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(11) | EP 2 431 179 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Litho printing apparatus |
| (57) A litho printing apparatus 2 comprises in sequence a plurality of litho units 4,
a coating unit 8 and a transfer unit 10. The transfer unit 10 is modified to include
film application and removal means for applying a film 28 to a substrate 20 passing
through the unit, and to remove said film from said substrate 20 after the substrate
20 has been dried or cured while in contact with the film 28.
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[0002] Litho printing apparatus typically comprises a plurality of litho printing presses arranged in series. A sheet substrate to be printed passes sequentially through the presses. Each press typically lays down a different coloured ink, varnish or pattern onto the substrate to build up a final image. In high quality printing, six or more litho presses can be provided in series.
[0003] After passing through the litho presses, the printed substrate also passes through a number of further units. Typically a first transfer unit is provided immediately downstream of the litho presses. This unit transfers the substrates to further units downstream and comprises suitable substrate transfer means such as transfer rollers or grippers. The unit may also comprise means for drying the inks etc applied by the litho presses. Such units are sometimes referred to as dummy drying units.
[0004] Downstream of the first transfer unit is typically provided a coating unit, typically a flexo-coating unit. This unit is typically used to apply a varnish or other finish coating to the printed sheet substrate.
[0005] Downstream of the coating unit is typically provided a second transfer unit. Typically this unit comprises drying means, such as ultraviolet lamps, to dry the varnish applied to the printed substrate. The unit also acts to transfer the printed and varnished substrate to further processing units downstream.
[0006] Such further processing units may include, for example, a second coating unit which may apply for example a different coating from the coating applied by the first coating unit. For example, the second unit may apply a matt varnish as opposed to possibly a gloss varnish applied by the first coating unit. From the second coating unit, the printed and varnished substrate passes to further downstream units, for example, collation and stacking units.
[0007] It is often desirable to produce a holographic or other decorative image on the printed sheet substrate. This is sometimes done by impressing a film, for example a film having an embossed surface, onto a wet coating of the substrate, drying the coating with the film in situ and then peeling off the film to leave a pattern or desired finish on the substrate. This process is sometimes termed a micro embossing transfer process.
[0008] In apparatus of the above type, this micro embossing transfer process can be cumbersome and expensive. In some apparatus, a completely separate embossing unit is added to the apparatus. However, this is not only expensive, but it requires additional space to accommodate the separate unit.
[0009] In an alternative approach, one of the coating units is adapted to supply the film to the sheet as it passes through the coating unit, using the application rollers of the coating unit to apply the film to the substrate. However, this has the considerable disadvantage that the coating unit cannot then be used to apply varnish. Consequently, one of the litho press units or another coating unit must be used to apply the varnish which receives the film. This reduces by one the number of inks or vanishes which can be applied to the substrate. This is clearly disadvantageous.
[0010] The present invention seeks to overcome or at least mitigate the above problems and from a first aspect provides a litho printing apparatus comprising, in sequence:
a plurality of litho units;
a coating unit; and
a transfer unit; wherein:
said transfer unit is modified to apply a film to a substrate passing therethrough, and to remove said film from said substrate after the substrate has been dried or cured in contact with said film.
[0011] The invention also extends to a method of modifying a litho printing apparatus which apparatus comprises, in sequence: a plurality of litho presses; a coating unit; and a transfer unit; wherein the modification comprises modifying said transfer unit to apply a film to a substrate passing therethrough and to remove said film from said substrate after the substrate has been dried or cured.
[0012] In accordance with the invention, therefore, a transfer unit is modified to apply and remove the film from a coated, e.g. varnished substrate rather than a coating unit as was used previously. This frees up the coating unit to apply another varnish or coating onto the substrate.
[0013] The film application and removal means may comprise an unreeling / reeling system, with the film being conducted through the unit over an appropriate path from an unreeling spool to a reeling spool. Suitable guide means, for example guide rollers, may be provided between the reeling and unreeling spools.
[0014] Whilst, as stated above, the transport unit comprises means for transferring the substrate (which is usually in the form of discrete sheets) through the unit, the unit will need to be modified in order to apply the film to the substrate surface. Accordingly, in one embodiment, the unit is therefore modified also to include a film application roller which is mounted so as to apply sufficient pressure to the film to press the film onto the underlying substrate.
[0015] The roller may be biased hydraulically or pneumatically to provide the appropriate contact force with the substrate sheet. Opposing rollers or cylindrical surfaces may be provided to trap the sheet and film between their nip.
[0016] A typical sheet substrate transport means comprises a transfer drum which cooperates with one or more sets of clamps which project from a cylindrical surface of the drum. Typically three sets of clamps are equally spaced circumferentially around the drum. The clamps typically have a hook portion which forms a stop for the sheet and which, as the drum rotates, is retracted towards the drum surface to clamp the end of the sheet on the drum.
[0017] In a preferred embodiment of the invention, the film application roller is arranged to nip the film and substrate between the film application roller and the cylindrical surface of the substrate transfer drum.
[0018] However, a problem may occur with such an arrangement in that the clamps cannot fully retract into the drum surface as to do so would damage the sheet. This incomplete retraction could result in the film tearing as it passes between the application roller and the clamps. It could also mean that the nip between the application roller and the drum may be lost thereby allowing air between the film and the substrate, possibly resulting in failure of the pattern transfer to the substrate. Also, the surface of the application roller itself (which may be rubber for example) may also be damaged.
[0019] To overcome this problem, the film application roller is preferably lifted away from the drum as the clamps approach the application roller.
[0020] This can be effected hydraulically, pneumatically or in any convenient manner, for example using the same means as used for biasing the application roller.
[0021] The application roller(s) must be positioned upstream of drying or curing means within the unit so as to ensure that the film is properly positioned on the substrate prior to the substrate being dried or cured with the film in situ. In general the film is so thin that the wet substrate surface under the film can easily be dried or cured through the film. Typically the drying means will comprise one or more UV sources e.g. lamps. As discussed above these lamps will normally already be present in the unmodified transfer unit.
[0022] The film may, for example, be an embossed film as discussed above. The process will then leave an embossed finish on the substrate. However, the invention is not limited to embossing processes and can also be applied to so called cold foiling processes. In such a process, the film supports a layer, e.g. a metallic layer, which is transferred from the film onto the substrate coating (for example a varnish or adhesive) under application of pressure, and is fixed on the surface by drying or curing so as to produce a foil like effect on the substrate. The film used in the modified apparatus may therefore comprises such a layer.
[0023] A preferred embodiment of the invention will now be described by way of example only with reference to the accompanying Figures in which:
Figure 1 which shows, schematically, an apparatus in accordance with the invention;
Figure 2 shows schematically a detail of the apparatus of Figure 1; and
Figure 3 shows a side elevation of Figure 2.
[0024] In the Figure, a litho printing apparatus 2 is shown. This particular apparatus illustrated is a Komori unit which comprises six litho presses 4 (only the last three of which are shown). Downstream of the litho presses 4 is arranged a first transfer or dummy drying unit 6, a first coating unit 8, a second transfer or dummy drying unit 10, a second coating unit 12 and an outfeed unit 14.
[0025] The first dummy drying unit 6 comprises drying means 16, e.g. UV lamps, for drying the inks or coating applied to a sheet substrate passing out of the litho units 4. It also comprises appropriate means to transfer the substrate into the downstream units.
[0026] The first coating unit 8 is in this embodiment a flexo coating unit applying a varnish or other coating to the substrate. Coating units other than flexo units may be used instead. The coating need not be applied over the entire substrate surface and can instead only be applied to regions where a desired surface finish is required.
[0027] The second dummy drying unit 10 is similar to the first dummy drying unit 6, except that it has been modified in accordance with the invention. Thus, similarly to the first dummy drying unit 6, the second dummy drying unit comprises sheet transfer rollers 16 and sheet transfer drum 18 between which the sheet 20 travels along a travel path 22. Also as is known and standard, the second dummy drying unit 10 comprises heaters, for example UV lamps 24, arranged along the travel path 22 for drying the coating applied by the first coating unit 8.
[0028] However, the second dummy drying unit has been modified to apply a film, e.g. a holographically embossed film 26 or some other film for providing a desired finish to the sheet 20, onto the sheet 20 as it passes through the unit. To this end the unit also comprises first and second film receiving spools 28, 30. The first spool 28 acts as an unreeling spool which initially receives the film 26, and the second spool 30 a reeling spool which reels back the film 26 after it has passed along its travel path 32 through the unit 10. A series of guide rollers (not shown) is provided along the travel path in an appropriate manner.
[0029] Also provided is an application roller 34 which presses the film 26 firmly down into contact with the sheet substrate 20 upon its entry into the unit 10. This roller may be biased by suitable means (not shown), such as pneumatic or hydraulic cylinders. This is shown in greater detail schematically in Figures 2 and 3.
[0030] The application roller 34 is mounted so as to cooperate with the cylindrical surface of a rotary transfer drum 36 which is arranged at the entrance to the unit 10. This transfer drum 36 is part of the unit 10 and does not need modification in accordance with the invention.
[0031] The transfer drum 36 comprises a cylindrical surface 38 which is provided with clamps 40 which are arranged in three circumferentially equi-spaced rows 42 across the drum. The clamps 40 are provided in pockets 44 in the drum surface 38. The clamps 40 project proud of the cylindrical surface 38 so that they may receive and stop the end of a sheet 20 against end 46. The clamps 40 can be partially retracted into the pockets 44 so as to grip the sheet 20 against the cylindrical surface 38, thereby pulling the sheet 20 into the unit 10 as the drum 36 rotates. When the sheet 20 has moved to the next transfer mechanism, the clamps 40 return to their fully projecting position to receive the next sheet 20.
[0032] However, the clamps 40 cannot retract fully into the pockets 44 as to do so would damage the sheet 20. This means that the clamps 40 may potentially damage the film 26 should it pass between the clamps 40 and the application roller. 34. To prevent this, the application roller 34 is retracted with respect to the drum 36 as the clamps 40 approach the application roller 34. This retraction may be effected pneumatically or hydraulically, for example through the biasing means discussed above.
[0033] The movement of the application roller 34 towards and away from the drum surface 38 may be controlled by any suitable means, for example by a suitable mechanical linkage or electrically, for example through a servo control system.
[0034] After leaving the second dummy drying unit, the sheet passes to further processing units such as a second coater, a collation unit and so on.
[0035] In use of the apparatus, then, a suitable varnish for receiving a holographic or other film 26 is applied to the sheet 20 by the first coating unit 8. The sheet 20 then enters the second dummy drying unit 10 where the film 26 is unwound from the spool 28 and pressed onto the sheet 20 by the application roller 34. The sheet 20 and film 26 are pressed firmly together in the nip between the application roller 34 and the cylindrical surface 38 of the gripper drum 36. However, to avoid damage to the film 26 due to the gripper teeth 40, the application roller 34 is lifted away from the gripper drum 36 when the gripper teeth approach. After the teeth have passed, the application roller 34 is once again biased towards the cylindrical counter surface 38 of the gripping drum 36 to press the sheet 20 and film 26 into firm contact once more.
[0036] The sheet 20 and film 26 then travel together through the unit 10, the coating being cured by the UV lamps 24 through the film which is typically very thin. This will cause the pattern embossed into the surface of the coating by the film 26 to solidify, such as to leave a pattern on the coating after the film 26 is removed from the sheet 20 by the reeling spool 30 as the sheet 20 leaves the unit 10.
[0037] In this way, the second dummy drying unit 10 applies the film 26 rather than a coating unit as was the case in the prior art, allowing the coating unit 8 to be used for its intended purpose, namely applying a coating. In this way, the litho units 4 may all be used to apply ink or other coatings rather than specifically applying a coating for receiving the film, leading to greater flexibility in the printing process.
[0038] It will be understood that in accordance with the invention, additional units may be positioned between the various units disclosed. Thus the reference to units being in sequence does not preclude intervening units being positioned therebetween.
[0039] Also, while the above embodiment has been described in terms of a micro embossing process using a holographic film, it may also be adapted to perform a cold foiling process by using a film which comprises a layer which is deposited in whole or in part onto the coated substrate surface. The layer may be continuous or discontinuous.
[0040] Whilst the clamping drum illustrated shows three sets of clamps, there may be any number, for example one or more. Also, while the clamps are shown as mounted in pockets in the drum, in an alternative arrangement, the clamps may be provided on separate chains which run through the machine and around the drum. The drum may therefore have recesses to accommodate such clamps. In such an embodiment , the clamps will still project from the drum surface and so the film application roller will still need to be retractably mounted relative to the drum.
1. A litho printing apparatus comprising, in sequence:
a plurality of litho units;
a coating unit; and
a transfer unit; wherein:
said transfer unit is modified to include film application and removal means for applying a film to a substrate passing through the unit, and to remove said film from said substrate after the substrate has been dried or cured while in contact with the film.
2. A method of modifying a litho printing apparatus which apparatus comprises, in sequence:
a plurality of litho units; a coating unit; and a transfer unit; wherein the modification
comprises modifying said transfer unit to include film application and removal means
which in use apply a film to a substrate passing therethrough and to remove said film
from said substrate after the substrate has been dried or cured.
3. An apparatus or method as claimed in claim 1 or 2 wherein the film application and
removal means comprises an unreeling / reeling system.
4. An apparatus or method as claimed in claim 3, wherein the film application and removal
means comprises an unreeling spool, a reeling spool and film guide means between the
reeling and unreeling spools.
5. An apparatus or method as claimed in any preceding claim wherein a film application
roller is provided in the transfer unit and which is mounted so as to press the film
onto the substrate.
6. An apparatus or method as claimed in claim 5 wherein the roller is biased hydraulically
or pneumatically to provide a contact force with the substrate.
7. An apparatus or method as claimed in claim 6 wherein the film and substrate are trapped
in the nip between the film application roller and a cylindrical counter-surface.
8. An apparatus or method as claimed in claim 7 wherein cylindrical counter surface is
provided on a substrate transfer drum, sheet clamps operating to clamp the substrate
to the drum.
9. An apparatus or method as claimed in claim 8 wherein the film application roller is
retracted from the transfer drum as the clamps approach the application roller.
10. An apparatus or method as claimed in claim 9 wherein the roller is lifted hydraulically
or pneumatically.
11. An apparatus or method as claimed in any preceding claim wherein the transfer unit
comprises drying or curing means.
12. An apparatus or method as claimed in claim 10 as dependent upon any of claims 5 to
11, wherein the application roller(s) are positioned upstream of drying or curing
means within the transfer unit
13. An apparatus or method as claimed in any preceding claim wherein the film is an embossed
film, for example a holographic film.
14. An apparatus or method as claimed in any of claims 1 to 12 wherein the film comprises
a layer for deposition onto the substrate surface.
15. A transfer unit for a litho printing apparatus comprising transfer means for transferring
a sheet through the unit, and a film application roller for applying a film to the
sheet, the transfer means comprising a drum and clamping elements for clamping the
sheet onto the drum, the sheet and film being fed together between the drum and the
film application roller, the film application roller being retractable relative to
the drum when a clamp passes between the drum surface and the roller.