Patent Application
20060233467
The present invention relates to bags formed from polymeric film and containing fluid-absorbent pads for absorbing fluids.
Poultry and meat are frequently sold in transparent plastic bags. A problem with this type of packaging is that the poultry or meat contains blood and other fluids that flow out of the meat after it has been packaged. The blood and other fluids accumulate in the package, detracting from its appearance. In addition, the blood and fluid sometimes leak from the package while the consumer is transporting it home from the market. To counter this problem, food bag manufacturers often insert an absorbent pad into the bag prior to packaging the food product. The pad absorbs the exuded blood and fluid and thereby enhances the appearance of the packaged product. In many cases, the absorbent pads are manually inserted into the bags. The manual labor associated with placing the absorbent pads in the bags prior to product packaging adds to the cost and time associated with this operation.
Meat and poultry are often packaged in heat-shrinkable bags, including “end seal” bags. In the making of heat-shrinkable end-seal bags, thermoplastic material is extruded from an annular die in the form of a seamless tubing, with the extrudate (known as a “tape”) being relatively thick and relatively narrow. The annular extrudate is then quenched. Optionally, the tape can then be irradiated and/or coated with one or more additional layers containing thermoplastic polymer. The tape is then reheated to its softening point by exposure to hot water or steam (or other heating means) and is stretched in its longitudinal and transverse directions while the polymer remains in the solid state, resulting in heat-shrinkable film in the form of a seamless tubing. The heat-shrinkable film tubing is then converted into end-seal bags by placing the tubing into a lay-flat configuration and heat-sealing across the tubing to heat-seal the inside surface of the tubing to itself. The seals across the tubing are made at intervals along the length of the tubing, these intervals corresponding with the desired bag lengths. The resulting sealed tubing is then converted into a plurality of heat-shrinkable bags by cutting across the tubing a short distance downstream of each of the transverse heat-seals, resulting in a plurality of lay-flat bags having an open top, two seamless side edges, a heat seal across the bag near the bottom edge of the bag, and a short section of tubing (commonly referred to as a “skirt”) below the transverse heat seal.
When end-seal bags extend across the entire width of the lay-flat tubing, such bags come off the production line one at a time, and each bag generally entails a separate sealing cycle and a separate printing cycle. It would be desirable to reduce the number of sealing cycles, printing cycles, and cutting cycles, to increase throughput of the process, and in some cases to provide bags of reduced width. It would also be desirable to provide such bags with absorbent pads and to do so in an automated fashion.
The present invention addresses the above needs and achieves other advantages, by providing a set of pre-padded end-seal bags and a process for making sets of such bags. The invention enables the number of printing cycles, as well as the number of cycles used to make the transverse seals, to be substantially reduced while making the same total number of bags, thereby enabling a substantial increase in the number of bags per extrusion die, as well as per print cycle and per transverse seal cycle. In addition, the sets of pre-padded bags in preferred embodiments have a lengthwise free shrink (i.e., shrink in the machine direction) that is less than the transverse free shrink (i.e., shrink across the width of the bags), so that during shrinking the bags have less tendency to distort flat, flexible, elongate products packaged in the bag.
The process can be used to produce sets of bags in which the bags of each set are connected with one another across the machine direction of the film being used to make the bags. Optionally, each set of bags can be provided with an appropriate number of longitudinal tear lines (i.e., tear lines running the length of the bags, i.e., in the machine direction) for ease in separating the bags from one another. Moreover, because the bags are connected to one another, the connected series of bags can be stretched out across the opening of a vacuum chamber without risk of overlap during sealing.
Additionally, the invention can be carried out so that each set of bags is connected to at least one other set of bags in a line of succession, e.g., resulting in a chain of sets of bags, which can be of indeterminate length as it comes off a production line. Optionally, this chain of sets of bags can be provided with transverse tear lines (i.e., a weakened region between the sets of bags, such as a line of perforations, etc.) so that each set of bags can be easily torn free of the chain of bags, as well as lengthwise (i.e., machine direction) tear lines between the bags of each set, so that the packaged product can be offered as singlets or any subset of the original set of bags.
In the sets of bags of the invention, the bag length of each of the bags in the set runs in the machine direction of the tubing or film. Likewise, the bag width of each of the bags in the set runs in the transverse direction across the tubing or film. A greater free shrink in the transverse direction is desirable for the packaging of a wide variety of products, particularly food products that tend to distort by bending along the length of the bag in which they are packaged. Various meat products, such as small beef and pork cuts, for example, beef and pork tenderloin, eye of round, single ribs, beef spare ribs, split beef back ribs, and various lamb cuts, tend to distort (i.e., bend) if packaged in a shrink bag having a higher shrink along the length of the bag than across the width of the bag. Such package distortion can be reduced or eliminated in the sets of bags of the invention, if the bags are provided with greater free shrink across the bag than along the length of the bag.
Sets of pre-padded bags in accordance with the invention can be made with various processes. In one embodiment, a chain of sets of pre-padded bags is made from two continuous polymer film webs that are positioned in overlying relation with each other. Absorbent pads are inserted between the two films and preferably adhered to one of the films. The pads are arranged in sets spaced at bag-length intervals along the films, the pads of each set being spaced transversely across the films. The films are then sealed with one or more longitudinal seals (e.g., one longitudinal seal in the case of sets of two bags, two spaced longitudinal seals in the case of sets of three bags, etc.) to form interior side seals of the bags. The films preferably are perforated longitudinally between the bags of each set to facilitate separating the bags of each set. The opposite longitudinal edges of the films are sealed together, and transverse seals are made across the films at spaced bag-length intervals. The films advantageously are perforated across the films adjacent each transverse seal to facilitate separating one set of bags from another.
In another embodiment, a chain of sets of pre-padded bags is made from a continuous lay-flat tubing. The lay-flat tubing is slit along at least one of its longitudinal edges to open the tubing, and absorbent pads are inserted between the two film portions of the slit lay-flat tubing, and preferably are adhered to one of the film portions of the slit lay-flat tubing. The pads are arranged in sets spaced at bag-length intervals along the lay-flat tubing, the pads of each set being spaced transversely across the lay-flat tubing. The tubing is then sealed with one or more longitudinal seals (e.g., one longitudinal seal in the case of sets of two bags, two spaced longitudinal seals in the case of sets of three bags, etc.) to form interior side seals of the bags. The tubing preferably is perforated longitudinally between the bags of each set to facilitate separating the bags of each set. The (or each) slit longitudinal edge of the tubing is sealed together, and transverse seals are made across the tubing at spaced bag-length intervals. The tubing advantageously is perforated across the films adjacent each transverse seal to facilitate separating one set of bags from another.
In still another embodiment, a chain of pairs of pre-padded bags is made from a single wide lay-flat film. Absorbent pads are placed onto the film and preferably adhered to the film. The pads are arranged in pairs spaced at bag-length intervals along the film, the pads of each set being spaced transversely on opposite sides of a centerline of the film. The film is then C-folded by bringing the opposite longitudinal edges of the film inwardly toward the centerline such that the pads are disposed between two overlying film portions and respective underlying film portions. The longitudinal edges of the overlying film portions are sealed with longitudinal seals to the underlying film portions to form interior side seals of the bags. The film preferably is perforated down the centerline to facilitate separating the bags of each set. Transverse seals are made across the film at spaced bag-length intervals. The film advantageously is perforated across the film adjacent each transverse seal to facilitate separating one set of bags from another.
In accordance with a further embodiment of the invention, a chain of sets of pre-padded bags is made from a single wide lay-flat film. Absorbent pads are placed onto the film and preferably adhered to the film. The pads are arranged in sets spaced at bag-length intervals along the film, the pads of each set being spaced transversely across half of the width of the film. The film is then folded down the middle (i.e., center-folded) by bringing one of the opposite longitudinal edges of the film over so as to overlie the other longitudinal edge of the film, such that the pads are disposed between an overlying film portion and an underlying film portion. The longitudinal edges of the film portions are sealed together with a longitudinal seal to form an outer side seal for one of the bags of each set of bags of the chain. The folded film is sealed with one or more longitudinal seals (e.g., one longitudinal seal in the case of sets of two bags, two spaced longitudinal seals in the case of sets of three bags, etc.) to form interior side seals of the bags. The film preferably is perforated longitudinally between the bags of each set to facilitate separating the bags of each set. Transverse seals are made across the film at spaced bag-length intervals. The film advantageously is perforated across the film adjacent each transverse seal to facilitate separating one set of bags from another.
A set of pre-padded bags made from a film in accordance with a first aspect of the invention comprises a first lay-flat bag and a second lay-flat bag joined along their respective lengths, with an end seal extending across both the first bag and the second bag. Each of the first and second bags contains an absorbent pad, preferably adhered to the film. The first bag has a first side seal extending the length of the first bag, and the second bag has a second side seal extending the length of the second bag. The first bag is connected with the second bag in an area between the first side seal and the second side seal. Both the first bag and the second bag having a total free shrink at 185° F. of at least 10 percent, and both the first bag and the second bag have a transverse free shrink at 185° F. which is greater than a longitudinal free shrink at 185° F.
In one embodiment, the set of bags has a first outer side edge and a second outer side edge, and at least one of the first outer side edge and the second outer side edge is a folded edge.
Preferably, the film has a total free shrink, at 185° F., of at least 15 percent; more preferably, at least 20 percent, more preferably, at least 25 percent; more preferably, at least 30 percent; more preferably, at least 35 percent; more preferably, at least 40 percent; more preferably, at least 45 percent. Preferably, the film has a total free shrink at 185° F. of from 15 to 150 percent; more preferably, from 20 to 140 percent; more preferably, from 25 to 130 percent; more preferably, from 30 to 120 percent; more preferably, from 35 to 110 percent; more preferably, from 40 to 100 percent; and, more preferably, from 45 to 90 percent.
Preferably, the end seal, the first side seal, and the second side seal are heat seals. In one embodiment of the invention, the end seal, the first side seal, and the second side seal are each a seal of an inside surface of a seamless tubing to itself. The end seal can be a straight seal or can be curved or have at least one curved region. If curved, preferably the end seal is curved so that the bottom of the lay-flat set of bags is convex.
Preferably, the set of bags further comprises a line of weakness between the first bag and the second bag, the line of weakness being between the first side seal and the second side seal. Preferably, the line of weakness between the first bag and the second bag comprises perforations.
Although the set of bags can comprise a pair of bags, the set of bags can further comprise first, second, and third bags, wherein the second bag is between the first bag and the third bag, the second bag having two side seals and an end seal. If the set of bags is a pair of bags, the first bag is preferably a mirror image of the second bag. Preferably, the first bag has a length equal to the length of the second bag. Preferably, first side seal is parallel to the second side seal.
Preferably, the film from which the set of bags is made is a multilayer film comprising a first outer film layer, a second outer film layer, and an inner O2-barrier layer comprising at least one polymer selected from the group consisting of vinylidene chloride/methyl acrylate copolymer, vinylidene chloride/vinyl chloride copolymer, ethylene/vinyl alcohol copolymer, polyamide, and polyethylene carbonate. Preferably, the multilayer film further comprises a fourth layer which serves as a tie layer between the barrier layer and the first outer film layer, and a fifth layer which serves as a tie layer between the barrier layer and the second outer layer.
Optionally, the first bag and the second bag have printing thereon.
In a second aspect, the present invention pertains to a plurality of sets of pre-padded bags, with each set being in accordance with the first aspect of the invention (described above). The first set of bags comprises a first bag and a second bag joined along their respective lengths, the first pair of bags having a first end seal extending across both the first bag and the second bag, the first bag having a first side seal extending the length of the first bag, and the second bag having a second side seal extending the length of the second bag, the first bag being connected with the second bag in an area between the first side seal and the second side seal. The second set of bags comprises a third bag and a fourth bag, the second set of bags having a second end seal extending across both the third bag and the fourth bag, the third bag having a third side seal extending the length of the third bag and the fourth bag having a fourth side seal extending the length of the fourth bag. The third bag is connected with the fourth bag in an area between the third side seal and the fourth side seal. The second set of bags is joined to the first set of bags in an area below the first end seal. Preferably, the third side seal is a continuation of the first side seal, and the fourth side seal is a continuation of the second side seal. Preferably, the second set of bags is joined to the first set of bags along a transverse line of weakness. Preferably, the line of weakness between the first set of bags and the second set of bags comprises perforations. Optionally, the set of bags further comprises a third set of bags which is joined to the second set of bags below the second end seal, and a fourth set of bags joined to the third set of bags below a third end seal, with the plurality of sets of bags being a portion of a chain of sets of bags, the chain being of indeterminate length. Unless inconsistent therewith, preferred embodiments of the second aspect of the invention correspond with preferred features of the first aspect of the present invention.
As a third aspect, the present invention pertains to a set of pre-padded bags made from a film. The set of bags comprises a first lay-flat bag and a second lay-flat bag joined along their respective lengths, and an end seal extending across both the first bag and the second bag, with the first bag connecting with the second bag at a heat seal between the first bag and the second bag, the heat seal extending the length of the first bag and the second bag, with both the first bag and the second bag having a total free shrink at 185° F. of at least 10 percent and a transverse free shrink at 185° F. which is greater than a longitudinal free shrink at 185° F. Each bag contains an absorbent pad, which preferably is adhered to the film.
In yet another aspect of the invention, pre-padded side-seal bags are provided as a continuous chains of serially connected bags.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which some but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
As used herein, the term “bag” is inclusive of L-seal bags, side-seal bags, backseamed bags, and pouches (i.e., “U-sealed” bags). An L-seal bag has an open top, a bottom seal, one side seal along a first side edge, and a seamless (i.e., folded, unsealed) second side edge. A side-seal bag has an open top and a seamless bottom edge, with each of its two side edges having a seal therealong. Although seals along the side and/or bottom edges can be at the very edge itself, (i.e., seals of a type commonly referred to as “trim seals”), preferably the seals are spaced inward (preferably about ¼ to ½ inch) from the bag side edges, and preferably are made using an impulse-type heat sealing apparatus, which utilizes a bar that is quickly heated and then quickly cooled. A backseamed bag is a bag having an open top, a seal running the length of the bag in which the bag film is either fin-sealed or lap-sealed, two seamless side edges, and a bottom seal along a bottom edge of the bag.
As used herein, the phrase “set of bags” refers to two or more bags that are connected with one another in a side-by-side relationship, with the bags extending across a tubing (seamed or seamless). The set of bags preferably comprises from 2 to 20 bags across the tubing, more preferably from 2 to 5 bags, more preferably 2 to 3 bags. Each bag preferably has a length of at least twice its width, more preferably three to ten times its width, with bag length and bag width being measured based on inside the bag dimensions while the bag is in a lay-flat position. The phrase “connected with”, as applied to the bags of a single set of bags, refers to the side-by-side relationship of the bags to one another, and does not require that the bags be directly adhered to one another. That is, two bags are connected with one another even if another bag is between them or even if a section of waste film is between them. Likewise, two bags are connected with one another if they share a common side seal, as illustrated in
The phrases “lay-flat film tubing”, “lay-flat bag”, and “lay-flat width” are known to those of skill in the flexible film art. A lay-flat film tubing is extruded through an annular die, with the extrudate being cooled and gathered by converging sets of rollers and wound up in flattened form. A lay-flat bag includes bags of various configurations including but not limited to end seal, side seal, L-seal, etc., which can be made by sealing the inside of a lay-flat film tubing to itself, following by cutting across the tubing to convert the tubing into, for example, an end-seal bag. A side-seal bag requires slitting one side edge of the tubing in addition to cutting across the tubing. Side seal and L-seal lay-flat bags can also be made by folding a flat film and sealing the inside surface of the folded film to itself. A pouch is often made by sealing two separate pieces of flat film to one another, with the seals extending up the sides of the pouch and across the bottom of the pouch, leaving the top of the bag open for the insertion of the product to be packaged.
As used herein, the phrase “line of weakness” refers to any line, whether straight or curved, whether wide or narrow, in which the film has been weakened by any means so that the film can readily be torn apart along the line. As one example, the line of weakness can be formed by perforating the film. Alternatively, the line of weakness can comprise one or more slits formed in the film along the line at which the film is desired to preferentially tear, the slits being configured so that one or more parts of said line are not slit (although they may be perforated) and thereby serve to keep the film portions on opposite sides of the line connected to each other until it is desired to separate the film portions.
As used herein, the phrases “heat-shrinkable film,” “heat-shrink film” and the like refer to a film that has been oriented while in the solid state (as opposed to a blown film, which is oriented at, above, or near the melting point of the polymer). The tension on a heat-shrinkable film increases upon the application of heat if the film is restrained from shrinking. As a corollary, the phrase “heat-contracted” refers to a heat-shrinkable film, or a portion thereof, which has been exposed to heat such that the film or portion thereof is in a heat-shrunken state, i.e., reduced in size (unrestrained) or under increased tension (restrained). Preferably, the heat-shrinkable film has a total free shrink (i.e., machine direction plus transverse direction), with the free shrink in each direction (measured in accordance with ASTM D 2732) of at least 5 percent at 185° C., more preferably at least 7 percent, still more preferably at least 10 percent, still more preferably at least 15 percent, and yet still more preferably at least 20 percent. The total free shrink at 185° F. can be from 10 to 150 percent, more preferably from 20 to 120 percent, more preferably from 40 to 100 percent.
As used herein, the phrases “inner layer” and “internal layer” refer to any layer, of a multilayer film, having both of its principal surfaces directly adhered to another layer of the film.
As used herein, the phrase “outer layer” refers to any film layer of film having less than two of its principal surfaces directly adhered to another layer of the film. The phrase is inclusive of monolayer and multilayer films. In multilayer films, there are two outer layers, each of which has a principal surface adhered to only one other layer of the multilayer film. In monolayer films, there is only one layer, which, of course, is an outer layer in that neither of its two principal surfaces are adhered to another layer of the film.
As used herein, the phrase “inside layer” refers to the outer layer of a multilayer film packaging a product, which is closest to the product, relative to the other layers of the multilayer film.
As used herein, the phrase “outside layer” refers to the outer layer, of a multilayer film packaging a product, which is farthest from the product relative to the other layers of the multilayer film. Likewise, the “outside surface” of a bag is the surface away from the product being packaged within the bag.
As used herein, the term “adhered” is inclusive of films that are directly adhered to one another using a heat seal or other means, as well as films that are adhered to one another using an adhesive that is between the two films.
Although the films used in the pre-padded bag according to the present invention can be monolayer films or multilayer films, the pre-padded bag comprises at least two films laminated together. Preferably, the pre-padded bag is comprised of films that together comprise a total of from 2 to 20 layers; more preferably, from 2 to 12 layers; and still more preferably, from 4 to 12 layers. In general, the multilayer film(s) used in the present invention can have any total thickness desired, so long as the film provides the desired properties for the particular packaging operation in which the film is used, e.g. abuse-resistance (especially puncture-resistance), modulus, seal strength, optics, etc.
The set 10 of bags is constructed by forming a first longitudinal seal 28 adjacent the first longitudinal edges 20 of the films, a second longitudinal seal 30 spaced in the transverse or width direction of the films from the first longitudinal seal 28 and located generally centrally of the width of the films, a third longitudinal seal 32 transversely spaced a short distance from the second longitudinal seal 30 in the direction of the second longitudinal edges 22 and located generally centrally of the width of the films, and a fourth longitudinal seal 34 adjacent the second longitudinal edges 22 of the films. A transverse seal 36 is formed across the width of the films to form end seals for the two bags 12, 14; that is, a first portion of the transverse seal 36 forms an end seal for bag 12 and a second portion of the transverse seal 36, which is a continuation of the first portion, forms an end seal for bag 14. The second and third longitudinal seals 30, 32 can comprise a single longitudinal seal rather than two separate, spaced seals. In any event, the longitudinal seals 28 and 34 form outer longitudinal seals of the bags 12, 14, respectively, and the generally centrally located longitudinal seals 30, 32 (or single centrally located longitudinal seal, in the alternative) form interior longitudinal seals of the bags 12, 14, respectively. The transverse seal 36 can be spaced a short distance from the transverse edges of the films so as to form a skirt 38 at the closed bottom ends of the bags. The opposite ends 42, 44 of the bags 12, 14, respectively, are open for loading products into the bags
It will be appreciated that a continuous chain of pre-padded bag pairs 60 can be formed from a continuous center-folded film or a continuous lay-flat seamless tubing that is slit along one longitudinal edge to enable the absorbent pads 24, 26 to be inserted between the film portions. Transverse lines of weakness can be formed in the continuous chain of bags adjacent each of the transverse seals, generally as previously described in connection with
A continuous chain of pre-padded bag sets 110 can be formed from continuous lengths of two films in a manner analogous to that described in connection with
Bag pair 110′ can also be formed from a seamless lay-flat tubing that is longitudinally slit along a centerline of one film portion to open the tubing for insertion of the pads 124, 126, followed by longitudinal sealing of the resulting two longitudinal edges with longitudinal seals 129, 130 as described above. In any event, a line of weakness 137 can be formed between bags 112′ and 114′ to facilitate separating the bags from each other
As yet another alternative, a chain of interconnected bag pairs 110′ can be formed from a seamless lay-flat tubing in a manner generally similar to that described in U.S. Patent Application Publication No. 2004/0255556 A1 to Boal et al., the entire disclosure of which is incorporated herein by reference. The lay-flat tubing has an upper layer and a lower layer. The method entails feeding the tubing to a perforator at which the upper layer and lower layer are perforated along a series of transverse lines spaced apart along the tubing's longitudinal direction at bag-length intervals. After the perforating step, the tubing is fed to a tube opener at which the upper layer is opened along the perforations to create an opening. Alternatively, a single station can sever the upper layer to create the opening and perforate the lower layer at the same time. Next, a pair of absorbent pads are inserted through each opening in the upper layer, generally in the manner described in the Boal '556 application. Once the pads have been inserted, a transverse seal is formed across the tubing adjacent each line of perforations. Longitudinal seals, and optionally a longitudinal line of weakness between the longitudinal seals, are then formed to complete the construction of the chain of bag pairs
In the various embodiments of bag sets as described above, the absorbent pads can be placed into the bags in either a flat unfolded configuration or in a folded configuration, and the positioning of the pad within the bag can vary depending on the particular needs in each instance.
Preferably, the film stock film from which the bags are formed has a total thickness of from about 1.5 to 5 mils; more preferably, 1.5 to 4 mils; more preferably, 2 to 3 mils; more preferably, 2 to 2.5 mils. Preferably the stock film from which the bag is formed is a multilayer film having from 1 to 20 layers; more preferably, 3 to 10 layers; more preferably, 4 to 8 layers
Preferably, the bag film, present in the form of a seamless tubing, backseamed tubing (lap seal, fin seal, or butt sealed backseamed tubing with butt seal tape) or as a flat film, has a total (i.e., L+T) free shrink at 185° F. of from about 45 to 125 percent, with a free shrink in the longitudinal (i.e., machine) direction of from 20 to 50 percent, and a free shrink in the transverse direction of from 25 to 75 percent, with the transverse free shrink being greater than the longitudinal free shrink. More preferably, the bag film has a total free shrink at 185° F. of from about 55 to 110 percent, with a free shrink in the longitudinal direction of from 25 to 45 percent, and a free shrink in the transverse direction of from 30 to 65 percent, again with the transverse free shrink being greater than the longitudinal free shrink. More preferably, the bag film has a total free shrink at 185° F. of from about 65 to 95 percent, with a free shrink in the longitudinal direction of from 30 to 40 percent, and a free shrink in the transverse direction of from 35 to 55 percent, again with the transverse free shrink being greater than the longitudinal free shrink.
Preferably, the transverse free shrink at 185° F. is higher than the longitudinal free shrink at 185° F. by an amount of from about 5 to 30 percent, more preferably from 8 to 20 percent higher. Preferably, the transverse free shrink is from 1.1 times to 1.8 times as high as the longitudinal free shrink, more preferably from 1.2 to 1.7 times as high, more preferably from 1.25 to 1.65 times as high.
Table I, below, provides a preferred multilayer film structure for making a set of bags in accordance with the present invention, including the composition, thickness, and general function of each of the film layers. This film, extruded from an annular die and thereafter extrusion coated, was in the form of a seamless tubing and had a total thickness of approximately 2.4 mils, and exhibited a total free shrink at 185° F. of 20% in the machine direction and 33% in the transverse direction.
In Table I, LLDPE #1 was DOWLEX® 2045 linear low density polyethylene, obtained from the Dow Chemical Company of Midland, Mich.
LLDPE #2 was ESCORENE® LL3003.32 linear low density polyethylene, obtained from Exxon Chemical Company of Baytown, Tex. SSPE#1 was AFFINITY® P11280 metallocene-catalyzed ethylene/octene copolymer, having a density of 0.900 g/cc and a melt index of 6 g/10 min, obtained from The Dow Chemical Company, of Midland, Mich. HDPE #1 was Fortiflex® T60-500-119 high density polyethylene, obtained from Solvay Polymers, of Deer Park, Tex. EVA No. 1 was ESCORENE® LD318.92 ethylene/vinyl acetate copolymer having a melt index of 2.0, a density of 0.930 g/cc, and a vinyl acetate mer content of 9 percent, this resin being obtained from the Exxon Chemical Company. EBA No. 1 was SP 1802 ethylene/butyl acrylate copolymer containing 18% butyl acrylate, obtained from Chevron Chemical Company, of Houston, Tex.
Table II, below, provides another preferred multilayer film structure for making the sets of bags in accordance with the present invention, the film having a total thickness of 3 mils and a free shrink at 185° F. of 28 percent in the machine direction and 36 percent in the transverse direction.
Table III, below, provides another preferred multilayer film structure for making the sets of bags in accordance with the present invention, the film having a total thickness of about 2.2 mils and a free shrink at 185° F. of about 31% in the machine direction and about 44% in the transverse direction.
Table IV, below, provides another preferred multilayer film structure for making the sets of bags in accordance with the present invention, the film having a total thickness of 2.3 mils and a free shrink at 185° F. of 25 in the machine direction and 41 in the transverse direction.
Table V, below, provides another preferred multilayer film structure for making the sets of bags in accordance with the present invention, the film having a total thickness of 2 mils and a free shrink at 185° F. of 31 in the machine direction and 46 in the transverse direction.
Table VI, below, provides another preferred multilayer film structure for making the sets of bags in accordance with the present invention, the film having a total thickness of 2 mils and a free shrink at 185° F. of 26 in the machine direction and 42 in the transverse direction.
Table VII, below, provides another preferred multilayer film structure for making the sets of bags in accordance with the present invention, the film having a total thickness of 2.2 mils and a free shrink at 185° F. of 36 in the machine direction and 51 in the transverse direction.
In Tables II through VII, SSPE1 was Dow Affinity® PL 1280 ethylene/octene copolymer, having a density of 0.900 g/cc and a melt index of 6 g/10 min. SSPE2 was Dow Affinity® PL 1850, having a density of 0.902 g/cc and a melt index of 3 g/10 min. SSCPE3 was DPF 1150.01 single site catalyzed ethylene/octene copolymer having a density of 0.901 g/cc and a melt index of 0.9 g/10 min, obtained from Dow. LLDPE1 was Exxon Escorene® LL3003.32 linear low density polyethylene having a density of 0.9175 g/cc and a melt index of 3.2 g/10 min. LLDPE2 was Dow Attane® 4203, having a density of 0.905 g/cc and a melt index of 0.8 g/10 min. LLDPE3 is Dow Dowlex® 2045.03 linear low density polyethylene, having a density of 0.92 g/cc and a melt index of 1.1 g/10 min. LLDPE4 was Exceed® 4518PA ethylene/hexene copolymer having a density of 0.918 and a melt index of 4.5 g/10 min. LDPE was Ruxell® V3401 ethylene/octene copolymer having a density of 0.911 g/cc and a melt index of 5.7 to 7.5 g/10 min, obtained from Huntsman. EVA1 was LD-713.93 ethylene/vinyl acetate copolymer, having a vinyl acetate content of 15 percent, a density of 0.933 g/cc and a melt index of 3.5 g/10 min, and was obtained from Exxon. EVA2 was Escorene® LD 761.36 ethylene/vinyl acetate copolymer having a density of 0.95 g/cc, a melt index of 5.7 g/10 min, and a vinyl acetate content of 28 percent, obtained from ExxonMobil. EVA3 was Escorene® LD 318.92 ethylene/vinyl acetate copolymer having a density of 0.93 g/cc, a melt index of 2 g/10 min, and a vinyl acetate content of 9 percent, obtained from ExxonMobil. EVA4 was Elvax® 3128 ethylene/vinyl acetate copolymer having a density of 0.928 g/cc, a melt index of 2 g/10 min, and a vinyl acetate content of 8.9%, obtained from DuPont. EMA was EMAC SP 1305 ethylene/methyl acrylate copolymer, having a methyl acrylate content of 20 percent, a density of 0.944 g/cc and a melt index of 2 g/10 min, also obtained from Exxon. EPD was Vistalon® 7800 ethylene/propylene/diene terpolymer, having a density of 0.87 g/cc and a melt index of 1.5 g/10 min, obtained from Exxon. VDC/MA was SARAN® MA-134 vinylidene chloride/methyl acrylate copolymer, obtained from the Dow Chemical Company. The epoxidized soybean oil was PLAS-CHEK® 775 epoxidized soybean oil, obtained from the Bedford Chemical Division of Ferro Corporation, of Walton Hills, Ohio. Bu-A/MA/bu-MA terpolymer was METABLEN® L-1000 butyl acrylate/methyl methacrylate/butyl methacrylate terpolymer, obtained from Elf Atochem North America, Inc., of 2000 Market Street, Philadelphia, Pa. 19103. MB1 was FSU 93E polyethylene masterbatch with slip and antiblock, having a density of 0.975 g/cc and a melt index of 7.5 g/10 min, obtained from A. Schulman. MB2 was 180637 light cream masterbatch having a density of 1.25 g/cc, obtained from Ampacet.
After cooling or quenching by water spray from cooling ring 146, tubing 144 is collapsed by pinch rolls 148, and is thereafter fed through irradiation vault 150 surrounded by shielding 152, where tubing 144 is irradiated with high energy electrons (i.e., ionizing radiation) from iron core transformer accelerator 154. Tubing 144 is guided through irradiation vault 150 on rolls 156. Preferably, tubing 144 is irradiated to a level of about 4.5 MR.
After irradiation, irradiated tubing 158 is directed through nip rolls 160, following which tubing 158 is slightly inflated, resulting in trapped bubble 162. However, at trapped bubble 162, the tubing is not significantly drawn longitudinally, as the surface speed of nip rolls 164 are about the same speed as nip rolls 160. Furthermore, irradiated tubing 158 is inflated only enough to provide a substantially circular tubing without significant transverse orientation, i.e., without stretching.
Slightly inflated, irradiated tubing 158 is passed through vacuum chamber 166, and thereafter forwarded through coating die 168. Second tubular film 170 is melt extruded from coating die 168 and coated onto slightly inflated, irradiated tube 158, to form two-ply tubular film 172. Second tubular film 170 preferably comprises an O2-barrier layer, which does not pass through the ionizing radiation. Further details of the above-described coating step are generally as set forth in U.S. Pat. No. 4,278,738, to Brax et al., which is hereby incorporated by reference thereto, in its entirety.
After irradiation and coating, two-ply tubing film 172 is wound up onto windup roll 174. Thereafter, windup roll 174 is removed and installed as unwind roll 176, on a second stage in the process of making the tubing film as ultimately desired. Two-ply tubular film 172, from unwind roll 176, is unwound and passed over guide roll 178, after which two-ply tubular film 172 passes into hot water bath tank 180 containing hot water 182. The now collapsed, irradiated, coated tubular film 172 is submersed in hot water 182 (having a temperature of about 210° F.) for a retention time of at least about 5 seconds, i.e., for a time period in order to bring the film up to the desired temperature for biaxial orientation. Thereafter, irradiated tubular film 172 is directed through nip rolls 184, and bubble 186 is blown, thereby transversely stretching tubular film 172. Furthermore, while being blown, i.e., transversely stretched, nip rolls 188 draw tubular film 172 in the longitudinal direction, as nip rolls 188 have a surface speed higher than the surface speed of nip rolls 184. As a result of the transverse stretching and longitudinal drawing, irradiated, coated biaxially-oriented blown tubing film 190 is produced, this blown tubing preferably having been both stretched in a ratio of from about 1:1.5-1:6, and drawn in a ratio of from about 1:1.5-1:6. More preferably, the stretching and drawing are each performed a ratio of from about 1:2-1:4. The result is a biaxial orientation of from about 1:2.25-1:36, more preferably, 1:4-1:16. While bubble 186 is maintained between pinch rolls 184 and 188, blown tubing film 190 is collapsed by rolls 192, and thereafter conveyed through nip rolls 188 and across guide roll 194, and then rolled onto wind-up roll 196. Idler roll 198 assures a good wind-up.
The polymer components used to fabricate multilayer films for use in making the bags of the present invention may also contain appropriate amounts of other additives normally included in such compositions. These include antiblocking agents (such as talc), slip agents (such as fatty acid amides), fillers, pigments and dyes, radiation stabilizers (including antioxidants), fluorescence additives (including a material which fluoresces under ultraviolet radiation), antistatic agents, elastomers, viscosity-modifying substances (such as fluoropolymer processing aids) and the like additives known to those of skill in the art of packaging films.
The multilayer films used to make the bags of the present invention are preferably irradiated to induce crosslinking, as well as corona treated to roughen the surface of the films which are to be adhered to one another. In the irradiation process, the film is subjected to an energetic radiation treatment, such as corona discharge, plasma, flame, ultraviolet, X-ray, gamma ray, beta ray, and high energy electron treatment, which induce cross-linking between molecules of the irradiated material. The irradiation of polymeric films is disclosed in U.S. Pat. No. 4,064,296, to BORNSTEIN, et al., which is hereby incorporated in its entirety, by reference thereto. BORNSTEIN, et al. discloses the use of ionizing radiation for crosslinking the polymer present in the film.
Radiation dosages are referred to herein in terms of the radiation unit “RAD”, with one million RADS, also known as a megarad, being designated as “MR”, or, in terms of the radiation unit kiloGray (kGy), with 10 kiloGray representing 1 MR, as is known to those of skill in the art. A suitable radiation dosage of high energy electrons is in the range of up to about 16 to 166 kGy, more preferably about 40 to 90 kGy, and still more preferably, 55 to 75 kGy. Preferably, irradiation is carried out by an electron accelerator and the dosage level is determined by standard dosimetry processes. Other accelerators such as a van der Graaf or resonating transformer may be used. The radiation is not limited to electrons from an accelerator since any ionizing radiation may be used.
As used herein, the phrases “corona treatment” and “corona discharge treatment” refer to subjecting the surfaces of thermoplastic materials, such as polyolefins, to corona discharge, i.e., the ionization of a gas such as air in close proximity to a film surface, the ionization initiated by a high voltage passed through a nearby electrode, and causing oxidation and other changes to the film surface, such as surface roughness.
Corona treatment of polymeric materials is disclosed in U.S. Pat. No. 4,120,716, to BONET, issued Oct. 17, 1978, herein incorporated in its entirety by reference thereto, discloses improved adherence characteristics of the surface of polyethylene by corona treatment, to oxidize the polyethylene surface. U.S. Pat. No. 4,879,430, to HOFFMAN, also hereby incorporated in its entirety by reference thereto, discloses the use of corona discharge for the treatment of plastic webs for use in meat cook-in packaging, with the corona treatment of the inside surface of the web to increase the adhesion of the meat to the adhesion of the meat to the proteinaceous material. Although corona treatment is a preferred treatment of the multilayer films used to make the pre-padded bag of the present invention, plasma treatment of the film may also be used.
A multilayer film is preferably converted to the bags of the present invention by heat sealing both across the film (i.e., a transverse heat seal) as well as heat sealing in the machine direction along the length of the film (i.e., a machine direction seal). The transverse seal is preferably made using a heat sealing method known as “impulse sealing”, which is carried out by placing a seal bar across the film and thereafter momentarily passing current through a heat seal wire on the seal bar. The seal wire heats up, transferring heat through a first side of the film tubing (or folded film) to the other side, causing the film to be sealed to itself. This sealing method is well known to those of skill in the art.
The lengthwise heat sealing (i.e., machine direction heat sealing) can be carried out using a seal bar and impulse sealing, i.e., in the same manner that the transverse seals are made. However, impulse heat sealing is generally carried out by forwarding the film intermittently in a direction along the length of the film tubing or sheet. If continuous forwarding of the film is desired during lengthwise heat sealing, a continuous band sealer can be used. Such continuous band heat sealers are described in U.S. Pat. No. 5,858,153, to Mack, entitled “Method for Making Tubular Containers”, as well as U.S. Pat. No. 6,344,258 B1, to Rasmussen, entitled “Heat-Sealing Polymer Films”, and U.S. Pat. No. 5,034,088, to Denker, entitled “Band Wheel and Tension Control”, each of which is hereby incorporated, in its entirety, by reference thereto. Continuous band sealers are available from, for example, Lamination Plus, 1142 West Flint Meadow Drive, P.O. Box 121, Kaysville, Utah, 84037, and Pierce Packaging Equipment, Inc., 217 South Claremont Street, San Mateo, Calif., 94401
It is also within the scope of the present invention to produce sets of pre-padded side-seal bags.
A chain of pre-padded side-seal bag sets alternatively can be formed from separate first and second films by disposing absorbent pads on the first film (and preferably adhering the pads to the film) and bringing the second film into overlying relation with the first film, longitudinally sealing one longitudinal edge of the first film to the corresponding longitudinal edge of the second film so as to form end seals for the bags, and then forming transverse seals (and optionally the lines of weakness) across the two films generally as described above in connection with
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific and/or preferred embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
