GB2324765A

GB2324765A - Reducing inkjet aerosol contamination using electrode(s)

Info

Publication number: GB2324765A
Application number: GB9806182A
Authority: GB
Inventors: Bradley B Branham; Yuan Kong; Michael F Klopfenstein; Donald W Huff
Original assignee: Hewlett Packard Co
Current assignee: HP Inc
Priority date: 1997-04-09
Filing date: 1998-03-23
Publication date: 1998-11-04
Anticipated expiration: 2018-03-23
Also published as: DE19810061A1; JPH10278252A; DE19810061B4; GB2324765B; GB9806182D0

Abstract

Aerosol contamination is reduced by inductively charging ink 70 (Fig. 8) within a printhead 38 (Fig.8) using a platen electrode 50 so that ink particles 78 (Fig.10), including aerosol particles (78c), ejected from a nozzle 68 (Fig.8) become charged. The platen also creates an electric field between the nozzle and a print medium 40, which interacts with the charged aerosol particles to help control their path. Depending on the charge of the particle and the polarity of the electric field the field either attracts the aerosol particle towards the medium, or it repels the particle towards the printhead where it can be collected and removed. A single electrode or network of electrodes can be used. The arrangement may be used in a carriage service station (80,Fig.11) wherein a spittoon electrode (84) diverts the aerosol particles received in the spittoon from the ink purged from a printhead (34).

Description

2324765 10960956 -)5

SYSTEM AIND METHOD FOR REDUCING AEROSOL CONTAMINATION IN AN INK-JET PRINTER BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to a system and method for reducing aerosol contamination in an ink-jet printer and, more particularly, to a system and method in which an electrode is used to inductively charge ink particles, including aerosol. ejected from the ink-jets of an ink-jet printer. The charged aerosol particles are ejected toward a print medium through an electric field such that they are either attracted toward the print medium where they contribute to the printing process or repelled back toward the print head where they canbe collected and disposed of.

2. Description of Related Art

Ink-jet printers are reliable and efficient printing devices. Typically, an ink-jet printer utilizes a print head mounted on a carriage which moves back and forth over a print medium. such as paper. The print head commonly has one or more ink jets which can be selectively activated to eject a small quantity of ink onto the print medium. A control system controls movement of the print head and selectively activates the appropriate ink-jets as the print head moves over the appropriaEe locations on the print medium to form desired images and characters.

There are two common types of ink-jets used in print heads for ink jet printers: 1) thermal ink-jets: and 2) piezo-electric ink-jets. In a thermal ink jet. a small ink chamber is typically defined with a substrate at one end and a nozzle at the other. A heating element. such as a resistor, is provided on the substrate. Activation of the heating element creates a bubble within the ink chamber which expels a small quantity of ink through the nozzle and toward the print medium. In a piezo-electric ink-jet, mechanical action of piezo- electric 10960956 elements serves to expel small quantities of ink from a small chamber. through a nozzle and toward the print medium.

In both of these types of ink-jets, as well as other less common types of ink-jeEs, the expulsion of ink through the nozzle frequently produces fine ink particles and fragments in addition to relatively larger particles. The relatively larger ink particles. referred to as drops. usually have sufficient mass and momentum to carry them directly to the priUE medium where they impact in the desired location. Smaller particles, referred to as spray, may have sufficient mass and momentum to reach the print medium. However. their path may be slowed or diverted by air currents or the like so that they do not necessarily impact the print medium at the intended location. This can detract from the qualiEy of the image being printed. Still smaller particles. referred to as aerosol, do not have sufficient mass or momentum to reach the print medium. Rather, Lhe small size and mass of these particles may aflow them to float Lin the various air currents within the printer until they settle on various surfaces in and around the printer.

The presence of this aerosol and the residue resulting from aerosol settling on various surfaces can have many undesirable results. For example, should the aerosol settle on circuit components, the various salts within the ink may cause corrosion and, eventually, failure of the circuit. Deposits of aerosol ink on moving parts. such as the carriage guide rod and the like, may increase friction or otherwise impair proper operation of the printer. This problem is worsened because such ink tends to trap dust. paper fibers and other debris which further impairs the proper operation of the moving components. Many ink-jet printers also use optical components. for example, to detect and monitor the position and movement of the print head or carriage. The build up of aerosol on and around these critical components may scatter, refract or block the light necessary for their proper operation.

10960956 Aerosol may also build up on surfaces which contact the print medium or the user. Should built-up aerosol contact the print medium, it may produce undesirable stray markings or smears. Similarly, the build up of aerosol on surfaces which contact the user may dirty the operator's hands and clothing.

Many of the efforts to increase print quality in other areas have worsened the problems associated with aerosol contamination. For example, smaller nozzles may be used to increase printer resolution. However, smaller nozzles can also eready increase the amount of aerosol created. Likewise. the salt concentrations in some inks have been increased in order to improve color.

color fastness. darkness and other characteristics of the ink. The increased salt content. however. makes the ink more corrosive and harmful to printer components. Increased use of surfactants in ink can promote the migration of the aerosol ink after it collects on printer surfaces. In addition, low evaporation solvents can cause aerosol ink to dry very slowly, thereby increasing the time during which the aerosol may migrate. cofiect debris and otherwise impair printer performance.

It should be appreciated that aerosol may be created any time ink is ejected from an ink-jet nozzle. Thus. aerosol may be created not only during normal printing operations, it may also be created during purging, an operation performed by some printers during which ink is ejected from the nozzles to remove clogs or obstructions, and other maintenance operations. Some ink- jet printers are provided with a service station to which the print head is moved to perform various maintenance operations, such as purging. Commonly, the service station is provided with a spittoon into which ink purged from the nozzles is ejected and collected. To reduce the adverse effects of aerosol created during such operations, the spittoon may be made as small as possible. Ln this mariner, the aerosol is more likely to collect on the internal walls of the spittoon and be captured within the spittoon. As a practical matter. however. if 10960956 the spittoon is too small it may fill with ink and no longer serve its intended purpose. Moreover, reducing Elie size of the spittoon has no effect on the aerosol created during printing.

In an attempt to control aerosol contamination, whether created during printing or purging, some printers are provided with a fan which is intended to blow aerosol laden air out of the printer. Typically, the fan directs the air through a filter. which may have electrostatic fibers, in an effort to remove at least some of the aerosol before the air leaves the printer. However, over time. such filters can become clogged and may offer only a short term solution. Moreover. the addition of the fan and its associated components adds EO the cost of the printer.

To help prevent the creation of aerosol and spray particles, visoelasLic long chain polymers are added to some inks. It is thought that these polymers help to hold the ink drops together as they are ejected through the nozzle, thus reducing the amount of aerosol and spray particles. However, the polymers also may increase nozzle clogging.

It is also possible to reduce the formation and effects of aerosol and spray particles by reducing the distance from the nozzle to the print medium. A shorter distance results in less aerosol and spray contamination because there is less oppominity for air currents and the like to divert or deflect ink particles before they impact the print medium. However, there are practical limitations to reducing the distance beyond a certain point. For example, many types of print media tend to wrinkle or cockle when they are wet. If the distance between the nozzle and the print medium is too smafl. these wrinkles may bump the nozzle, smearing the image or damaging the print medium. Further, many ink-jeE printers are designed to print on a variety of print media. Because the various print media may have varying thicknesses. the distance from the nozzle to the surface of the print medium may vary, even within the same printer.

10960956 Thus. in many printers the distance from the nozzle to the print medium is already at or near its practical i SUMMARY OF THE INVENTIO

Accordingly, it is an object of the current invention to provide a reliable system and method for reducing aerosol contamination associated with ink-jet printers.

It is another object of the invention to provide such a system which does not adversely affect other aspects of the printer and which can be inexpensively manufactured and easily incorporated into the printer.

In accordance with these and other objects. a system in accordance with a preferred embodiment of the present invention reduces aerosol contamination associated with an ink-jet printer by inductively charging ink within the ink-jet so that particles. including aerosol particles. ejected from the nozzle are charged. The particles are ejected into an electric field, typically between the nozzle and the print medium. The electric field interacts with the charged aerosol particles to help control their path. In particular. depending on the charge of the particle and the polarity of the electric field, the electric field either attracts the aerosol particle toward the print medium where it can contribute to printing or it repels the particle toward the print head where it can be collected and removed.

In one aspect of the present invention, the same electrode or network of electrodes can be used to both inductively charge the ink within the inkjet and to create the electric field. For example, an electric potential can be applied to a platen which supports the print medium.

In another aspect of the invention. an electric field may be created in a spittoon to control the flight of aerosol particles at the service station. Again, a single electrode or network of electrodes positioned in or near the spittoon may serve both to inductively charge ink within the ink-jet and to create an electric field within the spittoon.

10960956 Other objects and aspects of the invention will become apparent to those skilled in the art from the detailed description of the invention which is presented by way of example and not as a lin:Litation of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a partially cut-away, perspective view of an ink-jet printer incorporating an aerosol contamination reduction system in accordance with a preferred embodiment of the present invention.

Figure 2 is partially cutaway view of portions of the printer of FiguC 1.

Figure 3 is a cross-section view taken along line 3-3 in Figure 2.

Figure 4 is a cross section view taken along line 4-4 in Figure 2 and showing the platen in a towered position.

Figure 5 is a schematic cross section view of an ink-jet. print media and platen from a printer in accordance with a preferred embodiment of the present invention.

Figure 6 shows the components of Figure 5 during the initial stages of ink ejection.

Figure 7 shows the components of Figure 6 at a later stage of ink ejection.

ejection.

Figure 1.

Figure 8 shows the components of Figure 7 at a later stage of ink Figure 9 shows the components of Figure 8 at a later stage of ink Figure 10 shows the components of Figure 9 at a later stage of ink Figure 11 shows a perspective view of a spittoon from the printer of 10960956 DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

An ink-jet printer incorporating a preferred embodiment of the present system for reducing aerosol contamination is indicated in Figure I as reference numeral 20. The printer 20 includes a chassis 22 surrounded by a housing 24. Within the housing 24. is a printer controller 26 (illustrated schematically as a microprocessor) that receives instructions from a host device (not shown), such as a personal computer or the like. The controller 26 may also implement internal preprogrammed instructions or receive instructions through a keypad (not shown) on the printer 20. The controller 26 then controls the various systems within the printer 20 to implement the instructions.

For example. the controller 26 controls a carriage system and a paper feed system. The carriage system. seen in Figures 1-4, includes a carriage guide rod 32 which extends transversely across the printer 20. The carriage guide rod 32 supports a carriage 30 which. under the direction of the controller 26, travels back and forth along the carriage guide rod 32. The carriage 30 carries one or more ink pens 34, each of which is provided with at least one print head 36 having at least one ink-jet 38. Actuation of the ink-jets 38 is also controlled by the controller.

Still referring to Figures 1-4, the paper feed system serves to extract sheets of print media 40, such as paper, from a storage tray 42. As the print media 40 is extracted from the storage tray 42, it is engaged between several feed rollers 44 and a paper guide 46. The feed rollers 44 are mounted to a drive axle 48 which can be rotated, again under the direction of the controller 26. to advance the print media 40 beneath the carriage. A platen 50 is positioned to support the print media 40 in the area beneath the carriage. In this manner. the controller 26 controls the movement of the carriage 30, activation of the ink-jets 38. and the advancement of the print media 40 to print desired images.

10960956 It should be appreciated that there are a variety of known ink-jet printers having various types of controllers. carriage systems and paper feed systems which operate generally as described above. Similarly, various methods of constructing and using such systems are well known to those familiar with printers and need not be described. The present invention, a preferred embodiment of which is described below, may be implemented in a wide variety of such printers.

It should also be appreciated that while the present description is presented in tenns of an ink-jet printer of a type commonly used for home or office printing. the current invention is also applicable to a wide variety of other ink-jet printing devices. such as facsimile machines. plotters, portable printing units. copiers. cameras. video printers and the like.

In accordance with a preferred method of the present invention, ink within an ink jet is inductively charged so that particles, including aerosol particles. ejected from the nozzle are charged. Inductive charging of the ink can be accomplished by placing an electrode or electrode network, sometimes referred to as a charge electrode. in proximity to the ink-jet. In addition, an electric field is created about the ink-jet nozzle. The electric field is created by locating an electrode or electrode network. sometimes referred to as a field electrode. so as to create an electric field between the nozzle and the print medium.

The electric field interacts with charged aerosol particles to reduce aerosol contamination. In particular. depending on the polarity of the aerosol particle and the polarity of the field. the aerosol particle is either attracted toward the print medium where in impacts or it is repelled back toward the print head where it can be collected. In either case. the aerosol particle is contained so that it does not float uncontrolled about the printer.

In the illustrated embodiment. a single electrode serves as both the charge electrode and the field electrode. In particular, the platen 50 serves as

10960956 an electrode. The platen 50 is particularly desirable as an electrode because of its relatively close proximity to both the print media 40 and the ink- jets 38. In addition. the platen 50 extends transversely across the printer 20 and is general.ly coextensive with the printing path of the carriage 30. Of course, other electrodes or electrode networks could also be used. For example, in different embodiments. the drive axle 48 or the carriage guide rod 32 may be suitable. Alternatively. a dedicated electrode, that is an electrode that serves no other function. could be added to the printer as a charge electrode, a field electrode or both.

To facilitate its function as an electrode. the illustrated platen 50 is made of a conductive material and is elecuically isolated from ground. In the illustrated embodiment. the platen 50 is made of a carbon filled plastic material.

Preferably, the plastic material has at least 5 percent carbon fill. In the illustrated embodiment. the plastic material has between 5 percent and 30 percent carbon fill. Those skilled in the art wW recognize that other materials rnight also be suitable. Likewise, many suitable structures can be used to electrically isolate the platen from ground. For example, nonconductive bushings or bearings can be used to mount the platen within the printer. In the illustrated embodiment. the platen 50 is mounted to the drive axle 48 so as to allow the platen to rotate between an upper position. illustrated in Figure 3, during printing operations and a lower position, Wustrated in Figure 4, at other times. To isolate the platen 50, the bearing and bushings for the drive axle 48 are made of an insulating material such as nylon or plastic. In addition, the structures for moving and supporting the platen include insulating materials.

The platen 50 is charged by connecting it with a power source 52.

In the illustrated embodiment, the power source 52 is a direct current source designed to provide high voltage and low current. Although those skilled in the art will recognize that a wide variety of power sources, including alternating current power sources. might be used. the ilIustrated power source includes a 10960956 fly-back transformer with a secondary step-up winding with an associated diode rectifier and filter. For ease of manufacture, the power source 52 in the illustrated embodiment is mounted to the printers main logic board along with the controller 26.

The magnitude of the charge applied to the platen may vary from one type of printer to another depending on the particular geometry and constraints of the printer. Moreover, the strength of the electric field may vary across the width of the printer and vary with the type of print media being used. However, in the illustrated embodiment, it is desirable to create a field at the nozzle with a magnitude having an absolute value of greater than about 10 kv/meter and preferably between about 100 kv/meter and about 2 Mv/meter.

MOSE preferably the absolute value of the field magnitude at the nozzle should be about 100 kv/meEer. In the illustrated embodiment, with a distance from the platen to the nozzles of about I millimeter, a desirable field can be created by applying a potential of about 100 volts to the platen.

As seen best in Figures 2-4, the illustrated power source 52 is connected to the platen 50 through the drive axle 48. A contact 54 on the drive axle 48 provides electrical communication from the power source 52, via a cable 56, to the drive axle. The charge is transferred to the platen 50 by reason of its physical contact with drive axle 48. It is also possible for the power supply to be electrically coupled directly to the platen. Alternatively, a contact could be positioned on the printer chassis 22 such that it makes electrical contact with the platen when the platen is in its upper position and not when the platen is in the lower position. Using this structure. the platen is charged only when it is in the upper position for printing.

Figures 5-10 are schematic illustrations representing how the current invention is believed to operate to reduce aerosol contamination. Referring to Figure 5. the ink-jet 38 has a barrier layer 58 sandwiched between a substrate and an orifice plate 62 to define a nucleation chamber 64. A resistor 66 is 10960956 provided on the substrate 60 and a nozzle 68 is formed in the orifice plate. A small quantity of ink 70 is contained within the nucleation chamber. In the illustration, the platen 50 is provided with a positive charge (indicated by the plus signs). The positive charge on the platen 50 tends to cause the negative ions (represented by minus signs) in the ink 70 to migrate toward the platen 50 and the positive ions in the ink to migrate away from the platen Upon activation of the ink-jet 38 by the controller 26, a current is applied to the resistor 66 which heats and vaporizes the adjacent ink to generate a drive bubble 72. illustrated in Figure 6. which forces a small quantity of ink out of the nucleation chamber 64 and through the nozzle 68. Upon removal of the current from the resistor 66, the drive bubble 72 collapses, as shown in Figure 7- The collapsing drive bubble 72 retracts the ink within the nucleation chamber 64 and yields an ink drop 74, shown in Figure 8. Because of the charge distribution within the ink-jet ink 70, the ink drop 74 is inductively charged. Moreover, the distribution of ions within the ink drop 74 is not urfiform. As illustrated. negative ions are concentrated at the head while positive ions are concentrated near the tail.

During the flight of the ink drop 74 toward the print medium 40, it develops -pinch points" 76 or contractions, seen in Figure 9. Surface tension causes some of these pinch points 76 to fragment the tail of the ink drop 74 into smaller fragments 78a-c as shown in Figure 10. Because of the uneven charge distribution within the drop, the smaller fragments 78a-c will be charged.

The ink drop 74 has sufficient mass and momentum to carry it to the print medium where it will impact to form a part of a printed image. However, the smaller fragments 78a-c may not have sufficient ma s. In the absence of an electric field. some of the fragments 78a-b, referred to as spray particles, would be deflected by air currents or the like before reaching the print medium and other fragments 78c, referred to as aerosol particles, may be carried away by air currents or the like and never reach the paper medium. However, the presence 10960956 1 of the electric field helps to prevent this. Because the fragments are charged they are either attracted toward the print medium or repelled from the print medium. depending on their charge. For example. fragment 78c, a charged aerosol particle. has a positive charge and would be repelled from the print medium back to the print head. The fragment 78c would likely impact on the orifice plate of the print head where it could be removed during the periodic wiping and purging procedures normally conducted to maintain the print head.

In this manner. aerosol contamination is reduced by inductively charging aerosol particles and directing them through an electric field.

It is also believed that the present system may help prevent the formation of aerosol particles. In particular. because the drop 74 has oppositely charged ends. there is an attractive force between the head of the drop and the tail of the drop. This attractive force may help to hold the drop together and prevent or reduce fragmentation. This attractive force may also cause fragments that do form to reattach to the oppositely charged drop or to follow the oppositely charged drop to the print medium.

In the system described above. the platen serves as both a charge electrode and a field electrode. In this system, an ink drop is ejected in a path directly toward the field electrode. Thus. the drop is either attracted toward the medium or repelled away from the print medium, as opposed to a lateral deflection of the ink drop. It should be understood. however. that two separate electrodes or electrode networks may be used to perform these functions. For example a charge electrode having a particular polarity could be positioned at one end of the carriage guide rod 32 so that it came into close proximity. with the ink-jets 38 each time the carriage 30 traveled to that end of the guide rod.

This would serve to inductively charge the ink within the ink-jets. A separate field electrode. such as the platen or a dedicated electrode or electrode network.

could be provided near the print medium to create the electric field. One option

10960956 offered by such a system is that the polarity of the charge electrode may be opposite to that of the field electrode.

Also. it is not necessary that the electric field exist at all times or along the entire width of the printer. Rather. the field need only exist adjacent the print head during printing operations. Thus, it may be desirable to discharge the field electrode when not printing or to activate only a portion of the field electrode adjacent the print head at any given time.

The description above is directed primarily to reducing aerosol contamination which results during printing. However, the same concepts can be employed to control aerosol created during purging operations. For example. the illustrated printer 20 is provided with a service station 80, seen in Figure 1... The carriage 30 is periodically moved to this service station 80 for maintenance procedures. such as purging. The service station 80, seen best in Figure 11. includes a spittoon for receiving ink purged from the print head 36.

During a typical purge operation. the carriage is moved so that the print head is positioned over the spittoon and ink is ejected from the print head nozzles into the spittoon. Larger ink drops and spray particles fall to the bottom of the spittoon where they are collected. However. aerosol created during purge operations may float within the spittoon or drift to other areas of the printer or -)o the environment. To control this. the illustrated spittoon is provided with a spittoon electrode 84 to divert the aerosol particles, in the same manner described above. to locations where they may be collected. The power supply and voltage for the spittoon electrode 84 can be similar to that previously described. Alternatively, those skilled in the art will recognize many appropriate variations for the power supply. This detailed description is set forth only for purposes of illustrating examples of the present invention and should not be considered to limit the scope thereof in any way. Clearly, numerous additions, substitutions. and other

10960956 modifications can be made to the invention without departing from the scope of the invention which is defined in the appended claims and equivalents thereof.

10960956 1. A system for reducing aerosol contamination in an ink-jet printer 20 comprising: an ink-jet 38 having:

a chamber 64 for storing quantity of ink 70; a nozzle 68 adjacent the chamber 64 through which a portion 74 of said quantity of ink 70 is expelled toward a print medium 40, said portion 74 of ink comprising a plurality of ink particles 78a-c including at least one aerosol particle 78c; a charge electrode having an electric potential, the charge electrode positioned to inductively charge the ink 70 within the chamber 64 such that the aerosol particle 78c has a charge induced by the charge electrode; a field electrode having an electric potential of a single polarity, the field electrode being positioned to create an electric field between the nozzle 68 is and the print medium 40, whereby the electric field interacts with the aerosol particle 78c to influence the path of the particle.

2. The system of claim 1 wherein the charge electrode is a platen 50 which supports the print medium 40 during printing.

3. The system of claim 2 wherein the field electrode is a platen

50 which supports the print medium 40 during printing.

4. A method for controlling aerosol contamination in an ink-jet printer 20 having at least one ink-jet 38 with a chamber 64 for storing ink 70 to be ejected adjacent a nozzle 68 through which ink is ejected toward a print medium 40, the method comprising the steps of inductively charging ink within the chamber 64; ejecting a quantity 14 of charged ink through the nozzle 68 toward the print medium 40, the quantity 74 of ink breaking into a plurality of charged particles 78a-c at least one of which is an aerosol particle 78c; and 10960956 46- creating an electric field of a single polarity between the nozzle 68 and the print medium 40, whereby the electric field interacts with the charged aerosol particle 78c toinfluence its path.

5. The method of claim 4 wherein the step of inductively charging the ink 70 further comprises the steps of:

placing at least one charge electrode adjacent the nozzle 68; and applying an electric potential to the at least one charge electrode.

6. The method of claim 5 wherein the at least one charge electrode includes a platen 50 upon which the print media 40 rests during printing.

7. Ite method of claim 5 wherein the at least one charge electrode includes a drive axle 48 for a paper advance system in the printer.

8. The method of claim 5 wherein the step of creating an electric field further comprises the steps of:

placing at least one field electrode adjacent the nozzle 68; and applying an electric potential of a single polarity to the at least one field electrode.

9. I'lle method of claim 8 wherein the at least one field electrode is the same as the at least one charge electrode.

10. The method of claim 9 wherein the at least one field electrode and the at least one charge electrode are a platen 50 used to support the print media 40 during printing.