APPARATUS AND METHOD FOR GENERATING A RELIEF CARRIER BY IRRADIATION

Abstract

An apparatus for generating a relief carrier using a solidifiable material includes a support structure configured for providing a substantially cylindrical support surface. The support surface may be formed by a substrate intended to be part of the relief carrier to be generated or by a cylindrical support not intended to be part of the relief carrier to be generated. A container is provided for the solidifiable material, the container having a wall arranged substantially parallel to an axis of the support structure; a moving means to move the support structure relative to the wall such that subsequent areas of the support surface face the wall during the moving. Moving includes at least a rotation around the axis. An irradiating means sends irradiation, through the wall in a predetermined area between the support surface and the wall.

Claims

1. An apparatus for generating a relief carrier using a solidifiable material, said apparatus comprising: a support structure configured for providing a substantially cylindrical support surface, wherein the support surface is formed by a substrate to be part of the relief carrier to be generated or by a cylindrical support that will not be part of the relief carrier to be generated; a container for receiving the solidifiable material, said container having a wall arranged substantially parallel to an axis of the support structure, such that the support surface is at a determined distance of the wall; a moving means configured to move the support structure relative to the wall, such that subsequent areas of the support surface face the wall during the moving; said moving comprising at least a rotation around the axis; an irradiating means configured to send irradiation, through said wall, in a predetermined area between the support surface and the wall to solidify the solidifiable material at the support surface; wherein the wall is configured to allow said irradiation to pass through the wall.

2. The apparatus according to claim 1, wherein the support structure is configured for receiving a substrate in the form of a plate or sleeve forming the support surface.

3. The apparatus according to claim 1, wherein the movement means is configured to allow the support surface to be provided with solidified material over substantially 360°; and/or wherein the support surface describes a full cylinder.

4. (canceled)

5. The apparatus according to claim 1, wherein the moving means is configured to move the support structure relative to the wall such that the axis of the support structure is moved parallel relative to the wall of the container whilst rotating the support structure around the axis.

6. The apparatus according to claim 1, wherein the moving means is configured to translate and rotate the support structure relative to the wall such that for each degree of rotation of the support structure the support structure is translated relative to the wall over a distance which is within 10% of a value calculated as π multiplied with the outer diameter of the support surface divided by 360 (π*d/360).

7. The apparatus according to claim 1, wherein the moving means is configured to translate the support structure and/or to translate the container; wherein the apparatus further comprises an irradiation movement means configured to move an irradiating area of the irradiating means with respect to the wall in synchronization with the support structure.

8. (canceled)

9. The apparatus according to claim 1, further comprising an adjustment means configured to change the distance between the wall and the support structure.

10. The apparatus according to claim 1, further comprising a controller configured to control the movement means, the irradiation movement means and the irradiating means such that subsequent adjacent longitudinal zones of the support surface are irradiated, said longitudinal zones extending parallel to the axis of the support structure.

11. The apparatus according to claims 9, further comprising a controller configured to control the movement means, the irradiation movement means and the irradiating means such that subsequent adjacent longitudinal zones of the support surface are irradiated, said longitudinal zones extending parallel to the axis of the support structure; wherein the controller is configured to control the movement means, the adjustment means and the irradiating means such that one or multiple layers of solidified material are formed on the support surface; and/or such that during one or more rotations of the support structure at least one structured layer of solidified material is formed.

12. The apparatus according to claims 9, further comprising a controller configured to control the movement means, the irradiation movement means and the irradiating means such that subsequent adjacent longitudinal zones of the support surface are irradiated, said longitudinal zones extending parallel to the axis of the support structure; wherein the controller is configured to control the movement means, the adjustment means and the irradiating means such that during one or more rotations of the support structure at least one full layer of solidified material is formed on the support surface to form a floor, and during one or more subsequent rotations at least one imaged layer of structured solidified material is formed on the floor.

13. (canceled)

14. The apparatus according to claim 1, wherein the movement means is configured to translate the support structure relative to the wall in a forward direction from an initial position to an end position, whilst the support structure is being rotated, and next in a backward direction from the end position to the initial position.

15. The apparatus according to claim 1, wherein the wall is a bottom wall of the container; and wherein the wall is provided on a surface inside the container with an anti-stick coating configured to limit sticking to solidified material; wherein the wall is transparent to electromagnetic radiation and/or inhibitors.

16-17. (canceled)

18. The apparatus according to claim 1, wherein the irradiating means comprises one or more irradiating elements arranged in one or more lines parallel to the axis of the support structure; and wherein the irradiating means comprise any one of the following, or a combination thereof: a UV irradiating means, an infrared irradiating means, a laser means, a scanning means, a projection means, a LED array, a liquid crystal display, and an active matrix (O)LED display.

19. (canceled)

20. An apparatus for generating a relief carrier using a solidifiable material, said apparatus comprising: a support structure configured for providing a substantially cylindrical support surface, wherein the support surface may be formed by a substrate intended to be part of the relief carrier to be generated or by a cylindrical support not intended to be part of the relief carrier to be generated; a container for receiving the solidifiable material, said container having a wall arranged substantially parallel to an axis of the support structure, such that the support surface is at a determined distance of the wall; wherein the support surface is at a determined distance of the wall, said distance being smaller than 1 cm and/or wherein the support surface and the wall are shaped such that a gap is formed which, as seen in the movement direction, narrows toward the predetermined irradiated area; a moving means configured to move the support structure relative to the wall such that subsequent areas of the support surface face the wall during the moving; said moving comprising at least a rotation around the axis; and an irradiating means configured to send irradiation through said wall in a predetermined area between the support surface and the wall to solidify the solidifiable material at the support surface; wherein the wall is configured to allow said irradiation to pass through the wall.

21. A method for generating a relief carrier using a solidifiable material, said method comprising: providing a substantially cylindrical support surface, wherein the support surface is formed by a substrate that will be part of the relief carrier to be generated or by a cylindrical support that will not be part of the relief carrier to be generated; arranging said substantially cylindrical support surface at least partially in a solidifiable material in a container at a distance of a wall of the container and such that the wall is parallel to an axis of the substantially cylindrical support surface; moving said support surface relative to the wall such that subsequent areas of the support surface face the wall during the moving; solidifying the solidifiable material by irradiation through the wall in a predetermined area between the support surface and the wall.

22. The method according to claim 21, wherein the moving and the solidifying is performed such that the support surface is provided with solidified material over substantially 360°.

23. The method according to claim 21, wherein the moving comprises moving the axis parallel to the wall whilst rotating the support surface around said axis.

24. The method according to claim 21, wherein the solidifiable material is a viscous photosensitive coating material having a viscosity according to DIN 1342 that is higher than 400 mPa*s.

25. The method according to claim 21, wherein during one or more initial rotations of the support surface over 360° at least one full layer of solidified material is formed on the support surface to form a floor, and during one or more subsequent rotations at least one imaged layer of structured solidified material is formed on the floor to form a relief structure; and/or wherein during one or more initial rotations of the support surface at least one imaged layer of structured solidified material is formed on the floor to form a relief structure; and/or wherein the moving comprises translating and rotating the support surface relative to the wall such that for each degree of rotation of the support surface around the axis, the axis is translated relative to the wall over a distance which is within 10% of a value calculated as π multiplied with the outer diameter (d) of the support surface divided by 360 (π*d/360).

26-37. (canceled)

38. A relief carrier obtained by the method according to claim 21, wherein the relief carrier is for use as flexographic printing plate or sleeve, letterpress plate or sleeve, tampon printing plate or sleeve, intaglio printing plate or sleeve, microfluidic device, micro reactor, phoretic cell, photonic crystal or optical device.

39. (canceled)

Description

BRIEF DESCRIPTION OF THE FIGURES

[0058] The accompanying drawings are used to illustrate presently preferred non-limiting exemplary embodiments of devices of the present invention. The above and other advantages of the features and objects of the invention will become more apparent and the invention will be better understood from the following detailed description when read in conjunction with the accompanying drawings, in which:

[0059] FIGS. 1A, 1B and 1C illustrate a first exemplary embodiment of a method in which the container is fixed, whilst the support structure and irradiating means are being moved;

[0060] FIGS. 2A, 2B, 2C and 2D illustrate a second exemplary embodiment of a method in which the support structure is only rotated, whilst the container is being translated;

[0061] FIG. 3 illustrates a third exemplary embodiment of an apparatus for arranging a solidified material on a substrate or cylindrical carrier;

[0062] FIG. 4 illustrates a fourth exemplary embodiment of an apparatus for arranging a solidified material on a substrate or cylindrical carrier; and

[0063] FIG. 5 illustrates a schematic perspective view of an exemplary embodiment of an apparatus for arranging a solidified material on a substrate or cylindrical carrier;

[0064] FIG. 6 is a schematic cross section of an exemplary embodiment of a generated relief carrier;

[0065] FIG. 7 is a schematic cross section in more detail of a relief area of the relief carrier of FIG. 6;

[0066] FIGS. 8A, 8B, 8C show respectively a top view, a section along line B-B in FIG. 8A, and a section along line C-C in FIG. 8A of an exemplary embodiment of a relief area;

[0067] FIGS. 9A, 9B, 9C show respectively a top view, a section along line B-B in FIG. 9A, and a section along line C-C in FIG. 9A of an exemplary embodiment of a relief area; and

[0068] FIGS. 10A and 10B show respectively a top view and a section along line B-B in FIG. 10A of an exemplary embodiment of a relief area.

DESCRIPTION OF EMBODIMENTS

[0069] FIG. 1A illustrates schematically an apparatus for arranging a solidifiable material M on a cylindrical support surface S. The apparatus comprises a support structure in the form of a drum 100 on which a substrate may be fixed. In another embodiment the cylindrical drum 100 itself forms a support surface on which the relief carrier is built, without the use of a substrate. The apparatus further comprises a container 200 containing solidifiable material M, a moving means (not shown) configured to move the drum 100 parallel to a bottom wall 210 of the container 200, an adjustment means (not shown) configured to adjust the distance t between the drum 100 and the bottom wall 210, and an irradiating means 400. The container 200 has a bottom wall 210 and a side wall 220. The bottom wall 210 is arranged parallel to an axis A of the drum 100. The drum 100 is arranged in the container such that the support surface S is at a determined distance t of the bottom wall 210. The irradiating means 400 is configured to send irradiation through the bottom wall 210 in a predetermined area between the drum 100 and the bottom wall 210 to solidify the solidifiable material in that area such that it adheres to the support surface S in that area. The bottom wall 210 is configured to allow the irradiation to pass through the bottom wall 210. It is noted that the adjustment means (not shown) to adjust the distance t may be configured to move the container 200 in a vertical direction and/or to move the drum 100 in a vertical direction. If the container 200 is moved, the irradiating means may have to be adjusted as well.

[0070] In the figure description below, when referring to a support surface S, this may be a surface of a flat substrate or a sleeve arranged on the drum 100, or this may be a surface of the drum 100 itself. In yet another embodiment, support structure is not a drum and does not have a cylindrical support surface, but is a suitable mounting system for a cylindrical substrate. For example, the mounting system may comprise two cones.

[0071] The moving means (not shown) is configured to translate the drum 100 in a forward direction F parallel to the bottom wall 210, and to rotate the drum 100 around its axis A in a rotation direction R. FIG. 1A shows the drum 100 in an initial position on the right side of the container 200. FIG. 1B illustrates an intermediate position more or less in the middle of the container 200. Point P on the support surface S which is being irradiated in the initial position of FIG. 1A is located on top of the drum 100in the position of FIG. 1B. FIG. 1B further illustrates that a layer L of solidified material has been formed on the support surface S over substantially 180°. The drum 100 is further rotated and translated in the forwarded direction F towards the left side of the container 200, see FIG. 1C. The position shown in FIG. 1C corresponds with the end position of the drum 100. In this position a full layer L of solidified material has been formed on the support surface S and may extend over a large portion of the support surface, e.g. over substantially 360°. Now a second layer may be formed on the full layer L on the support surface S by moving the drum 100 in a backward direction B whilst rotating the drum 100 in an opposite rotation direction R. In the embodiment of FIGS. 1A-1C the irradiating means 400 is translated synchronously with the drum 100. However, it is also possible to provide an irradiating means which extends along the distance Dp between the initial position of FIG. 1A and the end position of FIG. 1C. In such an embodiment, the switching on of the lines of the irradiating means 400 may be synchronized with the translation movement of the drum 100.

[0072] In a possible embodiment, during one or more initial rotations of the support surface over 10° to 360° in the forward/backward direction F/B, at least one full layer of solidified material may be formed on the support surface S to form a floor. During one or more subsequent rotations over 10° to 360° in the forward/backward direction F/B at least one structured layer of solidified material may be formed on the floor to form a relief structure.

[0073] In a preferred embodiment, the distance Dp between the initial position and the end position is more or less equal to the circumference of the drum 100, i.e. Dp=π*d wherein d may be the outer diameter of the whole drum 100 including the substrate (if present) and any added layer(s) when present. In other words, the drum 100 is rolled over a virtual plane at a distance t of the bottom wall 210, from the initial position shown in FIG. 1A to the end position shown in FIG. 1C. Preferably, both the rotation speed of the drum 100 and the translation velocity in the forward/backward direction F/B is constant, and is such that for each degree of rotation of the drum 100 around the axis A, the axis A is translated relative to the bottom wall 210 over a distance which is within 10% of π*d/360.

[0074] The skilled person understands that instead of translating the drum 100 and the irradiating means 400 in the forward/backward direction F/B, it is also possible to translate the container 200 in the backward/forward direction B/F.

[0075] FIGS. 2A, 2B, 2C and 2D illustrate a second exemplary embodiment of an apparatus comprising a drum 100 arranged in a container 200. An irradiating means 400 sends irradiation through a bottom wall 210 of the container 200, in a similar manner as described above in connection with the embodiment of FIGS. 1A-1C. In the embodiment of FIGS. 2A-2D the container 200 is moved between an initial position shown in FIG. 2A and an end position shown in FIG. 2B. In this embodiment, the drum 100 is not rotated over 360° between the initial position and the end position, but is rotated over a smaller angle a as indicated in FIG. 2B. Note that point P has been moved from a first position in FIG. 2A to a second position in FIG. 2B over the angle a. Whilst the container 200 is being translated in the forward direction F from the initial position to the end position, the drum 100 is rotated in a rotation direction R, and the irradiating means 400 irradiate a predetermined area between the drum 100 and the bottom wall 210. In that manner, a layer L of solidified material is formed on the support surface S. This layer L extends over the angle α in the end position illustrated in FIG. 2B. Next, the container 200 is moved in the backward direction B from the end position of FIG. 2B to the initial position, see FIG. 2C. Now the container 200 is again translated in the forward direction F, whilst the drum 100 is being rotated in a rotation direction R, such that a further segment of the support surface S is covered with solidified material, see the layer L in FIG. 2D which extends over an angle equal to 2*a. In the embodiment of FIGS. 2A-2C, no irradiating is performed during the backward movement of the container 200.

[0076] The skilled person understands that instead of moving the container 200 in the embodiment of FIGS. 2A-2D, it is also possible to translate the drum 100 and the irradiating means 400 in the forward/backward direction F/B.

[0077] FIGS. 3 and 4 illustrate two further exemplary embodiments of an apparatus for arranging a solidified material on a support surface, wherein the same reference numerals refer to the same or similar components. In the embodiment of FIG. 3, the apparatus comprises a drum 100 on which a substrate may be fixed, a container 200 containing solidifiable material M, a moving means (not shown) configured to rotate the drum 100, an adjustment means (not shown) configured to adjust the distance between the drum 100 and a bottom wall 210 of the container 200, and an irradiating means 400. The container 200 has a bottom wall 210 and a side wall 220. The bottom wall 210 has an upwardly curved wall portion, here a bottom wall portion 215 with a cylindrical section arranged parallel to the axis A of the support structure, such that a gap is created between the cylindrical section 215 and the support surface S. Preferably, the irradiating means 400 are arranged to irradiate an area located between the axis A″ of the cylindrical section and the axis A of the drum, where the gap is smallest. The upwardly curved cylindrical section 215 faces a downwardly curved cylindrical section of the support surface S. By using such opposite cylindrical sections 215, 100 fresh solidifiable material can easily flow towards the area to be irradiated. The irradiating means 400 are preferably located centrally below the cylindrical bottom wall section 215, such that the area with the smallest distance between the drum 100 and the bottom wall 210 is irradiated.

[0078] In the embodiment of FIG. 4, the container 200 is formed as a cylinder or partial cylinder having an axis A′ which is parallel to the axis A of the support structure, here a drum 100. However, the support structure could also comprise a clamping structure to clamp a cylindrical carrier with its axis A parallel to the axis A′ of the container 200. The axes A, A′ of the container 200 and the drum 100 are located at a distance of each other and the diameter of the cylindrical container 200 is larger than the diameter of the completely built structure (drum 100 plus optional substrate plus built layers). The container 200 may be a closed cylinder (as indicated in dotted lines) which can be advantageous to keep the system free of dust and avoid evaporation of volatile material from the container 200. However, the container 200 may also be formed as an open or partial cylinder, which makes loading of the optional substrate and unloading of the generated relief carrier easier. The irradiating means 400 is arranged to irradiate an area between the drum 100 and the container 200, where the gap is smallest. In this setup the amount of solidifiable material in the container may be significantly reduced. Both the drum 100 and the container 200 may be rotated, see the arrows R and R′. For example, in order to limit any disturbance of the solidifiable material in the container, the drum 100 and the container 200 may be rotated in the same direction. However, for other purposes, it may also be envisaged to rotate the container 200 in the opposite direction. In yet other embodiments, the container 200 may be stationary. In yet another embodiment the drum 100 and/or the container may be stationary during the exposure while the irradiation means is moved on a cylindrical path around the container. With a set of LED arrays arranged around the container also an irradiation area may be moved by switching LEDs on and off. In a subsequent step, the drum is rotated to contact a further area of the drum with solidifiable material and subsequently exposed by moving the irradiation means.

[0079] In the embodiments of FIGS. 3 and 4, the solidified material on the support surface S can gradually be removed from the bottom wall of the container 200, whilst fresh solidifiable material flows towards the area to be irradiated.

[0080] FIG. 5 illustrates schematically an apparatus for arranging a solidified material on a support surface. The apparatus comprises a container 200, a drum 100, a moving means 300, an irradiating means 400, an adjustment means 600, and a controller 500. The controller 500 is configured to control the moving means 300, the irradiating means 400 and the adjustment means 600, as indicated with dotted lines in FIG. 5. The irradiating means 400 may be coupled with the moving means 300, such that the irradiating means are moved synchronously with the translation of the axis A of the drum 100. In the embodiment illustrated in FIG. 5, the drum 100 is provided with a shaft which is arranged in bearing blocks. The moving means are configured to move the bearing blocks along a guide means which extends in a direction perpendicular on the axis A of the drum 100, and parallel to the bottom wall 210 of the container 200. The adjustment means 600 is configured to adjust a distance between the drum 100 and a bottom wall 210 of the container 200. The adjustment means may be configured to move the axis A of the drum 100 vertically and/or to move the container 200. If the container 200 is moved vertically, this may be coupled with an adjustment of the irradiating means 400 so that the irradiating area is adjusted accordingly.

[0081] FIG. 6 is a sectional view of a relief carrier 1000 having a base layer 1100 and a relief layer 1200. The relief layer 1200 is formed as a stepped profile of solidified material. The stepped profile comprises a plurality of relief areas 1250, 1250′, 1250″, 1250″′. Preferably, the base layer 1100 is a cylindrical base layer. The cylindrical base layer 1100 may subscribe a full circumference such that a relief sleeve is formed, or it may extend over less than 360°. The base layer 1100 may correspond at least partially with the substrate, in embodiments where a substrate is used. In other embodiments where no substrate is used, the base layer 1100 may be a layer which is formed using the solidifiable material. The stepped profile may be provided over more than 10°, preferably over more than 90°, more preferably over more than 180°, even more preferably over more than 270°, and most preferably over substantially 360° of the outer surface of the relief carrier 1000.

[0082] FIG. 7 shows in detail one relief area 1250. The relief area 1250 has an upper landing 1251 and at least one flight of steps 1252 between the base layer 1100 and the upper landing 1251. The upper landing 1251 may be a curved surface, e.g. a cylindrical surface which is concentric with the cylindrical base layer 1100. Each flight of steps 1252 may comprise a plurality of steps, preferably at least three steps, more preferably at least five steps. In the illustrated example, for reasons of simplicity, the flight of steps comprises only three steps 1252, but the skilled person understands that much more steps may be provided. The flight of steps 1252 may extend all the way from the base layer 1100 to the upper landing, as shown in FIG. 7. However, as shown in FIG. 6, when adjacent relief areas 1250′, 1250″, 1250″′ are located close to one another, a flight of steps of a relief area 1250″ may not extend all the way to the base layer 1100, and may be merged with a flight of steps an adjacent relief area 1250′, 1250″′.

[0083] A step may correspond with a single layer L built during one pass of the irradiating means, but may also correspond with multiple layers L built during consecutive passes of the irradiating means. FIG. 7 further shows some dimensions of the steps 1252. Preferably, the height hs of a step 1252 of the stepped profile is smaller than 0.5 millimeter, more preferably smaller than 300 micrometer. The height hs may even be smaller than 200 micrometer or smaller than 100 micrometer. The base layer 1100 may have a thickness hb which is for example between 0.5 and 3 mm. The relief carrier 1000 may have a maximum thickness ht which is smaller than 10 mm, preferably smaller than 7 mm. The steps 1252 of the stepped profile are delimited by riser walls 1253, 1253′. Riser wall 1253′ is oriented at an angle α of less than 20° from a radial direction R, preferably less than 10° from the radial direction R. Preferably a riser wall 1253 is oriented substantially radially. The width w1, w2 of a step 1252 may vary, e.g. depending on the desired “steepness” of the flight of steps. For example, when two adjacent relief areas 1250 have to be positioned close to one another, the width w2 of an upper step may be relatively small, whilst one or more lower steps may have a width w1 which is larger than w2.

[0084] In a possible embodiment, the upper landing 1251 is substantially surrounded by the at least one flight of steps. In the embodiment of FIGS. 8A, 8B, 8C the upper landing 1251 has a substantially polygonal shape and there is provided a flight of steps 1252, 1252′ at each edge of the polygonal upper landing 1251, see also the section along line B-B shown in FIG. 8B and the section along line C-C shown in FIG. 8C. The direction of line C-C may correspond with the axial direction A of the support structure. In the illustrated example the shape of the upper landing 1251 is rectangular, but the skilled person understands that the upper landing 1251 may have any shape, e.g. depending on the image that has to be printed.

[0085] In another possible embodiment, the upper landing 1251 is not fully surrounded by the at least one flight of steps. In the embodiment of FIGS. 9A, 9B, 9C the upper landing 1251 has a substantially polygonal shape and there are provided two flights of steps 1252 at opposite sides of the polygonal upper landing 1251, see also the section along line B-B shown in FIG. 9B. The direction of line C-C may correspond with the axial direction A of the support structure. In the illustrated example the shape of the upper landing 1251 is rectangular, but the skilled person understands that the upper landing 1251 may have any shape, e.g. depending on the image that has to be printed.

[0086] In yet another possible embodiment, the upper landing 1251 is circular or rounded. In the embodiment of FIGS. 10A and 10B the upper landing 1251 has a substantially circular shape and there is provided a circular flight of steps 1252 around the upper landing 1251, see also the section along line B-B shown in FIG. 10B. Of course, any other regular or irregular shape of upper landing and its surrounding steps is possible whereby in general, the contours of the different layers are similar to the shape of the landing but they may be different as well.

[0087] By application and solidification of the layers in a curved form, the surface layers of the relief carrier are not mechanically stressed as comparable relief structures of the prior art, which are manufactured in a planar configuration and bent for mounting on a cylinder.

[0088] Further, by providing the steps to the relief areas, the relief areas 1250 are given additional stability. This may be especially useful for relief areas 1250 with a small upper landing 1251. In more advanced embodiments, the stepped profile may be determined in function of the image to be printed, and the number and/or size and/or shape of the steps may be adjusted in function of the image to be printed. For example, for large relief areas, less steps may be provided, whilst for small relief area more steps may be provided.

[0089] A person of skill in the art would readily recognize that steps of various above-described methods can be performed by programmed computers. Herein, some embodiments are also intended to cover program storage devices, e.g., digital data storage media, which are machine or computer readable and encode machine-executable or computer-executable programs of instructions, wherein said instructions perform some or all of the steps of said above-described methods. The embodiments are also intended to cover computers programmed to perform said steps of the above-described methods.

[0090] The functions of the various elements shown in the figures, including any functional blocks labelled as “controllers” may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared.

[0091] Whilst the principles of the invention have been set out above in connection with specific embodiments, it is to be understood that this description is merely made by way of example and not as a limitation of the scope of protection which is determined by the appended claims.