JP2011224861A - Oil inkjet printing method and ink set - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel pretreatment liquid, thereby to improve printing density, prevent strike through, and improve primary fixability of ink, in an oil inkjet printing system in which the pretreatment liquid is applied to a printing medium and thereafter oil ink containing a pigment and a solvent is ejected onto the printing medium, thereby printing is performed, particularly in an inkjet printing system performing printing on plain paper by using a line head type inkjet printer.SOLUTION: As a pretreatment liquid, a liquid containing inorganic particles having an average particle diameter of 1-20 μm and a solvent is used. The inorganic particles comprise 30-80 mass% of inorganic particles (P-1) each having a value of the following liquid absorptivity (A) of 0.2-0.6, and 20-70 mass% of inorganic particles (P-2) of a value of the liquid absorptivity (A) of 1.0-1.5. A=B/C (1), wherein A is liquid absorptivity of the inorganic particle, B is an oil absorption amount (ml/100g) of the inorganic particle, and C is a specific surface area (m/g) of the inorganic particle.

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, when plain paper is used as a printing medium, oil-based ink not only has excellent permeability and drying properties to the printing medium, but the solvent is less likely to evaporate than water-based ink and solvent ink. And is advantageous for high-speed printing, particularly high-speed ink jet printing using a line head method.

  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, there are various types of special papers having an ink receiving layer composed of inorganic particles and fixing resin on the surface in order to keep the color material on the paper surface. However, in order to obtain the same effect with plain paper, a means for keeping the color material on the paper surface during printing is required. In the case of water-based ink, as a method of keeping the coloring material on the surface of plain paper without penetrating with the solvent, a reactive substance is contained in the ink, and a treatment liquid containing a substance that reacts with the substance is prepared. There has already been proposed a method in which the treatment liquid is ejected over the ink and both substances are reacted on the paper surface, thereby aggregating the coloring material and making 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 paper is treated with a pretreatment liquid containing inorganic particles, the ink absorbability of the inorganic particles has a great influence on the print paper's processed paper, such as print density, back-through, and ink fixability. When the coating amount of inorganic particles is large, the ink absorption capacity of the coating layer increases, so the performance is greatly improved, but the fixing ability of the coating layer to the paper is reduced, and the texture of the printing paper is also reduced. There is a problem that the cost of printing paper increases. In order to avoid this problem, if the coating amount of the pretreatment liquid is reduced and the ink absorbability of the inorganic particles is not appropriate, the printing density, the back-through, and the primary fixability of the ink (ink drying property immediately after printing) The performance cannot be improved. If the primary fixing property is not appropriate, problems such as roll transfer contamination in the finisher occur when the printed material is post-processed.

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. An object of the present invention is to provide a novel pretreatment liquid in an ink jet printing system for printing on paper, thereby increasing the print density of printed matter, preventing back-through, and further improving the primary fixability of ink.

  As a result of intensive research under the above object, the present inventor causes the pretreatment liquid to contain inorganic particles having a specific particle diameter composed of two inorganic particles having different particle diameters in the oil-based inkjet printing system. As a result, the pigment in the oil-based ink ejected to the print medium is retained on the print medium and the penetration into the print medium is suppressed, so that the print density can be improved and at the same time the back-through can be prevented. The inventors have found that the primary fixability can be improved, and have completed the present invention.

  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 1 μm or more and 20 μm or less and a solvent, and the inorganic particles have a liquid absorbency (A) value of 0. 2 to 0.6 inorganic particles (P-1) 20 to 80% by mass, and the liquid absorbency (A) value is 1.0 to 1.5 inorganic particles (P-2) 20 to 80% by mass. An oil-based ink jet printing method is provided.

A = B / C (1)
A: Liquid absorbency of inorganic particles.
B: Oil absorption of inorganic particles (ml / 100 g).
C: Specific surface area of inorganic particles (m ² / g).
B was calculated | required with the linseed oil absorption amount measuring method by JISK-5101-21.
C was determined by a BET specific surface area measurement method.

  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 diameter of 1 μm or more and 20 μm or less and a solvent, wherein the inorganic particle is represented by the above formula (1). 20 to 80% by mass of inorganic particles (P-1) having a liquid absorbency (A) value of 0.2 to 0.6, and inorganic having a liquid absorbency (A) value of 1.0 to 1.5 An oil-based ink jet printing ink set comprising 20 to 80% by mass of particles (P-2) is provided.

  According to the present invention, inorganic particles having an average particle diameter of 1 μm or more and 20 μm or less are used as the inorganic particles of the pretreatment liquid, and the liquid absorption (A) value is 0.2 to 0. .6 inorganic particles (P-1) 20 to 80% by mass, and the liquid absorbency (A) value is 1.0 to 1.5 inorganic particles (P-2) 20 to 80% by mass. Therefore, by treating the surface of the print medium with the pretreatment liquid, the surface of the print medium is closed, and the pigment in the printed oil-based ink stays on the print medium and the color material The penetration into the printing medium is suppressed, the printing density is improved, and at the same time, the back-through and bleeding are prevented.

  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. It is preferable to use a solvent solubility parameter (SP value) of 6.5 (cal / cm ³ ) ^1/2 or more and 10.0 (cal / cm ³ ) ^1/2 or less, 7.0 ( It is more preferable to use a cal / cm ³ ) ^1/2 or more and 9.0 (cal / cm ³ ) ^1/2 or less.

  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 mass of a nonpolar solvent and 80 to 20% by mass of a polar solvent. More preferably, the solvent is composed of ˜45 mass% nonpolar solvent and 55-70 mass% 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” manufactured by ExxonMobil Co., Ltd. , Exor ”(all trade names),“ Nippon Oil Co., Ltd. “AF Solvent, Normal Paraffin H” (all trade names), Sun Petroleum “Sansen, Thamper” (all trade names), 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, etc., 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 and a 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 size of these inorganic particles needs to be 1 μm or more and 20 μm or less, preferably 1 μm or more and 15 μm or less, and more preferably 1 μm or more and 12 μm or less. In both cases where the average particle size is smaller than 1 μm and the average particle size is larger than 20 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 40% by mass, more preferably in the range of 5 to 30% by mass with respect to the total amount of the pretreatment liquid.

In the present invention, in order to improve the printing density, prevent backlining, and improve the primary fixability of the ink, the inorganic particles have a liquid absorbency (A) value of 0.2 to 0.2 represented by the above formula (1). From 20 to 80% by mass of 0.6 inorganic particles (P-1) and 20 to 80% by mass of inorganic particles (P-2) having a liquid absorbency (A) value of 1.0 to 1.5 Constitute. When the blending amount of the inorganic particles (P-1) is too large, particularly when the coating amount on paper is small (for example, when the amount of inorganic particles is 1.0 g / m ² or less), Since the liquid absorption is not sufficient, the ink absorption rate is decreased, the primary fixing property is deteriorated, and accordingly, the bleeding of the printed dots is increased, and the printing density is not sufficiently improved. Therefore, the blending amount of the inorganic particles (P-1) is preferably 30 to 70% by mass, and more preferably 45 to 55% by mass. When the amount of the inorganic particles (P-2) is too large, bleeding of printed dots is excessively suppressed, and particularly when the amount applied to paper is small (for example, 1.0 g / m in terms of the amount of inorganic particles). ² or less), it is effective in improving the printing density and suppressing the back-through, but a large amount of pigment in the ink stays on the paper surface and the primary fixing property is deteriorated. Transfer stains to the surface occur. In addition, if the amount of the inorganic particles (P-2) is too large, the liquid absorbency of the particles is high. Therefore, if the content of the inorganic particles in the treatment liquid is increased, the viscosity of the treatment liquid becomes too high, resulting in a uniform coating. Work becomes difficult. Therefore, the blending amount of the inorganic particles (P-2) is preferably 30 to 70% by mass, and more preferably 45 to 55% by mass. In the present invention, the entire inorganic particles need to satisfy the average particle diameter, but when both the inorganic particles (P-1) and the inorganic particles (P-2) fall within the average particle diameter range, Usually, the entire inorganic particles also satisfy the average particle size.

In addition, when the amount of inorganic particles (g / m ² ) is too large when the pretreatment liquid is applied to the printing paper, the bleeding of the printing dots becomes too small, and a solid image is printed when printing at a resolution of about 300 × 300 dpi. The dot size is not sufficient for formation, and show-through is suppressed, but a high-density printed matter cannot be obtained. Therefore, the coating amount of the pretreatment liquid is preferably from 0.3~2.5g / ^{m 2} and the amount of the inorganic particles, more preferably from 0.5 to 2 g / ^{m 2,} 0.5 Even more preferably, it is ˜1.5 g / m ² .

2-2. Solvent The solvent of the pretreatment liquid used in the present invention can be selected from the group consisting of water and organic solvents. The organic solvent may be a water-soluble organic solvent or a water-insoluble organic solvent as long as the solubility parameter is within a specified range.
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 chemical 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 chemical 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 chemical 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 chemical 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.
Specific examples of the water-insoluble organic solvent include dimethyl carbonate and diethyl carbonate.

In the present invention, the difference between the solubility parameter (SP value) of the solvent of the pretreatment liquid and the solubility parameter (SP value) of the solvent of the oil-based ink is preferably a predetermined value or more. In addition, the smaller the particle size of the inorganic particles, the more easily the inorganic particles themselves sink into the fibers of the printing paper, so the difference in SP value needs to be increased. When inorganic particles having an average particle diameter of 1 μm or more and 20 μm or less are used as the inorganic particles contained in the pretreatment liquid, the difference in SP value is preferably 1.0 (cal / cm ³ ) ^1/2 or more. . If the difference in SP value is too small, the ink is likely to penetrate due to the influence of the residual solvent in the printing medium and the dispersant used to disperse the particles, the concealability is lowered, and the printing density is not sufficiently improved. , Through-through and bleeding are likely to occur.

As the organic solvent, those having a solubility parameter (SP value) of 7.5 (cal / cm ³ ) ^1/2 or more and 17.0 (cal / cm ³ ) ^1/2 or less are preferably used. 0.0 (cal / cm ³ ) ^1/2 or more and 17.0 (cal / cm ³ ) ^1/2 or less are more preferable.

  The solvent of the pretreatment liquid may be composed of one or more selected from the group consisting of water and the above-mentioned various organic solvents. However, in order to obtain a solvent having a specific SP value, only one solvent is used. It is more convenient and preferable. When water is used as the solvent for the pretreatment liquid, if the printing medium is a printing paper such as plain paper, the paper is deformed, the transportability of the printing medium is lowered, and it becomes an obstacle to high-speed printing. So be careful. In order to prevent this, it is conceivable that the solvent of the pretreatment liquid is composed entirely of an organic solvent.

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.

  Among these, when water is used as the solvent of the pretreatment liquid, it is preferable to use polyvinyl alcohol having a polymerization degree of 500 or less and a saponification degree of 60 mol% or more as a fixing agent. When such polyvinyl alcohol is used, a high printing density can be obtained when printing at a relatively low resolution of 300 × 300 dpi or less. The polyvinyl alcohol is preferably contained in the range of 3.0 to 35.0% by mass and more preferably in the range of 6.0 to 30.0% by mass with respect to the amount of inorganic particles. When there is too much addition amount of polyvinyl alcohol, since dot size will become large and a brightness | luminance will become high, image quality will fall. Moreover, when there is too little addition amount of polyvinyl alcohol, the intensity | strength of coating layer itself will fall and it will become easy to peel from the printing medium surface.

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, it is preferable to discharge the oil-based ink after the pretreatment liquid has been applied to the print medium and the applied treatment liquid has permeated and evaporated to dryness. Therefore, when the amount of water in the pretreatment liquid is large, a drying step may be applied before printing the oil-based ink. For the drying step, an existing method such as applying hot air to the print medium after applying the pretreatment liquid or transporting the print medium under a heated roll can be used.

  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, since the pigment does not penetrate into the printing paper and stays on the surface of the printing paper, a great advantage is obtained in that the print density is improved and the back-through is reduced. .

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

Examples 1-8, Comparative Examples 1-6
(1) Preparation of pretreatment liquid containing inorganic particles Each component shown in Table 1 was premixed at a ratio shown in Table 1, and then dispersed for 1 minute with an ultrasonic disperser to obtain a pretreatment liquid.
(2) Preparation of oil-based ink Each component shown in Table 1 was premixed at the ratio shown in Table 1, and then zirconia beads having a diameter (φ) of 0.5 mm were put into a rocking mill (Seiwa Giken Co., Ltd.). For 60 minutes, and the resulting dispersion was filtered through a membrane filter (opening diameter: 3 μm) to prepare a black ink.

The SP value (δ _mix ) of the oil-based ink solvent that is a mixed solvent of three kinds of organic solvents was calculated according to the following formula (2).
δ _mix = δ _A φ _A + δ _B φ _B + δ _C φ _C (2)
δ _A , δ _B , δ _C : SP values of solvents A, B, C
φ _A , φ _B , φ _C : Volume fraction of solvents A, B, C

The details of the raw materials listed in Table 1 are as follows.
Mizukasil P-758: “Mizukasil P-758 (trade name)” (powdered silica having an average particle diameter of 13 μm) manufactured by Mizusawa Chemical Co., Ltd.
Mizukasil P-50: “Mizukacil P-50 (trade name)” (powdered silica with an average particle size of 8 μm) manufactured by Mizusawa Chemical Co., Ltd.
Mizukasil P-803: “Mizukacil P-803 (trade name)” (powdered silica with an average particle size of 5 μm) manufactured by Mizusawa Chemical Co., Ltd.
Mizukasil P-526: “Mizukacil P-526 (trade name)” (powdered silica having an average particle diameter of 7 μm) manufactured by Mizusawa Chemical Co., Ltd.
Demol EP: “Demol EP (trade name)” manufactured by Kao Corporation (special polycarboxylic acid type polymer surfactant, solid content 25%).
JMR-10M: “JMR-10M (trade name)” (polyvinyl alcohol having a degree of saponification of 65.0 mol% and a degree of polymerization of 250) manufactured by Nippon Vinegar Poval Co., Ltd.
Movinyl 965: “Movinyl 965 (trade name)” manufactured by Nippon Synthetic Chemical Co., Ltd. (styrene / acrylic emulsion resin, solid content 42%).
Slout 33: “Slout 33 (trade name)” (preservative) manufactured by Nippon Enviro Chemical Co., Ltd.
MA-11: “MA-11 (trade name)” (carbon black) manufactured by Mitsubishi Chemical Corporation.
Solsperse-28000: “Solsperse 28000 (trade name)” (pigment dispersant) manufactured by Lubrizol.
Exepal M-OL: “Exepal M-OL (trade name)” (methyl oleate) manufactured by Kao Corporation.
Exepal IPM: “Exepal IPM (trade name)” (isopropyl myristate) manufactured by Kao Corporation.
Normal paraffin H: “Normal paraffin H (trade name)” (hydrocarbon solvent) manufactured by Nippon Oil Corporation.

(3) Inkjet printing The oil-based ink listed in Table 1 is introduced into the discharge path of an inkjet printer HC5500 (trade name; manufactured by Riso Kagaku Co., Ltd.), and is used as a printing paper. (Trade name) ", the pretreatment liquid shown in Table 1 was applied to the entire surface of one side of the printing paper with a coating roller so that the amount of silica particles in the coating layer was a predetermined amount, and a heat roll After drying the solvent, the oil-based ink was ejected onto the treated surface of the printing paper to print a solid image. Printing was performed at a resolution of 300 × 300 dpi and an ink amount of 30 pl / dot. The primary fixability, print density, and back-through of the obtained printed matter were measured and evaluated by the following methods. The results are shown in Table 1.

Primary fixability: Immediately after printing a solid image, the ideal paper mat IJ (W) is layered on the printed matter, and then it is reciprocated 5 times with a plastic roller. did.
○: Almost unstained. Dirt is not noticeable.
Δ: Slightly noticeable dirt
X: Dirt is severe.

Print density of printed matter: The solid image printed matter was allowed to stand overnight, and then the printed image density (OD) on the surface of the solid image was measured using an optical densitometer (RD920: manufactured by Macbeth) and evaluated according to the following criteria.
○: 1.20 ≦ OD value Δ: 1.15 ≦ OD value <1.20
X: OD value <1.15

See-through of printed matter: After the solid image printed material was left overnight, the printed image density (OD) of the back surface of the solid image was measured using an optical densitometer (RD920: manufactured by Macbeth Co.) and evaluated according to the following criteria.
○: OD value ≦ 0.25
×: 0.25 <OD value

From the results in Table 1, the following can be understood.
In Examples 1 to 8 using the pretreatment liquid of the present invention, a sufficient printing density was obtained, and back-through was prevented, and further, primary fixability immediately after printing was good. On the other hand, in Comparative Example 1 in which the pretreatment liquid was not used, the primary fixing property was not sufficient, the printing density was low, and the showthrough occurred. In Comparative Examples 2 to 5 using the pretreatment liquid containing inorganic particles (P-1) or inorganic particles (P-2) alone, primary fixability and image density were insufficient. In Comparative Example 6 using the pretreatment liquid consisting of 90% by mass of inorganic particles (P-1) and 10% by mass of inorganic particles (P-2), the primary fixing property was sufficient, but the printing density was insufficient. there were.

  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 (10)

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 The inorganic particles include at least inorganic particles having a size of 1 μm or more and 20 μm or less, and a solvent, and the inorganic particles have a liquid absorbency (A) value of 0.2 to 0.6 represented by the following formula (1) (P− 1) An oil-based inkjet printing method comprising 20 to 80% by mass and 20 to 80% by mass of inorganic particles (P-2) having a liquid absorption (A) value of 1.0 to 1.5.
A = B / C (1)
A: Liquid absorbency of inorganic particles.
B: Oil absorption of inorganic particles (ml / 100 g).
C: Specific surface area of inorganic particles (m ² / g). The oil-based inkjet printing method according to claim 1, wherein the inorganic particles are silica or calcium carbonate. The printing method according to claim 1 or 2, wherein the coating amount of the pretreatment liquid is 0.3 to 2.5 g / m ² in terms of the amount of inorganic particles. The difference between the solubility parameter (SP value) of the solvent of the pretreatment liquid and the solubility parameter (SP value) of the solvent of the oil-based ink is 1.0 (cal / cm ³ ) ^1/2 or more. The oil-based inkjet printing method according to any one of the above. The oil-based inkjet printing method according to any one of claims 1 to 4, 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; The inorganic particles having an average particle diameter of 1 μm or more and 20 μm or less and a pretreatment liquid containing at least a solvent, and the inorganic particles have a liquid absorbency (A) value of 0.2 expressed by the following formula (1). 20 to 80% by mass of inorganic particles (P-1) of ~ 0.6, and 20 to 80% by mass of inorganic particles (P-2) having a liquid absorbency (A) value of 1.0 to 1.5 An oil-based ink jet printing ink set.
A = B / C (1)
A: Liquid absorbency of inorganic particles.
B: Oil absorption of inorganic particles (ml / 100 g).
C: Specific surface area of inorganic particles (m ² / g). The ink set according to claim 6, wherein the inorganic particles are silica or calcium carbonate. The ink set according to claim 7, wherein the pretreatment liquid is prepared so as to be used at a coating amount of 0.3 to 2.5 g / m ² in terms of the amount of inorganic particles. The difference between the solubility parameter (SP value) of the solvent of the pretreatment liquid and the solubility parameter (SP value) of the solvent of the oil-based ink is 1.0 (cal / cm ³ ) ^1/2 or more. The ink set according to any one of the above. The ink set according to any one of claims 6 to 9, wherein the oil-based ink is ejected onto the print medium by a line head type ink jet printer.