AU1064197A

AU1064197A - Dry offset three-colour printing

Info

Publication number: AU1064197A
Application number: AU10641/97A
Authority: AU
Inventors: Sokratis Kaloudis
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-12-11
Filing date: 1996-12-11
Publication date: 1997-07-03

Description

DRYOFFSETTHREE-COLOURPRINTING

FIELD OF THE INVENTION

This invention relates to printing.

In a particular aspect, this invention relates to dry offset printing.

In another particular aspect, this invention relates to dry offset printing onto cylindrical bodies such as of metal, plastic or paper such as containers for drinks or foodstuffs or other objects.

In a still further particular aspect, this invention relates to dry offset printing onto cylindrical cans formed of metal .

BACKGROUND TO THE INVENTION

Many techniques of printing have been developed over the ages and one particular excellent method of printing is a wet offset printing using three or four colours. If four colours are used, it is usual that one of those colours is black and that colour is usually referred to by the abbreviation "K".

The other three colours may be any colour desired but where it is desired to produce a finished product having a reasonably lifelike appearance such as of a person, a landscape, or a naturally occurring object, then the three colours need to be carefully chosen so as to be so complimentary to one another such that the resultant print has a lifelike appearance.

To obtain a lifelike appearance, there are still many, many colours that might be used but it has become an industry standard to print in the colours cyan (commonly known as "C"), magenta (commonly known as "M" ) and yellow (commonly known as "Y" ) .

Further, standards have grown up concerning what cyans are acceptable, what magentas are acceptable and what yellows are acceptable and for practical purposes, most of the industry follows a generally agreed standard in what is known as the "CMYK" printing process.

Other printing processes may involve the use of more colours and will produce superior results than the CMYK process but at vastly increased costs.

Thus, while not perhaps providing the best print possible, the CMYK process has become well accepted as producing a print of generally adequate quality.

When the CMYK process is applied in respect of wet offset printing, quite excellent results can be obtained.

However, wet offset printing is not particularly suitable to many mediums particularly such as steel or aluminium cans or plastic bodies.

Whereas in wet offset printing where it is possible for four colours to actually overlie a single spot on an acceptable medium, it is not possible for four colours to overlie a single spot if the medium is unsuitable as is the case with aluminium and steel cans or plastic bodies.

Having regard to the above constraint, the printing of aluminium and steel cans has been mostly done by a dry offset process in which colours are kept separate from one another or only merge to a very small degree.

As a result, it is not easy to obtain lifelike appearance when printing on a metal can body unless one is prepared to go to a six or more colour process.

However, a six colour process is considerably more expensive to use than a four colour process.

Since objects such as metal can bodies, which are often used for drinks, do not have a long life and are not regarded by many people as collector's items, it is not thought commercially feasible to often go to six colour printing processes merely for the purposes of making an attractive metal can body which, after consumption of the contents, will either be discarded or perhaps recycled because of the value of the base metal.

Thus, in practice, printing on metal can bodies has tended to be away from lifelike colour representation and more commonly takes the form of graphics using blocks of individual colours which, while often bright and attractive, are nevertheless not lifelike in the sense of representing a natural object.

To illustrate some of the problems with dry offset printing on metal can bodies, reference will be made to the accompanying representations.

ACCOMPANYING REPRESENTATIONS

Figure 1 is a schematic representation of an existing dry offset printing machine for use in printing on metal can bodies,

Figure 2 is a black and white version of what was a colour photograph,

Figure 3 is a black and white representation of a chemical proof taken from the photograph of Figure 2 using four colour wet offset printing on a suitable medium not being a metal can body, and

Figure 4 is a black and white enlargement of a conventional colour separation being part of the photograph of Figure 3.

INTEGER LIST

1. Disc transfer wheel

2. Deco chain

3. Disk transfer vacuum head

4. Infeed chute

5. Mandrel wheel 6. Pocket

7. Mandrel

8. Blanket wheel 9. Ink station

10. Plate cylinder

11. Overcoat unit

12. Deco chain sprocket 13. Main drive motor

21 - 26 Individual ink stations (9) each carrying a separate colour.

DETAILED DESCRIPTION WITH RESPECT TO THE DRAWINGS

The dry offset printing machine shown in Figure 1 is known as the "Concord Decorator" and is a six colour dry offset printing machine useful for printing metal can bodies.

In a process using the machine of Figure 1, can bodies are fed in at an infeed sheet 4 and are transferred to a mandrel wheel 5. The can bodies are carried over a pocket 6 to a mandrel 7 and are then brought into contact with a blanket wheel 8.

The blanket wheel 8 is inked by a number of ink stations 9 and which are individually represented by the reference numerals 21 - 26.

Each ink station 9 has a plate cylinder 10 together with other means for transferring ink to the plate cylinder 10 and thence to the blanket wheel 8.

Contact of the metal can bodies with the blanket wheel results in ink being transferred and thereafter the can bodies are passed to an overcoat unit 11 which applies a sealing coating and the can bodies are exited via a deco chain sprocket 12.

A main drive motor 13 is provided.

Each of the ink stations 21 - 26 applies a different colour to the blanket wheel and as a result can obtain a realistically lifelike appearance but at some substantial difficulty and cost and require substantial skill on the part of a printer.

The machine shown in Figure 1 may be used in the process of the present invention but need only use three or four colours.

Reference is made to US Patent No. 4,554,241.

While the process of US Patent No. 4,554,241 is excellent, and the pictures resulting are clear and of good quality, nevertheless the colour obtained is non-lifelike although well representational as only two colours are used, a red and a black, and the "white" that occurs is really only the medium upon which printing occurs.

Figure 2 is a black and white representation of a photograph produced by standard photographic techniques and photographic printing on photographic paper.

Figure 2 in its colour version shows lifelike colours.

Referring now to Figure 3, this is a black and white version of a print produced by a printing process from the photograph of Figure 2 and once again shows in its colour version excellent colour.

However, Figure 3 in its original was produced by wet offset printing onto a white high quality card stock.

In practical terms, while the photograph of Figure 2 could in fact be presently produced on a metal can body, it could only be done so to the quality of the print representationally shown in Figure 3 by using twelve or more colours and at substantial set up and at very substantial cost.

In particular, it must be noted that the original of print shown in Figure 3 actually has overlapping of four colours, CMYK, using inks which allow this to occur and which have a transparency allowing an overall colour result to be achieved.

Referring now to Figure 4, this is an enlargement at a six times enlargement and representation in black and white of a portion of the photograph of Figure 3 turned into a separation of one colour, which could be any colour, but using conventional screening techniques for use in the wet offset process.

SUMMARY OF THE INVENTION

The present invention provides: -

a method of dry offset three-colour printing comprising transferring ink from a transfer device to an object to be printed;

wherein prior to the transferring

ink is applied to the transfer device such that

a first colour of the three-colours is applied substantially only in a first group of rectangles

a second colour of the three-colours is applied substantially only in a second group of rectangles, and

a third colour of the three-colours is applied substantially only in a third group of rectangles;

wherein each of the rectangles is, in an orientation, about twice as wide as it is high;

wherein the rectangles are arranged in rows and columns with alternative rows being staggered by about half the width of the rectangles from the immediately adjacent row

and such that any one individual rectangle of any one of the first, second and third groups has

adjacent to it in its row at one end and the other end, respectively, a rectangle of one of the other groups and a rectangle of the other of said other groups,

and in a first adjacent row said any one individual rectangle is adjacent to a rectangle of said other of said other groups and a rectangle of said one of said other groups,

and in a second adjacent row said any one individual rectangle is adjacent to a rectangle of said one of said other groups and a rectangle of said other of said other groups.

PREFERRED ASPECTS OF THE INVENTION

Preferably there is provided a method of dry offset three- colour printing comprising transferring ink from a transfer device to an object to be printed;

wherein prior to the transferring

ink is applied to the transfer device such that

wherein the rectangles are arranged in rows and columns with alternative rows being staggered by about half the width of the rectangles from the immediately adjacent row;

wherein the rectangles in each row from one side of each row to the other side of the row are sequentially and repeatingly

a rectangle containing the first colour,

a rectangle containing the second colour, and

a rectangle containing the third colour;

the arrangement further being such that

for any one row and first and second adjacent rows

each rectangle in said one row containing the first colour is adjacent to three rectangles of the second colour and three rectangles of the third colour,

each rectangle in said one row containing the second colour is adjacent to three rectangles of the first colour and three rectangles of the third colour, and

each rectangle in said one row containing the third colour is adjacent to three rectangles of the first colour and three rectangles of the second colour. The present invention also provides a method of dry offset three-colour printing comprising transferring ink from a transfer device to an object to be printed;

wherein prior to the transferring

ink is applied to the transfer device such that

wherein the rectangles are arranged in rows and columns with alternative rows being staggered by less than the width of the rectangles from the immediately adjacent row

a rectangle containing the first colour,

a rectangle containing the second colour, and

a rectangle containing the third colour;

the arrangement further being such that

for any one row and first and second adjacent rows each rectangle in said one row containing the first colour is adjacent to three rectangles of the second colour and three rectangles of the third colour,

each rectangle in said one row containing the third colour is adjacent to three rectangles of the first colour and three rectangles of the second colour.

The present invention also provides a method of dry offset three-colour printing comprising transferring ink from a transfer device to an object to be printed;

wherein prior to the transferring

ink is applied to the transfer device such that

wherein the rectangles are arranged in rows and columns with alternative rows being staggered and such that

any one rectangle of the first colour has adjacent its perimeter and along about 50% of that perimeter, rectangles of the second colour and along about 50% of that perimeter, rectangles of the third colour,

any one rectangle of the second colour has adjacent its perimeter and along about 50% of that perimeter, rectangles of the first colour and along about 50% of that perimeter, rectangles of the third colour, and

any one rectangle of the third colour has adjacent its perimeter and along about 50% of that perimeter, rectangles of the first colour and along about 50% of that perimeter, rectangles of the second colour.

The present invention also provides a mask for colour separation of the first colour which, with other similar masks but appropriate to the second and third colours, can be used in the process.

The present invention also provides a dry offset printing machine set up to perform the process.

The nature of the transfer device is not critical and a flat surface may be used but it is preferred that it comprises a curved surface and it is more preferred that it comprises a drum or cylinder.

When a curved surface is used, it is preferred that the rectangles of ink and a medium on which printing is to occur is done in a manner involving relative movement of the medium and the rectangles in a direction along the longer sides of the rectangles but to run in the direction along the shorter sides of the rectangles may be advantageous in certain circumstances.

The rectangles are preferably separated from one another by trapping such as a hairline or less which is usually about 0.05mm. The rectangles may be of any desired size and to a large extent, this will depend upon the fineness of the printing to be achieved. However, a very practical size is 0.250mm by 0.125mm.

While the three colours may be any colour desired, subject to ink availability, in practical terms, they will usually be cyan, magenta and yellow (CMY) and as a matter of practical convenience the remaining description will be confined to CMY but it is to be remembered that other colours may be used.

If black is to be printed such as in CYMK then elimination of the whole or a part of relevantly positioned rectangles of CMY can be achieved by techniques well known in the printing art. Such elimination may be achieved by the use of a fourth mask or by effective incorporation with one or more of the three masks used.

The number of rows of rectangles per inch in the columns is not critical and will tend to be governed by the fineness of printing desired. For very fine printing, screen ruling may be used. In general 65-100 lines or rows per inch is very suitable for printing on metal cans.

The process of this invention will now be described by way of non-limiting example with reference to additional representations.

BRIEF DESCRIPTION OF THE VIEWS OF THE ADDITIONAL REPRESENTATIONS

Figure 5 is a representation of coloured rectangles produced by the process of this invention but in greatly enlarged view,

Figure 6 is a black and white diagrammatic equivalent of Figure 5 with labelling of the colours and once again, greatly enlarged,

Figure 7 is a black and white reproduction of one of the masks which can be used in the process of the invention but in greatly enlarged form,

Figure 8 is a flow chart representing one manner of putting the process of the present invention into effect in the preparation of negatives which can be used with the machine of Figure 1; an alternative process using positives is available and

Figure 9 is an enlargement of a colour separation produced by the process of the present invention and which is roughly equivalent to Figure 4 excepting that a mask as per Figure 7 was used to produce it.

DETAILED DESCRIPTION WITH RESPECT TO THE ADDITIONAL REPRESENTATIONS

Referring to Figure 5, this illustrates the rectangles of colour that can be laid down by the present invention.

It is particularly to be noted that each rectangle is fully filled with the relevant colour whereas in practice more often than not, the rectangles would only be partly filled with colour.

Referring now to Figure 6, this corresponds to Figure 5 but is in black and white and diagrammatic form and wherein the colours have been labelled with names.

It is to be noted that the colours are laid out in rectangles in rows and in columns with the columns staggered in alternate rows. It is to be noted that for any one particular colour, 50% of its perimeter is adjacent one other colour and the other 50% is adjacent another colour.

For instance, and referring to Figure 6, each yellow is bordered on its left by a cyan and on its right by a magenta and above it and on the left side is a magenta and on the right side, cyan and below it on the left side is magenta and on the right side, cyan.

Of course, this arrangement cannot occur at the very edges but it would be well understood by those in the printing art that what may well be correct for the interior mass is not likely to be correct at edges.

Referring to Figure 7, this is a greatly enlarged view of one of the screens.

Reference is now made to Figure 8 which illustrates a process for preparing colour separation negatives which can be used in the machine of Figure 1 to print in accordance with the process of the invention.

Referring to Figure 8, a colour picture is taken and using any one of a number of techniques, yellow, magenta, cyan and, if desired, black separations are made. Among the techniques that are known for preparing such separations include photographic techniques and computer techniques.

From the yellow separation and using a composite of unexposed film, one of the masks such as of Figure 7 and the yellow separation there is produced by exposure an exposed film which is thereafter processed to produce a yellow final negative image which can be used in the machine of Figure 1.

Similar is done with respect to magenta and cyan. If it is desired to print black, then the black separation can be combined together with the colour separations or otherwise dealt with to produce final positives for yellow, magenta and cyan and also a black final positive.

Reference is now made to Figure 9 which is a representation equivalent to Figure 4 but suitable for dry offset processing and is a colour separation positive using the masks but for use in the process of the present invention.

The claims, illustrations, photographs and drawings, if any, form part of the disclosure of this specification as does the description, claims, illustrations, photographs and drawings of any associated provisional or parent specification or of any priority document, if any, all of which are imported hereinto as part of the record hereof.

Finally it is to be understood that various alterations, modifications and/or additions may be incorporated into the various constructions and arrangements or parts without departing from the spirit and ambit of the invention.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:-

1. A method of dry offset three-colour printing comprising transferring ink from a transfer device to an object to be printed;

wherein prior to the transferring

ink is applied to the transfer device such that

wherein prior to the transferring

ink is applied to the transfer device such that

a rectangle containing the first colour,

a rectangle containing the second colour, and

a rectangle containing the third colour;

the arrangement further being such that

for any one row and first and second adjacent rows

wherein prior to the transferring

ink is applied to the transfer device such that

a rectangle containing the first colour,

a rectangle containing the second colour, and

a rectangle containing the third colour;

the arrangement further being such that

for any one row and first and second adjacent rows

4. A method of dry offset three-colour printing comprising transferring ink from a transfer device to an object to be printed;

wherein prior to the transferring

ink is applied to the transfer device such that

any one rectangle of the second colour has adjacent its perimeter and along about 50% of that perimeter, rectangles of the first colour and along about 50% of that perimeter, rectangles of the third colour, and any one rectangle of the third colour has adjacent its perimeter and along about 50% of that perimeter, rectangles of the first colour and along about 50% of that perimeter, rectangles of the second colour.

5. A mask for colour separation of the first colour which, with other similar masks but appropriate to the second and third colours, can be used in the method of any preceding claim.

6. A method or a mask as claimed in any preceding claim, wherein the rectangles are separated from one another by trapping such as a hairline or less which is usually about 0.05mm.

7. A method of dry offset printing substantially as hereinbefore described with reference to any one of the accompanying drawings.

8. A mask for dry offset printing substantially as hereinbefore described with reference to any one of the accompanying drawings.

9. The steps, features, compositions and compounds referred to or indicated in the specification and/or claims of this application, individually or collectively, and any and all combinations or any two or more of said steps or features.