vinylpyrrolidone, vinyl sulfonic acid or salts thereof, vinylt› rimethoxysilane, and vinyltriethoxysilane. 

[0070] Examples of the ally! compound monomers include allylsulfonic acid or salts thereof, allylamine, ally! chloride, diallylamine, and diallyldimethylammonium salts. 

[0071] Examples of the olefin monomers include ethylene, and propylene. Examples of the diene monomers include butadiene, and chloroprene. 

[0072] Examples of the oligomers having unsaturated car› bon atoms include styrene oligomers having methacryloyl groups, styrene-acrylonitrile oligomer having methacryloyl groups, methyl methacrylate oligomers having methacryloyl groups, dimethyl siloxane oligomers having methacryloyl groups, and polyester oligomers having acryloyl groups. 

[0073] In the presence of a strong alkali or strong acid, the water-dispersible resin may suffer from premature or uncon› trolled destabilization and/or swelling and/or breakage of the molecular chains, such as dispersion breakage and hydroly› sis, and thus the pH of the water-dispersible resin is preferably 4 to 12, and particularly, from the view point of miscibility with water-dispersible colorants, it is more preferably 6 to 11, and still more preferably 7 to 9. 

[0074] The water-dispersible resin preferably has a func› tion to fix the water-dispersible colorant on the surface of paper, to form a coat at normal temperature and to improve fixability of coloring material. Therefore, the minimum film forming temperature (MFFT) of the water-dispersible resin is preferably 60° C. or lower, more preferably 45° C. or lower, even more preferably 30° C. or lower. Alternatively, water dispersible resins having a higher MFFT, typically up to 100° C. may be used in combination with a plasticizing cosolvent in order to lower the MFFT of the latex composition. Further, if the glass transition temperature of the water-dispersible resin is -40° C. or lower, tucks may occur in printed matters because of the increased viscidity of the resin coat. Thus, the water-dispersible resin preferably has a glass transition tem› perature of -30° C. or higher. 

[0075] The content of the water-dispersible resin added in the ink of the present invention is preferably from 1-40 weight % based on the total weight of the ink, and it is more prefer› ably from 1.5-30 weight%, and it is still more preferably from 2-25 weight%. 

[0076] Even more preferably, the amount of the water-dis› persible resin contained in the inkjet ink, as a solid content, is 2.5 weight% to 15 weight%, and more preferably 3 weight% to 7 weight %, relative to the total ink composition. 

[0077] The average particle diameter (D50) of the water› dispersible resin is preferably from 10 nm-1 µm, it is more preferably from 10-500 nm, and it is still more preferably from 20-200 nm, and especially preferably it is from 50-200 nm. 

[0078] When the average particle diameter (D50) is equal to or less than 10 nm, significant effects in improving the image quality or enhancing transfer characteristics of the image cannot be fully expected, even if aggregation occurs. 

[0079] The average particle diameter (D50) of the water› dispersible resin is relevant to the viscosity of the dispersion liquid. In the case of water-dispersible resins having the same composition, the smaller the particle diameter, the higher is the viscosity at the same solid content. The average particle diameter (D50) of the water-dispersible resin is preferably 50 nm or greater to prevent the resulting ink from having exces› sively high viscosity. 

[0080] When the average particle diameter (D50) is equal to or greater than 1 µm, there may be a possibility that the ejection characteristics of the ink from the inkjet head or the storage stability of the ink will be deteriorated. In order not to impair the ink ejection stability, the average particle diameter (D50) of the water-dispersible resin is preferably 200 nm or smaller, and more preferably 150 nm or smaller. 

[0081] In addition, there are no specific restrictions to the particle size distribution of the polymer particles, and it is possible that the polymer particles have a broad particle size distribution or the polymer particles have a particle size dis› tribution of monodisperse type. 

[0082] In an embodiment, the ink composition according to the present invention comprises two or more water-dispers› ible resins selected from the above cited synthetic resins, synthetic copolymer resins and natural polymer compounds in admixture with each other. 

## Water-Dispersible Colorant 

[0083] A water-dispersible colorant may be a pigment or a mixture of pigments, a dye or a mixture of dyes or a mixture comprising pigments and dyes, as long as the colorant is water-dispersible. 

[0084] In the inkjet ink according to the present invention, a pigment is primarily used as a water-dispersible colorant in view of the weatherability, and, for the purpose of controlling color tone, a dye may be contained within the range not impairing the weatherability. The pigment is not particularly limited and may be suitably selected in accordance with the intended use. 

[0085] Examples of the pigment usable in the present invention include those commonly known without any limi› tation, and either a water-dispersible pigment or an oil-dis› persible pigment is usable. For example, an organic pigment such as an insoluble pigment or a lake pigment, as well as an inorganic pigment such as carbon black, is preferably usable. 

[0086] Examples of the insoluble pigments are not particu› larly limited, but preferred are an azo, azomethine, methine, diphenylmethane, triphenylmethane, quinacridone, anthraquinone, perylene, indigo, quinophthalone, isoindoli› none, isoindoline, azine, oxazine, thiazine, dioxazine, thiaz› ole, phthalocyanine, or diketopyrrolopyrrole dye. 

[0087] For example, inorganic pigments and organic pig› ments for black and color inks are exemplified. These pig› ments may be used alone or in combination. As the inorganic pigments, it is possible to use carbon blacks produced by a known method such as a contact method, furnace method and thermal method, in addition to titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red and chrome yellow. 

[0088] As the organic pigments, it is possible to use azo pigments (including azo lake, insoluble azo pigments, con› densed pigments, chelate azo pigments and the like), polycy› clic pigments (e.g., phthalocyanine pigments, perylene pig› ments, perynone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pig› ments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments), dye chelates ( e.g., basic dye type chelates, and acidic dye type chelates), nitro pigments, nitroso pigments, aniline black. Among these, particularly, pigments having high affinity with water are preferably used. 

[0089] Specific pigments which are preferably usable are listed below. 

