Fibrous composition, useful for preparing a sheet of paper, in particular security paper, its use, moisture resistant sheet of paper, security document and / or valuable document
Patent Information
- Application Number
- BR112022026571
- Authority / Receiving Office
- BR · BR
- Patent Type
- Patents
- Current Assignee / Owner
- Publication Date
- 2026-08-11
Smart Images
Figure 00000035_0000 
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Abstract
Description
Fibrous composition, useful for preparing a sheet of paper, particularly security paper; its use: sheet of paper with moisture resistance, security document and / or valuable document. Technical Field
[001] The present invention relates to the field of papers, particularly security papers, and particularly banknotes, produced from fibrous cellulosic compositions that require a high level of mechanical strength when wet. State of the art
[002] Cotton cellulosic fibers are commonly used for the production of banknotes, as they make it possible to provide these banknotes with very good mechanical performance, particularly high tear and folding resistance.
[003] Furthermore, the level of mechanical stress to which banknotes are subjected in very humid environments, particularly during circulation, but also during accidental contact with a large amount of water, for example, in a washing machine, has led central banks to impose a minimum wet strength (WS) level. This WS level is generally assessed by testing the tensile strength of the paper as is and after immersion in water under standardized conditions.
[004] Thus, in relation to other papers treated with WS, such as filter paper, toilet paper, absorbent paper, etc., the level of wet strength imposed on paper substrates for banknotes is extremely high.
[005] Several means, essentially chemical, have been proposed to provide satisfactory wet strength. Thus, melamine-formaldehyde resins have been widely used due to their performance. However, given the level of harmfulness of the formaldehyde present in these resins, their use has now been abandoned. Currently, the preferred agents are therefore thermally crosslinkable resins of the type Petition 870220121747, dated 12 / 23 / 2022, page 11 / 46 2 / 30 polyamide-polyamine epichlorohydrin, also called PAAE, of which there are different generations depending on the applications and uses.
[006] The reactivity of these polyamide polyamine epichlorohydrin (PAAE) resins is provided by the azetidinium (N+) function. Now, this function only has reactivity towards carboxylic functions, some of which are in fact present in cotton fibers, the base material of the paper considered for banknote manufacturing. Thus, alpha-cellulose, forming 85 to 90% by weight of cotton fibers, is devoid of carboxylic functions. Therefore, it is appropriate, to allow the fixation of epichlorohydrin (PAAE) resins to cotton fibers, to use an intermediate carboxylated fixing agent, which serves as a kind of bypass between the cotton fibers and the WS resins. As representatives of these fixing agents, mention can be made very particularly of guar gum or modified cellulose derivatives, such as carboxymethylcellulose (CMC).A chemical reaction occurs between the carboxyl and azetidinium functional groups in a humid environment and in the presence of cotton fibers intended for sheet production. The resulting sheet, once dried to allow crosslinking of the immobilized resin, is then advantageously provided with a three-dimensional network exhibiting relatively high wet strength.
[007] However, this method is limited in terms of the potential for fixing epichlorohydrin resins (PAAE) to fibers via the fixing agent. In fact, since the carboxylic functions are not supported by the fibers themselves, but by a polymer suspended in water, the fixation of epichlorohydrin resins (PAAE) depends on the specific characteristics of the fixing agent and its retention in the fibrous mat being formed. This chemistry actually requires optimization work, often empirical, to find a good balance and avoid having an excessive residue of unfixed epichlorohydrin resin (PAAE).
[008] The present invention has the precise aim of increasing the potential for bonding and fixing resins of this type to a fibrous cellulosic network and, Petition 870220121747, dated 12 / 23 / 2022, p. 12 / 46 3 / 30 thus, achieving an increased level of mechanical strength, both wet and dry, and advantageously with a significantly reduced residue of unfixed epichlorohydrin resin (PAAE).
[009] The present invention also aims to reduce the ecological footprint of security documents. Dissemination of the invention
[010] Thus, according to one of its aspects, the present invention relates to a fibrous composition, particularly useful for preparing a sheet of paper, particularly security paper, comprising at least - a fibrous cellulosic material based on cotton fibers and free of wood fibers, and - a wet-strengthening agent reactive to carboxylic functions, said fibrous cellulosic material additionally possessing cellulosic fibers, called hemicellulose fibers, having a hemicellulose content of at least 18% by weight relative to the total weight of said hemicellulose fibers and a hemicellulose content of at least 0.7% by weight relative to the total weight of said fibrous cellulosic material.
[011] Contrary to all expectations, the inventors have indeed found that the combination of specific cellulosic fibers with conventional cotton fibers proves to be particularly beneficial in improving the mechanical properties in the wet state of the corresponding paper, treated with a wet-strengthening agent and, in particular, an epichlorohydrin resin (PAAE). Contrary to all expectations, it is found that the self-rupture length of such paper, both wet and dry, is also advantageously increased. These gains are illustrated, in particular, in the examples provided below. Petition 870220121747, dated 12 / 23 / 2022, page 13 / 46 4 / 30
[012] According to a first variant, the composition according to the invention may be in wet form, particularly in the form of an aqueous fiber suspension.
[013] According to a second variant, the composition according to the invention may be in a dry form, particularly in the form of a fibrous substrate, particularly of paper type.
[014] According to a preferred variant, the fibrous cellulosic material contains, as a source of hemicellulose, fibers selected from sisal fibers, kenaf fibers and mixtures thereof and, preferably, at least sisal fibers.
[015] Sisal fibers are advantageous in several respects.
[016] As illustrated in the examples below, they make it possible to increase the mechanical strength properties, particularly tear strength or tensile strength, of a paper treated with a wet strength agent and, in particular, an epichlorohydrin resin (PAAE).
[017] According to a preferred variant, a fibrous composition according to the invention further comprises at least one intermediate carboxylated fixing agent.
[018] A fibrous composition according to the invention is very particularly interesting for manufacturing paper sheets, particularly security paper, more particularly banknotes, endowed with high levels of wet strength and self-rupture length.
[019] Thus, the present invention also relates to the use of a fibrous composition according to the invention to prepare a sheet of paper, particularly security paper.
[020] According to another aspect thereof, the invention relates to a wet-resistant paper sheet comprising a fibrous composition according to the invention. In particular, it also Petition 870220121747, dated 12 / 23 / 2022, p. 14 / 46 5 / 30 refers to a wet-resistant security paper sheet comprising a fibrous composition according to the invention.
[021] According to yet another of its aspects, the invention relates to a security document and / or valuable document comprising a sheet of paper according to the invention. Brief description of the figures
[022] Figure 1 shows the dry self-rupture length for four compositions according to the invention comprising 20% by weight of sisal fibers relative to the weight of the fibrous material (B, D, E and F) and a composition not according to the invention in which the fibrous material consists only of cotton fibers (G).
[023] Figure 2 shows the wet self-rupture length for four compositions according to the invention comprising 20% by weight of sisal fibers relative to the weight of the fibrous material (B, D, E and F) and a composition not according to the invention in which the fibrous material consists only of cotton fibers (G). Detailed description Fibrous composition
[024] The present invention relates primarily to a fibrous composition, particularly useful for preparing a sheet of paper, particularly security paper, comprising at least - a fibrous cellulosic material based on cotton fibers and free of wood fibers, and - a wet-strengthening agent reactive to carboxylic functions, said fibrous cellulosic material additionally possessing cellulosic fibers, called hemicellulose fibers, having a hemicellulose content of at least 18% by weight relative to the total weight of said hemicellulose fibers and a hemicellulose content of at least 0.7% by weight relative to the total weight of said fibrous cellulosic material. Petition 870220121747, dated 12 / 23 / 2022, page 15 / 46 6 / 30
[025] The cellulosic compositions according to the invention have the advantageous characteristics of possessing, when in the dry state and in sheet form, an improved self-rupture length, more particularly in a humid environment.
[026] They also have the advantageous feature of being devoid of wood fibers. Fibrous cellulosic material
[027] As stated above, the fibrous composition according to the invention comprises at least one fibrous material comprising cellulosic fibers, preferably natural. According to one embodiment, the fibrous cellulosic material according to the invention is formed only from natural cellulosic fibers.
[028] The fibrous material according to the invention has the original characteristic of having a hemicellulose content by weight of at least 0.7% relative to its total weight and very particularly comprising hemicellulose fibers. The inventors have indeed found that this specific type of cellulose proves to be able to interact directly with a wet-strengthening agent endowed with functions that are reactive with respect to free carboxylic functions. According to a preferred variant, these reactive functions are azetidinium functions and the wet-strengthening agent is selected from epichlorohydrin resins (PAAE).
[029] The presence of an adjusted amount of hemicellulose in the fibrous material advantageously makes it possible to immobilize an increased amount of wet-strengthening agent and thus significantly increase the mechanical properties without altering the wet-strength properties of the corresponding fibrous materials. This predisposition, obtained according to the invention, of the fibrous material directly immobilizing a wet-strengthening agent is, moreover, economically advantageous. Thus, with a fibrous material according to the invention, a significant decrease is observed in Petition 870220121747, dated 12 / 23 / 2022, page 16 / 46 7 / 30 of the residual wet-strengthening agent, i.e., the amount that did not interact, compared to a fibrous material devoid of hemicellulose. Furthermore, this reactivity of the fibrous material towards a wet-strengthening agent according to the invention makes it possible to consider a smaller amount of carboxylated fixing agent, which is conventionally required to immobilize a wet-strengthening agent in a fibrous material not according to the invention.
[030] According to a particular variant, the level of hemicellulose in the fibrous cellulosic material varies from 0.7 to 4% by weight and, preferably, from 1 to 4% by weight of hemicellulose relative to the total weight of the fibrous cellulosic material.
[031] The hemicellulose required in the fibrous cellulosic material according to the invention is present therein at least partially in the form of fibers called hemicellulose fibers.
[032] More particularly, in the sense of the invention, hemicellulose fibers are cellulosic fibers having a hemicellulose content of at least 18% by weight relative to their total weight or even preferably at least 21% by weight relative to their total weight.
[033] Hemicellulose fibers suitable for the invention may, in particular, be selected from esparto, kenaf, jute, flax, sisal, kapok fibers and mixtures thereof.
[034] In particular, hemicellulose fibers are selected from sisal fibers, kenaf fibers, jute fibers, kapok fibers and mixtures thereof.
[035] In particular, hemicellulose fibers are selected from sisal fibers, kenaf fibers, jute fibers and mixtures thereof and, preferably, from sisal fibers, kenaf fibers and mixtures thereof.
[036] Kenaf fibers are particularly characterized by an alpha-cellulose content by weight of 31% to 39% and a hemicellulose content of Petition 870220121747, dated 12 / 23 / 2022, page 17 / 46 8 / 30 21% to 23% in relation to their total weight. They are therefore particularly suitable for use in fibrous cellulosic material.
[037] Kapok fibers are particularly characterized by an alpha-cellulose content by weight of 35 to 64% and a hemicellulose content of 22 to 26% relative to their total weight. They are therefore very particularly suitable for use in fibrous cellulosic material.
[038] With regard to sisal fibers, they advantageously have a hemicellulose content by weight of 21% to 24% relative to their total weight, for an alpha-cellulose content by weight of 43% to 56% relative to their total weight. In addition to this particularly high hemicellulose content, which makes them particularly interesting as a source of hemicellulose in the context of the invention, sisal fibers also have other advantages.
[039] First of all, sisal fibers are morphologically similar to cotton fibers. They are therefore particularly suitable for replacing cotton fibers without loss of performance for paper sheets, particularly security paper, formed with such a composition.
[040] They also have the advantage of being thinner and therefore make it possible to achieve a higher fiber density per unit volume and an increase in the area of bonding and interaction with WS resins.
[041] Sisal fibers, therefore, allow a positive double interaction, physico-chemical and morphological, with the resins used as a wet strength agent.
[042] Finally, sisal fibers are also very advantageous due to their low environmental footprint. In fact, sisal cultivation requires little water, fertilizer or pesticides, and its residues can be utilized (biogas, pharmaceutical inputs, building material, fertilizer, animal feed). Moreover, sisal fibers are available, Petition 870220121747, dated 12 / 23 / 2022, page 18 / 46 9 / 30 particularly, as a local raw material in countries such as Brazil, Tanzania, Kenya, Madagascar or China.
[043] As examples of sisal fibers, we can mention the sisal fibers marketed by SWM, or the CELAVE C ECF, CELAVE E TCF or CELAVE D TCF fibers marketed by the company CELESA.
[044] According to a preferred variant, the fibrous material considered in the compositions according to the invention comprises, as hemicellulose fibers, at least sisal fibers, or even just sisal fibers, these sisal fibers particularly being derived from a bleached sisal pulp.
[045] In addition to hemicellulose fibers, the fibrous material of the invention contains at least cotton fibers.
[046] Cotton fibers are indeed effective fibers in terms of mechanical strength performance, particularly burst strength and tear strength.
[047] In particular, the fibrous cellulosic material comprises at least 50% by weight, preferably at least 80% by weight and more preferably 80 to 95% by weight of cotton fibers in relation to its total weight.
[048] For example, cotton fibers can be selected from comber-type fibers, linters-type fibers, or a mixture thereof. Comber-type fibers are long fibers obtained by combing. Linter-type fibers are cellulose fibers derived from the short bristles of the cotton flower. According to a particular embodiment, the fibrous cellulosic material comprises cotton fibers in the form of a mixture of comber-type and / or linters-type fibers, for example, in a weight ratio between 40 / 60 and 60 / 40, particularly in a weight ratio of 50 / 50.
[049] Obviously, the fibrous material according to the invention may contain, in addition to cotton fibers and hemicellulose fibers, fibers Petition 870220121747, dated 12 / 23 / 2022, page 19 / 46 10 / 30 additional selected fibers, particularly from bamboo fibers, abaca fibers and mixtures thereof.
[050] The fibers that make up the fibrous material of the invention can be obtained from bleached, semi-bleached or unbleached pulps, particularly bleached ones. Wet resistance agent
[051] As stated above, a composition according to the invention further comprises at least one moisture-resistant agent.
[052] This type of agent is crucial for increasing the mechanical properties of paper when wet.
[053] These agents are generally thermosetting polymers, which are added when the paper is still wet and which undergo crosslinking in the paper during drying.
[054] Suitable wet strength agents for the invention are compounds having one or more functions that are reactive to the carboxylic functions provided in the fibrous material by the cellulosic hemicellulose fibers. Advantageously, these reactive functions are azetidinium functions.
[055] Preferably, the wet strength agent comprises at least or even consists of one or more resins selected from polyamide polyamine epichlorohydrin (PAAE) based resins.
[056] The wet strength agent, preferably a polyamide polyamine epichlorohydrin resin, having interacted with the carboxylic functions of hemicellulose and thus being immobilized at the level of the fibrous material, undergoes crosslinking during the thermal drying of the composition according to the invention, generating cohesion between the fibers, thus significantly reinforcing the mechanical properties of the dry composition, in the wet or dry state, by the development of strong covalent bonds and, particularly, its strength in terms of self-rupture length. Petition 870220121747, dated 12 / 23 / 2022, page 20 / 46 11 / 30
[057] As illustrated by the examples provided below, this improvement in mechanical properties is, moreover, advantageously correlated with a significant reduction in the amount of free wet strength agent, i.e., free resin, after crosslinking. This characteristic is reflected in fact by the manifestation of a lower zeta potential and ionic demand on the part of the treated fibrous material. These two parameters can, in particular, be measured using the measurement methods described in the examples provided below. In particular, the ionic demand is measured by titration using an electrolyte: a specific quantity of a filtrate is neutralized with an electrolyte and, at the point of neutralization, the quantity of electrolyte used represents the value of the ionic demand.
[058] Clearly, the presence of hemicellulose fibers makes it possible to immobilize an increased amount of wet strength agent and therefore reduce the level of wet strength agent that has not been immobilized. This effect is beneficial in several respects. Indeed, when the wet strength agent is not immobilized and therefore remains in free form in the final fibrous material, it is, on the one hand, ineffective in increasing the mechanical strength of this material and, on the other hand, constitutes residual ionic pollution in the environment as well as a loss of material.
[059] In particular, a fibrous composition according to the invention may contain from 1% to 10% by dry weight, preferably from 1% to 5% by dry weight and more preferably from 1.5% to 4% by weight of wet strength agent(s) relative to the dry weight of the fibers. Other compounds
[060] According to a preferred variant, the fibrous composition of the invention further comprises at least one intermediate carboxylated fixing agent.
[061] The aforementioned agent also contributes to the cohesion of the fibrous composition. Petition 870220121747, dated 12 / 23 / 2022, page 21 / 46 12 / 30
[062] In particular, the fixing agent is selected from polymers comprising carboxylic functions. Preferably, it is selected from guar gums, cellulosic derivatives and mixtures thereof, particularly from carboxylated cellulosic derivatives. According to a preferred embodiment, the fixing agent comprises at least one carboxymethylcellulose (CMC), or even consists of one or more carboxymethylcelluloses.
[063] Advantageously, the content of intermediate fixing agent in the fibrous composition comprising hemicellulose according to the invention can be reduced compared to a fibrous composition whose fibrous material comprises less than 0.7% by weight of hemicellulose.
[064] A fibrous composition according to the invention may additionally comprise at least one filler, particularly mineral.
[065] More precisely, these fillers are intended, in particular, to increase the opacity, whiteness and / or printability of said fibrous substrate.
[066] The filler may be selected from mineral fillers, in particular calcium carbonate, kaolin, titanium dioxide, talc, silicas, hydrated aluminas, aluminum silicates and mixtures thereof and / or from organic fillers, in particular plastic fillers or pigments. Preferably, the fibrous composition comprises at least titanium dioxide.
[067] Additives or adjuvants commonly used in the paper manufacturing industry can also be used in a fibrous composition according to the invention.
[068] Among the additives, we can mention, for example, pigments and dyes, antimicrobial agents, antifoaming agents, retention agents, particularly for the retention of fillers or tracers. Petition 870220121747, dated 12 / 23 / 2022, page 22 / 46 13 / 30
[069] A fibrous composition according to the invention may additionally comprise synthetic fibers. The presence of synthetic fibers, mixed with cellulosic fibers, in the fibrous composition may make it possible to improve the tear and folding resistance properties of said substrate.
[070] As stated above, a fibrous composition may be in wet form, particularly in the form of an aqueous suspension. A fibrous composition of this type may be used in a method for preparing a substrate, generally employed in the papermaking industry, particularly in a papermaking process.
[071] It may also be in dry form. In particular, the fibrous composition may also be in the form of a paper-type fibrous substrate, preferably of the banknote type. For example, a fibrous substrate, particularly of the paper type, may be made from the fibrous composition in the form of an aqueous suspension, particularly by drainage, pressing and drying. Obviously, additional steps may be carried out depending on the required properties of the fibrous substrate.
[072] According to another particular embodiment, a dry fibrous composition according to the invention can also be combined with an anti-soiling type surface treatment, particularly hydrophobic and / or oleophobic, adapted to the intended use of the corresponding paper material. For example, a paper material according to the invention can receive surface treatment to form laminated or film-coated papers, such as those, for example, considered for food packaging, and / or can be provided with an anti-soiling treatment by impregnation, coating, coating and / or varnishing. As a variant and / or in combination, a dry fibrous composition according to the invention can also be combined with an antimicrobial surface treatment, particularly antibacterial, Petition 870220121747, dated 12 / 23 / 2022, page 23 / 46 14 / 30 antifungal, antiviral and / or antiyeast, for example, by impregnation, coating, coating and / or varnishing. Applications
[073] The present invention also relates to the use of a fibrous composition as described above to prepare a sheet of paper, particularly security paper. The sheet of paper, particularly security paper, can, in particular, be prepared by processing, particularly by cutting, printing and / or varnishing, the aforementioned fibrous substrate.
[074] It also refers to a wet-resistant paper sheet comprising a fibrous composition as described above. This paper sheet may, in particular, be characterized by forming a security paper sheet.
[075] In particular, the sheet of paper according to the invention comprises, by weight, at least: - 40% to 96% dry weight of fibers, particularly cellulosic fibers, in relation to the dry weight of the substrate, - from 1% to 20% by dry weight relative to the dry weight of fibers, of at least one anionic polymer having a glass transition temperature above -40 °C, which is, in particular, carboxylated, and - 0.5% to 5% by dry weight of at least one cationic precipitating agent, relative to the dry weight of fibers.
[076] As is clear from the examples given below, the combination according to the invention proves to be particularly advantageous at the level of the paper thus formed, since the hemicelluloses required according to the invention have carboxyl groups, which will participate in flocculation and thus make it possible to obtain a network (polymer(s), fibers with hemicelluloses and cotton fibers) with improved cohesion.
[077] In the sense of the present invention, an anionic polymer is a polymer exhibiting negative charges. It can be derived from functionalization Petition 870220121747, dated 12 / 23 / 2022, page 24 / 46 15 / 30 anionic polymers that are considered neutral since they are not charged.
[078] The anionic polymers suitable for the invention have a glass transition temperature above -40 °C.
[079] “Glass transition temperature” means the temperature below which the polymer is rigid. When the temperature increases, the polymer goes through a transition state, which allows the macromolecular chains to slide past each other, and the polymer softens.
[080] According to one embodiment of the invention, this anionic polymer is a polymer possessing carboxylated functions.
[081] Preferably, a polymer of this type is obtained by homopolymerization of at least one monomer or copolymerization of at least two monomers selected from acrylic acid, methacrylic acid, acrylonitrile, alkyl acrylate, alkyl methacrylate, acrylamide, methacrylamide, N-methylol acrylamide, styrene and butadiene.
[082] Preferably, the anionic polymer is selected from acrylic homo- and copolymers, acrylate homo- and copolymers, carboxylated styrene-butadiene copolymers and mixtures thereof.
[083] As acrylic copolymers, we can particularly mention: - vinyl-acrylic polymers, - styrene-acrylic polymers, and - polyurethane-acrylic polymers.
[084] In particular, the polymer in question is a carboxylated styrene-butadiene copolymer. Such copolymers are available, for example, from the Dow Chemical Company with various glass transition temperatures.
[085] According to another embodiment, this anionic polymer can also be non-carboxylated. Petition 870220121747, dated 12 / 23 / 2022, page 25 / 46 16 / 30
[086] As representatives of these other forms of anionic polymers, we can mention the anionic forms of polyacrylamides and polystyrene copolymers, such as, in particular, styrene-butadiene copolymers.
[087] According to a variant embodiment, the anionic polymer has a Tg above 23 °C.
[088] In particular, the polymer or polymers having a glass transition temperature above 23 °C are selected from polyacrylics, polyacrylates, polyacrylamides, the anionic forms of polystyrenes, polyvinyls, polyethylenes, polyurethanes and mixtures thereof.
[089] According to a preferred embodiment, the polymer or polymers having a glass transition temperature above 23 °C are selected from acrylic (or polyacrylic) polymers, that is, homopolymers or copolymers comprising at least one acrylic monomer, namely, acrylic homopolymers or acrylic copolymers.
[090] As acrylic copolymers, we can particularly mention: - vinyl-acrylics, for example, such as the Orgal VA-HP product marketed by the company Organik Kimya (Tg = +41 °C), - styrene-acrylics, for example, such as the Acronal DS2416 product marketed by BASF (Tg = +38 °C), and - Polyurethane-acrylics, for example, such as the Joncryl U6336 product marketed by BASF (Tg = +40 °C).
[091] Preferably, the polymer or polymers having a glass transition temperature above 23 °C are selected from the acrylic homopolymers.
[092] The aforementioned polymers are available in anionic dispersion, for example: - from the company Tanatex Chemicals, under the name Edolan AH (Tg = +36 °C), Petition 870220121747, dated 12 / 23 / 2022, page 26 / 46 17 / 30 - from the company Organik Kimya, under the name Orgal NA 302 (Tg = +26 °C), - from the company Icap Sira, under the name Acrilem 7105 (Tg = +50 °C), and - from the company BASF, under the name Acronal DS 2416 (Tg = +38 °C).
[093] The anionic polymer or polymers may be non-crosslinkable, crosslinkable using an external crosslinking agent, or self-crosslinkable.
[094] As anionic polyurethane, we can also particularly mention the anionic forms of polyurethane-polyesters, polyurethane-polyethers and polyurethane-polycarbonates and mixtures thereof. These polymers are available, for example, from Bayer, under the name Impranil DLC® (elongation at break = 600%; Tg = -34°C).
[095] The anionic polymer or polymers are generally used at a rate of 1% to 20% by dry weight, preferably 1% to 10% by dry weight, and more preferably 3% to 8% by dry weight of anionic polymer(s), relative to the dry weight of the fibers.
[096] A sheet of paper according to the invention may further comprise an effective amount of at least one cationic precipitating agent. This cationic precipitating agent, by modifying the electrostatic charge of the anionic cellulose fibers, allows, among other things, the fixation of the anionic polymer or polymer particles to the fibers.
[097] Preferably, the cationic precipitating agent is selected from aluminum polychlorides, water-soluble cationic polymers, particularly from cationic starches, polyamides, polyacrylamides, polyethyleneimines, polyvinylamines and mixtures thereof.
[098] Preferably, the cationic precipitation agent comprises at least one cationic resin.
[099] According to an advantageous embodiment, it should be noted that the compounds considered according to the invention as a wet-strengthening agent probably also have this ability to Petition 870220121747, dated 12 / 23 / 2022, page 27 / 46 18 / 30 precipitate the aforementioned anionic polymer on the surface of the fibers. This is particularly the case with polyamide-polyamine-epichlorohydrin resins, called PAAE resins, which are very particularly suitable for the invention as a wet strength agent. In this embodiment, a compound of this type can guarantee both functions, provided that its quantity is adjusted for its effectiveness.
[0100] Generally, the amount of cationic precipitating agent is adjusted to allow the precipitation of almost all, preferably all, anionic polymers on the fiber surface. It varies, in particular, from 0.5% to 5% by dry weight, particularly from 0.8% to 3.5% by dry weight relative to the dry weight of the fibers.
[0101] Finally, a sheet of paper may comprise, in addition to its fibrous composition, at least one security element. This security element allows, in particular, the authentication of said sheet.
[0102] In particular, said security element is selected from visual devices, particularly optically variable devices, called OVDs, holograms, lens devices, elements with an interference effect, particularly iridescent elements, liquid crystals, pigments with a magnetically orientable effect and multilayer interference structures. These optically variable devices may be present in security threads embedded in the fibrous substrate or in strips or stickers affixed or printed on the fibrous substrate.
[0103] As another element of visual security, we can also mention watermarks produced in the manufacturing process of the fibrous substrate.
[0104] In particular, the aforementioned security element is selected from so-called luminescent elements, detectable under UV or IR, said luminescent elements possibly Petition 870220121747, dated 12 / 23 / 2022, page 28 / 46 19 / 30 being in the form of particles, fibers, platelets, safety thread integrated at least partially into the fibrous substrate, strips or adhesives affixed or printed onto the fibrous substrate.
[0105] In particular, said security element is selected from elements that are automatically detectable, particularly optically or magnetically, these detectable elements commonly called markers or labelers being integrated into the fibrous substrate or into visual or luminescent security elements.
[0106] A sheet of paper, particularly security paper, according to the invention may also comprise a radio frequency identification device, called RFID, also providing the sheet of paper, particularly security paper, with an identification and traceability function.
[0107] The present invention further relates to a security document and / or valuable document comprising a sheet of paper according to the invention.
[0108] For example, a security document and / or valuable document is a means of payment, such as a banknote, a payment card, a check or a restaurant voucher, an identity document, such as an identity card, a visa, a passport or a driver's license, a card, particularly for access, a lottery ticket, a transport voucher or a ticket for entry to cultural or sporting events, a loyalty card, a service card, a subscription card, a game card or collection card, a discount voucher or other voucher.
[0109] For example, a banknote is a security document, since it comprises security elements, and a valuable document in the sense that it represents value, in contrast to a note which may have value, particularly exchange value, without being secure. In Petition 870220121747, dated 12 / 23 / 2022, pp. 29 / 46 In the case of an access card, it may be secure but have no value, particularly no exchange value.
[0110] Preferably, the security document and / or valuable document according to the invention is a banknote.
[0111] In particular, the security document and / or valuable document according to the invention is a banknote comprising a varnish, particularly an overprinting varnish. Examples Materials and measurement methods
[0112] The following raw materials were used: - Comber cotton fibers (also called "comber type") and "first cut linter" type; - Sisal fibers marketed by CELESA under the names CELAVE C ECF, CELAVE E TCF and CELAVE D ECF or marketed by SWM Papeteries de Saint-Girons; - polyamide polyamine epichlorohydrin (PAAE) type resin; - carboxymethylcellulose (CMC) with a degree of substitution between 0.65 and 0.90; - anatase-type titanium dioxide (TiO2); - Polyvinyl alcohol (PVA) grade 28 (viscosity at 4%) / 99 (degree of hydrolysis); - a cationic polyamide polyamine epichlorohydrin type insolubilizer 1. Zeta potential
[0113] Zeta potential is measured with a “System Zeta Potential” instrument, model Mütek SZP-06 from BTG. 2. Ionic demand
[0114] Ionic demand is measured with a “Particle load detector” instrument, model Mütek PCD-05 from the company BTG. 3. Dry tensile strength Petition 870220121747, dated 12 / 23 / 2022, pp. 30 / 46 21 / 30
[0115] To evaluate dry tensile strength, particularly the dry self-rupture length (or “dry self-rupture length”), we can measure the length at which the sheets break under the effect of their own weight according to ISO 19242. 4. Wet tensile strength
[0116] To evaluate wet tensile strength, particularly wet self-rupture length (or “wet self-rupture length”), we can measure the length at which the sheets break under the effect of their own weight according to ISO 3781. 5. Wet strength
[0117] Wet strength (WS) is defined as the ratio between the wet self-rupture length and the dry self-rupture length according to the following formula: [Mathematics 1] Wet self-rupture length WS = ________________ Dry self-rupture length 6. Resistance to dry bursting
[0118] Dry burst strength in the dry state (or “dry burst strength”) can be measured in accordance with ISO 2758.
[0119] The dry burst index (or “dry burst index”) is the quotient of the dry bursting strength, in kilopascals, by the paper weight determined according to ISO 536. 7. Resistance to wet bursting
[0120] The wet burst resistance (or “wet burst resistance”) can be measured according to ISO 3689. Petition 870220121747, dated 12 / 23 / 2022, pp. 31 / 46 22 / 30
[0121] The wet burst index (or “wet burst index”) is the quotient of the dry bursting strength, in kilopascals, by the paper weight determined according to ISO 536. Example 1: preparation of a fibrous paper-type substrate from compositions according to the invention and a composition not according to the invention.
[0122] Cotton fibers are first refined to achieve a refinement degree of 65 °SR (degrees Schopper-Riegler) and then mixed with sisal fibers, in the case of tests according to the invention, to form a fiber suspension in water at a concentration of 1 g / L. As a variant, the sisal fibers can also be refined before being mixed with the cotton fibers and / or the cotton fibers and sisal fibers can be refined as a mixture. Titanium dioxide (TiO2), carboxymethylcellulose (CMC) and PAAE resin are then successively added to the fiber suspension.
[0123] After homogenization, the fibrous paper-type substrates are prepared according to the existing papermaking process, that is, particularly by draining, pressing for 2 min at 7 bar and then drying for 20 min at 90 °C, with wet blotting paper, the aqueous suspensions, of which compositions A to F according to the invention and G not according to the invention are provided in Table 1 below, with the contents expressed in dry weight relative to the total weight of the fibers. [Table 1] First Cut Comber Linter Sisal PAAE CMC TÍÜ2 A 45% 45% 10% (Celave C) 2.5% 0.7% 5% B 40% 40% 20% (Celave C) 2.5% 0.7% 5% C 35% 35% 30% (Celave C) 2.5% 0.7% 5% D 40% 40% 20% (Celave D) 2.5% 0.7% 5% E 40% 40% 20% (Celave E) 2.5% 0.7% 5% Petition 870220121747, dated 12 / 23 / 2022, pp. 32 / 46 23 / 30 F 40% 40% 20% (SWM) 2.5% 0.7% 5% G (control) 50% 50% 0% 2.5% 0.7% 5% Example 2: zeta potential
[0124] The zeta potential of the fiber surfaces is measured for all compositions A to G of example 1 after mixing all components in aqueous solution. The results are presented in Table 2 below.
[0125] The zeta potentials of cottonseed and sisal pulps in the pure state are also measured and are similar. [Table 2] ABCDEFG Zeta potential (mV) -3.5 -5.3 -6.5 -2.0 -8.2 -6.3 +5.1
[0126] For all compositions comprising sisal fibers (A to F), a negative zeta potential is measured, reflecting the fact that there is no longer any PAAE resin free of positive charge, but all of it is fixed to the fibers. By contrast, for composition G not in accordance with the invention, the zeta potential is positive. This phenomenon is confirmed by tests A to C, which show that the zeta potential decreases as the sisal fiber content increases. There is, therefore, greater interaction of the PAAE resin with the sisal fibers than with the cotton fibers. Example 3: self-rupture length
[0127] The self-rupture length is measured in the dry and wet states for all fibrous substrates of composition A to G in example 1. The results are shown in Table 3 below and in Figs. 1 and 2. [Table 3] ABCDEFG Dry self-rupture length (m) 8073 7695 7861 7936 7862 8023 7384 Wet self-rupture length (m) 3192 3374 3280 3367 3596 3492 3159 Petition 870220121747, dated 12 / 23 / 2022, pp. 33 / 46 24 / 30
[0128] The self-rupture lengths, both dry and wet, of the compositions comprising sisal fibers (A to F) are greater than the self-rupture length in the test not in accordance with the invention (G). This result is valid for the various sisal fibers, but also for the various contents of sisal fibers. Thus, the mechanical properties of the fibrous substrates are improved in both the dry and wet states by the addition of sisal fibers. Example 4: preparation of a glued paper from compositions according to the invention and a composition not according to the invention.
[0129] Two fibrous compositions and fibrous substrates are prepared by the method described in Example 1 for the compositions in Table 4 below, according to invention (H) and not according to invention (I). [Table 4] Comber Linter first cut Sisal PAAE CMC T1O2 H 42.5% 42.5% 15% (Celave D) 2.5% 0.7% 5% I 50% 50% 0% 2.5% 0.7% 5%
[0130] The resulting fibrous substrates are then spliced in a splicing press (size press) with an aqueous composition comprising 4% PVA and 1% insolubilizer, to obtain a spliced paper, followed by 20 min of drying at 90 °C. Example 5: zeta potential
[0131] The 50 / 50 comber / linter cotton fiber blend and Celave D sisal fibers have zeta potentials of -14.7 mV and -17 mV, respectively, measured in aqueous suspension at identical concentrations. The zeta potentials of the different fiber types are therefore of the same order of magnitude.
[0132] The zeta potential (ZP) of the fiber surface is measured for compositions H and I in Example 4 for successive additions of titanium dioxide, CMC, and PAAE resin to the mixture of cotton fibers and sisal fibers, if applicable, in aqueous suspension at identical concentrations. The ZP Petition 870220121747, dated 12 / 23 / 2022, pp. 34 / 46 25 / 30 final is the PZ of the composition after the addition of PAAE resin and before sheet formation.
[0133] The results are presented in Table 5 below. [Table 5] PZ of fiber suspension PZ after addition of T1O2 PZ after addition of CMC PZ Final H -19.5 mV -20.6 mV -38.6 mV -2.8 mV I -14.7 mV -15.5 mV -47.7 mV +14.4 mV
[0134] The zeta potential is therefore little altered by the addition of TiO2, but then decreases rapidly, as expected, with the addition of CMC.
[0135] However, as already observed in example 2, the addition of PAAE resin alters the zeta potential differently between the composition according to the invention and the composition not according to the invention. For composition H, the zeta potential remains negative, close to zero, meaning that the composition no longer comprises free resin and most of the negative sites interact with the resin. By contrast, in the case of comparative example I, the zeta potential is largely positive, indicating the presence of free resin in the composition.
[0136] Finally, the final zeta potential approaches approximately zero, but remains largely positive in the case of comparative example I and slightly negative, for example, H according to the invention. Therefore, the PAAE resin is not in excess in example H. Example 6: Mechanical properties
[0137] The self-rupture and burst lengths are measured for the glued papers obtained with the various compositions in Example 4 and are presented in Table 6. [Table 6] Dry self-rupture length Wet self-rupture length Dry burst index Wet burst index H 7120 m 3667 m 4.28 kPa.m² / g 3.44 kPa.m² / g Petition 870220121747, dated 12 / 23 / 2022, pages 35 / 46 26 / 30 I 6217 m 3267 m 4.19 kPa.m2 / g 3.18 kPa.m2 / g
[0138] All self-rupture and burst length properties are improved, both dry and wet, by adding sisal fibers, as in test H according to the invention, compared to test I not according to the invention, without sisal fibers.
[0139] Thus, the composition according to the invention comprising hemicellulose fibers, particularly sisal fibers, makes it possible to obtain a gain in strength and, particularly, in wet strength. Example 7: preparation of a fibrous paper-like substrate from compositions according to the invention and a composition not according to the invention.
[0140] Two fibrous compositions are prepared by the method described in Example 1, one with 5% of the fibrous material formed from Celave C sisal fibers (test J according to the invention) and the other with 100% of the fibrous material formed from cotton fibers (test K not according to the invention), the remainder being kept identical between the two compositions. In both cases, the cotton fibers are formed from a 50 / 50 comber / linter blend and the PAAE, CMC and TiO2 contents are the same as for the compositions presented above. Example 8: zeta potential
[0141] The zeta potential is measured for the various compositions in example 7: - in the initial pulp, that is, in the fiber suspension, before adding the PAAE resin, CMC and TiO2, and - in the final composition, that is, after the addition of PAAE resin, CMC and TiO2, and before sheet formation. [Table 7] Fiber suspension voltage (mV) Final voltage (mV) Final ionic demand (equivalent / L) J -13.3 +16.1 +16 Petition 870220121747, dated 12 / 23 / 2022, pages 36 / 46 27 / 30 K -10.6 +33.1 +69
[0142] Thus, even for a sisal fiber content of 5% in the fibrous material, these hemicellulose-rich fibers make it possible to reduce the final zeta potential of the cellulosic fibers. Thus, they make it possible to reduce the final ionic demand, that is, the residual cationic charge bound to the free and unbound PAAE resin, by a factor of 4, reflecting a much better fixation of the resin to the fibers. Example 9: preparation of a fibrous paper-like substrate from compositions according to the invention and a composition not according to the invention.
[0143] Five fibrous compositions and fibrous substrates are prepared by the method described in Example 1 for the compositions in Table 8 below, according to the invention (L, M and N) and not according to the invention (O and P), varying the resin content and the CMC content. [Table 8] First Cut Comber Linter Sisal PAAE CMC TiO2 L 45% 45% 10% (Celave C) 1.8% 0.3% 3% M 45% 45% 10% (Celave C) 1.6% 0.3% 3% N 45% 45% 10% (Celave C) 1.8% 0.15% 3% O 50% 50% 0% 1.8% 0.3% 3% P 50% 50% 0% 1.8% 0.15% 3% Example 10: Ionic demand
[0144] The final ionic demand is measured for the compositions in Example 9 after the addition of PAAE resin and before sheet formation. The results are presented in Table 9 below. [Table 9] LMNOP Final ionic demand (equ / L) 9 6 24.5 32.2 51.5
[0145] When the resin content decreases, the ionic demand also decreases, since fewer positive charges are added to the system. In contrast, when the CMC content decreases, the ionic demand increases as fewer carboxylic functions are present to bind the resin. Petition 870220121747, dated 12 / 23 / 2022, pp. 37 / 46 28 / 30
[0146] Furthermore, the comparison of the L and O tests, or the N and P tests, confirms that the final ionic demand is systematically reduced by the presence of sisal fibers, which provides good confirmation of the interaction and fixation of the PAAE resin on the hemicellulose-rich fibers. Example 11: Mechanical properties
[0147] Dry and wet self-rupture lengths are measured and the wet strength is calculated from these two values according to formula 1 for the fibrous substrates obtained in example 9. [Table 10] Dry self-rupture length (m) 5683 5749 Wet self-rupture length (m) 2606 2611 Wet strength (WS, %) 45.9 45.4
[0148] Comparison of the O and M tests shows that the compositions according to the invention make it possible to reduce the wet strength agent content, due to the presence of sisal fibers, while maintaining an equivalent WS and wet self-rupture length. [Table 11] NP Dry self-rupture length (m) 5449 5152 Wet self-rupture length (m) 2428 2008 Wet strength (WS, %) 44.6 39.0
[0149] Comparison of tests N and P shows that the compositions according to the invention, comprising sisal fibers, make it possible to improve WS for reduced CMC contents. More precisely, reducing the CMC content relative to the fibers induces a 6.4% decrease in wet strength (WS) (tests O and P), while the decrease is only 0.8% WS for a composition comprising sisal fibers (test N relative to O). Petition 870220121747, dated 12 / 23 / 2022, pp. 38 / 46 29 / 30
[0150] In conclusion, the fixation of PAAE resin to hemicellulose-rich sisal fibers, demonstrated by ionic demand measurements, certainly makes it possible to improve the mechanical properties of the fibrous substrate, particularly in the wet state, in the compositions according to the invention. Furthermore, the presence of sisal fibers makes it possible to reduce the resin and / or CMC content with minimal performance loss, or even without any performance loss. Example 12: preparation of a pilot machine for a fibrous paper-type substrate from compositions according to the invention comprising an anionic polymer.
[0151] Three fibrous materials comprising only cotton fibers (comber / linter weight ratio of 50 / 50) and sisal fibers are prepared with sisal fiber proportions of 5%, 15% and 20%, respectively.
[0152] Fibrous compositions are formed by adding, to each of these fibrous materials, suspended in water, - 4% by dry weight relative to the dry weight of fibers, of at least one anionic carboxylated polymer having a glass transition temperature above -40 °C, - 2.5% by dry weight of a polyamide-polyamineepichlorohydrin resin, called PAAE resin, relative to the dry weight of the fibers, - 0.7% dry weight of CMC relative to the dry weight of fiber and - 5% by dry weight of TiO2 relative to the dry weight of the fibers. [ 0153] Next, in a test papermaking machine (called a pilot machine), several fibrous substrates are prepared from the three fibrous compositions thus obtained. [ 0154] The fibrous substrates formed are then impregnated in a sizing press with an aqueous composition comprising 4% PVA and 1% insolubilizer, to obtain a sizing paper, followed by 20 min of drying at 90 °C. Petition 870220121747, dated 12 / 23 / 2022, pp. 39 / 46 30 / 30
[0155] The wet strengths of the various substrates are indicated in the following table. [Table 12] Fibrous substrate 12a 12b 12c Dry fiber content of sisal fibers (%) 5 15 20 Wet strength (WS, %) 36 37 39
[0156] Moreover, good cohesion is found at the level of the three fibrous substrates. Petition 870220121747, dated 12 / 23 / 2022, pp. 40 / 46
Claims
1. A fibrous composition, useful for preparing a sheet of paper, particularly security paper, characterized in that it comprises at least - a fibrous cellulosic material based on cotton fibers and free of wood fibers, and - a wet-strengthening agent reactive to carboxylic functions, said fibrous cellulosic material additionally possessing cellulosic fibers, called hemicellulose fibers, having a hemicellulose content of at least 18% by weight relative to the total weight of said hemicellulose fibers and a hemicellulose content of at least 0.7% by weight relative to the total weight of said fibrous cellulosic material.
2. Fibrous composition, according to claim 1, characterized in that the level of hemicellulose in said fibrous cellulosic material varies from 0.7% to 4% and, preferably, from 1% to 4% by weight of hemicellulose relative to the total weight of the fibrous cellulosic material.
3. Fibrous composition, according to any one of claims 1 to 2, characterized in that said fibrous cellulosic material comprises at least 50%, preferably at least 80%, and more preferably from 80% to 95%, by weight of cotton fibers relative to its total weight.
4. Fibrous composition, according to any one of claims 1 to 3, characterized in that the hemicellulose fibers have a hemicellulose content of at least 21% by weight relative to their total weight.
5. Fibrous composition, according to any one of claims 1 to 4, characterized in that said fibrous cellulosic material contains, as a source of hemicellulose, fibers selected from sisal fibers, kenaf fibers, jute fibers, kapok fibers and mixtures thereof, preferably from sisal fibers, Petition 870250027792, dated 07 / 04 / 2025, page 12 / 19 2 / 4 kenaf fibers and mixtures thereof, and more preferably comprises at least sisal fibers, particularly derived from a bleached sisal pulp.
6. Fibrous composition, according to any one of claims 1 to 5, characterized in that it additionally comprises at least one intermediate carboxylated fixing agent.
7. Fibrous composition, according to any one of claims 1 to 6, characterized in that the wet strength agent comprises at least one or more resins selected from polyamide polyamine epichlorohydrin (PAAE) based resins.
8. Fibrous composition, according to any one of claims 6 to 7, characterized in that the fixing agent is selected from polymers comprising carboxylic functions, particularly guar gums, cellulosic derivatives and mixtures thereof, particularly from carboxylated cellulosic derivatives, and more particularly comprises at least one carboxymethylcellulose (CMC).
9. Fibrous composition, according to any one of claims 1 to 8, characterized in that it further comprises at least one filler selected from mineral fillers, particularly calcium carbonate, kaolin, titanium dioxide, talc, silicas, hydrated aluminas, aluminum silicates and mixtures thereof, and / or from organic fillers, particularly plastic fillers or pigments, and particularly comprising at least titanium dioxide.
10. Fibrous composition, according to any one of claims 1 to 9, characterized in that it is in the form of a fibrous substrate of the paper type, preferably of the banknote paper type.
11. Use of a fibrous composition, as defined in any one of claims 1 to 10, characterized in that it is for preparing a sheet of paper, particularly security paper. Petition 870250027792, dated 07 / 04 / 2025, page 13 / 19 3 / 4 12. Wet-resistant paper sheet, characterized in that it comprises a fibrous composition, as defined in any one of claims 1 to 10.
13. Paper sheet, according to claim 12, characterized in that it comprises, by weight, at least: - 40% to 96% by dry weight of fibers, particularly cellulosic, relative to the dry weight of said substrate, - 1% to 20% by dry weight relative to the dry weight of fibers, of at least one anionic polymer having a glass transition temperature above -40 °C, particularly carboxylated, and - 0.5% to 5% by dry weight of at least one cationic precipitating agent, relative to the dry weight of fibers.
14. A sheet of paper, according to any one of claims 12 to 13, characterized in that it comprises, in addition to the fibrous composition, at least one security element.
15. Security document and / or valuable document, characterized in that it comprises a sheet of paper, as defined in any one of claims 12 to 14.
16. Security document and / or valuable document, according to claim 15, characterized in that said document is a means of payment, such as a banknote, a payment card, a check or a restaurant voucher, an identity document, such as an identity card, a visa, a passport or a driver's license, a card, particularly an access card, a lottery ticket, a transport voucher or a ticket for entry to cultural or sporting events, a loyalty card, a service card, a subscription card, a game card or collection card, a discount voucher or a voucher, preferably said document is a banknote.
17. Security document and / or valuable document, according to any of claims 15 to 16, characterized by the fact that the Petition 870250027792, dated 07 / 04 / 2025, p. 14 / 19 4 / 4 said document is a banknote comprising a varnish, particularly an overprinting varnish.