JP2017047627A - Image recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image recording method with which an image having glossy feeling close to that of a recorded matter obtained by electrophotography can be recorded on a plain paper with an inkjet method.SOLUTION: An image recording method has: a step of applying a reaction liquid aggregating a pigment and resin particles in an ink to a plain paper; and a step of discharging an aqueous ink containing the pigment and the resin particles and having surface tension of 35 mN/m or less from an inkjet recording head, and recording an image by applying the aqueous ink to the plain paper to which the reaction liquid has been applied so as to be in contact with the reaction liquid. In the method, the content (mass%) of the resin particles in the ink is 2.0 times or more in terms of the mass ratio to the content (mass%) of the pigment in the ink, and in relation to aggregating property of the pigment and the resin particles in the case of contact of the reaction liquid with the ink, the aggregating property of the pigment is higher than that of the resin particles.SELECTED DRAWING: None

Description

  The present invention relates to an image recording method.

  Conventionally, it has been mainstream to use an electrophotographic method for recording business texts. However, in recent years, even when an ink jet recording apparatus is used, it has become possible to improve image fastness such as scratch resistance. Furthermore, the ink jet recording apparatus is advantageous from the viewpoint of energy, and tends to shift from an electrophotographic apparatus to an ink jet apparatus.

  As a method of recording an image on a recording medium such as plain paper, a method of recording an image using ink and a reaction liquid is known. For example, Patent Document 1 proposes an ink having specific characteristics in order to provide an ink having excellent ejection characteristics and capable of recording an image excellent in scratch resistance with respect to a water-soluble ink used together with a reaction liquid. ing. Further, Patent Document 2 discloses a technique for increasing the glossiness of an image recorded by an ink jet recording method, and causing a smoothness of the image by causing a difference in sedimentation speed between carbon black and resin fine particles contained in the ink. Has been proposed.

JP 2006-160850 A JP 2012-072361 A

  Conventionally, when a recording medium such as glossy paper is mainly used, efforts have been made to improve the glossiness of an image by using a pigment ink and a clear ink in combination. However, the glossiness of the image has not been emphasized on plain paper, which is a recording medium to which the reaction liquid is applied. That is, even with an image recording method in which ink is ejected from an inkjet recording head and applied to plain paper, it is not possible to record an image having a glossy feeling as a recorded matter obtained by an electrophotographic method.

  Accordingly, an object of the present invention is to provide an image recording method capable of recording an image having glossiness close to a recorded matter obtained by an electrophotographic method on plain paper by an ink jet method.

  The above object is achieved by the present invention described below. That is, according to the present invention, a step of applying a reaction liquid for aggregating pigments and resin particles in ink to plain paper, and an aqueous ink containing pigments and resin particles and having a surface tension of 35 mN / m or less. And a step of recording the image by ejecting it from an inkjet recording head and applying it to the plain paper to which the reaction liquid is applied so as to come into contact with the reaction liquid. When the content (mass%) of the resin particles in the ink is 2.0 times or more by mass ratio with respect to the content (mass%) of the pigment in the ink, the reaction liquid and the ink are in contact with each other The image recording method is characterized in that the cohesiveness of the pigment and the resin particles is higher in the cohesiveness of the pigment than in the cohesiveness of the resin particles.

  ADVANTAGE OF THE INVENTION According to this invention, the image recording method which can record the image with the glossiness close | similar to the recorded matter obtained by an electrophotographic system on plain paper by an inkjet system can be provided.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when the reactant is a salt, the salt is dissociated into ions in the reaction solution, but is expressed as “contains a salt” for convenience. In addition, water-based ink may be simply referred to as “ink”. Further, the physical property values are values at normal temperature (25 ° C.) unless otherwise specified.

  The reason why the glossiness of the image cannot be obtained in the conventional ink jet recording method using the reaction liquid and the ink in combination is that the resin that can increase the glossiness cannot be present on the pigment layer because it is an aqueous ink. It is. For example, it is conceivable that the resin layer is formed on the pigment layer by particularly increasing the content of the resin particles in the ink or by using a coating liquid containing resin particles in addition to the reaction liquid. . However, when the content of the resin particles in the ink is particularly increased, problems such as ejection properties may occur. In addition to the reaction liquid and the ink, when a coating liquid is used in combination, the total amount of liquid applied to the recording medium becomes too large, and it may be considered that it takes too much time to dry the recorded matter. In view of this, the present inventor did not use the above-described method, but studied to improve the glossiness of the image by devising the relationship between the reaction liquid and the ink.

  First, the present inventor has examined the conditions under which glossiness is felt in an image recorded on plain paper. As a result, it has been recognized that it is important that the gloss when an image recorded on plain paper is irradiated with light at an incident angle of 75 ° is 15 or more, that is, that the 75 ° gloss value is 15 or more. It was.

  The improvement in glossiness in the conventional ink jet recording method assumes an image recorded on glossy paper, and glossiness cannot be obtained even if this is applied to plain paper as it is. The inventor considers this reason as follows. In order to improve the glossiness of an image, it is important to efficiently provide a resin layer formed of a coating liquid on the pigment layer and to smooth the surface of the resin layer. Here, since glossy paper and plain paper have different ways of penetration of liquid components, in order to improve gloss when using plain paper as a recording medium, the design should be based on a concept different from that of glossy paper. There is a need to do.

  The ink jet recording method disclosed in Patent Document 2 mentioned above does not require a coating liquid, but is a technique for improving the glossiness of glossy paper. In this technology, for the ink containing carbon black as a pigment, the unevenness of the pigment layer formed on the glossy paper is made smooth by changing the sedimentation rate of the pigment and resin particles, thereby improving the glossiness. Yes. However, as a result of the study by the present inventor, it was found that the above mechanism is difficult to be exhibited due to the difference in sedimentation speed because the liquid component penetrates quickly in plain paper. Furthermore, when the ink and the reaction liquid described in Patent Document 2 are used in combination, the pigment and the resin particles start to aggregate rapidly with the contact. Therefore, since the specific water-soluble organic solvent described in Patent Document 2 causes aggregation before the resin particles swell and the sedimentation rate becomes different, the above mechanism is also used for this reason. Is hard to be demonstrated. That is, the glossiness cannot be improved by simply applying the glossiness improvement technique for glossy paper to plain paper.

  The inventor has reviewed the elements necessary to obtain gloss on plain paper. As a result, in order to efficiently form a resin layer on the pigment layer and improve glossiness, first, the resin particle content (mass%) in the ink is changed to the pigment content (mass%) in the ink. The present inventor has found that it is effective to set the mass ratio to 2.0 times or more. However, it has been found that even if these conditions are satisfied, the 75 ° gloss value of the image may not reach 15 or more. As a result of the inventor's investigation of the reason for this state, both the pigment and the resin particles react with the reaction solution, whereby a layer in which the pigment and the resin particles are mixed is formed, and the resin particles are present on the surface. It was found that there was a part that did not. For this reason, the pigment not covered with resin diffusely reflected incident light, and the 75 ° gloss value was not sufficiently increased.

  Therefore, the present inventor has studied to make the surface of the pigment layer covered with resin. As a result, the present inventor has obtained the knowledge that the cohesiveness of the pigment and the resin particles when the reaction liquid and the ink are in contact with each other may be in a specific relationship. Specifically, the resin layer is formed on the pigment layer by lowering the cohesiveness of the resin particles and the cohesiveness of the pigment and the resin particles when the reaction liquid and the ink are in contact with each other. The knowledge that it can be formed was obtained. By satisfying such a relationship, when ink is applied to the region of the plain paper to which the reaction liquid has been applied, the pigment having a relatively high cohesiveness first aggregates to form a large aggregate, which forms a pigment layer. . During this time, some of the resin particles pass through the gaps between the pigment aggregates and sink to the plain paper, but many of them are less agglomerated than the pigment, so that the aggregates slowly come into contact with the reaction solution. In order to form, it comes to be located on the pigment layer. As a result, it is considered that the resin layer can be efficiently formed on the pigment layer. In addition to this, the resin layer formed as described above is hard to contain a pigment that can hinder the filming action of the resin particles caused by the evaporation of moisture, so the smoothness of the surface is also increased and the glossiness is increased. . Contrary to the above, when the cohesiveness of the resin particles is higher than the cohesiveness of the pigment, the pigment layer is formed on the resin layer, resulting in low gloss.

  As a result of the study by the present inventors, it was found that the surface tension of the ink needs to be 35 mN / m or less while satisfying the relationship between the mass ratio and the cohesiveness. It has been found that satisfying all of these configurations allows the resin layer to be formed particularly efficiently on the pigment layer, and the 75 ° gloss value of the image to be 15 or more. On the other hand, if the surface tension of the ink is more than 35 mN / m, the penetration rate of the liquid component into the plain paper decreases, so that even if the cohesiveness relationship is satisfied, the pigment aggregate and the resin particle aggregate And the 75 ° gloss value of the image cannot be made 15 or more.

<Image recording method>
The image recording method of the present invention includes a step of applying a reaction liquid to plain paper, and a water-based ink containing pigment and resin particles is ejected from an inkjet recording head to react with the plain paper to which the reaction liquid is applied. And a step of recording the image by applying it so as to come into contact with the liquid. The reaction liquid aggregates pigments and resin particles in the ink. The water-based ink has a surface tension of 35 mN / m or less.

  The step of applying the reaction liquid to plain paper is performed by an application method such as a discharge method for discharging from an ink jet recording head, a roller coating method using a roller, and a bar coating method using a bar coater, as in the case of ink. be able to. Examples of the ejection method for ejecting from an ink jet recording head include a method for applying mechanical energy to the reaction liquid or ink, and a system for applying thermal energy to the reaction liquid or ink.

  In the present invention, in the step of recording an image by applying ink to plain paper, it is particularly preferable to employ a method in which thermal energy is applied to the ink and ink is ejected. In the step of applying the reaction liquid to plain paper, the reaction liquid is preferably applied to plain paper by a coating method such as a roller coating method. The step of applying a reaction liquid and the step of recording an image by applying ink are performed by an ink jet recording apparatus having a mechanism for applying the reaction liquid onto a recording medium by a roller and a recording head for discharging ink by thermal energy. be able to.

In the image recording method of the present invention, since the ink is applied to the plain paper to which the reaction liquid is applied, the step of applying the ink and recording the image can be performed after the step of applying the reaction liquid to the plain paper. it can. In order to sufficiently obtain reactivity by using the reaction liquid, the time interval for applying the reaction liquid and the ink is preferably 1 minute or less when the reaction liquid is applied by a discharge method. When applying the reaction solution by a coating method, it is preferably 30 seconds or less. The reaction liquid may be applied so as to include at least a region to which ink is applied. The applied amount of the reaction solution is preferably 0.5 g / m ² or more and 10.0 g / m ² or less, and more preferably 2.0 g / m ² or more and 5.0 g / m ² or less.

[Reaction solution]
The reaction solution is preferably colorless and transparent, but need not necessarily be one that does not absorb in the visible range. That is, even if absorption is shown in the visible region, absorption may be shown in the visible region as long as it does not affect the image. Preferably, the reaction liquid does not contain a coloring material.

(Reactant)
The reaction liquid used in the inkjet recording method of the present invention is a liquid containing a reactive agent. Any reactive agent may be used as long as it reacts with the pigment and the resin particles in the ink. For example, as long as pigments and resin particles are dispersed by the action of an anionic group, polyvalent metal ions generated by ion dissociation of polyvalent metal salts, organic acids, and the like can be used as reactants. More preferably, the reaction solution contains a polyvalent metal ion.

Examples of the polyvalent metal ion include divalent metal ions such as Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ , Zn ²⁺ , Sr ^2+, and Ba ²⁺ ; Al ³⁺ , Fe ^{3 And} trivalent metal ions such as ⁺ , Cr ³⁺ and Y ³⁺ . Examples of counter ions that form a polyvalent metal salt together with these polyvalent metal ions include Cl ⁻ , Br ⁻ , I ⁻ , ClO ⁻ , ClO ₂ ⁻ , ClO ₃ ⁻ , ClO ₄ ⁻ , NO ₂ ⁻ , and NO. Inorganic anions such as ₃ ⁻ , SO ₄ ²⁻ , CO ₃ ²⁻ , PO ₄ ³⁻ , HPO ₄ ²⁻ , and H ₂ PO ₄ ⁻ ; HCO ₃ ⁻ , HCOO ⁻ , (COO ⁻ ) ₂ , COOH (COO _{^{-), 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 ^- and organic anions such.

Examples of the polyvalent metal ion, is excellent in ^{reactivity, Ca 2+, Mg 2+, Sr} 2+, is preferably at least one selected from the group consisting of Al ³⁺ and Y ^3+, among others Ca ^{2 +} Is particularly preferred. Further, since the solubility in the aqueous medium constituting the reaction liquid is better, counterion (anion) of NO ₃ ^- is particularly preferably. For these reasons, in the present invention, it is particularly preferable to use Ca (NO ₃ ) ₂ when preparing the reaction solution. The polyvalent metal salt may be used in the form of a hydrate.

  In order to contain a polyvalent metal ion as a reactant in the reaction solution, a polyvalent metal salt capable of generating a polyvalent metal ion by ion dissociation may be used. The content of the polyvalent metal salt in the reaction solution is a content (mass%) in terms of polyvalent metal ions, and is 0.1% by mass or more and 15.0% by mass or less based on the total mass of the reaction solution. It is more preferable that it is 1.0 mass% or more and 12.0 mass% or less.

  As the organic acid, an organic acid having a carboxy group is preferably used. Specific examples of organic acids include salts of monocarboxylic acids such as formic acid, acetic acid, propionic acid, and butyric acid; phthalic acid, isophthalic acid, terephthalic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid Acids, fumaric acid, itaconic acid, sebacic acid, dimer acid, pyromellitic acid, and dicarboxylic acid salts and hydrogen salts such as trimellitic acid; tricarboxylic acid salts and hydrogen salts such as citric acid; oxysuccinic acid and DL-apple Examples thereof include salts of acids and hydroxycarboxylic acids such as tartaric acid. Examples of the cation forming the salt include alkali metal ions such as lithium, sodium, and potassium. The content (% by mass) of the organic acid in the reaction solution is preferably 1.0% by mass or more and 15.0% by mass or less based on the total mass of the reaction solution.

(Aqueous medium)
The reaction solution preferably contains water or a mixed solvent of water and a water-soluble organic solvent as an aqueous medium. An aqueous reaction solution containing at least water as the aqueous medium is preferable. It is preferable to use deionized water (ion exchange water) as the water. The content (% by mass) of water in the reaction solution is preferably 25.0% by mass or more and 95.0% by mass or less, based on the total mass of the reaction solution, and 50.0% by mass or more and 95.0% by mass. More preferably, it is% or less.

  As the water-soluble organic solvent, any known one generally used in a reaction liquid for inkjet can be used, and one or more water-soluble organic solvents can be used. Specific examples include alcohols, (poly) alkylene glycols, polyethylene glycols having a number average molecular weight of about 200 to 2,000, glycol ethers, and nitrogen-containing compounds. The content (% by mass) of the water-soluble organic solvent in the reaction solution is preferably 3.0% by mass or more and 70.0% by mass or less, and 3.0% by mass or more and 50% by mass or less based on the total mass of the reaction solution. More preferably, it is 0.0 mass% or less.

(Other ingredients)
In addition to the above components, the reaction solution may contain nitrogen-containing compounds such as urea and ethylene urea; and organic compounds that are solid at room temperature, such as trimethylolethane and trimethylolpropane, as necessary. Furthermore, in addition to the above components, the reaction solution may be a polymer compound, a pH adjuster, an antifoaming agent, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an anti-reduction agent, an evaporation accelerator, if necessary. Various additives such as an agent and a chelating agent may be contained.

[ink]
(Resin particles)
The ink used in the image recording method of the present invention contains resin particles. Examples of the resin particles include resin particles composed of acrylic resin, olefin resin, urethane resin, and the like. Especially, it is preferable to contain the resin particle comprised by acrylic resin. The acrylic resin only needs to have at least an acrylic component such as a unit derived from (meth) acrylic acid or a unit derived from (meth) acrylic acid ester. More specifically, a resin having a hydrophilic unit and a hydrophobic unit as constituent units is preferable. In the present specification, “(meth) acrylic acid” and “(meth) acrylate” mean “acrylic acid, methacrylic acid” and “acrylate, methacrylate”, respectively.

  The hydrophilic unit can be formed, for example, by polymerizing a monomer having a hydrophilic group. Specific examples of the monomer having a hydrophilic group include a monomer having a carboxy group such as (meth) acrylic acid, itaconic acid, maleic acid, and fumaric acid; a monomer having a sulfonic acid group such as styrenesulfonic acid; Monomers having a phosphonic acid group such as ethyl acrylate-2-phosphonate; anionic monomers such as anhydrides and salts of these acidic monomers; 2-hydroxyethyl (meth) acrylate and (meth) acrylic acid 3- Mention may be made of monomers having a hydroxy group such as hydroxypropyl. Examples of the cation constituting the salt of the anionic monomer include ions such as lithium, sodium, potassium, ammonium, and organic ammonium. The monomer which has a hydrophilic group can use 1 type (s) or 2 or more types. As the monomer having a hydrophilic group, a monomer having a carboxy group and a salt thereof are preferable, and (meth) acrylic acid and a salt thereof are more preferable.

  The hydrophobic unit can be formed, for example, by polymerizing a monomer having a hydrophobic group. Specific examples of the monomer having a hydrophobic group include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth) acrylate; ethyl (meth) acrylate, methyl (meth) acrylate, (iso) propyl ( And monomers having an aliphatic group such as (meth) acrylate, (n-, iso-, t-) butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate. The monomer which has a hydrophobic group can use 1 type (s) or 2 or more types. As the monomer having a hydrophobic group, a monomer having an aromatic ring is preferable, and styrene and benzyl (meth) acrylate are more preferable.

  The resin particles can be synthesized by a conventionally known polymerization method. Examples of the polymerization method include suspension polymerization and emulsion polymerization. From the viewpoint of obtaining resin particles having a volume average particle diameter of 150 nm or more and 200 nm or less, suspension polymerization in which the mixture of monomers described above and water as a solvent are stirred and suspended to perform polymerization is preferable.

  The acid value of the resin particles is preferably from 100 mgKOH / g to 300 mgKOH / g, and more preferably from 200 mgKOH / g to 300 mgKOH / g. The volume average particle diameter of the resin particles is preferably 150 nm or more and 200 nm or less. The resin particle content (% by mass) in the ink is preferably 5.0% by mass or more and 25.0% by mass or less based on the total mass of the ink.

(Pigment)
The ink used in the image recording method of the present invention contains a pigment as a color material. Examples of the pigment include inorganic pigments such as carbon black and organic pigments known in the art. 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, based on the total mass of the ink, and is 1.0% by mass or more and 10.0% by mass or less. More preferably it is. The volume average particle diameter of the pigment is preferably 70 nm or more and 150 nm or less.

  Examples of the pigment dispersion method include a method using a dispersant such as a resin and a method using no dispersant such as a resin. As a method using a dispersant such as a resin, (1) the resin is physically adsorbed on the pigment particle surface, and (2) the organic group in the resin is chemically bonded to the pigment particle surface for modification. Examples thereof include resin-bonded self-dispersing pigments and (3) microcapsule-type pigments coated with a resin. In addition, as a method that does not use a dispersant such as a resin, a self-dispersing pigment in which an anionic group is bonded to the particle surface of the pigment directly or via another atomic group can be mentioned. Combinations of pigments with different dispersion methods may be used. Among these, it is preferable to use a resin-dispersed pigment or a self-dispersed pigment in which the resin is physically adsorbed on the pigment particle surface, and it is more preferable to use a resin-dispersed pigment. In the present invention, in order to consider the reactivity with the reaction liquid, it is necessary to calculate the “pigment content” including a component that contributes to the dispersion of the pigment. For example, in the case of a method using a dispersing agent such as a resin, the content including the pigment and the resin is set as the “content of pigment”.

  The resin used as the dispersant is preferably an acrylic resin. The acrylic resin only needs to have at least an acrylic component such as a unit derived from (meth) acrylic acid or a unit derived from (meth) acrylic acid ester. Specifically, a resin having a constituent unit selected from the same constituent units as those described above as the constituent unit of the resin particles can be used. The resin used as the dispersant preferably has a weight average molecular weight of 1,000 or more and 30,000 or less. Further, the resin used as the dispersant preferably has an acid value of 50 mgKOH / g or more and 300 mgKOH / g or less, and more preferably 100 mgKOH / g or more and 200 mgKOH / g or less.

  The resin particle content E (% by mass) in the ink is a mass ratio with respect to the pigment content P (% by mass) in the ink and needs to be 2.0 times or more, and is 4.0 times or more. Preferably there is. If the mass ratio is less than 2.0 times, the glossiness of the image cannot be increased. The mass ratio is preferably 6.0 times or less. The total of the resin particle content (% by mass) and the pigment content (% by mass) in the ink is preferably 25.0% by mass or more based on the total mass of the ink. When the total content of the resin particles and the pigment is increased in this way, the effect of filling the irregularities on the surface of the plain paper is efficiently exhibited, so that the glossiness can be further improved. In this case, it is preferable to further perform a step of pressurizing the image. The total of the resin particle content (% by mass) and the pigment content (% by mass) is preferably 40.0% by mass or less based on the total mass of the ink from the viewpoint of ejection properties.

(Aqueous medium)
The ink is an aqueous ink containing at least water as an aqueous medium. The aqueous medium can further contain a water-soluble organic solvent. It is preferable to use deionized water (ion exchange water) as the water. The content (% by mass) of water in the ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink.

  As the water-soluble organic solvent, any known one generally used for ink jet inks can be used, and one or more water-soluble organic solvents can be used. Specific examples include alcohols, (poly) alkylene glycols, polyethylene glycols having a number average molecular weight of about 200 to 2,000, glycol ethers, and nitrogen-containing compounds. The content (% by mass) of the water-soluble organic solvent in the reaction solution is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink.

(Other ingredients)
In addition to the above components, the ink may contain nitrogen-containing compounds such as urea and ethylene urea; and organic compounds that are solid at room temperature such as trimethylol ethane and trimethylol propane as necessary. Further, in addition to the above components, the ink may be a polymer compound, a pH adjuster, an antifoaming agent, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an anti-reduction agent, an evaporation accelerator, if necessary. , And various additives such as chelating agents.

(Ink physical properties)
The surface tension at 25 ° C. of the ink used in the image recording method of the present invention is required to be 35 mN / m or less as described above. The surface tension of the ink is preferably 25 mN / m or more, and more preferably 30 mN / m or more, from the viewpoint of efficiently forming the resin layer on the pigment layer.

(Relationship between cohesiveness of resin particles and pigment)
In the present invention, the relationship between the cohesiveness of the pigment and the resin particles when the reaction liquid and the ink are in contact with each other requires that the cohesiveness of the pigment is higher than the cohesiveness of the resin particles. Aggregability is measured as follows. First, a magnification such as 500 times (volume basis) of an aqueous dispersion having a pigment content of 1.0% by mass, an aqueous dispersion having a resin particle content of 1.0% by mass, and ion-exchanged water. Prepare the reaction solution diluted in step 1 and use these as samples. Using a sample prepared using an aqueous dispersion of pigment or an aqueous dispersion of resin particles, the volume average particle diameter of the pigment and resin particles (volume average particle diameter of the pigment and resin particles before contact with the reaction liquid) is measured. To do. Next, two sample bottles containing 5 g of a sample diluted with the reaction liquid were prepared, and 1 g of a sample prepared using an aqueous dispersion of pigment or an aqueous dispersion of resin particles was dropped into each sample bottle and stirred. To do. Thereafter, the volume average particle diameter of the pigment and resin particles (volume average particle diameter of the pigment and resin particles after contact with the reaction solution) is measured. And the increase rate of each volume average particle diameter of the pigment and the resin particle before and after reaction (before and after contact with the reaction solution) is calculated, and the higher increase rate is determined to be high in cohesion. In the above description, the determination method using the aqueous dispersion is described as an example. However, the determination can be similarly performed using pigments and resin particles appropriately separated from the ink.

  The cohesiveness of the pigment and resin particles can be adjusted as follows. The cohesiveness of the pigment tends to be increased by lowering the acid value of the resin that can be used as the pigment dispersant, and by reducing the resin that can be used as the pigment dispersant relative to the pigment content. is there. For example, the acid value of the resin used as the dispersant is preferably 100 mgKOH / g or more and 200 mgKOH / g or less. The mass ratio of the content of the dispersant (resin) / the content of the pigment is preferably 0.2 times or more and 0.6 times or less. The cohesiveness of the resin particles tends to be lowered by increasing the acid value of the resin particles. More specifically, the acid value of the resin particles is preferably more than 200 mgKOH / g and not more than 300 mgKOH / g, and more preferably not less than 210 mgKOH / g and not more than 300 mgKOH / g.

(Relationship between volume average particle diameter of resin particles and pigment)
The ink used in the image recording method of the present invention is preferably such that the volume average particle diameter of the resin particles is larger than the volume average particle diameter of the pigment before contact with the reaction liquid (before reaction). In this case, glossiness can be further improved. When the volume average particle diameter of the resin particles is larger than the volume average particle diameter of the pigment, resin particles having relatively low cohesiveness are easily located on the pigment layer, and glossiness is easily improved.

  In addition, the lower the cohesiveness of the resin particles than the cohesiveness of the pigment, the higher the 75 ° gloss value. The influence on the 75 ° gloss value is due to the above-described relationship between the cohesiveness of the resin particles and the pigment. The relationship between the volume average particle diameter of the resin particles and the pigment is larger.

The “volume average particle size” in the present invention means a cumulative 50% particle size (D ₅₀ ) in a volume-based particle size distribution, and can be measured using a particle size distribution measuring device utilizing a dynamic light scattering method. it can. Specifically, it can be measured according to the following conditions. First, a measurement sample is prepared by diluting an aqueous dispersion of resin particles or an aqueous dispersion of pigment 50 times (volume basis) with pure water. And the particle size distribution measuring apparatus is used, The volume average particle diameter of the resin particle in a measurement sample is measured according to the measurement conditions shown below.
〔Measurement condition〕
SetZero: 30 seconds Number of measurements: 3 times Measurement time: 180 seconds Refractive index: 1.5
As the particle size distribution measuring device, a dynamic light scattering type particle size analyzer (for example, trade name “UPA-EX150”, manufactured by Nikkiso) can be used. Of course, the particle size distribution measuring apparatus and measurement conditions to be used are not limited to the above. In the above description, the method of measuring using an aqueous dispersion is described as an example, but the same measurement can be performed using resin particles and pigment appropriately separated from ink.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited at all by the following Example, unless the summary is exceeded. In addition, what is described as “parts” and “%” with respect to the component amounts is based on mass unless otherwise specified.

<Preparation of pigment dispersion>
16.0 parts of pigment (carbon black), 40.0 parts of an aqueous solution of a resin dispersant, and 44.0 parts of pure water were mixed. As an aqueous solution of the resin dispersant, a styrene-acrylic acid copolymer having an acid value of 100 mgKOH / g was neutralized with potassium hydroxide in an equivalent amount to the acid value and dissolved in ion-exchanged water (solid content). ) Content of 10.0% was used. The mixture was put into a batch type vertical sand mill (manufactured by IMEX), filled with 150.0 parts of 0.3 mm diameter zirconia beads, and dispersed for 5 hours while cooling with water. Thereafter, coarse particles are removed by centrifugation, the pigment content is 16.0%, the resin (solid content) content is 4.0%, and the pigment (resin content) content is 20.0. %, A pigment dispersion having a volume average particle diameter of the pigment of 150 nm was obtained.

<Synthesis of resin particles>
(Resin particles 1)
70.0 parts of styrene, 5.0 parts of benzyl methacrylate, and 25.0 parts of acrylic acid were mixed to obtain a monomer mixture. In a four-necked flask equipped with a stirrer, a reflux cooling device, and a nitrogen gas introduction tube, 50.0 parts of water was introduced, nitrogen gas was introduced into the reaction system, and the temperature was raised to 80 ° C. with stirring. . After putting the monomer mixture obtained above into this four-necked flask, 10.0 parts of 5% aqueous potassium persulfate solution was added dropwise over 3 hours. After aging for 2 hours, an appropriate amount of ion-exchanged water is added to adjust the solid content, and the content (solid content) of resin particles 1 having an acid value of 195 mgKOH / g and a volume average particle diameter of 150 nm is 30. An aqueous dispersion of resin particles 1 that was 0.0% was obtained.

(Resin particles 2)
50.0 parts of styrene, 5.0 parts of benzyl methacrylate, and 45.0 parts of acrylic acid were mixed to obtain a monomer mixture. Resin particle 2 in which the content (solid content) of resin particles 2 having an acid value of 350 mgKOH / g and a volume average particle diameter of 150 nm is 30.0%, except that this mixture is used. An aqueous dispersion was obtained.

(Resin particles 3)
The content (solid content) of the resin particles 3 having an acid value of 195 mgKOH / g and a volume average particle diameter of 200 nm is the same as the synthesis of the resin particles 1 except that the stirring speed at the time of dropping the potassium persulfate aqueous solution is changed. An aqueous dispersion of resin particles 3 that was 30.0% was obtained.

(Resin particles 4)
25.0 parts of styrene, 58.0 parts of methyl methacrylate, and 14.0 parts of acrylic acid were mixed to obtain a monomer mixture. Resin particles 4 having an acid value of 110 mgKOH / g and a volume average particle diameter of 150 nm of resin particles 4 (solid content) of 30.0%, except that this mixture is used. An aqueous dispersion was obtained.

<Preparation of reaction solution>
The components shown below were mixed and sufficiently stirred, and then pressure filtration was performed with a microfilter (manufactured by Fuji Film) having a pore size of 0.2 μm to prepare a reaction solution. As the surfactant, a nonionic surfactant (trade name “acetylenol E100”, manufactured by Kawaken Fine Chemicals) was used.
Calcium nitrate tetrahydrate: 18.0 parts Glycerin: 15.0 parts Triethylene glycol: 15.0 parts Surfactant: 1.0 parts Ion-exchanged water: 71.0 parts

<Measurement of cohesiveness>
First, each component (unit:%) shown in the upper part of Table 1 is mixed, sufficiently stirred, and a sample for measuring agglomeration (water dispersion having a pigment or resin particle content of 1.0%) 1) to 5 were prepared. Moreover, what diluted the reaction liquid obtained above 500 times (volume basis) with ion-exchange water was prepared. Sample 1 was used to measure the volume average particle diameter of the pigment before contact with the reaction solution (before reaction), and Samples 2 to 5 were each used before contact with the reaction solution (before reaction). The volume average particle diameter of the resin particles 1 to 4 was measured. Next, for each of the samples 1 to 5, 5 g of the diluted reaction solution and 1 g of the sample obtained above were mixed in a sample bottle and stirred for 1 minute. Thereafter, the volume average particle diameter of the pigment after contact with the reaction liquid (after reaction) and the volume average particle diameter of the resin particles were measured. For the measurement of each volume average particle size, using a particle size analyzer (trade name “Nanotrack UPA-EX150”, manufactured by Nikkiso), which is a measurement device using a dynamic light scattering method, under the above-described measurement conditions, The cumulative 50% particle size (D ₅₀ ) in the volume-based particle size distribution was measured. The values of the volume average particle diameters of the pigment and the resin particles 1 to 4 before and after the reaction with the reaction liquid measured as described above are shown in the lower part of Table 1. The lower part of Table 1 also shows the increase rate (times) of the volume average particle diameter before and after the reaction.

<Preparation of ink>
Each component (unit:%) shown in Table 2 was mixed and sufficiently stirred, and then pressure filtration was performed with a microfilter (manufactured by Fuji Film) having a pore size of 0.2 μm to prepare each ink. As the surfactant, a nonionic surfactant (trade name “acetylenol E100”, manufactured by Kawaken Fine Chemicals) was used. The lower part of Table 2 shows the ink characteristics such as the surface tension of the ink, the content P (%) of the pigment in the ink, the content E (%) of the resin particles in the ink, and the resin with respect to the content P of the pigment. The mass ratio (value of E / P) of the content E of particles was shown. The surface tension was measured using an automatic surface tension meter (trade name “DY-300”, manufactured by Kyowa Interface Science).

<Evaluation>
For the evaluation, an ink jet recording apparatus (trade name “PIXUS MX7600”, manufactured by Canon Inc.) was used. This recording apparatus includes a mechanism for applying a reaction liquid onto a recording medium with a roller, and a recording head for discharging ink by thermal energy. The amount of reaction liquid applied is adjusted to 3.0 g / m ^2, and a roller unit for pressurizing the image is provided on the paper discharge unit, with a nip pressure of 7.0 kgf / cm ² and a nip time of 0.9 seconds. The image was adjusted to pass under the conditions. In the present embodiment, a condition for applying one drop of ink having a mass per drop of 28 ng to a unit area of 1/600 inch × 1/600 inch is defined as a recording duty of 100%.

  The ink and reaction liquid obtained above were filled in a cartridge and set in the above-described ink jet recording apparatus. Then, after applying a predetermined amount of the reaction liquid to plain paper (trade name “PB Paper”, manufactured by Canon), a solid image of 5 cm × 5 cm having a recording duty of 100% is recorded, and further under the above conditions. The image was pressurized.

  About the obtained solid image, 75 degree gloss value was measured using the gloss meter (Brand name "VG2000", Nippon Denshoku Industries make). The higher the 75 ° gloss value, the higher the glossiness of the image. The results are shown in Table 3. Further, in the column of “aggregability” in Table 3, from the measurement result of aggregation property (see Table 1), the increase rate of the volume average particle diameter of the pigment and the increase rate of the volume average particle diameter of the resin particles used are These results showed that the higher rate of increase was determined to have high cohesiveness. In the column of “Aggregation” in Table 3, “resin particles <pigment” indicates that the agglomeration property of the pigment is higher than the agglomeration property of the resin particles, and “resin particle = pigment” indicates agglomeration of the resin particles. And the cohesiveness of the pigment are almost the same.

Claims (5)

A step of applying a reaction liquid for aggregating the pigment and resin particles in the ink to plain paper, and discharging an aqueous ink containing the pigment and resin particles and having a surface tension of 35 mN / m or less from an inkjet recording head. And applying to the plain paper to which the reaction solution has been applied so as to come into contact with the reaction solution and recording an image, and an image recording method comprising:
The resin particle content (% by mass) in the ink is 2.0 times or more in terms of a mass ratio with respect to the pigment content (% by mass) in the ink,
An image recording method characterized in that the cohesiveness of the pigment and the resin particles when the reaction liquid and the ink are in contact is higher in the cohesiveness of the pigment than in the cohesiveness of the resin particles. .   The image recording method according to claim 1, wherein the volume average particle diameter of the resin particles is larger than the volume average particle diameter of the pigment.   3. The image recording method according to claim 1, wherein the total of the content (mass%) of the resin particles and the content (mass%) of the pigment is 25.0 mass% or more based on the total mass of the ink. .   The image recording method according to claim 1, wherein the reaction liquid contains a polyvalent metal ion.   The image recording method according to claim 1, further comprising a step of pressurizing the image.