WO2006032491A1

WO2006032491A1 - Apparatus for printing microstructures

Info

Publication number: WO2006032491A1
Application number: PCT/EP2005/010243
Authority: WO
Inventors: Johannes Matthiesen
Original assignee: Securis Limited
Priority date: 2004-09-23
Filing date: 2005-09-20
Publication date: 2006-03-30
Also published as: GB0421174D0

Abstract

Surface relief microstructures such as holograms may be replicated rapidly and with accuracy on a web based in-situ polymerization replication (ISPR) printing apparatus. The apparatus of the present invention has a printing cylinder assembly (1) for ISPR utilizing a hollow printing cylinder (2) and in which assembly (1) the hollow cylinder (2) is retained under compression through the use of co-operating annular flanges (3,4) and annular elastomeric components (7, 8, 36, 37). The assembly (1) is robust and enables rapid and effective replacement of the printing cylinder (2) without removal of the assembly (1) from the printing apparatus.

Description

APPARATUS FOR PRINTING MICROSTRUCTURES

[0001] The invention relates to an apparatus for the manufacture of surface relief microstructures e.g. holograms and more especially to the design and operation of the surface relief microstructure printing cylinder.

[0002] The manufacture of surface structures with dimensions between the nanometer and micrometer level e.g. surface relief holograms has been undertaken in the past via a number of different methods. One commonly used method is thermal embossing where a hard embossing cylinder is utilized typically with pressure and temperature to transfer the image from the cylinder to a suitable thermoformable plastic such as PVC. A further method utilizes solvent casting where a plastic dissolved in a solvent is coated onto the master with surface relief hologram and allowed to dry by evaporation, and the resulting dry layer of plastic is peeled off the master surface relief.

[0003] A more recently developed method is that of in-situ polymerization replication (ISPR). With this technology a liquid polymer or resin, usually deposited on a substrate such as a polymer film or web, is cast or molded against the microstructure to be replicated e.g. holographic image or optically variable effect profile, in a continuous fashion. The molded profile is retained in the polymer or resin on or after removal from the microstructure mold by use of a curing stage. Examples of this approach are described in United States Patent Nos. 3,689,346, 4,758,296, 4,840,757, 4,933,120, 5,003,915, 5,085,514 and in DE-A-4, 132,476, WO88/09252 and WO94/18609. In most of these prior art techniques the microstructure to be molded is provided as a relief in a metal surface on a rotary cylinder. They all utilize radiation curable media as the liquid polymer or resin media for casting and therefore this technology is sometimes referred to as UV casting.

[0004] ISPR processes are attractive processes as they are web based and lend themselves to continuous/semi-continuous operations for bulk manufacture of surface relief images. In WO94/18609 the curing of the radiation curable resin is achieved by the use of a UV source that is located within the bore of a hollow quartz cylinder that carries the surface relief microstructure image to be molded into the radiation curable resin. One of the difficulties associated with this ISPR printing apparatus is accommodating the hollow quartz printing cylinder within the apparatus. The cylinder is typically made of quartz whereas the other components of the printer apparatus especially those associated with driving the rotation of the printing cylinder are manufactured out of metals such as aluminium or steel. During use there are relatively high pressures associated with the printing cylinder and associated components in the printing cylinder housing and this may lead to cylinder damage. A further problem is that the quartz cylinder must be securely engaged within the printing cylinder housing so that during use it does not move or shift in relation to the web passing through the housing and in contact with the cylinder; such movement would be detrimental to registration and therefore image and product quality. A further problem to be addressed with the ISPR printing apparatus of WO94/18609 is to enable the fast and efficient removal and replacement of the printing cylinder during use. Any downtime on the ISPR printing apparatus during use is costly and when part of an in-line process changing of the cylinder in the ISPR printing apparatus may be the rate determining step in restarting the production line. A key challenge therefore is to provide an apparatus that enables the rapid and efficient removal and replacement of the hollow printing cylinder, whilst also ensuring that the cylinder is held robustly in registration to ensure a high quality image and product is produced from the printing process. Typically such hollow cylinders have been bonded to the other components of the printing cylinder housing; this means that the whole housing needs to be removed and replaced when a change of cylinder is required. In other arrangements the cylinders have been retained by a clamping arrangement, located in the printing cylinder housing, which requires contact with the printing surface of the printing cylinder. This arrangement whilst being an improvement over the bonding technique in terms of ease of disassembly and replacement, has the drawbacks that pressure is applied to the printing surface of the cylinder, normally towards the edges, and this may result in damage to the cylinder. In addition the cylinder is driven through friction being applied to the printing surface of the cylinder. The hollow cylinder is one of the most expensive components of the ISPR printing apparatus and avoidance of damage is highly valuable to operators.

[0005] Thus there is a need for ISPR printing equipment based on the use of hollow printing cylinders which enable the rapid removal and replacement of the cylinder whilst ensuring image quality is maintained and the risk to cylinder damage is kept to a minimum.

[0006] The present invention addresses these technical challenges by providing a new design of ISPR printing apparatus that is more robust and flexible compared to the approaches previously considered.

[0007] The invention is based on a new design of printing cylinder station or assembly for hollow printing cylinders that enables rapid and effective assembly and disassembly of the printing cylinder station in-situ in the ISPR printing apparatus. The new design of station comprises two parts having flange surfaces that co-operate with each other to securely hold the hollow printing cylinder in position during use. These two flange components operate in a clamping fashion to engage indirectly with the two ends of the cylinder placing the cylinder into compression in a direction that is parallel wit the axis of the bore of the cylinder. The contact between these two flange components and the ends of the hollow cylinder is indirect but is achieved through the use of two intermediate elastomeric components e.g. o-rings, that are in contact with each of the clamping flange components and the ends of the hollow cylinder. The two flange components, whilst capable of rotational movement in the direction of the web and in the case of at least one flange component in a direction perpendicular to the direction of the web, are retained securely within the printing cylinder station and remain in-situ in the printing cylinder station on normal disassembly. The only components of the printing cylinder station that are removable on normal disassembly are the intermediate elastomeric components and the hollow cylinder itself. In one embodiment both flange components may be moved in a direction perpendicular to the direction of the web and parallel to the axis of the cylinder. At least one of the flange components is annular so that the UV source to be used may be inserted into and removed from the printing cylinder station after it has been assembled and on disassembly.

[0008] Therefore in a first aspect the present invention provides for a printing cylinder assembly for an ISPR printing process that utilizes a hollow printing cylinder having a surface relief microstructure, which assembly comprises a pair of co-operating flange surfaces at least one of which is annular, two elastomeric components for contact with the ends of the hollow cylinder and means for moving at least one of the flange surfaces relative to the other flange surface in a direction parallel to the axis of the bore of the hollow cylinder when located in the assembly, the flanges being capable of putting the hollow cylinder under compression through contact with the elastomeric components, which are in turn in contact with the ends of the hollow cylinder when located in the assembly.

[0009] In one embodiment both of the flange surfaces are annular. In this embodiment the second annular arrangement allows for passage of the UV source through the station from either side and/or for the provision of extraction means to the interior or the hollow cylinder during use. The extraction is desirable to remove ozone which is toxic and which may build up within the bore of the cylinder.

[0010] In a further embodiment one or both flange surfaces may have a driving means associated with them. The driving means is for rotation of the cylinder in situ during the printing process. In a preferred arrangement the driving means is a gear train driven by a motor e.g. an electric motor and one of the flange surfaces has a toothed outer edge for engagement and disengagement with the gear train. The drive means is preferably associated with the flange surface that is restricted for lateral movement within the printing cylinder assembly.

[0011] The means for moving at least one of the flange surfaces relative to the other flange surface in a direction parallel to the axis of the bore of the hollow cylinder may be any suitable means that allows the flange surface to be retained in the assembly but to move in both a rotational and lateral direction. This part of the assembly may be operated pneumatically to force the flange surface laterally into contact with one end of the cylinder and the other end of the cylinder into contact with the opposing flange surface through the elastomeric components. In this part of the assembly the flange surface may be secured against a bearing surface in a housing that is secured to the frame of the printing press but which may be moved perpendicular to the direction of the web towards the other flange surface.

[0012] Each flange surface may also have an additional feature that assists with assembly and disassembly of the printing cylinder assembly. This feature is in the form of projections from the surfaces of each of the flange surfaces, the projections being in a direction towards the opposing flange surface. Ideally the projections are in the form of a continuous band of metal that is proximate too and approximately follows the inner path of the annulus for about a third to one half of the annular circumference. These projections act as a cradle for the cylinder during assembly and disassembly by contacting the printing surfaces towards each end of the cylinder, which aids with the assembly and disassembly of the printing cylinder assembly.

[0013] In one embodiment the elastomeric components are in the form of o-rings. In this embodiment it is preferred that the flange surfaces are engineered to have a circular recess in their surfaces to accommodate the o- ring. The dimensions of the o-rings and the recesses are such that the o-ring will come into uniform contact with the annular ends of the cylinder and will ensure that these ends of the cylinder do not contact the flange surface when the printing cylinder assembly is assembled and the cylinder is under compression. Thus there is no direct contact between the flange surface and the end of the cylinder. When the cylinder is driven this is through the compressive contact with the elastomeric component. In a further embodiment each flange surface is engineered to have an annular lip edge which protrudes from each flange surface towards the opposing flange surface. This annular lip has an inner lip surface defining an inner circumference of the annular lip which is larger than the outer circumference of the surface of the hollow cylinder. In this embodiment the flange surfaces are not used with elastomer components that are in the form of an o-ring but with elastomeric components that are annular and have surfaces that contact the ends of the hollow cylinder the edge of the printing surface of the cylinder, the flange surface and the inner lip surface of the annular lip. This arrangement is preferred to the use of an o-ring as it provides for a more robust contact with the cylinder end and the flange surface ensuring minimum movement of the cylinder within the printing cylinder housing during use. In this arrangement the elastomeric component is in the form of a multi surface gasket.

[0014] The invention will now be illustrated by way of example only with reference to the following drawings in which:

[0015] Figure 1 is a sectional view perpendicular to the direction of rotation of a printing cylinder assembly according to the present invention in the assembled position,

[0016] Figure 2 is a plan view of a annular flange surface of Figure 1 ,

[0017] Figure 3 is a sectional view perpendicular to the direction of rotation of a further embodiment of a printing cylinder assembly according to the present invention in the assembled position, and [0018] Figure 4 a is a plan view of a annular flange surface of Figure 3 and Figure 4 b is a plan view of the elastomeric gasket of Figure 3.

[0019] Referring to the Figure 1 the printing cylinder assembly (1) in the assembled state consists of a hollow quartz cylinder (2) that is held under compression between two annular flange surfaces (3) and (4). Each annular flange surface has a recess (5) and (6) which engages with o-rings (7) and (8). The hollow cylinder (2) has a surface relief microstructure (9) adhered to its printing surface (10). In this embodiment annular flange surface (3) is able to rotate about axis X but is unable to move in a lateral direction along axis X. Annular flange surface (4) is also able to rotate about axis X but is also able to be moved along axis X as indicated by arrow Y. In this assembled state annular flange surface (4), which is movable along axis X in direction Y is held in position by a movable housing (not shown) and is being forced along axis X by suitable means e.g. pneumatic pressure (not shown) against o-ring (7) which is turn is in contact with the annular end (11) of the cylinder (2). The opposing annular end (12) of the cylinder (2) is being forced in contact with o-ring (8) which in turn is in forced contact with annular flange surface (3), which is held in position within the housing (13). Thus it can be seen that the whole assembly is under compressive load along axis X.

[0020] Referring to the Figure 2 the annular flange surface assembly (20) has a flange surface (21) in which is located a recess (22) for the o-ring (not shown).

[0021] Referring to the Figure 3 the printing cylinder assembly (30) in the assembled state consists of a hollow quartz cylinder (31) that is held under compression between two annular flange surfaces (32) and (33). Each annular flange surface has an annular lip edge (34) and (35) which engages with elastomeric gaskets (36) and (37) of L shaped cross-section. The elastomeric gaskets (36) and (37) also engage with flange surfaces (32) and (33) and the ends (40) and (41) of the cylinder (31). The hollow cylinder (31) has a surface relief microstructure (38) adhered to its printing surface (39). In this embodiment annular flange surface (33) is able to rotate about axis X but is unable to move in a lateral direction Y along axis X. Annular flange surface (32) is also able to rotate about axis X but is also able to be moved along axis X as indicated by arrow Y. In this assembled state annular flange surface (32), which is movable along axis X in direction Y is being held in a movable housing (not shown) and is being forced along axis X by suitable means e.g. pneumatic pressure (not shown) against elastomeric gasket (36) and the gasket is also in contact with annular lip edge (35), the elastomeric gasket is in contact with the annular end (41 ) of the cylinder (31 ). The opposing annular end (40) of the cylinder (31) is being forced in contact with elastomeric gasket (37) which in turn is in forced contact with annular flange surface (33) and annular lip edge (34), the annular flange surface is held in position within the housing (42). Thus it can be seen that the whole assembly is under compressive load along axis X.

[0022] Referring to the Figure 4a the annular flange surface assembly

(50) has a flange surface (51) and an annular lip edge (52). In Figure 4b the elastomeric gasket (53) has a surface (54) which contacts with the end of a hollow cylinder and a lip edge (55) which passes over the end of the hollow cylinder to contact the printing surface of the cylinder.

Claims

1. A printing cylinder assembly for an ISPR printing process that utilizes a hollow printing cylinder having a surface relief microstructure, which assembly comprises a pair of co-operating flange surfaces at least one of which is annular, two elastomeric components for contact with the ends of the hollow cylinder and means for moving at least one of the flange surfaces relative to the other flange surface in a direction parallel to the axis of the bore of the hollow cylinder, when located in the assembly, the flanges being capable of putting the hollow cylinder under compression through contact with the elastomeric components, which are in turn in contact with the ends of the hollow cylinder when located in the assembly.

2. A printing cylinder assembly for an ISPR printing process as claimed in claim 1 wherein both the flange surfaces are annular.

3. A printing cylinder assembly for an ISPR printing process as claimed in either claim 1 or claim 2 wherein the elastomeric component is an o-ring.

4. A printing cylinder assembly for an ISPR printing process as claimed in claim 3 wherein the annular flange surfaces comprise a recess for the o- ring.

5. A printing cylinder assembly for an ISPR printing process as claimed in any one of the preceding claims wherein the annular flange surface further comprises an annular lip edge.

6. A printing cylinder assembly for an ISPR printing process as claimed in claim 1 , 2 or 5 wherein the elastomeric component is an elastomeric gasket.

7. A printing cylinder assembly for an ISPR printing process as claimed in claim 6 wherein the gasket is of L shaped cross-section and is capable of contacting both the end and printing surface of the hollow cylinder when the assembly is in the assembled state.

8. A printing cylinder assembly for an ISPR printing process as claimed in claim 7 wherein the gasket is capable of contacting the annular lip edge of the annular flange surface when present and when the assembly is in the assembled state.

9. A printing cylinder assembly for an ISPR printing process as claimed in any one of the preceding claims which further comprises a source of UV radiation located within the bore of the hollow cylinder when the assembly is in the assembled state.

10. An ISPR printing process that utilizes a printing cylinder assembly according to any one of the preceding claims.

11. An ISPR printer incorporating a printing cylinder assembly according to any one of claims 1 to 9.

12. A hollow transparent cylinder having a surface relief microstructure and being adapted to be incorporated into a printing cylinder assembly according to any one of claims 1 to 9.