WO1994007671A1

WO1994007671A1 - Apparatus and process for washing and shredding film

Info

Publication number: WO1994007671A1
Application number: PCT/US1993/002881
Authority: WO
Inventors: Stanley R. Prew
Original assignee: Andritz Sprout Bauer Inc
Current assignee: Andritz Sprout Bauer Inc
Priority date: 1992-09-29
Filing date: 1993-03-26
Publication date: 1994-04-14
Anticipated expiration: 1995-03-29
Also published as: TW221392B

Abstract

An apparatus and process for washing and shredding scrap film. The apparatus includes a washer-shredder (32) unit upstream from the film cutter (14) in order to remove impurities from the film prior to cutting. The apparatus and process substantially reduce conventional problems with the film cutter (14) caused by impurities which customarily are present in unwashed film. The invention is particularly useful for recycling very thin scrap film.

Description

APPARATUS AND PROCESS FOR WASHING AND SHREDDING FILM

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus and process for washing and shredding film. The apparatus and process of the invention are particularly useful in the recycling of contaminated scrap film.

It is desirable to recycle used plastic products, including consumer goods such as grocery bags, laundry bags, plastic food wrap, and industrial materials such as stretch wrap, agricultural film, and composite substances, in order to reduce quantities of waste disposal and reduce the need for production of new plastic. In a conventional plastic recycling process, strips of plastic scrap are fed to a dry cutter or size reduction device, and are subsequently transferred to a separate wet wash device. Customarily, the cutter is of the granulator type, and particulate contaminants are removed only later, i.e. during the washing step, using hydraclones or sink-float tanks. The use of a cutter in a conventional apparatus for processing plastic scrap material can be problematic, as the cutter is very sensitive to contaminants such as dirt and metals. This makes cutting of thin film particularly troublesome. Furthermore, hydraclones and sink-float tanks generally do not remove sufficient amounts of paper fiber from the scrap film during the washing step.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a new and improved apparatus and a process for washing and shredding film.

Another object of the invention is to provide an apparatus and process for use in recycling thin film. A further object of the invention is to provide an apparatus and process which can be used to improve the operation of a film cutter that is used in the recycling of scrap film.

Another object of the invention is to provide an apparatus and process for use in recycling contaminated scrap film.

Yet another object of the invention is to provide an apparatus and method for use in efficiently recycling scrap film.

Other objects of the invention will be in part obvious and in part pointed out more in detail hereinafter.

The invention in a preferred form is an apparatus for washing and shredding film, particularly scrap film. The apparatus includes wetting means for wetting the film with a liquid. The wetting means is connected to washing and shredding means for washing and shredding the scrap film. The film from the washing and shredding means is transferred to a first separation means for separating the washed and shredded scrap film from particulate contaminants including at least one of dirt, metal, wood, glass, heavy plastic and heavy paper.

The wetting means, washing and shredding means, and first separation means preferably are all part of a single unit. Preferably, the apparatus further includes second separation means positioned upstream from the washing and shredding means for removing contaminants, including dirt, metal, wood, glass, heavy plastic, heavy paper and other particulate materials, particularly those having a higher specific gravity than the wetting liquid, from the film. In a particularly preferred embodiment of the invention, the second separation means includes a separation chamber, and the wetting means includes a wetting chamber and means for supplying a washing liquid and a surfactant to the wetting chamber. The washing and shredding means preferably comprises a washing-shredding zone in which the film is simultaneously washed and shredded. The washing-shredding zone preferably includes first and second counter-rotating, intermeshed rollers operating at different speeds at a ratio of about 1.5:1 to 15:1, or more preferably, 2:1 to 10:1. The first separation means preferably comprises settling means which includes agitation means for causing particulate contaminants having a slightly lower specific gravity than the liquid to sink. The apparatus preferably further includes cutting means positioned downstream from the first separation means for cutting the film.

Another preferred embodiment of the invention is a process for washing and shredding film. The process comprises wetting the film with an appropriate liquid in a wetting zone. The wet film is subsequently washed and shredded. Particulate contaminants including at least one of dirt, metal, glass, wood, heavy plastic, and heavy paper are subsequently removed from the washed and shredded film in a first separation means. In a preferred embodiment of the invention, the film is cut after it is removed from the first separation means.

Preferably, the liquid which is used according to the method of the invention is water, and a surfactant is added to the water. The first and second rotors preferably rotate at different speeds in a ratio of between about 1.5:1 and 15:1, or more preferably 2:1 to 10:1. The step of removing particulate impurities preferably is a multistage process taking place in multiple settling tanks. Washing and shredding preferably occur simultaneously.

The process of the invention preferably further includes the step of removing particulate impurities including at least one of dirt, metal, glass, wood, heavy plastics, and heavy paper from the scrap film before the washing and shredding step in a second separation means. Furthermore, the process preferably includes the steps of removing the film from the first separation means and cutting the removed film.

The apparatus and process of the invention are particularly useful for removing impurities from very thin scrap film, including film having a thickness of about 1/4 mil or less.

The invention accordingly comprises the several steps and the relation of one or more such steps with respect to each of the others, and the apparatus possessing the features, properties and the relation of elements exemplified in the following detailed disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a side elevational view of an apparatus and process for washing and shredding contaminated scrap film according to a preferred embodiment of the invention.

Fig. 2 shows a top view of the washer-shredder unit shown in Fig. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to Figs. 1 and 2, an apparatus for washing and shredding scrap film, particularly contaminated scrap film, is generally designated by the numeral 10. The washer-shredder unit 10 is connected to a cutter 14 for cutting the washed and shredded film.

Before the scrap film enters the washer-shredder unit 10, it is pre-shredded into strips which are about 1 - 2 inches wide by about 6 - 12 inches long. Depending upon the nature of the feedstock, the strips can be in single layers, or can be in layers of about 1-3 inches thick.

The pre-shredded scrap film is delivered to the washer-shredder unit 10 by a belt conveyor 20, shown in Fig. 1. The preferred washer-shredder unit 10 is a single unit which is divided into three sections, although it also is possible for the washer-shredder unit 10 to be formed from two, three or more separate and distinct sub-units. The first section of unit 10 is a wetting-settling zone 26, including a wetting-settling tank 28 in which hot water, preferably at a temperature of about ambient temperature to 195°F, and more preferably about 180°F, and an appropriate quantity of a surfactant are added to the scrap material through a wash water-surfactant inlet line 27. The addition of surfactant is automatically controlled by a conductance probe (not shown) . The relative amounts of water, film and surfactant can be any amounts which provide for cleaning of the film. Preferably, for every pound of scrap film, about 80 lbs. of water (±30%) are used. For every 3 gals, of water, about 1 oz. of surfactant is used. Sinking material, such as dirt, metal, wood, heavy plastic, heavy paper, glass, and other particles having a density greater than that of the liquid are removed from the lower end of the tank 28. Preferably, although not necessarily, the particulate impurities and liquid are removed in an approximate weight ratio of one-to-one. The inclusion of the surfactant in the soaking process in the wetting-settling zone 26 facilitates the removal of dirt and grease from the film. A paddle wheel-agitator 30 in the wetting-settling tank 28 keeps the film in suspension while the heavy particulate impurities are separated from the film.

The wet film in the wetting-settling tank 28 is delivered by the paddles of agitator 30 to the second section of the washer-shredder, i.e. the washing-shredding zone 32. Unlike conventional processes, in which dry cutting occurs in a step which is separate from and before the washing step, the preferred washing-shredding zone of the invention provides for simultaneous washing and shredding of the scrap film. In zone 32, the film is pre-shredded prior to cutting, and is violently agitated to loosen dirt from the film surface.

The washing-shredding zone 32 includes a pair of interlocking, counter-rotating, toothed shredder rotors 34a and 34b which rotate at different speeds. The rotors preferably are designed and operated under conditions sufficient to shred the film into segments of about 1/2" x 3" or smaller. As shown in Figs. 1 and 2, each rotor has a plurality of alternating large and small blades 140,142, respectively, which are mounted to a central shaft 144 at a spacing of about 0.03". Each blade is about 1 1/4" thick, and has a plurality of arched teeth 146. The larger diameter blades of one rotor run in close proximity (0.06") to the smaller diameter blades on the opposite rotor. As a result of this arrangement, there is both tip-to-tip interaction and side-to-side interaction between the teeth of the intermeshed blades. Preferably the speed ratio of the rotors is between about 1.5:1 and 15:1, the downstream rotor 34b having the faster rotation. Agitator 30 rotates clockwise in the view shown in Fig 1. Right rotor 34a rotates counterclockwise. Left rotor 34b rotates clockwise in the view shown in Fig. 1. As a result of this arrangement, the film tends to generally move upward between agitator 30 and rotor 34a, and downward between rotors 34a and 34b. The liquid level is at about the center of the rotors.

The drive means for the shredder rotors 34a, 34b is interlocked with other parts of the apparatus in order to stop all the equipment upstream from the shredder in the event of an overload. Furthermore, the rotors 34a, 34b will reverse automatically in order to clear themselves in the event of an overload, and will subsequently return to normal operation.

A second agitator 31, which rotates in a clockwise direction in the view shown in Fig. 1, follows the high-speed rotor 34b to provide a high shear zone for further separation of film and contaminants. The paddle wheel-agitator 31 also removes film from the washing-shredding zone 32 and transfers it to the third section of the washer-shredder 10, namely a settling zone 35.

The settling zone 35 includes three settling tanks 36. Between rotor 34b and agitator 31, the film is first moved upward by rotor 34b and then downward by agitator 31 into the first tank 36. In the settling tanks 36 the film is mildly agitated by the agitator 31 and paddles 38, which rotate clockwise in the view shown in Fig. 1. A single paddle 38 is located between each pair of adjacent tanks 36, and a third paddle 38 is located at the downstream end of the downstream settling tank.

In the tanks 36, the film is provided with a retention time sufficient to further loosen dirt and grease and allow further contaminants to sink. Preferably, the retention time is at least about one minute, however, this time period can be varied within the scope of the invention as long as the period is sufficient to allow impurities to settle. The tanks 36 have subtle agitation to allow wood or paper fiber which has a specific gravity slightly lower than that of the liquid to sink. The impurities are removed from the washer-shredder 10 through the bottom of the settling tanks 36 and through the bottom of wetting-settling tank 28 through double dump valves 37. The valves 37 are sequenced to open one at a time, to give a relatively constant flow. Liquid which is removed from the bottom of tanks 36 is clarified and recycled for use in wetting and washing.

The shredded and washed film is transferred from one settling chamber to the next by paddles 38. The downstream paddle 38 conveys the film into a discharge line 41 through which it falls into the cutter 14. The cutter 14, which is described in detail in U.S. Patent No. 4,738,404, incorporated herein by reference, can be the same type as is used in conventional scrap film processing. The cutter 14 cuts the washed film into 1/8" to 3/8" pieces to allow further separation of the dirt from the film. Furthermore, violent agitation is provided during the cutting action to loosen fine dirt particles from the film. The cut film is removed from the cutter 14 through line 40 and is conveyed to further film processing units for rinsing.

As will be apparent to persons skilled in the art, various modifications and adaptations of the structure and method described above will become readily apparent without departure from the spirit and scope of the invention, the scope of which is defined in the appended claims.

Claims

IN THE CLAIMS:

1. An apparatus for washing and shredding film, comprising: wetting means for wetting the film with a liquid, washing and shredding means for washing and shredding the wet film, and first separation means for separating particulate contaminants including at least one of dirt, metal, wood, glass, heavy plastic and heavy paper from the washed and shredded film, the wetting means, shredding and washing means, and first separation means being fluidly connected in series.

2. An apparatus according to claim 1, further comprising second separation means upstream from the washing and shredding means for removing particulate contaminants from the wet film.

3. An apparatus according to claim 1, wherein the second separation means includes a second separation chamber.

4. An apparatus according to claim 1, wherein the wetting means, washing and shredding means, and first separation means are part of a single unit.

5. An apparatus according to claim 1, wherein the wetting means includes a wetting chamber and means for supplying a washing liquid and a surfactant to the wetting chamber.

6. An apparatus according to claim 1, wherein the washing and shredding means comprises a washing-shredding zone in which the film is simultaneously washed and shredded.

7. An apparatus according to claim 1, wherein the washing and shredding means includes first and second counter-rotating, intermeshed rollers.

8. An apparatus according to claim 1, wherein the first and second rotors operate at different speeds at a ratio of about 1.5:1 to 15:1.

9. An apparatus according to claim 1, wherein the first separation means includes settling means.

10. An apparatus according to claim 9, wherein the settling means comprises agitation means for causing particulate contaminants having a specific gravity which is slightly lower than that of the liquid to sink.

11. An apparatus according to claim 1, further comprising cutting means for cutting the film, the cutting means being positioned downstream from the settling means.

12. A process for washing and shredding film, comprising: wetting the film with an appropriate liquid in a wetting zone, washing and shredding the wet film in a washing-shredding zone having first and second counter-rotating, intermeshed rotors, and removing particulate impurities including at least one of dirt, metal, glass, wood, heavy plastic, and heavy paper from the shredded and washed film in a first separation means.

13. A process according to claim 12, wherein the wetting liquid comprises water and a surfactant.

14. A process -according to claim 12, wherein the first and second rotors rotate at different speeds in a ratio of between about 1.5:1 and 15:1.

15. A process according to claim 12, wherein the step of removing particulate impurities is a multistage process taking place in multiple settling tanks.

16. A process according to claim 12, further comprising the step of removing particulate impurities including at least one of dirt, metal, glass, wood, heavy plastic, and heavy paper from the film in a second separation means before the shredding and washing step.

17. A process according to claim 12, wherein washing and shredding occur simultaneously.

18. A process according to claim 12, further comprising the steps of removing the film from the first separation means, and cutting the removed film.