Method of reducing kogation of heater of ink-jet recording head, ink-jet recording method, ink-jet recording apparatus, recording unit and method for prolonging service life of recording head

A method of reducing the kogation of a surface of a heater of an ink-jet recording head of an inkjet printer, the heater being adapted for applying thermal energy to ink in order to discharge the ink from an orifice and having a top surface protecting layer containing a metal and/or a metal oxide, said method comprising applying energy in the amount of Eop to the heater for generating the thermal energy,

• wherein the ink comprises
• (a) a coloring material,
• (b) water,
• (c) diglycolic acid, and
• (d) a cation selected from the group consisting of lithium ion, sodium ion, potassium ion, ammonium ion and amine ion, and
• wherein, if the minimal amount of energy to be applied to the heater in order to make the recording head discharge the ink therefrom is Eth, the ratio of EOP/Eth satisfies the relationship:
• 1.10≦Eop/Eth≦1.80.

An ink-jet recording method comprising a step of discharging ink from an ink-jet recording head provided with a heater by applying energy in the amount of Eop to the heater, the heater having a top surface protecting layer containing a metal and/or a metal oxide,

• wherein the ink comprises
• (a) a coloring material,
• (b) water,
• (c) diglycolic acid, and
• (d) a cation selected from the group consisting of lithium ion, sodium ion, potassium ion, ammonium ion and amine ion, and
• wherein, if the minimal amount of energy to be applied to the heater in order to make the recording head discharge the ink therefrom is Eth, the ratio of Eop/Eth satisfies the relationship:
• 1.10≦Eop/Eth≦1.80.

A set of inks for thermal ink-jet recording, said inks having different colors from each other and alleviating kogation on a heater of a thermal ink-jet head, and each of said inks comprising

• (a) a coloring material,
• (b) water, and
• (c) diglycolic acid,
• wherein the pH of each of said inks is regulated with a basic compound selected from the group consisting of lithium hydroxide, potassium hydroxide, ammonium hydroxide and an organic amine.