Patent Publication Number: US-8985015-B2

Title: Screen-printing squeegee and apparatus for screen printing

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention relates to a screen-printing squeegee having an elastic application element and a holding apparatus for the application element, the holding apparatus being divided, as viewed over the width of the application element, into a plurality of holding sections which can move with respect to one another. The invention also relates to an apparatus for screen printing having a screen-printing squeegee according to the invention. 
     The international laid-open specification WO 2005/035250 A1 has disclosed a screen-printing squeegee having an elastic application element in the form of a plate-shaped squeegee rubber. The plate-shaped squeegee rubber is provided with a holding apparatus, wherein impression cylinders which are also connected to a squeegee carrier act on the holding apparatus. For printing, the elastic application element is pressed by means of the impression cylinders in the direction of a printing screen and a printing table and is then moved by means of a movement of the squeegee carrier, parallel to the printing table, over the latter and/or the printing material. The division of the holding apparatus into a plurality of holding sections which can move with respect to one another is provided for the purpose of achieving a certain flexibility of the screen-printing squeegee. In order to print curved surfaces, the squeegee rubber itself is cut in accordance with the contour of the article to be printed. 
     The invention is intended to specify an improved screen-printing squeegee and an improved apparatus for screen printing which can be used in a flexible way for printing curved surfaces. 
     To this end, according to the invention, a screen-printing squeegee having an elastic application element and a holding apparatus for the application element is provided, the holding apparatus being divided, as viewed over the width of the application element, into a plurality of holding sections which can move with respect to one another, in which a leaf-spring element is provided interconnecting the holding sections which can move with respect to one another. 
     As a result of the provision of the leaf-spring element, the screen-printing squeegee is comparatively flexible in the plane of the application element, that is to say perpendicularly with respect to the provided printing direction, since, in this direction, the leaf spring makes a movement of the individual holding sections with respect to one another possible to a comparatively great extent. In contrast, the screen-printing squeegee is of substantially more rigid configuration in and counter to the printing direction, since the leaf-spring element makes only a very limited movement of the individual holding sections with respect to one another possible in this direction. The screen-printing squeegee is therefore of very rigid configuration in and counter to the printing direction, with the result that a precise print is made possible. As a result, curved surfaces can be printed by way of the screen-printing squeegee according to the invention, the flexible and resilient configuration of the screen-printing squeegee in the plane of the application element, that is to say perpendicularly with respect to the printing direction, making it possible to also adapt to changing curvatures and to ensure a uniform profile of the pressing force of the application element on the printing screen and the article to be printed. 
     The screen-printing squeegee according to the invention is also suitable for printing three-dimensionally curved surfaces, for example glass panes of bowl-like configuration for motor vehicles. The leaf-spring element is configured and arranged in such a way that a spring travel of the individual holding sections is made possible parallel to the plane of the application element, that is to say perpendicularly with respect to the provided printing direction, and a movement of the holding sections with respect to one another in and counter to the printing direction is largely suppressed. The spring action of the leaf-spring element ensures at the same time that an excessive movement of the holding sections with respect to one another is prevented and a continuous, uniform profile of the lower edge of the squeegee element is always ensured, said lower edge being decisive for the printing operation. 
     In one development of the invention, the leaf-spring element has a leaf spring which is contiguous, extends at least over the length of the squeegee, and from which fastening flanges extend to the individual holding sections. 
     By means of a contiguous leaf spring which has only one spring leaf in the embodiment which is shown, firstly the desired spring action parallel to the plane of the application element, that is to say perpendicularly with respect to the printing direction, and secondly the desired stiffening of the squeegee perpendicularly with respect to the plane of the application element, that is to say in and counter to the printing direction, can be achieved. The provision of fastening flanges makes the unproblematic arrangement of the leaf spring on the holding apparatus or the individual holding sections possible. In each case one leaf-spring element with holding flanges is advantageously provided in front of and behind the application element, as viewed in the printing direction. In this way, the leaf-spring elements themselves can be of smaller and lighter configuration, since the spring action and the stiffening of the squeegee are achieved by means of the two leaf-spring elements which are arranged in front of and behind the application element. 
     In one development of the invention, the leaf spring is formed from sheet-metal material and has a width which is greater than a thickness of the leaf spring, the leaf spring being oriented in such a way that the width dimension is arranged parallel to the printing direction and the thickness dimension is arranged perpendicularly with respect to the printing direction and with respect to the printing table. 
     An arrangement of this type of the leaf spring achieves a situation where a spring movement is possible substantially only perpendicularly with respect to the printing direction and with respect to the printing table, whereas a movement of the individual holding sections with respect to one another in and counter to the printing direction is largely suppressed. 
     In one development of the invention, the fastening flanges are configured integrally with the web. 
     In this way, a structurally simple design is achieved and the leaf-spring element can be mounted and dismantled in its entirety in a simple way. 
     In one development of the invention, the leaf-spring element is configured as a sheet-metal part and the fastening flanges are bent away starting from the web. 
     For example, the leaf-spring element can be configured in a simple way from spring steel and can be laser cut out, for example. In this case, the leaf spring consists merely of one spring leaf. 
     The problem on which the invention is based is also solved by an apparatus for screen printing having a screen-printing squeegee according to the invention, in which apparatus a plurality, in particular each, of the holding sections of the screen-printing squeegee are/is assigned an impression cylinder, the impression cylinders being connected firstly to the holding sections and secondly to a squeegee bar which can be moved in and counter to the printing direction, it being possible to set a pressure which loads the impression cylinders separately for at least some of the impression cylinders. 
     In this way, a different pressure can be set at the impression cylinders, as viewed over the width of the screen-printing squeegee, and a different contact pressure can be set in this way, as viewed over the width of the squeegee. This is of great importance if, when printing curved surfaces, a sufficient contact pressure is to be ensured even in the curvature regions. 
     In a screen-printing apparatus according to the invention, the impression cylinders are fastened firstly to in each case one holding section and secondly to a squeegee bar, the impression cylinders being arranged on the squeegee bar and/or on the holding sections such that they can be pivoted in each case about a pivot axis which is arranged substantially parallel to the printing direction. 
     In this way, the impression cylinders can be set in such a way that a force which is exerted on the application element by the impression cylinders acts substantially always perpendicularly with respect to the surface to be printed. The pivoting of the impression cylinders can take place during a setting operation, and the impression cylinders can be fixed in relation to the pivot axes after the setting operation. As an alternative, it can also be provided that the impression cylinders can also pivot about the pivot axes during the printing operation, for example when the curvature of the article to be printed changes as viewed in the printing direction. 
     In one development of the invention, a pivot axis is arranged approximately halfway up the squeegee bar. 
     In this way, a stable and geometrically favourable arrangement can be realized. 
     In one development of the invention, the pivot axis lies immediately above or in the region of the upper edge of the application element. 
     In this way, a perpendicular introduction of force, which is uniform and substantially perpendicular with respect to the pressing edge of the application element, is possible from the impression cylinders into the holding sections or the application element. 
     Further features and advantages of the invention result from the claims and the following description of preferred embodiments of the invention in conjunction with the drawings. Individual features which are shown in the different drawings and are described using the exemplary embodiments can be combined with one another in any desired way, without departing from the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an illustration of a screen-printing squeegee according to the invention in the partially mounted state, 
         FIG. 2  shows an enlarged illustration of a section of the screen-printing squeegee from  FIG. 1 , 
         FIG. 3  shows a partial illustration of a screen-printing apparatus according to the invention, and 
         FIG. 4  shows a section of the screen-printing apparatus from  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The illustration of  FIG. 1  shows a screen-printing squeegee  10  which has an elastic application element  12  and a holding apparatus  14  for the application element  12 . The application element  12  is configured in the form of a material strip which is elastic and of rectangular cross section. The holding apparatus  14  has a plurality of clip-like holding sections  16 , a total of nineteen holding sections  16  being provided as viewed over the width of the application element  12 . A printing direction is denoted by means of an arrow  18 . During a printing operation, the application element  12  is therefore moved over a printing screen in the printing direction  18  and, as a result, presses ink which is situated on the printing screen through openings in the printing screen onto a printing material which is arranged underneath the printing screen, for example a curved motor-vehicle pane. The width of the application element  12  lies perpendicularly with respect to the printing direction  18  and parallel to a printing table (not shown), and the length of the application element  12  lies parallel to the printing direction  18 . The application element  12  therefore has a width which is substantially greater than its length. 
     The holding sections  16  are in each case of clip-like configuration and engage over an upper edge of the elastic application element  12 . However, the individual holding sections  16  are configured as holding clips which are separate from one another, with the result that the individual holding sections  16  can be moved relative to one another. 
     The holding sections  16  are connected both on a front side of the screen-printing squeegee  10  and on a rear side of the screen-printing squeegee  10  to in each case one leaf-spring element  20 ,  22 . The leaf-spring elements  20 ,  22  are connected to the holding clips of the holding sections  16  above the application element  12 . 
     The two leaf-spring elements  20 ,  21  are configured in each case integrally as a sheet-metal flexible part and in each case have a leaf spring  24 ,  26  and a plurality of fastening flanges  28 ,  30  which are bent away from the leaf spring  24 . Each of the holding sections  16  is assigned in each case one fastening flange  28 ,  30 , and the fastening flanges  28  are fastened in each case by means of two threaded bolts  32  to the holding sections  16  which are configured as holding clips. 
     As can be seen in  FIG. 1 , a width of the leaf spring  24  is greater than a thickness of the leaf spring  24 . Here, the thickness direction runs perpendicularly with respect to the printing direction  18  and with respect to a printing table (not shown), and the width direction runs parallel to the printing direction  18 . The leaf spring  24  is therefore configured in the form of a single spring leaf and makes a spring movement possible substantially only perpendicularly with respect to the printing direction  18  and perpendicularly with respect to a printing table (not shown), that is to say in the thickness direction of the spring leaf in  FIG. 1  and therefore from bottom to top and vice versa. In and counter to the printing direction  18 , the leaf spring is substantially stiffer on account of its considerably greater width in comparison with the thickness, and therefore largely prevents a movement of the individual holding sections  16  in and counter to the printing direction  18 . The width of the leaf spring  24  is approximately from five to ten times greater than the thickness of the leaf spring  24 , it being possible for the ratio of width to thickness and the spring stiffness of the leaf spring to be adapted to the provided application. A plurality of spring leaves can also optionally be provided which are of different length, in order to achieve the desired spring action. 
     During a printing operation, the individual holding sections  16  can therefore move relative to one another perpendicularly with respect to the printing direction  18  and perpendicularly with respect to the printing table, and in this way the elastic application element  12  can be deformed in such a way that its pressing edge  34  runs in a curved manner thus adapting itself to the contour of an article to be printed. Nevertheless, yielding of the application element  12  and specifically of the pressing edge in and counter to the printing direction  18  is largely avoided, since a movement of the individual holding sections among one another in and counter to the printing direction  18  is largely prevented by the two leaf springs  24 ,  26 . 
     The screen-printing squeegee according to the invention is therefore very flexible perpendicularly with respect to the printing direction  18  and perpendicularly with respect to the printing table and can adapt itself to curvatures of an article to be printed. In contrast, the screen-printing squeegee  10  is very stiff in and counter to the printing direction and, as a result, makes a very precise printing operation possible. 
     In the illustration of  FIG. 2 , an enlarged illustration of a section of the screen-printing squeegee  10  can be seen. Merely two of the holding sections  16  are shown completely and two further holding sections  16  are shown partially. As has already been explained using  FIG. 1 , the holding sections  16  are configured in each case as holding clips and engage around the upper edge of the elastic application element  12 . The limbs of the said holding clips can be moved towards one another for a clamping operation, in order to clamp the elastic application element  12  reliably. 
     The leaf-spring element  20  has the leaf spring  24 , starting from which the fastening flanges  28  extend. The fastening flanges  28  are then fastened in each case to the limbs of the holding clips of the holding sections  16 , the fastening of the fastening flanges  28  taking place by means of the threaded bolts  32  to the holding sections  16  above an upper edge of the elastic application element  12 . In contrast, the leaf spring  24  is arranged approximately halfway up the application element  12  and approximately at the level of the free end of the limbs of the holding clips of the holding sections  16 . 
     The holding sections  16  are profiled in the form of holding grooves at their upper end which faces away from the application element  12 , with the result that they can be clamped into clamping jaws  56  of a squeegee receptacle, see  FIG. 4 . 
     The illustration of  FIG. 3  shows a screen-printing apparatus  40  according to the invention with a screen-printing squeegee  10  according to the invention, from the front, that is to say counter to the printing direction  18  in  FIG. 1 . The leaf-spring element of the screen-printing squeegee  10  is of slightly different configuration than in the embodiment of  FIG. 1 , but the illustration of  FIG. 3  serves substantially to clarify the construction of the screen-printing apparatus  40  according to the invention. 
     Each of the holding sections  16  is assigned in each case one impression cylinder  42 ,  48 . The impression cylinders  42 ,  48  are arranged firstly on the holding sections  16  and secondly on receiving elements  44 , the receiving elements  44  being arranged displaceably on a squeegee bar  46 . 
     As can be seen in the illustration of  FIG. 3 , the impression cylinders  42  are deflected partially out of their perpendicular position with respect to the squeegee bar  46 . With the exception of the two central impression cylinders  48 , the impression cylinders  42  are arranged such that they can be pivoted about a respective pivot axis  52 ,  54  both relative to the application element  12  on the squeegee bar  46  and relative to the holding sections  16 . The pivot axes  52 ,  54  all run parallel to the printing direction  18 , that is to say perpendicularly with respect to the plane of the drawing in  FIG. 3 . As can be seen in  FIG. 3 , an introduction of force can take place by means of the impression cylinders  42 , as a result, over the entire width of the screen-printing squeegee  10 , approximately perpendicularly with respect to its pressing edge  34  which, during a printing operation, rests on a printing screen (not shown) which in turn rests on a printing material to be printed (not shown) which in turn lies on a printing table  50 . It can be seen in the region of the left-hand and right-hand end of the screen-printing squeegee  10  that the introduction of pressure does not take place exactly perpendicularly with respect to the pressing edge  34 . An improvement is possible here as a result of the fact that the position of the pivot axis  52  is moved further in the direction of the pressing edge  34 . The pivot axis  52 , with which the impression cylinders  42  are arranged pivotably on the holding sections  16 , is advantageously arranged in the region of the upper edge of the elastic application element  12  or even below the upper edge of the application element  12 . 
     The squeegee angle can be set in a manner which is not shown, that is to say an angle between the application element  12  and the surface to be printed. This is realized by a curved slotted guide on the squeegee receptacle between the pivot axis  52  and the clamping jaws  56 . 
     The illustration of  FIG. 4  shows one of the impression cylinders  42 , the screen-printing squeegee  10  not being shown in  FIG. 4 . It can be seen that a pivot axis  52 , about which the impression cylinder  42  can be pivoted relative to the receiving element  44 , is arranged halfway up the squeegee bar  46 . The receiving element  44  is provided with two clamping screws and can be displaced along the squeegee bar  46 . The movement about the pivot axis  54  and about the pivot axis  52  can be blocked, with the result that, in a setting operation, the impression cylinders  42  are pivoted about the pivot axes  52 ,  54  and are then blocked. As an alternative, the pivoting of the impression cylinders  42  about the pivot axes  52 ,  54  can be made possible even during a printing operation, in order to make an adaptation of the screen-printing squeegee  10  possible to changing curvatures of the article  50  to be printed. This is advantageous, for example, when the article  50  to be printed is a bowl-like car pane, the curvature of which perpendicularly with respect to the printing direction and also in and counter to the printing direction changes over its length. 
     A squeegee receptacle with clamping jaws  56  and with a clamping screw is provided at the lower end of the impression cylinder  42 , in each case the holding sections  16  (see  FIG. 1  and  FIG. 2 ) then being clamped by way of the clamping jaws  56 . As a result, the screen-printing squeegee  10  is configured such that it can be mounted and dismantled in a simple way. 
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.