MXPA00010522A - Stretch film having heat-sealed edges - Google Patents

Abstract

A highly stretched film (40) has permanently heat-sealed edges (43) that are nearly invisible. A folding apparatus (30) folds the edge portions of a film to form folded edges (43). The folded film then is passed through a bridle mechanism having two heated rolls (15,16). A series of nips (13,17,18) apply pressure to the folded film as it is heated by the heated rolls (15,16). The nip pressure, combined with the heat imparted by the heated rolls (15,16), causes thermal welding of the folded edges resulting in permanent heat-sealed edges (43). Because the film edges are folded prior to the hot-stretching, the hot stretch process performs dual functions of stretching the film and heat sealing the folded edges (43). The resulting stretched film has permanently heat-sealed edges that do no separate, and which prevent tearing of the film edges during subsequent processing and use.

Description

STRETCHABLE FILM WHICH HAS HEAT SEALED EDGES FIELD OF THE INVENTION This invention is directed to a highly stretchable film having heat sealed edges and a method and apparatus for making the film. The film has resistant edges permanently sealed by heat that are almost invisible. The thickness and integrity of the heat sealed edges are controlled by the process of this invention, thus improving the appearance of the wound roll. BACKGROUND OF THE INVENTION Several cold processes for manufacturing a film with reinforced edges are known in the art. These reinforced films have good tear resistance characteristics to resist ripping at the edges. These films are used particularly to secure and pack goods for shipping. The related technology provides a cold process for providing longitudinal reinforcement of a film strip, as in U.S. Patent No. 4,905,451 issued to Jaconelli et al. Jaconelli et al. reveals guides positioned towards the fold areas of a strip to overlap each other in order to form a reinforcement zone. Salzsauler et al., In U.S. Patent 5, 531,393, discloses a cold process for making a stretchable film with bent edges comprising adjustable bending tab elements that cause the edges of a film to bend before stretching and recording the film . Scherer, in U.S. Patent No. 5,565,222 discloses a cold process for making a stretchable film having flat double-thickness hems at the opposite margins of the film. The prior art films and the procedures for making films with edges have certain disadvantages. One of the disadvantages is that the edges are produced through a cold process where the films bend to form edges. The edges are easily separated during application and / or use. Another disadvantage is that the thickness of the edges formed during cold processes is twice the thickness of the central portion of the film. Also the bent edges need to be wide enough to prevent them from unfolding. As a result of this, the films, which have these edges are difficult to wrap in a storage core. Unevenly coiled windings have a bad appearance and cause excessive pressure on the core which results in core failure. A method and a film produced through this process is needed to overcome the problems associated with the reinforced films of the prior art and the cold processes for making these films. SUMMARY OF THE INVENTION This invention is directed to a highly stretchable film having permanently sealed edges by heat that are almost invisible. The heat-sealed edges have a width of the order of 0.25 cm (0.10 inches) to 2.54 cm (1.0 inches). The edges sealed by heat do not separate, and prevent the film from tearing. The edges of the film can be folded once (to form a folded edge of two layers) or more than once (to form bent edges having three or more layers). In order to form the edges, a film is fed to a bending apparatus before stretching the film with the aid of heat. Any bending procedure is considered adequate, which bends the two edges of the film. In one method, the film advances on a first fold roll having a length that is less than the initial width of the film. As the film advances on the first bending roll, the edge portions project outwardly beyond the opposite ends of the first bending roll. A second bending roll is placed in relation to the first bending roll to direct the film at an angle with respect to the initial path of the film, keeping it under tension. As a result of this tension, the edge portions are folded down through the acute angles on the opposite ends of the first fold roller. A pair of bending members is placed between the first bending roll and the second bending roll. As the film proceeds through the fold members, the edge portions are bent until the edge portions come into contact with an end surface of the film to form bent edges. This procedure can be repeated if bent edges having multiple layers of film (more than two) are desired. Once the bent edges are formed, the film is fed to a high speed heating and drawing apparatus comprising a flange mechanism having a heated first roller and a heated second roller. The bent film passes through a compression upon contact with the first heated roller. The pressure of the compression, combined with the heat imparted by the first roller and the second roller, causes thermal welding of the bent edges resulting in permanent bends bent by heat. The resistance of the heat seals is conserved and, to a certain degree reinforced, during the hot stretching process. Because the film is bent before hot stretching, the hot drawing process performs double functions of stretching the film and sealing the bent edges. The resulting stretched film has permanently heat sealed edges that do not separate and which prevent tearing of the edges of the film during subsequent processes and use. With the foregoing in mind, it is a feature and advantage of this invention to provide a highly stretchable film having permanently heat sealed edges resistant to tearing and separation. The edges sealed by heat are almost invisible. The uniform controlled thickness of the bent edges minimizes the pressure load on the core and improves the appearance of the wound roll. Another feature and advantage of the present invention are to provide a high speed apparatus and method for forming edges in a film, heat sealing the edges and stretching the reinforced film about 100-450% of its initial pre-stretched length , until obtaining a final length that is of the order of 200 - 550% of the initial length. Another feature and advantage of the present invention is to provide a high speed apparatus and method for heating and stretching a reinforced film having bent edges, wherein the reinforced film is fed from a flange mechanism at a speed up to 2,500 fpm. The foregoing and other features and advantages of this invention will become more apparent from the following detailed description of the preferred embodiments, read in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a diagrammatic side view of the apparatus for high speed stretching according to one of the preferred embodiments of the invention. FIGURE 2 is a diagrammatic perspective view of the bending apparatus according to one of the embodiments of the invention. FIGURE 3 is a sectional diagrammatic view of the reinforced film produced by the apparatus of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT With reference to Figures 1 and 2, an apparatus 5, a bending apparatus 30, and a high-speed method for heating and stretching a film 40 while the bent edges are disclosed are disclosed. They are sealed with heat. The apparatus 5 comprises a structure 10. The bending apparatus 30 (FIGURE 2) supplies the apparatus 5 (FIGURE 1) with a stretchable reinforced film 40 of any known composition. For example, these films are often composed of polyethylene, polyvinyl, chloride, ethylene vinyl acetate, ethylene methyl acetate, and copolymers of ethylene with higher alpha olefins. With reference to Figure 2, a bending apparatus 30, as disclosed in U.S. Patent No. 5,565,222 issued to Scherer, the disclosure of which is incorporated herein by reference, can supply a reinforced film 40 to a high stretch apparatus. speed 5. The bending apparatus 30 can receive a film 40 from a supply roller 11 or in line from an extrusion apparatus (not shown). As shown in Figures 1 and 2, the apparatus 30 includes a first folding roller 31 rotatably mounted towards the entrance portion 6 of the structure 10. The first folding roller 31 has a length that is less than that of the initial width of the film 40. While the film 40 advances on the first folding roller 31, the edge portions 42 project outwardly protruding from the opposite ends 33 and 34 of the first folding roller 31. The second roller The fold 35 is rotatably mounted to the structure 10 and positioned relative to the first folding roll 31 to direct the film 40 at an angle to the initial path of the film 40, keeping the film 40 under tension. As a result of this tension, the edge portions 42 are bent outwardly through the acute angles on opposite ends 33 and 34 of the first bending roll 31, to initiate the bending procedure. The folding members 36 and 37 are placed between the first folding roller 31 and the second folding roller 35 and mounted to the structure 10. As the film 40 advances through the folding members 36 and 37, the portions of the edge 42 are bent until the edge portions 42 come into contact with a surface of the bottom 44 of the film 40 towards the formed edges 43 as shown in FIGURE 3. Before the stretch, the formed edges 43 have a width of the order of 0.25 cm (0.10 inches) to 2.54 cm (1.0 inches), preferably 0.63 cm (0.25 inches) to 1.27 cm (0.50 inches). By keeping the film 40 under tension, it is ensured that the film 40 and the edges 43 remain in a substantially flat position. Once the edges 43 are formed, the film 40 is stored on a roller or feeds an apparatus 5 (FIGURE 1) where the film 40 is heated, the bent edges are heat sealed 43, and stretched. A flange mechanism 14 is connected to the structure 10 and includes a first heated roller 15 and a second heated roller 16 operatively connected to the structure 10. The first heated roller 15 and the second heated roller 16 are rotatably mounted to the structure 10 and are preferably driven by independent motors at different speeds or, alternatively, by separate gear assemblies of different sizes driven by a common motor. The second heated roller 16 rotates at a speed greater than the speed at which the first heated roller 15 rotates during operation of the apparatus 5. The first heated roller 15 and the second heated roller 16 are preferably made of chromed steel, but can be manufactured of polished aluminum and other metals that have a smooth surface.

The rollers 15 and 16 can have an outer diameter (DE) of at least 30.48 cm (12 inches), preferably at least 45.72 cm (18 inches). The width of the first heated roller 15 and the heated second roller depends on the desired width in the film to be produced. In one embodiment, the rollers 15 and 16 have a width of about 1.63 m (64 inches). The large outer diameter and the softness of the heated rollers 15 and 16 allow maximum contact with the film 40 and the heat sealing of its edges. Also, rollers 15 and 16 are placed very close to each other and can, for example, have an interspace of about 0.02 cm (0.01 inches) between their nearest points. When placing the rollers and 16 together, the carry distance "d" is minimized. With reference to FIGURE 1, the carry distance "d" refers to the length of the film 40 between the rollers 15 and 16 that does not touch any of the rollers at any given time. The carry distance "d" must be of the order of 0.63 cm (0.25 inches) - 2.54 cm (1.0 inches), preferably 1.27 cm (0.50 inches) - 1.90 cm (0.75 inches). The combination of high surface contact and short haul distance minimizes narrowing. Narrowing is a reduction in the width of the film at the time the film is stretched and is the result of poor contact between the film and the stretching members, as well as too many stretch members and / or successive long distances between the members. of stretching. The narrowing of the films made by the inventive method is less than 15%, preferably about 10% or less, for 30.48 cm (12 inch) wide films. To achieve smoothness of the surface, the first heated roller 15 and the second heated roller 16 can have mirror surfaces 25 and 26 respectively. The outer mirror surfaces 25 and 26 may have a variation in surface finish, that varies from the lowest point to the highest point, in the order of 0 microns to 10 microns, preferably of the order of 0 microns to 5 microns . The smooth finish of the surface and the heat transferred from the heated rollers 15 and 16 to the film 40 allow a greater adhesion of the film 40 towards the heated rollers 15 and 16, and also improve the clarity of the film 40. Therefore , the film 40 can be fed through a flange mechanism 14 without the film 40 slipping, resulting in higher stretch ratios. Furthermore, the heat minimizes the fluctuation of the width of the film due to the coefficient of friction that is higher, the absence of air and the adhesion between the film 40 and the exterior mirror surfaces 25 and 26. A first compression of the stretch 13 it is rotatably connected to the structure 10 and operatively connected to the supply roller 11. The first stretch compression 13 is preferably made of rubber and has an outer diameter of less than 25.4 cm (10 inches), and suitably of about 15.24 cm (6 inches). The first stretch contraction 13 applies pressure, preferably of the order of 2-10 pounds per linear inch (pli), suitably of the order of 5 pli, against the outer mirror surface 25 of the first heated roll 15. The first stretch compression 13 initiates the heat sealing of the bent edges 43. The film 40 can be fed through the first compression 13 without slipping, thus preventing the formation of wrinkles and / or holes in the film 40. In one of the preferred embodiments of this invention, a second stretch compression 17 and a third stretch compression 18 are rotatably connected to the structure 10. The second stretch compression 17 and the third stretch compression 18 are preferably made of rubber and have an outer diameter less than 20.32 cm (8 inches), suitably of the order of 10.16 cm (4 inches). The second stretch compression 17 applies pressure, preferably about 2-10 pounds per linear inch ("pli"), suitably about 5 pli, against the outer mirror surface 25 of the first heated roll 15 and the third stretch compression 18 applies a similar pressure against the outer mirror surface 26 of the second heated roller 16. The second stretch compression 17 and the third stretch compression 18 pierce the film 40 against the respectively heated rolls 15 and 16, while the film it stretches between the rollers 15 and 16, thus minimizing slipping and further improving the heat sealing of the bent edges 43. Upon exiting the heated roller 16, the film passes between the heated roller 16 and the roller 19, which travels to the same tangential speed of the roller 16. A small pressure of the order of 2-10 pli is applied between the rollers. A guide roller 20, a laying roller 21 and a core are mounted to the structure 10 downwardly from the rollers 16 and 19. The laying roller 21 and the core 22 rotate at a slower tangential speed than the rollers 16 and 19, allowing the film 40 to relax or shrink after leaving the roller 19. The level of relaxation is less than 15% of the amount of the stretch, preferably about 5% or less. For example, a 30.48 cm (1 foot) long film sample can be stretched up to 1.22 m (4 ft), to obtain a final length of 1.81 m (4.6 ft). The annealed film is rolled and stored in the core 22, which is periodically filled and replaced. In one of the preferred embodiments of this invention, a dyed film having a thickness in the order of 23 microns comprising at least three layers with a first outer layer, a second outer layer and a second layer is heated and stretched. core. The first outer layer comprises a polyethylene of very low density (hereinafter VLDPE) comprising copolymers of ethylene with alpha olefin, available from Dow Chemical as Dow SC4105. The first outer layer has a thickness of about 2.8 microns. The VLDPE polymer has a density of the order of 0.910 to 0.911 g / cc and a melt index (ID) of 3.3 dg / min. The second layer and the core layer comprise a low density polyethylene (LLDPE) line, which is a copolymer of ethylene and octene, available from Dow Chemical as Dow 2288. The second outer layer has a thickness of about 1.8 microns. The core layer has a thickness of about 18.4 microns. The LLDPE polymer in these layers has a density of about 0.917 g / cc. In another embodiment, a blown film with a thickness of about 20 microns which includes at least three layers, with a first outer layer, a second outer layer and a core layer, is heated and stretched. The first outer layer has a thickness of about 1.6 microns which includes a VLDPE plastomer, which may be a catalyzed metallocene copolymer of ethylene with an alpha olefin, preferably 1-octene, resulting in a first outer layer having a density of around 0.870 g / cc and an ID of 1-0 dg / min. Dow Chemical Company sells a polymer that has these properties as Dow EG8100. VLDPE plastomers have lower densities than linear low density polyethylene (LLDPE) and are a class of materials different from linear low density polyethylene (LLDPE). These plastomers can be used in biaxially oriented films with superior properties comparable to those of films with LLDPE, including superior tensile strength and increased puncture resistance. The core layer can be manufactured from an ethylene LLDPE copolymer with hexene or octene, with a melt index of 1.0, and a density of 0.917-0.20 grams / cc. Suitable polymers include the Exxon LL3001 from Exxon Chemical Company, and Dowlex 2045 from the Dow Chemical Comp The core layer has a thickness of about 16.4 microns. The second outer layer includes an octene LLDPE with a density of the order of 0.925 g / cc and an IF of 1.9 dg / min. One of these polymers is available from Dow Chemical as Dow LD535I. The second outer layer has a thickness of the order of 2.0 microns. The invention is not limited in particular to these stretch film polymers, the thicknesses of the film, or the film constructions. Other stretchable films made from one or more combinations of layers and polymers can also be processed with this invention, including materials such as ethylene vinyl acetate (EMA), other VLDPE and LLDPE, certain catalyzed metallocene olefin polymers and copolymers and terpolymers of the same. The method of the invention can be described with reference to the apparatus. Referring again to Figures 1 and 2, in a high-speed process for heating and stretching the reinforced film 40 having edges 4, the film advances on a first guide roller 12 and is fed between the first stretch compression 13 and the first heated roller 15. The first stretch compression applies pressure, as explained above, against the outer mirror surface 25 of the first heated roller 15. The film 40 is fully engaged to the exterior mirror surface 25 of the first heated roller 15 , or free of wrinkles, holes and / or air pockets as a result of the pressure applied by the first stretch compression 13 and the smoothness of the outer mirror surface 25. The first heated roller 15 and the second heated roller 16 are They heat to a suitable temperature depending on the composition of the film. This temperature can be in the range of 37.77 ° C-176 ° C (100 - 350 ° F), suitably around 65.55 ° C - 121.11A (150-250 ° F). In a preferred film embodiment described above, the preferred temperature is of the order of 93.33 ° C (200 ° F) to about 104.44 ° C (220 ° F). The heating of rollers 15 and 16 is achieved by methods known to those skilled in the art, including internal steam, water, oil and electricity. Preferably, the first roller 15 is heated to a temperature of about 104.44 ° C (220 ° F). While the first heated roller 15 rotates, the film 40 is heated to about 71.11 ° C (160 ° F) while the film 40 passes around the outer mirror surface 25. The heat that is transferred from the film 40 , while the film 40 is passed around the first heated roller 15, promotes intermolecular melting along the edges 43. The film 40 is then fed through the second stretch compression 17, which applies pressure against the surface of the film. outer mirror 25, after the film 40 is separated from the first heated roller 15. After a brief separation of the two rollers 15 and 16, the film 40 is fed through a third stretching compression 18 which applies the appropriate pressure against the outer mirror surface 26 and the film 40 is adhered to the second heated roller 16. As a result of compression, and the second heated roller 16 rotates at a speed higher than the speed at which the first heated roller 15 rotates, the film 40 is stretched while the film 40 is transferred between the first heated roller 15 and the heated second roller 16. The shortest distance between the outer mirror surface 25 of the first heated roller 15 and the outer mirror surface 26 of the second heated roller 16 is known as the intermediate space of the roller. The interspace of the roller may vary with the thickness and type of film, and is typically of the order of 0.012 cm (0.005 inches) - 0.20 cm (0.08 inches), suitably about 0.025 cm (0.01 inches) - 0.05 cm (0.02 inches). The tangential distance between the point where the film 40 sates from the first heated roll 15 in the second stretch contraction 17 at the point where the film 40 first contacts the second heated roll 16 in the third stretch contraction 18 is known as intermediate carrying space. The intermediate space of the carry point is quite short, and is suitably of the order of 0.63 cm (0.25 inches) - 2.54 cm (1.0 inches), preferably 1.27 cm (0.50 inches) - 1.90 cm (0.75 inches). The short, intermediate space of carry decreases the narrowing associated with the stretch apparatus of prior technology.

Also, the fact that the film 40 only passes once means that the intermediate space of total carry is the same as the intermediate space of single-stage carry. While the second heated roller 16 rotates, the film passes around the outer mirror surface 26 and is heated. Preferably, the heated roller 16 is heated to a temperature within the ranges set forth above for the heated roller 15. The film is advanced on a rotary idler roller 19 and the film 40 is wound on the core (film roll) 22. In a of the preferred embodiments, the second guide roller 20 and a laying roller 21 are operatively connected to the idler roller 19 to prevent the film from slipping and further improve the heat sealing of the bent edges 43, improving the process of wound around the core 22. The film 40 is allowed to relax by up to 20%, preferably in the range of 5% to 15%, while the film advances between the idler roller 19 and the guide roller 20. The high stretch ratios, that is, the ratio of the end, the stretched length of the film 40 towards the initial one, and the pre-stretched length of the film, are the result of u The greater adhesion of the film 40 to the first heated roller 15 and the heated second roller 16. The "stretch ratio" is the ratio of the length of the film after stretching the initial length that is unstretched. Thus, a stretch ratio of 2: 1 means that a film increases its length by 100% due to stretching, while a ratio of 1: 1 means there is no stretching (ie, 0%). The stretching ratios resulting from the inventive process have a range of about 5.5: 1, and preferably between 2: 1 to about 4.5: 1. As a result, the apparatus 5 and the method of this invention have the ability to stretch the film 40 to about 450%, at a length which is about 550% of its initial pre-stretched length. Additionally, the apparatus 5 and the method of this invention have the ability to stretch the film 40 at a finished line speed of about 1,000 fpm to 3,000 fpm, preferably from about 1,500 fpm to about 2,500 fpm. The pressure, heat and rapid stretching force applied to the film 40 permanently heat-seal the bent edges 43. It should be understood that variations and modifications of the present invention can be made without departing from the scope of the present invention. It should also be understood that the scope of the present invention should not be construed as limiting itself to the specific embodiments disclosed herein. The scope of the invention is indicated in the appended claims, and all changes that fall within the meaning and range of equivalents are intended to be encompassed herein.

Claims (25)

1. CLAIMS 1. A method for manufacturing a film having bent edges sealed by heat comprising the steps of: advancing the film having a first portion of the edge and a second portion of the edge through a folding apparatus; folding the first edge portion and the second edge portion so that the first edge portion and the second edge portion come into contact with one surface of the film to form a first bent edge and a second bent edge; and heat seal the bent edges.
2. 2. The method of Claim 1, further comprising the step of passing the film through a hot drawing apparatus, wherein the bent edges are sealed and stretched with heat.
3. 3. The method of Claim 1, wherein the heat sealing step includes passage of the film through at least one contraction adjacent to the heated roll.
4. The method of Claim 3, wherein the heat sealing step further includes passing the film through a second contraction adjacent the heated roll.
5. 5. The method of Claim 4, wherein the step of heat sealing further includes passing the film through a third contraction adjacent to the heated roll.
6. The method of Claim 5, wherein the heat seal step includes adding the film through a fourth contraction adjacent a heated roll.
7. The method of Claim 1, wherein the first folded edge and the second folded edge have a width of up to 2.54 cm (1.0 inches).
8. The method of Claim 1, wherein the first folded edge and the second folded edge have a width of about 0.25 cm (0.1 inches) to about 2.54 cm (1.0 inches).
9. The method of Claim 1, wherein the first folded edge and the second folded edge have a width of about 0.63 cm (0.25 inches) to about 1.27 cm (0.5 inches)
10. 10. The method of Claim 2, wherein the film passes through the hot drawing apparatus at a speed of at least 304.80 m (1,000 feet) per minute.
11. 11. The method of Claim 1, wherein the first heated roller and the heated second roller are heated to a temperature of about 65.55 ° C (150 ° F) to 121.11 ° C (250 ° F).
12. 12. A film having permanently heat-sealed bent edges produced by the method of Claim 1.
13. 13. An apparatus for manufacturing a highly stretchable film having bent edges sealed with heat comprising: a structure; a bending device connected to the structure; and a hot drawing apparatus in communication with downwardly from the bending apparatus, the hot drawing apparatus comprises a flange mechanism having a first heated rotatable roller and a second heated rotatable roller.
14. 14. The apparatus of Claim 13 further comprises at least one compression adjacent to the first heated roller.
15. 15. The apparatus of Claim 14 further comprises a second compression adjacent to the first heated roller.
16. 16. The apparatus of Claim 13 further comprises at least one compression adjacent to the second heated roller.
17. 17. The apparatus of Claim 16 further comprises a second compression adjacent the second heated roller.
18. 18. The method of Claim 13, wherein the first heated roller and the heated second roller are heated to a temperature of about 65.55 ° C (150 ° F) to about 121.11 ° C (250 ° F).
19. 19. The apparatus of Claim 13, wherein the first heated roller and the heated second roller are heated to a temperature of about 93.33 ° C (200 ° F) to about 104.44 ° C (220 ° F).
20. 20. A stretched film with permanently heat sealed edges comprising: a first folded edge and a second folded edge having a width of up to 2.54 cm (1.0 inches).
21. 21. The stretched movie of the Claim 20, where the first edge and the second edge are bent before stretching.
22. 22. The stretched movie of the Claim 20, where the first folded edge and the second folded edge have a width of 0.25 cm (0.10 inches) to about 2.54 cm (1.0 inches).
23. 23. The stretched film of Claim 20, wherein the first folded edge and the second folded edge have a width of about 0.63 cm (0.25 inches) to about 1.27 cm (0.5 inches).
24. 24. The stretched film of Claim 20, wherein the first folded edge and the second folded edge comprise a single fold.
25. 25. The stretched film of Claim 20, wherein the first folded edge and the second folded edge comprise more than one fold.