DESC:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(Section 10 and Rule 13)

1. TITLE OF THE INVENTION:
SHRINK FILM

2. APPLICANT:
GARWARE HI-TECH FILMS LIMITED, an Indian company of the address Garware House, 50-A, Swami Nityanand Marg, Western Express Highway, Vile Parle(east), Mumbai-400057, Maharashtra, India.

The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF INVENTION
[1] The present disclosure relates to a method to prepare a film. More specifically, the present disclosure relates to a method to prepare a shrinkable co-polyester film having low density.
BACKGROUND OF INVENTION
[2] Films (or labels) are provided over packaged products (say, containers, bottles, boxes, etc.) to communicate product details as well as to enable the end consumer to identify said products. For example, dairy products, beverages, cosmetic formulations, pharmaceutical formulations, etc. have one or more labels provided over the said packaged products.
[3] While disposing or recycling such product containers having conventional films, numerous problems are observed. Firstly, it is very difficult to separate a conventional film from the container itself. This is problematic especially in the recycling industry, where it is imperative to separate the film from the respective container to obtain a higher quality recycled product (in terms of purity). For example, during container recycling process, residual labels can pollute (or adulterate) the product.
[4] Secondly, the conventional film fails to provide protection to the contents of the container from photo degradation, especially when the container is transparent. This leads to short shelf life of the product.
[5] In addition, the conventional films are themselves transparent thereby requiring extensive amount of ink for printing any form of graphical illustration. The said phenomenon not only contributes to solvent pollution but also compromises the innate mechanical properties of the film. Thus, reducing the durability of the film.
[6] Further, conventional films generally exhibit high noise, easy tearing, poor surface opacity/homogeneity (e.g., streakiness), or a combination thereof.
[7] Therefore, there is a need for a film which overcomes the aforementioned challenges associated with the conventional films.
SUMMARY OF INVENTION
[8] Particular embodiments of the present disclosure are described herein below with reference to the accompanying drawings, however, it is to be understood that the disclosed embodiments are mere examples of the disclosure, which may be embodied in various forms. Well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure in virtually any appropriately detailed structure.
[9] The present disclosure relates to a method of preparing a shrink film having low density. The method commences by polymerizing an ester to obtain a co-polymer. The co-polymer is homogenously mixed with at least one master batch to form a first mixture, the master batch including additives, optical brighteners, stabilizers, colorants, compatibilizers, pinning master batches, polypropylene based master batches. The first mixture is pre-heated at a pre-defined temperature for a pre-defined time period. The first mixture is extruded at a pre-defined temperature to obtain a melt. The melt is cooled to obtain a film having a pre-defined thickness ranging from 150 microns to 300 microns. The film is oriented by passing the film through a machine direction oven (MDO) set at a first pre-defined temperature ranging from 60 °C to 65 °C. Then, the film is pre-heated inside a transverse direction oven (TDO) set at a second pre-defined temperature ranging from 100 °C to 120 °C. The film is stretched at a third pre-defined temperature at a pre-defined stretch ratio in a transverse direction as the film travels in a machine direction at a pre-defined line speed. The third pre-defined temperature ranges from 80 °C to 100 °C. The pre-defined stretch ratio being 4 – 5 times an initial width of the film. The film is annealed at a fourth pre-defined temperature. The film has homogenously spread micro-voids, and a pre-defined thickness ranging from 40 microns to 60 microns.
BRIEF DESCRIPTION OF DRAWINGS
[10] The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the apportioned drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the disclosure is not limited to specific methods and instrumentality disclosed herein. Moreover, those in the art will understand that the drawings are not to scale.
[11] Fig. 1 depicts a method 100 to prepare a co-polymer to be used for making a low-density shrink film in accordance with an embodiment of the present disclosure.
[12] Fig. 2 depicts a method 200 to prepare a low-density shrink film in accordance with an embodiment of the present disclosure.
[13] Fig. 3 depicts percentage shrinkage of the low-density shrink film as a function of temperature in accordance with an embodiment of the present disclosure.
[14] Fig. 4 depicts percentage transmittance of light through the low-density shrink film as a function of wavelength of the light in accordance with an embodiment of the present disclosure.
DETAILED DESCRIPTION OF THE DRAWINGS
[15] Prior to describing the invention in detail, definitions of certain words or phrases used throughout this patent document will be defined: the terms "include" and "comprise", as well as derivatives thereof, mean inclusion without limitation; the term "or" is inclusive, meaning and/or; the phrases "coupled with" and "associated therewith", as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have a property of, or the like. Definitions of certain words and phrases are provided throughout this patent document, and those of ordinary skill in the art will understand that such definitions apply in many, if not most, instances to prior as well as future uses of such defined words and phrases.
[16] Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment, but mean “one or more but not all embodiments” unless expressly specified otherwise. The terms “including,” “comprising,” “having,” and variations thereof mean “including but not limited to” unless expressly specified otherwise. An enumerated listing of items does not imply that any or all of the items are mutually exclusive and/or mutually inclusive, unless expressly specified otherwise. The terms “a,” “an,” and “the” also refer to “one or more” unless expressly specified otherwise.
[17] Although the method steps of exemplary embodiments of the disclosed method may be described in a particular, sequential order for convenient presentation, it should be understood that the disclosed embodiments can encompass an order of method steps other than the particular, sequential order disclosed. For example, method steps described sequentially may in some cases be rearranged or performed concurrently. Further, descriptions and disclosures provided in association with one particular embodiment are not limited to that embodiment, and may be applied to any embodiment disclosed herein. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed system, method, and apparatus can be used in combination with other systems, methods, and apparatuses.
[18] Furthermore, the described features, advantages, and characteristics of the embodiments may be combined in any suitable manner. One skilled in the relevant art will recognize that the embodiments may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments. These features and advantages of the embodiments will become more fully apparent from the following description and apportioned claims, or may be learned by the practice of embodiments as set forth hereinafter.
[19] The present disclosure discloses a method to prepare a low-density shrink film (or film). The film may be used as a product label on a container of various consumer goods, for example, dairy products, beverages, cosmetic formulations, pharmaceutical formulations, etc. The film of the present disclosure has a low density, thus, floats on water.
[20] Now referring to the figures, Fig. 1 illustrates an exemplary method 100 to prepare a co-polymer (or co-polyester). The co-polymer acts as a precursor to prepare the film of the present disclosure. In an exemplary embodiment, the co-polymer includes Polyethylene terephthalate glycol (PETG).
[21] Although the present disclosure is described with the example of PETG, use of other co-polymers as a precursor to prepare the film is within the scope of the teachings of the present disclosure. For example, at least one co-polymer may be selected from a group of Polyethylene terephthalate glycol (PETG), Polypropylene (PP), Polyethylene, or a blend thereof.
[22] The method commences at step 101 by esterifying at least one dicarboxylic acid, and at least one diol component to produce an ester. The dicarboxylic acid is selected from a group of Terephthalic acid (PTA), Isophthalic acid, Orthophthalic acid, DimethylTerepthalate or a combination thereof. The diol component is selected from a group of Monoethylene glycol (MEG), Diethylene glycol (DEG), Neopentyl glycol (2,2-Dimethyl 1,3-Propanediol), Cyclo hexane di methanol (CHDM), or a combination thereof. The ester thus produced may chemically vary depending upon the dicarboxylic acid and the diol component used.
[23] The esterification may be carried out at a pre-defined temperature and pressure. The pre-defined temperature ranges from 250 °C to 265 °C. The pre-defined pressure ranges from 1 kg/sq.cm to 2 kg/sq.cm. In an exemplary embodiment, the esterification is carried out at 260°C and 1.2 kg/sq.cm.
[24] In an exemplary embodiment, the esterification is carried out between 100 mole% pure Terephthalic acid (on acid content basis), 20 mole% Neopentyl glycol or 1,4-cyclohexane-dimethanol, 71 mole% ethylene glycol and 9 mole% diethylene glycol (on diol basis) to produce 100 mole% of Bishydroxyl terephthalate (BHET). In other words, Bishydroxyl terephthalate (BHET) is an exemplary ester obtained from step 101.
[25] At step 103, the ester obtained at step 101 is subjected to a polymerization process to obtain the co-polymer. In an exemplary embodiment, the polymerization process is carried out in two stages, namely, a first stage i.e., a pre-polymerization stage, and a second stage i.e., a final polymerization stage.
[26] At least one additive at least one catalyst, at least one stabilizer are added and/or homogenously mixed with the ester to obtain a first product. The first product obtained after homogenous mixing ensures homogeneity in the material properties and quality of the resultant co-polymer. The additive(s) is added in a predefined concentration per unit weight of the ester. The additive(s) may be selected from silicon, titanium dioxide, or a combination thereof. Silica and/or titanium dioxide, as an additive, improves frictional properties of the ester.
[27] The stabilizers may be added in a pre-defined concentration per unit weight of the ester. The predefined concentration ranges from 0.04% (w/w) to 0.1% (w/w). The stabilizers may include at least one of organic phosphates such as triphenyl phosphate, trinonylphenyl phosphate, Trimethylphosphate, phospheric acid and the like. The stabilizers provide thermal stability to the resultant co-polymer.
[28] In an exemplary embodiment, 0.045 grams of silica, and 0.09 grams of triphenyl phosphate are added (and mixed) per 100 grams of Bishydroxyl terephthalate (BHET).
[29] The catalyst aids in the polymerization of the ester. The catalyst may include a compound selected from antimony trioxide, antimony triacetate, germanium dioxide, etc. The catalyst is added in a predefined concentration per unit weight of the ester. The predefined concentration ranges from 0.03% (w/w) to 0.06% (w/w). In an exemplary embodiment, 0.045 grams of antimony trioxide is added (and mixed) per 100 grams of bishydroxyl terephthalate (BHET).
[30] Additionally or optionally, the catalyst may be diluted in a diol component before being added to the ester. In an exemplary embodiment, antimony trioxide is diluted with monoethylene glycol (MEG) before being added to the bishydroxyl terephthalate (BHET).
[31] In the first stage, the first product is subjected to a first pre-defined temperature at a first pre-defined pressure for a first pre-defined time period to obtain a pre-polymerized product. The first pre-defined temperature ranges from 250 °C to 290 °C. The first pre-defined pressure ranges from 0.5 mm Hg to 3 mm Hg. The first pre-defined time period ranges from 120 minutes to 165 minutes. The first stage of the polymerization process helps to increase the viscosity of the polymer. In an exemplary embodiment, the first product is subjected to 285 °C at 0.5 mm Hg for 120 minutes to 165 minutes.
[32] In the second stage, after the first stage, the pre-polymerized product is subjected to a second pre-defined temperature at a second pre-defined pressure for a second pre-defined time period to obtain the co-polymer. The second pre-defined temperature ranges from 285 °C to 290 °C. The second pre-defined pressure ranges from 0.1 mm Hg to 0.5 mm Hg. The second pre-defined time period ranges from 120 minutes to 165 minutes. In an exemplary embodiment, the pre-polymerized product is subjected to 280 °C at 0.1 mm Hg for 120 minutes to 165 minutes.
[33] At step 105, the co-polymer obtained from step 103 is casted in the form of granules. In an exemplary embodiment, the Polyethylene terephthalate glycol (PETG) is casted into granules by cooling the co-polymer using underwater strand granulator. Casting of co-polymer granules helps in easy handling and storage of the co-polymer.
[34] Fig. 2 depicts an exemplary method 200 for extrusion of the co-polymer obtained from method 100 to form a film, i.e., the method 200 to prepare the film. The method 200 imparts directional properties, namely, a transverse direction (TD) and a machine direction (MD) to the resulting film.
[35] In an exemplary embodiment, the film obtained from the method 200 is rolled (or wound) to form a jumbo roll. Each jumbo roll includes a pre-defined length of the film and a pre-defined width. Then this jumbo roll may be slitted, using slitting machines, in various sizes. The length and width of the slit rolls may vary, on the basis of requirements of the customer (or end-user). The direction of the width of the film corresponds to the transverse direction of the film. The direction of the length of the film corresponds to the machine direction of the film.
[36] The method 200 commences at step 201 by homogenously mixing the co-polymer as obtained from the method 100 with at least one master batch to form a first mixture. The master batch includes, without limitation, additives (or pigments), optical brighteners, stabilizers, colorants, compatibilizers, pinning master batches, polypropylene based master batches, etc.
[37] The additives may be selected from Titanium dioxide, calcium carbonate etc. The additives may be added in a pre-defined concentration per unit weight of the co-polymer. The additives (or pigments) help to increase haziness, whiteness and opacity of the film.
[38] In an exemplary embodiment, Titanium dioxide is added in the concentration ranging from 1% (w/w) to 3% (w/w). Titanium dioxide provides white color to the film as well as helps the film to block Ultraviolet (UV) light.
[39] In an embodiment, calcium carbonate is added in the concentration ranging from 2 % (w/w) to 5 % (w/w). In an exemplary embodiment, 4.5% (w/w) calcium carbonate is added to the first mixture. Calcium carbonate helps to increase the haziness of the film, thus reducing the transparency and increasing the opaqueness.
[40] The optical brighteners are selected from UV tex, OB1, etc. The optical brighteners may be added in a pre-defined concentration per unit weight of the co-polymer. The pre-defined concentration ranges from 0.01% (w/w) to 0.05% (w/w). In an exemplary embodiment, 0.03% (w/w) of optical brightener is added to the first mixture. The optical brighteners help to improve the brightness and color of the film.
[41] The stabilizers may include Irgonox 1010 or the like. The stabilizers may be added in a pre-defined concentration per unit weight of the co-polymer. The pre-defined concentration ranges from 0.09% (w/w) to 0.5% (w/w). In an exemplary embodiment, 0.15% (w/w) stabilizer is added to the first mixture. The stabilizers help to stabilize the co-polymer by avoiding its degradation.
[42] The colorants (or color dyes) may include solvaparm red/blue or the like. The colorants may be added in a pre-defined concentration per unit weight of the co-polymer. The pre-defined concentration ranges from 0.0001 % (w/w) to 0.0004 % (w/w). In an exemplary embodiment, 0.0003% (w/w) solvaparm red/blue mix is added to the first mixture. The colorants help to improve the color of the film.
[43] The compatibilizers may include maleic unhydried grafted polyethylene copolymers, other grafted olefinic copolymers, cyclic olefinic copolymers, etc. The compatibilizers may be added in a pre-defined concentration per unit weight of the co-polymer. The pre-defined concentration ranges from 0.1 % (w/w) to 1.5 % (w/w). In an exemplary embodiment, 0.5% (w/w) compatibilizer is added to the first mixture. The compatibilizers helps to bind the polymers/co-polymers of the first mixture and improves impact resistance of the film.
[44] The pinning master batches may be added in a pre-defined concentration per unit weight of the co-polymer. The pre-defined concentration ranges from 0.01 % (w/w) to 0.06 % (w/w). In an exemplary embodiment, the pinning master batch includes 0.04% (w/w) of Di methyl sulfo isopthalate sodium salt (DMSI salt). The pinning master batches help to reduce the melt phase specific resistance.
[45] In an exemplary embodiment, the first mixture includes 71% (w/w) co-polymer, 0.5% (w/w) compatibilizer, 20% (w/w) titanium dioxide master batch, 4.5% (w/w) calcium carbonate master batch, 2% (w/w) pinning master batch, 0.5% (w/w) color master batch, 1% (w/w) stabilizer master batch, and 0.5% (w/w) optical brightener master batch.
[46] At step 203, the first mixture obtained at step 201 is pre-heated to a pre-defined temperature for a pre-defined time period. The pre-defined temperature ranges from 30 °C to 80 °C. The pre-defined time period ranges from 1 hour to 8 hours depending upon the moisture content of the first mixture. In an exemplary embodiment, the first mixture is heated to 30 °C to 60 °C. Pre-heating the first mixture helps to remove moisture content from the first mixture.
[47] In an exemplary embodiment, the step 201 and step 203 are performed in a feeding section of an extruder.
[48] At step 205, the first mixture is extruded, by using the extruder, to obtain a melt (or extruded product). The extruder is set at a pre-defined temperature ranging from 240 °C to 270 °C. In an exemplary embodiment, the extruder is set at 260 °C.
[49] In an exemplary embodiment, the first mixture, after extrusion, is forced through a coat hanger type film die to achieve sheet-like form of the melt.
[50] At step 207, the melt is cooled (or quenched) to a pre-defined temperature ranging from 25 °C to 55 °C to obtain the film (or cast film). In an exemplary embodiment, the melt is quenched over a chilled roller by using electrostatic pinning.
[51] The film obtained at step 207 has a pre-defined thickness ranging from 150 microns to 300 microns. In an exemplary embodiment, the film has a thickness of 250 microns. The thickness of the film may vary based on end-application of the film.
[52] Although the present disclosure describes preparation of films via extrusion process, other functionally equivalent processes are within the scope of the teachings of the present disclosure.
[53] At step 209, the film obtained from step 207 is oriented by a six-stage process. Orienting the film helps to achieve enhanced shrinkage.
[54] In a first stage of step 209, the film is passed through a machine direction oven (MDO) set at a first pre-defined temperature. The MDO is provided with a plurality of rollers. The film is passed in between the rollers of the MDO. The rollers of the MDO are maintained at the first pre-defined temperature. The first pre-defined temperature ranges from 60 °C to 65 °C. In an exemplary embodiment, the rollers of the machine direction oven (MDO) are set at 65 °C.
[55] Additionally or optionally, the film may be simultaneously subjected to infrared heating when the film is passed through the MDO. Passing the film through the machine direction oven (MDO) helps to pre-heat the film.
[56] In an optional second stage of step 209, one or more layers of coating is applied on at least one surface (or face) of the film. The layer of coating may be selected from an acrylic or a co-polymer base coating. In an exemplary embodiment, only one side of the film is online coated with a layer of acrylic base coating using a reverse gravure system. The coating improves surface roughness of the film by reducing friction thus, enabling the film to be smoothly printed with ink.
[57] In a third stage of step 209, the film is pre-heated inside a transverse direction oven (TDO) set at a second pre-defined temperature. The second pre-defined temperature ranges from 100 °C to 120 °C. The TDO is provided with a plurality of heating and/or cooling zones. The film is passed through the plurality of heating and cooling zones of the TDO. The plurality of heating zones of the TDO are maintained at the second pre-defined temperature. The temperature of the cooling zone is ranges from 15 °C to 25 °C. Pre-heating the film in the TDO helps to orient the film in the transverse direction.
[58] In a fourth stage of step 209, the film is stretched at a third pre-defined temperature at a pre-defined stretch ratio in the transverse direction as the film travels in the machine direction at a pre-defined line speed. The third pre-defined temperature ranges from 80 °C to 100 °C. Stretching the film yields a web width of the film. The pre-defined stretch ratio ranges from 4 – 5 times the initial width of the film. In other words, the web width of the film is 4 – 5 times the initial width of the film. In an exemplary embodiment, the web width of the film is less than 4 meters. The line speed of the tenter frame ranges from 40 m/min to 70 m/min. The pre-defined stretch ratio and the pre-defined line speed is selected basis the composition of the film obtained at step 207. Stretching the film in the transverse direction helps to improve the shrinkage of the film.
[59] In a fifth stage of the step 209, the film is subjected to heat setting (or annealing) at a fourth pre-defined temperature. The fourth pre-defined temperature ranges from 60 °C to 80 °C. In an exemplary embodiment, the film is annealed at an annealing section of the tenter frame by gradually reducing the temperature from 80 °C to 60 °C. Heat setting the film helps to improve stability of the film.
[60] Additionally or optionally, the annealing section of the tenter frame is retracted partially to relax the film, i.e., to remove any undue stress on the film. In an exemplary embodiment, the retraction of the annealing section of the tenter frame is expressed as a percentage of the maximum web width of the film.
[61] In a sixth stage of the step 209, the film is cooled to a fifth pre-defined temperature. The fifth pre-defined temperature ranges from 30 °C to 50 °C. In an exemplary embodiment, the surface of the film is air cooled.
[62] At step 211, the film obtained from step 209 is wound on Jumbo Winders and further slitted in to smaller widths and lengths., for easy storage and use. The film obtained at step 209 has a pre-defined thickness ranging from 40 microns to 60 microns depending upon the end-applications.
[63] The film obtained at step 209 have micro-voids spread homogenously. The formation of micro-voids within the film is attributed to steps 201 to 209 of method 200. Due to the presence of micro-voids in the film, the film has a pre-defined density that is less than water. In other words, the film floats on water. In an exemplary embodiment, the film has a density of 0.95 ± 0.03 g/cm3. Lower density of the film facilitates easy separability of the film in wet recycling processes, as the film separates from an underlying material (for example, a bottle) and floats on water.
[64] Further, due to the presence of micro-voids in the film, a production yield of the film from method 200 is increased by more than 30%.
[65] The film of the present disclosure has excellent shrinkage in the transverse direction, thereby enabling the film to snugly conform to any object/container the film is applied to. In an exemplary embodiment, the film has a shrinkage of more than 70% in the transverse direction and very low shrinkage of less than 5% in the machine direction.
[66] The film is at least partially opaque to UV light. In an exemplary embodiment, the film easily blocks transmittance of light having a wavelength ranging from 200 nm to 400 nm. Thus, the film protects photo perishable products/goods.
[67] The present disclosure will now be explained with the help of the following examples:
[68] Example 1 (Present disclosure): A first mixture containing 71% (w/w) of co-polymer (for e.g., Polyethylene terephthalate glycol (PETG) granules), 0.04% (w/w) of pinning master batch (for e.g., DMSI salt), 0.0002% (w/w) of color dyes, 0.5% (w/w) of compatibilizer (for e.g., Maleic unhydride grafted polyethylene copolymer), 1.5% (w/w) of titanium dioxide (master batch, in Polypropylene), 3.2% (w/w) of calcium carbonate (master batch, in Polypropylene), 0.1% (w/w) of stabilizer (for e.g., Irgonax 1010 master batch), 0.03% (w/w) of optical brightener master batch (for e.g., UvtexOB1) was made by homogenous mixing inside a feeding section of an extruder. The first mixture was heated at 30 °C to 80 °C for 1-8 hours to remove moisture.
[69] The first mixture was forced through the die set at a temperature of 270 °C to obtain a melt. The melt was quenched at a temperature ranging from 30 °C to 55 °C by passing the melt over chilled rollers using electrostatic pinning to obtain the film. The film had a thickness of more than 150 microns.
[70] The film was pre-heated by passing the film through a machine direction oven (MDO) set at a temperature ranging from 60 °C to 65 °C. One side of the film was coated with a layer of acrylic base coating using reverse gravure system.
[71] The film was then passed through the heating and cooling zones of a transverse direction oven (TDO). The heating zones of the TDO was set at a temperature ranging from 60 °C to 120 °C. Thereafter, the film was stretched (in the transverse direction) at a temperature ranging from 80 °C to 100 °C using a tenter frame at a stretch ratio of 4 to 4.5 times the initial width of the film. The film was allowed to travel at a line speed of 40 m/min to 70 m/min while the film was stretched using the tenter frame.
[72] The film was then allowed to anneal at a temperature ranging from 60 °C to 80 °C inside an annealing section of the tenter frame. The annealing section of the tenter frame was retracted partially. The film was then cooled at a temperature ranging from 30 °C to 50 °C. The film had a thickness ranging from 40 microns to 60 microns. The film had a density of 0.95 ± 0.03 g/cm3.
[73] The film had a white appearance, thereby not requiring white ink at the time of printing labels using the film. Skipping white ink printing preserved mechanical properties of the film thus, enhancing the shelf life of the film. Further, skipping white ink also reduced solvent pollution, energy consumption, production time at converters side.
[74] The film had high opacity, good strength, and no streaking from poor mixing.
[75] Example 2 (Present disclosure): The film, as obtained in Example 1, was physically characterized as follows:
S. No. Property of the film Quantification of the property
1. Wetting Tension (Uncoated side) 40 – 44 Dynes/cm
2. Wetting Tension (Coated side) 48 ± 4 Dynes/cm
3. Tensile strength in the machine direction (MD) 500 ± 150 Kg/cm2
4. Tensile strength in the transverse direction (TD) 1200 ± 300 Kg/cm2
5. Elongation at break in the machine direction (MD) 450 ± 150%
6. Elongation at break in the transverse direction (TD) 40 ± 20%
7. Shrinkage in the machine direction (MD)
[after the film was kept at 98 °C for 30 Sec. in water] <5%
8. Shrinkage in the transverse direction (TD)
[after the film was kept at 98 °C for 30 Sec. in water] 73 ± 3%
9. Transmittance (VLT) 25 ± 5%
10. Gloss (60 Degree) Gardner value 20 ± 10
11. Coefficient of Friction (Dynamic)
[one side of the film to other side of the film] 0.45 ± 0.15
12. Glass transition temperature (Tg) 74 ± 3 °C

[76] Example 3 (Present disclosure): The film, as obtained in Example 1, was tested for shrinkage in the transverse direction and the machine direction compared to an initial state of the film. The initial state of the film corresponds to a film cut-out having a length of 100 mm and a width of 100 mm. The said film was immersed in a water bath having a pre-defined temperature for 10 seconds. The amount of change in length and width of the film (expressed in %) was determined as a function of temperature of the water bath. In other words, the % change in length of the film corresponds to shrinkage in the machine direction (%MD) and the % change width of the film corresponds to shrinkage in the transverse Direction (%TD). The results obtained were tabulated as follows (and plotted as shown in Fig. 3):
Temperature (°C) 55 60 65 70 75 80 85 90 95 98
TD shrinkage (%) 0 1 13 42 56 65 68 70 72 73
MD shrinkage (%) 0 0 0 -2 -2 -2 -1 0 0 1

[77] Example 4 (Present disclosure): The film, as obtained in Example 1, was tested for percentage transmittance of light using a spectrophotometer. The percentage transmittance of the film, as observed on the spectrophotometer, is depicted in Fig. 4. It was observed that for light having wavelength below 315 nm, the light transmittance was less than 5%. Further, for light having wavelength between 315 nm and 400 nm, the light transmittance was less than 16%. And, for light having wavelength above 400 nm the light transmittance was below 30%. Thus, the film was able to protect photo perishable products/goods.
[78] Example 5 (Present disclosure): The film, as obtained in Example 1, was cut and applied over a cylindrical container (made of polyethylene terephthalate) using 1,3-dioxolane solvent. The film was heated to enable the film to conform to the shape of the cylindrical container, i.e., the film shrunk about 60% to conform to the shape of the cylindrical container.
[79] The film was removed from the cylindrical container and cut into small pieces. The small pieces of the film were put on water. It was observed that the small pieces of the film were floating on the water (at room temperature). The ability of the film to float on water, due to its low density, helps the film to easily separate from any container it is applied on and reduce adulteration of products received from, for example, container recycling via wet recycling processes.
[80] The scope of the invention is only limited by the appended patent claims. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used. ,CLAIMS:WE CLAIM
1. A method (200) to prepare a shrink film having low density comprising:
a. obtaining a co-polymer by polymerizing an ester;
b. homogenously mixing the co-polymer as obtained from step a. with at least one master batch to form a first mixture, the master batch including additives, optical brighteners, stabilizers, colorants, compatibilizers, pinning master batches, and polypropylene based master batches;
c. pre-heating the first mixture obtained from step b. at a pre-defined temperature for a pre-defined time period;
d. extruding the first mixture at a pre-defined temperature to obtain a melt;
e. cooling the melt obtained at step d. to obtain a film having a pre-defined thickness ranging from 150 microns to 300 microns; and
f. orienting the film obtained at step e. by:
i. passing the film through a machine direction oven (MDO) set at a first pre-defined temperature ranging from 60 °C to 65 °C,
ii. pre-heating the film inside a transverse direction oven (TDO) set at a second pre-defined temperature ranging from 100 °C to 120 °C,
iii. stretching the film at a third pre-defined temperature at a pre-defined stretch ratio in a transverse direction as the film travels in a machine direction at a pre-defined line speed, the third pre-defined temperature ranges from 80 °C to 100 °C, the pre-defined stretch ratio being 4 – 5 times an initial width of the film, and
iv. annealing the film at a fourth pre-defined temperature;
wherein, the film obtained from step f. has homogenously spread micro-voids and a pre-defined thickness ranging from 40 microns to 60 microns.
2. The method (200) as claimed in claim 1, wherein prior to polymerizing the ester, esterifying at least one dicarboxylic acid, and at least one diol component to produce the ester.
3. The method (200) as claimed in claim 2, wherein the dicarboxylic acid is selected from a group of Terephthalic acid (PTA), Isophthalic acid, Orthophthalic acid, DimethylTerepthalate or a combination thereof.
4. The method (200) as claimed in claim 2, wherein the diol component is selected from a group of Monoethylene glycol (MEG), Diethylene glycol (DEG), Neopentyl glycol (2,2-Dimethyl 1,3-Propanediol), Cyclo hexane di methanol (CHDM), or a combination thereof.
5. The method (200) as claimed in claim 1, wherein the obtaining the co-polymer includes polymerizing Bishydroxyl terephthalate (BHET) to produce Polyethylene terephthalate glycol (PETG).
6. The method (200) as claimed in claim 2, wherein the esterifying includes carrying out esterification at a pre-defined temperature ranging from 250 °C to 265 °C and a pre-defined pressure ranging from 1 kg/sq.cm to 2 kg/sq.cm.
7. The method (200) as claimed in claim 1, wherein the polymerizing the ester includes:
a. adding at least one additive at least one catalyst, and at least one stabilizer to the ester to obtain a first product;
b. subjecting the first product to a first pre-defined temperature at a first pre-defined pressure for a first pre-defined time period to obtain a pre-polymerized product, the first pre-defined temperature ranges from 250 °C to 290 °C, the first pre-defined time period ranges from 120 minutes to 165 minutes; and
c. subjecting the pre-polymerized product to a second pre-defined temperature at a second pre-defined pressure for a second pre-defined time period, the second pre-defined temperature ranges from 285 °C to 290 °C, the second pre-defined pressure ranges from 0.1 mm Hg to 0.5 mm Hg, the second pre-defined time period ranges from 120 minutes to 165 minutes.
8. The method (200) as claimed in claim 1, wherein the co-polymer is at least one of Polyethylene terephthalate glycol (PETG), Polypropylene (PP), Polyethylene or a blend thereof.
9. The method (200) as claimed in claim 1, wherein the additives include at least one of Titanium dioxide in the concentration ranging from 1% (w/w) to 3% (w/w), and calcium carbonate in the concentration ranging from 2 % (w/w) to 5 % (w/w).
10. The method (200) as claimed in claim 1, wherein the optical brighteners include at least one of UV tex, and OB1 in a pre-defined concentration ranging from 0.01% (w/w) to 0.05% (w/w).
11. The method (200) as claimed in claim 1, wherein the stabilizers include Irgonox 1010 in a pre-defined concentration ranging from 0.09% (w/w) to 0.5% (w/w).
12. The method (200) as claimed in claim 1, wherein the colorants include solvaparm red/blue in a pre-defined concentration ranging from 0.0001 % (w/w) to 0.0004 % (w/w).
13. The method (200) as claimed in claim 1, wherein the compatibilizers include at least one of maleic unhydried grafted polyethylene copolymers, other grafted olefinic copolymers, and cyclic olefinic copolymers in a pre-defined concentration ranging from 0.1 % (w/w) to 1.5 % (w/w).
14. The method (200) as claimed in claim 1, wherein the pinning master batches include Di methyl sulfo isopthalate sodium salt (DMSI salt) in a pre-defined concentration ranging from 0.01 % (w/w) to 0.06 % (w/w).
15. The method (200) as claimed in claim 1, wherein the pre-heating the first mixture includes pre-heating at 30 °C to 80 °C for 1 hour to 8 hours.
16. The method (200) as claimed in claim 1, wherein the extruding includes extruding the first mixture using an extruder set at a pre-defined temperature ranging from 240 °C to 270 °C.
17. The method (200) as claimed in claim 1, wherein the cooling includes cooling the melt to a temperature ranging from 25 °C to 55 °C.
18. The method (200) as claimed in claim 1, wherein passing the film through a machine direction oven (MDO) includes simultaneously subjecting the film to infrared heating.
19. The method (200) as claimed in claim 1, wherein after passing the film through a machine direction oven (MDO), applying one or more layers of coating on at least one surface of the film.
20. The method (200) as claimed in claim 19, wherein the layers of coating is at least one of an acrylic or a co-polymer base coating.
21. The method (200) as claimed in claim 1, wherein stretching the film includes, making the film travels in the machine direction at the pre-defined line speed ranging from 40 m/min to 70 m/min.
22. The method (200) as claimed in claim 1, annealing the film includes annealing the film by gradually reducing the temperature from 80 °C to 60 °C.
23. The method (100) as claimed in claim 1, wherein after annealing the film, cooling the film to a fifth pre-defined temperature ranging from 30 °C to 50 °C.