Fibrous composition for paper, in particular security paper

Abstract

The invention relates to a fibrous composition, especially suitable for the preparation of paper, in particular security paper, comprising at least: - a cellulose fibrous material based on cotton fibers and free of wood fibers, said cellulose fibrous material further having cellulose fibers known as 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 cellulose fibrous material, and - a wet strength agent reactive towards carboxyl functions. The invention also relates to a paper comprising it and to its use in security documents and / or value documents.

Description

Technical Field

[0001] This invention relates to the field of paper, particularly security paper and especially for banknotes (billets debanque), which is made of cellulose fibrous composition and must have a high level of mechanical strength in a wet state. Background Technology

[0002] Cotton's cellulose fibers are often used in banknote production because they provide these banknotes with very good mechanical properties, especially high tear and fold resistance.

[0003] Furthermore, the level of mechanical stress that banknotes experience in very humid environments, particularly during their circulation and when they are accidentally exposed to large amounts of water (e.g., in a washing machine), leads central banks to mandate minimum wet mechanical strength (REH) levels. This REH level is typically evaluated by examining the tensile strength of the paper under normal conditions and after immersion in water under standardized conditions.

[0004] Therefore, the mandatory wet strength level for paper substrates used in banknotes is extremely high compared to other REH-treated papers such as filter paper, toilet paper, and absorbent paper.

[0005] Several essentially chemical methods have been proposed to provide satisfactory REH. Melamine-formaldehyde resins have thus been widely used due to their properties. However, given the toxicity levels of formaldehyde present in these resins, their use has now been abandoned. Currently, the preferred reagent is therefore a thermally crosslinkable polyamide-polyamine epichlorohydrin type resin, also known as PAAE, which has different generations depending on the application and use.

[0006] The reactivity of these polyamide polyamine epichlorohydrin (PAAE) resins is determined by nitrogen-containing heterocyclic butane. The functional group (N+) is provided. However, this functional group only possesses reactivity associated with carboxyl functional groups, and in reality, very few carboxyl functional groups are present in cotton fibers, which are considered the base material for paper used in banknote manufacturing. In fact, α-cellulose, which forms 85-90% by weight of cotton fibers, lacks carboxyl functional groups. Therefore, in order to fix epichlorohydrin resin (PAAE) onto cotton fibers, it is suitable to use an intermediate carboxylation fixative, which to some extent acts as a bridging agent between the cotton fibers and the REH resin. Guar gum or modified cellulose derivatives such as carboxymethyl cellulose (CMC) can be specifically mentioned as representatives of these fixatives. In a wet environment and in the presence of cotton fibers considered for use in sheet manufacturing, the carboxyl functional group and the azacyclobutane... Chemical reactions occur between functional groups. Sheets formed in this way and dried to allow the fixed resin to crosslink advantageously possess a three-dimensional network with relatively high wet strength.

[0007] However, this method is limited in its ability to immobilize epichlorohydrin resin (PAAE) onto fibers using a fixative. This is because, since the carboxyl functional groups are carried not by the fiber itself but by the polymer suspended in water, the immobilization of PAAE depends on the properties of the fixative and its retention in the formed fiber mat. This chemistry practically requires often empirical optimization to find a good balance and avoid excessive residues of unfixed PAAE. Summary of the Invention

[0008] The exact object of the present invention is to increase the likelihood of bonding and fixation of this type of resin with the cellulose fiber network and thus achieve improved wet and dry mechanical strength levels, and advantageously significantly reduce the residue of unfixed epichlorohydrin resin (PAAE).

[0009] This invention also aims to reduce the ecological footprint of secure documents.

[0010] Disclosure of the present invention

[0011] Therefore, according to one aspect, the present invention relates to a fibrous composition particularly suitable for the preparation of paper, especially safety paper, the composition comprising at least

[0012] - Cellulose fibrous materials based on cotton fibers and free of wood fibers, and

[0013] -Wet-strength agents reactive to carboxyl functional groups

[0014] The cellulose fibrous material also has cellulose fibers referred to as hemicellulose fibers, having a hemicellulose content of at least 18% by weight relative to the total weight of the hemicellulose fibers, and a hemicellulose content of at least 0.7% by weight relative to the total weight of the cellulose fibrous material.

[0015] Contrary to all expectations, the inventors have indeed found that a combination of specific cellulose fibers with conventional cotton fibers proves particularly advantageous for improving the wet mechanical properties of the corresponding paper treated with wet strength agents, especially epichlorohydrin resin (PAAE). Contrary to all expectations, it has also been found that the breaking length of such paper is advantageously increased in both wet and dry conditions. These gains are particularly illustrated in the examples below.

[0016] According to the first variant, the composition according to the invention can be in wet form, particularly in the form of an aqueous suspension of fibers.

[0017] According to the second variant, the composition according to the invention can be in dry form, particularly in the form of a fibrous substrate, especially in the form of a paper-type fibrous substrate.

[0018] According to a preferred variant, the cellulose fibrous material comprises fibers as a hemicellulose source, selected from sisal fibers, kénaf fibers, and mixtures thereof, preferably at least sisal fibers.

[0019] Sisal fiber has several advantages.

[0020] As shown in the following examples, they enable the improvement of the mechanical strength properties of paper treated with wet strength agents, and in particular epichlorohydrin resin (PAAE), especially tear resistance or tensile strength.

[0021] According to a preferred variant, the fibrous composition according to the invention further comprises at least one intermediate carboxylation fixative.

[0022] The fibrous composition according to the invention is particularly advantageous for manufacturing paper, especially security paper, and even more particularly banknotes, with high levels of wet strength and breaking length.

[0023] Therefore, the present invention also relates to the use of the fibrous composition according to the invention in the preparation of paper, particularly safety paper.

[0024] According to another aspect, the present invention relates to wet-strength paper comprising a fibrous composition according to the invention. In particular, the invention also relates to wet-strength safety paper comprising a fibrous composition according to the invention.

[0025] According to another aspect, the present invention relates to secure documents and / or valuable documents comprising paper according to the invention. Attached Figure Description

[0026] [ Figure 1 The dry breaking lengths of four inventive compositions (B, D, E, and F) comprising sisal fibers at 20% by weight relative to the fibrous material, and a composition (G) not of the present invention in which the fibrous material consists only of cotton fibers, are shown.

[0027] [ Figure 2 The wet breaking lengths of four compositions of the present invention (B, D, E, and F) comprising sisal fibers at 20% by weight relative to the fibrous material, and a composition (G) not of the present invention in which the fibrous material consists only of cotton fibers, are shown. Detailed Implementation

[0028] Detailed description

[0029] fibrous composition

[0030] This invention first relates to a fibrous composition particularly suitable for preparing paper, especially security paper, the composition comprising at least

[0031] - Cellulose fibrous materials based on cotton fibers and free of wood fibers, and

[0032] -Wet-strength agents reactive to carboxyl functional groups

[0033] The cellulose fibrous material also has cellulose fibers referred to as hemicellulose fibers, having a hemicellulose content of at least 18% by weight relative to the total weight of the hemicellulose fibers, and a hemicellulose content of at least 0.7% by weight relative to the total weight of the cellulose fibrous material.

[0034] The cellulose compositions according to the invention have the advantageous property of having improved breaking length when they are in dry form and sheet state, especially in wet environments.

[0035] They also have the unique characteristic of being free of wood fibers.

[0036] Cellulose fibrous materials

[0037] As described above, the fibrous composition according to the invention comprises at least one fibrous material, which comprises cellulose fibers, preferably natural cellulose fibers. According to one embodiment, the cellulose fibrous material according to the invention is formed solely from natural cellulose fibers.

[0038] The ingenuity of the fibrous material according to the invention lies in having a hemicellulose weight content of at least 0.7% relative to its total weight and very specifically comprising hemicellulose fibers. The inventors have indeed discovered that this particular type of cellulose is capable of directly interacting with wet-strength agents having functional groups reactive relative to free carboxyl functional groups. According to a preferred variant, these reactive functional groups are aziridines. The (azetidinium) functional group is selected from epichlorohydrin resin (PAAE).

[0039] The presence of hemicellulose in this fibrous material allows for the advantageous fixation of an increased amount of wet strength agent, thus significantly improving mechanical properties without altering the moisture-proof properties of the corresponding fibrous material. This tendency, achieved by the fibrous material according to the invention, to fix the wet strength agent directly through itself, is also economically advantageous. It has thus been observed that, compared to fibrous materials without hemicellulose, the amount of residual (i.e., uninteracted) wet strength agent is significantly reduced using the fibrous material of the invention. Furthermore, the reactivity of the fibrous material according to the invention with respect to the wet strength agent allows for the consideration of a smaller amount of carboxylation fixative, which is conventionally necessary for fixing the wet strength agent to fibrous materials not according to the invention.

[0040] According to a particular variant, the hemicellulose ratio of the cellulose fibrous material is 0.7-4% and preferably 1-4% by weight of hemicellulose relative to the total weight of the cellulose fibrous material.

[0041] The hemicellulose required in the cellulose fibrous material according to the invention is present therein at least partially in the form of fibers called hemicellulose fibers.

[0042] More specifically, and in the sense of the present invention, the hemicellulose fiber is a cellulose fiber having a hemicellulose content of at least 18% by weight relative to its total weight, and even more preferably at least 21% by weight relative to its total weight.

[0043] The hemicellulose fibers suitable for use in this invention are particularly selected from North African sparte fiber, kenaf fiber, jute fiber, flax fiber, sisal fiber, kapok fiber, and mixtures thereof.

[0044] Specifically, the hemicellulose fiber is selected from sisal fiber, kenaf fiber, jute fiber, kapok fiber, and mixtures thereof.

[0045] Specifically, the hemicellulose fiber is selected from sisal fiber, kenaf fiber, jute fiber and mixtures thereof, preferably from sisal fiber, kenaf fiber and mixtures thereof.

[0046] Kenaf fiber is characterized in particular by its α-cellulose content of 31%-39% and hemicellulose content of 21%-23% relative to its total weight. They are therefore particularly well-suited for use in this cellulose fibrous material.

[0047] Kapok fibers are characterized in particular by their α-cellulose content of 35-64% and hemicellulose content of 22-26% relative to their total weight. They are therefore particularly well-suited for use in this cellulose fibrous material.

[0048] Regarding sisal fibers, they advantageously have a hemicellulose weight content of 21%-24% relative to their total weight and an α-cellulose weight content of 43%-56% relative to their total weight. In addition to this particularly high hemicellulose content (which makes them particularly advantageous as a hemicellulose source in this invention), sisal fibers have other advantages.

[0049] First, sisal fibers are morphologically similar to cotton fibers. They are therefore particularly suitable as a substitute for cotton fibers without sacrificing the properties of paper, especially security paper, formed from this composition.

[0050] They also have the advantage of being thinner, thus achieving a higher fiber density per unit volume and an increased bonding and interaction area with REH resin.

[0051] Sisal fibers thus enable a dual positive effect on the physicochemical and morphological properties of the resin used as a wet strength agent.

[0052] Finally, sisal fiber is particularly advantageous due to its low environmental footprint. This is because sisal cultivation requires very little water, fertilizer, or phytosanitary products, and its waste can be value-added (biogas, pharmaceutical ingredients, building materials, fertilizer, animal feed). Moreover, sisal fiber is particularly suitable as a local raw material in countries such as Brazil, Tanzania, Kenya, Madagascar, and China.

[0053] Examples of sisal fibers include sisal fibers sold by SWM, or CELAVE CECF, CELAVE E TCF, or CELAVE D TCF fibers sold by CELESA.

[0054] According to a preferred variant, the fibrous material considered in the compositions of the present invention comprises at least sisal fibers or even only sisal fibers as hemicellulose fibers, which are specifically derived from bleached sisal pulp.

[0055] In addition to hemicellulose fibers, the fibrous material of the present invention comprises at least cotton fibers.

[0056] Cotton fiber is actually an effective fiber in terms of mechanical strength properties (especially burst strength and tear resistance).

[0057] In particular, the cellulose fibrous material comprises at least 50%, preferably at least 80%, and more preferably 80-95% cotton fibers relative to its total weight.

[0058] For example, the cotton fibers may be selected from "combed" type fibers, "fluff" type fibers, or mixtures thereof. "Combed" type fibers are long fibers obtained through a combing machine. "Fluff" type fibers are cellulose fibers derived from the short fibers of cotton. According to a particular embodiment, the cellulose fibrous material comprises cotton fibers in the form of a mixture of "combed" type and / or "fluff" type fibers, for example, in a weight ratio of 40 / 60 to 60 / 40, particularly 50 / 50.

[0059] Of course, the fibrous material according to the invention may also contain additional fibers in addition to cotton fibers and hemicellulose fibers, said additional fibers being particularly selected from bamboo fibers, abaca fibers and mixtures thereof.

[0060] The fibers constituting the fibrous material of the present invention can be obtained from bleached, semi-bleached or unbleached pulp, especially bleached pulp.

[0061] wet strength agent

[0062] As described above, the composition according to the present invention further comprises at least one wet strength agent.

[0063] This type of reagent is crucial for improving the mechanical properties of paper in a wet state.

[0064] These reagents are typically thermosetting polymers that are added while the paper is still wet and crosslinked in the paper as it dries.

[0065] The wet strength agent suitable for use in this invention is a compound having one or more functional groups that are reactive relative to the carboxyl functional groups provided by hemicellulose fibers in the fibrous material. Advantageously, these reactive functional groups are azacyclobutane. Functional groups.

[0066] Preferably, the wet strength agent comprises at least one or more of the following substances or even consists of one or more resins selected from polyamide-polyamine epichlorohydrin (PAAE) based resins.

[0067] The wet strength agent (preferably polyamide polyamine epichlorohydrin resin) that has already interacted with the carboxyl functional groups of hemicellulose and is thus fixed to the fibrous material undergoes crosslinking during the heat drying process of the composition of the present invention, generating cohesive forces between the fibers, and thus significantly enhancing the mechanical properties of the dry composition in wet or dry conditions, particularly its resistance in terms of its breaking length, by forming strong covalent bonds.

[0068] As illustrated in the examples given below, this improvement in mechanical properties is also advantageously associated with a significant reduction in the amount of free wet strength agent (i.e., free resin) after crosslinking. This characteristic is manifested in the treated fibrous material exhibiting lower ion demand and zeta potential. These two parameters can be measured, in particular, using the measurement methods described in the following examples. Specifically, the ion demand is measured by means of electrolyte titration: a specific amount of filtrate is neutralized with an electrolyte, and at the neutralization point, the amount of electrolyte used represents the value of the ion demand.

[0069] Clearly, the presence of hemicellulose fibers allows for the fixation of increased amounts of wet strength agent, and thus reduces the proportion of unfixed wet strength agent. This effect is beneficial in several ways. This is because, when the wet strength agent is not fixed and therefore remains in a free form in the final fibrous material, it is ineffective in improving the mechanical strength of the material, and also contributes to residual ion pollution in the environment and material loss.

[0070] In particular, the fibrous composition according to the invention may contain a wet strength agent at a weight of 1-10% dry weight, preferably 1-5% dry weight and more preferably 1.5-4% dry weight relative to the dry weight of the fibers.

[0071] Other compounds

[0072] According to a preferred variant, the fibrous composition of the present invention further comprises at least one intermediate carboxylation fixative.

[0073] This reagent also contributes to the cohesiveness of the fibrous composition.

[0074] Specifically, the fixative is selected from polymers containing carboxyl functional groups. Preferably, it is selected from guar gum, cellulose derivatives, and mixtures thereof, particularly carboxylated cellulose derivatives. According to a preferred embodiment, the fixative comprises at least one carboxymethyl cellulose (CMC), or even consists of one or more carboxymethyl celluloses.

[0075] Advantageously, the content of intermediate fixative in the cellulose-containing cellulose composition according to the invention can be reduced compared to cellulose compositions containing less than 0.7% by weight of hemicellulose.

[0076] The fibrous composition according to the invention may further comprise at least one filler, particularly a mineral filler.

[0077] More precisely, these fillers are specifically designed to increase the opacity, whiteness, and / or printability of the fibrous substrate.

[0078] The filler may be selected from mineral fillers, particularly calcium carbonate, kaolin, titanium dioxide, talc, silica, hydrated alumina, aluminum silicate, and mixtures thereof, and / or from organic fillers, particularly plastic fillers or pigments. Preferably, the fibrous composition contains at least titanium dioxide.

[0079] Additives or auxiliaries commonly used in the papermaking industry can also be used in the fibrous composition of the present invention.

[0080] Among additives, examples include pigments and colorants, antimicrobial agents, defoamers, retention agents, especially filler retention agents, or tracers.

[0081] The fibrous composition according to the invention may further comprise synthetic fibers. The presence of synthetic fibers mixed with cellulose fibers in the fibrous composition enables the improvement of the tear and folding resistance of the substrate.

[0082] As mentioned above, the fibrous composition can be in wet form, particularly in the form of an aqueous suspension. This type of fibrous composition can be used in methods for preparing substrates, and is commonly used in the paper industry, especially in papermaking processes.

[0083] It can also be in dry form. In particular, the fibrous composition can also be in the form of a fibrous substrate of paper type (preferably banknote paper type). For example, the fibrous substrate (especially a paper-type fibrous substrate) can be prepared from a fibrous composition in the form of an aqueous suspension, especially by draining, pressing and drying. Of course, additional steps can be performed depending on the desired properties of the fibrous substrate.

[0084] According to another particular embodiment, the dry fibrous composition according to the invention can also be combined with antifouling surface treatments, particularly hydrophobic and / or oleophobic surface treatments, suitable for the specific use of the corresponding paper material. For example, the paper material according to the invention can be surface treated to form laminated or film-coated paper, such as those intended for food packaging, and / or antifouling treatments can be provided by impregnation, surface finishing, sizing, and / or varnishing. As variations and / or combinations, the dry fibrous composition according to the invention can also be combined with antimicrobial surface treatments, particularly antibacterial, antifungal, antiviral, and / or antiyeast surface treatments, for example by impregnation, surface finishing, sizing, and / or varnishing.

[0085] application

[0086] The present invention also relates to the use of the fibrous composition described above for the preparation of paper, particularly safety paper. This paper (particularly safety paper) can be prepared, in particular, by processing the aforementioned fibrous substrate, especially by cutting, printing, and / or applying a varnish.

[0087] The present invention also relates to wet-strength paper comprising the fibrous composition described above. Such paper is particularly characterized in that it forms safety paper.

[0088] In particular, the paper according to the invention comprises at least:

[0089] -40-96% dry weight fibers, especially cellulose fibers, relative to the dry weight of the substrate.

[0090] - At least one anionic polymer having a dry weight of 1%-20% relative to the fiber, the anionic polymer having a glass transition temperature above -40°C, particularly carboxylated ones, and

[0091] - At least one cationic precipitant with a dry weight of 0.5-5% relative to the dry weight of the fiber.

[0092] As can be clearly seen from the examples given below, the combination according to the invention has proven particularly advantageous for the paper thus formed, because the hemicellulose required according to the invention has carboxyl groups, which will play a role in the flocculation process, and thus a network (polymer, hemicellulose fiber and cotton fiber) with improved cohesiveness can be obtained.

[0093] In the context of this invention, anionic polymers are polymers carrying a negative charge. They can be derived from the anionic functionalization of polymers that are called neutral because they are uncharged.

[0094] The anionic polymers suitable for use in this invention have glass transition temperatures higher than -40°C.

[0095] The glass transition temperature refers to a temperature below which the polymer is rigid. As the temperature increases, the polymer undergoes a transition state, which allows the macromolecular chains to slide relative to each other and the polymer to soften.

[0096] According to one embodiment of the present invention, this anionic polymer is a polymer having carboxyl functional groups.

[0097] Preferably, this type of polymer 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-hydroxymethylacrylamide, styrene, and butadiene.

[0098] Preferably, the anionic polymer is selected from acrylic homopolymers and copolymers, acrylate homopolymers and copolymers, carboxylated styrene-butadiene copolymers, and mixtures thereof.

[0099] As an acrylic copolymer, it is worth mentioning that:

[0100] -Vinyl-acrylic polymers,

[0101] -Styrene-acrylic polymers, and

[0102] - Polyurethane-acrylic polymer.

[0103] Specifically, the polymer is a carboxylated styrene-butadiene copolymer. This copolymer, for example, is available from Dow Chemical Company and has different glass transition temperatures.

[0104] According to another implementation, this anionic polymer can also be non-carboxylated.

[0105] As representatives of these other forms of anionic polymers, polyacrylamide and anionic forms of polystyrene copolymers (such as styrene-butadiene copolymers in particular) can be mentioned.

[0106] According to one variant embodiment, the anionic polymer has a Tg higher than 23°C.

[0107] Specifically, the one or more polymers with a glass transition temperature above 23°C are selected from polyacrylic acid compounds, polyacrylates, polyacrylamide, anionic polystyrene, polyvinyl compounds, polyethylene, polyurethane, and mixtures thereof.

[0108] According to a preferred embodiment, the one or more polymers with a glass transition temperature higher than 23°C are selected from acrylic polymers (or polyacrylic polymers), i.e., homopolymers or copolymers containing at least one acrylic monomer, i.e., acrylic homopolymers and acrylic copolymers.

[0109] As an acrylic copolymer, it is worth mentioning that:

[0110] -Vinyl-acrylic compounds, such as Orgal VA-HP (Tg = +41℃) sold by Organanik Kimya.

[0111] -Styrene-acrylic compounds, such as Acronal DS2416 (Tg = +38℃) sold by BASF, and

[0112] - Polyurethane-acrylic, such as Joncryl U6336 (Tg=+40℃) sold by BASF.

[0113] Preferably, the one or more polymers with a glass transition temperature higher than 23°C are selected from acrylic homopolymers.

[0114] The polymer can be used in the form of anionic dispersions, for example:

[0115] - From Tanatex Chemicals, named Edolan AH (Tg=+36℃),

[0116] - From Organinik Kimya, named Organi NA 302 (Tg=+26℃),

[0117] - From Icap Sira, named Acrilem 7105 (Tg=+50℃), and

[0118] - From BASF, named Acronal DS 2416 (Tg=+38℃).

[0119] The one or more anionic polymers may be non-crosslinkable, crosslinkable using an external crosslinking agent, or self-crosslinkable.

[0120] As anionic polyurethanes, anionic forms of polyurethane polyesters, polyurethane-polyethers, and polyurethane-polycarbonates, and mixtures thereof, may also be specifically mentioned. These polymers are, for example, available from Bayer under the name Impranil. (Elongation at break = 600%; Tg = -34℃) was obtained.

[0121] The one or more anionic polymers are typically used at a ratio of 1%-20% dry weight, preferably 1%-10% dry weight, and more preferably 3%-8% dry weight relative to the dry weight of the fiber.

[0122] The paper according to the invention may also contain an effective amount of at least one cationic precipitant. This cationic precipitant, in particular, allows the particles of one or more anionic polymers to be fixed onto the fibers by altering the electrostatic charge of the anionic cellulose fibers.

[0123] Preferably, the cationic precipitant is selected from polyaluminum chloride, water-soluble cationic polymers, and particularly from cationic starch, polyamide, polyacrylamide, polyethyleneimine, polyvinylamine, and mixtures thereof.

[0124] Preferably, the cationic precipitant comprises at least one cationic resin.

[0125] According to an advantageous embodiment, it should be noted that compounds considered as wet strength agents according to the invention may also have the ability to deposit the anionic polymer onto the fiber surface. This is particularly suitable for polyamide-polyamine epichlorohydrin resins, known as PAAE resins, which are very particularly well-suited for use as wet strength agents in this invention. In this embodiment, this type of compound can guarantee both functions, provided that its amount is adjusted according to its effectiveness.

[0126] Typically, the amount of cationic precipitant is adjusted to allow almost all, preferably all, anionic polymers to precipitate on the surface of the fiber. This amount is particularly 0.5-5% of the dry weight of the fiber, especially 0.8-3.5% of the dry weight.

[0127] Finally, in addition to the fibrous composition, the paper may also contain at least one safety element. This safety element specifically allows for the verification of the paper.

[0128] Specifically, the security element is selected from visual devices, particularly optically variable devices called OVDs, holograms, lens devices, elements with interference effects, especially iridescent elements, liquid crystals, pigments with magnetic orientation effects, and multilayer interference structures. These optically variable devices may be present in security lines integrated into a fibrous substrate, or in strips or patches pasted or printed on a fibrous substrate.

[0129] As another visual safety element, watermarks generated during the manufacturing process of fibrous substrates can also be mentioned.

[0130] Specifically, the safety element is selected from so-called light-emitting elements that are detectable under UV or IR. The light-emitting element may be in the form of particles, fibrettes, slats, safety lines that are at least partially integrated into a fibrous substrate, strips or patches that are pasted or printed on a fibrous substrate.

[0131] In particular, the safety element is selected from automatically detectable elements, especially optical or magnetic automatically detectable elements, which are often referred to as markers or tracers and are integrated into fibrous substrates or visual or luminescent safety elements.

[0132] The paper (especially security paper) according to the invention may also include a radio frequency identification device called RFID, which provides identification and traceability functions for the paper (especially security paper).

[0133] The present invention also relates to security documents and / or valuable documents comprising paper according to the present invention.

[0134] For example, the security document and / or valuable document is a payment instrument such as banknotes, payment cards, checks or restaurant vouchers, identification documents such as ID cards, visas, passports or driver's licenses, cards, especially access cards, lottery tickets, transportation tickets or tickets to cultural or sporting events, loyalty cards, service cards, reservation cards, game cards or collection cards, discount coupons or vouchers.

[0135] For example, banknotes are both a secure document because they contain security elements and a valuable document because they represent value. In contrast, tickets may have value, especially exchange value, but are not secure. In the case of access cards, they may be secure, but they have no value, especially no exchange value.

[0136] Preferably, the security document and / or valuable document according to the invention is a banknote.

[0137] In particular, the security documents and / or valuable documents according to the invention are banknotes containing varnish, especially surimation varnish.

[0138] Example

[0139] Materials and Measurement Methods

[0140] The following raw materials were used:

[0141] - Combed cotton fibers (also known as "combed machine" type fibers) and "first-pass cotton linters" type cotton fibers;

[0142] - Sisal fiber sold by CELESA under the names CELAVE C ECF, CELAVE E TCF and CELAVE D ECF or by SWMPapeteries de Saint-Girons;

[0143] - Polyamide polyamine epichlorohydrin (PAAE) type resins;

[0144] -Carboxymethyl cellulose (CMC) with a degree of substitution of 0.65-0.90;

[0145] - Anatase titanium dioxide (TiO2);

[0146] - Polyvinyl alcohol (PVA) grade 28 (viscosity 4%) / 99 (degree of hydrolysis);

[0147] - Insolubilisant of cationic polyamide polyamine epichlorohydrin type.

[0148] 1. ζ-potential

[0149] The ζ-potential was measured using a BTG Mütek SZP-06 “System ζ-potential” instrument.

[0150] 2. Ion demand

[0151] Ion demand was measured using a BTG Mütek PCD-05 Particle Charge Detector instrument.

[0152] 3. Dry tensile strength

[0153] To evaluate dry tensile strength, especially the length of fracture in the dry state (or "dry fracture length"), the length of the sheet at which it breaks under its own weight can be measured according to standard ISO 1924-2.

[0154] 4. Wet tensile strength

[0155] To evaluate wet tensile strength, especially the length of breakage in the wet state (or “wet breakage length”), the length of the sheet when it breaks under its own weight can be measured according to standard ISO 3781.

[0156] 5. Wet strength

[0157] Wet strength (REH) is defined as the ratio of wet fracture length to dry fracture length according to the following formula:

[0158] [Math 1]

[0159]

[0160] 6. Dry bursting strength

[0161] The burst strength (or “dry burst strength”) can be measured in accordance with standard ISO 2758.

[0162] The bursting index (or "dry bursting index") is the quotient of the bursting strength (kPa) in the dry state and the paper basis weight as determined according to standard ISO 536.

[0163] 7. Wet bursting strength

[0164] The burst strength (or “wet burst strength”) can be measured in wet condition according to standard ISO 3689.

[0165] The bursting index in wet condition (or “wet bursting index”) is the quotient of the bursting strength (kPa) in wet condition and the paper basis weight as determined according to standard ISO 536.

[0166] Example 1: Preparation of paper-type fibrous substrates from the compositions of the present invention and non-composes of the present invention

[0167] First, the cotton fibers are refined to a refinement degree of 65°SR (Schoper-Riegler degree), and then mixed with sisal fibers under the conditions tested according to the invention to form a fiber suspension in water with a concentration of 1 g / L. As a variant, the sisal fibers may also be refined before being mixed with the cotton fibers, and / or the cotton and sisal fibers may be refined as a mixture. Titanium dioxide (TiO2), carboxymethyl cellulose (CMC), and PAAE resin are then added to the fiber suspension.

[0168] After homogenization, the paper-type fibrous substrate is prepared according to existing papermaking processes, specifically by the following methods: draining, pressing at 7 bar for 2 minutes, then drying at 90°C for 20 minutes, using wet absorbent paper, and the compositions of the aqueous suspension A to F (according to the invention) and G (not according to the invention) are given in Table 1 below, wherein the content is expressed as dry weight relative to the total weight of the fibers.

[0169] [Table 1]

[0170]

[0171] Example 2: ζ-potential

[0172] After mixing all components in an aqueous solution, the ζ-potential of the fiber surface of all compositions A to G in Example 1 was measured. The results are shown in Table 2 below.

[0173] The ζ-potential of cotton and sisal pulp in their pure state was also measured, and the results were similar.

[0174] [Table 2]

[0175] A B C D E F G ζ-potential (mV) -3.5 -5.3 -6.5 -2.0 -8.2 -6.3 +5.1

[0176] For all compositions (A to F) containing sisal fibers, a negative zeta potential was measured, reflecting the fact that no positively charged free PAAE resin was present; instead, all of it was fixed to the fibers. Conversely, for composition G, which is not according to the invention, the zeta potential was positive. This phenomenon was confirmed by tests A to C, which showed that the zeta potential decreased as the sisal fiber content increased. Therefore, the interaction of PAAE resin with sisal fibers is greater than its interaction with cotton fibers.

[0177] Example 3: Fracture Length

[0178] For all fibrous substrates of compositions A to G in Example 1, the breaking length was measured in both dry and wet conditions. The results are shown in Table 3 below. Figure 1 and Figure 2 .

[0179] [Table 3]

[0180] A B C D E F G Dry fracture length (m) 8073 7695 7861 7936 7862 8023 7384 Wet fracture length (m) 3192 3374 3280 3367 3596 3492 3159

[0181] The dry and wet breaking lengths of the compositions (A to F) containing sisal fibers are both greater than the breaking lengths in the test (G) not according to the invention. This result is effective for various types of sisal fibers and for various contents of sisal fibers. Therefore, by adding sisal fibers, the mechanical properties of the fibrous matrix are improved in both dry and wet conditions.

[0182] Example 4: Preparation of sizing paper from the compositions of the present invention and non-composes of the present invention

[0183] Two fibrous compositions and a fibrous substrate were prepared by the method described in Example 1, with respect to the compositions in Table 4 below according to the present invention (H) and non-present invention (I).

[0184] [Table 4]

[0185]

[0186] The obtained fibrous substrate was then sizing in a sizing press with an aqueous composition containing 4% PVA and 1% solvent-free material to obtain sizing paper, which was then dried at 90°C for 20 minutes.

[0187] Example 5: ζ-potential

[0188] The zeta potentials of a 50 / 50 blend of combed cotton / cotton lint and Celave D sisal fiber measured in aqueous suspensions of the same concentration were -14.7 mV and -17 mV, respectively. Therefore, the zeta potentials of different fiber types are of the same order of magnitude.

[0189] For compositions H and I in Example 4, titanium dioxide, CMC, and PAAE resin were successively added to a mixture of cotton and sisal fibers (if applicable) in an aqueous suspension of the same concentration, and the zeta potential (PZ) of the fiber surface was measured. The final PZ is the PZ of the composition after the addition of PAAE resin and before the formation of the sheet.

[0190] The results are shown in Table 5 below.

[0191] [Table 5]

[0192] PZ, fiber suspension <![CDATA[PZ, after adding TiO2]]> PZ, after adding CMC Final PZ H -19.5mV -20.6mV -38.6mV -2.8mV I -14.7mV -15.5mV -47.7mV +14.4mV

[0193] The ζ-potential therefore hardly changed with the addition of TiO2, but decreased rapidly as expected with the addition of CMC.

[0194] However, as observed in Example 2, the addition of PAAE resin alters the zeta potential differently between the compositions of the present invention and those of non-the present invention. For composition H, the zeta potential remains negative, close to zero, meaning that the composition no longer contains free resin and most negative sites interact with the resin. Conversely, in the case of Comparative Example I, the zeta potential is significantly positive, indicating the presence of free resin in the composition.

[0195] Finally, the final ζ-potential is almost zero, but remains significantly positive in Comparative Example I, while being slightly negative in Example H according to the present invention. Therefore, in Example H, the PAAE resin is not excessive.

[0196] Example 6: Mechanical Properties

[0197] The breaking and bursting lengths of the sizing paper obtained using the various compositions in Example 4 were measured and are shown in Table 6.

[0198] [Table 6]

[0199] Dry fracture length wet fracture length Dry burst index Wet burst index H 7120m 3667m <![CDATA[4.28kPa.m 2 / g]]> <![CDATA[3.44kPa.m 2 / g]]> I 6217m 3267 m <![CDATA[4.19kPa.m 2 / g]]> <![CDATA[3.18kPa.m 2 / g]]>

[0200] Compared to Test I without sisal fiber, which is not based on the invention, adding sisal fiber (as in Test H according to the invention) improves all properties, both dry and wet, in terms of breaking and burst length.

[0201] Therefore, the composition comprising hemicellulose fibers (especially sisal fibers) according to the present invention enables gains in strength, and especially wet strength.

[0202] Example 7: Preparation of paper-type fibrous substrates from the compositions of the present invention and non-composes of the present invention

[0203] Two fibrous compositions were prepared by the method described in Example 1: one containing 5% fibrous material formed from Celave C sisal fibers (Test J according to the invention), and the other containing 100% material formed from cotton fibers (Test K not according to the invention), with the remainder remaining the same in both compositions. In both cases, the cotton fibers were formed from a 50 / 50 mixture of combed cotton fibers / cotton lint, and the contents of PAAE, CMC, and TiO2 were the same as in the previously presented compositions.

[0204] Example 8: ζ-potential

[0205] Measure the ζ-potential of the various compositions in Example 7:

[0206] - In the initial slurry, i.e., in the fiber suspension before the addition of PAAE resin, CMC, and TiO2, and

[0207] - In the final composition, that is, after the addition of PAAE resin, CMC and TiO2 and before the formation of the sheet.

[0208] [Table 7]

[0209]

[0210] Therefore, even with sisal fiber comprising 5% of the fibrous material, these hemicellulose-rich fibers can reduce the final zeta potential of the cellulose fibers. They can thus reduce the final ion requirement (i.e., the residual cationic charge associated with free, unfixed PAAE resin) by a factor of 4, reflecting much better resin fixation on the fibers.

[0211] Example 9: Preparation of paper-type fibrous substrates from the compositions of the present invention and non-composes of the present invention

[0212] Based on the compositions in Table 8 below, five fibrous compositions and fibrous substrates were prepared by varying the resin content and CMC content using the method described in Example 1, according to the present invention (L, M, and N) and not according to the present invention (O and P).

[0213] [Table 8]

[0214]

[0215] Example 10: Ion Requirement

[0216] The final ion requirement of the composition in Example 9 was measured after the addition of PAAE resin and before the formation of the sheet. The results are shown in Table 9 below.

[0217] [Table 9]

[0218] L M N O P Final ion requirement (μ equivalent / L) 9 6 24.5 32.2 51.5

[0219] When the resin content decreases, the ion demand also decreases because less positive charge is added to the system. Conversely, when the CMC content decreases, the ion demand increases because there are fewer carboxyl functional groups available for binding the resin.

[0220] Moreover, tests comparing L and O or N and P confirmed that the presence of sisal fibers systematically reduced the final ion requirement, which fully affirmed the interaction and fixation of PAAE resin on hemicellulose-rich fibers.

[0221] Example 11: Mechanical Properties

[0222] For the fibrous substrate obtained in Example 9, the dry fracture length and wet fracture length were measured, and the wet strength was calculated from these two values ​​according to Formula 1.

[0223] [Table 10]

[0224]

[0225]

[0226] The comparison of tests O and M shows that, due to the presence of sisal fibers, the composition according to the invention can reduce the content of wet strength agent while maintaining equivalent REH and wet breaking length.

[0227] [Table 11]

[0228] N P Dry fracture length (m) 5449 5152 Wet fracture length (m) 2428 2008 Wet strength (REH, %) 44.6 39.0

[0229] The comparison of N and P tests shows that the composition containing sisal fiber according to the present invention can improve REH with reduced CMC content. More specifically, the reduction in CMC content relative to fiber leads to a 6.4% decrease in wet strength (REH) (tests O and P), while for the composition containing sisal fiber, the decrease in REH is only 0.8% (test N relative to O).

[0230] The examples demonstrate that the fixation of PAAE resin onto hemicellulose-rich sisal fibers, as revealed by measurements of ion requirements, undoubtedly improves the mechanical properties of the fibrous matrix in the compositions of this invention, particularly in the wet state. Furthermore, the presence of sisal fibers allows for a reduction in resin and / or CMC content with minimal or no performance loss.

[0231] Example 12: Preparation of paper-type fibrous substrates from the composition of the present invention containing an anionic polymer on a pilot-scale machine

[0232] Three fibrous materials were prepared, consisting of only cotton fiber (combed cotton fiber / cotton lint weight ratio of 50 / 50) and sisal fiber, with sisal fiber proportions of 5%, 15%, and 20%, respectively.

[0233] The fibrous composition is formed by adding the following substances to each of these fibrous materials suspended in water.

[0234] - At least one anionic carboxylated polymer with a glass transition temperature higher than -40°C relative to 4% of the fiber dry weight.

[0235] - Relative to 2.5% dry weight of the fiber, polyamide polyamine epichlorohydrin resin (referred to as PAAE resin),

[0236] - Relative to CMC at 0.7% dry weight of fiber, and

[0237] -TiO2 relative to 5% of fiber dry weight.

[0238] Then, on a test paper machine (called a pilot plant), various fibrous substrates were prepared from the three fibrous compositions obtained therefrom.

[0239] The resulting fibrous substrate is then impregnated on a sizing press with an aqueous composition containing 4% PVA and 1% solvent-free material to obtain sizing paper, which is then dried at 90°C for 20 minutes.

[0240] The wet strength of various substrates is shown in the table below.

[0241] [Table 12]

[0242] fibrous substrate 12a 12b 12c Dry fiber content (%) of sisal fiber 5 15 20 Wet strength (REH, %) 36 37 39

[0243] Moreover, good cohesion was found at the level of these three fibrous substrates.

Claims

1. A fibrous composition suitable for preparing paper, the composition comprising at least - Cellulose fibrous materials based on cotton fibers and free of wood fibers, and - A wet-strength agent reactive to carboxyl functional groups, the wet-strength agent comprising at least one or more resins selected from polyamide-polyamine epichlorohydrin (PAAE) based resins. The cellulose fibrous material also has cellulose fibers referred to as hemicellulose fibers, having a hemicellulose content of at least 18% by weight relative to the total weight of the hemicellulose fibers, and a hemicellulose content of at least 0.7% by weight relative to the total weight of the cellulose fibrous material.

2. The fibrous composition according to claim 1, wherein the paper is safety paper.

3. The cellulose composition according to any one of claims 1-2, wherein the hemicellulose ratio of the cellulose cellulose material is 0.7-4% by weight of hemicellulose relative to the total weight of the cellulose cellulose material.

4. The fibrous composition according to any one of claims 1-2, wherein the cellulose fibrous material comprises cotton fibers at least 50% by weight relative to its total weight.

5. The fibrous composition according to any one of claims 1-2, wherein the hemicellulose fiber has a hemicellulose content of at least 21% by weight relative to its total weight.

6. The fibrous composition according to any one of claims 1-2, wherein the cellulose fibrous material comprises fibers as a hemicellulose source, selected from sisal fibers, kenaf fibers, jute fibers, kapok fibers, and mixtures thereof.

7. The fibrous composition according to any one of claims 1-2 further comprises at least one intermediate carboxylation fixative.

8. The fibrous composition according to claim 7, wherein the fixative is selected from polymers containing carboxyl functional groups.

9. The fibrous composition according to any one of claims 1-2 further comprises at least one filler selected from mineral fillers and / or organic fillers.

10. The fibrous composition according to any one of claims 1-2, characterized in that, This fibrous composition takes the form of a paper-type fibrous substrate.

11. Use of the fibrous composition according to any one of claims 1-10 for the preparation of paper.

12. A wet-strength paper comprising the fibrous composition according to any one of claims 1-10.

13. The paper of claim 12, wherein the fibrous composition is in the form of a fibrous substrate of the paper type, the paper comprising, by weight, at least: - 40-96% dry weight fibers, relative to the dry weight of the substrate. - At least one anionic polymer having a dry weight of 1%-20% relative to the fiber, the anionic polymer having a glass transition temperature above -40°C, and - At least one cationic precipitant comprising 0.5-5% of the dry weight of the fiber.

14. The paper according to claim 12, characterized in that, In addition to the fibrous composition, the paper also contains at least one safety element.

15. Security documents and / or valuable documents comprising paper as described in any one of claims 12-14.

16. The secure document and / or valuable document of claim 15, wherein the document is a payment instrument, identification document, card, lottery ticket, transportation ticket or admission ticket for cultural or sporting event, discount coupon or voucher.

17. The secure document and / or valuable document of claim 16, wherein the payment instrument is selected from banknotes, payment cards, checks, or restaurant vouchers.

18. The secure document and / or valuable document of claim 16, wherein the identity document is selected from an identity card, visa, passport, or driver's license.

19. The secure document and / or valuable document according to any one of claims 15-17, characterized in that, The document in question is a banknote containing varnish.

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