IE60033B1

IE60033B1 - A method of printing

Info

Publication number: IE60033B1
Application number: IE260787A
Authority: IE
Original assignee: Clare Patents Ltd
Priority date: 1987-09-28
Filing date: 1987-09-28
Publication date: 1994-05-18
Also published as: GB2210328B; GB2210328A; ZA878233B; IE872607L; GB8818352D0

Abstract

A method multi-coloured/thermographic printing comprises the steps of printing onto sheet material at least two colours, at least one of which is a rubber-based ink, and distributing a sufficient amount of a nylon-based dust onto the wet or tacky rubber-based ink(s) to ensure the presence of an excess amount of dust. The excess dust is then removed and the sheet material and the dust is heated to a temperature sufficient to melt the dust and cause the rubber-based ink image(s) to rise relative to the sheet material. The resulting product is then cooled. In one embodiment, cyan, yellow and magenta inks are quick-drying oil-based inks. With black as the rubber-based ink provided the raised effects.

Description

Α METHOD OF PRINTING This invention relates to a method printing» In particular, it relates to a method of full colour photographic printing.

To produce full colour process printing, a printing press capable of producing high quality dot-for-dot register is required. Such printing presses are well known and the method of using them will only be briefly described here» There are four colours used in the colour printing process vis cyan, yellow, magenta and black» Each colour is printed onto sheet material in the form of tiny dots at the reauired locations» To achieve full colour accurate printing, all of the dots of each colour must be accurately juxtaposed relative to each other so that only 6 the actual colour required at a particular location is actually printed» In the printing process, the sheet material first passes that part of the press having the cyan colour followed immediately and In turn by the yellow, magenta and black colours. However, it will be appreciated that the order of printing is not critical but black is usually the last colour to be printed. Oil based inks are used in the printing process as the inks dry virtually instantaneously on application to the sheet material. Sometimes it is necessary to us© a drier to ensure that the ink is fully dry. The reason for this is that as the sheet comes off the printing press, it is stacked on top of the previous sheet. Accordingly, to prevent ink on the upper sheet of the stack transferring to the back of the sheet being placed thereon, it is imperative that the ink on the uppermost sheet be dry.

Thermographic printing is a well known technique. It is normally used in the production of raised printing on company stationery, letterheads, business cards, etc. The procedure of thermographic printing employs the use of a rubber based stay open ink. Rubber based inks do not dry very quickly which is an essential requirement in thermographic printing. The sheet material having been printed with a single colour rubber ink is then passed by a conveyer belt into a thermographic printing machine. In the machine, which includes a dusting section, nylon dust from a hopper is vibrated across the sheet material in the vicinity of the wet ink. The sheet material then passes through a vacuum unit of the machine which removes the surface dust leaving only the dust which has adhered to the wet ink. The heating causes the ink and the dust to rise relative to th® sheet material to give a raised printed texture. The sheet material then passes through a cooling section of the machine following which the sheet material is delivered to a delivery tray and stacked.

Heretofore, the thermographic printing employing a full colour printing process has not been employed chiefly because of the different types of ink required for each technique.

It is known to provide a three-dimensional effect in full colour printing by the use of a clear varnish ink being placed over those sections of the sheet material it is desired to raise. Th© problem with this method is that a fifth printing plate is required and furthermore © < 5 graphic artist has to draw separately the section to be raised. Both of these steps add substantial cost to the product and, accordingly,, are not generally employed.

It is an object of the present invention to overcome these problems.

Th© invention therefore provides a method of multi-coloured thermographic printing which comprises: (a) printing onto sheet material at least two colours at least one of which colours is a rubber based ink and at least one of which colours is an oil based ink; (b) distributing a sufficient amount of a nylon based dust onto the wet or tacky rubber based ink(s) to ensure the presence of an excess amount of the dust; (c) removing th© excess dust; (d) heating the sheet material and dust to a temperature sufficient to melt the dust and cause th© rubber based ink(s) to rise relative to the sheet material; (e) cooling the sheeting material.

The invention will be understood in greater detail from the following description which is given by way of ’ example only.

Having prepared four suitable plates - on© for each colour to be printed viz cyan, yellow, magenta and black, the plates are mounted on a conventional colour printing press such as a Heidleberg press to obtain full colour photographic printing. The rollers of the press are inked» At least one of the rollers is inked with an oil based ink, the remaining rollers being inked with a rubber based ink having open tacky additives» Sheet material is fed through the press so as to print in full colour the desired, image thereon. The thus printed sheet material, the rubber based ink of which is still tacky or wet, is fed sequentially onto a conveyor belt and into a thermographic printing machine. In the thermographic machine, the nylon dust is sprinkled over the sheet material and subsequently excess dust is vacuumed off the sheet material. The ink and the dust adhering thereto is heated so as to melt the dust and raise the ink relative to the sheet material. The sheet material is then cooled and ejected from the thermographic printing machine onto a stack.

It will be appreciated the above description relates to the thermographic printing of all four colours. However, it would be possible to thermographically print any combination from one to all four colours as desired. In that event, the colour or colours which it is desired to print thermographically should be applied to the sheet material last to ensure that the colour or colours are not dry prior to the step of applying the nylon dust to the sheet material. If desired, a drying stage could be employed for the inks it is desired not to thermographically print which stage would be located just prior to the printing of the colour or colours it is desired to thermographically print. It will be appreciated, therefore, that for ink which it is not desired to thermograph!cally print, then such inks should be oil based with the thermographically printed inks being of the rubber based type. Alternatively, any one of the rubber based inks it was desired not to thermographically print, a drying stage for that ink could be used as indicated above.

In the known technique of achromatic printing, the dark elements of the blue, yellow and magenta colours are removed during separation for the preparation of the printing plates and the required total concentration of black colour is added during the printing of the black colour. In this way, the other three colours are initially printed much lighter than in th© conventional non-achromatic printing. If the blue, yellow and magenta inks are oil based inks and therefore not subject to thermographic printing and only the black ink is a rubber based ink and therefore subject to thermographic printing, then a stronger raised effect can be obtained because of the increased concentration of black ink required for ©chromatic printing.

The invention is not limited by the specific embodiments described which can undergo considerable variation without departing from the scope of the invention

Claims

1. . A method of multi-coloured thermographic printing which comprises:(a) colours at ink and at ink; printing onto sheet material least one of which colours is least one of which colours is at least two a rubber based an oil based (b) distributing a sufficient amount of a nylon based dust onto the wet or tacky rubber based ink(s) to ensure the presence of an excess amount of dust; (c) removing the excess dust; (d) heating the sheet material temperature sufficient to melt the dust rubber based ink(s) to rise relative to and dust to a and cause the the sheet material; and (e) allowing the sheet material to cool.

2. A method as claimed in Claim 1 wherein the oil based ink(s) is applied first followed by the rubber based ink(s).

3. A method as claimed in Claim 1 or Claim 2 wherein the inks are selected from the group comprising cyan, yellow, magenta and black.

4. A method as claimed in any of Claims 1-3 wherein four colours are printed onto the sheet material vis. cyan, yellow, magenta and black to obtain full colour photographic printing.

5. A method as claimed in any of Claims 1-4 wherein the colours cyan, yellow and magenta are oil based inks and the black colour is a rubber based ink. S. A method of multi-coloured thermographic printing 5 substantially as hereinbefore described.

6.

7. Sheet material whenever printed by a method as claimed in any of Claims 1-6. F. R„ KELLY & CO., AGENTS FOR THE APPLICANTS.