HK1173846A - Assembly and method for reducing foil wrinkles - Google Patents

Description

Assembly and method for reducing foil wrinkles

Technical Field

The present invention relates to an assembly and a method for reducing wrinkles in an electron exit window foil of an electron beam generating device, which wrinkles can be generated due to excess foil present during assembly, which foil is glued to a support plate.

Background

Electron beam generating devices may be used in the sterilization of articles, such as for example in packaging materials, food packages or medical equipment, or they may be used in the curing of e.g. ink. Typically, these devices comprise an electron exit window assembly formed by at least one foil and a support plate. The support plate, which is preferably made of copper, has a plurality of holes through which electrons will be emitted from the electron beam generating device during operation. The support plate forms a wall of a vacuum-tight (vacuum-light) housing of the electron beam generating device, and the aperture of the support plate is covered by a foil in order to maintain the vacuum. The foil has a thickness of about 6-10 μm and is preferably made of titanium. Due to this thickness, most electrons are able to pass through it.

The foil is sealed to the support plate by gluing at or near the circumference of the support plate. The term adhesion should be construed herein as a general term. Possible bonding techniques may be laser welding, electron beam welding, soldering, ultrasonic welding, diffusion bonding and gluing.

During the delicate handling of the foil during assembly, surplus foil may occur, for example, due to the foil being stretched or in some other way. Since the foil and the support plate are fixed to each other at the bonding line, an excess of foil may result in wrinkles in the foil upon application of a vacuum in the housing. Large wrinkles are detrimental for the operation of the electron beam generating device not only because of the reduced efficiency of letting electrons through, but also because of the risk of cracks occurring along the wrinkles. The foil is in fact very fragile.

Disclosure of Invention

It is therefore an object of the present invention to provide an assembly of a support plate and an exit window foil, said support plate being designed to efficiently and carefully reduce wrinkles in the foil.

This object is achieved by an assembly of a support plate and an exit window foil for use in an electron beam generating device. The support plate is designed to reduce wrinkles in the foil which may arise due to surplus foil occurring during assembly, the foil being bonded to the support plate along a closed bonding line defining the boundary of the area of the support plate where the aperture and the foil support are provided, and in which area the foil is adapted to be used as a part of a wall of a vacuum-tight housing of an electron beam generating device. The assembly is characterised in that the support plate is provided in said area with a pattern (pattern) of holes and foil supports spaced from each other (alternally) adapted to form a topological profile that substantially absorbs any excess foil when a vacuum is generated in the housing.

It is important to recognize that where excess foil is generated, care needs to be taken in handling excess foil generated by, for example, an elongated foil. The support plate and the foil are glued to each other at a glue line and any movement between the foil and the support plate that would cause an accumulation of excess foil in certain areas would also cause wrinkles to occur. The surplus foil therefore needs to be absorbed as much as possible directly down into the support plate, i.e. in a direction perpendicular to the plane of the support plate. Thus, the foil can be controlled not to move significantly relative to the support plate in the direction of the plane of the support plate. Here and in the following, the term "absorbing" is used to indicate that the foil should be received on the contoured surface in such a way that any additional foil area is allowed to protrude downwards in a controlled manner to create a "tensioned" foil. Here and in the following the term "tensioned" is used to indicate that the foil is not able to form large uncontrollable wrinkles when a vacuum is created in the housing. However, the foil is not tensioned, meaning that tensile stresses are generated in the foil.

In a currently preferred embodiment of the assembly, the absorption is achieved in such a way that a substantial major bending of the foil occurs in the hole. It has been realized that the pattern of the support plate should promote a single bending of the foil and avoid double bending as much as possible. It has been found that detrimental wrinkling is more likely to occur in areas where the foil is significantly double bent. In the present invention, double bending is greatly reduced by giving the foil a dominant bend in each hole. Here and in the following, the term "predominantly curved" is defined as a predominantly single curve, or a single curve comprising a minor or minor double-curved component. It is difficult to eliminate the double bending of the foil completely, but if the foil is forced to protrude or bend in one direction as much as possible, resulting in a major bending in that direction, the effect of additional minor bending in any other direction can be reduced. The main bending is applied because it is highly desirable that the foil should be bent locally in each single hole of the support plate and because it is highly desirable that the foil should be bent entirely, i.e. over a number of adjacent holes.

Further currently preferred embodiments of the invention are described in the dependent claims 3-12.

The invention also comprises a method for reducing wrinkles in an exit window foil of an electron beam generating device, which wrinkles may arise due to surplus foil present during assembly, said foil being adhered to a support plate along a closed adhesion line defining the boundary of an area of the support plate where holes and foil supports are provided, and in which area said foil is adapted to be used as a part of a wall of a vacuum tight housing of the electron beam generating device. The method comprises the step of providing, in said area, a pattern of holes in the support plate and foil supports spaced from each other, which pattern is adapted to form a topological profile that substantially absorbs any surplus foil when a vacuum is generated in the housing.

The invention also comprises a method for sterilizing packaging material, such as for example a roll of packaging material, in a filling machine, comprising the step of using an electron beam generating device comprising an assembly according to claim 1.

Drawings

In the following, a currently preferred embodiment of the present invention will be described in more detail with reference to the accompanying drawings, in which:

FIG. 1 is an exemplary cross-sectional view of an electron beam generating apparatus according to the prior art;

FIG. 2 shows an exemplary cross-sectional view of a first embodiment of an assembly according to the present invention mounted to a partially shown housing of an electron beam generating device;

FIG. 3 shows an exemplary top view of the embodiment of FIG. 2;

FIG. 4 shows an isometric partial cross-sectional view of the support plate of the embodiment of FIGS. 2 and 3;

FIG. 5 shows an exemplary isometric partial cross-sectional view of a support plate and a foil, the foil shown subjected to a vacuum from inside a housing (not shown);

FIG. 6 shows a portion of the exemplary cross-sectional elevation view of FIG. 5, taken along line A of FIG. 3;

FIG. 7 shows a portion of the exemplary cross-sectional elevation view of FIG. 5, taken along line B of FIG. 3;

FIG. 8 shows a particular exemplary view in partial section taken along line C of FIG. 3, illustrating the coupling of the support bars of the second set of support bars and the foil;

FIG. 9 shows the main curvature in the small sketch D from FIG. 3;

FIG. 10 shows a partial top view of a second embodiment of a support plate;

FIG. 11 shows an exemplary top view of a support plate according to a third embodiment;

FIG. 12 shows a first support plate member of the support plate of FIG. 11, but in isometric partial cross-sectional view, an

Fig. 13 illustrates a particular exemplary view in partial cross-section taken along line D of fig. 11.

The same reference numerals are used for similar features in different embodiments.

Detailed Description

Fig. 1 shows a particular exemplary view of an example of an electron beam generating apparatus 10. The device comprises an electron exit window 12 through which electrons are emitted towards the target to be irradiated. In accordance with the design of the present invention, electron beam generating apparatus 10 generally includes a vacuum chamber 14 within which a filament 16 and a control grid 18 are provided. The filaments 16 are preferably made of tungsten. When current is passed through the filament 16, the electrical resistance of the filament causes the filament to be heated to a temperature on the order of 2000 ℃. This heating causes filament 16 to radiate a cloud of electrons. A control grid 18 is provided in front of the filaments 16 and helps to distribute the electrons in a controlled manner. The electrons are accelerated by the voltage between the grid 18 and the exit window 12. The electron beam generating apparatus 10 generally represents a low voltage electron beam emitter, typically having a voltage below 300 kV. In the design of the present invention, the acceleration voltage is in the order of 70-85 kV. This voltage generates kinetic (dynamic) energy of 70-85keV for each electron.

As shown in fig. 2, the electron exit window 12 is an assembly of a support plate 22 and an electron exit window foil 20. The foil 20 is attached to an outer surface 24 of the support plate 22, which in fig. 2 is shown as the upper surface of the support plate 22. Thus, the support plate 22 is provided inside the foil 20, i.e. the foil 20 faces the surroundings, whereas the support plate 22 faces inside the electron beam generating device 10.

The attachment of the foil 20 to the support plate 22 is effected along a continuous bonding line 26 (only shown as two spots in the drawings). The bond line 26, its entirety and the area bounded by it, is represented by the dashed line in fig. 3, which shows the assembly of fig. 2. In a preferred embodiment, the support plate 22 and the foil 20 are substantially rectangular and the bonding lines 26 define the boundaries of areas having substantially similar shapes. This area is called rectangular, but as can be seen from the figures, it has a substantially rectangular shape with rounded corners. The rectangle has a first side 1 and a second side 2 opposite the first side 1. And, the rectangle has a third side 3 and a fourth side 4 opposite to the third side 3. The sides of each pair of respective sides are substantially parallel. The first and second sides 1, 2 are substantially perpendicular to the third and fourth sides 3, 4. Possible bonding techniques for bonding the foil 20 to the support plate 22 may be e.g. laser welding, electron beam welding, soldering, ultrasonic welding, diffusion bonding and gluing. The bonding line 26 is continuous so as to be able to maintain a vacuum inside the electron beam generating apparatus 10. The term "continuous" is used to define a line that is circular or closed.

The foil 20 is substantially transparent to electrons and is preferably made of a metal, such as titanium, or of a laminate of materials. The thickness of the foil 20 is of the order of about 6-10 μm.

The support plate 22 serves as a support for the foil 20. In the shown embodiment the support plate 22 comprises two members, a first support plate member 22a supporting the middle part of the foil 20 and a second support plate member 22b having the shape of a frame provided with foil bonding wires 26. The term "frame" should here be interpreted as an element having a central hole configuration. The bond line 26 should be defined to extend along the aperture arrangement of the frame, but within the outer perimeter of the frame. Preferably, the bonding line 26 extends at a distance from the periphery of the frame.

Furthermore, at least one glue line 26 is made. Thus, two or more bond lines may be made. For example, inner and outer bond wires may be fabricated on the frame, and the two wires may be, for example, concentric with each other.

In the assembled state, the two support plate members 22a and 22b are bonded to each other. The two members may be made of different materials or of similar materials. In a preferred embodiment, the first support plate member 22a is made of copper or titanium, while the second support plate member 22b is made of stainless steel.

In fig. 2 and 3, the vacuum chamber housing 14 is also shown in part, with a support plate 22 attached thereto.

As shown in fig. 2, the bond line 26 is positioned on a plateau 28. The second support plate member 22b (i.e., the frame) is positioned relative to the first support plate member 22a in such a manner that: the upper surface of the frame forms a plateau 28, i.e. it forms a surface positioned at a higher level than the upper surface 30 of the first support plate member 22a, which means a surface elevated with respect to the upper surface 30 of the first support plate member 22 a.

A first embodiment is shown in fig. 3-9.

The first support plate member 22a is provided with a plurality of holes 32, and some of the holes 32 are through holes so that electrons can pass therethrough. The support plate 22 is provided with a foil support portion 34. The foil support 34 has a top surface which is designed to be in contact with the foil 22 when a vacuum is provided in the electron beam generating device 10. In the area bounded by the bond line 26, the support plate 22 is arranged in a pattern of these holes 32 and foil supports 34 spaced from each other, which pattern is adapted to form a topological profile of the foil 20 that substantially absorbs any surplus foil when a vacuum is generated in the housing 14. By absorbing the surplus foil, wrinkles can be largely avoided or at least reduced. The term "topological profile" is used to describe that the foil 20 will have a non-flat profile surface where some areas or points are raised and some areas or points are depressed relative to each other.

In the currently preferred embodiment, the pattern of holes 32 and foil support portions 34 is designed in such a way that: the main curvature of the foil 20 is formed in the hole 32. In this embodiment, the area bounded by the bond lines 26 is divided into three segments, wherein each segment includes a plurality of apertures 32. In each of these segments, a major bend is created in the adjacent holes 32 in the same direction. This will be described in more detail below in relation to the design of the support plate 22.

In this first embodiment, the foil support 34 of the first support plate member 22a is formed as a foil support strip 36. A first set of foil support strips is provided in a first section 38 of the area. The first section is an intermediate section of the first support plate member 22 a. In the following, these strips will be indicated as first support strips 36 a. A second set of foil support strips is provided in the second side sections 40 of the first support plate member 22a, wherein one such second side section 40 is provided on each side of the first middle section 38. In the following, these strips will be indicated as second support strips 36 b.

In fig. 3, a three-dimensional coordinate system has been added. The first axis of the coordinate system, denoted Y, defines a general direction and is directed perpendicular to the first and second sides 1, 2 of the rectangle constituting the area bounded by the bond line 26. A second axis, denoted X, defines another general direction and is directed perpendicular to the third and fourth sides 3, 4 of the rectangle. The supporting bars 36a of the first set of supporting bars extend along a first axis Y and the supporting bars 36b of the second set of foil supporting bars extend along a second axis X. This means that the respective support bars will have their lengthwise extension following the respective shaft. It will be shown that these axes should be construed as general and that in a preferred embodiment the strips have their actual extension along more specific and local axes.

The third axis, denoted Z, defines an additional general direction of depth that constitutes the assembly.

The first set of support bars 36a extend along a curved path. The curved path is substantially equal in shape to the arc and is formed as an arc. There is equal distance between the arc-shaped support bars 36a and they are oriented in the same direction so that the distance between the two arcs does not change along the second direction X. Also, the foil support upper surfaces 42 of these first set of support bars 36a are of equal height along the third axis Z, which is lower than the height of the upper surface of the plateau 28 where the foil 20 is adhered. This can be seen in fig. 6 and 7.

When in operation the electron beam generating device 10 is to be heated, the result is that the foil support plate 22 is also heated. The first set of support bars 36a are formed in an arc to control any potential changes in shape due to thermal expansion, i.e., any uncontrolled distortion or wrinkling of the first set of support bars 36a will be prevented. When heated, any thermal expansion in the material will carry the risk of creating forces on the support bar 36a which will cause the support bar to start to warp. By providing an arc-shaped support strip 36a, this force will directly have a component in the second direction X, which will promote further bending in this direction, i.e. the strip will become more curved.

As previously mentioned, a second support bar 36b is provided in the second outer side section 40 of the first support plate member 22a, the second support bar 36b being on each side of the first set of support bars 36 a. And, the second supporting bar 36b extends along the second direction X. Furthermore, they are substantially straight, substantially parallel to each other, and preferably equally distributed in the second section 40 so as to have an equal distance between them. However, other distributions and unequal distances are of course possible. Their bearing upper surfaces 44 are ramps, see fig. 4-7. The ramp is arranged such that the support strip 36b has its minimum height in the vicinity of the first support strip 36a and its maximum height in the vicinity of the bonding line 26. The minimum height of the upper surface 44 is less than the height of the upper surface 42 of the first support bar 36 a. The maximum height of upper surface 44 is less than the height of the upper surface of plateau 28, i.e., the upper surface of plateau 28 is the uppermost surface of support plate 22.

Between the first and each respective second section, indicated as third section, in the small interface region, there is provided a support strip 46 having a similar shape and extension to the arcuate first support strip 36 a. In the following, this supporting bar 46 is denoted as third supporting bar 46. Its upper surface 48 is positioned at a lower level than the upper surface 42 of the first support bar 36 a. The second support bar 36b is connected to the third support bar 46, and the upper surface 48 of the third support bar 46 is at a level equal to the level of the lowermost side of the inclined upper surface 44 of the second support bar 36 b.

As previously described, the apertures 32 are disposed between the support bars 36. In a first intermediate region between the first support strips 36a, the holes 32 are through-holes, i.e. the holes 32 extend completely through the support plate 22 so that the support plate 22 is transparent to electrons. However, the hole 32 is a non-through hole around the outer periphery of the first support plate member 22 a. Instead, the support bars 36, 46 are connected to one another here by an interconnection region 50 having an upper surface 52, the upper surface 52 being countersunk relative to the upper surfaces 42, 44, 48 of the support bars 36, 46. The distance between the upper surfaces 42, 44, 48 of the support bars 36, 46 and the upper surface 52 of the interconnect region 50 is large enough to ensure that the foil 20 does not contact the interconnect region 50.

As described above, the interconnecting region 50 extends around the periphery of the first support plate member 22 a. In fig. 3 and 4, it can be seen that the interconnection region 50 extends not only between the second support bar 36b and the third support bar 46, but also between the ends of the first support bar 36 a.

Also, in the middle region of the first supporting strip 36a, where the hole 32 is a through hole, a thin interconnection 54 is provided. From fig. 4-7, it can be seen that these interconnects 54 have upper surfaces 56 that have a height that is less than the height at which the upper surfaces 42 of the first support bars 36a are located. Along the third direction Z, the distance between the upper surface 42 of the first support bar 36a and the upper surface 56 of the interconnect 54 is large enough to ensure that the foil 20 does not contact the interconnect. The function of the interconnects 54 is to maintain the same distance between all of the first support bars 36 a.

The thin interconnecting portions 54 have their lengthwise extension in the second direction X, see fig. 3, but not a straight centre line, instead they are displaced a distance in the first direction Y from a (not shown) virtual centre line. Each second portion moves towards the first side 1 and the rest towards the second side 2 of the support plate 22, forming a zigzag line. By forming zigzag lines instead of straight lines along the second direction X, wrinkles can be prevented, i.e. straight lines of interconnects 54 may result in strips extending along the second direction X, which strips may form potential wrinkles.

The thickness of the arcuate support strip 36a along the second direction X is about 0.55mm and the thickness of the substantially centrally located interconnect 54 along the first direction Y is about 0.4 mm. The thickness of the third supporting strip 46 along the second direction X is about 0.55 mm. The thickness of the second support bar 36b along the first direction Y is about 0.55 mm.

In the following, with respect to fig. 5-8, it will be described how the foil 20 will be received in the support plate 22 upon application of a vacuum from the inside of the electron beam generating device 10. When a vacuum is applied, the holes 32 and foil supports 34 will form a topological profile of the foil 20 that substantially absorbs any excess foil that would otherwise create destructive wrinkles.

It is generally preferred that the foil 20 should protrude inwardly in the hole, resulting in a substantial main bending of the foil 20 around an axis substantially perpendicular to the bonding line 26 in an imaginary plane of the support plate 22. This means that, since the bond line is substantially rectangular in the preferred embodiment, the direction of the predominant bend in the first and second segments 38, 40 will preferably not be the same. In the first section 38, the foil 20 will project inwardly in the hole 32 between the support bars 36a, resulting in a substantially predominant bending of the foil 20 about the first axis Y. In the second side section 40, the substantially predominant bending between the support bars 36b will be about the second axis X.

In both cases the protrusion or absorption of the foil 20 will be effected along the negative direction of the third axis Z.

So far, the main bending in the first section 38 about the first axis Y has generally been described. However, it will be appreciated that this is somewhat a simplification of the real world situation. The first support bar 36a is arc-shaped and will form a primary bend along an axis that follows the shape of the arc. The axis may be defined by the axis Y of a random local coordinate system₁See, fig. 3 for a representation. Axis Y₁Will follow the shape of the arc and will therefore be different from each other at every point along the arc. Axis Y₁Should be considered as a small adjustment of the more general axis Y.

Fig. 9 shows the main bending of the foil in the small view D of fig. 3. It shows particularly exemplarily the space in the bore between two supporting bars. The foil having a direction about axis Y₁And protrudes downwards, i.e. in the direction of the third axis Z.

FIG. 8 shows a partial cross-section taken along line C of FIG. 3A particular exemplary view of a face showing the coupling of the support bars 36b from the second set of support bars with the foil 20. The purpose is to show the topological profile of the foil 20 along the first axis Y when a vacuum is applied. It can be seen that the foil 20 protrudes downwards in the holes 32 between the second supporting strips 36b and that here a major bending in each hole is achieved around the second axis X. Since the second supporting bar 36b is straight and has an extension along the second direction X, a general coordinate system can be used. However, in another preferred embodiment, the bars of the second set of support bars may have another configuration. Fig. 10 shows a partial view of a second embodiment of the support plate 22, in which the second support strip 36 b' is arranged in a fan-shaped configuration relative to the third support strip 46. The supporting bar 36 b' can in this embodiment for example be guided (direct) perpendicular to the tangent of the curved third supporting bar 46. In this example about the axis X of the local coordinate system₂The primary bending is achieved. Axis X₂Should be considered as a small adjustment of the more general axis X.

To achieve a smooth transition between the curves in the first and second segments 38, 40, referring to fig. 7, in the interface region, the upper surface 48 of the third support bar 46 is lower compared to the upper surface 42 of the first support bar 36 a. In this way the foil 20 will not be tensioned in this area and the foil 20 will not be pressed against the support bar in this area while being forced to move from one main bend to another. This is also the reason why the second supporting bar 36b is inclined at its lowest height toward the first supporting bar 36 a.

From fig. 5-8, but with particular reference to fig. 5, it is found that the foil 20 will not be arranged straight on the support plate 22, but will form a topological profile that absorbs any excess foil.

Fig. 11-13 show a third preferred embodiment of the support plate 22. In this embodiment, similar to the first and second embodiments, the primary curvature in the first middle section 38 is formed about the first axis Y and the primary curvature in the second side section 40 is formed about the second axis X. The first intermediate section 38 comprises the same foil support 34 as the support bars already described above with reference to the first and second embodiments, having the shape of the first support bar 36 a. Overall, the design in the first intermediate section 38 is at least substantially the same as in the first and second embodiments described above. Also the third section, being the small interface area between the first and second sections comprising the third support strip 46, is substantially the same as already described above. In this third embodiment, the interconnect region 50 having an upper surface 52 extending over both the first and second segments 38, 40 is also the same as in the previously described embodiments. However, the design and distribution of the foil support 34 in the second side section 40 is substantially different from that described above. The second side segments 40 each comprise a foil support as an oval element 58. The oval-shaped member 58 is positioned on the upper surface 52 of the interconnect region 50 and has an upper surface 60, the upper surface 60 being at the same elevation as the upper surface 42 of the first support bar 36 a. Also, the oval elements 58 are arranged in rows spaced apart from one another. The rows of elements 58 extend along a curved path. The curved path is arcuate. The arc substantially coincides with the arc of the first and third support bars 36a, 46. The rows of oblong elements 58 can therefore be seen in a sense to form additional strips corresponding to the first and third support strips 36a, 46. Each elliptical element 58 has its longest extension that follows the length of the arc. The length of each element 58 may be equal or may be different between elements 58. In the illustrated example, the elements 58 in the ends of the arc are longer than the elements 58 in the middle of the arc. The length interval is preferably between 2-4 mm. The thickness of the element 58 in a direction perpendicular to the length direction is about 1.6 mm.

As mentioned above, the primary bend formed in the second side section 40 about the second axis X. More specifically, in this example about axis X of a random local coordinate system₃Forming a primary bend. Axis X₃Should be considered a small adjustment of the more general axis X. Guiding the axis Y along a curved path₃And axis X₃Arranged substantially perpendicular to a tangent to the curved path. To obtain the desired predominant curvature, the distance or spacing between the rows of subsequent elements 58 is substantially equal to or longer than the distance fromThe distance of the element 58 to the third support bar 46 and the distance from the element 58 to the frame constituting the second support plate member 22 b. If the distances are equal, then X will still be around₃A major bend is created because the wrinkles are more likely to be created perpendicular to the bond lines 26, in this example perpendicular to the sides 3 and 4 of the rectangle. For better understanding, bond lines 26 have been added in fig. 11. Fig. 13 shows a particular exemplary view of a partial cross-section taken along line C of fig. 11, i.e., along a curved path along which the elliptical elements 58 are disposed. The figure shows the coupling of the oval element 58 with the foil 20. The purpose is to show the outline of the foil 20 over the oval elements 58 when a vacuum is applied. It can be seen that the foil 20 projects downwardly into the gaps between the oval elements 58 and forms here a main bend in each gap about the second axis X.

The invention also includes a method, which has been described to a large extent in relation to the described components. The method comprises the step of providing a pattern in said area in which the holes 32 in the support plate 22 and the foil support 34 are spaced from each other, which pattern is adapted to form a topological profile of the foil 20 that substantially absorbs any surplus foil when a vacuum is generated in the housing 14. Preferably, in this way, a substantial major bending of the foil 20 occurs in each hole 32.

The invention also comprises a method for sterilizing packaging material, such as for example a roll of packaging material, in a filling machine, said method comprising the step of using an electron beam generating device of the type initially described with reference to fig. 1, which electron beam generating device comprises an assembly according to the invention. A packaging material roll for use when forming a food package may comprise a packaging laminate comprising a paper core layer and inner and outer polymer layers. Before forming the roll into a package, the roll is sterilized by means of an electron beam generating device 10. The electron beam generating apparatus 10 includes components of the type described above.

An electron beam generating device having an assembly of the aforementioned kind may also be used for sterilizing the outer surface of the packaging container. Preferably, the electron beam generating device is directed towards the side of the packaging container and rotates the packaging container in order to achieve sterilization over the entire outer side surface.

An electron beam generating device suitable for sterilizing a conventional roll of packaging material will have an electron exit window assembly with a more regular rectangular shape than has been described previously in the figures. In practice, the transparent central portion of the assembly (i.e. the portion through which electrons can pass through the assembly) is about 40mm long (along the first direction Y) and about 400mm wide (along the second direction X). However, in a more regular rectangular shaped assembly, the overall design of the support plate 22 will not be substantially the same. Due to the greater width, the first section 38 of the support bar is larger due to having more first support bars 36 a.

During sterilization, the web of packaging material will pass through the electron exit window 12 of the electron generating device 10. The direction of travel of the roll will correspond to the first direction Y, i.e. the direction of travel is aligned with the first direction Y.

Although the present invention has been described in terms of the presently preferred embodiments, it will be understood that various modifications and changes may be made without departing from the spirit and scope of the invention as defined by the appended claims.

The first support bar 36a has been described as extending along a curved path and in the presently preferred embodiment is arcuate. Another way to describe a curved path is to use the mathematical term polynomial. The arc shown in fig. 3, for example, is a second order polynomial. In some applications, thermal expansion in the support bars of the support plate will be focused and it is desirable to minimize the effects of thermal expansion. Alternative designs of the support bars in those cases include, for example, third or fourth order polynomials. The interconnection between the supporting bars may be provided in the axis intersection of the polynomials.

Claims (15)

1. An assembly of a support plate (22) and an exit window foil (20) for use in an electron beam generating device (10), the support plate (22) being designed to reduce wrinkles in the foil (20) which can be generated by surplus foil occurring during assembly, the foil (20) being adhered to the support plate (22) along a closed adhesion line (26) bounding an area of the support plate (22) where holes (32) and foil supports (34) are provided, and in which area the foil (20) is adapted to be used as a part of a wall of a vacuum tight housing (14) of the electron beam generating device (10),

the assembly is characterized in that it is provided with,

the support plate (22) is provided in said area with a pattern of holes (32) and foil supports (34) spaced from each other, which pattern is adapted to form a topological profile of the foil (20) that substantially absorbs any surplus foil when a vacuum is generated in the housing (14).

2. Assembly according to claim 1, characterized in that the absorption is achieved in such a way that a substantially predominant bending of the foil (20) is generated in the hole (32).

3. An assembly according to claim 2, characterized in that the main bend is formed around an axis directed substantially perpendicular to the bonding line (26) in the plane of the support plate (22).

4. Assembly according to any one of claims 2-3, characterized in that the area delimited by the bonding line (26) is divided into at least two segments (38, 40), each segment comprising at least one hole (32), and in each respective segment (38, 40) the main bending is produced in the same direction in adjacent holes (32).

5. Assembly according to any one of claims 2-4, characterized in that the area bounded by the bonding line (26) is substantially rectangular and forms the main bend in a first intermediate section (38) around a first axis (Y) directed substantially perpendicular to a first side (1) of the rectangle and to a second side (2) opposite the first side (1), and in a second side section (40) around a second axis (X) directed substantially perpendicular to a third side (3) and to a respective fourth side (4) of the rectangle, the third and fourth sides (3, 4) of the rectangle being substantially perpendicular to the first and second sides (1, 2).

6. Assembly according to claim 5, characterized in that the foil support (34) is formed as a foil support strip (36).

7. Assembly according to claim 6, characterized in that a first set of foil support strips (36 a) is provided in the first middle section (38) of the support plate (22) and a second set of foil support strips (36 b, 36 b') is provided in a second side section (40) of the support plate (22), wherein one such second side section (40) is provided on each side of the first section (38) in the end area of the support plate (22).

8. Assembly according to claim 7, characterized in that the supporting bars (36 a) of the first set of supporting bars extend along the first axis (Y) directed substantially perpendicular to the first and second sides (1, 2) of the rectangle.

9. Assembly according to claim 8, wherein the foil support bars (36 a) of the first set of foil support bars extend along a curved path.

10. Assembly according to claim 7, characterized in that the foil support bars (36 b, 36 b') of the second set of foil support bars extend along a second axis (X) directed substantially perpendicular to the third side (3) and the respective fourth side (4) of the rectangle.

11. Assembly according to claim 5, characterized in that the foil support (34) in the second side section (40) is an element (58) arranged mutually separated in a row, which row substantially follows the first axis (Y).

12. Assembly according to any one of the preceding claims, characterized in that the bonding line (26) is positioned at a plateau (28) of the support plate (22).

13. A method for reducing wrinkles in an exit window foil (20) of an electron beam generating device (10), which wrinkles may arise due to surplus foil occurring during assembly, the foil (20) being adhered to a support plate (22) along a closed adhesion line (26) bounding an area of the support plate (22) where holes (32) and foil supports (34) are provided, and in which area the foil (20) is adapted to be used as part of a wall of a vacuum tight housing (14) of the electron beam generating device (10),

the method comprises the following steps:

in said area, a pattern of holes (32) provided in the support plate (22) and foil supports (34) spaced from each other is adapted to form a topological profile of the foil (20) that substantially absorbs any surplus foil when a vacuum is generated in the housing (14).

14. Method according to claim 13, wherein the absorption is effected in such a way that a substantially predominant bending of the foil (20) is generated in the hole (32).

15. A method in a filling machine for sterilizing packaging material, such as for example packaging material rolls, comprising the step of using an electron beam generating device comprising an assembly according to claim 1.