WO2018166869A1

WO2018166869A1 - A heat transmission system

Info

Publication number: WO2018166869A1
Application number: PCT/EP2018/055625
Authority: WO
Inventors: Peter Knudsen
Original assignee: K&f Industrial Coating Ivs
Current assignee: K&f Industrial Coating Ivs
Priority date: 2017-03-17
Filing date: 2018-03-07
Publication date: 2018-09-20
Anticipated expiration: 2019-09-17

Abstract

The present invention relates in general to a coating composition, a method for coating a material and a coated material as such. In particular, the present invention relates to a coating composition, a method for coating a material and a coated material as such for improving the energy transmission from a material surface. The coating composition according to the invention improving energy transmission from a material surface subjected to heating by radiation in the infrared spectrum. The coating composition before being applied to the material surface i.e. when in a ready-to-use state, comprises, or is constituted of, a mineral dissolved or suspended in an organic solvent or carrier, and the solvent or carrier comprises a carbon group having 3-10 carbon atoms. The mineral may be a white to pale grey or colourless mineral e.g. selected from the group CaSO₄, MgCO₃, SiO₂, TiO₂ or a mixture hereof, preferably TiO₂.

Description

A HEAT TRANSMISSION SYSTEM

Technical field of the invention

The present invention relates in general to a coating composition, a method for coating a material and a coated material as such. In particular, the present invention relates to a coating composition, a method for coating a material and a coated material as such for improving the energy transmission from a material surface.

Background of the invention

Radiant heat is invisible electromagnetic infrared radiation (IR) that heats objects in direct pathway of the IR rays which objects absorbs the energy immediately. Once the objects heat up, they radiate heat to other objects.

Radiant heat constitutes a considerable part of heat transfer from one object to another. E.g. at an oven-wall temperature of 200°C, radiant heat constitutes more than 60% and hence makes a larger heat contribution than the convection heat. Thus, in order to improve heat transfer from one object to another, it is of interest to adapt a material surface for absorbing the emitted IR radiation, e.g. from an oven wall.

Packing of foodstuffs in alu-foil followed by a heating procedure in a conventional oven prolongs the preparation time due to the good reflective properties of the aluminum material to IR heat radiation. As alu-foil is the most commonly used material for ready to eat meals, it has been attempted to produce both a dull and a glossy side on e.g. the alu-foil with improved heat transmission properties. The total heat transmission when heating foodstuffs in heat-resistant packaging can be estimated by the sum of convection and infrared or heat radiation. The effect of heat transmission and heat radiation differs from material to material, and at a surrounding temperature of 200°C, e.g. provided in an oven, heat radiation on a black element will dominate the total heat transmission by about 66 %. This is not the case with the heat radiation on an alu-foil. Here heat radiation constitutes only about 7 % of the total heat transmission.

For several years, it has been known that graphite applied to an alu-foil is an extremely efficient absorber of IR radiation, and over the years several attempts have been made within this field serving the purpose of using that idea to advantage. Thus, the issue is to utilize the effect which is known from the black body that absorbs IR heat radiation 100 %. Thus, US 4,220,134 describes the use of "black Teflon on an aluminum surface for ensuring the absorption of IR heat radiation". Another Patent: US 2006/153952 Al (Aromabag and aromafoil made of aluminum) also uses a black surface to advantage for optimally transferring radiant heat to an aluminum surface. For foodstuff, using black surfaces on aluminum foil are not particularly attractive from an aesthetical point of view, which is most likely the reason why foils of this kind have not found use for domestic purposes.

WO 2009/000272 describes a foil providing an improved heat transmission based on electromagnetic radiation, which foil has at least two coating layers, said at least two coating layers of the foil comprise a radiation-absorbing layer, e.g. carbon black, and a heat transmission layer, e.g. T1O2, wherein the wavelength spectre of the electromagnetic radiation of the radiation-absorbing layer and/or the heat transmitting layer, and the wavelength spectra of the electromagnetic radiation of the oven cavity are attuned to each other. The coating layers comprises an organic binder such as acryl styrene polymer or nitrocellulose and are applied to the foil in a thin layer, below 14 μιη, by printing technology to obtain a desired thin coating layer.

However, even though the prior art technologies may technically improve heat transmission, the prior art technologies are financially not interesting and there are a still increasing interest to be able to heat things faster, to save time on cooking and to save energy, to save time and money, to improve stability of a coating, and to benefit the environment.

Hence, an improved coating composition and method for applying the coating composition to a material would be advantageous, also obtaining a more efficient, stable, reliable, durably coating layer and a method of application of a coating composition resulting in less cracks and more efficient transmission of energy would be advantageous for the further benefit of the environment and to save time.

Summary of the invention

Thus, an object of the present invention relates to a coating composition, and a method for applying the coating composition to a material and an obtained coated material, for improving the energy transmission from a material surface.

According to an embodiment, a coating composition according to the invention does not relate to coatings or coated objects suitable to be subjected to heating by microwaves, i.e. electromagnetic radiation having a wavelength≥1 mm (1000 μιη). The coatings and objects according to the present invention is directed to coatings and coated objects suitable to be heated by infrared radiation.

In particular, it is an object of the present invention to provide a coating composition, a method for applying the coating composition to a material and a material obtained by application of the coating that solves the above-mentioned problems of the prior art with efficiency, providing a stable, durably coating composition and a method resulting in less cracks and hence more efficient in transmitting energy advantageous for the costs using the material, the environment and to save more time.

Thus, one aspect of the invention relates to a coating composition for improving the energy transmission from a material surface, the composition comprising a mineral and an organic solvent, wherein the solvent comprises a carbon group having 3-10 carbon atoms. The coating composition may comprise one or more additives in small amounts. The additives may comprise one or more components such as an emulsifier and/or a thickener and/or a fungicide or the like, or a combination of such components. Each additive is normally added in an amount below 5 wt%, e.g. below 1 wt% or below 0.5wt% providing a desired consistence or color or other functionality of the coating. A desired consistence may be determined by the method of application and a desired functionality may be determined by the intended use of the material to be covered by the coating. E.g. if the coating is applied to a foil covering food or the like, the coating may be added a fungicide or a component reducing bacterial growth. According to an embodiment, a coating composition improving energy transmission from a material surface subjected to heating by radiation in the infrared spectrum does not normally comprise or include an organic binder such as e.g. acryl styrene polymer or nitrocellulose.

According to an embodiment, a coating composition improving energy transmission from a material surface subjected to heating by radiation in the infrared spectrum does not comprise carbon black, e.g. the coating of the outer surface i.e. a surface facing away from the material to which the coating is applied, does not comprise carbon black, graphite or similar dark or black pigments. According to an embodiment, a coating composition improving energy transmission from a material surface subjected to heating by radiation in the infrared spectrum does not comprise a carboxyl vinyl polymer.

According to an embodiment, a coating composition improving energy transmission from a material surface subjected to heating by radiation in the infrared spectrum does not comprise a susceptor material in particulate form i.e. as powders or flakes or the like; where a "susceptor material" is defined as a conductive material such as nickel, antimony, copper, molybdenum, bronze, iron chromium, tin, zinc, silver, gold, alloys of metal, graphite, or a semi-conductive material such as silicon carbides or metal oxides. Another aspect of the present invention relates to a method for providing a material having an improved energy transmission of the material surface, the method comprises the steps of

(i) providing a material;

(ii) providing a coating composition according to the present invention;

(iii) applying the coating composition of step (ii) to the material of step (i)

providing a coated material having a coating layer thickness of at least 15 μπι, in dried state; and

allowing the coated composition to dry and cure providing the material having an improved energy transmission of the material surface.

Yet another aspect of the present invention relates to a coated material obtainable by a method according to the present invention.

Still another aspect of the present invention relates to a material or component having an energy transmitting coating on at least one material surface, wherein the energy

transmitting coating comprises a mineral and a coating layer thickness of at least 15 μιη, when in dried state.

Definition of concepts of the application:

Foil - a metal or similar material hammered or rolled into a thin flexible sheet, often used for covering or wrapping food, a common example is aluminium foil or as a flexible tray.

Layer or coating - the words "layer" and "coating" may be used interchangeably and may both refer to a layer of coating or a coating layer.

Sheet or sheet-like - a portion of something e.g. a material that is thin in comparison to its length and breadth.

Infrared radiation - Radiation is called "infrared (IR)" when the radiation has a wavelength spectrum between 750 nm - 1 mm (0.750 μιη - 1000 μιη) whereas "microwave" radiation has a wavelength spectrum between 1000 μιη and 1 m.

Carbon group - that a solvent or carrier used to prepare a coating composition according to the invention comprises a carbon group having 3-10 carbon atoms means that the solvent is constituted of molecules comprising 3-10 carbon atoms.

Detailed description of the invention

Controlling and optimising the heat transmission from different materials has gained more and more interest over the years as there have been an increasing demand for heat transmission and at the same time an increasing requirement to reduce the costs and the effect on the environment. Hence, the inventor of the present invention surprisingly found a method for applying a coating composition to the surface of a material resulting in an improved energy transmission from a material surface as well as a new coating composition for obtaining the desired effects.

Hence, a preferred embodiment of the present invention relates to a coating composition for improving the energy transmission from a material surface, the composition comprising a mineral and an organic solvent, wherein the solvent comprises a carbon group having 3-10 carbon atoms.

The coating composition according to the present invention comprises a solvent having a carbon group having 3-10 carbon atoms. The inventors found that in order to achieve the desired effects of a coated material, the coating layer should preferably be thick, e.g. in the range of 15-1000 μιη, when dried and in a state of ready-to-use. The advantage of this thick layer of the coating is in addition to improved effect in energy transmission, speed of energy transmission, that the coated material may have no or less cracks than coated materials provided with thin coating layers as described in the prior art, where the coating composition is applied using printing technologies. In general, a coating composition according to the present invention is not normally applied using printing technologies.

Furthermore, to apply a thick layer of a coating composition on a material or component, the vaporization of the solvent may preferably not be too fast as seen with the vaporization of the solvents used in the prior art. Therefore, it is of interest of the present invention to slow down vaporization of the solvent. The actual duration of the drying time or vaporization may be determined by a skilled person and will depend on the thickness of the coating composition, the composition of the coating composition and possibly the particle size distribution of the composition, and the solvent used in the coating composition. The duration of the drying may be controlled by controlling the temperature and the ventilation.

In an embodiment of the present invention the mineral may be a white to pale grey or colourless mineral. Preferably, the mineral is a white to pale grey or colourless mineral, and selected from the group CaSC , MgCC , S1O2, T1O2 or a mixture hereof. Preferably, the white to pale grey or colourless mineral is T1O2.

A coating composition according to the invention may further comprise flakes or particles of a good reflective material such as aluminium or silver. Being a "good reflective material" means that the flakes or particles has a high reflectance of infrared radiation. The flakes or particles may have a maximum dimension of at least 50 nm, or at least 100 nm, or at least 200 nm, or at least 300 nm, or at least 400 nm, or at least 500 nm (0.500 μιη), or at least 0.7 μιη, or at least 1 μιη, or at least 1.5 μιη, or the maximum dimension of the flakes or particles are in the range of 0.050-3 μιη, or the range of 0.100-3 μιη, or in the range of 0.500-3 μιη, or in the range of 1-3 μιη. The "maximum dimension" of a flake or particle is defined as the dimension, whether this is the length, height, width, obtaining the largest length measurement.

In the present context, the term "white to pale grey or colourless mineral" relates to a mineral mainly having energy transmitting activities and such mineral may also provide a more attractive and aesthetical surface of a coated material. The white to pale grey or colourless mineral is suitable for being coated as an energy transmitting layer. The term "energy transmitting activities" relates to a coating introduced for improving the effect of transmitting energy, some adsorption of energy may occur, but the primal function relies in transmitting energy.

In a further embodiment of the present invention the mineral may be a dark mineral such as carbon black or graphite. Preferably, the dark mineral, is carbon black. In the present context, the term "dark mineral" relates to a mineral mainly having energy adsorbing activities and suitable for being coated as an energy absorbing layer. The term "energy adsorbing activities" relates to a coating introduced for improving the effect of adsorbing energy, some transmission of energy occurs but the primal function relies on adsorbing energy.

In an embodiment of the present invention, the solvent and/or the coating composition is in liquid form or in the form of aerosols before and during application i.e. generally when in a ready-to-use-state. The mineral may be a solid material which may be suspended in the solvent, providing a slurry of the mineral in the solvent.

A polymeric resin may be dissolved in the solvent. The polymeric resin may provide a matrix holding and distributing the mineral in the solvent and on a surface of a material after drying, also the polymeric resin may act as a dispersing agent. The polymeric resin may be an acrylic resin such as polyether tetra-acrylate.

In an embodiment of the present invention, the mineral has an average particle size in the range of 50-500 nm, such as in the range of 100-400 nm, e.g. in the range of 200-300 nm, such as about 280 nm.

The coating composition may be provided in two forms, (1) a stock composition for storage, and (2) a ready-to-use composition. In an embodiment of the present invention, the coating composition comprises a white to pale grey or colourless mineral and during storage the coating composition may have a dry matter content in the range of 40-65% (w/w), such as in the range of 45-60% (w/w), e.g. in the range of 50-54% (w/w) or wherein the coating composition during application, i.e. when in a ready-to-use composition, has a dry matter content in the range of 20-50% (w/w), such as in the range of 25-45% (w/w), e.g. in the range of 30-40% (w/w), such as about 35% (w/w).

In a further embodiment of the present invention, the coating composition comprises a dark mineral and during storage the coating composition may have a dry matter content in the range of 15-45% (w/w), such as in the range of 20-40% (w/w), e.g. in the range of 24-30% (w/w) or wherein the coating composition, during application, ready to use composition, may have a dry matter content in the range of 10-35% (w/w), such as in the range of 12-30% (w/w), e.g. in the range of 15-25% (w/w), such as about 19% (w/w).

The coating compositions for storage may be diluted, preferably with the same solvent as originally used to provide a ready-to-use composition. This, dilution may be in a ratio (vol/vol) of coating composition to solvent of at least 2: 1, such as at least 3: 1, e.g. at least 4: 1, such as at least 6: 1, e.g. at least 8: 1, such as at least 10: 1, e.g. at least 15: 1.

In an embodiment of the present invention, the solvent may be a polar solvent or a combination of polar solvents. Preferably, the solvent may be a polar protic solvent or a combination of polar protic solvents. E.g. the solvent is a combination of at least 2, possibly 2-5 polar or polar protic solvents.

In a further embodiment of the present invention, at least one carbon group of the solvent comprises at least one oxygen group, preferably an alcohol and/or a ketone of said carbon group. The carbon group may be a straight carbon chain, a branched carbon chain or a cyclic carbon chain. Preferably, the carbon group may be propane, propanol, isopropanol, isopropylalcohol, butane, butanol, isobutanol, butyl acetate, isobutyl acetate, tert-butyl acetate, ethyl acetate, propyl acetate, butyl acetate, sec-butyl acetate, alkane-propyl acetate, such as ethoxy-propyl acetate or methoxy-propyl acetate, or a combination hereof.

In an embodiment of the present invention, the solvent has a vaporization temperature or a boiling point of 85°C or above, such as 90°C or above, e.g. 95°C or above, such as 100°C or above, e.g. 105 °C or above, such as 110°C or above, e.g. 115°C or above, such as 120°C or above, e.g. 125 °C or above. In a further embodiment of the present invention wherein the solvent is an organic solvent or a mixture of organic solvents, preferably the solvent is an acetate or a mixture of acetates or comprise at least one acetate or at least two acetates. One acetate solvent may comprise more than one acetate-group.

Normally, the solvent or mixture of solvents has a vaporization temperature or a boiling point of 85°C or above, such as 90°C or above, e.g. 95°C or above, such as 100°C or above, e.g. 105°C or above, such as 110°C or above, e.g. 115°C or above, such as 120°C or above, e.g. 125 °C or above.

Normally, the solvent or mixture of solvents has a vaporization temperature or a boiling point of 210°C or below, such as below 200°C, or below 180°C, or below 160°C or even below 130°C. Preferably, the solvent may be a mixture of ethyl acetate (boiling point approximately 77°C) and propyl acetate (boiling point approximately 102°C). Preferably the propyl acetate makes up at least 40% of the mixed solvent, such as at least 50%, e.g. at least 60%, such as at least 75%, e.g. at least 90%. Preferably, propyl acetate makes up 70-90% (such as about 80%) of the mixed solvent and ethyl acetate makes up 10-30% (such as about 20%) of the mixed solvent.

The coating composition may preferably be used in a method for providing a material having an improved energy transmission of the material surface, the method comprises the steps of

(i) providing a material;

(ii) providing a coating composition comprises a white to pale grey or colourless mineral according to the present invention;

(iii) applying the coating composition of step (ii) to the material of step (i)

(iv) allowing the coated composition to dry and cure providing a material having an improved energy transmission from the material surface.

In a preferred embodiment of the present invention the coating composition may be applied to the material in step (iii) by spraying, by dipping or by painting or a similar method where a desired thickness of the coating composition may be obtained.

The heat transmission of the material may be further improved by providing a duplex coating of the material surface. Such duplex coating of the material surface may be provided by coating both an energy absorbing layer and an energy transmitting layer on a material surface. The total thickness of a duplex layer may be at least 15 μιη in dried state, i.e. the total thickness of both layers of a duplex layer may be at least 15 μιη in dried state. E.g. at least one layer of a duplex coating, normally the outer or upper layer of the duplex coating - i.e. the layer furthest away from the material to be coated - has a thickness of at least 15 μπι, or possibly each layer of a duplex layer has a thickness of 15 μιη resulting in a total thickness of the duplex layer of at least 30 μιη.

Hence, in an embodiment of the present invention the material surface may be further coated with an energy absorbing layer. By coating the material surface with an energy absorbing layer comprising one or more dark minerals a duplex coated material surface may be provided. Preferably, the one or more dark minerals may be carbon black.

In an embodiment of the present invention, an energy absorbing layer may be a bottom layer (coated directly on or closest to the material surface) and an energy transmitting layer may be a top layer (coated on top of the energy absorbing layer).

In an embodiment of the present invention, an energy absorbing layer may be coated on one side of the material surface and an energy transmitting layer may be coated on the other side of the material surface, preferably located opposite to the energy adsorbing layer when the material is a sheet of material and at least thin enough to allow heat to be transferred from one side of the material to the opposite side of the material.

In an embodiment of the present invention, transmitted energy may be in form of heat convection and/or radiation, in particular, electromagnetic radiation. The coated material obtained by the present invention or the method described may have less cracks, be more efficient in transmitting energy and further benefit from faster heating of an object in contact with or covered by the coated material, thus save time during use, longer shelf-life of the material being coated and/or positive implications on the environment relative to the traditionally used and described coated materials.

A preferred embodiment of the present invention may be a material having an energy transmitting coating on at least one material surface, wherein the energy transmitting coating comprises a mineral and a coating layer thickness of at least 15 μιη, when the coating layer is in dried state.

In an embodiment of the present invention, a coating layer thickness, e.g. of an energy transmitting coating, of a energy absorbing layer or of a duplex coating, may be in the range of 15-1000 μιη, when in dried state, such as in the range of 16-750 μιη, e.g. in the range of 17-500 μιη, e.g. in the range of 18-400 μιη, such as in the range of 19-300 μιη, e.g. in the range of 20-200 μιη, e.g. in the range of 25-150 μιη, such as in the range of 30-100 μιη, e.g. in the range of 40-75 μιη.

The material may be further provided with an energy absorbing layer. The energy absorbing layer may be applied with a coating comprising or consisting of a temperature resistant organic matrix. Preferably, the coating may be applied as a duplex coating. Preferably, the bottom layer may be the energy absorbing layer and the uppermost layer may be the energy transmitting coating. The coating composition may be designed in such a manner that the wavelengths from the radiation-emitting or energy emitting surface (e.g. the oven wall) and the energy absorbing surface (a coated material surface of e.g. a foil) match.

This means that the wavelength spectra of the electromagnetic radiation of the one surface is attuned to that of the other surface, whereby e.g. the oven surface efficiently transmit the radiant heat to the coated material and any product covered or in contact with the coated material.

The advantage thus obtained may be that of using a material able to absorb radiation with an electromagnetic wavelength spectrum that is comprised e.g. within the lower half of an interval along with another material able to absorb radiation with an electromagnetic wavelength spectrum that is within e.g. the upper half of the interval in order to thereby accomplish a surface on the material that has an electromagnetic wavelength spectrum that uses all of this interval to advantage.

Hence, an embodiment of the present invention relates to a material comprising a coating comprising or constituted of an energy transmitting coating transmitting radiation at a wavelength spectrum attuned to that of a heat source, e.g. the wavelength spectrum of the electromagnetic radiation of an oven.

In an embodiment of the present invention the energy transmitting coating may be selected to be such that it reduces reflected radiation from the subjacent energy absorbing coating.

In a further embodiment of the present invention the energy absorbing coating may have a wavelength spectrum of an electromagnetic radiation which may be within the interval of 2500 - 10000 nm.

In another embodiment of the present invention the energy absorbing coating has a wavelength spectrum of an electromagnetic radiation which may be within the interval 8000 - 10000 nm. The material according to the present invention may be a material where it is of interest to direct energy, e.g. heat, from one side of the material to another side, either for heating the material or a product being covered or in contact with the material or for transporting heat across the material, e.g. to the air, in order to cool the material, extending shelf-life of the material.

In an embodiment of the present invention, the material may be a flexible material or an inflexible material. Preferably, the material may be of metal, plastic, polymer, paper, cardboard or other materials that are based on wood. The material may be formed as a flexible or non-flexible sheet i.e. be sheet-like, or as a plate where the distance between a first and a second opposite side is considerably smaller than the length or width of the material, the flexible sheet-like material may be a foil or the like and the inflexible sheet-like material may be a baking mold or a dish or a plate or the like. The material may also be formed as a more voluminous and inflexible component from which surface heat is released or received, e.g. a box-like structure, a radiator, a motor block or the like.

The material may be constituted of or comprising a material having a relatively high thermal conductivity able to transport heat from one surface of the material to another surface, i.e. through the material. The material may e.g. be constituted of a metal or a combination of metals, and may e.g. comprise aluminum having a thermal conductivity of 205 W/(m K), or the material may comprise or be constituted of one or a combination of materials or components resulting in a thermal conductivity of the material above 15 W/(m K). If the material comprises or is constituted of a sheet-like material, the material, the energy transmitting layer and/or the radiation absorbing layer may have a ductility of at least 5 %. Hereby it is accomplished that the surface of the material may be flexible, has high temperature resistance and high stability, which enables heating to 300°C for at least three hours without the material properties deteriorating significantly.

In an embodiment of the present invention the material may be a foil, a metal tray, a baking tin, or an engine block.

It is the object of the invention to provide an energy transmission system, preferably, based on electromagnetic radiation, a material and/or a coating composition, e.g. for applying aluminum packaging or aluminum foils for primary use within the foodstuffs industry with a view to obtaining surfaces that have unique properties in respect of quick heating via IR radiation/radiant heat from hot surfaces in ovens. This means that the surface on the foil is made of materials that are to the widest extent possible capable of transmitting radiation from an internal part of a hot surface of an oven to an outer surface of a product covered by or in contact with the foil.

In the present context, the term "energy transmission system" relates to the combination of the material (the coated material) according to the present invention and an energy source, such as a heating source or the surface of a heating source, e.g. an oven.

The energy transmission system is configured such that the wavelength of an IR-absorbing surface (a radiation adsorbing surface) is adapted to or matches the IR-radiation that is emitted from an energy source, e.g. the internal surface of an oven. For an oven applied with enamel, which is among the most frequently used materials for coating oven cavities, a coating is thus concerned that emits IR radiation with the highest intensity within the range 8000 - 10000 nm. The coated material according to the present invention is thus capable of primarily absorbing radiation of the same wavelength if the energy via radiant heat is to be performed quickly and efficiently. The energy is subsequently transmitted to the product, e.g. a ready to eat dish covered by a material, e.g. a foil or the like, coated according to the present invention.

The mineral selected may be selected according to their ability to absorb the energy (e.g. by IR radiation) at a given wavelength spectrum that characterizes the energy from the energy source, e.g. radiation from a hot oven wall. By applying the coating composition according to the present invention as a sandwich layer, where a first layer is configured for absorbing the IR-radiation and a second layer is configured for reflecting the energy, e.g. produced by radiation and emitted from a heated product wrapped in the foil, the heat from the product is thus reflected to the product.

The reason for this may be found in the so-called internal reflection between a bottom layer and a top layer. By combining optimally matching bottom layer coatings with a top layer coating that improves the internal reflection, higher temperatures have thus been measured on the inside of the material such as a foil than can be obtained via dark surfaces (carbon black).

The need for producing e.g. finished foodstuff products (such as ready to eat products) in aluminum packaging for being heated in radiation and convection ovens is ever increasing. The reasons for this are the desire to spend less time on cooking and to save energy.

Packing of foodstuffs in alu-foil followed by a heating procedure in a conventional oven prolongs the preparation time due to the good reflective properties of the aluminum material to IR heat radiation. It has been attempted to produce both a dull and a glossy side on e.g. the aluminum foil without having thereby improved the heat transmission properties significantly.

In an embodiment of the present invention, the coating composition on the material when used for food products, e.g. the aluminum foil, may preferably not have toxic or hazardous properties and it should preferably also be thermally stable up to 300°C, have a thickness above 15 μιη and exhibit sufficient mechanical properties in the application situation. What is intended by this is the usual way in which the material, such as alu-foil, is handled in an in- use situation. In a further embodiment of the present invention, the surface of the material, e.g. the foil, may be provided with a top coating that reduces the reflection of energy, such as IR radiation, from the surface and at the same time allows the energy, such as IR radiation to pass. Utilization of such duplex coatings may show to provide surprising measurement results that have given better values than the well-known "carbon black" surface mentioned above.

Hereby a distinctly more efficient energy transmission may be obtained which, in this context, enables shorter preparation time and/or energy savings since the energy input may be reduced.

The coated material according to the present invention comprises at least two layers, wherein the wavelength spectrum of the transmission energy, such as the electromagnetic radiation, of the coated material, e.g. a foil, may be attuned to that of an energy source, e.g. the wavelength spectrum of the electromagnetic radiation of an oven.

In a further embodiment of the present invention, the material may have an energy adsorbing layer and/or an energy transmitting layer that may be applied as a coherent layer or layers onto the surface of the material. In yet an embodiment of the present invention, an energy transmitting layer may be chosen such that it reduces reflecting radiation from a subjacent, energy absorbing layer.

According to a preferred embodiment a coating composition is prepared by mixing 10-20 grams of polymeric resin with 40 -60 grams with a mixture of organic solvents. Normally the mixture of organic solvents will comprise 2-3 solvents chosen amongst butyl acetate, isobutyl acetate, tert-butyl acetate, ethyl acetate, propyl acetate, butyl acetate, sec-butyl acetate, alkane-propyl acetate such as ethoxy-propyl acetate or methoxy-propyl acetate, propane, propanol, isopropanol, isopropylalcohol, butane, butanol and isobutanol. The polymeric resin is in form of a colorless powder which is soluble in the mixture of organic solvents. The polymeric resin may be an acrylic resin or a polyester resin or another resin with similar functionality. Polymeric resins and solvents are generally commercially available. The polymeric resin powder is mixed with the solvents during stirring at room temperature for 40-90 minutes, normally 50-70 minutes. The stirring is vigorously and may be performed in a kettle with a high-speed disperser.

During stirring is added 10-30 grams of heat transmission minerals such as CaSC , MgCC , S1O2, T1O2 in powder form and possibly aluminium flakes, or a mixture hereof, which powder and possibly flakes become part of the dry content of the coating.

After mixing is finished, a liquid coating having a dry matter content of 20-50% w/w is obtained, and the coating has a viscosity of 100-200 mPas. The coating is in a ready-to-use state and may be applied as a relatively thick layer i.e. a layer having a minimum thickness of 15 μιη to a material surface e.g. by spraying, dipping or painting.

Duplex systems have shown more efficient energy transmission properties. The reason for this may be found in the so-called internal reflection between the bottom layer coating and the top layer coating. By combining optimally matching bottom layer coatings with a top layer coating that improves the internal reflection, temperatures have thus been measured that are higher than those of single-layer "carbon black" on aluminum foil. By using a duplex system with "carbon black" as a component in a bottom layer coating and T1O2 as a component in a top layer coating, it is thus possible to combine the good absorbing property of carbon black with the appearance of T1O2. Besides, the IR radiation absorbing property is also improved since the total internal reflection within the coated material, between bottom layer and top layer, is improved due to the high refraction index of T1O2. For the process to be applicable, customized coating compositions may be made that comprises minerals that have matching properties with respect to the wavelength from the energy emitting surface (e.g. radiation emitted from an oven wall) and the energy absorbing surface. In a further embodiment of the present invention a coating composition may comprise an organic binder. Preferably, the organic binder may be selected from a group of compounds that is readily able to resist the achieved temperature. Preferably, the organic binder may be acryl styrene polymer and/or nitrocellulose or an organic binder having similar properties. In an embodiment of the present invention, a combination of minerals may be used. In this way, the minerals may cooperate to enable energy absorption across a wider spectrum than if only one mineral was used. Thus, the one mineral may e.g. have good absorption of radiant heat within a spectrum from a-b, another mineral from b-c, and optionally a third mineral from c-d. Thereby a combination of minerals may be provided that covers good heat absorption within a spectrum from a-d. Preferably, the combination of minerals comprises at least 2 different minerals, such as at least 3 different minerals, e.g. at least 4 different minerals, such as at least 5 different minerals, e.g. at least 6 different minerals.

In the present context, the term "different minerals" relates to a composition of minerals having difference in maximum energy absorption spectra allowing a coating to cover good energy absorption properties within a wider range of wavelengths, than a composition only comprising a single mineral.

In other words, the advantage may be cashed in on that it is possible to employ a mineral with an electromagnetic wavelength spectrum that is e.g. within the lower half of an interval along with another mineral with an electromagnetic wavelength spectrum that is e.g. within the upper half of the interval in order to achieve a surface on a material, e.g. the foil, that has an electromagnetic wavelength spectrum that utilizes the entire interval. It should be noted that embodiments and features described in the context of one of the aspects of the present invention also apply to the other aspects of the invention.

All patent and non-patent references cited in the present application, are hereby

incorporated by reference in their entirety.

References

US 4,220,134

US 2006/153952 Al

WO 2009/000272

Claims

1. A coating composition improving energy transmission from a material surface subjected to heating by radiation in the infrared spectrum, which coating composition before being applied to the material surface i.e. when in a ready-to-use state, comprises or is constituted of a mineral dissolved or suspended in an organic solvent or carrier, wherein the solvent or carrier comprises a carbon group having 3-10 carbon atoms.

2. The coating composition according to claim 1, wherein the mineral is a white to pale grey or colourless mineral e.g. selected from the group CaSC , MgCC , S1O2, T1O2 or a mixture hereof, preferably T1O2.

3. The coating composition according to anyone of the preceding claims, wherein the mineral has an average particle size in the range of 50-500 nm (0.050-0.500 μιη), such as in the range of 100-400 nm, e.g. in the range of 200-300 nm, such as about 280 nm.

4. The coating composition according to anyone of the preceding claims, wherein the coating composition during storage has a dry matter content in the range of 40-65% (w/w), such as in the range of 45-60% (w/w), e.g. in the range of 50-54% (w/w) or wherein the coating composition in a ready-to-use state or during application has a dry matter content in the range of 20-50% (w/w), such as in the range of 25-45% (w/w), e.g. in the range of 30-40% (w/w), such as about 35% (w/w).

5. The coating composition according to anyone of the preceding claims, wherein the carbon group is propane, propanol, isopropanol, isopropylalcohol, butane, butanol, isobutanol, butyl acetate, isobutyl acetate, tert-butyl acetate, ethyl acetate, propyl acetate, butyl acetate, sec-butyl acetate, alkane-propyl acetate, such as ethoxy-propyl acetate or methoxy-propyl acetate, or a combination hereof.

6. The coating composition according to anyone of the preceding claims, wherein the coating composition does not comprise a susceptor material in particulate form i.e. as powder, flakes, where a susceptor material is a conductive or semi-conducting material.

7. The coating composition according to anyone of claims 1-5, which coating composition further comprises flakes or particles of a conductive material such as aluminium.

8. A method for providing a material having improved energy transmission from a surface when the material is heated or subjected to heating by radiation in the infrared spectrum, the method comprises the steps of

(v) providing a material; (vi) providing a coating composition according to anyone of claims 1-5;

(vii) applying the coating composition of step (ii) to a surface of the material of step (i) providing a coated material having a coating layer thickness of at least 15 μιη, in dried state; and

(viii) allowing the coated composition to dry and cure providing a coated material having an improved energy transmission from the coated material surface.

9. The method according to claim 7, wherein the coating composition is applied to the material in step (iii) by spraying, by dipping or by painting.

10. A material coated by a coating composition according to anyone of claims 1-7, which material is either a flexible or an inflexible material, e.g. the material may have a ductility of at least 5%.

11. A material according to claim 10, wherein the material and the coating composition can withstand heating to 300 °C for at least 5 minutes without deteriorating significantly.

12. A material according to claim 10 or 11, wherein the material is shaped as a sheet or the like, e.g. a foil or plate or tray, or the material has a voluminous shape such as an engine block or the like.

13. A material according to claim 10, 11 or 12, wherein the material is constituted of metal or another material having a heat conductivity of at least 10 W/(m K), alternatively at least 15 W/(m K) or at least 50 W/(m K), or the material is constituted of plastic, or polymer, or paper, or cardboard and/or a materials based on wood, or the material is constituted of a combination of such materials.

14. A material according to claim 10, 11, 12 or 13, wherein the energy transmitting coating layer has a thickness of at least 15 μιη, when in dried state, alternatively the coating layer has a thickness is in the range of 15-1000 μιη, when in dried state, such as in the range of 16-750 μιη or 16-1000 μιη, e.g. in the range of 15-500 μιη or 17-500 μιη, e.g. in the range of 15-400 μιη or 18-400 μιη, such as in the range of 15-300 μιη or 19-300 μιη, e.g. in the range of 15-200 μιη or 20-200 μιη or 30-200 μιη or 40-200 μιη or 50-200 μιη.

15. A material according to anyone of claims 10-14, wherein a duplex coating is applied, the duplex coating comprising a bottom layer and an uppermost layer, where the bottom layer is closest to the material and comprises or constitutes an energy absorbing layer and the uppermost layer comprises or constitutes an energy transmitting layer according to one of claims 1-7.

16. A material according to anyone of claims 10-14, wherein the bottom layer and the uppermost layer are in direct contact with each other i.e. there are no layer between the bottom and the uppermost layer.

17. A material according to claim 15 or 16, wherein the energy transmitting layer, comprises a white to pale grey or colourless mineral e.g. selected from the group CaSC , MgCC , S1O2 or T1O2 or a mixture hereof, preferably T1O2.