, Description:
FIELD OF INVENTION
The present invention relates to foamed films. In particular, the present invention relates to a monolayered foamed film. The foamed film of the present invention finds its application as packaging aid.

BACKGROUND OF THE INVENTION
Polyolefin films are used for manufacture of various packaging solutions that include wraps, bags, films, sachets, labels, pouches. Depending on the article to be packaged, exposure of the packaged goods to various conditions during transport and logistics, the nature of packaging solutions differ widely.

In the wake of the current global concerns with regard to environment and sustainability, various attempts have been made to reduce the use of polymers from non-renewable sources, particularly poly-olefins in the manufacture of packaging goods.

Foamed packaging materials with reduced density have been in use in the packaging space since last decade. Foaming consist of incorporation of gas in the product like film, sheet or molding resulting in reduced density of the product, leading to reduction in the consumption of material.

US7341683 discloses a method of manufacturing a foamed-polyethylene blown-film specifically used for manufacture of trash-bags. Foamed films disclosed in US7341683 are manufactured through an extruder that comprises a die and a feed with varying temperature settings.

US8512837 relates to use of particular blends of LLDPE with high melt index and branched LDPE with low melt index together with specific fabrication conditions to make foamed sheets of thin gauge from about 1 to 10 mils thick with MD tear properties.

US10011697 relates to a foamed film comprising a polyethylene foam obtained by physically foaming of a low density polyethylene copolymer with a density between 910 kg/m.sup.3 and 935 kg/m.sup.3 (according to ISO 1183) and a melt index between 0.10 and 100 dg/minute (according to ASTM D1133) wherein the low density polyethylene is obtained by a high pressure polymerization process of ethylene in the presence of a di- or higher functional monomer.

There is a long felt need to develop foamed films with less plastic content that are robust and also possess good tensile strength and impact resistance.

OBJECTS OF THE INVENTION
It is an object of the present invention to provide a foamed film suitable for manufacture of various packaging aids.

It is an object of the present invention to provide a foamed packaging aid that requires relatively lesser amounts of polyolefin /polyethylene base materials for its manufacture without compromising on its thickness and strength.

It is another object of the present invention to provide a monolayer foamed film that can be used for manufacture of a wide variety of packaging aids.

It is yet another object of the present invention to provide a foamed film with improved specific strength and high impact resistance.

SUMMARY OF THE INVENTION
According to an aspect of the present invention there is provided a foamed film composition comprising:

HDPE 67 to 80 wt %;
Hexene co-polymer (HDPE) 20 to 30 wt %;
LDPE 3 to 6 wt % ;
wherein the density of HDPE is in the range of 0.94 to 0.97 g/ cc

According to another aspect of the present invention there is provided a foamed film composition further comprising a processing aid and a foaming agent.

According to another aspect of the present invention there is provided a foamed film composition wherein at least one HDPE polymer selected from the group consisting of HDPE and Hexene co-polymer has bimodal molecular weight distribution.

According to another aspect of the present invention there is provided a foamed film composition wherein the ratio of total LDPE content of the formulation to total HDPE content of the formulation is in the range from 1:20 to 1:24.

According to yet another aspect of the present invention there is provided a foamed film obtained from the foamed film composition having thickness in the range of 15 to 70 microns.

According to another aspect of the present invention there is provided a foamed film obtained from the foamed film composition wherein the density of the foamed film is in the range from 0.4 to 0.65 g/cc.

According to yet another aspect of the present invention there is provided a foamed film obtained from the foamed film composition wherein tensile strength of the film has MD from 15 MPa to 30 Mpa, and TD from 8 MPa to 15 Mpa.

According to yet another aspect of the present invention there is provided a foamed film wherein the film is a monolayer film, transparent and/or translucent.

According to yet another aspect of the present invention there is provided a method of preparing foamed film, the said method comprising the steps of:
a) Introducing the polymeric material comprising HDPE at 67 to 80% by weight; Hexene co-polymer (HDPE) at 20 to 30% by weight; LDPE at 3 to 6% by weight, optionally Ethylene Vinyl Acetate (EVA) at 3 to 7% by weight, in the hopper;
b) introducing a foaming agent in an amount ranging from 1 to 1.5% by weight;
c) setting the extruder barrel temperatures below 185°C;
d) setting the die end temperatures at 190°C to 205°C;
e) extruding the polymeric material from annular die in upward direction, inflated using air and pulled via nip rolls guiding further to the winding unit;
f) to obtain a foamed film on HDPE blown film machine having 5 zones with the following temperatures:

Zones Barrel 1 Barrel 2 Cross Head Die 1 Die 2
Temperature
(°C) 180
185
190
190 195-205

DETAILED DESCRIPTION OF THE INVENTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the scope of the invention as defined by the appended claims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, steps or components but does not preclude the presence or addition of one or more other features, steps, components or groups thereof.

It is to be understood that density of the high density thermoplastic homo-polymer (HDPE) polymers referred in the present context varies from about 0.94 to about 0.97 g/cc. It is to be understood that density of LDPE polymers in the present context varies from about 0.91 to about 0.93 g/ cc.

It is to be understood that density of the hexene co-polymer (HDPE) in the present context varies from about 0.94 to about 0.95 g/cc.

In the context of the present invention, the expression “high crystallinity polymer” refers to polymers with crystallinity of 45-75% such as HDPE and/or Hexene co-polymer (HDPE); while the expression “low crystallinity polymer refers to polymers with crystallinity of 15 to 35 wt% such as LDPE.

In the context of the present invention, a foamed film that allows a see through view of the packaged product is to be considered as transparent foam film.

According to an embodiment, the present invention provides a foamed film composition comprising
a. HDPE at 67 to 80% by weight;
b. Hexene co-polymer (HDPE) at 20 to 30% by weight ;
c. LDPE at 3 to 6% by weight and
wherein the density of (a) and (b) is in the range of 0.94 to 0.97 g/ cc.

In one embodiment, the present invention provides a foamed film composition comprising:
a high density thermoplastic homo-polymer (HDPE) in an amount ranging from about 67 to 80 wt%;
a hexene co-polymer (HDPE) in an amount ranging from 20 to 30 wt% and
a low density polyethylene (LDPE) in an amount ranging from about 3 to about 6 wt%;
optionally a processing aid in an amount of about 0.2 to 0.75wt %; and
foaming agent in an amount of about 1 to 1.5 wt% ;
wherein the density of high density thermoplastic homo-polymer and hexene co-polymer is in the range of 0.94 to 0.97 g/ cc and thickness of the obtained film is in the range from 15 microns to 70 microns.

In one of the embodiments, the composition of the present invention further comprises Ethylene Vinyl Acetate (EVA) in an amount ranging from 3 to 7% by weight, preferably 4 % by weight of the total composition. Presence of EVA renders the resultant film flexible and it also improves its impact properties.

In order to achieve a film with the desired thickness after foaming, the composition of the present invention employs at least one high crystallinity polymer with low MFI and bimodal molecular weight distribution. Typically, MFI of the polymer with bimodal molecular weight distribution varies in the range from 0.05 to about 1.2. Lower MFI values provide the melt strength required for blown film extrusion. Apart from MFI, molecular weight distribution in the high crystallinity polymer helps in imparting mechanical strength without compromising on the process-ability of the film. Without bound by theory, high molecular weight chains in the bimodal high crystallinity polymer provide good mechanical strength while the low molecular weight chains in the polymer provide ease in processing and good draw-downability.

Typically, the amount of bimodal HDPE in the high crystallinity polymer blend ranges from about 50 wt% to 90 wt% of total weight of the high crystallinity polymeric blend.

In one embodiment, the high crystallinity polymer with bimodal molecular weight distribution is a hexene co-polymer (HDPE). In one embodiment, the high crystallinity polymer with bimodal molecular weight distribution is (HDPE).

In one of the embodiments, the foamed film composition of the present invention comprises a combination of low-crystallinity polymer blend and a high crystallinity polymer blend in the ratio of about 1: 20 to about 1:24.

In one of the embodiments, the high crystallinity polymer blend comprises HDPE with density in the range of about 0.94 to 0.97 g/cc at 67 to 80 wt% and Hexene co-polymer (HDPE) with density in the range of about 0.94 to 0.95 g/cc at 20 to 30 wt % while the low crystallinity polymer present in the composition is LDPE with density in the range of about 0.91 to 0.93 g/cc in amount ranging from 3 to 6%.

In one of the embodiments, the high crystallinity polymer/HDPE blend comprises film grade HDPE while the low crystallinity polymer/LDPE polymer comprises film grade LDPE.

The composition of the present invention may further optionally comprise at least one processing aid selected from the group that consists of processing aid, nucleating agent, crosslinking agent, filler, antioxidant, pigment, stabiliser, antistatic agent and antioxidants or combinations thereof. Typically, the amount of processing aids in the composition varies from about 0.05 wt% to about 0.8 wt%; preferably 0.2 wt% to 0.75 wt%.

In one of the embodiments, composition of the present invention comprises polytetrafluoroethylene (PTFE) as a processing aid in an amount ranging from about 0.2 to 0.35 wt%.

The foaming agent in one of the embodiments is at least one inorganic compound selected from the group consisting of sodium bicarbonate, sodium borohydride and ammonium carbonate.

The foaming agent in one of the embodiments is at least one organic compound selected from the group consisting of Azodicarbonamide, modified Azodicarbonamide with zinc oxide or calcium carbonate and sodium bicarbonate modified with citric acid.

The recommended dosage of this foaming agent is from 1 to 1.5 wt %, preferably 1 wt %.

In still another aspect, the present invention provides a monolayered, foamed film prepared from the foamed film composition as described herein above. The thickness of the mono-layered foamed film in accordance of the present invention is varies in the range from 15 micron to 70 microns.

In an embodiment, the foamed film of the present invention is a monolayered foamed film with thickness below 20 microns. In another embodiment, the foamed film of the present invention has thickness below 30 microns. In a yet another embodiment, the foamed film has thickness below 50 microns and in a further embodiment; the foamed film of the present invention has thickness up to 70 microns.

Density of the monolayered foamed film of the present invention varies in the range of about 0.4 to about 0.65 g/cc.

Tensile strength MD (machine direction) of the monolayer foamed film of the present invention, ranges from 15 to 30 MPa while tensile strength TD (transverse direction) varies in the range from 8 MPa to 15 Mpa. The testing is carried out using an Universal Testing machine for measurement of the tensile properties as per ASTM D882 standard.

In an exemplified embodiment, tensile strength achieved for a 17 micron film is MD – 25 MPa (3625 psi), TD – 11 MPa (1595 psi).

Average size of the air bubbles in the monolayered foamed film of the present invention typically, varies in the range from 1.5 mm to 40 mm.

The monolayered foamed film of the present invention is easily sealable and printable. In one of the embodiments, the monolayered foamed film of the present invention is transparent. In another embodiment, the monolayered foamed film of the present invention is translucent.

The foamed film of the present invention does not rupture and runs at higher line speeds and is stable during processing even at a low thickness after foaming.

Further, the foamed film of the present invention has significantly higher specific strength in this density range as against the one mentioned in prior art. The use of bimodal polyethylene with the combination of processing aids, nucleating agent, cross linking agent, antioxidants and method of processing where machine configuration, process parameters equally contribute to the stable extrusion of a thin foamed film with higher specific strength.

In an embodiment of the present invention, the foamed film is air-bubbled.

Method of preparation
In another aspect, the present invention provides a method for preparation of a monolayered foamed film through an extrusion process.

The polymeric material comprising HDPE at 67 to 80% by weight; Hexene co-polymer (HDPE) at 20 to 30% by weight; LDPE at 3 to 6% by weight, optionally Ethylene Vinyl Acetate (EVA) at 3 to 7% by weight is introduced in the hopper. This is followed by introducing a foaming agent in an amount ranging from 1 to 1.5% by weight. The extruder barrel temperatures is set below 185°C and the die end temperatures is set at 190°C to 205°C. The polymeric material is extruded from annular die in upward direction, inflated using air and pulled via nip rolls guiding further to the winding unit. A foamed film is obtained on HDPE blown film machine having 5 zones.
Along with the composition, the extrusion process parameters play a key role in extrusion of the foamed film which is stable during processing and do not rupture. The extruder barrel temperatures are set below 185° C to avoid decomposition of foaming agent inside the barrel. The die end temperatures are set in such a way that the foaming agent decomposes when the polymer exits the die, releasing the gas to introduce foaming in the film. The die temperatures are maintained between 190° C to 205° C.

The screw design ensured there is no excessive shear heat generation as it affects the viscosity and the cell size.

Processing aid helps in uniformly controlling the viscosity of the melt in order to get uniform cell size.

The viscosity of the melt is controlled to have the required melt strength, so that the film does not rupture even after foaming at such a lower thickness (as low as 17 micron). Processing aids also help to reduce the stress on the material inside the extruder enabling smooth processability and product quality.

The foaming agent used in the present invention is Azodicarbonamide master batch (Azo MB).

The dosage of this foaming agent varies in the range from 1 to 1.5 wt %, preferably 1 wt%.

The film is extruded on a HDPE blown film machine having 5 zones with the following temperatures.

Zones Barrel 1 Barrel 2 Cross Head Die 1 Die 2
Temperature
(°C) 180
185
190
190 195-205

If the die temperature rises beyond 205 °C, there is increase in foaming that leads to significant increase in the thickness of the film and eventually breakage of the film.

The machine has variable frequency drive and hence the screw speed and the nip roll speed is set in terms of the frequency

Screw speed – 20 Hz (frequency)

Pulling speed – 36 Hz (frequency)

The present invention provides the following advantages:
• Reduction in density of up to 45%;
• Reduction in material consumption of up to 45%;
• Not opaque;
• Cost saving;
• Increased performance like reduced wrinkling, etc

EXAMPLES:

The following examples are meant to illustrate the present invention. The examples are presented to exemplify the invention and are not to be considered as limiting the scope of the invention.

Examples in accordance with the present invention:
Example 1:
The foamed film composition of the present invention

No Material Grade Make Density
(g/cc) MFI @
(ASTM
2.16/190) Formulation (%)
1 High density polyethylene** F55hm0003 GAIL 0.95 0.09 70.7
2 High density polyethylene Marlex HMTR144* Chevron Philips 0.94 0.18 24
3 Low density polyethylene HP 0323 N Sabic 0.92 0.3 4
4 Processing aid
PPA/8G AD-1083 Blend colours 0.91 – 0.95 1-10 0.3
5 Foaming Agent masterbatch (Azodicarbonamide) ADC 200 Kinetic Polymers - - 1 %
(0.2% ADC)
* Marlex HMTR144 - 0.1 MFI is a hexene copolymer.
**Film grade HDPE with Bimodal molecular weight distribution.

The Tensile strength as measured by ASTM D882 is as follows
MD – 25 MPa (3625 psi)
TD – 11 MPa (1595 psi)
Observation: Film stable, strength good, thickness achieved is around 17 to 19 microns.

Example 2:

The foamed film composition of the present invention

Material Formulation (wt %)
HDPE (Gail–F55HM0003 - 0.09 MFI ) 67 %
HDPE (Chevron Philips - Marlex HMTR144 - 0.1 MFI ) 23.7 %
LDPE (SABIC HP 0323 N – 0.3 MFI) 4%
Ethylene Vinyl Acetate (Elvax 40L-03) 4%
Processing aid 0.3%
Azo MB 1% (0.2%ADC)

Observation: Film stable, strength good, thickness achieved is around 25 to 30 micron.
The Tensile strength as measured by ASTM D882 is as follows
MD – 20 MPa (2900 psi)

Example 3

The foamed film composition of the present invention:

Material Formulation (wt %)
HDPE of 0.955 g/cc 70%;
Hexene copolymer (HDPE of 0.946 g/cc) 24.7%
LDPE of 0.923 g/cc 4%
PTFE 0.3%
Azodicarbonamide 1.0

Observation: Film stable, strength good, thickness achieved is around 50 microns.

The Tensile strength as measured by ASTM D882 is as follows
MD – 15 MPa (2175 psi)

Examples 4: (comparative) Non-working example
No. Material Grade Make Density
(g/cc) MFI @(2.16/190) Formulation (%)
1 High density polyethylene* Marlex HMTR Chevron Philips 0.95 0.18 73.50
2 Linear low density polyethylene F18S010U GAIL 0.92 1.0 20
3 Low density polyethylene HP 0323 N Sabic 0.92 0.3 5
4 Azodicarbonamide MB - - - - 1% (0.2%ADC)
* Non-bimodal HDPE

Observation: Process not stable, Bubble puncturing, Quality of film poor.
Film formation was not possible.

Example 5: (comparative), Non-working example.
One of the formulations is mentioned below with lower proportion of bimodal HDPE resin.

No. Material Grade Make Density
(g/cc) MFI @(2.16/190) Formulation (%)
1 High density polyethylene* F55hm0003 GAIL 0.955 0.09 62
2 High density polyethylene Marlex HMTR144 Chevron Philips 0.946 0.18 25.2
3 Low density polyethylene HP 0323 N Sabic 0.923 0.3 4
4 Ethylene Vinyl Acetate** Elvax 40L-03 Dow 0.96 3 7.5
5 Processing aid PPA/8G AD-1083 Blend colours 0.91 – 0.95 1-10 0.3
6 Azodicarbonamide MB - - - - 1% (0.2%ADC)
* Bimodal HDPE – Proportion of bimodal HDPE is outside the scope of the present invention.
**Proportion of Ethylene Vinyl Acetate is outside the scope of the present invention.
Observation: Tensile strength poor, Clarity not good.
The Tensile strength as measured by ASTM D882 is as follows
MD – 12 MPa (1740 psi)

Example 6:
Comparative data: Films when prepared with polymer composition not in accordance with that of the present invention:
Polymer composition Result
HDPE (Reliance - E52009 - 0.9 MFI) 98.5% and 1.5% Azo MB (0.3% ADC) Film not stable during extrusion, strength poor.
HDPE (Chevron Philips - Marlex HMTR144 - 0.1 MFI ) 98.5% and 1.5% Azo MB (0.3%ADC) Film stable, foaming not good, opaque.
HDPE (Chevron Philips - Marlex HMTR144 - 0.1 MFI ) 98 % and 2% Azo MB (0.4%ADC) Film not stable, Bubble puncturing, film surface bad, strength poor.
LDPE (SABIC HP 0323 N – 0.3 MFI) – 50% ; LDPE (Reliance - 24FS040 – 4 MFI) – 48.5% ; Azo MB 1.5% (0.3%ADC): Film stable, lower tensile strength.

The aforesaid compositions do not comprise a blend of High crystallinity and low crystallinity polymers or comprise only HDPE (high crystallinity polymer).
Thus beyond the scope of the present invention

Example 7:
Comparative data on physical properties of foamed films of the present invention vis-à-vis the prior arts.

Prior art reference/
Present invention Polymer compositions Thickness/observations
US8512837 High MFI (1.5 to 6) LLDPE rich with low MFI (0.2 to 1) LDPE to provide balance of mechanical strength, extensibility and stress relaxation 50 micron – 75 micron.

US 10011697 Core layer LDPE 20% and LLDPE 80 % 3 layer film (Thickness 100 micron) with foamed core layer (50 micron)
Foamed film of the present invention a. HDPE 67 to 80 wt% (0.955 /cc)
b. HDPE 20 to 30 wt % (0.946 g/cc)
c. LDPE 4 wt%
(0.923 g/cc) 15 to 70 microns

It is to be understood that the present invention is susceptible to modifications, changes and adaptations by those skilled in the art. Such modifications, changes, adaptations are intended to be within the scope of the present invention.

Claims:
1. A foamed film composition comprising
a. HDPE at 67 to 80% by weight;
b. Hexene co-polymer (HDPE) at 20 to 30% by weight;
c. LDPE at 3 to 6% by weight and
wherein the density of (a) and (b) is in the range of 0.94 to 0.97 g/ cc.

2. The foamed film composition as claimed in claim 1 comprising a processing aid in the range of 0.2 to 0.75 wt %.

3. The foamed film composition as claimed in claim 2 wherein in the processing aid is polytetrafluoroethylene (PTFE) in an amount ranging from 0.2 to 0.35 wt%.

4. The foamed film composition as claimed in claim 1 comprising a foaming agent in the range of 1.0 to 1.5 wt %.

5. The foamed film composition as claimed in claim 4 wherein the foaming agent is Azodicarbonamide master batch.

6. The foamed film composition as claimed in claim 1, comprising ethylene vinyl acetate in the range of 3 to 7% by weight.

7. The foamed film composition as claimed in claim 1, wherein at least one HDPE polymer selected from the group consisting of HDPE and Hexene co-polymer has bimodal molecular weight distribution.

8. The foamed film composition as claimed in claim 1, wherein the HDPE polymer has bimodal molecular weight distribution.

9. The foamed film composition as claimed in claim 1, wherein the ratio of total LDPE content of the formulation to total HDPE content of the formulation is in the range from 1:20 to 1:24.

10. The foamed film obtained from the foamed film composition as claimed in claim 1, wherein the thickness of the foamed film is in the range of 15 to 70 microns.

11. The foamed film obtained from the foamed film composition as claimed in claim 1, wherein the thickness of the foamed film is in the range from 15 to 30 micron.

12. The foamed film obtained from the foamed film composition as claimed in claim 1, wherein the thickness of the foamed film is in the range from 30 to 50 micron.

13. The foamed film obtained from the foamed film composition as claimed in claim 1, wherein the thickness of the foamed film is in the range from 50 to 70 micron.

14. The foamed film obtained from the foamed film composition as claimed in claim 1, wherein the density of the foamed film ranges from 0.4 to 0.65 g/cc.

15. The foamed film obtained from the foamed film composition as claimed in claim 1, wherein the tensile strength of the film has MD from 15 MPa to 30 Mpa, and TD from 8 MPa to 15 Mpa.

16. The foamed film obtained from the foamed film composition as claimed in claim 1, wherein the film is a monolayered film.

17. The foamed film obtained from the foamed film composition as claimed in claim 1, wherein the foamed film is transparent.

18. The foamed film obtained from the foamed film composition as claimed in claim 1, wherein the foamed film is translucent.

19. The method of preparing foamed film as claimed in any of the preceding claims, said method comprising the steps of:
a) Introducing the polymeric material comprising HDPE at 67 to 80% by weight; Hexene co-polymer (HDPE) at 20 to 30% by weight; LDPE at 3 to 6% by weight, optionally Ethylene Vinyl Acetate (EVA) at 3 to 7% by weight, in the hopper;
b) introducing a foaming agent in an amount ranging from 1 to 1.5% by weight;
c) setting the extruder barrel temperatures below 185°C;
d) setting the die end temperatures at 190°C to 205°C;
e) extruding the polymeric material from annular die in upward direction, inflated using air and pulled via nip rolls guiding further to the winding unit;
f) to obtain a foamed film on HDPE blown film machine having 5 zones with the following temperatures:
Zones Barrel 1 Barrel 2 Cross Head Die 1 Die 2
Temperature
(°C) 180
185
190
190
195-205