Patent Publication Number: US-10327475-B2

Title: Continuous mode heater assembly for aerosol-generating system

Description:
TECHNICAL FIELD 
     The present invention relates to a heater assembly for an aerosol-generating device, comprising a heater element, a reservoir comprising aerosol-generating liquid, and a condenser, for condensing excess vapours generated during use of the heater assembly. The present invention also relates to an aerosol-generating device, comprising such heater assembly and a method of manufacturing the heater assembly. 
     DESCRIPTION OF THE RELATED ART 
     In conventional electrically driven aerosol-generating devices such as e-cigarettes, an electrical heater is used to vaporize an aerosol-generating liquid, also called e-liquid. The e-liquid typically consists about 65 Vol.-% of propylene glycol, about 30 Vol.-% of glycerol, about 2 Vol.-% of water, about 2 Vol.-% of flavourants and about 1 vol.-% of nicotine. In conventional e-cigarettes the heater is operated in a temperature range between 250 and 300 degree Celsius. This temperature is high enough to volatize all constituents of the e-liquid. When a user draws at the e-cigarette an airstream is arranged to flow over the heater assembly and the generated aerosol inhaled by the user. Typically e-cigarettes comprise a puff detection system, which activates the heater and, thus, vaporization only during the puff. Between puffs, the heater element is switched off and no aerosol is generated. 
     One problem of conventional aerosol-generating systems concerns leakage of the e-liquid from the e-liquid reservoir within the aerosol-generating system. Leakage can be caused by malfunction of corresponding components, in particular malfunction of the e-liquid container. Another reason for leakage is deformation of components of the aerosol-generating system during use. Such deformation can be caused from mechanical stress exerted upon the aerosol-generating system. Deformation may also be caused by increased temperatures occurring within the aerosol-generating system. In particular conventional aerosol-generating systems, wherein heater elements are employed that locally generate temperatures of up to 300 degree Celsius, are prone to deformation of individual components due to high temperature effects. 
     SUMMARY 
     One or more of the problems of conventional aerosol heater can be alleviated by the heater assembly of the invention. 
     The heater assembly for aerosol-generating system of the present invention, comprises a heater element, a reservoir comprising aerosol-generating liquid, and a condenser. The condenser condenses excess vapours generated during use of the heater assembly, and is formed in such a way that the condensate is at least partially conveyed back into the reservoir. Preferably, the condenser is formed in such a way that at least 10% or at least 20%, or at least 50% or at least 80% by weight of the condensate is conveyed back in the reservoir. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be further described, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  shows a heater assembly according to an embodiment of the invention; 
         FIG. 2  shows individual components of the heater assembly as used in an e-cigarette; 
         FIG. 3  shows the changing procedure for exchanging the liquid reservoir in an e-cigarette with a two-part housing; 
         FIG. 4  shows an embodiment an e-cigarette wherein the condenser is used as secondary heater; and 
         FIG. 5  shows an alternative embodiment of an e-cigarette comprising a secondary heater. 
     
    
    
     DETAILED DESCRIPTION 
     Preferably the heater element is operated at temperatures in the range of between 80 and 240° Celsius, preferably between 120 and 200° Celsius, more preferably between 150 and 180° Celsius. The optimum temperature depends on the design of the aerosol-generating system and particularly on the exact composition of the e-liquid used. The operating temperatures are preferably lower than typically used operating temperatures of about 250 to 300 degree Celsius. The system is therefore subjected to less thermal stress in operation and therefore the risk of leakage caused by thermal deformation of components of the aerosol-generating system is reduced. 
     In contrast to typical aerosol-generating system, the heater assembly of the present invention is typically operated at such low temperatures that a continuous operation of the heater element is possible. In order to avoid that excess vapours generated between puffs are wasted, a condenser is provided which is used to condense these excess vapours, and conveys the condensed vapours back to the heater element or the e-liquid reservoir. 
     In order to increase its efficiency, in particular in order to facilitate return of the condensate to the reservoir, the condenser is preferably placed in direct vicinity to the aerosol generating liquid and in particular to the liquid-vapour interphase. The condenser is preferably placed in direct vicinity to the heater element. By direct vicinity it is meant a distance of less than 1 cm, preferably less than 5 mm, preferably less than 2 mm. 
     The condenser is preferably made from a non-porous, non-absorbing material. Further preferably the condenser is made from polymeric, metallic, or ceramic material. Most preferably the condenser is made from a material such that it has a non-wetting surface for the condensate. 
     In a preferred embodiment the condenser is located downstream from the heater element, has a conical shape and a hole at the apex. The hole in the apex preferably defines the only downstream passage for the aerosol out of the aerosol formation chamber. Preferably the condenser is oriented such that the apex point away from the heater element. Due to the conical shape of the condenser, the condensate preferably flows in radial outward direction and, when placed in the housing of an aerosol-generating system along the side surfaces of the housing of the aerosol-generating system towards the liquid reservoir. The peripheral shape of the condenser preferably corresponds to the cross-sectional shape of the housing of the aerosol-generating system in which the heater assembly is employed. Typically the peripheral shape of the condenser is therefore circular, oval, or quadratic with or without rounded edges. 
     The reservoir preferably comprises a porous material in which the aerosol generating liquid is absorbed. The porous material may be any porous material used in conventional e-cigarettes. Suitable materials include woven or non-woven material such as polyethylene or polypropylene fibers or thermal resistant polyethylene/polybutylene terephthalatefibers. Examples of suitable materials are a sponge or foam material, ceramic- or graphite-based materials in the form of fibres or sintered powders, foamed metal or plastics material, a fibrous material, for example made of spun or extruded fibres, such as cellulose acetate, polyester, or bonded polyolefin, polyethylene, terylene or polypropylene fibres, nylon fibres or ceramic. The material may have any suitable capillarity and porosity so as to be used with different liquid physical properties. The liquid has physical properties, including but not limited to viscosity, surface tension, density, thermal conductivity, boiling point and vapour pressure, which allow the liquid to be stored by the porous material of the reservoir. 
     Preferably the reservoir is resting on a support. The support may ensure that the reservoir is held at well-defined position within the heater assembly. The support may have a solid plane surface or may have the form of a mesh. In the latter form, air can flow through the support and through the reservoir supported thereon. 
     The reservoir can have any suitable shape and preferably has a shape and size that corresponds to the dimensions of the aerosol generating system in which the heater assembly is to be used. Preferably the reservoir is a cylindrical pad of HRM material. The thickness of the reservoir preferably ranges between 0.1 and 5 millimeters, preferably between 0.2 and 3 millimeters and preferably of about 2 millimeters. The reservoir preferably has a capacity of 5 milligramm to 1 gramm, preferably of 50 to 500 milligramm and most preferably of about 200 milligramm. 
     The reservoir preferably only holds liquid for about 20 puffs and has to be replaced thereafter. The reservoir therefore has to be replaced regularly after the aerosol-generating liquid has been consumed. Due to the reduced size and reduced storage capability of the reservoir the heater assembly comprises only a limited amount of liquid. Thus, even if leakage would occur, only a small amount of liquid is present that could leak. 
     The heater element preferably is a resistive heater, having a resistance between 0.1 and 10 Ohms, between 0.4 and 5 Ohms, more preferably between 0.8 and 2 Ohms, and most preferably of about 1.5 Ohms. The heater assembly preferably has a flat heater surface and a large heating surface. Further preferably the heater element may be a flat heating coil and more preferably the heater element is a flat etched stainless steel heater. An advantage of the flat shape of the heater is that the reservoir can be sandwiched between the generally flat surface of the support and the flat surface of the heater element, such that the heater element is in intimate contact with the reservoir providing ideal vaporization conditions. 
     In use of the heater assembly, the heater element may be placed in any suitable place in the vicinity of the reservoir. The heater element may be placed around the reservoir, between the reservoir and the condenser or opposite the condenser. Preferably, the heater element is placed between the reservoir and the condenser. The condenser may be situated downstream from the heater element. 
     The aerosol-generating liquid preferably comprises nicotine, having a boiling point of about 247 degree Celsius. The aerosol-generating liquid preferably comprises from 0.1% to 10% by weight, preferably from 0.2% to 5%, preferably from 0.5% to 2% by weight of nicotine. 
     The aerosol-generating liquid preferably comprises compounds having a vapour pressure at 200° Celsius comparable to the vapour pressure at 200° Celsius of nicotine. 
     The aerosol-generating liquid may comprise from 20% to 60%, preferably from 30% to 50%, by weight of compounds having a vapour pressure at 200° Celsius being at least 20%, preferably at least 50% of the vapour pressure of nicotine at 200° Celsius. 
     The aerosol-generating liquid preferably comprises compounds having a vapour pressure at 200° Celsius lower to the vapour pressure at 200° Celsius of nicotine. 
     The aerosol-generating liquid may comprise from 40% to 80% by weight, preferably from 50% to 70% by weight, of compounds having a vapour pressure at 200° Celsius being less than 50%, preferably less than 30% of the vapour pressure of nicotine at 200° Celsius. 
     The aerosol-generating liquid may comprise glycerol. Glycerol has a boiling point of about 290 degree Celsius. The aerosol-generating liquid may comprise from 20% to 80% or from 50% to 70% by weight of glycerol. 
     The aerosol-generating liquid may comprise water, preferably from 5% to 20% by weight of water, for example from 8% to 15% by weight of water. 
     The aerosol-generating liquid may comprise propylene glycol, preferably from 5% to 50% by weight of propylene glycol, for example from 10% to 40% by weight of propylene glycol. 
     The aerosol-generating liquid may comprise flavour, preferably from 0.1% to 5% by weight of flavour, for example from 0.5% to 3% by weight of flavour. 
     By varying the operating temperature and the concentration of nicotine, the vaporization performance can be adjusted such that the nicotine content of the generated aerosol corresponds to the nicotine content of conventional cigarettes or to a lower nicotine content 
     A further advantage of the heater assembly being operated in a continuous mode is that puff detection is not required in order to activate the heater during a puff. Accordingly the heater assembly and in particular aerosol generating systems employing this heater assembly is easier to manufacture and easier to use than conventional systems. 
     The present invention also relates to an aerosol generating system, preferably an e-cigarette, comprising the above discussed heater assembly. The aerosol-generating system has a housing that preferably comprises at least two connectable parts. The first part comprises a mouthpiece, the condenser and the heater element. The second part comprises a power source, control circuitry and the support for the reservoir. For assembly of the aerosol generating system a reservoir comprising the e-liquid is placed on the support of the second part. By attaching the first part to the second part the reservoir is tightly squeezed between the support and the heater element. Further, an electrical contact is established between the two parts such that the power source and the control circuitry of the second part is connected to the heater element of the first part. Attachment between the two parts of the housing can be established by any suitable attachment means including screw connection or clamp connection. This configuration of the two-part housing has the advantage that change of the reservoir is very simple. Such simple changeability is particularly important in the present case, since the reservoir only comprises a rather small amount of e-liquid and has thus to be changed very often. 
     The housing of the aerosol-generating system comprises an air inlet and an air outlet, typically the mouthpiece, between which an air flow path is defined. The air flow path leads through the aerosol-formation chamber, comprising the heater assembly. Blocking means are provided in the air flow path, in order to prevent air flow between puffs, i.e. when the user is not inhaling from the aerosol-generating system. The blocking means can be provided upstream, downstream or upstream and downstream from the aerosol formation chamber. The blocking means can be mechanical blocking means or air valves. Preferably the blocking means are electrically controlled via the electric circuitry. A puff detector may be used as a sensor for detecting whether a puff is drawn or not. Puff detectors are readily familiar to the skilled artisan. 
     The present invention is also directed to a method of manufacturing a heater assembly for an aerosol-generating system. The method comprises providing a heater element and a reservoir comprising aerosol-generating liquid, wherein in use of the aerosol-generating system the reservoir is located in direct contact with the heater element. The method further comprises providing a condenser, for condensing excess vapours generated during use of the heater assembly, wherein the condenser is formed in such a way that the condensate is at least partially conveyed back onto the heater or into the reservoir. 
     In a further aspect of the invention, the condenser is a secondary heater element. The secondary heater element is activated only during a puff. Between puffs the secondary heater assembly acts as condenser and excess vapours generated by the continuously operated first heater element are condensed at the secondary heater. When a user draws a puff the secondary heater element is activated such that the condensed vapours adhering to the secondary heater element are vaporized. 
     In a further aspect of the invention the heater assembly comprises a housing with two openings at opposite sides of the housing. The housing comprises porous material holding liquid aerosol generating substrate. A primary fluid permeable heater is provided at the first opening of the housing and is connected to an exhaust flow portion within the aerosol generating system. The first heater is continuously operated and continuously evaporated e-liquid that is exhausted from the system via the exhaust flow portion. The second opening is provided with a secondary heater which is only activated during puffs. The second opening is connected to the air flow path between an air inlet in the housing and the mouthpiece. When a user draws a puff the aerosol generated by the secondary heater is inhaled by the consumer. 
       FIG. 1  shows the heater assembly of the present invention, comprising a support  10 , a reservoir  12  for the e-liquid, a heater element  14  and a condenser  16 . The reservoir  12  is placed on the support  10  and is sandwiched between the support  10  and the heater element  14 . In peripheral areas of the support two feedthroughs  18  for the electrical contact portions  15  of the heater element  14  are provided. The heater element  14  is a flat etched stainless steel heater having a generally planar surface. The reservoir  12  is a generally cylindrical porous polymer disc made from thermo-resistant PET polymer. The thickness of the reservoir is about 2 millimeters. The reservoir  12  can store up to 250 milligramms of e-liquid. The e-liquid may have a composition of glycerol 50%, Propylene glycol 37%, nicotine 2%, water 10%, flavours 1% and the operating temperature of the heater element is 130 to 150 degree Celsius. The e-liquid may have a composition of glycerol 70%, Propylene glycol 14%, nicotine 2%, water 13%, flavours 1% and the operating temperature of the heater element is 150 to 200 degree Celsius. 
     In  FIG. 2  an e-cigarette with a two-part housing comprising the heater assembly of  FIG. 1  is depicted. For the sake of clarity only the second part of the housing  20  comprising a power source (not shown), electric circuitry (not shown) and an air inlet (not shown) is depicted. On the top side of the part  20 , electric contacts  22  for contacting the power source to the heater element  14  and air flow slit  24  are provided. Support  10  is placed on top of part  20 , such that the feedthroughs  18  of the support  10  coincide with the electric contacts  22  of part  20 . The support  10  also comprises slits  26  such that air can flow therethrough. 
     On the support  10  reservoir  12  is placed. The reservoir is laterally surrounded by a circular element  30  that ensures radial localization of the reservoir  12 . The circular element also has feedthroughs  32  for electric contacts  15  of the heater element. The outer dimensions of the circular element  30  correspond to the outer dimensions of the support  12 . The circular element  30  has a thickness such that its top edge lies in the same plane as the upper surface of the reservoir  12 . Heater element  14  is placed on top of the reservoir  12  and its electric contact portions  15  are inserted into the feedthroughs and connected to the below contacts  22  and via these contacts to the power source located in the second part  20  of the housing. Above the heater element  14  a cylindrical element  34  forming the side walls of the aerosol formation chamber  36 . A condenser  16  forming the top wall of the aerosol formation chamber  36  is placed above cylindrical element  34 . The condenser  16  has a conical shape with the conical apex pointing away from the heater element  14 . At the apex of the conical condenser  16  a hole  38  is provided through which aerosol may leave the aerosol formation chamber  36 . During a puff an air stream is created through the aerosol formation chamber and aerosol is inhaled by the consumer through the mouthpiece of the e-cigarette. The heater assembly is operated in continuous mode such that also between puffs e-liquid is vaporized. A large part of these excess vapors is condensed at the interior surface of the condenser. Due to the conical shape of the condenser the condensate flows along the side walls of the aerosol formation chamber and returns to the heater element and the surface of the reservoir in direct vicinity of the heater element. 
     In  FIG. 3  the e-cigarette of  FIG. 2  including the first part  40  of the two-part housing is depicted. The first part  40  includes a mouthpiece portion  42 . At its lower end  44  the first part  40  of the housing comprises the condenser  16 , the cylindrical element  34  the heater element  14  and the circular element  30  (not visible in  FIG. 3 ). The heater element  14  is preferably replaceable such that upon a defect of the heater element  14 , only the heater element  14  itself and not the complete first part  40  of the housing needs to be renewed. In order to insert or replace the reservoir  12  the two parts  20 ,  40  of the two-part housing are disconnected. The reservoir  12  is replaced or inserted on the support  10  and the two parts  20 ,  40  are reconnected again. In the embodiment shown in  FIG. 3 , the two parts  20 ,  40  of the housing are connected by a clamping connection. 
       FIG. 4  shows a further embodiment of the invention. The reservoir is a cylindrical container  50  comprising e-liquid absorbed in a porous material  52 , and comprising an opening  54  at the lower end. A primary heater  56  is provided in the opening  54  of the container  50 . The condenser is a secondary heater element  58 . The secondary heater element  58  is activated only during a puff. Between puffs the secondary heater assembly  58  acts as condenser and excess vapours generated by the continuously operated primary heater element  56  are condensed at the secondary heater  58 . An air flow channel  62  is defined between air inlets  60  and an outlet  64  of the aerosol forming chamber. Control circuitry  66  and a power supply  68  are provided for controlling and powering the heater elements  56 ,  58 . When a user draws a puff the secondary heater element  58  is activated such that the condensed vapours adhering to the secondary heater element  58  are vaporized. 
     In  FIG. 5  another embodiment of the invention is depicted. The heater assembly comprises a housing  70  with two openings  72 ,  74  at opposite sides of the housing  70 . The housing  70  comprises porous liquid absorbing material for holding liquid aerosol generating substrate. A primary fluid permeable heater  76  is provided at the first opening  72  of the housing  70  and is connected to an exhaust flow portion  78  within the aerosol generating system. The primary heater  76  is continuously operated and continuously evaporated e-liquid that is exhausted from the system via the exhaust flow portion  78 . The second opening  74  is provided with a secondary heater  80  which is only activated during puffs. The second opening  47  is connected to the air flow path  84  between an air inlet  82  and a mouthpiece. When a user draws a puff the aerosol generated by the secondary heater  80  is inhaled by the consumer.