FR2721859A1 - Continuous offset printing on support, esp. plastic, using two printing sets - Google Patents

Abstract

In a continuous offset printing process on a printing support, in which a printing support circulates between at least two printing sets, and where one or more first printings are made by means of the first set, and a final printing is made by means of the final set, the final set prints in the break in the printing surface caused by the first printing(s).

Description

 The present application relates to a continuous offset printing process of a printing medium, in particular for printing in micro or mini printing of films intended to be cut into so-called security threads, then inserted into the security papers, and print media so printed.

 The specialized paper industry uses for the production of security papers (application: banknotes, checks, identity papers, gray cards, credit cards), among others, the incorporation of so-called security threads in the thickness papers to protect and make it more difficult to tamper with the product.

 This wire generally consists of a thin strip of plastic film with a width of + or - 0.4 mm to 1.5 mm and + and a thickness of a few microns.

 To manufacture this "safety thread, the papermakers use a plastic film, mainly printed or unprinted polyester, but also possibly polypropylene, polyamide, polystyrene, PVC and other plastics which can be transformed into a film. and having the dimensional stability to be transformed. This wire is then cut to the determined widths.

 It is then rewound on reels identical to those used in spinning before being integrated into the paper during the manufacture thereof.

 The wire is generally micro-printed, metallized with or without reservation, and magnetic. It can also be printed in a solid or non-continuous solid color with inks invisible in daylight but identifiable and readable under a Wood lamp (ultra-violet rays, black light).

 The printing process used to make these security threads is rotogravure which allows printing without breaking.

 The other printing processes (wet or dry offset -waterless-, typography, flexography) are not used by manufacturers for technical reasons: these processes justifying the use of either plates and blankets, or plates, have for Consequently, the printing surface breaks in the direction of travel, called a non-printing "groove".

The process which is the subject of the invention described here had to face the following constraints:
- films printable and cut into thin strips
- seamless printing in the direction of travel
- a print identified in the cutting direction and provide
- the possibility of continuous printing of luminescent inks
- the possibility of heat-sealable coating
- a very good legibility of the characters and a high quality of reproduction of the texts.

 However, the Applicant has discovered that it is possible to offset offset a printing medium, in particular a plastic film, and this without breaking the printing in the direction of travel of said medium.

 This is why the present application relates to an offset process for continuously printing a printing medium, in which a printing medium circulates between at least two printing groups, and in which a or several first impressions using one or more first printing groups, then a final printing is carried out using a final printing group, the final printing group carrying out the impression in the rupture of the printing surface caused by the first impression (s).

 In fact, as those skilled in the art know, a printing unit in particular comprises two cylinders directly involved in printing. The first cylinder, called plate cylinder, in contact with the ink, carries a metal plate on which the elements to be printed are embossed (printing transfer). Said first cylinder is in contact with a second cylinder, called a blanket cylinder, comprising a rubber blanket on which the metal plate transfers the ink. The blanket thus inked in turn transfers the printing to the printing medium, paper or plastic for example.

 Both the plate and the blanket are fixed to their respective cylinders using a groove in which the ends of the plate and the blanket are inserted. At the level of this groove, a printing break is thus created, taking into account the existence of the groove.

However, unlike the prior art, in which the printer sought to synchronize the second printing group so that the second printing, for example of another color, coincides exactly with the first, the present method provides shifting the second impression relative to the first, so that a print is made at the print break due to printing by the first printing group. This impression at the level of the printing break can be obtained by several technical variants, and in particular the following
- The first printing group prints a continuous part of the printing circumference, while the next group prints the next part of the printing circumference. For example the first group prints the first half of the blanket printing circumference while the second group prints the second half of the blanket circumference.

 As is easily understood by those skilled in the art, the respective printing parts can be chosen within wide limits, the extreme case being that one of the groups proceeds to printing the entire circumference of the blanket to be except the throat and the other group prints only the width corresponding to the throat.

 - Another way is to alternate impressions. Thus, for example, one strip out of two of a print, for example repetitive, is printed by the first group, one of the non-printed strips corresponding to the break in the print due to the groove, while a second group of printing takes care of printing the other tapes. Thus, in the end, one strip out of two is printed by the first group, and one strip out of two is printed by the second group, the whole forming a continuous impression, without printing break.

 In the above cases, the minimum number of cylinders, i.e. two, was used to obtain continuous printing. It is clear to those skilled in the art that the aforementioned second cylinder is in this case the final cylinder.

 The above offsets between the printing units to achieve the continuous printing effect can be achieved by the well known methods themselves of printing units with respect to each other, but usually used to synchronize stackable prints and not to create a lag between prints.

 Depending on the machine used, this setting, called "no advance" can be obtained by mechanical and / or electronic control.

 The process which is the subject of the present invention can be implemented with all kinds of printing medium for paper, cardboard and in particular plastic material such as polypropylene, polyamide, polyvinyl chloride, polystyrene, etc., and more particularly polyester. . For the latter, a surface treatment is generally essential, for example by a corona treatment, an ink attachment device is then used, or by deposition of an attachment primer or varnish.

 The process which is the subject of the present invention can also be implemented both for positive prints and for negative prints, the printing being monochrome, or a full color alternation of monochrome prints. I1 can be used in particular with metallized inks.

 To the knowledge of the applicant, no printing had yet been carried out continuously using a metallic ink.

 In fact, the only continuous prints obtained so far have been rotogravure prints, using not metallic inks, but metallic particles.

 In this case, the offset printing process according to the invention makes it possible to envisage various and innovative applications as well as modifications in the manufacturing procedures to obtain a result whose appearance is similar to that obtained by gravure printing.

For example, to carry out a metallic impression by gravure printing, the following operations are carried out
- deposit of a lacquer corresponding to the characters which one wishes to print,
- metallization under reduced pressure by depositing an aluminum powder,
- demetallization, by passage through a bath, of the areas determined by the lacquer.

 Using the offset process according to the invention, direct printing is carried out with a metallic ink which may for example be silver, gold, red, green, blue.

 This is why the present application also relates to continuously printed printing supports, characterized in that they are printed by an offset process, in particular by the processes which are the subject of the present request.

 The present application also relates to a continuously printed printing medium, characterized in that a printing ink is a metallized ink.

 The offset process of the invention is a wet or dry offset process (or "waterless"). It can also apply to printing by typography and flexography.

The invention will be better understood if reference is made to the accompanying drawings, in which
FIG. 1 shows diagrammatically two successive printing units of an offset machine, as well as a simple device for adjusting printing synchronization.

 Figures 1b to 1 e show various printing methods according to the present invention.

 Fig 1 f shows a continuous offset printing using continuous plate cylinder and blanket.

 FIG. 2 shows a continuous printing, on the one hand in positive, on the other hand in negative, carried out on the same plate, half of the printing being carried out by a first printing unit, and the other part being produced using a second printing unit.

 FIG. 3 shows the result obtained by alternating on the one hand a printing carried out in black ink and on the other hand a printing carried out in blue ink, and this both in positive and in negative.

 In FIGS. 2 and 3, the direction of travel of the support for printing is from right to left.

 In FIG. 1 a, there is, on the right, the first printing group, comprising the plate cylinder 1 provided with its plate, a second cylinder 2 provided with a rubber blanket as well as a third cylinder 3, the pressure cylinder, used to press the printing medium 4 against the blanket. On the diagram, one exaggerated the size of the grooves 5 in which the ends are introduced as well of the plate of the cylinder plate 1 as of the blanket of the blanket cylinder 2, to highlight the cause of the printing break in the case of continuous printing of the prior art.

 Identical elements are found on the second printing unit. Any subsequent printing units are not shown. There has also been shown, between these two printing units, a simple synchronization adjustment device consisting of a baffle, comprising here three cylinders 6, 7, 8, and depending on whether the lowering or raising of the middle cylinder 7 for example, it is possible to adjust the printing synchronization of the second group (final) relative to the first (adjustment of the advance step).

 Figure 1b shows two printing groups.

By shifting 180, group B in relation to group A (by rotating the plate and blanket assembly in one direction or the other), and each group printing half of the surface to be covered, we obtains continuous printing without breakage as illustrated in FIG. 2.

FIG. 1 c shows diagrammatically two printing groups printing each of the marked bands and shifting the group
B compared to group A (see previous paragraph) of a printed bandwidth, continuous printing is carried out without breakage as illustrated in FIG. 3.

 Figure 1 d shows schematically a printing unit with a blanket 1C without groove (continuous), single and two plate cylinders 1A and 1B. By shifting cylinder A with respect to cylinder B (from x to 180 ") a continuous printing is transferred to the complete blanket.

 Figure 1 e schematically shows a printing group. The film after a first impression is pulled back and resumes the same impression (round trip of the support).

 Figure 1 f shows a printing group.

Plate and blanket are sleeved on the cylinders.

 In order to illustrate the synchronization of the prints, FIG. 2 represents such an imperfect synchronization, since on the negative print, at the bottom of the figure, one can observe on the one hand a very slight lateral offset, of the order d 'a half millimeter, of an impression compared to the other and, on the other hand, a slight overlap of the impressions. The level concerned is marked with an arrow.

 These imperfections, however existing at the level of the positive impression, above, are almost impossible to detect without being warned.

 In FIG. 3 which has been obtained by alternating printing of a strip using a first and a second group, each of the two groups being inked in a different color: blue for one ( B and lighter in the figure) and black for the other (N), we also observe here a very slight lateral offset, voluntary, of the order of half a millimeter each time the color changes, say every other band. Some of these offsets are targeted by arrows.

 On the other hand, the overlap of a strip of one color by a strip of another color is almost invisible here.

 At the top of the figure, the impression is in positive, and at the bottom in negative.

 The examples which follow illustrate the present invention without however limiting it.

 Two sets of films were produced by photogravure for the purpose of carrying out tests.

The first game consisted of a text "GMP
FRANCE "in alternation of pose, (ie a GMP film
FRANCE - a GMP FRANCE film) split into three types of text printed in mini-characters (height 0.9 mm).

The three types were:
- GMP FRANCE in positive and GMP FRANCE in positive,
- GMP FRANCE negative and GMP FRANCE negative,
- GMP FRANCE negative and GMP FRANCE positive.

 It therefore made it possible to print strips alternately on the same cylinder.

The second set of plates consisted of a single film with a length of 295.91 mm which was used to make two plates covering the development of a KOMORI machine
CHAMBON (591.82 mm) and which was divided into four parts
- two in micro-printing (text height 0.4 mm), one positive, one negative
- two in mini-printing (text height 0.9 mm), one positive, one negative.

 From these films, four plates were produced, two with the first set of films, two with the second set of films (a single film carried over twice).

 This second set was therefore used for printing strips on a half-cylinder.

EXAMPLE 1
The test was carried out on a KOMORI machine
CHAMBON, reference OR20, designed to print 5 colors in offset. The width is 525 mm while the development is 591.82 mm. The machine is conventionally made up of a film unwinder to be printed, an input voltage group, five offset printing groups, an electronic lateral and longitudinal automatic tracking system (ELTROMAT), a UV drying area, power 180/220 W, an output voltage group, and finally a rewinding of printed film.

The test was carried out with a polyester film with a thickness of 25 microns of the 10-23 / 25 type sold by the
RPF company. Two PLAST series inks were used
ULTRACURE, marketed by COATES LORILLEUX.

The colors used were black, reference 47 00, and blue, reference 47 25.

The plate installed on the cylinder-plate was of the SUPER SPARTAN type from the company HOWSON AL GRAPHY (Dupont de
Nemours). It is a plate with a thickness of 0.3 mm, the surface of which is in grained aluminum, which has been annealed after sunshine. It included an impression every other strip evenly spaced using the first set of plates.

 The wetting was carried out with water added with a wetting water adjuvant called VIOLET, sold by the company VEGRA, at the recommended dosage of 2-3%.

 Only printing groups 3 and 4 of the machine were used, the inking color of the third group being blue and the inking color of the fourth group being black.

 The speed used varied from 60 to 150 linear meters per hour.

 Group 3 therefore printed their text as follows: a printed strip, a strip without printing, a printed strip, a strip without printing, etc., blue in color.

 Group 4 for its part completed the printing in the non-printed parts, and this in black color, thanks to the adjustment of the advance step concerning groups 3 and 4, using the ELTROMAT.

 Continuous printing was thus obtained, with alternating printing in blue and in black in the direction of travel of the support. FIG. 3 illustrates such an impression, for its part concerning a positive impression and a negative impression.

EXAMPLE 2
We proceeded as indicated above, but the plates used were half-and-half plates (second set of plates), the printing group 3 continuously printing a part in blue and the printing group 4 continuously printing the next part in black, and so on. FIG. 2 illustrates such an impression, for the positive part and the negative part in mini-impression.

EXAMPLE 3
We proceeded as indicated in example 2, but the ink color was black for both group 3 and group 4.

EXAMPLE 4
The procedure was as in Example 1, but the ink color was black for the two groups used.

EXAMPLE 5
The procedure was as indicated in Example 1, but using for group 3 a silver ink, of the PLAST ULTRACURE series, reference Silver 43/34 and 44 21 of the
COATES LORILLEUX Company.

Claims (9)

 1. Offset process for continuously printing a printing medium, in which a printing medium circulates between at least two printing groups, and in which one or more first impressions are made using one or more first printing groups, then a final printing is carried out using a final printing group, the final printing group printing in the rupture of the surface d impression caused by the first impression (s).  2. Method according to claim 1, characterized in that the impression in the rupture of the printing surface caused by the first impression (s) is obtained by adjusting the advance step of the printing units with which they are provided this.  3. Method according to claim 1 or 2, characterized in that the first printing group prints a continuous part of the printing circumference, while the following group prints the next part of the printing circumference.  4. Method according to claim 1 or 2, characterized in that one strip out of two of a printing, for example repetitive, is printed by the first group, one of the non-printed strips corresponding to the break in printing due to the groove, while a second printing unit is responsible for printing the other bands.  5. Method according to one of claims 1 to 4, characterized in that the support is made of plastic.  6. Method according to claim 5, characterized in that the printing medium is made of polyester.  7. Method according to one of claims 1 to 6, characterized in that a printing ink is a metallized ink.  8. Printing medium printed continuously, characterized in that it is printed by an offset process.  9. Continuously printed printing medium, characterized in that a printing ink is a metallized ink.