JP2006110930A - Inkjet recording method and inkjet printer for use in it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording method, the attractiveness of which is prevented from being diminished, which is excellent in curling characteristics of recorded matter, which enhances the handleability of the recorded matter and which makes an image recorded on a water-absorbing recording medium by using a water-base ink, and an inkjet printer for use in the inkjet recording method. <P>SOLUTION: In this inkjet recording method, the image is recorded by ejecting the ink, containing water and a coloring agent, onto a recording medium from a recording head. In the recording medium, a coloring material fixing layer is provided on ordinary paper or a paper substrate which is equipped with solvent absorbing power. In the inkjet recording head, the number of nozzles is 5,000 or more; a driving frequency is 20 kHz or more; the amount of each ink droplet ejected from the inkjet recording head is 2.5 pL or less; and the gross mass of water and a water-soluble organic solvent component with a plurality of hydrogen-associative parts in an image area, where the adhesion amount of the ink is maximized, is in the range of 0.5-15 g/m<SP>2</SP>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink jet recording method in which curling of recorded matter obtained by using plain paper or coated paper having an absorbent support is suppressed, and improved handling of the recorded matter, and an ink jet printer used therefor.

  The ink jet recording method is a non-impact recording method in which an image is generated by depositing ink droplets on a recording medium in response to a digital signal to obtain a recorded matter.

  In addition to the inkjet recording method, examples of the recording method include a thermal transfer image recording method, a laser beam printer, and electrophotography. However, these methods require a large amount of heat for fixing and shorten the warm-up time. Therefore, the energy loss such as the need to keep the fixing member warm even when the fixing member is not used is large. This leads to a waste of enormous heat energy with the advanced information environment that is expected to expand rapidly on a global scale in the future. Further, since heat is applied to the recording material, there is a principle that the recorded material is deformed or curled due to heat.

  On the other hand, from the viewpoint of resource saving, attempts have been made to reduce the thickness of the recording material. However, not only the printability is impaired, but it is also difficult to maintain the texture as a recorded material, which is a limitation. In addition, for the purpose of facilitating recycling, a method of making paper by mixing natural materials such as starch other than cellulose is also known, but the recording material is discolored due to scoring and accompanying odor problems during heat fixing. Therefore, it is an obstacle to development or practical application.

  From the above, it is speculated that an ink jet recording method that does not require thermal energy at the time of image fixing is increasingly regarded as important from the viewpoint of environmental conservation.

  As inks used in ink jet recording, water-based inks, oil-based inks, solid-melt inks, and the like are generally used. Among these inks, expectations for water-based inks are increasing from the viewpoint of ease of production, handleability, odor, safety, and the like.

  Recording materials used for inkjet recording include plain paper such as PPC paper, water-absorbing coated paper, ink-jet exclusive paper with an ink-receiving layer on a water-absorbing support or a non-water-absorbing support, etc. Various recording materials are commercially available. Among these recording materials, plain paper, water-absorbent coated paper, etc. are most preferred for use in office documents that consume a large amount of paper from the viewpoint of manufacturing cost and ease of recycling. That position is not expected to change.

  However, in printing on plain paper or water-absorbing coated paper with water-based ink, there is a current situation in which deformation of the recording material called curl occurs during printing and the print quality is greatly reduced.

  It is assumed that the deformation of the recording material called curl occurs due to the following factors. That is, the paper base portion of plain paper or water-absorbent coated paper is rapidly dehydrated from the pulp state containing a large amount of water in the paper making process, and further pressed to be squeezed into a sheet. At this time, each of the cellulose fibers is not the original most stable shape, but is deformed by pressure. In this deformed state, hydrogen bonding force is activated between the cellulose fibers, and the cellulose is fixed in an unnatural deformed state. For this reason, the restoring force which a cellulose fiber tries to return to original is stored in paper. In ink jet printing, by applying ink to paper, this hydrogen bond is partially broken, and the stored restoring force is non-uniformly activated. The occurrence of this uneven restoring force is observed as a curl, resulting in a significant deterioration in quality as a printed matter.

  Various improvement methods have been proposed for curling that occurs during printing as described above.

  For example, JP-A-7-195683 discloses a recording method for preventing curling by drying with microwaves immediately after printing, and JP-A-9-30710 discloses that a heater is brought into contact with the printing surface side (surface) after printing. , A drying method for diffusing vapor such as an ink solvent to the non-printing surface side (back surface), and Japanese Patent Application Laid-Open No. 2001-239657 is a method of recording the ink discharge amount by feeding it back to the dryer and appropriately controlling the drying capacity. Each has been proposed. In addition, various drying methods have been proposed. By attaching a drying device, inkjet image recording that should not require fixing energy has resulted in wasting a lot of heat energy, making the inkjet attractive. This is a significant factor.

  On the other hand, JP-A-6-240189, JP-A-8-216384, JP-A-10-130550, JP-A-2004-136458, JP-A-2004-209758, JP-A-2004-209759, JP-A-2004-209762. In JP-A-2004-210902, JP-A-2004-210906, and JP-A-2004-210914, a hydrogen bond that is cleaved by water by adding a compound having a hydrogen bond property as an anti-curl agent to the ink. Although the force is compensated, the force that causes the curl is the restoring force of cellulose stored in advance, so it is difficult to stop the restoration of cellulose once hydrogen bonds are broken and can move freely It is. In addition, paper that has been reduced in thickness from the viewpoint of resource reduction, while increasing the hydrogen bond strength to obtain the strength of the paper is restored when the hydrogen bond strength is lost when wet. The force exceeds the effect of deformation reduction by the anti-curl agent. In general, paper containing waste paper has a tendency to promote crystallization of cellulose and has a high hydrogen bonding force due to waste paper components, so that the effect of reducing deformation of the anti-curl agent is surpassed as described above. In addition, since these anti-curl agents remain in the paper, they may act on and contaminate documents printed by other printing systems, such as electrophotographic toner and thermal recording colorants with anti-curl agents. There were many. For this reason, for example, a problem has been seen in saving the same saved file in an overlapping manner. In addition, many of the anti-curl agents that are particularly effective for preventing curling during long-term storage are highly viscous and require a large amount of addition, so sticking to the recording surface becomes a problem when storing over a file, Not suitable for long-term storage of documents.

For the above problems, there is a method for preventing curling by applying a transparent liquid containing water from the back side to the same place as the printed part on the front side, and making the degree of loss of hydrogen bonding power on the front side and the back side the same. It has been proposed (for example, see Patent Documents 1 to 3). However, if the front and back surfaces are not dried to the same extent in the drying after printing, there is a difference in the restoration of the hydrogen bonding force at the time of drying, which eventually leads to the occurrence of curling. Also, if the front and back surfaces are similarly dried in high-speed printing, the capacity of the dryer is twice that required for single-sided printing, resulting in an increase in waste of heat energy as described above. As a result, the attractiveness of the recording method is significantly reduced.
Japanese Patent Laid-Open No. 9-216389 Japanese Patent Laid-Open No. 10-151733 JP-A-10-272828

  As described above, the various methods proposed for the ink jet recording method for printing on plain paper or the like described in the prior art can suppress curling to some extent, but energy saving is an essential advantage of the ink jet recording method. In some cases, the recording property may be deteriorated or the preservability of the recorded material in a practical form may be inferior, and there is still room for improvement as a practical technique.

  Accordingly, an object of the present invention is to absorb water using an aqueous ink that has excellent curl characteristics of a recorded matter and improved handling of the recorded matter without impairing the attractiveness of the ink jet recording method that does not require excessive thermal energy. Another object of the present invention is to provide an ink jet recording method for recording an image on a recording medium and an ink jet printer used therefor.

  The above object of the present invention is achieved by the following configurations.

(Claim 1)
In an ink jet recording method for recording an image by discharging an ink containing at least water and a colorant onto a recording medium from an ink jet recording head.
The recording medium is a plain paper or a recording medium having a color material fixing layer on a paper support having a solvent absorption capability,
The inkjet recording head has a nozzle number of 5000 or more, a driving frequency of 20 kHz or more, and an ink droplet amount per droplet ejected from the inkjet recording head is 2.5 pl or less,
The total mass of the water-soluble organic solvent component having a plurality of water and hydrogen bonding sites in the image area where the ink adhesion amount is maximum is 0.5 g / m ² or more and 15 g / m ² or less. Inkjet recording method.

(Claim 2)
The total mass of the water-soluble organic solvent component having a plurality of water and hydrogen bonding sites in the image area where the ink adhesion amount is maximum is 1.0 g / m ² or more and 10 g / m ² or less. The inkjet recording method according to claim 1.

(Claim 3)
3. The ink jet recording method according to claim 1, wherein the amount of ink droplets ejected from the ink jet recording head is 0.3 pl or more and 1.0 pl or less.

(Claim 4)
The inkjet recording method according to any one of claims 1 to 3, wherein the content of the colorant in the ink is 7 mass% or more and 15 mass% or less.

(Claim 5)
In an ink jet printer provided with an ink jet recording head for recording an image by discharging an ink containing at least water and a colorant onto a recording medium,
The inkjet recording head has a nozzle number of 5000 or more, a drive frequency of 20 kHz or more, and ejects the ink onto a recording medium with an ink droplet amount of 2.5 pl or less per droplet,
The recording medium is a plain paper or a recording medium having a color material fixing layer on a paper support having a solvent absorption capability,
Image recording so that the total mass of water-soluble organic solvent components having a plurality of water and hydrogen bonding sites in the image area where the ink adhesion amount is maximum is 0.5 g / m ² or more and 15 g / m ² or less. An ink jet printer characterized by the above.

(Claim 6)
The total mass of the water-soluble organic solvent component having a plurality of water and hydrogen bonding sites in the image area where the ink adhesion amount is maximum is 1.0 g / m ² or more and 10 g / m ² or less. The inkjet printer according to claim 5.

(Claim 7)
The ink jet printer according to claim 5 or 6, wherein an ink droplet amount per droplet ejected from the ink jet recording head is 0.3 pl or more and 1.0 pl or less.

(Claim 8)
8. The inkjet printer according to claim 5, wherein a content of the colorant in the ink is 7% by mass or more and 15% by mass or less.

  According to the present invention, an ink jet recording method for recording an image on a water-absorbing recording medium using a water-based ink having excellent curl characteristics of a recorded matter and improved handling of the recorded matter without impairing the attractiveness of the ink jet recording method. And an ink jet printer used therefor.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

As a result of intensive studies in view of the above problems, the present inventor has disclosed an ink jet recording head for recording an image by discharging ink containing at least water and a colorant onto a recording medium from the ink jet recording head. However, the number of nozzles is 5000 or more, the drive frequency is 20 kHz or more, the amount of ink droplets ejected from the inkjet recording head is 2.5 pl or less, and the image area where the ink adhesion amount is maximum In the ink jet recording method, the total mass of the water-soluble organic solvent component having a plurality of water- and hydrogen-bonding sites is 0.5 g / m ² or more and 15 g / m ² or less. In the image formation using a recording medium having a color material fixing layer on a paper support having a solvent absorption capability, The present inventors have found that an ink jet recording method can be realized that has excellent curl characteristics of a recorded matter and improved handling of the recorded matter without detracting from the attractiveness of the print recording method.

  The reason why a high-quality recorded matter having excellent curl stability can be obtained by the above-described ink jet recording method defined in the present invention is presumed as follows.

One of the triggers for the occurrence of curling when printing on a recording medium having a colorant fixing layer on plain paper or a paper support having a solvent absorption capability using water-based ink is the multipolarity contained in the ink. If the adhesion amount of the solvent is 15 g / m ² or less, the proportion of hydrogen bonds to be broken is sufficiently smaller than the total hydrogen bonding force, and curling is unlikely to occur. In particular, the adhesion amount is preferably 12 g / m ² or less.

  Further, when ink is slowly printed with an ink jet recording head with a number of nozzles of less than 5000, curling appears remarkably even if the amount of ink droplets is reduced, but this is due to the cellulose against the restoring force that occurs following the breaking of hydrogen bonds. It is presumed that this is due to non-uniform deformation.

  Hereinafter, the mechanism will be described with reference to the drawings.

  FIG. 1 is a diagram showing an example of a mechanism of curling when low-speed printing is performed on a paper substrate.

  When printing at a slow printing speed, as shown in FIG. 1, the restoring force of the printing part B released by printing causes deformation of the paper, but the unprinted part A has no hydrogen bonds released, Small deformation due to restoring force. On the other hand, the print portion C that has already been printed has a hydrogen bond released and is greatly deformed by the restoring force. For this reason, the paper always deforms more on the downstream side of the printing, so that the curl is strongly generated. Further, when the printing further proceeds, the printing portion C is dried, and the generated deformation is maintained. The unprinted portion A, the printed portion B, and the printed portion C are each schematically described with springs. When the same stress is applied to the springs connected in series, the strong spring has a small deformation amount and the weak spring has a deformation amount. Since the difference is large, it can be understood more clearly that the amount of deformation varies depending on the location.

  FIG. 2 is a diagram illustrating an example of a mechanism of curling when high-speed printing is performed on a paper substrate.

  In the case of printing at high speed, as shown in FIG. 2, before the ink is driven into the printing portion E, the hydrogen bond is cut, and the restoring force is activated, the hydrogen bonding in the next region of the printing portion D to be continuously printed is performed. Is cut, deformation due to the restoring force is uniformly generated, curl is hardly generated, and drying is also uniformly generated, so that subsequent deformation does not occur. Here, if each of the printing part D, the printing part E, and the printing part F is schematically described with springs, it can be clearly understood that the difference in deformation amount is not easily generated.

  As a result of intensive studies, the present inventors have found that a remarkable effect is exhibited by setting the number of nozzles of the recording head to 5000 or more.

One of the triggers for the occurrence of cockling (wrinkle) in the recording medium is the amount of adhesion of the multipolar solvent. When the amount of adhesion is 15 g / m ² or less, the ratio of hydrogen bonds to be broken is all. It is sufficiently smaller than the hydrogen bonding force, and it is difficult to cause cockling. Particularly preferably, the adhesion amount is 10 g / m ² or less.

  If the amount of ink droplets per drop is too small, curling is improved, but a higher printing density is required, causing a reduction in printing speed. The ink droplet amount is desirably 0.3 pl or more.

  Further, from the viewpoint of image density, one of the characteristics is that the ink droplet amount is 2.5 pl or less, more preferably 2.0 pl or less, and most preferably 1.0 pl or less.

  The reason why the ink droplet amount and the image density are related can be considered as follows.

  FIG. 3 is a schematic diagram showing an example of a behavior when a large-sized pigment ink droplet has landed on a paper recording medium.

  When printing with large ink droplets, as shown in FIG. 3, when the pigment existing in the lower portion dispersed in the ink solvent S of the ink droplet D is pigment G and the pigment existing in the upper portion is H, After the pigment G has landed on the plain paper P, the non-penetrated ink solvent S portion penetrates into the plain paper P so as to push the pigment G from the top, and the pigment G is in the plain paper P and the pigment H is on the plain paper. Therefore, a decrease in image density is observed.

  FIG. 4 is a schematic diagram showing an example of a behavior when a small-sized pigment ink droplet has landed on a paper recording medium.

  On the other hand, when printing with small ink droplets, as shown in FIG. 4, first, after the pigment I dispersed in the ink solvent S of the ink droplet D ′ is applied, the ink of the ink droplet D ″ is printed. Although the pigment J dispersed in the solvent S is injected, since the ink droplet D ″ is small, the degree to which the pigment I is pushed into the plain paper P is small, and the image density remains high.

  In addition, it is one of the characteristics that the drive frequency when ejecting ink droplets from the ink jet recording head is 20 kHz or more, preferably 20 to 80 kHz, more preferably 20 to 50 kHz. If the drive frequency is 20 kHz or more, it is possible to maintain a sufficient printing speed and suppress curling. On the other hand, if the drive frequency is too high, the response speed of the ink droplets cannot catch up, so that the emission becomes unstable and a desired image cannot be obtained.

  Hereinafter, the present invention will be described in detail.

  First, the recording medium used in the present invention will be described.

  In the ink jet recording method of the present invention, the recording medium is a plain paper or a recording medium having a color material fixing layer on a paper support having a solvent absorbing ability.

  That is, plain paper (base paper) using pulp and filler as main raw materials, or absorbent coated paper provided with a colorant fixing layer that uses base paper as an ink absorption layer and further leaves liquid permeability on the base paper surface.

  Many of these recording media can be obtained as commercial products. For example, OK Kanto N, Esprit Coat, NK Double-sided Art, N Art Post, Kromote CO, Pearl Coat, Aurora Eight, POD Gloss Coat, POD Gloss coat chrysanthemum T and the like.

  The base paper used for the paper support is made from wood pulp as a main raw material, and if necessary, paper is made using synthetic pulp such as polypropylene, synthetic fiber such as nylon or polyester, or waste paper pulp in addition to wood pulp. As the wood pulp, any of LBKP, LBSP, NBKP, NBSP, LDP, NDP, LUKP, and NUKP can be used, but it is preferable to use more LBKP, NBSP, LBSP, NDP, and LDP with a short fiber content. However, the ratio of LBSP and / or LDP is preferably 10% by mass or more and 70% by mass or less.

  As the pulp, chemical pulp (sulfate pulp or sulfite pulp) with less impurities is preferably used, and a pulp whose whiteness is improved by bleaching is also useful. The freeness of the pulp used for papermaking is preferably 200 to 500 ml as defined by CSF, and the fiber length after beating is 24% by mass as defined in JIS-P-8207, and 42 mesh residue. 30 to 70% of the sum with the mass% of is preferable. In addition, it is preferable that the mass% of 4 mesh remainder is 20 mass% or less.

  In addition, a filler is added to the base paper in order to adjust opacity, whiteness, and surface smoothness. As fillers that can be used, calcium carbonate, kaolin, clay, titanium dioxide and the like can be mentioned as representatives, but other commonly used fillers can be used as long as the object effects of the present invention are not impaired. . The blending amount of the filler is preferably 5 to 30 parts by mass with respect to 100 parts by mass of the cellulose fiber, and particularly when the used paper is mixed and used, the addition amount is appropriately set in consideration of the ash content of the used paper. There is a need to.

  Further, a sizing agent may be added to the base paper, and examples of the internally added sizing agent include alkyl ketene dimer, alkenyl succinic anhydride, and neutral rosin sizing agent.

  The basis weight of the base paper is preferably 30 to 250 g, particularly preferably 50 to 200 g. The thickness of the base paper is preferably 40 to 250 μm.

The base paper can be imparted with high smoothness by calendering at the paper making stage or after paper making. The density of the base paper is generally 0.7 to 1.2 g / cm ³ (JIS-P-8118). Furthermore, the base paper stiffness is preferably 20 to 200 g under the conditions specified in JIS-P-8143.

  A surface sizing agent may be applied to the surface of the base paper. As the surface sizing agent, the same sizing agent as that which can be added to the base paper can be used.

The pH of the base paper is preferably 5 to 9 when measured by a hot water extraction method defined in JIS-P-8113.

  Next, a recording medium having a color material fixing layer on a paper support having a solvent absorbing ability will be described.

  The colorant fixing layer according to the present invention has a void structure like the ink receiving layer provided on a dedicated ink jet recording paper, and is mainly formed from a small amount of a hydrophilic binder and fine particles.

  As the fine particles used in the present invention, inorganic fine particles are preferable because they give a higher color density and easily obtain fine particles having a smaller particle diameter.

  Hereinafter, inorganic fine particles preferably used in the colorant fixing layer according to the present invention will be described.

  As the inorganic fine particles, various known solid fine particles conventionally used in ink jet recording paper can be used.

  Examples of inorganic fine particles include, for example, light calcium carbonate, heavy calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc hydroxide, zinc sulfide, zinc carbonate, hydro White inorganic pigments such as talcite, aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, synthetic amorphous silica, colloidal silica, alumina, colloidal alumina, pseudoboehmite, aluminum hydroxide, lithopone, zeolite, magnesium hydroxide, etc. Can be mentioned.

  The inorganic fine particles may be used as primary particles in a state of being uniformly dispersed in the hydrophilic binder, or may be added in a state of being dispersed in the hydrophilic binder by forming secondary agglomerated particles. The latter is more preferable.

  The shape of the inorganic fine particles is not particularly limited in the present invention, and may be a spherical shape, a rod shape, a needle shape, a flat plate shape, or a bead shape. The inorganic fine particles preferably have an average particle size of 3 to 200 nm. When fine particles having an average particle diameter exceeding 200 nm are used, the glossiness of the recording paper is lowered, or the maximum density is lowered due to light scattering on the surface, and it becomes difficult to obtain a clear image. The lower limit of the average particle diameter is not particularly limited, but is preferably about 3 nm or more, particularly preferably 6 nm or more from the viewpoint of particle production. Particularly preferred inorganic fine particles have an average particle diameter of 10 to 100 nm.

  The average particle size of the inorganic fine particles described above is obtained by observing the cross section or surface of the particle itself or the coloring material fixing layer with an electron microscope, and determining the particle size of a large number of arbitrary particles (number average). As required. Here, each particle size is represented by a diameter assuming a circle equal to the projected area.

  As the inorganic fine particles according to the present invention, composite particles composed of inorganic fine particles and a small amount of an organic substance (which may be a low molecular compound or a high molecular compound) are substantially regarded as inorganic fine particles. In this case, the particle diameter of the highest order particle observed in the dry film is taken as the particle diameter of the inorganic fine particles.

  The mass ratio of the organic matter / inorganic fine particle in the composite particle of the inorganic fine particle and a small amount of organic substance is approximately 1/100 to 1/4.

  The inorganic fine particles according to the present invention are preferably low refractive index inorganic fine particles from the viewpoint of low cost and high reflection density, more preferably silica, and particularly by a vapor phase method. Synthesized silica or colloidal silica is preferred. Further, cation surface-treated gas phase method silica, cation surface-treated colloidal silica and alumina, colloidal alumina, pseudoboehmite and the like can also be used.

  Examples of the hydrophilic binder that can be used in the color material fixing layer according to the present invention include gelatin, polyvinyl pyrrolidone, polyethylene oxide, polyacrylamide, and polyvinyl alcohol, with polyvinyl alcohol being particularly preferable. Polyvinyl alcohol has an interaction with inorganic fine particles, has a particularly high holding power to inorganic fine particles, and is a polymer with relatively small humidity dependency such as hygroscopicity, and has a comparative shrinkage stress during coating and drying. Therefore, the suitability for cracking during coating and drying, which is the subject of the present invention, is excellent. Examples of the polybilyl alcohol preferably used in the present invention include, in addition to ordinary polyvinyl alcohol obtained by hydrolysis of polyvinyl acetate, modified polyvinyl alcohol having a terminal cation modified, anion-modified polyvinyl alcohol having an anionic group, and the like. Polyvinyl alcohol is also included. As polyvinyl alcohol obtained by hydrolyzing vinyl acetate, those having an average degree of polymerization of 300 or more are preferably used, and those having an average degree of polymerization of 1000 to 5000 are particularly preferably used. The saponification degree is preferably 70 to 100%, particularly preferably 90 to 100%. Examples of the cation-modified polyvinyl alcohol have primary to tertiary amino groups and quaternary ammonium groups in the main chain or side chain of the polyvinyl alcohol as described in JP-A-61-110483. Polyvinyl alcohol, which is obtained by saponifying a copolymer of an ethylenically unsaturated monomer having a cationic group and vinyl acetate.

The amount of inorganic fine particles used in the void-type color material fixing layer depends largely on the required ink absorption capacity, the porosity of the color material fixing layer, the type of inorganic fine particles, and the type of hydrophilic binder. The amount is usually 3 to 30 g, preferably 5 to 25 g per 1 m ^{2 of} the recording medium.

  In addition, the ratio of the inorganic fine particles and the hydrophilic binder used for fixing the void-type color material is usually 2: 1 to 20: 1 by mass ratio, and particularly preferably 3: 1 to 10: 1.

  Examples of the method for applying the colorant fixing layer include a roll coating method, a rod bar coating method, an air knife coating method, a spray coating method, a curtain coating method, or U.S. Pat. Nos. 2,761,419 and 2,761. No. 791, a slide bead coating method using an hopper, an extrusion coating method and the like are preferably used.

  When using the slide bead coating method, the viscosity of each coating solution at the time of coating is preferably in the range of 5 to 100 mPa · s, more preferably in the range of 10 to 50 mPa · s. Moreover, when using a curtain application | coating system, the range of 5-1200 mPa * s is preferable, More preferably, it is the range of 25-500 mPa * s.

Further, the viscosity at 15 ° C. of the coating solution is preferably 100 mPa · s or more, more preferably 100 to 30,000 mPa · s, further preferably 3,000 to 30,000 mPa · s, and most preferably 10 , 30,000 to 30,000 mPa · s.
As a coating and drying method, it is preferable that the coating liquid is heated to 30 ° C. or higher and coated, and then the temperature of the formed coating film is once cooled to 1 to 15 ° C. and dried at 10 ° C. or higher. . More preferably, the drying conditions are a wet bulb temperature of 5 to 50 ° C. and a film surface temperature of 10 to 50 ° C. Moreover, as a cooling method immediately after application | coating, it is preferable to carry out by a horizontal set system from a viewpoint of the formed coating-film uniformity.

  Moreover, it is preferable to have the process preserve | saved 24 hours or more and 60 days or less on the conditions of 35 degreeC or more and 70 degrees C or less in the manufacture process. The heating condition is not particularly limited as long as it is stored under conditions of 35 ° C. or more and 70 ° C. or less for 24 hours or more and 60 days or less. 2 days to 2 weeks at 40 ° C. or 1 to 7 days at 55 ° C. By performing this heat treatment, the curing reaction of the water-soluble binder can be promoted, or the crystallization of the water-soluble binder can be promoted, and as a result, preferable solvent permeability can be achieved.

  Next, the ink used in the present invention will be described.

  As the ink used in the inkjet recording method of the present invention, specifically, an aqueous ink composition (for example, an aqueous inkjet ink containing 10% by mass or more of water per total mass of the ink) can be preferably used.

  As the colorant used in the ink, a water-soluble dye, for example, an acid dye, a direct dye, a reactive dye, or a disperse dye, a pigment, or the like can be used. It is particularly preferable from the viewpoint of safety.

  As the pigment used in the ink according to the present invention, organic pigments such as insoluble pigments and lake pigments, carbon black and the like can be preferably used.

  The insoluble pigment is not particularly limited. Dioxazine, thiazole, phthalocyanine, diketopyrrolopyrrole and the like are preferable.

  Specific pigments that can be preferably used include the following pigments.

  Examples of the magenta or red pigment include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of the pigment for orange or yellow include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. And CI Pigment Yellow 138.

  Examples of the pigment for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

  For these pigments, a pigment dispersant may be used as necessary. Examples of pigment dispersants that can be used include higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates. Acid salt, naphthalene sulfonate, alkyl phosphate, polyoxyalkylene alkyl ether phosphate, polyoxyalkylene alkyl phenyl ether, polyoxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, polyoxyethylene fatty acid amide, amine Activators such as oxides, or styrene, styrene derivatives, vinyl naphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives Block copolymer comprising a monomer of the above, a random copolymer and can be exemplified salts thereof.

  As a method for dispersing the pigment, for example, various dispersing machines such as a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker can be used. It is also preferable to use a centrifugal separator or a filter for the purpose of removing the coarse particles of the pigment dispersion.

  The average particle diameter of the pigment particles in the pigment ink is selected in consideration of stability in the ink, image density, glossiness, light resistance, etc. In addition, the image forming method of the present invention improves glossiness, textures. It is preferable to select the particle size as appropriate from the viewpoint of improvement.

  As the ink used in the inkjet recording method of the present invention, a water-soluble organic solvent can be used in combination as necessary. Examples of the water-soluble organic solvent that can be used in the present invention include alcohols (for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pentanol, hexanol, cyclohexanol, benzyl). Alcohol), polyhydric alcohols (for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol Etc.), polyhydric alcohol ethers (for example, ethylene glycol monomethyl ether, ethylene glycol) Ether monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether , Triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc.), amines (for example, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, mole) Phosphorus, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (eg, formamide, N, N-dimethylformamide, N , N-dimethylacetamide, etc.), heterocyclic rings (for example, 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, etc.), sulfoxides ( For example, dimethyl sulfoxide etc.), sulfones (for example, sulfolane etc.), urea, acetonitrile, acetone etc. are mentioned. These water-soluble organic solvents may be used alone or in combination.

  Further, in the ink according to the present invention, the functions are different between a solvent having a plurality of hydrogen bonding sites and a solvent having only one hydrogen bonding site. The hydrogen bonding site in the present invention refers to a functional group generally having hydrogen bonding properties such as a hydroxyl group and an amide group. Examples of organic solvents having a plurality of hydrogen bonding sites (also referred to as multipolar solvents) include ethylene glycol, glycerin, diethylene glycol, and triethylene glycol. On the other hand, examples of the solvent having only one hydrogen bonding site (also referred to as a monopolar solvent) include diethylene glycol monoethyl ether, dipropylene glycol monomethyl ether, and tetraethylene glycol monomethyl ether.

  Examples of the surfactant preferably used in the ink according to the present invention include anionic surfactants such as dialkylsulfosuccinates, alkylnaphthalenesulfonates and fatty acid salts, polyoxyethylene alkyl ethers, and polyoxyethylene alkyl. Nonionic surfactants such as allyl ethers, acetylene glycols, polyoxyethylene / polyoxypropylene block copolymers, and cationic surfactants such as alkylamine salts and quaternary ammonium salts. In particular, an anionic surfactant and a nonionic surfactant can be preferably used.

  Next, the ink jet printer of the present invention will be described.

In the ink jet printer of the present invention, as in the ink jet recording method described above, the ink jet printer provided with an ink jet recording head for recording an image by ejecting an ink containing at least water and a colorant onto a recording medium. The ink jet recording head has a nozzle number of 5000 or more, a drive frequency of 20 kHz or more, and ejects the ink onto the recording medium with an ink droplet amount of 2.5 pl or less per droplet. Or a water-soluble organic solvent component having a plurality of water- and hydrogen-bonding sites in an image area, which is a recording medium having a color material fixing layer on a paper support having a solvent absorption capability, and the amount of ink adhering to the maximum The image is recorded so that the total mass of the material is 0.5 g / m ² or more and 15 g / m ² or less.

  The ink jet printer of the present invention includes an ink jet recording head having a nozzle number of 5000 or more, a drive frequency of 20 kHz or more, and capable of ejecting the ink with an ink droplet amount of 2.5 pl or less per droplet.

  The ink jet recording head that can be used in the present invention may be an on-demand system or a continuous system. As a discharge method, any discharge method such as an electro-mechanical conversion method, an electric-thermal conversion method, or the like may be used.

  As a recording method of an ink jet printer, a serial head method and a line head method are mainly known. However, in recent years, an improvement in recording speed has been demanded, and an ink jet printer having high-speed printing suitability is desired. In general, a printer using a serial head method has a limit in improving the recording speed because the head needs to reciprocate. On the other hand, if the line head system has a recording medium width, the head can be fixed, and the printing speed can be dramatically improved.

  The outline of the line head type ink jet printer will be described below with reference to the drawings.

  In the ink jet printer of the present invention, a line head type ink jet recording head (hereinafter also referred to as a recording head or a head) used when performing image formation by ejecting the ink according to the present invention is an on-demand system. Also, as the discharge method, the above-mentioned electro-mechanical conversion method (single cavity type, double cavity type, bender type, piston type, shear mode type, shared wall type, etc.), electro-thermal conversion method (thermal ink jet type, bubble type) Any type of discharge method such as a jet (registered trademark) type may be used, but a head using a piezo method is preferable, and the share mode method is particularly suitable for performing high-speed and stable discharge over a long period of time. Is preferable.

  FIG. 5 is a perspective view showing an example of a main part of an ink jet printer using a line head.

  In FIG. 5, reference numeral 52 denotes a line head installed in the ink jet printer 1, which is connected to the control board 59 by a flexible cable 55 drawn from the line head 52. The recording medium P is held by the back roll 58 and is conveyed at a constant speed in the direction indicated by the arrow Y in the drawing by a paper conveyance mechanism (not shown) that conveys the recording medium P. The line head 52 is a holding unit by the back roll 58 and is disposed so as to face the surface PS of the recording medium P as illustrated. Although hidden in the drawing, an ink discharge port described later is provided on the surface of the line head 52 facing the surface PS of the recording medium P, and an image signal from the control substrate 59 is output from the ink discharge port. Accordingly, ink is ejected onto the recording medium P by one line at a time, and an image is formed on the recording medium P in combination with the conveyance of the recording medium P in the arrow Y direction.

  FIG. 6 is a schematic perspective view having a partially broken surface of the line head used in the present invention.

  The line head 52 is formed by bonding the lower substrate 1b and the upper substrate 1c made of lead zirconate titanate, which is a piezoelectric material, with an adhesive 6. The lower substrate 1b and the upper substrate 1c are polarized in opposite directions. A plurality of elongated grooves 2 are formed across the upper substrate and the lower substrate. Thereby, a plurality of parallel partition walls 4 and grooves 2 are formed.

  An electrode film 3 is provided on the inner surface of the plurality of grooves by vapor deposition. After attaching the electrode film 3 to the groove 2, a part of the upper surface of the substrate F is stepped to form a stepped portion 35. The lid 8 is bonded to the upper surface of the partition wall 4 with the adhesive 6, and the sealing groove 25 is attached to the end surface of the partition wall 4 with the adhesive. The surface of the electrode film 3 formed on the inner surface of the plurality of grooves is coated with an insulating film 17 such as parylene, and the surface of the insulating film 17 is hydrophilized by oxygen plasma treatment. The nozzle plate 10 having the nozzle holes 11 is adhered to the opening end face of the groove 2 by the same adhesive 6 to form the ink chamber 9 in every other groove 2. Nozzle holes are provided corresponding to the ink chambers. A common groove 5 is carved in the upper part of the lid 8 and a hole 12 for communicating with each ink chamber is provided. The groove 2 has both a nozzle hole 11 and a communication hole 12. An upper plate 14 having an ink supply hole 15 is bonded to the upper portion of the lid 8 with an adhesive 6 so as to cover the upper portion of the common groove 5.

  Each of the electrode films is connected to the lead wiring 7 exposed at the step portion 35 of the lid 8.

  Ink is supplied from the ink supply holes 15 to fill the ink chambers 9 formed in the parallel grooves 2 in FIG.

In the ink jet recording head (line head system) according to the present invention, the nozzle hole 11 is 5000 or more, the drive frequency is 20 kHz or more, and the ink droplet amount is 2.5 pl or less per droplet. On the water-absorbing recording medium, the total mass of the water-soluble organic solvent component having a plurality of water and hydrogen bonding sites in the image area where the amount of ink adhering is maximized is 0.5 g / m ² or more and 15 g / m ^2. By forming an image under the following conditions, curling of the recorded matter can be suppressed and handling of the recorded matter can be improved.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Example 1
<Preparation of ink>
[Preparation of Ink 1]
<Preparation of pigment dispersion 1>
Carbon black 30% by mass
Styrene-acrylic acid copolymer (molecular weight 7,000, acid value 150) 10% by mass
Glycerin 20% by mass
Ion exchange water 40% by mass
The above additives were mixed and dispersed using a horizontal bead mill (System Zetamini manufactured by Ashizawa Co., Ltd.) filled with 60% by volume of 0.3 mm zirconia beads to obtain pigment dispersion 1. The average particle size of the obtained black pigment was 75 nm.

<Preparation of ink>
Pigment dispersion 1 30% by mass
Ethylene glycol 10% by mass
Diethylene glycol 10% by mass
Surfactant (Surfinol 465 Nissin Chemical Industry Co., Ltd.) 0.1% by mass
Ion-exchanged water 49.9% by mass
The above compositions were mixed, stirred, and filtered through a 1 μm filter to prepare ink 1. The average particle diameter of the pigment in the ink 1 was 85 nm, and the surface tension γ was 35 mN / m. Further, the water-soluble organic solvent having a plurality of water and hydrogen bonding sites in the ink 1 was 88%.

[Preparation of ink 2]
<Preparation of pigment dispersion 2>
Carbon black 30% by mass
Styrene-acrylic acid copolymer (molecular weight 8,000, acid value 140) 10% by mass
Glycerin 20% by mass
Ion exchange water 40% by mass
The above additives were mixed and dispersed using a horizontal bead mill (System Zetamini manufactured by Ashizawa Co., Ltd.) filled with 60% by volume of 0.3 mm zirconia beads to obtain pigment dispersion 2. The average particle size of the obtained black pigment was 75 nm.

<Preparation of ink>
Pigment dispersion 2 30% by mass
Ethylene glycol 10% by mass
Diethylene glycol 10% by mass
Surfactant (Surfinol 465 Nissin Chemical Industry Co., Ltd.) 0.1% by mass
Ion-exchanged water 49.9% by mass
The above compositions were mixed, stirred, and filtered through a 1 μm filter to prepare ink 2. The average particle diameter of the pigment in the ink 2 was 85 nm, and the surface tension γ was 35 mN / m.

<< Inkjet image formation >>
Using the ink jet recording head shown in FIG. 6, as shown in Table 1, the ink-jet nozzle prepared above was applied to an ink jet recording apparatus having a width of 330 mm with a nozzle density per color of 2400 dpi or 2000 dpi as shown in Table 1. 2 is loaded into each cartridge, and A4 size plain paper (first class paper manufactured by Konica Minolta Business Technology) and a recording medium provided with a color material fixing layer on an A4 size paper support (manufactured by Oji Paper Co., Ltd.) First, a solid black image is formed using ink 1 under the conditions shown in Table 1 (ink droplet amount, printing density, ink adhesion amount, amount of applied multipolar solvent), leaving a 1 cm edge for POD gloss coating). The amount of ink required to do this (this is called 100% ink placement) to form an image, and then Further printed superimposed black solid image with 100% ink ejection rate similarly using the ink 2 on the image, a recorded material 1-35 200% total ink ejection rate.

  When obtaining an image that requires a resolution higher than the nozzle density, the recording medium was slid as much as necessary, and the image was formed so as not to return the paper in the transport direction. The ink supply system is composed of an ink tank, a supply pipe, a front chamber ink tank immediately before the recording head, a pipe with a filter, and a piezo head, and each ink droplet amount is 0.03 to 4 pl described in Table 1. Printing was performed by discharging at a droplet velocity of about 8 m / sec under voltage loading conditions. Each recording medium was at room temperature (23 ° C.). The above image formation was performed in an environment of 23 ° C. and 55% RH. In the present invention, dpi represents the number of dots per 2.54 cm.

<Evaluation of recorded materials>
Each of the produced recorded materials was evaluated according to the method described below.

[Evaluation of curl characteristics]
Each printed matter is left on a horizontal table for 10 minutes and 1 day under the environmental conditions of 23%, 20%, 55% and 80% relative humidity. The average value was measured as the curl amount, and the curl characteristics were evaluated according to the following criteria.

A: The curl amount is 10 mm or less in any time and environment, and there is no problem. O: The curl amount may be in the range of 10 mm to 15 mm depending on the standing time and the environment, but there is no problem in practical use. : Curling amount is 15 mm or more depending on the standing time and environment, and practically it is a level that requires temperature and humidity management for printing and document storage. ×: Curling amount is 15 mm or more under all conditions regardless of the environment. Practical, printing and document storage are difficult [Evaluation of cockling resistance]
The surface state of the overprinted black solid image was visually observed, and the cockling resistance was evaluated according to the following criteria.

◎: Cockling is not observed at all ○: Extremely weak cockling is observed, but the quality is acceptable for practical use ×: Strong cockling is generated, and the quality is not practical [Evaluation of printing speed]
According to the above printing method, the number of output sheets per minute of A4 size black solid print was obtained, and the printing speed was evaluated according to the following criteria.

◎ The number of output sheets per minute is 40 or more, which is not inferior to the system of copying machines, etc. △: The number of output sheets per minute is 30 or more and less than 40, approximating to the system of copying machines, etc. X: The number of output sheets per minute is less than 30, and the print speed is inferior to that of a system such as a copier. [Measurement of image density]
For the black solid image created above, the density is measured using an optical densitometer (X-Rite 938 manufactured by X-Rite), the maximum reflection density (Dmax) is measured, and the image density is evaluated according to the following criteria. went.

A: Image density is 1.6 or higher and very good. B: Image density is in the range of 1.4 or higher and lower than 1.6. X: Image density is lower than 1.4. Low image density obtained compared to other systems (evaluation of output stability)
Using the above ink jet printer, after discharging for 1 minute continuously at 23 ° C. and under relative environmental conditions of 20%, 55% and 80%, leaving the nozzle uncovered for 30 seconds and then again Ejection was performed, the ink ejection state at that time was visually observed, and ejection stability was evaluated according to the following criteria.

◎: Cleaning is not necessary for re-ejecting in all environments, and all nozzles are stably discharged ○: Ejecting from all nozzles by cleaning in all environments ×: Already bent at the time of continuous emission Table 2 shows the results obtained as described above.

  As is clear from the results shown in Table 2, the recorded matter of the present invention printed on a paper substrate according to the ink jet recording method having the configuration defined in the present invention has curl characteristics and cockling resistance compared to the comparative example. It can be seen that an excellent and high image density is obtained, and that the printing speed and the emission stability during printing are excellent.

Example 2
<< Inkjet image formation >>
According to the inkjet printer and printing method described in Example 1, the colorant concentration and ink droplet volume of the ink described in Example 1 on A4 size plain paper (first class paper manufactured by Konica Minolta Business Technology) The recorded matter 36 to 55 was prepared by changing the nozzle density, the ink application amount, the color material application amount, and the driving rate as shown in Table 3.

<Evaluation of recorded materials>
Each of the produced recorded materials was evaluated according to the method described below.

(Measurement of image density)
For the black solid image created above, the density is measured using an optical densitometer (X-Rite 938 manufactured by X-Rite), the maximum reflection density (Dmax) is measured, and the image density is evaluated according to the following criteria. went.

SS: An extremely high image density was obtained when the image density was 1.7 or more. S: An extremely high image density was obtained when the image density was 1.6 or more and less than 1.7. A: The image density was 1. A substantially good image density was obtained at 5 or more and less than 1.6. B: The image density is 1.4 or more and less than 1.5, and the image density is practically acceptable. C: The image density is 1. Less than 4 and undesirably practical image density [Evaluation of beading resistance]
The occurrence of mottled unevenness in the image caused by the ink droplet bias on the surface of the black solid image was visually observed while changing the evaluation distance, and beading resistance was evaluated according to the following criteria.

SS: Even when the observation distance is 10 cm, no beading is observed. S: The occurrence of beading is slightly observed at the observation distance of 10 cm. Generation of bedding is recognized, but the quality is acceptable in practical use. B: Generation of beading is observed even at an observation distance of 30 cm, and this is a quality that is problematic in practice. C: Clear beading even at an observation distance of 40 cm or more. The quality is unacceptable for practical use. [Evaluation of output stability]
Using the above ink jet printer, after discharging for 1 minute continuously at 23 ° C. and under relative environmental conditions of 20%, 55% and 80%, leaving the nozzle uncovered for 30 seconds and then again Ejection was performed, the ink ejection state at that time was visually observed, and ejection stability was evaluated according to the following criteria.

SS: There is no need for cleaning in order to re-discharge under the whole environment, and it was discharged stably from all the nozzles. S: In every environment, it was discharged stably from all the nozzles by one cleaning operation. A: Cleaning in a low humidity environment. B: Stable re-ejection by performing multiple times B: Re-ejection by multiple times of cleaning operation in all environments C: Bending of emission has already occurred during continuous emission, and stable even after cleaning Table 3 shows the evaluation results obtained as described above.

  As is apparent from the results shown in Table 3, the recorded matter of the present invention prepared according to the inkjet recording method of the present invention having the configuration defined in the present invention has a higher image degree than the comparative example, and It can be seen that the beading resistance is excellent. In addition, it can be seen that the inkjet recording method of the present invention is excellent in emission stability.

It is a figure which shows an example of the mechanism of the curl generation at the time of carrying out low speed printing on a paper base material. It is a figure which shows an example of the mechanism of the curl generation | occurrence | production at the time of high-speed printing on a paper base material. It is a schematic diagram showing an example of behavior when a large-sized pigment ink droplet landed on a paper recording medium. It is a schematic diagram showing an example of behavior when a small-sized pigment ink droplet landed on a paper recording medium. It is a perspective view which shows an example of the principal part of the inkjet printer which uses a line head. It is a schematic perspective view which has the partially broken surface of the line head used for this invention.

Explanation of symbols

D, D ′, D ″ Ink droplet S Ink solvent H, G, I, J Pigment 1 Inkjet printer 9 Ink chamber 11 Nozzle hole 15 Ink supply hole 52 Line head 55 Flexible cable 58 Back roll P Recording medium (plain paper)

Claims (8)

In an ink jet recording method for recording an image by discharging an ink containing at least water and a colorant onto a recording medium from an ink jet recording head.
The recording medium is a plain paper or a recording medium having a color material fixing layer on a paper support having a solvent absorption capability,
The inkjet recording head has a nozzle number of 5000 or more, a driving frequency of 20 kHz or more, and an ink droplet amount per droplet ejected from the inkjet recording head is 2.5 pl or less,
The total mass of the water-soluble organic solvent component having a plurality of water and hydrogen bonding sites in the image area where the ink adhesion amount is maximum is 0.5 g / m ² or more and 15 g / m ² or less. Inkjet recording method. The total mass of the water-soluble organic solvent component having a plurality of water and hydrogen bonding sites in the image area where the ink adhesion amount is maximum is 1.0 g / m ² or more and 10 g / m ² or less. The inkjet recording method according to claim 1. 3. The ink jet recording method according to claim 1, wherein the amount of ink droplets ejected from the ink jet recording head is 0.3 pl or more and 1.0 pl or less. The inkjet recording method according to any one of claims 1 to 3, wherein the content of the colorant in the ink is 7 mass% or more and 15 mass% or less. In an ink jet printer provided with an ink jet recording head for recording an image by discharging an ink containing at least water and a colorant onto a recording medium,
The inkjet recording head has a nozzle number of 5000 or more, a drive frequency of 20 kHz or more, and ejects the ink onto a recording medium with an ink droplet amount of 2.5 pl or less per droplet,
The recording medium is a plain paper or a recording medium having a color material fixing layer on a paper support having a solvent absorption capability,
Image recording so that the total mass of water-soluble organic solvent components having a plurality of water and hydrogen bonding sites in the image area where the ink adhesion amount is maximum is 0.5 g / m ² or more and 15 g / m ² or less. An ink jet printer characterized by the above. The total mass of the water-soluble organic solvent component having a plurality of water and hydrogen bonding sites in the image area where the ink adhesion amount is maximum is 1.0 g / m ² or more and 10 g / m ² or less. The inkjet printer according to claim 5. The ink jet printer according to claim 5 or 6, wherein an ink droplet amount per droplet ejected from the ink jet recording head is 0.3 pl or more and 1.0 pl or less. 8. The inkjet printer according to claim 5, wherein a content of the colorant in the ink is 7% by mass or more and 15% by mass or less.

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