1. Field of the Invention
The present invention relates to a thermal ink-jet ink having excellent storage stability and an ink cartridge for containing the ink.
2. Description of the Related Art
An ink-jet recording method is a recording method involving causing a small ink droplet to fly to plain paper or a dedicated glossy medium to form an image. The method has become rapidly widespread in association with advance of a reduction in price of a recording apparatus and an increase in recording rate of the apparatus. In particular, there has been a growing need for photograph picture quality because a digital camera has become widespread, so an additional improvement in image quality and printing at an additionally high speed have been requested. Accordingly, more sophisticated techniques than the conventional ones have been requested, and examples of the techniques include: a reduction in size of an ink droplet; an increase in density at which nozzles are arranged; an increase in length of a head in association with an increase in number of nozzles; and control of ejection of an ink droplet.
On the other hand, a thermal ink-jet recording mode is a mode involving: foaming ink by utilizing thermal energy; and ejecting the ink to a recording medium. The mode enables high-speed, high-density, high-definition, high-quality recording, and is suitable for colorization and a reduction in size of a recording apparatus. A general head to be used in the recording mode includes: a substrate for an ink-jet recording head on which a heat element for foaming ink and wiring to be electrically connected to the heat element are produced; and a flow path for ejecting the ink on the substrate.
In addition, the substrate for an ink-jet recording head is modified in various ways in order that electrical energy to be inputted may be saved and a reduction in lifetime of the substrate resulting from destruction of a heat generating portion in association with the foaming of ink may be prevented. In particular, a protective layer for protecting a heat element placed between a pair of wiring patterns from ink is modified in many ways.
It is advantageous for the protective layer to have a high thermal conductivity or a small thickness from the viewpoint of thermal efficiency. However, it is advantageous for the protective layer to have a large thickness from the viewpoint of protection of wiring to be connected to the heat element from ink. Accordingly, the thickness of the protective layer must be set to an optimum thickness from the viewpoints of energy efficiency and reliability. In particular, a layer in contact with ink are affected by both of cavitation damage due to the foaming of the ink, that is, mechanical damage, and damage due to a chemical reaction with an ink component at high temperature, that is, chemical damage, so influences of the mechanical damage and the chemical damage need to be sufficiently taken into consideration.
In view of the foregoing, the protective layer of an ink-jet substrate generally has a layer having high stability against mechanical damage and chemical damage as an upper layer (i.e., layer in contact with ink), and an insulating layer for protecting wiring as a lower layer. To be specific, in general, a Ta layer, which is a layer extremely stable both mechanically and chemically, is formed as the upper layer, and an SiN layer, SiO layer, or SiC layer, which can be easily formed by using an existing semiconductor producing device and is stable, is formed as the lower layer.
Detailed description of the foregoing is as described below. An SiN layer having a thickness in the range of from about 0.2 μm or more to 1 μm or less is formed as a protective layer on wiring, and then a protective layer as an upper layer is formed. A Ta layer has a thickness in the range of from 0.2 μm to 0.5 μm, which is referred to as a cavitation resisting layer, is formed as the upper layer because the layer serves as a layer to cope with cavitation damage. With this constitution, compatibility between the lifetime and reliability of a heat element of an ink-jet substrate is achieved.
Japanese Patent Application Laid-Open No. H05-330048 discloses, as an ink-jet technique using a thermal head, an ink-jet head using a material containing Si, N, or Ir at a specific ratio for a heat element to improve durability and thermal conversion efficiency. There is also disclosed an ink containing a chelating reagent at a specific concentration from the viewpoints of improvement in ejection durability of a thermal head and in suppression of a kogation to be deposited at a heat generating portion due to ejection (see Japanese Patent Application Laid-Open No. H06-093218). There is also disclosed an ink containing an ammonium salt of an acid having a methyl group or a methylene group, and a carboxyl group (see Japanese Patent Application Laid-Open No. 2002-012803). Those conventional arts each relate to suppression of erosion of a Ta layer in association with ejection duration or the suppression of a kogation to be deposited on the Ta layer when the Ta layer is arranged as the surface layer of the protective layer of a heat generating portion. In addition, ink contains a specific compound at a specific concentration, whereby a balance between the deposition of a kogation and the erosion of the Ta layer due to ejection duration is optimized for the lengthening of the lifetime of the ink.