Microwaveable package having a susceptor ink layer.

Microwaveable packaging composition

<u style="single">Detailed description of the invention</u>

On the one hand, the present invention is directed to a microwaveable package containing a dielectric substrate that is almost transparent to microwave radiation, and at least a portion of at least one surface of the substrate is coated with a dielectric substrate-containing A coating composition in which (A) a sufficient amount of microwave receptor material particles are dispersed in the substrate so that heat is generated when the coating composition is exposed to microwave radiation; and (B) a sufficient amount of shielding The agent particles are selected from calcium salt, zinc salt, zinc oxide, lithopone, silica and titanium dioxide, so that when the coating composition is subjected to a pre-selected microwave dose, the heat generated by the receptor material is controlled Within the pre-selected range.

On the other hand, the present invention is directed to a microwaveable packaging ink composition containing a liquid carrier, which has (A) a dielectric polymer material that is almost transparent to microwave radiation; (B) a microwave acceptor material And (C) at least one kind of screening agent particles, selected from calcium salt, zinc salt, zinc oxide, lithopone, silica and titanium dioxide; the microwave acceptor material and screening agent are present in such an amount that they are suitable for use When the coating formed by applying this ink receives a pre-selected dose of microwave radiation, the heat generated by the receptor material is controlled within a predetermined range.

On the other hand, the present invention is directed to a method of manufacturing such a microwaveable packaging composition.

The recent growth of microwave ovens for preparing and cooking food has created a need to make improved packaging to make certain types of food easier to cook with microwaves. Therefore, for example, certain foods, such as popcorn, cannot absorb enough microwave energy to generate enough heat to pop or cook. Other foods need to be scorched or crispy on their skins, which generally cannot be achieved with traditional food packaging compositions in microwave ovens.

In order to meet the needs of improved microwaveable packaging, many different approaches have been proposed.

A general way is to form a multi-layer wrapped composition composed of an energy absorbing receptor material and a plastic film or other dielectric substrate. This is, for example, US Patent No. 4,267,420 (Blasta) discloses a packaging material that is a plastic film or other dielectric substrate with a thin semiconducting coating, preferably evaporated aluminum. Somewhat similarly, U.S. Patent No. 4,434,197 (Patreiro et al.) shows a multi-layer laminated microwaveable packaging material, which contains an outer layer of PTFE, two intermediary colored PTFE layers and A central layer in which particles of energy absorbing acceptor material such as graphite, iron oxide or carbon are dispersed.

The second method that has been proposed involves the dispersion of the particles of the microwave absorbing composition in the polymerizable or ceramic-shaped material substrate. This is, for example, U.S. Patent No. 4,190,757 (Special Equality) discloses a microwaveable packaging material composed of a non-dissipative dielectric sheet material constituting the container body and a dissipative microwave absorbing heating body connected to it. This heating body generally contains microwave absorbing acceptor materials (including zinc oxide, gallium oxide, iron oxide, and metal alloy oxides such as manganese, aluminum and copper) in a ceramic adhesive (such as cement, plaster of Paris or sodium silicate) , Carbon and graphite) particles. Somewhat similarly, U.S. Patent No. 4,518,651 (Wulff) shows a microwaveable composite material containing a polymeric substrate in which electronically conductive particles are dispersed, and the substrate is bonded to a porous substrate. This patent tells us that it is very disadvantageous that at least a part of the polymer substrate under the surface of the base layer contains almost no electron conductive particles and is mixed with the base layer.

European Patent Publication No. 242,952 discloses a microwaveable packaging material that is a composite material. The composite material contains a dielectric material coated with a mixture of sheet-like conductive metals or metal alloys in a dielectric substrate. Material (for example, polyethylene terephthalate film). This patent shows that to obtain the best heating performance reproducibility, round sheets with flat surfaces and smooth edges should be used. Somewhat similarly, U.S. Patent No. 4,866,232 (Stone) discloses a food package for microwave ovens. This package is coated with a metalized ink containing metal particles suspended in an ink-like substance. Microwave can be made on a container formed by heat-resistant materials.

Although many of the above and similar microwaveable packaging compositions can be used to convert microwave energy into heat, there is still a need for improved packaging materials. This is because many of the suggested microwaveable packaging materials may not be able to control the heat in the microwave oven, resulting in carbonization of the packaging materials or even arcing, ignition and burning. Others cannot generate enough heat quickly, and many materials, although they function well, cannot be widely used because they are expensive.

Therefore, an object of the present invention is to provide a microwaveable package with higher control over the heat generated by exposure to microwaves.

Another object of the present invention is to provide a microwaveable packaging ink composition which, when plated on a dielectric substrate, will provide an improved control over the heat generated by exposure to microwave radiation.

Another object of the present invention is to provide a microwaveable packaging ink composition that can be used economically.

An additional object of the present invention is to provide a method of economically manufacturing a microwaveable package that provides enhanced control over the heat generated by exposure to microwave radiation.

These objectives, as well as other additional objectives, will become more fully understood from the following description and attached examples.

On the one hand, the present invention is directed to a microwaveable package, comprising: (A) a dielectric substrate that is almost transparent to microwave radiation; and (B) at least a portion of the substrate on at least one side of the substrate Coating, the coating contains a substrate composed of a dielectric polymer material dispersed in this polymer material; (i) a sufficient amount of microwave receptor material particles, so that when the coating composition is exposed to microwave When the coating composition is subjected to the predetermined In the case of microwave dose, the heat generated by the receptor material is controlled within a pre-selected range.

On the other hand, the present invention is directed to a microwaveable packaging ink composition containing a liquid carrier, which has: (A) a dielectric polymer material that is almost transparent to microwave radiation; (B) a microwave acceptor material Particles; and (C) a screening agent particle selected from calcium salt, zinc salt, zinc oxide, lithopone, silica and titanium dioxide; the microwave acceptor material and screening agent are present in such an amount that they are suitable for application When the coating formed by the ink receives a predetermined dose of microwave radiation, the heat generated by the receptor material is controlled within a predetermined range.

On the other hand, the present invention is directed to a method of manufacturing such a microwaveable packaging composition, the steps of which include: (A) manufacturing a coating composition, including: (i) a dielectric polymer material; ( ii) Microwave receptor material particles; and (iii) Screening agent particles, selected from calcium salt, zinc salt, zinc oxide, lithopone, silica and titanium dioxide; the amount of such microwave receptor material and screening agent is So that when the coating formed by applying this ink receives a predetermined dose of microwave radiation, the heat generated by the receptor material is controlled within a predetermined range; and (B) coating the composition on the microwave On at least a portion of at least one side of a dielectric substrate that is nearly transparent to radiation.

The microwaveable package of the present invention is composed of a dielectric substrate that is almost transparent to microwave radiation. At least a portion of at least one surface of the substrate is coated with a coating composition containing a dielectric polymer substrate. Incorporating (A) particles of microwave receptor material; and (B) particles of shielding agent.

Generally speaking, the dielectric substrate can be any kind with sufficient thermal and dimensional stability and can be used as a microwave oven, when you want to scorch or quickly heat food at high temperatures (for example, up to 150°C). And higher) packaging materials. Useful substrates include polymerizable films, for example, polyester films such as polyethylene terephthalate film and polymethylpentene film, and other thermally stable films such as polypropionate, polyamide, and polycarbonate , Polyetherimine, polyimine and other similar substances. Furthermore, as long as the required thermal and dimensional stability are met, porous structures such as paper or non-woven materials can also be used as substrates. For flexible packaging materials, the substrate is preferably about 8 to 50 microns thick. It is also possible to use thicker non-woven materials such as plates, lids, bowls and other similar materials.

As shown earlier, the substrate must have sufficient dimensional stability at the high temperature of microwave cooking to avoid uneven cooking of the substrate that may be caused by the loss of close contact between the packaging material and the cooked food. distortion. It is possible to use substrates that generally lack such high-temperature dimensional stability, if they are drawn into a film with another substrate layer that meets the thermal stability requirements of the original substrate. This layering can be achieved by using the adhesiveness of the thermoplastic substrate layer coated on the original base layer or by using any number of traditional adhesives to help form a stable layer. For example, a polyester copolymer coated with a polyethylene terephthalate film can be thermally bonded to another polyester film or paper or a heavier paper plate that can be used in a furnace. Another method is to apply another instilling agent from the solution before layering to increase the strength of the layered material. These auxiliary adhesives can be selected from many commercial items that have the required thermal stability. These include copolyesters, copolyester-polyurethanes and cyanoacrylates.

The dielectric polymer material forming the substrate of the coating composition formed in the present invention can be composed of many materials, which, when plated on a suitable substrate, exhibits sufficient thermal stability to allow the use of The high temperature caused by microwave cooking of food still maintains the dimensional integrity of the final packaging material.

The dielectric properties of the substrate formed by plating polymeric materials on packaging substrates at 915 MHz and 2450 MHz are an important variable. The reason is the heat generated per unit time at 2450 MHz. . Specifically, the dielectric material generally has a relative permittivity between 2.0 and about 10, preferably between about 2.1 and about 5, and generally should have a relative permittivity between about 0.001 and about 2.5. The relative dielectric loss index of is preferably about 0.01 to 0.6. The substrate preferably also exhibits the adhesive properties of the base layer and any additional base layer that can be stretched to increase dimensional stability of the composite.

Examples of suitable substrate materials are polyacrylates, polyesters, polyester copolymers, heat-formable resins such as copolyester-polyurethane and epoxy resins, polycarbonates, polyethers, poly Arylene, polyamide monoimide, polyimide, polyether ether ketone, poly-4-4'-isopropyldiene diphenylene carbonate, imidazole,<img file="TW216413B_D0001.tif" />Azole, and thiazole. These substances can be crystalline or non-crystalline. Preferred substrate materials include acrylic polymers and copolymers, such as polymethacrylate, polyacrylate, and styrene-acrylic acid copolymer. Particularly preferred polymeric materials are poly(methacrylate) and poly(ethylmethacrylate) with a molecular weight between about 1,500 and about 20,000.

The microwave acceptor material used in the practical operation of the present invention includes any material that can absorb the electric or magnetic radiation of the microwave field and convert the energy into heat. Suitable materials include metals such as powdered nickel, antimony, copper, molybdenum, brass, iron, chromium, tin, zinc, silver, gold, and aluminum. Other conductive materials such as semiconductor materials such as silicon carbide and magnetic materials such as metal oxides (if available in granular form) can also be used as acceptor materials. It is also possible to use abrasive metallized films. Particularly preferred acceptor materials include an alloy of copper, zinc and nickel, product number SF401 of Obron; and flake aluminum powder.

The acceptor material used in the actual operation of the present invention is in the form of particles. Such particles can be flakes or powder. The size of such particles will vary depending on many factors, including the particular receptor material selected, the heat to be generated, the way the coating composition is to be applied; and similar factors.

However, generally when the coating composition is to be applied in the form of an ink, due to the limitations of the printing process, the powder will have a diameter of no more than about 50 microns. In general, in this case, it is particularly preferred to use particles with a particle size between about 0.1 and about 25 microns. When the receptor material is applied in the form of a thin sheet, (for example, the form of thin aluminum), the thin sheet is generally used in the gravure ink technique for printing metal coatings.

The masking agent used in the practical operation of the present invention contains at least one compound including calcium salt, zinc salt, zinc oxide, lithopone, silica and titanium dioxide. Preferred masking agents include calcium carbonate, calcium sulfate, zinc oxide, silica and titanium dioxide, and calcium carbonate, with calcium carbonate being the most preferred.

The masking agent used in the actual operation of the present invention is generally used in the form of particles. The particle size of this masking agent is generally limited by the particular coating method used. The particle size is generally less than about 50 microns. For most masking agents, the particle size is between about 0.1 and about 25 microns is preferred. When calcium carbonate is used as a masking agent, the particle size is preferably between about 1 and about 10 microns, and the particle size is preferably between about 3 and about 7 microns.

Although not expecting to conform to any particular theory, the applicant has discovered that the presence of such a masking agent controls the amount produced by the receptor material. By controlling the ratio and amount of the masking agent to the receptor, and/or by changing the thickness of the applied ink, the heat generated by the microwave radiation of a predetermined dose can be conveniently controlled within a predetermined range.

The variables that must be considered for determining the precise receptor-to-screening agent ratio required for any particular application include the physical size, shape, and surface characteristics of the receptor and screening agent particles contained in the coating composition, and the application on the substrate. The amount of coating composition, the size of the portion, and the food that will be cooked in this application. By changing the variables used and the ratio of receptor:screening agent in this way, it can be heated to a high temperature in a conventional microwave oven in a relatively short time and in a controlled manner, for example, to about 150. °C or higher temperature, preferably within 120 seconds to 190 °C or higher 7 when receiving the microwave energy generated by the dose generally made with this kind of furnace; for example, 550 at 2450 MHz watt.

The content of the receptor in the substrate generally accounts for about 3 to about 80% by weight of the receptor screening agent/substrate combination composition. As mentioned above, the optimal content of the receptor material and the masking agent incorporated in the coating composition of the present invention depends on a number of factors, and these factors depend on the end use used. However, it has been found that in many cases, the weight ratio of the masking agent: receptor material of 1:4 or higher will effectively block the heating of the coating composition. This is when the microwave radiation generated by the traditional microwave oven is received. When the dose. A lower ratio of masking agent to receptor material results in a higher temperature. One of the general techniques in this art can easily use common experimental methods to determine the best ratio for any particular application. It is measured for a specific coating composition of a certain thickness.

The polymeric material is present in a sufficient amount to form a substrate for the masking agent and receptor material.

In addition to masking agents, polymeric materials, liquid carrier and receptor materials, the microwaveable packaging coating composition of the present invention can also include other traditional additives, such as wax and silicone surface modifiers, and anti-corrosion additives. Homogeneous dispersants of foaming agents, surface active agents, color enhancers such as dyes and colorants, and similar substances. These additives are well-known to those skilled in the art.

The microwaveable packaging ink composition of the present invention is composed of a liquid carrier, in which (A) an interfacial polymer material forming a substrate that is almost transparent to microwaves is dispersed or dissolved; (B) particles of an acceptor material; and ( C) Particles of masking agent.

The liquid carrier that can be used includes a mixture of organic solvents and water and the foregoing substances commonly used in the manufacture of inks. Examples of these solvents are liquid acetates such as isopropyl acetate and analogs; alcohols such as isopropanol, butanol and analogs; ketones such as methyl ethyl ketone and analogs; and aromatic hydrocarbons such as toluene and analogs . Particularly preferred solvents include water, acetic acid, isopropyl ester, and a mixture of isopropyl acetate and toluene.

When the ink composition of the present invention contains an aqueous carrier agent, the composition generally further contains one or more surfactants and/or dispersants. Therefore, use ethoxylated nonylphenol such as Tergitol NP-40, purchased from Union Carbide Company; dispersant such as the dispersant (bisperbyk) 182 purchased from Byk Chemical Company; wetting agent and Ruxiang Air Products purchased Surfynol 104 A as an anti-foaming agent; a combination with a protective colloid such as Anti-Tylar 207 purchased from Byk Chemical Company has been able to obtain good results. In addition, the usual addition of defoaming agents such as the non-foaming agents available from Rack Chemical Co., Ltd. often gives good results. The amount of each of these chemical components can be easily determined by a person with ordinary skills in the art using common experimental methods.

The packaging composition of the present invention can be manufactured in a number of ways. In one of the methods, the dielectric substrate can be dissolved or dispersed in any number of general organic solvents, such as tetrahydrofuran, methylene dichloride, ethyl acetate, methyl ethyl ketone or similar solvents, and then the acceptor and masking agent Disperse in water or in this solution. This solution is then applied to the base layer by any number of coating methods, such as quantitative coating repairer rolling coating method, gravure coating method, reverse rolling coating method or slot mold coating method. After the coating is applied, the liquid is removed using traditional furnace drying techniques to form the final coating composition.

When using a molten stable substrate, the second technique that can be used is very useful. The substrate material is melted in a conventional device, and the acceptor particles are mixed with the melt. This mixture is then applied to the base layer by extrusion or melting and liquefaction.

The receptor/screening agent/substrate can be applied to the base ruler in a pattern such that there are various temperature properties in the single-layer composite material. These graphics may include coating compositions with varying receptor to masking agent ratios, or may include coating compositions of different thicknesses, or both.

The microwaveable compositions of the present invention can be manufactured economically, making them commercially acceptable for mass production. Furthermore, this composition will provide enhanced control over the temperature produced in this microwave oven.

<u style="single">Instance</u>

The following examples are intended to further illustrate the present invention, and do not intend to limit the scope of the present invention in any way.

<u style="single">Example 1 and 2 and comparative experiment A</u>

In order to show the degree of control provided by the addition of a masking agent, two ink compositions were prepared by combining the following ingredients in a mixer:<tables><img file="TW216413B_D0002.tif" /></tables>

These compositions used gravure printing using No. 6 Meyer rods to apply to the back of the cardboard. These samples were placed in a high setting Samruns 450 watt microwave oven with the coating side down. The samples prepared with the formula of Comparative Experiment A ignite within 5 seconds, while those samples prepared with the formulas of Examples 1 and 2 after 60 seconds of irradiation, their surface showed a dark color, showing that they had produced High heat without igniting a fire.

<u style="single">Example 3 and Comparative Experiment B</u>

Using a mixer, prepare two ink compositions containing the following weight percentages:<tables><img file="TW216413B_D0003.tif" /></tables>

A hard paper plate was coated with the composition of Example 3 on one part and the composition of Comparative Experiment A on the adjacent part, using several Meyer rods to form a pair of raised strips. This hard paper plate was cut into 3 inch squares, half of the square was coated with the masking agent containing the formula of Example 3, and the other half was coated with the formula of Comparative Experiment B. A thin slice of white bread is placed between two such samples, the printed side is far from the bread, and the coating is arranged in a line, so that each half of the slice of bread is sandwiched between the same recipe. This structure was covered with paper towels and placed in a Cober Test Oven (LBM1.2A type) for 45 seconds, at which time the turntable and the agitator were activated. It was found that under these conditions, the bread segment sandwiched between the coatings of Example 3 did not change color, while the bread segment sandwiched between the coatings of Comparative Experiment B became quite black.

<u style="single">Examples 4-7 and Comparative Experiment C</u>

In order to show the effectiveness of many other materials as masking agents, a blender was used to formulate many additional formulas as follows:<tables><img file="TW216413B_D0004.tif" /></tables>

Use No. 6 Meyer stick to print on the back of the hard paper sample. This sample was then cut into 3 inch squares.

In order to test the effectiveness of the masking agent in controlling the temperature generated, a square sample was placed in a Cooper test furnace with the printing side facing down and placed in a 250 with 50 grams of water and the original temperature at 68°F. Under the beaker of milliliters. The furnace is operated at 600 Wh for 30 seconds, the turntable and the agitator are activated, and the discharge port is opened. The heat generated is calculated by measuring the increase in water temperature. 50 grams of water alone was heated in this way as a control experiment. The average value of 5 experiments for each example is summarized as follows:<tables><img file="TW216413B_D0005.tif" /></tables>

The above results show that under these conditions, zinc salt, zinc oxide, lithopone, and silica all exhibit the ability to regulate the heat generated by the acceptor material.

<u style="single">Example 8</u>

Using a stirrer, stir the following ingredients to form a water-based liquid carrier:<tables><img file="TW216413B_D0006.tif" /></tables><tables><img file="TW216413B_D0007.tif" /></tables>

The weight percentage of the above-mentioned carrier is mixed with 2% calcium carbonate (horse) and 20% Oberon-Atlantic Aluminum Super Bright 103 non-flake powder. The produced water-based ink is printed on the hard low plate. A thin white bread sample is placed between the two samples, with the printed side outside, and placed in the Cooper test furnace. The furnace is operated at 70% power for 45 seconds. At this time, the discharge port is opened, and the stirrer and the turntable are started. This treatment causes the slices of bread to be toasted under control.