Adhesives and Their Use in Microwave Packaging

1. Adhesives and Their Use in Microwave Packaging Li Xiong School of Packaging Michigan State University

2. Overview of Presentation Adhesives What Is It? How does it work? What We Have? Microwave Packaging What is microwave? Conventional Heating vs. Microwave Heating Microwave and Packaging Microwave Packaging Materials

3. Overview of Presentation (cont.) Microwave Packaging (cont.) Microwave Packaging Forms Active and Passive Microwave Packaging Primary and Secondary Packaging Popcorn Bags Evolution Adhesives Used in Microwave Packaging Effect of Adhesives on the Food Taste/Flavor Future of Microwave Packaging

4. Adhesives--What is it? Adhesive is defined as �any material that is capable of bonding and holding two surfaces�. --The Adhesion Committee of IoPP

5. Adhesives--What is it? (cont.) Liquid, solid or pressure sensitive Forms a joint or bonds two substrate together Specific formula, specific manufacturing process for specific use A typical adhesive formulation may be influenced by numerous factors: Manufacturing process Material base (natural or synthetic) Binders (binder agents provide toughness and cohesive strength and regulate properties, i.e. , what it will adhere to and what environment the bond will resist during the life cycle of a package) Modifiers Carriers (water, solvents, heat, or two-part) Anti-foaming Anti-mold growth additives Tackifiers pH additives Viscosity Additives Extenders Fillers A typical adhesive formulation may be influenced by numerous factors: Manufacturing process Material base (natural or synthetic) Binders (binder agents provide toughness and cohesive strength and regulate properties, i.e. , what it will adhere to and what environment the bond will resist during the life cycle of a package) Modifiers Carriers (water, solvents, heat, or two-part) Anti-foaming Anti-mold growth additives Tackifiers pH additives Viscosity Additives Extenders Fillers

6. Adhesives -- How does it work? Adhesive and cohesive bond Adhesive bond is the bond between adhesive and the adherend. Cohesive bond is the force of intermolecular attraction within the adhesive or adherend. Factors influencing adhesive/cohesive bond strength Adhesive: surface tension, solubility, and viscosity Cohesive: molecular and physical structure of the material Adhesive bonds: Adhesive forces: Because the inter-molecular forces (van der waals forces) require a distance of only 3-5 A to have reasonable strength, the neighboring molecules at the interface must be very close together for adhesion to occur. This has important practical implications: for effective adhesion, the adhesive, at the time of application, must be able to completely �wet� the adherend surface, and must have low enough viscosity to be able to flow into and fill any irregularities in the substrate surface, in order to bring the adhesive and substrate close together on a molecular scale. To obtain maximum adhesion, the adhesive bond strength between the adhesive and adherend should be greater than the cohesive bond strength of the adhesive. Cohesive bond: cohesive bond strength depends on both the chemical nature and the physical state of a material. Temperature and the MW of the adhesive are two important factors. Increasing MW of an adhesive increases its cohesive strength, but also increases its viscosity and decreases wettability.Adhesive bonds: Adhesive forces: Because the inter-molecular forces (van der waals forces) require a distance of only 3-5 A to have reasonable strength, the neighboring molecules at the interface must be very close together for adhesion to occur. This has important practical implications: for effective adhesion, the adhesive, at the time of application, must be able to completely �wet� the adherend surface, and must have low enough viscosity to be able to flow into and fill any irregularities in the substrate surface, in order to bring the adhesive and substrate close together on a molecular scale. To obtain maximum adhesion, the adhesive bond strength between the adhesive and adherend should be greater than the cohesive bond strength of the adhesive. Cohesive bond: cohesive bond strength depends on both the chemical nature and the physical state of a material. Temperature and the MW of the adhesive are two important factors. Increasing MW of an adhesive increases its cohesive strength, but also increases its viscosity and decreases wettability.

7. Adhesives -- How does it work? (cont.) Three mechanisms mechanical: physical or interlocking interface between the materials specific: molecular forces create bonding of two nonporous materials pressure-sensitive: two-stage bonding process Mechanical adhesion: the adhesive creates a physical or interlocking interface between the substrate. The adhesive will physically �wet out� and penetrate the surface of the substrates and hold the parts together permanently or temporarily. With porous substrates such as cloth, corrugated, paper, paperboard, or wood, mechanical adhesion works well. Specific adhesion: is achieved when molecular forces create bonding of two nonporous materials. Due to the nature of nonporous materials, adhesive penetration into the surface is minimal. The bond is created when molecular forces hold substrates together, e.g., water used to hold two plastic films or glass plates. Pressure-sensitive bonding: is a very viscous liquid and as such retains tack permanently. It is applied to one substrate and either cools or loses carrier to reach its high-viscosity immobile state. When the second adherent is brought into contact, the adhesive is still capable of wetting the surface and forming a bond. However, this bond is of much lower cohesive strength than that of other types.Mechanical adhesion: the adhesive creates a physical or interlocking interface between the substrate. The adhesive will physically �wet out� and penetrate the surface of the substrates and hold the parts together permanently or temporarily. With porous substrates such as cloth, corrugated, paper, paperboard, or wood, mechanical adhesion works well. Specific adhesion: is achieved when molecular forces create bonding of two nonporous materials. Due to the nature of nonporous materials, adhesive penetration into the surface is minimal. The bond is created when molecular forces hold substrates together, e.g., water used to hold two plastic films or glass plates. Pressure-sensitive bonding: is a very viscous liquid and as such retains tack permanently. It is applied to one substrate and either cools or loses carrier to reach its high-viscosity immobile state. When the second adherent is brought into contact, the adhesive is still capable of wetting the surface and forming a bond. However, this bond is of much lower cohesive strength than that of other types.

8. Adhesives -- What we have? Adhesives could be classified in three ways: Natural or synthetic Mechanism of bond formation Method of bonding

9. Adhesives -- Natural or Synthetic Natural: animal glue, casein, starch, dextrin, and natural rubber Pros: natural, biodegradable Cons: prone to attack by microorganisms, shorter shelf life Synthetic Pros: good bonding strength, multiple choices available Cons: most are not biodegradable nor recyclable

10. Adhesives -- Mechanism of bond formation Loss of carrier (water or solvent) Loss of heat Chemical reaction Usually an adhesive is applied as a liquid to one or both substrates to achieve adhesion and then becomes solid and results in cohesive strength after the two substrates have been brought together. The process by which this solid states is created is a most important consideration. Loss of carrier: the bond is formed when the carrier is lost through absorption into the substrate or evaporation into the air. When two impermeable substrates are to be bonded, such as in the lamination of plastic films, solvent-based or hot-melt adhesives may be used. It is also possible to achieve good wetting and, thus, good adhesion to plastic films with non-solvent-based adhesives. Loss of heat: molten adhesives solidifies as it cools creating a bond at a very fast rate. Good adhesion is achieved on both porous and impermeable substrates. Chemical reaction: a liquid material is applied and is then reacted chemically to create a solid with a high bond strength. This type of bond may be used in high-performance flexible laminates.Usually an adhesive is applied as a liquid to one or both substrates to achieve adhesion and then becomes solid and results in cohesive strength after the two substrates have been brought together. The process by which this solid states is created is a most important consideration. Loss of carrier: the bond is formed when the carrier is lost through absorption into the substrate or evaporation into the air. When two impermeable substrates are to be bonded, such as in the lamination of plastic films, solvent-based or hot-melt adhesives may be used. It is also possible to achieve good wetting and, thus, good adhesion to plastic films with non-solvent-based adhesives. Loss of heat: molten adhesives solidifies as it cools creating a bond at a very fast rate. Good adhesion is achieved on both porous and impermeable substrates. Chemical reaction: a liquid material is applied and is then reacted chemically to create a solid with a high bond strength. This type of bond may be used in high-performance flexible laminates.

11. Adhesives -- Method of bonding Single stage Wet bonding: Hot melt Two stage Heat seal Pressure-sensitive One Stage Wet bonding: the adhesive is applied and the substrates brought together while the adhesive is still in the fluid state. Two Stages Heat seal: The adhesive is applied to one substrate and solidified either by cooling or by carrier loss or when adherents are brought together and heated to melt the adhesive and wet the second adherent. Bonding formation is then by cooling. Pressure-sensitive: The adhesive is applied to one substrate but remains tacky as it cools or loss carrier. As a result, it is capable of wetting the surface and bonding to the second adherent when the time comes.One Stage Wet bonding: the adhesive is applied and the substrates brought together while the adhesive is still in the fluid state. Two Stages Heat seal: The adhesive is applied to one substrate and solidified either by cooling or by carrier loss or when adherents are brought together and heated to melt the adhesive and wet the second adherent. Bonding formation is then by cooling. Pressure-sensitive: The adhesive is applied to one substrate but remains tacky as it cools or loss carrier. As a result, it is capable of wetting the surface and bonding to the second adherent when the time comes.

12. Microwave Packaging What is Microwave? Conventional vs. Microwave Heating Microwave and Packaging Active and Passive Microwave Packaging Primary and Secondary packaging

13. What is Microwave? Microwaves are �a form of electromagnetic energy and are generally thought of as occupying the frequency spectrum from 0.3 to 300 GHz, or wavelengths of 1 mm to 1m�. Stanley Sacharow, Microwave Packaging GHz: gigahertz The commercial microwave oven has a nominal frequency of 2.45?0.05GHz which correspond to a wavelength of 12.2cm. GHz: gigahertz The commercial microwave oven has a nominal frequency of 2.45?0.05GHz which correspond to a wavelength of 12.2cm.

14. Conventional vs. Microwave Heating Conventional heating heating from surface to interior time consuming (thermal lags) could reach browning and crispness tends to heat evenly Microwave heating heating inside and outside at the same time very fast browned and crisped foods not easily obtained tends to heat unevenly The fact that microwaves heat foods directly without the need for a transferring medium such as hot air, water or oil, means that the air surrounding the foods are not easily achieved. High heating speed of microwave heating bring about another problem: foods tend to heat unevenly, the center of baby food may be boiling while the surface is deceptively cool. Shape: rectangular shapes will exhibit highest temp. at the corners and edges and may be considerably cooler in the center. Discontinuities: multi-component meals Ambient conditions: because of the lower ambient air temp. during heating, the surface of the food is usually considerably cooler than the interior due to heat losses form the surface and evaporative cooling. Browning or crisping is thus difficult without an auxiliary heat source. Materials could be classified depending on their interaction with microwaves: Transmitters: waves pass through with little or no absorption, air, paper, plastics, glass; Reflection: waves are reflected at the surfaces of metallic materials such as aluminium, steel with very little energy loss; Absorption: absorb microwave energy and so become heated, water, moist foods, wood, oils. They are called �lossy� materials or �lossy dielectrics�.The fact that microwaves heat foods directly without the need for a transferring medium such as hot air, water or oil, means that the air surrounding the foods are not easily achieved. High heating speed of microwave heating bring about another problem: foods tend to heat unevenly, the center of baby food may be boiling while the surface is deceptively cool. Shape: rectangular shapes will exhibit highest temp. at the corners and edges and may be considerably cooler in the center. Discontinuities: multi-component meals Ambient conditions: because of the lower ambient air temp. during heating, the surface of the food is usually considerably cooler than the interior due to heat losses form the surface and evaporative cooling. Browning or crisping is thus difficult without an auxiliary heat source. Materials could be classified depending on their interaction with microwaves: Transmitters: waves pass through with little or no absorption, air, paper, plastics, glass; Reflection: waves are reflected at the surfaces of metallic materials such as aluminium, steel with very little energy loss; Absorption: absorb microwave energy and so become heated, water, moist foods, wood, oils. They are called �lossy� materials or �lossy dielectrics�.

15. Some Facts of Microwave By 1991, about 85% of US households own at least one microwave oven; 100 million microwave ovens out of 150 millions worldwide are owned by Americans; US microwave market valued approximately US$2,000 million in the early 1990s; In Europe, Germany takes the lead, followed by France and the UK; In Asia, the leading microwave oven owners are Japanese and Australian.

16. Microwave and Packaging �Packaging holds the key to the future use of microwave heating�. -- Anon, Microwave packaging �The increased usage of microwave ovens highlighted the importance of the relationship between a food �and the right packaging� -- Stanley Sacharow, Microwave packaging The packaging must be designed to provide a container which assists the food in heating properly, be attractive and perhaps act as a serving dish or even be eaten from directly. The packaging must be designed to provide a container which assists the food in heating properly, be attractive and perhaps act as a serving dish or even be eaten from directly.

17. Microwaveable Foods in US Popcorn is the No.1 in US, with sales of about US$600 million in 1989. Others sold in US include pizza, vegetable and desserts; Total sale of microweveable foods in US amount to US$3 billion in 1992 compared to US$1 billion in 1987;

18. Microwave Packaging Materials Paperboard Glass Plastics Metals Paperboard: it is increasingly being used in the refrigerated and frozen foods. It is transparent to microwaves, many forms available, mechanical strength and stiffness, lack of thermo-plasticity and relatively economy. However, steps must be taken to improve its resistance to moisture and grease, re-sealability and shapeability. A properly designed paperboard/plastic/foil multi-layer will resolve all these shortcomings. The material currently being used is solid white bleached sulphate food grade board, with an extrusion coating of PET, or be coated with TPX (polymethylpentene). Glass: with the exception of glass jars, there are no examples yet of glass and ceramics labeled for heating in the microwave oven among packaged foods for retail sale. One particular advantage is there is no migration problem associated with food products. Plastics: polyolefins, polyesters, styrenics, engineering plastics and barrier materials are widely used. Metal: Aluminium is used in microwave tray ware in both coated and plain fomrs. The coated forms is preferred because it has virtually eliminated the potential for arcing (where electric fields in the microwave oven reach a high enough potential to overcome the insulating properties of air, leading to discharge.Paperboard: it is increasingly being used in the refrigerated and frozen foods. It is transparent to microwaves, many forms available, mechanical strength and stiffness, lack of thermo-plasticity and relatively economy. However, steps must be taken to improve its resistance to moisture and grease, re-sealability and shapeability. A properly designed paperboard/plastic/foil multi-layer will resolve all these shortcomings. The material currently being used is solid white bleached sulphate food grade board, with an extrusion coating of PET, or be coated with TPX (polymethylpentene). Glass: with the exception of glass jars, there are no examples yet of glass and ceramics labeled for heating in the microwave oven among packaged foods for retail sale. One particular advantage is there is no migration problem associated with food products. Plastics: polyolefins, polyesters, styrenics, engineering plastics and barrier materials are widely used. Metal: Aluminium is used in microwave tray ware in both coated and plain fomrs. The coated forms is preferred because it has virtually eliminated the potential for arcing (where electric fields in the microwave oven reach a high enough potential to overcome the insulating properties of air, leading to discharge.

19. Microwave Packaging Forms According to a Freedonia study in 1991, microwavable paperboard containers will grow 8% per year to 5 billion units, remaining the dominant materials. PET coated paperboard trays are predicted to increase 6.5% per year to 1.4 billion units. Led by demand for multilayer plastic tubs and trays for shelf-stable products, plastic microwave packaging grew nearly 18% per year to2.9 billion units by 1994. Demand for microwave popcorn packaging is expected to grow 8.3% annually to 2 billion units in 1994.According to a Freedonia study in 1991, microwavable paperboard containers will grow 8% per year to 5 billion units, remaining the dominant materials. PET coated paperboard trays are predicted to increase 6.5% per year to 1.4 billion units. Led by demand for multilayer plastic tubs and trays for shelf-stable products, plastic microwave packaging grew nearly 18% per year to2.9 billion units by 1994. Demand for microwave popcorn packaging is expected to grow 8.3% annually to 2 billion units in 1994.

20. Active and Passive Packaging Active packaging -- that constructed of material (susceptor) which is capable of focusing incident energy and converting into heat in a predetermined region of food. Passive packaging -- that does not modify the microwave energy field. Four basic microwave oven problem: uneven cooking inability to crisp dough products inability to brown uneven heating for multi-component needs Microwaves are not suited for crisping and browning processes requiring local temperature of >150C, which is not achievable in microwave oven. Susceptors such as thin coatings of either aluminium or ferrous alloys on various plastic substrates, usually PET. Susceptors: Most of susceptors in current use are rigid, consisting of pieces of aluminized PET film bonded to a paperboard substrate. These are used in packages for such items as pizza, fish products and popcorn, where the essentially planar geometry of the food adapts well to a flat rigid susceptor. However, flexible susceptors that can be wrapped around irregularly shaped foods are being used more and more.Four basic microwave oven problem: uneven cooking inability to crisp dough products inability to brown uneven heating for multi-component needs Microwaves are not suited for crisping and browning processes requiring local temperature of >150C, which is not achievable in microwave oven. Susceptors such as thin coatings of either aluminium or ferrous alloys on various plastic substrates, usually PET. Susceptors: Most of susceptors in current use are rigid, consisting of pieces of aluminized PET film bonded to a paperboard substrate. These are used in packages for such items as pizza, fish products and popcorn, where the essentially planar geometry of the food adapts well to a flat rigid susceptor. However, flexible susceptors that can be wrapped around irregularly shaped foods are being used more and more.

21. Primary and Secondary Packaging Primary packaging -- packaging system in direct, or potentially direct, contact with food. Secondary packaging -- those make no direct contact with food, but may become a source of odors when heated in the microwave oven. Primary packaging: a tray containing an entr�e is a primary package component, so is its lidding. If the food is frozen or otherwise held away from a package surface which it could contact if thawed or allowed free movement, the package surface is a primary food contact surface. Secondary Packaging: the odors may arise from the packaging material, paperboard or plastic from the ink (usually polymer-based materials), or from the adhesives used in bonding cartons. Coextrustion adhesives or tie layers are a distinct category quite different from other more conventional adhesives. The former are used in the coextrusion process to �tie� various multi-layers together. The latter are used in converting paper bags and for susceptors adhesion to bags. Primary packaging: a tray containing an entr�e is a primary package component, so is its lidding. If the food is frozen or otherwise held away from a package surface which it could contact if thawed or allowed free movement, the package surface is a primary food contact surface. Secondary Packaging: the odors may arise from the packaging material, paperboard or plastic from the ink (usually polymer-based materials), or from the adhesives used in bonding cartons. Coextrustion adhesives or tie layers are a distinct category quite different from other more conventional adhesives. The former are used in the coextrusion process to �tie� various multi-layers together. The latter are used in converting paper bags and for susceptors adhesion to bags.

22. Popcorn Bag Evolution (US) Over the past decade, the use of metallized polyester film to brwon, crisp, or provide spot heating in a variety of foods has become widespread. The primary application has been to heat oil to popcorn in a microwave oven and increase the yield of kernels. Well over 50% of all susceptor material produced today is going into popcorn bags (over 1 billion units)Over the past decade, the use of metallized polyester film to brwon, crisp, or provide spot heating in a variety of foods has become widespread. The primary application has been to heat oil to popcorn in a microwave oven and increase the yield of kernels. Well over 50% of all susceptor material produced today is going into popcorn bags (over 1 billion units)

23. Adhesives in Microwave packaging Primary packaging sealing lidding stock paperboard/seal material/flange sealing pouches and bags bonding susceptors Secondary packaging folding cartons for containing primary food packages coextrusion (tie layer) and coinjection adhesives Sealing lidding stock: lidding stocks are generally films of mono-layer construction or sheets of multi-layer film or foil/polymer construction. Responsibility for adherence to tray, bowl or cup shapes is provided by the container and the lidding with a heat seal. A common technique is to incorporate a coating on the stock which is heat sealed to the food container. Paperboard/seal material/flange: in this construction, the coating is mechanically bonded with the paper through the intermingling of fibers with polymer and the large surface area presented at the interface. Sealing pouches and bags: Seals are usually provided by the pouch or bag material itself. Polyolefins and olefin polymer coated polyester films are examples. Copolymers of vinylidene chloride with vinyl chloride or acrylates such as methyl are laid down as coating from latexes to provide seal coats on films. Solvent solutions of copolymers of vinylidene chloride with acrylonitrile or the acrylates are also used to provide heat sealable coatings on polyester,polyamide and polypropylene films. Coatings act also as barriers in some cases and as cold seals in others. Bonding susceptors: it is the most complicated task for adhesives so far encountered in microwave packaging. Temperature of the susceptor is elevated rapidly to 200-300C (390-570F) or more. There is concern that the integrity of the film supporting the susceptive coating may be damaged, opening a path for film or adhesive components or degraded products to migrate into the food. Sealing lidding stock: lidding stocks are generally films of mono-layer construction or sheets of multi-layer film or foil/polymer construction. Responsibility for adherence to tray, bowl or cup shapes is provided by the container and the lidding with a heat seal. A common technique is to incorporate a coating on the stock which is heat sealed to the food container. Paperboard/seal material/flange: in this construction, the coating is mechanically bonded with the paper through the intermingling of fibers with polymer and the large surface area presented at the interface. Sealing pouches and bags: Seals are usually provided by the pouch or bag material itself. Polyolefins and olefin polymer coated polyester films are examples. Copolymers of vinylidene chloride with vinyl chloride or acrylates such as methyl are laid down as coating from latexes to provide seal coats on films. Solvent solutions of copolymers of vinylidene chloride with acrylonitrile or the acrylates are also used to provide heat sealable coatings on polyester,polyamide and polypropylene films. Coatings act also as barriers in some cases and as cold seals in others. Bonding susceptors: it is the most complicated task for adhesives so far encountered in microwave packaging. Temperature of the susceptor is elevated rapidly to 200-300C (390-570F) or more. There is concern that the integrity of the film supporting the susceptive coating may be damaged, opening a path for film or adhesive components or degraded products to migrate into the food.

24. Adhesives and Microwave packaged Food Food safety must comply with government regulations. Food taste and flavor might be the results of degradation of adhesives being used to construct the package it�s still a blank area to be investigated When mcirowave packaging was first introduced, few researchers investigated the effect of microwave radiation on packaging adhesives. It was the introduction of susceptors capable fo bringing materials to high temp. that brought adhesive interactions into the realm of microwave packaging technology. While adhesive technology is now fairly well defined, less is known abut the effect of microwave radiation on coatings. In microwave oven heating, the type of adhesive used to laminate the film to the board, and whether or not a food load is present, is quite critical to the performance of susceptor. A functionally �good� adhesive will stabilize the film during heating such that a smooth, continuous surface is maintained up to the melting point of the film. Presence of food load could help to prevent the melting of film at high temperature. Clearly, the choice of adhesive can have a profound effect on susceptor performance in a functional sense. The strength and thermal properties of the adhesive-metal bond can affect the temperature rise and ultimate temperature that a susceptor reaches as well as the barrier properties of the polyester film. Through proper design of the adhesive, degree and placement of metallization, and other susceptor parameters, it is quite possible to avoid undesirable film rupturing and, instead, optimize food heating effects.When mcirowave packaging was first introduced, few researchers investigated the effect of microwave radiation on packaging adhesives. It was the introduction of susceptors capable fo bringing materials to high temp. that brought adhesive interactions into the realm of microwave packaging technology. While adhesive technology is now fairly well defined, less is known abut the effect of microwave radiation on coatings. In microwave oven heating, the type of adhesive used to laminate the film to the board, and whether or not a food load is present, is quite critical to the performance of susceptor. A functionally �good� adhesive will stabilize the film during heating such that a smooth, continuous surface is maintained up to the melting point of the film. Presence of food load could help to prevent the melting of film at high temperature. Clearly, the choice of adhesive can have a profound effect on susceptor performance in a functional sense. The strength and thermal properties of the adhesive-metal bond can affect the temperature rise and ultimate temperature that a susceptor reaches as well as the barrier properties of the polyester film. Through proper design of the adhesive, degree and placement of metallization, and other susceptor parameters, it is quite possible to avoid undesirable film rupturing and, instead, optimize food heating effects.

25. Potential Approaches Good choice of monomers, colloidal stabilizers, polymerization conditions and post-polymerization implies only to those whose principal component is one or more emulsion polymers; to eliminate low molecular weight materials; Choose right adhesive formula Control drying process in lamination So far, the most widely used adhesive formulation has been ethylene vinly acetate copolymer emulsion based formulations. Other choices include: Hot-melt adhesives: hot melt, typically applied at 175-200C (345-390F), are used primarily in carton and shipper sealing. Their low melting points limit their use in packaging for the microwave. Solvent-based adhesives: Solvent-based adhesives would be expected to continue their decline in use as water borne systems are developed for an increasing variety of uses.So far, the most widely used adhesive formulation has been ethylene vinly acetate copolymer emulsion based formulations. Other choices include: Hot-melt adhesives: hot melt, typically applied at 175-200C (345-390F), are used primarily in carton and shipper sealing. Their low melting points limit their use in packaging for the microwave. Solvent-based adhesives: Solvent-based adhesives would be expected to continue their decline in use as water borne systems are developed for an increasing variety of uses.

26. Future of Microwave Packaging Some trends include: increased shelf-stable and refrigerated markets; new susceptor technologies; increased environmental concerns health consciousness safety concern New susceptor technologies: focus on controlled shidlding and selective browning effects. The key objective is to limit susceptor temperatures to conform with FDA guidelines and to prevent runaway heating. Another objective is to provide multiple-use susceptor rather than single use. This will be accomplished by means of coating which limit the amount of microwave energy converted to heat. Final objective is to improve the uniformity of heat distribution in the susceptor structure so that consistent results are achieved front to back, side to side, and corner to corner.New susceptor technologies: focus on controlled shidlding and selective browning effects. The key objective is to limit susceptor temperatures to conform with FDA guidelines and to prevent runaway heating. Another objective is to provide multiple-use susceptor rather than single use. This will be accomplished by means of coating which limit the amount of microwave energy converted to heat. Final objective is to improve the uniformity of heat distribution in the susceptor structure so that consistent results are achieved front to back, side to side, and corner to corner.

27. Thanks and Any Questions?