US2870703A - Screen printing machines - Google Patents

Description

Jan. 27, 1959 w. BALMER 2,870,703

SCREEN PRINTING MACHINES United States Patent Z "asfrogra 'v SCREEN PRINTING MACHINES 'william Balma, Glasgow, scatena, assigner "to .Autoscreen Manufacturing `Company Limited, Edinligh, Scotland i Applicafin'mvemberab, iss, `623,409 Claims priant-y, appiicafioreat Britain- December 30, 1955 1 claim. (cl. 101-126) This invention has reference to screen printing machines.

The screen-printing process may be said to beA a stencilling process in which a stencil is mounted on a gauze screen which is brought into contact with the stock to be printed and the ink is forced `through the open areas of the stencil by means of a squeegee.

Two diierent types of machine are provided for screen printing.

One type is known as a flat bed. The screen is lowered on to a bed on which has been placed the stock, the squeegee drawn over the screen and thereafter the screen is raised. This machine has been mechanised so that the reciprocating movement of the squeegee and the lowering and raising of the screen is automatic. It has certain limitations of speed of operation, it does not readily lend itself to automatic feeding and what is known as line contact is not readily accomplished and is not always totally satisfactory.

The other type of screen printing machine incorporates a reciprocating screen with fixedv squeegee and a co-operating rotatably mounted impression cylinder provided with grippers. The grippers grip the stock and the cylinder rotates in unison with the travel of the screen so that the stock is carried around on the cylinder as printing takes place.

This type of machine, while overcoming certain disadvantages of the flat bed machine, has the fault that the stock must be in the form of paper or thin board. It cannot handle rigid or not-so-rigid stock as the stock must be wrapped around the cylinder during printing and such stock does not lend itself to this.

The present invention has therefore for its object to provide an improved construction of printing machine which will not have the limitations of defect of the existing two types of machine.

The invention will now be described with reference t the annexed drawings wherein- Figure 1 shows an elevationv of part of a screen printing machine in accordance with the invention; and

Figures 2, 3 and 4 respectively show the frame with screen at the beginning, at the middle and atthe end of its printing stroke.

The improved printing machine comprises la frame which supports a screen frame 18 to which is attached the printing screen 19. This frame is mounted to reciprocate in suitable guides and is reciprocated by any suitable power driven mechanism so that it travels backwards and forwards from the position shown in Figure 2 to that shown in Figure 4. y

ln the drawings such mechanism is shown comprising a motor driven shaft 19a on which is fast a cam 19b. The cam imparts a horizontal reciprocating movement to a member 19a pivotally connected at one end thereof to a connecting rod 19d. Said rod is pivotally connected to a fixture at its lower end and at its upper end is operatively connected to lugs 19e extending down- 2,870,703 Patented Jan. `27, 1959 "wardlyrfrom :theirame d8. tlhe rotation of the cam im- 1parts'1through :the :member 19e a `rocking vmovement -to fthe 'rod -'179d"which in turn freciproca'tes the frame -18 Suitablysupported byithe "mainiframe is fan ink reser- Amesh zithereof 7.whereritiis auncove're'dzby :the stencil.

The impression cylinder 17 is positioned immediately below the squeegee. Any suitable mechanism is provided to press the squeegee on the screen and to raise the impression roller during the printing stroke and to raise the squeegee and lower the impression cylinder during the non-printing or idle stroke. This may be effected by means of cams 20a fast on the shaft 19a, there being a cam at each side of the machine, which cams reciprocate vertically rods 20h which raise and lower the impression cylinder and squeegee.

At the rear of the impression cylinder is a tape conveyor 22 which is inclined downwards to the delivery end of the machine.

To the lugs 19e are secured plates 2lb providedwith guide slots 21a in which are fitted slipper blocks which carry the ends of a transverse rod 23 carrying grippers 23a. The slipper blocks also fit into guideways 24 which are parallel to the tape conveyor 22. Said grippers travel with the screen and, as they move away from the impression roller, are gradually moved downwards by the guideways, the ends of the rod 23 moving in the slots 21a.

Any suitable means may be provided to feed the stock between the screen and the impression cylinder so that the grippers 23aA can grip the leading edge thereof and draw the stock between the screen and impres-y sion cylinder.

When the machine is in operation stock represented by sheet 25 is fed to the grippers 23a which grip the leading end of the sheet and carry it along with the frame 18 as the latter is moved to the right in effecting a printing stroke, the impression roller 17 pressing the sheetV on the screen to effect line contact printing during this operation. As the grippers move away from the cylinder they gradually move vdownwards and thereby peel the printed sheet from the screen as printing proceeds. conveyor 22 which delivers the printed sheet as may be found desirable.

It is essentialthat during the printing stroke the grip-V pers do not stretch or tear the sheet or drag the sheet between the screen and impression cylinder and for that reason the slot 21a is not at right angles to the reciprocating frame. The slot should besuch that the distance between the line of contact of the cylinder on the screen to the top of the slot should be lthe same as the distance between said line of Contact and the foot of the slot which arrangement ensures that when the sheet is being peeled from the screen the grippers do not tend to stretch or tear the sheet or drag it between the cylinder and screen.

It will be understood from the foregoing that the improved machine represents a departure from normal practice wherein stock is locked to the cylinder during the printing stroke. By my improvements positive line contact is assured by reason of the fact that the sheet is peeled from the screen progressively throughout the printing stroke.

The cylinder may be either driven mechanically or may be free to rotate by frictional contact of the stock on its cylindrical surface. Further by my improved The printed sheet is thus deposited on the tape' ymeans paper or somewhat rigid sheets/heavy boards,

plastic, sheet metal and the like may all be printed by the improved machine.

What I claim is:

lIn a screen printing machine of the reciprocating screen and rotatablejcylinder type,`a transverse member which reciprocates with' the screen,Y grippers carried by .said members to grip the leading edge of the stock .by which the stock is drawn between the screen and cylinder, a delivery conveyor to receive.V the printed stock, guide means for the ends of the transverse member, said guide means being inclined relative to the'plane in which the screen reciprocates and further guide means for the ends l of said member', said further guide means reciprocating v l V2,870,703

10 stock. n

With'the screen 'and 'being' slightly inclinedy relative to the normal of said plane, the 4aforesaid guide `means combining to guide the transverse member so that the resultant travel imparted to the grippers during the printing stroke of the screen is progressively away from the screen but the linear travel isk never greater than that of the screen, and the stock gripped by the grippers is peeled progressively and .continuously throughout the printing stroke without danger of increasing the tension on the References Cited lledof this Apartent UNITEDf STATES PATENTS 2,579,461 Barlow Dec. 25, 1951

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