Note: Descriptions are shown in the official language in which they were submitted.
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SCREEN PRINTING STENCIL PRODUCTION
BACKGROUND TO THE INVENTION
Field of the Invention
The present invention relates to the production of
stencils for screen printing.
Related Background Art
The production of screen printing stencils is generally
well known to those skilled in the art.
One method, referred to as the "direct method" of
producing screen printing stencils involves the coating of a
liquid light-sensitive emulsion directly onto a screen mesh.
After drying, the entire screen is exposed to actinic light
through a film positive held in contact with the coated mesh
in a vacuum frame. The black portions of the positive do not
allow light to penetrate to the emulsion which remains soft
in those areas. In the areas which are exposed to light, the
emulsion hardens and becomes insoluble, so that, after
washing out with a suitable solvent, the unexposed areas allow
ink to pass through onto a substrate surface during a
subsequent printing process.
Another method, referred to as the "direct/indirect
method" involves contacting a film, consisting of a pre-coated
unsensitised emulsion on a base support, with the screen mesh
by placing the screen on top of the flat film. A sensitised
emulsion is then forced across the mesh from the opposite
side, thus laminating the film to the screen and at the same
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time sensitising its emulsion. After drying, the base support
is peeled off and the screen is then processed and used in the
same way as in the direct method.
In the "indirect method" a film base is pre-coated with
a pre-sensitised emulsion. The film is exposed to actinic
light through a positive held in contact with the coated film.
After chemical hardening of the exposed emulsion, the
unexposed emulsion is washed away. The stencil produced is
then mounted on the screen mesh and used for printing as
described above for the direct method.
In the "capillary direct method" a pre-coated and pre-
sensitised film base is adhered to one surface of the mesh by
the capillary action of water applied to the opposite surface
of the mesh. After drying, the film is peeled off and the
screen then processed and used as described for the direct
method.
In addition to the above methods, hand-cut stencils can
be used. These are produced by cutting the required stencil
design into an emulsion coating on a film base support. The
cut areas are removed from the base before the film is applied
to the mesh. The emulsion is then softened to cause it to
adhere to the mesh. After drying, the base is peeled off.
The screen is then ready for printing. This method is
suitable only for simple work.
One problem generally associated with all the prior art
methods is that many steps are necessary to produce the
screen, thus making screen production time-consuming and
labour-intensive.
Another problem is that normal lighting cannot be used
throughout the screen production process in any of the methods
except hand cutting. This is because the stencil materials are
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light-sensitive. In addition, it is necessary to provide a
source of actinic (usually W) light for exposing the stencil.
This usually incurs a penalty of initial cost, space
utilisation and ongoing maintenance costs.
Other methods of preparing printing screens are
available. CA-A-2088400 (Gerber Scientific Products, Inc.)
describes a method and apparatus in which a blocking
composition is ejected directly onto the screen mesh surface
in a pre-programmed manner in accordance with data
l0 representative of the desired image. The blocking composition
directly occludes areas of the screen mesh to define the
desired stencil pattern.
EP-A-0492351 (Gerber Scientific Products, Inc.) describes
a method where an unexposed light-sensitive emulsion layer is
applied to a screen mesh surface and a graphic is directly
ink-jet printed on the emulsion layer by means of a printing
mechanism to provide a mask through which the emulsion is
exposed before the screen is further processed.
Both the above methods require the use of very
specialised equipment (because of the need to handle large
complete screens) which incurs a certain cost as well as
imposing restrictions arising from the limitations of the
equipment, in particular in terms of the size of screen and
its resolution.
Ink-jet printers operate by ejecting ink onto a receiving
substrate in controlled patterns of closely spaced ink
droplets. By selectively regulating the pattern of ink
droplets, ink-jet printers can be used to produce a wide
variety of printed materials, including text, graphics and
images on a wide range of substrates. In many ink-jet printing
systems, ink is printed directly onto the surface of the final
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receiving substrate. An ink-jet printing system where an image
is printed on an intermediate image transfer surface and
subsequently transferred to the final receiving substrate is
disclosed in US-A-4538156 (AT&T Teletype Corp.). Furthermore,
S US-A-5380769 (Tektronix Inc.) describes reactive ink
compositions containing at least two reactive components, a
base ink component and a curing component, that are applied
to a receiving substrate separately. The base ink component
is preferably applied to the receiving substrate using ink-jet
printing techniques and, upon exposure of the base ink
component to the curing component, a durable, crosslinked ink
is produced.
SUMMARY OF THE INVENTION
According to the present invention there is provided a
method of producing a screen-printing stencil having open
areas and blocked areas for respectively passage and blocking
of a printing medium, the method comprising:
providing a receptor element comprising an optional
support base and an image-receiving layer capable of receiving
a first chemical agent in areas corresponding to the blocked
areas of the stencil to be produced;
applying the first chemical agent to the image-receiving
layer of the receptor element in the said corresponding areas;
applying a second, stencil-forming chemical agent to a
screen printing screen;
bringing the image-receiving layer of the receptor
element into contact with the stencil-forming agent, to allow
the first and second chemical agents to react to produce on
the screen a stencil-forming layer having areas of lower
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solubility corresponding to the said blocked areas and areas
of higher solubility in areas corresponding to the open
stencil areas;
removing any remaining unreacted part of the receptor
5 element; and
washing away the second chemical agent in the higher
solubility areas, thereby to produce the screen-printing
stencil.
In the method of the invention, the stencil is formed by
chemical means without the need to use either special lighting
conditions or actinic radiation.
Also, it is possible to carry out the method at reduced
expenditure of time and time labour, compared with the known
processes.
The steps of removing any remaining unreacted part of the
receptor element and of washing away the second chemical agent
in the higher solubility areas can be carried out in either
order or simultaneously. Thus, when the unreacted part of the
receptor element comprises a coherent film (for example the
optional support base referred to or the image-receiving layer
itself), the film can be removed, for example by being peeled
away, before the washing away step. Alternatively, the film
can be removed in the course of the washing away step, either
by the washing action or otherwise, or even be removed after
the washing away step. In some cases however the remaining
unreacted part of the receptor element may be a material which
is removed by the washing action, for example when the
optional support base is absent and the image-receiving layer
is insufficiently coherent to be removed as an intact layer,
for example by peeling away.
Advantageously, the first chemical agent is applied
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dropwise to the image-receiving layer.
Conveniently, the dropwise application is by use of an
ink-jet device, for example an ink-jet printer or plotter.
The device may have one or more ejection heads.
If desired, the first chemical agent may be produced in
situ by reaction between two or more precursor materials,
separately applied to the image-receiving layer, prior to
contact with the stencil forming agent, at least one of which
is applied in the said areas corresponding to the blocked
l0 areas of the stencil to be produced. This may con~reniently
be achieved by use of a plurality of drop-ejection heads.
When dropwise application is employed, the application
is preferably controlled according to data encoding the
desired pattern of blocked and open areas of the stencil to
be produced. This control is conveniently by a computer, for
example a personal computer. Thus, data representative of the
desired output pattern can be input to a controller as pre-
recorded digital signals which are used by the ejection head
to deposit or not deposit the liquid containing the chemical
agent as it scans the surface of the receptor element. The
invention is not however restricted to dropwise application
of the first chemical agent: other methods of application will
achieve the same essential end, for example, the first
chemical agent could be applied with a hand-held marker pen.
The method according to the invention can be carried out
using a material of the image-receiving layer which is
essentially unreactive with the first chemical agent. In such
a process, the image-receiving layer acts essentially as an
inert carrier for the first chemical agent. The stencil-
forming layer of the eventual stencil is thus derived
essentially from the second chemical agent applied to the
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screen.
Preferably however the material of the image-receiving
layer is selected to react with the first chemical agent to
produce lower solubility areas corresponding to the said
blocked areas and excess of the first chemical agent (or a
component of it, not necessarily the same as the component
that reacts with the image-receiving layer) remains in said
areas to react with the second chemical agent upon contact
between the image-receiving layer and the stencil-forming
l0 agent, whereby the respective lower solubility areas of the
image-receiving layer and of the stencil-forming layer
combine with one another and, after the higher solubility
areas are washed away, remain to form the blocked areas of the
screen-printing stencil.
In such a method, the stencil-forming layer of the
eventual stencil is derived in part from the second chemical
agent and in part from the image-receiving layer of the
receptor element. In this case, the thickness of the stencil-
forming layer can be such as to give the eventual screen a
"profile", that is a significant thickness to the closed areas
of the stencil beyond the thickness of the screen itself.
This is of benefit in terms of the quality of printed images
which are obtainable by use of the screen as it allows a
significant ink deposit to be applied during printing and
permits more precise control of the amount of ink deposited.
It also produces a flat printing surface which gives better
resolution and improved definition by limiting ink spread
during printing.
In one variant of the method of the invention, the second
chemical agent is applied to the screen printing screen from
one side thereof after the receptor element has been applied
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to the other side thereof with its image-receiving layer in
contact with the screen, whereby the image-receiving layer is
brought into contact with the second chemical agent.
In another variant, the second chemical agent is applied
to the screen printing screen and the receptor element is
subsequently brought into contact with the screen to bring the
image-receiving layer thereof into contact with the second
chemical agent.
DETAILED DESCRIPTION OF THE INVENTION
The invention will be described further by way of example
with reference to the drawings of this specification, in which
Figures 1 to 5 show schematically the successive steps
in the production of a printing screen in accordance with one
method according to the invention, and
Figures 6 to 10 show schematically the successive steps
in the production of a screen in accordance with a second
method according to the invention.
Referring to Figures 1 to 5, these show the formation of
a screen printing stencil shown in Figure 5, starting with a
receptor element shown in Figure 1.
Figure 1 shows the receptor element which consists of an
image-receiving layer 1 coated on a flexible film support base
2. In this example, the image-receiving layer is about 10 um
in thickness and the support base about 75 ~cm.
Figure 2 shows a first chemical agent 3 being applied to
the image-receiving layer 1 in droplets 3 which are ejected
from an ejection head (not shown? of, for example, an ink-jet
printer controlled by a computer. The first-chemical agent
3 is absorbed into the image-receiving layer 1 to form areas
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4 which correspond to the blocked areas of the stencil to be
formed.
Figure 3 of the drawings shows a screen mesh 5 to one
surface of which the receptor element of figure 2 has been
applied and to the other of which a stencil-forming agent 6
is being applied using a suitable spreader 7. In figure 3 the
image-receiving layer 1 of the receptor element is brought
into contact with the stencil-forming agent 6 when the latter
is forced through the mesh 5 by the spreader 7.
This contact could alternatively have been achieved by
first coating the mesh 5 with the stencil-forming agent 6 and
then applying the receptor element to the mesh 5.
Figure 4 of the drawings shows the receptor element 1
consisting of the support base 2 and the image-receiving layer
1, including the areas 4 where the first chemical agent was
absorbed, being peeled away from the image-receiving layer 1.
The areas of the stencil-forming agent 6 corresponding to the
areas 4 of the image-receiving layer have reacted with the
first chemical agent to produce areas 8 of insoluble material.
Figure 5 shows the final screen after the support base
2 has been peeled away and the screen washed out so that the
reduced-solubility areas of the stencil-forming agent and the
areas 4 of the image-receiving layer to which the first
chemical agent was applied remains and the higher solubility
areas have been washed away.
Figures 6 to 10 of the drawings correspond to figures 1
to S but show the production of a stencil using a receptor
element having an image-receiving layer which reacts with the
first chemical agent to produce areas which become
incorporated into the stencil-forming layer of the final
stencil.
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Reference numerals increased by "10" are used in figures
6 to 10 to identify integers corresponding to integers of
figures 1 to 5.
Figures 6 to 8 show operations corresponding to the
5 operations of figures 1 to 3. In figure 7 the first chemical
agent 13 reacts with the image-receiving layer 11 in the areas
14 but excess of the first chemical agent remains in those
areas, to react with the stencil-forming agent 16 as it is
applied as shown in figure 8.
10 Figure 9 therefore shows that, as the support base 12 is
peeled away, the areas 14 of the image-receiving layer have
become combined with the areas 18 of the stencil-forming layer
and, as shown in figure 10 after washing out, remain in the
final stencil to provide the desirable "profile" to which
reference has already been made. The remaining, unreacted
areas of the image-receiving layer are washed away with the
high solubility areas 16 of the stencil-forming layer in the
subsequent washing step.
When the image-receiving layer is substantially inert to
the first chemical agent it can comprise an inert polymer such
as methyl hydroxy propyl cellulose which is preferably present
in the image-receiving layer in an amount of 5 to 100 wt.%
with the balance comprising, for example, suitable other
polymers and/or suitable fillers, binders and plasticisers.
Numerous other inert polymers could alternatively be
utilised for use in the present invention. Suitable polymers
include those that have no chemical reaction or only an
insignificantly slow chemical reaction with the first chemical
agent to be used. Examples of such polymers are:
carboxymethyl cellulose;
polyvinylpyrrolidone; and
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polyacrylic acids.
In addition, papers, including ordinary papers, can be
used as the inert image-receiving layer, and, thereby, require
no supporting base.
The key criterium in selecting a suitable combination of
image-receiving layer and first chemical agent is that the
first chemical agent should form a good image on the layer;
for example, a drop of the first chemical agent should neither
be so repelled by the layer as to produce a defective image
nor it should not spread so far as to reduce the resolution
of the image. Moreover, it should not spread so
anisotropically (because of irregularities in the layer) as
to deform the image.
When the image-receiving layer reacts with the first
chemical agent and thus forms a part of the final screen
stencil, the image-receiving layer may comprise a polymer
which reacts with the first chemical agent. When the stencil
forming agent is applied and reacts with the first chemical
agent (or a component of it, not necessarily the same as the
component that reacts with the image-receiving layer), the
layer of stencil-forming agent and the reacted part of the
image-receiving layer become essentially one.
A typical example of such a polymer is polyvinyl alcohol
which is preferably present in an amount of 5 to 100 wt.% of
the image-receiving layer with the balance comprising, for
example, other suitable polymers and/or suitable fillers,
binders and plasticisers. The polyvinyl alcohol preferably
has a degree of hydrolysis of 20 to 99.9 mole % and,
independently thereof, a degree of polymerisation of 100 to
3500.
Numerous other reactive polymers could alternatively be
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utilised in the present invention. Suitable polymers include
those that change their solubility characteristics on
treatment with a suitable first chemical agent. Examples of
such polymers are:
gelatin and its derivatives;
carboxylated polymers capable of becoming water soluble on
addition of alkali, including carboxylated acrylics, ethylene-
acrylic acid and styrene-acrylic acid copolymers;
cellulose derivatives that are water soluble, including starch
and hydroxypropyl cellulose;
sulphonated polymers;
polyacrylamides;
epoxy resins; and
amino resins, including urea-formaldehyde and melamine-
formaldehyde.
In methods of either type according to the invention, the
polymers and other components are chosen so that the first
chemical agent forms a good image when applied. Layers that
are not compatible with any solvent used in the first chemical
agent (typically, water) will produce insufficient spread of
the liquid and a poor-quality image will result. If the layer
has too great an affinity with the first chemical agent, the
liquid will spread too far, giving a blurred, low resolution
image.
A receptor element can be with or without a support base.
Without the support base, the image receiving layer is
typically 6 to 250 ~.m in thickness. With a support base the
coating thickness is typically from 0.1 to SO ~,m.
The support base may comprise a non-reactive polymer,
preferably an organic resin support, e.g. polyethylene
terephthalate, polyethylene, polycarbonate, polyvinyl chloride
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or polystyrene. Alternatively a coated paper could be used as
the receptor element, the paper and coating constituting the
support base and the image-receiving layers, respectively.
An uncoated paper can alternatively constitute the image-
s receiving layer of a receptor element without a support base.
Such an image-receiving layer is usually removed as a coherent
film prior to washing away of the high solubility areas of the
stencil-forming layer. The thickness of the support base film
is preferably from 10 to 200 Vim. The organic resin supports
can optionally be coated with a subbing layer to give desired
adhesion properties with the image-receiving layer. When used,
the support base is usually removed as a coherent film in the
screen production method prior to the removal of the areas of
higher solubility, though it can be removed during this
process.
The first chemical agent is applied to the image-
receiving layer. The liquid may be applied dropwise,
conveniently by an ink-jet system such as (but not confined
to) an ink-jet printer or ink-jet plotter. Alternatively,
application can be continuous, for example by a hand held
delivery device, such as a pen. The liquid applied should
exhibit desirable stability, surface tension and viscosity
characteristics and may therefore contain surfactants,
viscosity modifiers, light stabilisers and/or anti-oxidants.
When the active components) of the first chemical agent
is/are not liquids, the first chemical agent may include a
suitable carrier, for example a suitable solvent or dispersant
for the active component(s).
Examples of suitable active components include boron
salts e.g. boric acid, Group I and Group II metal borates;
aldehydes, e.g. formaldehyde;
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dialdehydes, e.g. glyoxal and glutaraldehyde, optionally
activated by treatment with mineral acid;
isocyanates and their derivatives, e.g. toluenediisocyanate;
carbodiimides and their derivatives, e.g. 1,3
dicyclohexylcarbodiimide;
transition metal compounds and complexes, e.g.
pentahydroxy(tetradecanoate)dichromium and its derivatives;
aziridine and its derivatives;
amines;
multifunctional silane compounds, e.g. silicon tetraacetate;
N-methylol compounds, e.g. dimethylolurea and
methyloldimethylhydantoin; and
active vinyl compounds, e.g. 1,3,5-triacryloyl-hexahydro-s-
triazine.
For use in a dropwise application device such as an ink-
jet printer or plotter the invention provides a pre-filled
cartridge for such a device, the cartridge containing one or
more of the above chemical agents optionally in a suitable
liquid solvent or carrier.
In the method of the invention the receptor element
having had the first chemical agent applied to it may be
placed on a solid flat surface and a screen mesh is placed on
top such that there is close contact between the mesh and the
receptor element. The stencil-forming agent is then typically
applied to the screen mesh by a coating trough or squeegee
whereby the first chemical agent is brought into contact with
the stencil-forming agent, and reacts therewith so reducing
its solubility in predetermined areas. Alternatively, a thin
layer of the stencil-forming agent can be coated onto the
screen mesh, for example by a coating trough or squeegee and
the receptor element mounted manually with slight pressure,
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a technique well-known to those skilled in the screen printing
art.
A typical example of a stencil-forming agent comprises
an aqueous solution, dispersion or emulsion of polyvinyl
5 alcohol, with a degree of hydrolysis of 20 to 99.9 mole % and
a degree of polymerisation of 100 to 3500, as the reactive
polymer in proportion of 5 to 100 wt.% and the remainder of
the layer contains polymers, fillers, binders and plasticisers
as normally found in the art.
10 Numerous other active polymers could alternatively be
utilised as stencil-forming agents in the present invention.
Examples of such polymers are:
gelatin and its derivatives;
carboxylated polymers capable of becoming water soluble on
15 addition of alkali, including carboxylated acrylics, ethylene
acrylic acid and styrene-acrylic acid copolymers;
cellulose derivatives that are water soluble, including starch
and hydroxypropyl cellulose;
sulphonated polymers;
polyacrylamides;
epoxy resins; and
amino resins, including urea-formaldehyde and melamine-
formaldehyde.
If a support base is used, this can conveniently be
removed once the reaction of the first chemical agent with the
stencil-forming agent has substantially been completed. The
resulting screen stencil can be developed by washing away the
portion of higher solubility with a suitable solvent, thereby
leaving behind areas of reduced solubility to occlude areas
of the mesh (this act of washing could also remove the
optional support base and any other coherent film part of the
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receptor element if not removed earlier).
Optionally, the stencil can be further toughened by a
post-treatment, for example using extra chemicals, actinic
radiation or heat. The extra chemicals (or precursors
thereof) may be resident in the original image-receiving layer
or in the stencil forming agent, or may be supplied
externally. Examples of chemical toughening agents are ones
operating at pH 7 or higher and include dialdehydes
particularly glyoxal, and aqueous bases, for example aqueous
potassium carbonate. It is presently believed that these
toughening agents will only work when a boron salt is used as
the first chemical agent.
The screen produced is then ready for use as a printing
medium using techniques familiar to those skilled in the art.
Where the chemicals used are those cited in the Examples 1 to
8 which follow, the broad physical properties, chemical
resistances, washout solvent (water) and reclaim chemicals
(typically periodate systems) will in many cases be those used
routinely by screen printers. So, although the method of
producing the stencil is new, the resulting product will often
be familiar and highly acceptable to screen printers.
Surprisingly, we have found that when the active
component of the first chemical agent is a boron-containing
salt, the stencil can be reclaimed with dilute acid without
the use of the industry-standard periodate system. This low
cost and environmentally-friendlier reclaim system is a
distinct added advantage.
The advantages of the method of the present invention
include: a screen stencil can be produced directly from
digital information sources; unlike the methods disclosed in
CA-A-2088400 and EP-A-0492351 which ink-jet print onto a
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screen mounted in a frame, it is possible to use any general-
purpose ink-jet printer using rolls or sheets of film; it is
not necessary to use safe-lights during the stencil making
process; there is no requirement for an exposure step
utilising an actinic radiation source; and a finished stencil
can be produced in a shorter time than by conventional screen
printing techniques.
The present invention is illustrated by the following
examples without however being limited thereto. In these
examples, various commercially-available materials are listed
by their trade names; the following letters identifying the
following companies:
(a) 3M, UK
(b) Autotype international, UK
(c) DuPont, UK
(d) Nippon Gohsei, Japan
Examples 1 to 4 involve the use of non-reactive image-
receiving layers; examples 5 to 8 involve the use of reactive
image-receiving layers.
EXAMPLE 1
A liquid containing a first chemical agent was prepared
according to the formula:
water - 87 wt.%;
potassium tetraborate - 10 wt.%;
borax - 2 wt.%; and
"Fluorad FC-93" (a) (lwt. % aqueous solution) - anionic
fluorinated surfactant - 1 wt.%.
A receptor element was prepared. Methyl hydroxy propyl
cellulose (10 wt. % solution in water) was coated onto a
subbed 75 um polyethylene terephthalate film from an aqueous
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solution to form a receptor element comprising a polyethylene
terephthalate support base and an image receiving layer of IO
~cm thickness. The sub comprised a 1 wt.% methanol solution of
"Elvamide 8063" (c) - coated using a 6 thou. Meyer bar.
The resulting receptor element was passed through a
typical commercial ink-jet printer ( Hewlett Packard HP550 at
300dpi) connected to a personal computer and the liquid
containing the chemical agent was applied in a preprogrammed
manner to form the desired image. The receptor element was
then placed on a glass plate, with the coated layer facing
uppermost. The receptor element was covered with a screen mesh
of mesh count 62 threads per cm. Then a bead of a typical (but
unsensitized) polyvinylalcohol/polyvinyl acetate screen
emulsion - "2000" (b) - was placed on the upper side of the
mesh and drawn over the receptor element by means of a
squeegee so that a thin layer of emulsion was forced through
the mesh. After 1 minute, the polyethylene terephthalate
support base was removed from the mesh. The resulting screen
was left to dry and then washed out using cold running water,
until the portion of the assembly of higher solubility was
washed away to waste.
The stencil was then placed in a standard screen printing
machine and prints of an acceptable quality were obtained
using standard solvent-based screen printing inks.
EXAMPLE 2
A liquid containing a first chemical agent was prepared
according to the formula:
water - 50 wt.%; and
"Quilon C" (b) - pentahydroxy(tetradecanoate)dichromium, 50
wt
. o.
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"Quilon C" is itself a 25% solution in acetone/isopropyl
alcohol.
Polyvinylpyrrolidone (10 wt.% solution in water) was
coated onto a 75 ~.m polyethylene terephthalate film from an
aqueous solution to form a receptor element comprising a
polyethylene terephthalate support base and an image receiving
layer of 10 ~.m thickness.
The resulting receptor element was passed through a
typical commercial ink-jet printer (Hewlett Packard HP550 at
300dpi) connected to a personal computer and the liquid
containing the chemical agent was applied in a preprogrammed
manner to form the desired image. The receptor element was
then placed on a glass plate, with the coated layer facing
uppermost. The receptor element was covered with a screen mesh
of mesh count 62 threads per cm. Then a bead of a typical (but
unsensitized) polyvinylalcohol/polyvinyl acetate screen
emulsion - "2000" (c) - was placed on the upper side of the
mesh and drawn over the receptor element by means of a
squeegee so that a thin layer of emulsion was forced through
the mesh. The polyethylene terephthalate support base was
removed from the mesh. The resulting screen was left to dry
thoroughly using a hot air fan and then washed out using cold
running water, until the portion of the assembly of higher
solubility was washed away to waste.
The stencil was then placed in a standard screen printing
machine and prints of an acceptable quality were obtained
using standard solvent-based screen printing inks.
EXAMPLE 3
The procedure of Example 1 above was repeated exactly to
produce a screen stencil.
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This stencil was then treated with a 10 wt.% aqueous
solution of potassium carbonate, which was applied by brush
so as to cover the entire stencil area, then finally allowed
to dry. This produced a toughened stencil, which was placed
5 in a standard screen printing machine and prints of an
acceptable quality were obtained using standard solvent-based
screen printing inks.
EXAMPLE 4
10 The procedure of Example 1 above was repeated exactly to
produce a screen stencil.
This stencil was then treated with a 2 wt.% solution of
35 wt.% hydrochloric acid, which was applied by brush so as
to cover the entire stencil area. This treatment disrupted the
15 screen stencil and allowed the resulting residue to be washed
away to waste using a cold water spray, giving a reclaimed
screen with no observable stain present.
EXAMPLE 5
20 A liquid containing a chemical agent was prepared
according to the formula:
water - 87 wt.%;
potassium tetraborate - 10 wt.%;
borax - 2 wt.%; and
"Fluorad FC-93" (a) (lwt. % aqueous solution) - anionic
fluorinated surfactant - 1 wt.%.
Polyvinyl alcohol - "Gohsenol GH-20 (d) (10 wt.% solution
in water) of hydrolysis 88% and degree of polymerisation
2000, was coated onto a unsubbed 75 ~.m polyethylene
terephthalate film from an aqueous solution to form a receptor
element comprising a polyethylene terephthalate support base
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and an image receiving layer of 10 microns thickness.
The resulting receptor element was passed through a
typical commercial ink-jet printer (Hewlett Packard HP550 at
300dpi) connected to a personal computer and the liquid
containing the chemical agent was applied in a preprogrammed
manner to form the desired image.
The receptor element was dried, then placed on a glass
plate, with the coated layer facing uppermost. The receptor
element was covered with a screen mesh of mesh count 62
threads per cm. Then a bead of a typical (but unsensitized}
polyvinylalcohol/polyvinyl acetate screen emulsion - "2000"
(c) - was placed on the mesh and drawn over the receptor
element by means of a squeegee so that a thin layer of
emulsion was forced through the mesh. The screen was dried by
hot air fan until the polyethylene terephthalate support base
could be peeled cleanly from the mesh. The screen was left to
dry and then washed out using cold running water, until the
portion of the assembly of higher solubility was washed away
to waste.
The stencil was then placed in a standard screen printing
machine and prints of an acceptable quality were obtained
using standard solvent-based screen printing inks.
EXAMPLE 6
A 50:50 wt.o blend of polyvinyl alcohol - "Gohsenol GH
20" (d) and polyvinyl acetate was coated onto an unsubbed 75
~.m microns polyethylene terephthalate film from an aqueous
solution to form a receptor element comprising a polyethylene
terephthalate support base and an image-receiving layer of 10
~m thickness.
The resulting receptor element was passed through a
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typical commercial ink-jet printer (Hewlett Packard HP550 at
300 dpi) connected to a personal computer and liquid
containing a chemical agent was applied according to the
formula:
water - 50 wt.%; and
"Quilon C" (b) - pentahydroxy(tetradecanoate)dichromium, 50
wt.%. "Quilon C" is itself a 25% solution in acetone/isopropyl
alcohol.
The receptor element was then treated in exactly the same
manner as in Example 5 above.
The stencil was then placed in a standard screen printing
machine and prints of an acceptable quality were obtained
using standard solvent-based screen printing inks.
I5 EXAMPLE 7
The procedure of Example 5 above was repeated exactly to
produce a screen stencil.
This stencil was then treated with a 10 wt.% solution of
potassium carbonate which was applied by brush so as to cover
the entire stencil area, then finally allowed to dry. This
produced a toughened stencil, which was placed in a standard
screen printing machine and prints of an acceptable quality
were obtained using standard solvent-based screen printing
inks.
EXAMPLE 8
The procedure of Example 5 above was repeated exactly to
produce a screen stencil.
This stencil was then treated with a 5 wt.% solution of
glacial acetic acid, which was applied by brush so as to cover
the entire stencil area. This treatment disrupted the screen
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stencil and allowed the resulting residue to be washed away
to waste using a cold water spray, giving a reclaimed screen
with no observable stain present.
