Patent Application
20240239101
The disclosure of Japanese Patent Application serial No. 2021-163210, filed on Oct. 4, 2021, including the specification, drawings and abstract is incorporated herein by reference. The Japanese Patent Application serial No. 2021-163210 was published on Jan. 14, 2022, and is not prior art to the present application under 35 U.S.C. 102(b)(1)(a).
The present invention relates to a continuous inkjet printer, and more specifically to preventing dirtying of a printhead caused by ink rebounding off a printing surface.
Continuous inkjet printers have a configuration in which ink is ejected from a nozzle by a pump, ink droplets are electrically charged by a charging electrode at a position at which the ejected ink separates into such ink droplets, and furthermore the path of the ink droplets is deflected by deflection electrodes so that the ink droplets collide with a printing object at predetermined positions thereon to form ink dots.
In continuous inkjet printers, due to the nature of ejecting ink to print, constituent members of a printhead become dirtied with ink, and thus measures are taken according to the cause of the dirtying.
The first cause of dirtying is ink mist generated by ejected ink, and, in order to mitigate dirtying caused by ink mist, a printhead is covered with a head cover and positive pressure is maintained inside the cover (see JP 2018-83369A).
Specifically, a pressurizing means is used to maintain positive pressure inside the head cover such that ink mist floating around the constituent members of the printhead is discharged through an ink droplet passage slit. Thus, ink mist is kept from attaching to the constituent members and as incidental effects, foreign matter such as dust is prevented from entering the cover from the outside, and the formation of condensation inside the cover is also prevented.
The second cause of dirtying is minute ink particles formed due to ink droplets rebounding upon collision with a printing object.
Ink droplets flying from the printhead have kinetic energy and break apart under this kinetic energy upon collision with a printing object, and the thus ruptured ink particles rebound off and scatter around the printing surface. Some minute scattered ink particles enter the cover through a slit in the leading end of the head cover.
Ink particles that have entered the head cover via the slit attach to the surfaces of deflection electrodes and the like that constitute the printhead, and accumulate into solids. Also, conductive ink is used in continuous inkjet printers, and the main body of the head cover is made of metal. Accordingly, if ink is left to accumulate, in addition to the surfaces of electrodes and the like becoming dirty, the accumulated ink and the metal constituent members of the head included in the cover short-circuit, thus causing a malfunction.
In particular, a high DC voltage is applied to the deflection electrodes in order to deflect ink droplets, and thus leaving ink to accumulate may lead to a major incident.
Increasing the positive pressure in the cover to increase the flow amount of air blown out from the slit is conceivable as a method for preventing ink particles from entering through the slit, but changes in the flight direction of the ink droplets caused by the air leads to reduced printing quality, and thus the pressure cannot be simply raised.
As another method for preventing ink particles from entering through the slit, blowing air in a direction intersecting the flight direction of the ink droplets has been proposed (see JP 2014-100876A).
However, in the method disclosed in Patent Document 2, similarly to the method of increasing the pressure in the cover, when the blown air is strong, the flight direction of the ink droplets is deflected and the printing quality is reduced. Thus, there is a limit to the strength at which the air can be blown, and the entry of ink particles through the slit cannot be sufficiently suppressed.
Furthermore, blown ink particles attach to and dirty the surface of a conveyer for transferring printing objects, and thus a new issue arises where the conveyer needs to be cleaned each time printing is performed.
The present invention was made in view of the aforementioned conventional problems, and it is an object thereof to provide an inkjet printer that keeps dirtying of constituent members of the printhead and a transfer conveyer to a minimum without affecting printing quality.
In order to achieve the above-described object, the inkjet printer according to the present invention includes: a printhead including: a gun configured to generate continuous ink droplets by applying vibration having a constant period to ejected ink; a charging electrode configured to electrically charge the ink droplets by applying a stepped-wave voltage to the ink droplets in synchronization with the period of the ink droplets; a deflection electrode configured to deflect the electrically charged ink droplets in a vertical direction or a horizontal direction according to the amount of charge, and cause the ink droplets to land on a printing surface of a printing object; and a tubular head cover that houses the gun, the charging electrode, and the deflection electrode in a cavity portion, and that is provided with a slit through which the electrically charged ink droplets pass, the inkjet printer forming a character using rows of printed dots by causing the ink droplets ejected from the printhead to land on the printing object moving in the horizontal direction or the vertical direction, wherein the head cover is constituted by a tubular cover body having a rear end portion that is sealed, and a cap that is attached so as to cover a front portion of the cover body, the cap is provided with the slit and a blowing outlet that surrounds at least a portion of the slit, and air is blown out from the blowing outlet toward the printing object.
In the inkjet printer according to the present invention, the air blowing outlet is provided so as to surround at least a portion of the slit in the head cover, air is blown from the blowing outlet toward the printing object, and the entry of minute ink particles, which have rebounded off a printing object, into the cover via the slit is kept to a minimum.
Also, the air blowing outlet is formed independent of the slit, and the direction in which air is blown is substantially parallel to the flight direction of ink droplets, and thus the printing quality is unaffected.
Furthermore, minute ink particles that have been stopped from scattering by the blown air disperse in air, and the amount of ink that attaches to the surface of a transfer conveyer is largely reduced, and thus the number of times the conveyer needs to be cleaned can be reduced.
These and other objects, features and advantages of the present invention will become more apparent upon reading of the following detailed description along with the accompanied drawings.
Hereinafter, an inkjet printer according to an embodiment of the present invention will be described with reference to the drawings.
The constituent members of the printer 10 according to the present embodiment are largely classified into members related to supplying ink to the printhead 10 and performing printing (hereinafter, these constituent members are referred to as an “ink supply system”), and members related to supplying air for pressurization and dirt prevention to the printhead 10 (hereinafter, these constituent members are referred to as an “air supply system”). First, the ink supply system constituent members will be described.
As shown in
Members such as the gun 12 constituting the printhead 10 are actually disposed close together in a cavity portion 110 of the head cover 11, but
The gun 12 is configured to eject ink droplets ID toward a side surface of a printing object such as a decorative box 40 containing a product (see
The column of ink IP ejected from the hole of the nozzle 123 separates into ink droplets ID due to the vibration applied by the ultrasonic transducer 122, and the ink droplets ID are further electrically charged by the charging electrodes 13, and then only the ink droplets ID that are needed for printing are deflected by the deflection electrodes 15 according to their amount of charge, and pass through a slit 114 formed in the front portion of the head cover 11 to land on the printing surface of the printing object.
The decorative box 40 is a box whose surface is coated with a polyethylene or polypropylene film, and, after a food item or the like has been packed therein, takes shape as a final product when a production number, an expiration date, or the like is printed on the film.
When, as shown in
On the other hand, ink droplets ID that have not been electrically charged, and ink droplets ID that have been electrically charged but are not to be used for printing are not deflected, and fly into the gutter 16 for ink recovery so as to be collected in the ink tank 20. The ink collected in the gutter 16 is transferred to the ink tank 20 through the pipe 17b by the pump 30b, and is reused.
The operations of the printer 10 are controlled by a controller (not shown). The controller is constituted by a CPU, a memory (ROM, RAM, etc.), a timer, and a display, and controls the operations of the ultrasonic transducer 122 of the gun 12, a pulsation power supply 131 of the charging electrodes 13, the detection electrode 14, a DC power supply 151 of the deflection electrodes 15, and the pumps 30a and 30b.
Specifically, the controller drives the pump 30a to apply pressure to the ink stored in the ink tank 20 and supply the pressurized ink to the gun body 121. Also, the controller controls the timing at which a pulse voltage is applied to the charging electrodes 13 from the pulsation power supply 131, based on a signal detected by the detection electrode 14, so as to adjust the number of ink droplets ID to be electrically charged and the timing at which they are electrically charged. Furthermore, the controller controls the voltage of the DC power supply 151 so as to adjust the deflection amount of ink droplets ID to be deflected by the deflection electrodes 15.
Next, the air supply system of the printer 10 will be described with reference to the aforementioned
In the present invention, two functions are realized using air compressed by a compressor. Specifically, continuous printers realize the standard equipped functions of maintaining positive pressure in the head cover, and blowing air against ink particles that have rebounded off a printing surface to prevent ink particles from passing through a slit and entering the head cover.
Though not shown, first, a drain catch is used to remove excess moisture from air supplied from the compressor and through tubes, and oil mist is further removed by a mist separator.
Then, the air is split into two streams, namely, air AR 1 that has passed through a first tube is supplied to the cavity portion 110 of the head cover 11, and air AR 2 that branches into the second tube is supplied to an air blowing outlet 115 provided in the cap 112.
The functions of both air AR1 and AR2 will be described along with the configuration of the head cover 11. As shown in
The cover body 111 is made of metal in order to increase resistance to external noise, while the cap 112 is made of a resin in consideration of ease of molding.
First, the function of the first air AR1 will be described. A regulator (not shown) is attached at an intermediate position of first tube mentioned above to reduce the pressure of air compressed by the compressor to a suitable value, and the air AR1 whose pressure has been adjusted by the regulator is supplied to the head cover 11.
As shown in
In continuous printers, a portion of the ink ejected from the nozzle 123 floats as ink mist in the surrounding atmosphere, and attaches to and dirties the surfaces of the constituent members where it causes malfunctions, and thus members in the head cover 11 need to be cleaned regularly. Also, dust passes through the gutter and enters the ink circulation system where it causes malfunctions by clogging pipes and the like.
Thus, by housing the main members of the printhead 10 in the head cover 11, and maintaining positive pressure inside the head cover 11, the discharging of ink mist to the outside is promoted, and dust from the outside is prevented from entering the head cover 11. With such measures, the cycle at which the constituent members are to be cleaned can be delayed, and clogging of pipes and the like by dust can be avoided.
Next, the function of the second air AR2 that passes through the second tube and is supplied to the cap 112 of the head cover 11 will be described. The upper portion of a bottomed cylindrical cap 112 is provided with a thick portion 113, and the thick portion 113 is provided with the slit 114 through which ink droplets are ejected, and the blowing outlet 115 for blowing the air AR2 toward the printing object.
As shown in
As shown in
Note that, as shown in
When attaching the cap 112 to the cover body 111, the locking pieces 118 of the cap 112 are inserted into the front portion of the cover body 111, and then the locking pieces 118 are engaged with the locking holes 119, thus integrating the cover body 111 and the cap 112 into one piece.
As shown with solid arrows in
The blowing outlet 115 for the air AR2 is formed independent of the slit 114, and the direction in which the air AR2 is blown is substantially parallel to the flight direction of the ink droplets ID, and thus hardly any blown air meets the ink droplets ID that have passed through the slit and are flying toward the printing object. Accordingly, the flight path of the ink droplets ID is not deflected by the air AR2 and the printing quality is not degraded.
On the other hand, ink particles that have rebounded off the printing object are repelled by the air AR2 blown from the blowing outlet 115, and thus the amount of ink particles entering the head cover 11 via the slit 114 is suppressed.
As a result, dirtying of the constituent members of the printhead 10 by ink can be kept to a minimum. Furthermore, it is possible to avoid a situation where ink solids accumulate on the surfaces of electrodes and the like, and a short circuit occurs between the accumulated ink and the metal constituent members of the head that includes the cover, thus causing a malfunction in the printer.
Also, as a supplementary effect of the air AR2, drying of ink is promoted by blowing air onto the ink that has landed on the printing surface, and smudging and transfer of the ink can be prevented.
Note that, if the pressure of the air AR2 blown out from the blowing outlet 115 is excessively high, the excessive pressure affects the flight of ink droplets passing through the slit 114 and degrades the printing quality. Conversely, if the pressure of the air AR2 is low, more ink particles enter the head cover 11. Accordingly, the pressure of the air AR2 needs to be set through experimentation so as to not affect the flight of ink droplets and so as to be able to keep ink particles from entering the head cover 11.
In experiments, a cap provided with a slit with a center distance of 9 mm and a width of 2.6 mm was used in a conventional printhead. Also, a cap in which a blowing outlet with a width of 1 mm surrounded the aforementioned slit was used in the printhead according to the present invention. Also, the air AR1 was supplied to the conventional printhead, and air AR1 and AR2 were supplied to the printhead according to the present invention, and the pressure of the air was adjusted so that a slight amount of air was blown from the slits and so that air blown from the blowing outlet did not affect the flight of ink droplets.
As shown in
Conversely, as shown in
In
Embodiment 1 are given the same reference symbol. Also, the letter A is added to each reference symbol so as to distinguish it from the cap 112 of Embodiment 1.
As shown in
The cap 112 is often produced using injection molding, but if the channel 117 linking the port 116 and the blowing outlet 115 is complex, the manufacturing cost of the mold increases.
Conversely, in the cap 112A according to the present embodiment, as shown in
Air blown by the blowing outlet 115A according the present embodiment onto a printing surface has more bias in comparison to the blowing port 115 of Embodiment 1. However, it was found through experiments that the effect of preventing the attachment of ink using air blown out from the blowing port 115A is almost the same if the port 116A is formed such that air blown out from the blowing outlet 115A moves somewhat toward the center of the cylinder.
Thus, according to the specifications required of the printhead 10, a configuration may be employed in which an arc-shaped blowing outlet 115A and the channel 117A with a simple shape as illustrated in Embodiment 2 are formed instead of the blowing outlet 115 shaped so as to surround the slit 114 and the channel 117 with a complex shape as illustrated in Embodiment 1.
Note that, in the aforementioned embodiments, a cylindrical head cover was used as the head cover of the printhead, and main members were housed in the cavity portion of the head cover, but the head cover is not limited to being cylindrical. A head cover with a quadrangle or hexagonal cross section may be used so as to match the shape and arrangement of the constituent members.
Although a case in which printing is performed on a printing object moving in a horizontal direction is described in the embodiments described above, the movement direction of the printing object is not limited thereto, and even if, for example, the printing object moves in a vertical direction, a function for preventing dirtying of the printhead by ink that has rebounded off a printing surface can be implemented. In this case, ink droplets are deflected in the horizontal direction.
Herein after, preffered examples of the embodiment of the present invention will be collectively described.
Here, the cap is preferably provided with a port to which an air supply tube is connectable, and an air channel that links the port and the blowing outlet.
The cover body is preferably made of metal.
The blowing outlet is preferably formed so as to surround an end of the slit that is closer to an outer circumferential portion of the cap.
Furthermore, air is preferably supplied from an external compressor to the cavity portion of the head cover, and positive pressure is preferably maintained in the cavity portion while the printhead is driven.
Although the present invention has been fully described by way of example with reference to the accompanied drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art.
Therefore, unless otherwise such changes and modification from the scope of the present invention hereinafter defined, they should be construed as being included therein.
