JPH0643130B2 - Liquid jet recording head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention forms bubbles in a liquid by thermal energy, and discharges the liquid from an orifice by the pressure generated at that time, so that characters / images are recorded on a recording medium. The present invention relates to a liquid jet recording head that records such as.

[Prior Art] In this type of liquid jet recording head utilizing thermal energy, a heating resistor is laminated on a substrate of a liquid passage communicating with an orifice, and the liquid is generated by applying a pulse current to the heating resistor. In a dot-printing type liquid jet recording head that heats, it is important to effectively apply thermal energy to the liquid at each pulse, and at the same time to eject the liquid stably when the head is repeatedly driven in order to improve image quality. is there.

As a configuration for that, for example, as disclosed in Japanese Patent Laid-Open No. 55-154171, the thermal conductivity on the substrate is
a lower layer of k ₂ , specific heat c ₂ , density ρ ₂ and thickness L ₂ , a heating resistor layer of thermal conductivity k _H and thickness L _H , and thermal conductivity k ₁ ,
A heating resistor composed of a specific heat c ₁ and a density ρ ₁ and an upper layer of thickness L ₁ is laminated in this order, It is known that the material and dimensions may be determined so as to satisfy the following relational expression. However, τ ... Half-value width of electric signal input to heating resistor t ... Time from input of one electric signal to input of next electric signal S ... Heat acting surface on surface of heat acting portion of upper layer Area ΔT ... Average value of the difference between the surface temperature of the heat-acting surface and the substrate-side surface temperature of the lower layer Q ... The amount of heat generated per electric signal.

[Problems to be Solved by the Invention] By the way, as the shape of the heating resistor, a shape as shown in FIG. 9 is currently proposed. The requirements for defining such a shape are as follows. That is, the rectangular coordinate system XY is set on the surface of the heating resistor 1, φ (x, y) is the potential value at the point (x, y) on the resistor surface, and one of the electrodes on the boundary of the resistor is The boundary value of a certain value is given to the part which is in contact with 2, the boundary value different from the boundary value is given to the part which is in contact with the other electrode 3, and the normal direction of the peripheral boundary is given to the part which is not in contact with either electrode. When the Laplace equation ∂ ² φ / ∂x ² + ∂ ² φ / ∂y ² = 0 is solved for the heating resistor region by giving the boundary condition that the derivative of φ to 0 is 0, the slope of φ is large. It The maximum value of It is specified by the ratio with.

For example, the shape shown in FIG. 9 has a ratio of 1.13. The ratio value of the conventional example shown in FIG. 10 is infinite. If this value is 1.8 or less, the current concentration at the four corners of the heater is less than in the conventional case (infinity), that is, the heat concentration is less at the four corners, and therefore bubbling does not occur first from the four corners. The heating resistor 1 is first foamed from the entire surface. Also, a stable foam is thus obtained. To express this concretely, there is little fluctuation in the volume of the main bubbles (bubbles generated to eject the liquid) up to the ejection frequency of 10 KHz,
Therefore, fluctuations in the volume of the discharged droplets are reduced. That is, stable ejection can be obtained and good printing can be obtained. In addition, the current concentration at the four corners is small and the durability of the heating resistor is improved as compared with the conventional case.

Conventionally, the above formula (1) shown in JP-A-55-154171,
The film composition was determined by (2). However, the currently proposed shape of FIG. 9 is a heater (heating resistor).
Foaming does not occur first from the four corners, and the amount of heat that causes foaming differs from the conventional one. Therefore, when the film structure of the formula shown in JP-A-55-15417 is adopted, there is a problem that heat is accumulated and durability is lowered, and bubbles become unstable.

In the above equations (1) and (2), the lower layer serves as a barrier against heat transfer to the substrate during heating by pulsed current, and heat is transferred to the liquid from the heat acting part mainly through the upper layer. It defines the condition that the temperature of the recording head itself does not finally rise when it is repeatedly driven.

Therefore, in the liquid jet recording head satisfying the above equations (1) and (2), there is no problem in the heat transfer to the liquid for each pulse and the temperature condition of the recording head itself after the application of a large number of pulses, On the other hand, if there is a high temperature part that is higher than the heating limit temperature other than the position where the vapor bubble disappears when the bubble disappears, a streak-like secondary bubble will remain at that position along the liquid flow direction. There is.

The main bubbles generated to eject the liquid are crushed by the force of the liquid flow direction, that is, the liquid flow path direction,
The above-mentioned secondary bubbles that remain after the disappearance of the main bubbles are in the vicinity of the heat-acting surface, and because the height of the bubbles is low, they are not subjected to the force in the liquid flow direction, so Collapses vertically.

The cavitation of bubbles that collapse perpendicularly to the liquid flow path is very large and concentrated locally, and is several tens of times larger than the cavitation caused by the defoaming of the main bubbles. Therefore, due to the cavitation collapse of the bubbles, the upper protective layer of the heat-acting portion was destroyed, the heating resistor was destroyed, and the durability was often deteriorated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid jet recording head that eliminates the above-mentioned drawbacks and has significantly higher durability and higher quality recording properties than the conventional liquid jet recording head.

[Means for Solving the Problems] In order to achieve such an object, the present invention relates to a thermal action part that communicates with an orifice for ejecting liquid and applies thermal energy to the liquid to form bubbles in the liquid. For a heating resistor in a liquid jet recording head that has a heating resistor that generates thermal energy, set the Cartesian coordinate system XY on the resistor surface, and set φ (x, y) to the point (x, y ), The boundary value of the value that is in contact with one electrode of the peripheral boundary of the resistor is given, and the boundary value of the value that is different from the boundary value is given to the part that contacts the other electrode. A boundary condition that the derivative of φ with respect to the normal direction of the peripheral boundary is 0 is given to the part not in contact with the electrode, and the Laplace equation ∂ ² φ / ∂x ² + ∂ ² φ / ∂ is applied to the heating resistance pair region. when solved y ^{2 =} 0, the slope of φ I am come The maximum value of In a liquid jet recording head having a heating resistor having a shape with a ratio of less than 1.8, the heating resistor is formed by laminating a lower layer, a heating resistor layer and an upper layer in this order on a substrate,
In addition, the thermal conductivity of the substance at the position x measured in the layer direction from the boundary between the lower layer and the substrate toward the heat acting part is k (x), and the specific heat is
c (x), density ρ (x), the total thickness of the heating resistor is L, and τ _B is the time from the start of applying heat energy to the disappearance of bubbles, The material and thickness of the heating resistor are set so that

[Operation] The liquid jet recording head of the present invention is characterized in that the temperature of the heating resistor is sufficiently lowered by the time the bubbles disappear. In general, thermal conductivity k, specific heat c, density ρ
In the case where heat is transferred to the substance, when the distance at which heat is transferred after time t (that is, the distance at which the temperature distribution changes) is x, Have a relationship. Therefore, the condition that heat is dissipated by time t _B is Becomes Applying the condition of the above equation (4) to the heating resistor,
Position x of the heating resistor layer measured from the boundary between the lower layer and the substrate
Let k (x) be the thermal conductivity at, c (x) be the specific heat, and ρ (x) be the density. Becomes Here, L is the thickness of the heating resistor, that is, the sum of the thicknesses of the lower layer, the heating resistor layer and the upper layer, and τ _B
Is the life of the bubble, that is, the time from the generation of the bubble to its disappearance.

Therefore, if the heating resistor film is formed so as to satisfy the above equation (5) as in the present invention, the heat is dissipated from the heating resistor by the time τ _B when the bubble disappears, and the temperature is sufficiently increased. Since it completely drops, the problem that bubbles disappear and the bubbles remain in the high temperature part, or secondary bubbles are generated is solved. Oxidation of the heating resistor due to the adiabatic action of bubbles, cavitation when bubbles disappear, etc. Is not generated, it is possible to obtain remarkably high durability which is sufficiently satisfactory in practical use as compared with the conventional liquid jet recording head.

Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings.

First Embodiment FIGS. 1 to 3 show the steps of substrate preparation of the first embodiment of the present invention, and FIG. 4 shows an example of the configuration of the liquid jet recording head of the present embodiment. Here, 101 is a substrate, 102 is a heat generating part, 103,
104 is an electrode.

The substrate forming process of the heating resistor according to the present embodiment will be described. First, as shown in FIG. 2 (B), a 2 μm thick SiO ₂ film is formed by thermal oxidation of a Si wafer which is the substrate support 105. It is the lower layer 106 of the substrate 101. The heating resistor layer of HfB ₂ is formed by sputtering on the lower layer 106.
Form 107 to a thickness of 1300Å.

Subsequently, the Ti layer 50Å and the Al layer 5000Å are successively deposited by electron beam evaporation to form the common electrode 103 and the selection electrode 104. At this time, a circuit pattern as shown in FIG. 1 is formed by a photolithography (photolithography) process, and the heat acting surface of the heat generating portion 102 of the heat generating portion 111 has a dimension of 30 μm.
The width is 150 μm, including the resistance of Al electrodes 103 and 104.
Use a resistance value of 100 Ω.

Next, as shown in FIG. 2 (B), SiO ₂ is laminated as a first upper protective layer 108 to a thickness of 1.6 μm on the entire surface of the substrate 101 by a magnetron high rate sputtering method.

Then, as the second upper protective layer 110, as shown in FIGS. 2A and 2B, Ta is deposited to a thickness of 0.55 μm by a magnetron high rate sputtering method. Then, the second upper protective layer 11
0 is formed by a photolithography process into a pattern covering the upper portion of the heat generating portion 102 as shown in FIGS. 2 (A) and 2 (B).

Further, as shown in FIGS. 3 (A) and 3 (B), a photosensitive polyimide (trade name: Photo Nice) is applied as a third upper protective layer 109 on the first upper protective layer 108 of the substrate 101, and photolithography is performed. A circuit pattern as shown in FIG. 3 is formed by the process.

As shown in FIG. 4, a photosensitive resin dry film 400 having a thickness of 50 μm is laminated on the substrate 101 prepared in this way, and exposure and development are performed by a predetermined pattern mask to thereby obtain a liquid flow path. 401 and a common liquid chamber 404 are formed, and a ceiling plate 405 made of glass is adhered and laminated on the film 400 via an epoxy adhesive to form a liquid jet recording head. In addition, 402 is an orifice, 403 is an ink flow path wall, and 406 is an ink supply port.

As an example, the above-mentioned liquid channel 401 has a width of 50 μm and a height of 50 μm.
, 750 μm long. Also, the length from the front end of the heat generating part (heater) 111 to the orifice (discharging port) 402 is 150 μm.

When the defoaming time of the liquid jet recording head of this example was actually measured, it was 50 μs (microseconds) from the pulse application. However, the driving conditions at that time were a pulse width of 7 μs, a frequency of 2 KHz, and a driving voltage of 1.2 times the foaming voltage. The left side of equation (5) for this liquid jet recording head The value of is as follows by substituting the corresponding numerical value described above. The corresponding numerical values are shown in Table 1.

Also, since τ _B = 50 μsec = 50 × 10 ^-6 sec, the above equation
The value on the right side of (5) is as follows.

Therefore, since 4.35 × 10 ^-3 <1.4 × 10 ^-2 , It can be seen that the condition of the above equation (5) is satisfied.

The results of the durability test of the liquid jet recording head of this embodiment are shown in Table 2 below, together with the results of other embodiments.

Second Embodiment FIG. 5 shows a cross section of a substrate 101 prepared in the second embodiment of the present invention. As shown in the figure, in this embodiment, 5 μm is formed on the substrate support 105 of the Si wafer by magnetron sputtering.
A thick Al ₂ O ₃ film was formed as a lower layer 106 of the substrate 101, and SiO ₂ was laminated as a first upper protective layer 108 to a thickness of 1.9 μm by a magnetron high rate sputtering method. The other substrate forming steps, the structure and material of the liquid jet recording head, the dimensions, and the like are the same as those in the above-described first embodiment, and a detailed description thereof will be omitted.

When the defoaming time of the liquid jet recording head of this example prepared in this way was measured under the same conditions as in the first example, it was 50 μs from the pulse application. The left side of equation (5) for this liquid jet recording head The value of is calculated to be 4.29 × 10 ^{−3 in the same} manner as in the first embodiment.

Since τ _B = 50 μsec = 50 × 10 ^-6 sec, Is.

Therefore, since 4.29 × 10 ^-3 <1.4 × 10 ^-2 , The condition of Equation (5) is satisfied.

The results of the durability test of the liquid jet recording head of this embodiment are shown in Table 2 below together with the results of other embodiments.

Third Embodiment FIG. 6 shows a cross section of a substrate 101 prepared in the third embodiment of the present invention. As shown in this figure, in this embodiment, a SiO ₂ film having a thickness of 10 μm is formed on a substrate support 105 of a Si wafer by thermal oxidation to form a lower layer 106 of the substrate 101. The other substrate forming steps, the structure and material dimensions of the liquid jet recording head, etc. are the same as those in the above-described first embodiment, and detailed description thereof will be omitted.

When the defoaming time of the liquid jet recording head of this example prepared in this way was measured under the same conditions as in the first example, it was 50 μs from the pulse application. The left side of equation (5) for this liquid jet recording head The value of is 1.37 × 10 ^-2 when calculated in the same manner as in the first embodiment.

Since τ _B = 50 μsec = 50 × 10 ^-6 sec, the value on the right side of the above equation (5) is as follows.

Therefore, since 1.37 × 10 ^-2 <1.4 × 10 ^-2 , Therefore, the condition of the above equation (5) is satisfied.

The results of the durability test of the liquid jet recording head of this embodiment are shown in Table 2 below, together with the results of other embodiments.

First Comparative Example FIG. 7 shows an example of a heating resistor of a liquid jet recording head which does not satisfy the condition of the above expression (5) for comparison with the above-mentioned first to third embodiments. As shown in the figure, in this first comparative example, a 15 μm thick SiO ₂ film was formed on a substrate support 105 of a Si wafer by thermal oxidation to form a lower layer 106 of the substrate 101, and sputtering was performed on the lower layer 106. By HfB ₂ heating resistance layer 107
To a thickness of 1500Å, and the first upper protective layer 108
As a result, SiO ₂ was laminated to a thickness of 2.5 μm by a magnetron type high rate sputtering method. The other substrate forming steps, the structure, material, dimensions, etc. of the liquid jet recording head are the same as those in the above-described first embodiment, and therefore detailed description thereof will be omitted.

When the defoaming time of the liquid jet recording head of the first comparative example prepared in this way was measured under the same conditions as in the first example, it was 50 μs from the pulse application. The left side of equation (5) for this liquid jet recording head The value of is 2.0 × 10 ^-2 when calculated in the same manner as in the first embodiment.

Since τ _B = 50 μsec = 50 × 10 ^-6 sec, Is.

Therefore, since 2.0 × 10 ^-2 > 1.4 × 10 ^-2 , Therefore, it can be seen that the condition of equation (5) cannot be satisfied.

The results of the durability test of the liquid jet recording head of this comparative example are shown in the following Table 2 together with the results of other examples.

Second Comparative Example FIGS. 8A and 8B show a substrate of a head prepared as a second comparative example for the head of the present invention. As shown in this figure, this comparative example is different from the other examples in that the heater (heat generation part
111). Also, the substrate support 105 of the Si wafer
Substrate 101 is formed by forming 5 μm thick SiO ₂ on top by thermal oxidation.
As the lower layer. The other substrate forming steps and the structure, material, dimensions and the like of the liquid jet recording head are the same as those in the second embodiment described above, and thus detailed description thereof will be omitted.

Regarding the ejection frequency response, compared with the ejection frequency response of 20 KHz in the first to third examples and the first comparative example,
In the second comparative example, bubbles are unstable at a discharge frequency of 5 KHz, and the discharge volume is also unstable, resulting in poor print quality.

The results of the durability test of the liquid jet recording head of the second comparative example are shown in Table 2 below together with the results of the other examples and comparative examples.

Durability test result example Table 2 shows the results of the durability test of the liquid jet recording heads of the first to third examples and the first and second comparative examples.

The driving conditions are, as described in the first embodiment,
The driving voltage is 1.2 times the foaming voltage and its pulse width is 7μ
s, the frequency is 2 KHz.

As is clear from Table 2, the first to third examples show practically satisfactory durability. However, the first comparative example has practically unsatisfactory durability. Also,
The second comparative example has durability and print quality that are not practically satisfactory.

Therefore, the shape between the heat generating part 111 and the electrodes 101, 103 should be as shown in FIG. By satisfying the above condition, a liquid jet recording head having practically satisfactory durability and print quality can be obtained.

[Effects of the Invention] As described above, according to the present invention, the heating resistor of the liquid jet recording head has no corner, and the film structure is measured from the boundary between the lower layer and the substrate. The heat conductivity at the position x of the heating resistor layer is k (x), the specific heat is c (x), the density is ρ (x), the thickness of the heating resistor is L, and the life of bubbles is τ _B
And when Since the material and layer thickness are set so as to satisfy the conditions described in 1., the temperature of the heating resistor has fallen sufficiently by the time the bubbles disappear, delaying the disappearance of the bubbles, remaining bubbles and secondary The problem of the generation of bubbles is solved, and the oxidation of the heating resistor due to the bubbles and damage due to cavitation, etc. are prevented. There is an effect that it is possible to obtain a liquid jet recording head having excellent properties.

[Brief description of drawings]

FIGS. 1 to 3 show the steps of producing a substrate according to the first embodiment of the present invention, and FIGS. 1, 2 (A) and 3 (A) are plan views and FIG. 2 (B). ), Fig. 3 (B) is the XY of each corresponding diagram (A).
4 is a sectional view taken along the line, FIG. 4 is a perspective view showing the internal structure of the liquid jet recording head of the first embodiment when completed, and FIG. 5 is a sectional view showing the structure of the substrate of the second embodiment of the present invention. FIG. 6 is a sectional view showing the structure of the substrate of the third embodiment of the present invention, FIG. 7 is a sectional view showing the structure of the substrate of the first comparative example, and FIGS. 8 (A) and 8 (B) are the second parts. FIG. 9 is a plan view showing a configuration of a substrate of a comparative example and a cross-sectional view, FIG. 9 is a plan view showing a shape example of a heating resistor according to the present invention, and FIG. 10 is a shape example of a conventional general heating resistor. It is a top view. 101 ... substrate, 102 ... heating part, 103 ... common electrode, 104 ... selection electrode, 105 ... substrate support, 106 ... lower layer, 107 ... heating resistor layer, 108 ... first Upper protective layer, 109 ...... Third upper protective layer, 110 …… Second upper protective layer, 111 …… Heat generation part, 401 …… Liquid flow path, 402 …… Orifice, 403 …… Ink flow path wall , 404 ... common liquid chamber, 405 ... ceiling plate, 406 ... ink supply port.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirokazu Komuro 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP-A-62-73588 (JP, A)

Claims (1)

[Claims] 1. A liquid jet recording having a heat acting portion communicating with an orifice for ejecting liquid to apply heat energy to the liquid to form bubbles in the liquid, and a heating resistor generating the heat energy. In the heating resistor of the head, a rectangular coordinate system XY is set on the resistor surface, and φ
Let (x, y) be the potential value at the point (x, y) on the resistor surface, and give the boundary value of the value at the part of the peripheral boundary of the resistor that is in contact with one electrode, and the other electrode A boundary value different from the boundary value is given to the contacting portion, and a boundary condition in which the derivative of φ with respect to the normal direction of the peripheral boundary is 0 is given to the portion not in contact with either electrode. Laplace equation ∂ ² φ / ∂ x ² ＋
When ∂ ² φ / ∂y ² = 0 is solved, the magnitude of the inclination of φ The maximum value of In a liquid jet recording head having a heating resistor having a shape having a ratio of 1.8 or less, the heating resistor is formed by laminating a lower layer, a heating resistor layer and an upper layer in this order on a substrate, and The thermal conductivity of the substance at the position x measured in the layer direction from the boundary between the lower layer and the substrate toward the heat acting portion is k (x), the specific heat is c (x),
Assuming that the density is ρ (x), the total thickness of the heating resistor is L, and the time from the start of applying the thermal energy to the disappearance of the bubbles is τ _B , A liquid jet recording head, wherein the material and the thickness of the heating resistor are set so that