Patent Publication Number: US-11385573-B1

Title: End caps and films

Description:
BACKGROUND 
     Liquid electrophotographic (LEP) printing uses a special kind of printing fluid to form images on paper and other print substrates. LEP printing fluid usually includes charged polymer particles dispersed in a carrier liquid. The polymer particles are sometimes referred to as toner particles and, accordingly, LEP printing fluid is sometimes called liquid toner. LEP printing fluid may also include a charge control agent to help control the magnitude and polarity of charge on the particles. An LEP printing process involves placing an electrostatic pattern of the desired printed image on a photoconductor and developing the image by presenting a thin layer of LEP printing fluid to the charged photoconductor. The printing fluid may be presented to the photoconductor with a roller that is commonly referred to as a “developer roller.” Charged toner particles in the printing fluid adhere to the pattern of the desired image on the photoconductor. The printing fluid image is transferred from the photoconductor to a print substrate, for example through a heated intermediate transfer member that evaporates much of the carrier liquid to dry the printing fluid film, and then to the print substrate as it passes through a nip between the intermediate transfer member and a pressure roller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-B  illustrate an example end cap. 
         FIGS. 2A-B  illustrate another example end cap. 
         FIGS. 3A-C  illustrate an example developer unit. 
         FIG. 4  illustrates an example method. 
         FIG. 5  illustrates another example method. 
         FIG. 6  illustrates a further example method. 
         FIG. 7  illustrates yet another example method. 
     
    
    
     DETAILED DESCRIPTION 
     In liquid electrophotographic printing, a thin film of LEP printing fluid is applied to the exterior of a developer roller and then presented to a photoconductor at a nip between the developer roller and the photoconductor. A squeegee roller rotates against the developer roller to squeegee excess carrier liquid from the printing fluid film before the printing fluid is presented to the photoconductor. A cleaner roller rotates against the developer roller to remove residual printing fluid after printing fluid has been transferred to the photoconductor. The ends of each roller are sealed between end caps of a developer unit to help prevent printing fluid leaking away from the rollers. A developer unit comprises the end caps, the rollers and electrodes. The electrodes causes charged particles in the LEP printing fluid to adhere to the developer roller by electrostatically applying a thin layer of printing fluid to the surface of the developer roller along the electrodes as the developer roller is rotating. A voltage difference between the developer roller and the electrodes causes the charged particles in the LEP printing fluid to adhere to the developer roller. While the end caps can be attached to each other to form an enclosure of the developer unit, the developer unit can comprise a housing or tray as a transition piece supporting the end caps. During operation of the LEP printer, the developer unit contains printing fluid. The end caps have an inner surface facing the inside of the developer unit, the inner surface being exposed to the printing fluid during operation of the developer unit. Components of the printing fluid may accumulate onto such inner surface, sometimes leading to a build-up of solid components of the printing fluid. Such an accumulation can have an impact on the composition of the printing fluid, for example when a significant quantity of such accumulated solid components gets suddenly released from the inner surface into the developer unit, potentially leading to printing color instability. Preventing such accumulation reduces the risk of clumps of printing fluid solids falling off and potentially clogging a drain. Such an accumulation may also render cleaning of an end cap difficult, for example when such an end cap should be recycled. Avoiding or limiting such accumulation and facilitating cleaning of an end cap forms the foundation of the present disclosure. This is obtained as described in the present disclosure by applying a film, for example a film comprising both a pressure sensitive adhesive layer and a low surface energy layer, such film reducing accumulation of printing fluid components due to the low surface energy layer, and such film being peelable from the end cap due to the pressure sensitive adhesive layer, leading to easing the cleaning and recycling of end caps equipped with the film. 
       FIG. 1A  illustrates an example end cap system  100  for a developer unit in a LEP printer. An end cap should be understood as a mechanical piece for supporting the ends of shafts of rollers. An end cap may comprise a support surface supporting the end of shafts of the rollers, and end cap sides projecting from the support surface along a direction of the roller axis. In some examples, the end caps are made of a plastic material. In some examples, the end caps comprise cavities, sockets or through holes permitting supporting the shaft ends of the rollers. 
     The end cap system  100  comprises an end cap  110  and a film  120 . A film should be understood as a thin, flexible, planar structure. In some examples, the film has a thickness of less than 0.5 mm, of less than 0.2 mm, of less than 0.1 mm or of less than 0.09 mm. In some examples, the film has a thickness of more than 0.05 mm, of more than 0.06 mm, or of more than 0.07 mm. 
       FIG. 1B  illustrates the system  100  illustrated in  FIG. 1A , seen along the plane V illustrated in  FIG. 1A .  FIG. 1B  is at a different scale from  FIG. 1A  for purposes of clarity. The thickness of film  120  as illustrated in  FIG. 1B  was increased compared to the thickness of end cap  110  for the purpose of clarifying the illustration. The film  120  comprises a first outermost superficial layer  122  and a second outermost superficial layer  124  opposed to the first outermost superficial layer. A superficial layer should be understood as a layer of the film which extends itself across the film along dimensions normal to a direction of thickness of the film. Such extension may take place across the entire film, or across a portion of the entire film. An outermost superficial layer should be understood as a superficial layer which defines a superficial end of the film and is not covered by an additional layer of the film. In some examples, the first and second outermost superficial layers face each other. In some examples, the first and second outermost superficial layers both extend across the entire film. In some examples, one or both of the first and second outermost superficial layers extend across a portion of the entire film, in some examples across a different portion of the entire film. 
     The first outermost superficial layer is a pressure sensitive adhesive layer applied to a portion of an inner surface of the end cap. The inner surface of the end cap should be understood as the surface of the end cap oriented towards the inside of the developer unit. In some examples, such inner surface of the end cap is generally concave in order to contribute to containment of the printing fluid within the developer unit. Part or all of the inner surface of the end cap may be exposed to printing fluid when the LEP printer is operating. The pressure sensitive adhesive layer is applied to a portion of an inner surface of the end cap. Being applied should be understood in that the pressure sensitive adhesive layer is directly in contact with the portion of the inner surface of the end cap. The portion of the inner surface of the end cap may be a genus zero surface, i.e. a surface without a hole. The portion of the inner surface may be a genus non-zero surface, i.e. a surface comprising a hole or a plurality of holes, for example to accommodate components of the developer unit such as a roller shaft end, a printing fluid inlet, a printing fluid outlet, an alignment feature, a connector or a sensor, in which cases the film may comprises a cutout. In some examples, cutouts are provided which permit utilizing a same film with different endcaps having different features, configurations or components. The portion of the inner surface may comprise a single area of the inner surface, in which case the film comprises a single film section. The portion of the inner surface may comprise different separate areas of the inner surface, in which case the film comprises more than one film section. The configuration of the portion of the inner surface to which the pressure sensitive layer is applied may be configured and adapted to maintain the functionality of the end cap during operation of the printer, for example by ensuring that some areas of the inner surface of the end cap remain uncovered by the film, for example to permit rotation of a roller, to permit passage of printing fluid, of data, of power or of mechanical connections or to permit sealing a seal directly against the inner surface of the end cap. In some examples, the configuration of the portion of the inner surface to which the pressure sensitive layer is applied may be configured and adapted to focus on specific areas more likely to be exposed to printing fluid accumulation over time. In some examples, the inner surface of the portion of the end cap to which the pressure sensitive layer is applied corresponds to at least 10% of an entire inner surface of the end cap, in some examples at least 30%, in some examples at least 50%, in some examples at least 70% of an entire inner surface of the respective end cap. In some examples, the inner surface of the end cap comprises an intricate edge, for example an edge corresponding to an acute angle between sides projecting from the support surface, whereby the intricate edge is uncovered by the film in order to avoid difficulty when adhering the film or when removing the film, in particular by avoiding film breakoff during removal. 
     A pressure sensitive adhesive layer should be understood as a layer which adheres to the inner surface of the end cap while being peelable from such inner surface. In some examples, the pressure sensitive adhesive layer has a peel strength of 100 gf/25 mm or more at room temperature, at a peel rate of 5 mm/sec and a peel angle of 180 degrees. The pressure sensitive adhesive layer may comprise an acrylic polymer having a weight average molecular weight (Mw) of between 400,000 and 2,500,000. The weight average molecular weight is a conversion value to standard polystyrene that is measured by gel permeation chromatography (GPC). The pressure sensitive adhesive layer may include an epoxy acrylate, or a polyester acrylate, or a polyether acrylate. The pressure sensitive adhesive layer may comprise an epoxy-functional acrylic polymer. 
     The second outermost superficial layer is a low surface energy layer to be exposed to liquid photographic printing fluid during printing. A low surface energy layer should be understood as a layer which renders bonding difficult. In some examples, a low surface energy layer has a surface energy below 0.036 N/m. Example low surface energy layers may include polyolefin plastics such as polypropylene and polyethylene as well as “non-stick” surfaces such as polytetrafluorethylene (PTFE) or fluorinated polyurethane polymers. The low surface energy layer may include a polyol composition comprising a hydroxyl terminated polyester and/or a hydroxyl terminated polyether and a hydroxyl terminated polysiloxane. In some examples, the low surface energy layer comprises a silicone polymer. In some examples, the silicone polymer is the cross-linked product of a silicone oil and a cross-linker component. In some examples, the silicone polymer is the cross-linked product of a silicone oil, a cross-linker component and a cross-linking catalyst. In some examples, the silicone polymer is a polysiloxane that has been cross-linked using an addition cure process such that it contains Si—X—Si bonds, where X is an alkylene moiety. In some examples, the silicone polymer comprises the cross-linked addition cured product of: at least one silicone oil having alkene groups linked to the silicone chain of the silicone oil; a cross-linker comprising a silicone hydride component; and, in some examples, an addition cure cross-linking catalyst. In some examples, the silicone polymer comprises the cross-linked condensation cured product of at least one silicone oil, a condensation cure cross-linker component, and a condensation cure cross-linking catalyst. In some examples, the silicone polymer comprises the UV or IR radiation cross-linked cured product of at least one silicone oil, a photo cross-linker, and a photo-initiator. In some examples, the silicone polymer comprises the activated cross-linked cured product of at least one silicone oil, a cross-linker comprising a peroxide component, and an activated cure cross-linking catalyst. The low surface energy layer may comprise a silicone polyurethane polymer. 
       FIG. 2A  represents illustrates another example end cap system  200  for a developer unit in a LEP printer.  FIG. 2B  represents a view of the system  200  taken along the plane W illustrated in  FIG. 2A . 
     The end cap system  200  comprises an end cap  210  and a film  220 . The scales and proportions are adapted to render visible different layers of the film  220  in  FIG. 2B . In this example, the film  220  comprises a substrate layer  226  between the first outermost superficial layer  222  and the second outermost superficial layer  224  opposed to the first outermost superficial layer. 
     In this example film  220 , the substrate layer comprises a polyethylene terephthalate polymer, the low surface energy layer comprises a silicone polymer, and the pressure sensitive adhesive layer comprises an epoxy-functional acrylic polymer. This example film structure was found suitable for use for example in combination with and resistant to a printing fluid comprising carrier liquid including aliphatic hydrocarbons, isoparaffinic compounds, paraffinic compounds, dearomatized hydrocarbon compounds, and the like. In particular, such carrier liquids can include Isopar-G™, Isopar-H™, Isopar-L™, Isopar-M™, Isopar-K™, Isopar-V™ Norpar 12™, Norpar 13 ™, Norpar 15™, Exxol D40™, Exxol D80™, Exxol D100™, Exxol D130™, and Exxol D140™ (each sold by EXXON CORPORATION); Teclen N-16™, Teclen N-20™, Teclen N-22™, Nisseki Naphthesol L™, Nisseki Naphthesol M™, Nisseki Naphthesol H™, #0 Solvent L™, #0 Solvent M™, #0 Solvent H™, Nisseki Isosol 300™, Nisseki Isosol 400™, AF-4™, AF-5™, AF-6™ and AF-7™ (each sold by NIPPON OIL CORPORATION); IP Solvent 1620™ and IP Solvent 2028™ (each sold by IDEMITSU PETROCHEMICAL CO., LTD.); Amsco OMS™ and Amsco 460™ (each sold by AMERICAN MINERAL SPIRITS CORP.); and Electron, Positron, New II, Purogen HF (100% synthetic terpenes) (sold by ECOLINK™). It was indeed found that the composition of film  220  was resistant to such carrier liquids. 
     Film examples may comprise a substrate or substrates between the first and the second outermost layers. A substrate may comprise a single layer, or multiple layers. A substrate may comprise substrate material suitable to be coated on one side by a pressure-sensitive adhesive layer, and on the other side by a low surface energy layer. The substrate layer may comprise a polyethylene terephthalate, a polytetrafluoroethylene, a polyethylene, a polypropylene, a polybutene, a polybutadiene, a vinyl chloride copolymer, a polyurethane, an ethylene-vinyl acetate, an ethylene-propylene copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-methyl acrylate copolymer or a polyimide. The substrate layer may comprise a polyethylene terephthalate polymer. 
     In this example, the film  220  comprises a single film section and cutouts  232  and  234 . In this example cutout  232  is for a printing fluid inlet and cutout  234  is for a specific feature of the end cap, in this case an alignment feature. In this example, the film  220  has two cutouts and thereby corresponds to a genus two surface. In some examples such as this one, the cutout of the film is slightly larger than the feature or element for which the cutout is provided, in order to facilitate placement of the film, by introducing an offset distance whereby the inner surface of the end cap remains without film coverage and directly exposed to printing fluid in an area corresponding to this offset. Such offset distance may for example be of more than 0.5 mm, more than 1 mm, more than 2 mm or more than 3 mm. In this example, the inner surface of the end cap comprises an intricate edge  240 , the intricate edge being in this case contained within an acute angle  242  of less than 45 degree between end cap sides, or end cap side walls,  252  and  254  projecting from end cap support surface  256 . such intricate edge is left uncovered by the film in order to facilitate applying the film. 
     In this example, end cap system  200  comprises a top section comprising sockets  262 ,  264  and  266  which permit lodging and supporting, respectively, a developer roller, a squeegee roller, and a cleaner roller of a developer unit. The top section should be understood as a section which is oriented towards the top when the end cap is in operation, the printing fluid being primarily located in an opposite bottom section by gravity. 
       FIGS. 3A-3C  illustrate an example developer unit  310 , represented schematically in a cross section view as illustrated in  FIG. 3C  taken along a plane parallel to plane Z illustrated in  FIGS. 3A and 3B . Developer unit  310  includes a housing  312  housing a developer roller  314  (the circumference of which is represented in dashed lines), a squeegee roller  316 , a cleaner roller  318 , and a sponge roller  320 . Each end of each roller is in this example associated to respective seals illustrated by a circle concentrical to the respective rollers at the point at which their shaft intersects an end cap. Developer roller  314  is to present a layer of printing fluid to a photoconductor (not illustrated here), the developer roller being rotatable on a shaft. Printing fluid may be pumped to a local supply chamber  326  in developer unit  310  from an external reservoir through an inlet. Also, excess printing fluid may be reclaimed and collected in a local return chamber  332  and returned to reservoir through an outlet  334 . In operation, according to one example, supply chamber  326  is pressurized to force printing fluid up through a channel to the electrically charged developer roller  314 . A thin layer of printing fluid is applied electrically to the surface of the rotating developer roller  314  along electrodes  370 . A voltage difference between developer roller  314  and the electrodes causes charged particles in the printing fluid to adhere to roller  314 . Squeegee roller  316 , to squeegee printing fluid on the developer roller at an upstream nip between the developer roller and the squeegee roller, the squeegee roller being rotatable on a shaft, rotates along developer roller  314  to squeegee excess carrier liquid from the printing fluid on roller  314  while charged particles in the printing fluid continue to adhere developer roller  314 . 
     The now more concentrated printing fluid on developer roller  314  is presented to the photoconductor where some of the printing fluid is transferred in the pattern of a latent electrostatic image on the photoconductor at a nip between roller  314  and the photoconductor, as a desired image. A charged cleaner roller  318 , to clean printing fluid from the developer roller at a downstream nip between the developer roller and the cleaner roller, the cleaner roller being rotatable on a shaft, rotates along developer roller  314  to electrically remove residual printing fluid from roller  314 . In this example, cleaner roller  318  is scrubbed with a so-called “sponge” roller  320  that is rotated against cleaner roller  318 . Some of the printing fluid residue may be absorbed into sponge roller  320  and some may fall away. Excess carrier liquid and printing fluid drains to return chamber  332 , where it can be recycled to a reservoir. 
     Developer unit  310  also includes end caps  352 A,  352 B attached to housing  312  to support each roller  314 - 320  on its respective shaft, for example within supporting sockets such as sockets  262 - 266  as illustrated in the case of end cap  200  of  FIG. 2A . Such end caps are represented attached to housing  312  in  FIG. 3C  to form the developer unit  310 , and represented separately from the housing  312  in  FIGS. 3A and 3B  to illustrate their inner surface exposed to printing fluid during operation. 
     Developer unit  310  also includes seals compressed between each end cap and each end of the squeegee roller, of the cleaner roller and of the developer roller. An example roller sealing system includes seals to help prevent printing fluid from leaking off circular outer surfaces past the ends of the rollers. 
     Developer unit  310  further comprises films  362 ,  364  and  366 , each such film comprising a pressure sensitive adhesive layer applied to a portion of an inner surface of each end cap, the films further comprising a low surface energy layer to be exposed to liquid photographic printing fluid during printing. In this example, the portion of the inner surface of the end caps to which the pressure sensitive adhesive layer is applied is separate from a part of the inner surface of the end caps against which the seals are compressed, such part of the inner surface of the end caps against which the seals are compressed corresponding to a top section of the end caps for supporting the rollers. Such separation between the portion of the inner surface of the end caps to which the pressure sensitive adhesive layer is applied and the part of the inner surface of the end caps against which the seals are compressed permits avoiding that a film interferes with the sealing of the seals directly against the inner surface while benefiting from the effect of films  362 ,  364  and  366  on the areas which they are covering. 
     In the example of developer unit  310 , the housing  312 , to which the end caps are attached, comprises an inner surface  313  of the housing  312 , such inner surface  313  of the housing  312  comprising a sprayed low surface energy additive. Such sprayed low surface energy additive permits avoiding accumulation of printing fluid on such a surface. It was found that combining on one hand a sprayed low surface energy additive on the inner surface of the housing and on the other hand a film according to this disclosure on the inner surface of the end caps resulted in reducing printing fluid accumulation and in facilitating cleaning. The sprayed low surface energy additive may have a composition as hereby described for the low surface energy layers. 
     In the example of developer unit  310 , the developer unit comprises a top section comprising the rollers and a bottom section to collect printing fluid, whereby the portions of the inner surface of each end cap to which the films are applied correspond to the bottom section, which is more prone to printing fluid accumulation than the top section, due to the effect of gravity. 
     In the example of developer unit  310 , the developer unit comprises electrodes  370 , the films comprising a film section  364  located between the electrodes, such film section permitting avoiding printing fluid accumulation during operation, cleaning of end caps in this specific intricate area, and recycling of end caps. In this examples, the developer unit comprises two end caps, one end cap comprising a single film  366 , the other end cap comprising a pair of films  362  and  364 , the pair of films comprising a first film  364  surrounded by the electrodes, and a second film  362  surrounding the electrodes, thereby permitting obtaining the desired effect of the films without impacting the effect of the electrodes. 
     In the example of developer unit  310 , the films  362 ,  364  and  366  may each have a structure and composition as, for example, any of the films hereby described, including film  220  or film  120 . 
       FIG. 4  illustrates an example method  400  for recycling a used developer unit, such as, for example, developer unit  310 , of a liquid photographic printer; the method  400  comprising, in block  402 , peeling a first soiled film off a portion of an inner surface of a first end cap of the developer unit, the first soiled film being soiled with printing fluid. Such peeling is facilitated for example by employing a film comprising a pressure sensitive adhesive layer as hereby described, revealing a clean inner surface which was protected from soiling by the film as the film is peeled off the inner surface. 
       FIG. 5  illustrates an example method  500  comprising block  402  as described in the context of  FIG. 4 , as well as block  504  of applying a first clean film onto the portion of the inner surface of the first end cap in response to having peeled the first soiled film off as per block  402 . This permits preparing such first end cap for being protected in view of being reused. 
       FIG. 6  illustrates an example method  600  comprising block  402  as described in the context of  FIG. 4 , block  504  as described in the context of  FIG. 5 , as well as block  606  of peeling a second soiled film off a portion of an inner surface of a second end cap of the developer unit, the second soiled film being soiled with printing fluid. It should be noted that block  606  may take place prior to, concurrently to or following any of blocks  402  and  504 . 
       FIG. 7  illustrates an example method  700  comprising block  402  as described in the context of  FIG. 4 , block  504  as described in the context of  FIG. 5 , block  606  as described in the context of  FIG. 6 , as well as block  708  of applying a second clean film onto the portion of the inner surface of the second end cap in response to having peeled the second soiled film off as per block  606 . 
     Such example methods, applicable to example end caps hereby described, permit recycling of end caps and can further permit protecting end caps from printing fluid accumulation during operation.