JP2007185828A - Inkjet recording method and inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording method which is free from strike through and curling and brings about a high density, by using ink which contains a solvent satisfying specific conditions, and water. <P>SOLUTION: In the inkjet recording method, recording is made on plain paper by using the ink containing the water of 10-45 mass% and the solvent of 50-90 mass% of which the surface tension at 25°C is 25-40 mN/m, the viscosity at 25°C of 1-50 mPa s (Pascal second) and the vapor pressure at 25°C of 133 Pa or less. The plain paper undergoes a measure for reducing the moisture. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inkjet recording method and an inkjet printer.

  In recent years, the inkjet recording method can be easily and inexpensively produced images, and thus has been applied to various printing fields such as photographs, various printing, marking, and special printing such as color filters. In particular, ink jet recording devices that emit and control fine dots, ink with improved color reproduction range, durability, and emission suitability, ink absorbency, colorant color development, surface gloss, etc. are 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 capable of performing full color printing at high speed without being restricted by a recording medium (for example, plain paper, coated paper, art paper, plain paper double-sided printing, etc.).

  As for the composition of inkjet ink, it can print at high speed, has good character reproducibility on plain paper, and shows through when printing (a phenomenon in which the printed ink passes through the recording medium and the image appears on the back), feathering Various studies have been made from the viewpoints of no occurrence of image bleeding, rapid penetration into paper, and quick drying.

  As one of the methods, a so-called water-based ink-jet ink having a water content of 50% by mass or more is widely used as an ink-jet ink. An electrophotographic copy paper using such a water-based ink-jet ink is widely used. When recording images on plain paper such as high-quality paper and medium-quality paper, in addition to problems caused by penetrability such as image back-through and feathering, curling and cockling of the recorded plain paper is a major problem. Become.

  In order to solve the above problems, an ink jet recording method using an ink having improved penetrability by specifying a wetting time and an absorption coefficient for a recording medium in the Bristow method has been disclosed (for example, see Patent Document 1). However, in this method, since the colorant in the ink also penetrates into the plain paper at the same time, the image density is lowered and the ink shows through, which is not suitable for double-sided printing. Have

  Further, an inkjet ink containing a specific amide compound, pyridine derivative, imidazoline compound or urea compound as an anti-curl agent is disclosed (for example, see Patent Document 2). However, this method has a problem that clogging is likely to occur in the nozzle portion of the recording head as the ink liquid is dried.

  Further, as a method for improving the curl, an inkjet recording method supplement is proposed in which a solution containing water is applied to the back side of the image printing surface to optimize the curl balance (see, for example, Patent Document 3). . However, this method has the disadvantages that it does not have the ability to record on both sides, and the strength of plain paper decreases with the increase in the amount of ink and curl balance liquid attached to plain paper, and jamming is likely to occur during transportation. there were.

  Further, solvent-based inks that can perform printing at high speed instead of water-based inkjet inks have been studied. That is, by using an oil-based ink (solvent ink jet ink) that contains a volatile solvent and has improved drying properties, even when printing on plain paper, the penetration into the recording medium is fast and the drying time is short. High-speed printing is possible without curling or the like. However, solvent-based inks have high penetrability into plain paper media, resulting in poor character reproducibility and back-through on recording media, which is a major obstacle especially when printing on both sides of plain paper. It was.

  In order to solve such a problem, an ink-jet ink in which a solvent satisfying specific conditions and water are mixed to prevent curling and back-through is disclosed (for example, see Patent Document 4).

Further, it contains 10 to 45% by mass of water, has a surface tension at 25 ° C. of 25 mN / m or more and 40 mN / m or less, a viscosity at 25 ° C. of 1 mPa · s or more and 50 mPa · s or less, and at 25 ° C. It is disclosed that curl prevention and back-through prevention are compatible in an inkjet recording method for recording on plain paper using an ink containing 50 to 90% by mass of a solvent having a vapor pressure of 133 Pa or less (see, for example, Patent Document 5). However, there is still a problem with prevention of show-through and the print density is not sufficient.
JP 10-316915 A JP 9-176538 A JP-A-10-272828 Japanese Patent Laid-Open No. 2005-220298 JP 2005-220296 A

  An object of the present invention is to provide an ink jet recording method having a high density without back-through and curling by using an ink containing a solvent and water satisfying specific conditions.

  The above object of the present invention makes it possible to provide a means for obtaining a printed matter having a high density and no show-through and curl by the following configuration.

  1. Vapor pressure at 25 ° C. containing 10 to 45% by mass of water, having a surface tension at 25 ° C. of 25 mN / m to 40 mN / m, a viscosity at 25 ° C. of 1 mPa · s to 50 mPa · s. Ink-jet recording method for recording on plain paper using ink containing 50 to 90% by mass of a solvent having a viscosity of 133 Pa or less, wherein the plain paper is a paper provided with means for reducing moisture .

  2. 2. The ink jet recording method according to 1 above, wherein the plain paper is a paper having a water content of 0.1 to 6% by mass.

  3. 2. The ink jet recording method as described in 1 above, wherein the plain paper is a paper which is allowed to stand for 10 minutes or more in an environment having a humidity of 5 to 55% RH.

  4). 2. The ink jet recording method according to 1 above, wherein the plain paper is heat-treated paper.

  5. 2. The ink jet recording method according to 1 above, wherein the plain paper is paper irradiated with infrared rays or microwaves.

  6). 6. An ink jet printer wherein the inside of the ink jet printer used for the ink jet recording method according to any one of 1 to 5 is adjusted to a humidity of 5 to 55% RH.

  7). 6. An ink jet printer, wherein the inside of a paper feed tray of the ink jet printer used in the ink jet recording method according to any one of 1 to 5 is adjusted to a humidity of 5 to 55% RH.

  8). 2. An ink jet printer used in the ink jet recording method according to claim 1, wherein the ink jet printer has a mechanism for heating paper before ink jet recording.

  9. 2. An ink jet printer for use in the ink jet recording method according to claim 1, wherein the ink jet printer has a mechanism for irradiating the paper with infrared rays or microwaves before performing ink jet recording.

  According to the present invention, it is possible to provide an ink jet recording method having high density and no back-through and curling.

  The present invention will be described in more detail. Although details are unclear, as far as the ink according to the present invention is concerned, it has been found that there is a relation between the moisture content of paper before ink jet recording and the penetration property. Therefore, the paper was successfully dehumidified before printing, or dried by means such as heating, and succeeded in increasing the resistance to paper breakthrough. Furthermore, as a result of suppressing the show-through, the surface print density itself was also improved.

  In known water-based inks that do not satisfy the requirements of the ink in the present invention, there is no case in which the print density and the strike-through rate change with respect to the moisture in the paper, and this effect is achieved by using the ink used in the present invention. This is an effect obtained only when printing is performed on paper with a reduced moisture content.

  As an effect of the present invention, the print density is improved and the show-through is suppressed, which suggests that the color material is fixed on the surface layer side. Therefore, when the water content in the paper is small, the coloring material is liquid chromatographically because a strong interaction between the highly hydrophilic component and the paper fiber (in the ink of the present invention, the coloring material and water) tends to occur. The present inventors infer that the surface will be fixed by the principle of the graph and only the remaining solvent will permeate.

  The ink used in the present invention will be described. First, a solvent having a surface tension at 25 ° C. of 25 mN / m or more and 40 mN / m or less, a viscosity at 25 ° C. of 1 mPa · s or more and 50 mPa · s or less, and a vapor pressure at 25 ° C. of 133 Pa or less. explain.

  As described above, in the solvent (aqueous solvent) according to the present invention, as one requirement, the surface tension at 25 ° C. is 25 mN / m or more and 40 mN / m or less, preferably 25 mN / m or more. 32 mN / m or less. In addition, the viscosity at 25 ° C. is one of the characteristics that it is 1 mPa · s or more and 50 mPa · s or less, and preferably 1 mPa · s or more and 30 mPa · s or less. Moreover, although it is one of the characteristics that the vapor pressure in 25 degreeC is 133 Pa or less, Preferably it is 1-67 Pa.

  The solvent (aqueous solvent) that can be used in the present invention is not particularly limited as long as it satisfies all the three liquid properties defined above. For example, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl Ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, Propylene glycol monobutyl ether, dipropylene glycol monomethyl ether , Dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, diethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, tripropylene glycol monobutyl ether, tetrapropylene glycol monomethyl ether , Diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol diethyl ether, triethylene glycol dibutyl ether, dipropylene glycol dibutyl ether, tripropylene glycol dibutyl ether, 3-methyl-2,4-pentanediol, diethylene glycol monoethyl ether Or the like can be mentioned acetate.

  The ink used in the present invention contains various functional additives in addition to the above-described solvents.

  The ink used in the present invention contains a colorant in the above-mentioned solvent, and further contains each additive as described below, as the hue of the colorant used in the present invention, for example, Yellow, magenta, cyan, black, blue, green, and red are preferably used, and yellow, magenta, cyan, and black colorants are particularly preferable.

  The ink used in the present invention is a dye ink in which the colorant is a dye, or a pigment ink or a colorant that forms a dispersion containing fine pigment particles, in which the colorant is insoluble in the solvent constituting the inkjet ink. The present invention can be applied to various ink-jet inks such as a dispersion ink composed of a dispersion of a colored polymer.

  Examples of the dye that can be used in the present invention include azo dyes, methine dyes, azomethine dyes, xanthene dyes, quinone dyes, phthalocyanine dyes, triphenylmethane dyes, diphenylmethane dyes, and the specific compounds include: For example, the dye illustrated in Unexamined-Japanese-Patent No. 2002-264490 can be mentioned.

  In addition, for oil-soluble dyes that form colored fine particles together with the polymer or the like and serve as a colorant, they are usually soluble in organic solvents that do not have a water-soluble group such as carboxylic acid and sulfonic acid and are insoluble in water, such as dispersed A dye or the like is selected. Also included are dyes that exhibit oil solubility by salting a water-soluble dye with a long-chain base. For example, acid dyes, direct dyes, salt-forming dyes of reactive dyes and long-chain amines are known. .

  However, in the ink used in the present invention, it is preferable to use a pigment as the colorant, and a pigment having no solubility in the solvent system is preferable from the viewpoint of exerting the intended effect of the present invention.

  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.

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

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

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

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

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

In addition to the above, when red, green, blue and intermediate colors are required, the following pigments are preferably used alone or in combination. I. Pigment Red; 209, 224, 177, 194,
C. I. Pigment Orange; 43,
C. I. Vat Violet; 3,
C. I. Pigment Violet; 19, 23, 37,
C. I. Pigment Green; 36, 7,
C. I. Pigment Blue; 15: 6,
Etc. are used.

  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 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.

  The average particle size of the pigment dispersion used in the ink used in the present invention is preferably 10 nm to 200 nm, more preferably 10 nm to 100 nm, and still more preferably 10 nm to 50 nm. If the average particle size of the pigment dispersion exceeds 100 nm, the dispersion becomes unstable. In addition, even when the average particle size of the pigment dispersion is less than 10 nm, the stability of the pigment dispersion tends to deteriorate, and the storage stability of the ink tends to deteriorate.

  The particle size of the pigment dispersion can be determined by a commercially available particle size measuring device using a light scattering method, an electrophoresis method, a laser Doppler method or the like. It is also possible to obtain a particle image with a transmission electron microscope on at least 100 particles and perform statistical processing on the image using image analysis software such as Image-Pro (manufactured by Media Cybernetics). Is possible.

  By using the ink, it is possible to obtain a recorded matter having the same density as water-based ink, good curl, and high resistance to back-through.

  In the ink-jet ink used in the present invention, a surfactant can be used as an additive during dispersion. As the surfactant used in the present invention, any of cationic, anionic, amphoteric and nonionic can be used.

  Examples of the cationic surfactant include aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium salts, benzethonium chloride, pyridinium salts, imidazolinium salts, and the like.

  Examples of the anionic surfactant include fatty acid soap, N-acyl-N-methylglycine salt, N-acyl-N-methyl-β-alanine salt, N-acyl glutamate, acylated peptide, alkyl sulfonate, Alkyl benzene sulfonate, alkyl naphthalene sulfonate, dialkyl sulfosuccinate, alkyl sulfoacetate, α-olefin sulfonate, N-acylmethyl taurine, sulfated oil, higher alcohol sulfate, secondary higher alcohol Sulfate ester, alkyl ether sulfate, secondary higher alcohol ethoxy sulfate, polyoxyethylene alkyl phenyl ether sulfate, monoglyculate, fatty acid alkylolamide sulfate, alkyl ether phosphate ester, alkyl phosphate ester Examples include tellurium salts.

  Examples of amphoteric surfactants include carboxybetaine type, sulfobetaine type, aminocarboxylate, imidazolinium betaine and the like.

  Nonionic activators include polyoxyethylene secondary alcohol ether, polyoxyethylene alkylphenyl ether, polyoxyethylene sterol ether, polyoxyethylene lanolin derivative polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene glycerin fatty acid ester, Oxyethylene castor oil, hydrogenated castor oil, polyoxyethylene sorbitol fatty acid ester, polyethylene glycol fatty acid ester, fatty acid monoglyceride, polyglycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, sucrose fatty acid ester, fatty acid alkanolamide, polyoxyethylene Fatty acid amide, polyoxyethylene alkylamine, alkylamine oxide, acetyl Glycol, acetylene alcohol, and the like.

  Further, it is preferable to use a surfactant in order to accelerate the penetration of ink droplets after ink ejection into plain paper, and such a surfactant has an adverse effect on the ink, such as storage stability. The surfactant is not limited as long as it does not affect the surface, and the same surfactants as those used as an additive at the time of dispersion can be used.

  Further, in the ink used in 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 0.1 ppm. 5 ppm, particularly preferably 0.1 to 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 of the present invention, in addition to the above description, if necessary, the output stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other various performance improvement objectives are known. Various additives such as polysaccharides, viscosity modifiers, specific resistance regulators, film forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, antifungal agents, rust preventives, etc. may be appropriately selected and used. For example, oil droplet fine particles such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicon oil, ultraviolet absorbers described in JP-A-57-74193, 57-87988, and 62-261476, As described in Kaisho 57-74192, 57-87989, 60-72785, 61-146591, JP-A-1-95091 and 3-13376, etc. Anti-fading agents, fluorescent whitening agents described in JP-A Nos. 59-42993, 59-52689, 62-280069, 61-242871, and JP-A-4-219266 Can be mentioned.

  Next, the plain paper in the present invention will be described.

  Examples of the plain paper in the present invention include what are generally called high-quality paper, neutral paper, and copy paper. In the text, the term “recording paper” or “paper” means plain paper.

  The feature of the present invention is to control the water content in paper before ink jet recording.

  Hereinafter, a method for controlling the moisture in the paper will be described.

  When ink that satisfies the requirements of the present invention is used, a paper that has been subjected to a treatment for reducing the moisture content of the paper in advance can obtain a printed matter with a high print density and less show-through compared to the paper that was not used. Out.

  The moisture content in the present invention is the amount of water contained in paper, and is a value expressed in mass% based on the absolute dry mass of paper. The water content of the paper can be measured using any moisture measurement method. Specifically, it can be known by using an infrared moisture meter, an absolutely dry mass method, a dielectric constant method, a Karl Fischer method, or the like.

  From the viewpoint of ink jet recording density and see-through, the moisture content of the paper is preferably 6% by mass or less, more preferably 4% by mass or less, and the lower the better. On the other hand, in terms of means for controlling the moisture content, a moisture content of 2% by mass or less requires a means such as decompression. Therefore, it can be said that the moisture content is preferably 2% by mass or more from the viewpoint of simplicity.

  One method for reducing the moisture content of paper is to condition the paper in an atmosphere with a low relative humidity. This is due to the fact that the moisture content of the paper varies with the relative humidity of the environment. In the description of the present invention, the relative humidity refers to water vapor pressure / saturated water vapor pressure, and can be measured with a commercially available hygrometer such as a dry hygrometer, a hair hygrometer, a dew point hygrometer, an electric hygrometer, and the like.

  The range of the relative humidity for adjusting the humidity of the paper is preferably 5 to 55% RH, more preferably 5 to 30% RH.

  It is preferable to perform humidity conditioning for 10 minutes or more. When the humidity is adjusted in a state where the papers are stacked, it is preferable to adjust the humidity for 3 hours or more depending on the number of sheets. It is more preferable to adjust the humidity for 12 hours or more. The effect of the invention is not impaired when the humidity is adjusted for a long time.

  By dehumidifying the inside of the printer, the paper stocked in the printer can be automatically conditioned. At this time, the inside of the printer is preferably set to a relative humidity in the range of 5 to 55% RH, and more preferably set to a relative humidity in the range of 5 to 30% RH. Further, dehumidification of only the paper feed tray may be performed, and in this case, it is more preferable because the paper can be dehumidified without imposing a burden on the ink ejection mechanism.

  The moisture content of the paper can also be lowered by drying immediately before ink jet recording. In this case, unlike the adjustment of the moisture content of the paper by humidity control, a short time is required. For example, the set paper can be processed on-time by incorporating a drying mechanism on the transport mechanism, which is preferable.

  As a drying method, a method by heating or blowing, a method by radiation of electromagnetic waves, or the like can be performed, and these methods may be used in combination.

  When the paper is dehumidified by heating or electromagnetic wave irradiation, the surface temperature of the paper during drying is preferably in the range of 30 to 90 ° C. If it is 90 ° C. or lower, there is no risk of ignition, and if it is 30 ° C. or higher, paper drying is quick, which is preferable.

  Infrared rays or microwaves are preferably used as electromagnetic waves because they exhibit high drying efficiency in a short time. In the present invention, infrared refers to electromagnetic waves having a wavelength in the range of 0.1 μm to 1 mm, and microwave refers to electromagnetic waves having a wavelength in the range of 1 mm to 1 m.

  In the ink jet recording method of the present invention, for example, an ink jet print is obtained by ejecting ink as droplets from an ink jet head based on a digital signal and adhering it to plain paper with a printer loaded with ink jet ink.

  In the ink jet recording method of the present invention, the ink jet head to be used may be an on-demand system or a continuous system. Also, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an 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 them, in the ink jet recording method of the present invention, the ink of the present invention is ejected from a piezo ink jet recording head having a nozzle diameter of 30 μm or less, recording is performed on plain paper, and the nozzle diameter is 30 μm or less. It is desirable to perform recording on plain paper by discharging from a piezo-type ink jet recording head of the line head type. The printing characteristics of the ink of the present invention can be sufficiently extracted by printing on the shuttle head type recording head using a line head type recording head.

Example 1
[Preparation of pigment dispersion A]
After mixing 15 parts by mass of carbon black MA100 (manufactured by Mitsubishi Chemical Corporation) as a pigment, 15 parts by mass of Joncryl 501 as a dispersion resin, 5 parts by mass of tripropylene glycol monomethyl ether, and 65 parts by mass of water, a diameter of 0.5 mm was mixed. 200 parts by mass of zirconia beads were placed in a polypropylene plastic bottle and sealed, and dispersed for 5 hours with a paint shaker to obtain a black dispersion.

[Preparation of ink A]
The dispersion, solvent, and water were mixed at the following ratio, and stirred for about 30 minutes with a paint shaker. The numerical value of the addition amount in the table represents parts by mass. Thereafter, the beads were removed, and filtration and membrane deaeration treatment using a hollow fiber membrane were performed to prepare ink A.
Tripropylene glycol monomethyl ether 230 parts by weight Water 45 parts by weight Pigment Dispersion A 100 parts by weight [Preparation of Ink B]
The dispersion, solvent, and water were mixed at the following ratio, and stirred for about 30 minutes with a paint shaker. The numerical value of the addition amount in the table represents parts by mass. Thereafter, the beads were removed, and filtration and membrane deaeration treatment using a hollow fiber membrane were performed to prepare ink B.
Dipropylene glycol monomethyl ether 230 parts by weight Water 45 parts by weight Pigment Dispersion A 100 parts by weight [Preparation of Ink C]
The dispersion, solvent, and water were mixed at the following ratio, and stirred for about 30 minutes with a paint shaker. The numerical value of the addition amount in the table represents parts by mass. Thereafter, the beads were removed, and filtration and membrane deaeration treatment using a hollow fiber membrane were performed to prepare ink C.
2-Methyl-2,4, -pentanediol 200 parts by weight Water 75 parts by weight Pigment Dispersion A 100 parts by weight [Preparation of Ink D]
The dispersion, solvent, and water were mixed at the following ratio, and stirred for about 30 minutes with a paint shaker. The numerical value of the addition amount in the table represents parts by mass. Thereafter, the beads were removed, and filtration and membrane deaeration treatment using a hollow fiber membrane were performed to prepare ink D.
Triethylene glycol monobutyl ether 5 parts by mass Water 270 parts by mass Pigment Dispersion A 100 parts by mass Table 1 shows the configurations of the prepared inks A to D.

[Effect of dehumidification of paper]
As the print recording paper, A4 size of Shiraioi thin (manufactured by Daishowa Paper) was used. The recording paper was left overnight in a room adjusted to 23 ° C., 20% RH, 23 ° C., 50% RH, and 23 ° C., 80% RH, and three types of recording paper having different paper moisture contents were obtained. The moisture content was determined by measurement with a Karl Fischer moisture meter. The constant weight of paper at 105 ° C. was used as the absolute dry mass. The moisture content of each conditioned paper was as follows.

  Each of the inks A to D was replaced with a black cartridge of MC2000 manufactured by Seiko Epson Corporation, and printing was performed on three types of paper having different dehumidified states to prepare ink jet recording samples.

As an inkjet recording pattern, the margin from the four sides in the center of the A4 sheet is 2.5 cm, 720 dpi × 720 dpi (dpi represents 1 inch, that is, the number of dots per 2.54 cm), and the emission amount is Solid printing was performed with black ink so that the density was about 10 g / m ² .

Back-through evaluation method For each sample, the surface concentration and the back surface concentration one day after printing were measured. The results are shown in Table 3. For the measurement of the print density, Xrite 938 (Japanese lithographic equipment) was used, and the visual density in status A was used as a value.

Curl evaluation method The curl was evaluated according to the following criteria.
○: The total floating of the four corners of the paper when the paper is placed on a flat surface after one day of inkjet recording is within 0 to 1 cm. Δ: The floating of the four corners of the paper when the paper is placed on a flat surface after one day of inkjet recording. Total: within 1 to 12 cm x: One day after ink jet recording, the total of the four corners of the paper when the paper is placed on a flat surface is 12 cm or more, or rounded and cannot be measured.

  In Table 3, for inks A, B, and C that satisfy the configuration of the ink used in the present invention, the surface concentration increases and the back surface concentration decreases as the moisture content of the paper decreases. On the other hand, in the ink D which is not included in the configuration of the present invention, there is almost no influence due to the moisture content of the paper.

  From the above results, water is 10 to 45% by mass, the surface tension at 25 ° C. is 25 mN / m or more and 40 mN / m or less, the viscosity at 25 ° C. is 1 mPa · s or more and 50 mPa · s or less, and at 25 ° C. When an ink containing 50 to 90% by mass of a solvent having a vapor pressure of 133 Pa or less is used, it can be said that as the water content of the paper is reduced, an ink-jet recorded product having a high concentration and small show-through can be obtained.

Example 2
[Effect of paper drying]
As print recording paper, A4 size of Shiraioi thin (made by Daishowa Paper) was used. The ink A was replaced with a black cartridge of MC2000 manufactured by Seiko Epson Corporation, and ink jet recording was performed. As the ink jet recording pattern, solid printing was performed with black ink so that the margin from the four sides was 2.5 cm in the center of the A4 paper surface, 720 dpi × 720 dpi, and the output amount was about 10 g / m ² . .

  At this time, as for sample 1, recording paper that had been sufficiently dried with hot air by a drier was placed in a printer immediately after drying, and ink jet recording was performed by the above printing method.

  Sample 2 was a recording paper that had been irradiated with infrared rays for 15 seconds by a 400 W halogen lamp, and was set in a printer immediately after drying, and ink jet recording was performed by the above printing method.

  Sample 3 was not dried and ink jet recording was performed by the above method.

Back-through evaluation method For each sample, the surface concentration and the back surface concentration after one day of printing were measured. The results are shown in Table 4. For the measurement of the print density, Xrite 938 (Japanese lithographic equipment) was used, and the visual density in status A was used as a value.

Curl evaluation method The curl was evaluated according to the following criteria.
○: The total floating of the four corners of the paper when the paper is placed on a flat surface after one day of inkjet recording is within 0 to 1 cm. Δ: The floating of the four corners of the paper when the paper is placed on a flat surface after one day of inkjet recording. Total: within 1 to 12 cm x: One day after ink jet recording, the total of the four corners of the paper when the paper is placed on a flat surface is 12 cm or more, or rounded and cannot be measured.

  From the above results, it was possible to obtain a sample having a high surface concentration and a low back surface density by drying the paper before ink jet recording.

  10 to 45% by mass of water, the surface tension at 25 ° C. is 25 mN / m or more and 40 mN / m or less, the viscosity at 25 ° C. is 1 mPa · s or more and 50 mPa · s or less, and the vapor pressure at 25 ° C. is 133 Pa or less. By using an ink containing 50 to 90% by mass of the solvent and reducing the moisture in the paper in advance before printing, it is possible to provide a high-density ink jet recording method without back-through and curl. did.

Claims (9)

Vapor pressure at 25 ° C. containing 10 to 45% by mass of water, having a surface tension at 25 ° C. of 25 mN / m to 40 mN / m, a viscosity at 25 ° C. of 1 mPa · s to 50 mPa · s. Ink-jet recording method for recording on plain paper using ink containing 50 to 90% by mass of a solvent having a viscosity of 133 Pa or less, wherein the plain paper is a paper provided with means for reducing moisture . 2. The ink jet recording method according to claim 1, wherein the plain paper is a paper having a water content of 0.1 to 6% by mass. 2. The ink jet recording method according to claim 1, wherein the plain paper is a paper which has been allowed to stand for 10 minutes or more in an environment having a humidity of 5 to 55% RH. 2. The ink jet recording method according to claim 1, wherein the plain paper is heat-treated paper. 2. The ink jet recording method according to claim 1, wherein the plain paper is paper irradiated with infrared rays or microwaves. 6. An ink jet printer, wherein the inside of the ink jet printer used for the ink jet recording method according to claim 1 is adjusted to a humidity of 5 to 55% RH. 6. An ink jet printer, wherein the inside of a paper feed tray of the ink jet printer used in the ink jet recording method according to claim 1 is adjusted to a humidity of 5 to 55% RH. 2. The ink jet printer used in the ink jet recording method according to claim 1, wherein the ink jet printer has a mechanism for heating paper before ink jet recording. 2. The ink jet printer used in the ink jet recording method according to claim 1, wherein the ink jet printer has a mechanism for irradiating the paper with infrared rays or microwaves before performing ink jet recording.