JP2008155529A - Inkjet recording medium and inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To supply a high-grade inkjet recording medium and recorded matter which are excellent in the water resistance and perspiration resistance of a printed image, in inkjet recording using a water-based pigment ink. <P>SOLUTION: The inkjet recording medium is characterized by satisfying following conditions (1) to (3). (1) A surface pH of an ink accepting layer measured by a glass electrode method, i.e. the paper pulp testing method No. 45-1 of TAPPI, reaches the minimum value within 60 seconds after dripping of a wetting liquid. (2) The minimum value of the surface pH is 3.0 or below. (3) A difference between the minimum value of the surface pH and the surface pH reached five minutes after dripping of the wetting liquid is 1.0 or above. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an inkjet recording medium that can be suitably used for recording using an ink containing a pigment, and an inkjet recording method using the same.

  Various types of ink-jet recording media used for image formation by the ink-jet recording method have been known so far. In recent years, the use of inkjet recording methods and the enhancement of functionality have been advanced for electronic image information output in computers and the like, image information output captured by digital cameras, digital videos, scanners, and the like. . Along with this, the demands on the performance of ink jet recording media are becoming more diverse or advanced.

  Along with the higher definition of output images as described above, the amount of ink printed on an inkjet recording medium from an inkjet printer tends to increase. Therefore, as a high-absorption type ink jet recording medium capable of receiving a large amount of ink, a substrate provided with an ink receiving layer containing inorganic porous particles such as silica and alumina as a main component on a substrate has come to be used. It is coming. In this type of ink jet recording medium, the image is fixed by adsorbing the dye in the ink to the inorganic porous particles, and it becomes possible to improve the ink absorbability by adopting such a configuration. ing.

  Conventionally, water-soluble dyes have been widely used as inks for ink-jet recording. However, in the case of recordings for the purpose of improving weather resistance, water-based inks containing pigments are used as coloring materials. It has become to.

  The recorded matter using the aqueous pigment ink as described above is compared with the recorded matter using the dye ink to prevent fading due to light such as ultraviolet rays, and an image due to a small amount of gas (especially ozone) present in the atmosphere. The ability to prevent fading is very good. However, the usage environment of the recorded material has become severe year by year, and the recorded material may come into contact with various liquids other than water. For example, when human sweat, saliva, or the like adheres to a recorded matter using pigment ink, there is a problem that the pigment ink dissolves into the sweat, saliva, or the like and image blurring occurs. Further, further improvement in water resistance has been desired.

Therefore, studies have been made to improve the water resistance and sweat resistance of ink jet recording media. In Japanese Patent Publication No. 3-31594 (Patent Document 1), Japanese Patent Publication No. 4-15744 (Patent Document 2), and Japanese Patent Publication No. 6-30951 (Patent Document 3), a cationic resin is added to the ink receiving layer. An ink jet recording medium is disclosed. In these ink jet recording media, it is described that the water resistance of dye inks recorded with a cationic resin is improved.
Japanese Patent Publication No. 3-31594 Japanese Patent Publication No. 4-15744 Japanese Patent Publication No. 6-30951

However, in the ink jet recording media described in Patent Documents 1 to 3, the water resistance and sweat resistance of the recorded image recorded using the pigment ink have not sufficiently satisfied the required performance in recent years.
Therefore, as a result of intensive studies, the present inventors have determined that the surface pH of the ink receiving layer has a special value and a special temporal behavior when the ink receiving layer comes into contact with a predetermined liquid. Discovered that it can improve the performance and sweat resistance.
That is, an object of the present invention is to provide a high-quality ink jet recording medium and an ink jet recording method which are excellent in water resistance and sweat resistance of a printed image in ink jet recording using an aqueous pigment ink.

In order to solve the above problems, the present invention is characterized by having the following configuration.
1. An ink jet recording medium comprising: a base material; and an ink receiving layer provided on the base material, wherein the following conditions (1) to (3) are satisfied.

(1) TAPPI Paper Pulp Test Method No. 45-1: The surface pH of the ink receiving layer measured by the glass electrode method reaches a minimum value within 60 seconds after dropping the wetting liquid.
(2) The minimum value of the surface pH is 3.0 or less.
(3) The difference between the surface pH of the ink receiving layer and the minimum value of the surface pH 5 minutes after dropping the wetting liquid is 1.0 or more.

2. 2. The ink jet recording medium according to 1 above, wherein the substrate is a film substrate.
3. 2. The ink jet recording medium according to 1 above, wherein the base material is resin-coated paper.

4). 4. The ink jet recording medium according to any one of items 1 to 3, wherein the ink receiving layer contains vapor phase silica.
5. An inkjet recording method for performing recording using an ink on the inkjet recording medium according to any one of 1 to 4 above,
An ink jet recording method, wherein the ink is a water-soluble pigment ink having a pH of 7 or higher.

  The ink jet recording medium of the present invention can obtain a high-quality recorded image excellent in water resistance and sweat resistance of a printed image in ink jet recording using an aqueous pigment ink.

1. Inkjet recording medium The inkjet recording medium of the present invention has a base material and an ink receiving layer provided on the base material. Further, the surface of the ink receiving layer of the present invention has the following pH characteristics (1) to (3).

  (1) TAPPI Paper Pulp Test Method No. 45-1: The surface pH of the ink receiving layer measured by the glass electrode method reaches a minimum value within 60 seconds after dropping the wetting liquid.

  (2) The minimum value of the surface pH is 3.0 or less.

  (3) [(surface pH after 5 minutes) − (minimum value of surface pH)], which is the difference between the surface pH of the ink receiving layer and the minimum value of the surface pH 5 minutes after the wetting liquid is dropped. 1.0 or more.

  Note that TAPPI paper pulp test method no. 45-1: Ion-exchanged water (purified water (trade name), manufactured by Kishida Chemical Co., Ltd .; pH 6.8) is used as the wetting liquid for the glass electrode method.

  The ink receiving layer is formed, for example, using vapor phase silica and a binder as main components, and the surface of the ink receiving layer is formed by the layer including the vapor phase silica and the binder as main components. In the ink jet recording medium of the present invention, for example, the ink receiving layer can be composed of a single layer, and this layer can be formed with silica and a binder as main components. In addition, the ink receiving layer may have a multilayer structure of two or more layers, and at least the outermost layer may have a structure in which gas phase method silica and a binder are mainly formed.

  In the ink jet recording medium of the present invention, the ink receiving layer contains inorganic porous particles (such as vapor phase method silica) so that the pigment particles for coloring dispersed in the ink are contained in the ink receiving layer. Can be kept on and near the surface. As a result, a clear image with high image density can be obtained.

  Although the minimum value of the surface pH of the configuration (2) is 3 or less, it is preferably 2.0 or more and 2.8 or less. Also, [(surface pH after 5 minutes) − (minimum value of surface pH)], which is the difference between the surface pH of the ink receiving layer after 5 minutes and the minimum value of the surface pH of the above configuration (3), is 1. Although it is 0 or more, it is preferable that it is 1.5 or more. When the minimum value of the surface pH and [(surface pH after 5 minutes) − (minimum value of surface pH)] are within the above range, the inkjet recording medium of the present invention can fix the pigment particles after printing the ink and Absorption can be performed effectively. As a result, it is possible to have excellent image characteristics.

(Functional action)
An image recorded on a conventional inkjet recording medium has insufficient water resistance and sweat resistance for the following reasons. In other words, alkaline water-based pigment ink (water-soluble pigment ink) for ink jet recording is used. The reason for this is to improve the solubility of the anionic (alkali-soluble) water-soluble resin added as a dispersing agent to make the ink excellent in long-term storage stability.

  Here, when the aqueous pigment ink is recorded on the surface of the ink jet recording medium, the water-soluble resin contained in the ink remains on the surface of the ink jet recording medium. However, the water-soluble resin staying in the vicinity of the surface of the ink jet recording medium is alkali-soluble, and if it touches the sweat, saliva, etc. of an alkaline person after recording, it re-dissolves and remarkably impairs the quality of the printed image. It was.

  Here, in the present invention, by having the configuration of the above (1), the surface pH of the ink receiving layer is shifted to a minimum value within a short time of 60 seconds after the ink receiving layer comes into contact with water or sweat. be able to. Moreover, in this invention, by having the structure of said (2), surface pH can be shifted to the acidic side with the high acidity of 3.0 or less as this minimum value.

  In this way, even if the water-soluble resin staying on the surface of the ink receiving layer touches human sweat or water (neutral or alkaline) by shifting the equilibrium state of the hydrogen ion concentration to the acidic side. , This person can neutralize sweat and water. As a result, the water-soluble resin remaining on the surface of the ink receiving layer can be insolubilized, and the water resistance and sweat resistance of the ink jet recording medium on which the aqueous pigment ink is recorded can be improved.

  However, on the other hand, when the surface pH of the ink jet recording medium is on the acidic side having a low pH for a long time after touching human sweat or water, the agglomeration action of the ink fixed on the surface (fixed on the ink receiving layer) Aggregation of pigment particles) occurs. As a result, the image characteristics of the ink jet recording medium are hindered. Therefore, in the present invention, by having the configuration of (3) above, the surface pH of the ink jet recording medium can be increased and the acidity can be reduced 5 minutes after contact with human sweat or water. As a result, the ink cohesiveness can be weakened and excellent image characteristics can be maintained.

  In addition, the characteristics of the surface pH of the above (1) to (3) of the present invention are as follows. 45-1: It is based on the test based on the glass electrode method. In the present invention, ion-exchanged water (purified water (trade name), manufactured by Kishida Chemical Co., Ltd., pH 6.8) is used as a wetting liquid in this test method, and this ion-exchanged water is an ink jet recording medium after recording. It has characteristics similar to touching water and sweat. For this reason, the ink jet recording medium of the present invention has the above-described configurations (1) to (3), and thus has a minimum value even when the surface of the ink receiving layer is in contact with water or sweat. Becomes a low value on the acidic side. Further, a certain acidity becomes a weak pH 5 minutes after the surface of the ink receiving layer comes into contact with water or sweat.

  As described above, according to the present invention, by having the configurations (1) to (3), even when the surface of the ink receiving layer after recording is in contact with water or human sweat, excellent water resistance and Can have sweat properties.

  FIG. 1 shows the TAPPI paper pulp test method no. 45-1: An example of the result of the test by the glass electrode method is shown. In FIG. 1, the surface pH at time 0 cannot be measured and is not shown in the figure. FIG. 2 shows an example of the ink jet recording medium of the present invention. As shown in FIG. 2, the ink jet recording medium of the present invention is one in which an ink receiving layer 2 is provided on a substrate 1. Then, the surface pH of the surface 3) opposite to the base material of the ink receiving layer 2 is tested.

  As shown in FIG. 1, when the above test is performed on the surface 3 of the ink jet recording medium of the present invention (the surface opposite to the substrate side of the ink receiving layer), the surface pH of the ink receiving layer is acidic. Is configured to migrate to. For this reason, after dropping the wetting liquid (the time when the wetting liquid is dropped is set to time 0), the surface pH decreases with the passage of time, and falls to the minimum value at point A within 60 seconds after the wetting liquid is dropped. In addition, this minimum value is a value of pH 3.0 or less. After this, the surface pH starts to gradually increase from the minimum value (point A), reaches a certain value before 5 minutes have passed since the wetting liquid was dropped, and this value is 1.0% lower than the minimum value. This is a large value. For this reason, if the surface pH after 5 minutes from the start of the test is measured, it is possible to measure the stable surface pH by recovering from the minimum value.

It should be noted that the surface pH-time curve according to the above test may be a surface pH-time curve having a minimum value and having a stable steady-state surface pH 5 minutes after dropping the wetting liquid. It is not limited. For this reason, depending on the structure of the base material and the ink receiving layer of the present invention, a surface pH-time curve showing a behavior different from that shown in FIG. 1 may be used.
Hereinafter, the substrate and the ink receiving layer constituting the ink jet recording medium of the present invention will be described.

(Base material)
The base material of the present invention is not particularly limited, and may be transparent or opaque. Examples of the plastic film substrate include polyethylene, polypropylene, polyvinyl chloride, and polyester. In addition, as paper base materials, high-quality paper, baryta paper for photographic paper, RC paper for photographic paper (with olefin resin provided on both sides of photographic paper base paper), drawing paper, art paper, coated paper, cast coated paper, Examples include kraft paper, impregnated paper, and synthetic paper. These can be used as appropriate according to the intended use, but in consideration of the quality, glossiness, image density and the like of the resulting ink jet recording medium, a substrate such as a film substrate or RC paper is preferred.

  The substrate is preferably resin-coated paper. This resin-coated paper is a base material in which a resin layer having a thickness of about several tens of microns is provided on the surface of the paper base material, and the surface smoothness is very high like the film base material. For this reason, an ink jet medium in which an ink receiving layer is provided on resin-coated paper is also a very smooth medium with high glossiness. Therefore, a clear image having a high image density can be obtained.

  Further, since the resin-coated paper has a resin layer on the surface, the solvent component of the printed pigment ink does not penetrate into the base material and remains only in the ink receiving layer. In this way, when the ink component is retained on the surface of the ink receiving layer and the vicinity thereof, the component soluble in an alkaline solution such as a water-soluble resin in the ink is retained at a high concentration on the surface of the ink receiving layer and the vicinity thereof. Will be. As a result, the conventional ink jet recording medium using the base material of the resin-coated paper is greatly inferior in water resistance and sweat resistance. However, in the present invention, by having the constitutions (1) to (3) above, it is possible to prevent deterioration of water resistance and sweat resistance due to the use of the resin-coated paper base material, and to achieve better water resistance. And sweat resistance.

(Ink receiving layer)
Inorganic porous particles The ink receiving layer of the present invention preferably contains inorganic porous particles. As the inorganic porous particles, wet amorphous silica, dry silica, colloidal silica, alumina, boehmite and the like can be used, but gas phase method silica is preferable from the viewpoint of ink absorbability and color development of printed matter. . As the vapor-phase process silica, for example, those commercially available under the trade name Leoroseal of Tokuyama Co., Ltd. can be used, which can be easily obtained.

  Further, when the aqueous pigment ink is printed on the ink jet recording medium of the present invention, in order to color the pigment ink at a high concentration, the pigment particles for coloring dispersed in the ink are separated from the surface of the ink receiving layer and It is important to stay in the vicinity. This is because if the pigment particles enter the inside of the ink receiving layer, the pigment particles are shielded in the ink receiving layer and the color developability deteriorates.

Therefore, the vapor phase silica is preferably silica having a specific surface area of 50 m ² / g or more and 150 m ² / g or less by the BET method. When the specific surface area of the vapor-phase process silica is within this range, the color developability (printing density) of the pigment-based ink can be improved, and a clear image comparable to the photographic image quality can be obtained. Further, the occurrence of beading due to the pigment-based ink can be effectively prevented or suppressed, and a higher quality image can be obtained. Furthermore, the absorption speed of the pigment-based ink to the recording medium is further improved, and high-speed printing is possible.

  Further, since vapor phase silica does not have an internal surface area in the primary particles, the specific surface area obtained by the BET method corresponds to the primary particle diameter obtained from the transmission electron microscope. The primary particle diameter is preferably 15 nm or more and 30 nm or less.

  Furthermore, it is preferable that the largest gap of the ink receiving layer containing the vapor phase method silica is 0.1 μm or less in consideration of the particle diameter of ink pigment particles (generally around 100 nm). By setting the largest void diameter of the ink receiving layer in such a range, it is possible to obtain good color developability by keeping the pigment particles on the surface of the ink receiving layer. At the same time, the water-soluble resin added as a dispersant in the ink also stays on the surface of the ink receiving layer, and the adhesion between the ink pigment printed and recorded and the ink jet recording medium can be improved.

-Cationic resin The ink receiving layer of the present invention preferably contains a cationic resin. The aqueous pigment ink for printing on the ink jet recording medium of the present invention contains a dispersant for dispersing the colored pigment particles in the aqueous solution. This dispersant is anionic charged, and the pigment particles in the ink are protected by the dispersant and are stably dispersed in the aqueous solution by the charge repulsion of the dispersant.

  For this reason, the pigment particles in the ink can be agglomerated instantly due to the electric action of the opposite charge by containing a cationic resin having the opposite charge to the anionic resin used in the pigment ink in the ink receiving layer. It becomes. As a result, the pigment particles having an anionic charge can be closely fixed to the surface of the ink jet recording medium, and a clear and excellent image characteristic can be obtained.

  Examples of the cationic resin include acrylic resins having secondary to quaternary amine groups, which are made by copolymerizing a cationic acrylic monomer having an amino group or the like to give a neutralized salt, polyallylamine-based polymers and neutralized salts thereof, poly Examples include diallylamine-based polymers and neutralized salts thereof, polyaminesulfone, polyvinylamine, polyethyleneimine, polyamide-epichlorohydrin resin, polyvinylpyrrolidone, polyvinylpyridium halide, and polyvinylimidazole resin.

-Binder The ink receiving layer of the present invention preferably contains a water-soluble or hydrophilic binder in order to maintain the properties as a coating film. Examples of these binders include polyvinyl alcohol and modified products thereof, polyvinyl pyrrolidone, vinyl acetate, oxidized starch, etherified starch, casein, gelatin, soy protein, carboxymethyl cellulose, SB latex, NB latex, acrylic latex, and ethylene acetate. Vinyl latex, polyurethane, unsaturated polyester resin, etc. can be used.

  In the ink receiving layer of the present invention, at least one kind of these binders can be used, but the content is the minimum amount in consideration of the film forming property and film strength of the ink receiving layer. It is important to keep it at a minimum. This is because these hydrophilic binders are easily swollen by the solvent component of the ink, and may impair the absorbability of the pigment-based ink.

  The content of the binder is preferably 30% by mass or less, and more preferably 25% by mass or less, based on the total solid content mass of the ink receiving layer. The lower limit thereof can be selected so as to obtain the film formability and film strength required for the ink receiving layer, and is preferably 5% by mass or more, and more preferably 10% by mass or more.

  As this binder, it is more preferable to use polyvinyl alcohol, and even when two or more binders are mixed and used, it is preferable to use at least polyvinyl alcohol as one of them. The case where polyvinyl alcohol is used as the binder will be described in more detail below.

  Polyvinyl alcohol is obtained by a saponification reaction in which polyvinyl acetate is neutralized with an alkaline solution to replace an acetate group with a hydroxyl group. Polyvinyl alcohol has different properties such as film strength, crystallinity, water solubility, and viscosity depending on the degree of polymerization (molecular weight) and the degree of saponification.

  In the present invention, it is preferable to use polyvinyl alcohol having a saponification degree of 90 mol% or more. Thereby, the beading property of the pigment-based ink becomes better. Further, it is known that polyvinyl alcohol having a high degree of saponification tends to form a film having high crystallinity. Therefore, polyvinyl alcohol having higher crystallinity, that is, higher saponification degree, has lower water swellability, and therefore, the permeability of the solvent component into the ink receiving layer becomes higher when printing with pigment-based ink. As a result, it is considered that the beading property is improved. Moreover, it is preferable that the polymerization degree of polyvinyl alcohol is 1500 or more from a viewpoint of film | membrane intensity | strength.

  Further, as the binder, those capable of imparting a crosslinked structure to the ink receiving layer can be used. The cross-linked structure can be formed in the ink receiving layer by using a binder and a cross-linking agent in combination or using a cross-linking binder.

  Here, the crosslinking agent represents a monomer (monomer) or oligomer (medium molecular weight component) having a functional group (reactive group) capable of forming a covalent bond or a coordinate bond by heating or the like. For example, examples of the inorganic crosslinking agent include metal oxides such as boric acid and sodium borate and salts thereof. Examples of organic crosslinking agents include isocyanate compounds, epoxy compounds, N-methylol compounds, carbodiimide compounds, triazine compounds, aldehyde compounds, vinyl sulfone compounds, acryloyl compounds, ethyleneimine compounds, and siloxane compounds. There are compounds.

  Examples of the crosslinkable binder having a reactive functional group in the polymer include water-soluble acrylic resins having a methylol group, an epoxy group, a silanol group, and the like, and polyvinyl alcohol. By using such a crosslinkable binder, the film strength of the binder is increased, and the content of the binder in the ink receiving layer can be lowered. As a result, ink absorption inhibition due to the solvent component swelling the binder during ink absorption can be suppressed, and an ink receiving layer more suitable for ink absorption can be formed.

2. Method for Producing Inkjet Recording Medium The ink jet recording medium of the present invention can be produced by preparing a base material, applying a coating liquid for an ink receiving layer on the base material, and drying the coating liquid. .

The ink receiving layer coating solution can be prepared, for example, as follows.
First, gas phase method silica and binder powder are mixed in a liquid medium while stirring so that the solid content is 10 to 30% by mass, and a dispersion liquid in which these concentrations are adjusted as necessary is obtained. . In the coating solution, various components other than the vapor phase silica and the binder can be added as necessary. As the liquid medium for the coating liquid, water, water-soluble solvents such as alcohol solvents and ether solvents can be used, and a mixture of water and water-soluble solvents can also be used. As such a mixture, a liquid medium mainly composed of water can be used, and the content of water in the liquid medium in this case is preferably at least 90% by mass (including the case of 100% by mass). .

  The dispersion is further pulverized by a homogenizer, a colloid mill, a ball mill, a high-speed rotary mill, or the like to adjust the particle size of the silica secondary aggregate to obtain a coating solution for an ink receiving layer. At this time, from the viewpoint of adjusting the particle size and the stability of the dispersion, it is preferable to contain a dispersant in the coating solution.

  Here, in the aqueous pigment ink for printing on the inkjet recording medium of the present invention, the colored pigment particles are stably dispersed in the aqueous solution due to the charge repulsion of the anionic dispersant. Therefore, by containing a cationic resin having a charge opposite to that of the anionic resin used in the pigment ink in the coating liquid, the pigment particles in the ink can be instantaneously aggregated by an electric action due to the opposite charge during recording. It becomes possible. As a result, the pigment particles having an anionic charge can be closely fixed to the surface of the ink jet recording medium, and a clear and excellent image characteristic can be obtained. Furthermore, when considering the sweat resistance against human sweat and the like (especially for alkaline artificial sweat specified by JIS-L-0848), it is important that the pH of this dispersion is less than 3.

Next, an ink receiving layer coating solution is applied onto the substrate. At this time, general coating devices such as blade coaters, roll coaters, air knife coaters, bar coaters, gate roll coaters, curtain coaters, die coaters, short dwell coaters, gravure coaters, flexographic gravure coaters, etc. Can be used. The layer thickness of the ink receiving layer can be appropriately selected from layer thicknesses in which the coating weight after drying per unit area is in the range of 10 g / m ² or more and 30 g / m ² or less.

  In addition, the surface of the ink receiving layer such as calendering or casting may be applied to the ink receiving layer after coating the ink receiving layer within a range not impairing the effects of the present invention.

3. Inkjet recording method-Recording means As an inkjet recording method for recording ink on the inkjet recording medium of the present invention, an electrostatic suction method, an inkjet recording method using a piezoelectric element, an inkjet recording method using a heating element, or the like can be used. However, the method is not particularly limited.

Ink In the recording method of the present invention, it is preferable to use a pigment-based ink as the ink. Hereinafter, the pigment-based ink will be described.
The amount of the pigment contained in the pigment-based ink is preferably 1% by mass on the market, 20% by mass or less, and more preferably 2% by mass to 12% by mass with respect to the total mass of the ink. preferable. Examples of the pigment include inorganic pigments such as carbon black and titanium white, and organic pigments such as phthalocyanine pigments, monoazo pigments, disazo pigments, and quinacridone pigments. These pigments can be used alone or in combination of two or more as required.

  Examples of carbon black used for black ink include No. 2300, 900, MCF88, No. 2 33, 40, 45, 52, MA7, 8; 2200B (Mitsubishi Kasei), Raven 1170, 1255 (Made by Colombian Chemical), REGAL400R, 330R, 660R, Mogul L, Stirling MS, NSX76 (Made by Cabot), Color Commercial products such as Black FW1, FW18, S170, S150, and Special Black 4A (degussa) can be used.

  Examples of pigments used in yellow ink include C.I. I. Pigment Yellow 1, 2, 3, 12, 12, 14, 17, 17, 73, 74, 75, 83, 93, 95, 97, 98, 114, 128, 129, 151, 1154, and the like.

Examples of pigments used as magenta ink include C.I. I. Pigment R
ed 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca),
112, 122, 123, 168, 184, 202, 207 and the like.

As a pigment used as a cyan ink, C.I. I. PigmentBlue 1, 2, 3, 4, 15: 2, 15: 3, 15: 4, 16, 22, 22, 60, C.I. I. Vat Blue 4, 6, 19, 19, 23, 42 and the like.
However, the pigment is not limited to the above-mentioned pigment, and a pigment newly produced for the present invention can also be used.

  The ink used in the ink jet recording method of the present invention preferably contains a pigment dispersant. As this pigment dispersant, a water-soluble resin is used. This water-soluble resin is appropriately selected in consideration of the dispersion and storage stability of the pigment-based ink, the ejection property by inkjet, and the ejection stability.

  Examples of water-soluble resins that can be used as dispersants include styrene, styrene derivatives, vinyl naphthalene, vinyl naphthalene derivatives, aliphatic alcohol esters of α, β-ethylenically unsaturated carboxylic acids, acrylic acid, acrylic acid derivatives, and maleic acid. A hydrophilic copolymer obtained by copolymerizing at least two monomers selected from maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, etc. (of which at least one is a hydrophilic monomer) Examples thereof include a resin or a salt obtained by neutralizing these and making them water-soluble.

  Furthermore, N, N-dimethylaminoethyl methacrylate, N, N-dimethylaminoethyl acrylate, N, N-dimethylaminoacrylamide, N, N-dimethylaminomethacrylamide, N, N-dimethylaminopropylacrylamide, N, N -What used cationic dispersing agents, such as an acrylic copolymer containing the monomer unit which quaternized dimethylaminopropyl methacrylamide etc. with methyl chloride, dimethyl sulfuric acid, benzyl chloride, epichlorohydrin etc., may be used.

  Particularly preferred water-soluble resins are water-soluble resins having a structure such as a block copolymer or a graft copolymer. These resins are clearly separated in a hydrophobic molecular structure and a hydrophilic molecular structure, and exhibit a strong adsorptive power with respect to a hydrophobic pigment-based ink, so that the dispersibility in an aqueous solution is very good. Specifically, block-type water-soluble resins described in Japanese Patent Nos. 2635235 and 2675965 can be preferably used.

  One dispersant can be used alone, or two or more dispersants can be used in combination as required. The addition amount of the dispersant is set so as to obtain a desired dispersion state in the pigment-based ink. For example, 3 mass% or more and 15 mass% or less are preferable with respect to the total mass of ink, and 5 mass% or more and 10 mass% or less are still more preferable.

  This pigment-based ink is adjusted to be alkaline. Thus, since the ink is alkaline, the solubility of the water-soluble resin is improved, and the ink can be further excellent in long-term storage stability. In addition, the pH of the ink is more preferably in the range of 7 to 10 because it may cause corrosion of various members used in the ink jet recording apparatus. The ink can contain a pH adjuster. Examples of the pH adjuster include various organic amines such as diethanolamine and triethanolamine, inorganic alkali agents such as alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide, organic acids, and mineral acids. Is mentioned.

  In the ink used in the recording method of the present invention, an ink component such as a pigment and a water-soluble resin is dispersed or dissolved in an aqueous medium. As this aqueous medium, it is preferable to use a mixed solvent of water and a water-soluble organic solvent. Moreover, it is preferable to use ion-exchanged water (deionized water) instead of general water containing various ions.

In addition, as a solvent component that can be used in combination with water, for example, the following can be used as water-soluble organic solvents.
Alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol;
Amides such as dimethylformamide and dimethylacetamide;
Ketones or ketoalcohols such as acetone and diacetone alcohol;
Ethers such as tetrahydrofuran and dioxane;
Polyalkylene glycols such as polyethylene glycol and polypropylene glycol;
Alkylene glycols having an alkylene group containing 2 to 6 carbon atoms such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol;
Glycerin;
Lower alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether;
N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone.

  Of these many water-soluble organic solvents, polyhydric alcohols such as diethylene glycol and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl (or ethyl) ether are preferred. The water-soluble organic solvent can be used alone or in combination of two or more as required.

  Furthermore, it is effective to add 1% by mass or more of ethanol or isopropyl alcohol to the ink in order to improve the stability of ink ejection. By adding these alcohols, it is considered that foaming of the ink on the thin film resistor (discharge energy generating element) can be performed more stably.

  In general, the content of the water-soluble organic solvent in the pigment-based ink used in the recording method of the present invention is preferably in the range of 3% by mass to 50% by mass with respect to the total mass of the ink. More preferably, it is in the range of mass% or less. Further, the content of water in the ink is preferably 10% by mass or more and 90% by mass or less, and more preferably 30% by mass or more and 80% by mass or less of the total mass of the ink.

  In addition to the above-described components, a surfactant, an antifoaming agent, a preservative, and the like can be added to the pigment-based ink as necessary in order to obtain an ink having a desired physical property value. Furthermore, commercially available water-soluble dyes can also be added.

The surfactant is not particularly limited as long as it does not have an adverse effect such as storage stability on the ink. For example, fatty acid salts, higher alcohol sulfates, liquid fatty oil sulfates, alkyls Examples include anionic surfactants such as allyl sulfonates, nonionic surfactants such as polyoxyethylene alkyl esters, polyoxyethylene sorbitan alkyl esters, acetylene alcohol, and acetylene glycol. These surfactants can be used by appropriately selecting one kind or two or more kinds. The amount of the surfactant used in the ink varies depending on the dispersant, but is preferably 0.01% by mass or more and 5% by mass or less based on the total mass of the ink.
Further, as the particle diameter of the pigment particles in the pigment-based ink, the volume average particle diameter of the pigment particles is preferably 200 nm or less from the viewpoint of color developability.

-Manufacturing method of water-soluble pigment ink As a manufacturing method of the aqueous pigment ink used for the inkjet recording method of this invention, after adding a pigment in the aqueous solution containing a dispersing agent (water-soluble resin), it stirs first. To do. Next, a desired dispersion is obtained by performing a dispersion process using a dispersion means described later. In this case, the disperser to be used may be any disperser that is generally used, and examples thereof include a ball mill, a roll mill, and a sand mill. Among these, a high-speed sand mill is preferable, and examples thereof include a super mill, a sand grinder, a bead mill, an agitator mill, a glen mill, a dyno mill, a pearl mill, and a cobol mill (all are trade names).

Further, as a method for obtaining a pigment having a desired particle size distribution in the ink, the following methods are conceivable.
(1) Reduce the size of the pulverizing media of the disperser.
(2) Increase the filling rate of pulverized media.
(3) Increase the processing time.
(4) Reduce the discharge speed.
(5) After pulverization, classify with a filter or a centrifuge.
These methods can be used alone or in combination.

  Thereafter, a centrifugal separation process may be performed as necessary. Next, the compound used in the present invention (for example, the components listed above) is added to this dispersion and stirred to finally obtain the intended ink.

  When obtaining this ink, it is preferable to perform premixing for 30 minutes or more in advance before dispersing the aqueous solution containing the pigment. This premixing operation improves the wettability of the pigment surface and promotes the adsorptivity.

Hereinafter, the embodiment will be described in more detail.
(Preparation of silica dispersion 1)
Silica (inorganic porous particles; Tokuyama Corporation; Reolosil QS-07 (trade name); BET specific surface area: about 70m ² / g) and, polydiallyl methyl amine hydrochloride (Nitto Boseki Co., Ltd., a cationic resin ; PAS-M-1 (trade name); 5 mass% solution pH = 1.9) mixed with 20 mass% ion-exchanged water with stirring, and a silica coarse dispersion having a solid content of 20 mass% Got. The mass ratio of silica and cationic resin was 100: 3 (solid content mass ratio). Furthermore, this silica coarse dispersion was subjected to a dispersion treatment with a homogenizer to obtain silica dispersion 1. The silica was amorphous silica synthesized by a vapor phase method (vapor phase silica), and the silica dispersion had a pH of 2.8.

(Preparation of silica dispersion 2)
Silica (inorganic porous particles; Tokuyama Co., Ltd .; Reolosil QS-07 (trade name); specific surface area by BET method: about 70 m ² / g) is replaced with polydiallylamine ammonium chloride (Nittobo Co., Ltd .; PAS) as a cationic resin. -H-5L (trade name); 5 mass% solution pH = 3.2) was mixed with 20 mass% dissolved ion-exchanged water while stirring to obtain a silica coarse dispersion having a solid content of 20 mass%. It was. The mass ratio of silica and cationic resin was 100: 3 (solid content mass ratio). Further, this silica crude dispersion was subjected to a dispersion treatment with a homogenizer in the same manner as silica dispersion 1 to obtain silica dispersion 2. The silica was amorphous silica synthesized by a gas phase method (gas phase method silica), and the silica dispersion had a pH of 3.4.

(Preparation of silica dispersion 3)
Silica (inorganic porous particles; Tokuyama Corporation; Reolosil QS-07 (trade name); specific surface area by BET method: about 70m ² / g) of the cationic resin (manufactured by Nitto Boseki Co., Ltd., PAS-880 (trade name) PH = 2.2) of a 5 mass% solution was mixed with ion-exchanged water dissolved at 20 mass% with stirring to obtain a silica coarse dispersion having a solid content of 20 mass%. The mass ratio of silica and cationic resin was 100: 3 (solid content mass ratio). Further, this silica coarse dispersion was subjected to a dispersion treatment with a homogenizer in the same manner as silica dispersion 1 to obtain silica dispersion 3. The silica was amorphous silica synthesized by a gas phase method (gas phase method silica), and the pH of the dispersion was 2.7.

(Preparation of silica dispersion 4)
Silica (inorganic porous particles; Tokuyama Co., Ltd .; Leoroseal QS-07 (trade name); specific surface area by BET method: about 70 m ² / g) and cationic resin (Nittobo Co., Ltd .; PAA-CH ₃ COOH-L) (Product Name): pH = 5.9 of 5 mass% solution was mixed with ion-exchanged water dissolved at 20 mass% with stirring to obtain a silica coarse dispersion having a solid content of 20 mass%. The mass ratio of silica and cationic resin was 100: 3 (solid content mass ratio). Further, this silica coarse dispersion was subjected to a dispersion treatment with a homogenizer in the same manner as the silica dispersion 1, whereby a silica dispersion 4 was obtained. The silica was amorphous silica synthesized by a gas phase method (gas phase method silica), and the pH of this silica dispersion was 4.9.

(Preparation of silica dispersion 5)
Silica (inorganic porous particles; Tokuyama Co., Ltd .; Reolosil QS-07 (trade name); specific surface area by BET method: about 70 m ² / g) is mixed with ion-exchanged water while stirring to obtain a solid content of 20% by mass. A crude silica dispersion was obtained. Further, this silica crude dispersion was subjected to a dispersion treatment with a homogenizer in the same manner as the silica dispersion 1, whereby a silica dispersion 5 was obtained. The silica was amorphous silica (gas phase method silica) synthesized by a gas phase method, and the pH of this silica dispersion was 4.4.

(Preparation of silica dispersion 6)
Silica (inorganic porous particles; Tokuyama Corporation; Reolosil QS-09 (trade name); BET specific surface area: about 90m ² / g) and, polydiallyl methyl amine hydrochloride (Nitto Boseki Co., Ltd., a cationic resin ; PAS-M-1 (trade name); 5 mass% solution pH = 1.9) mixed with 20 mass% ion-exchanged water with stirring, and a silica coarse dispersion having a solid content of 20 mass% Got. The mass ratio of silica and cationic resin was 100: 3 (solid content mass ratio). Furthermore, this silica coarse dispersion was subjected to a dispersion treatment with a homogenizer to obtain silica dispersion 6. The silica was amorphous silica synthesized by a gas phase method (gas phase method silica), and the silica dispersion had a pH of 2.6.

(Example 1)
A coating liquid for the ink receiving layer having the following composition was prepared, and a slot was formed on a base material of white PET (Chrisper K1212; manufactured by Toyobo Co., Ltd.) having a thickness of 125 μm so that the coating weight after drying was about 25 g / m ^2. It was coated with a die coater. Thereafter, this was dried to obtain an ink jet recording medium.
(Combination)
Component-1: Silica dispersion 1 ... 100 parts by mass Component-2: Polyvinyl alcohol 8% by mass aqueous solution ... 83 parts by mass (Nippon Vinegar-Poval Corporation; JM-26 (trade name); Degree of saponification = 97%)
Pure water was added to the mixture of the above components-1 and -2 to dilute the solid content to 15% by mass.

(Example 2)
A coating liquid for the ink receiving layer having the following composition was prepared, and a slot was formed on a base material of white PET (Chrisper K1212; manufactured by Toyobo Co., Ltd.) having a thickness of 125 μm so that the coating weight after drying was about 25 g / m ^2. It was coated with a die coater. Thereafter, this was dried to obtain an ink jet recording medium.
(Combination)
Component-1: Silica dispersion 6 ... 100 parts by mass Component-2: Polyvinyl alcohol 8% by weight aqueous solution ... 34 parts by mass (Nippon Vinegar-Poval Corporation; JM-26 (trade name); degree of saponification = 97%)
Component-3: Crosslinking agent (3% by weight aqueous solution of boric acid) ... 23 parts by mass Component-4: Self-crosslinking cationic acrylic resin ... 3 parts by mass (Daicel Chemical Industries, Ltd .; AQ-903 (trade name) ); Solid content 26 mass%)
Pure water was added to the mixture of the above components-1 to -4 to dilute the solid content to 15% by mass.

(Example 3)
Prepared ink-receiving layer coating solution having the following formulation, a white PET with a thickness of 125 [mu] m; on the substrate (Crisper K1212 manufactured by Toyobo Co., Ltd.), as coating weight after drying of about 25 g / m ^2, slot It was coated with a die coater. Thereafter, this was dried to obtain an ink jet recording medium.
(Combination)
Component-1: Silica dispersion 3 ... 100 parts by mass Component-2: Polyvinyl alcohol 10% by mass aqueous solution ... 24 parts by mass (Kuraray Kuraray Poval Co., Ltd .; PVA-117 (trade name); degree of saponification = about 97%)
Pure water was added to the mixture of the above components-1 and -2 to dilute the solid content to 15% by mass.

Example 4
A coating solution for an ink receiving layer having the following composition was prepared, and a substrate (resin coated paper) coated with 15 μm of polyethylene resin on both sides of high-quality paper of 180 g / m ² was used as a substrate. The ink jet recording medium was obtained by coating the substrate with a slot die coater so that the coating weight after drying was about 25 g / m ² and drying.
(Combination)
Component-1: Silica dispersion 1 ... 100 parts by mass Component-2: Polyvinyl alcohol 8% by mass aqueous solution ... 83 parts by mass (Nippon Vinegar-Poval Corporation; JM-26 (trade name); Degree of saponification = 97%)
Pure water was added to the mixture of the above components-1 and -2 to dilute the solid content to 15% by mass.

(Comparative Example 1)
A coating liquid for the ink receiving layer having the following composition was prepared, and a slot was formed on a base material of white PET (Chrisper K1212; manufactured by Toyobo Co., Ltd.) having a thickness of 125 μm so that the coating weight after drying was about 25 g / m ^2. It was coated with a die coater. Thereafter, this was dried to obtain an ink jet recording medium.
(Combination)
Component-1: Silica dispersion 5 ... 100 parts by mass Component-2: Polyvinyl alcohol 8% by weight aqueous solution ... 83 parts by mass (Nippon Vinegar-Poval Corporation; JM-26 (trade name); Degree of saponification = 97%)
Pure water was added to the mixture of the above components-1 and -2 to dilute the solid content to 15% by mass.

(Comparative Example 2)
A coating liquid for the ink receiving layer having the following composition was prepared, and a slot was formed on a base material of white PET (Chrisper K1212; manufactured by Toyobo Co., Ltd.) having a thickness of 125 μm so that the coating weight after drying was about 25 g / m ^2. It was coated with a die coater. Thereafter, this was dried to obtain an ink jet recording medium.
(Combination)
Component-1: Silica dispersion 2 ... 100 parts by mass Component-2: 8% by weight polyvinyl alcohol aqueous solution ... 83 parts by mass (Nippon Vinegar Poval Co., Ltd .; JM-26 (trade name); degree of saponification = 97%)
Pure water was added to the mixture of the above components-1 and -2 to dilute the solid content to 15% by mass.

(Comparative Example 3)
A coating liquid for the ink receiving layer having the following composition was prepared, and a slot was formed on a base material of white PET (Chrisper K1212; manufactured by Toyobo Co., Ltd.) having a thickness of 125 μm so that the coating weight after drying was about 25 g / m ^2. It was coated with a die coater and dried.

(Combination)
Component-1: Silica dispersion 2 ... 100 parts by mass Component-2: 8% by weight polyvinyl alcohol aqueous solution ... 83 parts by mass (Nippon Vinegar Poval Co., Ltd .; JM-26 (trade name); degree of saponification = 97%)
Pure water was added to the mixture of the above components-1 and -2 to dilute the solid content to 15% by mass. Furthermore, a nitric acid solution having a pH of ² was applied with a bar coater so as to have a liquid mass of about 10 g / m ² and dried to obtain an ink jet recording medium.

(Comparative Example 4)
Prepared ink-receiving layer coating solution having the following formulation, a white PET with a thickness of 125; on a substrate (Crisper K1212 manufactured by Toyobo Co.), as coating weight after drying of about 25 g / m ^2, slot It was coated with a die coater. Thereafter, this was dried to obtain an ink jet recording medium.

(Combination)
Component-1: Silica dispersion 4 ... 100 parts by mass Component-2: 8% by weight polyvinyl alcohol aqueous solution ... 83 parts by mass (Nippon Vinegar Poval Co., Ltd .; JM-26 (trade name); degree of saponification = 97%)
Pure water was added to the mixture of the above components-1 and -2 to dilute the solid content to 15% by mass.

(Preparation of pigment-based ink)
Next, an ink was prepared by the following method. First, cyan ink was prepared by the following method.
(1) Preparation of dispersion First, an AB type block polymer having an acid value of 250 and a number average molecular weight of 3000 was prepared by a conventional method using benzyl methacrylate and methacrylic acid as raw materials. Further, this AB type block polymer solution was neutralized with an aqueous potassium hydroxide solution and then diluted with ion-exchanged water to prepare a homogeneous 50% by mass aqueous polymer solution.

  180 g of the above polymer aqueous solution, C.I. I. After mixing 100 g of Pigment Blue 15: 3 and 220 g of ion-exchanged water, the mixture was mechanically stirred for 0.5 hour. The mixture was then processed using a microfluidizer by passing it through the interaction chamber 5 times under a liquid pressure of about 10,000 psi (about 70 Mpa) to obtain a dispersion.

  Further, the dispersion obtained above was centrifuged (12,000 rpm, 20 minutes) to remove the non-dispersed material containing coarse particles, thereby preparing dispersion 1. The obtained dispersion liquid 1 had a pigment concentration of 10% by mass and a dispersant concentration of 10% by mass.

(2) Preparation of Ink The above dispersion liquid 1 was used to prepare the ink. The following components were added to this to obtain a predetermined concentration, and these components were sufficiently mixed and stirred. Thereafter, this was subjected to pressure filtration through a micro filter (manufactured by Fujifilm) having a pore size of 2.5 μm to prepare a cyan ink having a pigment concentration of 2 mass% and a dispersant concentration of 2 mass%. The volume average particle diameter of the pigment was 80 nm.
Dispersion 1: 20 parts by mass Glycerin: 5 parts by mass Ethylene urea: 10 parts by mass Polyoxyethylene cetyl ether (EO: 30, HLB: 19.5): 0.5 parts by mass Ion-exchanged water: 64.5 parts by mass Next, magenta ink was produced by the following method.

(1) Preparation of dispersion liquid 100 g of polymer solution used in dispersion liquid 1, C.I. I. After mixing 100 g of Pigment Red 122 and 300 g of ion-exchanged water, the mixture was mechanically stirred for 0.5 hour. The mixture was then processed using a microfluidizer by passing it through the interaction chamber 5 times under a liquid pressure of about 10,000 psi (about 70 Mpa) to obtain a dispersion.

  Furthermore, the dispersion obtained above was centrifuged (12,000 rpm, 20 minutes) to remove the non-dispersion containing coarse particles, thereby preparing dispersion 2. The obtained dispersion liquid 2 had a pigment concentration of 10% by mass and a dispersant concentration of 5% by mass.

(2) Preparation of Ink The above-mentioned dispersion liquid 2 was used to prepare the ink. The following components were added to this to obtain a predetermined concentration, and these components were sufficiently mixed and stirred. Thereafter, this was pressure filtered through a micro filter (manufactured by Fujifilm) having a pore size of 2.5 μm to prepare a magenta ink having a pigment concentration of 4 mass% and a dispersant concentration of 2 mass%. Further, the volume average particle diameter of the pigment was 97 nm.
Dispersion 2: 40 parts by mass Glycerin: 7 parts by mass Ethylene urea: 3 parts by mass 2-Pyrrolidone: 3 parts by mass 1,2,6 hexanetriol: 4 parts by mass Polyoxyethylene cetyl ether (EO: 20, HLB: 17) ): 1 part by mass acetylene glycol EO adduct (trade name: acetylenol EH, manufactured by Kawaken Fine Chemicals Co., Ltd.): 0.5 part by mass ion-exchanged water: 41.5 parts by mass Next, a yellow ink was prepared by the following method. did.

(1) Preparation of dispersion First, an AB type block polymer having an acid value of 300 and a number average molecular weight of 4000 was prepared by a conventional method using benzyl acrylate and methacrylic acid as raw materials. Further, this AB type block polymer solution was neutralized with an aqueous potassium hydroxide solution and diluted with ion-exchanged water to prepare a homogeneous 50 mass% aqueous polymer solution.

  110 g of the above polymer solution, C.I. I. After mixing 100 g of Pigment Yellow 128 and 290 g of ion-exchanged water, the mixture was mechanically stirred for 0.5 hour. The mixture was then processed using a microfluidizer by passing it through the interaction chamber five times under a liquid pressure of about 10,000 psi (about 70 Mpa) to obtain a dispersion. Furthermore, the dispersion liquid obtained above was centrifuged (12,000 rpm, 20 minutes) to remove coarse particles, thereby preparing dispersion liquid 3. The obtained dispersion 3 had a pigment concentration of 10% by mass and a dispersant concentration of 6% by mass.

(2) Preparation of Ink The above dispersion liquid 3 was used for preparation of the ink. The following components were added to this to obtain a predetermined concentration, and these components were sufficiently mixed and stirred. Thereafter, this was subjected to pressure filtration with a micro filter (manufactured by Fujifilm) having a pore size of 2.5 μm to prepare a yellow ink having a pigment concentration of 5 mass% and a dispersant concentration of 3 mass%. Moreover, the volume average particle diameter of the pigment was 84 nm.
Dispersion 3: 50 parts by mass Glycerin: 8 parts by mass Ethylene urea: 6 parts by mass Ethylene glycol: 5 parts by mass Polyoxyethylene oleyl ether (EO: 10, HLB: 14.5): 1.2 parts by mass Acetylene glycol EO Adduct (Surfinol 440 (trade name); manufactured by Air Products): 0.5 parts by mass Ion-exchanged water: 29.3 parts by mass Next, a black ink was produced by the following method.

(1) Preparation of dispersion First, an ABC type block polymer having an acid value of 350 and a number average molecular weight of 5000 was prepared by a conventional method using benzyl methacrylate, methacrylic acid and ethoxyethylene glycol methacrylate as raw materials. Further, the ABC type block polymer solution was neutralized with an aqueous potassium hydroxide solution and then diluted with ion-exchanged water to prepare a homogeneous 50% by mass aqueous polymer solution.

  After mixing 60 g of the 50% by mass polymer solution, 100 g of carbon black, and 340 g of ion-exchanged water, the mixture was mechanically stirred for 0.5 hour. The mixture was then processed using a microfluidizer by passing it through the interaction chamber five times under a liquid pressure of about 10,000 psi (about 70 Mpa) to obtain a dispersion. Furthermore, the dispersion liquid obtained above was centrifuged (12,000 rpm, 20 minutes) to remove coarse particles to obtain dispersion liquid 4. The obtained dispersion 4 had a pigment concentration of 10% by mass and a dispersant concentration of 3.5% by mass.

(2) Preparation of Ink The above dispersion liquid 4 was used to prepare the ink, and the following components were added to this to obtain a predetermined concentration, and these components were sufficiently mixed and stirred. Thereafter, this was pressure filtered through a micro filter (manufactured by Fujifilm) having a pore size of 2.5 μm to prepare a black ink having a pigment concentration of 3 mass% and a dispersant concentration of 1.05 mass%. The volume average particle diameter of the pigment was 91 nm.
Dispersion 4:30 parts by mass Glycerin: 3 parts by mass Ethylene urea: 6 parts by mass Triethylene glycol: 6 parts by mass 2-Pyrrolidone: 1.5 parts by mass Polyoxyethylene bephenyl ether (EO: 20, HLB: 16. 5): 1.5 parts by mass of acetylene glycol EO adduct (acetylene EH (trade name); manufactured by Kawaken Fine Chemical Co., Ltd.): 0.5 parts by mass of ion-exchanged water: 51.5 parts by mass.

(Image creation)
Inkjet recording media prepared in Examples 1 to 4 and Comparative Examples 1 to 4 by setting each of the above pigment-based inks of cyan, magenta, yellow, and black ink to a Canon inkjet printer (trade name: BJ-F870) A record was made. Next, these recorded materials were evaluated as follows.

1) Evaluation of water resistance Using the above printer, when 4.5 pl droplets of each of the above inks are printed at a density of 1200 dpi × 1200 dpi in a vertical and horizontal direction of 100%, 50% of each color is overprinted to make a total amount of 200% ink. The amount was printed. After printing, the recorded matter was allowed to stand indoors for 24 hours and dried sufficiently, and then 1 drop of pure water was dropped with a dropper. Thereafter, Kimwipe S-200 (trade name) manufactured by Crecia Co., Ltd. was pressed from above onto the printed portion after 1 minute and left for 1 minute, and then the Kimwipe was gently released in the direction perpendicular to the paper surface. Then, it evaluated visually as follows.
○: No color change is observed in the printed part. And there is no ink adhesion to Kimwipe.
Δ: Color change is not recognized in the printed part. However, there is a slight ink adhesion to the Kimwipe.
X: There is a color change in the printed part. Ink adheres to the Kimwipe.

2) Evaluation of sweat resistance When the above printer prints 4.5 pl droplets of each ink at a density of 1200 dpi in length and width of 1200 dpi, 100% of each color is overprinted to give a total amount of 200%. The amount of ink was printed. After printing, the recorded matter was allowed to stand indoors for 24 hours and sufficiently dried, and then an alkaline artificial sweat solution defined in JIS-L-0848 (Testing method for fastness to dyeing with sweat) was dropped with a dropper. Thereafter, Kimwipe S-200 (trade name) manufactured by Crecia Co., Ltd. was pressed from above onto the printed portion after 1 minute and left for 1 minute, and then the Kimwipe was gently released in the direction perpendicular to the paper surface. Then, it evaluated visually as follows.
○: No color change is observed in the printed part. And there is no ink adhesion to Kimwipe.
Δ: Color change is not recognized in the printed part. However, there is a slight ink adhesion to the Kimwipe.
X: There is a color change in the printed part. Ink adheres to the Kimwipe.

3) Evaluation of ink absorbency Using two colors of cyan ink and magenta ink prepared as described above, 20% to 200% ink was dropped onto an ink jet recording medium to form an image. Here, cyan ink and magenta ink were always recorded at a ratio of 1: 1. For example, in a 100% image, recording was performed so that cyan ink was 50% and magenta ink was 50%. The beading evaluation image of the image obtained as described above was visually evaluated as follows.
○: No graininess due to beading up to 160% ink ejection amount x: Graininess due to beading confirmed below 160% ink ejection amount.

  The image printing evaluations 1) to 3) were performed on the ink jet recording media obtained in Examples 1 to 4 and Comparative Examples 1 to 4. In addition, for each inkjet recording medium, the surface of the ink receiving layer was set to TAPPI paper pulp test method No. 45-1: Measured by the glass electrode method. At this time, ion-exchanged water (purified water (trade name), manufactured by Kishida Chemical Co., Ltd .; pH 6.8) is used as the wetting liquid, and whether or not the minimum value is reached within 60 seconds after the dropping is determined. The pH value after 5 minutes when the value and the pH value were sufficiently stable was measured using a pH meter (manufactured by Toko Chemical Laboratory Co., Ltd .; TP90-i (trade name)). The results are shown in Table 1.

  From the results of Table 1, in all of the inkjet recording media of Examples 1 to 4, the surface pH reached a minimum value within 60 seconds after the start of measurement of the surface pH, and the minimum value was 3.0 or less. I understand. In addition, it can be seen that [(surface pH after 5 minutes) − (minimum value of surface pH)] is 1.0 or more in all the ink jet recording media prepared in each example. All of the ink jet recording media of Examples 1 to 4 have a water resistance, a sweat resistance, and an ink absorptivity of “◯”, indicating that good results were obtained.

  On the other hand, the inkjet recording media of Comparative Examples 1 to 4 do not have a minimum value or have a minimum value of 3.0 or more. Furthermore, in the inkjet recording medium of Comparative Example 2, [(surface pH after 5 minutes) − (minimum value of surface pH)] is less than 1.0. And among the ink jet recording media of Comparative Examples 1 to 4, there are no water resistance, sweat resistance and ink absorbency that are all “◯”, and these ink jet recording media have water resistance, sweat resistance and ink absorbability. It turns out that it is inferior to.

TAPPI paper pulp test method no. 45-1: It is a figure showing the measurement result of pH by a glass electrode method. It is a figure showing an example of the inkjet recording medium of this invention.

Explanation of symbols

1 Substrate 2 Ink receiving layer 3 Ink receiving layer surface

Claims (5)

An ink jet recording medium comprising: a base material; and an ink receiving layer provided on the base material, wherein the following conditions (1) to (3) are satisfied.
(1) TAPPI Paper Pulp Test Method No. 45-1: The surface pH of the ink receiving layer measured by the glass electrode method reaches a minimum value within 60 seconds after dropping the wetting liquid.
(2) The minimum value of the surface pH is 3.0 or less.
(3) The difference between the surface pH of the ink receiving layer and the minimum value of the surface pH 5 minutes after dropping the wetting liquid is 1.0 or more.   The inkjet recording medium according to claim 1, wherein the substrate is a film substrate.   The inkjet recording medium according to claim 1, wherein the substrate is resin-coated paper.   4. The ink jet recording medium according to claim 1, wherein the ink receiving layer contains vapor phase silica. 5. An inkjet recording method for performing recording on an inkjet recording medium according to any one of claims 1 to 4, using ink,
An ink jet recording method, wherein the ink is a water-soluble pigment ink having a pH of 7 or higher.

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