JPH0698765B2 - Inkjet head - Google Patents

Description

TECHNICAL FIELD The present invention relates to an inkjet head, and more particularly, to a structure of an orifice portion in a bubble jet type inkjet head.

Prior Art The non-impact recording method has recently attracted interest in that noise generation during recording is negligibly small. Among them, high-speed recording is possible,
The so-called inkjet recording method, which can record on plain paper without requiring a special fixing process, is an extremely powerful recording method. Various methods have been proposed and commercialized with improvements. Some have been made, while others are still trying to be put into practical use.

Such an inkjet recording method is one in which droplets of a recording liquid, so-called ink, are ejected and adhered to a recording member to perform recording. The method is roughly classified into several methods according to a control method for controlling the flight direction of the generated recording liquid droplets.

First, the first method is disclosed in, for example, U.S. Pat. No. 30,60429 (Tele type method), in which droplets of a recording liquid are electrostatically attracted to generate a recording liquid droplet. The electric field is controlled according to the recording signal, and the recording liquid droplets are selectively deposited on the recording member to perform recording.

This will be described in more detail. An electric field is applied between the nozzle and the acceleration electrode to eject uniformly charged droplets of the recording liquid from the nozzle, and the ejected droplets of the recording liquid are used as recording signals. Accordingly, recording is performed by flying between xy deflection electrodes configured to be electrically controllable, and selectively depositing small droplets on the recording member according to changes in the strength of the electric field.

The second method is the method disclosed in, for example, US Pat. No. 3,596,275, US Pat.
et)), a droplet of a recording liquid with a controlled charge amount is generated by a continuous vibration generation method, and the generated droplet with a controlled charge amount is subjected to a uniform electric field. Recording is performed on the recording member by flying between the deflection electrodes.

Specifically, a nozzle orifice (ejection port) which is a part of a recording head provided with a piezoelectric vibration element.
The charging electrodes configured so that the recording signal is applied in front of are arranged a predetermined distance apart, and the piezoelectric vibrating element is mechanically vibrated by applying an electric signal of a constant frequency to the piezoelectric vibrating element, A small droplet of recording liquid is ejected from the ejection port. At this time, electric charges are electrostatically induced in the recording liquid droplets ejected by the charging electrodes, and the droplets are charged with an electric charge amount corresponding to the recording signal. The droplets of the recording liquid of which the charge amount is controlled are deflected according to the added charge amount when flying between the deflection electrodes to which a constant electric field is uniformly applied,
Only the droplets carrying the recording signal can be deposited on the recording member.

The third method is, for example, the method (Hertz method) disclosed in US Pat. No. 3,416,153, in which an electric field is applied between a nozzle and a ring-shaped charging electrode, and a small amount of recording liquid is generated by a continuous vibration generation method. It is a method of recording by generating and atomizing drops. That is, in this method, the atomization state of the small droplet is controlled by modulating the electric field strength applied between the nozzle and the charging electrode according to the recording signal, and the gradation of the recorded image is produced and recording is performed.

The fourth method is, for example, the method (Stemme method) disclosed in U.S. Pat.
The two methods are fundamentally different in principle.

That is, in all of the three methods, the droplets of the recording liquid ejected from the nozzles are electrically controlled during the flight, and the droplets carrying the recording signal are selectively deposited on the recording member. On the other hand, the Stemme method is used to perform recording by ejecting and ejecting a small droplet of recording liquid from an ejection port according to a recording signal.

In other words, the Stemme method applies an electrical recording signal to a piezo vibrating element provided with a recording head having an ejection port for ejecting a recording liquid, and converts this electrical recording signal into mechanical vibration of the piezo vibrating element. Instead, recording is performed by ejecting and ejecting a small droplet of the recording liquid from the ejection port according to the mechanical vibration and adhering it to the recording member.

These four conventional methods have their respective characteristics, but there are some points that can be solved in the other.

That is, in the first to third methods, the direct energy for generating the droplet of the recording liquid is electric energy, and the deflection control of the droplet is electric field control. Therefore, the first method is simple in construction, but it requires high voltage to generate small droplets, and it is difficult to form the recording head with multiple nozzles. Therefore, the first method is not suitable for high-speed recording.

The second method enables multi-nozzle recording heads and is suitable for high-speed recording, but it is complicated in structure, and the electrical control of recording liquid droplets is highly advanced and difficult. There is a problem that satellite dots are easily generated.

The third method has the feature that an image with excellent gradation can be recorded by atomizing recording liquid droplets, but on the other hand, it is difficult to control the atomized state, and fog occurs in the recorded image. And it is difficult to make the recording head multi-nozzle,
There are various problems such as being unsuitable for high-speed recording.

The fourth method has relatively many advantages as compared with the first to third methods. That is, the structure is simple, and since the recording liquid is discharged from the discharge port of the nozzle on-demand to perform recording, the droplets ejected and ejected as in the first to third methods are ejected. Medium, there is no need to collect small droplets that were not needed for image recording, and there is no need to use a conductive recording liquid as in the first and second methods, and it is not necessary to use a recording liquid substance. It has great advantages such as a high degree of freedom. On the other hand, on the other hand, it is difficult to form a multi-nozzle recording head because of problems in processing the recording head, miniaturization of a piezoelectric vibrating element having a desired resonance number, and the like. However, since the recording liquid droplets are ejected and ejected by the mechanical energy of mechanical vibration of the piezoelectric vibrating element, it is not suitable for high-speed recording.

Furthermore, JP-A-48-9622 (US Pat. No. 374712
(Corresponding to No. 0 specification), as a modified example, it is described that thermal energy is used instead of using mechanical vibration energy by means such as the piezoelectric vibration element described above.

That is, the above-mentioned publication describes a so-called bubble jet liquid jet recording apparatus that uses a heating coil that directly heats a liquid in order to generate vapor that causes a pressure increase, as a pressure increasing means instead of a piezoelectric vibrating element. There is.

However, in the above-mentioned publication, the liquid ink in a bag-shaped ink chamber (liquid chamber) having only one opening through which the liquid ink can flow in and out by energizing a heating coil as a pressure increasing means is directly vaporized. It is only described that, when performing continuous repeated liquid discharge, how to heat,
There is nothing to suggest. In addition, since the position where the heating coil is provided is provided at the deepest part of the bag-shaped liquid chamber far away from the liquid ink supply path, the head structure is complicated and continuous at high speed. For repeated use,
It is unsuitable.

Moreover, from the technical contents described in the above publication, it is not possible to promptly form the preparation state for the next liquid ejection after the liquid ejection is performed by the generated heat which is practically important.

As described above, the conventional method has advantages and disadvantages in terms of configuration, high-speed recording, multi-nozzle recording head, occurrence of satellite dots and occurrence of fog in recorded images. There was a constraint that it could only be applied.

Further, JP-A-55-107481 discloses that a recording liquid introduced into a liquid chamber is discharged and ejected as small droplets from an orifice communicating with the liquid chamber, and the small droplets are attached to a recording paper surface. In a liquid jet recording apparatus for recording, there has been proposed a recording head in which at least the peripheral portion of the orifice is processed to have an affinity for the liquid.
However, if the peripheral edge of the orifice is made compatible, in the case of a head with a high density array, when an ink droplet is ejected, the ink from the adjacent orifice will also be dragged (ejected) and fly. Due to the influence, there is a drawback that the jet direction is bent or the ink when it is dragged becomes satellite droplets and disturbs the image quality.

The present invention was made in view of the above-mentioned actual circumstances,
In particular, in an inkjet capable of high-density arrangement (4 orifices / mm or more) such as a bubble jet type inkjet, the purpose is to prevent mutual interference between adjacent orifices during ejection.

Structure In order to achieve the above object, the present invention has a plurality of ejection orifices arranged close to each other, and heats an ink containing water as a main solvent introduced into a liquid chamber communicating with each orifice. A heating element for applying energy, the heat generation of the heating element causes a state change instantaneously, and the action force of the state change causes the ink to be ejected and ejected as small droplets from the ejection orifices. In a bubble jet type ink jet head for recording by depositing droplets on a recording surface, each discharge orifice is formed in a common nozzle plate, and the orifice opening is
The nozzle plate is such that the edge lines forming the orifice end of each orifice are separated and independent from each other, and the outer surface of the nozzle plate is a water repellent nozzle plate, Nozzle plate having discharge orifices with a density higher than 16 / mm in one row, where 0.46l <d, where d is the opening size of the orifice and l is the distance between adjacent orifice edges. It is characterized by. Hereinafter, description will be given based on examples of the present invention.

The present invention relates to a multi-orifice type inkjet, and more particularly to a bubble jet type multi-orifice head capable of high density array (4 orifices / mm or more).
Conventionally, there is known an ink jet head that makes the peripheral portion of the orifice compatible with the above. However, in such a head, the peripheral edge of the orifice is wetted by the ink due to the affinity, so
When ink droplets are ejected from two orifices, the ink around them is also dragged, causing the droplets to fly and forming satellite droplets. Or, the ink droplets on the periphery can stabilize the ejection direction of the ink droplets. Without
In the case of a high-density array head, there is a drawback that ink droplets ejected simultaneously from the adjacent orifices merge during flight or ejection.

The present invention has been made in view of the above points, and proposes a head that does not cause dragging of the ink in the peripheral portion, instability of the ejection direction, merging of droplets during ejection or during flight, and the like.

The present invention will now be described in more detail with reference to examples.
First, an inkjet recording system to which the present invention is applied will be outlined with reference to FIG. For convenience of explanation, a single-orifice recording apparatus will be described below as an example. In FIG. 4, the recording liquid 3, which is generally called ink, is introduced into the liquid chamber 2 through the introduction pipe 1 in accordance with the heat generation of the electricity / heat converter 4 attached to the liquid chamber 2. Instantly change state. The converter 4 is for generating a thermal pulse signal by energizing it through the electrodes 5 ₁ , 5 ₂ connected thereto. In this way, due to the change in the state of the recording liquid 3, an acting force is applied to the recording liquid 3, and as a result, the recording liquid 3 is ejected and flies as small droplets 7 from the orifice 6 and recording on paper or the like. Recording is made by depositing on the member 10.

The converter 4 is provided on the substrate 8, the voltage of the power source 9 is applied according to the recording input, the converter 4 generates heat according to the input signal, and the recording corresponding to the input signal is recorded on the recording target member.
It is formed by the small droplets 7 flying and adhering on the surface 10.

The size (diameter) of the droplet 7 ejected from the orifice 6 and flying is the amount of electric energy input to the electric / thermal converter 4 as information, and the thermal energy converted therein is transmitted to the recording liquid 3. Efficiency, conversion efficiency of electricity / heat converter,
The diameter of the orifice 6, the inner diameter of the liquid chamber 2, the distance from the position of the orifice 6 to the converter 4, the acting force applied to the recording liquid 3, the amount of the recording liquid 3 to be acted on, the specific heat of the recording liquid 3,
It depends on thermal conductivity, boiling point, latent heat of vaporization, etc.

Therefore, the size of the droplet 7 can be easily controlled by changing any one or two or more of these elements, and on the recording member 10 with an arbitrary droplet diameter and spot diameter. You can make a record.

Incidentally, as the electric / heat converting body 4 shown in FIG. 4, a thermal print head (that is, a thermal head) which is widely used in the field of thermal recording in the past is applied. They are classified into thick film heads, thin film heads, and semiconductor heads, depending on the manufacturing method, heating resistor, etc., but all of them can be used in the present invention. However, it is currently desirable to utilize a thin film head, especially when recording at high speed and high resolution.

The recording liquid used in the present invention is water, ethanol,
It is prepared by dissolving or dispersing a wetting agent such as ethylene glycol or the like, a surfactant, and various dyes in a main solvent such as toluene. It should be noted that, in order to prevent the orifice from being clogged, it is effective to use a filter after preparation to pass through the filter or to provide a filter in the liquid chamber as in the case of the existing inkjet recording method.

FIG. 1 is an exploded view of a main part for explaining the configuration of a multi-orifice array device to which the present invention is applied. In the figure, 11 is a heating element substrate, 12 is a heating element (heater layer), 13 is an electrode, and 14 is a lid. A substrate, 15 is a flow path, and 16 is an orifice. On the Al ₂ O ₃ substrate 11 composed of fine particles, SiO ₂ which is the heat storage layer, HfB ₂ which is the heater layer 12 and Al which is the electrode layer 13 are sequentially laminated by the thin film forming technique and then selectively etched as shown in the figure. Made a different pattern.

The present invention exerts its effect in the case of a high-density arrangement. Now, the opening size of the orifice 16 is d (when the orifice is a circle, it means the diameter), and the interval between adjacent orifice edges is l.
Then, 4d> l is satisfied, that is, it is applied to heads arranged in high density. In the present invention, in the head as described above, the outer surface (hatched portion) of the orifice is water-repellent or oil-repellent treated as shown in FIG. The water-repellent or oil-repellent treatment is performed by immersing a prefabricated head in a treatment liquid (for example, a toluene solution of a silicone resin in the case of water-repellent treatment, gum arabic-phosphoric acid aqueous solution in the case of oil-repellent treatment), or This can be easily performed by a method such as spraying with a Teflon dispersion.

The experimental results are shown in Table 1 below. Table 1 shows the case where the orifice plate as in the case of FIG. 3 is used. The ink is a water-based ink and the surface treatment is a water repellent treatment. The nozzle shape is round.

From this, in the case of 4d-l <0, in all cases, good results can be obtained without connecting jets, but in the case of 4d-l> 0, good results are not always obtained. I understand. However, 4d-l> 0
It can be seen that even in the case of, even if the water repellent treatment is performed, good results are obtained. or, It is practical to set the degree to a good yield in order to manufacture the head. Optimally, 0.46l <d is satisfied and 1 per row
It is better to use a nozzle plate with discharge orifices formed at a density above 6 lines / mm.

Next, Table 2 shows the result of an experiment conducted using a head in the case of a so-called edge shooter type in which the tip of the flow path as it is in FIG. A major difference from the case of Table 1 is that the head, especially the orifice portion (nozzle portion) depends on the manufacturing method thereof, but the adjacent orifices are connected to each other by the edge line. Other than that, the water-based ink is used as in the case of Table 1, and the water repellent treatment is also the same.

From this, it is understood that in the case of the head as shown in FIG. 2, good results cannot be obtained unless the water repellent treatment is carried out regardless of the positive or negative of 4d-1. This is because the jets are easily connected to each other because they are connected to each other by the edge line of the ends of the adjacent orifices. Therefore, it goes without saying that the present invention is particularly effective for the orifice shown in FIG. 2 as well as for the orifice shown in FIG.

The present invention can also be applied to a structure in which the orifice plate 17 as shown in FIG. 3 is attached to the front surface of the head as shown in FIG. In the case of FIG. 2, the rectangular orifice has a lid substrate 14 having a channel groove 15 and a heating element substrate.
It is formed by laminating 11 pieces. Therefore, a part of the contour forming the edge of the orifice is connected (connected) to each other by the edge line of the end portion of the heating element substrate 11, and the ink is connected to each orifice by connecting the line on the outer side surface of the orifice. It becomes wet to all and is not preferable to the orifice plate as shown in FIG. Therefore, needless to say, the present invention is effective in the case of FIG. 3, but as shown in FIG. 2, physically (= by the edge line 18 at the end of the heating element substrate), This is especially effective when the ink is easy to contact.

Effect As is apparent from the above description, according to the present invention, in a high-density arrayed bubble jet, the ink jetting direction when ejecting ink droplets ejected from between adjacent orifices is caused by ink wetting on the orifice surface. It is possible to obtain a high image quality without causing merging due to curling, or dragging of ink due to wetting to generate satellite droplets.

[Brief description of drawings]

FIG. 1 to FIG. 3 are configuration diagrams of main parts for explaining an embodiment of the present invention, and FIG. 4 is a configuration diagram for explaining an example of an inkjet recording apparatus to which the present invention is applied. . 11 …… Heating element substrate, 12 …… Heating element, 13 …… Electrode, 14 ……
Lid substrate, 15 ... flow path, 16 ... Orifice.

Claims (1)

[Claims] 1. A heating element having a plurality of ejection orifices arranged close to each other, and providing heat energy to ink containing water as a main solvent introduced into a liquid chamber communicating with each orifice. Then, a state change is caused instantaneously by the heat generation of the heating element, and the ink is ejected as a small droplet from each of the ejection orifices by the acting force of the state change.
In a bubble jet type ink jet head for flying and performing recording by adhering these small droplets to a recording surface, each discharge orifice is formed in a common nozzle plate, and the orifice opening forms an orifice end portion of each orifice. Is a nozzle plate whose edges are separated from each other and independent of each other, and the outer surface of the nozzle plate is a water repellent nozzle plate, and the orifice opening dimension of each of the orifices is d, An ink jet head characterized in that it is a nozzle plate satisfying 0.46l <d when the distance between adjacent orifice edges is 1, and forming discharge orifices at a density higher than 16 lines / mm in one row.