Patent Publication Number: US-10773513-B2

Title: End deflectors for printing blades

Description:
The present invention relates to deflectors for printing blades, typically squeegee blades, in preventing the escape of print medium beyond the lateral ends of printing blades in a printing operation, deflector units comprising such deflectors and printing heads comprising such deflector units. 
     BACKGROUND AND PRIOR ART 
     Various deflectors, sometimes referred to as end deflectors, are available, such as disclosed in GB-A-2512038, US-A-2015/0336377 and U.S. Pat. No. 9,352,409. 
     The present inventor has recognized that existing end deflectors suffer from a number of drawbacks, in causing disruption of the print medium roll at the lateral ends of the printing blade, and also in causing coining of the printing screen, where the end deflectors dig into the printing screen with repeated operation. 
     It is an aim of the present invention to provide improved end deflectors for printing blades, typically squeegee blades, in preventing the escape of print medium beyond the lateral ends of printing blades in a printing operation. 
     It is also an aim to enable simplified deflector switching methods for different print media, such as printing paste and adhesive. 
     It is a yet further aim to provide a deflector which is resistant to damage from paste contamination. 
     SUMMARY OF THE INVENTION 
     In one aspect the present invention provides a deflector unit for use with a printing blade in printing a print medium through a printing screen, the deflector unit comprising: 
     a body which is disposable adjacent a respective one of the ends of a printing blade; 
     a deflector which is movably disposed to the body for a range of travel along a first axis and acts to contain print medium within a lateral extent of the printing blade; and 
     a biasing element which acts to bias the deflector from the body along the first axis; 
     wherein the biasing element is wholly enclosed within the body throughout the range of travel of the deflector. 
     Advantageously, the deflector includes a deflector member, which engages a surface of the printing screen in a printing operation. 
     In another aspect the present invention provides a deflector for use with a printing blade during a printing operation of printing a print medium through a printing screen to contain print medium within a lateral extent of the printing blade, wherein the deflector includes a deflector member, which has a first, engagement surface which engages a surface of the printing screen, a second, inwardly-facing surface which extends from the engagement surface and flares or tapers laterally outwardly in a first direction of printing, and a third, downwardly-facing surface which joins the second surface at a junction which is spaced at a distance from the first surface. 
     Preferably, the first surface extends over a substantially flat plane. 
     The second surface may extend over a substantially flat plane, or alternatively the second surface may be a curved or arcuate surface. 
     The second surface may have a first, rear edge and a second, forward edge, and a chord between the edges which encloses an angle (β) of less than about 45 degrees with the first direction of printing, optionally less than 40 degrees, optionally less than 35 degrees. 
     Preferably, the angle (β) may be greater than 20 degrees, optionally greater than 25 degrees, optionally greater than 30 degrees. 
     The second surface may extend substantially parallel to the first axis, optionally in a substantially vertical direction in use. 
     Preferably, the distance between the first and third surfaces is at least 5 mm. 
     Preferably, the distance between the first and third surfaces is at most 20 mm, optionally at most 15 mm, optionally at most 10 mm. 
     Preferably, the junction of the second and third surfaces encloses an angle of less than 110 degrees, optionally an angle of less than 100 degrees, optionally an angle of about 90 degrees. 
     The third surface may extend over a substantially flat plane. Alternatively, the third surface may be an arcuate or curved surface. 
     In a further aspect the present invention provides a deflector for use with a printing blade in printing a print medium through a printing screen to contain print medium within a lateral extent of the printing blade, wherein the deflector includes a deflector member which includes an elongate projection or recess, which is inclined substantially in parallel relation to the lateral edge of the printing blade and acts to reduce a pressure of the print medium at the junction of the deflector member and the printing blade in use. 
     The present invention also extends to a printing head, comprising: a support to which a printing blade is attachable; and first and second deflector units or deflectors as above described which are disposed adjacent respective ones of the lateral ends of the printing blade. 
     In one embodiment the deflector units are separable from the support. 
     In another embodiment the support and the deflector units are integrally formed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the present invention will now be described hereinbelow by way of example only with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates a perspective view of a printing head in accordance with one embodiment of the present invention; 
         FIG. 2  illustrates a perspective view of one end deflector unit of the printing head of  FIG. 1 ; 
         FIG. 3  illustrates an exploded perspective view of the end deflector unit of  FIG. 2 ; 
         FIG. 4  illustrates a fragmentary part-sectional view (along section I-I in  FIG. 1 ) of the printing head of  FIG. 1 , in a printing operation; and 
         FIG. 5  illustrates a fragmentary part-sectional view (along section II-II in  FIG. 1 ) of the printing head of  FIG. 1 , in a printing operation; 
         FIG. 6  illustrates a printing head in accordance with another embodiment of the present invention; 
         FIG. 7  illustrates a printing head in accordance with a further embodiment of the present invention; 
         FIG. 8  illustrates a modified deflector for the printing heads of  FIGS. 1 and 6 ; and 
         FIG. 9  illustrates another modified deflector for the printing heads of  FIGS. 1 and 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     The printing head comprises a support  3 , which is attached to a screen printing machine (not illustrated), a printing blade  7  which is attached to the support  3 , and first and second end deflector units  9 , which are attached to opposite ends of the support  3  to prevent print medium passing laterally beyond the respective ends of the printing blade  7  during a printing operation. 
     In this embodiment the print medium is a paste, such as a solder paste. 
     In this embodiment the support  3  comprises an elongate member  11  to which the printing blade  7  is attached. 
     In this embodiment the printing blade  7  has a first, lower edge  8  which contacts a printing screen PS in a printing operation, and the printing blade  7  depends downwardly from the support  3  to engage the printing screen PS, with a forwardly-inclined relation so as to create a main roll  15  of print medium, having an effective diameter of approximately d 1 , forwardly of the printing blade  7  in a direction of printing D 1 , at the junction of the printing blade  7  and the printing screen PS. 
     In this embodiment the printing blade  7  comprises a squeegee blade. 
     In this embodiment the end deflector units  9  each comprise a body  21  which is attached to a respective one of the ends of the support  3 , a deflector  23  which is movably disposed to the body  21  for a range of travel along a first, substantially vertical axis X and is disposed adjacent a respective one of the ends of the printing blade  7  so as to contain the print medium within the lateral extent of the printing blade  7 , and a biasing element  25  which acts to bias the deflector  23  in a downward direction D 2  along the first axis X. 
     In this embodiment the biasing element  25  is a compression spring. 
     In this configuration, with the deflector  23  being movably coupled to the support  3 , different pressures, which are applied to the printing blade  7  in various printing operations, can be accommodated, thereby providing that the deflectors  23  are self-adjusting and avoiding coining of the printing screen PS. 
     In this embodiment the body  21  includes a guide channel  27 , here an elongate bore, which receives a counterpart guide member  31  of the deflector  23 , as will be described in more detail hereinbelow. The guide channel  27  comprises two sections, a first, lower section in which the guide member  31  is accommodated, and a second, upper section in which the biasing element  25  is accommodated. The lower section is preferably of non-circular cross-section, which acts to prevent rotation of the guide member  31 , and hence deflector  23 , relative to the body  21 . The upper section is preferably of circular cross-section, for accommodating and allowing compression and extension of the compression spring biasing element  25 . It will be noted that this difference in cross-sections prevents the biasing element  25  from falling out of the body  21  if the deflector  23  is removed therefrom. The two sections are aligned and connected, such that the distal end of the guide member  31 , i.e. that end which extends furthest into guide channel  27 , contacts the biasing element  25  and is thereby biased in a downward direction. In this way the deflector  23  is biased towards the printing screen in use. 
     In this embodiment the biasing element  25  is held captive by a fixing  65 , here a screw fixing, which completely closes the upper section end of guide channel  27 . 
     In this embodiment the body  21  includes a lateral bore  28 , arranged generally orthogonally to the length of the guide channel  27  and in communication therewith, for receiving an engagement member  71 , as will be described in more detail hereinbelow. 
     In this embodiment the deflector  23  includes a deflector member  29  which engages a surface of the printing screen PS in a printing operation, and a guide member  31 , here an elongate shaft, which is counterpart to the guide channel  27  and is slidingly-disposed within the guide channel  27 , such that the deflector  23  is constrained to move along the first axis X in relation to the body  21  along its range of travel. The cross-sectional shape and dimension of the guide member  31  conforms closely to that of the guide channel  27 , which prevents paste or adhesive from entering the guide channel  27 , thus preventing contamination. 
     In this embodiment the deflector member  29  has a first, engagement surface  35  which engages the printing screen PS in a printing operation, and a second, inwardly-facing surface  37  which extends from the engagement surface  35  and flares or tapers laterally outwardly in the direction of printing D 1 . 
     In this embodiment the first surface  35  is a substantially planar surface. 
     In this embodiment the first surface  35  is profiled or textured, in the manner of tyre tracks, which promotes the transfer of any print medium at the first surface  35  laterally inwardly towards the printing blade  7 . 
     In this embodiment the second surface  37  is a substantially planar surface. 
     In another embodiment the second surface  37  could be a curved or arcuate surface. 
     In this embodiment the second surface  37  has a first, rear edge  41  and a second, forward edge  43 , and a chord between the edges  41 ,  43  encloses an angle β of less than 45 degrees with the direction of printing D 1 . 
     In this embodiment the angle β is 32 degrees. 
     In one embodiment the angle β is less than 45 degrees. 
     In another embodiment the angle β is less than 40 degrees. 
     In a further embodiment the angle β is less than 35 degrees. 
     In one embodiment the angle β is at least 20 degrees. 
     In another embodiment the angle β is at least 25 degrees. 
     In a further embodiment the angle β is at least 30 degrees. 
     In this embodiment the second surface  37  extends substantially perpendicular to the contact edge  8  of the printing blade  7 , here substantially parallel to the first axis X, in a substantially-vertical direction. 
     With this configuration, second, subsidiary rolls  47  of the print medium are developed at the respective deflectors  23 , having an effective diameter of approximately d 2 , smaller than diameter d 1 , which act to return the print medium which passes outwardly of the respective ends of the printing blade  7  back into the main roll  15  of print medium with little disturbance to the uniformity of the main roll  15  of print medium. 
     In this embodiment the deflector member  29  includes a third, downwardly-facing surface  51  which joins the second surface  37  at a distance d 3  from the lower surface  35  thereof. 
     In this embodiment the distance d 3  is 8 mm. 
     In one embodiment the distance d 3  is at least 5 mm. 
     In one embodiment the distance d 3  is at most 20 mm. 
     In one embodiment the distance d 3  is at most 15 mm. 
     In one embodiment the distance d 3  is at most 10 mm. 
     In this embodiment the junction of the second and third surfaces  37 ,  51  is a substantially square junction. 
     In this embodiment the junction of the second and third surfaces  37 ,  51  encloses an angle of about 90 degrees. 
     In another embodiment the junction of the second and third surfaces  37 ,  51  encloses an angle of less than 110 degrees. 
     In a further embodiment the junction of the second and third surfaces  37 ,  51  encloses an angle of less than 100 degrees. 
     In this embodiment the third surface  51  extends is a substantially flat surface. 
     In this embodiment the third surface  51  extends in substantially perpendicular relation to the second surface  37 . 
     In an alternative embodiment the third surface  51  could be an arcuate or curved surface. 
     The third surface  51  acts to prevent upward movement of the paste in use. This helps to prevent paste from entering the guide channel  27  at its lower end. Furthermore, the combination of third surface  51  and the angled second surface  37  acts to constrain the paste to create the rolls  47 , having a height approximately equal to d 3 , during the printing operation. This constrains the paste, reducing wastage and simplifying re-use. 
     In this embodiment the guide member  31  includes a recess  55 , here an elongate slot which extends axially along the guide member  31 , which defines first and second limit stops  57 ,  59 . Each body  21  of respective end deflector units  9  further comprises a detent  67 , which extends into the recess  55  in the guide member  31  to define the limit of travel of the deflector  23  along the first axis X by engagement with the limit stops  57 ,  59  of the recess  55 . 
     In this embodiment, the detent  67  is provided by an engagement member  71 , which is disposed in the bore  28  in the body  21 . 
     In this embodiment the engagement member  71  takes the form of a screw, which is threadedly engaged in the bore  28  and completely closes the same. This arrangement allows the position of the detent  67  with respect to the body  21  and recess  55  to be adjusted by rotation of the engagement member  71  within the bore  28 , whereby the detent  67  may be adjusted to provide sufficient engagement with the end stops  57 ,  59  to delimit the travel of the deflector  23  along the first axis X, such that the detent  67  is captively located within the recess  55 . 
     In this embodiment the guide member  31  includes a groove  61  which extends axially along the guide member  31  from the recess  55  to the distal end thereof, that is the end opposite to the deflector member  29 . 
     In this embodiment the groove  61  is a V-shaped groove. 
     By suitable adjustment of detent  67  by rotation of the engagement member  71 , the detent  67  can be drawn out of the recess  55  by manual application by an operator and along the groove  61 , against the frictional resistance with the groove  61 . 
     In this way, the groove  61  allows the deflector  23  to be fitted to and removed from the body  21  without requiring any tools, with the groove  61  being shaped and/or sized to allow an operator manually to overcome the frictional resistance with the detent  67 . With this configuration, an operator can readily change the deflectors  23 , such as for cleaning or replacement. This design also enables different types of deflector to be fitted in a modular fashion, for example to interchange between deflectors more suitable for paste application and deflectors more suitable for adhesive application, or to allow separate deflectors for leaded and lead-free paste. Furthermore, the inclusion of groove  61  on only one side of the guide member  31  prevents the guide member being inserted by an operator into the body  21  in an incorrect orientation. 
     It will be apparent that with the above-described configuration, the biasing element  25  is located internally of, and wholly enclosed within, the body  21 , throughout the deflector&#39;s range of travel, and that paste or adhesive, or indeed any other potential contaminant, is prevented from contaminating the biasing element  25 . In particular, no paste may enter the guide channel  27  at its lower opening due to the close conformance of the first section&#39;s cross-section with the cross-section of the guide member  31  and the barrier effect provided by third surface  51 , no paste may enter the guide channel  27  at its upper opening due to the closure by fixing  65 , and no paste may enter the guide channel  27  via lateral bore  28  due to the closure by engagement member  71 . 
       FIG. 6  illustrates a printing head in accordance with another embodiment of the present invention. 
     The printing head of this embodiment is very similar to that of the above-described embodiment, and thus, in order to avoid unnecessary duplication of description, only the differences will be described in detail, with like parts being designated by like reference signs. 
     The printing head of this embodiment differs from that of the above-described embodiment in that the support  3 , the printing blade  7  and the end deflectors  9  are formed as an integral unit. 
       FIG. 7  illustrates a printing head in accordance with a further embodiment of the present invention. 
     The printing head of this embodiment is quite similar to that of the first-described embodiment, and thus, in order to avoid unnecessary duplication of description, only the differences will be described in detail, with like parts being designated by like reference signs. 
     The printing head of this embodiment differs in that the deflector members  29  omit the second and third surfaces  37 ,  51 . 
     Although the omission of the second and third surfaces  37 ,  51  from the deflector members  29  does not allow for the formation of the subsidiary rolls  47  of the print medium at the lateral ends of the main roll  15  of the print medium, the deflector members  29  still advantageously are self-adjusting, independent of the pressure as applied to the printing blade  7 , thereby preventing coining of the printing screen PS. 
     This embodiment has particular application to print medium in the form of glues and inks. 
     Finally, it will be understood that the present invention has been described in its preferred embodiments and can be modified in many different ways without departing from the invention as defined by the scope of the appended claims. 
     For example, in one embodiment, as illustrated in  FIG. 8 , the deflector member  29  could include a raised, elongate projection  81 , which is inclined substantially in parallel relation to the printing blade  7 , and acts to reduce the pressure of the print medium at the junction of the second surface  37  and the printing blade  7 . This helps to reduce the formation of “snail trails”, i.e. thin trails of paste left in the wake of the printing blade  7  during the printing operation. 
     In this embodiment the projection  81  has the form of a ridge or bead, optionally a rounded ridge or bead. 
     Although illustrated in relation to the deflectors  23  of  FIGS. 1 and 6 , the projection  81  could have equal application to the embodiment of  FIG. 7 . 
     For example, in another embodiment, as illustrated in  FIG. 9 , the deflector  23  could include an inwardly-projecting member  91  at a rear, trailing edge in the direction of printing D 1 , which is located rearwardly of the printing blade  7  and includes a surface  93  which acts to transfer any print medium which remains on the printing screen PS after traversal of the print head  3  laterally inwardly into the printing region of the printing screen PS. This also helps to reduce the formation of “snail trails”. 
     Although illustrated in relation to the deflectors  23  of  FIGS. 1 and 6 , the inwardly-projecting member  91  could have equal application to the embodiment of  FIG. 7 .