Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02386593 2002-05-15
A-3492
Method and apparatus for structuring a surface to form
hydrophilic and hydrophobic regions
Description
The invention relates to a method for structuring a surface
which comprises at least a first layer which has a polymer to
form hydrophilic and hydrophobic regions by creating a latent
structure of the first layer by means of an assigned
modification device for producing a printing form for offset
printing.
Furthermore, the invention relates to an apparatus for
structuring a surface which comprises at least a first layer
which has a polymer to form hydrophilic and hydrophobic
regions by creating a latent structure of the first layer for
producing a printing form for offset printing.
Printing forms on which the surface has an outer layer of
polymer material, in particular polystyrene, styrene
copolymers and the like, and an inner layer of metallic
material, such as aluminum for example, have already been in
use for some time in the polygraphic industry. Printing forms
of this type are typically structured from an unstructured or
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undifferentiated state for use in offset printing to form
hydrophilic and hydrophobic regions or subareas according to
the subject to be printed. A common structuring method
comprises the locally selective modification of the outer
layer of the surface by temporally and spatially selective
exposure to the action of electromagnetic energy, in
particular laser radiation, and subsequent development of the
latent structure to form hydrophobic and hydrophilic regions
by removal, for example using chemicals, such as for example
printing form cleaning agents, of the non-modified regions of
the outer layer in such a way that hydrophilic regions of the
structure are formed essentially by the exposed inner layer of
the surface, while the modified regions of the outer layer are
the hydrophobic regions of the structure.
A printing form on which the surface can be structured by
means of exposure to the action of thermal laser energy and
subsequent chemical treatment to form hydrophilic and
hydrophobic regions is disclosed for example in EP 0 931 647
A1. In addition to a polymer containing carboxyl groups, the
surface in this case also has styrene. Furthermore, to
support the absorption of laser energy, an anionic dye is
provided in the surface or adjacent to it. In the document
EP 0 931 657 A1, a method for producing an offset printing
form is disclosed. Following the image-related exposure of
the printing form with infrared light, the image-related
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regions are developed by applying an aqueous liquid to the
surface of the printing form. This described method can be
carried out in particular on the printing form cylinder of a
printing unit or within a printing machine.
DE 44 26 012 C2 also discloses an erasing and hydrophilizing
apparatus on a printing unit in connection with printing forms
which can be erased, that is regenerated. A cleaning fluid, a
hydrophilizing agent, is sprayed either directly onto the
printing form or an assigned cleaning cloth. At the
circumference of the cylinder accommodating the printing form,
an image-setting device .is provided.
Conventional image-setting processes for printing forms, in
particular within printing units or printing machines, share
the common feature that the image-setting process or the
structuring process is essentially based on the interaction of
light, whether by -thermal or reactive effect, with the surface
of the printing form. Tile way in which this is realized
technically therefore requires an often sophisticated and
complex image-setting device, which comprises one or more
light sources, in particular laser .:Light sources. An image-
setting device of this type with laser light sources entails
not inconsiderable costs both in procurement and in use.
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The object of the present. invention is therefore to specify a
further method and a fl.~rther apparatus for structuring a
surface to form hydrophilic and hydrophobic regions.
This object is achieved according to the invention by a method
for structuring a surface to form hydrophilic and hydrophobic
regions with the features according to claim 1. Advantageous
developments of the invention are characterized in the
subclaims.
The method according to the invention for structuring a
surface which comprises at least a first layer which has a
polymer, for example polystyrene, polyimide, polysilane or the
like, to form hydrophilic and hydrophobic regions by creating
a latent structure of the first layer by means of an assigned
modification device for producing a printing form for offset
printing is distinguished by the fact that a gaseous, readily
volatile solvent is selectively applied as a modifying agent
to at least one locally .limited region of the surface over at
least one exposure time interval. Apart from the exposure
time interval, parameters for the gas flow, such as the gas
pressure, the flow rate, the extent of the flow field and the
like, are defined. In connection with the invention, a latent
structure is understood as meaning a structuring which
comprises regions of the surface with at least two contrasting
properties. An example of this which may be mentioned is the
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hydrophilicity-hydrophobicity, or else oleophilicity-
oleophobicity, property pairing. The term latent structure is
also to be understood as meaning that it may concern a
structure which potentially, possibly with the assistance of
one or more additional method steps, also referred to as
development, leads to a structure with at least two
contrasting properties.
If the surface, as preferred, comprises at least a first
layer, which has polystyrene, and a second layer, which may be
metallic or has polyester, in the method according to the
invention the latent structure is furthermore developed at
least in one region of the surface .in such a way that the
first layer is removed :in those regions which have not been
selectively modified. Tree second layer preferably has
aluminum. It is particularly advantageous if the modification
device can selectively reach regions of the surface along its
two dimensions spanning the latter, successively or at least
partly in parallel by translation.
According to the invention, the method for structuring a
surface which comprises at least two layers, the first layer
having polystyrene and the second layer possibly being
metallic or having polyester, by modification of the first
layer and subsequent development to form hydrophilic and
hydrophobic regions for producing a printing form for offset
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printing preferably comprises a number of steps. The first
layer of the surface of the printing form in the unstructured
state is assigned to a modification device; for example, this
assignment takes place by an arrangement in such a way that
the modification device lies opposite the surface. For
example, the printing form may be accommodated on a cylinder,
in particular a printing form cylinder within a printing unit,
rotatably about the axis of the cylinder. The modification
device can selectively reach regions of the surface along its
two dimensions, spanning the latter, successively or at least
partly in parallel by translation with suitable means, such as
actuators, linear drives, spindle drives and the like. The
cylinder is possibly assigned a drive for producing a
rotational movement about its axis. At the latest before the
modification of each selective region, the structure
information assigned to this region is made available at the
modification device. In this case, the structure information
corresponds at least to the structure of the desired subject
of printing. By selective application of a modifying agent to
regions of the surface, a latent structure is created. Used
here according to the invention as a modifying agent is a
gaseous, readily volatile solvent, which is applied to a
locally limited region of the surface over at least one
exposure time interval. The gaseous, readily volatile solvent
may in this case comprise an alcohol (R-OH) and/or an aldehyde
(R-HO) and/or a ketone (R.~-CO-Rz) and/or an ester (R1-COO-RZ).
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In connection with the invention, R, R1 or RZ may designate an
aliphatic radical, in particular a hydrocarbon chain, but also
an aliphatic radical substituted with further functional
groups, or an aromatic radical. R, R1 and R2 may be identical
or different. The latent structure is developed, at least in
one region of the surface, in such a way that the first layer
is removed in those regions which have not been selectively
modified. This results in a developed printing form with
hydrophilic and hydrophobic regions. The hydrophilic regions
are formed essentially by the exposed second layer and the
hydrophobic regions are formed essentially by the first layer
of the printing form, modified by the exposure to the action
of the gaseous, readily volatile solvent. The method
according to the invention represents a simple and low-cost
possible way of producing a printing form.
In advantageous developments of the method according to the
invention for structuring a surface, electromagnetic energy,
preferably emitted by a light source in the form of laser
radiation, is radiated at least onto the locally limited
region of the surface which is, has been or is to be modified
by applying the gaseous, readily volatile solvent. It may be
envisaged to provide the electromagnetic energy during the
application of the gaseous, readily volatile solvent to the
locally limited region. However, a type of pre-treatment or
type of post-treatment of the region to be modified by
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electromagnetic energy may also be advantageous. In other
words, the effective time interval of applying the gaseous,
readily volatile solvent may coincide essentially with the
time interval of exposure to electromagnetic energy or else be
different. It goes without saying that the intervals under
consideration may also in each case have a number of
subintervals. The energy provided by the light source on the
surface supports the action of the gaseous, readily volatile
solvent on the first layer of the surface in an advantageous
way.
The apparatus according to the invention for structuring a
surface which comprises <~t least a first layer which has a
polymer to form hydrophilic and hydrophobic regions by
creating a latent structure of the first layer for producing a
printing form for offset printing is distinguished by the fact
that a modification device applies a gaseous, readily volatile
solvent to a locally limited region of the surface over at
least one exposure time interval. The surface preferably
comprises at least a first layer, which has polystyrene, and a
second layer, which may be metallic or has polyester.
A preferred embodiment of the apparatus according to the
invention for structuring a surface which comprises at least
two layers, the first layer having polystyrene and the second
layer possibly being metallic or having polyester, by
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selective modification of the first layer and subsequent
development to form hydrophilic and hydrophobic regions for
producing a printing form for offset printing is distinguished
by the fact that a modification device applies a gaseous,
readily volatile solvent to a locally limited region of the
surface of the printing form over at least one exposure time
interval. The apparatus may typically comprise a control unit
or be connected to a control unit. At the latest before the
modification of each selective region, assigned structure
information is made available by the control unit at the
modification device. Furthermore, means for producing a
relative movement, for example by actuators, spindle drives,
servo motors, linear motors and the like, between the
modification device and the surface of the printing form are
provided. It is particularly advantageous if the modification
device reaches at least two locally limited regions of the
surface temporally and spatially in parallel. This makes it
possible to reduce the time for the modification of regions on
the overall surface by parallel processing.
In an advantageous development of the apparatus according to
the invention for structuring, it is additionally provided
that a light source, preferably a laser light source, radiates
electromagnetic energy onto at least one locally limited
region of the surface, in particular onto the locally limited
region to be modified of the surface. It goes without saying
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that means for producing a relative movement between the light
source and the surface analogous to those or identical to
those for producing the relative movement between the
modification device and the surface are possibly provided,
with the result that in each case the locally limited region
to be modified of the surface can be reached both by the
electromagnetic energy and by the modifying agent.
In a particularly advantageous embodiment of the invention,
the gaseous, readily volatile solvent comprises ethanol (C2H5-
OH) andlor 4-hydroxy-4-methyl-2-pentanone and/or 3-butoxy-2-
propanol and/or ethanal (CH3-CHO) and/or acetone (CH3-CO-CH3)
and/or acetic ether (CH3-COO-CZHS) .
The apparatus according to the invention for structuring a
surface may be advantageously used in a printing form exposer
or in a printing unit, known as a direct-imaging printing
unit. A printing machine according to the invention, which
for the processing of sheets typically comprises a feeder, one
or more printing units and a delivery unit or for the
processing of paper webs comprises a reel changer, at least
one printing unit, a dryer and a folder, is distinguished by
at least one printing unit which has at least one apparatus
according to the invention for structuring a surface.
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Further advantages and advantageous embodiments and
developments of the invention are represented on the basis of
the following figures and their descripts.ons. In the drawing
specifically:
Figure 1 shows a schematic representation of a preferred
embodiment of the method according to the invention for
structuring a surface on the basis of four subfigures,
Figure 2 shows a schematic representation of an embodiment of
the apparatus according to the invention with the advantageous
development of an additional light source,
Figure 3 shows schematic representations of two arrangements
of embodiments within a printing .form exposer or a printing
unit, and
Figure 4 shows schematic representations of two embodiments of
the apparatus according to the invention for the simultaneous
modification of more than one region of the first layer of the
surface.
Figure 1 shows a schematic representation of a preferred
embodiment of the method according to the invention for
structuring a surface on the basis of four subfigures. In
subfigure A, a printing form 10 with a first layer 12 and a
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second layer 14 is shown. In connection with the embodiments
described in figure 1 and the subsequent figures, the first
layer 12 may also be referred to as the outer layer and the
second layer 14 may also be referred to as the inner layer.
Apart from these layers on its surface, the printing form 10
may also comprise further layers in its depth or be
accommodated on a support; for the method according to the
invention, it is essentially immaterial whether the printing
form is flat or curved. The first layer 12 has in this case
polystyrene. In connection with the invention, polystyrene is
to be understood a:~ meaning both essentially pure polystyrene
and polystyrene copolymers, for example with polymers
containing carboxy_L groups. The second layer 14 may be
metallic, preferably comprises aluminum. An alternative
material which has proven to be advantageous comprises
polyester. Without. rest::ricting the generality with regard to
the initial state of the structure of the surface 10, the
method according to the invention starts out from an
unstructured first layer 12, as an embodiment in subfigure A
of figure 1 shows.
In subfigure B of figure 1 it is shown how the printing form
10 with the first layer 12 above the second layer 14 is
arranged lying opposite a modification device 16. A gaseous,
readily volatile solvent 18, comprising the substances
described above, is applied from the modification device 16 to
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a region of the printing form 10 in a locally limited manner,
for example through outlet nozzles. It is likewise
conceivable for the gaseous, readily volatile solvent 18 to be
applied to the surface of the printing form 10 by means of
flexible lines, such as hoses or the like. The action of the
gaseous, selective solvent 18 produces a modified surface 110.
The double-headed arrows indicate a first translational
direction 112 and <~ second translational direction 114, in
which t:he modification device 16 is movable in relation to the
printing form 10 in such a way that regions of the surface can
be selectively reached .in succession along the two dimensions
spanning the printing form. The modification device 16 is
preferably linked by means of a connection for the exchange of
data and/or control signals 116, which may also be partly
wireless, to a control unit 118. At the latest before the
modification of each selective region, structure information
assigned to the region to be modified is made available at the
modification device 16 by the control unit 118.
In subfigure C of figure l, a latent structure, created by
means of the modification device 16 and formed by a number of
modified surfaces 110, is shown on and/or in the first layer
12 of the printing form 10. The action of the gaseous,
readily volatile solvent is directed at the first layer 12 of
the printing form 10, but an increase in the adhesion of the
first layer 12 on the second layer 14 of the printing form 10
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can also be additionally achieved. The latent structure
corresponds to the hydrophobic component of the image-related
structuring, that is it comprises the ink-carrying hydrophobic
regions of the surface of the printing form in offset
printing.
For the development of the latent structure of the printing
form 10, at least in one region of the surface the first layer
12 is removed in taose regions which have not been selectively
modified. Removal of the first, non-modified layer 12 is
possible for examp.l_e by the use of a cleaning fluid, a common
printing-form cleaning agent. On account of the modification
of the first layer 12 in the method according to the
invention, a number of modified surfaces 110 remain on the
printing form, while the second layer 14 is exposed. The
second layer 14 is given the function of the hydrophilic
regions in offset printing. The structuring to form
hydrophilic and hydrophilic regions provided by the method
according to the invention is schematically represented in
subfigure D of figure 1.
Figure 2 is a schematic representation of an embodiment of the
apparatus according to the invention with the advantageous
development of an additional light source. A printing form 10
with a first layer 12 and a second layer 14 is shown. The
printing form 10 i~; arranged such that it lies opposite a
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modification device 16. The modification device 16 applies a
gaseous, readily volatile solvent 18 to a region of the
printing form 10 in a locally limited, temporally and
spatially selective manner. A modified surface 110 is
produced on the printing form 10. The modification device 16
is movable in a first translational direction 112 and a second
translational direction 114 in relation to the printing form
10. The modification device 16 is assigned a light source 20,
preferably a laser light source, emitting in particular in the
infrared wavelength range. A light beam 22 illuminates at
least the region of_ the printing form 10 which is modified by
the action of the gaseous, readily volatile solvent 18, with
the result that a modified surface 110 is produced.
Figure 3 schematically relates to two arrangements of
embodiments within a printing form exposer or a printing unit
of the apparatus according to the invention. Shown in
subfigure A of figure 1 is an arrangement as it may be
realized with preference in a printing unit in which the
printing form 10 with the first layer 12 and the second layer
14 is accommodated on .a cylinder 30. The cylinder 30 is
rotatable about its axis 32 :in rotational direction 34.
Assigned to the first layer 12 of the printing form 10 is the
modification device 16, which is movable along the
translational direction 36 essentially parallel in relation to
the axis 32 of the cylinder 30. Tn the combination of the
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rotational and translational movement, all the points of the
surface of the printing form 10 are reached by the
modification device 16. Shown in subfigure B of figure 3 is
an embodiment of what is known as an in-drum arrangement. In
other words, the printing form 10 with the first layer 12 and
the second layer 14 is accommodated in a concave manner, with
the result that the assigned modification device 16, located
on a shaft 38, reaches all the points of the surface of the
printing form 10 by movement in translational direction 36,
essentially parallel to the direction defined by the shaft 38,
and by rotation in rotatic>nal direction 34 about the axis
defined by the shaft 38.
Figure 4 is a schematic representation of two embodiments of
the apparatus accowding to the invention for the simultaneous
modification of more than one region of the first layer of the
surface. Shown in subfigure A of figure 4 is a number of
modification devices 16, here by way of example and without
restricting generality seven modification devices 16, which
are assigned to the first layer 12, lying opposite, of the
printing form 10 with the first layer 12 and second layer 14
accommodated on the cylinder. The cylinder 30 is rotatable
about its axis 32 i.n rotational direction 34. The number of
modification devices 16 are configured as an integrated
modification devices 40. In other words, this embodiment of
the apparatus according to the irrvention comprises an
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integrated modific:atior~ device 40 which has in a modular
manner a plurality of modification devices 16 for applying a
gaseous, readily volatile solvent to a locally limited region
of the surface of the printing form 10. It is shown in
subfigure B of figure 9 that, in an alternative embodiment of
the apparatus acct>rding to the invention, a number of
modification devices 16, here by way of example four, which
are arranged such that they lie opposite the printing form 10
accommodated on the cylinder 30, may be provided. Subregions
of the overall surface of the printing form 10 are in each
case reached by a modification device 16 and exposed in an
image-related manner to the gaseous, readily volatile solvent
18. With the embodiments shown in figure 4, a parallel or
simultaneous modification of at least two regions of the
surface of the printing .form 10 is at least partly possible.
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List of designations
printing form
12 first layer
5 14 second layer
16 modification device
18 gaseous solvent
110 modified surface
112 first translational direction
10 114 second translationa:l_ direction
116 connection for the exchange of data and/or control
sign als
118 control unit
light source
15 22 light beam
cylinder
22 axis
34 rotational direction
36 translational direction
20 38 shaft
integrated modification device
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