EP0044369B1 - Thermal engraving machine for relief printing - Google Patents

Abstract

A thermo-engraving machine has safety, energy conserving and convenience features. The thermo-engraving machine receives a freshly printed sheet, passes it through a device for depositing powder. It heats the powder to cause the powder to melt, then cools the sheet to create raised printed material. The deposition device in one case is a tank with a vertical partition that provides separate containers for powders of different types. The other deposition device is a cyclone type that is pivotal to allow easy cleaning and has toothed wheels in its suction manifold to retain the sheets. The oven has sidewalls that will laterally move to vary the width of the oven. Heater elements in the oven can be selectively turned off for smaller widths. The oven is held by a latch that releases the oven to spring upward should electricity be cut off to the solenoid that holds the latch in position. The cooling conveyor curves around from the back of the oven and leads to the front of the machine, preferably over the top of the oven. The cooling conveyor has a conveyor belt assembly and positive and negative plenums on its sides to retain the sheets in connection with the conveyor belt assembly and cool them at the same time.

Description

The present invention relates to thermogravure machines for relief printing.

Thermogravure or typo relief is a known process. It allows, from a typographic, offset or other printing, to obtain a relief printing imitating intaglio or stamping. The transformation into relief is simple and consists in sprinkling a freshly printed sheet of paper with a powder having the property of melting under the action of heat and of forming, after fusion, a film in relief. The wet ink retains only the powder and the excess is continuously recovered. The powdered print then passes under a tunnel oven and at its outlet, a jet of fresh air cools the paper and instantly freezes the film in viscous relief to prevent the sheets from sticking together. The automatic transformation into relief takes place in the following way: the paper, leaving the printing press, is received directly on conveyor belts and passes successively, under the powder block, inside the tunnel oven and on a last conveyor, to cool down, before being received in a receiving tank.

The powders used, shiny or mat, are transparent and retain their hues with the printing colors. On the other hand, pigmented powders give, whatever the printing color, a relief corresponding to their pigment. The particle size of the powder used determines the thickness of the raised film. The larger the powder, the greater the relief. The machines currently in service limit the possibilities of this process, since they have the following shortcomings and defects:

The tunnel ovens of these machines always operate at full size and in the majority of cases, the prints to be processed are of essentially variable widths. It is common to pass 10 cm wide prints in an oven allowing a passage of 35 cm or more, resulting in disproportionate and unnecessary energy expenditure.

These machines only process one type of powder at a time, but the bold characters require a large powder to give a sufficiently thick relief and-on the contrary, the lean characters require, to keep their finesse and sharpness, fine powders. Furthermore, when the print has texts of which certain parts must be without relief and others in relief of one or more colors, their execution requires several passages in the machine, which considerably increases the price of these printed matter.

These machines do not allow two-sided embossed prints to be processed, because the use of thermoplastic powder brings about a recasting of the film, on the second pass, which sticks to the conveyor of the tunnel oven and deteriorates. At the same time, when it is a matter of relief prints intended for making, for example, wrapping papers, wallpapers or labels, it would be advantageous for the film forming the relief to have a certain mechanical resistance, which is not not the current case, because the resins used are usually low molecular weight polyamides, which do not undergo any secondary action capable of improving their resistance.

The size of these machines is very large. This is mainly due to the fact that printing presses have high rates, of the order of 4 to 10,000 copies per hour, which requires a good length of tunnel ovens and cooling conveyors, especially when processing cards heavy weight.

These machines do not include automatic control of all of their adjustments as a function of the formats, grammages and rates of the successive printed matter to be processed. Their users are obliged to regulate separately and often in an arbitrary manner, the running speed of the conveyors and the temperature of the ovens.

In the case where the recycling of the surplus powder is obtained by suction through a "cyclone", the circular circular knives intended to prevent the paper from following the same trajectory as the powder, brake, by the lack of entry d air they cause at their level, good suction of the powder. It often follows that the periphery of these circular knives, running in contact with the powder and the paper, leaves traces of powder over the entire length of the paper, which is particularly troublesome in the case of colored powders. This defect is found, in another form, on the back of the print. In fact, the powder conveyor is in contact with the entire surface of the print and therefore tends to recover, despite the aspiration, grains of powder regardless of the precautions taken.

Thermogravure machines require frequent cleaning for proper functioning, because they process a large quantity of powder per hour, a small part of which is able to infiltrate inside. Currently cleaning operations are long and impractical because the parts to be cleaned lack accessibility.

These machines require long and tedious disassembly in the event of a mechanical or other incident, which leads to loss of time.

During its passage inside the oven, the paper is violently dehydrated; it loses its hold and does not find it until after a more or less long period of time depending on the humidity of the ambient air.

In the event of an incident, the operator must simultaneously stop the conveyors, dusting and precipitately raise the tunnel oven, otherwise the paper jammed below will ignite quickly.

Receiving embossed prints poses problems because the edge of the receiving sheet tends to hang on the parts embossed with the previous print.

The reception of relief prints on these machines is several meters from the printing press, which forces the operator to come and go to monitor the two machines.

The patent FR-A-2155 072 does not provide a new solution to the shortcomings exposed. Patent BE-A-705048 relates to continuous printing from roll paper and not from sheet-to-sheet printing. US-A-2230826 and French patents 2379458 present solutions to the thermal regulation of tunnel ovens but do not solve the problem of narrow width printed matter, such as business cards, processed from an oven whose passage width is often 4 to 5 times greater.

• Réaliser de larges économies d'énergie en utilisant rationnellement les calories nécessaires, en fonction de l'imprimé à traiter.

The present invention aims to remedy these various drawbacks and inadequacies and has as its object the production of thermogravure machines comprising characteristics providing the means capable of:

• Achieve large energy savings by rationally using the calories required, depending on the form to be processed.

Treat 1 or more types of powder simultaneously, of different types or colors.

Obtain a print whose embossed film will have a certain infusibility and good mechanical resistance.

Significantly reduce the size and mainly the length of these machines.

Fully automate these machines according to formats, grammages and rates.

Avoid as much as possible leaving on the print, both on the front and on the back, traces or grains of powder.

Simplify and minimize the different cleanings.

Allow mechanical disassembly, easy and quick, of the different elements, eliminating as much as possible any tools.

Incorporate humidifiers into these machines to rehydrate the paper as it comes out of the oven.

Raise the oven, stop the conveyors from running and drop the powder simultaneously using a single command in the event of an incident.

Receive the print on the raised side on the reception table, so that the edge of the next print meets only the smooth back of the previous print.

Receive the embossed print next to the reception of the printing press.

Cool the rollers of the metal conveyors.

The present invention as characterized in the claims, aims to provide thermogravure machines which, depending on their precise application, may include all or part of these characteristics. All of these characteristics and advantages of the invention will emerge from the description below, of an embodiment of these machines, given by way of nonlimiting example, with reference to the accompanying drawings.

Figure 1 shows an overview of a complete machine. 2 shows a cross section of the tunnel furnace with movable partitions. FIG. 3 represents a longitudinal section of this same tunnel oven. Figures 4 and 5 show an oven and its lifting device. Figures 6 and 7 show a pivoting cyclone and a dusting conveyor. Figures 8 and 9 show an assembly representing the instantaneous disassembly mechanism of a feed arm and free rollers or supporting all of the conveyors. Figure 10 shows a cooling conveyor. Figure 11 shows a dust removal wheel located inside the suction duct. Figure 12 shows an air-cooled roller.

Figure 1 shows in detail a body or frame 13 of a machine supporting a conveyor 12 for feeding sheets with its conveyor belts. The printed sheets, entrained by the rollers 9, pass into the reserve of the various powders 10 compartmentalized by the movable and adjustable partitions 11. The vibrating blade 14 detaches from the paper the excess powder not retained by the ink and returns to the inside the reserve 10. The metal conveyor 8 transports the paper under the tunnel oven 4. An insulating material 5 (rock wool) prevents the dispersion of the heat emitted by the heating elements 6. The lower wall of the oven 3, insulated, is inserted inside the metal conveyor 8: The paper, at the outlet of the tunnel oven, engages on the conveyor belts of the cooling conveyor 15 and passes under the blower box 1 supplied with air through the orifice 2. A vacuum cleaner 16, mounted on the suction box 17, sucks through the conveyor belts the printed relief and keeps it pressed, thus allowing it to be transported in any position during its cooling. In the case of light paper, the forced air is sufficient to keep it on the conveyor belts. A humidifier slightly wets the conveyor belts of the cooler, so as to rehydrate the paper while it cools. It consists of a tank 22 containing liquid in which a pick-up roller 21 transfers the liquid to the wringer roller 19, regulates the flow rate of the film and transfers it to the wetting roller for the strips 18. An access door 20, made of transparent plastic , allows to monitor the liquid level and to replenish the reserve in due time. The finished relief print is received on the recovery table 7.

Figures 2 and 3 show a machine body 13 on which is installed a tunnel oven consisting of a box 4 in which is placed the insulating material 5. The roof 6A of the oven supports and compartments the heating elements 6, in the form of longitudinal tubes or in coils. The mobile insulated partitions 6B move laterally and adjust to the desired widths and locations, thus restoring a elementary oven the width of the prints to be processed. An infrared probe 6C detects the rate of infrared emitted by the oven and transmits this data to the thermal controller. The movable side partitions 6B are supported, at each end of the oven, by the supports 23 and after adjustment blocked by the screws 23A. The heating elements 6 are maintained and supplied electrically, at their two ends by elastic clips 24 made of stainless steel. One of the two clamps is fixed on a movable rod 24A so as to serve as a switch in the raised position. The 24B soapstone insulator prevents the transmission of electric current from the clamp to the rod. These ovens, modulated according to the prints to be executed, allow significant energy savings and considerably reduce the cost price of relief prints. The electrical elements can be replaced by any other heating means obtained from gas, hot air, high-frequency partitioned oven, etc.

Figures 4 and 5 show a tunnel oven with its lifting and locking device. On the frame 13 is fixed the support 25 of the oven 4 with its hinge pin 25A. The lifting cylinders 25B are articulated on the axes 25C. In the low operating position, the hooking finger 26 of the oven is locked by the retaining hook 27 held by means of the electromagnet 28 in tension. In the event of a power failure, the electromagnet 28 releases the hook 27 which pivots on its axis 27A and is returned by the spring 27B. The oven is unlocked and rises by the push of its cylinders 25B in the rest position. The switch 24A and the metal conveyor 3 locate the position and the movement of the oven relative to the machine. By this principle, a switch simultaneously controls the electromagnet, the motor of the conveyors and the vibrator activating the powder container so that, in a single gesture, the operator stops: the conveyors, the fall of the powder and raises the oven. This procedure avoids, in the event of a malfunction, igniting the paper and allowing the powder to accumulate unnecessarily.

Figures 6 and 7 show a traditional powdering device whose cyclone 29 is integral with the sliding tube 29A so as to pivot around the guide rod 29B fixed to the frame of the machine, so as to completely release the cyclone from the body of the machine, to make all interventions, under the cyclone, easy. To release the cyclone, simply unscrew the retaining nut 29C, the lifting spring 29D lifts the cyclone and allows it to pivot. The dusting conveyor 30 is molded in rubber and has fine longitudinal ribs on the surface on which the print rests and has weak contacts, thus making it difficult to retain traces of powder. The suction nozzle 31, by which the excess powder is sucked, before recycling, is integral with the frame and is provided, in place of the circular knobs usually fitted to cyclones, notched knobs according to FIG. 11. The knobs, actuated by 'a rotary movement, have the action of preventing the paper from following the trajectory of the powder, inside the cyclone, when passing under the suction nozzle. These wheels have the advantage of not leaving traces of powder on the print, by mechanical effect, because they are in contact with the paper and the powder only by fine points. In addition, the air sucked in circulates freely between each tip, thus promoting good air entry into the nozzle and therefore, excellent dusting.

In the case of sheet-by-sheet treatment using powders of different colors or particle size, Figure 1, the suction tubes are replaced by two suction nozzles 2A, provided with serrated rollers according to Figure 11. With this powdering mode, the a print is produced simultaneously comprising raised portions of different colors or thicknesses. It is possible, for example, to treat powders with metallic or other pigmentation, at the same time as translucent powders and possibly interposed with powder-free zones, in the case of very fine characters or in order to contrast raised portions with d 'others without. In the same way, the particle size of the powder is selected from one compartment to another. In the case where these machines are intended to process printed matter of small formats, a variant is brought to the level of the movable partitions 11 and static dusting which separate the different powders 10. The movable partitions are doubled by rotary separators having the function of '' drive the print as it passes through the powder. They replace and double the action of the drive rollers 9. The movable partitions can be mounted on a transverse axis. Other powdering devices may be used to give an identical result. For example, the printed matter will be blended, on the machine, by known means and will pass successively under a certain number of basic powders, using the principle of recycling of the “cyclone” type, each treating an area of the printed matter. The bins distributing the powder will be closed and will only allow the powder to pass through in the desired parts.

Figure 8 shows a removable arm 32 supporting the removable roller 32A driving the conveyor belts 32B of the print. The arm is articulated on the axis 32C of the roller. The axis 32C enters its support 32D and latch 32E fixed to the frame 13 of the machine. The slide 32F allows the arm to be locked to the frame. The removable roller 32A is provided, at the end, with a gear 32G which takes its movement on the gear 32H, leading, itself driven by the pulley 321. This type of arm supports the feed conveyors, at the machine inlet and cooling outlet. They can be dismantled and reassembled in a few moments, without tools.

Figure 9 shows one of the rollers supporting all the conveyors of the machine. This roller 33 allows instant coupling with the drive pulley 33A set in motion by the general drive belt. The pulley 33A and the roller 33 each have a milling. The millings are complementary and thus form a dog. A boss 33B is fixed to the frame 13 of the machine and is connected to the pulley by the roller 33C. The axis 33D is connected to the roller 33 by two bearings. The assembly or disassembly of the roller is carried out by engaging or disengaging the axis 33D of the support 33E fixed to the frame and by extracting the ball joint from the axis of the drive pulley 33A. By pivoting the cyclone, all of the conveyors and arms are removable, without tools and in a very short time, hence great ease of troubleshooting and cleaning of the entire machine. The cyclone or the dusting vacuum cleaner for multi-powder powders will be fitted with a flexible, household flexible type and will be used for easy cleaning of these machines.

FIG. 10 shows in detail the device for cooling the print. The metal conveyor 8 fixed to the frame 13 passes under the tunnel oven 4 and brings the printed matter to the exit conveyor provided with conveyor belts 15. The air vacuum cleaner 16 fixed to the suction box 17, sucks through the conveyor belts 15 the embossed print and maintains it until the entry of the reception tray 7. The small intermediate belts 34 are interposed between the bands and run on the rollers supporting the conveyor belts which transmit their moisture to the paper during its cooling . On the other hand, this humidity accelerates by heat exchange, the cooling of the back of the paper. This humidifier consists of a tank, serving as a water reserve 22 from which comes a pick-up roller 21 which transfers a film of water to the wringing roller 19 which doses it and transfers it itself to the wetting roller 18 of the strips . A translucent access door 20 makes it possible to replenish the liquid reserve. In the case of light paper, the suction can be suppressed, the forced air sufficient to maintain the print on the conveyor belts. The receiving arm is removable. It can be positioned and worked horizontally or in other positions, if the printer has space and prefers, for personal reasons, to work in this way. The paper receiving tray 7 collects the paper from the side of the printing press, the relief being downwards, so that the edge of the piling up sheets only meets the smooth part of the back of the paper and thus avoids roll. Receiving paper in this area avoids operator fatigue and allows easy monitoring of these two machines. This operating method according to the invention makes it possible, by keeping it on the conveyors, to convey the printed matter on any plane, thus achieving very large savings in floor space. In the case of a hyper-compact machine, it can be extended to the tunnel oven which can work in any position. It does not matter how you press the paper on the conveyor, only the fact that the paper is now one with the different conveyors.

FIG. 11 represents a toothed wheel equipping the suction nozzle of the cyclone.

FIG. 12 represents a drive roller 35 of the metal conveyor passing under the tunnel oven, continuously cooled by air taken from the pipeline serving to supply the cooling arm. The forced air passes through the axis of the roller 35 and cools the drive pulley 35B and the bearings 35C. The heated air escapes at the other end of the axis and is discharged to the outside.

To allow two-sided printing and give mechanical properties to the film in relief, a generator equipped with ultraviolet lamps will be interposed between the oven and the cooler. This source of ultraviolet radiation polymerizes and infusibilises the film in relief. The resins used belong to the groups of vinyl, acrylic resins, etc. The molecular transformation leading to a certain infusibility is obtained by mineral or organic adjuvants and catalysts and under the action of internal reactions of short UV or laser wavelength .

A control of these machines is obtained from a computer system which takes into account the format of the print, its grammage and the rates displayed. This set processes these different data and achieves complete automation. An infra-red probe detects the infra-red rate emitted by the oven and transmits this data to the thermal regulator and to the control of the motor driving the conveyors. A balance is established, based on the fact that when the temperature of the oven drops, the engine instantly idles, for the time necessary for the thermal regulator to compensate for this cooling and vice versa. Sufficient space is left between each sheet to absorb these slight differences in speed of the conveyors, so that the sheets at the entrance to the machine never overlap.

All of these improvements to these machines provide their users with ease of use, great savings in space and energy and improve the quality of work, which greatly promotes the development of thermo-etching. In addition, the fact of being able to process simultaneously powders of different sizes or colors, of modifying, in certain cases, the film in relief to give it different characteristics, opens up new ways of applying the process which will find its usefulness. , apart from all commercial and advertising work, in fields as varied as continuous printing (wallpapers, wrapping paper, labels) or decoration of panels such as chipboard, aluminum sheet, steel etc. ..

Claims (28)

1. A thermographic machine, comprising in combination :

deposition means (10 Fig. 1) for depositing a heat sensitive powder deposit on wet ink of freshly printed individual sheets ;

heater means (4) for heating the sheets to melt the powder deposit, the heater means having an entrance and an exit ;

advancing means (8) for continuously and hori- zontaly advancing the sheets from a printing machine through the heater means ; and

cooling conveyor means (15) for cooling the sheets exiting from the heater means wherein the cooling conveyor means (15) extends upwardly from the exit of the heater means and turns back to generally an horizontal section located above the heater means (4) that terminates in a receiving tray (7) located generally above the deposition means (10).

2. A thermographic machine according to claim 1 wherein the cooling conveyor means comprises :

a plurality of conveyor belts sections (15) mounted end to end and driven to define a path for the sheets to the receiving tray ;

blower means (1, 2) for passing air transversely through the conveyor belts section to cause the sheets to frictionnally engage the conveyor belts section for transport along the path.

3. A thermographic machine according to claim 2 wherein plenum means (1) extending along the length of the conveyor belt assembly for passing air transversely through the conveyor belt assembly.

4. A thermographic machine according to claim 3 wherein a negative plenum mounted on the side of the conveyor belt assembly opposite the side that conveys the sheets, the conveyor belt assembly defining one wall of the negative plenum and having apertures for the passage of air transversely through the conveyor belt assembly; and blower means (16) for moving air through the apertures and passing the air from the negative plenum.

5. A thermographic machine according to claim 4 wherein an enclosed positive plenum having a discharge wall closely spaced from the side of the conveyor belt assembly that carries the sheets and extending substantially the length of the conveyor belt assembly, defining a clearance between the discharge wall and the conveyor belt assembly for the passage of the sheets ; and blower means for moving air through a plurality of apertures provided in the discharge wall.

6. A thermographic machine according to claim 5 wherein the conveyor belt assembly and the plenum means curve upwardly from the exit of the heater means and extend over the heater means ; and humidification means (18 to 22) for adding moisture to the sheets along the conveyor belt assembly.

7. A thermographic machine according to claim 6 wherein the humidification means comprises :

a tank (22) containing a liquid mounted at the termination of the conveyor belt assembly ; and roller means (18 to 21) having one rotating roller in the liquid in the tank for transferring a film of liquid to the conveyor belt assembly.

8. A thermographic machine according to any previous claim wherein the conveyor belt assembly has a roller (32 Fig. 8) located at the exit of the heater means over which a belt (32 B) of the first conveyor belt section is drawn, the roller having a gear (32 G) mounted to one end for engaging a gear (32 H) of the advancing means for driving the first conveyor belt section, the end of the roller opposite the gear having a shaft that engages an open ended slot formed in a bracket (32 F) mounted to the machine, enabling the conveyor belt assembly to be detached from the machine without tools by withdrawing the shaft from the slot and disengaging the gears.

9. A thermographic machine according to claim 8 further comprising a removable key (32 E) that engages the bracket transverse to the slot for retaining the shaft in the slot.

10. A thermographic machine according to claim 9 wherein the first conveyor belt assembly section has a second roller (33 Fig. 9) opposite the roller located at the exit of the heater means which comprises:

a drive member (33 A) rotatably mounted to one side of the machine and having a free end ;

a sleeve (33) rotatably supported on the other side of the machine and having a free end ; and

engaging means for releasably engaging the free ends to cause the sleeve to rotate with the drive member.

11. A thermographic machine according to any previous claim wherein deposition means (10) for depositing a powder comprises division means (11) for longitudinally dividing the deposition means into parallel segments that define separate containers for holding powder, enabling different types of powder to be placed on the material.

12. A thermographic machine according to claim 11 wherein the division means comprises at least one movable partition inserted in the tank parallel to the path, dividing the tank into at least two separate sections, each for containing powder.

13. A thermographic machine according to any previous claim wherein the deposition means for depositing powder comprises :

a tank through which the material passes ; and

at least one vertical partition placed in the tank parallel with the path to divide the tank into at least two separate sections, enabling each section to contain a different type of powder ; the lower edge of the partition being spaced above the bottom of the tank to enable the material to pass beneath the partition ; and

the partition being movable to different lateral positions to vary the width of the separate sections.

14. A thermographic machine according to claim 13 wherein the partitions are mounted on a transverse shaft.

15. A thermographic machine according to any previous claim wherein the deposition means further comprises :

vibration means (14) located along the path after the tank and before the heater means in an area sloping upwardly from the tank for vibrating the material to shake powder from the portions not containing wet ink for allowing the powder shaken from the material to slide down the area to return to the tank ;

suction means (2 A) located along the path after the vibration means and before the heater means for removing from the non wet ink portions of the material any traces of powder remaining after the vibration means.

16. A thermographic machine according to any previous claim wherein the deposition means comprises in combinaison :

a cyclone powdering assembly (29 Fig. 6, 7) of a type having feed means for feeding by gravity a metered stream of powder onto the path to cover the printed material with powder, the cyclone powdering assembly having recycling suction means for drawing from the path and printed material powder that has not contacted wet ink, the suction means including a nozzle (31) mounted over the path and a fan located above the nozzle, the feed means and fan being mounted in a housing ; and

mounting means (29 A, 29 B) for pivotally mounting the housing to the machine and for selectively pivoting the housing including the feed means and the fan to an open position out of the sheets path for cleaning.

17. A thermographic machine according to claim 16 wherein the housing separates from the nozzle (31 Fig. 11) when pivoted to the open position, leaving the nozzle mounted over the path.

18. A thermographic machine according to any previous claim further comprising :

a plurality of disks spaced apart from each other along a shaft extending across the nozzle, the disks being rotatable and adapted to contact the printed material on the path for preventing the printed material from being drawn into the nozzle as the printed material passes under the nozzle;

at least some of the disks having teeth extending around a circular periphery.

19. A thermographic machine according to claim 18 wherein a plurality of disks are mounted along a shaft extending across the nozzle at least some of the disks having teeth extending around a circular periphery, disks spaced apart from each other and adapted to rotatably contact the printed material and prevent the printed material from being drawn into the suction means.

20. A thermographic machine according to any previous claim wherein the heater means comprises :

a housing mounted over the path (4 Fig. 2, 3) having an entrance and exit for printed material to pass through, the housing having longitudinal sidewalls (6 B, 6 C) extending upwardly above the path, defining a heat zone ;

width varying means for varying the distance between the sidewalls to vary width of the heat zone for printed material of different widths.

21. A thermographic machine according to any previous claim wherein the width varying means comprises :

a pair of longitudinal sidewalls (6 B Fig. 2, 3) carried by the housing ; and

slide means (23) for moving at least one of the longitudinal sidewalls selectively toward and away from the other sidewall.

22. A thermographic machine according to any previous claim wherein the heat source means comprises a plurality of longitudinal extending heater elements (6 Fig. 3) mounted in the interior of the housing parallel with each other; and energizing means (24) for selectively energizing the heater elements so that selected heater elements can be deenergized while others remain energized.

23. A thermographic machine according to any previous claim wherein the heater means for melting the powder comprises an insulated heat barrier (5 Fig. 8) mounted to the machine over the path, the barrier having an entrance and an exit for printed material to pass underneath the barrier.

24. A thermographic machine according to claim 23 wherein the moving sidewalls are supported at both ends of the heater means with supports (23) provided with locker means (23 A) after selecting the width.

25. A thermographic machine according to claim 24 wherein the barrier has an insulated side located on the exterior of each sidewall.

26. A thermographic machine according to claim 25 wherein the housing is movable between a closed position in close proximity to the path and an open position spaced from the path ; and safety means for automatically moving the housing from the closed position to the open position should the advancing means cease moving the material.

27. A thermographic machine according to claim 26 wherein the safety release means comprises bias means (25 B Fig. 5) for urging the housing to the open position ;

latch means (27, 27 A, 27 B) for releasably securing the housing in the closed position ; and

signal means (28) for signaling the latch means to release the housing should the advancing means cease moving the material.

28. A thermographic machine according to claim 27 wherein the signal means comprises an electrically actuated solenoid (28).

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