Method for producing reusable and compostable lids made of natural fibres and low-temperature-resistant lids obtained using the method

Abstract

The invention relates to a method for producing reusable, recyclable and compostable lids made of natural fibres, with improved mechanical strength and sufficient detachment force such that the lid can be firmly secured without using additional fastening means and can be used over multiple use cycles, the structural rigidity thereof being preserved. The invention also provides lids resistant to low-temperature storage conditions, which maintain their structural rigidity even when exposed to sudden changes in temperature and humidity and which can be reused without losing their original shape.

Description

[0001] METHOD FOR PRODUCING REUSABLE AND COMPOSTABLE LIDS MADE OF NATURAL FIBERS AND LOW TEMPERATURE RESISTANT LIDS OBTAINED BY SAID METHOD

[0002] Field of Invention

[0003] The present invention relates to a method for producing reusable lids made of natural fibers, resistant to moisture and low temperatures, and more particularly relates to a method for producing biodegradable and compostable lids made of natural fibers, which allows obtaining lids with high resistance, adapted to be firmly secured to the containers where they will be used. Additionally, the present invention relates to biodegradable and compostable lids made of natural fibers, which can withstand multiple cycles of use without affecting the correct coupling of the lid and which are also resistant to low temperatures and humidity.

[0004] Background of the Invention

[0005] Caring for the environment is a necessity that is becoming more and more aware of every day, not only because pollution has an impact on health, but also because it is a factor causing various effects, including, for example, the alteration of ecosystems and climate change. Although there are various sources of pollution, in recent years special attention has been paid to plastic pollution. In modern life, plastics are present in the transportation, packaging, textile, cosmetic, electrical, construction, agricultural, medical, machinery, equipment, and packaging industries, to name a few uses.Plastic production and consumption have grown exponentially worldwide since the 1950s and are expected to triple by 2060 if activity continues as it is (OECD, Global Plastics Outlook: Economic Drivers, Environmental Impacts and Policy Options (Paris, OECD Publishing, 2022)). One of the sectors that generates the largest amount of single-use plastic waste in the world is the packaging sector, which produces more than 280 million tonnes of short-lived plastic products annually that end up in the trash.

[0006] Because packaging and packing are necessary for products to be handled, stored and sent to the final consumer in adequate conditions, there has been a concern both to develop better logistics processes in the supply chain, and to produce quality packaging that guarantees that the products will be in perfect condition for as long as necessary until they reach the final user.

[0007] The increase in waste generation and the saturation of storage spaces (landfills) have led to the search for options such as reuse and recycling; however, these alternatives have proven insufficient to counteract the environmental impact caused.

[0008] Product containers are mostly objects intended to be used only once, since the end consumer generally discards them once the contents have been removed. More recently, the use of reusable containers has been encouraged in order to avoid the generation of pollutants and a large amount of waste; however, even when using reusable containers, additional components such as lids are still discarded.The use of lids made from reusable materials such as recyclable plastics and metals like aluminum , has been a way to reduce the amount of waste associated with the use of reusable containers, since these materials, unlike conventional plastics used in containers, have the advantage of being able to be reused after being subjected to a recycling process, which means they can be given a second use, thus avoiding the generation of waste that must be thrown into landfills. However, even though recycling seems to be an attractive option to keep waste generation at controlled levels, in practice this is not the case, since most end consumers only discard the lids without making a selection and when they are discarded in landfills they are not degraded, thus contributing to the increase in the volume of waste.

[0009] Developing environmentally friendly products that meet the specifications required to replace those made from non-biodegradable materials, such as single-use plastics, has not been an easy task. From the selection of possible starting materials, their appropriate concentrations, treatment conditions, the steps and operating conditions of the processes, among others, require study and experimentation with the consequent investment of material and human resources.

[0010] Recent developments have proposed more environmentally friendly solutions, such as the use of packaging and lids made of biodegradable materials. Alternative materials include those based on natural fibers; however, the structural rigidity of products made from natural fibers is not very good, since the way they are obtained does not allow the production of objects that withstand impacts and are also resistant to low temperatures and humidity. Furthermore, in most developments of products based on natural fibers, the addition of binding agents, thickeners and the use of barrier coatings is necessary to prevent the loss of their shape.The inclusion of the agents described above not only makes the products less biodegradable because they are chemical products, but also, if shapes with grooves or anchoring surfaces at negative angles are required, the demolding processes are made more difficult, since due to their low malleability, it is not possible to demold the products without damaging them and / or deforming the anchoring surfaces molded into them.

[0011] In order to avoid the limitations of conventional natural fiber-based lid forming processes, alternatives have been developed that do not use binding agents, thickeners, or barrier coatings, such as those described in US Patent 9370912B2, which describes a process for producing lids that comprises softening a pulp of natural fibers such as virgin fibers of bamboo, sugar cane, wheat, wood, recycled paper, or any other fiber with similar characteristics; allowing the pulp to transform into a suspension; adding a food-grade agent to the suspension that provides resistance to water and oil; filtering the suspension; pumping the suspension to a molding tank; creating the lid on a vacuum mold by suctioning the fibers onto a mesh of said mold; dehydrating the molded lid; cutting off the excess from the lid; inspecting the lid; and sterilizing the lid by UV radiation.The process described in the aforementioned Patent makes it possible to obtain lids with surfaces that extend, increasing the volume of the lid, so the designs that can be obtained would be adapted to be placed on containers with a rolled edge at their end; however, due to the way in which the lids are produced, their configuration does not allow for a strong seal, so only a small force is required to detach them, which is incompatible with the requirements necessary to guarantee the seal in a container that is going to be transported under rigorous stowage conditions. Furthermore, due to the way in which the securing surfaces of the lids are generated, it is not possible to create deep grooves that allow for a stronger hold on the surfaces of the container.On the other hand, in the aforementioned Patent, it is not indicated that the lid can withstand severe storage conditions, such as those to which containers are subjected in cold storage and transport chains.

[0012] On the other hand, US Patent 10036126B2 describes a process for obtaining lids that comprises immersing a mold that includes a mesh in a mixture comprising a softwood fiber (SW) / bagasse in a proportion of between 7: 3 and 9: 1, between 1 and 4% of a stiffness component, and between 0. 5 and 10% of a moisture barrier component that may preferably be alkyl ketene dimer; creating a vacuum in the mold so that the fiber mixture accumulates on the mold; and removing the lid by using a piston that ejects the formed lid. In said Patent, since the lid is unmolded by means of a piston, it cannot have surfaces with deep grooves or negative angles, since during the unmolding process the formed structures would be deformed when a great tensile force is applied to them.

[0013] As can be seen from the above, the production methods for natural fibre lids do not allow for the production of reusable and compostable lids with a structural rigidity and shape adapted to remain firmly attached to the containers where they will be used, and which can also be subjected to multiple cycles of use without losing their shape. Furthermore, none of the developments available for the production of lids allow for the production of lids with good tolerance to low temperatures, which can also withstand sudden changes in temperature and humidity without losing their structural rigidity.

[0014] In view of the above problems, there is a need to provide a method that allows the production of reusable, recyclable and compostable natural fiber lids, with a composition and configuration that gives them improved resistance and support, which prevents them from coming loose from the containers where they will be placed, even during transport and storage maneuvers of said containers. Additionally, there is a need to provide a method to obtain natural fiber lids that allows obtaining lids that are resistant to low temperatures and sudden changes in temperature and humidity, such as those generated during storage and transportation operations of products intended for human consumption that require refrigeration.Likewise, there is a need to provide a method for producing natural fiber lids that do not lose their structural rigidity, even after being subjected to sudden changes in temperature and humidity, such as those generated during the transfer and storage operations of containers intended for the storage of products for human consumption.

[0015] Similarly, there is a need to provide reusable, recyclable and compostable lids made of natural fibers, with a suitable configuration to provide a firm temporary seal that prevents their involuntary detachment during the handling and transportation conditions of the containers in which they are arranged, but which at the same time can be removed by the final consumer without the need to use specialized tools.

[0016] Additionally, for specific cases in which the containers are intended for the storage of products that require storage at low temperatures and / or that are exposed to sudden changes in temperature and humidity, as is the case, for example, of containers of products stored in cold with dispensing valves that require protection, such as beer keg valves or others with similar characteristics, there is a need for reusable, recyclable and compostable lids that, in addition to providing a firm seal, do not lose their structural rigidity even after being subjected to low temperatures and sudden changes in temperature and humidity and that can also withstand multiple cycles of use without losing their shape and characteristics.

[0017] Summary of the Invention

[0018] In order to overcome the limitations of the processes for manufacturing lids made of natural fibers available, the present invention aims to provide a method for manufacturing reusable, recyclable and compostable products, made from natural fibers, which allows obtaining products, such as lids, with high resistance to storage conditions at low temperatures without losing their shape and structural rigidity.

[0019] Another objective of the present invention is to provide a method for obtaining products made from natural fibers, which provides the products with resistance to sudden changes in temperature and humidity, without modifications in their structure.

[0020] A further objective of the present invention is to provide a method for making molded products, including lids, comprising rolling the product with grooves or negative angles and sufficient structural rigidity to be firmly secured to the mouth of the container in which they are placed and withstand impacts and severe conditions such as those to which containers are subjected in storage and transportation chains.

[0021] It is also an object of the present invention to provide biodegradable and compostable lids made of natural fibers, which resist low temperatures, vibrations, impacts and sudden changes in temperature and humidity without losing their shape and structural rigidity.

[0022] An additional objective of the present invention is to provide compostable and biodegradable lids that can be firmly secured to the containers in which they will be used without the use of additional fixing means, remaining coupled to the containers during transfer and storage operations and at the same time can be detached or uncoupled from the container by the final consumers, without the need to use specialized tools, while preserving their integrity to be placed again in the container for the necessary number of use cycles, without modifying the holding force of the lid, in such a way that the lids obtained can be removed and subsequently placed again in the containers as many times as necessary until the entire contents of the containers are available.

[0023] Another objective of the present invention is to provide a compostable lid made of natural fibers, with grooves or negative angles with a depth suitable for interacting firmly with the mouths of the containers where it will be used.

[0024] A further objective of the present invention is to provide a biodegradable and compostable lid made of natural fibers, adapted to withstand peeling forces of up to 300 N, without losing its shape.

[0025] The aforementioned objectives, as well as other aspects and advantages of the present invention, will become apparent from the following detailed description thereof.

[0026] Brief Description of the Figures of the Invention

[0027] Figure 1 illustrates a top perspective view of a compostable lid made of natural fibers in accordance with an illustrative but non-limiting development of the present invention. Figure 2 shows a side view of the compostable lid made of natural fibers illustrated in Figure 1.

[0028] Figure 3 shows a side section through line AA of the compostable natural fiber lid in Figure 2, showing regions B and C in detail with enlargements of the same.

[0029] Detailed Description of the Invention

[0030] The present invention provides a method for producing biodegradable and compostable lids made from plant fibers, which allows obtaining lids with high mechanical resistance. Likewise, the method of the present invention allows obtaining lids made from natural fibers that resist low temperatures such as those used in refrigerated storage conditions, as well as sudden changes in temperature and humidity without losing their structural rigidity, and which also withstand multiple cycles of use without losing their coupling strength to the mouths of the containers where they are used.

[0031] Additionally, the method for producing natural fiber caps of the present invention allows obtaining caps with a configuration suitable for resisting detachment forces of up to 300 N, which are sufficient to prevent the detachment of the cap during transfer and storage operations, but which allow the detachment of the cap by the end user without requiring the use of tools for such purpose.

[0032] In order to achieve the above-described advantages, the method of the present invention comprises the steps of: a) suspending natural fibers, such as coconut, bamboo, wheat straw, barley, sugarcane, hardwood, softwood, bagasse, miscanthus, agave and hemp fibers, or combinations thereof, in water within a pulping tank, until reaching a consistency of between 2 and 10% w / v; b) adding to the pulping tank a suitable, environmentally friendly, wet strength additive in a percentage between 1 and 10% with respect to the total volume of the fiber suspension, and stirring the suspension for a time between 5 and 45 minutes to obtain a pulp suspension; c) transferring the pulp suspension from step b) to a feed tank, diluting it with water until obtaining a concentration between 0.1 and 1.5%;d) filling a suitable mold with the pulp suspension to obtain a lid with a configuration adapted to be received in a desired container; e) applying vacuum to the mold to extract the water from the pulp suspension, until having a solids content between 15 and 45%, to obtain a lid preform; f) transferring the lid preform to a drying mold, where a pressure of between 1000 N and 2000 KN is applied to it at a temperature between 135 and 270 ° C, to reduce the moisture content to between 0 and 20%, optionally applying vacuum to accelerate the drying time and / or optionally performing a die-cutting of the edge of the lid preform, in case there is an excess of material on said edge; g) moistening the lid preform obtained from step f) until obtaining a moisture content of between 5 and 40%;and h) placing the moistened lid preform in a rotating mold that rotates at a speed of between 20 and 350 revolutions per minute, and pressing the lid skirt with a beveled rotating disk to form a perimeter groove or negative angle in said skirt, with a depth suitable for providing the lid with a detachment force of between 50 and 300 N when said lid is placed on a container, thus obtaining the finished lid.

[0033] The method described above allows obtaining resistant compostable lids with good mechanical performance, and it is evident to an expert in the field that the configuration of the mould used in step d) may be any suitable one to obtain a lid with a shape that can adapt to the mouth of the containers where it will be placed.

[0034] The method of the present invention makes it possible to obtain compostable lids with improved mechanical performance without the need to resort to the use of hardening agents such as polymeric coatings or the inclusion of reinforcements such as prefabricated ribs or rings. Furthermore, thanks to the formation of negative angles by means of rolling in step h), the lids obtained by the method of the present invention provide adequate and sufficient fixing and sealing even under severe storage and transport conditions of the containers, with a release force of between 50 and 300 N, which is sufficient to prevent the lid from coming loose during handling and transfer of the containers, but at the same time allows the end user to separate the lid from the container, without resorting to the use of specialized tools.

[0035] Additionally, with the method of the present invention it is possible to obtain lids with sufficient structural integrity to withstand low temperatures of up to -6 ° C and sudden temperature changes of -6 ° C at room temperature and sudden humidity changes of between 30 and 95% without deforming or losing their structural rigidity, by adding during the dilution of step c), a suitable water-repellent additive, friendly to the environment, in a concentration of between 0.5 and 8% with respect to the total volume of the suspension.

[0036] In the method of the present invention, step d) is carried out in such a way that the molding of the lid allows to obtain a lid with a curved shoulder that extends from the upper surface or panel of the lid, the relationship between the distance that exists between two opposite points on the wall of the curved shoulder and the distance between two opposite points at the free end of the skirt being between 1:1.02 and 1:1.1, such that the skirt of the mold on which the groove or negative perimeter angle of the lid is formed in step h), has an inclination that improves its coupling to the mouth of the container where it will be used.

[0037] Additionally, in a more non-limiting illustrative example of the present invention, the lid may have a substantially circular configuration, and the height of the inclined skirt together with the height of the curved shoulder, add up to a height that is equivalent to between 10 and 17% of the distance that exists between two opposite points on the wall of the open edge of the skirt.

[0038] Likewise, in a further embodiment of the present invention, for containers with a threaded mouth, in step h), the rotating mold and / or the beveled rotating disk may have an inclination with respect to the vertical axis and / or a vertical movement so that when the skirt of the lid is pressed by the beveled rotating disk, a perimeter groove or negative spiral angle is formed, with a configuration suitable for the threaded mouth of the container, thus obtaining a compostable lid with thread, of high mechanical resistance, which can be used during multiple cycles of use and retain its structural rigidity even when subjected to impacts, low temperatures of up to - 6 ° C and sudden changes in temperature from - 6 ° C to room temperature and sudden changes in humidity between 30% and 95% without deforming.

[0039] It will be apparent to a person skilled in the art that the moulding in step d) may be made to provide a lid with a skirt inclination which will depend on the characteristics of the mouth of the container on which the lid will be placed.

[0040] On the other hand, the present invention provides reusable, recyclable and compostable lids made of natural fibers, which adapt firmly to the mouths of the containers without requiring additional seals, the fixation of the lid being ensured by the interaction between a groove or negative angle formed in the skirt of the lid, with the surface of the mouth of the container where it will be placed. The depth of the groove or negative angle formed in the lid is sufficient to provide the lid with a detachment force of between 50 and 300 N, which is sufficient to prevent the detachment of the lid during the handling and transfer of the containers, and at the same time allows the end user to separate the lid from the container without resorting to the use of specialized tools.The lids of the present invention may have any suitable shape that allows them to be joined to the receiving surfaces of the mouths of the containers where they will be used, it being evident to an expert in the matter that said shape of the lids may be selected from any that allows to guarantee the correct seal of the lid on the mouth of the container, for example, but without being limited to a specific shape, the lid may have a shape selected from a circular, oval, rectangular, square, triangular or any other shape that corresponds to the shape of the walls of the mouth of the container.The proper fixing of the lid to the mouth of the container, whatever its configuration, will be guaranteed by the lid obtained by the method of the present invention in which a negative angle is formed in the skirt of the lid, the depth of which is such as to provide the lid with a detachment force of between 50 and 300 N and the ratio between the distance existing between two opposite points on the wall of the curved shoulder and the distance between two opposite points on the outer perimeter edge of the skirt is between 1 : 1. 02 and 1 : 1. 1.

[0041] Likewise, the lids of the present invention have a high mechanical resistance, they retain their coupling force to the mouths of the containers where they are used, even after multiple cycles of use, and they retain their structural rigidity when they are subjected to impacts, low temperatures of up to - 6 ° C and sudden changes in temperature of - 6 ° C at room temperature and sudden changes in humidity of between 30% and 95% without deforming or losing their structural rigidity during the logistics that entail the transport operations and cold storage of the containers in which they are placed.Referring to Figure 1, there is illustrated by way of non-limiting example, a type of lid for containers with circular mouths, such as the lids that protect the dispensing valves of beer kegs from the entry of foreign bodies into the interior of the components of said dispensing valve, said lid comprising an upper panel (1) of substantially circular shape, ending in a curved shoulder (2), two points peripherally opposite the curved shoulder (2) being separated from each other by a distance (a). ■ said upper panel (1) having a thickness e) of between 0.5 and 2 % with respect to the distance (a); an inclined skirt (3) that extends from the curved shoulder (2) and has a distance (c) between two opposite end points, the ratio between the distance c) and the distance (a) being between 1.02:1 and 1.1:1 (c:a) , such that the height of said inclined skirt, together with the height of the curved shoulder (2) , extend a distance (b) that is equivalent to between 10 and 17% of the distance (c) , the inclined skirt (3) having a thickness (f) of between 0.7 and 2% with respect to the distance (a) . A perimeter groove or negative angle (4) is arranged in the inclined skirt (3), below its junction with the curved shoulder (2), such that said perimeter groove or negative angle (4) has a depth sufficient to be firmly secured against the wall that protects the dispensing valve of a beer keg, said depth in one embodiment of the present invention being able to be equivalent to between 2 and 6% of the distance (c), two opposite end points of the perimeter groove or negative angle (4) being separated by a distance (d) that is equivalent to between 90 and 94% of the distance (c).The configuration described above allows the lid to have a detachment force of between 50 and 300 N, which is sufficient to prevent its involuntary detachment from the beer barrels, even when said beer barrels are subjected to transfer operations from their storage sites to the final consumers, while allowing its easy detachment by the final users without having to resort to specialized tools. The lid of the exemplary embodiment described above may preferably be made with a combination of bamboo and wheat straw fibers, in a preferred concentration of between 30 and 50% bamboo fibers, and between 70 and 50% wheat straw fibers. Additionally, the lid of the previous embodiment may have a weight of between 3 and 6 g when said lid has a distance ( a ) of between 63 and 67 mm.

[0042] To demonstrate the advantages of the compostable plant fiber lid of the present invention, the finished lids were subjected to stress testing under real-life conditions. To this end, the lids were placed on conventional beer kegs as test containers to protect the bodies of their dispensing valves. The tests performed are described in more detail below.

[0043] Two different batches of the lid of the present invention (Batch 1 and 2) were produced using the method described above using as starting material a mixture of bamboo and wheat straw fibers in a concentration of 40% and 60% respectively.

[0044] Each batch was processed according to the guidelines established in the method of the present invention and stored in airtight bags until use to prevent variations in moisture content. The caps were subjected to an initial measurement of their dimensions and weight, to determine the uniformity of the caps obtained by the described method.

[0045] The caps were then fitted to cover the cavity protecting the body of the beer keg dispenser valve and subjected to a room temperature strength test to determine the force required to remove them once in place. The results of the tests are shown in Table 1 below.

[0046] Table 1. Measurement and endurance test results As can be seen from the results shown above, the natural fiber lids obtained by the method of the present invention have adequate performance to be used as sealing elements for containers such as beer barrels, since the force required for their detachment is on average 181.8 N, which is a force value sufficient to guarantee an adequate seal that resists the manipulation of the barrels without the lid coming off.

[0047] Two different batches of the lid of the present invention (Batch 1 and 2) were produced using the method described above using as starting material a mixture of bamboo and wheat straw fibers in a concentration of 40% and 60% respectively.

[0048] Each batch was processed according to the guidelines established in the method of the present invention and stored in airtight bags until use to prevent variations in moisture content. The caps were subjected to an initial measurement of their dimensions and weight, to determine the uniformity of the caps obtained by the described method.

[0049] The lids were then placed to cover the cavity protecting the body of the beer kegs' dispensing valve, and were refrigerated at a temperature of -6°C for the time required to simulate normal storage conditions in a refrigerated container prior to the sale of the product, and subsequently subjected to a strength test to determine the force required to remove them once in place.

[0050] The results obtained showed that the force required for its detachment is on average 120 N, which is a force value sufficient to guarantee an adequate seal that resists the manipulation of the barrels without the lid coming off, thus proving that the lids obtained by the method of the present invention retain their structural rigidity even after being subjected to low temperatures.

[0051] The tests described above also confirm that the lids obtained by the method of the present invention are resistant to changes in humidity, since it is evident to one skilled in the art that lids under low temperature storage conditions are subjected to humidity conditions different from those encountered during storage and use at room temperature. Because the force required to detach the lid stored at - 6 ° C did not decrease significantly with respect to that observed in lids stored at room temperature, it can be concluded that the structural integrity of the lids is maintained even after being subjected to different humidity conditions and to sudden changes in humidity such as those encountered when going from storage at - 6 ° C to room temperature.

[0052] The present invention has been described in accordance with a preferred embodiment; however, it will be apparent to one of ordinary skill in the art that modifications may be made to the invention without departing from its spirit and scope.

Claims

CLAIMS 1. - A method for producing reusable, recyclable and compostable caps made of natural fibers, characterized in that it comprises the steps of: a) suspending natural fibers in water in a pulping tank until reaching a consistency of between 2 and 10% w / v; b) adding a suitable, environmentally friendly, moisture resistance additive to the pulping tank in a percentage of between 1 and 10% with respect to the total volume of the fiber suspension, and stirring the suspension for a time of between 5 and 45 minutes to obtain a pulp suspension; c) transferring the pulp suspension from step b) to a feed tank, diluting it with water until obtaining a concentration of between 0. 1 and 1.5 % ; d) filling the pulp suspension into a mold suitable for molding a lid with a configuration determined according to the configuration of the mouth of the container in which said lid will be placed; e) applying a vacuum to the mold to extract the water from the pulp suspension, until obtaining a solids content of between 15 and 45 % , to obtain a lid preform; f) after transferring the lid preform to a drying mold, where a pressure of between 1000 N to 2000 KN is applied to it at a temperature of between 135 and 270 ° C, to reduce the moisture content to between 0 and 20 % ; g) moistening the lid preform obtained from step f) with water until obtaining a moisture content of between 5 and 40 %; and h) placing the moistened lid preform in a rotating mold that rotates at a speed of between 20 and 350. revolutions per minute, and pressing the skirt with a beveled rotating disc to form a groove or negative perimeter angle in said skirt, with a depth suitable and sufficient to provide the lid with a detachment force of between 50 and 300 N when said lid is placed on a container. 2.- The method according to claim 1, characterized in that the natural fibers of step a) are selected from the group consisting of coconut fibers, bamboo, wheat straw, barley, sugar cane, hardwood wood, softwood wood, bagasse, miscanthus, agave and hemp or combinations thereof. 3.- The method according to claim 2, characterized in that the natural fibers are a combination of bamboo fibers and wheat straw. 4.- The method according to claim 3, characterized in that the combination of bamboo and wheat straw fibers comprises between 30 and 50% bamboo, and between 70 and 50% wheat straw. 5.- The method according to claim 1, characterized in that it further comprises adding during the dilution of step c), a suitable water-repellent additive, friendly to the environment, in a concentration of between 0.5 and 8% with respect to the total volume of the suspension. 6.- The method according to claim 1, characterized in that step f) further comprises performing a die-cutting on the lid, when the skirt has irregular edges produced by an accumulation of excess material. 7.- The method according to claim 1, characterized in that step f) further comprises applying vacuum, to accelerate the extraction time. 8.- The method according to claim 1, characterized in that step d) is carried out in such a way that the molding of the lid allows obtaining a lid with a curved shoulder that extends from the upper surface or panel of the lid, the relationship between the distance that exists between two opposite points on the wall of the curved shoulder and the distance between two opposite points at the free end of the skirt being between 1:1.02 and 1:1.1, such that the skirt of the mold on which the slot or negative perimeter angle of the lid is formed in step h), has an inclination that improves its coupling to the mouth of the container where it will be used. 9.- The method according to claim 8, characterized in that the molding of the lid in step d) is carried out in such a way that the height of the inclined skirt together with the height of the curved shoulder, add up to a height that is equivalent to between 10 and 17% of the distance that exists between two opposite points on the wall of the open edge of the skirt. 10.- The method according to claim 1, characterized in that in step h), the rotating mold and / or the beveled rotating disk have an inclination with respect to the vertical axis and / or a vertical movement so that, when the skirt of the lid is pressed by the beveled rotating disk, a perimeter groove or negative spiral angle is formed, with a configuration suitable for the produced lid to be placed on the threaded mouth of a container and the depth of the negative perimeter angle on the skirt is adequate to provide the lid with high mechanical resistance, sufficient so that said lid can be used during multiple cycles of use and retain its structural rigidity.

11. A lid made of natural fibers obtained by the method according to any one of claims 1 to 9, characterized in that it is biodegradable, reusable, recyclable and compostable, of a configuration suitable for adapting to the mouth of the container in which it will be placed, comprising an upper surface or panel (1) with a curved shoulder (2) having a separation (a) between two perimetrally opposite points of said curved shoulder (2); an inclined skirt (3) extending from the curved shoulder (2) and having a distance (c) between two opposite end points thereof, the ratio between the distance c) and the distance (a) being between 1.02:1 and 1.1:1 (c:a) , such that the height of said inclined skirt, together with the height of the curved shoulder (2) , is a distance (b) that is equivalent to between 10 and 17 % of the distance (c) ; and a groove or negative perimeter angle (4) arranged in the inclined skirt (3) , such that said groove or negative perimeter angle (4) has a depth sufficient to firmly secure the lid to the mouth of the container in which it is placed and provide the lid with a detachment force of between 50 and 300 N, when it is placed on the mouth of said container, the structural rigidity of said lid being sufficient to withstand temperatures of up to -6 ° C, sudden changes in temperature of -6 ° C to room temperature and sudden changes in humidity of between 30 % and 95 % without deforming.

12. The lid according to claim 11, characterized in that the upper panel (1) has a thickness of between 0.5 and 2% with respect to the distance (a); and the inclined skirt (3) has a thickness (f) of between 0.7 and 2% with respect to the distance (a). 13.- The cover according to claim 11, characterized in that the depth of the groove or negative perimeter angle (4) is equivalent to between 2 and 6% of the distance (c), with two opposite end points of the groove or negative perimeter angle (4) being separated by a distance (d) that is equivalent to between 90 and 94% of the distance (c). 14.- The lid according to claim 11, characterized in that it is made with a combination of bamboo and wheat straw fibers, in a concentration of between 30 and 50% of bamboo fibers, and between 70 and 50% of wheat straw fibers. 15.- The lid according to claim 11, characterized in that when the upper surface or panel (1) is circular and the distance (a) is between 63 and 67 mm, said lid has a weight of between 3 and 6 g. 16.- A lid made of natural fibers obtained by the method according to claim 10, characterized in that it is biodegradable, reusable, recyclable and compostable, of a configuration suitable for adapting to the threaded mouth of a container in which it will be placed, and comprises an upper surface or panel (1) with a curved shoulder (2); a skirt (3) extending from the curved shoulder (2); and a perimeter groove or negative angle in spiral arranged on the skirt, such that said groove or negative spiral perimeter angle has a configuration suitable for the threaded mouth of the container, the structural rigidity of said lid being sufficient to withstand temperatures of up to - 6 ° C, sudden changes in temperature of - 6 ° C to room temperature and sudden changes in humidity of between 30% and 95% without deforming.

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