This invention relates to ink capsules for printing machines and
in particular for coding machines.
Inking systems for automatic marking machines comprising an ink reservoir
assembly are disclosed in US-A-2 756 674.
Coding machines are typically used for printing indicia on articles
to indicate, for example: a date of manufacture, an expiry date, prices, numbers
relating to the manufacture or packaging of an article etc.. A known coding machine
is the applicant's CC100 coder. The printing head on the coder picks up ink from
an ink capsule and prints the indicia on to the article. The ink capsule typically
includes an ink retaining pad which is conventionally made from felt. The use
of felt works well with conventional solvent based inks in which the solvent is
typically ethyl alcohol. However solvent based processes are no longer considered
desirable in that the solvent creates an unsuitable work environment and the waste
products from the process are environmentally unfriendly.
In view of the above problems there is now a trend towards the use
of water based printing mediums. Another advantage of water based codes, is that
they can, if desired, be removed by washing prior to sale of the marked goods.
The use of an aqueous medium allows for the use of a wide range of
different coloured inks, in particular inks which are coloured by the use of pigments.
The use of pigmented inks has given rise to problems in that the felt pads filter
out the pigment particles. Furthermore, if an alternative ink retentive material
is substituted for the felt, the ink capsule tends to leak since in use the face
of the ink capsule is generally vertical and the aqueous based inks are not self-sealing,
unlike solvent based inks. This may cause an unsightly mess on the article being
Object of the Invention
The present invention provides an ink capsule for use with aqueous
pigmented inks without the above problems.
Statements of Invention.
According to the present invention there is provided an ink capsule
for a printer, which comprises a container having a hollow shell with a mouth and
an inlet port through the container shell, a flexible impermeable liner sealed
to the container shell, the container and liner being filled with a resilient
polymeric foam, and the mouth of the container being closed by a porous closure.
The container may be moulded from a suitable plastics material such
as a polyolefin, preferably polyethylene in particular a high density polyethylene.
The liner is thin and pliable and is formed from resilient readily
deformable material such as an elastomer, for example natural rubber, butyl rubber,
nitrile rubber etc., or a laminate of different elastomers. A natural rubber latex
has been found particularly suitable. The porous disc is preferably a sintered
polymer, more preferably a fluoropolymer.
The foam, which in use retains the ink, is preferably an open cell
material such as polyethylene foam, or a polyurethane foam in particular a polyether
The invention also relates to an ink supply for a printer, which
includes an ink capsule according to the invention, wherein the supply includes
a variable volume fluid reservoir connected to the inlet port of the container
allowing for the movement of fluid between the reservoir and the container in
response to the expansion and contraction of the reservoir.
Movement of fluid into the container squeezes the foam within the
liner forcing ink through the porous closure to be transposed to the printing head,
and movement of fluid from the container causes the foam to expand, sucking the
excess ink back into the container.
Preferably the reservoir comprises a cylinder having a piston reciprocable
therein to displace fluid, being resiliently biased to an equilibrium condition
of maximum volume.
The maximum stroke of the piston is adjustable to control the squeeze
on the foam in the container by varying the volume of fluid displaced. The squeeze
on the foam may alternatively, or additionally, also be adjusted by controlled
bleed-off of the fluid displaced.
According to yet another aspect of the invention there is provided
a printing machine having an ink supply system as described above for a printing
head, wherein the printing head is operated by a pneumatic cylinder which is connected
to the reservoir so that a pulse of air pressure to the pneumatic cylinder also
pushes fluid into the container.
Description of the Drawings
The invention will be described by way of example and with reference
to the following drawings in which :
Detailed Description of the Invention
- Fig. 1
- is an exploded diagram in cross-section of an ink capsule according to the
- Fig. 2
- is a schematic drawing of an ink supply system for a printer which incorporates
a capsule as shown in Fig. 1, and
- Fig. 3
- is a printing head incorporating the capsule of Fig.1.
With reference to Fig 1, there is shown an ink capsule 10 for use
on a coder printer in particular a CC100 Coder which is sold by the applicant.
The capsule comprises a relatively rigid container 11 moulded from
a suitable plastic material e.g. high density polyethylene. The container 11 has
a hollow shell 14 with a mouth 11 having an external screwthread 12 formed thereon
for the attachment of a cap 13. The container shell 14 is provided with an inlet
port 15 passing through base 16 of the container.
The container 11 has an impermeable flexible rubber liner 17 inserted
therein to lie adjacent the shell 14 with the mouth 18 of the liner 17 having a
portion 19 extending back on itself for sealing between the container 11 and cap
13. The container 10 and liner 17 are filled with a block of foam 21 which is
a resilient open cell foam, preferably a polyether based polyurethane foam. The
density of the foam should be about 20-30 Kg per cubic metre, preferably 24-27
Kg per cubic metre. In use the foam contains the printing ink.
The mouth 18 of the liner is closed by a semi-rigid porous disc 22
which is formed from a sintered polymer, preferably a fluoropolymer, preferably
PTFE and is about 2mm thick. The disc 22 is held in place in the mouth 18 by the
cap 13. The cap 13 has a cylindrical sidewall 23 with an internal screwthread
24 which cooperates with the external thread 12 on the container. The end wall
25 of the cap 15 has an aperture 26 therein whereby a printing head (see Fig.3)
may access the ink.
With reference to Fig. 2, the capsule 10 is incorporated in an ink
supply 31 for a printer. The ink supply 31 comprises a fluid reservoir 41 in the
form of a cylinder having a cylindrical fluid chamber 42 with a piston 43 reciprocable
within the chamber 42 to vary the volume of the chamber. The chamber 42 is connected
through an outlet port 46 in its endwall 47, and via conduit 44, preferably a
flexible pipe, to the inlet port 15 of the capsule 10 so that a movement of the
piston 43 within the cylinder 41 causes the movement of fluid between the cylinder
41 and capsule 10.
A return spring 45 is located in the chamber 42 to bias the piston
to an equilibrium position against a stop 49 so that the chamber 42 is at maximum
volume in the at-rest condition. The external side of the piston 43 is open to
a second chamber 48 formed in the cylinder 41 between the piston and an end cap
51. The end cap 51 is connected through an inlet port 52 to a source of pulsed
air pressure (not shown).
A pulse of high pressure air enters the inlet port 52 causing the
piston 43 to move towards the cylinder endwall 47 displacing fluid, preferably
air, from the chamber 42 into the capsule 10 via the pipe 44. The displaced air
enters the capsule 10 through the inlet port 15 causing the flexible liner 17
to distort and thereby squeeze and distort the foam 21. Any ink retained in the
foam 21 is pushed through the porous disc 22 to lie on the exposed open surface
for contact with a printing head. When the air pulse stops, the spring 45 biases
the piston to its at-rest condition drawing the air from the capsule back into
the chamber 42 which sucks the surplus ink back into the capsule.
The volume of air displaced by the piston 43 should be about 50%
of the volume of the container 11. The actual volume may be controlled by having
a variable position stop 53 mounted in the endwall 47. The stop 53 may be an adjustable
screw passing through the end wall. The position of the stop 53 will be adjusted
to give optimum ink delivery to the surface of the disc 22. This will be dependent
upon many factors including the ink viscosity, porosity of the disc, density and
resilience of the foam, so that the actual stop position will be determined by
The volume of air displaced may also need to be adjusted during the
operating life of the capsule 10 to compensate for changes in falling ink levels
in the capsule, and changes in viscosity in the ink. An adjustable regulator 54
is connected to the pipe 44 between the fluid reservoir 41 and the capsule 10.
The flow regulator allows for a controlled exhausting, or bleed-off, of the displaced
air into the atmosphere.
With reference to Fig. 3, there is shown a printer 61 from a reciprocating
coder having a printing head 62 moved between the ink capsule 10 and an article
to be printed 63 by a pneumatic cylinder 64. The cylinder 64 is operated by pulses
of high pressure air (about 40 psi, that is about 3 bar) to cause the head 62 to
print. These air pulses can also be used to operate the piston 43 to squeeze ink
through the disc 22 ready for transfer to printing head.
The volumes of ink displaced through the disc are very small for
example a capsule of about 90 gms. of ink will print at least 50,000 codes and
probably up to 100,000 codes.