JP2007176966A - Ink set, inkjet recording method, inkjet recording apparatus, and ink tank for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink set which has no propensities to raise strike-through and is excellent in color development performance such as printing density and color reproducibility. <P>SOLUTION: Provided is an ink set comprising at least two different colors of pigmented ink and forming an image in such a way that the inks are sequentially ejected onto a recording medium in a manner that they are contiguous to each other, wherein at least one of the inks contains a resin, and the resin content in the first ejected ink is higher than the resin content in each of the other inks, (desirably, the resin content in each ink ejected second or later is equal to or lower than the resin content in the just precedingly ejected ink). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink set used for an image forming method using an ink jet method, an ink jet recording apparatus and an ink jet recording method using the ink set, and an ink tank for ink jet recording which stores the ink set.

  A so-called ink jet recording apparatus that discharges liquid or molten solid ink from a nozzle, slit, porous film or the like and records on paper, cloth, film, or the like has various advantages such as small size, low cost, and quietness. In recent years, not only black single-color printers that provide good print quality on so-called plain paper such as report paper and copy paper, but also many products that can perform full-color recording are commercially available.

  Dyes and pigments can be used as coloring materials for inks used in such ink jet recording, but pigments are used because they have excellent water resistance and weather resistance and can produce images with low image blur while having high image density. It is preferable. However, since the pigment is inherently hydrophobic, it is difficult to disperse in the ink. For this reason, in an ink using a pigment, a dispersant (resin) is often used to promote the dispersion of the pigment.

Pigment inks that achieve high speed and high image quality are required to have fast drying, high fixing properties, and high reliability, and particularly high image density and image quality without blurring.
On the other hand, for the purpose of improving bleeding and fixing, there has been proposed a method for reducing the ink permeability according to the printing order by adding a permeability imparting agent (see, for example, Patent Document 1).
JP-A-6-226999

  However, the above method is not sufficient from the viewpoint of improving the print density. Furthermore, as described above, an ink containing a resin (dispersant) has a high permeability to a paper medium, and in a system in which ink droplets such as secondary colors are superimposed and printed, the ink droplets printed later are printed on the paper medium. It has penetrated deeper into the back, and the occurrence of behind-the-scenes has become a problem.

  Accordingly, an object of the present invention is to prevent the occurrence of show-through and to provide an ink set excellent in color developability such as print density and color reproducibility, an ink jet recording method and an ink jet recording apparatus using the ink set, and the ink set Is to provide an ink tank for inkjet recording.

The above conventional problems are achieved by the present invention described below. That is, the present invention
<1> An ink set that has at least two colors of inks containing pigments, and that forms images by ejecting the two or more color inks so as to contact each other sequentially on a recording medium, The ink set is characterized in that at least one color or more of the ink contains a resin, and the resin content in the first ejected ink is equal to or higher than the resin content in each of the other inks.
<2> An ink set for forming an image by having at least three or more colors of ink containing a pigment, and ejecting the three or more color inks so as to sequentially contact each other on a recording medium, The ink set according to <1>, wherein the ink of at least one color contains a resin and the following condition (a) is satisfied by all the inks ejected after the second.
(A) The resin content is equal to or less than the resin content in the ink ejected immediately before. <3> The resin content in the first ejected ink is the resin content in the other inks. It is an ink set as described in said <1> or <2> characterized by having more.
<4> Any one of the above <1> to <3>, wherein a polymer containing at least one of an acrylic repeating structure and a styrene repeating structure in the main chain skeleton is used as the resin. The ink set according to any one of the above.
<5> The ink set according to any one of <1> to <4>, wherein a polymer having a weight average molecular weight of 7,000 or more is used as the resin.

  <6> An inkjet recording method in which an image is formed by using an ink set having at least two colors of inks containing pigments and ejecting the two or more colors of ink on a recording medium so that they are in contact with each other sequentially. An ink jet recording method, wherein the ink of at least one color contains a resin, and the content of the resin in the first ejected ink is equal to or higher than the content of the resin in each of the other inks. is there.

<7> An ink set having at least two droplet discharge means for discharging droplets and having at least two colors of ink containing a pigment is used, and the ink droplets of two or more colors are discharged from the droplet discharge means. Ink jet recording apparatus for forming an image by sequentially ejecting the ink on a recording medium so as to be in contact with each other, wherein the ink of at least one color contains a resin, and the first ink to be ejected contains the resin The ink jet recording apparatus is characterized in that the ratio is equal to or higher than the resin content in each of the other inks.
<8> The droplet discharge means is an ink jet recording head having a line head in which a plurality of nozzles are arranged in the width direction of the recording medium, and the ink jet recording head is arranged in the transport direction of the recording medium. The inkjet recording apparatus according to <7>, which is characterized in that

  <9> Removable from an ink jet recording apparatus provided with droplet discharge means, and having at least two colors of inks containing pigments, and the inks of the two or more colors are sequentially placed on a recording medium. An ink tank for ink-jet recording that stores an ink set that forms an image by being ejected in contact, and that supplies ink to the droplet ejection means in a state of being mounted on the ink-jet recording apparatus, wherein at least one color or more An ink tank for ink jet recording, wherein the ink contains a resin, and the resin content in the first ejected ink is equal to or higher than the resin content in each of the other inks.

  According to the present invention, an ink set which prevents occurrence of show-through and has excellent color development properties such as print density and color reproducibility, an ink jet recording method and an ink jet recording apparatus using the ink set, and the ink set are stored. An ink tank for ink jet recording can be provided.

The ink set of the present invention is used for forming an image in which a secondary color (superimposition of two colors), a tertiary color or higher colors are superimposed using at least two colors of ink containing a pigment. In the ink set, at least one color of the ink contains a resin, and the content of the resin in the first ejected ink is equal to that of the resin in the other inks (the ink ejected after the second). It is more than the content rate.
For example, if the ink set forms a black image of a tertiary color by superimposing cyan (C), magenta (M), and yellow (Y) inks in this order, the resin content in C is M and Y. It is an essential requirement that the content of each resin is equal to or greater than that.

Further, in the case of using three or more colors of ink, the resin content in each of the inks discharged after the second is equal to or less than the resin content in the ink discharged immediately before (that is, 2 The resin content of the second ejected ink is the same as the first, but less than that, and the third is the same as or less than the second, the nth is less than or equal to the n-1th) Is preferred.
The resin content in the first ejected ink is more preferably higher than the resin content in the other inks.

  In addition to the ink containing the pigment, the ink set may contain a resin or a liquid composition that aggregates the pigment (hereinafter referred to as “treatment liquid”). The ink may be ejected before the ink ejected in color, in the middle of the ink ejection such as between the first color and the second color, or may be ejected after all ink ejection. In addition, the treatment liquid may contain a resin as in the case of the ink.

  Hereinafter, the ink and treatment liquid used in the ink set of the present invention will be described in detail first.

(Ink-jet recording ink)
The ink in the present invention contains at least a pigment as a colorant, and optionally contains a resin, an additive, and the like, and is generally obtained by dispersing the above components in a solvent such as an organic solvent or water.

-Pigment-
The pigment used in the ink of the present invention is preferably a self-dispersible pigment or a pigment dispersed with a resin.

Self-dispersible pigment A self-dispersible pigment is a pigment that has a hydrophilic functional group on its surface, does not contain a so-called polymer dispersant, and can be dispersed in a solvent by itself.
In the present invention, whether or not a pigment is “self-dispersible” is confirmed by the following test.

  First, add the pigment to be measured in water, disperse it without a dispersant using an ultrasonic homogenizer, nanomizer, microfluidizer, ball mill, etc., and dilute with water so that the initial pigment concentration is about 5%. To prepare a dispersion. The initial pigment concentration and 100 g of the dispersion are put into a glass bottle having a diameter of 40 mm and allowed to stand for one day, and then the pigment concentration of the upper layer portion (10% dispersion from the liquid surface in the liquid depth direction) is measured. . When the ratio of the pigment concentration after standing for 1 day to the initial pigment concentration (hereinafter referred to as “self-dispersibility index”) is 98% or more, it was evaluated as “self-dispersibility”.

  At this time, the method for measuring the pigment concentration is not particularly limited, and any method such as a method of measuring the solid content by drying a sample or a method of obtaining the transmittance by diluting to an appropriate concentration may be used. If there is a method of obtaining accurately, it is of course possible to use that method.

  The hydrophilic functional group possessed by the pigment may be any nonionic, anionic or cationic hydrophilic functional group, and in particular, a carboxyl group, a hydroxyl group, a sulfonic acid group, a phosphoric acid group alone or 2 A combination of two or more species is preferable, and among them, a single carboxyl group or a combination of two or more types including a carboxyl group is more preferable.

  When it has a carboxyl group, a sulfonic acid group, or a phosphoric acid group, it can be used as it is in the free acid state, but a case where a part or all of them form a salt is advantageous and preferable in terms of dispersibility. At this time, examples of the substance that forms a salt include various basic substances, and alkali metals, ammonia, or organic onium compounds are preferably used alone or in combination of two or more. The number of hydrophilic functional groups on the pigment surface differs depending on the type of hydrophilic functional group and the type of substance that forms the salt when a salt is formed. 0.8-4 mmol / g is preferable.

  As a pigment into which a hydrophilic functional group is introduced, both inorganic and organic pigments can be used. As the black pigment, carbon black pigments such as furnace black, lamp black, acetylene black, channel black and the like are preferable. , Raven 1080ULTRA, Raven 1060 ULTRA, Raven 790 ULTRA, Raven 780 ULTRA, Raven 760 ULTRA (made by Columbia), Regal 400R, Regal 330R, Regal 660R, Mogu L Black Pearls L, Black Pearls 1300, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400 (manufactured by Cabot Corporation), Color B1, Color Black 18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex35, PrintexU, PrintexV, Printex140U, Printex140V, Special No. 6, Special Black 5, Special Black 4A, Special Black 4 (manufactured by Degussa), No. 6 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical Corporation) and the like can be used, but are not limited thereto. Further, magnetic fine particles such as magnetite and ferrite, titanium black and the like may be used as the black pigment.

  Examples of cyan pigments include C.I. I. Pigment Blue-1, C.I. I. Pigment Blue-2, C.I. I. Pigmet Blue-3, C.I. I. Pigmet Blue-15, C.I. I. Pigment Blue-15: 1, C.I. I. Pigment Blue-15: 3, C.I. I. Pigment Blue-15: 34, C.I. I. Pigment Blue-16, C.I. I. Pigment Blue-22, C.I. I. Pigment Blue-60 and the like, but are not limited thereto.

  Examples of magenta pigments include C.I. I. Pigment Red 5, C.I. I. Pigment Red 7, C.I. I. Pigment Red 12, C.I. I. Pigment Red 48, C.I. I. Pigment Red 48: 1, C.I. I. Pigment Red 57, C.I. I. Pigment Red 112, C.I. I. Pigment Red 122, C.I. I. Pigment Red 123, C.I. I. Pigment Red 146, C.I. I. Pigment Red 168, C.I. I. Pigment Red 184, C.I. I. Pigment Red 202 and the like, but are not limited thereto.

  Examples of yellow pigments include C.I. I. Pigment Yellow-1, C.I. I. Pigment Yellow-2, C.I. I. Pigment Yellow-3, C.I. I. Pigment Yellow-12, C.I. I. Pigment Yellow-13, C.I. I. Pigment Yellow-14, C.I. I. Pigment Yellow-16, C.I. I. Pigment Yellow-17, C.I. I. Pigment Yellow-73, C.I. I. Pigment Yellow-74, C.I. I. Pigment Yellow-75, C.I. I. Pigment Yellow-83, C.I. I. Pigment Yellow-93, C.I. I. Pigment Yellow-95, C.I. I. Pigment Yellow-97, C.I. I. Pigment Yellow-98, C.I. I. Pigment Yellow-114, C.I. I. Pigment Yellow-128, C.I. I. Pigment Yellow-129, C.I. I. Pigment Yellow-151, C.I. I. Pigment Yellow-154 and the like, but are not limited thereto.

In addition, for the present invention, a newly synthesized pigment may be used, or two or more pigments may be mixed and used.
In addition to the three primary color pigments of black and cyan, magenta, and yellow, specific color pigments such as red, green, blue, brown, and white, metallic luster pigments such as gold and silver, colorless extender pigments, and plastic pigments are used. May be. A particularly preferable pigment is carbon black.

  For these pigments, a known method or any of the newly invented methods can be used as a method for introducing a hydrophilic functional group on the surface of the pigment (surface modification treatment). For example, oxidation treatment with oxidizing agents (eg nitric acid, permanganate, dichromate, hypochlorite, ammonium persulfate, hydrogen peroxide, ozone, etc.), treatment with coupling agents such as silane compounds, polymer grafting In addition to known methods such as chemical treatment and plasma treatment, newly developed methods can also be used, and these methods may be combined.

  It is desirable to purify the obtained pigment with the hydrophilic functional group introduced by removing impurities such as the remaining oxidant, other inorganic impurities, and organic impurities. In particular, it is desirable that calcium, iron, and silicon in the ink be 10 ppm or less, preferably 5 ppm or less, respectively. In the present invention, the content of these inorganic impurities was measured by a high frequency inductively coupled plasma emission spectrometry. These impurities can be removed, for example, by washing with water, a reverse osmosis membrane, an ultrafiltration membrane, an ion exchange method or the like, or an adsorption method using activated carbon, zeolite or the like, alone or in combination.

  As the self-dispersible pigment into which these hydrophilic functional groups have been introduced, commercially available self-dispersible hydrophilic treated pigments can be used in addition to those newly prepared for the present invention. As a commercially available self-dispersible hydrophilic treatment pigment, for example, MICROJET BLACK CW-1 (manufactured by Orient Chemical Industry Co., Ltd.), MICROJET BLACK CW-2 (manufactured by Orient Chemical Industry Co., Ltd.), CAB-O-JET200 ( Cabot Corporation), CAB-O-JET300 (Cabot Corporation), and the like. All of these commercially available self-dispersible hydrophilic pigments have a self-dispersibility index of 100%.

  The self-dispersible pigment is preferably contained in the range of 2 to 15% by mass with respect to the total mass of the ink, more preferably 3 to 10% by mass, and particularly preferably 4 to 8% by mass. When the pigment content exceeds 15% by mass, the possibility of nozzle clogging increases. On the other hand, if it is less than 2% by mass, the print density may be lowered.

-Pigment dispersed with resin The pigment used in the present invention is preferably also dispersed with resin as described above.
The pigment used for this is the same as the pigment before the introduction of the hydrophilic functional group listed in the description of the “self-dispersible pigment”.

  In the case of using a pigment dispersed by a resin, the content of the pigment in the ink is preferably in the range of 2 to 15% by mass for the same reason as in the case of the “self-dispersible resin”, and 3 to 10% by mass. Is more preferable, and 4 to 8% by mass is particularly preferable.

-Resin-
In the ink set of the present invention, a resin is contained in at least one of the two or more inks. Whether the ink is an ink using the self-dispersible pigment or an ink using a pigment dispersed with the resin, the following resins are added, In the case of “ink using a pigment”, it is preferable to add a resin as a pigment dispersant.

  As the resin added to the ink, a nonionic compound, an anionic compound, a cationic compound, an amphoteric compound and the like can be used, for example, a copolymer of a monomer having an α, β-ethylenically unsaturated group. Can be used.

  Specifically, as a monomer having an α, β-ethylenically unsaturated group, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester, fumaric acid, fumaric acid mono Ester, vinyl sulfonic acid, styrene sulfonic acid, sulfonated vinyl naphthalene, vinyl alcohol, acrylamide, methacryloxyethyl phosphate, bismethacryloxyethyl phosphate, methacryloxyethyl phenyl acid phosphate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, styrene, α -Styrene derivatives such as methylstyrene and vinyltoluene, vinylcyclohexane, vinylnaphthalene, vinylnaphthalene derivatives, alkyl acrylate, acrylic acid Glycol ester, methacrylic acid alkyl esters, methacrylic acid phenyl ester, methacrylic acid cycloalkyl ester, crotonic acid alkyl ester, itaconic acid dialkyl esters, maleic acid dialkyl ester and the like.

A copolymer obtained by copolymerizing a single monomer or a plurality of monomers having an α, β-ethylenically unsaturated group is used as the resin (particularly in the case of an ink using a pigment dispersed by a resin, a pigment dispersant). As used). Specifically, polyvinyl alcohol, polyvinyl pyrrolidone, styrene-styrene sulfonic acid copolymer, styrene-maleic acid copolymer, styrene-methacrylic acid copolymer, styrene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer. Polymer, vinyl naphthalene-methacrylic acid copolymer, vinyl naphthalene-acrylic acid copolymer, alkyl acrylate ester-acrylic acid copolymer, alkyl methacrylate-methacrylic acid, styrene-alkyl methacrylate-methacrylic acid copolymer Examples thereof include a polymer, a styrene-alkyl acrylate ester-acrylic acid copolymer, a styrene-methacrylic acid phenyl ester-methacrylic acid copolymer, and a styrene-methacrylic acid cyclohexyl ester-methacrylic acid copolymer.

  The resins listed above added to the ink preferably have a weight average molecular weight of 7,000 or more, and the upper limit thereof is preferably 100,000 or less. When the molecular weight of the polymer substance is less than 7,000, the foaming property of the ink is increased, and there is a concern that ejection failure may occur due to the generation of bubbles in the ink flow path. On the other hand, even when the molecular weight exceeds 100,000, the ink viscosity There is a concern that a rise in the discharge rate is remarkable and ejection failure occurs. In addition, the more preferable weight average molecular weight of resin exists in the range of 10000-80000.

The weight average molecular weight of the resin can be measured by the following method.
For example, relative molecular weight can be obtained by using polystyrene as a standard sample in gel permeation chromatography (GPC) and dissolving and measuring the resin in a suitable solvent (THF, NMP, toluene, etc.).

  The content of the resin (dispersant) in the ink (including both the ink using the self-dispersible pigment and the ink using the pigment dispersed by the resin) is 0.1 to 10 It is preferable to be within the range of mass%. When the addition amount exceeds 10% by mass, the ink viscosity increases, and the ink ejection characteristics may become unstable. On the other hand, when the addition amount is less than 0.1% by mass, the dispersion stability of the pigment may be lowered. Furthermore, the range of 0.15-8 mass% is more preferable, and the range of 0.2-5 mass% is especially preferable.

  In addition, since the ink constituting the ink set of the present invention must contain at least one color of the resin, the ink containing the resin is “dispersed by the resin” from the viewpoint of storage stability. It is preferable to use “pigment”.

  Furthermore, in the case of an ink jet recording apparatus using black ink and color ink, the color ink may be one using a plurality of colors even if one color is selected from cyan, magenta, yellow ink and the like. It doesn't matter.

-Quantification of resin content in ink-
In the present invention, the aforementioned “resin contained in ink” refers to a component quantified by the following method. That is, the resin content is quantified by the following method.
The ink composition is weighed and the mass (A) is measured. This is heated to dryness, and the solid content (B) in the ink composition is weighed. The solid is weighed and the mass (C) of the solid content other than the pigment thermally decomposed is measured by thermogravimetric analysis. With (C) as the resin component, the amount of resin in (B) is known. Furthermore, the resin content in the ink can be determined using the ratio of (A) and (B).

-Other ingredients-
Further, the ink in the present invention may contain an antioxidant, an antifungal agent, a conductive agent, an ultraviolet absorber, a chelating agent, and the like as necessary. As these additives, all conventionally known additives can be used. For example, as a chelating agent, ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA), ethylenediamine-di (o-hydroxyphenylacetic acid) (EDDDHA). ), Nitrilotriacetic acid (NTA), dihydroxyethylglycine (DHEG), trans-1,2-cyclohexanediaminetetraacetic acid (CyDTA), diethylenetriamine-N, N, N ′, N ″, N ″ -pentaacetic acid (DTPA) Glycol ether diamine-N, N, N ′, N′-tetraacetic acid (GEDTA) and the like.

  Further, a surfactant can be added in order to adjust the surface tension of the ink in the present invention. As the surfactant, nonionic and anionic surfactants that do not easily affect the dispersion state of the pigment are preferable. Nonionic surfactants include, for example, polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan Fatty acid esters, fatty acid alkylolamides, acetylene alcohol ethylene oxide adducts, polyethylene glycol polypropylene glycol block copolymers, glycerin ester polyoxyethylene ethers, sorbitol ester polyoxyethylene ethers, and the like can be used.

  Examples of anionic surfactants include alkylbenzene sulfonates, alkylphenyl sulfonates, alkylnaphthalene sulfonates, higher fatty acid salts, sulfate esters of higher fatty acid esters, sulfonates, and higher alkyl sulfosuccinates. Can be used.

  Further, as the amphoteric surfactant, betaine, sulfobetaine, sulfate betaine, imidazoline and the like can be used. In addition, silicone surfactants such as polysiloxane polyoxyethylene adducts, fluorine surfactants such as oxyethylene perfluoroalkyl ether, biosurfactants such as splicrisporic acid, rhamnolipid, and lysolecithin can also be used.

  When the surfactant is included, it is preferable to select at least one from a nonionic surfactant and an anionic surfactant.

  In addition, as a method of adjusting the surface tension of the ink, there is a method of containing a polyhydric alcohol, a monohydric alcohol, or the like in addition to the inclusion of the surfactant. The total content of the compounds in the ink is preferably in the range of 0.01 to 3.0% by mass, more preferably in the range of 0.03 to 2.0% by mass, and 0.05 More preferably, it is in the range of -1.5% by mass. In particular, when the surfactant is used alone, the content is preferably in the range of 0.3 to 1.5% by mass.

  The surface tension of the ink adjusted by the above method is preferably adjusted in the range of 20 to 37 mN / m, more preferably in the range of 25 to 37 mN / m. When the surface tension is less than 20 mN / m, the ink permeability to the recording paper is too fast, the show-through density increases, and the suitability for double-sided printing may deteriorate. On the other hand, if it is larger than 37 mN / m, the ink permeability to the recording paper becomes slow, so that the drying property is deteriorated, and it becomes impossible to cope with high-speed printing, and the productivity may be lowered.

  In addition to methyl cellulose, ethyl cellulose and derivatives thereof, glycerins and polyglycerin and polyethylene oxide and polypropylene oxide adducts thereof, and addition of polysaccharides and derivatives thereof as viscosity modifiers in the ink of the present invention is also a preferred embodiment. . Examples of the viscosity modifier include glucose, fructose, mannitol, D-sorbitol, dextran, xanthan gum, curdlan, cycloamylose, maltitol and derivatives thereof.

  The viscosity of the ink in the invention is preferably in the range of 1 to 8 mPa · s (cP) at 20 ° C., more preferably in the range of 2 to 5 mPa · s (cP). If it is greater than 8 mPa · s (cP), the ejection tends to become unstable, which is not desirable. On the other hand, the case of less than 1 mPa · s (cP) is not desirable because the stability of ejection may not be obtained.

  The ink of the present invention can be adjusted for pH as necessary. Examples of components for adjusting pH include potassium hydroxide, sodium hydroxide, lithium hydroxide, ammonium hydroxide, triethanolamine, diethanolamine, ethanolamine, 2-amino-2-methyl-1-propanol, ammonia, and phosphoric acid. Ammonium, potassium phosphate, sodium phosphate, lithium phosphate, sodium sulfate, acetate, lactate, benzoate, acetic acid, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, propionic acid, P-toluenesulfonic acid, etc. . Alternatively, a general pH buffer can be used.

  Although not particularly limited, the pH range of the ink in the present invention is preferably about 3 to 11, more preferably about 4.5 to 9.5. In addition, in an ink having an anionic free radical on the pigment surface, the pH is preferably about 6 to 11, more preferably about 6 to 9.5, and still more preferably about 7.5 to 9.0. On the other hand, in an ink having a cationic free radical on the pigment surface, the pH is preferably about 4.5 to 8.0, more preferably about 4.5 to 7.0.

-Organic solvent-
As described above, the ink in the present invention is generally obtained by dispersing the above main components in a solvent such as an organic solvent or water.
In the present invention, a water-soluble organic solvent is particularly suitable, and the following specific examples can be given.
Specific examples of the water-soluble organic solvent include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, triethylene glycol monobutyl ether. 1,2-hexanediol, etc. Among these, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether are more preferable.

  Examples of other water-soluble organic solvents that can be used in combination with the water-soluble organic solvents mentioned in the preferred specific examples are ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, triethylene glycol, and 1,5-pentanediol. Polyhydric alcohols such as 1,2,6-hexanetriol and glycerin; Nitrogen-containing solvents such as pyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpyrrolidone and triethanolamine; ethanol, isopropyl alcohol, butyl alcohol and benzyl alcohol Alcohols such as thiodiethanol, thiodiglycerol, sulfolane, dimethyl sulfoxide, and the like; and propylene carbonate and ethylene carbonate.

In the present invention, the above water-soluble organic solvent may be used alone or in combination of two or more.
The content of the water-soluble organic solvent is preferably 2 to 30% by mass, more preferably 4 to 20% by mass, and particularly preferably 4 to 10% by mass in the total mass of the ink.

(Ink preparation method)
An example of the ink preparation method is shown below.
When the ink used in the present invention is an ink using a pigment dispersed with the resin, for example, a predetermined amount of the pigment is added to an aqueous solution containing a predetermined amount of the resin (dispersant), and After stirring, disperse using a disperser, remove coarse particles by centrifugation or the like, add the predetermined water-soluble organic solvent, the additive, etc., mix by stirring, and then perform filtration. Can do. At this time, it is also possible to use a method in which a concentrated dispersion of pigment is prepared in advance and diluted when preparing ink. Moreover, you may provide the grinding | pulverization process of a pigment before a dispersion | distribution process. Alternatively, after mixing a predetermined water-soluble organic solvent, water, and a dispersant, a pigment may be added and dispersed using a disperser.

  A commercially available dispersing machine can be used. For example, colloid mill, flow jet mill, slasher mill, high speed disperser, ball mill, attritor, sand mill, sand grinder, ultra fine mill, Eiger motor mill, dyno mill, pearl mill, agitator mill, cobol mill, 3 rolls, 2 rolls Examples thereof include a roll, an extruder, a kneader, a microfluidizer, a laboratory homogenizer, and an ultrasonic homogenizer. These may be used alone or in combination of two or more. In order to prevent mixing of inorganic impurities, it is preferable to use a dispersion method that does not use a dispersion medium. In that case, it is preferable to use a microfluidizer, an ultrasonic homogenizer, or the like.

  On the other hand, in the case of an ink using the self-dispersible pigment as the pigment, for example, the surface modification treatment is performed on the pigment, the obtained pigment is added to water, and the mixture is sufficiently stirred. It can be obtained by dispersing with the same disperser as described above, removing coarse particles by centrifugation or the like, then adding a predetermined resin, solvent, additive, etc., stirring, mixing, and filtering.

-Treatment liquid-
The liquid composition (treatment liquid) for aggregating the resin or pigment basically does not contain a coloring material component such as a pigment, and a component (aggregating agent) for aggregating the pigment or resin in the ink, water, etc. Those containing at least a solvent are used, and other components may be contained as necessary.

As the aggregating agent, an inorganic electrolyte, an organic amine compound, an organic acid, or the like is used.
As the inorganic electrolyte, a pH adjuster or a polyvalent metal salt is used. Specific examples of the pH adjuster include 2-pyrrolidone-5-carboxylic acid, 4-methyl-4-pentanolide-3-carboxylic acid, furan carboxylic acid, 2-benzofuran carboxylic acid, and 5-methyl-2-furan carboxylic acid. Acid, 2,5-dimethyl-3-furancarboxylic acid, 2,5-furandicarboxylic acid, 4-butanolide-3-carboxylic acid, 3-hydroxy-4-pyrone-2,6-dicarboxylic acid, 2-pyrone- 6-carboxylic acid, 4-pyrone-2-carboxylic acid, 5-hydroxy-4-pyrone-5-carboxylic acid, 4-pyrone-2,6-dicarboxylic acid, 3-hydroxy-4-pyrone-2,6- Dicarboxylic acid, thiophenecarboxylic acid, 2-pyrrolecarboxylic acid, 2,3-dimethylpyrrole-4-carboxylic acid, 2,4,5-trimethylpyrrole-3-propionic acid, Roxy-2-indolecarboxylic acid, 2,5-dioxo-4-methyl-3-pyrroline-3-propionic acid, 2-pyrrolidinecarboxylic acid, 4-hydroxyproline, 1-methylpyrrolidine-2-carboxylic acid, 5- Carboxy-1-methylpyrrolidine-2-acetic acid, 2-pyridinecarboxylic acid, 3-pyridinecarboxylic acid, 4-pyridinecarboxylic acid, pyridinedicarboxylic acid, pyridinetricarboxylic acid, pyridinepentacarboxylic acid, 1,2,5,6- Tetrahydro-1-methylnicotinic acid, 2-quinolinecarboxylic acid, 4-quinolinecarboxylic acid, 2-phenyl-4-quinolinecarboxylic acid, 4-hydroxy-2-quinolinecarboxylic acid, 6-methoxy-4-quinolinecarboxylic acid, Thiophenecarboxylic acid, potassium hydrogen phthalate, potassium dihydrogen phosphate, boric acid Sodium citrate, potassium citrate, potassium dihydrogen citrate, sodium tetraboron, tartaric acid, lactic acid, ammonium chloride, sodium hydroxide, potassium hydroxide, hydrochloric acid, coumaric acid, succinic acid, derivatives of these compounds, or these Examples of the compound include salts.
Preferably, pyrrolidone carboxylic acid, pyrone carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, nicotinic acid, potassium dihydrogen citrate, succinic acid, tartaric acid, lactic acid, potassium hydrogen phthalate Or a derivative of these compounds or a salt thereof. More preferably, it is pyrrolidone carboxylic acid, pyrone carboxylic acid, furan carboxylic acid, coumaric acid, or a compound derivative thereof, or a salt thereof.

On the other hand, as the polyvalent metal salt, alkali metal ions such as lithium ion, sodium ion, potassium ion, and aluminum ion, barium ion, calcium ion, copper ion, iron ion, magnesium ion, manganese ion, nickel ion, tin ion, Polyvalent metal ions such as titanium ion and zinc ion, hydrochloric acid, odorous acid, hydroiodic acid, sulfuric acid, nitric acid, phosphoric acid, thiocyanic acid, and acetic acid, oxalic acid, lactic acid, fumaric acid, citric acid, salicylic acid, benzoic Examples thereof include organic carboxylic acids such as acids and salts of organic sulfonic acids.
Specific examples include lithium chloride, sodium chloride, potassium chloride, sodium bromide, potassium bromide, sodium iodide, potassium iodide, sodium sulfate, potassium nitrate, sodium acetate, potassium oxalate, sodium citrate, potassium benzoate and the like. Alkali metal salts and aluminum chloride, aluminum bromide, aluminum sulfate, aluminum nitrate, sodium aluminum sulfate, potassium aluminum sulfate, aluminum acetate, barium chloride, barium bromide, barium iodide, barium oxide, barium nitrate, thiocyanate Barium acid, calcium chloride, calcium bromide, calcium iodide, calcium nitrite, calcium nitrate, calcium dihydrogen phosphate, calcium thiocyanate, calcium benzoate, calcium acetate, salicyl Calcium, calcium tartrate, calcium lactate, calcium fumarate, calcium citrate, copper chloride, copper bromide, copper sulfate, copper nitrate, copper acetate, iron chloride, iron bromide, iron iodide, iron sulfate, iron nitrate, oxalic acid Iron, iron lactate, iron fumarate, iron citrate, magnesium chloride, magnesium bromide, magnesium iodide, magnesium sulfate, magnesium nitrate, magnesium acetate, magnesium lactate, manganese chloride, manganese sulfate, manganese nitrate, manganese dihydrogen phosphate , Manganese acetate, manganese salicylate, manganese benzoate, manganese lactate, nickel chloride, nickel bromide, nickel sulfate, nickel nitrate, nickel acetate, tin sulfate, titanium chloride, zinc chloride, zinc bromide, zinc sulfate, zinc nitrate, thiocyanate Examples thereof include salts of polyvalent metals such as zinc acid and zinc acetate.

  Examples of the organic amine compound include primary, secondary, tertiary and quaternary amines and salts thereof. Specific examples include tetraalkylammonium salts, alkylamine salts, benzalkonium salts, alkylpyridium salts, imidazolium salts, polyamines, etc., for example, isopropylamine, isobutylamine, t-butylamine, 2-ethylhexylamine. , Nonylamine, dipropylamine, diethylamine, trimethylamine, triethylamine, dimethylpropylamine, ethylenediamine, propylenediamine, hexamethylenediamine, diethylenetriamine, tetraethylenepentamine, diethanolamine, diethylethanolamine, triethanolamine, tetramethylammonium chloride, tetraethylammonium Bromide, dihydroxyethyl stearylamine, 2-heptadecenyl-hydroxyethyl Imidazoline, lauryldimethylbenzylammonium chloride, cetylpyridinium chloride, stearamide methylpyridium chloride, diallyldimethylammonium chloride polymer, diallylamine polymer, monoallylamine polymer, and onium salts such as sulfonium salts and phosphonium salts of these compounds, Or phosphoric acid ester etc. are mentioned.

  Examples of the organic acid include the styrene-styrene sulfonic acid copolymer, styrene-maleic acid copolymer, styrene-methacrylic acid copolymer, styrene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer, vinyl naphthalene. -Methacrylic acid copolymer, vinyl naphthalene-acrylic acid copolymer, alkyl acrylate ester-acrylic acid copolymer, methacrylic acid alkyl ester-methacrylic acid copolymer, styrene-methacrylic acid alkyl ester-methacrylic acid copolymer Styrene-acrylic acid alkyl ester-acrylic acid copolymer, styrene-methacrylic acid phenyl ester-methacrylic acid copolymer, styrene-methacrylic acid cyclohexyl ester-methacrylic acid copolymer, and the like.

In the present invention, the flocculant may be used alone or in combination of two or more. Moreover, it is preferable that the addition amount of the flocculant in a process liquid is 0.01 mass% or more and 30 mass% or less. More preferably, it is 0.1 mass% or more and 15 mass% or less, More preferably, it is 0.25 mass% or more and 10 mass% or less. When the addition amount of the flocculant in the processing liquid is less than 0.01% by mass, the resin and the pigment are not sufficiently aggregated when the ink and the processing liquid are contacted and mixed on the recording medium. In some cases, the bleeding between colors deteriorates. On the other hand, when the addition amount exceeds 30% by mass, the ejection characteristics may be deteriorated and the liquid may not be ejected normally.
On the other hand, the same solvent as that used in the ink can be used as the solvent, and the same components as those used in the ink can be used as appropriate so that desired physical properties and characteristics such as viscosity and surface tension can be obtained. it can.

  When the treatment liquid contains the same resin as that used for the ink, the content is preferably in the range of 0.1 to 10% by mass. When the addition amount exceeds 10% by mass, there is a concern that the liquid viscosity increases and it becomes difficult to eject the liquid normally. On the other hand, even when the addition amount is less than 0.1% by mass, there is a concern that the liquid viscosity decreases and it becomes difficult to normally discharge the liquid. Furthermore, the range of 0.2-8 mass% is more preferable, and the range of 0.2-5 mass% is especially preferable.

-Various physical properties of ink and treatment liquid-
Next, preferred physical properties of the ink and treatment liquid used in the ink set of the present invention will be described.
When the ink set of the present invention includes an ink and a treatment liquid, and the ink is alkaline and the treatment liquid is an acidic combination, the pH of the ink is 7.5 to 10.5, and the pH of the treatment liquid Is preferably 2.5 or more and 7.0 or less. On the other hand, when the ink is acidic and the treatment liquid is an alkaline combination, the pH of the ink is preferably 2.5 or more and 7.0 or less, and the pH of the treatment liquid is preferably 7.5 or more and 10.5 or less. . More preferably, the pH of the alkaline liquid is preferably 7.5 or more and 10.0 or less, and more preferably 8.0 or more and 9.5 or less. On the other hand, as an acidic liquid, a preferable pH range is 3.0 or more and 7.0 or less, and more preferably 3.5 or more and 6.0 or less.

When the pH of the acidic liquid is less than 2.5, the ink flow path constituent portion of the recording head may be dissolved to cause the recording head to fail. On the other hand, if the pH of the acidic liquid exceeds 7.0, the resin and the pigment are not sufficiently agglomerated when the ink and the processing liquid are contacted and mixed on the recording medium, and the image density, bleeding, and color space are reduced. If the pH of the alkaline liquid is less than 7.5, the long-term jetting property of the liquid may decrease. If the pH exceeds 10.5, the ink flow path configuration of the recording head may be deteriorated. The part may be melted and the recording head may be broken.

  The surface tension of the ink is preferably 20 mN / m or more and 60 mN / m or less. More preferably, it is 20 mN / m or more and 45 mN / m or less, More preferably, it is 25 mN / m or more and 35 mN / m or less. If the surface tension is less than 20 mN / m, liquid may overflow on the nozzle surface of the recording head, and printing may not be performed normally. On the other hand, if it exceeds 60 mN / m, the permeability may be slow and the drying time may be slow.

  The viscosity of the ink is preferably 1.2 mPa · s or more and 8.0 mPa · s or less, more preferably 1.5 mPa · s or more and less than 6.0 mPa · s, and still more preferably 1.8 mPa · s or more. Less than 4.5 mPa · s. When the viscosity of the ink is greater than 8.0 mPa · s, the ejection performance may be degraded, and when it is less than 1.2 mPa · s, the long-term ejection performance may be degraded.

  On the other hand, the surface tension of the treatment liquid is preferably 20 mN / m or more and 45 mN / m or less. More preferably, it is 20 mN or more and 39 mN / m or less, More preferably, it is 25 mN / m or more and 35 mN / m or less. If the surface tension is less than 20 mN / m, the liquid may overflow on the nozzle surface and printing may not be performed normally. On the other hand, if it exceeds 45 mN / m, the permeability may be slow and the drying time may be slow.

  The viscosity of the treatment liquid is preferably 1.2 mPa · s or more and 8.0 mPa · s or less, more preferably 1.5 mPa · s or more and less than 6.0 mPa · s, and further preferably 1.8 mPa · s or more and 4 or more. Less than 5 mPa · s. When the viscosity of the treatment liquid is greater than 8.0 mPa · s, the dischargeability may be reduced, and when it is less than 1.2 mPa · s, the long-term jetability may be deteriorated.

(Inkjet recording method and inkjet recording apparatus)
Next, an ink jet recording method and an ink jet recording apparatus using the ink set of the present invention will be described.
The ink jet recording method using the ink set of the present invention forms an image by sequentially ejecting inks of two or more colors onto the surface of a recording medium such as paper so as to contact each other. Is used.

The ink jet recording apparatus of the present invention is a recording apparatus that includes at least a liquid droplet ejecting unit that ejects liquid droplets, and to which an ink jet recording method using the ink set is applied.
That is, the ink jet recording apparatus of the present invention forms an image by sequentially ejecting ink droplets from the droplet ejecting means so as to contact each other on the surface of the recording medium. A set is used.

  In addition, as the droplet discharge means, a so-called piezo-type droplet discharge means that applies pressure to the droplet to discharge the droplet, or a so-called thermal-type liquid that discharges the droplet by applying heat to the droplet. Any method such as droplet discharge means may be used.

The ink jet recording apparatus of the present invention is particularly preferably an ink jet recording apparatus used in an office or home, but may be used for industrial purposes. In the following description, it is assumed that the ink jet recording apparatus of the present invention is an ink jet recording apparatus, and the droplet discharge means is a recording head provided in the ink jet recording apparatus.
The ink jet recording apparatus of the present invention can supply ink or a treatment liquid as necessary to the recording head, and can be detached from the ink jet recording apparatus main body (hereinafter referred to as “ink tank”). May be provided). In this case, the ink set of the present invention may be stored in the ink tank.

The ink jet recording apparatus of the present invention can use a normal ink jet recording apparatus of a two-liquid (or more) printing method that can use the ink set of the present invention. Equipped with a heater or the like for controlling the temperature, an intermediate transfer mechanism, and a mechanism for discharging (printing) ink and processing liquid to the intermediate and then transferring it to a recording medium such as paper. There may be.
The ink tank can be attached to and detached from an ink jet recording apparatus equipped with a recording head, and can be used as long as it has a configuration capable of supplying ink and processing liquid to the recording head in a state of being attached to the ink jet recording apparatus. A known ink tank can be used. Here, the ink set of the present invention is stored in the ink tank.

In the ink jet recording method (apparatus) of the present invention, the ratio of the amount of ink applied per unit area applied to the recording medium surface and the amount of processing liquid applied (ink application amount: processing liquid application amount) is a mass ratio. And preferably within a range of 1.2: 1 to 20: 1.
The smaller the ratio of the applied liquid to the ink applied amount from the ratio of 20: 1, the less likely the problem of curl and cockle occurs. However, when the ratio is too small, the effect of the processed liquid becomes insufficient, and the image density and Image resolution may be reduced. On the other hand, if the ratio is out of 1.2: 1 and the amount of treatment liquid applied is large, the image density and the image resolution are good, but curl and cockle are likely to occur. A more preferable range of the ratio is 2: 1 to 16: 1, more preferably 3: 1 to 10: 1.

In the ink jet recording method (apparatus) of the present invention, the liquid mass per drop is preferably 25 ng or less for both the ink and the treatment liquid. More preferably, they are 0.5 ng or more and 20 ng or less, More preferably, they are 2 ng or more and 8 ng or less. If the liquid mass per drop exceeds 25 ng, bleeding may worsen. This is because the contact angles of the ink and the treatment liquid with respect to the recording medium change depending on the drop amount, and it is considered that the drop tends to spread in the paper surface direction as the drop amount increases.
However, in an ink jet apparatus capable of ejecting a plurality of drops from a single nozzle, the drop amount refers to the minimum drop amount that can be printed.

Further, the ink and the treatment liquid are applied on the recording medium so as to be in contact with each other. However, as long as they are in contact with each other, they may be applied so as to be adjacent to each other or to be covered. .
Further, in the present invention, inks of two or more colors are applied on the recording medium so as to contact each other. However, as long as they are in contact, they may be applied so as to be adjacent to each other or to be covered. ,either will do. In addition, from the viewpoint of obtaining the effect of the present invention more remarkably, it is preferable that the coating is provided so as to cover it.

Further, the order of application of the ink and the treatment liquid to the recording medium is not particularly limited, either of which may be applied first or substantially simultaneously, but the ink is applied after the treatment liquid is applied. It is preferable to do. This is because the resin and pigment in the ink can be effectively aggregated by applying the treatment liquid first. As long as the treatment liquid is applied, the ink may be applied at any time. Preferably, it is 1 second or less, more preferably 0.5 seconds or less after the treatment liquid is applied.
Further, as described above, the application of two or more colors of ink is preferably performed in descending order of the resin content, and the interval is preferably 0.5 seconds or less, and 0.3 seconds or less. Is more preferable.

  In the ink jet recording apparatus of the present invention, it is preferable that replenishment (supply) of the ink and the processing liquid to the recording head is performed from an ink tank (including the processing liquid tank) filled with each liquid of the ink and the processing liquid. The ink tank is preferably of a cartridge type that can be attached to and detached from the apparatus main body. By replacing the cartridge type ink tank, ink and processing liquid can be easily replenished.

  Hereinafter, preferred embodiments of the ink jet recording apparatus of the present invention will be described in detail with reference to the drawings. In the drawings, members having substantially the same functions are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a perspective view showing an external configuration of a preferred embodiment of an ink jet recording apparatus of the present invention. FIG. 2 is a perspective view showing an internal basic configuration of the ink jet recording apparatus (hereinafter referred to as an image forming apparatus) of FIG.

  The image forming apparatus 100 of this embodiment has a configuration that operates based on the above-described inkjet recording method of the present invention to form an image. That is, as shown in FIGS. 1 and 2, an image forming apparatus 100 mainly includes an external cover 6, a tray 7 on which a predetermined amount of recording medium 1 such as plain paper can be placed, and the recording medium 1 as an image forming apparatus. An image forming unit 8 (image forming unit) for forming an image by ejecting ink and processing liquid onto the surface of the recording medium 1; The main ink tank 4 is configured to supply ink and processing liquid to the sub ink tanks 5 of the forming unit 8.

  The conveyance roller 2 is a paper feed mechanism constituted by a pair of rollers rotatably disposed in the image forming apparatus 100, sandwiches the recording medium 1 set on the tray 7, and has a predetermined amount of recording medium 1. Are conveyed one by one into the image forming apparatus 100 at a predetermined timing.

  The image forming unit 8 forms an image with ink on the surface of the recording medium 1. The image forming unit 8 mainly includes a recording head 3, a sub ink tank 5, a power supply signal cable 9, a carriage 10, a guide rod 11, a timing belt 12, a driving pulley 13, and a maintenance unit 14. ing.

  The sub ink tank 5 has sub ink tanks 51, 52, 53, 54, and 55 in which different colors of ink and processing liquid are stored so as to be ejected from the recording head. These are filled with, for example, four inks of black ink (K), yellow ink (Y), magenta ink (M), and cyan ink (C), and are replenished from the main ink tank 4. It is paid.

  The sub ink tank 5 is provided with an exhaust hole 56 and a supply hole 57, respectively. When the recording head 3 moves to the standby position (or replenishment position), the exhaust pin 151 and the replenishment pin 152 of the replenishing device 15 are inserted into the exhaust hole 56 and the replenishment hole 57, respectively. 5 and the replenishing device 15 can be connected. The replenishing device 15 is connected to the main ink tank 4 via the replenishing pipe 16, and the replenishing device 15 replenishes ink or processing liquid from the main ink tank 4 to the sub ink tank 5 through the replenishing hole 57.

  Here, the main ink tank 4 also has main ink tanks 41, 42, 43, 44, 45 in which different colors of ink and processing liquid are stored. These are filled with processing liquids in addition to four inks, for example, black ink (K), yellow ink (Y), magenta ink (M), and cyan ink (C). 100 is removably stored.

  Furthermore, the power supply signal cable 9 and the sub ink tank 5 are connected to the recording head 3, and when external image recording information is input from the power supply signal cable 9 to the recording head 3, the recording head 3 detects the image recording information. Based on the above, a predetermined amount of ink is sucked from each sub ink tank 5 and discharged onto the surface of the recording medium. The power supply signal cable 9 also has a role of supplying power necessary for driving the recording head 3 to the recording head 3 in addition to the image recording information.

  The recording head 3 is arranged and held on a carriage 10, and the carriage 10 is connected to a guide rod 11 and a timing belt 12 connected to a driving pulley 13. With such a configuration, the recording head 3 extends along the guide rod 11 and is parallel to the surface of the recording medium 1 and perpendicular to the conveyance direction X (sub-scanning direction) of the recording medium 1 (main scanning direction). It can also be moved in the scanning direction.

  The image forming apparatus 100 includes control means (not shown) that adjusts the drive timing of the recording head 3 and the drive timing of the carriage 10 based on the image recording information. Thereby, an image based on the image recording information can be continuously formed in a predetermined region of the surface of the recording medium 1 that is transported at a predetermined speed along the transport direction X.

  The maintenance unit 14 is connected to a decompression device (not shown) via a tube. Further, the maintenance unit 14 is connected to the nozzle portion of the recording head 3 and has a function of sucking ink from the nozzles of the recording head 3 by reducing the pressure in the nozzles of the recording head 3. By providing the maintenance unit 14, if necessary, excess ink adhering to the nozzles during operation of the image forming apparatus 100 is removed, or evaporation of ink from the nozzles is suppressed when the operation is stopped. be able to.

  In the inkjet recording apparatus of the present invention, the recording head is preferably a line head in which a plurality of nozzles are arranged in the width direction of the recording medium, and the recording head is preferably arranged in the transport direction of the recording medium. The line head has a length substantially the same as the width of the recording medium (the number of recording elements is equal to the width of the recording paper × the resolution, for example, the width of the recording paper is the A4 width direction and the resolution is 600 dpi). Then, it is preferable to have about 5,000 recording heads (so-called full-width size recording heads) arranged in the paper width.

  FIG. 3 is a perspective view showing an external configuration of a preferred embodiment having the line head, which is the ink jet recording apparatus of the present invention. FIG. 4 is a perspective view showing an internal basic configuration of the ink jet recording apparatus (hereinafter referred to as an image forming apparatus) of FIG. The image forming apparatus 101 of the present embodiment has a configuration that operates based on the above-described inkjet recording method of the present invention to form an image.

  In the image forming apparatus 101 shown in FIGS. 3 and 4, the width of the recording head 3 is the same as or larger than the width of the recording medium 1, does not have a carriage mechanism, and is in the sub-scanning direction (conveying direction of the recording medium 1: arrow X). Direction) paper feed mechanism (the transport roller 2 is shown in the present embodiment, but it may be a belt-type paper feed mechanism, for example).

  Although not shown, the nozzle group for discharging each color (including the treatment liquid) is also provided in the same manner as the sub ink tanks 51 to 55 are sequentially arranged in the sub scanning direction (conveyance direction of the recording medium 1: arrow X direction). They are arranged in the sub-scanning direction. Other configurations are the same as those of the image forming apparatus 100 shown in FIGS. In the drawing, since the recording head 3 does not move, the sub ink tank 5 is always connected to the replenishing device 15. However, the sub ink tank 5 may be connected to the replenishing device 15 at the time of ink replenishment.

  In the image forming apparatus 101 shown in FIGS. 3 and 4, printing in the width direction (main scanning direction) of the recording medium 1 is performed collectively by the recording head 3, so that recording is performed at the time of printing as compared with the system having a carriage mechanism. Since only the sheet needs to be moved in one direction, the configuration of the apparatus is simple and the printing speed is increased.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. In the following examples, “parts” and “%” are based on mass unless otherwise specified.

<Preparation of ink using pigment having no surface functional group>
C. I. Pigment. Blue 15: 3 To 30 parts, resin (sodium neutralized salt of styrene-methacrylic acid copolymer) is added while adjusting the addition amount to the following composition ratio, and ion-exchanged water is further added to bring the total amount to 300. The part. This liquid was subjected to ultrasonic waves with an ultrasonic homogenizer to disperse the pigment. Further, this dispersion was centrifuged with a centrifugal separator to remove 100 parts of the residue.

Various cyan inks (used in Examples 1, 3, 5, 6, 7, and Comparative Examples 2 and 4) using pigments processed according to the above-described pigment processing method and using pigments having the following composition and having no surface functional groups are used. Prepared.
・ C. I. Pigment. Blue 15: 3 (pigment, no surface functional group): 5%
Resin (polymer dispersant, styrene-methacrylic acid copolymer sodium neutralized salt, weight average molecular weight = 10000): amount described in Tables 1 and 2 diethylene glycol: 10%
・ Diethylene glycol monobutyl ether: 3%
-Acetylene glycol ethylene oxide adduct: 1%
・ Ion exchange water: balance

The C.I. I. Pigment. Blue 15: 3, C.I. I. Pigment. Various magenta inks using a pigment having no surface functional group were prepared in the same manner except that the composition was changed to Red122.
Further, the C.I. I. Pigment. Blue 15: 3, C.I. I. Pigment. Various yellow inks using a pigment having no surface functional group were prepared in the same manner except that the color was changed to Yellow 74.

<Preparation of ink using pigment having surface functional group>
-Surface modification treatment of pigment-
The aqueous sulfanilic acid solution was heated, and 100 g of a pigment (CI Pigment. Blue 15: 4) was added while stirring. The mixture was cooled to room temperature with stirring, and 14 g of concentrated nitric acid was added dropwise. To this solution, 10 g of an aqueous NaNO ₂ solution was added and stirred until the reaction was completed. The pigment was desalted. The obtained surface-treated pigment was added with ion-exchanged water so that the pigment concentration was 12%, adjusted to pH 7.5, and then dispersed using an ultrasonic homogenizer. The dispersion was subjected to centrifugal separation (8000 rpm × 30 minutes) with a centrifugal separator, and the residue (20% with respect to the total amount) was removed to obtain a surface-treated pigment dispersion.

  Next, the surface-modified C.I. I. Pigment. Blue 15: 4 To 30 parts, resin (sodium neutralized salt of styrene-methacrylic acid copolymer) is added while adjusting the addition amount to the following composition ratio, and ion exchange water is further added to make a total amount of 300 The part. This liquid was subjected to ultrasonic waves with an ultrasonic homogenizer to disperse the pigment. Further, this dispersion was centrifuged with a centrifugal separator to remove 100 parts of the residue.

Various cyan inks (used in Examples 2 and 4 and Comparative Examples 1 and 3) using a pigment having a surface functional group having the following composition were prepared using the pigment treated according to the pigment treatment method.
・ C. I. Pigment. Blue15: 4 (pigment, with surface functional groups): 5%
Resin (polymer dispersant, styrene-methacrylic acid copolymer sodium neutralized salt, weight average molecular weight = 10000): amount described in Tables 1 and 2 diethylene glycol: 10%
・ Diethylene glycol monobutyl ether: 3%
-Acetylene glycol ethylene oxide adduct: 1%
・ Ion exchange water: balance

The C.I. I. Pigment. Blue 15: 4, C.I. I. Pigment. Various magenta inks using a pigment having a surface functional group were prepared in the same manner except that it was changed to Red122.
Further, the C.I. I. Pigment. Blue 15: 4, C.I. I. Pigment. Various yellow inks using a pigment having a surface functional group were prepared in the same manner except that it was changed to Yellow 74.

<Preparation of treatment liquid (aggregated liquid composition)>
The processing liquid used for Example 1, 2, 5, 6 and the comparative examples 1 and 2 was prepared by the following composition.
・ Diethylene glycol: 25%
Flocculant (2-pyrrolidone-5-carboxylic acid): 5%
Resin (polyvinylpyrrolidone, weight average molecular weight 100,000,000): amount described in Tables 1 and 2 Sodium hydroxide: 0.8%
-Acetylene glycol ethylene oxide adduct: 1%
・ Ion exchange water: balance

<Measurement of surface tension>
Using the surface tension meter CBVP-Z manufactured by Kyowa Interface Science Co., Ltd., the surface tension of the ink and the treatment liquid prepared as described above was measured.

<Quantification of resin content>
With respect to the ink and the treatment liquid prepared by adjusting the resin content, the amount of the resin was quantified again by the following method.
The ink composition (or treatment liquid) is weighed and the mass (A) is measured. This is heated to dryness, and the solid content (B) in the ink composition (or treatment liquid) is weighed. The solid is weighed and the mass (C) of the solid content other than the pigment thermally decomposed is measured by thermogravimetric analysis. With (C) as the resin component, the amount of resin in (B) is known. Furthermore, the resin content in the ink was determined using the ratio of (A) and (B).

<Evaluation>
Printing was performed on FX-P paper (Fuji Xerox Co., A4) using an 800 dpi, 256 nozzle piezo print head and Fuji Xerox WorkCentre B900. Specifically, in the example using the treatment liquid (liquid composition), the treatment liquid was first ejected, and ink was ejected therefrom. The print patterns include secondary color B (ink ejection order is C → M), G (also C → Y), R (also M → Y), and tertiary color process black PK (also C → M → A solid image of Y) was formed, and each print pattern was evaluated for show-through and print density according to the following criteria. The results are shown in Tables 3 and 4.

-Evaluation of strikethrough-
After the solid image was formed, the back of the paper was observed.

−Print density−
The printing density (OD) was measured using a spectral densitometer (trade name: X-Rite 404, manufactured by X-Rite Co., Ltd.). Based on the measured print density results, the following criteria were used for evaluation.
・ Secondary color evaluation
◎: OD1.1 or more
○: OD1.0 or more and less than 1.1
Δ: OD 0.9 or more and less than 1.0
×: OD 0.8 or more and less than 0.9
XX: Less than OD0.8 ・ Evaluation of tertiary color
◎: OD1.2 or more
○: OD1.1 or more and less than 1.2
X: OD1.0 or more and less than 1.1
XX: Less than OD1.0

1 is a perspective view showing an external configuration of a preferred embodiment of an ink jet recording apparatus of the present invention. FIG. 2 is a perspective view showing an internal basic configuration of the ink jet recording apparatus of FIG. 1. 1 is a perspective view showing an external configuration of a preferred embodiment of an ink jet recording apparatus of the present invention. FIG. 4 is a perspective view showing an internal basic configuration of the ink jet recording apparatus of FIG. 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Recording medium 2 Conveyance roller 3 Recording head 4 Main ink tank 5 Sub ink tank 6 External cover 7 Tray 8 Image forming part 9 Power supply signal cable 10 Carriage 11 Guide rod 12 Timing belt 13 Driving pulley 14 Maintenance unit 15 Replenishing device 16 Replenishment pipe 41, 42, 43, 44, 45 Main ink tanks 51, 52, 53, 54, 55 Sub-ink tank 56 Exhaust hole 57 Replenishment hole 100, 101 Image forming apparatus 151 Exhaust pin 152 Replenishment pin

Claims (4)

An ink set that has at least two colors of inks containing pigments, and that forms images by ejecting the two or more color inks so as to contact each other sequentially on a recording medium,
A resin is contained in the ink of at least one color,
An ink set, wherein the resin content in the first ejected ink is equal to or higher than the resin content in each of the other inks. Using an ink set having at least two colors of ink containing a pigment,
An ink jet recording method for forming an image by sequentially ejecting the two or more colors of ink on a recording medium so as to contact each other.
A resin is contained in the ink of at least one color,
An ink jet recording method, wherein the resin content in the first ejected ink is equal to or higher than the resin content in each of the other inks. At least a droplet discharge means for discharging droplets,
Using an ink set having at least two colors of ink containing a pigment,
An ink jet recording apparatus that forms an image by ejecting ink droplets of two or more colors on a recording medium sequentially from the droplet ejecting means,
A resin is contained in the ink of at least one color,
An ink jet recording apparatus, wherein a content ratio of the resin in the first ejected ink is equal to or higher than a resin content ratio in each of the other inks. It is detachable from an ink jet recording apparatus provided with a droplet discharge means,
Containing at least two or more inks containing pigments, and containing an ink set for forming an image by sequentially ejecting the two or more inks in contact with each other on a recording medium;
An ink tank for ink-jet recording that supplies ink to the droplet discharge means in a state of being mounted on the ink-jet recording apparatus,
A resin is contained in the ink of at least one color,
An ink tank for ink-jet recording, wherein the resin content in the first ejected ink is equal to or higher than the resin content in each of the other inks.

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