Ink composition for inkjet recording, recording method and record

Background of the invention

<u style="single">Field of invention</u> INDUSTRIAL APPLICABILITY The present invention is an ink composition for inkjet recording and an ink composition thereof, which are excellent in glossiness, color reproducibility, ejection stability, and clogging recovery even in various recording media, particularly printing paper. The present invention relates to an inkjet recording method using.

<u style="single">Background technology</u> The inkjet recording method is a printing method in which droplets of ink are made to fly and adhere to a recording medium such as paper for printing. In recent years, innovative advances in inkjet recording technology have led to the use of inkjet recording methods in the field of high-definition printing, which has been realized only by silver halide photography and offset printing. Along with this, a high-gloss recording medium comparable to photographic paper and art paper used in the fields of silver-salt photography and offset printing, so-called special paper, is used for inkjet recording, and the glossiness is comparable to that of silver-salt photography. Inkjet recording inks that can realize images with the above have been developed. Inkjet recording inks have been developed that can achieve image quality comparable to that of silver halide photographs even when plain paper is used.

As the ink used for inkjet recording, a water-based ink containing water as a main component and containing a colorant and various additives is generally used. As a colorant, pigments are superior to dyes in terms of weather resistance such as light resistance, gas resistance, water resistance, and moisture resistance, and therefore pigment-based inks that take advantage of the characteristics of pigments are being developed. .. For example, in Japanese Patent Application Laid-Open No. 2005-194500 (Patent Document 1), a polysiloxane compound is used as a surfactant and an alkanediol such as 1,2-hexanediol is added as a solubilizing agent to eliminate bleeding. , An ink composition having excellent glossiness with respect to special paper is disclosed. Further, in JP-A-2001-72905 (Patent Document 2) and JP-A-2003-12583 (Patent Document 3), 1,2-hexanediol, which is a water-soluble alkanediol, and a poorly water-soluble alkanediol are used. An ink in which a certain 1,2-octanediol is added to an ink and has less bleeding than plain paper is disclosed. Further, Japanese Patent Application Laid-Open No. 2005-263970 (Patent Document 4) contains an acetylene glycol compound and a polysiloxane compound as surfactants, and further uses 1,2-octanediol for high printing on plain paper. An ink composition capable of achieving a density is disclosed.

By the way, in recent years, with the spread of image forming technology from digital data, the needs for digital color proof (DTP) are increasing, especially in the printing field, and the inkjet recording method has begun to be applied to DTP. Since DTP requires color reproduction and stability reproduction of printed matter, special paper for inkjet recording is usually used when producing a proof by an inkjet recording method. However, there is a high demand for color proofing applications, and if it can be output directly to the printing paper without using special paper and used as the final proofing sample, it is considered that the cost of proofing can be significantly reduced. This printing paper is a coated paper provided with a layer that receives oil-based ink on its surface, and because the coating layer has a poor ink absorption capacity, it is a water-based pigment ink that is generally used for inkjet recording. When used, the penetrability of the ink into the recording medium is low, and blurring and uneven aggregation may occur in the image.

To solve such a problem, if a highly permeable ink containing the above-mentioned polysiloxane-based surfactant and 1,2-hexanediol as a solubilizing agent thereof is used, bleeding is improved, but bleeding is improved. In some cases, proofs, final printed matter, color reproduction, and stable reproducibility became problems.<patcit num="1"><text>Japanese Patent Application Laid-Open No. 2005-194500</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 2001-72905</text></patcit><patcit num="3"><text>Japanese Unexamined Patent Publication No. 2003-12583</text></patcit><patcit num="4"><text>Japanese Unexamined Patent Publication No. 2005-263970</text></patcit>

Outline of the invention

The present inventors have recently added two specific types of alkanediol and a polyorganosiloxane compound as a surfactant to an ink in combination to make them glossy even in various recording media, especially printing paper. It was found that an ink composition having excellent ejection stability and clogging recovery as well as excellent color reproducibility can be realized. The present invention is based on such findings.

Therefore, an object of the present invention is to obtain an ink composition for inkjet recording which is excellent in glossiness, good color reproducibility, ejection stability and clogging recovery even in various recording media, especially printing paper. To provide.

The ink composition for inkjet recording according to the present invention is an ink composition for inkjet recording containing at least a colorant, water, an alkanediol, and a surfactant, and the alkanediol is water-soluble. 1,2-Alkanediol and the poorly water-soluble 1,2-Alkanediol are contained, and the surfactant is polyorganosiloxane.

According to the present invention, it is possible to realize an ink composition for inkjet recording having excellent glossiness and good color reproducibility even in various recording media, particularly printing book paper.

Specific description of the invention

The ink composition for inkjet recording according to the present invention contains a colorant, water, an alkanediol, and a surfactant as essential components, and the alkanediol includes a water-soluble 1,2-alkanediol. , Two types of alkanediols, which are poorly water-soluble 1,2-alkanediols, are used, and polyorganosiloxane is used as the surfactant. Hereinafter, each component will be described.

&lt;Alkanediol&gt; The alkanediol used in the ink composition for inkjet recording according to the present invention includes at least two types of alkanediols, a water-soluble 1,2-alkanediol and a poorly water-soluble 1,2-alkanediol. contains. By using these two specific types of alkanediol together with the surfactant described below, an image having excellent glossiness and good color reproducibility even on a recording medium having a surface coated with a resin such as printing paper. Can be realized. Further, even when applied to plain paper, strike-through is improved, so that it can be suitably used for double-sided printing. The reason for this is not clear, but it can be considered as follows.

As described above, the highly permeable ink used for conventional inkjet recording is preferably 1,2-hexanediol or 4-methyl-1,2-pentanediol in order to reduce surface tension and improve bleeding. It is used. However, in order to add only water-soluble 1,2-alkanediol such as 1,2-hexanediol to make the surface tension extremely low, it is necessary to add a large amount. For example, the surface tension of a 15 wt% aqueous solution of 1,2-hexanediol or 4-methyl-1,2-pentanediol is 25 to 26 mN / m. This increases the viscosity of the ink and thus reduces the ink weight of the dots. Therefore, it becomes difficult to precisely control the ink weight of the dots, and when the ink is ejected from the head, the landing position may shift, mist formation may occur, or printing durability may deteriorate. As a result, the color development property may be lowered, the graininess may be deteriorated, uneven aggregation and intercolor bleeding may occur, which may cause printing defects. On the other hand, if only the poorly water-soluble 1,2-alkanediol such as 1,2-octanediol is added, the poorly water-soluble 1,2-alkanediol in the ink may separate and cause printing defects, especially at a low temperature. It may also be inferior in storage stability at low and high temperatures. On the other hand, when dissolved using an acetylene glycol-based surfactant as in the ink described in JP-A-2005-263970, the storage stability at high temperature may be inferior.

Further, when the ink droplets adhere to the recording medium, the surfactant selectively and preferentially permeates into the recording medium, and there is a transient permeation period in which the relative amount of the surfactant of the ink droplets staying on the surface of the recording medium becomes insufficient. To do. In this transient permeation period, the surface tension of the ink rises sharply, so that the ink cannot completely permeate the recording medium and overflows, resulting in agglutination spots and poor drying. In particular, when a conventional ink containing alkanediol is applied to the printing paper, the ink receiving layer is thin and the amount of ink absorbed by the recording medium is lower than that of the inkjet recording paper, so 1 inch / m.²It is considered that the weight of ink per ink (amount of coloring material) is reduced and the color reproducibility is deteriorated. In the present invention, the relative amount of the surfactant is deficient by adding two specific types of alkanediol, a water-soluble 1,2-alkanediol and a poorly water-soluble 1,2-alkanediol. Even in the transient permeation period, the surface tension is suppressed from rising sharply, and by containing the lipophilic, poorly water-soluble alkanediol, the affinity with the printed book paper having an oil-based coating layer causes poor permeation. Overflow, cohesive spots, and poor drying can be reduced.

In addition, an ink composition containing a large amount of a water-soluble penetrant such as water-soluble 1,2-alkanediol may be inferior in color development property on plain paper due to its remarkable permeability, but it is poorly water-soluble 1, By appropriately emulsifying or completely dissolving an oil such as 2-alkanediol with a water-soluble penetrant such as 1,2-alkanediol, deterioration of color development can be prevented. This is a color material pigment in which the poorly water-soluble 1,2-alkanediol, which is an oily substance, permeates the fiber of plain paper preferentially, swells the fiber, and is dispersed in the water-soluble component. It is considered that the penetration between the fiber layers of the fiber is hindered.

In the present invention, as the water-soluble 1,2-alkanediol, 1,2-alkanediol having 5 or 6 carbon atoms, which may have branches, is preferable, and 4-methyl-1,2-pentanediol, 1 , 2-Pentanediol, 3,3-dimethyl-1,2-butanediol, 1,2-hexanediol. In particular, among these, it is preferable to use 1,2-hexanediol and / or 4-methyl-1,2-pentanediol.

The water-soluble 1,2-alkanediol is preferably contained in an amount of 3% by weight or more, more preferably 3 to 15% by weight, based on the entire ink composition. Within this range, the separation of the poorly water-soluble 1,2-alkanediol can be suppressed and the discharge is stable.

As the poorly water-soluble 1,2-alkanediol, it is preferable to use one having 1,2-alkanediol having 8 or more carbon atoms which may have a branch, and 4,4-dimethyl-1,2. -Pentanediol, 5-methyl-1,2-hexanediol, 1,2-heptanediol, 1,2-octanediol can be mentioned. In particular, it is preferable to use 1,2-octanediol.

The poorly water-soluble 1,2-alkanediol is preferably contained in an amount of 0.3 to 15.0% by weight, more preferably 0.3 to 3.0% by weight, based on the entire ink composition. Within this range, the separation of the poorly water-soluble 1,2-alkanediol can be suppressed and the discharge is stable. Further, even if the amount of water-soluble 1,2-alkanediol exceeding 15 wt% is not contained, the surface tension can be extremely lowered, which is effective in lowering the viscosity, suppressing aggregation, and storing stability. For example, the surface tension of an aqueous solution containing 7 wt% 4-methyl-1,2-pentanediol and 3 wt% 1,2-octanediol is 25 mN / m or less.

In the present invention, the content ratio of the water-soluble 1,2-alkanediol to the poorly water-soluble 1,2-alkanediol is preferably 10: 1 to 1: 1 on a weight basis. By setting the mixing ratio in this range, the separation of the poorly water-soluble 1,2-alkanediol can be suppressed and the discharge is stable. In addition, strike-through and / or agglomeration spots can be further reduced.

Further, in the present invention, the penetrating solvent includes 1.2-alkanediol and / or lactams and / or lactones having 5 to 10 carbon atoms to which a polyoxyethylene chain and / or a polypropylene chain is added. May be good.

&lt;Surfactant&gt; The ink composition for inkjet recording according to the present invention contains a surfactant as an essential component. By using a surfactant as the recording medium, the surface of which is coated with a resin for receiving ink, the glossiness is more important even in a recording medium such as photographic paper. It is possible to realize an image having. In particular, even when a recording medium such as this printing paper in which a coating layer for receiving oil-based ink is provided on the surface receiving layer, bleeding between colors can be prevented. At the same time, it is possible to prevent whitening due to reflected light of light generated as the amount of ink adhered increases.

Further, the penetrating solvent may contain 1.2-alkanediol and / or lactams and / or lactones having 5 to 10 carbon atoms to which a polyoxyethylene chain and / or a polypropylene chain is added.

&lt;Surfactant&gt; The ink composition for inkjet recording according to the present invention contains a surfactant as an essential component. By using a surfactant as the recording medium, the surface of which is coated with a resin for receiving ink, the glossiness is more important even in a recording medium such as photographic paper. It is possible to realize an image having. In particular, even when a recording medium such as this printing paper in which a coating layer for receiving oil-based ink is provided on the surface receiving layer, bleeding between colors can be prevented. At the same time, it is possible to prevent whitening due to reflected light of light generated as the amount of ink adhered increases.

As the surfactant used in the present invention, an organopolysiloxane-based surfactant is used. When an organopolysiloxane-based surfactant is used, since it contains the above-mentioned two specific types of alkanediol, the solubility of the surfactant in the ink is improved and the generation of insoluble matter and the like can be suppressed. Therefore, an ink composition having more excellent ejection stability can be realized.

In addition, as an organopolysiloxane-based surfactant, the following formula:<chemistry num="1"><img file="JP2007277342A_D0001.tif" /></chemistry>(In the formula, R represents a hydrogen atom or a methyl group, a represents an integer of 7 to 11, m represents an integer of 20 to 70, and n represents an integer of 2 to 5.) It is more preferable that it contains two or more compounds. By using such a specific organopolysiloxane-based surfactant, uneven ink aggregation can be further improved.

Further, as another preferred embodiment of the present invention, in the polysiloxane compound represented by the above formula, R represents a hydrogen atom or a methyl group, a represents an integer of 2 to 5, and m represents an integer of 20 to 70. Representing, n represents an integer of 2 to 4, and may contain one or more compounds.

When each of the above polyorganosiloxane compounds is contained, as a surfactant, in the above formula, R represents a hydrogen atom or a methyl group, a represents an integer of 9 to 13, and m represents 2 to 4. It represents an integer, and n preferably contains a polysiloxane compound representing 1 or 2. By using such a polysiloxane compound in combination, uneven ink aggregation can be further improved.

The reason why the agglutination unevenness of the ink can be improved by containing the specific polyorganosiloxane compound as described above is considered as follows. That is, for example, in an aqueous solution containing 20 wt% of glycerin (glycerol), 10 wt% of 1.2-hexanediol, and 0.1 wt% of the above-mentioned surfactant, the surface tension of the aqueous solution at 1 Hz becomes 25 mN / m or less, which is described above. It is considered that this is because the aqueous solution containing glycols can have an extremely low surface tension by containing the surfactant. The surface tension of Surfinol 465, which is an acetylene glycol-based surfactant, is 25 mN / m or more when it is made into an aqueous solution having the same composition as described above.

Commercially available surfactants as described above may be used, for example, KF-954A, KF-353A, KF6017, X-22-6551, AW-3 (all manufactured by Shin-Etsu Chemical Co., Ltd.). Etc. can be used.

The surfactant is preferably contained in the ink composition according to the present invention in an amount of 0.01 to 2.00% by weight, more preferably 0.05 to 0.50% by weight. In particular, when the above-mentioned surfactant in which R is a methyl group is used, it is preferable to increase the content as compared with the case where the above-mentioned surfactant in which R is H is used.

In the ink composition according to the present invention, other surfactants, specifically, fluorine-based surfactants, acetylene glycol-based surfactants, anionic surfactants, nonionic surfactants, amphoteric surfactants and the like are further added. It may be added.

Among these, examples of the acetylene glycol-based surfactant include 2,4,7,9-tetramethyl-5-decine-4,7-diol and 3,6-dimethyl-4-octyne-3,6-. Examples include diols, or 3,5-dimethyl-1-hexin-3ol, 2,4-dimethyl-5-hexin-3-ol, and the like. Commercially available products of acetylene glycol-based surfactants can also be used, for example, Orphine E1010, STG, Y (trade name, manufactured by Nissin Chemical Co., Ltd.), Surfinol 61, 104,82,465,485 or TG (trade name, trade name,). (Manufactured by Air Products and Chmicals Inc.).

&lt;Colorant&gt; As the colorant used in the ink composition for inkjet recording according to the present invention, both dyes and pigments can be used, but pigments can be preferably used from the viewpoint of light resistance and water resistance.

As the pigment, an inorganic pigment and an organic pigment can be used, and each of them can be used alone or in combination of two or more. As the inorganic pigment, for example, in addition to titanium oxide and iron oxide, carbon black produced by a known method such as a contact method, a furnace method, or a thermal method can be used. Examples of the organic pigment include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, etc.), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, etc. Dioxazine pigments, thioindigo pigments isoindolinone pigments, quinofuralone pigments, etc.), dye chelate (for example, basic dye type chelates, acidic dye type chelates, etc.), nitro pigments, nitroso pigments, aniline black and the like can be used.

Specific examples of the pigment may be appropriately given according to the type (color) of the ink composition to be obtained by using the pigment dispersion liquid according to the present invention. For example, as pigments for yellow ink compositions, CI Pigment Yellow 1, 2, 3, 12, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114 , 128, 129, 138, 139, 147, 150, 151, 154, 155, 180, 185, etc., and one or more of these are used. Of these, it is particularly preferable to use one or more selected from the group consisting of CI Pigment Yellow 74, 110, 128 and 147. Examples of pigments for magenta ink compositions include CI Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, 123, 168, 184, 202, 209; CI Pigment Violet 19, etc., and one or more of these are used. Of these, it is particularly preferable to use one or more selected from the group consisting of CI Pigment Red 122, 202, 209 and CI Pigment Violet 19. Examples of pigments for cyan ink compositions include CI Pigment Blue 1, 2, 3, 15: 2, 15: 3, 15: 4, 15:34, 16, 22, 60; CI Bat Blue 4, 60 etc. are mentioned, and one or more of these are used. Of these, CI Pigment Blue 15: 3 and / or 15: 4 is particularly preferred, and CI Pigment Blue 15: 3 is particularly preferred. Examples of pigments for black ink compositions include carbon blacks (CI pigment black 7) such as furnace black, lamp black, acetylene black and channel black, and inorganic pigments such as iron oxide pigments; aniline black (CI pigment). Examples include organic pigments such as black 1).

In the present invention, the pigment is preferably a pigment that has been kneaded with a dispersant described later, and even a pigment that has not been surface-treated can form an excellent color image.

&lt;Dispersant&gt; The ink composition according to the present invention preferably contains a copolymer resin of a hydrophobic monomer and a hydrophilic monomer as a dispersant for dispersing the colorant. These copolymer resins are adsorbed on the pigment to improve the dispersibility.

4-Butanediol dimethacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, polyethylene Glycol diacrylate, polyethylene glycol dimethacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, dipropylene glycol diacrylate, dipropylene glycol dimethacrylate, trimethylpropantriacrylate , Trimethylolpropan trimethacrylate, glycerol acrylate, glycerol methacrylate, styrene, methylstyrene, vinyltoluene and the like. These may be used alone or in admixture of two or more.

Specific examples of the hydrophilic monomer include acrylic acid, methacrylic acid, maleic acid, itaconic acid and the like.

The copolymer resin of the hydrophobic monomer and the hydrophilic monomer has both glossiness of a color image, bronze prevention, and storage stability of the ink composition, and can form a color image having more excellent glossiness. , Styrene- (meth) acrylic acid copolymer resin, styrene-methylstyrene- (meth) acrylic acid copolymer resin, or styrene-maleic acid copolymer resin, (meth) acrylic acid- (meth) acrylic acid ester copolymer resin , Or at least one of a styrene- (meth) acrylic acid- (meth) acrylic acid ester copolymer resin.

The copolymer resin may be a resin (styrene-acrylic acid resin) containing a polymer obtained by reacting styrene with acrylic acid or an ester of acrylic acid. Alternatively, the copolymerized resin may be an acrylic acid-based water-soluble resin. Alternatively, these salts such as sodium, potassium and ammonium may be used.

The content of these copolymer resins is 100 parts by weight of the pigment from the viewpoint of achieving both glossiness of a color image, bronze prevention, and storage stability of the ink composition and forming a color image having more excellent glossiness. On the other hand, it is preferably 10 to 50 parts by weight, and more preferably 10 to 35 parts by weight.

Examples of preferable surfactants as dispersants include fatty acid salts, higher alkyl dicarboxylates, higher alcohol sulfate esters, higher alkyl sulfonates, condensates of higher fatty acids and amino acids, sulfocarbonate ester salts, and naphthene. Anionic surfactants such as acid salts, liquid fatty oil sulfate esters, alkylallyl sulfonates; cationic surfactants such as fatty acid amine salts, tetraammonium salts, sulfonium salts, phosphoniums; polyoxyethylene alkyl ethers , Polyoxyethylene alkyl esters, sorbitan alkyl esters, polyoxyethylene sorbitan alkyl esters and the like, nonionic surfactants and the like can be mentioned. Needless to say, the above-mentioned surfactant also functions as a surfactant by being added to the ink composition, but it is necessary to add the above-mentioned surfactant so that the contact angle with the recording medium is within the above range. is there.

(3) Water and Other Components The ink composition for inkjet recording according to the present invention contains the above-mentioned specific solvent, surfactant, and various other additives, and also contains water as a solvent. As the water, it is preferable to use pure water such as ion-exchanged water, ultra-filtered water, reverse osmosis water, distilled water, or ultrapure water. In particular, water obtained by sterilizing these waters by irradiating them with ultraviolet rays or adding hydrogen peroxide is preferable because it prevents the growth of mold and bacteria for a long period of time.

The ink composition for inkjet recording according to the present invention can further contain an organic amine. When forming a recording image, the wettability to the recording surface such as a recording medium can be enhanced to enhance the permeability of the ink, and the pH of the ink composition can be easily adjusted to a suitable range. .. As the organic amine, a tertiary amine can be preferably used.

Examples of the tertiary amine include alkanolamines such as triethanolamine. The pH of the ink composition according to the present invention is preferably 8 to 12, particularly preferably 8 to 10. When the pH is within the applicable range, deterioration of the member in contact with the ink can be prevented.

The content of the organic amine with respect to the total weight of the ink composition is 0.1% by weight or more, but when forming a recording image, it is possible to improve the wettability to the recording surface such as a recording medium and enhance the ink permeability. It is possible, and from the viewpoint of ink ejection stability, storage stability, and high-speed printing, it is preferably 0.1 to 8.0% by weight, more preferably 0.5 to 5.0% by weight, and further preferably 1.0 to 3.0% by weight.

Further, the ink composition according to the present invention preferably contains a penetrant in addition to the above components.

As the penetrant, glycol ethers can be preferably used.

Specific examples of glycol ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-iso-butyl ether, and ethylene glycol mono-tert. -Butyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, diethylene glycol mono-iso-propyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono-tert-butyl ether, triethylene Glycol mono-n-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-iso-propyl ether, propylene glycol mono-n-butyl ether, propylene glycol mono-tert- Butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol-iso-propyl ether, dipropylene glycol mono-n-butyl ether, dipropylene glycol mono-tert- Examples thereof include butyl ether and 1-methyl-1-methoxybutanol, which can be used as one or a mixture of two or more of these.

Among the above glycol ethers, alkyl ethers of polyhydric alcohols are preferable, and especially ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether, and triethylene. Glycol monomethyl ether, triethylene glycol monoethyl ether or triethylene glycol mono-n-butyl ether is preferred. More preferably, it is triethylene glycol mono-n-butyl ether.

The amount of the penetrant added may be appropriately determined, but is preferably about 0.1 to 30% by weight, more preferably about 1 to 20% by weight.

Further, the ink composition according to the present invention preferably contains a recording medium dissolving agent in addition to the above components.

As the recording medium solubilizer, pyrrolidones such as N-methyl-2-pyrrolidone and / or lactones such as γ-butyrolactone can be preferably used. The amount of the recording medium dissolving agent added may be appropriately determined, but is preferably about 0.1 to 30% by weight, more preferably about 1 to 20% by weight.

Further, the ink composition for inkjet recording according to the present invention preferably contains a wetting agent. As the wetting agent, polyhydric alcohols and / or sugars can be preferably used. Specific examples of the polyhydric alcohols include glycerin, ethylene glycol, diethylene glycol, triethylene glycol, trimethylolpropane and the like. Specific examples of saccharides include monosaccharides, disaccharides, oligosaccharides (including trisaccharides and tetrasaccharides) and polysaccharides, preferably glucose, mannose, fructose, ribose, xylose, arabinose, galactose, aldonic acid, etc. Glucitol, (Solbit), martose, cellobiose, lactoose, sucrose, trehalose, maltotriose, etc. can be mentioned. Here, polysaccharide means a sugar in a broad sense, and is used to include substances widely present in nature such as alginic acid, α-cyclodextrin, and cellulose. Further, as a derivative of these saccharides, the reducing sugar of the above-mentioned saccharide (for example, sugar alcohol (general formula HOCH))₂(CHOH)_nCH₂OH (represented here as an integer of n = 2 to 5), oxidized sugars (eg, aldonic acid, uronic acid, etc.), amino acids, thiosaccharides, etc.). Sugar alcohols are particularly preferable, and specific examples thereof include maltitol, sorbitol, and xylitol. As a commercially available product, HS500 (manufactured by Hayashibara Shoji) can also be preferably used. As the hyaluronate, those commercially available as a 1% aqueous solution of sodium hyaluronate (molecular weight 350,000) can be used. Further, trimethylolpropane and 1,2,6-hexatriol can also be preferably used.

The amount of the wetting agent added may be appropriately determined, but is preferably 0.1 to 30% by weight, more preferably about 1 to 20% by weight, and further preferably 6 to 16% by weight. It is clear to those skilled in the art that some of the above-mentioned penetrating solvents also act as wetting agents.

The ink composition according to the present invention may further contain a nozzle clogging inhibitor, a preservative, an antioxidant, a conductivity regulator, a pH regulator, a viscosity regulator, a surface tension regulator, an oxygen absorber, and the like. it can.

Examples of preservatives and fungicides include sodium benzoate, sodium pentachlorophenol, sodium 2-pyridinethiol-1-oxide, sodium sorbate, sodium dehydroacetate, 1,2-dibenzinethiazolin-3-one ( ICI's Proxel CRL, Proxel BND, Proxel GXL, Proxel XL-2, Proxel TN) and the like can be mentioned.

Further, examples of pH adjusters, solubilizers or antioxidants include amines such as diethanolamine, triethanolamine, propanolamine and morpholin and their variants, potassium hydroxide, sodium hydroxide, lithium hydroxide and the like. Inorganic salts, ammonium hydroxide, quaternary ammonium hydroxide (such as tetramethylammonium), potassium carbonate, sodium carbonate, carbonates such as lithium carbonate and other phosphates, or N-methyl-2-pyrrolidone, urea, thiourea. , Ureas such as tetramethylurea, alohanates, alohanates such as methylalohane, biurets such as biuret, dimethylbiuret, tetramethylbiuret, and the like, L-ascorbic acid and salts thereof.

In addition, the ink composition according to the present invention may contain an antioxidant and an ultraviolet absorber, for example, Tinuvin 328, 900, 1130, 384, 292, 123, 144 of Ciba Specialty Chemicals. , 622, 770, 292, Irgacor 252 153, Irganox 1010, 1076, 1035, MD1024, oxides of lanthanide and the like.

The ink composition according to the present invention can be produced by dispersing and mixing each of the above components by an appropriate method. Preferably, the pigment, the polymer dispersant and the water are first mixed with a suitable disperser (eg, ball mill, sand mill, attritor, roll mill, agitator mill, Henschel mixer, colloid mill, ultrasonic homogenizer, jet mill, ong mill, etc.). Mix to prepare a uniform pigment dispersion, then add a separately prepared resin (resin emulsion), water, water-soluble organic solvent, sugar, pH adjuster, preservative, antifungal agent, etc. to dissolve sufficiently. Prepare an ink solution. After sufficiently stirring, filtration can be performed to remove coarse particle diameters and foreign substances that cause clogging to obtain the desired ink composition.

<u style="single">Inkjet recording method</u> In the inkjet recording method according to the present invention, droplets of the above ink composition are ejected and the droplets are adhered to a recording medium for printing, and the ejected ink droplets are arranged so that dots overlap. It is attached to a recording medium. In the recording method according to the present invention, it is preferable to use a printed book paper as a recording medium, and even when such a specific recording medium is used, an image having excellent glossiness and good color reproducibility can be realized.

Further, in the inkjet recording method of the present invention, it is preferable to eject droplets of the ink composition so that the dot arrangements in the direction perpendicular to the scanning direction of the recording head are alternately arranged. When the dots are formed so as to have such a checkered pattern arrangement, when the ink composition of the present invention described above is used, the aggregation unevenness is remarkably improved as compared with the conventional ink composition.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

&lt;Preparation of Ink Composition&gt; Each ink was prepared by mixing each component according to the composition shown in Table 1 below and filtering with a 10 μm membrane filter.<tables num="1"><img file="JP2007277342A_D0002.tif" /></tables><tables num="2"><img file="JP2007277342A_D0003.tif" /></tables> The styrene-acrylic acid resin in the table is a copolymer having a molecular weight of 1600 and an acid value of 150.

&lt;Evaluation&gt;<u style="single">Discharge stability</u> Using an inkjet printer (PX-G900, manufactured by Seiko Epson), solid and line patterns were continuously printed at 5 ° C (low temperature) in the recommended clean mode of photo paper for each ink. We observed missing ink dots and flying bends within 1000 pages of printing, and evaluated them based on the following criteria. A: There are no missing dots or flying bends. B: 10 or less missing dots and flying bends. C: There are more than 10 missing dots and flying bends.

The evaluation results are as shown in Table 2 below.

<u style="single">Evaluation of clogging recovery</u> Using the above inkjet printer, fill the head with each ink and check that the ink is ejected from all the nozzles, then remove the ink cartridge and remove the recording head in order to accelerate the drying state at the nozzles. With the head cap removed, it was left in an environment of 40 ° C 20% RH for 1 week.

After being left unattended, the cleaning operation was repeated until all nozzles ejected at the same level as the initial discharge, and the ease of recovery was evaluated according to the following criteria. A: It recovers to the same level as the initial one by cleaning within 3 times. B: Recovers to the same level as the initial stage by cleaning within 6 times. C: After 6 cleaning operations, after leaving for 6 hours, recovers to the same level as the initial stage with one more cleaning.

The evaluation results are as shown in Table 2 below.

<u style="single">Color development</u> Install Ink Set 1 in the ink cartridge of the same inkjet printer as above, select "Plain Paper Recommended Clean Mode", and set "No Gloss Optimizer" to 720 x 720 dpi on Xerox 4024 paper (manufactured by Xerox). After solid printing at 25 ° C and leaving for 24 hours at 25 ° C, the OD value of the recording surface was measured using SPM50 manufactured by Gretag. The color development of the image was evaluated based on the following criteria. A: OD value is 1.2 or more B: OD value is 1.1 or more and less than 1.2 C: OD value is less than 1.1

Similarly, the color reproducibility of ink sets 2 to 9 was evaluated. The evaluation results are as shown in Table 2.

<u style="single">Strike through</u> Install ink set 1 in the ink cartridge of the same inkjet printer as above, select "Photo paper recommended clean mode", and set "No gloss optimizer" to Xerox 4024 paper (manufactured by Xerox) at 1440 x 720 dpi. After solid printing at 25 ° C and leaving for 24 hours at 25 ° C, the OD value of the back surface of the recording surface was measured using SPM50 manufactured by Gretag. The degree of strike-through was evaluated based on the following criteria. A: OD value is less than 0.06 B: OD value is 0.06 or more

Similarly, the color reproducibility of ink sets 2 to 9 was evaluated. The evaluation results are as shown in Table 2.

<u style="single">Ink agglomeration unevenness</u> For each ink obtained above, attach the ink set 1 to the ink cartridge of the same inkjet printer as above, and print on OK Topcoat Plus (manufactured by Oji Paper Co., Ltd.), which is the main printing paper, at a resolution of 1440 x 1440 dpi. went. As a printing condition at this time, the ink ejection amount was adjusted so that the dot weight was 7 ng in the unidirectional recording method in which the resolution was 720 × 180 dpi by one drive of the recording head. The drive head is 200 cps.

In the obtained recorded material, the unevenness of ink aggregation was evaluated according to the following criteria. AA: 5.2mg / inch²Even with the ink weight of, there is no uneven aggregation A: 4.4 mg / inch²Even with the ink weight of, there is no uneven aggregation, but 5.2 mg / inch²At the ink weight of, agglomeration occurs. B: 3.6mg / inch²Even with the ink weight of, there is no uneven aggregation, but 4.4 mg / inch²At the ink weight of, agglomeration occurs. C: 3.6mg / inch²Even with the weight of the ink, uneven aggregation occurs.

Similarly, the aggregation unevenness was evaluated for the ink sets 2 to 9. The evaluation results are as shown in Table 2.<tables num="3"><img file="JP2007277342A_D0004.tif" /></tables>