JPH0372464B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ink-on-demand type inkjet, and particularly to an inkjet head that can be mass-produced at low cost.

As shown in FIG. 1, the ink-on-demand type ink jet head is composed of a head substrate 1, a diaphragm 2, and a piezoelectric element 3, and has a very simple structure. However, because the diameter of the nozzle 4 is small, it is quite difficult to actually mass-produce the head. At present, heads made of photo-etched photosensitive glass are in practical use, but they are difficult to mass produce and are expensive.

The inventors of the present invention have been developing plastic heads by injection molding in order to mass produce inkjet heads at low cost, but it has become clear that the thickness of the head substrate must be increased due to the low elastic modulus of plastic. came. That is, if the thickness of the head substrate is thinner than the laminated plate of the piezoelectric element and the diaphragm, pressure will escape to the head substrate, and the electrical energy applied to the piezoelectric element will not be used sufficiently to eject ink.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an inkjet head with a thin head that can be manufactured at low cost.

The gist of the present invention is to suppress an increase in the thickness of the head by adhering to the head substrate a reinforcing member having a higher elastic modulus than that of the head substrate.

A schematic cross-sectional view of an embodiment of the invention is shown in FIG.
On the surface of the head substrate 1 made of ABS resin, there are nozzles 4,
Ink flow paths such as the pressurizing chamber 5 and the supply path 6 are formed as grooves. Head board 1 and diaphragm 2 made of the same material
are bonded with dope cement, and the piezoelectric element 3 is bonded at a position corresponding to the pressurizing chamber 5. The head substrate 1 is bonded with epoxy resin to a reinforcing plate 7 made of steel that has been punched into a predetermined shape using a press. At the same time, a head substrate 1' laminated on a piezoelectric element 3' and a diaphragm 2' is adhered to the opposite surface of the reinforcing plate 7. Here, the head substrate 1 and the diaphragm 2', and the head substrate 1' and the diaphragm 2 are the same parts, and the piezoelectric elements 3, 3'
The glued side functions as a diaphragm.

In the above configuration, in order to prevent the drive energy of the piezoelectric elements 3, 3' from escaping due to the deflection of the opposing head substrates, the thickness of the head substrates 1, 1',
The thickness of the reinforcing plate 7 needs to be sufficiently thick. Quantitatively, energy escape can be estimated from the amount of change in volume with respect to the same pressure on the diaphragm side and the head substrate side, that is, compliance.

If the shapes of the pressurizing chamber 5 and the piezoelectric element 3 are calculated as circles, the compliance C ₁ of the laminated plate of the diaphragm 2 and the piezoelectric element 3 can be expressed as follows. Here, the subscript p represents a piezoelectric element, and the subscript v represents a diaphragm.

C ₁ = πa ⁶ (1-νv) (7+νv)/16Evh ₁ ³ … h ₁ = hv+k ₁・hp … where a: piezoelectric element radius, Ep, Ev: longitudinal elastic modulus, νp, νv: Poisson's ratio, hp, hv: thickness, h ₁ :
Equivalent thickness of laminate, k ₁ : Equivalent coefficient that converts piezoelectric element thickness to diaphragm thickness.

Similarly, the compliance _C2 of the laminate of the head substrates 1, 1' and the reinforcing plate 7 can be expressed as follows. Here, the subscript m represents the reinforcing plate, the subscript b represents the head substrate, and E, v, h, etc. are the constants described above.

C ₁ = πa ⁶ (1-νb) (7+νb)/16Ebh ₂ ³ … h ₂ = 2hb+k ₂ hm … However, h ₂ : Equivalent thickness of the laminate, k ₂ : Equivalent coefficient for converting the thickness of the reinforcing plate to the thickness of the head board.

Since the pressure escape to the head board side can be considered as the ratio of the volume change on the board side and the diaphragm side due to the same pressure, in order to reduce the pressure escape to a predetermined ratio K or less, C ₂ ≦KC ₁ ... holds true. Just do it. Since the diaphragm and head board are made of the same material, Ev = Eb, νv = νb, and the formula ~
To summarize the formula, hm≧1/k ₂ (hv+k ₁ hp/k1/3-2hb)...

Specifically, Ep=5.9×10 ¹⁰ N/m ² , νp=0.3, hp
=0.15mm, Ev=Eb=2.1×10 ⁹ N/m ² , νv=νb=
0.37, hv=hb=0.3mm, Em=2.1=10 ¹¹ N/m ² ,
By substituting νm=0.3 and K=0.1 into the equation, hm≧
It becomes 0.23mm. If this is to be satisfied by increasing the thickness of the head substrate without using a reinforcing plate, the thickness will be k2 _times larger, and hm≧1 mm. Therefore, assuming the thickness of the head substrate section to be hm+2hb, the thickness of the head substrate section, which was required to be 1.6 mm, can be reduced to 0.83 mm by inserting a steel plate as a reinforcing plate, and the same effect can be obtained.

As stated above, by using a reinforcing plate with a thickness that satisfies the formula as an intermediate substrate, an inkjet head with low pressure loss and no adverse effects from vibration leakage on both sides can be obtained, and the thickness of the head can be made thinner. .

The formula , , is for the case where the diaphragm 2 and the head board 1 are supported circumferentially, and when the state of the bond between the diaphragm 2 and the head board 1 can be considered to be fixed circumferentially, C ₁ = πa ⁶ (1−νv ² )/16Evh ₁ ³ … C ₁ = πa ⁶ (1−νb ² )/16Ebh ₂ ³ …′ It is better to find it by substituting it into the formula. Specifically, when calculating with the same constant as used before, hm≧0.13
mm.

In addition, when the pressurizing chamber 5 and the piezoelectric element 3 are rectangular, when they can be regarded as peripheral support, Just substitute it into the formula. Specifically, when calculated using the same constant as before, hm≧0.22mm.

Also, when it can be considered that the periphery is fixed, Just substitute it into the formula. At this time, when calculated in the same way as before, hm≧0.13mm.

In each of the calculation examples above, K = 0.1, but in order to further suppress injection instability due to vibration leakage to the back side, the pressure loss is set to 5% or less, and if K = 0.05, the circular shape and peripheral support are determined by the formula. If it can be considered, km≧0.32mm, if it can be considered as peripheral fixed,
Km≧0.2mm, Km≧0.19 if rectangular and peripheral fixed
The thickness of the reinforcing plate should be selected in mm.

The embodiment shown in FIG. 2 shows a double-sided head in which the head board is bonded to both sides of the reinforcing plate, but if the head board is bonded to only one side of the reinforcing plate, 2hb may be replaced by hb in the equation.

Various values can be taken for the value of K, but when priority is given to the thinness of the head, K = 0.1, and when priority is given to preventing increases in voltage and instability, K = 0.05 may be selected.

Ceramic and various metals can be used as the reinforcing plate, but steel plates, stainless steel plates, etc., which have a high modulus of elasticity, are particularly suitable.

In addition to ABS, AS resin, acrylic resin, polysulfon, etc. are suitable for the head substrate in terms of head assembly adhesiveness, transparency, etc.

As can be seen from the embodiment shown in FIG. 2, according to the present invention, a reinforcing plate having a higher modulus of elasticity than the head substrate is bonded to the head substrate, thereby resulting in a thinner inkjet head with less pressure loss.

In particular, mass production of low-cost heads becomes possible by welding the diaphragm to the plastic head substrate made by injection molding. Furthermore, since the thickness of the diaphragm and head board can be thin, there are fewer sink marks during injection molding and the flatness is improved, so the amount of solvent cement applied during bonding can be reduced, and therefore the nozzle can be sealed with solvent cement. It becomes less likely to occur. Furthermore, since the diaphragm and head board are thin, the pressing force of the assembly jig can be weak, and the nozzle is less likely to collapse.

In addition, since the pressurized chamber is covered with a metal plate, it is less likely that ink will evaporate through the plastic or that air will enter.

Furthermore, the weight of the head can be reduced compared to a head made only of photosensitive glass or metal, and the energy and drive motor for moving the head are also advantageous.

Furthermore, since the head substrate can be made thinner, the width w of the front surface of the nozzle becomes smaller, the accumulation of ink is reduced, and the stability of ink ejection is increased. In particular, if a material with good ink wettability, such as a metal plate, is used as the reinforcing plate, the ink on the front surface of the plastic nozzle will be less likely to be pulled by the reinforcing plate and accumulate. In particular, if the reinforcing plate 7 is provided at a position lowered from the nozzle front face 9 as in the embodiment shown in FIG. 2, the ink 10 on the nozzle front face 9 will be pulled by the reinforcing plate 7 like the ink 8, and the effect will be even greater. For example, in the embodiment shown in FIG. 2, when the ink colors on both the left and right sides are red and black, the mixing of red and black inks is reduced.

Furthermore, in the embodiment shown in Fig. 2, the right and left head parts are made common and only the bonding surface of the piezoelectric element is changed, so there is an advantage in mass production that only one type of injection mold, assembly jig, etc. is required. be.

As described above, the present invention not only can provide a thin head with little pressure loss, but also has many effects and can be widely applied to serial printers, line printers, plotters, cobia, facsimile machines, etc.

As described above, according to the present invention, by laminating a metal plate with a high elastic modulus on the outside of a synthetic resin substrate, the elastic modulus of the substrate is improved, and the pressure generated in the pressure chamber is transferred to the substrate side. This enables efficient ink jetting and good inkjet recording. Further, even if this occurs on the synthetic resin substrate, it is corrected by the lamination of the metal plates, ensuring close contact between the substrates, and preventing ink from going around to adjacent channels and preventing pressure from escaping.

In addition, since a metal plate is laminated on a synthetic resin substrate to cover pressure chambers, etc., ink evaporation through the substrate,
This prevents air from entering the inside, and prevents clogging and deterioration of the ink due to ink drying.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional inkjet head, and FIG. 2 is a sectional view of an embodiment of the present invention. 1, 1'... Head board, 2, 2'... Vibration plate,
3, 3'... Piezoelectric element, 4... Nozzle, 5... Pressurizing chamber, 7... Reinforcement plate.

Claims (1)

[Scope of Claims] 1. A pressure chamber that connects a nozzle for ejecting ink to generate pressure for ejecting ink, and an ink supply path that supplies ink to the pressure chamber are formed between laminated substrates. A laminated ink jet head according to the present invention, wherein the substrate is made of synthetic resin, and a metal plate having a high elastic modulus is laminated on the outside of the substrate.