Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-02-29
2002-09-10
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S010000, C347S011000
Reexamination Certificate
active
06447085
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driving method of an ink-jet recording head in which thermal energy is made to act on ink and ink is discharged on the basis of a bubble generated thereby, and an ink-jet recording apparatus for performing the recording method.
2. Related Background Art
An ink-jet recording method, in which ink is heated to generate a bubble, ink is discharged on the basis of the generation of the bubble, and it is made to adhere onto a medium to perform image formation, has the advantages that high-speed recording is possible, the recording quality is relatively high, and the generated noise level is low.
In addition, this method has many superior advantages such as color image recording is relatively easy, recording can be performed even on a plain paper or the like, miniaturization of apparatus is feasible, and further, because the discharge outlets of a recording head can be disposed at a high density, a high-resolution and high-quality image can be recorded at a high speed. A recording apparatus using this method has been used as information output means in a copier, a printer, a facsimile, or the like,
The general construction of a recording head, in which such an ink-jet recording method is performed, comprises discharge outlets for discharging ink, ink flow passages communicating with them for ink supply and electrothermal transducing elements (heating elements) provided within those ink flow passages for generating thermal energy. Each of the heating elements is generally made of a thin-film resistance element. Thermal energy is generated by electrifying each of the heating elements through electrode wiring in a pulse manner (applying drive pulse).
When an overheated liquid layer for storing foaming energy is to be formed in ink by applying thermal energy to ink near the heating element, in a case that the state of the heating element surface (ink heating surface) has partially changed due to scorching of ink, damage, or the like, or impurities or gas has mixed in the ink, heat is hindered from flowing into the overheated liquid layer because a foaming nucleus has been generated in an early stage of heating. As a result, unevenness of foaming start times in the ink on the heating element surface occurs. Because such unevenness of foaming start times causes unevenness of foaming energy of bubbles, there may arise a change in the discharge quantity or discharge velocity of ink to deteriorate image quality.
Therefore, in order to provide an ink-jet recording head good in reproducibility of discharge characteristics of ink droplets such as discharge velocity, it is required to decrease unevenness of foaming start times. For this purpose, it is important to increase the temperature rise rate dT (t0) at the foaming time t=t0. The reason for this will be described below with reference to FIG.
16
.
Although foaming probability of ink depends on the temperature distribution in the ink, it changes from 0 to 1 when the temperature T of the portion at the highest temperature in the ink shifts from the lower temperature side to the higher temperature side of the temperature range T1<T<T2 near the overheat limit.
FIG. 16
is a diagram showing a change in the temperature T of ink in contact with a heating element surface being at the highest temperature. When the temperature rise rate at the foaming time t=t0 is dT (t0), unevenness &Dgr;t of foaming times is given by:
Δ
t
≈
T2
-
T1
d
T
(
t
o
)
(
1
)
Therefore, for decreasing the unevenness &Dgr;t of foaming start times, the temperature rise rate dT (t
0
) should be increased.
For decreasing &Dgr;t, it is known that rapid heating is effective in which the temperature of ink near a heating element surface is rapidly heated to the homogeneous nucleation temperature before a foaming nucleus is generated at the boundary surface (or interface) between ink and the heating element surface (A. Asai et al., “Bubble Generation Mechanism in the Bubble Jet Recording Process”, Journal of Imaging Technology, Vol. 14, pp. 120-124, 1988).
In case of performing rapid heating, the shorter applying time of the drive signal causes a lesser heat quantity that can fully flow into the ink, at a point in time, and so a lesser thickness of ink (overheated liquid layer) in such an overheated state that a foaming nucleus can grow to a bubble results.
A large quantity of evaporative latent heat required by the overheated liquid layer that has started the homogeneous nucleation in rapid heating is mainly supplied from the heating element side. But, there is ink at a low temperature outside the overheated liquid layer, and a large quantity of heat flows out of the thin overheated liquid layer to the ink side outside the overheated liquid layer, which is at a great difference in temperature from the overheated liquid layer. For this reason, if rapid heating is performed with shortening the applying time (heating time) of the drive signal, the essentially required quantity of evaporative latent heat cannot fully be supplied to the overheated liquid layer.
Therefore, if the heating time is shortened, foaming energy decreases, and it becomes hard to obtain a sufficient discharge velocity. (A. Asai, “Bubble Dynamics in Boiling Under High Heat Flux Pulse Heating”, J. Heat Transfer, Vol. 11B, pp. 973-978, 1991; Mitsuya et al., “Nucleus Boiling and Ink Discharge Characteristics in Ultra-rapid Heating”, Japan Hardcopy '96, A-40)
As a result, when rapid heating is performed with a shortened heating time, “initial discharge performance” is reduced and there is the possibility of no discharge in the worst case. (In case of performing no ink discharge for a certain time after an ink droplet is discharged through a nozzle, when an ink droplet is next discharged through the nozzle, trouble may arise that stable discharge cannot be performed due to an increase in viscosity of ink, and so printing falls into disorder. The discharge performance of the next droplet is referred to as “initial discharge performance”.)
Besides, unevenness in resistance of the thin film resistance bodies of recording heads or unevenness in film thickness of protection layers formed on the thin film resistance bodies, which has not been at issue in conventional driving methods, readily results in unevenness in thickness of overheated liquid layers of the recording heads. This may cause unevenness in discharge quantity, discharge velocity, or the like, of the recording heads. Similarly, if there is a change in resistance of a thin film resistance element while foaming is repeated, it causes a change in discharge characteristics of the same recording head.
As described above, in such a driving method of a rapidly-overheated region in which unevenness of foaming start times can be reduced by rapid heating but foaming energy decreases, the discharge characteristics of recording heads may be unstable and uneven due to small foaming energy, which may deteriorate image quality.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above problems, and aims to provide a driving method of an ink-jet recording head capable of performing stable ink discharge, wherein:
(1) unevenness of foaming start times is small to perform stable foaming; and
(2) foaming energy is great to ensure a sufficient discharge quantity and a sufficient discharge velocity, and to provide a recording apparatus in which such recording method is performed.
A driving method of an ink-jet recording head according to the present invention to attain such objects is a driving method of an ink-jet recording head that comprises a discharge outlet for discharging ink, an ink flow passage communicating with said discharge outlet, and a heating element for heating ink in said ink flow passage by applying a drive signal so as to generate a bubble, said head discharging ink through said discharge outlet on the basis of the generation of said bubble, wherein
said
Asai Akira
Furukawa Tatsuo
Okamura Yoshimasa
Shinjo Katsuhiko
Tsukada Mamoru
Barlow John
Dudding Alfred E
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