JP2005305687A - Inkjet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recording method, preferably an ink jet, which can improve bleeding and substantially improve color developability without impairing fixability, and also satisfies the problem of back-through of colored ink in a recording medium and can perform high-speed printing. Provide a recording method.
The reaction liquid has polyvalent metal ions, and among the plurality of pigment inks of the same color, the dark ink having the highest pigment concentration does not contain substantially achromatic fine particles. An ink jet recording method, wherein the other pigment ink has pigments and substantially achromatic fine particles.
[Selection] Figure 3

Description

  The present invention relates to a recording method, preferably an ink jet recording method, and more particularly to an ink jet recording method capable of obtaining a high-quality color image on a recording medium having fibers that absorb ink components such as plain paper.

  In the ink jet recording method, recording is performed by causing a droplet of a recording liquid (ink) to fly and adhere to a recording medium such as paper. By using an electrothermal converter as the discharge energy supply means and ejecting liquid droplets by applying thermal energy to the ink and generating bubbles, it is possible to easily realize a high density multi-orifice of the recording head. High resolution and high quality images can be recorded at high speed (see Patent Documents 1 to 3).

  However, inks used in conventional ink jet recording generally contain water as a main component, and generally contain water-soluble high-boiling solvents such as glycol for the purpose of preventing drying and clogging. When recording on plain paper using ink, the ink penetrates into the inside of the recording paper, and a sufficient image density cannot be obtained, or the filler and sizing agent on the surface of the recording medium (recording paper) are not uniform. The image density seemed to be uneven due to uneven distribution.

  In particular, when trying to obtain a color image, the inks of a plurality of colors are stacked one after another before fixing, so that the color is blurred or mixed unevenly at the boundary portion of the different color image. Accordingly, satisfactory images (hereinafter referred to as bleeding) were not obtained.

  As one means for improving bleeding, it is disclosed to use an ink in which a compound that enhances permeability such as a surfactant is added to the ink (see Patent Document 4). However, in the former method, the penetrability of the ink into the recording paper is improved and bleeding is suppressed to some extent, but the ink colorant penetrates deep into the recording paper, so that the image density decreases or the image There are inconveniences such as a decrease in the sharpness of the image and an image appearing on the back surface of the recording medium. Further, since the wettability with respect to the surface of the recording paper is improved, the ink is likely to spread, resulting in a decrease in resolution and occurrence of bleeding.

  Further, a method is disclosed in which a liquid that makes a good image adhere to the recording paper prior to the ejection of the recording ink. For example, a method has been proposed in which a solution of a polymer such as carboxymethyl cellulose, polyvinyl alcohol, polyvinyl acetate or the like is jetted onto a recording medium before printing (see Patent Document 5). There is a concern that the drying property itself is poor and the fixing property is lowered.

  In order to improve this, a method of recording an ink containing an anionic dye after attaching a liquid containing an organic compound having two or more cationic groups per molecule (see Patent Document 6), Further, a method of recording ink after attaching an acidic liquid containing succinic acid or the like (see Patent Document 7), and a method of attaching a liquid that insolubilizes the dye before recording (see Patent Document 8) are disclosed. Has been.

  However, in any of the above cases, although bleeding can be suppressed to some extent, since the reaction liquid penetrates into the recording medium and is present in the recording medium and disappears from the surface of the medium, the colored ink is applied. Since the reaction occurs in the recording medium, there are a problem that the color developability is not improved and a problem that the colorant is visually recognized on the back surface of the recording medium.

  As described above, there is a concern that when the reaction liquid is on the recording medium, the fixing property is poor when the reaction liquid is on the recording medium, and when the reaction liquid is in the recording medium, the coloring property is poor.

  In addition, a proposal has been made to prevent bleeding by utilizing a reaction between a polyvalent metal ion and a carboxyl group (see Patent Document 9). In this case, although the bleeding is effectively suppressed by the reaction between the polyvalent metal ink and the carboxyl group, the liquid containing the polyvalent metal ion is impregnated in the recording medium and then reacted with the colored ink. When the colored ink has high penetrability with respect to the recording medium, there is a concern that the color developability deteriorates and the back-through occurs. Therefore, although this proposal is highly effective for preventing bleeding, it has a poor color development viewpoint, and there remains a problem for high color development.

Japanese Patent Publication No. 61-59911 Japanese Patent Publication No. 61-59912 Japanese Examined Patent Publication No. 61-59914 JP 55-65269 A JP-A-56-89595 JP 63-29971 A Japanese Unexamined Patent Publication No. 64-9279 JP-A-64-63185 JP-A-5-202328

  As described above, as a means for improving bleeding, various proposals using a colored ink and a reaction liquid have been made. Among them, prevention of bleeding by the reaction of polyvalent metal ions and carboxyl groups is effective, but the present situation is that no proposal has been made to obtain high color development after preventing bleeding.

The present invention has been made in view of this point. The object of the present invention is to improve bleeding without sacrificing fixability while improving bleeding, and to prevent the color ink from appearing through the recording medium. An object of the present invention is to provide an ink jet recording method which satisfies the problems.
Another object of the present invention is to obtain a recorded matter in which a highly color-developing image is formed on a recording medium containing a plurality of fibers such as plain paper.

  The above object is achieved by the present invention described below. That is, the present invention provides a recording method for performing recording by applying a plurality of pigment inks of the same color after applying a reaction liquid to a recording medium, with respect to the reaction liquid applied to the upper surface of the recording medium. A step of applying the pigment ink having a surface tension lower than the surface tension, and a step of forming a film-like aggregate formed by aggregation of aggregates at an interface where the reaction liquid and the pigment ink are in contact with each other. The reaction liquid has polyvalent metal ions, and in the plurality of pigment inks, the dark ink having the highest pigment concentration in these inks does not contain substantially achromatic fine particles, The pigment ink other than the dark ink contains the pigment and substantially achromatic fine particles, and is substantially the same as the mass concentration of the pigment contained in the dark ink and the pigment in the ink other than the dark ink. Total mass with achromatic particles Degree is, an ink jet recording method is characterized in that approximately the same among the plurality of pigment inks.

  In a preferred embodiment of the ink jet recording method of the present invention, in the above, the plurality of pigment inks of the same color are substantially free from the mass concentration of the pigment in the dark ink and the pigment in each pigment ink other than the dark ink. The total mass concentration with the chromatic fine particles is such that the ratio of these mass concentrations is between 0.85 and 1.15 between the pigment inks, and the plurality of pigment inks of the same color The mass concentration of the pigment in the dark ink, and the total mass concentration of the pigment in each pigment ink other than the dark ink and the substantially achromatic fine particles is 3 to 10% by mass, Examples of the achromatic fine particles include inorganic oxides, and examples of the substantially achromatic fine particles include organic compounds.

  According to the present invention, there is provided a recording method in which color developability is improved without impairing fixability. This recording method is particularly effective for a recording medium containing a large number of fibers such as plain paper, and obtains a recorded matter in which a high color-developing image is formed on a recording medium containing a plurality of fibers. be able to.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. First, an ink jet recording method which is a premise of the present invention will be described with reference to FIGS.
FIG. 3 shows the basic concept of the present invention. FIG. 3A shows a step of bringing the reaction liquid 20 and the pigment ink 30 into contact with the upper surface of the recording medium 10. The pigment ink 30 is applied to the recording medium 10 to which the reaction liquid 20 has been applied in advance. The moment of contact with the reaction solution 20 is shown. Here, from the viewpoint of bringing the reaction liquid and the pigment ink into contact with each other in liquid form and promptly fixing the film-like aggregate, the permeability of the pigment ink is made higher than the permeability of the reaction liquid. Specifically, the surface tension of the pigment ink is made lower than the surface tension of the reaction liquid. The relationship between the surface surface forces can be adjusted, for example, by changing the content ratio of the surfactant in the reaction liquid and the pigment ink.

  Although the application | coating method of the reaction liquid 20 is not prescribed | regulated in this invention in particular, the application | coating by the inkjet method which is a well-known technique can be used conveniently. Further, in order to bring the reaction liquid 20 and the pigment ink 30 into contact with each other on the upper surface of the recording medium 10, it is necessary to apply the pigment ink 30 before the reaction liquid 20 applied to the recording medium 10 completely penetrates the recording medium 10. . In other words, the pigment ink is brought into contact with the upper surface of the recording medium while the reaction liquid is in a liquid state. In order to realize this, it is preferable to use a reaction solution 20 having low permeability. If the reaction liquid 20 has low permeability to the recording medium 10, it is easy to set suitable printing conditions because a certain amount of time can be set until the pigment ink 30 is applied.

In order to make the reaction solution 20 have low permeability with respect to the recording medium 10, it can be achieved by suppressing the addition amount of a surfactant or the like that becomes a penetration accelerator. On the other hand, there is a Bristow method as one method for evaluating the permeability of the reaction liquid 20 to the recording medium 10. The Bristow method is JAPANTAPPI paper pulp test method no. 51, “Liquid absorbency test method for paper and paperboard”, wetting time Tw, absorption coefficient Ka (mL / m ² · ms ^1/2 ) and roughness index Vr (mL / m ² ) are defined. Since many commercial books have explanations, detailed explanations are omitted here, but only examples of absorption curves are shown in FIG.

  The reaction solution 20 starts to penetrate into the recording medium 10 when the wetting time Tw has elapsed. Accordingly, by applying the pigment ink 30 and bringing it into contact with the reaction liquid 20 by the time when the permeation is not completely completed, the pigment ink can be brought into contact with the interface of the reaction liquid existing on the upper surface of the recording medium.

Therefore, when the time difference for applying the reaction liquid 20 and the pigment ink 30 to the recording medium 10 is Td, the relationship with the wetting time Tw is
Td <2.0 × Tw
Printing conditions, preferably, before the reaction solution 20 starts to penetrate into the recording medium 10,
Td <1.0 × Tw
According to the printing conditions, the reaction liquid 20 and the pigment ink 30 are brought into contact with each other on the upper surface or above the recording medium 10.

  However, as shown in FIG. 4, the calculation method of the wetting time Tw in the present invention is represented by the approximate straight line A by the least square method for calculating the absorption coefficient Ka, the liquid transfer amount V, and the roughness index Vr. The time until the intersection AB with the straight line B of V = Vr. Further, in general, the liquid absorbency of various plain papers can be controlled with the surface tension of the liquid as a main factor, and in a general ink jet recording method, the landing time difference Td is several milliseconds or more. Therefore, the surface tension of the reaction solution is desirably 35 mN / m to 60 mN / m.

  Next, FIGS. 3B, 3 </ b> C, and 3 </ b> D show a process of forming a film-like aggregate 31 c at the interface where the reaction liquid and the pigment ink are in contact. This step is to form a film-like aggregate 31c formed by aggregation of pigment aggregates 31b immediately after the previous step. The manner in which the aggregates 31b are aggregated to form a film-shaped aggregate 31c will be described in detail with reference to FIG.

  In order to form the aggregate 31b constituting the film-shaped aggregate 31c, it is necessary to react with components contained in the pigment ink 30 to cause aggregation of the pigment. The most suitable method is a method in which polyvalent metal ions are contained in the reaction solution to agglomerate. In this method, the reaction solution is made to have a low pH and an acid precipitation phenomenon is used, or a cationic organic substance is contained. A method of aggregating them can be used in combination.

  The polyvalent metal ions 21 contained in the reaction solution react by colliding with carboxylate ions, sulfonate ions, phosphate ions, etc. in the pigment ink 30, thereby reducing the dispersibility of the pigment, resulting in a result. In particular, pigment aggregation occurs. The aggregation of the pigment is more likely to occur as the collision probability increases. Therefore, the polyvalent metal ion 21 contained in the reaction liquid 20 is preferably contained in a larger amount than the total charge concentration of the reverse polarity ions that react with the polyvalent metal ion 21 in the pigment ink 30.

  Here, the total charge concentration is the number of polyvalent metal ions per unit mass in the reaction liquid, and the number of reverse polarity ions such as carboxylate ions, sulfonate ions, phosphate ions per unit mass in the pigment ink. Defined.

  Then, when the pigment ink is brought into contact with the reaction liquid while it is in a liquid state on the upper surface of the recording medium, as shown in FIG. Bonding between the carboxylate ions, sulfonate ions, phosphate ions, etc. therein and the polyvalent metal ions occurs, and the pigment particles 31a are generated in which the electric repulsion of the pigment particles 31 in the dispersed state is lost. Then, as shown in FIGS. 3C and 3D, the aggregate 31b is rapidly formed by the pigment particles 31a due to the van der Waals attractive force acting between the pigment particles 31a, and these aggregates 31b are aggregated. As a result, a film-like aggregate 31c is formed.

  Here, the mechanism for forming the film-like aggregate 31c, which is an aggregate of the aggregates 31b, will be described in more detail with reference to FIG. FIG. 5 is an enlarged view of a portion indicated by a broken line frame in FIGS. First, as shown in FIG. 5A, the aggregate 31 b formed immediately after the pigment ink 30 contacts the reaction liquid 20 moves along with the surfactant 32 on the surface of the reaction liquid 20. The aggregate 31b and the surfactant 32 move on the surface of the reaction liquid 20 because the surfactant 32 in the pigment ink 30 is reacted with the reaction liquid because the content of the surfactant 32 in the pigment ink 30 is increased. This is because the surface of the reaction solution 20 is oriented and moved when it comes into contact with 20, and the agglomerate 31b also moves with the flow of the surfactant. Thereafter, as shown in FIG. 5B, the aggregate 31b stops at the boundary between the reaction solution 20 and the recording medium 10, and the subsequent aggregate 31b also moves. Then, as shown in FIG. 5 (c), the aggregates 31 b formed one after another are oriented on the surface of the reaction solution 20. Eventually, as shown in FIG. 5D, the density of the aggregate 31b is increased, and a film-like aggregate 31c formed by aggregation of the aggregate 31b on the surface of the reaction solution 20 is formed.

  Returning to FIG. 3, FIGS. 3E and 3F will be described. FIGS. 3E and 3F show a process in which the process of promoting the permeability of the reaction liquid 20 with respect to the recording medium 10 and the process of fixing the film-like aggregate 31c on the surface of the recording medium 10 proceed almost simultaneously. It is expressed in time series.

  The penetration accelerator and the solvent represented by the surfactant 32 contained in the pigment ink 30 diffuse into the reaction liquid 20, and along with this diffusion, the permeability of the reaction liquid increases, This solvent component and the solvent component in the pigment ink 30 quickly permeate the recording medium 10.

  FIG. 3E shows a state in which this process has progressed. Finally, as shown in FIG. 3F, the film-like aggregate 31c is composed of the recording medium 10 (for example, a plurality of fibers). The agglomerated film 31d is formed by fixing so as to cover the surface of the plain paper.

  Actually, since the surface of the plain paper has undulations due to the unevenness of the fibers, as shown in FIG. 6A, after the film-like aggregate 31c is formed, the solvent component and the pigment in the reaction solution 20 The solvent component in the ink 30 quickly penetrates into the recording medium 10, and the film-like aggregate 31c is covered along the undulations formed by the fiber irregularities as shown in FIG. The agglomerated film 31d is fixed. As a feature of the agglomerated film 31d at this time, a bridge-like agglomerated film 31d that covers a trough (concave portion) between fibers is covered, or that the agglomerated film 31d is cracked. There is also.

  FIG. 8A is an electron micrograph of the surface of plain paper that has not been printed. However, according to the actual recording method of the present invention, as shown in FIG. cover. According to FIG. 8C, it can be seen that the aggregated film 31d covers the plurality of fibers and the aggregated film 31d is cracked. By this step, both fixing ability and coloring ability can be achieved. That is, the mixed liquid component of the reaction liquid 20 and the pigment ink 30 quickly permeates the recording medium 10, and the film-like aggregate 31c is quickly fixed on the surface of the recording medium, whereby fast fixing can be achieved. Further, high color developability can be achieved by the aggregated film 31d which is a film-shaped aggregate fixed so as to cover the surface of the recording medium.

  On the other hand, a case where each of the ink jet recording methods as the preconditions described above is missing will be described. First, one of the characteristics is that the reaction liquid 20 and the pigment ink 30 are brought into contact with the upper surface of the recording medium 10, but when this characteristic is not provided, that is, when the reaction liquid is not on the upper surface of the recording medium 10. A case where ink is brought into contact will be described. When the recording medium 10 is impregnated with the reaction liquid 20 and brought into contact with the pigment ink 30, most of the reaction occurs in the recording medium 10, so that the distribution of pigment particles increases inside the surface of the recording medium 10. Therefore, high color developability cannot be obtained. Further, since the aggregate 31b is not generated at the interface of the reaction solution, the film-like aggregate 31c, which is an aggregate of the aggregate 31b, should not be formed. For this reason as well, high color developability is obtained. I can't. Further, there is a problem of see-through where the colorant can be seen from the back surface of the recording medium.

  Next, in the present invention, the formation of a film-like aggregate 31c formed by aggregation of the aggregates 31b is mentioned as one of the characteristic matters. However, when this feature is not provided, that is, the film-like aggregate 31c is formed. A case where the aggregate 31c is not formed will be described. Even if the pigment particles lose their electrical repulsion and aggregate, they do not form a film and may maintain the state of the aggregate 31b. According to the study by the present inventors, the size of the aggregate 31b is often 10 μm or less. In such a state, as the liquid components of the reaction liquid 20 and the pigment ink 30 permeate, it is shown in FIG. Thus, it has been found that most of the aggregate 31b flows between the fibers of the recording medium 10 together with the liquid component. For this reason, even if the fixing property is excellent, there is a possibility that the recorded matter has a low coloring property.

  FIG. 8 (b) is an electron micrograph when the aggregate 31b flows between the fibers of the plain paper, and is observed so as not to be much different from FIG. 8 (a), clearly in FIG. 8 (c). Thus, the aggregated film 31d is not formed, and the recorded matter has a low color developability.

  In summary, (i) while the reaction liquid containing the polyvalent metal salt is in a liquid state on the recording medium, a pigment ink having a permeability higher than that of the reaction liquid is brought into contact. (Ii) Since a film-like aggregate 31c formed by aggregation of aggregates 31b as shown in FIG. 5 (d) and FIG. 6 (a) is formed at the contact interface, (iii) Finally, an aggregated film 31d as shown in FIG. 6B or FIG. 8C can be formed on the surface of the recording medium. In particular, when the present invention is applied to a recording medium composed of a large number of fibers such as plain paper, an aggregated film that covers the plurality of fibers can be formed across the plurality of fibers. And it becomes possible to obtain high coloring property by this aggregated film.

  On the other hand, in the above-described conventional techniques (the techniques described in Patent Documents 1 to 9), knowledge that a film-like aggregate 31c formed by aggregation of aggregates 31b at the contact interface between the pigment ink and the reaction liquid is formed. These conventional techniques cannot form the film-like aggregate 31c. In these conventional techniques, since the film-like aggregate 31c is not formed, the aggregate as shown in FIGS. 7 and 8B is only formed on the final recording medium surface. In other words, it is not possible to obtain the high color developability as when the aggregated film is formed.

  Next, there is a change in the permeability of the reaction liquid due to the diffusion of the penetration accelerator in the pigment ink into the reaction liquid 20. If the penetration accelerator does not diffuse into the reaction liquid 20, a reaction is caused. The liquid permeability does not change, and the liquid component of the pigment ink 30 is held on the film-like aggregate 31c. For this reason, the printing unit dries the solvent over a long period of time, which causes a problem that the fixability is lowered. Similarly, when the pigment ink does not have a penetration accelerator, the permeability of the reaction liquid 20 does not change, and the printing section retains the liquid for a long time, resulting in a problem that the fixability is lowered. To do.

  Recently, new knowledge was obtained when the above-described aggregate 31c was not formed instantaneously. In order to form the aggregate 31c instantaneously, the total mass concentration of the pigments of the plurality of pigment inks of the same color and the substantially achromatic fine particles is substantially the same between the plurality of inks of the same color. Can be achieved. This is a feature of the present invention.

  Even if the pigment particles in the ink lose their electric repulsive force due to the reaction liquid and aggregate, the film-like aggregate 31c is not formed, but the formation of the aggregate 31b in which several pigment particles gather together is merely This is because the particle density of the pigment particles is low. Pigment particles that have lost their electrical repulsion generate aggregates due to van der Waals forces, but when the concentration of pigment particles in the ink is low, some aggregates are sparse in distance, so the aggregates are Does not further agglomerate to grow the agglomerates, and as a result, the fine agglomerates 31b are generated. Therefore, as a method for increasing the particle density due to aggregation without impairing the color developability, the particle density in the ink can be increased by adding substantially achromatic fine particles other than pigment particles, and the electric repulsion is lost. The aggregates 31c can be formed by generating large aggregates because the aggregates are in a dense state with distance due to the pigment particles and the substantially achromatic fine particles.

  Therefore, an agglomerate 31c similar to the dark ink of the same color is generated by adding achromatic fine particles to a light color ink that does not generate the aggregate 31c, that is, an ink having a low pigment concentration (an ink having a low pigment particle density). This makes it possible to record color images that can improve printing without sacrificing both fixability and color developability, satisfying the problem of color ink see-through in recording media, and capable of high-speed printing. Can be achieved.

  Next, the substantially achromatic fine particles in the present invention will be described. The achromatic fine particles that can be used in the present invention can be used as long as they have the property of aggregating with a reaction solution. One class is fine particles composed of inorganic oxides, and one is fine particles composed of organic compounds. Silica, alumina, zinc oxide, tin oxide, yttrium oxide and the like can be used as the fine particles made of the inorganic oxide, but silica can be most preferably used. An inorganic oxide having a particle size of 30 nm or less, preferably 20 nm can be used. Commercially available products include silica (made by C.I. Kasei) and zinc oxide (made by Sumitomo Cement).

  On the other hand, a white pigment or the like can be used as the fine particles made of an organic compound. Some white pigments are composed of alkylene bismelamine derivatives. Commercially available products include Shigenox OWP, Shigenox OWP L, Shigenox FWG, Shigenox FWP, Shigenox UL, Shigenox U (manufactured by Hackol Chemical) and the like.

  In addition, the amount of achromatic fine particles added is the same as the pigment mass of the pigment ink having the highest pigment concentration among the plurality of pigment inks of the same color, while other pigment inks add achromatic fine particles. Thus, it has been found that the print quality is substantially equal by blending the pigment and the achromatic fine particles so that the total mass is substantially equal. Therefore, it is preferable that the ratio of the total mass concentration of the pigment and the substantially achromatic fine particles is 0.85 to 1.15 among a plurality of pigment inks of the same color. Further, in order to prevent the formation of the fine agglomerates described above, the total mass concentration of the pigment and the substantially achromatic fine particles is desirably 3% by mass or more, and 10 mass from the viewpoint of the storage stability of the pigment ink. % Or less is desirable.

Next, the reaction solution in the present invention will be described.
As the reactive agent that reacts with the pigment ink contained in the reaction liquid in the present invention, a polyvalent metal salt is most preferable. The polyvalent metal salt is composed of a divalent or higher polyvalent metal ion and an anion that binds to the polyvalent metal ion. Specific examples of the polyvalent metal ions include divalent metal ions such as Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ and Zn ²⁺ , and trivalent metal ions such as Fe ³⁺ and Al ^3+. Is mentioned. Examples of the anion include Cl ⁻ , NO ₃ ⁻ , SO ₄ ^{2− and the} like. In order to form an aggregated film by reacting instantaneously, it is desirable that the total charge concentration of the polyvalent metal ions in the reaction solution is twice or more the total charge concentration of the reverse polarity ions in the pigment ink.

  Examples of water-soluble organic solvents that can be used in the reaction solution in the present invention include amides such as dimethylformamide and dimethylacetamide, ketones such as acetone, ethers such as tetrahydrofuran and dioxane, polyalkylenes such as polyethylene glycol and polypropylene glycol, and the like. Glycols, ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, alkylene glycols such as thiodiglycol, hexylene glycol, diethylene glycol, ethylene glycol methyl ether, diethylene glycol monomethyl ether, tri Lower alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl ether, ethanol, isopropyl alcohol In addition to monohydric alcohols such as n-butyl alcohol and isobutyl alcohol, glycerin, N-methyl-2-pyrrolidone, 1,3-dimethyl-imidazolidinone, triethanolamine, sulfolane, dimethylsulfoxide and the like can be mentioned. . Although there is no restriction | limiting in particular about content of the said water-soluble organic solvent in the reaction liquid in this invention, 5-60 mass% of the reaction liquid total mass, More preferably, 5-40 mass% is a suitable range.

  In addition, the reaction solution in the present invention may further contain additives such as a viscosity adjuster, a pH adjuster, a preservative, and an antioxidant as necessary, but a penetration enhancer. The selection and addition amount of the surfactant functioning as a caution must be taken to suppress the permeability of the reaction liquid to the recording medium. Furthermore, the reaction liquid in the present invention is more preferably colorless, but it may be light in a range that does not change the color tone of each color ink when mixed with ink on a recording medium. Furthermore, as a preferable range of the various physical properties of the reaction solution in the present invention as described above, the viscosity at about 25 ° C. is 1 to 30 cps. What was adjusted so that it might become the range of this is preferable.

Next, the pigment ink will be described.
The pigment of the pigment ink used in the present invention is used in a mass ratio of 1 to 20 mass%, preferably 2 to 12 mass%, based on the total mass of the pigment ink. Specific examples of the pigment used in the present invention include carbon black as a black pigment. For example, carbon black produced by a furnace method or a channel method having a primary particle size of 15 to 40 μm. (Nm), having a specific surface area by BET method of 50 to 300 m ² / g, DBP oil absorption of 40 to 150 ml / 100 g, volatile content of 0.5 to 10% by mass, pH value of 2 to 9, etc. Is preferably used. Examples of commercially available products having such characteristics include No. 2300, no. 900, MCF88, No. 33, no. 40, no. 45, no. 52, MA7, MA8, no. 2200B (above, manufactured by Mitsubishi Kasei), Raven 1255 (above, made in Colombia), REGAL400R, REGAL330R, REGAL660R, MOGUL L (above made by Cabot), Color Black FWl, Color Black FW18, Color Black S170, Color Black S170, ColorSack 35 Printex U (above, manufactured by Degussa) and the like can be preferably used.

  Examples of yellow pigments include C.I. I. Pigment Yellow 1, C.I. I. Pigment Yellow 2, C.I. I. Pigment Yellow 3, C.I. I. Pigment Yellow 13, C.I. I. Pigment Yellow 16, C.I. I. Pigment Yellow 83 and the like. Examples of magenta pigments include C.I. I. Pigment Red 5, C.I. I. Pigment Red 7, C.I. I. Pigment Red 12, C.I. I. Pigment Red 48 (Ca), C.I. I. Pigment Red 48 (Mn), C.I. I. Pigment Red 57 (Ca), C.I. I. Pigment Red 112, C.I. I. Pigment Red 122 and the like. Examples of cyan pigments include C.I. I. Pigment Blue 1, C.I. I. Pigment Blue 2, C.I. I. Pigment Blue 3, C.I. I. Pigment Blue 15: 3, C.I. I. Pigment Blue 16, C.I. I. Pigment Blue 22, C.I. I. Vat Blue 4, C.I. I. Vat Blue 6 etc. are mentioned. Of course, the present invention is not limited to these. In addition to the above, a newly produced pigment such as a self-dispersing pigment can of course be used.

  The pigment dispersant may be any water-soluble resin, but preferably has a weight average molecular weight in the range of 1,000 to 30,000, more preferably 3,000 to 15, The one in the range of 000 is used. Specific examples of such a dispersant include styrene, styrene derivatives, vinyl naphthalene, vinyl naphthalene derivatives, aliphatic alcohol esters of α, β-ethylenically unsaturated carboxylic acids, acrylic acid, acrylic acid derivatives, At least two or more monomers selected from maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, vinyl acetate, vinylpyrrolidone, acrylamide, and derivatives thereof (of which at least 1 One is a block copolymer comprising a hydrophilic polymerizable monomer), a random copolymer, a graft copolymer, or a salt thereof. Alternatively, natural resins such as rosin, shellac and starch can also be preferably used. These resins are soluble in an aqueous solution in which a base is dissolved, and are alkali-soluble resins. In addition, it is preferable to contain the water-soluble resin used as these pigment dispersants in the range of 0.1 to 5% by mass with respect to the total mass of the pigment ink.

  In particular, in the case of a pigment ink containing a pigment as described above, the entire pigment ink is preferably adjusted to be neutral or alkaline. This is preferable because the solubility of the water-soluble resin used as the pigment dispersant can be improved, and the pigment ink can be further excellent in long-term storage stability. However, in this case, since it may cause corrosion of various members used in the ink jet recording apparatus, it is desirable that the pH range is 7-10. Examples of the pH adjuster used in this case include various organic amines such as diethanolamine and triethanolamine, inorganic alkali agents such as alkali metal hydroxides such as sodium hydroxide, lithium hydroxide and potassium hydroxide, Examples include organic acids and mineral acids. The above-described pigment and dispersant water-soluble resin are dispersed or dissolved in an aqueous liquid medium.

In the pigment ink containing the pigment used in the present invention, a suitable aqueous liquid medium is a mixed solvent of water and a water-soluble organic solvent, and the water is not general water containing various ions but ion exchange. It is preferred to use water (deionized water).
Examples of the water-soluble organic solvent used by mixing with water include carbon atoms of 1 such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and the like. Alkyl alcohols of -4; 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; Ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol Alkylene glycols having 2 to 6 carbon atoms, such as coal; glycerin; ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether, etc. Lower alkyl ethers of monohydric alcohols; N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like. Among these many water-soluble organic solvents, polyhydric alcohols such as diethylene glycol and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl (or ethyl) ether are preferred.

  The content of the water-soluble organic solvent as described above in the pigment ink is generally in the range of 3 to 50% by mass, more preferably in the range of 3 to 40% by mass, based on the total mass of the pigment ink. The water content used is in the range of 10 to 90% by mass, preferably 30 to 80% by mass, based on the total mass of the pigment ink.

  In addition to the above-described components, a surfactant, an antifoaming agent, a preservative, and the like are appropriately added as a pigment ink in the present invention in order to obtain a pigment ink having desired physical properties as necessary. be able to. In particular, the surfactant functioning as a penetration accelerator needs to be added in an appropriate amount to play a role of promptly penetrating the liquid components of the reaction liquid and the pigment ink into the recording medium. As an example of the addition amount, 0.05 to 10% by mass, preferably 0.5 to 5% by mass is suitable. As examples of the anionic surfactant, any commonly used ones such as a carboxylate salt type, a sulfate ester type, a sulfonate salt type, and a phosphate ester type can be preferably used.

  As a method for preparing a pigment ink containing the pigment as described above, first, the pigment is added to an aqueous medium containing at least a water-soluble resin as a dispersant and water, mixed and stirred, and then described later. The desired dispersion is obtained by performing dispersion using the dispersion means and performing a centrifugal separation process as necessary. Next, a sizing agent and appropriately selected additive components such as those mentioned above are added to this dispersion and stirred to obtain a pigment ink used in the present invention.

  In addition, when using an alkali-soluble resin as described above as a dispersant, it is necessary to add a base in order to dissolve the resin. In this case, the bases include monoethanolamine, Organic bases such as diethanolamine, triethanolamine, aminomethylpropanol and ammonia, or inorganic bases such as potassium hydroxide and sodium hydroxide are preferably used.

  In addition, in the method for preparing a pigment ink containing a pigment, it is effective to perform premixing for 30 minutes or more before stirring and dispersing the aqueous medium containing the pigment. That is, such a premixing operation is preferable because it improves wettability of the pigment surface and promotes adsorption of the dispersant on the pigment surface. The disperser used in the above-described pigment dispersion treatment may be any disperser that is generally used, and examples thereof include a ball mill, a roll mill, and a sand mill. Among these, a high speed type sand mill is preferably used. Examples of such include a super mill, a sand grinder, a bead mill, an agitator mill, a glen mill, a dyno mill, a pearl mill, and a cobol mill (all are trade names).

  In addition, as a pigment in the pigment ink, a pigment having an optimum particle size distribution is used in the ink jet recording method because of demands for clogging resistance and the like. As a method for obtaining a pigment having a desired particle size distribution, a disperser is used. Reducing the size of the grinding media, increasing the filling rate of the grinding media, increasing the processing time, slowing the discharge speed, classifying with a filter or centrifuge after grinding, etc. Examples include a combination of methods.

  Next, the ink jet recording method of the present invention will be described. Specific examples of the liquid composition cartridge, the recording unit, the ink jet recording apparatus, and the liquid discharge head suitably used in these apparatuses, to which the liquid composition of the reaction liquid and the pigment ink having the above-described structure is preferably applied. Will be described with reference to FIGS.

  FIG. 1 shows an example of a liquid discharge head as an ink jet recording head of an ejection method suitable for the ink jet recording apparatus used in the present invention and communicating bubbles with the atmosphere at the time of discharge, and an ink jet printer as a liquid discharge apparatus using this head. It is a schematic perspective view which shows the principal part.

  In FIG. 1, the ink jet printer includes a conveyance device 1030 that intermittently conveys a sheet 1028 as a recording medium provided in the casing 1008 along the longitudinal direction in a direction indicated by an arrow P shown in the drawing, A recording unit 1010 that is reciprocated along a guide shaft 1014 substantially parallel to an arrow S direction substantially orthogonal to the conveyance direction P of the paper 1028 by the conveying device 1030, and a moving drive as a driving unit that reciprocates the recording unit 1010. Part 1006.

  The movement drive unit 1006 is disposed substantially parallel to the pulleys 1026a and 1026b arranged on the rotation shafts opposed to each other with a predetermined interval, the belt 1016 wound around the pulleys, the roller units 1022a and 1022b, and the roller unit. A motor 1018 that drives a belt 1016 coupled to the carriage member 1010a of the portion 1010 in the forward direction and the reverse direction.

  When the motor 1018 is activated and the belt 1016 rotates in the direction of arrow R in FIG. 1, the carriage member 1010a of the recording unit 1010 is moved by a predetermined amount of movement in the direction of arrow S in FIG. When the motor 1018 is activated and the belt 1016 rotates in the direction opposite to the arrow R direction shown in the figure, the carriage member 1010a of the recording unit 1010 is in the direction opposite to the arrow S direction in FIG. Is moved by a predetermined amount.

  Further, a recovery unit 1026 for performing an ejection recovery process of the recording unit 1010 is disposed at one end portion of the movement driving unit 1006 at a position serving as a home position of the carriage member 1010a so as to face the ink ejection port array of the recording unit 1010. Is provided.

  The recording unit 1010 includes ink jet cartridges (hereinafter sometimes simply referred to as “cartridges”) 1012Y, 1012M, 1012C, and 1012B as pigment inks containing each color, for example, yellow, magenta, cyan, and black pigments, and 1012S as a reaction liquid. The carriage member 1010a is detachably provided.

  FIG. 2 shows an example of an ink jet cartridge that can be mounted on the above-described ink jet recording apparatus. The cartridge 1012 in this example is of a serial type, and the main part is composed of the ink jet recording head 100 and a liquid tank 1001 that stores a liquid such as ink.

  The inkjet recording head (liquid ejection head) 100 has a large number of ejection ports 832 for ejecting liquid, and liquid such as a liquid composition is ejected from the liquid tank 1001 through a liquid supply passage (not shown). The head 100 is led to a common liquid chamber (not shown). A cartridge 1012 shown in FIG. 2 is formed by integrally forming an ink jet recording head 100 and a liquid tank 1001 so that liquid can be supplied into the liquid tank 1001 as necessary. A structure in which a liquid tank 1001 is connected to 100 in a replaceable manner may be adopted.

  The recording method of the present invention is particularly effective in an ink jet recording head or recording apparatus that performs recording by forming flying droplets using thermal energy among ink jet recording methods. As for the typical configuration and principle, for example, those performed using the basic principle disclosed in US Pat. Nos. 4,723,129 and 4,740,796 are preferable. .

  This method can be applied to both the so-called on-demand type and the continuous type. In particular, in the case of the on-demand type, it corresponds to a sheet or a liquid path that holds liquid (ink). By applying at least one drive signal that corresponds to the recorded information and gives a rapid temperature rise exceeding the film boiling to the arranged electrothermal transducer, thermal energy is generated in the electrothermal transducer, and recording is performed. This is effective because film boiling occurs on the heat acting surface of the head, and as a result, bubbles in the liquid (ink) corresponding to this 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 the pulse-shaped drive signal at this time, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. Further excellent recording can be performed by adopting the conditions described in US Pat. No. 4,313,124 related to the invention concerning the temperature rise rate of the heat acting surface.

  The ink cartridge, the recording unit, and the recording head constituting the ink jet recording apparatus used in the present invention include a combination of an ejection port, a liquid path, and an electrothermal transducer as disclosed in the above specifications. U.S. Pat. No. 4,558,333 and U.S. Pat. No. 4, which disclose a configuration in which the heat acting portion is arranged in a bent region in addition to the configuration (straight liquid flow path or right-angle liquid flow path) It is also preferable to use the thing of the structure using 459,600 specification.

  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. It 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 recording medium in the maximum range that can be recorded by the recording apparatus, the length is obtained by combining a plurality of recording heads as disclosed in the above specification. Either a configuration satisfying the above or a configuration as a single recording head formed integrally may be used.

  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. A cartridge type recording head provided with a tank can also be used.

  In addition, it is preferable to add a recovery means for the recording head, a preliminary auxiliary means, etc. provided in the ink jet recording apparatus of the present invention, since the effects of the present invention can be further stabilized. Specifically, capping means for the recording head, cleaning means, pressurization or suction means, electrothermal converter or a heating element different from this, or preheating means by a combination of these, recording and In order to perform stable recording, it is also effective to perform a preliminary discharge mode in which another discharge is performed.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the following description, “part” or “%” is based on mass unless otherwise specified. The surface tension of the ink and the reaction liquid was measured using CBVP-Z manufactured by Kyowa Interface Chemical Co., Ltd.
[Example 1]
First, cyan pigment inks each containing a pigment and an anionic compound were obtained as described below.
(Pigment ink)
<Preparation of pigment dispersion>
-Styrene-acrylic acid-ethyl acrylate copolymer (acid value 240, weight average molecular weight = 5,000) 1.5 parts-Monoethanolamine 1.0 part-Diethylene glycol 5.0 parts-Ion-exchanged water 81.5 Part

The above components are mixed and heated to 70 ° C. in a water bath to completely dissolve the resin component. To this solution, 10 parts of newly prepared Pigment Blue 15 and 1 part of isopropyl alcohol were added, and after 30 minutes of premixing, dispersion treatment was performed under the following conditions.
・ Disperser: Sand grinder (Igarashi Machine)
・ Crushing media: Zirconium beads, 1 mm diameter ・ Filling rate of grinding media: 50% (volume ratio)
-Grinding time: 3 hours Further, centrifugal separation (12,000 rpm, 20 minutes) was performed to remove coarse particles to obtain a pigment dispersion.

<Preparation of Cyan Pigment Ink C1>
Using the above dispersion, components having the following composition ratios were mixed to produce an ink containing a pigment, which was designated as cyan pigment ink C1.
-Pigment dispersion 30.0 parts-Glycerol 10.0 parts-Ethylene glycol 5.0 parts-N-methylpyrrolidone 5.0 parts-Ethyl alcohol 2.0 parts-Acetylenol EH (manufactured by Kawaken Fine Chemicals) 1.0 Parts / ion-exchanged water 47.0 parts The surface tension of the cyan pigment ink C1 obtained above was 32 mN / m.

<Preparation of Cyan Pigment Ink C2>
Using the above dispersion liquid, components having the following composition ratios were mixed to produce an ink containing a pigment, which was designated as cyan pigment ink C2.
-5.0 parts of the above pigment dispersion-40% zinc oxide slurry (Sumitomo Cement) 6.3 parts-10.0 parts glycerin-5.0 parts ethylene glycol-5.0 parts N-methylpyrrolidone-ethyl alcohol 2 1.0 part acetylenol EH (manufactured by Kawaken Fine Chemicals) 1.0 part ion-exchanged water 65.7 parts The surface tension of the cyan pigment ink C2 obtained above was 31 mN / m.

(Reaction solution S1)
Next, after mixing and dissolving the following components, pressure filtration with a membrane filter (trade name: Fluoropore filter, manufactured by Sumitomo Electric) having a pore size of 0.22 μm, and the pH is adjusted to 3.8. A liquid S1 was obtained.
<Composition of reaction liquid S1>
-Diethylene glycol 10.0 parts-Methyl alcohol 5.0 parts-Magnesium nitrate 7.0 parts-Acetylenol EH (manufactured by Kawaken Fine Chemicals) 0.1 part-Ion-exchanged water 77.9 parts of the reaction solution S1 obtained above The surface tension was 46 mN / m.

  Using the reaction liquid S1 and the cyan pigment inks C1 and C2, the reaction liquid S1 is first applied to PB paper (manufactured by Canon) that is plain paper, and then the reaction liquid S1 and the cyan pigment inks C1 and C2 are applied. The pigment inks C1 and C2 were applied so as to be in contact with the reaction liquid S1 so that the time difference until the time was 5 milliseconds, and solid printed matters A1 and A2 each having a 1 cm square were prepared. The recording head used here had a recording density of 1,200 dpi, and the driving condition was a driving frequency of 15 kHz. Further, a 4 pl head was used for the ejection volume per dot. The environmental conditions for the print test are unified at 25 ° C./55% RH. The color development of the printed matter A1 and A2 produced was not fading, although there was a difference in shade of pigment, there was no problem with the sharpness of the edge of the pattern, and there was no problem with the color show-through.

[Example 2]
In the same manner as in Example 1, cyan pigment inks each containing a pigment and an anionic compound were obtained as described below.
(Pigment ink)
<Preparation of pigment dispersion>
A pigment dispersion was prepared in the same manner as in Example 1.

<Preparation of Cyan Pigment Ink C3>
Using the above dispersion liquid, components having the following composition ratios were mixed to prepare an ink containing a pigment to obtain a cyan pigment ink C3.
-Pigment dispersion 30.0 parts-Glycerol 10.0 parts-Ethylene glycol 5.0 parts-N-methylpyrrolidone 5.0 parts-Ethyl alcohol 2.0 parts-Acetylenol EH (manufactured by Kawaken Fine Chemicals) 1.0 Parts / ion-exchanged water 47.0 parts The surface tension of the cyan pigment ink C3 obtained above was 32 mN / m.

<Preparation of Cyan Pigment Ink C4>
Using the above dispersion, components having the following composition ratios were mixed to produce an ink containing a pigment, which was designated as cyan pigment ink C4.
-5.0 parts of the above pigment dispersion-25.0 parts of Shigenox OWP 10% slurry (manufactured by Hakko Chemical)-10.0 parts of glycerin-5.0 parts of ethylene glycol-5.0 parts of N-methylpyrrolidone-ethyl alcohol 0 part acetylenol EH (manufactured by Kawaken Fine Chemicals) 1.0 part ion-exchanged water 47.0 parts The surface tension of the cyan pigment ink C4 obtained above was 33 mN / m.

(Reaction solution S2)
A reaction solution S2 was prepared in the same manner as in Example 1 with the following composition.
<Composition of reaction liquid S2>
・ Diethylene glycol 10.0 parts ・ Methyl alcohol 5.0 parts ・ Aluminum chloride 10.0 parts ・ Acetylenol EH (manufactured by Kawaken Fine Chemicals) 0.1 part ・ Ion-exchanged water 74.9 parts The surface tension was 47 mN / m.

  Using the reaction liquid S2 and the cyan pigment inks C3 and C4, the reaction liquid S2 is first applied to PB paper (manufactured by Canon) which is plain paper, and then the reaction liquid S2 and the cyan pigment inks C3 and C4 are applied. The pigment inks C3 and C4 were applied so as to be in contact with the reaction liquid S2 so that the time difference until the completion was 5 milliseconds, thereby producing solid prints A3 and A4 each having a 1 cm square. The color development of the printed matter A3 and A4 produced was not fading, although there was a difference in shade of the pigment, there was no problem with the sharpness of the edge of the pattern, and there was no problem with the color show-through.

[Comparative Example 1]
In the same manner as in Example 1, cyan pigment inks each containing a pigment and an anionic compound were obtained as described below.
(Pigment ink)
<Preparation of pigment dispersion>
A pigment dispersion was prepared in the same manner as in Example 1.

<Preparation of Cyan Pigment Ink C5>
Using the above dispersion, components having the following composition ratios were mixed to produce an ink containing a pigment, which was designated as cyan pigment ink C5.
-Pigment dispersion 5.0 parts-Glycerol 10.0 parts-Ethylene glycol 5.0 parts-N-methylpyrrolidone 5.0 parts-Ethyl alcohol 2.0 parts-Acetylenol EH (manufactured by Kawaken Fine Chemicals) 1.0 Parts / ion-exchanged water 72.0 parts The surface tension of the cyan pigment ink C5 obtained above was 32 mN / m.

  Using the reaction liquid S1 and cyan pigment inks C2 and C5, the reaction liquid S1 is first applied to PB paper (manufactured by Canon), which is plain paper, and then the reaction liquid S1 and the cyan pigment inks C2 and C5 are applied. The pigment inks C2 and C5 were applied so as to be in contact with the reaction liquid S1 so that the time difference until the time was 5 milliseconds, thereby producing solid printed matters A5 and A6 each having a 1 cm square. The printed matter A5 and A6 produced had poorer color developability of A6 than A5, had density unevenness in a 1 cm square solid pattern, and had a problem of color show-through.

1 is a schematic perspective view illustrating an example of an ink jet printer. FIG. 2 is a schematic perspective view illustrating an example of an inkjet cartridge. FIG. 3 is a schematic cross-sectional view showing the behavior of ink on a recording medium by the ink jet recording method of the present invention. Absorption curve in Bristow method. The figure which showed a mode that the aggregate 31b aggregated and the film-form aggregate 31c was formed. The figure which showed a mode that the film-like aggregate 31c fixed to the surface of a recording medium, and the aggregated film 31d was formed. The figure which showed the mode of the surface of the recording medium in case the aggregated film 31d is not formed. The figure which showed the mode when the surface of a recording medium was image | photographed using the electron microscope.

Explanation of symbols

10: Recording medium 10a: Print surface 20 of the recording medium: Reaction liquid 21: Multivalent metal ion 30: Pigment ink 31: Pigment particle 31a in a dispersed state: Pigment particle 31b in which electric repulsion has disappeared: Aggregate 31c: Film Aggregate 31d: Aggregated film 32: Surfactant 100: Inkjet recording head 832: Discharge port 1001: Liquid tank 1006: Movement drive unit 1008: Casing 1010: Recording unit 1010a: Carriage member 1012: Cartridge 1012Y, M, C B, S: inkjet cartridge 1014: guide shaft 1016: belt 1018: motor 1022a, 1022b: roller unit 1024a, 1024b: roller unit 1026: recovery unit 1026a, 1026b: pulley 1028: paper 1030: transport device R: rotation of belt Countercurrent S: conveying direction in a direction substantially perpendicular to the paper

Claims (5)

In a recording method for performing recording by applying a plurality of pigment inks of the same color after applying a reaction liquid to a recording medium, the surface tension of the reaction liquid applied to the upper surface of the recording medium is lower than the surface tension of the reaction liquid A step of applying the pigment ink having surface tension, and a step of forming a film-like aggregate formed by aggregation of aggregates at an interface where the reaction liquid and the pigment ink are in contact with each other.
The reaction liquid has polyvalent metal ions, and in the plurality of pigment inks, the dark ink having the highest pigment concentration in these inks does not contain substantially achromatic fine particles, and other than the dark ink. The pigment ink includes a pigment and substantially achromatic fine particles, and the mass concentration of the pigment contained in the dark ink, and the pigment in the ink other than the dark ink and the substantially achromatic fine particles The total mass concentration of the ink is substantially the same among the plurality of pigment inks.   The plurality of pigment inks of the same color have a mass concentration of the pigment in the dark ink and a total mass concentration of the pigment in each pigment ink other than the dark ink and the substantially achromatic fine particles between the pigment inks. The inkjet recording method according to claim 1, wherein the mass concentration ratio is 0.85 to 1.15.   The plurality of pigment inks of the same color have a mass concentration of the pigment in the dark ink and a total mass concentration of the pigment in each pigment ink other than the dark ink and substantially achromatic fine particles of 3 to 10% by mass. The inkjet recording method according to claim 1 or 2.   The inkjet recording method according to claim 1, wherein the substantially achromatic fine particles are inorganic oxides. The inkjet recording method according to claim 1, wherein the substantially achromatic fine particles are an organic compound.