GB2097331A - Method of multi-colour printing on cylindrical containers - Google Patents

Abstract

Layers of different coloured ink formulations are transferred from a plurality of patterned rollers (30a, 30b) on to predetermined areas of the outer periphery of a single transfer roller (33), and the body of a cylindrical container (10) is pressed against said transfer roller and rotated as many times as the number of said patterned rollers (30a, 30b), the length in the circumferential direction of each area on the transfer roller (33) corresponding to the circumference of the container (10). There may be similar additional transfer rollers (43). If the colours are to overlap on the container, the rack value of transferred layers should decrease from the first to the last layer. <IMAGE>

Description

SPECIFICATION Method of multicolour printing on cylindrical containers The present invention relates to a method of multi-colour printing (including multi-layer printing) on the exterior surface of the side wall of a cylindrical container with ink form rollers.

It is known to perform multi-colour printing on the exterior surface of the side wall of cylindrical containers such as plastics tubes and cans, and many containers having multi-colour patterns printed thereon are available on the market. In one type of multi-colour printing, different coloured inks are applied to a container without overlapping each other, and in the other type, different colour inks are applied to the container so that they partially overlap. These two types of printing are illustrated in Figures 1 and 2 of the accompanying drawings, respectively, in which the side wall bearing a printed pattern is shown in a flat form. In FIG. 1 , the side wall is painted with white paint U which is dried and baked to form a base-coat which is then printed with red (W), green (X), yellow (Y) and blue (Z) inks to form completely discrete areas.In FIG. 2, the side wall has a base layer coated with white paint U', and red, green, yellow and blue areas formed by the respective coloured inks W', X', Y' and Z'. FIG. 3 is a cross section of FIG. 2 taken on the line II I-Ill, and as shown, part of the area formed by W' is covered with X', and part of X' is covered with Y', and part of Z' is covered with Z'. Each of the ,overlapped portions has the tone of the upper layer colour, with a hint of the colour of the layer underneath.

The first type of multi-colour printing, or printing without forming overlapped layers, is generally performed with a.four-colour printing machine. A typical example of the known fourcolour printing machine is shown schematically in FIG. 4 of the accompanying drawings. In the figure, a printing table is indicated generally by 1.

This table supports a rotary disc 2 for transport of cans, and the disc rotates about a shaft 4. A container (A), typically a can, passes through a supply channel 6 and is fitted on a mandrel 10 mounted on the disc 2. The can is transported to a printing site 11 by the rotation of the disc 2. An ink form roller is generally indicated by 3, and it rotates about a shaft 5 in a direction opposite to that of the rotation of the disc 2. At the printing site 11, different coloured inks that have been transferred from four ink conductors 20d, 20c, 20b, and 20a are transferred on to the exterior surface of the can A. Respective ink formulations are supplied to these conductors from known ink fountains 21 d, 21 C, 21 b and 21 a. Over-print varnish is applied to the printed surface of the can by an application roller 7.The varnish is supplied from a pair of varnish retaining rollers 8. The can with four colours of ink printed thereon and finished with varnish is subsequently discharged through a discharge channel 9. The can A on the mandrel 10 is transported to the printing site 11 by the rotation of the disc 2, and at that site, makes rolling -- and press-contact with the ink form roller 3 so that the ink on the outer circumference of the roller 3 is transferred on to the exterior surface of the can.

The embodiment shown in FIG. 2, assumes that the form roller 3 rotates counterclockwise, so the transfer of ink on to the form roller 3 starts with a rolling contact of the roller 3 with the ink conductor 20d which supplies a predetermined coloured ink on a predetermined area of a given section. By reference to FIG. 1 ,for example, red ink W is supplied in a rectangular area of the section of the side wail coated with white paint U.

Subsequently, a second ink formulation (say, green ink X) is supplied from the roller 20c on to an area of the same section which does not overlap the area of red ink, and a third ink formulation (say, yellow inkY) is supplied from the roller 20b on to an area which does not overlap either of the areas formed by red and green ink formulations, and finally a fourth ink formulation (blue ink Z) is supplied from the roller 20a on to an area which does not overlap with any of the areas formed by red, green and yellow ink formulations.

The ink form roller 3 having four coloured inks supplied in predetermined areas within a given section without overlapping each other is presscontacted by the exterior, white painted surface of the can at the printing site 11, and when the can makes one turn, the four coloured inks are transferred on to the exterior surface of the can in a pattern as illustrated by FIG. 1. Subsequently, the can is coated with overprint varnish and transported through the discharge channel 9 into drying and baking zones.

One defect of the printing machine described above is that it is not capable of performing multicolour printing wherein different colours of ink are applied to form overlapping layers. As will be described in detail below, overlapping layers of ink can be formed on the form roll when the tack value of ink decreases from the base layer to the top layer. This means that the topmost layer and thus the exterior surface of the can is formed by the lowest tack value ink. When the can comes out of contact with the form roll, half the thickness of the top-most ink layer is transferred on to the can, leaving the other half of the topmost layer and the underlying layers of ink on the roller.

The conventional method of multi-layer printing, the result of which is schematically illustrated in FIG. 2 uses one form roller per colour.

A certain colour ink is first transferred on to the exterior surface of a can, and after drying the resulting ink layer, another coloured ink is applied on to an area that overlaps the area coated previously, and after drying the second ink layer.

still another coloured ink is applied in a like manner, followed by drying. Application and drying is repeated in this way until a desired number of overlapping ink layers is formed. This method can achieve both types of multi-colour printing, but since it involves repeated application and drying of ink layers, the number of process steps is increased and the process time prolonged.

Among the recently developed printing methods is the wet-on-wet method wherein a wet layer of one paint is overlaid by a layer of another paint and both layers are dried and baked simultaneously. When this method is performed with the conventional four-colour printing machine described above, ink formulations can be transferred on to the form roller from the respective ink conductors, but when the ink formulations are transferred on to the exterior surface of the can, only the top-most ink layer is picked up by the can and the underlying ink layers are left on the form roller, and as a result, the desired muiti-colour printing cannot be achieved.

An object of this invention is to provide a simple method of achieving a multi-colour printing by forming overlapping ink layers without experiencing the defects of the conventional technique.

Another object of this invention is to provide a method of multi-colour printing that is also capable of forming discrete patterns of different colours.

According to the present invention there is provided a method of muiti-colour printing on the side wall of a cylindrical container by bringing the exterior surface of the container into a press- and rolling-contact relationship with an ink form roller, wherein two or more ink formulations of different colour are sequentially transferred in a like manner from two or more ink conductors on to the outer periphery of the ink form roller, a first ink formulation being transferred from a first ink conductor on to a first area of the outer periphery of said ink form roller which extends in a circumferential direction of said outer periphery and whose length is equal to that of the outer periphery of the side wall of the container, and a second ink formulation of a colour different than that of the first ink formulation being transferred from a second ink conductor on to a second area of the outer periphery of said ink form roller whose length is equal to that of the first area and which is adjacent said first area and extends in a circumferential direction of said outer periphery, and the exterior surface of the side wall of said container is brought into a press- and rollingcontact relationship with the surface of the ink form roller to which the layers of the desired ink formulations here been transferred, the number of revolutions of said container being equal to the number of said ink conductors employed so that the respective ink layers are transferred on to the exterior surface of the side wall of said container from said ink form roller.

Embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings, in which: FIG. lisa schematic representation of the side wall of a container treated with multi-colour printing to form discrete patterns of different colours, the side wall being shown in a flat form for the sake of clarity; FIG. 2 is a schematic representation of the side wall of a container treated with multi-colour printing to form overlapping ink layers of different colours, the side wall also being shown in a flat form for the sake of clarity; FIG. 3 is a cross section of FIG. 2 taken at the line Ill-Ill with the thickness of the respective ink layers being exaggerated; FIG. 4 is a schematic line drawing of essential parts of the conventional four-colour printing machine; and FIG. 5 is a schematic line drawing showing one embodiment of the method of this invention.

FIGS. 1 to 4 have already been described above.

One embodiment of the method of this invention is now described by reference to FIG. 5.

In this figure, as in FIG. 4, a rotary disc to which cans A are supplied through a can supply channel (not shown) and fitted on a mandrel 10 is generally indicated at 2. Upper and lower form rollers 33, 43 are positioned adjacent to the rotary disc 2. In this figure, 11 indicates an upper printing section at which the can A on the mandrel 10 receives ink from the upper ink form roller 33 as it is advanced (revolved about the axis of the disc 2) by the rotation of the disc 2; 11' indicates a lower printing section at which the can likewise receives ink from the lower ink form roller 34; 30a is a first ink conductor which transfers a first ink formulation on to the upper from 33; 30b is a second ink conductor for transfer of a second ink formulation; 31 is a first ink layer deposited on the first ink conductor 30a; 32 is a first ink layer that has been transferred from said first ink conductor 30a on to a first area 132 of the ink form roller 33.

Said first area 132 is that part of the outer periphery of the ink form roller 33 which extends in circumferential direction of the roller 33 and whose length is equal to that of the outer periphery of the side wall of the can, and the first layer deposited on the first ink conductor 30a is transferred on to this first area 132. Generally, when two rollers holding ink in position and rotating at equal speeds come out of engagement, an ink layer about the same thickness is left on each roller.

When the form roller 33 continues to rotate and the first area 1 32 has passed under the second ink conductor 30b to reach an area indicated by 132', a second ink layer 34 deposited on said conductor 30b is transferred on to a second area 135 of the roller 33. The second inl < layer thus transferred is indicated at 35. The second area 1 35 is adjacent and equal in length to said first area that has been brought to the area 132' by the rotation of the ink form roller 33 and extends in a circumferential direction of said roller.

Each of the length of the two areas 132,135 is equal to the length of the outer periphery of the side wall of the can which is indicated by I in FIG. 2.

The two areas 132, 135 on to which the ink formulations have been transferred, advance further until they come into a press-contact relationship at a point 50 on the pass line of the can with the can A that has been transported on the rotary disc 2. The point 50 is also the starting point of the upper printing section 11. When the centre of the can A reaches this point, the leading edge of the first area 132 having the ink layer 32 transferred on to the first area 132 on the form roller 33 comes into contact with the exterior surface of the side wall of the can A.The can A, while it remains in press-contact relationship with the roller 33, continues to revolve about the axis of the disc 2 until it reaches a point 55 intermediate the starting point 50 and a point 51 where it is no longer in press-contact with the roller 33, and at this point 55, the can stops being in press-contact relationship with the first area 132 which is equal in length to the outer periphery of the side wall of the can. At the same time, the can starts to make press-contact with the leading edge of the second area 135 (which is also the trailing edge of the first area 132).Therefore, when the can A moves from the starting point 50 to the intermediate point 55, the upper ink form roller 33 rotates from a position where the leading edge 36 of the first area 132 faces the starting point 50 (i.e. a point where the line connecting the starting point 50 and the centre of the upper ink from roller crosses the circle formed by the outer periphery of the ink for roller) to the position indicated in FIG. 5 (the first area 132 is indicated by 132"), and in consequence, the can A is caused to make one turn so that the ink layer 32 transferred on to the first area 1 32 is again transferred on to the side wall of the can A. In FIG. 5, an ink layer which is left untransferred on the roller 33 is indicated by 32".Subsequently, the can A moves from the intermediate point 55 to the end point 51, and during this period, the second ink layer 35' transferred on to the second area 135 (which has moved to a position indicated by 135') of the upper ink form roller 33 is again transferred on to the exterior surface of the side of the can.

The above procedure is enough to achieve twocolour printing. In a preferred embodiment of this invention, four-colour printing is performed using a lower ink form roller 43 for printing the other two colours. As shown in FIG. 5, the form roller 43 is positioned along a path where the can A advances and it is ahead of the upper ink form roller 33. In FIG. 5, third and fourth ink conductors are indicated at 40a and 40b, respectively. Details of the lower ink form roller, and the third and fourth ink conductors are not described herein because they have the same construction and function as those of the upper ink form roller 33 and the first and second ink ductors 30a and 30b.

In the figure, 41 and 44 are ink layers deposited on the third and fourth ink ductors 40a and 40b, respectively; and 42 and 45 are third and fourth ink layers transferred on to third and fourth areas 142 and 145 of the ink form roller 43. Like the first and second areas 132 and 135, the third and fourth areas 142 and 145 are adjacent each other and equal in length to the outer periphery of the side wall of the can. The start point and end point of the lower printing section 11' are indicated at 52 and 53 which correspond to the points 50 and 51, respectively.In FIG. 5, the lower ink form roller 33 is represented as if only the first ink layer has been transferred on to the side wall of the can A, and the lower ink form roller 43 is represented as if the can A' has made two turns to come out of contact with the third and fourth areas (which are indicated by 142" and 145' in the figure).

The can A' to which the first and second ink layers have been transferred from the upper ink form roller 33 in the upper printing section 11 continues its revolution about the axis of the disc 2, and in the lower printing section 11', the can has the third and fourth ink layers transferred on to its side wall from the lower ink form roller 43 as in the upper printing section 11. The can having the four ink layers transferred thereto is indicated by A". Subsequently, the can continues to revolve about the axis of the disc 2 and is dislodged from the mandrel and sent to drying and baking zones through a discharge channel. The first to fourth ink layers according to the embodiment described above correspond to the inks W, X, Y and Z referred to in FIG. 1.

The embodiment described above assumes the use of two ink form rollers, but it is to be understood that four-colour printing can be effected with a single form roller having formed thereon four areas that correspond to the first and fourth areas 132, 135, 142 and 145. It is also to be understood that three or more form rollers may be used. A printing method wherein four coloured inks transferred on to a single ink form roller are sequentially transferred on to the can, one colour for one turn of the can, permits the use of a fairly simple printing machine. In the embodiment described above, two colours of ink are transferred on to each one of two ink form rollers, and this method has the advantage of high-speed printing as compared with the former type of four-colour printing using only one ink form roller.

The method of performing four-colour printing to form overlapping ink layers according to this invention will now be described. This method is possible by controlling the tack value of different ink formulations, and except for this point, the explanation of the method of four-colour printing to form four discrete patterns applies, so that the following description provides only a brief outline of the method of performing four-colour printing to form overlapping ink layers.

To form overlapping ink layers so that a first ink layer transferred on to the can is partially overlapped by a second ink layer, the first mentioned ink layer must have a tack value lower than that of the second ink layer. One plausible reason for this necessity is as follows: as already described, when the can is rotated in a press contact relationship with an ink form roller to transfer ink to the can, the thickness of the ink layer transferred is about half the initial thickness of the ink layer on the form roller. When the form roller carrying a subsequent ink layer is brought into a press-contact relationship with the can while the previously transferred ink layer is still wet, two wet ink layers are formed between the can and the form roller.When the can and form roll rotating in a rolling-contact relationship gradually come out of engagement, the ink layer having a lower tack value is divided into two.

Therefore, if the ink layer first transferred on to the can body has a tack value lower than that of the ink layer transferred next, the first ink layer is separated into two, and as a result, one half of the first ink layer is left on the can body whereas the other half and all of the subsequently transferred ink layer are left on the form roller. On the other hand, if the previously transferred ink layer has a higher tack value, one half of the subsequently applied ink layer is transferred on to the previously applied ink layer to provide a can body having ink layers of different colours printed thereon.

The above embodiment is now described by reference to FIGS. 5 and 2: for instance, red ink (W') is transferred on to the first area 132 of the upper form roller 33 to provide a pattern as shown in FIG. 2, and green ink (X') having a lower tack value than W' is applied to the second area 135 in a pattern as shown in FIG. 2, and the two overlapping ink layers W' and X' are transferred on to the exterior surface of the can A in the upper printing section 11. Yellow ink (Y') having a lower tack value than X' is transferred on to the third area 142 of the lower form roller 43 in a pattern as shown in FIG. 2, and blue ink (Z') having the lowest tack value is transferred on to the fourth area 145 in a pattern as shown in FIG. 2, and the two overlapping ink layers Y' and Z' are transferred on to the exterior surface of the can A' in the lower printing section 11'.

The tack value of the ink decreases from the first applied ink formulation to that last applied, so that an ink formulation can be transferred on to the exterior surface of the can body to partially overlap the layer formed by the previously applied ink. Because of this, the method of this invention can be used with advantage for providing gradation in dot printing. Overlapping ink layers of different colours can be provided by using one or more ink form rollers. High-speed printing can be achieved with more than one ink form roller.

As described in the foregoing, according to the method of this invention, a single ink form roller bearing one ink layer in each of a plurality of predetermined areas of the roller is brought into a rolling- and press-contact relationship with the can body to transfer an ink layer of one colour on to the exterior surface of the can body per turn of the can. As a result, this invention can provide not only discrete patterns of different colours but also overlapping ink layers by decreasing the tack value of ink from the first transferred ink layer to the last transferred ink layer. As a further advantage, this invention uses only one ink form roller to transfer more than one colour of ink layer and achieves a higher degree of registration than the conventional multi-colour printing method for providing both discrete and overlapping patterns.

Claims (4)

1. A method of multi-colour printing on the side wall of a cylindrical container by bringing the exterior surface of the container into a press- and rollingcontact relationship with an ink form roller, wherein two or more ink formulations of different colour are sequentially transferred in a like manner from two or more ink conductors on to the outer periphery of the ink form roller, a first ink formulation being transferred from a first ink conductor on to a first area of the outer periphery of said ink form roller which extends in a circumferential direction of said outer periphery and whose length is equal to that of the outer periphery of the side wall of the container, and a second ink formulation of a colour different than that of the first ink formulation being transferred from a second ink conductor on to a second area of the outer periphery of said ink form roller whose length is equal. to that of the first area and which is adjacent said first area and extends in a circumferential direction of said outer periphery, and the exterior surface of the side wall of said container is brought into a press- and rollingcontact relationship with the surface of the ink form roller to which the layers of the desired ink formulations have been transferred, the number of revolutions of said container being equal to the number of said ink conductors employed so that the respective ink layers are transferred on to the exterior surface of the side wall of said container from said ink form roller.

2. A method according to Claim 1 wherein a plurality of ink form rollers are used to transfer the layers of the respective ink formulations on to the exterior surface of the side wall of the container.

3. A method according to Claim 1 or 2 wherein the tack value of overlapping ink layers successively transferred to the exterior surface of the side wall of the container decreases from the first to the last transferred ink layer.

4. A method of multi-colour printing substantially as herein described with reference to and as illustrated in FIG. 5 of the accompanying drawings.