Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
2001-08-07
2002-10-29
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
C347S096000
Reexamination Certificate
active
06471350
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of protecting the surface of the heater of an ink-jet recording head, an ink-jet recording apparatus, a recording unit and a method of prolonging the service life of an ink-jet recording head.
2. Related Background Art
Various techniques have been proposed for printing using an ink-jet recording system. For instance, Japanese Patent Application Laid-Open No. 54-51837 describes an ink-jet method (a so-called bubble jet method) of ejecting ink droplets under the effect of thermal energy. This method provides a remarkable advantage of producing high quality images at high speed and low cost on ordinary plain paper not carrying any special coat layer because the method allows to prepare a high density multi-nozzle head with ease. With this method, the heater of the recording head is rapidly heated to cause the liquid laid on the heater to generate a bubble and quickly increase its volume so that liquid droplets (ink droplets) are ejected from the nozzle that is arranged at the front end of the recording head under the effect of the quick voluminal expansion of the liquid. Then, the ejected ink droplets are forced to fly and hit the target recording medium for printing.
However, when ink of a certain type, or ink containing alkali metal ions (sodium ions, lithium ions or the like) to be more specific, is used with this bubble jet method to produce a large volume of printed paper, the surface of the heater (heat generating resistor) of the recording head can become dissolved. Therefore, it is of vital importance to suppress or prevent the phenomenon of a dissolved surface of the heater of the recording head in order to provide high quality images on a stable basis, prolong the service life of the recording head and consequently reduce the load on the part of the environment. Thus, it has been and still is a technological challenge to provide improved recording heads from the above described point of view.
Japanese Patent Application Laid-Open No. 5-320550 discloses an ink composition containing ammonium salt such as ammonium halogenide or ammonium sulfonate up to 0.2 wt % in an attempt to dissolve this problem. However, halogenide ions and sulfonic acids are strongly acidic and corrosive. Therefore, when ink having such a composition is contained in the recording apparatus for a long time, the areas of the apparatus held in contact with the ink can become corroded and the effect of preventing a surface of the head of the recording head from being dissolved (etched) can be significantly lowered.
U.S. Pat. No. 5,462,590 (Japanese Patent Application Laid-Open No. 6-220386) discloses an ink composition containing water, a coloring material and an amine compound expressed by the general formula shown below to be used for thermal ink-jet recording;
(where any one or each of any two of R1, R2 and R3 represents an alkyl group with one to five carbon atoms substituted by a carboxyl group, a sulfonic acid group or the Li, Na, K or ammonium salt thereof and each of the remaining two or the remaining one, whichever appropriate, of them represents an alkyl group with one to five carbon atoms substituted by a hydrogen atom, a hydroxyl group or a carbamoyl group).
Specific examples of amine compounds that can be used for the above ink composition include N,N-bis(2-hydroxyethyl)-2-aminosulfonic acid, N,N-bis(2-hydroxyethyl)glycine and aminoethane sulfonic acid (taurine). However, U.S. Pat. No. 6,048,390 (Japanese Patent Application Laid-Open No. 10-36735), the applicant of which is same as that of the above identified patent, describes that the addition of primary amine as covered by the above U.S. Pat. No. 5,462,590 does not necessarily result in any noticeable improvement in terms of kogation and the primary amine reacts itself near the heater due to the rapid temperature rise and becomes insoluble to aggravate the kogation when a dye having a carboxyl group is used and the pH level is regulated to between 6 and 8. In short, the patent document describes that the use of primary amine is far from advantageous under certain conditions.
SUMMARY OF THE INVENTION
Ink and the related liquid composition can contain alkali metal ions produced from hydroxide of alkali metal (such as lithium hydroxide, sodium hydroxide or potassium hydroxide) and operating as counter ions relative to the carboxyl group or the sulfonic acid group in the molecule of the coloring material in order to prevent the nozzle of the ink-jet recording head from clogging. As a result of a series of studies of the inventors of the present invention, it was found that, when solution containing an alkali metal ion is ejected repeatedly from a bubble jet system, the metal and/or the metal oxide of the outermost surface protection layer of the heater can become dissolved and the heater can give rise to broken wires to make the bubble jet system no longer able to eject ink and the related ink composition. The inventors of the present invention presume that, as the liquid composition (including ink) containing an alkali metal ion is heated excessively by the heater, the concentration of the alkali metal ion rises near the heater to make the composition highly alkaline, which by turn dissolves the protection layer on the outermost surface that is made of metal such as tantalum and/or metal oxide.
On the basis of this technological presumption, the inventors of the present invention examined the effect of adding primary amine that is denied in the above identified patent document to ink containing an alkali metal ion to find that the behavior of the added primary amine is vitally affected by the rate at which energy is applied to the heater. In other words, it is possible to maximally suppress the phenomenon of scraping the heater of ink containing both primary amine having a structure as shown in formula (1) below and an alkali metal ion by controlling the rate at which energy is applied to the heater. Additionally, the side effect of raising the level of kogation due to the addition of primary amine can be suppressed. The inventors of the present invention also found that the effect of energy control is not dependent on the type of the coloring material of the ink. More specifically, the effect of the present invention was proved for ink containing a dye having a carboxyl group with a pH level regulated to between 6 and 8 for which U.S. Pat. No. 6,048,390 reports that any addition of primary amine does not necessarily result in any noticeable improvement in terms of kogation.
On the basis of the above finding, it is therefore an object of the present invention to provide a method of protecting a surface of a heater of an ink-jet recording head to be used for applying thermal energy to the ink in the recording head and causing the recording head to eject ink.
Another object of the present invention is to provide an ink-jet recording apparatus that can print images with improved image quality and operate with a prolonged service life.
Still another object of the present invention is to provide a recording unit having a prolonged service life for printing. A further object of the present invention is to provide a method of prolonging the service life of a recording head that can print images with improved image quality at reduced cost.
In an aspect of the present invention, there is provided a method of protecting an outermost surface protection layer of a heater of an ink-jet printer having a recording head, the outermost surface protection layer of the heater containing at least metal or oxide thereof, said heater being used for an ink-jet printing process comprising the step of applying energy (E
op
) to the heater to eject the liquid composition from the recording head,
the liquid composition comprising a liquid medium, an alkali metal ion and a compound expressed by the following general formula (1):
H
2
N—(CHY)
n
—(CH
2
)
m
—X (1),
X representing a carboxyl group or a sulfonic acid group, Y representing a hydrogen atom, a carboxyl group o
Katsuragi Ryuji
Shioya Makoto
Yokoi Hideto
Barlow John
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Shah Manish
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