Note: Descriptions are shown in the official language in which they were submitted.
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Fleld of the Invention.
The present invention relates to a cylindrical sleeve
structure for an offset cylinder of a rotary printing machine
and more particularly to such a sleeve structure which has
a resiliently compressible cover.
Background.
Blanket cylinders of offset printing machines can be
an endless, cylindrical sleeve or an interrupted cover,
clamped in a clamping groove. German Patent Disclosure
Document DE-OS 27 08 689 describes an offset printing machine
havlng a continuous cylindrical cover wbich is replaceable
applied on an offset printing cylinder. Elastic materials ar~
used for the coating.
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The referenced textbook, Walenski: "Linf~hrung in den
Offsetdruck" ("Introduction to Offset Printing"), published
by Hanns Eggen GmbH & Co. KG, Hannover, Fed. Rep. Germany,
pp. 262, 263, describes rubber blankets for use in customary
offset rotary printing machines which are elastically deformable,
but not volume compressible. Rubber blankets of this type are
referred to as incompressible or non-compressible blankets.
Only gaseous materials are volume compressible. Liquids and
solid materials are not volume compressible. Rubber blankets
having in~ermediate rubber layers of micro-compressible
material, connected by air channels or pores, have not found
acceptance in offset printing machine sleeves. Use of
customary, that is, elastic but not volume compressible
material, is not suitable since, in contrast to blankets which
are clamped in clamping grooYes,continuous sleeves do not
permit release of tension or bulges which form ~n operation.
Practical use of coated, continuous carrier sleeves,
particularly for wide or axially long printing cylinders was
not possible. Such sleeves could not be made,either in form
of a compact inherently elastic sleeve, or as an elastic
coating on a sleeve, and foamed coatings were impossible to use.
Customary materials in order to make foamed structures,
such as cast polyurethane, had been considered. Yet, use
of previously known uolume compressible material was not
econamically possible, even if, theoretically, the technical
use would have been possible.~
The Invention.
It is an object to provide a cylindrical sleeve in which kno~
difficulties of offset print subject matter carriers do not arise,
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which are economically in manufacture and provide for
desirable roll-off and printing to thereby result in
improved printing quality of a resulting printed product.
Briefly, a cylindrical carrier has a cylindrical
cover placed thereover which is formed of a multi-component
material having a foam of a base substance which becomes
volume compressible during its application. The foam
substance includes a blowing agent and an inhibitor, both
applied by free foaming on the surface of the carrier.
In accordance with a feature of the invention, the carrier
is rotated and a thi~otropic base substance, in liquid
form, is applied thereon in a spiral stripç, for example
by axially feeding or translating the carrier as it rotates,
the thixotropic substance, including the blowing agent and
inhibitor, being appli~d in an essentially spiral layer in a
condition in which it is still spreadable and somewhat flowable
to form a uniform cover over the cylindrical carrier.
The resulting structure, made by the method, has the
advantage of low damping and high rebound or bounce-back
elasticitiy.
"Free foaming" as used herein means that the material is
applied and can foam as it is being applied, without
constraint by a mold, that is, is free to form microcells or
micropores, not externally constrained but inherent in the
material a~ it is formed and, if of the curing type, as
it foams and cures.
Drawing:
The single figure is a highly schematic cross-sectional
view through a carrier sleeve forming an offset sleeve cover
for an offset cylinder of a rotary offset printing machine,
in which the offset cylinder has been omitted and is shown,
X
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schematically, only by its center line and shaft extensions.
Detailed Description.
An offset printing machine cylinder 1, for example
as used in rotary offset printing machines to transfer a
printed image from an inked plate on a substrate has t~o
shaft extensions for supporting the cylinder in suitable
bearings in side walls of a printing machine. The cylinder
has a replaceable sleeve 2 thereon. The replaceable sleeve 2
has a substrate or carrier layer 5 and a volume compressible
layer 3. A cover layer 4 is applied on top of the volume
compressible layer 3.
In accordance with the present invention, microcells
or micropores are formed in the volume compressible layer
3, are located within the material, and formed during
application of the layer 3; they are not applied externally
from the outside.
The cover layer 4 is not strictly necessary but is
usually provided.
The cylindrical body 1 may be, itself, a hollow
cylindrical sleeve-like structure; the sleeve 2
likewise, may be a separate cylindrical structure. Either
one of the cylindrical structures may be made of plastic,
for example reinforced with carbon or graphite fibers or
the like; the carrier 5 may also be a metallic tube or
sleeve, for example made of aluminum. The wall thickness of the
carrier S, depending on the material, is, preferably,
between 0.02 and 0.3 mm.
The volume compressible layer 3,which forms the base
for the cover layer 4, is, preferably, a materlal based on a
polyol " such as polyurethane; or a material based on a silicone
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Layer 3, preferably, has a thickness of between 1 to 5 mm,
althoug~it may be somewhat thinner or thicker. The top cover
layer 4, if used, can be applied on the volume compressible
base layer 3. Cover layer 4-is not volume compressible and
may, for example, be made of a material based on polyurethane,
or based-on rubber. The thickness of the layer 4 is usually
less than 0.5 mm and may be as small as only a few hundredths mm.
In accordance with a feature of the invention, the
materials used to generate the volume compresslble base layer
3 are exothermic upon cross-lin~ing by addition of cross-linking
or curing`agents which, upon cross-linking, generate heat.
The base layer 3, in accordance with a feature of the
invention, will have microcells or micropores of less than
0.01 mm. The volumetric portion of the cells should be
greater than 50% and, preferably, the number of their
occurrence should increase towards the outer circumference.
The volume:compressible layer 3 has a density of between
about 0.30 g/cm3 and 0.6 g/cm . The rise time or build-up
time of the material of the volume compressible layer 3 should
be between about 2 and 15 seconds. The proportion of the
pores or cells formed upon manufacture of the layer should be
greater than the proportion of the pores or cells which are
open; in other ~ords, there should be more closed pores than
pores which are connected by ducts or channels or other
communication, or which terminate at the surface.
The contacting portion of the compact cover layer 4
on the composite layer is, preferably, greater than 50%.
The damping of the volume compressible layer 3 is smaller
than 25%. The volume compressible layer 3 permits, in
a desirable manner, consideration of spring characteristics in
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printing. From a spring diagram of surface
pressure, width of printing impression lines, and the path distance
thereto, the specific desired characteristics can be determined.
The size of the cells or pores should be less than
0.0~ mm, and the relationship of pore volume to wall
thickness should be greater thah 1.5 : 1 and, preferably,
about 2.5 : 1. The rebound or bounce-back elasticity
~ill be more than 95%, and the remanent deformation due
to pressure will be less than 5~ and, desirably and
preferably, usually less than 2~.
It is a specific advantage of the sleeve construction
that the layer is volume compressible throughout the
entire thickness thereof.
Method of making the volume compressible sleeve:
In accordance with a preferred feature of the invention,
a thixotropic base material, provided in form of a gel within
a container is stirreduntil it becomes readily flowable and
liquid. Due to the thix~tropic characteristics of the material,
it will revert to a gel after stirring. The material, further,
can be filled, thickened and reinforced by additives to increase its
consistency and "body". In accordance with the invention,
the volume compressible layer is applied in liquid form of
the thixQtropic material on the carrier sleeve,
preferably by rotating and axially feeding the carrier
sleeve, so that the material is applied in spiral layers,
and can still flow so that no bulges, ridges, or free
spots will form. The material, then, solidifies. By use of
suitable hardeners, the solidifying step can be controlled.
In accordance with the invention, generally, a
cylindrical carrier sleeve is provided for rotary printing
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~achlnes, particularly offset printing machines, which have
a continuous, that is seamless, coating of plastic material whic~
is formed with separate micropores or microcells which are
n~ connected among each other.
A suitable thixotropic material is a polyol based
with silicic acid. Suitable addltives are chalk or
talcum.
In contrast to known processes, the invention provides
the possibility to form a volume compressible layer whlch can
foam freely as it is applied, that is, it does not require
a molding form, as known methods do. By use of expanding,
blowing or foaming agents and inhibitors, the characteristics
of the material using ~he foregoing process can be controlled
by suitable stirring and adding of curing or hardening
agents, so that the desired size and number of micropores
or microcells will result. The hardeners to be used influence
the resting or curing time which, preferably, is
between 2 to 10 seconds. The expanding or blowing agents and
the inhibitors, which also are operative as activat~rs,
inltia~e and will result in closed , for example at the surface,
forming an elastic foam. The volume, compactness, size of cells, proportion
of c~ll walls to overall volume, and the proportion of cells to overall
vol~me can be varied within wide ranges, easily determined by expsriments
to provide the desired material. Basically, the present invention provides
a cylindrical carrier sleeve for rotary printing machines, particularly offset
printing machines, which has a closed, continuous, that is, seamless outer
coating of plastic material, formed with separate, that is, not connected
microcells or micropores. The process described in detail above is a
preferred method of its manufacture.
Inhibitors, as used herein, are activators with indirect action. A
suitable inhibitor is a tertiary amine. The inhibitors change the base
characteristics of the basic materials which are used in accordance with the
desired characteristics. Expanding, blowing or foaming agents are materials
which, themselves, liberate gas, for example methylenechloride.
'~`
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The cover layer 4 can be applied in a suitable and
well known manner, for example also uslng the above-described
principle and method.
The size of the cells can be influenced decisively
by the energy applied during the stirring and the speed
- of stirring as the material is prepared. The distribution
of the space within the layer 3 depends, temporally,
on the application time, the foaming rise time, the speed of
rotation of the carrier, and the hardening time.
The cover layer 4 is preferably formed by a compact
elastomer, wlh a surface which is a fine smooth surface
with the required roughness or, better expressed, the
required smoothness. The thickness of the layer 4 can be
less than 0.5 mm, and may be made of any suitable material,
such as a rubber-based materi-al, a silicone or a polyurethane.
The sIeeve 2 so formed has advantages-with respect to the
construction of printing machines, as well as advantages in
use, that is, upon printing. Additionally, it can be made
inexpensively.
Seamless offset sleeves are not subjected to the
stresses arising on changeable compression and tension loading,
which interferes with print quality, register, and output;
additionally, they permit a paper path which is gentle on
the paper. The power requirement to drive_the machine,
further, is reduced. It is not necessary to form the
machine cylinder which carries the sleeve as a massive
solid element, which is frequently the case in current machines.
In accordance with the present inven~ion, thevolume compressible
material does not "knead"; thus,-all problems of the formation
of bulges, ridges and the like, are eliminated.
-~Y
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The cover, preferably made according to the
described method, has a furt-her advantage: From a printing
quality point of view, excellent reproduction is obtainable
because the impression line only compresses the layer of the
carrier material, without spreading out, since no material
is displaced. This advantage is obtainable with a seamless
or continuous cover, that is, one without being clamped in a
clamping groove. As a result, the impression line ls precisely
transferred from a printing plate on the offset cylinder and
by the offset cylinder precisely transferred to the printing
substrate. The s~rlngy characteristics or resiliency
characteristics, namely compression and reset to normal
or uncompressed dimension, is a gas dynamic process which is
essentially isothermal, that is, no heat of any consequence
is liberated. Heating of the gas by compression is balanced
by cooling upon expansion of the gas after the compression
is released.
The substantially smaller mechanical stresses which
are applied on the cover layer 2, and especially the
elimination of kneading, and pushing and pulling as well as
stretching and clamping of the cover, which occurred in the
prior art, and in combination with the highly wear accepting
material, provides for long operating time of the cover 2.
The cover can be made quite inexpensively, and has the
additional advantage that, due to the circular geometry, it can
be easily handled. The shape and the position is predetermined.
This is in contrast to blankets which are stretched over a
cylinder. Likewise, the size of the cover can be easily
predetermined since the material can be so influenced that its
behavior, that is, the behavior of the compressible layer upon
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compression, is determinable. Another advantage which
contributes to low cost is that the material cures in an exo-
thermal reaction, that is, it liberates heat. This is in
contrast to vulcanizing a rubber blanket, which requires heat.
No holding or counter mold or form is necessar~ as, for
example, in the manufacture of generally known polyurethane
rollers, which are cast with compact material between a mold
core ol form and a mold shell.
The invention is particularly applicable to cylindrical
carrier sleeves, that is, sleeves which are coated and which
can receive printed image subject matter, to replace prior
art rubber blankets, for transfer of the printed image on a
substrate, for example in the well known offset process.
The coating, and the method thereof, in accordance with the
present invention may be applied also to other types of
cylinders or rollers, for example to any kind of essentially
cylindrical elements, for example for image transfer via
a cylinder, as well as for other applications, for example
as ink application rollers, forme rollers, or roller elements
within various roller trains utilized in printing machines.
--10--
~"
201~376
Example 1:
A carrier sleeve of 22 cm diameter and 10O cm length is
placed in a holder which permits the carrier sleeve to
rotate, and carry out axially longitudinal movement wlth
respect to a coating application head. The cylinder was
rotated at a speed of 60 rpm, and fed
longitudinally at a rate of 30 meters per hour.
The coating was provided by mixing polyurethane of 1 kg
with iso cyanate of 0.370 kg, to obtain, within a
containerJ a gel which, by stirring, was rendered liquid.
Additives of talcum of 0.04 kg to increase the "body" were
added during mixing.
A foaming agent, namameiln~ ~ Frigen Ofo.50 kg
as well as a curing agent, a tertiary ` f 0.5kg was added
to the stirred liquid, and immediately applied by an
application head or spreader on the now rotating and axially
fed cylinder 5. The cylinder continued to rotate unti' it
was coated through its entire length, and then was continued
to be rotated, without application of further coating
material, for 2 minutes. The entire process was
carried out at room temperature. A coating of 3 mm
thickness was obtained. The layer 4 was applied over the
foamed layer 3, formed upon curing. Alternatively, the
layer 4 can be applied before the layer is entirely cured
and while it is still slightly tacky. It can be applied by
any well known coating process, for example by casting,
by rolling, or by applying with a blade.
The layer 4 was formed of compact polyurethane,namely Vulkolan.
The thickness of the layer 3 was 2.5 mm, the thickness
of the layer 4 was 0.5 mm, and the density of the volume
compressible layer 3 was 0.4 g/cm , with a damping of the
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volume compressible layer 3 of 3 % and a rebou~d
elastlcity of 95 Z.
Example 2:
A roller as explained in Example 1 was similarly
coated, except that the coating composition was: 1 kg
of base material with 0.4 kg gel forming material;
the foaming or blowing agent and inhibitor or curing agents
were: 0.3 kg of water or a polyvalent alcohol with Rll gas or R12 gas.
The layers 3 and 4 were similar to the layers of
l~xample 1, except that the density was Z 0-3 g/cm
and the rebound elasticity was 98 %.
Example 3:
A roller as explained in Example 1 was similarly coated, except
that the coating composition was: 1 kg of base material with 0.4 kg gel
forming material; the foaming or blowing agent and inhibitor or curing
agents were: 0.3 kg of water or a polyvalent alcohol with Rll gas àr
R12 gas.
The layers 3 and 4 were similar to the layers of Example 1, except
that the density was 0.35 g/cm3 and the rebound elasticity was 96 %
and 90 Shore A.
~.. ,~
