US2613596A - Stencil printing apparatus - Google Patents

Description

Oct. 14, 1952 w. MEISSNER STENCIL PRINTING APPARATUS 3 Sheets-Sheet 1 Filed Feb. 9, 1949 i 3k awe @641 96L 1952 K. w. MEISSNER 2, 33

STENCIL PRINTING APPARATUS Filed Feb. 9, 1949 3 Sheets-Sheet 2 45 HHHI I.

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///'s ATTORNEY Oct. 14, 1952 K. W. MEISSNER STENCIL PRINTING APPARATUS Filed Feb. 9, 1949 3 Sheets-Sheet 3 YO ZJ INVENTOR.

Patented Oct. 14-, 1952 UNITED STATES PATENT OFFICE STENCIL PRINTING APPARATUS Karl W. Meissner, New York, N. Y.

Application February 9, 1949, Serial No. 75,321

7 Claims.

This invention relates to printing methods and apparatus in which a viscous ink or pigment paste is applied to the paper through a stencil mounted on woven material, such as silk. The mesh openings are left exposed where printing is to take place. Ink is applied to the top of the stencil and forced through the exposed mesh openings by a rubber squeegee. By this method a much greater thickness of color can be applied than by the more usual contact printing blocks or rolls.

It has been customary heretofore manually to apply the ink and remove the excess ink by a squeegee, and the principal object of this invention is to provide an automatic method and apparatus for stencil printing.

' In manual operation the stencil is laid on top of the paper so that every part of the paper tobe printed on is in contact with the stencil throughout the printing operation. Along each end of the stencil is a supply of viscous or pasty ink. The squeegee is dipped into that supply and then moved across the stencil, thereby pushing a .line .of the ink across the top of the stencil to the other end of the latter. The squeegee performs three functions: first, applying ink to the stencil; second, forcing'a part of the ink through the interstices; and, third, wiping off the excess ink and pushing it ahead across the stencil.

-An entirely different mode of operation is required for stencil printing by means of a rotary printing press of the Miehle type. Such a machine calls for a stencil .reciprocating beneath a continuously rotating roll which carries the paper to and from the stencil. This means that the ink, instead of being forced downwards through the pores in the stencil as in the manual method, must be pushed upwardly through them. .Also, with the paper carried by a roll there is only line contact between the .paper and the stencil and not simultaneous contact of all parts of the paperwith the stencil.

This means, first, that the squeegee must be located along the line of contact between the paper and stencil, but below the latter. Second, the ink must be lifted from a reservoir and applied to the underside of the stencil ahead of the squeegee. There is no paper in contact with the top ofthe stencil at the point where the ink is applied to prevent the latter being forced through the openings in the stencil if any substantial pressure is applied. If there is ink on top of the stencil before the paperfis pressed against it, such ink will be squeezed out sideways and smudging will result. Consequently, the

ink-applying means must be such that the ink is brought into substantially pressureless contact with the underside of the stencil.

A convenient method for applying the ink without pressure is by means of an inking roller having grooves in its outer surface to receive ink. The ridges between the grooves which contact the stencil are kept substantially free of ink. At the same time the grooves are kept brimful. With such an arrangement pressure between the inking roller and the stencil will not force ink through the latter as the pressure is confined to the inkless ridges. The stencil picks up the ink from the grooves by adhesion.

This desirable result may be obtained in various ways, one being to locate the inking roller completely above the level of the ink in the reservoir and transfer ink to it by a'se'cond rubbersurfaced roller whose lower part dips into the ink pool, while its upper part contact the ink applying roller. As the second roller contacts the ridges between the grooves in the inking roller, it will return to the ink pool all ink in excess of that required to fill the said grooves.

One suitable form of construction is illustrated, by way of example, in the accompanying drawings, in which: I

Fig. 1 is a somewhat diagrammatic side elevation, partly in section, of a stencil-printing machine embodying the presentlinvention;

Fig. 2 is a plan view of the squeegee, ink reservoir, ink-applying rollers, and associated mechanism; I v

Fig. 3 is a section .on the line 3-3 of Fig. 2

Fig. 4 is a section on the line 4-4 of Fig. 2;

Fig. 5 is a section on the line 5-5 of Fig. 2;

Fig. 6 is a section on the line -66 of Fig. 4; and

Figs. '7 and 8 show diagrammatically the relative positions of the printing roll, squeegeeand inking roller with respect to the stencil on the printing and non-printing strokes of the latter.

The machine as a whole is similar to that of the rotating roll and reciprocating platen printing machines of the well known Miehle type, in which the platen is reciprocated back and forth under a continuously rotating roll which carries the paper to and from the surface of the platen. ,In the present machine there is a frame l0 carrying a stencil l I instead of the customary platen. The reciprocating mechanism i that used in standard presses "of the Miehle type. It includes two racks l2 and [3 on the frame respectively above and below 'a continuously rotating gear l4, When the gear is in mesh with the lower rack 13, the stencil frame moves to the left. At the end of the stroke the gear is raised to bring it into engagement with the upper rack l2. Then the frame moves to the right. Above the stencil is the usual printing r011 I5. This roll is driven in synchronism with the gear l4 and is raised and lowered with the latter, so that when the stencil is moving to the left the paper carried by the roll is in contact with the stencil. See full line position of roll. On the other hand, when the stencil is moving to the right, the roll is clear of the stencil. See dotted line position. A suitable mechanism for operating the gear l4, printing roll l5, and associated parts is shown in U. S. Patent to Miehle, No. 1,111,604.

Between the upper and lower parts of the stencil-carrying frame is a stationary ink reservoir 20. At the lefthand end (Fig. 1) of this reservoir is the support for the squeegee 2|. Journalled in the upper part of the reservoir is a roller 22 for applying ink to the underside of the stencil prior to its passage between the squeegee and the roll I5. For reasons given above, this roller is provided with a series of grooves, conveniently circumferential as shown in Fig. 2, for retaining ink. The roller 22 is supplied with ink from the ink pool in the reservoir by a rubber-surfaced roller 23 whose lower part dips into the ink pool and whose upper part closely contacts the ridges between the grooves in the roller 22. In view of the close contact between such ridges and the roller 23, substantially no ink is applied to the ridges and any excess beyond that required to fill the grooves is returned to the ink pool.

A third roller 24 is provided for the purpose of aiding the maintenance of proper distribution of ink in the reservoir. The ink used in stencil printing is a viscous liquid almost pasty in consistency. Without the roller 24, the continuous rotation of the roller 23 would transfer the bulk of the ink from the righthand end (Fig. 1) of the reservoir into the lefthand end. The roller 24 pushes the ink in the opposite direction to that given by roller 23 and so maintains equable distribution of the ink. Rollers 23 and 24 are separated slightly so that the former can feed the requisite amount of ink to the roller 22.

The three rollers 22, 23 and 24 are all positively driven by gearing, as shown in Fig. 3, so connected to the gearing which drives the gear l4 that the peripheral speed of the roller 22 is the same as the linear velocity of the stencil. Also that part of the roller which contacts the stencil during the printing stroke of the latter is moving in the same direction as the stencil. The roller 22, like the gear 14 and printing roll l5, rotates continually. However, on the return stroke of the stencil, the latter is out of contact with the roller 22.

As previously stated, the stencil is normally formed of flexible woven material like silk. The machine is set up so that the margins of the stencil attached to its supporting frame lie in a plane intermediate the upper and lower positions of the roll I 5. When the roll is down, it depresses the central portions of the stencil sufiiciently to cause the stencil to contact with the squeegee and inking roller 22. When the roll I is up, the elasticity of and the tension in the stencil causes it to rise sufficiently to be clear of the squeegee and inking roller 22. At the same time it does not rise as much as the roll I5, so that there is no contact between such roll and the stencil on thereturn stroke of the latter. To permit the roll Hi to depress the central parts of the stencil to bring it into contact with the squeegee and ink-applying roller, it is necessary that the area of the stencil inside its supporting frame be considerably greater than the area contacted by the roll I5. In other words, the length of the stencil between the ends of the frame must be considerably in excess of the length of the stroke of the frame. Alsov thewidth of the stencil between the sides of the frame is considerably greater than the effective length of the roll [5. Such proportioning of the parts allows the marginal parts of the stencil to sag downward under the pressure of roll I5 without tearing it or stretching it beyond its elastic limit.

The squeegee is a stiff rubber strip capable of bending laterally somewhat so that the edge which is in contact with the underside of the stencil produces a steady pressure on the lower side of the stencil, holding it against the paper to be printed and its supporting roll l5. As the strip is stiff to give the necessary pressure, it follows that such pressure is very sensitive to the relative positions of the operative edge-of the squeegee and the roll l5. Consequently, the vertical position of the operative edge of the'squeegee requires careful adjustment vertically to give the desired upward pressure against the bottom of the roll [5. Further, this adjustment must take care of the position of such edge throughout'its length. i a

The squeegee forces part of the ink through the pores of the stencil and pushes the remainder along the underside of the stencil. There are two forces exerted on the ink: one operating vertically upwards forcing it through the pores, and the other operating horizontally pushing it over the lower surface of the stencil. The ratio between these two forces is a function of the angle A (Fig. 4) between the face of the squeegee and the stencil. The smaller that angle, the greater the vertical upward pressure on the ink, and vice versa. The optimum vertical pressure depends on the nature of the ink, its viscosity and other factors. It is desirable, therefore, to mount the squeegee so that such angle may be varied as desired. To avoid having to make simultaneous adjustments in the vertical position not only of the squeegee but also of the inking roll and other parts, it is desirable to mount the squeegee so that it can be swung in an arc about its op.- erating edge as a center.

Two adjustments are, therefore, highly desirable. First, an adjustment in a vertical or generally vertical direction and, second, an angular adjustment. Both are provided for in the construction illustrated. I

The squeegee 2| consists of a stiff rubberstrip mounted between two plates 26 and.21 attached along their lower margins to a bar 28, these parts forming part of the carrying frame for the strip. In the lower part of the space between the plates 26 and 21 is a loose bar 29 on which the lower edge of the rubber strip rests. At its ends this bar 29 has longitudinally bevelled channel-section portions on its underside, as shown more particularly in Fig. 6. On top of the bar 28 are slidable wedges 30 and 3| which engage the bevelled channel-section portions on the bar 29. These wedges are adjustable longitudinally by screws 32 and 33. Plates 39 engaginggrooves in the screws 32 and 33 prevent longitudinal movement ofthe latter.

The screw 33 isturned bya knurledhead 40 mounted directly on the screw. The screw 32 is turned by a short shaft 4| having worm and worm-wheel connection with the screw. By adjusting the position of the wedges 30 and 3|, the operative edge of the squeegee can be raised or lowered at one or both ends.

To the ends of the bar 28 are attached plates 35 of arcuate form. The circles of which the edges of these plates form parts both have their centers along the operative edge of the strip 21. See Fig. 4. The outer peripheries of these plates rest on complementarily curved blocks 35 secured to the walls 3! of the ink reservoir. The inner peripheries of these plates bear against complementarily curved blocks 33 also attached to the walls 31.

Movement of the plates 35 along the curved path defined by the blocks 36 and 33 is brought about by an adjustment screw 42 passing through a nut 43 pivotally mounted on a pin M. The inner end of the screw 4?. is journalled in a block 45 pivotally connected to the squeegee support ing frame by a pin t6. A plate t? engaging a groove in the screw prevents longitudinal movement of the screw and the block at.

I claim:

1. A stencil printing machine comprising a stencil, an ink reservoir below the stencil, inkapplying means above the level of the ink in the reservoir and below the stencil, means for transferring ink from the reservoir to the ink-applying means, a horizontally stationary squeegee above the reservoir and below the stencil to remove excess ink from the underside of the sten oil and return such excess to the reservoir, means for reciprocating the stencil to and fro above the squeegee and ink-applying means, means for pressing a sheet of paper against the top of the stencil on alternate strokes of the latter, and means for bringing the stencil into contact with said squeegee and ink-applying means on such alternate strokes.

2. A printing machine of the continuously rotating roll and reciprocating platen type, comprising a reciprocating stencil, a horizontally stationary ink reservoir below the stencil, means for lifting ink from said reservoir and applying it to the underside of the stencil including a roller adapted to contact the stencil and a squeegee of angular cross-section for forcing a part of the ink through the stencil and returning the excess to said receptable, the upper edge of said squeegee being at all times directly below the axis of the roll whereby on the printing stroke of the stencil the roll holds the paper in contact with the stencil and the latter in contact with the squeei gee.

3. A printing machine as in claim 2, in which the roller has recesses in its surface for the reception of ink for transfer tothe stencil, and said ink-lifting and applying means also includes means for removing and returning to the reservoir the excess ink above the level of the portions between the recesses prior to contact between the roller and the stencil.

4. A printing machine as in claim 2, which also include a frame carrying the squeegee having arcuate end sections, complementary arcuate supporting means for said frame, the centers of the arcs of said end sections and supporting means being substantially in line with the operative edge of the squeegee, and means for adjusting the position of the end sections relatively to their supporting sections to change the angle of the squeegee relatively to the stencil without appreciably raising or lowering said operative edge relatively to the stencil.

5. A printing machine as in claim 2, in which the ink-applying roller is wholly above the top of the ink in said receptacle and which also includes a second roller dipping into the ink and having its upper part in rolling contact with the first roller to transfer ink from said receptacle to the first roller.

6. A printing machine as in claim 5, in which the ink-applying roller has a grooved surface H whereby, as the second roller makes rolling contact with the first, any ink above the level of the ridges between the grooves will be returned to the reservoir.

7. A stencil printing machine comprisin a reciprocating stencil, a squeegee below the stencil, a grooved inking roller below the stencil, means for bringing the stencil into contact with the squeegee and roller on alternate strokes of the stencil, a roll in close rolling contact with the inking roller, and an ink reservoir for supplying ink to said roll for transfer to the grooves in the inking roller.

KARL W. MEISSNER.

nnrnnnnoss siren The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 513,212 Stackhouse Jan. 23, 1894 1,832,216 Johnston et a1 Nov. 17, 1931 1,840,071 Werner et al Jan. 5, 1932 1,861,610 Respess June '7, 1932 FOREIGN PATENTS Number Country Date 207,550 Great Britain Feb. 5, 1925

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