Patent Application
20240401278
The present disclosure relates to the field of paper-based materials.
The current legislative trends regarding packaging are driving consumers and brands to change their packaging from plastic to paper. There are many large market segments where barrier papers are required to effectively replace traditional plastic packaging and demand for paper-based solutions is growing strongly. Examples include flow wrapped products, bags and other wrappings.
Flow wrapping is a horizontal-motion process in which products of any shape are wrapped in a wrapping material. It is used to pack single solid items, such as confectionery bars or multiple products already collated in trays. Traditionally, the wrapping material has been a clear plastic film or a printed opaque plastic film. The package resulting from the flow wrapping process has a longitudinal fin seal and end fin seals. The longitudinal fin seal is typically folded over so that the fin lies flat on the backside wall of the package rather than projecting from it.
The vertical form fill sealing (VFFS) machine is a type of automated assembly-line product packaging system. It is commonly used in the packaging industry for food and a wide variety of other products. The machine often constructs plastic bags out of a flat roll of plastic film, while simultaneously filling the bags with product and sealing the filled bags. Both solids and liquids can be bagged using this packaging system.
The present disclosure aims to provide a paper-based material that can replace plastic films in packaging in for example flow wrapping processes, sealed paper bags, e-commerce bags, tissue wrapping and bedding wrappings. The inventors have realized that such a paper-based material, to be commercially successful, should meet the majority, preferably all, of the following criteria:
Accordingly, the present disclosure provides the following listing of itemized embodiments:
(A % ash in B g/m2 base paper+X1% pigment in Y1 g/m2 in first coating layer+X2% pigment in Y2 g/m2 second coating layer)/Z g/m2; wherein
As a first aspect of the present disclosure, there is provided a coated paper product comprising:
The second coating layer is preferably applied on the first coating layer, i.e. directly on top of the first coating layer forming a dual superposed coating arrangement.
The paper substrate is typically a machine-glazed (MG) paper or a machine finished (MF) paper. The paper substrate may be calendered. The MG or MF paper is typically a kraft paper, and typically at least 80%, preferably at least 90%, by dry weight of the fibres used to produce the MG or MF paper are never-dried fibres (i.e. virgin fibres).
An MG paper has glazed side and a non-glazed side. The glazed side is the side that faced the Yankee cylinder (a polished metal cylinder sometimes referred to as a MG cylinder) used for drying the paper web in the MG papermaking machine. The contact with the polished metal surface during drying makes the glazed side smoother than the non-glazed side. Typically, the first coating layer is applied to the less smooth, non-glazed, side of the paper substrate. Onto the first coating layer, the second coating layer is applied. The opposite side, i.e. the smooth, glazed side, in such case is typically printed. It is beneficial to apply the coating on the non-glazed side to provide the glazed side for printing. The glazed side may be coated with a thin layer of starch (≤1 g/m2) for curl prevention. A lacquer may be provided on the optional print, e.g. to modify gloss, friction and/or release properties.
An MF paper is produced by a drying technique using a large number of smaller, steam-heated cylinders to dry the paper which is alternately wrapped one way and then the other way so that both sides of the paper receive the same finish. The finish on both sides of an MF paper is similar to the non-glazed side of an MG paper.
The paper substrate may have been treated in a size press or similar to smoothen the surface and thereby avoid too great penetration of the first coating layer into the paper substrate.
The grammage measured according to ISO 536:2020 of the paper substrate is typically 40-135 g/m2, 40-100 g/m2, such as 40-90 g/m2, such as 40-60 g/m2, such as 42-55 g/m2. A suitable density (measured according to ISO 534:2011) for the paper substrate is 800-900 kg/m3. A too low density is disadvantageous since such paper is too porous for application of a thin barrier.
Typically, if the paper is used for flow wrapping, a suitable thickness (measured according to ISO 534:2011) of the paper substrate is 50-64 μm, such as 52-61 μm. A too high grammage or thickness makes the paper not suitable for a flow wrapping process as the paper should be flexible.
The paper substrate may be bleached, e.g. has an ISO Brightness according to ISO 2470 of at least 77.
The first coating may comprise a rheology modifier to facilitate the coating operation. The first coating layer typically comprises pigment and the pigment is preferably talc and/or calcium carbonate (CaCO3).
Typically, at least 50% by weight of the total pigment content in the second coating layer is talc.
It is beneficial for combining coating ductility, barrier properties, non-blocking, recyclability, heat sealability and possibility to coat with a sealant layer that the first coating layer comprises EAA or VACA or SA or acrylic latex as well as talc and/or CaCO3 in the first coating layer and EAA as well as talc in the second coating layer, wherein the dry weight ratio of EAA to talc in the second coating layer is between 100:5 and 100:70. The first coating layer may also be free of pigments.
The first coating layer preferably comprises talc in a EAA or VACA or SA or acrylic latex to talc ratio of 100:30 and 100:110, such as between 100:30 and 100:75, or CaCO3 in a EAA or VAcA or SA or acrylic latex to CaCO3 ratio of 100:20 and 100:70, such as between 100:30 and 100:65. The dry weight ratio of EAA to talc in the second coating layer is preferably between 100:10 and 100:70, such as between 100:10 and 100:60, such as between 100:15 and 100:60, such as between 100:15 and 100:40. It is advantageous with such filler to EAA or VACA or SA or acrylic latex ratios in the first and second coating layers with respect to coating ductility, blocking, barrier properties and heat-sealability.
The coated paper product is typically heat-sealable. EAA is inherently heat-sealable and by addition of a dry weight ratio of EAA to talc in the second coating layer of between 100:5 and 100:70, this heat-sealability is typically maintained. A higher talc content impairs the sealability as well as the barrier crack resistance. Typically, the maximum heat seal strength measured according to ASTM F88 & EN 868-5 of the coated paper product is at least 2.8 N measured on a 15 mm test strip sealed for 0.5 s at 160° C., and 3 bar. This means that 2.8 N is required to separate the sealed strip. It is advantageous for the coated paper product to be heat-sealable in order to allow the formation of a flow-wrap packaging by sealing the paper to itself.
The second coating layer typically forms a surface to which a sealant layer can be applied, typically a cold-sealant layer. To facilitate the application of the sealant layer, the contact angle between water and the second coating layer surface is preferably less than 95°, such as less than 90°, such as less than 80°. The contact angle may be measured according to TAPPI T 558. This standard stipulates measuring the contact angle at different checkpoints. Suitably, the contact angle at the 1.0 s checkpoint is selected. Moreover, the contact angle between di-iodomethane (DIM) and the second coating layer surface is preferably less than 60° and the surface energy is at least 30 mJ/m2 at the 1.0 s checkpoint measured according to TAPPI T 558. The surface energy is derived from the contact angle measurements by plotting (1+cosθ)/2*(σL/σLd)1/2) vs (σLP/σLd)1/2, wherein θ is the contact angle formed between the liquid drop and solid surface, σL is the liquid surface tension, and superscripts d and p stand respectively for dispersive and polar components of the liquid surface tension. After plotting, the points are fitted to a straight line to calculate σsP and σsd from the slope and intersection with the vertical axis, respectively. σs is the solid surface free energy and the surface energy is the sum of σsP+σsd.
It is advantageous that the second coating layer typically can either be heat-sealed without the need for an additional sealant layer or coated by and sealed by an additional sealant layer, typically a cold seal layer.
The coat weight of the first coating layer is typically 4-10 g/m2. The coat weight of the second coating layer is typically 3-9 g/m2. There is preferably a higher coat weight of the first coating layer than the second coating layer. This is advantageous especially if the first coating layer comprises a higher filler content thereby making the first coating layer more economically favourable and environmentally friendly.
The grammage measured according to ISO 536:2020 of the coated paper product is typically 52-142 g/m2, 52-110 g/m2, such as 52-95 g/m2, such as 52-71 g/m2, such as 56-68 g/m2. A suitable density (measured according to ISO 534:2011) of the coated paper product is 950-1100 kg/m3. Typically, if the paper is used for flow wrapping, a suitable thickness (measured according to ISO 534:2011) of the coated paper product is 52-68 μm, such as 54-66 μm.
In a particularly preferred embodiment of the coated paper product the first coating layer comprises EAA to talc in a ratio of between 100:30 and 100:75 and the second coating layer comprises EAA to talc in a ratio of 100:15 to 100:40. Such embodiment is advantageous as it combines barrier properties, barrier crack resistance, blocking resistance, grease resistance, heat sealability and possible application of a sealant layer.
In another particularly preferred embodiment of the coated paper product the first coating layer comprises VAcA to pigment in a ratio of between 100:30 and 100:75 and the second coating layer comprises EAA to talc in a ratio of 100:15 to 100:70. Such embodiment is beneficial in terms of combining recyclability with barrier crack resistance, blocking resistance, low ash content and possible application of a sealant layer.
In yet another particularly preferred embodiment of the coated paper product the first coating layer comprises VAcA to pigment in a ratio of between 100:30 and 100:75 and the second coating layer comprises EAA to talc in a ratio of 100:15 to 100:40. Such embodiment is beneficial in terms of combining barrier crack resistance, blocking resistance, grease resistance, recyclability, low ash content and possible application of a sealant layer.
In yet another particularly preferred embodiment of the coated paper product the first coating layer comprises acrylic latex to pigment in a ratio between 100:30 and 100:110 and the second coating layer comprises EAA to talc in a ratio between 100:50 and 100:70. Such embodiment is beneficial in terms of combining mineral oil barrier properties as well as water vapour barrier properties with barrier crack resistance, blocking resistance, grease resistance, recyclability and possible application of a sealant layer.
As a second aspect of the present disclosure, there is provided a flow-wrapped product obtained by flow-wrapping a product in a coated paper product according to the first aspect, wherein the flow-wrapped product has a longitudinal fin seal and end fin seals.
The examples and embodiments discussed above in connection to the first aspect apply to the second aspect mutatis mutandis.
As a third aspect of the present disclosure, there is provided a sealed bag, such as a gusseted bag or a pillow bag, having a longitudinal seal and each end portion is sealed by a fin seal produced from a coated paper product according to the first aspect.
A filled gusseted bag is obtainable from a VFFS machine. Such bag has a longitudinal seal adhering two overlapping ends of the paper material to each other to form a lap seal. In an alternative embodiment of the filled bag, the longitudinal seal is a fin seal. Further, the bag has a top end sealed by a fin seal and a bottom end sealed by a fin seal.
A filled pillow bag is obtainable from a VFFS machine. Such bag has a longitudinal seal adhering two overlapping ends of the paper material to each other to form a lap seal. In an alternative embodiment of the filled bag, the longitudinal seal is a fin seal. Further, the bag has a top end sealed by a fin seal and a bottom end sealed by a fin seal.
The examples and embodiments discussed above in connection to the first and second aspect apply to the third aspect mutatis mutandis.
As a fourth aspect of the present disclosure, there is provided use of a coated paper product according to the first aspect for wrapping a product, such as flow-wrapping a product, in sealable paper bags, such as a gusseted bag or a pillow bag, in e-commerce packaging, in bedding packaging, such as pillow packaging, or in tissue wrapping.
The examples and embodiments discussed above in connection to the first, second and third aspect apply to the fourth aspect mutatis mutandis.
As a fifth aspect of the present disclosure there is provided a method of producing a coated paper product comprising the steps of:
In one embodiment, the method comprises drying between the application of the first coating layer and the application of the second coating layer. Drying is typically performed with non-contact drying, such as IR and/or hot air, or contact drying, such as a drying cylinder, or a combination of non-contact and contact drying.
The coating is typically conducted with blade coating. The coating may also be conducted with rod coating, air-knife coating, rotogravure coating and/or curtain coating. The first and second coating layers may be applied with the same coating technique or different coating techniques.
The first and second coating layers may be applied in-line (also referred to as on-line). In such case, the productivity is increased by eliminating the handling operations linked to off-line treatment and by eliminating, or at least reducing, the amount of waste. When an in-line process is conducted, the coating weight is typically below 10 g/m2 in both the first and second coating layers to allow for sufficient drying between coating steps as well as prior to reeling. A non-blocking coating is in such case also advantageous.
The examples and embodiments discussed above in connection to the first, second, third and fourth aspects apply to the fifth aspect mutatis mutandis.
A typical product to be flow-wrapped in the paper-based material of the present disclosure is a protein bar, a snack bar or a chocolate bar.
A typical product to be packed in a sealed barrier bag made from the paper-based material of the present disclosure are dry foods, such as confectionary or baked goods. Alternatively, the product is cosmetics and toiletries.
Coating of paper
Pigment (talc (Finntalc C15B2), kaolin clay (Barrisurf LX), CaCO3 (Setacarb HG-ME 75%)) was added to and dispersed in an ethylene acrylic acid (EAA) latex (Michem Flex HS 1130) having a solids content of about 45% or vinyl acetate acrylate copolymer (VAcA) latex (CHP 125) having a solids content of about 50% or acrylic latex (Rhobarr 214, DOW) having a solids content of about 45%.
A machine-glazed (MG) base paper produced from never-dried bleached SW pulp was coated on the non-glazed side with a pilot-scale blade coater for samples 1-17 & 20-23.
The properties of the MG base paper is shown in Table 1 below.
Two samples (sample 18-19) were produced by coating a machine finished (MF) base paper with a grammage of 70 g/m2 (sample 18) and a grammage of 80 g/m2 (sample 19) in the same way as on the MG base paper.
A first coating layer comprising latex and pigment (samples 1-16 & 18-22) or latex but no pigment (sample 17) was coated onto the paper. The coated paper was dried by IR and a drying cylinder. Thereafter a second coating layer comprising latex and pigment (samples 1-18 & 22-23) or latex but no pigment (samples 20-21) was coated so that the paper was coated on one side with a dual superposed coating. The coating was dried by IR, hot air and a drying cylinder. The composition of each coating is presented in Table 2.
To evaluate the barrier properties against water vapour, the water vapour transmission rate (WVTR) was measured according to ISO 15106-1 at 23° C., and 50% relative humidity (RH) as well as at 30° C., and 80% RH.
To evaluate mineral oil migration barrier properties, the hexane/heptane vapour transmission rate (HVTR) was measured. The determination of the hexane vapour transmission rate (HVTR) was performed in a permeability cup (evaporation chamber) with a sealable closure fixable with screws. The closure has an open surface area which is sealed with the barrier material. A volume of hexane or heptane (9-10 ml) is filled into the evaporation chamber onto a sponge (to reach a liquid/gas equilibrium as quickly as possible) and the weight of hexane/heptane vapour that goes through the exposed surface of a functional barrier, is expressed in gram per square meter of the surface area per day. The samples were prepared by using a punch and visually inspected to see that there were no surface defects or damages (e.g. creases or pin holes). Under controlled experimental conditions (23°±1° C., and 50+2% relative humidity), the paper sample was fixed into the closure head, the barrier coatings facing the inner side. The chamber was closed as quickly as possible. The filled evaporation chamber is then weighed after 1, 2, 4 hrs and 1 day. The HVTR was then calculated according to:
The results of WVTR and HVTR measurements are presented in Table 3 and the sample numbering is the same as in Table 2.
By measuring the folded oil resistance from the barrier side, the ductility is measured, i.e. how well the formed barrier resists cracking. The methods is described in detail herein.
Rape seed oil was mixed with 1% colorant (Sudan blue II) and stirred on a magnetic stirrer until fully mixed.
In a cobb ring a blotting paper was arranged with one paper sample on top of the blotting paper. The paper sample had the barrier coated side upwards. The coloured rape seed oil (10 ml) was dosed into the ring and evenly distributed over the paper sample immediately. After 2 minutes the paper sample was taken out from the ring and excess oil was removed with additional blotting papers and lint-free drying paper.
Within 10 minutes from the removal, the paper sample was scanned in a computer scanner and the number of visible blue dots counted manually. The blue dots appear where the barrier has cracked and oil could enter into the paper. The criteria for evaluation are shown in Table 4 below. The analysis was performed in triplicate and the presented result in Table 6 is the average result.
After coating of the paper with the first and second coatings layers the paper was reeled up. After about 24 h, the paper was reeled out and blocking was evaluated according to the following criteria presented in Table 4.
The maximum heat seal strength was measured according to ASTM F88 & EN 868-5 and settings were 0.5 s, 160° C., and 3 bar on 15 mm wide samples. The results are presented in Table 6.
A high barrier crack resistance in combination with blocking resistance as well as good barrier properties against both water vapour and mineral oil was obtained for both pigmented pre-coating (samples 11-16, 18-19 & 23) as well as a pre-coating free of pigments (sample 17). The same applies to the lower grammage MG paper (samples 11-17 & 23) as well as the higher grammage MF paper (samples 18-19), and heat-sealibilty was obtained independently of MG paper (samples 11-12) or MF paper (sample 18).
Water and di-iodomethane (DIM) contact angle was measured according to TAPPI T 558 on the surface of the second coating layer to evaluate the wetting of the surface. The surface energy is derived from the contact angle measurements by plotting (1+cosθ)/2*(σL/σLd)1/2) vs (σLP/σLd)1/2, wherein θ is the contact angle formed between the liquid drop and solid surface, σL is the liquid surface tension, and superscripts d and p stand respectively for dispersive and polar components of the liquid surface tension. After plotting, the points were fitted to a straight line to calculate σsP and σsd from the slope and intersection with the vertical axis, respectively. σs is the solid surface free energy and the surface energy is the sum of σsP+σsd.
The contact angle as well as surface energy reflects the ability of the surface to be coated, i.e. wetted, with a sealant layer. The measurement was conducted at the 1.0 s checkpoint. The results are presented in Table 7.
To further evaluate the possibility to coat the surface with an additional sealant, a cold-seal (Loctite Liofol CS 22-422, Henkel) was applied onto the second coating by using a lab rod coater. If a uniform coating was formed, i.e. did coating did not form pearls, the surface could be wet by the cold-seal.
The total surface energy is the key factor to wetting. Moreover, it is believed by the inventors that it is the top-coating that contributes the most to the total surface energy. A similar top-coat to that in samples 9-11 is therefore fair to assume that such top-coat is also wettable with a cold-seal.
The show through times of palm kernel oil is a measure of grease resistance and was measured according to Standard ISO 16532-1. Minimum time as well as average time are presented in Table 8.
The recyclability was measured according to PTS Method PTS-RH 021/97 and the results are presented in Table 8.
To fulfil food-grade packaging legislation in Italy it is required that the ash content is below 10%.
The ash content was calculated according: (3% ash in 48 g/m2 base paper+X1% pigment in Y1 g/m2 in first coating layer+X2% pigment in Y2 g/m2 second coating layer)/Z g/m2; wherein
The calculated ash contents are presented in Table 8.
There are four sublevels of recyclability (level A+, A, B, C). The result of the assessment according to the PTS Method PTS-RH 021/97 was that the coated paper product samples having a recyclability of at least 80% were classified as level A recyclable.
Both for the lower grammage MG paper and the higher grammage MF paper a level A recyclable classification was measured and obtained for samples 8, 12-16, 23 (MG paper) and 18 (MF paper).
| Number | Date | Country | Kind |
|---|---|---|---|
| 21199210.2 | Sep 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/076813 | 9/27/2022 | WO |
