Title: An improved polyethylene film and a process of manufacturing thereof
Field of the invention:
The present invention relates to the field of packaging films.
More particularly, the invention relates to the field of polyethylene films.
Even more particularly, the present invention relates to an improved film having a wide thickness range, from very low thickness to higher side, such that the said film can be used for a wider range of applications.
The invention also provides a manufacturing process for making such a film.
Background and prior art of the invention:
From years, polyethylene films have been used in film packaging. The low-density polyethylene (LDPE), linear low density polyethylene (LLDPE) and high density polyethylene (HDPE), are often combined in one film to obtain the best balance of properties for the application. Products can be combined by blending and by co-extrusion.
The blown film extrusion process is used very commonly across the globe. Polymers are typically conveyed to the extrusion line bya vacuum conveying system. The feed system typicallycontains a number of hoppers for receiving different resinsand a mixing system for blending multiple resins. Modernlines typically have gravimetric systems for controlling theblending process and also for metering the resins to theextruders. In the extrusion process, homogeneous polymermelt delivered at a constant rate from one or more extruderscrews is extruded through an annular die togive a tube of controlled diameter and wall thickness.
Upward vertical extrusion is almost universally used,but downward or horizontal extrusion is employed in somecircumstances. The extruded melt is air-cooled in thevicinity of the die via a cooling ring and the tube of filmis inflated to a bubble of the required diameter by airintroduced through the center of the die mandrel. The film is hauled off between a pair of nip rolls so that a constant volume of inflation air is contained within the bubble formed between the nip rolls and the die.
2
Co-extrusion of multiple layers within a film can increasethe options available in designing films. For example, eachlayer can be optimized to perform a different function.
Reference is made to United States Patent9,284,440, dated March 15, 2016, by Effler Jr. et al, titled “Polyethylene blend composition suitable for blown film, method of producing the same, and films made therefrom”.
This invention provides a polyethylene blend composition suitable for blown film, method of producing the same, and films made therefrom. The polyethylene blend composition suitable for blown film according to the present invention comprises the melt blending product of: (a) less than or equal to 4 percent by weight of a low density polyethylene (LDPE); (b) 90 percent or greater by weight of a heterogenous linear low density polyethylene (hLLDPE); (c) optionally a hydrotalcite based neutralizing agent; (d) optionally one or more nucleating agents; and (e) optionally one or more antioxidants. When the polyethylene blend-composition is formed into a film via blown film process, the output rate is improved at least 6 percent relative to a similar linear low density polyethylene.
The said polyethylene blend-composition is formed into a film via blown film process, the output rate is improved at least 6percent relative to a similar linear low density polyethylene. The total haze is improved by at least 15 percent relative to a blown film consisting essentially of a linear low density polyethylene. The gloss is improved by at least 10 percent relative to a blown film consisting essentially of a linear low density polyethylene.
Further reference is made to United States Patent9,096,745, dated August 4, 2015, by NOVA Chemicals (International) S.A., titled “Polyethylene blend compositions and film”.
This invention provides a polymer blend comprising first and second polyethylene copolymers is presented which has good processability, and which when made into film shows good toughness-stiffness balance, reasonable MD tear, as well as good optical properties. The polymer blend comprising: a) from about 5 to about 95 wt % of a first polyethylene copolymer; and b) from about 95 to about 5 wt % of a second polyethylene copolymer which is a linear low density polyethylene (LLDPE) different from the first polyethylene copolymer.
3
Another reference is made to United States Patent 9,080,082, dated July 14, 2015, by ExxonMobil Chemical Patents Inc., titled “Medium density polyethylene film layer and multilayer film comprising same”.
This invention relates to a multilayer film structure including (a) a core layer having a first side and a second side, the core layer including at least one core polymer; (b) a first tie layer having a first side and a second side, the second side of the first tie layer on the first side of the core layer; (c) a second tie layer having a first side and a second side, the first side of the second tie layer on the second side of the core layer; (d) a sealant skin layer having a side on the first side of the first tie layer; and (e) a second skin layer having a side on the second side of the second tie layer, is provided.
The sealant skin layer is comprising a blend of from 25 wt % to 75 wt % of a polyethylene polymer, from 25 wt % to 75 wt % random copolymer or terpolymer and from 0.3 wt % to 1 wt % antiblock agent.
The second skin layer having a side on the second side of the second tie layer, is comprising a polymer selected from the group consisting of polyethylene (PE), polypropylene (PP), ethylene-propylene (EP) copolymer, propylene-butylene (PB) copolymer, ethylene-propylene-butylene (EPB) terpolymer, ethylene-vinyl alcohol (EVOH) polymer, and blends thereof.
The said sealant skin layer is from 0.5 .mu.m to 4.0 .mu.m thickness, said first tie layer is from 0.5 .mu.m to 5.0 .mu.m thickness, said core layer is from 10 .mu.m to 50 .mu.m thickness, said second tie layer is from 0.5 .mu.m to 5.0 .mu.m thickness and said second skin layer is from 0.5 .mu.m to 4.0 .mu.m thickness.
The film structure is biaxially oriented from three to six times the extruded length in the machine direction and from four to ten times the extruded width in the transverse direction. The second skin layer is metalized by vacuum deposition of a metal selected from the group consisting of aluminum, copper, silver, chromium, and mixtures thereof.
However, none of these inventions teach about a film having thickness in the range of 7.5 to 15 micro meter. Nor do they provide any process for
4
manufacturing such a thin film using same machinery and process, as is used for making a thick film. The present invention provides these innovative solutions having a wide range of applications and advantages.
Objectives of the invention:
The main objective of the present invention is to provide an improved packaging film.
Another objective of the present invention is to provide an improved and environment-friendly polyethylene film with better properties.
Another objective of the present invention is to provide an improved film having a very low thickness, which can be used for a wider range of applications.
Another objective of the present invention is to provide an improved manufacturing process for making improved packaging film.
Summary of the invention:
The present invention provides an improved environment-friendly polyethylene film and a novel process of manufacturing. Further, the invention provides a polyethylene film with improved and modified machinery. The polyethylene film is manufactured having a thickness of 7.5 to 15 micro-meters scale. The film is manufactured in this wide range of thickness using the same machinery and process. This reduces the burden of extra costs for requirement of different range of film thickness.
Disclosed herein is a polyethylene film comprises low density polyethylene, high density polyethylene and linear low density forms are mixed in required ratios and are extruded. Further, temperature of 250 to 300 degrees is used for melting and polymerization. The bubble formation takes place at the top of layer. But the die gap, process, gauzing and other factors associated have optimized such that even when drying takes place for molten film using high temperature, the thin film bubble does not burst and stay stable without any wrinkles is obtained having thickness up to 7.5 micrometer low.
Embodiment of the invention, an auto Gauging system is developed for controlling and monitoring the properties of the film being manufacturing. Further, air chillers are used for blowers for cooling off the film.
5
Brief description of the drawings:
Figure 1: is a schematic representation of a blown film extrusion process.
Figure 2: is a schematic representation of extruder and Co-extrusion Line with 5 Extruders.
Figure 3: is schematic representation of dies.
Figure 4: is schematic representation of Cooling Ring for Blown Film Extrusion.
Figure 5: is schematic representation of film slitting machine and film treater for blown film.
Statement of the invention:
Accordingly, the present invention provides an improved and environment-friendly polyethylene film with modified properties, and a process for manufacturing thereof, said film having a wider range of thickness, suitable for higher range of applications, wherein said film is having low density polyethylene (LD), high density polyethylene (HD) and linear low density polyethylene (LLDPE) as main components, and said film is prepared by extrusion process using machines well known in the art at highly modified process parameters.
Detailed description of the invention:
It should be noted that the particular construction and mode of application/usage set forth hereinabove is merely exemplary of the wide variety and arrangement of instructions which can be employed with the present invention. The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. All the features disclosed in this specification may be replaced by similar other or alternative features performing similar or same or equivalent purposes. Thus, unless expressly stated otherwise, they all are within the scope of present invention. Various modifications or substitutions are also possible without departing from the scope or spirit of the present invention. Therefore, it is to be
6
understood that this specification has been described by way of the most preferred embodiments and for the purposes of illustration and not limitation.
The present invention provides a polyethylene film with improved properties, having a thickness range of 7.5 to 15 micro meters.
The innovative film has been manufacturing using an improved and modified machinery and a novel process for manufacturing the film has been provided. The film is possible to manufacture in this wide range of thickness using the same machinery and process. There is no need to change the machinery for making film of variable thickness.
All forms of polyethylene, i.e. low density polyethylene, high density polyethylene and linear low density polyethylene are mixed in required ratios and are extruded. Three separate extruders are used.
The normal ration for LD + HD + LLDPE is USUAL RATIO IS 1-2-2.
THEIR CONTENTs Vary AND DEPEND UPON REQUIREMENTS.
Even in the reduced thickness of film, the same quantity of sealant can be applied which was used on higher thickness films. So, there is no change in application part, in fact the thinner film can be used for very wide ambit of applications.
A temperature of 250 to 300 degrees is used for melting and polymerization. The bubble formation takes place at the top of layer. But the die gap, process, gauzing and other factors associated have been optimized such that even when drying takes place for molten film using high temperature, the thin film bubble DOES NOT BURST and a stable film without any wrinkles is obtained having thickness as low as 7.5 micro meter.
The speed of running the machine is the same as that used for manufacturing a film with higher range of thickness. An auto Gauging system has been developed for controlling and monitoring the properties of the film being manufacturing.
The improved process as developed in this invention uses air chillers instead of blowers for cooling off the film.
7
Blown film extrusion is carried out vertically upwards; however horizontal and downward extrusion processes are now becoming more common. This procedure consists of four main steps:
1. The polymer material starts in a pellet form, which are successively compacted and melted to form a continuous, viscous liquid. This molten plastic is then forced, or extruded, through an annular die.
2. Air is injected through a hole in the center of the die, and the pressure causes the extruded melt to expand into a bubble. The air entering the bubble replaces air leaving it, so that even and constant pressure is maintained to ensure uniform thickness of the film.
3. The bubble is pulled continually upwards from the die and a cooling ring blows air onto the film. The film can also be cooled from the inside using internal bubble cooling. This reduces the temperature inside the bubble, while maintaining the bubble diameter.
4. After solidification at the frost line, the film moves into a set of nip rollers which collapse the bubble and flatten it into two flat film layers. The puller rolls pull the film onto windup rollers. The film passes through idler rolls during this process to ensure that there is uniform tension in the film. Between the nip rollers and the windup rollers, the film may pass through a treatment center, depending on the application. During this stage, the film may be slit to form one or two films, or surface treated.
Extrusion is the basic process for converting pelletized raw material into a homogeneous melt for delivery to a die and forming into the final shaped product, in this case a thin blown film.
The extruder consists essentially of a cylindrical heated barrel within which rotates a close-fitting Archimedean screw. The polyethylene pellets are fed to one end of the screw from a feed-hopper and are forced forward by the rotating screw, being melted partly by heat conducted through the walls of the barrel from external heater band sand partly by frictional heat generated by the shearing action of the screw. The molten and compacted polymer is then forced through an annular die as a thin tubular film, cooled and hauled off by nip rolls.
8
The functions of the blown film die are to meter the polymer melt at constant pressure and uniform rate, and to transform it into a thin-walled tube, while maintaining uniformity of the melt temperature. For more information on extrusion dies, refer to the Extrusion publication. For blown film extrusion, the die comprises a metal outer body and an internal mandrel to form an annular aperture through which the molten polymer is forced to produce a tubular extrudate. The lips of the die are in the form of hardened-steel rings which can be integral with the mandrel and body but more often are bolted on to allow for replacement. The die is heated to maintain uniform melt temperature. Air for inflating the film bubble is introduced via a channel in the core of the mandrel.
Extruder process-
The extruded polyethylene tube on exiting the die is inflated into a bubble of the desired diameter and film thickness by mean so fan internal injection of air introduced through the die mandrel at a pressure of 15 to 35k Pa. This air is trapped within the film bubble formed between the die and the nip rolls. The ratio of the diameter of the bubble relative to the diameter of the die is known as the blow-up ratio. Blow-up ratios a slow as 1.5:1 can be used but these can lead to excessive machine direction orientation. Generally blow-up ratios between 2:1 and 3:1 are used. Higher blow-up ratios may lead to bubble instability problems and film creasing.
Further, the film cooling process is very important because the cooling can affect the output rate, gauge uniformity, film density, and a number of film properties. The cooling system has four main functions:
1. To remove heat from the melt exiting the die and cool the film bubble to the solid state, so that it can be subsequently flattened and wound-up.
2. To stabilize and support the bubble on its exit from the die and minimize gauge variations.
3. To control the film density and a number of film properties including impact strength, tear strength and optical.
4. To determine the maximum output rate at which the film can be produced without blocking problems.
9
5. To prevent blocking, the temperature of the film reaching the nip rolls should be less than 40°C
As the film exits from the die annulus, it is in the molten state and must be cooled as soon as possible to stabilize the bubble and achieve a low degree of crystalline. The freeze line or frost line is the ring-shaped zone where the polymer solidifies after being cooled from the molten state and the bubble reaches its final diameter.
The basic form of cooling unit is an air ring which is fitted above the die. The air ring is designed to direct an air stream uniformly onto the exterior circumference of the film bubble as it emerges from the die. For maximum cooling efficiency, a combination of a high volume of low pressure air at the highest practical velocity must be used. It should not be an air blast of such force as to damage the bubble or to induce flutter. Any variations in the air temperature or flow rate around the circumference of the air ring will give rise to non-uniform cooling rates and as a consequence, irregularities in the bubble and poor film thickness tolerance.
Prior to entering the nip rolls, the film bubble is collapsed into a flattened tube by means of a pair of angled collapsing frames or boards (sometimes called the A-frame or bat wings). These can take various forms and can be either of solid or hollow construction, or in the form of rollers. Friction between the film and the surfaces of the collapsing system should not be too high, as this will cause the ragging or grabbing of the film, giving rise to wrinkles and creasing. This effect becomes more notice able if the film is hot or the area of contact between the boards and the film is too large. It can largely be overcome by slightly roughening the surfaces or using coatings to reduce heat build-up and film drag. Each collapsing frame should be aligned tangentially to the nip roll and positioned symmetrically relative to the vertical.
The collapsed bubble passes through nip rolls which flatten the tubular film before the wind-up stage, trap the inflation air in the film bubble, and regulate the take-off speed of the film. The wall thickness of the film can be controlled by changing the speed of the nip rollers. Then IP roll assembly comprises two rollers, typically one constructed of steel and the other covered with are salient material such as rubber, to take up flaws in the film. Then IP rolls should be mounted vertically above the
10
extrusion die, at a height of at least two meters, and directly in line with the collapsing frames. When only the conventional air cooling ring is used for cooling the film, the height of then IP rolls above the die has a marked effect on the film production speed, more after-cooling being obtained with higher nip rolls. However very high nip rolls can lead to bubble in stability, especially when extruding LLDPE polymers. The pressure between the two rolls should be even along their length and just sufficient to maintain the steady linear take-off speed and prevent escape of air from the film bubble. If then IP roll pressure is too high, blocking and weak edge-folds will result. Blocking will also occur if the film entering the nip rolls is too hot.
Further, if sheet film is required, the lay-flat is slit at its edge so rat any points across its width to form a number of reels of the desired size. The edge trim and off-cuts so formed can be removed with a vacuum system. The amount of this scrap should be minimized to reduce waste and it is often prudent to reclaim it.
SLITTER TREATER:
TREATMENT OF POLYETHYLENE FILM
The surface of polyethylene film is highly non-polar and inert because of the hydrophobic chemical nature of the polymer. This means that the receptivity of the film surface to inks, coatings, adhesives, etc. is poor and adhesion of these materials to the surface is unsatisfactory. This non-polar nature of the surface is the biggest limitation in the subsequent processing (printing, adhesive lamination) of the film for high quality packaging applications. Traditionally, surface receptivity has been considerably improved by electrical corona discharge treatment, which oxidizes the surface, increases the polarity, and provides acceptable adhesion for subsequent printing and laminating operations.
ADDITIONAL SETUP TO ACHIEVE LOWER MICRON STABLIZATION AND WASTE REDUCTION
As the film passes through dandy free rolls to rewind axis, there is a setup of two/ three vertical blade assembly for removal of extra or non-required or GSM variation prone area removal. That trimmed length or material sent to an assembly especially
11
designed to shred the same into FLAKES (very little pieces) and next to this process, a motor operated blower fan with high air pressure to send these FLAKES travels through a pipeline in to the hopper of the middle layer online. It helps to control the heat the thinner layer from bursting.
Die GAP plays an eminent role to control, stabilize and alteration the thinner gauge.
Chilled air provided for better cooling and controlling the thin gauge bubble.
Online fully automatic gauge controlling system incorporated to control the gauge variation of the thinner film.
Extrusion is the basic process for converting pelletized raw material into a homogeneous melt for delivery to a die and forming into the final shaped product, in this case a thin blown film.
The extruder consists essentially of a cylindrical heated barrel within which rotates a close-fitting Archimedean screw. The polyethylene pellets are fed to one end of the screw from a feed-hopper and are forced forward by the rotating screw, being melted partly by heat conducted through the walls of the barrel from external heater band sand partly by frictional heat generated by the shearing action of the screw. The molten and compacted polymer is then forced through an annular die as a thin tubular film, cooled and hauled off by nip rolls
The functions of the blown film die are to meter the polymer melt at constant pressure and uniform rate, and to transform it into a thin-walled tube, while maintaining uniformity of the melt temperature.
For blown film extrusion, the die comprises a metal outer body and an internal mandrel to form an annular aperture through which the molten polymer is forced to produce a tubular extrudate. The lips of the die are in the form of hardened-steel rings which can be integral with the mandrel and body but more often are bolted on to allow for replacement. The die is heated to maintain uniform melt temperature. Air for inflating the film bubble is introduced via a channel in the core of the mandrel.
The extruded polyethylene tube on exiting the die is inflated into a bubble of the desired diameter and film thickness by means of an internal injection of air introduced through the die mandrel at a pressure of 15 to 35 kPa. This air is trapped within the
12
film bubble formed between the die and the nip rolls. The ratio of the diameter of the bubble relative to the diameter of the die is known as the blow-up ratio.
Blow-up ratios as low as 1.5:1 can be used but these can lead to excessive machine direction orientation. Generally blow-up ratios between 2:1 and 3:1 are used. Higher blow-up ratios may lead to bubble instability problems and film creasing
BUBBLE COOLING
The film cooling process is very important because the cooling can affect the output rate, gauge uniformity, film density, and a number of film properties. The cooling system has four main functions:
1. To remove heat from the melt exiting the die and cool the film bubble to the solid state, so that it can be subsequently flattened and wound-up.
2. To stabilize and support the bubble on its exit from the die and minimize gauge variations.
3. To control the film density and a number of film properties including impact strength, tear strength and optical.
4. To determine the maximum output rate at which the film can be produced without blocking problems.
5. To prevent blocking, the temperature of the film reaching the nip rolls should be less than 40°C
As the film exits from the die annulus, it is in the molten state and must be cooled as soon as possible to stabilize the bubble and achieve a low degree of crystalline. The freeze line or frost line is the ring-shaped zone where the polymer solidifies after being cooled from the molten state and the bubble reaches its final diameter.
The basic form of cooling unit is an air ring which is fitted above the die. The air ring is designed to direct an air stream uniformly onto the exterior circumference of the film bubble as it emerges from the die. For maximum cooling efficiency, a combination of a high volume of low pressure air at the highest practical velocity must be used. It should not be an air blast of such force as to damage the bubble or to induce flutter. Any variations in the air temperature or flow rate around the
13
circumference of the air ring will give rise to non-uniform cooling rates and as a consequence, irregularities in the bubble and poor film thickness tolerance.
COLLAPSING THE BUBBLE
Prior to entering the nip rolls, the film bubble is collapsed into a flattened tube by means of a pair of angled collapsing frames or boards (sometimes called the A-frame or bat wings). These can take various forms and can be either of solid or hollow construction, or in the form of rollers. Friction between the film and the surfaces of the collapsing system should not be too high, as this will cause dragging or ‘grabbing’ of the film, giving rise to wrinkles and creasing. This effect becomes more noticeable if the film is hot or the area of contact between the boards and the film is too large. It can largely be overcome by slightly roughening the surfaces or using coatings to reduce heat build-up and film drag. Each collapsing frame should be aligned tangentially to the nip roll and positioned symmetrically relative to the vertical
Nip Rolls
The collapsed bubble passes through nip rolls which flatten the tubular film before the wind-up stage, trap the inflation air in the film bubble, and regulate the take-off speed of the film. The nip roll assembly comprises two rollers, typically one constructed of steel and the other covered with a resilient material such as rubber, to take up flaws in the film. The nip rolls should be mounted vertically above the extrusion die, at a height of at least two meters, and directly in line with the collapsing frames. When only the conventional air cooling ring is used for cooling the film, the height of the nip rolls above the die has a marked effect on the film production speed, more after-cooling being obtained with higher nip rolls. However very high nip rolls can lead to bubble instability, especially when extruding LLDPE polymers.
The pressure between the two rolls should be even along their length and just sufficient to maintain the steady linear take-off speed and prevent escape of air from the film bubble. If the nip roll pressure is too high, blocking and weak edge-folds will result. Blocking will also occur if the film entering the nip rolls is too hot.
Slitting: If sheet film is required, the lay-flat is slit at its edges or at any points across its width to form a number of reels of the desired size. The edge trim and off-cuts so
14
formed can be removed with a vacuum system. The amount of this scrap should be minimized to reduce waste and it is often prudent to reclaim it.
Slitter Treater
TREATMENT OF POLYETHYLENE FILM
The surface of polyethylene film is highly non-polar and inert because of the hydrophobic chemical nature of the polymer. This means that the receptivity of the film surface to inks, coatings, adhesives, etc. is poor and adhesion of these materials to the surface is unsatisfactory. This non-polar nature of the surface is the biggest limitation in the subsequent processing (printing, adhesive lamination) of the film for high quality packaging applications. Traditionally, surface receptivity has been considerably improved by electrical corona discharge treatment, which oxidizes the surface, increases the polarity, and provides acceptable adhesion for subsequent printing and laminating operations.
ADDITIONAL SETUP TO ACHIEVE LOWER MICRON STABLIZATION AND WASTE REDUCTION
As the film passes through dandy free rolls to rewind axis, there is a setup of two/ three vertical blade assembly for removal of extra or non-required or GSM variation prone area removal. That trimmed length or material sent to an assembly especially designed to shred the same into FLAKES (very little pieces) and next to this process, a motor operated blower fan with high air pressure to send these FLAKES travels through a pipeline in to the hopper of the middle layer online. It helps to control the heat the thinner layer from bursting.
Die GAP plays an eminent role to control, stabilize and alteration the thinner gauge.
Chilled air provided for better cooling and controlling the thin gauge bubble.
Online fully automatic gauge controlling system incorporated to control the gauge variation of the thinner film.
So accordingly, the present invention provides an improved and environment-friendly polyethylene film with modified properties, and a process for manufacturing thereof, said film having a wider range of thickness, suitable for higher range of applications, wherein said film is having low density polyethylene (LD), high density polyethylene
15
(HD) and linear low density polyethylene (LLDPE) as main components, and said film is prepared by extrusion process using machines well known in the art at highly modified process parameters.
In an embodiment, said film is manufactured having a wider thickness range, from as low as 7.5 micro meters up to 15 micro meters using highly modified process parameters.
In an embodiment, the preferred ratio is which said ingredients are used is preferably as LD: HD: LLDPE at 1 :2 :2.
In an embodiment, even with highly reduced thickness, said film requires the same quantity of sealant applications for using in same applications as of thicker films.
In an embodiment, said process for manufacturing said film comprises vertical blown film extrusion, by following the steps of: (a) melting the raw material polymers pellet form so as to form a continuous, viscous liquid; (b) extruding the molten plastic as obtained in step (a) through an annular die; (c) injecting air through a hole in the center of the die, so that the pressure makes the extruded melt to expand into a bubble; at the same time replacing the air entering the bubble with the air leaving it; so that even and constant pressure is maintained so as to ensure uniform thickness of the film; (d) pulling the bubble continually upwards from the die and blowing a cooling air ring blow into the film and alternatively, cooling the film from the inside using internal bubble cooling so as to reduce the temperature inside the bubble, while maintaining the bubble diameter; (e) after solidification at the frost line, moving the film moves into a set of nip rollers to collapse the bubble and flatten it into two flat film layers; (f) rolling the film through a series of rolls so there is uniform tension in the film and optionally passing film through a treatment in between depending on the application; (g) finally slitting the film to form one or two films, or surface treating the film to obtain the final product as per the requirement.
In an embodiment, said process for manufacturing the film comprises a temperature of 250 to 300 degrees for melting and polymerization with bubble formation taking place at the top of the layer, in a way that the die gap, process, gauzing and other factors associated are so optimized that even when drying takes place for molten film using high temperature, the thin film bubble DOES NOT BURST and a stable film without any wrinkles is obtained having thickness as low as 7.5 micro meter.
16
In an embodiment, said process comprises a die gap which efficiently controls, stabilizes and alters the thinner gauge and also with chilled air being used for better cooling and controlling the thin gauge bubble with the involvement of fully automatic gauge controlling system to control the gauge variation of the thinner film.
In an embodiment, said process comprises of controlling the thickness of the film by changing the speed of the nip rollers.
In an embodiment, said process comprises running the machine at a speed as that used for manufacturing a film with higher thickness; and using an auto gauging system developed for controlling and monitoring the properties of the film being manufactured.
In an embodiment, said process for manufacturing said film comprises preferably an air-ring as basic form of cooling unit which is fitted above the die, said ring designed to direct an air stream uniformly onto the exterior circumference of the film bubble as it emerges from the die.
In an embodiment, said process as developed in this invention preferably uses air chillers instead of blowers for cooling off the film.
The present invention provides an improved and environment-friendly polyethylene film with modified properties, and a process for manufacturing thereof, substantially as hereinbefore described with reference to the accompanying specification, drawings and any of the claims.
17
Advantages of the invention:
The polyethylene film can be manufactured in the wider thickness range of 7.5 to 15 microns using the same machinery and equipment of the invention as described in the specification.
The process is environment friendly as less amount of film serves the same purpose.
The reduction in thickness from the normal 18 microns to lower level offers it for very wide range of applications. The film can be used for many more industries.
There is less use of plastic, lesser wastage and hence environment friendly product and process of making it.
There are applications of re-using it.
There is less wastage of product.
Associated benefit of cost reduction.
There is no issue in sealant base application, the same amount and base is maintained even with lesser thickness.
The life cycle and shelf-life of packaged product increases.
It would be easier to transport the products with this film

We claim:
1. An improved and environment-friendly polyethylene film with modified properties, and a process for manufacturing thereof, said film having a wider range of thickness, suitable for higher range of applications, wherein said film is having low density polyethylene (LD), high density polyethylene (HD) and linear low density polyethylene (LLDPE) as main components, and said film is prepared by extrusion process using machines well known in the art at highly modified process parameters.
2. The improved and environment-friendly polyethylene film as claimed in claim 1, wherein said film is manufactured having a wider thickness range, from as low as 7.5 micro meters up to 15 micro meters using highly modified process parameters.
3. The improved and environment-friendly polyethylene film as claimed in claim 1, wherein the preferred ratio is which said ingredients are used is preferably as LD: HD: LLDPE at 1 :2 :2.
4. The improved and environment-friendly polyethylene film as claimed in claim 1, wherein even with highly reduced thickness, said film requires the same quantity of sealant applications for using in same applications as of thicker films.
5. The improved and environment-friendly polyethylene film as claimed in claim 1, wherein said process for manufacturing said film comprises vertical blown film extrusion, by following the steps of:
a) melting the raw material polymers pellet form so as to form a continuous, viscous liquid;
b) extruding the molten plastic as obtained in step (a) through an annular die;
c) injecting air through a hole in the center of the die, so that the pressure makes the extruded melt to expand into a bubble; at the same time replacing the air entering the bubble with the air leaving it; so that even and constant pressure is maintained so as to ensure uniform thickness of the film;
d) pulling the bubble continually upwards from the die and blowing a cooling air ring blow into the film and alternatively, cooling the film from the inside using internal
19
bubble cooling so as to reduce the temperature inside the bubble, while maintaining the bubble diameter;
e) after solidification at the frost line, moving the film moves into a set of nip rollers to collapse the bubble and flatten it into two flat film layers;
f) rolling the film through a series of rolls so there is uniform tension in the film and optionally passing film through a treatment in between depending on the application;
g) finally slitting the film to form one or two films, or surface treating the film to obtain the final product as per the requirement.
6. The improved and environment-friendly polyethylene film as claimed in claim 5, wherein said process for manufacturing the film comprises a temperature of 250 to 300 degrees for melting and polymerization with bubble formation taking place at the top of the layer, in a way that the die gap, process, gauzing and other factors associated are so optimized that even when drying takes place for molten film using high temperature, the thin film bubble DOES NOT BURST and a stable film without any wrinkles is obtained having thickness as low as 7.5 micro meter.
7. The improved and environment-friendly polyethylene film as claimed in claim 5, wherein said process comprises a die gap which efficiently controls, stabilizes and alters the thinner gauge and also with chilled air being used for better cooling and controlling the thin gauge bubble with the involvement of fully automatic gauge controlling system to control the gauge variation of the thinner film.
8. The improved and environment-friendly polyethylene film as claimed in claim 5, wherein said process comprises of controlling the thickness of the film by changing the speed of the nip rollers.
9. The improved and environment-friendly polyethylene film as claimed in claim 5, wherein said process comprises running the machine at a speed as that used for manufacturing a film with higher thickness; and using an auto gauging system developed for controlling and monitoring the properties of the film being manufactured.
10.The improved and environment-friendly polyethylene film as claimed in claim 5, wherein said process for manufacturing said film comprises preferably an air-ring
20
as basic form of cooling unit which is fitted above the die, said ring designed to direct an air stream uniformly onto the exterior circumference of the film bubble as it emerges from the die.
11.The improved and environment-friendly polyethylene film as claimed in claim 5, wherein said process as developed in this invention preferably uses air chillers instead of blowers for cooling off the film.
12.An improved and environment-friendly polyethylene film with modified properties, and a process for manufacturing thereof, substantially as hereinbefore described with reference to the accompanying specification, drawings and any of the proceeding claims.