Patent Application
20240033130
The present disclosure is directed generally to forming films with perforations having controlled tearing characteristics. More particularly, the present disclosure is directed to obtaining flame-perforated films in a manner that eliminates or reduces the impact of thermal creep skewing perforations in the film, whereby the perforations have controlled tear characteristics in both the lengthwise or machine direction (MD), and the crosswise or transverse direction (TD).
Currently to obtain polymeric films with tear characteristics in the machine and crosswise directions, a simultaneously biaxially oriented polypropylene (SBOPP) film is utilized. A backing roll of a flame-perforating apparatus provides a supporting surface for the film as the latter is advanced through the apparatus. An exemplary flame-perforating apparatus is described in commonly assigned U.S. Pat. No. 7,037,100. The backing roll includes a plurality of lowered portions or etched wells formed in the backing roll surface. Each of the etched wells has a generally oval shape with a major axis oriented at 45 degree angles to crosswise or TD line of the advancing film web. Perforations are formed in the film over the etched wells as heat is applied to the advancing film by flames positioned over the etched wells. Collectively the noted wells are arranged in a generally herringbone pattern and, as such, it is expected that the resulting film perforations formed thereby would provide comparable tear characteristics in both the MD and TD directions. However, in practice, balanced tearing characteristics are relatively difficult to obtain. This is due to the impact of so-called thermal creep. Thermal creep as the term is used in the present application means the simultaneous application of heat and tension to the film during the flame-perforating process that results in the film undergoing thermal and physical stresses, such that the film stretches or elongates in the MD direction and shrinks or contracts in the TD dimension. As a result, the major axes of the resulting perforations are skewed in that they have angular orientations other than the 45 degrees intended to be imparted and other than the 45 degree orientation of the etched wells in the backing roll surface. As such, the tearing characteristics in both the MD and TD are unbalanced relative to their intended characteristics.
The condensation control process is one known approach for offsetting the impact of thermal creep causing skewing of the perforations particularly during a flame-perforating process. In particular, a film of water is generated on the backing roll while heat is applied by the flames. The resulting film of water causes adhesion between the film, preferably along the edges, and the backing roll. Adhesion inhibits the film slippage on the backing roll that arises, during the flame-perforating process, from the general simultaneous longitudinal expansion and transverse contraction of the film due to thermal creep. While condensation control has proven effective in minimizing the impact of thermal creep, such success has, however, been generally limited to situations involving relatively low tension forces being applied to the film or when low stresses from thermal creep are present. As a consequence, condensation control may not be as robust a process for large-scale commercial applications since significant tension forces must be applied to the larger and wider rolls of the film typically used commercially. The stresses imparted by thermal creep will also be larger in large-scale commercial equipment. In addition, the condensation control process requires utilization of control structures and methods for controlling the formation of the film of water, in order to provide successful implementations during the actual process. As such, this adds to overall commercialization costs and process complexity. Furthermore, because web tension forces are generally kept relatively low, any problems with uneven caliper in the input film cannot be overcome by increasing web tension.
Hence, needs exist for providing methods, systems, and apparatus for controlling tear characteristics of films, such as flame-perforated films. These needs further include being able to easily and reliably perforate film during a flame-perforating process, such that skewing of perforation orientations that are due to thermal creep are minimized or eliminated. These needs further include being able to provide tear characteristics wherein polymeric films, such as flame-perforated polymeric films, have comparable tear characteristics in both the lengthwise or machine direction (MD), and the crosswise or transverse direction (TD). These needs further include being able to correct for positional skewing of perforations in films, such as flame-perforated films, by thermal creep. These needs further include being able to, in a low cost manner, offset the impact of thermal creep skewing the orientations of perforations in the film. These needs further include being able to offset the impact of thermal creep skewing the orientation of perforations formed in the film in a manner that lessens the need for adhesion created by a water film, or the relatively expensive and complex water film control methods and mechanisms used during the actual process. The needs further include the ability to increase web tensions during the process so as to enable commercial processing of films requiring relatively high tension forces. Without such needs being satisfied the true potential for perforating films providing enhanced tear characteristics will not be fully achieved, especially in a simple, reliable, and less costly manner.
Accordingly, efforts are being undertaken for continuing the generation of improvements in this field that minimize the affects of thermal creep skewing the perforations in film during flame-perforating as well as being efficient and economical to implement.
In one exemplary embodiment, the present disclosure is directed to a method of correcting for positional skewing of perforations from a predefined angle of inclination relative to a generally transverse reference line of flame-perforated film produced by a flame-perforating process under a first set of conditions, the method comprising: determining the degree of angular deviation of the major axis of each of the one or more perforations in the flame-perforated film from the predefined angle of inclination; and forming one or more perforation-forming structures in a film supporting structure adapted for use in a subsequent flame-perforating process using the first set of conditions, wherein each of the perforation-forming structures has a major axis being angularly offset to the predefined angle of inclination by an inverse amount related to the angular deviation of the one or more corresponding perforations of the previously flame-perforated film.
In another exemplary embodiment, the present disclosure is directed to a film-supporting apparatus adapted to form perforations in film supported thereon during a flame-perforating process, wherein each of the formed perforations has a major axis positioned at a predefined angle of inclination relative to a generally transverse reference line, the apparatus comprises: a body having a film supporting surface, and one or more perforation-forming structures positioned on the film supporting surface, wherein each perforation-forming structure has a major axis angularly offset from the predefined angle of inclination of the major axis of each corresponding formed perforation by a predetermined amount.
In another exemplary embodiment, the present disclosure is directed to a roller adapted for use in a flame-perforating apparatus for perforating film, the roller comprises: a body; a film supporting surface on the body adapted to support and convey film to be perforated; and one or more perforation-forming structures on the supporting surface, each of which has a major axis having an angular orientation that is angularly offset to a predefined angle of inclination that is established relative to a generally transverse reference line across the film to be supported, wherein the angular offset is by an amount that is inversely related to the angular deviation relative to the predefined angle of inclination of one or more corresponding skewed perforations formed in previous flame-perforated film, the film supporting surface thus configured forms perforations in the film to be flame-perforated during a flame-perforating process that offsets the impact of thermal creep skewing the resulting one or more perforations, such that the major axis of each of the resulting one or more formed perforations is generally coincident with the predefined angle of inclination.
In another exemplary embodiment, the present disclosure is directed to a method of controlling tear characteristics of film, comprising: providing a polymeric film to be flame-perforated; providing a flame supporting apparatus that includes a body having a film supporting surface including one or more perforation-forming structures, each of the one or more perforation-forming structures has a major axis with an angular orientation that is angularly offset to a predefined angle of inclination established relative to a generally transverse reference line of film to be supported by the film supporting surface, wherein the angular offset is by an amount that is inversely related to the angular deviation relative to the predefined angle of inclination of one or more corresponding skewed perforations formed in previous flame-perforated film; and applying heat and tension forces to the film as it is advanced by the film supporting apparatus to form resulting perforations in the film; such that the film supporting surface thus configured forms perforations in the film supported thereby that offset the impact of thermal creep skewing the one or more resulting perforations, whereby the major axis of each of the resulting one or more perforations is generally coincident with the predefined angle of inclination.
In another exemplary embodiment, the present disclosure is directed to a method for use in an apparatus for flame-perforating a film, wherein the apparatus includes a film-supporting apparatus as noted above, the method of obtaining perforations during a flame-perforating process comprising: using the film-supporting apparatus as noted above during a flame-perforating process such that the formed perforations have a major axis at a predefined angle of inclination relative to a generally transverse reference line.
In another exemplary embodiment, the present disclosure is directed to a flame-perforated film made according to the above noted method of controlling tear characteristics in flame perforated film.
In another exemplary embodiment, the present disclosure is directed to a film comprising: first and second major surfaces; one or more perforations formed in at least one of the first and second major surfaces, wherein the one or more perforations in the film is formed by providing a film supporting apparatus that includes a film supporting surface having one or more perforation-forming structures thereon, each of the perforation-forming structures has a major axis with an angular orientation that is angularly offset to a predefined angle of inclination established relative to a generally transverse reference line of film to be supported by the film supporting surface, wherein the angular offset is by an amount that is inversely related to the angular deviation relative to the predefined angle of inclination of one or more corresponding skewed perforations formed in previous flame-perforated film; and applying heat and tension forces to the film as it is advanced by the film supporting apparatus such that the film supporting surface thus configured forms perforations in the film supported thereby during a flame-perforating process that offsets the impact of thermal creep skewing the resulting one or more perforations, such that the major axis of each of the resulting one or more formed perforations is generally coincident with the predefined angle of inclination to form perforations in the film.
In another exemplary embodiment, the present disclosure is directed to a flame-perforating apparatus for flame-perforating a film; the flame-perforating apparatus comprises: a frame; a first device coupled to the frame for applying heat to the film to form perforations in the film; and a second device coupled to the frame for advancing the film under tension through the apparatus, the second device includes a film supporting apparatus, the flame supporting apparatus includes a body having one or more perforation-forming structures on a film supporting surface thereof, each of the perforation-forming structures has a major axis with angular orientation angularly offset to a predefined angle of inclination established relative to a generally transverse reference line of film to be supported by the film supporting surface, wherein the angular offset is by an amount that is inversely related to the angular deviation relative to the predefined angle of inclination of one or more corresponding skewed perforations formed in previous flame-perforated film.
In another exemplary embodiment, the flame-perforating apparatus includes a water condensation control apparatus for controlling the formation of a film of water on the film supporting surface during the flame-perforating process.
In another exemplary embodiment, the present disclosure is directed to a system comprising: film comprising: first and second major surfaces; one or more perforations formed in at least one of the first and second major surfaces; and a flame-perforating apparatus for flame-perforating the film; the flame-perforating apparatus includes: a first device for applying heat to the film to form perforations in the film; and a second device for advancing the film under tension through the flame-perforating apparatus, the second device includes a film supporting apparatus, the film supporting apparatus includes one or more perforation-forming structures on a film supporting surface thereof, each of the perforation-forming structures has a major axis with an angular orientation that is angularly offset to a predefined angle of inclination established relative to a generally transverse reference line of film to be supported by the film supporting surface, wherein the angular offset is by an amount that is inversely related to the angular deviation relative to the predefined angle of inclination of one or more corresponding skewed perforations formed in previous flame-perforated film.
In another exemplary embodiment, the present disclosure is directed to an adhesive tape comprising: a flame-perforated film having first and second major surfaces as constructed above; a first film on one of the first and second major surfaces of the flame-perforated film; and a layer of adhesive coated on at least one of the first film and the other of the first and second major surfaces opposed to the surface having the first film thereon.
Thermal creep as the term is used in the present application means the simultaneous application of heat and tension to the film during the flame-perforating process that results in the film undergoing thermal and physical stresses, such that the film stretches or elongates in the MD direction and shrinks or contracts in the TD direction.
Perforation as the term is used in the present application means an opening made in or through something.
Transverse as the term is used in the present application is not limited to being perpendicular to an axis.
Skewing as the term is used in the present application to describe the perforations means that the major or longer axis of each of the perforations is at an angle that deviates from an intended angle.
Major axis as the term is used in the present application means a longitudinal axis of the larger of two axes of symmetry of a perforation or perforation-forming structure.
Angular offset as the term is used in the present application means the deviation between the actual major axis and the intended major axis.
Inverse amount as the term is used in the present application means an equal and opposite amount.
Perforation-forming structure as the term is used in the present application means any structure that results in the formation of a perforation in a flame-perforating process.
Typically, the film support surface 15 of the backing roll 14 is temperature-controlled, relative to the ambient temperature around the flame-perforating apparatus 10. The film support surface 15 of the backing roll 14 may be temperature-controlled by any means known in the art. Typically, the film support surface 15 of the backing roll 14 is cooled by providing cooled water into the inlet portion 56a of hollow shaft 56, into the backing roll 14, and out of the outlet portion 56b of the hollow shaft 56. The backing roll 14 rotates about its axis 13. The flame-perforating apparatus 10 includes a motor 16 attached to the lower portion 12b of the frame. The motor 16 drives a belt 18, which in turn rotates the hollow shaft 56 attached to the backing roll 14, thus driving the backing roll about its axis 13.
The flame-perforating apparatus 10 includes a burner 36 and its associated burner piping 38. The burner 36 and burner piping 38 are attached to the upper portion 12a of the frame 12 by burner supports 35. The burner supports 35 may pivot about pivot points 37 by actuator 48 to move the burner 36 relative to the film support surface 15 of the backing roll 14. The supports 35 may be pivoted by the actuator 48 to position the burner 36 a desired distance either adjacent or away from the film support surface 15 of the backing roll 14, as explained in more detail with respect to
In one exemplary embodiment of the present invention, the flame-perforating apparatus 10 includes a preheat roll 20 attached to the lower portion 12b of the frame 12. The preheat roll 20 includes an outer roll layer 22. The outer roll layer 22 includes an outer surface 24. Typically, the outer roll layer 22 is made of an elastomer; more typically, the outer roll layer is made of a high-service-temperature elastomer. Typically, the preheat roll 20 is a nip roll, which may be positioned against the backing roll 14 to nip the film between the nip roll 20 and backing roll 14. However, it is not necessary that the preheat roll 20 be a nip roll 20 and instead, the preheat roll may be positioned away from the backing roll 14 so as to not contact the backing roll 14. The nip roll 20 freely rotates about its shaft 60 and is mounted to roll supports 62. Linkage 46 is attached to roll supports 62. The nip roll 20 may be positioned against the backing roll 14, using actuator 44. When the actuator 44 is extended (as shown in
In another embodiment, the flame-perforating apparatus 10 includes a temperature-controlled shield 26 attached to the nip roll 20 by brackets 66 to form one assembly. Accordingly, when the actuator 44 rotates the nip roll 20, as explained above, the temperature-controlled shield 26 moves with the nip roll. The temperature-controlled shield 26 may be positioned relative to the nip roll 20 by bolts 32 and slots 34 attached to the brackets 66. The temperature-controlled shield 26 typically includes a plurality of water-cooled pipes 28. However, other approaches of providing a temperature-controlled shield may be used, such as water-cooled plate, air-cooled plate, or other means in the art. Typically, the temperature-controlled shield 26 is positioned between the burner 36 and the nip roll 20. In this position, the shield 26 protects the nip roll 20 from some of the heat generated from the burner 36, and thus, can be used to control the temperature of the outer surface 24 of the nip roll 20, which has the benefits of reducing wrinkles or other defects in the film at the flame-perforating step performed by the burner 36, while maintaining high film speeds.
In yet another embodiment, the flame-perforating apparatus 10 includes an optional applicator 50 attached to the lower portion 12b of frame 12. The flame-perforating apparatus 10 includes a plurality of nozzles 52. In one exemplary embodiment, the applicator 50 is an air applicator for applying air onto the backing roll 14. In another embodiment, the applicator 50 is a liquid applicator for applying liquid onto the backing roll 14. Typically, the liquid is water; however, other liquids may be used instead. If the liquid is applied by the applicator 50, then typically, air is also supplied to the individual nozzles to atomize the liquid prior to application on the backing roll. The manner in which the air or water may be applied to the backing roll 14 may be varied by one skilled in the art, depending on the pressure, rate, or velocity of the air or water pumped through the nozzles 52. As explained below, without wishing to be bound by any theory, it is believed that if air or water is applied to the film support surface 15 of the backing roll 14, prior to contacting the film to the film support surface 15, then this application of air or water helps either remove some of the condensation built up on the film support surface 15 or applies additional water to actively control the amount of water between the film and the support surface, and thereby helps in eliminating wrinkles or other defects formed in the film at the flame-perforating step conducted by the burner 36.
The flame-perforating apparatus 10 includes a first idle roller 54, a second idle roller 55, and a third idle roller 58 attached to the lower portion 12b of the frame 12. Each idle roller 54, 55, 58 includes its own shaft and the idle rollers may freely rotate about their shafts.
The temperature of the outer film support surface 15 of the backing roll 14 may be controlled by the temperature of the water flowing through the backing roll 14 through shaft 56. The temperature of the outer film support surface 15 may vary depending on its proximity to the burner 36, which generates a large amount of heat from its flames. In addition, the temperature of the film support surface 15 will depend on the material of the film support surface 15.
The temperature of the outer surface 24 of the outer layer 22 of the nip roll 20 is controlled by a number of factors. First, the temperature of the flames of the burner affects the outer surface 24 of the nip roll 20. Second, the distance between the burner 36 and the nip roll 20 affects the temperature of the outer surface 24. For example, positioning the nip roll 20 closer to the burner 36 will increase the temperature of the outer surface 24 of the nip roll 20. Conversely, positioning the nip roll farther away from the burner 36 will decrease the temperature of the outer surface 24 of the nip roll 20. The distance between the axis of nip roll 20 and the center of the burner face 40 of the burner 36, using the axis 13 of the backing roll 14 as the vertex of the angle, is represented by angle α. Angle α represents the portion of the circumference of the backing roll or the portion of the arc of the backing roll between the nip roll 20 and the burner 36. It is typical to make angle α, as small as possible, without subjecting the nip roll to such heat from the burner that the material on the outer surface of the nip roll starts to degrade. For example, angle α is typically less than or equal to 45°. Third, the temperature of the outer surface 24 of the nip roll 20 may also be controlled by adjusting the location of the temperature-controlled shield 26 between the nip roll 20 and the burner 36, using bolts 32 and slots 34 of the brackets 66. Fourth, the nip roll 20 may have cooled water flowing through the nip roll, similar to the backing roll 14 described above. In this embodiment, the temperature of water flowing through the nip roll may affect the surface temperature of the outer surface 24 of the nip roll 20. Fifth, the surface temperature of the film support surface 15 of the backing roll 14 may affect the surface temperature of the outer surface 24 of the nip roll 20. Lastly, the temperature of the outer surface 24 of the nip roll 20 may also by impacted by the ambient temperature of the air surrounding the nip roll 20.
Typical temperatures of the film support surface 15 of backing roll 14 are in the range of 45° F. to 130° F., and more typically are in the range of 50° F. to 105° F. Typical temperatures of the nip roll surface 24 of nip roll 20 are in the range of 165° F. to 400° F., and more typically are in the range of 180° F. to 250° F. However, the nip roll surface 24 should not rise above the temperature at which the nip roll surface material may start to melt or degrade. Although the temperatures of the support surface 15 of the backing roll 14 and the typical temperatures of the nip roll surface 24 of the nip roll 20 are listed above, one skilled in the art, based on the benefits of the teachings of this application, could select temperatures of the film support surface 15 and nip roll surface 24 depending on the film material and the rotational speed of the backing roll 14 to flame-perforate film with reduced numbers of wrinkles or defects.
Returning to the process step, at this location between the preheat roll 20 and backing roll 14, the preheat roll preheats the first side 72 of the film 70 prior to contacting the film with the flame of the burner. The temperature of the preheat roll 20 assists in eliminating wrinkles or other defects in the film at the flame-perforating step.
In the next step of the process, the backing roll 14 continues to rotate moving the film 70 between the burner 36 and the backing roll 14. This particular step is also illustrated in
After the burner 36 has flame-perforated the film, the backing roll 14 continues to rotate, until the film 70 is eventually pulled away from the film support surface 15 of the backing roll 14 by the idler roller 55. From there, the flame-perforated film 70 is pulled around idler roll 58 by another driven roller (not shown). The flame-perforated film may be produced by the flame-perforating apparatus 10 in long, wide webs that can be wound up as rolls for convenient storage and shipment. Alternatively, the film 70 may be combined with a layer of pressure-sensitive adhesive or other films to provide tape, as discussed in reference to
As mentioned above, the flame-perforating apparatus 10 may include the optional applicator 50 for either applying air or water to the film support surface 15 of the backing roll 14, prior to the film 70 contacting the support surface between the backing roll 14 and the nip roll 20. Without wishing to be bound by any theory, it is believed that controlling the amount of water between the film 70 and the film support surface 15 helps reduce the amount of wrinkles or other defects in the flame-perforated film. There are two ways in which to control the amount of water between the film 70 and the film support surface 15. First, if the applicator 50 blows air onto the support surface, then this action helps reduce the amount of water build up between the film 70 and film support surface 15. The water build up is a result of the condensation formed on the backing roll surface when the water-cooled film support surface 15 is in contact with the surrounding environment. Second, the applicator 50 may apply water or some other liquid to the film support surface 15 to increase the amount of liquid between the film 70 and the support surface. Either way, it is believed that some amount of liquid between the film 70 and the film support surface 15 may help increase the fraction between the film 70 and the film support surface 15, which in turn helps reduce the amount of wrinkles or other defects in the flame-perforated film. The position of the nozzles 52 of the applicator 50 relative to the centerline of the burner 36 is represented by angle β where the vertex of the angle is at the axis 13 of the backing roll 14. Typically, the applicator 50 is at an angle β greater than angle α so that the air or water is applied to the backing roll 14 prior to the nip roll 20.
Maintaining some level of water in between the backing roll and the film improves overall quality of the perforated film. However, it was also observed that poor perforation quality would also result with an excess of water applied to the indentation pattern of the backing roll because water that is either partially or completely filling the indentations provides such good heat conductivity that the film over the indentations is not exposed to sufficient heat to form perforations in the film.
There are several distances represented by reference letters in
In
Typically, the film 70 is a polymeric substrate. The polymeric substrate may be of any shape that permits perforation by flame and include, for example, films, sheets, porous materials and foams. Such polymeric substrates include, for example, polyolefins, such as polyethylene, polypropylene, polybutylene, polymethylpentene; mixtures of polyolefin polymers and copolymers of olefins; polyolefin copolymers containing olefin segments such as poly(ethylene vinylacetate), poly(ethylene methacrylate) and poly(ethylene acrylic acid); polyesters, such as poly(ethylene terephthalate), poly(butylene phthalate) and poly(ethylene naphthalate); polystyrenes; vinylics such as poly(vinyl chloride), poly(vinylidene dichloride), poly(vinyl alcohol) and poly(vinyl butyral); ether oxide polymers such as poly(ethylene oxide) and poly(methylene oxide); ketone polymers such as polyetheretherketone; polyimides; mixtures thereof, or copolymers thereof. For example, the polymeric material is from a group that comprises simultaneously or sequentially biaxially oriented polypropylene film and uniaxially oriented polypropylene film. Typically, the film is made of oriented polymers and more typically, the film is made of biaxially oriented polymers. Biaxially oriented polypropylene (BOPP) is commercially available from several suppliers including: ExxonMobil Chemical Company of Houston, Tex.; Continental Polymers of Swindon, UK; Kaisers International Corporation of Taipei City, Taiwan and PT Indopoly Swakarsa Industry (ISI) of Jakarta, Indonesia. Other examples of suitable film material are taught in the aforenoted PCT Publication, WO 02/11978, titled “Cloth-like Polymeric Films,” (Jackson et al.).
The perforation pattern formed in polymeric film 114 has a strong influence on the tear and tensile characteristics of the perforated films and tape backings of the invention. In
As explained above in reference to
The films described herein are suited for many adhesive tape backing applications. The presence of a top film over the perforation pattern can provide an appearance similar to a poly-coated cloth-based tape backing in certain embodiments. This appearance, combined with the tensile and tear properties, makes the film useful as a backing for duct tape, gaffer's tape, or the like. Because the backing is conformable, it is also useful as a masking tape backing.
Polymeric tape 112 further includes a top film 122 and a bottom layer 124. In the embodiment illustrated, top film 122 provides durability to the polymeric tape 112, and can further increase the strength and impart fluid impermeability to tape 112. Bottom layer 124 is, for example, an adhesive composition. Additional or alternative layers can be used to create tape 112. The arrangement of the layers can also be changed. Thus, for example, the adhesive can be applied directly to the top film 122 rather than to the perforated film 114.
The operation of the apparatus 10 will be further described with regard to the following detailed examples. These examples are offered to further illustrate the various embodiments and techniques. It should be understood, however, that many variations and modifications may be made while remaining within the scope of the application.
The custom-designed flame perforation system described above was used to generate the examples below, wherein the perforated film is made of biaxially oriented polypropylene (BOPP). Dust-filtered, 25° C. compressed air was premixed with a natural gas fuel (having a specific gravity of 0.577, a stoichiometric ratio of dry air:natural gas of 9.6:1, and a heat content of 37.7 kJ/L) in a venturi mixer, available from Flynn Burner Corporation, of New Rochelle, NY., to form a combustible mixture. The flows of the air and natural gas were measured with mass flow meters available from Flow Technology Inc. of Phoenix, AZ. The flow rates of natural gas and air were controlled with control valves available from Foxboro-Eckerd. All flows were adjusted to result in a flame equivalence ratio of 0.96 (air:fuel ratio of 10:1) and a normalized flame power of 20,000 Btu/hr-in. (2135 W/cm2). The combustible mixture passed through a 3 meter long pipe to a ribbon burner, which consisted of a 68 cm×1 cm, 8-port corrugated stainless steel ribbon mounted in an extruded aluminum housing, supplied by Flynn Burner Corporation, New Rochelle, NY.
The burner was mounted adjacent a 61 cm diameter, 76 cm face-width, steel, spirally-wound, double-shelled, chilled backing roll, available from F. R. Gross Company, Inc., Stow Ohio. The temperature of the backing roll was controlled by a 240 l/min recirculating flow of water at a temperature of 50° F. (10° C.). The steel backing roll core was plated with 0.5 mm of copper of a 220 Vickers hardness, and then engraved by Custom Etch Rolls Inc. of New Castle, PA, with a perforation pattern shown in
An electric spark ignited the combustible mixture. Stable conical flames were formed with tips approximately 7 mm from the face of the burner housing. The ribbons were recessed 3 mm from the face of the burner. A thermally extruded, biaxially oriented polypropylene (BOPP) homopolymer film, which was 1.2 mil (0.03 mm) thick and 68.5 cm wide, was guided by idler rolls to wrap around the chilled backing roll and processed through the system at an adjustable speed. The upstream tension of the film web was maintained at approximately 2.2 N/cm and the downstream tension was approximately 2.6 N/cm.
To insure intimate contact between the BOPP film and the chilled backing roll, a 23 cm diameter, 76 cm face-width, inbound nip roll, available from American Roller Company, Kansasville, WI, covered with 6 mm of VN 110 (80 Shore A durometer) VITON fluoroelastomer, was located at an adjustable position of approximately 45 degrees relative to the burner, on the inbound side of the chilled backing roll. A water-cooled shield was positioned between the nip roll and the burner which was maintained at a temperature of 50° F. (10° C.) with recirculating water. The nip roll-to-backing roll contact pressure was maintained at approximately 50 N/lineal cm. The film speed through the flame perforation system was 91 m/min.
A custom-built air impingement system utilizing 6 air nozzles was installed to blow compressed air onto the chilled backing roll at a pressure of 10 PSI (69 kPa/m 2) to controllably reduce the amount of water condensation accumulating on the patterned portion of the backing roll. The air nozzles were located approximately 45 degrees prior to the nip roll, relative to the axis of the backing roll.
As noted, the perforations 902 have their orientations skewed relative to the orientations of the perforations in the films depicted in
An undesirable aspect of skewing is that it alters the tearing characteristics desired to be imparted by the pattern and orientations of the perforations. Because of skewing comparable tear characteristics in the MD and TD are diminished. Skewing, as noted, results from thermal creep. As noted, the foregoing process set forth in
Each of the perforations 902 has its major axis 908 coincident with an illustrated perforation skew line 912. The perforation skew line 912 defines an angle A with a generally transverse reference line 914. The perforation skew line assumed by the major axis of the perforation is offset relative to its intended angular orientation. In an exemplary embodiment, angle A is 51 degrees.
The transverse reference line 914 need not be perpendicular to a longitudinal axis 916 of an advancing film being supported by a supporting backing roll (not shown). In this embodiment, however, the transverse reference line 914 is generally coincident to the transverse direction (TD) of the film and is perpendicular the longitudinal axis 916 as well. Transverse reference lines having angles other than 90 degrees to the longitudinal axis 916 are contemplated. The perforation skew line 912 has an angular deviation relative to a predefined angle of inclination illustrated by reference line 918. The predefined angle of inclination line 918 is measured relative to a same transverse reference line 914. The predefined angle of inclination line 918 defines an angle B relative to the transverse reference line 914. The predefined angle of inclination line 918 is the line that is intended to be coincident to the intended angle the major axis of each perforation has with respect to the generally transverse reference line 914. As noted, such a relationship will enable the perforations to impart the desired tearing characteristics. In the exemplary embodiment, the angle B is 45 degrees and assists in obtaining comparable tear characteristics in the MD and TD. An angle C of deviation is provided that represents the angular deviation of the skew line 912 including the major axis 908 of a perforation with respect to the predefined angle of inclination 918. The angle of deviation (angle C) is directly attributable to the thermal creep and represents the angular amount of deviation of the perforations 902.
Reference is made to
The film supporting apparatus 1000 includes a film supporting surface 1020 that is adapted to support and convey the film (not shown) through the flame-perforation apparatus 10. In one exemplary embodiment, the film supporting apparatus 1000 is implemented as a backing roll 1000. The backing roll 1000 may have a 610 mm diameter, with a 760 mm face width. The backing roll 1000 may be a water-cooled steel backing roll for flame-perforation. Such a surface may be polished to a finish suitable for etching of one or more perforation-forming structures 1030 therein. The one or more perforation-forming structures 1030 can be arranged with a pattern as will be described so as to reduce or eliminate skewing caused by thermal creep.
Essentially, the present disclosure is directed to a method of correcting for positional skewing of perforations, such as illustrated in
It will be appreciated that the corrections that are to be introduced by offsetting the perforation-forming structures 1030, in a manner to be described, are effective so long as the set of flame-perforating process conditions that caused the skewing in the first place are the same or are a similar set of conditions that will be used in subsequent flame-perforating process with the improved film supporting apparatus 1000. In other words, the improved film supporting apparatus 1000 may not obtain the desired perforation offsetting in subsequent flame-perforating steps even if operating in the flame-perforating apparatus, should the operating conditions which caused the skewing in the first instance be changed significantly.
The method of this disclosure comprises determining the degree of angular deviation (i.e., angle C), see
To correct for the skewing in film 900 according to the present disclosure, the operator then forms a corresponding one or more perforation-forming structures 1030 in the backing roll 1000 (
The perforation-forming structures 1030 may be etched wells 1030. Such a backing roll 1000 with such etched wells 1030 may be available from Custom Etch Rolls, Inc. of New Castle PA. In an exemplary embodiment, the backing roll 1000 may be plated with a 0.5 mm of copper of 220 Vickers hardness. The illustrated pattern of etched wells, in this embodiment, is a biased pattern that was etched to a depth of 0.23 mm using techniques known in the art. It will be understood, that the present invention contemplates using film supporting apparatus other than backing rolls. For example, the film supporting apparatus may be other equivalent film supporting and conveying devices, such as conveying belts (not shown) or the like.
After etching, the backing roll surface 1020 may be washed with a suitable acid, polished, plated with about 10 microns of chrome, and then re-polished to a mirror finish (4-8 RMS). Such a backing roll 1000 is mounted in the flame-perforating apparatus of the noted U.S. Pat. No. 7,037,100.
In one example (i.e., sample #1), balanced simultaneously biaxially oriented polypropylene (SBOPP) film was then perforated on a bias pattern backing roll by the method described above. This perforation condition is denoted as Standard in Table 1, below.
In another example, another sample (i.e., sample #2) was run, the BOPP film was perforated on a so-called “dry roll”, that is without the presence of a condensed water film on the backing roll 1000 and using a backing roll held at a temperature of 10° C. (50° F.) described in the last noted patent. The dry roll condition was achieved by blowing all of the condensed water off of the backing roll 1000 with intense jets of air through the applicator 50 directed against the backing roll with the condensation air flow control at maximum. Samples were collected at least 10 minutes after process conditions appeared to stabilize.
The total condensation control air-flow using a condensed layer of water method was 450 l/min (16 cfm) while the total condensation-control air flow at the maximum flow was 1290 l/min (45.5 cfm).
Various perforated films were tested for TD and MD tear by a method similar to the “Pinch Tear” test described in Col. 15 of commonly assigned U.S. Pat. No. 7,138,169 which patent is incorporated herein by reference. In preparing Table 1 infra, approximately seventy-five 8 cm×30 cm portions of perforated film samples were cut so that the 30-cm dimensions was oriented in either the TD or MD. For testing for TD tear or MD tear, respectively. Several small 1-cm—long slits were then made with a razor blade (not shown) along the 8-cm edge of the samples to be tested. These slits provided a site for tear initiation. The samples were then torn in accordance with the Pinch tear test noted above. Samples were judged to “fail” the tear test if the number of adjacent rows of perforations across which the tear propagates is equal to or greater than two.
The results of the tear test are reported as “percent failure.” The “hole angle” is the measurement of angle (A) on the perforated film. The “desired angle” is the angle (B) in
As evident from the data, the samples of the BOPP perforated film using a bias-patterned backing tool as noted above has a hole angle or major axis at the desired 45 degrees, thereby generating tear that is straight in both the MD and TD with a minimal number of tear failures. The data also illustrates that a significant advantage arises from the patterning of the present invention in that acceptable tear characteristics can be obtained with a so-called dry backing roll (i.e., with the condensation control air flow at a maximum). As sample #2 indicates, the use of biased pattern instead of the use of controlled water condensation on the backing roll would result in a significant improvement in the robustness of a manufacturing scale perforation process. The data of sample #2 is to be compared to the data generated for sample #4, wherein the biasing of the present invention was not utilized with a dry backing roll.
The data also illustrates that a significant advantage arises from the biased patterning of the present invention in that acceptable tear characteristics can be obtained even when a known standard condensation control approach, such as described in the noted U.S. Pat. No. 7,037,100, (i.e., with a water condensation control procedure and apparatus) is utilized. As sample #1 indicates the use of a biased pattern even with a controlled water condensation process on the backing roll would result in a significant improvement compared to the sample #3 wherein a biased pattern was not used.
The present disclosure envisions correcting for any angular offset of the perforation-forming structures from a desired angle of inclination. More typical offsets may range from about 1-15 degrees. This angular offset may either be greater than or less than the desired angle, which in the exemplary embodiment is 45 degrees. Other even more typical ranges for the angular offset may be about least 6-10 degrees greater than or less than the 45 degrees. In one exemplary embodiment as described above, the angular offset of the perforation-forming structures was 6 degrees.
The films described herein are suited for many adhesive tape backing applications, such as described above in regard to
According to the present disclosure methods, systems, and apparatus are provided for making film having controlled tear characteristics of films, such as flame-perforated films. Aspects of the present disclosure implement being able to easily and reliably perforate film during a flame-perforating process, such that skewing of perforation orientations that are due to thermal creep are minimized or eliminated. Aspects of the present disclosure implement being able to provide tear characteristics wherein polymeric films, such as flame-perforated polymeric films, have comparable tear characteristics in both the lengthwise or machine direction (MD), and the crosswise or transverse direction (TD). Aspects of the present disclosure implement being able to correct for positional skewing of perforations in films, such as flame-perforated films, by thermal creep. Aspects of the present disclosure further include being able to, in a low cost manner, offset the impact of thermal creep skewing the orientations of perforations in film. Aspects of the present disclosure implement further being able to offset the impact of thermal creep skewing the orientation of perforations formed in the film in a manner that lessens the need for adhesion created by a water film, or the relatively expensive and complex water film control methods and mechanisms used during the actual process. Aspects of the present disclosure implement the ability to increase web tensions during the process so as to enable commercial processing of films requiring relatively high tension forces without being affected by thermal creep. According to the present disclosure prior needs are being satisfied such that the true potential for perforating films providing enhanced tear characteristics can be fully achieved, especially in a simple, reliable, and less costly manner.
The aspects described herein are merely a few of the several that can be achieved by using the disclosure. The foregoing descriptions thereof do not suggest that the disclosure must only be utilized in a specific manner to attain the foregoing aspects.
The above embodiments have been described as being accomplished in a particular sequence, it will be appreciated that such sequences of the operations may change and still remain within the scope of the disclosure.
This disclosure may take on various modifications and alterations without departing from the spirit and scope. Accordingly, this disclosure is not limited to the above-described embodiments, but is to be controlled by limitations set forth in the following claims and any equivalents thereof
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2021/061521 | 12/9/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63124167 | Dec 2020 | US |
