Dec. 11, 2014  5  US 2014/0364548 Al  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.  [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.  Water-Dispersible Colorant 