EP-4735689-A1 - METHOD FOR WATERPROOFING A LAYER OF PAPER

Abstract

The invention relates to a method for waterproofing a layer of paper, by using an aqueous dispersion comprising a combination of particles of a polyvinyl acetal-based resin and particles of a resin other than a polyvinyl acetal-based resin. It also relates to a bag comprising a layer of paper waterproofed by means of such a method, as well as to the use of such a bag for packaging materials in powder form, such as plaster or cement.

Inventors

• TEULERE, CORALIE
• RIEGERT, Maeva
• LEIVA MUÑOZ, Raul
• LOZE, Jacques
• Bequin, Philippe

Assignees

• Saint-Gobain Weber France
• Vicat

Dates

Publication Date

20260506

Application Date

20240627

Claims (16)

1. A method of sealing a paper layer, comprising applying an aqueous dispersion to a surface of said paper layer to form a coating, and drying said coating, wherein said aqueous dispersion comprises water, particles of a poly(vinyl acetal)-based resin, particles of a resin other than a poly(vinyl acetal)-based resin, one or more plasticizers, and one or more emulsifiers, wherein the total content of resin particles is from 5 to 50% by weight.
2. The method of claim 1, wherein the poly(vinyl acetal) based resin is poly(vinyl butyral) based.
3. The method of claim 2, wherein the poly(vinyl butyral) based resin comprises residual alcohol and acetate functions.
4. Method according to claim 2 or 3, in which the poly(vinyl butyral)-based resin comes from the recycling of laminated glazing.
5. Process according to any one of claims 1 to 4, in which said aqueous dispersion further comprises one or more crosslinking agents, preferably chosen from silanes, preferably from alkoxysilanes optionally comprising a functional group reactive with respect to carboxylic acid, carboxylate or hydroxy functions, such as an epoxy or amine group.
6. Method according to claim 5, in which the weight ratio between the content of crosslinking agent and the content of resin based on poly(vinyl acetal) is between 0.001 and 0.10, in particular between 0.002 and 0.06.
7. Process according to any one of claims 1 to 6, in which the aqueous dispersion further comprises one or more fillers, the filler content preferably being between 5 and 80% by weight, relative to the total weight of the dispersion.
8. A method according to claim 7, wherein the fillers are selected from calcium carbonate, calcium stearate, clays, talc, dolomite, mica, silica sands, ground basalt, barium sulfate, kaolin, and mixtures of two or more of these compounds.
9. A method according to any one of claims 1 to 8, wherein said resin other than a poly(vinyl acetal) based resin is selected from styrene-acrylic resins, styrene-butadiene resins, acrylic resins, alkyd resins, and a mixture of two or more of these resins, preferably from alkyd resins.
10. A method according to any one of claims 1 to 9, wherein the aqueous dispersion further comprises from 0.1 to 20% by weight of pigments, relative to the total weight of the dispersion.
11. Process according to any one of claims 1 to 10, in which the total weight content of emulsifier(s) is between 0.1% and 10%.
12. Process according to any one of claims 1 to 11, in which the weight ratio between the plasticizer content and the poly(vinyl acetal)-based resin content is between 0.1 and 1, in particular between 0.2 and 0.5.
13. Process according to any one of claims 1 to 12, in which the amount of water is between 10 and 70% by weight, in particular between 20 and 60% by weight, relative to the total weight of the dispersion.
14. A method according to any one of claims 1 to 13, wherein the weight ratio between the content of particles of resin other than a poly(vinyl acetal)-based resin and the content of particles of a poly(vinyl acetal)-based resin is between 0.05 and 20, preferably between 0.1 and 10, or even between 1.0 and 5.0.
15. A bag comprising a paper layer, and a sealing layer at least partially covering the paper layer, the sealing layer being formed by the method as defined in any one of claims 1 to 14.
16. Use of a bag as defined in claim 15, for packaging plaster or cement-based powders.

Description

Method for sealing a layer of paper The invention relates to a method for sealing a paper layer, using an aqueous dispersion comprising a combination of particles of a poly(vinyl acetal)-based resin and particles of a resin other than a poly(vinyl acetal)-based resin. It also relates to a bag comprising a paper layer sealed by means of such a method, as well as the use of such a bag for packaging materials in powder form, such as plaster or cement-based powders. Paper bags require protection against the penetration of atmospheric water vapor through the layers of the bag. Since paper is a porous and hydrophilic substrate, it is difficult to avoid the adsorption and transport of water or water vapor to prevent the loss of quality of the packaged materials. In particular, gypsum and cement powders can harden in the presence of water and thus lose their properties. Polyethylene plastic films are usually inserted between two plies of paper as a permeability barrier. However, due to their hybrid composition, these packaging bags are not recyclable. One strategy is to replace the current bags with a recyclable two-ply bag without a plastic-based sheet, in which one of the plies would have a very thin polymer-based coating, to ensure good water barrier properties. However, these coatings are typically based on petroleum resources, which contribute to global warming. From a sustainable perspective, there is growing interest in alternative films and coatings with similar sealing properties. In response to the demand for more environmentally friendly packaging materials, bio-based polymers have been used to replace petroleum-based coatings. Some of them show the ability to biodegrade or be compostable. Most of the bio-based polymers found in the literature consist of semi-crystalline polymers such as polyesters that are coated onto paper by extrusion or other high-temperature processes. The use of aqueous polyester dispersions allows for application at room temperature using conventional wet coating processes. Although this method allows for easier and more environmentally friendly application, it is necessary, after application, to heat the coating to a temperature above its melting point to obtain homogeneous films. Usually, the temperature of these bio-based polyesters is high and the process is not suitable for the paper application process, due to paper degradation or oven temperature limitation. In this context, the inventors have developed an aqueous dispersion overcoming the above-mentioned limitations. Specifically, they have demonstrated that an aqueous dispersion combining poly(vinyl acetal) resin particles, in particular poly(vinyl butyral), with other polymer resin particles, could be deposited on a paper substrate at room temperature, and form a coating offering very good barrier properties to liquid or vapor water. This invention is particularly relevant for paper bags used for packaging construction materials, such as cement or plaster powders, or any other moisture-sensitive product. Paper bags comprising such a coating also have the advantage of having a lower carbon footprint than the sealed paper bags currently used. Thus, the present invention relates to a method for sealing (in particular for water-proofing) a paper layer, comprising applying an aqueous dispersion to a surface of said paper layer to form a coating, and drying said coating, wherein said aqueous dispersion comprises water, particles of a poly(vinyl acetal)-based resin, particles of a resin other than a poly(vinyl acetal)-based resin, one or more plasticizers, and one or more emulsifiers, wherein the total content of resin particles is from 5 to 50% by weight. In some embodiments, the poly(vinyl acetal)-based resin is poly(vinyl butyral)-based. In some embodiments, the poly(vinyl butyral) based resin includes residual alcohol and acetate functionalities. In some embodiments, the poly(vinyl butyral)-based resin is derived from the recycling of laminated glazing. In certain embodiments, said aqueous dispersion further comprises one or more crosslinking agents, preferably chosen from silanes, preferably from alkoxysilanes optionally comprising a functional group reactive with respect to carboxylic acid, carboxylate or hydroxy functions, such as an epoxy or amine group. In some embodiments, the weight ratio of crosslinking agent content to poly(vinyl acetal) resin content is between 0.001 and 0.10, especially between 0.002 and 0.06. In some embodiments, the aqueous dispersion further comprises one or more fillers, the filler content preferably being between 5 and 80% by weight, relative to the total weight of the dispersion. In some embodiments, the fillers are selected from calcium carbonate, calcium stearate, clays, talc, dolomite, mica, silica sands, ground basalt, barium sulfate, kaolin, and mixtures of two or more of these compounds. In some embodiments, said resin other than a poly(vinyl acetal) based resin is selected from styre