Hydrophobic paper or cardboard with self-assembled nanoparticles and method for the production thereof

Abstract

A hydrophobic paper or cardboard that has self-assembled silicon-oxide nanoparticles with functional silane groups and fluorocarbonated compounds linked directly to cellulose fibers of at least one surfaces thereof, with a Cobb value of 8 to 25 g/m.sup.2 and water contact angles of 100° to 140°, which can be used for packing foodstuffs. The hydrophobic paper or cardboard may be printed, is recyclable and exhibits improved adhesion in areas requiring adhesive bonding of paper or cardboard.

Claims

1. A hydrophobic paper or cardboard comprising: cellulose fibers; and self-assembled silicon-oxide nanoparticles functionalized with amine free functional silane groups and fluorocarbonated compounds; wherein the amine free functional silane groups are selected from the group consisting of 3-Mercaptopropyltrimethoxysilane (MPTMS), 3-Glycidoxypropyltrimethoxysilane (GLYMO), Bis[3-(triethoxysilyl)propyl] tetrasulfide (TETRA-S), 1,2-Bis(triethoxysilyl)ethane (BTSE), dichlorodiphenylsilane, 3-isocyanatopropyltrimethoxysilane, 1,2-Bis (chlorodimethylsilyl)ethane, N-[3-(trimethoxysilyl)propyl]aniline, 3-(Mercapto methyl)octyl)silane-triol, 2-(2-Mercaptoethyl)pentyl)silane-triol, and combinations thereof; wherein the fluorocarbonated compounds are selected from a group consisting of 2,3,5,6-tetrafluoro-4-methoxystyrene, monomers of acrylamide fluoridated, or 1H,1H,2H,2H-Perfluorooctyltrietoxysilane, and combinations thereof; and wherein the self-assembled silicon-oxide nanoparticles are linked directly by covalent bonds at pH from 3 to 4.5 to cellulose fibers through the amine free functional silane groups.

2. The hydrophobic paper or cardboard of the claim 1, wherein it has a Cobb value from 8 to 25 g/m.sup.2.

3. The hydrophobic paper or cardboard of claim 1, wherein it has a water contact angle from 100° to 140°.

4. The hydrophobic paper or cardboard of claim 1, wherein at least a surface of the paper or cardboard has an amount of self-assembled silicon-oxide nanoparticles less than 3.5 g/m.sup.2 per square meter of paper or cardboard.

5. A method for producing a hydrophobic paper or cardboard comprising the steps of: preparing a dispersion of self-assembled silicon-oxide nanoparticles functionalized with amine free functional silane groups and fluorocarbonated compounds in a hydro-alcoholized medium at pH from 3 to 4.5; wherein the amine free functional silane groups are selected from the group consisting of 3-Mercaptopropyltrimethoxysilane (MPTMS), 3-Glycidoxypropyltrimethoxysilane (GLYMO), Bis[3-(triethoxysilyl)propyl] tetrasulfide (TETRA-S), 1,2-Bis(triethoxysilyl)ethane (BTSE), dichlorodiphenylsilane, 3-isocyanatopropyltrimethoxysilane, 1,2-Bis (chlorodimethylsilyl)ethane, N-[3-(trimethoxysilyl)propyl]aniline, 3-(Mercapto methyl)octyl)silane-triol, 2-(2-Mercaptoethyl)pentyl)silane-triol, and combinations thereof; and wherein the fluorocarbonated compounds are selected from a group consisting of 2,3,5,6-tetrafluoro-4-methoxystyrene, monomers of acrylamide fluoridated, or 1H,1H,2H,2H-Perfluorooctyltrietoxysilane, and combinations thereof; applying the dispersion on at least one surface of a paper or cardboard; and drying and curing the paper or cardboard to directly link the self-assembled silicon-oxide nanoparticles with the cellulose fibers of the paper or cardboard by covalent bonds through the amine free functional silane groups.

6. The method of the claim 5, wherein the dispersion has a density from 0.96 to 0.99 g/cm.sup.3.

7. The method of making paper or cardboard of the claim 5, wherein the step of preparing a dispersion of self-assembled silicon-oxide nanoparticles, the hydro-alcoholized medium includes an alcohol selected from a group consisting of ethanol, propanol, methanol, and combinations thereof.

8. The method of the claim 5, wherein the step of preparing a dispersion of self-assembled silicon-oxide nanoparticles, the self-assembled silicon-oxide nanoparticles are dispersed by mechanical stirring with ultrasonic support.

9. The method of the claim 8, wherein the ultrasound is performed at a continuous or pulsed frequency.

10. The method of the claim 8, wherein the ultrasound is performed at a frequency from 10 to 150 KHz.

11. The method of the claim 5, wherein the step of applying the dispersion on at least one surface of a paper or cardboard consists in immersion-extraction of the paper or cardboard in the dispersion.

12. The method of the claim 11 wherein further the step of applying the dispersion on at least one surface of a paper or cardboard, includes the step of evenly dosing and distributing the dispersion on the surface of the paper or cardboard by means of a scraper.

13. The method of the claim 5, wherein the step of applying the dispersion on at least one surface of a paper or cardboard, the dispersion is applied in an amount less than 3.5 g/m.sup.2 per square meter of the paper or cardboard.

14. The method of the to claim 5, wherein the step of drying and curing the paper or cardboard is performed at a temperature from 80 to 170° C.

15. The method of the claim 5, wherein the paper or cardboard has a Cobb value from 8 to 25 g/m.sup.2.

16. The method of the claim 5, wherein the step of preparing a dispersion of self-assembled silicon-oxide nanoparticles is performed at a temperature from 10 to 250° C.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Other features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It should be understood, however, that the drawings are made only as an illustration and not as a limitative definition of the invention, in which:

(2) FIG. 1 shows a diagram of silane linking on the surface of silicon-oxide nanoparticles formed according to the invention.

(3) FIG. 2 shows a diagram of a crust by polymerizing fluorocarbonated compounds into nanoparticles according to the invention.

(4) FIGS. 3A, 3B, and 3C show a diagram of physicochemical fixation of the silicon-oxide nanoparticles with the fibers of the paper or cardboard by dehydration of free silanol groups according to the invention.

(5) FIG. 4 shows a block diagram of the steps of the process of applying hydrophobic coatings on paper and cardboard, based on self-assembled silicon-oxide nanoparticles according to the present invention.

(6) FIG. 5 shows a photograph of the water contact angle of the paper or cardboard of the present invention.

(7) FIG. 6 shows a photomicrograph obtained by scanning electron microscopy of an uncoated paper or cardboard of the prior art, illustrating the cellulose fiber matrix.

(8) FIG. 7 shows a photomicrograph obtained by scanning electron microscopy of a cellulose fiber of an uncoated paper of the prior art.

(9) FIG. 8 shows a photomicrograph obtained by scanning electron microscopy of a paper or cardboard with a coating of the Michelman® type according to the prior art, where the cellulose fiber matrix is shown covered by a film-like coating.

(10) FIG. 9 shows a microphotograph obtained by scanning electron microscopy of a cellulose fiber of a paper or cardboard with a coating of the Michelman® type according to the prior art, where the film-like coating is shown as extending to other cellulose fibers.

(11) FIG. 10 shows a microphotograph obtained by scanning electron microscopy of a paper or cardboard with a coating according to the invention, wherein it is illustrated that there is no film formation on the matrix, but the cellulose fibers are coated.

(12) FIG. 11 shows a microphotograph obtained by scanning electron microscopy of a cellulose fiber of a paper or cardboard with a coating according to the invention, where the coating is shown on the cellulose fibers.

(13) FIG. 12 shows a microphotograph obtained by scanning electron microscopy of the cellulose fibers of the paper or cardboard coated with self-assembled silicon-oxide nanoparticles according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(14) The characteristic details of the invention are described in the following paragraphs together with the figures that accompany it, which are for the purpose of defining the invention but not limiting its scope.

(15) The object of the present invention is to reduce the amount of water that can be absorbed by the paper or cardboard, once the fibers of at least one its surfaces has been coated with self-assembled silicon-oxide nanoparticles, and propose a new method of producing such paper or cardboard that achieves Cobb values between 8 and 25 g/m.sup.2. The Cobb value indicates the capacity of water absorption by paper and cardboard, as well as the amount of liquid penetrating the same; that is, it indicates the weight of water absorbed in a specified time per 1 m.sup.2 of paper or cardboard under normal conditions.

(16) According to the present invention, hydrophobicity properties are conferred to the paper and cardboard through the use of coatings of self-assembled silicon-oxide nanoparticles and functionalized with fluorocarbonated compounds and groups such as functional silanes groups, in a colloidal hydro-alcoholized dispersion agitated by ultrasound.

(17) Fluorocarbonated compounds used are for example: 2,3,5,6-tetrafluoro-4-methoxystyrene, monomers of acrylamide fluoridated, or 1H,1H,2H,2H-Perfluorooctyltrietoxysilane.

(18) The functional silane groups used are: 3-Mercaptopropyltrimethoxysilane (MPTMS), 3-Glycidoxypropyltrimethoxysilane (GLYMO), Bis[3-(triethoxysilyl)propyl] tetrasulfide (TETRA-S), 1,2-Bis(triethoxysilyl)ethane (BTSE), dichlorodiphenylsilane, 3-isocyanatopropyltrimethoxysilane, 1,2-Bis (chlorodimethylsilyl)ethane, N-[3-(trimethoxysilyl)propyl]aniline, (3-Aminopropyl)triethoxysilane (APTES), 3-(Mercapto methyl)octyl)silane-triol, 2-(2-Mercaptoethyl)pentyl) silane-triol, Bis[3-(trimethoxysilyl)propyl] amine (BAS).

(19) The hydrophobic characteristics of the coatings of self-assembled silicon-oxide nanoparticles on paper are maximized when the paper is immersed in hydro-alcoholic suspension and continuously agitated by some mechanical means, either supported by ultrasound or not, and the resulting coating is dried and cured at temperatures of about 80° C. to about 170° C. After applying the heat to evaporate the solvents in the dispersion and at the same time promote the anchorage or direct linking of the particles on the paper fibers, Cobb values can be obtained of about 8 g/m.sup.2 to about 25 g/m.sup.2.

(20) This invention stands out from the above, because the application procedure of the coating does not affect the printing of paper or cardboard, further improving the adhesion on the wings or areas requiring gluing of the cardboard boxes obtained. Moreover, the coating application process, according to the present invention, on paper and cardboard does not prevent recycling of packaging and facilitates their adaptation to industrial machines for manufacturing boxes. The paper and cardboard products thus produced have high levels of moisture resistance and a high water contact angle-coating.

(21) A fundamental concept when considering the use of hybrid or composite materials to achieve a particular functionality in a material as hydrophobicity of cellulose and its derivatives is compatibility between organic or polymeric materials and inorganic materials. This compatibility is usually characterized by a certain degree of antagonism, since many of the inorganic materials have a hydrophilic character, while polymers have a hydrophobic character. However, this property that can be antagonistic between the separate materials, can have a synergic effect in one sense or in the other as required in the hybrid or composite materials.

(22) This situation means that an important part of the preparation of composite materials is focused on how to improve this compatibility by way of modifying the hydrophilic nature of the inorganic materials to achieve better linking of the inorganic material-organic matrix on the interfaces of both materials. So if we wish to take advantage of the barrier effect of the inorganic materials, these must be tightly bound to the matrix.

(23) Adhesion between the inorganic materials and the polymer matrix can be attributed to a number of mechanisms that can occur on the interface, as isolated phenomena or as an interaction between them. The physical and chemical methods for modifying the interface, promote different levels of adhesion between the inorganic material and the polymer matrix. Physical treatments can change the structural and surface properties of inorganic aggregates, influencing the mechanical links with the polymer matrix. However, many highly polarized aggregates are incompatible with hydrophobic polymers. When two materials are incompatible, it is possible to introduce a third material called coupling agent, which has intermediate properties between the other two, and thus creates a degree of compatibility.

(24) Chemical compounds containing methanol groups (—CH.sub.20H) form stable covalent bonds with cellulose loads. Hydrogen linking between aggregate and matrix, can also be formed in this reaction.

(25) The surface energy of the inorganic aggregate is closely related to the hydrophilicity and hydrophobicity of the composite materials. The silanes as coupling agents that may contribute to hydrophilic or hydrophobic properties of the interface. Organosilanes are the main group of coupling agents for polymers with glass or silicon oxide aggregates. Silanes have been developed to couple different polymers to the mineral aggregates in the manufacture of composite materials.

(26) Coupling agents based on silane, can be represented by the following formula: R—(CH.sub.2)n-Si(OR′).sub.3, where n functional =0-3, OR′ is a hydrolyzable alkoxy group, and R is the organic group.

(27) The organic functional group (R) on the coupling agent produces the reaction with the polymer. Acts as a copolymerization agent and/or for the formation of an interpenetrating network. The alkaline silanes undergo hydrolysis in the step of forming links, both in an acid medium and in a basic medium. These reactions of silanes with the surface hydroxyls of the aggregates surface may lead to the formation of polysiloxane structures.

(28) In the present invention, the use of self-assembly techniques is contemplated for the functionalization of silicon-oxide nanoparticles prior to their dispersion in a polymer matrix.

(29) Self-assembly can be defined as the spontaneous formation of complex structures from smaller pre-designed units. The self-assembled monolayers are ordered molecular units which are formed by spontaneous absorption (chemisorption) of a surfactant onto a substrate, wherein the first a functional group with affinity to this substrate.

(30) The reaction sequence of self-assembly is performed according to this invention with the purpose of preparing a hybrid material to assign paper or cardboard a hydrophobic character or resistance to water absorption as described below.

(31) For the preparation of SiO.sub.2 nanoparticles with the intention to generate dispersions in a hydro-alcoholic solution, TEOS was used as starting material dissolved in a mixture of ethanol-water and stabilized at a pH of about 3.5 to about 3.75; this is allowed to react at temperatures of about 25° C. to about 40° C. for approximately 15 minutes to approximately 90 minutes, forming a transparent or white colloidal solution.

(32) ##STR00001##

(33) Subsequently, the TEOS tends to hydrolyze generating cores of formula (SiO.sub.2)x

(34) ##STR00002##

(35) Other functional silanes groups were employed such as: 3-Mercaptopropyltrimethoxysilane (MPTMS), 3-Glycidoxypropyltrimethoxysilane (GLYMO), Bis[3-(triethoxysilyl)propyl] tetrasulfide (TETRA-S), 1,2-Bis(triethoxysilyl)ethane (BTSE), dichlorodiphenylsilane, 3-isocyanatopropyltrimethoxysilane, 1,2-Bis (chlorodimethylsilyl)ethane, N-[3-(trimethoxysilyl)propyl]aniline, (3-Aminopropyl)triethoxysilane (APTES), 3-(Mercapto methyl)octyl)silane-triol, 2-(2-Mercaptoethyl)pentyl) silane-triol, Bis[3-(trimethoxysilyl)propyl] amine (BAS), and combinations thereof, with the objective of substituting the hydroxyl groups and of generating functional groups on the silicon-oxide nanoparticles surface that are able of originating self-assembly reactions on the surfaces of the generated silicon oxide nanoparticle cores. FIG. 1 shows how these silanes can form links on the surface of the silicon-oxide nanoparticles that are formed.

(36) The third stage of the synthesis process of silicon-oxide nanoparticles functionalized consists of the creation of the crust of the nanoparticles. The crust of these nanoparticles is formed of fluorocarbon chains of molecules. These crusts are prepared by polymerization reactions or condensation on the surface of the nanoparticle cores. Depending on the type of functional group, different molecules are used for fluorocarbon crust formation.

(37) In some of these polymerizations, intervention is necessary of small amounts of catalysts; these catalysts are of an acid type, such as carboxyl groups, compounds of Cu(I), basic medium such as ammonia or potassium carbonate. A reaction scheme is shown in FIG. 2.

(38) It is necessary to use a bis-silane, such as BAS, TETRA-S, or BTSE and the fluorocarbonated compound with functional silane groups. These reactions are performed at pH 3.5 and allowed to react during 30 minutes at 25° C. From these reactions in three stages, particles were prepared of sizes between 10 nm and 130 nm. Fluorocarbon groups were used such as 2,3,5,6-tetrafluoro-4-methoxystyrene, monomers of acrylamide fluoridated, or 1H,1H,2H,2H-Perfluorooctyltrietoxysilane. The silane groups used are: 3-Mercaptopropyltrimethoxysilane (MPTMS), 3-Glycidoxypropyltrimethoxysilane (GLYMO), Bis[3-(triethoxysilyl)propyl] tetrasulfide (TETRA-S), 1,2-Bis(triethoxysilyl)ethane (BTSE), dichlorodiphenylsilane, 3-isocyanatopropyltrimethoxysilane, 1,2-Bis (chlorodimethylsilyl)ethane, N-[3-(trimethoxysilyl)propyl]aniline, (3-Aminopropyl)triethoxysilane (APTES), 3-(Mercapto methyl)octyl)silane-triol, 2-(2-Mercaptoethyl)pentyl) silane-triol, Bis[3-(trimethoxysilyl)propyl] amine (BAS), and combinations thereof.

(39) The former in order to avoid agglomeration and precipitation of the colloidal nanoparticles. In this invention, an alternative method is proposed by the use of ultrasound and the synergic effect of cavitation generated by ultrasound and self-assembly which prevents dispersed nanoparticles, once dispersed to re-agglomerate. Because of exerted repulsion between particles, in a suitable dispersion medium and due to surface functionalization of the same, it is possible to achieve a good dispersion of said particles, even at concentrations above 25%.

(40) In general, ultrasonic dispersion is performed using an ultrasonic generator across one or more piezoelectric transducers that convert the electrical signal into a mechanical vibration. This vibrational energy is transmitted to the liquid at a rate of up to 200,000 oscillations per second. These oscillations of pressure and vacuum create a large amount of microbubbles, which implode at high speed to contribute to the disintegration of the clusters of nanoparticles.

(41) The combined use of ultrasound and/or ultrasound pulses at frequencies of about 10 KHz to about 150 KHz, and at temperatures of about 10° C. to about 250° C. in aqueous or organic solvents results in the disintegration of the clusters of nanoparticles. Furthermore, the addition of molecules with ability to functionalize the nanoparticle surface by self-assembly, allows obtaining nanopowders with high disintegration of the particles in an ultrasonic bath, primarily due to the functional groups of the same that prevent these from being added due to electrostatic interactions between the nanoparticles. Furthermore, the functionalized auto-assembled nanoparticles allow greater dispersion and prevent clusters of nanoparticles or aggregates from appearing.

(42) The dispersion of the self-assembled nanoparticles is performed in a hydro-alcohilized medium, wherein the dispersion has a density of approximately 0.96 g/cm.sup.3 to approximately 0.99 g/cm.sup.3 and a pH from approximately 3 to approximately 4.5.

(43) The alcohol used for preparing the dispersion may be ethanol, propanol, methanol, and combinations thereof.

(44) Deposition of colloidal solutions of silicon-oxide nanoparticles on at least one surface of the paper or cardboard results in deposited nanoparticles, without these remaining fixated for any chemical or physicochemical interaction thereon, except a physical occlusion in the holes of the paper or cardboard. For physicochemical fixation of the silicon-oxide nanoparticles with the fibers of paper or cardboard with at least one of their outer surfaces, dehydration is required of the free silanol groups leading to a three-dimensional network as shown in FIG. 3A.

(45) Subsequently, during the immersion-extraction process of the paper, the silanols migrate and deposit on the paper or cardboard as shown in FIGS. 3B and 3C. According to experimental tests carried out by the inventors and despite the functionalization of silicon-oxide nanoparticles, it is necessary to maintain good dispersion and prevent said nanoparticles from agglomerating in the container of the suspension of silicon-oxide nanoparticles. Generally, it is understood that the mixtures of organic polymers with inorganic or metallic particles give rise to a phase separation agglomeration of nanoparticles that subsequently results in poor properties. Moreover, when the particles have diameters below 50 nanometers, it is actually very difficult to obtain a homogeneous mixture if the added amount exceeds 5% by weight, or when polymers that are used have a high melt viscosity. For this reason we need new methods such as ultrasound to achieve these requirements in terms of dispersion.

(46) Finally, a heat treatment achieves the polimerization of the coating.

(47) This heat treatment is critical to obtain a superhydrophobic coating on the surface of paper or cardboard.

(48) In summary, but not limiting the method to produce hydrophobic paper or paperboard of the present invention, the invention is shown schematically by the block diagram of FIG. 4 which indicates the stages of the method by different numbers and which are described below:

(49) In step 100, alternatively, in case of not having the self-assembled nanaoparticles, a synthesis is performed by self-assembling the silicon-oxide nanoparticles with functional silane groups and the fluorocarbonated compounds in a hydro-alcoholized medium agitated by ultrasound.

(50) In the present invention, self-assembled silicon-oxide nanoparticles functionalized with amine free functional silane groups and fluorocarboned compounds are used.

(51) Once nanoparticles have been self-assembled, in step 200, a dispersion is prepared by mechanical stirring of the self-assembled silicon-oxide nanoparticles with functional silane groups and fluorcarbonated compounds in a hydro-alcoholized medium. The dispersion of the nanoparticles can be supported by the application of ultrasound with a continuous or pulsed frequency of approximately 10 KHz to approximately 150 KHz.

(52) Once the dispersion is prepared, in step 300 the dispersion is applied on at least one surface of paper or cardboard, where the hydrophobic property is required. This application can be by immersion-extraction of the paper or cardboard in the dispersion of nanoparticles in order to react and link the Si—OH groups of the nanoparticles with the OH groups of the cellulose fibers of paper or cardboard. This application in turn can be dosed and distributed evenly on the surface of paper or paperboard by means of a scraper.

(53) Finally, in step 400, the paper or cardboard is dried and cured to directly link the self-assembled silicon-oxide nanoparticles with functional silane groups, and fluorcarbonated compounds with the cellulose fibers of paper or cardboard.

(54) It is important to note that although a skilled expert in the art may find that independently each of the stages belong to the prior state of the art, the synergic effect of all five steps comprising the method of application of nanoparticles, dispersed and functionalized according to the present invention, produces effects that are not formerly reported in the state of the art, and that if any of the steps set forth is not carried out it is not possible to obtain the hydrophobicity properties, nor coating improvements reported in the present invention.

(55) As it has been observed experimentally, very important factors that directly affect the curing reactions of cardboard are time and temperature of the heat treatment, which have a close relationship with the crosslinking level of the active components of the coating, and consequently with Cobb values.

(56) According to the above, it was observed that the longer and higher temperature of curing, the lower Cobb values of coatings are obtained.

(57) As discussed previously, the process of curing and drying is key to obtain a superhydrophobic coatings on the surface of the paper or cardboard, that is, it is the heat which helps directly in the fixation of nanomaterials on the paper or cardboard surface, not only generating this linking with the fibers, but also promotes the interactions between the nanoparticles so as to produce a nanoparticle coating which enables nanostructured greater lotus effect, causing the paper to present a greater resistance to moisture.

(58) As the cross-linking process between the fibers of paper or cardboard and applied nanoparticles is based on the dehydration of the functional groups Si—OH of fluorocarbon and —OH cellulose, the improvement of Cobb values depends directly on the dehydration process of said groups, and on the phenomenon of cross-linking of Si—OH groups and their interaction with cellulose fibers. This interaction makes a greater amount of these groups react and increase the linking of the silicon-oxide nanoparticles to the surface of each fiber, so that by increasing the temperature and the curing time an optimization of the cellulosic surface curing is achieved. During these thermal processes occurring at a temperature of approximately 80° C. to approximately 170° C., the paper or cardboard fiber loses a certain amount of chemically bound water, which after the curing process must be recovered to prevent destabilization in the fiber arrangement and rigidity.

(59) Thus, it was determined that the curing conditions for preparing paper or cardboard of the present invention with Cobb values close to 20 g/m.sup.2 correspond to a temperature of 150° C. and a time of 180 seconds by using an immersion time in the suspension of 10 seconds and coating amounts close to 3.5 g/m.sup.2.

(60) Just as for the curing temperature, excess of the heat treatment time results in a reduction of the humidity resistance values, which could be verified in tests at 170° C. for 240 seconds.

(61) The water contact angle with the surface with self-assembled nanoparticles on paper or cardboard of the present invention is approximately 100° to approximately 140° as illustrated in FIG. 5.

EXAMPLES OF EMBODIMENT OF THE INVENTION

(62) The invention will now be described with respect to the following examples, which are solely for the purpose of representing the way of carrying out the implementation of the principles of the invention. The following examples are not intended to be an exhaustive representation of the invention, nor intended to limit the scope thereof.

(63) For preparing hydrophobic coatings of self-assembled and functionalized silicon-oxide nanoparticles, according to the present invention, a colloidal hydro-alcoholized dispersion of nanoparticles was used with fluorocarbons with a density of 0.98 g/cm.sup.3 and a pH of 3.6. This suspension was stirred with ultrasound for 30 minutes. After the stirring process the suspension was poured into a tray and the paper was started to be covered.

(64) Two types of cardboard were prepared; one with a compressive strength of 220.63 kPa (32 lb/in.sup.2), and one with a resistance of 303.37 kPa (44 lb/in.sup.2). Both complied with the standardized method ECT. The composition of the cardboards for each case was as follows: Resistance of 32 ECT (Liner L33A, Midium M110U, Liner LT170) and resistance of 44 ECT (Liner L42A, Midium M150U, Liner LT170t).

(65) Test 1. Paper of 44 ECT

(66) Table 1 shows the temperature conditions of the different critical process parameters.

(67) TABLE-US-00001 TABLE 1 Temperature ° C. Cylinder 170 Paper cold part 84 Corrugator roll 145 Paper after cylinder 105

(68) The production rate was 80 m/min. In this test it was observed that when the dispersion is no longer stirred, the product in the tray is not homogeneous. Stirring was then started again. In that way it was possible to observe that the effect decreased and the product became homogeneous again.

(69) Test 2. Paper of 44 ECT

(70) Table 2 shows the temperature conditions of the different critical process parameters.

(71) TABLE-US-00002 TABLE 2 Temperature ° C. Cylinder 170 Paper cold part 91 Corrugator roll 134 Paper after cylinder 116

(72) The production rate was 60 m/min.

(73) Test 3. Paper of 32 ECT

(74) Table 3 shows the temperature conditions of the different critical process parameters.

(75) TABLE-US-00003 TABLE 3 Temperature ° C. Cylinder 168 Paper cold part 93 Corrugator roll 167 Paper after cylinder 123

(76) The production rate was 80 m/min.

(77) With sheets of coated paper boxes were produced, which were manipulated such that the coating was obtained on the inner face and the outer face.

(78) Table 4 shows a comparison of the Cobb values obtained, the contact angle, the passage speed of the water, and the amount of material used for each test.

(79) TABLE-US-00004 TABLE 4 Cobb Water contact Water flow gwater/m.sup.2 Amount of angle rate g/s Card- material Test Paper Cardboard Paper Cardboard Paper board g/m.sup.2 1 118.1 117.4 0.036 0.005 16.7 26.8 0.627 2 111.9 128.9 0.004 0.040 15 25.0 0.81  3 121.0 128.8 0.047 0.005 25 25.2 0.630

(80) The amount of material per square meter is less than 1 g/m.sup.2 in the tests in general, the best Cobb values are 15 for cardboard where water contact angles larger than 128° were obtained and low penetration of liquid. These water contact angles are far superior to those obtained with commercial coatings of the Michelman® type.

(81) Is important to note that in commercially available coatings such as Michelman®, the amount of material required to achieve Cobb values between 25 and 30 is between 4 g/m.sup.2 to 16 g/m.sup.2.

(82) FIGS. 6 to 11 illustrate a photomicrograph obtained by scanning electron microscopy both for paper or cardboard of the prior art uncoated (see FIG. 6) and its corresponding details of cellulose fiber (see FIG. 7), paper or cardboard with a coating of the Michelman® type according to the prior art (see FIG. 8) and its corresponding details of cellulose fibers (see FIG. 9), as well as paper or cardboard with a coating according to the invention (see FIG. 10) and its corresponding details of cellulose fibers (see FIG. 11), so that one can observe the comparative effect between a film type coating (see FIGS. 8 and 9) with the effect of fiber coatings of the present invention (see FIGS. 10 and 11).

(83) Table 4 also shows the results obtained according to the Cobb values, the water contact angle and the water flow rate. In this table the Cobb values are observed as very low in all tests (from 16.7 g.sub.water/m.sup.2 to 26.8 g.sub.water/m.sup.2) for water flow rates of 0.036 g/s to 0.005 g/s, which shows a significant reduction of the water flow in both paper and cardboard due to the coating. From additional experimental tests, it was proved that with the process of the present invention Cobb values can be controlled within a range of 8 g.sub.water/m.sup.2 to 25 g.sub.water/m.sup.2. Also, high water contact angles can be observed for all cases (from 118.1° to128.9°), which confirms the great hydrophobicity of the coatings applied to both paper and cardboard. In highly hydrophobic surfaces the water contact angle is greater than 100°, in these cases water rests on the surface, but it does not wet nor spread over the surfaces, giving rise to the so-called lotus effect. In the present invention, the lotus effect is promoted by the self-assembled silicon-oxide nanoparticles that cover the cellulose fibers, resulting in a nano-rough topography on the surface thereof as shown in FIG. 12.

(84) To evaluate the degree of hydrophobicity, the water contact angle was used and to measure the humidity absorption capacity of paper and cardboard the standards IMPEE-PL020 and TAPPI are used, which allow quantifying Cobb values and the rate of water penetration.

(85) When conducting industry-wide testing it was found that the nanostructured hydrophobic coating prepared and applied in accordance with the present invention does not affect the printing of paper or cardboard, and improves adhesion on the wings or areas requiring bonding of cardboard boxes that were obtained. The former, because the silicon-oxide nanoparticles are directly linked to the cellulose fibers as shown in FIG. 5, unlike other commercial products where a monolithic layer is produced which covers the surface of paper or cardboard, modifying the printing and the gluing of cardboard when making boxes. In addition to tests at the industrial level, it was confirmed that the well dispersed nanostructured coatings of silicon-oxide nanoparticles reduce the amount of hydrophobic material required per surface unit of paper or cardboard, thus facilitating the process of recycling of such packaging.

(86) Although the invention has been described with respect to a preferred embodiment, those skilled in the art will understand that various changes may be realized and equivalents may substitute its components without departing from the scope of the invention. Moreover, many modifications may be made to adapt a particular situation or material to the contents of the invention, without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.