Molecular structure & Morphology of BOPP-PP

Biaxially oriented polypropylene (BOPP) film, one major type of biaxially oriented film, has been developed since the 1960s through the mass production of polypropylene. This film is today widely used in commercial packaging because of advantages that include high transparency, good moisture resistance, high mechanical strength and dimensional stability, low density, environmental friendliness, and printability. The production of BOPP film involves a sequential biaxial stretching process, in which films are cold drawn in two consecutive steps at two different temperatures. The temperatures of the orientation processes are usually chosen in the vicinity of the melting point of polypropylene. With the increasing commercial demand for BOPP film, wider and faster production lines have been introduced to produce films of high quality and competitive manufacturing price.

Various investigations on BOPP film and optimization of its production conditions have been extensively performed from many points of view, such as the effect of temperature, draw ratio, and morphology on the properties of the final product. The results indicate that the orientation processes can be optimized through varying the starting morphology, stretching conditions, and polymer structure. For improving the stretching process, various methods have been proposed, among which broadening of the molecular weight distribution (MWD) and additional molecules with ultra-high molecular weight has proven most successful. Consequently, the raw PP resin used for BOPP film production today is considerably designed. As is known, isotactic polypropylene (iPP) has a high tendency to crystallize when cooled from the melting state or precipitated from its dilute solution. From a general melt crystallization condition, iPP forms the so called α phase, which belongs to the monoclinic phase based on its threefold helical conformation, and possesses the unit cell dimensions of a=0.650 nm, b=2.096 nm, c=0.638 nm, β=99.3°. Similar to the crystallization process of most other polymers, the development of polypropylene crystals is determined by both nuclear formation rate and the subsequent several steps segment movements, which is definitely dependent on the molecular weight and structure.

Optical Microscope studies

Polarized light optical micrographs of two different PP samples (BOPP grade & Injection molded grade) indicate that number of crystal nuclei of BOPP grade is almost five times that of Injection molded PP within the same area. So the molecular structure and molecular weight distribution of the both PP samples will be quite different. Generally BOPP grade PPs have a small amount of ultra-high molecular weight component, and also a considerable amount of very low molecular weight part, while injection molded PP grades has a narrow molecular weight distribution as compared to BOPP-PP. Therefore, the abundance of crystal nuclei from BOPP-PP as shown in POM micrographs can be attributed due to the ultra-high molecular

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weight molecules in this sample, because only these PP chains can nucleate at a temperature that is still too high for the remaining chains to form nuclei, which gives rise to a large amount of nuclei as the sample cooled down from the complete melting state. In contrast, low molecular weight polymers require a long time to nucleate and finally result in a low number of large spherulites.

Polarized optical micrographs of BOPP and Injection Molded grade PP

TEM studies

If these two different PP samples are viewed under TEM, it can give better idea of their crystal morphologies. Both the morphology itself and electron diffraction patternindicate that the BOPP-PP crystals are dentrite, while Injection-PP crystals more or less develops into general spherulites. TEM images of BOPP-PP Injection-PP

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Fig showing TEM bright image at higher resolution

The reason we always obtain dentrite structures from BOPP-PP is due to the specially designed molecular weight distribution in the sample, in which a small number of polymer chains with ultra-high molecular weight crystallize first, followed by the crystallization process of the low molecular weight part, which attaches to the possible defects at the main bones. However, the proportion of ultra-high molecular weight component in the composite sample is so small that no complete backbone of a spherulite can be built. As a consequence, a kind of crystal morphology dominated by the uncompleted spherulites or dentrite structure is finally obtained. In contrast, the common spherulites are observed in sample injection-PP owing to its uniform molecular weight distribution, to which a classic crystallization process can be applied.

A material with a unique molecular weight distribution will result in some special characters of condensed state. Correspondingly, BOPP-PP possesses many unique advantages for orientation processing. For example, a small amount of ultra-high molecular weight polymer component can maintain stretching stability in the high orientation procedure owing to the improved rheologic properties. Moreover, a rapid crystallization process from the same component also results in a large number of nuclei, which finally leads to small but uniform crystals in the product. On the other hand, the low molecular weight part provides PP resin high mobility when it is stretched at high temperature and contributes to a BOPP film with better “feel” owing to its high crystallinity in the subsequent cooling process.

Morphology differences between the two crystals arise mainly for two reasons. First, BOPP-PP exhibits smaller crystal size than injection-PP, and all these tiny crystals

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are connected by an amorphous phase. Second, more defects exist in the BOPP-PP crystals than in Injection-PP crystals, in which long and complete lattices are frequently observed. These differences are mainly attributed to the different isotacticities between the two samples. The small number and random occurrence of ethylene monomers along the PP chain in the BOPP-PP sample destroy the intrinsically uniformed 31 helix structure of the isotactic polypropylene, which compel PP molecules to introduce more disordered packing sites into their crystals. Therefore, the obtained crystals possess many more defects and exhibit lower crystallinity and smaller crystal size. However, these characteristic crystal morphologies allow the final film product to exhibit high transparency to visible light, which is the fundamental requirement for high-quality BOPP film.

These special morphological characteristics, e.g., unique dentrite crystals, uncompleted spherulites, small crystal size, more defects in the crystal lattice, and so on, all satisfy the fundamental requirements for producing high-quality BOPP film and also make it more suitable for highly efficient processing in modern wide and fast production lines.

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There are two main principles for its production:

          The sequential manufacturing process is a two-step (1.longitudinal, 2. transverse) direction stretching process. The image given below shows the necessary machinery.  95 - 99 % of all biax stretching lines in the world are sequential lines.

          The simultaneous manufacturing process is a one-step stretching process. The film is stretched (oriented) in the longitudinal and transverse direction at the same time. The MDO and the TDO are combined to one unit. Because of its multiple advantages DMT's simultaneous stretching system (MESIM) will be the leading system in future

BOPP film, a part of the flexible packaging industry has emerged as one of the most popular, high growth films in the world. Lower costs and convenience has added to the growth of BOPP in the past few years, along with other flexible packaging materials. Moreover, the growth in demand for this film has been substantial both in developed as well as emerging markets on account of its recyclable nature and applications in a variety of non-food and food products.

The BOPP films are categorized into two different segments - commodity and specialty films. Among the two categories, the commodity film comprises of around 80% of the market, as this is categorized by low margins and price competitiveness, while the specialty films which are mainly consumed in the developed markets account for the remaining 20%. Recent years has seen the consumption of BOPP in different markets such as food industry, tape/ adhesives, tobacco, certain industrial products, among others.

The worldwide demand for BOPP film has been growing rapidly and since 2002, the global BOPP film industry has expanded by 72% with China accounting for the major production and consumption. Geographically, Asia was the largest market for BOPP, followed by Europe, and North America region. In the last few years, the emerging economies have witnessed an improved standard of living, urbanization and increased per capita consumption, and this has led to an increase in demand for BOPP films.

Although the BOPP industry has continued to witness growth on account of favorable demographic and market factors, it continues to be plagued by the problem of over capacity as well as raw materials prices, particularly PP resins

Jindal 

Latest state-of-the-art production lines from leading global equipment suppliers…

(CAPACITY IN TPA)

LocationBOPET Films

BOPP Films

Metalliser Plants

Polymer Chips

Coating Plant

Total Existing Capacity 127,000 180,000 45,000 111,600 4,500

Proposed expansions in financial year 2010-2011

- - 8600   -

Proposed expansions in financial year 201-2012

60,000 66,000 31,700 - -

Proposed expansions in 30,000 66,000 39,700 - -

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financial year 2012-2013

Total Capacity Post Current Expantions

217,000 312,000 125,000 111,600 4,500

Production

Cosmo Films has multi-location manufacturing facilities in India with an annual capacity of 56,000 MT in BOPP and 22,000 MT in thermal lamination.We have the most advanced BOPP equipments from DMT and Brueckner, as well as high speed slitters from Atlas and metallizer from Gallileo.We are adding a new line in Baroda of 40,000 MT per annum capacity in March 2009. The company has an installed capacity of 22000 MT of extrusion coated films, which are made in state of the art extrusion coating machines. The company has recently acquired a PVDC and Acrylic coating plant from France and has started making inroads in the high barrier packaging material as well as coated Label segments. Certified for ISO 9001 and ISO 14001, our products are popular in domestic and overseas markets. By following the principle of “Quality First, Customer Supreme”, Cosmo Films Ltd is devoted to being a world class packaging as well as thermal lamination film supplier. We have has our own captive power plant of 8 MW capacity in Aurangabad to ensure uninterrupted ,stable power supply to our production lines which is essential to get consistent quality of production as well as to meet committed deliveries to our esteemed customers. At Cosmo, we are very much concerned with the environment. At Baroda, we have opted for natural gas as power source.

Bopp Films FeaturesThe main feature of Bopp films are improved stiffness, high tensile strength, excellent optics and good water barrier properties. They range from 15 to 50 microns and are most commonly 15 to 30 microns. These bopp packaging films can be monolayer or coextuded structures, and transparent, opaque, or metallized. They also have the advantage of being non-toxic and fully recyclable.

In films, it is common to add antistatic, slipping and anti-blocking agents to avoid powder attraction, as well as the adhesion of one surface to another once the film is coiled and to facilitate their handling in processes that are performed after the extrusion.

BOPET FILMS

BIAXIALLY ORIENTED POLYETHYLENE TERAPTHALATE FILMS

FLEXPET™

Engineering Innovated Films,

Customised for Your Applications

Flex Films produce over 1,60,000 MT/Annum (350 Million Lbs)

of BOPET Films on its seven state-of-the-art plants.

RANGE 8 - 75 MICRONS AVAILABLE IN :

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PLAIN, ON-LINE CORONA TREATED, CHEMICALLY PRIMED, MATT, HEAT SEALABLE, METALLIZABLE,

ENVIRONMENT FRIENDLY, CLEAR, EXTRA CLEAR VARIETIES

FLEXPET™ Performing Properties

1. Superior mechanical properties

2. Improved resistance to chemicals

3. Good barrier against oxygen

4. Dimensional stability at elevated temperatures

5. Good optical clarity

6. Excellent surface treatment & primer coatings

7. Excellent surface smoothness

8. Resistance to abrasion

APPLICATIONS

1. Printing & Lamination

2. Metallizing

3. Industrial Coating

4. Thermal Lamination

5. Encapsulation

6. Hot Stamping

7. Cable Wrapping

8. Metallic Yarn

9. Electrical & Thermal Insulation

10. Pressure Sensitive Tapes

11. Heat sealable films

12. Lidding (Dairy products)

13. Release Film

14. Retort Applications

15. Silicon Coating

16. Extra clear film for Embossing & Holograms and many more

BOPP Films

BIAXIALLY ORIENTED POLYPROPYLENE FILMS

FLEXOPP™

Engineering Innovated Structures,

Customised for Your Applications

Flex Films produce over 72,000 MT/Annum (160 Million Lbs) of FLEXOPP™ on

three state-of-the-art PLC controlled lines.

FLEXOPP

RANGE 8 - 75 MICRONS AVAILABLE IN:

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PLAIN, HEAT-SEALABLE, METALLIZABLE, MATT, PEARLISED, CAVITATED, OVERWRAP, WHITE OPAQUE,

SPECIALTY FILM GRADES

FLEXOPP™ Performing Properties:

1. Good mechanical strength

2. Good chemical resistance

3. Good dimensional stability

4. Excellent barrier against water

5. Superior optical clarity

6. One or both side heat sealable

7. Good stiffness

8. RResistance to tear and abrasion

Applications

1. Packaging & Conversion

2. Metallizing

3. Industrial Coating

4. Printing and Lamination

5. Photo Albums

6. Encapsulation

7. Overwraps (CDs, Cigarettes)

8. Synthetic Papers

9. Holography

10. Adhesive Tapes

11. Textile Bags

12. Hot & Cold Antifog

13. Cables over wrap

14. Reams/Sheets wrapping

15. Confectionery packaging

16. Biscuit/Sandwich over wrap

17. Inner wrap

18. Embossing

19. Anti-fog (Food products)

20. Thermal Lamination

21. Shrink wrap and many more

CPP FILMS

Cast Polypropylene Films

FLEXCPP™

Engineering Innovated Films, customized for your applications

Engineering Innovated Films,

Customised for Your Applications.

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FLEXCPP™ is a highly dynamic and versatile film with exceptional gloss, excellent transparency, heat sealability,

good twisting property and excellent tear strength. Flex Film’s Cast Polypropylene film line has a capacity of

16,000 MT / Annum (35 Million Lbs) and can be supplied in widths upto 3000 mm, thickness range of 18-200

microns. The film can be offered with corona treatment on either one or both sides.

FLEXCPP™ RANGE 18 - 200 MICRONS

AVAILABLE IN :

PLAIN, HEAT-SEALABLE, METALLIZABLE, POLISHED, MIRROR, EMBOSSED SURFACE, GLOSS / MATTE

FINISH, STIFF, FLEXIBLE, CLEAR, OPAQUE VARIETIES

FLEXCPP™ Performing Properties:

1. New aesthetic possibilities for enhanced shelf appeal

2. Good gloss, transparency and heat sealability

3. Versatile structural properties

4. Good oxygen and moisture barrier

5. Customisable for special applications

Applications

1. Packaging & Conversion

2. Food Wraps

3. Lamination

4. Anti-fog

5. Candy/confectionery Wrap

6. Garment Bags

7. Retort Packaging

8. Stationery Packaging

9. Vacuum Metallization

10. Deep Freeze Application

11. Over Wrap

12. Floral Wraps, and many more

Metallized Films

BOPP, BOPET & CPP Films

FLEXMETPROTECT™

Engineering Innovated Barriers for your Applications

FLEXMETPROTECT™ high barrier metallized films is the ultimate solution for packaging a wide variety of

products that require extended shelf life apart from host of applications in the textile and capacitor industries.

Armed with seven state-of-the-art metallizers, with Plasma treatment facilities for better metal to film adhesion,

Flex Films is producing over 45,000 MT (100 Million Lbs) of Barrier Metallized films per annum with optical

density ranging from 0.4 to 3.5 upto a width of 2,850 mm.

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FLEXMETPROTECT™ RANGE

8-75 microns for BOPET 8-75 microns for BOPP 18-200 microns for CPP

APPLICATIONS

1. Converting and Laminating

2. Synthetic Zari & Metallic Yarn

3. Electronic Goods Packaging

4. Insulation Ducting

5. Decorative Applications

6. Lidding Applications

7. Embossing & Holograms

8. Sandwitch Lamination

9. Twist Wrap & Confectionery, and many more

Blown film versus the cast film processPrint

RSS

Modified: Friday, 09 January 2009 02:55 PM by mcurenton - Categorized as: Consultants Corner

» Blown film versus the cast film process

Blown film versus the cast film process Vol. 22 #3, December 1995 

Blown Film:

1. Better balance of film physical properties (MD vs TD): This is especially true of linear polyolefins like HDPE and even LLDPE. The monoaxial drawdown in the cast film process coupled with the web neck-in tends to give very splitty cast film from resins like HDPE. Physical properties of most resins, such as tear strength and elongation, tend to be more balanced in the blown film process thus promoting better dart drop impact strength.

2. Denser film, stiffer, with better barrier properties: The lower cooling rate in the blown film process allows more crystallite formation and a higher film density. This generally promotes higher film modulus and lower rates of moisture and gas transmission for the same polymer.

3. Less trim, regrind: Because of the tendency to edge bead and because many cast film line dies are fixed slot width, the amount of edge trim that must be taken is a much higher percentage of the total web. This becomes less so as the cast film line is wider. The bubble diameter in a blown film line can be adjusted to give just the right size for mini mum edge trim.

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4. Lower investment per annual pound for equipment: Because the line speed for a cast film line running the same lb/ hr. width and thickness is twice that for a blown film line, the takeoff drive system is more sophisticated and expensive. The web handling and winding systems are designed for much higher speeds, are more sophisticated, and more expensive. Automatic gage control is almost mandatory for cast film and adds about $200,000 to the price of a cast film line. Typical machinery investment numbers for blown film lines are 14 to 28 cents per annual pound of film production and for cast film lines is 25 to 50 cents.

5. Short runs are less expensive: Because the width is easily changeable on a blown film line, short runs are less ex pensive as less changeover scrap is run and less trim is taken during the run.

6. Thinner films can be made: Because the drawdown occurs in two directions (MD and TD), a thinner film can be made from the same resin on a blown film line than can be made on a cast film line. In addition, the web handling is easier because two thicknesses are transported to the winder at a slower line speed instead of one at a higher line speed.

7. 100% LLDPE does not have the drawdown instability problems with blown film that it has in cast film (draw down resonance).

Cast Film:

1. Better gage uniformity: The slot die can be adjusted from one point to the next and the adjustment can be made automatically by a computer control system.

Typical operating gage control for LDPE on a cast film line is within + or - 2%. Typical blown film gage uniformity is within + or- 10%, which can be reduced to = or - 5% with a good TD automatic gage control system. The viscosity of the melt in a cast film line is usually much less than that in a blown film line because of the resins used and because cast film generally is done at higher melt temperatures, (475 deg. F vs 375 deg. F).

2. Better optical properties: The quench rate at the casting roll contact area of a cast film line is much higher than the cooling rate in an air cooled blown film bubble. This tends to delay the crystallization and tends to make the film more amorphous with less haze and more gloss. Because of this, the transparency (see through) of cast film is much better. This is especially true for homopolymer polypropylene.

3. Better embossing quality: The embossing that can be done at the casting roll surface can be much finer in definition and have more retention with heat and time exposure than that which is done on blown film after the collapsing process.

4. Higher rates of production per total inch of web width are achieved in the cast film process because the cooling at the casting roll surface is so much more effective. Typical numbers for the blown film process are 10 to 20 lb/hr per inch of layflat tubing or 5 to 10 lb/hr per inch of bubble 

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circumference, depending on resin and film thickness. Typical rates for cast film are 15 to 30 lb/hr per inch of web width, usually three times that for blown film. For a given width of take off, the cast film line will usually run 50% more pounds per hour than a blown film line (the blown film line makes two thicknesses for one web width of production).

5. Lower density, softer film: The same characteristic cited as a disadvantage for cast film in item 2. under blown film can sometimes be an advantage, especially if soft drapable film is desirable.

6. Allows some resins not readily runnable on blown film to run: A good example is polypropylene homopolymer. In the air cooled blown film process, polypropylene homopolymer produces a very hazy splitty film because the crystallites are so large. Rapid quenching in the cast film process produces a clear, soft film that is very useful for dry goods packaging and photo album pages. Note: some tubular water or mandrel quench processes exist that can run PP homopolymer film. The cast film process can run resins with low melt strength, (typically higher melt index) whereas the blown film process requires those with higher melt strength. LLDPE is an exception here and must be modified to prevent drawdown resonance.

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Blown Film Extrusion - An IntroductionBy: Cantor, Kirk © 2006 Hanser Publishers