Offset litho conversion from letterpress equipment

Abstract

Web letterpress equipment is converted to offset lithographic equipment by modification of a driven letterpress impression cylinder to receive an offset blanket, thereby producing an offset blanket cylinder. A letterpress plate cylinder is modified to become an offset plate cylinder with accompanying offset inking and dampening equipment. In one embodiment a drive letterpress plate cylinder of a color hump is packed to become an offset impression cylinder cooperating with the offset blanket cylinder. In a second embodiment the letterpress plate cylinder of the color hump is modified to an offset color plate cylinder and a driven offset impression cylinder is added to cooperate with the offset blanket cylinder. In this manner at least two colors may be offset printed on one side of a web. When used in combination with similarly converted letterpress plate, impression and color hump plate cylinders, at least three colors may be offset printed on one side of a web or multiple colors printed on opposite sides thereof. The press tower is rewebbed to print with proper registration in the bight between the respective offset blanket cylinders and offset impression cylinders.

Description

BACKGROUND OF THE INVENTION

This application relates to web printing presses and more particularly to the conversion of web letterpress equipment, of the type heretofore commonly used for printing newspapers, to offset lithographic equipment which utilizes an offset blanket to transfer the image.

Due in part to the considerable convenience and savings that modern methods of producing lithographic plates provide over letterpress plate methods, there has been substantial recent interest, particularly among newspapers, in converting letterpress equipment to offset lithographic equipment. In converting such letterpress equipment to offset litho, each printing unit is suitably equipped with a water dampening device whereby the necessary moisture for proper image separation is provided. Also, the conversion usually involves the "packing" or "saddling" of the thin litho plates (compared to letterpress plates) to bring them up to the printing height of the letterpress plates, for which the equipment was designed.

The advantages of such offset litho conversion, in comparison to investing in new web offset presses, include monetary savings and less printing down time for the change required to modernize letterpress equipment, as well as the ability to obtain additional life out of existing such equipment. However, even though the monetary savings by conversion are substantial, the cost to effect the conversion is considerable and sometimes prohibitive.

This invention is concerned with reducing the cost of the conversion to the point where it becomes economical under most conditions. Such conversions are of equipment which include common letterpress equipment having or adapted to receive, color humps, that is, an additional letterpress plate cylinder in a tower so that two letterpress plate cylinders are cooperating with a single letterpress blanket or impression cylinder.

By way of explanation, letterpress equipment, especially newspaper web letterpress equipment, generally comprises multiple printing towers, each of which includes a letterpress plate cylinder and a letterpress impression roll or cylinder driven in cooperative relation, with the web wrapped about the impression cylinder over an included angle of about ninety to about three hundred degrees, thereby utilizing the impression cylinder to aid in driving the web and maintaining registry with other printing units. Certain of the printing towers have an additional letterpress plate cylinder cooperating with the letterpress impression cylinder, producing a so-called "color hump" by which a color image may be printed during the same web pass through the tower. In letterpress equipment where a "color hump" is used, the web wraps around the impression cylinder and is engaged by both plate cylinders. Those towers which do not have color hump cylinders are often constructed so that such cylinders can be easily added.

The amount of web wrap around the letterpress impression cylinder is believed to be far in excess of that necessary, but the letterpress equipment was so designed because this helped insure proper registration, it simplified structure and there appeared to be no appreciable adverse effects in doing so.

Many printing applications require the use of at least two color print, therefore it is advantageous to be able to convert letterpress equipment to offset lithographic having the ability to print two or more colors on one side of a web. Again because of monetary considerations, it is important to provide a simple and relatively inexpensive method of adding offset "color" printing in combination with offset "black" print. (It should be noted that the term "black" normally refers to the color first printed by a tower, whereas "color" refers to the second color printed therein. In fact the "black" cylinder may print any color and the "color" cylinders could print black.)

In practice of this invention, a letterpress impression cylinder is modified to receive an offset blanket and one of the letterpress plate cylinders is adapted to carry a lithographic offset plate, with associated inking and dampening equipment.

In one embodiment of the present invention a second letterpress plate cylinder, normally the color hump cylinder, is packed so as to become an offset impression cylinder. The web may then be fed, with substantially less wrap about the letterpress impression cylinder (now the offset blanket cylinder), through the bight between the offset blanket cylinder and the offset impression cylinder. Since both the offset blanket cylinder and the offset impression cylinder are driven, if desired for registration purposes, increased wrap may be utilized about the offset impression cylinder by adjusting the position of suitable idler rolls. To facilitate the modified webbing, the three cylinders are driven in the opposite direction than normally used for letterpress purposes, however, this generally does not present a problem since common letterpress equipment is designed to anticipate the rollers being driven in either direction.

In another embodiment of the present invention the second "color hump" letterpress plate cylinder is converted to an offset color plate cylinder with dampening and inking equipment and a driven offset impression cylinder is added to cooperate with the offset blanket cylinder. Images are transferred from both offset plate cylinders to the offset blanket cylinder creating a reverse multicolor image on the offset blanket cylinder. The web is guided through the bight between the offset blanket cylinder and the offset impression cylinder. The multicolor image is transferred to the web from the offset blanket cylinder, whereby at least two colors are offset printed on one side of a web.

In another embodiment, additional letterpress equipment is converted to offset lithographic as described. This second converted offset lithographic press cooperates with the first, in conjunction with a web properly fed through both and registered therewith, to print at least two offset colors on one side of a web with at least one offset color being printed on an opposite side thereof or alternatively to print at least three offset colors on one side of a web.

OBJECTS AND SUMMARY OF THE INVENTION

Therefore the principal objects of the present invention are: to provide an improved method for converting web letterpress printing equipment to offset litho equipment; to provide such a method which is relatively inexpensive and easily accomplished; to provide such a method which allows simple and inexpensive addition of multicolor offset printing; to provide such a method which offset prints at least two colors on one side of a web; to provide apparatus to accomplish the methods of the invention and the completed apparatus associated therewith; and to provide such methods and apparatus produced thereby, which are reliable, quickly operational and well suited for their intended purpose.

Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawings wherein are set forth by way of illustration and example certain embodiments of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified, schematic elevational view of a typical section of prior art web letterpress equipment.

FIG. 2 is a schematic illustration of a portion, or printing tower, of the prior art equipment of FIG. 1, enlarged from the broken line rectangle, illustrating a typical prior art web path in a printing unit having a color hump cylinder.

FIG. 3 is a view similar to that of FIG. 2 but showing an altered web path and cylinder identity as a result of one embodiment of the practice of this invention.

FIG. 4 is a view similar to that of FIG. 2 but showing an altered web path and cylinder identity as a result of a second embodiment of the practice of this invention.

FIG. 5 is a view similar to that of FIG. 2 but showing an altered web path and cylinder identity as a result of a third embodiment of the practice of this invention.

FIG. 6 is a view similar to that of FIG. 2 but showing an altered web path and cylinder identity as a result of a fourth embodiment of the practice of this invention.

FIG. 7 is a view similar to that of FIG. 2 but showing an altered web path and cylinder identity as a result of a fifth embodiment of the practice of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As required, detailed embodiments of the present invention are disclosed herein, however, it is to be understood that the disclosed embodiments are merely exemplary of the invention which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure.

Referring to the drawings in more detail:

FIGS. 1 and 2 illustrate portions of typical prior art letterpress printing equipment 1 which includes letterpress printing or plate cylinders 2, 3 and 4 each having, respectively, printing plates 5, 6 and 7 secured in the usual manner to the surface thereof and suitably inked by well known apparatus, not shown. The letterpress plate cylinder 2 is associated with a letterpress blanket or impression cylinder 8 and the letterpress plate cylinders 3 and 4 are associated with a single letterpress blanket or impression cylinder 9. A web 10 passes over an idler or directing roller 11 and is wrapped, in this example, approximately ninety degrees about the blanket cylinder 8 from which it is directed to another idler or directing roller 12. From the roller 12 the web 10 is wrapped, in this example, approximately two hundred and forty degrees about the blanket cylinder 9, from which it passes about an idler roller 13 while traveling to another section of the equipment 1 for other operations such as further printing, collating with other webs, cutting, folding, etc. The printing cylinders 2, 3 and 4 simultaneously engage the web 10, which is supported by the blanket cylinders 8 and 9 and the ink image is thereby transferred by the respective plate cylinders to the web 10.

Various embodiments of the present invention are depicted in FIGS. 3, 4, 5, 6 and 7. Similar parts appearing in the modified embodiments of FIGS. 3, 4, 5, 6 and 7 and the prior art are represented by the same, corresponding reference numeral except for the addition of the suffixes "a," "b," "c," "d," or "e" respectively.

Referring to FIG. 3 in comparison with FIG. 2, by way of example in the practice of this invention, the letterpress impression cylinder 9 is suitably modified by known methods to receive an offset printing blanket 14a, thereby becoming an offset blanket cylinder 15a. The lower letterpress plate cylinder 3 is adapted through suitable known modifications to carry a lithographic offset plate 16a, thereby being converted into an offset plate cylinder 17a. Appropriate offset inking and dampening equipment 18a is associated with the plate cylinder 17a for supporting its intended function. The other letterpress plate cylinder 4, formerly the color hump cylinder, is appropriately packed so as to become an offset impression roll or cylinder 19 mating with the offset blanket cylinder 15a.

Conveying means such as an additional idler or directing roller 20 is desirably aligned with a juncture or bight 21 between the cylinders 15a and 19 for guiding the web therefrom. The web 10a may then be fed, with substantially less wrap than in the prior art letterpress equipment, about the center or offset blanket cylinder 15a, however, if increased wrap is desired for registration purposes the position of the idler roller 20 may be suitably changed. The modified press of FIG. 3 is webbed so that no paper passes between the former printing bight 22 between the unmodified letterpress plate and impression cylinders 3 and 9, as seen in FIG. 2, since in the embodiment of this invention shown in FIG. 3, this becomes bight 22a which is the transfer line of the image from the offset plate cylinder 17a to the offset printing blanket 14a. The web 10a receives the offset image from the offset printing blanket 14a at the bight 21.

In the example illustrated in FIG. 3, the three modified cylinders 15a, 17a and 19 are driven in the opposite direction from the prior art letterpress cylinders 9, 3 and 4 respectively to facilitate the new web path. Preferably the offset impression cylinder 19 is positively driven and mechanically synchronized to the offset blanket cylinder 15 whereby the web engaging surfaces thereon move with the same velocity at the bight 21.

Referring to FIG. 4 in comparison to FIGS. 2 and 3, a second embodiment of the present invention is shown wherein the letterpress plate cylinder 3 is converted to carry an offset plate 16b, thereby becoming an offset plate cylinder 17a, also referred to as an offset black plate cylinder, along with appropriate offset inking and dampening equipment 18b. The letterpress impression cylinder 9 is modified by known methods to receive an offset printing blanket 14b to produce offset blanket cylinder 15b. The other letterpress plate cylinder 4, formerly the color hump cylinder, is also converted by known methods to carry a second offset plate cylinder 24b, thereby becoming a second offset plate cylinder 25b, also referred to as an offset color plate cylinder. Appropriate offset inking and dampening equipment 26b is associated with the second offset plate cylinder 24b. An offset impression roll or cylinder 27b is placed adjacent the offset blanket cylinder 15b and cooperates therewith. The size and position of the offset impression cylinder 27b can be varied, as long as sufficient space therefor exists in the letterpress equipment being converted, wherein the impression cylinder 27b can be mounted. Preferably the impression cylinder 27b is positively driven, such that the surface thereof rotates at the same speed as the offset blanket cylinder 15b.

In the embodiment shown in FIG. 4, a web 10b is guided by conveying means such as a suitable idler or directing roller 28 to the bight 29b between the offset blanket cylinder 15b and the offset impression cylinder 27b. Each offset cylinder 15b, 17b and 25b rotates in the opposite direction as original letterpress cylinders 9, 3 and 4 respectively. An ink image is made upon each of the offset plate cylinders 17b and 25b by their respective inking and dampening equipment 18b and 26b respectively. Both ink images on the offset plate cylinders 17b and 25b are consequently transferred to the offset blanket cylinder 15b at bights 30b and 31b respectively. The image produced on the offset blanket cylinder 15 is thus multicolor provided that different color inks are used on the offset plate cylinders 17b and 25b. The multicolor image on the offset blanket cylinder 15b is then transferred to the web 10b at the bight 29b, whereupon one web printing side 32b has at least two colors offset printed thereon.

Referring to the embodiment appearing in FIG. 5, the letterpress equipment is converted to offset equipment as described herein above for the embodiment in FIG. 4, such that offset black and color plate cylinders 17c and 25c have appropriate offset inking and dampening equipment 18c and 26c respectively and cooperate with an offset blanket cylinder 15c bights 30c and 31c respectively. An impression roll or cylinder 27c is added which engages the offset blanket cylinder 15c at bight 29c slightly removed from such engagement in the previously described embodiment. In addition a second black letterpress plate cylinder 2 and a second letterpress impression cylinder 8, as seen in FIG. 2, are respectively converted to a second offset black plate cylinder 34c and a second offset blanket cylinder 33c respectively. Preferably the second offset impression black plate and blanket cylinder 34c and 33c are converted from letterpress equipment in the same press tower as or adjacent to said first offset black plate and blanket cylinders 17c and 15c. Appropriate offset inking and dampening equipment 35c is provided for the offset plate cylinder 34c. A second offset impression cylinder 36c cooperates with the offset blanket cylinder 33c at a bight 37c therebetween. A web 10c is suitably guided to the first impression cylinder 27c whereat a first web printing side 32c is multicolor offset printed as described for the embodiment in FIG. 4. The web 10c is also directed and properly registered by suitable conveying means such as idler or directing rollers 38 and 39 to the bight 37c between the second offset impression and blanket cylinder 36c and 33c. The second offset black plate cylinder 34c has an image transferred thereto by the inking and dampening equipment 35c which is thereafter transferred to the second offset blanket cylinder 33c at a bight 40c therebetween. This image is then transferred to a web second printing side 41c as the web 10c passes between the second offset impression cylinder 36c and second offset blanket cylinder 33c at bight 37c, whereby the web 10c has at least two colors offset printed on the web first printing side 32c and at least one color offset printed on the second printing side 41c. It is readily foreseen that the second offset impression cylinder 36c could also be a converted letterpress second plate cylinder which is a part of a color hump. All offset cylinders of FIG. 5 rotate in reverse direction in comparison to their corresponding former unmodified letterpress cylinders.

Referring to the embodiment shown in FIG. 6, the letterpress equipment is converted to offset equipment substantially as described hereinabove with reference to the discussion about the embodiment appearing in FIG. 5, thereby producing offset first black and color plate cylinders 17d and 25d cooperating with a first offset blanket cylinder 15d, a first offset impression cylinder 27d engaging the first offset blanket cylinder 15d at bight 29d, a second offset black plate cylinder 34d cooperating with a second offset blanket cylinder 33d, and a second offset impression cylinder 36d engaging the second offset blanket cylinder 33d at bight 37d.

A web 10d having first and second printing sides or surfaces 32d and 41d is directed by an idler or directing roller 42 to and between the second offset impression cylinder 36d and second offset blanket cylinder 33d, receiving an image having at least one color therein transferred from the second offset blanket cylinder 33d to the web first printing side 32d. The web 10d then partially wraps about the second offset impression cylinder 36d after which the web 10d is directed to the first offset impression cylinder 27d partially wrapping thereabout and passing between the first offset impression cylinder 27d and the first offset blanket cylinder 15d at bight 29d, whereupon the second web printing side engages the first offset blanket cylinder 15d and has offset printed thereupon an image having at least two colors therein. It is foreseen that the web 10d could be guided through a number of somewhat altered paths to produce the described offset images thereon. All offset cylinders of FIG. 6 rotate in reverse direction in comparison to their corresponding former unmodified letterpress cylinders.

Referring to the embodiment depicted in FIG. 7, the letterpress equipment is again converted to offset equipment substantially as described in the discussion regarding the embodiment shown in FIG. 5, thereby producing offset first black and color plate cylinders 17e and 25e cooperating with a first offset blanket cylinder 15d, a first offset impression cylinder 27e engaging the first offset blanket cylinder 15e at bight 29e, a second offset black plate cylinder 34e, and a second offset impression cylinder 36e engaging a second offset blanket cylinder 33e at bight 37d.

A web 10e having a first printing side 32e thereon is suitably directed to pass between the second offset impression cylinder 36e and the second offset blanket cylinder 33e at bight 37e with the first printing side 32e engaging and receiving an offset printed image from the offset blanket cylinder 33e. The web 10e is also directed by suitable guides such as an idler or director roller 43 to pass between the first offset impression cylinder 27e and first offset blanket cylinder 15e, partially wrapped about the former, with the web first printing side 32e engaging the first offset blanket cylinder 15e at bight 29e, whereupon an image having two additional colors if offset printed thereupon. Thus the web first printing side 32e has at least a three color image printed thereon. (It should be noted that although both offset plate cylinders 34e and 17e are referred in the trade as "black," the term is not meant to limit such cylinders to printing only the color black. Thus either or both cylinders 17e and 34e may produce an image color other than black transferred therefrom.) The offset first black and color plate cylinders 17e and 25e and the first offset blanket cylinder 15e of the embodiment shown in FIG. 7 rotate in reverse direction to their corresponding former unmodified letterpress cylinders.

Thus, the relatively simple modifications above noted allow existing letterpress equipment, and particularly web letterpress, to be easily and inexpensively changed to offset printing capability having the advantage of higher printing quality in conjunction with the convenience and savings offered thereby. In addition the equipment converted to offset printing according to this invention can be used to easily print in multiple colors on a printing web.

It is to be understood that while certain embodiments of this invention have been illustrated and described herein, it is not to be limited thereto except insofar as such limitations are included in the following claims.

Claims

1. The process of modifying conventional, continuous web and non-interchangeably convertible letterpress newspaper printing equipment, including cooperating first letterpress impression and plate cylinders generally horizontally spaced from and cooperating with second letterpress impression and plate cylinders within a single tower frame, to continuous web offset equipment; which process includes the steps of:

(a) modifying the first letterpress plate cylinder to accept an offset plate and thereby function as a first plate cylinder;

(b) mounting dampening and inking equipment on the tower frame in cooperation with said first offset plate cylinder;

(c) modifying said first letterpress impression cylinder to accept an offset blanket and thereby function as a first offset blanket cylinder;

(d) positioning a first offset impression cylinder in the tower frame so as to cooperate with said first offset blanket cylinder at a first bight removed from said first offset plate cylinder; said first offset impression cylinder not extending outwardly from said tower such that adjacent towers may be placed in close proximity without interference from said first offset impression cylinder;

(e) rotating said first offset impression cylinder; such that the speed of the surfaces of said first offset impression cylinder and said first offset blanket cylinder at said first bight are substantially the same;

(f) modifying a second letterpress plate cylinder to an offset plate cylinder to thereby function as a second offset plate cylinder;

(g) mounting dampening and inking equipment on the tower frame to cooperate with said second offset plate cylinder;

(h) modifying said second letterpress impression cylinder to accept an offset blanket and thereby function as a second offset blanket cylinder;

(i) positioning a second offset impression cylinder on the tower frame so as to cooperate with said second offset blanket cylinder at a second bight removed from said second offset plate cylinder; said second offset impression cylinder not extending outwardly from said tower such that adjacent towers may be placed in close proximity without interference from said second offset impression cylinder;

(j) rotating said second offset impression cylinder, such that the speed of the surfaces of said second impression cylinder and said second offset blanket cylinder at said second bight are substantially the same; and

(k) directing a continuous web between said first offset blanket cylinder and said first offset impression cylinder at said first bight and directing said web between said second impression cylinder and said second offset blanket cylinder at said second bight;

(l) modifying a third letterpress plate cylinder to accept a third offset plate within the tower frame and thereby function as a color third offset plate cylinder; said third offset plate cylinder cooperating with said first offset blanket cylinder and said first offset plate cylinder so as to transfer two colors to said first offset blanket cylinder;

(m) wherein said first impression cylinder is a new cylinder mounted in said letterpress tower frame; and including the steps of:

(n) directing said web to said first bight between said first offset blanket cylinder and said first offset impression cylinder; and

(o) directing said web to said second bight between said second offset blanket cylinder and said second offset impression cylinder, such that at least two colors are printed on one side of said web.

2. The process according to claim 1 wherein:

(a) said second offset impression cylinder is an adapted existing third letterpress plate cylinder of a letterpress color hump;

(b) said first offset impression cylinder is an additional cylinder added to and mounted within the tower frame; and

(c) said process of converting is accomplished without substantial modification to the tower frame.

3. The process according to claim 1 wherein:

(a) said third offset letterpress plate cylinder is an existing portion of a letterpress color hump.

4. The process according to claim 1 wherein:

(a) said third offset letterpress plate cylinder is an existing portion of a letterpress color hump;

(b) said first offset impression cylinder is an added cylinder; and including the steps of:

(c) first directing said web to said second bight between said second offset blanket cylinder and said second offset impression cylinder;

(d) second wrapping said web substantially about said second offset impression cylinder; and

(e) third directing said web to said first bight between said first offset impression cylinder and said first offset blanket cylinder.

5. The process according to claim 1 wherein:

(a) said third offset letterpress plate cylinder is an existing portion of a letterpress color hump;

(b) said first offset impression cylinder is an added cylinder; and including the steps of:

(c) first directing said web to said second bight between said second offset blanket cylinder and said second offset impression cylinder; and

(d) second directing said web to said first bight between said first offset impression cylinder and said first offset blanket cylinder, such that three colors are printed on one side of said web.

6. The process according to claim 3, 4 or 5 wherein:

(a) said first impression cylinder is mounted between said first and second offset blanket cylinders within the tower frame and said first and second offset blanket cylinders are positioned whereat said first and second letterpress impression cylinders respectively were positioned with respect to the tower frame.