Methods, apparatus, and chemical compositions for selectively coating fiber-based food containers

Abstract

A method and apparatus for vacuum forming and subsequent topical coating of a fiber-based food container. The slurry includes one or more of an embedded moisture barrier, a vapor barrier, and an oil barrier, and the topical coating includes one or more of a vapor barrier, a moisture barrier, an oil barrier, and an oxygen barrier. For food containers with deep sidewalls, the spray coating system includes a first nozzle for applying a full cone spray pattern to the bottom surface of the container and a second nozzle for applying a hollow cone spray pattern to the inside surface of the sidewall.

Description

[Technical Field]

[0001] REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of, and claims priority to, U.S. Patent Application No. 15 / 220,371, filed July 26, 2016, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates generally to spray coatings for use with vacuum-formed, molded fiber food containers, and more specifically to the selective combination of slurry chemistries and surface coatings to produce desired oil, water, steam, and / or oxygen barriers. [Background technology]

[0003] Pollution caused by single-use plastic containers and packaging materials is epidemic, damaging global landscapes and threatening delicate ecosystems and the life forms that inhabit them. Single-use containers migrate along waterways and into the oceans in the form of Styrofoam and expanded polystyrene (EPS) packaging, take-out containers, bottles, thin film bags, and photodegraded plastic pellets.

[0004] This marine debris accumulates in huge patches of highly concentrated plastic islands located in each of our ocean eddies. Sunlight and waves gradually break down floating plastic into smaller particles, which never completely disappear or biodegrade. Furthermore, plastic particles act as sponges for water-soluble pollutants such as pesticides. Fish, turtles, and even whales eat plastic objects, which can make them sick or kill them. Smaller marine animals ingest the microscopic plastic particles, which are passed on to us when we eat seafood.

[0005] Sustainable solutions for reducing plastic pollution are gaining momentum. However, continued adoption requires that these solutions not only be environmentally beneficial, but also competitive with plastics from both a performance and cost perspective. This invention involves replacing plastics with an innovative technology of molded fibers without compromising product performance, offering a competitive cost structure within an ecologically responsible framework.

[0006] As a brief background, molded paper pulp (molded fiber) has been used to make containers, trays, and other packaging since the 1930s but experienced a decline in the 1970s after the introduction of plastic foam packaging. Paper pulp can be produced from old newsprint, corrugated cardboard boxes, and other plant fibers. Today, molded pulp packaging is widely used for electronic components, household goods, auto parts, and medical products, as well as for edge / corner banding or pallet trays for shipping electronic and other fragile components. A mold is formed as a mirror image of the finished package, with a screen attached to its surface. A vacuum is drawn across the screen, accumulating the fiber particles into the shape of the finished product.

[0007] The two most common types of molded pulp are classified as Type 1 and Type 2. Type 1 has walls between 3 / 16 inch (4.7 mm) and 1 / 2 inch (12.7 mm) and is commonly used for support packaging applications. Type 1 molded pulp production, also known as "dry" production, uses a fiber slurry made from ground newsprint, kraft paper, or other fibers dissolved in water. A mold mounted on a platen is dipped or immersed in the slurry, and a vacuum is applied to the generally convex backside. The vacuum pulls the slurry onto the mold, forming the shape of the package. While still under vacuum, the mold is removed from the slurry tank, allowing the water to drain from the pulp. Air is then blown through the tool to extrude the molded fiber pieces. The parts are typically deposited on a conveyor within a drying oven.

[0008] Type 2 molded pulp production, also known as "wet" production, is typically used for packaging electronics, cell phones, and household goods with containers having walls between 0.02 in. (0.5 mm) and 0.06 in. (1.5 mm). Type 2 molded pulp uses the same materials and follows the same basic process as Type 1 production, up to the point where a vacuum pulls the slurry onto a mold. After this step, a transfer mold mates with the fibrous packaging, and the formed "wet part" is transferred to a hot press, which compresses and dries the fibrous material to increase density and provide a smooth exterior surface finish. See, for example, stratasys.com / solutions / additive-manufacturing / tooling / molded-fiber, keiding.com / molded-fiber / manufacturing-process / , Grenidea Technologies PTE Ltd. European Patent Publication No. EP1492926B1, published April 11, 2007, entitled "Improved Molded Fiber Manufacturing," and afpackaging.com / thermoformed-fiber-molded-pulp / , the contents of all of the foregoing being incorporated herein by reference in their entirety.

[0009] Fiber-based packaging products are biodegradable, compostable, and, unlike plastics, do not migrate into the ocean. However, currently known fiber technologies are not well suited for use with meat and poultry, prepared meals, produce, microwaveable foods, or as closures for beverage containers such as hot coffee. In particular, selectively integrating one or more oil, water, steam, and / or oxygen barriers into a slurry and / or selectively applying one or more barrier layers to all or a portion of the surface of a finished packaging product can be laborious, time-consuming, and expensive.

[0010] Therefore, there is a need for methods, devices, spray systems, and chemical formulations that overcome the limitations of the prior art.

[0011] Various features and characteristics will also become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background section. Summary of the Invention

[0012] Various embodiments of the present invention relate to methods, chemical formulas, spray systems, and nozzle configurations for producing vacuum-formed, fiber-based packaging and container products and selectively applying barrier coatings to selected surfaces thereof, including, among others: i) meat, produce, horticulture, and utility containers embodying novel geometric features that promote structural rigidity; ii) meat, produce, and horticulture containers with embedded and / or localized moisture, oil, oxygen, and / or vapor barriers; iii) microwavable, oven-heated, frozen food, ready-to-eat, yogurt, salad, prepared food, macaroni and cheese, and other containers embodying embedded and / or localized moisture, oil, oxygen, and / or vapor transmission barriers and / or retention aids to improve chemical bonding within the fiber matrix; and iv) meat containers embodying moisture / vapor barriers that maintain structural rigidity over extended shelf lives.

[0013] It should be noted that the various inventions described herein are illustrated in the context of, but not limited to, a conventional slurry-based vacuum forming process. Those skilled in the art will understand that the inventions described herein contemplate any fiber-based manufacturing modality, including drying or fluffing processes that may or may not involve vacuum forming, including 3D printing techniques.

[0014] Various other embodiments, aspects, and features are described in more detail below. [Brief explanation of the drawings]

[0015] Exemplary embodiments are described below in conjunction with the accompanying drawings, in which like numerals refer to like elements. [Figure 1]FIG. 1 is a schematic block diagram of an exemplary vacuum forming process using a fiber-based slurry, according to various embodiments. [Figure 2] FIG. 1 is a schematic block diagram of an exemplary closed-loop slurry system for controlling the chemical composition of a slurry, according to various embodiments. [Figure 3] FIG. 1 is a perspective view of the bottom of an exemplary meat tray, according to various embodiments. [Figure 4] FIG. 4 is a side elevational view of the meat tray of FIG. 3 according to various embodiments. [Figure 5] 5 is a top plan view of the meat tray of FIGS. 3 and 4 in accordance with various embodiments. FIG. [Figure 6] FIG. 6 is an end view of the meat tray of FIG. 5 according to various embodiments. [Figure 7] 1 is a schematic perspective view of a spray coating system for meat trays according to various embodiments; FIG. [Figure 8] FIG. 1 is a schematic perspective view of a spray coating system using a full cone and hollow cone dual nozzle system for use with microwave ovens, frozen foods, ready meals, and other food containers with deep sidewalls, according to various embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0016] The following detailed description of the present invention is merely exemplary in nature and is not intended to limit the present invention or the application and uses of the present invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

[0017] Various embodiments of the present invention relate to fiber-based or pulp-based products for use both within and outside the food and beverage industry. By way of non-limiting example, the present disclosure relates to specific chemical formulations of slurries and topical films or coatings adapted to address the unique challenges facing the food industry, including oil barriers, moisture barriers, vapor barriers, water vapor barriers, oxygen barriers, strength additives, and retention aids, the lack of which has heretofore limited the range of fiber-based products that can effectively replace single-use plastic containers in the food industry. By combining novel slurry chemistries and surface coating techniques (e.g., spray coating, dipping), fiber-based products can be used in a wide variety of applications, such as frozen, refrigerated, and non-refrigerated foods, medical, pharmaceutical, and biological applications, microwaveable and ovenable food containers, beverage cups and lids, edible and non-edible liquids, materials that liberate water, oil, and / or water vapor during storage, shipping, and preparation (e.g., cooking), horticultural applications including consumable and landscape / garden plants, flowers, herbs, shrubs, and trees, chemical storage and dispensing devices (e.g., paint trays), packaging, lids, cups for produce (including human and animal foods such as fruits and vegetables), salads, prepared foods, meat, poultry, and fish. and industrial, automotive, marine, aerospace, and military components such as cups, bottles, guides and separators for the above-mentioned processing and display, edge and corner pieces for packaging, storage, and shipping of electronics, mirrors, artwork, and other fragile components, buckets, tubes, gaskets, spacers, sealants, cushions, and the like, as well as related molds, wire mesh forms, recipes, spray system and spray nozzle configurations and processes, chemical formulas, tools, slurry distribution, chemical monitoring, chemical injection, and related systems, apparatus, methods, and techniques for manufacturing the above-mentioned components.

[0018] Various embodiments of the spray coating technology provide an oil and / or vapor barrier to microwave bowls and meat trays to address the phenomenon of water and / or oil penetrating the tray surface and peeling off with the meat after freezing. Additionally, the spray coating may have applicability to beverage lids, for example, to mitigate unwanted staining (e.g., lipstick).

[0019] In some embodiments, the microwave bowl, steamer, or tray is spray coated only on the inside surface, while other embodiments contemplate spray coating both the inside and outside surfaces. For spray applications, the spray nozzle may be configured to apply a spray pattern that approximates the surface to be coated (e.g., circular, annular, rectangular, and the like).

[0020] Various spray, dip, or other coating methods use chemicals tailored to produce desired performance characteristics in the finished product. Various chemical formulations include alginates (e.g., algae derivatives) mixed with polyester emulsions and applied to the surface of a container to mitigate water vapor transmission through the container wall (e.g., bottom surface) upon heating (e.g., using a microwave or conventional oven). Various chemical formulations may also include a calcium carbonate component to promote bonding of the coating to the surface of the fiber-based container. In many applications, the coating also effectively mitigates oil transmission.

[0021] These coating chemistries may be used instead of (or in addition to) incorporating TG8111-based fluorochemicals into the slurry, as described elsewhere herein. In some embodiments, the surface coating may have secondary oil barrier properties in addition to primary vapor and / or water barrier properties, although it may still be desirable to embed an oil barrier component into the slurry.

[0022] Various surface coating embodiments contemplate chemical as well as process aspects (e.g., the manner in which the formulation is applied to the surface to achieve the desired coverage objectives). Process considerations include, but are not limited to, spray droplet size, atomizer configuration and orientation, spray geometry, and the "fill and transfer" technique in which a container (e.g., yogurt) is filled with the coating formulation and rapidly emptied to create a film on the interior surface.

[0023] In this regard, vapor barriers (e.g., to prevent frozen foods from drying out during freezing) and oxygen barriers (to maintain freshness and shelf life during freezing) typically require complete (e.g., 100%) coverage of the protective surface, while moisture (e.g., water) barrier coatings (e.g., to prevent meat from sticking to a meat tray after one or more freeze / thaw cycles or to prevent starch from sticking to a microwave bowl) can be effective with less than substantially complete surface coverage.

[0024] In various embodiments, spray and other coating processes may be used to apply a steam, oxygen, moisture, and / or oil barrier to the surface of the finished container in addition to, or instead of, incorporating one or more barrier chemicals into the slurry used to vacuum-form the container. In preferred embodiments, for example, when only the interior surface is to be coated (e.g., in the case of a non-stick barrier), a moisture barrier component is mixed into the slurry and an oil and / or vapor barrier is applied to the formed container.

[0025] Spray coating applications are intended for microwave bowls, frozen foods, and meat trays, among others. Depending on the application, spray coating with one or more of water, steam, oil, and oxygen barriers may be desirable. In the case of microwave bowls, 100% coverage may not necessarily be required, as long as shelf life is the issue. Spray technology can be used to apply a water and / or steam barrier, but can also be used to prevent "sticking" (not requiring 100% coverage) so that meat does not tear the paper fibers when removed from the tray in a frozen state (after one or more freeze / thaw cycles). Yogurt and other applications use spray coatings for water vapor and oxygen barriers, which typically require nearly 100% coverage.

[0026] Spray coating use cases generally involve: i) the chemical formulation of the coating to be applied; ii) the thermophysical, rheological, and viscoelastic properties; iii) the equipment for applying the coating to one or more surfaces (or portions of surfaces) of a container, packaging, or other workpiece; and iv) process parameters such as drying time and temperature.

[0027] A typical use case involving a spray coating is to surround the coating of a meat tray with a moisture barrier to help prevent the meat from sticking to the fiber tray after freezing. A top (surface) coating may be applied (via spray or otherwise) to reduce the extent to which the meat sticks to the tray after freezing. The coating also helps to maintain the strength and rigidity of the tray without freezing, for example, while meat and secretions are placed within the tray in a refrigerator.

[0028] An exemplary method for producing a spray-coated meat tray can start with an aqueous fiber-based slurry containing up to 100% OCC, or any desired combination of OCC and double-lined kraft (DLK) paper. (Alternatively, the various slurry bases described herein can include a mixture of recycled and virgin fibers, or the slurry base can include 100% virgin fibers (e.g., hardwood, softwood, or a combination thereof), as discussed below in conjunction with microwave bowls.)

[0029] A water / moisture barrier (e.g., 2-5%, preferably about 4% AKD), a dry strength additive (e.g., 0.5-4.5%, preferably about 4%, starch, Hercobond 6950 or modified starch), and a wet strength additive (e.g., Kymene) may be added to the slurry. After the trays are vacuum formed (e.g., dried in a heat press for about 55 seconds), the trays are transferred to a stacker and the stack of trays is transferred to a spray coating station where they are unnested and dropped into their respective pockets on a conveyor, after which a supplemental moisture coating is applied to each tray in either a serial or parallel fashion.

[0030] In various embodiments, the auxiliary coating may be applied using a system including two fixed nozzles disposed above the tray, each nozzle outputting a spray pattern in the form of a wall or curtain (much like an air knife) as the tray passes underneath. In this manner, each nozzle (or combination of nozzles) produces a spray pattern that preferably terminates in a line perpendicular to the direction of travel of the workpiece. In one embodiment, one nozzle may be angled forward (toward the direction of tray travel) and the other nozzle may be angled backward to ensure complete coating of sloped sidewalls, structural ribs, and any other geometric features.

[0031] Alternatively, for substantially flat trays with limited sidewall depth, or for applications where film uniformity is less important, a single curtain-type spray configuration may be used.

[0032] One metric for assessing whether a tray has received sufficient coverage (e.g., is sufficiently coated) involves comparing the weight of the tray before and after coating to determine whether the weight of the coating material applied to the tray meets a predetermined threshold (or range of values). Alternatively or additionally, the thickness of the applied film can be measured to determine whether the coating thickness meets a predetermined threshold (or range of values).

[0033] In some embodiments, the uniformity of the applied coating may also be measured, and process parameters adjusted as necessary to promote uniformity in application to future trays; in this regard, uniformity involves at least two considerations: i) whether the film layer is too thin at a local point or area, thereby not forming an effective barrier, and ii) whether the film layer is too thick at a local point or area, thereby preventing the finished tray at that point from drying completely, resulting in staining or peeling (where the top layer of the film slides off or otherwise peels off from the film).

[0034] The coated tray is then dried in an oven at a temperature ranging from 70 to 180°C, preferably about 80 to 110°C, and most preferably about 95°C for about one (1) minute to remove moisture from the film layer and otherwise cure as appropriate. Infrared (IR) sensors may be used to check the temperature of the meat tray at one or more points to ensure the proper curing temperature has been achieved.

[0035] For meat trays, the coating composition may include 25% acrylic and 75% water, where the acrylic may include an acrylic copolymer latex or similar material, such as Rhobarr 110 binder available from DOW Chemical Corporation. In this context, the coating functions as an anti-stick layer to prevent the top layer of the meat tray from peeling off when the frozen meat is removed from the tray.

[0036] In some embodiments, some or all of the opposite side of the tray (including the bottom surface and / or exterior sidewall) may also be coated to reduce to some extent the likelihood that frozen secretions from the meat (e.g., blood, oil, water) will adhere to the outside of the tray if, for example, the secretions leak around the seal between the tray and the outer plastic wrap when the package is stored on its side.

[0037] Meat trays typically do not require a separate oil barrier, but a vapor and / or anti-fouling barrier may also effectively inhibit oil penetration.

[0038] As an alternative to, or in addition to, acrylic, pea emulsion and alginate can also be used for meat trays, microwave bowls, and / or other packaging components.

[0039] After drying, the trays are stacked, boxed, and shipped.

[0040] The term "ready to eat" (RTE) trays describes containers in which salads, fruit, prepared meals, and other foods are packaged using a plastic film sealed around the perimeter of the tray and often stored in a refrigerator. RTE trays may be coated to provide an oxygen barrier to improve freshness and shelf life.

[0041] RTE trays without a local membrane barrier can be made by adding to an OCC / DLK slurry containing 30-100% OCC / DLK and 0-70% virgin pulp, and preferably about 100% OCC / DLK, i) an oil barrier containing 1-5%, preferably about 4%, Daikin 8111, ii) a moisture / water barrier containing 2-5%, preferably about 3.5%, AKD, and iii) a reinforcing component containing 3% starch, such as Hercobond.

[0042] RTE trays with a localized film barrier can be made in substantially the same manner as described above (but potentially omitting the 8111 oil barrier and / or increasing the AKD to 4%) and may also add a localized oxygen barrier comprising an acrylic in aqueous solution (e.g., 25% Robar 110 and 75% water). For RTE trays and containers (e.g., yogurt cups), the film is typically thicker than that described above in the context of meat trays to ensure more complete (e.g., 100%) coverage.

[0043] Uncoated microwave bowls can be made using slurries containing up to 100% virgin fibers (softwood, hardwood, or a combination thereof). In one embodiment, the slurry base includes about 45% bleached hardwood, about 35% bleached softwood, and about 25% unbleached softwood. The slurry may also include an oil barrier (e.g., 2.5% 8111), a water barrier (e.g., 3% AKD), a dry strength additive (e.g., 2.5% starch), a retention additive (e.g., 0.15% Nalco), and a defoaming component to remove entrained air (e.g., 1.5% Expair).

[0044] The coated microwave bowl may be made using a substantially virgin fiber slurry base as described above with respect to the uncoated microwave bowl, further comprising about 3% water barrier (AKD) and about 2.5% starch, but excluding oil barrier, retention additives, and antifoaming agents. The coating formulation may include about 27.5% solids in an aqueous solution. The 27.5% solids may include any suitable combination of the following five (5) ingredients (sometimes referred to as the DWP formulation): i) 25% acrylate, ii) 1.8% rice bran wax (which may reduce stickiness), iii) 0.4% pectin (which may promote the formation of a vapor barrier and also reduce stickiness to facilitate de-nesting of stacked bowls), iv) 0.3% pea protein (which may promote the emulsion of the rice bran wax), and v) 0.2% liquid ammonium or other additive to adjust the pH and thereby promote acrylate cure.

[0045] For bowls and other packaging components with deep sidewalls, a curtain-type spray output terminating in a line is insufficient. To address this challenge, the inventors developed a two-nozzle spray paradigm with a full cone spray pattern combined with a hollow cone spray pattern, which together provide adequate coverage of the bottom surface as well as sidewall features without overspraying the bottom surface.

[0046] In a preferred embodiment, the coating is applied to microwave bowls using a two-nozzle system disposed above a conveyor that carries the bowls through the spray coating station. A first "full cone" nozzle is configured to cover the center (bottom) of each bowl, and a second "hollow cone" nozzle is configured to cover the inside sidewall of each bowl. The full cone and hollow cone spray patterns are suitably configured to ensure complete coverage while minimizing excess film thickness in the area where the full cone pattern overlaps the hollow cone pattern.

[0047] In a preferred embodiment, as a bowl or other packaging component advances along the conveyor, the nozzle system also advances along the same path for a predetermined period of time, so that the nozzle or nozzles do not translate relative to the bowl during spraying. Thus, the nozzles can remain "stationary" relative to each bowl without compromising throughput.

[0048] The coated yogurt cup may be made using a substantially virgin fiber slurry base as described above in connection with the uncoated microwaveable bowl, further comprising approximately 4% water barrier (AKD) and 3% starch. Instead of (or in addition to) the spraying method described above, the topical oxygen barrier layer may be applied using either: i) a full immersion process in which the cup is immersed in a pool of coating solution, thereby coating both the interior and exterior surfaces; or ii) a "fill and discard" technique in which the coating solution is poured into the cup until it is full, and then discarded to coat the interior surface of the cup. In this context, the same or more diluted (lower acrylate concentration) versions of the DWP formulations described above may be used. Additionally, the poured solution may be recirculated in an open-loop or closed-loop system to reduce waste.

[0049] The coated cups may then be dried in an oven at about 95° C. for about 1 minute, before being stacked, boxed, and shipped.

[0050] In a traditional bowl of macaroni and cheese (mac and cheese), the pasta is dry and the cheese is typically packaged separately in a plastic or foil envelope, so an oxygen barrier layer may or may not be required. If an oxygen barrier is desired, it may be applied using, for example, either the full immersion or pour-and-dump technique (or both) described above. If an oxygen barrier is not required, an anti-stick coating may be applied, as described above.

[0051] An alternative version of the DWP formulation involves omitting the 0.3% pea protein (which is a powder) and using 0.05% Tween 80 (an emulsifier) ​​to perform essentially the same function as emulsifying the rice wax.

[0052] Additionally, instead of using powdered pectin, we use a water-based version that is easy to mix.

[0053] The formulation for the topical coating may include: [Table 1] [Table 2] [Table 3]

[0054] Generally, DWP spray coatings can be described as aqueous formulations containing total solids in the range of 15-40% by weight, preferably 25-30% by weight, and most preferably about 27.5% by weight. One component in the formulation may include an acrylic polymer that crosslinks and polymerizes upon curing to promote the formation of a desired moisture, oil, and / or oxygen barrier layer. The formulation also contains rice bran wax to provide non-stick properties and a non-glossy surface finish to the coated surface. The wax is emulsified with pea protein for a stable aqueous dispersion. The formulation also contains pectin as a viscosity modifier for optimal adhesion to hydrophobic fiber surfaces during spray coating. The pH of the formulation is approximately 9.0 with the addition of ammonia to maintain solubility of the acrylic polymer.

[0055] An exemplary method for preparing a solution to be applied as a topical coating will be described in the context of a seventy-five (75) gallon batch using the following definitions. RBW: Rice bran wax PP: Pea protein Pec: pectin G: Gallon L: Liter kg: kilogram

[0056] Heat 35.6 gallons of water to at least 185°F and mix 5.1 kg of RBW at high speed for approximately 12 minutes until the wax pellets are completely dissolved and the temperature of the solution returns to 185°F. Add 0.85 kg of PP to the mixture over approximately 1 minute. Mix the PP for an additional 10 minutes or more until no lumps are visible. Add 1.14 kg of Pec over 5 minutes and mix the contents for an additional 15 minutes or more until no lumps are visible. Continue mixing at low speed to bring the batch temperature to approximately 120°F. While mixing, add 37.5 gallons of Rhobarr 110 to the batch and continue mixing for 10 minutes. Slowly pour 2.15 L of 4% ammonia into the batch and continue mixing for an additional 10 minutes.

[0057] 1, an exemplary vacuum forming system and process 100 using a fiber-based slurry includes a first stage 101 in which a mold (not shown for clarity) in the mirror image shape of the product to be produced is encased in a thin wire mesh form 102 to match the contours of the mold. A supply 104 of fiber-based slurry 104 is introduced at pressure (P1) 106 (typically ambient pressure). By maintaining a lower pressure (P2) 108 inside the mold, the slurry is drawn through the mesh form, capturing the fiber particles in the shape of the mold, and excess slurry 110 is drained and recycled back into the system.

[0058] Continuing with reference to FIG. 1 , the second stage 103 involves building up a fiber layer 130 around the wire mesh in the shape of the mold. When the layer 130 reaches the desired thickness, the mold enters the third stage 105 for either wet curing or dry curing. In the wet curing process, the formed part is transferred to a heated press (not shown) where the layer 130 is compressed and dried to the desired thickness, thereby producing a smooth exterior surface finish for the finished part. In the dry curing process, heated air is passed directly over the layer 130 to remove moisture therefrom, resulting in a more textured finish, much like that of a traditional egg carton.

[0059] According to various embodiments, the vacuum forming process operates as a closed-loop system in that unused slurry is recirculated back to the liquid bath where the product is formed. As such, some of the chemical additives (discussed in more detail below) are absorbed into the individual fibers, while some of the additives remain in the aqueous solution. During vacuum forming, only the fibers (which have absorbed some of the additives) are trapped in the form, and the remaining additives are recirculated back to the tank. As a result, only the additives trapped within the formed section need to be replenished, as the remaining additives are recirculated with the slurry in solution. As described below, the system maintains a steady-state chemical balance within the vacuum tank at a predetermined volumetric ratio of the components that comprise the slurry.

[0060] 2, there is a closed-loop slurry system 200 for controlling the chemical composition of a slurry. In the illustrated embodiment, a tank 202 is filled with a fiber-based slurry 204 having specific desired chemistries, and then a vacuum forming mold 206 is immersed in the slurry bath to form a molded part. After the molded part has been formed to a desired thickness, the mold 206 is removed for subsequent processing 208 (e.g., forming, heating, drying, top coating, and the like).

[0061] In a typical wet pressing process, the hot pressing temperature range is about 150-250°C, and the hot pressing pressure range is about 140-170 kg / cm.2 The density of the final product is approximately 0.5 to 1.5 g / cm 3 , and most likely about 0.9-1.1 g / cm 3 The thickness of the final product is about 0.3 to 1.5 mm, preferably about 0.5 to 0.8 mm.

[0062] Continuing with reference to FIG. 2 , a fiber-based slurry containing pulp and water is introduced into tank 202 via slurry input 210. In various embodiments, a grinder may be used to break up the pulp fibers and create additional bond sites. One or more additional components or chemical additives may be provided via respective inputs 212-214. The slurry may be recirculated using a closed-loop conduit 218, adding additional pulp and / or water as needed. To maintain a steady-state balance of the desired chemical additives, a sampling module 216 is configured to measure or otherwise monitor the constituents of the slurry and dynamically or periodically adjust the respective additive levels by controlling the respective inputs 212-214. Typically, the slurry concentration is about 0.1-1%, most ideally about 0.3-0.5%, and preferably about 0.4-0.5%. In one embodiment, the various chemical components are maintained at predetermined desired volume percentages; alternatively, the chemicals may be maintained based on weight percentages or any other desired control manner.

[0063] The pulp fibers used in 202 can also be mechanically comminuted to improve interfiber bonding and improve bonding of chemicals to the fibers. In this way, the slurry undergoes a modification process that alters the freeness or drainage rate of the fibrous material. Physical modification modifies the fibers to make them smaller and more flexible, resulting in better bonding. The modification process can also increase the tensile strength and burst strength of the final product. In various embodiments, freeness is related to the surface condition and swelling of the fibers. The freeness (CSF) is suitably in the range of 200 to 700, preferably about 350 to 550, for many of the processes and products described herein.

[0064] Various chemical formulations (sometimes referred to herein as "chemicals"), spray coating and dipping systems, and nozzle and product configurations for various fiber-based packaging and containers, as well as various methods for applying topical coatings, are further described in conjunction with Figures 3-8.

[0065] FIG. 3 is a perspective view of a meat tray 300 illustrating the underside of the bottom surface 302 and the outer surface of the sidewalls 304.

[0066] FIG. 4 is a side elevational view of the meat tray 402 of FIG.

[0067] FIG. 5 is a top plan view of the meat tray of FIGS. 3 and 4 illustrating the upper surface 502 of the bottom region of the tray and respective side walls 504 and 506.

[0068] FIG. 6 is an end view of the meat tray 602 of FIG.

[0069] FIG. 7 is a schematic perspective view of a spray coating system 700 useful for spray coating meat trays, according to various embodiments.

[0070] More specifically, system 700 includes a conveyor 708 having pockets 710 for holding trays as they are transported along the direction indicated by arrow 730. The trays include a bottom panel 704 having structural features (e.g., ribs) 706 and are surrounded by sidewalls 702.

[0071] 7, the illustrated spray system includes a first spray nozzle 712 and a second spray nozzle 718. Nozzle 712 is configured to deliver a substantially planar spray pattern 715 bounded by a side edge 714 and terminating in a line 716 substantially perpendicular to direction 730. Nozzle 718 is configured to deliver a substantially planar spray pattern 721 bounded by a side edge 720 and terminating in a line 716 substantially perpendicular to direction 722. As the tray passes under the spray nozzles, spray lines 716 and 722 apply a coating to all or selected portions of bottom surface 704 and / or the inner surface of sidewall 702.

[0072] 8 is a schematic perspective view of a spray coating system 800 including a full cone nozzle 810 configured to deliver a full cone spray pattern and a hollow cone nozzle 814 configured to deliver an annular (or "donut") shaped spray pattern. In particular, system 800 is configured to apply a full cone spray pattern 812 to an inner bottom surface 802 of a workpiece (bowl). System 800 is further configured to apply a hollow cone spray pattern 816 to an inner surface of a workpiece sidewall 804.

[0073] Continuing with reference to FIG. 8, conveyor 806 is configured to convey trays along the direction defined by arrow 830 (to the right in FIG. 8). In one embodiment, conveyor 806 may be configured to sequentially index in the direction of arrow 830 to position successive trays under stationary nozzles 810, 814 lowered from stationary platen 820. In this position, the bowl on the left may be bottom spray coated while the bowl on the right is sidewall spray coated. After indexing to the next position, the bowl previously under nozzle 810 is then disposed under nozzle 814, and so on.

[0074] In an alternative embodiment, total workpiece throughput may be increased by operating conveyor 806 in a continuous (as opposed to sequentially indexed) manner. To maintain positional registration between the nozzle system and the underlying workpieces during application of the spray coating, platen 820 may be configured to advance to the right with conveyor 830, temporarily suspending relative motion between the nozzles, and then shift leftward to align the nozzles with the next series of workpieces to be coated.

[0075] While FIG. 8 illustrates two workpieces and one each of a full-cone and hollow-cone nozzle, one skilled in the art will understand that the system can be scaled to accommodate any number of nozzles and workpieces per reciprocating motion of the platen 820.

[0076] As briefly described above, the various slurries used to vacuum form containers according to the present invention comprise a fiber-based mixture of pulp and water to which chemical ingredients have been added to impart desired performance characteristics tailored for each particular product application. The base fiber may comprise any one or combination of at least the following materials: softwood (SW), bagasse, bamboo, old corrugated cardboard (OCC), and newsprint (NP).Alternatively, the base fiber may be selected according to the following resources, the entire contents of which are incorporated herein by reference: "Lignocellulosic Fibers and Wood Handbook: Renewable Materials for Today's Environment," edited by Mohamed Naceur Belgacem and Antonio Pizzi (Copyright 2016 by Scrivener Publishing, LLC) and available from https: / / books.google.com / books?id=jTL8CwAAQBAJ&printsec=frontcover#v=onepage&q&f=false; "Efficient Use of Flourescent Whitening Agents and Shading Colorants in the Production of Wood" by Liisa Ohlsson and Robert Federe, published October 8, 2002 in African Pulp and Paper Week, available from tappsa.co.za / archive / APPW2002 / Title / Efficient_use_of_fluorescent_w / efficient_use_of_fluorescent_w.html of White Paper and Board,” Cellulosic Pulps, Fibres and Materials: Cellucon '98 Proceedings, edited by J.F. Kennedy, G.O. Phillips, and P.A. Williams, 200 Copyright by Woodhead Publishing Ltd., available at books.google.com / books?id=xO2iAgAAQBAJ&printsec=frontcover#v=onepage&q&f=false. and U.S. Patent No. 5,169,497A, entitled "Application of Enzymes and Flocculants for Enhancing the Freeness of Paper Making Pulp," issued December 8, 1992.

[0077] For vacuum-formed product containers made using either wet or dry pressing, a fiber system of OCC or OCC / DLK and NP may be used, with the OCC / DLK component being 50% to 100%, preferably about 70% OCC / DLK and 30% NP or VNP, with an added moisture / water repellent in the range of 1 to 10% by weight, preferably about 1.5% to 4% by weight, most preferably about 4% by weight. In a preferred embodiment, the moisture / water barrier may comprise alkyl ketene dimer (AKD) (e.g., Hercon 79, Hercon 80) and / or long chain diketene, available from FOBCHEM at fobchem.com / html_products / Alkyl-Ketene-Dimer%EF%BC%88AKD-WAX%EF%BC%89.html#.V0zozvkrKUk and Yanzhou Tiancheng Chemical Co., Ltd. at yztianchengchem.com / en / index.php?m=content&c=index&a=show&catid=38&id=124&gclid=CPbn65aUg80CFRCOaQod0JUGRg.

[0078] To produce specific colors for molded pulp products, cationic or fiber-reactive dyes can be added to the pulp. Fiber-reactive dyes, such as Procion MX, bond with the fibers at a molecular level, chemically becoming part of the fabric. Adding salt, soda ash, and / or increasing the pulp temperature can also help further trap the absorbed dye within the fabric, preventing color bleeding and improving color depth.

[0079] To improve structural rigidity, a starch component can be added to the slurry, for example, liquid starches commercially available as Topcat® L98 cationic additive (or Hercobond 6950 available from Solenis LLC), Hercobond, and Topcat® L95 cationic additive (available from Penford Products Co., Cedar Rapids, Iowa). Alternatively, liquid starch can also be combined with low-charge liquid cationic starches, such as those available as Penbond® cationic additive and PAF 9137 BR cationic additive (also available from Penford Products Co., Cedar Rapids, Iowa).

[0080] For dry pressing processes, Topcat L95 or Hercobond 6950 may be added at 0.5% to 10% by weight, preferably about 1% to 7% by weight, most preferably about 6.5% by weight for products that require strength to be maintained in high humidity environments, otherwise most preferably about 1.5 to 2.0% by weight. For wet pressing processes, dry strength additives such as Topcat L95 or Hercobond 6950, which are made from modified polyamines that form both hydrogen and ionic bonds with fibers and particulates, are used. Dry strength additives increase dry strength, aid in drainage and retention, and are also effective in immobilizing anions, hydrophobic materials, and sizing agents on textiles. These additives may be added at 0.5% to 10% by weight, preferably about 1% to 6% by weight, most preferably about 3.5% by weight. Additionally, both wet and dry processes can benefit from the addition of a wet strength additive, such as a polyamide-epichlorohydrin (PAE) resin such as Kymene 920A or 1500, or a similarly formulated solution available from Ashland Specialty Chemical Products at ashland.com / products. In a preferred embodiment, Kymene 920A or 1500 can be added in an amount ranging from 0.5% to 10% by volume, preferably about 1% to 4% by volume, and most preferably about 2% by volume or equivalent to the dosage of the dry strength additive. Kymene 920A or 1500 is part of a class of polycationic materials that contain an average of two or more amino groups and / or quaternary ammonium salt groups per molecule. Such amino groups tend to protonate in acidic solution to generate cationic species. Other examples of polycationic materials include polymers derived from the modification of amino-containing polyamides with epichlorohydrin, such as those prepared from condensed adipic acid and dimethylene triamine, commercially available as Hercosett 57 from Hercules and Catalyst 3774 from Ciba-Geigy.

[0081] The inventors have discovered that molded fiber containers can be made suitable as single-use food containers suitable for use in microwave ovens, convection, and conventional ovens by embedding barrier chemicals in the slurry, adding a topical coating to the finished vacuum-formed container, or both. In particular, the slurry and / or topical coating chemicals should advantageously address one or more of the following three performance metrics: i) moisture barrier, ii) oil barrier, and iii) water vapor (condensation) barrier to avoid condensation from placing a hot container on a surface having a cooler temperature than the container.

[0082] In this context, the extent to which water vapor penetrates the container is related to the porosity of the container, which is what the present invention seeks to reduce. That is, even if the container is effectively impermeable to oil and water, water vapor penetration into the container can detract from the user's experience, especially if the water vapor condenses on cold surfaces and leaves behind a moisture ring. The inventors have further determined that condensation problems are uniquely manifested in fiber-based applications because water vapor typically does not penetrate plastic barriers.

[0083] Thus, for microwaveable containers, the present invention contemplates a fiber- or pulp-based slurry containing water, oil, and vapor barriers, as well as optional retention aids. In one embodiment, a softwood (SW) / bagasse fiber base may be used in the range of about 10% to 90%, preferably at a ratio of about 7:3. As a moisture barrier, AKD may be used in the range of about 0.5% to 10%, preferably about 1.5% to 4%, most preferably about 3.5%. As an oil barrier, grease and oil repellent additives are often aqueous emulsions of fluorine containing fluororesin or other fluorine-containing polymer compositions, such as UNIDYNE TG 8111 or UNIDYNE TG-8731, available from Daikin or World of Chemicals at worldofchemicals.com / chemicals / chemical-properties / unidyne-tg-8111.html. The oil barrier component of the slurry (or topical coating) may be present in a weight percentage range of 0.5% to 10% by weight, preferably about 1% to 4% by weight, and most preferably about 2.5% by weight. As a retention aid, an organic compound such as Nalco 7527 available from Nalco Company of Naperville, Ill., may be used in a range of 0.1% to 1% by volume, preferably about 0.3% by volume. Finally, to strengthen the finished product, dry strength additives such as inorganic salts (e.g., Hercobond 6950, available at solenis.com / en / industries / tissue-towel / innovations / hercobond-dry-strength-additives / , see also sfm.state.or.us / CR2K_SubDB / MSDS / HERCOBOND_6950.PDF) may be used in the range of 0.5% to 10% by weight, preferably about 1.5% to 5% by weight, and most preferably about 4% by weight.

[0084] As mentioned above, vapor barrier performance is directly affected by the porosity of the fiber tray. Reducing the porosity of the fiber tray, and therefore improving its vapor barrier performance, can be achieved using at least two approaches. One is by improving the freeness of the tray material by grinding the fibers. The second method is by topical spray coating, for example, using Daikin S2066, a water-based long-chain fluorine-containing polymer. Spray coating can be implemented using a concentration in the range of about 0.1% to 3% by weight, preferably about 0.2% to 1.5% by weight, and most preferably about 1% by weight.

[0085] Currently known meat trays, such as those used in grocery stores for displaying poultry, beef, pork, and seafood, are typically made from plastic-based materials such as polystyrene and Styrofoam, primarily for their excellent moisture barrier properties. The inventors have determined that variations of the aforementioned chemistries used for microwaveable containers can be adapted for use in meat trays, particularly with respect to moisture barrier (oil and porosity barriers are typically less important in meat trays than in microwaveable containers).

[0086] Therefore, for meat containers, the present invention contemplates a fiber- or pulp-based slurry containing a water barrier and an optional oil barrier. In one embodiment, a fiber base of softwood (SW) / bagasse and / or bamboo / bagasse may be used in a range of about 10% to 90%, preferably about a 7:3 ratio. As a moisture / water barrier, AKD may be used in a range of about 0.5% to 10%, preferably about 1% to 4%, most preferably about 4%. As an oil barrier, a water-based emulsion, such as UNIDYNE TG 8111 or UNIDYNE TG-8731, may be used. The oil barrier component of the slurry (or topical coating) may be present in a weight percentage range of 0.5% to 10% by weight, preferably about 1% to 4% by weight, most preferably about 1.5% by weight. Finally, to strengthen the finished product, a dry strength additive such as Hercobond 6950 may be used in the range of 0.5% to 10% by weight, preferably about 1.5% to 4% by weight, and most preferably about 4% by weight.

[0087] As discussed above in relation to produce containers, slurry chemistry and / or spray coating chemistry, in combination with structural features, can provide long-term rigidity over time by preventing moisture / water from penetrating the tray.

[0088] Therefore, a method for manufacturing a meat tray is provided, the method including providing a wire mesh mold approximating the shape of the meat tray, preparing an aqueous fiber-based slurry including at least one of old corrugated container (OCC) and double-lined kraft (DLK) paper, adding an embedded moisture barrier to the slurry, immersing the mold in the slurry, drawing a vacuum across the mold within the slurry until a desired thickness of fiber particles accumulates on the surface of the mold, removing the accumulated particles from the mold, drying and pressing the accumulated particles in a press to thereby form the meat tray, transferring the meat tray from the press to a coating station, and applying a supplemental moisture barrier layer to the surface of the meat tray at the coating station.

[0089] In one embodiment, the embedded moisture barrier comprises 2% to 5% alkyl ketene dimer (AKD).

[0090] In one embodiment, the method further comprises adding a dry strength additive to the slurry.

[0091] In one embodiment the dry strength additive comprises 0.5% to 4.5% starch.

[0092] In one embodiment, the coating station comprises a spray system and a conveyor configured to move the meat trays along a travel direction into engagement with the spray system.

[0093] In one embodiment, the spray system includes a first nozzle configured to dispense a first predetermined spray pattern onto the meat tray.

[0094] In one embodiment, the first predetermined spray pattern includes a substantially vertical curtain terminating in a line on the meat tray, the line having a predetermined thickness and oriented substantially perpendicular to the direction of travel.

[0095] In one embodiment, the spray system further includes a second nozzle configured to discharge a second predetermined spray pattern onto the meat tray, the first spray pattern being angled toward the direction of travel and the second spray pattern being angled away from the direction of travel.

[0096] In one embodiment, the auxiliary moisture barrier layer comprises an acrylic copolymer latex in an aqueous solution.

[0097] In one embodiment, the auxiliary moisture barrier layer comprises a solution of about 1:3 acrylic and water.

[0098] A method is also provided for producing a microwave bowl of the type characterized by a substantially flat, circular bottom region bounded by a circumferential sidewall. The method includes providing a wire mesh mold approximating the shape of the bowl, preparing an aqueous fiber-based slurry including at least one of hardwood virgin fibers and softwood virgin fibers, adding an embedded moisture barrier to the slurry, immersing the mold in the slurry, drawing a vacuum across the mold within the slurry until a desired thickness of fiber particles accumulates on the mold surface, removing the accumulated particles from the mold, drying and pressing the accumulated particles in a press to thereby form a bowl, transferring the bowl from the press to a coating station, and applying a topical oil barrier layer to at least a portion of the bowl at the coating station.

[0099] In one embodiment, the embedded moisture barrier comprises 2% to 5% alkyl ketene dimer (AKD).

[0100] In one embodiment, the method further comprises adding a dry strength additive to the slurry, wherein the dry strength additive comprises 0.5% to 4.5% starch.

[0101] In one embodiment, the topical oil barrier layer comprises about 27.5% solids in an aqueous solution.

[0102] In one embodiment, the solids include acrylates, rice bran wax, pectin, and pea protein.

[0103] In one embodiment, the coating station includes a spray system and a conveyor configured to move the bowl along a travel direction beneath the spray system.

[0104] In one embodiment, the spray system includes a first nozzle configured to discharge a full cone spray pattern onto the bottom region of the bowl and a second nozzle configured to discharge a hollow cone spray pattern onto the inner surface of the circumferential sidewall.

[0105] In one embodiment, the method further includes moving the spray system along a direction of travel so that i) a first nozzle is disposed above the bowl and remains stationary relative to the bowl for a first predetermined period of time, and ii) a second nozzle is disposed above the bowl and remains stationary relative to the bowl for a second predetermined period of time.

[0106] In one embodiment, the first period of time is one of: i) greater than the second period of time, ii) equal to the second period of time, and iii) less than the second period of time.

[0107] A method is provided for producing a fiber-based microwave bowl of the type including a substantially circular bottom portion bounded by a sloped circumferential sidewall. The method may include providing a wire mesh mold approximating the shape of the bowl, preparing an aqueous fiber-based slurry including up to 100% virgin fibers, adding an embedded moisture barrier to the slurry, immersing the mold in the slurry, drawing a vacuum across the mold within the slurry until a desired thickness of fiber particles accumulates on the mold surface, removing the accumulated particles from the mold, drying and pressing the accumulated particles in a press to thereby form a bowl, transferring the bowl from the press to a coating station, and applying an acrylic oil barrier layer to the surface of the bowl at the coating station.

[0108] In one embodiment, the embedded moisture barrier comprises 2% to 5% alkyl ketene dimer (AKD).

[0109] In one embodiment, the oil barrier layer includes a calcium carbonate component to promote bonding to the bowl surface.

[0110] In one embodiment, the oil barrier layer comprises a pea emulsion.

[0111] In one embodiment, the oil barrier layer comprises an alginate.

[0112] In one embodiment, the oil barrier layer comprises an aqueous solution comprising about 25% acrylate and a first auxiliary component configured to reduce tackiness.

[0113] In one embodiment, the first adjunct component comprises about 1.8% rice bran wax.

[0114] In one embodiment, the first accessory ingredient comprises about 0.4% pectin.

[0115] In one embodiment, the oil barrier layer comprises a second adjunct ingredient configured to facilitate emulsification of the first adjunct ingredient.

[0116] In one embodiment, the second accessory component comprises about 0.3% pea protein.

[0117] In one embodiment, the oil barrier layer includes a third adjunct component configured to adjust the pH level of the oil barrier coating, thereby facilitating acrylate curing.

[0118] In one embodiment, the third adjunct component comprises about 0.2% liquid ammonium.

[0119] In one embodiment, the coating station includes a spray system and a conveyor configured to move the bowl along a travel direction into engagement with the spray system.

[0120] In one embodiment, the spray system includes a first nozzle configured to deliver a full-cone spray pattern onto the bottom of the bowl.

[0121] In one embodiment, the spray system includes a second nozzle configured to deliver a hollow cone spray pattern onto the inner surface of the sidewall.

[0122] In one embodiment, the oil barrier layer comprises a solution of about 1:3 acrylic and water.

[0123] A method is also provided for manufacturing a microwave bowl of a type characterized by a substantially flat, circular bottom region bounded by a circumferential sidewall, comprising: providing a wire mesh mold approximating the shape of the bowl; preparing an aqueous fiber-based slurry including at least one of hardwood virgin fibers and softwood virgin fibers; adding an embedded moisture barrier to the slurry; immersing the mold in the slurry; drawing a vacuum across the mold within the slurry until a desired thickness of fiber particles accumulates on the surface of the mold; removing the accumulated particles from the mold; drying and pressing the accumulated particles in a press to thereby form a bowl; transferring the bowl from the press to a coating station; and applying a localized oil barrier layer to at least a portion of the bowl at the coating station, the localized oil barrier layer comprising about 27.5% solids in an aqueous solution.

[0124] In one embodiment, the solids include acrylates, rice bran wax, pectin, and pea protein.

[0125] The microwave bowl may be manufactured using any of the methods described herein.

[0126] While the present invention has been described in the context of the foregoing embodiments, it will be understood that the invention is not so limited. For example, various spray system and nozzle configurations, slurry chemistries, and spray coat chemistries can be tailored to suit additional applications based on the teachings of the present invention.

[0127] As used herein, the term "exemplary" means "serving as an example, instance, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments, nor is it intended as a model to be literally copied.

[0128] While the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing various embodiments of the invention, it should be understood that the specific embodiments described are merely examples and are not intended to limit the scope, applicability, or configuration of the invention in any way. On the contrary, various changes may be made in the function and arrangement of the described elements without departing from the scope of the invention.

Claims

1. 1. A method for manufacturing a microwave bowl of the type characterized by a substantially flat bottom region bounded by a circumferential sidewall, comprising: providing a wire mesh mold approximating the shape of the bowl; preparing an aqueous fiber-based slurry comprising at least one of hardwood virgin fibers and softwood virgin fibers; adding an embedded moisture barrier to the slurry; immersing the mold in the slurry; drawing a vacuum through the slurry and across the mold until a desired thickness of fiber particles accumulates on the mold surface; removing the accumulated particles from the mold; drying and pressing the accumulated particles in a press to thereby form the bowl; transferring the bowl from the press to a coating station; applying a topical oil barrier layer to at least a portion of the bowl at the coating station; the coating station A spray system; a conveyor configured to move the bowl along a direction of travel beneath the spray system; the spray system comprising: a first nozzle configured to deliver a full conical spray pattern onto the bottom region of the bowl; a second nozzle configured to discharge a hollow conical spray pattern onto the inner surface of the circumferential sidewall.

2. The method described in claim 1, wherein the bottom region is circular.

3. The method of claim 1 , wherein the embedded moisture barrier comprises 2% to 5% alkyl ketene dimer (AKD).

4. 10. The method of claim 1, further comprising adding a dry strength additive to the slurry, wherein the dry strength additive comprises 0.5% to 4.5% starch.

5. 10. The method of claim 1, wherein the topical oil barrier layer comprises about 27.5% solids in solution.

6. The method of claim 5 , wherein the solid comprises a sticky component and an emulsifier.

7. 2. The method of claim 1, further comprising the step of moving the spray system along the direction of travel so that i) the first nozzle is disposed above the bowl and remains stationary relative to the bowl for a first predetermined period of time, and ii) the second nozzle is disposed above the bowl and remains stationary relative to the bowl for a second predetermined period of time.

8. 8. The method of claim 7, wherein the first period of time is one of: i) greater than the second period of time, ii) equal to the second period of time, and iii) less than the second period of time.

9. 10. A microwave bowl made from the method of claim 1.

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