Patent Publication Number: US-2012045258-A1

Title: Preheating of Marking Material-Substrate Interface for Printing and the Like

Description:
BACKGROUND 
     The present disclosure is related to transfer lamination methods (such as printing) and systems therefor, and more specifically to the pre-heating of the interface at which an imaging material, such as a toner, is applied to a substrate, such as paper. 
     Transfer lamination systems use one of a variety of devices to apply a marking material onto a substrate. One well-known example is an electrophotographic device, used for example for printing, copying, facsimile, etc. In such devices, a photosensitive drum or web is exposed by light to form a latent image thereon. The image is developed, typically with toner. The toner is transferred to a substrate such as paper, where by way of heat and pressure the toner is fused to the substrate, thereby creating a permanent image from the latent/developed image. 
     In a typical fusing stage of an electrophotographic device, two rollers are in contact with one another at a desired pressure, thereby forming a nip along the line of contact between the rollers. One or both rollers are heated, for example by an electrical element forming a part of the roller sleeve or core. Therefore, such systems are referred to as hot pressure fusers (HPF). In one variation, a web or belt replaces one of the rollers, and either the roller or belt or both are heated. The area of contact between the roller and the belt forms the nip. In either case, when a toner-bearing substrate (with a developed image) passes through the nip, the heat and pressure causes the toner to soften or melt, and thereby fuse with the substrate and adjacent toner particles. 
     However, hot pressure fusers are typically a significant, if not the major consumer of the overall energy budget of an electrophotographic device. In addition, a typical hot pressure fuser is relatively slow to heat to operating temperature, and is therefore a major contributor to the time required for an electrophotographic device to warm up to operating conditions. 
     In order to reduce energy consumption and operational wait-time, alternatives to HPF are being investigated. Such alternatives include cold pressure fusing (CPF) and warm pressure fusing (WPF). As their names suggest, these alternatives attempt to fuse toner at ambient and slightly-above ambient temperature, respectively. To accomplish this, special toners have been developed which fuse at relatively low temperatures. However, while fusing of toner particles has been demonstrated at low temperatures, a significant problem encountered with both CPF and WPF is the poor fix of the toner to the substrate. It is speculated that one reason for this is low flow of toner into the interstices (e.g., pores between fibers or coating material) of the substrate surface, which in turn results in poor mechanical adhesion. 
     It is known that in place of heating the substrate with the toner already applied, the blank substrate may be heated prior to application of the toner. This is useful in multi-pass systems and systems that use a photosensitive web and a pressure transfer nip. However, such substrate pre-heating systems still use two rollers, or one roller and a belt, with an electric heating element as part of the roller(s), belt or both. As used herein, the term pre-heating refers to heating an element of the system, such as substrate, marking material, etc., prior to the application of the marking material to the substrate. 
     It is also known that the toner itself may be preheated prior to fusing. This is accomplished either by drawing the toner from a heated pool or applying the toner to a heated transfer web or drum. However, in these methods either the toner is bulk heated without regard to heating one surface or another of the toner, or the toner is heated from a side opposite of that which ultimately contacts the substrate. 
     There has been inadequate attention paid in the art to selective placement of a device to heat one or both elements of the interface of marking material and substrate in order to minimize the energy consumed in heating the interface for fixing before pressure fusing. Still further, there has been inadequate investigation into types of heat sources and heat transfer members that minimize the energy consumed in heating the interface between the marking material and substrate for fixing before pressure fusing. Finally, there is a need to provide a faster heating cycle of the marking material and/or substrate to address the device warm-up time issues discussed above. 
     SUMMARY 
     Accordingly, the present disclosure is directed to systems and methods for providing efficient, low energy consumption for the fixing or fusing of marking material to a substrate, for a transfer lamination system, for example in an electrophotographic marking system. The present disclosure is also directed to systems and methods for providing rapid warm-up times in an electrophotographic marking system, particularly in regard to the fixing of marking material to a substrate. 
     According to one aspect of the disclosure a heat transfer member such as a cylinder is provided with a heat source that imparts heat energy to a portion of the substrate, the marking material, or both, by absorption, conduction, convection, etc. where the substrate and marking material come into contact with one another—i.e., the marking material-substrate interface. As used herein, “absorption” is intended to mean absorption of radiation, such as absorption of light energy. In one embodiment, the heat source is a resistive heater. In other embodiments, the heat source may be another electrical, electromechanical, radiant (e.g., filament, laser, etc.) or electrochemical heat source. The heat transfer member is proximate or in physical contact with a substrate that is to receive and have fused thereon a marking material. The energy driving the heat source, and hence the amount of heat produced by the heat source, is controlled such that only the minimum amount of heat energy is transferred to the substrate to permit toner fusing into the substrate. Typically, this means that the point at which the heat transfer member imparts heat to the substrate is in close physical proximity to the nip at which the marking material is applied to the substrate. While different systems into which the present disclosure is integrated will define different degrees of closeness between the point of heat transfer and the nip, the concept of the present disclosure and the use of the term close physical proximity is meant to encompass the purposeful design of the system elements and operation of the system to minimize the distance between point of heat transfer and nip yet still provide effective pre-heating. 
     The minimized distance between point of heat transfer and nip means there is a minimized time for heat dissipation. That is, the amount of heat energy required to pre-heat the substrate is minimized. Furthermore, this typically means that only a portion of the thickness of the substrate is heated, preferably a portion extending from the surface at which the marking material is to be applied partway, but not all of the way, to the opposite surface, again further minimizing the needed heat energy for effective substrate pre-heating. 
     According to another aspect of the disclosure, in place of a resistive heater the heat source is an optical source, such as a light emitting diode (LED) bar or array, solid-state laser bar or array, and so forth. It will be understood here that “optical” is intended to mean any electromagnetic source of any output wavelength, whether visible to the unaided human eye or not (e.g., visible, infrared, etc.) In this case, the cylindrical heat transfer member may include a heat absorption layer of a material selected to be highly optically absorptive at the wavelengths of light emitted by the optical source. The optical source may be disposed within a transparent cylinder having an absorptive coating applied thereto. The optical source illuminates the absorptive coating through the transparent cylinder. Alternatively, the optical source may be disposed proximate and outside of the cylinder such that the optical source directly illuminates the absorptive coating. One advantage of the optical source is the ability to selectively heat portions of the heat transfer member (and ultimately the substrate), reducing the energy consumed in pre-heating the substrate (i.e., saving the energy that would go towards heating portions of the substrate that do not receive marking material). Another advantage of the optical source is the ability to rapidly heat the desired portions of the heat transfer member, thus reducing device warm-up time. 
     According to yet another aspect of the disclosure, the heat transfer member is a web or belt provided with a heat source. Again, the heat source may be by absorption, conduction, convection, etc., and may comprise a resistive heater or other electrical, electromechanical or electrochemical heater, or may be an optical source. One advantage provided by this aspect of the disclosure is that the belt remains in contact with the substrate for a longer period of time, thereby providing a more effective heat transfer from heat transfer member to substrate. 
     According to still another aspect of the disclosure, in place of pre-heating the substrate, the marking material is pre-heated. Typically, this may be accomplished by directing heat energy from a heat source to a region of the drum, web or plate carrying marking material to be deposited onto the substrate. The heat source again may be a resistive heater or other electrical, electromechanical or electrochemical heater or may be an optical source. The energy driving the heat source, and hence the amount of heat produced by the heat source, is controlled such that only the minimum amount of heat energy is transferred to the substrate to permit the marking material to fuse into the substrate and with any adjacent marking material. Typically, this means that the point at which the heat transfer member imparts heat to the marking material is physically close to the nip at which the marking material is applied to the substrate. Furthermore, this typically means that only a portion of the thickness of the marking material pile on the drum, web or plate is heated, preferably a portion extending from the surface of the marking material which is applied to the substrate partway, but not all of the way, to the opposite surface in contact with the drum, web, plate, etc. Of course both the substrate and the marking material may be pre-heated by the arrangements described above as well. 
     According to a still further aspect of the disclosure the heat transfer member is neither a roller nor web, but rather a member sized and shaped to be placed very close to the point at which marking material is applied to the substrate. The precise cross-sectional shape of this member will vary from application to application, but one example is a member with a roughly triangular cross-section for fitting closely in the wedge-shaped region between the pressure drum on the marking material side of the substrate and the substrate surface receiving the marking material. According to this aspect, the heat transfer member may employ a heat source comprising a resistive heater or other electrical, electromechanical or electrochemical heater. Alternatively, the heat source may be an optical source directed through an appropriately shaped mirror or lens, such as a prism, such that the optical energy is applied very close to the point at which the marking material is applied to the substrate. The heat source may heat the substrate, the marking material, or both. An advantage of this aspect of the disclosure is that the amount of time for heat energy to dissipate prior to the application of the marking material to the substrate surface is minimized, meaning that the total amount of energy required to drive the heat source can be kept to a minimum. 
     In each of the above described aspects, the amount of energy driving the heat source, and hence the amount of heat energy produced by the heat source, is limited to that amount needed to provide effective fixing of the marking material to the substrate. The actual amount of energy required will depend on many factors, such as the marking material, substrate, the pressure applied at the nip, the operating environment temperature, humidity, and pressure, the speed of travel of the substrate through the system, etc. However, by locating the pre-heating member(s) physically close to the point at which the marking material is applied to the substrate, energy consumed for heating the substrate and/or marking material to assist with fixing can be minimized. Furthermore, in applications that benefit from reduced warm-up time, selection of the proper heat source, such as an optical source, can provide both minimized energy usage and reduced warm-up time. Following the fixing of the material to the substrate other means, such as application of pressure across the marking material and substrate, can be used to complete the fusing of the marking material. The result is a marking material layer which is fused well and fixed well to the substrate. 
     The above is a summary of a number of the unique aspects, features, and advantages of the present disclosure. However, this summary is not exhaustive. Thus, these and other aspects, features, and advantages of the present disclosure will become more apparent from the following detailed description and the appended drawings, when considered in light of the claims provided herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings appended hereto like reference numerals denote like elements between the various drawings. While illustrative, the drawings are not drawn to scale. In the drawings: 
         FIG. 1  is a side view of a first embodiment of a portion of an electrophotographic printing system including a substrate pre-heating heat transfer member according to the present disclosure. 
         FIG. 2  is another side view of the embodiment of the portion of an electrophotographic printing system including a substrate pre-heating heat transfer member shown in  FIG. 1 , illustrating heat transfer to the substrate. 
         FIG. 3  is a side view of another embodiment of a portion of an electrophotographic printing system including a substrate pre-heating heat transfer member according to the present disclosure, illustrating heat transfer to both the substrate and marking material prior to application of the marking material to the substrate. 
         FIG. 4  is a side view of another embodiment of a portion of an electrophotographic printing system including an optical heating mechanism according to the present disclosure, which also illustrates heat transfer to the substrate. 
         FIGS. 5A and 5B  are cut-away perspective views of a roller heat transfer member with internally disposed optical heating mechanisms which are operated together and operated independently, respectively. 
         FIG. 6  is a side view of yet another embodiment of a portion of an electrophotographic printing system including a belt-type substrate pre-heating heat transfer member according to the present disclosure. 
         FIG. 7  is a side view of still another embodiment of a portion of an electrophotographic printing system including a marking material-specific pre-heating arrangement according to the present disclosure. 
         FIG. 8  is a side view of a still further embodiment of a portion of an electrophotographic printing system including a substrate pre-heating heat transfer member shaped and disposed for minimal spacing from the marking nip according to the present disclosure. 
         FIGS. 9A ,  9 B, and  9 C are side views of several variations of another embodiment of a portion of an electrophotographic printing system including a substrate pre-heating heat transfer member including an optical member such as a mirror, lens, or prism, respectively, and optical heat source, each disposed for minimal spacing from the marking nip according to the present disclosure. 
         FIGS. 10 and 11  are system and component side views, respectively, of a heat pipe heat transfer member according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Initially, descriptions of well-known starting materials, processing techniques, components, equipment and other well-known details are merely summarized or are omitted so as not to unnecessarily obscure the details of the present disclosure. Thus, where details are otherwise well-known, we leave it to the application of the present disclosure to suggest or dictate choices relating to those details. 
     With reference to  FIG. 1 , there is shown therein a first embodiment of a portion of an electrophotographic printing system  10  according to the present disclosure. System  10  comprises a pair of pressure/guide drums  12 ,  14 . Pressure/guide drum  12  carries a transfer surface web  16  for delivering marking material  18  to a first surface  20  of a substrate  22 . Belt  16  may be a transfix belt, meaning that marking material  18  is transferred thereto from a photosensitive member (not shown) after development, or may itself be a photosensitive member. It will also be understood that while the embodiment of  FIG. 1  shows marking material  18  carried by web  16 , the teachings of this disclosure apply equally to systems in which marking material  18  is carried directly by drum  12 , or when web  16  is replaced by other elements with similar functionality. 
     System  10  further comprises a pair of heat transfer members  26 ,  28 . Heat transfer member  26  is located proximate surface  20  of substrate  22 , which receives marking material  18 , while heat transfer member  28  is located proximate surface  24  opposite surface  20 . In one embodiment, heat transfer members  26 ,  28  are rollers, disposed so as to be in physical contact with substrate  22  as it passes through system  10 . Heat transfer member  26  is provided with a heating mechanism  30 , which heats at least the outer surface of heat transfer member  26 . In one embodiment, heating mechanism  30  is a resistive heating element disposed within heat transfer member  26  such that when energized (i.e., a current is applied thereto) heating mechanism  30  provides radiant heat energy to the surface of heat transfer member  26 . In other embodiments, heating mechanism  30  may be located external to heat transfer member  26 , and may be a radiant filament heater, hot air heater or, in fact, any form of electrical, electromechanical or electrochemical heater which can controllably heat the surface of heat transfer member  26 . Heat transfer member  28  will typically not be associated with a separate heating mechanism, and its surface generally will be at ambient temperature during operation. 
     In operation, as substrate  22  passes between heat transfer members  26 ,  28  surface  20  of substrate  22  is heated. As discussed further below, in order to minimize power consumption substrate  22  is heated only enough that marking material applied to surface  20  may fuse therewith. Substrate  22  then exits heat transfer members  26 ,  28  and marking material  18  is applied to surface  20  at nip  32  when the surface of web  16  carrying the marking material is brought into physical contact (or close proximity) with surface  20 . 
     With reference to  FIG. 2 , the heating of substrate  22  is further explained. Fundamentally, the goal is to impart only the minimum amount of heat energy needed to facilitate fusing of the marking material  18  to substrate  22  (and fusing of marking material particles together at the point of fusing to substrate  22 ). To accomplish this, surface  20  passes by heat transfer member  26 . Heat energy is thereby transferred into substrate  22  to create a bounded isotherm within substrate  22 . The temperature of the surface of heat transfer member  26  is controlled such that the heat energy transferred into substrate  22  is just sufficient that, when taking into account the dissipation of heat energy in substrate  22  between its contact with the heat transfer member  26  and nip  32 , the temperature of surface  20  at nip  32  permits fusing of the marking material into substrate  22 . For example, the shaded region  34  illustrates the heat coming out of heat transfer member  26 , including formation of the bounded isotherm  34 ′ within substrate  22 , as shown in  FIG. 2 . Bounded isotherm  34 ′ is generally limited to a lateral section roughly between the region of contact of heat transfer member  26  with surface  20  and the region of contact of web  16  with surface  20 . Furthermore, if t is the thickness of substrate  22 , then the depth, d 1 , of heated region  34  may be such that d 1 &lt;t, provided the temperature of substrate  22  in the region of nip  32  is sufficient to permit fusing. Since the temperature of substrate  22  at nip  32  is sufficient to facilitate fusing of marking material  18 , any additional heat energy imparted to substrate  22  would be wasted. 
     It will be appreciated from the above description that in order to reduce the energy consumed in pre-heating the substrate, it is desirable to locate heat transfer member  26  close to nip  32 . That is, it is desirable to minimize the distance S 1  between the region of contact of heat transfer member  26  with surface  20  and the region of contact of web  16  with surface  20 . This can beneficially lead to the condition illustrated in  FIG. 3 , in which the heat radiated by heat transfer member  26  pre-heats not just substrate  22 , but also marking material  18  on web  16  as it passes close to heat transfer member  26 . In certain embodiments this may be advantageous as less heat energy need be provided to substrate  22 . In certain embodiments, this means that less of substrate  22  need be heated (i.e., d 2 &lt;d 1 ). This implies that in such embodiments a lower overall energy consumption may be possible. 
     In the embodiments discussed above, the heating mechanism has been assumed to be electrical, electromechanical or electrochemical. The present disclosure is not so limited. With regard to  FIG. 4 , there is shown a system  40  in which the heating mechanism  42  is an optical heat source, such as a light emitting diode (LED) bar or array, solid-state laser bar or array, and so forth. An advantage of the optical source is the ability to rapidly cycle between on and off, thus rapidly heating the desired portions of the heat transfer member  44  when needed, and only when needed, thereby reducing device warm-up time and excess energy usage. Another advantage of the optical source is the ability to selectively heat certain portions, while not heating other portions, of heat transfer member  44 , as will be discussed further below. 
     Heat transfer member  44  is comprised of a roller or cylindrical drum  46  that is optically transparent at the wavelength of emission of optical heating mechanism  42 . A thermal absorption layer  48 , of a material that is highly absorptive at the wavelength of light emitted by the optical source, is applied to roller  46 , typically on the outer surface thereof. Roller or cylindrical drum  46  defines a cylindrical cavity in which optical heating mechanism  42  may be disposed. Optical energy (beam  50 ) from optical heating mechanism  42  is transmitted in a direction from a radially inward surface of drum  46  to a radially outward surface of drum  46  (i.e., radially outward through drum  46 ) and absorbed by layer  48 , resulting in heat energy being propagated into region  34 ,  34 ′ as described above. An anti-reflective coating (not shown) on the inward surface of drum  46  may improve the absorption and/or the rate of absorption by layer  48 . 
     While optical heating mechanism  42  may be a single emitter device that emits a single beam as illustrated in  FIG. 4 , the optical heating mechanism may be a multiple emitter device capable of producing multiple optical beams generally parallel to beam  50  extending along the axial length of roller  46 . This is illustrated in  FIG. 5A , which illustrates 4 light emitting diode bars, although this number is arbitrary, and may be larger or smaller, and may be bars providing a one-dimensional row of beams or may be arrays providing two-dimensional arrays of beams, depending on the application of the present disclosure. 
     In certain embodiments, each emitter in the bars or arrays comprising optical heating mechanism  42  are operated together, as shown in  FIG. 5A . In other embodiments, such as illustrated in  FIG. 5B , the individual emitters in each bar or array are operated independently. Independent operation provides the desirable option that certain regions of substrate  22  may be heated when fusing is to occur in those regions, while regions not receiving marking material are not provided with heat energy. For example, at a given time t 1 , certain emitters are operated while others are not. At a later time t 2 , a different set of emitters may be operated. Software may be used to coordinate the operation of the emitters with the placement of marking material, so that where marking material is to be applied selected emitters are operated to heat the portions of the substrate that are to receive the marking material, on a line-by-line or pixel-by-pixel basis. Individually addressable optical sources permit selective heating of portions of the heat transfer member  44  (and ultimately substrate  22 ), reducing the energy consumed in pre-heating substrate  22 . 
     While the embodiments described immediately above comprise optical heating mechanism  42  disposed within the core of heat transfer member  44 , it is within the scope of the present disclosure to provide the optical heating element external to heat transfer member  44  (not shown). Single or multiple emitter laser diodes, lasers, raster optical scanners, and other devices and systems capable of producing multiple optical beams are examples of such external sources. In such a case, the output of the optical heating mechanism  42  is directed to the absorptive layer  48 . Such an arrangement obviates the need for roller  46  to be optically transparent, as well as the need for the relatively large hollow region within roller  46  required to accommodate optical heating mechanism  42 . 
     While the aforementioned embodiments have utilized a roller as a heat transfer member, other arrangements are contemplated herein. For example,  FIG. 6  illustrates a system  60  which includes a pair of heating belts  62 ,  64 . In the embodiment shown in  FIG. 6 , an optical heating mechanism  66  is employed, although an electrical, electromechanical or electrochemical heating mechanism may be substituted therefor in a manner previously described herein. Belt  64  is selected to have a surface that is absorptive at the wavelength of light emitted by optical heating mechanism  66 . Furthermore, while the contact region between belt  62  and surface  20  is shown as linear, other arrangements are possible, such as contact over a large radius curve, which permits tensioning of belt  62  against surface  20 . In general, the larger contact area and longer contact between belt  62  and surface  20  permits a more efficient transfer of heat energy from belt  62  to substrate  22 . In addition, belt  62  is driven by and/or rides on rollers  68 ,  69 , which generally will be of smaller diameter than the roller comprising the heat transfer member described above (i.e., member  26 ,  FIG. 1 ). This permits positioning the source of heat energy closer to the nip (i.e., reducing the length s), further reducing the amount of energy required to heat substrate  22  to permit fusing. 
     In the embodiment described immediately above, the heating mechanism was optical, and disposed external to belt  62 . However, it will be appreciated that heating mechanism  66  may be located between rollers  68 ,  69 , and illuminate (heat) web  62  from the backside (i.e., from the inside). Furthermore, heat energy may be provided by an electrical, electromechanical or electrochemical heater, which may be located between rollers  68 ,  69  or within one or both of rollers  68 ,  69  (not shown). 
     An alternative to heating a drum or belt is to heat the marking material such that fusing with the substrate and other marking material is facilitated. One embodiment for doing so has been described above with regard to  FIG. 3 . While the embodiment shown in  FIG. 3  heats both the substrate and the marking material, embodiments that heat only the marking material are contemplated by the present disclosure. The heat transfer member  26  may be positioned such that it does not heat substrate  22 , but heats only marking material  18  as described above. However, in another embodiment shown in  FIG. 7 , an embodiment  70  comprises an optical heating mechanism  72  capable of individually addressing marking material piles carried by web  16 . Again, optical heating mechanism  72  may comprise a light emitting diode (LED) bar or array, solid-state laser bar or array, and so forth. Each emitter of optical heating mechanism  72  may be individually addressable so that light is only generated and made incident on marking material piles, not on the bare surface of web  16 , in order that the total overall driving energy is minimized. This typically means that only a portion of the thickness of the marking material pile  18  on the web (or drum or plate) is heated, preferably a portion extending from the surface of the marking material which is applied to the substrate partway, but not all of the way, to the opposite surface in contact with the drum, web, plate, etc. And again, the light energy required is controlled so as to be only the minimum required to heat the marking material to facilitate fusing. It should be noted that heat transfer between marking material particles is poor because of the small effective contact area between particles. Thus, heat absorbed by ‘interfacial’ marking material particles is largely confined to those particles until pressure is applied which drives the sintering of marking material particles to each other and to the substrate. 
     One aspect of minimizing the energy required to pre-heat either the substrate or the marking material for fusing is minimizing the time between heating either or both the substrate and marking material and the application of the marking material to the substrate at the marking (transfer) nip. The throughput rate of the system is fixed. This limits system design to minimizing the distance between heat application and nip. Thus, according to another embodiment of the present disclosure, the heat transfer member is neither a roller nor belt, but rather a member sized and shaped to be placed very close to the nip at which marking material is applied to the substrate. The precise cross-sectional shape of this member will vary from application to application, but one example  80  is illustrated in  FIG. 8 . In addition to elements previously described, system  80  comprises heat transfer member  82  with a substantially wedge-shaped or triangular cross-section for fitting very closely into the wedge-shaped region between the marking material side of web  16  as it wraps around pressure drum  12  and substrate surface  20 . According to this embodiment, heat transfer member  82  may employ a heat source comprising a resistive heater or any other energy source such as an electrical, electromechanical or electrochemical heater. 
       FIGS. 9A ,  9 B, and  9 C illustrate several variations of another embodiment which facilitates providing heat energy to a substrate (or equivalently, the marking material) very close to the point at which marking material is applied thereto, thus enabling the preheating of the substrate (or equivalently, the marking material) with minimal unused heat energy. With reference to  FIG. 9A , heat transfer member  86   a  comprises an optical heating mechanism  88   a  (LED bar, array, solid-state laser, etc.) which produces an optical beam B, which is directed to surface  20  (or to marking material  18 , not shown) by an appropriately positioned and optical element  90   a , which in the embodiment illustrated in  FIG. 9A  comprises a mirror. With reference to  FIG. 9B , again, heat transfer member  86   b  comprises an optical heating mechanism  88   b  (LED bar, array, solid-state laser, etc.) which produces an optical beam B. In this variation, beam B is focused by lens  90   b  onto surface  20 . Finally, with reference to  FIG. 9C , heat transfer member  86   c  again comprises an optical heating mechanism  88   c  (LED bar, array, solid-state laser, etc.) which produces an optical beam B. In this variation, beam B is directed by prism  90   c  onto surface  20 . 
     In each embodiment described herein, the optical heating element may comprise a monolithic, multiple emitter device, multiple discrete devices connected for simultaneous operation, or multiple discrete devices connected for independent operation, in each case either on a device-by-device basis or on an emitter-by-emitter basis. 
     Each of the embodiments of  FIGS. 9A ,  9 B, and  9 C are merely illustrative of the broader concept disclosed herein of intentionally designing and disposing a heat transfer member in close proximity to the point at which marking material is applied to a substrate so that only a minimum amount of heat energy is needed to facilitate or assist with marking material fusing at the substrate. 
     With reference to  FIGS. 10 and 11 , according to another embodiment  100  of the disclosure, heat transfer member  102  may include or be comprised of a heat pipe. Heat transfer member  102  itself comprises a heating mechanism  104 , and at least one sealed, fluid-filled cavity  106 , within a cylindrical housing  108  (e.g., double cylindrical walls with an enclosed annular cavity forming the heat pipe structure). 
     Cavity  106  maintains a controlled internal pressure corresponding to the vapor pressure of the enclosed fluid near the temperature at which effective heat transfer is desired for the particular application. Through constant phase change (vaporization) at a “hot” (i.e., heat source) portion of cavity  106  followed by transfer of the vaporized fluid to a “cold” (i.e., heat sink) portion of cavity  106 , and its subsequent condensation near the heat sink portion, large amounts of heat can be quickly transferred due to the rapid phase change heat transfer effects. This heat transfer can be more efficient than a purely thermal conduction through solid walls (e.g., the wall of heat transfer member  26 ,  FIG. 1 ). Typically, a wicking material  110  is also used to transfer the condensed (liquid) fluid back to the “hot” region within the heat pipe so as to continue the heat transfer cycle. Thus, heat generated (sourced) at (by) the heating mechanism  104  may be quickly and efficiently transferred to the outer surface of cylindrical housing  108  for subsequent coupling to substrate  22 . 
     It will be appreciated that by minimizing the distance between the point of heat application to the substrate (or marking material) and the marking nip in the embodiments described above, the amount of time for heat energy to dissipate prior to the application of the marking material to the substrate surface is minimized, meaning that the total amount of energy required to drive the heat source can be kept to a minimum. 
     It should be understood that the description above merely illustrates exemplary embodiments with the scope of the disclosure, and that the limitations of the claims following define the boundaries of the present disclosure, up to and including those limitations. To further highlight this, the term “substantially” may occasionally be used herein in association with a description above or in a claim limitation (although consideration for variations and imperfections is not restricted to only those limitations used with that term). While as difficult to precisely define as the limitations of the present disclosure themselves, we intend that this term be interpreted as “to a large extent”, “as nearly as practicable”, “within technical limitations”, and the like. 
     Furthermore, while a plurality of preferred exemplary embodiments have been presented in the foregoing detailed description, it should be understood that a vast number of variations exist, and these preferred exemplary embodiments are merely representative examples, and are not intended to limit the scope, applicability or configuration of the disclosure in any way. Various of the above-disclosed and other features and functions, or alternative thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications variations, or improvements therein or thereon may be subsequently made by those skilled in the art which are also intended to be encompassed by the claims, below. 
     Therefore, the foregoing description provides those of ordinary skill in the art with a convenient guide for implementation of the disclosure, and contemplates that various changes in the functions and arrangements of the described embodiments may be made without departing from the spirit and scope of the disclosure defined by the claims thereto.