System and method for producing polymeric film

Information

  • Patent Grant
  • 6277314
  • Patent Number
    6,277,314
  • Date Filed
    Wednesday, February 4, 1998
    27 years ago
  • Date Issued
    Tuesday, August 21, 2001
    23 years ago
Abstract
Efficient, improved output systems and methods for producing polymeric film are described. Such systems include a feed assembly for positively and substantially constantly feeding polymeric raw material to a grooved feed extruder. The system also includes suitable apparatus for forming the molten polymer output from the extruder into film. The raw material may consist of 100% pelletized polymer, 100% polymer fluff, or any combination of the two. If necessary, a blending apparatus is included to blend the pellets and fluff prior to feeding the raw material to the extruder.
Description




FIELD OF THE INVENTION




The present invention is directed to systems and methods for producing polymeric film, and more particularly to such systems and methods wherein improved output and efficiencies are realized.




BACKGROUND OF THE INVENTION




A wide variety of polymeric films are produced using extrusion technology. The composition of the film is dependant upon the end use to which the film is put. Examples of polymeric materials suitable for processing in an extrusion system for the production of film are polyethylene (high density, low density and linear low density), EVA, EVOH, polyamides, etc. Such materials can be processed in an extrusion system for blown film of single layer and co-extruded films with up to seven or more layers, including barrier and tie-layers. Typically, blown films or sheet films have thicknesses in the range of 0.4 to 40 mils. These films are useful in the food packaging and other packaging industries, as well as agricultural, automotive and a wide variety of other industries.




There are two principle types of extruders for melting and extruding polymeric materials in film production systems. The first is a “smooth bore” or smooth barrel extruder which has a smooth barrel over its entire length. There are numerous North American manufacturers of smooth bore extruders, including Davis Standard, Gloucester Engineering, Cincinnati Milacron and Brampton Engineering, among others.




In the production of polymeric film using a smooth bore extruder, generally the polymeric resin raw material is fed to the extruder in the form of pellets. Because waste and scrap film are generated during production of the polymeric film, which material can be recycled within the production facility, it is not uncommon to blend some proportion of the recycled material with the pellets. The scrap film is chopped using techniques and equipment well known in the art and is often referred to as “fluff” or “flake”. This fluff can be fed into a smooth bore extruder along with the “virgin” resin pellets at ratios up to 50/50. If the equipment is specially designed, as much as 100% fluff can be fed into a smooth bore extruder. This is typically accomplished by a speed-controlled (ratio controlled) auger located in a hopper above the screw of the extruder. With this technique, there is no pre-mixing of the fluff with the virgin pellets and there is no control of the “head pressure” on the extruder throat. Another method for feeding fluff into a smooth bore extruder is to mix the fluff and pellets together and then introduce the blend into the throat of the extruder. This blend is force fed into the extruder using a specific type of feeder equipment commonly referred to as a “crammer” feeder. The force exerted by the crammer feeder pushes the blend into the extruder and is principally controlled by a torque setting. The speed of the crammer feeder auger is then adjusted to maintain the torque setting and thus the “head pressure” on the extruder screw. Because a smooth bore extruder's feed/pump rate output is significantly affected by the head pressure at the inlet, the second method for feeding fluff may be considered superior to the first because of the relative constancy of the head pressure.




The second common type of extruder is called a grooved feed extruder. Although used worldwide, these are commonly built in Germany and are available from companies such as Hosokawa Alpine Aktiengesellschaft of Augsburg, Germany. Such extruders were initially developed for processing high molecular weight, high density, polyethylene (HMWHDPE). Subsequently it was found that the pumping and melting characteristics of such extruders had certain advantages in the processing of other polymers also, particularly in blown film production applications. A grooved feed extruder has longitudinal grooves formed in the barrel beginning just downstream from the barrel inlet. These grooves do not extend the length of the barrel. As is well known in the art, the grooves are highly efficient at transferring energy from the extruder motor to the polymer and cause the polymer to rapidly melt very close to the extruder inlet.




Conventional wisdom has suggested that making extruded film in a grooved feed extruder utilizing fluff in the raw material, in any percentage, is not possible or not likely to be successful. It has been known to run in the range of 5-10% fluff into a grooved feed extruder via a typical gravity feed-type hopper. However, because of the perceived problems and problems actually experienced in feeding fluff to grooved feed extruders, manufacturing facilities that use grooved feed extruders typically send their scrap film (fluff) through an additional process step of re-pelletization and simply recycle and reuse the scrap in pellet form. It was and is believed that the reasons fluff cannot successfully be processed through a grooved feed extruder are: (1) that the fluff melts in the grooves and either plugs them or carbonizes or forms gels, which then may break loose and appear in the extruded film, thus rendering it non-usable; and (2) that fluff cannot readily and efficiently be fed to the grooved bore extruder and thus extruder output and capacity are diminished, thereby resulting in increased film cost.




What is needed is an efficient, enhanced output system and method for production of polymeric film in which productivity from the extruder is increased and a system and method are capable of utilizing anywhere from 0%-100% fluff in the feed material for the extruder.




SUMMARY OF THE INVENTION




In its broadest aspects, the present invention is directed to a system and method for producing polymeric film. The system includes as its primary components a grooved feed extruder force fed with polymeric raw material by means of a crammer feeder. The raw material, which can be any one or more of a wide variety of polymeric materials suitable for extrusion and subsequent processing into film, may contain in the range of 0 to 100% fluff in combination with 0 to 100% virgin pelletized polymeric material. Upstream of the crammer feeder, which itself is well known in the art, is an appropriate blending system for blending the fluff and pelletized feed material and feeding it to the crammer feeder, or for feeding pure fluff or pure pellets to the crammer feeder. The blending system is capable of processing raw material at ratios of 100% pellets and 0% fluff up to 100% fluff and 0% pellets, and any combination thereof in between. Downstream of the extruder is suitable processing equipment for forming sheet film, blown film, or any other desired form of polymeric film. The specific processing equipment downstream of the extruder for forming the final film product is not a critical part of the system of the present invention, and because many varieties of such processing equipment are known in the art, it will not be described in detail herein.




The system of the present invention has been operated and compared to a film forming system which utilizes a standard gravity feed hopper for feeding raw material to a grooved feed extruder. By way of comparison, the system of the present invention has resulted in increased output (as measured in pounds extruded per hour per revolution of extruder screw) on the order of 25% to 35% when a crammer feeder is used in combination with the grooved feed extruder, versus a system using the same extruder and a gravity feed-type hopper. This significant increase in output is at a level of 0% fluff in the raw material. When 100% fluff is used the extruder output improvement declines somewhat such that at 100% fluff the extruder output is approximately equivalent to a system using 100% pelletized feed material fed via a gravity feeder. Although this output is equivalent, the system of the present invention is still highly advantageous vis-a-vis the gravity feed system because it is operating with 100% fluff, rather than pelletized feed material, and thus the cost associated with re-pelletization is removed. Furthermore, when others were feeding up to 5-15% fluff into a grooved feed extruder without the use of a crammer feeder, output actually decreased by a percentage commensurate with the fluff percentage (i.e., 15% fluff resulted in approximately 15% decrease in output). The problems heretofore experienced and/or believed to exist with regard to utilizing fluff in a grooved feed extruder have not materialized. The film quality output from the system of the present invention is on par with that found in smooth bore extruders and grooved feed extruders that do not utilize any fluff in the feed material.




As the term is used herein, a crammer feeder is an apparatus for feeding the raw materials to the extruder and which consists of a hopper (typically conical) having a feed auger. The auger is driven by a torque-controlled motor but may also be a hydraulic-controlled motor. The essence of the crammer-type feeder is the application of constant torque on the auger which therefore may fluctuate in its rotational speed depending on the density of the feed material (i.e., speed will vary depending on the fluff/pellet ratio) and on the back pressure from the extruder (which also varies depending on the composition of the feed material). It will be appreciated that any suitable feeder assembly can be used in the context of the present invention so long as the raw material is fed substantially constantly and positively to the extruder.




While not forming an integral part of the system and method of the present invention, downstream of the extruder output is appropriate processing equipment to form the polymeric film. Such systems include lines for producing blown film in which the output from the extruder is in tubular form which is then expanded and ultimately slit and wound into rolls. The system and method of the present invention are equally applicable to single-layer and co-extruded films having up to seven layers or more. Materials which are suitable for processing include high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene, EVA, etc. Furthermore, for barrier films materials such as low density polyethylene, linear low density polyethylene, polyamides, EVOH, and various tie layers are also contemplated. Furthermore, metalecene polymers are contemplated. The output from the film production system can be used for plastic films in a wide variety of applications, including general packaging, food packaging, carrier bags, shrink and stretch wrap films, etc.




In operation, the method of the present invention contemplates feeding raw material comprising in the range of 0 to 100% fluff and 100 to 0% pelletized polymeric material, blended if desired or necessary, to a crammer feeder. The raw material is metered and fed to a grooved feed extruder via the crammer feeder and is processed in the extruder and extruded therefrom. Subsequently the polymeric material is formed into a film.




These and other features and advantages of the present invention will be appreciated and more fully understood with reference to the following detailed description taken in conjunction with the accompanying drawings.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a perspective view, partially broken away, of a portion of one embodiment of the present invention;





FIG. 2

is a partial cross-sectional view taken on lines


2





2


of

FIG. 1

;





FIG. 3

is a cross-sectional view of the extruder shown in

FIG. 1

taken on lines


3





3


of

FIG. 1

; and





FIG. 4

is a schematic representation of a blending system for the raw material used in the system of the present invention.











DETAILED DESCRIPTION OF THE INVENTION





FIG. 1

shows several of the components of the apparatus of the present invention. More particularly,

FIG. 1

shows an extruder


10


having an input end


12


and an output end


14


. Extruder


10


is a readily available grooved feed extruder such as is available from Hosokawa Alpine Aktiengesellschaft of Augsburg, Germany. In particular, an Alpine HS65 or HS90 grooved feed extruder can be utilized in the practice of the present invention. Mounted on inlet end


12


of extruder


10


is a crammer feeder assembly


16


such as Model CF-2V crammer feeder assembly available from Foremost Machine Builders of Fairfield, N.J. Extruder


10


further includes a drive motor


18


, having a cooling fan


20


mounted thereon and a gear box


22


. Although not explicitly shown, the output from extruder


10


via output end


14


then is processed in a film production apparatus such as blown film equipment also available from Hosokawa Alpine AG. The details of the film forming equipment are not necessary to critical to an understanding of the present invention and therefore are not described in greater detail herein. Suffice it to say that any available film forming equipment that can be operably connected to the output end of an extruder for forming any variety of polymeric film will be acceptable. As shown, and as is typically found in grooved feed extruders, extruder


10


includes an outer housing


24


and an internal bore


26


in which resides the extruder screw


28


which has helical flights


30


thereon.




Mounted to the inlet end


12


of extruder


10


is an assembly that substantially constantly and positively feeds the raw material to the extruder


10


. One such assembly is crammer feeder assembly


16


. Assembly


16


includes a torque or hydraulic-controlled motor


32


and a gear box


34


for driving auger


36


. Crammer feeder assembly


16


is fed with raw material via inlet pipe


38


in the direction of the arrow. The torque or hydraulic-controlled motor for crammer feeder assembly auger


36


is set to provide a constant energy usage and thus the actual speed of the motor fluctuates up and down so as to provide a constant force on the extruder. This is to be differentiated from variable speed motors which simply can be set at a specific speed requirement and then the force on the extruder fluctuates as the motor torque changes to maintain the same auger speed.




The details of the inner face of crammer feeder assembly


16


and extruder


10


can be seen more specifically with reference to

FIG. 2

, which is a partial cross-sectional view taken on lines


2





2


of FIG.


1


. As will be appreciated, the raw material fed to crammer feeder


16


is directed downwardly in the direction of the arrows within the conical housing


40


of crammer feeder


16


. The torque-controlled auger drives and forcibly feeds the raw material into the throat section of the extruder adjacent at the input end


12


thereof. The raw material then travels along the barrel of extruder


10


by virtue of the action of extruder screw


28


. Extruder barrel


26


is shown in cross-section in FIG.


3


and depicts the core of the extruder screw


28


as well as the helical flights


30


thereon. For a length of approximately 2-3 screw diameters at the input end of extruder


10


are longitudinal grooves


42


formed therein. The extruder is housed within an outer housing


44


at the input end. As is common in the use of grooved feed extruders (and all types of extruders) the back pressure within the extruder is monitored. The drive control is adjusted to maintain constant or nearly constant screw speed and therefore constant output. This is particularly important in the context of extrusion in film production lines where variances in extruder output will result in different thicknesses of material which can therefore deleteriously result in variations in thickness of the output of film, which is generally unacceptable. Furthermore the torque-controlled motor for the crammer feeder assembly


16


is operated to provide a constant torque to the crammer feeder auger


36


. The importance of a constant or relatively constant torque results in a uniform amount of material being supplied to the extruder which again translates into a more uniform output in the film production equipment downstream of the extruder


10


.




With reference to

FIG. 4

there is shown a blending system


46


which blends and supplies the raw materials via downcomer


38


to crammer feeder assembly


16


. Blending system


46


can be any suitable system for blending raw material in the form of pelletized polymer and/or fluff. One suitable blending system is the Foremost fluff blending system Model No. CLWB-3 available from Foremost Machine Builders, Fairfield, N.J. Additionally, suitable fluff blending systems are available from Process Control Corporation. Blending system


46


itself comprises at least two hoppers


48


and


50


for the pelletized and fluff raw material, respectively. Each hopper


48


,


50


may include a load cell


52


,


54


for monitoring the weight and controlling the feed rate of raw material in the system. Additionally, each hopper


48


,


50


has an auger


56


,


58


associated therewith that can be set to control the feed rate of raw material. This may be accomplished using a constant speed auger or a uniform weight output auger. The augers


56


,


58


are driven by control motors


60


,


62


, respectively, to feed the raw material to catch hopper or mixer


64


, which itself may include an agitator (not shown). It is contemplated that the blending system can be utilized to blend a variety of pellet and fluff compositions. In certain contexts it may not be necessary to utilize a blending apparatus.




In use, the system of the present invention is readily adaptable to process 100% pelletized polymeric raw material containing 0% fluff and likewise is fully capable of processing 100% fluff raw material with 0% pelletized polymer. Also, any ratio of pellets/fluff in between 100%/0% and 0%/100% is processable in the system of the present invention for producing suitable polymeric film. As stated previously, a wide variety of raw materials can be processed through the system of the present invention to produce polymeric films of any suitable composition. Examples of suitable polymeric materials include high and low density polyethylene, linear low density polyethylene, polypropylene, EVA, polyamides and EVOH, etc. Once the desired blend ratio of fluff to pellets is selected, the system is operated and raw material blending system


46


blends the proper mix of raw material and supplies that via downcomer


38


to crammer feeder assembly


16


. Assembly


16


, in turn, forcibly and under constant torque on auger


36


, feeds the blended raw material to the inlet end of extruder


12


. The action of the grooved feed extruder


10


serves to melt and mix the polymer or polymer blend as it is conveyed along the length of extruder


10


to the output end


14


whereupon it is taken up and processed further through suitable film forming equipment. The result is polymeric film of desired composition which is of exceptional quality and consistency. Because of its capacity for processing fluff in any quantity ranging from 0% to 100% of the raw material, the system of the present invention is highly advantageous vis-a-vis prior film processing apparatus and systems.




While the invention has been described with reference to specific embodiments thereof, including crammer feeders, the invention is not intended to be so limited and various modifications and changes will become apparent to and appreciated by persons skilled in the art. The invention is therefore defined by and its scope is commensurate with that defined in the appended claims.



Claims
  • 1. A method of producing polymeric film, comprising:positively feeding polymeric raw material to the input end of a grooved feed extruder by means of a crammer feeder operated at substantially constant torque; melting the polymeric raw material in the grooved feed extruder and extruding molten polymeric material from an output end thereof; forming a polymeric film from the molten polymeric material extruded from the output end of the grooved feed extruder.
  • 2. The method of claim 1 further comprising blending the polymeric raw material prior to feeding it to the extruder.
  • 3. The method of claim 1 wherein the polymeric raw material comprises in the range of 0% to less than 100% pelletized polymer and greater than 0% fluff, and combinations thereof.
US Referenced Citations (93)
Number Name Date Kind
2366673 Paley Jan 1945
2382655 Nichols Aug 1945
2540146 Stober Feb 1951
2912041 Boggs Nov 1959
3175807 Gouveia Mar 1965
3183553 Slater May 1965
3256562 Heard, Jr. Jun 1966
3278986 Welt Oct 1966
3310617 Dygert et al. Mar 1967
3342901 Kosinsky et al. Sep 1967
3344218 Chopra et al. Sep 1967
3345690 Hagen Oct 1967
3360821 Marcus et al. Jan 1968
3418694 Strauss Dec 1968
3459840 Wood Aug 1969
3520027 Amos et al. Jul 1970
3535408 Ronden Oct 1970
3538203 Overcashier et al. Nov 1970
3645659 Schott, Jr. Feb 1972
3672803 Rees Jun 1972
3746489 Rizzi et al. Jul 1973
3773586 Koch et al. Nov 1973
3797702 Robertson Mar 1974
3862594 Stölting et al. Jan 1975
3920229 Piggott Nov 1975
3976730 Cushing Aug 1976
4003498 Moneghan Jan 1977
4014462 Robertson Mar 1977
4063860 Cushing Dec 1977
4108334 Moller Aug 1978
4125069 Smith et al. Nov 1978
4134714 Driskill Jan 1979
4139309 Billingsley Feb 1979
4148100 Moller Apr 1979
4201485 Walker May 1980
4222728 Bacher et al. Sep 1980
4228005 Covington, Jr. et al. Oct 1980
4243629 Tramezzani Jan 1981
4244903 Schnause Jan 1981
4249877 Machen Feb 1981
4287147 Hungerford Sep 1981
4303344 Müller Dec 1981
4319871 McAlister Mar 1982
4333789 McAlister Jun 1982
4353851 Godfrey et al. Oct 1982
4353967 Hungerford Oct 1982
4361373 Gallusser et al. Nov 1982
4385016 Gwinn May 1983
4385883 Hanslik May 1983
4413969 McDonald Nov 1983
4426018 Ward Jan 1984
4440702 Susnjara Apr 1984
4446094 Rossiter May 1984
4448737 Johnson May 1984
4467969 Godfrey et al. Aug 1984
4493806 Hatzkelis et al. Jan 1985
4500481 Marx, III Feb 1985
4564349 Brown Jan 1986
4619799 Teerling Oct 1986
4659301 Yoshida Apr 1987
4714573 Yoshida Dec 1987
4738808 Hammer et al. Apr 1988
4797237 Hammer et al. Jan 1989
4812048 Newmann et al. Mar 1989
4824627 Hammer et al. Apr 1989
4832889 Johnson May 1989
4863652 Chang Sep 1989
4877568 Austin Oct 1989
4894001 Petschner Jan 1990
4925512 Briand May 1990
4937034 Sewell Jun 1990
4958770 Mitchell Sep 1990
4976904 Bilhorn Dec 1990
5259749 Meixner et al. Nov 1993
5261743 Moller Nov 1993
5290498 Shiraki et al. Mar 1994
5304618 Atwell et al. Apr 1994
5332309 Ramazzotti et al. Jul 1994
5358327 Derezinski et al. Oct 1994
5366365 Sullivan et al. Nov 1994
5369202 Atwell et al. Nov 1994
5424013 Lieberman Jun 1995
5433593 Berger Jul 1995
5465503 Oates Nov 1995
5468436 Kirtland Nov 1995
5474722 Woodhams Dec 1995
5503790 Clements Apr 1996
5534204 Aoki et al. Jul 1996
5556581 Aoki et al. Sep 1996
5569713 Lieberman Oct 1996
5589203 Sato Dec 1996
5599099 Bullivant Feb 1997
5607700 Kando et al. Mar 1997
Foreign Referenced Citations (3)
Number Date Country
230821 Nov 1985 DE
0298256 Jan 1989 EP
06099460 Apr 1994 JP
Non-Patent Literature Citations (3)
Entry
Processing Technologies, Inc., Trident Series Extrusion Systems Brochure.
Foremost, Product Review: Crammer Feeders Brochure.
HydReclaim product information—Fluff Feeding (Aug. 13, 1997), http://hydreclaim.com/index9.html.