Patent Application
20220275582
The invention relates to a method to manufacture and the use of metallized multilayer sheet material having a reduced Water Vapour Transmission Rate for use in packaging water sensitive equipment or foodstuff.
Nanometer vacuum deposition of metals, metal alloys and metal oxides onto impervious fossil-based plastic films has been well documented to improve oxygen and water vapour barrier properties.
However, the use of metallized impervious fossil-based plastic films has come under pressure due the slow biodegradability, and hence gives environmental concerns.
On permeable substrates, bio-based readily biodegradable, such as cellulosic fibrous papers, cellulosic films, polylactic acid and others, nanometer deposition of metals, metal alloys and metal oxides were much less effective than on plastic films in achieving water vapour and oxygen barrier levels sufficient for the food and sensitive instrument parts packaging industries where a WVTR (Water Vapour Transmission Rate) should be around 1 g/m2/day at 38° C. in a relative humidity (RH) of 90%. Impervious plastic films already have appreciable WVTR & OTR (Oxygen Transmission Rate) barrier properties prior to enhancement with nanometer metal deposition. Minimal damage occurs to the deposited metal barrier layer on films due to clean room handling and smooth backside surface contact upon winding prior to bare metal overcoating protection. Although vacuum deposition of layers of above 20 nm of metals, metal alloys and metal oxides onto permeable renewable biodegradable substrates can impart adequate water vapour barrier performance, acceptable barrier performances can be reached only by carefully selecting the best sampled areas with a high degree of homogeneity of metal layer and free of scratches through the metal layer. Moreover, even on those selected samples the variability in water vapour barrier loss due to imperfections in the metal layer increases to the extent of not meeting required packaging performance due to paper dust on the pre-metal surface falling off after metallization leaving a metal pinhole as well as metal layer damage from the rough paper backside abrasion upon winding prior to protective post-metal coating.
The applicant has therefore deemed it necessary to propose a new metallized material incorporating a permeable substrate, possibly bio-based biodegradable, having reduced water vapour transmission rate (WVTR) variability which meets required packaging performance.
To this purpose, the invention relates to a process for preparing a metallized multilayer sheet material for packaging having a WVTR of below 5 g/m/day at 38° C. RH:90% comprising:
Packaging here refers to wrapping, packing, overpacking or covering macroscopic objects or food products, sensitive to humidity and intends to exclude the micro or nanoelectronics applications.
The invention also relates to the product directly obtained by the process, which is a metallized multilayer sheet material having a WVTR of below 5 g/m2/day at 38° C. RH:90% comprising:
Preferably, when the sheet substrate has a rough surface, i.e. not smooth enough to reliably apply a homogeneous metallic layer, the sheet material of the invention further comprises a dried solvent based polymeric coating applied directly onto one or both sides of the sheet substrate wherein a metallized layer is applied (to the one or both sides). For example, the substrate could be smooth due to the presence of a permeable biofilm (bio-based polymers, like PLA films, cellulosic films or others . . . , preferably biodegradable) surface allowing for homogeneous metal deposition to be accomplished which is characterized by adequate adhesion.
Preferably, the metallized multilayer sheet material of the invention has a WVTR of below 3 g/m2/day at 38° C. RH: 90% and still preferably below 1.5 g/m2/day at 38° C. RH: 90%.
The steps of the method of the invention are not meant to be performed in the recited sequence. Metallization and polymer coating can be performed alternatively. Additional steps can also be performed. For example, several layers of solvent based coatings can be applied onto each other, to confer various properties to the material.
Furthermore, the metallized multilayer sheet material of the invention can also be obtained by laminating on top of each other two or more sheets, each sheet possibly containing none, one or more metallized layers. When using lamination, the material obtained comprises two water vapour permeable sheet substrates and at least two metallized layers.
Lamination can be performed with identical or different metallized sheets. When similar sheets are used, they can be assembled in a symmetrical or unsymmetrical manner.
In some embodiments, the metallized layers are on the same side of the substrate. In that case, a dried solvent based polymeric coating is applied directly onto the side of the sheet substrate wherein the metallized layers are applied. In other embodiments, the metallized layers are on opposite sides of the substrate. In that case, dried solvent based polymeric coatings are applied directly onto both sides of the sheet substrate wherein the metallized layers are applied.
The optical density (OD) of the cumulated metallized layers refers to an optical density measured without taking the substrate into account. The optical density is measured by the well-known method of measurement with a calibrated densitometer. Preferably, the cumulated metallized layers have an optical density (OD) comprised between 2.5 and 6.5, still preferably between 3 and 4. Preferably, the cumulated metallized layers have a thickness comprised between 15 nm and 100 nm, still preferably between 20 nm and 50 nm.
Typically, the water vapour permeable substrate has a water vapour barrier of over 150 g/m2/day at 38° C. and 90% RH, and still preferably 100 g/m2/day at 38° C. and 90% RH.
Depending on the nature of the water vapour permeable substrate, the process can comprise a first step of applying a solvent polymeric coating(s) onto one or both sides of the substrate, followed by a solvent evaporation step(s), prior to depositing a metallized layer. For example, when the substrate is a cellulosic paper or a substrate with a rough surface topology, it aids in achieving a smoothed continuous surface for improved adhesion and homogeneity of the deposited metallized layer. Some commercially available water vapour permeable substrates are already coated with a mineral filler in a latex binder matrix on one side (C1S) or on both sides (C2S) inline on the specialty paper products paper mills manufacturing equipment.
Preferably, the method of the invention comprise a first step of applying a solvent polymeric coating(s) onto one or both sides of the substrate, followed by a solvent evaporation step(s), prior to depositing a metallized layer, when the substrate is not already provided or acquired with such a layer, by the user of the method of the invention.
The solvent based coating refers to either a polymer dissolved in an organic solvent or an aqueous polymeric emulsion or dispersion when it is applied, and which is subsequently dried by evaporation of the solvent (organic, water or mixed), in order to achieve adequate adhesion of the metal and obtain the desired WVTR barrier performance. The top or outermost layer serves to protect the metal from a high propensity for abrasion damage, which would increase the variability of water vapour barrier performance.
The metallized multilayer sheet material of the invention can comprise more than two metallized layers, provided that a solvent based polymeric coated and dried layer(s) or the permeable sheet substrate is separating the two or more consecutive metallized layers, the outermost of which have a solvent based polymeric coated and dried protective layer(s).
The sheet substrate may be any suitable water vapour permeable material, preferably renewably sourced, flexible, for example paper which can be processed through production equipment applying coatings and metallization, as reels.
A metallized layer can be any metal selected from the group of aluminium, copper, tin, zinc, silver, gold, titanium, indium, silicon, and/or alloys and/or oxides and/or combinations thereof.
It is preferably deposited by vacuum deposition, or by any other relevant technique well known to the skilled in the art. The thickness of a single metallized layer is preferably not thinner than 5 nm, rather not thinner than 10 nm, and not thicker than 100 nm, and preferably rather not thicker than 50 nm or 30 nm, or even 15 nm. Ideally, it has an optical density of between 1.5 and 6.0, preferably between 2.0 and 4.5, and still preferably between 2.5 and 3.5.
The metallized layers can be the same or different.
A solvent based polymeric coating layer can be any suitable coating, know to a person skilled in the art, suitable for the purpose of the final product. They can for example be acrylic polymer based, polyester polymer based, nitrocellulose based, polyvinyl acetate based or others. Each dried solvent based polymeric coating thickness is above 0.3 μm. This coating serves to confer homogeneity to the surface of the substrate and impart adequate adhesion of the metallized layer.
Preferably, it has a gram per square meter of between 0.3 and 6.0 to ensure proper protection of the metallized layer, while ensuring the flexibility of the sheet material.
Water based polymeric emulsion and dispersion layers can be applied at a thickness of above 0.5 μm and below 10 μm. They can serve to bring additional barrier properties, other than water vapour barrier, to the material, such as mineral oil barrier, oxygen barrier properties or scuffing resistance.
The process of the invention enables to obtain a flexible material, suitable to wrap food products or water sensitive products. The biodegradable metallized multilayer sheet material of the invention should have a water vapour transmission rate (WVTR) below 5 g/m2/day at 38° C. RH:90%, and preferably below 2 g/m2/day and still preferably below 1 g/m2-day, and preferably in all areas of the finished reel utilized for producing packaging structures. Such a good water vapour barrier performance is reached by applying multiple metal layers (at least two), whose thicknesses sum is above 20 nanometres, separated by dried solvent based polymeric coatings.
It is well known in the field that an effective water barrier, on a water vapour permeable substrate, could only be achieved by the presence of a thick metallized layer having an optical density (OD) of above 2.4. However, the applicant has demonstrated that a statistically reduced variability of the water barrier properties over the area can be achieved by applying at least two distinct metallized layers, separated by solvent evaporated polymeric coatings and/or a substrate, having a final structure OD above 2.4 and preferably below 6.0.
The functionally increased water vapour barrier full surface area performance of the packaging material of the invention was hypothesized to come from the scientific concept that the individual localized areas of damage that may be present in a given metallized layer do not line up with those defects in the other metallized layer(s), thus creating a tortuous or impeded path for water vapour migration through the entire sheet structure.
The sheet material according to the invention is for use as packaging sheet, for example to package food material sensitive to humidity, or any non-food material also sensitive to humidity and/or oxygen, like chemicals, elements for electronic devices, or non-electronic devices. The packaging sheet of the invention can be used to manufacture any type of packaging like containers, boxes, bags, trays, bottles, cups, or having any shape for the intended application using usual techniques such as folding, cutting, gluing, heat sealing, pressing, etc . . . the only limitation being that the packaging manufacturing process should not degrade or alter the properties of the sheet. The packaging can be fully or partially made with the sheet material of the invention. It can for example be used for the whole box or for the sealing sheet of a tray or for the lid of a cup.
Such packaging can typically be cubic, parallelepiped, cylindrical, or have any other suitable shape. To manufacture of such packaging, the sheet of the invention can be reinforced with or associated to one or several additional layers, for example cardboard or paper, to ensure sufficient rigidity for conservation of the shape.
The invention will be better understood with the following description of several examples, referring to the accompanying drawing on which:
The metal layer used in the examples below is aluminium, the thickness of the metal layers has been correlated to the Optical Density, as well known to a person skill in the art (see for example McClure, D. J.; Copeland, N. Evaporated Aluminium on Polyester: Optical, Electrical, and Barrier Properties as a Function of Thickness and Time (Part II). Available online: httplidnn.convertingquarterly.com/Portals/1/files/matteucci-awards/2010-Evapourated-Aluminum-on-Polyester-p2.pdf)
The relationship between OD and thickness is not linear but is well established for a number of materials.
While OD can easily be measured for aluminium layers, as disclosed in the examples below, a person skilled in the art knows that other deposited layers, like for example metal oxides, for which their deposition thickness cannot be reliably quantified by OD measurement, other physical methods can be effectively applied to measure the thickness.
Units in g/m2/day is equivalent to g H2O/m2/day.
A multilayer metallized sheet material, according to the prior art, is prepared as follows:
This material represents the prior art, where only one thick metal layer is present in the sheet material, with an OD>2.5.
The material was characterized by WVTR values between 5.22 and 12.36 g-/m2/day, showing a variability (Δ)=7.14 g/m2/day with an average=8.56 g H2O/m2/day measured at 38° C. and relative humidity 90% on six selected samples.
A single metallized layer sheet material, according to the prior art, is prepared as follows:
This material represents the prior art, where only one thick metal layer is present in the sheet material, with an OD>2.5.
The material was characterized by WVTR values between 2.15 and 6.72 g/m2/day, showing a variability Δ=4.58 g H2O/m2/day with an average=4.81 g/m2/day measured at 38° C. and relative humidity 90% on six selected samples.
A multilayer metallized sheet material, as illustrated on
The total thickness of aluminium layers 4 and 6 amounts to an OD of 3.5-4.0. The material has WVTR values between 0.33 and 1.76 g/m2/day, showing a Δ=1.43 g/m2/day with an average=0.80 g/m2/day measured at 38° C. and relative humidity 90%, exhibiting superior average WVTR with significantly reduced variability among six randomly chosen test samples.
A multilayer metallized sheet material, as illustrated on
The total thickness of aluminium (
A multilayer metallized sheet material, comprising a sequence of layers as illustrated on
The total thickness of aluminium layers 4 and 6 amounts to an OD of 3.8-4.1. The material has WVTR values for the six random test samples was between 2.18 and 4.18 g/m2/day, showing a Δ=2.00 g/m2/day with an average=2.83 g/m2/day measured at 38° C. and relative humidity 90%.
A single metallized sheet material (Comparative example 3A), is compared to multilayer metallized on one side of the sheet, comprising a sequence of layers as illustrated on
This material represents the prior art, where only one thick metal layer is present in the sheet material. The material was characterized by WVTR values between 1.75 and >110 g (one sample over-ranged Permatran-W Model 3/61)/m2/day, showing a Δ>108 g/m2/day with an average>20 g/m2/day measured at 38° C. and relative humidity 90% on six random test samples.
Double metallization on one side with OD=4.9-5.4, sequence of layers as on
The material was characterized by WVTR values between 0.12 and 0.26 g/m2/day, showing a Δ=0.14 g/m2/day with an average 0.20 g/m2/day measured at 38° C. and relative humidity 90% with five random test samples.
Single metallization's on both sides with OD=6.3-6.8, sequence of layers as illustrated on
The material was characterized by WVTR values between 0.77 to 1.41 g/m2/day, showing a Δ=0.64 g/m2/day with an average 1.13 g/m2/day measured at 38° C. and relative humidity 90% with six random test samples.
Futamura NatureFlex™ Renewable and Compostable Cellulosic double-sided heat sealable coated NVS with WVTR=600 g H2O/m2/day at 38° C., 90% RH and OTR=5 cc O2/m2/day at 23° C., 50% RH packaging films, was prepared as follows:
Single metallized sheet materials, 30NVS or 23NVS, (comparative examples 4A and 4B) are compared to multilayer metallized on one side of the sheet material 30NVS (examples 4C and 4D) according to the sequence of layers illustrated on
Single metallization directly on raw base sheets 30NVS (two WVTR test samples) and 23NVS (two WVTR test samples) with OD=2.5-4.0
This material represents the prior art, where only one thick metal layer is present in the sheet material. The materials were characterized by WVTR values between 2.52 to 3.99 g/m2/day, showing a Δ=1.47 g/m2/day with an average 3.09 g/m2/day measured at 38° C. and relative humidity 90% with four test samples.
Single metallization on coated sheet OD=4.1-5.4, was prepared as follows:
This material represents the prior art, where only one thick metal layer is present in the sheet material. The material was characterized by WVTR values between 2.15 to 3.15 g/m2/day, showing a Δ=1.00 g/m2/day with an average 2.91 g/m2/day measured at 38° C. and relative humidity 90% with two test samples.
Double metallization on one side with first metal deposited directly onto the raw base with final substrate OD=2.7-3.8
The material was characterized by WVTR values between 1.23 to 1.32 g/m2/day, showing a Δ=0.09 g/m2/day with an average 1.27 g/m2/day measured at 38° C. and relative humidity 90% with two test samples.
Double metallization on one side with both metal layers deposited onto polyester polymer coated 30NVS with final structure OD=3.6-5.3
The material was characterized by WVTR values between 1.83 to 1.99 g/m2/day, showing a Δ=0.16 g/m2/day with an average 1.90 g/m2/day measured at 38° C. and relative humidity 90% with two test samples.
Single metallization's on both sides of 30NVS raw stock with OD=3.1-4.0 (
The material was characterized by WVTR values between 3.90 to 4.22 g/m2/day, showing a Δ=0.32 g/m2/day with an average 4.06 g/m2/day measured at 38° C. and relative humidity 90% with two test samples.
White Sack Kraft Paper 70 Gsm Non-Machine Finished, sheet material 5, high puncture resistance with final structure OD=3.3-4.4 (
The material was characterized by WVTR values between 1.31 to 3.56 g/m2/day, showing a Δ=2.25 g/m2/day with an average 2.21 g/m2/day measured at 38° C. and relative humidity 90% with six test samples.
A multilayer metallized sheet material, according to the prior art, is prepared as follows:
This material represents the prior art, where only one thick metal layer is present in the sheet material, with an OD>2.5.
The material was characterized by WVTR after folding according to the set method described as follows.
180° folding of metallized WVTR barrier papers single sheets and laminated structures was accomplished by the following procedure:
Resulting in values between 11.79 and 19.21 g/m2/day, showing a variability Δ=7.42 g/m2/day with an average=15.61 g/m2/day measured at 38° C. and relative humidity 90% on six selected samples.
A multilayer metallized sheet material, according to the prior art, is prepared as follows:
The total thickness of aluminium layers 4 and 6 amounts to an OD of 4.5-5.0.
The material has WVTR after folding according to the set method described for Comparative example 6 resulted in values between 2.84 and 7.19 g-/m2/day, showing a variability Δ=4.35 g/m2/day with an average=4.77 g-/m2/day measured at 38° C. and relative humidity 90% on six selected samples.
A multilayer metallized sheet material, according to the prior art, is prepared as follows:
This metallized paper was then laminated onto itself, such that the final structure further has, on top on the third layer, the following layers:
The total thickness of aluminium layers 54, 56, 54a and 56a amounts to an OD of 4.0-5.1. The material has WVTR values between 0.99 and 1.47 g-/m2/day, showing a variability Δ=0.48 g/m2/day with an average=1.22 g-/m2/day measured at 38° C. and relative humidity 90%, exhibiting superior average WVTR with significantly reduced variability among nine randomly chosen test samples.
A single metallized layer sheet material, according to the prior art, is prepared as follows:
This metallized paper has further been laminated to the polyester layer of a coated paper prepared as follows:
Note that layers #54a, 55a,56a, 57a, 56 and 57 in
The material was characterized by WVTR after folding according to the set method described at Comparative Example 6 resulting in values between 3.22 and 17.36 g/m2/day, showing a variability Δ=14.64 g/m2/day with an average=9.29 g/m2/day measured at 38° C. and relative humidity 90%.
A single metallized layer sheet material, according to the prior art, is prepared as follows:
This metallized paper has been laminated to itself, in a symmetrical manner, such that the final structure further comprises the following layers onto layer #55:
Note that layers #56a, 57a, 56 and 57 in
The material was characterized by WVTR after folding according to the set method described at Comparative Example 6 resulting in values between 1.48 and 4.88 g/m2/day, showing a variability Δ=3.40 g/m2/day with an average=2.59 g/m2/day measured at 38° C. and relative humidity 90%.
A multilayer metallized sheet material, according to the prior art, is prepared as follows:
This metallized paper has been laminated to itself, in a symmetrical manner such that the final structure has the following layers on top of layer #57:
The material was characterized by WVTR after folding according to the set method described at Comparative Example 6 resulting in values between 1.79 and 4.00 g/m2/day, showing a variability Δ=2.21 g/m2/day with an average=2.44 g/m2/day measured at 38° C. and relative humidity 90%.
Examples Summary Tables
These examples show that the multilayer metallized sheet materials of the invention enable to improve the WVTR along with reducing the variability over the surface of the material.
These examples show that the multilayer metallized sheet materials of the invention display low WVTR and low variability, both when the two aluminium layers are on the same side of the paper and on each side of the paper.
These examples show that the multilayer metallized sheet materials of the invention enable reduce the variability of WVTR over the surface of the material, whether the aluminium is deposited directly on the substrate or whether an intermediate layer is applied.
These examples show that the multilayer metallized sheet materials of the invention enable to improve the WVTR along with reducing the variability over the surface of the material, even after folding.
This example shows that the multilayer metallized sheet materials of the invention enable to improve the WVTR along with reducing the variability over the surface of the material, after lamination.
These examples show that the multilayer metallized sheet materials of the invention, obtained by lamination of two metallized sheet materials enable to improve the WVTR along with reducing the variability over the surface of the material, even after folding.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19189748.7 | Aug 2019 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/071671 | 7/31/2020 | WO |
