than 100, the polymer dispersant may not be dissolved in the aqueous medium, or the dispersion of the pigment dispersion dispersed with the polymer dispersant may be poor and an aggregate may be generated. It is not preferable. On the other hand, an acid value exceeding 350 is not preferable because the dispersion stability of the pigment dispersion dispersed with such a polymer dispersant increases, and the reactivity with the polyvalent metal salt decreases. That is, an ink made of such a pigment dispersion is not preferable because it penetrates deeper into the recording medium and lowers the image density.

  The ink used in the present invention controls the reactivity of the reaction liquid and the ink within a desired range in addition to the anion component that reacts with the polyvalent metal salt in order to control the penetration of the coloring material into the recording medium. Ingredients suitable to do so may be included. Examples of components that control the reactivity of the reaction liquid and the ink within a certain range include highly hydrophilic nonionic substituents such as a hydroxyl group of a polyol such as polyvinyl alcohol and an ether group such as polyethylene ether. For example, it is preferable to contain a copolymer of a (meth) acrylic acid ester having a polyethylene glycol substituent, a radical polymerizable monomer, and another radical polymerizable monomer. Such components can change the amount of polyethylene glycol introduced into the dispersant and the ether chain length (repeating unit) of polyethylene ether by changing the copolymerization ratio. The reactivity with a valent metal salt can be arbitrarily controlled, which is preferable.

  The polymer dispersant as described above is preferably used as long as it is within the range of 20 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the pigment. When the amount is less than 20 parts by mass, the film forming property by the polymer dispersant is insufficient, and the scratch resistance and the marker resistance are insufficient. On the other hand, when the amount exceeds 200 parts by mass, the amount of the polyvalent metal salt necessary to cause sufficient aggregation reaction between the pigment dispersion and the polyvalent metal salt increases, or the increase in the polymer dispersant increases the amount of the ink. The viscosity may increase, which is not preferable. That is, when ink with increased viscosity is printed by the ink jet method, ejection may become unstable.

<Pigment>
Examples of the pigment constituting the ink used in the present invention include the following carbon black and organic pigments.
(Carbon black)
As carbon black, various carbon black pigments, such as furnace black, lamp black, acetylene black, channel black, can be used, for example. Commercially available carbon blacks such as those listed below can be used. For example, Raven 7000, 5750, 5250, 5000, 3500, 2000, 1500, 1250, 1200, 1190 ULTRA-II, 1170, 1255 (above Colombia);
Black Pearls L;
Regal 400R, Legal 330R, Legal 660R;
Mogul L;
Monarch 700, Monak 800, Monak 880, Monak 900, Monak 1000, Monak 1100, Monak 1300, Monak 1400;
Vulcan XC-72R (above Cabot);
Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170;
Printex 35, Printex U, Printex V, Printex 140U, Printex 140V;
Special Black 6, Special Black 5, Special Black 4A, Special Black 4 (manufactured by Degussa);
No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical Corporation), etc .;
Can be mentioned. However, it is not limited to these, and conventionally known carbon black can be used. Further, magnetic fine particles such as magnetite and ferrite, titanium black and the like can be used as the black pigment.

(Organic pigment)
As the organic pigment, those listed below can be used. For example, insoluble azo pigments such as Toluidine Red, Toluidine Maroon, Hansa Yellow, Benzidine Yellow, and Pyrazolone Red, soluble azo pigments such as Ritolol Red, Helio Bordeaux, Pigment Scarlet and Permanent Red 2B;
Derivatives from vat dyes such as alizarin, indanthrone, thioindigo maroon;
Phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green;
Quinacridone pigments such as quinacridone red and quinacridone magenta;
Perylene pigments such as perylene red and perylene scarlet;
Isoindolinone pigments such as isoindolinone yellow and isoindolinone orange;
Imidazolone pigments such as benzimidazolone yellow, benzimidazolone orange, and benzimidazolone red;
Pyranthrone pigments such as pyranthrone red and pyranthrone orange;
Indigo pigments;
Condensed azo pigments;
Thioindigo pigments;
Other pigments such as flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo yellow, copper azomethine yellow, perinone orange, anthrone orange, dianthraquinonyl red, dioxazine violet;
Is mentioned.

The organic pigments that can be used in the present invention are indicated by the color index (CI) number, and the following are listed. For example, C.I. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 109, 110, 117, 120, 125, 128, 137, 138, 147, 148, 151, 153, 154, 166, 168;
C. I. Pigment orange 16, 36, 43, 51, 55, 59, 61;
C. I. Pigment Red 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175, 176, 177, 180, 192, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240;
C. I. Pigment violet 19, 23, 29, 30, 37, 40, 50;
C. I. Pigment blue 15, 15: 3, 15: 1, 15: 4, 15: 6, 22, 60, 64;
C. I. Pigment green 7, 36;
C. I. Examples thereof include CI Pigment Brown 23, 25, 26, and the like. Of course, conventionally known organic pigments can be used in addition to the above.

  The content of the pigment in the ink used in the present invention is 0.1% or more and 15% or less, particularly 1% or more and 10% or less, based on mass, based on the total amount of ink (percentage in the ink). It is preferable to set it as the range. By setting it within this range, the pigment dispersion can maintain a sufficiently dispersed state when it is contained in the ink. Furthermore, for the purpose of adjusting the color tone of the ink, a dye may be added as a coloring material in addition to the pigment dispersion.

<Aqueous medium>
The water-based ink used in the present invention is obtained by dissolving or dispersing a color material containing the above-described pigment in an aqueous medium. Hereinafter, the aqueous medium that can be used in the present invention will be described. The aqueous medium is not particularly limited, and an aqueous medium used for a conventionally known aqueous ink can be used. An aqueous medium similar to the ink can be used for the reaction liquid described later. In particular, when the water-based ink used in the present invention is attached to a recording medium by an inkjet method [for example, bubble jet (registered trademark) method, etc.], an aqueous medium is appropriately selected so as to have inkjet ejection characteristics, The ink is preferably prepared so as to have a desired viscosity and surface tension.

Examples of the aqueous medium used in the ink used in the present invention include water or a mixed solvent of water and a water-soluble organic solvent. As the water-soluble organic solvent, those having an anti-drying effect are particularly preferable. Specifically, for example, alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol;
Amides such as dimethylformamide and dimethylacetamide;
Ketones or ketoalcohols such as acetone and diacetone alcohol;
Ethers such as tetrahydrofuran and dioxane;
Polyalkylene glycols such as polyethylene glycol and polypropylene glycol;
Alkylene glycols in which the alkylene group contains 2 to 6 carbon atoms such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol ;
Lower alkyl ether acetates such as polyethylene glycol monomethyl ether acetate;
Glycerin;
Lower alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether;
Polyhydric alcohols such as trimethylolpropane and trimethylolethane;
N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like can be mentioned. The water-soluble organic solvents as described above can be used alone or as a mixture. It is desirable to use deionized water as the water.

  The content of the water-soluble organic solvent contained in the ink used in the present invention is not particularly limited, but it is preferably contained in the range of 3% or more and 50% or less on the mass basis with respect to the total amount of the ink. . The content of water contained in the ink is preferably in the range of 50% or more and 95% or less on the mass basis with respect to the total amount of the ink. In the ink used in the present invention, in addition to the above-mentioned components, a moisturizing agent may be added as necessary. In addition, in order to obtain an ink having a desired physical property value, a surfactant and an antifoaming agent are used. Further, an antiseptic, an antifungal agent and the like may be added.

[Reaction liquid components]
The ink set of the present invention comprises a plurality of water-based inks configured as described above and a reaction liquid containing a polyvalent metal. Hereinafter, components for forming the reaction liquid will be described.

<Polyvalent metal ions and salts thereof>
Specific examples of the polyvalent metal ion that can be used in the reaction solution include divalent metals such as Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ , Zn ^2+, and Ba ^{2+. Examples} thereof include ions and trivalent metal ions such as Al ³⁺ , Fe ³⁺ , Cr ³⁺ , and Y ³⁺ . The salt is a metal salt composed of the polyvalent metal ions mentioned above and anions that bind to these polyvalent metal ions, but is soluble in water. Cost. Examples of the anion for forming the salt include SO ₄ ²⁻ , Cl ⁻ , CO ₃ ²⁻ , NO ₃ ⁻ , I ⁻ , Br ⁻ , ClO ₃ ^−, CH ₃ COO ⁻ , HCOO ^{− and the} like. Of course, the present invention is not limited to the above compounds.

  In view of the effect of the present invention, the content of the metal salt described above in the reaction solution is preferably 0.01% or more and 20% or less in terms of mass. Further, the reaction solution preferably contains no color material and is transparent, but it does not necessarily have to exhibit no absorption in the visible region. That is, even if absorption is shown in the visible range, absorption may be shown in the visible range as long as it does not substantially affect the image.

<Aqueous medium>
Examples of the aqueous medium used for the reaction liquid include water or a mixed solvent of water and a water-soluble organic solvent. As the water-soluble organic solvent, those having an effect of preventing the reaction solution from drying are particularly preferable. Specifically, the same aqueous medium as mentioned above as the ink component can be used. The water-soluble organic solvent can be used alone or as a mixture. It is desirable to use deionized water as the water.

  Although content of the water-soluble organic solvent contained in the reaction liquid used by this invention is not specifically limited, The range of 3% or more and 50% or less is suitable on a mass basis with respect to the reaction liquid whole quantity. Moreover, the content of water contained in the reaction solution is preferably in the range of 50% or more and 95% or less on a mass basis with respect to the total amount of the reaction solution. Furthermore, in addition to the above components, surfactants, antifoaming agents, preservatives, antifungal agents, and the like can be added as appropriate in order to obtain a reaction solution having desired physical property values, if necessary. .

<Other components of reaction solution>
Moreover, the reaction liquid used by this invention can contain the component mentioned below other than an above-described component.

(Polymer compound)
The reaction liquid used in the present invention can further contain a polymer compound, and by adopting such a configuration, the scratch resistance of the recorded matter obtained using the ink set of the present invention can be improved. it can. The polymer compound used as a component for forming the reaction liquid is a nonionic water-soluble polymer that does not directly participate in the reaction between a component such as a coloring material in the ink and a polyvalent metal ion in the reaction liquid. It is preferable. Specifically, for example, polyacrylamide, polyvinylpyrrolidone;
Water-soluble cellulose such as carboxymethylcellulose, hydroxymethylcellulose, hydroxypropylcellulose;
Examples of the resin include polyvinyl methyl ether, polyvinyl acetal, and polyvinyl alcohol, but are not limited thereto. For example, when an image is formed, a polymer compound in which an anion unit or a cation unit is added to these nonionic polymers may be used as long as the basic performance of the ink and the reaction liquid can be maintained. . Furthermore, the above-described polymer compound is satisfactory as long as it is water-soluble, but may be a dispersion such as latex or emulsion. A preferable addition amount of the polymer compound as mentioned above is preferably 0.01% or more and 20% or less on a mass basis with respect to the total amount of the reaction solution.

<Ink set>
The color of the ink other than the yellow ink when the ink set of the present invention is configured by combining the ink described above and the reaction liquid described above is not particularly limited. For example, an ink showing one color tone selected from magenta, cyan, red, green, blue, and black may be used. Specifically, the color material can be appropriately selected from the above-described color materials so that the ink has a desired color tone. In addition, when any one of the inks constituting the ink set combined with the reaction liquid comes into contact with the above-described reaction liquid on the recording medium in which the coloring material is dissolved or dispersed in the aqueous medium by the action of the ionic group. Any ink that forms color material aggregates may be used. Of course, all the inks constituting the ink set may be inks having the above functions.

<Recording method>
The image forming method on the recording medium of the present invention comprises (i) a step of applying the aqueous ink constituting the ink set described above to the recording medium by an ink jet recording method, and (ii) constituting the ink set. A step of applying the reaction liquid to the recording medium, performing the step (ii) prior to the step (i), and contacting the aqueous ink and the reaction liquid on the recording medium. It is characterized by performing. By such a method, when the ink having the configuration according to the present invention and the reaction liquid come into contact with each other on the recording medium, high image density and color development are improved, and the ambiguity of the image outline is improved, resulting in color bleeding. In addition, it is possible to form a high-quality image having excellent resistance to see-through. Here, the resistance to see-through is the bleeding of the coloring material to the back side of the print caused by excessive penetration of ink. Therefore, when applying the reaction liquid and the ink to the recording medium, it is preferable that the reaction liquid is applied at least to the area of the recording medium to which the ink is applied. More preferably, the reaction solution is applied to a wider area.

  In the present invention, a plurality of ink sets of the reaction liquid and ink having the configuration according to the present invention described above, or an ink set of the reaction liquid and ink having the configuration described above and an ink having another configuration are used. It may be a combination. In either case, an ink set that can be suitably used for forming a high-quality color image is provided. When such an ink set is used, for example, when black ink is printed with the ink set having the configuration according to the present invention so that the black image portion and the color image portion are adjacent to each other, bleeding is performed. Can be suppressed very effectively.

  Examples of the method for applying the reaction liquid to the recording medium according to the present invention include a method using an ink jet recording system as in the case of an ink, and a method for applying the reaction liquid of the present invention to a recording medium with a roller or the like. In these, the application | coating with a roller etc. which does not need to consider discharge property etc. is preferable. A specific application method will be described later.

The amount of the reaction liquid applied to the recording medium can be appropriately adjusted according to the polyvalent metal ion species in the reaction liquid, the amount thereof, or the ink to be reacted therewith. For example, it is preferably 0.5 g / m ² or more and 10 g / m ² or less from the viewpoint of the solid uniformity and fixability of the image of the obtained recorded matter. A more preferable amount of the reaction liquid applied to the recording medium is more than ² g / m ² and not more than 5 g / m ² .

<Ink characteristics; inkjet ejection characteristics, permeability to recording media>
The ink set of the present invention is particularly suitable for inkjet recording. As the ink jet recording method, there are a recording method in which mechanical energy is applied to ink to eject droplets, and a recording method in which thermal energy is applied to ink and ink droplets are ejected by foaming of the ink. Not only the ink of the present invention but also a reaction liquid can be used. In that case, it is preferable that the reaction liquid and the ink having the above-described configuration according to the present invention have characteristics that can be ejected from an inkjet head. From the viewpoint of dischargeability from the inkjet head, it is preferable that the characteristics of these liquids are as follows. For example, the viscosity is 1 mPa · s to 15 mPa · s, the surface tension is 25 mN / m (dyne / cm) or more, in particular, the viscosity is 1 mPa · s to 5 mPa · s, and the surface tension is 25 mN / m (dyne / cm). cm) to 50 mN / m (dyne / cm) or less.

  Particularly in the case of the reaction liquid, it is preferable that the reaction liquid is applied to at least the printing area of the recording medium to which the ink is applied, so that the surface tension is 25 mN / m (dyne / cm) or more and 35 mN / m (dyne). / Cm) or less. Further, when the reaction liquid is applied to the recording medium by roller coating or bar coating, the surface tension of the reaction liquid is 20 mN / m (dyne / cm) or more and the viscosity is 100 mPa · s or less. It is desirable that the viscosity is 25 mN / m (dyne / cm) or more and 35 mN / m (dyne / cm) or less and the viscosity is 5 mPa · s or more and 60 mPa · s or less from the viewpoint of controlling the applied amount and applying uniformly on the recording medium.

<Inkjet recording apparatus>
FIG. 1 shows an example of an ink jet recording apparatus. This image forming apparatus employs a serial type ink jet recording system, and includes a recording head 1, a paper feed cassette 16, and a driving means for reciprocating the recording head in a direction orthogonal to the recording paper conveyance direction. And control means for controlling driving of these components. The above-described paper feed cassette 16 is a unit in which a paper feed tray 17 for feeding a recording medium (hereinafter also referred to as recording paper) 19 and a means for applying the reaction liquid of the present invention are integrally formed. It is.

  The recording head 1 is mounted on the carriage 2 so that the surface on which the ink discharge ports are formed is oriented toward the platen 11. Although not shown, the recording head 1 includes the ink discharge port, a plurality of electrothermal transducers (for example, heating resistance elements) for heating the ink liquid, and a substrate that supports the electrothermal transducer. The recording head 1 has an ink cartridge mounted in the carriage on the top thereof. The carriage 2 carries the recording head 1 and can reciprocate along two guide shafts 9 extending in parallel along the width direction of the recording paper 19. The recording head 1 is driven in synchronism with the reciprocating movement of the carriage and ejects ink droplets onto the recording paper 19 to form an image.

  The paper feed cassette 16 can be detached from the image forming apparatus main body. The recording paper 19 is stacked and stored on a paper feed tray 17 in the paper feed cassette 16. At the time of paper feeding, the uppermost sheet is pressed against the paper feed roller 10 by a spring 18 that presses the paper feed tray 17 upward. The sheet feeding roller 10 is a roller having a substantially half moon shape in cross section, and is driven and rotated by a motor (not shown) to feed only the uppermost sheet (recording paper 19) by a separation claw (not shown).

  The separated recording paper 19 is fed along the conveyance surface 16A of the paper feed cassette 16 and the conveyance surface 27A of the paper guide 27 by the large-diameter intermediate roller 12 and the small-diameter application roller 6 that is in pressure contact therewith. Are transported. These transport surfaces are formed by curved surfaces that draw a concentric arc concentric with the intermediate roller 12. Therefore, the recording paper 19 reverses its transport direction by passing through these transport surfaces 16A and 27A. That is, the surface on which the recording paper 19 is printed is directed downward until it is conveyed from the paper feed tray 17 and reaches the intermediate roller 12, but when facing the recording head 1, it is directed upward (recording). Turn to the head side. Therefore, the printing surface of the recording paper always faces the outside of the image forming apparatus.

  The reaction solution applying means is provided in the paper feed cassette 16 and is a replenishment tank 22 for supplying the reaction solution 15 and an intermediate portion rotatably supported with a part of the peripheral surface immersed in the tank 22. The roller 12 and the application roller 6 are arranged so as to be parallel to the intermediate roller and are in contact with the intermediate roller 12 and rotate in the same direction. The application roller 6 is arranged so that the intermediate roller 12 for conveying the recording paper 19 is in contact with and parallel to the peripheral surface. Therefore, when the recording paper 19 is transported, the intermediate roller 12 and the application roller 6 rotate with the rotation of the intermediate roller 12. As a result, the reaction liquid 15 is supplied to the peripheral surface of the application roller 6 by the supply roller 13, and the reaction liquid is evenly applied to the printing surface of the recording paper 19 sandwiched between the application roller 6 and the intermediate roller 12 by the supply roller 6. Is done.

  In the image forming apparatus, the float 14 is provided in the replenishing tank 22. The float 14 is a substance having a lighter specific gravity than the reaction solution 15 and floats on the surface of the reaction solution 15 so that the remaining amount of the reaction solution can be visually confirmed from the outside through the remaining amount display window 21 which is a transparent member.

  FIG. 2 is a front view of the remaining amount display portion. The remaining amount display portion is provided with a display indicating the level of the remaining amount along the longitudinal direction of the remaining amount display window 21. In the figure, the liquid level of the reaction solution or the float 14 has reached the position indicated as “Full”, which is a full state. On the other hand, when the liquid level of the reaction solution or the float 14 is present at the position labeled “Add”, it indicates that the reaction solution is low. Therefore, it can be seen at a glance that the reaction solution 15 should be replenished when the reaction solution 15 is gradually reduced and the float 14 is lowered to the Add line.

  As a method of replenishing the reaction solution, as shown in FIG. 3, the tip of the injection device 23 is inserted into the injection port 20 made of a cut rubber member in a state where the paper feed cassette 16 is pulled out from the image forming apparatus main body. By inserting, the reaction liquid is injected into the replenishing tank 22.

  In this way, the recording paper coated with the reaction liquid is then fed by a predetermined amount by the main transport roller 7 and the pinch roller 8 in pressure contact therewith and transported to the recording unit, and ink is applied from the recording head 1. The The recording sheet 19 fed and printed in the above configuration is discharged and conveyed by the discharge roller 3 and the spur 4 in pressure contact with the discharge roller 3 and stacked on the discharge tray 5.

<Recording head>
As an embodiment of a recording head of an ejection method that can be suitably used in the present invention and communicates air bubbles with the atmosphere at the time of ejection, for example, as described in Japanese Patent No. 2783647, a so-called edge shooter type or a side shooter type effective in practice in recent years Is mentioned. The present invention provides an excellent effect particularly in an ink jet recording head and a recording apparatus that perform recording by forming flying droplets using thermal energy among ink jet recording methods. As the typical configuration and principle, for example, those performed using the basic principle disclosed in US Pat. Nos. 4,723,129 and 4,740,696 are preferable. . This method can be applied to both the so-called on-demand type and continuous type. In particular, in the case of the on-demand type, it is arranged corresponding to the sheet or liquid path holding the liquid (ink). By applying at least one drive signal corresponding to the recorded information and giving a rapid temperature rise exceeding the film boiling to the electrothermal transducer, the thermal energy is generated in the electrothermal transducer, and the recording head This is effective because film boiling occurs on the heat acting surface of the liquid and, as a result, bubbles in the liquid (ink) corresponding to the drive signal on a one-to-one basis can be formed. By the growth and contraction of the bubbles, liquid (ink) is ejected through the ejection opening to form at least one droplet. It is more preferable that the drive signal has a pulse shape, since the bubble growth and contraction is performed immediately and appropriately, and thus it is possible to achieve discharge of a liquid (ink) having particularly excellent responsiveness.

  As this pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. Further excellent recording can be performed by employing the conditions described in US Pat. No. 4,313,124 of the invention relating to the temperature rise rate of the heat acting surface. As the configuration of the recording head, in addition to the combination configuration (straight liquid channel or right-angle liquid channel) of the discharge port, the liquid channel, and the electrothermal transducer as disclosed in each of the above-mentioned specifications, the thermal action A configuration using US Pat. No. 4,558,333 and US Pat. No. 4,459,600 which disclose a configuration in which a portion is disposed in a bent region is also included in the present invention. . In addition, for a plurality of electrothermal transducers, Japanese Patent Application Laid-Open No. 59-123670 that discloses a configuration in which a common slit is used as a discharge portion of the electrothermal transducer, or an aperture that absorbs pressure waves of thermal energy is provided. The present invention is also effective as a configuration based on Japanese Patent Application Laid-Open No. 59-138461 which discloses a configuration corresponding to the discharge unit.

  Furthermore, as a full-line type recording head having a length corresponding to the width of the maximum recording medium that can be recorded by the recording apparatus, the length is set by combining a plurality of recording heads as disclosed in the above specification. Either the satisfying configuration or the configuration as a single recording head formed integrally may be used, but the present invention can exhibit the above-described effects more effectively. In addition, by mounting on the apparatus main body, the ink can be integrated with the replaceable chip type recording head that can be electrically connected to the apparatus main body and supplied with ink from the apparatus main body, or the recording head itself. The present invention is also effective when a cartridge type recording head provided with a tank is used.

  In addition, it is preferable to add recovery means for the recording head, preliminary auxiliary means, and the like provided as the configuration of the recording apparatus of the present invention, since the effects of the present invention can be further stabilized. Specifically, the capping means, the cleaning means, the pressurizing or suction means for the recording head, the preheating means by the electrothermal converter or another heating element or a combination thereof, and the recording Performing a preliminary discharge mode for performing another discharge is also effective for performing stable recording.

  Further, the recording mode of the recording apparatus is not limited to the recording mode of only the mainstream color such as black, but the recording head may be configured integrally or may be a combination of a plurality of colors. The present invention is extremely effective for an apparatus having at least one of full colors.

  In the above description, the ink is described as a liquid. However, the ink solidifies at room temperature or lower and is softened at room temperature, or is a liquid, or in the above-described inkjet system, the ink itself is 30. In general, the temperature is adjusted so that the viscosity of the ink is within the stable discharge range by adjusting the temperature within the range of from 70 ° C. to 70 ° C. Good.

  In addition, positive temperature rise by thermal energy is prevented by using it as energy for changing the state of the ink from the solid state to the liquid state, or ink that is solidified in the standing state is used to prevent ink evaporation. In any case, thermal energy such as ink that is liquefied by application of thermal energy according to a recording signal and discharged as liquid ink, or that already starts to solidify when reaching the recording medium. The use of ink having the property of being liquefied for the first time is also applicable to the present invention. In such a case, the ink is held as a liquid or solid in a porous sheet recess or through-hole as described in JP-A-54-56847 or JP-A-60-61260, It is good also as a form which opposes with respect to an electrothermal converter. In the present invention, the most effective one for each of the above-described inks is to execute the above-described film boiling method.

  In addition, as a form of the recording apparatus according to the present invention, a copying apparatus combined with a reader, as well as a transmission / reception function, in addition to those provided as an image output terminal of an information processing device such as a word processor or a computer. It may be in the form of a facsimile machine having the same.

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

[Preparation of reaction solution]
First, the reaction liquid 1 was prepared as follows.
(Reaction solution 1)
The following components were mixed, sufficiently stirred and dissolved, followed by pressure filtration with a micro filter (manufactured by Fuji Film) having a pore size of 1.0 μm to prepare a reaction solution.
・ Calcium nitrate (tetrahydrate) 18 parts ・ Trimethylolpropane 15 parts ・ Glycerin 5 parts ・ Diethylene glycol 5 parts ・ Acetylene glycol ethylene oxide adduct (trade name: acetylenol EH) 1 part ・ Water 56 parts

[Preparation of water-based ink]
Next, cyan, magenta and yellow inks were prepared as follows.
(Preparation of cyan ink 1)
<Preparation of pigment dispersion C1>
First, pigment dispersion C1 was prepared as follows. In this case, C.I. I. Pigment Blue 15: 3 (product name: Fastgen Blue FGF, manufactured by Dainippon Ink & Chemicals, Inc.) was used, and an anionic polymer P-1 was used as the polymer dispersant. The anionic polymer P-1 is obtained by solidifying a styrene / ethyl acrylate / acrylic acid copolymer (copolymerization ratio (mass ratio) = 40/30/30) having an acid value of 214 and a weight average molecular weight of 8,500. An aqueous solution containing 10% min. Potassium hydroxide was used as the neutralizing agent. A material obtained by mixing 10 parts of the pigment, 40 parts of the anionic polymer P-1 and 50 parts of pure water was charged into a batch-type vertical sand mill (manufactured by IMEX), and 150 zirconia beads having a diameter of 0.3 mm were added. The dispersion treatment was carried out over 5 hours while partly filling and cooling with water. After the dispersion, this dispersion was centrifuged to remove coarse particles to obtain a pigment dispersion C1. Pigment dispersion C1 as the final preparation had a solid content of about 13% and a weight average particle size of 120 nm.

<Composition of cyan ink 1>
The components having the following composition including the pigment dispersion C1 obtained above were mixed, sufficiently stirred and dissolved, and then filtered under pressure with a microfilter (manufactured by Fuji Film) having a pore size of 1.0 μm. Prepared.
-Pigment dispersion C1 30 parts-Glycerol 9 parts-Diethylene glycol 6 parts-Acetylene glycol ethylene oxide adduct (trade name: acetylenol EH) 1 part-Water 54 parts

(Preparation of magenta ink 1)
<Preparation of pigment dispersion M1>
First, a pigment dispersion M1 was prepared as follows. In this case, C.I. I. Pigment Red 122 (Dainippon Ink Chemical Co., Ltd.) was used, and the same anionic polymer P-1 as that used for preparing the pigment dispersion C1 was used as the polymer dispersant. Then, 10 parts of the pigment, 40 parts of the anionic polymer P-1 and 50 parts of pure water are mixed, and the mixed material is charged into a batch type vertical sand mill (made by IMEX), and zirconia beads having a diameter of 0.3 mm. Was dispersed over 5 hours while cooling with water. After the dispersion, the dispersion was centrifuged to remove coarse particles to obtain a pigment dispersion M1. The pigment dispersion M1 as the final preparation had a solid content of about 12% and a weight average particle size of 155 nm.

<Composition of magenta ink 1>
The components having the following composition including the pigment dispersion M1 obtained above were mixed, sufficiently stirred and dissolved, and then filtered under pressure with a microfilter (manufactured by Fuji Film) having a pore size of 1.0 μm. Prepared.
-Pigment dispersion M1 30 parts-Glycerol 9 parts-Diethylene glycol 6 parts-Acetylene glycol ethylene oxide adduct (trade name: acetylenol EH) 1 part-Water 54 parts

(Preparation of yellow ink 1)
<Preparation of pigment dispersion Y1>
First, a pigment dispersion Y1 was prepared as follows. In this case, C.I. I. Pigment Yellow 180 (product name: Nova Palm Yellow PH-G, manufactured by Hoechst) was used, and an anionic polymer P-2 was used as the polymer dispersant. The anionic polymer P-2 is a styrene / butyl acrylate / acrylic acid copolymer (copolymerization ratio (mass ratio) = 40/30/30) having an acid value of 195 and a weight average molecular weight of 9,000. An aqueous solution containing 10% solids. Potassium hydroxide was used as the neutralizing agent. Then, 10 parts of the pigment, 40 parts of the anionic polymer P-2 and 50 parts of pure water were mixed, and the mixed material was charged into a batch type vertical sand mill (manufactured by IMEX), and 0.3 mm diameter zirconia beads 150 parts were filled and dispersed for 5 hours while cooling with water. After the dispersion, this dispersion was centrifuged to remove coarse particles to obtain a pigment dispersion Y1. Pigment dispersion Y1 as the final preparation had a solid content of about 12.5% and a weight average particle size of 130 nm.

<Composition of yellow ink 1>
Components having the following composition including the pigment dispersion Y1 obtained above were mixed, sufficiently stirred and dissolved, and then filtered under pressure with a micro filter (manufactured by Fuji Film) having a pore size of 1.0 μm. Prepared.
-Pigment dispersion Y1 30 parts-Glycerol 9 parts-Diethylene glycol 6 parts-Acetylene glycol ethylene oxide adduct (trade name: acetylenol EH) 1 part-Water 54 parts

(Preparation of yellow ink 2)
<Preparation of pigment dispersion Y2>
First, a pigment dispersion Y2 was prepared as follows. At this time, C.I. I. Pigment Yellow 180 (product name: Nova Palm Yellow PH-G, manufactured by Hoechst) was used, and an anionic polymer P-3 was used as the polymer dispersant. The anionic polymer P-3 has a styrene / M90G (manufactured by Shin-Nakamura Chemical Co.) / Acrylic acid copolymer (copolymerization ratio (mass ratio)) = 20 having an acid value of 190 and a weight average molecular weight of 9,000. / 50/30) at a solid content of 10%. Potassium hydroxide was used as the neutralizing agent. Then, 10 parts of the pigment, 40 parts of the anionic polymer P-3 and 50 parts of pure water are mixed, and the mixed material is charged into a batch type vertical sand mill (manufactured by IMEX), and 0.3 mm diameter zirconia beads 150 parts were filled and dispersed for 5 hours while cooling with water. After the dispersion, this dispersion was centrifuged to remove coarse particles to obtain a pigment dispersion Y2. Pigment dispersion Y2 as the final preparation had a solid content of about 12.5% and a weight average particle size of 140 nm.

(Composition of yellow ink 2)
The components having the following composition including the pigment dispersion Y2 obtained above were mixed, sufficiently stirred and dissolved, and then filtered under pressure with a microfilter (manufactured by Fuji Film) having a pore size of 1.0 μm. Prepared.
-Pigment dispersion Y2 30 parts-Glycerol 9 parts-Diethylene glycol 6 parts-Acetylene glycol ethylene oxide adduct (trade name: acetylenol EH) 1 part-Water 54 parts

[Example 1]
The ink set of Example 1 was prepared by combining the ink of each color prepared above and the reaction liquid 1 as follows.
・ Reaction solution 1
・ Cyan ink 1
・ Magenta ink 1
・ Yellow ink 1

[Comparative Example 1]
The ink set of Comparative Example 1 was prepared by combining the ink of each color prepared above and the reaction liquid 1 as follows.
・ Reaction solution 1
・ Cyan ink 1
・ Magenta ink 1
・ Yellow ink 2

[Evaluation test]
Using the ink sets of Example 1 and Comparative Example 1 prepared above, image recording was performed as follows. First, the reaction liquid 1 is adjusted to a coating amount of 2.5 g / cm ² using an application roller having a configuration as shown in FIG. Application was performed. Immediately after application, image recording was performed using an inkjet recording apparatus BJS700 (manufactured by Canon) having an on-demand multi-recording head that ejects ink by applying thermal energy corresponding to a recording signal to the ink. Then, the obtained image was evaluated. The evaluation items are shown below. Three types of commercially available copy paper, bond paper, and recycled paper were used as printing materials.

(1) Reactivity of ink and reaction liquid The ink sets of Example 1 and Comparative Example 1 were mixed under the following conditions, the absorbance was measured, and the reactivity between the reaction liquid and aqueous ink was evaluated. The obtained results are shown in Table 1.

[A] First, a 400-fold diluted aqueous solution of the reaction solution 1 and a 5-fold diluted aqueous solution of each of the cyan ink 1, the magenta ink 1, the yellow ink 1, and the yellow ink 2 were prepared. Then, a 400-fold diluted aqueous solution of reaction liquid 1 and a 5-fold diluted aqueous solution of each aqueous ink were mixed at a mixing ratio of 50: 1, and after 15 minutes, filtered with a 1.0 μm filter, a mixed sample for measurement It was. The amount of each water-based ink contained in the obtained mixed sample is 1/255. About each obtained sample, the light absorbency in wavelength 550nm was measured, and the obtained value was set to (A). Cyan ink 1, magenta ink 1 and yellow ink 1 or yellow ink 2 were each diluted with water to prepare a 255-fold diluted aqueous solution, and each was used as a measurement sample. About the obtained measurement sample, the light absorbency in wavelength 550nm was measured, and the value was set to (B). The value of reactivity (A) / (B) was calculated | required using the value of (A) and (B) obtained above. The obtained results are shown in Table 1.

[B] A 800-fold diluted aqueous solution of the reaction solution and a 5-fold diluted aqueous solution of each of the cyan ink 1, magenta ink 1, yellow ink 1 and yellow ink 2 were prepared. Then, an 800-fold diluted aqueous solution of reaction solution 1 and a 5-fold diluted aqueous solution of each aqueous ink were mixed at a mixing ratio of 50: 1, and after 15 minutes, filtered with a 1.0 μm filter, a mixed sample for measurement Respectively. The amount of each water-based ink contained in the obtained mixed sample is 1/255. About each obtained sample, the value obtained by measuring the light absorbency in wavelength 550nm was set to (C). Using the absorbance (B) at a wavelength of 550 nm of a 255-fold diluted aqueous solution of the water-based ink obtained by diluting the water-based ink previously measured and the value of (C) obtained above, the reactivity (C) / (B) The value was determined. The obtained results are shown in Table 1.

(2) Color Tone of Mixed Color Image The gray tone of cyan, magenta, and yellow was expressed with a duty of 60% each, and the color tone was evaluated by comparing the color tone at a distance of about 30 cm according to the following criteria. The results are shown in Table 1 below. The evaluation criteria are as follows.
a: Color tone of natural gray image b: Color tone looks different

  The ink sets of Example 1 and Comparative Example 1 described above differ only in the yellow ink, and only in the reactivity with the reaction liquid used in combination with the yellow ink. More specifically, the difference between the ink of Comparative Example 1 and the ink of Example 1 is that the ink of Comparative Example 1 is different from the ink of Example 1, and (A) / (B) <0 described above. .8 requirement not satisfied. As a result of forming an image using each of the ink sets of Example 1 and Comparative Example 1, as shown in Table 1, an image formed with the ink set of Comparative Example 1 that does not satisfy the above requirements is shown in Example 1. Compared with the image formed with the other ink set, the color tone was clearly different.

It is sectional drawing which shows an example of the inkjet recording device used by this invention. It is the figure which looked at the residual amount display part of the apparatus of FIG. 1 from the front. It is a figure for demonstrating the method to replenish a reaction liquid to the apparatus of FIG.

Claims (5)

  In an ink set in which a reaction liquid containing a polyvalent metal and at least two types of water-based inks including at least a yellow ink are combined, the water-based ink is at least an anion on a pigment or surface dispersed with an anionic substance. An ink set comprising a pigment having a reactive group and having a reactivity between the yellow ink and the reaction liquid higher than a reactivity between the aqueous ink other than the yellow ink and the reaction liquid . Visible after the 400-fold diluted aqueous solution of the reaction solution and the 5-fold diluted aqueous solution of any of the water-based inks constituting the ink set were mixed at a mixing ratio of 50: 1 and filtered with a 1.0 μm filter after 15 minutes. Any aqueous ink constituting an ink set, where (A) is the absorbance at the maximum absorption wavelength of the region, and (B) is the absorbance at the maximum absorption wavelength in the visible region of the 255-fold diluted aqueous solution of the aqueous ink. The ink set according to claim 1, wherein the condition of the following formula (1) is satisfied.
(A) / (B) <0.8 Formula (1) Visible after the 800-fold diluted aqueous solution of the reaction solution and the 5-fold diluted aqueous solution of any of the water-based inks constituting the ink set were mixed at a mixing ratio of 50: 1 and filtered with a 1.0 μm filter after 15 minutes. Any water-based ink constituting the ink set, where (C) is the absorbance at the maximum absorption wavelength of the region and (B) is the absorbance at the maximum absorption wavelength in the visible region of the 255-fold diluted aqueous solution of the water-based ink. The ink set according to claim 1 or 2, which satisfies the condition of the following formula (2).
(C) / (B)> 0.3 ... Formula (2) An image forming method on a recording medium,
(I) a step of applying an aqueous ink constituting the ink set according to any one of claims 1 to 3 to the recording medium by an inkjet recording method; and (ii) any one of claims 1 to 3. Applying the reaction liquid constituting the ink set according to item 1 to the recording medium,
An image forming method, wherein the step (ii) is performed prior to the step (i), and the aqueous ink and the reaction liquid are in contact with each other on the recording medium. The image forming method according to claim 4, wherein the reaction liquid of the step (ii) is applied to a region wider than the ink application region of the step (i).

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