Abstract:
The invention relates to an improved ink jet pen for an ink jet printer. The pen includes a pen body having raised end walls, a recessed substantially planar portion between the end walls containing two or more printheads and flexible circuits therefor, the flexible circuits being attached to the pen body in the recessed portion between the raised end walls. A polymeric material is disposed between adjacent flexible circuits in the recessed portion having a height sufficient to protect a wiper from damage from exposed edges of the flexible circuits between adjacent printheads during a printhead cleaning operation. The improved pen lends itself to simplified manufacturing processes yet provides enhanced mechanical protection of the wiper and critical electrical structures and enhanced corrosion resistance from ink.

Description:
FIELD OF THE INVENTION 
     The invention relates to ink jet printers and in particular to an improved ink jet pen having a printhead surface adaptable for cleaning and to methods for making ink jet pens. 
     BACKGROUND OF THE INVENTION 
     During the lifespan of an ink jet pen containing one or more printheads, ink mist, dried ink and debris from the print media tend to accumulate on the nozzle plates of the printheads adjacent orifice holes therein. If not removed, the debris may accumulate to the point it blocks or partially blocks ejection of ink from the nozzle holes. Periodically, therefor, it is necessary to remove the debris from adjacent the nozzle holes so that the performance of the pen will not be impaired. Cleaning of the nozzle plates may be conducted using solvents or preferably by passing a flexible wiper across the nozzle plate to loosen and remove ink mist, dried ink and debris such as paper fibers therefrom. A wide variety of wipers and wiper blade designs are used for cleaning ink jet printhead nozzle plates. 
     In order to effectively clean a nozzle plate of a printhead with a wiper device, the pen must have a structure or configuration which lends itself to effective wiping across the nozzle plate or plates of the printheads. A single color ink jet pen contains a single printhead and a flexible circuit connected to a silicon substrate containing heater resistors and control devices for selectively ejecting ink from one or more nozzle holes of the printhead. Typically, the flexible circuit surrounds the nozzle plate or is integrally formed with the nozzle plate and is attached to a printhead carrier structure or pen body in a recessed portion therein. The raised sides of the pen body are often sufficient to protect the wiper from the relatively sharp edges of the flexible circuit as the wiper traverses the nozzle plate during a cleaning operation. 
     As contrasted with a single color ink jet pen, a multi-color pen contains multiple nozzle plates and associated flexible circuits for the printheads thereof. Typically, only the raised portions of the pen body adjacent the outermost edges of the flexible circuits protect the wiper as the blade of the wiper traverses the nozzle plates. It is difficult to adequately protect the wiper from interior edge portions of the flexible circuits remote from the raised portions of the pen body between adjacent nozzle plates because of printhead spacing tolerances. Thus these interior portions of the flexible circuits are often exposed. During a cleaning operation, as the flexible wiper blade traverses across the printhead surface of the pen body, the exposed edges of the flexible circuits can damage and/or cause excessive wear on the wiper. 
     SUMMARY OF THE INVENTION 
     With regard to the foregoing, the invention provides an improved ink jet pen for an ink jet printer. The ink jet pen includes a pen body having raised end walls, a recessed substantially planar portion between the end walls containing two or more printheads and flexible circuits therefor, each flexible circuit having at least one exposed edge. The flexible circuits are attached to the pen body in the recessed portion between the raised end walls and a polymeric thermoplastic material is disposed between adjacent flexible circuits in the recessed portion. The polymeric material has a height sufficient to protect a wiper from damage from the exposed edges of the flexible circuits between adjacent printheads during a printhead cleaning operation. 
     In another aspect the invention provides a method for protecting a wiper of a printhead cleaning station of an ink jet printer from damage from edges of a flexible circuit attached to an ink jet pen body during a printhead cleaning operation. The method includes providing a pen body having raised end walls and a recessed substantially planar portion between the end walls. A thermoplastic adhesive film is applied to the planar portion of the pen body and one or more printheads and one or more flexible circuits therefor are attached to the adhesive film in the recessed portion of the pen body. The one or more flexible circuits have first and second edges. Once attached to the adhesive film, the flexible circuits and film are heated under pressure to a temperature sufficient to cause the adhesive film to flow and encapsulate at least one of the first or second edges of the flexible circuits. The flowed adhesive film is then cooled in the encapsulated state to harden the flowed film and provide the first and second edges in a protected state sufficient to protect the wiper from damage from exposed edges of the flexible circuit during a printhead cleaning operation. 
     In yet another aspect the invention provides an ink jet printer having a printer housing and a printhead cleaning station and including an ink jet pen and ink cartridge containing ink attached to the pen. The pen contains a pen body having raised end walls, a recessed substantially planar portion between the end walls and two or more printheads and flexible circuits therefor, each flexible circuit having at least one exposed edge. The flexible circuits are attached to the pen body in the recessed portion between the raised end walls. A thermoplastic polymeric material is disposed between adjacent flexible circuits in the recessed portion and has a height sufficient to protect a wiper from damage caused by exposed edges of the flexible circuits during a printhead cleaning operation. 
     An advantage of the devices and methods of the invention is that the edges of flexible circuits attached to a multi-color ink jet pen body are protected so as to reduce damage and/or excessive wear to the flexible wiper blade and/or flexible circuit during printhead cleaning operations. Another advantage is that the polymeric material effectively encapsulates the edges of the flexible circuits thereby improving the ink resistance of the flexible circuits. Still another advantage is that the devices and methods enable cost effective manufacturing techniques and eliminate the need for applying individual encapsulant materials to the edges of the flexible circuit. 
     For the purposes of this invention the terminology “exposed edges” means those edges of the flexible circuits which if left unencapsulated provide relative sharp edges which could contact and cause damage or excessive wear to a wiper blade during a printhead cleaning. For the most part, exposed edges include the edges of the flexible circuits between adjacent printheads. The edges of the flexible circuits adjacent the sides of the pen body are somewhat protected by raised end walls on the pen body as described in more detail below and thus may be exposed, partially exposed or unexposed depending on the height of the end walls and the proximity of the edges to end walls. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages of the invention will become apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale, wherein like reference numbers indicate like elements through the several views, and wherein: 
     FIG. 1 is a top plan view of an ink jet pen and pen body containing a single printhead; 
     FIG. 2 is a cross-sectional view of an ink jet pen containing a single printhead and wiper therefor; 
     FIG. 2A is a cross-sectional view of a wiper for cleaning pens according to the invention; 
     FIG. 3 is a plan view of an ink jet pen and pen body containing multiple ink jet printheads according to the invention; 
     FIG. 4 is a cross-sectional view of an ink jet pen body containing multiple ink jet printheads and flexible circuits therefor; 
     FIG. 5 is a cross-sectional view of a multi-color ink jet pen according to the invention; 
     FIG. 6 is a plan view of an adhesive film according to the invention; and 
     FIGS. 7 and 8 are sequential cross-sectional views of a method for protecting a wiper and/or flexible circuits on an ink jet pen according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For the purpose of background and with reference to FIGS. 1 and 2 there is shown the operating surface of an ink jet pen  10  containing a printhead  12  and a flexible circuit  14  attached to the pen body  16  by means of adhesive  17  between raised end walls  18  and  20 . During a printhead cleaning step, a wiper  22  traverses the printhead  12  and flexible circuit  14  in a direction crosswise to the longest dimension of the printhead  12  as generally indicated by arrow  24 . As the blade  23  of the wiper  22  traverses the printhead  12 , debris, dried ink and/or ink mist deposits are swept from the face of the printhead nozzle plate thereby improving printer performance and reducing the build up of deposits on the printhead which could affect the ejection of ink from the printhead. 
     The wiper  22  is preferably made from a polyester-based polyurethane such as a product available from Bayer Corporation-Polymers Division. of Pittsburgh, Pa. under the trade name TEXIN. Suitable polyester-based polyurethane materials preferably have a durometer of approximately 85 Shore A hardness. The wiper  22  may have a generally rectangular shape. A particularly preferred wiper  22  is shown in cross-section in FIG.  2 A and has a flexible body including a mounting portion  25 , a wiper blade  23  containing a wiping portion  27  and a beam portion  29  connecting the blade  23  to the mounting portion  25 . The wiping portion  27  includes an upper substantially planar surface  31  having first and second opposing wiping edges  33  and  35  and first and second opposing side surfaces  37  and  39  opposite the upper surface  31  which diverge at an acute angle from the first and second wiping edges  33  and  35  respectively and intersect the beam portion  29  on opposing sides thereof. Wipers  22  suitable for use with the ink jet pens of the invention are described more fully in U.S. Pat. No. 5,612,722 to Francis et al. issued Mar. 18, 1997, the disclosure of which is incorporated by reference as if fully set forth herein. 
     Other features of a mono or single color pen are shown in cross-sectional view in FIG.  2 . As can be seen, the pen body  16  has a recessed substantially planar portion  26  between raised end walls  18  and  20  to which the flexible circuit  14  and printhead  12  are attached, preferably by an adhesive  17 . The raised end walls  18  and  20  have a height which is substantially equal to or greater than the thickness T of the flexible circuit  14  and adhesive  17  such that the upper surfaces  28  and  30  of end walls  18  and  20 , respectively, are no lower than the planar surface  32  defined by exposed surface of the printhead  12  and flexible circuit  14 . Accordingly, as the wiper  22  traverses the printhead and flexible circuit  14  from end wall  18  to end wall  20  in the direction of arrow  24  and from end wall  20  to end wall  18  in a direction opposite to arrow  24 , the wiper  22  does not engage the edges  33  and  35  of the flexible circuit  14 . Hence, in the single printhead embodiment, there are no exposed edges of the flexible circuit  14  which can cause damage to the wiper  22 . 
     A plan view of a multi-color ink jet pen  40  is illustrated in FIG. 3. A typical multi-color pen  40  contains at least three colors such as cyan, magenta and yellow and preferably contains a black printhead  42  and flexible circuit  44  therefor, a cyan printhead  46  and flexible circuit  48  therefor, a magenta printhead  50  and flexible circuit  52  therefor and a yellow printhead  54  and flexible circuit  56  therefor. The printheads  42 ,  46 ,  50  and  54  which include a semiconductor chip such as chip  55  and flexible circuits  44 ,  48 ,  52  and  56  are attached to a pen body  58  (FIG. 4) between end walls  60  and  62  in chip pockets  64  of the pen body  58 . An adhesive  66  is preferably used to attach the printheads  42 ,  46 ,  50  and  54  to the chip pockets  64  of the pen body  58 . Adhesive  68  is used to attach flexible circuits  44 ,  48 ,  52 , and  56  to the recessed surfaces  70  of the pen body between the individual printheads  42 ,  46 ,  50  and  54  and between printhead  42  and end wall  60  and between printhead  54  and end wall  62 . 
     One or more edges  69 ,  71 ,  72 ,  74 ,  76 ,  78 ,  80  or  82  of flexible circuits  44 ,  48 ,  52  and  56  may be exposed so that upon traversal of a wiper  84  across the surface of the printheads in the direction of arrow  86 , or in a direction opposite arrow  86 , the exposed edges  69 ,  71 ,  72 ,  74 ,  76 ,  78 ,  80  or  82  of the flexible circuits may damage or otherwise excessively wear the wiper  84  or the wiper  84  may urge the flexible circuits  44 ,  48 ,  52  and  56  away from the recessed surface  70  of the pen body. Likewise, the flexible circuits  44 ,  48 ,  52  and  56  may be damaged or worn by the wiper  84  as the wiper  84  traverses across the printheads in the direction of arrow  86 . As shown in FIG. 4, end walls  60  and  62  provide minimal protection to edges  69  and  82  of flexible circuits  44  and  56  respectively. However, even if end walls  60  and  62  protect edges  69  and  82 , exposed edges  71 ,  72 ,  74 ,  76 ,  78  and  80  are still subject to damaging the wiper  84 . Likewise, ink which deposits or accumulates between the printheads may corrode or otherwise attack any exposed metal traces on the flexible circuits thereby causing premature pen failure. 
     Ideally, the body  58  of such a multicolor pen should include recessed portions  70  between raised walls for each of the printheads  42 ,  46 ,  50  and  54  and their corresponding flexible circuits  44 ,  48 ,  52  and  56 . However, as the spacing between adjacent printheads is decreased, it becomes increasingly more difficult to provide raised walls between adjacent flexible circuits without affecting the alignment of the printheads and flexible circuits on the pen body  58  and increasing the overall width of the pen. The present invention enables a reduction in the spacing between the printheads which provides a relatively narrower overall width for the pen and ink cartridge attached thereto. A narrower width enables use of a narrower printer box resulting in significant cost savings due to reduced material costs. 
     An improved ink jet pen  90  according to the invention is illustrated in cross-sectional view in FIG. 5. A pen body  58  contains printheads  42 ,  46 ,  50  and  54  attached to semiconductor chips such as chip  55  and flexible circuits  44 ,  48 ,  52  and  56  therefor. Each of the printheads  42 ,  46 ,  50  and  54  and corresponding chips  55  is attached to the pen body  58  in a chip pocket  64  using an epoxy adhesive  66  and each of the flexible circuits  44 ,  48 ,  52  and  56  is attached to a recessed surface  70  of the pen body  58  by means of a thermoplastic adhesive  92 . The adhesive, as described in more detail below, is caused to flow between adjacent flexible circuits, between flexible circuit  44  and raised end wall  60  and between flexible circuit  56  and raised end wall  62  forming raised portions  94 ,  96 ,  98 ,  100  and  102  which have a height at least equal to or above a plane defined by the exposed surface  104  of the printheads and flexible circuits which is opposite adhesive  92 . 
     As shown in FIG. 5 in comparison to FIG. 4, the raised portions  94 ,  96 ,  98 ,  100  and  102  of the adhesive  92  solidify when cooled and effectively encapsulate the edges of flexible circuits  44 ,  48 ,  52  and  56 , therefore protecting wiper from damage caused by the edges of the flexible circuits during a wiping or cleaning operation. Additional benefits of the encapsulation of the edges of the flexible circuits are that any exposed metal traces on the flexible circuits are protected from corrosion from ink or other materials and there is less tendency for the wiper to urge the flexible circuits away from the recessed surfaces  70  of the pen body  58 . 
     In a preferred fabrication method for an ink jet pen  90  according to the invention, first a nozzle plate is bonded to a semiconductor chip such as chip  55  using well known bonding techniques. The nozzle plate/chip assembly is then bonded to a flexible circuit such as flexible circuit  44 . In a separate step, a thermoplastic adhesive  92  is applied to the recessed portions  70  of the pen body  58 . An epoxy adhesive  66  is dispensed in the chip pockets  64  of the printhead body  58 , the nozzle plate/chip/circuit assemblies are aligned and attached to the printhead body  58  and the epoxy adhesive  66  is cured in an oven. The plate/chip/circuit assemblies may be held in place until the epoxy is cured by use of a UV curable adhesive which is also dispensed in the chip pockets  66 . Finally, the flexible circuits  44 ,  48 ,  52  and  56  are heat staked into the thermoplastic adhesive  92  and heat is applied to the exposed surface of the flexible circuits  44 ,  48 ,  52  and  56  which is sufficient to cause the adhesive  92  to flow and encapsulate the edges of the flexible circuits. 
     In accordance with the invention, a particularly preferred thermoplastic adhesive  92  is in the form of an adhesive film  108  which may be applied to the recessed portions  70  of the pen body  58  before attaching the plate/chip/circuit assemblies to the body  58 . A particularly preferred adhesive film  108  is illustrated in plan view in FIG.  6 . The adhesive film is preferably a flexible polyolefin, non-curing thermoplastic bonding film  108  such as available from Minnesota Mining and Manufacturing Company of Saint Paul, Minn. under the trade name 3M THERMO-BOND 845. Such film  108  has a thickness ranging from about 2.0 to about 5.0 mils and includes a polyolefin based-resin having a softening point in the range of from about 80° to about 150° C. Under heat and pressure of from about 5 to about 60 psig, the film  108  is caused to soften and flow thereby bonding the flexible circuits to the pen body  58 . As the film soften and flows, it also extrudes between the flexible circuits and then solidifies or hardens as it cools to form the raised portions  94 ,  96 ,  98 ,  100  and  102  as shown in FIG.  5 . Such a film is particularly useful for pen bodies  58  which are made of polymeric materials such as NORYL polymer available from General Electric company of New York, N.Y. having a softening point of from about 130° to about 150° C. In the case of pen bodies made of a higher temperature polymer or metal, a higher softening temperature thermoplastic film such as a polyurethane ether, non-curing thermoplastic bond film available from Deerfield Urethane, Inc. of South Deerfield, Mass. under the trade name DEERFIELD PT 9300 having a softening point in the range of from about 150° to about 250° C. under a pressure of about 10 to about 100 psig may be used as film  108 . 
     It is preferred that the film  108  not be tacky at room temperature because the alignment of the chips  55  to the pen body  58  (FIG. 5) is critical to the proper functioning of the ink jet pen. Accordingly, as described above, the nozzle plate/chip/flexible circuit assembly is aligned and placed on the printhead body  58  in the chip pockets  64  and the chip adhesive  66  is cured prior to bonding the flexible circuits  44 ,  48 ,  52  and  58  to the adhesive film  108 . If the film  108  has a tacky surface, the flexible circuits  44 ,  48 ,  52  and  58  would stick to the film and likely cause the plate/chip/flexible circuit assembly to shift out of alignment. 
     In order to enable proper placement of the plate/chip/flexible circuit assembly in the chip pockets  64  of the pen body, it is preferred that the film  108  contain apertures  110 ,  112 ,  114  and  116  corresponding to the printheads  42 ,  46 ,  50  and  54 . If the film  108  were solid and contained no openings or apertures  110 ,  1   12 ,  114  and  116 , the film would have to be cut to insert the plate/chip assemblies therethrough as the plate/chip assemblies are attached in the chip pockets. 
     Reference is now made to FIGS. 7 and 8, which illustrate a sequence for attaching flexible circuits to an ink jet pen body. According to the method, an adhesive film  108  is placed in a recessed area  70  of the ink jet pen body  58  with apertures  110 ,  112 ,  114  and  116  (FIG. 6) aligned with chip pockets  64  in the body  58 , and adhesive  66  is placed in chip pockets  64 . Next the nozzle plate/chip assemblies  118 ,  120 ,  122  and  124  associated flexible circuits  44 ,  48 ,  52  and  56  are aligned so that ink feed ports of the pen body  58  such as feed port  126  are in flow communication with ink vias such as via  128  in the nozzle plate/chip assemblies  118 ,  120 ,  122  and  124 . Once the nozzle plate/chip assemblies  118 ,  120 ,  122  and  124  are placed and aligned in the chip pockets  64 , the adhesive  66  is cured to adhesively bond the nozzle plate/chip assemblies  118 ,  120 ,  122  and  124  to the chip pockets  64 . After curing the nozzle plate/chip assemblies  118 ,  120 ,  122  and  124 , a hot bar  130  is pressed in the direction of arrows  132  against the flexible circuits  44 ,  48 ,  52  and  56  to heat the flexible circuits and adhesive film  108  thereunder and cause the film to soften and flow to fill gaps  134 ,  136  and  138  between flexible circuits  44 ,  48 ,  52  and  56  and to fill gaps  140  and  142  between flexible circuits  44  and  56  and raised end walls  60  and  62  of the pen body  58 . The temperature of the hot bar 130 preferably ranges from about 80° to about 150° C. Too high a temperature may cause damage to the delicate electronic parts and/or pen body  58  while too low a temperature may not be sufficient to cause the thermoplastic adhesive to soften and flow. The pressure applied by the hot bar 130 preferably ranges from about 5 to about 60 psig. 
     As shown in FIG. 7, it is preferred that the hot bar 130 contain recessed areas  144 ,  146 ,  148  and  150  corresponding to nozzle plate/chip assemblies  118 ,  120 ,  122  and  124  so that excessive heat and/or pressure are not applied to the assemblies during the heating and pressure steps. Additional indentations  152 ,  154  and  156  may be provided in the hot bar  130  to enable the adhesive material to encapsulate the entire edge of each of the flexible circuits  44 ,  48 ,  52  and  56  so that the adhesive material has a height which is on the same plane as the flexible circuits or slightly above the surface as shown by protrusions  160 ,  162 ,  164 ,  166  and  168 . Because none of the edges of the flexible circuits  44 ,  48 ,  52  and  56  extend above the protrusions  160 ,  162 ,  164 ,  166  and  168  formed by the extruded film  130  or above raised end walls  60  and  62  (FIG.  8 ), the wiper  84  (FIG. 4) can easily glide over the printheads and nozzle plates without significantly wearing or damaging the flexible circuits or the wiper  84 . 
     Having described various aspects and embodiments of the invention and several advantages thereof, it will be recognized by those of ordinary skills that the invention is susceptible to various modifications, substitutions and revisions within the spirit and scope of the appended claims.