Impervious treatment of paper or paperboard and impervious paper or paperboard obtained thereby

Abstract

This invention describes a method for treating the surface of paper or paperboard to make it impermeable to water, oil, and atmospheric gases, particularly oxygen. The invention also relates to the resulting impermeable paper or paperboard, which is particularly suitable for the production of food packaging or tableware.

Description

Technical Field

[0001] This invention describes a method for treating the surface of paper or paperboard to make it impermeable to water, oil, and atmospheric gases, particularly oxygen. The invention also relates to the resulting impermeable paper or paperboard, which is particularly suitable for the production of food packaging or tableware. Background Technology

[0002] Most food industry products are transported and sold in containers or packaging that must be impermeable to water (or water-based liquids, such as brine), alcoholic liquids (e.g., cocktails), oils, or gases. These properties are necessary to prevent liquids or gases from leaking out of the packaging, for example, to prevent degassing in the case of carbonated beverages, or to prevent condiment leakage in the case of ready-to-use food containers; and in some cases, to prevent the entry of substances from the outside, typically gases, such as moisture or oxygen that can cause food spoilage and degradation; finally, impermeability (especially to gases) is required to prevent cross-exchange between the inside and outside, and when the packaged product is in a modified atmosphere (e.g., under nitrogen), it is necessary to prevent the product from being modified due to leakage of packaging gases and the simultaneous entry of atmospheric gases. Typical applications of impermeable materials include cups and straws for beverage production, bags for vegetables, cold chain bags, packaging for long-term foods, packaging for fresh foods, containers for long-term and short-term liquids; and some applications unrelated to the food industry, such as the production of pots for flower cultivation.

[0003] Another category of products used in relation to food and the food industry is disposable tableware (plates, knives, glasses and similar items); in this case, impermeability to liquids is still necessary, while impermeability to gases is not strictly necessary.

[0004] Currently, most food packaging or single-use products for food are made of various plastics, especially polyethylene terephthalate (PET, mainly used in the production of beverage bottles), polyethylene (PE), polypropylene (PP), and polystyrene (PS); in some cases, these plastics are combined with a thin metal layer (usually aluminum) to achieve airtightness, or with Tetra... The packaging combines cardboard (a registered trademark of a company with the same name).

[0005] However, it is well known that the vast quantities of plastic produced each year and the improper disposal of plastics have led to extremely serious environmental problems. In particular, when released into rivers, lakes, and oceans, they form floating islands that can trap and kill fish populations, release secondary polluting components (e.g., plasticizers used in their production), and generate microplastics (material fragments smaller than 5 mm) that can be ingested by animals and ultimately enter the human food chain. These problems are exacerbated by the very long time, even centuries, required for these materials to degrade.

[0006] Despite these problems, plastic wrapping and packaging, or plastic tableware, are still widely used today because glass and metal are much heavier and more expensive than other materials used in the food industry (in addition to the risk of glass breaking), and paper does not have suitable impermeability properties unless it is bonded with layers of different materials.

[0007] Combining paper with polymer layers does not overcome the drawbacks of plastics, and even if it were possible, it would make recycling the paper components troublesome.

[0008] Patent application JP 2008-50380A describes a method for imparting superhydrophobicity to glass or paper articles. The method involves depositing a solution containing an alcohol, a tetraalkoxysilane, hydrophobic silica particles, hydrochloric acid, and water onto the surface of the article to be treated, and allowing the composition to dry on the surface at ambient temperature for 30 minutes. The document also describes that, to increase the durability of the superhydrophobic layer, a buffer layer can be prepared on the surface of the glass or paper article before forming the superhydrophobic layer; this buffer layer is obtained by depositing a solution containing an alkyltrialkoxysilane or a mixture of alkyltrialkoxysilane and tetraalkoxysilane onto the bare surface of the article, and drying the solution; the superhydrophobic layer is then prepared on this buffer layer. Although they possess superhydrophobic properties, the coatings described in this document do not exhibit the good liquid impermeability, particularly water impermeability, as demonstrated in the experimental section of this specification. Furthermore, the time required to dry the initial liquid composition on the surface to be coated is very long, therefore the method described in this document is not suitable for industrial-scale applications.

[0009] The object of this invention is to provide a material that has liquid and gas impermeability properties similar to those of plastics, thus allowing it to replace plastics in packaging applications. Furthermore, it is easily recyclable and does not cause the pollution problems associated with the use of plastics. Another object of this invention is to provide a method for producing said material. Summary of the Invention

[0010] According to the invention, these objectives are achieved. A first aspect of the invention relates to a method for treating paper or paperboard to make it impermeable to liquids and gases, the method comprising:

[0011] A) Applying a treatment solution to the surface of paper or paperboard, said treatment solution comprising:

[0012] a.1) An aqueous solution of 35wt%-100wt% containing 5wt%-20wt% micron-sized silica, 15wt%-40wt% hydrolyzed tetraalkoxysilane, and 25wt%-40wt% hydrolyzed alkyl-trialkoxysilane.

[0013] And optionally one or more other components selected from the following:

[0014] a.2) 10 wt% - 50 wt% of C1-C6 alcohols or mixtures thereof;

[0015] a.3) An alkali selected from NaOH and KOH, used in an amount that maintains the pH within the range of 2.3-4.5; and

[0016] a.4) 2wt%-15wt% of glycerin used for coloring with colorants approved for use in food;

[0017] B) Heat-treat the paper or paperboard treated with the treatment solution in step A) at a temperature of 100-250°C.

[0018] In a second aspect, the present invention relates to impermeable paper or paperboard obtained by the above method. Attached Figure Description

[0019] Figure 1 An oven is schematically shown for performing the heat treatment in step B) of the method of the present invention;

[0020] Figure 2 A scanning electron microscope image of a paper sample obtained by the method of the present invention is shown;

[0021] Figure 3 Paper samples obtained using the method of the present invention are shown in greater than 1000 mm. Figure 1 Two scanning electron microscope images at magnification;

[0022] Figure 4 Enlarged views of relevant portions of the FTIR spectra of the paper and the same paper after coating treatment according to the present invention are shown;

[0023] Figure 5 Two photographs of paper samples treated by the method of the present invention, taken from different angles, are reproduced, highlighting the water-repellent and oil-repellent properties of the samples.

[0024] Figure 6 The photographs reproduce the hydrophobic paper samples obtained according to the present invention (right) and according to the prior art (left);

[0025] Figure 7 A photograph of a hydrophobic paper sample obtained according to the prior art, taken 10 minutes after contact with a water droplet, is reproduced.

[0026] Figure 8 The photographs reproduce the cardboard stir bar obtained according to the prior art (top of the image) and the present invention (bottom of the image) after 30 seconds of contact with hot coffee;

[0027] Figure 9 and Figure 10 The photographs (at different angles) show water droplets on a cardboard surface treated with different solutions according to the present invention. Detailed Implementation

[0028] In the following description, unless otherwise specified, all percentages are by weight.

[0029] In the first step of the present invention, A) the surface to be made into impermeable paper or paperboard is treated with a treatment solution.

[0030] The water used to prepare all of the following solutions is demineralized water; the presence of different ion species can actually alter the reactivity of the components used in the solution, making the method control unreproducible.

[0031] The treatment solution may consist solely of an aqueous solution of a.1, or it may be prepared by adding one or more of the components a.2-a.4.

[0032] The solution in a.1 is an aqueous solution containing 5 wt%-20 wt% micron-sized silica, 15 wt%-40 wt% hydrolyzed tetraalkoxysilane, and 25 wt%-40 wt% hydrolyzed alkyl-trialkoxysilane. Preferably, the amount of alkyl-trialkoxysilane in the aqueous solution is higher than the amount of tetraalkoxysilane, and under this preferred condition, the content of tetraalkoxysilane in the solution is between 15 wt% and 25 wt%.

[0033] This solution is prepared by mixing three separate solutions of the three components in appropriate proportions, which are referred to below as the primary solution for clarity.

[0034] The first of these primary solutions is a suspension containing micron-sized silica. Micron-sized silica is amorphous silica in powder form; this powder is made by the aggregation of primary particles of nano-sized silica (i.e., less than 1 micrometer (μm), typically 5-100 nm) into secondary particles of micron-sized size, ranging in size from about 1 μm to 100 μm. This material can be produced by burning the vapor of silicon tetrachloride (SiCl4) and oxygen in a special chamber; in this case, the material is also referred to in the art as "pyrolytic silica" or "fumed silica". Alternatively, silica powder can be obtained by precipitation from a dilute aqueous solution of alkali metal silicates (e.g., water glass solution, i.e., sodium silicate solution of the general formula Na2O.xSiO2, where x = 2-4) with a dilute acid (e.g., sulfuric acid or hydrochloric acid); in this case, the resulting amorphous silica is referred to in the art as "precipitated silica". Considering the intended use of the product of this invention (in contact with food), the purity of the micron-sized silica should be no less than 99.5%; this characteristic can be confirmed by chemical analysis, and is essentially guaranteed by the fumed silica obtained through the aforementioned combustion process. Micron-sized silica is widely commercially available, and is, for example, marketed under the trade name Evonik Resource Efficiency GmbH (Essen, Germany). (For example, products) OX 50) sold, or by Cabot Corporation (Boston, Massachusetts (USA)) under the trade name Cab-O- For sale. The concentration of micronized silica in the water-silica suspension can vary between 10 wt% and 70 wt%, preferably between 10 wt% and 65 wt%, and even more preferably between 20 wt% and 40 wt%. To obtain a homogeneous suspension, mechanical stirring, such as with Ultra- Series mixers (by Stauffer, Germany) -Werke GmbH & Co. KG manufactures and sells) or similar devices that add micron-sized silica to water.

[0035] The second primary solution is an aqueous solution of hydrolyzed tetraalkoxysilane. Tetraalkoxysilane is a compound of the general formula Si(OR)4, where R is an alkyl group. For the purposes of this invention, R is a C1-C4 alkyl group, preferably methyl, and even more preferably ethyl; the tetraalkoxysilanes corresponding to these alkyl groups are tetramethoxysilane (also known as the abbreviation TMOS) and tetraethoxysilane (also known as the abbreviation TEOS). The concentration of tetraalkoxysilane in this solution is 10 mol%-20 mol%; in the preferred case of using TEOS, these molar concentrations correspond to a concentration of 56 wt%-74 wt%. Before mixing with the other two primary solutions, the tetraalkoxysilane is hydrolyzed by bringing the solution to an alkaline pH of 9-14 (preferably 9-10); preferably, this pH is obtained by adding NaOH or KOH to the solution.

[0036] Finally, the third primary solution is an aqueous solution of hydrolyzed alkyl-trialkoxysilane. Alkyl-trialkoxysilanes are compounds of the general formula R'-Si(OR")3, wherein R' and R" are C1-C4 alkyl groups that are the same or different from each other; preferably R' is a C1-C3 group, and even more preferably methyl (C1). The preferred compound for the purposes of this invention is an alkyl-trialkoxysilane, wherein R' = methyl and R" = ethyl, i.e., methyltriethoxysilane compounds known in the art with the abbreviation MTES. The concentration of alkyl-trialkoxysilane in this solution is 30 mol%-50 mol%; in the preferred case using MTES, these molar concentrations correspond to a concentration of 80 wt% to 90 wt%. The alkyl-trialkoxysilane is hydrolyzed by adding an inorganic acid, such as HCl or HNO3, to bring the solution to an acidic pH of 1-3 before mixing with the other two primary solutions.

[0037] Once prepared, the three primary solutions are mixed in proportions suitable for obtaining the desired composition within the aforementioned range, namely, 5 wt%-20 wt% micron-sized silica, 15 wt%-25 wt% hydrolyzed tetraalkoxysilane, and 25 wt%-40 wt% hydrolyzed alkyl-trialkoxysilane. Preferably, the following molar ratio is obtained in the solution thus prepared:

[0038] (tetraalkoxysilane + alkyl-trialkoxysilane) / SiO2: the ratio is between 1 and 2, or even more preferably between 1.5 and 1.7;

[0039] (Tetraalkoxysilane + Alkyl-trialkoxysilane) / H2O: The ratio is between 0.05 and 0.1.

[0040] One or more of components a.2-a.4 may be optionally added to the solution of a.1 prepared as described above.

[0041] Component a.2 is an alcohol having 1-6 carbon atoms, or a mixture of such alcohols. When used, this component can be added in an amount of 10%-50%, preferably 15%-30%, of the total weight of the treatment solution. The addition of component a.2 allows for accelerated drying of the treatment solution on a paper or paperboard carrier. Furthermore, this component allows for intervention in the viscosity of the treatment solution, which decreases as the amount of alcohol increases; this allows the operator additional control parameters to optimize the properties of the product based on the dispensing method on the paper or paperboard or the type of paper or paperboard (with more or less "closed" texture, i.e., with more or less closed fibers).

[0042] Component a.3 is an alkali selected from NaOH and KOH. When this component is present, it is added to the treatment solution to increase its initial pH, typically to 2.3-2.5, with a maximum of 5.5, and preferably 4.5. It is important that the pH does not exceed 5.5, as this will accelerate the gelation of the treatment solution, thus affecting its distribution on the paper surface. If the alkali is used in the form of a 1M solution, the pH is controlled within this range by adding 0.20%-0.50%, preferably 0.30%-0.45% of the alkali solution relative to the weight of the treatment solution. Component a.3 reduces the time required to dry the treatment solution when dispensing it onto the paper or paperboard carrier.

[0043] Finally, when it is desired to impart color to the treatment solution (and thus to the treated paper or cardboard obtained at the end of the method), component a.4 is added. This component consists of glycerol dyed with a suitable colorant appropriate for food use; in Europe, colorants permitted for use in food are designated with the initial letter E#, where # is a number between 102 and 143. The purity of the glycerol used should be not less than 99.5%. When this component is present, it may be added to the treatment solution in an amount of 2%–15%, preferably 4%–10%, depending on the color intensity obtained on the paper or cardboard carrier.

[0044] The glycerol used for staining can be added to the product in two operating modes. According to the first method, glycerol is added to the primary solutions of tetraalkoxysilane and alkyl-trialkoxysilane used to prepare solution a.1; glycerol is added to these solutions before their hydrolysis; this method allows glycerol to be more uniformly dispersed throughout the treatment solution. The second method involves adding glycerol as a final step in the preparation of the treatment solution; in this case, the resulting mixture should be stirred for at least 20 minutes to allow the glycerol to be fully dispersed in the solution; this second method is suitable for preparing treatment solutions containing a low percentage of glycerol.

[0045] The treatment solution thus prepared can be distributed on the surface of paper or paperboard to prevent seepage using various industrial techniques known in the printing field; for example, the distribution of the treatment solution on the surface of paper or paperboard can be achieved using techniques such as, for example, rotary gravure printing, flexographic printing, offset printing, air knife printing, inverted printing (the latter more commonly known as reverse printing) or spraying techniques.

[0046] Depending on the specific intended use, the solution can be applied to one or both sides of the paper or paperboard surface; for example, in the case of paperboard used to produce plates or glass, coating the inner surface may be sufficient (i.e., the surface that will come into contact with food), while in the case of cutting tools, the paperboard must be fully coated, and also coated on its side surfaces. Application to both surfaces also increases the gas barrier properties of the product.

[0047] There are no particular limitations on the thickness of paper or paperboard coated with the above solution, and it depends on the intended use.

[0048] In the case of paper, its thickness can vary between 0.03 mm and 0.6 mm, and its weight can be 20 g / m³. 2 and 400g / m 2 The changes between them.

[0049] In the case of cardboard used for producing tableware, its thickness can be 1mm-3mm, and its area weight is typically about 400g / m². 2 -1400 g / m 2 .

[0050] The paper that can be processed in the method of the present invention can be kraft paper (such as plain white paper), tissue paper, parchment, coated paper, or paper combined to form the desired thickness. Depending on the type of product to be obtained, the use of paper having fibers arranged more or less tightly together can be evaluated; this characteristic determines the paper's "closure," another parameter used by the operator to check the impermeability properties of the final product.

[0051] The treatment of this invention is typically applied to blank paper, and primarily to food-grade paper; however, excellent results have also been obtained using non-food or recycled paper. Recycled paper contains oils / fats derived from printing inks, which are almost never used for food purposes; the inventors have observed that by using these papers in the method of this invention, in addition to achieving the desired impermeability to water and oil, it is possible to prevent the leakage of these oils and fats contained in the paper itself into the food that comes into direct contact with it.

[0052] Depending on the technology used, a printing press is used to distribute or spread the material, resulting in a uniform application of 2.5 g / m² onto the paper substrate. 2 -30g / m 2A sufficient amount of solution has been shown to be usable for achieving the desired purpose of this invention.

[0053] In step B) of the method of the present invention, the paper or paperboard treated with the solution of step A) is heat-treated in one or more ovens at a temperature of 100-250°C, preferably at a temperature of about 120-180°C. Even if the ignition temperature of the paper is about 235°C, heat treatment can be carried out at a temperature up to 250°C if the duration is short (e.g., not exceeding 10 seconds), because the heat transferred to the coated paper is initially consumed in the evaporation of the liquid components of the coating.

[0054] One or more ovens can be of any type, such as enclosed and static ovens, in which several sheets of treated paper or paperboard are placed on a special tray, preferably made of metal mesh, to expose both surfaces of the paper or paperboard to hot air.

[0055] However, preferably, in order to improve the productivity of the method, in the case of paper, the oven is a tunnel oven and the paper is guided from one end to the other across its length.

[0056] This preferred configuration is in Figure 1 The figure is shown in a highly schematic manner. In the drying system 10 for the solution deposited in step A), the paper 11 is initially wound onto roller 12, and the necessary length of paper is unwound from the roller to hook its ends onto a second roller 15. In this system, the paper 11 is conveyed in the direction of the arrow: the paper 11 is unwound from roller 12 and moves on rotary guides 13, 13', ... through tunnel oven 14, and is rewound onto roller 15 downstream for drying. The heating device (not shown) in tunnel oven 14 can be a resistor, an infrared lamp, or any other useful heating device. The movement of paper 11 in system 10 may be solely due to the traction force applied by roller 15; however, preferably, to avoid the risk of paper breakage, both rollers 12 and 15 are rotated about their axes by mechanical means, and under the control of a differential system, the rotational speeds of the two rollers vary during the paper movement in the system to ensure that the linear unwinding speed of paper 11 from roller 12 is always the same as the rewinding speed of paper onto roller 15; however, this speed need not be constant throughout the process and can be adjusted in the same process according to the degree of dryness observed at the oven outlet.

[0057] The temperature inside the oven is not necessarily constant; a gradually increasing heat distribution is preferred, for example, a temperature of 120°C at the oven inlet and 180°C at the outlet. For industrial production that results in sustainable product costs, the paper conveying speed in the system should be at least 100 m / min. The inventors have observed that, under these preferred conditions, using a tunnel oven with a heat distribution of 120°C to 180°C from inlet to outlet as defined above, the length of the oven should be at least 15 m.

[0058] In a second aspect, the present invention relates to impermeable paper or paperboard obtained by the above method.

[0059] The treated paper or paperboard has a nano-thick layer of silica material on its surface, which does not change the appearance of the paper or paperboard, but makes it resistant to the passage of liquids, greases and gases.

[0060] The resistance to the passage of liquids (water (and water-based liquids) and oil) is measured by the hydrophobicity and oleophobicity of the treated paper or paperboard, which can be evaluated by contact angle measurement. This is denoted by the symbol θ. c The contact angle is defined by the tangent at the point where the droplet surface contacts the surface being evaluated; this angle is measured between the tangent and the portion of the solid surface in contact with the liquid. In the case of water, a contact angle θ greater than 90° is formed when a droplet on the surface... c When this surface is called hydrophobic, or even water-repellent, it is considered superhydrophobic if the angle is greater than 150°. Similarly, a surface on which an oily liquid forms a contact angle greater than 90° is defined as oleophobic. The inventors have observed that paper or paperboard samples treated with the method of the present invention are both hydrophobic and oleophobic; these properties prevent liquids (water, oil, or components containing alcohol) from being absorbed through the liquid-absorbing action between the paper or paperboard fibers and thus initiating the process through the paper or paperboard.

[0061] Therefore, the paper or paperboard obtained by the method of the present invention is water and oil resistant, and it has been observed that it also improves the barrier properties against oxygen and water vapor, achieving values ​​very similar to those of plastics for certain types of paper.

[0062] The present invention is further illustrated by the following embodiments.

[0063] Methods, Instruments and Materials

[0064] The product was obtained through the following analytical characterization:

[0065] - The paper obtained after treatment by the method of the present invention was visually evaluated by scanning electron microscopy (SEM); the instrument used was a LEO 1525 Zeiss SEM.

[0066] - Fourier transform infrared spectroscopy (FT-IR) was used to study the composition of the starting product and the products obtained after the treatment of this invention; the instrument used was a Varian 640-IR FT-IR spectrophotometer;

[0067] - Gas permeation test, used to evaluate the transfer of gas through treated paper; the instrument used is a MULTIPERM O2 / H2O sold by Permtech Srl, Pieve Fosciana, Italy.

[0068] Example 1

[0069] This embodiment relates to the preparation of a paperboard sample processed according to the method of the present invention.

[0070] Three primary solutions of micron-sized silica, tetraalkoxysilane, and alkyl-trialkoxysilane were prepared respectively.

[0071] The first primary solution is a 30 wt% aqueous solution of micron-sized silica, which is obtained by passing 300 g of Evonik Resource Efficiency Add OX 50 silica to 700ml of distilled water and use Ultra- The resulting suspension is homogenized using a mixer.

[0072] The second primary solution was obtained by mixing 670g of tetraethoxysilane (TEOS) and 330ml of distilled water, stirring the solution with a mechanical stirrer until homogeneous, adding NaOH to adjust the pH to 10, and allowing the system to react for 8 hours.

[0073] The third primary solution was prepared by adding 870g of methyltriethoxysilane (MTES) to 130g of distilled water, stirring the solution with a mechanical stirrer to make it homogeneous, adding HCl to adjust the pH to 1, and allowing the system to react for 8 hours.

[0074] The three primary solutions obtained in this way are mixed to obtain a treatment solution, which contains:

[0075] -SiO2: 10%;

[0076] -TEOS: 22.3%;

[0077] -MTES: 29%;

[0078] -Water: 38.7%.

[0079] For the purpose of testing in this embodiment, a thickness of 2.55 mm and a weight of 970 g / m² were used.2 Cardboard.

[0080] A portion of the treatment solution prepared as described above was distributed onto both sides of the aforementioned paperboard sample with dimensions of 18 × 20 cm using a roller system. A result of 5 g / m² was obtained. 2 The coating of the dried product (i.e., after the water and alcohol formed during the hydrolysis of TEOS and MTES are evaporated following the drying process).

[0081] The cardboard sample was heat-treated at 160°C for 3 minutes in a static oven (laboratory oven) and then dried.

[0082] The paperboard samples obtained in this way were characterized in terms of morphology, IR, water repellency, and oil repellency.

[0083] Morphological characterization was performed using SEM analysis. Results were obtained at low magnification. Figure 2 The report includes photomicrographs, as well as two photomicrographs of the same sample reproduced at higher magnification. Figure 3 The report includes micrographs. The micrographs show that the openings between the cellulose fibers of the cardboard, which are tens of micrometers in size, are not completely blocked by the silica coating, confirming that the silica coating has a micrometer-sized structure.

[0084] FT-IR analysis was performed on the cardboard used in Example 1 before and after treatment. Figure 4 In the image, these spectra were reproduced at approximately 720 cm⁻¹. -1 and 1440cm -1 Enlarged views of the relevant portions; dashed lines represent untreated cardboard, and solid lines represent treated cardboard. In the spectrum obtained on the sample treated according to the present invention, an observation was made at 759.005 cm⁻¹. -1 The peak is at 1269.590 cm. -1 The peaks at 1000-1100 cm⁻¹ (these two values ​​were determined by the instrument's built-in software) are not present in uncoated paperboard. According to the documented data, these two values ​​are attributed to the CH₃ rocking and CH₃ symmetric bending in the Si-CH₃ groups, respectively, while the peaks at 1000-1100 cm⁻¹ are attributed to the Si-O bonds in the documented data. -1 The peaks within the range overlap with the stripes on the cardboard below.

[0085] Figure 5 Two photographs of the cardboard sample obtained after the treatment in Example 1, taken from different angles, are reproduced; specifically, the upper image is taken from an angle closer to perpendicular to the surface of the cardboard, while the lower image is taken from a more oblique angle; in both images, the droplet on the left is water, and the droplet on the right is edible oil. The two photographs show that water and oil do not wet the sample, confirming the latter's hydrophobic and oleophobic properties.

[0086] Example 2 (Comparison)

[0087] This embodiment relates to the preparation of paper samples processed according to the method of patent application JP 2008-50380A.

[0088] To prepare a sol according to the embodiment described in paragraph

[0021] of JP 2008-50380A, the following components were mixed in a given weight percentage:

[0089] - Ethanol: 96.26%;

[0090] -SiO2: 3%;

[0091] -TEOS: 0.54%;

[0092] -H2O: 0.16%;

[0093] -HCl: 0.04%.

[0094] According to the description in the Japanese application, the silicon dioxide used is RX 300 is a micron-sized fumed silica that becomes hydrophobic through treatment with HMDS (hexamethyldisilazane).

[0095] Ethanol and silica were mixed for 30 minutes, followed by ultrasonic treatment for 30 minutes. Then, the above-mentioned amounts of TEOS, H2O and HCl were added to the resulting suspension, the mixture was stirred for 2.5 hours, and then ultrasonicated for 30 minutes.

[0096] Using a manual coating roller, the obtained sol was applied to a coating area of ​​90 g / m². 2 The tissue paper. Dry the sol at room temperature for 30 minutes.

[0097] Example 3

[0098] Example 3 was repeated using the sol of the present invention prepared as described in Example 1, and the coated paper was dried in air at 165°C for 2 minutes.

[0099] Example 4 (Comparison)

[0100] This embodiment relates to the process described as a second implementation in duplicate patent application JP 2008-50380A.

[0101] JP 2008-50380A also describes the possibility of applying a first (buffer) layer of silica-based material to a substrate, followed by the possibility of the layer described in Comparative Experimental Example 2. Although this possibility is only illustrated by example with glass as the substrate in paragraph

[0030] of the document, the described process has been repeated and applied to a rod obtained from a cardboard with a thickness of 1.3 mm.

[0102] The buffer layer is obtained from a sol having the following weight percentage composition:

[0103] Ethanol: 60%;

[0104] H2O: 20%;

[0105] TEOS: 10.5%

[0106] MTES: 9%

[0107] 1N HCl: 0.5%.

[0108] First, ethanol, TEOS and MTES are mixed under stirring for 30 minutes, then water and HCl are added, and stirring is continued for 3 hours to prepare a sol.

[0109] The paper rods described above were coated with the sol and dried at 105°C for 20 minutes.

[0110] The pretreated bar was then coated with the sol from Example 2 and allowed to dry at room temperature for 30 minutes.

[0111] Example 5

[0112] The preparation of Comparative Example 4 was repeated using the sol of the present invention prepared as described in Example 1, without applying a buffer layer, and with the coated paper stick dried in air at 165°C for 2 minutes.

[0113] Example 6

[0114] The hydrophobicity of the coated paper samples prepared in Examples 2 and 3 was tested by depositing a drop of water on the sample surface.

[0115] Figure 6 These are photographs of two samples shortly after water droplet deposition. The left side shows a sample from the prior art, and the right side shows a sample from the present invention.

[0116] Initially, both samples showed hydrophobicity, although droplets on the prior art sample appeared to show an increased tendency to spread on the surface.

[0117] However, after 10 minutes, the paper sample treated according to the present invention appeared unchanged, while the sample treated according to JP 2008-50380A showed ripples corresponding to water droplets, as... Figure 7 As shown, this indicates that water has penetrated the silica-based coating and wetted the paper.

[0118] Example 7

[0119] The oxygen permeability of the coated paper samples prepared in Examples 2 and 3 was tested; this is a characteristic relevant to food packaging.

[0120] Table 1 shows the data obtained from the tests conducted on the two samples described above. For comparison, data obtained from samples of the starting paper used in Examples 2 and 3 are also listed. Tests were conducted at 23°C, and the temperature was kept constant throughout the tests using the instrument's thermostat system.

[0121] Table 1

[0122]

[0123] The results reported in Table 1 indicate that the treatment of JP 2008-50380A does not impart gas impermeability to the paper, while the treatment of the present invention achieves good gas impermeability, which is reduced by about 5 orders of magnitude compared to the starting paper, and reaches values ​​comparable to some paper / plastic bilayers currently available on the market.

[0124] Example 8

[0125] Samples of the coated paper prepared in Examples 4 and 5 were tested to examine their resistance to liquid absorption.

[0126] These relatively thick cardboard sticks are typically used to stir beverages (e.g., coffee or tea from a vending machine), so they must be able to withstand soaking for at least a few minutes.

[0127] Weigh three samples of the present invention and three samples of the prior art, soak them in hot coffee (65°C) for 30 seconds, then remove and weigh them again.

[0128] Six samples taken from the hot coffee are shown below. Figure 8 In Example 4 (Prior Art), sample AC was obtained, and in Example 5 (In this invention), sample DF was obtained.

[0129] As can be seen from the figure, the prior art sample AC shows obvious discoloration in the lower part of the coffee immersion, while the discoloration intensity of the present invention sample DF is much lower (almost invisible in the figure).

[0130] Table 2 reports the initial (P0) and final (P1) weights and weight changes (ΔP) of six samples; the last column reports the average ΔP of samples from the prior art and the present invention.

[0131] Table 2

[0132]

[0133] The data in the table above clearly show that paper treated according to JP 2008-50380A absorbs more liquid than paper treated according to the present invention.

[0134] Example 9

[0135] Prepare and mix the three primary solutions as described in Example 1 to obtain a first mixture containing:

[0136] -SiO2: 5%;

[0137] -TEOS: 35%;

[0138] -MTES: 35%;

[0139] Water: 25%.

[0140] Ethanol is added to the first mixture thus obtained, wherein the weight ratio of the first mixture to EtOH is 6:4.

[0141] Use a spray gun to apply 6g / m 2 The treatment solution thus obtained is applied to an area with a weight of 210 g / m². 2 On the surface of the cardboard.

[0142] The treated cardboard was dried in a closed oven at 165°C for 1 minute.

[0143] Water is deposited onto the resulting coated paperboard, forming droplets on the treated surface; Figure 9 With similar Figure 5 The two views (top view and tilted view) show two images of the water droplet. The hydrophobic properties of the treated cardboard are clearly visible in the images.

[0144] Example 10

[0145] Two primary solutions of micron-sized silica and TEOS were prepared as described in Example 1. 725g of methyltriethoxysilane (MTES) was added to 130g of distilled water, and the solution was stirred with a mechanical stirrer until homogeneous. HCl was added to adjust the pH to 1, and then 145g of glycerol, which was dyed light blue, was added. The system was allowed to react for 8 hours to prepare a third primary solution.

[0146] The three primary solutions are mixed to obtain a first mixture, which contains:

[0147] -SiO2: 18%;

[0148] -TEOS: 15%;

[0149] -MTES: 35%;

[0150] -Water: 25%;

[0151] - Glycerin: 7%.

[0152] The solution was applied to an area weight of 60 g / m² using a flexographic printing press. 2 On the cotton paper.

[0153] The treated paper was dried in a closed oven at 165°C for 1 minute.

[0154] Water is deposited onto the coated paper thus obtained, forming droplets on the treated surface; Figure 10 With Figure 5 The image shows two similar views (top view and tilted view) of a water droplet. The hydrophobic properties of the treated cardboard are clearly visible in the image.

Claims

1. A method for treating paper or paperboard to make said paper or paperboard impermeable to liquids and gases, comprising: A) Applying a treatment solution to the surface of the paper or paperboard, the treatment solution comprising: a.1) A 35 wt% - 100 wt% aqueous solution containing 5 wt% - 20 wt% micron-sized silica, 15 wt% - 40 wt% hydrolyzed tetraalkoxysilane, and 25 wt% - 40 wt% hydrolyzed alkyl-trialkoxysilane; wherein the micron-sized silica exists in the form of secondary particles of 1 μm to 100 μm micron size formed by the aggregation of primary particles of nano-sized silica; wherein the aqueous solution is obtained by mixing the following: - A primary suspension of micron-sized silica in water, with a concentration of 10 wt% - 70 wt%, wherein the purity of silica is not less than 99.5%; - A second primary solution of hydrolyzed tetraalkoxysilane in water, with a concentration of 10 mol% - 20 mol%, wherein the general formula of the unhydrolyzed tetraalkoxysilane is Si(OR)4, wherein R is a C1-C4 alkyl group, and wherein the hydrolysis of the tetraalkoxysilane is carried out by making the pH of the solution 9-14. - A third primary solution of hydrolyzed alkyl-trialkoxysilanes in water, with a concentration of 30 mol% - 50 mol%, wherein the general formula of the alkyl-trialkoxysilane before hydrolysis is R'-Si(OR")3, wherein R' and R" are C1-C4 alkyl groups that are the same or different from each other, and wherein the hydrolysis of the alkyl-trialkoxysilane is carried out by adjusting the pH of the solution to 1-3; and a.3) An alkali selected from NaOH and KOH, used in an amount that keeps the pH within the range of 4.5-5.5; And optionally one or more other ingredients selected from the following: a.2) 10 wt% - 50 wt% of C1-C6 alcohols or mixtures thereof; and a.4) 2 wt% - 15 wt% of glycerin used for coloring with colorants approved for use in food; B) Heat-treat the paper or paperboard treated with the treatment solution in step A) at a temperature of 100-250°C.

2. The method according to claim 1, wherein the aqueous solution of a.1) contains 15 wt% - 25 wt% of the hydrolyzed tetraalkoxysilane.

3. The method according to claim 1 or 2, wherein in the aqueous solution of a.1), the molar ratio of (tetraalkoxysilane + alkyl-trialkoxysilane) / silica is 1-2, and the molar ratio of (tetraalkoxysilane + alkyl-trialkoxysilane) / water is 0.05-0.

1.

4. The method according to claim 1, wherein the tetraalkoxysilane is selected from tetramethoxysilane (TMOS) and tetraethoxysilane (TEOS), and the alkyl-trialkoxysilane is methyltriethoxysilane (MTES).

5. The method according to claim 1, wherein the stained glycerol of a.4) is added to one of the first primary suspension or the second or third primary solution used to prepare the aqueous solution of a.1), or is added at the end of the preparation of the treatment solution.

6. The method according to claim 1, wherein in step A), the treatment of the paper or paperboard surface with the treatment solution is performed using a technique selected from rotary gravure printing, flexographic printing, offset printing, air knife printing, inverted printing, and spraying techniques.

7. The method of claim 6, wherein only one or both sides of the paper or paperboard surface are treated, the paper having a thickness of 0.03-0.6 mm and a g / m² of 20-400 g / m³. 2 The paperboard has a weight of 1-3 mm and a density of 400-1400 g / m². 2 The area weight, and 10-20 g / m² 2 The amount of the treatment solution is applied to the surface of the paper or paperboard.

8. The method according to claim 1, wherein in step B) of the method, the paper or paperboard treated with the treatment solution of step A) is heat-treated in one or more ovens at a temperature of 100°C to 250°C.

9. The method according to claim 8, wherein the heat treatment is performed using a tunnel oven (14), and the paper or cardboard (11) treated with the treatment solution of step A) is guided from one end to the other, through the length of the tunnel oven, and wherein the temperature of the inlet portion of the tunnel oven is lower than the temperature of the outlet portion of the tunnel oven.

10. Paper or paperboard obtained by the method according to any one of claims 1-9, wherein the paper or paperboard is waterproof, impermeable to liquids containing alcohol and oil, and has a barrier effect against gases and vapors.

Images