US2491090A - Printing plate - Google Patents

Description

Dec. 13, 1949 w, w, DAvlDsoN 2,491,090

PRINTING PLATE Filed March l, 1946 Patented Dec. 13, 1949 PRINTING PLATE William Ward Davidson, Evanston, Ill., assignor to Davidson Manufacturing Corporation, a corporation of Illinois Application March 1, 1946, Serial No. 651,159

13 Claims.

My invention pertains to planographic printing plates and relates more specifically to a thin ilexible type of planographic plate adapted to preventI buckling of the plate under the influence of lithographie dampenng solutions.

One of the primary objects of my invention is to provide a planographlc printing plate ofthe type described formed in such manner as to prevent wrinkling or buckling of the plate on the press under the action of lithographie fluids.

This and other objects of my invention will become apparent from the following description and from the drawing in which Figure 1 is a sectional view of my plate attached to the drum of a rotary lithographie press of the offset type;

Figure 2 is a partial end view of my plate as applied to the drum;

Figure 3 is an end section of one form of my invention;

Figure 4 is an end section of another form of my invention; and

Figure 5 is and end section of still another modification of my plate.

There are two general types of thin flexible planographic plates ordinarily employed commercially. One class consists essentially of a thin sheet of metal foil such as aluminum .ordinarily backed with some type of reinforcing medium such as paper. The second class consists of a thin flexible web of organic material such aS paper treated to render the material more suitable for use as a printing plate and to provide a lithographie surface. The materials employed in forming plates of this class are usually cellulosic in nature. In many cases, the structure of the cellulose is wholly destroyed as is the case with plates formed of synthetic plastics and in others, the structure may be altered only partially as illustrated by various parchmentized types of planographic plates. In coated or impregnated types of plates, the fibrous structure of the paper web usually remains substantially undisturbed and since this type of plate is usually the leastl expensive, it is widely used.

It is essential that a planographic plate be capable of retaining on all non-image areas of its surface a film of moisture and for this reason many types of plates in this class have high water absorption. Although plates of this nature are often treated to render the fibers waterproof without making them waterrepellent, substantially all of the plates of this class exhibit some expansion or stretching when dampened by lithoiol-415.1)

nounced in paper plates and the least noticeable when plastic sheet ls employed as a web.

This invention is concerned primarily with paper base planographic plates but is equally applicable to other similar plates wherein the expansion upon dampening constitutes a potential source of difficulty.

Referring to the drawings, a printing drum I D is rotatably mounted about an axis A and includes a printing surface or periphery Ii. A portion of the printing surface il is cut away. as is common in such drums, to provide recessed areas in which plate clamping means I6 may be positioned. The clamping means may take many forms and are not material to this invention but may suitably comprise a roller or bar l2 mounted parallel to the axis of the drum iii for eccentric rotation and positioned coact with an abutment i3 formed on ends i9 of the drum i@ in such manner that rotation of the bar l2 will bring its surface into contact with that of the abutment i3 thereby clamping a plate iii rinly to the roller. The leading clamping means i@ is fixed, but the following clamping means may be pivotally mounted as at i 'i and urged inwardly by a spring is in order to apply a continuous tension to the plate M.

Since the inking and dampening rollers pass over the surface of the plate iii every revolution, it is obvious that the printing surface of the drum iii must be smooth and that no portion of the clamping means l@ extend outwardly beyond the surface. It is customary to dispose the grain of printing plates expansible by dampening in a. direction which will minimize the expansion normal to the axis A of the drum l0. Any expansion occurring in this direction is therefore small and is compensated by the spring tensioning means i8. This type of structure, however, permits considerable expansion of the plate Hl in the direction parallel to the axis which, if unrestrained, would not be objectionable since it does not tend to throw the press out of registry. The clamping means i6, however, and particularly the bar I2, will usually extend substantially the entire length of the dr-um i0 and therefore serves to normally restrict the expansion of the plate lf3 parallel to the axis of the drum i0. Furthermore, the dampening rollers do not contact the portion of the plate disposed between the clamp l@ and the end i9 of the drum. Expansion of the plate i4 parallel to the axis A therefore results in a series of folds or buckles unusually forming on the printing surface Il near the ends i9 and graphic fluids. This phenomena is most prowhich project upwardly a distance suillcient to force them into rm contact with the inking rollers. Because of the resulting abrasive action and increased pressure, ink is deposited on these buckles or folds and is in turn deposited by the press on the work.

I have found that this difficulty can be substantially eliminated by forming on an end of the plate Il a series of substantially linear mutilated areas extending from a point adjacent the end ol the plate towards the center of the plate a distance sufficient to position the inner ends of the mutilated areas on or near the printing surface adjauent the ends Il. These mutilated areas, which greatly reduce the resistance of the section of the, plate on which they are disposed to expansion, are preferably formed on the plate after the coating or impregnating steps, if any. have been completed and in their most effective form resemble substantially straight parallel lines normal to the axis of the drum A and normal to the direction of expansion. Since the maximum diiliculty is encountered at the leading edge of the plate, the mutilated areas are most advantageously formed at this point but are preferably formed to both ends of the plate I4.

The width and spacing of the mutilated areas is not critical, but I have found that substantially linear areas, that is areas which greatly exceed the width, are highly elective when spaced about one-sixteenth of an inch apart. The mutilated areas may be formed by placing the edge of the plate on a yielding surface such as rubber and embossing or indenting the mutilated areas on the sufrace of the plate with a blunt instrument to form areas of parallel linear indentations 2|. Wheels or discs of the type used for precreasing paper, operating against a rubber pressure roll, are satisfactory for this purpose. The indenting or scoring action causes a distortion of the web material immediately below the instrument and is preferably sufficient to cause ridges 24 to appear on the opposite surface of the plate immediately below the indentations 2|. If the plate employs a fibrous web, the indentations should be suiliciently deep to produce a visible set or distortion of the fibers.

The instrument used for forming the indentations 2| should be blunt in order to avoid complete rupture or tearing of the web and to insure that small portions of the ber or web material do not project upwardly beyond the general surface of the plate. It is, of course, obvious that the ridges 24 and, to a certain extent, the plate areas lying between the indentations 2| will project slightly beyond theV plane of the plate but the amount of projection is not great enough to cause pickup cf ink.

The indentations 2| may be arranged relative to eachother in a number of ways; for example, as illustrated in Figure 3, the indentations 2| may be formed only on the surface of the plate or, as illustrated in Figure 4, alternately on the face and back of the plate I4.

Another method of forming mutilated areas is to form a series of slits 22 substantially similar in length and-disposition to the indentations 2|. In this modification, however, the slits 22 should not extend to the edge of the plate because of the difllculty in handling which would obviously be encountered.

I prefer to terminate the slits a short distance inwardly from the edge of the plate leaving as nslit section 23 interposed between the end of the slits 22 and the end of the plate Il. However, the unslit strip 23 should not be of such depth that 4 the slits 22 will be uncovered by the clamping means Il since the most eiilcient operation of my plate requires that the mutilated areas extend substantially to the clamping means Il. If desired, the indentations 2| could be similarly formed, leaving an unmutilated strip adjacent the end of the plate I4 but since this serves no usef-ul purpose where indentations are employed, I ordinarily prefer to continue the indentations 2| to the end of the plate.

Although I do not wish to bind myself to 'IU theory of operation, it is believed that mutilation of the type described produces lines oi' weakness or variable strength which may serve to distribute the buckling areasevenly across the plate in such manner that no single buckle is suniciently great to cause the Plate to pick up ink. Furthermore, the plate after indenting has a pleated appearance indicating that there may have been a flow of material coupled with a compensating contraction which reduces the resistance of the section bearing the indentations to expansion.

Planographic plates treated in accordance with the teachings of my invention can be placed directly on the printing drum without prior treatment without danger of buckling near the drum ends. This not only reduces the degree of skill required by the operator but increases the utility of the plate for, in many instances, the highest degree of skill cannot prevent buckling of ordinary plates. Furthermore, the manufacturer of paper plates is enabled vto employ certain less expensive materials in the manufacture of the plate which have heretofore been considered un usable because of excessive expansion.

In compliance with Section 4888 of the Revised Statutes, I have herein described only certain preferred modifications of my invention but it is to be understood that I do not wish to be limited to the specific details herein described except in so far as described in the appended claims.

I claim:

l. A flexible printing plate comprising a thin flexible web of material expansible by dampening and adapted for attachment to a rotatable drum, the plate being characterized by a series of substantially uniform linear and parallel mutilated areas adjacent one end of the plate.

2. A flexible printing plate comprising a thin flexible web of material expansible by dampening' and adapted for attachment to a rotatable drum, the plate being characterized by a series of substantially uniform linear mutilated areas adjacent one end of the plate.. said areas being generally normal to the axis of the drum.

3. A flexible planographic plate comprising a thin flexible web of material expansible by dampening and adapted for attachment to a rotatable printing drum, the plate being characterized by a series of substantially linear uniform mutilated areas adjacent one end of the plate. said areas being generally normal to the axis of the drum and of sulcient length to extend onto the surface of the drum.

4. A generally rectangular flexible planographic plate comprising a web of flexible fibrous material expansible by dampening and adapted for attachment to a printing press, the plate being characterized by a plurality of substantially uniform linear mutilated areas approximately parallel to the long dimension of the plate and disposed adjacent one end of the plate.

5. A generally rectangular planographic plate comprising a web of paper expansible by dampening and adapted for attachment to a printing press, the plate being characterized by a plurality of substantially uniform linear mutilated areas approximatelyy parallel to the long dimension of the plate and disposed adjacent one end of the plate.

6. A llexible printing plate comprising a thin flexible web of material expansible by dampening and adapted for attachment to a rotatable printing drum, the plate being characterized by a series of substantially linear surface indentations generally normal to the axis of the drum and extending inwardly from an end of the plate a distance suicient to reach the printing surface when attached to the printing drum.

7. A flexible printing plate comprising a thin flexible web of material expansible by dampening and adapted for attachment to a rotatable printing drum, the plate being characterized by a series of substantially linear surface indentations formed alternately on the face and back of the plate and generally normal to the axis of the drum, said indentations extending inwardly from an end of the plate a distance sufiicient to reach the printing surface of the plate when attached to the printing drum.

8. A ilexible printing plate comprising a thin flexible web of material expansible by dampening and adapted for attachment to a rotatable printing drum, the plate being characterized by a series of slits generally normal to the axis of the drum and of sufcient length to extend from approximately the edge of the printing surface to a point short of the end of the plate when attached to the printing drum.

9. A exible planographic printing plate comprising a paper web adapted for attachment to the drum of a rotary press, a lithographie coating on one surface of the plate, and a series of substantially linear surface indentations generally normal to the axis of the drum extending inwardly from an end of the plate a distance suf- :llcient to reach the supporting plane of the drum.

10. A flexible planographic printing plate comprising a paper web adapted for attachment to the drum of a rotary press, a lithographic coating on one surface of the plate,and a series of substantially linear surface indentations formed alternately on the surface and back of the plate generalLv normal to the axis of the drum extendi'ng inwardly from an end of the plate a distance sumcient to reach `the supporting plane of the drum.

1l. A planographic printing plate comprising a brous web expansible by dampening, a lithographic surface on the web, said web being adapted for attachment to the drum of a rotary press, and a series of substantially parallel linear rotation of the press and characterized by distortion of the ber structure beneath each of said areas, said distortion being of such character as to substantially prevent protrusion of adjacent areas above the plane of the plate surface.

13. A planographic printing plate comprising a web of organic material expansible by dampening, a lithographic surface on the web, said web being adapted for attachment to the drum of a rotary press, and a series of substantially parallel linear mutilated areas adjacent one end of the plate, said areas being generally normal to the axis of rotation of the press and characterized by distortion of the structure of the web beneath each of said areas.

WILLIAM WARD DAVIDSON.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS

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