Method of protecting heater surface of ink-jet printer, ink-jet recording apparatus, recording unit and method of prolonging service life of ink-jet recording head

An ink-jet recording apparatus comprising a liquid composition container containing a liquid composition, an ink-jet recording head having a heater for applying thermal energy to the liquid composition and a means for applying a pulse-shaped electric signal to said heater according to the information to be recorded, said heater having an outermost surface protection layer containing at least metal or oxide thereof;

• said liquid composition comprising an aqueous liquid medium, an alkali metal ion and a compound expressed by the following general formula (1):
• H2N—(CHY)n—(CH2)m—X (1)
• X representing a carboxyl group or a sulfonic acid group, Y representing a hydrogen atom, a carboxyl group or a sulfonic acid group, n representing 0 or 1, m representing an integer from 0 to 2;
• said apparatus satisfying the relation as defined by the following formula (2):
• 1.10≦Eop/Eth≦1.90 (2),
• Eop representing the energy applied to the heater in order to cause the recording head to eject the liquid composition, Eth representing the minimum energy required by the recording head to eject the liquid composition.

A recording unit comprising a liquid composition container containing a liquid composition and an ink-jet recording head having an orifice for ejecting the liquid composition under the effect of thermal energy, said ink-jet recording head being provided with a heater for applying thermal energy to the liquid composition, said heater having an outermost surface protection layer containing at least metal or oxide thereof;

• said liquid composition comprising an aqueous liquid medium, an alkali metal ion and a compound expressed by the following general formula (1):
• H2N—(CHY)n—(CH2)m—X (1),
• X representing a carboxyl group or a sulfonic acid group, Y representing a hydrogen atom, a carboxyl group or a sulfonic acid group, n representing 0 or 1, m representing an integer from 0 to 2:
• said recording unit satisfying the relation as defined by the following formula (2):
• 1.10≦Eop/Eth≦1.90 (2),
• Eop representing the energy applied to the heater in order to cause the recording head to eject the liquid composition, Eth representing the minimum energy required by the recording head to eject the liquid composition.

A method of prolonging a life span of a recording head to be used for an ink-jet recording method comprising a step of applying thermal energy to a liquid composition and causing it to be ejected through an orifice, said recording head being provided with a heater for applying thermal energy to the liquid composition, said heater having an outermost surface protection layer containing at least metal or oxide thereof;

• said liquid composition comprising an aqueous liquid medium, an alkali metal ion and a compound expressed by the following general formula (1):
• H2N—(CHY)n—(CH2)m—X (1),
• X representing a carboxyl group or a sulfonic acid group, Y representing a hydrogen atom, a carboxyl group or a sulfonic acid group, n representing 0 or 1, m representing an integer from 0 to 2;
• said method satisfying the relation as defined by the following formula (2):
• 1.10≦Eop/Eth≦1.90 (2),
• Eop representing the energy applied to the heater in order to cause the recording head to eject the liquid composition, Eth representing the minimum energy required by the recording head to eject the liquid composition.