IES80478B2 - A method of producing a printed varnished sheet - Google Patents

Abstract

UV curable varnish is fed into a varnish trough (1). An uncoated metal trough roller (2) is rotated through the varnish in the trough (1) and varnish from the trough roller (2) is applied to a predefined surface of an elastomeric coating (3) on a feed roller (4). Varnish is delivered from the coating (3) on the feed roller (4) to an uncoated metal surface of an oscillating roller (6) which applies the varnish to two metal form rollers (7,8). The varnish from the form rollers (7,8) is applied onto a varnishing cylinder (9) having a varnishing stencil (10) applied thereto so that the varnish is applied in a predetermined pattern. Varnish from the varnishing cyclinder (9) is applied to a blanket varnishing cylinder (11) in a predetermined pattern. A printed sheet (20) is passed between the blanket cylinder (11) and an impression cylinder (21) which delivers the varnish to a predetermined area of the printed sheet (20). The printed sheet (20) from the impression cylinder (21) is picked up by grippers (25) and delivered by a chain link arrangement and lifted so that it drops onto the surface of a conveyor (30). The conveyor (30) is mounted on a frame (35) which is movable on wheels (36) into and out of alignment with a sheet take-off station (32) as required. A varnished printed sheet is conveyed along the conveyor (30) under a guide means (38) to an infeed section (39) to a UV light applying station (40) having a bank of UV curing lights which are applied to the varnish to cure it.

Description

Introduction The invention relates to a method of producing a printed varnished sheet.

The technology of printing has advanced considerably to the stage that by sufficient capital investment it is possible to print several different colours and apply coatings in one pass on a large printing machine. Such machines, however, are not only expensive capital items but also are expensive to run. Consequently, for maximum efficiency they are run for as long as possible on a single print job. This however creates difficulties particularly for shorter run specialist jobs, in that the set up time and costs may not warrant using such machines for some types of products. Indeed, some products cannot in any event be easily nm on such machines because of the need to adjust a number of parameters on-the-run to achieve the highest quality finish.

This invention is therefore directed towards providing an improved method of producing a printed varnished sheet.

Statements of Invention According to the invention there is provided a method of producing a printed varnished sheet comprising the steps of: feeding a UV curable varnish into a varnish trough; rotating an uncoated metal trough roller through the varnish in the trough; applying varnish from the trough roller to a predefined surface of an elastomeric coating of a feed roller; delivering the varnish from the coating of the feed roller to an uncoated metal surface of an oscillating roller; applying the varnish from the metal oscillating roller to an elastomeric coating on a pair of form rollers; applying the varnish from the form rollers onto a varnishing cylinder having a varnishing stencil applied thereto; applying varnish from the varnishing cylinder to a blanket varnishing cylinder in a predetermined pattern; passing a printed sheet between the blanket cylinder and an impression 15 cylinder; gripping the printed varnished sheet and placing it onto a conveyor; conveying the printed sheet with the varnish applied thereto under a guide 20 means at an infeed section of the conveyor; curing the varnish on the sheet as the sheet is moving along the sheet conveyor by applying UV light from a bank of UV lights positioned above the conveyor; and guiding the printed varnished sheet along an outfeed section of the sheet conveyor for final curing and stacking.

In one embodiment of the invention the method includes the step of oscillating the oscillating roller longitudinally with respect to the axis of rotation of the roller as the varnish is being applied, the amplitude of the oscillation being from 1 mm to 5 mm.

Preferably the amplitude of the oscillation is approximately 2 to 3 mm.

Ideally the sheet conveyor and UV curing unit are moveable for interengagement with a varnished sheet take off from the sheet gripping means.

In a particularly preferred embodiment of the invention the surface of the elastomeric coating of the feed roller is defined by selecting one of three feed rollers with differing lengths of elastomeric covering thereon.

Preferably in this case the method includes the step of controlling the application of varnish to a least one marginal edge of the coating on the feed roller.

Preferably the application of varnish is controlled by positioning a varnish cut-off device at a predetermined position on the metal trough roller.

In a prefered arrangement the application of varnish is controlled by positioning a varnish cut-off device in the form of a plate having a trough roller engaging edge adjacent a side marginal edge of the coating on the feed roller and clamping the varnish cut-off plate in position so that on rotation of the trough roller varnish is removed from an area of the metal trough roller prior to application to the coating on the feed roller.

Preferably the varnish is delivered into the varnish trough by feeding the varnish into the trough from a supply vessel at a feed rate approximately corresponding to the rate of take up of varnish from the feed trough by the metal trough roller. To optimise varnish usage preferably excess varnish flows over a weir means in the trough for collection to be recycled.

Brief description of the drawings The invention will be more clearly understood form the following description thereof given by way of example only with reference to the accompanying drawings in which; Fig 1 is a side view illustrating a method of producing printed varnished sheets in accordance with the invention; Fig 2 is a view similar to Fig 1 with some of the apparatus in a different position; Fig 3 is a side view illustrating a method of applying varnish; Fig 4 is a perspective view of a varnish trough and applicator rollers used in the method of the invention; Fig 5 is a cross sectional view on the line V - V in Fig 4 Fig 6 is another view of the varnish trough and rollers; Fig 7a to 7c are perspective views of feed rollers used in the method of the invention; Fig 8 is a perspective view of a varnish applying stencil used in the method of the invention; and Fig 9 is a perspective view of a UV curing station used in the method of the invention.

Detailed description Referring to the drawings there is illustrated a method of producing a printed varnished sheet. UV curable varnish is fed into a varnish trough 1. An uncoated metal trough roller 2 is rotated through the varnish in the trough 1 and varnish from the trough roller 2 is applied to a predefined surface of an elastomeric coating 3 on a feed roller 4. Varnish is delivered from the coating 3 on the feed roller 4 to an uncoated metal surface of an oscillating roller 6 which applies the varnish to two metal form rollers 7, 8. The varnish from the form rollers 7, 8 is applied onto a varnishing cylinder 9 having a varnishing stencil such as the stencil 10 illustrated in Fig 8, applied thereto so that the varnish is applied in a predetermined pattern. Varnish from the varnishing cylinder 9 is applied to a blanket varnishing cylinder 11 in a predetermined pattern. A printed sheet 20 is passed between the blanket cylinder 11 and an impression cylinder 21 which delivers the varnish to a predetermined area of the printed sheet 20. The printed sheet 20 from the impression cylinder 21 is picked up by grippers 25 and delivered by a chain link arrangement in the direction of the arrow A over guide wheels 28, 29 and lifted so that it drops at the end of the guide chain onto the surface of a conveyor 30.

The conveyor 30 is mounted on a frame 35 which is movable on wheels 36 into and out of alignment with a sheet take-off station 32 as required. The conveyor 30 is shown in a retracted position in Fig 2. A varnished printed sheet is conveyed along the conveyor 30 under a guide means 38 to an infeed section 39 to a UV light applying station 40 having a bank of UV curing lights which are applied to the varnish to cure it. The printed varnished sheet is then passed over an outfeed guide station 41 along a curing section 42 of the conveyor 30 for final stacking at a stacking station 45. It will be noted that the bank of UV lights may be lifted using a ram means 48.

In more detail, varnish is delivered into the trough 1 from a container 50 having a delivery pipe 51. The rate of delivery of varnish into the trough 1 is controlled to correspond as closely as possible with the take up of varnish by the trough roller 2.

Excess varnish in the trough 1 travels over a weir 51 through an outlet pipe 52 into a container 53 for recycling. In this way, the flow of varnish in the trough is optimised for maximum take up efficiency of varnish. The surface of the trough metal roller 2 delivers the varnish onto a predetermined surface of the elastomeric coating 3 on the feed roller 4. For efficient varnishing we have found that it is essential to control the amount and path of delivery of varnish as closely as io possible. For this reason a range in this case three, feed rollers 4 are provided each with a different length of coating 3 thereon as illustrated in Figs 7a to 7c. Only the amount of varnish required for varnishing a particular print job is taken off the trough roller 2 by the coating 3 on the feed roller 4. The amount of varnish is even more closely controlled by using a number of die plates 60 which are bent at one end 61 over a support bar 62 and which are engaged at the other end 63 against the surface of the trough roller 20. A pressure pad formed by a rubber block 65 is provided on the tip of the plate 60 to avoid metal to metal contact. The guide strips 60 are clamped in a desired position on the trough roller by a series of clamping elements 70 which are pivotable from a released position for positioning the metal strips 60 to a clamping engaged position in which the metal strips 60 are retained in position. The strips 60 are positioned to control the application of varnish at the side marginal edges of the coating 3 on the rollers 4. In combination with the use of a range of individual rollers 4 a close control of the varnish applied can thus be achieved.

We have found that for optimal application the trough roller 2 is a metal roller in which the varnish is taken up in a clear film and then applied to an elastomeric coating 3 on the feed roller 4 which takes the film of varnish and applies it to the metal surface of the oscillating roller 6. For optimum varnish-applying conditions we have found that the oscillation of the roller 6 along the longitudinal axis of the roller should be restricted to an amplitude of from 2 to 5 mm, and preferably, approximately 2 to 3 mm. In this way, application of the varnish is ensured without disturbing the integrity of the film of the varnish to be applied. Similarly the surface of the form rollers 7, 8 to which the varnish is applied from the oscillating roller 6 is an elastomeric material which ensures that the film of varnish is applied through the stencil 10 to the printing cylinder 9. Thus, the varnish taken up by the printing blanket cylinder 11 and delivered onto the printed sheet 20 as it passes between the impression cylinder 21 and printing cylinder 11 is highly efficiently applied to provide a very high quality finish.

The delivery of the varnished printed sheets by grippers along a pathway before being dropped directly onto a conveyor 30 gives an opportunity for some preliminary drying of the varnish on the sheet. Passing the sheet under the guide means 38 ensures that it is in a flat condition on presentation to the UV curing lamps 40 for optimum curing conditions.

The curing system frame 35 is mobile to increase the flexibility of the system. Ideally the varnishing system described is preceded by a single printing station so that the printing unit may be used for printing alone without applying varnish. When it is required to use the varnishing station for conventional printing the various rollers and cylinders are replaced with corresponding printing rollers and cylinders. Thus the maximum flexibility is achieved and we have found that because of the optimising of the varnishing system a printing station in advance of the varnishing unit may be used for direct printing followed by direct varnishing of, for example, single or two colour sheets.

Thus the invention provides a highly flexible and efficient process for producing a printed varnished sheet which ensures that all the production elements in a printing works are working to maximum efficiency. This leads to efficient printing scheduling with high rates of output and minimum production time so that tum-around times for a customer are considerably improved without sacrificing product quality.

Many variations on the specific embodiments of the invention will be readily apparent and accordingly the invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail.

Claims (5)

1. A method of producing a printed varnished sheet comprising the steps of: feeding a UV curable varnish into a varnish trough; rotating an uncoated metal trough roller through the varnish in the trough; applying varnish from the trough roller to a predefined surface of an elastomeric coating of a feed roller; delivering the varnish from the coating of the feed roller to an uncoated metal surface of an oscillating roller; applying the varnish from the metal oscillating roller to an elastomeric coating on a pair of form rollers; applying the varnish from the form rollers onto a varnishing cylinder having a varnishing stencil applied thereto; applying varnish from the varnishing cylinder to a blanket varnishing cylinder in a predetermined pattern; passing a printed sheet between the blanket cylinder and an impression cylinder; gripping the printed varnished sheet and placing it onto a conveyor; conveying the printed sheet with the varnish applied thereto under a guide means at an infeed section of the conveyor; curing the varnish on the sheet as the sheet is moving along the sheet conveyor by applying UV light from a bank of UV lights positioned above the conveyor; and guiding the printed varnished sheet along an outfeed section of the sheet conveyor for final curing and stacking.

2. A method as claimed in claim 1 including the step of oscillating the oscillating roller longitudinally with respect to the axis of rotation of the roller as the varnish is being applied, the amplitude of the oscillation being from 1 mm to 5 mm, preferably approximately 2 to 3 mm.

3. A method as claimed in any preceding claim wherein the sheet conveyor and UV curing unit are moveable for interengagement with a varnished sheet take off from the sheet gripping means, preferably the surface of the elastomeric coating of the feed roller is defined by selecting one of three feed rollers with differing lengths of elastomeric covering thereon, preferably the method includes the step of controlling the application of varnish to a least one marginal edge of the coating on the feed roller, preferably the application of varnish is controlled by positioning a varnish cut-off device at a predetermined position on the metal trough roller, preferably the application of varnish is controlled by positioning a varnish cut-off device in the form of a plate having a trough roller engaging edge adjacent a side marginal edge of the coating on the feed roller and clamping the varnish cut-off plate in position so that on rotation of the trough roller varnish is removed from an area of the metal trough roller prior to application to the coating on the feed roller.

4. A method as claimed in any preceding claim wherein the varnish is delivered into the varnish trough by feeding the varnish into the trough from a supply vessel at a feed rate approximately corresponding to the rate of take up of varnish from the feed trough by the metal trough roller, preferably excess varnish flows over a weir means in the trough for collection to be recycled.

5. Printed UV cured varnished sheets whenever produced by a method as claimed in any preceding claim.