Patent Application
20100225715
Printing systems may use liquid inks which are stored in ink tanks. These liquid inks are pumped from the ink tanks through the printing system during the printing process. In some cases it may be desirable to change the color or type of inks used by the printing system. For example, a new print run may require the replacement of a particular ink with a specialized spot color ink to achieve a desired metallic, fluorescent, or tint effect. Ideally, the entire printing system would be cleaned to remove residuals of the first ink to avoid cross contamination of the replacement ink. The process of changing inks may be a manual and lengthy process which requires the operator to remove the ink tank, drain the current ink from the ink tank, clean the ink tank, purge the supply lines and printing apparatus to remove residuals of the first ink from the system, and then refill the ink tank with the replacement ink. To facilitate the flexibility and ease of changing inks within a printing system, it is desirable to automate the ink color change process.
Additionally, it may be desirable to periodically clean the printing system even if the colors of the ink remain the same. These maintenance cleanings can improve the printing performance of the system, extend the lifetime of various components, and improve the efficiency of the printing system. Manual maintenance cleanings can take a significant amount of time and training to perform. During this time period, the printing system is typically idle. By automating these maintenance cleanings, the cleanings could be performed more quickly, accurately, and with less training.
The accompanying drawings illustrate various embodiments of the principles described herein and are a part of the specification. The illustrated embodiments are merely examples and do not limit the scope of the claims.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.
Digital printing refers to a printing process in which a printed image is created directly from digital data. In contrast to typical printing processes, the words, pages, text and images are created with electronic layout and/or desktop publishing programs and printed by the digital printer without any intermediate steps. In a non-digital printing process, these intermediate steps restrict the flexibility and speed at which new printing jobs can be started. For example, these intermediate steps may include film processing, imagesetters, plates, photochemicals, plate mounting, and registration. Because digital printers do not require any manual configuration between print jobs, digital printers are capable of printing different images on each sheet of substrate and rapid reconfiguration. This versatility makes digital printers well suited to shorter print runs and specialized printing tasks.
However, in some cases it may be desirable to change the color or type of a source ink used by the printer. For example, a new print run may require the replacement of a particular ink with a specialized spot color ink to achieve a desired metallic, fluorescent, or tint effect. The process of changing inks is primarily a manual process which requires the operator to remove the ink tank, drain the current ink from the tank, clean the tank, purge the supply lines and printing apparatus to remove ink from the system, and then refill the tank with the new ink. To facilitate the flexibility and ease of changing inks within a printing system, it is desirable to automate the ink color change process.
Additionally, it may be desirable to periodically clean the printing system even if the colors of the ink remain the same. These maintenance cleanings can improve the printing performance of the system, extend the lifetime of various components, and improve the efficiency of the printing system. Manual maintenance cleanings can take a significant amount of time and training to perform. During this time period, the printing system is typically idle. By automating these maintenance cleanings, the cleanings could be performed more quickly, accurately, and with less training.
In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present systems and methods. It will be apparent, however, to one skilled in the art that the present apparatus, systems and methods may be practiced without these specific details. Reference in the specification to “an embodiment,” “an example” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least that one embodiment, but not necessarily in other embodiments. The various instances of the phrase “in one embodiment” or similar phrases in various places in the specification are not necessarily all referring to the same embodiment.
The term “electrostatically printing” refers to a process of printing whereby a colorant or other material is arranged into a pattern or a layer by an electric field. This can occur by passing a colorant or other material through an electric field onto an electrostatic surface. One example of electrostatic printing is the LEP process.
The term “liquid electro printing” (LEP) refers to a process of printing in which ink is printed through an electric field onto a surface to form an electrostatic pattern. In most LEP processes, this pattern is then transferred to at least one intermediate surface, and then to a substrate. The term “liquid electro printer” refers to a printer capable of LEP.
According to one illustrative embodiment, an image is formed on the photo imaging cylinder (105) by rotating a clean, bare segment of the photo imaging cylinder (105) under the photo charging unit (110). A uniform static charge is deposited on the photo imaging cylinder (105) by a corona wire. As the photo imaging cylinder (105) continues to rotate, it passes through the laser imaging portion of the photo charging unit (110). A number of diode lasers dissipate the static charges in portions of the image area to leave an invisible electrostatic charge pattern that replicates the image to be printed.
A number of ink tanks (160) contain inks which are supplied to corresponding Binary Ink Developer (BID) units (115). There is one BID unit (115) for each ink color. According to one illustrative embodiment, the ink is supplied in concentrated form in an ink can (155). Concentrated ink paste is dispensed from the ink can (155) into the ink tank (160). In the ink tank (160), the concentrated paste is mixed with imaging oil to form the ink. The characteristics of the ink in the ink tank (160) are carefully controlled to maintain the printing quality of the system. For example, the ink tank (160) may contain a number of sensors which detect the temperature, density, amount, and flow rate of the ink. If any of these parameters drift out of a set range, appropriate correction is taken. For example, if the temperature of the ink is too high, coolant may be circulated through a heat exchanger in the ink tank to cool the ink. If the density of the ink is too low, more ink solids may be added from the ink can (155). A pump inside the ink tank (160) provides the associated BID (115) with the desired amount of ink through a tube (150). The excess ink from the BID is returned to the ink tank (160) through a separate return line. This excess ink is reconditioned in the ink tank (160) and recirculated to the BID (115).
During printing, the appropriate BID unit is engaged with the photo imaging cylinder (105). The engaged BID unit presents an inking roller which has a uniform film of ink to the photo imaging cylinder (105). The ink contains electrically charged pigment particles which are attracted to the opposing electrical fields on the image areas of the photo imaging cylinder (105). The ink is repelled from the non-image areas. The photo imaging cylinder (105) now has a single color ink image on its surface. According to illustrative embodiment, the photo imaging cylinder (105) continues to rotate and transfers the ink image to a blanket cylinder (120). The process of transferring the ink image from its origin on the photo imaging cylinder is called “offset printing.” The offset printing method has several advantages. First, the offset process protects the photo imaging cylinder from wear which would occur if the substrate was to directly contact the photo imaging cylinder. Second, the blanket cylinder (120) is covered with a renewable rubber blanket. This rubber blanket compensates for unevenness of the substrate surface and deposits ink uniformly into the bottom of any depressions or grain. Consequently, the illustrative digital LEP system can print on a very wide range of substrate surfaces, textures, and thicknesses.
The substrate (140) enters the printing system (100) from the right, passes over a feed tray (125), and is wrapped onto the impression cylinder (130). As the substrate (140) contacts the blanket cylinder (120), the single color ink image is transferred to the substrate (140).
The photo imaging cylinder (105) continues to rotate and brings the portion of the cylinder surface which previously held the ink image into a cleaning station (135). The cleaning station (135) serves multiple purposes, including cleaning any stray particulates or fluids from the photo imaging cylinder (105) and cooling the outer surface of the photo imaging cylinder (105). The creation, transfer, and cleaning of the photo imaging cylinder (105) is a continuous process, with hundreds of images being created and transferred per minute.
To form a single color image (such as a black and white image), one pass of the substrate between the impression cylinder (130) and blanket cylinder (120) completes transfer of the image. For a multiple color image, the substrate is retained on the impression cylinder and makes multiple contacts with the blanket cylinder (120). At each contact, an additional color is placed on the substrate. For example, to generate a four color image, the photo charging unit (110) forms a second pattern on the photo imaging cylinder (105) which receives the second ink color from a second binary ink developer. As described above, this second ink pattern is transferred to the blanket cylinder (120) and impressed onto the substrate as it continues to rotate with the impression cylinder (130). This continues until the desired image is formed on the substrate. Following the complete formation of the desired image on the substrate (140), the substrate (140) can exit the machine or be duplexed to create second image on the opposite surface of the substrate (140).
As shown in
The advantages of the illustrative digital offset LEP system described above include consistent dot gain, optical densities, and colors. Because the printing system is digital, the operator can change the image being printed at any time and without any reconfiguration. Further, the printing system produces uniform image gloss, a broad range of ink colors, compatibility with a wide variety of substrate types, and instantaneous image drying.
The color A ink paste (242) enters the ink tank (160), where it is mixed with imaging oil (270). The imaging oil (270) serves as a fluid carrier for the ink particles and is supplied as needed from an imaging oil reservoir (265) by an oil pump (245).
As discussed above, the ink tank (160) contains a number of sensors and conditioning devices. For example, the ink tank (160) may contain a temperature sensor, heating coil, and a cooling coil. To be effective, many of these sensors and conditioning devices must be in direct contact with the ink in the ink tank (160). Consequently, the ink coats the surfaces of the sensors and conditioning devices.
During a printing run, the in-tank pump (260) provides conditioned color A ink (255) to the BID (115) at a pressure and flow rate within acceptable ranges through a feed line (205). The feed line passes through a feed valve (220) and connects to the BID (115). The BID (115) presents a uniform film of color A ink to the photo imaging cylinder (105,
A number of additional components can be present within the system to facilitate the automatic cleaning within the system. These components include the feed valve (220) which can be used to divert the output of the in-tank pump (260) into a recycle tank (230). A three way valve (210) can be used to divert the returning ink flow through a filter (235) and out of a sprayer (250).
The in-tank pump (260) continues to operate until all the accessible color A ink (255) is pumped into the recycle tank (230). However, color A ink (255) is still present throughout the ink tank (160), on surfaces of components within the ink tank (160), within the in-tank pump (260), and in the feed line (205,
According to one illustrative embodiment, a large volume of clean imaging oil (270) is not required for the washing process. For example, if the capacity of the ink tank (160) is four liters, only about one liter of clean imaging oil (270) is pumped into the ink tank (160).
The filter (235) removes the color A ink particles from the return flow and allows the imaging oil (270) to pass into the ink tank (160) through a sprayer (250). The filter (235) may use a variety of mechanisms to separate undesirable particulates or fluids from the imaging oil (270). By way of example and not limitation, the filter (235) may use filter media with pore sizes which trap the majority of the particulates but allow the imaging oil to pass through. Filter media may be fibrous media, ceramic media, or a bed of granular material. The filter may require periodic replacement or cleaning to open pores blocked by particulates. Additionally or alternatively, the filter may include a permanent magnet which attracts ferrous particulates which may be generated during the operation of the equipment.
The sprayer (250) is configured to distribute imaging oil throughout the interior of the ink tank (160) to wash color A particulates off of the various surfaces. According to one illustrative embodiment, a single sprayer is configured to distribute imaging oil throughout the ink tank (160). For example, the sprayer (250) may have nozzles which direct the imaging oil in all directions within the ink tank. Additionally or alternatively, the sprayer (250) may move to further distribute the streams of imaging oil throughout the tank (160). In one illustrative embodiment, the sprayer has relatively few nozzles, but rotates about its axis to direct relatively high velocity streams of imaging oil throughout 360 degrees.
In some embodiments, multiple fixed sprayers may be used. For example, a first fixed sprayer may be located in one of the upper corners of the ink tank (160) and a second fixed sprayer may be located in a second upper corner of the ink tank (160). In this configuration, each object within the ink tank (160) may receive stream of imaging oil from two separate directions.
A variety of additional components may be incorporated into the system to achieve the desired purging and cleaning action. For example, an additional pump may be included between the filter (235) and the sprayer (250) to provide higher pressure washing action by the sprayer (250). An agitator may be included to circulate the imaging oil (270) within the bottom of the ink tank (160). A number of sensors may be included to monitor the cleaning process. For example, an optical sensor could be incorporated to monitor the amount of suspended solids in the imaging oil or to measure surface contamination.
The operation of the system as shown in
At this point, the entire path through which color A ink flows has been cleaned. If a maintenance cleaning is being performed and the color of the ink is not being changed, the color A ink which has been pumped into the recycle tank (230,
Those of skill in the art will recognize that the examples described above have been presented only to illustrations and that many modifications and variations are possible in light of the above teaching.
By incorporating all necessary washing components within the ink tank (925), no modification to the printing apparatus (905) is required to implement automatic cleanings. Rather, the replacement of an ink tank is all that is required to implement automatic color changes. This may be particularly advantageous in systems where the process colors are rarely, if ever, changed. However, the spot colors may be much more frequently changed. The ink tanks which supply the spot colors could be replaced with ink tanks which incorporate the in-tank washing system (900), thereby providing automatic ink color changes for the most frequently changed colors.
The automatic cleaning process described above provides for an enclosed and automatic purge of a first color for maintenance cleanings or in preparation for the use of a second color within the printing system. This reduces the manual intervention by an operator. This can reduce the exposure of the operator to printing and cleaning chemicals, reduce the need for washing facilities and storage of washing fluids in the printing area, and shorten the time required to make an ink change. By automating the process, variability in color changing process can be reduced when compared to manual washing procedures. The operator training can be simplified because the operator only monitors the color change process rather than performing all of the steps manually. In some illustrative embodiments, manual intervention could be performed. For example, the fluid switches and pump operation could be manually performed if desired.
Further, the amount of volatile organic compounds released during the process is reduced because the color change process may be enclosed. No storage, manual open air handling, or disposing of additional carrier liquids is required. The ease of performing color changes facilitates the use of the on-site mixture of spot colors, thereby increasing variety and quality of prints produced.
The purging and washing process can remove virtually all of the free flowing ink solids and liquids from the ink tank and connected systems. Additionally, sludge residues can be removed from internal tank parts, including the walls, cover, electronics, pump, and tubing. This cleaning can increase the lifetime of the components and result in a reduced need for maintenance. For example, by removing sludge residues from the BID, overflows and other malfunctions can be minimized. Further, by cleaning and recycling the imaging oil, the system waste is reduced.
In some embodiments, the printing process may continue while the automatic cleaning process is ongoing. For example, if a first spot color is being switched for a second spot color, the process colors may be unaffected and can still be used. In this illustrative embodiment, the automatic cleaning of the spot color does not disrupt the operation of the printing system or delivery of process colors.
In sum, the automatic color changing system provides for more efficient changes between ink colors. Operator safety is improved and the need for operator training is reduced. Cross contamination between inks is reduced or eliminated, resulting in improved print quality. Additionally, normal printing operation can continue while the color changing process is being performed.
The preceding description has been presented only to illustrate and describe embodiments and examples of the principles described. This description is not intended to be exhaustive or to limit these principles to any precise form disclosed. Many modifications and variations are possible in light of the above teaching.
