Technical field

The present disclosure relates to a device and a method for measuring absorption into a substrate due to surface condensation.

Background

Fiber-based material used in packages or cups for liquids or frozen food is usually provided with barrier coatings on the inside facing the packed item to protect the content, e.g. food content. The barrier coating applied on the inside makes the material resistant against e.g. liquids, grease and/or aroma and enables it to withstand the influence of the packed item on the packing material. The outside of the package facing the surrounding climate is subjected to e.g. water vapor and condensation that is formed on the surface due to temperature fluctuations or temperature differences between outside vs inside, e.g. when filled with content having a temperature lower than the surrounding). Commonly, therefore also the outside (the print side) of the package material is provided with a barrier coating to protect not only the packed item, but also the package itself from losing its shape and function.

Barriers are normally created by coating the fiber-based substrate with a composition which gives the substrate desired barrier properties. The most commonly used materials when forming a barrier on a fiber-based product, are polyolefins, such as polyethylene (PE) or polypropylene (PP). Today, also biobased versions thereof are used including other bio-based polymers such as PLA. Liquid packaging board is usually provided with polymer coating on both sides and often comes with an additional aluminum coating layer included in the inside barrier layer. Paperboard intended for cold cups is often provided with a polyolefin coating to provide a barrier both on the inside towards the liquid content and on the outer/print side to provide a barrier against moisture arising from e.g. condensation. Environmental concerns, increasing oil prices, improved recyclability and legislative requirements have created an interest in reducing the use of fossilbased barrier materials, and even eliminate laminate layers when possible to save resources and avoid, or at least minimize, plastic content. This has led to development of new packaging materials aiming to fulfill these demands, e.g. by removing at least the outer polyolefin coating.

Novel materials for packaging in its turn require new ways of evaluating their properties, such as barrier function, in order to test and optimize a substrate to the intended use (e.g. hot and cold cups, frozen food package, meat package, cool liquid containers etc.).

There is a need for a method to measure research development, benchmark internal initiatives and competitor solutions with a method that can give relevant data at different climates to meet customer needs.

Objects of the invention

It is an object of the present invention to provide an improved method and device for measuring amount of absorbed water into a packaging material, where such water has been produced for instance due to surface condensation. It is a further object of the present invention to provide a quick and reliable way of testing barrier materials in a standardized way.

The above-mentioned objects, as well as other objects that will be realized by the skilled person in the light of the present disclosure, are achieved by the various aspects of the present disclosure.

Summary of the invention

The objects of the invention are achieved at least partially by means of a device for determining the liquid absorption of a substrate, where said substrate comprises at least one liquid barrier layer, and said device comprises: -a receptacle for receiving a volume of matter, said receptacle comprising a closed proximal end (a bottom) and an open peripheral end (an open top/mouth), wherein said open peripheral end is arranged to receive a sample of the substrate;

-a retaining arrangement arranged to sealingly retain said sample at said open peripheral end; wherein said liquid barrier layer of the sample is positioned so as to face said receptacle, and wherein said sample substrate sealingly separates the inside volume of said receptacle from ambient air when retained by the retaining arrangement.

Said “volume of matter” herein refers to a content to be added to the receptacle so as to imitate a packed item. The volume of matter is a substance that has a defined mass, volume and temperature and may be in liquid or solid state. For example, said “volume of matter” may be liquid water or solid ice or a mixture of the two. Also other substances are conceivable for mimicking packed items such as fresh, frozen or canned food stuff and/or drinks, but is not limited to be foodstuff

The invention according to the present invention also relates to a method for measuring absorption into a substrate. Said method comprises the steps of: a. providing a device according to the invention; b. adding a volume of matter having a predetermined temperature to said receptacle; c. providing a sample of a substrate to be measured, wherein said substrate comprises a liquid barrier layer; d. positioning said sample substrate at said open peripheral end in such a way that the barrier-side of said sample is facing said receptacle; e. sealingly positioning said sample substrate at said open peripheral end by means of said retaining arrangement in such a way that said receptacle becomes sealed; f. placing said sealed device in a controlled environment/climate (e.g. in a climate receptacle) for a predetermined time period; and g. removing the sample from the device and measure the amount of liquid absorbed by said substrate during said time period. A standardized measuring method can be achieved by means of performing test series during the same controlled circumstances, such as e.g. adding the same predetermined volume of liquid having the same temperature; keeping the sealed device in the climate receptacle for a predetermined time period in the same ambient temperature and humidity, etc. For example, a common (non-limiting) setup for test in a climate receptacle is 38°C and 90% relative humidity (RH) for 300 seconds or 600 seconds.

Thanks to the invention, there is provided a quick and reliable way of measuring liquid absorption into a flat substrate. Being able to measure on a flat sample (i.e. not three dimensional) leads to several advantages such as low costs, short detection time and also the possibility of setting up a standardized testing scheme where flat samples of the same size and same preconditioning may be compared and evaluated. Furthermore, the device allows for measuring absorption into a substrate e.g. due to condensation on the outer surface of the substrate which, to our knowledge, is not previously suggested. The same device also allows for measuring absorption into the substrate by direct contact with water, meaning that the same device can be used for measuring water absorption both from the inside as well as from the outside of a packaging material (a sample substrate).

Moreover, the device allows for long-term conditioning of a substrate sample, that is, mimicking the conditions that a substrate with a barrier will be subjected to in reality such as being stored, shipped, and subjected to external temperature variations. Such conditioning may be performed by e.g. storing an assembled device with said sample attached to the liquid-containing receptacle for a pre-set period (such as a few days) in a controlled climate. The hereby conditioned sample may then be removed from the device and tested for selected properties such as water absorption, mechanical strength, oxygen transmission rate and/or vapor transmission rate.

Another advantage is that the measurement can be performed both in a horizontal as well as in a vertical position, depending on what package to simulate. In a vertical position, for instance, condensed water is allowed to run off the outer surface as to simulate what would happen e.g. with a cup that contains cold liquid in a hot and humid climate, and also include other impacts besides hydrophobicity, e.g. the effect of surface roughness and other surface features. Some surfaces may comprise a quality which retains water droplets created as a result of condensation, whereas other surfaces lead to that droplets are dispersed and/or roll off. In other words, the invention allows for measuring liquid absorption as well as properties related to liquid surface contact.

According to one aspect of the invention, the receptacle and retaining arrangement are made from metal material such as stainless steel or aluminum.

According to another aspect of the invention, said receptacle and retaining arrangement are made from plastic material.

According to another aspect of the invention, said receptacle and retaining arrangement are made from a combination of metal and plastic material.

According to another aspect of the invention, the receptacle is arranged with an isolating material. Hereby, heat diffusion through the receptacle material is prevented and thus temperature of the content inside the receptacle can be maintained for a longer time.

According to another aspect of the invention, the device comprises a temperature detecting sensor for continuously measuring the temperature in said receptacle.

The device according to any one of the previous claims, comprising a temperature regulating member arranged to keep the temperature inside said receptable at a predetermined level. For example, the device may be arranged with internal peltier cooler/s for electrically cooling the interior of said receptacle. Such a set-up allows for imitating a package containing cold or frozen items and detecting how a certain packaging material is affected in a specific climate. Cooling of the inside of the receptable in an assembled device also leads to cooling of the sample, and thereby to condensation at the side facing ambient air. The properties of the material when subjected to condensation can thus be measured. Other ways of regulating and/or controlling the receptacle inside temperature are conceivable. As an example, the temperature regulating member may be arranged with circulating fluid comprising a specific temperature in order to e.g. cool the receptacle interior.

According to another aspect of the invention, said receptacle has an inner volume between 0.001-10 Liters.

According to another aspect of the invention, the device comprises an arrangement for providing supplementary liquid to said receptacle after sealingly attaching and retaining said sample substrate at said open peripheral end. Hereby, it is possible to fill up the entire volume of the receptacle during measurement.

According to yet another aspect of the invention, said substrate is a flat sheet, such as a single-ply sheet, a multi-ply sheet or a film. Preferably, said substrate is a packaging material, i.e. intended for use in packages and/or cups for liquids or frozen food. Thanks to the invention, the effects of e.g. condensation on an outside surface of a packaging material can be evaluated, for instance by measuring liquid absorption of the substrate, without the need of converting the substrate into a product prototype. Insufficient barrier quality in a material intended for e.g. holding liquids leads to leakage/diffusion of water or moisture into the fiber material which in turn destroys the mechanical properties, making the product soggy and leads to a risk that the product becomes unstable and even may rupture. In a known instrument for testing of the grip strength of paper cups, a ready-made 3D cup of a selected material containing liquid is provided and placed in a test chamber wherein the cup is subjected to external pressing. The strength loss of the cup material after being subjected to condensation at set testing conditions can be detected by the instrument. However, this method is limited to 3D products which sometimes is inadequate, for example by limitation in production and converting of new types of material. The strength of a cup is very dependent on how the cup is formed, the dimensions, how the rim is formed and how it is sealed. Thanks to the present invention, however, a flat sheet of any packaging material can be tested for liquid absorption and/or to study effects on mechanical strength due to e.g. poor barrier quality. According to yet another aspect of the invention, the substrate is made from cellulose-based or lignocellulose-based material, such as any one of a packaging paper, a paperboard or a film.

According to yet another aspect of the invention, one side of the sample comprises at least one liquid barrier. According to one aspect of the invention, said liquid barrier layer is a water impermeable barrier layer. The term water impermeable is understood to refer to that said barrier prevents water from penetrating through. An example of a commonly used water-impermeable barrier is polyethylene coating on top of an aluminum foil, i.e. PolyAI barrier. However, many other barriers are conceivable. The side of the sample opposite of the barrier-side may or may not comprise a barrier layer.

According to yet another aspect of the invention, said substrate comprises a first liquid barrier layer arranged to face the receptacle when said sample is positioned as in step d) above, and a second barrier layer arranged to face the ambient air.

Brief Description of the Drawings

In the following, embodiments of the invention will be described with reference to the drawing, in which:

Fig. 1 is a perspective view of a partially disassembled device according to an exemplary embodiment of the invention;

Fig. 2 is another perspective view of a partially disassembled device according to an exemplary embodiment of the invention;

Fig. 3 illustrates an assembled device according to an exemplary embodiment of the invention, placed in a climate chamber;

Figs. 4A shows a schematic illustration of a side-view in cross section according to an exemplary embodiment of the invention; and

Fig. 4B displays a detailed view according to IVB in Fig. 4A.

Detailed Description of the Drawings The device and method according to the invention will now be described with reference to the appended figures.

Fig. 1 shows a perspective view of a partially disassembled device 1 according to an example of the invention, comprising a receptacle 3 which, in this example, is in the form of a cylindrical container having a closed base 30 and an open top 31 (also referred to as a closed proximal end 30 and an open peripheral end 31 respectively). The cylindrical container defines an inner chamber having a defined volume meaning it can receive and hold a defined volume of matter 4 in e.g. liquid or solid state. In the example seen in Fig. 1 , the receptable contains a defined volume of liquid water 4. A sample 2 of a substrate is also seen in Fig. 1 , which herein is a circular, flat piece of fiber-based material. The device 1 also comprises a clamping arrangement 5 and associated clamping devices 50 such as screws, shown in Fig. 2 and Fig. 3 respectively. As understood by the skilled person, other clamping devices than screws may be used. Said clamping arrangement 5 comprises a central opening 51 arranged to display the sample 2 when attached on the device 1.

When testing a substrate for liquid absorption, a sample 2 of said substrate is provided and placed at the top of the receptacle 3 such that the entire opening is covered by said sample. Said clamping arrangement 5 is positioned so as to clamp and retain the sample 2 between itself and the top of the receptacle 3 by a fastening pressure obtained by tightening said screws until said sample 2 sealingly separates the inside volume of said receptacle 3 from ambient air 6. In this assembled configuration, a first side of the sample 2 is subjected to the inside of the receptable 3 and an opposite second side of the sample 2 is subjected to ambient air 6 via said central opening 51 of the clamping arrangement 5.

Fig. 3 shows an assembled device 1 according to an example of the invention, wherein a sample 2 of a substrate to be tested is attached and retained on a receptacle 3 by means of a clamping arrangement 5 (also referred to as “retaining arrangement” 5), said receptacle possibly containing a volume of matter 4 such as water. The device 1 in Fig. 2 has been placed inside a climate chamber in a vertical position. “Vertical” herein refers to the position of the sample 2 retained by the device 1 , i.e. in Fig. 3 the device is placed so that the retained sample 2 is in a vertical position.

Figs. 4A-B show in a schematic way a cross-sectional side-view of an assembled device 1 in a vertical position. As shown herein, in particular in the detailed view of Fig. 4B, the surface of said sample 2 which is facing the receptacle 3 and the content 4 therein comprises a liquid barrier layer 7. This liquid-barrier side is supposed to mimic an inside of a package and is therefore referred to as the inside 20 of the sample 2. Accordingly, the side of the sample 2 opposite of the inside 20, facing the ambient air 6 when retained by the device 1 , is referred to as the outside 21 of the sample 2. The outside 21 of the sample 2 may or may not comprise a barrier 8.

The use and function of the device for determining liquid absorption of a substrate is now to be described, referring to Figs. 1-4.

A sample 2 of the substrate to be tested is provided and conditioned to get the correct starting weight, i.e., so all materials that are tested are in their equilibrium state. Suitable conditioning is performed in 23°C and 50% RH.

The substrate may be any material suitable for measuring liquid absorption such as fiber-based substrates including paper, board, films etc.

The substrate comprises a liquid barrier 7 on at least one surface 20 which corresponds to the surface intended to face the inside of a package after converting. Preferably, the liquid barrier 7 is a water impermeable barrier meaning that no water, or very limited amounts, can penetrate through. The skilled person understands that by “very limited amounts” in this context means that also reliable liquid barriers may have a minimal, yet present, water diffusion.

A device 1 according to the invention is provided and a predefined volume of matter is added into the receptacle 3. The volume of matter 4 may be in liquid or solid state or a mixture thereof, that is for instance liquid water or solid ice or water which contains ice. In order to set up a standardized test scheme, the temperature of the volume of matter 4 is regulated and/or controlled for instance according to a defined scheme. As an example, it may be that liquid water of a certain volume and temperature is mixed with a predetermined number of ice cubes of a specific size. This allows for comparison of test results of different samples. As an option to adding a volume of matter, the device 1 may be arranged with a temperature regulating member (not shown) whereby the temperature inside the receptacle 3 can be adjusted and controlled simulating a content having a certain temperature, e.g. frozen food content. Of course, it is possible to combine the addition of a content (volume of matter 4) with a temperature regulating member when designing a test set-up. A non-limiting example of a temperature regulating member is a peltier cooler.

A peltier cooler is based on the thermoelectrical phenomenon that direct current allowed to flow through different metals or semiconductors produces a heat pump that cools on one side of the element and heats on the other side. It is within the ambit of the present invention to modify the device 1 in such a way that a temperature regulating member, e.g. peltier element, is installed so as to cool the inside of the receptacle 3.

Said sample 2 is positioned at the open peripheral end 31 of the receptacle 3 in such a way that the inside 21 of said sample 2 is facing the inside of said receptacle. Next, the sample 2 is tightly sealed against the opening by means of the clamping arrangement 5 separating the inside volume of said receptacle 3 from ambient air 6. At this point, the testing device 1 is assembled and ready to be used for testing. Testing is initiated by means of placing the sealed device 1 in a controlled environment or controlled climate, such as in a climate chamber, for a predetermined period of time. A controlled environment such as a climate chamber provides predetermined climate conditions such as temperature and air humidity. After said predetermined period of time, the sample 2 is detached from the device 2 and the amount of liquid absorbed by the substrate is measured by means of weighing said sample 2 and calculate the result based on the weight difference between the weight at the start of the measurement and the weight after the predetermined period of time has passed.

The inventive test method allows for a number of different evaluations of material properties by simulating how a material absorbs moisture at a specific climate and with a specific temperature of the content inside a package. As an example, the liquid absorption due to outer surface condensation can be measured. This can be valuable information when developing packaging materials intended to hold cold/frozen content in warm and humid climate (e.g. tropical climate). Thanks to the present invention, such circumstances can be simulated in a controlled way and different materials with various outer surface qualities and surface treatments can be examined and compared in an early stage of the development using plain sheets, independent of different package/product design solutions, as shown in the Example 1 where two different surface treatments are compared.

As another example, the liquid barrier 7 facing on the inside surface 20 can also be evaluated for long-term diffusion from the content inside the package through the barrier 7 and into the bulk of the substrate.

As understood by the skilled person, the results from measurements will differ depending on surface weight and material thickness of the sample 2 since bulk density affects isolating property as well as heat transfer properties of the material. Such differences are, however, representing the reality and are to be taken into account when comparing various materials/barriers /surface treatments.

Example 1

A board material was subjected to two different surface treatments, both treatments aiming to achieve a hydrophobic surface to resist water absorption due to condensation. A flat sample sheet was cut out from each of the materials to be evaluated and each sample was conditioned in 23°C and 50%RH before initiating the measurements. The respective barrier qualities were evaluated by measuring liquid absorption, and untreated board material was compared with each of the two treated samples. Two measurement methods were used: standard Cobb (“Determination of water absorptiveness” - ISO 535:2014) for 300 seconds and evaluation according to the invention (the latter referred to as “Condensation Device” in Table 1 below). The results are shown in Table 1.

Both for standard Cobb and method according to the invention, the amount of liquid absorbed by the respective substrate was measured by means of weighing said sample and calculate the result based on the weight difference between the weight at the start of the measurement and the weight after a predetermined period of time has passed. After said predetermined test period, each sample was blotted to remove excess liquid and thereafter weighed. When comparing the samples by means of the standard Cobb measurement for 300 seconds, both samples showed the same result: 15 g/m ² However, when using the device according to the invention in a warm and humid climate (38°C/90 % RH) for 600 seconds, Surface 2 shows a better protection, with a Cobb-value which is half of the value obtained for Surface 1 .

Standard Cobb measurement is performed in a horizontal position and the whole surface is covered with water. With the device according to the present invention, the measurement was done in vertical position to mimic a standing paper cup containing cold water. This means both surface chemistry and surface structure impact water absorption, which better represents a real situation.

Table 1