GB2323071A - Method for covering a carton with a printed sheet - Google Patents

Abstract

A method for covering a carton comprises printing a colour image onto the front surface of a sheet and guide lines onto the rear surface 2. Applying adhesive to the rear surface 5 and bringing the carton into contact with the rear surface 9 so that the carton is aligned with the guide lines. Adhering the carton to the rear surface and wrapping the sheet uniformly around the carton so as to cover it 11. The printing is done by an electrographic printing system (20, figure 2) and the sheet material is of 135 g/m<SP>2</SP> gauge with a double-sided gloss. Once printed the sheet is cut to the requisite size by a guillotine (40, figure 3) and is then laminated 4 with 27Ám polypropylene. A water based adhesive (50:50 water/solvent mix) is applied 5 and the sheet is conveyed on a vacuum conveyor (70, figure 6). From the conveyor the sheet is transferred to a vacuum jig (80, figure 7) where the carton is adhered to it in registry with the guide lines. The completed carton may then be conveyed through a pressing system (130, figure 10) to ensure that there are no air bubbles.

Description

"A Carton Production Method" The invention relates to the production of cartons of a relatively small size and on which a large amount of colour information is printed. An example is a carton for a software product.

Typically, such cartons are produced by printing a carton blank with an offset rotary printing machine such as those described in US5351616 (MAN Roland), US4930414 (Heidelberger), or US5154041 (Schneider).

Such a production method involves pre-press image processing to produce a set of colour separation files, and then colour separation films for use by the printer in setting up the offset printing machine. Such machines are effective for high volume runs - directly printing the image onto many thousands of carton blanks. The carton blanks are subsequently assembled into cartons, and are then ready for use.

Such a production method is quite efficient for high-volume runs. However, for short runs (such as hundreds of units) the pre-press and printing set-up time and cost often make the unit cost prohibitively high. Further, the number of situations in which short runs are required is increasing. This is because of the progress towards just-in-time production to avoid obsolescence and to reduce work-in-progress where there are frequent changes of product. For example, some software products might have production runs of only some hundreds of units, for example, a software version in the language of a country having a small market.

The invention is therefore directed towards providing a production process for such cartons which is efficient for low-volume production and provides cartons of a high quality.

According to the invention, there is provided a method of producing a printed carton, the method comprising the steps of: printing a colour image on a front surface of a high-strength sheet; printing carton panel edge guide lines on a rear surface of the sheet; applying adhesive to the rear surface of the printed sheet; bringing a carton into contact with the printed sheet at the rear surface with panel edges in registry with the guide lines; uniformly adhering the printed sheet to the carton to cover adjoining carton panels; and curing the adhesive.

By printing onto a high-strength sheet, printing techniques can be used which require relatively little pre-press and print set-up time to achieve a quality colour image. The edge guide lines on the rear surface allow the carton to be brought into registry with the sheet in a simple manner so that direct printing can be simulated. The invention therefore provides a very simple solution to the problem of low-volume production runs where high-quality colour printing is required.

Preferably, the carton is assembled and pressed flat before being brought into registry with the printed sheet. This minimises the extent of folding of the printed sheet which is required after it adheres to the carton, while at the same time allowing simple registry of the carton with the sheet.

in one embodiment, the printed sheet is adhered to the carton by wrapping around completely. Thus, there is only one seam to provide excellent simulation of direct printing.

Preferably, the printed sheet is wrapped around to the extent of overlapping at the extremities. This provides a neat appearance and allows relatively quick production to minimise registry time.

In one embodiment, the method comprises the further steps of cutting excess sheet according to the panel guide lines before contact with the carton. This allows a generic sheet to be used for a variety of different carton types - the sheet being cut exactly to the dimensions required with the assistance of the guide lines.

in one embodiment, the carton is brought into registry with the printed sheet on a jig having adjustable alignment guides and vacuum apertures to hold the printed sheet in position. This arrangement helps to achieve registry in a quick and efficient manner.

In one embodiment, the printed sheets are conveyed on a porous conveyor belt to which a suction is applied from below to maintain printed sheets in a flat configuration and to aid penetration of the adhesive. This achieves the effect of conveying the sheets to the jig, allowing comprehensive penetration of the adhesive in a uniform manner, and maintenance of the sheet in a stable flat configuration.

Preferably, the printed sheet is laminated on the front surface. This provides an excellent end-product appearance, and carton protection.

In one embodiment, the sheet is laminated with a transparent film having a thermally-activated adhesive. This is a particularly robust lamination and provides a high-gloss.

In one embodiment, the sheet is printed by a digital printing machine having an electrophotographic press. Such machines are particularly flexible and require short set-up times for particular images.

In one embodiment, the method comprises the further step of pressing the carton after application of the printed sheet to exclude any trapped air.

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which: Fig. 1 is a flow diagram illustrating a carton production method of the invention; Figs. 2(a) and 2(b) are perspective views showing printing of sheets; Fig. 3 is a diagram showing printed sheets and the manner in which they are cut; Fig. 4 is a diagrammatic representation of lamination of a printed sheet; Figs. 5(a) and 5(b) are perspective and aoss-sectional diagrammatic views respectively showing application of adhesive to a printed sheet; Fig. 6 is a diagrammatic cross-sectional view showing a buffer conveyer for a sheet after application of adhesive; Fig. 7 is a perspective view from above of a jig for application of a printed sheet to a blank carton; Figs. 8(a) and 8(b) are diagrammatic cross-sectional views showing operation of an alternative jig of the invention; Fig. 9 is a perspective view showing a generic blank carton which is used in the process; Fig. 10 is a perspective view from above showing a carton being pressed; and Fig. 11 is a perspective view showing an end-product carton.

Referring to Fig. 1, a method 1 for producing a carton is indicated by a set of steps 2 to 12 inclusive. The manner in which these steps are performed is illustrated in Figs.

2 to 11. In step 2 of the process there is digital printing using a printing press 19 shown in Figs 2(a) and 2(b). The press 19 is a digital colour press of the electrophotographic type having an LED array which exposes a charged photoconductor drum to different light levels. Small toner particles having a diameter of 4 microns or less adhere to the charged areas of the drum, thus forming an image which is transferred to paper. The drum is re-charged with each rotation.

The paper which is used is maintained in a temperature controlled environment which is stable at 20"C. The paper is of 135 g/m2 gauge and has a double-sided gloss.

As shown in Fig. 2(a), a spool 21 of the paper is mounted in an input stage 20 having a housing 22 and a cover 23. The printing drums are mounted in a cabinet 24, and the printed sheets are delivered at output trays 25.

Referring now the Fig. 3, a printed sheet 30 is illustrated. The sheet 30 has carton colour printed indicia 31 printed on a front surface. The india 31 are printed to provide a margin 32. In addition, the printing operation prints guide lines 33 and 34 on the rear surface. The guide lines 34 indicate the alignment for cutting by a guillotine machine 40, also shown in Fig. 3. The interrupted lines 34 correspond to panel side edges of a carton to which the sheet 30 is to be adhered. The sheets 30 are cut in step 3 using the guillotine machine 40.

Referring now to Fig. 4, in step 4 the printed sheet is laminated with a layer of transparent polypropylene having a thickness of 27 pm. The purpose of this lamination is to enhance the gloss effect on the sheet, to avoid cracking at the panel side edges, and to provide improved wear resistance. The sheet is laminated using a system 50 to which the printed sheets 30 are delivered by a conveyor 51. A lower, pressure roller 52 supports the printed sheet 30 as the polypropylene layer 54 is applied by a heated drum 53 from above. The layer 54 is drawn from a reel 55 and around a tension roller 56, the latter providing sufficient tension for the heated roller 53. The elevated temperature of the roller 53 activates an adhesive to secure the layer on the front surface of the printed sheet 30.

In step 5 adhesive is applied to the rear surface of the printed sheet by an adhesive application system 60. The system 60 comprises an adhesive tray 61 above which there is an adhesive-collecting drum 62, an adhesive-applying drum 63, fixed guides 64, and a pair of drive rollers 65. The printed sheet 30 is fed by the drive rollers 65 over the adhesive-application roller 63. The fixed guides 64 ensure that the sheet 30 separates from the drum 63. An important aspect of adhesive application is that the adhesive used is water-based with a 50::50 water/solvent mix. The temperature and the water content are regularly monitored to ensure that there is a uniform application over the full rear surface of the sheet 30. An important aspect is that the viscosity is maintained to a level only slightly higher than that of water.

Referring now to Fig. 6, the sheet is then conveyed on a vacuum buffer conveyor 70 in step 6. The buffer conveyor 70 is shown in Fig. 6, and it comprises a mesh conveyor 71, supported underneath its upper portion by a plate 72 having vent apertures through which air is drawn by fans 73. The air flow streams are indicated by the arrows 74. The conveyor 71 moves at a speed of 3m/min and during transit each sheet 30 is maintained in a flat configuration by application of the suction for approximately 1 min. Also, the suction for the delay period provided by the conveyor 70 allows for comprehensive penetration of the adhesive to the extent required for uniform bonding across the full rear surface. Thus, the conveyor 70 effectively conditions the printed sheet in order to ensure the necessary quality of the end product.

In step 7 a sheet 30 is transferred from the conveyor 70 to a jig 80 shown in Fig. 7.

The jig 80 has a steel plate 81 with vacuum apertures 82, side edge guides 83 and lower guides 84. The guides have elongate slots and wing nuts to allow adjustment.

An alternative jig 90 is shown in Figs. 8(a) and 8(b). The jig 90 comprises a plate 91 having suction apertures 92 and a recessed slot 93 housing a roller 94.

In use, the printed sheet is laid front surface down on a jig in alignment with some or all of the guides 83 and 84. A generic blank carton 100 produced in step 8 is then placed in step 9 on top in registry according to the guide lines 33 and 34. A generic blank carton 100 is shown in Fig. 9. Such a carton design may be used for many types of carton, the margin-cutting step 3 reducing the printed sheet to the exact size.

The guide lines 33 and 34 are very important to ensure accurate registry of the blank carton with the sheet so that when the sheet is wrapped fully around the carton and held in place it simulates direct printing of the sheet. The sheet is wrapped around the carton in step 10 either manually, or automatically as shown in Figs. 8(a) and 8(b), depending on the configuration of the carton and sheet.

In step 11 the carton with the sheet adhered to it is conveyed through a pressing system 130 having upper and lower pressure rollers 131 and 132 respectively. This step is very simple and it effectively ensures that there is no trapped air and that there is uniform bonding between the sheet and the carton. This operation produces an end product 140 which is ready to receive contents.

It will be appreciated that the invention provides a simple and effective method for producing cartons having comprehensive colour indicia printed on the outside surface. The method achieves simulation of a directty-printed carton and so avoids the cost involved in pre-press and print set-up for rotary offset printing. There is excellent flexibility afforded by the fact that the print set-up is quick and simple.

Differences from one batch to another do not reflect in the production process itself, other the printing step. Once the sheet has been printed, the subsequent steps are similar in nature, the registry guide lines 33 and 34 ensuring accurate placement.

The invention is not limited to the embodiments described, but may be varied in construction and detail within the scope of the claims.

Claims (13)

Claims

1. A method of producing a printed carton, the method comprising the steps of: printing a colour image on a front surface of a high-strength sheet; printing carton panel edge guide lines on a rear surface of the sheet; applying adhesive to the rear surface of the printed sheet; bringing a carton into contact with the printed sheet at the rear surface with panel edges in registry with the guide lines; uniformly adhering the printed sheet to the carton to cover adjoining carton panels; and curing the adhesive.

2. A method as claimed in claim 1, wherein the carton is assembled and pressed flat before being brought into registry with the printed sheet.

3. A method as claimed in claim 2, wherein the printed sheet is adhered to the carton by wrapping around completely.

4. A method as claimed in claim 3, wherein the printed sheet is wrapped around to the extent of overlapping at the extremities.

5. A method as claimed in any preceding claim, wherein the method comprises the further steps of cutting excess sheet according to the panel guide lines before contact with the carton.

6. A method as claimed in any preceding claim, wherein the carton is brought into registry with the printed sheet on a jig having adjustable alignment guides and vacuum apertures to hold the printed sheet in position.

7. A method as claimed in claim 6, wherein the printed sheets are conveyed on a porous conveyor belt to which a suction is applied from below to the front surface to maintain printed sheets in a flat configuration and to aid penetration of the adhesive.

8. A method as claimed in any preceding claim, wherein the printed sheet is laminated on the front surface.

9. A method as claimed in claim 8, wherein the printed sheet is laminated with a transparent film having a thermally-activated adhesive.

10. A method as claimed in any preceding claim, wherein the sheet is printed by a digital printing machine having an electrophotographic press.

11. A method as claimed in any preceding claim, comprising the further step of pressing the carton after application of the printed sheet to exclude any trapped air.

12. A method substantially as described with reference to the drawings.

13. A carton whenever produced by a method as claimed in any preceding claim.