JP2018118433A - Inkjet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet recording method allowing for recording of an image in which a change in color tone before and after high temperature storage of ink is suppressed.SOLUTION: A plurality of recording heads 20 are arrayed in a conveyance direction of a recording medium. Color ink contains at least a pigment, resin particles and water. Out of the plurality of color inks, the orders of the color inks applied to the recording medium are set to be the first to the N-th in which the orders of the color inks is the orders of application of the inks. A coagulation speed of a solid content in a first liquid obtained by preparing each of the color ink is represented by V, and a coagulation speed of a solid content in a second liquid obtained by preparing each of the color ink after the color inks are stored at 60°C for two weeks is represented by V. A coagulation speed ratio before and after each of the color inks are stored is represented by R=(V/V)×100, a relationship between a coagulation speed ratio Rof the color ink of the K-th (1≤K<N) and a coagulation speed ratio Rof the color ink of the (K+1)-th (2≤K+1≤N) satisfies R<R.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ink jet recording method.

  The ink jet recording method is one of the image recording methods that have been remarkably developed in recent years because it can easily record a high-quality color image with a simple principle. In addition to recording images such as documents and photographs at home, which have been mainstream until now, they are rapidly spreading in offices and industrial applications.

  Conventionally, various ink compositions have been studied for the purpose of improving the optical density of an image recorded on a recording medium such as plain paper. For example, there has been proposed an ink capable of recording an image with good color development, in which a self-dispersing pigment to which a functional group having a high calcium index value is bonded and a dispersion of a polyurethane prepolymer are blended (Patent Document 1).

Special table 2013-535548 gazette

  As a result of studies by the present inventors, it has been found that if the ink proposed in Patent Document 1 is used, an image with good color development can be recorded. However, it has also been found that if the ink proposed in Patent Document 1 is stored for a certain period of time at a high temperature of, for example, about 60 ° C., the color developability of the recorded image decreases.

  Accordingly, an object of the present invention is to provide an ink jet recording method capable of recording an image in which a change in color tone before and after high temperature storage of ink is suppressed.

The above object is achieved by the present invention described below. That is, according to the present invention, there is provided an inkjet recording method for recording an image on a recording medium by ejecting a plurality of color inks from a plurality of inkjet recording heads, wherein the plurality of recording heads convey the recording medium. The color ink contains at least a pigment, resin particles, and water, and the plurality of color inks in order from the first color ink applied to the recording medium in advance. N-th, each color ink was diluted 500 times with water and calcium chloride was added at a concentration of 2.0 mmol / L, and the solids aggregation rate in the first liquid prepared as V _before , After each color ink was stored at 60 ° C. for 2 weeks, it was diluted 500 times with water, and calcium chloride was added at a concentration of 2.0 mmol / L. When the aggregation rate of the solid content in the produced second liquid is V _after and the aggregation rate ratio of each color ink before and after the storage is R = (V _after / V _before ) × 100, the Kth (1 and aggregation rate ratio R _K color inks ≦ K <N), the relationship between the coagulation speed ratio R _{K + 1} of the color ink (K + 1) -th (2 ≦ K + 1 ≦ N ), satisfies the R _K <R K _{+ 1} An ink jet recording method is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the inkjet recording method which can record the image by which the color tone change before and after high temperature storage was suppressed can be provided.

It is a schematic diagram which shows the outline | summary of the inkjet recording device used for the inkjet recording method of one Embodiment of this invention. It is a schematic diagram which shows each line head which comprises the ink provision part in an inkjet recording device. It is a graph which shows an example of the absorption curve for demonstrating the absorption coefficient Ka of the water of a recording medium.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments, but the present invention is not limited to the following embodiments. In this specification, ink jet ink (including color ink) may be simply referred to as “ink”. Further, the physical property values are values at normal temperature (25 ° C.) unless otherwise specified.

  As a result of studying the color developability using a plurality of color inks, the present inventors have reached the configuration of the present invention. That is, a method has been reached in which the aggregation speed ratio before and after storage of the ink and the ink recording order are taken into consideration.

  In order to record an image with excellent color developability, the pigment in the ink needs to stay in the vicinity of the surface of the recording medium as much as possible without penetrating into the recording medium. It is important to suppress the penetration of the pigment into the recording medium. That is, if the aggregation of the pigment is earlier than the penetration, the pigment stays in the vicinity of the surface of the recording medium, so that an image having a high optical density and excellent color developability can be recorded.

  In order to quickly aggregate the pigment on the surface of the recording medium, for example, the collision frequency of the pigments in the ink is increased to improve the probability of aggregation, or the pigment may be changed due to environmental changes such as changes in ion concentration or pH in the recording medium. It is necessary to take measures such as causing distributed destruction. In addition, a countermeasure such as agglomeration of the pigment by reaction with ions eluted from the recording medium due to ink landing may be considered. That is, (i) increasing the solid content concentration in the ink; (ii) decreasing the pH of the ink; (iii) increasing the salt strength of the ink; (iv) a pigment having functional groups capable of reacting with ions bonded to the particle surface. A method such as using can be considered.

  However, when an ink containing a pigment in a high concentration is exposed to a high temperature during transportation or storage, the collision frequency between the pigments further increases, and the pigment is likely to aggregate in the ink. Similarly, when ink that has weakened repulsion between pigments due to a decrease in pH or an increase in salt strength is exposed to high temperatures during transportation or storage, the pigment with increased collision frequency tends to aggregate in the ink. . As a result, the dispersion stability of the pigment is lowered, and precipitation and thickening are likely to occur. In the case of a pigment in which a functional group that reacts with ions is bonded to the particle surface, the functional group is desorbed at a high temperature, and the reactivity with ions eluted from the recording medium is reduced, so that the pigment aggregates on the surface of the recording medium. It becomes difficult to occur and the color developability of the image decreases.

  With reference to FIG. 1, the configuration and operation of an ink jet recording apparatus that can be used in the ink jet recording method of one embodiment of the present invention will be described. FIG. 1 is a schematic diagram showing an outline of an ink jet recording apparatus used in an ink jet recording method according to an embodiment of the present invention. As shown in FIG. 1, the inkjet recording apparatus 100 records an image by ejecting ink onto a recording medium based on image data received from, for example, an external computer and recording conditions (for example, whether or not double-sided printing is performed). As the recording medium P, for example, plain paper can be used. When the recording medium supply unit 10 is transporting the recording medium P, ink is ejected from the ink applying unit 20 toward the recording medium P, and an image is recorded on one side (recording surface) of the recording medium P by the ink. . The ink applicator 20 includes line heads 20a, 20b, 20c, 20d,... 20x that eject inks of two or more different colors.

  Next, the configuration of the ink applying unit 20 will be described mainly with reference to FIG. FIG. 2 is a schematic diagram showing each line head constituting the ink application unit 20. Each line head 20 is a line-type long recording head. The plurality of line heads 20a, 20b, 20c, 20d,... 20x are arranged in the conveyance direction (X direction) of the recording medium P. Each of the line heads 20a to 20d and 20x extends in a direction (Y direction) orthogonal to the conveyance direction (X direction) of the recording medium P. The lengths of the line heads 20a to 20d and 20x are preferably larger than the width of the recording medium P. As a result, it is possible to record images collectively in the width direction.

  Each of the line heads 20a to 20d and 20x preferably includes a plurality of ejection units 30 arranged in a direction (Y direction) orthogonal to the conveyance direction (X direction) of the recording medium P. Each of the line heads 20a to 20d and 20x ejects ink from each ejection unit 30 in accordance with the image signal. In the ink jet recording apparatus 100, the line heads 20a to 20d and 20x are sequentially ejected with ink to record an image on the recording medium P. Specifically, the line heads 20a, 20b, 20c, 20d,... 20x... Are arranged in this order from the upstream (X1 side) to the downstream (X2 side) in the conveyance direction of the recording medium P. Ink is ejected. As a result, ink can be ejected to the same position on the recording medium P. As a result, an image can be recorded on the recording medium P.

  For example, when the line head 20a is filled with the first ink and the line head 20b is filled with the second ink, the first ink is applied to the recording surface of the recording medium P first, and then the second ink is applied. Ink is applied. Further, when the first ink is applied to the recording medium P, the calcium (Ca) component in the recording medium and the pigment in the first ink are aggregated and fixed. Thereafter, when the second ink is applied to the recording medium P, a part of the pigment in the second ink is aggregated and fixed to Ca in which the pigment in the first ink is not aggregated. Then, a part of the pigment in the second ink that could not be fixed penetrates into the lower layer portion of the recording medium P and is fixed.

  It was found that the ink used in the study had almost no color change when recording was performed with primary colors, even though the aggregation rate was changed before and after storage at 60 ° C. for 2 weeks. However, it was found that when recording was performed with a secondary color, the color developed by the ink applied later was lowered. Further, it was found that when recording was performed from an ink having a large change in aggregation rate before and after storage for 2 weeks at 60 ° C., the color change was smaller than when the ink was applied from a small change in aggregation rate to a recording medium. This is because the recording medium has sufficient Ca that can aggregate the pigment when the ink using the pigment whose aggregation rate changes largely before and after storage is recorded on the upstream side, and the aggregation ability is high. Even if it falls, it can aggregate with Ca, and it is thought that it does not lead to a color development fall.

From the above examination, an ink jet recording method for recording an image on a recording medium by ejecting a plurality of color inks from a plurality of ink jet type recording heads is configured as follows, so that the ink is stored either before or after high-temperature storage. It is possible to record an image with excellent color developability. That is, a plurality of recording heads used in the ink jet recording method are arranged along the recording medium conveyance direction. As the color ink, an ink containing at least a pigment, resin particles, and water is used. Here, among the plurality of color inks, the color inks that are applied first to the recording medium are first to Nth in order. On the other hand, the solid aggregation rate in the first liquid prepared by diluting each color ink 500 times with water and adding calcium chloride at a concentration of 2.0 mmol / L is defined as V _before . In addition, after each color ink was stored at 60 ° C. for 2 weeks, it was diluted 500 times with water and calcium chloride was added at a concentration of 2.0 mmol / L, and the solids aggregation rate in the second liquid prepared _Is V _after . Further, the aggregation speed ratio of each color ink before and after storage is R = (V _after / V _before ) × 100 (%). At this time, the relationship between the K-th (1 ≦ K <N) color and aggregation rate ratio R _K of the ink, K + 1 th aggregation rate ratio R _{K + 1} of the color inks (2 ≦ K + 1 ≦ N ) of, R _K <R _{K + 1} is satisfied.

(Measuring method of aggregation rate)
The aggregation rate (V _before and V _after ) of the solid content in the first and second liquids can be measured with reference to the descriptions in the following documents. That is, after a predetermined amount of calcium chloride solution is added to the ink diluent, the change in the particle size of the pigment over time is measured, and the increase rate of the particle size is measured and calculated as the “aggregation rate”.
(Reference)
“International Conference on Digital Printing Technologies, September 2002; p. 383-387, Yuan Yu et. Al.“ Coagulation Kinetics of Surface Modified ”.

  As a pigment particle size measuring device, a dense particle size analyzer (trade name “FPAR-1000”, manufactured by Otsuka Electronics Co., Ltd.) can be used. After adding and mixing a predetermined amount of calcium chloride solution to ink diluted 500 times with water, measurement of the particle size of the pigment is started immediately. The particle size of the pigment is measured for 900 seconds at 2 second intervals. After the measurement is completed, the initial slope of the particle size change is determined and used as the aggregation rate. The ink dilution rate was set to 500 times (mass basis), which gives a measurable density in order to maintain the interaction between the inks.

<Ink>
In the inkjet recording method of one embodiment of the present invention, a plurality of color inks are used. This color ink contains at least a pigment, resin particles, and water. Examples of the color ink include cyan ink, magenta ink, and yellow ink. Further, in the ink jet recording method of one embodiment of the present invention, an ink set having a plurality of color inks can be used. In this ink set, black ink may be used in addition to a plurality of color inks. Hereinafter, each component of the ink will be described.

[Pigment]
Examples of the type of pigment (pigment particles) include inorganic pigments such as carbon black and organic pigments. As the pigment, any known pigment that can be used in the ink can be used, and one kind of pigment can be used alone, or two or more kinds can be used in combination. An organic pigment is preferably used as the pigment (color pigment) used in the color ink, and carbon black is preferably used as the pigment used in the black ink.

  The content (% by mass) of the pigment in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, more preferably 1.0% by mass or more and 8.0% by mass based on the total mass of the ink. It is below mass%. When the content of the pigment in the ink is less than 0.1% by mass, the optical density of the image may not be sufficiently obtained. If the content of the pigment in the ink exceeds 15.0% by mass, ink jet characteristics such as adhesion resistance may not be sufficiently obtained.

  It is preferable to use a copper phthalocyanine pigment as the pigment for the cyan ink. Specific color index No. As C.I. I. Pigment blue 1, 2, 3, 15, 15: 2, 15: 3, 15: 4, 16, 22, 60, and the like.

  A quinacridone pigment is preferably used as the magenta ink pigment. Specific color index No. As C.I. I. Pigment Red 5, 7, 12, 48, 48: 1, 57, 112, 122, 123, 146, 168, 184, 202, 207 and the like.

  As the pigment for yellow ink, an azo pigment is preferably used. Specific color index No. As C.I. I. Pigment yellow 12, 13, 14, 16, 17, 74, 83, 93, 95, 97, 98, 114, 128, 129, 151, 154, and the like.

  Carbon black is preferably used as the pigment for the black ink. Examples of the carbon black include Raven: 1060, 1080, 1170, 1200, 1250, 1255, 1500, 2000, 3500, 5250, 5750, 7000, 5000 ULTRAII, 1190 ULTRAII (manufactured by Columbian Carbon); Black Pearls L; MOGUL-L; Regal: 400R, 660R, 330R; Monarch: 800, 880, 900, 1000, 1300, 1400 (above, manufactured by Cabot); Color Black: FW1, FW2, FW200, 18, S160, S170; Special Black: 4, 4A, 6; Printex: 35, U, 140U, V, 140V (above, manufactured by Degussa); 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, no. 2600, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical) and the like.

  The pigment is preferably a pigment that can be dispersed in water. Examples of the pigment dispersion method include self-dispersion type pigments (hydrodispersion pigments) in which hydrophilic groups are bonded directly or via other atomic groups to the pigment particle surface, and resin dispersion type pigments using a resin as a dispersant. The method using is mentioned. It is also possible to use pigments with different dispersion methods in combination with the ink.

(Self-dispersing pigment)
The color ink used in the ink jet recording method of one embodiment of the present invention preferably contains a self-dispersing pigment as a pigment, and the self-bonded phosphonic acid group is directly or via other atomic groups on the pigment particle surface. More preferably, it contains a dispersed pigment. In the ink, the form of the phosphonic acid group of the self-dispersing pigment may be any form in which a part thereof is dissociated or all is dissociated.

  The content (% by mass) of the self-dispersing pigment in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, and 1.0% by mass or more and 8.0% by mass or less based on the total mass of the ink. More preferably, it is more preferably 3.0% by mass or more and 6.0% by mass or less. If the content of the self-dispersing pigment is less than 0.1% by mass, sufficient color developability may not be obtained. If the content of the self-dispersing pigment exceeds 15.0% by mass, ink ejection stability may not be sufficiently obtained. The average particle size of the self-dispersing pigment is preferably 50 nm or more and 200 nm or less.

Examples of the phosphonic acid group include a PO ₃ HM group and a PO ₃ M ₂ group. M in these formulas represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. Among them, phosphonic acid group, and more preferably has a structure _{-CQ (PO 3 M 2) 2} . Q in this formula represents R ′, OR ′, SR ′, or NR ′ ₂ , and R ′ independently represents a hydrogen atom, an alkyl group, an acyl group, an aralkyl group, or an aryl group. Specifically, examples of the alkyl group include a methyl group and an ethyl group; examples of the acyl group include an acetyl group and a benzoyl group; examples of the aralkyl group include a benzyl group; examples of the aryl group include a phenyl group and a naphthyl group. . Among these, —CH (PO ₃ M ₂ ) _{2 in} which R ′ is a hydrogen atom is preferable.

As other atomic groups (—R—), amide group, amino group, ketone group, ester group, ether group, alkylene group having 1 to 12 carbon atoms, substituted or unsubstituted phenylene group, substituted or unsubstituted And an unsubstituted naphthylene group. Among these, it is preferable that another atomic group (—R—) contains —C ₆ H ₄ —CONH— (benzamide structure) or —C ₆ H ₄ —SO ₂ NH— (benzenesulfonamide structure). Moreover, the some phosphonic acid group may couple | bond with the carbon atom of another atomic group (-R-). Specific examples include self-dispersing pigments in which an atomic group to which a bisphosphonic acid group or a triphosphonic acid group is bonded is bonded to the surface. Among these, self-dispersed pigments to which an atomic group to which a bisphosphonic acid group is bonded are bonded are preferable from the viewpoint of achieving both image fastness and long-term storage stability of the pigment.

  A method for verifying whether or not the pigment contained in the ink is a self-dispersing pigment is as follows. Specifically, the ink is acidified and then centrifuged to collect a precipitate. In the case of a pigment dispersion, the precipitate is collected after acid precipitation of the pigment dispersion. The collected sediment is poured into a petri dish, stirred and redispersed. After 1 day, if no precipitate is formed in the petri dish and the pigment is dispersed, it is judged as a self-dispersion type pigment. Further, when the pigment contained in the ink is a self-dispersing pigment, it can be verified by an ICP emission analyzer whether or not it has a phosphonic acid group. Specifically, using an ICP emission analyzer, if a phosphorus element is confirmed, it is determined that the phosphor has a phosphonic acid group.

(Resin dispersion type pigment)
As a resin dispersion type pigment using a resin as a dispersant, a resin dispersed pigment using a resin dispersant, a microcapsule pigment in which the pigment particle surface is coated with a resin, and an organic group containing a resin on the pigment particle surface are chemically used. For example, resin-bonded pigments bonded to each other can be used. It is also possible to use pigments with different dispersion methods in combination.

  The resin used as the dispersant in the resin dispersion type pigment preferably has a hydrophilic part and a hydrophobic part. Specifically, a resin obtained by copolymerizing a monomer having a carboxy group such as acrylic acid and methacrylic acid and a monomer having an aromatic group such as styrene; polymerization using a diol having an anionic group such as dimethylolpropionic acid And urethane resin.

  As the resin used as the dispersant, any of those conventionally used in inks can be used. The resin used as the dispersant is preferably water-soluble. That is, when a resin dispersion type pigment is used as the pigment to be included in the ink, the pigment is preferably a pigment dispersed with a water-soluble resin. In the present specification, the fact that the resin is water-soluble means that the resin does not have a particle diameter when neutralized with an alkali equivalent to the acid value. That is, in this specification, the water-soluble resin is different from resin particles (having a particle size) described later.

  Specific examples of the monomer used when preparing the resin used as the dispersant include the following, and resins synthesized using at least two of these monomers can be given. At this time, at least one is preferably a hydrophilic monomer. Usable monomers include styrene, vinyl naphthalene, aliphatic alcohol ester of α, β-ethylenically unsaturated carboxylic acid, acrylic acid, methacrylic acid, maleic acid, itaconic acid, fumaric acid, vinyl acetate, vinyl pyrrolidone, acrylamide Or derivatives thereof. Among these, acrylic acid or methacrylic acid is preferably used as the hydrophilic monomer. In particular, a copolymer having a structural unit derived from at least acrylic acid and (meth) acrylic acid is more preferable. Examples of the resin include a block copolymer, a random copolymer, a graft copolymer, or a salt thereof. Furthermore, natural resins such as rosin, shellac and starch may be used.

  The resin used as the dispersant preferably has a polystyrene-equivalent weight average molecular weight in the range of 1,000 to 30,000, which is obtained by GPC (gel permeation chromatography), and is in the range of 3,000 to 15,000. Are more preferred. The acid value of the resin is preferably from 50 mgKOH / g to 350 mgKOH / g, more preferably from 80 mgKOH / g to 250 mgKOH / g. By being within this range, the dispersion stability of the pigment by the resin is improved, and preferable ejection stability of the ink can be obtained. The acid value of the resin is determined by potentiometric titration.

  The content (% by mass) of the resin used as the dispersant is preferably 0.1% by mass or more and 5.0% by mass or less, more preferably 0.2% by mass or more and 4.% by mass or more based on the total mass of the ink. It is 0 mass% or less, More preferably, it is 0.5 mass% or more and 3.0 mass% or less. The content of the resin-dispersed pigment in the ink (the total content of the pigment and the resin dispersant) is preferably 0.1% by mass or more and 15.0% by mass or less based on the total mass of the ink. More preferably, it is 0.0 mass% or more and 8.0 mass% or less. If the content of the resin dispersed pigment in the ink is less than 0.1% by mass, the effect of improving the optical density of the image may not be sufficiently obtained. If the content of the resin-dispersed pigment in the ink exceeds 15.0% by mass, sufficient adhesion resistance may not be obtained.

  A method for determining whether or not the pigment contained in the ink is a pigment dispersed by a resin is as follows. The liquid prepared by concentrating or diluting the ink so that the total solid content is about 10% by mass is centrifuged at 12,000 rpm for 1 hour. As a result, a water-soluble organic solvent, a resin that does not contribute to dispersion, and the like are included in the liquid layer, so that the precipitated component including the pigment is recovered. At this time, if the sediment component containing the pigment contains a resin, it can be determined that the pigment is dispersed by the resin. The resin contained as a main component in the precipitation component containing the pigment is a resin that contributes to the dispersion of the pigment (resin dispersant), and the resin contained as the main component in the liquid layer is used for the dispersion of the pigment. It is a resin that does not contribute.

[Resin particles]
In the present specification, “resin particles” means a resin that is dispersed in a solvent and has a particle size. The 50% cumulative volume average particle diameter (D ₅₀ ) of the resin particles is preferably 1 nm or more and 100 nm or less, and more preferably 5 nm or more and 50 nm or less. D ₅₀ of the resin particles is obtained by diluting the resin particle dispersion 50 times (volume basis) with pure water and using UPA-EX150 (manufactured by Nikkiso), SetZero: 30 s, number of measurements: 3 times, measurement time: The measurement may be performed under the measurement conditions of 180 seconds and refractive index: 1.5.

  Any known resin particles can be used, but it is preferable to use at least one selected from the group consisting of polyurethane resin particles and acrylic resin particles. Hereinafter, each of the polyurethane resin particles and the acrylic resin particles will be described.

<1> Polyurethane resin particles (Physical properties of polyurethane resin particles)
The polystyrene equivalent weight average molecular weight (Mw) obtained by GPC of the polyurethane resin particles is preferably 5,000 or more and 150,000 or less, and more preferably 8,000 or more and 100,000 or less. When the Mw is less than 5,000, the strength of the polyurethane resin particles becomes low, and the effect of improving the scratch resistance of the image may not be sufficiently obtained. If Mw is greater than 150,000, ink storage stability and ejection stability may not be sufficiently obtained. In this specification, the measurement of Mw of polyurethane resin particles is performed using an apparatus: Alliance GPC 2695 (manufactured by Waters), a column: Shodex KF-806M quadruple column (manufactured by Showa Denko), and a detector: RI (refractive index). Can be done. For the calculation of Mw, PS-1 and PS-2 (manufactured by Polymer Laboratories) can be used as polystyrene standard samples.

  The acid value of the polyurethane resin particles is preferably 100 mgKOH / g or less, and more preferably 5 mgKOH / g or more and 30 mgKOH / g or less. The acid value of the polyurethane resin particles can be measured by a titration method. For example, the acid value may be measured by dissolving polyurethane resin particles in THF and performing potentiometric titration with a potassium hydroxide ethanol titrant using an automatic potentiometric titrator AT510 (manufactured by Kyoto Electronics Industry).

  The glass transition temperature (Tg) of the polyurethane resin particles is preferably −80 ° C. or higher, and more preferably −50 ° C. or higher. The Tg of the polyurethane resin particles is preferably 120 ° C. or lower, and more preferably 100 ° C. or lower.

(Polyurethane resin particle content)
The content of the polyurethane resin particles is preferably 0.1% by mass or more and 10.0% by mass or less based on the total mass of the ink. If the content of the polyurethane resin particles in the ink is less than 0.1% by mass, the effect of improving the scratch resistance of the image may not be sufficiently obtained. On the other hand, when the content of the polyurethane resin particles in the ink exceeds 10.0% by mass, the ink ejection stability may not be sufficiently obtained.

(Production example of polyurethane resin particles)
Any conventionally used method can be used as a method for producing polyurethane resin particles. For example, polyurethane resin particles can be produced by the method described below. A polyol having no acid group is sufficiently stirred and dissolved in an organic solvent such as methyl ethyl ketone, and then a polyisocyanate and a diol having an acid group are added and reacted to obtain a urethane prepolymer solution. Subsequently, after neutralizing the obtained urethane prepolymer solution, ion-exchange water is added and it emulsifies by stirring at high speed with a homomixer. After emulsification, a chain extender is added to carry out a chain extension reaction.

The material which comprises a polyurethane resin particle is demonstrated below.
(1) Polyisocyanate The polyurethane resin particles preferably have a structural unit derived from polyisocyanate. “Polyisocyanate” means a compound having two or more isocyanate groups. Examples of polyisocyanates include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates, and araliphatic polyisocyanates. The proportion of structural units derived from polyisocyanate in the polyurethane resin particles is preferably 10.0% by mass or more and 80.0% by mass or less.

  Examples of the aliphatic polyisocyanate include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, and 2-methylpentane. -1,5-diisocyanate, 3-methylpentane-1,5-diisocyanate and the like.

  Examples of the alicyclic polyisocyanate include isophorone diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane 4,4′-diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, and 1,3-bis (isocyanate methyl). And cyclohexane.

  Examples of the aromatic polyisocyanate include tolylene diisocyanate, 2,2′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate, 4,4′-dibenzyldiisocyanate, 1,5- Examples thereof include naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, and 1,4-phenylene diisocyanate.

  Examples of the araliphatic polyisocyanate include dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α, α, α, α-tetramethylxylylene diisocyanate.

  As the polyurethane resin particles, one kind or two or more kinds of polyisocyanates can be used as necessary. Among the polyisocyanates, it is preferable to use at least one selected from the group consisting of isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane 4,4'-diisocyanate.

(2) Polyol having no acid group The polyurethane resin particles preferably have a structural unit derived from a polyol having no acid group. The proportion of the structural units derived from the polyol having no acid group in the polyurethane resin particles is preferably 0.1% by mass or more and 80.0% by mass or less.

  Examples of the polyol having no acid group include polyester polyol, polyether polyol, and polycarbonate diol. The polyol having no acid group preferably has 13 to 250 carbon atoms. Moreover, it is preferable that the polystyrene conversion number average molecular weight obtained by GPC of the polyol which does not have an acid group is 600 or more and 4,000 or less.

  Examples of the polyester polyol include esters of an acid component and a polyalkylene glycol, a dihydric alcohol, or a trihydric or higher polyhydric alcohol. Examples of the acid component constituting the polyester polyol include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, and aliphatic dicarboxylic acids. Examples of aromatic dicarboxylic acids include isophthalic acid, terephthalic acid, orthophthalic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, biphenyldicarboxylic acid, and tetrahydrophthalic acid. It is done. Examples of alicyclic dicarboxylic acids include hydrogenated aromatic dicarboxylic acids. Aliphatic dicarboxylic acids include malonic acid, succinic acid, tartaric acid, oxalic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, alkyl succinic acid, linolenic acid, maleic acid, fumaric acid, mesacone Examples include acids, citraconic acid, itaconic acid and the like. In addition, a reactive derivative such as an acid anhydride, an alkyl ester, or an acid halide of these acid components can be used as an acid component constituting the polyester polyol. The acid component which comprises said polyester polyol can use 1 type (s) or 2 or more types as needed. Examples of the polyalkylene glycol include polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, and ethylene glycol-propylene glycol copolymer. Examples of the dihydric alcohol include hexamethylene glycol, tetramethylene glycol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 4,4′-dihydroxyphenylpropane, 4 , 4'-dihydroxyphenylmethane and the like. Examples of the trihydric or higher polyhydric alcohol include glycerin, trimethylolpropane, 1,2,5-hexanetriol, 1,2,6-hexanetriol, pentaerythritol and the like. These polyester polyols can use 1 type (s) or 2 or more types as needed.

  Examples of the polyether polyol include polyalkylene glycols and addition polymerization products of alkylene oxide and a dihydric alcohol or a trihydric or higher polyhydric alcohol. Examples of the polyalkylene glycol include polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, and ethylene glycol-propylene glycol copolymer. Examples of the dihydric alcohol include hexamethylene glycol, tetramethylene glycol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 4,4′-dihydroxyphenylpropane, 4 , 4'-dihydroxyphenylmethane and the like. Examples of the trihydric or higher polyhydric alcohol include glycerin, trimethylolpropane, 1,2,5-hexanetriol, 1,2,6-hexanetriol, and pentaerythritol. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, α-olefin oxide and the like. These polyether polyols can use 1 type (s) or 2 or more types as needed.

  As the polycarbonate diol, a polycarbonate diol produced by a conventionally known method can be used. For example, polycarbonate diol obtained by making carbonate components or phosgene, such as alkylene carbonate, diaryl carbonate, and dialkyl carbonate, react with an aliphatic diol component is mentioned. These polycarbonate diols can be used alone or in combination of two or more as required.

  Among the polyols having no acid group, polyether polyol is preferably used. By using the polyether polyol, the flexibility of the resin film is moderately exhibited, so that the image scratch resistance is easily improved. Furthermore, since the polyether polyol has relatively high hydrophilicity, it is excellent in ink ejection stability. Among the polyether polyols, it is more preferable to use polypropylene glycol.

(3) Diol having an acid group The polyurethane resin particles preferably have a structural unit derived from a diol having an acid group. The diol having an acid group means a diol having an acid group such as a carboxy group, a sulfonic acid group, or a phosphoric acid group. The diol having an acid group may be present in the form of an alkali metal salt such as Li, Na or K, or an organic amine salt such as ammonia or dimethylamine. As the diol having an acid group, dimethylolpropionic acid or dimethylolbutanoic acid is preferably used. These can use 1 type or 2 types as needed. The proportion of the structural unit derived from the diol having an acid group in the polyurethane resin particles is preferably 5.0% by mass or more and 40.0% by mass or less.

(4) Chain extender When manufacturing polyurethane resin particles, a chain extender may be used. The chain extender is a compound that reacts with a residual isocyanate group that has not formed a urethane bond among the structural units derived from polyisocyanate in the urethane prepolymer. Examples of chain extenders include, for example, trimethylol melamine and derivatives thereof, dimethylol urea and derivatives thereof, dimethylol ethylamine, diethanolmethylamine, dipropanolethylamine, dibutanolmethylamine, ethylenediamine, propylenediamine, diethylenetriamine, hexylenediamine, Examples include triethylenetetramine, tetraethylenepentamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogenated diphenylmethanediamine, polyhydric amine compounds such as hydrazine, polyamide polyamine, and polyethylene polyimine. Further, ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, Ethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, 3-methyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexanediol 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, glycerin, trimethylolpropane, pentaerythritol and the like. These chain extenders can use 1 type (s) or 2 or more types as needed.

<2> Acrylic resin particle In this specification, "acrylic resin particle" means the acrylic resin which disperse | distributes in a solvent in the state which has a particle size. If the water-soluble acrylic resin does not have a particle size, it adsorbs to the recording medium and has a surface-active action, so that the penetration of the pigment in the depth direction of the recording medium is promoted. It is considered that a level of color developability cannot be obtained.

(Physical properties of acrylic resin particles)
The polystyrene-reduced weight average molecular weight (Mw) obtained by GPC of the acrylic resin particles is preferably greater than 100,000 and not greater than 3,000,000, and preferably not less than 300,000 and not greater than 1,000,000. More preferred. When the Mw is 100,000 or less, the strength of the acrylic resin particles becomes low, and the image scratch resistance may not be sufficiently obtained. If Mw is greater than 3,000,000, ink storage stability and ejection stability may not be sufficiently obtained. In this specification, the measurement of Mw of acrylic resin particles is performed using an apparatus: Alliance GPC 2695 (manufactured by Waters), a column: Shodex KF-806M quadruple column (manufactured by Showa Denko), and a detector: RI (refractive index). Can be done. For the calculation of Mw, PS-1 and PS-2 (manufactured by Polymer Laboratories) can be used as polystyrene standard samples.

  The acid value of the acrylic resin particles is preferably 150 mgKOH / g or less, and more preferably 25 mgKOH / g or more and 140 mgKOH / g or less. The acid value of the acrylic resin particles can be measured by a titration method. For example, the acid value may be measured by dissolving acrylic resin particles in THF and performing potentiometric titration with a potassium hydroxide ethanol titrant using an automatic potentiometric titrator AT510 (manufactured by Kyoto Electronics Industry).

  The glass transition temperature (Tg) of the acrylic resin particles is preferably −20 ° C. or higher, more preferably −10 ° C. or higher, and further preferably 25 ° C. or higher. The Tg of the acrylic resin particles is preferably 120 ° C. or less, and more preferably 100 ° C. or less.

(Acrylic resin particle content)
The content of the acrylic resin particles is preferably 0.1% by mass or more and 10.0% by mass or less based on the total mass of the ink. If the content of the acrylic resin particles in the ink is less than 0.1% by mass, the effect of improving the scratch resistance of the image may not be sufficiently obtained. On the other hand, if the content of the acrylic resin particles in the ink exceeds 10.0% by mass, ink ejection stability may not be sufficiently obtained.

(Monomer composing acrylic resin particles)
Examples of the monomer constituting the acrylic resin particles include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, lauryl ( Examples include (meth) acrylic acid alkyl esters such as (meth) acrylate and stearyl (meth) acrylate; (meth) acrylic acid such as acrylic acid and methacrylic acid. A homopolymer of these monomers may be used, a copolymer of two or more of these monomers, or a copolymer with other monomers may be used. Examples of monomers to be copolymerized with the above monomers include vinyl esters, olefins, styrenes, crotons, itacones, maleic acids, fumaric acids, acrylamides, allyl compounds, vinyl ethers, vinyl ketones, and glycidyl esters. , And unsaturated nitriles.

(Production example of acrylic resin particles)
Any conventionally used method can be used as the method for producing acrylic resin particles. For example, acrylic resin particles can be produced by the method described below. A predetermined amount of monomer and 100 g of distilled water as a solvent are weighed into a 300 mL four-necked flask. Next, a stirring seal, a stirring rod, a reflux condenser, a septum rubber, and a nitrogen introduction tube are attached, and nitrogen substitution is performed for 1 hour while stirring at 300 rpm in a constant temperature bath at 70 ° C. Furthermore, an initiator dissolved in 100 g of distilled water is injected into the flask with a syringe to initiate polymerization. The polymerization state is monitored by GPC and NMR to obtain a desired polymerization reaction product. The acrylic resin particles are purified in the state of an aqueous dispersion by repeating the step of centrifuging the generated acrylic resin and redispersing it in distilled water. The purified aqueous dispersion of acrylic resin particles may be concentrated by an evaporator or ultrafiltration, if necessary.

  As an initiator, what is used by normal radical polymerization etc. can be used. Specific examples of the initiator include potassium persulfate and 2,2'-azobis (2-amidinopropane) dihydrochloride. In the polymerization, an emulsifier, a chain transfer agent, a neutralizing agent and the like can be used in addition to the initiator. As the neutralizing agent, ammonia and hydroxides of inorganic alkalis such as sodium hydroxide and potassium hydroxide are preferable. As the emulsifier, for example, an anionic surfactant such as sodium lauryl sulfate, a nonionic surfactant, and an amphoteric surfactant can be used. Examples of the chain transfer agent include xanthogens such as dimethylxanthogen disulfide and diisobutylxanthogen disulfide, and t-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan, dipentene, indene, 1,4-cyclohexadiene, dihydrofuran, And xanthene.

[Aqueous medium]
The ink used in the ink jet recording method of one embodiment of the present invention is a water-based ink containing at least water. As water, it is preferable to use deionized water (ion exchange water). The content of water in the ink is preferably 50% by mass or more and 90% by mass or less based on the total mass of the ink.

  The ink used in the ink jet recording method of one embodiment of the present invention preferably contains a water-soluble organic solvent as an aqueous medium in addition to water. In the present specification, the “water-soluble organic solvent” means “an organic solvent having a solubility in water at 20 ° C. of 500 g / L or more”. As the water-soluble organic solvent, any known water-soluble organic solvent that can be used for ink can be used.

  Examples of the water-soluble organic solvent include alcohols, glycols, alkylene glycols, polyethylene glycols, nitrogen-containing compounds, and sulfur-containing compounds. These water-soluble organic solvents can be used alone or in combination of two or more. From the viewpoint of adjusting the viscosity of the ink, the water-soluble organic solvent is preferably glycerin, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol having a weight average molecular weight of 10,000 or less, 1,3-propanediol, and diglycerol. Furthermore, polyethylene glycol and glycerin are more preferable. The number average molecular weight of polyethylene glycol is preferably 400 or more and 2,000 or less. The content of the water-soluble organic solvent in the ink is preferably 50% by mass or less, more preferably 5% by mass or more and 45% by mass or less, based on the total mass of the ink.

[Surfactant]
The ink used in the ink jet recording method of one embodiment of the present invention preferably contains a surfactant. As the surfactant, any known surfactant that can be used for ink can be used, and one kind of surfactant can be used alone or two or more kinds can be used in combination. Among the surfactants, nonionic surfactants are preferable. Among the nonionic surfactants, ethylene oxide adducts such as polyoxyethylene alkyl ether and acetylene glycol are more preferable, and surfactants represented by the following general formula (1) are more preferable. Examples of the commercially available products include acetylenol series (manufactured by Kawaken Fine Chemical Co., Ltd.), surfinol series (manufactured by Air Products), and dynol 604, 607, 800, 810 (manufactured by Air Products).

In general formula (1), R ^{1 to} R ⁴ each independently represents an alkyl group having 1 to 3 carbon atoms. x and y each independently represents a number of 1 to 5. m + n represents a number from 0 to 10. As the surfactant represented by the general formula (1), the sum of m and n in the general formula (1) (m + n) is preferably 8 or less, and more preferably 5 or less. Further, the surfactant is more preferably one in which both x and y in the general formula (1) are 2.

  The content of the surfactant represented by the general formula (1) is preferably 0.5% by mass or more and 3.0% by mass or less, based on the total mass of the ink, and 0.7% by mass or more and 1. More preferably, it is 5 mass% or less. When the content of this surfactant is less than 0.5% by mass, color development may not be sufficiently obtained from the surface of dot formation. On the other hand, when the content of the surfactant exceeds 3.0% by mass, the effect of improving the color developability of the image may not be sufficiently obtained. The ink may contain a surfactant different from the surfactant represented by the general formula (1).

[Additive]
The ink used in the ink jet recording method of one embodiment of the present invention includes a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an anti-reduction agent, an evaporation accelerator, and a chelation as necessary. You may contain various additives, such as an agent. For example, as the pH adjuster, it is preferable to use an amine compound having a buffering ability, and it is particularly preferable to use N-butyldiethanolamine.

<Ink cartridge>
In an ink jet recording method according to an embodiment of the present invention, an ink cartridge including an ink storage unit that stores the ink described above can be used. As the ink cartridge, those conventionally used in the ink jet recording method can be used. For example, as an ink cartridge structure, the ink storage portion includes an ink storage chamber that stores liquid ink, and a negative pressure generation member storage chamber that stores a negative pressure generation member that holds the ink therein by negative pressure. The structure which has can be mentioned. Further, the ink cartridge may be provided with an ink storage portion that is configured not to include an ink storage chamber for storing liquid ink but to hold the entire amount of ink by a negative pressure generating member. Furthermore, the ink cartridge may include an ink storage unit and a recording head.

<Inkjet recording method>
An ink jet recording method according to an embodiment of the present invention is a method of recording an image on a recording medium by discharging a plurality of color inks from a plurality of ink jet recording heads. The ink jet recording method according to an embodiment of the present invention may include an ink application process in which the ink described above is used as the color ink and the ink is applied to the recording medium. Furthermore, this method preferably includes a transporting process for transporting the recording medium and a heating process for heating the recording medium to which ink has been applied.

  In the ink jet recording apparatus 100 shown in FIG. 1 described above, a mode is shown in which recording is performed using a recording medium wound in a roll shape, and then wound into a roll shape again. The ink jet recording apparatus 100 includes a recording medium supply unit 10, an ink application unit 20, and a recording medium collection unit 11. The recording medium supply unit 10 is a unit for holding and supplying the recording medium P wound in a roll shape. The ink applying unit 20 is a unit for applying ink to the recording medium P. The recording medium recovery unit 11 is a unit for winding up the recording medium P on which an image is recorded. Further, the ink jet recording apparatus 100 can include a heating unit 400 that is a unit for heating the recording medium P. The recording medium P is transported by transport means including a pair of rollers and a belt along the transport path of the recording medium P, which is indicated by a solid line in the drawing, and is processed by each unit. In addition, the recording medium P wound up in a roll shape by the recording medium recovery unit 11 is supplied to another apparatus or the like, and the recording medium P is cut into a desired size or bound. Also good.

  In the inkjet recording method of one embodiment of the present invention, the speed of conveying the recording medium in the conveying step of conveying the recording medium is preferably 50 m / min or more, and more preferably 100 m / min or more. .

  In the ink jet recording method of one embodiment of the present invention, it is preferable that tension is applied to the recording medium during conveyance. That is, it is preferable that the ink jet recording apparatus has a tension applying unit that generates tension. As a specific method, in the transport mechanism between the recording medium supply unit 10 and the recording medium recovery unit 11 in FIG. 1, a tension applying unit that generates tension on the recording medium P and a tension adjustment that adjusts the tension of the recording medium. A part or the like may be provided. When tension is applied to the recording medium P, swelling of the fibers of the recording medium due to water in the ink is suppressed. When the fibers of the recording medium P swell, the gap between the fibers increases and the ink penetration rate increases. However, when the ink penetration rate increases, the ink tends to penetrate deeply in the direction perpendicular to the surface of the recording medium. In some cases, the optical density of the image cannot be obtained sufficiently. As described above, by applying tension to the recording medium P, the swelling of the fibers of the recording medium P due to the water in the ink is suppressed, so that it is possible to suppress a decrease in the optical density of the image due to an increase in the permeation speed of the ink. it can.

  The tension applied to the recording medium is preferably 20 N / m or more. By applying a tension of 20 N / m or more to the recording medium, the swelling of the fibers of the recording medium due to water in the ink is more efficiently suppressed. From this viewpoint, the tension applied to the recording medium is more preferably 30 N / m or more, and further preferably 40 N / m or more and 100 N / m or less.

(1) Ink application step As a method for applying ink to a recording medium, an ink jet method can be used. The ink jet method may be a thermal ink jet method or a piezo ink jet method. The thermal ink jet method is a method in which thermal energy is applied to ink and ink is discharged from the discharge port of the recording head. The piezo ink jet method is a method in which ink is ejected from an ejection port of a recording head using a piezo element. In the ink jet recording method of one embodiment of the present invention, the piezo ink jet method is preferable from the viewpoint of ink ejection stability.

  The recording head may be a serial type recording head or a full line type recording head. The serial type recording head is a recording head that records an image by scanning the recording head in a direction intersecting with the conveyance direction of the recording medium. The full-line type recording head is a recording head in which a plurality of nozzles are arranged in a range that covers the maximum width of the recording medium. The recording head is preferably a full line type ink jet recording head. In the full-line type ink jet recording head, it is preferable that nozzle rows are arranged in a direction perpendicular to the conveyance direction of the recording medium. In addition, a plurality of full-line type ink jet recording heads are provided for each type of ink (usually ink color), and the recording heads are arranged in parallel along the recording medium conveyance direction. It is preferable that

(2) Heating step In the heating step, it is preferable to heat the recording medium to which the ink is applied so that the surface temperature becomes 70 ° C. or higher. The “surface temperature of the recording medium to which ink has been applied” means the surface temperature of the recording medium at a position where the ink has been transported for 0.5 seconds, assuming that the time when the ink was applied to the recording medium is 0 second. For example, it is assumed that the conveyance speed of the recording medium is “V” m / min. In this case, the surface of the recording area X at a position where the ink recording area X on the recording medium has moved “(V × 0.5) / 60” m along the transport direction from the position where the ink is applied. What is necessary is just to measure temperature. In the case of a full-line type ink jet recording head, the “position to which ink is applied” means a position immediately below the recording head.

  In the heating step, it is more preferable to heat the recording medium to which the ink is applied so that the surface temperature is 80 ° C. or higher. Further, from the viewpoint of preventing the recording medium from being deformed by heat, the surface temperature of the recording medium to which the ink has been applied is preferably 140 ° C. or lower. Examples of the method for heating the recording medium include a method in which a heater is provided to heat the recording medium from the front surface side (the ink application side), a heating method from the back surface side, and a heating method from both sides. it can.

  The heating in the heating step may be continuously performed from before the ink is applied to after the ink is applied. Before the ink is applied to the recording medium, the surface temperature of the recording medium is preferably lower than 70 ° C., more preferably 60 ° C. or lower, even if heated, even if heated. More preferably, it is as follows.

  Further, in the heating step, when the recording medium is heated, for example, a pressure roller may be used to press the recording medium. By fixing the recording medium, the fixability of the image can be improved. When pressurizing the recording medium, it is not necessary to apply pressure throughout the entire heating process, and it may be applied only during a part of the heating process. Further, the recording medium may be pressurized in multiple stages, and may further include a pressing process after the heating process.

[recoding media]
As the recording medium, any conventionally used recording medium can be used. Among them, a recording medium having a water absorption coefficient Ka of 0.1 mL · m ⁻² · ms ^−1/2 or more is preferable, and is 0.2 mL · m ⁻² · ms ^−1/2 or more. A recording medium is more preferable, and a recording medium of 0.3 mL / m ⁻² · ms ^−1/2 or more is further preferable. Thus, it is preferable to use a recording medium with high ink absorbability.

As a method for deriving the water absorption coefficient Ka of the recording medium, the JAPAN TAPPI paper pulp test method No. 1 was used. The Bristow method described in 51 “Test method for liquid absorbency of paper and board” is used. Since the Bristow method is described in many commercial books, detailed description is omitted, but the absorption coefficient Ka (mL · m ⁻² · ms ⁻ ) is determined by the wetting time Tw and the roughness index Vr (mL / m ² ). ^1/2 ) is defined. FIG. 3 is a diagram showing an example of an absorption curve for explaining the water absorption coefficient Ka of the recording medium. The absorption curve shown in FIG. 3 is based on a permeation model in which permeation into the inside of the recording medium begins after a wetting time Tw after the liquid contacts the recording medium. The slope of the straight line after the wetting time Tw is the absorption coefficient Ka. This absorption coefficient Ka corresponds to the penetration speed of the liquid into the recording medium. As shown in FIG. 3, the wetting time Tw is an approximate straight line A by the least square method for calculating the absorption coefficient Ka, and a straight line of “V = Vr” represented by the liquid transition amount V and the roughness index Vr. An intersection AB with B is obtained, and the time until the intersection AB is calculated. The temperature of the liquid (water) that permeates the recording medium is 25 ° C. That is, the water absorption coefficient Ka in this specification is the water absorption coefficient Ka of 25 ° C.

  As the recording medium, for the purpose of improving the whiteness and opacity, it is preferable to use a recording medium provided with minerals such as kaolin and talc, and fillers such as calcium carbonate, titanium dioxide, and silica on the surface. . Of these, calcium carbonate is preferable because it has higher whiteness than kaolin and talc and is cheaper than titanium dioxide and silica. The recording medium contains calcium, and the content of calcium in the recording medium is preferably 1% by mass or more and 5% by mass or less based on the total mass of all elements other than hydrogen. The recording medium may be cut in advance to a desired size, or may be cut to a desired size after recording an image using a recording medium wound in a roll shape. . As described above, since it is easy to apply tension to the recording medium, it is preferable to use a recording medium wound in a roll shape.

[Treatment solution]
The ink jet recording method of one embodiment of the present invention may include a step of applying a treatment liquid containing a polyvalent metal salt. When using the treatment liquid, it is preferable to apply the treatment liquid to the recording medium before the color ink is applied to the recording medium. Examples of the polyvalent metal ion in the polyvalent metal salt include divalent metal ions such as Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ , Zn ²⁺ , Sr ²⁺ , and Ba ²⁺ , and Mention may be made of trivalent metal ions such as Al ³⁺ , Fe ³⁺ , Cr ³⁺ and Y ³⁺ . Counter ions that form salts with these polyvalent metal ions include, for example, Cl ⁻ , Br ⁻ , I ⁻ , ClO ⁻ , ClO ₂ ⁻ , ClO ₃ ⁻ , ClO ₄ ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , Inorganic anions such as SO ₄ ²⁻ , CO ₃ ²⁻ , PO ₄ ³⁻ , HPO ₄ ²⁻ , and H ₂ PO ₄ ⁻ ; HCO ₃ ⁻ , HCOO ⁻ , (COO ⁻ ) ₂ , COOH (COO ⁻ ), Mention may be made of organic anions such as CH ₃ COO ⁻ , C ₂ H ₄ (COO ⁻ ) ₂ , C ₆ H ₅ COO ⁻ , C ₆ H ₄ (COO ⁻ ) ₂ and CH ₃ SO ₄ ^— . The polyvalent metal salt may be used in the form of a hydrate.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the configurations of the following examples. In the following description, “parts” and “%” are based on mass unless otherwise specified.

<Preparation of ink>
As the ink components, each component (unit:%) shown in the upper part of Tables 1-1 to 1-3 is mixed, dispersed with sufficient stirring, and filtered with a glass filter AP20 (MILLIPORE), thereby allowing each ink. Was prepared. In addition, the content (%) of the pigment and the resin particle in the table below is the solid content (%) of the pigment and the resin particle in the ink, respectively. Also, the table shows the aggregation rate V _before solid content in the first liquid prepared using each ink, and the second liquid prepared in the above-mentioned second liquid prepared after storage at 60 ° C. for 2 weeks. The solid content aggregation rate V _after and the ratio thereof (aggregation rate ratio R) are shown. Further, the abbreviations in the table are as described below.

[Pigment]
In the ink, the following self-dispersing pigments were used as pigments in which phosphonic acid groups were bonded directly or via other atomic groups to the pigment particle surface.
COJ450C: CAB-O-JET450C (Cabot, cyan pigment dispersion)
COJ465M: CAB-O-JET465M (manufactured by Cabot, magenta pigment dispersion)
COJ470Y: CAB-O-JET470Y (manufactured by Cabot, yellow pigment dispersion)
The phosphonic acid groups possessed by the COJ450C, COJ465M, and COJ470Y are all bisphosphonic acid groups.

[Resin particles]
(Acrylic resin particles A)
Polymerization was performed using “ethyl acrylate 90 g, ethyl methacrylate 5 g, methyl methacrylate 10 g” as monomers in accordance with the above-mentioned “Production Example of Acrylic Resin Particles”. Thereafter, purification and concentration were performed to obtain an aqueous dispersion of acrylic resin particles A having a solid concentration of 10%.

(Acrylic resin particles B)
Polymerization was carried out using “butyl acrylate 30 g, butyl methacrylate 15 g, acrylate-2-ethylhexyl 40 g, styrene 45 g” in accordance with the above-mentioned “Examples of production of acrylic resin particles”. Then, the aqueous dispersion of the acrylic resin particle B with a solid content concentration of 10% was obtained by performing purification and concentration.

(Acrylic resin particle C)
Polymerization was carried out using “butyl acrylate 30 g, butyl methacrylate 15 g, acrylate-2-ethylhexyl 40 g, α-methylstyrene 50 g” in accordance with the above-mentioned “Example of production of acrylic resin particles”. Thereafter, purification and concentration were performed to obtain an aqueous dispersion of acrylic resin particles C having a solid content concentration of 10%.

(Acrylic resin particles D and E)
As an aqueous dispersion of acrylic resin particles D, a trade name “JONCRYL711” manufactured by BASF was used. Further, as an aqueous dispersion of acrylic resin particles E, a trade name “BT-9” manufactured by DSM was used.

(Polyurethane resin particles A)
In accordance with the above-mentioned production example of polyurethane resin particles, polymerization was performed using 10 g of isophorone diisocyanate, 20 g of polytetramethylene ether glycol, 5 g of dimethylolpropionic acid, and 8 g of triethylamine for neutralization. Thereafter, purification and concentration were performed to obtain an aqueous dispersion of urethane resin particles A having a solid content concentration of 35%.

(Polyurethane resin particles B and C)
As an aqueous dispersion of polyurethane resin particles B, a trade name “W5661” manufactured by Mitsui Chemicals was used. Further, as an aqueous dispersion of the polyurethane resin particles C, a trade name “R4000” manufactured by DSM was used.

(Water-soluble organic solvent)
As the water-soluble organic solvent, glycerin (referred to as “Gly” in the table) and polyethylene glycol having a number average molecular weight of 1,000 (referred to as “PEG1000” in the table) were used.

(Surfactant)
As the surfactant, trade name “Acetyleneol E100” (referred to as “AE100” in the table) manufactured by Kawaken Fine Chemical Co., Ltd. and trade name “Dynol 800” (referred to as “D800” in the table) manufactured by Air Products. Was used. In addition, acetylenol E100 is ethylene oxide of acetylene glycol represented by the above general formula (1) (wherein R ^{1 to} R ⁴ are all methyl groups, x = 1, y = 1, m + n = 10). It is an adjunct. Dinol 800 is a surfactant represented by the above general formula (1) (wherein x = 2, y = 2, m + n = 4 to 6).

[Ink set]
Each ink obtained above was used by being filled in an ink cartridge. The number of line heads used in Examples and Comparative Examples (see FIGS. 1 and 2), and combinations of inks or treatment liquids supplied to the respective line heads are shown in the left column of Tables 2-1 to 2-5. In Examples 9 and 41 to 45, in addition to the color ink, the components shown below were mixed and the prepared treatment liquid was used. In Tables 2-1 to 2-5, the aggregation rate ratio R (= (V _after / V _before ) × 100) of each ink shown in Tables 1-1 to 1-3 is shown again. Further, 20a to 20d in Tables 2-1 to 2-5 correspond to the reference numerals in FIGS. 1 and 2, and the inks supplied to the line heads in the order of the line heads 20a, 20b, 20c, and 20d or Indicates that the processing liquid has been discharged.

[Preparation of treatment solution]
In Examples 9 and 41 to 45, a treatment liquid prepared with the following formulation was used.
Glycerin: 20 parts Calcium chloride tetrahydrate: 8 parts Acetylenol E100 (manufactured by Kawaken Fine Chemicals): 1 part Pure water: 71 parts

[Preparation of image samples]
For image recording, an inkjet recording apparatus having the configuration shown in FIG. 1 and equipped with a piezo inkjet line head (trade name “KJ4”, manufactured by Kyocera, nozzle density 600 dpi) was used. Further, the trade name “DL9084” (manufactured by Mitsubishi Paper Industries, basis weight 91 g / m ² ) was used as the recording medium. A solid image of 3 cm × 3 cm (recording duty is 100%) is recorded on this recording medium using the ink jet recording apparatus and the ink or processing liquid shown in Tables 2-1 to 2-5, and an image sample is manufactured. did. Three solid images were used: Red (Magenta 100% duty-Yellow 100% duty), Blue (Cyan 100% duty-Magenta 100% duty), and Green (Cyan 100% duty-Yellow 100% duty). In all of the recording conditions, the temperature was 25 ° C., the relative humidity was 55%, the ink discharge frequency was 39 kHz, the recording medium conveyance speed was 100 m / s, and the ink discharge volume during recording was about 13 pL. In the ink jet recording apparatus, the condition for applying one dot of 13 ng ink droplets to a unit area of 1/600 inch × 1/600 inch with a resolution of 600 dpi × 600 dpi is defined as a recording duty of 100%. When using the treatment liquid, it was recorded at 100% duty.

Immediately after the preparation of each ink, each ink was put in a sealed container, stored at 60 ° C. for 2 weeks, and then returned to room temperature (25 ° C.). did. Using the ink before and after storage, the Lab value of each obtained image sample was measured using a spectrocolorimeter (trade name “i1 public pro2”, manufactured by X-rite). The lightness in the image recorded with the ink before storage is L ₁ , the chromaticity is a ₁ and b ₁ , the lightness in the image recorded with the ink after storage is L ₂ , and the chromaticity is a ₂ and b ₂ . The value of ΔE was determined based on the formula (2).

Then, according to the following evaluation criteria, the color developability (change in color tone) of the ink before and after storage was evaluated. In the following evaluation, A and B were set as preferable levels, and C was set as an unacceptable level. The evaluation results are shown in the right column of Tables 2-1 to 2-5.
A: The color difference ΔE was less than 2.
B: The color difference ΔE was 2 or more and 3 or less.
C: Color difference ΔE was greater than 3.

Claims (7)

An inkjet recording method for recording an image on a recording medium by discharging a plurality of color inks from a plurality of inkjet recording heads,
The plurality of recording heads are arranged along a conveyance direction of the recording medium,
The color ink contains at least a pigment, resin particles, and water,
Among the plurality of color inks, the first to Nth in order from the color ink applied to the recording medium first,
V _before the aggregation rate of solids in the first liquid prepared by diluting each color ink 500 times with water and adding calcium chloride at a concentration of 2.0 mmol / L,
Each color ink was stored at 60 ° C. for 2 weeks, diluted 500 times with water, and calcium chloride was added at a concentration of 2.0 mmol / L. V _after ,
When the aggregation rate ratio before and after the storage of each color ink is R = (V _after / V _before ) × 100,
And aggregation rate ratio R _K of the color inks K-th (1 ≦ K <N), the relationship between the coagulation speed ratio R _{K + 1} of the color ink (K + 1) -th (2 ≦ K + 1 ≦ N ), R K <R K An inkjet recording method characterized by satisfying ₊₁ .   2. The ink jet recording method according to claim 1, wherein the color ink contains, as the pigment, a self-dispersing pigment in which a phosphonic acid group is bonded to the particle surface of the pigment directly or through another atomic group.   The inkjet recording method according to claim 2, wherein the phosphonic acid group is a bisphosphonic acid group.   The inkjet recording method according to claim 1, wherein the color ink contains polyethylene glycol and glycerin. The inkjet recording method according to claim 1, wherein the color ink contains a surfactant represented by the following general formula (1).

(In the general formula (1), R ^{1 to} R ⁴ each independently represents an alkyl group having 1 to 3 carbon atoms, x and y each independently represents a number 1 to 5, and m + n is Represents a number from 0 to 10.)   The inkjet recording method according to claim 5, wherein the surfactant includes a surfactant in which both x and y in the general formula (1) are 2. 7.   The ink jet recording method according to claim 1, further comprising a step of applying a treatment liquid containing a polyvalent metal salt to the recording medium.

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