Title of Invention

A POLYMERIC COMPOSITION SUITABLE FOR MANUFACTURING HEAT SEALABLE FILMS OR SHEETS

Abstract

A polymeric composition suitable for manufacturing heat sealable films or sheets comprising, polyethylene terephthalate (PET) to the extent of about 80 % to 95 % by mass of the total composition; a polymer additive for lowering the melting point of the composition selected from Polyethylene Naphthalate (PEN), Polytrimethylene Naphthalate (PTN), in-situ formed Polyethylene Naphthalate (PEN) and in situ formed Polytrimethylene Naphthalate (PTN) to the extent of about 20 % to 5 % by mass of the total composition; a nucleating agent to the extent of about 200 to 1500 ppm by mass of the composition; a polycondensation catalyst to the extent of about 30 to 300 ppm by mass of the composition; a clear fast reheat (CFRH) additive to the extent of about 10 to 30 ppm by mass of the composition; a color toner to the extent of about 0.75 to 25 ppm by mass of the composition; and a heat stabilizer to the extent of about 20 to 55 ppm by mass of the composition.

Full Text

FORM - 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 PROVISIONAL Specification (See section 10 and rule 13) RESIN COMPOSITIONS FUTURA POLYESTERS LIMITED an Indian Company of Paragon Condominium, 3rd floor, Pandurang Budhkar Marg, Mumbai 400 013, Maharashtra, India THE FOLLOWING SPEC IFICATION DESCRIBES THE INVENTION. Field of Invention: The present invention relates to resin compositions. In particular, this invention relates to resin compositions for manufacturing heat sealable top layer film or sheet for sealing containers like thermoformed CPET trays used in food packaging Background: In packaging food materials oriented polyester films "OPET" as pouches or thermoformed dual ovenable trays made from "CPET" are nowadays very common. The use of such polyester containers needs a cover, lid or seal which can both seal the container to prevent leakage of the contents during storage and as well protect the contents from external atmosphere. The top layer or seal should be easily peeled without tear from the container. The lid or seal normally comprises a flexible composite polymeric film consisting of a base polymer layer and a sealable layer of another polymer or a coating layer of another polymer. A strong seal with easy peeling properties is required at both low, e.g ambient and high temperatures. Also the heat seal layer should be transparent, haze free and optically clear. However, heat sealing PET containers is extremely difficult in comparison with other plastic containers because of PET's high melting point of ~ 260°C and its reasonably fast crystallization rates at temperatures between 100 and 240°C. This makes the heat sealing process difficult and if forcibly sealed at high temperature the material will become brittle due to crystallization and polymer degradation. Thus it becomes important to inhibit crystallization of the polyester composition at the time of heat sealing in order to increase the strength of the heat seal. 2 Prior Art: Polyester resins for heat sealable films are known as early as from 1970s. US 4020141 describes the method of making heat-sealable, heat shrinkable, biaxially oriented polyester film wherein the polymer consisted primarily of PET with additional monomeric units selected from a second acid or a second glycol. EP 0035835 deals with polymer film composites with a primary layer comprising an oriented layer of a first linear polyester and a heat sealable secondary layer adherent to the primary layer which comprises essentially an amorphous second linear polyester. It also states that the preferred polyester resin is an amorphous copolyester resin comprising PET and PIA (polyethylene isophthalate) or hexahydroterephthalic acid based co polyester with a preferred composition of PET:PIA as 80:20. US 4765999 describes multilayer non oriented heat sealable films with a base substrate layer of PET or its co polymer and a heat sealable surface layer of a copolyester consisting of DEG or PETG. JP 63202429 describes a polyester shrink film with excellent heat sealing property. Here the polyester composition constituted PET as the major component and 3 -50 mole % of neopentyl glycol as the glycol modifier. JP 1165627 deals with a polyester sheet for heat sealing thermoformed objects and the polyester resin comprised PET with 1-15 parts by weight of a block co polyester of PBT and poly tetramethylene glycol and 2-20 parts by weight of PP resin. 3 EP 0379190 deals with a laminated polyester film with excellent heat sealing ability consisting of a base polyester layer and a heat sealing layer. The resin composition used in the heat-sealing layer comprises either a glygol modified polyester or a dicarboxylic acid modified polyester which includes acids like adipic acid, azelaic acid , isophthalic acid etc. It also gives data on sealing energy, antiblocking property etc. US 5484632 describes a non oriented heat sealing polyester film PET, EG and 7-15 mole % of CHDM, a glycol modifier. WO 9619333 discloses a polyester based film with a substrate layer and a coating layer containing a copolyester of aliphatic or aromatic dicarboxylic acid, which includes isophthalic acid, along with at least one polyalkylene glycol. The film is suitable for use as a lid for a container with strong heat sealing and easy peeling property. US 5721028 discloses a heat-sealed closure for polyester container. The closure composed of a laminate of a heat seal layer comprising mainly a copolyester resin modified with aliphatic or aromatic dicarboxylic acids or glycol modified co polyesters. US 5972445 discloses a multilayer polyester sheet with a base layer comprising a polyester resin and a sealing layer comprising a polyester resin with a Tg less than that of the base layer by at least 5°C. The sealing layer co polyesters are modified by NDC or IP A or DEG or CHDM or neopentyl glycol. 4 US 2002/0015835 describes sealable polyester film comprising modified co polyesters with NDC, cycloaliphatic or aromatic diols and/or dicarboxylic acids. US 6623821 discloses a packaging film comprising heat sealable polyester film comprising a homopolyner or copolymer of PET and coated with a solvent bases heat seal coating of an amorphous co polyester. The amorphous heat sealing copolyester has a composition consisiting of PET and other diacids like succinic acid, isophthalic acid etc. US 2005/0061708 describes a coextruded heat sealable and peelable polyester film having high peeling resistance. The film comprises a base layer and a heat sealable top layer. The polymer of the heat sealable layer has a melting point of US 2005/0249906 discloses a process for the production of coated heat sealable polymeric film. The heat sealable layer consists of a co polyester with repeat units of one or more aliphatic or aromatic dicarboxylic acids whose concentration ranges from 40 to 70 mole %. Objects of the Present Invention: An object of the present invention is to develop a polyester based resin which can be converted to a heat sealable film or sheet. Another object of the present invention is to develop a polyester based resin the composition of which comprises a co polyester. 5 Yet another object of the present invention is to ensure that the co polyester resin suitable for making heat sealable film or sheet has a Tg and melting point lower than the PET in the co polyester thereby facilitating the heat sealing of the film or sheet at sufficiently low temperature when compared to the melting point of PET. Another object of the present invention is to develop the heat sealable resin giving a film or sheet with sufficient seal strength at ambient and high temperatures to withstand storage during the shelf life of the container like an APET/CPET thermoformed tray followed by its heating in the oven. Yet another object of the present invention is to develop a resin for making heat sealable film or sheet which is easily peelable without tearing from the container. One more object of the present invention is to ensure that the co polyester resin in accordance with this invention gives an optically clear film or sheet with low or nil haze. Yet another object of the present invention is to develop a copolyester resin which will prevent or reduce crystallization tendency in the heat sealable film or sheet so that the film or sheet does not degrade and lose strength during heat sealing with time and temperature and also sagging of the film or sheet during the extrusion process is attenuated. Yet another object of the present invention is to add suitable additives which help in quick heat up while processing the resin to film or sheet and saves energy during extrusion. 6 The invention with the recipe and the process for making the copolyester resin suitable for the application of heat sealable film or sheet is described below in the example. Example: 184 kg of IPA (8 % on PET calculated on the basis of 2300 kg, which excludes the naphthalate comonomer, along with 80 kg of MEG are taken in the Esterification reactor. Appropriate quantities of PTA and EG for a 2300 kg of PET batch are made into a paste and fed to the Esterification reactor. In the present example 1803 kg of PTA and 919 kg of MEG are used for a PTA:MEG mole ratio of 1:1.07. 146.2 g of Cobalt Acetate powder, 3.45 g of Red Toner powder, 2.88 g of Blue Toner powder as Color improving additives and toners, 994 g of Germanium based catalyst as a suspension, and 460 g of Nyacol consisting of 30 % silica by weight in MEG as a suspension are added to the esterification reactor. Esterification is carried out between 245 and 265°C. After the completion of esterification 852 g of heat stabilizer i.e. triethylphosphono acetate (TEPA) followed by 165 g of orthophosphoric acid (OPA) are added to the esterifier. Prior to the transfer of the prepolymer formed to the poly reactor 27.6 g of tungsten based clear fast reheat (CFRH) additive is added and held for 5 minutes. The prepolymer with all the additives is transferred via a 20 micron filter to the polycondensation reactor or autoclave. 115 kg (5 weight % on 2300 kg) of amorphous PEN chips of intrinsic viscosity (I.V.) between 0.45 and 0.55 dL/g are added to the poly reactor and held for 10 minutes for temperature stabilization i.e 265°C. Polymerization is conducted between 265 and 284°C with a peak temperature of 288°C to achieve the required I.V. in the melt. After reaching the required I.V. the amorphous co polyester resin melt is extruded out as strands and cut under water and collected as amorphous chips. These amorphous chips are dried and precrystallized before subjecting to 7 solid state polymerization (SSP) for increasing the I.V. beyond ~ 0.55 obtained in the amorphous melt. Table 1 gives the details of the raw materials and additives for a typical batch. Table 2 gives the important properties of the amorphous and SSP chips of the co polyester resin. TABLE 1: Raw Materials and Additives for a 2415 kg Batch of Co Polyester Resin Additives are based on 2300 kg batch weight excluding the addition of PEN S.No. Raw Materials / Additives Quantity Unit ppm or % ;1. PTA 1803 kg ... . j. .__j. ._. { 2. MEG 919 kg 3. IPA 184 kg |8.0 wt. % on PET 4. PEN 115 kg 5.0 wt. % on PET 5. Sb203 catalyst 345 gi 150 ppm as Sb 6. Cobalt Acetate Powder 146.2 g 15 ppm 7. RT - Powder 3.45 g 1.5 ppm 8. BT - Powder 2.88 jg 1.25 9. Germanium based Catalyst as a suspension■ i ■ 994 g 130 ppm 10.! _ Nyacol Silica 460 !g 200 ppm.... j .. ......... _. j 11. TEPA 852 g 50 ppm as P 12. OPA 165 g 20 ppm as P 13. Clear FRH 27.6 g 12 ppm additive 8 TABLE 2: Properties of Amorphous and SSP Co Polyester Resin PARAMETERS AMORPHOUS SSP COPOLYESTER COPOLYESTER I.V. dL/g 0.55 ±0.01 0.800 + 0.01 L* Min. 78 Min. 83 A* -1.0 + 0.2 -1.2 + 0.2 B* -7.0 + 0.5 -3.5 + 0.5 Tm 228 + 2°C 228 + 2°C Tg ~74°C ~77°C COOH, meq/kg Max. 35 Max. 30 DEG wt. % Max. 1.5 Max. 1.5 The co polyester resin made as described above is converted to sheets by extrusion and its heat sealing characteristics are measured and compared with a PVC heat seal sheet. The sheets exhibited good clarity and the weld strength test results measured at different temperatures and cycle times indicated good sealing strength Table-3 gives the details of heat seal strength. TABLE - 3: Heat Seal Strength of the Co Polyester CYCLE TIME Weld Strength, Weld Strength, Weld Strength, Weld Strength, (sec) lbf lbf lbf lbf 121°C 129°C 140°C 149°C 0.80 0.00 0.57 3.90 7.07 1.00 0.30 5.05 18.30 17.70 1.20 2.48 5.20 19.70 17.20 1.50 0.28 10.50 19.20 14.00 It can be seen the heat seal strength are higher and adequate even at a low heat seal 9 temperature of 140° C. While considerable emphasis has been placed herein on the specific steps of the preferred process, it will be appreciated that many changes can be made in the preferred steps without departing from the principles of the invention. These and other changes in the preferred steps of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation. 10

Documents:

1837-mum-2007-abstract(19-9-2008).doc

1837-MUM-2007-ABSTRACT(19-9-2008).pdf

1837-MUM-2007-ASSIGNMENT(7-6-2013).pdf

1837-MUM-2007-CLAIMS(19-9-2008).pdf

1837-MUM-2007-CLAIMS(AMENDED)-(13-6-2012).pdf

1837-MUM-2007-CLAIMS(AMENDED)-(3-10-2013).pdf

1837-MUM-2007-CLAIMS(MARKED COPY)-(3-10-2013).pdf

1837-MUM-2007-CORRESPONDENCE(12-11-2008).pdf

1837-MUM-2007-CORRESPONDENCE(16-4-2009).pdf

1837-MUM-2007-CORRESPONDENCE(19-9-2008).pdf

1837-MUM-2007-CORRESPONDENCE(7-6-2013).pdf

1837-mum-2007-correspondence-received.pdf

1837-mum-2007-description (provisional).pdf

1837-MUM-2007-DESCRIPTION(COMPLETE)-(19-9-2008).pdf

1837-MUM-2007-FORM 13(3-10-2013).pdf

1837-MUM-2007-FORM 18(16-4-2009).pdf

1837-mum-2007-form 2(19-9-2008).pdf

1837-MUM-2007-FORM 2(TITLE PAGE)-(19-9-2008).pdf

1837-mum-2007-form 2(title page)-(provisional)-(20-9-2007).pdf

1837-MUM-2007-FORM 26(7-6-2013).pdf

1837-MUM-2007-FORM 3(12-11-2008).pdf

1837-mum-2007-form 3(20-9-2007).pdf

1837-MUM-2007-FORM 5(19-9-2008).pdf

1837-MUM-2007-FORM 6(7-6-2013).pdf

1837-mum-2007-form-1.pdf

1837-mum-2007-form-2.doc

1837-mum-2007-form-2.pdf

1837-mum-2007-form-26.pdf

1837-mum-2007-form-3.pdf

1837-MUM-2007-MARKED COPY(13-6-2012).pdf

1837-MUM-2007-MARKED COPY(22-10-2013).pdf

1837-MUM-2007-OTHER DOCUMENT(3-10-2013).pdf

1837-MUM-2007-REPLY TO EXAMINATION REPORT(13-6-2012).pdf

1837-MUM-2007-REPLY TO HEARING(22-10-2013).pdf

1837-MUM-2007-REPLY TO HEARING(3-10-2013).pdf

1837-MUM-2007-SPECIFICATION(AMENDED)-(13-6-2012).pdf

1837-MUM-2007-SPECIFICATION(AMENDED)-(22-10-2013).pdf