Method for coating a hollow container containing a molded pulp

Abstract

The present disclosure relates generally to a method for providing a barrier coating on a hollow container (100) containing a molded pulp. The method comprises providing a polymeric powder coating to at least a portion of the inner surface (105a) and outer surface of the container (100) prior to curing and / or melting the powder coating. The present disclosure also relates to a hollow container (100) formed by the method.

Description

Technical Field

[0001] This disclosure generally relates to a method for providing a barrier coating on a hollow container containing a molded slurry. The method includes providing a polymer powder coating onto at least a portion of the inner and outer surfaces of the container before curing and / or melting the powder coating. The invention also relates to a hollow container formed by this method. Background Technology

[0002] Plastic containers, trays, and bottles are widely used for storing food, such as liquid foods and beverages. Plastic products can be easily molded, stretched, and produced at a relatively low cost. However, the use of plastics is associated with environmental problems. To mitigate the environmental burden, efforts are being made to replace plastic containers and bottles with renewable materials such as molded pulp.

[0003] Formed pulp products such as paper containers and bottles can be formed by feeding a pulp (e.g., pulp for papermaking) into a split die and then dehydrating the pulp with heat and / or pressure, as disclosed, for example, in WO16055072.

[0004] Although paper is considered a sustainable packaging material, it has many disadvantages compared to traditional plastics. Paper is generally more permeable to gases, greases, and moisture. Prolonged exposure to moisture (typically during beverage storage) can lead to deterioration of the inner walls of paper containers.

[0005] For this purpose, the inner wall of paper containers can be coated with a barrier coating to protect the container from deterioration due to exposure to liquids and moisture. The barrier coating can also be used to control the container's humidity, sealing performance, aroma, etc.

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

[0007] In recent years, powder coating has received attention in order to reduce emissions of volatile organic compounds (VOCs) and coating waste.

[0008] Powder coatings are dry, finely granulated solid materials typically used on conductive metal substrates. Powder deposition is usually achieved via electrostatic forces. For example, powder can be charged via corona discharge and then sprayed onto a grounded substrate. Thus, a powder layer is applied to the substrate, which is then heated, causing the powder to melt and form a continuous film on the substrate.

[0009] However, due to the inherent non-conductive properties of this substrate, depositing powder coatings onto the molded slurry substrate is challenging. The coating is not aided by electrostatic attraction, which can lead to poor powder-substrate adhesion and uneven powder deposition.

[0010] If the product to be coated is shaped like a hollow container, such as a bottle, the complexity of the powder coating process increases. In this case, it may also be necessary to coat the upper outer portion of the container, i.e., the part surrounding the opening of the container. This part of the product is typically repeatedly exposed to moisture and liquid during consumption or pouring from the container.

[0011] Therefore, there is a need for a simplified method for applying a powder coating to a molded slurry container for storing flowable food or beverage, wherein the surface of the container, which is primarily exposed to moisture and liquid, is provided with a protective and durable barrier coating. Summary of the Invention

[0012] In view of the above, there is a need for an improved and simplified method for providing a powder coating on a hollow container containing a molded slurry, which produces a liquid- and moist barrier coating that protects the most exposed part of the container.

[0013] According to a first aspect, a method is provided for providing a barrier coating on a hollow container containing a molded slurry, the method comprising:

[0014] a) Provides a hollow container comprising a molded slurry, wherein the hollow container includes a main portion and an upper portion; the hollow container extends along a longitudinal centerline, wherein the longitudinal extension of the upper portion corresponds to 5% to 30% of the maximum longitudinal extension of the hollow container, and wherein the longitudinal extension of the main portion corresponds to 70% to 95% of the maximum longitudinal extension of the hollow container, wherein the hollow container includes a bottom surface and sidewalls extending from the bottom surface to an opening of the hollow container; the sidewalls and the bottom surface define an outer surface and an inner surface of the hollow container.

[0015] b) Depositing polymer powder onto the inner surface of a hollow container using a spraying device capable of electrifying the polymer powder before or during deposition, wherein at least a major portion of the hollow container is grounded during polymer powder deposition.

[0016] c) Depositing polymer powder onto the outer surface of at least a portion of the upper part of the hollow container using a spraying device.

[0017] d) After steps b) and c), the hollow container is treated with heat or radiation under conditions that melt and / or solidify the polymer powder.

[0018] This disclosure is based on the understanding that a portion of both the inner and outer surfaces of a hollow container can be coated prior to heat or radiation treatment; that is, prior to the formation of a continuous barrier coating. Therefore, the most “vulnerable” part of the container; that is, the part primarily exposed to moisture and liquids during use, can be coated in a single step, and the method requires only one heating or radiation step.

[0019] Depositing powder coatings onto these portions of a hollow container involves complex processability issues. First, because the molded slurry substrate itself is non-conductive. Second, because coating the inner and outer surfaces of the upper portion of the container cannot typically be done in a single step. In most applications, it is generally necessary to first provide the inner powder coating, then melt and / or cure it, and then provide the outer coating in a separate step, followed by melting and / or curing it in a second step.

[0020] The hollow container formed according to the method of this disclosure requires only one step of heat treatment or radiation treatment after the inner and outer surfaces of a portion of the upper part are coated. Therefore, significant savings in time and cost, as well as a more simplified method, are provided.

[0021] Polymer powder particles become charged upon passing through the spraying device, and due to their negative (or positive) charge, the powder will seek out grounded surfaces with more positive (or negative) charge. Therefore, the powder particles will adhere to the container surface. During a subsequent heating or radiation step, the applied polymer powder coating melts and solidifies, providing a uniform and durable protective barrier coating.

[0022] In an exemplary embodiment, the hollow container has a moisture content of 3% to 15%, for example 5% to 10%, during the polymer powder deposition step.

[0023] The moisture content within the above range 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.

[0024] In an exemplary embodiment, the polymer powder deposition step b) of the method is performed in a molding apparatus containing a conductive material; the molding apparatus is configured to surround at least a portion of the main part of the hollow container.

[0025] Typically, the molding device is constructed to enclose the entire main part of the hollow container.

[0026] Therefore, most of the hollow container is charged during the polymer powder deposition step, and a uniform powder coating is applied to the inner surface of the hollow container.

[0027] The molding apparatus can include any conductive material.

[0028] If the conductive material is, for example, a metal, a higher moisture content may be required during the polymer powder deposition step, such as a moisture content in the range of 8% to 15%.

[0029] In an exemplary embodiment, the molding apparatus includes a formable conductive material.

[0030] The inventors discovered that the use of formable conductive materials has enhanced adaptability to or conformability to the shape of hollow containers. Thus, the polymer powder deposition step can be carried out in a low moisture content range, for example, from 3% to 10%, or, for example, from 5% to 10%. Furthermore, a uniform coating thickness is achieved.

[0031] In an exemplary embodiment, the method further includes the steps of: a') adjusting the hollow container to an ambient relative humidity of 30% to 100%, and after step a), providing the hollow container containing the molded slurry.

[0032] In embodiments using formable conductive materials, conditioning is typically performed at an ambient relative humidity of 30% to 100%, for example, 30% to 75%.

[0033] In an embodiment where the polymer powder deposition step b) of the method is carried out in a molding apparatus containing metal as a conductive material, the adjustment of the hollow container is preferably carried out at an ambient relative humidity of 60% to 100%, for example, from 75% to 95%.

[0034] Prior to the polymer powder deposition step; i.e. steps b) and c) of the method, adjusting the relative humidity of the hollow container within the range described above allows for the provision of a homogeneous and uniform coating before the step of curing or melting the powder coating.

[0035] The moisture content of a hollow container affects its ability to be coated on both the inner and outer surfaces of at least the upper portion.

[0036] The moisture content within the aforementioned range allows at least a portion of the upper part to be coated without being connected to a grounded conductive surface; that is, only a portion of the hollow container needs to be connected to a grounded conductive surface during powder deposition. Typically, since the slurry is inherently non-conductive, a grounded conductive surface is required for the powder to adhere to the slurry container. However, this is not necessary when the moisture content is within the aforementioned range.

[0037] The moisture content of a hollow container can be selectively manipulated and controlled based on the container's size and intended use. For example, in some cases, it may be necessary to coat a large portion of the upper part of the container, while in others, only a smaller portion may be desired. Adjustments can be made to suit specific circumstances by modifying the moisture content and / or relative humidity level during conditioning.

[0038] Furthermore, the moisture content within the aforementioned range allows for simultaneous or sequential deposition of polymer powder on both the inner and outer surfaces of the container wall. Therefore, a melting and / or curing step is not required between steps b) and c) of this method.

[0039] In an exemplary embodiment, polymer powder deposition steps b) and c) are performed simultaneously.

[0040] This can be achieved by arranging the spraying device, specifically the tip of the spraying device, close to 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 container wall, while also at least partially covering the outer surface of the upper portion of the container.

[0041] The polymer powder deposition step c) can be performed by positioning the spraying device at a distance d1 from the opening of the hollow container, which is 10 mm to 250 mm, preferably 40 mm to 150 mm.

[0042] If necessary, the tip of the spraying device is typically arranged along the longitudinal centerline so that the flow of polymer powder particles can cover the entire surface of the upper portion.

[0043] Therefore, the spraying device can be inserted into the opening during the first polymer powder deposition step b), or positioned near the opening during spraying. The charged polymer powder particles will be electrically attracted to the inner surface of the hollow container and are allowed to adhere to it.

[0044] Subsequently, the spraying device can be removed from the container opening and positioned at a distance d1 from the container opening. The nozzle or tip of the spraying device is typically arranged vertically from the container opening; that is, along the longitudinal centerline of the container. This is to ensure that the powder is covered on the large surface of the upper part of the hollow container.

[0045] As described above, polymer powder deposition step b) can be performed in a molding apparatus containing conductive material.

[0046] In such an embodiment, the molding apparatus may include at least a first removable portion and a second removable portion, wherein the first removable portion is configured to surround the upper portion of the hollow container, and wherein the second removable portion is configured to surround the main portion of the hollow container.

[0047] The spraying apparatus applies an electric field, causing the polymer powder particles to become charged and electrically attracted to the grounded and conductive surface of the hollow container. During polymer powder deposition step b), the first and second removable portions of the molding apparatus can be arranged to surround both the main and upper portions of the hollow container. Therefore, during polymer powder deposition in the inner portion of the container, the entire inner surface of the container becomes charged. The stream of charged polymer powder particles is guided to the inner surface of the hollow container and adheres thereto. By ensuring effective grounding and surrounding both the main and upper portions of the container during polymer powder deposition step b), the charge carried by the grounded surface will be distributed across the entire area of ​​the inner surface. Therefore, a uniform powder coating will be applied to the inner surface of the hollow container.

[0048] In embodiments where the hollow container has a moisture content in the range of 3% to 15%, for example 5% to 15%, the polymer powder deposition step b) can be performed with only the second removable portion present.

[0049] Therefore, in step b), a spraying device such as a spray gun can be inserted into (or near) the opening of the hollow container to coat the inner surface of the container.

[0050] In an exemplary embodiment, the first removable portion is removed from the molding apparatus during polymer powder deposition step c).

[0051] After polymer powder deposition step b), the first removable portion (configured to surround the upper portion of the container) can be removed, and the spraying device can be removed from the inside of the container or the opening and positioned at a distance from the container. Spraying of at least a portion of the upper portion of the container can then be completed. During this step (step c), the upper portion of the container is not connected to a grounded conductive surface.

[0052] Therefore, a simplified method for providing an inner barrier coating and an outer barrier coating is provided. This method requires only one or two spraying sequences and only one heat treatment or radiation treatment after the spraying sequence.

[0053] Furthermore, this is advantageous because only the outer surface of the upper portion will be coated. Preferably, the outer surface of the main part of the container does not include any barrier coating; that is, it does not have a barrier coating containing polymer powder. This is to create a more paper-like and "raw" feel on the main part of the container.

[0054] In a preferred embodiment, the hollow container is a bottle-shaped member, wherein 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 surround at least an opening of the bottle-shaped member, and wherein the shoulder portion is arranged to taper between the main portion and the neck portion.

[0055] In one embodiment, at least the neck portion of the upper part of the bottle-shaped component is coated in polymer powder deposition step c).

[0056] In the case of bottle-shaped containers, the neck portion is preferably coated because it is exposed to moisture and liquid when people drink from the bottle or when pouring out flowable food or liquid from the bottle.

[0057] In this embodiment, the entire upper portion of the hollow container is coated in polymer powder deposition step c).

[0058] In some cases, it may be necessary to cover the entire upper portion of the bottle-shaped component. In such embodiments, a higher moisture content in the hollow container may be required during polymer powder deposition (steps b and c).

[0059] In the final step d) of the method disclosed herein, after steps b) and c), the hollow container is treated with heat or radiation under conditions of melting and / or solidifying the polymer powder.

[0060] In this embodiment, curing step d) is performed by heating the hollow container at a temperature of 120°C to 220°C for 1 to 30 minutes.

[0061] Therefore, a uniform barrier coating is provided on the inner and outer surfaces of the upper portion of the container.

[0062] The thickness of the barrier coating formed by the method of this disclosure can be in the range of 5 μm to 300 μm, for example, 20 μm to 100 μm.

[0063] According to another aspect of this disclosure, a hollow container formed by the aforementioned method is provided.

[0064] The hollow container includes a main portion and an upper portion; the hollow container extends along a longitudinal centerline, wherein the longitudinal extension of the upper portion corresponds to 5% to 30% of the maximum longitudinal extension of the hollow container, and wherein the longitudinal extension of the main portion corresponds to 70% to 95% of the maximum longitudinal extension of the hollow container, wherein the hollow container includes a bottom surface and sidewalls extending from the bottom surface to an opening of the hollow container; the sidewalls and the bottom surface define an outer surface and an inner surface of the hollow container, wherein the hollow container includes a barrier coating containing polymer powder on the inner surface of the hollow container and on at least a portion of the outer surface of the upper portion of the hollow container.

[0065] In one embodiment, the hollow container is a bottle-shaped member. In such an 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 surround at least an opening of the bottle-shaped member, and wherein the shoulder portion is arranged to taper between the main portion and the neck portion, and wherein the bottle-shaped member includes a barrier coating containing polymer powder on the inner surface of the bottle-shaped member and at least the outer surface of the neck portion of the bottle-shaped member.

[0066] The thickness of the barrier coating can be in the range of 5 μm to 300 μm, preferably 20 μm to 100 μm.

[0067] Therefore, the moisture-proof performance of hollow containers is improved.

[0068] In this embodiment, the outer surface of the main part of the bottle does not have a barrier coating containing polymer powder.

[0069] This is to achieve a "raw" paper-like appearance on the outer surface of the main part of the bottle. Therefore, only the parts of the bottle exposed to moisture and liquid are provided with a barrier coating.

[0070] Further features and advantages of this disclosure will become apparent when examined in light of the appended claims and the following description. Those skilled in the art will recognize that different 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

[0071] Various aspects of this disclosure, including its specific features and advantages, will be readily understood from the following detailed description and accompanying drawings, wherein:

[0072] Figure 1A The steps of providing an internal barrier coating portion according to an exemplary embodiment of the method of this disclosure are illustrated schematically.

[0073] Figure 1B The steps of providing an external barrier coating on the upper portion of a container are illustrated schematically according to an exemplary embodiment of the method of this disclosure.

[0074] Figure 2 The illustration shows, including, according to Figures 1A to 1B Bottle-shaped parts of molded slurry formed by the method shown.

[0075] Figure 3A A bottle-shaped component comprising a molded slurry coated according to the method of this disclosure is shown, wherein the bottle-shaped component has been conditioned at a relative humidity of 90%.

[0076] Figure 3B The heat-treated product is shown. Figure 3A Bottle-shaped components. Detailed Implementation

[0077] The present disclosure will now be described more fully with reference to the accompanying drawings, in which presently preferred embodiments of the disclosure are illustrated. However, the disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to achieve thoroughness and completeness and to fully communicate the scope of the disclosure to those skilled in the art. Throughout the application, the same reference numerals refer to the same elements.

[0078] exist Figures 1A to 1B The present invention conceptually illustrates a method for providing a barrier coating on a hollow container containing a molded slurry. Figure 2 A hollow container, i.e. a bottle-shaped piece, formed by the method of this disclosure is shown.

[0079] The methods disclosed herein include:

[0080] a) A hollow container 100 comprising a molded slurry is provided, wherein the hollow container includes a main portion 101 and an upper portion 102; the hollow container extends along a longitudinal centerline 103, wherein the longitudinal extension of the upper portion 102 corresponds to 5% to 30% of the maximum longitudinal extension of the hollow container, and wherein the longitudinal extension of the main portion 101 corresponds to 70% to 95% of the maximum longitudinal extension of the hollow container, and wherein the hollow container includes a bottom surface 104 and sidewalls 105 extending from the bottom surface to an opening of the hollow container; the sidewalls 105 and the bottom surface 104 define an outer surface and an inner surface 105a of the hollow container.

[0081] b) Polymer powder is deposited onto the inner surface 105a of the hollow container 100 by a spraying device 107 capable of electrifying the polymer powder before or during deposition, wherein at least a major portion 101 of the hollow container 100 is grounded during polymer powder deposition.

[0082] c) Polymer powder is deposited onto the outer surface of at least a portion of the upper portion 102 of the hollow container 100 using the spraying device 107.

[0083] d) After steps b) and c), the hollow container is treated with heat or radiation under conditions that melt and / or solidify the polymer powder to form a barrier coating.

[0084] 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-shaped piece. In this embodiment, the hollow container has rotational symmetry about its longitudinal centerline. For example, the hollow container is typically cylindrical in shape.

[0085] As used herein, the term "molded pulp" refers to a pulp or mixture of pulps that has been shaped, pressed, and dried. Molded pulps 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.

[0086] 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.

[0087] 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.

[0088] There are no limitations on the polymer powder used for coating hollow containers. For example, the powder may contain thermoplastic polymers selected from polyolefins such as polyethylene or polypropylene and their copolymers, polyamides, and polyesters and their copolymers. The polymer powder may also contain 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 5 μm to 100 μm, or for example 10 μm to 50 μm. These ranges allow for uniform coating and also allow for the charging of the polymer powder particles by a spraying device.

[0089] The longitudinal extension of the upper portion 102 corresponds to 5% to 30%, preferably 10% to 20%, of the maximum longitudinal extension of the hollow container. The longitudinal extension of the upper portion... Figure 2 In this context, it is represented by e1.

[0090] The longitudinal extension of the main portion 101 corresponds to 70% to 95%, preferably 80% to 90%, of the maximum longitudinal extension of the hollow container. The longitudinal extension of the main portion 101 in... Figure 2 In Chinese, it is represented by e2.

[0091] Hollow containers containing molded slurry can be provided in ways known to those skilled in the art. For example, a hollow container can be provided by depositing a slurry mixture into a mold, such as a split mold, activating a pressing tool, or using an impermeable balloon-like object, such as within the internal cavity of the mold, to shape the slurry into a balloon-like form, thereby forming the inner and outer walls of the hollow container. The molded slurry can then be discharged, thereby removing excess water. A process for providing a hollow container is described, for example, in WO16055073. Other methods for providing hollow containers containing molded slurry are also conceivable.

[0092] The hollow container can then be removed from the split mold, and the hollow container can be adjusted before the powder coating is applied to the inner and outer walls of the container.

[0093] In an alternative embodiment, the step of providing a hollow container containing the molded slurry is performed in the same molding apparatus used to provide the inner and outer coating portions in steps b) and c) of the method.

[0094] like Figures 1A to 1B As shown, the spraying device 107 for polymer powder coating is a spray gun. The method is by no means limited to using a spray gun, but can use any spraying device capable of charging the powder before or during powder deposition. Typically, the powder is charged by corona charging; that is, 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 allows the powder particles to adhere firmly to and bond to the grounded and conductive portion of the hollow container.

[0095] like Figures 1A to 1B As shown, the spraying device 107 includes a nozzle 107a that is inserted into a hollow container, i.e., inserted into a bottle-shaped component.

[0096] During the polymer powder deposition step, the hollow container may have a moisture content of 3% to 15%, for example 5% to 10%.

[0097] "Moisture content" refers to the amount of water contained in a molded slurry container, expressed as a percentage of the total weight of the container. Moisture content is typically measured at a temperature of approximately 20°C.

[0098] When the moisture content is within the above range, the polymer powder tends to adhere to the inner and outer surfaces of the hollow container.

[0099] The polymer powder deposition step b) can be performed in a molding apparatus 108 containing conductive material; the molding apparatus 108 is configured to surround at least a portion of the main part of the hollow container.

[0100] exist Figures 1A to 1B In the method shown, polymer powder deposition step b) is performed in a molding apparatus 108 containing conductive material; the molding apparatus 108 includes at least a first removable portion 108a and a second removable portion 108b, wherein the first removable portion 108a is configured to surround the upper portion 102 of the container, and wherein at least the second removable portion 108b is configured to surround the main portion 101 of the container.

[0101] exist Figures 1A to 1BIn the illustrated embodiment, the molding apparatus 108 further includes a third removable portion 108c. The first removable portion 108a is configured to surround the upper portion 102 of the hollow container, and the second removable portion 108b and the third removable portion 108c are configured to surround the main portion 101 of the hollow container.

[0102] In this document, the term "encircle" means that the removable mold portion surrounds and contacts the hollow container portion, thereby achieving a uniformly grounded and conductive surface. In embodiments, the corresponding removable mold portion has a shape that matches the shape of the hollow container portion.

[0103] The molding device 108 is configured to surround the hollow container 100 to ensure grounding and contact with a conductive surface during polymer powder deposition.

[0104] The molding apparatus 108 may include, for example, a metal, such as aluminum.

[0105] In an alternative embodiment, the molding apparatus includes a formable conductive material.

[0106] The term "formable" refers to the ability of a conductive material in a molding apparatus to conform to or adapt to the shape of a hollow container when a moderate load is applied. For example, a formable conductive material can be a conductive thermoplastic elastomer copolyester (TPC-ESD), conductive foam including, for example, polyurethane, conductive felt such as polyester fabric, or conductive rubber. Formable conductive materials can also be coated with metal.

[0107] The inventors discovered that a more uniform coating thickness can be obtained by utilizing a formable molding device. Furthermore, the deposition of the polymer powder is less dependent on the moisture content of the hollow container. By utilizing a formable conductive material, a moisture content in the range of 3% to 10% can be utilized during the polymer powder deposition steps (steps b and c).

[0108] In embodiments where the molding apparatus 108 includes metal, a moisture content typically in the range of 8% to 15%, for example 10% to 15%, is used during the polymer powder deposition steps (steps b and c).

[0109] The method may also include the following steps:

[0110] a') After step a) of providing a hollow container containing the molded slurry, the hollow container is conditioned to an ambient relative humidity of 30% to 100%, preferably 30% to 70%.

[0111] In embodiments where the molding apparatus includes metal as a conductive material, the method may further include the following steps:

[0112] a') After step a), the hollow container containing the molded slurry is conditioned to an ambient relative humidity of 60% to 100%, for example, 75% to 95%.

[0113] Polymer powder deposition step b) is typically performed directly after conditioning step a') to maintain the moisture content of the hollow container during powder coating.

[0114] At an ambient relative humidity of 60% to 100%, for example 75% to 95%, the conditioning time can be at least 2 hours, for example at least 10 hours, preferably at least 15 hours. Conditioning is typically carried out at room temperature.

[0115] like Figure 1A As shown, during polymer powder deposition step b), the main portion 101 and the upper portion 102 of the container are surrounded by the molding device 108.

[0116] The internal powder coating can be provided by continuously spraying the inside of the hollow container for about 1 to 20 seconds, for example, 2 to 10 seconds. Charged particles are blown from the nozzle 107a toward the inner surface 105a of the container. A uniform electric field is achieved by the molding device 108 surrounding the main part and the upper part of the container. Thus, a flat and uniform barrier coating covering substantially all parts of the inner wall of the container is achieved.

[0117] Figure 1B The step of providing an external coating on the outer surface of the upper portion 102 of the container 100 is shown. In this step, the first removable portion 108a is removed from the molding apparatus 108.

[0118] The tip of the spraying device 107 is arranged at an axial distance d1 of 10 mm to 250 mm, preferably 40 mm to 150 mm, from the opening of the container. Generally, spraying is achieved by arranging the tip or nozzle of the spraying device 107 in a vertical position relative to the center of the opening of the container; that is, in a position along the longitudinal centerline.

[0119] Hollow containers are preferably bottle-shaped. For example... Figure 2 As shown, the bottle-shaped component includes a bottom surface 104 and sidewalls 105 extending from the bottom surface 104 to an opening 106 of the bottle-shaped component; the sidewalls 105 define a main portion 101 and an upper portion 102 of the bottle-shaped component. The bottle-shaped component may have rotational symmetry about a longitudinal centerline 103. The bottle-shaped component generally has a substantially cylindrical shape.

[0120] The upper portion 102 includes a shoulder portion 102a and a neck portion 102b, wherein the neck portion 102b has a smaller cross-sectional area than the main portion 101 and is configured to surround at least an opening 106 around the bottle-shaped member, and wherein the shoulder portion 102a is arranged to taper between the main portion and the neck portion.

[0121] The shoulder section typically tapers at an angle of approximately 5 to 75 degrees, for example, 20 to 60 degrees, between the main section and the neck section.

[0122] exist Figure 2 In the illustrated embodiment, the neck portion 102b is threaded. Threaded neck portions may be advantageous in various bottle-shaped applications, but this disclosure is not limited to threaded neck portions.

[0123] The neck portion 102b of the bottle-shaped component is the part most susceptible to moisture and liquid. This portion is coated in step c) of the method. The neck portion has a smaller cross-sectional area than the rest of the upper portion 102 of the bottle-shaped component.

[0124] In embodiments where the neck portion 102b has threads, the threaded portion typically has a trapezoidal structure; that is, a “threaded profile” that allows the cap to be screwed onto it.

[0125] The main part 101 and the upper part 102 (including the neck part and the shoulder part) of the hollow container are integrally molded.

[0126] In the step of providing the external coating (step c), at least the neck portion 102b of the upper portion is coated.

[0127] Following polymer powder deposition steps b) and c), the hollow container is subjected to heat and / or radiation treatment under conditions of melting and / or solidifying polymer powder.

[0128] When polymer powder is exposed to high temperatures or radiation such as ultraviolet radiation, the deposited polymer powder coating softens, melts, and / or solidifies, providing a continuous barrier coating.

[0129] Therefore, a uniform barrier coating without pinholes was obtained.

[0130] The heat treatment steps can vary depending on the properties of the polymer particles and the required thickness of the barrier coating.

[0131] In this embodiment, the hollow container is subjected to heat treatment at a temperature of 100°C to 300°C. The heat treatment time can be between 1 minute and 30 minutes.

[0132] Alternatively, the powder-coated portion can be treated with ultraviolet (UV) light, which typically allows the powder-coated portion to melt and solidify rapidly.

[0133] In an exemplary embodiment, the curing step d is performed by heating the hollow container at a temperature of 120°C to 220°C for 1 to 30 minutes.

[0134] For example, the curing step can be carried out by heating the hollow container at a temperature of 150°C to 200°C, preferably 170°C to 190°C, for 5 to 20 minutes, preferably 6 to 15 minutes.

[0135] The method disclosed herein allows for coating of both the inner and outer surfaces prior to heat (or radiation) treatment. Therefore, the method requires only one curing or melting step. This is advantageous because the method is significantly simplified and time-saving compared to situations where heating must be performed, for example, after the corresponding coating steps b) and c).

[0136] The steps of providing the inner and outer coating portions in the same spraying sequence, i.e., before heating or radiating the polymer powder coating portion, can be related to the moisture content of the hollow container. If the moisture content is high, the outer surface of the upper portion of the hollow container can be coated during polymer powder deposition without connecting to a grounded conductive surface. The moisture content can vary depending on the material used as the conductive material in the molding apparatus.

[0137] The method disclosed herein is not limited to a specific slurry, but can be used with any slurry.

[0138] In an exemplary embodiment, the molded slurry is formed from a mixture of a first slurry and a second slurry, wherein...

[0139] - The first slurry comprises 65% to 90%, such as 70% to 84% by dry weight, of a first slurry having a Schopper-Riegler (SR) number of less than 48, preferably less than 40, more preferably less than 30 according to ISO 5267-1; and

[0140] - The second slurry contains 10% to 35%, such as 16% to 30% of a second slurry by dry weight, having a Schopper-Riegler (SR) number of 60-90, preferably 70-90, more preferably 77-90 according to ISO 5267-1.

[0141] This slurry mixture allows for increased strength in the container walls and also affects the rate at which the slurry dehydrates in the mold. Therefore, the process of providing hollow containers can be achieved in a faster and more robust manner.

[0142] The first slurry may be unrefined or only moderately refined.

[0143] The second pulp typically has a higher degree of refining than the first pulp. Therefore, the average fiber length in the first pulp is greater than the average fiber length in the second pulp.

[0144] The first slurry and / or the second slurry may include “market slurry”; that is, a slurry produced at one location, dried, and transported to another location for further processing.

[0145] Preferably, the first and / or second slurry is at least 50%, for example at least 75%, for example at least 90% by dry weight, of cork pulp. This mixture of slurries allows for the provision of more robust container walls.

[0146] The thickness of the barrier coating formed by the method according to this disclosure can be in the range of 5 μm to 300 μm, for example 10 μm to 200 μm, for example 20 μm to 100 μm.

[0147] 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 radiation under conditions that melt and / or cure the polymer powder.

[0148] On the other hand, a hollow container formed according to the method described above is provided.

[0149] See Figure 2 The hollow container includes a main portion 101 and an upper portion 102. The hollow container extends along a longitudinal centerline 103, wherein the longitudinal extension of the upper portion 102 corresponds to 5% to 30% of the maximum longitudinal extension of the hollow container 100, and wherein the longitudinal extension of the main portion 101 corresponds to 70% to 95% of the maximum longitudinal extension of the hollow container 100. 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 105a of the hollow container. The hollow container includes a barrier coating containing polymer powder on the inner surface 105a of the hollow container and on at least a portion of the outer surface of the upper portion 102 of the hollow container.

[0150] Preferably, the hollow container is a bottle-shaped piece; the upper portion 102 includes a shoulder portion 102a and a neck portion 102b; wherein the neck portion has a smaller cross-sectional area than the main portion and is configured to surround at least an opening 106 of the bottle-shaped piece, and wherein the shoulder portion is arranged to taper between the main portion and the neck portion; wherein the bottle-shaped piece includes a barrier coating containing polymer powder on the inner surface 105a of the bottle-shaped piece and on at least the outer surface of the neck portion 102b of the bottle-shaped piece.

[0151] The outer surface of the main portion 101 of the bottle-shaped component preferably does not include any barrier coating. In other words, the outer surface of the main portion of the bottle-shaped component does not have a barrier coating containing polymer powder. Therefore, the main portion of the outer surface of the bottle-shaped component will have a paper-like appearance and no gloss.

[0152] Example 1: Powder-coated portions of the inner and outer surfaces of a bottle-shaped component containing a molded slurry.

[0153] The purpose of the test is to apply a polymer powder coating to the inner surface and the outer surface of the upper part of the bottle, i.e., the neck part of the bottle, before subjecting the coating to heat treatment.

[0154] Three paper bottle-shaped containers were used in the test. Each container contained a slurry formed from a mixture of chemical and mechanical slurries.

[0155] The bottle-shaped component is installed in an aluminum molding device, such as Figures 1A to 1B The inverted structure is shown. The aluminum molding unit comprises three removable sections. The spray gun used for the powder coating section is a Nordson Encore HD automated powder coating gun. The polymer powder used is HDPE powder with a particle size distribution of 0μm-80um.

[0156] Insert the spray gun nozzle into each bottle-shaped part, approximately 10 mm from the bottom surface of the bottle. The spraying sequence lasts approximately 5 to 7 seconds and is performed continuously as the spray gun is removed from the bottle-shaped part.

[0157] Next, remove the portion of the molding device that covers the upper part of the bottle-shaped part, cover the screw holes, and then spray the bottle-shaped part again by holding the spray gun approximately 100mm away from the opening of the bottle-shaped part (see...). Figure 1B The report describes powder adhesion and coverage on the outer neck and shoulder of the vial; that is, on the upper portion of the vial.

[0158] Three different bottle-shaped containers were used in the test. Two of the containers were conditioned overnight at 23°C and 90% RH (moisture content approximately 14%), and one container was conditioned overnight at 23°C and 50% RH (moisture content approximately 7%).

[0159] The bottle, conditioned at 90% relative humidity (RH), exhibited excellent coverage and a complete upper portion; that is, the neck of the bottle showed a uniform outer coating. The results are as follows... Figure 3A and Figure 3B As shown. Figure 3A The external coating on the upper portion of the bottle-shaped component 300 is shown. The main portion 101 of the bottle-shaped component 300 has no coating on its outer wall. Figure 3B The cured bottle-shaped part 300 is shown.

[0160] For bottle-shaped parts cured at 50% RH, a smaller powder coverage area is achieved on the outer surface of the upper portion of the bottle-shaped part.

[0161] Example 2: Powder deposition using a molding apparatus containing a formable conductive material – coating thickness on the sealing area

[0162] The purpose of this test was to apply a polymer powder coating to the inner and outer surfaces of a bottle-shaped part with a lower moisture content than in Example 1, using a formable molding apparatus. The molding apparatus was made of a conductive thermoplastic elastomer copolyester in the shape of the bottle. When the bottle-shaped part was placed in the molding apparatus, approximately 15 mm of the neck area was left uncovered, i.e., not in direct contact with the molding material, allowing both the outer and top surfaces of the bottle-shaped part to be coated.

[0163] The spray gun used for the powder coating section is the Nordson Encore HD automated powder coating gun. The polymer powder used is HDPE powder with a particle size distribution of 0 μm to 100 μm.

[0164] Mount the bottle upside down in a grounded, formable forming device. Position the spray gun nozzle approximately 40 mm from the bottle's inlet. Powder coating begins as the nozzle moves toward the bottle's neck / inlet. The nozzle continues coating, stopping approximately 10 mm from the bottom inner surface of the bottle. The nozzle then returns to its starting position, approximately 40 mm from the bottle's inlet, and statically coats the uncovered neck area of ​​the bottle. The total coating time is 4 seconds.

[0165] A total of nine paper bottle-shaped containers were used during the test. Five of the containers had a moisture content of 8.5% (measured at approximately 20°C), and four had a moisture content of 5.2% (measured at approximately 20°C).

[0166] The bottle-shaped parts were sprayed according to the above procedure, and the weight of the coated portion was measured immediately. For bottle-shaped parts with a moisture content of 8.5%, the average weight of the coated portion was 3.06g (standard deviation 0.07g). For bottle-shaped parts with a moisture content of 5.2%, the average weight of the coated portion was 3.24g (standard deviation 0.16g).

[0167] After measuring the weight of the coated portion, the bottle was placed in an oven at 180°C for 10 minutes. Then, the thickness of the coating around the circumference of the sealing area was measured using an optical microscope.

[0168] The average coating thickness of the sealing area of ​​the bottle-shaped component with a moisture content of 8.5% was 103.6 μm (standard deviation 29.7 μm). A total of 219 locations were measured in the sealing areas of the five bottle-shaped components. The average coating thickness of the sealing area of ​​the bottle-shaped component with a moisture content of 5.2% was 95.3 μm (standard deviation 28.5 μm). A total of 173 locations were measured in the sealing areas of the four bottle-shaped components.

[0169] Example 3: Powder deposition using a molding apparatus containing a formable conductive material—coating thickness on the inner surface of a bottle-shaped component.

[0170] The purpose of this test was to apply a more uniform polymer powder coating to the inner surface of the bottle-shaped part using a formable molding device and an optimized spraying sequence. Similar to Example 2, the molding device was made of a conductive thermoplastic elastomer copolyester into the shape of the bottle, with approximately 15 mm of the neck portion left uncovered.

[0171] For these tests, the spray gun nozzle was initially positioned 10 to 15 mm from the inner surface of the bottom of the bottle. Powder coating began as the nozzle started moving downwards towards the neck / inlet of the bottle. The nozzle continued coating while traveling approximately 40 mm outside the inlet of the bottle and then stopped. The nozzle then remained stationary in that position and coated the neck and threaded sections of the bottle. The total coating time was 5 seconds.

[0172] Four bottle-shaped components were used in the test, all with a moisture content of 5.2% (measured at approximately 20°C). The average weight of the coated portion was 3.48g (standard deviation 0.09g).

[0173] After spraying, the weight of the coated portion was measured directly, and the bottle was placed in an oven at 180°C for 10 minutes. Then, the thickness of the coating layer on the inner surface was measured by dividing the bottle in half and observing the coating layer on the cut surface using an optical microscope.

[0174] The average coating thickness in the bottle-shaped components was 169.2 µm (standard deviation 49.9 µm). A total of 720 measurements were taken at different locations along the complete cut surfaces of all four bottle-shaped components.

[0175] Example 4: Moisture-proof performance

[0176] The purpose of this test is to evaluate the moisture resistance of a molded device containing a formable conductive material and a bottle-shaped component coated with a spraying sequence as described in Example 2.

[0177] Four paper bottle-shaped components were used in total during the testing. The paper bottle-shaped components were conditioned at 50% relative humidity (23°C). For all bottle-shaped components, the moisture content (when polymer powder was applied) was approximately 7%. The average weight of the coated portion was 3.4 g (standard deviation 0.1 g). After measuring the weight of the coated portion, the bottle-shaped components were placed in an oven at 180°C for 6 minutes to melt the powder and form a continuous film. The moisture resistance of the bottle-shaped components was then measured using Permatran. During the testing, the neck of the bottle-shaped components was sealed to a steel plate with epoxy resin. The measured average WVTR (23°C, 50%RH) was 0.006 g / day, and the average WVTR (38°C, 90%RH) was 0.04 g / day.

[0178] Therefore, all four bottle-shaped components exhibit excellent moisture-proof performance.

[0179] The terms, definitions, and implementation methods of all aspects of this disclosure are applied to other aspects of this disclosure with the necessary modifications.

[0180] 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.

[0181] 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 providing a barrier coating on a hollow container (100) containing a molded slurry; the method comprising the steps of: Step a): Provide a hollow container (100) containing a molded slurry, wherein the hollow container (100) includes a main portion (101) and an upper portion (102); the hollow container extends along a longitudinal centerline (103), wherein the longitudinal extension of the upper portion (102) corresponds to 5% to 30% of the maximum longitudinal extension of the hollow container (100), and wherein the longitudinal extension of the main portion (101) corresponds to 70% to 95% of the maximum longitudinal extension of the hollow container (100), 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 (105a) of the hollow container. Step b): The polymer powder is deposited onto the inner surface (105a) of the hollow container (100) by a spraying device (107) capable of electrifying the polymer powder before or during the deposition of the polymer powder, wherein at least the main portion (101) of the hollow container (100) is grounded during the deposition of the polymer powder, wherein step b) of the polymer powder deposition is performed in a molding device (108) comprising a conductive material, wherein the molding device (108) includes at least a first removable portion (108a) and a second removable portion (108b), wherein the first removable portion (108a) is configured to surround the upper portion (102) of the hollow container (100), and wherein the second removable portion (108b) is configured to surround the main portion (101) of the hollow container (100). Step c): Polymer powder is deposited onto the outer surface of at least a portion of the upper portion (102) of the hollow container (100) by means of the spraying device (107), wherein the outer surface of the main portion (101) does not contain a barrier coating portion containing polymer powder, wherein step c) of polymer powder deposition is performed by arranging the spraying device (107) at a distance d1 from the opening (106) of the hollow container at a distance of 10 mm to 250 mm, wherein during step c) of polymer powder deposition, the first removable portion (108a) is removed from the molding device (108); Step d): Following steps b) and c), the hollow container is treated with heat or ultraviolet radiation under conditions that melt and / or solidify the polymer powder. During steps b) and c) of polymer powder deposition, the moisture content of the hollow container is 3% to 15%.

2. The method according to claim 1, wherein, The molding apparatus includes a formable conductive material.

3. The method according to claim 1 or 2, further comprising the following step: Step a'): After step a), the hollow container containing the molded slurry is provided, the hollow container is adjusted to an ambient relative humidity of 30% to 100%.

4. The method according to claim 1 or 2, wherein, After step a), which provides the hollow container containing the molded slurry, step a') includes adjusting the hollow container to an ambient relative humidity of 60% to 100%.

5. The method according to claim 1 or 2, wherein, Steps b) and c) of polymer powder deposition are performed simultaneously.

6. The method according to claim 1 or 2, wherein, The hollow container is a bottle-shaped piece, wherein the upper portion (102) includes a shoulder portion (102a) and a neck portion (102b), wherein the neck portion has a smaller cross-sectional area than the main portion, and the neck portion is configured to surround at least the opening (106) of the bottle-shaped piece, and wherein the shoulder portion (102a) is arranged to taper between the main portion (101) and the neck portion (102b).

7. The method according to claim 6, wherein, In step c) of polymer powder deposition, at least the neck portion (102b) of the upper portion (102) is coated.

8. The method according to claim 6, wherein, In step c) of the polymer powder deposition, the entire upper portion (102) of the hollow container (100) is coated.

9. The method according to claim 1 or 2, wherein, Step d is performed by heating the hollow container (100) at a temperature of 120°C to 220°C for 1 minute to 30 minutes.

10. A hollow container (100) formed by the method according to any one of claims 1 to 9, wherein, The hollow container includes a main portion (101) and an upper portion (102); the hollow container extends along a longitudinal centerline (103), wherein the longitudinal extension of the upper portion (102) corresponds to 5% to 30% of the maximum longitudinal extension of the hollow container (100), and wherein the longitudinal extension of the main portion (101) corresponds to 70% to 95% of the maximum longitudinal extension of the hollow container (100), wherein the hollow container includes a bottom surface (104) and extends from the bottom surface (104)... The sidewall (105) extends to the opening (106) of the hollow container; the sidewall (105) and the bottom surface (104) define the outer surface and inner surface (105a) of the hollow container, wherein the hollow container includes a barrier coating containing polymer powder on the inner surface (105a) of the hollow container and on the outer surface of at least a portion of the upper portion (102) of the hollow container, wherein the outer surface of the main portion (101) does not have a barrier coating containing polymer powder.

11. The hollow container according to claim 10, wherein, The hollow container is a bottle-shaped part; the upper part (102) includes a shoulder part (102a) and a neck part (102b), wherein the neck part has a smaller cross-sectional area than the main part, and the neck part is configured to surround at least the opening (106) of the bottle-shaped part, and wherein the shoulder part is arranged to taper between the main part and the neck part, wherein the bottle-shaped part includes a barrier coating containing polymer powder on the inner surface (105a) of the bottle-shaped part and on at least the outer surface of the neck part (102b) of the bottle-shaped part.

12. The hollow container according to claim 10 or 11, wherein, The thickness of the barrier coating is in the range of 5 μm to 300 μm.

13. The hollow container according to claim 10 or 11, wherein, The thickness of the barrier coating is in the range of 20 μm to 100 μm.

14. The hollow container according to claim 11, wherein, The outer surface of the main portion (101) of the bottle-shaped component does not contain a barrier coating of polymer powder.

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