Patent Publication Number: US-4545300-A

Title: Screen printing apparatus and process comprising chamber with movable upper surface-squeegee combination

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to printing apparatuses and processes, and more particularly to automated or manual printing by silk screening. It further relates to all types of ink printing presses using squeegee and flood bar mechanisms. 
     Numerous printing apparatuses are known, including those recent ones shown in U.S. Pat. Nos. 4,268,545 and 4,404,903, the contents of which are hereby incorporated by reference in their entirety. Basically they show a support frame positionable on top of a screen frame. Means attached to the support frame deposit ink on the screen and then force it through the screen pattern onto an underlying substrate. Solvents can be sprayed on the ink to keep it at its proper consistency and to keep it from drying out. However, these harmful solvents and other chemicals are thereby released into the environment endangering the health of the operator and others standing nearby. Another problem associated with prior screen printing apparatus is that the ink rapidly dries on the screen and the whole process must be shut down so that the screen can be cleaned. 
     OBJECTS OF THE INVENTION 
     Accordingly, it is the principal object of the present invention to provide an improved apparatus and process for screen printing. 
     Another object of the present invention is to provide an improved screen printing apparatus that works on all types of presses, manual or automated, and with all types of inks. 
     A further object of the present invention is to provide a novel screen printing apparatus that reduces the contamination of the atmosphere by harmful solvents and chemicals. 
     A still further object of the present invention is to provide an improved screen printing apparatus that exposes the operator thereof to considerably smaller amounts of harmful solvents. 
     Another object is to provide an improved screen printing apparatus that keeps the ink at its proper consistency for longer periods of time and also keeps it from drying out. 
     A further object is to provide a novel screen printing apparatus that reduces the frequency of the down time needed to clean the dried ink from the screen thereby increasing the productivity of the screen printing process. 
     A still further object is to provide an improved screen printing apparatus that is able to print finer details and half tones with a solvent base ink system than previously was possible. 
     Other objects and advantages of the present invention will become more apparent to those persons having ordinary skill in the art to which the present invention pertains from the foregoing description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a screen printing apparatus embodying the present invention. 
     FIG. 2 is a top plan view of the apparatus of FIG. 1 without the track and carriage system and having parts thereof broken away for the sake of clarity. 
     FIG. 3 is a cross-sectional view, partially broken away, taken along line 3--3 of FIG. 2. 
     FIG. 4 is an enlarged partial cross-sectional view taken along line 4--4 of FIG. 2. 
     FIG. 5 is an enlarged perspective view of the screen sealing means of the apparatus of FIG. 3 illustrated in isolation. 
     FIG. 6 is an enlarged top plan view of a portion of the connection and attachment mechanism for the plastic sheets of FIG. 2 with the parts thereof shown in exploded relation. 
     FIG. 7 is a side elevational view of the mechanism of FIG. 6. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a screen printing apparatus embodying the present invention is illustrated. It comprises generally a support frame 12 to which all of the components of the apparatus are attached, a silk screen frame 14 positioned underneath support frame 12 and supporting a silk screen having the desired pattern thereon, and a press bed or substrate 16 which comprises a level surface on which the stock to be imprinted is placed and on which screen frame 14 rests. Press bed 16 supports a generally horizontal, U-shaped carriage track 18 suspended above the length of support frame 12. A printing head carriage 20 holding the squeegee 22 and flood bar 24 moves in carriage track 18 along the length of support frame 12. Squeegee 22 and flood bar 24 are positioned in a sealed chamber as shown generally at 26 in FIG. 3, and first coat the silk screen 27 with a coating of ink and then sequentially force the ink through the screen onto the substrate. Sealed chamber 26 provides a controlled environment for depositing the ink and for spraying the solvents, thereby being a safer and more productive screen printing apparatus than previously possible. 
     Support frame 12 is made from aluminum U-channel, as shown in FIG. 5, cut and welded to size. Attached to squeegee 22 and flood bar 24 is a plastic flexible sheet 28 which extends generally the entire width and length of the support frame. The sheet is attached to squeegee 22 the flood bar 24 and moves with it along the length of the frame. A pair of opposed shaft or rod assemblies 30, 32 mounted at their ends in bearings 34, 36, respectively, which are bolted to the underneath of the top surface of support frame 12 and the sheet is designed to roll over each of the shaft assemblies, as best illustrated in FIG. 3. Tension springs 38, 40 are positioned in each of the shaft assemblies keeping the sheet in a constant rolled up and taut position as it moves relative to support frame 12. Front and back seals shown generally at 42 and 44 extending the width of support frame 12 are mounted to the lower surface of the frame inside of their respective rod assemblies. Referring to FIGS. 3 and 5, it is seen that front and back seals 42, 44 each comprise a curved U-shaped extruded plastic member bolted to the lower surface of the frame and extending upwardly. The seals extend upward against the taut sheet, apply pressure against the sheet and thereby form a seal. Along the edges of the sheet, side seals 46, 48 are provided extending generally the length of frame 12 between front and back seals 42, 44. Side seals 46, 48 comprise extruded plastic members formed with a thin space going down their center and are configured so that the edges of the plastic sheet travel freely within the thin space but are sealed therein. Thus, sealed chamber 26 is defined in part by plastic sheet on the top 28, the side seals 46, 48 along the sides and the front and back seals 42, 44 along the ends over the silk screen. 
     Into chamber 26 inert gas, such as CO 2  or nitrogen, is pumped through a line 50, replacing the oxygen in the chamber and preventing the ink from drying out. Further, suitable solvents can be sprayed into the chamber via line 52 shown in FIG. 2. The solvent is contained within the chamber and does not exhaust into the atmosphere thereby endangering the health of the operator or others in the vicinity. The inert gas minimizes the danger of the contained solvents exploding. It is also possible in this sealed inert gas chamber to print finer details and half tones than were previously possible with other solvent base ink systems. Since the ink does not dry as rapidly, the down time needed to clean the dried ink is reduced and productivity is thereby increased. Also, the ink is kept at its proper consistency. As shown in FIGS. 1 and 2, inking caps 54, 56 extending through the surface of sheet provide access to the inside of chamber 26 to deposit the ink. 
     Further details of the flexible sheet and the flood bar 24 and squeegee 22 attachment are shown in FIGS. 3, 6 and 7. Referring thereto it is seen that the sheet comprises two portions: a front sheet 60 to which squeegee 22 is attached, and a back sheet 58 to which the flood bar squeegee enclosure unit 62 is attached. This squeegee and flood bar enclosure unit is formed from individual parts made from extruded aluminum and plastic, and when manufactured come in two parts. These two parts are then bolted together as best shown in FIGS. 6 and 7. An attachment member 64 is provided to attach to the side of the squeegee handle. As best shown in FIG. 2, a squeegee opening 66 and a flood bar opening 68 and suitable rubber seals 70, 71, 72 are provided in the sheet. 
     In a conventional manner, printing head carriage 20 moves to the front of the press by a typical motorized means, flood bar 24 lays a deposit of ink on the silk screen stencil. Then when the carriage moves by carriage drive 74 to the back of the frame the flood bar lifts up by flood bar lift 76 shown in FIG. 1 and squeegee 22 comes in contact with the silk screen thereby forcing the ink through the silk screen pattern onto the substrate. The sheet moves with the carriage and is sealed to the frame at all times thereby forming the sealed chamber. The press illustrated is a semi-automatic clam shell type press that is hinged in the back and lifts the screen frame in the front. However, this invention will work on all types of silk screen presses both manual or automated, and can be used with all types of inks. 
     A gasket or closed cell neoprene rubber gasket 78 is adhered to the bottom of the metal frame to create a seal between silk screen frame 14 and support frame 12, which are clamped together by suitable tabbed clamps 80 as shown in FIG. 1. This gasket clamping mechanism creates a good seal between the two frames. 
     It is to be understood that the form of the invention herein shown and described is to be taken as an illustrative embodiment only of the same, and that various changes in the shape, size and arrangement of parts, as well as various procedural changes, may be resorted to without departing from the spirit of the invention, which is limited only by the appended claims.