JP2017132973A - Ink, ink cartridge, and image recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink that can achieve both optical density and fixability at a high level as well as that can record an image in which the feathering and strike-through are suppressed.SOLUTION: Provided is an ink containing a pigment, a water-soluble organic solvent and a surfactant, and having a viscosity at 25°C of 5 mPa s or more. The static surface tension of this ink measured at 25°C by the Wilhelmy method is 30.5 mN/m or more and 35.0 mN/m or less. Further, the dynamic surface tension of this ink measured at 25°C by the maximum bubble pressure method is 30.5 mN/m or more and 37.0 mN/m or less at a lifetime of 150 m sec.SELECTED DRAWING: None

Description

  The present invention relates to an ink, an ink cartridge, and an image recording method.

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

  In the case of a printer for home use or office use, a printing speed is limited because a short serial type head scans a recording surface of a recording medium a plurality of times to perform printing. On the other hand, a long line type head has been developed in recent years. If a recording apparatus such as a printer equipped with such a line type head is used, an image corresponding to the head width can be recorded by one scanning (one pass). For this reason, the ink jet recording method is beginning to be adopted also in the commercial printing industry that requires printing at higher speed.

  In the commercial printing industry, it is necessary to be able to print large quantities at a lower cost. For this reason, it is hoped that high-quality images can be recorded not only on inexpensive and thin paper that is generally called printing paper but also on thin paper that does not have an ink-receiving layer called plain paper. It is rare.

  In image recording on plain paper, when the ink applied to the recording medium comes into contact with a member such as a conveyance roller in the recording apparatus, the fixability indicating the time until the member is not soiled, and the optical density of the image are: Traditionally, it has been an important design item. On the other hand, the inks sold in the market are so-called super-penetrating ink (ink having high penetrability to the recording medium) that emphasizes fixability, and so-called overlay ink (recording medium) that emphasizes the optical density of the image. Ink with low penetrability into ink).

  Super penetrating ink contains a lot of penetrating solvents (glycol ether, diol, etc.), and ink droplets applied to the surface of the recording medium (plain paper) penetrate into the gaps between the cellulose fibers that make up the plain paper. It is characterized by a rapid penetration time in milliseconds.

  In the overlay ink, ink droplets applied to the surface of the recording medium penetrate into the cellulose fiber itself, and the penetration time into the recording medium is on the order of several seconds. For this reason, since the color material remains on the relatively surface of the recording medium, the optical density can be increased efficiently. Japanese Patent Application Laid-Open No. H10-228561 describes an overlay ink that fixes a pigment near the surface of plain paper.

JP-A-5-179183

  The above-mentioned super-penetrating ink can be said to be suitable for high-speed recording because it penetrates quickly into a recording medium (plain paper). On the other hand, there are problems that the ink bleeds along the paper fibers (hereinafter also referred to as feathering) and that the optical density of the image tends to be low. The reason why the optical density of the image tends to be low is considered to be because the color material penetrates from the surface of the recording medium to the back. In order to increase the optical density of the image in high-speed recording, it is conceivable to increase the density of the color material in the ink. However, in the ink for inkjet, when the concentration of the color material in the ink is increased, the color material is likely to be deposited near the nozzle opening in the recording apparatus. As a result, an undischarge phenomenon that makes it impossible to discharge ink is likely to occur, and there is a limit to increasing the density of the color material in the ink. In addition, when super-penetrating ink is used, there is a possibility of so-called back-through, in which the image can be seen through from the back side of the recording medium. It is difficult to improve the concentration.

On the other hand, the present inventors have examined that an overlay ink such as the ink described in Patent Document 1 can record an image with a high optical density, but has a low fixability and is suitable for high-speed recording. It turned out to be an insufficient level. For example, in order to obtain sufficient color on plain paper, it is necessary to apply about 1 mg of ink per 1 cm ^{2 of} plain paper. However, when printing on one pass is performed at a high speed of 75 m / min or more on the plain paper. In some cases, the conveying roller in contact immediately after recording was soiled.

  Accordingly, an object of the present invention is to provide an ink capable of recording an image in which the optical density and the fixability are compatible at a high level and the feathering and the back-through are suppressed. Another object of the present invention is to provide an ink cartridge and an image recording method using the ink.

  The above object is achieved by the present invention described below. That is, according to the present invention, an ink containing a pigment, a water-soluble organic solvent, and a surfactant and having a viscosity at 25 ° C. of 5 mPa · s or more and measured at 25 ° C. by the Wilhelmy method. Tension is 30.5 mN / m or more and 35.0 mN / m or less, and dynamic surface tension measured at 25 ° C. by the maximum bubble pressure method is 30.5 mN / m or more and 37.0 mN / m or less at a lifetime of 150 msec. There is provided an ink characterized in that.

  According to the present invention, it is possible to provide an ink capable of recording an image in which both the optical density and the fixability are compatible at a high level and the feathering and the back-through are suppressed. In addition, according to the present invention, it is possible to provide an ink cartridge and an image recording method using the above ink.

It is a schematic diagram which shows an example of the image recording apparatus used for the image recording method of this invention. It is a graph which shows an example of the absorption curve for demonstrating the absorption coefficient Ka of the water of a recording medium.

  Embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments. Various physical property values in this specification are values at normal temperature (25 ° C.) unless otherwise specified.

  The inventors of the present invention have found that when the recording medium is transported at a high speed of 75 m / min or more and one pass recording is performed using the superposition-based ink, the ink fixing property is low, resulting in the inside of the recording apparatus. We paid attention to the problem that the transport rollers of the camera become dirty. In order to improve the fixability of the ink on the recording medium, the inventors of the present invention need to reduce the ink permeation time to the recording medium to about 1 second, which is shorter than the conventional overlay ink. Thought.

  On the other hand, inkjet heads used for the above-described high-speed recording are commercially available from, for example, April, Scitex Vision (Hewlett Packard), Spectra, Xaar, Ricoh, Kyocera, and Seiko. In these inkjet heads, it is the mainstream that ink in a range of 5 mPa · s to 15 mPa · s is usually used at 25 ° C. Such a relatively high-viscosity ink has an advantage that coalescence hardly occurs on the recording medium in addition to the advantage of high ejection stability. In coalescence, ink droplets immediately after ink is applied to the recording medium come into contact with each other, and the spread of ink, that is, the bleeding rate is reduced. Become. In high-speed recording, it is essential that ink droplets are concentrated and fixed on a recording medium in a short time. Therefore, in order to prevent coalescence, the viscosity of the ink is preferably 5 mPa · s or more. . However, since such relatively high-viscosity ink is difficult to penetrate into the recording medium, the ink penetration time into the recording medium is shortened to about 1 second, which is shorter than the conventional low-viscosity type ink. Requires a more advanced penetration time control technique than before.

  Conventionally, static surface tension is known as a physical property related to control of the permeation time of ink into a recording medium. The present inventors have used various solvents and surfactants to adjust the static surface tension of the ink in order to achieve both the optical density and the fixability of the image, thereby adjusting the ink droplet recording medium (plain paper). ) To increase the permeability to cellulose fibers. As a result, it was found that inks having a permeation time of about 1 second required for high-speed recording have different optical densities of images even with the same static surface tension.

  Therefore, the present inventors have conducted intensive studies, and considered that it is important to control the dynamic surface tension in addition to the static surface tension of the ink, and further studied. As a result, if the dynamic surface tension of the ink within a short time is adjusted to a specific range suitable for high-speed recording, it is excellent in fixability to a recording medium even with an overlaid ink and prevents the conveyance roller from being stained. It has been found that an image with a high optical density can be obtained.

<Ink>
That is, the ink of the present invention contains a pigment, a water-soluble organic solvent, and a surfactant, and has a viscosity at 25 ° C. of 5 mPa · s or more. The ink of the present invention has a static surface tension of 30.5 mN / m or more and 35.0 mN / m or less, and a dynamic surface tension of 30.5 mN / m or more and 37.0 mN / m at a lifetime of 150 msec. It is as follows. Static surface tension is a value measured at 25 ° C. by the Wilhelmy method. The dynamic surface tension is a value measured at 25 ° C. by the maximum bubble pressure method.

  With the ink of the present invention having the above-described configuration, it is possible to record an image in which the optical density and the fixability are compatible at a high level and the back-through is suppressed. The mechanism for obtaining the effect is considered as follows.

  When the ink droplets of the present invention are applied to a recording medium (plain paper), the ink penetrates into the cellulose fibers themselves constituting the recording medium. It has been considered that the penetration of ink droplets into the cellulose fiber itself as seen in conventional overlay inks is influenced by the static surface tension of the ink droplets. However, considering the adaptability to high-speed recording, in order to set the ink droplet permeation time to the recording medium to about 1 second, the dynamic surface within a short time immediately after the ink droplet is applied to the recording medium. It is necessary to pay attention to tension.

  On the surface of the ink droplet ejected from the inkjet nozzle and applied to the recording medium, the orientation of the surfactant in the ink droplet collapses due to the impact and deformation of the droplet shape when applied to the recording medium. For this reason, when the ink droplet is applied to the recording medium, the dynamic surface tension of the droplet is considerably higher than the static surface tension. Thereafter, the degree of orientation of the surfactant on the droplet surface is increased, the dynamic surface tension of the ink is decreased, and the penetration of the ink into the recording medium starts. As described above, the overlay ink suitable for high-speed recording needs to penetrate in about 1 second after being applied to the recording medium. For this purpose, the dynamic surface tension of the ink needs to drop rapidly immediately after the ink is applied to the recording medium, and needs to be sufficiently low in 150 milliseconds after the ink is applied to the recording medium. is there.

  On the other hand, when the dynamic surface tension of the ink in 150 milliseconds after the ink is applied to the recording medium is a high value exceeding 37.0 mN / m, it takes time for the ink to penetrate into the recording medium, and the fixing property is increased. Will fall. On the other hand, if the dynamic surface tension of the ink at 150 milliseconds after the ink is applied to the recording medium is so low as to be less than 30.5 mN / m, depending on the type of paper, the ink may be in gaps between the cellulose fibers. It penetrates. Therefore, in this case, a sufficient optical density cannot be obtained as in the case of conventional super-penetrating ink. Therefore, in addition to the static surface tension, it is necessary to design the ink while paying attention so that the dynamic surface tension at 150 milliseconds after the ink is applied to the recording medium is in an appropriate range.

  As described above, an ink containing a pigment, a water-soluble organic solvent, and a surfactant, having a viscosity at 25 ° C. of 5 mPa · s or more, and having a specific static surface tension and dynamic surface tension is used. That is, the static surface tension measured by the Wilhelmy method is 30.5 mN / m or more and 35.0 mN / m or less, and the dynamic surface tension measured by the maximum bubble pressure method is 30.5 mN / m at a lifetime of 150 msec. An ink having a viscosity of 37.0 mN / m or less is used. With this ink, the pigment can remain in the vicinity of the surface of the recording medium. As described above, each component in the ink synergistically effects, so that it is possible to record an image in which the optical density and the fixing property are compatible at a high level and the show-through is suppressed. Therefore, the ink of the present invention can be suitably used for an ink jet recording apparatus capable of performing high-speed recording at a recording medium conveyance speed of 75 m / min or more, and also can print an image in one pass at the conveyance speed. It can be suitably used for a recordable ink jet recording apparatus. Furthermore, the ink of the present invention can be suitably used for a high-speed continuous form printer.

(Ink physical properties)
The viscosity of the ink of the present invention at 25 ° C. is 5 mPa · s or more. When the viscosity of the ink is 5 mPa · s or more, the ink has high ejection stability, and coalescence (condensation) hardly occurs on the recording medium. From this viewpoint, the viscosity of the ink at 25 ° C. is preferably 5.5 mPa · s or more. The upper limit of the viscosity at 25 ° C. of the ink is preferably 17.0 mPa · s or less, more preferably 15.0 mPa · s or less, from the viewpoint of continuous ejection stability of the ink. In the present specification, the viscosity of the ink is a value measured at 25 ° C. using a rotary viscometer.

  The static surface tension measured at 25 ° C. by the Wilhelmy method (also referred to as plate method or vertical plate method) of the ink of the present invention is 30.5 mN / m or more and 35.0 mN / m or less. If the static surface tension of the ink exceeds 35.0 mN / m, the ink droplets applied to the recording medium may be reduced without spreading. Further, when the static surface tension of the ink is less than 30.5 mN / m, a phenomenon that ink bleeds along the paper fibers (so-called feathering) may occur in some types of plain paper. There is. From the viewpoint of obtaining an image in which feathering is further suppressed, the static surface tension of the ink is preferably 31.0 mN / m or more.

  The dynamic surface tension measured at 25 ° C. by the maximum bubble pressure method of the ink of the present invention is 30.5 mN / m or more and 37.0 mN / m or less at a lifetime of 150 msec. If the dynamic surface tension of the ink is less than 30.5 mN / m, breakthrough is likely to occur. From the viewpoint of obtaining an image in which show-through is further suppressed, the dynamic surface tension of the ink is preferably 31.0 mN / m or more, and more preferably 31.5 mN / m or more. If the dynamic surface tension of the ink exceeds 37.0 mN / m, the penetration time of the ink into the plain paper becomes long in some of the various plain papers, and the image fixability is poor. There is. From the viewpoint of obtaining an image having high fixability, the dynamic surface tension of the ink is preferably 36.0 mN / m or less, and more preferably 35.0 mN / m or less.

  As described above, the ink of the present invention contains a pigment, a water-soluble organic solvent, and a surfactant. Next, components constituting the ink of the present invention will be described.

(Pigment)
Examples of the type of pigment (pigment particles) include inorganic pigments such as carbon black and organic pigments, and any known pigment that can be used for ink can be used. As the pigment, pigments that can be dispersed in water such as self-dispersed pigments and resin-dispersed pigments described below are preferable.

(Self-dispersing pigment)
The self-dispersing pigment means a pigment in which at least one hydrophilic group is bonded to the surface of the pigment particle directly or through another atomic group (—R—). Examples of the hydrophilic group include a carboxylic acid group (—COOM), a sulfonic acid group (—SO ₃ M), and a phosphonic acid group (—PO ₃ HM, —PO ₃ M ₂ ). “M” in the above formula is preferably a hydrogen atom, an alkali metal, ammonium, or organic ammonium. Compared with the case where “M” in the above formula is a hydrophilic group which is ammonium or organic ammonium, the ink ejection stability is improved, so that “M” is an alkali metal such as lithium, sodium or potassium. More preferred is a hydrophilic group.

  Examples of the other atomic group (—R—) include an alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, and a substituted or unsubstituted naphthylene group. A plurality of phosphonic acid groups may be bonded to the carbon atom of the other atomic group (—R—). As the self-dispersing pigment, it is more preferable to use a self-dispersing pigment (bisphosphonic acid-based self-dispersing pigment) in which bisphosphonic acid groups are bonded directly or via other atomic groups to the surface of the pigment particles. In addition, the form of the hydrophilic group in the ink may be any form in which a part of the hydrophilic group is dissociated or a part of the hydrophilic group is dissociated.

  Suitable self-dispersing pigments include pigments (self-dispersing inorganic pigments) in which hydrophilic groups are bonded directly or via other atomic groups to the surface of inorganic pigment particles such as carbon black. Examples of the self-dispersing inorganic pigment (self-dispersing carbon black) in which the inorganic pigment is carbon black include CAB-O-JET200, 300, 352K, 400 (manufactured by Cabot) under the trade name.

  Examples of suitable self-dispersing pigments include pigments (self-dispersing organic pigments) in which hydrophilic groups are bonded directly or via other atomic groups to the surface of organic pigment particles. Examples of the pigment type in the self-dispersing organic pigment include a cyan pigment, a magenta pigment, and a yellow pigment. As the cyan pigment, a copper phthalocyanine pigment is preferable. I. Pigment Blue 1, 2, 3, 15, 15: 2, 15: 3, 15: 4, 16, 22, 60, and the like. Examples of the self-dispersing cyan pigment include CAB-O-JET250C, 450C, and 554B (above, manufactured by Cabot) under the trade name. The magenta pigment is preferably a quinacridone pigment. I. Pigment Red 5, 7, 12, 48, 48: 1, 57, 112, 122, 123, 146, 168, 184, 202, 207 and the like. Examples of self-dispersing magenta pigments include CAB-O-JET260M, 265M, and 465M (above, manufactured by Cabot) under the trade names. As the yellow pigment, an azo pigment is preferable. I. Pigment Yellow 12, 13, 14, 16, 17, 74, 83, 93, 95, 97, 98, 114, 128, 129, 151, 154 and the like. Examples of the self-dispersing yellow pigment include CAB-O-JET270Y, 470Y, and 740Y (above, manufactured by Cabot) by trade names.

  When a self-dispersing pigment is used as the pigment, the content of the self-dispersing pigment in the ink is preferably 0.1% by mass or more and 10.0% by mass or less based on the total mass of the ink, and 1.0% by mass. More preferably, it is 7.0 mass% or less. If the content of the self-dispersing pigment in the ink is 0.1% by mass or more (more preferably 1.0% by mass or more), the effect of improving the optical density of the image can be sufficiently obtained. Further, if the content of the self-dispersing pigment in the ink is 10.0% by mass or less (more preferably 7.0% by mass or less), ink ejection stability can be sufficiently obtained.

(Resin dispersion pigment)
The resin dispersed pigment means a pigment dispersed by a resin dispersant (resin dispersant) different from the resin particles. As the resin dispersant, any of those conventionally used for ink (preferably ink for inkjet) can be used. The resin dispersant is preferably water-soluble. In the present specification, “the resin is water-soluble” means that when the resin is neutralized with an alkali equivalent to the acid value, the resin has no particle size in the aqueous medium.

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

  The weight average molecular weight in terms of polystyrene of the resin dispersant, measured by gel permeation chromatography (GPC), is preferably 1,000 or more and 30,000 or less, and preferably 3,000 or more and 15,000 or less. More preferred. The acid value of the resin dispersant is preferably 50 mgKOH / g or more and 350 mgKOH / g or less, and more preferably 80 mgKOH / g or more and 250 mgKOH / g or less. When a resin dispersant having an acid value within the above range is used, pigment dispersion stability and ink ejection stability are improved. The acid value of the resin dispersant can be measured by potentiometric titration.

  The resin-dispersed pigment is preferably such that the mass ratio of the pigment particle content to the resin dispersant content (pigment particle content / resin dispersant content) is 1.0 to 10.0 times. . Such a resin-dispersed pigment can be favorably dispersed in the ink.

  The content of the resin-dispersed pigment in the ink (total content of pigment particles and resin dispersant) is preferably 0.1% by mass or more and 10.0% by mass or less based on the total mass of the ink. More preferably, it is 0 mass% or more and 7.0 mass% or less. If the content of the resin-dispersed pigment in the ink is 0.1% by mass or more (more preferably 1.0% by mass or more), the effect of improving the optical density of the image can be sufficiently obtained. Further, if the content of the resin-dispersed pigment in the ink is 10.0% by mass or less (more preferably 7.0% by mass or less), the ink ejection stability can be sufficiently obtained.

(Surfactant)
The kind of surfactant contained in the ink of the present invention is not particularly limited. Suitable surfactants include, for example, nonionic surfactants, anionic surfactants, fluorine surfactants, acetylene glycol surfactants, and silicone surfactants. A commercially available surfactant can be used for the ink.

  Specific examples of nonionic surfactants are Emulgen 103, 108, 123P, Amite, and Emazole (above, Kao); Neugen, Epan, and Sorgen (above, Daiichi Kogyo Seiyaku); In addition, narroacty, emalmin, sannonic (manufactured by Sanyo Chemical Industries, Ltd.) and the like can be mentioned.

  Specific examples of anionic surfactants include Emar, Latem, Perex, Neoperex, and Demol (above, Kao); and Sannole, Lipolane, Lipon, and Lipar (above, Lion). Can be mentioned.

  Specific examples of the fluorosurfactant include, for example, trade names such as Megafac F-114, F-410, F-440, F-447, F-553, and F-556 (manufactured by DIC); And Surflon S-211, S-221, S-231, S-233, S-241, S-242, S-243, S-420, S-661, S-651, and S-386 (AGC Seimi Chemical) Etc.).

  Specific examples of the acetylene glycol surfactant include, under the trade name, Surfynol 104, 82, 420, 440, 465, 485, TG, 2502, Dynal 604, and Dynal 607 (above, manufactured by Air Products); Orphine E1004 , E1010, PD004, and EXP4300 (manufactured by Nissin Chemical Industry); acetylenol EH, E40, E60, E81, E100, and E200 (manufactured by Kawaken Fine Chemical).

  Specific examples of the silicone-based surfactant include trade names of FZ-2122, FZ-2110, FZ-7006, FZ-2166, FZ-2164, FZ-7001, FZ-2120, SH 8400, FZ-7002, FZ-2104, 8029 ADDITIVE, 8032 ADDITIVE, 57 ADDITIVE, 67 ADDITIVE, and 8616 ADDITIVE (above, manufactured by Toray Dow Corning); KF-6012, KF-6015, KF-6004, KF-6013, KF-6011, KF -6043, KP-104, 110, 112, 323, 341, and 6004 (manufactured by Shin-Etsu Chemical); and BYK-300 / 302, BYK-306, BYK-307, BYK-320, BYK-325, BYK- 330, BY K-331, BYK-333, BYK-337, BYK-341, BYK-344, BYK-345 / 346, BYK-347, BYK-348, BYK-375, BYK-377, BYK-378, BYK-UV3500, BYK-UV3510, BYK-310, BYK-315, BYK-370, BYK-UV3570, BYK-322, BYK-323, BYK-350, BYK-352, BYK-354, BYK-355, BYK-358N / 361N, BYK-380N, BYK-381, BYK-392, BYK-340, BYK-Silclean 3700, BYK-Dynwet800 (above, manufactured by BYK Chemie) and the like can be mentioned.

  The ink may contain one type of surfactant or two or more types. The content of the surfactant in the ink is preferably 0.6% by mass or more, and more preferably 5.0% by mass or less, based on the total mass of the ink. The content of the surfactant contained in the ink can be adjusted as appropriate according to the miscibility and cleaning properties of the ink, the wettability to the inner wall of the flow path, the ink jetting properties, and the like.

(Water-soluble organic solvent)
The ink of the present invention contains a water-soluble organic solvent. In the present specification, “water-soluble organic solvent” means “an organic solvent having a solubility in water at 20 ° C. of 500 g / L or more”. As the water-soluble organic solvent, any known water-soluble organic solvent can be used. Examples of the water-soluble organic solvent include alcohols, glycols, alkylene glycols, polyethylene glycols, nitrogen-containing compounds, and sulfur-containing compounds. These water-soluble organic solvents can be used alone or in combination of two or more as required. The content of the total water-soluble organic solvent in the ink is preferably 50% by mass or less, more preferably 5% by mass or more and 45% by mass or less, based on the total mass of the ink.

  The ink is a water-soluble organic solvent such as glycerin, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol having a weight average molecular weight of 2,000 or less, 1,2-hexanediol, 1,3-propanediol. It is preferable to contain at least one selected from the group consisting of 1,4-butanediol, and diglycerol. Hereinafter, in the present specification, a water-soluble organic solvent included in the group may be referred to as a “first water-soluble organic solvent”, and a water-soluble organic solvent other than the first water-soluble organic solvent may be referred to as “other water-soluble organic solvent”. It may be described as “water-soluble organic solvent”.

  The total content of the first water-soluble organic solvent in the ink is preferably larger than the total content of the other water-soluble organic solvents. In this case, the first water-soluble organic solvent is used as the water-soluble organic solvent in the ink. Only the solvent may be contained. Further, the total content of the first water-soluble organic solvent in the ink is preferably 3 times or more, more preferably 10 times or more, by mass ratio with respect to the total content of other water-soluble organic solvents. preferable. Furthermore, the total content of the first water-soluble organic solvent in the ink is preferably 50% by mass or less, more preferably 5% by mass or more and 45% by mass or less, based on the total mass of the ink. More preferably, it is 10 mass% or more and 40 mass% or less.

  The ink preferably contains water in addition to the water-soluble organic solvent. As water, it is preferable to use deionized water (ion exchange water). The content of water in the ink is preferably 50% by mass or more and 90% by mass or less based on the total mass of the ink.

(Resin particles)
The ink of one embodiment of the present invention preferably contains resin particles. In the present specification, the “resin particles” means “particles made of a resin that can exist in a dispersed state in an aqueous medium”. The resin particles are more preferably at least one selected from the group consisting of polyurethane resin particles, acrylic resin particles, styrene-acrylic resin particles, fluorine resin particles, and silicone resin particles. Among these, polyurethane resin particles and acrylic resin particles are more preferable.

  The polyurethane resin constituting the resin particles is a polymer or copolymer having a urethane bond, and is obtained, for example, by reacting a polyol and a polyisocyanate. The acrylic resin constituting the resin particles is a polymer or copolymer having a structural unit derived from an acrylic monomer such as (meth) acrylic acid alkyl ester or (meth) acrylic acid alkylamide. It can be obtained by emulsion polymerization of monomers. The styrene-acrylic resin constituting the resin particle is a copolymer having a structural unit derived from the acrylic monomer and a structural unit derived from styrene. For example, the acrylic monomer and styrene are emulsion-polymerized. Obtained. The fluorine resin constituting the resin particles is a polymer or copolymer of olefin (fluoroolefin) containing fluorine. The silicone resin constituting the resin particles is a polymer or copolymer having a siloxane bond in the main skeleton. Commercially available products can be suitably used for these resin particles.

  The resin particle content in the ink is preferably 10.0% by mass or less based on the total mass of the ink. When the content of the resin particles in the ink is 10.0% by mass or less, the ink ejection stability can be sufficiently obtained. Moreover, when the resin particles are contained in the ink, the content of the resin particles in the ink is preferably 0.1% by mass or more.

(Additive)
The ink according to an embodiment of the present invention includes, as necessary, a surfactant other than the above, a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an anti-reduction agent, an evaporation accelerator, and Various additives such as a chelating agent may be contained.

<Ink cartridge>
The ink cartridge of the present invention includes an ink storage portion that stores ink. The ink of the present invention described above is stored in the ink storage portion. Examples of the ink storage unit include an ink storage chamber that stores liquid ink and a negative pressure generation member storage chamber that stores a negative pressure generation member that holds the ink therein by a negative pressure. Can do. Further, the ink cartridge may be provided with an ink storage portion that is configured not to include an ink storage chamber for storing liquid ink but to hold the entire amount of ink by a negative pressure generating member. Furthermore, the ink cartridge may include an ink storage unit and a recording head.

<Image recording method>
The image recording method of the present invention includes an ink application process for applying the above-described ink to a recording medium. The image recording method of one embodiment of the present invention preferably further includes a transporting step of transporting the recording medium, and preferably includes a heating step of heating the recording medium to which ink has been applied.

  FIG. 1 is a schematic diagram illustrating an example of an image recording apparatus used in an image recording method according to an embodiment of the present invention. In the image recording apparatus shown in FIG. 1, a form is shown in which recording is performed using a recording medium wound in a roll shape, and then wound into a roll shape again. This apparatus includes units of a recording medium supply unit 1, an ink application unit 2, a heating unit 3, and a recording medium collection unit 4. The recording medium supply unit 1 is a unit for holding and supplying a recording medium wound in a roll shape. The ink applying unit 2 is a unit for applying ink to a recording medium, and includes a recording head, for example. The heating unit 3 is a unit for heating the recording medium. The recording medium collection unit 4 is a unit for winding up a recording medium on which an image is recorded.

  The recording medium is transported along a transport path between the recording medium supply unit 1 and the recording medium recovery unit 4 by a transport unit such as a pair of rollers and a belt, and is processed by the above units. The image recording apparatus shown in FIG. 1 includes transport rollers 5 and 6 as a transport unit. The recording medium wound up in a roll shape by the conveyance roller 6 and the recording medium recovery unit 4 is supplied to another apparatus or the like, and processing such as cutting the recording medium into a desired size or bookbinding is performed. Also good.

  The speed of transporting the recording medium in the transporting process (recording medium transport speed) is more preferably 75 m / min or more, and further preferably 100 m / min or more. In the image recording method of the embodiment of the present invention, the ratio of the recording medium conveyance speed to the recording resolution (conveyance speed / recording resolution) is preferably 0.0625 m / min · dpi or more, and 0.125 m. More preferably, it is at least / min · dpi.

  When the recording medium is transported, it is preferable that tension is applied to the recording medium. That is, it is preferable that the image recording apparatus has a tension applying unit that generates tension. As a specific method, in the transport unit between the recording medium supply unit 1 and the recording medium recovery unit 4 in FIG. 1, a tension applying unit that generates tension on the recording medium and a tension adjusting unit that adjusts the tension of the recording medium. Etc. may be provided. When tension is applied to the recording medium, swelling of the fibers of the recording medium due to water in the ink is suppressed. When the fibers of the recording medium swell, the gap between the fibers increases and the ink penetration rate increases.However, if the ink penetration rate increases, the ink tends to penetrate deeply in the direction perpendicular to the surface of the recording medium. In some cases, sufficient optical density cannot be obtained. As described above, by applying tension to the recording medium, the swelling of the fibers of the recording medium due to the water in the ink is suppressed, so that a decrease in the optical density of the image due to an increase in the permeation speed of the ink can be suppressed.

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

(Ink application process)
The ink application process is a process of applying ink to the recording medium. As a method for applying ink to the recording medium, it is preferable to adopt an ink jet method. That is, the image recording method of the present invention is preferably an ink jet recording method. The ink jet method may be a thermal ink jet method or a piezo ink jet method. The thermal ink jet method is a method in which thermal energy is applied to ink and ink is ejected from the ejection port of the recording head. The piezo ink jet method is a method in which ink is ejected from an ejection port of a recording head using a piezo element.

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

The amount of ink applied to the recording medium in the ink application step is preferably 0.5 mg / cm ² or more and 0.9 mg / cm ² or less per ink type from the viewpoint of drying property, etc. cm and more preferably ² or more 0.8 mg / cm ² or less.

(Heating process)
In the heating step, it is preferable to heat the recording medium to which the ink is applied so that the surface temperature becomes 70 ° C. or higher. The “surface temperature of the recording medium to which ink has been applied” means the surface temperature of the recording medium at a position where the ink has been transported for 0.5 seconds, assuming that the time when the ink was applied to the recording medium is 0 second. For example, it is assumed that the conveyance speed of the recording medium is “V” m / min. In this case, the surface of the recording area X at a position where the ink recording area X on the recording medium has moved “(V × 0.5) / 60” m along the transport direction from the position where the ink is applied. What is necessary is just to measure temperature. In the case of a full-line type ink jet recording head, the “position to which ink is applied” means a position immediately below the recording head. In an example described later, a non-contact infrared thermometer digital radiation temperature sensor (trade name “FT-H20”, manufactured by KEYENCE) is used, and the recording medium is moved from a position approximately 10 cm away from the surface of the recording medium in a substantially vertical direction. The surface temperature was measured.

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

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

(recoding media)
As the recording medium, any conventionally used recording medium can be used. In particular, the water absorption coefficient Ka of the recording medium is preferably 0.1 mL / (m ² · ms ^1/2 ) or more and 3.0 mL / (m ² · ms ^1/2 ) or less. In addition, the image recording method according to an embodiment of the present invention preferably includes an ink application process in which the above-described ink is applied to the recording medium in the range of the absorption coefficient Ka to record an image in one pass. .

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

  The thickness of the recording medium is not particularly limited. As described above, the ink used in the image recording method of one embodiment of the present invention is capable of recording an image in which the back-through is suppressed. A recording medium of 08 mm or less can also be suitably used.

  The recording medium may be cut in advance to a desired size, or may be a long length wound in a roll shape and cut to a desired size after image recording. As described above, since it is easy to apply tension to the recording medium, it is preferable to use a long recording medium wound in a roll shape.

  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 the following description, “parts” and “%” are based on mass unless otherwise specified.

<Pigment>
As pigments, bisphosphonic acid-based self-dispersing magenta pigments (trade name “CAB-O-JET465M”, manufactured by Cabot, hereinafter sometimes referred to as “Pigment 1”), and the following resin dispersion pigments (hereinafter “Pigments”) 2 ”).

[Preparation of pigment dispersion]
A 500 mL eggplant flask equipped with a mechanical stirrer was placed in a tank of an ultrasonic generator. In this eggplant flask, 1 g of a styrene-acrylic acid random copolymer (acid value: 80 mgKOH / g) as a water-soluble resin dispersant and 120 mL of tetrahydrofuran as a solvent were placed, and the contents were stirred while applying ultrasonic waves. In another container, C.I. I. 5 g of Pigment Blue 15: 3 and 120 mL of tetrahydrofuran as a solvent were added. After mixing using a planetary stirrer (manufactured by Kurabo Industries) until the surface of the pigment particles is sufficiently wet with the solvent, add the mixture of the pigment particles and the solvent into the eggplant flask and mix well with the water-soluble resin dispersant. Mixed. Next, a potassium hydroxide aqueous solution was dropped and phase-inverted until the neutralization rate of the water-soluble resin dispersant became 100%, and then premixed for 60 minutes. Thereafter, the mixture was dispersed for 2 hours using a atomizer (trade name “Nanomizer NM2-L200AR”, manufactured by Yoshida Kikai Kogyo Co., Ltd.) to obtain a dispersion. Tetrahydrofuran was distilled off from the dispersion using a rotary evaporator, and the concentration was adjusted to obtain a resin dispersion pigment dispersion having a resin dispersion pigment (pigment 2) content of 6.0%. This resin-dispersed pigment dispersion has a mass ratio of pigment (pigment particle) content to pigment-containing water-soluble resin dispersant content (pigment content / water-soluble resin dispersant content) of 5.0 times. there were.

<Preparation of ink>
By mixing each component so that it becomes the content described in the upper stages of Tables 1 to 4 (all units are mass%), sufficiently stirring and dispersing, and filtering with a glass filter AP20 (MILLIPORE), Each ink was prepared. In addition, the description of “residue” of the water content in the table means an amount in which the content of each component including water is 100% in total. Moreover, the content (mass%) of the pigment and resin particle in a table | surface is content (mass%) of the solid content of the pigment and resin particle in an ink, respectively. Abbreviations in the table are as follows.

(Surfactant)
“E103”: trade name “Emulgen 103” (manufactured by Kao, polyoxyethylene lauryl ether)
"E108": Trade name "Emulgen 108" (manufactured by Kao, polyoxyethylene lauryl ether)
“E123P”: trade name “Emulgen 103” (manufactured by Kao, polyoxyethylene lauryl ether)
“AE100”: trade name “acetylenol E100” (manufactured by Kawaken Fine Chemicals, acetylene glycol surfactant)

(Water-soluble organic solvent)
“Gly”: Glycerin (manufactured by Kishida Chemical)
“12HD”: 1,2-hexanediol (manufactured by Tokyo Chemical Industry)
“PEG1000”: Polyethylene glycol 1000 (polyethylene glycol having a weight average molecular weight of 1000, manufactured by Pure Chemical)

(Resin particles)
"W5661": Trade name "Takelac W5661" (Mitsui Chemicals, urethane resin emulsion)
“PDX7430”: Trade name “Johncrill PDX-7430” (BASF, acrylic resin emulsion)
All of these resin particles formed a particle form even in the prepared ink.

  About each prepared ink, the viscosity, static surface tension, and dynamic surface tension in 25 degreeC were measured by the method described below. The results are shown in Tables 1 to 4 together with the evaluation results described later.

[Measurement of ink viscosity]
Using a rotational viscometer (trade name “RE80 type viscometer”, manufactured by Toki Sangyo Co., Ltd.), the viscosity (mPa · s) at 25 ° C. of each prepared ink was measured and listed in Tables 1 to 4.

[Measurement of static surface tension of ink]
For each ink prepared, a static surface tension (mN / m) at 25 ° C. using an automatic surface tension meter (trade name “CBVP-A3”, manufactured by Kyowa Interface Science) using a Wilhelmy method and a platinum plate. Was measured.

[Measurement of dynamic surface tension of ink]
For each ink prepared, a dynamic surface tension meter (mN) at a lifetime of 150 msec at 25 ° C. using a dynamic surface tension meter (trade name “BP2-Mk2 Bubble Pressure Tensimeter”, manufactured by KRUSS) using a maximum bubble pressure method. / M) was measured.

<Evaluation>
For image recording, an ink jet recording apparatus having a configuration shown in FIG. 1 and equipped with a piezo type ink jet head (trade name “KJ4”, manufactured by Kyocera, nozzle density 600 dpi) was used. Also, high-quality paper (trade name “OK Prince Quality”, made by Oji Paper Co., Ltd., basis weight 64 g / m ² , thickness 0.07 mm) was used as the recording medium. The recording conditions were a temperature of 25 ° C., a relative humidity of 55%, an ink discharge frequency of 39 kHz, a recording medium conveyance speed of 75 m / min, and about 13 pL per dot of ink discharge volume during recording. The ratio of the conveyance speed of the recording medium to the recording resolution (conveyance speed / recording resolution) was 0.125 m / min · dpi, and the applied amount of ink was 0.8 mg per cm ² . In the ink jet recording apparatus, the condition for applying one dot of 13 ng ink droplets to a unit area of 1/600 inch × 1/600 inch with a resolution of 600 dpi × 600 dpi is defined as a recording duty of 100%. In this example, in the evaluation criteria for the following evaluation items, “A” and “B” are preferable levels, and “C” is an unacceptable level.

(Image fixability)
Using the above-described inkjet recording apparatus, a solid image of 20 cm × 20 cm size and a non-printing area with a length of 10 cm in the recording medium conveyance direction on the above recording medium (quality paper), a recording medium conveyance speed of 75 m / Continued recording for 1 hour in minutes. Thereafter, the surface of the transport roller 6 (see FIG. 1) was observed, and the image fixability was evaluated according to the following evaluation criteria.
A: Although a slight discoloration of 20 cm width was visible on the roller surface, the boundary was not visible.
B: There was a slight discoloration of 20 cm width on the roller surface, and the boundary was faintly visible.
C: There was a strong discoloration of 20 cm width on the roller surface, and the boundary was clearly visible.
At the level C, the non-printing area printed just before the end of printing was discolored. Since the color material once adhering to the roller is considered to have adhered again, C was set to an unacceptable level.

(Color development of images)
Using the above-described inkjet recording apparatus, a solid image (image sample 1) having a recording duty of 100% on the recording medium (quality paper) on the recording medium (quality paper) having a recording duty of 100%. ) Was recorded. At this time, the ratio of the conveyance speed of the recording medium to the recording resolution (conveyance speed / recording resolution) was 0.125 m / min · dpi. The amount of ink applied was 0.8 mg per cm ² . The optical density of the image sample 1 was measured with a reflection densitometer (trade name “RD19I”, manufactured by Gretag Macbeth), and the color developability of the image was evaluated according to the following evaluation criteria.
A: The optical density was 1.3 or more.
B: The optical density was 1.2 or more and less than 1.3.
C: The optical density was less than 1.2.

(Background image)
The same image as the image sample 1 on the front surface was recorded on the surface (back surface) opposite to the surface (front surface) on which the image sample 1 was recorded in the recording medium used in the evaluation of the “image color development”. The image sample 1 on the back surface is projected on the back surface so that the projected area overlaps by an area of 10 cm × 20 cm when the image sample 1 on the front surface and the image sample 1 on the back surface are projected. Recording was performed at a position shifted by 10 cm from the position. Then, by visually observing the surface of the recording medium, the back-through state of the image sample 1 recorded on the back surface of the recording medium was evaluated according to the following evaluation criteria.
A: It was recognized that the image of the image sample 1 recorded on the back surface of the recording medium slightly penetrated into the area where the image of the image sample 1 on the front surface of the recording medium was not recorded.
B: It was recognized that the image of the image sample 1 recorded on the back surface of the recording medium was seen through in the area where the image of the image sample 1 on the front surface of the recording medium was not recorded. However, the boundary portion between the image sample 1 recorded on the front surface of the recording medium and the image sample 1 recorded on the back surface of the back-recorded recording medium can be determined.
C: It was recognized that the image of the image sample 1 recorded on the back surface of the recording medium was seen through in a region where the image of the image sample 1 on the front surface of the recording medium was not recorded. In addition, it is difficult to determine the boundary portion between the image sample 1 recorded on the front surface of the recording medium and the image sample 1 recorded on the back surface of the back-recorded recording medium.

(Image feathering)
Using the above-described inkjet recording apparatus, a 36-point ruled line was recorded on the recording medium (quality paper) at a recording medium conveyance speed of 75 m / min to produce Image Sample 2. At this time, the heating step was adjusted so that the surface temperature of the paper was 80 ° C. This was allowed to stand at room temperature for 5 minutes, and then the radgetness value Ra was measured. A personal image quality evaluation system Personal IAS (Quality Engineering Associates) was used for the measurement of the radgetness value Ra. Then, the degree of feathering was evaluated from the value of Ra according to the following evaluation criteria. In this evaluation, the degree of blurring of the ruled line width is measured by the above evaluation system. If the value of Ra is small, it means that the ruled line width is constant and excellent.
A: Ra was 13 or less.
B: Ra exceeded 13 and was 15 or less.
C: Ra exceeded 15.

Claims (9)

An ink containing a pigment, a water-soluble organic solvent, and a surfactant and having a viscosity at 25 ° C. of 5 mPa · s or more,
The static surface tension measured at 25 ° C. by the Wilhelmy method is 30.5 mN / m or more and 35.0 mN / m or less,
An ink having a dynamic surface tension measured at 25 ° C. by a maximum bubble pressure method of 30.5 mN / m or more and 37.0 mN / m or less at a lifetime of 150 milliseconds.   The ink according to claim 1, wherein the content of the surfactant is 0.6% by mass or more based on the total mass of the ink.   3. The resin particle according to claim 1, comprising at least one resin particle selected from the group consisting of urethane resin particles, acrylic resin particles, styrene-acrylic resin particles, fluorine resin particles, and silicone resin particles. ink.   The pigment is a resin-dispersed pigment in which the mass ratio of the pigment particle content to the resin dispersant content is 1.0 to 10.0 times, or the surface of the pigment particle has a bisphosphonic acid group directly or other The ink according to any one of claims 1 to 3, which is a self-dispersing pigment bonded through an atomic group. An ink cartridge comprising ink and an ink containing portion for containing the ink,
The ink cartridge according to claim 1, wherein the ink is an ink according to claim 1. An image recording method including an ink application process for applying ink to a recording medium,
The image recording method according to claim 1, wherein the ink is the ink according to claim 1.   The image recording method according to claim 6, wherein a ratio of the conveyance speed of the recording medium to the recording resolution (conveyance speed / recording resolution) is 0.125 m / min · dpi or more.   The image recording method according to claim 6 or 7, wherein the recording medium has a thickness of 0.1 mm or less. The application amount of the ink into the recording medium, first ink species per image recording according to any one of claims 6 to 8 which is 0.6 mg / cm ² or more 0.8 mg / cm ² or less in the range Method.

Images