JP2007181974A - Inkjet image recorder and inkjet image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet image recorder which has a high image quality and superior curling characteristics, and prevents a rear face of a printing surface from being stained even when the apparatus is used for a long period of time, and to provide an inkjet image forming method. <P>SOLUTION: In the inkjet image recorder which forms an image by making an ink for inkjet ejected from an inkjet head onto a recording paper 14 conveyed by a conveyance belt 7, the ink for inkjet includes at least water, water-soluble organic solvents and pigments. A content of the water is not smaller than 10 mass% and smaller than 50 mass% of a total ink mass. Moreover, among the water-soluble organic solvents, the water-soluble organic solvent which has an SP value ((MPa)<SP>1/2</SP>) of not smaller than 16.5 and smaller than 24.6 is contained by 30 mass% or more of the whole ink. An angle of contact between the ink for inkjet and the belt is not smaller than 60°. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inkjet image recording apparatus and an inkjet image forming method.

  In recent years, the inkjet recording method can easily and inexpensively create an image, and thus has been applied to various printing fields such as photographs, various printing, marking, and special printing such as a color filter. In particular, inkjet recording devices that emit and control fine dots, ink with improved color reproduction gamut, durability, and emission suitability, ink absorbency, colorant color development, surface gloss, etc. have been dramatically improved. It is also possible to obtain image quality comparable to silver halide photography using special paper.

  However, in an inkjet image recording system that requires dedicated paper, there are problems in that the recording media that can be used are limited and the cost of the recording media is increased.

  On the other hand, in the office, there is an increasing need for a system that can perform full color printing at high speed without being restricted by recording media (for example, plain paper, coated paper, art paper).

  In particular, it is desired to perform high-quality printing at high speed on plain paper (for example, PPC paper, non-coated paper for printing, etc.) that is inexpensive and easily available. When water-based ink is used, curling and cockling after printing have been major issues. On the other hand, when oil-based ink is used, there is no problem with curling and cockling, but there are problems such as higher penetrating power than water-based ink, character image quality, bleeding, and low reflection density. Various studies have been conducted so far, including the composition of the recording liquid, in order to solve the problem of printing on plain paper, but ink that satisfies all of curling, cockling, image density, and character quality has not been obtained. It was.

  As a method for preventing curling and cockling during recording on plain paper using an aqueous ink, a technique of adding a specific diol to the ink is disclosed (for example, see Patent Document 1). However, even in this method, there is a problem that curling and cockling occur when an image with a large amount of ink is printed. Alternatively, a technique for preventing curling and cockling by adding caseins into the ink is disclosed (for example, see Patent Document 2). However, this method has a problem of deteriorating dispersion stability with respect to ink containing a pigment.

  As a technology that focuses on curling when using plain paper, a technology that suppresses curling and improves character quality and light output by containing a specific organic solvent in a specific ratio has been disclosed. (For example, refer to Patent Documents 3 to 5.) In addition, these inks have a feature of excellent emission stability, and it has been reported that the ink can be emitted stably because there is little change in viscosity even during so-called intermittent emission, in which a time is provided between emission and emission. For this reason, it has been found that even when applied to a so-called line head type printer, an image can be stably formed.

  Here, a line head type inkjet head will be described. In this head, inkjet heads are arranged in a line in the width of the recording paper, and high-speed image recording is possible only by transporting the recording paper. Since the heads arranged in a row are very large as a whole, the head is moved to the side of the recording paper, which is used in a conventional shuttle head type printer, and it is discharged or cleaned with a blade. It was difficult to perform maintenance operations.

  Although the maintenance load can be reduced by using the inks described in Patent Documents 3 to 5, it has been desired to incorporate some maintenance mechanism in order to further improve the safety of emission.

  In a line head type ink jet printer, a method for preliminarily ejecting ink onto a conveyance body (conveyance belt) to ensure emission stability has been proposed (see, for example, Patent Documents 6 to 8). It has been reported that the pre-discharged ink is wiped and cleaned by a cleaning roller or the like. However, it has been found that it is difficult to completely clean these methods, and when used for a long period of time, it is not possible to completely remove the dirt on the transporting body, which contaminates the back surface of the recording medium.

There has been proposed a method of ensuring ejection stability by providing a concave portion in a conveyance body for conveying recording paper and preliminarily discharging ink prior to recording (see, for example, Patent Document 9). Since the concave portion is not in contact with the back surface of the recording medium, the back surface of the recording medium is not contaminated. However, since it is mechanically complicated, there is a problem that it leads to high cost and is inferior in stability of operation.
JP-A-6-157955 JP-A-5-208547 JP 2005-220296 A Japanese Patent Laid-Open No. 2005-220297 Japanese Patent Laid-Open No. 2005-220298 JP 2000-127362 A JP 2000-263801 A JP 2000-272110 A JP 2005-178246 A

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an ink jet image recording apparatus and ink jet image forming that have high image quality, excellent curl characteristics, and the back surface of the printed surface is not contaminated even after long-term use. It is to provide a method.

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

1. In an inkjet image recording apparatus for forming an image by ejecting an inkjet ink onto a recording paper conveyed by a belt from an inkjet head, the inkjet ink contains at least water, a water-soluble organic solvent, and a pigment, and the water content Is 10 mass% or more and less than 50 mass% of the total ink mass, and among the water-soluble organic solvents, all of the water-soluble organic solvents having an SP value ((MPa) ^1/2 ) of 16.5 or more and less than 24.6 are included. An ink jet image recording apparatus characterized by containing 30% by mass or more of the ink and having a contact angle of 60 ° or more between the ink for inkjet and the belt.

2. 2. The inkjet according to 1 above, wherein the vapor pressure at 20 ° C. of the water-soluble organic solvent having an SP value ((MPa) ^1/2 ) of 16.5 or more and less than 24.6 is 0.01 Pa or more and 133 Pa or less. Image recording device.

3. When a water-soluble organic solvent having an SP value ((MPa) ^1/2 ) of 16.5 or more and less than 24.6 is mixed with water, a water-soluble organic solvent that exhibits a maximum viscosity by its mixing ratio is used, and the maximum 3. The inkjet image recording apparatus as described in 1 or 2 above, wherein water and the water-soluble organic solvent are mixed at a ratio in the vicinity of the portion.

  4). 4. The inkjet image recording apparatus according to any one of items 1 to 3, wherein image recording is performed by a line head type inkjet printer.

  5. 5. An inkjet image forming method using the inkjet image recording apparatus according to any one of 1 to 4 above.

  According to the present invention, it is possible to provide an ink jet image recording apparatus and an ink jet image forming method that have high image quality, excellent curl characteristics, and that do not contaminate the back surface of the printed surface even when used for a long period of time.

  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 found that, in an inkjet image recording apparatus that forms an image by ejecting from an inkjet head onto a recording paper conveyed by a belt, the inkjet ink is at least water, water-soluble organic It contains a solvent and a pigment, the water content is 10% by mass or more and less than 50% by mass of the total ink mass, and the SP value ((MPa) ^1/2 ) of the water-soluble organic solvent is 16.5 or more. An ink jet image recording apparatus having a feature of containing a water-soluble organic solvent of less than 24.6 in an amount of 30% by mass or more of the total ink, and having a contact angle between the ink for inkjet and the belt of 60 ° or more, and the ink jet It has been found that the object of the present invention can be realized by an image forming method performed using an image recording apparatus, and the present invention has been achieved.

  Hereinafter, the present invention will be described in detail.

  The inkjet image recording apparatus and the image forming method used in the present invention are characterized in that the contact angle between the conveyance belt for conveying the recording paper and the inkjet ink of the present invention is 60 ° or more.

  As described above, it is difficult to introduce a maintenance mechanism in a line head type ink jet printer. For this reason, means such as preliminary ejection of ink onto the conveyor belt have been proposed, but the belt itself becomes contaminated by long-term use, which may contaminate the back side of the recording paper, or a complicated cleaning mechanism is required. It was said.

  Here, when such preliminary ejection onto the belt is applied to the ink of the present invention, the ink of the present invention has high wettability due to a high organic solvent ratio, and thus ink droplets are likely to spread on the belt. The ink spread on the belt is difficult to remove from the belt surface even if a removing means such as a cleaning roller is used, and there is a problem that the back surface of the recording paper is more easily contaminated than a normal aqueous ink. However, if the organic solvent ratio is reduced to prevent the backside contamination, the problem of curling after recording and degrading the quality becomes significant. For this reason, it has been difficult to improve only by changing the ratio of a simple organic solvent.

  Therefore, when we studied to overcome the above problems by changing the organic solvent type and improving the conveyor belt, we achieved the goal by controlling the belt surface so that the contact angle between the inkjet ink and the belt was 60 ° or more. It turns out that you can. Here, when the contact angle is smaller than 60 °, it has been found that even if cleaning is performed, a so-called wiping residue remains, which accumulates on the belt and eventually leads to contamination of the back surface.

  There are various methods for making the contact angle between the inkjet ink and the belt 60 ° or more. However, the method can be controlled easily and appropriately by changing the material of the belt or performing a surface treatment. it can. It can also be controlled by changing the ink solvent.

  In the present invention, the contact angle between the inkjet ink and the belt is preferably 120 ° or less, more preferably 90 ° or less. If the contact angle exceeds 120 °, the back side of the recording paper is likely to be repelled, which adversely affects the transportability.

  Examples of materials constituting the conveyor belt include various polymers. For example, PET (polyethylene terephthalate), PEI (polyetherimide), PVDF (polyvinylidene fluoride), PC (polycarbonate), ETFE (ethylene-tetrafluoroethylene). Ethylene copolymer), PTFE (polytetrafluoroethylene) and the like.

  The conveyance belt according to the present invention may be formed of a single material or may be formed of a multilayer structure formed of a plurality of materials. Moreover, even if it forms from a single raw material, you may form a laminated structure so that electrical resistance may differ for every layer, for example. The belt having such a structure can be used, for example, in a conveyor belt device using electrostatic attraction force.

The ink-jet ink used in the present invention contains at least water, a water-soluble organic solvent and a pigment, and the water content is 10% by mass or more and less than 50% by mass of the total ink mass, and the water-soluble organic solvent Among these, a water-soluble organic solvent having an SP value ((MPa) ^1/2 ) of 16.5 or more and less than 24.6 is characterized by containing 30% by mass or more of the total ink.

  When the water content in all the inks is 50% by mass or more, curling and cockling are inferior. If it is less than 10% by mass, the dispersion stability of the pigment becomes poor even with other solvent compositions.

  The water content in the total ink is more preferably 20% by mass or more and less than 40% by mass.

The ink according to the present invention is characterized by containing 30% by mass or more of a water-soluble organic solvent having an SP value ((MPa) ^1/2 ) of 16.5 or more and less than 24.6. When this addition amount is less than 30% by mass, curling and cockling during recording on plain paper become extremely large. If the SP value ((MPa) ^1/2 ) of this organic solvent is also less than 16.5, the compatibility with water is deteriorated and separation occurs. Conversely, an organic solvent having an SP value ((MPa) ^1/2 ) of 24.6 or more has an insufficient curl suppressing effect.

The range of the SP value ((MPa) ^1/2 ) of the organic solvent is more preferably 16.5 or more and less than 22.5.

The solvent solubility parameter (SP value) referred to in the present invention is a value represented by the square root of molecular cohesive energy. F. Fedors, Polymer Engineering Science, 14, p147 (1974). The unit is (MPa) ^1/2 and refers to the value at 25 ° C.

Examples of water-soluble organic solvents having an SP value ((MPa) ^1/2 ) of 16.5 or more and less than 24.6 are shown below together with the SP value ((MPa) ^1/2 ). Needless to say, the present invention is not limited to this.

Ethylene glycol monomethyl ether (SP value ((MPa) ^1/2 ): 24.5)
Ethylene glycol monoethyl ether (23.5)
Ethylene glycol monobutyl ether (22.1)
Ethylene glycol monoisopropyl ether (22.3)
Diethylene glycol monomethyl ether (23.0)
Diethylene glycol monoethyl ether (22.4)
Diethylene glycol monobutyl ether (21.5)
Diethylene glycol diethyl ether (16.8)
Triethylene glycol monomethyl ether (22.1)
Triethylene glycol monoethyl ether (21.7)
Triethylene glycol monobutyl ether (21.1)
Propylene glycol monomethyl ether (23.0)
Propylene glycol monophenyl ether (24.2)
Dipropylene glycol monomethyl ether (21.3)
Tripropylene glycol monomethyl ether (20.4)
1,3-dimethyl-2-imidazolidinone (21.8)
Further, among the water-soluble organic solvents having an SP value ((MPa) ^1/2 ) of 16.5 or more and less than 24.6, all of the water-soluble organic solvents having a vapor pressure at 20 ° C. of 0.01 Pa or more and 133 Pa or less are used. It is preferable to contain 30% by mass or more of the ink, and it is more preferable to contain an organic solvent of 0.01 Pa to 66 Pa. Examples of water-soluble organic solvents corresponding to this include tripropylene glycol monomethyl ether (3.99 Pa), triethylene glycol monomethyl ether (less than 1.33 Pa), triethylene glycol monobutyl ether (less than 1.33 Pa), diethylene glycol monomethyl. Examples include ether (24.00 Pa), diethylene glycol monoethyl ether (17.33 Pa), and the like.

  In the present invention, various water-soluble organic solvents can be used in combination with the water-soluble organic solvent. Examples of water-soluble organic solvents preferably used include alcohols (eg, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pentanol, hexanol, cyclohexanol, benzyl alcohol, etc.), 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, 1,3 -Propanediol, 1,4-butanediol, 1,5-pentanediol, 1,2-pentanediol 1,2-hexanediol, 1,2,6-hexanetriol, etc.), amines (eg, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine) , Diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, etc.), Heterocycles (eg 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, 2-oxazolidone etc.), sulfoxides (eg dimethyl sulfoxide) ), Sulfones (e.g., sulfolane), urea, acetonitrile, ketones (e.g., acetone, methyl ethyl ketone, etc.).

  Among the water-soluble organic solvents in the ink according to the present invention, it is preferable to use an organic solvent that exhibits a maximum viscosity by its mixing ratio when mixed with water, and at a ratio in the vicinity of the maximum. Mixing with a water-soluble organic solvent is one of the more preferable embodiments in terms of light emission and decap. The vicinity mentioned here means within 10% above and below the ratio indicating the maximum when the total mass ratio of water and the water-soluble organic solvent is 100%. For example, when the ratio of water to the organic solvent is 50:50 and indicates the maximum, 40:60 to 60:40 is set as the vicinity.

  Examples of the solvent that exhibits the maximum viscosity when mixed with water include ethylene glycol monoalkyl ethers (eg, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether), diethylene glycol, and the like. Monoalkyl ethers (eg, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, etc.), triethylene glycol monoalkyl ethers (eg, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether) Etc.), propylene glycol monoalkyl ethers (eg propylene glycol) Monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, etc.), dipropylene recall monoalkyl ethers (eg, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, etc.), tri Propylene recall monoalkyl ethers (for example, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monobutyl ether, etc.) can be mentioned, preferably dialkylene glycol monoalkyl ethers or trialkylene glycol mono Alkyl ethers.

  As the pigment that can be used in the present invention, conventionally known pigments can be used without particular limitation, and any of water-dispersible pigments, solvent-dispersible pigments, and the like can be used. For example, organic pigments such as insoluble pigments and lake pigments, An inorganic pigment such as carbon black can be preferably used.

  Although it does not specifically limit as an insoluble pigment, For example, azo, azomethine, methine, diphenylmethane, triphenylmethane, quinacridone, anthraquinone, perylene, indigo, quinophthalone, isoindolinone, isoindoline, azine, oxazine, thiazine, 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. Pigment red 202, C.I. I. Pigment red 222, C.I. I. Pigment violet 19 and the like.

  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 15: 3, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 138, C.I. I. And CI Pigment Yellow 150.

  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 15: 4, C.I. I. Pigment blue 15: 6, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

  Examples of black pigments include C.I. I. Pigment black 1, C.I. I. Pigment black 6, C.I. I. Pigment black 7 and the like.

  The average particle size in the dispersed state of the pigment contained in the inkjet ink according to the present invention is preferably 50 nm or more and less than 200 nm. If the average particle diameter of the pigment dispersion is less than 50 nm or 200 nm or more, the stability of the pigment dispersion tends to be poor, and the storage stability of the recording liquid tends to deteriorate.

  The particle size of the pigment dispersion can be determined by a commercially available particle size measuring instrument using a dynamic light scattering method, an electrophoresis method, or the like. Accurate and often used.

  The pigment used in the present invention is preferably used after being dispersed by a disperser together with a dispersant and other necessary additives according to desired purposes. As the disperser, a conventionally known ball mill, sand mill, line mill, high-pressure homogenizer, or the like can be used. In particular, the particle size distribution of the ink produced by dispersion with a sand mill is sharp and preferable. The material of the beads used for sand mill dispersion is preferably zirconia or zircon from the viewpoint of contamination of bead fragments and ionic components. Furthermore, the bead diameter is preferably 0.3 to 3 mm.

  As the dispersant used in the present invention, a conventionally known polymer dispersant can be preferably used, and among them, acrylic polymers and urethane polymers can be preferably used.

  In the ink according to the present invention, a known pigment dispersant, for example, higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, naphthalenes, together with the above polymer dispersants or independently. Interface of sulfonate, alkyl phosphate, polyoxyalkylene alkyl ether phosphate, polyoxyalkylene alkyl phenyl ether, polyoxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, polyoxyethylene fatty acid amide, amine oxide, etc. It does not prevent the use of an activator or the like.

  Next, components of the ink according to the present invention other than those described above will be described.

  The pH of the ink according to the present invention is preferably 7.0 or more, more preferably 8.05 to 10.0, and by using the above pH, the emission stability is good and the concentration is preferable. This is preferable from the viewpoint of obtaining a glossy image.

  Examples of the pH adjuster used in the ink according to the present invention include various organic amines such as monoethanolamine, diethanolamine, and triethanolamine, and alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide. Inorganic alkaline agents such as organic acids and mineral acids.

  The surface tension of the ink according to the present invention is preferably 25 to 50 mN / m at 25 ° C. More preferably, it is 25-40 mN / m, More preferably, it is 25-35 mN / m. When the surface tension of the ink is less than 25 mN / m, the absorption speed to the recording medium is increased, causing aggregation due to the pigment particles, resulting in the occurrence of bronzing, reduction in gloss and abrasion resistance. On the other hand, when the surface tension of the ink exceeds 50 mN / m, the ink droplets that have landed on the recording medium cause color turbidity due to staying for a long time, and a high-definition image cannot be obtained.

The surface tension referred to in the present invention can be adjusted to a desired surface tension by appropriately adjusting the type and amount of addition using, for example, various water-soluble organic solvents and the following various surfactants. The method for measuring tension is described in general interface chemistry and colloid chemistry reference books. For example, New Experimental Chemistry Course Vol. 18 (Interface and Colloid), edited by The Chemical Society of Japan, published by Maruzen Co., Ltd. : P. 68-117 can be referred to, and specifically, it can be determined by using a ring method (Dunoi method) or a vertical plate method (Wilhelmy method).

  Various surfactants can be used as one means for achieving the surface tension. Each surfactant that can be used in the present invention is not particularly limited, and examples thereof include anionic surfactants such as dialkyl sulfosuccinates, alkyl naphthalene sulfonates, fatty acid salts, polyoxyethylene alkyl ethers, polyoxy Nonionic surfactants such as ethylene alkylallyl 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.

  In the present invention, it is preferable to use an acetylene-based surfactant as the surfactant from the viewpoint of obtaining an image having good emission stability, favorable gloss at a high concentration, and excellent uniformity.

  There is no particular limitation as long as it is an acetylene-based surfactant, and examples thereof include acetylene glycols and acetylene alcohols, and more preferable are surfactants having an acetylene group and an alkylene oxide chain. 465 (manufactured by Nissin Chemical Industry Co., Ltd.).

  In the ink according to the present invention, the ink viscosity is preferably 1 to 40 mPa · s at 25 ° C., more preferably 5 to 40 mPa · s, and further preferably 5 to 15 mPa · s. Further, in the ink according to the present invention, the dissolved oxygen concentration in the ink is preferably 2 ppm or less at 25 ° C. By using this dissolved oxygen concentration condition, the formation of bubbles can be suppressed, and in high-speed printing. In addition, an ink jet recording method having excellent emission stability can be realized. As a method for measuring the dissolved oxygen dissolved in the ink, for example, it can be measured using a dissolved oxygen measuring device DO-14P (manufactured by Toa Radio).

  Further, in the ink according to the present invention, the total content of calcium ions, magnesium ions and iron ions, which are polyvalent metal ions of the ink, is preferably 10 ppm or less, more preferably 0.1 to 5 ppm, particularly preferably Preferably it is 0.1-1 ppm.

  By setting the content of polyvalent metal ions in the inkjet ink to the amount specified above, an ink having high dispersion stability can be obtained. The polyvalent metal ion according to the present invention is contained in sulfates, chlorides, nitrates, acetates, organic ammonium salts, EDTA salts and the like.

  In the ink according to the present invention, in addition to the above description, various known types may be used depending on the purpose of improving the emission stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other various performances as necessary. Additives such as viscosity modifiers, specific resistance modifiers, film forming agents, ultraviolet absorbers, antioxidants, fading inhibitors, antifungal agents, rust inhibitors, etc. can be appropriately selected and used, for example, Oil droplets such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicone oil, ultraviolet absorbers described in JP-A-57-74193, JP-A-57-87988, and JP-A-62-261476, JP-A-57-74192, JP-A-57-87989, JP-A-60-72785, JP-A-61-146591, JP-A-1-95091 and JP-A-3-13376 Described in JP-A-59-42993, JP-A-59-52689, JP-A-62-280069, JP-A-61-228771 and JP-A-4-219266. Examples thereof include fluorescent brighteners.

  In the image forming method using the ink jet ink according to the present invention, for example, the ink is ejected as a droplet from the ink jet recording head based on the digital signal by an ink jet printer loaded with the ink jet ink and is attached to the recording medium. Thus, an inkjet print can be obtained.

  When an image is formed by ejecting the ink according to the present invention, the ink jet recording head to be used may be an on-demand system or a continuous system. As the discharge method, an electro-mechanical conversion method (for example, single cavity type, double cavity type, bender type, piston type, shear mode type, shared wall type, etc.), electro-thermal conversion method (for example, thermal ink jet) Any ejection method such as a mold, a bubble jet (registered trademark) mold, or the like may be used.

  Among these, when the inkjet ink according to the present invention is used, recording is performed on a recording material by discharging from a piezo-type inkjet recording head having a nozzle diameter of 30 μm or less, and a line having a nozzle diameter of 30 μm or less. Recording is performed on a recording material by ejecting it from a head-type piezo ink jet recording head, and an image is recorded on the recording material at a printing speed of 20 ppm or more using a piezo ink jet recording head having a nozzle diameter of 30 μm or less. It is preferable.

  As a printing method of an ink jet printer, printing can be performed sufficiently with respect to a shuttle head type recording head by using a line head type recording head. It is possible to achieve a very good dot shape (roundness) and printing accuracy when the droplets land on the recording material.

  In addition, the ink according to the present invention has characteristics excellent in emission stability and decap resistance, has excellent characteristics in high-speed printing, and is preferably printed at a high speed of 20 ppm or more as a printing speed. Preferably they are 20 ppm or more and 200 ppm or less, More preferably, they are 50 ppm or more and 200 ppm or less. In the present invention, “ppm” refers to the number of pages printed per minute (Page Per Minute) of an A4 size recording material.

  The recording material used for the inkjet ink according to the present invention can be used without limitation as long as it has the absorbability and retention of the ink to be printed, for example, a non-absorbent support or an absorbent support. Ink-jet recording materials provided with an ink absorbing layer that absorbs and retains ink on the body, and paper supports such as coated paper and non-coated paper can be used, but image printing using plain paper as the recording material It is preferable from the viewpoint of obtaining the effect of preventing the show-through and high quality image according to the present invention.

  Although there is no restriction | limiting in particular as such a plain paper, 80-200 micrometers uncoated paper which belongs to a part of non-coating paper, special printing paper, and information paper is desirable. The construction of the plain paper according to the present invention is made by a conventional method using mainly chemical pulps represented by LBKP and NBKP, sizing agents and fillers, and using other paper making aids as necessary. As the pulp material used for the plain paper according to the present invention, mechanical pulp or recycled paper recycled pulp may be used in combination, and there is no problem even if these are used as the main material.

  Examples of the sizing agent internally added to the plain paper according to the present invention include rosin size, AKD, Alnicel succinic anhydride, petroleum resin-based size, epichlorohydrin, cationic starch, and acrylamide.

  Examples of the filler internally added to the plain paper according to the present invention include finely divided silicic acid, aluminum silicate, diatomaceous earth, kaolin, kaolinite, halloysite, nacrite, dickite, pyrophyllite, sericite, titanium dioxide, bentonite. Etc.

  Further, the plain paper according to the present invention may contain a water-soluble polyvalent metal salt from the viewpoint of enhancing the back-through of the ink according to the present invention and the fixability of the colorant.

  The water-soluble polyvalent metal salt that can be used for the plain paper according to the present invention is not particularly limited. For example, aluminum, calcium, magnesium, zinc, iron, strontium, barium, nickel, copper, scandium, gallium, It is added as a metal salt such as indium, titanium, zirconium, tin or lead, a salt such as sulfate, nitrate, formate, succinate, malonate, chloroacetate or p-toluenesulfonate. Further, a water-soluble inorganic polymer such as polyaluminum chloride may be used as a salt of a water-soluble polyvalent metal ion. The water solubility is preferably at least 0.1% by mass, more preferably 1% by mass. Among these, a water-soluble salt composed of aluminum, calcium, aluminum, magnesium, and zinc is preferable because its metal ion is colorless. Particularly preferred are aluminum chloride, aluminum sulfate, aluminum nitrate, aluminum acetate, calcium chloride, calcium sulfate, calcium nitrate, calcium acetate, magnesium chloride, magnesium sulfate, magnesium nitrate, magnesium acetate, zinc chloride, zinc sulfate, zinc nitrate, Zinc acetate.

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

  First, the ink jet image recording apparatus used in the present invention will be described.

  FIG. 1 shows a line head type inkjet image recording apparatus preferably used in the present invention.

  In FIG. 1, 1 to 4 represent line head type ink jet heads. The heads are arranged in parallel with the width of the recording paper in the direction perpendicular to the paper surface, and are arranged in four rows for each color of yellow, magenta, cyan, and black.

  The recording paper 14 is placed in a stacked state, and is pulled out from there by a recording feed roller 15 and a recording paper guide 13, passes between the driving roller 12 and the suppression roller 16, and is transported by the transport belt 7. The recorded recording paper 5 is attracted to the transport belt 7 by the electrostatic force generated by the electrostatic attraction plate 17.

  Here, the ink stains adhering to the transport belt 7 are wiped off by the cleaning roller 9 positioned with the tension roller 11 interposed therebetween, and the stains are removed by the cleaning liquid stored in the cleaning tank 8 and the squeezing roller 10. For example, when so-called borderless printing is performed, image recording is performed in such a manner that the edge of the image slightly protrudes between the recording paper and the recording paper. It will remain. In addition, for example, when preliminary ejection is performed between recording sheets, ink remains on the conveyance belt. Here, when the contact angle between the ink and the belt is smaller than 60 °, the cleaning is incomplete, and further, the coloring material is re-dyed from the cleaning tank to the cleaning roller, and dirt is accumulated on the belt. End up. On the other hand, when the surface condition of the belt is controlled to be 60 ° or more, the remaining ink is completely removed by the cleaning roller, and the reattachment of the coloring material accumulated in the cleaning tank is also suppressed, so that the stain on the belt Does not accumulate.

  Next, the inkjet image forming method of the present invention will be described. In the following examples, “part” or “%” is used, but “part by mass” or “% by mass” is expressed unless otherwise specified.

Example 1
<< Preparation of Pigment Dispersions 1-16 >>
Each component was mixed at the ratio shown in Table 1, and dispersed using a horizontal bead mill (System Zeta Mini manufactured by Ashizawa Co., Ltd.) filled with zirconia beads having a diameter of 0.5 mm at a volume ratio, and then the zirconia beads were removed. Pigment dispersions 1 to 16 were obtained.

[Preparation of inks 1 to 16]
After adding a solvent and water so that it may become the addition amount shown in Table 2 to each prepared said pigment dispersion, the deaeration process was performed under pressure reduction, and the inks 1-16 were prepared.

  The details of each additive described in abbreviations in Tables 1 and 2 are as follows.

(solvent)
TPGmME: Tripropylene glycol monomethyl ether 1,2-HDO: 1,2-hexanediol t-BuOH: Tertiary butanol DEG: Diethylene glycol (Vapor pressure, viscosity, and SP value of each solvent alone ((MPa) ^1/2 ))
TPGmME: Viscosity = 6.2 mPa · s, Vapor pressure = 4 Pa, SP value ((MPa) ^1/2 ) = 20.4
1,2-HDO: viscosity> 30 mPa · s, vapor pressure <1.3 Pa, SP value ((MPa) ^1/2 ) = 27.4
t-BuOH: Viscosity = 3.6 mPa · s, Vapor pressure = 4.08 kPa, SP value ((MPa) ^1/2 ) = 22.3
DEG: Viscosity = 30 mPa · s, vapor pressure <1.3 Pa, SP value ((MPa) ^1/2 ) = 30.6
Water: Viscosity = 0.87 mPa · s, Vapor pressure = 3.16 kPa
About the said viscosity and SP value, all are the values in 25 degreeC, and vapor pressure is a value in 20 degreeC.

(Viscosity characteristics of solvent and water mixed solvent)
About the solvent set of each of the above solvents and water, each solvent was prepared by changing the mixing ratio by 10% by mass from 100: 0 to 0: 100 with solvent: water, and the viscosity of these mixed solvents was measured. The results obtained are as follows.

  Solvent composition of TPGmME / water: TPGmME: Water showed a maximum viscosity (10.1 mPa · s) under a mixing condition of 80:20.

  1,2-HDO / water solvent composition: As the ratio of 1,2-HDO increased, the viscosity increased monotonously. Under a mixing condition of 1,2-HDO / water of 60:40, the viscosity was 7.8 mPa · s.

  Solvent composition of t-BuOH / water: The maximum viscosity (4.0 mPa · s) was exhibited under a mixing condition of 60:40 of t-BuOH: water.

  DEG / Water solvent composition: Viscosity increased monotonically as the ratio of DEG increased. Under a mixing condition of DEG / water of 60:40, the viscosity was 6.6 mPa · s.

(Pigment)
Y: C.I. I. Pigment Yellow 138
C: C.I. I. Pigment Blue 15: 3
M: C.I. I. Pigment Red 122
K: Carbon black (pigment dispersant)
F760: Floren TG-760W (manufactured by Kyoeisha Chemical Co., Ltd.)
J501: Jonkrill 501 (manufactured by Johnson Polymer)
B190: Disperbyk-190 (by Big Chemie Japan)
[Preparation of ink sets 1 to 4]
Using the inks prepared above, ink sets 1 to 4 were prepared in combination as shown in Table 3.

[Evaluation of ink]
《Image evaluation》
(Evaluation of curl characteristics after printing)
An evaluation image was created using the ink set prepared above by the ink jet printer shown in FIG. Here, as the recording head, 12 share mode piezo-type recording heads having a nozzle diameter of 25 μm, an ejected ink droplet amount of 4 pl, and a number of nozzles of 256 are arranged in parallel in the width direction of the recording material. A total of 4 units were used, each having a nozzle resolution of 720 dpi (dpi in the present invention represents the number of dots per 2.54 cm) and a total of 3072 nozzles, one for each color.

  Further, the drive voltage of the recording head was adjusted so that the droplet velocity was 8 m / sec and the ink droplet amount was 4 pl. Here, the surface of the conveyor belt was treated with a corona discharge treatment and a silicone release agent for each ink set so that the contact angle between the ink and the conveyor belt was as shown in Table 4.

  The contact angle was ranked according to the following criteria.

◎: Contact angle is 70 ° or more ○: Contact angle is 60 ° or more and less than 70 ° ×: Contact angle is 50 ° or more and less than 60 ° XX: Contact angle is less than 50 °

Next, using A4 size Konica Minolta Business Technology's business class plain paper (J paper) as the recording material, the transport direction becomes the short side length of A size, and the environment is 23 ° C. and 30% RH. Below, the image density is adjusted so that the output amount of each color ink is 3 ml / m ² at a resolution of 720 dpi × 720 dpi at a recording speed of 10 ppm (speed of printing 10 sheets of A4 size plain paper per minute). A four-color solid image of 200 mm × 280 mm was recorded.

  Next, the recorded plain paper was left on a flat table in an environment of 23 ° C. and 20% RH for 1 week with the recording surface facing up, and then the raised heights of the four corners were measured. In addition, about the sample of the negative curl which the center part floats, after standing upside down for another day, the lift height of four corners was measured. The raised heights of the four corners were measured as described above, and the curl characteristics were evaluated according to the following criteria.

A: Almost flat, even at the most floating part at the four corners, the lifting height is less than 5 mm. B: The lifting height at the most floating part at the four corners is not less than 5 mm and less than 10 mm. The raised height of the portion is 10 mm or more and less than 20 mm. D: The raised height of the most floating portion at the four corners is 20 mm or more or rounded into a cylindrical shape, and measurement is impossible.

(Evaluation of backside contamination during continuous recording)
Continuous recording was performed on 3001 recording sheets by the above method. At that time, the ink was discharged 1 ml / m ² on the belt every 50 sheets. After recording, the back surfaces of the 501st, 1001st, 2001th, and 3001st recording papers were visually observed, and the backside contamination during continuous recording was evaluated according to the following criteria.

a: No contamination on the back side of any recording paper is observed b: A slight amount of contamination is observed on the back side of the 3001st recording paper c: Although contamination is observed on the back side of the 2001st and 3001st sheets No problem in practical use d: Contamination was confirmed from the back surface of the 501st sheet, which is not suitable for printing on the back surface.

  The results are shown in Table 4.

  As is apparent from the results shown in Table 4, the ink set and the image forming method showing the contact angle that are out of the scope of the present invention are inferior in curl and back surface contamination during continuous use, or in all performances. As a result. On the other hand, in the case of the inkjet image forming method of the present invention, it was found that a good recorded image having excellent curling and no back surface contamination can be obtained.

This is a line head type inkjet image recording apparatus preferably used in the present invention.

Explanation of symbols

1-4 Line Head Type Inkjet Head 5 Recorded Recording Paper 6 Conveying Roller 7 Conveying Belt 8 Cleaning Tank 9 Cleaning Roller 10 Aperture Roller 11 Tension Roller 12 Drive Roller 13 Recording Paper Guide 14 Recording Paper 15 Recording Feed Roller 16 Suppression Roller 17 Static Electroadsorption plate

Claims (5)

In an inkjet image recording apparatus for forming an image by ejecting an inkjet ink from a inkjet head onto a recording paper conveyed by a belt, the inkjet ink contains at least water, a water-soluble organic solvent, and a pigment, and the water content Is 10 mass% or more and less than 50 mass% of the total ink mass, and among the water-soluble organic solvents, all of the water-soluble organic solvents having an SP value ((MPa) ^1/2 ) of 16.5 or more and less than 24.6 An inkjet image recording apparatus characterized by containing 30% by mass or more of the ink, and having a contact angle of 60 ° or more between the inkjet ink and the belt. 2. The vapor pressure at 20 ° C. of a water-soluble organic solvent having an SP value ((MPa) ^1/2 ) of 16.5 or more and less than 24.6 is 0.01 Pa or more and 133 Pa or less. Inkjet image recording apparatus. When a water-soluble organic solvent having an SP value ((MPa) ^1/2 ) of 16.5 or more and less than 24.6 is mixed with water, a water-soluble organic solvent that exhibits a maximum viscosity by its mixing ratio is used, and the maximum 3. The ink jet image recording apparatus according to claim 1, wherein water and the water-soluble organic solvent are mixed at a ratio in the vicinity of the portion. The inkjet image recording apparatus according to claim 1, wherein the image recording is performed by a line head inkjet printer. An ink jet image forming method using the ink jet image recording apparatus according to claim 1.

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