US3785284A

US3785284A - Screen printing machine

Info

Publication number: US3785284A
Application number: US00253764A
Authority: US
Inventors: J Vertegaal
Original assignee: Stork Brabant BV
Current assignee: Stork Brabant BV
Priority date: 1969-01-28
Filing date: 1972-05-16
Publication date: 1974-01-15
Anticipated expiration: 1991-01-15
Also published as: DE2000481A1; CH493334A; NL6901386A; AT310700B; FR2029520A1

Abstract

A screen printing machine comprising a plurality of cylindrical screens capable of printing a travelling web which is temporarily affixed to a supporting belt, said machine comprising means for discharging said web immediately beyond the last screen under an acute angle with said belt.

Description

United States Patent Vertegaal Jan. 15, 1974 SCREEN PRINTING MACHINE [75] Inventor: Jacobus Gerardus Vertegaal, [56] References Cited Boxmeer, Netherlands UNITED STATES PATENTS 73 Assignee; Stork B b m N v Boxmeer 2,139,164 12/1938 KHOlvVlIOI] 226/171 X Netherlands 2,522,224 9/1950 Hedmger 226/170 X 3,102,469 9/1963 Sherman 10l/l28.4 X [22] Filed: May 16, 1972 3,198,109 8/1965 Dwyer et a1. l01/l28.3 X

l [2 1 App] No 253764 Primary Examiner-C1yde I. Coughenour Related U.S. Application Data Att0rneyEdmund M. Jaskiewicz [63] Continuation-impart of Ser. No. 887,977, Dec. 24,

I969, abandoned. 57 S C A screen printing machine comprising a plurality of [30] Foreign Apphcatlon Priority Data cylindrical screens capable of printing a travelling web Jan. 28, 1969 Netherlands 6901386 which is temporarily affixed to a pp g belt7 Said 1 machine comprising means for discharging said web [52] US. Cl 101/118, 101/232, 226/170 immediately beyond the last screen under an acute [51] Int. Cl B411 13/06, B65h 17/34 angle with Said hem [58] Field of Search 101/118, 119,120,

3 Claims, 4 Drawing Figures PATENTEDm 15 I974 SCREEN PRINTING MACHINE RELATED APPLICATIONS The present application is a continuation-in-part of the co-pending application Ser. No. 887,977 filed on Dec. 24, 1969, now abandoned, by the same named inventor.

BACKGROUND OF THE INVENTION My invention relates to a screen printing machine consisting of at least one cylindrical stencil and a driven endless belt on which the web to be printed can be temporarily affixed e.g., by means of glue for support and guiding in the printing track. With not so closely woven fabrics symptoms may occur which can give rise to faults as will be explained hereinafter.

After the last color has been pressed through the cylindrical stencil the web is still taken along over a certain distance with the belt (the so called blanket) before it is pulled off. At the slightest irregularity of the glue film, the web is loosened along a sharply broken line. When the web is separated from the belt along a horizontal extension of the printing track, an irregular loosening of the web results. In closely printed patterns this non-uniform loosening appears as an irregularity.

Expecially when the web is thin, such as thin nylon, when the paint is pressed through it may occur that the web locally adheres either more or less to the supporting belt which results in that the dreaded irregularities of the pattern are produced. This irregular loosening is visible in the ultimate printed product in view of the printing paste which has dried differently, depending upon the time lapse during which the ink or paste is indirectly in contact with the glue film on the lower face of the web in the period in which the web still adheres to the belt.

SUMMARY OF THE INVENTION Considerable attention has been directed to the problem of separating along a straight line a web which has been adhered to a body by an adhesive. The web is glued to the belt so that the web may be transported past the printing stencils at the same speed at which the belt is travelling. A layer of glue is uniformly applied to the underside of the web to adhere the web uniformly over its area to the belt. Immediately after the web has left the printing track, the web is separated from the moving belt along a straight line which is perpendicular to the direction of movement of the beltand web. By separating the printed web from the belt along a straight line, a uniform drying of the ink will occur in the web and this will prevent variations in the colors printed in the web. While it has been previously proposed to provide a friction or non-slipping surface upon a belt so as to transport a web along a printing track at the same speed as the belt, there was no problem involved in separating a web from such a nonslipping belt. Since there is no adhering or adfixing between the web and a friction surface on the belt, the web will separate naturally from the belt as the web and belt follow divergent paths. However, the problem is substantially different where the web is glued by an adhesive to the belt. The mere movement of web and belt along divergent paths after the web has left the printing track is not of itself sufficient to assure a uniform straight line separation of the web from the belt to which it has been glued.

It is an object of my invention to make improvements in this respect which is attained in that provisions are available for discharging the web in such a manner, after having passed by the last stencil, that an acute angle is enclosed between this web and the associated part of the supporting belt. Due to this feature the web after having passed by the last stencil is immediately pulled off the supporting belt and there is obtained a straight and therefore uniform area of detachment.

It is a further object of my invention to pull off the web immediately after the last stencil has imprinted the desired pattern and to transfer thereupon the web without any material contact to a usual floating drier. Another object of the invention is to avoid irregularities described above by creating a sharp and straight separating zone between the web and the belt immediately after passing of the last cylindrical stencil of the printing path.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a diagrammatical side elevational view of a part of a screen printing machine.

FIGS. 2 and 3 show in plan view the difficulties experienced on pulling off the web of fabric when the invention is not applied.

DESCRIPTION OF THE PREFERRED EMBODIMENT The screen printing machine to which my invention relates and which is partially represented in FIG. 1 is extensively described in the U.S. Pat. Nos. 3,291,044, 3,304,860, 3,313,232, 3,420,167 and in application Ser. No. 395,964 now abandoned. Such a machine comprises a number of cylindrical stencils 1 and a driven endless belt 2 on which the web 3 to be printed is temporarily affixed for support and guiding in the printing track A. Within each stencil l is provided in a usual way a doctor blade e.g., of the type described in the application Ser. No. 81 1,787 filed on Apr. 1, 1960. The supporting belt 2 is guided over two sprockets 4 one of which is depicted in the drawing. In the printing track A a number of supporting rollers 5 corresponding to the number of stencils 1 are situated under the supporting belt 2. The supporting roller 5 has a diameter which is considerably smaller than the diameter of the cylindrical printing stencil 1. This reduced diameter of the supporting roller 5 greatly increases the nip angle between the web 3 and the belt 2. This pronounced increase of the nip angle contributes significantly to the sharp and precise separation of the web 3 from the belt 2 in order to obtain the straight line perpendicular to the direction of travel of the belt.

In the conventional printing machines the part of the supporting belt 2, which is situated beyond the printing track A still remains for some time in contact with the web 3. On pulling off this web an irregular strike-off line is obtained as depicted in FIG. 2. This can be visible under particular circumstances in the final product since same is not quite evenly printed.

The provision according to the invention consists, in the embodiment according to FIG. 1, in a particular position of the sprocket 4 situated near the location at which the web is discharged, this sprocket being disposed at a level lower than that of the printing track A. In this manner there is a straight strike-off line or loosening-area, whereby two difficulties so far encountered are avoided. The first drawback has been discussed hereinbefore and relates to the irregularity in tightly crammed patterns.

A second drawback which is eliminated lies in the formation of folds which may occur due to the swelling up of the fibres of closely woven fabrics under the influence of moisture absorption from the printing paste. Since the back ground is printed as last color the symptoms of swelling up and thereby getting loose from the supporting belt will especially occur in the area past the last stencil. Due to the provision according to the invention this is no longer possible because the web after having passed by this stencil is then immediately pulled off. The cause of this formation of folds is depicted in the FIGS. 3 and 3A.

As is apparent from FIG. 1 the web 3, after having been detached from the belt 2 is transferred without change of direction to a usual floating dryer 6. The angle between the web 3 and the belt 2 after passing by the printing area of the last stencil 1 amounts to at least 5.

When the web is rather thin, the presence of a film of glue along the lower side of the web is of importance in eventually obtaining a quality of color which complies with exacting customer specifications. ln FIGS. 2 and 3, it is illustrated that in the conventional process the glue loosens from the web in an irregular manner such that there are parts from the web in which the contact between the color face printed upon the web and the glue against the lower side of the web is different from other parts of the web. This leads unavoidably to variations in color which may not be readily apparent to the layman but which are easily recognizable by persons skilled in the art. These color variations have the effect of significantly lowering the prices of the final printed product.

Thus, the use ofa film of glue on the lower side of the material to be printed has a specific influence upon the drying characteristics ofthe ink printed upon the upper side of the material. lt is not the adherance of the web upon the supporting belt which is important but it is the use of a glue film which has a particular consequence. This invention is not directed to the glueing or adhering of the web upon the belt but the manner of separating the web from the belt after the last printing operation so that there is no irregularity in the time lapse during which the web is in contact with the film of glue. It has not been previously appreciated in the art that a cause of a non-uniform grade of color in a printed material is the non-uniform or irregular duration of contact between the web and the film of glue along the full width of the web. This relationship has been discovered and it is apparent that the present invention has solved the problem as set forth above based upon this relationship.

While a preferred embodiment of my invention has been shown and described, it is to be understood that changes and variations may be made without departing from the spirit and scope of my invention as defined in the appended claims.

What is claimed is:

1. A screen printing machine of the endless belt support type consisting of at least one cylindrical stencil and first and second rollers, a driven endless adhesive belt on which the web to be printed is temporarily and uniformily adhered by said adhesive for support and guide in a printed track, a nip formed at the intersection of one cylindrical stencil and said first roller, said first roller having a substantially smaller diameter than said one cylindrical stencil, said second roller being located on the exit side from the nip and beyond and below said first roller to form an acute angle between said printing track and said endless belt supported by said rollers for separating the adhered web from the belt along a straight line perpendicular to the direction of travel of the belt and web immediately after the web has passed under the one cylindrical stencil of the printing track and after emerging from the nip.

2. A screen printing machine as claimed in claim 1, wherein supporting belt is guided between said first and second guide rollers, the first roller lying at the end of the printing track and the second beyond the printing track, said second being disposed at a level lower than the printing track and near the location where the web is discharged.

3. A screen printing machine as claimed in claim 2 wherein the diameter of the first roller is considerably less than the diameter of the cylindrical stencil at the end of the printing track and the second roller is larger in diameter than said first roller.