NO830892L - PROCEDURE FOR PREPARING A CLOSELY WRAPPING PACKAGING - Google Patents

Description

The present invention generally relates to tubular food casings made of laminated film and more particularly to casings which tightly enclose a foodstuff extruded into or stuffed into the casing.

Many foodstuffs are pressed into a casing during their processing, for example the foodstuffs can be liquid

.state flow under pressure into the tubular casing. j(iNvrlæuéernt ltilae nev gr asmv otmyipdyhydtietslnk elreit nlfogigrekmn aen ret ee ylvbtleeetr ad errdbtlreeigyt idkerkkiae nfg yn bleellaailrgnlg rber eeis i dsdaei els gon etc. ehryFønrls .nefdokinersmgt . eedn eer melts r e in oonmpæshråtye warm-ini-g-s-medium cheese cover with butter or solid cheese .The encased cheese is then allowed to solidify or set off and under ideal conditions the encasement will be uniformly filled with a loosing roll of uniform diameter. Ideally, these tubular |bm encasements should possess material properties such that they can be said to form "an exact fit". This means that the wrapping is possibly deformed radially during pressure filling so that the food roll formed therein exhibits a substantially equal diameter along its length. Furthermore, even radial deformation is not prevented, which weakens the wrapping and promotes cracking and spillage of the food product. .the term "exact fit" implies that the ideal casing has dimensional memory sl ik that when the introduced custom food product cools or sets, contraction of the wrapping will be sufficient to keep the wrapping securely and evenly stretched over the shrunk food roll in the wrapping.

Conventionally, such wraps consist of a fibrous wrap built up from a fibrous web of non-woven paper, possibly impregnated with various synthetic polymers or laminated to achieve desired combined properties for a particular application, such as low transmission of oxygen and water vapour. such as, for example, shown in US patent no. 4,026. 985. When used, these cellulose-based wraps must be soaked in hot water immediately before filling to make the oIra wrap sufficiently flexible and elastic for a uniform I ■if' woolling, as the wrap before water treatment_en__f_o.r_el_igg.eI<r>;i| a shrunken and collapsed configuration. Furthermore, the water treatment serves to wash away preservation micelles, this type of wrapping is burdened with a number of disadvantages in that soaking in hot water is necessary, since if a curing operation is interrupted the already soaked wrappings cannot be used.

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Furthermore, the soaking water will be a source of contamination and, as a result of the high moisture permeability, the storage time for the filled casings must be relatively short in order to prevent the food from drying out. It is also important to note that the filled casings can easily burst.

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In contrast to this, the present invention provides a coating that has no tendency to brittleness but

Instead, it will undergo a significant uniform plastic deformation due to the loss of the introduced nutrient, if the casing is intentionally filled beyond the elastic limit, and at the same time provide an enhanced apparent elasticity and thereby promote a tighter and more even fit. Furthermore. the wrappings can be moistened in good time before filling, but will still appear dry in a moist state and should the wrappings dry out, they can be re-soaked and any interrupted packaging cycle repeated.

According to the invention, the wrapping, which in the following for the sake of simplicity will be referred to as the packaging, comprises a non-fibrous, polymeric tubular laminate with an outer layer of crystallized and moistened nylon, thereby maximizing the elastic area and the elastic limit of the packaging at the same time keeping it in a plastic yielding state. In one application, the packaging is stored in a humid environment to prevent the outer layer of nylon from drying out. In an alternative way where the packaging is allowed to dry out during storage, the nylon layer will be re-moistened before filling. Optionally, the packaging can be filled and will thereby be subjected to a filling load that is less than that in the apparent elastic limit so that the radial deformation I will be uniform along the length of the tubular packagingj

As the exposed, outer nylon layer dries out, the multi-layer packaging will surprisingly shrink uniformly which further: will cause an elastically firm contraction over the introduced il

jfood rolls in the packaging. This contraction on drying will provide an apparent increase in the packaging's i ■

gel elasticity. In the case where the filled foodstuff is hot, this delayed shrinkage will counteract thermal concentration when cooling the filled foodstuff and thereby provide a wrinkle-free, tight packaging. According to a method feature of the invention, a method is provided for the production of a packaging with exact adaptation and comprises the production of a tubular polymeric laminate with an outer layer of crystallized nylon and in

moisten this nylon layer. In an advantageous embodiment, the method includes melt forming a tubular polymer laminate with an outer nylon layer, then quenching and solidifying the tubular laminate so that the nylon layer is essentially amorphous, while the diameter is set to approx. the predetermined working diameter and then heat treat the tubular laminate to crystallize the nylon layer while simultaneously wetting the nylon layer to saturation.

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According to the invention, an exact ^ntait lpmaesd set et emybtare llalasg jea, v omkrfyatsttaenldle iseert t røorg fofrumkettet,ponylylmoen rot g laemti-

internal moisture barrier layer. In an advantageous embodiment, the packaging is further characterized by the fact that the nylon layer is heat crystallized from a substantially amorphous state and simultaneously saturated with water, provided that the nylon layer was made substantially amorphous during a simultaneous sizing of the tubular laminate to the predetermined in-use diameter, the thickness of the nylon layer is chosen so that the elastic range of the force-extension profile of the emba..jlass at least covers the range of the in-use load,

According to the invention, there is also a device for the production of an exactly suitable food packaging.

Jbcooling and solidification of the resulting tubular laminate, '

. js such that the nylon layer is essentially made amorphous, means

for heat treatment of the tubular laminate to crystallize the nylon layer, as well as agents for moistening the nylon layer. In an advantageous embodiment, the apparatus comprises further means for rapid cooling of the becoming tubular laminate at the same time as the diameter of the laminate is set to be approximately equal to the predetermined use diameter, as well as means for simultaneous heat treatment and moistening of the nylon layer.

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Further details of the invention will appear from the attached drawings in which

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[Fig. 1 schematically shows a flowchart for a preferred

■embodiment when manufacturing the packaging according to the invention.

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Shut up. 2 is a stress-elongation diagram in which the packaging according to the invention is compared with a conventional fibrous wrapping in a dry and wet state.

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The laminate structure according to the present invention is directed to a multilayer, tubular packaging with an outer nylon layer; s6m adheres to one or more inner layers including one or more moisture barrier layers, for example the structure is 'nylon (outer)/adhesive/barrier (inner layer. Conventionally nylon is present in food packaging laminates to serve as an oxygen barrier to prevent indiffusion of oxygen and to provide high strength to the laminate, while a polyolefin, such as polyethylene, EVA, wound or surlyn, including copolymers and terpolymers thereof, is used as an inner surface which is relatively impermeable to moisture and chemically inert in relation to the food. It must, however, be emphasized that the aforementioned composition is only an example and that the packaging according to the invention may comprise several inner layers which can be selected to achieve desired composite properties which may be necessary for a git_

[use, provided that the packaging is in compliance

■with the invention. As discussed above, it is essential that

i il the nylon layer is formed as the outer layer of the packaging and immediately bring.e the nylon layer into a condition for a selected heat;-^ treatment, moistening and drying conditions. According to a particularly advantageous embodiment of the invention, the nylon layer is characterized by a selected crystalline micro-structure, produced by a special manufacturing step. This selected microstructure manifests itself in a special stress-elongation profile, which will be discussed in the following and which exhibits a distinctive yield point and elastic elongation, as well as moisture-absorbing properties compared to previously known tubular food packaging and which in the wetted state retains a plastic, not -brittle properties with considerable plastic elongation.

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With regard to developing preferred tension-elongation profiles in tubular food packaging, reference can be made to!.

US patent no. 4,303,711 in which it is stated that the electrical range of an envelope is extended to close to the ultimate thing by choosing a treatment step that includes biaxial orientation and thereby reducing the ability of the packaging to undergo irreversible plastic deformation during pressure filling of the packaging.

(Advantageously, the nylon layer in the packaging according to the invention consists of a heat-crystallisable nylon with a moisture absorption of at least 8%, such as nylon 4,6 or 66 or more

'preferred a moisture absorption of 15%. A preferred laminate structure for the packaging is nylon 6 or 6 6/Plexar/ polyethylene. The adhesive Plexar (TM), (the-Chemplex Company) and variants thereof are described in US patents nos. 4,087,587, 4,087,588 and 4,303,711. Plexar 2 adhesive can general

is characterized as an adhesive of a type comprising mixtures of a graft copolymer of HD polyethylene and at least one unsaturated, ring-condensed carboxylic anhydride and this

in mixture with one or more resin copolymers of ethylene and ethylenic unsaturated ester. Plexar 3 is preferred in the preceding embodiment and comprises mixtures of a graft copolymer of HD polyethylene and at least one unsaturated, ring-condensed carboxylic acid anhydride mixed with a polyethylene resin with <1>eh or more homopolymers, of. ethylene,..ko.pjolyjBere__ay..._ethylene

, and an alpha olefin or a mixture of all of these. More generally, the adhesives which are suitable for the present invention comprise a chemically modified polyolefin such as ethylene-vinyl acetate polymer, HD polyethylene and rubber modified with HD polyethylene, each of which is chemically modified by providing functional groups to the polymer and which exhibit]: a strong affinity for nylon and which will form a strong bond to nylon under heat and pressure in coextrusion, s!.ik

as set forth in US Patent No. 4,233,367. An alternative but less preferred structure partially utilizes the technology described in; US Patent No. 4,104. 404 for "Cross-Linked Amide/OlefinIPolymeric Tubular Film CoextrudedLaminates", in which amide/olefin films are indicated and which are relatively resistant to lamination when used in a heated state. The adhesive used is of the type that contains monomeric units that can be cross-linked by irradiation, the main component being olefinic units with the proviso that the olefins in the adhesive; is the same as in the polyolefin layer.

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I i !iUs' ntdi•elr linhgensmvåitsne infg or teiml bafligla. s1 jen so.m i vheinsehr old en tfiol roeptprufkiknnet elfsreneijn.-

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I A multi-layer coating is extruded tubularly through a cone-Ijv-e2n4 smjo/ns emll ends ydse a 1u1t, geåeknsdeme preølvr i1s 2 meld et a trhaekskteigs hefrt a pdå y7se,n 6<m>so</>m<s>

indicated at 13. The remaining pipe is drawn carefully with pressure rollers 14 over a calibration spindle 15 and through a cooling device 16 which provides a water cascade from a conventional water ring, or by water immersion or spraying, j The extrusion speed is sufficient so that when the formed tube is fed into the cooling zone, the outer nylon layer will remain in an essentially amorphous state. The cooling device ;16 has a sufficient capacity to cool the nylon layer: so that it maintains an extruded amorphous state ime

li the nylon layer to below its glass transition temperature. Preferably, the calibration spindle 15 is internally cooled to promote the cooling rate, as indicated by the coolant piping 17. As discussed below, it has been found that the diameter of the spindle 15 should be selected to

met to be equal to the desired application diameter for the packaging, i.e. equal to the desired diameter for the food roll to be contained in the packaging. After cooling, the advancing wrap collapses and is pulled through the press rollers 14 and fed to a subsequent take-up roller 13. Rolls with the wrap are then heat-treated in the presence of moisture at a temperature and time sufficient to crystallize the amorphous nylon layer in the packaging. The heat treatment is preferably carried out by immersing the roll in a i

In a warm water bath (not shown). Such a heat treatment is preferably carried out for 1-12 hours, preferably 1-4 hours depending

of the desired degree of crystallization, the temperature of the water bath is in the range 80-100°C. Alternatively, heat treatments j can be carried out by continuously passing the advanced tube directly j through a heat treatment medium before winding on the take-up I roll so that a shorter treatment time may be appropriate, I representative 1-60 min., due to the relatively quick response

jav the exposed nylon for heat treatment. The method mentioned in i is particularly suitable for unit production of: the packaging according to the invention. In an alternative process which is less preferred, the nylon layer is melt formed as a single sheet, crystallized and wetted and then laminated. nerted with the desired substrate and then formed into a tube or tube.

The term "crystalline" is used in the conventional sense to denote the existence of a wide range of three-dimensionally ordered atoms or repetitions at the atomic scale within the material. The term "amorphous" is also used in its conventional sense and as synonymous with the term "non-crystalline" to denote the absence of a wide range of ; atomic periodicity inside the material. The degree of ordered atoms I can be determined by conventional techniques, such as X-ray diffraction techniques to determine the probability density of central atoms. As a first approximation can ! a material is characterized as essentially crystalline if the material exhibits a defined melting point or melting point range, while a material can be characterized as bom i! the all-important if the material becomes less viscous] vec heating without exhibiting a defined melting point or melting point range.

The packaging that is ultimately used in the production of learning agent rolls where a pasta-type foodstuff, such as a hot melted cheese, is filled under pressure in the packaging which is j cut up and closed to desired lengths. The packaging is typically filled from a wrinkled state in a conventional rna t product filling apparatus, for example as shown in US patent no. I 4j. 3 07.48 9 which relates to pre-treatment of "gathered" packaging. The flexibility of the packaging is important for an even filling; ling of the packaging. According to the present invention j, the newly produced packaging has, after the above-mentioned heat treatment, been carefully moistened and is thus in a relatively flexible state. Preferably packaging is packed, I is cut and cutting clips are applied in a flat stack and

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stored in an environment saturated with moisture to prevent drying out. Alternatively, the packaging can if it is allowed to dry out in

I during storage times is re-moisturized before filling to j regain flexibility. During filling, the cheese melt J will be extruded into the wrinkled packaging under pressure so that the packaging I is stretched within its elastic range and thereby

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! prevent non-uniform plastic deformation of the packaging, which would lead to uneven filling and uneven shape of the cheese roll. Advantageously, the thicknesses of the nylon layer are chosen so that in the elastic range of the stress-elongation profile of the packaging at least covers the range of the end-use load.

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bone-filled packaging is then closed with clips and allowed to cool and dry. Contraction of food products by ! cooling and setting tend to give a smaller to-! fitment of the packaging for the raw material product, however, drying out of the nylon layer in the packaging which normally occurs in the course of approx. 30 min. the packaging will contract as

due to remaining elasticity and drying out thereby eliminating the effect of the thermal contraction of cheese rolls and thus achieving a tight, wrinkle-free fit. It can thus be said that the new packaging has a supervisory tendency

I, oemlaråsdteis. itSoem t uttiodvleir gedree t ankognivtetn, shjoovneedlt redsuefltinaetrett e of elaopsptifsiintneetlss-en

includes the ratio between the diameter of the spindle 15 and the final diameter of the filled packaging, namely that the diameter of the filled and dried packaging will be approximately equal to the selected diameter of the spindle 15. For example;

packaging produced according to the above-mentioned method using a spindle diameter of 82 mm and consisting of 0.05 mm nylon g/0.01 "Plexar 3"/0.04 mm or

LDPE (inside). The newly produced packaging after the heating process and kept in a saturated state had a diameter of

In 78.84 mm and after drying the diameter was 76.81 mm. The moist packaging was filled with a cheese melt at approx. 71°C to a diameter of 419 mm: After cooling and drying, the filled package had a diameter of 416 mm. The diameter of the finished filled packaging was thus very close to the d,en of the calibration spindle 15. Furthermore, it should be noted that the packaging exhibited a contraction upon drying of approx.

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3%, which is a significant proportion in relation to the packaging's elastic area.

Furthermore, for a multi-layer packaging it was observed that

in it underwent contraction in a unitary manner, i.e. the entire airbal layer followed the outer nylon layer without shrinkage or separation of the individual layers.

Compared to conventional fibrous packaging, the present packaging has been found to exhibit significant advantages in other ways. Water solution immediately before filling is eliminated, thereby eliminating surface water on packaging

j the load. Although the nylon layer may be in a saturated state I, it will apparently not be wet, thereby eliminating

! damp conditions at and around the filling machine area. Packaging

in! the load has been found to exhibit dimensional stability along its length, for example it has been found that the diameter i filled to-

<i>j stand was within the 0.5 mm tolerance and thereby produced a cheese roll with a substantially uniform shape. In the event that the elastic area of the packaging is exceeded during filling, the packaging will be plastically extended and will not undergo spraying--

breakage and thereby preventing leakage of the food product - and spillage. It has been found, for example, that the packaging according to the invention has a typical plastic extension of approx. 500%,

compared to an extension of 20% for the above-mentioned conventional packaging. During storage, the food content will not dry out significantly because the packaging according to the invention is non-porous and thus enables a considerable storage time. The moist state of the packaging according to the invention is reversible so that the packaging can be remoistened before filling in the event that the packaging has dried out during storage. As this process is reversible for the packaging according to the <1>invention, loss of packaging will be prevented in the case where the food filling process is interrupted over a longer period of time. Furthermore, as a result of the highlighted, apparent elasticity of the packaging, this provides a tight "secone skin fit" and the food product contained in the packaging will achieve an appealing, semi-mixed surface after the packaging

the material has been removed from the food roll.

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I I fig. 2 shows force-elongation profiles in the transverse direction within the electrical range in which a packaging according to the invention is compared with a conventional j non-woven fibrous packaging. Curves A and B show, the ! elastic extension of a conventional packaging in

in dry and wet conditions respectively. The conventional packaging

j i lage must be filled in a wet state and is relatively exposed to over-i loading and cracking because the curve B lies significantly below i

Curve A. Curve C is typical for the moistened packaging according to the invention and can be seen to be comparable to the substantially stronger conventional packaging in a dry state.

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i There are several features of the invention that are important,

j As stated above, the packaging according to the invention has an iI reinforced apparent elasticity area which manifests itself in that the moistened outer nylon layer of the filled packaging

The layer dries out and shrinks, thereby promoting a tight, even fit. Another feature relates to the improved flow rate. limit and reinforced • elastic area attributed}

during crystallizing heat treatment as discussed above.

Each of these improvements serves to extend the elastic range of the packaging and thereby promote dimensional stability during filling, i.e. less possibility of non-uniform, plastically irreversible deformation or bulging of the filled packaging. It is an advantage that this highlighted elastic area does not occur at the expense of plastic elongation in the case where the packaging is inadvertently overloaded, in which case the packaging will yield plastic and not brittle. It is believed that the advantageous I mechanical properties of the packaging according to inventions,

can be further enhanced by the manner of crystallization

of the outer nylon layer is performed on. Firstly, in a preferred embodiment, the nylon layer is crystallized by reheating from the essentially solid amorphous, cooled state as opposed to crystallization from a melt.

And not least, a highly reproducible method for producing the packaging has been provided by conditionally

in the ices for the nylon layer just before the heat treatment is velc.ef i - ! in here. Secondly, the crystallization heat treatment 1 is carried out in the presence of moisture, which is believed to have an impact on the crystallization process as well as to promote a high moisture

j density absorption and plasticity of the nylon layer. More generally, the invention encompasses in its broadest scope crystallization of the outer nylon layer to promote the mechanical properties in the elastic range and moistening of the nylon layer to promote the elastic flexibility and.plastic ! extensibility to provide additional apparent elasticity upon desiccation, with the surprising overall j result that the multi-layer packaging exhibits these properties for the outer nylon layer in a substantially uniform manner.

<1>Table I shows a comparison of the mechanical properties

between a sample of the packaging with an outer nylon layer, in relation to a sample with a nylon layer inside a packaging lock-

' laminate. The packaging samples were essentially produced

according to the above-described preferred method so that the respective nylon layers were originally in an essentially amorphous state...

I which is a typical temperature for hot filling. The packaging marked SDX244 consisted of a laminate with the structure: "nylon 6

(external/binder/PE/binder/PE, and where the nylon layer was 0.05 mm thick and the total thickness of the laminate was 6.10 mm. The sample labeled SDX246 had a total thickness of

0.10 mm and the nylon layer a thickness of 0.05 mm, as for the previous sample, but had the structure: PE/adhesive/

nylon 6/adhesive/PE. The table shows data for yield strength and elongation at yield for condition A which is not heat treated, dry condition, for condition B which indicates heat treatment in a hot water bath at 82 oC for 1 min. and for condition C indicating heat treatment in hot _ water at 82°C for 1 hour. The term "yield strength" must be understood in the conventional sense that indicates the stress value that produces a small, irreversible deformation or settlement in the material. The yield strength was determined using

In a conventional force-elongation breaking load machine "Instron"<1>where a sample is stretched under constant extension rate j and where force and extension are measured. The samples were strips j with a width of 2.5 cm and a length of 10 cm and were drawn with ei at a constant clamping speed of approx. 5 cm/min. The sample labeled SDX244 with an outer nylon layer can be seen to react quickly to the heat treatment, i.e. within a minute as can be seen by comparing columns A and B. With further continued heat treatment it can be seen that after one hour a significant increase is achieved in further buoyancy as well as elongation : by displacement. In contrast, it can for the sample ! marked SDX24 6 which has an inner nylon layer which is not directly exposed to hot water during the heat treatment then is achieved ! essentially no effect within 1 min. After , 1 hour it can be seen that a certain effect has taken place. It is significant that, as can be seen from the sample marked SDX24 4 with an outer nylon layer, according to the invention, shows a significant response to the heat treatment within a very short time. It should be noted that 1 standard deviation for each test condition is given in parentheses and shows that the statistical spread of the test results was relatively narrow, indicating good reproducibility of the test. In table II is !. the same comparison carried out at 23°C, which gave itJ

Claims (1)

1. Method for the production of exactly suitable adhesive coating, characterized by forming a tubular polymeric laminate with an outer layer of cross- in tallized nylon; and moisten the nylon layer. 21 Method according to claim 1, characterized in that the nylon layer is crystallized by first melt-forming a remaining nylon layer, then cooling and solidifying the nylon layer so that it essentially remains amorphous and then heat-treating the nylon layer to crystallize it. IN 1 13 Method according to claim 1, characterized <.> . i y y y e d yes), melt form a permanent polymer laminate with an outer nylon layer, bl cooling and solidifying the tubular laminate so that the nylon layer remains essentially amorphous, <c> ). heat treating the tubular laminate to crystallize the nylon layer, and !d) moisten the nylon layer. j 4 i Method according to claims 1-3, character-i :certain in that the heat treatment and moistening are carried out at the same time by heat treatment in hot water and that the cooling is carried out at the same time that the diameter of the tubular laminate is set to approximately the predetermined intended final diameter, for example by passing the laminate over a cooled A spindle with a diameter approximating the intended final diameter. ! in in !5i Method according to claims 1-4, characterized in that the heat treatment is carried out at 82-100°C L l,min. to 12" hours. j In the 6th ! Device for carrying out the method in accordance with claim 1 • Ir5, characterized in that it includes means for melt forming a permanent tubular polymeric laminate with an outer nylon layer, means for cooling and solidifying the tubular layer such as; The nylon layer is essentially made amorphous, mgii dli is deft ovr evsaenrmtelbigehe ankdrylisntg alalv isderet t rnyørlofonr, mesdame tlaminat to in agents for moistening the nylon layer. 7. Apparatus according to claims 1-6, characterized by a spindle for dimensioning the diameter of the tubular laminate, which spindle is optionally cooled, <!> in in