METHOD FOR PRODUCING PAPER IMPREGNATED BY A SUPERCRITICAL-PRESSURE FLUID, AND IMPREGNATED, PARTICULARLY COLOURED PAPER

Abstract

In the field of papermaking and more particularly a method for producing paper impregnated with a molecule of interest, particularly colored paper, and the associated product, i.e. impregnated paper, there is a disclosed a method implementing a supercritical-pressure fluid. Such paper, particularly colored paper, obtained from a formulation of paper pulp or paper including latex, does not bleed when it comes into contact with water.

Claims

1-27. (canceled)

28. Method for impregnating a paper and in particular dyeing, by means of a supercritical-pressure fluid, comprising a step of impregnation by putting paper into contact with molecules of interest in the presence of a fluid in the supercritical or subcritical state, said paper comprising, (i) at the core, a polymeric additive introduced in the form of latex and/or (ii) on the surface, a polymeric additive applied in the form of latex, identical or different from the polymeric additive possibly present at the core and/or a molecule, in particular a polymer that can be impregnated by a molecule of interest, in particular a hydrophobic molecule, by means of the supercritical-pressure fluid.

29. Method according to claim 28, wherein the step of impregnation is carried out on a dry paper.

30. Method according to claim 28, wherein the supercritical-pressure fluid is carbon dioxide in the supercritical or subcritical state or a mixture of carbon dioxide with an organic solvent, for example an alcohol, in particular ethanol.

31. Method according to claim 28, wherein the molecules of interest are chosen from dye molecules, reactive disperse dyes, optical brightening agents, fluorophores, antioxidants, molecules that absorb ultraviolet rays, surfactants, polymers and paraffinic waxes.

32. Method according to claim 28, wherein the dye molecules are formed by a dispersed hydrophobic dye or a mixture of dispersed hydrophobic dyes, the dye or dyes being added at a level of from 0.1 to 10% by dry weight of dye or dyes relative to the weight of the paper.

33. Method according to claim 28 comprising the steps of: a) Loading into a reactor, dry paper to be impregnated with a molecule of interest, in particular with a dye or a mixture of dyes, and a determined quantity of molecule of interest, in particular a dye or a mixture of dyes, followed by the closure of the reactor, b) Loading a fluid, in particular CO.sub.2, at the storage pressure of the fluid, c) Heating the reactor and/or pumping the fluid until obtaining the conditions of pressure and temperature that allow the solubilization of the molecule of interest, in particular the dye or dyes, in the fluid in the supercritical or subcritical state, and impregnating the molecule of interest, in particular the dye or dyes, in the thickness of the paper, d) Circulating the supercritical-pressure fluid loaded with the molecule of interest, in particular the dye or dyes, through the paper, e) Sweeping with clean supercritical-pressure fluid under conditions of temperature and pressure that are supercritical or, where appropriate, subcritical, identical or different from those of the step c., in order to eliminate the non-fixed molecule of interest, in particular the non-fixed dye or dyes, f) Depressurizing the reactor to precipitate the remaining dye or dyes and allowing the fluid in the supercritical or subcritical state to return to the gaseous state, g) Recovering the dry paper, colored at the core and/or on the surface.

34. Method according to claim 28, wherein the supercritical-pressure fluid is carbon dioxide and the temperature during the supercritical-pressure impregnation phase is greater than or equal to the ambient temperature and in particular less than or equal to 200 C., for example less than or equal to 150 C., in particular in the range from 70 C. to 130 C. and the pressure during the supercritical-pressure impregnation phase is greater than or equal to 75 bars and less than 1000 bars.

35. Method according to claim 28, wherein the paper is obtained from a paper pulp comprising: i) a fibrous suspension based on cellulose fibers in water having a concentration of cellulose fibers from 2 to 50 g/l, the cellulose fibers being comprised of a mixture of cellulose fibers of different origin and/or size, said suspension being refined to a degree of at least 17 SR; ii) a polymeric additive in the form of latex, said latex being added to the fibrous suspension in a proportion from 0.5 to 50% by weight of dry product, in particular from 0.5 to 20% by weight of dry productrelative to the dry weight of the cellulose fibers.

36. Method according to claim 28, wherein the paper is obtained: i) from a paper pulp comprising a fibrous suspension based on cellulose fibers in water having a concentration of cellulose fibers from 2 to 50 g/l, the cellulose fibers being comprised of a mixture of cellulose fibers of different origin and/or size, said suspension being refined to a degree of at least 17 SR, and a polymeric additive in the form of latex, said latex being added to the fibrous suspension in a proportion from 0.5 to 5 0% by weight of dry product, in particular from 0.5 to 20% by weight of dry product relative to the dry weight of the cellulose fibers and ii) according to a method of manufacturing paper comprising a step of depositing on the surface of the paper, a polymeric additive in the form of latex in a proportion from 0.5 to 25% by weight relative to the weight of the paper.

37. Method according to claim 28, wherein the latex is an aqueous ionic dispersion of particles of polymer, in particular of copolymer, where applicable crosslinked or crosslinkable, in particular thermally or self-crosslinking, or thermoplastic, in particular whose chains comprise Lewis base groups, for example ethers, carbonyl, carboxyl or phenyl groups or mixtures thereof, said copolymer having a glass transition temperature less than 100 C.

38. Method according to claim 28, wherein the latex is obtained from a copolymer, at least one of the monomers of which is chosen from ether monomers, vinyl monomers, styrene monomers, acrylic monomers, in particular methacrylic, urethane and dienic monomers.

39. Method according to claim 38, wherein the latex is obtained from a polymer chosen from the group of styrene-butadiene copolymers in particular a carboxylated styrene-butadiene copolymer of styrene-acrylic copolymers, acrylic ester-acrylonitrile copolymers, vinyl acetate-ethylene copolymers, ether-urethane copolymers, and vinyl chloride-vinyl acetate-ethylene copolymers.

40. Method according to claim 38, wherein the latex is obtained from a polymer chosen from the group of copolymers of styrene and acrylate (in particular butyl acrylate), copolymers of acrylic ester and acrylonitrile, copolymers of acrylate and vinyl acetate, copolymers of styrene butadiene, copolymers of ethylene and vinyl acetate, polyacrylate, ether-urethane copolymers, copolymers of acrylic ester, styrene and acrylonitrile, polyurethane, copolymers of vinyl chloride and ethylene.

41. Method according to claim 38, wherein the latex is obtained from a polymer chosen from the group of copolymers of styrene and acrylate (in particular butyl acrylate), copolymers of acrylic ester and acrylonitrile, copolymers of acrylate and vinyl acetate copolymers, copolymers of styrene butadiene, copolymers of ethylene and vinyl acetate.

42. Method according to claim 35, wherein the paper pulp comprises a retention agent formed by a cationic compound capable of fixing the latex on the cellulosic fibres.

43. Method for preparing according to claim 42, wherein the cationic compound is chosen from cationic flocculation agents, cationic resins capable of reacting with the cellulosic fibers, in particular crosslinkable resins on the cellulosic fibers, and cationic starch.

44. Method according to claim 43, wherein the cationic resin is a polyamide-amine-epichlorhydrine resin.

45. Method according to claim 38, wherein the retention agent is added to the latex in conditions enabling the retention of the latex in the fibrous mat comprising the cellulose fibers, by forming ionic bonds with said fibers, said conditions comprising for example the addition of a retention agent according to a retention agent/latex ratio expressed as a percentage of dry retention agent/dry weight of latex from 0.1% to 20.

46. Method according to claim 34, wherein the cellulose fibers are a mixture of fibers of different lengths chosen from short fibers of length in the range from 0.1 to 0.49 mm, medium fibers of length in the range from 0.5 to 1.5 mm and long fibers of length in the range from 1.6 to 3 mm.

47. Method according to claim 34, wherein the proportion of cellulosic fibers of a first determined length is from 40 to 50% and the proportion of cellulosic fibers of a second determined length is from 60 to 50%, in particular the mixture is comprised of 40% long fibers and 60% short fibers or is comprised of 50% long fibers and 50% short fibers.

48. Method according to claim 34, wherein the formulation of the pulp is adjusted by adding fillers, pigments, bonding agent, dry resistance agent, wet resistance agent, fluorescent agent, fire-proofing agent, liquid barrier or gas barrier product.

49. Method for manufacturing impregnated paper by means of a supercritical-pressure fluid, in particular colored paper, comprising the following steps: a. Preparing in a pulper a paper pulp according to claim 34, b. If needed, adjusting the prepared pulp and/or diluting to the desired concentration, before it is sent into the headbox for the purpose of homogeneous distribution in particular on the wire cloth of a flat table, c. Draining the pulp distributed beforehand over the wire cloth of the paper machine, the drainage being in particular carried out via gravity and by suction using suction boxes, to produce a sheet of paper, d. Dewatering the sheet obtained in the step c., for example by means of a press comprised of cylinders and where applicable drying felt for example by means of steam-heated to obtain a sheet with the moisture content less than or equal to 7%, e. Where applicable, applying a surface treatment to the dried sheet, for example sizing by means of a size or a bath of a determined composition, supplied by a size-press, f. Where applicable, drying in a post-drying zone, g. Where applicable, modifying of the surface state of the sheet by an operation of calendering or smoothing or coating, h. Impregnating, in particular coloring, the sheet obtained by implementing the method for impregnating.

50. Colored paper that is obtainable or obtained by implementing the method according to claim 28, wherein the paper is obtained from a fibrous suspension and in particular the paper has a composition of short fibers and long fibers in a ratio of 50/50, is refined to 30-35 SR and comprises from 0.5 to 20%, in particular from 1 to 15%, in particular from 1 to 10% and more particularly from 1 to 5% or from 5 to 10% of polymeric additive in the form of latex introduced in bulk and retained in the fibers by means of a cationic retention agent, said paper comprising on the surface a layer of polymeric additive, where appropriate applied in the form of latex identical or different from the polymeric additive introduced in bulk, and comprising from 0 to 20% by dry weight of polymer relative to the weight of the dry paper.

51. Colored paper according to claim 50, wherein the latex is obtained from a copolymer, at least one of the monomers of which is chosen from ether monomers, vinyl monomers, styrene monomers, acrylic monomers, in particular methacrylic, urethane and dienic monomers.

52. Colored paper according to claim 50, wherein the latex is obtained from a polymer chosen from the group of styrene-butadiene copolymers in particular a carboxylated styrene-butadiene copolymer of styrene-acrylic copolymers, acrylic ester-acrylonitrile copolymers, vinyl acetate-ethylene copolymers, and ether-urethane copolymers.

53. Colored paper according to claim 50, wherein the latex is obtained from a polymer chosen from the group of copolymers of styrene and acrylate (in particular butyl acrylate), copolymers of acrylic ester and acrylonitrile, copolymers of acrylate and vinyl acetate c, copolymers of styrene butadiene, copolymers of ethylene and vinyl acetate, polyacrylate, ether-urethane copolymers, copolymers of acrylic ester, styrene and acrylonitrile, polyurethane, copolymers of vinyl chloride and ethylene.

54. Colored paper according to claim 50, wherein the latex is obtained from a polymer chosen from the group of copolymers of styrene and acrylate (in particular butyl acrylate), copolymers of acrylic ester and acrylonitrile, copolymers of acrylate and vinyl acetate, copolymers of styrene butadiene, copolymers of ethylene and vinyl acetate.

Description

[0109] The invention shall be illustrated and described in more detail in the following examples and figures.

[0110] FIG. 1 describes the diagram of supercritical CO.sub.2 impregnation assembly. The references numbered 1 to 7 designate the valves with function as shown in the following examples.

[0111] FIG. 2 shows the values of K/S for the equation K/S=(1-R).sup.2/2R which determine the color intensity of the treated papers. In this equation, R is the minimum value of the reflectance curve, which is measured over the range of the wavelength between 400 and 700 nm using a spectrophotometer. The term (K/S), proportional to the dye concentration, evaluates the color intensity.

EXAMPLE 1

[0112] Sheet former containing 1, 5 or 10% of a polymer introduced in the form of latex in bulk, retained in the fibrous mat thanks to a polyamide-epichlorhydrine (PAE) type resin.

[0113] a) Preparation of the Fibrous Suspension and the Various Elements Used in the Composition

[0114] i. Preparation of the Fibrous Suspension

[0115] The composition chosen is a mixture of long fibers (Sodra Black R) and short fibers (Cenibra). Note that the fibers of the Cenibra type are cellulosic wood fibers derived from eucalyptus, with an average length within the range from 0.5 to 1.5 mm, and that the fibers of the Sodra Black R type are long cellulosic wood fibres derived from softwoods, with an average length within the range from 1.5 to 3 mm. At 500 g of pulp, formed from a mixture at of the Cenibra type fibers and of the Sodra Black R type fibers, 22 L of water is added then refining is carried out until a refining degree of about 45 SR (or Schopper-Riegler degrees) is reached.

[0116] ii. Preparation of Latexes

[0117] Different commercial latexes have been chosen and evaluated. The list and the technical characteristics provided by the suppliers are shown in Table 1.

TABLE-US-00001 TABLE 1 Technical data of the different latexes tested. Commer- Glass transition Dry cial Acrylate or Acrylo- Vinyl Buta- Vinyl temperature (Tg extract Presence of Crosslinking name Supplier Chemical Nature Styrene acrylic ester nitrile acetate diene Ethylene Ether Urethane chloride in C.) pH (%) plasticizer nature Acronal BASF Aquesous dispersion of a * * with R = butyl 46 6 46 NO Thermal S 996 S butyl and styrene acrylate (120 C.) copolymer, crosslinkable in temperasture. Contains no plasticizers or solvents. Acronal BASF Aqueous dispersion of an * * 39 6.5 51 NO Thermal (T.sub.amb- LN 838 S acrylate ester and >150 C.) acrylonitrile copolymer, crosslinkable in temperature. Contains no plasticizers or solvents. Acronal BASF Aqueous dispersion of an * * 7 5.5 50 NO Thermal (T.sub.amb- LN 579 S acrylate ester and >150 C.) acrylonitrile copolymer, crosslinkable in temperature. Contains no plasticizers or solvents. Acronal BASF Aquesous dispersion of a, * with R * 13 3-5 50 NO (without 500 D acrylate copolymer sometimes = H specific containing carboxylic and additives) vinyl acetate groups. Styrofan BASF Aqueous dispersion of a * * 23 5.5 49 2430 styrene butadiene copolymer Styronal BASF Aqueous dispersion of a * * 6-7 50 NO D 809 styrene butadiene copolymer Vinnapas WACKER Aqueous dispersion of a self- * * 15 4-6 52 NO Thermal (T.sub.amb- EN 428 crosslinking copolymer, >150 C.) without plasticizer, produced from vinyl acetate and ethylene monomers. Epotal BASF Aqueous dispersion of an * with R 53 2-3 45 Thermal A 816 acrylate copolymer sometimes = (110 C.) containing carboxylic H groups. Epotal BASF Aqueous dispersion of a * * 7 53 FLX 3621 polyether polyurethane elastomer. Acronal BASF Anionic aqueous dispersion * * with R butyl 23 6.5-7.5 50 NO S 728 of a styrene and n-butyl acrylate copolymer. Contains no plasticizers or solvents. Acronal BASF Aqueous dispersion of a self- * * 7 5.5 51 Thermal (Tamb- LA 47 S crosslinking copolymer with >150 C.) an acrylic ester and acrylonitile base. Acronal BASF Aqueous dispersion of a * * * 31 8.5 50 Thermal (Tamb- S 888 S copolymer (thermally >150 C.) crosslinkable) of acrylic ester and styrene, manufactured by a method incorporating acrylonitrile. Emuldur BASF Anionic aqueous dispersion * 8 40 NO (without 360 A of polyurethane. specific additives) Acronal BASF Aqueous dispersion of a * with different R * 36 3.5 50 Thermal (Tamb- A 273 S copolymer (thermally >120 C.) crosslinkable) of different acrylates in the manufacture of which acrylonitrile is also used. Vinnol WACKER Dispersion of a self- * * 35 5-7 50 NO YES CEN 203 crosslinking copolymer of ethylene and of vinyl chloride. Contains no plasticizers. Acronal BASF Aqueous dispersion of a * * 38 4.5 50 YES DS 2416 copoymer with an acrylic ester and styrene base. Vinnapas WACKER Aqueous dispersion of small- * * 20 7.5-8.5 50 SAF 364 size particles of a copolymer produced from styrene and acrylic ester monomers.

TABLE-US-00002 Repeat units present in the latexes tested Acrylate or Styrene acrylic ester Acrylonitrile [00001] [00002] [00003] Vinyl acetate Butadiene Ethylene [00004] [00005] [00006] Ether Urethane Vinyl chloride [00007] [00008] [00009]

[0118] Before use, each latex was diluted in order to reach a solid particle content of about 10%, controlled and recalculated by a measurement of dry extract. The pH of each latex was also adjusted to the pH of the fibrous suspension, i.e. about 7.1 and a visual inspection was conducted after a few hours or a few days in order to detect any destabilization of the solution.

[0119] iii. Preparation of the Retention Agent

[0120] The retention agent used is a cationic polyelectrolyte: a resin of the PAE (cationic polyamide-epichlorohydrine) type, Kymene 617. In the same way as above, the PAE is diluted and its pH is adjusted to 7.1.

[0121] b) Study of the Retention and Optimization of the Ratio [Retention Agent: Latex]

[0122] After having carried out the various preparations, the quantity of PAE required for the total retention of each one of the latexes on the fibres is defined in the following way: [0123] Bottles suitable for centrifugation are filled with a known and identical quantity of fibrous suspension. [0124] In each one of the bottles, a determined quantity of PAE is then added. As such, a series of bottles containing respectively 0%, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3% and 1.5% of dry PAE/mass of dry fibres is prepared and stirred for 4 min using an orbital shaker. [0125] The latex is then added to each bottle at a level of 10% dry/mass of dry fibres. An additional bottle, referred to as the control, containing water to which the same quantity of latex will be added, is also prepared. The solutions are again stirred for 4 min using the orbital shaker. [0126] A centrifugation of all of the bottles is carried out and the results are read. The control bottle is first examined in order to verify that no sedimentation of the latex is visible. Then the supernatants of each one of the bottles is examined, and the ratio [retention agent: latex] is determined by the presence of a perfectly transparent supernatant without Tyndall effect.

[0127] Rhe ratios [retention agent: latex] thus defined for each one of the latexes and are listed in Table 2 below:

TABLE-US-00003 TABLE 2 Ratios [retention agent:latex] determined by each PAE + latex pair. Ratio[retention agent:latex] expressed as Latex a % of dry PAE/dry mass of latex Acronal S 996 S 9% Acronal LN 838 S 13% Acronal LN 579 S 11% Acronal 500 D 11% Styrofan 2430 7% Styronal D 809 7% Vinnapas EN 428 5% Epotal A 816 13% Epotal FLX 3621 13% Acronal S 728 11% Acronal LA 471 S 11% Acronal S 888 S 7% Emuldur 360 A 5% Acronal A 273 S 13% Vinnol CEN 203 7% Acronal DS 2416 7% Vinnapas SAF 364 7%

[0128] c) Preparation of Sheet Formers

[0129] For each one of the latexes several sheet formers were prepared containing 1%, 5% or 10% of latex (dry/mass of the fibres). To do this, in a recipient under mechanical stirring, to the fibres in suspension the required quantity of PAE was added, predetermined in the preceding step. This mixture was stirred for 4 min. The latex was then added. The mixture was homogenized again 4 min before carrying out the production of the sheet. A sample can be taken and centrifuged in order to check the correct retention of the latex on the fibres.

[0130] In order to manufacture the sheet former, a sampling of the quantity of pulp required, a dilution in a sheet former device, a stirring, a filtration, a pressing and a drying were successively carried out.

[0131] d) Characterization of the Mechanical Properties of Sheet Formers

[0132] Different characteristic properties of the sheet former were evaluated: the paper basis weight and the bulk or specific volume, the resistance to bursting and tearing, but also the force at break, elongation as well as the breaking length. All of these characteristics were compared with those of a control sheet former containing only cellulose and are listed in Table 3 hereinbelow.

TABLE-US-00004 TABLE 3 Evaluation of the various mechanical properties of the sheet formers into which were introduced 1, 5 or 10% of latex (in dry weight/dry weight of fibres). Force Paper at Breaking % of latex weight Main break length Latex introduced (g/m.sup.2) (cm3/g) Burst (kPa) Tear (nM) (N) Elongation (%) (km) None 0% 114 1.53 308 1203 88.9 3.0 5.3 Acronal 1% 107 1.44 435 1054 92 4.0 5.8 S 996 S 5% 112 1.45 556 1022 103 3.5 6.3 10% 120 1.40 744 1079 144 4.4 8.2 Acronal 1% 117 1.59 573 1153 122 5.6 7.1 LN 838 S 5% 115 1.54 677 1257 121 6.4 7.1 10% 116 1.57 704 1140 127 5.5 7.5 Acronal 1% 114 1.54 357 1149 107 4.4 6.4 LN 579 S 5% 118 1.46 357 1149 107 4.3 6.1 10% 126 1.45 661 1148 131 6.5 7.1 Acronal 1% 111 1.50 345 992 85 3.3 5.1 500 D 5% 115 1.52 445 1312 95 4.2 5.6 10% 119 1.47 505 1134 102 4.9 5.8 Styrofan 1% 125 1.60 463 1110 85 4.5 4.6 2430 5% 135 1.61 517 1224 105 4.5 5.2 10% 146 1.56 629 1428 133 5.4 6.2 Styronal 1% 121 1.51 597 1149 102 4.7 5.7 D 809 5% 114 1.49 664 1071 121 5.3 7.2 10% 115 1.59 768 1059 115 7.0 6.8 Vinnapas 1% 127 1.61 439 1130 99 4.8 5.3 EN 428 5% 137 1.62 461 1210 101 4.1 5.0 10% 109 1.67 415 945 91 6.0 5.7 Epotal A 1% 141 1.59 481 1267 98 3.4 4.9 816 5% 137 1.57 590 1281 144 6.4 7.0 10% 132 1.58 701 1349 130 5.0 6.7 Epotal 1% 106 1.81 358 1112 68 4.3 4.4 FLX 3621 5% 105 1.77 370 965 76 5.6 4.9 10% 118 1.79 527 1157 95 5.7 5.4 Acronal 1% 137 1.55 450 1487 106 3.5 4.9 S 728 5% 126 1.58 470 1130 101 5.0 5.6 10% 163 1.56 694 1795 139 4.9 5.9 Acronal 1% 115 1.45 327 1122 82 3.5 4.8 LA 471 S 5% 121 1.51 463 1161 107 4.9 6.0 10% 115 1.56 553 912 115 7.5 6.8 Acronal 1% 117 1.63 420 1090 102 5.4 6.0 S 888 S 5% 152 1.63 555 1502 124 5.4 5.6 10% 129 1.60 655 1182 124 5.5 6.5 Emuldur 1% 147 1.58 518 1470 96 3.4 4.5 360 A 5% 133 1.61 448 1216 98 4.4 5.0 10% 129 1.60 454 1255 89 4.5 4.7 Acronal 1% 109 1.68 387 1034 90 5.4 5.6 A 273 S 5% 110 1.69 417 1149 76 4.3 4.7 10% 110 1.63 420 1026 75 5.1 4.6 Vinnol 1% 122 1.68 446 1149 108 5.7 6.1 CEN 203 5% 132 1.63 499 1355 102 3.9 4.9 10% 128 1.59 550 1485 117 4.5 5.6 Acronal 1% 143 1.60 440 12308 111 3.6 5.5 DS 2416 5% 114 1.58 526 1017 93 4.8 5.7 10% 158 1.54 594 1685 156 6.4 6.9 Vinnapas 1% 141 1.61 432 1298 98 4.4 4.7 SAF 364 5% 119 1.58 464 1122 96 6.0 5.5 10% 125 1.55 522 1094 114 5.1 6.2

[0133] As such, it was verified that no degradation of the mechanical properties was observed following the addition of one or the other of the latexes in the sheet. The sheet formers containing a polymer in the form of latex have even better mechanical properties.

[0134] e) Dyeing of Sheet Formers

[0135] The paper produced as such was colored by a method of dyeing or impregnation by means of a supercritical fluid which is supercritical CO.sub.2. For this, the paper was placed inside a closed reactor wherein a known quantity of dispersed dye was added (more preferably treated beforehand with Soxhlet extraction in order to eliminate therefrom most of the dispersants). In the context of this example, the dye used was Blue Foron RD-E (Archroma) which was pre-treated via Soxhlet extraction with acetone. It was then dried in order to eliminate any trace of solvent before being finely ground. Then, 1 g of this pre-treated dye was added to the bottom of the reactor.

[0136] This reactor was provided with an accessory which guides the flow of CO.sub.2 through the paper. Paper discs of 3 cm in diameter were cut in order to be perfectly adjusted to the inner diameter of the accessory. This accessory is comprised of a hollow and threaded rod, which is connected to the internal tapping of the reactor corresponding to the flow inlet. This rod is then welded to a metal cylinder having an inner diameter is 3 cm and the lower pierced portion which can be detached from the assembly in order to introduce the samples to be impregnated.

[0137] The closed reactor was then loaded with liquid CO.sub.2 to about 80-90 bars. To do this, the valves (1), (2), (3), and (4) are open, while the valves (5), (6) and (7) are closed. Then the whole was heated and the conditions were adjusted to 100 C.-300 bars. When the experimental conditions were reached (100 C.-300 bars), an overpressure is generated in the core of the reactor by starting the pump so that the supercritical CO.sub.2, loaded with dye, passes through the paper for 2 hours. The excess pressure generated is continuously removed thanks to the overflow set to 300 bars. At the end of the 2 h, we conducted a sweeping of the paper with clean CO.sub.2. For this, the valves (1), (3) and (4) are closed, the valve (2) remains open and the valves (5) and (6) are open. The sweeping is maintained for 5 to 10 min then the assembly is depressurized (under a light flow of clean CO.sub.2) thanks to the valve (7). Depressurization, on the one hand, precipitates the dyes to the bottom of the reactor and, on the other hand, turns the fluid in the supercritical state into the gaseous state and allows to obtain at the end of the impregnation method, samples of paper that are perfectly dry and colored on the surface as well as at the core.

[0138] Kubelka-Munk's equation, K/S=(1-R).sup.2/2R, is used in order to determine the color intensity of the paper treated as such. In this equation, R is the minimum value of the reflectance curve, which is measured over the range of the wavelengths between 400 and 700 nm using a spectrophotometer. The term (K/S), proportional to the concentration in dye, evaluates the color intensity. Thus, in the context of this example and of the examples presented hereinafter, the higher K/S is, the more intense the coloration is.

[0139] Measurements were taken on these sheets. As intense level of color was obtained. Depending on the latex added and its quantity, the K/S values in Table 4 hereinbelow were obtained.

TABLE-US-00005 TABLE 4 Value of K/S obtained on sheet formers wherein were introduced 1, 5 or 10% of latex (in dry weight/dry weight of fibres) and coloured by impregnation with supercritical CO.sub.2. % of latex Latex introduced K/S None 0% 1.2 Acronal S 996 S 1% 3.5 5% 7.3 10% 9.6 Acronal LN 838 S 1% 5.0 5% 7.3 10% 9.5 Acronal LN 579 S 1% 2.2 5% 6.3 10% 9.0 Acronal 500 D 1% 2.8 5% 5.7 10% 8.3 Styrofan 2430 1% 1.4 5% 2.7 10% 6.9 Styronal D 809 1% 3.1 5% 4.2 10% 6.2 Vinnapas EN 428 1% 0.9 5% 1.6 10% 6.2 Epotal A 816 1% 2.6 5% 5.0 10% 6.2 Epotal FLX 3621 1% 2.6 5% 5.0 10% 6.2 Acronal S 728 1% 1.8 5% 3.6 10% 5.6 Acronal LA 471 S 1% 2.2 5% 3.5 10% 5.7 Acronal S 888 S 1% 2.2 5% 3.5 10% 5.7 Emuldur 360 A 1% 2.5 5% 3.3 10% 5.0 Acronal A 273 S 1% 2.5 5% 3.3 10% 5.0 Vinnol CEN 203 1% 1.3 5% 3.1 10% 5.0 Acronal DS 2416 1% 2.3 5% 2.9 10% 4.1 Vinnapas SAF 364 1% 0.8 5% 2.3 10% 4.3

[0140] f) Non-Bleeding Test

[0141] The samples of colored paper were tested in contact with water according to standard EN NF 646. As such, two sheets of non-colored glass fiber paper were immersed into the test liquid: distilled water. After saturation, the latter are freed from the excess liquid by wiping them on the edge of the recipient.

[0142] A sheet of non-colored glass fibre paper was laid down, smooth face upwards, on a glass plate. The test piece (sample of paper tested) was then immediately placed on this sheet. It was covered with a second sheet of saturated glass fiber paper n such a way that the smooth face of the latter is also in contact with the test piece. Another glass plate was placed on the second sheet of non-colored glass fibre paper then the assembly was wrapped in a polyethylene film in order to prevent the edges from drying out. The assembly was placed under a load of 1 kg and left to rest for 24 hours away from any direct penetration of light.

[0143] After 24 hours, the assembly was disassembled. The sheets of non-colored glass fibre paper were placed on three adjacent glass rods, with the face having been respectively in contact with the test piece facing upwards. The sheets of glass fibre paper were protected from light by being covered without contact, then left to dry in the air at ambient temperature.

[0144] The coloration of the glass fibre papers was then evaluated in relation to a control, a new non-colored glass fibre paper. In all of the cases, no coloration was observed, which corresponds to a total absence of bleeding.

EXAMPLE 2

[0145] a) Preparation of Sheet Formers

[0146] In the same way as described in example 1, sheet formers the composition of which is detailed in Table 5 hereinbelow were prepared.

TABLE-US-00006 TABLE 5 Description of the sheet formers produced. Sheet formers containing: 0% of latex 1% of latex 5% of latex 10% of latex Fibrous Mixture of 3/5 Cenibra and of 2/5 Sodra Black R composition Refining: 45SR Concentration 22.5 g/L Addition 1: Solvitove PLV Solvitove PLV Solvitove PLV Solvitove PLV cationic starch 3% dry/fibres 3% dry/fibres 3% dry/fibres 3% dry/fibres Stirring: 50 min Stirring: 50 min Stirring: 50 min Stirring: 50 min Addition 2: Calprec PA Calprec PA Calprec PA Calprec PA calcium 8% dry/fibres 8% dry/fibres 8% dry/fibres 8% dry/fibres carbonate Stirring: 10 min Stirring: 10 min Stirring: 10 min Stirring: 10 min Addition 3: Acronal S 996 S Acronal S 996 S Acronal S 996 S Acronal S 996 S latex 0% dry/fibres 1% dry/fibres 5% dry/fibres 10% dry/fibres Stirring: 10 min Stirring: 10 min Stirring: 10 min Stirring: 10 min Addition 4: Aquapel F215 Aquapel F215 Aquapel F215 Aquapel F215 AKD 0.15% dry/fibres 0.15% dry/fibres 0.15% dry/fibres 0.15% dry/fibres Stirring: 2 min Stirring: 2 min Stirring: 2 min Stirring: 2 min Forming Dilution in the sheet former, stirring, draining (1 min 30) Pressing (1 min) Drying in temperature at 100 C.-10 min

[0147] The retention of the latex was verified by taking a sample before the production of the sheet former by centrifugation according to parameters of power and of time which were further adjusted using different control samples. The parameters chosen are such that a highly diluted solution of latex does not sediment while a solution containing a small quantity of calcium carbonate in water has a perfectly clear supernatant.

[0148] b) Characterization of the Sheet Formers

It was verified that the mechanical properties of the sheets were not altered by the presence of the polymer introduced in the form of latex. The results of the evaluation of the mechanical properties are shown in Table 6 hereinbelow.

TABLE-US-00007 TABLE 6 Mechanical properties of the sheet formers produced. Paper Force at Breaking % of latex weight Main Cobb break Elongation length Latex introduced (g/m.sup.2) (cm.sup.3/g) (mL/min) Burst (kPa) Tear (mN) (N) (%) (km) Acronal 0% 111 1.61 34 543 1110 112 6.4 6.8 S 996 S 1% 110 1.55 32 521 1191 98 8.1 6.1 5% 112 1.58 32 572 1030 117 7.2 7.1 10% 111 1.54 26 575 1051 120 6.1 7.4

[0149] The calcium carbonate content retained in each one of the sheet formers was also estimated. The results are logged in Table 7 hereinbelow.

TABLE-US-00008 TABLE 7 % CaCO.sub.3/total weight of the dry paper according to the percentage of latex introduced. % of latex % CaCO.sub.3 estimated by thermogravimetric/total Latex introduced weight of the dry paper analyses Acronal 0% 7.2 S 996 S 1% 6.6 5% 5.8 10% 5.9

[0150] c) Coloration of the Sheet Formers

[0151] The paper produced as such was coloured by the method of coloration described in example 1 paragraph e.

[0152] Measurements via spectrophotometry were taken on these sheets. As such, a level of intense coloration was obtained and the values of K/S measured are contained in Table 8.

TABLE-US-00009 TABLE 8 Value of K/S obtained on sheet formers into which were introduced 1, 5 or 10% of latex (in dry weight/dry weight of fibres) and coloured by impregnation with supercritical CO.sub.2. Latex % of latex introduced K/S Acronal 0% 1.2 S996S 1% 2.0 5% 5.5 10% 7.8

[0153] d) Characterization of the Bleeding

[0154] Bleeding tests were carried out according to the protocol described in example 1, paragraph f. In all of the cases, no coloration was observed after 24 hours on the non-colored glass fibre papers, which corresponds to a total absence of bleeding.

EXAMPLE 3

[0155] a) Manufacture of the Paper

[0156] A paper pulp was prepared in a pulper by mixing fibres in water. The composition of the mixture of cellulosic fibre is 50% by dry weight of short cellulosic fibres of the Cenibra type (wood fibres coming from eucalyptus) and 50% by dry weight of long cellulosic fibres, of the Pacifico type (wood fibres coming from softwoods). The pulp prepared as such was refined to a Schopper degree between 30 and 35.

[0157] To this mixture were added, based on the dry weight of the cellulose fibres, 0.6% by dry weight of latex of the Acronal S728 type, 0.4% by dry weight of fluorinated resin of the Asahi Guard E061 type and 0.1% by dry weight of cationic polyamide-epichlorhydrine resin of the Kymene 617 type (retention agent).

[0158] Before being sent to the headbox, the composition of this pulp was adjusted by continuously adding 2.5% by wet weight (in relation to the weight of the pulp before adjustment) of fluorinated resin of the Asahi Guard E061 type and 0.7% by wet weight of bonding agent of the Aquapel J215 type.

[0159] The pulp prepared as such was sent into the headbox of the paper machine then was uniformly distributed on the moving web of the flat table, where it underwent draining through the meshes of the wire cloth, by gravity and by suction using suction boxes, for the purpose of producing a sheet, as is known to those skilled in the art.

[0160] Once formed, the sheet of paper passed through the press section of the paper machine, then a dryer comprised of a series of steam-heated cylinders.

[0161] When the moisture of the sheet was greatly reduced, for example about 5%, the sheet underwent a coating treatment on the surface by passing through a size-press, comprised for example of two rollers arranged side-by-side horizontally in order to form a bowl supplied with a size of a determined composition. The sheet is then passed between the rollers in such a way as to coat its two opposite faces.

[0162] In the context of this example, the compositions of the size were as follows: [0163] Between 8 and 12% by dry weight of a latex of the Acronal S 728 type [0164] About 0.9% by dry weight of a styrene acrylic compound of the Baysize BMP type [0165] About 1.8% by dry weight of a polyvinylic alcohol (P.V.A.) of the BF 17 type

[0166] The sheet is then passed into a so-called post-drying section, in which it again comes into contact with one or several steam-heated rollers, to a temperature of about 120 C.

[0167] b) Characterization of the Properties of the Paper

[0168] The physical properties of the paper produced as such were evaluated. Various characteristic measurements were taken, such as the tensile strength, tearing strength or bursting strength. An evaluation of the printability by measurement of the pulling off IGT was also conducted. The various results are logged in Table 9 hereinbelow.

TABLE-US-00010 TABLE 9 Properties of the test roll Paper weight (g/m.sup.2) 90 Main (cm3/g) 1.32 Bendtsen porosity (mL/min) 510 Bendtsen roughness (mL/min) Front Back 234 294 Burst (kPa) 298 Tear (mN) Machine direction Cross direction 353 698 Traction Machine direction Cross direction Force (N) 116 71 Elongation (%) 2.4 6.1 Breaking length (km) 8.8 5.4 Dry pulling off IGT Machine direction Cross direction (pressure 35 kgf - increasing Thumbwheel Absence of linting Absence of linting speed 0 to 7 m/s - ink 3804) Strip No pulling off point No pulling off point Cobb (mL/min) 25

[0169] c) Coloration of the Paper and Intensity Measurements

[0170] The paper produced as such was colored by a method of dyeing or impregnating by means of a supercritical fluid which is supercritical CO.sub.2. For this, a roll of paper was placed inside a closed reactor wherein a known quantity of dispersed dye was added (more preferably treated beforehand with Soxhlet extraction in order to eliminate therefrom most of the dispersants).

[0171] In the context of this example, several dyes or mixture of dyes were used. These dyes are all commercial dispersed dyes supplied by Archroma and were all pre-treated via Soxhlet extraction with acetone. As such, the following colorations were successively carried out: [0172] Yellow coloration with Yellow Foron Brilliant RD-E [0173] Green Coloration using a mixture Yellow Foron Brilliant RD-E (75%) and Blue Foron RD-E (25%) [0174] Blue coloration with Blue Foron RD-E [0175] Black coloration noire with Black Foron RD-RM 400

[0176] The reactor used is designed so that the flow of CO.sub.2 is guided through the thickness of a roll of paper. After loading of the paper, a quantity of dye equivalent to 2.5 to 5% of the weight of the paper to be impregnated was placed in the reactor. Once the reactor is closed, the first step consisted in loading the reactor with CO.sub.2 at the storage pressure (40-50 bars) then simultaneously the reactor was heated and CO.sub.2 pumped in order to reach the working conditions: a temperature between 100 and 115 C. and a pressure between 270 and 300 bars. A circulation was provided using a pump. As such, the supercritical CO.sub.2 loaded with dissolved dye was sent through the thickness of the roll, radially from the inside to the outside. After 2 hours in the predefined supercritical conditions, a sweeping was carried out with clean CO.sub.2 at a temperature of 100 to 115 C. and at a pressure of 250 bars for 30 min in order to eliminate the non-fixed dye before depressurizing which generated on the one hand, the precipitation of the remaining dye and, on the other hand, turned the fluid in the supercritical state into the gaseous state. At the end of the impregnation method, perfectly dry paper samples, colored on the surface as well as at the core, and whose color does not bleed when in contact with water were obtained.

[0177] Measurements via spectrophotometry were taken on these sheets. As such, levels of intense color were obtained and the values of K/S measured at the maximum absorption wavelengths are shown in Table 10 hereinbelow.

TABLE-US-00011 TABLE 10 Value of K/S obtained on the test rolls colored by impregnation with supercritical CO.sub.2 in different colours. Wavelength corresponding to the peaks or absorption maximums Colour Dye (nm) K/S Yellow Yellow Foron Brilliant RD-E Yellow: 460 4.6 Green Yellow Foron Brilliant RD-E Yellow: 440 5.8 (75%) + Blue Foron Bleu: 620 2.1 RD-E (25%) Blue Blue Foron RD-E Bleu: 580 6.7 Black Black Foron RD-RM 400 Maximum: 600 6.3

[0178] d) Bleeding Tests

[0179] Bleeding tests were carried out according to the protocol described in example 1, paragraph f. In all of the cases, regardless of the dye or mixture of dyes used, no coloration was observed after 24 hours on the non-coloured glass fibre papers, which corresponds to a total absence of bleeding.

EXAMPLE 4

[0180] a) Manufacture of the Paper

[0181] Papers having the compositions identical to those of the sheet formers presented in the example 2 are produced.

[0182] As such, a paper pulp is prepared in a pulper by mixture of fibres in water. The composition of the mixture of cellulosic fibre is of short cellulosic fibres of the Cenibra type (wood fibres from eucalyptus) and of long cellulosic fibres, of the Sodra Black R type (wood fibres from softwoods). The pulp thus prepared is refined to a Schopper degree between 40 and 42.

[0183] To this mixture is added, relative to the dry weight of the cellulose fibres, 3% of cationic starch (Solvitose PVL prepared at 3% in water). The mixture is stirred for about 1 h. Then, fillers of the calcium carbonate type (Calprec PA) are introduced into the mixture at a rate of 8% by dry weight relative to the dry weight of the fibres and stirred for 20 minutes.

[0184] According to the paper desired, a defined quantity of latex is then added. The papers no. 1, 2, 3 and 4 correspond to the addition respectively of 0, 1, 5 and 10% dry relative to the weight of the fibers of a butyl acrylate and styrene latex, Acronal S 996 S. The mixture is then homogenized for 10 to 20 minutes before it is sent to the headbox.

[0185] During the transfer of the pulp to the headbox, the composition of this pulp is adjusted by the continuous adding of 0.15% by dry weight relative to the weight of the fibers of a bonding agent of the AKD type (alkylketene dimers). In the context of this example, Aquapel F215 is used.

[0186] The pulp thus prepared is sent into the headbox of the paper machine and then uniformly distributed on the moving web of the flat table, where it will undergo draining through the meshes of the wire cloth, by gravity and by suction using suction boxes, for the purpose of producing a sheet of 80 g/m.sup.2, as known to those skilled in the art.

[0187] Once formed, the sheet of paper passes through the section of the presses of the paper machine, then a dryer comprised of a series of stem-heated cylinders.

[0188] After cutting of this paper into a format, a post-treatment is carried out in the laboratory. The sheet undergoes coating treatment on the surface by passing through a laboratory size-press, comprised of two rollers arranged side-by-side horizontally in order to form a bowl supplied with a size of a determined composition. The sheet is then passed between the rollers in such a way as to coat its two opposite faces. This post-treatment is representative of a treatment in size-press on an industrial paper machine.

[0189] In the context of this example, the compositions of the sizes are as follows:

TABLE-US-00012 TABLE 11 Composition of the sizes used during deposits in size-press. Aqueous sizes containing: Total dry 2.7% 10.7% 20.6% extract Addition 1: Acronal S 996 S (commercial solution at 46% in water) latex 2% dry 10% dry 20% dry Addition 2: Blanose 7M65 (preparation at 2% in water rheological 0.71% dry 0.66% dry 0.61% dry agent

[0190] The exact masses deposited on each sheet are then calculated using the actual dry extracts of the sizes and of the wet masses deposited per surface unit.

[0191] The sheet then goes into an oven at a temperature of about 120 C. for 2 minutes.

[0192] b) Dyeing of the Sheets

[0193] The paper produced as such is colored by the method of dyeing described in example 1 paragraph e.

[0194] Measurements via spectrophotometry were taken on these sheets. As such, a level of intense color can be obtained and the values of K/S measured are represented on the graph in FIG. 2.

[0195] The papers produced without depositing latex on the surface are homogeneously colored over the entire thickness. As the intensity of the color depended on the quantity of latex added, it is thus possible to produce paper having the colors varying from a pastel tone to a very intense color.

[0196] The adjustment of the ratio of latex between the bulk and the surface makes it possible in certain cases to increase the intensity of color while still retaining homogeneity in the color in the thickness of the paper. This is the case for example of paper no. 3 containing 5% of latex in mass and on which a deposit on the surface of 2.7 g/m.sup.2 was conducted.

[0197] In other cases, this produces low-end papers by limiting the quantity of latex used. The latter, for example the paper no. 2, on which a deposit of 3.76 g/m.sup.2 of latex was carried out, has a strong intensity of coloron the surface but a color gradient is visible during tearing.

COMPARATIVE EXAMPLE 5

[0198] A colored paper was produced according to the teaching of patent application FR 3 015 988 by using amphiphilic molecules (CTAB and AOT in an equimolar mixture) as additives for the preparation of the paper.

[0199] a) Manufacture of the Paper

TABLE-US-00013 TABLE 12 Description of the manufacture of sheet formers Sheet former Control (without surfactants) CTAB:AOT in a ratio 1:1 w/w Fibrous Mixture of Cenibra and of Mixture of Cenibra and of Sodra Black R Sodra Black R composition Refining: 45SR Refining: 45SR Concentration 22.5 g/L Concentration 22.5 g/L % of pulp used 100% 50% 50% Addition 1: Amylofax PW-A (DS 0.035) Amylofax PW-A (DS cationic starch 0.035) (binder) 3% dry/fibres 3% dry/fibres Stirring: 50 min Stirring: 50 min Addition 2: Calprec PA Calprec PA calcium 10% dry/fibres 10% dry/fibres carbonate Stirring: 10 min Stirring: 10 min (filler) Addition 3: AKD Aquapel J 215 Aquapel J 215 (bonding agent) 0.15% dry/fibres 0.15% dry/fibres Stirring: 2 min Stirring: 2 min Addition 4: None CTAB cationic 5% dry/fibres surfactant Stirring: 2.5 min Addition 5: None AOT anionic 5% dry/fibres surfactant Stirring: 2.5 min Transfer into Dilution All of the pulp is put into the presence in the the bowl of the bowl of the sheet former and diluted. sheet former Addition 6: Retaminol K Retaminol K polyamine 0.05% dry/fibres 0.05% dry/fibres (retention agent) Agitation Agitation Forming Draining (1 min 30) Draining (1 min 30) Pressing (1 min) Pressing (1 min) Drying in temperature at Drying in temperature at 100 C.-10 min 100 C.-10 min

[0200] b) Characterization of the Properties of the Paper

[0201] The physical properties of the paper produced as such were evaluated. Various characteristic measurements were taken, such as the tensile strength, tearing strength or bursting strength. An evaluation of the printability through measurement of IGT tearing was also conducted. The various results are shown in the table hereinbelow.

TABLE-US-00014 TABLE 13 Physical properties of the sheet formers produced. Sheet former Control CTAB:AOT (1:1) % of additive of the 0% 10% dry/fibres surfactant type introduced Paper weight (g/m.sup.2) 114 110 Burst (kPa) 504 222 Burst index (kPa .Math. m.sup.2/g) 4.42 2.02 Tear (mN) 1096 546 Tear index (mN .Math. m.sup.2/g) 9.61 2.46 Bendtsen porosity (mL/min) 100 311 Internal cohesion (Scott unit) 210 131 Traction Force (N) 111.4 54.7 Elongation (%) 3.6 1.9 Breaking length (km) 6.6 3.4 Cobb (mL/min) 28 261 Dry pulling off IGT Thumb No pulling off point Strong pulling off (pressure 35 kgf - wheel increasing speed Strip Strong linting Front 4.44 m 0 to 7 m/s - ink 3804) Back 4.13 m

[0202] These measurements, compared to those listed in table 6 and in table 9 for paper according to the invention, show superior mechanical properties of the paper according to the invention as well as superior printability and the adequacy of its ability to absorb water.

[0203] c) Coloration of the Sheet Formers

[0204] The paper produced as such is colored by the method of dyeing described in example 1 paragraph e.

[0205] Measurements by spectrophotometry were taken on these sheets. As such, an intense level of color is obtained and the values of K/S measured are shown in the table hereinbelow.

TABLE-US-00015 TABLE 14 Value of K/S obtained on sheet formers into which were introduced 10% (in dry weight/dry weight of fibres) of a mixture of CTAB/AOT in a ratio 1:1 and coloured by impregnation with supercritical CO.sub.2. Additive % introduced K/S CTAB:AOT (1:1) 10% 7.3

[0206] d) Characterization of the Bleeding

[0207] Bleeding tests were conducted according to the protocol described in example 1, paragraph f. In this case, substantial bleeding is already observed after 1 hour on the non-colored glass fiber papers.

COMPARATIVE EXAMPLE 6: CHARACTERIZATION OF THE BLEEDING OF AN INTENSE BLUE COMMERCIAL PAPER

[0208] Bleeding tests were conducted according to the protocol described in example 1, paragraph f. In the case of an intense blue commercial paper whose color is obtained by a standard paper-making method, substantial bleeding is already observed after 1 hour on the non-colored glass fiber papers.

REFERENCES

[0209] 1] Soluble anionic trisazo dyes of aromatic seriesfor natural and synthetic fibres, esp. leather. Brevet BE-834146, 1976. [0210] 2] Halogen-contg. isoindoline pigmentsuseful for colouring plastics, paint, etc. in yellow shades. Brevet DE2805234, 1978. [0211] 3] Anthraquinone pigmentsand vat dyes, for cellulose fibres, paints, printing inks and plastics. Brevet DE2123963, 1972. [0212] 4] Disazo dispersion pigment dyesfor synthetic fibres paints, printing inks, and plastics. Brevet DE2138014, 1973. [0213] 5] Azo dyes having one or two triazinyl- or pyrimidyl-acetic acid ester or amide coupling component radicals. Brevet BE-820674, 1973. [0214] 6] Blue cationic oxazine dye contg. tert. and prim. aminofor dyeing or printing paper leather and polyacrylonitrile etc. Brevet IT7949811, 1978. [0215] 7] Azo anthraquinone pigments. Brevet CH-635218, 1976. [0216] 8] Monazo dyes free of sulphonic acid groups. Brevet BE-740009, 1968. [0217] 9] Reactive polymeric monochlorotriazine dyes. Brevet GB-923429, 1958. [0218] 10] Dyes substd. by imidazolyl-methyl gps.esp. for colouring paper. Brevet DE3044563, 1980. [0219] 11] Dyeing paper with 2, 1-benzoisothiazole sulphonic acid azo dyestuffgiving brilliant light-fast dyeing. Brevet DE3041838, 1980. [0220] 12] Fixation of dyes on colored paper. U.S. Pat. No. 1,926,614, 1931. [0221] 13] Dip dyeing type paper dyeing method. Brevet CN102877363, 2012. [0222] 14] Colorant composition and method of coloring. Brevet WO2006112452, 2006. [0223] 15] K. Blus, J. Czechowski and A. Kozirog, New Eco-friendly Method for Paper Dyeing, Fibres & Textiles in Eastern Europe, pp. 121-125, 5 (107) 22, 2014. [0224] 16] Supercritical CO2. Brevet EP 2 876 203, 2013. [0225] 17] Method for colouring cellulose. Brevet WO/2015/140750, 2015. [0226] 18] Imprgnation d'un papier l'aide d'un fluide supercritique. Brevet FR3015988, 2015. [0227] 19] Latex containing papers. U.S. Pat. No. 4,510,019, 1985. [0228] 20] Paper sheet having a very high proportion of latex, process for preparing same and applications thereof particularly as a substitution product for impregnated glass webs. U.S. [0229] 21] Latex-saturated paper. Brevet CA 02211776, 1997. [0230] 22] Feuille de papier transparente or translucide, son method de fabrication and emballage le containing. Brevet FR2916769, 2008. [0231] 23] Method of making paper. Brevet WO 2011/146367 A1, 2011. [0232] 24] Support plan hydrophobe. Brevet WO 2014/177586 A1, 2014.