Patent Publication Number: US-11022913-B2

Title: Carrier evaporators for liquid electrophotography printing

Description:
BACKGROUND 
     Liquid Electrophotography Printing (LEP) is a printing method in which a suspension of a printing dye and a carrier liquid is transferred or printed on to an intermediate print target, sometimes referred to as a blanket. Thereafter, the carrier liquid is evaporated such that the printing dye, substantially free of the carrier liquid, is transferred to the print target. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing will be apparent from the following more particular description of the examples provided herein, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the examples provided herein: 
         FIG. 1  is an illustrative example of a Liquid Electrophotography Printing (LEP) system, according to some of the examples presented herein; 
         FIG. 2  is a graphical example of an amount of vapour evaporation vs temperature of the air flow used in evaporating the carrier liquid Isopar L, according to some of the examples presented herein; 
         FIG. 3  is a graphical example of an amount of vapour evaporation vs an amount of heat applied to the hot air flow used in evaporating the carrier liquid Isopar L, according to some of the examples presented herein; 
         FIG. 4  is a hardware example of a carrier evaporator, according to some of the examples presented herein; 
         FIG. 5  is an example of a filter in the form of a vain demister; 
         FIG. 6  is an example of a filter in the form of an electrostatic demister, according to some of the example presented herein; 
         FIG. 7  is a further hardware example of the carrier evaporator, according to some of the examples presented herein; and 
         FIG. 8  is a flow diagram illustrating example operations which may be taken by the carrier evaporator, according to some of the examples presented herein. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for the purposes of explanation and not limitation, specific details are set forth, such as particular components, elements, techniques, etc. in order to provide a thorough understanding of the examples provided herein. However, the examples may be practiced in other manners that depart from these specific details. In other instances, detailed descriptions of well-known methods and elements are omitted so as not to obscure the description of the examples provided herein. 
     Example aspects presented herein are directed towards effective and efficient means of evaporating a liquid carrier in a Liquid Electrophotography Printing (LEP) system. Specifically, some aspects described herein make use of increased temperatures during evaporation. The use of a hot air flow allows for a lesser amount of air at, for example, a lower flow rate in the evaporation process thereby utilizing less energy in maintaining the temperature for absorbing the evaporated carrier. 
       FIG. 1  illustrates an example of a LEP system. The LEP printing system comprises a first drum  10  in which a suspension of a liquid carrier, for example Isopar L and printing dyes of various colors  12  are supplied. The printing dye may originally be in a powder form. The printing dye will be mixed with the liquid carrier and supplied to the first drum via the use of an electric charge. The first drum will comprise an electric potential in portions where dye is meant to be transferred thereby creating the printing pattern. While the use of a drum is discussed, other elements may also be utilized such as a belt or other transfer member. 
     The first drum  10  is in proximity to an electrically biasable Intermediate Transfer (ITM) drum  14 . The ITM drum  14  receives the suspension of the liquid carrier and the printing dye in the printing pattern from the first drum  10 . The liquid carrier is thereafter evaporated and the printing dye, in the printing pattern, is transferred to the print target 
     The evaporation of the liquid carrier is provided via a heating system  20 . Once the ITM drum  14  comprising the suspension is rotated towards the heating system  20 , the liquid carrier is evaporated  22  such that the printing dye, substantially free of the carrier liquid, is transferred to the transfer drum  16  and subsequently to the print target  18 . 
     During the evaporation of the liquid carrier, the suspension of the liquid carrier and the printing dye is typically heated via a flow of air at room temperature. Once the suspension is heated, the liquid carrier vapour  22  is passed through a filter (not shown) whereby liquid carrier particles, for example, condensed drops of liquid vapour, may be collected and recycled for subsequent printing cycles. 
     According to the some of the example aspects presented herein, a carrier evaporator for the LEP system is provided. Specifically, some aspects described herein provide for the heating system  20  to provide an air flow which is above room temperature (RT)  21 , thereby providing a hot air supply. With the use of the hot air supply, the carrier evaporator provides an efficient and low cost means of evaporating the liquid carrier from the suspension of liquid carrier and the printing dye. 
       FIG. 2  illustrates a graph representing the relationship between the concentration of the carrier vapour evaporation (e.g., Isopar L) vs temperature. As shown in the graph, as the temperature of the flow of air which heats the suspension is increased, the concentration of the vapour which is evaporated is also increased. As shown from the graph, the relationship between the concentration of evaporated liquid carrier and the temperature of the applied hot air flow is an exponentially increasing logarithmic function. Data comprised in  FIG. 2  has been obtained experimentally using Isopar L as the carrier liquid. 
       FIG. 3  illustrates a graph representing the relationship between the concentration of evaporated carrier vapour vs the amount of heat applied to the air flow utilized in the carrier vapour evaporation. As shown from the graph, the relationship between the concentration of evaporated liquid carrier and the temperature applied to the hot air flow used in the evaporation is an increasing linear function. Data comprised in  FIG. 3  has been obtained experimentally using Isopar L as the carrier liquid. 
     From  FIG. 3 , it is shown that greater amounts of concentration of the liquid carrier utilize larger amounts of heat to be applied to the hot air flow used in the evaporation. A greater amounts of heat being applied to the hot air flow is typically associated with increased operational costs as more energy will be utilized to provide the increased levels of temperature to the air flow. Therefore, in order to maintain lower production costs, it is common to heat the suspension of carrier liquid and printing dye using an air flow maintained at room temperature. 
     However, as shown in  FIG. 2 , since the relationship between the concentration of evaporated liquid carrier and the temperature of the air flow used in the evaporation is an exponential logarithmic function, a substantial amount of additional heat is not utilized for providing a significant increase in the concentration of evaporated carrier vapour. Furthermore, the amount of air which needs to be heated is also reduced 
     According to some aspects, it has been appreciated that an increase in heating temperature results in a greater amount of carrier liquid being evaporated. Points  3  and  7  of  FIGS. 2 and 3 , respectively, illustrate a working point of LEP evaporators using air flows at room temperature to evaporate liquid carriers. Points  5  and  9  of  FIGS. 2 and 3 , respectively, illustrate an LEP evaporator using a hot air flow to evaporate liquid carriers, according to some of the aspects described herein. 
     While it is generally thought that an increase of heating results in increased power and operational costs, aspects presented herein have appreciated that with an increased heating temperature as larger amounts of carrier liquid may be evaporated, lower flow rates may be employed. Thus, a reduced amount of power may be used to provide an air flow in an increased temperature thereby resulting in a greater concentration of evaporated liquid carrier. 
       FIG. 4  illustrates a detailed view of the carrier evaporator  20  within the LEP printing system. As discussed in relation to  FIG. 1 , the ITM drum  14  comprises the suspension of the liquid carrier and the printing dye in a printing pattern. As the surface of the ITM drum  14  passes the carrier evaporator  20 , the suspension will be heated and the liquid carrier will be evaporated. 
     The carrier evaporator  20  provides a low flow rate hot air supply. According to some aspects, the hot air supply is at a temperature higher than room temperature. According to some aspects, the hot air supply is at a temperature of at least 120° C. According to some aspects, the hot air supply is at a temperature within a range of 160° C.-165° C. According to some aspects the hot air supply is provided at a low flow rate. Specifically, the hot air supply may be provided at a flow rate of at most 8 L/s at a printing productivity level of 0.6 m 2 /s. According to some aspects, the flow rate may be a rate of at most 5 L/m 2  of a printing target area. 
     According to some aspects, the carrier evaporator  20  provides the air supply via a blower/pump  36 . The air supply is then heated with the use of an air heater  34 , thereby providing the hot air supply  30 . According to some aspects, the heater may be a ceramic, tungsten spiral or an infused heater. According to some aspects, a blanket heater  38  may also assist in regulating the temperature of the hot air supply. 
     The carrier evaporator  20  applies the hot air supply to the surface ITM drum  14  via an air knife  32 . The application of the hot air supply results in an absorption of an evaporated carrier liquid resulting in a flow rate of air comprising a carrier vapour. As a lower flow rate is used in the hot air supply, reduced power levels may be achieved. According to some aspects, the evaporator may supply the hot air supply upon receiving a power level of less than 1 kW at a printing productivity level of 0.6 m 2 /s. According to some aspects, the power level may be less than 0.6 J/m 2  of a printing target area. 
     The carrier vapour is then enters an evacuator and heat exchanger unit  40 . The evacuator portion of unit  40  evacuates at least a portion of the carrier vapours. The heat exchanger of unit  40  decreases a temperature of the reaming carrier vapour. The decrease in temperature results in transforming the air flow comprising the carrier vapour to an air flow comprising carrier particles. According to some aspects, the heat exchanger of unit  40  may decrease the temperature of the carrier vapour to 5° C.-10° C. 
     The air flow comprising the carrier particles thereafter passes through a filter  42 . According to some aspects, the filter  42  removes the carrier particles from the air flow.  FIG. 5  illustrates a filter in the form of a vain demister  52 . As illustrated in  FIG. 5 , the rate of air passes through the demister  52 . The demister  52  separates the carrier particles from the air flow. The separated carrier particles may thereafter pass through a fine filter  54  in which the carrier particles are combined. The combined carrier particles comprise an increased weight and therefore drop, due to the force of gravity, into a carrier drain. The remaining air flow which exists the demister is clear air. The dropped carrier particles are thereafter recycled for future printing. 
     According to some aspects, it is herein appreciated that at lower flow rates, the air flow, comprising the carrier particles, may pass through a filter such as the vain demister of  FIG. 5  thereby not providing effective filtering.  FIG. 6  illustrates an electrostatic demister  60  which may be used as the filter  42  of  FIG. 4 . 
     According to some aspects, the electrostatic demister  60  comprises at least two parallel ionized plates.  FIG. 6  illustrates three ionized plates  61 - 63 . Any number of ionized plates (two or more) may be utilized. The parallel ionized plates define a first path P 1  for the air flow. According to some aspects, the ionized plates are charged such that as the air flow enters the first path P 1 , the carrier particles within the air flow become electrostatically charged. Either a positive of negative electrostatic charge may be applied to the carrier particles. 
     The air flow, comprising the charged carrier particles, may then enter a second path P 2  defined by at least two parallel collection plates.  FIG. 6  illustrates the use of 5 parallel collection plates  64 - 68 . Any number (two or more) of collection plates may be utilized. According to some aspects, the collection plates form an electric field within the second path P 2 . As the low flow rate air flow enters the second path P 2 , the electrostatically charged carrier particles become attracted to a collection plate and thereafter become neutralized. Specifically, the carrier particle will become neutralized by gaining its lost electron or proton. 
     According to some aspects, the electrostatic demister  60  also comprises a carrier drain  70  which is positioned to collect the neutralized carrier particles as they fall from the collection plates due to the force of gravity. Thereafter, the neutralized carrier particles may be recycled and used for future printing. The electrostatic demister  60  of  FIG. 6  provides an efficient and effective means of filtering carrier particles traveling in a low flow rate air flow. 
       FIG. 7  illustrates a control unit  73 . According to some aspects, the control unit  73  may be used to control operations of the carrier evaporator, including the different components thereof, discussed above. The control unit  73  may comprise any number of network interfaces  75  which may be configured to receive and transmit any form of heating, evaporation or sensing related information and/or instructions. According to some aspects, the network interface may also comprise a single transceiving interface or any number of receiving and/or transmitting interfaces. 
     The control unit  73  may further comprise at least one memory  77  that may be in communication with the network interfaces. The memory  77  may store received or transmitted data and/or executable program instructions. The memory may also store information relating to the evaporating or heating of the liquid carrier as described herein. The memory may be any suitable type of machine readable medium and may be of a volatile and/or non-volatile type. 
     The control unit  73  may also comprise at least one processing unit  79  which may be configured to process received information related to the evaporating or heating provided by the evaporator for the LEP printing system. The processing unit may be any suitable computation logic, for example, a microprocessor, digital signal processor (DSP), field programmable gate array (FPGA), or application specific integrated circuitry (ASIC) or any other form of circuitry. 
       FIG. 8  illustrates a flow diagram depicting example operations which may be taken by the evaporator, for example comprising the control unit of  FIG. 7 , in the LEP printing system as described herein. 
       FIG. 8  comprises some operations which are illustrated in a solid border and some operations which are illustrated with a dashed boarder. The operations which are comprised in a solid border are operations which are comprised in the broadest aspect. The operations which are comprised in a dashed boarder are example aspects which may be comprised in, or a part of, or are further operations which may be taken in addition to the operations of the broader example aspects. The operations of  FIG. 8  need not be performed in order. Furthermore, not all the operations need to be performed. The example operations may be performed in any order and in any combination. 
     Operation  80   
     The evaporator is configured to apply a hot air supply. The heater (e.g., at least any one of components  30 - 38 ) may be configured to supply or maintain the temperature of the hot air supply. The processing unit may be configured to provide computer readable instructions to supply such a hot air supply. 
     According to some aspects the use of a hot air flow allows for less air to be used as compared to systems with rely on air at room temperature. Furthermore, less energy and system resources are utilized to maintain the temperature of the air flow above room temperature. According to some aspects, the hot air supply and resulting air flow comprise low flow rates. 
     Example Operation  81   
     According to some aspects, the applying  80  further comprises applying  81  the hot air supply at a temperature greater than room temperature. The heater (e.g., at least any one of components  30 - 38 ) may be configured to supply or maintain the temperature of the hot air supply at a temperature above room temperature. The processing unit may be configured to provide computer readable instructions to supply such a hot air supply at a temperature above room temperature. 
     Example Operation  82   
     According to some aspects, the applying  80  further comprises applying  82  the hot air supply at a temperature greater than 120° C. The heater (e.g., at least any one of components  30 - 38 ) may be configured to supply or maintain the temperature of the hot air supply at a temperature above 120° C. The processing unit may be configured to provide computer readable instructions to supply such a hot air supply at a temperature above 120° C. 
     Example Operation  83   
     According to some aspects, the applying  80  further comprises applying  83  the hot air supply at a temperature between 160° C.-165° C. The heater (e.g., at least any one of components  30 - 38 ) may be configured to supply or maintain the temperature of the hot air supply at a temperature between 160° C.-165° C. The processing unit may be configured to provide computer readable instructions to supply such a hot air supply at a temperature between 160° C.-165° C. 
     Example Operation  84   
     According to some aspects, the applying  80  further comprises applying  84  the hot air supply at a flow rate of at most 8 L/s at a printing productivity level of 0.6 m 2 /s. The heater (e.g., the blower/pump  36 ) may be configured to supply the hot air supply at a rate of at most 8 L/s at a printing productivity level of 0.6 m 2 /s. The processing unit may be configured to provide computer readable instructions to supply such a hot air supply at a rate of at most 8 L/s at a printing productivity level of 0.6 m 2 /s. 
     Operation  85   
     The evaporator is further configured to absorb  85  a carrier liquid with the hot air supply, where the absorbing results in a first air flow comprising a carrier vapour. The suction of the unit  40  is configured to absorb the carrier liquid with the hot air supply. The processing unit is configured to provide computer readable instructions to control the absorbing. 
     As explained above, the absorbing of the carrier liquid may be provided via the application of heat to the blanket comprised on the ITM drum of the LEP printing system. According to some aspects, the liquid carrier may be a dielectric volatile liquid, for example mineral oil. As example of such a mineral oil is an isoparaffin such as Isopar L. 
     Operation  86   
     The evaporator is further configured to transform the first air flow comprising the carrier vapour to a second air flow comprising carrier particles via a decrease of temperature of the carrier vapour. The heat exchanger of unit  40  is configured to transform the first air flow comprising carrier vapour to a second air flow comprising carrier particles via the decrease of temperature of the carrier vapour. The processing unit is configured to provide computer readable instructions to facilitate the decrease of temperature. According to some aspects, an evacuator may also be used to evacuate a portion of the carrier vapour prior to the decrease in temperature. 
     Example Operation  87   
     According to some aspects, the transforming  86  may further comprise decreasing  87  the temperature of the first air flow comprising the carrier vapour to 5° C.-10° C. The heat exchanger of unit  40  may decrease the temperature of the first air flow comprising the carrier vapour to 5° C.-10° C. The processing unit may be configured to provide computer readable instructions to facilitate the decrease of temperature to 5° C.-10° C. 
     Operation  88   
     The evaporator is further configured to filter  88  the carrier particles from the second air flow. A filter  42  is configured to filter the carrier particles from the second air flow. The processing unit may be configured to provide computer readable instructions to facilitate the filtering of the carrier particles. 
     Example Operation  89   
     According to some aspects, the filtering  88  may further comprise supplying  89  an electrostatic charge between at least two parallel ionized plates defining a first path. Ionized plates (e.g., plates  61 - 63 ) of an electrostatic demister  60  may be configured to supply the electro static charge. The processing unit may be configured to provide computer readable instructions to supply the electrostatic charge between the at least two parallel ionized plates defining the first path. This example operation is further described in at least  FIG. 6 . 
     Example Operation  90   
     According to some aspects, the filtering  88  and supplying  89  may further comprise electrostatically charging  90  carrier particles in the second air flow once the second air flow passes through the first path. The at least two parallel ionized plates (e.g., plates  61 - 63 ) of an electrostatic demister  60  may be configured to electrostatically charge the carrier particles in the second air flow. The processing unit may be configured to provide computer readable instructions for electrostatically charging the carrier particles. 
     Example Operation  91   
     According to some aspects, the filtering  88 , supplying  89  and electrostatically charging  90  may further comprising supplying  91  an electric field between at least two parallel collection plates defining a second path. At least two collection plates (e.g., collection plates  64 - 68 ) may supply the electric field. The processing unit may be configured to provide instructions for supplying the electric field between the at least two parallel collection plates. 
     Example Operation  92   
     According to some aspects, the filtering  88 , supplying  89 , electrostatically charging  90  and supplying  91  may further comprising neutralizing  92  the electrostatically charged carrier particle as the second air flow passes through the second path and the electrostatically charged particle becomes attracted to one of the parallel collection plates. The at least two collection plates of the electrostatic demister may neutralize the electrostatically charged carrier particle. The processing unit may provide computer readable instructions to control an electric field in order to neutralize the electrostatically charged carrier particle as the air flow passes through the second path and the electrostatically charged particle becomes attracted to one of the parallel plates. 
     Example Operation  93   
     According to some aspects, the filtering  88 , supplying  89 , electrostatically charging  90 , supplying  91  and neutralizing  92  may further comprise collecting  93  the neutralized carrier particles via a carrier drain. The processing unit may provide computer readable instructions to facilitate the collecting of the neutralized carrier particles. 
     Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or examples. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise expresses singular use similar. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context otherwise expresses singular use similar. 
     Features, integers, characteristics, groups described in conjunction with a particular aspect or examples are to be understood to be applicable to any other aspect or examples described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the operations of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or operations are mutually exclusive. The examples presented herein are not restricted to the details of any foregoing aspects. The examples extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the operations of any method or process so disclosed.