JP2001071494A - Thermal ink-jet printer head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal ink-jet printer head which discharges ink drops with an energy as little as possible for forming a necessary dot landing diameter. SOLUTION: An orifice plate is formed in a thickness of 25 μm or smaller, preferably 17 μm whereby a discharge resistance becomes small. A heating resistor is formed to have a relatively small area of 25×25 μm whereby a discharge energy becomes 1 μJ. A ratio of the thickness of the orifice plate and an inner diameter of a discharge nozzle (orifice plate thickness/discharge nozzle inner diameter) is variously changed by variously changing a diameter of the discharge nozzle. Whether a printing quality is good or not is judged through visual measurement. Given that an allowable range of an aspect ratio is from an evaluation level '5' when a landing dot having almost proper diameter and position as a printing dot is obtained to an evaluation level '4' when the position of the landing dot in one-dot range becomes irregular, a proper aspect ratio is 0.75-1.3. The diameter of the discharge nozzle can be set on the basis of the proper aspect ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal ink jet printer head capable of ejecting ink droplets capable of forming a required dot landing diameter with as little energy as possible.

[0002]

2. Description of the Related Art In recent years, ink jet printers have been widely used. This inkjet printer uses a thermal jet method in which ink droplets are ejected by pressure generated by air bubbles, or a piezoresistive element (piezoelectric element).
There is a piezo method in which ink droplets are ejected by the pressure due to the deformation of the ink.

[0003] In these methods, a process in which ink as a color material is formed into ink droplets and directly ejected toward recording paper requires a lower printing energy as compared with an electrophotographic system using a toner as a powdery printing material. It is easy to colorize by mixing ink, and it is possible to reduce the size of printing dots, so that high image quality is achieved, the amount of ink used for printing is not wasted, and cost performance is excellent. This is the printing method used.

There are two types of the above-mentioned thermal jet system depending on the direction of ink droplet ejection. That is, there is a configuration that discharges in a direction parallel to the heating surface of the heating resistor, and a configuration that discharges in a direction perpendicular to the heating surface of the heating resistor.

FIGS. 4 (a), 4 (b) and 4 (c) show a top shooter type (also referred to as a roof shooter type) thermal ink jet printer head which discharges in a direction perpendicular to the heat generating surface of a heat generating resistor. It is a sectional side view which shows a structure and its operation | movement typically. As shown in FIG. 1A, the thermal ink jet printer head 1 has a heating resistor 3 formed on a silicon substrate 2. An orifice plate 4 is laminated on a partition (not shown), thereby forming an ink flow path 5 having a height corresponding to the thickness of the partition.

The heating resistor 3 of the orifice plate 4
A discharge nozzle 6 for discharging ink is bored at a position facing. The heating resistor 3 is connected to an electrode (not shown), and ink is constantly supplied to an opposing portion between the heating resistor 3 and the discharge nozzle 6 via the ink flow path 5.
When the heating resistor 3 is on standby, the ink 7 forms a meniscus at the outlet of the discharge nozzle 6.

When the heating resistor 3 generates heat by energizing the heating resistor 3 via an electrode (not shown) in accordance with image information, nuclear bubbles are generated at the interface between the heating resistor 3 and the ink 7, As shown in FIG. 3 (b), the nuclear bubbles coalesce and grow as film bubbles 8, which push the surrounding ink 7, whereby the ink 7 'is pushed out from the discharge nozzle 6, and The extruded ink 7 'is formed as an ink droplet 7 "as shown in FIG. 4C, and is discharged from the discharge nozzle 6 toward a sheet surface (not shown).

After that, the above-mentioned film bubbles shrink and disappear,
As shown in FIG. 7A, the next heating of the heating resistor 3 is on standby. A series of steps repeated as shown in FIGS. 5A, 5B, 5C, and 5A is performed in a very short time of several tens of microseconds.

The discharge amount and discharge speed of the ink droplet 7 ″ are determined by the shape of the heating resistor 3, the thickness of the orifice plate 4,
(a), (b) and (c) are significantly affected by the shape of the partition not shown, the shape of the discharge nozzle 6, and the like. In other words, the configuration of each section greatly affects the quality of a printed image formed by ejection.

[0010]

In general, an ink jet printer requires a landing diameter of dot pitch × √2 in order to obtain a desired image quality. That is, the landing diameter of the ink droplet 7 ″ must be larger than the diameter of the ejection nozzle 6 so that the adjacent printing dots landed on the paper surface and the printing dots overlap each other at the ends.

The impact diameter of the ink droplet 7 ″ depends on the shape of the heating resistor 3, the shape of the partition wall,
It is affected by various factors such as the height of the partition wall and the shape of the discharge nozzle 6, and particularly depends on the shape of the discharge nozzle 6 for discharging ink droplets, that is, the nozzle diameter and the nozzle length of the discharge nozzle 6. I do.

On the other hand, the length of the discharge nozzle 6 is short so that the fluid resistance is as small as possible in view of the energy efficiency of discharging the ink droplet 7 ″ due to the heat generated by the heat generating resistor 3.
That is, it is desirable that the thickness of the orifice plate 4 be thin. However, in this case, unless the nozzle diameter of the discharge nozzle 6 is appropriately set, a problem arises in that the required landing diameter of the ink droplet 7 ″ cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances,
An object of the present invention is to provide a thermal ink jet printer head capable of discharging ink droplets capable of forming a required dot landing diameter with as little energy as possible.

[0014]

The construction of the thermal ink jet printer head according to the present invention will be described below.

The thermal ink jet printer head according to the present invention has a plurality of heating elements arranged in parallel at a predetermined interval on a substrate so as to generate air bubbles to exert a pressure on the ink, and the above-mentioned heating element is provided in a region where the heating elements are arranged. A partition wall provided on the substrate for forming a flow path for supplying ink corresponding to each of the heating elements, and facing the heating element for discharging the pressured ink in a predetermined direction. And a plurality of ejection nozzles provided in the ink jet printer head, wherein the nozzle length L of the ejection nozzle in the direction of ejecting the ink is 25 μm or less,
The aspect ratio “L / D” between the nozzle length L and the inner diameter D of the nozzle cross section is configured to be 0.75 to 1.3.

[0016] For example, in the nozzle cross section of the discharge nozzle, it is preferable that a projected figure projected onto the heating element falls within an area of the heating element. Further, for example, as described in claim 3, the area of the heating element is square, and the discharge nozzle is
Preferably, it is cylindrical. Further, for example, as described in claim 4, the heating element has a size of 6 per inch.
Arranged at a density of 00, and the partition walls have a height of 10 μm.
The following is preferred.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1A, 1B, and 1C schematically show a configuration of a thermal ink jet printer head according to an embodiment. FIG. 1A is a plan view and FIG.
(b) is an enlarged cross-sectional view taken along the line AA 'in FIG. (a), and FIG.
FIG. 2A is an enlarged view showing a main part inside the thermal ink jet printer head without an orifice plate.
In FIG. 3C, the ejection nozzles formed on the orifice plate are shown by broken lines so that the positional relationship with the heating resistors can be understood.

In the thermal ink jet printer head 10 shown in FIGS. 1A, 1B and 1C, a plurality of heating resistors 12 are arranged on a silicon substrate 11 and the heating resistors 12 are arranged in parallel. Partition wall 13 (seal partition wall 1)
3-1 and the partition 13-2) are stacked. An orifice plate 14 is further laminated on the seal partition 13-1 and the partition 13-2, whereby a common ink flow having a height corresponding to the thickness of the seal partition 13-1 and the partition 13-2 is formed. A passage 15 and an individual ink passage 16 are formed.

The heating resistor 1 of the orifice plate 14
2 is located at a position facing the discharge nozzle 1 for discharging ink.
7 are drilled. Each heating resistor 12 has a pair of electrodes (not shown) connected to both ends thereof.
Are provided through the common ink flow path 15 to the individual ink flow paths 16 provided respectively as shown by the arrow B in FIG.
The ink is constantly supplied, and the ink is turned into fine ink droplets by the heat generated by the heat generating resistor 12, and is indicated by an arrow C in FIG.
As shown by, the ink is ejected toward the paper surface (not shown).

As a method of manufacturing a thermal ink jet printer head of this type, there is a method in which a plurality of heating resistors, individual driving circuits, and orifices are collectively formed monolithically using a silicon LSI forming technique and a thin film forming technique. is there. According to the method, for example, a resolution of 600
In the case of creating a thermal ink jet printer head of dpi (dot / inch), for example, 15 mm
300 heating resistors 12, a driving circuit for individually driving these heating resistors 12, and 300 ejection nozzles 1
7 are formed at an arrangement pitch of 42.3 μm.

The ink discharge due to the heat generated by the heat generating resistor 12 is configured so that the partition wall 13-2 is provided so that the ink is hardly influenced by the adjacent heat generating resistor 12 and the heat generating resistor 12. . It is difficult to make the width a of these partition walls 13-2 too small in manufacturing. For example, when the height of the partition wall 13-2 is 10 μm, the width a is about 13 μm in the current technology. Is required.

Also in this example, the thickness (height) of the seal partition 13-1 and the partition 13-2 is set to 10 μm. Also, from the point of energy efficiency, the orifice plate 1
The thickness of No. 4 is set to 17 μm, which is extremely thin as compared with a normal orifice plate having a thickness of 35 to 40 μm.

FIG. 2A is a diagram showing two examples of the degree of image quality by visual measurement of a print image formed by the thermal ink jet printer head 10 of this embodiment described above.
(b) is a diagram showing the measurement results of the ejection speed of the ink droplets in these two examples.

FIG. 3A shows the value obtained by dividing the thickness of the orifice plate 14 by the diameter of the discharge nozzle 17 on the horizontal axis, that is, the aspect ratio between the orifice plate thickness and the discharge nozzle diameter (hereinafter simply referred to as the aspect ratio). From 0.4 to 1.6, and the vertical axis indicates the degree of image quality by visual measurement of the printed image. In this example, since the thickness of the orifice plate 17 is fixed to 17 μm as described above, the change in the aspect ratio shown here is obtained by substantially changing the diameter of the discharge nozzle 17.

In FIG. 2A, a characteristic curve b indicates a degree of image quality corresponding to a change in aspect ratio when the size (area) of the heating resistor 12 is 25 × 25 μm, and a characteristic curve c indicates a heating resistor. The size (area) of 12 is 30 × 25 μm
5 shows the degree of image quality corresponding to the change in the aspect ratio.

A predetermined margin is required between the heating resistor 12 and the partition 13-2 shown in FIG. 1C so that the heating resistor 12 does not directly contact the partition 13-2. It is. The arrangement pitch of the heating resistors 12 is 42.3 μm as described above, and the width a of the partition wall 13-2 is
Is 13 μm, the width of the heating resistor 12, that is,
The width d in the X direction of FIG.
It must be formed with a size smaller than the value obtained by subtracting the above margin from the value obtained by subtracting 13 μm from 3 μm, ie, 29.3 μm. Accordingly, 30 μm of the dimension 30 × 25 μm of the heating resistor 12 in the characteristic curve c of FIG. 2A corresponds to Y in FIG.
Direction width e.

The criteria for visually evaluating the image quality are “5” and “1” when it is observed that landing dots whose diameters and positions are substantially appropriate as printing dots are obtained.
"4" when disturbance of the landing dot position within the dot range is observed, "3" when disturbance of the landing position over one dot range is observed, and "3" when the landing image is somehow recognizable. Five evaluation levels were set, "2", and "1" when only ink droplets could be ejected.

According to actual measurements, as the aspect ratio increases, the amount of ink droplets to be ejected gradually decreases. In other words, if the diameter is smaller than the length of the ejection nozzle 17, the amount of the ejected ink droplet is smaller. Then, when the printed image was visually measured, the evaluation level was “4”.
This is when the aspect ratio is 0.8 or more. The size of the heating resistor 12 is 25 × 2 as described above.
In either case of 5 μm or 30 × 25 μm, the evaluation level becomes lower than “4” near the aspect ratio of 1.3.

On the other hand, in the characteristic diagram showing the measurement results of the ink droplet ejection speed shown in FIG. 2B, the horizontal axis shows the aspect ratio from 0.4 to 1.6 similarly to FIG. The vertical axis indicates the ink droplet ejection speed. As shown in FIG. 2B, the characteristic curve f when the size of the heating resistor 12 is 25 × 25 μm and the characteristic curve g when the size of the heating resistor 12 is 30 × 25 μm have the aspect ratios. As the size increases, the ejection speed of the ink drops increases, and the aspect ratio becomes 1.
It shows that the equilibrium point is almost reached near 2.

The phenomenon that the image quality is lowered when the aspect ratio is further increased after peaking at a certain point shown in the characteristic diagram of FIG. 2A is considered as follows. In other words, the entire integral of the film bubbles generated by the heat generated by the heat generating resistor 12 should be able to be ejected as ink droplets. However, in actuality, since the ink droplets are ejected from the ejection nozzle 17, there is ejection resistance. It is considered that the ink droplet of the total integral of the film bubble is not ejected from the ejection nozzle 17, but a part thereof is pushed back to the common ink channel 15 side.

That is, the area of the heating resistor 12 is invariable,
If the height of the partition wall 13 is not changed, the conditions for generating the film bubble are the same, and the pressure of the total integral of the film bubble is applied to the ink. However, the smaller the diameter of the discharge nozzle 17 (the larger the aspect ratio). It is considered that this is because the ejection resistance of the ink droplets ejected from the ejection nozzle 17 increases, and the ejected ink droplets decrease (the amount decreases).

On the other hand, the characteristic diagram of FIG. 2 (b) shows that the ejection speed increases as the ejected ink droplet passes through a place where the ejection resistance is large. It is thought that the same principle can be used as if the tip of the connected hose was pinched with a finger and made thinner, the momentum of the released water improved.

As a result, as described above, 2
Both the case of the heating resistor of 5 × 25 μm and the case of the heating resistor of 30 × 25 μm show a similar tendency, and although the aspect ratio increases and the ejection speed increases, there is a certain point in the landing dots of the image. , The quality is degraded with the peak as a peak, and the overall image quality is good when the aspect ratio is near “1.0”.

The energy required for discharging the ink droplet is proportional to the surface area of the heating resistor 12. For example,
With the heating resistor 12 of 25 × 25 μm indicated by the characteristic curve b in FIG. 2A, printing was possible at about 1 μJ. Meanwhile, the same figure
(b) Heating resistor 1 of 30 × 25 μm indicated by characteristic curve c
In the case of 2, about 1.4 μJ of energy is required.
Therefore, from the viewpoint of energy saving, 600
In the thermal ink jet printer head 10 of dpi, it can be said that the heating resistor 12 of 25 × 25 μm is appropriate.

The 25 × curve shown in the characteristic curve b of FIG.
In the case of the heating resistor 12 of 25 μm, the reason why the evaluation level exceeds “4” is that the aspect ratio is “0.81”, that is, 2
The discharge nozzle 17 is provided for the heating resistor 12 of 5 × 25 μm.
Is when the nozzle diameter is 21 μmφ. At this time, it has been experimentally confirmed that a diameter of the landing dot of 60 μmφ was obtained. In this case, the length h formed so as to extend toward the common ink flow path 16 side of the partition wall 13-2 shown in FIG. 1C was 35 μm.

That is, 60 μmφ (42.3 μm × √2), which is the landing diameter required for a good print image of 600 dpi.
In order to obtain the landing dots, the thermal inkjet printer head 10 requires, for example, a heating resistor area of 25 × 25 μm, a partition height of 10 μm, a partition partition width of 13 μm, and a discharge nozzle nozzle diameter. 21 μm
φ and the nozzle length (the thickness of the orifice plate) may be set to 17 μm.

Further, it has been found that even when the orifice plate 14 is made thicker, the image quality draws a mountain-like characteristic having a peak of substantially the aspect ratio "1" as in FIG. 2 (a). For example, when an experiment similar to the above is performed using an orifice plate 14 having a thickness of 31 μm, the thermal resistance 12
Is 25 × 25 μm and the aspect ratio is “1”, the best image can be obtained. However, the absolute quality of the image is reduced, and the evaluation level of the image quality is between “3” and “4”. It is considered that this is because the orifice plate is as thick as 31 μm, so that the ejection resistance of the ink droplet is large, the ejection energy is insufficient, and the ejection is adversely affected.

Here, assuming that the evaluation level of the image shown in FIG. 2 (a) is "4" or more, which is within the allowable range of high quality image quality, from the above measurement results, in this embodiment, the orifice used in the above experiment is used. It is expected that an orifice plate having a thickness approximately halfway between the thicknesses of the plate 14 of 17 μm and 31 μm, that is, a thickness of 25 μm will provide an image in a desired allowable range, and this has been confirmed by experiments. That is, since an extremely good result has already been obtained when the thickness of the orifice plate is 17 μm, the appropriate thickness of the orifice plate is 25 μm or less.

On the other hand, in order to obtain a good image, the lower limit of “0.75” and the upper limit of “1.3” are obtained from the characteristic diagram of FIG. Have been. Therefore, in order to get a good image,
The thickness of the orifice plate 14 is set to 25 μm or less.
It turns out that it is better to set the nozzle diameter of the discharge nozzle 17 so as to be "5 to 1.3".

As described above, in the above-described embodiment, the size of the heating resistor when the best image is obtained near the aspect ratio of “1” is 25 × 25 μm or 30 × 25.
μm. Also, in this case, it has been found that the nozzle diameter of the discharge nozzle that forms a good image is 25 μm or less. In other words, this means that the nozzle diameter of the discharge nozzle, that is, the projected figure on the heating resistor in the cross section of the nozzle falls within the size of the heating resistor.

That is, assuming that the area of the heating resistor is square and the cross section of the discharge nozzle is a perfect circle, the nozzle diameter of the discharge nozzle 17 is just inside the heating resistor 12 as shown in FIG. Can be said to be a proper shape of the discharge nozzle.

In the above-described embodiment, the cross section of the discharge nozzle is a perfect circle. However, the present inventor has confirmed by experiments that the present invention is applicable to a case other than a perfect circle. In this case, the nozzle diameter D that determines the aspect ratio of the discharge nozzle was an average value of the maximum inner diameter DL and the minimum inner diameter DS as shown in FIGS. 3 (a) to 3 (f).

FIGS. 6A and 6B show an elliptical cross section, and FIG. 6C shows a rectangular cross section. The long axis is indicated by the maximum inner diameter DL, and the short axis is indicated by the minimum inner diameter DS. . In this case, the aspect ratio D is D = (DL + DS) / 2.

FIG. 4D shows an example of a cross section of an isosceles triangle. In this case, the maximum inner diameter DL and the minimum inner diameter DS are each defined by a perpendicular line extending from each vertex to an opposite side. The maximum and minimum lengths were used. FIG. 11E shows an example of a deformed pentagonal cross section, which is the same in this case. It has been confirmed by experiments conducted by the present inventors that these five types of discharge nozzles each exhibit the same characteristics as those shown in FIG.

[0045]

As described in detail above, according to the present invention, in a thermal ink jet printer head having an orifice plate thickness of 25 μm or less, the ratio of the orifice plate thickness to the inner diameter of the discharge nozzle (orifice plate thickness / By setting the discharge nozzle inner diameter to 0.75 to 1.3,
It is possible to provide a thermal inkjet printer head that forms an image of good print quality with energy efficiency.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams schematically showing a configuration of a thermal ink jet printer head according to an embodiment, wherein FIG. 1A is a plan view, FIG. 1B is an enlarged cross-sectional view taken along line AA ′ of FIG. Is (a)
FIG. 3 is an enlarged view showing the orifice plate of FIG.

FIGS. 2A and 2B show two examples of the degree of image quality by visual measurement of a print image formed by a thermal inkjet printer head according to an embodiment, and FIG. 2B shows the measurement results of the ejection speed of the ink droplets. FIG.

FIGS. 3A to 3F are diagrams illustrating examples in which the cross section of the discharge nozzle of the thermal inkjet printer head according to the embodiment is not a perfect circle;

FIGS. 4A, 4B, and 4C are side sectional views schematically showing the configuration and operation of a conventional thermal ink jet printer head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermal inkjet printer head 2 Silicon substrate 3 Heating resistor 4 Orifice plate 5 Ink channel 6 Discharge nozzle 7, 7 'ink 7 "Ink drop 10 Thermal inkjet printer head 11 Silicon substrate 12 Heating resistor 13 Partition 13-1 Seal partition 13-2 Partition partition 14 Orifice plate 15 Common ink flow path 16 Individual ink flow path 17 Discharge nozzle

Claims (4)

[Claims] A plurality of heating elements arranged in parallel at a predetermined interval on a substrate to generate air bubbles to apply pressure to the ink; and a flow path for supplying the ink to a region where the heating elements are arranged. A partition wall erected on the substrate to form a partition corresponding to each of the heating elements, and a plurality of partitions provided opposite the heating elements to discharge the ink under pressure in a predetermined direction. An ink jet printer head comprising: a nozzle length L in the direction in which the ink is discharged from the discharge nozzle is 25 μm or less; and an aspect ratio between the nozzle length L and the inner diameter D of the nozzle cross section. "L / D" is 0.75
1.3. A thermal ink jet printer head, characterized in that: 2. The thermal ink jet printer head according to claim 1, wherein a projected figure projected onto the heating element falls within an area of the heating element in a cross section of the discharge nozzle. 3. The heating element has a square area.
3. The thermal ink jet printer head according to claim 1, wherein the discharge nozzle has a cylindrical shape. 4. The heating element according to claim 1, wherein the heating element is 600
4. The thermal ink jet printer head according to claim 1, wherein the partition walls are arranged at the same density, and the partition walls have a height of 10 μm or less.