JP2005298652A - Ink set, recording property-improving liquid and image-forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording property-improving liquid capable of giving an excellent inkjet recording image, which gives a sufficient image density with an excellent letter quality while having high-speed fixability, performs high uniformity of a solid image, is bleed-less, and gives an image having good color reproducibility and high definition, when color inkjet recording is applied onto a regular paper sheet, in particular; and to provide an ink set and an image-forming method using the ink set. <P>SOLUTION: The ink set comprises the recording property-improving liquid which improves recording properties of an inkjet ink, and the inkjet ink which forms an image onto a recording medium by inkjet recording. The recording property-improving liquid contains at least colorless or white fine particles and the inkjet ink contains an organic pigment as a colorant. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a recording technique for reducing bleeding that occurs in the formation of a color image on plain paper and having good color development of a recorded image, and in particular, a recording performance improving liquid that is optimally used for image formation using an ink jet recording system. The present invention also relates to an ink set using the recording performance improving liquid and an image forming method using the ink set.

  In the ink jet recording method, ink droplets are ejected and ink is attached to a recording medium such as paper to perform recording. In particular, according to an ink jet recording method in which droplets are ejected by using an electrothermal transducer as the ejection energy supply means and generating thermal bubbles by applying thermal energy to the ink, the recording head is made to have a high density multi-orifice. This can be easily realized, and high-resolution and high-quality images can be recorded at high speed (see, for example, Patent Documents 1 to 3).

  However, inks used in conventional ink jet recording methods generally contain water as a main component and contain a water-soluble high-boiling solvent such as glycol for the purpose of preventing drying and preventing nozzle clogging. Therefore, when recording is performed on plain paper using such ink, sufficient fixing properties cannot be obtained, or it is presumed that this is due to uneven distribution of filler and sizing agent on the surface of the recording paper. Problems such as the generation of a uniform image occurred. In particular, when trying to obtain a color image, a plurality of color inks are superimposed one after another before the ink of a certain color is fixed on the recording paper. There is a problem that a satisfactory image cannot be obtained due to non-uniform mixing (hereinafter, this phenomenon is called bleeding).

  On the other hand, as a means for improving the fixability, a method of adding a compound that enhances permeability such as a surfactant into the ink is disclosed (for example, see Patent Document 4). Further, it is disclosed to use an ink mainly composed of a volatile solvent (see, for example, Patent Document 5). However, the former method of adding a surfactant or the like to the ink increases the ink permeability to the recording paper and improves the fixing property and bleeding of the ink to some extent. Since it penetrates deeply, inconveniences such as a decrease in image density and saturation occur. In addition, the spread of the ink in the lateral direction also occurred, resulting in problems such as a decrease in edge sharpness and a decrease in resolution. On the other hand, in the case of the latter method using ink mainly composed of a volatile solvent, in addition to the same inconvenience as in the former case, clogging due to evaporation of the solvent at the nozzle portion of the recording head occurs. It was easy to do and was not preferable.

  Further, in order to improve the above-described problem, a method has been proposed in which a liquid that makes a good image appear in advance on a recording medium prior to ink ejection. For example, a method is disclosed in which a liquid containing an organic compound having two or more cationic groups per molecule is deposited on a recording medium and then recorded with an ink containing an anionic dye ( For example, see Patent Document 6). Further, a method is disclosed in which an acidic liquid containing succinic acid or the like is deposited on a recording medium and then recorded with an ink containing an anionic dye (see, for example, Patent Document 7). Further, Patent Document 8 discloses a method in which a liquid for insolubilizing a dye is applied prior to ink recording (see, for example, Patent Document 8).

  However, since any of the above-described methods is intended to improve image bleeding and water resistance by precipitation of the dye itself, the above-described bleeding suppression effect between the color inks is insufficient, and the precipitated dye However, since it tends to be non-uniformly distributed on the recording paper, the coverage of the recording paper on the pulp fibers is poor, and the sharpness, uniformity, etc. of the image are reduced.

Japanese Patent Publication No. 61-59911 Japanese Patent Publication No. 61-59912 Japanese Examined Patent Publication No. 61-59914 JP 55-65269 A JP-A-55-66976 JP 63-29971 A Japanese Unexamined Patent Publication No. 64-9279 JP-A-64-63185

Accordingly, the object of the present invention has been made in order to solve all of the following problems in view of the above situation. That is, the following points can be cited as problems when performing inkjet recording on plain paper.
(1) The print quality is good while having good fixability.
(2) A sufficient image density is obtained, and the solid image has high definition and uniformity.
In addition to the above-mentioned problems, the following problems can be cited as problems when forming color images on plain paper.
(3) Prevent bleeding.
(4) The color reproducibility is good and a high-definition image can be obtained.

  The above object is achieved by the present invention described below. That is, the present invention relates to [1] an ink set comprising a recording performance improving liquid for improving the recording performance of an ink jet ink and an ink jet ink for forming an image on a recording medium by an ink jet recording method. However, the ink set contains at least colorless or white fine particles, and the ink-jet ink contains an organic pigment as a colorant.

（ただし、Ｒは、水素原子、炭素数１〜４の低級アルキル基又は脂環式基のいずれかを示す。又、Ｒ₁、Ｒ₂、Ｒ₃及びＲ₄はそれぞれ独立に、水素原子、炭素数１〜４の低級アルキル基を示し、窒素原子と共に複素環式基を形成してもよい。又、Ｘは炭素数２〜３の低級アルキレン基を示す。） Preferred forms of the ink set include the following [2] to [5]. [2] The ink set according to [1], wherein the colorless or white fine particles are organic fine particles made of an organic compound. [3] The ink set according to [2], wherein the organic fine particles are dispersed with a cationic resin. [4] The ink set according to [3], wherein the organic fine particles are bismelamine compounds represented by the following general formula (I). [5] The ink set according to [4], wherein the recording performance improving liquid contains a water-soluble polyvalent metal salt.

(However, R shows a hydrogen atom, a C1-C4 lower alkyl group, or an alicyclic group. Moreover, R < ₁ >, R < ₂ >, R < ₃ > and R < ₄ > are respectively independently a hydrogen atom, A lower alkyl group having 1 to 4 carbon atoms may be formed together with a nitrogen atom to form a heterocyclic group, and X represents a lower alkylene group having 2 to 3 carbon atoms.

（ただし、Ｒは、水素原子、炭素数１〜４の低級アルキル基又は脂環式基のいずれかを示す。又、Ｒ₁、Ｒ₂、Ｒ₃及びＲ₄はそれぞれ独立に、水素原子、炭素数１〜４の低級アルキル基を示し、窒素原子と共に複素環式基を形成してもよい。又、Ｘは炭素数２〜３の低級アルキレン基を示す。） Another embodiment of the present invention is [6] a recording performance improving liquid for improving the recording performance of an ink-jet ink, which is colorless or hav- er composed of a compound of the following general formula (I) dispersed with a cationic resin. It is a recording performance improving liquid characterized by containing white fine particles.

(However, R shows a hydrogen atom, a C1-C4 lower alkyl group, or an alicyclic group. Moreover, R < ₁ >, R < ₂ >, R < ₃ > and R < ₄ > are respectively independently a hydrogen atom, A lower alkyl group having 1 to 4 carbon atoms may be formed together with a nitrogen atom to form a heterocyclic group, and X represents a lower alkylene group having 2 to 3 carbon atoms.

  Another embodiment of the present invention is [6] using the ink set according to any one of [1] to [5] or the recording performance improving liquid according to [6]. Image forming method.

  As described above, according to the present invention, in particular, when color ink jet recording is performed on plain paper, a high-quality image can be obtained with a high printing quality and a sufficient image density can be obtained, and a uniform solid image can be obtained. A recording performance improving liquid, an ink set, and an image forming method using the same that can provide an excellent ink jet recording image capable of providing a high-definition image having high reproducibility and excellent color reproducibility in a breathless manner are provided. .

  Next, the present invention will be described in more detail with reference to preferred embodiments. First, a recording performance improving liquid containing colorless or white fine particles will be described. The recording performance improving liquid of the present invention is characterized by containing at least colorless or white fine particles. Preferably, the colorless or white fine particles are colorless or white fine particles composed of an organic compound (hereinafter referred to as organic type). And the use of the organic fine particles after dispersion treatment with a cationic resin.

  Next, regarding the role of the recording performance improving liquid when the recording performance improving liquid mainly composed of colorless or white fine particles is used for image formation, the colorless or white fine particles are preferably dispersed with a cationic resin. A description will be given taking the form as an example. The recording performance improving liquid according to the present invention contains an anionic compound, for example, when used together with an ink containing an organic pigment dispersed in an anionic resin as a coloring material, on a recording paper or a position penetrating into the recording paper. In the recording performance improving liquid, for example, a cationic substance such as a cationic resin for dispersing colorless or white fine particles and an anionic compound in the ink are ionized. As a result of mechanical interaction, association occurs, and the pigment in the ink aggregates instantaneously, causing separation from the solution phase. At that time, since colorless or white fine particles dispersed in the cationic resin are simultaneously taken into the aggregate, the concealability of the colored layer is improved. As a result, the sharpness and density of the image are greatly improved. For the above reasons, by combining the above-described ink and the recording performance improving liquid, the formed image can achieve both improvement in print quality and improvement in fixability. Moreover, the effect of improving the light fastness of the formed image can also be obtained by the above-mentioned shielding effect of colorless or white fine particles.

  The ink set according to the present invention is characterized in that the recording performance improving liquid configured as described above is combined with a recording ink containing at least an anionic compound. The colored ink for recording used in combination with the recording performance improving liquid contains an organic pigment as at least a colorant, and preferably further contains an anionic compound and an organic pigment.

  The components to be contained in the recording performance improving liquid according to the present invention are preferably (1) colorless or white fine particles and a cationic compound (more preferably, a cationic resin). The components to be contained in the colored ink according to the present invention are preferably (2) an organic pigment and an anionic compound. Hereinafter, each of the preferred embodiments will be described.

(1) A recording performance improving liquid in a form containing at least colorless or white fine particles and a cationic compound In a preferred form of the recording performance improving liquid according to the present invention, it contains colorless or white fine particles and a cationic compound. . As the cationic compound used in the recording performance improving liquid, it is preferable to use a cationic water-soluble resin as shown below. These resins are contained to disperse colorless or white fine particles in the aqueous medium, but may be added separately from the dispersant as described later.

As the cationic water-soluble resin in the above, for example, a copolymer of a cationic monomer and a hydrophobic monomer is preferably used. Examples of the cationic monomer used in the present invention include the following quaternized compounds of monomers.
N, N-dimethylaminoethyl methacrylate [CH ₂ ═C (CH ₃ ) —COO—C ₂ H ₄ N (CH ₃ ) ₂ ],
· N, N-dimethylaminoethyl acrylate _{[CH 2 = CH-COO-} C 2 H 4 N (CH 3) 2],
· N, N-dimethylacrylamide _{[CH 2 = CH-CON (} CH 3) 2]
· N, N-dimethyl methacrylamide _{[CH 2 = C (CH 3} ) -CON (CH 3) 2], · N, N- dimethylaminopropyl acrylamide _{[CH 2 = CH-CONH-} C 3 H 6 N (CH ₃ ) ₂ ],
· N, N-dimethylaminopropyl methacrylamide _{[CH 2 = C (CH 3} ) -CONH-C 3 H 6 N (CH 3) 2]

  In addition, when quaternizing the above-mentioned compounds, for example, methyl chloride, dimethyl sulfate, benzyl chloride, epichlorohydrin and the like may be used in a conventional manner.

  Examples of the hydrophobic monomer used for the cationic water-soluble resin include styrenes such as styrene, α-methylstyrene, vinyltoluene, acrylonitrile, and (meth) acrylic acid alkyl esters. Here, as the (meth) acrylic acid alkyl ester, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, sec-butyl (Meth) acrylate, tert-butyl (meth) acrylate, 2-methylbutyl (meth) acrylate, 2-ethylbutyl (meth) acrylate, 3-methylbutyl (meth) acrylate, 1,3-dimethylbutyl (meth) acrylate, pentyl ( (Meth) acrylate, 3-pentyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, -Ethoxyethyl acrylate, 3-ethoxypropyl acrylate, 2-ethoxybutyl acrylate, 3-ethoxybutyl acrylate, and dimethylaminoethyl acrylate are listed. Examples of alcohol components used for half-esterification include methanol, ethanol, and propanol. Examples of the monomer that can be optionally used include (meth) acrylamide, N-methylol (meth) acrylamide, diacetone acrylamide, and the like.

  When the cationic monomer and the hydrophobic monomer are copolymerized as described above, the mass ratio of the cationic monomer to the hydrophobic monomer in the copolymer is in the range of 10:90 to 40:60. It is preferable that These resins are soluble in water or in an aqueous solution adjusted to be acidic. Such a water-soluble resin is preferably contained in the recording performance improving liquid according to the present invention in the range of 0.1 to 5% by mass of the whole liquid.

  Any pH adjuster may be used as long as it exhibits acidity in an aqueous solution, for example, a compound having hydrochloric acid, acetic acid and a carboxyl group, a compound having carbonic acid, a sulfuric acid and a sulfone group, or nitric acid. , Phosphoric acid compounds, sulfurous acid, nitrous acid and the like. However, it is not limited to these as long as it shows acidity in an aqueous solution.

  Next, colorless or white fine particles which are components characterizing the recording performance improving liquid according to the present invention will be described. The amount of colorless or white fine particles is 0.1 to 20% by mass, preferably 0.5 to 10% by mass of the whole liquid. Further, the colorless or white fine particles in the present invention are incorporated into the aggregate when the components in the recording performance improving liquid cause aggregation with the components in the ink as described above. Any material can be used as long as it satisfies the performance of improving the concealability of the colored layer. For example, an inorganic pigment such as titanium oxide may be used, but the use of organic fine particles, which will be described below, is suitable for ink jetting, abrasion resistance of a recorded image, and a recording paper surface of a colored pigment contained in a colored ink. It is more preferable from the standpoints of the above-described inking properties [the degree of ink deposition (coloring property)] and the stability during ink storage (precipitation).

（ただし、Ｒは、水素原子、炭素数１〜４の低級アルキル基又は脂環式基のいずれかを示す。又、Ｒ₁、Ｒ₂、Ｒ₃及びＲ₄はそれぞれ独立に、水素原子、炭素数１〜４の低級アルキル基を示し、窒素原子と共に複素環式基を形成してもよい。又、Ｘは炭素数２〜３の低級アルキレン基を示す。） Specific examples of organic fine particles suitable in the present invention include compounds represented by the following general formula (I).

(However, R shows a hydrogen atom, a C1-C4 lower alkyl group, or an alicyclic group. Moreover, R < ₁ >, R < ₂ >, R < ₃ > and R < ₄ > are respectively independently a hydrogen atom, A lower alkyl group having 1 to 4 carbon atoms may be formed together with a nitrogen atom to form a heterocyclic group, and X represents a lower alkylene group having 2 to 3 carbon atoms.

  Previously, the cationic resin for stably dispersing the organic fine particles constituting the recording performance improving liquid according to the present invention in the ink has been described. However, in the present invention, the following will be described separately. An organic cationic substance and / or a water-soluble polyvalent metal salt may be contained. In particular, when the organic white fine particles represented by the above general formula (I) are used in the recording performance improving liquid according to the present invention, it is preferable that a soluble polyvalent metal salt coexists.

Preferable specific examples of the organic cationic substance used above include ethyleneamines represented by the following general formula (II), polyethyleneimine represented by the following general formula (III), spermidine, spermine and the like. However, it is not limited to these.

  Furthermore, a cationic surfactant can also be used as the organic cationic substance. Specifically, the following can be used. For example, primary, secondary and tertiary amine salt type compounds, specifically hydrochlorides such as laurylamine, coconut amine, stearylamine, rosinamine, acetates, etc .; quaternary ammonium salt type compounds, specifically Lauryltrimethylammonium chloride, cetyltrimethylammonium chloride, lauryldimethylbenzylammonium chloride, benzyltributylammonium chloride, benzalkonium chloride, etc .; pyridinium salt type compounds, specifically cetylpyridinium chloride, cetylpyridinium bromide, etc .; imidazoline Type cationic compounds, specifically 2-heptadecenyl-hydroxyethyl imidazoline, etc .; ethylene oxide adducts of higher alkylamines, specifically dihydroxyethyl stearylamine, etc. Masui.

Furthermore, in the present invention, other amphoteric surfactants that exhibit a cationic property in a certain pH range can be preferably used as the cationic substance. Specifically, for example, amino acid type amphoteric surfactant; R—NH—CH ₂ —CH ₂ —COOH type compound; betaine type compound, specifically, carboxylic acid such as stearyl dimethyl betaine, lauryl dihydroxyethyl betaine, etc. In addition to acid salt type amphoteric surfactants, examples include amphoteric surfactants such as sulfate ester type, sulfonic acid type, and phosphate ester type. Of course, when these amphoteric surfactants are used, the recording performance improving liquid according to the present invention is adjusted so that the pH is lower than the isoelectric point thereof, or the recording performance improving liquid is applied to the recording medium. It is necessary to take any method of adjusting the pH to be equal to or lower than the isoelectric point when mixed with ink. In addition, although the example of the low molecular weight cationic compound was mentioned above as a cationic substance, it cannot be overemphasized that the cationic substance which can be used by this invention is not necessarily limited to these.

  The amount of the organic cationic substance as described above contained in the recording performance improving liquid according to the present invention is preferably in the range of 0.05 to 20% by mass, more preferably 0.5 to Although it is the range of 10 mass%, it is necessary to determine the optimal range by the combination of each substance to be used. For example, the amount of the water-soluble cationic surfactant is preferably in the range of 0.05 to 10% by mass.

In the present invention, a water-soluble polyvalent metal salt can be used in addition to the water-soluble organic cationic substance. The polyvalent metal salt is composed of a divalent or higher polyvalent metal ion and an anion that binds to the polyvalent metal ion. Specific examples of polyvalent metal ions include divalent metal ions such as Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ and Zn ²⁺ , and trivalent metal ions such as Fe ³⁺ and Al ^3+. A metal ion is mentioned. In addition, examples of the anion which is a counter ion include Cl ⁻ , NO ₃ ⁻ , SO ₄ ^{2− and the} like. The content is preferably 0.1 to 20% by mass, more preferably 1 to 10% by mass in the recording performance improving liquid according to the present invention.

  Next, other components constituting the recording performance improving liquid according to the present invention will be specifically described. The recording performance improving liquid according to the present invention is usually composed of water, a water-soluble organic solvent and other appropriate additives in addition to the above-described components, and is a colorless or light-colored liquid substance. Examples of the water-soluble organic solvent that can be used in the recording performance improving liquid according to the present invention include amides such as dimethylformamide and dimethylacetamide, ketones such as acetone, ethers such as tetrahydrofuran and dioxane, polyethylene glycol, polypropylene glycol, and the like. Polyalkylene glycols, ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, alkylene glycols such as thiodiglycol, hexylene glycol, diethylene glycol, ethylene glycol methyl ether, diethylene glycol monomethyl Lower alkyl ethers of polyhydric alcohols such as ether and triethylene glycol monomethyl ether, ethanol, isopropyl alcohol In addition to monohydric alcohols such as coal, n-butyl alcohol and isobutyl alcohol, glycerin, N-methyl-2-pyrrolidone, 1,3-dimethyl-imidazolidinone, triethanolamine, sulfolane, dimethylsulfoxide, etc. Preferably used. Although there is no restriction | limiting in particular about content of the said water-soluble organic solvent, 5-60 mass% of the total mass of a recording performance improvement liquid, More preferably, 5-40 mass% is a suitable range.

  In addition, the recording performance improving liquid according to the present invention may further contain additives such as a viscosity adjusting agent, a pH adjusting agent, a preservative, various surfactants, an antioxidant and an evaporation accelerator as necessary. It doesn't matter. The selection of the surfactant is particularly important for adjusting the permeability of the liquid into the recording medium. The recording performance improving liquid according to the present invention is more preferably colorless. However, the recording performance improving liquid may be a light color in a range that does not change the color tone of each color ink when mixed with ink on a recording medium or the like. Furthermore, as a suitable range of various physical properties of the recording performance improving liquid as described above, the pH is set to 3 to 12, preferably 3 to 8, more preferably 3 to 5, and the surface tension is set to 10 to around 25 ° C. 60 dyn / cm (mN / m), more preferably 10 to 40 dyn / cm (mN / m), and a viscosity of 1 to 30 cps. (MPa · s). The surface tension of the recording performance improving liquid according to the present invention is preferably lower than the surface tension of the ink used together with the recording performance improving liquid.

  Next, the ink constituting the ink set according to the present invention will be described. The ink used in the present invention uses an organic pigment as a coloring material. The organic pigment referred to in the present invention includes carbon black. More preferably, an anionic compound is used in combination. The ink used in the present invention further includes water, a water-soluble organic solvent and other components such as a viscosity adjuster, a pH adjuster, a preservative, a surfactant, an antioxidant and the like. Is included as needed.

The amount of the pigment in the ink used in the present invention is 0.1 to 20% by mass, preferably 0.5 to 10% by mass with respect to the total mass of the ink. The following are mentioned as a kind of organic pigment used in this invention. Carbon black can be used as a black ink. For example, carbon black produced by a furnace method or a channel method has a primary particle diameter of 15 to 40 nm and a specific surface area by a BET method of 50 to 300 m. ² / g, DBP oil absorption of 40 to 150 ml / 100 g, volatile content of 0.5 to 10%, pH value of 2 to 9 and the like are preferably used. Examples of commercially available products having such characteristics include No. 2300, no. 900, MCF88, No. 33, no. 40, no. 45, no. 52, MA7, MA8, no. 2200B (above, manufactured by Mitsubishi Kasei), RAVEN 1255 (above, made in Colombia), REGAL400R, REGAL330R, REGAL660R, MOGUL L (above, made by Cabot), Color Black FWl, Color Black FW18, Color Black S170, Color Black S170, ColorSla 35, , Printex U (manufactured by Degussa) and the like can be preferably used.

  Examples of organic pigments used in yellow ink include C.I. I. Pigment Yellow 1, C.I. I. Pigment Yellow 2, C.I. I. Pigment Yellow 3, C.I. I. Pigment Yellow 13, C.I. I. Pigment Yellow 16, C.I. I. Pigment Yellow 83 and the like.

  Examples of organic pigments used in magenta ink 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 (Ca), C.I. I. Pigment Red 48 (Mn), C.I. I. Pigment Red 57 (Ca), C.I. I. Pigment Red 112, C.I. I. Pigment Red 122 and the like.

Examples of organic pigments used for cyan ink include C.I. I. Pigment Blue 1, C.I. I. Pigment Blue 2, C.I. I. Pigment Blue 3, C.I. I. Pigment Blue 15: 3, C.I. I. Pigment Blue 16, C.I. I. Pigment Blue 22, C.I. I. Vat Blue 4, C.I. I. Vat Blue 6 and the like can be mentioned, but are not limited thereto.
In addition to the above, organic pigments newly synthesized for the present invention can of course be used. As the coloring material of the ink used in the present invention, in addition to the above pigment, a disperse dye, a water-soluble dye, and the like may be appropriately mixed and used in combination with the above-described organic pigment.

  Further, since the ink used in the present invention uses the organic pigments listed above, a dispersant is usually used. As the dispersant, any water-soluble resin can be used, but those having a weight average molecular weight in the range of 1,000 to 30,000 are preferable, and more preferably 3,000 to 15,000. Those in the range of are preferably used. Examples of such 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, maleic acid, maleic acid, and the like. At least two monomers selected from acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, vinyl acetate, vinylpyrrolidone, acrylamide, and derivatives thereof (of which at least one is hydrophilic) Monomer), a random copolymer, a graft copolymer, or a salt of these copolymers. Alternatively, natural resins such as rosin, shellac and starch can be preferably used. These resins are soluble in an aqueous solution in which a base is dissolved, and are alkali-soluble resins. In addition, it is preferable to contain the water-soluble resin used as these pigment dispersants in the range of 0.1 to 5% by mass with respect to the total mass of the ink.

  In particular, in the case of an ink containing a pigment as described above, the entire ink is preferably adjusted to be neutral or alkaline. This is preferable because the solubility of the water-soluble resin used as the pigment dispersant can be improved and the ink can be further improved in long-term storage stability. However, in this case, since it may cause corrosion of various members used in the ink jet recording apparatus, it is desirable that the pH range is 7-10. Examples of the pH adjuster used at this time 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, Examples include organic acids and mineral acids. The above-described pigment and dispersant water-soluble resin are dispersed or dissolved in an aqueous liquid medium.

  A suitable aqueous liquid medium in the ink used in the present invention is a mixed solvent of water and a water-soluble organic solvent, and the water is not general water containing various ions but ion-exchanged water (deionized water). Is preferably used.

  Examples of the water-soluble organic solvent used by mixing with water include carbon atoms of 1 such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and the like. Alkyl alcohols of -4; 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; Ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol Alkylene glycols having 2 to 6 carbon atoms, such as coal; glycerin; ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether, etc. Lower alkyl ethers of monohydric alcohols; N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like. 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 content of the water-soluble organic solvent in the ink as described above is generally in the range of 3 to 50% by mass, preferably in the range of 3 to 40% by mass with respect to the total mass of the ink. The water content used is in the range of 10 to 90% by mass, preferably 30 to 80% by mass, based on the total mass of the ink.

  In addition to the above-mentioned components, the ink used in the present invention is appropriately added with a surfactant, an antifoaming agent, a preservative, etc., if necessary, in order to obtain an ink having a desired physical property value. be able to. Moreover, a water-soluble dye etc. can also be added suitably as a coloring material. The surface tension of the ink is preferably larger than the surface tension of the recording performance improving liquid according to the present invention described above. For this purpose, it is preferable to adjust the surface tension of the ink in such a manner by using a surfactant or the like contained in the ink.

  As a method for producing the ink containing the pigment as described above, first, the pigment is added to an aqueous medium containing at least a water-soluble resin as a dispersant and water, and after stirring, a dispersion means described later is used. The desired pigment dispersion is obtained by carrying out dispersion using a centrifugal separation treatment if necessary. Next, an aqueous medium, a sizing agent, and appropriately selected additive components such as those mentioned above are added to the pigment dispersion and stirred to obtain an ink used in the present invention.

  In addition, when an alkali-soluble resin as described above is used as a pigment dispersant, it is necessary to add a base in order to dissolve the resin. Organic amines such as amine, diethanolamine, triethanolamine, aminemethylpropanol and ammonia, or inorganic bases such as potassium hydroxide and sodium hydroxide are preferably used.

  In addition, in a method for producing an ink containing a pigment, it is effective to perform premixing for 30 minutes or more before the pigment is placed in an aqueous medium and stirred and dispersed. That is, such a premixing operation is preferable because wettability of the pigment surface is improved and adsorption of the dispersant on the pigment surface can be promoted.

  The disperser used in the above-described pigment dispersion treatment may be any disperser that is generally used, and examples thereof include a ball mill, a roll mill, and a sand mill. Among them, a high-speed sand mill is preferably used, 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).

  In addition, when an ink containing a pigment is used in an inkjet recording method, a pigment having an optimum particle size distribution is used because of demands such as clogging resistance. As a method for obtaining a pigment having a desired particle size distribution, Reducing the size of the grinding media of the disperser, increasing the filling rate of the grinding media, increasing the processing time, slowing the discharge speed, classifying with a filter or centrifuge after grinding, and A technique such as a combination of these techniques can be mentioned.

  In addition to the various components described above, an anionic compound such as an anionic surfactant or an anionic polymer substance is preferably added to the ink containing the pigment used in the present invention. . In particular, when an anionic compound is not used as the dispersant, it is necessary to add such an anionic substance. The addition amount at this time is 0.05 to 10% by mass, preferably 0.2 to 5% by mass. It is also a preferred embodiment that the amphoteric surfactant is adjusted to a pH below its isoelectric point. As examples of the anionic surfactant used in this case, any commonly used ones such as a carboxylate type, a sulfate type, a sulfonate type, and a phosphate type can be preferably used. . Examples of the anionic polymer include alkali-soluble resins, specifically, sodium polyacrylate, or a polymer obtained by copolymerizing acrylic acid, Of course, it is not limited to these.

  An image forming method that can suitably use the ink set according to the present invention will be described. The ink set according to the present invention includes a step of adhering the recording performance improving liquid as described above to the image forming region on the recording medium, or the image forming region and its vicinity, and at least a pigment as a colorant. It is preferably applied to an image forming method including an ink jet recording process in which ink is ejected as droplets from a discharge orifice to a recording medium in accordance with a recording signal.

  The recording medium used in the above-described image forming method is not particularly limited, and so-called plain paper such as copy paper and bond paper, which has been conventionally used, is preferably used. Of course, a coated paper specially prepared for inkjet recording and a transparent film for OHP are also preferably used. Furthermore, it can be suitably used for general high-quality paper and glossy paper.

  As a method for adhering the recording performance improving liquid on the recording medium, for example, a method of adhering the recording performance improving liquid to the entire surface of the recording medium with a spray or a roller is conceivable. This is performed by an ink jet recording method in which a recording performance improving liquid can be selectively and uniformly attached only to an image forming area and the vicinity of the image forming area. In this case, various ink jet recording methods can be used, but a method of discharging droplets using bubbles generated by thermal energy is particularly preferable.

  Next, a recording apparatus used in the above case will be described. In the present invention, a method of giving a recording signal to the recording ink of the recording head and discharging droplets by the generated thermal energy is preferable. The configuration of the recording head which is the main part of the apparatus is shown in FIGS. 1 is a cross-sectional view of the head 13 along the ink flow path, and FIG. 2 is a cross-sectional view taken along the line AB of FIG.

  The head 13 includes a heat generating head 15 having a glass, ceramic, or plastic plate having a groove 14 through which ink passes and a heat generating resistor used for thermal recording (though a thin film head is shown in the figure, this is not limitative). It is obtained by adhering The heat generating head 15 includes a protective film 16 formed of silicon oxide or the like, aluminum electrodes 17-1 and 17-2, a heat generating resistor layer 18 formed of nichrome or the like, a heat storage layer 19, a substrate with good heat dissipation such as alumina. It is 20.

  The recording ink 21 reaches the discharge orifice 22, and a meniscus 23 is formed by the pressure P. Here, when an electrical signal is applied to the aluminum electrodes 17-1 and 17-2, the region indicated by n of the heat generating head 15 rapidly generates heat, and bubbles are generated in the ink 21 in contact therewith. The meniscus 23 protrudes, becomes an ink droplet 24 from the ejection orifice 22, and flies toward the recording medium 25. FIG. 3 shows a schematic view of a recording head in which a large number of nozzles shown in FIG. 1 are arranged. The recording head is made by closely adhering a glass plate or the like 27 having a large number of flow paths and a heating head 28 similar to that described in FIG.

  FIG. 4 shows an example of an ink jet recording apparatus incorporating the head. In FIG. 4, reference numeral 61 denotes a blade as a wiping member, one end of which is held by a blade holding member to become a fixed end, and forms a currant lever. The blade 61 is disposed at a position adjacent to the recording area by the recording head 65, and in this example, is held in a form protruding in the moving path of the recording head 65. Reference numeral 62 denotes a cap on the discharge port surface of the recording head 65, which is disposed at a home position adjacent to the blade 61, moves in a direction perpendicular to the moving direction of the recording head 65, contacts the ink discharge port surface, A capping configuration is provided. Further, 63 is an ink absorber provided adjacent to the blade 61 and, like the blade 61, is held in a form protruding in the movement path of the recording head 65. The blade 61, the cap 62, and the ink absorber 63 constitute a discharge recovery portion 64, and the blade 61 and the ink absorber 63 remove moisture, dust, and the like from the ink discharge port surface.

  65 is a recording head that has discharge energy generating means and discharges ink onto a recording medium facing the discharge port surface on which the discharge port is arranged, and 66 is mounted with the recording head 65 to move the recording head. The carriage. The carriage 66 is slidably engaged with the guide shaft 67, and a part of the carriage 66 is connected to a belt 69 driven by a motor 68 (not shown). As a result, the carriage 66 can move along the guide shaft 67, and the recording area and its adjacent area can be moved by the recording head 65.

  Reference numeral 51 denotes a paper feed unit for inserting a recording medium, and 52 denotes a feed roller driven by a motor (not shown). With these configurations, the recording medium is fed to a position facing the discharge port surface of the recording head 65, and is discharged to a discharge portion provided with a discharge roller 53 as recording progresses.

  In the above configuration, when the recording head 65 returns to the home position due to the end of recording or the like, the cap 62 of the ejection recovery unit 64 is retracted from the moving path of the recording head 65, but the blade 61 protrudes into the moving path. As a result, the ejection port surface of the recording head 65 is wiped. When the cap 62 is in contact with the ejection port surface of the recording head 65 to perform capping, the cap 62 moves so as to protrude into the moving path of the recording head.

  When the recording head 65 moves from the home position to the recording start position, the cap 62 and the blade 61 are at the same position as that at the time of wiping. As a result, the ejection port surface of the recording head 65 is wiped even during this movement. The movement of the recording head 65 to the home position is not only at the end of recording or at the time of ejection recovery, but also at the home position adjacent to the recording area at a predetermined interval while the recording head 65 moves the recording area for recording. The wiping is performed along with this movement.

  FIG. 5 is a diagram showing an example of an ink cartridge 45 that contains ink supplied to the head via an ink supply member, for example, a tube. Here, reference numeral 40 denotes an ink container, for example, an ink bag, which contains ink for supply, and a rubber stopper 42 is provided at the tip thereof. By inserting a needle (not shown) into the stopper 42, the ink in the ink bag 40 can be supplied to the head. An ink absorber 44 receives waste ink. As the ink storage portion, a liquid contact surface with ink is preferably formed of polyolefin, particularly polyethylene.

  The ink jet recording apparatus used in the present invention is not limited to the one in which the head and the ink cartridge are separated as described above, but the one in which they are integrated as shown in FIG. 6 is also preferably used.

  In FIG. 6, reference numeral 70 denotes a recording unit, in which an ink storage portion that stores ink, for example, an ink absorber, is stored. The ink in the ink absorber is transferred from a head portion 71 having a plurality of orifices. It is configured to be ejected as ink droplets. As a material for the ink absorber, for example, polyurethane can be used. Reference numeral 72 denotes an atmosphere communication port for communicating the inside of the recording unit with the atmosphere. The recording unit 70 is used in place of the recording head shown in FIG. 4 and is detachable from the carriage 66. In the above description of the recording apparatus used in the present invention, an example of an inkjet recording apparatus that ejects ink droplets by applying thermal energy to the ink has been given. However, a piezoelectric type inkjet recording apparatus that uses a piezoelectric element may also be used. It can be used as well.

  When carrying out the image forming method to which the ink set according to the present invention is applied, for example, a recording apparatus in which five recording heads shown in FIG. 3 are arranged on a carriage is used. FIG. 7 shows an example. Reference numerals 81, 82, 83, and 84 denote recording heads for ejecting recording inks of yellow, magenta, cyan, and black, respectively. Reference numeral 85 denotes a head for discharging a colorless recording performance improving liquid. The head is disposed in the above-described recording apparatus, and ejects recording ink of each color according to a recording signal. Further, for example, prior to that, the colorless recording performance improving liquid is attached in advance to a portion where at least the recording ink of each color adheres to the recording medium. FIG. 7 shows an example in which five recording heads are used. However, the present invention is not limited to this. As shown in FIG. 8, recording performance of yellow, magenta, cyan, black, and colorless is achieved with one recording head. It is also preferable to carry out the improvement liquid by dividing the liquid flow path. Of course, the head may be arranged such that the recording order of the recording performance improving liquid and the ink is opposite to the above order.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In the text, “parts” and “%” are based on mass unless otherwise specified. The weight average molecular weight of the pigment ink dispersant was measured by a GPC method using styrene polymer as a standard.

<< Examples 1 and 2 >>
[Preparation of recording performance improving liquid]
(Preparation of organic fine particle dispersion)
50 parts of styrene, 40 parts of N, N-dimethylaminoethyl methacrylate and 10 parts of ethyl acrylate were solution polymerized in a conventional manner in a mixed solvent of toluene and isopropyl alcohol. After completion of the polymerization, chloromethylation was carried out to obtain a copolymer having a number average molecular weight of 7,500 and a weight average molecular weight of 13,000. Next, 4 parts of the polymer, 82 parts of ion-exchanged water, and 4 parts of ethylene glycol are mixed and heated to 60 ° C. in a water bath to completely dissolve the resin component. To this solution, 16 parts of organic fine particles having the following structural formula and 2 parts of ethyl alcohol were added, premixed for 30 minutes, and then dispersed under the following conditions.

・ Disperser: Sand grinder (Igarashi Machine)
・ Crushing media: Zirconium beads 1mm diameter ・ Filling rate of grinding media: 50% (volume)
-Grinding time: 3 hours Further, centrifugal treatment (12,000 RPM, 20 minutes) was performed to remove coarse particles to obtain an organic fine particle dispersion.

(Preparation of recording performance improving liquid A)
Using the organic fine particle dispersion obtained above, components having the following composition ratio were mixed to prepare a liquid composition containing organic fine particles, and this was used as a recording performance improving liquid A. The obtained recording performance improving liquid A was white.
・ The above organic fine particle dispersion 30.0%
・ Glycerin 10.0%
・ Ethylene glycol 5.0%
・ Surfinol 465 (trade name, manufactured by Nissin Chemical Industry Co., Ltd.)
0.2%
・ Ion exchange water 54.8%

(Preparation of recording performance improving liquid B)
In the same manner as described above, components having the following composition ratio were mixed to prepare a liquid composition containing the organic fine particle dispersion prepared earlier, and this was used as a recording performance improving liquid B.
・ The above organic fine particle dispersion 30.0%
・ Glycerin 10.0%
・ Ethylene glycol 5.0%
・ Magnesium nitrate 3.0%
・ Surfinol 465 (trade name, manufactured by Nissin Chemical Industry Co., Ltd.)
0.2%
・ Ion exchange water 51.8%

<Preparation of colored ink set 1>
A black pigment dispersion 1 was prepared from the components shown below, and a black ink Bk1 was produced using the black pigment dispersion 1 as described below. Furthermore, yellow, magenta and cyan pigment dispersions were obtained in the same manner as in the preparation of the black pigment dispersion 1, except that the colorant was changed as follows. Then, using the obtained pigment dispersion liquid of each color, pigment inks Y1, M1, and C1 were obtained, and a set having a combination of the pigment inks Bk1, Y1, M1, and C1 was defined as a colored ink set 1.

(Preparation of colored pigment dispersion 1)
-Styrene-acrylic acid copolymer (weight average molecular weight 8,000, acid value 200) 3.0 parts-Potassium hydroxide 10% aqueous solution 7.2 parts-Ion-exchanged water 69.8 parts-Ethylene glycol 5 parts

  The above components are mixed and heated to 60 ° C. in a water bath to completely dissolve the resin component. To this solution, 15 parts of carbon black (NIPEX 160 IQ, manufactured by Degussa Co., Ltd.) and 1 part of isopropyl alcohol were added, and a black pigment dispersion liquid 1 was prepared under the same conditions as those for preparing the organic fine particle dispersion liquid. .

(Preparation of ink)
[Black ink Bk1]
Using the black pigment dispersion obtained above, the following components were added and mixed and stirred to prepare a black ink Bk1.
・ Black dispersion 1 30 parts ・ Glycerin 2 parts ・ Diethylene glycol 15 parts ・ Surfinol 465 (trade name, manufactured by Nissin Chemical Industry Co., Ltd.)
1 part ・ Ion-exchanged water 52 parts

[Yellow ink Y1]
The pigment-containing yellow ink Y1 was prepared in the same manner as the black ink Bk1, except that 15 parts of carbon black (NIPex 160 IQ, manufactured by Degussa) used in the preparation of the black ink Bk1 was replaced with pigment yellow 74. Prepared.

[Magenta ink M1]
The pigment-containing magenta ink M1 was prepared in the same manner as the black ink Bk1, except that 15 parts of carbon black (NIPEX 160 IQ, manufactured by Degussa) used in the preparation of the black ink Bk1 was replaced with Pigment Red 122. Prepared.

[Cyan ink C1]
A pigment-containing cyan ink was prepared in the same manner as the black ink Bk1, except that 15 parts of carbon black (NIPEX 160 IQ, manufactured by Degussa) used in the preparation of the black ink Bk1 was replaced with pigment blue 15: 3. C1 was prepared.

  A set 1 according to Example 1 is configured using the previously prepared recording performance improving liquid A and the colored ink set 1 obtained as described above, and an image recording test is performed on PPC paper (manufactured by Canon). went. As the ink jet recording apparatus used for the test, a recording apparatus similar to that shown in FIG. 4 was used, and a color image was formed using the five recording heads shown in FIG. At this time, the recording performance improving liquid A was preliminarily deposited on the recording paper and then each ink constituting the colored ink set 1 was adhered. The recording head used here had a recording density of 600 dpi, and the driving condition was a driving frequency of 15 kHz. The discharge volume per dot was yellow, magenta, and cyan ink, and for the recording performance improving liquid A, a 6 pl head was used, and for black ink, a 10 pl head was used per dot. These recording conditions are the same throughout the examples and comparative examples in the case of using the ink containing the dye described below. The environmental conditions for the print test are unified at 25 ° C./55% RH.

<< Example 2 >>
<Creation of colored ink set 2>
A black pigment dispersion 2 was prepared from the components shown below, and a black ink Bk2 was produced using the black pigment dispersion 2. Furthermore, yellow, magenta and cyan pigment dispersions were obtained in the same manner as in the preparation of the black pigment dispersion 2, except that the colorant was changed as follows. Then, using the obtained pigment dispersion liquid of each color, pigment inks Y2, M2, and C2 were obtained, and a set having a combination of the pigment inks Bk2, Y2, M2, and C2 was set as a colored ink set 2. Next, a set 2 according to Example 2 was obtained in combination with the recording performance improving liquid A previously obtained using the obtained colored ink set 2. Then, using the obtained set 2, an image formation test was performed in the same manner as in Example 1.

(Preparation of pigment dispersion)
-1.5 parts of styrene-acrylic acid-ethyl acrylate copolymer (weight average molecular weight 7,000, acid value 180)-5.0 parts of diethylene glycol-90.5 parts of ion-exchanged water

  The above components are mixed and heated to 70 ° C. in a water bath to completely dissolve the resin component. To this solution, 1 part of newly produced carbon black (NIPEX 180 IQ, manufactured by Degussa) and 1 part of isopropyl alcohol were added, premixed for 30 minutes, and dispersed under the same conditions as in the case of producing black ink Bk1. Processed.

[Black ink Bk2]
Using the black pigment dispersion obtained above, components having the following composition ratio were mixed to prepare an ink containing a pigment, which was designated as black ink Bk2.
-30 parts of the above pigment dispersion-2 parts of glycerin-15 parts of diethylene glycol-Surfynol 465 (trade name, manufactured by Nissin Chemical Industry Co., Ltd.)
0.6 part ion-exchanged water 52.4 parts

[Yellow ink Y2]
A yellow ink containing a pigment in the same manner as the black ink Bk2, except that 1 part of carbon black (NIPEX 180 IQ, manufactured by Degussa) used in the preparation of the black ink Bk2 was replaced with pigment yellow 74 Y2 was prepared.

[Magenta ink M2]
Magenta ink M2 containing a pigment in the same manner as in the preparation of black ink Bk2, except that 1 part of carbon black (NIPEX 180 IQ, manufactured by Degussa) used in the preparation of black ink Bk2 was replaced with Pigment Red 122 Was prepared.

[Cyan ink C2]
Cyan containing pigment as in the preparation of black ink Bk2, except that 1 part of carbon black (NIPEX 180 IQ, manufactured by Degussa) used in the preparation of black ink Bk2 was replaced with pigment blue 15: 3 Ink C2 was prepared.

<< Examples 3 to 6, Comparative Example 1 >>
Instead of the recording performance improving liquid A constituting the set 1, the set using the recording performance improving liquid B obtained previously is set as the set 3 of the example 3, and the same as the example 1 except that the set 3 is used. An image formation test was conducted by the method described above. Instead of the recording performance improving liquid A constituting the set 2, the set using the previously obtained recording performance improving liquid B is set as the set 4 of the fourth embodiment, and the same procedure as in the second embodiment is performed except that the set 4 is used. An image formation test was conducted. Further, the image forming test of Example 5 was performed in the same manner as in Example 1 except that the set 1 used in Example 1 was used, and the recording performance was changed and the recording performance improving liquid A was post-printed. Further, the image formation test of Example 6 was performed in the same manner as in Example 2 except that the set used in Example 2 was used, and the recording performance was changed and the recording performance improving liquid A was post-printed. Further, the image formation test of Comparative Example 1 was conducted in the same manner as in Example 1 except that only the coloring set 1 used in Example 1 was used and the recording performance improving liquid A was not used.

  Table 1 below collectively shows image forming conditions in Examples 1 to 6 and Comparative Example 1.

[Evaluation]
Table 2 shows the evaluation results for the respective recorded images obtained under the image forming conditions in Examples 1 to 6 and Comparative Example 1 shown in Table 1 above. Evaluation was performed by the following evaluation method and evaluation criteria.

(1. Black image density)
A solid image is formed using a recording performance improving liquid and black ink (only ink is used in Comparative Example 1) constituting each set, and then left for 12 hours, and the reflection density of the image after being left is measured by a reflection densitometer. Measurement and evaluation were performed with Macbeth RD915 (manufactured by Macbeth). The evaluation criteria are as follows.
A: Reflection density is 1.40 or more.
A: The reflection density is 1.35 or more and less than 1.40.
(Triangle | delta): Reflection density is 1.25 or more and less than 1.35.
X: Reflection density is less than 1.25.

(2. Character quality)
Using the recording performance improving liquid and black ink (only ink in Comparative Example 1) constituting each set, alphanumeric black characters were printed, and the obtained images were visually evaluated. The evaluation criteria were ◎ when the feathering was hardly noticeable, ◯ when the feathering was slightly noticeable but practically acceptable, and × when the level was less than that.

(3. Breeding)
The printing mode is 1-pass, bi-directional printing, the recording performance improving liquid constituting each set, and the solid portions of each color ink of yellow, magenta, cyan and black (each ink in Comparative Example 1), Printing was performed so as to be adjacent to each other, and the degree of occurrence of bleeding at the boundary of each color was visually observed and evaluated. The evaluation criteria were “A” when almost no bleeding occurred, “O” when bleeding was slightly occurring but at a level where there was substantially no problem, and “X” when the level was not.

(4. Color image sharpness (color ink color development))
A solid image is formed using the recording performance improving liquid constituting each set and yellow, magenta, and cyan color inks, and after leaving for 12 hours, the set of Comparative Example 1 that does not use the recording performance improving liquid is used. The difference in the sharpness was visually evaluated by comparing the image printed on the inkjet dedicated paper HR-101 (manufactured by Canon Inc.). Evaluation criteria are evaluated as ◎ when the sharpness of the image is equal to or higher than that of the inkjet paper, ○ when the sharpness is slightly inferior, and × when it is lower than that. did.

  The area where the recording performance improving liquid adheres to the recording medium in the above evaluation is the same area as the ink image forming area, and the printing duty is 25% for the recording performance improving liquid and 100% for the colored ink. I went there.

  Table 2 below shows the evaluation results for the images obtained in Examples 1 to 6 and Comparative Example 1 for the above-described evaluation items. As is apparent from Table 2 below, in the examples, good images were obtained in terms of character quality, image density, bleeding, and color image sharpness (color ink color developability), whereas Comparative Example 1 However, only images with low character density and poor character quality were obtained, and bleeding and color image sharpness (color ink colorability) were also poor.

  In the case of performing color ink jet recording on plain paper, the application example of the present invention provides high image quality with a high printing quality while being high-speed fixability, and high uniformity of solid images. A recording performance improving liquid capable of providing an excellent ink jet recording image capable of obtaining a high-definition image with good color reproducibility, an ink set comprising a combination of the recording performance improving liquid and a colored ink, and the same There is an image forming method.

It is a longitudinal cross-sectional view of the head of the inkjet recording device which can be used by this invention. It is a cross-sectional view of the head of the ink jet recording apparatus that can be used in the present invention. FIG. 2 is an external perspective view of a head in which the head shown in FIG. It is a perspective view which shows an example of the inkjet recording device which can be used by this invention. It is a longitudinal cross-sectional view of an ink cartridge that can be used in the present invention. It is a perspective view showing an example of a recording unit that can be used in the present invention. FIG. 3 is a perspective view showing a recording unit in which a plurality of recording heads used in an embodiment of the present invention are arranged. It is a perspective view of another recording head used for the present invention.

Explanation of symbols

13: head 14: ink groove 15, 28: heating head 16: protective film 17-1, 17-2: aluminum electrode 18: heating resistor layer 19: heat storage layer 20: substrate 21: ink 22: ejection orifice (micropore )
23: Meniscus 24: Ink droplet 25: Recording medium 26: Multi groove 27: Glass plate 28: Heat generating head 40: Ink bag 42: Plug 44: Ink absorber 45: Ink cartridge 51: Paper feed unit 52: Paper feed Roller 53: Paper discharge roller 61: Blade 62: Cap 63: Ink absorber 64: Discharge recovery unit 65: Recording head 66: Carriage 67: Guide shaft 68: Motor 69: Belt 70: Recording unit 71: Head unit 72: Air Communication port 81, 82, 83, 84, 85: recording head

Claims (7)

In an ink set comprising a recording performance improving liquid for improving the recording performance of an inkjet ink and an inkjet ink for forming an image on a recording medium by an inkjet recording method,
An ink set, wherein the recording performance improving liquid contains at least colorless or white fine particles, and the inkjet ink contains an organic pigment as a colorant.   The ink set according to claim 1, wherein the colorless or white fine particles are organic fine particles made of an organic compound.   The ink set according to claim 2, wherein the organic fine particles are dispersed with a cationic resin. The ink set according to claim 3, wherein the organic fine particles are bismelamine compounds represented by the following general formula (I).

(However, R shows a hydrogen atom, a C1-C4 lower alkyl group, or an alicyclic group. Moreover, R < ₁ >, R < ₂ >, R < ₃ > and R < ₄ > are respectively independently a hydrogen atom, A lower alkyl group having 1 to 4 carbon atoms may be formed together with a nitrogen atom to form a heterocyclic group, and X represents a lower alkylene group having 2 to 3 carbon atoms.   The ink set according to claim 4, wherein the recording performance improving liquid contains a water-soluble polyvalent metal salt. A recording performance improving liquid for improving the recording performance of an ink-jet ink, comprising colorless or white fine particles comprising a compound of the following general formula (I) dispersed with a cationic resin: .

(However, R shows a hydrogen atom, a C1-C4 lower alkyl group, or an alicyclic group. Moreover, R < ₁ >, R < ₂ >, R < ₃ > and R < ₄ > are respectively independently a hydrogen atom, A lower alkyl group having 1 to 4 carbon atoms may be formed together with a nitrogen atom to form a heterocyclic group, and X represents a lower alkylene group having 2 to 3 carbon atoms. An image forming method using the ink set according to any one of claims 1 to 5 or the recording performance improving liquid according to claim 6.

Images