Composite metal-coated polyester films with barrier properties

Abstract

This invention concerns composite metal-coated polyester films with good barrier properties relative to gases. More precisely, it concerns a biaxially drawn composite metal-coated film based on polyester and having improved barrier properties relative to gases, characterised in that it comprises a base polyester film of 5 to 50 μm, coated on one of its two surfaces with a deposit containing polyvinyl alcohol and a water dispersible copolyester with sulphonyloxy units, the deposit containing polyvinyl alcohol and a water dispersible copolyester which is itself coated with a metal deposit, said composite film having permeability to oxygen measured at 23° C. under 50% relative humidity, not more than 0.4 cm 3 /m 2 /24 h [cm 3 /m 2 24/h] composite metal-coated films have, besides their barrier properties, excellent resistance to mechanical stresses such as crumpling.

1 . A composite metallized film stretched biaxially, based on a polyester and having improved barrier properties to gases, characterised in that it includes a polyester film base of 5 μm to 50 μm, coated on one of its two faces with a layer including a polyvinyl alcohol which has an average degree of polymerisation in number equal to or in excess of 350 and a water-dispersible copolyester with sulphonyloxy residues, the layer including the polyvinyl alcohol and the water-dispersible copolyester being in turn coated with a metal layer, said composite film exhibiting a permeability to oxygen measured at 23° C. under a relative humidity of 50% (the measurements being carried out using an <<OXTRAN>> apparatus, type 300 H from the firm MODERN CONTROL INC.) equal to or lesser than 0.4 cm 3 /m 2 / 24 h.  
     
     
         2 . A film according to  claim 1 , characterised in that the polyester is selected from polyterephthalates or from polynaphthalene dicarboxylates of alkylene diols.  
     
     
         3 . A film according to  claim 2 , characterised in that the polyester is selected from polyterephthalates of ethylene glycol or of 1,4-butanediol and the copolyesters including at least 80% in moles of ethylene glycol terephthalate residues.  
     
     
         4 . A film according to one of  claims 1  to  3 , characterised in that the average roughness Rz of the film base (such as defined in standard DIN 4768) is lesser than or equal to 0.40 μm on the face of the film carrying the layer of the polyvinyl alcohol and of the water-dispersible copolyester and this face exhibits, on the average, not more than 20 peaks having a height equal to or in excess of 1 μm and not more than 150 peaks having a height comprised between 0.4 and 1 micrometre, per square millimetre, when the thickness of the layer including the polyvinyl alcohol and the water-soluble copolyester with sulphonyloxy residues is lesser than 0.6 μm.  
     
     
         5 . A film according to one of  claims 1  to  4 , characterised in that the face of the film base carrying the layer of the polyvinyl alcohol and of the water-dispersible copolyester has, on the average, not more than 20 peaks having a height equal to or in excess of 1 micrometre and no more than 100 peaks having a height comprised between 0.4 and 1 micrometre, per square millimetre.  
     
     
         6 . A film according to one of  claims 1  to  5 , characterised in that the water-dispersible copolyesters with sulphonyloxy residues combined with the polyvinyl alcohol in the coating is selected from copolyesters derived from at least one aromatic dicarboxylic acid and from at least one aliphatic diol, and carrying a plurality of sulphonyloxy groups of the general formula (I):  
       —(—SO 3 —) n M  (I)  
       in which n is equal to 1 or 2, M is a hydrogen atom, an alkali metal, an earth-alkali metal, a cationic ammonium or a cationic quaternary ammonium.  
     
     
         7 . A film according to  claim 6 , characterised in that the aromatic dicarboxylic acid used for preparing the water-dispersible copolyester is selected from terephthalic acid, isophthalic acid, orthophthalic acid, naphthalene 1,4-dicarboxylic acid and their mixtures.  
     
     
         8 . A film according to  claim 7 , characterised in that the aromatic dicarboxylic acid is selected from mixtures of terephthalic acid with one or several other aromatic dicarboxylic acids.  
     
     
         9 . A film according to  claim 8 , characterised in that the aromatic dicarboxylic acid is selected from mixtures of terephthalic acid with isophthalic acid.  
     
     
         10 . A film according to one of  claims 6  to  9 , characterised in that the amount of terephthalic acid expressed in moles is in the range from 20 to 99% of the total number of moles of non sulphonated diacids and in that the water-dispersible copolyester includes sodium 5-oxysulphonyl-isophthalate residues.  
     
     
         11 . A film according to  claim 10 , characterised in that the amount of terephthalic acid expressed in moles is in the range from 30 to 95% of the total number of moles of non sulphonated diacid.  
     
     
         12 . A film according to one of  claims 6  to  11 , characterised in that the diol entering into the composition of the water-dispersible copolyesters with sulphonyloxy groups, is selected from ethylene glycol, 1,4-butanediol, 1,5-butanediol, 1,3-propanediol, 1,2-propanediol, 2,2-dimethyl-1,3-propanediol (or neopentylglycol), 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol and cyclohexane dimethanol.  
     
     
         13 . A film according to  claim 12 , characterised in that the diol entering into the composition of the water-dispersible copolyester with sulphonyloxy groups, is selected from ethylene glycol and its oligomers.  
     
     
         14 . A film according to one of  claims 6  to  13 , characterised in that in the water-dispersible copolyester, the dicarboxylic acid residues with sulphonyloxy groups amount to 5-30 moles for 100 moles of the dicarboxylic acid residues.  
     
     
         15 . A film according to  claim 14 , characterised in that in the water-dispersible copolyester, the dicarboxylic acid residues with sulphonyloxy groups amount to 8-15 moles for 100 moles of the dicarboxylic acid residues.  
     
     
         16 . A film according to one of  claims 1  to  15 , characterised in that the coating of the polyvinyl alcohol and of the water-dispersible copolyester exhibits a weight ratio of the polyvinyl alcohol to the water-dispersible copolyester of 99/1 to 50/50.  
     
     
         17 . A film according to  claim 16 , characterised in that the coating of the polyvinyl alcohol and of the water-dispersible copolyester exhibits a weight ratio of the polyvinyl alcohol to the water-dispersible copolyester comprised between 97/3 and 80/20.  
     
     
         18 . A film according to one of  claims 1  to  17 , characterised in that the coating of the polyvinyl alcohol and of the water-dispersible copolyester has a thickness equal to or lesser than 3 μm.  
     
     
         19 . A film according to one of  claims 1  to  18 , characterised in that said composite film further carries on the free face of the coating of the polyvinyl alcohol and of the water-dispersible copolyester, a layer of polyvinyl alcohol.  
     
     
         20 . A film according to one of  claims 1  to  19 , characterised in that the metal layer, which is deposited on the surface of the coating of the polyvinyl alcohol and of the water-dispersible polyester not in contact with the polyester film or which is deposited on the free face of the additional layer of the polyvinyl alcohol, is made of a metal selected from aluminium, copper, chromium, nickel and silver.  
     
     
         21 . A film according to  claim 20 , characterised in that the metal layer, which is deposited on the surface of the coating of the polyvinyl alcohol and of the water-dispersible polyester not in contact with the polyester film or which is deposited on the free face of the additional layer of the polyvinyl alcohol, is made of aluminium.  
     
     
         22 . A film according to one of  claims 1  to  21 , characterised in that the thickness of the metal layer is in the range from 0.01 μm to 0.06 μm.  
     
     
         23 . A film according to one of  claims 1  to  22 , characterised in that the polyester base film is comprised of two layers exhibiting different roughnesses Rz.  
     
     
         24 . A film according to  claim 23 , characterised in that the dissymetric polyester film base is produced with a technique of co-extrusion of 2 polyesters having different filler contents and possibly including fillers of differing nature.  
     
     
         25 . A film according to  claim 24 , characterised in that the polyester used is the same for the two co-extruded layers and in that the layer receiving the polyvinyl alcohol layer is the less filled one.  
     
     
         26 . A process for the production of metallized composite films according to one of  claims 1  to  25 , characterised in that the polyester film base is coated on one of its faces with an aqueous solution including a polyvinyl alcohol having, in a 4% aqueous solution and at 20° C., a viscosity which is equal to or in excess of 4 mPa.s (measured using a Brookfield LV viscosimeter) and a water-dispersible copolyester, the coating of the polyvinyl alcohol and of the water-dispersible polyester being in turn coated, if desired, with an aqueous solution of a polyvinyl alcohol, and in that said coated film is subjected to a thermal treatment at a temperature equal to or in excess of 170° C. and in that a metal layer is deposited on the coating of the polyvinyl alcohol and of the water-soluble copolyester or, on the additional layer of polyvinyl alcohol when such a layer is provided.  
     
     
         27 . A process according to  claim 26 , characterised in that the face of the polyester film carrying the coating of the polyvinyl alcohol and of the water-dispersible copolyester exhibits an average roughness Rz (such as defined in standard DIN 4768) lesser than or equal to 0.40 μm and carries, on the average, not more than 20 peaks having a height equal to or in excess of 1 micrometre, and not more than 150 peaks having a height comprised between 0.4 and 1 micrometre per square millimetre, when the desired thickness of the coating including the polyvinyl alcohol and the water-dispersible copolyester is lesser than 0.6 micrometres.  
     
     
         28 . A process according to one of claims  26  or  27 , characterised in that the coating of the polyester film base with an aqueous solution of the polyvinyl alcohol and of the water-dispersible copolyester is carried out on line or as a separate operation.  
     
     
         29 . A process according to  claim 28 , characterised in that the coating is carried out on-line.  
     
     
         30 . A process according to one of  claims 26  to  29 , characterised in that the aqueous solution of the polyvinyl alcohol and of the water-dispersible copolyester is used at a concentration in the range from 1% to 20% in weight/weight.  
     
     
         31 . A process according to  claim 30 , characterised in that the aqueous solution of the polyvinyl alcohol and of the water-dispersible copolyester is used at a concentration in the range from 5% to 15% in weight/weight.  
     
     
         32 . A process according to one of  claims 26  to  31 , characterised in that the weight ratio of the polyvinyl alcohol to the water dispersible copolyester in the aqueous solution is from 99/1 to 50/50.  
     
     
         33 . A process according to  claim 32 , characterised in that the weight ratio of the polyvinyl alcohol to the water dispersible copolyester in the aqueous solution is between 97/3 and 80/20.  
     
     
         34 . A process according to one of  claims 26  to  33 , characterised in that the temperature at which the coated film is treated, is between 180° C. and 240° C.  
     
     
         35 . A process according to  claim 34 , characterised in that the temperature at which the coated film is treated, is between 200° C. and 230° C.