JPS62103149A - Liquid jet recording head - Google Patents

Abstract

PURPOSE:To raise the durability of the titled head, by setting an impressed voltage so that the minimum value of the voltage impressed onto the heat resistance material in which bubbles appearing at the heat acting part separately from bubbles for forming liquid drops are generated and the voltage impressed on the heat resistance material meet specific interactions. CONSTITUTION:Vapor bubbles are generated in the heat acting part filled by recording liquid material and pushed out from a liquid drop orifice. When the vapor bubble has been constricted by itself thereafter, the threshold voltage for executing the generation of secondary vapor bubbles is made to be VR. A drive voltage Vop is determined by making reference to this threshold voltage VR to be within a range conforming to the relation Vop<=1.15VR. Thereby, because of making reference to the threshold voltage VR set from thermal problem, the optimum drive voltage Vop in heat resistance can be set and driven in the optimum state for durable life and practical use.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid jet recording head that jets recording liquid from an orifice to form flying droplets.

[Prior Art] Regarding this type of liquid jet recording head, for example, Japanese Patent Laid-Open No. 54
-51837 Publication and German Publication (DOLS) No. 2
The liquid jet recording method described in Publication No. 843084 has a different feature from other liquid jet recording methods in that thermal energy is applied to the liquid to obtain the driving force for ejecting droplets. .

That is, in the recording method disclosed in the above-mentioned publication, the liquid subjected to the action of Q energy is overheated to generate bubbles, and the acting force based on the generation of bubbles causes the liquid to be ejected from the orifice at the tip of the recording head. This method is characterized in that flying droplets are formed, and the droplets adhere to a recording member to record information.

A recording head applied to this recording method generally includes an orifice provided for ejecting liquid, and a heat-acting section that communicates with the orifice and acts on the liquid in order to eject droplets. The apparatus includes a liquid discharge part having a liquid flow path which is a part of the configuration, and a heating resistor as a heating resistor which is a means for generating thermal energy.

Incidentally, a shape as shown in FIG. 6 is currently proposed as a shape of a heating resistor. The requirements for defining such a shape are as shown below.

That is, a rectangular coordinate system X-Y is set on the surface of the heating resistor 1, and φ(x, y) is the potential value at a point (x, y) on the resistor surface, and among the surrounding boundaries of the resistor, A boundary value of a certain value is given to the part in contact with one electrode 2, a boundary value of a value different from the boundary value is given to the part in contact with the other electrode 3, and the said surrounding boundary is given to the part not in contact with either electrode. Given the boundary condition that the differential coefficient of φ with respect to the normal direction of and (eφ/ax)2+(;) at the center of the resistor
Φ/ay) Defined as a ratio of 2.

For example, the shape shown in FIG. 6 has a ratio of 1.13. The value of this ratio in the conventional example shown in FIG. 7 is infinite. If this value is 1.8 or less, there is less current concentration at the four corners of the heater than in the conventional case (infinity), that is, there is less heat concentration at the four corners, and therefore foaming does not occur from the four corners first. , the entire surface of the heating resistor l is first foamed. Also, stable foam is therefore obtained. Expressing this specifically, up to an ejection frequency of 10 kHz, there is little variation in the volume of one bubble (a bubble generated to eject liquid) for each ejection, and therefore, there is less variation in the volume of the ejected droplet. That is, stable ejection can be obtained and good printing can be obtained. Furthermore, compared to the conventional case, current concentration at the four corners is reduced and the [1lP1 durability of the heating resistor is improved.

Further, the above-mentioned heating resistor has a pair of electrodes, and this electrode generally consists of a selection electrode and a common electrode, and by passing current between these electrodes, heat is generated for ejecting droplets from the above-mentioned orifice. Energy is generated from the heating resistor. The main factor that determines the repeated use life (durable life) of such a liquid jet recording head is mechanical impact force called cavitation collapse. Cavitation collapse occurs when vapor bubbles self-contract and disappear. Specifically, the liquid near the heating resistor becomes superheated due to the sudden heat generation by the heating resistor, and vapor bubbles are generated when the liquid reaches its superheating limit temperature.The sudden increase in volume at this time causes the liquid to jump out of the orifice. After flying droplets are formed, cavitation collapse occurs as the bubbles (vapor bubbles) self-contract and disappear. The impact on the heating resistor due to this cavitation collapse was the main factor in determining the durability of the recording head.

There are several measures that can be taken to avoid such causes of failure and improve the durable life of the recording head. For example, the heating resistor may be constructed of a material with good cavitation resistance. Alternatively, a protective layer with good cavitation resistance is provided at least between the heating resistor and the recording liquid. Furthermore, the liquid flow path is designed to weaken the impact force caused by cavitation collapse. Conventionally, these measures have been used to improve the durability of the recording head.

[Problems to be Solved by the Invention] However, even in a liquid jet recording head whose durable life has been improved by the above-mentioned measures, it is often impossible to achieve a sufficient durable life due to the electrical driving conditions applied to the heat generating resistor. there were. The cause of this is, for example, when steam bubbles are generated by applying an electric signal to a heating resistor and then self-contract, there are other high-temperature areas that are higher than the superheating limit temperature in addition to the position where the steam bubbles disappear. If there is, there is a phenomenon in which secondary bubbles remain in the form of streaks along the flow direction of the liquid at that position.

One bubble generated to discharge liquid is collapsed by force from the direction of liquid flow, that is, from the direction of the liquid flow path.
The above-mentioned secondary bubbles that remain even after the bubbles disappear are near the heat-active surface, and because the height of a is low, they do not receive force in the flow direction of the liquid, and therefore are not perpendicular to the liquid flow path. It collapses in the direction of.

The cavitation caused by bubbles collapsing perpendicular to the liquid flow path is extremely large and locally concentrated, and is actually dozens of times larger than the cavitation caused by one bubble defoaming. Therefore, the cavitation collapse of the bubbles often destroyed the upper protective layer of the heat-acting part and the heating resistor, resulting in poor durability.

Conventionally, as shown in Japanese Unexamined Patent Publication No. 58-1571, in order to prevent secondary bubbles, the driving voltage ■P is set to 1, It is proposed to reduce the number to 3 times or less. However, in the currently proposed head having a heating resistor shaped like the one shown in Figure 6, there is no initial bubble formation from the four corners as in the conventional case, so even if the film structure is the same, the boundary voltage Generally, the boundary voltage vth increases. Therefore, if the drive voltage Vop is set to 1.3 times or less of vth using the conventional boundary voltage vth as a reference, the durability may be lowered due to the generation of secondary bubbles.

In view of the above-mentioned problems, the present invention changes the standard for setting the drive voltage of the recording head from the conventional boundary voltage vth, and uses a new rule to generally define the most suitable applied voltage VOp in terms of durability and practical use. An object of the present invention is to provide a liquid jet recording head that can perform the following steps.

[Means for Solving the Problems] In order to achieve the present object, the present invention includes a heat acting part that communicates with a liquid discharge orifice and applies thermal energy to the liquid to form bubbles in the liquid; In a heat generating resistor in a liquid jet recording head having a heat generating resistor that generates energy, a rectangular coordinate system X-Y is taken on the surface of the resistor, and φ(x, y) is a point (14) on the surface of the resistor. The potential value is given as a potential value at the peripheral boundary of the resistor, a boundary value of a certain value is given to the part in contact with one electrode, a boundary value of a value different from the boundary value is given to the part in contact with the other electrode, and a boundary value of a value different from the boundary value is given to the part in contact with the other electrode. A boundary condition is given in which the differential coefficient of φ with respect to the normal direction of the surrounding boundary is O for the part that is not in contact with the area, and the magnitude of the slope, εpd> /21K) is applied to the region of the heating resistor. +(4/)y
)' maximum value and (Dφ/Px)2+ at the center of the resistor
('; aφ/) In a liquid jet recording head having a heat generating resistor having a shape in which the ratio to Set the minimum value of the voltage applied to the heating resistor at which bubbles (secondary bubbles) occur to be vR, so that the voltage applied to the heating resistor Vop satisfies the relationship 1°15≧VOP/VR. , the applied voltage Vop is set.

[Action record: When a vapor bubble is generated in a heat-active part filled with a liquid and self-contracts after being pushed out of a droplet orifice, the generation of secondary bubbles of the base bubble occurs. Let vR be the threshold voltage for The present invention determines the drive voltage Vop based on this threshold voltage vR, and sets the drive voltage Vop to Yap≦1. It is characterized by being within a range that satisfies the relationship: +5 vR. Therefore, according to the present invention, since the threshold voltage vR, which is set based on thermal issues, is used as the standard, even a head having a heating resistor shaped as shown in Fig. 6 can be optimized in terms of heat resistance. It becomes possible to set the driving voltage Vop according to the conditions, and it is possible to drive in a state suitable for the durability life and practical use, and high durability with improved durability life can be obtained.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

(1) First Embodiment FIGS. 1 to 3 show the process of producing a substrate according to the first embodiment of the present invention, and FIG. 4 shows an example of the structure of the liquid jet recording head of this embodiment. Here, 101 is the board.

102 is a heat generating part, and 103 and 104 are electrodes.

To explain the process of manufacturing the substrate of the heating resistor according to this embodiment, first, as shown in FIG. 2(B), the substrate support 105 is
A 5102 film with a thickness of 5 μm is formed by thermal oxidation of a Si wafer, which serves as the lower layer 1013 of the substrate 101. H is applied onto this lower layer 106 by sputtering (sputtering).
The heating resistance layer 107 of fB2 is formed to have a thickness of 1300λ.

Next, 50 Ti layers and 50 A standing layers were formed by electron beam evaporation.
00 people are successively deposited to form a common electrode 103 and a selective electrode 1.
04. At this time, a circuit pattern as shown in FIG. 1 is formed by a photolithography process, and the heat-active surface of the heat-generating portion 102 of the heat-generating portion 111 is set to have a width of 30 pm and a length of 15 OILII.
The resistance value including the resistance of the A pattern electrodes 103 and 104 is set to 100Ω.

Next, as shown in FIG. 2(B), a first upper protective layer 10 is formed.
8, 5i02 is laminated to a thickness of 1.8 uLm over the entire surface of the substrate 101 by magnetron high rate sputtering.

Subsequently, as the second upper protective layer 110, as shown in FIG.
As shown in (B), Ta is deposited to a thickness of 0.54 m by magnetron high rate sputtering.

Next, a second upper protective layer 110 is formed in a pattern covering the upper part of the heat generating portion 102 as shown in FIGS. 2(A) and 2(B) by a photolithography process.

Furthermore, as shown in FIGS. 3(A) and (B), the third
As the h-section protective layer +09, photosensitive polyimide (trade name: Photonice) is coated on the first upper protective layer 108 of the substrate 101, and a circuit pattern as shown in FIG. 3 is formed by a photolithography process.

As shown in FIG. 4, a photosensitive resin dry film 40 with a thickness of 50 gm is placed on the substrate 101 thus created.
A liquid flow path 401 and a common liquid chamber 404 are formed by laminating 0 and performing exposure and phenomenon using a predetermined pattern mask, and then a glass ceiling is formed on the film 400 with an epoxy adhesive. A liquid jet recording head is created by laminating the plates 405 with adhesive. In addition, 402 is an orifice,
403 is an ink flow path wall, and 406 is an ink supply port.

- As an example, the liquid flow path 401 described above has a width of 5 olm.

It is formed to have a height of 50 gm and a length of T50 pLm.

Further, the length from the front end of the heat generating part (heater) 111 to the oriice 402 is set to 150 m.

When the above-mentioned threshold voltage (minimum applied voltage) VR of the liquid jet recording head of this example prepared in this manner was measured, it was found to be 22. It was OV. Also, the firing boundary voltage vth
was 20V. However, the pulse width of the drive signal is 7gs.
, the frequency is 2kHz. Further, when the recording head of this example was driven at voltages shown in Table 1 below, durability as shown in Table 1 was obtained. However, the driving conditions at that time were a pulse width of 7 gs and a frequency of 2 kHz, and the ink composition was 50% water, 15% N-series P (N-methylpyrrolidone), and 30% DEC (diethylene glycol).
, 5% dye.

■Second Embodiment FIG. 5 shows a cross section of a substrate 101 prepared in a second embodiment of the present invention. A 5i02 film with a thickness of 2.5 gm was formed as the lower layer 106, and a heat generating resistor layer 107 with a thickness of 1 fB2 (1 fB2) was formed on the lower layer 10e to a thickness of 1600 gm. In addition, the resistance value of the heat acting surface of the heat generating part 111 is
The resistance was 80Ω including the resistance. Furthermore, as a first upper protective layer, 5i07 was deposited to a thickness of 1.9 gm by magnetron high rate sputtering.

The other substrate preparation steps, the structure of the liquid jet recording head, etc. are the same as in the first embodiment described above, so a detailed explanation thereof will be omitted.

When the threshold voltage vR of the liquid jet recording head of the second example prepared in this manner was measured, the 2B, OV tear, mata, and foaming boundary voltage vth was 23.5V. However, the pulse width of the drive signal is 7ps, and the frequency is 2kHz.
It is z. Further, when the recording head of this example was driven at the voltage shown in Table 2 below, durability as shown in Table 2 was obtained. However, the driving conditions at that time were a pulse width of 7 gg and a frequency of 2 kHz, and the ink composition was 50% water.
NMP 15%, DEC 30%.

The dye content is 5%.

(2) Comparative Example FIG. 8 shows a substrate prepared in a comparative example of the present invention. As shown in this figure, the difference from the first embodiment is the shape of the heater (heat acting section). The other substrate preparation steps, the structure of the liquid jet recording head, etc. are the same as in the first embodiment described above, so a detailed explanation thereof will be omitted.

The bubble boundary voltage vth of the liquid jet recording head of the third example prepared in this manner was 19.2V. However, the pulse width of the drive signal is 71hs, and the frequency is 2k)lz.
When the recording head of this comparative example was driven at the voltages shown in Table 3 below, the durability shown in Table 3 was obtained. However, the driving conditions at that time are a pulse width of 74 seconds and a frequency of 2.
kHz, the ink composition is 50% water, 15% NMP, DE
C30%, dye 5%.

■Example of durability test results Table 1 shows the durability test results of the first example, Table 2 shows the durability test results of the second example, Table 3 shows ■Durability of the comparative example (third example) 1 Table Δ: Remaining recording head of 50% or more to less than 100% ×:
0% or more to less than 50% of the recording head remaining.

Table 2 Q: 100% recording head remaining Δ: 50% or more to less than 100% recording head remaining ×:
0% or more to less than 50% of the recording head remaining.

Table 3 ○: 100% recording head remaining Δ: 50% or more to less than 100% recording head remaining ×:
Indicates a recording head sand retention of 0% or more to less than 50%.

The foaming boundary voltage vth of the first example and the comparative example is 2, respectively.
0. OV, 19.2V. Although the film configuration and dimensions are the same, the boundary voltage Vth is different. Also, the comparative example is v
It has good durability at 25V, which is 1.3 times th.

Therefore, it is possible to achieve good durability by driving with a driving voltage Vop that is 1.3 times or less the boundary voltage vth shown in Japanese Patent Laid-Open No. 58-1571. On the other hand, the first
In the example, durability is poor when driven at 26V, which is 1.3 times the boundary voltage vth. Therefore, JP-A-58-1571
The method disclosed in the above publication in which the drive voltage Vop is determined based on 1.3 times the boundary voltage vth or less, that is, vth as a reference, ends up having poor durability. Therefore, I thought as follows.

As can be seen from Tables 1 and 2, durability deteriorates when the voltage exceeds a certain level. For example, in the first embodiment, the durability deteriorates when the driving voltage Vop is 28V or more as described above (Table 1).If we take the threshold voltage vR for secondary vapor bubble generation as a standard, then The threshold voltage VR is 22V as mentioned above.
Therefore, it becomes Vop/VR-1,18. In the second embodiment, the durability deteriorates when the driving voltage Vop exceeds 30V as described above (Table 2).If the threshold voltage vR is taken as a reference, the threshold voltage vR of the second embodiment is 2BY as described above.
Therefore, Vop/VR-1.15.

Therefore, it has been demonstrated that by setting Vop/VR≦1.15, the durability of the recording head can be obtained for practical use.

[Effects of the Invention] As explained above, according to the present invention, the drive voltage is
p, threshold voltage is vR, Vop /vR≦1
．． Since the liquid jet recording head is driven at a driving voltage Vop that satisfies the condition No. 15, the liquid jet recording head can be driven in a state suitable for durability and practical suspension, and high durability can be obtained.

[Brief explanation of drawings]

1 to 3 show the process of manufacturing a substrate according to the first embodiment of the present invention, and FIG. 1, FIG. 2 (A), and FIG. ), Figure 3 (B) is the corresponding figure (A
), FIG. 4 is a perspective view showing the internal structure of the completed liquid jet recording head of the first embodiment, and FIG. 5 is the structure of the substrate of the second embodiment of the present invention. FIG. 6 is a plan view showing an example of the shape of a heating resistor according to the present invention; FIG. 7 is a plan view showing an example of the shape of a conventional general heating resistor; FIG. 8 is a plan view showing an example of the shape of a heating resistor according to the present invention FIG. 2 is a plan view showing the configuration of a substrate created for comparison with FIG. 101...Substrate, 102...Heating portion, 103...Common electrode, 104...Selection electrode, 105...Substrate support, toe...Lower layer, 107...Heating resistor layer , 108... First upper protective layer, 109... Third upper protective layer, 110... Second upper protective layer, 111... Heat generating section, 401... Liquid flow path, 402... Orifice, 403... Ink channel wall, 404... Common liquid chamber, 405... Ceiling plate, 40G... Ink supply port. ) 1f, J1 Oita Sobu's Guidance Anti-creation Technique I's Ten Faces Figure 1
Figure 2 (A) Figure 2 (B)
) Top view of the base of the Mouse 1 Suspicion I column, Figure 3 (A > ¥1 Award Nabei 1 Su) (= P-I Makune Reaction Work, No. 3 counter entrance of 4v) Figure (B) Figure 5, ``Ninvention''; / ll. Figure 7 of the ten-sided diagram showing the four members of the book.

Claims (1)

[Scope of Claims] A liquid having a heat acting part that communicates with a liquid discharge orifice and applies thermal energy to the liquid to form bubbles in the liquid, and a heating resistor that generates the thermal energy. In the heating resistor in the jet recording head, a rectangular coordinate system X-Y is taken on the surface of the resistor, and φ(x, y)
Let be the potential value at the point (x, y) on the surface of the resistor, give a boundary value of a certain value to the part in contact with one electrode among the peripheral boundaries of the resistor, and give the boundary value of a certain value to the part in contact with the other electrode. A boundary value different from the above value is given, and a boundary condition is given where the differential coefficient of φ with respect to the normal direction of the surrounding boundary is 0 in the part that is not in contact with either electrode. When the equation ∂^2φ/∂x^2+∂^2φ/∂y^2=0 is solved, the magnitude of the slope of φ((∂φ/∂x)^2+(∂
The maximum value of φ/∂y)^2) and √(((
The ratio of ∂φ/∂x)^2+(∂φ/∂y)^2) is 1.
In a liquid jet recording head having a heat generating resistor having a shape of 8 or less, the heat generation generates bubbles (secondary bubbles) that appear in the heat acting area separately from the bubbles (main bubbles) for forming droplets. The applied voltage Vop is set so that the voltage applied to the heating resistor satisfies the relationship 1.15≧Vop/V_R with respect to the minimum value V_R of the voltage applied to the resistor. liquid jet recording head.