Language selection

Search

Patent 1037103 Summary

Third-party information liability

Some of the information on this Web page has been provided by external sources. The Government of Canada is not responsible for the accuracy, reliability or currency of the information supplied by external sources. Users wishing to rely upon this information should consult directly with the source of the information. Content provided by external sources is not subject to official languages, privacy and accessibility requirements.

Claims and Abstract availability

Any discrepancies in the text and image of the Claims and Abstract are due to differing posting times. Text of the Claims and Abstract are posted:

  • At the time the application is open to public inspection;
  • At the time of issue of the patent (grant).
(12) Patent: (11) CA 1037103
(21) Application Number: 213290
(54) English Title: METHOD FOR PREPARING PRINTING PLATE FOR USE IN LITHOGRAPHY
(54) French Title: METHODE DE PREPARATION DE CLICHES D'IMPRESSION UTILISES EN LITHOGRAPHIE
Status: Expired
Bibliographic Data
(52) Canadian Patent Classification (CPC):
  • 101/61
  • 314/8
(51) International Patent Classification (IPC):
  • G03G 13/28 (2006.01)
  • B41C 1/10 (2006.01)
  • G03G 13/16 (2006.01)
(72) Inventors :
  • YAMADA, YOSHIHIKO (Not Available)
  • ANDO, ITSURO (Not Available)
(73) Owners :
  • RANK XEROX (Not Available)
(71) Applicants :
(74) Agent:
(74) Associate agent:
(45) Issued: 1978-08-22
(22) Filed Date:
Availability of licence: N/A
(25) Language of filing: English

Patent Cooperation Treaty (PCT): No

(30) Application Priority Data: None

Abstracts

English Abstract




METHOD FOR PREPARING PRINTING PLATE
FOR USE IN LITHOGRAPHY

ABSTRACT OF THE DISCLOSURE
Printing masters of improved contrast are obtained by
forming and developing an electrostatic latent image comprising
a conductive substrate, an abhesive ink-releasing silicone
surface layer and a photoconductive layer, said method of
imaging comprising primary charging the master, selectively
illuminating said master with an image pattern to effect charge
migration, secondary charging said master, uniformly
illuminating said master wherein a developable electrostatic
latent image is formed on the exposed surface of said abhesive
layer, and developing said image.


Claims

Note: Claims are shown in the official language in which they were submitted.




The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:


1. A method of preparing a waterless lithographic
master comprising forming an image on a non-imaged master
comprising a photoconductive layer, a conductive substrate,
and an abhesive ink releasing silicone surface layer, the
imaging comprising primary charging the master, selectively
illuminating said master with an image pattern to effect
charge migration, secondary charging said master, uniformly
illuminating said master wherein a developable electrostatic
latent image is formed on the exposed surface of said
abhesive layer, and developing the image by deposition of
marking material.
2. The method of Claim 1 wherein the image is
developed with an ink accepting particulate toner.

12

Description

Note: Descriptions are shown in the official language in which they were submitted.


~037~03
BACKGROUND OF THE INVENTION
This invention relates to a xerographic method for
preparing a printing plate for use in lithography, and more
particularly to a method for preparing a printing plate for
use in lithography in which no fountain solutions or dampen-
ing solutions are required in the non-image area in order to
prevent adhesion of inX thereto.
In general, lithography is based on the principle
that if an oily ink is applied to the surface of a printing
plate having a non-imaged bearing area which has been dampened
with a fountain solution, the non-imaged areas repel the oily
ink while the oily ink adheres to the imaged area which is
oleophilic and hydrophobic.
Heretofore, various methods for preparing a printing
plate have been employed. These methods, however, involve
special treatments and in order to produce a copy conforming
to the quality of the original image and to sustain uniformity
in the copies obtained, the balance between the ink and water
required must be carefully controlled.
It has recently been discovered that if the non-
imaged areas of the printing master are formed of an abhesive
silicone elastomer, lithographic ink is readily released from
said areas even in the absence of fountain solution or dampen-
ing solution. This offers considerable simplification in
process control and printing apparatus. This process has been
called variously dry lithography, waterless lithography, or
driography.
A particularly advantageous method for preparing
printing plates for dry lithography takes advantage of the
fact that xerographic toner which may be made of ink receptive
materials, may be deposited in image patterns on a photocon-
~,- . .

--2--


10371Q3
ductive plate whose surface comprises an ink releasing silicone
elastomer. Typical of such photoconductive configurations are
- zinc oxide dispersions in cured silicone elastomer binders.
~hile such photoconductive masters have good photosensitivity,
they do not make very effective printing plates for waterless
or dry lithography. This is apparently because a large portion
(typically 20 - 40%) of the surface area comprises exposed (or
only thinly covered) photoconductive pigment which is inherently
ink~receptive. The bac~ground areas of the imaged plate accord-
ingly tend to accept ink after the first thin surface coating of
binder has been abraded and the underlying pigment becomes
exposed to the ink. Typically this occurs after the first 10 -
50 prints have been run, and contrast is rapidly degraded there-
after. Accordingly conventional silicone elastomers with
photoconductive materials do not offer satisfactory printing
surfaces for long run waterless lithography. It is to this
problem to which this invention is directed.
SUMMAR~ OF THE INVENTIO~
It has now been discovered that the aforesaid defects
can be obviated and prints of excellent contrast obtained,
employing masters having ink releasing abhesive surface layers
of any desired thickness without the need for photosensitive
particles dispersed therein.
In accordance with one aspect of this invention there
is provided a method of preparing a waterless lithographic
master comprising forming an image on a non-imaged master
comprising a photoconductive layer, a conductive substrate, and
an abhesive ink xeleasing silicone surface layer, the imaging
comprising primary charging the master, selectively illuminating
said master with an image pattern to effect charge migration,
secondary charging said master, uniformly illuminating said

~ _3_

1037103
master wherein a developable electrostatic latent image is
formed on the exposed surface of said abhesive layer, and
developing the image by deposition of marking material.




-3~-

",~,

- - \

~037103
DETAILED DESCRIPTION OF THE I~V~NTION
Methods of imaging, suitable ink releasing abhesive
materials and other aspects of the invention will now be dis-
cussed in detail.
The printing master consists essentially of a con-
ductive supporting substrate, an abhesive ink releasing sili~
cone surface layer and a photoconductive layer. The substrate
may be formed of a metal such as aluminum, a sheet of paper with
a metallic foil bonded thereto, a sheet of paper rendered con-

ductive by chemical treatment or other similar material.
The photoconductive layer may comprise any conven-
tional photosensitive material optionally dispersed in a suit-
able binder. Typical photosensitive materials include amorphous
selenium, cadmium sulfide, cadmium sulfoselenide, zinc oxide,
or an organic photoconductive material such as poly(vinyl car-
bazole) complexed with trinitrofluorenone. Typical binders
include dielectric polymeric materials such as polyesters,
alkyd resins, silicone resins and copolymers of styrene and
butadiene.
Conventional silicone elastomer gums can be employed
in the invention. These include those having only methyl con-
taining groups in the polymer chain such as polydimethylsil-
oxane, gums having both methyl and phenyl containing groups in
the polymer chain as well as gums having both methyl and vinyl
groups, methyl and fluorine groups, or methyl, phenyl and
vinyl groups in the polymer chain.


7103
Exemplary of suitable room temperature vulcanizable
gums which can be cured at ambient temperature and atmospheric
conditions include RTV-108, 106, and 118 polydimethylsiloxane
gums available from General Electric Company. Room tempera-
ture vulcanizable gums can be cured by using poly-functional
silanes and siloxanes as crosslinking agents together with
certain catalysts. The preferred crosslinking agents are
methoxy and ethoxy silanes or polysiloxanes because of their
reactivity. Suitable catalysts are supplied by the manufac-
turer of the gum.
Typical silicone gums which are curable at elevated
A~ temperature and suitable for use in the invention are Syl Gard
~F
#182, Syl Off #22 and #23, manufactured by E~ow Corning Corpora-
tion; Y-3557 and Y-3602 silicone gums supplied by Union Carbide
Company and #4413 and #4427 heat curable silicone gums supplied
by General Electric Company. Typical catalysts include diiso-
cyanates such as toluene diisocyanate and peroxides such as
dibenzoyl peroxide which are available from the manufacturer
of the gum.
Ink releasable copolymers which can be employed and
coalesced at elevated temperature comprise heterophase block
copolymeric compositions consisting of an organopolysiloxane
material and a non-silicone polymeric material. Polymeric
materials which can be employed as the non-silicone component
of the heterophase polymeric composition include materials
such as poly ( ~C -methylstyrene), polycarbonate, polysulfone,
polystyrene, polyester, polyamide, acrylic polymers, poly-
urethané, and vinyl polymers. The present invention is not
intended to be limited by the material for this non-silicone
phase.


~037103
While not limiting, preferred proportions for the
heterophase polymeric composition comprise a ratio by weight
of between about 95 to 50 parts organopolysiloxane to 5 to 50
parts of the non-silicone polymeric phase. This ratio range of
organopolysiloxane to non-silicone polymer, provides suitable
ink release materials for the ink release layer of the instant
printing master. Copolymers of the above type, could be typi-
cally prepared in a manner as is illustrated by the procedure
for preparation of an organopolysiloxane polystyrene block-

copolymer as described in Macromolecules, Volume 3, January-
February 1970, pages 1-4.
The silicone mixture can be applied to the photocon-
ductive layer by conventional techniques such as solvent casting,
dip coating or draw-bar coating after dissolution in organic
solvents which typically may be solvents such as benzene, hexane,
heptane, tetrahydrofuran, toluene, xylene, as well as other
common aliphatic and aromatic solvents. Powdered photoconductors
may be applied to the substrate by first coating a thin layer of
oil thereover and then cascading the powder against the oiled
surface. Vacuum evaporation is a desirable method for coating
materials such as amorphous selenium.
In a preferred embodiment of the invention, the
master is imaged by the Katsuragawa Process. This process
comprises the steps of applying a first electric field across
the photosensitive layer to deposit an electric charge of a
first polarity on the surface of the silicone insulating layer,
applying a second electric field across the photosensitive
element to deposit an electric charge of a polarity opposite
to the first charge on the surface of the insulatlng layer and
projecting a light image concurrently with the application of
the second field to form an electrostatic latent image on the




-6-

1037103
surface of the insulating layer. The entire master is then
subjected to blanket exposure by light and the latent image
developed to produce the imaged printing master. This is the
most photosensitive process and exhibits high electrostatic
contrast. The Katsuragawa Process is described in more detail
in an article titled, "Electrophotographic Processes Using a
Dielectric Layer Bonded to a Photoconductive Layer as in the
- Katsuragawa Process" by Nakamura ~IEEE Transactions on Electron
Devices, Volume 19, ~4, April, 1972).
Another imaging process which can be employed is the
Canon Process. In this process, the master is first given a
primary charge followed by simultaneous image exposure and A.
C. corona discharge, and finally blanket light exposure.
During the primary charge, opposite polarity charge is formed
at the interface between the insulating silicone layer and
the photoconductive layer. In this step the charging polar-
ity depends on the character of the photoconductor. That is,
~l positive charge is applied to n-type photoconductors and neg-
`I ative charge to p-type photoconductors. During the second
step of simultaneous image exposure and A.C. discharge, the
primary charge on the top surface of the light-exposed ~ortion
is eliminated by an A.C. corona discharge and the charge at
I the interface of the light-exposed portion is also eliminated
In the dark portion, the primary charge on the insulating
layer is difficult to discharge and almost all charge remains
without decay because the charged layer at the interface is
not discharged but remains as it was. During the final step
of blanket illumination, the electrostatic charge remaining at

-



103~103
the interface in the dark portion is partly eliminated and the
latent image is formed by the primary charge remaining in the
dark portion. The Canon Process is discussed in more datail
in an article titled, "CanQgraphy (canon NP Process) in Elec-
trophotography" by Mitsui (IEEE Transactions on Electron De-
vice~, Volume 19, #4, April, 1972).
Finally, the Hall method of imaging may be employed
(described in U.S. Patent 3,234,019), which is herein incor-


porated by reference. By the Hall Process, the master is first
sensitized by applying a uniform electrostatic charge to the

exposed surface or primary charged, followed by a second stepof selectively illuminating the plate in accordance with an
image pattern to effect charge migration. The plate is then
subjected to a secondary charging to bring the exposed surface
to a uniform potential and finally a blanket illumination
whereby a developable latent electrostatic image is formed on
the exposed surface of the master which is then developed.
Further, while the master has been described as having three
.
layers, improved results may be obtained if one or more insu-
lating layers are present such as for example a non-conductive

plastic, resin or other film-forming member sandwiched between
the photoconductive layer and the master substrate.
The thickness of the various layers will depend upon
the particular materials employed, but generally the substrate
will have a thickness between about 5 and about 50 microns.

The thickness of the silicone surface layer is based upon the
relative thickness of the photoconductive intermediate layer.
It is generally advisable that the dielectric thickness



~ -8-


~037~a3
(dielectric thickness being defined as the geometrical thick-
ness/dielectric constant) of the silicone surface layer
relative to the photoconductive layer be in the range of from
about 0.1:1 to about 10:1 and preferably from about 0.5:1 to
about 2:1. For example


,




:,
'
:'

::,
. .

:
.:




--8A--


~03~7~03
the master might comprise a conductive substrate of aluminum
10 microns thick, a photoconductive layer of amorphous
selenium approximately 0.5 microns in thickness and a
silicone elastomer overcoating of about 10 microns.
The thickness of the various layers will depend upon
the particular materials employed but generally the substrate
will have a thickness between about 5 and about 50 microns, the
photosensitive layer between about 30 and about 50 microns, and
the abhesive silicone layer between about 5 and about 40 microns.
Conventional particulate imaging materials, commonly
referred to in the art as toner, can be employed as the marking
material to develop the electrostatic latent image. Typical
toners are finely divided thermoplastic polymers combined with
a carrier such as glass and metal beads and a pigment such as
}5 carbon black. Typical imaging polymers include styrene polymers
such as poly(styrene), styrene-n-butyl/methacrylate copolymer,
and styrene-butadiene copolymer. Other materials which can be
employed include: poly(ethylene), poly(propylene), ethylene-
vinyl acetate copolymers, acetals, acrylics, poly(amides),
poly (imides), phenoxies, and vinyls.
Typical inks can be employed in the printing method
of the invention to include inks of the oleophilic type having
the vehicle component for the ink pigments derived from various
oleophilic materials such as aromatic and aliphatic hydro-
carbons, drying oil varnishes, lacquers and solvent type resins.
Other suitable inkg include the glycol and rubber based inks.
The imaged printing master can thereafter be employed
in a planographic printing operation, including direct or
offset lithography, with the dampening system removed to
provide good quality prints over an extended period of operation.


_g_

~0;~7103
The following examples will serve to illustrate the
invention and embodiments thereof. All parts and percentages
in said Examples a~d elsewhere in the specification and claims
are by wei~ht unless otherwise specified.
EXAMPLE I
A printing master is prepared as follows~ An
aluminum master substrate is coated with a xylene slurry of
cadmium sulfide powder incorporated in a thermoplastic acrylic
resin consisting of a copolymer of n-butyl and isobutyl meth-
acrylate. The photoconductive powder and acrylic resin are
present in equal volume amounts. The formed layer is then
air dried and further dried at 80c for several hours. Several
coatings are applied to obtain a dry film thickness of 40
microns. An insulating thermosetting acrylic resin is then
coated on the photoconductive layer to a thickness of about
10 microns, the resin is cured by heat and then a silicone
elastomer gum, curable at an elevated temperature, applied
thereon to a thickness of about 30 microns and this layer cured
by heat. The master is then imaged by primary charging the
master to a positive polarity followed by a secondary charging
of negative polarity which is effected simultaneously with
the exposure of the image. The master is then subjected to
blanket exposure whereby an electrostatic latent image is
formed on the surface of the master. The image is developed
by electrostatically depositing a toner comprising carbon
black and a polyethylene thermoplastic polymer. The developed
image is fixed to the master by heat, the master inked and
prints made therefrom without prior application of a~ueous
fountain solution. Prints of excellent contrast are obtained.


--10--

1037103
EXAMPLE II
The general procedure of Example I is repeated but
for the exception that the insulating thermosetting acrylic
resin layer is omitted. The total thickness of the photo-
conductive layer is 40 microns and a 25 micron layer of General
Electric silicone RTV 108 elastomer gum is coated over this
and cured under ambient conditions. The photoreceptive master
is then charge exposed and developed to provide a waterless
lithographic master. The master is inked and excellent prints
are obtained.
EXAMPLE III
,
The general procedure of Example I is repeated but
for the exception that the photoconductive composition employed
is an equimolal complex of 2,4,7-trinitro-9-fluorenone with
lS poly-N-vinylcarbazole. The coating is prepared by dissolving
the polyvinylcarbazole in tetrahydrofuran, whereafter the
trinitrofluorenone is added to the polymer sol~tion. The
solution is coated on the aluminum substrate by using a
:
doctor blade to a dry film thickness of 20 microns. The dried
photoconductive film is overcoated with a 20 micron thick layer
of silicone elastomer (General Electrlc RTV 108) and cured.
- The master is charged to a negative potential, imagewise-
exposed, recharged to a zero potential while simultaneously
::~
subjecting the master to blanket exposure and the latent image
developed with toner. The toner is fused, the master inked
: '
and excellent prints are made therefrom.
Having described the invention with reference to these
specific embodiments, it is to be understood that numerous
variations can be made without departing from the spirit of t`ne
invention and it is intended to encompass such reasonable
variations or equivalents within its scope.


' ` -11-

Representative Drawing

Sorry, the representative drawing for patent document number 1037103 was not found.

Administrative Status

For a clearer understanding of the status of the application/patent presented on this page, the site Disclaimer , as well as the definitions for Patent , Administrative Status , Maintenance Fee  and Payment History  should be consulted.

Administrative Status

Title Date
Forecasted Issue Date 1978-08-22
(45) Issued 1978-08-22
Expired 1995-08-22

Abandonment History

There is no abandonment history.

Owners on Record

Note: Records showing the ownership history in alphabetical order.

Current Owners on Record
RANK XEROX
Past Owners on Record
None
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.
Documents

To view selected files, please enter reCAPTCHA code :



To view images, click a link in the Document Description column. To download the documents, select one or more checkboxes in the first column and then click the "Download Selected in PDF format (Zip Archive)" or the "Download Selected as Single PDF" button.

List of published and non-published patent-specific documents on the CPD .

If you have any difficulty accessing content, you can call the Client Service Centre at 1-866-997-1936 or send them an e-mail at CIPO Client Service Centre.


Document
Description 
Date
(yyyy-mm-dd) 
Number of pages   Size of Image (KB) 
Description 1994-05-16 12 462
Drawings 1994-05-16 1 6
Claims 1994-05-16 1 22
Abstract 1994-05-16 1 19
Cover Page 1994-05-16 1 17