This invention relates to improvements in toner bonding
It has long been recognised that toner deposition systems
have a number of weaknesses that make them unsuitable for use with data that is
vulnerable to alteration.
Two of these weaknesses are related to the way the toner
is bonded to the surface of the paper and both affect the security of the document.
A third is associated with the material composition of toner.
The first is the effect that variations in paper surface
have on the bond, it has been shown that indentations i.e. watermarks and normal
variation to surface characteristics of the paper can reduce the strength of the
bond between the toner and the surface. This can result in the toner breaking off
during the life of the document or in the extreme cases not bonding at all. Documents
with poor bonding or incomplete characters from this problem impact upon the detection
of deliberate alterations, as the persons checking the document become use to seeing
variations within the characters on genuine data and therefore becomes less able
to determine what is altered.
The second problem is that, as the bond of the toner does
not penetrate the surface of the paper it means that the bond can be broken by physical
force alone and this may mean that the level of distribution to the surface of the
substrate is low which means the detection by visual means is very difficult. The
third problem is due to the material used to produce the toner. Toner was never
intended for use as a security feature and therefore the majority of common toners
do not contain materials that lend themselves to detection by machine-readable techniques.
With the increasing demand for higher speeds in personalisation
of security documents, the use of toner deposition systems has increased and this
process has been developed to tackle these three major problems. It is a process
that will give increased security to toner produced data and will introduce a method
by which the integrity of the coating can be verified by machine-readable techniques.
In EP A 0839670 we propose a method of security coating
of documents wherein a coating is applied to fused markings such as laser printed
characters in order to protect the markings against wear and tampering.
US 5045426 proposes that before a document is laser printed,
a carrier web should be prepared by application of an adhesion-enhancing composition
to the web in at least selected places where the web is to be printed, and the application
may be carried out by printing with a flexographic press, a process adopted for
use in particulate with plastics webs. The web is then laser printed in the areas
which have been so prepared but there is no teaching of providing a coating over
the markings to protect these against wear or tampering, although adhesion to the
web is improved by the pre-printing coating.
The object of this process is three-fold the first is to
produce a surface that gives a stronger bond to toner than the surface of the paper.
The second is to add a security coating to selected areas of the document, that
will improve the security of the toner allowing the integrity of the data below
to be validated by machine reading techniques. This process also allows the materials
to be applied only where the toner-generated data may be applied, minimising the
use of materials.
The invention provides a process for security coating of
a document, characterised in that the process comprises the steps of first applying
a pre-coating by printing a coating material onto selected areas of a substrate,
printing with hot melt toner on the selected areas to provide a toner image and
fusing the toner image, and applying an over-coating by printing a further coating
material onto the toner image.
The process is for coating a secure bond for toner deposition
images and the application of a secure coating and may comprise a selective coating
applied to selective areas of the fused toner.
The coating applied on to the fused toner may be machine
readable by the use of transmission and reflectance of any or a combination of visible
light, Ultra violet light and/or infra red light.
The material applied to the surface of the substrate may
be cured by the use of one or more external energy sources comprising any of IR,
UV radiation, Electron beam or any other suitable energy source.
The coating applied on top of the toner may be cured by
the use of one or more external energy sources comprising any of IR, UV radiation,
Electron beam or any other suitable energy source.
The coating to the substrate is applied by using a printing
process i.e. a lithographic process, a flexographic and Gravure process or any or
any other printing process.
The coating applied on top of the toner is applied by using
a printing process i.e. lithographic process, flexographic and Gravure process or
any other printing process.
A separate coating may be applied to the substrate and
a further coating then applied on top of the fused toner.
The first step in the process is preferably to print a
coating onto the surface of the paper in at least the areas where the toner would
be applied. This coating is preferably applied on the top of any other printed designs.
The coating can be applied by a printing process such a lithographic, Gravure or
flexographic or any other printing process. The documents may then be processed
in toner deposition system and the toner is then fused as normal within the machine.
The fused images are than preferably coated with a material
over all or some of the toner generated marking. The coating is applied by the flexographic
lithographic printing process or Gravure or any other printing process.
With the use of this process the toner bonding variations
that occur naturally on the surface of the paper can be reduced thus increasing
the bonding of the toner to the paper. The coating gives improved security against
deliberate remove of toner by physical means and a method by which the area of toner
generated data can be scanned using machine reading techniques.
A process according to the invention will now be explained
by way of an example.
Example Laser Printing
In accordance with the invention, the first process step
is to print a coating on to the document to be laser (toner-deposition) printed
in at least the areas where the toner is to be deposited on to the substrate. This
is done using a printing process and the material is applied on top of any other
printings on the document, in at least the areas onto which the toner is to be applied.
The second process is to laserprint the variable details onto the document. The
toner is then fused in the standard way.
The document with the fused toner is then coated with a
second layer using a printing process; the coating is used to cover at least the
most sensitive toner generated data. The document is then issued, once the document
is used and returned for reconciliation it can be passed along a track with a reader
that checks if the coating is till intact and therefore if the data safety has been