EP0258099A1 - Method of gilding or marking in relief upon thermographical printing - Google Patents

Abstract

Gilding or relief-marking process which starts with any typographic, offset or other impression and converts it into relief of variable thickness, by the known thermography principle, but employing a hot-melt powder endowing the film forming the relief with adhesive properties capable, after it has solidified, of transferring and retaining on its surface a marking material.

Description

Gilding, printing or hot stamping, is a known process used in various industries such as printing, cardboard, factories of plastic materials, bookbinding workshops, etc.

Schematically, the marking principle is as follows:
a roll consisting of a polyester film is covered, on one side, with a thin marking film, metallic or not, on which is then deposited a heat-reactive hot-melt adhesive. During the marking operation, a browning iron, the raised parts of which represent the image to be marked, is heated and pressed against the marking film and the receiving support. Only the parts of the film and of the receiving support in contact and pressure with the raised parts of the browning iron are heated, which allows the reactivated adhesive in these areas to adhere and fix themselves with the marking film on the support. receiver. The transfer of the marking film, from the film to the receiving support, takes place, at each cycle, when the pressure is released and the press when opening moves the film away from the support. At the origin of this process, the metallic film was produced with gold leaf. Nowadays, very often, the strip is vacuum metallized and colored aluminum has replaced gold. Different pigments or decorative marking materials are sometimes substituted for the metallic film. The manufacturers of these marking films offer users a range of products whose decorative effects, much sought after, lead to countless applications.

All kinds of plate or roller presses are equipped to carry out this hot stamping and include devices allowing the strip to run intermittently, with a variable advance according to the length of the pattern to be reproduced and systems to heat and maintain in temperature the iron to mark.

The pressure required to transfer the film from marking on a card-type receiver support is of the order of 250 Kg / cm2.

In many cases, to improve the decorative effect and the readability, a pushing back of the support, in the marked parts, makes it possible to highlight them. The technique currently used gives very good results with regard to the quality obtained, but has a certain number of major faults due to the basic principle of the process and to the means necessary for its implementation.

These faults are defined as follows:
- transfer machine, press or heating cylinder, very heavy, unwieldy and representing a significant investment,
- high cost of the materials to be used such as gilding irons or to repel having repercussions on the cost prices of the printed matter and being very difficult to incorporate into its selling price, mainly in the very frequent cases of prints of little copies,
- lack of flexibility of use and too long implementation time of the process limiting its possibilities of development,
- need to use highly qualified operators, because they are faced with a set of difficulties to overcome to achieve quality marking.

These difficulties are broadly listed as follows:
- relative thickness irregularity in different areas of the same support,
- variable surface condition from one support to be marked to another,
- pressure phenomena very often difficult to control and mainly on platen presses where it is very difficult to obtain a perfect distribution of the pressure and mainly when it is a question of simultaneously treating patterns comprising large printing surfaces next to fine lines,
- poor general distribution of the temperature of the heating plates on which the printing plates are fixed, causing transfer defects in the marking film,
- relatively very low hourly production.

In addition, and in order to fully appreciate the care required to carry out sation of a good marking, it should be known that the marking film and the fusible adhesive covering film each have a thickness of the order of a micron and admit, in most cases, only temperature differences and very low pressure.

On the other hand, the embossing to obtain the relief is also a matter for specialists, because this extremely delicate operation requires solid experience and mainly when one uses marking irons making it possible to brown and repel simultaneously. The object of the present invention is an extremely simple process, enabling any printer to obtain relief prints coated, on the surface, with the same type of marking film as usually used.

According to the present invention, the obtaining of relief printing is carried out on the basis of the known principle of thermogravure, by modifying the powder products usually used, with products having particular adhesive properties.

The relief printing is then coated with a traditional marking film, the transfer of its support strip being carried out using the adhesive properties of the film forming the relief image.

The operation is carried out schematically as follows:

1 - Traditional printing which, depending on the receiving medium, can be wet offset, dry offset, typographic, screen printing, flexographic, heliographic, etc. The only criterion to remember is that the ink, printing varnish or overlay or other material used to form the image to be transformed into relief, ie moist on the surface.

2 - Transformation in relief of this impression by the known principle of thermogravure, which consists in sprinkling a flat impression whose ink is still wet, of a hot-melt powder having the property of melting under the action of the heat generally associated to that of infrared radiation, to form a semi-liquid relief film, which freezes when passing under a jet of fresh air to avoid its deformation and the adhesion of the sheets to one another when these pile up one above the other. Excess powder not retained by the wet ink is continuously vacuumed and recycled. The present invention, while using the principle of thermogravure for its relief printing, provides an important variant as regards the powdered materials traditionally used for this process.

Indeed, the powders usually used in thermogravure must have physical characteristics allowing them to withstand a significant rise in temperature, without having a tacky surface state, so as to avoid any risk of adhesion of the sheets to each other. The adhesiveness of these powders appears when they pass into the semi-liquid phase.

These properties are contrary to those necessary for the application of the process which is the subject of the present invention where the adhesiveness of the film in relief must be obtained after its solidification, as long as it retains or regains a surface temperature of the order of 50 ° centigrade. It must also, when using powders of small particle size, keep its adhesiveness in the semi-liquid state.

3 - Surface coating of the image in relief with any traditional marking material, the transfer of which takes place thanks to the thermoadhesive properties of the film in relief, generally accompanied by a slight calendering made from a flexible material. By this method, the fusible adhesive covering the marking material of the films usually used becomes useless but can possibly be preserved, because its adhesive reactivation is obtained at a much higher temperature than that of the raised layer and therefore remains inert in does not intervene in the transfer phase of the marking material.

When producing thermogravure printing, the minimum particle size generally used is of the order of fifty microns. This is not the case in the present invention where one can obtain an impression covered with a marking material with a practically zero relief, starting from powder whose average particle size will be between five and twenty microns, giving a laminated film, depending on the porosity of the support of the order of five to ten microns. In this if the process is applied, a long tunnel oven is avoided since the melting and film-forming state of the fine powder film can be obtained simultaneously by calendering at a slight temperature during the transfer operation, or calendered cold with a slight preheating of the powdery print.

One of the essential differences characterizing the present invention resides in the fact of retaining, on the surface of the support, an adhesive layer forming the image to be reproduced by marking, of a variable thickness and always sufficient, whatever the porosity of the object. to be marked, to obtain an easy transfer in all cases. This is not possible in the usual process, because the fusible film is intimately linked to the marking material it covers and can therefore hardly exceed one micron in thickness, without the risk of causing irregular peeling and tearing. of the marking material during its transfer, providing a poor definition of the contours of the image on the receiving medium. This constraint results in the need to use for the transfer of reliefs and very high pressures of the order of 250 Kg / cm2.

The process which is the subject of the present invention requires average pressures of the order of 1 to 2 kg / cm 2.

By way of nonlimiting example, one of the operating methods of the method is described below with reference to the accompanying drawings.

An offset printing press 1 Fig. 1 places a form 2 on the feed conveyor 3 of a 1 A heat-etching machine. This form 2 passes successively on the powdering conveyor 4 where it is covered over its entire surface with a film of powder from the powder 5. Cyclone 6 continuously sucks up and recycles up to the inside of the powder container 5 the excess powder not retained by the wet ink. At the outlet of the powder block 7, the powdered print only in the printing areas continues its cycle and is conveyed by the fusion conveyor 8 inside the tunnel oven 9 where the powder image becomes a covered image a film in relief in the semi-liquid state which is solidified on the cooling conveyor 10 under the action of the fresh air pulsed by a turbine 11, with adjustable flow rate, blowing inside the perforated box 12. The print 2 whose embossed film is solidified but whose adhesiveness is still very high then passes on the margin conveyor 13 of the transfer device 1 B and under the pressure cylinder 14 where the marking strip 15 is applied to the print 2 to effect the transfer of the marking material. The conveyor 16 conveys the "marked" print to the reception table 17.

FIG. 2 represents a top view of the margin and output conveyors of the device for transferring the marking material.

Figure 3 shows a front view of the entire transfer device.

Using these 2 figures, we understand the detailed operation of the marking operation, which is defined as follows:
the printed matter transformed into relief and whose film is still viscous engages, after solidification of its mass, on the margin conveyor 13 FIG. 2-3. The pneumatic margin rectifier 13 A Fig. 2 presses by means of compressed air jets at low pressure (about six bars) on the oblique strip 13 B Fig. 2 to straighten and tack the paper on the cleat 13 C Fig. 2. The set of conveyors and cylinders ensuring the advance of the belt is driven using a stepping motor 18 Fig. 2 or direct current provided with an encoder controlled by an electronic device, programmable as a function of the location of the marking areas of the print to be processed. A gear train 18 A Fig. 2 ensures the connection of the training of the various conveying bodies of the print. An optical sensor 19 Fig. 2-3 detects the arrival of printed form 2 and starts the marking cycle according to the established program. The marking cycle includes the following functions executed simultaneously:
a) advance of the blank marking strip 15 FIG. 3 previously rewound and supported by the axis of the reel 15 A FIG. 1-3 whose drive is provided by the towed reel 15 B Fig. 1-3 recovering from a reel the strip used 15,
b) the blank marking strip 15 Fig. 1 and 3 pass under the elastic pressure cylinder 14 Fig. 1 and 3, the pressure of which is exerted via the pneumatic cylinder 14 A FIG. 1 and 3 on the back pressure cylinder 14 B Fig. 1, 2 and 3. The back pressure cylinder 14 B and the outlet conveyor 16 Fig. 1, 2 and 3 are under vacuum through the suction box 20 Fig. 3 fitted with a 20 A helical turbine Fig. 2 and 3, so as to flatten and maintain the print 2 during and at the end of its marking, so as to cause a precise detachment of the marking film. The reception table 17 Fig. 1, 2 and 3 retrieve the form at the end of treatment. The desk 21 Fig. 1 and 2 of the digital control allow programming for each new type of print. The compressor 22 Fig. 3 supplies the air jets 13 A Fig. 2 of the feeder and the pneumatic cylinder 14 A Fig. 1 and 3.

In the case where the printer wishes to obtain the relief by a traditional embossing, it is enough for him to start from a printed matter whose transfer of marking is obtained using powder of small particle size. It is quite obvious that without departing from the scope of the present invention, the reactivation of the adhesiveness of the film forming the relief can be obtained by means other than heat by using, for example, a hot-melt powder whose adhesiveness of surface will be reactivated by humidity.

The granulometry of the powder, according to the applications, has no real limit, it will however generally be between 5 and 1000 microns.

As an example, two powder formulas give good transfer results. The first is similar to powder formulas usually used, modified in order to use the manufacturing waste of these powders. The second is chemically very different and has a lower cost price.

First formula: known traditional polyamide whose schematic average formula is established as follows per 100 by equivalent weight:

- fatty diacid (dimer): 71.43
-stearic acid: 28.57
- ethylene diamine: 100.00

To obtain a kilogram of transfer material, take 650 grams of this polyamide to which we add:
- 295 grams of rosin
- 25 grams of butyl phthalate or other plasticizer
- 20 grams of attactic polypropylene
- 10 grams of glycerol monostearate

Second formula: mixture as a percentage of:

- styrene oleophthalic resin: 65%
- acrylic resin: 15 to 20%
- plasticizer like Unimol 66 from Bayer 10 to 15%
- microcrystalline wax to adjust the tack 5 to 10%

In the case where, for particular reasons, it is desired to reactivate the adhesiveness by humidity, the acrylic resin used could be chosen from the range of water-soluble thermoplastic acrylic resins.

A very large number of products can be formulated according to and by country of the facilities and costs of supply.

The process which is the subject of the present invention will find a wide field of applications in all kinds of industries, since its basic principle gives it great flexibility of use. It allows it to "mark" practically any support and material provided that suitable printing methods and powders are formulated to obtain good adhesion and sufficient mechanical resistance, depending on the type of use sought.

In the field of printing and cardboard, a whole range of applications is open to him as well in sheet-by-sheet printing as in continuous printing where the process of thermogravure is usually used. For these continuously "marked" prints, it suffices at the exit of the marking device, to replace the reception table 17 FIG. 1 by the material usually used, such as rewinder or other depending on the additional treatment applied to these impressions.

Furthermore, a simple ballpoint pen with fatty ink makes it possible to produce a drawing capable of being transformed into relief by dusting and therefore of being "marked" by the process which is the subject of the invention, hence again a potential application. very important.

Claims (11)

1 - Gilding or embossed marking process characterized by starting from an impression, transforming it into relief with variable thickness by the known process of thermogravure and making use of the adhesive properties imparted to the film forming the image in relief, to transfer and retain, on its surface, any marking material.
The means used for its application include, in combination, a printing press 1 Fig. 1, coupled to a thermogravure machine 1 A, to which is added or not directly a transfer device 1 B of the marking material on the film forming the relief image. 2 - gilding process or embossed marking according to claim 1 characterized by the fact of using, for its realization, any type of printing such as typographic, offset, heliographic, screen printing, etc ... or any means image formation, the only requirement being that this image has the possibility of retaining a film of powder on its surface. 3 - A process of gilding and embossing marking according to claims 1 and 2, characterized by the fact of leaving, at will, sheet-by-sheet printing or continuous printing. 4 - Gilding or embossed marking method according to any one of the preceding claims, characterized in that it can be applied to virtually any support. 5 - Process for gilding and embossed marking according to any one of the preceding claims, characterized by the fact of using hot-melt powders of any kind whatsoever having adhesive properties, after melting and solidification, from low temperature of the order of 50 ° centigrade up to temperatures very high erasures. 6 - A method of gilding or embossed marking according to any one of the preceding claims, characterized by the fact of using powders having physical properties adapted to the various receptive supports used. 7 - Gilding or embossed marking method according to any one of the preceding claims, characterized by the fact of using adhesive hot-melt powders after solidification, the particle size of which will be between and of the order of 5 to 1000 microns. 8 - Gilding and embossing marking method according to claim 1, characterized in that all of the elements allowing the transfer of the marking film will be driven by a stepping or direct current motor 18 Fig. 2, controlled by control electronics. 9 - gilding process and embossed marking according to claims 1 and 8, characterized in that the margin conveyor of the transfer device 1 B is provided with a pneumatic margin tracking device 13 A, 13 B and 13 C Fig. 2. 10 - gilding process and embossed marking according to claims 1, 8 and 9, characterized in that the pressure cylinder 14 Fig. 1, 2 and 3 is actuated by a pneumatic cylinder 14 A Fig. 1 and 3. 11 - Gilding and embossing marking method according to claims 1, 8, 9 and 10, characterized in that the back-pressure cylinder 14 B Fig. 1, 2 and 3 and the outlet conveyor 16 Fig. 1, 2 and 3 are kept under vacuum.

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