WO2003044604A1

WO2003044604A1 - Fusers and intermediate transfer members

Info

Publication number: WO2003044604A1
Application number: PCT/IL2001/001033
Authority: WO
Inventors: Ilan Romem
Original assignee: Hewlett-Packard Indigo B.V.
Priority date: 2001-11-06
Filing date: 2001-11-06
Publication date: 2003-05-30
Also published as: US20040250985A1; AU2002223981A1

Abstract

Drum intermediate transfer member or fuser apparatus, for use in a printer or copier, comprising: a drum having a drum surface and including a liquid-containing region in the interior of the drum thermally connected to the drum surface, such that the liquid is capable of heating and cooling the drum surface; and a liquid transfer system including a hot liquid reservoir, a cold liquid reservoir, at least one pump, pipes and optionally at least one valve arranged to selectively pump liquid between the liquid-containing region and the hot liquid reservoir, and between the liquid-containing region and the cold liquid reservoir.

Description

FUSERS AND INTERMEDIATE TRANSFER MEMBERS

FIELD OF THE INVENTION The present invention is related to the field of printers and copiers and more particularly to fusers, intermediate transfer members, and/or elements that function as both fusers and intermediate transfer members and to printers or copiers that utilize the same.

BACKGROUND OF THE INVENTION Printers and copiers are well known. Modern copiers that utilize powder or liquid toners comprising toner particles to form visible images generally form a latent electrostatic image on an image forming surface (such as a photoreceptor), develop the image utilizing a toner (such as the aforementioned powder or liquid toners) to form a developed image and transfer the developed image to a final substrate. The transfer may be direct, i.e., the image is transferred directly to the final substrate from the image forming surface, or indirect, i.e., the image is transferred to the final substrate via one or more intermediate transfer members. In general, the image on the final substrate must be fused and fixed to the substrate. This step is achieved in most copiers and printers by heating the toner image on the substrate. In some copiers and printers the fusing and fixing of the image is performed simultaneously with the transfer of the image to the substrate. This is achieved by utilizing a heated intermediate transfer member to perform the transfer and by pressing the intermediate transfer member against the final substrate. This combination of heat and pressure softens the toner particles and fixes them to the substrate. In other copiers and printers, the image is first transferred to the final substrate, and then fused by a separate fuser. Once the transferred image has been fused, it is desirable for the surface of the intermediate transfer member or fuser to cool below a certain temperature while it is still in contact with the final substrate, so that none of the toner sticks to it.

In several prior art devices, a drum used as an intermediate transfer member or fuser contains water or another liquid in its interior. These include devices described in PCT Publication WO 00/31593, EP 0 772 100 A2, JP Publication 08320625, US Patent 4,172,976, PCT Application PCT/IL00/00652 filed October 13, 2000, and a PCT Application titled "Fusers and Intermediate Transfer Members" filed October 30, 2001 at the Israel Patent Office by Ilan Romem of Indigo N. V., the disclosures of all of which are incorporated herein by reference. There are two reasons for including liquid inside the drum. The first reason is that the liquid can keep the outer surface of the drum at a uniform temperature. This is important for obtaining good image quality, and especially for avoiding "short-term memory" effects, in which an image can be affected by the previous image. Such short-term memory effects are believed to be caused by lower surface temperatures in regions where the drum previously had liquid toner, which cools the surface locally when it evaporates. Having liquid inside the drum has been found to practically eliminate short-term memory. The second reason for using liquid, described in WO 00/31593, is that when the liquid gets hot, the vapor pressure of the liquid inside the drum can support a thin membrane, allowing it to conform slightly to the surface of the substrate that it is in contact with, when transferring images or fixing images. That could also be accomplished by maintaining air under pressure inside the drum, or by including a layer of compliant spongy material underlying the outer surface of a drum whose interior is rigid. But maintaining air under pressure inside the drum would require a pumping system, and a spongy layer can easily become damaged, and thermally insulates the surface from the source of heat inside the drum. Another advantage of using a thin membrane supported by gas pressure is that the heat capacity on transfer is low, so the image cools and hardens during transfer.

There are some disadvantages to using a drum with liquid in it, particularly a drum whose outer surface is a thin membrane supported by gas pressure. The liquid can have a high heat capacity, and hence take a long time to heat up. This means there may be a long waiting time when the copier or printer is first turned on, until it is ready to print. To avoid waiting, the drum may be kept hot all the time, but this can be dangerous, because someone inadvertently touching the drum could be burned, and because the drum could explode if the gas pressure inside gets too high. Also, toner particles on the drum could be burnt onto the drum. If the surface of the drum is a thin somewhat flexible membrane, then it cannot be built to withstand very high pressure. Using liquid with high heat capacity also means that, if the gas pressure does get too high, it will take a long time to bring the pressure down by cooling off the liquid. The heating problem is especially acute if a large amount of liquid is used.

SUMMARY OF INVENTION An aspect of some embodiments of the invention is concerned with rapidly changing the temperature of a drum containing a liquid used as an intermediate transfer member or fuser, in a printer or copier. An aspect of some embodiments of the invention is concerned with rapidly heating such a drum, in order to bring it up to the temperature required for printing, and rapidly cooling the drum once the printing is completed.

An aspect of some embodiments of the invention is concerned with rapidly cooling such a drum, in order to reduce the gas pressure, if it gets too high.

An embodiment of the invention comprises a reservoir of hot liquid and a reservoir of colder liquid, and pipes connecting the reservoirs to the interior of the drum. The embodiment also comprises valves which can be opened and closed, to control the flow of liquid between the interior of the drum and the reservoirs. When the printer or copier is idle, the drum contains colder liquid, so that it is safe to touch, and there is no danger of explosion or fusing toner to the drum. Before the printer or copier begins to print, the colder liquid is pumped out of the drum back to the colder liquid reservoir, and hot liquid is pumped from the hot liquid reservoir to the drum, which transfer heats up the drum very quickly, especially if the drum has a cylindrical surface formed of a thin membrane. Once printing is done, hot liquid is pumped out of the drum back to the hot liquid reservoir, and colder liquid is pumped into the drum from the cold liquid reservoir. If the drum becomes too hot and the gas pressure gets too high in the middle of printing, and/or if there is a paper jam, the gas pressure and temperature can be quickly reduced to a safe level by pumping at least some of the hot liquid out of the drum, and/or pumping some colder liquid into the drum. This is particularly true when the cylindrical surface is thin so that the heat capacity of the liquid is much higher than that of the cylinder, but it is not necessary for the surface to be thin. The valves can be arranged so that this transfer of liquid is done automatically, and in a fail-safe way, whenever the gas pressure gets too high. The colder liquid need not be colder than room temperature, it could be room temperature or even hotter than room temperature.

In an embodiment of the invention, a heater within the drum is used to replace heat transferred to the final substrate and other rollers of the system. Alternatively or additionally, this heat is provided by the heater in the reservoir, for example, in response to a temperature measurement of the drum surface and/or the temperature of the liquid in the drum.

The volatile liquid used to produce gas pressure in the drum in some embodiments need not be the liquid that is being pumped into and out of the drum to heat and cool the drum. The liquid transfer system which is used to pump the liquid into and out of the drum will work best if it uses a non- olatile liquid, free of gas. The volatile liquid used to produce gas pressure could be in a thin outer region just beneath the outer surface of the drum. The liquid being pumped into and out of the drum could fill a separate, more central portion of the drum, below the outer region, sealed off from the outer space but in good thermal contact with it.

In some embodiments, the hot liquid reservoir has a heating element and thermostat, and/or the cold liquid reservoir has a refrigeration element and a thermostat, to maintain the hot liquid and the cold liquid at the desired temperature. The hot liquid reservoir, unlike a drum with a thin membrane, can be kept well insulated thermally, and it can be kept some distance away from the parts of the printer or copier that require frequent handling (for example, to remove paper jams), so there will be little danger that someone will be burned by touching it. The hot liquid reservoir can also be designed to withstand much higher gas pressure than a drum using a thin membrane, since it can have thick walls, so there will be little danger of it exploding. It can also be kept at a higher temperature than the desired final temperature of the liquid, so that the final temperature, after the change of liquid in the drum, will be the desired final temperature. For both these reasons, it will be safe to keep the liquid in the hot liquid reservoir heated all the time. Having good thermal insulation around the hot liquid reservoir and the cold liquid reservoir also means that it will not require much power to maintain the hot liquid and the cold liquid at their desired temperatures.

There is thus provided, in accordance with an embodiment of the invention, a drum intermediate transfer member or fuser apparatus, for use in a printer or copier, comprising: a drum having a drum surface and including a liquid-containing region in the interior of the drum thermally connected to the drum surface, such that the liquid is capable of heating and cooling the drum surface; and a liquid transfer system including a hot liquid reservoir, a cold liquid reservoir, at least one pump, pipes and optionally at least one valve arranged to selectively pump liquid between the liquid-containing region and the hot liquid reservoir, and between the liquid- containing region and the cold liquid reservoir.

In an embodiment of the invention, the liquid-containing region and the liquid transfer system are sealed from the outside, and are substantially free of gas. In an embodiment of the invention, the liquid-containing region does not rotate when the drum rotates.

In an embodiment of the invention, there is at least one rotating seal used to transfer liquid into and out of the liquid-containing region. In an embodiment of the invention, the optional at least one valve comprises a three-way valve and including an outlet pipe connecting the liquid-containing region directly or indirectly to the three-way valve, controllable to direct liquid leaving the liquid-containing region into either the hot liquid reservoir or the cold liquid reservoir.

In an embodiment of the invention, the optional valve comprises a three-way valve and including an input' pipe connecting the liquid-containing region directly or indirectly to a three-way valve, controllable to direct liquid from either the hot liquid reservoir or the cold liquid reservoir into the liquid-containing region.

In an embodiment of the invention, there is a heating element in the hot liquid reservoir. In an embodiment of the invention, there is a temperature sensor in the hot liquid reservoir.

Optionally, the temperature in the hot liquid reservoir is maintained in a certain range by using feedback from the temperature sensor to control the heating element.

In an embodiment of the invention, there is a refrigerating element in the cold liquid reservoir.

In an embodiment of the invention, there is a temperature sensor in the cold liquid reservoir.

Optionally, the temperature in the cold liquid reservoir is maintained in a given range by using feedback from the temperature sensor to control the refrigerating element. In an embodiment of the invention, there is an accumulator in the hot liquid reservoir which allows the volume of liquid in the hot liquid reservoir to change substantially without a commensurate change in liquid pressure.

In an embodiment of the invention, there is an accumulator in the cold liquid reservoir which allows the volume of liquid in the cold liquid reservoir to change substantially without a commensurate change in liquid pressure.

Optionally, the accumulator in the hot liquid reservoir is linked to the accumulator in the cold liquid reservoir, so that when one reservoir increases in volume, the other reservoir decreases in volume by the same amount. Optionally, the accumulators comprise a movable sealed barrier between the hot liquid reservoir and the cold liquid reservoir.

In an embodiment of the invention, there is an accumulator in the liquid-containing region which allows the volume of liquid in the liquid-containing region to change substantially without a commensurate change in liquid pressure.

Optionally, the liquid-filled region is largely drained of liquid of one temperature, before it is filled with liquid of a different temperature.

In an embodiment of the invention, the liquid-containing region heats and cools the surface of the drum indirectly through a separate thin region which also contains liquid.

In an embodiment of the invention, the liquid in the thin region is volatile and increases the gas pressure in the thin region when the liquid therein is heated.

In an embodiment of the invention, different liquids are used in the liquid- containing region and in the thin region. In an embodiment of the invention, the liquid in the liquid-containing region has low volatility in the operating range of temperature.

In an embodiment of the h vention, there is a pressure sensor in the thin region.

In an embodiment of the invention, at least part of the boundary between the liquid-containing region and the thin region is flexible, so that an increase in pressure in the thin region will lead to an increase in pressure in the liquid-containing region.

In an embodiment of the invention, there is a pressure sensor in the liquid- containing region or in the liquid transfer system, and a controller that controls one or more of said at least one pump and at least one valve, wherein the controller causes hot liquid to flow out of the liquid-containing region and/or causes cold liquid to flow into the liquid-containing region, if the pressure in the liquid-containing region or in the liquid transfer system rises higher than a given value.

In an embodiment of the invention, there is an overflow valve in the liquid- containing region or in the liquid transfer system, wherein the valve opens and relieves the pressure in the liquid-containing region and in the thin region, if the pressure rises higher than a given value.

In an embodiment of the invention, there is an overflow valve in the liquid transfer system or the liquid-containing region that allows excess liquid to leave the liquid transfer system or the liquid-containing region. Optionally, the overflow valve is forced open mechanically when the hquid pressure rises higher than a given value.

In an embodiment of the invention, there is a pressure sensor in the liquid- containing region or in the liquid transfer system. In an embodiment of the invention, there is an overflow reservoir, wherein excess liquid that flows through the overflow valve enters the overflow reservoir, and liquid can flow from the overflow reservoir into the liquid transfer system or the hquid-containing region when the pressure falls below a given value.

In an embodiment of the invention, there is a controller that controls one or more of said at least one pump and at least one valve, wherein the controller causes hot liquid to flow out of the liquid-containing region and/or causes cold liquid to flow into the liquid- containing region, if the pressure in the thin region rises higher than a given value.

In an embodiment of the invention, the controller receives data from the pressure sensor and opens the overflow valve when the pressure rises higher than a given value. In an embodiment of the invention, there is a controller that controls one or more of said at least one pump and said at least one valve, thereby to control selective pumping.

In an embodiment of the invention, there is a bleed valve for removing unwanted gas from the apparatus.

In an embodiment of the invention, there is a shut-off valve closable to prevent liquid from flowing into the liquid-containing region.

BRIEF DESCRIPTION OF THE DRAWING Exemplary embodiments of the invention are described in the following section with reference to the drawing. The drawing is generally not to scale. Fig. 1 is a schematic diagram showing the elements of an embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS The embodiment shown in Fig. 1 has a drum 10, with a region 12 filled with a liquid. Optionally, there is a thin outer region 11, between region 12 and the outer surface of drum 10, which contains its own liquid, optionally a different liquid more volatile than the liquid in region 12, which maintains gas pressure supporting the outer surface when the drum is hot. Generally, the liquid in region 12 need not be replaced when the temperature of the drum is to be changed. Region 12 is connected to a liquid transfer system 13, consisting of pipes, connectors, valves, and reservoirs. An outlet 14 of region 12 connects region 12 to a return pipe 16. In those embodiments where there is an outer region 11 between region 12 and the outer surface of drum 10, region 12 optionally remains fixed in place while drum 10 is rotating. In this case, outlet 14 is optionally an ordinary pipe connector. If region 12 rotates with the outer surface of drum 10, then outlet 14 optionally comprises a rotating seal. Return pipe 16 is optionally connected to a three- way valve 18, with connections to both a hot liquid reservoir 20 and a cold liquid reservoir 22. The three-way valve 18 can be electrically controlled by a controller 19, to allow liquid from the return pipe 16 to flow into either the hot liquid reservoir 20 or the cold liquid reservoir 22. The hot liquid reservoir has a heating element 24 and a thermostat 26. The cold liquid reservoir has a refrigeration element 28, and optionally also has a thermostat. Controller 19 optionally maintains the hot liquid reservoir and/or the cold liquid reservoir at desired temperatures by using feedback from the thermostats to control the heating element and refrigeration element. Hot liquid reservoir 20 has an outlet 30, and cold liquid reservoir 22 has an outlet 32, which both connect to a three-way valve 34, which also connects to a pump 36. Three-way valve 34 can be electrically controlled by controller 19, to selectively control the pump to pump liquid out of either the hot reservoir 20 or the cold reservoir 22. Controller 19 can also turn the pump on and off. The outflow of pump 36 connects to a pipe 38, which connects to an inlet 40 to drum 10. Pipe 38 has a bleed valve 42 somewhere along its length, which allows trapped air or other gas to be removed from liquid transfer system 13. Trapped gas in the liquid transfer system may make it operate less efficiently, or, in an extreme situation, not operate at all. Pipe 38 also has a shut-off valve 43 somewhere along its length, which can be used to prevent liquid from flowing into region 12. Pipe 38 also has an overflow valve 44 somewhere along its length, which allows liquid from the liquid transfer system to flow into an overflow reservoir 46 and relieve the pressure, if the liquid pressure gets too high. Overflow valve 44 can also allow liquid transfer system 13 to draw liquid from overflow reservoir 46, if the liquid pressure gets too low. The overflow valve can allow liquid to flow in each direction automatically, when the pressure difference exceeds some value. Alternatively, a pressure sensor 47 in pipe 38, or elsewhere in liquid transfer system 13, triggers controller 19 to open overflow valve 44. In some embodiments, pressure data is not used by the controller for this purpose; it may still be used to notify an operator of a problem. Too high a pressure could lead to leaking or even catastrophic failure of the liquid transfer system. Too low a pressure could lead to cavitation, which would adversely affect the performance of the pump. Even before those extreme conditions are reached, the shape of the drum can be distorted, or the compliance of the drum can be less than or greater than optimal, if the pressure is too high or too low. Because, in a desired operating range of pressures, the liquid is essentially incompressible, and it is generally desirable not to have any trapped gas in the liquid transfer system, hot reservoir 20 and cold reservoir 22 optionally change their volumes as liquid is pumped into and out of them. One way to do this, illustrated in Fig. 1, is to have a movable barrier 48 between hot reservoir 20 and cold reservoir 22. In response to a small difference in pressure between hot reservoir 20 and cold reservoir 22, barrier 48 moves to increase the volume of one reservoir and decrease the volume of the other reservoir by the same amount. With this configuration, cold liquid preferably flows into region 12 at the same rate as hot liquid is being pumped out, and vice versa. This can lead to some mixing of hot and cold liquid in region 12, when both hot and cold liquid are present there. An alternative scheme is to have separate accumulators in region 12, hot reservoir

20, and cold reservoir 22. Each accumulator independently changes the volume of its region or reservoir in response to a small change in pressure. Each accumulator may consist of a gas-filled balloon or bellows, or any other kind of accumulator known to the art. In this scheme, it is possible to largely or completely empty the hot liquid from region 12 before starting to pump in the cold liquid, and vice versa. Also, because barrier 48 between hot reservoir 20 and cold reservoir 22 is not necessarily movable, it might be easier to make the barrier a better thermal insulator, and to avoid having liquid leak past it. In this embodiment, hot reservoir 20 and cold reservoir 22 do not have to be adjacent to each other, which makes it even easier to thermally insulate them, and to prevent liquid leaking from one reservoir into the other.

Another alternative scheme is to have separate accumulators in hot reservoir 20 and cold reservoir 22, but not in region 12. Like the first scheme, this scheme may require that when liquid is pumped from region 12 to one reservoir, an equal volume of Hquid is pumped from the other reservoir into region 12. However, in this scheme the hot and cold reservoirs could be some distance apart, and better insulated from each other. A disadvantage of this scheme, compared to the first scheme, is that there will be larger transient increases in pressure if the pumping starts suddenly, which can lead to noise and vibrations that could damage the liquid transfer system. In some embodiments, drum 10 has a thin outer region 11 between region 12 and the outer surface of the drum, containing a volatile liquid which produces gas pressure to support the outer surface when the drum is hot. The boundary between outer region 11 and region 12 could either be rigid or flexible. If the boundary is flexible, then raising the gas pressure in outer region 11 will also cause the liquid pressure to rise in region 12. This relationship is optionally used to prevent the gas pressure from getting too high or too low. For example, raising the liquid pressure in region 12 above a given level could force open a valve at outlet 14, allowing liquid from region 12 to flow through pipe 16, past the 3-way valves, reservoirs and pump, and through overflow valve 44, even without the pump running. The resulting increase in volume of outer region 11, as the flexible boundary expands at the expense of region 12, would immediately decrease the gas pressure. (Having a flexible boundary between region 12 and outer region 11 might not work, however, if region 12 had its own accumulator, since this would tend to prevent the gas pressure in the outer blanket from changing.) Alternatively or additionally, a pressure sensor in outer blanket 11 or region 12 optionally triggers the pump to draw hot liquid out of region 12 and to pump cold liquid into region 12, if the pressure exceeds a given value, or the pressure sensor triggers the pump to pump more hot liquid into region 12 if the pressure falls below a given value. Pressure sensor 47, even it is located in pipe 38 or elsewhere in liquid transfer system 13, optionally is used for this purpose. The invention has been described in the context of the best mode for carrying it out. It should be understand that not all features shown in the drawing may be present in an actual device, in accordance with some embodiments of the invention. Furthermore, variations on the method and apparatus shown are included within the scope of the invention, which is limited only by the claims. As used herein, the terms "have", "include" and "comprise" or their conjugates mean "including but not limited to."

Claims

1. Drum intermediate transfer member or fuser apparatus, for use in a printer or copier, comprising: a drum having a drum surface and including a liquid-containing region in the interior of the drum thermally connected to the drum surface, such that the liquid is capable of heating and cooling the drum surface; and a liquid transfer system including a hot liquid reservoir, a cold liquid reservoir, at least one pump, pipes and optionally at least one valve arranged to selectively pump liquid between the liquid-containing region and the hot liquid reservoir, and between the liquid- containing region and the cold liquid reservoir.

2. Apparatus according to claim 1 wherein the liquid-containing region and the liquid transfer system are sealed from the outside, and are substantially free of gas.

3. Apparatus according to claim 1 or claim 2 wherein the liquid-containing region does not rotate when the drum rotates.

4. Apparatus according to claim 1 or claim 2 and comprising at least one rotating seal used to transfer liquid into and out of the liquid-containing region.

5. Apparatus according to any of the preceding claims wherein the optional at least one valve comprises a three-way valve and including an outlet pipe connecting the liquid- containing region directly or indirectly to the three-way valve, controllable to direct liquid leaving the liquid-containing region into either the hot liquid reservoir or the cold liquid reservoir.

6. Apparatus according to any of the preceding claims wherein the optional valve comprises a three-way valve and including an input pipe connecting the liquid-containing region directly or indirectly to a three-way valve, controllable to direct liquid from either the hot liquid reservoir or the cold liquid reservoir into the liquid-containing region.

7. Apparatus according to any of the preceding claims and including a heating element in the hot liquid reservoir.

8. Apparatus according to any of preceding claims 1-6 and including a temperature sensor in the hot liquid reservoir.

9. Apparatus according to claim 7 and including a temperature sensor hi the hot liquid reservoir.

10. Apparatus according to claim 9 wherein the temperature in the hot liquid reservoir is maintained in a certain range by using feedback from the temperature sensor to control the heating element.

11. Apparatus according to any of the preceding claims and including a refrigerating element in the cold liquid reservoir.

12. Apparatus according to any claims 1-10 and including a temperature sensor in the cold liquid reservoir.

13. Apparatus according to claim 11 and including a temperature sensor in the cold liquid reservoir.

14. Apparatus according to claim 13 wherein the temperature in the cold liquid reservoir is maintained in a given range by using feedback from the temperature sensor to control the refrigerating element.

15. Apparatus according any of the previous claims and including an accumulator in the hot liquid reservoir which allows the volume of liquid in the hot liquid reservoir to change substantially without a commensurate change in liquid pressure.

16. Apparatus according to any of claims 1-14 and including an accumulator in the cold liquid reservoir which allows the volume of liquid in the cold liquid reservoir to change substantially without a commensurate change in liquid pressure.

17. Apparatus according to claim 15 and including an accumulator in the cold liquid reservoir which allows the volume of liquid in the cold liquid reservoir to change substantially without a commensurate change in liquid pressure.

18. Apparatus according to claim 17 wherein the accumulator in the hot liquid reservoir is linked to the accumulator in the cold liquid reservoir, so that when one reservoir increases in volume, the other reservoir decreases in volume by the same amount.

19. Apparatus according to claim 18 wherein the accumulators comprise a movable sealed barrier between the hot liquid reservoir and the cold liquid reservoir.

20. Apparatus according to any of claims 1-16 and including an accumulator in the liquid-containing region which allows the volume of liquid in the liquid-containing region to change substantially without a commensurate change in liquid pressure.

21. Apparatus according to claim 17 and including an accumulator in the liquid- containing region which allows the volume of liquid in the liquid-containing region to change substantially without a commensurate change in liquid pressure.

22. Apparatus according to claim 21 wherein the liquid-filled region is largely drained of liquid of one temperature, before it is filled with liquid of a different temperature.

23. Apparatus according to any of claims 1-20 wherein the liquid-containing region heats and cools the surface of the drum indirectly through a separate thin region which also contains liquid.

24. Apparatus according to claim 23 wherein the liquid in the thin region is volatile and increases the gas pressure in the thin region when the liquid therein is heated.

25. Apparatus according to claim 23 or claim 24 wherein different liquids are used in the liquid-containing region and in the thin region.

26. Apparatus according to any of claims 1-20, 23, or 25 wherein the liquid in the liquid-containing region has low volatility in the operating range of temperature.

27. Apparatus according to claim 21 or claim 22 wherein the liquid-contafriing region heats and cools the surface of the drum indirectly through a separate thin region which also contains liquid.

28. Apparatus according to claim 27 wherein the liquid in the thin region is volatile and increases the gas pressure in the thin region when the liquid therein is heated.

29. Apparatus according to claim 27 or claim 28 wherein liquids are used in the liquid- containing region and the thin region.

30. Apparatus according to any of claims 21, 22, 27 or 29 wherein the liquid in the liquid-containing region has low volatility in the operating range of temperature.

31. Apparatus according to any of claims 23-26 and including a pressure sensor in the thin region.

32. Apparatus according to any of claims 27-30 and including a pressure sensor in the thin region.

33. Apparatus according to any of claims 23-26 or 31, wherein at least part of the boundary between the liquid-containing region and the thin region is flexible, so that an increase in pressure in the thin region will lead to an increase in pressure in the liquid- containing region.

34. Apparatus according to claim 33 and including a pressure sensor in the liquid- containing region or in the liquid transfer system, and including a controller that controls one or more of said at least one pump and at least one valve, wherein the controller causes hot liquid to flow out of the liquid-containing region and/or causes cold liquid to flow into the liquid-contaimng region, if the pressure in the liquid-containing region or in the liquid transfer system rises higher than a given value.

35. Apparatus according to claim 33 and including an overflow valve in the liquid- containing region or in the liquid transfer system, wherein the valve opens and relieves the pressure in the liquid-containing region and in the thin region, if the pressure rises higher than a given value.

36. Apparatus according to any of claims 1-32, and including an overflow valve in the liquid transfer system or the liquid-containing region that allows excess liquid to leave the liquid transfer system or the liquid-containing region.

37. Apparatus according to claim 35 or claim 36 wherein the overflow valve is forced open mechanically when the liquid pressure rises higher than a given value.

38. Apparatus according to any of claims 1-33, and including a pressure sensor in the liquid-containing region or in the liquid transfer system.

39. Apparatus according to any of claims 35-37, and including a pressure sensor in the liquid-containing region or in the liquid transfer system.

40. Apparatus according to any of claims 35-37 or 39, and including an overflow reservoir, wherein excess liquid that flows through the overflow valve enters the overflow reservoir, and liquid can flow from the overflow reservoir into the liquid transfer system or the liquid-containing region when the pressure falls below a given value.

41. Apparatus according to claim 31 and including a controller that controls one or more of said at least one pump and at least one valve, wherein the controller causes hot liquid to flow out of the liquid-containing region and or causes cold liquid to flow into the liquid-containing region, if the pressure in the thin region rises higher than a given value.

42. Apparatus according to claim 32 and including a controller that controls one or more of said at least one pump and at least one valve, wherein the controller causes hot liquid to flow out of the liquid-containing region and/or causes cold liquid to flow into the liquid-containing region, if the pressure in the thin region rises higher than a given value.

43. Apparatus according to claim 41, wherein at least part of the boundary between the liquid-containing region and the thin region is flexible, so that an increase in pressure in the thin region will lead to an increase in pressure in the liquid-containing region.

44. Apparatus according to claim 43 and including a pressure sensor in the liquid- containing region or in the liquid transfer system, wherein the controller causes hot liquid to flow out of the liquid-containing region and/or causes cold liquid to flow into the liquid-containing region, if the pressure in the liquid-containing region or in the liquid transfer system rises higher than a given value.

45. Apparatus according to any of claims 34, 43 or 44 and including an overflow valve in the liquid-containing region or in the liquid transfer system, wherein the valve opens and relieves the pressure in the liquid-containing region and in the thin region, if the pressure rises higher than a given value.

46. Apparatus according claim 41 or claim 42, and including an overflow valve in the liquid transfer system or the liquid-containing region that allows excess liquid to leave the liquid transfer system or the liquid-containing region.

47. Apparatus according to claim 45 or claim 46 wherein the overflow valve is forced open mechanically when the liquid pressure rises higher than a given value.

48. Apparatus according to any of claims 41-43 and including a pressure sensor in the liquid-containing region or in the liquid transfer system.

49. Apparatus according to any of claims 45-47, and including a pressure sensor in the liquid-containing region or in the liquid transfer system.

50. Apparatus according to any claim 49, wherein the controller receives data from the pressure sensor and opens the overflow valve when the pressure rises higher than a given value.

51. Apparatus according to any of claims 45-47, 49 or 50, and including an overflow reservoir, wherein excess liquid that flows through the overflow valve enters the overflow reservoir, and liquid can flow from the overflow reservoir into the liquid transfer system or the liquid-containing region when the pressure falls below a given value.

52. Apparatus according to any of claims 1-33, or 35-40, and including a controller that controls one or more of said at least one pump and said at least one valve, thereby to control selective pumping.

53. Apparatus according to any of the preceding claims, and including a bleed valve for removing unwanted gas from the apparatus.

54 . Apparatus according to any of the preceding claims, and including a shut-off valve closable to prevent liquid from flowing into the liquid-containing region.