JPH06134988A - Bubble-jet print head - Google Patents

Abstract

PURPOSE:To obtain the excellent printing quality without the printing-dot deviation by suppressing thermal interference between heating dots, and equalizing the timings of the generations of bubble films. CONSTITUTION:An insulating substrate 1, on which heating resistors 2 are formed, is fabricated in a comb shape. The heating resistors 2 are provided on the approximately entire surfaces of the edge surfaces of the comb teeth. Heat separating members 15 having the lower heat conductivity than the insulating substrate 1 are embedded in the comb-shaped gap parts furthermore.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a print head of a bubble jet printer which is one type of ink jet printer.

[0002]

2. Description of the Related Art FIG. 4 shows a configuration example of a conventional bubble jet print head and the principle of ink ejection. In FIG. 4, 1 is an insulating substrate, 2 is a heating resistor, 3 is an electrode for energizing the heating resistor 2, and 4 is a protective layer for protecting the heating resistor 2. An undercoat 5 is usually formed between the insulating substrate 1 and the heating resistor 2 for protecting the insulating substrate 1 and for causing appropriate heat storage.

The Joule heat generated in the heating resistor 2 by the voltage pulse applied through the electrode 3 heats the protective layer 4, and the surface 6 of the protective layer 4 instantly reaches a high temperature. Therefore, the ink in contact with the surface 6 boils and a bubble film 7 is generated.
The expansion of the bubble film 7 causes the ink 8 to be ejected from the orifice 9.

FIG. 5 is a sectional view taken along the plane AA 'of FIG. The insulating substrate 1 is flat, and the heating resistors are not separated.

[0005]

The generation principle of the bubble film will be described in detail. The phenomenon applied in the bubble jet printer is the film boiling phenomenon. When the heat transfer surface in contact with the liquid (ink) is rapidly heated and the temperature of the heat transfer surface is instantly raised to the superheat limit TS of the liquid, the liquid in contact with the heat transfer surface is boiled and film-like bubbles are formed. . The initial internal pressure of this bubble film is very high, and the bubble film expands rapidly. FIG. 6 shows the timing of the applied pulse, the temperature rise of the heat transfer surface and the generation of the bubble film. The bubble film starts to be generated immediately after the temperature of the heat transfer surface reaches the overheat limit. Therefore, in order to perform printing without dot deviation in the bubble jet printer, it is necessary to make the time t _{B at} which the bubble film is generated constant regardless of the heating element.

Here, consider the case where five consecutive dots in a conventional bubble jet print head are energized and generate heat. Thermal interference occurs between the adjacent dots through the insulating substrate and the protective layer, and the rate of temperature rise is higher and the peak temperature is also higher than when one dot is energized to generate heat. Therefore, when successive dots (a) to (e) are simultaneously energized and heated, the dot temperature distribution at a certain point during pulse application becomes as shown in FIG. 7, and the generation of the bubble film at the central dot (c) is the earliest. The dots at the edges are the slowest. This indicates that ink is ejected from the orifices of the print head at different timings, which causes deviation of print dots.

In fact, when the present inventors investigated the shape of the bubble film by stroboscopic observation, it was found that the bubble film of the central dot was the largest and the bubble film became smaller toward the end during the growth process of the bubble film. Was confirmed. This indicates that the generation of the bubble film at the central dot is the fastest.

As described above, the conventional bubble jet print head has a problem that the heat separation between the adjacent heating resistors is poor and thermal interference is likely to occur, resulting in the deviation of print dots.

[0009]

In order to solve the above problems, according to the present invention, an insulating substrate having a high thermal conductivity is formed in a comb shape, and a heating resistor is formed on almost the entire tip surface of the comb teeth. And a thermal separator having a lower thermal conductivity than that of the insulating substrate is embedded in the comb-shaped void.

[0010]

By the above means, the heat separation between the heating dots can be enhanced, and the thermal interference can be suppressed even when a plurality of dots are simultaneously energized and heated. The print quality is constant regardless of the above, and therefore good print quality without deviation of print dots can be obtained.

[0011]

【Example】

(Embodiment 1) FIG. 1 shows a first embodiment. Insulating substrate 1
Is formed in a comb shape, and the heating element resistor 2 is formed on almost the entire tip surface of the comb shape. When the heating resistor 2 is energized with such a structure, the amount of heat not used for film boiling is mainly transferred in the direction of the arrow in the figure and diffused to the base 10, so that thermal interference with adjacent dots is suppressed.

The thermal isolation increases as the depth D of the comb teeth of the insulating substrate 1 increases. A nozzle wall and a top plate 11 having ink holes are joined to the insulating substrate 1 to form a print head. (Example 2) In Example 1, since the insulating substrate has a gap, the step coverage of the protective layer may not be sufficient.
Further, when a high-density print head is manufactured, there is a possibility that a space for forming an electrode wiring for applying a voltage pulse is insufficient, or it becomes difficult to align a position with a nozzle wall.

In order to improve this point, FIG.
As shown in FIG. 3, a material having a thermal conductivity λ2 smaller than the thermal conductivity λ1 of the insulating substrate 1 is embedded in the void of the insulating substrate 1 as the heat separating material 15. On the insulating substrate 1 flattened by this heat separating material, the heating resistor 2, the electrode 3,
The protective layer 4 is formed. The larger the thermal conductivity ratio λ 1 / λ 2 is, the higher the thermal separability is, and the greater the effect on the printing quality is.

FIG. 3 shows an example of a manufacturing process when a Si substrate is used as the insulating substrate and a polyimide resin is used as the heat separating material. The SiO ₂ layer 13 is formed by thermal oxidation of the Si substrate 12. Since the SiO ₂ layer 13 also functions as a heat storage layer, the thickness is determined according to the required characteristics.

S to be removed by photoetching
The SiO2 layer corresponding to the i-substrate 12 is removed. The unnecessary portion of the Si substrate 12 is removed by etching. At this time, if the Si substrate 12 is designed so that the etched side surface 14 becomes the (111) plane, the deep groove can be accurately formed by anisotropic etching.

A varnish-like polyimide resin 16 is spin-coated and cured, and then unnecessary portions are removed to flatten the Si substrate. When photosensitive polyimide is used, the unnecessary portion can be removed by exposure and development. On the insulating substrate manufactured as described above, the heating resistor 2,
The electrode 3 and the protective layer 4 are formed.

In this case, the thermal conductivity λ 1 of the Si substrate is about 1.
70W / mk, thermal conductivity λ2 of polyimide resin is about 0.
Since it is 1 W / mk, the ratio of the thermal conductivities of both is very large, and most of the heat generated in the heating resistor 2 is diffused to the base through the Si substrate 12 and does not impair the thermal separability at all. If SiO ₂ is used as the protective layer 4, the thermal conductivity of SiO ₂ is about 1 W / mk.
Since the thermal conductivity of the i substrate is much lower than that of the i substrate, thermal interference through the protective layer has almost no effect.

[0018]

As described above, according to the present invention, the insulating substrate on which the heating element is formed is provided with a space between the heating elements or is replaced with a heat separating material having a lower thermal conductivity than the insulating substrate, and the adjacent dots are Since the heat interference between the heating elements is suppressed, a bubble film can be generated at the same timing even when a plurality of heating elements are heated at the same time, and thus, it is possible to obtain good print quality without print dot deviation. .

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a sectional view of another embodiment of the present invention.

FIG. 3 is a cross-sectional view of the manufacturing process of the example of the present invention.

FIG. 4 is a structural example of a conventional bubble jet print head.

FIG. 5 is a structural example of a conventional bubble jet print head.

FIG. 6 is a timing explanatory diagram of bubble film generation.

FIG. 7 is a heat generation distribution diagram of a conventional head.

[Explanation of symbols]

1 Insulating Substrate 2 Heating Resistor 3 Electrode 4 Protective Layer 5 Undercoat 6 Protective Layer Surface 7 Bubble Film 8 Ink 9 Orifice 10 Base 11 Top Plate 12 Si Substrate 13 SiO ₂ Layer 14 Si Etching Side 15 Thermal Separation Material 16 Polyimide Resin

Claims (2)

[Claims] 1. A plurality of heating resistors arranged in a line on at least an insulating substrate, means for heating the heating resistors, and nozzles formed corresponding to the heating resistors. In the bubble jet print head that heats the heating resistor to boil the ink in contact with the heating resistor and eject the ink by the expansion pressure of the generated bubble film, the insulating substrate is comb-shaped. A bubble jet print head, characterized in that the heating resistor is provided on substantially the entire tip surface of the comb tooth. 2. The heat separating material having a thermal conductivity lower than that of the insulating substrate is embedded in the void portion of the comb-shaped insulating substrate. Bubble jet print head.