Field Of Invention

The present invention relates to an apparatus and method of drying of polymeric film. More particularly, it relates to the quick removal of water from and drying the film which has been extruded as hot melt from the extrusion machine at higher speeds.

Background Of Invention

Polymeric films which are typically manufactured from resins, each with its own unique physical properties that are differently suited to different applications. Such film can be produced from film extrusion technique of the molten material such as polypropylene, polyolefin more particularly termed as LDPE/ HDPE/PP. Besides all the different materials it can be made from, a polymeric film can be clear, coloured, smooth, rough, functionally embossed, opaque, or semitransparent.

Finished films can be either laminated by several methods, or stretched (oriented) in machine direction, or cross-machine direction or biaxially. Stretched films are often annealed when desired. Other common treatments of finished polymeric films are surface treatment and metallization.

Typical uses of polymeric films include packaging, bags, labels, in automotive, aerospace, electrical and electronic, in chemical industry, optical industry, in the military, and in building construction and landscaping.

In the film extrusion technique, the polymeric molten material is made to fall into the quenching device where due to the sudden cooling and difference in temperature, the molten film solidifies and gain the shape of the film which is passed through various processes such that film passed through water as quenching medium is dried and water is removed.

The film after passing through the quenching device is dried and passed over the heating and stretching unit so that film can be stretched and molecules can be monoaxially oriented, also the film can regain its properties such as strength. However such film if it is wet, due to heating at later stages will tends to tear or break.

Thus, proper drying of the film is very essential so that further processing of the film can be done in an efficient manner.

In the conventional system of drying, as shown in figure 1, the molten material from the extruder (2) is dipped into the water tank (3) to form a polymeric film (1) which is passed over the first and second roller (5,7). The first and second roller (5,7) are mounted on a dancer arm (6) such that the dancer arm (6) deflects up and down to compensate the film (1) movement with respect to the line speed of the machine. The film (1) is now passed through the wiper & scraper unit (8) where the water which is carried by the film (1) is removed. However, this unit does not completely remove the water from the surface of the film (1). First set of suction pipe (9) and second set of suction pipe (10) is present through which suction is created and film (1) when passes besides it is dried as these suction pipes (9) suck the water droplets. The film (1) is driven by the first drive unit (12) and second drive unit (13) such that it can be moved in the vertical direction smoothly. The drive units (12, 13) comprise a set of rollers which can be rubbery in nature to provide a cushion to the fragile film (1).

Further, the film (1) enters parallel to the air drying unit (18) which comprises of first pair of air dryer (19) which are placed at a height ‘Hl’. The air dryer (19) pair is further placed perpendicular to the film (1). By first and second drive unit (12, 13) a difference in the speed in movement of fdm (1) is created such that fdm (1) is slightly loosen near the first pair of air dryer (19) area. Such looseness is created so that due to high pressure of air thrust by the air dryer (19) on the film (1) does not damage the film (1).

Further, air dryers (19) well-known as air knife with blower unit is used in the conventional high end system to remove by jet of air. Patent WO 03/055369 (‘5369) discloses blower operated air knife for directing elongated air curtains for various purposes such as drying, cooling, or cleaning items conveyed transversely through the air curtain. A problem with such low air pressure operated air knives is that the volume and velocity of the discharging air can be limited, which in turn can limit the effectiveness of the air curtain, including its effective transverse width, i.e. the width of the curtain in the direction of travel of items conveyed through the air curtain.

Due to the multiple drive units in the system, there is a difficulty to synchronise the drive units (12, 13) with respect to the movement of the film (1). Thus, if due to some mechanical or electrical failure in the drive unit (12, 13) there will be failure in the synchronisation of the drives (12, 13) which will eventually create puncture in the film (1). A first pair of air dryers (19) is located opposite to each other such that both the top and bottom layer of the film (1) is dried up by them.

Atleast a pair of trays (14) is present so that any water which is drained out by the second drive unit (13) can be accumulated in the tray (14) and is removed out by any of the means through hose or by manual extraction.

Film (1) now guided to the next station through the set of rollers mounted on the holder (17) wherein next station is defined as cutting unit (22) in which film (1) is slitted into tapes of desired width. One of the drawbacks of the above conventional system is that pair of air dryer (19) are situated at a height ‘Hl ’ which is in close proximity to the water tank (3), though the height Hl is greater yet it does not suffice the problem of carrying wet film without drying. This is because at greater speed lesser dwell time will be there for film to be exposed for drying. In addition to it, the air supply is to be done at high height Hl where the air dryers are installed which consume high power for the supply. The dryers (19) are mounted on the support plate (4) which is connected to the water tank (3) such that film moving at higher speed does not get enough time to stay at the dryers and thus it won’t dry the film (1) adequately. Also, the construction appears to be too complex which eventually reduces the overall efficiency of the system.

The pressure required for the air dryer (19) to efficiently work will be higher as the film (1) is moving at high speed and ideal time require by film (1) to stay at the air dryer station will be less, so operator must reduce the speed of the machine in order to compensate the overall efficiency.

In addition to it, in the conventional system, these air knives or air drying system are integrated with the quenching device such that as soon as the molten material is converted into film, then it is made to pass through the air drying unit. Since the distance of travel after quenching to the air drying unit is very less, there is no effective drying operation takes place because of which there is a decrease in efficiency with the increase in the speed of movement of film.

Thus, there is a requirement of a drying system that makes a film dry at high speed movement produced from the extruded molten material.

Objects of Invention:

The main object of the present invention is to provide a method and an apparatus for drying polymeric film in more efficient manner at high-speed movement that has been produced from the extruded molten material.

Another objective of the present invention is to produce a fdm with improved properties for succeeding operations in extrusion line.

Yet another objective of the present invention is to dry the film moving at high speed.

Further objective of the present invention is to provide an apparatus which can be integrated in an automated extrusion line.

Another objective of the present invention is to increase overall efficiency of the extrusion line.

Brief Description Of Figures:

Figure 1 shows the conventional system of drying polymeric film.

Figure 2 shows the drying system of drying polymeric film.

Figure 3 shows air dryer and mechanism of water removal from the film.

List of Parts:

1. Polymeric film

1 A. Top layer or surface of the film

IB. Bottom layer or surface of the film

2. Extruder

3. Water tank

4. Support plate

5. First roller

6. Dancer arm

7. Second roller

8. Wiper & scraper unit 9. First set of suction pipe

10. Second set of suction pipe

11. Scraper

12. First drive unit

13. Second drive unit

14. Tray

15. Third set of suction pipe

16. Fourth set of suction pipe

17. Holder

18. Air drying unit

19. First pair of Air dryers

19’ top first air dryer

19” bottom first air dryer

20. Side plate

21. Base frame

22. Cutter unit

23. Second pair of air dryers

23 ’ top second air dryer

23 ’ ’ bottom second air dryer

24. Nozzle

25. Chamber

26. Air input hose a air-blowing angle

0 film angle

Summary Of Invention:

In the tape extrusion machine, the polymeric film particularly polypropylene film is extruded in the form of hot melt from extruder die. Extruded molten film solidifies due to the direct contact with the cooling medium. Such kind of cooling medium can be water, oil, soft soap, emulsion of oil and water, ethylene glycol etc. The solidification of the molten material takes place due to the coiling of the molecules in random direction to form a film. After passing through the quenching medium such as water, the film produce carries the water along with it. During initial stages of film transfer, some of the water droplets are removed with the help of the wiper or scraper unit.

But due to the high speed movement of the film these wipers and scraper unit are not efficient enough to remove all the water content over the film.

In the conventional systems, air drying unit is placed just after the wiper or scraper unit. This air drying unit is mounted such that its axis is perpendicular to the movement of the film. The pressurized air is made to flow from these airdrying units over the top and bottom surfaces of the film which removes additional water droplets. Due to the position of the air drying unit so close to the wiper or scraper unit as well as the mounting as described above, these drying unit are not efficient enough to remove the water from the film which is moving at high speed.

The present invention discloses an apparatus in a high speed automated tape extrusion line for drying of the film that is constructed such that it is placed far away from the wiper or scraper unit. However, apparatus of the present invention tends to remove the water from the film which is moving at high speed as well.

Thus, polymeric film is made to pass between at least one pair of the air drying unit, more preferably called air dryers such that a controlled air is passed over the top and bottom surfaces of the film in stages such that it removes the water content which lies over the film effectively and completely.

In the drying system of the present invention, the polymeric film which is moving at high speed which matches with the line speed of tape extrusion machine preferably at 750-800 mpm is provided enough time to enter the air dying unit such that water can be removed or sprinkled away from the film due to its selfweight.

In the present invention, the air drying unit is placed at a height ‘H’ lower than the height at which film is discharged after wiper or scraper unit such that its forms a film angle 0 with the air drying unit. At least one pair of air dryers or more preferably two pairs are used in the inventive system such that the water is moved completely.

Air dryers with different cross section preferably circular cross section help to provide even flow of the air inside the chamber which distributes the air over the film evenly. The air blowing units are placed at a close distance to the air drying unit which supplies the enough air to the air dying unit. An air reservoir is present which stores the extra amount of air such that in the event of pressure drop, the air can be supplied without any hindrance.

At least a pair of air dryers are installed after the quench unit (which in this case is a water tank (3)), such that these are far from it and the film get enough time to get dried before entering into the next processing unit namely cutter unit (22) in which film (1) is slit into tapes of desired width and thereby made to enter into Hot air oven. These air dryers are capable of removing water or any liquid content from the upper as well as lower layer of the film.

Thus, such kind of technique can be quite beneficial for the tape extrusion machine to work at higher speed and supply of dry film to the subsequent unit for further processing in efficient way. Detail Description Of Invention:

Figure 2 shows the drying system of the present invention. The molten film from the extruder (2) is dipped into the water tank (3) to form a polymeric film (1) which is passed over first and second rollers (5, 7). The first and second roller (5, 7) are mounted on a dancer arm (6) such that the dancer arm (6) deflects up and down to compensate the film (1) movement with respect to the line speed of the machine. The film (1) is now passed through the wiper & scraper unit (8) where the water carried by the surface of the film (1) is removed. However, this unit does not completely remove the entire water from the surface of the film (1) completely. First set of suction pipes (9) and second set of suction pipes (10) is present through which suction is created and film (1) when passes besides it is dried as these suction pipes (9) suck the water droplets.

The film (1) is driven by a single drive unit, namely second drive unit (13), such that it can be moved in the vertical direction smoothly. The second drive unit (13) comprises a set of rollers to provide a cushion to the fragile film (1). The rollers can be made of inside hard material with a coating of softer material such as polyurethane, elastomers or any kind of soft material which provide cushion effect and does not damages the film. Below the second drive unit (13) a set of trays (14) is provided such that the water which is drained out by the rolling action of the second drive unit (13) percolates into the tray (14) and is being regularly removed through drain pipes or manually. Scraper (11) is present which can be in set or in pairs such that extra water is removed from the film (1) top and bottom side.

Further the film (1) passes through the air drying unit (18) which is placed far away from the water tank (3) which will eventually provide film (1) more time to travel and thereby drying the film due to the ambient temperature well before entering into the air drying unit (18). The air drying unit (18) is placed at a height ‘H’ such that it provides a slant profile to the film (1) which enters the air drying unit (18) at a film angle 0. The film angle 0 can be 25 to 85 degrees, preferably 45 degrees or more preferably 65 degrees such that the water will drops down due to self-weight. Before passing into the air drying unit (18), fdm (1) is optionally guided over the third and fourth set of suction pipes (15, 16) which are mounted on the holder (17). These multiple stage suction pipes (15, 16) will tends to remove the moisture contents at greater instant.

The air drying unit (18) comprises of a base frame (21) over which side plate (20) is mounted. The base frame (21) can be constructed by square or rectangular or circular cross section profde which are fabricated together by welding process. The base frame (21) however, can also be constructed by solid plates or rods welded or bolted together to form a sturdy structure. The side plate (20) can be made from the structural steel which are mounted on the base plate. These mounting can be done by any mechanical joints such as welding or bolting. On the side plate (20) at least one pair preferably two set of air dryer unit (19, 23) is mounted. The two sets of air dryers can be termed as first pair of air dryers (19) and a second pair of air dryers (23). Each pair of air dryer (19, 23) comprises dryers mounted opposite to each other such that the air can be blown on the film (1) from the top as well as from the bottom.

An experiment has been performed using single pair of air dryer on an automated tape extrusion line and it was found that some water droplets were present after the drying unit as well which passes to the next processing station such as hot air oven, the efficiency of the hot air oven drastically reduces by 15-20% due to the moisture content in the film as it require high temperature for curing. Whereas when two pair of the air dryer unit placed in close proximity are used, the efficiency for the hot air oven increased by 5-10 %. Here the close proximity refers to the optimal distance in range of 1 - 10 metres more preferably 7 metres such that film travelling at a speed of 700-750 metres per minute is continuously dried by the pair of dryers. The nozzle (24) of the air dryer (19) from which air is blown out is placed at an angle such that the pressurised air does not create any puncture in the moving fdm as shown in figure 3. Air dryer (19, 23) most commonly consist of a structure, usually made from aluminium, steel or plastic, that houses a chamber (25) and includes a unique shape of oblong cross section on one side, formed from two blades joined together, in the shape of nozzle (24), these blades which are made from sharp steel sheets provide a sharp edge to the air flow without any hinderance. Air dryers (19, 23) come from their ability to produce a particular type of air flow. When air is ejected through the nozzle (24), it forms a laminar air flow. Laminar air flow is a unique and useful type of air movement. It occurs when air moves at the same speed and in the same direction, with no crossover.

Further figure 3 shows top air dryer (19’) which comprises of a chamber circular in cross section to provide a smooth flow of air inside it. The pressurised air from the air input hose (26) is made to enter the chamber (25) and passed the exit through the nozzle (24) onto the top film (1A) The high pressurized air disturbed the water or liquid film and remove it completely from the top layer (1A). Thus, a dry region is obtained. The top air dryer (19’) is mounted such that it forms an airblowing angle (a) with the direction of the travel of film (1). The air-blowing angle (a) is less than 90 degrees, preferably in the 45 to 60 degree range. The higher the air-blowing angle (a), the greater is the force is applied on the top layer of film due to air pressure which can damage the film. Since the nozzle (24) becomes perpendicular to the film so the air which is ejected from it directly bombard over the top layer of the film (1A) in order to remove water and due to continuous process, the air pressure damages the film. After performing many experiments, it was concluded that after inclining the nozzle (24) at the airblowing angle (a) as defined above, the film (1A) is secure from the damages. The same construction and mounting arrangement are replicated for the bottom air dryer (19”) as well. Further, can be applied for second pair of the air dyer (23) as well.

Now the dried film (1) is passed to the subsequent unit namely cutter unit (22) in which film (1) is slit into tapes of desired width and thereby made to enter into Hot air oven.

As an example, it is observed in the tape extrusion machine while using the conventional system of drying the film, the maximum speed at which tapeline can be operated is in the range of 550-600 mpm (meters per minute) to get the desired film output which is dry in nature while in the same tapeline when drying system of the present invention is used the maximum speed of the tapeline can be achieved in the range of 700-750 mpm. Thus, the film can be dried quickly which the help of inventive system at high speed as well without any damage to the film.

Following steps are involved in drying polymeric film at high speed:

1) The molten material from the extruder (2) is dipped into water tank (3) to solidifies as a film (1) and passed over the rollers (5, 7) mounted on the dancer arm (6).

2) Film (1) now passed over the wiper & scraper unit (8) to remove excess water.

3) The film (1) passes further over the pair of suction units (9, 10) such that water is sucked.

4) Second drive unit (13) carries the film (1) to the subsequent units in the upright position in the vertical direction, whereafter said film (1) is sent through a set of first and second suction pipes (15, 16) at a film angle 0.

5) Film (1) is made to transfer to the air dryer unit (18) where the pair of air dryers (19, 23) are present at a height H and at given air blowing angle (a), preferably between 45 and 60 degrees, to remove water from the top as well as botom of the film (1A, 1B) by throwing air over it by the blowers (not shown).

6) Finally, dried film (1) is passed to the subsequent unit namely cuter unit (22) in which film (1) is slit into tapes of desired width and thereby made to enter into Hot air oven.

The following example illustration the effect of using air dryers which are placed after quenching unit (i.e. the water tank (3)) in an automated tape extrusion line as a present invention works. The film (1) of 1200 denier was produced by an inventive system working at a speed of 650-750 mpm which is made to pass through the pair of the air dryers which are placed after quenching unit (i.e. the water tank (3)) at height ‘H’ such that the film is completely dried where ‘H’ is preferably A of ‘Hl’ and made to pass through the cuter unit where it is slit in form of tape of width 2mm. Now the tapes are entered into the hot air oven operating at a set temperature of apparatus was 160 °C. The air-flow velocity was set at 10 to 11 m/s using individual air-flow regulators present at the top and botom chambers of hot air oven. Temperature of the tape was measured at various locations across the width of the oven at randomly chosen location along its length. It was found that the variation of the temperature of the tape from the set temperature was between 0.3% and 1.92%. This is much lower than the variation of 0.54% to 3.9% which was experienced using a conventional system of drying. Since in the conventional system the water which carries with the film in the hot air oven hinders the process inside the hot air oven. This represents nearly 100% reduction in variation of temperature as compared with the treated using conventional method. Further during the maintenance or in breakdown due to tape breakages also reduces by 50-60%.

While the above description contains much specificity, these should not be construed as limitation in the scope of the invention, but rather as an exemplification of the preferred embodiments thereof. It must be realized that modifications and variations are possible based on the disclosure given above without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.