JPH05338192A - Line type inkjet recording device - Google Patents

Abstract

(57) [Abstract] [Purpose] Even if the device is installed at an inclination, the liquid level does not change, and the negative pressure in the nozzle that depends on the height difference between the liquid level in the ink tank and the nozzle is set. (EN) Provided is a line type ink jet recording apparatus which does not greatly change even if an angle changes, and has good characteristic in the head without variation in characteristics. .. A plurality of independently controllable nozzles 20 are divided into nozzle groups, and each nozzle group communicates with a corresponding specific ink tank 21, 22, 23 ,. A communication window 38 connects the ink tanks.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet recording device. In particular, the present invention relates to a line-type inkjet recording apparatus that performs recording by ejecting ink onto a recording material by a line-type recording head.

[0002]

2. Description of the Related Art As an ink jet printer, there is known a method of scanning by a line type ink jet recording head in which a plurality of nozzles are arranged in a direction orthogonal to a conveying direction of a recording paper for recording (Japanese Patent Laid-Open No. 3-187771). In such an apparatus, the recording head can be configured to have a large number of nozzles, and an apparatus capable of high-speed recording can be realized.

[0003]

In the above structure, the recording head is a long head which is long in the nozzle arrangement direction. Therefore, in order to equalize the negative pressure acting on each nozzle, the recording head is installed in the device. It is arranged horizontally.

However, even with such a configuration, there is a problem that the allowable range of the installation angle of the device is small. This is explained below.

As shown in FIG. 6, n nozzles of the recording head 60 are designated as 1 #, ..., J # (nozzles located at the center) ,. It is assumed that the ink 62 contained in the ink tank 61 provided below is ejected by pulling up the distance H by the distance H by the capillary force. When the installation angle of the device is from horizontal to θ, the value of the negative pressure applied to each nozzle is as follows.

P1 (negative pressure applied to the 1 # nozzle) = H · cos (θ) − (L / 2) · sin (θ) Pj (negative pressure applied to the j # nozzle) = H · cos (θ) Pn ( n # Nozzle negative pressure) = H.cos (.theta.) + (L / 2) .sin (.theta.) Therefore, a negative pressure difference of L.sin (.theta.) occurs between the nozzles at both ends. On the other hand, the ejection characteristics of the inkjet head are greatly affected by the negative pressure.

This is because the amount of ink flowing into the nozzle at the time of ejection is regulated by the difference between the supply negative pressure, which is the sum of the negative pressure and the flow path resistance of the supply path, and the capillary force of the nozzle portion. If the negative pressure value is large, as a result, the supplied negative pressure value becomes large and the amount of ink supplied to the head becomes insufficient,
The amount of ejected ink is reduced and a predetermined image cannot be formed. In an extreme case, as a result of the decrease in the ink amount in the nozzle part, the ink surface (meniscus) cannot be restored to the normal position, and when the pressure chamber part leading to this is largely retracted, the capillary force is greatly reduced. However, air is drawn into the inside of the inkjet head, resulting in malfunction.

In the opposite case, when the negative pressure shifts to the positive pressure side, the ink ejection form changes, the dot shape does not become normal, and the ink leaks from the nozzle.

The appropriate value of the negative pressure depends on the ejection specifications (frequency, ejected ink amount, etc.), ink jet head shape conditions (nozzle size, flow path resistance, etc.), and ink fluid characteristics (surface tension, specific gravity, viscosity, etc.). .. As a typical value that the present inventor has conducted an experiment with, as an example, the range of the allowable negative pressure (absolute value) is 0-150 mm hydrohead when expressed by the hydrohead value. Further, the allowable negative pressure range was ± 5 mm hydrohead in order to obtain characteristics that did not vary among the nozzles.

In this case, H = 100 mm and L = 2
The allowable range of installation angle θ when 00 mm is sin θ <
From 0.05, θ <2.9 °.

It is difficult to suppress the inclination within the above range of θ in the actual use state, and there is a problem that it becomes a restriction in use of the apparatus.

The present invention solves this problem, and an object thereof is to obtain a line type ink jet recording apparatus having a large installation angle allowable range of the apparatus.

[0013]

SUMMARY OF THE INVENTION The present invention is a line type ink jet recording apparatus for performing recording by ejecting ink onto a recording material by a line type ink jet recording head, and a plurality of nozzles of the recording head do not have ink circulation with each other. The nozzle group is characterized in that the nozzle group is communicated with a corresponding specific ink tank.

[0014]

According to the above structure, the negative pressure of the nozzle portion depends on the height difference between the ink surface of the ink tank and the nozzle portion.
Since the ink surface of the ink tank is divided by the partition wall, it does not change significantly depending on the installation angle. Therefore, even if the installation angle changes, the negative pressure in the nozzle portion does not change significantly, the difference in negative pressure between the nozzles is small, and good ejection characteristics are maintained.

[0015]

EXAMPLES Examples of the present invention will be described.

FIG. 1 is a perspective view of the ink jet printer of the first embodiment. This printer has a structure in which an ink image is formed on the transfer drum 1 and then transferred onto a recording paper 8 which is a recording material, and the recording head 2 scans the transfer drum 1. The ink is an emulsion in which colored particles are dispersed in an ink dispersion medium. The ink dispersion medium is a petroleum solvent, that is, a high resistance low dielectric constant aliphatic hydrocarbon solvent (for example, Isopar G manufactured by Exxon Chemical Co.). The colored particles are composed of Raven 1255 of Colombian Carbon Co., Ltd. as a pigment and ethyl cellulose as a resin, which are made into fine particles having an average particle size of 1 μm and dispersed in the above dispersion medium together with an organic amine as a dispersion stabilizer as an additive. is doing.

The ink is diluted with an ink dispersion medium so that the solid content concentration defined by the following definition is 25 wt% so that the ink can be ejected from the recording head 2.

Solid content concentration = (weight of colored particles) / (weight of colored particles + weight of dispersion medium + weight of additive) The transfer drum 1 has an image forming layer 17 formed of a silicone rubber layer around a metal tube 16. Consists of Silicone rubber does not repel ink drops and has the property that ink drops do not spread greatly. Furthermore, the ink image releasability is good, and pressure transfer to a recording medium is possible at low pressure. In addition, since the surface of the recording paper is deformed due to the unevenness of the surface of the recording paper due to elasticity, the transfer drum 1 is not affected by the smoothness of the recording paper.
It has the characteristic that the above ink image can be faithfully transferred to the recording paper. Therefore, it is suitable for the image forming layer 17. A pressure roller 9 is provided as a pressure applying unit that presses the recording paper 8 toward the transfer drum 3.

Next, the structure of the recording head 2 will be described with reference to FIGS.

In FIG. 2, an electromechanical conversion means 31 is provided corresponding to each nozzle 20 so that ink can be ejected independently from each nozzle 20. This uses a piezo element to expand in the direction of arrow B by applying voltage control and deform the metal thin film 44 to increase the pressure in the pressure chamber 35 (the space between the metal thin film 44 and the nozzle filled with ink). , Eject ink drops. The pressure chamber 35 is connected to a nozzle group including specific nozzles by an ink supply path 32, and the ink supply path 32 is located in the rear portion of the recording head 2 with ink tanks 21, 22, 23, 24, 25, 26. , 27. As shown in FIG. 2, the ink tank (which will be described as a representative of 24) is separated by a partition having an ink communication window 38 in the upper part, and the drain ports provided in the ink tanks 21 and 27 at both ends. Except for 43, they have the same sectional shape. Each ink tank is configured to communicate with a specific nozzle group through each ink supply path and supply ink to the corresponding nozzle group.

In FIG. 3, the recording head 2 has a plurality of nozzles (typically represented by 20) on the front surface facing the transfer drum 1. A supply pipeline 6 for supplying ink from the ink container 3 using a pump 4 is connected to the ink tanks 21 and 27 at both ends. The supply conduit 6 has an ink end detector 51, which issues an ink end signal when the liquid level in the ink container 3 drops and air flows in. As a detector used for this purpose, a pair of light-emitting and light-receiving elements having an optical path orthogonal to the transparent portion of the supply conduit 6 is used. When the ink flows through the conduit, the emitted light is absorbed by the ink and does not reach the light receiving element, but when the air flows through the conduit, the light is transmitted through the conduit and is received, thereby performing detection. The air sent immediately before the ink end floats on the liquid surface immediately after being sent to the ink tanks 21 and 27,
Since it escapes to the atmosphere, it does not enter the ink supply path 32. Since the ink according to this embodiment has a light absorption characteristic of absorbing almost all infrared light, a pair of light emitting and light receiving elements using infrared light is suitable. It is needless to say that even when an ink other than this embodiment such as a color is used, it can be applied by using light having a wavelength corresponding to the light absorption characteristics of the ink used for the light emitting element, the ink tanks 21 and 27 at both ends are provided with the wall 43. , 44, and the recovery tanks 28, 29 are connected to the ink container 3 via the drain conduit 5. During the recording operation, the discharge amount of the pump 4 is increased or decreased by the overflow detector 52 so that a small amount of ink always flows out to the drain conduit 5. A detector having the same configuration as the ink end detector 51 is used as the detector.

Next, the operation will be described.

First, the image forming operation will be described.

In FIG. 1, the transfer drum 1 rotates in the direction of arrow A during operation. The recording head 2 selectively ejects ink droplets from a plurality of nozzles, and the recording head 2 transfers the ink drops onto the transfer drum 1.
Form an ink image. Since the ink dispersion medium has an evaporating property and the image forming layer 17 has a property of absorbing the ink solvent, the ink solvent is removed from the ink image on the transfer drum 1 and colored particles are formed on the transfer drum 1. An ink image having a high density is formed. Next, the recording paper 8 is brought into contact with the transfer drum 1 and pressed by the pressure roller 9 to transfer the ink image.

Since the ink image has a high density on the transfer drum 1, the ink is soaked in the recording paper fiber in the transfer process and the image is faithfully transferred without blurring the edges. The image is obtained.

Next, the ink supply operation to the recording head 2 will be described with reference to FIGS. 3 and 4. FIG. 4 is a view seen from the direction of arrow G in FIG.

The recording head 2 includes an ink tank 21, ...
Ink is supplied from the ink container 3 to the ink tanks 21 and 27 at both ends by using the pump 4. Ink tanks at both ends (represented by 21) are raised in level by the supply of ink, and when they reach the ink communication window 38, they flow into the adjacent ink tanks 22. Further, when the ink level in the ink tank 22 exceeds the communication window 38, the ink level flows into the adjacent ink tank 23. Thus, all the ink tank liquid level reaches the ink communication window 38, the ink level further rises, and when it exceeds the drain port 43 which is set slightly higher than the ink communication window 38, the recovery tank 28
To the ink container 3 through the drain conduit 5. During the recording operation, the discharge amount of the pump 4 is increased / decreased by a drive circuit (not shown) so that the ink always flows out to the drain conduit 5 by the overflow detector 52, and the ink level is maintained without excess or deficiency with minimum power consumption. be able to.

Next, the change in the negative pressure of the nozzle portion when the apparatus is installed at an inclination will be described with reference to FIG.

When the installation posture changes, the ink tank (25
Since the ink surface in (indicated by 1) is kept horizontal, the ink that has passed the lower portion of the ink communication window 38 flows into the adjacent ink tank 26. In the ink tank 27, the ink is collected in the collection tank 28 after passing through the drain port 43.
A certain amount of ink remains in each ink tank, but since the ink tanks are divided, there is little difference in the negative pressure of the nozzles of the nozzles that communicate with the same ink tank. Further, since the ink tanks have the same cross-sectional shape except for the drain port 43 which is provided slightly higher than the communication windows 38 provided in the ink tanks 21 and 27 at both ends, the liquid surface of each ink tank is blunt. It becomes the same and no difference occurs between the nozzle groups.

In the structure of this embodiment, the line type recording head is divided into a plurality of nozzle groups which do not circulate with each other and communicates with a specific ink tank corresponding to this nozzle group, so that the apparatus is installed at an inclination. Even in this case, the difference in negative pressure between the nozzles in each nozzle group is small. Furthermore, by making the shape of each ink tank the same, there is an effect that there is no difference between the groups of nozzle groups corresponding to each ink tank.

[0031]

In the line type ink jet recording apparatus of the present invention, the negative pressure of the nozzle portion depends on the height difference between the liquid surface of the corresponding ink tank and the nozzle portion, but the ink liquid surface of the ink tank is divided by the partition wall. To be done. Therefore, even if the installation angle changes, the negative pressure applied to each nozzle does not change significantly. Therefore, even if the installation angle changes, good ejection characteristics are maintained, and it is possible to obtain a line type inkjet recording apparatus having a large installation angle allowable range.

[Brief description of drawings]

FIG. 1 is a perspective view of a line type inkjet recording apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an internal configuration of a recording head of a line type inkjet recording apparatus according to an embodiment of the present invention.

FIG. 3 is a perspective view showing a configuration of a recording head of the line type inkjet recording apparatus according to the embodiment of the present invention.

FIG. 4 is a diagram illustrating ink supply when the line-type inkjet recording apparatus according to the embodiment of the present invention is installed horizontally.

FIG. 5 is a diagram showing ink behavior in the ink tank when the installation angle of the line type inkjet recording apparatus according to the embodiment of the present invention is θ.

FIG. 6 is a diagram illustrating the installation angle dependency of the negative pressure of the nozzle portion.

[Explanation of symbols]

1: Transfer Drum 2: Recording Head 3: Ink Container 4: Pump 5: Drain Pipeline 6: Ink Supply Pipeline 8: Recording Paper 21, 22, 23, 24, 25, 26, 27, 61: Ink Tank 28, 29: Recovery tank 38: Communication window 43: Drain port 62: Ink

Claims (1)

[Claims] 1. A line type ink jet recording apparatus for performing recording by ejecting ink onto a recording material by a line type ink jet recording head, wherein nozzles are divided into a plurality of nozzle groups having no ink circulation, and the nozzles are divided. The group is a line type ink jet recording apparatus characterized by communicating with a corresponding specific ink tank.