Abstract:
A preferably dark coated freezer storage bag on the basis of a black body radiator and a method of making it. The freezer bag is coated on the outside with a coating having a thermal emissivity higher than 0.56, mostly used black 100% virgin polyethylene with an emissivity of (ε=0.92) or black carbon with an emissivity of (ε=0.88). The invention pertains to a process of minimising the freezing and defrosting time of foodstuff inside and outside the refrigerators by optimising the thermal transfer.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     This invention relates to a black coloured freezer storage bag. The outside of the bag is coated with a black pigment or the pigment is combined with the polymer structure of the foil. During the freezing process the dark coloured outside of the bag enables to a higher emission of thermal radiation and reduces the freezing time of the foodstuff compared with standard sizes of mostly transparent freezer bags. The black freezer bag is functioning on the basis of a black body radiator. It maximises the emission of thermal radiation during the freezing process and minimises the defrosting time due to its higher grade of absorption of thermal radiation when being outside the refrigerator in contact with a higher ambient temperature.  
         [0003]     2. Description of the Prior Art  
         [0004]     Freezer bags made out of plastic already exists in various versions. The mostly performed standard size of a freezer bag is made of transparent polyethylene foil. The main function of standard freezer bags is the prevention of the so called freezer burn (see “Packaging Foods With Plastics”, by Wilmer A. Jenkins and James P. Harrington, published in 1991 by Technomic Publishing Co., Inc., at page 305).  
         [0005]     The patent applications CA2162681/EP877051 relates to copolymers of ethylene and a C4-C12 monomer having a relatively narrow composition distribution and to the production and use of such copolymers. It relates to linear low density polyethylene resins (LLDPE) that have much better processability and film properties like clarity, gloss and low reblock. The application do not relate to any solution to produce a polyethylene foil with a higher grade of thermal emission on the basis of black-body radiators.  
         [0006]     The application WO1997029966/EP880457 made by S. C. Johnson/Dowbrands comprises a freezer multibag that consists of a inner liner bag and an outer support bag to reduce freezer burn. The use of multibags does not relate to any improvement of thermal emission of radiation and a reduction of freezing time.  
         [0007]     The application U.S. Pat. No. 5,840,800 relates to improvements in polymer foil production and leads to an aqueous dispersion of crosslinked pre-formed silicon modified organic polymer which upon drying, yields to an elastomer, but it does not give a solution to an increasing thermal emission of radiation.  
         [0008]     DE69232195 relates to a freezing mould bag. It leads to ice cubes with a defined shape and give no answer to the essential problem solved by the present invention.  
         [0009]     The patent application DE2658150 relates to process of splitting the fruits from its fruit juice during the freezing process and give no support for increasing the emission or absorption of thermal radiation.  
         [0010]     All standard sizes of freezing storage bags don&#39;t give any solutions to the problem of heat exchange and thermal transfer during the freezing and defrosting process of foodstuff that is packaged in freezing bags made of polyethylene.  
         [0011]     The applications WO0176976 and WO2005000690 relate to a multilayer heat sealable packaging material for foodstuff that reduces light and UV-transition by using a carbon pigment combined with titanium oxide in one inner layer (not the outside layer) to produce a grey colour of the foil. The outside surface of such a multilayer composition is glossy and has no black pigment and the grey colour of the inner layer leads to a reduction of thermal emission of radiation.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention solves the problem described above, by providing a black coloured freezer storage bag that increases the grade of emission and absorption of thermal radiation according to the ambient temperature. It optimises the heat exchange in order to reduce freezing and defrosting time. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]     The problem of the invention is solved by the use of black coloured freezer storage bags according to the claims  1  to  8 .  
         [0014]     A possible composition of a multilayer freezer bag comprises: 
        a substrate with a thickness from 5 mu m up to 300 mu meter, which is selected from the group consisting of:     a thermoplastic material like 100% virgin polyethylene according to the US government specification LP378 or conformant to the FDA regulation 177.1520,     an aluminium foil.     an outer surface coated with a pigment that has a emissivity ε&gt;0.56. That might be a dark coloured pigment, especially a carbon black modification (ε&gt;0.8), like FW200 or inorganic iron(II,III) oxides (ε=0.56) to increase thermal transfer. But also white coloured pigments might be for some applications useful, especially Titanium oxide with Potassium Silicate (ε=0.92) or Zinc Oxide with Sodium Silicate (ε=0.92).        
 
         [0019]     The emissivity is the ratio of the power W [Watt/m 2 ] or radiation a surface emits into a surrounding hemisphere and the total radiant power a perfect black body radiator emits, given by W 8  [Watt/m 2 ]=σT 4  where σ=Stefan-Boltzmann constant. (see: Radiometric Properties of Isothermal Diffuse Wall Cavity Sources, Applied Optics, Vol. 13, page 2142, September 1974).  
         [0020]     The given average emissivity values have been taken from the list published by Electro Optical Industries, Inc., 859 Ward Drive, Santa Barbara Calif. 93111, www.electro-optical.com.  
         [0021]     It is also useful for a higher thermal emission to produce a non bright, mat surface and not glossy like one of the already existing conductive bags.  
         [0022]     Useful binders are all polymeric binders used in foodstuff applications that do not hinder thermal transfer and are applicable in temperature ranges that occur in standard refrigerators, like for example polysiloxane or polyorganosiloxanes (silicones), especially all sorts of polyester and epoxide modified silicone resins. Among these are the polyester-modified methylphenyl polysiloxanes and hydroxyl functional silicone resins published in U.S. Pat. No. 6,696,511 and DE10035641 in combination with aluminium as a substrate. In addition to this a mixture of hydrolyzable trialkoxysilane and hydrolyzable dialkoxysilane, water, acidifying agent from about 2.8 to 6, published in the 20 years old application U.S. Pat. No. 4,439,239 (page 2, line 5-7; page 4, line 25-57; page 9, line 1-32).  
         [0023]     Among the binders selected from the group of Polysiloxanes are the so called inorganic-organic siloxane-based hybrid polymers that encapsulate the pigment in three-dimensional networks in a Sol-Gel transformation. They are more and more used in foodstuff applications and some examples are given in the applications WO00/59555 (page 3, line 26 page 8 line 1-19, page 9 line 29), EP1201721 (column 1, line 49-61; column 5, line 4; column 7, line 14 and examples 1-3) and EP1484372.  
         [0024]     Another example of a useful binders consisting of organic-inorganic polymeric chains that are linked to Ormosil monomers (Fraunhofer-Institut für Silicatforschung ISC Neunerplatz 2;97082 Würzburg Germany; www.isc.fhg.de).  
         [0025]     For example Tetraethylorthosilicate that is linked to di- tri-or tetrafunctional silicon alkoxides three-dimensional networks by Sol-Gel transformation. More flexible for the use in combination with polyethylene as a substrate are the Ormocer hybrids published by the Fraunhofer Gesellschaft in Munich, Germany.  
         [0026]     In addition to this all sorts of acrylate resins, like polyacrylates or acrylate elastomers can be used according to the non-toxic premiss of the application.  
         [0027]     Another example of a polymer-based composition and useful coating of the outside of the freezer bag is described in the application WO0177215. In contradiction to the composition in WO0177215 for the present invention it is necessary to use only carbon black as a pigment and no titanium oxide in order to bring the freezer bag into line with a black-body radiator.  
         [0028]     Another possible composition of a black freezer bag comprises a bag made out of a thermoplastic 100% virgin polyethylene, especially high density polyethylene according to the US government specification LP378 and the FDA regulation 177.1520 that is entirely black coloured, for example with carbon black. The average emissivity of black polyethylene is ε=0.92 and is high enough for a good energy emission. If a multibag is used as a freezer bag to prevent freezer burn like in application WO97/29966 of S. C. Johnson, at least the outside bag must be made out of black polyethylene.  
         [0029]     To realize a better thermal transfer from the inside of the bag to the surface it is useful to take aluminum foil as a substrate. The metal foil has a much better thermal conductivity compared with polyethylene as material. The inside of the aluminium foil can be coated with a non-stick surface in order to hinder the sticking of the foodstuff and it also prevents any chemical reaction of the foodstuff and the aluminium.  
         [0030]     Especially the freezer bag can be modified as a aluminium container that can be closed in an airtight manner. When polyethylene is selected as a substrate, there can be a small window of transparent polyethylene left on one side of the bag in order to make the frozen foodstuff clearly visible for the user.  
         [0031]     The foregoing examples have been presented for the purpose of illustration and description only and are not to be construed as limiting the scope of the invention any way.  
         [0032]     The scope of invention is to be determined from the claims appended thereto.