Method for providing a non-uniform barrier coating on a hollow container and hollow container

Abstract

The present disclosure relates generally to a method for providing a non-uniform barrier coating on a hollow container (100) comprising a molded pulp and a hollow container. The method comprises depositing a polymer powder on the interior container surface of at least one predetermined portion (105a-105d) of the hollow container and, subsequently, treating the container with heat or irradiation. The present disclosure also relates to a hollow container (100) comprising a non-uniform polymer powder coating.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to a method for providing a non-uniform barrier coating on a hollow container comprising molded pulp. The method comprises depositing a polymer powder on the inner container surface of at least one predetermined portion in the hollow container, and subsequently treating the container with heat or irradiation. The present disclosure also relates to a hollow container comprising a non-uniform polymer powder coating. BACKGROUND

[0002] Plastic containers, packaging trays and bottles are widely used for storing food products such as flow food and beverages. Plastic articles can easily be molded, stretched and produced at relatively low cost. However, the use of plastic is associated with environmental problems. In order to mitigate the environmental burden, attempts are made to replace plastic containers and bottles with renewable materials such as molded pulp.

[0003] Shaped pulp products such as paper containers and bottles can be formed by feeding pulp, e.g. paper pulp, into a double-action mold and subsequently dewatering the pulp using heat and / or pressure, as disclosed in WO16055072.

[0004] Although paper is considered a sustainable packaging material, paper has many disadvantages compared to traditional plastic. Paper is generally more permeable to gases, grease and moisture. Long exposure to moisture, as typically occurs during storage of beverages, can lead to deterioration of the inner walls of the paper container.

[0005] To this end, the inner walls of a paper container can be coated with a barrier coating to protect the container from deterioration due to liquid and moisture exposure. Barrier coatings can also be used to control the humidity, sealing properties, aroma, etc. of the container.

[0006] Barrier coatings typically comprise a polymer such as a polyolefin polymer, and the barrier coating can be applied to the container inner wall in various ways, for example by extrusion coating or as a liquid coating.

[0007] If a molded pulp product is shaped into a hollow container, e.g. a can, a tray, a cup, a bowl or a bottle, certain inner regions of such a container can require additional barrier protection. For example, in the case of a typically cylindrical container or bottle, it can be desirable to have additional “protection” near the opening of the container, which can also be referred to as the “neck portion”. This portion is typically exposed to moisture and liquids during use, for example when drinking or pouring from the container. Furthermore, this portion is typically sealed by a lid or foil seal, which puts requirements on this portion during use and manufacturing.

[0008] Furthermore, in case the container is provided with labels or printings, the inner surface of the container should be able to resist the stresses associated with such labels and printings.

[0009] Furthermore, if the bottom surface of the container is uneven or comprises sharp indentations or edges, such parts can benefit from additional barrier protection.

[0010] Therefore, there is a need to provide a means to protect the inner parts of a molded pulp container in a more controlled manner, such that the container can withstand exposure to moisture and liquids and the requirements put on the container during manufacturing, handling and transportation. SUMMARY

[0011] In view of the above, there is a need to provide an improved and more controlled means to protect specific areas of a hollow container during use.

[0012] According to a first aspect, there is provided a method for providing a non-uniform barrier coating on a hollow container, the method comprising:

[0013] a) providing a hollow container comprising molded pulp, wherein the hollow container comprises a bottom part, a main part and an upper part, wherein the main part is arranged between the bottom part and the upper part, wherein the hollow container comprises a bottom surface and a sidewall extending from the bottom surface to an opening of the hollow container; the sidewall and the bottom surface defining an outer surface and an inner surface of the hollow container,

[0014] b) depositing a polymer powder onto the inner surface of at least one predetermined part of the hollow container by a spraying device capable of charging the polymer powder before or during deposition of the polymer powder, wherein at least the predetermined part is grounded,

[0015] c) treating the hollow container with heat or irradiation in case the polymer powder is melted and / or solidified,

[0016] wherein the electrical conductivity of the at least one predetermined part is higher than the electrical conductivity of the remaining part of the hollow container during the polymer powder deposition step b).

[0017] The present disclosure is based on the recognition that a non-uniform barrier coating on the inner wall of a container can be provided by varying the electrical conductivity across the container. The thickness of the barrier coating can be selectively controlled and manipulated such that the most vulnerable parts of the container, i.e. the predetermined parts, are protected in a more effective manner. These vulnerable parts can for example be parts of the container that are exposed to a large amount of moisture and liquids, or parts that are more sensitive to damage during manufacturing, transportation or use of the container.

[0018] In the method of the present disclosure, the polymer powder particles are charged by means of a spraying device, and due to their negative (or positive) charge, the powder will seek a grounded surface with a more positive (or negative) charge. Hence, the polymer powder particles will be electrically attracted to the inner surface of the predetermined portion of the hollow container. The charged polymer powder particles will mainly adhere to the predetermined portion of the inner surface; i.e. the inner wall with a higher electrical conductivity. However, the powder can also adhere to the remaining portion of the inner surface of the container. For example, a thinner barrier coating can be provided in these portions.

[0019] The barrier coating formed by the polymer powder is advantageous as this coating technique reduces the emission of volatile organic compounds (VOC) and coating waste. It is also a simple and relatively fast coating technique.

[0020] A powder coating is a dry, finely divided solid material, typically used on electrically conductive metal substrates. However, due to the inherently non-conductive nature of such substrates, it is challenging to deposit a powder coating onto a molded paper pulp substrate. The coating is not assisted by electrostatic attraction, which would normally result in a poor adhesion of the powder to the substrate. By implying means to make the predetermined portion of the container electrically conductive, a non-uniform barrier coating can be achieved. The barrier coating can be configured to cover the entire inner surface of the side wall, but the coating applied to the predetermined portion; i.e. the portion that typically needs the most “protection” will be thicker.

[0021] Thereafter, the coating is treated or irradiated in case the polymer powder is melted or cured. Hence, a durable protective barrier coating is formed, wherein the thickness of the coating varies in the selected portions on the inner surface of the hollow container

[0022] In embodiments, the hollow container extends along a longitudinal centerline, wherein the longitudinal extension of the bottom portion corresponds to 5-30% of the maximum longitudinal extension of the hollow container, the longitudinal extension of the main portion corresponds to 40-80% of the maximum longitudinal extension of the hollow container, and the longitudinal extension of the upper portion corresponds to 5-30% of the maximum longitudinal extension of the hollow container.

[0023] Hence, the main portion of the container is typically the largest portion of the hollow container.

[0024] In embodiments, at least one predetermined portion of the hollow container is arranged to be in contact with an electrically conductive material that is grounded during the polymer powder deposition step b).

[0025] The electrically conductive material is typically arranged to contact but not adhere to the outer surface of the predetermined portion of the hollow container. The container is at least grounded at the predetermined portion, which allows the powder to be attracted to these portions. The electrically conductive material ensures that the charge carried by the grounded surface will spread to a larger area.

[0026] The predetermined portion can form the upper portion, main portion, and / or bottom surface portion of the hollow container.

[0027] These parts of a hollow container can benefit from a thicker barrier coating. A thicker coating on the bottom surface can, for example, help protect against sharp edges and dents caused by features such as oriented lugs or non-flat bottom surface construction. Furthermore, a thicker coating may also be advantageous in predetermined sections of the main body of the hollow container, such as where labels or printing will be applied.

[0028] In one embodiment, the upper portion of the hollow container includes a shoulder portion and a neck portion, wherein the neck portion has a smaller cross-sectional area than the main portion, and the neck portion is configured to at least surround the opening of the container, and wherein the neck portion is arranged to taper between the main portion and the neck portion.

[0029] Therefore, hollow containers can be shaped into bottles.

[0030] The predetermined portion can form the shoulder and / or neck portion of a hollow container; that is, a bottle.

[0031] Depending on the circumstances, the barrier coating can be thicker in more than one predetermined section of the container.

[0032] Therefore, in an exemplary embodiment, the electrical conductivity is high in at least two predetermined portions of the hollow container, wherein the first predetermined portion forms part of the neck portion, and wherein the second predetermined portion forms part of the main portion, shoulder portion, or bottom surface of the hollow container during polymer powder deposition step b).

[0033] The neck section is constructed to surround the opening of the bottle. This section is typically exposed to moisture and liquid during drinking and pouring from the container. Furthermore, this section is usually sealed by a cap-like or foil seal, and therefore a thicker coating in this section of the container may be advantageous.

[0034] In this embodiment, the conductive material is a conductive wire, such as a metal wire, which is configured to be wound around at least one predetermined portion during the polymer powder deposition step b).

[0035] The conductive wire is grounded, and it can be wound around a larger or smaller surface area, depending on the specific needs, purpose, and application. The conductive wire ensures that a thicker coating is applied evenly to the intended area.

[0036] In one embodiment, the conductive material is a conductive molding device configured to encapsulate at least one predetermined portion during polymer powder deposition step b), wherein the at least one predetermined portion forms part of the main portion and / or shoulder portion of the hollow container.

[0037] Therefore, a large portion of the inner surface of the hollow container is provided with a thicker barrier coating. Furthermore, the molding apparatus ensures that a uniform, thick coating is applied to the inner surface of the predetermined portion. The molding apparatus may, for example, comprise a metal such as aluminum.

[0038] In an implementation method, the method further includes the following steps:

[0039] b') Polymer powder is deposited onto the outer surface of at least a portion of the upper part of the hollow container using a spraying device.

[0040] Therefore, the outer surface of the upper portion will also be coated with polymer powder. This is advantageous because this portion is repeatedly exposed to moisture and liquid during drinking, pouring, and attaching and removing the cap. Preferably, the neck portion of the container is provided with a barrier coating.

[0041] In this embodiment, the polymer powder deposition step b') is performed before the step c) of heating or irradiating the hollow container.

[0042] This can significantly save time and improve the processability of the method. Typically, during coating application, a curing or melting step is required after each spraying step. The hollow container formed according to the method of this disclosure requires only one heat treatment or irradiation treatment step after the inner and outer surfaces of a portion of the upper part have been coated. Therefore, a significantly time- and cost-effective and simplified method is provided.

[0043] In this embodiment, during the powder deposition step b), the hollow container has a moisture content of 3% to 15%, for example, a moisture content of 5% to 10%.

[0044] "Moisture content" refers to the amount of water contained in a molded pulp container, expressed as a percentage of the total weight of the molded pulp container. Moisture content is typically measured at a temperature of approximately 20°C.

[0045] The moisture content range mentioned above allows for the application of a uniform polymer powder coating. If the moisture content is too high, the surface of the hollow container may repel the polymer powder, resulting in an uneven coating. If the moisture content is too low, the polymer powder may not adhere properly to the surface of the hollow container.

[0046] In one implementation, the method includes an additional step of adjusting the hollow container after step a).

[0047] For example, the method may also include the following steps:

[0048] a') After step a) of providing a hollow container comprising molded pulp, the hollow container is conditioned at an ambient relative humidity of 30% to 100%.

[0049] The inventors have discovered that the moisture content of the hollow container affects the distribution of the polymer powder coating on the inner surface of the container's sidewalls. For example, a lower moisture content is preferable if a more localized coating distribution is needed, while a higher moisture content is preferable if a uniform coating distribution over a larger surface is desired. This can be customized, for example, by adjusting the hollow container under different conditions. For instance, in cases where localized coating distribution is required, the ambient relative humidity during adjustment can be in the range of 30% to 55%, and, for example, in cases where a more uniform coating distribution is desired, it can be in the range of 60% to 100%, such as in the range of 75% to 95%. In the case of a uniform coating over a larger surface, an internal barrier coating can then be applied to the entire inner surface, but will be thicker in predetermined portions with higher electrical conductivity.

[0050] Furthermore, a moisture content within the range mentioned above; i.e., 3% to 15%, for example 5% to 10%, allows for direct coating of the outer surface of the upper portion of the container after polymer powder deposition step b); i.e., before curing or melting the polymer powder. Therefore, only one heating or irradiation step is required in this method. Thus, a significantly time- and cost-saving and more simplified method is provided.

[0051] The moisture content of a hollow container can be selectively manipulated and controlled depending on the container's size, intended use, and the specific purpose of the powder coating. For example, in some cases, a thick, localized coating may be required in selected sections, i.e., predetermined portions of the container. In other cases, a uniformly distributed coating is needed, but with locally thicker areas in specific parts of the container. Furthermore, the proportion of powder coating on the outer surface of the upper container can be customized and adjusted to meet specific needs. This customization is achieved by tailoring the moisture content and adjusting it at a specific relative humidity.

[0052] According to another aspect of this disclosure, a hollow container is provided, wherein the hollow container includes a bottom portion, a main portion, and an upper portion, wherein the main portion is disposed between the bottom portion and the upper portion, wherein the hollow container includes a bottom surface and a sidewall extending from the bottom surface to an opening of the hollow container; the sidewall and the bottom surface define an outer surface and an inner surface of the hollow container, wherein the inner surface of the hollow container includes a barrier coating comprising a polymer powder, and wherein the thickness t1 of the barrier coating in at least one predetermined portion of the hollow container is greater than the thickness t2 of the barrier coating in the remaining portion of the hollow container.

[0053] In one embodiment, the upper portion includes a shoulder portion and a neck portion, wherein the neck portion has a smaller cross-sectional area than the main portion and is configured to at least surround the opening of the container, and wherein the shoulder portion is arranged to taper between the main portion and the neck portion, wherein at least one predetermined portion forms part of the neck portion, shoulder portion, main portion or bottom surface of the hollow container.

[0054] The thickness t1 of the barrier coating in at least one predetermined portion may be at least 10% higher than the thickness t2 of the barrier coating in the rest of the container, preferably at least 20% higher.

[0055] In one embodiment, at least a portion of the outer surface of the upper part of the hollow container includes a barrier coating.

[0056] This is advantageous because this part of the hollow container is specifically exposed to moisture and liquids during use.

[0057] Other features and advantages of this disclosure will become apparent from the appended claims and the following description. Those skilled in the art will recognize that the various features of this disclosure can be combined to create embodiments other than those described below, without departing from the scope of this disclosure. Attached Figure Description

[0058] Various aspects of this disclosure, including its specific features and advantages, will be readily understood from the following detailed description and accompanying drawings, in which:

[0059] Figure 1 A hollow container shaped as a bottle according to an exemplary embodiment of the present disclosure is schematically shown, along with an apparatus for selectively applying a polymer powder coating to a predetermined portion of the container.

[0060] Figure 2A The steps of depositing polymer powder on the inner surface of a hollow container are illustrated schematically.

[0061] Figure 2B The steps of depositing polymer powder on the outer surface of the upper portion of a hollow container are illustrated schematically. Detailed Implementation

[0062] This disclosure will now be described more fully below with reference to the accompanying drawings, which illustrate presently preferred embodiments of the disclosure. However, this disclosure may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness and to fully convey the scope of this disclosure to those skilled in the art. The same reference characters refer to the same elements throughout.

[0063] Reference Figure 1 and Figures 2A-2B A method is provided for applying a non-uniform barrier coating on a hollow container. The method includes:

[0064] a) A hollow container 100 comprising molded pulp is provided, wherein the hollow container 100 includes a bottom portion 101, a main portion 102, and an upper portion 103, wherein the main portion 102 is disposed between the bottom portion 101 and the upper portion 103, wherein the hollow container includes a bottom surface 104 and a sidewall 105 extending from the bottom surface 104 to an opening 106 of the hollow container; the sidewall 105 and the bottom surface 104 define an outer surface and an inner surface of the hollow container.

[0065] b) Polymer powder is deposited onto the inner surface of at least one predetermined portion 105a-105d of the hollow container by a spraying device 107 capable of charging the polymer powder before or during polymer powder deposition.

[0066] c) Treating hollow containers with heat or irradiation in the case of melting and / or solidifying polymer powder.

[0067] During polymer powder deposition step b), at least one predetermined portion 105a-105d has a higher conductivity than the remaining portion of the hollow container.

[0068] As used herein, the term "hollow container" refers to any type of container such as a can, tray, cup, bowl, or bottle. In the embodiment shown in the accompanying drawings, the hollow container is a bottle. In this embodiment, the hollow container has rotational symmetry about its longitudinal centerline. For example, the hollow container is typically cylindrical in shape.

[0069] As used herein, the term "molded pulp" refers to pulp or pulp mixtures that have been shaped, pressed, and dried. Molded pulp can be made, for example, from paper or wood fibers. For example, pulp can be a fibrous material produced by mechanically or chemically reducing a woody plant to its constituent parts and then suspending it in a fluid such as water.

[0070] A “non-uniform” coating is a coating with a thickness gradient. The non-uniform coating is thicker in selected locations; that is, the non-uniform coating is thicker in at least one predetermined portion of the hollow container.

[0071] The "inner surface" of a hollow container is defined by the container's side walls and bottom surface. The inner surface can also be referred to as the inner wall.

[0072] The “outer surface” is defined by the side walls and bottom surface of the container. The outer surface can also be referred to as the outer wall.

[0073] There are no restrictions on the polymer powder used for coating hollow containers.

[0074] For example, the powder may include thermoplastic polymers, polyamides, and polyesters, and copolymers thereof, wherein the thermoplastic polymer is selected from polyolefins such as polyethylene or polypropylene and copolymers thereof. The polymer powder may also include water-soluble synthetic polymers, such as polyvinyl alcohol, or polysaccharides such as cellulose. The powder particles typically have an average size in the range of 1 μm to 200 μm, for example, an average size in the range of 5 μm to 100 μm, or an average size in the range of 10 μm to 50 μm. These ranges allow for uniform coating and, furthermore, allow for charging of the polymer powder particles via a spraying device.

[0075] "Pre-defined portion" refers to a part that forms a component of the hollow container. The pre-defined portion may form a part of the upper portion, such as the neck portion, shoulder portion, main portion, and / or bottom surface of the hollow container. The dimensions of the pre-defined portion may vary. The pre-defined portion may constitute the entire bottom surface, the main portion, the neck portion, or the shoulder portion, or only a part thereof. In the context of this disclosure, the pre-defined portion does not mean the entire hollow container, but only a part thereof.

[0076] The hollow container extends along the longitudinal centerline 109, wherein the longitudinal extension of the bottom portion 101 corresponds to 5% to 30% of the maximum longitudinal extension of the hollow container 100, the longitudinal extension of the main portion 102 corresponds to 40% to 80% of the maximum longitudinal extension of the hollow container 100, and the longitudinal extension of the upper portion 103 corresponds to 5% to 30% of the maximum longitudinal extension of the hollow container 100.

[0077] The step of providing a hollow container comprising molded pulp (step a) can be provided in a manner known to those skilled in the art. For example, the hollow container can be provided by depositing a pulp mixture into a mold (e.g., a double-sided mold), or by activating a pressing tool (e.g., an impermeable balloon within the internal cavity of the mold to shaped the pulp into a balloon), thereby forming the inner and outer walls of the hollow container. The molded pulp can then be discharged, thereby removing excess water. The treatment used to provide the hollow container is, for example, described in WO16055073. Other methods for providing a hollow container comprising molded pulp are also conceivable.

[0078] The hollow container can then be removed from the double-sided mold and can be further adjusted before applying the powder coating to the inner wall and to the outer wall of the container in the embodiment.

[0079] Reference Figure 2A The step of depositing polymer powder (step b) can be achieved by a spraying device 107 capable of charging the polymer powder before or during polymer powder deposition. The spraying device can be a spray gun, but any spraying device that charges the powder before or during powder deposition can be used. Typically, the powder is charged by corona charging; that is, the powder particles pass through a charged corona field at the tip or nozzle of the spray gun, which applies a negative (or positive) charge to each polymer powder particle. This causes the powder particles to adhere firmly to and bond to the grounded and conductive surface of the container. The particles will primarily adhere to the inner surface of the predetermined portion.

[0080] The deposition of polymer powder can be achieved by inserting the spraying device 107 or the nozzle 107a of the spraying device into the opening during spraying, or by arranging the spraying device or nozzle near the opening. Charged polymer powder particles will be electrically attracted to the grounded and conductive internal components of the hollow container; i.e., the predetermined portion. Figures 2A-2B In this figure, the predetermined portion forms the main part of the hollow container. The predetermined portion is encapsulated by a grounded conductive molding device 111. Polymer powder is deposited onto the inner surface of the upper portion (as shown in...). Figure 2A As shown) and on the outer surface (as shown in) and on the outer surface (such as on Figure 2B The same principle applies regardless of which predetermined portion is to be coated and regardless of how this conductive surface is provided.

[0081] During polymer powder deposition step b), at least one predetermined portion 105a-105d has a higher conductivity than the rest of the hollow container. Therefore, a thicker coating will be provided in these portions.

[0082] The internal powder coating can be applied by continuously spraying the inside of the hollow container for approximately 1 to 20 seconds, for example, 2 to 10 seconds. Charged particles are blown from nozzle 107a toward the inner wall of the container.

[0083] In the final step d) of the method disclosed herein, the hollow container is treated with heat or irradiation while melting and / or solidifying the polymer powder.

[0084] When polymer powder is exposed to high temperatures or irradiation, such as ultraviolet radiation, the deposited polymer powder coating softens, melts, and / or solidifies, providing a continuous barrier coating. This results in a uniform, pinhole-free barrier coating.

[0085] The heat treatment steps can vary depending on the properties of the polymer particles and the required barrier coating thickness.

[0086] In one embodiment, the hollow container is heat-treated at a temperature ranging from 100°C to 300°C, for example, at a temperature ranging from 120°C to 220°C. The heat treatment time can be between 1 and 30 minutes.

[0087] In the embodiment, the curing step d) is performed by heating the hollow container at a temperature from 150°C to 200°C, preferably at a temperature from 170°C to 190°C for 5 to 20 minutes, and preferably at a temperature of 6 to 15 minutes.

[0088] Alternatively, ultraviolet (UV) light can be used to treat powder coatings, which typically allows the powder coatings to melt and / or cure rapidly.

[0089] Using the method of this disclosure, a thicker barrier coating can be provided on the inner surface of a predetermined portion of a hollow container. An exemplary predetermined portion is... Figure 1 As shown in the figure, and exemplary predetermined portions are indicated as 105a-105d.

[0090] exist Figure 1 In the hollow container 100, the shape is that of a bottle. The upper portion 103 of the hollow container, i.e., the bottle, includes a shoulder portion 103a and a neck portion 103b, wherein the neck portion 103b has a smaller cross-sectional area than the main portion 102, and the neck portion 103b is configured to at least surround the opening 106 of the bottle, and wherein the shoulder portion 103a is arranged to taper between the main portion 102 and the neck portion 103b.

[0091] The shoulder section typically tapers at an angle of approximately 5 to 75 degrees between the main section and the neck section, for example, at an angle of 20 to 60 degrees.

[0092] In one embodiment, the neck portion 103b is threaded. A threaded neck portion may be advantageous in various bottle applications, but this disclosure is by no means limited to threaded neck portions. In embodiments where the neck portion 103b is threaded, the threaded portion may have a trapezoidal construction; i.e., a “thread profile,” which allows the cap-like element to be screwed onto it.

[0093] The neck portion typically has a smaller cross-sectional area than the rest of the upper portion 103 of the bottle.

[0094] The bottom part 101, the main part 102, and the upper part 102 (including the neck part and the shoulder part) of the hollow container are integrally molded.

[0095] Figure 1 An example of a predetermined portion of a hollow container 100 is shown exemplarily. This predetermined portion may form the neck portion 103b of the hollow container 100 (see...). Figure 1 105a in the middle), shoulder portion 103a (see Figure 1 The portions of 105b), main portion 102 (not shown), and / or bottom surface 104 (see 105c-105d).

[0096] Depending on the specific purpose or use of the hollow container, in some implementations it may be necessary to apply a thicker coating to at least two different portions of the inner surface of the container.

[0097] Therefore, in the embodiment, at least two predetermined portions have high electrical conductivity, wherein the first predetermined portion 105a forms a portion of the neck portion 103b, and wherein, during the polymer powder deposition step b), the second predetermined portions 105b to 105d form a portion of the main portion 102, shoulder portion, or bottom surface 104 of the hollow container.

[0098] During polymer powder deposition step b), at least one predetermined portion 105a-105d of the hollow container 100 may be arranged to contact a grounded conductive material.

[0099] like Figure 1 As shown, the conductive material can be a conductive wire, for example, a metal wire 108 configured to be wound around at least one predetermined portion 105a-105d during polymer powder deposition step b).

[0100] The conductive wire 108 may be wound around a predetermined portion 105a of the portion forming the neck portion 103b of the hollow container. Alternatively or additionally, the conductive wire 108 may be wound around a predetermined portion 105b of the portion forming the shoulder portion 103a of the hollow container.

[0101] Conductive wire 108 can be wrapped to cover a larger surface area, for example, to cover the formation Figure 1 The predetermined part 105b of the shoulder portion 103a.

[0102] Alternatively, the conductive wire 108 can be wrapped to cover a smaller surface area, such as Figure 1 The neck portion 103b is shown in the diagram. Figure 1 In the first predetermined portion 105a, the second predetermined portion 105b is larger.

[0103] like Figure 1 As shown, predetermined portions 105c to 105d may form portions of the bottom surface 104 of the hollow container 100.

[0104] In embodiments where a localized powder coating is required on the bottom surface, the conductive material may be at least one piece of conductive material, such as a metal arranged to contact at least one predetermined portion 105a-105d of the hollow container 100 during polymer powder deposition step b).

[0105] exist Figure 1 In this configuration, two conductive materials 110 (e.g., two metals) can be arranged to contact predetermined portions 105c and 105d. The conductive element 110 can form part of the support device 112. The support device can include an electrically insulating material, such as plastic, in the area surrounding the conductive element 110. This configuration may be advantageous if a more localized barrier coating is required. For example, this configuration may be necessary to protect against sharp dents and edges on the bottom surface 104.

[0106] The conductive sheet 110 is not limited to a specific size or shape. In some embodiments, the conductive element is formed of metal. A piece of conductive material may also be disposed on the main portion 102 of the hollow container 100 (not shown). In this case, the conductive element may be larger, and the purpose of providing a thicker internal coating in this portion may be to protect the area where a label or print will be placed. A thicker coating may also be beneficial in protecting against dents or sharp corners caused by, for example, embossing or recessing.

[0107] like Figure 2A and Figure 2B As shown, the conductive material is a grounded conductive molding device 111, which is configured to encapsulate a portion of the main part 102 and / or the shoulder part 103a of the hollow container 100.

[0108] This may be desirable if a larger and more uniformly distributed coating is required in the intended portion. The molding apparatus may include any conductive material, such as a metal like aluminum. Alternatively, the molding apparatus may include a formable conductive material such as a conductive thermoplastic elastomer copolyester (TPC-ESD), a conductive foam including, for example, polyurethane, a conductive felt including, for example, polyester fabric, or a conductive rubber. The formable conductive material may also be coated with metal.

[0109] During the polymerization powder deposition step b), by ensuring effective grounding surrounding the main or shoulder portion, the charge carried by the grounded surface will diffuse to a larger area on the inner surface of the predetermined portion. Therefore, a uniform powder coating will be applied to the inner surface of the predetermined portion of the hollow container.

[0110] In an alternative embodiment, the molding device 111 may be configured to encapsulate the upper portion 103 or the bottom portion 101 of the hollow container.

[0111] In an implementation method, the method further includes the following steps:

[0112] b') Polymer powder is deposited onto the outer surface of at least a portion of the upper portion 103 of the hollow container 100 using a spraying device.

[0113] The outer surface of the upper part, especially the outer surface of the neck part; that is, the part around the opening of the container, is preferably coated because this part of the container is exposed to a large amount of moisture and liquid.

[0114] Preferably, the polymer powder deposition step b') is performed before the step c) of heating or irradiating the hollow container.

[0115] Therefore, this method requires only one heating or irradiation step.

[0116] Figure 2B The steps of depositing polymer powder onto the outer surface of the upper portion 103 of container 100 are shown.

[0117] After the inner surface has been coated with polymer powder, remove the spraying device from the opening or interior of the container. (In polymer powder deposition step b) Figure 2A As shown, the spraying device can be inserted into the opening or positioned near the opening during spraying.

[0118] Subsequently, the spraying device 107 is removed from the container opening and positioned at a distance d1 from the container opening. The tip of the spraying device, such as the tip of nozzle 107a, is typically positioned perpendicular to the container opening; that is, along the longitudinal centerline of the container. The axial distance d1 from the tip of the spraying device to the container opening can range from 10 mm to 250 mm, for example from 40 mm to 150 mm. This is to ensure that the powder covers the large surface of the neck portion (and upper portion) of the hollow container.

[0119] In this embodiment, polymer powder deposition steps b) and c) are performed simultaneously.

[0120] This can be achieved by positioning the tip of the spraying device 107 near the opening of the hollow container and along the longitudinal centerline of the container. In this way, the stream of charged polymer powder particles is guided toward the inner surface of the hollow container, while also at least partially covering the outer surface of the upper portion of the container.

[0121] During the powder deposition step b), the hollow container 100 may have a moisture content of 3% to 15%, for example, 5% to 10%.

[0122] If a more localized coating distribution is required, a lower moisture content can be used. If a uniform coating distributed over a larger surface is required, a higher moisture content can be used. The polymer powder barrier coating of this disclosure can then be applied to the entire inner surface of the container, but will be thicker in predetermined portions with higher electrical conductivity.

[0123] The method disclosed herein may include, after step a), an additional step of adjusting the hollow container to an ambient relative humidity of 30% to 100%.

[0124] The moisture content and conditioning of the hollow container within the aforementioned scope also allow for coating the outer surface of the upper portion of the container directly (or simultaneously) after polymer powder deposition step b), prior to curing or melting the polymer powder. Therefore, only one heating or irradiation step is required in this method.

[0125] At ambient relative humidity levels ranging from 30% to 100%, such as from 50% to 95%, the conditioning time can be at least 2 hours, such as at least 10 hours, preferably at least 15 hours. The hollow container can be conditioned at room temperature.

[0126] Polymer powder deposition step b) is typically performed directly after the conditioning step to maintain the moisture content of the hollow container during powder coating.

[0127] The moisture content can be selectively manipulated and controlled depending on the size of the container, its intended use, and the specific purpose of the powder coating. For example, in some cases, it may be necessary to provide a thick, localized coating in selected areas; i.e., a predetermined portion of the container. In other cases, a uniformly distributed coating is required, but with locally thicker areas in specific locations; i.e., predetermined portions of the container. Furthermore, the proportion of powder coating on the outer surface of the sidewalls of the upper container can be customized and adjusted to meet specific needs and requirements.

[0128] According to another aspect, a hollow container is provided, wherein the hollow container 100 includes a bottom portion 101, a main portion 102, and an upper portion 103, wherein the main portion 102 is disposed between the bottom portion 101 and the upper portion 103, wherein the hollow container includes a bottom surface 104 and a sidewall 105 extending from the bottom surface 104 to an opening 106 of the hollow container; the sidewall 105 defining an inner surface and the bottom surface 104 include a barrier coating comprising a polymer powder, wherein the thickness t1 of the barrier coating in at least one predetermined portion of the hollow container is greater than the thickness t2 of the barrier coating in the remaining portion of the hollow container 100.

[0129] The container is preferably formed by the method described above.

[0130] like Figure 1 As shown, the upper portion 103 includes a shoulder portion 103a and a neck portion 103b, wherein the neck portion 103b has a smaller cross-sectional area than the main portion 102, and the neck portion 103b is configured to at least surround the opening 106 of the container, and wherein the shoulder portion 103a is arranged to taper between the main portion 102 and the neck portion 103b, wherein predetermined portions form portions of the neck portion 103b, shoulder portion 103a, main portion 102, or bottom surface 104 of the hollow container 100.

[0131] The barrier coating thickness t1 of at least one predetermined portion 105a-105d may be at least 10% higher than the barrier coating thickness t2 of the rest of the hollow container, preferably at least 20% higher.

[0132] For example, the thickness t1 of the barrier coating in the predetermined part can be in the range of 10 μm to 200 μm, such as from 30 μm to 120 μm.

[0133] The thickness t2 of the barrier coating in the remaining part can be in the range of 5 μm to 150 μm, for example, from 10 μm to 80 μm.

[0134] The thickness of the barrier coating refers to the thickness of the cured barrier coating; that is, the thickness of the coating after the hollow container has been treated with heat or irradiation in the case of melting and / or curing polymer powder.

[0135] The outer surface of the upper portion 103 of the hollow container 100 may include a barrier coating.

[0136] This is to provide additional protection against liquids and moisture during the use and manufacturing of the container.

[0137] Preferably, the outer surfaces of the main body and bottom of the bottle have no barrier coating. This is to achieve a matte, "raw" paper-like appearance on the outer surface of the main body of the container. Therefore, only the most vulnerable parts of the container are provided with a barrier coating.

[0138] Example: Providing a non-uniform coating

[0139] The following materials and facilities were used in the experiment:

[0140] - Pure white 135gsm (A4 size, 210 mm x 297 mm) paper, conditioned overnight at 20°C and 50% RH (moisture content approximately 7%).

[0141] - Pure white 135gsm (A4 size, 210 mm x 297 mm) paper, conditioned overnight at 20°C and 90% RH (moisture content approximately 14%).

[0142] - Polymer powder: HDPE powder with a particle size distribution from 0 μm to 80 μm

[0143] - Spray gun: PGC Type 1 electrostatic powder gun

[0144] Tests were conducted to demonstrate that coating thickness in predetermined portions of two different sheets of paper can be optimized by positioning one or more grounded and conductive metal parts at predetermined locations on the paper.

[0145] Secure the paper to the plastic sheet. Cut off the plastic sheet in the section where you will place the grounding conductive material (metal in this example).

[0146] Two different setups were tested. In the first test, a single metal piece (15 mm x 15 mm) was placed in the center of the paper. In the second test, four metal pieces (15 mm x 15 mm) were arranged near the corners of the paper, forming a square. The distance between each metal piece was 150 mm to 200 mm.

[0147] For the first test, six sheets of paper were tested, three of which were conditioned at 20°C and 50% RH (moisture content of approximately 7%), and three of which were conditioned at 20°C and 90% RH (moisture content of approximately 14%).

[0148] For the second test, seven sheets of paper were tested, four of which were conditioned at 20°C and 50% RH, and three of which were conditioned at 20°C and 90% RH.

[0149] All sheets of paper were marked with 20 dots, forming a grid on the paper surface. The thickness of the paper was measured twice at each dot using an Elcometer 456 film thickness meter, and the results were reported.

[0150] The polymer powder was sprayed onto the paper from a distance of approximately 100 mm for a period of three seconds while the spray gun was moved downwards. The weight of each sheet was measured before and after the spraying sequence.

[0151] The paper was subjected to heat treatment in an oven at 180±10°C for 10 minutes. After heat treatment, the thickness at each point was measured again and reported.

[0152] In the first test, for paper conditioned at 50% RH (approximately 7% moisture content), the coating was concentrated on the metal part. The coating extended approximately 20 mm from the edge of the metal part. The thickness was measured at 20 points. For the point located on the metal part, a coating thickness of approximately 100 μm was measured.

[0153] For paper conditioned at 90% RH (approximately 14% moisture content) using a central metal element, the coverage was better compared to paper conditioned at 50% RH. Almost the entire sheet was completely covered with powder. This was also confirmed in thickness measurements. A coating thickness gradient was observed, with the coating at the metal element being approximately 50% thicker than either the coating applied approximately 100 mm from the metal element or the coating applied approximately 50% thicker at the metal element.

[0154] The same trend was observed in the second test (which included four different metal parts). For paper conditioned at 50% RH, the coated area was concentrated at the location of the metal parts and extended approximately 20 mm from the edge of the metal parts. Thickness was measured at 20 points. Measurements only at the metal parts showed significant coating thickness.

[0155] For paper conditioned at 90% RH, the coverage is significantly better than that of paper conditioned at 50% RH. Almost the entire surface area of ​​the paper is covered with powder. A gradient in coating thickness is still observed. Measurements show that the coating thickness at the metal parts is significantly higher than at points farther from the metal parts.

[0156] These results indicate that polymer powder deposition can be selectively directed to specific sections and areas requiring a thicker coating. Furthermore, these results demonstrate that relative humidity and moisture content affect the distribution or coverage of the powder coating. Therefore, relative humidity and moisture content can be tailored to determine whether a more localized or more distributed coating is desired.

[0157] The terms, definitions, and implementation methods of all aspects of this disclosure are adapted to other aspects of this disclosure as necessary.

[0158] Although this disclosure has been described with reference to specific exemplary embodiments thereof, many different changes, modifications, etc. will become apparent to those skilled in the art.

[0159] Those skilled in the art, upon practicing this disclosure, can understand and implement variations of the disclosed embodiments by studying the accompanying drawings, this disclosure, and the appended claims. Furthermore, in the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality.

Claims

1. A method for applying a non-uniform barrier coating to a hollow container, characterized in that, The method includes: Step a) provides a hollow container (100) comprising molded pulp, wherein the hollow container (100) includes a bottom portion (101), a main portion (102), and an upper portion (103), wherein the main portion (102) is disposed between the bottom portion (101) and the upper portion (103), wherein the hollow container includes a bottom surface (104) and a sidewall (105) extending from the bottom surface (104) to an opening (106) of the hollow container; the sidewall (105) and the bottom surface (104) define an outer surface and an inner surface of the hollow container. Step b) Depositing the polymer powder onto the inner surface of at least one predetermined portion of the hollow container using a spraying device (107) capable of charging the polymer powder before or during polymer powder deposition. In this embodiment, at least one predetermined portion of the hollow container (100) is arranged to contact a grounded conductive material during step b) of the polymer powder deposition, the at least one predetermined portion forming a portion of the upper portion (103), the main portion (102), and / or the bottom surface (104) of the hollow container (100), and wherein the conductive material is a conductive wire (108) or a conductive molding device (111), the conductive wire being configured to be wound around at least one predetermined portion (105a-105d) of the hollow container during step b) of the polymer powder deposition, and the conductive molding device (111) being configured to encapsulate at least one predetermined portion (105a-105d) during step b) of the polymer powder deposition. Step c) Treating the hollow container with heat or irradiation while melting and / or solidifying the polymer powder. During step b) of the polymer powder deposition, the conductivity of at least one of the predetermined portions is higher than that of the remaining portions of the hollow container.

2. The method according to claim 1, wherein, The hollow container extends along a longitudinal centerline (109), wherein the longitudinal extension of the upper portion (103) corresponds to 5% to 30% of the maximum longitudinal extension of the hollow container (100), the longitudinal extension of the main portion (102) corresponds to 40% to 80% of the maximum longitudinal extension of the hollow container (100), and the longitudinal extension of the upper portion (103) corresponds to 5% to 30% of the maximum longitudinal extension of the hollow container (100).

3. The method according to claim 1 or claim 2, wherein, The upper portion (103) of the hollow container includes a shoulder portion (103a) and a neck portion (103b); wherein the neck portion (103b) has a cross-sectional area smaller than that of the main portion (102), and the neck portion (103b) is configured to at least surround the opening (106) of the hollow container, and wherein the shoulder portion (103a) is arranged to taper between the main portion (102) and the neck portion (103b).

4. The method according to claim 3, wherein, During step b) of the polymer powder deposition, the electrical conductivity in at least two predetermined portions of the hollow container is higher than that in the remaining portions of the hollow container, wherein a first predetermined portion (105a) forms a portion of the neck portion (103b), and wherein a second predetermined portion (105b-105d) forms a portion of the main portion (102), the shoulder portion (103a), and / or the bottom surface (104) of the hollow container.

5. The method according to claim 1 or claim 2, wherein, The conductive wire is a metal wire.

6. The method according to claim 3, wherein at least one of the predetermined portions forms part of the shoulder portion (103a) of the upper portion (103) of the hollow container (100).

7. The method according to claim 1 or claim 2, wherein, The method further includes the following steps: Step b') The polymer powder is deposited onto the outer surface of at least a portion of the upper portion (103) of the hollow container (100) by means of the spraying device.

8. The method according to claim 7, wherein, Step b') of the polymer powder deposition is performed before step c) of heating or irradiating the hollow container.

9. The method according to claim 1 or claim 2, wherein, During step b) of the polymer powder deposition, the hollow container has a moisture content of 3% to 15%.

10. The method according to claim 1 or claim 2, wherein, During step b) of the polymer powder deposition, the hollow container has a moisture content of 5% to 10%.

11. The method according to claim 1 or claim 2, further comprising the following steps: Step a') After providing the hollow container comprising the molded pulp in step a), the hollow container is conditioned at an ambient relative humidity of 30% to 100%.

12. A hollow container comprising molding pulp, the hollow container being formed by the method according to any one of claims 1 to 11, wherein, The hollow container (100) includes a bottom portion (101), a main portion (102), and an upper portion (103), wherein the main portion (102) is disposed between the bottom portion (101) and the upper portion (103), wherein the hollow container includes a bottom surface (104) and a side wall (105), the side wall (105) extending from the bottom surface (104) to the opening (106) of the hollow container; the side wall (105) and the bottom surface (102) 4) Define the outer surface and inner surface of the hollow container, wherein the inner surface includes a barrier coating comprising a polymer powder, wherein the thickness t1 of the barrier coating in at least one predetermined portion of the hollow container is greater than the thickness t2 of the barrier coating in the remaining portion of the hollow container (100), wherein the thickness t1 of the barrier coating in at least one predetermined portion is at least 10% greater than the thickness t2 of the barrier coating in the remaining portion of the hollow container (100).

13. The hollow container according to claim 12, wherein, The thickness t1 of the barrier coating in at least one of the predetermined portions is at least 20% greater than the thickness t2 of the barrier coating in the remaining portions of the hollow container (100).

14. The hollow container according to claim 12, wherein, At least a portion of the outer surface of the upper portion (103) of the hollow container (100) includes a barrier coating.

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