METHOD FOR THE PRODUCTION OF PAPER ARTICLES MADE WATERPROOF BY SILICA-BASED COATINGS AND ARTICLES OBTAINED THUS

Description

P024183IT-01 Notarbartolo & Gervasi SpA “METHOD FOR THE PRODUCTION OF WATERPROOF PAPER ARTICLES WITH SILICA-BASED COATINGS AND ARTICLES OBTAINED THUS” ***** ***** ***** FIELD OF INVENTION 5 The present invention refers to the sector of paper products, often of the disposable type throws, which for their creation require the gluing of two separate parts of paper or two sections or flaps of the same part on itself. STATE OF THE ART There are numerous products and artifacts that are formed by joining together through gluing 10 of different parts made of paper, which can be initially separate parts or sections of a single part, such as a single sheet. For example, gluing separate parts together is used to produce cardboard or sheets of paper of relatively high thickness and weight elevated, gluing together sheets of a thickness lower than the desired one; the gluing of flaps of the same sheet is instead used to allow the formation of objects of the shape 15 complex, such as glasses, capsules, containers, bags, etc. The use of paper products has also accelerated in recent years in consequence of the push to replace plastic with non-plastic based alternative products plastic polymers, or with a reduced content of the same, which guarantee good recyclability, biodegradability and compostability. For example, in the European Union it has entered into force 20 The SUP Directive (from the English “Single Use Plastic”) comes into force in 2021, which prohibits the use of certain single-use plastic products for which alternatives exist on the market. A direction along which research has moved with the aim of replacing the artefacts in plastic is that of paper covered with silica or modified silica, using the sol- 25 gel. In this technique, a solution or suspension (sol) of silica precursors is prepared. in an aqueous or hydroalcoholic solvent; the precursors react in solution forming a gel, that is, a viscous liquid phase that is distributed on the paper to which it remains adherent precisely due to viscosity; subsequently, the gel-coated paper is subjected to a treatment P024183IT-01 Notarbartolo & Gervasi SpA thermal at temperatures typically in the range 120-200 °C, causing the evaporation of the volatile components of the gel and the final solidification of the inorganic part, which forms on the paper a glassy layer impermeable to liquids and resistant even to temperatures hot drinks. Paper and paper products made waterproof in this way are described for 5 example in patent applications WO 2020 / 261198 A1 and WO 2022 / 171893 A1, both at name of the applicant. Even the production of paper articles made waterproof with silica coating Today it requires the use of adhesives to obtain complex shapes; for example, the Patent application EP 4043362 A1 describes the production of paper cups covered with 10 silica, in which the closure of two edges of a sheet to give a truncated cone shape and the fixing of the bottom to the smaller base of the truncated cone are achieved using polymeric adhesives. Nowadays, gluing paper parts is done with adhesives, such as cold (vinyl, acrylic, polyurethane, etc.), hot melt adhesives, thermo-lacquers (vinyl, acrylic) and UV adhesives. 15 The use of adhesives requires the adoption of dedicated equipment in the production plants production of paper products, for example devices (rollers, dispensers, ...) that allow the application of the adhesive in selected areas of the sheet of paper, which will then be involved in the gluing operation; this also implies that the production process includes a dedicated step for distributing the adhesive onto a selected surface 20 of the sheet (register printing). Similarly, at least for some types of stickers, it is necessary an additional device and a further process step dedicated to consolidation of the adhesive, for example a UV lamp and an irradiation step in the case of stickers which cross-link along this path. The purpose of the present invention is to provide a process 25 simplified for the production of paper products made waterproof by covering with siliceous material, which require at least one gluing step between two paper parts or two flaps of the same piece of paper. SUMMARY OF THE INVENTION P024183IT-01 Notarbartolo & Gervasi SpA This and other purposes are achieved with the present invention, which in its first aspect concerns a process for the production of a paper product covered on at least one surface with siliceous material, said artifact comprising at least one gluing area of two areas of two sheets or of the same sheet of paper, said process comprising the following 5 steps: a) prepare one or more sheets of coated paper on at least one side or of calendered paper or supercalendered, in which said one or more sheets are optionally shaped into a any time before step d); b) cover at least one face of each of said one or more sheets of coated paper, 10 calendered or super-calendered with a solution of one or more silica or silica precursors modified, with the condition that if the sheet of paper is coated on one side only, the the face covered with said solution is the patinated one; c) cause the sheet or sheets of paper covered with the solution to dry b), resulting in the formation of a layer of silica or modified silica on said face of 15 one or more said sheets of paper; d) joining two parts of a single sheet or parts of at least two sheets, obtained in the step c), so that the contact areas of the said two parts of the single sheet or of the said at least two sheets are covered with the layer of silica or modified silica; e) subject the parts or sheets placed side by side to a heat compression treatment at a 20 temperature of at least 100 °C exerting a pressure of at least 300 N, or an ultrasound treatment that applies a pressure of at least 150 kPa, causing the adhesion of the interposed siliceous material. In its second aspect the invention concerns the artefacts obtained with the above method. described. 25 BRIEF DESCRIPTION OF THE FIGURES The invention will be described in detail below with reference to the figures, in which: - Fig. 1 schematically represents a section of a sheet of coated paper on a single face; P024183IT-01 Notarbartolo & Gervasi SpA - Fig. 2 schematically represents a section of a sheet of coated paper, calendered or supercalendered on both sides; - Fig. 3 schematically represents a section of a sheet of coated paper and with coating of siliceous material on one side only; 5 - Fig. 4 schematically represents a section of a sheet of coated paper, calendered or supercalendered with silica coating on both faces; - Fig. 5 schematically represents the welding area of ​​two parts in cross-section paper in which only one of the two faces is covered with siliceous material; - Fig. 6 schematically represents the welding area of ​​two parts in cross-section 10 papers that have a siliceous coating on both sides. DETAILED DESCRIPTION OF THE INVENTION The invention is based on the observation made by the inventor that, surprisingly, if a siliceous material, produced by sol gel, is deposited on a coated paper surface, calendered or supercalendered, the deposit has adhesive properties if subjected to treatment 15 thermocompression or with ultrasound. This phenomenon was completely unexpected: in the sector it was believed that in order to obtain the adhesion of two paper parts covered with siliceous material required the use of a traditional adhesive (polymeric); in fact, the inventor is not aware of any documents describing the adhesive properties of the silica layer alone. Furthermore, the inventor observed that the 20 layer of silica material presents these adhesive characteristics only when it is produced on coated, calendered or supercalendered paper; a similar siliceous deposit produced on uncoated paper having these characteristics, for example handmade paper, kraft paper and similar, does not present adhesiveness. This observation of the inventor allows to eliminate in the production processes of 25 paper products the step of dispensing adhesives on selected areas, as well as eliminate the related dispensing devices from the machines. The invention also allows for eliminate traditional polymer adhesive, helping to reduce material load similar to plastics in the final product. P024183IT-01 Notarbartolo & Gervasi SpA In the figures cited in the following description, an equal number corresponds to an element equal. Furthermore, the figures are not to scale, and in particular the thicknesses are greatly augmented to highlight the layers that make up the covered paper sheets of the invention. The first step of the invention, a), consists in preparing one or more sheets of paper 5 coated, calendered, or supercalendered. In the case of coated paper, this can be coated on one surface or both; patination consists in coating the surface of the sheet with a mixture of materials, including kaolinite, calcium carbonate, bentonite and talc, possibly added with a binder, or a polymer. In the case of calendered paper or supercalendered obviously the two surfaces of the sheet have the same characteristics because the 10 The calendering process applies a compressive force symmetrically on both faces. Fig. 1 shows a schematic cross-section of a sheet 1 of coated paper on a single face; the paper support, 10, is coated on one side with a coating layer, 11, while the opposite face has no cladding or finishing. Fig. 2 shows, in a similar view to that of Fig. 1, a sheet 2 of paper with finishes on both sides; in this case the two 15 finishing layers, 21 and 21', can be patination layers or layers of cellulose fibers plus tablets obtained through calendering or supercalendering processes. Sheet or sheets 1 or 2 may be shaped or not, depending on the final product you want. you want to produce. If this is simply a cardboard obtained by joining two or more sheets on their entire surface, the shaping step is not necessary. In the case, more 20 commercially important, where an article with a particular shape has to be produced, for example a glass, the sheet of paper must be shaped; for example, in the case of the glass, the shape is a section of a circular crown, so that by overlapping the two sides straight lines you get a truncated cone shape, to which the bottom of the glass will then be added at the minor base. The shaping can take place at any time before 25 of the juxtaposition of the parts to be joined together, therefore at any time before the step d) of the process. In step b) of the invention process, the paper from step a) is covered on at least one face with a solution of one or more silica or modified silica precursors, P024183IT-01 Notarbartolo & Gervasi SpA according to methods known in the sol-gel technique. In the case of paper coated on one side only, the silica or modified silica coating is done on the coated face. In this technique a solution is prepared in a solvent chosen between water or a hydroalcoholic mixture, of at least one precursor of the final siliceous layer; this precursor is 5 typically be a tetraalkoxysilane, an alkyltrialkoxysilane, or nanosized silica or their mixtures. When the sheet must subsequently be folded, rolled or otherwise deformed, the precursor must contain at least one alkyltrialkoxysilane. Tetraalkoxysilanes are compounds with the general formula Si(OR)4, where R is a radical alkyl. For the purposes of this invention, R is a C1-C4 alkyl radical, 10 preferably methyl and even more preferably ethyl; the tetraalkoxysilanes corresponding to These alkyl radicals are respectively tetramethoxysilane, also known as the abbreviation TMOS, and tetraethoxysilane, also known by the abbreviation TEOS. Alkyltrialkoxysilanes are compounds with the general formula R'-Si(OR”)3, where R' and R”, equal or different from each other, they are C1-C4 alkyl radicals; preferably R' is a C1- radical 15 C3, and even more preferably is methyl (C1). A preferred compound for the purposes of this invention is the alkyl-trialkoxysilane in which R' = methyl and R” = ethyl, i.e. the compound methyltriethoxysilane known in the industry by the abbreviation MTES. Nanoscale silica is a form of silica made up of primary silica particles of nanometer dimensions (i.e., dimensions smaller than a micrometer, µm) generally 20 aggregates to form secondary particles of micrometric size. This material is also known in the art as “colloidal silica” or “fumed silica”. For contact application with food (for example, in the case of glasses), the nanometric silica must have a purity not less than 99.5%. Nanoscale silica is widely available commercially and is sold for example from the company Evonik Resource Efficiency GmbH of Essen (Germany) under the name ® ® 25 AEROSIL (for example, the product AEROSIL OX 50), or from the Cabot company ® Corporation of Boston, Massachusetts (USA) under the name Cab-O-Sil. The solution used to cover the paper is generally prepared in a room acidic, with a pH of about 2-3, typically obtained by adding mineral acids such as HCl or P024183IT-01 Notarbartolo & Gervasi SpA HNO . The solution may also contain, as optional components, one or more C1- alcohols C6, a base (chosen, for example, between NaOH and KOH) in an amount sufficient to regulate the pH in the range between 2.3 and 4.5, and glycerin pigmented with a colorant permitted for use food. 5 A preferred solution for the purposes of the present invention contains, by weight, between 35% and 45%, preferably 40% of MTES, between 15% and 25%, preferably 20% of TEOS, and between 35% and 45%, preferably 40% water, plus a small amount of an acid solution (for example, a 1 N HCl solution) sufficient to bring the pH into the range 2-3. Covering with the solution at least one side of the sheet, already shaped or not, 10 can be done by any known method, for example by immersion, spraying, brushing and the like; alternatively, it is possible to resort to typical printing methods flexographic, in which the solution described above is collected from a tank and, thanks to a roller system, is transported, dosed by an anilox roller (for the purposes of the invention it is a roller with a low number of surface cells per centimetre is sufficient, approximately between 80- 15 250) and deposited on the support to be coated; finally, another method for transferring the solution on the surface of the paper is that described in patent application WO 2020 / 261198 A1, in which the sheet of paper is passed between two rollers, at least one of which is hollow and filled with the solution, and has a cylindrical surface perforated and covered with felt, so that the solution soak the felt and it will distribute it on the sheet of paper as you roll it. 20 After the solution has been spread on at least one surface of the sheet of paper, in the step c) let the sheet dry. In theory this could be achieved by leaving simply the sheets spread out in a suitable conditioned room, even at a temperature environment; to achieve rapid drying times, compatible with process timings industrial, this operation is carried out by treating the sheet at a temperature between 25 between 100 and 250 °C, typically between 120 and 200 °C. Although the temperature of 250 °C is higher to that of self-combustion of paper, a treatment at this temperature for very long times short is possible because the paper, as long as it is wet by the solution, is protected from the combustion. P024183IT-01 Notarbartolo & Gervasi SpA In this step, the liquid components of the solution (water, alcohols) are eliminated. added voluntarily or resulting from the hydrolysis of tetraalkoxysilanes or alkyl-trialkoxysilanes) and a layer of vitreous silica is formed; in the preferred case of using part of alkyl- trialkoxysilane, the glassy layer is not composed of pure silica but of a chemically modified silica 5 modified by the presence of alkyl groups bonded to part of the silicon atoms; this condition favors the flexibility of the glass layer. For simplicity, in the following we will only use the definition silica to indicate both pure silica (i.e., of exact composition SiO ) and silica modified. The paper obtained at this point in the process is impermeable to water, oils and fats, even at the temperatures of hot foods, and partly to gases. Figures 3 and 4 represent in 10 schematically, respectively, a sheet 3 covered with a silica layer 30 only on one face, and a sheet 4 covered with silica layers 30 and 30' on both faces. In step d) of the process of the invention two parts of the sheet, or two sheets, obtained in step c), they are placed next to each other. For simplicity, in the following with the definition of two parts that are joined or fixed together, it is understood that the two parts can be two 15 separate sheets (or parts of two separate sheets), or two portions of the same sheet. In the simplest case of forming sheets of greater thickness than the initial sheets, two or more sheets are simply overlapped in a coincident manner (i.e. such that no part of one sheet protrudes beyond the adjacent sheet). In the more industrially interesting case, where a shaped artefact has to be created 20 more complex, two parts of a single sheet are placed next to each other. The joining of the two parts must be done in such a way that each of the two turn towards the other a surface covered with a layer of silica obtained in the passage previous. In case only one surface of the sheet is covered with silica, the sheet must be folded in such a way that two edges of the same surface face each other; this 25 situation is schematically represented in Fig. 5, in which the area is shown in section of overlapping and adhesion of the folded sheet on itself. Most commonly, both surfaces of the sheet are covered with silica, and in this case the two parts can be simply superimposed obtaining a flat adhesion area; this situation is P024183IT-01 Notarbartolo & Gervasi SpA schematically represented in Fig. 6; in this figure, for clarity of representation, only the numerical references of the two silica layers 30 and 30' are shown which determine the adhesion of the two paper parts. Finally, in the last step of the invention process, e) in the area where they have been 5 the parts to be connected are placed next to each other and a treatment is carried out which causes the adhesion of the facing silica layers. The treatment can be a heat sealing, in which the area in which to obtain the adhesion It is compressed with suitable heated tools, for example a hot blade welder, pliers, jaws and the like. The temperature to which the silica must be brought is at least 100°C, 10 preferably between 120 and 200 °C, and the pressure exerted by the tool must be equal to the at least 300 N. Under these conditions, the time required to obtain the adhesion of the two surfaces is less than 1 s, and for the highest values ​​of temperature and pressure even less than 0.5 s. Alternatively, adhesion of the two silica-coated surfaces can be achieved by 15 ultrasonic treatment. In this case, a sonotrode with a surface that comes into contact with the paper having a shape corresponding to the adhesion area. The sonotrode It is the part of an ultrasonic welding apparatus that comes into direct contact with the part to be welded. welding and transfers the ultrasonic energy to said part. The use of the ultrasonic welding machine ultrasonic does not require the application of a temperature, and the part to be welded eventually 20 heats up due to mechanical agitation caused by vibration; the pressure to be applied with the ultrasound must be at least 150 kPa. The reasons why these treatments unexpectedly achieve the adhesion of the two silica layers, have not been clarified; it is possible to hypothesize that these two layers present on the their surface of free -OH groups, which during these treatments react with each other forming 25 Si-O-Si bridges between the two different silica layers, resulting in adhesion. Step e) can be repeated several times to obtain objects of complex shape. For for example, in the case of a glass, a first weld is made to fix the two together straight edges of a sheet shaped like a circular crown, obtaining a truncated cone P024183IT-01 Notarbartolo & Gervasi SpA with the two free bases; in a second step, with the same method, at the base of diameter a bottom is fixed, also made of silica-coated paper at least on a surface. In a second aspect, the invention concerns the artefacts that can be produced 5 with the process described above; these can be bags, envelopes, tea bags, trays, cutlery, capsules or other thermoformed products with complex geometries in which they are foreseen overlaps. For example, in the case of an envelope, this can be produced starting from a sheet of Fig. 3, folded on itself so that the two halves face each other surface with the silica coating, and welding the two sides perpendicular to the line of 10 folding. Other products, such as capsules and trays, can be produced by welding the silica-coated surfaces of previously shaped paper parts. The invention will be further described through the following experimental part. EXAMPLE 1 This example refers to the creation of a weld using thermocompression. 15 of modified silica coated coated paper. A solution was prepared comprising, by weight, 40% MTES, 20% TEOS and 40% water, to which 0.38% by weight of a 1 N HCl solution was added. The solution was applied with a hand felted roller on both surfaces of a sheet of commercial coated paper (Burgo 270) measuring 30 x 30 cm; the quantity of 20 applied solution, measured by weight difference before and after covering the sheet, was of approximately 10 g / m per side of the sheet. The sheet thus covered was dried in an oven for 2 minutes at 150 °C. The dry sheet was rolled up by overlapping the two short sides of the sheet by 0.5 cm and subjected to heat sealing treatment at 120 °C with a force of 500 N for 0.3 s with a 25 Twin 406 hot plate welders manufactured by Raima Srl of Cernusco sul Naviglio (ME). The welding efficiency was verified with tensile tests carried out according to the ® DIN EN ISO 1924-3 standard with an Instron 8801 instrument; in the test the P024183IT-01 Notarbartolo & Gervasi SpA two pieces of paper glued together and their resistance to detachment is evaluated. The test result was that the paper delaminated with an applied tensile force of 5.8 N, but the two edges welded they did not separate; this means that the weld resists tractions greater than the value detected. 5 EXAMPLE 2 Example 1 was repeated with the only difference that the welding was done with an ultrasonic welder PSX 20 from the Sonomax company of Fenegrò (CO), applying a force of 300 kPa for 0.3 s. During the tensile test the weld did not open, and instead delamination occurred. 10 of the paper when the tensile force has reached the value of 4.1 N.

Claims

P024183IT-01 Notarbartolo & Gervasi SpA 1. Process for the production of a paper product covered on at least one surface with siliceous material, said artifact comprising at least one gluing area of two areas of two sheets or of the same sheet of paper, said process comprising the following steps: a) prepare one or more sheets (1; 2) of coated paper on at least one side or of paper calendered or supercalendered, in which said one or more sheets are possibly shaped at any time before step d); b) cover at least one face of each of said one or more sheets of coated paper, calendered or super-calendered with a solution of one or more silica or silica precursors modified, with the condition that if the sheet of paper is coated on one side only, the the face covered with said solution is the patinated one; c) cause the sheet or sheets of paper covered with the solution to dry b), obtaining the formation of a layer of silica or modified silica (30, 30') on said face of one or more of the said sheets of paper; d) joining two parts of a single sheet or parts of at least two sheets, obtained in the step c), so that the contact areas of the said two parts of the single sheet or of the said at least two sheets are covered with the layer of silica or modified silica; e) subject the parts or sheets placed side by side to a heat compression treatment at a temperature of at least 100 °C by exerting a pressure of at least 300 N, or an ultrasound treatment that applies a pressure of at least 150 kPa, causing the adhesion of the interposed siliceous material.

2. Process according to claim 1, wherein said solution of one or more precursors of silica or modified silica includes a tetraalkoxysilane, an alkyl-trialkoxysilane, silica nanometric or a mixture thereof in a solvent consisting of water or a mixture hydroalcoholic.

3. Process according to claim 2, wherein said tetraalkoxysilane has general formula P024183IT-01 Notarbartolo & Gervasi SpA Si(OR) , where R is a C1-C4 alkyl radical, and said to be an alkyl-trialkoxysilane has general formula R'-Si(OR”), where R' and R”, equal or different from each other, are radicals C1-C4 alkyls.

4. Process according to any preceding claim, wherein when said one or more sheets must be folded, rolled or deformed after step b), said solution of one or more silica or modified silica precursors comprises at least one alkyl- trialkoxysilane.

5. Process according to any of the preceding claims, wherein said solution of silica precursors or modified silica comprises, by weight, between 35% and 45% CH - Si(OCH CH ), between 15% and 25% Si(O CH CH ), between 35% and 45% water, and an acid in 2 3 3 2 3 4 quantity sufficient to bring the pH of the solution into the range 2-3.

6. Process according to any of the preceding claims, wherein step b) It is made by dipping, spraying, brushing, flexographic printing or by passage of said one or more sheets of paper between two rollers, of which at least one is hollow, filled with the solution, and has a perforated cylindrical surface covered with felt to allow the passage of the solution from inside the cylinder towards said one or more sheets of paper.

7. Process according to any of the preceding claims, wherein step c) is produces by treating said one or more sheets at a temperature between 100 and 250°C.

8. Process according to any of the preceding claims, wherein said sheet of coated, calendered or supercalendered paper is shaped in the form of a crown section circular, such that the superposition of the two rectilinear sides gives rise to a shape three-dimensional truncated cone.

9. Paper product produced according to the method of any of the claims previous, chosen between a bag, an envelope, a tea bag, a tray, a cutlery or a capsule.