Ink-jet print head and method thereof

Details Ink-jet print head and method thereof Ink-jet print head and method thereof

2002-12-04

2003-12-16

Stephens, Juanita (Department: 2853)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

C029S890100, C029S611000

Reexamination Certificate

active

06663226

ABSTRACT:

This application claims the benefit of Korean Patent Application No. 2001-80902, filed Dec. 18, 2001, in the Korean Industrial Property office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink-jet print head, and more particularly, to an inkjet print head having a nozzle plate, a heat element formed on the nozzle plate, and a thermal shunt formed in the nozzle plate such that thermal accumulation on the nozzle plate can be effectively prevented
2. Description of the Related Art
Ink ejection mechanisms of ink-jet print heads include an electro-thermal transducer having a heat source generating bubbles to eject ink by using a bubble-jet method, and an electromechanical transducer having a piezoelectric device varying a volume of the ink caused by deformation of the piezoelectric device to eject the ink.
The bubble-jet method of the electro-thermal transducer is classified into a top-shooting method, a side-shooting method, and a back-shooting method according to a relationship between a growing direction of the bubbles and an ejecting direction of an ink droplet of the ink. In the top-shooting method, the growing direction of the bubbles is the same as the ejecting direction of the ink droplet, in the side-shooting method, the growing direction of the bubbles is perpendicular to the ejecting direction of the ink droplet, and in the back-shooting method, the growing direction of the bubbles is opposite to the ejecting direction of the ink droplet.
A basic principle of the back-shooting method and a structure of an ink-jet print head using the same are disclosed in U.S. Pat. No. 5,760,804 to Heinzl et al. issued Jun. 2, 1998. In addition, various structures used for the back-shooting method are disclosed in U.S. Pat. No. 4,847,630 to Bhaskar et al. issued Jul. 11, 1989 and U.S. Pat. No. 6,019,457 to Silberbrook issued Feb. 1, 2000.
FIG. 1
is a cross-sectional view of a conventional ink-jet print head.
A chamber
1
a
having a hemispheric shape is formed in a substrate
1
, which is formed of silicon, etc., and an ink inlet
1
b
connected to an ink supply source (not shown) is formed in a lower portion of the chamber
1
a
. A nozzle plate
2
is formed on the substrate
1
and above the chamber
1
a
, a nozzle
3
is formed in the nozzle plate
2
, and an ink droplet
15
a
is ejected from the nozzle
3
.
The nozzle plate
2
includes a thermal insulation layer
2
a
and a chemical vapor deposition (CVD) overcoat
2
b
formed on the thermal insulation layer
2
a
. The insulation layer
2
a
and the CVD overcoat
2
b
correspond to a portion of the substrate
1
. The insulation layer
2
a
has a first surface facing the substrate
1
and a second surface contacting the heat element
8
.
A heat element
8
is disposed adjacent to the nozzle
3
to surround the nozzle
3
. The heat element
8
is disposed in an interface area between the thermal insulation layer
2
a
and the overcoat
2
b
, and a thermal shunt
9
transferring heat from the heat element
8
to ink
15
in the chamber
1
a
and transferring redundant heat to the substrate
1
through the insulation layer
2
a
is formed above an upper side of the heat element
8
.
In the conventional ink-jet print head, if a current pulse is applied to the heat element
8
, the heat is generated from the heat element
8
, and bubbles
7
are formed from the first surface of the insulation layer
2
a
. After that, while heat is continuously generated from the heat element
8
, the heat is continuously supplied to the bubbles
7
, and thus the bubbles
7
expand. Due to the expansion of the bubbles
7
, pressure is applied to the ink
15
disposed in the chamber
1
a
, and thus the droplet
15
a
of the ink
15
in a vicinity of the nozzle
3
is ejected to an outside of the nozzle plate
2
through the nozzle
3
. After that, additional ink
15
is sucked into the chamber
1
a
along an ink channel or passage direction
5
, and thus the chamber
1
a
is refilled with the additional ink
15
.
In the conventional ink-jet print head using the back-shooting method, as described above, the heat element
8
arranged around the nozzle
3
of the nozzle plate
2
is formed between the insulation layer
2
a
and the overcoat
2
b
, which constitute the nozzle plate
2
, and the heat element
8
is connected to an electric line (not shown) to receive current from a power source. The electric line is also formed between the insulation layer
2
a
and the overcoat
2
b.
If the current is supplied to the heat element
8
, heat generated from the heat element
8
is transferred to the ink
15
in the chamber
1
a
, and thus the bubbles
7
are formed in the ink
15
. However, remaining redundant heat may be accumulated on the nozzle plate
2
, but the thermal accumulation of the remaining redundant heat is prevented by the thermal shunt
9
. In other words, the thermal shunt
9
prevents the thermal accumulation on the nozzle plate
2
. The temperature of the nozzle plate
2
raised by the remaining redundant heat, which is has not been transferred to the ink
15
in the chamber
1
a
, is lowered when the remaining redundant heat is transmitted to the substrate
1
. If the temperature of the nozzle plate
2
is increased to more than a predetermined temperature, a lifetime of the ink-jet print head is shortened, and the performance of an ink-jet ejection operation is lowered. The problem with the thermal accumulation may not occur in a structure in which the heat element
8
is directly formed on the substrate
1
but occurs in another structure having the heat element
8
formed on a portion spaced-apart from the substrate
1
, for example, on the nozzle plate
2
having a membrane structure with a large heat transfer resistance as shown in FIG.
1
.
Likewise, in the ink-jet print head having the heat element
8
formed on the nozzle plate
2
, the thermal shunt
9
is used to improve the above thermal accumulation. However, with the thermal shunt
9
of the conventional ink-jet print head, it is very difficult to efficiently transfer or radiate the remaining redundant heat to the substrate
1
. In addition, the thermal shunt
9
is made of a conductor, such as aluminum, and is extended above the heat element
8
and between upper and lower material layers. Since the thermal shunt
9
is disposed very close to the heat element
8
, cracks are generated due to the thermal stress caused by a difference between thermal expansion coefficients of the thermal shunt
9
and the upper and lower material layers.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide an inkjet print head, which is capable of more effectively preventing excessive thermal accumulation on a nozzle plate.
Additional objects and advantageous of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the above and other objects, there is provided an ink-jet print head. The ink-jet print head includes a substrate, a channel formed on the substrate to supply ink in an ink passage direction, a nozzle plate connected to the substrate and including a nozzle corresponding to the channel, a heat element disposed in the nozzle plate to surround the nozzle, a thermal conduction layer formed on an upper side of the heat element, an intermediate insulation layer formed between the thermal conduction layer and the heat element, and a first thermal shunt spaced-apart from the heat element by a predetermined interval in a direction parallel to a major surface of the nozzle plate not to overlap the heat element and connecting the thermal conduction layer to the substrate.
The thermal conduction layer is made of diamond like carbon (DLC) or silicon carbide (SiC), and a passivation layer is formed on an upper surface of the thermal conduction layer, and a hydrophobic layer is formed on the passivation

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