NL8300515A - METHOD FOR MANUFACTURING A CLOSURE FOOD COVER - Google Patents

Description

i ψ · s, -i

A method of manufacturing a form-fitting food casing

The invention generally relates to a tubular food casing of laminated film, more particularly to casings tightly enclosing a food product that has been extruded or stuffed into the casing.

Many treated foods are stuffed into a casing during treatment, i.e. the food product, when in a flowing state, flows under pressure into a tubular casing. The food product, when enclosed in the casing, may be further treated or it may be stored in the casing pending further treatment or sale. For example, cheese rolls are typically formed by pressure filling a tubular food casing with a hot cheese melt or solid cheese curd. The coated cheese is then allowed to solidify or bind together, and under ideal conditions, the envelope is uniformly filled and forms a cheese roll of uniform diameter.

Ideally, these tubular casings have such material properties that they can be said to form an "exact fit." This means that the casing deforms radially uniformly during pressurization, so that the food roll formed therein has a substantially uniform diameter along its length. Furthermore, uniform radial deformation is not prevented from weakening the casing, thereby promoting cracking and wasting of the food product. Furthermore, the term "exact fit" includes that the ideal casing has a size memory such that 8300515 $ Λ t \ -..... 2 when the trapped food product cools or binds together, contraction of the casing is sufficient to keep the casing safe and uniform stretched over the shrunk food roll contained therein.

Normally, such sheaths are typically fibrous sheaths, which are made up of a fibrous nonwoven paper web, possibly with different synthetic polymer impregnations or laminations to obtain properties of the composite required for a particular application, such as low permeability. for oxygen and water vapor, as disclosed in U.S. Pat. No. 4,026,985. In use, these cellulose casings must be soaked in hot water, shortly before filling, to make the casing sufficiently flexible and elastic for uniform filling of a pleated or wrinkled configuration and to wash away all preservatives. There are a number of drawbacks to the use of this type of casing in that soaking in hot water is required, while in the event of production failure, soaked casings 20 cannot be saved. Furthermore, the drinking water is a source of contamination and, due to the relatively high moisture permeability, storage times of the filled casings must be relatively short to prevent food from drying out. It is also significant that these filled shells are susceptible to cracking in the manner of brittle failure.

In contrast, the invention provides a sheath that is not susceptible to brittle failure, but undergoes substantial uniform plastic deformation, without wasting food, when the sheath is inadvertently filled beyond the elastic limit, and provides greater apparent elasticity, thereby providing a firmer, more uniform fitting is promoted. In addition, the casings can be wetted well before filling and still appear dry in the wetted condition; however, if the casings are allowed to dry out, they can be re-soaked and thus 8300515 * 3 * · · <% can be used repeatedly.

Summary of the Invention The sheath of the invention thus comprises a non-fibrous polymer tubular laminate with an outer layer of crystallized and wetted nylon, thereby maximizing the elastic range and the elastic limit of the sheath while retaining a plastic failure behavior. In one application form, the casing is stored in a humid environment to prevent drying of the nylon outer layer. In another form, where the casings are allowed to dry out during storage, the nylon layer is re-wetted before filling. Finally, the sheath is filled and thereby subjected to a fill load less than about its elastic limit, so that radial deformation is uniform along the length of the tubular sheath. When the exposed outer nylon dries out, the multi-layer casing surprisingly shrinks uniformly, further stretching it tightly elastically over the food roll contained therein. In fact, this contradiction on drying out gives an apparent increase in the elasticity of the casing. In case the food filling is hot, this delayed shrinkage counteracts thermal contraction upon cooling of the food filling 25, thereby providing a crimp-free form-fitting package.

According to the method aspects of the invention, there is provided a method of making a form-fitting food casing comprising molding a tubular polymer laminate with an outer layer of crystallized nylon and wetting this nylon. In an advantageous embodiment, the method further comprises melt-molding a resulting tubular polymer laminate with a nylon outer layer; then quenching and solidifying the resulting tubular laminate such that the nylon is made amorphous, while at the same time setting the tubing diameter 8300515 to approximately equal to a predetermined final application diameter; and then the tubular laminate is heat treated to crystallize the nylon, simultaneously wetting the nylon to saturate.

In the product aspects of the invention, there is provided a form-fitting fitting envelope comprising a tubular polymer laminate with an outer layer of crystallized and wetted nylon and an inner moisture barrier layer. In an advantageous embodiment, the sheath is further characterized in that the nylon is crystallized hot from an amorphous state and simultaneously saturated with water, with the proviso that the nylon is made amorphous, the tubular laminate being adjusted to a predetermined end-use diameter , and the thickness of the nylon is selected such that the elastic range of the stress-strain profile of the sheath is at least about the same size as the range of the final application load.

According to the device aspect of the invention, there is provided an apparatus for manufacturing a form-fitting food casing comprising means for melt-molding a resulting tubular polymer laminate with a nylon outer layer; quenching and solidifying means of the resulting tubular laminate such that the nylon is made substantially amorphous; heat treatment means of the tubular laminate for crystallizing the nylon and means for wetting the nylon. According to an advantageous embodiment, the device further comprises means for quenching the resulting tubular laminate, at the same time setting the laminate to a diameter approximately equal to a predetermined final application diameter; and means for simultaneously heat treating and wetting the nylon.

8300515 φ "* -. 5 ____________________ - _ _____________ .... ......, ..

Brief description of the drawing.

Further details are set forth below with reference to the drawing, in which Figure 1 is a schematic flow chart of a preferred embodiment for manufacturing the casing of the invention; and FIG. 2 is a stress-strain diagram comparing a wrapper according to the invention with a conventional fibrous wrapper in a dry and soaked condition.

Description of the Preferred Embodiments The laminate structure of the invention is directed to a multilayer tubular food casing with a nylon outer layer, which is bonded to one or more inner layers, including one or more moisture barrier layers, for example, the structure nylon (outer) / adhesive / barrier ( within).

Normally, nylon is present in food casing laminates as an oxygen barrier to prevent the inward diffusion of oxygen 20 and to impart a relatively high strength to the laminate, while a polyolefin, such as polyethylene, EVA, saran or surlyn, including copolymers and terpolymers thereof, is used as an inner surface, which is relatively impermeable to moisture and chemically inert to many nutrients. However, it is emphasized that this assembly is an example and that the casing according to the invention comprises multiple biennial layers to obtain the desired compositional properties required for a particular application, depending on the essential features of the invention. As discussed below, it is essential that the nylon layer is formed as the outer layer of the shell to make the nylon directly suitable for selected heat treatment, wetting and drying conditions. According to a particularly advantageous embodiment of the invention, the nylon 8300515-4-4 is further characterized according to selected crystalline microstructure developed by selected process steps. This selected microstructure is evidenced by a selected stress-strain profile, as will be discussed hereinafter, which exhibits higher yield strength and elastic stretch and moisture absorption, compared to prior art tubular food casings, in the wetted state of which a plastic, non-brittle plastic failure mode elongation is maintained. Of general interest, at the point of developing selected stress-strain profiles in tubular food casings, the casings of U.S. Pat. No. 4,303,711, which disclose that the elastic range of a casing is extended to near the fracture stress by selection, are 15 process steps, which include biaxial orientation, which decreases the sensitivity of the casing to irreversible plastic deformation during pressurization of the casing.

Advantageously, the nylon layer of the casing according to the invention consists of a warmerized nylon with a moisture absorption capacity of at least about 8%, for example nylon 4, 6 or 66, and most preferably about 15%. A preferred laminate structure for the shell is nylon 6 or 66 / Plexar / polyethylene. The adhesive Plexar (TM) is commercially available from the Chemplex Company. Plexar variants are described in U.S. Pat. Nos. 4,087,587, 4,087,588 and 4,303,711, the contents of which are to be considered incorporated herein. Plexar 2 adhesive can be broadly characterized as an adhesive of the type containing mixtures of a graft copolymer of a high density polyethylene and at least one condensed ring unsaturated carboxylic anhydride mixed with one or more resin copolymers of ethylene and an ethylenically unsaturated ester. Plexar 3 35 is preferred in the aforementioned embodiment and contains blends of a graft copolymer of a high density polyethylene 8300515 P: 7. at least one condensed ring unsaturated carboxylic anhydride mixed with a polyethylene resin of one or more homopolymers of ethylene, copolymers of ethylene and an alpha olefin and one or all of them. More generally, in the invention, suitable adhesives containing a chemically modified polyolefin are selected from the group consisting of ethylene vinyl acetate polymer, high density polyethylene and rubber modified high density polyethylene, each chemically modified by the presence of functional groups on the polymer which have a strong affinity for nylon and which will form a strong bond with nylon under the heat and pressure of coextruding, as described in U.S. Patent 4,233,367.

Another structure, although less preferred, partially utilizes the technology described in US Patent 4,104,404 for "cross-linked amide / olefin polymer tubing coextruded laminates", which is to be considered interleaved herein, disclosing amide / olefin films. , which are relatively resistant to delamination when used in warm conditions. The adhesive used is of the type which has irradiated cross-linked monomer units, the main component of which are olefin units, with the proviso that the olefins in the adhesive and in the polyolefin layer are the same.

Fig. 1 schematically illustrates a preferred method for manufacturing the casing according to the invention. The multilayer casing is coextruded tubularly through a conventional die 11, for example, at a rate of about 25 to 80 fpm, the resulting tube 12 being lightly pulled from the die, as shown at 13. The resulting tube is pulled lightly by pinch rollers 14 over a calibration mandrel 15 and through 35 quenching members 16, where quenching takes place with water • · r.

uxt a conventional watering, or by rinsing or spraying 8300515 * 4 t 8 with water. The extrusion rate is sufficient such that the resulting tube enters the quenching zone with the outer nylon layer in the amorphous state. The quenches 16 have sufficient capacity to quench the nylon layer to maintain the extruded amorphous condition in the nylon below the glass transition temperature.

Preferably, the calibration mandrel 15 is internally cooled to increase the quench rate, as indicated by the coolant lines 17. As explained further below, it has been found that the diameter of the mandrel 15 is selected approximately according to the desired final diameter of the casing. that is, according to the desired diameter of the feed roll being introduced therein. After quenching, the advancing casing 15 is flattened and pulled by pinch rollers 14 and passes to the take-up roll 18. Casing rolls are then heat treated in the presence of moisture at a temperature and for a time sufficient to crystallize the amorphous nylon layer of the casing . Preferably, heat treatment is carried out by immersing a roller in a hot water bath (not shown). Representatively, such heat treatment is continued for about 1 to 12 hours, preferably about 1 to 4 hours, depending on the degree of crystallization desired, and at a temperature in the range of 180 to 212 ° F. On the other hand, heat treatment may take place by continuously passing the advancing tube directly through a heat treatment medium for recording onto the take-up roller, so that a shorter treatment time is suitable, typically about 1 minute to 1 hour, due to the relatively rapid response of the exposed nylon on heat treatment. The method described above is particularly suitable for unitizing the casing according to the invention. In another embodiment, although less preferred, the nylon layer can be formed as a single layer sheet, crystallized and wetted, laminated with the 8300515

V

- »* 9 t desired substrate and then formed into a tube.

The term "crystalline" is used in the usual sense to indicate the existence of three-dimensional atomic order or periodicity over a gret distance on the atomic scale in a material. The term "amorph'1 is also used in the usual sense as being synonymous with the term" non-crystalline "to indicate the absence of long-range atomic periodicity in a material. The degree of atomic order can be determined by conventional methods , such as X-ray diffraction methods, for determining radial atomic probability density As a first approximation, a material can be characterized as crystalline, when the material has a certain melting temperature or range, while a material can be characterized as amorphous, when the material gradually becomes less viscous when heated without exhibiting a particular melting point or range.

The casings are ultimately used to form a food roll or block, whereby a pasta-type food, such as a hot cheese melt, is pressurized into a casing which is cut to the desired length. The casings are typically filled from a pleated configuration on conventional feed fillers, such as described in U.S. Patent No. 4,307,489. Thus, sheath flexibility is important for uniform sheath filling. In the present invention, the fresh casings, following the heat treatment steps discussed above, are fully wetted and therefore in a relatively flexible state. Preferably, the shells are packed, cut in a flat lay-up, and stored in a saturated moist environment to prevent drying. If the casings are allowed to dry out during storage, they can be re-wetted before filling to restore flexibility. During the filling, the cheese melt is below 8300515

V

10 extruded pressure into the pleated casing such that the casing is stretched in the elastic range, thereby preventing non-uniform plastic deformation of the casing resulting in non-uniform filling and irregular formation of the cheese roll. It is advantageous to select the thickness of the nylon layer such that the elastic range of the force-stretch profile of the envelope coincides at least approximately with the range of the final application loading.

The filled casing is then cut and allowed to cool and dry. Contraction of the food product upon cooling or curing loosens fitting of the casing to the food product; however, upon drying out the nylon layer of the casing, which takes place in about 0.5 hours, the casing contracts due to the residual elasticity and drying, thereby eliminating thermal contraction of the cheese roll to maintain a snug, crimped fit freely. It can therefore be said that the sheath has an increased apparent elasticity above the elastic range, as defined normally. As mentioned above, the key result of the invention includes the relationship between the diameter of the mandrel 15 and the final loaded diameter of the casings, namely, the diameter of the loaded and dried casing will be approximately equal to the selected diameter of the mandrel 15. Casings were manufactured, for example, by the previously described process, using a 3.243 inch mandrel diameter and with a composite structure of 2 mils nylon 6 / 0.5 mil Plexar 3 / 1.5 mils LDPE (inner). The fresh casings after heat treatment had a diameter of 3,104 inches in the saturated state and a diameter of 3,024 inches after drying. The wetted casings were filled with a cheese melt at about 160 ° C to a diameter of 3.275 inches. The filled shells had a diameter of 3.25 inches after cooling and drying. Therefore, the diameter of the final filled casing was quite equal to. that of the calibration steam 15. It is further noted that the sheath exhibits a drying contraction of about 3%, a considerable amount with respect to the elastic range of the sheath.

In addition, it was observed that; the multilayer casing underwent contraction in a uniform manner, that is, the entire casing followed the outer nylon layer, without crimping or separating the component layers.

Furthermore, the sheath of the invention, compared to conventional fibrous sheaths, has been shown to have significant advantages in other respects. Watering immediately before filling is eliminated, eliminating surface water on the casing. While the nylon may be in the saturated state, it will not be visibly wet, eliminating wet conditions around the area of the filling machine. The casing was found to be dimensionally stable along its length, for example, the loaded diameter was found to be within a tolerance of 0.02 inches, thereby providing a uniform cheese roll. In case the elastic trajectory of the casing is exceeded during filling, the casing stretches plastically and the failure is not brittle, preventing break-out and waste of food products. For example, the sheaths of the invention were found to have a plastic elongation of about 500% compared to an elongation of about 20% for the conventional sheaths discussed above. When stored, the food filling does not dry out to a significant degree, because the casing according to the invention is not porous, whereby a considerable storage time is obtained. The wetted condition of the cases according to the invention is reversible, so that the cases for filling can be re-wetted in case the cases dry out during storage. Since this process is reversible for the casings of the invention, spillage of the casings is prevented in the event that the food filling process is interrupted for a considerable time. Finally, due to the increased apparent elasticity of the wrapping, which provides a snug second skin, an attractive semi-gloss surface is obtained on the food product contained therein after stripping the wrapping from the food roll.

Fig. 2 shows shear-strain profiles in the elastic range, comparing the above-described housing according to the invention with a conventional non-woven fibrous housing. Profiles A and B

demonstrate the elastic response of the conventional shell in the dry and wet state. The conventional casings must be filled in the wet state and are thus relatively susceptible to overfilling and cracking, since profile B is considerably lower than A. Profile C refers to the elastic profile of a typical wetted casing according to the invention, which is comparable with the significantly higher strength of the conventional casing in the dry state.

There are several aspects of the invention that deserve emphasis.

As noted above, the inventive sheaths have an increased apparent elastic range, which manifests as the wetted nylon outer layer of the filled sheath dries and shrinks, thereby promoting a snug, uniform fit. Another aspect includes an increased yield point and an increased elastic range, due to the crystallizing heat treatment discussed above. Each of these improvements serves to increase the elastic range of the envelope, thereby promoting dimensional stability during filling, i.e., a lower sensitivity to non-uniform, plastic, irreversible deformation or bulge of the filled envelope. However, this extension of the elastic range is not at the expense of plastic stretch, if the casings are accidentally overloaded, in 8300515%, in which case the casings will fail plastically and not brittle. It is believed that the favorable mechanical properties of the casings according to the invention can be further improved by the manner of crystallization of the nylon outer layer. In the preferred embodiment, the nylon is crystallized upon reheating the solid amorphous cooled state as opposed to melt crystallization. At the very least, a highly reproducible process for manufacturing the casings is provided in that the state of the nylon is determined just prior to heat treatment. Secondly, the crystallizing heat treatment is preferably carried out in the presence of moisture, which is believed to promote the crystallization mode as well as promote high moisture absorption and plasticity of the nylon. More generally, the broad aspects of the invention include crystallizing the nylon outer layer to improve the mechanical properties in the elastic range and wetting the nylon layer to increase elastic flexibility and plastic elongation and to provide additional apparent elasticity on drying, with the surprising overall result that the multilayer casing exhibits these properties of the nylon outer layer 25 in a uniform manner.

Table 1 compares the mechanical properties of nylon shell coated samples and nylon coated samples inside the shell laminate. The casing samples 30 were prepared by the preferred method described above, so that the respective nylon layers were initially in an amorphous state. The comparison was made at 160 ° F, which is a typical hot fill temperature. Casing type SDX244 consisted of a laminate with the structure nylon 6 (outer) / adhesive / PE / adhesive / PE, the nylon layer being 2 mils thick and the laminate having an 8300515 ... 14 t total thickness of 4 mils. Sample type SDX246 had a total thickness of 4 mils and a nylon layer thickness of 2 mils, as in the previous sample, but had the structure FE / adhesive / nylon 6 / adhesive / PE. The table shows fracture-5 strength and elongation at break for condition A, which is the non-heat-treated dry condition, for condition B, which means heat treatment in a hot water bath at 180 ° for 1 minute, and for condition C, which means heat treatment in hot water at 180 ° for 1 hour.

The term "yield strength" is used in the conventional sense and refers to the stress value which causes a small irreversible deformation or settlement in the test material. The yield strength was determined using an Instron conventional force-strain stress test machine, which stretches a constant strain rate sample, with force-? measurements at values of increasing elongation. The samples were strips 1 inch wide and 4 inches long and drawn at a constant crosshead speed of about 2 inches per minute. Sample type SDX244 with the 20 "nylon outer layer appears to respond quickly to heat treatment, i.e. within 1 minute, as shown by comparing columns A and B. Continued heat treatment shows that after 1 hour a significant increase in yield strength as well as elongation at breakage is obtained, on the other hand, in sample type SDX246 with the nylon outer layer, which is not directly exposed to the hot water heat treatment, there is no effect within 1 minute. After 1 hour, some effect occurs. Essential, it has been demonstrated that sample type SDX244 shows a strong response to heat treatment in a very short time with the nylon outer layer of the invention It is noted that a standard deviation is given in parentheses for each test condition, showing that the statistical spread was relatively narrow, which is on a relatively consistent sample Behavior In Table 2, the same comparison is made at 73eF to obtain the self the overall result.

8300515 «τ '^ 15

Table 1; properties 160 ° F

YS-Transverse yield strength, psi, and (Standard deviation) E- Transverse elongation at break,%, and (Standard deviation)

Monster Condition

Type Abc SDX244 YS 1670 (40) 2070 (120) 2250 (60) (nylon E 21 (4) 19 (4)> 25 outside) SDX246 YS 1410 (140) 1400 (220) 1840 (30) (nylon E 23 ( 2) 22 (7)> 25 in)

Condition A: not heated, dry

Condition B: hot water treatment, 180 ° F, 1 minute.

Condition C: hot water treatment, 180 ° F, 1 hour.

Table 2: Properties 73 “F

SDX244 YS 2770 (70) 2990 (30) 3130 (24) E 14> 25 24 (1) SDX246 YS 2800 (90) 2470 (190) 2180 (90) E 9 24 (0) 25

While the invention has been described with reference to the preferred embodiments, it will be appreciated that modifications and variations can be made without departing from the principles and scope of the invention, as will be apparent to those skilled in the art.

8300515

Claims (27)

A method of manufacturing a form-fitting food casing, characterized by a) melt molding a resulting tubular polymer laminate with a nylon outer layer; then b) quenching and solidifying the resulting tubular laminate such that the nylon is made amorphous, then c) heat treating the tubular laminate before crystallizing the nylon; and c d) wetting the nylon. 2. A method according to claim 1, characterized in that the heat treatment and the moistening take place simultaneously and before natural aging of the nylon takes place. Method according to claim 2, characterized in that the heat treatment and moistening take place in a hot water bath. 4. Method according to claim 1, characterized in that the tubular laminate is stored in a humid environment before use. Method according to claim 1, characterized in that the quenching takes place and at the same time the tubular laminate is calibrated to a diameter which is approximately equal to a predetermined final application diameter. A method according to claim 5, characterized in that the resulting tubular laminate is quenched when it is passed over a mandrel of approximately the predetermined end-use diameter. Method according to claim 6, characterized in that the mandrel is cooled internally. Method according to claim 6, characterized in that the quenching is quenching with water. 9. Method according to claim 1, characterized in that the melt-forming takes place by coextruding. 8300515 Λ. a*· * A method of manufacturing a form-fitting tubular food casing, characterized by a) coextruding a resulting tubular polymer laminate with a nylon outer layer; then b) quenching and solidifying the resulting tubular laminate such that the nylon is made amorphous while at the same time making the tube diameter approximately equal to a predetermined final application diameter; and then c) heat treating the tubular laminate to crystallize the nylon, while simultaneously wetting the nylon to saturation. 11. Method according to claim 1 or 10, characterized in that the heat treatment takes place in a range from about 180 to 212 ° C for about 1 minute to 12 hours. A method according to claim 1 or 10, characterized in that the nylon comprises a heat-crystallizable nylon with a moisture absorption capacity of at least about 8% and the tubular laminate contains an inner moisture barrier layer. The method according to claim 12, characterized in that the composite structure of the tubular laminate comprises nylon (outer) / adhesive / polyolefin (inner). Method according to claim 13, characterized in that the nylon comprises nylon 6 or nylon 66. 15. A method according to claim 13, characterized in that the polyolefin comprises polyethylene and the adhesive comprises a chemically modified polyolefin selected from the group consisting of ethylene vinyl acetate polymer, high density polyethylene and high density rubber modified polyethylene, each chemically modified by the presence of functional groups on the polymer, which have a strong affinity for nylon and which will form a strong bond to nylon when extruded under heat and pressure. 16. Tight-fitting food casing, characterized 8300515 by a tubular melt-formed polymer laminate with an outer layer of crystallized and wetted nylon and an inner moisture barrier layer, the nylon layer being hot crystallized from an amorphous state and simultaneously wetted. Casing according to claim 16, characterized in that the thickness of the nylon is selected such that the elastic range of the force-stretch profile of the casing coincides at least approximately with the range of the final application load. Casing according to claim 16, characterized in that the nylon is made amorphous in advance, whereby the tubular laminate is brought to a predetermined end-use diameter. Casing according to claim 16, characterized in that the nylon comprises a heat-crystallizable nylon with a moisture absorption capacity of at least about 8%. Casing according to claim 19, characterized in that the structure of the tubular laminate comprises nylon 20 (outer) / adhesive / polyolefin (inner). Casing according to claim 20, characterized in that the nylon comprises nylon 6 or nylon 66. 22. Casing according to claim 20, characterized in that the polyolefin comprises polyethylene and the adhesive comprises a chemically modified polyolefin selected from the group consisting of ethylene-vinyl acetate polymer, high-density polyethylene and rubber-modified high-density polyethylene, which all are chemically modified by the presence of functional groups on the polymer, which have a strong affinity for nylon and which will form a strong bond with the nylon when coextruded under heat and pressure. 23. Device for manufacturing a snug food casing, characterized by a) melting members of a resulting tubular polymer laminate with a nylon outer layer and an 8300515 ψ ψ - V moisture barrier inner layer; b) means for quenching and solidifying the resulting tubular laminate, such that the nylon is made amorphous, while at the same time making the tube diameter about 5 equal to a predetermined final application diameter; and c) heat treatment means of the tubular laminate to crystallize the nylon and simultaneously wet to saturate the nylon. The device according to claim 23, characterized in that the melt molding member comprises a coextruding member. 25. Device according to claim 23, characterized in that the means for adjusting the diameter of the laminate comprises a mandrel with the predetermined final application diameter. An apparatus according to claim 25, characterized in that the quenching means comprises a water quenching means. Device according to claim 25, characterized in that the mandrel is cooled internally. 8300515