MULTILAYER FILM FOR PACKAGING
FIELD OF INVENTION
[0001] The present invention relates to a multilayer film for packaging of bitumen. In particular, the invention relates to a multilayer film that can withstand hot bitumen filling at 100°C with external cooling and dissolves into hot bitumen in the molten stage at 150°C.
BACKGROUND OF THE INVENTION
[0002] Bitumen, also known as asphalt, is a versatile construction material, which is widely used in road building, construction, waterproofing, roofing and other applications. Majority of bitumen produced worldwide is a result of distillation of crude oil through processes such as vacuum distillation process. Bitumen is a complex mixture of various substances, most of which are hydrocarbons that include asphaltenes, saturates, aromatics and resins and a host of other elements like sulfur and metals like iron, copper, calcium, aluminum among others. Bitumen is solid at room temperature and liquid at elevated temperature.
[0003] Transportation of bitumen is usually done either in bulk, where the molten bitumen is pumped into tankers and transported at high temperature in order to keep it in molten state for easy pumping out at the user end, or transported in containers such as drums. In case of bulk bitumen transportation from the refinery, hot bitumen at 150°C to 170°C is transferred into truck mounted tankers of 10MT or more capacity with superior insulation. The insulation is required to maintain the high temperature of the bitumen till it reaches the customer destination and the content can be pumped out from the tank without re-heating the bitumen. It is generally observed that up to 30 hours from the time of loading, bitumen is hot enough to be pumped out without reheating, beyond which it requires re-heating. Also, prolonged heating of the bitumen at an elevated temperature affects the properties of the bitumen in some instances.

[0004] If the bitumen is transferred in drums, it becomes solid at room temperature after filling and it has to be reheated in order to unload. Unloading of molten bitumen from drums involves a loss of 2-3% of bitumen, as it is practically impossible to unload the entire quantity of bitumen due to its high viscosity and stickiness. Another problem associated with the drum container is the disposal of the empty drums since these drums cannot be recycled due difficulty in removing the layer of bitumen sticking inside. Also the heavy weight of the drum and thereby addition of unnecessary freight adds up to the cost of transportation. Last but not the least, handling of the molten bitumen is a potential health hazard and according to the Shell Bitumen Handbook (5th edition), 50% of all the bitumen related accidents and loss of working days occur during the delivery of bitumen.
[0005] An alternative to using drums or other container based packaging/ distributing means for bitumen is the use of polymer bags and films. Conventional packaging materials like polyethylene and polypropylene do not melt and dissolve into bitumen so easily due to incompatibility of these materials with bitumen. They are often found to agglomerate and coalesce on the surface of molten bitumen, for example as disclosed in WO 93/07219. Making a homogeneous mixture of bitumen with such polyolefin type materials involves high energy shear mixing, which is both cost intensive and expects the customers to build facilities at their end. Even after shear mixing these polymers undergo phase separation and tend to separate and float at the surface while cooling at the ambient temperature.
[0006] It is therefore crucial for the poly pack to dissolve completely into the hot bitumen; else there is a possibility that it will choke the outlet pipe thereby preventing the molten bitumen to pass to the mixing chamber. Any accumulation of polymeric material resulting in clogging of the flow line into the tank would be unacceptable to the customer as it would add an extra step of removal of the accumulated polymeric material as is described in the WO publication no. 2004/096917, involving flushing of the undissolved polymeric materials and further attempting to incorporate it into the packaged material

during recycling. Such an extra step not only adds to overall costs but also increases inconvenience to the end user.
[0007] It is thus necessary to develop a polymeric film material which not only melts into bitumen at 150°C but is also compatible with bitumen and mixes easily without the help of any high energy mixing process. U.S. Patent 3,366,233 discloses the use of double-walled polymeric bags for bitumen packaging. The patent discloses the use of a two layer polypropylene/polyethylene sheets laminated either by using an adhesive or heat treating the surface the sheets. The sheets of the '233 patent suggest the incorporation of small amount of plasticizers such as tricresyl phosphate to facilitate the dissolution the polymeric bag into the melted bitumen.. The patent, however, does not disclose whether the double-walled polymeric bag can be used to fill molten bitumen at 100°C.
[0008] Few prior arts do discuss films that can melt and dissolve into bitumen at about 150°C but fail to withstand filling at 100°C. On the other hand, few films with high heat resistance can withstand temperature of 100°C during bitumen filling but do not melt at 150°C to dissolve into bitumen. [0009] Polyolefins like polyethylene and polypropylene are not compatible with molten bitumen. It is thus realized that the polymeric material should contain polar functional group in order to be compatible with bitumen melt. Ethylene/ester group of copolymers is one such example, comprising ethylene and a wide variety of esters like vinyl acetate, methyl acrylate, butyl acrylate etc. Among several ethylene/ester copolymers it is found that ethylene-vinyl-acetate copolymer (EVA) is particularly suited for this application. [00010] US 4894107 discloses a three layer packaging film consisting of outer and inner layers of 30-35% LLDPE and 65-70% EVA (and one inner layer of vinylidene chloride-methyl acrylate or vinylidene chloride-vinyl chloride as the oxygen barrier layer). Addition of LLDPE to the outer layer adds to the toughness to the film with significant reduction of the package failure.

[00011] WO 01/43962 discloses a four layer film in which the inner layer consists of a mixture of two types of EVA, plastomer of ethylene and a-olefin, VLDPE or LLDPE, followed by a oxygen barrier core layer, the abuse layer which is a combination of EVA, plastomers, ethylene and a-olefin, polybutene VLDPE or LLDPE, and the outer layer which is a combination of EVA, plastomers, ethylene and a-olefin, polypropylene, VLDPE or LLDPE. It was claimed that the addition of the VLDPE and LLDPE to the EVA improves the heat sealing properties.
[00012] US 6299984 discloses a five layer film containing the outer layer consisting of 50% LLDPE, 25% EVA (4.5% VA) and 25% MDPE, 0.1% silica and 0.3% Erucamide, Tie layer containing anhydride grafted LLDPE and polyamide core layer as barrier layer.
[00013] US 2008/0311261 discloses a three layer film for food packaging of which the sealant layer comprises of 44-72% of EVA and varying proportions of LLDPE, polybutylene.
[00014] However, the disclosures stated above either do not pertain to bitumen packaging or do not show a multilayer film that can easily withstand hot bitumen filling at 100°C with external cooling and completely dissolve into molten bitumen at 150-160°C without having any adverse effect upon the quality of the bitumen. Such citations typically state the application of EVA in multilayer film compositions. There is therefore a need of a multilayer film having the right composition for packaging and filling bitumen and melting into it at appropriate temperatures.
OBJECTS OF THE INVENTION
[00015] It is an object of the invention to provide a multilayer film
composition for packaging molten bitumen.
[00016] It is an object of the invention to provide a multilayer film
composition that dissolves completely into molten bitumen at 150-160°C.
[00017] It is an object of the invention to provide a multilayer film
composition that withstands hot bitumen filling at 100°C with external cooling.

[00018] It is an object of the invention to provide a multilayer film
composition that withstands rough handling.
[00019] It is an object of the invention to provide a multilayer film
composition that does not have any adverse effect upon the quality of the
bitumen.
[00020] It is an object of the invention to provide a multilayer film
composition that improves the quality of the bitumen.
[00021] It is an object of the invention to provide a multilayer film
composition that has good heat seal strength.
[00022] It is an object of the invention to provide a multilayer film
composition that can withstand the side effects of UV radiations.
[00023] It is an object of the invention to provide a multilayer film
composition that has high shelf life.
SUMMARY OF THE INVENTION
[00024] The present invention relates to a multilayer film composition for packaging bitumen. The multilayer film is developed to withstand hot bitumen filling at 100°C with external cooling and dissolve completely into molten bitumen at 150°C. The multilayer film comprises of an inner layer in contact with the bitumen comprising of 75-100% ethylene-vinyl acetate copolymer and 0-25% of a polymer selected from a group comprising of ethylene alpha-olefin copolymer and branched ethylene homopolymer and a plurality of outer layers comprising of 100% ethylene-vinyl acetate copolymers. The multilayer film composition further comprises of additives to improve the properties of the film. The invention also discloses a method of packaging hot molten bitumen using the multilayer film.

DETAILED DESCRIPTION OF THE INVENTION
[00025] The present invention is directed to development of a multilayer film for bitumen packaging at 100°C, with external cooling, wherein the multilayer film dissolves completely into the molten bitumen at a temperature range of 150-160°C. The film comprises of multiple layers, blown simultaneously and then merged together to form a single multilayer film, wherein the inner layer, also referred to as the contact layer hereinafter, comprises of ethylene-vinyl acetate (EVA) copolymers and a polymer selected from a group comprising of ethylene alpha-olefin copolymer and branched ethylene homopolymer. The film can further comprise of a plurality of outer layers.
[00026] In an embodiment, the multilayer film comprises of an inner layer and a plurality of outer layers. The inner layer can include 75-100% ethylene-vinyl acetate (EVA) copolymer and 0-25% of a polymer selected from a group comprising of ethylene alpha-olefin copolymer or branched ethylene homopolymer. Each of the plurality of outer layers can be 100% ethylene-vinyl acetate (EVA) copolymer.
[00027] In an embodiment, the EVA copolymer comprises of 75-85% by weight of ethylene comonomer and 15-25% by weight of vinyl acetate comonomer. The ethylene vinyl acetate copolymer can have a density in the range of 0.93-0.945 g/cm3 and MFI in the range of 2-2.5 g/10 min. [00028] The ethylene alpha-olefin copolymer comprises of linear low density polyethylene (LLDPE) and is derived from ethylene and comonomer selected from a group comprising C4-C8 alpha olefins. The linear low density polyethylene can be a homogeneous linear low density polyethylene or a heterogeneous linear low density polyethylene. In an embodiment, the ethylene alpha-olefin copolymer can have density in the range of 0.915 g/cm3 to 0.925g/cm3 and MFI in the range of 1.0-1.5 g/10 min.
[00029] The branched ethylene homopolymer, on the other hand, comprises of low density polyethylene (LDPE). The low density polyethylene can have a

density in the range of 0.92 g/cm3 to 0.93g/cm3 and MFI in the range of 3.5 -4.5 g/10 min.
[00030] Addition of the LLDPE and/or LDPE improves the heat seal strength as well as heat retention capacity of the bag during hot filling of the bitumen at 100°C. LLDPE and LDPE are heat sealing polymers and are used to heat seal two adjacent layers at a variety of time, pressure and temperature conditions. In an embodiment, the heat sealing materials can be any material conventionally used for heat sealing purposes.
[00031] In a preferred embodiment, the multilayer film is a three layer film, wherein the inner layer comprises of a blend of 75-100% ethylene-vinyl acetate copolymer and 0-25% of a polymer selected from a group comprising of ethylene alpha-olefin copolymer and branched ethylene homopolymer. The middle and the outer layers comprise of 100% ethylene-vinyl acetate copolymer. In another embodiment, the inner and the outer layer includes Slip and Anti-block additives (AB) in the form of Master-Batch. In yet another embodiment, the outer layer includes UV stabilizers.
[00032] Slip additives reduce the coefficient of friction between two adjacent film surfaces. Such reduction in the coefficient of friction helps in the easy handling of the film during packaging. Slip additives help the multilayer films to slide more easily over each other. The commonly used slip additives are fatty acid amides, of which erucamide is the most commonly used slip additive. Erucamide has a high thermal stability allowing it to be used at high processing temperature without the risk of getting degraded. Degradation of the slip additive imparts coloration to the film. Anti-block additives prevent blocking of the film surfaces. Blocking prevents smooth unwinding of the film roll during the packaging. With the addition of Anti-block additives, the multilayer film surface becomes rough thereby reducing the adhesion of the film surface. Inorganic solids such as silica and talc are generally used as Anti-block additives.

[00033] UV stabilizers are used to protect the films from prolonged exposure to the sunlight. Several UV stabilizers such as benzophenone and HALS are available for this application.
[00034] In an embodiment, the multilayer film composition can have an average thickness of about 150-300 micron. Seal strength of the inner layer is at least 5 N/25 mm according to ASTM F88.
[00035] Tensile strength at break of the film is at least 10 N/mm2 (machine direction and transverse) according to IS 2508-1984. Preferable range for the tensile strength is between 10-20 N/mm2 (L/W) and 12 - 22 N/mm2 (T/W). Elongation at break of the film is at least 500 % (longitudinal and transverse) according to IS 2508-1984 and preferably in the range of 645 - 900 % (LAV) and 740 -985 % (T/W). In another embodiment, the maximum Co-efficient of Friction for the film is 0.1 according to IS 2508-1984 and preferably in the range of 0.05-0.09.
[00036] In one preferred embodiment, a three layer film of 100% EVA in the inner and/or contact layer is prepared with 1000 ppm each of Slip, Anti-block additives.
[00037] In another preferred embodiment, a three layer film with the inner layer including 1-50%, more preferably 5-15% branched ethylene homopolymer (LDPE) and 99-50%, more preferably 95-85% EVA, along with 100 ppm each of Slip and Anti-block additives is prepared. The middle layer includes 100% EVA resin. The outer layer includes 100% EVA along with 100 ppm each of Slip, Anti-block additives and UV stabilizer. [00038] In yet another preferred embodiment, a three layer film has been described with the inner layer including 1-50%, more preferably 5-15% ethylene alpha-olefin copolymer (LLDPE), and 99-50%, more preferably 95-85% EVA, along with 100 ppm each of Slip and Anti-block additives. The middle layer includes 100% EVA resin. The outer layer includes of 100% EVA along with 100 ppm each of Slip, Anti-block additives and UV stabilizer. [00039] Each film of distinct composition was subjected to various property analyses such as for compatibility and/or solubility into molten bitumen at

150°C. Property analysis of the resultant bitumen obtained thereof was also done.
[00040] Addition of branched ethylene homopolymer (LDPE) and ethylene alpha-olefin copolymer (LLDPE) to the inner and/or contact layer imparts higher heat-seal strength and heat retention temperature to the inner layer. The purpose of adding Slip and Anti-block additives to the inner and/or contact layer of the film is to reduce the coefficient of friction and blocking of the film surface that in turn helps easy packaging. The purpose of addition of UV stabilizer in the outer layer is to increase the shelf life of the film and the material contained therein. The purpose of adding a third layer is to improve the strength of the film and to minimize the use of additives.
EXAMPLE
The present invention is further explained in the form of following examples. However, these examples should not be construed as limiting the scope of the invention.
EXAMPLE 1
A three-layer polymer film was blown using a three screw extruder film blowing plant. Thickness of each layer was kept at approximately 60 micron. Blowing of the polymer film was done using a three layer plant of extruder size 1.5 m length and 45 cm diameter, consisting of four heating zones. The extruder temperatures were maintained between 150- 200°C and the speed was maintained at 80 RPM. The various compositions of the films are given in Table-1.
Bitumen (60/70) or (80/100) filled poly-bags of 2 Kg net weight were prepared. The proportions of the films with respect to the total weight of the bags were kept approximately 1%. The filled poly-bags, when solidified at room temperature, were melted at the temperature mentioned in Table-2. After 2.5 h, when the melting was complete, the bitumen samples were mixed thoroughly to ensure complete homogenization of the film into the bitumen. The resultant molten bitumen was then passed through a 5 mm mesh and poured into a drum. It was observed that the entire quantity of the resultant molten bitumen passed through the mesh without any trace of the film on the mesh, or without choking the mesh. No phase separation was observed even after a week of dissolving the film into molten bitumen. The bitumen samples were tested for softening point, elastic recovery and penetration and compared with the properties of the base bitumen. To illustrate the effect of mechanical agitation on the quality of the bitumen samples with the molten film, the samples were further subjected to mechanical agitation using overhead stirrer for 20-30 min, and were tested for the above properties.
Table 1: Composition of the various films
(Table Removed)

In a separate set of trials, 10 Kg poly-bags were tested for filling hot bitumen at 100°C using a sprinkler assembly. The empty poly-bags were attached inside the inner-cage of the assembly, and water was sprinkled to the outer wall of the empty bag using the sprinkler nozzles attached to the outer cage of the assembly. 10 Kg hot bitumen at 100°C was poured into each poly-bag through a funnel and allowed to settle at the bottom. The bag was sealed from the top and allowed to cool. The poly-bag filling trials had more than 99% success. Various compositions of the films tested are given in the Table-1 and their respective properties are given in the Table-2.
Table 2: Properties of the films
(Table Removed)

Table-3: Analysis of the bitumen samples with Bitumen 60/70
(Table Removed)

Table-4: Analysis of the bitumen samples with Bitumen 80/100
(Table Removed)

ADVANTAGES OF THE INVENTION
(1) The present invention describes a multilayer film composition that easily dissolves into molten bitumen at 150-160°C and withstands hot bitumen filling at 100°C with external cooling.
(2) The multilayer film composition withstands rough handling and does not have any adverse effect upon the quality of the bitumen.
(3) The multilayer film composition has good heat seal strength and high shelf life.

WE CLAIM
1. A multilayer film composition for packaging molten bitumen
comprising,
an inner layer comprising of 75-100% ethylene-vinyl acetate copolymer and 0-25% of a polymer selected from a group comprising of ethylene alpha-olefin copolymer and branched ethylene homopolymer; and
a plurality of outer layers comprising of 100% ethylene-vinyl acetate copolymers.
2. The multilayer film composition as claimed in claim 1, wherein the ethylene-vinyl acetate copolymer comprises 75-85% by weight of ethylene comonomer and 15-25% by weight of vinyl acetate comonomer.
3. The multilayer film composition as claimed in claim 1, wherein the ethylene alpha-olefin copolymer comprises of linear low density polyethylene derived from ethylene and comonomer selected from a group comprising C4-C8 alpha olefins.
4. The multilayer film composition as claimed in claim 1, wherein the branched ethylene homopolymer comprises of low density polyethylene.
5. The multilayer film composition as claimed in claim 1, wherein the multilayer film is a three layer film.
6. The multilayer film composition as claimed in claim 1, wherein the plurality of outer layers and the inner layer further comprise of slip and anti-block additives.

7. The multilayer film composition as claimed in claim 6, wherein the slip additives comprise of fatty acid amides.
8. The multilayer film composition as claimed in claim 7, wherein the fatty acid amides comprise of erucamide.
9. The multilayer film composition as claimed in claim 6, wherein the anti-block additives are selected from silica and talc.
10. The multilayer film composition as claimed in claim 1, wherein the plurality of outer layers further comprises of UV stabilizing additives.
11. The multilayer film composition as claimed in claim 10, wherein the UV stabilizing additives are selected from benzophenone and HALS.
12. The multilayer film composition as claimed in claim 1, wherein the multilayer film is sealed into poly-bags.
13. The multilayer film composition as claimed in claim 12, wherein the multilayer film sealed poly-bags are filled with hot bitumen at 100°C with external cooling.
14. The multilayer film composition as claimed in claim 1, wherein the multilayer film completely dissolves into molten bitumen in the temperature range of 150 - 160°C.
15. The multilayer film composition as claimed in claim 1, wherein the multilayer film has an average thickness in the range of 150-300 micron, tensile strength at break of at least 10 N/mm2 (L/W) and 10 N/mm2 (T/W), and elongation at break of at least 500% (L/W) and 500% (T/W).

16. The multilayer film composition as claimed in claim 1, wherein the inner layer has a maximum coefficient of friction of 0.1 and seal strength of at least 5 N/25 mm.
17. The multilayer film composition as claimed in claim 1, wherein the multilayer film composition when melted into bitumen grade 60/70 at 150-160°C gives a resultant bitumen having softening point value in the range of 51.5°C - 54.1°C, elastic recovery value in the range of 23 -32%, and penetration value in the range of 55-67.
18. The multilayer film composition as claimed in claim 1, wherein the multilayer film composition when melted into bitumen grade 80/100 at 150-160°C gives a resultant bitumen having softening point value in the range of 45.2°C - 49.5°C, elastic recovery value in the range of 18-26 %, and penetration value in the range of 68-88.
19. The multilayer film composition as claimed in claim 1, wherein the multilayer film withstands corona discharge.
20. A method of packaging hot molten bitumen, wherein said method comprises:
a. preparing poly-bags with a multilayer film composition, wherein
the multilayer film comprises of an inner layer comprising of a
blend of 75-100% ethylene-vinyl acetate copolymer and 0-25%
of a polymer selected from a group comprising of ethylene alpha-
olefin copolymer and branched ethylene homopolymer and a
plurality of outer layers comprising of 100% ethylene-vinyl
acetate copolymer;
b. attaching the poly-bags to a sprinkler assembly to sprinkle water
on outer surface of the poly-bags;
c. filling the poly-bags with the hot molten bitumen; and

d. allowing the bitumen to settle at the bottom, and sealing it from the top to cool.
21. The method as claimed in claim 20, wherein the weight of the multilayer film is about 1% of the weight of the filled poly-bags.