EP1702110A1

EP1702110A1 - Security paper highly resistant to double folding and method for making same

Info

Publication number: EP1702110A1
Application number: EP04817614A
Authority: EP
Inventors: Henri Rosset; Pierre Doublet
Original assignee: ArjoWiggins SAS; ArjoWiggins Security SAS
Current assignee: ArjoWiggins Security SAS
Priority date: 2003-12-30
Filing date: 2004-12-29
Publication date: 2006-09-20
Also published as: US7754314B2; BRPI0418257A; FR2864557B1; BRPI0418257B1; CA2550574A1; FR2864557A1; US20070164556A1; CA2550574C; WO2005073464A1

Abstract

The invention concerns a security paper comprising at least two plies of paper, wherein at least one intermediate layer arranged between the two plies of paper comprises at least one element providing the paper with high double folding resistance, such as defined by the NF ISO 5626 standard, the two plies and said intermediate layer being closely assembled. The invention also concerns a method for making said paper whereby the intermediate layer is deposited by spraying.

Description

SECURITY PAPER HAVING HIGH DOUBLE-FOLD RESISTANCE AND MANUFACTURING METHOD THEREOF

The present invention relates to a security paper and, more particularly to a security paper used for the production of banknotes, passports, certificates of authenticity, checks. The invention also relates to the method of manufacturing said security paper. A large number of printed documents require increasing resources to ensure their authentication and security. The documents range from banknotes to transport tickets and also include scratch-off game tickets, playing cards, checks, identity cards or passports. To allow the user or the holder of the security document a simple and reliable verification of the authenticity thereof, it is common to include in the mass of the material of the document authentication elements. The inclusion of such elements is also intended to prevent malicious people from forging said document, by reproducing the identical or almost identical characteristics of the said document. As such, it is common to provide areas of reduced thickness within the fibrous layer, thus forming a watermark in the final security document, said watermark preventing in particular the reproduction of said document by photocopying. In addition to these problems linked to the authentication and prevention of counterfeit security documents, it is also essential to ensure sufficient durability for these security documents, which are subjected to repeated constraints during their use. In particular, in the case of a bank note in particular, account must be taken of frequent handling, in particular folding and unfolding of the note repeatedly, which, if no adaptation of the fibrous structure has been envisaged to this level, can lead to rapid deterioration or even tearing of said ticket. In patent application EP-A-628408, a reinforced security paper is described which consists of two sheets of paper between which a plastic sheet is laminated. This sheet has the advantage, in addition to that of comprising an authentication element, of improving the fold resistance of the security paper. However, this manufacturing process requires several bonding steps to assemble the different sheets together and which are done offline from the paper machine, once the paper sheets have been produced (and therefore dried). The paper could therefore on the one hand delaminate fairly easily and on the other hand be fairly easily manufactured by counterfeiters who can laminate sheets of paper with a plastic sheet. It may also be advantageous to introduce certain reinforcing materials within the fibrous layer. Sheet formation problems may, however, arise when adding too much reinforcing material. The Applicant has noted in particular that the introduction of synthetic fibers into a fibrous layer, in order to increase its mechanical strength, in fact degrades the quality and rendering of a watermark formed within this layer. One of the aims of the invention is therefore to propose a new security paper and a method of obtaining security documents making it possible to reconcile both correct and reliable securing of said document, while giving it mechanical or chemical resistance, adapted to its usual use. As such, one can consider adding reinforcing elements using a coating technique. In most applications requiring a support having better mechanical or physical characteristics, it is known to apply a layer on a basic support of the cellulose type. Such layers are traditionally applied on both sides of a sheet of dry paper using a size press, which consists of a pair of rollers forming a nip through which the sheet passes. However, this layer deposition method has a number of disadvantages which reduce the efficiency of the paper machine as a whole. The size presses indeed have a large number of moving parts, which require frequent adjustments and lead to significant maintenance and cleaning times. In certain applications, additional coating devices have also been provided, positioned after the paper machine itself. These devices have the major drawback of greatly increasing the space occupied by the paper machine and of generating increased energy consumption for drying the paper thus rewetted. Another object of the invention is therefore to propose a new process for depositing a layer on a fibrous strip, the process being both simple, inexpensive and easily adaptable to existing paper machines. As such, the Applicant had the idea of using liquid spraying devices to deposit a layer containing reinforcing elements on the surface of a paper being formed. These liquid spraying devices indeed have few moving parts and require reduced maintenance. They are moreover easily adaptable to existing paper machines. Furthermore, noting that depositing a layer on only one side of the paper led to an asymmetry in the physical and mechanical properties of the paper between the coated side and the uncoated side, the Applicant also had the idea of projecting the layer between two jets of paper then assembled, pressed together and dried in the traditional way. This technique also has the advantage of not modifying the surface properties of the base paper, which can be useful in particular for papers intended for printing. The object of the present invention is therefore to provide a security paper comprising at least two paper jets, in which, at least in one zone, at least one intermediate layer disposed between the two paper jets comprises at least one conferring element high resistance to double-fold paper, as defined in standard NF ISO 5626, the element being in "diffuse" form and / or in the form of particles and the two jets and said intermediate layer being intimately assembled.

“Diffuse” is understood to mean that the element was dissolved or in emulsion in the composition of the layer and is found distributed in a diffuse manner between said jets. The term “element in the form of particles” means an element in the form of pigments, fibers, agglomerates and more generally of diverse shape and of small size. The pigments can be of the order of a hundred micrometers to a nanometer; the fibers can be round or flat fibers, a few micrometers or millimeters or even centimeters long and a few micrometers or nanometers in diameter or in width.

It is understood by "the two jets and said intermediate layer being intimately assembled" that the constituents of each of the jets and also those of the composition of the layer (including said element) have partially interpenetrated; once the paper is dry, it would be impossible to separate the jets neatly where they meet. A cross-sectional observation under a microscope, in particular electronic, makes it possible to see the intimate assembly of these two jets and of said element whereas if the layer had been placed between the two papers once dry, we would observe a less intimate assembly both between the jets and also with the constituents of the layer. Such an assembly can be obtained as described below by directly assembling the two jets and the composition, that is to say that the composition is sprayed between the jets, in particular on at least one of the two jets, which are still wet and are assembled immediately (when wet). More particularly, said intermediate layer has been arranged by spraying, in particular by spraying, of a composition comprising said element. Preferably the surface between the two jets is entirely covered by said layer. According to a preferred embodiment of the invention, the resistance to double-fold of the paper is greater than a value DPmin, with DPmin = 75000 E, E being the percentage by dry weight of the element in the paper. According to a particular embodiment of the invention, said element is chosen from mineral pigments, in particular clays or titanium dioxide, pigments organic, natural or synthetic binders, in particular starches or polyvinyl alcohols or polyurethanes or styrene-butadiene copolymers, natural or synthetic fibers, in particular polyester or polyamide, and their mixtures. As organic pigments, plastic coating pigments can be used, for example solid or hollow polystyrene microspheres. As natural fibers, it is possible to use, for example, textile fibers such as abaca, hemp, flax or chinook fibers and their mixtures. More particularly, when the element is a binder, such as polyurethanes or styrene-butadiene copolymers, it can be used in the form of a latex, that is to say an emulsion of a polymer in an aqueous medium. Preferably, the grammage of each jet is between 30 and 60 g / m ² . According to another particular embodiment of the invention, at least one of the paper jets has a watermark. According to another particular embodiment of the invention, the intermediate layer also includes at least one authentication element. According to another particular mode of the invention, the authentication element is detectable optically. According to another particular embodiment of the invention, the authentication element is chosen from iridescent particles, fluorescent particles, phosphorescent particles, colored particles, planchettes. In particular, these particles can be fibers. According to another particular mode of the invention, the authentication element reacts to certain stimuli by giving a specific signal detectable using an adapted device. According to another particular mode of the invention, the authentication element is chosen from substances reacting to electromagnetic fields, in particular of the microwave or infrared or ultraviolet type. The elements providing resistance to the double fold can also play the role of authentication elements. Another object of the invention is to protect a process for manufacturing a security paper having a high double-fold resistance in accordance with standard NF ISO 5626, as defined above, comprising the following steps: a first paste composition on a first drip cloth, the first dough composition is drained so as to form a first fibrous mat, a second dough composition is deposited on a second drip cloth, - the second composition is drained of paste so as to form a second fibrous mat, a liquid mixture comprising at least one soluble element or in emulsion or in the form of particles conferring said high resistance to double ply is sprayed onto at least one of said fibrous mat, assembling said first fibrous mattress to said second fibrous mattress so as to form a unitary fibrous mattress. The term “liquid composition” means a composition produced in a liquid medium; such a liquid composition may be a suspension, an emulsion or a solution. Preferably the liquid medium is aqueous. Preferably, said composition is sprayed. According to a particular embodiment of the invention, at least one watermark is formed in the first and / or in the second fibrous mat. According to another particular embodiment of the invention, a liquid composition containing at least one authentication element is projected onto said first and / or said second fibrous mat. According to another particular embodiment of the invention, the draining of the first or of the second paste composition is carried out using a Fourdrinier cloth, a double cloth or a cylinder of round shape. According to another particular embodiment of the invention, additional steps are provided for pressing and drying the unitary fibrous mat. The invention will be better understood using the examples presented below.

Comparative example 1:

A series of sheets of square format paper with a surface is produced from a fibrous composition containing, by dry weight, 100 parts of pure cotton cellulose fibers. 310 cm.

The grammage of the paper obtained is 85 g / m.

In addition, the laboratory formatter apparatus has been adapted to apply a watermark pattern in the mass of the paper obtained.

Comparative example 2:

A fibrous composition containing, on a dry weight basis, 100 parts of pure cotton cellulose fibers and 12 parts of synthetic polyethylene terephthalate fibers is produced, and using a laboratory formwork apparatus, a series of square sheets of paper with a surface area of 310 cm. The grammage of the paper obtained is 85 g / m.

Example 3:

A ﬁ rst composition of square-shaped sheets of paper is produced from a fibrous composition containing, by dry weight, 100 parts of pure cotton cellulose fibers, and using a laboratory formwork apparatus. surface of 310 cm. The grammage of the paper in this first series is 40 g / m. In addition, the laboratory formatter in this series has been adapted to apply a watermark pattern in the mass of the paper.

Then produced from a fibrous composition containing, by dry weight, 100 parts of pure cotton cellulose fibers and using a laboratory formatter, a second series of sheets of paper of square format and having an area of 310 cm ² .

The grammage of the paper in this second series is 40 g / m. Using a small manual sprayer, approximately 8 g / m ² by dry weight of a coating composition comprising a carboxylated styrene butadiene copolymer latex ( in aqueous emulsion). Then, in the wet state, a sheet of the first series is assembled with a sheet of the second series, the coated side of the sheet of the second series being covered by the sheet of the first series. The complex obtained is dried. In this complex, the percentage by dry weight of latex is then about 0.09.

Comparative example 4:

It is made from a fibrous composition containing, by dry weight, 100 parts of pure cotton cellulose fibers and using a paper machine of the round shape type - forming two jets of paper.

In the wet state, the jet from the round machine and the jet from the former are assembled. About 2.5 g / m dry weight of a coating composition comprising a carboxylated polyvinyl alcohol is deposited by means of a size press.

The complex obtained is dried.

The grammage of the complex obtained is then 83.1 g / m.

Example 5:

One spray on one side of the paper jet coming from the forming, using a ramp of three spray nozzles spaced 10 cm apart and positioned about 9 cm from the sheet, about 2.5 g / m dry weight a coating composition comprising a carboxylated polyvinyl alcohol.

In the wet state, the jet of the machine in the round shape and the jet of the former are assembled, the coated side of the jet coming from the former being covered by the jet of the round former. The complex obtained is dried.

The grammage of the complex obtained is then 82.7 g / m ² . In this complex, the percentage by dry weight of polyvinyl carboxylated alcohol is then about 0.03.

Tests carried out in examples 1 to 3: The mechanical strength of the paper was first evaluated using standardized tests in each of examples 1 to 3.

By applying standard NF EN 21974, the tear index of the papers obtained was thus evaluated.

By applying standard NF ISO 5626, the double-ply resistance was also evaluated.

The rendering of the watermark was then evaluated visually in each of Examples 1 to 3.

Tests carried out in Examples 4 and 5:

The mechanical strength of the paper was first evaluated using standardized tests in each of Examples 4 and 5.

By applying the NF ISO 5626 standard, the resistance to double ply was thus evaluated. The surface condition of the papers obtained in Examples 4 and 5 was also compared. By applying standard NF ISO 2470, the whiteness of the papers was thus evaluated.

Test results:

Table 1 below gives the results of the tests carried out for Examples 1 to 3.

It is found that the mechanical resistance of the paper increases when a latex is sprayed between the paper jets and when synthetic fibers are introduced into the fibrous composition. However, it can be seen that the rendering of the watermark remains correct in Example 3 corresponding to the invention, whereas, in Comparative Example 2, this watermark has practically disappeared.

Table 2 gives the results of the tests carried out for Examples 4 and 5.

It can be seen that the whiteness of the paper in Comparative Example 4 is slightly lower than that of Example 5 according to the invention. This confirms that a surface layer deposition tends to affect the surface characteristics of the paper, while the spray deposition between two jets of paper, as envisaged by the invention, is of no consequence for these same characteristics. Furthermore, a minimum double-ply resistance DPmin has been defined for each of the examples, a value corresponding to a limit below which the paper must be considered as not being sufficiently resistant, taking into account the needs of the users. This value has been expressed, for reasons of simplification, in a single formula in order to be able to adapt it to the different types of paper present, in particular as a function of the weight of layer deposited.

In fact, the more the layer rate increases in the paper, the greater the minimum double-fold resistance required.

By extrapolation, we defined a minimum DP min value of double-ply resistance by the formula: DP min = 75000 X (percentage by dry weight of the mechanical reinforcement elements present in the layer compared to the paper) This value was calculated , in Table 1, using the percentage by dry weight of latex in the paper of Example 3 and, in Table 2, using the percentage by dry weight of polyvinyl carboxylated alcohol in the paper of Example 5 It can be seen that, in comparative examples 1, 2 and 4, the double-ply resistance values are all lower than the imposed DP min value. On the contrary, in the examples according to the invention, these values are quite much higher than the imposed value DP min.

TABLE 1

TABLE 2

Claims

1) Security paper comprising at least two jets of paper in which, at least in one zone, at least one intermediate layer disposed between the two jets of paper comprises at least one element giving the paper a high double-ply resistance, such as defined in standard NF ISO 5626, said element being in “diffuse” form and / or in the form of particles and the two jets and said intermediate layer being intimately assembled.

2) Security paper according to claim 1, characterized in that said layer has been arranged by projection of a composition comprising said element. 3) Security paper according to one of the preceding claims, characterized in that the surface between the two jets is entirely covered by said layer.

4) Security paper according to one of the preceding claims, characterized in that the grammage of each jet is between 30 and 60 g / m ²

5) Security paper according to one of the preceding claims, characterized in that the resistance to double-fold of the paper is greater than a value DPmin, with: DPmin = 75000 E, E being the percentage by dry weight of the element in the paper.

6) Security paper according to one of the preceding claims, characterized in that the said element is chosen from mineral pigments, in particular clays or titanium dioxide, organic pigments, natural or synthetic binders, in particular starches or polyvinyl alcohols, polyurethanes or styrene-butadiene copolymers, natural or synthetic fibers, in particular polyester or polyamide and their mixtures.

7) Security paper according to one of the preceding claims, characterized in that at least one of the paper jets has a watermark.

8) Security paper according to one of the preceding claims, characterized in that the intermediate layer also comprises at least one authentication element.

9) Security paper according to the preceding claim 8, characterized in that the authentication element is detectable optically.

10) Security paper according to the preceding claim 9, characterized in that the authentication element is chosen from iridescent particles, fluorescent particles, phosphorescent particles, colored particles, planchettes.

11) Security paper according to one of claims 8 to 10, characterized in that the authentication element reacts to certain stimuli by giving a specific signal detectable using a suitable device. 12) Security paper according to the preceding claim 11, characterized in that the authentication element is chosen from substances reacting to electromagnetic fields, in particular of the microwave or infrared or ultra-violet type. 13) Security paper according to one of the preceding claims 8 to 12, characterized in that the element providing resistance to the double ply is also an authentication element. 14) Method for manufacturing a security paper, having a high double-fold resistance as defined in standard NF ISO 5626, according to one of the preceding claims, comprising the following steps: depositing a first pulp composition on a first drip cloth, - the first dough composition is drained so as to form a first fibrous mat, a second dough composition is deposited on a second drip cloth, the second dough composition is drained so as to forming a second fibrous mattress, a liquid composition containing a soluble or emulsion element or in the form of particles conferring said high double-ply resistance is projected onto at least one of said fibrous mattress, said first fibrous mattress is assembled to said second mattress fibrous to form a unitary fibrous mattress.

15) Method according to the preceding claim 14, characterized in that said composition is sprayed. 16) Method according to one of claims 14 to 15, characterized in that at least one watermark is formed in the first and / or the second fibrous mat.

17) Method according to one of claims 14 to 16, characterized in that one projects on said first and / or said second fibrous mat a liquid composition containing at least one authentication element. 18) Method according to one of claims 14 to 17, characterized in that the draining of the first paste composition or the second paste composition is carried out using a Fourdrinier cloth, a double cloth or a round cylinder.

19) Method according to one of claims 14 to 18, characterized in that it comprises additional steps of pressing and drying of the unitary fibrous mat.