JPS59187871A - Ink jet recording head - Google Patents

Abstract

PURPOSE:To realize the speed up in gradation recording by a method wherein outlet areas of plural nozzles are made to be different to each other and at the same time, the construction reaching the outlet of respective nozzle (nozzle length, taper angle etc.) are made to be different under the conditions where all fluid resistance of respective nozzle are equalized. CONSTITUTION:In the on-demand type ink jet printer carrying out gradation recording, outlet areas of plural nozzles 10a-10d provided to printer head are respectively made to be different to each other and at the same time, internal constructions reaching outlets of respective nozzles 10a-10d (for example, nozzle length, taper angle etc.) are made different to let the fluid resistance of ink the same to all nozzles 10a-10d. Further, the fluid resistance G at nozzle part is expressed as G=KvDv<2>/Lv (K represents coefficient and v is the kinematic viscosity of ink).

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an ink jet printer 1 to a recording head, and particularly to a monochrome or multicolor recording head having a plurality of nozzles with different cross-sectional areas for excellent gradation recording. The present invention relates to an on-demand inkjet recording head.

(b) Prior art and problems In conventional inkjet recording heads, gradation recording (
In order to express color shading), a recording head system that uses multiple nozzles with different cross-sectional areas in parallel and has a structure that changes the size of ejected ink droplets can be considered.

Figures 1 to 3 show an example of a recording head, in which Figure 1 is a plan view, Figure 2 is a sectional view taken along line AA in the same figure,
FIG. 3 is a side view of the nozzle seen from the front. In the figure, a head base 1 is provided with one ink chamber 2, four ink supply paths 3, four piezoelectric elements 4 for individually controlling ink ejection, and one nozzle plate 5. Board 5
Four nozzles 6a, 6b, 6c, and 6d, each communicating with the four ink supply paths 3 and having different cross-sectional areas, are formed in the nozzles 6a, 6b, 6c, and 6d. Since the nozzle is generally cylindrical, the cross-sectional area is changed by changing the nozzle diameter, and the nozzle 6a
The diameter is the largest, and the diameters are successively smaller, 6b, 6c, and 6d.

By the way, when the cross-sectional area of the nozzles differs in this way, the size of the ejected ink particles changes and it is possible to perform gradation recording, but on the other hand, when the ink has the same physical properties (viscosity, etc.), each nozzle part There is a problem that the fluid resistance differs between the two.

For this reason, differences arise in the particle formation characteristics of each nozzle, especially in the particle formation frequency characteristics, and the recording speed of the entire head is determined by the nozzle with the worst particle formation frequency characteristics, which is a drawback in that the recording speed cannot be increased. Hail! Therefore, it is necessary to eliminate this difference in particle frequency characteristics.

One possible way to adjust this is to change the physical properties of one ink for each nozzle with a different cross-sectional area, but this would require separate ink chambers (ink reservoirs), and the fixing time of the ink would be limited. This is not a practical method because it causes differences in recording characteristics such as recording density and recording density.

In addition, if each nozzle is inevitably used with different fluid resistance, the rate of change in atomization characteristics due to changes in the temperature around the head will be different for each nozzle, making it extremely difficult to control the temperature of the entire head. There's a problem.

(C) Object of the Invention The object of the present invention is to reduce the number of nozzles by equalizing the fluid resistance of a plurality of nozzles having different cross-sectional areas without employing the above-mentioned difficult method. The purpose of the present invention is to provide an on-demand inkjet recording head that eliminates the difference in atomization characteristics caused by the difference in fluid resistance of the inkjet recording head, and is capable of stable and high-speed recording.

(d+ Structure of the Invention The object of the invention is to provide a plurality of nozzles that can individually control the ejection of ink, each of the plurality of nozzles having an exit shape with a different cross-sectional area, and furthermore, the plurality of nozzles has a plurality of nozzles that eject ink. This can be achieved by using inkjet recording heads that have different structures leading to the nozzle exits so that the fluid resistance is all equal. This is taper adjustment.

tel　Embodiments of the invention Examples will be described in detail below with reference to two drawings.

FIG. 4 is a sectional view of one cylindrical nozzle 6 used in an on-demand type head, where Dn indicates the diameter of the nozzle and Ln indicates the length of the nozzle. Now, assuming that the fluid resistance of the nozzle portion is G, G is expressed by the following equation.

G = K v Dn2/Ln However, K is a coefficient and υ is the kinematic viscosity of the ink.

Therefore, from this formula, the cross-sectional area of the nozzle part π(Dn/2
) 2 and it is clear that the fluid resistance G changes as the nozzle length Ln changes.

Incidentally, in an on-demand recording head, the upper limit of the graining frequency is determined by the time Tg required for the meniscus to return to an equilibrium state after graining. This Te is called the residual vibration damping completion time, and the ink kinematic viscosity υ minimizes this Te. should exist. The smaller the Te, the higher the particle formation frequency and the faster the recording speed.

From this point of view, various heads were prototyped. FIG. 5 is a chart based on the experimental results, where Dn=50 μmφ.

This is the relationship data between the ink kinematic viscosity and the residual vibration damping completion time when Ln=300 μm and the ejected ink particle diameter is about 70 μmφ. From this, the ink kinematic viscosity is 5×10 =
m/s, the residual vibration damping completion time Te becomes the minimum. Therefore, it can be seen that there is an ink kinematic viscosity that allows the atomization frequency to be maximized at this time and minimizes Te.

Next, since such optimal ink kinematic viscosity is thought to depend on the nozzle shape, an experiment was conducted to determine this. FIG. 6 is a graph showing the relationship between the nozzle diameter Dn and the optimum ink kinematic viscosity based on the results. Data is Dn-30crmφ, 40.1
71Tlφ, 50μmφ, Ln-100μm, 20
Although the values are taken as 0 μm, it can be seen that the smaller the nozzle diameter, the lower the optimal ink kinematic viscosity value, and the longer the nozzle length, the lower the optimal ink kinematic viscosity value. FIG. 7 is a chart showing the relationship between the nozzle length and the optimum ink kinematic viscosity, assuming Dn=50 μmφ.

Therefore, in the present invention, a recording head was created in which the length of the nozzles was adjusted in order to match the optimum ink kinematic viscosity values of nozzles with different diameters and to equalize the atomization frequency characteristics of each nozzle. FIG. 8 shows a cross-sectional structural diagram of a nozzle according to an embodiment of the present invention, and the nozzle 10a has Dn=60 μmφ,
Ln=230#m, nozzle 10b has Dn=50μmφ,
I, n = 200 /1 m', nozzle 10c is 1) 1
=4Qμmφ, Ln=160, 1-1m.

The nozzle 10d was set to Dn=30pmψ and Ln=100μm. The optimal ink kinematic viscosity at this time is 10 to 15
It was 10-6 m2/s.

With such a nozzle, the pulse width applied to the piezoelectric element is set to 2.
When recorded as 0 μs, the diameter of each jetted particle is 90 μs.
μmφ, 75μmφ, 60μmφ.

The diameter was 45 μm, and a stable gradation image was recorded.

Next, FIG. 9 shows another example of nozzle structure according to the present invention, in which adjustment is made by changing the taper angle θ of the nozzles in order to match the optimum ink kinematic viscosity values of nozzles with different diameters. This is what I did.

According to this method, the length of the nozzle can be kept constant, so it is easy to manufacture. FIG. 10 shows an example of this, in which the nozzle length is Ln-200 μm, and the nozzle 11a is Dn-60 μm.
μmφ, θ-90°, Drl=50μm for nozzle 10b
φ, θ=87°, nozzle 10”'c Dn=40μmφ
, θ-81°, nozzle 10d has Drl=30μmφ, θ
When set to -68°, the optimum ink kinematic viscosity becomes almost equal.

In the above embodiment, a single color head is composed of a plurality of nozzles, but in the case of a multicolor head, color gradation recording can be obtained by arranging a plurality of types of such a plurality of nozzles.

ff) Effects of the Invention As is clear from the above explanation, according to the present invention, it is possible to obtain a plurality of nozzles having substantially the same particle formation characteristics and different cross-sectional areas. It is possible to record monochromatic or multicolor gradation (characters or images) of extremely high quality at high speed without any difference.

[Brief explanation of drawings]

Figures 1 to 3 are examples of conventional recording heads (Figure 1 is a plan view, Figure 2 is an AΔ sectional view of the same figure, Figure 3 is a side view seen from the front of the nozzle), Figure 4 9 is a model sectional view of the nozzle, FIGS. 5 to 7 are data charts, FIG. 8 is a sectional view of the head of one embodiment of the present invention, and FIG. 10 is another embodiment of the present invention. FIG. In the figure, 1 is the base, 2 is the ink chamber, 3 is the ink supply path, 4
The piezoelectric element 35 is a nozzle plate, and 6 and 10 degrees 11 are all nozzles. Figure 1 Figure 4) S-Ln -) Nozzle 9 threads (jW') Figure 7 Nozzle (mm) Figure 8 Figure 10

Claims (3)

[Claims] (1) It is equipped with a plurality of nozzles that can individually control the ejection of ink, and each of the plurality of nozzles has an exit shape with a different cross-sectional area, and furthermore, the plurality of nozzles have the same fluid resistance of the ejected ink. The ink side recording head is characterized in that each nozzle has a different structure leading to its exit. (2) The inkjet recording head according to claim 1, wherein said different nozzle structure is an adjustment of nozzle length. (3) The inkjet recording head according to claim 1, wherein the different nozzle structure is adjustment of the nozzle taper.