Ink jet print head

Abstract

An ink jet print head comprises a substrate formed with a heating resistor, an ink path defining member for defining an ink supply path, and an orifice plate, and in the orifice plate, there is formed an ink outlet at the position opposing the heating resistor. Further, a heating zone surrounding the heating resistor is formed at the position corresponding to the heating resistor of the ink supply path. The channel resistance of the ink supply path is set so that a relationship is established between a quantity q of the discharged ink drop, a sectional area A of the ink outlet, and a maximal projection h that a meniscus of the ink has when it projects from the ink outlet after it has restored the exit level from a retreat position it had after the drop of the ink had been discharged such that 0<h<0.3q/A 0<h<0.25q/A. Consequently, there is obtained a high-speed printing of high quality without dispersion.

Description

BACKGROUND OF THE INVENTION

The present invention relates to an ink jet print head for discharging ink drops from ink outlets by use of thermal energy.

Description of the Related Art

Recently, in contrast with the wire dot printing methods, non-impact recording method is attracting interest became the recording noise level is negligible. In particular, an ink et recording method is attractive as it permits high-speed recording on ordinary paper without the need of a deposition treatment on the paper side. In the field, therefore, aiming at an optimal ink discharge performance, various approaches have been made, with associated implementations.

In the ink jet recording method, a recording is effected with discharged droplets of recording liquid, called "ink" deposited on a recordable material. This method is categorized into several systems according to the manner in which the drops of recording liquid are formed.

FIG. 1 illustrates a bubble jet recording system as a conventional example. The conventional system includes a substrate 32 provided with a heating resistor 30, a channel plate member 36 for defining an ink supply path 34, and an orifice plate 40 formed with an orifice as an ink outlet 38 communicating with the ink supply path 34. The heating resistor 30 rapidly heats to vaporize a volume of ink supplied on a heating zone surrounding the resistor 30, causing ink bubbles 42 to grow, exerting pressures therearound so that an ink drop is discharged from the ink outlet 38, with trailing droplets 50, 52 as shown in FIG. 2.

Grown bubbles 42 become deflated as they are cooled by surrounding ink, and fade out with ink vapour therein condensed to be liquidated.

A consumed volume of ink by the discharge is supplemented from an ink pool through the ink supply path 34, due to capillary forces acting on an ink meniscus 44 retreating inside the ink outlet 38.

To permit a high-speed recording, it is desirable to repeat a discharge of an ink drop in a short period, supplementing at a high speed a volume of ink consumed during every discharge through the ink outlet 38.

In a conventional implementation, the diameter of the ink outlet 38 is reduced to have an increased capillary force, and the channel resistance of the ink supply path 34 is reduced.

Thus, ink is supplemented at an increased speed, and with an increased momentum, which causes, as shown in FIG. 1, an elongated ink pillar 46 to project from the ink outlet 38, before it deforms into an ink drop. In the deformation, the elongated ink pillar 46 is broken so that a leading upper portion is changed into a main drop 48 and a trailing lower portion is separated into a number of relatively large low-speed satellites 50, 52 such as in FIG. 2. Such satellites adversely affect the printing.

Moreover, as a volume of ink is supplemented with an increased momentum, as shown in FIG. 3, an ink meniscus 44 at a top end of the ink outlet 38 has an increased tendency to convex outside and concave inside of the outlet 38. The meniscus 44 thus vibrates with a reduced damping ratio. That is, the vibration of the meniscus 44 is not readily stopped.

As the ink discharge is repeated in a short period, a subsequent discharge occurs immediately after the supplement of ink, so that it may occur when the ink meniscus 44 starts convexing above the ink outlet. This causes an undesirable deformation of an ink drop and an undesirable development of low-speed satellites, resulting in a reduced quality of recording.

Further, some volume of ink may flood over a surface area around the ink outlet 38, causing an ink drop to be discharged in an oblique direction, or bubbles to be involved, stopping the discharge, with a reduced reliability of recording.

A probable solution to such problems may include entering subsequent discharge after a sufficient damping of vibration, which however is inconsistent with an intended high-speed recording.

The present invention has been achieved with such points in mind.

SUMMARY OF THE INVENTION

It therefore is an object of the present invention to provide an ink jet print head with criteria such as on an sectional area of an ink outlet and a fluid resistance of an ink supply path to achieve an optimal high-speed ink discharge with an increased reliability and an improved cost effect, without additional elements.

In the present invention, an ink outlet is tapered, with a gradually reduced diameter, toward an orifice plate surface. Supposing a straight aperture of a diameter, it is typical that the quantity Q of an ink drop discharged from a print head of an identical resolution is substantially identical, as well as the volume of a void defined by an ink outlet and an ink meniscus drawn back therein just after a discharge of an ink drop, i.e., the quantity Q_r of ink to be supplemented.

Letting t_r be a time for the drawn back ink meniscus to restore to an exit level of the ink outlet, and v be a mean flow velocity in the ink outlet,

v=Q_r /(A·t_r),

Letting ρ be an ink density, and M be a mean momentum per unit volume,

M=ρ·Q_r /(A·t_r),

Thus, the larger the diameter of the ink outlet is, the smaller the mean momentum becomes, with a reduced frequency of occurrence of an overshooting ink meniscus.

As the overshooting meniscus convexes like a paraboloid of revolution, letting Q_o be an overshooting volume of ink and h be an overshooting height or projection of ink,

h=2·Q_o /A.

Thus, the larger the diameter of the ink outlet is, the smaller the overshooting volume of ink becomes.

For a quantity of ink supplemented in a time the larger the diameter of the ink outlet is, the overshooting ink might have the smaller projection h. However, experiments showed that the projection h of an ink overshoot depends on a sectional configuration of the ink supply path, i.e., a channel resistance or flow resistance thereof.

This fact means that an optimized relationship between an ink outlet sectional area and a channel resistance permits a high-speed recording without low-speed satellites.

The inventors found that a subsequent discharge of ink immediately after a concaved meniscus of the ink has restored to an exit level of an ink outlet can be free from an undesirable deformation of a drop of the ink, when an overshooting height or projection h of the ink falls within a range such that:

0<h<0.25q/A, more specifically, h=0.2 q/A.

Further, between the quantity q of an ink drop and the sectional area A of the ink outlet 14 a setting is made such that:

π{(3q)/(4π)}^2/3≦A≦π{(3a)/(2q)}^2/3.

When a driving pulse is applied between the individual electrode and the common electrode to heat the heating resistor 4, the ink above the heating resistor 4 is rapidly heated and boiled, and as a result, a bubble 18 (as a collective term of bubbles) is developed from vapours of ink components as shown in FIG. 7. The bubble 18 extrudes the ink above it out from the ink outlet 14, thereby forming an ink pillar 20.

The condition "π{(3q)/(4π)}^2/3≦A" means that the diameter of the ink outlet 14 is larger than that of an ink drop which provides an intended ink drop quantity. Therefore, the ink pillar 20 will not elongate, but is formed into a combination of an ink drop 22 and negligible droplets, as shown in FIG. 8. Accordingly, an excellent printing quality without dispersion or scattering is obtained.

If the diameter of the ink outlet 14 is unnecessarily large, the flow velocity of the ink at a discharge of an ink drop becomes slow. Therefore, the velocity or the momentum of an ink drop becomes slow or small, with increased influences of disturbances. Further, as the nozzle action for the discharge of ink drops from the ink outlet 14 becomes less effective, the discharge direction of an ink drop becomes irregular, which causes an irregular deposition of ink drops on the target paper. As a result, a deterioration is caused in the printing quality.

However, since the present embodiment operates under the condition "A≦π{(3q)/(2π)}^2/3 ", that is, the diameter of the ink outlet 14 is smaller than that of a hemisphere which provides an expected ink drop quantity, the side surface of the ink pillar 20 becomes right angled to the surface of the orifice plate 12. Consequently, the ink outlet 14 functions as a nozzle free of irregularities in the spattering direction of an ink drop.

After formation of the ink pillar 20, the internal pressure and temperature begin to fall due to the cooling effect of the adiabatic expansion and surrounding ink, and the bubble 18 starts to contract, as shown in FIG. 8. As described above, the ink pillar 20 is changed into an ink drop 22 to be discharged toward the recording medium, while the ink meniscus 24 is drawn inside the ink outlet 14.

Then, the ink meniscus 24 recovers, heading toward the exit level of the ink outlet 14, driven by a capillary force, which is a resultant force of the surface tension. Due to the inertial force of the ink, the ink meniscus 24 reaches the exit level of the ink outlet 14, and although the capillary force is gone, the meniscus 24 does not stop instantly but projects out from the exit level of the ink outlet 14, as shown in FIG. 9.

However, since the channel resistance value is set as to meet the condition "h=0.2q/A" in the present embodiment, although the ink is supplemented at high-speed, the projection h is considerably smaller as compared to the prior art. Therefore, even though a sequential discharge is executed immediately after the arrival of the ink meniscus 24 to the exit level, there is neither an undesirable deformation of an ink drop nor development of low-speed satellites. Moreover, since an ink overflow hardly occurs, there is no deterioration in the printing quality caused by the irregularity in the discharge direction, and also, no discharge error is caused by a bubble.

Further, since the projection h of the ink meniscus 24 is considerably smaller as compared to the prior art, the periodic damping time of the meniscus 24 becomes extremely short as shown in FIG. 10, and thereby the unfavorable effect of the vibration to be caused at the subsequent discharge is avoided. In the figure, t₁ represents the time for the ink meniscus 24 to reach the exit level of the ink outlet 14.

Therefore, by driving the ink jet print head 2 under the condition of 0.9×t₁ <t_min <1.1×t₁, in which t₁ represents a time for the ink meniscus 24 to reach the exit level of the ink outlet 14 and t_min represents a minimum operation period of the ink jet print head 2, the discharge interval is minimized with the excellent discharge performance kept, and as at result, a high-speed printing is achieved.

With the constitution described above, the measurement data of the present embodiment is compared with that of the conventional case as shown in FIG. 11.

As it is clear from FIG. 11, according to the ink jet print head of the present embodiment, a printing without dispersion is permitted in high-speed, which is almost twice the speed of the conventional print head.

Preferably, for the MIN value, where the diameter of the ink outlet 14 is 63 μm, a relationship is established such that 0<h<0.24 (q/A), and for the MAX value, where the diameter of the ink outlet 14 is 70 μm, a relationship is established such that 0<h<0.21(q/A).

While each associated member is illustrated in a particular shape in the embodiment, be present invention is not to be restricted by them, for example, the shape of the ink outlet 14 can be defined to a polygon or other. As long as the above-mentioned condition is satisfied, the elements are permitted to be property selected and exchanged.

According to the present invention, there is provided an excellent ink jet print head which enables a non-dispersed high-speed printing without additional members or devices.

While the present invention has been described with reference to the particular illustrative embodiment, it is not to be restricted by this embodiment but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiment without departing from the scope and spirit of the present invention.

Claims

1. An ink jet print head comprising:

a substrate member formed with a heating resistor;

an ink path defining member provided on the substrate member, for defining an ink supply path including a heating zone in a vicinity of the heating resistor; and

an orifice plate member formed with an ink outlet communicating with the ink supply path and laminated on the substrate member, with the ink path defining member interposed therebetween coupled to the ink path defining member,

said ink jet print head generating heat from the heating resistor to discharge a drop of ink from the ink outlet,

said ink supply path having a fluid resistance so that a relationship is established such that:

0<h<0.3(q/A) 0<h<0.25(q/A),

where q is a quantity of the drop of the ink, A is a sectional area at an exit level of the ink outlet, and h is a maximumal projection that a meniscus of the ink has when it projects from the ink outlet after it has restored the exit level from a retreat position it had after the drop of the ink had been discharged.

2. An ink jet print head according to claim 1, wherein another relationship is established such that:

π{(3q/4π)}^2/3≦A<π{(3q/2π)}^2/3.

3. An ink jet print head according to claim 1, wherein another relationship is established such that:

0.9×t₁ <t_min <1.1×t₁,

where t₁ is a time for the meniscus of the ink to restore the exit level from the retreat position, and t_min is a minimal period by which said ink jet print head discharges the drop of the ink.

4. An ink jet print head comprising:

a substrate member formed with a heating resistor:

for defining an ink supply path including a heating zone in a vicinity of the heating resistor; and

an orifice plate member formed with an ink outlet communicating with the ink supply path and coupled to the ink path defining member,

said ink jet print head generating heat from the heating resistor to discharge a drop of the ink outlet,

said ink supply path having a fluid resistance so that a relationship is established such that:

0<h<0.24(q/A),

where q is a quantity of the drop of the ink, A is a sectional area at an exit level of the ink outlet, and h is a maximum projection that a meniscus of the ink has when it projects from the ink outlet after it has restored the exit level from a retreat position it had after the drop of the ink had been discharged.

5. The ink jet print head according to claim 4, wherein another relationship is established such that:

π{(3q/4π)}^2/3≦A≦π{(3q/2π)}2/3.. Iadd.

6. The ink jet print head according to claim 4, wherein another relationship is established such that:

0.9×t₁ <t_min <1.1×t₁

where t₁ is a time for the meniscus of the ink to restore the exit level from the retreat position, and t_min is a minimal period by which said ink jet print head discharges the drop of the ink.

7. An ink-jet print head comprising:

a substrate member formed with a heating resistor;

an ink path defining member provided on the substrate member for defining an ink supply path including a heating zone in a vicinity of the heating resistor; and

an orifice plate member formed with an ink outlet communicating with the ink supply path and coupled to the ink path defining member,

said ink jet print head generating heat from the heating resistor to discharge a drop of the ink outlet,

said ink jet print head generating heat from the heating resistor to discharge a drop of the ink outlet,

said ink supply path having a fluid resistance so that a relationship is established such that:

0<h<0.21(q/A),

where q is a quantity of the drop of the ink, A is a sectional area at an exit level of the ink outlet, and h is maximum projection that a meniscus of the ink has when it projects from the ink outlet after it has restored the exit level from a retreat position it had after the drop of the ink had been discharged.

8. The ink jet print head according to claim 7, wherein another relationship is established such that:

π{(3q/4π)}^2/3≦A≦π{(3q/2π)}^2/3.

9. The ink jet print head according to claim 7, wherein another relationship is established such that:

0.9×t₁ <t_min <1.1×t₁

where t₁ is a time for the meniscus of the ink to restore the exit level from the retreat position, and t_min is a minimal period by which said ink jet print head discharges the drop of the ink.

10. An ink jet print head comprising:

a substrate member formed with a heating resistor;

an ink path defining member provided on the substrate member, for defining an ink supply path including a heating zone in a vicinity of the heating resistor, and

an orifice plate member formed with an ink outlet communicating with the ink supply path and coupled to the ink path defining member,

said ink jet print head generating heat from the heating resistor to discharge a drop of the ink outlet,

said ink supply path having a fluid resistance so that a relationship is established such that:

0<h≦0.2(q/A),

where q is a quantity of the drop of the ink, A is a sectional area at an exit level of the ink outlet, and h is a maximum projection that a meniscus of the ink has when it projects from the ink outlet after it has restored the exit level from a retreat position it had after the drop of the ink had been discharged.

11. The ink jet print head according to claim 10, wherein another relationship is established such that:

π{(3q/4π)}^2/3≦A≦π{(3q/2π)}^2/3.

12. The ink jet print head according to claim 10, wherein another relationship is established such that:

0.9×t₁ <t_min <1.1×t₁

where t₁ is a time for the meniscus of the ink to restore the exit level from the retreat position, and t_min is a minimal period by which said ink jet print head discharges the drop of the ink.

13. An ink jet printing method for generating a drop of an ink from an ink outlet of an ink jet print head, said ink outlet being connected to an ink supply path on an substrate formed with a resistor in said ink jet printing head, said method comprising the steps of,

heating said resistor for generating a bubble in said ink supply path to discharge the drop of the ink, and

providing a fluid resistance in said ink supply path so that a relationship is established such that:

0<h<0.25(q/A),

where q is a quantity of the drop of the ink, A is a sectional area at an exit level of the ink outlet, and h is a maximum projection that a meniscus of the ink has when it projects from the ink outlet after it has restored the exit level from a retreat position it had after the drop of the ink had been discharged.

14. The ink jet printing method according to claim 13, wherein said relationship is established such that:

0<h<0.24(q/A),

where q is a quantity of the drop of the ink, A is a sectional area at an exit level of the ink outlet, and h is a maximum projection that a meniscus of the ink has when it projects from the ink outlet after it has restored the exit level from a retreat position it had after the drop of the ink had been discharged.

15. The ink jet printing method according to claim 13, wherein said relationship is established such that:

0<h<0.21(q/A),

where q is a quantity of the rop of the ink, A is a sectional area at an exit level of the ink outlet, and h is a maximum projection that a meniscus of the ink had when it projects from the ink outlet after it has restored the exit level from a retreat position it had after the drop of the ink had been discharged.

16. The ink jet printing method according to claim 13, wherein said relationship is established such that:

0<h≦0.2(q/A),

where q is a quantity of the drop of the ink, A is a sectional area at an exit level of the ink outlet, and h is a maximum projection that a meniscus of the ink has when it projects from the ink outlet after it has restored the exit level from a retreat position it had after the drop of the ink had been discharged.

17. An ink jet printing device for printing an image on a recording material by discharging a drop of an ink from an ink jet print head,

wherein said ink-jet print head comprises;

a substrate member formed with a heating resistor;

an ink path defining member provided on the substrate member, for defining an ink supply path including a heating zone in a vicinity of the heating resistor; and

an orifice plate member formed with an ink outlet communicating with the ink supply path and coupled to the ink path defining member,

said ink jet print head generating heat from the heating resistor to discharge a drop of the ink outlet,

said ink jet print head generating heat from the heating resistor to discharge a drop of the ink outlet,

said ink supply path having a fluid resistance so that a relationship is established such that;

0<h<0.25(q/A),

where q is a quantity of the drop of the ink, A is a sectional area at an exit level of the ink outlet, and h is a maximum projection that a meniscus of the ink has when it projects from the ink outlet after it has restored the exit level from a retreat position it had after the drop of the ink had been discharged.

18. The ink jet printing device according to claim 17,

wherein said relationship is established such that;

0<h<0.24(q/A),

where q is a quantity of the drop of the ink, A is a sectional area at an exit level of the ink outlet, and h is a maximum projection that a meniscus of the ink has when it projects from the ink outlet after it has restored the exit level from a retreat position it had after the drop of the ink had been discharged.

19. The ink jet printing device according to claim 17, wherein said relationship is established such that;

0<h<0.21(q/A),

where q is a quantity of the drop of the ink, A is a sectional area at an exit level of the ink outlet, and h is a maximum projection that at meniscus of the ink has when it projections from the ink outlet after it has restored the exit level form a retreat position it had after the drop of the ink had been discharged.

20. The ink jet printing device according to claim 17, wherein said relationship is such that:

0<h≦0.2(q/A),

where q is a quantity of the drop of the ink, A is a sectional area at an exit level of the ink outlet, and h is a maximum projection that a meniscus of the ink has when it projects from the ink outlet after it has restored the exit level from a retreat position it had after the drop of the ink had been discharged.