JPH0820110A - Thermal inkjet printer - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to a thermal inkjet printer, and an object of the present invention is to provide a head capable of eliminating density control without impairing print density and color balance. [Structure] SiO having a thickness of 2 μm or less on a Si substrate
_The ink is formed by applying a voltage having a constant pulse width of 3 μS or less to the heating resistor, which has a heating substrate in which _two layers and a heating resistor without a protective layer are sequentially stacked, an ink discharge nozzle, and a liquid path. In an ink jet printer for recording by causing fluctuation nucleate boiling in a part of the ink in the liquid path and discharging the ink from the ink discharge nozzle by the expansion force of the bubble, the height of the ink liquid path is more than 30 μm. The structure is such that the vertically projected image of the bottom of the ink ejection nozzle onto the heating resistor surface overlaps the heating resistor within ± 5 μm, and the viscosity of the ink used for this has a value of 0.7 to 6 C.P. Use water-based ink.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called thermal ink jet printer, which is a recording apparatus of a type in which thermal energy is used to eject ink droplets toward a recording medium.

[0002]

2. Description of the Related Art Two methods have been put into practical use for an ink ejection head used in a thermal ink jet printer. One is that the heating resistor formed on one wall surface (substrate) of the ink liquid path and the ink ejection direction are parallel to each other (JP-A-54-161935, JP-A-55-27281). No. 55-27282), and the other one is vertical (JP-A-54-5).
1837). In both cases, it is the same that a portion of the ink is rapidly vaporized by pulse heating, and the ink droplets are ejected from the orifice by its rapid expansion and contraction. The basic constitution of the heating resistor is a thin film resistor It is the same in that it is covered with a protective layer of (Hewlet
t Packard Journal, Aug.1988 and Nikkei Mechanical 19
(See p. 58 of December 28, 1992).

It is well known that the print density changes depending on the head temperature as a characteristic common to the two types of ink ejection heads that have been put to practical use.

FIG. 3 shows the Electrophotographic Society of Japan, Vol. 28, No. 4 (1).
989) published on P82, it is shown that the head temperature rises by printing and the image density rises proportionally.

The reason why the image density depends on the head temperature is
This is related to the fact that the viscosity of ink greatly changes with temperature as shown in FIG. Therefore, in order to prevent the image density from changing, an actual printer is provided with means for adjusting the temperature such as heating and cooling so that the head temperature can be kept constant.

The above-mentioned measures for keeping the head temperature constant becomes a little complicated in the case of a full-color printer using a plurality of heads. That is, since the duty (the number of times of printing per unit time) of the heads of each color is different, there is a difference in the temperature rising rate of each head, and it is not easy to eliminate the difference in head temperature in batch air cooling that is normally used. Can not.
Further, it is difficult to completely match the viscosity of each color ink and its temperature dependence, and in the end, the head with a low duty is subjected to extra heating so as to match with a head with a high duty. By doing so, it is possible to keep the density and color balance constant for the first time.

[0007]

In the conventional thermal ink jet printer, "initial heating" for ensuring a constant density in the initial state of printing is indispensable in addition to the above-mentioned accurate control of the head temperature. Time for warming up is also required.

An object of the present invention is to provide a head which can eliminate the need for temperature control without impairing the print density and color balance, and to provide a simple thermal ink jet printer which is easy to use.

[0009]

The above object is to provide a heat generating substrate in which a SiO ₂ layer having a thickness of 2 μm or less and a heat generating resistor without a protective layer are sequentially laminated on a Si substrate, and to the heat generating resistor surface. An ink discharge nozzle oriented vertically or substantially vertically and a liquid path communicating with the ink discharge nozzle for supplying ink are provided, and a voltage having a constant pulse width of 3 μS or less is applied to the heating resistor. In this way, in the ink jet printer for performing recording by causing fluctuation nucleate boiling in a part of the ink in the ink liquid passage, and discharging the droplet ink from the ink discharge nozzle by the expansion force of the bubble, Has a height of less than 30 μm, and a vertical projection image of the bottom of the ink discharge nozzle onto the heating resistor surface overlaps the heating resistor within ± 5 μm. The viscosity of the click is accomplished by an aqueous ink having a value of 0.7~6C.P..

[0010]

When the head constructed as described above is filled with water-based ink having a viscosity in the above range and ejected, the ejected ink droplet ejects a fixed amount of ink without causing tailing and sub-drops. It becomes possible. That is, according to the printer configured as in the present invention, even if the head temperature changes and the ink viscosity changes, the ejected ink amount does not change, and therefore the print density does not change. Therefore, the energy required to raise the temperature of the head to a predetermined temperature and adjust the temperature is also unnecessary.

As described above, the printer having the configuration of the present invention can maintain the print density and the color balance in good condition without controlling the temperature of the head, and is not affected by the environmental temperature. I understand.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of a thermal ink jet print head according to the present invention, and FIG.
A B'cross section is shown.

On the silicon substrate 1, S having a thickness of 1 to 2 μm is formed.
An iO ₂ thermal oxide film (not shown) and a heating resistor 2 which does not require a protective layer are sequentially laminated to form a heating substrate. Examples of the heating resistor 2 that does not need the protective layer include C described in Japanese Patent Application Laid-Open No. 6-71888 by the present inventor.
A heating resistor 2 composed of an r-Si-SiO alloy thin film resistor and a Ni thin film conductor is formed. In addition, in the efficient ink ejection by the heating resistor without the protective layer, the amount of electric power applied to the head can be reduced to 1/10 or less, so that the head temperature hardly increases due to printing.

Although only the heating resistor portion is shown in FIGS. 1 and 2 for the sake of simplification, in the case of an actual head, a patent application invention by the present inventor, Japanese Patent Application No. 5-90123.
As disclosed in Japanese Patent Application No. 5-272452, a driver circuit is formed on the silicon substrate 1 to be monolithic.

In order to form a liquid path on the silicon substrate 1, a partition wall 3 is formed with a photosensitive resin or the like, and its height (thickness) is formed.
G was 30 μm or less, here 20 μm. The width W of the individual ink passage (liquid passage) 7 is 50 μm, and the pitch thereof is 62.5 μm (400 dot / inch). The heating resistor 2 has a square shape, and one side thereof has a length of 40 μm. In this step, the ink groove 5 is formed in the silicon substrate 1, the orifice plate 4 is adhered and cured on the partition wall 3, and R = 40 μm is formed by photo dry etching.
The mφ discharge nozzle 8 is formed. In this case, the orifice plate 4 is made of a polyimide film having an epoxy adhesive layer and a thickness of 60 μm. By this process,
It is possible to manufacture a large number of heads that are accurately aligned with each other on a 5 inch or 6 inch Si wafer with a high yield.

The head exemplified in this embodiment is 400 dpi.
In this process, a linear array of orifices is 800 dpi, and a head of 1600 dpi can be manufactured by arranging the orifice arrays on both sides of one ink groove 5. Moreover, 4 sets of these, the same S
By making it on the i substrate, it is possible to manufacture even a full color line head of 1600 dpi.

With the above arrangement, Japanese Patent Application No. 6-
As described in No. 21060, the amount of ink ejected at one time is almost equal to the amount of ink up to the meniscus existing on the heating resistor.

The print densities when the heads shown in FIGS. 1 and 2 are filled with the water-based inks (a), (b) and (c) shown in FIG. 4 respectively, and the head temperature is changed from 5 ° C. to 40 ° C. I checked. However, in order to exclude the influence of the extension of the refill time due to the ejection on the low temperature side, the ejection repetition frequency was evaluated as 2 KHz, which is sufficiently slow for this head. It should be noted that when using pure water to discharge at 5 ° C, 15 KH
It has been confirmed by stroboscopic observation that the ejected water droplets are stable with respect to the ejection repetition frequency of z.

The image density results are shown in FIG. As can be seen from these results, the image density decreases when the viscosity of the water-based ink exceeds 6 C.P., but as long as the viscosity is 6 C.P.
The image density does not change even if the head temperature is raised to 40 ° C. Then, using pure water, the head temperature was 40 ° C. (the viscosity of pure water at this time was about 0.7 C.P.), and the discharge water droplets were observed with a strobe. I have confirmed that it is not different from the case of. That is, as long as the viscosity is at least in the range of 0.7 to 6 C.P., the volume of the ejected ink droplet is invariable, so that the image density is constant. It is considered that the reason why the image density is lowered when the amount exceeds 6 C.P. is that the amount of ink remaining on the inner wall surface of the ejection nozzle increases.

As described above, as long as the viscosity is in the range of 0.7 to 6 C.P., it is possible to print with a constant image density even if the head temperature changes. It is also easy to keep constant.
That is, it has been shown that it is not necessary to match the temperature dependence of the viscosity of the full-color ink, without limiting.

However, in the case of an ink having a high viscosity, the refill time becomes long and it becomes impossible to follow the high-speed ejection repetition frequency, resulting in a decrease in density. Further, as the viscosity becomes higher, the ejection speed of ink drops becomes slower. Therefore, the ejection repetition frequency may be set according to the relationship between the lower limit of the head temperature and the ink viscosity. Of course, this is not the case when the head scanning speed in the case of serial scan recording is slow.

Even if the head temperature is 5 ° C. or lower,
If the ink viscosity is 6 C.P. or less, there will be no hindrance to normal printing. However, in general, the viscosity of the ink sharply rises to make the printing unstable, and the evaporated water after printing condenses on the head and the periphery of the head, causing various problems. To prevent this, a method of exhausting air from the surface of the recording paper immediately after printing (Japanese Patent Application No.
However, keeping the head temperature at 5 ° C. or higher is a very effective method for preventing dew condensation.

[0023]

According to the present invention, since the print density does not depend on the environmental temperature and the print conditions, it is not necessary to control the temperature of the head, and a small size, low cost and high quality printer can be realized. . This is a great advantage when applied to a full-color printer, and constant and invariant color balance can be easily realized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view (cross-sectional view taken along the line AA ′ in FIG. 2) showing an embodiment of a thermal inkjet printhead according to the present invention.

FIG. 2 is a sectional view taken along line B-B ′ of FIG.

FIG. 3 is a reference diagram showing changes in head temperature and image density when serial scan recording is performed (Electrophotographic Society Vol. 28 No. 4 (1989) P. 82).

FIG. 4 is a characteristic diagram showing temperature changes in viscosity of pure water and typical water-based inks.

FIG. 5 is a characteristic diagram showing the head temperature dependence of image density when the head of the present invention is used.

[Explanation of symbols]

1 is a silicon substrate, 2 is a heating resistor, 3 is a partition wall, 4 is an orifice plate, 5 is an ink groove, 6 is a common ink passage, 7 is an individual ink passage, 8 is an ejection nozzle, 9 is an ink meniscus, and R is The inner diameter of the discharge nozzle (more precisely, the inner diameter of the bottom of the discharge nozzle), G is the distance between the heating resistor 2 and the bottom surface of the orifice plate 4, T is the thickness of the orifice plate, and H is H.
Is the length of one side of the square heater, and W is the width of the individual ink passage 7.

Claims (1)

[Claims] 1. A SiO substrate having a thickness of 2 μm or less on a Si substrate.
A heat generating substrate in which _two layers and a heat generating resistor without a protective layer are sequentially laminated, an ink discharge nozzle oriented in a direction perpendicular or almost perpendicular to the heat generating resistor surface, and the ink discharge nozzle for supplying ink. And a liquid passage communicated with
A fluctuation pulse nucleate boiling is caused in a part of the ink in the ink liquid path by applying a voltage of a constant pulse width of 3 μS or less to the heating resistor, and the expansive force of the bubble causes a droplet shape from the ink discharge nozzle. In an ink jet printer that ejects ink to perform recording, the height of the ink liquid path is lower than 30 μm, and a vertical projection image of the bottom of the ink ejection nozzle onto the heating resistor surface is within ± 5 μm with the heating resistor. A thermal ink jet printer characterized by having an overlapping structure and using an aqueous ink having a viscosity of 0.7 to 6 C.P.