Abstract:
Disclosed is a method for producing substantially seamless, circumferentially closed flexible embossing or printing tapes ( 2 ), wherein a free-flow material is fed into an annular mold space ( 14 ) defining the profile of the tape ( 2 ), said mold ( 1 ) comprising an external sidewall ( 6 ), delimiting the external radial extent of an annular space ( 14 ), and a core ( 12 ), delimiting the internal radial extent of the annular space ( 14 ). A device for carrying out such a method is also disclosed.

Description:
FIELD OF THE INVENTION 
     The invention relates to a method and a device for the manufacture of substantially seamless, flexible circumferentially closed embossing or printing tapes, as well as an embossing tape. 
     BACKGROUND OF THE INVENTION 
     The term “printing or embossing tape” as referred to herein will be understood to mean a tape having a surface structure formed on its surface for printing or embossing. Such surface structure may for example be a micro or nano scale structure. 
     For embossing or printing a replication/transfer tool having microsurface or nanosurface structures may typically be formed on a rigid surface such as a cylinder, with the structures having a negative imprint of the desired final pattern. The pattern is then used to either transfer an ink or to replicate a structure on a substrate. For example, WO2008/024947A2 discloses a method and apparatus for fabricating durable replication tools. 
     There is a desire to provide such surface structures on a flexible tape which may then be mounted on rollers to print or emboss a surface, particularly if said surface is non-planar, irregular or flexible such that printing or embossing with a rigid cylinder may be difficult. 
     Thus, an object of embodiments of the invention is to create a method and a device for the manufacture, substantially seamless, circumferentially closed flexible embossing or printing tapes. Furthermore, it is an object of embodiments of the invention to create a substantially seamless, circumferentially closed flexible embossing or printing tape. 
     The term “substantially seamless” as referred to herein will be understood to mean a tape which is manufactured in a single step without the need for a separate joining process. Substantially seamless tapes may include both tapes which are entirely seamless (i.e. no discontinuity is detectable or visible) and tapes which have a limited discontinuity (for example as a result of a joint in the mould with which the tape is formed) It will be appreciated that an embossing or printing tape as referred to herein may alternatively be referred to in the art as a belt, form or tool. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention there is provided, a method for the manufacture of substantially seamless, circumferentially closed flexible embossing or printing tapes, comprising the steps:
         providing a mould space defining the profile of the tape, said mould comprising an external sidewall, delimiting the external radial extent of an annular space, and a core, delimiting the internal radial extent of the annular space;   face-end introduction of a free-flow material into the annular space;   curing of the free-flow material; and   demoulding of the cured material.       

     The external side wall may comprise a plurality of side elements. The step of demoulding may comprises the steps of: outwardly radially displacing the side elements away from the core to open said annular space; and removing the tape from the core. 
     The step of providing a negative mould may further comprise the step of: providing an insert mould onto one of the walls delimiting the annular space, the insert mould defining a surface relief pattern to be formed on the tape. The insert mould may be provided as a circumferential sleeve around the core. In some arrangements an insert mould may be provided on both walls of the annular space (one or both of which may be provided with a surface relief pattern). 
     The free-flow material may be introduced, sucked into or injected into the annular space by means of capillary action. The free flow material may, for example, be drawn into the annular space under a vacuum. 
     The free-flow material may be cured by means of light radiation, such as UV, or heat radiation. Alternatively, the free flow material may be cured by a chemical reaction. For example, the free flow material may be mixed with a curing agent before or during flow into the annular space. The free flow material may be a silicon polymer. 
     At least one body surface may be textured, in that the free-flow material is conducted past an insert mould of the texture to be depicted. 
     According to a further aspect of the invention there is provided, a device for producing seamless, circumferentially closed flexible embossing or printing tapes, the device comprising:
         a multi-part housing comprising a side wall for delimiting the radially external extent of an annular space, a bottom wall and a lid wall for delimiting the respective face-ends of the annular space;   a core for the radially internal delimiting of the annular space;   an inlet for introducing a free-flow material; and   a vent for ventilating the annular space.       

     The inlet may be formed on the bottom wall side and may, for example, comprise a plurality of inlet openings, which in the assembled state lead into the annular space at the face end. 
     The vent may be provided on the lid wall side and may, for example, comprise a plurality of outlet openings, which in the assembled state extend out of the annular space at the face end. 
     A vacuum pump may be provided for connection to the vent for evacuating the annular space. 
     The side wall may be designed in multiple parts with a plurality of side elements. The side elements may comprise a plurality of circumferential segments. The side elements may be are arranged so as to be outwardly radially displaceable to enable the annular space to be opened. It is advantageous to be able to open the annular space by radial movement of the side elements since there pressure, adhesion and or friction between the cured material and the side elements acts to strongly resist and sliding motion between the mould parts. Additionally, when moulding a tape having micro or nano structural features it may not be possible to utilise a release coat since it might fill features of the mould. In some embodiments of the invention, therefore, a release coat may be provided on only the blank or unstructured wall of the mould. 
     For example, the side elements may be outwardly rotatable. The side wall may comprise two halves joined at a fixed pivot (for example in a clamshell type arrangement). The halves may or may not be equal. A half may comprise a plurality of side elements. For example the side wall may comprise two halves each comprising two side elements. Each adjacent side element in a single half may be pivotally engaged. Advantageously, this arrangement may enable a compound rotation of at least some of the segments (i.e. a rotation of the half about its fixed pivot and a rotation of the adjacent segment about the pivot between adjacent side elements) to maximise the space between the side wall and core in the open position. The adjacent side elements may be self-centring to each other. Adjacent side elements seen in circumferential direction may be arranged to make possible a mutual tolerance offset. 
     A seal may be provided between adjacent side elements. The seal may for example comprise an inflatable seal (which may be an inflatable elastomer seal). 
     An insert mould may be provided introducing a texture in a body surface. The insert mould will typically be a positive surface structured insert mould which creates a negative on the tool or tape (which in turn is used to create positive on the final substrate). The insert mould may be flexible. In the assembled state, the insert mould may close longitudinal gaps between the side elements or core. For example, the insert mould may cover discontinuities which could for example be the result of the joining of outer wall segments, magnets provided in the walls or moveable sections of the core. 
     The insert mould may be provided on either the side wall or the core. The insert mould may be a sheet or may be pre formed into a cylindrical insert. The insert mould may be magnetic and one of the side wall or the core may be provided with plurality of magnets. For example the insert mould may be formed of a metallic sheet, for example a nickel alloy sheet. 
     The core may have multiple parts. Alternatively, or additionally, the core may be provided with an expandable diameter. For example the core may be mechanically or pneumatically expandable. The core may comprise at least one circumferential segment which is radially displaceable. The core may comprise a plurality of displaceable segments, for example opposing segments. The plurality of segments may be arranged to expand equally to provide an even change of diameter across the core. The core may be radiation-permeable, for example to UV-radiation. The device may further comprise a curing device, such as a UV-radiation source or a heater. The curing device may be positioned in the core. 
     The invention includes an embossing or printing tape produced according to a method according to an embodiment of invention or with a device according to an embodiment of the invention. 
     Whilst the invention has been described above, it extends to any inventive combination set out above or in the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, preferred exemplary embodiments of the invention are explained in more detail by means of schematic representations, in which: 
         FIG. 1  is a perspective representation of a casting mould of a device according to an embodiment of the invention; 
         FIG. 2  is an embossing tape according to an embodiment of invention; 
         FIG. 3  is a horizontal section through the casting mould of  FIG. 1 ; 
         FIG. 4  is a detail from  FIG. 3 ; 
         FIG. 5  is a section of a insert mould of the device; 
         FIG. 6  is a positioning of the insert mould in the casting mould; 
         FIG. 7  is a lateral view of the casting mould; 
         FIG. 8  is a side element of a side wall; 
         FIG. 9  is a bottom wall of the casting mould; 
         FIG. 10  is a lid wall of the casting mould; 
         FIG. 11  is a 3-dimensional view of a casting mould of a device according to an alternate embodiment of the invention; 
         FIG. 12  is a partial plan view of the mould of  FIG. 11  with the exterior wall in an open position; 
         FIG. 13  is a plan view of the mould of  FIG. 11  with the exterior wall in a closed position; 
         FIG. 14  is a cross section of the assembled mould of  FIG. 11 ; and 
         FIG. 15  is an expandable core for use in embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  shows a casting mould  1  of a device according to an embodiment the invention for producing an embossing tape  2  shown in  FIG. 2 . The embossing tape  2  is a seamless circumferentially closed flexible body with an external texture. In use, the embossing tape  2  rotates for example about rollers and is simultaneously moved over a surface to be embossed so that a counter-texture of the texture is depicted in the surface. The texture has for example a plurality of tooth-like elevations  4  arranged in transverse direction. The overall thickness of the embossing tape  2  is for example 3 mm. The elevations  4  per se are for example 45 μm high and spaced from one another at a spacing of 90 μm. 
     As shown in the  FIGS. 1, 3 and 4 , the casting mould  1  has a multi-part housing with a side wall  6 , a bottom wall  8 , a lid wall  10  and a core  12 . The core  12  is arranged in the housing and with the side wall  6  delimits an annular space  14 . The annular space  14  serves for the receiving of a free-flow product for forming the embossing tape  2 . At the face end, the annular space  14  is delimited by the floor wall  8  and by the lid wall  10 . 
     For introducing the external texture in the embossing tape  2  the casting mould has an insert mould  16  having a textured or partially textured surface as shown in sections in  FIG. 5 . The insert mould  16  is magnetic and flexibly designed in such a manner that it can be rolled about the vertical axis of the casting mould  1 . It is more preferably sheet-metal like. It has an elevation-free external surface  18  and a textured internal surface  20 , in which depressions  22  are formed in such a manner that the elevations  4  are formed as positive (or negative) moulds. As shown in  FIG. 6 , the insert mould  16  with its external surface  18  in the assembled state is in contact with the side wall  6  and thus delimits the annular space  14  radially outside. The insert mould  16  has for example a wall thickness of 0.25 mm. The depressions  22  have an extension corresponding to the elevations  4  and thus a depth of 45 μm in the shown exemplary embodiment. Its lateral spacing is in accordance with the lateral spacing of the elevations  4  and thus 90 μm. The orientation of the depressions  22  and their shape depends on the texture to be depicted. For arrangement in the annular space  14 , the latter has a radial extension corresponding to the sum of the insert mould  16  and the overall thickness of the embossing tape  2 . In the shown exemplary embodiment the annular space  14  thus has a width of 3.25 mm prior to the insertion of the insert mould  16 . Following the insertion, the annular space  14  has a width of 3 mm and thus a width corresponding to the embossing tape  2 . 
     As already shown in  FIG. 3  and numbered as in  FIG. 7 , the side wall  6  is designed in multiple parts with at least two side elements  24 . At their longitudinal sides, the side elements  24  can be releasably connected to one another via closure elements. In particular, the closure elements  26  make possible a mutual tolerance offset in circumferential direction of the side elements  24 . For the self-centring of the side elements  24 , their longitudinal sides can be provided with a V-protrusion  28  or with a V-groove  30  for receiving the respective V-protrusion  28 . According to the representation in  FIG. 8 , a plurality of magnets  32  is arranged in the side elements  24  for the temporary fixing of the insert mould  16 , which can be embodied both as permanent magnets as well as electromagnets. Alternatively or additionally magnets may be provided on the wall core support cylinder such that an insert mould may be provided on either or both of the radial surfaces of the annular mould space. 
     As shown in  FIG. 9 , the bottom wall  8  has an annular standing surface for the positioning of the side wall  6 . In addition, it comprises an integrated inlet for introducing the free-flow material. The inlet has a central bore  34 , radial channels  36  and an inlet opening ring  38 . The channels  36  extend between the bore  34  and the inlet opening ring  38 , which in the assembled state is arranged on the face end of the annular space  14  and which has a plurality of inlet openings. 
     The lid wall  10 , as shown in  FIG. 10 , has a vent with a plurality of annularly arranged outlet openings  40 , which are arranged in such a manner that in the assembled state these are located at the face end of the annular space  14  so that the latter can be ventilated. The vent can lead into the outside surroundings so that the annular space  14  is pressure-relieved or can be connected for example with a vacuum pump of the device for subjecting the annular space  14  to a vacuum. 
     The core  12  is a cylindrical body having an elevation-free circumferential surface  42  (see  FIG. 4 ). It can consist of a translucent material, more preferably a UV-permeable material. In particular, it is not magnetic. For simplifying a demoulding the core  12  can be designed in multiple parts. 
     For curing the free-flow material a curing device such as a UV-radiation source or a heater can be integrated in the casting mould  1 . The UV-radiation source is more preferably positioned in the casting mould  1  in the core  12 . 
     In the following, a preferred method for the manufacture of the embossing tape  2  shown in  FIG. 2  is explained. The casting mould  1  is assembled, wherein the insert mould  16  is fixed on the side elements  24  by means of the magnets in such a manner that their structural internal surface  20  delimits the annular space  14  radially outside. Longitudinal gaps between the side elements  24  are covered by the insert mould  24 , thus closing these. Radially inside, the annular space  14  is delimited by the circumferential surface of the core  12 . The vent is connected to a vacuum pump and the annular space  14  is evacuated. Following the evacuation, the inlet tied to an inflow device is opened and the free-flow material is sucked into the annular space  14  at the face end via the inlet openings on the bottom. The free-flow material is sucked in the direction of the lid-sided vent until the annular space  14  is completely filled with the free-flow material. In the process, it enters into the depressions  22 . After the filling, the material starts to cure. This can take place automatically, for example by using a material on two-component bases or with the help of the curing device. Following the curing, the casting mould  1  is disassembled and the embossing tape  2  demoulded. Externally, the embossing tape  2  is now provided with a texture having a plurality of elevations  4 . 
     Obviously, the device can also be used for introducing a texture in the embossing tape  2  on the inside. To this end, the insert mould is fixed about the core  12 . For example, this can also take place through magnetism, but in suitable magnets will then have to be integrated in the core  12 . Alternatively, the embossing tape  2  following the demoulding can be turned or inverted such that the texture is arranged on the inside. Obviously, the embossing tape  2  can also be provided with a texture each on the inside and outside. 
     It is also noteworthy that the free-flow material can also be injected into the annular space  14  or flow into the annular space  14  by means of capillary action. 
     A casting mould  101  according to an alternate embodiment is shown in  FIGS. 11-14 . In this embodiment the mould  101  is provided on a support table  103 . The mould comprises a core  112  which is generally held in a fixed position on the table  103 . The core may be metallic and may in some cases be provided with magnets for retaining an insert mould (this embodiment is generally intended for use in moulding an internal texture, although the skilled person will appreciate that this can easily be reversed). 
     In this embodiment, the side wall  116  comprises four side elements  124   a ,  124   b ,  124   c ,  124   d . Each element is formed of a quarter circumference segment. A fixed pivot shaft  150  is provided at the rear of the table  103  to which the adjacent, rear, side elements  124   b ,  124   d  are attached. The remaining, front, side elements  124   a ,  124   c  are pivotally attached to the rear side elements  124   b ,  124   d  by hinges  152   a  and  152   b  respectively. As such the side elements pairs  124   a ,  124   b  and  124   c ,  124   d  form a clamshell arrangement rotatable about the pivot  150  between an open position (as shown in  FIGS. 11 and 13 ) and a closed position (as shown in  FIG. 12 ). Additionally the front side elements  124   a ,  124   c  are able to rotate relative to the respective rear side elements  124   b ,  124   d  about the hinges  152   a ,  152   b . As such it will be noted that the front doors may be rotated radially outward in a compound motion so as to maximise the opening of the annular space. Bolts  127  and closure elements  124  are provided for clamping the side elements in the closed position so as to define the annular space between the outer surface of the core  112  and the inner surface of the elements  124 . 
     The hinges  150 ,  154   a ,  154   b  between adjacent side elements  124  are provided radially outside of the side wall and the adjacent side elements have sealing surfaces which are arranged to provide a flush mating surfaces. One of the adjacent sealing surfaces may be provided with a resilient seal  154  (which may be held in a recessed seal seat). It is particularly important that a strong seal is formed between the surfaces when vacuum forming a flexible tape since any ingress of air from outside of the casting mould may result in bubbles, voids or other imperfections in the tape. As such, elastomer inflatable seals are preferably provided between the side elements. One such commercially available seal which would be suitable for use in embodiments of the invention is the Cefilair® range of pneumatic seals from Garlock Sealing Technologies. As shown in  FIG. 14 , O-ring seals are preferred for sealing between the bottom wall  108  and lid  110 . A pair of O-rings  160   a ,  160   b  and  162   a ,  162   b  are provided respectively at both the bottom wall  108  and the lid  110  so as to seal either side of the annular space  114 . 
     While an inset mould may be provided as a sheet  16  (for example a nickel shim) as described above it may be desirable to use a nickel shim which has been formed into a cylindrical sleeve. For example, the insert mould  16  may be formed from as a sleeve by rolling and welding the ends. An advantage of such sheets is that any discontinuities which would form a seam effect in the final tape may be further reduced. However, in order to keep its shape and dimensions such cylindrical sleeve inserts must be fixed very precisely to the core. As such, an expandable core  112  as shown in  FIG. 15 , may be provided. The expandable core is provided with at least one circumferential section  113   a  which is radially moveable between a retracted and expanded position (in the direction shown by arrow A). In some embodiments multiple sections, for example opposing sections, may be radially expandable. For example four expandable sections may be provided, in radially opposing pairs. In order to maintain the shape tolerance of the annular mould space  114  the segments should be arranged to expand equally. To provide for accurate fixing of the mould to the core  112  a further portion  113   b  of the circumference of the core  112  is fixed. The expandable section of the core provides sufficient clearance in its retracted position to enable a sleeve to be slid over the core. Once in position pneumatic air is pumped into the core to radially expand portion  113   a  and retain the insert mould sleeve in position. 
     Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims. 
     It will be appreciated that the printing or embossing belt of the invention may be utilised in, for example: UV Casting/UV Embossing of nano and microstructures on to rigid or flexible substrates, for Optical and function surfaces; in the printing (print and coating) industry as a means of transferring inks or coatings from the flexible form/matrix to a flexible or rigid substrate similar to roller or plate related print technologies (and in particular for flexo-graphic, roto-gravure, off set and digital off set) or where the ink is first transferred to the flexible belt (in place of a conventional roller) and then printed on to or transferred on to the intended substrate material; Printed electronics, utilising the same technologies as printing but with the use of metallic or conductive inks and coatings. 
     The skilled person will appreciate that in some embodiments the insert mould may not be required and rather the detailed surface structure may be formed directly upon the surface of the core or external wall defining the annular space. In particular, such an arrangement may be preferred where there is a need for the final tape to be entirely seamless (particularly if the tolerance is to the micro or nano scale) since an insert sleeve will typically provide seam effects where the ends of the insert are overlapped or joined. However, this significantly increases the cost of replacing the mould (for example if it is damaged or if it needs to be modified) and as such insert moulds are generally preferred in the embodiments of the invention described above. 
     Flexible belts in accordance with embodiments of the invention are typically formed from silicone polymers, for example PolyDimethylsiloxane (PDMS). It will be appreciated that Silicone polymers have a backbone of alternating silicon and oxygen atoms, that is they are polysiloxanes. The simplest Simplest is polydimethyl siloxane (side groups from Silicon of two methyls) but is a liquid and is formed as a solid using, for example, cross bridges. Silicone resins have many such branched structures. 
     Such polymers may typically be used in a two part formulation of a highly viscous liquid silicone elastomer and curing agent. However, the skilled person will appreciate that other polymers may be used without departing from the scope of the invention, for example PET, PMMA, PVC. The material chosen will generally depend upon the particular application (for example, the required thickness of the tape or the required wear resistance).