CA2126275C - Laminated films - Google Patents
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- CA2126275C CA2126275C CA 2126275 CA2126275A CA2126275C CA 2126275 C CA2126275 C CA 2126275C CA 2126275 CA2126275 CA 2126275 CA 2126275 A CA2126275 A CA 2126275A CA 2126275 C CA2126275 C CA 2126275C
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Abstract
The invention provides a heat-shrinkable thermoplastics packaging film comprising a laminate of two or more individual heat-shrinkable thermoplastics packaging films, where each of the individual films is substantially identical in composition and layer construction. The films are preferably prepared from double wound film, especially biaxially oriented film comprising LLDPE. The invention also provides a process of preparing such a film, comprising: a) providing two layers of heat-shrinkable thermoplastics packaging film, namely a first layer and a second layer, each of the first and second layers having inner and outer surfaces, the inner surfaces being adjacent to each other; b) treating the outer surface of the first layer to enable the first layer to adhere to the second layer; and c) winding the two layers together into a roll, such that the treated outer surface of the first layer adheres to the outer surface of the second layer to form a laminate. The laminated films of the invention have good strength as well as being advantageously thin.
Description
1.
IMPROVEMENTS IN AND/OR RELATING TO LAMINATED FILMS
This invention relates to a packaging film, and in particular to a laminated film, and to a process for preparing the same.
At present, single wound, irradiated polyolefin high shrink film is typically used for packaging, by manual overwrapping, of bone-in frozen or chilled meat cuts, especially pork or lamb ,.~.ut~~. Such films include the Cryovar_T"' DL19 film of W R Grace (Na) Ltd. The overwrapping concept requires operators to use wrapping techniques that provide multiple layers of film t;o cover the sharp bones of the meat cuts and prevent subsequent film tearing or puncturing during the shrink process and re:~ulting packaging rejection.
For applications such as these, a t.hi:n :hi.gh shrink film having good tensile strength wo~~zld be desirable.
IMPROVEMENTS IN AND/OR RELATING TO LAMINATED FILMS
This invention relates to a packaging film, and in particular to a laminated film, and to a process for preparing the same.
At present, single wound, irradiated polyolefin high shrink film is typically used for packaging, by manual overwrapping, of bone-in frozen or chilled meat cuts, especially pork or lamb ,.~.ut~~. Such films include the Cryovar_T"' DL19 film of W R Grace (Na) Ltd. The overwrapping concept requires operators to use wrapping techniques that provide multiple layers of film t;o cover the sharp bones of the meat cuts and prevent subsequent film tearing or puncturing during the shrink process and re:~ulting packaging rejection.
For applications such as these, a t.hi:n :hi.gh shrink film having good tensile strength wo~~zld be desirable.
It is an object of the present invention to go some way towards meeting the above desiderata or at least to offer the public a useful choice.
Accordingly, in a first aspect the present invention consists in a heat-shrinkable thermoplastics packaging film comprising a laminate of two or more individual heat-shrinkable thermoplastics packaging films, wherein each of said individual films is substantially identical in composition and layer construction.
In a preferred embodiment, the laminate comprises two individual films, the films together comprising double wound biaxially oriented film. The thickness of each of the individual films is preferably from about 10 to about 30~m, more preferably from about 15 to about 25~m.
In a preferred embodiment, the individual films contain polyethylene, preferably linear low density polyethylene (LLDPE).
In particularly preferred embodiments, the individual films are selected from the group consisting of:
W ."
' ~ 'w/
.y 1) a monolayer comprising 1:,LDPE, 2) a three layered film. comprising a core layer comprising LLDPE, and two outside layers each comprising LI DPE containing a slip agent; and 3) a three layered film comprising a core layer comprising LLDPE, and two outside layers each comprising a blend of LLDPE, ethylene vinyl acetate copolymer (EVA), polypropylene and a slip agent.
When the individual filin is 1), preferably the thickness of said individual film is from about 15 to about l9,um. When the individual film is 2), preferably the thickness of said individual film is about l9~cm. When the individual film is 3), preferably the thickness of said individual film is from about 19 to about 25~cm.
The laminate is also preferably printed, and the print is trapped between the individual films of the laminate.
In a further aspect the present invention may broadly be said to consist in a .
process of preparing a heat shrinkable thermoplastics packaging filin, comprising the step of laminiating two or more individual heat-shrinkable thermoplastics packaging films, wherein each of said individual films is substantially identical in composition and layer construction.
In preferred embodiments, the laminated film is as described above.
In a further aspect the present invention consists in a process of preparing a laminated heat-shrinkable thermoplastics packaging film, comprising the steps of:
a) providing two layers, each layer comprising an individual heat-shrinkable thermoplastics packaging film, said two layers comprising a first layer and a second layer, each of said first and second layers having inner and outer surfaces, said inner surfaces beinø a~iiacent t~ each other ' '~ ' 4 21~6~'~5 b) treating the outer surface of the first layer to enable the first layer to adhere to the second Layer; and c) winding the two layers together into a roll, such that the treated outer surface of the first layer adheres to the outer surface of the second layer to form a Laminate of the first and second layers.
The layers are preferably wound onto a cylinder, and the process preferably also includes the further step of unwinding the unadhered portion of the first layer from the roll.
In a preferred embodiment the two layers are substantially identical in composition and layer construction and together comprise double wound film. The double wound film preferably comprises biaxially oriented film containing LL.DPE, each layer having a thiclmess of from about 10 to about 30~m, more preferably from about 15 to about 25~cm, and the layers are selected from the group consisting of:
1) a monolayer comprising LLDPE;
2) a three layered film comprising a core layer comprising LLDPE, and two outside layers each comprising I.,LDPE and containing a slip agent; and 3) a three layered film comprising a core layer comprising L.LDPE, and two outside layers each comprising a blend of 1..LDPE, EVA, polypropylene and a slip agent.
In a preferred embodiment, the laminated film is printed, and the printing and treatment steps are carried out on a printing press, more preferably a central ' impression drum ffexographic printing press.
In one form of the invention, the treatment step (b) comprises applying laminating varnish to the outer surface of the first layer. In this form of the invention, preferably '' ' ~ ~ ~
' ~-~ 5 21262' the outer surface of the first layer is printed before the laminating varnish is applied, and the varnish is applied using a full laminating varnish plate.
In an alternative form of the invention, the treatment step (b) comprises flame treatment or electrical discharge treatment. In this form of the invention, preferably the outer surfaces of both of the first and second layers are treated, and the outer surface of the first layer is printed after the treatment bas been carried out.
In a further aspect the present invention consists in a heat-shrinkable thermoplastics packaging film comprising a laminate of two or more individual heat-shrinkable thermoplastics packaging films, wherein each of said individual films has a thickness of 25 ~m or less.
In a preferred embodiment the laminate comprises two individual films substantially identical in composition and layer construction, and the films together comprise double wound biaxially oriented film.
Preferably each individual film comprises 11 nPE and has a thickness of from to 25~cm.
In still a further aspect the present invention consists in a process of preparing a heat-shrinkable thermoplastic packaging fiha,, comprising the step of laminating two or more individual heat-shrinkable thermoplastics packaging fihms, wherein each of said individual films has a thickness of 25~m or less.
In a further aspect the present invention consists in a laminated film produced by a process as herein defined.
Preferred forms of the present invention will now be described in more detail with reference to the accompanying drawings, in which:
Figure 1 is a diagrammatic view; of a typical central impression drum flexographic printing press, on which the process of the present invention may be carried-out, and showing the various stages in the process;
Figures 2A and 2B are diagrammatic cross-sections of a roll of wound-up laminate produced according to the proces s of the present invention, showing the.
final step in the process in which the top layer of the laminate is unwound back on itself;
and Figure 3 is a diagrammatic cross section showing the structure of a laminated film of the present invention.
In a preferred form of the inventioy the laminated films of the invention are produced from a starting material comprising a double wound, heat shrinkable thermoplastics packaging film. The term "double wound" refers to a film which has been produced from an extruded collapsed film bubble which has had its two edges slit out.
The films are preferably of a gauge ranging from about l0,um to 3U~Cm, more preferably from 15 to 25,um. Biaxially oriented films containing LLI?PE are particularly suitable. Single layer films and coextruded multi-layered films may all be used.
Examples of preferred films which may be used are (1) the DL19 film of W R
Grace (NZ) Ltd, which is an irradiated biaxially oriented film comprising a monolayei,- of LLDPE, with a gauge. of 15 or 19~m, (2) the MD film of W R Grace & Co-Conn, which is a non-irradiated biaxially oriented three layered structure consisting of a core layer of LLDPE and two outside layers each comprising LLDPE with Slip lVlasterbatch, with a gauge of l9~cm, and (3) the MR film of W R Grace & Co-Conn, which is an irradiated biaxially oriented three layered structure consisting of a core layer of .LLDPE, and balanced inner and outer layers of a blend of LLDPE, EVA, TM
polypropylene and Slip Masterbatch, with a gauge of 19 or 25,um. 'The term "Slip TM
~'l~Iasterbatch" refers to a blend of clays, waxes and sGp additives, which imparts antiblock characteristics to the film. ~.lternative fzlm.s suitable for use in the present invention are the Cryovac BDF barrier films.
21~62'~5 It is preferred that the individual films to be laminated are identical, but laminates produced from different individual elms are also within the scope of the invention.
In a preferred form of the invention, the laminates of the present invention are prepared using a printing press, preferably a central impression drum (CI) flexographic printing press. Such printing presses are well known in the art.
Referring to Figure 1, a double layer of film 10 is first loaded into an unwind press station 1, and threaded through the press as a double layer in the same manner as single layer material would be processed. The arrows show the direction of the film through the press. At a treatment station 2, the top (outer) surface of the upper layer of material is - treated to enable later printing of the surface to be performed. The treatment reduces the surface tension of the film to match it to the surface tension of the inks to be used for printing. Flame treatment is typically the treatment used, but electrical discharge treatment ('Corona' treatment) may also be used. After the surface layer has been treated, the elm advances to the drum 3 where printing of the top surface of the upper layer, as desired, is carried out at printing stations 4 to 8 (each of which will comprise a different coloured ink). Preferred inks for use in the invention include the W R Grace & Co-Conn R.D system inks.
Interstation drying is carried out between each print station. Laminating varnish is then applied at station 9, to the top surface of the upper layer of the film, preferably as a complete web overlay. The laminating varnish treatment is the treatment which enables subsequent lamination of the two layers, i.e. it facilitates adhesion of the two layers. A preferred laminating varnish for'use in the present invention is a "Morrisons Printing Ink" proprietary ink, code No. WI5437. Other suitable materials will be apparent to those skilled in the art.
21262'~~ w The preferred varnish treatment is achieved using a full laminating varnish plate, although grid plates and strip plates may also be used. A "tall plate" Is a Oat plate covering the surface of the plate cylinder (which carries the printing plates), "strip plates" arc placed in strips around the plate cylinder, and a "grid plate" is a plate with a raised grid design covering the surface of the plate cylinder.
After the printing and lamination adhesive application processes have been completed, the material travels (still as a double layer with the t«p surface of.the top layer printed and with varnish applied) through the press tunnel 12 (where further drying is carried out) to a press rewind station 11. It is preferred that any reverse angle rollers which will come into contact with the varnish-containing top surface of the tap layer, during this process, are covered with a thin layer comprising a teflon coating.
This Prevents any adhesion hctween the varnish and the rollers occurring. The material is then rewound, still ac a doable layer. The winding up of the material laminates the upper and lower layers together. That is, as the film is wound up, the top (outward.
facing) surface of the upper layer will adhere to the bottom (outward facing) surface . of the' lower layer. This is shown more clearly in Figure 2A, in which the two llycrs 20.°
and 21 are shown, wound up on a roll 24. The treated upper surface of the top layer 20 is indicated by numeral 22 and the continuous wavy line. The arrows show the adhesion between the surfaces. ' When the material has been wound up, the top layer 20 is wound hack on itself, that is, unwound, for nearly one revolution in the dircctlott indicated by the arrow in Figure 2A. The treated surface of the unwound portion of the tap layer 20 will contact the bottom surface of the bottom layer 21 and adhere to it, locking the two layers together as shown in Figure 2B. The surplus material 23 of'the top layer which has no corresponding portion of bottom layer to adhere to, may be slit off if desired. The laminated material is thereby conveniently already wound up and presented ready for use.
In an alternative form ~f the present invention, laminating varnish is not used. It has been found, for example, that lamination of the DL19 film can be achieved by using only the flame or electrical discharge treatment whica is carried out before the printing process. The flame or electrical discharge treatment imparts a. blocking or bonding characteristic to the DL 14 film. ttt this form of the invention, the outer surfaces of both the first and second layers will be treated i~ this wanner. This cart be achieved by using a 'Corona' press trcater, which can treat both iilrn surfaces in one pass before printing. A.ltcrnatively, if press flame trcatrnent is used, in which only one surface eau he treated with each pass, the film is run through the press twice. The first piLSs through the press treats one outer surface only. The second pass treats the opposite outer surface. Print is then applies! to one outer surface. After tile second press pa.u and rewinding of the material, the treated printed surface is wound back onto the unprintcd treated surface (as shown in Figure 2D;., thus laminating the film.
It can be seen that by carrying out the process of the present .invention the printed matter will be trapped between the two layers of the laminate. Figure 3 shows a laminated film according to the present invention, having inner and outer layers 20 and 21 adhered together by a layer of v~.rnisit 22.
>;xamples Laminated films were. prepared using the process described above, 1'he films and varnish plate used, as well as results of puncture energy tests carried out on the .
laminated films using an Instron Model 4301 (standard test prugrarnme programmed into the machine), are detailed in Table 1 below. The re.~ults for the same tests performed on single layer MD and I~L19 films arc also shown in the table.
,o~ 2126275 TABLE 1 .
. ra 1 P nk l:nererPeak Filtn nd at Stress Gauee Test nd ikg) i8m) ~kg/mm2)Gym) MD: full laminating varnish plate 6.SZ 20.$ 3.71 1.9/19 MR: full .laminating varnish plate 10.1 3fi.U 4.74 25/25 MR: grid laminating varnish plate 7.65 24.8 4.SS 1/19 DL19: full laminating varnish plate 7.94 23.3 5.04 19/19 MD: single layer3.21 1U:9 4.04 19 DL19: single 4.76 12S 6.02 19 lnycr As can be seen from the results in Table I, the double layer films were approximately twice as ~uong as the corresponding single layer films.
1n an alternative form of the invention, a single layer of film only may be loaded into the unwind press station 1, and subjected to the treatment, printing and laminating varnish application processes described above. The second layer of film tray then be introduced after the lust layer has emerged from the press tunnel 12, and directly laminated unto the first layer.
~.r ~ 11 The lamiaatcJ films of the present invention offer a number of advantugea.
First a laminate of two films of for example 19~m thickness cacti, will be considerably stronger than a single, i.e. non-laminated, film of 38~ra. Thus, d,e present invention provides hc:tt-shrinkable laminated Glms of improved strength, which arc st111 acceptably thin. The trapping of the print hetween the two IayCrs of the laminate also avoids the problem of damage caused to printed labels ac frozen cuts move against adjacent cuts in a rarton of packaged cuts.
Also, a-s will he apparent front the foregoing description, in a preferred embodiment of the invention, the films of the present invention are prepared by tha efficient process of simply extruding or coextruJing a single monolayer or multilayer material; which is then slit and Double wound in preparation for the lamination process JesaibeJ above.
~e (acninateJ filme of the present invention may also allow the use of a wide range of sctni-automatic and automatic cyuipment for packaging bone-in meat cuts.
For example, a pillow pack (horizontal form, fill and seal) could be used. The preferred sealing or closure method for such app(icatioos would be the trim-sealing of the hlm.
Although the invention has been described with reference to a particular embodiment, other variations and modifications will be apparent to a person skilled in the art without departing from the scope of the invention as defined itt the following claims.
Accordingly, in a first aspect the present invention consists in a heat-shrinkable thermoplastics packaging film comprising a laminate of two or more individual heat-shrinkable thermoplastics packaging films, wherein each of said individual films is substantially identical in composition and layer construction.
In a preferred embodiment, the laminate comprises two individual films, the films together comprising double wound biaxially oriented film. The thickness of each of the individual films is preferably from about 10 to about 30~m, more preferably from about 15 to about 25~m.
In a preferred embodiment, the individual films contain polyethylene, preferably linear low density polyethylene (LLDPE).
In particularly preferred embodiments, the individual films are selected from the group consisting of:
W ."
' ~ 'w/
.y 1) a monolayer comprising 1:,LDPE, 2) a three layered film. comprising a core layer comprising LLDPE, and two outside layers each comprising LI DPE containing a slip agent; and 3) a three layered film comprising a core layer comprising LLDPE, and two outside layers each comprising a blend of LLDPE, ethylene vinyl acetate copolymer (EVA), polypropylene and a slip agent.
When the individual filin is 1), preferably the thickness of said individual film is from about 15 to about l9,um. When the individual film is 2), preferably the thickness of said individual film is about l9~cm. When the individual film is 3), preferably the thickness of said individual film is from about 19 to about 25~cm.
The laminate is also preferably printed, and the print is trapped between the individual films of the laminate.
In a further aspect the present invention may broadly be said to consist in a .
process of preparing a heat shrinkable thermoplastics packaging filin, comprising the step of laminiating two or more individual heat-shrinkable thermoplastics packaging films, wherein each of said individual films is substantially identical in composition and layer construction.
In preferred embodiments, the laminated film is as described above.
In a further aspect the present invention consists in a process of preparing a laminated heat-shrinkable thermoplastics packaging film, comprising the steps of:
a) providing two layers, each layer comprising an individual heat-shrinkable thermoplastics packaging film, said two layers comprising a first layer and a second layer, each of said first and second layers having inner and outer surfaces, said inner surfaces beinø a~iiacent t~ each other ' '~ ' 4 21~6~'~5 b) treating the outer surface of the first layer to enable the first layer to adhere to the second Layer; and c) winding the two layers together into a roll, such that the treated outer surface of the first layer adheres to the outer surface of the second layer to form a Laminate of the first and second layers.
The layers are preferably wound onto a cylinder, and the process preferably also includes the further step of unwinding the unadhered portion of the first layer from the roll.
In a preferred embodiment the two layers are substantially identical in composition and layer construction and together comprise double wound film. The double wound film preferably comprises biaxially oriented film containing LL.DPE, each layer having a thiclmess of from about 10 to about 30~m, more preferably from about 15 to about 25~cm, and the layers are selected from the group consisting of:
1) a monolayer comprising LLDPE;
2) a three layered film comprising a core layer comprising LLDPE, and two outside layers each comprising I.,LDPE and containing a slip agent; and 3) a three layered film comprising a core layer comprising L.LDPE, and two outside layers each comprising a blend of 1..LDPE, EVA, polypropylene and a slip agent.
In a preferred embodiment, the laminated film is printed, and the printing and treatment steps are carried out on a printing press, more preferably a central ' impression drum ffexographic printing press.
In one form of the invention, the treatment step (b) comprises applying laminating varnish to the outer surface of the first layer. In this form of the invention, preferably '' ' ~ ~ ~
' ~-~ 5 21262' the outer surface of the first layer is printed before the laminating varnish is applied, and the varnish is applied using a full laminating varnish plate.
In an alternative form of the invention, the treatment step (b) comprises flame treatment or electrical discharge treatment. In this form of the invention, preferably the outer surfaces of both of the first and second layers are treated, and the outer surface of the first layer is printed after the treatment bas been carried out.
In a further aspect the present invention consists in a heat-shrinkable thermoplastics packaging film comprising a laminate of two or more individual heat-shrinkable thermoplastics packaging films, wherein each of said individual films has a thickness of 25 ~m or less.
In a preferred embodiment the laminate comprises two individual films substantially identical in composition and layer construction, and the films together comprise double wound biaxially oriented film.
Preferably each individual film comprises 11 nPE and has a thickness of from to 25~cm.
In still a further aspect the present invention consists in a process of preparing a heat-shrinkable thermoplastic packaging fiha,, comprising the step of laminating two or more individual heat-shrinkable thermoplastics packaging fihms, wherein each of said individual films has a thickness of 25~m or less.
In a further aspect the present invention consists in a laminated film produced by a process as herein defined.
Preferred forms of the present invention will now be described in more detail with reference to the accompanying drawings, in which:
Figure 1 is a diagrammatic view; of a typical central impression drum flexographic printing press, on which the process of the present invention may be carried-out, and showing the various stages in the process;
Figures 2A and 2B are diagrammatic cross-sections of a roll of wound-up laminate produced according to the proces s of the present invention, showing the.
final step in the process in which the top layer of the laminate is unwound back on itself;
and Figure 3 is a diagrammatic cross section showing the structure of a laminated film of the present invention.
In a preferred form of the inventioy the laminated films of the invention are produced from a starting material comprising a double wound, heat shrinkable thermoplastics packaging film. The term "double wound" refers to a film which has been produced from an extruded collapsed film bubble which has had its two edges slit out.
The films are preferably of a gauge ranging from about l0,um to 3U~Cm, more preferably from 15 to 25,um. Biaxially oriented films containing LLI?PE are particularly suitable. Single layer films and coextruded multi-layered films may all be used.
Examples of preferred films which may be used are (1) the DL19 film of W R
Grace (NZ) Ltd, which is an irradiated biaxially oriented film comprising a monolayei,- of LLDPE, with a gauge. of 15 or 19~m, (2) the MD film of W R Grace & Co-Conn, which is a non-irradiated biaxially oriented three layered structure consisting of a core layer of LLDPE and two outside layers each comprising LLDPE with Slip lVlasterbatch, with a gauge of l9~cm, and (3) the MR film of W R Grace & Co-Conn, which is an irradiated biaxially oriented three layered structure consisting of a core layer of .LLDPE, and balanced inner and outer layers of a blend of LLDPE, EVA, TM
polypropylene and Slip Masterbatch, with a gauge of 19 or 25,um. 'The term "Slip TM
~'l~Iasterbatch" refers to a blend of clays, waxes and sGp additives, which imparts antiblock characteristics to the film. ~.lternative fzlm.s suitable for use in the present invention are the Cryovac BDF barrier films.
21~62'~5 It is preferred that the individual films to be laminated are identical, but laminates produced from different individual elms are also within the scope of the invention.
In a preferred form of the invention, the laminates of the present invention are prepared using a printing press, preferably a central impression drum (CI) flexographic printing press. Such printing presses are well known in the art.
Referring to Figure 1, a double layer of film 10 is first loaded into an unwind press station 1, and threaded through the press as a double layer in the same manner as single layer material would be processed. The arrows show the direction of the film through the press. At a treatment station 2, the top (outer) surface of the upper layer of material is - treated to enable later printing of the surface to be performed. The treatment reduces the surface tension of the film to match it to the surface tension of the inks to be used for printing. Flame treatment is typically the treatment used, but electrical discharge treatment ('Corona' treatment) may also be used. After the surface layer has been treated, the elm advances to the drum 3 where printing of the top surface of the upper layer, as desired, is carried out at printing stations 4 to 8 (each of which will comprise a different coloured ink). Preferred inks for use in the invention include the W R Grace & Co-Conn R.D system inks.
Interstation drying is carried out between each print station. Laminating varnish is then applied at station 9, to the top surface of the upper layer of the film, preferably as a complete web overlay. The laminating varnish treatment is the treatment which enables subsequent lamination of the two layers, i.e. it facilitates adhesion of the two layers. A preferred laminating varnish for'use in the present invention is a "Morrisons Printing Ink" proprietary ink, code No. WI5437. Other suitable materials will be apparent to those skilled in the art.
21262'~~ w The preferred varnish treatment is achieved using a full laminating varnish plate, although grid plates and strip plates may also be used. A "tall plate" Is a Oat plate covering the surface of the plate cylinder (which carries the printing plates), "strip plates" arc placed in strips around the plate cylinder, and a "grid plate" is a plate with a raised grid design covering the surface of the plate cylinder.
After the printing and lamination adhesive application processes have been completed, the material travels (still as a double layer with the t«p surface of.the top layer printed and with varnish applied) through the press tunnel 12 (where further drying is carried out) to a press rewind station 11. It is preferred that any reverse angle rollers which will come into contact with the varnish-containing top surface of the tap layer, during this process, are covered with a thin layer comprising a teflon coating.
This Prevents any adhesion hctween the varnish and the rollers occurring. The material is then rewound, still ac a doable layer. The winding up of the material laminates the upper and lower layers together. That is, as the film is wound up, the top (outward.
facing) surface of the upper layer will adhere to the bottom (outward facing) surface . of the' lower layer. This is shown more clearly in Figure 2A, in which the two llycrs 20.°
and 21 are shown, wound up on a roll 24. The treated upper surface of the top layer 20 is indicated by numeral 22 and the continuous wavy line. The arrows show the adhesion between the surfaces. ' When the material has been wound up, the top layer 20 is wound hack on itself, that is, unwound, for nearly one revolution in the dircctlott indicated by the arrow in Figure 2A. The treated surface of the unwound portion of the tap layer 20 will contact the bottom surface of the bottom layer 21 and adhere to it, locking the two layers together as shown in Figure 2B. The surplus material 23 of'the top layer which has no corresponding portion of bottom layer to adhere to, may be slit off if desired. The laminated material is thereby conveniently already wound up and presented ready for use.
In an alternative form ~f the present invention, laminating varnish is not used. It has been found, for example, that lamination of the DL19 film can be achieved by using only the flame or electrical discharge treatment whica is carried out before the printing process. The flame or electrical discharge treatment imparts a. blocking or bonding characteristic to the DL 14 film. ttt this form of the invention, the outer surfaces of both the first and second layers will be treated i~ this wanner. This cart be achieved by using a 'Corona' press trcater, which can treat both iilrn surfaces in one pass before printing. A.ltcrnatively, if press flame trcatrnent is used, in which only one surface eau he treated with each pass, the film is run through the press twice. The first piLSs through the press treats one outer surface only. The second pass treats the opposite outer surface. Print is then applies! to one outer surface. After tile second press pa.u and rewinding of the material, the treated printed surface is wound back onto the unprintcd treated surface (as shown in Figure 2D;., thus laminating the film.
It can be seen that by carrying out the process of the present .invention the printed matter will be trapped between the two layers of the laminate. Figure 3 shows a laminated film according to the present invention, having inner and outer layers 20 and 21 adhered together by a layer of v~.rnisit 22.
>;xamples Laminated films were. prepared using the process described above, 1'he films and varnish plate used, as well as results of puncture energy tests carried out on the .
laminated films using an Instron Model 4301 (standard test prugrarnme programmed into the machine), are detailed in Table 1 below. The re.~ults for the same tests performed on single layer MD and I~L19 films arc also shown in the table.
,o~ 2126275 TABLE 1 .
. ra 1 P nk l:nererPeak Filtn nd at Stress Gauee Test nd ikg) i8m) ~kg/mm2)Gym) MD: full laminating varnish plate 6.SZ 20.$ 3.71 1.9/19 MR: full .laminating varnish plate 10.1 3fi.U 4.74 25/25 MR: grid laminating varnish plate 7.65 24.8 4.SS 1/19 DL19: full laminating varnish plate 7.94 23.3 5.04 19/19 MD: single layer3.21 1U:9 4.04 19 DL19: single 4.76 12S 6.02 19 lnycr As can be seen from the results in Table I, the double layer films were approximately twice as ~uong as the corresponding single layer films.
1n an alternative form of the invention, a single layer of film only may be loaded into the unwind press station 1, and subjected to the treatment, printing and laminating varnish application processes described above. The second layer of film tray then be introduced after the lust layer has emerged from the press tunnel 12, and directly laminated unto the first layer.
~.r ~ 11 The lamiaatcJ films of the present invention offer a number of advantugea.
First a laminate of two films of for example 19~m thickness cacti, will be considerably stronger than a single, i.e. non-laminated, film of 38~ra. Thus, d,e present invention provides hc:tt-shrinkable laminated Glms of improved strength, which arc st111 acceptably thin. The trapping of the print hetween the two IayCrs of the laminate also avoids the problem of damage caused to printed labels ac frozen cuts move against adjacent cuts in a rarton of packaged cuts.
Also, a-s will he apparent front the foregoing description, in a preferred embodiment of the invention, the films of the present invention are prepared by tha efficient process of simply extruding or coextruJing a single monolayer or multilayer material; which is then slit and Double wound in preparation for the lamination process JesaibeJ above.
~e (acninateJ filme of the present invention may also allow the use of a wide range of sctni-automatic and automatic cyuipment for packaging bone-in meat cuts.
For example, a pillow pack (horizontal form, fill and seal) could be used. The preferred sealing or closure method for such app(icatioos would be the trim-sealing of the hlm.
Although the invention has been described with reference to a particular embodiment, other variations and modifications will be apparent to a person skilled in the art without departing from the scope of the invention as defined itt the following claims.
Claims (13)
1. A heat-shrinkable thermoplastic packaging film comprising a laminate of two or more individual heat-shrinkable thermoplastic packaging films, wherein each of said individual films is selected from the group consisting of:
1) a monolayer film comprising LLDPE;
1) a monolayer film comprising LLDPE;
2) a three layered film comprising a core layer comprising LLDPE, and two outside layers each comprising LLDPE
and containing a slip agent; and
and containing a slip agent; and
3) a three layered film comprising a core layer comprising LLDPE, and two outside layers each comprising a blend of LLDPE, EVA, polypropylene, and a slip agent.
2. A film as claimed in claim 1 comprising a laminate of two identical films, wherein said films together comprise double wound biaxially oriented film.
3. The film as claimed in claim 1 or 2 wherein the thickness of each of said individual films is from about 10 to about 30µm.
2. A film as claimed in claim 1 comprising a laminate of two identical films, wherein said films together comprise double wound biaxially oriented film.
3. The film as claimed in claim 1 or 2 wherein the thickness of each of said individual films is from about 10 to about 30µm.
4. A film as claimed in claim 1 or 2 wherein each individual film is a monolayer film comprising LLDPE, and having a thickness of from about 15 to about 19µm.
5. A film as claimed in any one of claims 1 to 4 wherein print is trapped between two individual films.
6. A film as claimed in claim 1 or 2 wherein each individual film has a thickness of from 15 to 25µm.
7. A film as claimed in claim 1, wherein each of the individual films is substantially identical in composition and layer construction.
8. A process for preparing a heat-shrinkable thermoplastic packing film, comprising the step of laminating two or more individual heat-shrinkable thermoplastic packaging films as defined in claim 1.
9. The process as claimed in claim 8 wherein the individual heat-shrinkable films have a thickness of from 10 to about 30µm.
10. The process as claimed in claim 9 wherein the thickness is from about 15 to about 25µm.
11. The process as claimed in claim 8 wherein each individual heat-shrinkable film comprises LLDPE and has a thickness of from about 15 to about 19µm.
12. The process as claimed in any one of claims 8 to 11 wherein print is trapped between two individual films.
13. The process as claimed in any one of claims 8 to 12 wherein the individual films are substantially identical in composition and layer construction.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NZ247940A NZ247940A (en) | 1993-06-21 | 1993-06-21 | Heat-shrinkable thermoplastics packaging film comprising at least two identical films |
| NZ247940 | 1993-06-21 | ||
| NZ24794994 | 1994-06-16 | ||
| NZ247,940 | 1994-06-16 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2126275A1 CA2126275A1 (en) | 1994-12-22 |
| CA2126275C true CA2126275C (en) | 2003-10-21 |
Family
ID=29405447
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2126275 Expired - Fee Related CA2126275C (en) | 1993-06-21 | 1994-06-20 | Laminated films |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2126275C (en) |
-
1994
- 1994-06-20 CA CA 2126275 patent/CA2126275C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2126275A1 (en) | 1994-12-22 |
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| Date | Code | Title | Description |
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| EEER | Examination request | ||
| MKLA | Lapsed |