JPH02184430A - Heat sensitive material - Google Patents

Abstract

PURPOSE: To provide a product capable of converting a part of microwave energy to heat energy by constituting a microwave susceptor of a thin metal layer supported by a paper-based material. CONSTITUTION: A metal layer 14 is constituted of a conductive metal material capable of being formed into a thin film having thickness effective to convert microwave energy to heat energy. Stainless steel is especially suitable but another metal like aluminum or copper can be also used. The thickness of the metal layer 14 ranges from about 10 Å to about 150 Å generally. The metal layer is directly adapted to a base material 12 without any intermediate layer. The thickness of the base material 12 can range from about 12 1b. /ream to the thickness of the cardboard of about 20 points, preferably from about 10 mil to about 40 mil. It is preferable to use the base material having a smooth surface.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION This invention relates to a novel thermally sensitive structure for use in converting the harmonic energy A. of Merta into thermal energy.

Prior Art Thin films of conductive metals are capable of converting incident microwave energy into thermal energy to achieve external heating of foods during microwave rehydration or heating of foods such as bob corn, pizza, and french fries. It is known that this kind of effect is used in

For this purpose, the metal is commonly supported on a polymeric substrate, such as polyester, commercially available under the trade name Mylar. The thickness of the metal film required to achieve thermal energy generation will vary based on the conductive material selected. Metals commonly used for this purpose, such as aluminum, have a thickness of about 0.01 to about 0.08 optical density;
In particular, it can vary from about 0.2 to about 0.3 optical density. Other metals that can be used include copper or stainless steel.

To protect the polymerized substrate from distortion during the application of microwave radiation to metal films, the heavy substrate is coated with relatively strong paper or pole paper or two such layers using a conventional laminating adhesive. Usually laminated into a single seam sandwiched between seams I and I. ]-) is shown in U.S. Pat. No. 4.64.1.005.

A conflict of interest has been demonstrated by a competent authority that the heat generated by the application of microwave energy to metal films can result in deterioration of polymeric substrates or laminating adhesives due to gaseous by-products that are harmful to the food environment. There is.

A search was conducted at the facilities of the United States Patent Office regarding the prior art related to this invention. As a result of this search, the following US patents are noted as highly pertinent prior art.

1st 4th. ．． 210. '1.24 Hughes Rain etc., No. 4
, No. 248.687 Fan, No. 4,267.420 Blastat, No. 4,351.
No. 997 Mattison et al., No. 4.363, 851 Misina et al., No. 4. ．． No. 364.995 Crowport et al., No. 11.5
14. ．． 446';'3 Power 1 Heno etc., No. 4.528.2
No. 34 Kaiho et al., No. 4,592, 91.4-Henbecker No. 11. ．．
No. 599,275 Hayaji et al., No. 4.64. ],,005
Zuichi Seifers, 4th. ．． No. 702,963 Phillips et al., No. 4, 703, No. 14.8 Mikulski et al., No. 4.735, 51.3 Wa1-Kins et al., No. 4,7
77.05: No. 3 Toberman et al., No. 4,785. ], 6
No. 60 bar 1~.

Related to this prior art, U.S. Pat. No. 4,210.1.
No. 24, published in 1999, describes a dish structure with a microwave reflective metal foil coating and a microwave structured metal-interactive metal oxide film. The base material is made of porcelain, fired silica, or similar materials.

U.S. Pat. No. 4.248.687, No. 4. ．． 26742
No. 0, No. 4. ．． No. 363,851, No. 4. , 5 ],
, No. 4446, No. 4,528.234, No. 4. ．． 5
99°275, No. 4.64. ],,0005 No. 11
．． No. 702963, No. 4,735,513, No. 4.7
No. 85160 describes any construction that requires the combination of a microwave active metal layer, typically aluminum, supported on a polymeric film substrate.

US Patent Tube 4. ．． 351. ．． No. 997, Mei S, describes a 1-ray structure in which the metal layer is described as a foil and a reflector of microwave material.

U.S. Pat. No. 4,364,995 describes a general method of forming metal and metal oxide coatings on substrates.

US Patent Tube 4. ．． No. 592,91.4 describes the construction of a container with a microwave absorbing layer that is a metallized PlusDeck film and a microwave reflective layer that is described as a foil coated on paper.

U.S. Pat. No. 4.703.148 and No. 4.
No. 777.053 describes a package for microwave heating with a microwave reflective foil layer and a microwave-sensitive metal film on a polymeric film.

Problem to be Solved by the Invention The present invention provides that it is possible to provide a microwave sensitive body provided with a thin metal layer directly supported by a paper substrate. None of this prior art describes or suggests.

In accordance with the present invention, a novel heat sensitive material having a thickness of a conductive material such as a metal such as aluminium, copper or stainless steel or directly supported on a paper, pole paper or other similar fibrous material substrate is provided. A structure is set up. It was not previously known that thermal susceptors could be provided by applying a metal film directly to a paper substrate, and contrary to common understanding of the art. The term "thermal susceptor thickness," as used herein, is the thickness at which the material becomes conductive or semi-conductive due to electrical resistance or dissipation of heat when exposed to microwave energy. It means that.

Accordingly, in one feature of the present invention, a base layer made of constituent fibrous materials is supported in direct engagement with one side of the base layer and has a thickness effective to convert microwave energy into thermal energy. A product is provided which consists of a layer of electrically conductive material and is capable of converting a portion of the applied microwave energy into thermal energy.

Placing the conductive material in direct contact with the fibrous material substrate, typically paper, eliminates the prior art need for laminating adhesives and polymeric film layers, thus reducing the potential for formation of gaseous by-products of such materials. Sexually excluded.

It was previously believed that it was possible to provide a thin film metal susceptor for the conversion of microwave energy to thermal energy other than by supporting a polymeric substrate laminated to a piece of paper, or by the features involved in this technique. do not have.

For example, in discussing the invention leading to the above-mentioned U.S. Patent Section 4.64].

``Vacuum deposition of aluminum onto cardboard substrates has not produced active layers with sufficient microwave heating properties.''
' and '91 (any attempt made to achieve a sufficiently thin aluminum layer capable of microwave heating by direct vacuum deposition on the raw material is not possible).

The reasons given for this description regarding the vacuum deposition of aluminum, among others, are that (a) the expected effect requires that the surface on which the aluminum is deposited be very smooth (no wobbling), and (b) Either it is not possible to form a continuous layer of aluminum on the surface of the paper, or it is possible to coat the surface of each individual fiber with a highly irregular layer of aluminum; (c) the moisture generally present in the paper; The problem is that scum is released into the vacuum, thereby interfering with the expected amount of material being vacuum deposited.

These considerations are made for the vacuum deposition of aluminum, but nothing is said about other metals or other deposition techniques.

It is therefore a great surprise that the applicant is able to produce a microwave susceptor supported directly by a thin metal layer or paper substrate.

SUMMARY OF THE INVENTION As noted above, in a broad aspect of the invention, the invention provides an article of manufacture comprising two components: a substrate and a layer of conductive material supported on the substrate. It is something to do. The construction is very simple and allows a wide range of packaging structures for food heating to achieve various effects, for example during microwave heating or reconstitution of fried and browned foods. The second coating of the conductive material thickness of the heat sensor is such that it achieves an enhanced heating effect from the two layers. It can be applied to a substrate opposite from the first layer of material.

The conductive material layer is usually a metal layer, or can be a metal oxide such as carbon. The metal layer can be comprised of a conductive metal material that can be formed into a thin film of effective thickness to convert microwave energy into thermal energy. Stainless steel is preferred for reasons discussed below, but other metals such as aluminum or copper can also be used. Other possibilities include buttons, gold, silver, or platinum.

Stainless steel, such as 316 stainless steel, is a useful metal for the structures of this invention for a variety of reasons.

Stainless steel is inert to oxidation under normal room temperature conditions and therefore maintains a stable Sea I resistance over the storage and packaging life of the package. Many metals, particularly aluminum 18, oxidize over time and the resulting metal oxide becomes less effective as a thermal sensor without being heated by the applied microwave energy.

As is well known, stainless steel essentially consists of iron,
It is an alloy containing chromium and carbon. Resistance to oxidation is
Based on the constituent chromium that migrates through the surface, it is oxidized to act as a barrier to the oxidation of subsurface iron.

The stainless steel layer of the structure of this invention is heated by the application of microwave energy. Because stainless steel is a resistant metal, there is a limit to the range of temperature rise in stainless steel, which is indicated by the temperature at which natural oxidation occurs, which is around 425°F, the ideal temperature of the paper packaging environment of the susceptor used. There is.

However, although the upper limit of self-oxidation for aluminum is around 675°F, this temperature varies widely due to the existing oxidation state of the aluminum, so the continuous action of microwave energy on the aluminum layer is Burning or burning of the paper base material is to be avoided, causing a continuous rise in temperature which may be disadvantageous for some time.

In order to be effective as a microwave sensitive material for browning or crispy frying, the metal layer should be approximately 300%
the required heating time during which the microwave energy is applied to the food, rapidly heating it to a temperature of from °F to about 400 °F;
This temperature should normally be maintained for about 5-10 minutes.

Based on the resistance of stainless steel, temperatures in the range of about 200 to about 420 degrees Fahrenheit can be achieved with the structure of the present invention and maintained for as long as possible, from about 30 minutes on application. .

All the microwave energy incident on the microwave sensitive body is reflected by the surface, absorbed by the metal layer, or transmitted through the sensitive body structure. Only the energy absorbed by the metal layer can be converted into thermal energy.

The absorbed microwave energy causes the electrons within the metal to oscillate at the frequency of the oscillating microwave electric field. In a typical microwave oven, the frequency is 2
, 45 kilohertz.

The semiconducting thickness of the metal resists the movement of electrons, and the resulting energy is dissipated as heat from the metal layer.

The heat output obtained from the metal varies from about 50 ohms to about 500 ohms.
0 oats, well, iE suitable for about 100 ohms to about 2
It is based on the resistance of the metal layer, which can vary within a range of up to 1,000 ohms. The resistance is sized by the thickness of the metal layer, which can vary in depth across the surface of the metal layer based on the properties of the base layer, as will be discussed in more detail below. The thickness of the metal layer generally varies from about 10 angstroms to about 150 ounces).

A number of individual effects are observed as the resistance of a metal layer decreases with increasing metal thickness, e.g. at a minimum sheet resistance (thicker layers) around 25% before rapidly dropping around 10%.
The absorption increases slowly from a value of 0 to a maximum value of about 50%, and the minimum sheet resistance increases slowly from about 5% to about 25% at the point of maximum absorption before rapidly increasing to about 90%.

Therefore, when the SEI resistance is decreased from the value of maximum absorption and heat generation corresponding to about 50% of the incident microwave energy, absorption decreases, reflection increases, and transmission decreases. Similarly, as sheet resistance increases from the value of maximum absorption, absorption decreases, reflection decreases, and transmission increases.

In order to generate maximum heat output from the metal layer, it is preferable to make the resistance of the metal layer to occur within about 5% of the peak absorption that falls in the metal layer. However, a resistance that results in absorption of at least about 45% of the microwave energy allows for a wide range of reflection and conduction balances in the remaining microwave energy. In this context, the reflected 4
The resistance range of the metal layer allows for a selection of reflection vs. transmission ranging from 5% and 10% transmitted to 10% reflected and 45% transmitted, which is substantially the same as the thermal output from the heat sensitive body. The present invention allows considerable flexibility in the application of the susceptor to a variety of packaging structures. The degree of transmission of microwave energy by the new structure can be achieved by providing a microwave transmitter on one side of the structure and a microwave receptor on the other side. ) can be determined by determining the portion of the incident microwave energy from the transmitter.

A metal layer of the required thickness can be applied to the substrate by conventional substrate coating techniques or practical techniques depending on the metal used. As previously noted, the preferred metal is stainless steel and it is preferred to use a sputter link method to coat the substrate with a layer of stainless steel. Sputter linking is a well-known coating method, for example, as described in the second lecture of Hsieh Matensi, "Electronic beam evaporation and DC magnetron sputter linking in roll coating" at the 30th technical conference of the Vacuum Coating Society on July 28, 1987. has been done.

The metal layer is applied directly to the substrate without the need for an interlayer, thereby eliminating the need for polymeric film layers and laminating adhesives as previously required.

Structures constructed in accordance with the present invention may be constructed using adhesives or polymers (
By not using polymers or other heat sensitive materials, concerns about thermal breakdown of such materials in the structures of the present invention are eliminated, thereby overcoming problems with previously available structures. At the same time, L(material-1
A greater heat output is achieved by the structure of the present invention than by providing the same thickness of metal.Furthermore, paper or hole paper is shown to be a better substrate than polyester film. .

A second thin metal layer can be provided on the side of the substrate opposite the first layer, if desired, as described above.

Due to the paper sheet substrate, the thermal output from two metal layers of a thermal susceptor thickness when compared to the heat output obtained from a single metal layer of thickness corresponding to the total thickness of the two metal layers is Temporarily) 2 can be used to achieve the heating effect.

The substrate provided on the second side of the metal layer can be made from any suitable fibrous material, such as wood fiber or glass fiber provided in the form of a sheet. The fiber stock, when used in packaging structures, serves to provide structural strength to the novel product as well as support in the metal layer. The fiber raw material is made to withstand the cooking temperatures generated by the metal layer.
(-) is a low-density material with relatively high thermal insulation ability and thermal stability.

For use in packaging structures, the base layer is most conveniently formed from paper stock, or alternatively whole paper or flat wood sheets can be used. It is a feature of the present invention that the base layer can support a metal layer of electrical resistance, such as that generated in the application of microwave radiation applied with thermal energy.

The substrate on which the structure is placed is a paper stock ranging in thickness from about 12 bonds/ream to about 20 points/ream, preferably about 1 to 1 pole paper.
The required thickness can vary from 0 mils to about 40 mils to match the end use.

The substrate sheets 1-- can generally be formed from cellulose material fibers, such as wood fibers or glass fibers. In the latter case, the substrate sheet resists combustion, which can occur in the case of substrates made from cellulose fiber materials, if overheating occurs.

It is preferred to use a substrate with a smooth surface, since this allows a uniform degree of heating to be obtained from all parts of the surface of the metal layer. Recommended examples of such smooth-surfaced papers are high-gloss gloss papers and greaseproof papers.

Generally, a macroscopically continuous metal film is required on a substrate that generates heat from incident microwave energy. Therefore, a rough surface is required to fill the ``trough'' before a continuous film is formed on the ``peak'' than in the case of a smooth surface, and to fill the trough in the latter case. Since it is narrower or absent, it is necessary to apply a heavy coating of metal to the substrate to ensure the presence of a continuous film.

''As a couple, the portion of the incident microwave energy absorbed and the degree of heating obtained are due in part to the electrical resistance of the coating, which is based on thickness. As mentioned above, when the electrical resistance of the metal layer decreases and the metal layer becomes thicker, the absorption rate decreases, so less heat is generated. To this end, providing a metal layer on a smooth substrate surface results in a more even heat release from the metal layer and a greater value of such heat release.

In the product of the invention, the metal layer extends the same length as the base layer as a result of the forming method. In applications involving horizontal corpses, heat radiation is generated when microwave energy is applied.
It is advantageous to provide a surface area that does not generate heat and to generate thermal energy from the remaining surface area. Such a configuration can be used, for example, to bond a product to another surface by means of an adhesive that is applied in areas that do not contain thermal energy without fear of thermal breakdown of the adhesive.

Various techniques are available to achieve such results.

One such method involves the use of a mask during the coating process to prevent deposition of the metal layer on portions of the substrate that are desired to be free of metal. However, masking is impractical for continuous manufacturing methods.

It has been found that mechanical wiping of the metal layer or scratching of the metal layer is sufficient to prevent heat generation from this part of the surface being mechanically treated.

Another method that may be used is to print the substrate in parts of the mold where heating is not required with a suitable emissive material, such as a silicone emissive material, to which no metal is bonded prior to metallizing the substrate surface. Following metallization of the processed sheet,
Appropriate techniques such as brushing to remove metal,
Metal can be removed from the molded part by removing metal using an electromagnet or the like.

The structure of the present invention can be used for a variety of purposes requiring converting a portion of incident microwave energy into thermal energy.

The main uses of the new structure include microwave heating and reconstitution of a wide range of food products. By varying the parameters of the metal layer, in particular electrical resistance, improved properties of energy absorption, reflection and transmission of incident microwave energy, and different suitable values of heat generation can be achieved. The particular selection of such characteristics is based on the application to which the structure of the present invention will be placed.

The new structure can be fabricated by placing the structure in the desired location of the packaging material, typically paper sheet I, where heating is required, generally by using conventional fastening means. Used on the body. Generally, a suitable adhesive is used, but mechanical bonding of the parts together can also be used.

In order to minimize the possibility of thermal breakdown of such adhesives when microwave energy is applied, with the potential for formation of undesirable decomposition products, ensure 1.1 bonding. If the smallest such adhesive is applied to the surrounding area of the body, 9.
Commonly used. To further minimize the possibility of such decomposition, the periphery of the structure can be made free of metal by using one of the demetallization techniques mentioned above.
As a result, the lateral corpse is glued to the packaging material with such peripheral portions raised. In such a configuration, there is no metal in the area where the adhesive is located, so there is no risk of thermal destruction of the adhesive.

The novel structure is not bonded to the packaging material, such as the paper sheet I, in the metal layer or the part that is heated when microwave energy is applied to the packaging structure, so that the adjacent surfaces of the novel structure and the paper sheet are The air trapped between the pouch and the pouch is expanded by the metal layer as heat is generated, providing some thermal insulation against heat passing from the heat sensitive body out of the bag. In this manner, most of the heat generated by the metal layer when exposed to microphone single wave energy is used to heat the food product.

The invention will be explained in more detail below by means of illustrative embodiments with reference to the accompanying drawings, in which: FIG.

Embodiment Referring to the drawings, FIG. 1 shows a diagram according to an embodiment of the present invention.
) and comprising a base layer 12 of paper supporting a metal layer 4 ] 0 is shown in a perspective view. The metal layer ] 4 extends co-extensive with the base layer 12 .

FIG. 2.3 shows an example in which the present invention is applied to a microwave bob corn heating bag 20.
It is formed from polymerized paper sheets 22, 23 joined by ridges 26 to allow expansion of the inner bob cone.

According to the present invention, the three bodies are glued to the bottom paper sheets 1 to 2/I inside the bag by means of an adhesive 32 suitably provided at the peripheral part of the structure 3o. As shown, the metal layer 34 is on both sides or on the paper layer 3G.
and is in contact with the bob cone 38 on the outside.

The paper layer 3G is provided with a layer of a high temperature emissive material of some kind, such as silicone, between the bob cone 38 and the paper layer 36. However, the positions of the third layer 34 and the paper layer 36 can be reversed. When such a configuration is used, a polymeric layer of emissive material can be provided over the metal layer 34. j′,
Alternatively, the structure 30 can be glued to the outside of the bob cone 38 to the end 20 of the bob cone 38.

In this example, the structure 3 on which the adhesive 32 is installed
The surrounding area 40 of 0 is either a metal part or not, or there is a metal part that is made inert by mechanically rubbing it, for example with an extinguisher, so that it absorbs the thermal energy of the microwave energy. Since no heating occurs in this area as a result of the conversion, no thermal breakdown of the adhesive occurs.

When the bag 20 is exposed to microwave energy radiation, the bob cone 38 along with the used oil is exposed to the microwave energy and heated by the thermal energy produced by the metal N34, as shown in FIG. The bob corn is then heated to fill the interior cavity 28 of the bag 20.

When the bobcorn heating is complete, the bag 20 can be opened and the bobcorn can be eaten.

Another use of the principles of this invention is in a deep frying pan 50, as shown in FIG. 4.5.

The deep tray 50 consists of a plurality of layers that are laminated together into the final structure. The inner layer 52 adjacent the deep pie crust is comprised of a polymeric film with a thin metal layer 54 of the same size as the polymeric film layer and of a thickness effective to convert incident microwave energy into thermal energy adhered to the polymeric film. has been done.

Following the metal layer 54 is a heat sensitive body according to the invention which supports another thin metal layer 58 of a thickness sufficient to convert the incident microwave energy into thermal energy. It consists of a base layer 56 of paper. Base layer 56
and a thin metal layer 58 extend into the raw material portion of the deep-by plate 50. An outer layer 60 of pole paper completes the laminated structure.

] U.S. 1J + Patent No. 37 filed on June 30, 989
No. 4,655, referenced herein, states that the configuration of two metal layers in the base portion of the dish is more effective than would be obtained with a wall portion with a single fabric layer. Large heat generation can be obtained.

The structure consists of a thin metal layer that generates heat when a 17-wave microphone is placed in a dish. The greatest amount of heat is generated at the bottom of the pan, and the least amount of heat is generated at the side walls. The combination of 17-wave radiation from the microphone and the heat generated from the metal film ensures even cooking of deep pies or even filling of the stuffed pies, resulting in even baking of the pie crust. You can choose to have the same effect as you want.

The invention is illustrated by the following examples.

30 lb paper sheet (Kolgar 1~) and 30 Bong 1~
An oil-resistant sheet (Ramopac) was coated with stainless steel in a spun-vacuum chamber to a metal thickness with an electrical resistance ranging from about 500 ohms to about 5000 ohms.

Each heat generated by the high temperature heat generated in the thick coating when exposed to microwave energy1. Details of heat generation and time for various samples are shown in the graph in Figure 6. It is indicated by.

In summary of this description, the present invention is useful for a variety of applications requiring the conversion of microwave energy to thermal energy, and that directly relates to paper or pole paper that does not generate decomposed vapors during the application of microwave energy. To provide a novel thermally sensitive structure of an acoustically supported thin metal layer or other conductive thermally sensitive material. Improved heat generation is obtained when compared to conventional polyester substrates, while providing an inexpensive construction and a reduced radiation construction. Various modifications are possible within the scope of this invention.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a product manufactured according to an embodiment of the present invention; FIG. 2 is a perspective view of a microwave bob cone heating bag used in the novel structure constructed according to the present invention;
3 is a partially cutaway view of the bob corn heating bag of FIG. 2 after roasting the bob corn; FIG. 4 is a perspective view of a deep pie pan using the novel structure constructed in accordance with the present invention; and FIG.
Figure 4 shows the disassembly of the deep pie plate in Figure 4, which shows the laminated constituent layers. In the figure, 10: Product, 12: Lambda layer, 14.34
, metal layer, 20° bag, 22.24.36 Paper sheet 1~.
30 structure, 32 adhesive, 38 bob cone, 40
Peripheral portion, 50 Deep pizza plate, 52 Inner layer, 511. Metal layer, 56 Paper base layer, 58 Metal layer, 60: Outer layer.

Claims (10)

[Claims] (1) A base layer made of constituent fibrous materials, consisting of a layer of conductive material that is directly engaged with and supported on one side of the base layer and has a thickness effective to convert microwave energy into thermal energy. A product capable of converting a portion of the microwave energy that is applied to it, characterized by: (2) The product according to claim 1, wherein the base layer is a paper material. (3) A product according to claim 2, characterized in that the paper stock is made of cellulose fiber material or glass fiber material. (4) The product according to claim 2 or 3, wherein the base paper layer has a smooth surface. 5. The product of claim 4, wherein the smooth surface paper is a high gloss gloss paper. (6) characterized by a second layer of electrically conductive material having a thickness effective to convert microwave energy into thermal energy supported in direct engagement with one surface and an opposite surface of the fibrous material; A product according to any one of claims 1 to 5. 7. Article according to claim 1, characterized in that the layer of electrically conductive material is stainless steel applied to the base layer by a sputtering process. (8) The layer of conductive material has a surface temperature of 200° to 420° F, at which the absorbing portion of the incident microwave energy can be maintained for up to 30 minutes, preferably 300° to 4, at which the absorbing portion of the incident microwave energy can be maintained for up to 30 minutes.
It is characterized by being made of stainless steel with electrical resistance such that a surface temperature of 00°F can be quickly converted into heat energy to heat the food, thereby effectively browning and crisping the food. A product according to any one of claims 1 to 7. 9. The article of claim 8, wherein the stainless steel layer absorbs at least 45% of the incident microwave energy. 10. The article of claim 1, wherein the layer of electrically conductive material is a continuous film thickness of stainless steel giving an electrical resistance of 50 to 5000 ohms.