Process for making high aspect ratio reflective metal flakes

Abstract

A process for making high aspect ratio metal flakes comprises applying a multi-layer sandwich of vapor deposited metal and release coats in alternating layers to a rotating chilled drum or suitable carrier medium contained in a vapor deposition chamber. The alternating metallized layers are applied by vapor deposition and the intervening release layers are preferably solvent-soluble materials applied by suitable coating or vapor deposition sources contained in the vapor deposition chamber. The release coat materials can be a thermoplastic solvent-soluble polymer. The multi-layer sandwich built up in the vacuum chamber is removed from the drum or carrier and treated with a suitable solvent to dissolve the release coating from the metal in a stripping process that leaves the metal flakes essentially release coat free. The solvent and dissolved release material are then removed by centrifuging to produce a cake of concentrated flakes which can be air milled and let down in a preferred vehicle and further sized and homogenized for final use in inks, paints or coatings. In one embodiment the finished flakes comprise single-layer thin metal flakes and in another embodiment the flakes are coated on both sides with protective polymeric coatings that were applied from vacuum deposition sources contained in the vapor deposition chamber. In an alternative embodiment the release coat can be a thermoset material which is lightly cross-linked in the vacuum chamber and then later treated with a de-polymerizing solvent material that breaks the chemical bonds sufficiently to separate the layers.

1 . Apparatus for making flakes comprising: 
 a vapor deposition chamber;    a deposition surface in the vacuum deposition chamber; and    a release coat source and a flake deposition source in the vacuum deposition chamber, each directed toward the deposition surface,    the release coat source and flake deposition source arranged relative to the deposition surface and adapted for depositing a multi-layer vapor deposit on the deposition surface under vacuum in alternating layers comprising a vaporized polymeric release coat layer deposited from the release coat source and a vapor deposited layer of flake material deposited from the flake deposition source to thereby build up in sequence said multi-layer vapor deposit of flake material layers separated by and deposited on corresponding intervening release coat layers;    the release coat source adapted to deposit a thermoplastic polymeric material vaporizable under vacuum to form a smooth continuous solvent soluble and dissolvable barrier layer and support surface on which each of the layers of flake material is formed,    the multi-layer vapor deposit removable from the vacuum deposition chamber and the deposition surface for separating the multi-layer vapor deposit into flakes by treatment with a solvent which dissolves the release coat layers and yields flakes with smooth, flat surfaces which are essentially free of the release coat material.    
     
     
         2 . Apparatus according to  claim 1  in which the flake deposition source deposits flake layers comprising a vapor deposited material selected from the group consisting of metal in elemental form, an inorganic material, and a non-metal.  
     
     
         3 . Apparatus according to  claim 2  in which the non-metal comprises silicon monoxide, silicon dioxide, a polymeric material, and the inorganic material is selected from the group consisting of magnesium fluoride, silicon monoxide, silicon dioxide, aluminum oxide, aluminum fluoride, indium tin oxide, titanium dioxide and zinc sulfide.  
     
     
         4 . Apparatus according to  claim 1  in which the release coat source deposits a release coat material selected from styrene or acrylic polymers or blends thereof.  
     
     
         5 . Apparatus for making flakes comprising: 
 a vapor deposition chamber;    a deposition surface in the vacuum deposition chamber; and    a release coat source and a flake deposition source in the vacuum deposition chamber, each directed toward the deposition surface,    the release coat source and flake deposition source arranged relative to the deposition surface and adapted for depositing a multi-layer vapor deposit on the deposition surface under vacuum in alternating layers comprising a vaporized polymeric release coat layer deposited from the release coat source and a vapor deposited layer of flake material deposited from the flake deposition source to thereby build up in sequence said multi-layer vapor deposit of flake material layers separated by and deposited on corresponding intervening release coat layers;    the release coat source adapted to vapor deposit a resinous material comprising a monomer or polymer which is lightly cross-linked or polymerized by chain extension and is organic solvent soluble or dissolvable sufficient to separate from the layers of flake material when treated with an organic solvent, the resinous material vaporizable under vacuum to form a smooth continuous barrier layer and support surface on which each of the layers of flake material is formed,    the multi-layer vapor deposit removable from the vacuum deposition chamber and the deposition surface for separating the multi-layer vapor deposit into flakes by treatment with said organic solvent which dissolves the release coat layers and yields flakes with smooth flat surfaces which are essentially free of the release coat material.    
     
     
         6 . Apparatus according to  claim 5  in which the release coat material comprises an acrylic resinous material.  
     
     
         7 . Flakes of high aspect ratio in which the flakes have an average particle size from about 4 to about 12 microns and a single layer thickness from about 200 to about 400 angstroms, the flakes produced by vapor deposition of multiple layers of the flake material on corresponding intervening layers of vapor deposited release coat material, the layers of release coat material forming a smooth continuous barrier layer and support surface on which each of the layers of flake material has been deposited, the release coat material comprising a polymeric material vapor deposited under vacuum and solvent soluble and dissolvable for separating the layers of flake material from the release coat layers by treatment with a solvent which dissolves the release coat layers and yields the flakes having smooth essentially flat surfaces essentially free of the release coat material.  
     
     
         8 . The product according to  claim 7  in which the flake material comprises a metal.  
     
     
         9 . The product according to  claim 7  in which the release coat layer has a thickness in the range of about 200 to about 400 angstroms.  
     
     
         10 . The product according to  claim 7  in which the flake material comprises a metal layer selected from the group consisting of aluminum, copper, silver chromium, tin, zinc, indium and nichrome.  
     
     
         11 . The product according to  claim 10  in which the optical density of the vapor deposited metal layer is below about 2.8 (MacBeth densitometer).  
     
     
         12 . The product according to  claim 7  in which the flakes have an aspect ratio of 300 or more.  
     
     
         13 . Apparatus for making metal flakes comprising: 
 a vacuum deposition chamber containing a deposition surface;    a release coat source and a metal deposition source in the vacuum deposition chamber, each directed toward the deposition surface; and    a multi-layer vapor deposit which has been deposited on the deposition surface under vacuum in alternating layers comprising a vaporized polymeric release coat layer deposited from the release coat source and a vapor deposited metal layer deposited from the metal deposition source to build up in sequence said multi-layer vapor deposit of metal layers separated by and deposited on corresponding intervening release coat layers;    the release coat layers comprising a thermoplastic polymeric material which was vaporized under vacuum to form a smooth continuous barrier layer and support surface on which each of the metal layers is formed, the vapor deposited thermoplastic polymeric release coat layer dissolvable in an organic solvent;    the metal layers comprising vapor-deposited metal in elemental form deposited to a film thickness of less than about 400 Angstroms;    the multi-layer vapor deposit adapted for separating into metal flakes by treatment with an organic solvent which dissolves the release coat layers and yields single layer metal flakes which are essentially free of the release coat material.    
     
     
         14 . Apparatus according to  claim 13  in which the release and metal layers are in thermal contact with a chilled rotating drum.  
     
     
         15 . Apparatus process according to  claim 13  in which the is release coat material has a glass transition temperature combined with thermal conductivity to the release coat such that the heat of condensation of the deposited metal layer does not melt the previously deposited release layer.  
     
     
         16 . Apparatus according to  claim 13  in which the vacuum deposition chamber includes a primary vacuum pump and an auxiliary turbo pump.  
     
     
         17 . Apparatus according to  claim 13  in which the release coat material is selected from styrene or acrylic polymers or blends thereof.  
     
     
         18 . Apparatus according to  claim 13  in which the metal layer is selected fro the group consisting of aluminum, copper, silver, chromium, tin, zinc, indium and nichrome.  
     
     
         19 . Apparatus according to  claim 13  in which the optical density of the vapor deposited metal layer is below about 2.8 (MacBeth densitometer).  
     
     
         20 . Apparatus according to  claim 13  in which the release coat layer has a thickness in the range of about 200 to about 400 angstroms.  
     
     
         21 . Apparatus according to  claim 13  in which the metal flakes have an aspect ratio of 300 or more.  
     
     
         22 . Apparatus according to  claim 13  in which the release coat/metal layer combination is repeatedly deposited at least ten times to build up the vapor deposit.  
     
     
         23 . Apparatus for making reflective metal flakes comprising: 
 a vacuum deposition chamber containing a deposition surface;    a release coat source in the vacuum-deposition chamber, each directed toward the deposition surface; and    a multi-layer vapor deposit which has been deposited on the deposition surface under vacuum in alternating layers a compromising vaporized polymeric release coat layer deposited from the release coat source and a vapor deposited reflective metal layer deposited from the metal deposition source to build up in sequence said multi-layer vapor deposit of metal layers separated by and deposited on corresponding intervening release coat layers;    the release coat layers comprising a thermoplastic polymeric material comprising polystyrene or acrylic resin or blends thereof which was vaporized under vacuum to form a smooth continuous barrier layer and support surface on which each of the metal layers is formed, the vapor deposited thermoplastic polymeric release coat layer dissolvable in an organic solvent;    the reflective metal layers comprising vapor-deposited aluminum in elemental form applied to a film thickness of less than about 400 Angstroms;    the multi-layer vapor deposit adapted for separating into metal flakes by treatment with an organic solvent which dissolves the release coat layers and yields single layer aluminum flakes having highly reflective mirror-like surfaces essentially free of the release coat material.    
     
     
         24 . Apparatus according to  claim 23  in which the release coat/metal layer combination is repeatedly deposited at least ten times to build up the vapor deposit.  
     
     
         25 . Apparatus for making multi-layer metal flakes with protective outer coatings comprising: 
 a vacuum deposition chamber containing a deposition surface;    a release coat vapor deposition source, a metal vapor deposition source and a protective coating vapor deposition source in the vacuum deposition chamber, each directed toward the deposition surface; and    a multi-layer vapor deposit which has been vapor deposited on the deposition surface under vacuum, in the following sequence, (1) a layer of release coat material deposited from the release coat vapor deposition source, (2) a first polymeric protective outer coating deposited from the protective coating vapor deposition source, (3) a metal layer deposited from the metal vapor deposition source, (4) a second polymeric protective coating deposited from the protective outer coating vapor deposition source, and (5) a further layer of a release coat material deposited from the release coat vapor deposition source, to build-up in sequence said multi-layer vapor deposit of flake material comprising metal layers each bonded to first and second polymeric protective outer coatings with intervening release coat layers between adjacent layers of multi-layer flake material;    the release coat layers comprising thermoplastic polymeric material which was vaporized under vacuum to form a smooth continuous barrier layer and support surface on which each layer of multi-layer flake material is formed, the vapor deposited thermoplastic polymeric release coat layer dissolvable in an organic solvent;    the metal layers comprising vapor-deposited metal in elemental form applied to a film thickness of less than about 400 Angstroms;    the vapor deposit of multi-layer flake material adapted for separating into flakes by treatment with an organic solvent which dissolves the release coat layers and yields multi-layer flakes comprising metal layers bonded on opposite sides to the first and second protective outer layers, the flakes having their surfaces essentially free of the release coat material.    
     
     
         26 . Apparatus according to  claim 25  in which the protective outer coating comprises a transparent polymeric material applied from its corresponding vapor deposition source and cured in the vacuum chamber to a thermoset condition.  
     
     
         27 . Apparatus according to  claim 25  in which the protective outer coating comprises a vapor deposited inorganic material selected from the group consisting of magnesium fluoride, silicon monoxide, silicon dioxide, aluminum oxide, aluminum fluoride, indium tin oxide, titanium dioxide, and zinc sulfide.  
     
     
         28 . Apparatus according to  claim 25  in which the release coat/flake material combination is repeatedly deposited at least ten times to build up the vapor element.  
     
     
         29 . Apparatus for making flakes comprising: 
 a vacuum deposition chamber containing a deposition surface;    a release coat source and an inorganic flake material deposition source in the vacuum deposition chamber, each directed toward the deposition surface; and    a multi-layer vapor deposit which has been vapor deposited on the deposition surface under vacuum in alternating layers comprising a vaporized polymeric release coat layer deposited from the release coat source and a vapor deposited inorganic material from the flake material deposition source to build up in sequence said multi-layer vapor deposit of inorganic flake material separated by and deposited on corresponding intervening release coat layers;    the release coat layers comprising a thermoplastic polymeric material which was vaporized under vacuum to form a smooth continuous barrier layer and support surface on which each of the inorganic flake material layers is formed, the vapor deposited thermoplastic release coat layer dissolvable in an organic solvent;    the inorganic flake material layers comprising a vapor-deposited inorganic material selected from the group consisting of magnesium fluoride, silicon monoxide, silicon dioxide, aluminum oxide, aluminum fluoride, indium tin oxide, titanium dioxide and zinc sulfide;    the multi-layer vapor deposit adapted for separating into flakes of inorganic material by treatment with an organic solvent which dissolves the release coat layers and yields single layer flakes of inorganic material essentially free of the release coat material.    
     
     
         30 . Apparatus according to  claim 29  in which the release coat/flake material combination is repeatedly deposited at least ten times to build up the vapor deposit.  
     
     
         31 . Apparatus for making non-metal flakes comprising: 
 a vacuum deposition chamber containing a deposition surface;    a release coat source and a non-metal deposition source in the vacuum deposition chamber, each directed toward the deposition surface; and    a multi-layer vapor deposit which has been deposited on the deposition surface under vacuum in alternating layers comprising a vaporized polymeric release coat layer from the release coat source and a vapor deposited non-metal layer from the non-metal deposition source to build up in sequence a multi-layer vapor deposit of non-metal layers separated by and deposited on corresponding intervening release coat layers;    the release coat layers comprising a thermoplastic polymeric material which was vaporized under vacuum to form a smooth continuous barrier layer and support surface on which each of the non-metal layers is formed, the vapor deposited thermoplastic polymeric release coat layer dissolvable in an organic solvent;    the non-metal layers deposited to a film thickness of less than about 400 Angstroms;    the multi-layer vapor deposit adapted for separating into non-metal flakes by treatment with an organic solvent which dissolves the release coat layers and yields single layer non-metal flakes which are essentially free of the release coat material.    
     
     
         32 . Apparatus according to  claim 31  in which the release coat/non-metal layer combination is repeatedly deposited at least ten times to build up the vapor deposit.  
     
     
         33 . Apparatus according to  claim 31  in which the non-metal material comprises silicon monoxide, silicon dioxide or a polymeric material.  
     
     
         34 . Apparatus for making flakes comprising: 
 a vacuum deposition chamber containing a deposition surface;    a release coat source and a flake deposition source in the vacuum deposition chamber, each directed toward the deposition surface; and    a multi-layer vapor deposit which has been deposited on the deposition surface under vacuum in alternating layers comprising a vaporized polymeric release coat layer deposited from the release coat source and a vapor deposited layer of flake material deposited from the flake deposition source to build up in sequence said multi-layer vapor deposit of flake material layers separated by and deposited on corresponding intervening release coat layers;    the release coat layers comprising a thermoplastic polymeric material which was vaporized under vacuum to form a smooth continuous solvent soluble and dissolvable barrier layer and support surface on which each of the layers of flake material is formed;    the multi-layer vapor deposit adapted for separating into flakes by treatment with a solvent which dissolves the release coat layers and yields flakes with smooth, flat surfaces which are essentially free of the release coat material.    
     
     
         35 . Apparatus according to  claim 34  in which the release coat/flake layer combination is repeatedly deposited at least ten times to build up the vapor deposit.  
     
     
         36 . Apparatus according to  claim 34  in which the flake layer comprises a vapor-deposited material selected from the group consisting of metal in elemental form, an inorganic material, and a non-metal.  
     
     
         37 . Apparatus according to  claim 36  in which the non-metal comprises silicon monoxide, silicon dioxide or a polymeric material, and the inorganic material is selected from the group consisting of magnesium fluoride, silicon monoxide, silicon dioxide, aluminum oxide, aluminum fluoride, indium tin oxide, titanium dioxide and zinc sulfide.  
     
     
         38 . Apparatus according to  claim 37  in which the release coat material is selected from styrene or acrylic polymers or blends thereof.  
     
     
         39 . Apparatus according to  claim 38  in which the flake layers are deposited to a film thickness of less than about 400 angstroms.  
     
     
         40 . A process for making flakes comprising: 
 providing a vacuum deposition chamber containing a deposition surface;    providing a release coat source and a flake deposition source in the vacuum deposition chamber, each directed toward the deposition surface;    depositing on the deposition surface under vacuum in alternating layers a vaporized polymeric release coat layer from the release coat source and a vapor deposited layer of flake material from the flake deposition source to build up in sequence a multi-layer vapor deposit of flake material layers separated by and deposited on corresponding intervening release coat layers;    the release coat layers comprising a resinous material which was vaporized under vacuum to form a smooth continuous solvent soluble and dissolvable barrier layer and support surface on which each of the layers of flake material is formed, said resinous release coat material comprising a monomer or polymer which is lightly cross-linked or polymerized by chain extension and is organic solvent soluble or dissolvable sufficient to separate from the layers of flake material when treated with an organic solvent; and    removing the multi-layer vapor deposit from the vacuum chamber and separating it into flakes by treatment with a solvent which dissolves the release coat layers and yields flakes with smooth, flat surfaces which are essentially free of the release coat material.    
     
     
         41 . The process according to  claim 40  in which the release coat/flake layer combination is repeatedly deposited at least ten times to build up the vapor deposit.  
     
     
         42 . The process according to  claim 40  in which the flake layer comprises a vapor-deposited material selected from the group consisting of metal in elemental form, an inorganic material, and a non-metal.  
     
     
         43 . The process according to  claim 42  in which the non-metal comprises silicon monoxide, silicon dioxide ora polymeric material, and the inorganic material is selected from the group consisting of magnesium fluoride, silicon monoxide, silicon dioxide, aluminum oxide, aluminum fluoride, indium tin oxide, titanium dioxide and zinc sulfide.  
     
     
         44 . The process according to  claim 43  in which the release coat material is selected from styrene or acrylic polymers or blends thereof.