JP3639290B1 - Water-based ink for stencil printing and stencil printing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-based ink for stencil printing which has excellent fixability of an image of a printed matter and does not cause defective discharge even after the printing press is left unused.
A monovalent metal salt or amine salt of an unsaturated carboxylic acid-based water-soluble polymer and an ammonium salt of an alkali-soluble resin are blended.
[Selection figure] None

Description

  The present invention relates to a water-based ink for stencil printing, particularly a water-based ink for stencil printing suitable for use in a rotary digital stencil printing machine, and a stencil printing method using the same.

Compared with printing methods such as offset printing, gravure printing and letterpress printing, the stencil printing method does not require complicated operations such as cleaning after use, and has excellent operability such as not requiring a specialized operator, Easy to use. Since the use of the thermal plate making method with a thermal printing head as a device, digitization of image processing has become possible in the stencil printing method, and it has become possible to easily obtain high-quality printed materials in a short time. The convenience of the terminal is increasingly recognized.
2. Description of the Related Art A rotary stencil printing machine in which master plate making, plate making, discharging operation, ink supply operation and printing operation are automatically controlled is widely used in offices and schools under the name of digital stencil printing machine.

Conventionally, water-in-oil (W / O) emulsion inks have been used as stencil printing inks. W / O emulsion ink has a function to suppress changes in the composition and physical properties of the ink even if the ink inside the printing press is in contact with the air when the printing press is left unused. Yes. That is, since the water that is the inner phase component of the emulsion ink is covered with the oil that is the outer phase component, its evaporation is suppressed.
The drying of the ink in the printed matter printed with the W / O type emulsion ink causes the emulsion to become oily by penetrating between the paper fibers of the printing paper that is the printing medium (printing medium) and contacting with the paper fibers. It is believed that the water is the main component of the ink and gradually evaporates in contact with the atmosphere and is gradually separated into a phase and an aqueous phase. However, since the water in the ink transferred to the printing medium cannot be brought into contact with the atmosphere within a short time after printing, the drying property immediately after printing depends on osmotic drying. Since the viscosity of the O-type emulsion ink is designed to be high to some extent, the permeation speed is not fast, and therefore the ink drying property immediately after printing cannot be said to be sufficient.
Accelerating the drying of printed matter is an extremely important issue for stencil printing. This is because if the printed matter is not dried, the operator cannot handle the printed matter, and the advantage of “obtaining high-quality printed matter in a short time” of stencil printing cannot be fully utilized.

Therefore, various improvements have been made to improve the drying property of the printed matter. For example, an ultraviolet curable ink for stencil printing that is fixed and dried by ultraviolet irradiation is known (Patent Document 1). In addition, water-based inks for stencil printing have been developed from the viewpoint of environmental conservation and safety, and a stencil printing method is known in which a base is added to the printing surface immediately after printing to increase the permeability of water-based ink to paper. (Patent Document 2).
JP 2002-30238 A JP 2001-302955 A

However, with conventional water-based inks for stencil printing, the fixability of the image after the printed matter dries is not sufficient, the image becomes thin when the printed part is rubbed with an eraser, and the printed characters are blurred due to a water-based pen or water-based marker was there. In addition, the conventional water-based ink for stencil printing has a problem that the fluidity of the ink is lost when the printing press is left unused and the ink in the printing press is left in an open system. Had. In particular, when a fixing agent is contained in the ink, the printed master on which the ink is adhered adheres to the printing drum due to the action of the fixing agent, which may cause defective master discharge. . On the other hand, when a fixing method using a chemical reaction is used, a curing energy irradiation device, a reaction liquid coating device, energy for that, and the like are required.
Therefore, the present invention is excellent in fixability to a printing medium (printing medium) such as printing paper without using special means, devices, energy, etc. such as application of heat, light, and reactive substances, and An object of the present invention is to provide a water-based ink for stencil printing that does not cause defective master discharge even when the printing press is left unused, and a stencil printing method using the same.

The present invention relates to a water-based ink for stencil printing comprising a monovalent metal salt or amine salt of an unsaturated carboxylic acid-based water-soluble polymer and an ammonium salt of an alkali-soluble resin.
Another aspect of the present invention relates to a stencil printing method using the water-based ink for stencil printing according to the present invention.

  Since the water-based ink for stencil printing of the present invention contains a monovalent metal salt or amine salt of an unsaturated carboxylic acid-based water-soluble polymer and an ammonium salt of an alkali-soluble resin, it can be fixed to a printing medium. In addition, it does not solidify even when left in an open system inside the printing press, and does not degrade the master's plate removal. Therefore, by using the water-based ink for stencil printing of the present invention, the ink fixing property is excellent, and even if the printed part is rubbed with an eraser, the image does not become thin, and printed characters may be blurred by an aqueous pen or an aqueous marker. High-quality printed matter can be provided, and printing can be resumed without any trouble even after the printing press is left unused. In addition, the present invention does not require special means, devices, energy, etc., such as application of heat, light, reactive substances to the printing material, etc. Excellent in terms.

  The water-based ink for stencil printing according to the present invention (hereinafter, water-based ink for stencil printing is simply referred to as “ink”) contains water and a colorant, and is a monovalent metal salt of an unsaturated carboxylic acid-based water-soluble polymer or It contains an amine salt and an ammonium salt of an alkali-soluble resin. Hereinafter, (meth) acrylic acid means acrylic acid and methacrylic acid, and a derivative of (meth) acrylic acid means a derivative of acrylic acid and a derivative of methacrylic acid.

（式中、Ｒ_１，Ｒ_２，Ｒ_３はそれぞれ独立にＨ、ＣＨ_３、（ＣＨ_２）ｎＣＯＯＨ（ｎは０または１の整数）を表す。）で示される繰り返し単位を含む水溶性の高分子を意味する。２以上のカルボキシル基を含む場合に、それらが酸無水物を形成していてもよい。共重合体となっている場合の共重合形式は、ランダム型、交互型、ブロック型、グラフト型等のいずれの形態であってもよい。また、高分子鎖の構造は、直鎖型であっても分子内に架橋構造を有する架橋型であってもよい。 The monovalent metal salt or amine salt of the unsaturated carboxylic acid-based water-soluble polymer acts as a thickener for the ink. In the present invention, the unsaturated carboxylic acid-based water-soluble polymer is represented by the following formula (1):

(Wherein R ₁ , R ₂ and R ₃ each independently represents H, CH ₃ , (CH ₂ ) nCOOH (n is an integer of 0 or 1)) Means a molecule. When two or more carboxyl groups are contained, they may form an acid anhydride. In the case of a copolymer, the copolymerization form may be any form such as a random type, an alternating type, a block type, and a graft type. Further, the structure of the polymer chain may be a linear type or a crosslinked type having a crosslinked structure in the molecule.

  Examples of the unsaturated carboxylic acid thickener include one or more unsaturated carboxylic acids selected from the group consisting of acrylic acid, methacrylic acid, maleic anhydride, maleic acid, fumaric acid, crotonic acid and itaconic acid. Examples thereof include water-soluble polymers contained in the main chain, and salts thereof are also included. More specifically, for example, poly (meth) acrylic acid, polycrotonic acid, polyitaconic acid, polymaleic acid, polyfumaric acid, acrylic acid-methacrylic acid copolymer, (meth) acrylic acid-itaconic acid copolymer, (meta ) Acrylic acid-maleic acid copolymer, (meth) acrylic acid- (meth) acrylamide copolymer (ie, acrylic acid-acrylamide copolymer, acrylic acid-methacrylamide copolymer, methacrylic acid-acrylamide copolymer) , Methacrylic acid-methacrylamide copolymer), (meth) acrylic acid- (meth) acrylic acid ester copolymer (that is, acrylic acid-acrylic acid ester copolymer, acrylic acid-methacrylic acid ester copolymer, methacrylic acid) Acid-acrylic acid ester copolymer, methacrylic acid-methacrylic acid ester Copolymers), (meth) acrylic acid-sulfonic acid monomer copolymers, (meth) acrylic acid-vinyl pyrrolidone copolymers, maleic anhydride-alkyl vinyl ether copolymers, etc. Is mentioned. Examples of the monovalent metal salt include alkali metal salts such as sodium and potassium, and examples of the amine salt include alkanolamine salts such as triethanolamine.

  More specifically, as a monovalent metal salt or amine salt of an unsaturated carboxylic acid water-soluble polymer, poly (meth) acrylate sodium, poly (meth) acrylate potassium, poly (meth) acrylate triethanolamine , Sodium polyitaconate, sodium polymaleate, sodium acrylic acid-methacrylic acid copolymer, sodium (meth) acrylic acid-maleic acid copolymer, sodium (meth) acrylic acid- (meth) acrylamide copolymer (ie acrylic Acid-acrylamide copolymer sodium, acrylic acid-methacrylamide copolymer sodium, methacrylic acid-acrylamide copolymer sodium, methacrylic acid-methacrylamide copolymer sodium) and the like can be preferably used. These can be used alone or in combination of two or more.

  As a monovalent metal salt or amine salt of an unsaturated carboxylic acid-based water-soluble polymer, an unneutralized unsaturated carboxylic acid-based water solution can be used instead of or in addition to the above neutralized salt. It is also possible to use an aqueous solution obtained by mixing a water-soluble polymer and an alkaline neutralizer such as sodium hydroxide, potassium hydroxide, triethanolamine, diisopropanolamine or the like in water.

  The content of the unsaturated carboxylic acid-based water-soluble polymer varies depending on the type and desired ink viscosity, but is preferably 0.01% by weight or more in order to obtain stable ink properties. From the viewpoint of balance with the content of the components and printing operability after the printing press is left in a non-use state, it is preferably 5% by weight or less, more preferably 0.05 to 3% by weight, 0.1 to 2% by weight is more preferable.

In addition to the unsaturated carboxylic acid-based water-soluble polymer, the ink of the present invention may contain one or more other water-soluble polymer-based thickeners and clay mineral-based thickeners as necessary. .
Other water-soluble polymer thickeners optionally blended include, for example, plant-based natural polymers such as gum arabic, carrageenan, guar gum, locust bean gum, pectin, tragacanth gum, corn starch, konjac mannan, agar; pullulan Microbial natural polymers such as gelatin, casein and glue; cellulosic semisynthetic polymers such as ethylcellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose, hydroxypropylmethylcellulose, etc. ; Starch-based semi-synthetic polymers such as hydroxyethyl starch, carboxymethyl starch sodium, cyclodextrin; sodium alginate, propylene glycol alginate Alginate semi-synthetic polymers such as sodium hyaluronate; polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl methyl ether, poly N-vinylacetamide, polyacrylamide, polyethylene oxide, polyethyleneimine, polyurethane, and other synthetic polymers can be used. .
As the clay mineral-based thickener, for example, smectite-based clay minerals such as montmorillonite, hectorite, and saponite can be used.
The amount of other thickeners optionally blended is preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 2% by weight or less in the ink.

An ammonium salt of an alkali-soluble resin is used as a fixing agent for a colorant on a printing medium such as printing paper. When a pigment is used as the colorant, it can also be used as a pigment dispersant.
In the present invention, the alkali-soluble resin means a polymer that is insoluble in water but becomes water-soluble in the presence of alkali. Therefore, even if the compound name is the same, for example, acrylic acid-acrylic acid ester copolymer, in the present invention, it is classified into a water-soluble polymer or an alkali-soluble resin depending on its solubility.

  Examples of the ammonium salt of the alkali-soluble resin include styrene- (meth) acrylic acid copolymer, styrene-α methylstyrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid ester- (meth) acrylic. Acid copolymer (ie, styrene-acrylic acid ester-acrylic acid copolymer, styrene-acrylic acid ester-methacrylic acid copolymer, styrene-methacrylic acid ester-acrylic acid copolymer, styrene-methacrylic acid ester-methacrylic acid) Acid copolymer), styrene-maleic anhydride copolymer, vinylnaphthalene- (meth) acrylic acid copolymer, vinylnaphthalene-maleic acid copolymer, isobutylene-maleic anhydride copolymer, (meth) acrylic acid Ester- (meth) acrylic acid copolymer (ie acrylic acid Stealth-acrylic acid copolymer, methacrylic acid ester-acrylic acid copolymer, acrylic acid ester-methacrylic acid copolymer, methacrylic acid ester-methacrylic acid copolymer), acrylic acid ester-methacrylic acid ester- (meth) Each ammonium salt of an acrylic acid copolymer can be used. These can be used alone or in combination of two or more. Usually, the alkali-soluble resin ammonium salt is used as an aqueous solution of an alkali-soluble resin ammonium salt obtained by dissolving an alkali-soluble resin in an aqueous ammonia solution.

  The alkali-soluble resin is preferably contained in the ink in an amount of 0.1% by weight or more, more preferably 0.3% by weight or more in terms of solid content, in order to exert the effect as a fixing agent. On the other hand, if it is contained in a large amount, the printing performance after nonuse of the printing press may be hindered. Therefore, it is preferably contained in a range of 5% by weight or less in terms of solid content, more preferably 3% by weight. It is as follows.

The unsaturated carboxylic acid-based water-soluble polymer and the alkali-soluble resin are contained in a blend ratio of 1: 9 to 4: 1 as a weight ratio in terms of solid content, and the fixing property of the printed image and the non-use of the printing press It is preferable from the viewpoint of the subsequent printing performance, more preferably 1: 6 to 3: 1, and still more preferably 1: 4 to 2: 1.
In the present invention, the alkali-soluble resin does not act as a fixing agent inside the printing press, and exerts a great effect as a fixing agent on a printing medium such as printing paper. The reason is considered as follows. That is, even if the printing press is left unused and the ink is left in an open system and ammonia is evaporated from the ammonium salt of the alkali-soluble resin, a large amount of ink exists as a continuous phase inside the printing press. Since the monovalent metal or amine component, which is a non-volatile component in the adhesive, moves through the ink and becomes a water-soluble alkali-soluble resin monovalent metal salt or amine salt, the alkali-soluble resin in the ink is used as an ink fixing agent. It is thought that it does not work. On the other hand, the amount of ink transferred to the printing paper is small compared to the amount present in the printing machine and penetrates and diffuses into the printing paper, so that the ink becomes a discontinuous phase on the printing paper, resulting in an alkali-soluble resin ammonium salt. From this, ammonia is gradually evaporated to produce an insoluble resin (alkali-soluble resin), which is considered to act as an ink fixing agent.

  As the water-soluble organic solvent, an organic compound that is liquid at room temperature and is soluble in water is used. For example, lower alcohols such as methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, 2-methyl-2-propanol; ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, penta Glycols such as ethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol; glycerin; acetins (monoacetin, diacetin, triacetin); triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, Triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene Glycol monoethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol derivatives of diethylene glycol such as ether, triethanolamine, beta-thiodiglycol, it may be used sulfolane. Polyethylene glycol having an average molecular weight of 200, 300, 400, 600 or the like in the range of 190 to 630, diol type polypropylene glycol having an average molecular weight of 400 or the like in the range of 200 to 600, average molecular weight of 300, 700, or the like A low molecular weight polyalkylene glycol such as a triol type polypropylene glycol having an average molecular weight of 250 to 800 can also be used. These water-soluble organic solvents can be used alone or in combination of two or more.

  The content of the water-soluble organic solvent in the ink is preferably 5% by weight or more, and more preferably 10% by weight or more. On the other hand, the upper limit of the amount of the water-soluble organic solvent is not particularly limited, but is preferably about 45% by weight or less, and more preferably about 35% by weight or less in order to reduce the back-through of the image. By containing 5% by weight or more of a water-soluble organic solvent having a boiling point higher than that of water, more preferably a boiling point of 150 ° C. or higher, drying of the master perforated part during printing can be effectively prevented.

  From the viewpoint of improving the drying property of the printed matter, water is preferably contained in the ink in an amount of 50% by weight or more, and more preferably 65% by weight or more. On the other hand, the upper limit of the amount of water is not particularly limited, and is preferably set as appropriate from the balance with other components.

  As the colorant, a pigment or a dye can be used, and two or more kinds may be used in combination. Examples of the pigment include organic pigments such as azo, phthalocyanine, dye, condensed polycyclic, nitro, and nitroso (brilliant carmine 6B, lake red C, watching red, disazo yellow, hanza yellow, phthalocyanine blue, Phthalocyanine green, alkali blue, aniline black, etc.); metals such as cobalt, iron, chromium, copper, zinc, lead, titanium, vanadium, manganese, nickel, metal oxides and sulfides, and ocher, ultramarine, bitumen, etc. Carbon blacks such as inorganic pigments, furnace carbon black, lamp black, acetylene black and channel black can be used. Examples of the dye include a basic dye, an acid dye, a direct dye, a soluble vat dye, an acid mordant dye, a mordant dye, a reactive dye, a vat dye, a sulfur dye, and the like. Water-soluble dyes can be used. Either or both of a pigment and a dye may be used as a colorant. However, the use of a pigment is preferable because an ink having less bleeding and show-through and excellent weather resistance can be obtained.

  The content of the colorant in the ink is usually 1 to 15% by weight, and preferably 3 to 12% by weight. In order to further increase the printing density of the printed material, it is more preferable to contain 5% by weight or more. If the content of the colorant exceeds 15% by weight, the printing performance after the printing machine is put into a non-use state may be impaired.

In addition to the above-described components, the ink of the present invention may appropriately contain a pigment dispersant, other fixing agents, antifoaming agents, surface tension reducing agents, pH adjusters, antioxidants, preservatives, and the like.
For example, the ink can contain an oil-in-water (O / W) type resin emulsion and can be used as a fixing agent for a colorant on a printing medium such as printing paper. In the case where a pigment is used as the colorant, this resin emulsion can also be used as a pigment dispersant.
Examples of the oil-in-water (O / W) type resin emulsion include polyvinyl acetate, ethylene-vinyl acetate copolymer, vinyl acetate- (meth) acrylate ester copolymer, poly (meth) acrylate ester, polystyrene, Resin emulsions such as styrene- (meth) acrylic acid ester copolymer, styrene-butadiene copolymer, vinylidene chloride- (meth) acrylic acid ester copolymer, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyurethane Can be used. Two or more of these may be used in combination.
The resin emulsion may be included in the ink in a range of 5% by weight or less in terms of solid content, more preferably, since there is a possibility that the printing performance after the non-use of the printing press may be hindered when the resin emulsion is contained in a large amount. 2% by weight or less.

  In addition to the ink thickener, the water-soluble polymer exemplified as the thickener can be used as a colorant fixing agent for printing paper, etc., depending on the type and amount thereof. Moreover, when using a pigment as a coloring agent, it can also be used as a pigment dispersant.

In order to improve the image quality of the printed matter, extender pigments can be included in the ink.
As the extender pigment, for example, white clay, talc, clay, diatomaceous earth, calcium carbonate, barium carbonate, barium sulfate, alumina white, silica, kaolin, mica, aluminum hydroxide can be used, and two or more of these can be used in combination. May be.
If the extender pigment is contained in a large amount, it may hinder the fixing of the colorant to the printing material or may impair the printing performance after the printer is not used. More preferably, it is 2 wt% or less.

Furthermore, as a pigment dispersant, an antifoaming agent, a surface tension reducing agent, etc., an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant, or a polymer-based, silicone-based, or fluorine-based interface. An activator can be included in the ink.
In order to adjust the viscosity and pH of the ink, an electrolyte can be added to the ink. Examples of the electrolyte include sodium sulfate, potassium hydrogen phosphate, sodium citrate, potassium tartrate, and sodium borate, and two or more kinds may be used in combination. Sulfuric acid, nitric acid, acetic acid, sodium hydroxide, potassium hydroxide, ammonium hydroxide, triethanolamine, and the like can also be used as an ink thickening aid or pH adjuster.

  By blending an antioxidant, the ink components can be prevented from being oxidized and the storage stability of the ink can be improved. As the antioxidant, for example, L-ascorbic acid, sodium L-ascorbate, sodium isoascorbate, potassium sulfite, sodium sulfite, sodium thiosulfate, sodium dithionite, sodium pyrosulfite can be used.

  By blending a preservative, the ink can be prevented from being spoiled and the storage stability can be improved. Examples of preservatives include 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, and 1 Isothiazolone preservatives such as 1,2-benzisothiazolin-3-one; triazine preservatives such as hexahydro-1,3,5-tris (2-hydroxyethyl) -s-triazine; 2-pyridinethiol sodium-1- Pyridine quinoline preservatives such as oxide and 8-oxyquinoline; Dithiocarbamate preservatives such as sodium dimethyldithiocarbamate; 2,2-dibromo-3-nitrilopropionamide, 2-bromo-2-nitro-1,3 -Propanediol, 2,2-dibromo-2-nitroethanol, 1,2-dibromo-2,4-dicia Brominated organic preservatives such as butane; p-hydroxybenzoate, p- hydroxybenzoate ethyl, potassium sorbate, sodium dehydroacetate, can be used salicylic acid.

The ink of the present invention comprises water, a colorant, a monovalent metal salt or amine salt of an unsaturated carboxylic acid-based water-soluble polymer, an ammonium salt of an alkali-soluble resin, and the above-described components that are appropriately blended as necessary. It can be produced by mixing. For example, a part of water, a pigment, and a pigment dispersant are mixed, and the pigment is dispersed using a dispersing means such as a ball mill or a bead mill, while the remaining water, a thickener, a fixing agent, and a water-soluble organic solvent. And may be mixed together.
The viscosity of the ink varies depending on the printing pressure of the printing apparatus and the like, but is generally about 0.5 to about 20 Pa · s (viscosity at 20 ° C., shear rate 100 / s), and (pseudo) The plastic fluidity is suitable for stencil printing.

Next, the stencil printing method according to the present invention is performed using the ink of the present invention. Specifically, a step of preparing a master for making a plate and a step of transferring the ink to the printing medium by passing the ink of the present invention from the perforated part of the master by press-contacting the master for printing and the printing medium. Contains.
The stencil printing machine to be used is not particularly limited, but it is preferable to use a digital stencil printing machine from the viewpoint of excellent operability.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Hereinafter, “% by weight” is simply referred to as “%”.
(Example 1)
Carbon black (“# 40” manufactured by Mitsubishi Chemical Co., Ltd.) 6.0% as a colorant, and polyoxyethylene nonylphenyl ether which is a nonionic surfactant as a pigment dispersant (“NP-10” manufactured by Nikko Chemicals Co., Ltd.) 1.0% and 20.0% distilled water were mixed and sufficiently dispersed with a bead mill to prepare a pigment dispersion. Dissolve 1.0% sodium polyacrylate, a monovalent metal salt of unsaturated carboxylic acid-based water-soluble polymer as a thickener, in 30.0% distilled water. In addition, 27.0% of the pigment dispersion prepared earlier, an aqueous solution of acrylic acid-acrylate copolymer ammonium as an alkali-soluble resin (“Jurimer AT-510” manufactured by Nippon Pure Chemical Co., Ltd., solid content 30%) 10 0.02%, tetraethylene glycol 20.0% as a water-soluble organic solvent, and the remaining distilled water (12.0%) were added and mixed to obtain the ink of Example 1.

(Examples 2 to 4, Comparative Examples 1 and 2)
An ink of each example was obtained in the same manner as in Example 1 except that the formulation shown in Table 1 was used. In Table 1, the acrylic acid-methacrylic acid ester copolymer is “Carbopol ETD2020” manufactured by BF Goodrich, and the styrene-α-methylstyrene-acrylic acid copolymer ammonium aqueous solution is “John Crill 60 manufactured by Johnson Polymer Co., Ltd. (Solid content 34%). In Examples 2 and 4, 1.0% acrylic acid-methacrylic acid ester copolymer was dissolved in 30.0% distilled water and neutralized by adding 2.0% triethanolamine to form an amine salt. Although used, in Comparative Example 2, triethanolamine was not used. In Examples 3 and 4, the pigment was dispersed using an alkali-soluble resin without using a nonionic surfactant.

Using each of the inks prepared in the above examples and comparative examples, printing is performed on printing paper (“Ideal paper thin mouth” manufactured by Riso Kagaku Kogyo Co., Ltd.) using a stencil printing machine (lithograph RP370, manufactured by Riso Kagaku Kogyo Co., Ltd.) Then, the fixability of the ink (image of the printed matter) and the discharge operation were evaluated as follows.
(Eraser resistance) An image obtained after 1 hour of printing was rubbed with an eraser, and an image in which the image was hardly erased was evaluated as ◯ and a thinned image was evaluated as ×.
(Water-resistant pen resistance) The image obtained 1 hour after printing was traced with an aqueous fluorescent pigment pen. The case where there was almost no bleeding of the image was evaluated as “◯”, and the case where the bleeding was large was evaluated as “×”.
(Discarding operability) After printing, the printing machine was left as it was for 14 hours. After that, the master was able to remove the plate without any problem, and the master was stuck to the printing drum, so that the plate could not be removed was evaluated as x.
The respective evaluation results are also shown in Table 1.

  All of the inks of the examples were excellent in the fixability of the image of the printed matter, and the printing plate operability was also good.

Claims (5)

  A water-based ink for stencil printing comprising a monovalent metal salt or amine salt of an unsaturated carboxylic acid-based water-soluble polymer and an ammonium salt of an alkali-soluble resin.   The water-based ink for stencil printing according to claim 1, wherein the content of the alkali-soluble resin is 0.1 to 5% by weight in terms of solid content.   The water-based ink for stencil printing according to claim 1 or 2, comprising a pigment as a colorant, wherein the pigment is dispersed with an ammonium salt of the alkali-soluble resin.   The unsaturated carboxylic acid-based water-soluble polymer and the alkali-soluble resin are contained at a blending ratio of 1: 9 to 4: 1 as a weight ratio in terms of solid content. Water-based ink for stencil printing.   A stencil printing method using the water-based ink for stencil printing according to any one of claims 1 to 4.