Package comprising a multilayer sheet

Disclosed is a tray comprising a liner. The liner has at least two layers comprising a water-wicking material, such as a nonwoven material, with a moisture-vapor transmission rate of at least about 20,000 g/m2-day and a hydrostatic head pressure of less than about 5 cm H2O and an absorbent and highly-thermally insulating material.

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Description

This application claims the benefit of U.S. provisional application Ser. No. 60/554566, filed Mar. 19, 2004, the entire description of which is incorporated herein by reference.

The invention relates to a thermoplastic tray comprising a liner and the liner comprises a multilayer sheet.

BACKGROUND OF THE INVENTION

Composite or multilayer sheets or wraps have long been used for packaging foods. Such sheets aim to keep freshly-made food hot from the time it is prepared until it is consumed. Current commercial sheets or wraps include polyethylene-coated paper or tissue, hot-melt coated paper, foil/tissue laminations, tissue/aluminum foil/polyethylene film, dry wax, etc. These wrap materials are of high moisture resistance to maximize heat retention. Liquid water from condensation is often still left in contact with food, which can leave the food undesirably soggy.

Most of the known sheets or wraps involve an absorbent layer and an impermeable layer. See, for example, U.S. Pat. No. 5,128,182; U.S. Pat. No. 5,310,587; and Japanese Patent Application 11094260. The resulting food quality of using these wraps and sheets is less than optimum. Thus, there exists a need to improve packaging for hot foods to maintain freshly-cooked characteristics, such as by improving heat retention and moisture control in the package, especially for packaging freshly-cooked foods for the “take-out” market.

SUMMARY OF THE INVENTION

The invention includes a rigid, thermoplastic tray comprising a bottom portion and a lid wherein the lid fits over the bottom portion to generally seal along the perimeter where the lid and bottom portion meet; the tray comprises or is produced from a liner; the liner comprises a multilayer sheet comprising or produced from at least two layers including a first layer, a second layer, and optionally a third layer; the first layer comprises or is produced from a water-wicking material; the second layer comprises or is produced from an absorbent and insulating material; and the third layer comprises or is produced from a structural material.

The invention further includes packages such as trays, lids and boxes comprising package liners comprising the liner.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional view of a specific embodiment of the multilayer sheet illustrating a fiberfill batt as the insulating and absorbent material of the second layer, positioned between and adhesively bonded to a film, as the structural material of the outermost layer, and a water-wicking material, as the inner layer, via two separate adhesive layers.

FIG. 2 is a cross-sectional view of another specific embodiment of the multilayer sheet illustrating a fiberfill batt as the insulating and absorbent material of the second layer, positioned between a film, as the structural material of the outermost layer, and a water-wicking material, as the inner layer, employing an adhesive layer between the fiberfill baft and inner water-wicking material.

DETAILED DESCRIPTION OF THE INVENTION

A multilayer sheet that can be used for packaging hot foods can comprise or be produced from a combination of a first inner layer comprising a water-wicking material with a second layer comprising an absorbent and highly-thermally insulating material. The multilayer sheet can provide moisture control while maintaining heat retention. Freshly-cooked food quality can be maintained (e.g., “crispness” especially in fried or baked foods) for time periods of at least about 10, or 20, or 30 minutes under ambient conditions, and the food quality is judged to be “excellent”. The multilayer sheet may be used in various packaging embodiments and can be used for the “take-out” food packaging market.

The first layer of the multilayer sheet of the invention comprises a water-wicking material. This layer can be the innermost layer of the sheet, and is the layer in direct contact with the hot food or interior of the package containing the hot food. The water-wicking capability is one key to preventing the build-up of moisture in the package as the hot food cools, thereby avoiding undesirably soggy food.

The first layer facilitates the passage of water and moisture vapor (i.e., wicks) from the interior of the package to the second layer of the multilayer sheet. To do so, the water-wicking material can have a non-condensable surface and can have a moisture-vapor transmission rate of at least about 20,000 g/m2/day, or at least about 150,000 g/m2/day, or at least about 170,000 g/m2/day, as tested by ASTM D-6701. Further, the water-wicking material can have a hydrostatic head pressure of less than about 5 cm H2O, or less than about 2 cm H2O, as tested under MTCC Method 127-1989.

The first layer can comprise a nonwoven fabric, preferably a “spunlaced” or “hydroentangled” fabric. The term “spunlaced fabric” or “hydroentangled fabric” refers to a nonwoven fabric that is produced by entangling fibers in the web to provide a strong fabric that is free of binders. Such spunlaced fabrics can be prepared by supporting a nonwoven web of fibers on a porous support such as a mesh screen and passing the supported web underneath water jets, such as in a hydraulic needling process. The fibers can be entangled in a repeating pattern.

The nonwoven fabric can be made out of fibers such as polyester, nylon 6,6, or, preferably, a combination of wood pulp and staple poly(ethylene terephthalate) fibers. Such fabrics are available from E. I. du Pont de Nemours and Company, Wilmington, Del. (DuPont) under the trade name Sontara® and the thickness can be varied, though generally in the range of about 10-50 mils (0.01 to 0.05 inches).

In preparing such fabrics, the starting nonwoven layer comprises a thin, supple web of staple fibers, continuous filaments, plexifilamentary strands or the like. The term “fibers” collectively includes each of these fibrous materials. The fibers may be natural fibers, e.g., cellulosic, or may be formed from synthetic organic polymers. The fibers may not bond to each other. Suitable starting nonwoven fibrous layer can be substantially not bonded, and composed of fibers that inherently can absorb or wick liquid, e.g., polyester and wood pulp, or rayon and wood pulp.

The first layer may also comprise paper, preferably with sufficient porosity to function as a water-wicking material.

The multilayer sheet includes a second layer comprising an absorbent and insulating material. This layer can be highly thermally insulating and somewhat absorbent. The high thermal insulating capability effectively retains heat, slows condensation and thereby reduces liquid moisture formation within a given package. At the same time, any condensate that is produced is wicked through the first layer and absorbed by the second layer. These combined characteristics of high thermal insulating capability and some absorbency may prevent the build-up of condensate in the package and avoid undesirably soggy food.

Though not bound by any particular theory, it appears that the multilayer sheet may work successfully because the absorbent and insulating material in the second layer aims to keep the temperature within a given package above the dew point, preventing condensation from forming within the package. If the temperature falls just below the dew point, the water-wicking material of the first layer wicks the liquid from the package interior to the second layer. Hence, the interior of the package is warm but free of liquid moisture that can cause crisp food to turn soggy.

The second layer can have a thermal resistance, as measured in units of insulation, or CLO, of at least about 0.05, or at least about 0.1, or about 0.1 to about 2.5, or 0.1 to 0.5.

The CLO unit is defined as a unit of thermal resistance of a garment. The Si unit of thermal resistance is the square-meter kelvin per watt (m2·K/W) (See “Textile Terms and Definitions”, Tenth Edition, The Textile Institute, (1995), pp. 66, 350). Thus, the range of thermal resistance in SI units of the absorbent and insulating material of the present invention is at least about 0.0077, preferably at least about 0.0154 m2·K/W. CLO is defined in terms of a garment, but it can be used to describe the thermal resistance of any textile system, and is used herein to describe the thermal resistance of the absorbent and insulating material of CLO values depend on the material used for the layer and its thickness.

For the “take-out” food packaging market, the necessary level of thermal resistance can be high enough to maintain the temperature within the package above the dew point for at least about 10 or 20 or 30 minutes when the package is exposed to ambient conditions. The water-wicking material of the first layer may also contribute some thermal resistance.

The second layer can have some absorbency due to the high efficiency of the insulating capability, and the resulting minimization of condensation formation. In most cases, the absorbency, in terms of water pressure resistance, may be less than about 50 cm H2O.

The second layer may comprise an organic thermoplastic fiber-based material comprising, e.g., polyester, polyethylene or polypropylene. The thermal insulating layer can be a fiberfill batt comprising polyester. A fiberfill batt sold as Thermolite® Active Original by DuPont can be used. The fiberfill batt useful can have an areal weight in the range of 10 gm/m2 to 200 gm/m2, and a bulk density of less than about 0.3 gm/cm3. The thermal insulating layer may comprise melt-blown fibers, such as melt-blown polyolefins, sold as THINSULATE®, by 3M.

Many other variations of material for the absorbent and insulating material may be used to provide the thermal resistance disclosed here. For instance, the absorbent and insulating material may possibly comprise an inorganic thermoplastic fiber-based material comprising glass wool, borosilicate glass or rockwool.

Alternatively, the absorbent and insulating material may comprise a knit fabric made, for example, from a tetrachannel or scalloped oval fiber, sold under the trademark Coolmax® by DuPont. Or the absorbent and insulating material may be a woven or fleece material. The absorbent and insulating material could also comprise some sort of nonwoven, such as felt, or a highloft nonwoven or needled nonwoven fabric.

The thickness of the second layer may vary or depend on the desired level of insulating capability, i.e., thermal resistance. As more thermal resistance is required, the thickness of the layer may increase. Generally, the thickness can fall in the range of about 10 mils to about 500 mils, or about 10 to about 200 mils, or about 10 to about 50 mils. For a second layer comprising polyester fiberfill batt, and within the preferred range for the thermal resistance, the thickness for the layer can range from about 10 to about 500 mils.

The multilayer sheet may comprise an optional third, outermost layer comprising a structural material. Use of the third layer may be helpful for certain considerations in designing a practical package (e.g., impermeability, strength, flexibility).

Generally, the structural material may comprise film, foil, paper and/or fabric. A film may be made of a thermoplastic material comprising, e.g., polyester, polyethylene or polypropylene. For many uses where impermeability and flexibility are desired, films of oriented polypropylene or oriented polyester can be used. Films of oriented polyester are available from DuPont Teijin Films of Wilmington, Del. (DuPont Teijin) under the trade names Mylar® and Melinex®.

The choice of material for the third layer may depend on how the multilayer sheet is used in the packaging, e.g., what type of package is used and what type of food product is packaged. For example, if the desired packaging is a bag or pouch, then paper, foil or a film may be useful. If the multilayer sheet is used as a liner in a package, then it may have the structural material contain an adhesive layer to adhere the multilayer sheet to the inside of the package. A peelable backing can also be useful in such a case.

One specific example of a film that is suitable for use as a structural material is Melinex® 854, commercially available from DuPont Teijin. Melinex® 854 is a multilayered film, one layer being heat-sealable. This can allow for heat-sealing between the second and third layers.

Melinex® 854 is a 120 gauge (0.0012 inch, or 0.0030 cm.) thick co-extruded biaxially oriented polyester film. The first layer of the film is made from a standard polyester homopolymer, intrinsic viscosity of about 0.590, containing 2500 ppm of inorganic slip additive particles. This layer comprises approximately 65% of the total film thickness. A co-polyester resin comprised of 18 weight % isophthalic acid, intrinsic viscosity of about 0.635, containing 2300 ppm inorganic slip additive particles, is co-extruded to form the heat-sealable layer and comprises 35% (or 15-40%) of the total film thickness. The surface of the first layer opposite the heat sealable layer can be coated in-line by a gravure coater (during the film manufacturing process) with a print primer coating based on an aqueous polyester dispersion at a dry coat-weight of 0.03 g/m2.

The multilayer sheet or liner can further comprise an additive. The additive can be a desiccant such as silica, thermal and ultraviolet (UV) stabilizers, UV absorbers, antistatic agents, processing aids, fluorescent whitening agents, pigments, lubricants, etc. These additives may be present in the compositions used in this invention in quantities that are generally from 0.01 to 20, or 0.1 to 15, weight.

The structural material may be modified on the surface facing away from the second layer to facilitate printing thereon by a corona discharge treatment. In addition, surface modification (i.e., coating or corona discharge treatment) may be used to facilitate bonding to another surface with an adhesive layer, as mentioned above. In order to bond to another surface, an adhesive primer layer may be applied to the untreated surface of the structural material or to the corona discharge treated surface. This adhesive primer layer is pressure sensitive to enable application of the multilayer sheet to a container to function as a package liner.

Generally, the layers of the multilayer sheet of the invention may be joined by various methods known in the art, one such method being lamination, i.e., uniting layers of material by an adhesive or other means. The adhesive can be applied in various ways, e.g., pattern-application or spray application, or through the use of an adhesive layer, e.g., a thermoplastic adhesive scrim, which is a web-like layer of adhesive. The use of pattern-application adhesive or an adhesive scrim achieves a similar effect within the multilayer sheet, i.e., there is no complete barrier to moisture transport due to the abundance of free space or holes within the adhesive layer which allows moisture to flow through. This is desirable when laminating the first and second layers. Other means of joining the layers may include pinpoint embossing, needling and quilting, among others known to those of skill in the art. These methods may allow for the free transport of moisture between layers.

The adhesive may be a heat-sealable coating on one of the layers to be joined, e.g., on the structural material. The multilayer sheet may be sealed, such as with a hot knife, at its edges so that fluid cannot penetrate the edges.

The multilayer sheet may be used in various ways to package hot foods. One embodiment is simply to use the multilayer sheet in sheet form as a packaging wrap to directly wrap hot foods.

The multilayer sheet may be formed into a pouch or bag for wrapping hot foods, e.g., hot sandwiches. The pouches or bags may be manufactured according to any well-known method. A “pouch” means an enclosure sealed on at least two of four sides, though generally sealed on three of four sides with the fourth side being an opening. A pouch is made from a flat web of film by forming a tubular film therefrom with a longitudinal seal and subsequently flattening the tubular film at a first position and transversely heat-sealing said tubular film at the flattened position. A “bag” may be a pouch, but is also meant to include a “stand-up pouch”, similar to the commonly-known paper lunch bag, comprising four sides and a rectangular bottom opposite an opening.

After inserting the hot food into a pouch or bag of the invention herein, the pouch or bag can be sealed or closed in various ways known to those of skill in the art. The closing may be done mechanically, such as flaps or tabs that can be folded over and/or tucked in; and/or adhesive, such as pressure sensitive adhesive, among others.

The multilayer sheet may be used in sheet form or as a liner in a package. The package may be a rigid, thermoplastic tray, a box, or even a pouch or bag as discussed above, among others. The box may be a conventional-type box made from paperboard, or possibly could be made from other materials including polymers or foams.

Rigid, thermoplastic trays are used often for storing hot food in the “take-out” food market. Such trays generally comprise a bottom reservoir portion and a lid. The bottom reservoir portion typically comprises a reservoir for holding the food, and the lid is similar in size and shape to the bottom portion. The lid is constructed to fit over the bottom portion to generally seal along the perimeter where the bottom portion and lid meet. The lid and bottom portion may lock together by a variety of mechanisms known in the art, e.g., through the use of small protruding notches on the perimeter of the lid which fit into matching cavities in the bottom portion, or vice versa. The material used for the tray and/or lid may be any suitable thermoplastic such as polyester or oriented polystyrene. The tray and/or lid material may also be foam comprising polystyrene, polypropylene or polyester, preferably polystyrene.

The multilayer sheet can be used as a liner to improve heat retention and moisture control within the tray. As demonstrated in the Examples, improvement in food temperature and food quality can be attained by affixing the liner to the inside lid of such a package. It is possible that extending the duration of desired temperature and moisture levels within the package could also be attained by affixing the liner to other areas within a package, such as the inside, bottom, of the package.

The invention also includes a lid for covering a package, wherein a liner comprising the multilayer sheet is affixed thereto. The lid can be made to cover a variety of package types. Such packages can come in a variety of sizes, shapes and materials and the lid comprising the multilayer sheet disclosed herein. In this embodiment the lid and the package it covers can certainly be made of different materials. Polyester or oriented polystyrene can be useful as materials for lids.

A flexible, impermeable layer may be used to prevent leakage of moisture from the food to the consumer. The multilayer sheet can be used in sheet form to act as liner within a package (e.g., take-out tray, box, bag, etc.), or even on the exterior of a package (e.g., covering perforations in a take-out tray lid).

The method for making a multilayer sheet can involve laminating a first inner layer to a second inner layer under suitable pressure and heat depending on the type of adhesive method used. Adhesives may be activated by chemical reaction, or be activated by heat, i.e. heat-sealable. Depending on the materials for the first and second layers, other methods known in the art for laminating the layers may also be used, e.g., pinpoint embossing, as discussed above.

Pressure may be useful when laminating two layers to facilitate even bonding across the layers, to ensure contact between the two layers to be joined, e.g., for adhesives that are activated by chemical reaction. Heat may be applied for heat-activated adhesives, such as the thermoplastic adhesive scrim described in Examples 1 and 2.

The first inner layer may be coated with a suitable pattern-applied adhesive on one side, which is the side placed in contact with the second layer prior to lamination. A thermoplastic adhesive scrim can be interposed between the first inner layer and second layer prior to lamination. These methods may be used to join the second layer to an optional third layer. Many other lamination methods known in the art could be used. The multilayer sheet can also be produced by co-extrusion known to one skilled in the art.

The following examples are intended to illustrate, not to limit, the scope of the invention. The test method used to determine thermal resistance is also disclosed.

Thermal Resistance—CLO Measurement

For measurement of insulating capability, CLO was measured on a “Thermolabo II”, which is an instrument with a refrigerated bath, commercially available from Kato Tekko Co. L.T.D., of Kato Japan, and the bath is available from Allied Fisher Scientific of Pittsburgh, Pa. Lab conditions were 21° C. and 65% relative humidity. Each sample was a one-piece sample measuring 10.5 cm×10.5 cm.

The thickness of the sample (in inches) at 6 gm/cm2 was determined using a Frazier Compressometer, commercially available from Frazier Precision Instrument Company, Inc., of Gaithersburg, Md. To measure thickness at 6 g/cm2, the following formula was used to set PSI (pounds per square inch) (kilograms per square centimeter) on the dial: (6.4516 cm2/in2) (6 g/cm2) /453.6 g=0.8532 lb/in2.

A reading of 0.8532 on the Frazier Compressometer Calibration Chart (1 in., or 2.54 cm. diameter presser foot) showed that by setting the top dial to 3.5 psi (0.2 kg/cm2), thickness at 6 g/cm2 was measured.

The Thermolabo II instrument was then calibrated. The temperature sensor box (BT box) was then set to 10° C. above room temperature. The BT box measured 3.3 inch×3.3 inch (8.4 cm×8.4 cm). A heat plate measuring 2″×2″ was in the center of the box, and was surrounded by Styrofoam. Room temperature water was circulated through a metal water box to maintain a constant temperature. A sample was placed on the water box, and the BT box was placed on the sample. The amount of energy (in watts) required for the BT box to maintain its temperature for one minute was recorded. The sample was tested three times, and the following calculations were performed: Heat ⁢   ⁢ Conductivity ⁢   ⁢ ( W ⁢ / ⁢ cm ⁢ ° ⁢   ⁢ C . ) = ( W ) ⁢ ( D × 2.54 ) ( A ) ⁢ ( Δ ⁢   ⁢ T )
where W=Watts and D=Thickness of sample measured in inches at 6 g/cm2 (6 g/cm2 was used because the weight of the BT box is 150 g, the area of the heat plate on the BT box was 25 cm2). Multiplying the thickness by 2.54 converted it to centimeters.

    • A=Area of BT Plate (25 cm)
    • ΔT=10° C.
    • CLO=Thickness×0.00164/Heat Conductivity

The value 0.00164 was a combined factor including the correction of 2.54 (correcting thickness from inches to cm) times the correction factor of 0.0006461 to convert thermal resistance in cm2×° C./Watts. To convert heat conductivity to resistance, conductivity was put in the denominator of the equation.

EXAMPLE 1 Preparation of Multilayer Sheet

A multilayer sheet for hot food packaging was made according to the process described above and as illustrated in FIG. 1 wherein the first layer, 1, is a water-wicking material, second layer, 2, s an absorbent and insulating material, and a third layer, 3, is a structural layer. In this example, interposed between these layers are porous, thermoplastic adhesive scrims, 4. These adhesive scrims, 4, are constructed of polyester materials that are spunlaced. They provide a web-like layer, with an abundance of holes, through which water vapor or condensed water can easily pass through. These layers were bonded together by thermal lamination means on a tunnel laminator with a calendar roll, such as the one provided by Inta-Roto Machine Company of Richmond, Va. The adhesive layers, 4, were activated at temperatures between 240 and 350° F. (116-177 C).

In this example the structural layer, 1, was a film of the type sold by DuPont Teijin under the trade name Mylar®. The film was 1.2 mils (0.0012 inch or 0.0030 cm) thick. The absorbent and insulating material, 2, was a fiberfill batt of the type sold by DuPont under the trademark Thermolite® Active Original. The fiberfill batt, 2, had an areal weight of 80 gm/m2 at a specified thickness of 0.25 inch (0.63 cm) or a bulk density of 0.013 gm/cm3. The water-wicking material, 3, was a nonwoven fabric available from DuPont under the trademark Sontara®. Sontara® used in this example comprised hydroentangled, white fibers (45% polyester/55% wood pulp), having an areal weight of 68 g/m2 and thickness of 13 mils (0.013 in or 0.033 cm). The adhesive webs were of the type sold by Bostik Findley, Inc., and were about 8-10 mils (0.008 to 0.01 inches) thick. (The thickness varied depending on how much pressure was applied to the web during measuring.)

EXAMPLE 2 Preparation of Multilayer Sheet:Bicomponent Third Layer

A multilayer sheet for hot food packaging was made according to the process described above and as illustrated in FIG. 2 wherein the first layer, 1, was a water-wicking material, second layer, 2, was an absorbent and insulating material, and a third layer, 3, was a structural layer. In this example, the structural layer, 3, was a bicomponent film of polyester and a heat-sealable layer. The heat-sealable layer acts as the adhesive required to laminate the structural layer to the absorbing and insulating layer. An adhesive scrim, 4, as described in Example 1 (above) was used to adhere the absorbent and insulation layer, 2, to the water-wicking nonwoven layer, 1. These layers were bonded together by thermal lamination means on a tunnel laminator with a calendar roll, such as the one provided by Inta-Roto Machine Company of Richmond, Va. The adhesive layers were activated at temperatures between 240 and 350° F. (116-177 C).

In this example the structural film layer, 3, was of the type sold by DuPont Teijin under the trade name Mylar® OL. Mylar® OL is a biaxially oriented PET film having a heat-sealable layer. In this embodiment, the film was 1.5 mils (0.0015 inch or 0.00375 cm) thick. The composition of the heat-sealable layer was an isophthalic acid-base copolyester and comprised 10-50% of the thickness of the total film thickness; 15-30% was preferred. The absorbing and insulating material, 2, was a fiberfill batt of the type sold by E.I. du Pont de Nemours and Company under the trademark Thermolite® Active Original. The fiberfill batt had an areal weight of 80 g/m2 at a specified thickness of 0.25 inch (0.63 cm) or a bulk density of 0.013 g/cm3. The water-wicking layer, 1, was a nonwoven fabric available from DuPont under the trademark Sontara®. The Sontara® used in this example comprised hydroentangled, white fibers (45% polyester/55% wood pulp), having an areal weight of 68 g/m2 and thickness of 13 mils (0.013 in or 0.033 cm). The adhesive webs were of the type sold by Bostik Findley, Inc., and were about 8-10 mils (0.008 to 0.01 inches) thick. (The thickness varied depending on how much pressure was applied to the web during measuring.)

EXAMPLE 3 Chicken Nuggets—Insulated v. Un-insulated Trays

Using a small-scale deep fryer, two portions of chicken nuggets were produced to test the effectiveness of the multilayer sheet in packaging for heat retention with moisture control. The deep fryer was filled with vegetable oil and set to 340° F. A batch consisting of 18 frozen “Banquet” brand chicken nuggets was placed into the hot oil for 4 minutes. After cooking, the hot nuggets were allowed to drain for 15 seconds. After draining, the nuggets were quickly placed into a “take out”-style, polyester (PET) tray, typically available in supermarkets or restaurants for packaging fresh, hot foods.

The PET tray typically comprises a bottom tray reservoir portion and a top tray or lid, similar in size and shape to the bottom tray. The lid fits over the bottom portion to generally seal along the perimeter (where the lid and bottom portion meet) and lock in place, typically through the use of small protruding notches on the perimeter of the lid which fit into matching cavities in the bottom portion, or vice versa, thus locking and sealing the tray container. The trays used for this test were Ivex Model #5720-9MO, Microwave Supreme, medium entreé style trays. One tray was insulated using a multilayer sheet as described in the invention herein. The multilayer sheet was placed on the interior on the inside lid (Ex. 3). The multilayer sheet comprised a first layer Sontara®, a second layer fiberfill batt, and an outer layer Mylar®, as disclosed in Example 2. The other tray was not insulated. (Comparative Ex. I)

After loading the tray with the hot food product, chicken nuggets, the lid was snapped into place and two separate digital temperature probes were inserted into the interior of the tray. One probe was used to measure the temperature of the air space in the top of the container, while the second probe was placed in the bottom of the tray among the food. The container was placed on a countertop at ambient conditions and readings were taken from one to twenty minutes at various intervals as shown in Table 1.

TABLE 1 Un-insulated - Comp. Ex. I Insulated Ex. 3 Top ° F. Bottom ° F. Top ° F. Bottom ° F. Time (min) 157 154 164 157 1 154 168 169 1.5 153 157 169 178 2 151 166 169 184 2.5 152 165 169 188 3 169 189 3.5 155 163 168 190 4 156 161 167 190 4.5 156 160 166 189 5 154 155 163 186 7 149 149 161 181 9 147 146 160 180 10 136 135 155 171 15 149 162 20

After preparation and measuring of the chicken nuggets, it was determined that the tray containing the multilayer sheet of the invention herein the inside lid, Ex. 3, offered an advantage when compared to the un-insulated one. The nuggets from the insulated tray were both hotter and crisper.

EXAMPLE 4 Chicken Breast Strips—Tray Liner and Pouch

An experiment was conducted as described in Example 3, except that the food product used was frozen chicken breast strips, rather than chicken nuggets. Four chicken strips were placed in each package. Temperature, humidity, and dew point were recorded using a digital hygrometer. Three different packaging methods were tested; two being modifications to the PET “take-out” tray. The package for Example 4A had the multilayer sheet of the invention herein (similar to that described in Example 2) attached to the lid on the exterior of the PET tray covering holes that were punched in the lid to allow moisture to escape from inside the container. Each hole was ½ inch in diameter, and there were 36 holes in the lid, for a total area of 7 square inches. The package used in Example 4B was a pouch formed from the multilayer sheet of the invention herein (similar to that described in Example 2). The pouch was formed as described in Example 6. The package used in Example 4C was a PET “take-out” tray with a liner comprising the multilayer sheet of the invention herein attached to the inside lid. The results are shown in Table 2.

TABLE 2 Example 4A Example 4C Bottom Example 48 bottom Time Top ° F. ° F. Top ° F. Top ° F. ° F. (min) 117 114 106 140 151 1 121 118 108 148 151 1.5 151 150 2 128.5 122 112.5 153 149 2.5 130.2 123 115 155 147.5 3 131.5 123.1 116 156 146.5 3.5 132.3 123.2 115.7 156 145 4 132.8 123.2 115.6 156.5 144 4.5 133 123 115.2 156.3 142 5 132 121 113.5 154 137 7 129 119 111 151 132.9 9 128 117 110 148.6 130 10 123 113 105 141 123 15 Dew Dew Dew point point point RH % ° F. RH % ° F. RH % ° F. 100 100 103.7 100 118 1 100 100 108.9 100 1.5 100 99 110 100 123.3 2 100 112 93 110 88 122.5 2.5 100 113.2 88 110 83.5 121.6 3 100 113.4 86.5 110.4 80 122 3.5 100 114 86 110.1 78 122 4 100 115.1 82.3 109.5 77 121.2 4.5 100 116.1 76.8 106.6 75.4 121 5 91.6 114 75.7 103.8 74 118.5 7 87.7 112 78.5 102.8 67 113.5 9 87.1 110.8 78.9 101.7 67 112 10 87.5 107 86.9 100.2 72.3 108.6 15

EXAMPLE 5 Chicken Breast Strips—Tray Liner

Testing was performed using chicken breast strips as the food product using the procedure described in Examples 3 and 4. In this example, the trays used for Examples 5A, 5B and 5C were similar to that in Example 4C, that is, a PET “take-out” tray with a liner comprising the multilayer sheet of the invention herein attached to the inside lid. In Examples 5D and 5E the multilayer sheet of the invention herein was attached to the exterior lid of the PET tray covering holes in the lid as described in Example 4. Comparative Example II used an uninsulated tray. Results are shown in Tables 3 (internally insulated) and 4 (Examples 5D and 5E were externally insulated while Comparative Example II was sulated). Time shown in the table is minutes.

TABLE 3 Example 5A Example 5B, Example 5C, Top RH DP Top RH DP Top RH DP Time ° F. (%) (° F.) ° F. (%) (° F.) ° F. (%) (° F.) 1 125.2 100 123.7 135 100 110.5 120 100 119 1.5 130.1 100 127.9 128.4 100 113 123.5 98.6 121.4 2 135.7 100 129.7 125.9 100 114 124.7 92 121.2 2.5 138.6 100 129.6 123.8 100 114.3 127.7 89 121.1 3 139.5 100 131.2 122.9 100 114.8 128.4 84 121.5 3.5 140.2 100 131.5 122.2 100 115.5 128.5 83 122.1 4 141.1 100 132 121.4 99 115.5 128.5 81 122.3 4.5 141.4 100 132.4 120.7 97.7 115.2 128.3 80.3 121.7 5 141 100 133.8 120 98 115 127.5 79 121.1 7 138.2 96.8 133.5 118 95.7 113 124 71 115.7 9 135.7 86.3 125.9 116.6 96.4 110 121.2 71 115 10 134.2 85.3 125.4 115.9 96.6 110.9 120.2 70.2 113.5 15 129 86.7 120.1 113.2 94.4 107.1 116.1 72.1 109.5 20 123.9 92.3 116.3 112 94.4 105.7 112.1 79.5 107.1 25 120.9 96.5 114.2 110.5 100 104.4 108.2 88 106 30 117.2 98.5 111.1 107.5 100 101 103.7 93.15 103.6

TABLE 4 Example 5D, Example 5E, Comp. Example II Top RH DP Top RH DP Top RH DP Time ° F. (%) (° F.) (° F.) (%) (° F.) (° F.) (%) (° F.) 1 117 100 112 121 100 113 110.3 100 109 1.5 120.2 100 116 123.9 100 116.2 2 120.8 100 118 127.7 100 117.6 117.9 100 115.9 2.5 121.4 100 120.2 130.4 100 117.8 3 121.5 100 120.6 131.2 100 117.9 122.7 100 117.1 3.5 121.8 100 121 131.4 100 117.8 4 122.4 100 121.4 131.1 100 117.6 125.4 100 117 4.5 122.7 100 121.5 130.7 100 117 5 122.9 100 121.4 130.1 100 116.7 126.4 100 117.3 7 121 100 121.7 126.4 100 115.3 126 100 119.9 9 119.4 100 121.7 124 100 113.5 124.3 97.6 117.8 10 118.8 100 121.6 123 100 112.8 123 96.7 116.8 15 114.9 100 115.7 118.1 100 108.6 117.5 90.8 109.2 20 110.7 100 113 113.2 100 106 112.6 94.1 105.2 25 105.3 100 108 108.8 100 103.5 107 97.1 102.2 30 101.3 100 103.8 103.4 100 100 101.8 99.1 98.2

For Example 5A, after 30 minutes the internal chicken temperature was 140° F., and the external air temperature was 1 17° F. Subjective testing by a food taster rated the product as “excellent”. The food quality rating was focused on the crispness of the food and the scale ran from “excellent”, “very good”, “satisfactory”, to “poor”.

In Example 5B, the internal chicken temperature was 137° F. after 30 minutes, and the external temperature was 129° F. The product was again rated as “excellent”. Also, by way of comparison, one freshly cooked chicken finger was left outside of the container for 30 minutes to observe how the temperature changed during cooling without any packaging to retain heat. The external temperature was 86° F. while the internal temperature was 93.5° F. after 30 minutes.

In Example 5C, the internal chicken temperature was 137° F. and the

external chicken temperature was 133° F. after 30 minutes. Product was rated as “excellent”. Again, by way of comparison, a freshly cooked chicken finger was left outside the test package for 30 minutes. After 30 minutes, the internal temperature was 103° F. while the external temperature was 94° F.

In Example 5D, after 30 minutes the internal chicken temperature was 138° F. and the external temperature was 133° F. The food product was rated as “very good”.

In Example 5E, the internal chicken temperature was 126° F., and the external temperature was 122° F. after 30 minutes. The food product was rated as “very good”.

In Comparative Example II, the internal chicken temperature was 127° F., and the external temperature was 119° F. after 30 minutes. The food product was rated as “poor to satisfactory”.

In these examples, the hot, freshly-cooked chicken strips that were packaged in take-out trays, with a multilayer sheet of the invention herein attached to the inside lid, better retained heat and food quality (i.e., were judged to taste better, generally hotter and crisper, more like freshly-cooked) as compared to chicken packaged in take-out trays with the multilayer sheet on the exterior of the tray.

EXAMPLE 6 Chicken Tenders and Steak Fries—Pouches

An experiment was conducted as described in Example 3, except the food product used was chicken tenders (Barber brand “Italian style”) and the packaging tested was a pouch made from a multilayer sheet as constructed and described in Example 1 (Example 6A). Two pieces of the multilayer sheet, each the same size (approximately 12 in.×12 in.) were used to form a pouch by aligning the two sheets and sealing on three sides with masking tape.

TABLE 5 Chicken Tenders in Pouch Time (min) Temp (° F.) RH DP (° F.) 1 106 100 103.7 1.5 108 99 108.9 2 110 2.5 112.5 93 110 3 115 88 110 3.5 116 86.5 110.4 4 115.7 86 110.1 4.5 115.6 82.3 109.5 5 115.2 76.8 106.6 7 113.5 75.7 103.8 9 111 78.5 102.8 10 110 78.9 101.7 15 105 86.9 100.2

After 15 minutes, the internal temperature of the chicken tenders was 150° F. and the food was rated as “satisfactory”.

Steak fries were tested in a similar manner (Example 6B). A sample of approximately 370 g of frozen steak-style french fries (Ore-Ida brand) were cooked at 375° F. for four minutes, drained of cooking oil for 15 seconds, and added to the pouch. Temperature, relative humidity and dew point were recorded for 15 minutes. Results are shown in Table 6.

TABLE 6 Steak Fries in Pouch Time (min) Temp (° F.) RH DP (° F.) 1 107 100 104.6 1.5 113.9 100 112.7 2 116.6 100 117.5 2.5 118.8 100 117.5 3 120.7 100 120 3.5 122.5 100 123.2 4 124 100 124.4 4.5 125 100 125.3 5 125.6 100 125.8 7 126.5 100 126.5 9 125.5 100 125.7 10 124.7 100 124.6 15 118 100 117.8

The internal temperature of the fries was 153° F. after 15 minutes.

By way of comparison, freshly cooked chicken tenders (Barber brand “Italian style” chicken tenders) and steak fries (Ore-Ida brand) were also placed in un-insulated pouches made from Mylar® film. The pouches were formed as discussed above. This constituted Comparative Examples III and IV. Temperature, relative humidity and dew point were recorded for 15 minutes. Results are shown in Tables 7 (Comparative Example III) and 8 (Comparative Example IV).

TABLE 7 Chicken tenders, un-insulated pouch Time (min) Temp (° F.) RH DP (° F.) 1 87.8 100 89.7 2 97.8 100 95 3 98.5 100 98.3 5 96.5 100 98.7 7 95.2 100 98.9 9 91.9 100 94.9 10 91.3 100 89.8 15 92.1 100 86

Condensation was observed in the pouch after 2 minutes. Crispness was rated as “poor to satisfactory”. Internal temperature of product was 144° F. after 15 minutes.

TABLE 8 Steak fries, un-insulated pouch Time (min) Temp (° F.) RH DP (° F.) 1 87.7 100 109.9 2 102.8 100 112.6 3 107.5 100 112.8 5 108.7 100 110.9 7 103.9 100 106 9 101.3 100 101.6 10 100.5 100 99.9 15 99.7 100 100

There was a large amount of condensation evident in the pouch after 4 minute. The internal temperature of the food was 138° F. after 15 minutes. Steak fries were rated as “poor”.

Comparative Example V Pouch with Melt-blown Polyolefin Nonwoven First Layer

This example was conducted in a manner similar to that in Example 6. The pouches were made from a multilayer sheet similar to that described in Example 1 with the exception that the first inner layer was a polyolefin nonwoven, available under the trade name Tyvek® from DuPont. The pouch was formed from two pieces of the multilayer sheet, each the same size, here approximately 10 in.×10 in., sealed on three sides with masking tape.

Four pieces of chicken tenders (approximately 240 g) were cooked at 240° F. for four minutes, drained of cooking oil for 15 seconds, and then placed in the pouch. Temperature, relative humidity and dew point were recorded for 15 minutes. The results are shown in Table 9.

TABLE 9 Time Temp (° F.) RH Dew Point (° F.) 1 75.6 65.5 60.1 2 80.1 100 74.2 3 82.8 96.3 73.4 5 79.7 94 72.3 7 81.7 100 74 9 83.9 100 81.5 10 84 100 81.8 15 83.9 100 81.5 20 81.7 100 79.5 25 80.3 100 78.4 30 78.4 100 76.8

The results show >20 degree drop in temperature (83.9° F. v. 105° F.) within the pouch after 15 minutes when compared to the chicken tenders in Example 6 (Table 5), while the relative humidity remained very high (100% v. 86.9%). With a resulting lower temperature and higher humidity within the pouch, one would expect the food quality and crispness to be less desirable as compared to Example 6A.

Physical Property Data on Sontara®

The following tables provide various physical parameters on spunlaced, nonwoven fabrics used as the water-wicking material and sold under the trade name Sontara®. The various grades listed in Tables 10 and 11 comprise hydroentangled, white, staple polyester fibers, as well as varying percentages of wood pulp. Moisture-vapor transmission rate (MVTR) was tested using ASTM D-6701. Hydrostatic head was tested using AATCC Method 127-1989.

TABLE 10 Bulk Wt % Wood Thickness Ai Re Ri MVTR (g/m2) Pulp (mils) Ae(mL/m2) (mL/g) (mL/m2/s) (mL/g/s) (g/m2-day) A 54  0 14 200,000 B 136   0 40 ˜25,000 C 68 55 13 290 4.25 1864 27.4 200,000 D 51 54 12 258 4.99 2043 39.9 E 63 25 16 286 4.63 2154 34.9 170,000

TABLE 11 Hydrostatic head (cm H2O) A 1.5 +/− 0.4 B Wets out (˜0)

Claims

1. A rigid, thermoplastic tray comprising a bottom portion and a lid wherein the lid fits over the bottom portion to generally seal along the perimeter where the lid and bottom portion meet; the tray comprises or is produced from a liner; the liner comprises a multilayer sheet comprising or produced from at least two layers including a first layer, a second layer, and optionally a third layer; the first layer comprises or is produced from a water-wicking material; the second layer comprises or is produced from an absorbent and insulating material; the third layer comprises or is produced from a structural material; and the multilayer sheet optionally comprises an additive including a desiccant, thermal and ultraviolet (UV) stabilizer, UV absorber, antistatic agent, processing aid, fluorescent whitening agent, pigment, lubricant, or combinations of two or more thereof.

2. The tray of claim 1 wherein the first layer has a moisture-vapor transmission rate of at least about 20,000 g/m2-day.

3. The tray of claim 1 wherein the first layer has a moisture-vapor transmission rate of at least about 150,000 g/m2-day.

4. The tray of claim 1 wherein the first layer has a hydrostatic head pressure of less than about 5 cm H2O.

5. The tray of claim 4 wherein the first layer has a moisture-vapor transmission rate of at least about 170,000 g/m2-day.

6. The tray of claim 5 wherein the first layer is, or is produced from, a nonwoven.

7. The tray of claim 6 wherein the nonwoven comprises a spunlaced fabric comprising a mixture of fibers of poly(ethylene terephthalate) and wood pulp.

8. The tray of claim 1 wherein the second layer has a thermal resistance, as measured in units of insulation, of at least about 0.0077 m2.K/W (0.05 CLO).

9. The tray of claim 7 wherein the second layer has a thermal resistance, as measured in units of insulation, of at least about 0.0077 m2.K/W (0.05 CLO).

10. The tray of claim 8 wherein the second layer comprises fiberfill batt, melt-blown fibers, foam, knit material, felt, or combinations of two or more thereof.

11. The tray of claim 9 wherein the second layer comprises fiberfill batt, melt-blown fibers, foam, knit material, felt, or combinations of two or more thereof.

12. The tray of claim 9 wherein the second layer comprises the fiberfill batt, which comprises or is produced from poly(ethylene terephthalate).

13. The tray of claim 12 wherein the second layer ranges in thickness from about 10 mils to about 100 mils.

14. The tray of claim 13 wherein the multilayer sheet comprises the third layer and the structural material is oriented polypropylene, oriented polyester, or combinations thereof.

15. The tray of claim 14 wherein the first layer is a nonwoven comprising a spunlaced fabric having a moisture-vapor transmission rate of at least about 20,000 g/m2-day and a hydrostatic head pressure of less than about 5 cm H2O, and the second layer has a thermal resistance of at least about 0.0077 m2.K/W (0.05 CLO).

16. The tray of claim 15 wherein the spunlaced fabric comprises a mixture of fibers of poly(ethylene terephthalate) and wood pulp, and the second layer is fiberfill batt.

17. The tray of claim 16 wherein the lid is substantially the same in size and shape as the bottom portion and the liner is affixed to the inside of the lid.

18. A lid for covering a package comprising a liner affixed thereto wherein the liner is as recited in claim 1.

19. The lid of claim 18 wherein the lid comprises oriented polystyrene and the liner is as recited in clam 16.

20. A box for packaging hot foods comprising paperboard and a liner wherein the liner is as recited in claim 16.

Patent History
Publication number: 20050260367
Type: Application
Filed: Mar 21, 2005
Publication Date: Nov 24, 2005
Inventors: Jeffrey Chambers (Hockessin, DE), Donna Visioli (Lower Gwynedd, PA), William Grassel (Delmont, PA), Bruce Robbins (Richmond, VA), Donald Smith (Gibsonia, PA), Robert Speer (Upper Burrell, PA)
Application Number: 11/085,722
Classifications
Current U.S. Class: 428/34.200; 428/35.700