U.S. patent number 3,785,286 [Application Number 05/175,224] was granted by the patent office on 1974-01-15 for wiping cylinder of steel engraving printing machine and method of making it.
This patent grant is currently assigned to De La Rue Giori S.A.. Invention is credited to Gualtiero Giori.
United States Patent |
3,785,286 |
Giori |
January 15, 1974 |
WIPING CYLINDER OF STEEL ENGRAVING PRINTING MACHINE AND METHOD OF
MAKING IT
Abstract
The wiping cylinder of a steel engraving printing machine is
coated with a plurality of thin plastic layers over a rubber base
layer. When the wiping cylinder is to be cleaned with an organic
solvent, the plastic coatings are of a thermoplastic synthetic
resin that is soluble in water but not in organic solvents, for
example polyvinyl alcohol that is partially saponified and contains
acetyl groups. When the wiping cylinder is to be cleaned by an
aqueous solution, the coatings are of a synthetic resin such as
polyvinyl chloride that is not soluble in water. The thin plastic
layers are applied successively by means of a doctor blade assuring
smoothness, uniformity and exact thickness of the layers, and each
layer is hardened before the next is applied.
Inventors: |
Giori; Gualtiero (Lausanne,
CH) |
Assignee: |
De La Rue Giori S.A. (Lausanne,
CH)
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Family
ID: |
26329314 |
Appl.
No.: |
05/175,224 |
Filed: |
August 26, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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833622 |
Jun 16, 1963 |
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462355 |
Jun 8, 1965 |
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Foreign Application Priority Data
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Jun 18, 1964 [IT] |
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48397/64 |
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Current U.S.
Class: |
101/155; 101/348;
428/909; 101/425; 492/53 |
Current CPC
Class: |
B41N
10/005 (20130101); Y10S 428/909 (20130101) |
Current International
Class: |
B41N
10/00 (20060101); B41f 009/08 () |
Field of
Search: |
;29/130,132
;101/155,148,348,401.1 ;161/401 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Coughenour; Clyde I.
Attorney, Agent or Firm: Robert E. Burns et al.
Parent Case Text
This application is a continuation-in-part of my copending
application, Ser. No. 833,622, filed June 16, 1969 which was in
turn a continuation-in-part of application Ser. No. 462,355 filed
June 8, 1965, both now abandoned.
Claims
What I claim and desire to secure by Letters Patent is:
1. In a steel engraving printing machine, in combination with a
plate cylinder carrying an engraved plate and means for applying
ink to said plate, a rotating wiping cylinder in wiping engagement
with said plate to press the ink in the engravings of the plate and
to remove the ink from the plenum areas of said plate, said wiping
cylinder comprising a cylindrical base, a rubber layer surrounding
said base and a plurality of thin plastic seamless layers overlying
said rubber layer, each of said plastic layers having a uniform
thickness of from 0.1 to 1 mm and the total thickness of said
plastic layers being between 1 and 4 mm, said plastic layers
comprising at least one under layer and at least one cover layer of
a different composition and having a greater hardness than said
under layer the outermost of said layers having a smooth
cylindrical surface precisely concentric with the axis of rotation
of said wiping cylinder, said under layer being of a first
homogenous mixture composed of 100 parts by weight of polyvinyl
chloride, 30-50 parts by weight of dioctylphthalate, 30- 50 parts
by weight of tricresylphosphate and 0.5 to 3 parts by weight of a
stabilizer, said first mixture being heat hardened in situ to a
hardness of approximately Shore A 60 to 70, and said cover layer
being of a second homogeneous mixture composed of 100 parts by
weight of polyvinyl chloride, 25-40 parts by weight of
dioctylphthalate, 15-30 parts by weight of tricresylphosphate, 3-10
parts by weight of CaCO.sub.3, 2-5 parts by weight of graphite and
0.5-3 parts by weight of a stabilizer, said second mixture being
heat hardened in situ to a hardness of approximately Shore A 80 to
95.
2. A wiping cylinder according to claim 1, in which said under
layer has a Shore hardness of about A 65 and said cover layer has a
Shore hardness of about A 90.
3. A wiping cylinder according to claim 1, in which said rubber
layer has a Shore hardness between A 40 and A 90.
4. A wiping cylinder according to claim 1, in which gauze is
embedded in the plastic layer immediately superposed on said rubber
layer.
5. A wiping cylinder according to claim 1, in which said rubber
layer is a mixture of nitrile and vinyl polymers having a Shore
hardness of A 70 to A 75.
6. In a steel engraving printing machine, in combination with a
plate cylinder carrying an engraved plate and means for applying
ink to said plate, a wiping cylinder engaging said plate to press
the ink in the engravings of the plate and to remove the ink from
plenum areas of said plate, said wiping cylinder comprising a
cylindrical base, a rubber layer surrounding said base and a
plurality of superposed thin plastic seamless layers overlying said
rubber layer, said layers comprising an inner layer having a
uniform thickness of 0.1 to 0.2 mm and formed of a first
homogeneous mixture having the following composition:
said first mixture being heat hardened to a hardness of
approximately Shore A 60 to 70, an outer layer having a uniform
thickness of 0.1 to 1.0 mm and formed of a homogeneous mixture
having the following composition:
said second mixture being heat hardened to a hardness of
approximately Shore A 80 to 95, and a plurality of intermediate
layers formed of one of said compositions, each of said
intermediate layers having a uniform thickness of 0.1 to 1.0 mm and
the total thickness of said inner layer and intermediate layers
being 1 to 4 mm, each of said plastic layers being individually
heat set on the underlying layer.
Description
The invention relates a wiping cylinder for steel engraving
printing machines and to a method of producing and renewing the
surface layer of such wiping cylinder.
With steel engraving printing it is known to use at least one
wiping cylinder as a wiping device for the engraved printing plate
or the engraved cylinder, which has the task of pressing into the
engraving grooves of the printing plate or the engraved cylinder
the color or colors applied on the printing plate or the engraved
cylinder by the single-color rollers and to clean the color from
the plenum, i.e., the non-printing surface outside the engraving
grooves.
To obtain good quality printing, use is preferably made of two
wiping cylinders contacting the printing plate in sequence, of
which the first cylinder has the function of pressing the colors
into the engraving grooves and or removing already a substantial
part of the color to be found on the plenum, whereas the second
wiping cylinder has the function of cleaning the plenum completely
free from color.
In all cases, the surface of the wiping cylinder must comply with
quite definite requirements if satisfactory wiping is to be
obtained. Furthermore, the surface layer of the wiping cylinder
must be adapted to be capable of being cleaned continuously of
colors adhering thereto, so that the wiping cylinder surface coming
each time afresh in contact with the printing plate is completely
free from color. For this purpose it is known to clean the wiping
cylinder surface continuously with a preferably organic solvent. As
a cleaning bath, trichlorethylene or a similar organic compound has
heretofore been used practically exclusively.
As trichlorethylene is comparatively costly and, for economical
use, requires a recovery plant, it has already been proposed to use
as a solvent a considerably less expensive solution, for example
petroleum.
Even more advantageous and still cheaper, it has already
furthermore been proposed to use simply water, to which detergents
and tension relieving means usual in the trade have been added.
As the dissolving capacity of all other solvents for the colors
used in steel engraving printing is not so great as that of
trichlorethylene, it has also already been proposed to free the
wiping cylinder surface mechanically of the greater part of the
adherent color before contact with the petroleum bath by means of a
scraping blade. This also provides at the same time the advantage
that the greater part of the generally speaking valuable printing
color can be recovered.
With the use of petroleum or simple aqueous cleaning fluids, it is,
generally speaking, necessary to use a scraper device to free the
wiping cylinder surface of the liquid film adhering thereto as it
comes out of the cleaning bath.
Up to the present, a gelatine layer has commonly been used as the
surface layer for the wiping cylinder. The gelatine layer is stuck
on the jacket of the wiping cylinder by means of a cloth base. Such
known gelatine layer, has, however, a number of disadvantages:
1. The gelatine layer has only a very restricted length of life.
From experience it can only be used for approximately 60,000
printings, which with modern printing machine corresponds to a
duration of two days, whereupon the gelatine layer must be renewed,
and this process is comparatively costly.
2. The gelatine layer is extraordinarily sensitive and can be
scratched, for example by sharp engraving edges or small particles
of dirt, whereby the said layer immediately becomes unusable and
must be replaced in its entirety.
3. The gelatine layer is also very sensitive to outside influences,
such as variations in temperature and the moisture content of the
air. Accordingly, it is necessary that a wiping cylinder coated
with a gelatine layer should not be left in the machine overnight
or during long interruptions in the work, but has to be stored in a
heated cupboard or where there is air conditioning. This always
means dismantling, and at the beginning of the work, the
reinstallation of the wiping cylinder. If this were not done, the
gelatine mass, under the effect of variations in the temperature,
would "work" which easily brings the risk of the formation of
cracks.
4. As the gelatine layer is put on a cloth base which itself must
be glued to the wiping cylinder jacket, the said layer necessarily
has an overlapping joining part, which is very disadvantageous on
two counts; in the first place the said overlapping place must
naturally never come into contact with the printing plate or the
engraved cylinder to be wiped, so that care must be taken to see
that the wiping cylinder always turns in phase with the printing
plates or the engraved cylinders, and this means that it is always
exactly the same sections of the gelatine layer which carry out the
actual wiping function and come into contact with the printing
plates. Accordingly, it is always exactly the same portions of the
gelatine layer that are subjected to strain and are used up, with
resultant rapid wear and tear of the wiping cylinder surface.
Furthermore, the seam of the gelatine layer makes it impossible for
the scraping blade to glide smoothly over the wiping cylinder
surface so as to remove the adhering color in the main part from
the wiping cylinder surface or, after treatment in the cleaning
bath, to free it from the adhering liquid film. Still less, because
of the said overlapping place, is a rubbing clean of the wiping
cylinder surface possible by means of a strip wiping device, i.e.,
without the use of solvents.
For the cleaning of wiping cylinders equipped with a gelatine
layer, one is accordingly still forced to use a highly effective
organic solvent, i.e., trichlorethylene.
5. If the surface of the gelatine layer is once made unusable by
wear or by the occurring of the scratches, then it is necessary to
remove the whole layer together with its cloth base from the
cylinder jacket, and to replace it in its entirety with a new
layer. It is not possible to renew the damaged cover layer of the
gelatine mass.
The aim of the invention is to overcome the above mentioned
disadvantages previously known with wiping cylinder layers. The
method proposed for this purpose for the production of the surface
of the wiping cylinder in single color or multicolor steel
engraving printing machines, has the feature that a cylinder coated
with a rubber layer is covered with a first layer of a synthetic
plastic which is flowable in the state of use and has good
strengthening properties; this plastic layer is evenly distributed
by means of at least one blade adjustable as described hereinafter
disposed parallel to the axis of the cylinder and moveable relative
to this; finally this first inner layer is allowed to harden at
least partially, and then with repetition of the operations
described, a determined number of further plastic layers are
applied in sequence to the cylinder surface until the total layer
thickness reaches a prearranged value and in the hardened out
state, the covering layer gives the surface of the cylinder
suppleness and good gliding properties. To prevent shrinking
effects during the hardening of the layer which can result in
cracks or unevenness, the thickness of each layer is chosen
sufficiently small, in general less than 1 mm.
When the wiping cylinder is to be cleaned during the printing
process with an organic solvent, for example trichlorethylene, a
particularly suitable synthetic resin for the process in accordance
with the invention is a synthetic resin that is soluble in water,
but in which in organic solvents dissolve with difficulty if at
all, viz a polyvinyl alcohol that is partially saponified and
contains acetyl groups. A thermoplastic synthetic resin of this
type is known under the registered Trade Mark "Mowiol" and is
produced by the Farbwerke Hoechst A.G. Germany. If the wiping
cylinder is to be cleaned with an aqueous solution, a synthetic
resin nonsoluble in water such as a polyvinyl chloride is
recommended, for example, that known under the Trade name "Solvic"
340 (produced by Solvay Cie, Brussels, Belgium), or under the Trade
name "Hostalit P/VP 3475" (produced by Farbwerke Hoechst A.G.
Germany).
The product known under the registered Trade Mark "Mowiol"
designates a group of polyvinyl alcohols of various degrees of
polymerization and hydrolysis, which with water form highly viscous
solutions with good protective colloidal effect. The aqueous
solution dries to a clear comparatively solid film and was
previously used preferably in the adhesive, paper and textile
industries as layers for nylon yarn, as a gel agent for the
production of cosmetics and the like.
The plastic layer of the invention overcomes all the disadvantages
mentioned under points 1 to 5 found with the previously known
gelatine-covered wiping cylinder. The holding power of such plastic
layer is effective for at least 3 to 6 months on a basis of
approximately 30,000 printings per day. It is practically resistent
to all external influences, in particular to variations in
temperature and variations in the moisture content of the air. The
wiping cylinder accordingly does not need to be stored in a
cupboard with air circulation during intervals in the work, but can
remain positioned ready for use in the printing machine. The
plastic layer has no seam or joining place, but a completely smooth
surface, so that work can be done with a continual "phase
displacement" of the parts of the layer coming in contact with the
printing plate. This means that all regions of the wiping cylinder
layer are brought to an equal extent into the actual wiping
function, and accordingly are evenly stressed. It is possible
therefore to take care, for example, that the region of the wiping
cylinder surface coming in contact with the pressure plate on each
turn is displaced each time through an angle of 6.degree., so that
it is only after 60 printings that the original wiping cylinder
place then comes in contact with the pressure plate. Furthermore,
with the seamless synthetic layer, scraping blades can be used for
mechanically stripping off the color and/or the liquid film from
the wiping cylinder surface. Similarly, the wiping cylinder surface
can be rubbed clean with a strip wiping device.
The synthetic layer is also substantially less sensitive to the
formation of cracks than is a layer of gelatine.
A further important advantage consists in that after the wear and
tear of the cover layer of the plastic mass, one is not forced to
renew the whole wiping cylinder layer, but it is sufficient simply
to remove the damaged cover layer mechanically, and here, in the
case of a water-soluble plastic, which dissolves with difficulty if
at all in organic solvents, the cover layer can be softened or
dissolved previously in water before being mechanically removed,
whereupon by putting on a new plastic cover layer, the original
diameter of the wiping cylinder surface is again produced. The long
life of the plastic layer of the invention as well as the
possibility of simple renewal of only the cover layer, represent an
extraordinary saving in expense in comparison with the previously
known wiping cylinder layers.
It has furthermore been seen that the quality of the printing
produced with the wiping cylinder is improved with the use of a
plastic layer.
The invention will now be described in greater detail with
reference to the accompanying drawings in which:
FIG. 1 is a schematic view of a steel engraving printing machine
having a wiping cylinder in accordance with the present
invention.
FIG. 2 is a schematic view on a larger scale of the wiping cylinder
and associated parts.
FIG. 3 is a schematic end view, partially in cross section, of a
wiping cylinder, the thickness of the layers being exaggerated for
clarity.
FIG. 4 is a diagrammatic view of a device for applying a surface
layer to a wiping cylinder.
FIG. 5 is a similar diagrammatic view illustrating the scraping off
of the used cover layer of the wiping cylinder using a water
soluble synthetic resin.
In FIG. 1, there is shown schematically a steel engraving printing
machine having a wiping cylinder 1 in accordance with the present
invention. The wiping cylinder 1 is mounted in position to engage a
plate on the plate cylinder 22 to which ink is supplied by one or
more inking rollers 23, 24 and 25 with their associated inking
devices 26, 27 and 28 respectively. A paper web 30 to be printed
passes between the plate cylinder 22 and an impression cylinder 31.
The directions of rotations of the respective cylinders and rollers
and the direction of travel of the paper web are indicated by
arrows. It will be seen that the inking rollers 23, 24 and 25 turn
in the opposite direction from the plate cylinder 22 and hence have
a rolling engagement with a plate on the plate cylinder while the
wiping cylinder 1 turns in the same direction as the plate cylinder
and hence has a wiping engagement with the plate. After ink has
been applied to a plate on the plate cylinder by the inking rollers
23, 24 and 25, the plate is wiped by the wiping cylinder 1 to press
the ink into the engraved grooves and remove it from the plenum of
the plate before it reaches the impression cylinder 31.
The wiping cylinder 1 is kept clean by a cleaning bath in a
container 32 as shown in FIGS. 1 and 2. Rotating brushes 33 and 34
are shown in the bath. A doctor blade 35 removes the cleaning fluid
from the wiping cylinder. In case it is desired to reclaim a
portion of the ink or to reduce the contamination of the cleaning
bath, a doctor blade 36 is provided in position to engage the
surface of the wiping cylinder before it enters the bath. When an
aqueous solution is used for the cleaning bath, a water spray 37,
squeegee 38 and air drying pipe 39 are provided following the
doctor blade 35. When trichlorethylene is used as the cleaning
bath, the elements 37, 38 and 39 are not needed.
As shown schematically in FIG. 3, the wiping cylinder 1 has a shaft
or axle 2. The periphery of the cylinder body is covered with a
base 3 of rubber on which a plurality of plastic layers 4 has been
successively applied.
A device 6 for applying the successive layers is shown
schematically in FIG. 4. This device can also be used for replacing
the worn cover layer as illustrated schematically in FIG. 5. In
applying the successive plastic layers to the wiping cylinder 1,
the cylinder is mounted for rotation about its axle or shaft 2.
During the process the cylinder is put into rotation by suitable
means which are not shown in the drawings, the direction of
rotation being indicated by an arrow. As the cylinder is rotated, a
layer of plastic is progressively applied by the device 6.
As shown in FIG. 4 the device 6 comprises an elongated container 7
which extends lengthwise of the cylinder to be treated. The
container 7 comprises an inclined base 8, an inclined rear wall 9,
opposite end walls 7a and a removable cover plate 15. On the edge
of the base 8 toward the wiping cylinder, there is provided a
scraper blade 8a which extends parallel to the cylinder axis over
the entire length of the jacket of the cylinder. It is naturally
also possible for the scraper blade 8a to form part of the base
plate 8 itself. The scraper blade 8a is disposed at a small angle
of inclination to a plane defined by the edge of the scraper blade
and the axis of the cylinder when the container is in operative
position as shown in FIG. 4.
The container 7 is tiltably mounted by means of a shaft 10 on a
support 13. An abutment 14 on the support 13 is engageable by the
base 8 of the container to position the container relative to the
support. The support 13 and the container 7 carried by it are
movable toward and away from the wiping cylinder 1 by means of a
threaded shaft 11 which is rotatable in the mechanism framework
which is not shown in detail and is rotatable by means of a handle
12. The threaded shaft 11 and associated parts comprise in effect a
micrometer device which makes possible accurate and readable
adjustment of the support 13 and hence the container 7 in relation
to the jacket of the cylinder 1.
In FIG. 4 the device is shown diagrammatically in position for
applying a layer of plastic to the cylinder. The cylinder is
represented as being coated with a base layer of rubber 3 on which
there has also been applied one or more plastic layers 4. The
plastic mass 5 of which a layer is to be applied to the cylinder is
distributed on top of the cover 15 which as shown is disposed
somewhat at an angle so that the plastic mass engages the surface
of the cylinder.
When the cylinder 1 turns in the direction of the arrow, a fresh
layer of the plastic mass 5 is applied to the cylinder through the
small gap between the scraping edge of the blade 8a and the layer
of plastic 4 which had already been applied to and has solidified
on the cylinder. The plastic mass is distributed evenly by the
blade edge 8a and the thickness of the layer being applied is
accurated controlled by adjusting the blade 8a toward or away from
the cylinder by means of the threaded shaft 11. Accordingly a
further layer of plastic is applied with a completely smooth
surface and an exactly defined thickness. When the first layer has
been completely applied to the cylinder jacket, the cover 15 is
removed so that the blade 8a can smooth out any remaining uneven
spots without supplying fresh plastic mass.
Finally the blade 8a is removed from the cylinder by tilting the
whole container 7 upwardly and rearwardly about the shaft 10. A
heating and drying device 17 disposed in the peripheral region of
the cylinder 1, which can work with radiation and/or hot air,
speeds up the drying and hardening of the freshly applied plastic
layer.
When the drying and hardening is completed, the next synthetic
layer is applied in the same way as described.
There is further shown in FIG. 4 a water bath 16 which can be put
in a perpendicularly raised position as can be seen in FIG. 5, and
in which the cylinder is partially immersed in the water. This
water bath is used for the more rapid cooling of a layer that has
been applied. In the case of water soluble synthetic resin, the
water bath is used only when renewing the cover layer.
In FIG. 5 there is shown diagrammatically the position of the
device in which the worn cover layer 4 of a water soluble synthetic
mass is softened or already partially dissolved in the water bath
16 through which the cylinder 1 turns in the direction of the
arrow. The softened cover layer is then lifted off or scraped off
by the same blade 8a, which is moved successively towards the
cylinder by means of the micrometer device 11, 12, 13. The plastic
mass removed by the blade 8a collects in the container on the base
8 and is taken away via a discharge opening 8b optionally for
further use.
There is described below a detailed example for the preparation of
the plastic mass used and also for the advantageous applying of the
first plastic layer onto the cylinder jacket in the case of the use
of a plastic which is not soluble in water.
EXAMPLE 1
Use is made here for example of polyvinyl chloride known under the
Trade name of "Hostalit P/PV 3475." Two differing initial masses A
and B are produced, the first of which, A, is used at least for the
formation of the first base layer and has particularly good
strength whilst the other, B, is used at least for the formation of
the outer cover layer which when hardened gives suppleness to the
surface of the wiping cylinder and has good gliding and wear
properties.
The plastic mass A is composed of 100 parts by weight of polyvinyl
chloride PVC, 30 to 50 parts by weight, preferably 40 parts by
weight of dioctyl-phthalate (DOP), 30 to 50 parts by weight,
preferably 40 parts by weight, of tricresylphosphate (TCP) and 0.5
to 3 parts by weight, preferably 1 part by weight, of a stabilizer
known in the trade. DOP and TCP are used as softeners.
The plastic mass B is composed of 100 parts by weight of PVC, 25 to
40 parts by weight, preferably 33 parts by weight of DOP, 15 to 30
parts by weight, preferably 22 parts by weight, of TCP, 3 to 10
parts by weight, preferably 5 parts by weight of calcium carbonate,
2 to 5 parts by weight, preferably 3 parts by weight, of graphite
as a lubricant, and 0.5 to 3 parts by weight, preferably 1 part by
weight, of a stabilizer known in the trade.
The calcium carbonate contributes to increasing the wiping effect
of the wiping cylinder surface on the base plate to be wiped, and
the finely distributed graphite helps to improve the smooth
gliding.
USE OF THE PLASTIC MASS A
For applying the first plastic base layer onto the wiping cylinder
provided with a rubber jacket, the said rubber surface is roughened
so that the plastic can have a good hold on the rubber surface. A
rubber base layer with Shore hardness A amounting to between 40 and
90, and preferably between 70-75, is particularly suitable for the
applying of the plastic layer. While the thickness of the rubber
base layer can be varied, it is desirably between 0.3 mm and 4.0 mm
and preferably about 1 mm. Then the wiping cylinder jacket is
covered over its whole extent with a gauze strip, this being done
preferably by arranging that the wiping cylinder to be treated is
pressed against a pressing cylinder, and with locking of the
pressing cylinder, to prevent its rotation, the cylinder to be
treated is rotated, the gauze strip being inserted between the
cylinders. In this way the gauze strip is wound around the cylinder
to be treated smoothly, without folds or puckers. At the same time
between the two cylinders, a suitable amount of the plastic
solution A is poured, so that the gauze strip is completely
saturated with this solution. The plastic mass here serves as
adhesive by which the gauze strip is fixed onto the rubber surface.
After the stripping off of the superfluous plastic mass by means of
a blade such as blade 8a, FIG. 4 which produces an evenly
distributed layer having a thickness of 0.3 to 1 mm, preferably of
0.8 mm and after the hardening of the plastic, there is formed a
thin, even base film, in which the gauze strip is embedded.
The plastic mass when it is applied has a temperature between
20.degree.C and 60.degree.C, which is selected in such a way that
viscosity during use is kept as low as possible. After the applying
of the first base layer, the hardening out takes place at a
temperature between 200.degree.C and 250.degree.C for at least 5
minutes, in order to obtain a good adhesion of the plastic mass,
gauze strip and rubber jacket.
When preferably a mixture of nitrile and vinyl polymers is used for
the rubber jacket having a Shore hardness A 70-75, no gauze strip
is necessary, because such a rubber jacket produces an excellent
adhesion between the rubber surface and the first PVC layer.
When a sufficient hardening of the layer is obtained, there is a
delay in the putting on of the next plastic layer until the wiping
cylinder surface has again cooled off to a temperature between
20.degree.C and 60.degree.C. For speeding up this cooling, the
wiping cylinder can be immersed at least partially in a cooling
water bath by raising the pan 16 as is shown diagrammatically in
dotted lines in FIG. 4.
The strength of the hardened plastic layer produced from the mass A
can be, for example, of Shore hardness A 60 to A 70 and preferably
about A 65.
For the further plastic layers forming the midlayers, one can use
optionally either the plastic mass A or B, the only thing that is
important being that the plastic mass B is used at least as the
last outer cover layer. The mass A can be used accordingly for the
production of the further plastic layers.
After the initial treatment described, the cylinder is provided
with a firmly adhering base layer and can be covered with further
plastic layers, successively, preferably with the device shown in
FIG. 4, the thickness of which at all times preferably lies between
0.3 and 1 mm. Each of the said layers is put on at a temperature
between 20.degree.C and 60.degree.C and then is hardened by heating
to a temperature between 150.degree.C and 250.degree.C, preferably
to approximately to 200.degree.C. When the hardening process is
completed, the layer is again cooled to 20.degree.C to 60.degree.C,
and here for speeding up the cooling, the water bath 16 can be
used. The process cycle is repeated until the whole thickness of
the layer has reached a value which differs only by at least one
layer thickness from the desired thickness, which in all can amount
to 2 to 3.5 mm. For instance, four layers of plastic mass A each
having a thickness of 0.8 mm are applied amounting to a total
thickness of 3.2 mm. It has been found that the thickness of the
individual layers and the total thickness of the layers is critical
to obtain a smooth, crack-free and durable cover for the wiping
cylinder.
USE OF THE PLASTIC MASS B
For the outer cover layer or layers, as already mentioned, the
plastic mass B is used. The application of the outer cover layer
differs from the treatment of the inner layers, in that for the
hardening of this outermost layer, preferably an increased
temperature in the range of 200.degree.C to 250.degree.C is used
e.g., 200.degree.C, in order to obtain good hardness of the said
layer, which is subjected to stress during the subsequent wiping
process in the printing process. All other layers are heated to
approximately 200.degree.C. Whilst the strength of the hardened
inner layers produced from the mass A, as indicated, would
correspond to approximately Shore hardness A 65, for the strength
of the cover layer produced from the mass B one preferably selects
a strength which corresponds to Shore hardness A 80 to A 95 and
preferably A 90. The thickness of the outer layer or layers of the
plastic mass B is likewise between 0.3 and 1 mm. If a single layer
of plastic mass B having a thickness of 0.8 mm is applied over four
layers of plastic mass A each having a thickness of 0.8 mm, the
total thickness is 4 mm.
If after a certain amount of use of the wiping cylinder in the
printing process the cover layer shows a certain amount of wear and
tear, this cover layer can be renewed by removing it initially
mechanically for example by means of a lathe tool on a lathe, down
to a depth at which all cracks, damaged areas and uneven places are
done away with. Thereupon the said cover layer, which has been
removed mechanically in this way is replaced by a new plastic layer
of the mass B, which is then brought to a temperature between
20.degree.C and 60.degree.C and then is hardened at a temperature
between 200.degree.C and 250.degree.C.
The point of time of the completed hardening out can easily be
recognized with the use of Solvic PVC, as the plastic layer takes
on a transparent appearance.
EXAMPLE 2
As second example will be described the production of plastic
masses from a water soluble resin, and also the applying of this
plastic mass. For this purpose use is made of three polyvinyl
alcohol types which are customary in the trade, i.e., Mowiol 30 to
88, Mowiol 50 to 88 and Mowiol 70 to 88, which are partially
saponified, and are polyvinyl alcohols containing acetyl groups.
The first figure in the type designation characterises the length
of the molecule chain and accordingly the relative polymerization
degree of the polyvinyl acetate used; the second figure of the type
designation indicates the degree of saponification.
To produce the solution A for the base layer; one mixes 150g Mowiol
30 to 88, 150g Mowiol 50 to 88 and 900g Mowiol 70 to 88.
To this power mixture is added approximately 300g ethyl alcohol.
For this, use is made for example of "Halethyl PCB" 1,002, which is
a compound of 20 parts by weight of ethyl alcohol, 30 parts by
weight of methylethyl-ketone and 50 parts by weight of ether. The
resulting swelling paste is ground fine to a thoroughly homogenous
mass, to which is then added approximately 510 parts by weight of
hot water which is near its boiling point. Still maintaining the
temperature, the resulting solution is thoroughly homogenized. The
said homogenous solution then has added to it approximately 30
parts by weight of glycerine of pharmaceutical quality.
The thus prepared solution is filtered, and the resulting filtrate
changes after the cooling into a mass which remain viscous and
which is ready for applying. At room temperature the useful life of
this mass is 3 to 5 days till it is dried and hardened to the
extent that it requires a further treatment for reuse.
Production of the solution B for the cover layer: approximately 1.5
litres of the above described solution A is heated in a water bath
to approximately 80.degree.C. This heated solution has added to it
approximately 50 ml of chalk white (calcium carbonate CaCO.sub.3)
which previously has been suspended in a small amount of cold water
to form a homogeneous paste.
After thorough mixing, the said solution has added to it
approximately 10 ml of tannic acid which was previously dissolved
in a small amount of hot water. After cooling, the solution B
produced in this way is ready for applying.
Additionally or in place of the chalk white mentioned, the solution
A -- as in the case of the PVC -- can also have added to it an
equal amount of graphite which was previously suspended in a small
amount of alcohol, with the formation of a homogeneous paste.
APPLYING THE PLASTIC MASSES A AND B
The applying of the first plastic base layer using a gauze strip,
onto the roughened rubber jacket of the cylinder corresponds to the
process step described for PVC. The mass, however, in this case is
applied at room temperature, whilst the subsequent hardening out
needs to take place only at moderate temperatures. The hardening is
carried out to provide a Shore hardness of A 60 to A 70 and
preferably about A 65.
The separate layer thicknesses are only 0.1 to 0.3 mm and the total
thickness is selected at 1 to 2 mm. If one wishes to obtain a total
layer thickness of 2 mm and one assumes that the said base layer
has a thickness of 0.2 mm, then by means of the device of FIG. 4
for example 8 layers are applied in sequence of 0.15 mm each, using
the plastic solution A. Before the applying of the subsequent
layer, the last layer must always be well dried and hardened.
For producing the cover layer areas, one uses the above mentioned
solution B in place of the solution A. In the case considered, four
further plastic layers each 0.15 mm thick of the plastic mass B are
applied and each layer is dried and hardened before applying a
succeeding layer. The cover layers should have a hardness greater
than the under layer or layers, for example a Shore hardness
between A 80 and A 95 and preferably about A 90.
Naturally the thickness of the cover plate which is produced from
the plastic mass B can be varied at will; all that is needed is
simply that the number of the layers produced from solution A and
from solution B must form the total combination required.
In the dimensioning of the thickness of the separate plastic layers
or of the dimensioning of the total thickness, in the case of
Mowiol, one has to take into account the shrinking effect of the
plastic mass. The shrinking is also the reason why one applies one
at a time only comparatively thin layers. If one were to apply too
great layer thicknesses all at once there would be the danger that
during the hardening the layer would show uneveness or even cracks,
as a result of the shrinking.
For the renewing of a used cover layer all that has to be done is
to immerse the cylinder in a water bath and to soften or dissolve
the cover layer with simultaneous stripping off or scratching off
by means of the blade 8a, as in FIG. 5. When the drying is
completed, one or more fresh surface layers are put on, as
described, using the solution B.
EXAMPLE 3
The plastic material utilized is a polyvinyl chloride which lends
itself particularly well to the formation of mixtures with
plasticizers. These mixtures are commonly called "Plastisol."
The plastisol is a liquid characterized by a certain viscosity
which is greater when the content of the plasticizers is smaller.
When the Plastisol is heated, the viscosity at first decreases (at
a temperature of 40.degree.-50.degree. C.) then at about 60.degree.
there is a very rapid increase of the viscosity and the mass
becomes solid, attaining a stage called "pre-gelatinization." The
compact mass thus obtained is friable and has a very low mechanical
strength. When the heating is continued to about
180.degree.-200.degree. C. there is obtained a complete
"gelatinization" and after cooling it results in a material
resembling rubber which is insensible to water, aqueous solutions,
acids and alkalies, alcohol and hydrocarbons. This material is
characterized by a very high mechanical strength and the Shore
hardness of the final product is a function of the type and the
quantity of the plasticizer used. For covering wiping cylinders for
use with water, there is used a Plastisol, the characteristics of
which permit obtaining not only a good coating (for which the
viscosity should not be too high) but also the desired qualities of
the final product (hardness, mechanical strength, characteristics
of the coating, etc.).
The products used to obtain this effect are as follows:
1. Polyvinyl Chloride (PVC):
"Hostalite P/VP-3475" made by Hoechst AG Frankfort, West Germany.
This is a white powder obtained by the polymerization in emulsion
of vinyl chloride. The form and size of the molecules are such as
to provide very fluid Plastisol. While the powder is not
hygroscopic, it is advisable to store it in closed vessels.
2. Trioctyle-phosphate (TOP):
This plasticizer is manufactured by the Bayer Company.
3. Dioctyle-sebacate (DOS):
This plasticizer is supplied by the Swiss Company Oel-Chemie.
4. Plastolein 9789:
This polymeric plasticizer is supplied by the Unilever Company,
Emery, Holland.
5. Stabilizer:
During the rapid heating necessary to effect gelatinization, the
PVC has a tendency to degrade by producing hydrochloric acid while
the color changes from white to yellow to brown and to black. This
inconvenience is completely eliminated by the addition of
stabilizers. A suitable stabilizer for this purpose is the tin base
PROSPER-DBM supplied by the Commer Company.
6. Additives:
Calcium carbonate and graphite. These additives contribute to
modifying the characteristics of the final product to improve its
wiping quality and to reduce the coefficient of friction.
PREPARATION OF THE PLASTISOL
The different components should be perfectly disbursed in the
mixture which should be absolutely free of air bubbles and
moisture. For this purpose it is desirable to use a planetary mixer
which working under vacuum effects the mixing, the extraction of
air and the elimination of moisture. The different phases of the
operation are as follows:
1. The several components are placed in the mixing vessel according
to the proportions indicated below.
2. The mixer is put into operation for thirty minutes and the
vacuum pump is then put into operation. At first, the mass swells
and becomes frothy. The air discharge valve is eventually opened
slowly while the mass is observed through a porthole to prevent the
froth reaching the upper part of the vessel. After some minutes,
the valve can be completely closed, whereupon the mixer is
continued in operation for at least one hour.
3. The mixer is stopped while opening the air valve with caution
and then the mass is filtered through a bronze screen into a second
mixing vessel.
4. The blades are thoroughly cleaned and the mass is again mixed
under vacuum, the vacuum pump being maintained this time in
operation until bubbles of air are practically eliminated.
5. The mixer is stopped, the air valve is opened with caution and
finally the vacuum pump is stopped.
The Plastisol is then ready to be applied to the cylinder. It is
recommended that a freshly prepared batch be used (within 24 hours)
because in time the viscosity increases and coating becomes more
difficult.
PREPARATION OF THE SURFACE OF THE RUBBER
It is very important for the surface of the rubber to be prepared
before the application of the plastic mass in such manner as to
assure a perfect bonding of the plastic on the rubber. The
necessary operations are as follows:
1. The cylinder to be coated is placed on the coating machine, the
heating hood is lowered and the cylinder is turned at a speed of
five revolutions per minute and heated for thirty minutes (all of
the central resistances being put into operation during the last
twenty minutes). The heating is then discontinued and the cylinder
is allowed to cool while continuing to rotate for a quarter of an
hour.
2. While rotating the cylinder it is again heated for 20 minutes
(using all of the resistances during the first 10 minutes and then
only the central resistances during the last 10 minutes). Heating
is then discontinued for 15 minutes and resumed for another 20
minutes (10 plus 10 minutes).
3. The cylinder is then cooled with water, wiped dry and the
surface of the cylinder is very carefully and uniformly treated
with emery paper in order to eliminate all residual oil or grease
from the surface of the rubber. The entire surface as thus treated
should have a black color.
4. The cylinder is carefully brushed to totally eliminate the
particles rubber, is wet with water and is dried with a rubber
cloth (which cannot leave any residue).
5. The cylinder is again heated for 15 minutes (10 plus 5 minutes)
and then allowed to cool without turning until it reaches a
temperature of about 40.degree. C. The cylinder is then ready for
application of the first coat of plastic.
APPLICATION OF THE PLASTIC
First Coat
The plastisol has the following composition:
"Hostalite P/VP-3475" -- 1,000 gr.
Trioctyle-phosphate (TOP) -- 240 gr.
Dioctyle-sebacate (DOS) -- 120 gr.
Graphite -- 15 gr.
Calcium carbonate -- 15 gr.
Prosper DBM -- 10 gr.
The speed of the cylinder is regulated to 5 revolutions per minute.
When the cylinder is cold it is heated several minutes until the
surface attains a temperature of about 40.degree. C.
With the cylinder stopped, the blade and the counterblade are
brought in toward the cylinder in such manner that they barely
touch the surface of the cylinder without pressure. A small
quantity of the Plastisol is then spread along the whole length of
the blade above the line of contact between the blade and the
cylinder. The cylinder is then put in rotation and after one
complete turn the blade is slowly withdrawn so that a thin coating
(0.1 - 0.2 millimeters) is applied over the entire surface of the
cylinder. After removing the blade, the cylinder is allowed to
rotate cold for several minutes and then the heating hood is
lowered and heat is applied for 23 minutes (using all of the
resistances during the first 8 minutes and then only the central
resistances during the last 15 minutes). The heat is then turned
off but the heating hood is left in its lower position several
minutes. Then it is raised and the cylinder is cooled with water to
a temperature of about 40.degree. C. The cylinder is then wiped
dry, washed with ordinary alcohol, and when the surface is
perfectly dry, it is ready to receive a second coating. Additional
coatings of the same composition may be applied in like manner but
at least the outer coating is of a different composition as
described below.
Outer Coating
A Plastisol having the following composition is utilized:
"Hostilite P/VP-3475" -- 1,500 gr.
Trioctyle-phosphate (TOP) -- 360 gr.
Dioctyle-sebacate (DOS) -- 180 gr.
Plastolein 9789 -- 150 gr.
Graphite -- 45 gr.
Calcium carbonate -- 45 gr.
Prosper DBM -- 15 gr.
The procedure is the same as for the first coating while using a
somewhat larger quantity (about 450 cc.). During application of the
plastic, the blades are withdrawn until almost the entire amount of
plastic has been applied to the cylinder - a small quantity of
plastic, however, remaining on the blade. The curing, cooling with
water, washing with alcohol and the drying are effected as for the
first layer.
The operation of coating is repeated until the diameter of the
cylinder exceeds 266 millimeters. At the beginning of each coating
the cylinder should have a temperature of about 40.degree. C. In
the case where the cylinder is cold it is necessary to heat it
several minutes tubing the surface to this temperature.
Rectifying and Polishing
Experience has shown that it is rarely possible to obtain a
perfectly cylindrical layer of plastic by coating. To overcome this
inconvenience there has been provided a machine for truing the
plastic coated cylinder. After the last layer has been applied it
is advisable to let the cylinder sit at least over night before
proceeding with the truing. The truing operation is carried out
with the cylinder dry and comprises rotating the cylinder while
removing any high portions by a cutting tool or abrasive. One or
more operations are required according to the initial amplitude of
the irregularities. After the cylinder has been trued, it is
moistened with water and polished with an extremely fine emery
paper until the surface is perfectly smooth and uniform.
Regeneration of the Coated Cylinders
When a coated cylinder is to be renewed, it is necessary first of
all to true it until all of the surface irregularities have
disappeared. Then its diameter is checked. When the diameter is
greater than 264 millimeters the cylinder can be polished and
reused.
On the contrary if the diameter is found to be too small, it will
be necessary to apply one or more layers of plastic and to true and
polish the surface when the diameter has been brought anew to 265
millimeters.
In a case where after rectification small cavities appear on the
surface of the plastic (indicating a decomposition of the plastic)
it will be necessary to proceed with the rectification until the
basic layer of rubber is reached whereupon all of the coating
operations are repeated as described above.
The following is the list of chemicals and supplies required:
Suppliers Polyvinyl chloride Farbwerke Hochst Hostalite P/VP-3475*
or Ormag Dioctyle-sebacate (DOS) Oel-Chemie or Ormag
Trioctyle-phosphate (TOP) Bayer or Ormag Plastolein 9789**
UNILEVER, Emery or Ormag PVC Stabilizer PROSPER DBM Commer or Ormag
Calcium Carbonate Ormag Graphite Ormag Alcohol Local Brush Local
Emery Pater - Coarse grain and Ormag or Local fine grain
List of Equipment and Accessories Required:
Suppliers Planetary Mixer with vacuum pump Ormag Special Plastic
Coating Machine Ormag with Heating Hood and Ventilator for drawing
off the vapors Set of seven special receptacles Ormag for the
plastic mass with small devices for retouching Five meters of metal
cloth Ormag (bronze screen) with stainless steel frame for
filtering the mixture Mobile crane for introducing the wiping Ormag
cylinders into the coating machine Machine for rectifying or truing
the Rastelli plastic coated cylinders Polishing equipment Ormag *
Emulsion polymerized PVC. ** High molecular weight polymer
plasticizer and tackifier based on dibasic fatty alcohols and
acids.
The above-described arrangements for the production of the plastic
masses to be applied are naturally given as examples only and are
to be evaluated as such; the process of the invention can be
carried out with other synthetic plastic which are or are not
soluble in water, and similar in their properties to PVC or to the
polyvinyl alcohols, and here naturally also the constituents of the
given mixtures can be varied in type and amount.
* * * * *