Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C59/00—Surface shaping of articles, e.g. embossing; Apparatus therefor
  • B29C59/02—Surface shaping of articles, e.g. embossing; Apparatus therefor by mechanical means, e.g. pressing
  • B29C59/04—Surface shaping of articles, e.g. embossing; Apparatus therefor by mechanical means, e.g. pressing using rollers or endless belts
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C59/00—Surface shaping of articles, e.g. embossing; Apparatus therefor
  • B29C59/02—Surface shaping of articles, e.g. embossing; Apparatus therefor by mechanical means, e.g. pressing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C59/00—Surface shaping of articles, e.g. embossing; Apparatus therefor
  • B29C59/02—Surface shaping of articles, e.g. embossing; Apparatus therefor by mechanical means, e.g. pressing
  • B29C59/04—Surface shaping of articles, e.g. embossing; Apparatus therefor by mechanical means, e.g. pressing using rollers or endless belts
  • B29C59/046—Surface shaping of articles, e.g. embossing; Apparatus therefor by mechanical means, e.g. pressing using rollers or endless belts for layered or coated substantially flat surfaces
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
  • B29D11/00—Producing optical elements, e.g. lenses or prisms
  • B29D11/00009—Production of simple or compound lenses
  • B29D11/00278—Lenticular sheets
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
  • B29D11/00—Producing optical elements, e.g. lenses or prisms
  • B29D11/00009—Production of simple or compound lenses
  • B29D11/00365—Production of microlenses
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
  • B29D7/00—Producing flat articles, e.g. films or sheets
  • B29D7/01—Films or sheets
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/40—Manufacture
  • B42D25/405—Marking
  • B42D25/425—Marking by deformation, e.g. embossing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
  • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
  • B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
  • B29C35/0805—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation
  • B29C2035/0822—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation using IR radiation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
  • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
  • B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
  • B29C35/0805—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation
  • B29C2035/0827—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation using UV radiation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C59/00—Surface shaping of articles, e.g. embossing; Apparatus therefor
  • B29C59/02—Surface shaping of articles, e.g. embossing; Apparatus therefor by mechanical means, e.g. pressing
  • B29C59/022—Surface shaping of articles, e.g. embossing; Apparatus therefor by mechanical means, e.g. pressing characterised by the disposition or the configuration, e.g. dimensions, of the embossments or the shaping tools therefor
  • B29C2059/023—Microembossing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
  • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C59/00—Surface shaping of articles, e.g. embossing; Apparatus therefor
  • B29C59/02—Surface shaping of articles, e.g. embossing; Apparatus therefor by mechanical means, e.g. pressing
  • B29C59/026—Surface shaping of articles, e.g. embossing; Apparatus therefor by mechanical means, e.g. pressing of layered or coated substantially flat surfaces

Definitions

• the invention relates to methods and apparatus for forming non-diffractive light control structures such as focusing lenses in or on a surface of a polymer substrate, for example arrays of microlenses used in the construction of optical devices such as moire magnifiers and the like.
• the invention can be used for security devices for securing documents and articles of value such as banknotes, cheques, passports, identity cards, certificates of authenticity, fiscal stamps and other secure documents.
• Another optical device is a so-called "lenticular" device formed by an array of elongate focusing lenses having widths of up to a few hundred microns located over a corresponding array of image strips. The optical effect is observed by viewing the combined device at different rotational angles so that different combinations of image strips are viewed at the different angles.
• Examples of known lenticular devices can be found in US-A-4892336, WO-A-03/052680, US- A-4402150 and WO-A-201 1/051668.
• optical devices incorporating arrays of microlenses are described in WO-A-2006/125224.
• One of the reasons why these devices make good security devices is the difficulty of fabricating lens arrays, particularly microlens arrays.
• the microlenses are formed on a security thread for incorporation in a paper substrate using a UV cast curing technique although other options have been disclosed such as extrusion embossing, injection moulding and the like. These techniques generally involve the provision of an additional material on the surface of the substrate which can be formed with the lenses.
• a method of manufacturing a security document comprising non-diffractive light control structures in a surface of a polymer substrate of the security document comprises thermally embossing non-diffractive light control forms into the surface of the substrate while the substrate is at a temperature at which the surface can be deformed; chilling the embossed substrate; and, before, during or after either of the steps of thermally embossing and chilling, coating at least partially one or both surfaces of the substrate with a, preferably opaque, coating layer such that at least the non-diffractive light control structures are uncoated.
• apparatus for manufacturing a security document comprising non-diffractive light control structures in a surface of a polymer substrate comprises:
• an embossing die carrying embossing forms corresponding to the light control structures and which, at an embossing location, engages the surface of the polymer in use to emboss the non-diffractive light control structures into the surface;
• a heating system for heating the polymer substrate, in the vicinity of the embossing die, to a temperature at which the surface can be deformed; chilling apparatus to chill the embossed substrate; and a coating system to coat at least partially one or both surfaces of the substrate with a, preferably opaque, coating layer such that at least the non- diffractive light control structures are uncoated.
• the chilling process could be carried out in a variety of ways, for example by spraying a cold fluid such as water onto the embossed polymer, passing the polymer through a chilled atmosphere or the like but in the preferred case, the chilling apparatus comprises at least one chilling roller which engages the embossed substrate.
• the chilling apparatus comprises at least one chilling roller which engages the embossed substrate.
• a plurality of chilling rollers are provided in sequence. Each could be maintained at the same temperature or each chilling roller downstream of the first being maintained at a lower temperature than the preceding chilling roller. In the latter case, the chilling process is carried out in a sequence of sub-steps in which the substrate is chilled to successively lower temperatures.
• the chilling process could be carried out after the substrate has been separated from the embossing die or while it remains in contact with the embossing die.
• the embossing process is carried out by passing the polymer substrate through a nip between an embossing die and an impression roller, wherein at least part of the chilling process is performed by the impression roller.
• the polymer substrate can be held under tension against the embossing die with sufficient force that the light control structures are embossed into it.
• the apparatus further comprises a pressure roller forming a nip with the embossing die through which the substrate is fed. This increases the pressure with which the polymer substrate is urged against the embossing die.
• one or both of the embossing die and pressure roller, if provided, are heated whereby heat is transferred to the substrate.
• the temperature to which the polymer substrate must be raised to enable it to be deformed will depend upon the material of the substrate.
• Typical polymer materials include polypropylene (PP) (most preferably bi-axially oriented PP (BOPP)), polyethylene terephthalate (PET), polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), nylon, acrylic, Cyclic Olefin Polymer (COP) or Cyclic Olefin Copolymer (COC), or any combination thereof.
• PP polypropylene
• BOPP bi-axially oriented PP
• PET polyethylene terephthalate
• PE polyethylene
• PC polycarbonate
• PVC polyvinyl chloride
• nylon acrylic, Cyclic Olefin Polymer (COP) or Cyclic Olefin Copolymer (COC), or any combination thereof.
• COP Cyclic Olefin Polymer
• COC Cyclic Olefin Copolymer
• a temperature at which deformation is possible at a certain pressure can be ascertained using the Vicat softening point test using the ASTM D 1525 and ISO 306 standards.
• the Vicat softening point is taken as the temperature at which the specimen is penetrated to a depth of 1 mm by a flat-ended needle with a 1 mm 2 circular or square cross- section.
• a heating rate of 50°C/hr is used with a loading rate of 50N.
• apparatus for forming non-diffractive light control structures in the surface of a polymer substrate comprises:
• an embossing die roller carrying embossing forms corresponding to the non-diffractive light control structures and which, at an embossing location, engages the surface of the polymer in use to emboss non-diffractive light control structures into the surface;
• a pressure roller defining a gap with the embossing die roller through which the polymer substrate passes in use as the rollers rotate;
• a heating system for heating the polymer substrate, in the vicinity of the embossing die roller, to a temperature at which the surface can be deformed, wherein the embossing forms are provided on radially outwardly projecting pedestals of the embossing die roller whereby each pedestal forms a respective nip with the pressure roller as the rollers rotate thereby causing non- diffractive light control structures to be embossed into the surface of the polymer substrate.
• This third aspect provides another approach to solving the problem outlined above which is to increase the embossing pressure as compared to that experienced with a conventional embossing die roller without raised pedestals.
• Increasing the embossing pressure enables a reducing embossing temperature. That in turn means that the risk of shrinkage and warping after embossing is also lowered.
• the increase in pressure is achieved by utilizing pedestal forms on the embossing die roller so that as each pedestal form engages the polymer material at the nip, there will be an increase in pressure compared with the pressure involved with a conventional embossing die roller having a generally constant radius.
• the pedestals will project beyond the circumference of the embossing die roller by between 3 and 5pm.
• a further advantage of this aspect of the invention is that the modified embossing die roller with pedestals can be installed into a conventional embossing machine and provide much higher pressures at the nip without the need for adjusting the process conditions of the machine.
• the embossing roller carries a plurality of radially outwardly projecting pedestals.
• each pedestal is provided with a plurality of embossing forms.
• each pedestal may emboss a region or sub-region of lenses or other non-diffractive light control structures.
• each pedestal comprises a two-dimensional array of embossing forms that correspond to a two-dimensional array of embossed non-diffractive light control structures.
• a method of forming non-diffractive light control structures comprises:
• thermoplastic, curable coating providing a polymer substrate with a thermoplastic, curable coating
• curing will depend upon the nature of the coating but typically is one of UV, IR and thermal curing. It will be appreciated here that curing is a chemical process which involves the formation of cross-links between polymer chains to increase the hardness or toughness of the coating material.
• the method includes the step of thermally embossing non-diffractive light control structures into the thermoplastic, curable coating while the coating is at a temperature at which it can be plastically deformed.
• the curable coating is heated beyond its glass transition temperature at the point of embossing such that it may be plastically deformed.
• the curing may occur while the curable coating is in contact with any embossing structure, or, because it has been plastically deformed, it may be removed from the embossing structure before curing to harden and fix the embossed structure in its surface.
• the curable coating is a thermoplastic that is preferably solid, dry and non-tacky before embossing to aid handling. This is in contrast to, for example, cast-cure processes, in which a material is in a liquid state prior to its curing.
• a method of forming non-diffractive light control structures in a first surface of a polymer substrate comprises:
• a (typically non-fibrous) polymer substrate having either a skin region of the substrate at the first surface of the substrate comprising a radiation absorbing material, or a radiation absorbing material affixed to the first surface of the polymer substrate;
• the radiation absorbing material absorbs the radiation and heats up the first surface of the polymer substrate to a temperature at which the surface can be locally deformed
• thermal embossing non-diffractive light control structures into the first surface of the substrate
• the amount of the substrate which is caused to be deformable is restricted to a region near the surface thereby avoiding elastic and/or plastic deformation of the bulk of the polymer substrate.
• This is achieved by providing a radiation absorbing material on the surface of the polymer substrate to absorb radiation and thus heat up so as to heat the adjacent surface of the polymer substrate.
• a typical radiation absorbing material will comprise a polymer in which is provided a radiation absorbing additive.
• a typical example comprises:
• a radiation e.g. infrared, absorber
• a polymeric binder a polymeric solution or a monomer formulation which can be converted to a polymer layer on the exposure of heat or UV or both.
• the polymeric binder layer usually consists of substantially linear chains specially those of low T g ( ⁇ 100C). Monofunctional acrylic precursors are specially suited for this.
• Typical Infrared absorbers can be:
• a preferred infrared absorber is an infrared dye due to the narrower absorption spectrum
• infrared dyes examples are:
• Suitable inorganic infrared pigments include:
• Suitable inorganic infrared pigments can also be carbon blacks including:
• Typical concentrations of additive are 0.01 to 2.0 g/m 2 , more preferably in an amount of 0.1 to 1 g/m 2 .
• radiation absorbing materials transparent to optical wavelengths are preferred.
• the radiation absorbing materials are transparent to at least some wavelength(s) in the visible spectrum, preferably transparent across the entire visible spectrum.
• a method of forming non-diffractive light control structures in or on the surface of a transparent or translucent polymer substrate comprises: (i) embossing, under predetermined conditions, non-diffractive light control structures into the surface of the substrate or into a material provided on the surface of the substrate;
• non-diffractive light control structures are focussing elements.
• apparatus for forming non-diffractive light control structures in or on a surface of a polymer substrate comprises:
• an embossing die carrying embossing forms corresponding to the non- diffractive light control structures and which, at an embossing location, engages the surface of the polymer in use to emboss non-diffractive light control structures into the surface;
• apparatus for forming non-diffractive light control structures in or on a surface of a polymer substrate comprises:
• an embossing die carrying embossing forms corresponding to the non- diffractive light control structures and which, at an embossing location, engages the surface of the polymer in use to emboss non-diffractive light control structures into the surface;
• a detector such as a camera, for detecting the optical effect resulting from viewing the or each indicia in conjunction with, for example through, the light control structures;
• a system for generating a feedback signal based on the detected optical effect and using the feedback signal to change the predetermined embossing conditions based on the feedback signal a system for generating a feedback signal based on the detected optical effect and using the feedback signal to change the predetermined embossing conditions based on the feedback signal.
• indicia can be provided on the opposite surface of the substrate itself or the substrate can be located over indicia on another surface. Alternatively, the indicia may be provided on one or more rollers for conveying the substrate.
• the non-diffractive light control structures are focussing elements, such as lenses.
• determining the resultant optical effect is not satisfactory typically comprises determining whether or not the indicia are in focus.
• Other means of determining the resultant optical effect could comprise identifying other optical effects such as a moire magnified effect, integral image and the like.
• one or more of the predetermined conditions can be changed and these predetermined conditions can include embossing temperature, embossing pressure, and/or the tension under which the substrate is held during the embossing process.
• non-diffractive light control structures are envisaged for use with this invention including a series of parallel linear microprisms with planar facets arranged to form a grooved surface, a ruled array of tetrahedra, an array of square pyramids, an array of corner- cube structures, an array of hexagonal- faced corner-cubes and a saw-tooth microprismatic array.
• the invention is principally concerned, however, with non-diffractive light control structures in the form of focusing elements such as lenses which may be concave or convex.
• the light control structures that are embossed into the polymer substrate may be sufficient by themselves to achieve the desired light control but in some cases could be provided with reflection enhancing coatings such as metallisations, ceramic materials including zinc sulphide or the like, etc.
• microlenses can be preferably defined as lenses having an active dimension such as a diameter or width in the range 5-250 microns. In some cases, lens diameters less than 5 microns are possbile. Examples of microlenses are one or more of spherical, aspherical, polygonal base, and elongate microlenses. Particularly preferred microlenses for use in optical devices such as moire magnifiers are spherical microlenses having a base diameter of less than 250pm, preferably less than 50pm.
• the thickness of the polymer substrate is determined by the focal length of the microlenses which in turn relates to their diameter.
• a typical thickness for the polymer substrate will be in the rangel 0-500 microns and more preferably 10- 100 microns even more preferably 50-100 microns and most preferably substantially 70pm.
• Typical examples of polymer materials which can be used are polypropylene (PP) (most preferably bi-axially oriented PP (BOPP)), polyethylene terephthalate (PET), polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), nylon, acrylic, Cyclic Olefin Polymer (COP) or Cyclic Olefin Copolymer (COC), or any combination thereof.
• PP polypropylene
• BOPP bi-axially oriented PP
• PET polyethylene terephthalate
• PE polyethylene
• PC polycarbonate
• PVC polyvinyl chloride
• nylon acrylic, Cyclic Olefin Polymer (COP) or Cyclic Olefin Copolymer (COC), or any combination thereof.
• the polymer substrate may be opaque, particularly where the light control structures are reflective (in which case a reflective coating may be provided on the embossed forms) but preferably is transparent or translucent. This then enables indicia to be provided on the opposite surface of the substrate to the light control structures and the formation of security devices such as moire magnifiers, lenticular devices and the like.
• the methods may further comprise coating at least partially one or both surfaces of the substrate with a, preferably opaque, coating layer while leaving at least the light control structures uncoated.
• This coating step may be carried out before or after the embossing process and indeed could be carried our partially before and partially after the embossing process.
• one side of the polymer substrate could be coated before the embossing process and the other side after.
• the method may further comprise, where the polymer substrate is transparent or translucent, before or after the embossing process, providing on the side of the substrate opposite to the light control structures, and in alignment with the structures, indicia that co-operate with the light control structures to create an optical effect.
• the indicia may be provided directly on the opposite side of the substrate or on a layer joined or coated on that side of the substrate.
• the coatings on opposite sides could both be partial so as to define a full window including the light control structures and indicia or microimages, or could be full on the side of the indicia so as to define a half-window.
• the method of providing the indicia can be chosen from a wide variety of known possibilities as for example described in WO-A-201 1/107788, WO-A- 2006/125224, WO-A-2014/070079 and WO-A-2008/000350.
• the invention has many applications, particularly in the security industry, for producing security devices for use in securing documents and articles of value such as banknotes, cheques, passports, identity cards, certificates of authenticity, fiscal stamps and other secure documents. Further examples include use of a security thread or stripe, a passport laminate or a layer in a passport data page,
• FIG. 1 is a schematic diagram of a first example of embossing apparatus according to the invention
• FIG. 1 illustrates examples of different ways to implement microimages
• Figure 3 is a schematic cross-section through part of a banknote with lenses made according to examples of the invention
• Figure 4 is a view similar to Figure 1 but of a second example of embossing apparatus
• Figure 5 is an enlarged view of part of an embossing die provided with pedestals according to an example of the invention.
• Figures 6A and 6B are enlarged, schematic views of the embossing die shown in Figure 5 in conjunction with a polymer substrate at different stages;
• Figures 7A and 7B are views similar to Figures 6A and 6B but using a modified embossing die
• Figures 8A-8C are enlarged, schematic views of a further example of an embossing die and of a polymer film embossed with embossing dies having different lens forms;
• Figure 9 illustrates schematically another example of a polymer substrate having a curable coating
• Figure 10 illustrates an example of a polymer substrate having a radiation absorbing coating
• Figure 1 1 is a schematic block diagram of apparatus for detecting manufacturing errors and applying a feedback control to the embossing apparatus.
• non-diffractive light control structures in the form of focusing lenses (both convex and concave) will be described. It should be understood, of course, that the techniques can also be used for non-diffractive light control structures of many other types including, for example, a series of parallel linear microprisms with planar facets arranged to form a grooved surface, a ruled array of tetrahedra, an array of square pyramids, an array of corner- cube structures, an array of hexagonal-faced corner-cubes and a sawtooth microprismatic array.
• Figure 1 illustrates a first example of apparatus for forming focusing lenses in a polymer substrate 1.
• the substrate may comprise a clear plastic substrate preferably formed from a typically transparent, polymeric material such as polypropylene (PP) (most preferably bi-axially oriented PP (BOPP)), polyethylene terephthalate (PET), polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), nylon, acrylic, Cyclic Olefin Polymer (COP) or Cyclic Olefin Copolymer (COC), or any combination thereof but advantageously is made of at least one biaxially-oriented polymeric film, such as BOPP.
• the substrate can comprise a single layer or multiple layers.
• the substrate 1 is fed in web form into a nip 2 defined between an embossing die roller 3 having a shore hardness of at least 95 on the A scale and a pressure or impression roller 4 (of high shore hardness).
• the embossing roller 3 carries embossing forms shown schematically at 5 about its circumference in a predetermined pattern and in the shape of the inverse of a desired lens form.
• the embossed forms on the roller 3 will be concave.
• the temperature T E of the embossing roller 3 for soft embossing will be in the range 150-180°C for nip pressures less than 5N/mm 2 and typically as low as 1 N/mm 2 while the temperature Ti of the impression roller 4 will be in the range 50-80°C. This then generates a temperature gradient between the two rollers 4,5 such that the web 1 is heated to an average temperature across its thickness of about 100°C at which the polymer material is deformable. Increasing the nip pressure to between 5-15N/mm 2 would be considered medium pressure embossing and would enable T E to be reduced by 10-15°C. Increasing the nip pressure above 15N/mm 2 would be considered high pressure embossing and would enable T E to be reduced by a further 10-15°C.
• rollers 4,5 rotate in opposite senses as shown as the web 1 passes through the nip 2 and the desired lens forms are imparted into the polymer.
• the web 1 is maintained under tension as it passes through the embossing apparatus shown in Figure 1 (by means not shown).
• chilling apparatus 10 which comprises in sequence a large diameter chill roller 12 and two smaller diameter chill rollers 13, 14.
• the web 1 after embossing and passing through the nip 2, extends around the three chill rollers 12-14.
• the chill rollers 12-14 are maintained at a low, chill temperature (T c ) so that the web 1 is rapidly cooled from the deforming temperature used at the nip 2.
• T c chill temperature
• the temperature T c is preferably less than 50°C and most preferably less than 30°C.
• embossed side of the web 1 does not contact the chill rollers 12 to avoid compression of the lenses.
• the lenses embossed into the polymer web 1 are preferably microlenses such as spherical, aspherical, polygonal base, and elongate, cylindrical microlenses. They will typically have active dimensions, for example diameters, of no more than 250pm and preferably less than 50pm.
• the thickness of the polymer material 1 is typically in the range 10-500 microns and more preferably 10-100 microns, even more preferably 50-100 microns and most preferably substantially 70pm for use in a polymer banknote, and will usually correspond to the focal length of the lenses.
• BOPP polyethylene terephthalate
• PE polyethylene
• PC polycarbonate
• PVC polyvinyl chloride
• nylon acrylic
• COP Cyclic Olefin Polymer
• COC Cyclic Olefin Copolymer
• the finished polymer could be used in its own right to provide an array of lenses for a variety of applications including a verifying device such as described in WO-A-94/27254.
• a verifying device such as described in WO-A-94/27254.
• an array of microimages or other indicia can be provided in association with the microlenses, typically on the opposite side of the web (the web being translucent or transparent), the microimages cooperating with the microlenses to define an optical device such as a moire magnifier, integral imager, lenticular device or the like.
• the association of the microimages with the microlenses can be achieved in a variety of ways known in the art.
• the microimages are printed onto the web.
• the microimages can be provided on a separate layer which is then laminated with the web. Examples of high resolution printing techniques suitable for forming microimages are described in WO-A-2014/070079 and WO-A-2008/000350.
• Figure 2A illustrates embossed or recessed image elements.
• Figure 2B illustrates debossed image elements.
• Figure 2C illustrates image elements in the form of grating structures while Figure 2D illustrates moth-eye or other fine pitch grating structures.
• Figure 2E illustrates image elements formed by gratings in recesses areas while Figure 2F illustrates gratings on debossed areas.
• Figure 2G illustrates the use of a rough embossing.
• Figure 2H illustrates the provision of print on an embossed area while Figure 21 illustrates "Aztec" shaped structures.
• Figure 2J illustrates ink filled recesses.
• a very important application of an embossed web having an array of lenses on one side and an array of microimages or other indicia on the other side is in the formation of a security document such as a banknote.
• An example is shown schematically in Figure 3.
• the transparent or translucent polymer web 1 is shown in cross-section and has on one side a two-dimensional array of embossed, spherical microlenses 20 and on the opposite side a two-dimensional array of microimages 21 which are sufficiently aligned with the microlenses 20 to generate a moire magnified image when the device is viewed in transmission.
• the web 1 has been provided with an ink receptive coating 23 on the side with the lenses 20 and an ink receptive coating 24 on the side with the microimages 21.
• the coatings 23,24 define gaps 25,26 respectively which are aligned, contain the lenses and microimages 20,21 and thereby form a window.
• the coatings 23,24 carry printed indicia (not shown) relating to the security document, in this case a banknote, such as its denomination and other security patterns.
• the ink receptive layers or coatings are preferably opaque or opacifying layers of printed material on which indicia relevant to the security document can be provided.
• the layers of opacifying ink may comprise pigmented coatings comprising pigments such as titanium oxide dispersed within a binder or carrier or cross-linkable polymeric material.
• the opacifying layers may be printed using any conventional printing technique including offset, gravure, intaglio printing and the like.
• polymeric-based security articles are described in WO 83/00659 and EP-A-1054778 which also describe how indicia receptive coatings can be provided.
• the provision of the coatings 23,24 can be carried out downstream of the embossing apparatus shown in Figure 1 but as an alternative, one or both of the coatings 23,24 could be provided on the web 1 upstream of the embossing apparatus with the embossing apparatus being designed to provide the lens array only in the window 25.
• FIG 4 A second example of an embossing apparatus is shown in Figure 4. This is a modification of the apparatus shown in Figure 1 in which the embossing roller 3 is located between two impression rollers 4A.4B, with which it defines respective nips 2A.2B.
• the rollers 3,4A,4B are maintained at temperatures T E and Ti respectively as in Figure 1 .
• This configuration has the benefit of minimizing deflection of the embossing roller 3 and also allows the option of using a clamped embossing plate.
• a separate embossing plate carrying the desired lens forms is provided on the embossing roller 3 and has an impression length equal to one half of the overall roller circumference.
• first chilling apparatus 10A including a chill roller 30 around which the web is wrapped through an angle of about 180°, the roller 30 contacting the non-embossed side of the web where the objective is to cool the substrate below the softening temperature of the substrate such that no further relaxation of the embossed lens relief occurs.
• the web is then guided around a number of guide rollers 32, which may be further chill rollers, around a further chill roller 33 before passing into a nip 2B between the rollers 3,4B.
• the chill rollers 30,33 are water cooled to a temperature T c of less than 50°C, preferably less than 30°C.
• both impression rollers 4A.4B will either be coated with a very high shore hardness polymer or may even be steel. The higher the shore hardness, the less the roller surface compresses, which in turn results in a higher nip pressure for a given cylinder load.
• the web passes into second chilling apparatus 10B comprising chill rollers 35,36 water cooled to a temperature T c less than 50°C, preferably less than 30°C, from where the cooled web then passes on for further downstream processing as described in more detail with respect to the Figure 1 example.
• Figure 5 illustrates the principle of an alternative embossing die 3A for using in place of the embossing die 3 in the previous embodiments.
• the Figure shows in a very schematic and enlarged form, part of the embossing die 3A having a main body or base substrate 50 on which are provided individual raised pedestals 52 on which embossing die forms 54 are provided.
• the die forms 54 define convex lens forms which will be used to emboss corresponding concave lens forms into the polymer substrate.
• the main difference between the embossing dies 3 and 3A is the insertion of the pedestal section 52 having a height H.
• the sagittal height (or depth) of the lens forms 54 is also shown at S referred to as "SAG height".
• the embossing die 3A is provided with pedestals having a small height H relative to the SAG height S of the lenses, movement of the polymer and die being from left to right.
• the total area occupied by the lens array regions will be a small fraction of the total web area and more pertinently if an imaginary line is drawn across the nip width then the lens regions will occupy some fraction of that nip width.
• this value for a particular design is 25%, then it follows that if we elevate the relief then initially at least contact will occur only in the raised lens area thus increasing the nip width by a factor of 4.
• This scenario is shown in Figure 6, where the pedestal height H is much less than the SAG height S (> 30% but less than 90%). Initially only the lens sag profile contacts the substrate 1 , leading to an elevated contact pressure (for a given roller load) to impress the lens profile into the substrate by using the minimum softening temperature.
• the amount of heat transferred into the substrate 1 is reduced via direct conduction simply because the direct physical contact between substrate and tool is initially at least limited to the lens region.
• Figure 6B As the lens profile pushes into the softened substrate displacing substrate material ( Figure 6B), eventually a state is achieved wherein the displaced substrate material flows up to contact the embossed die / surface at least in those areas adjacent to the lens regions.
• pedestal height and for lens SAG height values in the range 9-15pm, then in the scenario of Figure 6 a pedestal height (H) of only 1 -3pm would be sufficient to limit both pressure and heat transfer to the lens regions only, for most of the emboss depth
• a pedestal height (H) greater than 3pm would ensure that pressure and heat transfer contact was always limited to the lens regions for all of the emboss stroke or cycle. If the pedestal height is too high then it will tend to leave a proud relief on the opposing side of the substrate and therefore pedestal height should ideally be limited to less than half the SAG height.
• Figure 8A is a view similar to Figure 5 but showing part of an embossing die 3B with pedestals 82 on a base substrate 80 and carrying embossing lens forms 84 for embossing convex lenses into the polymer substrate.
• the major difference is that the pedestal height H needed to prevent full contact with the base plate of the embossing die 3B throughout the majority of the embossing stroke / cycle should have a minimum value approaching that of the SAG height S (i.e. H > 0.75S).
• H indeed slightly exceeds the value of S then little or no contact will occur between substrate and base substrate 80 throughout the embossing process and hence a higher contact emboss pressure is achieved and also reduced heat transfer into the substrate film in areas not being impressed with lenses.
• Such a die can be used to reduce or eliminate the elevation of the lenses above the base substrate thus reducing any negative impact on other downstream, print processes.
• Figure 8B shows the embossed film 1 scenario where H ⁇ S and thus the peaks of the embossed lenses 86 lie slightly above the base substrate of the polymer film 1.
• Figure 8C shows the scenario H > S and the lenses 86 lie below the surface of the substrate 1.
• the benefit here in addition to print processes is that the recessed convex lenses should have improved wear and soil resistance.
• Figure 9 illustrates another embodiment of polymer film 1A for use in the embodiments of Figures 1 -4 or indeed with other conventional embossing apparatus.
• the polymer substrate 1 A comprises a primary substrate layer 90 made of any of the materials previously mentioned in connection with the substrate 1 , the preferred material being biaxially-oriented polypropylene, the primary layer 90 being coated with a layer 92 containing a cross-linking chemical group.
• the group that provides secondary curing preferably has 2 curing groups- one based on an - acrylic- which cures during the pre-polymerisation and is a part of network; and a second group which cures during the secondary curing reaction.
• the cross-linking additive layer 92 is chosen so that prior to embossing the layer 92 has, or can be modified to have, a deformation temperature which is lower than that of the layer 90.
• the layer 92 will be deformable at a lower temperature than layer 90.
• Figure 9 shows this modified substrate 1A in conjunction with the embossing die 3A of Figure 7 although it could be used with any of the embossing dies previously described.
• the layer 92 is embossed by the embossing die so as to create, in this case, concave focusing lenses in the surface of the layer 92 (but not the layer 90).
• the embossed substrate although the embossing is not shown in Figure 9
• the curing radiation could be UV, IR or heat.
• the softening or embossing temperature of the layer 92 will be less than that of the layer 90 so, when the layer 90 is BOPP, the embossing temperature of the layer 92 will be less than 100°C, for example 60-90°C.
• the cross-linkage bond formation increases the hardness of the layer 92 to provide similar mechanical properties to layer 90.
• the material to form the layer 92 may be partially pre-cured and then coated on the layer 90 so that the layer 92 is soft and can easily be deformed during the embossing stage. This pre-curing allows the coating to be applied on flat surfaces and yields a dry, tack-free surface with sufficient deformability after drying.
• the material used to form the layer 92 is not pre- cured and instead is applied as a substantially solid layer, e.g. by co-extrusion with the polymer substrate, or by applying the layer 92 in a molten state and cooling to solidify.
• the thermoplastic nature of the material ensures that, as it is heated in the thermal embossing process to a point at which it can be embossed, it is plastically deformable during the embossing process.
• Materials that are applied without any pre-curing that are nevertheless solid prior to embossing may provide a dry, non-tacky surface that facilitates handling.
• the coating 92 is capable of undergoing a second curing step leading to a hard coating with increased chemical and mechanical resistance as a result of further cross linking.
• Acrylatic monomers with secondary functionalities such as Glycidyl, Oxetane and Hydroxy are the main examples of suitable materials for synthesising such polymer coatings in combination with normal monofunctional acrylate components. There are multiple other functionalities which provide the same mechanism. The most common examples of such precursors are:
• Glycidyl methacrylate (GMA) or
• Trimethylolpropane oxetane acrylate (TMPO acrylate)
• a solvent such as Isopropanol, Butanol, MIBK, MEK, Ethyl acetate, Butyle Acetate, Gamma Butyrolactone or a mixture thereof;
• monofunctional acrylate monomers are:
• the same monomers are also available for multiple chemical suppliers/ Manufacturers, including Allnex, IGM, BASF, Bayer, Miwon, Doublebond etc.
• initiators are:
• Free radical based thermal initiators such as AIBN (Azobisisobutyronitrile), 1 ,1 '-Azobis (cyclohexanecarbonitrile), Benzoyl peroxide or tert-Butyl hydroperoxide
• Initiator concentration 4-5% (w/w) of free radical type photo-initiators (eg, Irgacure 819) and 3% (w/w) of PAG type initiators- Cyracure 6974.
• a pre-polymer was first synthesised by reacting a mixture of 1 or more low Tg acrylate monomers (examples given below) and either- Glycidyl methacrylate (GMA) or / and
• Trimethylolpropane oxetane acrylate (TMPO acrylate) or/and
• a solvent such as Isopropanol, Butanol, MIBK, MEK, Ethyl acetate, Butyle Acetate, Gamma Butyrolactone or a mixture thereof.
• a free radical based thermal- or photo- initiator and a Photoacid generator As it is known to a technician trained in the art that exposure of UV light (a Few minutes) or heat (100 to 150 degree C for 14 hrs) would be required for initiating the polymerisation.
• This pre-polymer can be further chemically modified to enhance chemical reaction or cross linking density in particular, as required for modifying the hardness appropriate for the applications. This can be achieved by introducing additional expoy, oxetane or hydroxyl groups in the prepolymer - such as by adding 1 -15% of bisphenol-A novalac glycidyl ether with 8 epoxy groups (commonly known as SU8) or similar amount of isocyanate terminated monomers/ oligomers or other similar high functionality Epoxy's or other chemical reactants.
• This pre-polymer can also be further concentrated or diluted to required concentration appropriate for coating applications or additional additives can be added to it.
• This pre-polymer was coated on the polymer substrate and dried to tack-free transparent coatings of thickness in the range of 0.5 to 100 microns. Lenses were thermally embossed onto this layer by heating the pre-polymer coated substrates to ⁇ 100 C following by embossing using a hard lens tool.
• the layer was exposed to strong UV light (>1000mj/cm2) for 1 to 2 min and subsequently heated at 80 to 100 degree for 2 min. This led to production of further cross-links and hardening of lenses.
• Figure 10 illustrates yet another embodiment of the invention.
• the substrate 1 of the previous example is replaced by the substrate 1 B comprising a primary layer 100 formed of a polymeric plastics material of the type described above in connection with the substrate 1 , the substrate 100 being coated with a radiation absorbing layer 102 adapted to absorb, typically infrared, radiation.
• a radiation absorbing layer 102 adapted to absorb, typically infrared, radiation.
• upstream of the embossing die 3A is located an irradiation station 104 where infrared radiation from a laser or the like is applied to the layer 102 where it is absorbed.
• the layer 100 is transparent to the selected infrared radiation wavelength so that only the layer 102 absorbs the infrared radiation and heats up.
• This heating causes the adjacent surface region of the layer 100 to be raised to a temperature at which it is deformable while the remainder of the layer 100 remains below that temperature or indeed is unaffected.
• the temperature to which the layer 102 is raised is in the range 150-180°C while the base layer 100 remains unheated or at least is not heated to a value approaching the point at which the base layer is deformable. It is preferable if the layer 102 is transparent in the optical wavelength range.
• PET is substantially transparent in the infrared spectrum and so wavelength selection for IR source and absorber is not critical and therefore medium wave IR (2-4pm) or long wave IR (4-1000pm) radiation is acceptable.
• BOPP has absorption bands at 3 and 6pm and therefore long-wave IR radiation above 6pm is preferred.
• Figure 11 illustrates schematically apparatus for checking the accuracy of lenses embossed into the substrate 1 and can be used with any of the examples previously described.
• the embossing apparatus is shown at 1 10 and the embossed substrate 1 is fed from the embossing apparatus to a checking station 1 12 where it is brought over a fixed surface 114 carrying indicia 1 16.
• the indicia 1 16 correspond to indicia that would in a final product be provided, such as printed, on the underside of the substrate 1 in alignment with the lenses.
• the superposed lenses and indicia 1 16 are then viewed in transmission (the surface 1 14 being provided on a transparent plate 1 18) and the resultant optical effect viewed by a camera 120.
• the received image is then analysed by a processor 122 to determine if it is in focus. If it is not, this indicates that one of the process parameters for controlling the embossing apparatus 1 10 needs to be adjusted and the processor 122 outputs a suitable control signal to affect that adjustment.
• the reason for the out of focus condition would typically be because the lenses are not provided at the correct pitch.
• Suitable parameters that can be adjusted include the tension of the substrate 1 in the embossing apparatus 1 10, the temperature of the embossing roller, the speeds of the rollers, embossing temperature and the like.
• the processor 122 could simply display the required adjustment on a monitor or the like and the adjustment would then be manually made by an operator.
• the indicia 116 could be provided, for example printed or laminated, on the underside of the substrate 1 thus avoiding the need for the plate 118.
• the indicia 1 16 could be provided as markings on one or more rollers used to convey the substrate 1.
• the camera 120 views the indicia through the lenses in reflection.

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• 2015
  • 2015-07-10 GB GBGB1512122.1A patent/GB201512122D0/en not_active Ceased
• 2016
  • 2016-07-11 GB GB1911616.9A patent/GB2575564B/en not_active Expired - Fee Related
  • 2016-07-11 AU AU2016293298A patent/AU2016293298A1/en not_active Abandoned
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