JP4640195B2 - Inkjet recording method - Google Patents

Description

  The present invention relates to a novel ink jet recording 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, an inkjet recording apparatus that emits and controls fine dots, an inkjet ink (hereinafter, also referred to as ink) with improved color reproduction range, durability, ejection suitability, etc., and ink absorbability, coloring material coloring property, It is also possible to obtain image quality comparable to silver halide photography by using special paper with dramatically improved surface gloss.

  However, in an inkjet image recording system that requires special paper, there is a problem that a recording medium that can be used is limited and the cost of the recording medium 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, double-sided printing on plain paper, etc.). Further, it is being applied to so-called POD printing taking advantage of the fact that no printing plate is required.

  The ink composition can also be printed 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) and curls occur. In addition, various studies have been made from the viewpoint of rapid penetration into paper and quick drying. However, the so-called water-based ink in which water, which is generally used as an ink, is a main component of a solvent, easily causes curling on plain paper. This is considered to occur because the hydrogen bond of cellulose in paper shifts from the original position after swelling, and various improvements have been studied (for example, see Patent Document 1), but it is still insufficient.

  On the other hand, the non-aqueous ink has a feature that the influence on the hydrogen bond of cellulose is small and curling is difficult, but the non-aqueous ink has a problem that the showthrough is large (see, for example, Patent Document 2).

  For paper, demands for weight reduction and thinning (ie, lower basis weight) due to economic conditions such as postage cost increases, social demands such as resource saving and environmental issues, and consumer convenience, etc. Is big. However, when water-based ink is printed on plain paper with a low basis weight, there is a problem that curling and back-through are worsened and feathering is also worsened.

  Also, in a paper craft called paper craft, there is a method of printing a pattern on plain paper by inkjet, but when making and using origami or paperback book cover paper by such a method, if the paper is thin The crease may be broken. In particular, when repeatedly touched like a book cover of a paperback book, there is a problem that the crease part is gradually broken and the decorativeness is lowered.

Furthermore, the paper having a low basis weight has a problem that the printed image does not look good because the opacity and whiteness are low.
JP 2004-217930 A JP 2005-193660 A

  An object of the present invention is to provide an ink jet recording method in which curling is suppressed and printing with less feathering is possible even in a low basis weight plain paper recording, crease breakage is less likely to occur, and a printed image is clear. There is.

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

1. An ink jet recording method for printing on plain paper having a basis weight of 20 to 60 g / m ² using an ink jet printer, wherein the ink used contains at least a pigment, an organic solvent and water, and the water content in the ink is all 10 mass% or more and less than 50 mass% of the ink mass, and at least one of the organic solvents is an SP calculated by the method described in SP value (RF Fedors, Polymer Engineering Science, 14, p147 (1974)). Value) is a water-soluble organic solvent having a value of 16.5 or more and less than 24.6, and the content of the water-soluble organic solvent is 50% by mass or more and 80% by mass or less of the total ink mass Recording method.

2. An ink jet recording method for printing on plain paper having a basis weight of 20 to 40 g / m ² using an ink jet printer, wherein the ink used contains at least a pigment, an organic solvent and water, and the water content in the ink is all 10 mass% or more and less than 50 mass% of the ink mass, and at least one of the organic solvents is an SP calculated by the method described in SP value (RF Fedors, Polymer Engineering Science, 14, p147 (1974)). Value) is a water-soluble organic solvent having a value of 16.5 or more and less than 24.6, and the content of the water-soluble organic solvent is 50% by mass or more and 80% by mass or less of the total ink mass Recording method.

3. An ink jet recording method for printing on plain paper having a basis weight of 20 to 60 g / m ² using an ink jet printer, wherein the ink used contains at least a white pigment, an organic solvent and water, and the water content in the ink is It is 10 mass% or more and less than 50 mass% of the total ink mass, and at least one kind of the organic solvent was calculated by the method described in SP value (RF Fedors, Polymer Engineering Science, 14, p147 (1974)). SP value) is 16.5 or more and less than 24.6 water-soluble organic solvent, and the content of the water-soluble organic solvent is 50% by mass or more and 80% by mass or less of the total ink mass. Inkjet recording method.

4). An ink jet recording method for printing on plain paper having a basis weight of 20 to 40 g / m ² using an ink jet printer, wherein the ink used contains at least a white pigment, an organic solvent and water, and the water content in the ink is It is 10 mass% or more and less than 50 mass% of the total ink mass, and at least one kind of the organic solvent was calculated by the method described in SP value (RF Fedors, Polymer Engineering Science, 14, p147 (1974)). SP value) is 16.5 or more and less than 24.6 water-soluble organic solvent, and the content of the water-soluble organic solvent is 50% by mass or more and 80% by mass or less of the total ink mass. Inkjet recording method.

  According to the present invention, an ink jet recording method in which curling is suppressed and printing with less feathering is possible even in low-basis-weight plain paper recording, crease tearing is less likely to occur, and the printed image has good sharpness. be able to.

The present inventor has found an ink that can simultaneously prevent a characteristic that exists between a water-based ink and a non-water-based ink and has a trade-off relationship between curling and back-through. The content of water in the ink is 10% by mass or more and less than 50% by mass of the total ink mass, and at least one of the organic solvents has an SP value (R. F. Fedors, Polymer Engineering Science, 14, a water-soluble organic solvent having an SP value calculated by the method described in p147 (1974) of 16.5 or more and less than 24.6, and the SP value of 16.5 or more and less than 24.6 The ink content is 50% by mass or more and 80% by mass or less of the total ink mass. With such a solvent structure, both of the characteristics of water-based inks that are less likely to curl but easily curl, and the characteristics of non-aqueous inks that are less likely to curl but easily pass through when printing on plain paper. You can take advantage of the advantages, and both disadvantages can be kept to a satisfactory level.

Furthermore, the ink according to the present invention can suppress curling even when a plain paper having a basis weight of 20 to 60 g / m ² is used as a plain paper for printing, and it is possible to prevent blurring from worsening. I found out.

  The reason is considered as follows. When the same amount of ink is printed as compared with thin paper and thick paper, the amount of ink contained per unit volume in the thin paper increases, so that the amount of water increases and curling tends to occur. In addition, curl lifts itself, so from this point it is easier to curl lighter, lighter paper. 2. Description of the Related Art Conventionally, as described in, for example, Japanese Patent Application Laid-Open No. 2004-210902, a method for printing by adding an anti-curl agent in ink to reduce curling is known. As the anti-curl agent, for example, a saccharide such as D-sorbitol is used. However, it is considered that the anti-curl agent prevents curling by blocking the hydroxyl group of cellulose, and the strength of the paper is lowered by its use. In contrast, in the method of the present invention, the decrease in paper strength is slight. Further, when the ink pigment penetrates into the inside, the density on the back side naturally increases in the case of thin paper. However, since the ink according to the present invention has curling resistance and back-through resistance by devising the solvent composition, it is hardly affected even when the paper becomes thin.

  In general, in order to reduce the basis weight of paper, in order to prevent a decrease in paper strength, a measure is taken to increase the blending ratio of softwood pulp having a long fiber length, as described in, for example, JP-A-8-137790. . When the pulp having a long fiber length increases, the feathering that occurs because the ink moves along the fiber is likely to occur. However, in the ink according to the present invention, due to the devising of the solvent composition, the affinity of the ink to the fibers is also low, so it is considered that feathering is unlikely to occur.

  Furthermore, since the paper strength is reduced due to the lower basis weight, the ink tends to become brittle due to the influence of the moisture of the ink, and the crease is likely to break, but this is also improved by devising the solvent composition in the ink according to the present invention. .

  In addition, by printing the non-image area with the ink having the solvent composition of the present invention using a white pigment, a white background having a high surface concentration without being exposed can be obtained, and a printed matter in which a color image can be enhanced while curling is suppressed is obtained. It is done.

"solvent"
The solvent composition in the ink according to the present invention contains at least water and an organic solvent, the water content is 10% by mass or more and less than 50% by mass of the total ink mass, and at least one of the organic solvents is: A water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6, and the content of the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 is 50% by mass of the total ink mass. As described above, it is characterized by being 80% by mass or less , and by using this solvent composition, it is excellent in the emission stability and decap resistance, the character quality of the formed image, the resistance to show through, and the printed recording material. It is possible to improve the curl characteristics.

  If the water content in the total ink mass is less than 50 mass%, the occurrence of curling and cockling is suppressed. Moreover, if it is 10 mass% or more, favorable dispersion stability of the pigment can be obtained. The content of water in the total ink mass is preferably 20% by mass or more and less than 40% by mass.

The ink according to the present invention contains a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 at least 30% by mass of the total ink mass. The occurrence of curling and cockling can be drastically suppressed. In the present invention, a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 is 50% by mass or more and 80% by mass of the total ink mass. containing the following.

  In the ink according to the present invention, the SP value of the main organic solvent is 16.5 or more and less than 24.6, but if it is 16.5 or more, the compatibility with water becomes good and the separation from water is achieved. And high dispersion stability of the pigment particles can be maintained. Moreover, if SP value is less than 24, 6, the inhibitory effect with respect to the curl resulting from an organic solvent can be acquired. In the present invention, the range of the SP value of the organic solvent is more preferably 16.5 or more and less than 22.5.

The SP value (solubility parameter) of the solvent referred to in the present invention is a value represented by the square root of the molecular aggregation energy, and is described in Polymer HandBook (Second Edition) Chapter IV Solubility Parameter Values. The unit is (MPa) ^1/2 and refers to the value at 25 ° C. In addition, R.D. F. It can be calculated by the method described in Fedors, Polymer Engineering Science, 14, p147 (1967). Hereinafter, examples of water-soluble organic solvents having an SP value of 16.5 or more and less than 24.6 are shown together with the SP value. Needless to say, the present invention is not limited to this.

Ethylene glycol monomethyl ether (SP value: 24.5)
Ethylene glycol monoethyl ether (23.5)
Ethylene glycol monobutyl ether (22.1)
Ethylene glycol mono-isopropyl ether (22.7)
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)
Dipropylene glycol monomethyl ether (21.3)
Tripropylene glycol monomethyl ether (20.4)
In the ink according to the present invention, in addition to a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6, various conventionally known water-soluble organic solvents can be used in combination. 1,3-dimethyl-2-imidazolidinone is preferred because it does not adversely affect the dispersibility of the pigment and has the effect of lowering the ink viscosity.

<Pigment>
As the pigment that can be used in the ink according to 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 Pigments and inorganic pigments such as carbon black can be preferably used. The pigment is present in a dispersed state in the water-based ink. The dispersion method may be any of self-dispersion, activator dispersion, polymer dispersion, and microcapsule dispersion, but the polymer dispersion and microcapsule dispersion are fixed. From the viewpoint of sex.

  The insoluble pigment is not particularly limited, 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. 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 pigments, when red, green, blue, or intermediate colors are required, the following pigments are preferably used alone or in combination. I. Pigment Red; 209, 224, 177, 194, C.I. I. Pigment Orange; 43, C.I. I. Vat Violet; 3, C.I. I. Pigment Violet; 19, 23, 37, C.I. I. Pigment Green; 36, 7, C.I. I. Pigment Blue; 15: 6 or the like is 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 average particle size of the pigment dispersion used in the ink according to the present invention is preferably 50 nm or more and less than 200 nm. When the average particle size of the pigment dispersion is less than 50 nm or 200 nm or more, 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 instrument using a dynamic light scattering method, an electrophoresis method, or the like. The accuracy is 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 various desired purposes. As the disperser, a conventionally known ball mill, sand mill, line mill, high-pressure homogenizer, or the like can be used. Among them, the dispersion by sand mill is preferable because the particle size distribution is sharp when the dispersion is aimed at an average particle diameter of around 100 nm. 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 0.1 to 0.5 mm.

<Pigment dispersant>
Examples of the polymer dispersant for dispersing the pigment include higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, naphthalene sulfonates, alkyl phosphates, and polyoxyalkylene alkyl ethers. Activators such as phosphate, polyoxyalkylene alkylphenyl ether, polyoxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, polyoxyethylene fatty acid amide, amine oxide, or styrene, styrene derivatives, vinyl naphthalene derivatives, acrylic Block copolymers, random copolymers and two or more monomers selected from acids, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid and fumaric acid derivatives Mention may be made of these salts.

  In the present invention, the addition amount of the pigment dispersant is preferably 10 to 100% by mass with respect to the pigment.

<Surfactant>
In dispersing the pigment, a surfactant can be used as an additive. As the surfactant used in the present invention, any of cationic, anionic, amphoteric and nonionic surfactants can be used, but it is particularly preferable to use a nonionic surfactant from the viewpoint of dispersion stability.

  Nonionic activators include, for example, polyoxyethylene secondary alcohol ether, polyoxyethylene alkylphenyl ether, polyoxyethylene sterol ether, polyoxyethylene lanolin derivative polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene glycerin fatty acid ester , Polyoxyethylene 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, poly Oxyethylene fatty acid amide, polyoxyethylene alkylamine, alkylamine oxide , Acetylene 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.

《Polyvalent metal ion》
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, is preferably 10 ppm or less, more preferably 0.1 to 5 ppm, particularly preferably. Is 0.1-1 ppm.

  By setting the content of the polyvalent metal ions in the ink to the amount specified above, an ink having high dispersion stability can be obtained. Multivalent metal ions are contained in sulfates, chlorides, nitrates, acetates, organic ammonium salts, EDTA salts and the like.

《Other additives》
In addition to the above description, the ink according to the present invention is publicly known 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. Various additives such as polysaccharides, viscosity modifiers, specific resistance regulators, film forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, anti-fouling agents, rust inhibitors, etc. For example, oil droplet fine particles such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicone oil, ultraviolet absorbers described in JP-A-57-74193, 57-78988 and 62-261476, JP-A-57-74192, 57-87989, 60-72785, 61-146591, JP-A-1-95091 and 3-13376, etc. Examples of the fading-inhibiting agent described in JP-A-59-42993, JP-A-59-52689, JP-A-62-280069, JP-A-61-228771 and JP-A-4-219266 Can do.

  In addition, the dissolved oxygen concentration in the ink according to the present invention is preferably 2 ppm or less at 25 ° C. By setting this dissolved oxygen concentration condition, the formation of bubbles can be suppressed, and emission is also possible in high-speed printing. An ink jet recording method having excellent 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).

"Recording method"
In the image recording method using ink according to 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 to plain paper by a printer loaded with ink jet ink. It is done.

  When forming an image by ejecting the ink according to the present invention, an ink jet head to be used may be an on-demand system or a continuous system. In addition, 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, a thermal type) Any discharge method such as an ink jet type or a bubble jet (registered trademark) type may be used.

  Among them, in the ink jet recording method of the present invention, the ink according to the present invention is ejected from a piezo ink jet recording head having a nozzle diameter of 30 μm or less, and recording is performed on plain paper, and the nozzle diameter is 30 μm or less. It is preferable to perform recording on plain paper by discharging from a piezo-type ink jet recording head having a line head.

  As a printing method of an ink jet printer, the printing characteristics of the ink according to the present invention can be sufficiently obtained by printing with a recording head of a shuttle head method using a recording head of a line head method. Very good isot shape (roundness) and printing accuracy can be achieved when the droplets land on plain paper.

  In particular, it is preferable to apply the ink according to the present invention to an ink jet recording system in which images are printed on both sides of plain paper from the viewpoint that the object and effects of the present invention can be exhibited.

  In double-sided printing, after printing on one side, plain paper is often turned over and transported with the printing side down. Since there is no bleeding of characters and characters, high density and excellent character quality are obtained on any surface, and no conveyance failure occurs and the conveyance belt is not contaminated with ink.

"recoding media"
In the ink jet recording method using the ink according to the present invention, the effect is exhibited with plain paper having a basis weight of 20 to 60 g / m ² . Furthermore, even a plain paper having a basis weight of 20 to 40 g / m ² is effective.

  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 and the like. Is mentioned.

  Further, the plain paper according to the present invention may contain a water-soluble polyvalent metal salt from the viewpoint of improving the ink see-through and pigment fixing property according to the present invention. The water-soluble polyvalent metal salt is not particularly limited, and examples thereof include aluminum, calcium, magnesium, zinc, iron, strontium, barium, nickel, copper, scandium, gallium, indium, titanium, zirconium, tin, and lead. It is added as a salt such as a metal salt, 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. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

<Preparation of ink>
[Preparation of black pigment dispersion]
The following additives are mixed, put together with 200 g of zirconia beads having a diameter of 0.5 mm in a polypropylene plastic bottle, sealed, and dispersed for 0.5 hour using a paint shaker. The black pigment content is 15%. A black pigment dispersion was prepared.

C. I. Pigment Black 7 15 parts Disperbyk190 (Byk-Chemie, 40% solids aqueous solution)
15 parts Tripropylene glycol monomethyl ether 55 parts Water 15 parts [Preparation of black ink 1]
Tripropylene glycol monomethyl ether and water are added to the black pigment dispersion prepared above so that the pigment concentration in the ink is 4.5% and tripropylene glycol monomethyl ether / water = 92/8, and the mixture is sufficiently stirred. It was. Next, this mixed solution was filtered through a # 3500 mesh metal filter, and deaerated with a hollow fiber membrane, whereby a black ink 1 was prepared.

[Preparation of black inks 2 to 5]
Black inks 2 to 5 were prepared in the same manner as the black ink 1 except that the ratio of tripropylene glycol monomethyl ether and water was changed as shown in Tables 1 and 2.

[Preparation of Black Ink 6]
Part of the solvent and water of black ink 1 was replaced with D-sorbitol, an anti-curl agent, and tripropylene glycol monomethyl ether (TPGME) / water = 92/8 was replaced with TPGME / water / D-sorbitol = 35/60 / A black ink 6 was prepared in the same manner as the black ink 1 except that 5.

《Printing evaluation》
An on-demand ink jet printer having a maximum recording density of 720 × 720 dpi using a piezo head having a nozzle diameter of 25 μm, a driving frequency of 12 kHz, a nozzle number of 128, and a nozzle density of 180 dpi (hereinafter, dpi represents the number of dots per 2.54 cm). (Made by Konica Minolta) was used, and evaluation was performed using commercially available plain paper having a basis weight of 55 g / cm ² and a basis weight of 35 g / cm ² .

[Feathering]
Characters were printed, feathering was judged visually, and evaluation was performed according to the following criteria.

A: No feathering at all B: Slight feathering is generated but not a quality that causes a practical problem C: A weak feathering is generated but a quality that causes a practical problem D: Strong feathering Is unacceptable quality [curl]
A solid image was printed, visually observed, and evaluated according to the following criteria.

A: No curl at all B: Slightly curled but not a quality that is practically problematic C: A weak curl is produced, and the quality is just below the practical level D: Slight expansion and contraction is observed, strong curl E: Quality that is a problem in practical use E: Shrinkage is clearly observed, fairly strong curl is generated, and it is an unacceptable quality.
The back side of the solid image was visually observed and evaluated according to the following criteria.

A: No ink bleed or show-through on the back side B: Ink bleed or show-through on the back side is slightly recognized, but it is not a quality that causes practical problems C: Ink bleed or show-through occurs on the back side Slightly recognized, but practically of the quality D: Ink bleeds on the back side, and back-through is a quality that is practically problematic E: Ink bleed on the back side and back-through is severely unacceptable quality [Crack of crease]
The operation of folding the solid image portion by hand and opening it again was repeated 100 times, and then the crease portion was visually observed and evaluated according to the following criteria.

A: The crease had no problem at all. B: The white background inside the paper was slightly visible at two to three places of the fold, but the quality was not a problem in practical use. C: The white background inside the paper was at the five or more places of the fold. Although it is visible, the quality is almost the limit of practical use. D: Many parts of the crease are torn, and the white background inside the paper is quite visible and is a problem that is practically problematic. E: The entire crease is torn, and the white background inside the paper. Is clearly unacceptable, and the holes are partially unacceptable. Table 1 shows the results of printing on plain paper with a basis weight of 55 g / cm ² , and Table 2 shows ordinary results with a basis weight of 35 g / cm ² . The result printed on paper is shown .

When black ink according to the present invention is printed on plain paper having a basis weight of 55 g / cm ^{2, all} of feathering, curling, back-through, and crease cracking are good in rank A, but black ink 1 with a large solvent ratio When black was used, it was defective in see-through, and in black ink 5 having a high water ratio, feathering, curling, and crease cracks were defective.

When the black ink according to the present invention is printed on plain paper with a basis weight of 35 g / cm ² , all of feathering, curling, back-through, and crease cracks are B ranks, and there is no practical problem. On the other hand, when printing on plain paper having a basis weight of 64 g / cm ² , the feathering, curl, and crease cracks of the sample prepared with the black ink 5 are C rank, which is practically the quality.

  Black ink with an anti-curl agent has an effect on curling, but the crease cracking worsened because the paper strength was weakened.

[Preparation of white pigment dispersion]
The following additives are mixed, put together with 200 g of zirconia beads having a diameter of 0.5 mm in a polypropylene plastic bottle, sealed, and dispersed for 5 hours using a paint shaker. A white pigment with a white pigment content of 15% A dispersion was prepared.

Titanium oxide (anatase type: particle size 0.2 μm) 15 parts Jonkrill 501 (manufactured by Johnson Polymer, solid content 30% aqueous solution) 15 parts tripropylene glycol monomethyl ether 55 parts water 15 parts [Preparation of white ink 1]
Tripropylene glycol monomethyl ether and water are added to the white pigment dispersion prepared above so that the pigment concentration in the ink is 4.5% and tripropylene glycol monomethyl ether / water = 92/8, and the mixture is sufficiently stirred. It was. Next, this mixed solution was filtered through a # 3500 mesh metal filter, and deaerated with a hollow fiber membrane, whereby white ink 1 was prepared.

[Preparation of white ink 2-5]
White inks 2 to 5 were prepared in the same manner as the white ink 1 except that the ratio of tripropylene glycol monomethyl ether and water was changed as shown in Tables 3 and 4.

《Printing evaluation》
An on-demand ink jet printer having a maximum recording density of 720 × 720 dpi using a piezo head having a nozzle diameter of 25 μm, a driving frequency of 12 kHz, a nozzle number of 128, and a nozzle density of 180 dpi (hereinafter, dpi represents the number of dots per 2.54 cm). (Made by Konica Minolta) was used, and evaluation was performed using commercially available plain paper having a basis weight of 55 g / cm ² and a basis weight of 35 g / cm ² .

  The character image was printed with black ink 3 on the paper, and the other portions were solid printed with white ink.

[Image clarity]
Ten subjects scored the vividness of the character image in five stages, and the average was evaluated. A: Image sharpness was excellent B: Image sharpness was excellent C: Image Sharpness is not so good D: Image sharpness is inferior E: Image sharpness is very poor Table 3 shows the results of printing on plain paper with a basis weight of 55 g / cm ^2. The result of printing on plain paper with a basis weight of 35 g / cm ² is shown .

When the ink according to the present invention is printed on plain paper having a basis weight of 55 g / cm ^{2, all} of the feathering, curling, back-through, and crease cracks reproduce the result of the black ink, and the non-image area is opaque. The image becomes clearer due to the increased brightness and whiteness.

When the ink according to the present invention was printed on plain paper having a basis weight of 35 g / cm ² , the sharpness was slightly reduced but was an excellent level.

On the other hand, when printing on plain paper with a basis weight of 65 g / cm ² , the feathering, curl, and crease breakage of the sample prepared with the white ink 2 is C rank, which is practically the quality, and the image sharpness. Was not so good (results not shown).

Claims (4)

An ink jet recording method for printing on plain paper having a basis weight of 20 to 60 g / m ² using an ink jet printer, wherein the ink used contains at least a pigment, an organic solvent and water, and the water content in the ink is all 10 mass% or more and less than 50 mass% of the ink mass, and at least one of the organic solvents is an SP calculated by the method described in SP value (RF Fedors, Polymer Engineering Science, 14, p147 (1974)). Value) is a water-soluble organic solvent having a value of 16.5 or more and less than 24.6, and the content of the water-soluble organic solvent is 50% by mass or more and 80% by mass or less of the total ink mass Recording method. An ink jet recording method for printing on plain paper having a basis weight of 20 to 40 g / m ² using an ink jet printer, wherein the ink used contains at least a pigment, an organic solvent and water, and the water content in the ink is all 10 mass% or more and less than 50 mass% of the ink mass, and at least one of the organic solvents is an SP calculated by the method described in SP value (RF Fedors, Polymer Engineering Science, 14, p147 (1974)). Value) is a water-soluble organic solvent having a value of 16.5 or more and less than 24.6, and the content of the water-soluble organic solvent is 50% by mass or more and 80% by mass or less of the total ink mass Recording method. An ink jet recording method for printing on plain paper having a basis weight of 20 to 60 g / m ² using an ink jet printer, wherein the ink used contains at least a white pigment, an organic solvent and water, and the water content in the ink is It is 10 mass% or more and less than 50 mass% of the total ink mass, and at least one kind of the organic solvent was calculated by the method described in SP value (RF Fedors, Polymer Engineering Science, 14, p147 (1974)). SP value) is 16.5 or more and less than 24.6 water-soluble organic solvent, and the content of the water-soluble organic solvent is 50% by mass or more and 80% by mass or less of the total ink mass. Inkjet recording method. An ink jet recording method for printing on plain paper having a basis weight of 20 to 40 g / m ² using an ink jet printer, wherein the ink used contains at least a white pigment, an organic solvent and water, and the water content in the ink is It is 10 mass% or more and less than 50 mass% of the total ink mass, and at least one kind of the organic solvent was calculated by the method described in SP value (RF Fedors, Polymer Engineering Science, 14, p147 (1974)). SP value) is 16.5 or more and less than 24.6 water-soluble organic solvent, and the content of the water-soluble organic solvent is 50% by mass or more and 80% by mass or less of the total ink mass. Inkjet recording method.