IL99932A - Multilayer bag containers with improved heat processability properties - Google Patents

Description

MULTILAYER BAG CONTAINERS WITH IMPROVED HEAT PROCESSABILITY PROPERTIES MULTILAYER BAG CONTAINERS WITH IMPROVED HEAT PROCESSABILITY PROPERTIES This invention relates to container such as a made of which has improved seal and improved heat In the field of thermoplastic films being increasingly used in order to provide a balance of requested properties such as mechanical and abuse gae barrier attractive good optical properties and good heat seal Particularly in food a required property is often which io provided by subjecting film to orientation by or Amongst the many prior art references relating to multilayer the following can he mentioned as of a interest in connection with the present Patent issued et discloses a layer laminate with a core layer of a hydrolised and two outer layers of a mixture of copolymer of ethylene and vinyl acetate and a copolymer of lene end ethylene or linear low density The multilayer lajninate film of the reference can be made heat and has gas barrier discloses a container adhesive and additional layers of polypropylene or ethylene propylene a et discloses a container an adhesive and additional oi polypropylene or ethylene propylene Patent issued to enristensan et al appears to disclose a pouch having a linear low density polyethylene heat seal a second layer of a blend of linear low density polyethylene and propylene ethylene optional and layers of propylene ethylene a sixth layer of an anhydride modified a seventh layer of an eighth layer of a ninth layer of Patent issued to Mueller discloses a shrink film having two skin layers each comprising a blend of polypropylene and propylene Also of Interest is to Rosenthal et al which discloses a composite having a biaxally oriented polypropylene based laminated on at least one surface with a multilayer structure including a barrier layer a hydrolyzed ethylene vinyl acetate and a layer adjacent to the baee and a heat outer layer nay for modified EFO Patent Application a heat tubular film having a gas barrier layer of Vinylidene Chloride outer layers of such as propylene polypropylene and mixtures at least one intermediate layer of for example a and adhesive layers disposed between any of the above Patent Application GB disclosed a preferably coextruded heat scalable film having a surface layer of a heat scalable polymer such as linear low density polyethylene or blended with other such as an and a layer of These layers can bonded by polymeric adhesive Patent Application GB 2 221 a composite film with improved heat properties comprising a core layer of a copolymer propylene and one or heving a Vicat point of and two outer layers of a crystalline polypropylene resin having melting point or BUCn prior art references appears to relate to multilayer thermoplastic films having improved seal performance both in cold and hot conditions as provided by the container of the presen It an object or the present invention to provide a such as a bag having at least sealed area and having seal performance in of cold seal strength and thermal It is another object of the present invention to provide container structure having a unique balance of impact and abuse sealaJbility and thermal It is a further object of the present invention to provide a container structure fit for use in heat resistant These and further objects are achieved by a heat treatable container made of a multilayer film comprising at least an outer heat seal layer and a core gas barrier said heat layer comprising polymers of propylene with from 1 to by weight of two or more having from 2 to carbon The heat seal layer according to this invention preferably a polymer of propylene vith 3 to 10 by weight of said a of propylene with any or store having up to 8 carbon atoms can be a preferred a terpolymer of propylene with ethylene and The weight ratio between the ethylene and butene ly from l to A specific embodiment of the terpolymer consists thus of parts by weight of a further embodiment of the heat sealing layer a blend of propylene terpolyner or higher polymer an additional propylene in a proportion of to by of the terpolymer and 1 to by weight the additional said percentages being referred to the whole additional propylene copolymer comprises to by weight of propylene and from 1 to by weight of a selected from with to 8 carbon preferably from ethylene and n most packaging applications the multilayer film of which the container of this invention addition heat outer layer and barrier core a further outer structural The gae barrier layer is of conventional with gas barrier properties such as alcohol copolymers having for example an ethylene content of 30 to poiyvynlllaene chloride copolymers with vinyl chloride or methyl acrylate or or or or blends thereof with The outer structural layer can be made of the same propylene polymer as the neat sealing layer or or conventional polymers Xnown to impart mechanical strength to the Such polymers can be selected for instance from polyethylenes of very low density of high density or linear low density t acetate copolymers with VA content of 2 to preferably of 6 to ethylene copolymers with acrylic and olefinio polymers and copolymers modified witn functional polyamidesi and their Examples acrylic and eomonomers usable in euch ethylene copolymers are acrylic and aethacrylio and acryiates and with moieties such as butyl methyl acrylate and ethyl modified or not with factional euch with particularly Said modified polymers and copolymers be selected from polyethylene and while said can be selected from Nylon Nylon and Nylon an icnenerie polymer the one available froa tie under trademark can be The multilayer films of bags of the invention are made preferably produced by or sequential or the various component layers with interposition of tie producing tie known for such uses can be employed such as for ethylene copolymers modified or not With in particular anhydride modified ethylene Illustrative of such polymers and copolymers are modified by nctional groups and having a VA content of 6 to polyethylene or polypropylene polymers by functional of acryiate aoid or acid modified or with functional and blends Preferably the multilayer making up the container structure of this invention comprises an at least structure of the following the aultilayer film useful in the present invention comprises a structure like the Structural the inner and outer structural layers can be the or different and are selected from the polymers mentioned above for the outer structural beg of this invention is prepared by providing the aultilayer by or preferably by coextrueion in a tubular using this latte technique either all layers are and then whole multilayer film is by using conventional irradiation or first a substrate comprising of the layers is then it is irradiated in order to these layers and finally a coating is extruded on the Another alternative of the whole structure according to a specific a substrate can be formed by coextruding the heat sealant with an inner layer and optionally with a first tie then by sub substrate to by ana finally by coating over the substrate the remaining layers such as a second tie structural The various adhesive tie layers oan be the or different depending also on the nature or layers to be adhered When preparing heat shrinkabie tubular film obtained stated above is then to orientation by or stretching in the or by known stretching For instance the atretc blowing of the extrusion Thereafter bags are formed by cutting lengths of the tubular film and sealing such transversely to the direction of the tubular so providing bags with a bottom or providing bags with two side seals to be noted that these latest bags with side seals are not obtainable on industrial processing equipment from conventional multilayer films having seal layers different from those according to the present invention because of the poor processin performance of such conventional sealing The bags to this invention show outstanding properties in cold and hot seal when bags are used in food packaging the food item inserted in the the is vacuumized and then closed by heat coaling or clipping the package as a whole can subjected to various heat treatments such as cocking at a temperature up to about for several say or pasteurization treatment at far about to 1 The bags stand such treatments without revealing damages or weakening Of the seal or damages to the integrity of the whole pack for example by These properties are important in preserving the integrity of the packed food which in the presence damaged should the packages made with the bags of this invention stand without breaking or damages of sealed area electrical treatment aimed at improving the bag adhesion to the food in particular when meat being so as to better preserve the packed food and improve appearance of the The examples which follow as purely illustrative of the by the inventive Example 1 A multilayer for producing the bags according to invention and a control multilayer film have been prepared by of all the respective layers in tubular form and subsequent of the film by The two films had the following Control Sealing 2 of this Sealing 2 a copolymer of p Propylene Ethylene Scaling of EVA l is an inner structural layer with a VA content of by weight EVA 2 is an outer structural layer with a VA content of by weight Tie is an EVA copolymer with a VA content of 14 and modified with anhydride Typical physical and mechanical properties 0Γ the two reported in table TABLE 1 PHYSICAL MECHANICAL PROPERTIES OF THIS INVENTION THICKNESS 60 TENSILE STRENGTH 400 420 TD 430 450 MD 190 120 130 SHRINK at MD 24 33 32 10 10 MD Machine Direction TD Transverse Direction t b films have been converted 300 X 500 mm bottom of each type Οί fils have been tested for cold seal by measuring the burst resistance at room temperature of the 38 after rwo an average value of water pressure at burst in inches are given in the following table Table 2 Burst resistance As prepared After ageing Control 137 136 Furt hot strength of these bogs has been also by the seal in hot water bath at and applying internal pressure until burst The bags made of the inventive and those cr control film showed comparably good hot Example 2 and control of have been used cooking and testa result whereof are reported in the following Tables and Table 3 COOKING TEST 5 cooked ham cuts TEMPERATURES TOTAL CONTROL EX 1 COOKING TIME WIDE WIDE X 5h OR X 1 h X 1 h 7 OK X a h 3 REJECT OK NEXT 2 REJECTS 1 REJECT PASTEURIZATION TEST 5 cooked TEMPERATURES TOTAL CONTROL EX 1 COOKING TIME WIDE WIDE X OK X 4 h 4 OK X 4h REJECT OK X h s X h 6 1 REJECT X 3 h 7 3 REJECT i As it can be noted the bags of invention have a better performance at higher temperatures for prolonged treatment 3 The control and inventive bags of 1 after having been to corona hove also been subjected to the corona treatment in the of the onto the packed meat ao product presentation and packaging The bags with inserted cute have been heat treated at for and finally tested by moaeuring the strength requested to tear o a strip of 23mm cut tne bag adhered on meat contact with the The results shown in Table 5 indicate the improved performance or tne inventive Table T A D H E S I O N 1 Control insufficientOCRQuality

Claims (1)

1. CIAI2S5 A heat treatable container of a multilayer comprising at least an o seal layer and a core barrier said neat layer comprising of propylene copolymerized with from 1 to by weight of two having from 2 to 8 The container cf claim wherein the heat seal layer comprises cf propylene copolymerized with 3 to 10 by sai two or The container of 1 or 2 wherein said heat seal layer coapricea of propylene with ethylene The container of wherein said heat seal layer comprises blend of SS to by weight of said propylene with 1 to by weight of at least an additional lene with a comonomer selected rrom z 8 carbon container of claim 4 wherein said additional propylene copolymer comprises to by weight of said container of claim A or 5 wherein said additional propylene copolymer comprises a comonomer selected ethylene and container of claim i wherein said gas barrier layer is selected PVDC and and their mixtures with further container of 1 of a multilayer film comprising at least a neat seal layer a core gas barrier and further outer structural The container of claim 8 comprising said further outer layer selected from eaid polymers of propylene copolymerized from 1 to by weight of two or more having from 2 to 8 carbon polyethylenes of very low density of high density or linear low density acetate copolymers with content or 2 to ethylene copolymers with acrylic and methacrylic comonooers polymers and copolymers modified with functional and their The container of claim 9 wherein said acrylic and methacrylic selected from acrylic and methacryllc and and methacrylatee with or not with functional modified and are selected from polyethylene and polypropylene and said are selected from Nylon Nylon Nylon and The container or claim e further comprising adhesive layers interposed between said outer and core layers which are from ethylene polymers modified or not functional container of claim 1 or 8 made of in tubular form and a bottom seal transverse to axial of eaid tubular container of claim or a made or multilayer film provided in form a having two seals parallel to the axial dimension of said tubular The container of any of the claims has been made by at least a monoaxlal of said container of anyone of the preceding claims wherein said multilayer film has at least layer which has been container of claim 17 wherein said multilayer is fully by The container of anyone of claims 12 to 16 wherein said neat seal layer has been uorona treated or protein adhesion properties container according to anyone of the preceding claims for uae in heat A heat comprising a container according to anyone of claims 1 to A method for packaging heat items comprising inserting said item into container according to any one or claims to is an subjecting the package to a dry or wet heat of polymers of propylene with from 1 to by of two or more having from 2 to a carbon for producing a heat sealing outer layer in a multilayer heat treatable container as described i n the Use according to claim 21 of terpolymera of propylene with ethylene and butene as descri bed in the speci For the Appl B7283 insufficientOCRQuality