US2775199A

US2775199A - Flexible printing plate locking device

Info

Publication number: US2775199A
Application number: US338338A
Authority: US
Inventors: Claff Clarence Lloyd; Carl A Moeller
Original assignee: MB Claff and Sons Inc
Current assignee: MB Claff and Sons Inc
Priority date: 1953-02-24
Filing date: 1953-02-24
Publication date: 1956-12-25
Anticipated expiration: 1973-12-25

Description

Dec. 25, 1956 c cLAFF ET AL 2,775,199

FLEXIBLE PRINTING PLATE LOCKING DEVICE Filed Feb. 24, 1953 Fig. I I5 INVENTORS CLARENCE LLOYD CLAFF CARL A. MOELLER ATTORNEYS r 2,775,199 FLEXIBLE PRINTING PLATE LOCKING DEVICE Clarence Lloyd Clafi' and Carl A. Moeller, Randolph, Mass., assignors, by mesne assignments, to M. B. Clalf & Sons, Inc., Randolph, Mass., a corporation .of Massachusetts Application February 24, 1953, Serial No. 338,338

1 Claim. (Cl. 101-4151) The present invention relates to lithographic printing presses, duplicating machines, and the like, and more particularly to an improved device for securing a flexible lithographic plate or other sheet printing means to the surface of the plate cylinder.

A lithographic plate consists, essentially, of a base material or support and a coating on a surface of the support adapted to be prepared for selective wetting by a printing ink. A considerable variety of base materials may be used. in the case of rotary lithographic presses it .is necessary that such materials be deformable into a cylindrical shape. This permits the image to be transferred to the coating while the support is flattened in a plane, as in the case of photolithography, or wrapped upon a radius differing from that of the plate roll or cylinder, as in the case of typewritten lithographic printing. The support may then be wrapped upon the cylinder and securedthereto by its ends. In usual practice, the surface of the plate cylinder is relieved to form a slot running parallel to the axis of rotation, and means are provided to secure the ends of the support within the The specific form and mode of operation of the plate securing means depend to a considerable extent upon the selection of the base material. The relevant properties of this material include its stifiness and elasticity as respects bending or folding, and its strength and resistance to tearing. These and other properties, as will be understood by those familiar with this art, determine the amount, if any, of circumferential stretching force to be applied to insure a smooth, fiat fit upon the cylinder. They also determine the means to be used in gripping the ends of the plate, whether for example by screws, by bolts or rivets, by jaws or clamps of one type or another, by frictional devices, or by some combination of these or other suitable means.

It is a principal object of the present invention to provide an improved plate securing device, especially, although not exclusively, adapted for securing relatively thin fiexibleplates having base materials consisting of paper, plastic, cloth, or similar materials, characterized by flexibility and relatively low tear strength.

gins to form a resilient filler structure for frictionally binding the ends of the lithographic plate Within the slot.

The invention is further characterized by a construction which permits the plate locking device to be inserted Withinthe slot in the plate cylinder in a manner facilitating the removal of folds and wrinkles in the plate, as well as even distribution of the clamping forces acting upon the ends of the plate.

Other features Will be evident from the following description of the preferred embodiment, taken in conjunction with the drawings, in which:

Fig. 1 is an end view of a plate cylinder with the novel plate securing device in place, taken in a plane perpendicular to the axis of the cylinder.

Fig. 2 is an oblique view of the plate securing device.

Fig. 3 is a sectional view of a portion of the plate cylinder at the slot, taken on the line 3-3 of Fig. l and showing the locking device in operative position.

Referring to Fig. l, the plate cylinder 4 is constructed in any desired manner, being mounted for rotation about the axis of a shaft 5, and has a more or less continuous cylindrical surface, with a depression or slot running parallel to its axis. The sides 6 of the slot are preferably rounded very slightly, as shown in the drawing, at the intersection between the slot and the cylinder periphery. Also, the cylinder periphery adjacent the slot on each side is relieved very slightly for a short distance, to permit the portion of the plate in the vicinity of the slot to lie a slight distance radially inward from the periphery of the main portion of the plate, for a purpose hereinafter described.

As a further object, the plate securing device should be of simple design, suitable for rapid mounting and removal of the plate with a minimum of effort, yet so constructed as to insure a consistently smooth and wrinklefree fit of the plate upon the surface of the cylinder.

A further object is to provide means for adjusting the securing device for various thicknesses of base material, such as different weights of paper, as well as to insure an even distribution of the gripping force along the margins of the material within the slot.

With these objects in view, a principal feature of this invention resides in a plate-locking device of laminated construction consisting of two strips of rigid material separated by a layer of rubber or rubber-like material, with adjustable means for drawing the strips together to cause the rubber to protrude at the longitudinal mar- The plate 8, when in secured position, is wrapped around the cylinder with its ends projecting into the slot toward, but preferably not reaching, the bottom of the slot. It is effectively secured in this position frictionally by the plate securing device, which presses each end or margin of the plate against a wall of the slot.

The construction of a preferred form of the securing device is shown generally in Fig. 2. The device comprises spaced

strips

10 and 12 of rigid material, preferably but not necessarily metal, with a strip 14 of rubber or rubber-like material interposed between the strips and projecting slightly beyond the longitudinal margins of the strips. The bottom strip 12 is preferably provided with a notch 16 at one end for engagement under the head of a screw 18 threaded into the cylinder 4. The width of the strip is slightly less than the clearance in the slot with the plate 8 in position as shown in Fig. 1. Its length is preferably somewhat greater than the transverse end dimension of the plate 8. The top strip 10 is of the same width, and preferably of substantially the same length, but associated with the bottom strip in longitudinally off set relation so as to provide clearance at one end above the notch 16, while affording a projection 20 at the other end to facilitate removal from the slot by a prying action with the fingers or other suitable device.

The. two strips are separated by the layer of rubber or rubber-like substance 14, which is preferably of the same width as the strips, when uncompressed. The length of this layer may be the same as, or slightly greater than, the transverse width of the sheet material to be secured (the lithographic plate). Its preferred thickness is a function of its elastic properties, as well as of the extent by which it is desired to project or bulge the rubber outwardly to obtain the requisite clamping pressure in the slot.

To secure the sandwich of metal strips and interposed rubber layer, fiat-headed screws 22 pass through unthreaded holes in the strip 10, through the rubber layer 14, and into threaded holes in strip 12. These screws hold the laminae together, and permit the

strips

10 and 12 to be drawn together to bulge the rubber layer so that Patented Dec. 25, 1956 V it protrudes the required distance beyond the edges of the strips. They also permit adjustments of the bulge at various points in the longer dimension, since the strips and 12 are capable offlexure, whereby their compressive action on the rubberstrip may be varied from one screw to the next to achieve the desired lateral clamping pressure at any point. This is particularly useful in producing an equal distribution of clamping pressure upon the inturned margins of plate 8, which is important where printing plates of low tear strength are employed. It also facilitates interchangeability of cylinders and plate locking devices since, even though variations are encountered in the widths of the slots on different plate cylinders, the plate securing device may be quickly adjusted to a proper clamping engagement within the slot.

It will be understood that the number of screws 22 is to be principally determined by the choice of rubber or rubber-like material and the thickness and flexibility of the

strips

10 and 12. For example, more screws would be required where the rubber material is extremely stiff and great force is necessary to achieve the req uired protrusion. Similarly, more screws could be used where the rubber material is soft if either or both of the

strips

10 and 12 is flexible, permitting localization of the effect of each individual screw upon the rubber layer.

As heretofore stated, the structure just described is so adapted as to insure a consistently smooth and wrinklefree fit of the printing plate upon the surface of the cylinder. To illustrate this feature, the procedure of mounting a lithographic plate upon the cylinder will next be described.

The screws 22 will have been preferably tightened on the basis of a previous test, in which a test plate, or material of the same thickness as the plate to be used, is placed in the slot. The test may be so performed as to ascertain whether the clamping pressure is evenly distributed. Strips of the plate material may be placed side by side in the slot, on each side, and each strip may be subjected to a pull to determine the tension at which it begins to slip out of the securing device. Other tests of a more or less complicated nature 'will suggest themselves to those skilled in this art.

Once the proper adjustments of the screws 22 have been made, a lithographic plate may be mounted. The plate is first wrapped around the cylinder, and its ends folded over the edges of the slot. In this folding step, the plate may crack. To avoid the possibility of this crack picking up ink and transferring it to the blanket roll, the surface of the cylinder is relieved very slightly on each side of the slot, as described above, to allow such portions of the plate to lie slightly below the active peripheral portions of the plate.

The plate securing device is then inserted in place. First, the securing device is held at an acute angle with respect to the slot and the end with the notch 16 is inserted beneath the head of the screw 18. At this time, two corners of the plate, one on each end, are held in the slot by the pressure of short segments of the rubber extending into the slot near the screw.

The securing device is then pushed into place with a rotary motion about the screw 18. As this is done, the

length of the rubber extending into the slot gradually increases in the direction away from the screw. Progressively, from one end of the cylinder toward the other, a localized, circumferential, tensioning force is exerted upon each end of the plate due to the sliding of the rubber against the sides of the slot. This force, which is simultaneously applied at each end of the plate, removes the wrinkles in the plate, starting with the originally fitted side and working toward the other side. This action is facilitated by the rounded edges of the slot. Thus, the entire plate is drawn into smooth and snug engagement with the plate cylinder when the securing device reaches its final position in the slot.

Removal of the securing device is extremely simple, and involves merely prying it loose by inserting a finger or suitable tool under the projecting end 20 of the device lifting upward until the notch end 16 is free of the screw.

It willbe understood that the invention has been described with reference to a preferred embodiment, and that numerous modifications of form and details of construction may be incorporated without departing from the spirit or scope of the invention. Some of these modifications are discussed above, and others will occur to those skilled in this art in connection with specific applications.

Having thus described our invention, we claim:

In a rotary printing press, the combination of a plate cylinder having a transverse slot in its surface adapted to receive the inturned ends of a printing plate of thin flexible material, said slot having substantially parallel walls, a projection in one end of the slot, and plate locking means comprising a pair of elongated flexible strips narrower than the width of the slot and adapted to be disposed therein with their edges adjacent the slot walls, resilient material capable of developing friction with the plate intermediate the said strips, and a number of indiviually adjustable means spaced along the strips, each of said means being adapted to compress the resilient material between the strips in a substantially local area to cause the margins of the resilient material to extend laterally beyond the edges of the strips and thereby to provide frictional engagement of the inturned ends of the plate against the sides of the slot, said plate locking means being adapted to be retained at one end under said projection and to be lowered with a rotary motion until it lies in the slot, said resilient material frictionally engaging the inturned margins of the printing plate during said rotary motion and thereby exerting a laterally progressive circumferential pull on the plate around the cylinder.

References Cited in the file of this patent UNITED STATES PATENTS Faeber Dec. 16, 1952