MMP Reportdsafasdf

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MMP Final Report Polyester Film Metallization Process Farhan Zafar Khan - 1445108 BhaweshRathi - 1345141 Submitted to Miss TanzilaYounas

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Transcript of MMP Reportdsafasdf

Page 1: MMP Reportdsafasdf

MMP Final ReportPolyester Film Metallization Process

Farhan Zafar Khan - 1445108

BhaweshRathi - 1345141

Submitted to

Miss TanzilaYounas

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ContentsIntroduction.................................................................................................................................................1

Film Extrusion..............................................................................................................................................1

Description of Polyolefin and polypropylene...........................................................................................1

Production of polyolefin (specifically LDPE).............................................................................................1

Blown Film Extrusion Process..................................................................................................................2

Description of process.........................................................................................................................2

Blown Film Extrusion Equipment.........................................................................................................2

Film Extrusion Equipment................................................................................................................2

Film Forming Dies............................................................................................................................5

Cooling Systems...............................................................................................................................7

Windup Equipment..........................................................................................................................7

Metallization Process..................................................................................................................................8

Description of metallization process:......................................................................................................8

Applications:............................................................................................................................................8

Description of the metallizer platform:...................................................................................................9

Coating trials conducted:.....................................................................................................................9

Optical Density Measurements:........................................................................................................10

Barrier measurements:......................................................................................................................10

Conclusion.................................................................................................................................................10

Works Cited...............................................................................................................................................11

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IntroductionThe purpose of this report is to describe the process for the production of metallized thin films used commonly in a variety of packaging applications from food to decorative wrapping papers.

Film Extrusion(Production of Polypropylene film by extrusion… BOPP and BOPET processes)

Description of Polyolefin and polypropylenePolyolefins are plastic resins which are polymerized from petroleum based gases. The two principal gases are ethylene and propylene which are used to make polyethylene and polypropylene respectively.

Polyolefins are classified as thermoplastics, which means that they can be melted, set and then melted again. In comparison, thermoset plastics cannot be remelted once they have been set.

Most polyolefin resins for film extrusion generally are used in pellet form. The pellets are about 1/8 inch thick and 3/16 inch in diameter, usually somewhat translucent and white in color. Polyolefin resins sometimes will contain additives, such as thermal stabilizers.

Production of polyolefin (specifically LDPE)Polyolefins are plastics made from high purity alkenes such as ethylene, propylene and butane. These gases are obtained from purification of gas from gas fields, or from refineries as by products. For high quality end products it is important that high purity gases be used as raw materials.

LDPE

To make LDPE (Low Density Polyethylene), high pressure,high temperature polymerization reactors are used. Ethylene gas, pumpedinto the reactors, is activated by acatalyst and polymerizes intopolyethylene. The LDPE formedflows to a separator where unused gas is removed. Next, the LDPEgoes to a compounding extruderwhere additives are added prior topelletizing.

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Figure 1: LDPE production process[1]

Blown Film Extrusion ProcessDescription of processThe film extrusion process occurs in a few steps. The resin in pellet form is added to an extruder, which melts and mixes the resin into a continuous form ready to be molded into a sheet. The extruder is heated in stages so that the resin is gradually melted, and a screw in the extruder helps to mix the resin and push it forward into the adapter. The adapter is a connection point between the extruder and the die. The die is the main step in this process. It is used to take the molten resin and convert it into sheet form. Many different types of dies exist and they are used for a variety of different compounds. The two most common ones, blown film dies, and cast film dies are discussed in the next section. After the resin has been converted to sheet form, it goes through a cooler to undergo sufficient cooling, and is then passed through a winding setup to be collected into rolls. Details of these equipment and processes are also discussed in the following section.

Blown Film Extrusion EquipmentThere are two basic methods used in the production of film, cast film, and blown film extrusion. In both of these methods, the resin is melted using heat and pressure in an extruder and then forced through a narrow slit in the die. The slit may be either a straight line or a circle. The resulting thin film is either in the form of a sheet or a tube. The equipment used in this process is described below.

Film Extrusion Equipment

ExtruderAn extruder consists of a hopper, a heated barrel, a rotating screw, a screen changer, a die adapter and a base.

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Figure 2: Standard extruder setup[1]

Hopper

Resins are droppedinto the extruder feed throatthrough a round or square funnel,called the hopper. An automaticloader on top of the hopperperiodically feeds resin into it.Two basic types of automatichopper feeding systems exist:volumetric feeders, which refill the hopperon a schedule based on theextrusion system’s output; andgravimetric feeders,directly feed resin into theextruder.

The hopper throat can be cooled using water to prevent pellets from sticking together. If an extruder is run at heat then during shut down, the feed screw must be kept turning until all of the resin has been cleared out, to prevent it from sticking and bridging over the gap.

Barrel

A barrel is a long tunnel where the heating processes for the resin take place, before sending it to the die to be shaped. Most barrels have smooth bores. However, for some low melting point resins, the mouth of the barrel may be water cooled and have helical grooves. This allows low melt resins to be processed at high extrusion rates.

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Figure 3: Barrel with screw.[1]

Heater

For fast extruder start-up,barrel heating is necessary andusually done by electrical barrelheating bands. They are PID controlled, respondrapidly, and are easy to adjust.The heater bands are distributedalong the barrel length in zones. Generally, the barrelis divided into three to six zones.Blowers in each zone decrease theheat when necessary to rapidlycool the barrel when the extruder isto be shut down. Water-cooledzones also are used by somemanufacturers for faster heattransfer.

Thermocouple

Thermocouples are inserted in the barrel wall, and insome cases into the melt, tomonitor processing temperature.Signals from the thermocouplesactivate temperature controllingmechanisms to regulate the heaterbands and cooling devices.

Screw

A motor-driven screw rotateswithin the barrel. Screw speedsrange from 50 to250 rpm. As the screw rotates, the resin is forced forward, the screwchannels become shallowerand the resin is heated, compressed, melted and mixed. The four basic sections of the screw are shown in the figure below.

Figure 4: Different sections of a screw[1]

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A long, properly designedscrew allows better melting andmixing of the resin, as well asbetter film appearance, closergauge tolerance and increasedproduction rate. Screws are specifiedby their length to-diameter(UD) ratio and compression ratio.Ideally, the screw should be at least24 times, as long as its diameter. A larger UDratio allows enhanced mixing. Thecompression ratio is the ratio of thechannel volume of one screw flightin the feed section to that of onescrew flight in the metering section.

Screen Pack and Breaker Plates

After traveling through the screw, the molten resin passes through a screen pack, the supporting breaker plate and through the adapter to the die.The functions of a breakerplate are to:• Support the screen pack• Reinforce the screen pack’s action• Develop back pressure• Straighten out the spiral flow ofthe melt caused by the screw• Serve as a melt seal betweenthe barrel and the adapter(which a loose breaker platecannot do)• Help align the barrel andadapter.

Adapter

The adapter guides the resin melt from the barrel to the die as quickly and uniformly as possible. Uneven flow would mean dead areas where some of the melt could be held back, excessively heated and decomposed chemically. A hinged collar generally serves to attach the adapter tightly to the barrel. Adapter heaters keep the adapter at a specified temperature. Maintaining the temperature of the melt when it leaves the extruder to be formed into film is very important. Melt temperatures can be checked by using athermocouple that extends throughthe adapter or die wall and into themelt stream.

Film Forming DiesThe film forming die is attached to the adapter. Its purpose is to smooth and complete melt flow, thus preventing resin degradation from overheating. The functions of the die are to:

Force the melt into a form approaching its final shape. Maintain the melt at a constant temperature. Meter the melt at a constant pressure and rate to the die land for uniform film gauge, with

allowance for gauge reduction.

The die consists of a body, mandrel or pin, heaters and lands. The die lands decrease the speed of the melt flow and build-up back pressure in the die and adapter. The die mandrel can beadjusted to change the die openingin order to control gauge uniformity.Most film extrusion dies are dividedinto heating zones and die heatersare automatically controlled.

Many different types of dies are available for the extrusion process. Some of them are:

Blown Film Dies Rotating Dies Coextrusion Blown Film Dies Cast Film Dies Coextrusion Cast Film Dies

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Blown Film Dies

In blown film extrusion, the melt is forced through spiral grooves around the surface of a mandrel inside the die and extruded through the circular die opening in the form of a thick-walled tube. The tube is expanded into a long “bubble” of desired diameter and decreased thickness. This expansion results from the volume of air inside the bubble, which is introduced into the tube through the center of the mandrel. Blown film dies have a number of circular heating zones. Most blown film dies for polyethylenes are positioned vertically to push the tube upward. However, downward extrusion also occurs.

The gap between the mandrel and the die ring ranges from 0.5 to 3 mm. In some dies, this opening can be changed by moving the mandrel lengthwise in the die. Most dies require a change in mandrels in order to adjust the die gap opening. This adjustment changes the extruded tube thickness. A wider ring opening increases output slightly, but due to uneven flow, it may make gauge control more difficult. It also tends to promote film snap-off, particularly when the film is drawn down to a gauge of less than 13 microns. Blown film dies can be as large as 80 inches in diameter, producing film with 125 inches or more of flat width.

Figure 5: Setup of a blown film die[1]

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Cast Film DiesThe most common cast film dies are the “keyhole” and “coat hanger” designs. In a keyhole die, the cross section of the manifold is constant. In a coat hanger die, the cross section decreases across the manifold from the center of the die to the outer edges.

The coat hanger die’s manifold distributes the incoming melt across a steadily widening flow. Then the die land forms the melt into its final thickness before the melt exits the die. Cast film dies can vary in size from a few inches to 180 inches in width. The larger the die, the more important film gauge control becomes. The die gap is the opening or distance between die lands. For film with a gauge of 1-3 mils (25-75 microns), the typical die gap is 20 mils (0.5mm). Usually, one of the die lands is adjustable to assist in controlling film gauge.

The output of film per inch of die width and the temperature of the die are usually higher in cast film extrusion than in the blown film process. Cast film die temperatures range from 450 to 550°F (230 to 290°C). Narrow multiple heating zones are used to maintain die temperature uniformity which is also an important factor in gauge control.

Cooling SystemsBlown Film Cooling System

The film bubble produced by the die in blown film extrusion is cooled using ambient chilled air. There are several ways to cool this bubble:

• By air from a single- or dual lipped air ring

• By adding air from single- or dual-lipped air rings inside the bubble to air from similar rings outside the bubble

• By water sprayed on the outside of a bubble that is extruded either downward or upward. This method is most often used with PolyPropylenehomopolymer.

Cast Film Cooling Systems

In the cast film process, the molten resin falls onto a water cooled chill roll. This chill roll may have a pattern or texture on it, which may be imprinted on to the film.

Generally in chill roll operations, the film is cooled by two or more chill rolls. This allows the film to be cooled in stages. For example, the first roll has a temperature between 40 and 65 C, and it takes out a lot of the heat from the film. Further cooling rolls are then set up to cool the sheet and their temperatures are set based on the initial cooling temperature.

Windup EquipmentAfter extrusion and cool down the next stage in film production is takeoff and windup. That is the plastic film is wound into rolls. The setup for blown film is shown below:

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Figure 6: Setup of a winding operation for blown film dies[1]

Metallization Process(Evaporated aluminum on polyester: optical, electrical, and barrier properties as a function of thickness)

Description of metallization process:We have produced aluminum films on polyester at various thicknesses using a high speed modern move to-roll metallizer and described them utilizing a scope of systems. This work is displayed in two papers. For this first paper, we have measured the optical, electrical, and boundary properties for every example as a component of aluminum film thickness what's more, time. We have additionally measured the variety in the optical thickness as a component of down web and cross web position on the substrate. The movies were created in thicknesses comparing to optical densities of around 0.5 to 2.5 in 0.5 OD steps which compares to physical thicknesses of around 6-40 nm. A partner paper (Part II) will depict a suite of diagnostic estimations to portray the film thicknesses and will examine the utility of film thickness in anticipating the optical and electrical properties of the movies.For several decades, aluminium thin films have been successfully deposited on various polymer base substrates for the following applications.[2]

Applications: Barrier protection Reflection/ absorption requirements (Optical) Low energy requirements (Electrical)

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Description of the metallizer platform:

The machine stage utilized for the metal thickness trials was a 2007 General Vacuum Equipment K4000 vacuum roll-toroll coater with a warm resistive PVD source. The machine had a greatest viable covering width of 1650 mm and can suit move distances across of up to 1000 mm. The most extreme line rate of the machine was 840 m/min.[3]

The vacuum chamber had two independently pumped zones, which worked at two distinctive weight administrations, specifically the winding zone and the dissipation zone. The pumping gathering for the winding zone comprised of a two stage mechanical blower framework (12865 m3/hr and a 4035 m3/hr) upheld by a variable pitched screw dry pump with a pumping pace of 630 m3/hr, and the vanishing zone is pumped by 3 x 10,000 lpm dispersion pumps upheld with a 4035 m3/hr mechanical blower and a further 630 m3 /hr screw dry pump. A polycold quick cycle water vapor cyro pump is likewise utilized in the vanishing zone with a hypothetical pumping pace of up to 300,000 l/sec.

Coating trials conducted:Five beginning covering trials were directed on a 12 micron crown treated polyethylene leatherette base substrate fluctuating the wire food rate to get the required optical thickness levels. The trial set is compressed in table

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Optical Density Measurements:OD estimations were taken in the vacuum move coater utilizing an as a part of line non-contact optical screen utilizing a 5 mm spot size at 626 nm wavelength outlined by General Vacuum Equipment Ltd. Sender and collector pitching was set to 100 mm and situated in-line over each evaporator watercraft. With the in-line optical screen adjusted with a guaranteed lens, the covering trials on the machine were directed in open circle control and the wire food rate was physically changed in accordance with accomplish the craved OD target level, to be specific 0.5, 1.0, 1.5, 2.0 and 2.5 OD. A static completely oxidized reference test of covered film was additionally situated in the measuring width of the pillar to guarantee the OD levels got were exact amid handling and didn't float with time, vacuum or temperature varieties.

Barrier measurements:Regular polymers utilized for bundling applications have penetration values for oxygen and water vapor that would either make them unsatisfactory for obstruction bundling or require to a great degree thick movies. Today thin film obstruction layers, for example, metal also, metal-oxides are utilized and give much lower dispersion coefficients than the polymerization.The warm dissipation of aluminum from an earthenware evaporator onto polymer movies is a standard strategy that has been around for a long time. Such movies are generally utilized for sustenance bundling, ornamental, intelligent and other specialized applications. For sustenance bundling, gas saturation is of awesome significance keeping in mind the end goal to augment the items time frame of realistic usability, and assurance against light, oxygen and water vapor saturation is vital. Amid the most recent fifteen years, the comprehension of the metallized film boundary advancement has enhanced, and expansive film hindrance properties can be appeared as far as fragrance, dampness and oxygen obstruction for an extensive variety of metallized movies.

ConclusionThe process for producing metallized films is highly technical and requires a number of precise steps so that the end product is of high quality. However, it is one of the most important and widely used processes in the production industry as the number of end products related to this manufacturing process is vast and it is linked to every other industry in one way or another.

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Works Cited

[1] Equistar, "A guide to polyolefin film extrusion".

[2] "Wikipedia," Wikipedia, 2015. [Online]. Available: https://en.wikipedia.org/wiki/Metallised_film. [Accessed 2015].

[3] R. A. Nick Copeland, "Evaporated aluminium on polyester: optical, electrical, and barrier properties as a," 12/09/2010.

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