HK1023095B - Apparatus for reducing mottling in printing presses - Google Patents

Description

Device for reducing spot contamination in a printing press

Technical Field

The present invention relates to an apparatus and method for reducing mottle contamination in a printing press. More particularly, the present invention relates to an ink supply apparatus for reducing solid mottle contamination in an offset printing press.

Background

Offset printing presses are well known in the printing art. In an offset printing press, an image cylinder or plate cylinder containing an image to be printed on its outer surface is rotated into contact with a web or sheet to be printed with an image or, preferably, a transfer cylinder or blanket cylinder for transferring an image from the plate cylinder to the web or sheet. The ink is transferred to a plate cylinder and then directly to the web or sheet, or first through a transfer cylinder and then transferred to the web or sheet.

There are several known methods for supplying ink to the plate cylinder in offset printing presses. The most common method of supplying ink to the plate cylinder is by using an ink reservoir. An ink reservoir is a device in which an ink reservoir cylinder is mounted against an ink fountain containing ink. A group of ink keys is arranged at the junction of the bottom of the ink fountain (namely the ink reservoir) and the ink storage roller. The ink keys are movable toward and away from the ink reservoir cylinder, and the distance between the end of each ink key and the surface of the ink cylinder determines the thickness of ink applied to the outer surface of the ink cylinder by the ink key. The ink cylinder is adjacent to a metering cylinder in an area that is behind the ink key in the direction of ink rotation.

The metering cylinder delivers ink to an ink delivery chain consisting of one or more cylinders, which may include distribution cylinders, vibrating cylinders, oscillating cylinders, and a forming roller. The forming roller transfers the ink to the plate cylinder. The prior art forming roll is formed by an elastomeric outer surface which is relatively soft on the order of 22-28 shore a. The elastomeric outer surface is cylindrical and has a uniform outer diameter.

One disadvantage that can be found in existing offset printing presses is solid mottle. Solid mottle contamination is a condition in which ink is not uniformly distributed on paper in a printed image, thereby producing a mottled image which cannot have an appropriate optical density throughout the image. To compensate for solid spot contamination, it is often necessary in prior art devices to increase the amount of ink transferred to the paper.

Disclosure of Invention

The present invention relates to an apparatus and method that can reduce solid mottle contamination in a printing press. As a result, the present invention significantly improves the quality of the images printed by the printer by ensuring that the ink solids are deposited on the printing web or sheet throughout the printed image. In addition, the present invention can ensure the proper optical density and reduce the consumption of ink compared with available technology.

To achieve the above objects, in the apparatus and method of the present invention, one or more forming rollers having a hard elastomeric outer surface having a hardness of between about 60 and 90 on the Shore A scale are used to transfer ink to the plate cylinder. The hardness of the outer surface of the cylinder may also be between 50 and 100 shore a. The use of this type of former ensures smooth application of ink to the plate cylinder, which in turn ensures uniform application of ink to the blanket cylinder and the photographic web. If more than one forming roller is used, it is preferred that at least the last forming roller, i.e. the one with which the plate cylinder last contacts in the direction of rotation, is a forming roller having a hard elastomeric outer surface. The effect is significantly increased if all of the former rolls have a hard elastomeric outer surface. In addition, the present invention allows at least the final shaping rollers to be made convex along their axial length such that the diameter of the hard elastomeric surface at the axial center is greater than the diameter of the hard elastomeric surface at the axial ends. This ensures proper contact between the forming roller and the plate cylinder.

More specifically, according to one aspect of the present invention, there is provided an ink supply for use in a rotary printing press comprising a plurality of forming rollers in contact with a plate cylinder, the forming rollers having an inner portion and an outer layer, wherein the hardness of the outer layer of the last forming roller in the direction of rotation of the plate cylinder is between 50 and 100 Shore A, and further wherein the outer layer of the last forming roller has an outer surface which is convex along the axial length of the outer layer.

Preferably, the hardness of the outer layer of the last forming roll is between 60 and 90 Shore A, preferably 80 Shore A.

Advantageously, the outer layer of the last forming roll comprises an elastomeric material, preferably rubber.

The invention also comprises a printing press which can achieve high print quality with low ink consumption. This is because the form roll of the present invention can smoothly and uniformly distribute ink onto the plate cylinder, thereby requiring less ink to be used on the plate cylinder to achieve a particular level of lithographic quality. As a result, the present invention is a significant improvement over prior art printing presses, where a significant consumption of ink is required for a particular lithographic quality.

The present invention also includes a printing process that reduces solid speck contamination and reduces ink consumption for equivalent optical densities as compared to the prior art.

Drawings

These and other features of the present invention will become more readily apparent to those of ordinary skill in the art upon reading the following detailed description and by referring to the accompanying drawings.

FIG. 1 is a schematic front view of an ink delivery chain in an offset printing press according to the present invention;

FIG. 2 is a partially cut-away elevational view of a first embodiment of the forming roll of the present invention;

fig. 3 is a partially cut-away front view of a second embodiment of the forming roll of the present invention.

Detailed Description

The printing press of the present invention is schematically shown in fig. 1. A web W, e.g. a paper web, passes over a blanket cylinder B_UAnd a lower blanket cylinder B_LIn a middle section, andin contact with them. Can be arranged on a blanket cylinder B_U、B_LOn the outer surface of which an adhesive pad 12 is mounted. The web W runs in the direction indicated by the arrow, the blanket cylinder B_U、B_LIt is rotated in the direction indicated by the arrow. For clarity, for transferring an ink image to the upper blanket cylinder B_UThe plate cylinder and the ink applicator on are not shown; it will be appreciated that these components are also useful for transferring an ink image to the lower blanket cylinder B_LThe above components are the same or similar.

The ink may be applied to the former F by any known form of applicator₁、F₂、F₃The above step (1); in fig. 1, an ink feed chain 1 is shown. The ink chain 1 transfers ink to a plate cylinder P which in turn transfers an ink image to a lower blanket cylinder B_LThe above. An ink reservoir cylinder I is disposed adjacent to an ink reservoir 10 and rotates to transfer a layer of ink from the ink reservoir 10 to a metering cylinder M. The manner in which the ink reservoir 10 delivers a layer of ink to the reservoir cylinder I is well known in the art. The metering cylinder M, in turn, transfers a layer of ink onto a set of distribution cylinders D. From the distribution cylinder D, the ink is transferred to a number of vibrating cylinders V, a swinging cylinder S and a large distribution cylinder L. Ink is applied by a vibrating cylinder V to one or more forming rollers F₁、F₂、F₃The above. Shaping roller F₁、F₂、F₃A layer of ink is transferred onto the plate cylinder P.

The printing press according to the invention may comprise a buffer 2 for the plate cylinder P to be offset from the lower cylinder B_LWhen the plate cylinder P is separated from the plate cylinder P, the plate cylinder P is buffered.

As is well known in the art, the plate cylinder P includes a printing plate 11 on its outer surface for transferring an ink image to the lower blanket cylinder B_LTo subsequently print the image on web W. Shaping roller F₁、F₂、F₃Controlling the quantity and quality of the layers of ink transferred onto the plate cylinder PThe amount and thus the quality of the ink image photocopied on the web W.

FIGS. 2 and 3 show a forming roll F used in the present invention₁、F₂Or F₃Two embodiments of (a). Shaping roller F₁、F₂Or F₃Includes an inner portion 30 that is made of a relatively durable and rigid material, such as steel. Inner portion 30 may include journals 22 at each end thereof for rotatably mounting form roll F₁、F₂Or F₃. The inner portion 30 is preferably hollow to reduce weight. The hollow of the inner portion 30 may contain a suitable cooling means, such as a coolant channel, to prevent the forming roll F₁、F₂Or F₃Overheated during operation.

An outer layer 21 is mounted over at least a portion of the axial length of the inner portion 30. The outer layer 21 is made of an elastomeric material such as a Buna rubber (Buna * rubber) composite or any suitable compressible material. The elastomeric material in outer layer 21 is manufactured to have a relatively high durometer, which may be between 50-100 Shore A, preferably about 60-90 Shore A, and preferably about 80 Shore A. The greater the hardness of outer layer 21, the better the result is produced, since the hardness of outer layer 21 may cause the ink to form on plate cylinder P and forming roller F₁、F₂Or F₃With a finer and more uniform pattern. After transfer of ink from plate cylinder P to lower impression cylinder B_LThis improved ink distribution pattern may then result in improved quality of the solid ink deposited on the web W. This smoother transfer of ink ensures that images of high quality and optical density are obtained while consuming less ink than in the prior art.

Due to the forming roll F of the invention₁、F₂Or F₃The outer layer 21 of the upper part, so that the former F is comparable to the former of the prior art₁、F₂Or F₃Has higher bending rigidity. As a result, if a standard, uniform outer diameter forming roller is used, the line of contact or "strip" between the forming roller and the plate cylinder can vary. In order to prevent the use of the forming roll F of the present invention₁、F₂Or F₃The line of contact varies, and a forming roller F having a convex shape along the axial length may be used₁、F₂Or F₃. In a male forming roll F according to this feature of the invention₁、F₂Or F₃Diameter d located near the end of outer layer 21₁Smaller than the diameter d located near the axial center of the outer layer 21₂. The convexity, i.e. the shape of the convex curve forming the outer diameter of the outer layer 21, can be calculated according to a standard beam bending algorithm or a calculation model in which the forming roll F is to be formed₁、F₂Or F₃Taking into account the axial length, diameter and material of the shaft.

If more than one former is used, it has been found that the most effective way is to place the former having a hard outer layer 21 in the last position in the direction of rotation of the plate cylinder P, i.e. former F in FIG. 1₃The position of (a). If each forming roll F₁、F₂And F₃The effect is further enhanced by having a high hardness outer layer 21.

At the forming roll F₁、F₂Or F₃The use of a high hardness layer for the outer surface of (a) results in the forming roll F₁、F₂Or F₃The temperature rises during rotation. Therefore, it is desirable to have a mold roll cooling system (not shown) running, for example, through mold roll F₁、F₂Or F₃Is provided. Such a cooling system may be included in the forming roll F₁、F₂Or F₃Internal coolant passages.

In the above description of the present invention, various improvements, changes and modifications will occur to those skilled in the art. Various improvements, changes and modifications within the skill of the art are deemed to be covered by the claims.

Claims (5)

1. An inking device for rotary printing presses, comprising a plurality of forming rollers (F) in contact with a plate cylinder (P)₁、F₂、F₃) Forming roll (F)₁、F₂、F₃) Having an inner portion (30) and an outer layer (21), wherein the last forming roller (F) in the direction of rotation of the plate cylinder (P)₃) Has a hardness of between 50 Shore A and 100 Shore A, the last forming roller (F)₃) Has an outer surface, wherein the outer surface is convex along the axial length of the outer layer (21)And (4) shaping.

2. An ink supply device as claimed in claim 1, characterised in that the last former (F)₃) Has a hardness of between 60 Shore A and 90 Shore A.

3. An ink supply device as claimed in claim 2, characterised in that the last former (F)₃) The hardness of the outer layer (21) is 80 Shore A.

4. An ink supply device as claimed in claim 1, 2 or 3, characterised in that the last former (F)₃) Comprises an elastomeric material.

5. The ink supply of claim 4 wherein the elastomeric material is rubber.