Classifications

• • 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
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/36—Layered products comprising a layer of synthetic resin comprising polyesters
• • 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
  • B32B15/00—Layered products comprising a layer of metal
  • 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
• • 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
  • B32B15/00—Layered products comprising a layer of metal
  • 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
  • B32B15/09—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 comprising polyesters
• • 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
  • B32B15/00—Layered products comprising a layer of metal
  • B32B15/18—Layered products comprising a layer of metal comprising iron or steel
• • 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
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
• • 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
  • 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
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/32—Phosphorus-containing compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/49—Phosphorus-containing compounds
  • C08K5/51—Phosphorus bound to oxygen
  • C08K5/52—Phosphorus bound to oxygen only
  • C08K5/521—Esters of phosphoric acids, e.g. of H3PO4
• • 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
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L83/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
  • C08L83/04—Polysiloxanes
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L91/00—Compositions of oils, fats or waxes; Compositions of derivatives thereof
  • C08L91/06—Waxes
• • 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
  • B32B2439/40—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
• • 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 Bisphenol A (“BPA”) free multi-layer film, such as a biaxially oriented polyester (BOPET) film, for lamination on metal sheets, which could be used for food containers. More particulary, 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.
• BPA Bisphenol A
• 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. [0006] The above sterilization temperatures are needed for short-term inactivation (within a few seconds) of spores of Bacillus or Clostridium. These spores can also be killed at slightly lower temperatures, but longer heat treatment periods may be applied in such cases to arrive at the same level of heat treatment.
• 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.
• these epoxy polymers may contain a residual amount of a chemical building block called BPA, which has faced much scrutiny from consumer advocacy groups. Under Proposition 65, California has proposed for the second time to list BPA as a cause of reproductive toxicity. Thus, there is a desire to eliminate BPA-based expoxy resins as protective coatings.
• Laminating polyester films to metal prior to forming the container parts is one solution for replacing containers lined with an epoxy coating.
• Biaxially oriented polyethylene terephthalate (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; (b) 0.1 - 2 wt.% of a silicone resin comprising a polydiemthylsiloxane resin; (c) optionally 0.001 to 0.09 wt.% of a wax component; and 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 film structure comprising at least an outer release layer A, further comprises 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. % of an amorphous copolyester resin or a polyester resin having a melting point of least 20 °C below that of the polyester resin P2; and (c) 0.1-15 wt.% of an antiblock comprising organic or inorganic particles.
• the polyester film further comprises a heat- sealable layer C having the same or substantially the same composition as that of the heat- sealable layer B.
• the polyester film further comprises a heat-sealable layer C having a different composition from that of the heat-sealable layer B.
• the polyester P2 comprises an aromatic polyester.
• 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 is essentially polybutylene terephthalate (PBT) resin.
• Another embodiment is related to a laminated metal sheet comprising a polyester film of the embodiments herein.
• the silicone resin has a kinematic viscosity ranging from 10-50 x 10 6 centistokes at room temperature.
• the patent or application file contains at least one drawing executed in color.
• 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 a jar 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.
• Figure 9 shows a plot of relative crystallinity values (counts per second) determined by XRD (X-ray diffraction test) measured at different locations of the film of Comparative Example 8 after steel lamination at the indicated lamination and post-bake temperature settings.
• Figure 10 is a plot showing relative crystallinity values (counts per second) determined by XRD (X-ray diffraction test) measured at different locations of the film of Example 7 after steel lamination at the indicated pre-heat and post-heat temperature settings.
• 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/phosphoric 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. as part of the continuous lamination process.
• 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 polyethylene terephthalate (PET) 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.
• PET polyethylene terephthalate
• 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.%.
• Release layer A can further contain a wax component for more robust release performance.
• wax component refers to a component containing a wax or wax-like material.
• Waxes are a diverse class of organic compounds that are hydrophobic, malleable solids near ambient temperatures. They include higher alkanes and lipids, typically with melting points above about 40 °C (104 °F), melting to give low viscosity liquids. Waxes are insoluble in water but soluble in organic, nonpolar solvents. Natural waxes of different types are produced by plants and animals and occur in petroleum (source: https://en.wikipedia.org/wikiAVax).
• a "wax-like material” refers to a mateial that has properties of a wax but is not a wax.
• the amount of wax component adeded is is 0.001 to 0.090 wt.%.
• waxes are mentioned in US patent 6,905,774, incorporated herein by reference in its entirety.
• examples of the wax compounds which can be used here are the esters of aliphatic carboxylic acid compounds and aliphatic alcohol compounds, and the amides of aliphatic carboxylic acid compounds and aliphatic amine compounds, and preferably the wax is composed of a compound in which the total number of carbons is 30 to 120, and more preferably 40 to 100.
• synthetic or natural waxes comprising aliphatic esters like stearyl stearate, carnauba wax, candelilla wax, rice wax, pentaerythritol full ester, behenyl behenate, palmityl myristate and stearyl triglyceride, are preferred from the point of view of compatibility with the polyester.
• carnauba wax is preferred and especially refined carnauba wax.
• the term "robust perfomance" relates in particular to commercial metal lamination installations, where, due to process limitations, there is a variability across the web width, in terms of heat history, and, correspondingly, in terms of the final morphology of the laminated film.
• Such an installation is described in US patent 9,358,766.
• a commercial metal lamination line has two key factors affecting such morphology: one is the preheat temperature of the steel sheet just prior to coming in contact with the polyester film at the point of lamination (a pair of nip rolls one or both of which are also heated). For biaxially-oriented PET-based film this temperature is between 320 ⁇ 430 °F, preferably 360 -430 °F.
• the second is the temperature setting at the post-heat station (for example an infrared (IR)-heated oven), which serves to stabilize the initial bond between the plastic film and the steel created during the lamination step.
• the post-heat station for example an infrared (IR)-heated oven
• this temperature is between 350-500 °F, preferably 420 - 460 °F.
• post-bake the variability in the morphology of the laminated polyester film is manifested for example by the crystallinity (determined for example by X-ray difraction— XRD) at different spots across the laminate width; that crystallinity is also affected by both the preheat temperature and the post-heat temperature.
• the amount of wax required for meat release is lower than that present in a film which uses solely wax for release properties (such as LumirrorTM grade FN8 polyester film from Toray Industries. That film is impregnated with carnauba wax compounded at a level in the range prescribed by US Patent 6,652,979 (0.1 - 2 wt.%) or US Patent 6,905,774 (0.1 - 5 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, based on overall film thickness.
• 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 are 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 substrate of the can).
• Core layer B may include 100 wt% PET resin ("base resin"). If there is no C layer, then layer B may also contain anti-block-containing 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. crystalline 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 trimethylene 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, and the like.
• PTT poly(trimethylene terephthalate)
• 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 or sodium
• 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 resin and 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.
• metal compound a metal-containing compound of which the metal element is at least one member selected from the group consisting of Na, Li and K
• a metal compound the metal element is at least one member selected from the group consisting of S
• 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 transesterification catalyst and confer electrostatic characteristics such as the resistivity of the polyester resin.
• 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.
• biaxially oriented PET film is stretched about 100%-400% in the MD and 100%-600% in the TD.
• the biaxially oriented film can be heat-set at temperatures 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 .
• PET Resin P4 PET Resin anti-block masterbatch type F18M, containing 2% silica particles of average size 2 ⁇ (Fuji Silysia 310P) manufactured by Toray Plastics America (IV
• 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 resin.
• Low-melting point polyester resin P5 Polybutylene terephthalate (PBT) resin Crastin® FG6130 from E.I. DuPont De Nemours, having melting point 223 °C.
• PBT Polybutylene terephthalate
• the Carnauba wax component was added in the form of of of a masterbatch ("Wax MB") containing 2 wt.% wax, available under the trade name W030 from Toray Industries.
• 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 polymer melt streams flow through a die to form the laminate coextruded structure and is 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 width 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 (TFS) with a thickness of 0.0075" was preheated to 400 F (except where otherwise indicated).
• the steel and film were passed through a set of nipped rolls forming the initial bond of film to steel.
• the film and steel laminate structure were then passed through a secondary heating operation ("post-bake") at 460 F for 20 seconds, then cooled to room temperature.
• 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.
• 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.
• Film crystallinity were measured by X-Ray Diffraction method on a PANalytical X'Pert PRO system with Cu X-Ray source (40 kV, 20 mA) and a Xe gas proportional type detector.
• the incident X-ray beam is directed at the sample over a spectrum of angles and the intensity of the diffracted beam is measured at each angle as the count of the number of pulses per second.
• a measure of crystallinity specified as "Counts per Second" (cps) is reported based on the count of the number of pulses at peak intensity of the diffracted beam.
• 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:
• BOPET film was cut to sheet sizes large enough to fit in the jar and hold the food mix as decribed in the following steps • A sheet of film was placed on top of the jar can (meat release side up) and then the metal disk on top of it, with the food contact side facing upward
• test jars were placed on top of the plate and retort (pressure cooker) cover was applied securely.
• the retort was placed on a hot plate set to medium-high and retorted for 90 minutes 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 Microsoft PaintTM software. The number of grid squares 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).
• the acceptance rating, based on percentage, is as follows: (based on US pat. 6,905,774)
• testing was conducted by a qualified laboratory (named at the time of testing 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) under the following specifications for each of the conditions of use, and then determining the levels of choloroform-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.
• the extrusion conditions were the same as those listed in Comparative Example 5.
• the silicone masterbatch content in layer A was 0.5%, corresponding to silicone content 0.25 wt.%.
• 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 difference that the major polyester resin (base resin) was P2 (standard 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.
• base resin P2 (standard film-grade PET)
• PET resin alkali metal phosphate and phosphoric acid (such as PI)
• alkali metal phosphate and phosphoric acid such as PI
• Example 2a was repeated with the only 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.
• base resin base resin
• PET resin standar film-grade PET
• alkali metal phosphate and phosphoric acid such as PI
• 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 , 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.
• Tables 1 and 2 respectively.
• this Comparative Example comprised 2.0 wt% of silicone masterbatch in layer A, corresponding to silicone content 1 wt.%
• Table 4 The results of the food release test are listed in Table 4.
• Comparative Example 5 was repeated with the only difference being that the silicone masterbatch content in layer A was 4.0 wt%, 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 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 being considered suitable for internal container liner with food release properties, namely LumirrorTM grade FN 8 polyester film from Toray Industries. That film is impregnated with carnauba wax compounded at a level in the range prescribed by US Patent 6,652,979 (0.1 - 2 wt.%) or US Patent 6,905,774 (0.1 - 5 wt.%).
• Blend Composition (in wt%) of Layer C (examples not shown have only A and B C. Ex. 4 - 85% - - 15% 1.5
• 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:
• Comparative Example 8 (This is a Comparative Example ⁇ no wax ⁇ for the wax addition Example 7 that follows).
• Two-layer biaxially oriented polyester film, having layer composition as shown in Tables 1 and 2 was produced on a film production line consisting of a main extruder and a subextruder , casting drum, machine-direction stretching and transverse direction stretching (stenter oven). Stretch ratios were 4.8 in the MD direction and 3.7 in the TD direction. Maximum stretch temperaures were 121 °C in the MD and 104 °C in the TD. Following TD orientation, there was a 5% relaxation section at 233 °C. Final line speed was 288 m/min.
• the final film product was subsequently laminated on a sheet of tin-free metal sheet on the B-layer side underthe following conditions: lamination temperature 370-380 °F (188-193 °C); post bake 430-440 °F ( 2221-227 °C).
• Food release was tested according to the procedure described earlier at six different locations across the laminate width, depending on the position in the lamination machine: drive side (DS), midde distance between drive side and center (“DSC”), two points at the center on either side of the true center, i.e. center left (“C-L”) and center-right (“C-R”), midde distance between tending side and center (“TSC”), and tending side (“TS”).
• the score expressed as percentage of total area occupied by food remains is listed in Table 4.
• Example 7 Comp. Example 8 was repeated with the exception that 4.5 wt.% wax masterbatch (resulting in 0.9 wt.% wax) was added in layer A, as shown on Table 1.
• the PBT level (resin "P5") in layer B was increased to 35 wt% for reasons unrelated with the scope of this invention and should not affect the release results.
• Process chamges vs. Example 7 were a lower MD ratio (4.5) and small adjustments in MD and TD max. temperatures ( 116 °C and 123 °C respectively); also TD relaxation temperature was 216 °C.
• the final film product was subsequently laminated on a sheet of tin-free metal sheet on the B-layer side at the following conditions: lamination temperature 370-380 (188-193 °C) post bake 430-440 °F ( 2221-227 °C).
• Food release was tested according to the procedure described earlier at five different locations across the laminate width, depending on the position in the lamination machine: drive side (DS), midde distance between drive side and center (“DSC”), center, midde distance between tending side and center (“TSC”), and tending side (“TS”).
• the score, expressed as percentage of total area occupied by food remains is listed in Table 4.
• Table 4 Results of food release testing at different locations across the lamination width for Example 7 and Comp. Example 8.
• Example 7 and Comparative Example 8 The results of the food release tests on Example 7 and Comparative Example 8, along with the crystallinity testing support the fact that the addition of wax, whereas not improving crystallization, it helps nevertheless to mitigate the effect of loss of crystallinity on food release properties. This is evident, for example, by the food release score around the center (where crystallinity almost vanishes in both Examples) which is much better for the wax-containing sample (Example 7) vs. the control (Comp. Example 8). Overall, these Examples demonstrate that wax addition to the original design (food-contact skin A comprising a polyester using an alkali metal phosphate in the catalyst package and a silicone), which may fall short under certain laminatin circumstances, adds robustness to the meat release properties.

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