Inkjet ink and printing method using the same

Abstract

A inkjet ink and a method for printing on hydrophobic media such as offset coated media using the inkjet ink. An inkjet contains a pigment, water, a surfactant and 40 to 75 weight % of a polar non-protic solvent with a molecular weight of 40 to 130 which has permeability to a hydrophobic surface such as the coating of an offset coated medium.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application is a first division of copending application Ser. No. 11 / 631,346, filed Jul. 17, 2007, which is a U.S. national stage application of PCT application serial number PCT / JP2005 / 021206, filed Jun. 30, 2005.TECHNICAL FIELD[0002]The present invention relates in particular to an inkjet ink suitable for printing on hydrophobic media, such as offset coated media, and a method for printing on hydrophobic media using the inkjet ink.BACKGROUND ART[0003]Generally with a conventional inkjet printing method using an aqueous inkjet ink, printing is performed on a bond paper or other normal type of paper or on a specialized paper, typically designed to have a high ink absorbing property, etc. However, offset coated media that are suitable for offset printing are not suited for printing using an aqueous inkjet ink, because a substrate surface is coated with a smooth, hydrophobic, and non-porous coating.[0004]Even if printing using an aqueou...

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Benefits of technology

[0017]In the inkjet ink described in Patent Document 3, an aprotic polar solvent is contained at a content proportion of 5 to 40 weight % with respect to the total amount of the inkjet ink. Examination by the present inventor has shown that within this content proportion range, the effect of increasing permeability into a coating or other hydrophobic surface of an offset coated medium to improve the drying property, etc., of a print cannot be adequately obtained.

[0018]Although in order to increase the permeability into a coating, etc., a larger amount of a polar aprotic solvent must be contained, when a polar aprotic solvent that is high in molecular weight is contained at a proportion of no less than 40 weight % with respect to the total amount of the inkjet ink, the viscosity of the inkjet ink increases and this may cause degradation of discharge stability during discharge from fine nozzles of a head of an inkjet printer.

[0019]In contrast, in the present invention, because among the polar aprotic solvents described in Patent Document 3, a polar aprotic solvent having a low molecular weight of no more than 130 is used selectively and the content proportion thereof is limited to no less than 40 weight %, the permeability with respect to a hydrophobic surface can be increased to improve the drying property of a print, etc., over the conventional case while suppressing the increase of viscosity of the inkjet ink to maintain good discharge stability. Thus, according to the inkjet ink of the present invention, better printing than at present can be performed on hydrophobic media such as offset coated media.

[0020]In the present invention, the molecular weight of the polar aprotic solvent is limited to no less than 40 because when a low molecular weight polar aprotic solvent with a molecular weight less than 40 is used, the inkjet ink dries readily and tends to readily cause clogging of the above-described fine nozzles, etc. The content proportion of the polar aprotic solvent limited to no more than 75 weight % because when the content proportion exceeds 75 weight %, even if the molecular weight of the polar aprotic solvent is limited to no more than 130, the viscosity of the inkjet ink becomes high and degrades the discharge stability during discharge from the fine nozzles.

[0021]In the present invention, the polar aprotic solvent preferably has a boiling point of 150 to 250° C. When the boiling point of the polar aprotic solvent is less than 150° C., the inkjet ink dries readily and tends to readily cause clogging of the nozzles, etc. When the boiling point exceeds 250° C., the inkjet ink conversely causes difficulty in drying and the drying property after printing may degrade. In contrast, when the boiling point of the polar aprotic solvent is 150 to 250° C., the above problems can be prevented and even better printing can be performed on hydrophobic media.

[0022]As a favorable polar aprotic solvent that meets these conditions, at least one type of solvent selected from the group consisting of 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, 2-pyrrolidone, formamide, N-methylformamide, N,N-dimethylformamide, N,N-diethylpropionamide, and γ-butyrolactone can be cited. When any of these polar aprotic solvents is used, not only the various effects mentioned above can be provided but, although the details are not clear, the dispersion stability of the pigment in the inkjet ink can also be improved.

Problems solved by technology

However, offset coated media that are suitable for offset printing are not suited for printing using an aqueous inkjet ink, because a substrate surface is coated with a smooth, hydrophobic, and non-porous coating.

Even if printing using an aqueous inkjet ink is performed, because the coating does not absorb the aqueous inkjet ink, the inkjet ink is repelled by or bleeds on the coating surface and a clear print with sharp edges cannot be obtained.

Further, because the print is poor in drying property and inadequate in fixing property even upon drying, bleeding occurs readily when the print is rubbed.

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