Barrier papers

Abstract

A barrier paper, preferably for use in tropical conditions, comprising, in this order: a paper-based substrate layer, comprising, in this order, a base paper layer, a first base paper overcoat layer comprising a polymer, a second base paper overcoat layer comprising a polymer, an inorganic layer, optionally, a protective layer comprising a polymer, characterized in that the paper-based substrate layer has a hygroexpansion of less than 0.5%, and preferably of 0.33% or less, and more preferably of 0.25% or less.

1 . A barrier paper, preferably for use in tropical conditions,
 comprising, in this order:
 a paper-based substrate layer, comprising, in this order, 
 a base paper layer, 
 a first base paper overcoat layer comprising a polymer, 
 a second base paper overcoat layer comprising a polymer, 
   an inorganic layer,   a protective layer comprising a polymer,   characterized in that the paper-based substrate layer has a hygroexpansion of less than 0.5%, wherein the polymer of the protective layer is a thermoplastic polyolefin chosen from polyethylene, polypropylene, ethylene vinyl acetate or ethylene acrylic acid copolymer.   
     
     
         2 . The barrier paper according to  claim 1 , wherein at least one chosen from the base paper layer, the first or second base paper overcoat, and the inorganic layer comprises aluminum (Al) or an oxide of aluminum. 
     
     
         3 . The barrier paper according to  claim 1 , wherein the polymer in the first base paper overcoat layer is present in an amount of 2 to 8 g/m 2  and/or wherein the polymer in the second base paper overcoat layer is present in an amount of 2 to 8 g/m 2 . 
     
     
         4 . The barrier paper according to  claim 1 , wherein the polymer in the first base paper overcoat layer is styrene-butadiene or styrene-acrylic, and wherein the first base paper overcoat further comprises mineral particles, wherein the mineral comprises aluminium (Al). 
     
     
         5 . The barrier paper according to  claim 1 , wherein the inorganic layer has a thickness of 5 to 250 nm, and wherein the inorganic layer comprises an inorganic material selected from the group consisting of metals, metal oxides, and non-metal oxides. 
     
     
         6 . The barrier paper according to  claim 1 , wherein the polymer in the second base paper overcoat layer is selected from the group consisting of polymers of vinyl alcohol, copolymers of vinyl alcohol mixtures of ethylene vinyl alcohol copolymer (EVOH) with a polysaccharide or a protein, proteins, and a polysaccharides. 
     
     
         7 . The barrier paper according to  claim 1 , wherein the barrier paper further comprises a graphic layer that is adjacent to the paper-based substrate layer, on the side opposite of the inorganic layer, and wherein the graphic layer comprises a mineral particles and wherein the mineral comprise aluminium. 
     
     
         8 . The barrier paper according to  claim 1 , wherein the second base paper overcoat layer is obtained by applying a same composition two or more times on the first base paper overcoat. 
     
     
         9 . The barrier paper according to  claim 1 , wherein the protective layer is heat-sealable and the protective layer is obtained by applying an aqueous composition comprising the thermoplastic polyolefin of the protective layer. 
     
     
         10 . The barrier paper according to  claim 1 , wherein the paper-based substrate layer and the inorganic layer are adjacent to each other and/or the inorganic layer and the protective layer are adjacent to each other. 
     
     
         11 . The barrier paper according to  claim 1 , wherein the base paper layer comprises kaolin particles. 
     
     
         12 . The barrier paper according to  claim 1 , wherein the barrier paper has a WVTR of less than 1 g/m 2* day at tropical condition when measured according to ISO 2528 at 38° C. and 90% relative humidity and/or a OTR of less than 1 cm 3 /m 2* day a when measured according to ISO 2528 at 38° C. and 50% relative humidity and/or an aluminium migration of less than 1 mg/l when measured according to EN 645:1994-01. 
     
     
         13 . A food packaging material comprising
 a barrier paper, comprising, in this order,   a paper-based substrate layer, comprising, in this order,
 a base paper layer, 
 a first base paper overcoat layer comprising a polymer, 
 a second base paper overcoat layer comprising a polymer, 
   an inorganic layer,   a protective layer comprising a polymer,   characterized in that the paper-based substrate layer has a hygroexpansion of less than 0.5%, wherein the polymer of the protective layer is a thermoplastic polyolefin chosen from polyethylene, polypropylene, ethylene vinyl acetate or ethylene acrylic acid copolymer   wherein the food packaging material is configured such that when the packaging material is in use the barrier paper is in direct contact with a food.   
     
     
         14 . A method of packaging food, the method comprising using a barrier paper comprising, in this order:
 a paper-based substrate layer, comprising, in this order,
 a base paper layer, 
 a first base paper overcoat layer comprising a polymer, 
 a second base paper overcoat layer comprising a polymer, 
   an inorganic layer,   a protective layer comprising a polymer,   characterized in that the paper-based substrate layer has a hygroexpansion of less than 0.5%, wherein the polymer of the protective layer is a thermoplastic polyolefin chosen from polyethylene, polypropylene, ethylene vinyl acetate or ethylene acrylic acid copolymer as a food packaging material.   
     
     
         15 . A process to produce a barrier paper, the process comprising
 providing a paper-based substrate layer,   applying to the substrate layer, in this order,   a base paper layer,   a first base paper overcoat layer comprising a polymer,   a second base paper overcoat layer comprising a polymer,   
       an inorganic layer, and 
       a protective layer comprising a polymer, and 
       in the drying section of a paper or paperboard machine equipped with a drying device:
 drying a dewatered paper base layer precursor, using the drying device, to form the paper base layer; or 
 drying a dewatered base paper layer precursor coated with a coating composition for the first base paper overcoat layer comprising a polymer, using the drying device, to form the base paper layer and the first base paper overcoat layer comprising a polymer, 
 wherein the drying device is configured to prevent drying shrinkage, and wherein preferably the drying device configured to prevent drying shrinkage is a Yankee dryer.