JP2887971B2 - Thermal inkjet head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal ink jet head in which a concave portion defining a bubble generation region is formed of a thermosetting resin layer.

[0002]

2. Description of the Related Art Conventionally, in a thermal ink jet head, as described in JP-A-61-249767, a polyimide resin or a polyamide resin is used as a material for forming a portion in contact with ink such as an ink flow path. The use of a thermosetting resin such as the above has been proposed, and the durability as an ink jet recording head has been improved, and high reliability can be obtained.

On the other hand, as described in Japanese Patent Application Laid-Open No. 62-33648, a concave portion for the purpose of limiting the bubble growth region and preventing air from being caught from a nozzle (this concave portion is also referred to as a pit). A thermal ink jet head is known in which a heating element is disposed in the concave portion, and a thermosetting resin is also effectively used for forming the concave portion.

In the thermal ink jet head proposed in Japanese Patent Application No. 2-212525, a concave portion is formed by a thermosetting resin layer, and the boundary of the concave portion is set inside the boundary of the heat generating region of the heat generating element. Things. In this structure, the life of the electrode can be prolonged by protecting the step portion near the electrode where a failure easily occurs with a thermosetting resin.

By the way, as a method of forming a thermosetting resin layer, usually, a varnish of a desired resin is applied to a substrate such as glass, ceramic or a Si wafer, and then a desired pattern is formed. A method of curing the applied resin layer by performing the method is employed.

However, by performing the heat treatment, the applied resin layer thermally contracts, and as a result, the edge of the pattern formed by the heat-treated resin layer rises in a frame shape. FIG. 8 is a model diagram for explaining the phenomenon. In the figure, 10 is a heater substrate,
17 is a thermosetting resin layer, 20 is a channel substrate,
FIG. 8A is a cross-sectional view showing a state after pattern exposure and development, and shows a state before heat curing.
(B) shows the state after the heat curing treatment. When the thermosetting resin layer 17 in the state shown in FIG. 8A is heat-treated at, for example, 400 ° C., heat shrinkage occurs in the film thickness direction and also in the plane direction. In the curing, the edge portion proceeds first. Since the dimension of the portion where the thermosetting resin layer 17 is in contact with the heater substrate 10 does not change, a large distortion is generated in the thermosetting resin layer 17 and the end has a high height as shown in FIG. The raised portion a of the height h occurs in a frame shape.

An example of the degree of excitement will be described. As a thermosetting resin layer, as a photosensitive polyimide varnish,
Probimide® (Ciba-Geig)
(manufactured by Company y) at 350 ° C. for 2 hours. When the thickness of the resin layer before curing is 55 μm, the thickness after curing is 33 μm.
m, and a bulge having a height of 8 μm occurred thereon. Another photosensitive polyimide varnish, P
It heated at 350 degreeC for 2 hours using yralin PI2722 (made by Du-Pont). When the resin layer thickness before curing is 55 μm, the film thickness after curing is 33 μm,
Further, a swell of 8 μm was generated thereon.

When such a phenomenon occurs, the following problems occur when assembling an ink jet recording head. That is, as a method of forming the nozzles of the ink jet recording head, as shown in FIG. 9, a heat acting portion (not shown) is formed on the heater substrate 10, and pits are formed thereon using the above-described resin. After the thermosetting resin layer 17 is formed in a desired pattern, a method of bonding a channel substrate 20 on which a nozzle 21, an ink supply port 23, a filter 24 and the like are formed to the heater substrate 10, or as shown in FIG. In addition, a method is adopted in which a partition wall 31 is formed of the above-described resin on the heater substrate 10 on which the heat acting section is formed, and the partition wall 31 is covered with a top plate 30 to form the nozzle 21. However, in any case, as long as heat treatment is performed in a normal forming method, a phenomenon in which the edge of the pattern of the thermosetting resin layer always rises in a frame shape occurs.

[0009] The frame-like bulge at the end of such a pattern has a large correlation with the resin film thickness, and becomes larger as the thickness increases. Therefore, when the film thickness is small,
Although this does not cause much problem, if practicality as an ink jet recording head is considered, at least 5 to 1
Since a relatively thick resin film of about 00 μm is required, the frame-shaped swelling described above cannot be avoided by the conventional method. As a result, the contact with the channel substrate or the top plate could not be completely achieved, and the yield was lowered, and the reliability as an ink jet recording head was significantly lowered.

The frame-shaped bulge at the end of the pattern has a strong correlation not only with the film thickness of the resin but also with the temperature at the time of heat treatment for curing the resin (hereinafter referred to as the curing temperature). It has been found that the higher the temperature, the greater the climax. One example is the same Pr as in the above example.
A case in which a resin film having a thickness of 55 μm before curing is heated for 2 hours using obimide will be described. At a curing temperature of 200 ° C., the film thickness after curing is 50 μm, on which a swelling of 2 μm occurs. On the other hand, at a curing temperature of 400 ° C., the film thickness after curing is 30 μm, and a swelling of 10 μm is generated thereon. Pyra
Even in the case of lin PI2722, the film thickness before curing is 55
When the μm resin film is heated for 2 hours, the curing temperature is 200 ° C.
Then, the film thickness after curing becomes 50 μm, and 1 μm
At the curing temperature of 400 ° C.
The film thickness after curing was 30 μm, and a swell of 9 μm was generated thereon.

That is, if the curing temperature is lowered, the height of the swelling is reduced. However, the resin layer cannot be completely cured at a low curing temperature. In the case of the polyimide resin as described above, the imidization ratio, which is a measure of curing, reaches 95% or more at a curing temperature of 400 ° C., but remains at about 80% at a curing temperature of 200 ° C. know.

No consideration is given to the curing characteristics of the resin layer in the thermosetting resin layer in the case of the thermal ink jet head proposed in the above-mentioned Japanese Patent Application No. 2-21425. Therefore, in order to suppress the swelling height of the heat-treated resin film, heat treatment is performed at a curing temperature at which swelling does not become a problem, for example, at 200 ° C., so that the yield in bonding the channel substrate or the top plate to the heater substrate is increased. It is conceivable to improve the quality.

However, when a resin film that has been heat-treated at 200 ° C. is used, the following problems occur with the ejection of ink droplets. This will be described below with reference to FIGS. FIG. 4 and FIG. 5 are cross-sectional views of the vicinity of a thermal action area of a conventional thermal inkjet head. In the figure, 10 is a heater substrate, 11 is a heat storage layer, 12 is a common electrode, 13 is an individual electrode, 14 is a heater layer, 15 is a heater protective film, 16 is an electrode protective film, 17 is a thermosetting resin layer, and 18 is Recess, 20
Denotes a channel substrate, 21 denotes a nozzle, and 22 denotes an ink flow path. FIG. 4 shows a thermosetting resin film 1 heat-treated at 200 ° C.
In this state, the heater substrate 10 having the substrate 7 and the channel substrate 20 are bonded and then diced. Since ink droplets are not ejected, the thermosetting resin layer 17
Is formed such that the cross-sectional shape of the recess 18 is substantially perpendicular to the heating surface. However, as shown in FIG. 5, the cross-sectional shape of the thermosetting resin layer pit layer 17 after ejecting about 100 million ink droplets is such that a portion close to the heater heating portion is caused by cavitation or chemical corrosion. The shape will look like it has been shaved. As a result, there is a problem that the effect of the thermosetting resin layer 17 as a protective film is weakened, and the heater is likely to fail.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and it has been proposed to reduce the height of a thermosetting resin after curing, thereby providing a channel substrate, a top plate and a heater. The yield in the process of bonding to the substrate is high, and the thermosetting resin layer in the vicinity of the heat generating portion is almost completely cured, and the adhesion to the lower layer is also high, which is an effect as a protective film of the thermosetting resin layer. Is intended to realize an excellent thermal inkjet head.

[0015]

According to the present invention, a concave portion for defining a bubble generation region is formed by a thermosetting resin layer, a heating element is provided at a bottom portion of the concave portion, and a boundary of the concave portion is defined by the boundary. In a thermal ink jet head set inside a boundary of a heat generating region of a heat generating element, the thermosetting resin layer is formed of a plurality of layers, and at least a lowermost layer is sufficiently thermoset. It is.

The imidization ratio of at least the lowermost thermosetting resin layer can be 85% or more, preferably 95% or more. The opening size of the thermosetting resin layer above the lowermost layer may be larger than the opening size of the lowermost thermosetting resin layer. The thermosetting resin layer may be formed by setting the curing temperature of the lower layer higher than the curing temperature of the upper layer.

[0017]

The thermosetting resin layer of the present invention is formed into a plurality of layers by repeating patterning and subsequent heat treatment a plurality of times. After patterning at least the lowermost layer of the plurality of thermosetting resin layers, a heat treatment is performed at a high temperature to sufficiently thermoset and form a layer having a high protective effect. The thermosetting resin layer forms pits in the thermal ink jet head, and sets the boundaries of the pits near the electrodes closer to the center of the heating section than the boundaries of the heating section to prevent damage near the step at the boundary of the heating section. Can be prevented.

Further, by forming the thermosetting resin layer by a plurality of layers, the swelling at the end can be reduced, and the swelling at the end can be suppressed by setting the heat treatment temperature of the upper layer low. It is.

Further, by forming the opening size of the lower thermosetting resin layer to be smaller than the opening size of the upper thermosetting resin layer, the thermosetting resin layer functions as a protective film and the concave portion is formed. Volume can be secured.

[0020]

FIG. 2 is a perspective view of a completed thermal ink jet head obtained by bonding a heater substrate and a channel substrate according to a first embodiment of the present invention. FIG. FIG. In the figure, the same parts as those in FIG. 17a and 17b are thermosetting resin layers. The heater substrate 10 and the channel substrate 20 are formed on a Si substrate by photolithography. After bonding the two, the substrate is cut by a dicing saw, and the head shown in FIGS. 1 and 2 is manufactured.

The structure of the heater substrate 10 will be described in more detail. In this embodiment, the heat storage layer 11 is a thermal oxide film on a Si substrate, and the heater layer 14 is formed of polysilicon (poly-Si). Common electrode 1
2 and the individual electrodes 13 are formed of Al, and the electrode protection layer 16 thereon is SiO ₂ . Heater protection layer 1
5 is composed of two layers of Si ₃ N ₄ and Ta, and Ta is an upper layer. The thermosetting resin layers 17a and 17b are formed on the heater protection layer 15 and the electrode protection layer 16. Electrode protection layer 1 formed under thermosetting resin layer 17a
Since No. 6 is SiO ₂ , heat conduction is not good. In this embodiment, the boundary of the heat action region is located at the end of the electrode protection layer 16 as shown by b. Therefore, the boundary between the thermosetting resin layers 17a and 17b is set closer to the center of the heat generating portion, which is inside the boundary of the heat action region.

Each of the thermosetting resin layers 17a and 17b has the above-mentioned Probimide (registered trademark) (Ciba-Gei).
gy). That is, in this embodiment, the pit layer is composed of two thermosetting resin layers 17a and 17b. Hereinafter, a method for forming the pit layer will be described. (A) A varnish of a thermosetting resin is applied on a heater substrate on which a film other than the pit layer has been formed to a predetermined thickness by a method such as spin coating or roll coating. (B) Perform baking and dry the varnish of the thermosetting resin. (C) Exposing the thermosetting resin varnish through a mask corresponding to a desired pattern. (D) Develop by a method suitable for the thermosetting resin varnish to form a desired pattern. (When a thermosetting resin having no photosensitivity is used, after (b), an appropriate resist is applied, and then exposure and development are performed.) (E) Baking at a predetermined temperature for a predetermined time To cure the thermosetting resin layer.

In this embodiment, the above-described steps (a) to (e) are repeated twice to form a pit layer having a two-layer structure. The film thickness of the first thermosetting resin layer 17a before the curing in the step (a) is 9 μm, and the curing temperature and the curing time in the step (e) are 400 ° C. and 2 hours. As a result, the first layer having a thickness S _1, the height of the raised shown 5μm next, h of FIG. 8 (B), was only 1μm because the film is thin.

Next, a second thermosetting resin layer 17b was formed. The film thickness before curing in step (a) of the second layer is 2
The curing temperature and the curing time in the step (e) are 200 ° C. and 2 hours. As a result, the film thickness S ₂ of the second layer is 20 μm, and the height of the swelling shown by h in FIG. 8B is 1 μm due to the low curing temperature.
It was only.

The bulge having a height of 1 μm after the formation of the first layer was absorbed and flattened after the application in the step (a) of the second layer. However, the unevenness of the first layer itself having a thickness of 5 μm is substantially maintained. As a result, the total film thickness of the first and second layers was 25 μm, and the height of the protrusion was 1 μm. Since the height of the swell was only 1 μm, it did not hinder the adhesion to the channel substrate 20 in FIG.

FIG. 3 is a cross-sectional view showing the vicinity of a heat working area of a second embodiment of the thermal ink jet head according to the present invention.
In the figure, the same parts as those in FIG. The outline of the perspective view of the completed head obtained by bonding the heater substrate and the channel substrate is the same as FIG.
In this embodiment, the opening of the concave portion of the upper thermosetting resin layer 17b of the two thermosetting resin layers 17a and 17b forming the pit layer is different from that of the embodiment described in FIG. The size is larger than the opening of the concave portion formed by the thermosetting resin layer 17a. Further, as the thermosetting resin, the aforementioned Pyr
alin PI2722 (manufactured by Du-Pont) was used. The pit layer is formed by repeating steps (a) to (e) twice, similarly to the method described with reference to FIG.
A pit layer having a two-layer structure was formed. The thickness of the first thermosetting resin layer 17a before curing in the step (a) is 9 μm, and the mask in the step (c) has a pit size of 50 μm.
μm × 100 μm is used, and the curing temperature and curing time in the step (e) are 4
00 ° C. for 2 hours. As a result, the film thickness S1 of the _first thermosetting resin layer 17a becomes 5 μm, and h of FIG.
The height of the swelling shown in Table 1 was only 1 μm due to the thin film thickness. Next, a second thermosetting resin layer 17b was formed. The film thickness S ₂ before curing in the step (a) is 22
The mask used in the step (c) is designed to have a pit size of 60 μm × 110 μm. The curing temperature and the curing time in the step (e) are 200 ° C. and 2 hours. As a result, the film thickness S ₂ of the _second thermosetting resin layer 17b was 20 μm, and FIG.
The height of the bulge indicated by h in (B) was only 1 μm due to the low curing temperature. The rise of 1 μm in height after the formation of the first thermosetting resin layer 17a was absorbed and flattened after the application of the second thermosetting resin layer 17b in the step (a). As a result, the total film thickness of the first and second layers was 25 μm, and the height of the protrusion was 1 μm. Since the height of the swell was only 1 μm, it did not hinder the adhesion to the channel substrate 20 in FIG.

FIG. 6 is a perspective view of a main part of a third embodiment of the thermal ink jet head of the present invention. In the figure, 1
0 is a heater substrate, 21 is a nozzle, 30 is a top plate, 31
a and 31b are thermosetting resin layers. In this example,
Unlike the first or second embodiment, the thermosetting resin layer 3
1a and 31b are used for forming a partition. The used thermosetting resin is the above-mentioned Probimide (registered trademark), but it is of course possible to use other thermosetting resins. Also in this embodiment, the above-mentioned (a) to (e)
Step 2 is repeated twice to obtain the thermosetting resin layer 31
The partition walls were formed in a two-layer configuration of a and 31b. The manufacturing conditions for the first and second layers were exactly the same as in the first embodiment.
As a result, the thickness of the finally manufactured partition wall was 25 μm,
The height of the swell was 1 μm. The height of the swell was only 1 μm, and did not hinder the adhesion to the top plate 30 as in the above-described embodiment. In this embodiment, the present invention is applied to the production of a thermal inkjet head, but other inkjet recording heads requiring a partition,
Alternatively, the present invention can be applied to manufacture of a recording head of another system.

FIG. 7 is a front view of a main part of a fourth embodiment of the thermal ink jet head according to the present invention. In the figure, the same parts as those in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted.
This embodiment also uses the thermosetting resin layers 31a and 31b for forming the partition. The thermosetting resin layer used is
Although the above is Pyralin PI 2722, it is of course possible to use other thermosetting resins. Also in this example, the above-described steps (a) to (e) were repeated twice to form the partition 14 with a two-layer structure. As the mask in the step (c) of the first thermosetting resin layer 31a, a mask designed so that the ink flow path width was 70 μm was used. Other manufacturing conditions were exactly the same as in the second embodiment. As a result, the thickness of the finally manufactured partition wall was 25 μm.
m, and the height of the swell was 1 μm. The height of the swell is only 1 μm, and as in the third embodiment,
The adhesion to the top plate 30 did not hinder. This embodiment also employs another inkjet recording head that requires a partition,
Alternatively, the present invention can be applied to manufacture of a recording head of another system.

In the embodiment described above, the thermosetting resin layer has a two-layer structure. However, it is of course possible to form the thermosetting resin layer with three or more layers. At that time, the curing temperature of the lowermost layer is set higher than the curing temperature of at least one other layer, but it is not always necessary to set the curing temperature of the lowermost layer higher than the curing temperature of any other layer. However, the thickness of the lowermost layer and the height of the swelling at that time depend not on the curing temperature of the layer but on the highest temperature that the lowermost layer subsequently experiences.

[0030]

As described above, according to the present invention, a multi-layered thermosetting resin layer is used for a pit layer or a partition wall, and the lowermost layer of the thermosetting resin layer is sufficiently thermoset. Thereby, the following effects can be obtained. Since the curing temperature other than the lowermost layer of the thermosetting resin layer can be lowered, the swelling that occurs in a frame shape at the end of the pattern of the thermosetting resin can be almost eliminated. as a result,
In the step of forming the nozzles of the ink jet recording head, the adhesion between the thermosetting resin layer and the top plate or the grooved substrate is improved, and the yield is greatly improved. By setting the curing temperature of the lowermost layer of the thermosetting resin layer sufficiently high, the curing of the lowermost layer proceeds almost completely, and it is possible to prevent chemical erosion due to ink and mechanical erosion due to cavitation damage when bubbles are crushed. as a result,
Even after a large number of ink droplet ejections, the lowermost layer is not eroded, the effect as a protective film is not weakened, and a long-life inkjet recording head can be realized. The chemical erosion due to the above-described ink and mechanical erosion due to cavitation damage are concentrated on the lowermost layer of the thermosetting resin layer close to the heating surface near the electrode, and the other layers are insufficiently cured. However, no problem arises. Since the curing temperature of the lowermost layer of the thermosetting resin layer is sufficiently high,
The curing of the lowermost layer proceeds almost completely, and at the same time, the adhesive strength to the lower layer is enhanced. As a result, the thermosetting resin layer peels off from the layer below it after discharging ink droplets many times,
It is possible to provide a highly reliable inkjet recording head having excellent ejection durability without causing ejection failure or heater failure. By reducing the opening size of the lower layer and increasing the opening size of the upper layer, the thermosetting resin layer can be formed with little loss of the volume required for the pits.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a first embodiment of a thermal ink jet head according to the present invention, showing the vicinity of a heat action zone.

FIG. 2 is a perspective view of the thermal inkjet head according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view showing the vicinity of a heating area of a second embodiment of the thermal inkjet head of the present invention.

FIG. 4 is a cross-sectional view showing the vicinity of a heat action area of a conventional thermal inkjet head.

FIG. 5 is an explanatory diagram of a damaged state of a conventional thermal inkjet head.

FIG. 6 is a perspective view of a main part of a third embodiment of the thermal inkjet head of the present invention.

FIG. 7 is a front view of a main part of a fourth embodiment of the thermal ink jet head of the present invention.

FIG. 8 is an explanatory diagram of a heat-treated state of a thermosetting resin layer.

FIG. 9 is a cross-sectional view showing the vicinity of a heat action area of an example of a conventional thermal inkjet head.

FIG. 10 is a perspective view of a main part of another example of a conventional thermal inkjet head.

[Explanation of symbols]

10 heater substrate, 11 heat storage layer, 12 common electrode,
13 individual electrode, 14 heater layer, 15 heater protective film, 16 electrode protective film, 17, 17a, 17b, 31
a, 31b thermosetting resin layer, 18 recess, 20 channel substrate, 21 nozzle, 22 ink flow path, 30
Top board.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/05

Claims (1)

(57) [Claims] 1. A concave portion for defining a bubble generation region is formed by a thermosetting resin layer, a heat generating element is provided at a bottom portion of the concave portion, and a boundary of the concave portion is larger than a boundary of a heat generating region of the heat generating element. In the thermal ink jet head set inside, the thermosetting resin layer is formed of a plurality of layers, and at least the lowermost layer is sufficiently thermoset.