Printing – Printing members – Rolling contact
Reexamination Certificate
1999-09-01
2001-06-26
Hilten, John S. (Department: 2854)
Printing
Printing members
Rolling contact
C101S376000
Reexamination Certificate
active
06250222
ABSTRACT:
DESCRIPTION
FIELD OF THE INVENTION
This invention relates to an apparatus for the continuous treatment of sheet material under reduced pressure, particularly for the low pressure processing of photographic sheet material, such as X-ray film, pre-sensitised plates, graphic art film and paper, and offset plates.
BACKGROUND OF INVENTION
A number of processes are known which take place under conditions of reduced pressure. Examples include plasma cleaning, sputtering and vaporising. The material to be treated is often in the form of a sheet.
In International patent specification WO 91/17561 (Eastman Kodak) an apparatus for the plasma treatment of material in continuous form under vacuum is described. The apparatus comprises a housing defining a treatment cell having a sheet material path extending therethrough from an entrance to an exit, the entrance and exit each being closed by a roller pair. A vacuum is applied to the treatment cell.
The sealing of the rollers to the housing is an important feature if desirable consistent conditions of reduced pressure in the treatment cell are to be achieved. In the apparatus described in W091/17561, the rollers are sealed to the housing by the use of fixed sealing members. We have found that the use of fixed sealing members is often unsatisfactory, leading to undesirable leakages.
In European patent specification EP 0 384 041-A, (Agfa-Gevaert NV), a process is described for the coating of a web support under vacuum conditions with a layer of vapour depositable material followed by the lamination of the coated material with a protective organic resin layer.
Although the process described operates satisfactorily, the apparatus used requires both the vapour deposition and the lamination to take place in the same vacuum chamber. This chamber is therefore of a considerable volume, requiring the consumption of significant energy and time during start-up. Furthermore, once a batch of web support has been so coated and laminated, it can only be removed by releasing the vacuum to enable the chamber to be opened. Time and energy is therefore repeatedly wasted in shut-down and start-up of the apparatus.
OBJECTS OF INVENTION
It is an object of the present invention to provide an apparatus in which the continuous treatment of sheet materials can be carried out under reduced pressure, in a convenient and reliable manner.
SUMMARY OF THE INVENTION
We have discovered that this objective and other useful benefits may be achieved wherein the rollers closing the entrance and exit are drive rollers and rotatable sealing means are provided for sealing each drive roller to the housing.
According to the invention there is provided an apparatus for the continuous treatment of sheet material under reduced pressure, comprising
a housing defining a treatment cell having a sheet material path extending therethrough from a sheet material entrance to a sheet material exit, the entrance and exit each being closed by a respective path-defining roller in contact with a reaction surface to define a nip therebetween through which the sheet material path extends, and
means for establishing a reduced pressure within the treatment cell, characterised in that each said path-defining roller is a drive roller and rotatable sealing means are provided for sealing each drive roller to the housing.
The apparatus according to the invention provides the possibility for continuous processing, overcoming the time and energy wasted in start-up and shut-down in a non-continuous process.
Furthermore, the construction of the apparatus according to the invention enables the treatment cell volume to be reduced since other processing steps, not relying on the use of reduced pressure, can take place outside the treatment cell. By the use of a treatment cell of reduced volume, the start-up time and energy requirement is reduced.
By the use of a rotatable sealing member in place of a stationary sealing member, the torque which needs to be applied to the drive roller can be significantly reduced. This reduces the power needed by the processor, reduces wear on the drive roller, reduces the mechanical deformation thereof and thereby extends the expected life time. This construction also improves the control of pressure distribution over the sheet material.
Each drive roller may comprise a rigid core provided with a covering of elastomeric material, although it is possible for the drive roller to be elastomeric throughout its cross-section. By the term “core” we mean an axially inner member, which is usually cylindrical and which is relatively rigid compared to the elastomeric material covering. The core may be solid or hollow. Usually, drive to the roller will be applied to the core. In a preferred embodiment, each of the ends of the elastomeric material covering are in sealing contact with a surface of end plates of the housing. The surface of each end plate may be formed of, or coated with, a low friction material such as polished metal, or polytetrafluoroethylene. The elastomeric material may extend beyond the ends of the core to define a space into which the elastomeric material of the covering may be deformed as a result of a sealing force between the covering and the end plate. Such an arrangement improves the sealing between the drive roller and the end plate. In a preferred embodiment, the roller comprises an inner layer of elastomeric material having a relatively low hardness, and an outer region of elastomeric material having a relatively high hardness positioned over the inner layer. Such a roller minimises leakage as the sheet material passes through the nip without damage to the sheet material while enabling the roller to successfully function as a drive roller. Alternatively, the elastomeric material of the inner layer has substantially the same hardness as the elastomeric material of the outer layer, and the outer layer is doped with a surface modifying material.
In a preferred embodiment, each roller comprises a main body member, a shaft fixed to the main body member and extending from one end thereof. An end member is positioned in contact with the main body member, the end member comprising wear resistant material for face-to-face sliding contact with an end plate of the housing and being mounted on the shaft in a replaceable manner. The shaft may be fixed to the main body member by bonding the roller core to an end piece of the roller shaft by glue positioned in a bonding chamber between bonding surfaces of the core and the shaft end piece. The bonding chamber may be provided with an entrance and an exit, enabling the roller to be fabricated by introducing liquid glue into the bonding chamber while allowing air to be expelled through the exit until the bonding chamber is at least substantially full of the glue.
As the sheet material leaves the treatment cell, in view of the nature of elastomeric material, it is in fact impossible to totally eliminate any gap between the drive roller surface at the edges of the sheet material as it passes through the nip. It is desirable that the drive roller surface be in contact with the reaction surface within as short a distance as possible from the edges of the sheet material i.e. that the size of the leak zone should be minimised. It is important however that the force between the drive roller and the reaction surface is sufficient to prevent leakage when no sheet material is passing through. However, the force must not be so high as to risk physical damage to the sheet material as it passes through the nip.
The objective of a minimum leak zone referred to above can be achieved if the ratio of the diameter of the drive roller to its length is above a critical limit. In particular, the drive roller preferably comprises a rigid core carrying a covering of elastomeric material, the ratio (&phgr;/L) of the maximum diameter (&phgr;) of the elastomeric material covering to the length (L) thereof being at least 0.012, most preferably between 0.03 and 0.06.
The elastomeric material covering preferably has a thickness of between 1 mm and 30 mm. The elast
Verhoest Bart
Verlinden Bartholomeus
AGFA-GEVAERT
Baker & Botts L.L.P.
Hilten John S.
Nguyen Anthony H.
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