WO1999020471A2

WO1999020471A2 - Dyesheet cassette and printing apparatus

Info

Publication number: WO1999020471A2
Application number: PCT/GB1998/003163
Authority: WO
Inventors: Keith William Gilbert; Jeffrey Michael Howell; Terence John Burch; Peter Charles William Butcher; Scott Thomas Mazar; David Schouweiler; Richard Keeney; Kevin Arnal
Original assignee: Imperial Chemical Industries Plc
Priority date: 1997-10-22
Filing date: 1998-10-22
Publication date: 1999-04-29
Also published as: GB9722370D0; WO1999020471A3

Abstract

A dyesheet cassette (3) contains a dyesheet (2) mounted between supply and take-up spools (5 and 6) for printing to e.g. a slide (1) using a laser beam (8) focussed by a rod lens (7). The cassette (3) comprising a moulded casing (13) having a base (14), and supply and take-up spool housings (15 and 16) into which the spools (5, 6) are placed during manufacture, before end caps (35, 36) (not shown) are added. The casing (13) includes integrally moulded leaf spring (17) for urging the spools (5 and 6), against the end caps (35, 36) and against drive shafts (not shown) of a printer. The cassette (3) includes a ribbon insertion guide (12) which moves between an extended position in which it engages the ribbon (2) and also seals the ribbon supply opening (15a) in the housing (15), and the shown retracted position, in which it passes about the lens (7) to leave the ribbon (2) thereon. The guide (12) has a pad (53) thereon which cleans the lens (7) during retraction or extension of the guide. The take-up spool (6) is longer in length than the supply spool (5) to prevent snagging of the ribbon (2). The cassette (3) is accurately positioned on printing apparatus by placing locating cylinders (18, 18b) over locating rods (47). It also includes a shield (11) for preventing dye resublimed from the slide (1) during flash fixing from reaching the flash fixing tubes (9).

Description

Dye Sheet Cassette and Printing Apparatus

The present invention relates to dye thermal transfer printing, and particularly to a cassette for holding a dye transfer ribbon and to apparatus for use with the same. The invention especially relates to dye sheet cassettes and printing apparatus for 35 mm slide printing. In dye thermal transfer printing, selected regions of a dye donor sheet are heated to cause dye to pass from the heated regions of the donor sheet to corresponding regions of a receiver sheet to form an image therein. The heating may be carried out in a number of ways, for example by a thermal head comprising a number of heatable elements or by a scanning laser beam which is modulated as it is scanned.

Transfer of the dye may be by a diffusion process in which the donor and receiver sheets are held in intimate contact with one another. Alternatively, transfer may be by a sublimation process in which there is a gap of typically a few microns between the donor and receiver sheets. In sublimation transfer, the heated dye enters the vapour phase, crosses the gap between the sheets, and condenses onto the relatively cool surface of the receiver sheet. Typically, the gap is provided by spacer particles, such as microbeads, mounted in the surface of the donor and/or receiver sheets.

The dye sheets are often in the form of transfer ribbons, which, in colour printing, may include repeating sequences of each primary colour (e.g. cyan, magenta and yellow) and any other materials to be transferred (e.g. black dyes) . These ribbons are generally mounted within a cassette.

Typically, the cassette consists of a casing which houses a supply spool of unused ribbon and a take-up spool of used ribbon. A window is provided in the cassette casing between the spools to expose the ribbon for printing purposes, and an opening is provided at one end of each of the supply and take-up spool housings to allow drive shafts of the printer to engage with spindles of the spools.

When the cassette is placed in the printer, the spools are engaged by the drive shafts, and a receiver sheet and print head are located either side of the ribbon exposed in the cassette window. Printing may then be carried out .

Typically in the prior art, the cassette casing comprises a pair of opposed moulded halves, each having a pair of semi-cylindrical portions that each define one longitudinal half of either the housing of the take-up spool or the housing of the supply spool. During construction of the cassette, the spools are sandwiched between the casing halves.

Springs are generally provided at one end of each of the spool housings, opposite to the drive shaft openings, so as to ensure that the spools engage with the printer drive shafts. The springs also ensure that the spools are engaged with transit locks when the cassette is removed from the printer and when it is in transit, which prevent the spools from unwinding.

Examples of prior art cassettes are shown in e.g. US-A-5492422, WO-A-9519889 and JP-A-8-58201.

The present invention aims to provide an alternative cassette for housing a dye sheet ribbon, which is particularly suitable for use with ribbon for 35 mm slide printing.

Viewed from one aspect, the present invention provides a transfer ribbon cassette for use in dye thermal transfer printing, the cassette comprising a moulded casing having a base and a pair of tubular spool housings extending up from the base into which a supply spool and a take-up spool may be inserted longitudinally, each spool housing having a spring member at its base end and an end cover at its opposite end.

The arrangement provides a cassette of simple and inexpensive construction. The cylindrical spool housings provide the cassette with strength and assist in the assembly of the cassette by acting as receptacles for the supply and take-up spools. Further, the construction uses a limited number of parts, and enables the close control of critical dimensions, many of these dimensions being contained within the cassette base and therefore not being dependent upon the correct assembly and accurate positioning of the cassette.

A cassette according to the invention is particularly suitable for housing ribbon for printing to 35 mm slides, as the narrow width of the ribbon makes the moulding of the cassette more simple. A cassette for a wide ribbon would require a long opening stroke on an injection mould tool and an increased draft angle to cope with the increased depth of the moulding. The spring members urge the spools towards the end covers of the spool housing, which will have openings therein for allowing engagement of the spindles of the spools by drive shafts of the printer. The springs hold the spools onto the printer datums and take up excess clearance. They provide axial thrust and may therefore maintain contact with spool anti-rotation ribs during transport of the cassette.

The spring members may be separate elements, e.g. of metal, which are attached to the casing during manufacture. Preferably, however, the spring members are moulded integrally with the casing, and preferably comprise cantilevered springs extending e.g. from the inner edge of an opening in the base end of each spool housing. The openings allow for the moulding of the springs and their cantilevered action. The spring may be a leaf spring, e.g. formed by a U-shaped opening in the cassette base, the opening defining a cantilevered tongue portion of the base as the spring means . Each spool preferably has means thereon for engaging the spring member, for locating the spool accurately in the housing, and for closing the opening in the casing base. The spools preferably have base end caps including a central pip for engaging the spring member and preferably a circumferential rim for engaging with a rim or stepped portion of the base about the springs . The rim of the cap may provide protection for the pip, whilst also helping to ensure correct location of the spools in the cassette and providing a dust seal over the openings around the springs .

The spools preferably have flanges at their other ends to provide a dust seal over the drive shaft openings. Preferably, these flanges include ribs and/or grooves which cooperate with corresponding ribs/grooves on the inner surface of the casing end covers . As the spring members urge the spools against the end covers, the ribs/grooves cooperate to prevent slip in the spools and to prevent ribbon unwind during transit.

The spools may connect with the drive shafts of the printer in any suitable manner through any suitable means. Preferably, the spools comprise hollow spindles for holding the ribbon, the spindles receiving the drive shafts therein and preferably having splines running longitudinally along their inner surfaces for engagement by the drive shafts.

The spring-engaging end caps of the spools may be e.g. integral with the spools, but are preferably a push fit into the ends of the spool spindles, and may include clips that engage with a horizontal rib on the inside of the spindles .

The spools may include stop means which engage with the drive shafts of the printer to locate the spools at the correct position on the shafts. Preferably, the spring-engaging end caps include a central stop pip extending into the hollow spool spindles for locating the spindles a set length along the drive shaft. The spools are preferably of different lengths, and preferably the take-up spool is between about 2 mm and about 6 mm, e.g. 4 mm, longer than the supply spool for a 35 mm slide ribbon cassette. This 2 mm to 6 mm difference in size may also be used for spools associated with any other width of ribbon.

It is preferable for the supply spool to have flanges close to the edges of the dyesheet to ensure that any telescoping of the ribbon on the spool is contained within the flanges and kept to a low level . The lengths of the spools between their flanges determines the maximum lateral movement that can be permitted, and this is able to be kept small for the supply spool, because, at the factory, the transfer ribbon may be wound onto the supply spool with great accuracy - e.g. to a tolerance of about ± 0.5 mm. However, during use, the winding of the ribbon onto the take-up spool is not so accurate. This can lead to snagging and turn-up of the edges of the taken-up ribbon, which can affect the smoothness of the ribbon unwind. By having the take-up spool longer than the supply spool, however, this snagging and turn-up can be prevented .

The differently sized spools may be accurately positioned longitudinally with respect to one another through the engagement of the printer drive shafts by e.g. the above-mentioned stop pips. Thus, the take-up spool may be centred on the supply spool, so that it extends 1 to 3 mm past either end of the supply spool, by using stop pips in the spindles of differing lengths, with the stop pip of the take-up spool being 1 to 3 mm shorter than the stop pip of the supply spool .

In a particularly preferred form, the cassette includes a ribbon insertion guide between the two spool housings which may move between an extended and a retracted position. In one position of the ribbon insertion guide, the transfer ribbon is held away from the print head, whilst in the other position the ribbon cooperates with the print head.

Preferably, when the cassette is not in use, the ribbon insertion guide is held in the extended position, with the transfer ribbon between the two spools passing about the ribbon insertion guide, and, when the cassette is in use and mounted on the printer, movement of the ribbon insertion guide into its retracted position causes the transfer ribbon to engage with the print head and to disengage from the ribbon insertion guide. Thus, on insertion of the cassette into the printer, the ribbon insertion guide holds the ribbon away from the print head and then moves the ribbon into contact with the print head.

The ribbon insertion guide may be moved by e.g. an arm or other means of the printer apparatus with which it engages on insertion of the cassette into the printer apparatus . The ribbon insertion guide may have a hook or other suitable means thereon for engagement by the arm or other means . The ribbon insertion guide is preferably mounted between one or more guide grooves or ribs in the base of the cassette casing and one or more guide grooves or ribs in one or both of the spool housing end covers, preferably in the supply housing end cover. The portion of the casing which houses the supply spool has an opening for feeding the ribbon to the take- up spool . This opening is wide enough to cope with the extremes of the supply spool ' s diameter from when the ribbon is fully wound about the spool to when the ribbon has been mostly unwound. Preferably, the ribbon insertion guide is designed, when extended, to seal this opening, e.g. against dust. For example, the ribbon insertion guide may have a side wall portion which extends across the opening when in the extended position.

In one preferred form, the ribbon insertion guide comprises a body having first and second elongate sides in a substantially L-shaped cross-sectional configuration, one (first) side cooperating with the base of the cassette casing, and the other (second) side facing the supply spool housing to provide a seal for the housing's opening when the ribbon insertion guide is extended. A longitudinal edge of the second side may run in a guide groove in the end cover of the supply housing, and a groove in the first (base-cooperating) side may be mounted over a guide rib on the cassette's base . The ribbon insertion guide preferably has a guide portion at the front thereof over which the ribbon passes when the ribbon insertion guide is in the extended position.

The mounting of the cassette and the print head on the printer is preferably arranged so that when the cassette is on the printer, the front guide portion of the ribbon insertion guide is positioned between the print head and the receiver's print position, and, on movement of the ribbon insertion guide to its retracted position, the front guide portion is preferably retracted past the print head leaving the transfer ribbon in contact with the print head.

The front guide portion of the ribbon insertion guide may take any suitable form, and for example for the above-mentioned L-shaped insertion guide may be in the form of a pair of prongs extending up from the first (base-cooperating) side of the ribbon insertion guide, one of these prongs possibly being the front end edge of the second side of the ribbon insertion guide. Preferably, the front guide portion is in the form of a window through which the print head may pass when the ribbon insertion guide is retracted, the print head engaging with the ribbon on passing through the window to lift the ribbon away from the window. The print head is preferably mounted on the printing apparatus in a cantilevered fashion, so as to enable it to pass through the window.

Preferably, the cassette is used in a printing system in which the print head comprises a rod lens, cylindrical lens or the like, the lens focussing a laser beam onto the transfer ribbon to cause the dye to transfer to the receiver. Such a system is disclosed in USSN 08/682,905 filed on 16 July 1996 (corresponding to EP 96305216.2 and JP 8-220270), the contents of which are incorporated herein by reference.

The ribbon insertion guide preferably includes a cleaning means thereon, which cleans the print head, e.g. optical elements such as the above-mentioned rod lens, as the ribbon insertion guide moves between the extended and retracted positions. In this case, the ribbon insertion guide may be moved between its retracted and extended positions to provide cleaning at any suitable time, e.g. after each complete slide has been printed or after each one of a number of colour images has been printed on a slide.

The cleaning head is preferably a pad that wipes the head. Cleaning may be accomplished by moving the pad into contact with the active surface of the print head, then drawing it across the surface, e.g. in a wiping action, so that any debris is moved away from the active surface . The pad surface may be e.g. a fibrous rough surface, which moves relative to the print head surface and captures loose particles in its meshwork.

Alternatively, the surface may be smooth so that it wets the print head, with particles sticking preferentially to the pad when the surfaces separate. In this case, the head and/or the pad surface should preferably be convex so that one can roll over the other.

The pad should preferably be compliant, by virtue of its substance or support, so that it conforms closely to the print head when it is cleaning.

The cleaning head is preferably hinged to the ribbon insertion guide, e.g. on the side of the L-shaped insertion guide facing the supply spool housing opening.

The ribbon insertion guide preferably includes camming means that engage with a portion of the casing, e.g. the supply spool housing, to provide the necessary action for the cleaning pad to clean the head as the ribbon insertion guide is moved. The camming action may determine the pressure of the pad during cleaning and ensure adequate clearance between the pad and head at other times . In a preferred form, the pad is preferably made from silicon rubber, and may be in the form of an elongate strip mounted along a front edge of a cleaning arm on the ribbon insertion guide. The pad may be mounted on the arm in any suitable manner, e.g. by double-sided tape, glue or mechanically (such as by rivets) .

The cleaning means preferably comprises a sprung arm, e.g. of leaf-spring type construction, which is urged by the camming means towards the print head and which springs back from the print head when the camming action ends .

The camming means may take the form of one or more trapezoidal elements (e.g. in the form of a truncated triangular form) on the opposite side of the cleaning arm to the cleaning pad. When the ribbon insertion guide is in the extended position, the camming elements may lie in the opening of the supply spool housing and when the ribbon insertion guide is retracted or moved back to its extended position, the camming elements may engage with a side edge of the opening to urge the arm away from the opening and towards the print head. The cleaning pad is thus urged into contact with the print head during movement of the ribbon insertion guide between its extended and retracted positions, but is spaced from the print head when the ribbon insertion guide is at either of its two limit positions.

Where a rod lens is the print head, the design of the pad and other cleaning elements is preferably such that debris greater than about 10 microns is removed from the lens, and the softness of the pad should be such that no scratching results from dust, etc., retained on the pad. Where the cleaning action occurs after each slide has been printed, the pad should be able to survive e.g. about 200 passes, that is 100 cleaning actions of the ribbon insertion guide moving between its extended and retracted position and back again. The pad may be made to withstand correspondingly more passes, e.g. three times more, where it cleans between each single colour print to a slide.

The pad may e.g. be 36.00 ± 0.50 mm long, 9.13 ± 0.50 mm wide and may have a thickness of 2.00 ± 0.50 mm. The width is calculated from a 7.13 mm wiping stroke plus 2 x 1 mm oversize to prevent peel of the pad.

Preferably, the pad should not extend beyond the arm on which it is mounted, as any overhang may result in the pad peeling off of the arm and onto the print head.

A locking means is preferably provided on the base of the cassette casing for holding the ribbon insertion guide in the extended position when not in the printer. Preferably the locking means is released automatically on insertion of the cassette into the printer, e.g. by a cooperating member on the printer. The locking means may comprise a spring element, e.g. a leaf spring formed integrally in the base of the cassette, the spring having a stop portion that engages with the ribbon insertion guide (e.g. at a rear edge thereof) to hold it in place, the printer mechanism having means, e.g. a pin, for urging the spring out of contact with the insertion guide to allow the guide to move freely.

The cassette is preferably designed to accommodate a flash source adjacent the print station for fixing the dye into the receiver medium after printing in accordance with the flash fixing process described in International Patent Application No. PCT/GB 97/01050, - li the contents of which are incorporated herein by reference. In this method, an infra-red absorber is incorporated in the receiver medium and the medium is exposed to a burst of infra-red rich light after printing to heat the medium and so fix the dye therein. The cassette may therefore for example have a recess for accommodating an array of flash tubes . Preferably, the cassette includes a transparent shield which extends between the flash source and the receiver medium during use, the shield preventing dye sublimed off of the receiver sheet during fixing from building up on the flash tubes .

The shield is preferably fixed onto the cassette by a rib and groove arrangement. The casing end cover for the take-up spool housing may close the channels in which the shield is mounted after fitment, so as to secure the shield in place.

Such a shield is disclosed in a co-pending International patent application based on GB 9722332.5 to Imperial Chemical Industries PLC entitled "Apparatus and Method for Dye Thermal Transfer Printing" filed on the same date as this application, the contents of which are incorporated herein by reference.

In the prior art, the cassette is normally located in the printing apparatus by holes and pins. The present cassette, however, preferably includes tubular locating cylinders, preferably extending substantially the full width of the cassette, for accurately mounting the cassette on corresponding locating rods on the printer. The cylinders are structurally superior to holes, and are more resistant to damage which could prevent the cassette from being inserted into the printer. They provide good three axes stability. Preferably, one cylinder is provided at each end of the cassette. The locating cylinders are able to contribute to the structural integrity of the cassette design.

Preferably, one of the cylinders is elongate, e.g. oval, in cross-section, so as to allow for accurate positioning of the cassette on the printer, independent of the dimensional variability of the cassette and printer. The elongate cross-section ensures that one hole provides accurate location whilst the other limits the degree of freedom with respect to angular movement between the cassette and printer. The elongate section allows movement in the other plane thereby making it independent of manufacturing tolerances of both the printer and cassette in this second plane. The cassette will preferably be mounted vertically, with one spool housing above the other. The elongate cylinder is preferably the bottom cylinder.

The cassette may be made from any suitable materials, e.g. Acrylonitrile-Butadiene-Styrene (ABS) plastic.

The invention also extends to a method of making a dye transfer ribbon cassette comprising the steps of providing a moulded casing having a base and a pair of tubular spool housings, providing a spring member at the base end of each spool housing, inserting supply and take-up spools in the housings, and closing the housings with end covers. Preferably, a ribbon insertion guide and a shield, as discussed above, are mounted on the base before the end covers are placed over the spool housings.

The provision of the above-mentioned casing with moulded springs thereon is a particularly advantageous feature of the present invention, and viewed from a further aspect, the present invention provides a transfer ribbon cassette for use in dye thermal transfer printing, the cassette comprising a moulded casing having a base and a pair of tubular spool housings extending up therefrom into which supply and take-up spools may be inserted longitudinally, each spool housing having a spring member integrally moulded at its base end and an end cover at its opposite end.

The use of spool lengths of different sizes is in itself a new invention which may be used with any suitable design of cassette, and, viewed from a further aspect, the invention provides a transfer ribbon cassette for dye thermal transfer printing, in which the ribbon mounting portion of the take-up spool is longer than the ribbon mounting portion of the supply spool . The use of a ribbon insertion guide is also in itself a new invention over the prior art which may be used with any suitable design of cassette, and, viewed from a further aspect, the invention provides a transfer ribbon cassette in which a retractable ribbon insertion guide is mounted on the cassette for spacing the ribbon from the print head on insertion of the cassette into the printer. The ribbon insertion guide may have any of the above-described ribbon insertion guide features. The invention also extends to printing apparatus for receiving such a cassette, the apparatus including means for moving the ribbon insertion guide between its two positions .

The use of locating cylinders is further itself a new improvement which may be used with any suitable design of cassette, and, viewed from a still further aspect, the invention provides a transfer ribbon cassette having locating cylinders for locating the cassette accurately on the printer. The invention also extends to a printer for dye thermal transfer printing which includes rods for locating a cassette in place on the printer, the rods being received by locating cylinders in the cassette.

Viewed from a further aspect, the present invention provides a dye transfer ribbon cassette comprising a moulded casing having a base and a pair of tubular spool housings extending up therefrom into which supply and take-up spools may be inserted longitudinally, each spool housing having a spring member at its base end and an end cover at its opposite end, with a ribbon insertion guide mounted between the base unit and the supply end cover, the ribbon insertion guide being adapted to engage the ribbon with the print head of a printer when it moves from an extended position, in which it engages the ribbon and provides a seal for the feed opening of the supply housing, to a retracted position. An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 shows schematically apparatus for printing and fixing an image onto a 35 mm slide in accordance with an embodiment of the present invention;

Fig. 2 is a perspective view of a casing for the dye sheet cassette shown in Fig. 1;

Fig. 3 is a perspective view of the flash tube shield of Fig. 1; Fig. 4 shows a ribbon insertion guide element for the cassette of Fig. 1;

Fig. 5 shows the portion of the printing apparatus of Fig. 1 on which the dye sheet cassette is mounted;

Figs . 6 and 7 show respective ends of a spool which may be used as a take-up or supply spool in the cassette of Fig. 1;

Figs . 8 and 9 are front and side views of a base end cap for the spool of Figs . 6 and 7 ;

Figs. 10 and 11 show respectively take-up and supply end covers for the cassette casing of Fig. 1;

Figs. 12-16 show various views of the ribbon insertion guide of Fig. 5; and

Fig. 17 is a plan view of the cassette of Fig. 1 with the ribbon insertion guide in its extended position.

Referring to Fig. 1, printing apparatus is shown for printing and fixing an image onto a 35 mm slide 1 by laser sublimation transfer printing. Dye is transferred to the receiver portion of the slide 1 from a dye sheet ribbon 2 mounted in a dye sheet cassette 3. Fig. 1 shows the slide 1 in the printing position, with the fixing position shown in phantom.

The slide 1 is mounted on a suitable support 4 so as to contact the dye sheet ribbon 2 which is mounted between supply and take-up spools 5,6 of the dye sheet cassette 3. The slide 1 contacts the ribbon 2 at the point where the ribbon passes about a rod lens 7 of the printing apparatus .

The slide 1 may take a form as disclose in International Patent Application No. PCT/GB98/01324 , the contents of which are incorporated herein by reference. Such a slide has a sheet of unprinted receiver material mounted between a pair of frame halves, one of which has a larger aperture than the other for accommodating the rod lens 7 and dye sheet 2. Of course, similar apparatus to that shown in Fig. 1 could be used to print to any suitable receiver, including to a receiver sheet that is placed in a slide mount after printing and fixing.

In use, a modulated laser beam 8 is scanned along the length of the rod lens 7 (in a direction perpendicular to the plane of Fig. 1) , and is focussed by the lens 7 into the dye sheet 2. Dye from the heated portions of the dye sheet 2 transfers onto the slide 1 to form an image therein. During printing, the slide support 4 moves the slide 1 across the rod lens 7 in a direction perpendicular to the laser beam scan direction to produce a 2D scan of the slide, the ribbon 2 being wound on during this scan.

The beam 8 is orientated with respect to the lens 7 so that the beam is focussed into the dye sheet 2 along a line which is offset slightly from the pinch of the lens 7 and slide 1, at a point where the dye sheet ribbon 2 and slide 1 do not touch. This produces a gap between the ribbon 2 and slide 1 that allows for dye sublimation transfer printing. Such a printing method is disclosed in the above-mentioned USSN 08/682,905. After printing, the slide 1 is moved by its support 4 to a position opposite to an array of, e.g. xenon, flash tubes 9. The tubes 9 are then flashed in order to fix the dye into the body of the dye receiving material of the slide 1. This method of fixing the dye is discussed in the above-mentioned International Patent Application PCT/GB97/01050. The flash tubes 9 produce a flash rich in infrared light, and an infrared absorber included in the slide receiving material is heated by the flash to cause the transferred dye on the surface of the receiver material to diffuse into its body.

A reflector 10 is mounted behind the flash tubes 9 to direct the light from the flash forward onto the slide 1.

Once the dye has been fixed into the slide 1, the slide may be removed and a new slide inserted.

In colour printing, the dye ribbon 2 may have alternate areas of e.g. magenta, cyan and yellow dyes, and the slide 1 may be printed to three times, each time winding on the ribbon 2 to a different colour area. In this case, the slide may be moved opposite the flash tubes 9 for fixing between each individual colour dye transfer and/or after all three coloured dyes have been transferred.

The cassette 3 includes a shield 11 which is transparent to the infrared radiation and extends over the flash tubes 9 in use, so as to prevent dye which is resublimed by the fixing flash from building up on the flash tubes 9 and reflector 10.

A ribbon insertion guide 12 is mounted in the cassette 3 for moving the ribbon 2 into and out of engagement with the rod lens 7.

A casing 13 for the cassette 3 of Fig. 1, and the shield 11 and ribbon insertion guide 12 of Fig. 1, are shown separately in Figs. 2, 3 and 4 respectively. The elements of the printing apparatus which cooperate with the cassette 3 are shown in Fig. 5.

The casing 13 may be moulded from ABS plastic, and comprises a base portion 14, a supply spool housing portion 15, a take-up spool housing portion 16, biasing leaf springs 17 for the take-up and supply spools 5 and 6, locating cylinders 18a, 18b, a channel 19 and locking mechanism 20 for the ribbon insertion guide 12, and guide slots 21 for mounting the shield 11.

The shield 11 comprises a four-sided polycarbonate tubular member 22 having a pair of ribs 23 that engage with the guide slots 21 on the cassette casing 13. As can be seen from Fig. 1, the cassette 3 is configured so as to accommodate the flash tubes 9, with the take-up side of the cassette to which the shield 11 is mounted being somewhat recessed. The printing apparatus has the flash tubes 9 and rod lens 7 closely adjacent one another to facilitate the mounting of the flash shield 11 on the cassette.

The supply and take-up spools 5,6 are constructed from a spool portion 24 shown in Figs. 6 and 7, and base end caps 25 shown in Figs. 8 and 9. The spool portions 24 comprise a hollow spindle 26 and a flange 27. The end caps 25 clip onto the unflanged ends of the spindle 26 via clips 28 that engage with a rib 29 on the inside of the spindles 26. The end caps 25 have a central pip 30 that engages with one of the casing springs 17, and a rim portion 31 that protects the pip 30 and also extends over a raised portion 32 (see Fig. 2) of the casing base to ensure proper location of the spool in the housing and to provide a dust seal over the opening 33 surrounding the spring 17.

The hollow spindles 26 receive the drive shafts 34 of the printer, with protrusions 35 of the drive shafts 34 engaging with longitudinal splines 36 of the spindles 26 to drive the spools in rotation. A stop pip 37 on the inner surface of the end caps 25 stops the spool portions in the correct longitudinal position along the drive shafts 34.

The ribbon insertion guide 12 shown in Fig. 4 is placed in the channel 19 of the casing 13, and supply and take-up end covers 35 and 36 shown in Figs. 10 and 11 respectively are mounted on the housing portions 15,16. The end covers 35,36 clip onto the casing 13 via pins 37 that push into openings 38 (see Fig. 1) on the casing 13. The ribbon insertion guide 12 is substantially L-shaped, and includes a guide edge 39 that runs in a guide slot 40 on the supply end cover 35, and a guide slot 41 which is mounted over a guide ridge 42 (see Fig. 1) of the casing base 14.

The end covers 35 and 36 have ribs 43 thereon. Ribs 44 of the spool flanges 27 of the spool portions 24 are biased against the ribs 43 by the springs 17 in order to prevent unwind and to keep tension in the ribbon 2 between the spools when the cassette is not in the printer, e.g. during transit of the cassette

The shield 11 is placed on the casing 13 before the end covers 35 and 36, and pins 45 and 46 of the take-up cover 36 engage with the ends of the shield guide slots 21.

The cassette 3 is mounted accurately in place on the printer apparatus through the placing of the locating cylinders 18a, 18b over locating rods 47 of the printer apparatus . As can be seen from Figs. 1 and 2, the locating cylinder 18b is elongate in cross-section. The use of the elongate cross-section allows accurate positioning to be achieved independent of the dimensional variability of the cassette and printer. The ribbon insertion guide 12 is used to hold the ribbon 2 out of contact with the rod lens 7 on placing the cassette 3 into the printer apparatus. It is normally held in place by the locking mechanism 20 in an extended position, as shown in Fig. 17. In this position, during e.g. storage, it seals the ribbon supply opening 15a in the supply housing 15.

The locking mechanism 20 comprises a leaf spring 20a integrally moulded in the base 14 of the casing 13 and having a moulded raised stop portion 20b which engages with the rear edge of the ribbon insertion guide 12 to prevent its rearward movement. A portion 20c of the leaf spring 20a extends past the ribbon insertion guide 12 for engagement by a release pin 48 of the printer apparatus (see Fig. 5) , the pin 48 pushing the leaf spring 20a out of the plane of the casing base 14, so as to move the stop portion 20b out of engagement with the guide 12. When the cassette 3 is mounted on the printer apparatus, the locking mechanism 20 is engaged by the release pin 48, and a hook 49 of the ribbon insertion guide 12 is engaged by an arm of the printer apparatus . The arm then moves the ribbon insertion guide 12 into the retracted position shown in Fig. 1.

As can be seen from Fig. 5, the rod lens 7 is mounted in a cantilevered fashion on an optical plate 50 (which also mounts the locating rods 47 and the flash tubes 9) . The cantilevered mounting allows the rod lens 7 to pass through a window 51 of the ribbon insertion guide 12 during retraction of the ribbon insertion guide, so as to contact with the dye sheet ribbon 2 in readiness for printing.

Also shown mounted on the optical plate 50 is a further lens 52 of the optical system for focussing the laser beam 8.

The laser beam 8 may be produced by a multimode laser diode, which is first collimated, then anamorphically expanded in its multimode axis, and then separately focused onto the transfer ribbon 2 in its single mode axis by optical mens including the lens 55 and then in its multimode axis by the rod lens 7.

To remove the cassette 3, the printer arm which engages the hook 49 of the ribbon insertion guide 12 is pivoted forward to move the ribbon insertion guide into its extended position. This moves the ribbon 2 away from the rod lens 7, and allows the cassette 3 to be easily removed.

The movement of the ribbon insertion guide 12 to its extended position causes an elastomeric cleaning pad 53, e.g. of silicon rubber, on the ribbon insertion guide 12 to wipe against the rod lens 7 and so clean it . The cleaning pad 53 has a tacky surface which removes and retains debris .

The cleaning pad 53 is mounted to a leaf-spring portion 54 of the guide 12 formed on the side of the guide 12 that is opposite to the supply spool housing. The pad portion 54 has trapezoidal camming elements 55 thereon which engage with the edge of the supply spool housing's ribbon opening, so that when the guide 12 is moving between its two limit positions the portion 54 and so the pad 53 is urged towards the print head to provide the necessary cleaning movement to the pad 53. At each limit position of the guide 12, the portion 54 springs back away from the head.

Rod lens 7 rotates as it is stroked by the pad 53, and a portion of its circumference is cleaned by contact with the tacky surface.

The ribbon insertion guide 12 is shown in further detail in Figs 12-16. The lengths of the groove 41 and rib 42 define the limits to which the guide 12 may extend and retract . Besides holding the ribbon 2 out of contact from the rod lens 7 on placing on the cassette into the printing apparatus, the ribbon insertion guide 12 may also be moved between its retracted and extended positions at any suitable times to clean the lens 7, e.g. cleaning may take place after the printing of each slide 1.

The supply spool 5 has its flanges (defined by end cap 25 and flange 27) close to the edges of the dyesheet ribbon 2 to ensure that any telescoping of the ribbon 2 on the spool 5 is contained within the flanges and kept to a low level. The take-up spool 6 is, in a preferred embodiment, of longer spool length than the supply spool, e.g by about 2 to 6 mm, preferably 4 mm. The reason for this is that during use, the winding of the ribbon onto the take-up spool is not accurate, and normally this can lead to snagging and turn-up of the edges of the taken-up ribbon, which can affect the smoothness of the ribbon unwind. By using a longer take-up spool, however, this snagging and turn-up can be prevented. The problem is not encountered for the supply spool 5, because the transfer ribbon may be wound onto the supply spool at the factory with great accuracy - e.g. to a tolerance of about ± 0.5 mm. The spools may be accurately positioned longitudinally with respect to one another through the engagement of the printer drive shafts 34 by the above- mentioned stop pips 37. Thus, the take-up spool 6 may be centred on the supply spool 5 so that it extends 1 to 3 mm past either end of the supply spool, by using stop pips 37 of differing lengths, e.g. the stop pip of the take-up spool being 1 to 3 mm shorter than the stop pip of the supply spool .

The above described embodiments are examples only, and various alternatives and modifications are possible. Although the invention is well suited to the production of 35 mm slides, the invention may also be applied to any other suitable receiver mediums . The rod lens could be replaced by a cylindrical lens or a transparent roller with focusing optics upstream thereof. Further, the locating cylinders, ribbon insertion guide and casing features do not need to be used together, and the invention extends to cassettes using any individual ones of these features separate from the others . Any other suitable method of dye transfer could be used, such as by a thermal head comprising a number of heatable elements, flash printing or ultrasonic means.

Claims

1. A transfer ribbon cassette for use in dye thermal transfer printing, the cassette comprising a moulded casing having a base and a pair of tubular spool housings extending up from the base into which a supply spool and a take-up spool may be inserted longitudinally, each spool housing having a spring member at its base end and an end cover at its opposite end.

2. The cassette of claim 1, wherein the cassette houses a ribbon for printing to 35 mm slides

3. The cassette of claim 1 or 2 , wherein the spring members are moulded integrally with the casing.

4. The cassette of claim 1, 2 or 3 , wherein the spring members comprise cantilevered springs.

5. The cassette of any preceding claim, wherein each spool has a base end cap for closing an opening in the cassette base about the spring members .

6. The cassette of claim 5, wherein the base end caps include a projection for engaging the spring members.

7. The cassette of claim 5 or 6, wherein the base end caps have a circumferential rim for engaging a raised portion of the base about the spring members.

8. The cassette of claim 5, 6 or 7, wherein the base end caps are push fit into the ends of the spool spindles .

9. The cassette of any of claims 5 to 8 , wherein the spools have hollow spindles, and wherein the base end caps include a central stop extending into the hollow spindles for locating the spindles a set length along drive shafts of a printing apparatus in use.

10. The cassette of any preceding claims, wherein the spools have flanges at the ends thereof which extend over drive shafts of a printing apparatus in use, the flanges providing a seal over drive shaft openings provided in the cassette end caps .

11. The cassette of any preceding claim, wherein the supply and take-up spools are of different lengths.

12. The cassette of claim 11, wherein the take-up spool is between about 2 mm and about 6 mm longer than the supply spool .

13. The cassette of claim 11, wherein the take-up spool is about 4 mm longer than the supply spool .

14. The cassette of any preceding claim, wherein the cassette includes a ribbon insertion guide between the two spool housings which engages with the ribbon and is movable between an extended in which the ribbon is held away from a print head in use, and a retracted position in which the ribbon is able to engage a print head in use.

15. The cassette of claim 14, wherein the ribbon insertion guide includes engagement means which in use are engaged by actuating means of a printer apparatus for moving the guide between the extended and retracted positions .

16. The cassette of claim 14 or 15, wherein the ribbon insertion guide is mounted between one or more guide grooves or ribs in the base of the cassette casing and one or more guide grooves or ribs in one or both of the spool housing end covers.

17. The cassette of claim 14, 15 or 16, wherein the ribbon insertion guide is configured such that, when extended, it seals an opening in the casing for feeding the ribbon from the supply spool .

18. The cassette of any of claims 14 to 17, wherein the ribbon insertion guide comprises a body having first and second elongate sides in a substantially L-shaped cross- sectional configuration, one side cooperating with the base of the cassette casing, and the other side facing the supply spool housing to provide a seal for a ribbon supply opening of the housing when the ribbon insertion guide is extended.

19. The cassette of any of claims 14 to 18, wherein the ribbon insertion guide has a guide portion at the front thereof over which the ribbon passes when the ribbon insertion guide is in the extended position, and which is arranged such that, on movement of the guide to its retracted position in use, the front guide portion is able to be retracted past a print head leaving the transfer ribbon in contact with the print head.

20. The cassette of claim 19, wherein the front guide portion is in the form of a window through which a print head may pass when the ribbon insertion guide is retracted, the print head engaging with the ribbon on passing through the window to lift the ribbon away from the window .

21. The cassette of any of claims 14 to 20, wherein the ribbon insertion guide includes a cleaning means thereon, which in use cleans a print head of the printing apparatus on which the cassette is mounted, as the ribbon insertion guide moves between extended and/or retracted positions.

22. The cassette of claim 21, wherein the cleaning means is a pad that wipes the head.

23. The cassette of claim 22, wherein the pad has a fibrous rough surface.

24. The cassette of claim 22, wherein the pad has a smooth surface that wets the print head.

25. The cassette of any of claims 21 to 24, wherein the cleaning means is hinged to the ribbon insertion guide.

26. The cassette of any of claims 21 to 25, wherein the ribbon insertion guide includes camming means that engage with a portion of the casing, to cause movement of the cleaning means .

27. The cassette of claim 26, wherein the cleaning means comprises a sprung arm, which is urged in use by the camming means towards a print head and which springs back from the print head when the camming action ends.

28. The cassette of claim 27, wherein the camming means takes the form of one or more trapezoidal elements on the opposite side of the cleaning arm to a cleaning pad.

29. The cassette of claim 28, wherein when the ribbon insertion guide is retracted or extended, the camming elements engage with a side edge of an opening in the supply spool housing to urge the arm away from the opening and in use towards a print head.

30. The cassette of any of claims 14 to 29, wherein a locking means is provided on the base of the cassette casing for holding the ribbon insertion guide in the extended position when not mounted in a printing apparatus .

31. The cassette of claim 30, wherein the locking means comprises a spring element having a stop portion that engages with the ribbon insertion guide to hold it in place.

32. The cassette of any preceding claim, wherein the cassette includes a transparent shield which in use extends between a flash fixing source and a receiver medium.

33. The cassette of claim 32, wherein the shield is fixed onto the cassette by a rib and groove arrangement, and the casing end cover for the take-up spool housing closes the grooves in which the shield is mounted after fitment .

34. The cassette of any preceding claim, wherein the cassette includes tubular locating cylinders for mounting the cassette on corresponding locating rods on a printer.

35. A method of making a dye transfer ribbon cassette comprising the steps of providing a moulded casing having a base and a pair of tubular spool housings, providing a spring member at the base end of each spool housing, inserting supply and take-up spools in the housings, and closing the housings with end covers.

36. The method of claim 35, wherein a ribbon insertion guide is mounted on the base before the end covers are placed over the spool housings, the guide being movable between an extended in which the cassette ribbon is held away from a print head in use, and a retracted position in which the ribbon cooperates with the print head in use.

37. A transfer ribbon cassette for use in dye thermal transfer printing, the cassette comprising a moulded casing having a base and a pair of tubular spool housings extending up therefrom into which supply and take-up spools may be inserted longitudinally, each spool housing having a spring member integrally moulded at its base end and an end cover at its opposite end.

38. A transfer ribbon cassette for dye thermal transfer printing, in which the ribbon mounting portion of the take-up spool is longer than the ribbon mounting portion of the supply spool .

39. A transfer ribbon cassette in which a retractable ribbon insertion guide is mounted on the cassette for spacing the ribbon from a print head on insertion of the cassette into a printer.

40. The cassette of claim 39, in which the ribbon insertion guide includes any of the ribbon insertion guide features of claims 14 to 31.

41. Printing apparatus for receiving a cassette according to claim 39 or 40, the apparatus including means for moving the ribbon insertion guide between its two positions.

42. Apparatus for dye thermal transfer printing, comprising a printing means and a dye donor ribbon cassette, the cassette having locating cylinders thereon for receiving rods mounted on the printing means for locating the cassette in place on the printing means .

43. A dye transfer ribbon cassette comprising a moulded casing having a base and a pair of tubular spool housings extending up therefrom into which supply and take-up spools may be inserted longitudinally, each spool housing having a spring member at its base end and an end cover at its opposite end, with a ribbon insertion guide mounted between the base and the supply spool housing end cover, the ribbon insertion guide being adapted to engage the ribbon with the print head of a printer when it moves from an extended position, in which it engages the ribbon and provides a seal for the feed opening of the supply housing, to a retracted position.

44. A printing system comprising a printing apparatus and a cassette according to any preceding cassette claim.

45. The system of claim 44, wherein the print head of the printing apparatus comprises a rod lens, cylindrical lens or the like, the lens focussing a laser beam onto the transfer ribbon to cause dye to transfer to a receiver.