EXHAUST HOOD

In one example, an exhaust hood includes an enclosure having a perimeter defining an exhaust area and a fluid flow path. The fluid flow path includes a perimeter intake slot through which air is sucked into the flow path during an exhaust operation and a flow channel in fluid communication with the perimeter intake slot and configured to carry fluid away from the intake slot and out of the enclosure.

BACKGROUND

Ink used in liquid electro-photographic (LEP) printing contains tiny pigments encapsulated in a polymer resin, forming polymer particles that are dispersed in a carrier liquid. The polymer particles are sometimes referred to as toner particles and, accordingly, LEP ink is sometimes called liquid toner. In one type of LEP printing process, an electrostatic pattern of the desired printed image is formed on a photoconductor for each color of the image. Each color is developed by applying a thin layer of LEP ink to the photoconductor. Charged polymer particles in the ink adhere to the electrostatic pattern on the photoconductor to form the desired pattern of liquid ink for that color. Each color pattern is commonly referred to as a “separation.” Each liquid ink color separation is transferred from the photoconductor to an intermediate transfer member and heated to evaporate the carrier liquid and melt the polymer particles into a smooth film. The film is transferred from the intermediate transfer member to the print substrate by direct contact.

The same part numbers refer to the same or similar parts throughout the figures. The figures are not necessarily to scale.

DESCRIPTION

In some LEP printers, the intermediate transfer member is a belt that rotates in an endless loop past a series of printing units. Each printing unit applies a liquid ink color separation to the surface of the rotating belt one after another to form a liquid ink image on the belt. The belt is heated to dry the liquid ink image to a molten film. The molten film is transferred from the belt to the print substrate at a nip between the belt and a pressure roller. Infrared lamps are commonly used to heat the intermediate transfer belt to dry the ink and to keep the molten film hot to the point of transfer.

Evaporating the carrier liquid to dry the ink generates vapors that include unwanted contaminants, sometimes referred to as “VOCs” (volatile organic compounds). To prevent the release of VOCs and to reclaim carrier liquid, the contaminated air is evacuated to a condenser where the carrier vapor is condensed back to a liquid and removed from the air. The clean air is exhausted to the environment or recirculated inside the printer. Currently in an inline LEP printer, higher suction air flows are used to evacuate the full volume of the exhaust hoods to capture carrier vapors from the comparatively large surface area of the intermediate transfer belt while preventing vapor escaping the hood to the surrounding environment. For example, a total suction air flow of more than 1,000 L/s from four inline exhaust hoods is used to capture carrier vapors from approximately 1 m2of belt surface area in a six color in-line LEP printer. A higher suction air flow means a lower concentration of vapor in the flow. Condensing carrier liquid from an air flow with a lower concentration of vapor is less efficient and therefore more costly compared to condensing carrier liquid from an air flow with a higher concentration of vapor.

A new exhaust system has been developed to enable the use of lower suction air flows to effectively evacuate carrier vapors from the surface of an intermediate transfer belt in an inline LEP printer. Examples of the new system use an exhaust hood with perimeter intake slots connected to a central suction duct. Since the area of the intake slots is much smaller than the total area covered by the hood, carrier vapor may be captured effectively at lower suction (differential pressure) and lower overall suction air flow, while still preventing vapor escaping the hood to the surrounding environment. Lower suction air flow means a higher concentration of carrier vapor in the flow. Condensing carrier liquid from an air flow with a higher concentration of vapor is more efficient and therefore less costly compared to condensing carrier liquid from an air flow with a lower concentration of vapor. Cost savings may justify the added expense of chilling the air to lower temperatures to increase the concentration of vapor in the air flow even more to condense out more VOCs and thus further lower the ppm of VOCs remaining the air discharged to the environment or recirculated in the printer. Examples of the new exhaust hood may also include one or multiple interior intake slots extending across the exhaust area between perimeter intake slots.

Examples are not limited to LEP printing but may be implemented in other printing and/or non-printing applications. The examples shown in the figures and described herein illustrate but do not limit the scope of the patent, which is defined in the Claims following this Description.

As used in this document “and/or” means one or more of the connected things; “LEP ink” means a liquid that includes polymer particles in a carrier liquid suitable for electro-photographic printing; and a “slot” means an opening with a ratio of length to width (L/W) at least 60, where length is the longer dimension of the slot and width is the shorter dimension of the slot.

FIG.1is an elevation view showing one example of an exhaust system10over a work surface12. Work surface12is giving off vapors14inFIG.1.FIG.2is a bottom plan view looking up at system10inFIG.1. Surface12is omitted fromFIG.2to more clearly show some of the features of exhaust system10. Referring toFIGS.1and2, system10includes an exhaust hood16and a fan18. Hood16includes an enclosure20with walls22defining a rectangular perimeter24surrounding an exhaust area26. Hood16also includes an intake slot28along substantially the full perimeter24of enclosure20such that intake slot28surrounds exhaust area26. “Substantially” the full perimeter of enclosure20means enough of the perimeter to suck in air along the full perimeter even though there be gaps in perimeter intake slot28. The orientation of hood16and work surface12inFIG.1is just one example. Other orientations are possible. For example, hood16could be located alongside a vertically oriented work surface12. For another example, hood16could be located under a down facing work surface12.

Hood16inFIGS.1and2also includes a discharge port30and a flow channel32between perimeter intake slot28and discharge port30. Perimeter intake slot28, channel32, and discharge port30together form a fluid flow path34through exhaust hood16. In an exhaust operation, fan18sucks air and vapor into slot28and through channel32to discharge port30, as indicated by flow arrows36. The air/vapor fluid can then be exhausted from system10, as indicated by exhaust arrow38, for example to vapor removal. In this example, flow channel32is integral to enclosure walls22. Also in this example, perimeter intake slot28is surrounded on both sides by a flange35that stiffens walls22to help maintain a uniform width along the full length of slot28.

For a rectangular perimeter24inFIGS.1and2, exhaust area26is the product of the length L and width W of perimeter24. Intake slot28covers an intake area40that is the product of the length and width of slot28. Although the ratio of intake area40to exhaust area26to achieve the desired flow characteristics will vary depending on the volume of enclosure20, the amount of vapor14, the configuration of flow path34, and the volume and the operating characteristics of fan18, testing and flow simulation show an intake area40less than 10% of exhaust area26will be adequate in many LEP printing applications to effectively evacuate enclosure20while developing a sufficient pressure difference at slot28to prevent any significant amount of vapor14from escaping enclosure20.

FIG.3is an elevation view showing another example of an exhaust system10over a work surface12. Work surface12is giving off vapors14inFIG.3.FIG.4is a bottom plan view looking up at system10inFIG.3. Surface12is omitted fromFIG.4to more clearly show some of the features of exhaust system10. Referring toFIGS.3and4, system10includes an exhaust hood16and a fan18. Hood16includes an enclosure20with walls22defining a rectangular perimeter24surrounding an exhaust area26. Hood16also includes a perimeter intake slot28along substantially the full perimeter of enclosure20such that perimeter intake slot28surrounds exhaust area26. In this example, hood16also includes crosswise interior intake slots42and a lengthwise interior intake slot44. Interior intake slots such as slots42,44inFIGS.3and4may be desirable, for example, to effectively evacuate a larger volume enclosure20and/or greater amounts of vapor14.

Hood16inFIGS.3and4also includes a discharge port30and a flow channel32between intake slots28,42,44and discharge port30. Intake slots28,42,44, channel32, and discharge port30together form a fluid flow path34through exhaust hood16. In an exhaust operation, fan18sucks air and vapor into slots28,42,44and through channel32to discharge port30, as indicated by flow arrows36. The air/vapor fluid can then be exhausted from system10, as indicated by exhaust arrow38, for example to vapor removal.

FIG.5an elevation view illustrating an inline LEP printer46implementing one example of an exhaust system10to evacuate vapors generated while drying the ink. Referring toFIG.5, printer46includes multiple LEP printing units48, an intermediate transfer belt50, and a pressure roller52. Although six printing units48are shown for six color separations, more or fewer printing units48could be used for more or fewer color separations. Belt50rotates in a loop around rollers54past printing units48and pressure roller52. Each printing unit48applies an LEP ink color separation to the rotating belt50. The color separations are gathered together on belt50as a full color ink image.

Although not shown inFIG.5, an LEP printing unit48usually includes a photoconductor, a scanning laser or other suitable photo imaging device, and a developer. The laser exposes select areas on photoconductor to light to form a charge pattern on the photoconductor corresponding to the respective color separation. The developer applies a thin layer of LEP ink to the patterned photoconductor. Ink from the developer adheres to the charge pattern on the photoconductor to develop a color separation on the photoconductor. Each liquid ink color separation is transferred from the photoconductor to intermediate transfer belt50. An idler roller56opposite each printing unit48helps keep belt50properly positioned with respect to the corresponding photoconductor.

The color separations on belt50are dried to a molten film by a series of dryers58. The pressure roller52presses a paper or other printable substrate59against the rotating belt50to transfer the molten film from the belt to the substrate59. In the example shown inFIG.5, each dryer58includes two IR lamps or other suitable heaters60, an air knife62, and an exhaust hood16to contain and evacuate vapors produced while drying the ink on belt50. Each hood16includes an enclosure20with a perimeter intake slot28along substantially the full perimeter of enclosure20and crosswise interior intake slots42. Each hood16also includes a discharge port30and a flow channel32between intake slots28,42and discharge port30. Exhaust hoods16are part of an exhaust system10that includes a condenser64and a fan18. (Belt50is the work surface12for exhaust system10.) In operation, fan18sucks air and vapor into slots28,42, along channel32to discharge port30and through condenser64where the vapor is removed from the air and the condensate recycled or discarded. The clean air is recirculated inside the printer or discharged to the environment.

Printer46inFIG.5also includes a controller86with the programming, processing and associated memory resources, and the other electronic circuitry and components to control fan18. In the example shown inFIG.5, controller86includes a processor88and a computer readable medium90with control instructions92operatively connected to processor88. Control instructions92represent programming that, when executed, controls fan18to generate the desired flow characteristics for exhaust system10in printer46. For example, as described in more detail below, controller86executing instructions92controls fan18to generate a pressure difference of 1.0-3.0 Pa at intake slots28,42with a suction flow of 25-100 L/s per square meter (L/s/m2) of the exhaust area. Controller86inFIG.5may be implemented as a discrete controller dedicated to fan18, or some or all of the components of controller86may be part of a system, print engine and/or printer controller.

FIGS.6-11illustrate an example exhaust hood16such as might be used in a printer46shown inFIG.5.FIGS.6and7are bottom isometric views of hood16. Hood16is partially exploded inFIG.7.FIGS.8and9are top isometric views of hood16. Hood16is partially exploded inFIG.9.FIG.10is a top plan view of the interior of hood16showing one example for the layout of the flow channel conduits.FIG.11is a bottom plan view of hood16. The flow channel conduits are omitted inFIGS.6-9and11for clarity to not obscure other features of hood16. Not all part numbers are repeated for all parts in all ofFIGS.6-11.

Referring first toFIGS.6-9, exhaust hood16includes an enclosure20with a base66and a cover68. The outer walls22of enclosure base66define a rectangular perimeter surrounding the exhaust area. Perimeter intake slots28are formed along substantially the full perimeter of enclosure base66. Crosswise interior intake slots42are formed along the interior walls70of enclosure base66. Referring now also toFIGS.10and11, the air flow path34through hood16includes an intake port72connected to each intake slot28,42, a conduit74connected to each intake port72, and a central manifold76near the top of the enclosure to collect the flows from conduits74into a single flow at discharge port30. Conduits74are shown inFIG.10. Each intake port72and corresponding conduit74inFIG.10along with manifold76forms a flow channel32between a respective intake slot28,42and discharge port30.

In this example, each intake port72is implemented as a tapered duct integral to a respective wall22,70of enclosure base66. Thus the walls22,70form a suction frame supporting a cover68to contain the vapors while they are sucked out through the frame. Each intake slot28,42forms an inlet to the larger, upstream part78of a corresponding intake port72. Flanges35may be formed along each intake slot28,42to strengthen walls22,70and guide air into slots28,42. As shown inFIG.10, each conduit74is connected between an outlet80from the smaller, downstream part82of a corresponding intake port72and an inlet84on manifold76. In this example, each intake slot28is integral to an intake port72and each intake port72is integral to a section of wall22,42in a module that provides both structure for enclosure base66and a flow path for the exhausted air. A modular configuration such as that shown inFIGS.6-11may be desirable, for example, to standardize manufacturing and to more easily adapt an exhaust hood16to different size exhaust areas.

In the example shown inFIG.10, each conduit74is implemented as flexible hose for easier routing, for example around and over heat lamps60and air knives62shown inFIG.5. A two part enclosure20with a separate cover68that can be removed provides easier access to interior parts including, for example, heat lamps60and air knives62shown inFIG.5. In may be desirable in some implementations to make all conduits74the same length for a consistent flow from all intake slots28,42. In may be desirable in other implementations to vary the length of conduits74, for example shorter conduits74from perimeter intake slots28for a higher flow at the perimeter to help seal against vapor leaking around the hood, without increasing the flow at discharge port30. Testing and flow simulations indicate tapered intake ports72, in which the intake flow at each slot28,42is funneled toward an outlet80through a narrowing flow channel, promotes uniform flow in a compact space.

Testing and flow simulations also show that, even with comparatively low flows at discharge port30, a sufficient pressure difference can be generated at perimeter intake slots28to seal the perimeter against any significant vapor escaping hood16while still evacuating substantially all of the vapor from the exhaust area. For example, a total flow of 46-54 L/s at discharge ports30(e.g., 11-14 L/s at each of four ports30inFIG.5) with 4 mm wide intake slots28,42covering about 5.5% of the exhaust area that, together with flow channels32, generate an intake pressure difference of about 1.8 Pa, will be sufficient to exhaust 120-150 L/s of vapors from a total exhaust area of about 1 m2. Due to the lower discharge air flow, e.g. 46-54 L/s/m2compared to more than 1,000 L/s/m2for conventional exhaust hoods, it is easily possible to cool the discharge air to a very low temperature (e.g. −20° C.) to dramatically increase the volume of vapor removed from the discharge air at condenser64and thus reduce the concentration of vapor remaining in the air leaving the condenser, for example from 1.5 g/m3entering the condenser to 0.2 g/m3leaving the condenser, well below the current regulatory threshold. While the configuration and flow parameters for an exhaust system10will vary depending on the particular application, it is expected that, for a typical inline LEP printer, an acceptable level of vapor exhaust can be achieved with a suction flow of 25-100 L/s per square meter (L/s/m2) of exhaust area and a pressure difference of 1.0-3.0 Pa at the intake slots, and with a total intake area less than 10% of the total exhaust area.

As noted above, the examples shown in the figures and described herein illustrate but do not limit the scope of the patent, which is defined in the following Claims.

“A” and “an” in the Claims means one or more. For example, an intake slot means one or more intake slots and subsequent reference to the intake slot means the one or more intake slots.