US2787213A - Dampener for offset lithographic printing - Google Patents

Description

April 2, 1957 '5. w. HUBBARD DAMPENER FOR OFFSET LITHOGRAPHIC PRINTING Filed Sept. 50, 1954 INVENTCR. Bruce Hubbard ATTORNEYS United States Patent DAMPENER FOR OFFSET LITHOGRAPHIC PRINTING Bruce W. Hubbard, Oak Park, Ill., assignor to Ideal Roller and Manufacturing Company, Chicago, Ill, a corpora fion of Illinois Application September 30, 1954, Serial No. 459,258

2 Claims. (Cl. 101-447) This invention relates to the so-called dampener roll used in offset lithographic printing to receive water from a ductor roll and wet the nonsensitized areas of the lithographic plate during operation of the offset lithographic printing press.

The general object of the invention i to provide a dampener surface which is much less costly than the so-called molleton surface now in common use, which possesses improved water receptive characteristics, and which may be removed and replaced easily and quickly without the necessity of removing the supporting roller from the printing press.

Another object is to provide an improved dampener roll having a thin water receptive covering mountable on a base roll by simply wrapping a flexible sheet of the covering material around the roll.

A further obiect is to achieve cheapness and ease of repiaceability through the use of sheetmaterial composed of cellulose fibers initially combined in a paper making machine.

Still another object is to provide a water receptive element composed of cellulose fibers joined or reinforced by a nonfibrous substance which possesses adequate wet strength and is suificiently water pervious to permit of use of the composite sheet as the covering for a dampener roll.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings, in which Figure l i a schematic view showing the elements of an offset lithographic printing press with the dampener roll constructed in accordance with the present invention.

Fig. 2 is a cross section of the dampener roll.

Fig. 3 is a perspective view illustrating the manner of applying the dampener roll covering.

In the operation of an offset lithographic printing press, the printing plate having sensitized and nonsensitizcd areas 11 and 12 is Wrapped around and attached to a rotary cylinder 1% whose surface is contacted continuously by an inking roller 13 and a water roller 14. The latter runs in contact with and receives water from a rigid roll which in most ofiset lithographic printing presses is vibrated axially back and forth and operates to wet the nonprinting areas 32 of the lithographic plate so as to confine the transfer of ink from the roll 13 to the plate areas 11 from which the ink is transferred to a blanket to on a roll which makes the printing impression on a sheet 13 backed by the impression roll 19. The base 23. of the water roll is usually composed of relatively firm rubber or other yieldable material.

The present invention contemplates the provision on the dampener roll 14 of a covering 263 which possesses improved water receptive properties as compared to the surfaces heretofore used and which at the same time may be applied in the form of a rectangular sheet by wrapping or spiraling around the circumference of the roller base 21. The attainment of these new results is based on my 2,787,213 Fatented Apr. 2, 1957 discovery that so-called vegetable parchment paper possesses unusual water receptive properties as Well as other characteristics not recognized or utilized heretofore but correlated closely with the requirements for a dampener roller covering in offset lithographic: printing. These unusual properties are developed in the initial formation of the paper and so-called parchmentizing of part of the cellulose fibers.

A soft highly absorbent sheet is first formed in an ordinary paper making process during which the cellulose fibers, although interlocking effectually with each other, tend to aline themselves along the length of the paper or the direction of advance through the paper-making machine. The so-called waterleaf thus formed is passed quickly through a bath of carefully controlled regenerating chemical, usually sulphuric acid, which immediately attacks the sheet dissolving some of the fibers into a jelly or gelatin-like substance known as amyloid. This substance fills up the pores and effectually cements the remaining fibers into a cohesive mass.

After momentary immersion in the acid bath, the sheet is washed free of acid to interrupt the parchmentizing action after which the sheet is dried in the usual way. While the paper thus parchmentized may be of different weights and thicknesses, it is preferred to employ a sheet weighing about 15 pounds per 1,000 square feet.

Paper formed in the above manner has been found to be unusually water receptive, that is, capable of absorbing and holding a substantial quantity of water. This is believed to be due to the fact that a substantial part of the fibers of the original paper remain unchanged in the short acid treatment and, perhaps due to the somewhat porous character of the amyloid cementing them together, these fibers are readily accessible for absorbing a substantial amount of water. At the same time, no loose fibers are exposed on the paper surface and the latter remains completely lint free-an important requirement of a dampener surface.

The paper also possesses ample strength when wet to withstand the forces to which the surface is subjected while running in contact with the plate and adjacent steel cylinders of an offset lithographic printing press. The amyloid cement is believed to be responsible for this important characteristic since it is a non-fibrous substance possessing uniform tensile strength in all directions particularly when reinforced by the cellulose fibers that become embedded in the parchmentizing process.

A final characteristic utilized in practicing the invention is the ability of the paper sheet to adapt itself accurately to the convex curvature of the base roller periphery and form itself into a smooth unwrinkled layer of uniform thickness in spite of the fact that the trailing end of the sheet overlaps the remainder of the sheet and is left exposed after the wrapping. To mount the sheet and form such a covering, advantage is taken of the tendency of the paper, when it is wet, to stretch enough in all directions to adapt itself to the contour of the roll and thus eliminate any wrinkles that may exist in the sheet initially or after Wrapping around the base roll. With some papers the avoidance of wrinkles in the final wet covering may be facilitated by taking advantage of the tendency of the paper to curl in a direction transversely of the length of the fibers 23 (Fig. 3) which, in the paper forming process, tend to aline themselves in the direction of advance of the sheet during its formation. When wetted, there is some tendency for the sheet to curl in a direction perpendicular to the fibers. Accordingly, it is sometimes desirable, though not essential, to arrange the sheet on the base roller so that the fibers 23 parallel the roller axis.

While the paper sheet may be fastened to the roll at its leading edge 22, it has been found that no securing means is actually required. Thus, the preferred procedure in forming the covering 20 is to first cut a paper sheet of a length substantially equal to the axial length of the base roll and of a width somewhat greater than the roll circumference. One edge 22 of the sheet is laid along the roller periphery parallel to the axis 24. The roller is then turned in the direction in which it revolves during actual printing thus Winding or Wrapping the sheet around the roll with the trailing end 27 overlapping the initially laid part of the sheet as shown in Fig. 2. By Wetting the paper and continuing the turning slowly while the roll is in contact with the adjacent steel roll 15, any wrinkles in the sheet will be ironed out automatically and disappear completely leaving the Wrapped around layer tightly contracted around the base and secured frictionally against turning relative to the latter. At the same time, the trailing end portion and the initially .laid or underlying part of the sheet become so matted together that the end 27 virtually disappears leaving a smooth surface which, in spite of the double thickness ever part of the circumference, is sufliciently uniform in diameter to provide proper contact at all times With the surface of the plate cylinder during actual printing.

One thickness of the paper covering the base roll has been found to be sufiicient to provide the desired dampening action. If desired, however, the sheet may be made long enough to extend two or even more times around the base roll.

The dampener constructed as above described possesses numerous advantages over the so-called molleton now in common use. Most important is the improved quality of the printing which has been noted due to the unusual manner in which Water is absorbed, retained, and distributed over the printing plate surface. The Wet covering has been found to possess ample strength to resist the frictional forces to which it is subjected in ordinary service use in an otfset lithographic printing press even when the Water transfer roller is vibrated axially through a substantial range. The cost of the paper sheet both initially and for replacement in service is only a small fraction of the cost of molleton sleeves. In fact, the cost of the entire covering is so small that it may be disposed of and replaced frequently thus avoiding the high labor and equipment costs heretofore involved in cleaning and replacing the expensive molleton fabric. Finally, since the covering is discarded after one use, it may be stripped off from the base while the latter remains in the press. Then, since the covering is applied in the form of a sheet wrapped around the base, it may be renewed without disassembly of the press or roller mounting. These advantages combine to overcome a serious handicap Which has been recognized for years in the offset printing art.

I claim as my invention:

1. An offset lithographic printing press having, in combination, a plate cylinder carrying a sensitized lithographic printing plate, and a dampener roll for said plate comprising a base, a resiliently yieldable covering thereon,

and a thin sheet of vegetable parchment paper snugly wrapped around said covering with the trailing end of the sheet left free, said sheet presenting a continuous water receptive outer surface for contacting said printing plate.

2. An offset lithographic printing press having, in combination, a plate cylinder carrying a sensitized lithographic printing plate, and a dampener roll for said plate comprising a base, a resiliently yieldable covering thereon, and a thin sheet of vegetable parchment paper snugly Wrapped around said covering and presenting a continuous water receptive outer surface contacting said printing plate.

References Cited in the file of this patent UNITED STATES PATENTS 683,478 Meyer Oct. 1, 1901 1,972,448 Jenkins Sept. 4, 1934 1,976,039 Rowell Oct. 9, 1934 2,230,981 Toland et a1. Feb. 4, 1941 2,312,853 Toland et al Mar. 2, 1943 2,530,388 Gullixson Nov. 21, 1950

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