Classifications

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  • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
  • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
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  • B32B27/28—Layered products comprising a layer of synthetic resin comprising synthetic resins not wholly covered by any one of the sub-groups B32B27/30 - B32B27/42
  • B32B27/283—Layered products comprising a layer of synthetic resin comprising synthetic resins not wholly covered by any one of the sub-groups B32B27/30 - B32B27/42 comprising polysiloxanes
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
  • C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
  • C08G63/16—Dicarboxylic acids and dihydroxy compounds
  • C08G63/18—Dicarboxylic acids and dihydroxy compounds the acids or hydroxy compounds containing carbocyclic rings
  • C08G63/181—Acids containing aromatic rings
  • C08G63/183—Terephthalic acids
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  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/18—Manufacture of films or sheets
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L67/00—Compositions of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Compositions of derivatives of such polymers
  • C08L67/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
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  • B32B2307/514—Oriented
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• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B32B2439/00—Containers; Receptacles
  • B32B2439/40—Closed containers
  • B32B2439/66—Cans, tins
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2439/00—Containers; Receptacles
  • B32B2439/70—Food packaging
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
  • C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds

Definitions

• This invention relates to a butylene terephthalate-containing multi-layer film, such as a biaxially oriented polyester (BOPET) film, preferably free of Bisphenol A, for lamination on metal sheets, which could be used for food containers. More particulalry, the multi-layer film has an outer release layer, which aids in the release of food, such as a high protein food source, when food is cooked and sterilized in direct contact with the outer release layer.
• BOPET biaxially oriented polyester
• Clostridium is more heat resistant than Bacillus. Temperatures of 110°C will kill most Bacillus spores within a short time. In the case of Clostridium temperatures of up to 121°C are needed to kill the spores within a relatively short time.
• Meat products suitable for canning Practically all processed meat products which require heat treatment during preparation for consumption are suitable for heat preservation. Meat products which do not receive any form of heat treatment before being consumed, such as dried meat, raw hams or dry sausages, are naturally not suitable for canning as they are preserved by low pH and/or low water activity.
• the following groups of meat products are frequently manufactured as canned products: cooked hams or pork shoulders; sausages with brine of the frankfurter type; sausage mix of the bologna or liver sausage type; meat preparations such as corned beef, chopped pork; and ready-to-eat dishes with meat ingredients such as beef in gravy, chicken with rice soups with meat ingredients such as chicken soup or oxtail soup.
• Metal food and beverage containers e.g., cans
• a coating on the interior surface is essential to prevent corrosion of the container and contamination of food and beverages with dissolved metals.
• the coating helps to prevent canned foods from becoming tainted or spoiled by bacterial contamination.
• the major types of interior coatings for food containers are made from epoxy resins, which have achieved wide acceptance for use as protective coatings because of their exceptional combination of toughness, adhesion, formability and chemical resistance. Such coatings are essentially inert and have been used for over 40 years. In addition to protecting contents from spoilage, these coatings make it possible for food products to maintain their quality and taste, while extending shelf life.
• Laminating polyester films to metal prior to forming the container parts is one solution for replacing containers lined with an epoxy coating.
• Biaxially oriented polyester (BOPET) films are used for multiple applications such as food packaging, decorative, and labels for example.
• An embodiment herein relates to a polyester film comprising at least one layer comprising: (a) 0.1-99.9 wt.% of a polyester resin PI comprising an alkali metal phosphate in an amount of 1.3 mol/ton of the polyester resin PI to 3.0 mol/ton of the polyester resin PI, and phosphoric acid in an amount of from 0.4 to 1.5 times by mole that of the alkali metal phosphate; and (b) 0.1 - 2 wt.% of a silicone resin comprising a polydiemthylsiloxane resin; wherein the polyester film is free of Bisphenol A.
• the polyester resin PI comprises an aromatic polyester.
• the aromatic polyester comprises at least 50 wt.% ethylene terephthalate as a constituent component of the aromatic polyester.
• the at least one layer comprises an outer release layer having a food area coverage of about 10% or less as measured according to Food Release Test.
• the at least one layer comprises an outer release layer, further comprising a heat-sealable layer B comprising (a) 0.1-100 wt.% of a polyester resin P2, wherein the polyester resin P2 is crystallizable and different from the polyester resin PI; (b) 0.1-100 wt.
• the polyester film further comprises a heat-sealable layer C having a same or substantially a same composition as that of the heat-sealable layer B. In one embodiment, the polyester film further comprises a heat-sealable layer C having a different composition from that of the heat-sealable layer B. In one embodiment, the polyester P2 comprises an aromatic polyester. In one embodiment, the polyester resin P2 comprises at least 50 wt.% ethylene terephthalate as a constituent component of the polyester resin P2.
• component (b) of the polyester resin having a melting point of at least 20 °C below that of polyester resin P2 comprises polybutylene terephthalate (PBT) resin, preferably, essentially polybutylene terephthalate (PBT) resin.
• the silicone resin has a kinematic viscosity ranging from 10-50 x 10 6 centistokes at room temperature.
• Fig. 1 shows pictures of the different ingredients used in preparing the food mix for Food Release Test.
• Fig. 2 shows pictures of BOPET laminated metal disks and of a non- laminated BOPET film.
• FIG. 3 shows pictures of inserting of the food mix into ajar that is sealed with cap having a BOPET laminated metal disk, where the BOPET film contacts the food mix.
• FIG. 4 shows pictures of multiple sealed jars containing the food mix in a pressure cooker, and the pressure cooker on a heated stove.
• Fig. 5 shows pictures showing removal of the BOPET laminated metal disk from the cooked food mix.
• Fig. 6 shows pictures of BOPET laminated metal disks demonstrating good and bad release of the cooked food mix from the BOPET film surface of the BOPET laminated metal disks.
• Fig. 7 shows pictures of a BOPET laminated metal disk ("Test Sample") after the food release test with a grid overlaid on the BOPET laminated metal disk to calculate the percentage of food area coverage where the cooked food mix remains stuck to the BOPET film.
• Fig. 8 shows a plot of percentage of food area coverage where the cooked food mix remains stuck to the BOPET film as a function of weight percent of the ultra high molecular weight silicone.
• Embodiments herein relate to a polyester film, namely a BOPET film, which has superior heat resistance to be able to withstand the temperatures associated with retort sterilization temperatures and barrier properties to provide corrosion resistance to a metal container by a food product.
• the BOPET film is capable of being laminated and formed to metal plates for the container forming process. Furthermore, the BOPET film is capable of providing a sufficient release surface to enable high protein food (meat products) to be easily removed from the container after high heat sterilization.
• the inventors have found that the release action imparted by incorporating silicone comprising ultra-high-molecular weight siloxane is greatly enhanced when using a polyester resin carrier formulated with an alkali metal phosphate and phosphoric acid during polymerization.
• the original purpose of the alkali metal phosphate/phosphoirc acid package was to improve hydrolysis resistance and the added benefit of the enhancement of silicone's release action was a surpising finding.
• the BOPET film may comprise one or more layers, preferably at least 2 layers.
• a multilayered BOPET film may include one or more of each of: a container- side or inside layer (i.e., heat seal or metal bonding layer), a food or outside layer, a food release layer.
• a container- side or inside layer i.e., heat seal or metal bonding layer
• a food or outside layer i.e., heat seal or metal bonding layer
• a food release layer i.e., a food or outside layer
• core layers between the layer bonded to the metal surface and the food side layer that is in direct contact with the food stored inside the container.
• the film which can be laminated to a metal plate for canning which is typically made of tin-free steel (TFS), electro tin plated steel (ETP), or aluminum, said film characterized by a dimensional change of not more than 2.0% after a heat treatment of 210°C.
• the films disclosed herein include two-layer or three-layer coextruded and biaxially drawn structures.
• the outer release layer and an optional lower “skin” layer are generally thinner than the core “main” layer.
• the outer release layer (thereafter referred to as “skin A”), typically contains an ultra high molecular weight silicone (based on siloxane) resin, that has been pre-blended with a copolyester elastomer resin to form a "masterbatch,” which is then added at low levels in the outer release layer during coextrusion.
• UHMW PDMS ultra high molecular weight silicone
• PDMS polydiemthylsiloxane
• kinematic viscosities ranging from 10-50 x 10 6 centistokes at room temperature.
• an advantage of UHMW PDMS is that it forms stable droplet domains in various thermoplastic carriers as pellets, so as to allow easy addition of the additive directly to the thermoplastic during processing.
• Another advantage of UHMW PDMS is that it does not bleed-out from the BOPET while at the same time migrates to the surface of the BOPET film, thereby providing desirable release charatceristics.
• the typical UHMW silicone concentration in the masterbatch is 50 wt. %.
• Masterbatch addition levels in the outer release layer range between 0.2 and 4 wt.%, resulting in net siloxane content in the range 0.1 - 2%.
• the remaining components of the outer release layer are PET resin polyester resin composition comprising an alkali metal phosphate as a phosphorus compound in an amount of 1.3 mol/ton to 3.0 mol/ton, and phosphoric acid as another phosphorus compound in an amount of 0.4 to 1.5 times (by mole) that of the alkali metal phosphate, (major component), and optionally inorganic particles for anti-blocking purposes.
• Typical inorganic particle compositions in this case is silica (silicon dioxide, S1O 2 ) in sizes ranging from sub- micron up to a few microns.
• the silica particles are typically added during coextrusion in the form of a concentrate PET chip ("silica masterchip") made by adding silica in the polymerization.
• Typical silica content in the silica masterchip is 1 -3 wt.%; typical addition level of the silica masterchip in the outer release layer is 1 - 15 wt%, resulting in net silica content around 0.1 - 3 wt.%.
• layer “B” for the core layer
• skin layer “C” for the skin layer lying on the opposite side versus the A skin layer.
• Thickness distribution ranges between 5 - 30%, 40 - 95%, and 0 - 30 % for layers A, B, and C respectively.
• Typical total film thickness after biaxial stretching is 10 - 25 microns, preferably 12 microns - 23 microns.
• the two-layer or three-layer film structure is laminated onto a metal sheet (steel or aluminum) which is then formed into a container. Both sides of the metal sheet may be laminated with plastic film but the films of this invention intended for lamination on the metal sheet side that is intended to become the inside surface of the container and in such a way that the outer release layer containing the silicone is the food-contact layer (i.e. the layer away from the metal).
• Core layer B may include 100% PET resin ("base resin"). If there is no C layer, then layer B may also contain anti-block masterbatches or low-melting- temperature copolyesters, described below in more detail for optional layer C.
• Optional skin layer C can be a lower-temperature-melting (vs. PET) or amorphous polyester copolymer or a blend of PET base resin with a lower melting (or amorphous) polyester copolymer.
• a lower-melting polyester are resins comprising butylene terephthalate repeat units such as poly(butylene terephthalate) (“PBT”) resin and copolymers thereof with other dicarboxylic acids or diols, such as isophthalic acid, naphthalene dicarboxylic acid, azelaic acid, sebacic acid, adipic acid, ethylene glycol, 1,3 -propanediol, 1-2 propanediol, neopentyl glycol, 1,4-cyclohexyldimethanol, and the like.
• PBT poly(butylene terephthalate)
• PBT polybutylene terephthalate
• polyesters comprising trimetyhyelne terephthalate repeat units such as poly(trimethylene terephthalate) PTT resins and copolymers thereof with other dicarboxylic acids or diols such as isophthalic acid, naphthalene dicarboxylic acid, azelaic acid, sebacic acid, adipic acid, ethylene glycol, 1,4-butanediol, 1-2 propanediol, neopentyl glycol, 1,4-cyclohexyldimethanol, abd the like.
• trimetyhyelne terephthalate repeat units such as poly(trimethylene terephthalate) PTT resins and copolymers thereof with other dicarboxylic acids or diols such as isophthalic acid, naphthalene dicarboxylic acid, azelaic acid, sebacic acid, adipic acid, ethylene glycol, 1,4-butaned
• PTT polytrimethylene terephthalate
• Sorona DuPont
• Corterra Shell
• Ecoriex SK Chemicals
• the purpose of adding the lower melting or amorphous polyester copolymer in that layer is to facilitate easier adhesion to metal during thermal lamination.
• the addition of such a copolymer is not necessary for making the metal contact layer heat-sealable, as the temperature of lamination and subsequent oven treatment can be adjusted to a value that makes the metal-contact side tacky enough to bond to the metal.
• PET polyester has a melting point peak around 250 °C
• melting initiation occurs at around 205 °C (400 F) , which is consistent with lamination temperature conditions and facilitates initial bonding at the pressure of the lamination nip rolls, which is further strengthened by oven treatment of the laminated structure at around 460 °F.
• the resin in layer A is a polyester resin, "PI", comprising a buffer soluble in ethylene glycol, and containing a substance exhibiting ion dissociation.
• a buffer agent is preferably an alkali metal salt, e.g., salts of phthalic acid, citric acid, carbonic acid, lactic acid, tartaric acid, phosphoric acid, phosphorous acid, hypophosphorous acid; alkali metal salt of polyacrylic acid compound or the like.
• the alkali metal is potassium orsodium, therefore specific alkali metal salt examples such as sodium dihydrogen hydroxycitrate, potassium citrate, potassium hydrogen hydroxycitrate, sodium carbonate, sodium tartrate, potassium tartrate, sodium lactate, sodium carbonate, sodium hydrogen phosphate, potassium hydrogen phosphate, potassium phosphate, sodium dihydrogen phosphate, sodium hypophosphite, sodium hypochlorite, sodium polyacrylate, etc. can be cited.
• PI is a polyester resin composition
• an alkali metal phosphate as a first phosphorus compound in an amount of 1.3 mol/ton to 3.0 mol/ton of polyester resin, and phosphoric acid as a second phosphorus compound in an amount of 0.4 to 1.5 times (by mole) that of the alkali metal phosphate.
• its acid component contains a dicarboxylic acid component in a molar amount of 95% or more.
• a terephthalic acid component is preferred in view of the mechanical characteristics.
• the glycol component contains a straight-chain alkylene glycol having 2 to 4 carbon atoms in an amount of 95% by mole or more.
• ethylene glycol which has two carbon atoms, is preferred from the point of view of moldability and crystallization of the polyester resin.
• additional polyester raw materials e.g. diacids such as isophthalic acid, naphthalene dicarboxylic acid or diols such as 1,4- cyclohexyldimethanol, diethylene glycol, 1,3-prolylene glycol, 1,4-butylene glycol, may be present in the polyester composition polymerization mix as copolymerized components at levels up to 5 mole% of the total diacid or diol.
• the polyester resin composition contains an alkali metal phosphate in an amount of 1.3 mol/ton to 3.0 mol/ton of polyester resin. It is preferably 1.5 mol/ton to 2.0 moles/ton of polyester resin.
• the content of the alkali metal phosphate is less than 1.3 mol/ton of polyester resin, long term hydrolysis resistance may be insufficient.
• the alkali metal phosphate is contained in an amount exceeding 3.0 mol/ton of polyester resin, this is likely to cause phase separation (precipitation) of the alkali metal phosphate.
• alkali metal phosphate examples include sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, lithium dihydrogen phosphate, dilithium hydrogen phosphate, trilithium phosphate.
• alkali metal phosphate are alkali metal dihydrogen phosphates and alkali metal phosphates.
• Alkali metal phosphates in which an alkali metal is Na or K are preferred from the viewpoint of long-term hydrolysis resistance.
• Particularly preferred examples of alkali metal phosphate are sodium dihydrogen phosphate and potassium dihydrogen phosphate.
• the phosphoric acid is 0.4 to 1.5 times that of the alkali metal phosphate in a molar ratio. It is preferably from 0.8 to 1.4 times. If it is smaller than 0.4 times, long term hydrolysis resistance may deteriorate.
• the polyester resin composition contains an alkali metal element in an amount of 1.3 mol/ton of polyester resin to 9.0 mol/ton of polyester resin and a phosphorus in an amount of 1.8 mol/ton of polyester resin to 7.5 mol/ton of polyester resin.
• the polyester resin composition preferably contains an alkali metal element in an amount of 1.3 mol/ton of polyester resin to 6.0 mol/ton of polyester resinand a phosphorus in an amount of 1.8 mol/ton of polyester resin to 7.5 mol/ton of polyester resin.
• the total content of phosphorus compounds contained in the polyester resin composition of the present composition is from 30 PPM to 150 PPM by weight of the polyester resin composition, in terms of the amount of phosphorus element. It is more preferred that this content is 60 PPM to 150 PPM.
• the composition of polyester resin P 1 comprises a metal- containing compound ("metal compound") of which the metal element is at least one member selected from the group consisting of Na, Li and K, a metal compound of which the metal element is at least one member selected from the group consisting of Mg, Ca,Mn and Co, and a metal compound, the metal element is at least one member selected from the group consisting of Sb, Ti and Ge, and the total amount of these metal elements is adjusted to 30 PPM or more and 500 PPM or less based on the entire of the polyester resin composition. By adjusting the total amount of metal elements within this range, the amount of terminal groups COOH can be reduced in the polyester resin toimprove its heat resistance. It is more preferred that this content is 40 PPM to 300 PPM.
• the elements Na, Li and Ka are alkali metal elements.
• the elements Mg, Ca, Mn and Co, which are divalent metal elements, are
• Sb, Ti and GE are metal members having an ability to catalyze the polymerization of the polyester resin and serve as polymerization catalyst.
• the multi-layer PET film is biaxially oriented prior to laminating it to the metal substrate.
• a raw material PET resin is supplied in solid form to a melt processing device, preferably a continuous screw extruder.
• the heating of the melt processor is controlled to maintain the PET resin above its melting point but below polymer degradation temperature.
• PET molten resin is extruded from an appropriately shaped die to form a thin, flat ribbon of polymer melt.
• the polymer ribbon is quenched in air and or on a chilled roll to form a solid, self-supporting film.
• the film is taken up by sets of rollers turning at different rotation speeds that stretch the film in the direction of continuous forward motion, referred to as the machine direction ("MD").
• MD machine direction
• the stretching can be accompanied by heating of the film to establish crystal orientation in the MD.
• the mono-directionally oriented film is clamped at its opposite edges in and stretched in the transverse machine direction ("TD") laterally perpendicular to the MD in a tenter oven.
• the tenter oven is heated to temperatures operative to establish crystal orientation in the TD thus forming a biaxially oriented PET film.
• the biaxially oriented film can be heat set at temperatures can be preferably between about 300°F and about 490°F, more preferably about 350°F to about 460 °F.
• Resin materials for films mentioned in the examples were as follows:
• PET Resin PI PET resin comprising alkali metal phosphate and phosphoric acid
• PET Resin P2 ordinary film-grade PET resin, not comprising alkali metal phosphate
• PET Resin P3 Bottle-grade PET resin 8712A from Invista with an IV of 0.75 .
• Silicone Resin Masterbatch Dow Corning MB50-010 containing 50% of an ultra-high molecular weight polymerized siloxane ("Silicone Resin") and 50% of a polyester elastomer carrier.
• Low-melting point polyester resin P5 Polybutylene terephthalate (PBT) resin Crastin FG6130 from E.I. DuPont De Nemours, having melting point 223 °C. Test Methods
• IV Intrinsic viscosity of the film and resin were tested according to ASTM D 4603. This test method is for the IV determination of poly(ethylene terephthalate) (PET) soluble at 0.50 % concentration in a 60/40 ratio of phenol / 1, 1,2,2- tetrachloroethane solution by means of a glass capillary viscometer.
• PET poly(ethylene terephthalate)
• melt point of copolyester resin is measured using a TA Instruments Differential Scanning Calorimeter model 2920. A 0.007 g resin sample is tested, substantially in accordance to ASTM D3418-03. The preliminary thermal cycle is not used, consistent with Note 6 of the ASTM Standard. The sample is then heated up to 300 °C temperature at a rate of 10 °C/minute, while heat flow and temperature data are recorded. The melting point is reported as the temperature at the endothermic peak.
• the Multi-layer coextruded BOPET film was made using a 1.5m-wide pilot- line sequential orientation process
• the coextruded film is cast onto a chill drum using an electrostatic pinner, oriented in the machine direction through a series of heated and differentially sped rolls, followed by transverse direction stretching in a tenter oven.
• the multilayer coextruded laminate sheet is coextruded by means of a main extruder for melting and conveying the core blend to the die and by means of one or two sub extruders for melting and conveying the skin blends to the die.
• Extrusion through the main extruder takes place at processing temperatures of ca. 270° to 285°C.
• Extrusion through the Sub Extruders takes place at processing temperatures of ca. 270°C to 280°C.
• Both the Main and the Sub streams flow through a die to form the laminate coextruded structure and cast onto a cooling drum whose surface temperature is controlled at about 21 °C to solidify the non-oriented laminate sheet at a casting speed of about 9 mpm.
• the non-oriented laminate sheet is stretched in the longitudinal direction at about 75°C to 85°C at a stretching ratio of about 3 times the original length and the resulting stretched sheet is annealed at about 70°C to obtain a uniaxially oriented laminate sheet.
• the uniaxially oriented laminate sheet is introduced into a tenter at a line speed of ca. 27 mpm and preliminarily heated at 80°C, and stretched in the transverse direction at about 90°C at a stretching ratio of about 4 times the original length and then heat-set or annealed at about 210°C to reduce internal stresses due to the orientation and minimize shrinkage and give a relatively thermally stable biaxially oriented sheet.
• Tin-Free Steel with a thickness of 0.0075" was preheated to 400 F (except where otherwise indicated).
• the steel and film are passed through a set of nipped rolls forming the initial bond of film to steel.
• the film and steel laminate structure is then passed through a secondary heating operation ("post-bake") at 460 F for 20 seconds, then cooled to room temperature.
• post-bake secondary heating operation
• the film side laminated to steel was the side opposite that of the silicone- comprising side (food contact side; side A in the examples), i.e. the lamination side was side B or C in the examples.
• the food area coverage on the food contact side of the polyester film laminated to steel is measured according to a food release test, referred herein as "Food Release Test.”
• Food Release Test The procedure of the Food Release Test is descibed below.
• a food mixture of chicken egg/ground beef/flour at a ratio of 3/2/1 was prepared, as follows:
• the retort was placed on a hot plate set to medium-high and retorted for 90 min after the pressure valve started oscillating (inside pressure 14.7 psig, temperature around 260 °F).
• Retort process means a procedure in which the inside or outside of a metal container with a wall composed of a composite of a metal substrate having a polymer film laminated onto the inside, the outside or both sides of the substrate is treated with live steam or super heated water for a period of time.
• Live steam means that steam directly contacts the surface of the container.
• the steam is usually superheated, i.e., above the boiling point of water.
• a nominal retort process calls for exposure to steam at temperature of 260°F for 90 minutes.
• the temperature and duration of exposure of the retort process can vary to provide an approximately equivalent sterilization and food pasteurization effectiveness. For example, the temperature might be higher for a shorter duration or lower for a longer duration.
• the release performance was rated by producing a photographic image of the test laminated disk after release and superposing a rectangular grid image using MS Paint software. The number of grid quares occupied by food remained adhering was then counted and expressed as percentage of the total number of grid squares. The lower the percentage the better the food release performance ( Figure 7)
• testing was conducted by a qualified laboratory (named at the time of testing as follows: National Food Lab, Livermore, CA— renamed and relocated at the time of filing as follows: Covance Laboratories, Madison, WI) ) under the conditions prescribed by Code of Federal Regulations, Title 21CFR177.1630, conditions (f), (g), (h).
• the testing consists of exposing the food-contact surface (layer A in this case) unde the following specifications for each of the conditions of use, and then determining the levels of cholorform-soluble extractives present in the exposure medium:
• 3-layer BOPET film structures were produced by melt extrusion from three extruders supplying the resin blends corresponding to layers A, B, and C as shown on Tables 1, 2, and 3 respectively.
• the silicone masterbatch content in layer A was 0.5%, corresponding to silicone content 0.25 wt.%.
• the differences between compositions 1 and la were with respect to the antiblock masterbatch (P4) content in layer A and with respect to the amorphous copolyester (CoPl) content in layer C (and the resulting differences in the content of the majority resin balance PI and P2 in layers A and C repsectively).
• the cast film was formed into a biaxially oriented film by stretching 3 times along the machine direction at a temperature of 82 °C and subsequently stretching 4 times along the transverse direction through an oven held at a temperature 85-93 °C in the stretch zone and 204 °C in the anneal zone and collected in roll form by means of a rotating winder at a linear speed of 32 m/min.
• Examples 1 and la were repeated with the only major difference being that the silicone masterbatch content in layer A was 1.0%, corresponding to silicone content 0.5 wt.%. using an A/B/C three-layer structure as shown in Tables 1,2,3 respectively.
• the Results of the food release test are listed in Table 4.
• Example 1 was repeated with the only major difference being that the silicone masterbatch content in layer A was 2.0%, corresponding to silicone content 1.0 wt.%. making an A/B/C three-layer structure as shown in Tables 1, 2, 3 respectively.
• the Results of the food release test are listed in Table 4.
• a 2-layer BOPET film structures was produced by melt extrusion from two extruders supplying the resin blends corresponding to layers A and B as shown in Tables 1, 2, respectively.
• Layer B contains 15% PBT.
• a 2-layer BOPET film structure was produced by melt extrusion through two extruders supplying the resin blends corresponding to layers A and B and then formed into a biaxially oriented film by casting on a cooling drum held at 21 °C and rotating at a linear speed of , stretching 3 times along the machine direction at a temperature of 82 °C, and subsequently stretching 4 times along the transverse direction through an oven held at a temperature 85-93 °C in the stretch zone and 204 °C in the anneal zone, and collected in roll form by means of a rotating winder at a linear speed of 32 m/min.
• the final A/B biaxially -oriented two-layer structure is shown in Tables 1 and 2 respectively.
• the silicone masterbatch content in layer A was 0.5%, corresponding to silicone
• Example 4 was repeated with the only difference being that the weight ratio of PBT in layer B was increased to 30%.
• Example 5 was repeated with the only difference being that the weight ratio of PBT in layer B was increased to 45%.
• Example la was repeated with the only major difference being that no silicone masterbatch was added in layer A, making an A/B/C three-layer structure as shown in Tables 1,2,3 respectively.
• the Results of the food release test are listed in Table 4
• Example la was repeated with the only major difference that the major polyester resin (base resin) ws P2 (standar film-grade PET) and no PET resin comprising alkali metal phosphate and phosphoric acid (such as PI) was used, making an A/B/C three-layer structure as shown in Tables 1,2,3 respectively.
• this comparative example comprised 0.5% of silicone masterbatch
• Table 4 The results of the food release test are listed in Table 4
• Example 2a was repeated with the only major difference being that the major polyester resin (base resin) ws P2 (standar film-grade PET) and no PET resin comprising alkali metal phosphate and phosphoric acid (such as PI) was used, making an A/B/C three-layer structure as shown in Tables 1,2,3 respectively.
• this comparative example comprised 1.0% of silicone masterbatch in layer A
• the results of the food release test are listed in Table 4
• Example 4 The extrusion conditions were the same as those listed in Example 4.
• the final A/B biaxially-oriented two-layer structure is shown in Tables 1 and 2 respectively.
• this comparative example comprised 2.0% of silicone masterbatch in layer A, corresponding to silicone content 1 wt.%
• the results of the food release test are listed in Table 4
• Comparative Example 6 Comparative Example 6 was repeated with the only major difference being that the silicone masterbatch content in layer A was 4.0%, corresponding to silicone content 2.0 wt.%. making an A/B two-layer structure as shown in Tables 1 and 2 respectively. The Results of the food release test are listed in Table 4
• Comparative Example 3 was repeated (0.5 wt.% silicone masterbatch in the A layer corresponding to 0.25 wt.% silicone) with the only major difference being that the major resin in layer A was P3, making an A/B/C three-layer structure as shown in Tables 1 and 2 respectively.
• the Results of the food release test are listed in Table 4
• the reference example is represented by a commercial film currently been considerd suitable for internal container liner with food release properties, namely Lumirror grade FN8 from Toray Industries. That film is impregnated with carnauba wax compound at a level in the range prescribed by US Patent 6,652,979 (0.1 - 2 wt.%) or US Patent 6,905,774 (000.1 - 5 wt.%).
• Table 2 Blend Com osition of La er B
• Table 3 Blend Com osition of La er C
• Figure 2 plots those results versus silicone content in the A layer in the following way:
• One data series groups the data (C. Ex. 1 and examples 1, la, 2, 2a, and 3) corresponding to films comprising resin PI as the major PET resin in layer A;
• another data series groups the data (C. Ex. 2, 4, 5, 6) comprising resin P2 as a major resin in layer A.
• a single data point plots the data for the film of comparative example 7 (comprising resin P3 and 0.25% silicone). It is evident that:

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