JPH09169111A - Ink jet printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stable ink liquid droplet quantity by rapidly restoring a meniscus to the original position after emission even when high viscosity ink is used to emit ink at the same meniscus position every time. SOLUTION: In an ink jet printers, the diameter of the nozzle 5 of an ink jet head is set to 50-70μm to lower the resistance to the flow of ink with viscosity of 10-100 cp at the part of the nozzle and ink is rapidly supplied to a cavity chamber from an ink manifold after emission to perform printing in the liquid droplet quantity and drive frequency corresponding to resolving power. By this constitution, ink is emitted in the same liquid droplet quantity every time to obtain a printing result of high quality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet printer that ejects ink from a nozzle to adhere it to a recording material for recording, and more specifically, to recover the ink amount inside the nozzle after ejecting the ink. The present invention relates to an inkjet printer in which the ejection amount is stabilized in consideration.

[0002]

2. Description of the Related Art A conventional ink jet printer has been designed to eject ink from a small diameter nozzle having a diameter of about 30 μm on the assumption that ink having a low viscosity (about 1 cP (centipoise)) is used. If the viscosity of the ink is low, ink is replenished quickly from the ink manifold into the nozzle where the amount of ink has decreased due to ejection. Therefore, even if the nozzle diameter is small, the meniscus (ink-air interface) inside the nozzle after ejection The ink can be ejected at the same meniscus position every time even when high-speed printing is performed, and printing can be performed with a stable ink droplet amount.

[0003]

However, in recent years, in order to deal with a variety of recording materials, high-viscosity ink that is difficult to bleed has been used. However, if the ink viscosity is high, for example, about 20 cP, it takes time for the meniscus to return after ejection. Therefore, when high-speed printing is performed, the next ejection is performed before the meniscus has sufficiently recovered.

This state is shown in FIG. FIG. 8A shows a state before the first ejection, in which the meniscus is substantially at the same position as the outer surface of the nozzle 5. (B) is a state in which the ink droplets 9 have been ejected from the state of (a). Then, (c) is a state immediately after (b), and the meniscus is largely retracted as compared with the state of (a). Then, in this state, the next ejection is performed as shown in (d). In the case of this (d), since the amount of the ejected ink droplet 9 is smaller than the original amount, the size of the dot formed on the recording material is small, and therefore, as shown in FIG. A gap is formed without being filled, and as a result, the print mark becomes light.

The next ejection may be performed after waiting until the meniscus is sufficiently returned.
When printing is performed at a resolution of i or higher, or when performing color printing, the time required to print one sheet becomes too long, which is impractical. Therefore, from the viewpoint of printing time, it is preferable to secure at least about 5 kHz as the driving frequency of the inkjet head.

On the other hand, if the amount of ink droplets per ejection is reduced, the retreat of the meniscus itself can be reduced and the recovery time can be shortened. However, there is an appropriate dot size according to the resolution of printing, and it is achieved. The amount of droplets required to do so has been determined. That is, as shown in FIG.
If the amount of droplets is small, then there will be gaps between the dots, which is not desirable for print quality. Therefore, it is impossible to extremely reduce the amount of droplets in order to achieve high-speed printing. Incidentally, 300-
When printing about 360 dpi, the droplet amount should be 60 p
It has been confirmed by experiments by the present inventor that it is preferable to set it to 1 or more, and it is preferable to set the droplet amount to 20 pl or more when printing about 600 to 720 dpi.

When printing at a low resolution (for example, about 300 dpi), the amount of droplets per ejection is large in order to increase the dot size. Therefore, the variation in the amount of ejected droplets due to the poor recovery of the meniscus is caused. In particular, it was a cause of impairing print quality. Further, these phenomena often occur when the viscosity exceeds 10 cP of the ink, and have been remarkably exhibited in the ink jet printer using the hot melt ink having a relatively high viscosity among the inks.

The present invention has been made in order to solve the above-mentioned conventional problems. Even when a high-viscosity ink is used, the meniscus quickly recovers to its original position after ejection, and the same meniscus position is maintained every time. It is an object of the present invention to provide an ink jet printer that is ejected by the method and can obtain a stable ink droplet amount, and enable high-quality high-speed printing.

[0009]

In order to achieve the above object, the invention according to claim 1 provides an ink cavity filled with an ink having a viscosity in the range of 10 to 100 cP, and an ink cavity provided in the ink cavity. An ink jet printer including an ink jet head having a nozzle for ejecting ink, an ink manifold for refilling the ink cavity with ink, and an energy generating element for pressurizing ink in the ink cavity to eject ink from the nozzle. And a droplet amount varying means capable of changing the droplet amount of the ink ejected from the nozzle by adjusting the waveform of the signal applied to the energy generating element. It is characterized by being in the range of 70 μm.

In this ink jet printer, when a signal is applied to the energy generating element of the ink jet head, the energy generating element pressurizes the ink cavity, and ink is ejected from the nozzles provided in the ink cavity to perform printing. Done. Here, since the waveform of the signal applied to the energy generating element is adjusted by the droplet amount varying means, the droplet amount of ink suitable for the printing purpose is ejected. When the ink is ejected from the nozzle, the ink in the ink cavity decreases and the meniscus recedes, so that the ink is replenished from the ink manifold. Here, the nozzle diameter is 50 μm or more and 70
Since the thickness is less than μm, resistance to movement of the meniscus in the nozzle portion is small, and recovery of the meniscus position by replenishment of ink is promptly performed. Therefore, even when the waveform of the signal is adjusted by the droplet amount varying means to increase the ink droplet amount, the ink is ejected at the same meniscus position each time, and the ink droplet amount is stabilized.
In particular, it is excellent in that the amount of droplets is stable despite the use of high-viscosity ink having relatively large resistance to meniscus movement such as hot melt ink.

Here, the ink viscosity range is 10 to 100c.
The reason why P is set is that the recovery of the meniscus poses almost no problem in the low viscosity ink of less than 10 cP, and 10
An extremely high viscosity of more than 0 cP makes it difficult to eject as droplets from the nozzle before the problem of meniscus recovery (it is difficult to cut at the end of ejection, etc.) and is suitable for use in an inkjet printer. Because it does not exist. Preferably, when the viscosity range of the ink is 20 to 40 cP, it is further excellent from the viewpoint of easy control of the droplet amount, bleeding on the paper, and ink shortage.

Therefore, the invention according to claim 2 is the ink jet printer according to claim 1, wherein the viscosity of the ink is in the range of 20 to 40 cP.

The invention according to claim 3 is the ink jet printer according to claim 1 or 2, wherein the droplet amount varying means prints at a resolution within a range of 300 to 360 dpi. It is characterized in that the amount of ink droplets ejected from the nozzle is within a range of 60 to 130 pl.

In this ink jet printer, 300
When printing with a resolution not so high in the range of up to 360 dpi, the waveform of the signal is adjusted by the droplet amount varying means, and the droplet amount of the ink ejected from the nozzle is 60 to 1
It is set within the range of 30 pl. Even if the resolution is relatively low and the amount of droplets per ejection is large, if it is within such a range, the position of the meniscus is promptly recovered after the ejection as described above, and the droplet amount of ink is stable. ing. In printing within this range, excellent gradation and proper optical density are obtained, and high-quality images are stably formed at high speed.

The invention according to claim 4 is the ink jet printer according to any one of claims 1 to 3, wherein the droplet amount varying means is 600 to 720.
When printing with a resolution within the range of dpi, the amount of ink droplets ejected from the nozzle is set within the range of 20 to 45 pl.

In this ink jet printer, 600
When printing at a high resolution of up to 720 dpi, the waveform of the signal is adjusted by the droplet amount varying means so that the droplet amount of the ink ejected from the nozzle is within the range of 600 to 720 dpi. In this case, although the droplet amount is smaller than that in the above case, the driving frequency of the inkjet head is high and the time interval from one ejection to the next ejection is short in order to achieve the resolution of 600 to 720 dpi. However, as described above, the position of the meniscus is quickly recovered after the ejection, so that the ink droplet amount is stable.

The invention according to claim 5 is the ink jet printer according to any one of claims 1 to 4, wherein when the droplet amount varying means prints at a resolution of 600 dpi or more, the nozzle is used. The amount of ink droplets ejected from the recording medium is 1.0 × 10 ^{7 to} 1.7 × 10 ⁷ pl / inch when the amount of ink adhered on the recording medium is solid recording.
It is characterized in that it is controlled within the range of ² . Here, "solid recording" refers to ejecting ink from all nozzles each time to fill the printing range on the recording medium with all dots.

In this ink jet printer, 600
When printing at a high resolution of not less than dpi, the waveform of the signal is adjusted by the droplet amount varying means, and the amount of ink adhered on the recording medium in the case of solid recording is 1.0 × 10 ⁷ or more.
The droplet amount of the ink ejected from the nozzle is controlled so as to be within the range of 1.7 × 10 ⁷ pl / inch ² . In printing within this range, excellent gradation and proper optical density are obtained, and high-quality images are stably formed at high speed. Therefore, even if printing is performed at a high resolution of 600 dpi or more, the optical density and gradation are excellent.

The invention according to claim 6 is the ink jet printer according to any one of claims 1 to 5, wherein the ink is a solid at room temperature and is liquefied by heating and melting. Is characterized in that.

In this ink jet printer, hot melt ink is used as the ink. The hot-melt ink has a viscosity in the range of 10 to 100 cP, which is higher than that of a normal liquid ink even in a state of being heated and melted and liquefied. However, in this inkjet printer, the position of the meniscus after ejection is as described above. Since the ink recovers promptly, the ink droplet amount is stable.

The invention according to claim 7 is the inkjet printer according to any one of claims 1 to 6, characterized in that the driving frequency of the inkjet head is 8 kHz or more.

In this ink jet printer, the driving frequency of the ink jet head is as high as 8 kHz or more. Generally, at such a high frequency, meniscus recovery tends to be a problem, but in this ink jet printer, the position of the meniscus is quickly recovered after ejection as described above, and thus the ink droplet amount is stable.

The invention according to claim 8 is the ink jet printer according to any one of claims 1 to 7, which has at least two types of print modes having different resolutions, and the variable droplet amount. The means is characterized in that the amount of ink droplets ejected from the nozzle and the driving frequency of the inkjet head are changed according to the selected print mode. As the two types of print modes, for example, a high resolution mode (about 600 to 720 dpi) and a low resolution mode (about 300 to 360 dpi) can be considered.

In this ink jet printer, when the print mode is selected, the waveform of the signal is adjusted by the liquid drop amount varying means, and the liquid drop amount of the ink ejected from the nozzle becomes a value according to the selected print mode. Controlled as. At the same time, the drive frequency of the inkjet head is also adjusted, and control is performed so that ink is ejected from the nozzles at a frequency according to the selected print mode.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the ink jet printer according to the present invention will be described in detail below with reference to the drawings. As shown in the sectional view of FIG. 1, an inkjet head 1 mounted in an inkjet printer 1
In general, the cavity plate 4 and the piezoelectric element plate 2 are joined together via a vibrating plate 3 which is an elastic body, and the base plate 10 which is a base is installed.

A nozzle plate 8 having a nozzle hole 5 is provided at one end of the cavity plate 4, and a cavity chamber 6 for supplying ink to the nozzle hole 5 from the inside is provided inside the cavity plate 4. . The cavity chambers 6 and the nozzle holes 5 are provided in parallel with each other in the thickness direction of the paper, and the respective cavity chambers 6 face the piezoelectric element plate 2 via the vibration plate 3. The diameter of each nozzle hole 5 is 55 μm, and its meaning will be described later. The cavity plate 4 is further formed with an ink manifold 7 which is a common ink supply path to each cavity chamber 6. Each cavity chamber 6 and ink manifold 7 are filled with ink, and the viscosity of the ink is higher than that normally used (about 1 cP).
It is a hot-melt ink melted by heating having a cP level.

The piezoelectric element plate 2 is made of a material having a piezo effect such as PZT, and an electrode is provided at a position facing each cavity chamber 6 through the vibrating plate 3 to form a vibrating portion 2a. The vibrating sections 2a are provided in parallel with each other in the thickness direction of the paper in the same manner as the respective cavity chambers 6 and are provided in a one-to-one correspondence, and are selectively driven according to an input signal. Thereby, each of the cavity chambers 6 can be selectively pressurized.

An ink jet printer equipped with the ink jet head 1 has a control system shown in FIG. This control system includes a CPU 3 which is a known arithmetic processing unit.
It is mainly composed of 5. The CPU 35 is a host computer 3 such as a personal computer via the interface 34.
3 and is configured to perform printing according to a command from the host computer 33.

The CPU 35 has a switch panel 41, R
AM43 and ROM42 are connected. The switch panel 41 is for selecting and displaying a print mode for designating print resolution and other parameters. RAM43
Is for temporarily storing necessary data such as print data received from the host computer 33.

The ROM 42 stores various programs and data tables necessary for control. One of the data tables stored here is the relationship between the printing resolution (dpi) and the ink droplet amount per ejection. According to the table, for example, when printing with a resolution of 360 dpi, the droplet amount is 70 pl,
When printing with a resolution of 20 dpi, it is set to 30 pl. The relationship between the printing resolution and the driving frequency of the inkjet head 1 is also stored as a data table. For example, the frequency is 8 kHz when printing at a resolution of 360 dpi, and 10 kHz when printing at a resolution of 720 dpi. It

The CPU 35 has a droplet amount changing unit 30 for driving the ink jet head 1 and a drive circuit 3.
1 are connected. These are the switch panel 41
The droplet amount changing unit 30 determines the droplet amount to be ejected according to the print mode selected in step 1, and the drive circuit 31 generates a pulse height drive signal for ejecting the ink of the droplet amount. The drive signal is applied to the piezoelectric element plate 2 (more specifically, the vibrating portion 2a) of the inkjet head 1.

The operation of this ink jet printer will be described.

When the CPU 35 receives a print command from the host computer 33, the ink droplet amount corresponding to the print mode selected on the switch panel 41 is stored in the ROM.
The droplet amount is read from 42, and the droplet amount is instructed to the droplet amount changing unit 30. Then, the droplet amount changing unit 30 determines the drive voltage of the vibrating unit 2 a for ejecting the instructed droplet amount from the nozzle hole 5. For example, if the droplet amount is 70 pl, it is 40 V, and if it is 30 pl, it is 30 V.

Then, the drive circuit 31 selectively applies the pulse signal of the drive voltage to each vibrating portion 2a of the piezoelectric element plate 2 according to the print data. The waveform of this signal has the height instructed by the droplet amount changing unit 30, as shown in FIG. 3 (droplet amount 30 pl) or FIG. 4 (droplet amount 70 pl), but slightly reverses just before application. It is driven (indicated by R in the figure). The reason is that the meniscus may be slightly retracted inside the nozzle hole 5, so that the ink is sucked out from the ink manifold 7 to compensate for it.

Thus, in the ink jet head 1, one of the vibrating portions 2a of the piezoelectric element plate 2 to which the pulse signal is applied expands, and the expansion causes the corresponding cavity chamber 6 to be pressurized. The pressure generated by this pressurization is propagated to the corresponding nozzle holes 5, and ink droplets 9 are ejected from the nozzle holes 5 as shown in FIG. 5 to perform printing. Here, FIG. 5A shows the state immediately before ejection, in which the inside of the nozzle hole 5 is filled with ink and the meniscus is located at the forefront. FIG. 5B shows a state in which ejection is being performed. The droplet amount of the ink droplet 9 at this time is the amount instructed by the droplet amount changing unit 30.

FIG. 5C shows a state after the end of the ejection. In this ink jet head 1, the nozzle holes 5 have a relatively large diameter of 55 μm and have a low resistance to the flow of ink as described above.
The ink inside, that is, the cavity chamber 6 is immediately replenished from the ink manifold 7, and the meniscus position is recovered to almost the same level as in the state (a). Therefore,
Immediately after that, even if the next ejection is performed, the ink droplets 9 having a droplet amount almost the same as in the case of (b) are ejected as shown in (d) of FIG.

At this time, the meniscus position and the ink droplet 9
Tables 1 and 2 show the relationship between the droplet amount and the droplet velocity, compared with the case where the diameter of the nozzle hole 5 was 45 μm.
Table 1 shows that the printing resolution is 360 dpi and the drive frequency is 8k.
Table 2 shows a printing resolution of 720d.
This is the case where the driving frequency is 10 kHz in pi.

[0038]

[Table 1]

[0039]

[Table 2]

Taking Table 1 as an example, the meniscus position (retraction amount) immediately before the first discharge is 45 μm.
In both cases of the m diameter and the 55 μm diameter, it is 0 μm, and therefore there is almost no difference in the droplet amount at that time. The droplet speed is slightly higher when the diameter is 45 μm. The retreat amount of the meniscus immediately before the second discharge is as large as 23.5 μm when the diameter is 45 μm, and is 5.9 μm when the diameter is 55 μm, which is smaller than the nozzle diameter. Therefore, in the second discharge, both the droplet amount and the droplet velocity are 45 μm.
In the case of the diameter, the diameter is drastically reduced as compared with the case of the first discharge, but in the case of the diameter of 55 μm, it hardly changes. In the case of the diameter of 45 μm, since the droplet amount of the second ejection is small, there is a tendency to recover slightly in the third ejection to approach the data of the first ejection.

In the case of 720 dpi in Table 2, the same tendency as in Table 1 is observed. In the case of 720 dpi, the ejected droplet amount is smaller than that in the case of 360 dpi, but the time interval from ejection to the next ejection is short accordingly.

In this way, the diameter of the nozzle hole 5 is 55 μm.
According to the inkjet head 1 described above, the characteristics of each discharge are uniform, and almost the same droplet amount is secured for printing. Therefore, as shown in FIG. Is secured.

Further, as a result of investigating the discharge characteristics by changing the diameter of the nozzle hole 5 variously, as shown in the graph of FIG. 7, it was found that good characteristics can be obtained if the nozzle diameter is about 50 μm or more. . However, the nozzle diameter is 70
If it exceeds μm, the ink leaks from the nozzle hole 5 even when the ejection is not performed, which is not preferable.

Further, by using the ink jet printer thus constructed, the ink droplet amount is variously changed as shown in Tables 3 and 4 under a predetermined resolution (recording density), and the most general recording medium is used. The image quality when printed on economical plain paper was examined. Table 3 shows the results of the image quality measurement experiment in the case of 300 dpi and in the case of 360 dpi,
Table 4 shows the results of image quality measurement experiments for 600 dpi, 720 dpi, and 900 dpi.

[0045]

[Table 3]

[0046]

[Table 4]

In the evaluation, sample images with variously changed ink droplet amounts are shown to 30 panelists, and a qualitative evaluation is made based on the support rate of the print quality, while the coverage (jet droplets) is evaluated. Number / number of dots that make up the unit area) and dot diameter, and perform a quantitative evaluation with an emphasis on optical density and gradation, and show a comprehensive evaluation that includes both evaluations. There is.

As is clear from Table 3, when the ink droplet amount is within the range of 50 to 160 pl, preferably within the range of 70 to 130 pl at the resolution of 300 dpi, the optical density is high and the gradation is high. You can see that you can print well. If the droplet amount is less than 70 pl, gaps are formed between the dots as shown in FIG. 9, resulting in an image with low optical density. On the other hand, when the droplet amount is 130 pl or more, the dot diameter becomes large, and even if the coverage is low, the actual optical density of the image becomes too high, and the gradation expression becomes poor. It should be noted that when the droplet amount exceeds 200 pl, variations in the droplet amount begin to occur, and image disturbance occurs. On the other hand, at a resolution of 360 dpi, the ink droplet volume is in the range of 40 to 150 pl, preferably 60 to 120.
It can be seen that if it is within the range of pl, printing with high optical density and good gradation can be performed.

Similarly, from Table 4, at a resolution of 600 dpi, the ink droplet volume is within the range of 20 to 55 pl,
It can be seen that when the thickness is preferably in the range of 30 to 45 pl, printing with high optical density and good gradation is possible. 7
At a resolution of 20 dpi, the ink droplet amount is 15 to
It can be seen that when the thickness is within the range of 40 pl, preferably within the range of 20 to 30 pl, printing with high optical density and good gradation can be performed.

As is clear from Tables 3 and 4, the suitable droplet amount differs depending on the resolution. However, when the amount of droplets is converted into the amount of ink adhered per square inch at the time of solid recording and the recording densities are compared, a tendency common to high resolution areas is recognized. That is, 600 dp
At a resolution of i or higher, the ink adhesion amount is 7.2 × 10 ⁶
It can be seen from Table 4 that excellent recording quality is obtained when it is in the range of up to 2.1 × 10 ⁷ pl / inch ² .

Therefore, when designing and manufacturing an ink jet printer having a recording density of 600 dpi or more, the amount of ink adhered during solid recording is 7.2 × 10 ^{6 to} 2.1 × 10 ⁷ pl.
/ Inch ² range, preferably 1.0 × 10 ^{7 to} 1.7 ×
By setting the droplet amount so that it falls within the range of 10 ⁷ pl / inch ² and setting the driving signal (for example, the driving voltage) so as to obtain the droplet amount, continuous gradation is maintained. Recording quality with high optical density can be ensured.

As described in detail above, in the ink jet printer according to the present embodiment, the diameter of the nozzle hole 5 in the ink jet head 1 is set to 55 μm to reduce the resistance to the ink flow. Even when using, the ink is quickly replenished from the ink manifold 7 into the cavity chamber 6 after the ink is ejected, and the meniscus in the nozzle hole 5 immediately returns to the original position. In this state, ink is ejected from the next time onward, so that the ink droplets 9 with the same ejection amount and the same droplet amount are ejected every time. Therefore, even when performing high-speed printing, the same droplet amount is secured every time, and printing can be performed with the original density.

Further, the control system is provided with a droplet amount changing unit 30,
Since the ejection droplet amount and the driving frequency corresponding to the resolution corresponding to the selected print mode are determined, the ejection amount of the droplet suitable for the resolution is performed. Here, as described above, the meniscus returns quickly after ejection, so that the ejection amount is ensured every time even in the case of low resolution printing in which the amount of droplets of one ejection is large and in the case of high resolution printing in which the driving frequency is high. It is possible to print with high quality without making the printed traces light.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various improvements and modifications can be made without departing from the gist of the present invention. That is, although various numerical values are shown and described in the above-mentioned embodiment, the present invention is not limited to these numerical values.

For example, in the above embodiment, the viscosity is 20c.
Although the ink jet printer using the ink of P is shown, it is not limited to this viscosity, and when it is applied to the ink jet printer using the ink of 10 cP or more in which the receding of the meniscus is likely to be a problem because the viscosity is relatively large, preferable effects can be obtained. It has been confirmed. However, the viscosity is 1
If it exceeds 00 cP, besides the receding of the meniscus, there is a problem that the ink is not easily broken and the ejection environment of the ink droplets is significantly deteriorated, which is not suitable as an inkjet ink. Therefore, the application range of the present invention is an inkjet printer using an ink having a viscosity within the range of 10 to 100 cP. Ink having a viscosity in the range of 20 to 40 cP, which has less bleeding, has good ink breakability, and easily forms ink droplets of various droplet volumes, is particularly preferable.

[0056]

As is apparent from the above description, according to the first aspect of the invention, the meniscus quickly recovers to its original position after ejection even when the high viscosity ink within the range of 10 to 100 cP is used. There is provided an inkjet printer that discharges at the same meniscus position each time to obtain a stable ink droplet amount, and high-quality, high-speed printing is possible. Further, according to the second aspect of the invention, since the ink viscosity is within the range of 20 to 40 cP, it is easy to control the droplet amount and the print quality is particularly excellent.

According to the third aspect of the invention, the ink droplet amount is stable even when low-resolution printing is performed in which the droplet amount per ejection is relatively large. Further, according to the invention of claim 4, the amount of ink droplets is stable even when performing high-resolution printing in which the driving frequency of the inkjet head is high. According to the invention of claim 5, 600 dpi
Even when printing is performed at the above high resolution, print quality excellent in optical density and gradation can be obtained.

According to the sixth aspect of the invention, the hot melt ink having a relatively high viscosity even in the liquefied state is used.
The amount of ink droplets is stable. According to the invention of claim 7, the driving frequency of the ink jet head is high, but the amount of ink droplets is stable, and a high quality printing result can be obtained. According to the invention of claim 8, printing is performed with an appropriate droplet amount and drive frequency in accordance with the selection of the printing mode.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an inkjet head according to an embodiment.

FIG. 2 is a block diagram illustrating a control system of the inkjet printer.

FIG. 3 is a diagram showing an example of a pulse signal applied to a driving unit of a piezoelectric element.

FIG. 4 is a diagram showing an example of a pulse signal applied to a driving unit of a piezoelectric element.

FIG. 5 is a diagram showing a state of ink droplet ejection from a nozzle.

FIG. 6 is a diagram showing how dots are formed by ink droplets.

FIG. 7 is a graph showing the relationship between the nozzle diameter and the droplet amount of the second discharge.

FIG. 8 is a diagram showing a state of ejection of ink droplets from nozzles in a conventional inkjet printer.

FIG. 9 is a diagram showing a dot formation state in a conventional inkjet printer.

[Explanation of symbols]

 2 Piezoelectric element plate 2a Vibration part 5 Nozzle hole 6 Cavity chamber 7 Ink manifold 30 Droplet amount changing part

Claims (8)

[Claims] 1. An ink cavity filled with ink having a viscosity within a range of 10 to 100 cP, a nozzle provided in the ink cavity for ejecting ink, and an ink manifold for replenishing the ink cavity with ink. In an inkjet printer including an inkjet head having an energy generating element that pressurizes ink in the ink cavity to eject ink from the nozzle, the nozzle is adjusted by adjusting a waveform of a signal applied to the energy generating element. An ink jet printer having a droplet amount varying means capable of changing a droplet amount of ink ejected from the nozzle, wherein the diameter of the nozzle is within a range of 50 to 70 μm. 2. The inkjet printer according to claim 1, wherein the viscosity of the ink is in the range of 20 to 40 cP. 3. The inkjet printer according to claim 1 or 2, wherein the droplet amount varying means has a resolution within a range of 300 to 360 dpi (dots per inch, vertical and horizontal (the same applies below)). When printing, the amount of ink droplets ejected from the nozzle is 60 to 130 pl (picoliter (= 10
An ink jet printer characterized in that it is within the range of ^-9 cm ³ )). 4. The ink jet printer according to any one of claims 1 to 3, wherein when the droplet amount varying means prints at a resolution within a range of 600 to 720 dpi, the ink ejected from the nozzle is An ink jet printer characterized in that the amount of droplets is in the range of 20 to 45 pl. 5. The ink jet printer according to any one of claims 1 to 4, wherein when the droplet amount varying means prints at a resolution of 600 dpi or more, the droplet amount of ink ejected from the nozzle is set. An ink jet printer characterized in that the amount of ink deposited on a recording medium is controlled to be within a range of 1.0 × 10 ^{7 to} 1.7 × 10 ⁷ pl / inch ² during solid recording. 6. The inkjet printer according to claim 1, wherein the ink is a hot melt ink that is solid at room temperature and is heated and melted to be liquefied. 7. The inkjet printer according to claim 1, wherein the driving frequency of the inkjet head is 8 kHz or higher. 8. The ink jet printer according to claim 1, wherein the ink jet printer has at least two types of print modes having different resolutions, and the droplet amount varying means is in accordance with a selected print mode. The inkjet printer is characterized by changing the amount of ink droplets ejected from the nozzle and the driving frequency of the inkjet head.