JPH05208496A - Ink jet printing head - Google Patents

Abstract

PURPOSE:To create a halftone image with a high image quality in a simple manner by a method wherein the magnitude of a dot to be printed can be easily changed by simply and automatically changing the magnitude of a bubble to be produced. CONSTITUTION:One end of a heater 9 is connected to a common line 14. A plurality of electrodes 10, 10a, 10b, 10c are provided at intervals between both ends of the heater. These electrodes are connected to a switching means to be selected. In this manner, the magnitude of a bubble can be adjusted stepwise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet type print head which ejects ink by generating bubbles by heating with a heater.

[0002]

2. Description of the Related Art FIG. 7 shows a conventional print head of this type. In the figure, 1 is a top plate made of ceramic,
Reference numeral 2 is a base plate made of an aluminum plate, 3 is an adhesive member layer for adhering between the top plate 1 and the base plate 2, 4 is a plurality of nozzle portions formed by photolithography, and all nozzle portions 4 are at the rear end. And communicates with the common liquid chamber 5. Reference numeral 6 denotes a heater portion, on which insulating members 7 and 8 are formed on the base plate 2, and a heater 9 is formed thereon corresponding to each nozzle portion 4. Further, an electrode 10 for energizing the heater 9 is formed, and an antioxidant film 11 for preventing oxidation due to contact between the heater 9 and ink is formed on the heater 9, and a bubble (bubble) is formed thereon. Cavitation protective film 1 for protecting the heater 9 from the force of crushing
2. Further, an insulating film 13 is formed on it.

[0003]

In the conventional print head, there is one electrode 10 for each heater 9,
In the print head thus configured, the size of the bubble generated cannot be controlled by the voltage applied to the heater 9, and is determined by the size of the heater 9 and the structure of the nozzle unit 4.

Therefore, when an attempt is made to express a halftone image using this print head, it must be expressed by the area gradation of the matrix structure. For example, when the resolution of the print head is 300 dpi and halftones are represented by an 8 × 8 matrix as shown in FIG. 8, the number of grayscales that can be represented is 64, but the resolution is 8 minutes. The image quality was lowered to 1, and satisfactory image quality could not be obtained.

The present invention pays attention to the characteristic that the size of the bubble generated depends on the size of the heater, and the size of the bubble can be easily and automatically changed for printing. The size of dots can be easily changed so that a halftone image can be expressed with good image quality.

[0006]

In the print head according to the present invention, the heater is provided with a plurality of electrodes so that the energization length of the heater can be divided into several stages. For example,
One end of the heater is connected to a common line, a plurality of electrodes are provided between the one end and the other end of the heater with a space between each other, these electrodes are connected to a switching means, and the switching means connects the plurality of electrodes to each other. By selecting one of the above, the energization length of the heater between the electrode and the common line can be varied stepwise.

[0007]

The heater has a heating area divided into several stages by a plurality of electrodes, and the size of bubbles can be adjusted stepwise by selecting the electrodes.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a cross-sectional structure of a print head as an example of the present invention. The cross-sectional structure of the print head in this example is the same as the conventional example shown in FIG. 7, 1 is a top plate made of ceramics, 2 is a base plate made of an aluminum plate, 3 is a space between the top plate 1 and the base plate 2. Adhesive member layers 4 for adhering in 1. are a plurality of nozzle portions formed by photolithography, and all nozzle portions 4 communicate with a common liquid chamber 5 at their rear ends. Reference numeral 6 denotes a heater part, which is formed with insulating members 7 and 8 on the base plate 2 and Hf is formed thereon.
A heater 9 made of B ₂ is formed corresponding to each nozzle portion 4. Furthermore, in order to energize each heater 9, an electrode 10 made of an aluminum plate is formed at the end of each heater 9,
Further, on the heater 9, in order to prevent the oxidation due to the contact between the heater 9 and the ink, the antioxidant film 1 made of resin is formed.
1. A cavitation protective film 12 made of Ta for protecting the heater 9 from the force of crushing bubbles, and an insulating film 13 made of SiO are further formed thereon.

In the present invention, the electrode structure of each heater 9 is different from the conventional one, and FIG. 2 shows a plan configuration of two heaters 9 arranged in parallel. One end of each heater 9 is connected to a common wire 14 which is an electrode common to all the heaters 9. Each heater 9 is provided with the above-mentioned electrode 10 at the other end, and, for example, three electrodes 10a, 10b, 10c are provided in the middle part.
The heaters 9 are provided at intervals in the longitudinal direction of the heater 9.

FIG. 3 shows an equivalent circuit of such a structure. The electrodes 10, 10a, 10b, ...
10c is a switching element 1 for selecting these.
Connected to 5. Since the position of the connection point between the heater 9 and the electrodes 10, 10a, 10b, 10c becomes farther in the order of 10c, 10b, 10a, 10 with respect to the common line 14, the heat generation range of the heater 9 is the electrode 10. 10a ・ 1
The switching element 1 is almost aligned with the positions of 0b and 10c.
When the electrode 10 is selected in 5, the heater 9 has the largest heat generation area, and then the heat generation area gradually decreases in the order of 10a, 10b, and 10c. Therefore, the switching element 1
By selecting the electrodes 10, 10a, 10b, 10c with 5, the size of the generated bubble can be changed stepwise.

FIG. 4 shows a process from the generation of bubbles due to heating of the heater 9 to the ejection of ink from the nozzle portion 4. Since the thermal time constant of the heater 9 is small, the temperature rises rapidly when a current flows. Now, assuming that the electrode 10b is selected, in the heater 9, a current mainly flows between the common wire 14 and the electrode 10b, and this range becomes high in temperature, and as shown in FIG. Many nuclear bubbles 30
Occurs. As shown in (B), the nuclear bubbles 30 combine to form a film bubble 31, which grows and the ink droplet 32 starts to project from the tip of the nozzle portion 4 as shown in (C). The heat is taken away by the surrounding ink 33 and the ink droplet 32 contracts as shown in (D), and the ink droplet 32 is contracted by the inertial force of the ink droplet 32.
As shown in (E), the recording paper 34 collides with the recording paper 34 from the leading edge of the recording paper. On the other hand, the film bubble 31 completely disappears by the pulse input for the next heater heating.

Therefore, four electrodes 1 are provided in each heater 9.
By selecting 0, 10a, 10b, or 10c, the diameter of the printed dots changes in four steps as shown in FIG.

Therefore, the print head having such a structure expresses a halftone, for example, the resolution of the print head is 3
When it is set to 00 dpi and 64 gradations are expressed, it can be expressed by a 4 × 4 matrix as shown in FIG. That is, 4 × 4 × 4 = 64 gradations. In this case, the actual resolution is 300/4 = 75 dpi, and a satisfactory image quality can be achieved in terms of the number of gradations and the resolution.

[0014]

According to the present invention, the size of the generated bubble can be changed stepwise by selecting the electrode of the heater. That is, the diameter of the dots to be printed can be changed stepwise by a simple control of selecting the electrodes of the heater, so that a halftone image can be expressed easily and with good image quality.

[Brief description of drawings]

FIG. 1 is a perspective view showing a cross-sectional structure of a print head according to the present invention.

FIG. 2 is a plan configuration diagram of a heater in the print head.

FIG. 3 is an equivalent circuit diagram of the above.

FIG. 4 is an operation explanatory diagram showing a process from bubble generation due to heating of a heater to ink ejection from a nozzle portion.

FIG. 5 is a diagram showing that the diameter of a printed dot changes stepwise.

FIG. 6 is a diagram showing an example in which a print head according to the present invention represents 64 gradations with a 4 × 4 dot matrix.

FIG. 7 is a perspective view showing a cross-sectional structure of a conventional print head.

FIG. 8 is a diagram showing an example in which 64 gradations are expressed by an 8 × 8 dot matrix by a conventional print head.

[Explanation of symbols]

 9 Heater 10 ・ 10a ・ 10b ・ 10c Electrode 14 Common line 15 Switching element

Claims (2)

[Claims] 1. An ink jet type print head for ejecting ink by generating bubbles by heating with a heater, wherein a plurality of electrodes are provided on the heater and the energization length of the heater is divided into several stages. , Inkjet print head. 2. One end of the heater is connected to a common wire,
2. The ink jet print head according to claim 1, wherein a plurality of electrodes are provided between the one end and the other end of the heater at a distance from each other, and these electrodes are connected to a switching means.