JPH054336A - Thermal ink jet printer - Google Patents

Abstract

PURPOSE: To prevent a printing head from being overheated to keep printing quality even when printing speed increases by absorbing thermal energy by a heat sink made of phase transition materials at the back of a print head nozzle. CONSTITUTION: A print head 8 is composed of a main body 3 with ink reservoir, ink injecting multiple nozzles 11 that are arranged at the main body 3 and connected to the ink reservoir, and an electric heater 9 that heats ink to inject from the nozzles 11. A heat sink 15 made of phase transition materials that changes thermal energy physical states of the print head 8 is arranged at the main body exposing to the print head 8 so that the heat sink 15 changes its physical states to absorb thermal energy of the print head 8. This prevents the printing head from being overheated to keep printing quality even when printing speed increases.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a thermal ink jet printer with a phase change cooling system.

[0002]

BACKGROUND OF THE INVENTION Thermal ink jet printing devices such as print cartridges are used to print text and images on media such as paper. Such devices include an inkjet printhead mounted on a substrate fixed to the body of the printing device and comprising a nozzle or orifice plate in fluid communication with the supply of ink in an ink chamber or bladder within the body.
When a small electric heater, each in the form of a small resistor in the ink path of each nozzle, is pulsed with an electric pulse, it heats the ink and ejects it as a drop of ink from the nozzle.

A typical nozzle plate structure is CS Chan filed on Nov. 22, 1985.
U.S. Pat. Nos. 4,694,308 and 1989.
U.S. Pat. No. 4,812,859 filed Mar. 14, 1996, and is specifically illustrated in FIG.

A typical thermal ink jet printing device consists of a print head having a glass or single crystal silicon silicon substrate structure on which a silicon dioxide barrier is deposited. Individual heater resistors are each deposited on the silicon barrier in the ink passages or priming cavity of each nozzle, with individual circuit traces for each resistor providing conduction to separate electrical energy sources. As is well known, resistors are fired in a variable order to print the characters or images selected by this order of organization. The heat of the resistor is transferred to the ink, causing the ink to boil. Ink droplets are ejected from the nozzle by the expanding bubbles. The heat of the resistor also heats the silicon substrate structure. In high-density printing, the number or resolution of resistors to be fired is set to, for example, 300 dots / inch to 600 dots / inch.
Printheads tend to heat up, such as by increasing inches or by firing more often. Thermal inkjet printhead performance degrades when the printhead temperature becomes too high. The temperature at which the print quality deteriorates varies greatly depending on the design of the inkjet print head.

A thermal ink jet printing apparatus often employs a plastic body on which a print head is mounted. Without a heat sink, a print speed limit must be set and not exceeded to avoid print quality degradation. Other attempts to solve this overheating problem have included all-metal printing device bodies to dissipate heat, or metal fins coupled to air convection cooling. The metal acted as a capacitor or bucket, but when the metal was heated, print quality deteriorated. Convective cooling helped to dissipate the heat, but was expensive and required air velocities that adversely affected the ink flight path, which reduced print quality. If the ejection frequency of ink drops is reduced, the heat flux is reduced. This keeps the head cooler. It is also possible to employ various print modes in which the pen scans one line multiple times to obtain the desired output. For example, if every other nozzle is fired, two passes are required to complete one line or the like. This reduces hardcopy throughput.

[0006]

SUMMARY OF THE INVENTION According to the present invention, an improvement over conventional devices and methods is provided by providing a printing device having a heat sink employing a phase change material for absorbing the thermal energy of the print head. Will be realized.
The heat sink may consist of a heat pipe containing a circulating phase change material. Alternatively, in the presently preferred embodiment and the best mode of the invention, from a heat pipe comprising a solid material disposed in heat exchange relationship with the printhead, for example near or in contact with the printhead substrate. Can be configured. Such solid phase change materials are solid in the temperature environment for the printhead such that acceptable print quality is achieved and preferably melt at a temperature below that at which print degradation occurs.
Such heat sinks utilize the heat of fusion of solid phase change materials. A heat pipe is a heat transfer device consisting of a sealed container containing a small amount of fluid in a partial vacuum. Heat is absorbed at one end by evaporation of this fluid in heat exchange relationship with the printhead, and is condensed at the other end of the container where it is released and removed from the end. Condensate returns to the sump along the side of the sealed container. The heat of vaporization thus absorbs the thermal energy of the printhead.

Thermal energy from the printhead is used to change the physical state of the phase change material. This thermal energy is absorbed or passed to the thermal energy used to change the physical state of the material by this means, thereby removing it from the substrate and the adjacent printer body.

When changing the physical state of a material, the thermal energy applied to the liquid or solid material is used to break the molecular bonds and does not heat the material much. As for solids, once the solid material has completely melted, the temperature of the melt will of course begin to rise if the printing speed is unchanged. With a heat pipe, the change in physical state is continuous unless its heat capacity is exceeded. Using this phase change principle, the heat generated by a thermal inkjet printhead is used to act on the physical state of the material. The printhead is kept at a constant and acceptable temperature as long as the physical state of the material changes.

Although the principles of the present invention have been described with reference to printheads, it should be apparent that the principles can be extended and used to cool integrated circuits and other electrical components.

Furthermore, the glass transition of the material can be used for cooling purposes in these applications.

[0011]

DETAILED DESCRIPTION OF THE INVENTION In many thermal ink jet printers, the potential for hardcopy throughput cannot be realized due to overheating of the printhead and the consequent loss of print quality. According to the present invention, the printing speed can be increased by adopting the heat sink for the print head that employs the material whose physical state changes at the upper limit of the operating temperature of the print head. Figure 1 is a heat vs. temperature diagram, which typically shows the thermal energy input when changing the physical state of a material, such as melting a solid or evaporating a fluid, where the physical state of the material is continuous. It plots the relatively constant temperature that exists over varying periods. If the material is solid, the temperature of the liquid will increase when the phase change is complete, unless the thermal energy input is reduced.
During this phase change period, thermal energy is used to change the physical state.

The use of a heat sink requires space within the printing device to receive the heat sink and place the phase change material in close proximity to the print head where heat exchange occurs. The solid heat sink material is preferably a thermally conductive material that melts at or below the print head temperature, above which print quality degradation becomes unacceptable. This heat sink provides temperature control during the period required to achieve a complete change in physical state. The phase change material storage capacity of the print head is the capacity that allows solid printing for about 4 minutes on the tested print head, as described below.
Therefore, without reducing the printing speed during use,
Enables implementation of many variable print density printing schemes that periodically require high print density. This can be further optimized over a longer period of time.

The use of a fixed amount of solid phase change material in the cavities of the print body provides a convenient solution to the printhead overheating problem. However, the high density printing period can be extended or continuous by using a configuration that circulates the phase change material, such as in a heat pipe. The heat pipe can also consist in part of the body cavity, and
It may be a self-contained unit having a heat contact and a cold contact for heat input and heat output, in which the heat from the print head is received and the cold contact removes the heat. The general requirements for the materials in this example are the same as for solid materials as far as the temperature at which the change in phase or physical state occurs. The advantage of heat pipes is that the duration of temperature control for the printhead is continuous.

One type of printer embodying the present invention is shown in the exploded perspective view of FIG. 2, but the invention is not so limited. The printing device 1 comprises a printing body 3 sealed in an ink chamber 5 with a gasket 7 or other suitable seal. A thermal ink jet print head 8 (see FIG. 3) including a resistor substrate 9 and an orifice or nozzle plate 11 is liquid-tightly bonded and fitted into the recess 3a. The recess 3a is filled with the resistor substrate and the printing main body 3 Is sealed on the top surface of. The slot 3b in the recess 3a of the printing body 3 is the ink chamber 5
It is connected to the ink inside. Print head assembly 8
Is sealed in the recess 3a, the slot 9a in the resistor substrate 9 allows the ink in the ink chamber 5 to reach the nozzle plate 11.
It is aligned with the slot 3b that passes through the back surface of the. As will be seen in FIG. 4, which will be described later, the passages 11b in the printhead structure behind the back surface of the nozzle plate 11 lead to ink channels or slots 9a in the resistor substrate 9 and allow ink to be delivered to each nozzle 11a individually. Through the ink cavity or the priming cavity 11c. Each resistor 9b on the resistor substrate 9 has a respective nozzle 11
It is arranged to face a. When the resistor is energized, the ink just above the resistor evaporates and bubbles form. As the bubble grows, the momentum is transmitted to the ink on the bubble, and the ink is ejected from the nozzle 11a. The resistor 9b is individually incorporated into any known system for organizing resistor firing using a flexible circuit 13 having individual circuit traces 13a connected to the individual resistors, only a portion of which is shown here. Is bound to. As can be seen in FIG. 2, these flexible circuits are shaped to fit the slanted sides of the print body 3.

The printing device 1 of FIG. 2 and the print head 8 of FIG. 3 are shown in a convenient position for the purpose of explanation. In some applications, the printing device 8 occupies a position as shown in FIG. 8, in which position the print head body 3
And the print head 8 is arranged in a substantially vertical plane. Placing the printing device 1 in this position causes the ink to flow to the print head 8 by gravity. Of course, the printing device can be in another position.

An outline of temperature control of the print head 8 using the phase change heat sink 15 is shown in FIGS. The heat sink cavity 15a is formed by the wall of the printing body 3. The open back side of the printing body 3 is closed by a gasket 7 backed by the end face 5a of the ink chamber 5, as can be seen in FIG. The solid material 15b having a melting point below the maximum allowable temperature of the print head contacts the back surface of the substrate 9 to fill the cavity 15a in a heat exchange relationship therewith.

The ink passage between the ink chamber 5 and the priming cavity 11c is best seen in the cross-sectional view of FIG. 5, showing the assembled printing device 1.
The ink passage includes an opening 5b in the end surface 5a of the ink chamber 5 and an opening 7a in the gasket 7. Both of these openings are located in the priming cavity 1 behind the nozzle plate 11 via slots 9a in the resistor substrate 9.
It is aligned with the slot 3b of the printing body 3 leading to 1c.

Details of this ink distribution system to the individual nozzles 11a are apparent in FIG. This is a partial sectional view taken along the section IV-IV in FIG.
The printing body 3 of the substrate 9 of the print head 8 only in a
The attachment of the cavity 3a at the upper end of the to the slot 3b is shown representatively. The printing body 3 is a gasket 7 (see FIG. 2)
Is sealed in the ink chamber 5. The print head 8 is a single crystal silicon substrate 9c sealed in the recess 3a.
From now, silicon dioxide that acts as a thermal capacitor barrier (Sio ₂₎ layer 9d is deposited thereon.
Only one individual resistor 9b of tantalum aluminum TaAl is shown here, but these are deposited on this silicon dioxide layer 9d. Individual resistor 9b
Circuit trace or conductor 9bb for resistor 9b
Deposited on top, but the resistor portion at or opposite nozzle 11 remains exposed. A passivation layer and resistor protection layers 9p and 9q are subsequently deposited on the resistor 9b. Layer 9p is silicon carbide S
iC or silicon nitride SiN. The layer 9q is tantalum Ta. The passivation layer allows the transfer of heat from the resistor to the ink in the priming cavity while providing physical, chemical, and electrical isolation from the ink.

Barrier layer 11e of photoimageable polymer
Form an ink cavity, which includes a priming cavity 11c for each nozzle and a manifold passage or cavity 11b. Nozzle plate 11
Is usually electroformed with nickel, covering and adhering to the barrier layer. Each nozzle 11a communicates with each priming cavity 11c. An approximate meniscus line of ink is located at the opening of the nozzle 11a. Each nozzle 11
The priming cavities 11c of a are joined together by a manifold cavity 11b. This manifold cavity 11b is a slot 9a in the resistor substrate 9
This slot 9a extends through all layers of the substrate as shown. Sealant 9e
Seals the substrate 9 around the slot 3b and inside and around the recess 3a. Figures 6, 7 and 8 show a plastic printing body 3 of the type employed in the practice of this invention using a solid phase change material from which the test data shown in the temperature diagram of Figure 9 was taken. .. In this embodiment, the print head recess 3a in the print body 3 is sealed from the heat sink cavity 15a in the print head 3 by an integral end plate portion 3d that seals the recess 3a except for the opening of the slot 3b. In FIG. 6, the print head 8 and the flexible circuit are removed in order to clearly show the end plate 3d. However, FIG. 7 is a cross-sectional view taken along section line VII-VII in FIG.
Contains these features. The integral end plate 3d eliminates a sealing failure between the heat sink 15 and the print head 8. Direct heat exchange between the resistor substrate and the phase change material 15 no longer occurs, requiring the printhead to operate at a slightly higher temperature with the same heat sink material.
However, this can be compensated for if necessary by selecting a heat sink material that melts at a lower temperature to compensate for the heat drop in the end plate 3d.

FIG. 8 is a sectional view taken along the section line VIII-VIII in FIG. This cross section includes the major axis of the slot 3b and defines the internal structure of the slot 3b forming a passage 3bb between opposing sides or openings of the slot 3b. At the position of the printing device 1 shown in FIG. 8, it is clear that there is a gravity-induced flow of ink to the print head at the opening outside the slot 3b. In addition, the ejection of ink from the nozzle acts as a pump for drawing the ink into the priming cavity of the printhead.

Solid materials suitable for heat sink applications include gallium and polyethylene glycol. Low temperature solder can also be used. The melting point of the solid phase change material used is determined for each printhead in relation to the upper temperature limit at which the printhead can operate without unacceptable print quality degradation. An experiment using a 300 dpi print head of a plastic body shows that there is a large variation in the allowable upper limit of the temperature of the thermal inkjet print head. Therefore, the solid phase change material selected for this application must have a melting point below the already known upper temperature limit of the particular printhead to obtain acceptable print quality in any case. Experiments with plastic body printheads show that the material is required to change its physical state at temperatures below the printhead temperature limit and to have reasonable thermal conductivity. Thermal conductivity is about 10 w / m / ° k for tested solids
Is. The choice of solid or liquid material depends only on the upper temperature limit of the printhead. Thermal conductivity is a coefficient of the rate of change of physical state required to absorb the rate of supply of thermal energy.

In experiments conducted with a 300 dpi thermal ink jet pen or printhead with a plastic case and no heat dissipation equipment, the temperature of the printhead continued to rise during printing. Another experiment using the same type of thermal ink jet pen or printhead with a plastic case and a heat sink with gallium as the phase change material showed that printing during printing during the melting period of the phase change material. The head temperature was constant at an acceptable level. Applications of heat sinks with solid phase change materials show significant improvements in thermal management based on these experiments.

For example, if gallium is used as the phase change material in the heat sink of a print head assembly of the same type, the print head will operate in high density print mode for 3-4 minutes without exceeding the maximum operating temperature of the print head. It was found that continuous ejection was possible. As one example of a specific success of the test, 100% optical print density A-size diagrams could be printed without slowing down.
As a second successful test example, it was possible to print ten sheets of A size with a density of 50% in succession without deterioration of print quality. The performance varies depending on the number of nozzles, the size of the silicon substrate, the ejection frequency, and the resolution (300 dpi).

The test results described above are shown in FIG. This figure shows test data obtained from a test of a 300 dot / inch printing device 1 with a printing body 3 of the type of FIGS. 6, 7 and 8 constructed of plastic material. Four tests were performed, one without a heat sink and three with different heat sink materials. All tests were carried out with this plastic printing body 3, which is marked in FIG. 9 as a manifold. The print head 8 was ejected for about 260 seconds in the high density mode as shown and then stopped. With no heat sink, the printhead temperature exceeded 100 ° C at the end of the test period. When a heat sink using polyethylene glycol as the phase change material was used, the upper limit of the temperature of the print head decreased by about 16 ° C. However, there is an upper limit followed by a gradual increase in temperature during the test period, where again the concept of this invention worked, but the use of other materials with phase change temperature and thermal conductivity properties that better suit this application. Was urged. As shown in the third test, the addition of copper fibers to polyethylene glycol improved the thermal conductivity and slightly lowered the upper temperature limit at the end of the test period. The last test recorded in Figure 9 used gallium as the heat sink material,
Significant improvements in heat management were seen compared to using only the plastic print body 3 or the manifold. In the final test, the printhead temperature remained constant for the duration of the test once the gallium began to melt.

10 to 14 show the heat pipe and the printer 1.
Indicates its application to 0. In these figures,
Components corresponding to those in FIGS. 2 to 8 are designated by the same reference numerals. The printing device 10 includes a main body 30 including the ink bladder 31 shown in FIG. A print head 8 having a substrate 9 is sealed in a recess in the body 30. Ink bladder 31
Has a neck portion 31a shown in FIG. 11, the outlet of which is a slot 9b on the back side of the substrate 9 of the print head 8 (see FIG. 14).
It is sealed around the. At this position, the ink in the bladder 31 communicates with the slot 9b and supplies the ink to the priming cavity 11c and the nozzle 11a of the nozzle plate 11 (see FIG. 4).

The heat pipe 25 is arranged inside the main body 30 of the printing apparatus 10. This heat pipe consists of a pair of tubes 25a and 25b which can be joined on the neck portion 31a of the bladder, these tubes being at the lower ends 25c and 25d, respectively, and at the open enlarged upper end 25.
e and 25f. The lower ends 25c and 25d are also open, the ends of which are indicated by outlines 25g and 25h on the back surface of the substrate 9 opposite to the ink supply slot 9a and the neck portion 31a of the bladder 31 shown in FIG. Are bonded and sealed with, for example, an epoxy type sealant. The open upper ends 25e and 25f are similarly
Here, it is adhesively sealed to a cold junction composed of a plate 33 of high thermal conductivity such as aluminum or copper which is shown to project from the upper inclined surface of the main body 30 of the printer 10.
It rejects heat to the ambient environment or cold junction metal clamps on plate 33, such as the highly conductive heat of body 30. The heat pipe fluid 25j at the bottom of each heat pipe tube 25a, 25b is in contact with the back surface of the substrate 9, and wetting regions are formed within the outlines 25g and 25h. These wetted areas should be as large as possible in the substrate space to maximize the area exposure of the heat pipe fluid to the substrate 9.

As in the case of the solid phase change material, the thermal energy generated on the substrate 9 by discharging the resistor 9b causes a physical change. In this case, the heat pipe fluid evaporates. Warm steam rises in the heat pipe tubes 25a and 25b as indicated by the dotted arrows in FIG. At the expanded upper ends 25e and 25f of the heat pipes 25a and 25b, the steam is cooled by the cold junction plate 3
It contacts the inner surface of 1, where it cools, changing phase states and returning to a fluid. This is indicated by the solid arrows flowing through the wall of the heat pipe tube to the fluid source 25j.

In one embodiment, the heat pipes were pressurized and each contained about 1 cc of fluid 25j. An atmospheric pressure range P from 0 ° C. to 70 ° C. was applied to each fluid shown in the table below.

[0029] Heat consumption rate: mh _fg m = mass flow rate (g / sec) h _fg = heat of vaporization (joule / g) For Freon, the heat of vaporization h _fg is 180 j / g

From the above, the choice of phase change material corresponds to the rate of heat dissipation to provide a change in the physical state of the phase change material at a rate simply equal to the upper temperature limit of the printhead and the rate at which thermal energy increases. It can be seen that it is based on the thermal conductivity.

Although the present invention has been described above in the application to a printing apparatus having a plastic printing main body, the principle of the present invention has at least the same advantages when applied to a case where a metal printing main body is adopted. is there. We named specific solid and liquid phase change materials and provided data about them, but when we know the upper temperature limit and velocity of the printhead at which thermal energy is generated, the physics of materials that can make use of other materials are known. It can be easily selected from the characteristic table. Therefore, it is believed that changes in the physical state of the material, such as glass transition within the temperature range of acceptable print quality, can be used for cooling purposes.

[0032]

As described above, according to the present invention, it is possible to prevent the print head from being overheated, and as a result, the print quality does not deteriorate even if the printing speed is increased.

[Brief description of drawings]

FIG. 1 is a graph of temperature versus time showing the thermal energy required to transform the physical state of a solid material into a liquid.

FIG. 2 is an exploded perspective view of a thermal inkjet printing apparatus embodying the principles of the present invention.

3 is an enlarged perspective view showing assembly of a print head and attachment of a flexible circuit of the printing apparatus of FIG.

FIG. 4 is a partially enlarged cross-sectional view of the print head taken along the line IV-IV in FIG.

5 is an enlarged cross-sectional view taken along the line VV in FIG.

FIG. 6 is a plan view of a print head main body in another embodiment in which a flexible circuit is removed in a state in which a print head and a flexible circuit are removed.

7 is a sectional view taken along line VII-VII in FIG.

8 is a sectional view taken along line VIII-VIII in FIG.

FIG. 9 is a graph of printhead temperature from the same printhead test with and without a heat sink using different solid materials.

FIG. 10 is a perspective view of a printing apparatus in another embodiment in which thermal pulp is carried out by using a print head of the type shown in FIGS. 3 and 4;

11 is a partial side view of the printing device of FIG.

12 is a perspective view of the heat pipe of FIGS. 10 and 11. FIG.

13 is a side sectional view of the heat pipe of FIG.

FIG. 14 is a rear view of the print head substrate.

[Explanation of symbols]

 1: Printing device 3: Printing main body 3a: Recess 3b: Slot 5: Ink chamber 8: Printing head 9: Resistor substrate 11: Nozzle plate 15: Heat sink 15a: Heat sink cavity

Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location 8804-2C B41J 29/00 Q (72) Inventor Zyon El Stuthuel San Diego Diego Columbus Street, California 8049 ( 72) Inventor William Dei Kuppel Loveland Houses West 18th Street, Colorado, USA 665 (72) Inventor Bruce Day Miular, Escondide Cantry Club Drive, California, United States 1812 (72) Inventor Gerardo・ Gie Huar 14141 Poway Ezralane, California California

Claims (1)

Claim: What is claimed is: 1. A main body having an ink reservoir, a print head having a plurality of nozzles arranged in the main body for ejecting ink in association with the ink reservoir, and heating the ink. An electric heater for ejecting ink from each of the nozzles and a phase change member that changes the physical state of the heat energy of the print head are exposed to the print head, and the heat of the print head is changed by changing the physical state. A thermal ink jet printer comprising: a heat sink arranged on the main body so as to absorb energy.