Thermal transfer ribbon cassette system

A thermal transfer ribbon cassette system for use with a thermal transfer printer comprises supply and take-up spools, a thermal transfer ribbon extending between the spools with one end loaded onto the supply spool and the other onto the take-up spool, a cassette casing (10) with spool-locating means (15, 16) to locate and retain the two ribbon-carrying spools (5) spaced-apart, parallel and rotatable during printing, the spacing between the spools being predetermined to fit the printer, and a disposable loading member (20) comprising a rigid body portion (21) shaped to be manually transportable and having spool-holding means (23) releasably to hold the loaded spools (5) parallel, non-rotatable and spaced apart with the same predetermined spacing as the spool-locating means (15, 16); the spools (5), casing (10) and loading member (20) being adapted to enable the spools (5) to be inserted into the spool-locating means (15, 16) of the casing (10) while being held by the loading member (20), and to enable the loading member (20) thereafter to be withdrawn while the spools (5) are retained in the casing (10).

FIELD OF THE INVENTION 
The invention relates to thermal transfer printing, and in particular to 
means for holding the thermal transfer ribbons during storage and during 
use in thermal transfer printers. 
BACKGROUND OF THE INVENTION 
Thermal transfer printing is a process for generating printed images by 
transferring thermally transferable colorant from a thermal transfer 
ribbon to a receiver. The ribbon usually comprises a base sheet coated on 
one side with a transfer coat comprising a non-transferable binder 
containing one or more thermally transferable dyes, or a fusible ink which 
is all transferable. Printing is effected while the transfer coat is held 
against the surface of the receiver, by heating selected areas of the 
ribbon so as to transfer the dyes or inks from those selected areas to 
corresponding areas of the receiver. This generates an image according to 
the areas selected. By repeating the transfer process with each of the 
three primary colours, full colour images can be obtained. Black may also 
be used. 
Thermal transfer printers using a thermal head with a plurality of tiny 
heaters to heat the selected areas, have been gaining widespread attention 
in recent years, mainly because of its ease of operation in which the 
areas to be heated can be selected by electronic control of the heaters 
(e.g. according to a video or computer-generated signal), and because of 
the clear, high resolution images which can be obtained in this manner. 
Alternative thermal energy sources, such as addressable laser systems, are 
also being developed. 
Transfer sheets for such primers are normally in the form of long ribbons, 
having repeated sequences of print size panels of each primary colour and 
any other materials to be transferred (e.g. black dyes or ink), such 
sequence being repeated along the ribbon to enable it to be used for as 
many prints as there are repeats of the sequence. The ribbons are rolled 
up and stored in a cassette. These consist essentially of supply and 
take-up spools, the thermal transfer ribbon extending between the spools 
with one end loaded onto the supply spool and the other onto the take-up 
spool, and a casing having spool-locating means to locate and retain the 
spools spaced apart, parallel and rotatable during printing with the 
spacing between the spools being predetermined to fit the printer. The 
cassettes may also be supplied with a small anti-rotation member which is 
plugged into the ends of the spools to prevent their rotation during 
transit to the consumer. 
Cassette casings typically comprise two parallel spool-housings having end 
portions interconnected by bridge members such that the housings and 
bridge members together define an open access port through which the 
transfer ribbon is exposed as it extends from one spool to the other. 
However, there is at present no overall industry standard for thermal 
transfer printers and cassettes, and the specific configurations of the 
latter are largely determined by the printers with which they are to be 
used, both in respect of the overall shape and size (e.g. they must fit 
correctly into the space provided), and also in respect of the functional 
requirements (e.g. they must meet the requirements of various sensors 
normally built into the printer). There may also be differences between 
cassettes for printers using thermal heads to effect transfer and those 
which are laser driven. 
Such casings can represent a substantial proportion of the cost of the 
cassette, but after all the transfer ribbon has been used up, they are 
usually discarded. However, some known cassettes do have an open 
configuration which leaves the spools and their spent transfer ribbons 
accessible for replacement. Such replacement may be facilitated by 
permitting longitudinal movement of the spools in the casing from a free 
to a retained position, and some form of spring, e.g. leaf springs or coil 
springs around the spool ends, provided to bias the spools into their 
retained positions. 
Unfortunately, ribbon replacement is not without its difficulties. The 
colorants used in the ribbons are intended to be readily transferred to a 
receiver on application of heat, and when handled some of the colorant may 
become similarly transferred to the hands or clothing. Moreover the 
transfer sheet can itself become damaged by such handling, even when no 
colorant is actually transferred. Particularly susceptible to this are 
transfer coats comprising thermally transferable dyes held in a static 
binder from which they diffuse during printing, because such dyes are 
generally soluble in finger grease. Where the transfer coats are handled, 
any grease deposited may cause such dyes to diffuse to the surface where 
they accumulate and form crystals. These make the transfer sheets even 
more dirty, and may produce noticeable unevenness in a print made from 
that part of the transfer sheet. 
SUMMARY OF THE INVENTION 
We have now invented a cassette system wherein the ribbon can more easily 
be replaced with a new refill without contact between the transfer coat 
and the operator's hands, and the refill can be packaged in a form ready 
to be inserted into the casing by the consumer. 
According to a first aspect of the present invention there is provided a 
thermal transfer ribbon cassette system for use with a thermal transfer 
printer, the system comprising supply and take-up spools, a thermal 
transfer ribbon extending between the spools with one end loaded onto the 
supply spool and the other onto the take-up spool, and a cassette casing 
with spool-locating means to locate and retain the two ribbon-carrying 
spools spaced-apart, parallel and rotatable during printing, the spacing 
between the spools being predetermined to fit the printer; the system also 
including a disposable loading member comprising a rigid body portion 
shaped to be manually transportable and having spool-holding means 
releasably to hold the loaded spools parallel, non-rotatable and spaced 
apart with the same predetermined spacing as the spool-locating means; the 
spools, casing and loading member being adapted to enable the spools to be 
inserted into the spool-locating means of the casing while being held by 
the loading member, and to enable the loading member thereafter to be 
withdrawn while the spools are retained in the casing. 
A purpose of the loading member is to enable an operator to hold a refill 
manually by the loading member rather than by the loaded spools. 
Consequently these need to shaped to be manually transportable, but such 
shaping can be minimal provided the function is available. Thus for 
example, the body may be moulded with an integral handle, which provides 
an economical way of shaping the body portion to be comfortable to hold 
and transport manually, with the advantage of improved rigidity; but there 
are also suitable alternatives, including forming an integral flange 
around part or all the periphery of the body portion to give a broader 
edge that can be gripped twixt finger and thumb, for example. In extreme 
cases the body may be moulded with sufficient thickness to enable it to be 
gripped without such peripheral flanges, eg by having a foamed core, but 
this may not be the most economical way to provide manual 
transportability. 
Supply and take-up spools typically have two end portions located either 
side of a bobbin portion onto which the respective ends of the thermal 
transfer ribbon are loaded, with one corresponding end portion of each 
spool being hollow by way of having an axial cavity for engaging driving 
means in the printer. The spool-holding means of the loading member can 
then comprise two parallel spaced-apart rods extending orthogonally from 
the body portion to fit securely but releasably in the respective 
cavities. The simplest way of gripping the spools is then for the rods to 
have extended end portions which are an interference fit in the respective 
cavities. The lengths of the rods and cavity depths need only to be 
sufficient to hold the loaded spools parallel as they extend from the body 
portion. When the rods are pushed home sufficiently to support the spools, 
they can also prevent rotation of the spindles during transit, and can be 
withdrawn after the refill has been located in the casing, simply by 
overcoming the friction of the interference fit. 
A preferred cassette system is one wherein each spool-locating means for 
locating and retaining the hollow end portion of a spool comprises two 
arcuate upstands forming a major portion of an incomplete retaining ring 
with a gap between the ends of the upstands which is less than the 
external diameter of the hollow end portion of the spool, and each of the 
rods has at least a portion with a smaller diameter than the spool, being 
less than the width of the gap, and wherein the retaining rings are of a 
size to receive the hollow end portions with freedom for the spools and 
rods to move axially between a free position in which the smaller diameter 
portion is aligned with the gap to enable it to pass therethrough, and a 
retained position in which the hollow end portion is aligned with the gap 
to prevent the spool passing therethrough, whereby the spools held on the 
holding means can be inserted into the free position within the cassette 
by passing the rods through the gaps, then moved axially into the retained 
position and the holding means separated and removed. The casing suitably 
contains means to bias the spools from the free position into the retained 
position, thereby to maintain the spools in the retained position after 
removal of the spool-holding means. 
Each of the rods with a diameter which provides an interference fit in the 
spool cavity, suitably has the diameter which is less than the width of 
the gap provided as a reduced diameter in just an intermediate portion of 
the rod. This gives a waisted shape, as produced, for example, by a 
circumferential groove, but depending on the method of construction, we 
find it is often simpler to reduce the diameter of the intermediate 
portion of the rod in one diametric direction only, by the provision of a 
slot on each side of the rod. 
According to a second aspect of the present invention there is provided a 
refill unit for a thermal transfer ribbon cassette having a casing with 
spool-locating means to locate and releasably secure two ribbon-carrying 
spools spaced-apart, parallel and rotatable during printing, the refill 
unit comprising supply and take-up spools having a thermal transfer ribbon 
loaded onto and extending between them, and a disposable loading member 
comprising a rigid body portion shaped to be manually transportable and 
having spaced spool-holding means holding the loaded spools and 
maintaining them parallel, non-rotatable and spaced apart with the same 
predetermined spacing as the spool-locating means, said loading means 
being releasable from the spools after the latter have been loaded into 
and are retained by the spool-locating means. 
According to a third aspect of the present invention, a method of refilling 
a thermal transfer cassette having a casing with spaced spool-locating 
means, comprises the steps of loading a thermal transfer ribbon onto a 
pair of spools, providing a loading member comprising a rigid body having 
spaced means for holding the loaded spools, engaging the spool-holding 
means and the spools so that the latter are held parallel, non-rotatable 
and spaced apart with the same spacing as the spool-locating means, 
inserting the spools into the casing while held by the loading member, 
thereafter allowing or causing relative movement between the casing and 
the spools until the spools are held by the spool-locating means, 
releasing the spools from the loading member and withdrawing the latter 
leaving the loaded spools retained in the casing. 
The cassette system and refill unit of the present invention provide a 
number of advantages over previously known cassettes and refill methods. 
In particular it reduces the amount of wasted material and expense by 
enabling discarded mouldings to be limited to a minimal loading member, 
rather than a full cassette casing. This frees the cassette designer to 
produce a cassette with optimum performance characteristics, such as 
including reinforcement to give optimum rigidity, without commercial 
constraints of minimising the cost of mouldings discarded with the used 
ribbons. Compared with other refillable systems, the provision of the 
loading member enables a non-technical consumer to perform the refilling 
act without risk of damaging the ribbon or soiling their hands or clothes, 
because all that needs to be handled is the loading member. 
As may have been noted from the above discussions of the prior art, 
cassettes have previously been supplied with small disposable 
anti-rotation devices which plugged into the ends of the spools to prevent 
their rotation during transit to the consumer. However, these were 
employed with filled cassettes, rather than refills, and were not suitable 
for use with those cassettes as a loading member according to the present 
invention.

DETAILED DESCRIPTION OF THE INVENTION 
The refill 1 comprises two spools each having a broad spindle portion 3 at 
one end and a narrower spindle portion 4 at the other. Between the two 
spindle portions are bobbin portions (obscured) on which are wound a 
dyesheet ribbon 5. Between the broad spindle portion 3 and the bobbin 
portion is provided a circumferential flange 6. The broad spindle portions 
are hollow, having an axial printer-drive-receiving cavity 7 with internal 
knurls for engaging driving means in the printer. 
The casing 10 comprises two parallel spool-housings 11, having end portions 
interconnected by bridge members 12 and 13, such that the housings and 
bridge members together define an open access port 14. At each end of the 
housings are first and second spool-locating means 15 and 16 to receive 
corresponding end portions of the spools with freedom to move 
longitudinally between a free position as shown in FIG. 3, and a retained 
position as shown in FIG. 4. Each first spool-locating means 15 comprises 
a box with a spindle-receiving hole 17 and containing spring means (not 
shown) to bias the spools into the retained position, and each second 
locating means 16 comprises two arcuate upstands to form a major portion 
of an incomplete retaining ring 18, with a gap 19 between the ends of the 
upstands. The hole 17 and ring 18 are sized to provide bearings in which 
the respective spindle portions of the spools can be rotatably mounted, 
and to provide retaining means to retain the spindle portions in the 
bearings when the spools are in the retained positions. 
The loading member b comprises a rigid body portion 21 having an integral 
handle 22, and two spool-holding means. The latter are parallel rods 23 
extending from the rigid body portion 21, each with tapered extended ends 
24 and a waisted portion 25 formed by a recess on both sides only one of 
which can be shown on each rod). The rods 23 are a firm interference fit 
in the cavities 7 of the broad spindle portions 3 at one end of the 
spools. The integral handle provides an economical way of shaping the body 
portion to be comfortable to hold and transport manually, and improve the 
rigidity at the same time. 
The refill unit is first assembled by combining the refill 1 and the 
loading member 20, as shown in FIG. 2. To achieve this the tapered 
extended ends 24 of rods 23 on the loading member, are pressed into the 
cavities 7 of the refill, up to but not including the waisted portion 25 
of the rods. The interference fit between the rods 23 and the knurls in 
the cavity 7 provides the loading member with a good non-rotatable hold on 
the refill, whilst keeping the spools spaced apart and parallel. The 
refill unit can then readily be picked up and transported manually by 
using the handle 22, with little danger of the user inadvertently touching 
the spooled ribbon. 
The refill unit is inserted into the casing as shown by guide lines 30 in 
FIG. 2. First the narrow spindle portions 4 are inserted into the holes 17 
until resistance by the spring means in the boxes 15 is felt, and then 
continued until the waisted portions 25 of the rods 23 become adjacent to 
the gaps 19. The loading member is then lowered through the gaps so that 
those waisted portions enter into the rings 18 of the second bearings as 
shown in FIG. 3. This is the "free position" referred to above, in which 
the spindles are still free to be lifted out of the retaining rings 18 and 
removed. 
On withdrawing the loading member from the hollow ends of the spools (as 
indicated by the arrow 31 in FIG. 4), bias from the spring means causes 
longitudinal movement of the refill spools in the casing from the free 
position shown in FIG. 3, until the flanges 6 contact the rings 18, and 
prevent further movement. In so moving the refill unit, the gaps 19 in the 
second bearing portions 16 come into alignment with the broader spindle 
ends of the spools 3 (instead of the waisted portions of the loading 
member rods), which are not able to pass back out through the gaps 19, 
thus retaining the refill in place. Hence this is the "retained position" 
referred to above, and is shown in FIG. 4. 
The loading member thereafter plays no active role in the operation of the 
refilled cassette during printing, and may be discarded or recycled as 
part of a fresh refill unit, as desired. Being a smaller, simpler moulding 
than the cassette, whether the loading member is discarded or recycled, 
this represents an environmentally more friendly option than doing the 
same with the full cassette, and is a more user-friendly way of refilling 
the cassette than handling the refills directly.