Patent Application
20080300121
The present invention relates generally to the art of bag making. More specifically, it relates to bag making machines and a bag making method that create bags from a film or web and form seals and perforations or a line of weakness separating adjoining bags made from the web.
There are many known bag machines. One style is a rotary drum machine. Rotary drum machines are well known, and a detailed description may be found in U.S. Pat. Nos. 6,117,058, 4,934,993, 5,518,559, 5,587,032 and 4,642,084 (each of which is hereby incorporated by reference).
A detailed description of the operation of rotary bag machines may be found in the patents above, but their general operation may be seen with respect to
The web is provided through dancer assembly 203 to drum 208. Drum 208 includes a plurality of seal bars 209. The seals bars are heated and create the seals forming the bags from web 201. Web 201 is held against drum 208 (and the seals bars) by a Teflon® coated blanket. The distance between seals created by the drum is related to the bag length (for bags formed end to end) or the bag width (for bags formed by making side seals). End to end bags are formed with one seal from the drum, and side to side bags are formed with a pair of seals. The drum diameter may be adjusted and/or less than all of the seal bars turned on to determine the distance between seals, and hence bag size.
Generally, rotary motion machines registers a downstream rotary knife to perforate between two seals, or beside a seal. Variations due to tension, film gauge variation, machine variations etc., occasionally causes seals to get cut off.
The prior art of
Controller 221 is connected to the various components to control speed, position, etc. Sensors may be used to sense print on the web to form the seals and/or register the perforation (place it in the correct location with respect) to the seal. Also, sensors may detect seals to try and create the perforation in the correct location. Sensing the seal has proven to be difficult. One prior art example of a system that sensed seals is described in U.S. Pat. No. 6,792,807, hereby incorporated by reference. If the perforation is placed too close to one side seal, then the seal may be cut off, rendering the bag useless.
Because sensing the seal is difficult, much waste is generated in bag making, or bags are ruined. The wasted web, (i.e. the web between a seal and the adjacent perforation), or the web used to make the ruined bag, can be very costly, particularly for high speed bag machines where the number of bags made per hour is great.
Another problem of prior art machines is that perforations may be skewed with respect to the seals, because the perforations are created downstream, and the web can wander or stretch. Also, a mechanical perforation knife must be adjusted every few days to continue to perform properly. Generally, sharp mechanical knives cannot be adjusted to change the perforation strength, and they can be costly, complex, and difficult to use.
Other type of bag machines, such as intermittent motion machines (not rotary drum machines) use burn off seals to seal and cut or perforate at the same time but speed is limited to about 300 fpm due to the reciprocating motion, dwell time, and difficulty handling the loose bags. Other intermittent motion machines, such as the CMD Icon™, have seal bars with an integral toothed blade. The CMD CM300™ machine has oscillating motion to move seal bars that have an integral toothed blade. Generally, intermittent motion machines are not as fast as rotary drum continuous machines, and thus produce far fewer bags per machine hour.
Accordingly, a method and machine for making bags that enhances the ability to locate the perforations close to the seals is desirable. Preferably this can be done without a downstream knife, to avoid problems associated therewith. Also, this is preferably done on a continuous motion machine, to avoid the slowness and difficulties associate with intermittent machines.
A bag machine, according to a first aspect of the invention, includes an input section, a rotary drum, and an output section, wherein a web travels from the input section, to the rotary drum, to the output section. The rotary drum includes at least one seal bar which has a single sealing zone that forms a single seal, and further includes a weakening zone within the first sealing zone, that forms a weakened zone within the single seal.
The weakening zone is a heated perforator, and/or includes a heating wire, and/or a thin film heater according to various embodiments.
The heating wire has, connected thereto, a source of power that is at an adjustable voltage or magnitude, and/or pulsed, and/or a feedback loop is provided in other embodiments.
The heating wire is a nickel chromium resistance wire, preferably about 80% nickel and about 20% chromium, and/or a thin film heater, and/or a resistance heater, and/or disposed to be make intermittent contact with the web, and/or has a resistance of about 4 ohms/ft, and/or disposed in an insert and/or cartridge on the seal bar in various embodiments.
The insert is comprised of Muscovite® mica, Phlogopite® mica, Glastherm® composite, or similar electro-insulating material and/or has a plurality of holes disposed along a line in the cross direction in other embodiments.
The single seal extends at most 0.125 or 0.25 inches in the machine direction in various embodiments.
The weakening zone is disposed to create a line of weakness that varies in intensity, and/or is a separating zone, and/or includes a heat film, and/or includes a toothed blade, and/or includes a row of pins, and/or includes a source of air directed at the web, and/or includes a source of vacuum in various embodiments.
The toothed blade is retractable in accordance with another embodiment.
The first sealing zone includes a plurality of independently controlled temperature zones capable of making side seals and tape seals and/or includes at least two parallel sealing subzones, extending in the cross machine direction, and the perforating zone is disposed between the at least two parallel sealing subzones in various embodiments.
The single sealing zone include a plurality of independently controlled temperature zones capable of making side seals and tape seals, and/or include cartridge heaters with a plurality of heat zones, and/or include a source of air disposed to cool at least a portion of the single sealing zone, and/or include at least one port for directing heated air to the web, and/or include at least one of a source of ultrasonic energy, microwave energy, and/or of radiative heat in various embodiments.
A sealing blanket is disposed to hold the web against the rotary drum and may be made of polyester material with a silicone layer that contacts the web in other embodiments.
The rotary drum has an adjustable diameter in another embodiment.
According to a second aspect of the invention, a bag is made by receiving a web, forming a single seal on the web using a seal bar on a rotary drum, and forming a weakened area within the single seal. The weakened area is formed during at least a portion of the time the first seal is being formed.
The weakened area is formed for less than the time the first seal is being formed, and formed for about half the time the first seal is being formed in various embodiments.
Forming a weakened area includes, forming a consistently weak line, and/or forming a perforation, and/or forming a line of weakness that varies in intensity, and/or separating adjoining bags, and/or applying a vacuum to the web, and/or directing air at the web in other embodiments.
Forming a perforation includes heating a wire, and/or resistance heater, and/or thin heat film, and/or contacting the web with a toothed blade that may or may not be retracted after the perforation is formed, and/or contacting the web with a row of pins, and/or forming an auxiliary seal adjacent the perforation in various embodiments.
The wire has power applied thereto at an adjustable voltage, and/or that is pulsed in other embodiments.
A signal indicative of heat in the wire is monitored and the power applied is controlled in response thereto in various embodiments.
The single seal extends at most 0.125 or 0.25 inches in the machine direction in various embodiments.
Forming a single seal includes bringing at least two parallel sealing subzones into thermal contact with the web, and forming the weakened area includes bringing a weakening zone disposed between the parallel sealing subzones into thermal contact with the web in another embodiment.
The single seal has a plurality of independently controlled temperature zones, and/or are cooled, and/or are formed using ultrasonic energy, microwave energy, and/or radiative heat in various embodiments.
According to a third aspect of the invention a perforator for a rotary bag machine is an insert for a rotary drum including a single sealing zone and a weakening zone within the single sealing zone. It may or may not be retrofitted to existing machines.
According to other embodiments, the sealing zone is comprised of a heating wire, an electrical insulating layer/release layer, a glastherm or mica layer, and an aluminum block, in that order, where the wire and electrical insulating layer/release layer come into contact with the film.
According to another aspect of the invention a bag machine includes an input section, a rotary drum, and an output section, disposed to receive the web from the rotary drum. The rotary drum has at least one seal bar that includes a sealing zone that forms a single seal, and a heating wire that is a weakening zone within the sealing zone, that forms a weakened zone within the single seal. There is a release layer on at least a part of the at least one sealing zone.
The release layer may be comprised of a first material in the weakening zone, and a second material on the remainder of the sealing zone, such as Kapton® and/or Teflon® tape, and the heating wire is stitched into the sealing zone and stitched into the first material in one embodiment.
The sealing zone surface may be a cap and/or have an arcuate shape that contacts the film in other embodiments.
The sealing zone and/or the weakening zone include a draw tape area where the release layer is raised in the draw tape area relative to the remainder of the sealing zone in one embodiment.
The sealing zone can be an aluminum block heater in one embodiment.
The heating wire is mounted in and between the plurality of holes in the aluminum block heater in one embodiment.
According to other embodiments, the sealing zone is comprised of a double sided tape, a heater, a heat conductive layer, a wire and a release layer, in that order, where the release layer comes into contact with the film.
Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims.
Before explaining at least one embodiment of the invention in detail it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. Like reference numerals are used to indicate like components.
While the present invention will be illustrated with reference to a particular bag machine, it should be understood at the outset that the invention can also be implemented with other machines, and using other components. Bag machine, as used herein, includes a machine used to make bags such as draw tape bags, non-draw tape bags, and other bags. Any input section (unwinds and dancers, e.g.) and any output section (winders, folders, e.g.) may be used with the present invention. Bags may be comprised of traditional poly material, other materials such as starch, polyactic acid (PLA), cellulose, polyhydroxy alkanoates (PHA), and lignin, and/or be biodegradable, compostable, etc., such as Mater-Bi®, Ecoflex®, Ecovio®, Bioplast GF106®
Generally, the present invention provides for a rotary bag machine with an input section, a drum section, and an output section. A perforation or line of weakness is formed on the rotary drum, for at least part of the time the seal is being formed. For example, on a rotary bag machine the web might be in contact with the drum for about one-half of the drum cycle, and the perforator formed in one quarter of the drum cycle. The seal bar includes a sealing zone and applies heat as the drum rotates, thus forming the seal. Seal bars, as used herein, includes an assembly, such as on a rotary drum, that applies heat to and seals the web, and the mounting mechanisms, perforators, etc. Sealing zone, as used herein, includes the portion of a seal bar that creates the seal.
The seal bars can have independently controlled temperature zones, for example for applying more heat to a hem or draw tape portion of a side seal. Independently controlled temperature zones, as used herein, includes temperature zones along a sealing zone that can be controlled or caused to be different temperatures.
A perforator or weakening zone can be mounted on the seal bar, for example as part of an insert. The weakening zone can create a perforation or weakened area as the seal is being formed. The perforation can be created with heat, radiation, or by mechanical contact. Weakening zone, as used herein, includes the portion of a seal bar that creates a weakened area. Weakened area, as used herein, includes an area on the web which is weakened, such as by a perforation or a portion of the web being melted or burned off.
The insert can alternatively include a separating zone for separating adjoining bags. This typically requires more heat than weakening or perforating. Separating zone, as used herein, includes the portion of a seal bar that separates adjoining bags. The insert can be retrofitted, and/or sold as a replacement part. One embodiment includes a laminate that is adhered to an insert or seal bar. The laminate is replaced as it wears.
If the bag is a side seal bag, made with a pair of seals, the perforator is preferably disposed adjacent and between the pair of sealing zones. Adjacent, as used herein, includes being mounted with or close to. Between the sealing zones, as used herein, means the region, on a single seal bar assembly, between two heated seal tips.
Thus, the perforation is located consistently and correctly next to the seal. Less film is wasted because the distance between the pair of side seals is less. While typical prior bag machines have one inch between side seals, the preferred embodiment provides about 0.5 inches, more preferably 0.3 inches, and most preferably as little as about 0.01 inches between side seals. About, as used herein, includes a magnitude being close enough to a given value to function substantially the same as if the magnitude were the given value.
The perforator replaces a downstream perforator that needed to be readjusted every few days with an insert that does not need readjusting, although it might need to be replaced (such as monthly). Insert, as used herein with reference to a seal bar, includes an assembly mounted on or with the seal bar that is in addition to the sealing zone that creates the seal or seals.
A wide variety of perforators can be used, such as a heating wire, heat film, toothed blades, etc. Heat film, as used herein, includes a film used to apply heat to a specific area. The perforation strength may be adjusted by controlling the amount of heat (or pressure) applied at the perforator. The perforation may be clearly defined, a line of weakness, or a line of weakness that varies in intensity. Line of weakness that varies in intensity, as used herein, includes varying web strength along a line or curve, such as a perforation or such as a line where the web is not removed, but alternates between low and higher strength regions.
Using a heated perforator can advantageously create an auxiliary sealed area at the edge of the perforation or line of weakness. Heated perforator, as used herein, includes a device that uses thermal energy to perforate, through contact, convection, conduction or radiative heat. Heating wire, as used herein, is a wire used to heat, such as by passing electrical current therethrough. Auxiliary sealed area, as used herein, includes a sealed area formed by forming a perforation using heat. The edges of the perforation may include a strip where the web is sealed. This is in addition to the web being sealed by a distinct sealing zone. Radiative heat, as used herein, includes heat in the form of electromagnetic radiation, ultrasonic radiation, thermal radiation, etc.
Another embodiment provides for creating a single seal, such as an auxiliary sealed area, with the perforation created as part of the single sealed area. The single sealed area can be created using two seals that melt to form a single seal, or a weakening zone that provides sufficient heat to seal the web or film surrounding the weakened zone. In either case, the single seal is comprised of two parallel sealing subzones, with a perforation or weakened area within the single seal. Other sealing techniques may be used. The single seal embodiment can be combined with other embodiments described above or below, such as hem or draw tape seals, varying intensity seals and perforations, etc.
Sealing subzones, as used herein portions of a seal formed by heat from different sources. Within the sealing zone, as used herein, includes, within the boundaries of a single sealing zone. Within a single seal, as used herein, includes, within the boundaries of a single seal. Single seal, as used herein, includes, an area of film that is melted to form a seal without unsealed portions that extend a substantial distance in the cross machine direction. A single seal may have small gaps in the seal, either intentionally or inadvertently.
The heated perforator may include a wire in intermittent contact with the web, to create the perforation pattern. Intermittent contact between the web and a sealing or perforating element, as used herein, includes the web being in contact with the element at some locations and not in contact at other locations, such as contact and no contact alternations along a cross-machine direction line.
One embodiment provides for retrofitting existing machines by placing an insert on existing seal bars, or by replacing seal bars with seal bars designed to have a weakening zone, such as with an insert.
The blanket may be blankets such as those found in the prior art, although the preferred embodiment includes a blanket that is a belt consisting of 2-ply polyester material with 1/32″ ground silicone top cover Silam K® (55 durometer) with an endless length. Other blankets, preferably able to handle the high intermittent temperatures (600-800 F) that can be reached while burning a perforation and that have good release characteristics so the film does not stick to the belting, are contemplated in various embodiments, and may be Teflon®, silicon, hybrids, etc. Another embodiment uses a fine fabric mesh impression in the silicon surface of the blanket. This results in an impression made in the film that can aid in sealing or perforating and also improve the release characteristics.
Turning now to
Drum 200 is preferably one similar to the CMD 1270GDS Global Drawtape System® and has approximately 0.5 seconds of seal dwell time at 600 fpm and has an adjustable diameter to easily change product repeat lengths. It has 4 seal bars equally spaced around the circumference that span across a 50″ web width. This drum can be used for making trash can liners or garbage bags, for example. Other drums could consist of more or less seal bars, larger or smaller diameter, or narrower or wider web widths.
Referring now to
Seal bar 300 preferably has a uniform temperature range across a given width of a web, with an independently controlled temperature zone at the edge for making a side seal while simultaneously making a tape seal with bar 401. Cartridge heater 310 is a custom wound heat zone such as those available from Watlow® or Thermal Corp. in the preferred embodiment. The temperature profile for specific or different temperature setting combinations (desirable especially on thin films) may be controlled using compressed air cooling of hot zones, as described below. Air cooling is also used for isolating different temperature zones which are located next to each other but are set at greatly different temperatures such as 300 F (bar 304) for side seals but 450 F (bar 401) for tape seals, in various embodiments.
Referring now to
One alternative embodiment provides for seal bars that form side seals only, with no drawtape seal zone. Another embodiment, provides for a seal bar that makes a bottom seal with only one seal (the perforation preferably does not have an auxiliary seal in this embodiment).
Cartridge heater 310 is replaced with a flexible silicone rubber heater 901 and 903, as shown in
An alternative seal bar 1000 is shown in
Another embodiment is seal bar 1200, shown in
Laser or focused light directed with a moving or pivoting mirror or lens is used on other embodiments. The laser can be positioned in the center of drum 200, and a pivoting mirror (or a linear actuator) can be used to direct the laser light through a glass seal bar at the periphery of the drum (again, the glass can be coated for easier release). The seal bar can have a continuous line of glass for forming seals, and alternating intermittent regions of opaque and clear for creating perforations.
Another alternative seal bar 1300 is shown in
Insert 306 has, in the preferred embodiment, a Ni—Cr wire woven into a shape that produces intermittent contact with the web (such as areas of contact where film is burned away, and areas of no contact where film is not burned away to create perforations). The Ni—Cr wire is pulsed on for the first half of the dwell time (the time the web is against the seal bar) and allowed to cool the second half of the dwell time so the perforations are non-molten when the web separates from the perforator. This allows a stronger web, reduces film sticking to the wire, and eliminates the chance of the perforation melting shut.
Referring now to
One alternative designs is shown in
Another embodiment of the invention includes an insert 2600, shown in
The side view of insert 2600, shown in
The NiCr wire may be turned on and off (current flow) to control temperature of the wire/sealing. For example, the wire may be turned on immediately after contacting the film (or blanket), and turned off immediately after the contact with the film (or blanket) ends. Alternatives include connections other than serial between wires 2701 and 2703, more heat zones (and wire connections/types), controlling heat with external resistors/potentiometers or current magnitude, such as with PWM. If a pot is used the user could adjust the relative temperature by adjusting the pot. Other embodiments includes combining these features, or other on/off schemes. This and other embodiments may be used with any other bag where a perforation needs to be placed next to a seal, such as t-shirt bags, including reinforced t-shirt bags, draw tape bags, side seal bags, etc. The wire may be off for part of the time the seal is being made and on for at least a portion of the time the first seal is being formed. One embodiment calls for preheating the wire when it is not in contact with the film so it is turned off while in contact with the film, relying on the wires retained heat to burn the perforations.
The blanket preferably has a 0.03-0.012 in. thick silicone rubber top surface with a matte finish, durometer 50-90 Shore A, initially seasoned with a talc powder. The wire may be held in the holes using a Resbond® high temperature adhesive, injected into the holes using a syringe. Hard or flexible adhesives, or both, alternating, e.g.) may be used. Flexible adhesives allow the wire to flex, which can occur when it is heated and cooled. The insert may be held in place with five cone point set screws 2605 or with flat tip set screws.
Another alternative is shown in
Other alternatives are shown in
Other alternatives provide for wire 1502 to be round, a rectangular ribbon, straight or woven at a uniform or varying pitch, uniform thickness or non-uniform thickness along their length (to create hot/cold spots), Toss® wire, tapered, or profiled to make two side seals between a burn off cut. Profiled wire may have intermittent copper plating to perforate rather than clean cut. Varying pitch for a woven wire or different hole spacing creates a weakened area of varying weakness, that allows the bag to be torn by hand easier at the edge than in the middle of the web. Other designs contemplated include flexible silicone rubber heaters, thick film heating technology, sintered ceramic, or the like available from Watlow Electric Manufacturing Co. Yet other alternatives include using thin film heating technology mounted on a PNEUSEAL™ rubber inflatable diaphragm that can stay hot all the time but physically move in and out of contact with the film by inflating and deflating the diaphragm.
Other alternatives includes a wire that is constantly hot but is physically moved in and out of contact with the web during the seal dwell phase. Hot wire segments (stitches) could be connected to a power source in parallel or in series. Parallel is preferred to reduce the amount of current required. Hot wires are preferably potted into a replaceable insert that can be easily replaced in the field and mass produced. Hot wires could be coated with substance to improve release characteristics.
Alternative perforators include a toothed blade 2301 (see
Another alternative is to use hot compressed air jets 2402 (
The preferred embodiment controls the heat of a burn-perf wire by controlling the voltage of a DC circuit. Preferably the lowest voltage that provides an acceptable perforation is used. For example, a 0.013″ diameter 80/20 Ni—Cr wire woven alternating between 0.25 inch in contact with the web and 0.12 inches below the mica requires approximately 20 watts per inch of web width to burn perforations in 0.75 mil LLDPE film two layers thick at 600 feet per minute. Thus, a 2 inch long perforator would use 10 volts pulsed on for about 0.25 seconds as soon as the film is sandwiched between the perforator and the seal blanket. With a 0.5 second dwell time, the perforation has about 0.25 seconds to cool. The preferred embodiment thus allows the perforation to be quickly heated and cool down. The adjustable voltage is supplied by a DC motor controller in one embodiment. Other embodiments includes a mechanical rheostat, potentiometer, or adjustable resistor. An adjustable AC voltage can preferably be used.
A controller may be used to compensate for resistance changes over the life of the wire. For example, a Toss® controller has current sensing feedback and adjusts voltage accordingly to maintain a more consistent temperature. Cartridge heaters may be controlled with thermocouple feedback using PID temperature control, as is well known in the industry.
The preferred embodiment provides for consistent incoming tension and consistent incoming accumulation to consistently form seals and perforations. The preferred embodiment includes a servo infeed nip with ultrasonic accumulation loop feedback. Alternatives includes a mechanical lay-on roll assembly. Static induction pinning is used to help the film lay flat against the sealing blanket.
A tension zone isolator nip, also called a chill roll nip, is used as the web exits the sealing drum area. The preferred embodiment uses a 2″ wide double groove diamond shape is cut into the face of the roll to allow minor air bubbles or wrinkles to flush out rather than build up ahead of the nip.
After leaving the drum the web is provided to folding boards. Hard-board filler plates with ¼″ diameter holes 3″ from the tip of standard V-board with symmetrical geometry near the tip of the V-board are provided to reduce tension surges due to wrinkles or air entrapment. Also, transporting the folded web over two idlers before going through a rubber nip and an additional ¼″ thick air relief blade is inserted between film layers just prior to the rubber nip to allow air to bleed out rather than getting trapped inside wrinkles.
Air cooling of hot zones, briefly referred to above, generally includes ports or channels in seal bar, for example created by drilling or machining, to allow compressed air to flow through a desired zone or zones.
Another embodiment provides for using a single seal bar, with a perforation within the seal. Referring now to
The single seal/perforation may be created using a contoured seal bar, a previous embodiment with the temperature controlled to burn through in places, fine fabric impression (bumpy or textured) blanket, such as a Habasit® WVT-136 silcone rubber blanket, where the pressure of the “bumps” burns through the plastic.
The single seal may also be created using two seal bars such as those described above, but disposed close to one another, or made wider, such that the two seals blend together to form a single seal (i.e., no unsealed web between them) comprised of two sub-seals. The sub seals are generally parallel and extend across the web or film in the cross machine direction, and a weakened area is formed between the generally parallel sub-seals. The perforation may be made using any of the alternatives described above. Another embodiment provides for using one of the embodiments above, but is used by turning the side seal temperature very low so that the seals are not formed. The perforator then forms the perforation and the seals are the auxiliary seals from the perforation.
Referring to
Seal bar 2900 forms a single seal on a web or film 2912. A cartridge heater 2901 disposed within an aluminum block 2903 provides steady heat to seal bar 2900. Wire or resistance heater 2911 provides additional heat that creates the seal and weakened area. Wire 2911 is preferably a NiCr wire 0.009-0.013 inches in diameter. The different sources of heat combine so that both add heat to the seal zone and the weakening zone, although in this embodiment wire 2911 primarily provides heat for the weakening area, and heater 2901 primarily can be thought of preheating the assembly.
Alternatives provide for a flat or other shaped resistance wire. The flat wire can have a raised ridge or be curved to form the weakening zone, with cutouts where the solid portions between perforation holes are located. Air under the bend can act as an insulator to affect the heat profile of the ribbon.
A shim 2905 can be used, particularly for retrofits, to force wire 2911 into tighter contact with web 2912. Other embodiments call for greater shimming in the hem or draw tape area (of about 0.020 inches in one embodiment), so the web in that area is under greater pressure than the remaining portion of the film, thus providing greater heat transfer for this region, or no shim at all. Another embodiment provides for a backing wheel behind the blanket in a hem or draw tape region that forces the blanket against the web and provides greater pressure in that region.
An insert 2907 is preferably comprised of, or coated with, an electrical or thermal insulating material to insulate wire 2911. In various embodiments insert 2907, or the electrical insulating material, is comprised of mica, glastherm, fiberglass phenolic, plastics, polymers, aluminum (with an electrically insulating coating) or other materials. Glastherm™, as used herein, includes, a composite material of glass fibers and heat resistant thermosetting resins
A releasing layer 2909 is disposed over insert 2907, and is preferably comprised of Teflon®, Rulon®, or Kapton® tape. The releasing layer or releaser is chosen to be of a material that releases melted film, but able to withstand the temperatures needed to seal and perforate the film. Releasing layer on a seal bar or insert, as used herein, includes, a layer that, compared to other materials of the seal bar or insert, reduces the buildup of melted film on the seal bar or insert. This embodiment provides that the film touches only the wire and tape (over the insert), although other embodiments provide that the film touches the insert directly, and/or touches the aluminum block heater. Alternatives provide for coating the wire with a releaser instead of or in combination with the releasing layer. The release maybe an application of a liquid layer that later dries such as Resbond®, Rescor®, Teflon® paint, silicone paint, or the like.
The single seal can extend across the entire film width, or across part of the film with two seals used in one region, such as a hem or draw tape region. The two seals may be formed as described above. Another embodiment provides for two sub seals to be used only in the draw tape area, and a single seal without sub seals formed elsewhere or vice versa.
The selection of various materials, such as the releaser, insulater, heater, wire, etc., is should be made in consideration of the film thickness, the temperatures desired for perforating (up to 600 F or more in one embodiment) and sealing the major portion of the film and any hem or draw tape region, and the ability of the sealing surface to release melted film. Improper selection could result in premature wear of the material, or premature buildup of melted film on the sealing surface. Alternatives provide for turning on the wire earlier to preheat it, so it can be turned off sooner, removing the built up film during the time the film is not in contact with the seal bar by, for example, mechanical action, heating, brush, or air blast, etc.
Other design concerns include the range of types and thicknesses of films that will be used with the machine, heat migrating between the hem and other regions, the perforation and the seal, blanket material, dwell time, removing or addressing wrinkles in the film, ink from the web building up on the sealing surface, and providing different pressure zones.
Referring to
Referring to
Referring to
Referring to
One modification of this embodiment provides for the releaser to be a tape placed over the wire, and there may or may not be holes or slits on the releaser aligned with the locations where the perforations holes are to be made, so that the wire contacts the film in these locations.
Referring not to
The row of pins or needles are in an unheated or heated seal bar and press against a Kevlar® sealing blanket material, which will be less likely to be damaged from the sharp pins penetrating into it, in another alternative. The rows of pins or needles could be placed in blanket, and be held in phase with seal bars on the drum, to create the perforation. Similarly, thin film heaters and/or pins on a belt or blanket can press against a simple drum face. No drum would be required if pressure is applied by the belts against one another, such as by an elliptical shaped belt path for both belts.
Another embodiment provides for the seal and perforation to be formed using magnetic fields or inductive heat. A magnet (permanent or electric) on the seal bar, with metal in the backing blanket causes extra pressure in the perforation area to melt holes where desired and less pressure in the sealing area. The magnetic fields can be created to be disposed in a line across the film.
Another embodiment provides for the seal and perforation to be formed together on a non-circular loop, such as an oval or oblong, or on a shuttle machine. generally, the invention of these embodiments call for the creation of a seal when and where a perforation is created.
Other methods of perforating and sealing at the same time in a rotary drum to preferably create a perforation down the middle of one narrow seal are included withing this invention. For example, three staggered rows of Ni—Cr wire stitches may be used where the outer two rows create the seals and the inner row creates the perforation. Inner refers to the inner in the machine direction.
One seal may be made with one rounded seal tip when the film is under tension such that the center of the seal thins/weakens/perforates during the sealing process. The seal bar may have a bumpy surface at the crest to create the perforations.
A seal bar may comprise a resistive coating placed over a shaped electrically non-conductive material so the heat is generated at exactly the sealing surface where it is needed and a complex shape with various sealing heights can be achieved. This could be done adapting thin film heater technology.
Another embodiment calls for increase sealing blanket pressure, such as by factor of 5, 10 or 20, preferably 10, so the burn-perforation temperatures can be lowered from 550 F-600 F to a lower temperature where a wider variety of coatings and materials are available (many materials have a 500 F maximum operating temperature).
Yet another embodiment provides for a sealing bar comprising two parallel heated strips that separate 0.03″ to 0.06″ during sealing to stretch the film into a line of weakness or perforations between the two strips.
Film could be tucked into a ⅛″ deep recess in the drum seal bar such that perforations can be cut or burned below the surface of the drum without damaging the sealing blanket. The tucking can be mechanical or vacuum assisted.
Other methods of creating the seal and perforation could be used, such as using radiant heat, microwaves, or light waves tuned to especially heat and perforate the web. Hot glue could be applied, or a liquid from inside drum such that it heat seals the two poly webs together. The perforations could be done simultaneously if hot liquid burns perforation holes at the same time. A hot solid such as sand or poly pellet, or a hot liquid, such as oil, could be forced through web such that it perforates the web while forming a seal at the same time. Or the web could be chemically treated to react with an additive such that film melts together and melts perforation holes where excess chemical is applied. Another alternative includes applying a time activated acid in the drum which allows the web (non-sealed and non-perforated) to be wound and placed inside a carton; then the time activated acid creates a burn-off seal so the web later becomes multiple sealed/separated bags.
The web could be sealed with conductive heat sealing, and before the dwell time is over the web could be cryogenically frozen in a perforation pattern such that the film fractures at each perforation spot when it is flexed downstream.
Turning now to
Another single sealing area 3612 under a release layer 3613 forms a single seal across the remainder of the web (the non-draw tape area). The single seal created may have a non-uniform intensity but has sufficient strength throughout to be a single seal with sufficient integrity. Release layers 3603 and 3613 are preferably Teflon® tape, but alternatives provide for the release material to be Rulon® tape, Kapton® tape, Mica® tape, Resbond® painting, Rescor® paint, and/or RP Polyimide resin poured and baked onto the surface (available from Unitech in VA). One embodiment omits the release layers. Release layer 3603 and 3613 extends over the side areas adjacent (and outside) the sealing zone in one embodiment, and does not in another embodiment.
Single sealing zone 3602 extends under release layers 3603, and under a release layer 3605. Release layer 3605, with a perforator/heating wire 3607 create a perforation or weakened zone in the draw tape region of the web. Release layer 3605 is preferably Kapton® tape, but could be Teflon® tape, Rulon® tape, Mica® tape, Resbond® painting, Rescor® paint, RP Polyimide resin poured and baked onto the surface (available from Unitech in VA), and/or other non-stick materials. Release layer 3605 is omitted in one embodiment. Release layers 3603 and 3605 are shown terminating at the edge of the top surface of the heater, but could be folded over the edge, or terminate short of the edge.
An electrically insulating coating is used if the seal bar is aluminum, to prevent shorting of wire 3607. If a cap (described below) is used, and the cap is conductive, the insulating coating is used with the cap. Alternatively, the cap could be made of a non-conductive material.
A heating wire 3607, preferably NiCr, is disposed withing the draw tape area. Heating wire 3607 is stitched into single sealing zone 3602, and is also stitched through release layer 3605. Alternatively, wire 3607 may be stitched into a cap 3801 (
The ratio of the perforator wire 3607 height to the seal area width (areas 3603 and 3605) should be selected to obtain good perforations and good seals at the same time for a given application, and can be different for the draw tape area relative to the rest of the seal. When making a single seal 0.65 inches wide, the height of wire 3607 can be between 0.015 and 0.020 inches taller than the sealing surface in some applications.
A similar arrangement is provided for in the non-draw tape region, with cap 3801 (or a different cap, not shown), release layers 3613 and 3615 and wire 3617. Cap 3801 may be one continuous cap, or more than one cap extending across the web. The draw tape region has heating wire 3607 and sealing zones 3603 raised so that extra pressure is applied, and thus more melting occurs, in the draw tape area. Alternatively only one of, or neither of, the perforating zone and sealing zone can be raised. A draw tape area is raised relative to the remainder of the sealing zone when the draw tape area projects closer to the sealing blanket, thus resulting in greater pressure in the draw tape area.
Heating 3607 is preferably 80% nickel and about 20% chromium, and/or a thin film heater, and/or a resistance heater, and/or disposed to be make intermittent contact with the web, and/or has a resistance of about 4 ohms/ft, and/or disposed in an insert and/or cartridge on the seal bar in various embodiments.
The surface of sealing area 3603 and/or the surface of cap 3801 is arcuate shaped to help create greater pressure throughout the draw tape seal region and thus to transfer more heat and make a satisfactory seal through the extra layers of film present in the draw tape hem. Arcuate shape, as used herein, includes a surface that curves rather than a straight surface, and thus an arcuate sealing surface has a different pressure profile than a straight sealing surface. Alternatives provide for an arcuate shape throughout the entire seal region, or other profiles, including flat.
The various alternatives may be combined as desired, to design a bag machine suited to a specific need.
Numerous modifications may be made to the present invention which still fall within the intended scope hereof. Thus, it should be apparent that there has been provided in accordance with the present invention a method and apparatus for making bags that fully satisfies the objectives and advantages set forth above. Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11937870 | Nov 2007 | US |
| Child | 12145913 | US | |
| Parent | PCT/US2007/000981 | Jan 2007 | US |
| Child | 11937870 | US | |
| Parent | 11331466 | Jan 2006 | US |
| Child | PCT/US2007/000981 | US |
