DE69625829T2 - freeze bag - Google Patents

Abstract

The present invention provides a freezer bag comprising a multibag (90) having at least an inner liner bag (91) and an outer support bag (92), the inner liner bag having a first sidewall (94) and a second sidewall (94') attached together along respective lateral edges forming edge seals, each sidewall having a top edge (95, 95'), and the liner bag having a folded edge defining the bottom of the liner bag, the outer support bag having two sidewalls (96, 96') attached together along respective lateral edges forming edge seals, each sidewall having top edges defining the opening to the multibag, and the support bag having a folded edge defining the bottom of the multibag, the top edges of the liner bag being attached to an inner surface of each respective sidewall of the support bag wherein the liner is thermoplastic and has a thickness of less than 2.0 mil (50.8 micron).

Description

The present invention relates to freezer bags, a method and an apparatus for their manufacture and their use for preventing freezer burn during the storage of meat. The invention arose from attempts to provide "freezer bags" for the repacking and storage of raw meat in freezers by the end user in a way that reduces so-called "freezer burn". However, the invention also has aspects that extend to the commercial packaging or repackaging of food, for example in the supermarket or slaughterhouse.

Multi-sealable plastic storage bags have been around for a long time. Today they are typically available to the public in boxes that are labeled according to the recommended purpose (e.g. storage, heavy-duty freezer bags, vegetable bags, garbage bags). The purpose is often also indicated on the bag itself - e.g. "ZIPLOC BRAND Heavy Duty Freezer Bags".

The term "freezer bag" is used here to refer to a bag that has a significant functional benefit in the storage of food in a freezer. "Freezer bags" are typically available in 2 gallons (7.57 liters), 1 gallon (3.785 liters), 1/2 gallon (1.9 liters) folded, 1 quart (0.95 liters), and 1 pint (0.47 liters) sizes.

The term "freezer burn" is the name given to the dehydration that occurs when unpackaged or improperly packaged foods are stored in the low-humidity atmosphere of a freezer (see "Packaging Foods With Plastics" by Wilmer A. Jenkins and James P. Harrington, 1991, Technomic Publishing Com., Inc., page 305). Consumers typically describe freezer burn by three main visual attributes: ice crystal formation, dehydration, and discoloration.

Freezer burn remains one of the main complaints among consumers - despite the commercial success of freezer bags made of thick plastic film. In the long term, however, freezer burn leads to a complex impairment of food quality with undesirable textural changes, followed by chemical changes such as pigment degradation and oxidative rancidity of lipids. Taste, aroma, mouthfeel and color can all be lost. Freezer burn of raw red meat is particularly critical because of its effect on its color.

The previously mentioned book "Packaging Foods With Plastics" provides an excellent summary of the state of the art, with all information on "commercial" packaging of fresh red meat collected in Chapter 7. Strangely, however, the book does not mention freezer burn; it is only defined in the glossary.

"Keeping Food Fresh" is the title of an article in the magazine "Consumer Reports", March 1994, pp. 143-147. This article is too new to be relevant to the present application as prior art. Nevertheless, its content is interesting because it shows the absence of certain types of known technology and therefore argues in favor of the patentability of the present invention.

The article in Consumer Reports attempts to answer the question of which packaging material (plastic, aluminum, wax paper, bags, wraps, or reusable containers) is best suited to (1) keep food fresh for a long time, (2) do so at the lowest total cost, and (3) cause the least possible environmental damage. The product that receives the highest rating is "ZIPLOC Pleated Freezer Bags" (see page 145). It points out that freezer burn can occur on food stored in plastic containers if the container contains too much air. As for wraps (plastic film and freezer paper), the article advises against double wrapping for cost and environmental reasons, and states that tests have shown that double wrapping does not provide any significant additional protection anyway. The invention described below is neither disclosed nor suggested in this article.

The patent literature contains descriptions of various types of bags with linings or double walls with some space between the latter. Some of these patents relate to the transportation and storage of food. US-PS 4,211,091 (Campbell) relates to an "Insulated Lunch Bag". US-PS 4,211,267 (Skovgaard) describes a "Carrying Bag" for carrying frozen food home before thawing it. US-PS 4,797,010 (assigned to Nabisco Brands) discloses a paper double bag as a "reheatable, resealable package for fried food". US Patent No. 4,358,466 (assigned to The Dow Chemical Company) relates to an improved "Freezer To Microwave Oven Bag". This bag is formed by two wing-shaped bags on either side of a standing tap-like outlet. US Patent No. 5,005,679 (Hjelle) relates to carrying bags with a cooling chamber. All of these bags and bags for food appear to have very thick side walls in contact with the bag contents compared to the invention described below. None of these patents focuses on freezer burn.

Books on home freezing techniques are of interest to the present invention. As for wrapping meat for passage through a freezer, Rodale's Complete Book of Home Freezing by Marilyn Hodges and the Rodale Test Kitchen staff (1984) suggests the hardly practical method of wrapping meat piece by piece in a single layer of freezer paper and sucking out the air with a drinking straw (trying not to get blood in your mouth) to reduce the amount of dehydration in the freezer.

As consumer surveys have shown, there appears to be a significant need to improve existing methods of packaging fresh meat - coupled with the fact that in the US alone there is a huge retail market that consumes many millions of dollars worth of packaging annually.

In contrast to the state of the art, it has now surprisingly been found that certain types of multi-walled plastic bags (hereinafter referred to as "multi-bags") are better suited for use as functional freezer bags for freezer burn-free storage of meat than corresponding single-wall freezer bags (of the same or higher weight as multi-wall bags).

An example of a multi-bag is given in GB 2 097 361, which is the basis of the preamble of claim 1. Each layer of the multi-bag is made of a plastic film of approximately 11 micrometers thickness, although a thickness range of 4-100 micrometers is mentioned. The freezer burn problem is not discussed in this document.

According to a first aspect of the present invention, a freezer bag is provided for freezer burn-free storage of meat, which has a multi-bag with at least one inner lining bag and an outer support bag, each made of thermoplastic material, wherein the lining bag has a first and a second side wall which are attached to one another along corresponding side edges to form tight seals, each side wall has an upper edge and the lining bag has a folded edge which forms the bottom of the lining bag, the outer support bag has two side walls which are attached to one another along associated side edges so that edge seals are formed, the side walls each have upper edges which form the opening of the multi-bag, and the support bag has a folded edge which forms the bottom of the multi-bag, and wherein the lining bag is attached with the upper edges to an inner side of each associated side wall of the support bag, characterized in that the support bag has a nominal sidewall thickness of 33 um to 76 um (1.3 to 3.0 mils) and the liner bag has a nominal sidewall thickness of 7.6 um to 25 um (0.3 to 1.0 mils).

According to a further aspect, the present invention provides a method for producing multi-bags according to one of claims 1 to 6 for A freezer burn-free storage system for meat comprising at least one inner liner bag and one outer support bag, comprising the steps of: feeding a first thermoplastic film web having a thickness of 33 µm to 76 µm (1.3 to 3.0 mils) and a first transverse web width between parallel edges; feeding at least one second thermoplastic film web having a thickness of 7.6 µm to 25 µm (0.3 to 1.0 mils) and a second transverse web width between parallel edges, the second web width being less than the width of the first thermoplastic film; laying the second thermoplastic film web on the first thermoplastic film web between the parallel edges of the first film web; securing the second thermoplastic film web to the first thermoplastic film web along the parallel edges of the second thermoplastic film web; folding the films transversely at longitudinal intervals to form the bottom of the bag; and cutting the folded films to form a seal to form the bags.

According to yet another aspect of the invention, there is provided an apparatus for producing multi-bags according to any one of claims 1 to 6 for freezer burn-free storage of meat, which have at least one inner liner and one outer support bag, with means for feeding a first thermoplastic film web having a thickness of 33 µm to 76 µm (1.3 to 3.0 mils) and a first web width in the transverse direction between parallel edges; means for feeding at least one second thermoplastic film web having a thickness of 7.6 µm to 25 µm (0.3 to 1.0 mils) and a second web width in the transverse direction between parallel edges, the second web width being smaller than the width of the first thermoplastic film; means for laying the second thermoplastic film web on the first thermoplastic film web between parallel edges of the first film web; means for securing the second thermoplastic film web to the first thermoplastic film web along parallel edges of the second thermoplastic film web; means for folding the films transversely at longitudinal intervals to form the bag bottom; and means for cutting the folded films transversely to form a seal to form bags.

The invention also relates to the use of the bags for preventing freezer burn when storing meat.

Fig. 1A is a front view of a known multi-sealable thermoplastic single-wall bag with zip closure;

Fig. 1B is a section along line 1B-1B of Fig. 1A;

Fig. 2A is a front view of a double-walled bag according to the invention having (i) a thinner inner wall panel or liner and (ii) common side closures between the inner and outer wall panels and optionally (iii) a vent opening in the outer wall panel to connect the space between the inner and outer wall panels to the atmosphere outside the outer wall panel;

Fig. 2B is a partial sectional view taken along line 2B-2B of Fig. 2A;

Fig. 2C is a partial sectional view taken along line 2C-2C of Fig. 2A;

Fig. 3A is a front view of another double-wall bag according to the invention with separate side closures, wherein the liner bag is attached longitudinally over the entire length of the inner surfaces of the side wall panels of the support bag;

Fig. 3B is a partial sectional view taken along line 3B-3B of Fig. 3A;

Fig. 3C is a section along line 3C-3C of Fig. 3B;

Fig. 4A is a front view of another double-walled bag according to the invention, wherein the liner bag is fitted longitudinally over a portion of the total length of the inner surfaces of the side wall panels of the support bag and the space between the wall panels of the liner and support bags is connected to the space in the liner bag;

Fig. 4B is a partial sectional view taken along line 4B-4B of Fig. 4A;

Fig. 4C is a partial sectional view taken along line 4C-4C of Fig. 4B;

Figure 5A is a front view of a 3-layer multi-bag according to the invention with an inner film layer between the liner and support bags, the liner bag containing microholes;

Fig. 5B is a partial sectional view taken along line 5B-5B of Fig. 5A;

Fig. 5C is a partial sectional view taken along line 5C-5C of Fig. 5A showing an optional third layer between the liner and support bags of Fig. 5A;

Fig. 6A is a front view of a package of "meat in a sealed bag" according to the invention;

Fig. 6B is a section taken along line 6B-6B of Fig. 6A;

Figure 7 is a diagrammatic flow chart for a manual process for making experimental freezer bags according to the invention;

Fig. 8 is a diagrammatic flow chart for a method of making freezer bags with a common edge seal between the liner and support bags according to the invention;

Fig. 9A is a front view of a double-walled bag according to the invention in which a liner bag with a textured - in particular an embossed film on at least the inner side;

Fig. 9B is a section taken along line 9B-9B of Fig. 9A;

Fig. 9C is an enlarged section of a cover closure for attaching the upper edges of the liner bag to the side wall surfaces of the support bag;

Fig. 9D is an enlarged sectional view of another embodiment of a cover closure for attaching the upper edges of the liner bag to the side wall surfaces of the support bag;

Fig. 10 is an isometric view of a method for preparing and closing bags according to the invention with a cover closure;

Fig. 11-16 show, in enlarged section and plan views, various preferred embossing patterns for embossing one or both side wall surfaces of the liner bag; and

Fig. 17 shows in section a preferred method for producing the bags according to the invention.

Some terms used in this description are defined as follows:

A "multi-wall bag" is a bag with side walls made of more than one layer;

a "double bag" consists of two bags placed inside each other, which can be separated into two separate bags, from which the double bag can then be formed again (e.g. for bagging goods in a supermarket);

a "duplex bag" is defined as a unitary bag consisting of an outer support bag and an inner liner bag, the liner bag being partially (but not completely) bonded to the support bag;

a "multi-bag" is defined here as a unitary bag with at least one outer support bag and one inner liner bag, where the liner bag is partially (but not completely) attached to the support bag attached or connected to it and there can be additional layers between the lining bag and the support bag. The simplest form of a multi-bag is the duplex bag.

An embodiment of the multi-bag according to the invention is shown generally in Figures 2A-2C. As shown in Figure 2A, the multi-bag 10 has an outer or support bag 12 and an inner or liner bag 11. The support bag 12 is formed by edge closures 21, 21' and the fold edge 26 as shown by line dc. The support bag 12 has a reusable closure 14 such as a male and female element or profile with which the multi-bag 10 can be openably closed. The support bag 12 has a venting device such as a vent hole 99 in the side wall 19. The liner bag 11 has edge closures shown by lines ad, bc and a fold edge 24 according to line dc. The liner bag 11 and the support bag 12 use common edge closures, i.e. the edge closures shown with the lines ad, bc are formed together with a part of the total length of the edge closures 21, 21'.

As shown in Figures 2A and 2B, the upper edges 28, 28' of the liner bag are longitudinally attached across the inner surfaces 20, 20' of the side walls 19, 19' of the support bag and form the mouth or opening 13 of the liner bag. The liner bag is longitudinally attached to the support bag at a preselected distance from the opening 15 of the multi-bag. Other means for attaching the upper edges 28, 28' of the liner bag to the side walls 19, 19' of the support bag are described below.

As shown in detail in Figs. 2B and 2C, the side walls 19, 19' and 17, 17' of the support and liner bags are generally separable from one another - with the exception of the edge closures ad, bc and the connection ab - and have a space 23 between them. As Fig. 2B shows, the liner bag 11 is attached longitudinally to the edges 28, 28' of the liner bag across the side walls 19, 19' of the support bag so that when the closure 14 is pulled apart to form the opening 15, filling material (food) that can be introduced into the liner bag 11 through the opening 15 and the opening 13 of the liner bag and contacts the liner bag 11; With minimal manipulation of the bag, the lining bag 11 adapts to the shape of the contents, as shown in Fig. 6A and 6B.

The closure 14 may be any closure capable of being opened and closed multiple times. Examples of useful, reusable closures and methods of making and attaching them to bags can be found in U.S. Patent Nos. 4,561,109, 4,363,345, 4,528,224 and 5,070,584.

One or more ventilation holes 99 can be provided at any location in at least one side wall 19 or 19' of the support bag 12 or in at least one side wall 17 or 17' of the lining bag or in one or both side walls of both the lining bag and the support bag. Likewise, one or more ventilation holes 99 can be provided in the fold edge 24 or 26 of the lining or support bag or in both fold edges. The support bag 12 preferably contains more than one ventilation hole 99, preferably in a side wall 19 of the support bag 12 below the attachment area where the lining bag 11 is attached to the side walls 19, 19' of the support bag 12. A ventilation hole 99 causes the support bag 12 to be ventilated at the surrounding atmosphere and allows an air space 23 between the side walls 17, 17' and 19, 19' of the lining bag 11 and the support bag 12, respectively.

Venting to the outside atmosphere increases the area of adhesion or contact between the liner bag film and the meat. Venting allows the inner liner to conform closely to the meat because the liner bag can now move more independently of the support bag than would be possible if the space between the two film layers was closed and the volume of the support bag was fixed. The support bag film is generally stiffer than the liner bag film and, without venting, tends to pull the liner bag away from the meat. The vent holes in the support bag also prevent air bubbles from forming between the film layers and the film layers from sticking together when the multi-bag is made.

The number of ventilation holes in the liner or support bag and their diameter should be as small as possible so that they are less noticeable to the consumer. However, they must be large enough to allow air to escape steadily between the film layers during manufacture and for the consumer to be able to squeeze it out between the liner and support bags during use. Therefore, the number of ventilation holes in one or both bags will generally depend on the size of the holes.

Generally, there will be at least one vent hole in the liner or support bag; there is practically no upper limit to the number of vent holes in the bags. The number of vent holes in either or both of the bags may range from a minimum of 1 to 28, more likely from 6 to 28 and preferably from 9 to 17. In general, the diameter of the ventilation holes is more than 450 micrometers, more likely 450 to 750 micrometers and preferably 450 to 500 micrometers.

The means for attaching a liner bag to a support bag to form a multi-bag according to the invention can be any known in the art. The liner bag can be attached continuously and evenly or discontinuously or intermittently along its upper edges. Useful examples of attachment means known in the art are heat seal hem seal with hot air, extrusion lamination (pressing a thermoplastic film between the film layers), hot melt adhesive (on or under the upper edges of the liner bag), welding, heated rollers or belts, adhesive film strips and ultrasonic, infrared, high frequency or vibration welding. The liner bag can also be attached during manufacture by subsequently attaching closure profiles on and over the edges of the liner film, as described below. The use of any of the foregoing means for joining two film webs depends largely on the chemical and physical properties of the film webs used to make the liner and support bags. Preferably, the liner bag 11 is joined along the upper edges 28, 28' by means of a hinge-type blanket seal 97, as described in more detail below and shown in Fig. 9C.

To apply the present invention, the user inserts the filling material to be packaged (food or meat) through the opening in the multi-bag into the lining bag, passes the filling material by hand through the bag so that it clings to the outside of the filling material on the surface 9 and air is squeezed out of it, and then closes the support bag while attempting to prevent a backflow of air into the lining bag. Figs. 6A, 6B show meat 300 packed in a multi-bag with an inner lining bag 11 and an outer support bag 12.

Fig. 3A and Fig. 3B-3C show a further embodiment of a multi-bag 40 according to the invention. The multi-bag 40 has a lining bag 41 and a support bag 42. The support bag 42 has a reusable closure 14 and edge closures 44, 44' on the side walls 46, 46' (Fig. 4B) and a fold edge 26. The liner bag 41 has the edge closures shown by the lines ad, bc connecting the side walls 49, 49' (Fig. 4B) and a fold edge 24. As Figs. 3B and 3A show, the upper edges 48, 48' of the liner bag 41 are lengthwise attached across the inner surfaces 43, 43' of the side walls 46, 46' of the support bag which form the opening 13 of the liner bag. The edge closures bc, ad of the liner bag 41 are separate from the edge closures 44, 44' of the support bag 42 - in contrast to the edge closures bc and ad of the multi-bag 10 of Fig. 2A, which share a portion of the edge closures 21, 21' of the support bag 26. As in the embodiment of Fig. 2A, a space 23 is located between the side walls 46, 46' of the support bag and the side walls 49, 49' of the liner bag. The liner bag 41 can be attached to the support bag 42 along its upper edges 48, 48' by means of the attachment means described above. Preferably, the liner bag 41 is attached along its upper edges 48, 48' to the support bag 42 by means of a hinged cover closure 97, as described in more detail below and shown in Fig. 9C.

A further embodiment of the multi-bag according to the invention is shown with the multi-bag 50 of Fig. 4A and Fig. 4B-4C. The multi-bag 50 has a lining bag 51 and a support bag 52 with a multi-closable closure 14 on the top edge of the bag. The liner bag 51 forms edge closures ad, bc connecting the side walls 57, 57' (Fig. 4B) and has a fold edge 54. The support bag has edge closures 60, 60' connecting the soap walls 58, 58' (Fig. 4B) and a fold edge 56. As Fig. 4B shows in more detail, the top edges 53, 53' of the liner bag are attached along the line ab, longitudinally across the inner surfaces 59 of the side walls 58, 58', as shown in Fig. 4A. In this embodiment, the liner bag 51 and the support bag 52 have separate edge closures. As shown in more detail in Figs. 4A, 4C, the upper edges of the lining bag 53, 53' are not attached to the side walls 58, 58' of the support bag over the entire width of the side walls 58, 58'. This connection of the lining bag 51 to the support bag 52 creates an opening leading into the support bag 52 at the edge closures ad, bc of the lining bag. This opening 63 leading into the support bag is open to the atmosphere when the closure 14 is open. The lining bag 51 can be attached to the support bag 52 along the upper edges 53, 53' of the lining bag by means of the attachment devices described above.

Another embodiment of a multi-bag according to the invention is shown with the multi-bag 70 of Fig. 5A and Fig. 5B-5C. The multi-bag 70 generally comprises the liner bag 71 and the support bag 72 with a multi-closable closure 14. The liner bag 71 is formed by edge closures marked with the lines ad, bc, which connect the side walls 80, 80' (Fig. 5B) to each other, and has a folding edge 76. As shown in Figs. 5A, 5C, the liner bag 71 contains in the side walls 80, 80' a plurality of micro or minute holes 78 (described below). Fig. 5B shows the upper edges of the lining bag 83, 83' intermittently welded over the longitudinal extent of the side walls 82, 82' to the holes 75 and the attached areas 79. The upper edges of the lining bag 83, 83' attached to the side walls 82, 82' of the support bag form the opening 81 of the lining bag. Fig. 5C shows the multi-bag 70 with an inner film layer 77 between the lining bag 71 and the support bag 72.

The holes 75 and the welded areas 79 are formed by intermittently welding the upper edges 83, 83' of the liner bag to the side walls 82, 82' of the support bag. The holes 75 are those areas of the upper edges 83, 83' of the liner bag that are not connected to or attached to the side walls 82, 82' of the support bag. In this embodiment of the present invention, the upper edges 83, 83' of the liner bag are intermittently welded to the side walls 82, 82' of the support bag where parts of the inner layer 77 have been removed. In this embodiment, the inner film layer 7 consists, for example, of a material that cannot be welded to the liner or the support bag. However, in any embodiment of the present invention, the liner bag may be attached to the support bag with an intermittent connection. A discontinuous or intermittent connection of a liner bag to a support bag may also be made using conventional or hot melt adhesives, hot air seam welding or the like, as described above and known in the art.

When the closure 14 is open, the holes 75 open to the interior of the support bag and to the atmosphere, allowing the user to escape from the space between the The holes 75 are located only along the area where the liner bag is attached to the support bag. The holes 75 perform essentially the same function as the vent holes 99, but are typically much larger than the vent and micro holes 99 and 78, respectively.

The micro-holes 78 are evenly distributed over at least one side wall of a bag. On the other hand, vent holes are not generally evenly distributed over at least one side wall of a bag. The micro-holes 78 can be distinguished from the vent holes 99 in that the latter are present in much smaller numbers than the micro-holes in a side wall of a bag. Normally, a multi-bag according to the invention does not contain both micro-holes and vent holes, since the micro-holes allow air to escape as well as water to pass from the meat to the inner film layer. Both the support and liner bags can contain micro-holes in the side walls. Preferably, only the liner bag of the multi-bag of Figs. 5A-5C has micro-holes.

In practice, filling material such as meat is placed in the multi-bag 70 and comes into contact with the lining bag 71. Water passes through the tiny holes 78 of the lining bag 71 and is absorbed by the hygroscopic inner film layer 77, whereby the latter swells slightly so that the lining bag 71 adheres evenly to the surface of the meat. The even contact of the lining bag with the meat prevents freezer burn.

"Uniformly distributed" means that the pinholes are substantially identical and substantially equally spaced over the entire area of a sidewall or sheet. The pinholes are preferably in a dot matrix pattern and have a diameter of 50 to 950 micrometers, more preferably 100 to 500 micrometers, and preferably 200 to 300 micrometers. In general, the number of pinholes per unit area is 3 to 81 pinholes/in.² (0.465 to 12.65 pinholes/cm²), more preferably 5 to 50 pinholes/in.² (0.775 to 7.75 pinholes/cm²), and preferably 8 to 30 pinholes/in.² (1.24 to 4.65 pinholes/cm²). A method and apparatus for perforating films is described in US-PS 5,405,561.

Generally, a third or inner film layer 77 may be made of the same or different material as the liner and support bags. Useful materials include thermoplastic polymers, cellulosic polymers, paper, cotton, polyvinyl alcohol, a synthetic fiber matrix such as TYVEX™ (DuPont), a polyester fabric such as RAYON™ or DACRON™, an elastic fabric such as LYCRA™, or a generally hygroscopic material in film form. Preferably, the inner layer 77 is a film of a hygroscopic material such as a cellulose ether or a polyvinyl alcohol; most preferably, the inner film layer is a film of a hydroxypropyl methyl cellulose resin such as METHOCEL (trademark of The Dow Chemical Company; available from Polymer Films, Inc., Rockville, Connecticut, USA).

A preferred embodiment of a multi-bag according to the invention is shown with the multi-bag 90 of Fig. 9A. The multi-bag 90 consists of a lining bag 91 and a support bag 92 with a multi-closable closure 14. The lining bag 91 is closed by the Edge closures ad, bc and a fold edge 24. The support bag 92 is formed by the edge closures 89, 89' and the fold edge 26. The edge closures ad, bc are common to the liner and support bags 91, 92. As shown in Fig. 9A, the upper edges 95, 95' of the liner bag 91 are attached longitudinally over the inner surfaces 101, 101' by means of a cover closure 97 in the machine direction to the side walls 96, 96' of the support bag 92. The upper edges 95, 95' attached to the side walls 96, 96' of the support bag form the mouth of the liner bag. The side walls 94, 94' and 95, 95' of the liner and support bags are generally separable, but not at the edge closures ad, bc and at the cover closure 97 (described below), to form a space therebetween as shown in Fig. 9B. The support bag 92 includes a plurality of vent holes 99 in the side wall 96 below the cover closure 97. The liner bag 92 has textured interior surfaces 98 as shown in Figs. 9A, 9B. Preferably, the textured surfaces are embossed. Vent holes 99 may also be located in a side wall 94, 94' of the liner bag below the cover closure 97.

As shown in particular in Fig. 9C, a hinged web-like cover closure 97 is formed by placing a closure tape 100 of extruded material across the top edges of the liner bag 95 in the machine direction of the liner and support bags. The method of applying a closure tape and forming a cover closure is described below. The closure tape 100 is applied to the side walls of the support bag generally in area 103 and is attached to the edges of the liner bag generally in area 102. The top edges of the liner bag are not welded to the side walls of the support bag in this embodiment. By attaching the closure tape 100 to both the side wall 96 and the top edge 95, a type of hinged web is formed, as a result of which the upper edge 95 can be pulled away from the side wall 96, creating a T-structure at the attachment point. The attachment strength of the closure tape to the support and liner bags is preferably such that the film of the liner bag tears in the T-tensile test. The closure tape 100 used to form a hinged cover closure can be made from a suitable thermoplastic material or a combination of thermoplastic materials that can be welded to at least parts of the thermoplastic films to be joined. The closure tape is preferably polyethylene, most preferably low-density polyethylene or another material that is compatible with the support and liner bag materials described below.

Another type of cover seal useful in the present invention is one which is sealed to the material of both the support and liner bags and causes the liner material to fuse to the support bag material. As shown in Figure 9D, the cover seal 110 includes a sealing tape 112 which is placed over the top edges of the liner bag 95 and contacts the support bag 96 and is generally located at regions 114, 116. The top edge 95 of the liner bag is generally sealed and rigidly connected to the support bag 96 at region 118. The cover seal is formed when the sealing tape can transfer enough heat through the liner bag film to fuse it to the support bag film. Sufficient heat transfer from the sealing tape will occur when the temperature, heat capacity and mass of the sealing tape are sufficiently high and the liner bag film is thin enough and its sealing temperature is low enough. The sealing tape 112 can be made from the same material as described above for the sealing tape 100. usable. As described below, in order to form a weld-on cover closure, the materials of the support bag and the liner bag must be weldable to one another.

Surprisingly, the liner bag film exhibits improved performance when it is textured or embossed. This improved performance of an embossed liner bag film is attributed to the increased surface area of the film, which causes the film to adhere more strongly to a meat surface than an unembossed liner film. Embossing also reduces the overall film stiffness, which also improves the adhesion of the liner bag film to the meat surface.

In general, any embossed pattern can be used on the liner bag or support bag. Useful embossed patterns and shapes include elongated diamonds (Fig. 11), honeycombs (Fig. 12), squares, spheres (Fig. 13), triangles (Fig. 14), cones (Fig. 15), and pyramids (Fig. 16). Uniform discrete geometric patterns also provide air channeling when air is expelled between the film layers. Other embossed patterns useful in the present invention and their preparation are described in U.S. Patent No. 5,113,555. Preferably, the embossed pattern on the liner bag is a rhombus, preferably a square or a uniform diamond with a pyramidal cross section. Preferably, embossed patterns protrude from the interior surface of the liner bag to contact with the meat or other contents. The density of the embossed elements of the pattern on the liner bag may generally be 6 to 50, preferably 10 to 20, per linear inch (25.4 mm) of the surface of the liner bag.

The support and liner bags of the multi-bags of the invention are generally made of a thermoplastic material or a blend of thermoplastic materials, which may be the same or different. The films may be conventionally cast or blown. Useful thermoplastic materials include polyolefins such as high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and propylene (PP); thermoplastic elastomers such as styrene block copolymers, polyolefin blends, elastomer alloys, thermoplastic polyurethanes, thermoplastic copolyesters and thermoplastic polyamides; Polymers and copolymers of polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), Saran polymers, ethylene/vinyl acetate copolymers, cellulose acetates, polyethylene terephthalate (PET), ionomers (Surlyn), polystyrene, polycarbonates, styrene acrylonitrile, aromatic polyesters, linear polyesters, thermoplastic polyvinyl alcohols, and those materials identified above as useful in making an inner film layer. Preferably both the support and liner bags are made of polyethylene, most preferably a blend of low density polyethylene (LDPE; density 0.92) and linear low density polyethylene (LLDPE; density 0.925). The film of the liner bag preferably has a density of less than 0.930 g/cm3.

Generally, the film of the liner bag of the multi-bag of the present invention has a 2% transverse direction secant modulus (TDSM) of less than 40,000 psi (2.75 x 108 Pa) and preferably less than 27,000 psi (1.86 x 108 Pa), as determined by ASTM D832-83, Method A, with a 4 inch wide jaw gap, a 1 inch sample width, an initial deformation rate of 0.25 inch/inch/min, and a transverse head speed of 1 inch/min. The modulus of a film in its transverse or machine direction is generally a measure of its stiffness.

Typically, thermoplastic polyolefin films made by known casting processes have a TDSM of less than 27,000 psi (1.86 x 10⁸ Pa), while thermoplastic polyolefin films made by known blowing processes have a TDSM of 20,000 to 40,000 psi (9.30 x 10⁸ to 1.86 x 10⁸ Pa). Examples of commercially available resins that produce cast or blown films with these tensile properties include LDPE 748 and LDPE 690 from The Dow Chemical Company.

Another useful property of the film for the liner bag is its Z-number. The Z-number is defined by the relationship

t³ · TDSM

where t is the film thickness in mils (10-3 inches) and TDSM is the transverse modulus as defined above. The Z-number describes the relative stiffness of the film as a function of its thickness and modulus. Generally, the liner bag film has a Z-number below 60,000 mil³·psi (6.7 mm³·kPa), more likely from 2,000 to 10,000 mil³·psi (0.22 to 1.1 mm³·kPa), and preferably from 3,000 to 6,000 mil³·psi (0.33 to 0.66 mm³·kPa).

The support bag preferably has a Z-value in the range of 50,000 to 150,000 mil³·psi (5.6 to 16.9 mm³·kPa).

Generally, the support bag has a nominal sidewall thickness of 1.3 to 3.0 mils (33 to 76 microns), and preferably 1.5 to 2.0 mils (38 to 50.8 microns). "Nominal thickness" means the film thickness prior to any surface treatment such as slitting, texturing, and embossing.

Generally, the liner bag has a nominal sidewall thickness of 0.3 to 1.0 mil (7.6 to 25.4 microns), preferably 0.5 to 0.7 mil (13 to 17.8 microns).

Preferably, the inner surface of the raw beef juice liner bag has a contact angle in the range of 65º to 75º at 20ºC as determined by determining the pre-run contact angle with a contact goniometer (e.g., Model No. A-100 from Rame-Hart). The contact angle is defined as the angle formed between a horizontal substrate and a tangent to the surface of a liquid drop at the point where the surface of the liquid drop meets the horizontal substrate. The contact angle is dependent on the surface tension of the liquid. A smaller contact angle indicates greater wetting or adhesion of the liquid to the substrate.

The procedure for measuring the contact angle is as follows: 1. Drops of the liquid to be measured (approximately 1 microliter) are placed on the measuring surface (liner bag film) of the contact goniometer. 2. Contact angles are measured on either side of each of five drops. 3. Step 2 is repeated on various areas of the liner bag surface and the results are averaged to give a mean contact angle. Examples of films with a contact angle between 65º and 75º at 20ºC for raw beef juice include a blend of LDPE and LLDPE available from The Dow Chemical Company.

The multi-bags according to the invention can further comprise one or more layers of film or substrate between the support bag and the lining bag. Useful films and substrates include those described above for the Lining and support bags as well as paper, cellulose polymers, fabrics and elastic fabrics.

The multi-bags of the invention can also be made from differently colored films to emphasize the bag-in-a-bag construction to the consumer. For example, the liner and support bags can be differently colored; likewise, they can be individually or both opaque or clear.

Furthermore, the multi-bags according to the invention can have a lining and/or support bag made of a film or a substrate that has been corona-treated in order to improve the wetting properties of the film and thus its adhesion to meat and/or its printing properties. Preferably, the inner surface or the side of the lining bag that comes into contact with the contents is corona-treated. Useful disclosures on the process of corona-treating plastic films are contained in US Pat. No. 5,328,705.

The multi-bags according to the invention can also have a printable area on the support and/or the liner bag. Printable or writable areas are used as a writing surface on which information about the bag contents can be recorded. The writing surface can also be strategically arranged on the support and/or liner bag so that it covers ventilation holes.

Likewise, the multi-bags of the invention may comprise a liner and/or support bag that is folded.

Without wishing to be bound by any particular theory, the means by which the multi-bags of the invention prevent freezer burn is believed to be a thin inner film layer in the form of a bag that fits tightly to the surface of the meat, preventing moisture loss from it and keeping air out of it. The exclusion of liquid loss and air from the surface of the meat reduces the formation of ice crystals that cause freezer burn or dehydration of the meat.

Figure 7 shows a block diagram of a method for making the multi-bags of the invention by hand. As indicated in the step indicated by box 200, an inner liner film is cut, the edge seals of an existing polyethylene freezer bag are cut off, and the freezer bag is unfolded. In step 210, the liner film is placed on the unfolded freezer bag and aligned so that the edges of the liner film lie between the closure profiles of the freezer bag. In step 220, the liner film is placed on the freezer bag film with a bar welder so that the two films are welded together along the parallel edges of the liner film. In step 230, the placed films are folded so that the closure profiles match each other and the film edges are welded to form a multi-bag. The edge seals are made by conventional welding. In step 240, excess plastic film is trimmed off; the bag is inspected and then packaged in a dispenser in step 250.

A method according to the invention for producing a multi-bag with at least one inner liner bag and an outer support bag generally comprises the following steps: feeding a first thermoplastic film web having a thickness of over 1 mil and a first transverse web width between parallel edges; feeding at least a second thermoplastic film web having a thickness of less than 2 mils and a second transverse web width, the second transverse web width being less than the width of the first thermoplastic film; laying the second thermoplastic film web on the first thermoplastic film web between the parallel edges of the latter; securing the second to the first thermoplastic film along parallel edges of the former; folding the films in the transverse direction; and simultaneously sealing and cutting the folded films to form bags.

Fig. 8 shows an embodiment of the method according to the invention in a flow chart. In step or box 300, the lining or second film can be extruded or fed from an unwinding stand. The extrusion of the lining film can be carried out as a blow or cast extrusion of the thermoplastic material, as known from the prior art. Step 310 provides that the support or first film is extruded with zip closure profiles on the film edges. The extrudate can be a conventional cast or blown film. An example of a film casting process is disclosed in US Pat. No. 4,263,079. Preferably, both films are cast extruded. In step 320, the inner or second film is placed on the first. The second film is aligned so that its edges lie between the closure profiles of the first film. The second film is placed and aligned on the first using conventional guides such as rollers or pairs of rollers. In step 330, the parallel edges of the liner or second foil are welded to the support or first foil. The foils can be welded using conventional welding equipment - for example, a heated rod or hot air welding device, heated rollers and belts or extrusion laminating devices. Preferably, the foils are sealed with a hinged cover closure The method for forming such a top seal is described below. In step 340, the web of stacked films is folded over and the closure profiles are placed against one another. The web can be folded over using conventional means known in the art. In step 350, the folded web is cut to form a seal to form bags which are then stacked and packaged in batches. The secured films can be folded and cut as described in U.S. Patent No. 5,062,825. The closure profiles are preferably pressed together after the films are folded over and before they are simultaneously sealed and cut. The finished bags can be stacked, dispensed and packaged as described in U.S. Patent Nos. 5,302,080, 5,108,085 and 5,185,987. The method according to the invention for producing a multi-bag with at least two bags also provides for the assembly of more than two film webs.

The first and second films can be textured individually or together - e.g. provided with an embossing. The first and second films can be corona-treated individually or together before or after joining. Preferably, the second thermoplastic film is corona-treated and embossed before it is placed on the first.

The second or liner film web can be microperforated prior to being placed on the first or support film using a method and apparatus described in US-PS 5,405,561. Ventilation holes 99 can be made in one or both film webs using any perforating device or method - for example, according to those of US-PS 5,405,561. Ventilation holes can also be made in one or both film webs using a laser or a puncturing device, in which pins protrude from a rubber roller. Preferably, ventilation holes 99 are made in the film by perforating with an unheated perforating device. Preferably, at least one ventilation hole 99 is provided in the support or first thermoplastic film web below the area where the films are placed together and before the films are placed on top of each other. The ventilation hole 99 in the support film web prevents air from becoming trapped between the webs and causing bubbles to form or the film to wrinkle when passing between pressure rollers or when the web is folded over.

Preferably, the closure profiles are formed and applied to the first thermoplastic film after the film webs have been joined together. The closure profiles can be extruded through a nozzle with the desired cross-section and then pressed onto the film in a known manner. An example of a process for extrusion with subsequent application of a closure profile is described in US Pat. No. 5,049,223.

A preferred method of producing the film web for producing the multi-bags of the invention is shown in Fig. 17, and a method of joining the two film webs is shown in Fig. 10. Fig. 17 is a side perspective view of the method of providing and joining the film webs 400, and Fig. 10 is an isometric view of a method of joining the film webs prior to actual bag formation. In Fig. 17, the process 400 generally includes a means for supplying a support or first film web 410, a means for supplying a liner or second film web 430, a tension control means 440, and a welding means generally shown at 450. The means 410 generally includes an extrusion means 412 in extrusion alignment with a casting roll 416. The extrusion means 412 extrudes a thermoplastic material 413 onto a casting roll 416 to form a backing or first film 414. The means for producing the first film web may be any known means in an extrusion process such as that described in U.S. Patent 5,049,223. The film web 414 passes through a conventional thickness control means 418 to a corona treatment means 420 in which the first film web 414 is corona treated in preparation for optional later printing.

A liner or second film web 432 is unwound from a roll or unwind stand 431. The second film 432 may also be produced by a conventional blowing or casting process. The second film web has a transverse web width that is smaller than that of the first film web 414. The film webs 414, 432 are fed into a tension control device such as the roller pair 440 to adjust the deformation of the films to one another. The film webs 414, 432 are aligned on the roller 434 and laid on top of one another to form the web 436. The web 436 is fed into a welding device, shown generally at 450. The web 436 changes orientation at the roller 438 and is fed into the welding device 450, which generally includes an extruder 452, the roller 454 and the pressure roller 456. A preferred sealing apparatus is shown in Figure 10 and described below. The extruder 452 provides a closure tape 458. The closure tape 458 is dispensed onto the web 436 and overlaps the parallel edge of the liner or second film 432. The closure tape 458 on the web 436 passes between the roller 454 and the pressure roller 456, forming a cover closure. The extrusion apparatus or extruder 456 provides closure profiles 460. The closure profiles 460 are applied to opposite parallel edges of the first film 414, for example as described in U.S. Patent 5,049,223, wherein a web 462 is provided with a cover closure and closure profiles. The web 462 with the closure profiles is then folded over, welded and cut, stacked and packaged as shown and described in Fig. 8.

As noted above, either or both of the film webs may be textured or corona treated. Either or both of the film webs may be microperforated or provided with vent holes as described above.

The second thermoplastic or liner film can be attached to the first thermoplastic or support film by means of an extruded cover seal (overlapping the edge of the liner film) as previously described with reference to Figures 9C and 9D, hot air seam welding, extrusion lamination (extruded film between film layers), hot melt adhesive (on or under the edge of the top film layer), ultrasonic welding, heated rollers or belts, adhesive film strips, and infrared, radio frequency or vibration welding. The use of any of the above-mentioned devices or methods for attaching the two film sheets together depends largely on the chemical and physical properties of the film sheets. Preferably, the liner is attached to the support film using an extruded hinged web-type cover seal 97 as shown in Figure 9C, as described below. The process of Fig. 17 can be carried out stepwise or continuously. Preferably, it is carried out continuously.

Fig. 10 shows a method for attaching the second thermoplastic film web 432 to the first thermoplastic film web 414, which is generally designated 450a. When attaching a second thermoplastic film web 432 to a first thermoplastic film web 414 according to the invention along parallel edges 470 of the former, the latter is aligned with and superimposed on a first thermoplastic film web to form web 452. The film webs pass between pressure rollers 472 and under a fastener tape extruder 452. A fastener tape 458 of molten thermoplastic material is extruded onto the machine direction leading webs so as to overlap the edge 470 of the second film web and contact both film webs, securing them together. The secured film webs are then passed through a set of pressure rollers 454, 456 which form a cover seal 459. A conventional second fastener tape extruder (not shown) secures the opposite parallel edge of the second film web to the first. The film web 436 with a cover closure 459 then passes through conventional guide rollers 474, 476 to properly orient the web 436 for folding and sealing/cutting to form bags.

The blanket seal 459 can be a hinged blanket seal 97 (Fig. 9C) or a heat seal type blanket seal 110 (Fig. 9D). Preferably, it is a hinged blanket seal 459. Advantages of this blanket seal process include that the films can be joined together in a continuous process at a relatively high process speed; furthermore, the blanket seal has a solid and pleasant appearance for the consumer. Finally, the process is insensitive to other process changes and, in contrast to known processes, does not produce any film lag.

In general, the fastening tapes can be applied in any way to attach the two films to each other. Preferably, the first thermoplastic film has fastening elements in the form of male and female profiles along opposite web edges and the fastening tapes are applied equidistant from their associated closure profiles. Even better, the closure strips are applied equidistant from the corresponding edges of the first thermoplastic film so that the plug/receiver closure profiles can be applied to the support or first thermoplastic film after the film strips have been put together.

In general, the closure tapes can be made of any suitable thermoplastic material or combination of materials that is weldable to at least portions of the thermoplastic films to be joined. Preferably, the closure tape is polyethylene, more preferably low density polyethylene. An example of a commercially available LDPE suitable for the present invention is LDPE 748 (The Dow Chemical Company).

When forming a hinged cover closure, the width of the closure tape can generally be from 3 mm to the width of the support or first film web. The closure tape is preferably 3 to 76 mm wide, preferably 6 to 19 mm.

Generally, the fastener tape for forming a hinged cover closure has a thickness of 13 to 254 micrometers (0.5 to 10 mils), more preferably 25 to 51 micrometers (1 to 2 mils), and preferably 25.5 to 28.3 micrometers (1.0 to 1.5 mils).

The closure tapes can be tinted, colored or textured to emphasize the double bag structure for the consumer.

Since the sealing tape does not normally weld the second film onto the first, it can advantageously be used to seal films tightly together which cannot be welded together. However, if the temperature, heat capacity and mass of the sealing tape are sufficient and the liner film has an appropriate thickness and sealing temperature, the extruded sealing tape will transfer enough heat through the liner film to weld it to the backing film.

Generally, the liner or second film web is less wide than the first film web so that no part of the fastener tape hangs over the edge of the first film web after application. Preferably, the liner or second film is so much less wide than the first film that the male/female fastener profiles can be applied along opposite parallel edges of the first film web.

In the relevant technology, it is generally known that when two webs are placed on top of each other, the percentage stretch of the two webs at the point of joining should be as equal as possible. This avoids cross-rolling when the tension is removed. In the elastic range, the tension in each web in the machine direction can be expressed as follows:

σ = E·ε = T/t

with σ = voltage (psi)

E = elastic modulus (psi)

ε = elongation (inch/inch)

T = Train (PLI)

t = thickness (inch)

By transforming we obtain: ε = σ/E = T/t·E

To avoid wrinkling in the machine direction when an inner lining film is attached to an outer film,

εinner f. = εoutside.

TInnenf. = TAußenf·[(tInnenf.·EInnenf.)/(tAußenf.·EAußenf.)]

For elastic films, it is known that a material under tension in the machine direction will contract in the transverse direction depending on a material property known as Poisson's ratio ν. This value is the ratio of the lateral to the axial deformation and is typically 0.3 for polyethylene. If the lateral to the axial deformation is used as a ratio using Poisson's ratio, a similar derivation as above for the adjusted transverse deformation and the avoidance of wrinkling in the machine direction results in

TInnenf. = TAußenf.·[νAußenf.·tInnenf.·EInnenf.)/(νInnenf.·tAußenf.·EAußenf)]

In practice, one generally wants to match the deformations in both the machine and cross directions. Wrinkling can be minimized in various ways - including placing webs with a similar modulus and/or Poisson's ratio next to one another.

For a given set of materials, wrinkling can be minimized by running the films at low tension where they are joined together, so that there is little pull-back. Depending on the application, wrinkling in the cross direction can sometimes be considered negligible compared to that in the machine direction.

It is therefore desirable to maintain a relatively low tension in both webs and to keep the stretch in the machine direction as equal as possible where they are joined. From the relevant technology It is known that for effective web transport, a recommended machine direction tension is in the range of 10-25% of the yield point (measured in PLI). At less than 10%, film tracking may become inaccurate. While machine direction tension can be maintained in any web from 0-100% of the yield point, it has been found that above 25% there is a risk of localized thin spots forming in the web where the yield point is exceeded, causing the web to be inelastically stretched. It has been found that for successful application of extruded fastener tapes, it is preferable to maintain tension in the range of 2-15% of machine direction yield point.

For the preferred embodiment, the use of lightweight idler rollers with roller bearings has proven advantageous in order to minimize the tension resistance between the feed point of the liner film and the point at which a cover closure is applied. Even then, the tension in the liner film at the feed point is often so low that a compromise must be made between a tension which is low enough to avoid wrinkling or stretching on the one hand and sufficient for adequate synchronization on the other. As a result, the embodiment of Fig. 10 has a set of nip rollers between the two web run-up points and the point at which a cover closure is applied. The tension between the two webs in front of the nip rollers can then be set somewhat higher, e.g. to 15% of the yield point. Pinch rollers allow different tension control zones. The stretch of the webs can be controlled by suitable tension control between the run-up points and the nip rollers. The pressure roller is allowed to run at a slightly lower speed than the nip rollers in order to relieve part of the tension in the machine direction and bring it into the target range for the top sealing tape to be placed (2-15%). Optionally, a second set of nip rollers can be added so that that the two webs each run through their own printing nip and are tension-controlled separately immediately before the separate webs are brought together, as shown in Fig. 17.

Returning to the process shown in Figure 17, the tension of the liner or second thermoplastic film is generally controlled in the range of 0.05 to 1 lb. per linear inch width (PLI) (0.6 mil PE) using a set of nip rolls 440, as is known. In the preferred embodiment, the film webs each pass through nip rolls to match their stretch to one another. Thus, the tension applied to each film web can be different to match their stretch to one another. Alignment of the liner or second film is accomplished using conventional edge guides and/or by trimming the film web edges to the desired width.

As shown in Figure 10, the tension of the combined films is generally controlled in the range of 0.2 to 2.0 PLI (PE films) after the closure tape is applied to avoid stretching of the hot tapes. The tension of the combined film tapes can be controlled using conventional nip rolls 472. Stretching of the cover tapes can cause "waves" and/or wrinkles to appear in the final product.

An alternative method according to the invention for welding at least two film webs comprises the following steps: feeding at least one first and one second film web which can be welded together; placing the second film web on the first; feeding at least one sealing tape made of a material with a temperature, mass and heat capacity sufficient to weld the second thermoplastic film onto the first thermoplastic film; and applying the tape of sealing material onto the superimposed film webs. This method is similar to that of Fig. 10, but the fastener tape extruder 452 can be positioned over any portion of the film web 436 to join the film webs together in the machine direction at any transverse position of the web. Preferably, the fastener tape is compressed between the rollers 454, 456 after application. A plurality of fastener tape extruders 452 are used to apply a plurality of fastener tapes 458 in the machine direction of the film web to apply a plurality of sealing cover tapes - see Fig. 9D. The film webs can be fed by extrusion or from an unwind stand. The film webs to be welded can be made of any thermoplastic materials - including those specified above - that can be welded together. The film webs can have the same or different widths. In general, the fastener tape can be made of any extrudable material with which the film webs can be welded. Preferably, the closure tape is made of a thermoplastic material such as LDPE 748 from The Dow Chemical Company.

In general, the sealing tape has a temperature, heat capacity and mass sufficient to weld the two films together. In general, the temperature of the sealing tape is the temperature at which the respective material can be extruded without loss of quality.

In general, the thickness of the film to be welded should allow heat transfer from the sealing tape to the film such that the film can be welded to the underlying film web. In general, the thickness of the sealing tape to form a welded cover seal can be in the range of 0.5 to 10 mils (13 to 254 microns), more preferably 1.5 to 3.0 mils (38 to 76 micrometers) and preferably 1.5 to 2 mils (38 to 50.8 micrometers).

In general, the width of the closure tape for forming a welded cover closure is in the range from 3 mm to the width of the support or first film web, better from 3 to 76 mm and preferably from 6 to 19 mm.

Another method according to the invention for joining together at least two film webs comprises the following steps: feeding at least one first and one second film web with a first and second width, respectively, the second width being less than the first; laying the second film web on the first between parallel edges of the latter; feeding at least one band of closure material; and applying the band of closure material along and over parallel edges of the second film web. Preferably, the closure band 458 is applied to the film webs with one or more extruders 452 (Fig. 10). The extruders 452 can be arranged at any location above the film webs at which the film webs can be joined together by forming a hinge-like cover closure in the machine direction. For example, several extruders 452 can be arranged offset over the parallel edges of three or more film webs in order to attach them to one another one after the other. Preferably, the closure tape 452 is compressed between the rollers 454, 456 after being applied to the parallel edges of the film web or webs.

Preferably, the closure tapes used to form hinged web-type cover closures are applied equidistant from the corresponding edges of the first thermoplastic film. In general, the closure tape may be made of any suitable thermoplastic film or Combination of thermoplastic materials that can be welded to at least the film web areas to be joined together. The webs to be joined together can be, for example, thermoplastic as described above, non-thermoplastic, fabrics, nonwovens and coextruded films. The film substrates are joined together with the closure tape as shown in Fig. 9C.

When forming a hinge-like cover closure, the width of the closure band can generally be from 3 mm to the width of the support or first film web, better from 3 to 76 mm and preferably from 6 to 19 mm.

Generally, the fastener tape used to form a hinged cover closure has a thickness of 13 to 254 micrometers (0.5 to 10 mils), more preferably 25 to 50.8 micrometers (1 to 2 mils), and preferably 25.5 to 38.2 micrometers (1.0 to 1.5 mils).

EXAMPLES OF THE INVENTION

The experimental work leading to the aspects of the invention claimed below required the time-consuming manual preparation of numerous different "multi-bags" as defined above, the repacking of meat into these multi-bags and an evaluation of the behavior of the multi-bags relative to each other and to other control bags, i.e. commercially available freezer bags, during and after storage in a deep freezer for several months.

During the experiments, three main types of prototypes were evaluated - types A, B and C described below.

TYPE A PROTOTYPES

The Type A prototypes were all 3-layer multi-bags manufactured as shown in Fig. 5A, 5B, 5C with a support and a liner bag and a third layer, with ventilation holes provided to ventilate the space between the liner and support bags to the space in the liner bag.

In particular, the Type A1 multi-bags were manufactured as follows:

a. A support bag made of an outer layer of polyethylene film (to make a 1.75 mil (44.4 micron) ZIPLOC® bag);

b. A liner bag made of an inner layer of 1.75 mil (44.4 micron) polyethylene film with 800 10 micron diameter pinholes for ventilation, allowing moisture to move freely into and out of the middle layer.

c. A third layer of a hygroscopic film of 1.5 mil (38 micrometers) thickness and about 10% by weight moisture content (cellulose ether film METHOCEL® from Polymer Films, Inc., Rockville, Connecticut, USA; METHOCEL® is a registered trademark of The Dow Chemical Company). In particular, typical properties of the film can be found in a data sheet from Polymer Films Inc. dated June 1986 for a product called "EM IIDO Water Soluble Film". The main component of the product was identified as hydroxypropylmethylcellulose resin with the CAS number 009004-65-3.

Furthermore, it can be seen from Fig. 5A that the support bag has the edge closures AD, BC essentially in common with the edge closures ad, bc of the lining bag.

TYPE B PROTOTYPES

The Type B prototypes were all 3-layer multi-bags essentially similar to Type A, but the liner bag had a thickness of 1.2 mils (30.5 micrometers) instead of 1.75 mils (44.4 micrometers); the liner bag contained no pinholes and the space between the liner and support bags was essentially completely unventilated.

TYPE C PROTOTYPES

The Type C prototypes were all duplex multi-bags as shown in Figs. 2A, 2B, 2C, 3A, 3B, 3C, 4A, 4B and 4C, with the support bag being 1.75 mil (44.4 microns) thick and the liner bag being 0.6 mil thick, with no third layer or wall between them.

The Type C multi-bags were given a secondary classification (designated by the letter C or S depending on whether the edge closures were common (C) or separate (S) between the bags. The edge closures of the liner bag are indicated by lines ad, bc in Figs. 2A, 3A and 4A, and those of the support bag are indicated by lines AD, BC in Figs. 2A, 3A and 4A. As can be clearly seen, in Fig. 2A the edge closures are essentially "common" but in Figs. 3A and 4A they are "separate".

The bags were manufactured manually. Fig. 7 shows a flow chart for the production of multi-bags of type CC.

The Type C multi-bags were given a tertiary classification (1, 2 or 3) depending on whether the space between the support and the liner bag was (1) ventilated to the interior of the liner bag (see Fig. 4C), (2) not ventilated (see Figs. 3A, 3B and 3C) or (3) ventilated to the surrounding atmosphere (see the dashed ventilation hole 99 in Figs. 2A and 2B).

EVALUATION

All multi-bag prototypes were essentially evaluated relative to control bags in the manner specified below, with the bags being used as potential freezer bags with boneless beef steak as the filler.

1. Beefsteak samples were first weighed before being packed into the bags. Each bag contained one beefsteak. The bags were placed in a commercial freezer with a set point of 0ºF (-17.8ºC).

2. The freezer was opened and closed occasionally for the purpose of observing the samples.

3. For the Type A and B prototypes, observations (including conformation of the bags to the steak shape, formation of ice crystals, visible dry spots, discoloration) were made daily for the first two weeks and then once a week for the next eight months; the Type C prototypes were observed for a period of three months. Color photographs were taken of the frozen beefsteaks inside and outside the bags; the beefsteaks were then thawed and photographed again.

4. The percentage loss and the amount of dripping were measured on the thawed steaks. The amount of dripping is defined as the blood-like liquid that comes out of the frozen meat when it is thawed.

5. “Unexpected effects” were recorded where appropriate.

SHORT-TERM RESULTS - TYPES A, B AND C

Different Type A and Type B prototypes were evaluated simultaneously and sequentially.

The Type A1 bags described above were evaluated because the film was hygroscopic and was expected to help prevent moisture from escaping from the meat during freezer storage.

However, an unexpected result occurred almost immediately. In particular, it was discovered that when a hygroscopic film layer was placed between the liner and support bags, the hygroscopic layer and the liner bag changed shape very quickly and conformed to the beefsteak. In other words, it was very useful for removing air from the space surrounding the beefsteak.

As a second significant surprise and short-term phenomenon, in the Type B multi-bag, the lining bag also clung tightly to the steak.

The obvious success of the Type B multi-bag led to the design of the Type C multi-bag. Two types of Type C multi-bag were evaluated: Type CC2 and Type CS2. Again, a surprising result emerged. The Type CC2 multi-bag appears to conform more easily to the shape of the beefsteak during packaging and prior to storage in the freezer (see Fig. 6A). In hindsight, the fact that there is an essentially constant air mass in the unventilated bag between the liner and support bags allows for speculation.

LONG-TERM RESULTS - TYPES A AND B

Beefsteaks in regular freezer bags (control) showed numerous large ice crystals and significant discoloration (bright red to pale brown). The steak showed large discolored dry spots when frozen and thawed.

Beefsteaks in the 3-layer multi-bags type A (with perforated inner layer) showed excellent condition. The formation of ice crystals was significantly reduced, the bright red color was retained and no discoloration was observed, nor was there any freezer burn on the steak surface.

The 3-layer multi-bags of type B with non-perforated film as inner layer showed similar results to those obtained with multi-bags of type A.

A key retrospective observation that may explain the significant difference in behavior between the control and 3-layer bags is that the middle and inner layers of the 3-layer bags were tightly wrapped around the steak, reducing air pocket and subsequent ice crystal formation.

A comparison of weight loss and drip rate between treatments showed that the weight loss of the steaks correlates well with the amount of ice crystals formed. Beefsteaks stored in regular freezer bags showed significant weight loss (20.5%) and drip rate of 2.06% over eight months. Beefsteaks stored in 3-layer bags (perforated inner layer) showed significantly lower weight loss (4.3%) than the control samples; drip rate was 1.93%. The lowest weight loss (1.9%) and drip rate (0.26%) were measured in steaks stored in 3-layer bags (non-perforated inner layer). The difference in performance between the 3-layer bags and the control bags is due to the ability of the former to conform tightly to the meat, minimizing air pocket formation. As a result of this conformation, drainage leading to freezer burn was significantly reduced.

It was concluded that the quality of frozen beefsteaks stored in 3-layer multi-bags of type A and type B was much higher than that of samples stored in regular freezer bags (control). Freezer burn was significantly reduced due to the tight fit of the inner and middle layers of the 3-layer bags to the beefsteaks.

LONG-TERM RESULTS - TYPE C

The CC2 and CS2 multi-bags also performed much better than the commercial freezer bags used as controls. Their superior performance can be attributed - albeit in hindsight - to the tendency of the liner bag to cling to the contents and minimize the headspace available for ice formation. It should perhaps be noted that the performance advantages of these prototypes were less pronounced in tests on contents with irregular shapes - broccoli, bone-in chicken.

Various properties of the Type C liner and support bags were measured and compared to the corresponding properties of commercially available freezer bags. For example, the relative stiffness (determined by the equation Z = t3 TDSM) of the Type C liner bag was one to two orders of magnitude lower than that of commercially available freezer bags (e.g., 5300 mils3 psi (9.59 mm3 kPa) compared to 304000 mils3 psi (34 mm3 kPa)).

In another experiment, a Type CC multi-bag as described above was compared to a Type CC multi-bag with an embossed liner bag. Five different types of meat were repackaged and the multi-bags were compared to each other and to a commercial freezer bag using a simplified five-point rating scale. The control bags tested were ZIPLOC FREEZER BAGS.

PROTOTYPES

The multi-bags used were duplex bags with a sidewall thickness of 1.75 mil (44.4 micrometers) for the support bag and 0.6 mil (15.2 micrometers) for the liner bag. One multi-bag contained an embossed liner (hereinafter referred to as "embossed liner"), the other contained a smooth liner (hereinafter referred to as "smooth liner"). Both multi-bags were made of polyethylene. The embossed pattern on the embossed liner bag consisted of uniform diamonds with a density of 16 diamonds per linear inch (25.4 mm).

Five samples each of ground beef, Denver steak, chicken breast (boneless and skinless), fish fillet and pork chop were placed (one piece each) in multi-bags with smooth and embossed liner bags and in ZIPLOC FREEZER BAGS and the bags were placed in a commercial freezer with a set point of 0ºF. The freezer was opened at various intervals to observe and evaluate the samples.

RATING SCALE

A rating scale was developed to visually assess the ice crystal formation on the surface of the meat samples tested. The rating levels are "weak-weak", "weak-medium", "medium", "medium-strong" and "strong".

"Weak-weak" means the presence of no or very small and very fine ice crystals on the meat surface in ice crystal areas 1/4 to 1/2 inch² (1.6 to 3.2 cm²) in size, but no freezer burn.

"Weakening" refers to the beginning of the formation of three-dimensional ice crystals on the meat surface as a result of some lifting of the film, but no freezer burn on the meat surfaces touched by the film.

"Medium" means the presence of numerous ice crystals on the meat surface in patches of 1/2 inch² (3.2 cm²) or larger, with at least 1/4 of the total meat surface having lost contact with the film, and freezer burn.

"Medium-severe" refers to the presence of numerous three-dimensional ice crystals on more than 1/3 of the meat surface as a result of a major loss of film contact; freezer burn is also present.

"Severe" means the presence of ice crystals on at least 50% of the total surface area of the meat and/or freezer burn.

RESULTS

The results of the tests with a duration of 17 weeks and 8 months are summarized in Table 1. The numbers in each evaluation category indicate the number of meat samples (of the five tested) with the specified rating in the specified time interval. The results show that the two multi-bags according to the invention - in comparison with a control sample - prevented ice crystal formation and freezer burn on the tested meat samples.

Although specific embodiments of the invention have been described above, it will be understood that modifications and variations thereof will be apparent to those skilled in the art within the scope of the invention. TABLE 1

FIGURE CAPTIONS Fig. 1A, B

Prior art State of the art

Fig.7

200 Cut top inner foil (template);

Cut off the bottom side welds of the existing bag

210 Stacking and aligning

220 Manually weld with heating device

230 Fold and close sides

240 Trimming and checking

250 Packaging

Fig.8

300 Extrude/unwind thin film

Extrude 310 film with zip closure

320 Add inner foil

330 Place inner foil on outer foil

Add 340 folds and zip closure

350 Welding, stacking and packaging

Claims (10)

1. Freezer bag for freezer burn-free storage of meat, with a multi-bag (10, 40, 50, 70, 90) with at least one thermoplastic inner liner bag (11, 41, 51, 71, 91) and a thermoplastic outer support bag (12, 42, 52, 72, 92), the inner liner bag (11, 41, 51, 71, 91) having a first side wall and a second side wall (17, 17', 49, 49', 57, 57', 80, 80', 94, 94') which are attached to one another along associated side edges so as to form edge finishes, and each side wall having a top edge and the liner bag having a fold edge (24, 54, 74) which forms the bottom of the liner bag, wherein the outer support bag has two side walls (58, 58', 82, 82', 96, 96') which are attached to one another along associated side edges so that edge closures (21, 21', 60, 60', 73, 73', 89, 89') are created, the side walls each have upper edges which form the opening of the multi-bag, and the support bag has a folding edge (26, 56, 76) which forms the bottom of the multi-bag (10, 40, 50, 70, 90), and wherein the upper edges (28, 28', 48, 48') of the lining bag (11, 41, 51, 71, 91) are attached to an inner side (43, 43', 59) of each associated side wall (19, 19', 46, 46', 58, 58') of the support bag (12, 42, 52, 72, 92), characterized in that the support bag (12, 42, 52, 72, 92) has a nominal sidewall thickness of 33 um to 76 um (1.3 to 3.0 mils) and the Liner bag (11, 41, 51, 71, 91) has a nominal sidewall thickness of 7.6 µm to 25 µm (0.3 to 1.0 mils). 2. Freezer bag according to claim 1, wherein the side walls (17, 17', 49, 49', 57, 57', 80, 80', 94, 94') of the lining bag (11, 41, 51, 71, 91) have a nominal thickness from 13 µm to 17.8 µm (0.5 to 0.7 mils) and/or the support bag has a sidewall thickness of 38 µm to 50.8 µm (1.5 to 2.0 mils). 3. Freezer bag according to claim 1, further comprising an inner film layer (77) between the liner and the support bag, preferably made of a hygroscopic material such as cellulose ether or polyvinyl alcohol, preferably made of hydroxypropylmethylcellulose or polyvinyl alcohol. 4. Freezer bag according to one of the preceding claims, in which at least the inner surface of the liner bag is textured and corona treated. 5. Freezer bag according to one of the preceding claims, in which the support bag has paired, nestable or pluggable closure elements (14) along opposite inner surfaces of the support bag and/or the upper edges of the lining bag are attached to the side walls of the support bag by means of a web-like or heat-welded top closure (97, 110, 459). 6. Freezer bag according to one of the preceding claims, in which the support or the lining bag or a combination thereof in a side wall contains at least one ventilation hole (99) and/or the lining bag contains a plurality of evenly distributed micro-holes (78) and in which the attachment of the upper edges (83, 83') of the lining bag (71) to the side walls (82, 82') of the support bag (72) is discontinuous. 7. A method for producing multi-bags according to one of claims 1 to 6 for freezer burn-free storage of meat, which have at least one inner liner bag and an outer support bag, with the following steps: - feeding a first thermoplastic film web (414) having a thickness of 33 µm to 76 µm (1.3 to 3.0 mils) and a first web width in the transverse direction between parallel edges; - feeding at least a second thermoplastic film web (432) having a thickness of 7.6 µm to 25 µm (0.3 to 1.0 mils) and a second web width in the transverse direction between parallel edges, the second web width being less than the width of the first thermoplastic film (414); - placing the second thermoplastic film web (432) on the first thermoplastic film web (414) between the parallel edges of the first film web; - Attaching the second thermoplastic film web (414) to the first thermoplastic film web along the parallel edges of the second thermoplastic film web; - folding the films lengthwise in the transverse direction to form the bottom of the bag; - Cutting the folded films in the transverse direction while sealing them to form the bags. 8. Method according to claim 7, with the step of attaching paired attachable or pluggable closure elements along opposite parallel edges of the first thermoplastic film web, wherein the films are attached by attaching a web-like or a heat-welded ceiling finish, wherein preferably the second thermoplastic film web is placed on the first thermoplastic film web between the closure elements. 9. Device (400) for producing multi-bags according to one of claims 1 to 6 for freezer burn-free storage of meat, which have at least one inner lining bag and one outer support bag, with means (410) for feeding a first thermoplastic film web (414) having a thickness of 33 µm to 76 µm (1.3 to 3.0 mils) and a first transverse web width between parallel edges; means (430) for feeding at least a second thermoplastic film web (432) having a thickness of 7.6 µm to 25 µm (0.3 to 1.0 mils) and a second web width in the transverse direction between parallel edges, the second web width being less than the width of the first thermoplastic film (414); means (434) for laying the second thermoplastic film web (432) on the first thermoplastic film web between parallel edges of the first film web; means (450) for securing the second thermoplastic film web (432) to the first thermoplastic film web (414) along parallel edges of the second thermoplastic film web (432); a device for folding the films lengthwise in the transverse direction to form the bag bottom; and a device for cutting the folded films in the transverse direction while sealing them to form bags. 10. Use of a bag according to any one of claims 1-6 for preventing freezer burn when storing meat.