Screen printing machine with improved device for aspirating excess ink

Abstract: A screen printing machine with an improved device for aspirating excess ink, comprising a printing bed (11) for supporting a glass plate (12) to be printed, which is provided in an upward region with a frame (13) with a mesh surface (15) forming a permeable portion. Ink is placed on the frame. The machine has a doctor unit (16) comprising a doctor and a complementary doctor whose dimensions are equal to the width of the frame and which are adapted to move along the frame from one end to the other in order to respectively distribute and collect the ink. The machine further comprises a suction unit (23) provided with a suction nozzle (27) and means for guiding the nozzle along a preset path. The suction nozzle moves on the mesh surface (15) so as to follow the path traced by a perimetric edge of the glass plate (12) in order to aspirate the excess ink.

Description: The present invention relates to a screen printing machine with an improved device for aspirating excess ink. The screen-printing method is currently widely used to reproduce images, words, drawings or figures and the like on paper, glass plates, plastic backings or fabrics etcetera. In particular, this printing method, when used to apply images to glass plates, uses a mesh frame which is arranged above a fixed supporting surface and whereon minute through openings are formed, which, as a whole, form the image to be printed. The mesh frame is spread with ink (which can be black or colored); the ink can pass only through the openings, thus reaching the item to be printed and fixing thereon so as to form the image. This printing method is usually used mainly on windshields and on rear and side windows of motor vehicles. All these components must in fact be screen-printed with borders at their perimetric edges. The borders are aesthetically indispensable because they conceal the region where each component is assembled in its respective seat. Currently it is in fact customary to assemble, for example, windshields by arranging them in the complementarily shaped seat of the structure of the vehicle by means of adhesives, without having to first insert therein special weather stripping inside which the seat for the windshield used to be formed. Currently, therefore, the border of the windshield and of all the other glass parts must conceal the underlying coupling region and accordingly must be printed with maximum precision and accuracy. Unfortunately, screen-printing machines are unable to work according to the printing process known in the field as "edge to edge" without producing excess ink on the edge of the glass plate. This excess produces deposits (ink drops) which are not allowed on the edge of the windshield because they dirty the glass. Machines are currently available which have a mechanical ink scraping device that acts on the mesh frame from below. This device, however, after a certain number of production cycles, inevitably produces an application of ink on the printing region which causes smudges and shadows. Other screen-printing machines are commercially available which have scraping devices which operate in combination with pads, for example rolls of paper, by means of which an attempt is made to delete shadows and smudges without however achieving their full elimination. Finally, there are at present machines which are provided with an aspirator with a suction nozzle which acts on the upper part of the mesh frame, i.e., on the part on which the ink is spread. Such a machine is disclosed in document EP-A-642923. The aspirator is capable of aspirating ink and any residues thereof on all of the exposed region of the frame by means of the suction nozzle, whose dimensions are at least equal to the width of the frame and which is actuated by a mechanical device which makes it shift along all of the frame. This last machine, however, is unable to perfectly aspirate only the excess ink on the edge; most of all, it produces uneven image definition on the glass plate. These machines are in fact designed and built to work in a continuous cycle and to print one glass plate after the other. The aspirator instead aspirates ink on the frame and in a short time dries the ink between the openings of the frame, making it difficult for new ink to pass through to print a subsequent glass plate. Accordingly, constant cleaning of the frame is necessary to clear the openings formed in the frame from the clogging produced by the dried ink. The aim of the present invention is to provide a screen printing machine which eliminates the above-mentioned conventional drawbacks. Within the scope of this aim, an object of the present invention is to provide a screen printing machine which allows to print images onto a glass plate up to the edge without smudges and most of all without leaking excess ink. Another object of the present invention is to provide a screen printing machine which has a simple constructive structure. Another object of the present invention is to provide a machine which operates according to an effective and practical process. Another object of the present invention is to provide a screen printing machine which can work without requiring the intervention of specialized personnel. Another object of the present invention is to provide a screen printing machine which requires neither particular maintenance nor frequent cleaning of the frame. Another object of the present invention is to provide a screen printing machine which can produce prints having excellent ink uniformity characteristics. This aim, these objects and others which will become apparent hereinafter are achieved by a screen printing machine comprising a printing bed for supporting a glass plate to be printed which is provided in an upward region with a frame with a mesh surface, which forms a permeable portion and above which ink can be placed, a doctor unit which comprises a doctor and a complementary doctor whose dimensions are equal to the width of said frame and which are suitable to move along said frame from one end to the other in order to respectively distribute and collect said ink, a suction unit provided with a suction nozzle and means guiding said nozzle along a preset path, said nozzle moving on said frame so as to follow said path which is traced by a perimetric edge of said glass plate, in order to aspirate excess ink. Further characteristics and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment thereof, illustrated only by way of non-limitative example in the accompanying drawings, wherein: Figure 1 is a perspective view of a screen printing machine with a suction unit according to the present invention; Figure 2 is a side view of a detail of a screen printing machine with a suction unit according to the invention; Figure 3 is a top view of a screen printing machine with a suction unit according to the invention; Figures 4, 5 and 6 are side views of the screen printing machine with a suction unit according to the invention in three successive steps of its operation. With reference to the above figures, a screen printing machine according to the invention is generally designated by the reference numeral 10 and comprises a printing bed 11 above which a glass plate 12 to be screen printed is arranged. A frame 13 is superimposed on the printing bed 11 and is supported by a border 14 which provides the supporting structure for a mesh surface 15. The mesh surface 15 forms a printing image by means of an ink-permeable portion which in this case is formed at its perimetric edge. The border 14 is meant to support a doctor unit 16 constituted by a first framework 17 which can slide longitudinally along the entire frame 13 from one end to the opposite end and viceversa. The doctor unit 16 is actuated, in a per se known manner, by a first drive (not shown in the above figures) along a track 18 formed on the border 14 of the frame 13. The first framework 17 is constituted by a first bridge 19 and by a second bridge 20 which is parallel to the first one. These bridges respectively support a doctor 21 and a complementary doctor 22 of the per se known type which are adapted to respectively distribute and collect the ink on the mesh surface 15 of the frame 13. The machine 10 further comprises, in particular, a suction unit 23 which is constituted by an aspirator 24 which is connected, by means of a flexible hose 25, to an ink collection tank 26 and is provided with a suction nozzle 27 through which it draws ink in order to convey it into the collection tank 26. The suction unit 23 is supported by a second framework 28 which is operated automatically by a second drive, not shown in the figures, which is fully independent of said first drive and is suitable to make the second framework 28 also move along the track 18. The second framework 28, in particular, comprises a bridge 29, along which a slider 30 can slide, and is parallel to the first framework 17. The second framework 28 constitutes the supporting skeleton for the duct 25 of the suction unit 23. In particular, the suction nozzle 27, which is fixed to the slider 30 which can slide along the bridge 29, is arranged at right angles to the printing bed 11 and can be arranged itself in contact with the mesh surface 15, with a lifting and lowering movement, at the perimetric edge of the glass plate 12. In this manner, the suction nozzle 27 can, when lowered, aspirate the excess ink from the mesh surface 15; otherwise said excess ink, by passing through the permeable portion of the mesh surface 15, would reach the glass plate 12 and would drip along its edge so as to form deposits constituted by one or more drops. The doctor unit 16 is actuated automatically and fully independently of the suction unit 23. The screen printing process that can be performed with a machine 10 according to the invention consists first of all in arranging the glass plate 12 on the printing bed 11 and in centering its position with respect to the print image formed by the permeable portion of the mesh surface 15 of the frame 13. In order to perfectly print the glass plate 12 to its edge, since the edge is rounded, the print image formed on the mesh surface 15 by the ink-permeable portion is larger than the dimensions of the glass plate 12 and accordingly the frame 13 and the plate 12 must be conveniently centered with respect to each other. The doctor unit 16 is then arranged at a first end 31 of the frame 13, so that the suction unit 23 is arranged between the doctor unit 16 and the border 14 of said first end 31. The operating process continues with the application of ink above the mesh surface 15; this is usually performed manually by an operator. Immediately thereafter, the doctor unit 16 actuates the doctor 21 so that the doctor moves down until it makes contact with the mesh surface 15; at the same time, the doctor unit 16 moves parallel to the printing bed 11, moving along the track 18 from the first end 31 to the second end 32 of the frame 13, in the direction indicated by the arrow 33. While the doctor 21 distributes the ink so that by passing through the mesh surface 15 only in the permeable region it prints the intended image on the glass plate 12, the suction unit 23 moves starting from the point 34, which is on the longitudinal centerline 35 of the frame 12, and moves, while the suction nozzle 27 is conveniently lowered, along the curve that corresponds to the perimetric edge of a first half 36 of said glass plate 12 with respect to the centerline 35, so as to aspirate only the excess ink which would otherwise produce deposits. Accordingly, when the doctor 21, in its right-to-left motion in the direction of the arrow 33, has reached the second end 32 of the frame 13, the suction nozzle 27 has correspondingly reached the point 37 of said second end 32 on the centerline 35. The suction nozzle 27 is capable of accurately following, on the mesh surface 15, the path that corresponds to the edge of the glass plate 12 by means of its combined movement along the two perpendicular axes and up and down, ensured by the slider 30, which is slideable on the bridge 29, and by the movement of said bridge 29 along the track 18. Once this operating step has been reached, the doctor 21 moves upward while the complementary doctor 22 moves downward until contact with the mesh surface 15 is achieved. Then the doctor unit 16 and the suction unit 23 start to move and while the suction unit, preceding the doctor unit in its left-to-right translatory motion, moves along the profile that corresponds to the edge of the second half 38 of the glass plate 12, so as to aspirate the excess ink from the mesh surface 15, the complementary doctor 22 collects all the ink. At this point, the complementary doctor 22 moves upward, the printed glass plate 12 can be replaced in the printing bed 11 with a new glass plate to be printed, and the machine 10, which has returned to the initial position, is ready to screen-print the new glass plate 12. No downtimes are present with the above-described process and the doctor unit 16 and the suction unit 23 work independently but are mutually synchronized. The machine 10 according to the invention is particularly suitable for continuous screen printing processes. In practice, it has been observed that the present invention fully achieves the aim and all the intended objects. An important advantage is achieved with the present invention in that a screen printing machine has been provided which allows to produce screen printing on glass up to the edge without imperfections and smudges and without forming deposits of excess ink. Another important advantage of the present invention is that a screen printing machine has been provided which has a simple structure and ensures effective and practical operation. Another advantage of the present invention is that the machine requires neither specialized personnel for its use nor any particular labor. Another advantage is achieved with the present invention in that a screen printing machine has been provided which requires no frame cleaning operations. Another advantage is achieved with the present invention in that a screen printing machine has been provided which achieves excellent printing uniformity. Another important advantage is ensured with the present invention in that a screen printing machine has been achieved which produces images printed with edges which are outlined with extreme precision and accuracy. The present invention is susceptible of numerous modifications and variations, all of which are within the scope of the same inventive concept. All the details may also be replaced with other technically equivalent elements. The materials employed, as well as the dimensions, may be any according to requirements. The disclosures in Italian Patent Application No. PD97A000191 from which this application claims priority are incorporated herein by reference. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims: A screen printing machine (10) comprising a printing bed (11) for supporting a glass plate (12) to be printed which is provided in an upward region with a frame (13) with a mesh surface (15), forming a permeable portion and above which ink can be placed, a doctor unit (16) which comprises a doctor and a complementary doctor whose dimensions are equal to the width of said frame and which are suitable to move along said frame from one end to the other in order to respectively distribute and collect said ink, and a suction unit (23) provided with a suction nozzle (27) characterized in that it comprises means guiding said nozzle along a preset path such that said nozzle moves on said frame so as to follow said path which is traced by a perimetric edge of said glass plate, in order to aspirate the excess ink. The screen printing machine according to claim 1, characterized in that said suction unit (23) comprises an aspirator (24) and a collection tank (26) which are connected by means of a flexible hose (25) to said suction nozzle. The screen printing machine according to claim 2, characterized in that said suction unit is actuated by a drive which is independent of said doctor unit. The screen printing machine according to claim 3, characterized in that said suction unit (23) is supported by a bridge-like framework (28) which can slide on guides along said frame from one end to the other parallel to said doctor unit. The screen printing machine according to claim 4, characterized in that said bridge-like framework (28) has a slider (30) which is slideable on it and with which said suction nozzle (27) is arranged in a position which is perpendicular to said mesh surface (15) and can be moved along said perpendicular position for lifting and lowering the nozzle until contact with said mesh surface occurs.

Inventors: DI PRISCO ALDO, MAZZOCCHI BENEDETTO, DI PRISCO, ALDO, MAZZOCCHI, BENEDETTO
Applicants: IANUA S P A, IANUA S.P.A
Application year: 1998
Main classification: B41F15
IPC codes: B41F17, H05K3, B41F35, B41F15