FIELD OF INVENTION
The present invention relates to a printed film for packaging of baked food products.
More particularly, the present invention relates to a moisture resistant printed film for
packaging of baked food products.
BACKGROUND AND PRIOR ART
Conventional laminate is generated using different polymeric films and laminating them
using an adhesive such that the benefits of different polymeric films are encompassed in
the laminate. To further improve specific barrier property requirements, individual layers
can be metallized or various form of web treatments. All such treatments (Corona,
Chemical, Plasma, metallization) tend to reduce its efficacy over a period of time and
involve additional process followed by lamination with different film substrate. Thereby
it increases the overall price of the laminate.
US 4442158 relates to a food package and more particularly to an improved snack food
package. The package comprises an outer layer of polypropylene, a polyvinylidene
chloride middle layer and an inner ionomer resin layer. The invention also comprises a
unique method for making the snack food package which includes a plurality of steps
especially adapted to provide the required lamination between the layers.
US 4916198 discloses a normally solid, high molecular weight, gel-free, propylene
polymer material, branching index of which less than 1, that has strain hardening
elongational viscosity. It discloses formation of polymer material by extrusion coating
wherein polypropylene is used. However there is no mention of the use of such extrusion
coating to form printed films for packaging baked food on a horizontal form fill seal
machine.

Thus there is a need to provide an improved film which ensures efficient moisture barrier
enabling improved baked food freshness and flavour, with reduced material consumption
and reduced number of conversion processes.
The present inventors surprisingly found that reverse printed BOPP film provided with
extrusion coating of polypropylene provides excellent moisture barrier properties and at
the same time provide defined coefficient of friction for ease of machinability. This
avoids additional coating and lamination thus making the product cost effective and yet
making the film appropriate for packing baked food preserving its freshness.
OBJECTS OF THE INVENTION
It is an object of the present invention to overcome the drawbacks of the prior art.
It is another object of the present invention to provide a printed film for packaging of
baked food products formed by polypropylene extrusion coating.
Another object of the present invention is to provide a printed film for packaging of
baked food products formed by propylene extrusion coating wherein said film having
moisture resistant with Co-efficient of Friction (COF) is 0.16-0.17 for smooth
machinability.
A further object is to provide a printed film for packaging which is scuff resistant, such
that the print matter is not easily destroyed on use.
It is another object of the present invention to provide a laminate that can run on high
speed horizontal packaging machines i.e., have consistent interlayer bonds strength and
COF values.

SUMMARY OF THE INVENTION
Accordingly the present invention relates to a printed film for baked food products
formed by polypropylene extrusion coating wherein said film has moisture resistant
properties of water vapour transmission rate (WVTR) less man 3.7 g/sqm/24 hrs at 38°C
and relative humidity of 90% with optimum Co-efficient of friction (COF) of 0.16-0.17
for smooth machinability.
The present invention provides a printed film for baked food products formed by
polypropylene extrusion coating wherein the melt flow index (MFI) of the polypropylene
is 15-17 g/10mins.
DETAILED DESCRIPTION OF THE INVENTION

The present invention relates generally to composites of various plastic films , to flow
wrap a food product. In addition to the general function of containment, protection
required for the product, the film provides barrier to internal and external environment of
a package or product. The barrier provided by the film safeguards the enclosed product
against the major causes of loss of food freshness and flavour, namely, oxygen or water
vapour flow into the package and/or exposure to ultraviolet light. For smooth usage of the
film, it has to be smooth function with respect to machinability, by having right slip
properties and co-efficient of friction. Moreover, the said film provides good seal
integrity ensuring no permeation between the internal and external environment along the
seal area.
The film structure of present invention does not involve product formed by one film
conversion process and lamination process. Additionally the film of the present invention
eliminates requirement of adhesive unlike conventional laminate structure. Further unlike
US'198 the extrusion coating is carried out on printed film which provide specific
moisture resistance and COF properties. Moreover the print and the extrusion being on

the same side makes the print scratch resistant since the print matter ( design) is
sandwiched between the top BOPP film and the bottom PP extrusion coating.
The present invention provides a packaging film that is capable of providing optimum
barrier properties to oxygen and water vapour transmission required for optimum shelf
life of packaged baked products.
The printed BOPP film of the present invention is scuff resistance since it is reverse
printed with coloured heat resistant inks . Further white ink is eliminated from the print
and is substituted by adding white master batch in the Polypropylene extrusion coating
to give a white base coat to the design and protecting the product against the ultraviolet
light.
The present invention provides a packaging film that can run on high speed horizontal
packaging machines, i.e., having consistent interlayer bonds strength and COF values.
The present invention provides a reverse printed BOPP film wherein the said BOPP film
is extrusion coated with Polypropylene layer using an extrusion process. Moreover, the
film of the present invention involves reduced overall plastic consumption and controlled
necking thereby leading to meeting optimal functional and performance parameters.
The invention is now described by way of non limiting illustrative example
One side treated PET or BOPP or polyethylene or Polyvinyl chloride film in thickness
ranging from 10 microns to 30 microns is taken and printed using gravure process using
heat resistant inks. The printed web is loaded on the unwound shaft of the extrusion
coating machine. The printed web is passed through an on-line priming station for better
polymeric adherence. The hopper of extrusion machine is loaded with either polyethylene
or polypropylene granules mixed with 5% to 8% white master batch, basis the desired
aesthetic requirement. For the process of extrusion coating the following conditions are
maintained namely barrel temperatures of 290-300°C; adapter temperature of 260-290°C;

air gap of 120mm-150mm; chill roll temperature of 19-22°C; nip pressure of 3.5 kgs;
linear speed range of take up system: 90 m/min; neck-in (cms): 3" The extruder
temperature across different zones is maintained between 260-290°C and the polymeric
melt is extruded between 8 microns to 30 microns thickness. To ensure proper oxidation
and thereby the bond strength the length between the die lip and the nip is maintained
between 120-150 mm. Proper infeed and outfeed tension controls are maintained for
optimum bond strength.
The melt flow index (MFI) of 15-17 g/10 minutes of the polypropylene or polyethylene is
critical with respect to involved 'neck-in' and consistency of thickness of the extruded
layer. For consistent bond and ensuring no gauge band, the chill drum temperature is
maintained between 19°C to 22°C.
The extrusion coating of polypropylene or polyethylene on printed BOPP or PET film
results into a film structure with good moisture barrier properties of water vapour
transmission rate (WVTR) less than 3.7 g/sqm/24 hrs at 38°C and 90% relative humidity,
consistent seal strength of 0.7 -1 kg/15mm, with better possibility of hermetic sealing
and optimum COF of 0.16 - 0.17 for smooth machinability on horizontal flow wrap
machine. Accordingly the film provides adequate moisture barrier properties and other
properties essential for maintaining freshness of baked food without formation of a
laminate structure and without used of adhesives. Thus providing a cost effective yet
appropriate film package for baked food product.

WE CLAIM:
1. A printed film for baked food products formed by polypropylene extrusion
coating wherein said film has moisture resistant properties of water vapour
transmission rate (WVTR)is less than 3.7 g/sqm/24 hrs at 38°C and relative
humidity of 90%.
2. A printed film as claimed in claim 1 having optimum Co-efficient of friction
(COF) of 0.16-0.17 for smooth machinability.
3. A printed film as claimed in claim 1, wherein the melt flow index of the
polypropylene is 15-17 g/10 mins.
4. A printed film as claimed in claim 1, wherein the said film is printed on the
same side of the extrusion coating.
5. A printed film as claimed in claim 1, wherein the said film is scuff resistant.

A printed film for baked food products formed by polypropylene extrusion coating wherein said film has moisture resistant properties of water vapour transmission rate (WVTR) less than 3.7 g/sqm/24 hrs at 38°C and relative humidity of 90% with optimum Co-efficient of friction (COF) of 0.16-0.17 for smooth machinability.