Food Science Packaging – R. Jefferson Babbitt, Exopack Technology LLC
Abstract for “Microwave food packaging with printed-on susceptor.”
“A gusseted microwave package is provided. It includes a printed-on susceptor that has reduced microwave activity under its gussets. The new susceptor prevents the package from being charred by microwave heating. The susceptor should be printed in small patterns to avoid unwanted edge heating effects. This invention’s printed-on susceptor may be made from graphite or metallic inks. It is preferably printed on a non-contact surface. You can use the invention with many different susceptor designs, provided that the print coverage and microwave activity under the gussets are reduced to prevent charring and burning.
Background for “Microwave food packaging with printed-on susceptor.”
“It was discovered that the problems of charring of gusseted packaged can be solved by providing a printed-on susceptor with a patterned susceptor that is broken down into sub-patterns to reduce the edge heating effect. Also, the microwave activity of sub-patterns can be adjusted so that the microwave activity in the susceptor below the gussets is less than that of the center of the package that is not under the gumsets. It has been shown that runaway heating can also be prevented by reducing microwave activity in the area of the susceptor under the gussets on a microwave food package. Microwave activity, as used in this document, refers to how the susceptor reacts to microwave energy to produce heat. This can be controlled most easily with the printed-on susceptor by “print coverage”, which refers to either the area covered by the susceptor or the thickness (density), of the susceptor. It also indicates the concentration of microwave active particle in that area. The susceptor should be made from a coating with microwave active particles such as graphite and metal that is applied to a substrate during a printing operation. This method is easy and cheap.
The present invention is a microwave food packaging with gussets at opposite ends and an opening to allow food to be introduced into it. If the package contains oils or fats it will be greaseproof. It also includes an inner substrate that can hold the food and an outer substrate that can surround and attach to the inner substrate. A printed-on susceptor comprises a coating of a microwave reactive compound printed on the inner or outer surfaces of the inner substrates. The pattern has a first microwave activity in the center of the package. Under the gussets there is a second microwave activation, which is less than the first microwave activation. The susceptor’s first and second microwave activities have been selected to ensure uniform temperatures during microwave heating. This susceptor significantly reduces the risk of food being charred by the microwave heating. According to a preferred embodiment, the food comprises popcorn and oil. The center portion of the package is heated during initial heating. The inner and outer substrates can be made into bags, such as a microwave popcorn bag that opens automatically or one that is pillow-shaped, to hold the popcorn and oil.
“In accordance to the invention, the printed on susceptor is composed of sub-patterns spaced in a relation adapted to moderate heat generated by microwave energy across the pattern. This prevents substantial charring of the outer and inner substrates during microwave heating. You can adjust the area coverage, thickness, concentration, or combination of these factors to alter the microwave activity. Preferably, sub-patterns located in the middle portion of the microwave activity are determined. Sub-patterns below the gussets are similarly determined by second microwave activity. This invention may allow for the use of many sub-patterns such as squares and rectangles, circles and triangles.
“A first embodiment is distinguished by the fact that the coverage of the microwave active area’s surface area is approximately 60% to 90%. In the middle portion of the microwave active area, approximately 20% to 80% of the surface is covered by the pattern. Preferable embodiments have the second print coverage covering approximately 40% to 60% the area of the microwave food packaging under the gussets. The difference in microwave activity between the first and second areas as determined by the coverage of the pattern should be less than ten percent (10%) or forty percent (40%). Similar percentages are applicable to microwave activity as determined by the thickness or concentration of microwave interactive particles in ink.
“The susceptor can be made from many types of microwave reactive materials. The preferred microwave composition material is graphite-based inks. However, metal-based inks and inks containing carbon black containing particles could be used.
“This invention also contains a method for manufacturing a microwave food packet with gussets at opposite ends and an opening that allows food to be introduced into a microwave oven. This method according to the invention is preferred to include the following steps:
“Provide a greaseproof inner substrate, and an outer substrate;
“Printing on either the outer or inner surface of an outer substrate a susceptor consisting of a coating of a microwave reacting composition in a pattern with a first microwave activation in a central portion of the microwave food packaging and a second microwave activity, less than the second microwave activity under the gussets. The first and second microwave activities are selected to substantially prevent the food from charring under the gussets while still allowing for microwave heating;
“Laminating the inner substrate’s outer surface to the inner substrate’s outer substrate with the susceptor sandwiched between; and
“Forming the laminated substrates into the microwave package with the gussets, and openings for the introduction to food.”
The shaping step can be done by either transferring laminated substrates into a bag-making machine, or by transferring laminated substrates onto a form fill and seal machine. The preferred embodiment of the microwave food package contains popcorn.
“FIGS. “FIGS. The bag’s top end may be sealed to the bag’s backside 14 using known techniques. Gussetted side panels 18 extend from the bag’s top to the conventional bottom section 20. The bag 10 can expand when heated by the gussets 18. The majority of popcorn and oil are located in the middle of the bag between fold lines 22, 24 when used as a microwave popcorn bag. Further, a printed-on susceptor 28, which is in accordance to this invention, is provided in the central portion of the package. This can be illustrated by printing the susceptor28 in accordance the techniques described below.
“FIGS. 2A and 2B show another embodiment of a microwave-safe food container. It is a pillow-style bag 100 with a printed susceptor 28. FIG. 100 shows the pillow-style bag 100. 2A features a sealed side seam 101, an opening 104 to accept food products such as popcorn or oil, and a sealed bottom stitch 106. The susceptor 28 includes a first microwave activ area 34, bordered by fold lines 110 and 110; and a second microwave activate area 32 that extends below the fold lines 110 to 112.
“FIG. 2B is a top view of the partially expanded pillow-style bag. It has been filled with popcorn and sealed to better illustrate the close proximity of the food load. We will discuss the significance of this later. To provide self-venting, an adhesive 108 should be placed at the opening 104.
FIGS. 1 and 2 show the microwave food container of the invention. FIGS. 1 and 2 show gusseted sides 18 that allow for compact storage and shipping, as well as expansion of the bag during heating to store popped popcorn. This invention is for microwave food containers. The printed-on susceptor 28 of the general type is designed to maintain a uniform temperature throughout the susceptor according to the amount of food within the susceptor. The heating efficiency of the printed on susceptor 28 depends on the load. Therefore, the susceptor has been modified to prevent the substrate from burning or charring at small loads. These portions typically include the sections under the gussets of bags of the type illustrated in FIGS. 1, 2, 2A, and 2B. It is also forbidden to charring or burn areas that initially have no food load but later have food loads. These areas are typically found between fold lines 110, 112 or sealed ends 108,106.
“As mentioned above, the susceptor 28, in accordance to the invention, has patterns that are adapted for substantially uniform temperatures across a substrate during heating. This is in contrast with susceptors described by Maynard and al. Others where the microwave interactive element’s pattern is chosen to direct heat to specific areas, thus creating heat gradients. Separating the susceptor into subpatterns can result in uniform temperatures across the susceptor. This is to avoid the edge heating effect. Temperature gradients across susceptors can be substantially avoided by breaking the pattern into sub-patterns. This invention also reduces the amount of print coverage on the susceptor that is exposed to heat (such as under the gassets), which results in the suppression of burning and charring.
The susceptor 28 is best created by printing the susceptor-ink onto the packaging materials. This susceptor ink usually contains dispersed microwave active particle, such as graphite and carbon black particles in an ink. This invention’s susceptor can be printed using any printing method, including flexographic, relief or intaglio. For metal-based inks, it is possible to use prior art metallization or polymeric impregnation methods to create the susceptor pattern.
“The printed-on susceptor according to this invention preferably includes a susceptorink containing microwave active particles suspended within a suitable vehicle with the viscosity required for proper printing transfer. Preferably, the microwave active particles in this invention are graphite particles. They can be used for moderate heating and do not require compensators like those used in the prior arts. The microwave active particles absorb microwave energy and then convert it into heat when the susceptor ink has been dried on a suitable substrate. To ensure a uniform conversion of microwave energies, microwave active particles must be approximately the same size as the ink vehicle and should be distributed in the ink vehicle in a uniform manner during printing. The preferred size of the microwave active particles is between 4-10 microns. The microwave active particles in a particular embodiment are graphite particles, such as Micro 270. Asbury Graphite Mills (Asbury NJ ) manufactured and sold the particles
It is preferred that the susceptor ink has a solids content including microwave active particles greater than 35% according to the desired viscosity. A solids content below 35% is preferred for gravure printing, while a solids contents of around 50% is preferable for flexographic printing. Here is an example of the preferred ink formula for flexible printing according to the present invention:
“A defoaming agents may be added as required.”
“The preferred printing ink contains a graphite substance suspended within a vehicle with resin and solvent. This ink composition is best suited for printing on a paper substrate, according to those skilled in the art. The art is also able to appreciate that the ink composition must be adapted for printing on other substrates than paper. For example, polyethylene. Unirez? You can also use rosin-based graphite inks to print the substrate according to this invention.
“When applied to food containers, such as the ones shown in FIGS. “When applied to food containers such as those shown in FIGS. 1 and 2, the susceptor 28, is preferably printed on an outer ply a two-ply substrate. However, the susceptor 28 can also be printed on inside the outer ply. The preferred embodiment of a microwave popcorn bag is made from an inner ply that is greaseproof, such as 25# greaseproof papers. On the other hand, the outer substrate may be a 30# machine glazed kraft paper. Once the susceptor has been printed, a laminating adhesive like a National Starch Resyn33-9138 can be used to attach the outer ply and inner ply. PVAc-based adhesives such as Duracet 30, adhesive 108, are preferred for the top and bottom of the bag. Below are more details about the fabrication of a food container according to the invention.
“As mentioned above, susceptors can be used in microwave food packages with gussets such as the microwave popcorn bags shown in FIGS. 1, 2 and 3, heat buildup underneath the gussets can cause scorching and charring to the bag. This problem can be solved by reducing susceptor print coverage below the gussets. FIGS. 3 and 4 illustrate an example of such a susceptor according to the invention. FIGS. 3 and 4.
“The susceptor 28 is shown in FIGS. There are two main components to FIGS. 3 and 4. To eliminate edge heating, the entire susceptor pattern has been broken down into smaller squares (30-40). The second is that the second print coverage 32 and 44 are located under the gussets 18. This print coverage is intended to be lower than 34 and 42 which are located in the middle section 36 of the microwave food containers. The print coverage 34 found within the middle section 36 of the microwave food container is dense because the food product, e.g., popcorn, is located in this area. This area is used mainly for heating oil and popcorn. The first print coverage 34 covers a large portion of the heating area. To provide heat, a large amount of load must be provided. The load under the 18 gussets is usually lower than the portion of the microwave container that has the first print coverage 34, because less food is normally found under the 18 gussets before the microwave container expands. Because of this lower load, the print coverage under the gussets 32 is decreased so less heat can be applied to the load. The temperature of the microwave food container can be kept relatively constant by reducing the print coverage 32 under the susceptor 28, as well as the central section 36, by reducing its print coverage. Similar to the above, it is possible to reduce the print coverage at both the ends and the center section 36 of a food container. It has been shown that the temperature of the microwave food container can be controlled by changing the print coverages at the ends 36 and 18 of the gussets 18. This is highly recommended as it prevents the substrate from burning and charring, while also allowing for optimal microwave heating.
“In FIG. 3. The susceptor according to the invention has a surface coverage 34 within the center section 36 of the order 78%, and an outside coverage 32 in the areas of the susceptor below the gussets 18, and at the ends 36 of the order 40%. FIG. FIG. 4 shows a similar pattern to a susceptor38 with sub-patterns40. The first surface area of the print coverage 42 is in the center section of the susceptor 36, and the second area of print coverage 44 is at the ends of the center section 36. These print coverages are only an example and one skilled in art will know that different print coverages can be used depending on the load in the center 36 or under the gussets 18. A skilled artist will also be able to see that the second and third print coverages can have similar variations depending on the thickness of the susceptor, or the concentration of microwave interactive particles in ink. The preferred print coverage 34 of the susceptor 28, 36, is between 60-90 percent, while 32 of the susceptor 28, under the gussets 18, is between 20-60%. However, a 32 print coverage between 40-60% is preferable. It is important that the difference between center and outer sections be chosen to ensure uniform heating. The difference between the center and outer sections should be greater than ten percent (10%) or less than forty percent (40 %).”).
“Those who are skilled in the art will be able to appreciate FIGS. FIGS. 3 and 4 show different coverages of the same surface area. As mentioned above, you can alter the thickness of the susceptor and/or the concentrations of conductive particles within the susceptor ink to change the coverage. These variations can be made at the discretion of the skilled.
FIG. 2 shows a susceptor in accordance to the present invention. 5. The susceptor 28 includes sub-patterns 30, which are preferably printed on the outer surface or inner ply of a 2-ply, gusseted microwave popcorn bags of the type shown at FIGS. 1. and 2. Preferably, the substrate is a laminated newspaper such as a 25# greaseproof or laminated to a 30# machine-glazed paper.
“In FIG. “In FIG. The typical wavelength of microwaves used in commercially-available microwave ovens is about 12 cm. Therefore, it is preferable that dimensions A and B not exceed 3 cm. FIGS. For example, in FIGS. 3 and 4, the sub-patterns can be 0.156 in2 in blocks within the first print coverage 34, located within the middle sections 36, 0.109 In2 blocks under gussets 18, and in the end portions 36 of FIG. 3. and 0.135 In2 blocks under the gussets 18, and in the end sections of center section 36, in the embodiment shown in FIG. 4.”
“The sub-patterns 30 and 40 of the FIGS. 3, 4 and 5 need not be restricted to squares. FIG. 6. Squares can be replaced with rectangles 46, in which A>B. Similar to FIG. As shown in FIG. 7, the susceptor 28 could also include a plurality 48 of circles that are offset from adjacent rows. To increase the area of the printed surface, interstitial circles 49 can be used in this embodiment. As shown in FIG. 8 Suceptor 28 can include a plurality equilateral triangles 50, and a plurality a right triangles 52 at each end of each row. The length of the hypotenuse 52 of each right triangular 52 is substantially the same as the side of an adjacent triangular 50. Many other patterns are possible according to the invention. To achieve the benefits of the invention, any such patterns must have reduced print coverages under the gussets to ensure that the susceptor is heated in a microwave-safe area.
“EXAMPLES”
Once the ink has been prepared, you can prepare the microwave popcorn bag by using a greaseproof inner layer such as a 25# greaseproof newspaper. An outer ply can be made from machine-glazed 30# paper. The bag graphics, such as brand, directions, and the like, are printed on the outer ply by any method. The inside of the outer layer is coated with a laminating adhesive, such as National Starch Resyn 31-3138.
The ink composition should then be applied to the greaseproof inner plly at the desired thickness. However, one skilled in the art may recognize that the susceptor can also be applied to the inner ply. The graphite particle concentration or coating thickness can be varied to achieve a reduced print coverage below the gussets. However, FIGS. The coating thickness should be nearly equal in FIGS. 3 and 4. Combining these techniques is possible, however. The preferred embodiment of the invention’s ink composition is intended for use in a flexible printing apparatus. However, it should be noted that other printing methods, such as letter press, rotogravure and lithograph, may also be used. The preferred flexographic printing process requires ink viscosity of 20-40 seconds (#3 Zahn). Other printing processes may have different viscosity requirements. The above-mentioned range of viscosity should not be considered a limit.
“In a flexographic printing process, the ink is measured onto an anilox roll with an engraved network of cells of a specified size and depth. This defines the coating weight for the ink layer. The ink is then transferred to a photopolymer plat on an application roll which in turn applies it to the paper sheet. The ink does not need to be applied to any substrate that contacts food. Therefore, there is no FDA-approved coating. The ink is applied using a pattern that has a reduced print coverage below the gussets, in accordance with the invention. FIGS. 3. Any of the FIGS. patterns can be used. The patterns shown in FIGS. 5-8 can also be used, provided that the coverage below the gussets are less than the one in the middle of the ply. Although printing and laminating are best done on one machine, this is not always necessary.
The microwave popcorn bag is made by laminating the outer and the inner plys, with the susceptor sandwiched between them using a rolling nail laminator that operates at the required speed. The appropriate portions of the greaseproof paper are then sealed with a heat seal adhesive like 4#/3MSF Duracet 30. The rollstock is then dried and rolled. The rollstock can then be transferred to a bag-machine for conversion into bags that allow for food insertion or can be filled and sealed using a suitable packaging machine. The bag can be, for example, a 2-ply self-opening style (FIG. 1.) or a 2-ply pillow style (FIG. 2) Microwave popcorn bag
“FIG. “FIG. 9” illustrates a sheet of 76 that can be used to make a microwave popcorn bag, or other similar food packaging in accordance with this invention. The sheet 76 is part a continuous web of 78 which will allow for the manufacture of many bags. To form individual bags, the sheet 76 must be cut along line 80. Pre-applied adhesive coating 82 to the sheet’s inside surface is made according to any of the methods described above. This adhesive 82 coating covers the tongues 84. It extends laterally over the slits of 86 and 88, and along the length of line 90. As illustrated, a second strip of adhesive can be placed along cut line 92. It is possible to place a strip adhesive along web 78’s side edges. This will allow the sides of the bag to be joined during the bag-forming operation. The invention includes a susceptor 28 that is printed between the inner and outer plies.
The resulting sheet 76 can be made into a pillow-style bag, as shown in FIG. 2, or a bag that opens automatically, as shown in FIG. 1. FIG. 1 shows the bag in its entirety. FIG. 1 shows the bag fully opened. 10. For the desired shape upon inflation, the bag’s side walls can be folded in a centrally or off-center manner. In any way known, transfer fold lines 94-96 and diagonal fold lines 99-100 are formed. It is not shown but it will be appreciated by those who are skilled in the art that lines similar to lines 95, 98, and 100 can also be formed on the side of bag where the flap 102 is made. The typical method for making such bags is to first form sheet 76 into tubes by joining its sides edges. After that, the tube is flattened using inwardly folded gussets 18, and then manipulated as flattened. The bag can then be sealed by applying heat and pressure. This creates a self-venting bag with a susceptor 28 printed either on the outer surface of an inner ply, or on the inner surface of an outer ply. 10.”
“As mentioned above, the desired print coverage can be adjusted in accordance to the shape of the microwave package by changing the surface area or thickness of the ink on the substrate. The microwave conductive material concentration can also be adjusted to obtain the desired effect.
“COMPARATIVE EXAMPLE”
“A microwave popcorn bag with a susceptor pattern like FIG. The above procedure was used to prepare 3. A control microwave popcorn bag with a susceptor pattern 120, without reduced print coverage below the gussets (see FIG. The above method was used to prepare 11 as well. The popcorn bags were then punctured in the four designated areas. The MIW-2 temperature probes were connected to a Luxtronx. The holes were made by inserting the Model 755 Fluoroptic temperature sensor. The probes were placed in the holes so that the probe tips touched the marked areas in FIG. 11. A first probe was inserted into hole 140 so that its tip was at 142. A second probe was then inserted through the hole 130 so that its tips were at 132. A third probe was then inserted through hole 134, so that its top was at 136. Finally, a fourth probe was placed through hole 138 so that its tip was at 140. Kapton was then used to cover the probe tips and holes. Heat resistant tape. FIG. 11 were chosen to ensure that two tips were placed under the gussets 18, and two tips were located centrally in 36 for comparison purposes.”
“For microwave popcorn bags with the susceptor pattern and reduced print coverage, however, the temperature rise in the middle (curve 126) is more similar to that in the center (curve 126). Thus, FIG. FIG. 12 shows that the temperature of the printed suceptor is dependent on the load. Accordingly, a reduced load can be achieved by reducing the coverage below the gussets. The present invention also reduces the amount of coverage under the gussets to provide better control over runaway heat. This is in contrast to the prior art which required the use of thermocompensators or the like.
The printed susceptor patterns of this invention, which reduce the print coverage below the gussets, substantially prevent microwave food containers from burning or charring and provide better control over microwave heating. The invention allows for the temperature of microwave food packages to be maintained at the same temperature by recognising that susceptor heating is dependent on load and adapting the susceptor’s print coverage according to the amount of food being heated at each location. For flexible, expandable gusseted microwave foods packages, very little food can be found underneath the gussets, until the package has been fully inflated. This is where the invention comes in handy.
“While the exemplary embodiments have been described in detail, those skilled in art will quickly appreciate that there are many other modifications possible to the exemplary embodiments. However, they do not materially depart from the inventive teachings and benefits. Metal-based inks can be used instead of graphite ink in the preferred embodiment. Graphite inks can be used for moderate heating, but not without thermocompensators, as metal inks will crack under severe loads, which adversely affects their heating efficiency. Thermocompensators can be used for intense heating.
“A further embodiment of susceptor according to the invention may have graduated print coverage that decreases from the center of susceptor pattern towards the edges under the gussets. The print coverage may be uniform in the middle of the susceptor, while it is possible that the coverage below the gussets will vary according to the package’s outer edges. Another embodiment may have uniform print coverage throughout the food container, but not under the gussets. FIG. FIGS. 3 and 4 show the center portions 34, 42 and 42 that may extend to the containers’ ends. These designs must be considered to ensure that the container doesn’t burn or char due to a lower load. All such modifications are included in the scope of the invention as described in the following claims.
Summary for “Microwave food packaging with printed-on susceptor.”
“It was discovered that the problems of charring of gusseted packaged can be solved by providing a printed-on susceptor with a patterned susceptor that is broken down into sub-patterns to reduce the edge heating effect. Also, the microwave activity of sub-patterns can be adjusted so that the microwave activity in the susceptor below the gussets is less than that of the center of the package that is not under the gumsets. It has been shown that runaway heating can also be prevented by reducing microwave activity in the area of the susceptor under the gussets on a microwave food package. Microwave activity, as used in this document, refers to how the susceptor reacts to microwave energy to produce heat. This can be controlled most easily with the printed-on susceptor by “print coverage”, which refers to either the area covered by the susceptor or the thickness (density), of the susceptor. It also indicates the concentration of microwave active particle in that area. The susceptor should be made from a coating with microwave active particles such as graphite and metal that is applied to a substrate during a printing operation. This method is easy and cheap.
The present invention is a microwave food packaging with gussets at opposite ends and an opening to allow food to be introduced into it. If the package contains oils or fats it will be greaseproof. It also includes an inner substrate that can hold the food and an outer substrate that can surround and attach to the inner substrate. A printed-on susceptor comprises a coating of a microwave reactive compound printed on the inner or outer surfaces of the inner substrates. The pattern has a first microwave activity in the center of the package. Under the gussets there is a second microwave activation, which is less than the first microwave activation. The susceptor’s first and second microwave activities have been selected to ensure uniform temperatures during microwave heating. This susceptor significantly reduces the risk of food being charred by the microwave heating. According to a preferred embodiment, the food comprises popcorn and oil. The center portion of the package is heated during initial heating. The inner and outer substrates can be made into bags, such as a microwave popcorn bag that opens automatically or one that is pillow-shaped, to hold the popcorn and oil.
“In accordance to the invention, the printed on susceptor is composed of sub-patterns spaced in a relation adapted to moderate heat generated by microwave energy across the pattern. This prevents substantial charring of the outer and inner substrates during microwave heating. You can adjust the area coverage, thickness, concentration, or combination of these factors to alter the microwave activity. Preferably, sub-patterns located in the middle portion of the microwave activity are determined. Sub-patterns below the gussets are similarly determined by second microwave activity. This invention may allow for the use of many sub-patterns such as squares and rectangles, circles and triangles.
“A first embodiment is distinguished by the fact that the coverage of the microwave active area’s surface area is approximately 60% to 90%. In the middle portion of the microwave active area, approximately 20% to 80% of the surface is covered by the pattern. Preferable embodiments have the second print coverage covering approximately 40% to 60% the area of the microwave food packaging under the gussets. The difference in microwave activity between the first and second areas as determined by the coverage of the pattern should be less than ten percent (10%) or forty percent (40%). Similar percentages are applicable to microwave activity as determined by the thickness or concentration of microwave interactive particles in ink.
“The susceptor can be made from many types of microwave reactive materials. The preferred microwave composition material is graphite-based inks. However, metal-based inks and inks containing carbon black containing particles could be used.
“This invention also contains a method for manufacturing a microwave food packet with gussets at opposite ends and an opening that allows food to be introduced into a microwave oven. This method according to the invention is preferred to include the following steps:
“Provide a greaseproof inner substrate, and an outer substrate;
“Printing on either the outer or inner surface of an outer substrate a susceptor consisting of a coating of a microwave reacting composition in a pattern with a first microwave activation in a central portion of the microwave food packaging and a second microwave activity, less than the second microwave activity under the gussets. The first and second microwave activities are selected to substantially prevent the food from charring under the gussets while still allowing for microwave heating;
“Laminating the inner substrate’s outer surface to the inner substrate’s outer substrate with the susceptor sandwiched between; and
“Forming the laminated substrates into the microwave package with the gussets, and openings for the introduction to food.”
The shaping step can be done by either transferring laminated substrates into a bag-making machine, or by transferring laminated substrates onto a form fill and seal machine. The preferred embodiment of the microwave food package contains popcorn.
“FIGS. “FIGS. The bag’s top end may be sealed to the bag’s backside 14 using known techniques. Gussetted side panels 18 extend from the bag’s top to the conventional bottom section 20. The bag 10 can expand when heated by the gussets 18. The majority of popcorn and oil are located in the middle of the bag between fold lines 22, 24 when used as a microwave popcorn bag. Further, a printed-on susceptor 28, which is in accordance to this invention, is provided in the central portion of the package. This can be illustrated by printing the susceptor28 in accordance the techniques described below.
“FIGS. 2A and 2B show another embodiment of a microwave-safe food container. It is a pillow-style bag 100 with a printed susceptor 28. FIG. 100 shows the pillow-style bag 100. 2A features a sealed side seam 101, an opening 104 to accept food products such as popcorn or oil, and a sealed bottom stitch 106. The susceptor 28 includes a first microwave activ area 34, bordered by fold lines 110 and 110; and a second microwave activate area 32 that extends below the fold lines 110 to 112.
“FIG. 2B is a top view of the partially expanded pillow-style bag. It has been filled with popcorn and sealed to better illustrate the close proximity of the food load. We will discuss the significance of this later. To provide self-venting, an adhesive 108 should be placed at the opening 104.
FIGS. 1 and 2 show the microwave food container of the invention. FIGS. 1 and 2 show gusseted sides 18 that allow for compact storage and shipping, as well as expansion of the bag during heating to store popped popcorn. This invention is for microwave food containers. The printed-on susceptor 28 of the general type is designed to maintain a uniform temperature throughout the susceptor according to the amount of food within the susceptor. The heating efficiency of the printed on susceptor 28 depends on the load. Therefore, the susceptor has been modified to prevent the substrate from burning or charring at small loads. These portions typically include the sections under the gussets of bags of the type illustrated in FIGS. 1, 2, 2A, and 2B. It is also forbidden to charring or burn areas that initially have no food load but later have food loads. These areas are typically found between fold lines 110, 112 or sealed ends 108,106.
“As mentioned above, the susceptor 28, in accordance to the invention, has patterns that are adapted for substantially uniform temperatures across a substrate during heating. This is in contrast with susceptors described by Maynard and al. Others where the microwave interactive element’s pattern is chosen to direct heat to specific areas, thus creating heat gradients. Separating the susceptor into subpatterns can result in uniform temperatures across the susceptor. This is to avoid the edge heating effect. Temperature gradients across susceptors can be substantially avoided by breaking the pattern into sub-patterns. This invention also reduces the amount of print coverage on the susceptor that is exposed to heat (such as under the gassets), which results in the suppression of burning and charring.
The susceptor 28 is best created by printing the susceptor-ink onto the packaging materials. This susceptor ink usually contains dispersed microwave active particle, such as graphite and carbon black particles in an ink. This invention’s susceptor can be printed using any printing method, including flexographic, relief or intaglio. For metal-based inks, it is possible to use prior art metallization or polymeric impregnation methods to create the susceptor pattern.
“The printed-on susceptor according to this invention preferably includes a susceptorink containing microwave active particles suspended within a suitable vehicle with the viscosity required for proper printing transfer. Preferably, the microwave active particles in this invention are graphite particles. They can be used for moderate heating and do not require compensators like those used in the prior arts. The microwave active particles absorb microwave energy and then convert it into heat when the susceptor ink has been dried on a suitable substrate. To ensure a uniform conversion of microwave energies, microwave active particles must be approximately the same size as the ink vehicle and should be distributed in the ink vehicle in a uniform manner during printing. The preferred size of the microwave active particles is between 4-10 microns. The microwave active particles in a particular embodiment are graphite particles, such as Micro 270. Asbury Graphite Mills (Asbury NJ ) manufactured and sold the particles
It is preferred that the susceptor ink has a solids content including microwave active particles greater than 35% according to the desired viscosity. A solids content below 35% is preferred for gravure printing, while a solids contents of around 50% is preferable for flexographic printing. Here is an example of the preferred ink formula for flexible printing according to the present invention:
“A defoaming agents may be added as required.”
“The preferred printing ink contains a graphite substance suspended within a vehicle with resin and solvent. This ink composition is best suited for printing on a paper substrate, according to those skilled in the art. The art is also able to appreciate that the ink composition must be adapted for printing on other substrates than paper. For example, polyethylene. Unirez? You can also use rosin-based graphite inks to print the substrate according to this invention.
“When applied to food containers, such as the ones shown in FIGS. “When applied to food containers such as those shown in FIGS. 1 and 2, the susceptor 28, is preferably printed on an outer ply a two-ply substrate. However, the susceptor 28 can also be printed on inside the outer ply. The preferred embodiment of a microwave popcorn bag is made from an inner ply that is greaseproof, such as 25# greaseproof papers. On the other hand, the outer substrate may be a 30# machine glazed kraft paper. Once the susceptor has been printed, a laminating adhesive like a National Starch Resyn33-9138 can be used to attach the outer ply and inner ply. PVAc-based adhesives such as Duracet 30, adhesive 108, are preferred for the top and bottom of the bag. Below are more details about the fabrication of a food container according to the invention.
“As mentioned above, susceptors can be used in microwave food packages with gussets such as the microwave popcorn bags shown in FIGS. 1, 2 and 3, heat buildup underneath the gussets can cause scorching and charring to the bag. This problem can be solved by reducing susceptor print coverage below the gussets. FIGS. 3 and 4 illustrate an example of such a susceptor according to the invention. FIGS. 3 and 4.
“The susceptor 28 is shown in FIGS. There are two main components to FIGS. 3 and 4. To eliminate edge heating, the entire susceptor pattern has been broken down into smaller squares (30-40). The second is that the second print coverage 32 and 44 are located under the gussets 18. This print coverage is intended to be lower than 34 and 42 which are located in the middle section 36 of the microwave food containers. The print coverage 34 found within the middle section 36 of the microwave food container is dense because the food product, e.g., popcorn, is located in this area. This area is used mainly for heating oil and popcorn. The first print coverage 34 covers a large portion of the heating area. To provide heat, a large amount of load must be provided. The load under the 18 gussets is usually lower than the portion of the microwave container that has the first print coverage 34, because less food is normally found under the 18 gussets before the microwave container expands. Because of this lower load, the print coverage under the gussets 32 is decreased so less heat can be applied to the load. The temperature of the microwave food container can be kept relatively constant by reducing the print coverage 32 under the susceptor 28, as well as the central section 36, by reducing its print coverage. Similar to the above, it is possible to reduce the print coverage at both the ends and the center section 36 of a food container. It has been shown that the temperature of the microwave food container can be controlled by changing the print coverages at the ends 36 and 18 of the gussets 18. This is highly recommended as it prevents the substrate from burning and charring, while also allowing for optimal microwave heating.
“In FIG. 3. The susceptor according to the invention has a surface coverage 34 within the center section 36 of the order 78%, and an outside coverage 32 in the areas of the susceptor below the gussets 18, and at the ends 36 of the order 40%. FIG. FIG. 4 shows a similar pattern to a susceptor38 with sub-patterns40. The first surface area of the print coverage 42 is in the center section of the susceptor 36, and the second area of print coverage 44 is at the ends of the center section 36. These print coverages are only an example and one skilled in art will know that different print coverages can be used depending on the load in the center 36 or under the gussets 18. A skilled artist will also be able to see that the second and third print coverages can have similar variations depending on the thickness of the susceptor, or the concentration of microwave interactive particles in ink. The preferred print coverage 34 of the susceptor 28, 36, is between 60-90 percent, while 32 of the susceptor 28, under the gussets 18, is between 20-60%. However, a 32 print coverage between 40-60% is preferable. It is important that the difference between center and outer sections be chosen to ensure uniform heating. The difference between the center and outer sections should be greater than ten percent (10%) or less than forty percent (40 %).”).
“Those who are skilled in the art will be able to appreciate FIGS. FIGS. 3 and 4 show different coverages of the same surface area. As mentioned above, you can alter the thickness of the susceptor and/or the concentrations of conductive particles within the susceptor ink to change the coverage. These variations can be made at the discretion of the skilled.
FIG. 2 shows a susceptor in accordance to the present invention. 5. The susceptor 28 includes sub-patterns 30, which are preferably printed on the outer surface or inner ply of a 2-ply, gusseted microwave popcorn bags of the type shown at FIGS. 1. and 2. Preferably, the substrate is a laminated newspaper such as a 25# greaseproof or laminated to a 30# machine-glazed paper.
“In FIG. “In FIG. The typical wavelength of microwaves used in commercially-available microwave ovens is about 12 cm. Therefore, it is preferable that dimensions A and B not exceed 3 cm. FIGS. For example, in FIGS. 3 and 4, the sub-patterns can be 0.156 in2 in blocks within the first print coverage 34, located within the middle sections 36, 0.109 In2 blocks under gussets 18, and in the end portions 36 of FIG. 3. and 0.135 In2 blocks under the gussets 18, and in the end sections of center section 36, in the embodiment shown in FIG. 4.”
“The sub-patterns 30 and 40 of the FIGS. 3, 4 and 5 need not be restricted to squares. FIG. 6. Squares can be replaced with rectangles 46, in which A>B. Similar to FIG. As shown in FIG. 7, the susceptor 28 could also include a plurality 48 of circles that are offset from adjacent rows. To increase the area of the printed surface, interstitial circles 49 can be used in this embodiment. As shown in FIG. 8 Suceptor 28 can include a plurality equilateral triangles 50, and a plurality a right triangles 52 at each end of each row. The length of the hypotenuse 52 of each right triangular 52 is substantially the same as the side of an adjacent triangular 50. Many other patterns are possible according to the invention. To achieve the benefits of the invention, any such patterns must have reduced print coverages under the gussets to ensure that the susceptor is heated in a microwave-safe area.
“EXAMPLES”
Once the ink has been prepared, you can prepare the microwave popcorn bag by using a greaseproof inner layer such as a 25# greaseproof newspaper. An outer ply can be made from machine-glazed 30# paper. The bag graphics, such as brand, directions, and the like, are printed on the outer ply by any method. The inside of the outer layer is coated with a laminating adhesive, such as National Starch Resyn 31-3138.
The ink composition should then be applied to the greaseproof inner plly at the desired thickness. However, one skilled in the art may recognize that the susceptor can also be applied to the inner ply. The graphite particle concentration or coating thickness can be varied to achieve a reduced print coverage below the gussets. However, FIGS. The coating thickness should be nearly equal in FIGS. 3 and 4. Combining these techniques is possible, however. The preferred embodiment of the invention’s ink composition is intended for use in a flexible printing apparatus. However, it should be noted that other printing methods, such as letter press, rotogravure and lithograph, may also be used. The preferred flexographic printing process requires ink viscosity of 20-40 seconds (#3 Zahn). Other printing processes may have different viscosity requirements. The above-mentioned range of viscosity should not be considered a limit.
“In a flexographic printing process, the ink is measured onto an anilox roll with an engraved network of cells of a specified size and depth. This defines the coating weight for the ink layer. The ink is then transferred to a photopolymer plat on an application roll which in turn applies it to the paper sheet. The ink does not need to be applied to any substrate that contacts food. Therefore, there is no FDA-approved coating. The ink is applied using a pattern that has a reduced print coverage below the gussets, in accordance with the invention. FIGS. 3. Any of the FIGS. patterns can be used. The patterns shown in FIGS. 5-8 can also be used, provided that the coverage below the gussets are less than the one in the middle of the ply. Although printing and laminating are best done on one machine, this is not always necessary.
The microwave popcorn bag is made by laminating the outer and the inner plys, with the susceptor sandwiched between them using a rolling nail laminator that operates at the required speed. The appropriate portions of the greaseproof paper are then sealed with a heat seal adhesive like 4#/3MSF Duracet 30. The rollstock is then dried and rolled. The rollstock can then be transferred to a bag-machine for conversion into bags that allow for food insertion or can be filled and sealed using a suitable packaging machine. The bag can be, for example, a 2-ply self-opening style (FIG. 1.) or a 2-ply pillow style (FIG. 2) Microwave popcorn bag
“FIG. “FIG. 9” illustrates a sheet of 76 that can be used to make a microwave popcorn bag, or other similar food packaging in accordance with this invention. The sheet 76 is part a continuous web of 78 which will allow for the manufacture of many bags. To form individual bags, the sheet 76 must be cut along line 80. Pre-applied adhesive coating 82 to the sheet’s inside surface is made according to any of the methods described above. This adhesive 82 coating covers the tongues 84. It extends laterally over the slits of 86 and 88, and along the length of line 90. As illustrated, a second strip of adhesive can be placed along cut line 92. It is possible to place a strip adhesive along web 78’s side edges. This will allow the sides of the bag to be joined during the bag-forming operation. The invention includes a susceptor 28 that is printed between the inner and outer plies.
The resulting sheet 76 can be made into a pillow-style bag, as shown in FIG. 2, or a bag that opens automatically, as shown in FIG. 1. FIG. 1 shows the bag in its entirety. FIG. 1 shows the bag fully opened. 10. For the desired shape upon inflation, the bag’s side walls can be folded in a centrally or off-center manner. In any way known, transfer fold lines 94-96 and diagonal fold lines 99-100 are formed. It is not shown but it will be appreciated by those who are skilled in the art that lines similar to lines 95, 98, and 100 can also be formed on the side of bag where the flap 102 is made. The typical method for making such bags is to first form sheet 76 into tubes by joining its sides edges. After that, the tube is flattened using inwardly folded gussets 18, and then manipulated as flattened. The bag can then be sealed by applying heat and pressure. This creates a self-venting bag with a susceptor 28 printed either on the outer surface of an inner ply, or on the inner surface of an outer ply. 10.”
“As mentioned above, the desired print coverage can be adjusted in accordance to the shape of the microwave package by changing the surface area or thickness of the ink on the substrate. The microwave conductive material concentration can also be adjusted to obtain the desired effect.
“COMPARATIVE EXAMPLE”
“A microwave popcorn bag with a susceptor pattern like FIG. The above procedure was used to prepare 3. A control microwave popcorn bag with a susceptor pattern 120, without reduced print coverage below the gussets (see FIG. The above method was used to prepare 11 as well. The popcorn bags were then punctured in the four designated areas. The MIW-2 temperature probes were connected to a Luxtronx. The holes were made by inserting the Model 755 Fluoroptic temperature sensor. The probes were placed in the holes so that the probe tips touched the marked areas in FIG. 11. A first probe was inserted into hole 140 so that its tip was at 142. A second probe was then inserted through the hole 130 so that its tips were at 132. A third probe was then inserted through hole 134, so that its top was at 136. Finally, a fourth probe was placed through hole 138 so that its tip was at 140. Kapton was then used to cover the probe tips and holes. Heat resistant tape. FIG. 11 were chosen to ensure that two tips were placed under the gussets 18, and two tips were located centrally in 36 for comparison purposes.”
“For microwave popcorn bags with the susceptor pattern and reduced print coverage, however, the temperature rise in the middle (curve 126) is more similar to that in the center (curve 126). Thus, FIG. FIG. 12 shows that the temperature of the printed suceptor is dependent on the load. Accordingly, a reduced load can be achieved by reducing the coverage below the gussets. The present invention also reduces the amount of coverage under the gussets to provide better control over runaway heat. This is in contrast to the prior art which required the use of thermocompensators or the like.
The printed susceptor patterns of this invention, which reduce the print coverage below the gussets, substantially prevent microwave food containers from burning or charring and provide better control over microwave heating. The invention allows for the temperature of microwave food packages to be maintained at the same temperature by recognising that susceptor heating is dependent on load and adapting the susceptor’s print coverage according to the amount of food being heated at each location. For flexible, expandable gusseted microwave foods packages, very little food can be found underneath the gussets, until the package has been fully inflated. This is where the invention comes in handy.
“While the exemplary embodiments have been described in detail, those skilled in art will quickly appreciate that there are many other modifications possible to the exemplary embodiments. However, they do not materially depart from the inventive teachings and benefits. Metal-based inks can be used instead of graphite ink in the preferred embodiment. Graphite inks can be used for moderate heating, but not without thermocompensators, as metal inks will crack under severe loads, which adversely affects their heating efficiency. Thermocompensators can be used for intense heating.
“A further embodiment of susceptor according to the invention may have graduated print coverage that decreases from the center of susceptor pattern towards the edges under the gussets. The print coverage may be uniform in the middle of the susceptor, while it is possible that the coverage below the gussets will vary according to the package’s outer edges. Another embodiment may have uniform print coverage throughout the food container, but not under the gussets. FIG. FIGS. 3 and 4 show the center portions 34, 42 and 42 that may extend to the containers’ ends. These designs must be considered to ensure that the container doesn’t burn or char due to a lower load. All such modifications are included in the scope of the invention as described in the following claims.
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