JP2011098454A - Inkjet printing method using oil-based ink and ink set - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new pretreatment liquid which can contribute to enhancing the print density of printed matter, and inhibiting the feathering phenomenon and strike-through of an ink and the distortion of a printing medium and thereby, keeping the conveyability of the printing medium successful, in an inkjet printing system using oil-based ink for performing a printing operation by discharging the oil-based ink containing a pigment to the surface of a printing medium after applying a pretreatment liquid to the printing medium, especially, an inkjet printing system for printing a paper by using a line head type inkjet printer. <P>SOLUTION: The pretreatment liquid contains at least an inorganic particle with the average particle diameter of 0.15 to 15 μm, water and a water-soluble organic solvent. In addition, it is recommended that the pretreatment liquid is used which has the mass ratio of the content of the water-soluble organic solvent to the content of water of the pretreatment liquid (the content of the water-soluble organic solvent/the content of water) is within the range of 0.1 to 0.8. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an oil-based inkjet printing method for improving printing density by suppressing penetration of ink into a printing medium and preventing back-through and bleeding, and an ink set used for the printing method.

  In recent years, inkjet printing systems are increasingly required to be able to perform full-color printing at high speed without being restricted by recording media. In order to meet this demand, the use of a line head type ink jet printer is suitable. In that case, the penetration into plain paper is fast, the drying is fast, the printing density is high, and there is little bleeding and show-through. Ink that provides a high-quality print image is required.

Ink jet inks used in the ink jet printing system are roughly classified into water-based inks and non-water-based inks.
Since water-based ink contains water as a solvent, when plain paper is used as the printing medium, the solvent easily penetrates into the printing medium and the pigment tends to stay on the surface of the printing medium. While it is easy to obtain an image, there is a drawback in that the print medium is likely to curl and cockling, adversely affects the transportability of the print medium, and is an adverse effect of high-speed printing.

Non-aqueous inks are roughly classified into solvent inks mainly containing a highly volatile organic solvent as a solvent and oily inks mainly containing a low volatile organic solvent as a solvent.
The solvent ink is excellent in drying properties, but the use environment is limited because a large amount of the solvent is volatilized. On the other hand, oil-based inks, when using plain paper as a printing medium, have excellent penetrability and drying properties on the printing medium, while the solvent is less volatile than water-based inks and solvent inks. This is advantageous in that it does not easily occur and the number of times of cleaning of the ink nozzles can be reduced, and is suitable for high-speed printing, particularly high-speed ink jet printing of the line head system.

  However, oil-based inks have poor colorant and solvent detachability on the print medium, and particularly when plain paper is used as the print medium, the colorant and solvent tend to penetrate the fiber gaps of the print medium together. There are drawbacks in that the density is lowered, the back-through is increased, and the printed dots are blotted to deteriorate the image quality of the printed image.

  Conventionally, with water-based inks, as a method for keeping the coloring material on the surface of plain paper without penetrating with the solvent, a reactive liquid is contained in the ink, and a treatment liquid containing a substance that reacts with the substance is prepared. In addition, a method has been proposed in which the treatment liquid is ejected over the ink and both substances are reacted on the paper surface to aggregate the color material and make it difficult to penetrate (Patent Document 1 and Patent Document 2). . Further, a method has been proposed in which a pretreatment liquid containing cationic inorganic particles and a water-based ink containing an anionic dye are reacted and fixed (Patent Document 3). However, no method has yet been proposed that shows the same effect for non-aqueous inks.

  In addition, when treating plain paper with a pretreatment liquid containing inorganic particles, it is preferable to use water with good dryness and safety as a solvent for the pretreatment liquid, but the amount of water in the pretreatment liquid is large. As a result, the plain paper is deformed, which adversely affects the transportability of the print medium and becomes an obstacle to high-speed printing.

JP 08-281930 A JP 2000-198263 A JP 2007-276387 A

  The present invention relates to an oil-based ink jet printing system that performs printing by applying a pretreatment liquid onto a print medium and then discharging an oil-based ink containing a pigment onto the print medium, particularly using a line head ink jet printer. In an inkjet printing system that prints on paper, by providing a new pretreatment liquid, the print density of the printed matter is increased, bleeding and back-through are prevented, and deformation of the printing medium is prevented, thereby conveying the printing medium. It aims at maintaining favorable.

  As a result of intensive research under the above-mentioned object, the present inventor, in the oil-based ink jet printing system, comprises at least inorganic particles having an average particle diameter of 0.15 μm to 15 μm, water, and a water-soluble organic solvent, and the pretreatment Use a pretreatment liquid in which the mass ratio of the content of the water-soluble organic solvent to the content of water in the liquid (water-soluble organic solvent content / water content) is in the range of 0.1 to 0.8. As a result, the pigment in the oil-based ink discharged to the print medium is retained on the print medium and the penetration into the print medium is suppressed, so that not only can the printing density be improved but also the back-through and bleeding can be prevented. The present inventors have found that the deformation of the print medium can be prevented and the transportability of the print medium can be maintained well, and the present invention has been completed.

  That is, according to one aspect of the present invention, in the oil-based inkjet printing method of performing printing by applying a pretreatment liquid to a print medium and then discharging an oil-based ink containing at least a pigment and a solvent onto the print medium. The pretreatment liquid comprises at least inorganic particles having an average particle diameter of 0.15 μm to 15 μm, water and a water-soluble organic solvent, and the content of the water-soluble organic solvent relative to the content of water in the pretreatment liquid An oil-based inkjet printing method in which the mass ratio (water-soluble organic solvent content / water content) is in the range of 0.1 to 0.8 is provided.

  According to another aspect of the present invention, there is an ink set used for oil-based inkjet printing in which printing is performed by ejecting oil-based ink onto the print medium after applying a pretreatment liquid to the print medium, An oil-based ink comprising at least a pigment and a solvent, and a pretreatment liquid comprising at least an inorganic particle having an average particle size of 0.15 μm to 15 μm, water and a water-soluble organic solvent, and the water in the pretreatment liquid An ink set for oil-based ink jet printing in which the mass ratio of the content of the water-soluble organic solvent to the content of (water-soluble organic solvent content / water content) is in the range of 0.1 to 0.8 is provided.

  According to the present invention, the pretreatment liquid is constituted by dispersing inorganic particles having an average particle diameter of 0.15 μm to 15 μm in a solvent composed of water and a water-soluble organic solvent. By treating the surface of the print medium with the above, the surface of the print medium is sealed, and the pigment in the printed oil-based ink stays on the print medium and the penetration of the coloring material into the print medium is suppressed. Concealment and bleeding are prevented at the same time as the concentration is improved. Furthermore, the solvent of the pretreatment liquid contains water and a water-soluble organic solvent in a mass ratio (water-soluble organic solvent content / water content) of 0.1 to 0.8. Even when the surface is treated, the print medium is not deformed such as curling, and the transportability of the print medium is kept good, so that high-speed printing is not hindered.

  Hereinafter, the present invention will be described in more detail.

1. Oil-based ink The oil-based ink used in the present invention is mainly composed of a solvent and a pigment, but may contain other components as necessary.

1-1. The solvent solvent is not particularly limited as long as it functions as an ink solvent, that is, a vehicle, and may be either a volatile solvent or a hardly volatile solvent. However, in the present invention, from the environmental viewpoint, the solvent preferably contains a hardly volatile solvent as a main component. The boiling point of the hardly volatile solvent is preferably 200 ° C. or higher, more preferably 240 ° C. or higher.

  As a solvent, any organic solvent of a nonpolar organic solvent and a polar organic solvent can be used. These may be used alone or in combination of two or more as long as they form a single phase. In the present invention, a nonpolar organic solvent and a polar organic solvent are preferably used in combination, and the solvent is preferably composed of 20 to 80% by weight of a nonpolar solvent and 80 to 20% by weight of a polar solvent, More preferably, the solvent is composed of ˜45 wt% nonpolar solvent and 70 ˜55 wt% polar solvent.

1-1-1. Non-polar solvent As the non-polar organic solvent, petroleum hydrocarbon solvents such as naphthenic, paraffinic and isoparaffinic solvents can be used. Specifically, aliphatic saturated hydrocarbons such as dodecane, “Isopar , Exor ”(all trade names),“ AF Solvent ”(trade name) manufactured by Nippon Oil Corporation,“ Sansen, Thumper ”(all trade names) manufactured by Sun Oil Co., Ltd., and the like. These can be used alone or in combination of two or more.

1-1-2. Examples of the polar solvent polar organic solvent include ester solvents, alcohol solvents, fatty acid solvents, ether solvents, and the like. These can be used alone or in combination of two or more.

  Examples of the ester solvent include higher fatty acid esters having 5 or more, preferably 9 or more, and more preferably 12 to 32 carbon atoms in one molecule. For example, isodecyl isononanoate, isotridecyl isononanoate, and isononanoic acid. Isononyl, methyl laurate, isopropyl laurate, isopropyl myristate, isopropyl palmitate, isooctyl palmitate, hexyl palmitate, isostearyl palmitate, isooctyl isopalmitate, methyl oleate, ethyl oleate, isopropyl oleate, oleic acid Butyl, hexyl oleate, methyl linoleate, isobutyl linoleate, ethyl linoleate, butyl stearate, hexyl stearate, isooctyl stearate, isopate isostearate Pill, 2-octyldodecyl pivalate, soybean oil methyl, soybean oil isobutyl, tall oil methyl, tall oil isobutyl, diisopropyl adipate, diisopropyl sebacate, diethyl sebacate, propylene glycol monocaprate, trimethylol tri-2-ethylhexanoate Examples thereof include propane and glyceryl tri-2-ethylhexanoate.

  Examples of the alcohol solvent include aliphatic higher alcohols having 12 or more carbon atoms in one molecule. Specifically, higher alcohols such as isomyristyl alcohol, isopalmityl alcohol, isostearyl alcohol, and oleyl alcohol. Examples include alcohol.

  Examples of the fatty acid solvent include fatty acids having 4 or more, preferably 9 to 22 carbon atoms in one molecule, such as isononanoic acid, isomyristic acid, hexadecanoic acid, isopalmitic acid, oleic acid, and isostearic acid. Can be mentioned,

  Examples of ether solvents include glycol ethers such as diethyl glycol monobutyl ether, ethylene glycol monobutyl ether, propylene glycol monobutyl ether, propylene glycol dibutyl ether, and acetates of glycol ethers.

1-2. The pigment pigment is not particularly limited, and may be any organic pigment or inorganic pigment that is generally used in the technical field of printing. Specifically, carbon black, cadmium red, chrome yellow, cadmium yellow, chromium oxide, pyridian, titanium cobalt green, ultramarine blue, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, isoindo Rinone pigments, dioxazine pigments, selenium pigments, perylene pigments, thioindigo pigments, quinophthalone pigments, metal complex pigments and the like can be suitably used. These pigments may be used alone or in combination of two or more.

  The pigment is preferably contained in the range of 0.01 to 20% by mass with respect to the total amount of the oil-based ink.

1-3. Pigment Dispersant It is preferable to add a pigment dispersant to the oil-based ink in order to improve the dispersion of the pigment in the oil-based ink. The pigment dispersant that can be used in the present invention is not particularly limited as long as the pigment is stably dispersed in a solvent. For example, a hydroxyl group-containing carboxylic acid ester, a salt of a long-chain polyaminoamide and a high molecular weight acid ester, High molecular weight polycarboxylic acid salt, long chain polyaminoamide and polar acid ester salt, high molecular weight unsaturated acid ester, high molecular weight copolymer, modified polyurethane, modified polyacrylate, polyether ester type anionic active agent, naphthalene sulfone Acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, polyoxyethylene nonylphenyl ether, polyester polyamine, stearylamine acetate and the like are preferably used, and among them, a polymer dispersant is preferably used.

  Specific examples of the pigment dispersant include “Solsperse 5000 (phthalocyanine ammonium salt type), 13940 (polyesteramine type), 17000, 18000 (fatty acid amine type), 11200, 22000, 24000, 28000” manufactured by Nippon Lubrizol (any) Product name), "Fuka 400, 401, 402, 403, 450, 451, 453 (modified polyacrylate), 46, 47, 48, 49, 4010, 4055 (modified polyurethane)" manufactured by Efka CHEMICALS (both products) Name), “Demol P, EP, Poise 520, 521, 530, Homogenol L-18 (polycarboxylic acid type polymer surfactant)” manufactured by Kao Corporation (all trade names), “Disparon KS-” manufactured by Enomoto Kasei Co., Ltd. 860, KS-873N4 (polymer polyester (All trade names), “Dacol 202, 206, OA-202, OA-600 (multi-chain polymer nonionic)” (all trade names) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Etc.

  Among the pigment dispersants, a comb-type polyamide dispersant having a plurality of side chains made of polyester chains is preferably used. A comb-type polyamide dispersant having a plurality of side chains comprising a polyester chain is a compound having a plurality of nitrogen atoms in the main chain, such as polyethyleneimine, and a plurality of side chains amide-bonded via the nitrogen atoms. The side chain is a polyester chain, for example, 3 to 80 per main chain molecule composed of polyalkyleneimine such as polyethyleneimine as disclosed in JP-A-5-177123. And a dispersant having a structure in which the poly (carbonyl-C3-C6-alkyleneoxy) chain is bonded as a side chain by an amide bridge. Examples of the comb-type polyamide-based dispersant include Solsperse 11200 and Solsperse 28000 (both trade names) manufactured by Nippon Lubrizol Corporation.

  The content of the pigment dispersant is sufficient as long as the pigment can be sufficiently dispersed in the organic solvent, and can be appropriately set.

1-4. Other components In the oil-based ink of the present invention, other than the organic solvent, pigment, and pigment dispersant, for example, other dyes, surfactants, fixing agents, preservatives, and the like, as long as the properties of the ink are not adversely affected. Ingredients can be added.

1-5. Production method of oil-based ink The oil-based ink of the present invention is dispersed by introducing all components into a known disperser such as a bead mill in a lump or divided and, if desired, passing through a known filter such as a membrane filter. Can be prepared. For example, after preparing a mixed liquid in which a part of the solvent and the whole amount of the pigment are uniformly mixed in advance and dispersing with a disperser, the remaining components are added to this dispersion and the mixture is passed through a filter. can do.

2. Pretreatment liquid The pretreatment liquid used in the present invention comprises at least inorganic particles, water, and a water-soluble organic solvent, and may contain other components as necessary.

2-1. As inorganic particles, inorganic particles used as extender pigments can be used. For example, silica, calcium carbonate, barium sulfate, titanium oxide, alumina white, aluminum hydroxide, white clay, talc, clay, diatomaceous earth, kaolin And inorganic particles such as mica. The average particle diameter of these inorganic particles needs to be 0.15 μm to 15 μm, and preferably 1 μm to 12 μm. In both cases where the average particle size is smaller than 0.15 μm and the average particle size is larger than 15 μm, the sealing action on the printing medium is not sufficient, and the effect of improving the printing density is not sufficiently obtained.

  The inorganic particles are preferably contained in the range of 0.01 to 20% by mass, and more preferably in the range of 5 to 20% by mass with respect to the total amount of the pretreatment liquid.

2-2. Solvent The solvent of the pretreatment liquid used in the present invention comprises water and a water-soluble organic solvent.
Water-soluble organic solvents include glycol solvents, glycol ethers, glycol ether acetates, lower alcohols, glycerol, diglycerol, triglycerol, polyglycerol, imidazolidinone solvents, 3-methyl-2,4-pentane. Examples include diols. These may be used alone or in combination of two or more as long as a single phase is formed.

  Examples of the glycol solvent include alkylene glycols such as ethylene glycol, diethylene glycol, triethylene glycol, and propylene glycol.

  Examples of glycol ethers include alkylene glycol alkyl ethers and polyalkylene glycol alkyl ethers (herein, both are collectively referred to as (poly) alkylene glycol alkyl ethers). For example, compounds represented by the following formula (1) Is mentioned.

(In Formula (1), R ¹ and R ² are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, preferably 4 to 6 carbon atoms, and n is an integer of 1 to 4).

  Specific examples of the (poly) alkylene glycol alkyl ether represented by the above formula (1) include, for example, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol mono Propyl ether, triethylene glycol monobutyl ether, triethylene glycol monohexyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, tetraethylene glycol monopropyl ether, tetraethylene glycol monobutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl Ether, triethylene glycol diethyl ether, and triethylene glycol dibutyl ether.

  Specific examples of other (poly) alkylene glycol alkyl ethers include compounds represented by the following formula (2).

(In Formula (2), R ¹ and R ² are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, preferably 4 to 6 carbon atoms, and n is an integer of 1 to 4).

  Specific examples of the (poly) alkylene glycol alkyl ether represented by the above formula (2) include, for example, propylene glycol monobutyl ether, propylene glycol dibutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono Examples include propyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monopropyl ether, tripropylene glycol monobutyl ether, tetrapropylene glycol monomethyl ether, dipropylene glycol dibutyl ether, and tripropylene glycol dibutyl ether.

  Examples of the lower alcohol include aliphatic alcohols having 1 to 6 carbon atoms in one molecule, and specific examples include ethyl alcohol, propyl alcohol, isopropyl alcohol, and butyl alcohol.

  Of these water-soluble organic solvents, glycol solvents, glycol ethers, glycerin, diglycerin, triglycerin and polyglycerin are preferably used.

The mass ratio of the content of the water-soluble organic solvent to the content of water in the pretreatment liquid used in the present invention (water-soluble organic solvent content / water content) is in the range of 0.1 to 0.8. It is necessary to be within a range of 0.1 to 0.7. In both cases where the mass ratio is smaller than 0.1 and larger than 0.8, when the printing medium is a printing paper such as plain paper, the paper is deformed, and the transportability of the printing medium is increased. This is a hindrance to high-speed printing. In order to prevent such deformation of the paper, the solubility parameter (SP value) of the water-soluble organic solvent is 8.5 (cal / cm ³ ) ^1/2 or more, 17.0 ( cal / cm ³ ) ^1/2 or less is preferably used.

2-3. Other components In the pretreatment liquid used in the present invention, other components such as a dispersant, a surfactant, a fixing agent, a preservative, etc., in addition to the solvent and the inorganic particles, as long as the properties are not adversely affected. Can be added. In particular, the fixing agent is useful for preventing bleeding of a printed image. As the fixing agent, various water-soluble polymers or water-dispersible polymer particles can be used. Polymer types include acrylic acid copolymer, acrylic / styrene copolymer, polyurethane, polyester, polyvinyl alcohol, polyvinyl chloride, polyvinyl acetate, styrene-butadiene rubber (SBR), starch, alkyd resin, poly Acrylamide, polyvinyl acetal and the like are preferable.

2-4. Manufacturing method of pretreatment liquid The pretreatment liquid used in the present invention is, for example, a known disperser such as a bead mill or the like, and all components are batched or divided and dispersed, and if desired, a known filter such as a membrane filter is used. Can be prepared. For example, after preparing a mixed liquid in which a part of the solvent and the whole amount of the pigment are uniformly mixed in advance and dispersing with a disperser, the remaining components are added to this dispersion and the mixture is passed through a filter. can do.

3. Inkjet printing method The inkjet printing method of the present invention is performed by applying a pretreatment liquid to a printing medium and then discharging oil-based ink onto the printing medium. The pretreatment liquid may be applied to the printing medium by uniformly coating the surface of the printing medium using a brush, roller, bar coater, or the like, or by printing means such as inkjet printing and gravure printing. This may be done by printing an image. For example, using an ink jet printer, printing may be performed by discharging a pretreatment liquid onto a print medium and then discharging oil-based ink continuously over the pretreatment liquid. In the present invention, after applying the pretreatment liquid to the print medium, the oil-based ink may be discharged before the applied treatment liquid is dried, or the oil-based ink is applied after the applied treatment liquid is dried. It may be discharged. ■

  It is advantageous to configure and sell an ink set including at least the pretreatment liquid and the oil-based ink so that the ink jet printing method of the present invention can be easily carried out.

  In the present invention, the printing medium is not particularly limited, and plain paper, glossy paper, special paper, cloth, film, OHP sheet and the like can be used. In particular, according to the present invention, even when printing on plain paper, the pigment stays on the surface of the printing paper without penetrating the printing paper, so that the printing density is improved, and the back-through and bleeding are reduced. The curling of the printing paper inside is prevented, and a great merit that high-speed printing is not hindered is obtained.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention in detail, this invention is not limited only to this Example.

Production Example 1 (Preparation of pretreatment liquid containing inorganic particles)
Each component shown in Table 1 is premixed at the ratio shown in Table 1, and then dispersed in a bead mill (using zirconia beads having a diameter (φ) of 2.0 mm), and the resulting dispersion is subjected to a membrane filter (opening diameter: 200 μm). ) To obtain a pretreatment liquid.

The details of the raw materials listed in Table 1 are as follows.
Snowtex AK-YL: “Snowtex AK-YL (trade name)” manufactured by Nissan Chemical Co., Ltd. (colloidal silica, solid content 31%).
Mizukasil P-73: “Mizukacil P-73 (trade name)” (powdered silica) manufactured by Mizusawa Chemical Co., Ltd.
Mizukasil P-74F: “Mizukacil P-74F (trade name)” (powdered silica) manufactured by Mizusawa Chemical Co., Ltd.
Aron SD-10: Dispersant “Aron SD-10 (trade name)” manufactured by Toagosei Co., Ltd. (polyacrylic acid copolymer / solid content 40%)
Elitel KZT-0507: “Elite KZT-0507 (trade name)” (polyester resin emulsion, solid content 30%) manufactured by Unitika Ltd.

Production Example 2 (Preparation of oil-based ink)
Each component shown in Table 2 was premixed at the ratio shown in Table 2, and then dispersed in a bead mill (using zirconia beads having a diameter (φ) of 0.5 mm), and the resulting dispersion was subjected to a membrane filter (opening diameter: 3 μm). ) To obtain an oil-based ink.

Carbon black MA-100: “MA-100 (trade name)” (carbon black) manufactured by Mitsubishi Chemical Corporation.
Solsperse-11200: “Solsperse 11200 (trade name)” manufactured by Lubrizol (pigment dispersant containing 50% aliphatic hydrocarbon (nonpolar) solvent).
Solsperse-28000: “Solsperse 28000 (trade name)” (pigment dispersant) manufactured by Lubrizol.
Fine Oxocol 140N: “Fine Oxocol 140N (trade name)” (higher alcohol) manufactured by Nissan Chemical Industries, Ltd.
AF Solvent No. 7: “AF7 (trade name)” (hydrocarbon solvent) manufactured by Nippon Oil Corporation.

Examples 1-5, Comparative Examples 1-5
The oil-based inks listed in Table 2 were introduced into the discharge path of an inkjet printer “HC5500 (trade name)” manufactured by Riso Kagaku Kogyo Co., Ltd. Is applied to the entire surface of one side of the printing paper with a bar coater so that the solid content after drying is 3 g / m ^2. The oil-based ink was ejected on the surface to print a solid image. Printing was performed at a resolution of 300 × 300 dpi and an ejection condition with an ink amount of 30 pl per dot. The print density and back-through of the obtained printed matter were measured and evaluated by the following methods. Moreover, the printing dot area, printing dot density, and paper deformation were measured and evaluated by the following methods. The results are shown in Table 3.

Print density of printed matter: The printed image density (OD) of the surface of the solid image of the obtained printed matter was measured using an optical densitometer (RD920: manufactured by Macbeth).

Back-through of printed matter: The printed image density (OD) of the back side of the solid image of the obtained printed matter was measured using an optical densitometer (RD920: manufactured by Macbeth).

Printed dot area: Printed image obtained by printing an image in which a plurality of dots are arranged instead of a solid image in the same manner as described above, with a zoom microscope (AZ-100: manufactured by Nikon Instruments Company), an exposure time of 10 mS, and a captured pixel The image was taken with a 1 × objective lens under the condition of several 4076 × 3116 pixels. The resulting image is converted to 8-bit 256 gray scales with the image editing software Adobe PhotoShop (manufactured by Adobe Systems), and the area of about 900 dots by the image measurement / analysis software Image Pro Plus (manufactured by Rover). Was measured, and the average value was defined as “printing dot area” and evaluated according to the following criteria.
Evaluation criteria:
○: 8000 μm ² ≦ printing dot area <12000 μm ²
Δ: 12000 μm ² ≦ printed dot area <17000 μm ² ×: 17000 μm ² ≦ printed dot area

Sheet deformation: 1 second after printing a solid image, the printed material was placed on a flat surface, and the height (deformation amount) of the most curled portion of the sheet was measured and evaluated according to the following evaluation criteria.
Evaluation criteria:
○: Deformation amount is less than 11 mm Δ: Deformation amount is 11 mm or more and less than 20 mm x: Deformation amount is 20 mm or more up to a cylindrical shape

From the results in Table 3, the following can be understood.
In Examples 1 to 5 using the pretreatment liquid of the present invention, a sufficient printing density was obtained and at the same time, back-through was prevented and deformation of the printing paper was also suppressed.

  On the other hand, in Comparative Example 1 in which no pretreatment liquid was used, the printing density was low, and show-through and bleeding occurred. Further, in Comparative Example 2 using the pretreatment liquid whose solvent was composed only of water, the printing paper was deformed. In Comparative Examples 3 and 4 using the pretreatment liquid containing inorganic particles having an average particle diameter outside the range of the present invention, the printing density was low, and show-through and bleeding occurred. Further, in Comparative Example 5 using the pretreatment liquid containing excessive water-soluble solvent, the printing paper was deformed.

  The ink-jet printing method and ink set of the present invention can be easily implemented by an ink-jet printer that can print on the treated surface of a print medium by ejecting oil-based ink from a nozzle head after the surface treatment of the print medium with a pretreatment liquid. Can be widely used in the field of inkjet printing.

Claims (8)

In the oil-based inkjet printing method in which printing is performed by applying an oil-based ink containing at least a pigment and a solvent onto the print medium after the pretreatment liquid is applied to the print medium, the pretreatment liquid has an average particle size of It comprises at least 0.15 μm to 15 μm of inorganic particles, water and a water-soluble organic solvent, and the mass ratio of the content of the water-soluble organic solvent to the content of water in the pretreatment liquid (water-soluble organic solvent content / The oil-based inkjet printing method whose water content is in the range of 0.1 to 0.8. The solubility parameter (SP value) of the water-soluble organic solvent contained in the pretreatment liquid is 8.5 (cal / cm ³ ) ^1/2 or more and 17.0 (cal / cm ³ ) ^1/2 or less. The oil-based inkjet printing method according to claim 1, wherein: The mass ratio of the content of the water-soluble organic solvent to the content of water in the pretreatment liquid (water-soluble organic solvent content / water content) is in the range of 0.1 to 0.7. The oil-based inkjet printing method of description. The oil-based inkjet printing method according to claim 1, wherein the oil-based ink is discharged onto the print medium by a line head type inkjet printer. An ink set for use in oil-based inkjet printing in which printing is performed by applying a pretreatment liquid to a print medium and then discharging the oil-based ink onto the print medium, and an oil-based ink comprising at least a pigment and a solvent; A pretreatment liquid comprising at least an inorganic particle having an average particle size of 0.15 μm to 15 μm, water and a water-soluble organic solvent, and the content of the water-soluble organic solvent relative to the water content in the pretreatment liquid An oil-based ink jet printing ink set having a mass ratio (water-soluble organic solvent content / water content) in the range of 0.1 to 0.8. The solubility parameter (SP value) of the water-soluble organic solvent contained in the pretreatment liquid is 8.5 (cal / cm ³ ) ^1/2 or more and 17.0 (cal / cm ³ ) ^1/2 or less. The ink set according to claim 5, wherein: The mass ratio of the content of the water-soluble organic solvent to the content of water in the pretreatment liquid (water-soluble organic solvent content / water content) is in the range of 0.1 to 0.7. The ink set described. The ink set according to claim 5, wherein the oil-based ink is ejected onto the print medium by a line head type ink jet printer.