Waterproof paper-based tray and method of making such tray

Abstract

The present invention relates to a waterproof paper-based tray having a paper tray body comprising a paper panel having a load-bearing upper side and paper legs connected to the paper panel. The essence of the invention is that the whole outer surface of the paper tray body is provided with a coating formed by spraying a solvent-free polyurethane system, a polyurea system or a composite polyurea system. The invention also relates to a method for producing such a paper-based tray.

Description

Technical Field

[0001] The present invention relates to a waterproof paper-based tray having a paper tray body, the paper tray body including a paper panel having a load-bearing upper side and paper legs connected to the paper panel.

[0002] The present invention also relates to a method of manufacturing a paper-based tray. Background Art

[0003] Today, paper trays are becoming increasingly popular due to their low cost and ease of production. More and more manufacturers are now using paper tray production technology, which has the advantages of automation, precise dimensions, and the ability to use recycled paper as raw material, and the produced trays are cheap, lightweight, and recyclable. However, paper trays also have obvious disadvantages, such as:

[0004] - Sensitivity to water and moisture,

[0005] - Fragility,

[0006] - Limited lifespan due to the above reasons,

[0007] - Limitations in load-bearing capacity,

[0008] - Flammability.

[0009] Attempts are being made to address these disadvantages, but with limited success.

[0010] For example, common methods of improving water resistance / moisture resistance are to apply thin coatings, varnishes, paints, waxes. However, these solutions have limited use in eliminating water and moisture sensitivity. The main problem is the fragility of the surface, which is very likely to occur during use, and once damaged, it no longer provides waterproof and moisture-proof protection.

[0011] An example of using a waterproof coating can be seen in patent application CN100547157C.

[0012] Another common solution is to use shrink film. This provides a somewhat higher level of mechanical protection against damage, but it still does not meet the requirements of warehousing and transportation, and is not suitable for complete surface protection, i.e., it cannot protect the tray from moisture, high humidity, or condensation caused by temperature differences, for example, from below. In the case of a paper tray, this will result in a direct and measurable deterioration of quality / performance, and in most cases, render the tray unusable.

[0013] To prevent mechanical damage and increase load capacity, many manufacturers attempt to strengthen the load surface of the tray, for example, by adding additional paper layers. Using a thicker and denser distribution of legs is also used to increase load capacity. However, these methods increase the size and weight of the tray, while not significantly improving mechanical resistance and load capacity.

[0014] Hungarian Patent Application No. HU1700062A2 discloses a paper pallet which, under bending load, owes its specific load-bearing capacity to laterally arranged cross-reinforcing profile elements on the pallet base element, and the profile elements are hollow closed profile elements formed by folding cardboard. The load-bearing capacity of the paper pallet is improved by using forming elements in its structure, preferably designed with rolling-up devices, and its structural stability increases with the number of rolled-up plate elements. However, the resulting paper pallet still only has a load capacity of about 800 - 1,500 kg, which is generally insufficient for construction applications.

[0015] The above method does not solve or only slightly solves the flammability problem. Paper pallets are inherently flammable, and if necessary, chemical methods are used to reduce this flammability, but this does not help to overcome the other mentioned drawbacks, and the paper pallets lose their environmentally friendly characteristics and are likely to lose their recyclability. Summary of the Invention

[0016] The object of the present invention is to provide a paper-based pallet without the drawbacks of the prior art solutions. The object of the present invention is to provide such a solution that can eliminate the above-mentioned drawbacks (water and moisture sensitivity, mechanical fragility, low load capacity, flammability), while retaining the advantages of traditional paper pallets (low-cost production, low weight, recyclability).

[0017] The present invention is based on the recognition that by coating a traditional paper pallet body with a coating of a sprayable PU system with a thickness of a few millimeters, the resulting paper-based pallet not only has improved water resistance and reduced flammability, but also has a significantly increased static and dynamic load capacity, usually increased by at least 35 - 220%.

[0018] Based on the above recognition, the problem is solved by a waterproof paper pallet having a paper pallet body, which includes a paper panel having a load-bearing upper side and paper legs attached thereto. The present invention is characterized in that the paper pallet body has a coating of a synthetic polymer system around its entire outer surface, and the synthetic polymer system is selected from polyurethane systems, polyurea systems, and composite polyurea systems. The coating material is thus a solvent-free polyurethane system and / or polyurea system and / or composite polyurea system. These systems are hereinafter collectively referred to as PU systems, where PU can refer to solvent-free polyurethane, polyurea, and composite polyurea. Since polyurea systems and composite polyurea systems are also solvent-free, the PU system forming the coating according to the present invention is a solvent-free PU system. The coating is produced by spraying, and the spraying can be carried out with a high-pressure, heated spraying device capable of spraying a sprayable PU system. Therefore, in the context of the present invention, a sprayable PU system is understood to be a sprayable solvent-free PU system that can be used as a coating, but not a foam.

[0019] The PU coating preferably has a thickness of 1 - 8 mm, more preferably 1 - 5 mm, for example 1 - 3 mm or 3 - 5 mm.

[0020] The present invention also relates to a method for producing a waterproof paper-based tray according to the present invention, wherein a spraying machine is used to produce a PU coating with a thickness of preferably 1 - 8 mm, more preferably 1 - 5 mm, on the entire outer surface of the paper tray body from a sprayable PU system.

[0021] The inventors have also recognized that if more stressed parts of the paper body (such as the load-bearing upper side, legs, bending edges, glued joints) are reinforced with a fiber reinforcement material and a coating of the sprayable PU system is formed together therewith, so that the reinforcement material is embedded in the coating, the increase in load capacity is even more significant.

[0022] According to the above recognition, in a particularly preferred embodiment of the present invention, the fiber reinforcement layer is at least partially arranged on the upper side and / or legs and / or bending edges and / or glued joints of the paper panel of the paper tray body, and the fiber reinforcement layer is also coated with a PU coating.

[0023] The fiber reinforcement material is preferably selected from building facade nets, plastic nets, glass nets, glass fabrics, glass fibers, metal wool, steel cord, carbon fiber reinforcement materials, carbon fibers, hemp fibers, and chopped glass fiber reinforcement materials.

[0024] An alternative way of using the fiber reinforcement material is to mix the fiber reinforcement material into the sprayable PU system. This can be technically achieved by mixing the fiber reinforcement material into the spray stream of the sprayable PU system during the spraying process.

[0025] It has been further recognized that in order to ensure proper waterproofing of the hollow layered paper material in the case where there are gaps between layers (for example, in the case of single-layer or multi-layer cardboard paper, where corrugated paper separates flat paper layers), the outward-facing cut edges of the paper tray body (i.e., providing the outer surface) must be sealed, otherwise the sprayed PU system will diffuse into the gaps at the cut edges and a solid waterproof surface will not be formed. Based on this recognition, if the material of the paper tray body is preferably multi-layer cardboard with a hollow structure, the cut edges forming the outer surface of the paper tray body are covered with an edge covering element, and the covering element is also coated with a PU coating. Particularly preferably, the covering element is a layer including a fiber reinforcement material having perforations with a diameter of up to 5 mm. If the paper tray body is made of pressed non-hollow paper, the cut edges forming the outer surface do not need to be covered for the waterproofing of the PU coating, but it may be advantageous to increase the load capacity. In addition, the pressed paper can have deeper grooves, which are also beneficial for covering with the covering element and spraying a PU coating on top of the covering element.

[0026] Due to the extremely short setting time of the PU system that can be used as the coating of the present invention (less than 60 seconds, usually 10 - 30 seconds), the PU system is sprayed with a heated spraying device under high pressure, preferably at 140 - 250 bar, usually 160 - 210 bar. With this spraying device, the spraying is usually carried out at a temperature of 40 - 90 °C, preferably 60 - 80 °C. Description of the Drawings

[0027] Further details of the present invention will be described with reference to the accompanying drawings. In the drawings:

[0028] Figure 1 is a perspective top view of an exemplary, state-of-the-art paper tray;

[0029] Figure 1a is according to Figure 1 a schematic side view of the longer side of the paper tray body;

[0030] Figure 1b is according to Figure 1 a schematic side view of the shorter side of the paper tray body;

[0031] Figure 2a schematically shows the position of the sprayed PU coating according to the present invention around Figure 1a the outer surface of the paper tray body in the

[0032] Figure 2b schematically shows the position of the sprayed PU coating according to the present invention around Figure 1b the outer surface of the paper tray body in the

[0033] Figure 3a shows the position of an exemplary covering element of the paper-based tray according to the present invention on Figure 1a the outer cutting edge of the paper tray body in the

[0034] Figure 3b shows the position of an exemplary covering element of the paper-based tray according to the present invention on Figure 1b the outer cutting edge of the paper tray body in the

[0035] Figure 4a shows the preferred position of the layer of the paper-based tray according to the present invention, the layer of which contains a fiber-reinforced material on Figure 1a the outer surface of the paper tray body in the

[0036] Figure 4b shows the preferred position of the layer of the paper-based tray according to the present invention, which Figure 1b contains a fiber-reinforced material on the outer surface of the paper tray body in the Detailed Description of the Invention

[0037] Figure 1 A perspective view of an exemplary state-of-the-art paper pallet body 10 is shown, in this case the paper pallet body 10 is the paper pallet disclosed in Hungarian patent application HU1700062A2. Other views of such a paper pallet can be found in the publication of HU1700062A2.

[0038] To more easily distinguish the paper pallet according to the present invention from the paper pallet used as the initial paper pallet, the initial paper pallet is referred to as the paper pallet body.

[0039] The paper-based pallet according to the present invention can be manufactured starting from any paper pallet body, not just from Figure 1 the paper pallet body 10 exemplarily shown therein.

[0040] The paper pallet body 10 includes a paper panel 12, the paper panel 12 having a load-bearing upper side 11 and paper legs 14 connected thereto. It should be noted that the panel 12 and the legs 14 can also be formed as a single element (integrally), which is common, for example, in the case of a pressed paper pallet, but according to the functions performed, a distinction can be made between the panel 10 having the load-bearing upper side 11 and the legs 14 connected thereto.

[0041] In this embodiment, three rectangular legs 14 extend parallel to the longest side of the panel 12 (which is also the longest side of the paper pallet body 10). The legs 14 have a base plate 15 and side walls 17, in which two through openings 18 are constructed. The forks of a forklift can be guided through the through openings 18 in order to move the paper pallet body 10. The panel 12 has covering flaps 12a on the longer sides and covering flaps 12b on the shorter sides, which are folded and glued to the legs 14. The covering flaps 12a, 12b are bounded by cutting edges 13, which define a part of the outer surface of the paper pallet body 10.

[0042] According to Figure 1 the paper pallet body 10 of Figure 1a and 1b is schematically shown in side view from the longer side and the shorter side respectively.

[0043] Figure 2a and 2b show the paper-based pallet 20 according to the present invention in views corresponding to Figure 1a and 2b where the starting point is the paper pallet body 10 according to Figure 1 . In the pallet 20 according to the present invention, there is a spray-applied PU coating 21 with a thickness of 1 - 8 mm, which is formed by a sprayable PU system surrounding the entire outer surface of the paper pallet body 10, the profile of which is shown in Figure 2a and 2bis schematically shown by a dashed line therein. In Figure 2a and Figure 2b the PU coating 21 covers the entire surface within the contour indicated by the dashed line (except for the through-opening 18). The outer surface of the paper tray body 10 is any surface that comes into contact with the external environment, and thus the PU coating 21 also covers the inner sidewall 17 of the leg 14 and the surfaces that define the through-opening 18, as well as the side surfaces not shown in the figure.

[0044] Several types of sprayable PU systems are known, and all of them are suitable for producing the PU coating 21 according to the present invention. Examples of such sprayable PU systems are:

[0045] · Sprayable solvent-free polyurethane systems, including, for example:

[0046] - Sprayable solvent-free TDI (toluene diisocyanate) or MDI (methylene diphenyl diisocyanate) polyurethane systems (composition: isocyanate + polyol)

[0047] · Sprayable polyurea systems (composition: isocyanate + amine), including, for example:

[0048] - Sprayable TDI (toluene diisocyanate) or MDI (methylene diphenyl diisocyanate)

[0049] polyurea systems (composition: isocyanate + amine)

[0050] · Sprayable composite polyurea systems (composition: isocyanate + polyol + amine), including, for example:

[0051] - Sprayable TDI (toluene diisocyanate) or MDI (methylene diphenyl diisocyanate)

[0052] composite polyurea systems (composition: isocyanate + polyol + amine)

[0053] The sprayable PU system according to the present invention is a two-component system and is solvent-free. There are also sprayable polyurethane systems containing solvents, but the inventors have found that the solvents in the sprayable polyurethane systems containing solvents (usually in an amount of 30 - 40% by weight) "migrate" into (enter) the structure of the paper after spraying and weaken the strength of the adhesive there, as well as weaken the structural integrity of the paper by wetting. In addition, even after drying, the solvents do not completely disappear from the coating and the paper structure, which also adversely affects the paper structure and the combined load-bearing capacity of the paper and the coating.

[0054] This effect does not occur with the solvent-free PU system, and therefore, the load-bearing capacity of the paper-based tray coated with the solvent-free PU system will be significantly better.

[0055] We note here that the polyurea systems and composite polyurea systems according to the invention are also solvent-free. The polyurea system consists of an isocyanate + amine complex and is solvent-free. In the case of the composite polyurea system (isocyanate + amine complex + polyol), the alcohol (polyol - various types and / or various alcohols) cannot be considered a solvent (although in fact in many cases alcohols are used as solvents), because here the polyol is a natural part of the system and, in terms of its function, it is a chain-forming material rather than a solvent. The composite polyurea system is also solvent-free.

[0056] Solvent-free polyurethane systems, polyurea, and composite polyurea systems are essentially systems with a rapid setting time (short pot life / open time), with a setting time usually less than 60 seconds, and on average 10 - 30 seconds. To produce the PU coating 21 according to the invention, a sprayable PU system with a setting time of 10 - 30 seconds is preferably used.

[0057] The sprayable PU system is sprayed onto the outer surface of the paper tray body 10 by using a suitable high-pressure heated spraying machine. The spraying is preferably carried out at a pressure of 140 - 250 bar, preferably 160 - 210 bar, with a spraying device heated to 40 - 90°C, preferably 60 - 80°C. The technology of spraying the PU system is well-known (for example, see: "The Scheer Polyurethane Handbook", Dr. Michael Scheer, CRC Press, 2013), and for this purpose, many types of spraying machines are commercially available. Suitable spraying machines include those from the manufacturer GRACO, such as the Reactor E-XP2 (which is a high-pressure, heated spraying machine with a nozzle optimized for elastomer systems). This spraying device separately heats (separately from each other) the two components that make up the PU system and transports them to the spray head, where they are mixed due to high-pressure spraying, and the chemical reaction begins, which produces a bond that cures the PU system in a very short time (less than 60 seconds, usually 10 - 30 seconds).

[0058] The thickness of the resulting PU coating 21 can be controlled in a known manner by adjusting the spraying flow rate, spraying distance, and spraying pattern, as well as by repeating the spraying process, which allows the PU coating 21 of the required thickness to be constructed from several spray layers.

[0059] If the material of the paper tray body 10 is a multi-layer cardboard with a hollow structure, which has a cut edge 13 forming the outer surface of the paper tray body 10, then in order to ensure sufficient waterproofness, it is preferable to cover the cut edge 13 with a covering element 23 before forming the PU coating 21, as Figure 3a and 3bAs shown, a sprayable PU system is sprayed onto the outer surface of the covering element 23 using a spraying machine such that the coating 21 is placed on the covering element 23 at the cutting edge 13. If the covering element 23 is not used, the sprayed PU system can be sprayed into the inner cavity of the multi-layer cardboard at the cutting edge, and either a very large amount of PU must be sprayed on the cutting edge 13 to fill the cavity structure, which makes production more expensive, or the sprayed PU system does not form a solid waterproof surface.

[0060] It should be noted that the cutting edge 13 can be elsewhere, for example along the facing edge of the through-opening 18, which is not visible in the two side views. All cutting edges 13 are covered by the covering element 23, which will prevent or complicate the waterproofing of the PU coating 21.

[0061] Anything that can seal the gap leading to the hollow interior of the cardboard can be used as the covering element 23. The covering element 23 can be, for example, the paper itself, which is glued to the cutting edge 13, or it can be, for example, a self-adhesive tape, etc. In a preferred embodiment, the covering element 23 is a layer containing a fiber-reinforced material, such as a building facade mesh, a plastic mesh, a glass mesh, a glass fabric, glass fibers, metal wool, steel cord, a carbon fiber-reinforced material, carbon fibers, hemp fibers, a cut glass fiber-reinforced material. When using a layer containing a fiber-reinforced material as the covering element 23, it should be noted to ensure that the fiber-reinforced material preferably has perforations with a diameter not greater than 5 mm, because in the case of overly large perforations, the covering element 23 does not perform its function and it cannot properly cover the gap in the inner hollow structure of the paper material.

[0062] If the material of the paper tray body 10 is pressed paper, which is not hollow, then the cutting edge 13 forming the outer surface does not need to be edge-covered for the watertightness of the PU coating 21, but this is also beneficial for increasing the load-bearing capacity.

[0063] In addition to the cutting edge 13 with a hollow structure, there may be other openings on the commercially available paper tray body 10 leading to internal cavities or grooves, the surfaces of which cannot be properly coated by spraying technology through the openings. It is also desirable to cover these openings with a covering element 23 of appropriate size before spraying the PU system. The openings 18 for the forks of the forklift are not included here because they are large enough to allow the surfaces adjacent to the openings 18 to be sprayed. Of course, if there are additional openings on these boundary surfaces leading to cavities that cannot be accessed by the spraying machine, these additional openings must also be covered with a covering element 23 of appropriate size.

[0064] Figure 4a and 4bAn embodiment is shown in which, in order to increase the static and dynamic load-bearing capacity, the parts of the paper tray body 10 that are exposed to greater stress (for example, on the load-bearing upper side 11 of the panel 12, on the lower side of the base plate 15, along the legs 14, especially along the curved edges and glued joints) contain layers 25a, 25b, 25c of fiber-reinforced material for reinforcement, and a sprayable PU system is sprayed on their outer surfaces such that the PU coating 21 not only surrounds the outer surface of the paper tray body 10 but also surrounds the layers 25a, 25b, 25c containing the fiber-reinforced material.

[0065] In addition to the reinforcement positions mentioned by way of example, the layers 25a, 25b, 25c containing the fiber-reinforced material can be used elsewhere, but it is also possible to use only one or the other of the shown layers 25a, 25b, 25c. The reinforcement positions should be selected according to the required application.

[0066] In this case, the fiber-reinforced material is preferably also a building facade net, a plastic net, a glass net, a glass fabric, glass fibers, carbon fiber reinforcement, or chopped glass fiber reinforcement.

[0067] The layers 25a, 25b, 25c containing the fiber-reinforced material can also be used as the covering element 23, provided that the perforations are small enough to form a continuous PU coating 21 due to spraying on the outer surfaces of the layers 25a, 25b, 25c. Of course, it is also possible to use the layers 25a, 25b, 25c containing the fiber-reinforced material and the covering element 23 in combination. In this case, there is no need to pay attention to the size of the perforations in the layers 25a, 25b, 25c containing the fiber-reinforced material because there is the covering element 23 or the outer surface of the paper tray body 10 itself below, so a solid and continuous PU coating 21 is produced overall by spraying.

[0068] An alternative way of using the fiber-reinforced material is to add the fiber-reinforced material to the sprayable PU system during the spraying process. This is technically achieved by introducing a fiber-reinforced material stream into the spray jet of the sprayable PU system. Suitable spraying machines are commercially available. For example, the FRP Chop system of GRACO Inc. is such a chopped fiber spraying / feeding device. The fiber-reinforced material mixed into the sprayable PU system can be combined with the previously proposed techniques. Therefore, for example, by using the covering element 23 and / or the layers 25a, 25b, 25c containing the fiber-reinforced material, a tray 20 with an even higher load capacity can be obtained.

[0069] In order to determine the characteristics of the tray 20 according to the present invention, a number of experiments were carried out in two test phases.

[0070] The first test phase

[0071] In the first test phase, as a first step, the inventors checked whether the PU coating 21 could be properly applied to the paper surface and whether it adhered properly. To do this, several different qualities of PU coatings were developed on cardboard, which is hereinafter referred to as paper. The PU systems used were solvent-free TDI / MDI polyurethane systems, pure polyurea systems, and composite polyurea systems.

[0072] First, it was found that the PU systems had excellent adhesion to paper without any surface preparation. The two layers "fused" together.

[0073] Then, the inventors tested the water resistance of the PU-coated paper. The prepared PU-coated and uncoated papers were placed in a sealable plastic container of about 0.125 m 3 and then a commercially available evaporator was placed beside them, and a humidity of about 90% was generated in the test space, where the coated and uncoated papers spent 24 hours under these conditions. The effects of water vapor were studied using both subjective and objective methods.

[0074] Within the framework of the subjective test, the inventors checked the perceptible properties (feel / texture / strength) of the PU-coated paper taken out of the steam chamber compared to the paper without the PU coating. It was found that although the uncoated paper became wet, wavy, and also softened, no changes were found in the PU-coated paper compared to the conditions before the steam chamber.

[0075] In the objective study, the tensile strengths of the PU-coated and uncoated papers from the steam chamber were compared with their tensile strengths measured before the steam chamber. It was found that before being treated in the steam chamber, the tensile strength of the PU-coated paper increased by about 7 times compared to the uncoated paper. After the steam chamber, the tensile strength of the uncoated cardboard decreased to almost zero, while the tensile strength of the PU-coated cardboard did not change after spending 24 hours in the steam chamber.

[0076] Overall, it was found that all the types of PU coatings tested provided almost 100% moisture protection for the paper surface in the moisture chamber, while the uncoated paper was not suitable for use as a paper tray.

[0077] Then the PU-coated paper was subjected to further mechanical tests.

[0078] In this case, the abrasion resistance was tested, and it was found that the PU-coated paper actually provided the abrasion resistance expected of the PU coating.

[0079] Since preventing surface rupture will be particularly important for paper trays, the present inventors conducted drop ball tests on coated and uncoated paper before and after the steam chamber to test this. To measure the relative tolerance to point loads, the present inventors statically and then dynamically loaded a test sample weighing 1 kg and having a base size of 1 cm onto the experimental cardboard by dropping the test sample from a height of 1 m onto the surface. 2 After repeating the test 50 times, the inventors observed the percentage of cases that resulted in permanent deformation or rupture. The results are summarized in the following two tables:

[0080] Title Rupture - Static Load Uncoated Dry Paper Permanent Deformation ~10% / Rupture 30% Uncoated Paper, after Steam Chamber Rupture 100% PU Coated Paper Permanent Deformation 0% / Rupture 0% PU Coated Paper, after Steam Chamber Permanent deformation < 5% / Rupture < 10%

[0081] Table 1

[0082] Table 1 clearly shows that the PU coating significantly increases the protection against permanent deformation and rupture caused by point static loads. It can be considered a significant result that while in a total of 40% of the cases, the uncoated paper tested suffered permanent deformation or rupture under static point loads, no such deformation or rupture was observed for the PU-coated paper. It should also be noted that the uncoated paper was 100% permeated due to moisture, while when the PU coating was applied, this value dropped below 10%.

[0083] Title Rupture - Dynamic Drop from 1m Height Uncoated Dry Paper Permanent Deformation ~30% / Rupture 70% Uncoated Paper, after Steam Chamber Rupture 100% PU Coated Paper Permanent Deformation 10% / Rupture 10% PU Coated Paper, after Steam Chamber Permanent Deformation 10% / Rupture 10%

[0084] Table 2

[0085] The results of the series of dynamic drop tests summarized in Table 2 show even more significant results. Even under dry conditions, the untreated paper still had a measured rupture rate of 70%, while the PU-coated paper showed a rupture rate of less than 10%. In addition, when exposed to the steam chamber, the crack resistance of the PU-coated paper did not change.

[0086] From the above, it can be concluded that by applying the PU coating, the life cycle of conventional paper can be significantly extended even when the paper is used in a humidity-protected place. In highly humid and moist environments, the PU coating is essential for ensuring sufficient mechanical protection.

[0087] Second test phase

[0088] After that, in the second test phase, trays 20 with a PU coating 21 according to the invention obtained by spraying are tested. In this second test phase, the inventors coated commercially available 5-layer paper trays with different PU coatings 21 in different ways (with and without reinforcement) and with different layer thicknesses (single layer with a thickness of 1 - 3 mm and double layer with a thickness of 3 - 5 mm). The resulting paper-based trays 20 provided with a PU coating 21 are tested under industrial conditions, and comparative tests are carried out on the initial paper trays without a coating and with various other types of coatings. The other coatings tested are: solvent-based polyurethane coating, varnish coating, polyurethane paint coating. The test results are presented in Figure 5 In.

[0089] The paper-based trays according to the invention are sprayed with various polyurea and composite polyurea systems of ERA polymers in various thicknesses, and further for comparison, with a commercially available solvent-based polyurethane system named ERASPRAY ES81A HB system, with Borma shellac-type paint, and with solvent-based polyurethane paint. Due to spraying non-uniformity, in the case of a single layer, the thickness of the PU coating 21 varies between 1 mm and 3 mm, so the average thickness of the PU coating 21 is about 2 mm, and in the double layer, the thickness of the PU coating 21 varies between 3 mm and 5 mm, so the average thickness is 4 mm. A series of experiments are carried out with polyurea and composite polyurea systems of various hardnesses.

[0090] During the tests, paper trays of the standard EUR tray size made of 5-layer cardboard are used. These trays are coated with various polyurea and composite polyurea materials using high-pressure heated spraying equipment.

[0091] Check the load-carrying capacity of the coated trays: static load-carrying capacity, dynamic load-carrying capacity, and shelf load-carrying capacity.

[0092] - Static load-bearing capacity test: When the tray stands on a flat surface, the maximum load-carrying capacity of the tray is tested using standard measuring equipment, and the maximum load when the tray does not suffer permanent deformation is measured.

[0093] - Dynamic load-bearing capacity test: The load on the tray is increased on a vibrating table, and the maximum load at which the tested tray does not suffer permanent deformation is measured.

[0094] - Shelf load-bearing capacity test: This test is the same as the static load test, but in this case, the trays stand on a metal frame corresponding to a "typical" shelf system, i.e., they are not supported in the middle.

[0095] In the comparative tests, the solvent-based polyurethane was also applied in a single layer (1 - 3 mm thickness), and the other two comparative coatings were applied in a conventional manner, the varnish in a single layer thickness (30 - 120 microns) and the polyurethane paint in two layer thicknesses (100 - 300 microns). In this way, the above three types of tests were carried out on both the coated trays and the reference uncoated trays.

[0096] For a series of experiments, trays 20 were also produced, starting from 5 - layer paper trays, and chopped glass fibers were added to the PU coating 21 during spraying, thus obtaining a glass fiber-reinforced PU coating 21.

[0097] Thereafter, the behavior of the initial 5 - layer paper trays, the trays 20 formed therefrom according to the invention, and the trays with other coatings produced for comparison were examined under operating conditions.

[0098] Using the paper - PU composite system, the static, dynamic and shelf load - bearing capacities of the tested paper trays have been increased to such an extent that the trays are now suitable for any general transportation and storage tasks.

[0099] Using the single - layer PU coating 21 according to the invention, compared with the original paper trays, the static load - bearing capacity increased by 33 - 65%, and in the case of applying a second layer, the static load - bearing capacity increased by up to 15%. There was an even more significant improvement in the dynamic load - bearing capacity. In the case of applying only one layer, the dynamic load - bearing capacity increased by 47 - 116%, and the second layer led to an additional 10 - 20% increase. The greatest improvement occurred in the shelf load - bearing capacity: applying only one layer of the PU coating increased the shelf load - bearing capacity by more than 97%, and when applying two layers, we even experienced a 230% increase. The glass fiber reinforcement greatly increased each type of load - bearing capacity. Even when applying a single - layer PU coating, the inventors measured a 109% increase in the static load - bearing capacity, a 323% increase in the dynamic load - bearing capacity, and a 291% increase in the shelf load - bearing capacity.

[0100] On the other hand, it is clear from the comparative measurements that the paint layer and the two - layer traditional polyurethane paint hardly led to any improvement. The paint layer did not increase the measured load - bearing capacity by even 1%, and in the case of the polyurethane paint, the static load - bearing capacity and the shelf load - bearing capacity increased by about 1%, and even the dynamic load - bearing capacity increased by only 7%.

[0101] The coatings produced by the two - component solvent - based polyurethane system also significantly lagged behind the polyurea and composite polyurea coatings of the same thickness. Here, the static load - bearing capacity increased by 19%, the dynamic load - bearing capacity increased by 15%, and the shelf load - bearing capacity increased by 69%. The significant differences are largely due to the adverse effects of the solvents as described above.

[0102] In all cases, several longer tests are carefully carried out at each stage.

[0103] Summary of Results

[0104] The PU coating 21 according to the invention provides sufficient moisture protection for the paper. The inventors found that the water resistance / moisture protection of the tray 20 with the PU coating 21 (without a damage coating) can be up to 100%.

[0105] The inventors observed a significant improvement in the load-bearing capacity of the paper. As a result of the tests, it was found that with the coating system of the invention, even without fiber reinforcement, the inventors achieved an increase in the static load-bearing capacity of the test trays by 33 - 70%, an increase in the dynamic load-bearing capacity by 47 - 224%, an increase in the shelf load-bearing capacity by 97 - 230%, and the inventors minimized the possibility of mechanical damage to the trays, thus increasing the expected lifespan and the number of cycles spent in use.

[0106] In general, it can be concluded that even at a layer thickness of a few millimeters, the PU coating 21 formed by spraying increases the load-bearing capacity of the initial paper tray body 10 in an unexpected way, which can be further increased by using fiber reinforcement materials, without a significant increase in the weight of the tray 20. The tray 20 also becomes waterproof, and due to the continuous PU coating 21 completely surrounding the outer surface of the paper tray body 10, the flammability of the tray 20 is significantly reduced. The production cost only increases moderately, which is easily compensated for by the increased cycle time of the tray 20 and its wider applicability due to its higher load-bearing capacity.

[0107] Various modifications to the embodiments disclosed above will be apparent to those skilled in the art without departing from the scope of protection determined by the appended claims.

Claims

1. A waterproof paper-based tray with a paper tray body, the paper tray body comprising a paper panel having a load-bearing upper side and paper legs connected to the paper panel, characterized in that, The paper tray body has a coating of a sprayable synthetic polymer system formed by spraying around its entire outer surface, wherein the synthetic polymer system is selected from a solvent-free polyurethane system, a polyurea system, and a composite polyurea system.

2. The waterproof paper-based tray according to claim 1, characterized in that, The paper tray body is made of multi-layer cardboard with a hollow structure, wherein the cutting edges of the cardboard material forming the outer surface of the paper tray body are covered with edge covering elements, and the covering elements are also coated.

3. The waterproof paper-based tray according to claim 2, characterized in that, The covering element is a layer of fiber-reinforced material having perforations with a diameter of up to 5 mm.

4. The waterproof paper-based tray according to claim 1, characterized in that, The paper tray body is made of pressed paper or multi-layer cardboard.

5. The waterproof paper-based tray according to any one of claims 1 to 4, characterized in that, The fiber-reinforced layer is at least partially provided on the upper side and / or legs and / or curved edges and / or glued joints of the paper panels of the paper tray body, and the fiber-reinforced layer is also coated with a coating.

6. The waterproof paper-based tray according to claim 3 or 5, characterized in that, The fiber-reinforced material is selected from building facade nets, plastic nets, glass nets, glass fabrics, glass fibers, metal wool, steel cord, carbon fiber-reinforced materials, carbon fibers, hemp fibers, and cut glass fiber-reinforced materials.

7. The waterproof paper-based tray according to any one of claims 1 to 6, characterized in that, The fiber-reinforced material is added to the sprayable synthetic polymer system during spraying.

8. The waterproof paper-based tray according to any one of claims 1 to 7, characterized in that, The coating thickness is 1 to 8 mm, preferably 1 to 5 mm.

9. A method for producing a waterproof paper-based tray with a paper tray body, the paper tray body comprising a paper panel having a load-bearing upper side and paper legs connected to the paper panel, characterized in that, The coating is produced by spraying a sprayable synthetic polymer system around the entire outer surface of the paper tray body, wherein the synthetic polymer system is selected from a solvent-free polyurethane system, a polyurea system, and a composite polyurea system.

10. The method according to claim 9, characterized in that, The paper tray body is made of multi-layer cardboard material with a hollow structure, and before forming the coating, the cutting edges forming the outer surface of the paper tray body are covered with edge covering elements, and the sprayable synthetic polymer system is sprayed onto the outer surface of the covering elements.

11. The method according to claim 10, characterized in that, The covering element is a layer of fiber-reinforced material having perforations with a diameter of up to 5 mm.

12. The method according to claim 9, characterized in that, The paper tray body is made of pressed paper or multi-layer cardboard.

13. The method according to any one of claims 9 to 12, characterized in that, A layer comprising a fiber-reinforced material is at least partially arranged on the upper side and / or legs and / or curved edges and / or glued joints of the paper panels of the paper tray body, and the sprayable synthetic polymer system is sprayed onto the outer surface of the layer comprising the fiber-reinforced material.

14. The method according to claim 11 or 13, characterized in that, The fiber-reinforced material is selected from building facade nets, plastic nets, glass nets, glass fabrics, glass fibers, metal wool, steel cord, carbon fiber-reinforced materials, carbon fibers, hemp fibers, and cut glass fiber-reinforced materials.

15. The method according to any one of claims 9 to 14, characterized in that, During the spraying of the synthetic polymer system, a fiber-reinforced material, preferably cut glass fiber, is added to the spray stream of the synthetic polymer system.

16. The method according to any one of claims 9 to 15, characterized in that, The coating thickness is 1 to 8 mm, preferably 1 to 5 mm.

17. The method according to any one of claims 9 - 16, characterized in that, The synthetic polymer system is sprayed under high pressure, preferably at a pressure of 140 - 250 bar, more preferably at a pressure of 160 - 210 bar.

18. The method according to claim 17, characterized in that, The synthetic polymer system is sprayed with a spraying device heated to a temperature of 40 - 90 °C, preferably 60 - 80 °C.

19. A waterproof paper-based tray, which has a paper tray body, the paper tray body comprising a paper panel having a load-bearing upper side and paper feet connected to the paper panel, characterized in that, It is produced by the method according to any one of claims 9 to 18.

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