Damping roller for a printing press

A damping roller for the damping unit in a printing press has a roller body that carries a glass, glass ceramic, or enamel outer material, layer, or coating. Suitable coatings can be produced, for example, by enamelling, plasma spraying, or attaching the outer layer to the body with a sealing compound. In another embodiment, the glass, glass ceramic, or enamel material acts as the self-supporting roller member accommodated solely by the journals. Preferably, the outer surface of the roller is polished. The damping roller of the invention has the ability to dispense an optimum amount of damping medium while eliminating or reducing damping medium additives such as alcohol to less than 6% of the total mixture.

FIELD OF THE INVENTION 
The present invention relates generally to a damping roller for use in a 
printing press damping unit. More particularly, this invention relates to 
an improved damping roller which can provide an increase in the amount of 
damping medium applied by the roller without the need to combine costly 
additives such as alcohol to the damping medium. 
BACKGROUND OF THE INVENTION 
The general purpose of a damping roller within a damping unit of a printing 
press is to apply a damping medium to some preselected surface, such as a 
printing plate carried on a rotating plate cylinder. To this end, it is 
desirable to have a damping roller with an optimum amount of 
"wettability." A damping roller which is wettable can receive and apply 
the damping medium. A damping roller with comparatively increased 
wettability denotes that this particular damping roller can receive 
comparatively increased quantities of damping medium. On the other hand, a 
decrease in roller wettability results not only in a decrease in the 
damping medium application rate but also often results in a non-uniform 
application of the damping medium. Without an optimum damping medium 
application rate, the printing process yields ink variations and 
associated printing problems. It is essential to a successful printing 
process to maintain a steady damping application rate. 
Intimately related to the wettability and the damping medium application 
rate of a particular damping roller is the damping roller's surface 
material. A large variety of materials, coverings, or surface structures 
are known for damping rollers. Damping units traditionally have rollers 
made of steel, rubber, or textile coverings. Other damping roller surfaces 
are made of material permeable to a liquid such as porcelain or fired clay 
(DE-PS 580 963). Prior art damping roller coverings have also been made of 
elastic yarn (DE-PS 2 607 255) or plastic fibers embedded in resin (EP 0 
293 551). Yet another patent (EP 0 400 621) discloses a damping roller 
whose shell is coated with ceramic/metal carbides. In some cases, these 
roller surfaces can become "wettable" only if hydrophilic agents, such as 
gum arabic, are applied to the damping roller surface. 
The main disadvantage of these damping rollers is that alcohol or another 
suitable agent must be added to the damping medium to increase the 
roller's wettability. If the alcohol is eliminated or if the ratio of the 
alcohol to the total mixture is reduced to less than 6%, the wettability 
of these rollers significantly decreases. In contrast, however, damping 
media that contain less than 6% alcohol in the total damping mixture are 
considered optimum in the printing business. Hence, a need exists for a 
damping roller which uses a low damping medium additive concentration 
while still maintaining a high wettability. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, it is the object of the invention to provide a damping roller 
whose outer surface will provide an optimum degree of wettability when the 
total damping medium mixture is less than 6% alcohol or other wettability 
enhancing additive. 
In accordance with the present invention, the above object is realized by 
providing an outer layer of glass, glass ceramic, or enamel disposed 
concentrically on a roller base or body. These layers may be applied onto 
the roller body through the use of a sealing compound or plasma process. 
Furthermore, the invention also contemplates that a roller base body may 
be eliminated and that the damping roller would consist entirely of the 
glass, glass ceramic or enamel material. 
Pursuant to another aspect of the invention and after the outer material is 
affixed to the roller shell, a polishing operation is performed. The 
polished mantle surface brings about a high wettability for the damping 
media without requiring additional operations such as adding alcohol to 
the damping media. In comparison to conventionally smooth surfaces it has 
been found that with the execution according to the present invention, the 
damping medium applied off of the polished surface remains constant for a 
substantially longer time. 
Another advantage of the damping roller of the present invention is that 
there is no need for the otherwise conventional treatment of the roller 
surface with hydrophilic agents. The steady damping medium application 
rate of the present invention results in a uniform film of damping medium 
on the printing plate. Moreover, ink variation and register difficulties 
are reduced and the addition to the damping medium of alcohol, which is 
harmful to health and the environment, is reduced to an unobjectionable 
degree or is completely eliminated. 
These and other features and advantages of the invention will be more 
readily apparent upon reading the following description of a preferred 
exemplified embodiment of the invention and upon reference to the 
accompanying drawings.

While the invention will be described and disclosed in connection with 
certain preferred embodiments and procedures, it is not intended to limit 
the invention to those specific embodiments. Rather it is intended to 
cover all such alternative embodiments and modifications as fall within 
the spirit and scope of the invention. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now to the drawings, a cross section of a damping or moistening 
roller for a printing press is shown in FIG. 1. A glass layer 3 is applied 
concentrically to a roller body 1 carried by two journals 5; the two parts 
1 and 3 being stuck together by means of a sealing compound 2. Sealing 
rings 4 are disposed at the ends of the body and also act as centering 
rings for the outer layer. 
As shown in the embodiment of FIG. 1, there is a small gap between the 
glass layer 3 which, in the present example, is in the form of a glass 
tube, and the roller body 1. The sealing compound 2 is introduced into 
this gap through an entry aperture 6 in the shell 1, in conjunction with 
the venting bore 7. The sealing rings 4 at the roller body ends center the 
glass tube relative to the roller shell and simultaneously seal off the 
gap. When the sealing compound 2 has set, the outer surface of the glass 
coating 3 is polished. 
In FIG. 2, an alternative damping roller is shown. Here, a glass layer or 
ceramic coating 3 is applied directly to the shell 1. Preferably, this is 
done by spraying it on by means of a gas plasma process or the like. The 
outer surface of the glass ceramic coating 3 is then also polished. 
Another construction of a damping roller can be obtained by eliminating the 
roller body 1, the journals 5 themselves directly carrying the 
appropriately dimensioned glass or glass ceramic material 3. In addition, 
reinforcing material, such as wire gauze or fiber glass, may additionally 
be introduced into the glass or glass ceramic coating 3 to increase 
stability and prevent fracturing thereof.