FIELD OF INVENTION
This invention relates to a thermal lamination film particularly to an extrusion coated biaxially oriented nylon (BON) base film for thermal lamination on various paper based printed substrates. Thermal lamination by using this film involves a process wherein two webs are combined under pressure and or temperature. As this process eliminates the use of solvent, it is eco-friendly. This is made possible by having a low melting polymer coated on to one of the web and this layer combines both the webs.
BACKGROUND OF THE INVENTION
Lamination is a process of pasting two different or similar substrates together to achieve hybrid properties. In case of book cover lamination, printed paper and plastic film are laminated to protect the paper against weather, water, stain and tear. This lamination is generally done by coating adhesive over plastic film and then laminating it with printed paper or paperboard. This process, which is called as "Wet Lamination" is widely used world over and predominantly in India. In USA and in few European countries, the process employed is different. Plastic films such as BOPP, Polyester or Nylon are extrusion coated with low density polyethylene (LDPE), ethylene vinylacetate (EVA) etc.. This coated film and printed paper are passed over heated rolls under pressure and thereby inducing lamination. This process is called "Thermolamination". Industry refers this as dry lamination.
Thermal laminating materials and methods are known for protecting printed substrates by adhering a protective thermoplastic polymer cover film or sheet to one or both of the major surfaces of a printed substrate. Thermal film lamination provides immediate benefits to printed materials-most notably, an attractive look and polished feel. With thermal lamination, printed materials enjoy greater durability. Unlike UV or other coatings, thermal lamination provides protection against scratching and smudging. The life of the printed materials is extended in a number of ways because thermal lamination makes paper more tear resistant and protects inks on printed substrates.
Based on various applications, the following features are required in the film.
Film for thermal lamination should be made in extra ordinary glossy varieties. Total film thicknesses for glossy should be 24^, 21 \a & 30|j..

Laminating surface should be low melting, polar & easy flowing. The opposite surface should be hot slip modified without any locking issue when laminated on both surfaces, good scuff resistance, good antistatic property to enable better & smooth runnability at elevated temperatures.
Unlike other finishes, the present invention of thermal lamination is a very safe and waste free process. It does not emit harmful volatiles and other substances into the atmosphere. Accordingly, thermal lamination is a significant breakthrough in finishing practices and contributes greatly toward preserving the environment. Earlier, less productive solvent-and water-based systems are now being changed over to thermal lamination.
PRIOR ART
U.S. Patent No. 5,626,969 teaches a method of one sided laminating and a one sided laminated product using nylon laminating film reduces the tendency of one-sided laminations to curl toward the laminating side due to moisture swelling of the paper side of the lamination.
A patent document WO 0140395 teaches a laminatory film for thermal adhesion to a substrate. This film comprises an over-laminate layer of a heat-sealeable film, a first adhesive layer of a low-density polyethylene or its copolymers contacting the overlaminate layer and a second layer contacting the first adhesive layer. The second adhesive layer comprises a material having an amount of maleic anhydride to increase adhesion of the second adhesive layer to the substrate. The over laminate layer is selected from polypropylene, nylon and polyethylene terephthalate.
Reference is also made to copending application No. 2972/DEL/2005 dated 8th November 2005 in respect of "biaxially oriented polypropylene film".
The known films however suffer from drawback in that these require higher temperature for lamination, due to which it is not possible to do lamination at high speed and yet obtain a good bond strength.
OBJECTS OF THE INVENTION

In order to over come the drawbacks of the film known in the art the present invention has the following objects.
The principal object of this invention is to propose an extrusion coated Biaxially oriented nylon base film for thermal lamination.
Another object of this invention is to propose a thermal lamination film which does not use a solvent and hence is ecofriendly.
A further advantage provided by the present invention is that new and improved thermal laminating films provide very good bonding with aqueous coated paper.
A further advantage provided by the present invention laminating surface is of low melting, point and easy flowing.
Another specialty of present invention is that the extrusion coating is possible with such thinner micron of base BON film.
The present invention also provides finished single side or both side thermal laminated assembly products which gives excellent scuff resistance and excellent optics.
The present invention also provides the opposite surface should be hot slip modified without any locking issue when laminated on both surfaces, good scuff resistance, good antistatic property to enable better & smooth runnability at elevated temperatures.
This film provides good oxygen and aroma barrier when the product is used in packaging application.
This film provides excellent flex crack resistance.
Further object of this invention is to propose a film for thermal lamination coated with a thermoplastic which is polar enough to allow chemical bond and adherence with paper substrates, ink formulations etc.
Other advantages and objects of invention will be apparent from the ensuing description. It is to be understood that the features and concepts of the invention can be adopted to various

embodiments by making changes, modification by those skilled in the art. Such variants are intended to be within the scope of the present invention.
STATEMENT OF THE INVENTION
According to the present invention there is provided a thermal laminating film comprising: a base layer of biaxially oriented nylon (BON) film having a primer coating and a thermal laminating layer disposed on the surface, wherein the said thermal laminating layer comprises 100% by weight of an ethylene vinyl acetate, copolymer containing from about 10% to about 20% by weight of vinyl acetate units and having melt flow index of 18 to 30.
According to the another aspect of the invention relates to a process for preparing a thermal laminating film comprising step
(a) feeding the biaxially oriented nylon (BON) base film to the coating rolls from
payoff roll or unwind roll amounting to decrease the diameter;
(b) coating the BON base film with a thin hot film of poly-olefin resin;
(c) passing the said thin hot film and BON base film in between two rolls under
suitable pressure for proper boding;
(d) rapid cooling the combined film of (BON) base film and polyolifin resin film
by chill roll.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Figure 1 shows the layer structure of the thermal film.
Figure 2 shows the schematic diagram of extrusion coating line.
Figure 3 shows the extrusion coating line.
Figure 4 shows the thermal laminating equipment.
Figure 5 shows the schematic diagram of process of thermal lamination m/c.
DETAILED DESCRIPTION OF THE INVENTION

Thermal or heat activated laminating films are constructed by a layer of Biaxially oriented nylon (BON) base film having a primer coating and a layer of adhesive resin (EVA), bonded together. During the lamination process, the adhesive resin is softened or liquefied and permanently bonded to the document. Once liquefied, the adhesive is spread across the surface and with pressure, forced into the pores of the paper. The adhesive then hardens as it cools creating a permanent bond between paper and film.
Pressure Sensitive laminating films are often referred to as cold films. The reason is that they require no heat or very limited amount of heat to adhere to any particular document during the laminating or mounting process'. The adhesive layer in cold film is constantly in a tacky state since no heat is used in the sealing process (only pressure). This gives the need for a paper or film liner, that keeps the film from adhering to itself when it is rolled. Pressure sensitive laminating films will adhere to almost any substrate but is best used for heat sensitive or previously heat activated materials. These films work great for overlaminating and mounting on such substrates as gator board, foam board, wood, Plexiglass or delicate print materials such as photostats, transparencies, cyberchromes and thermal transfers.
Extrusion coating is a variation of the extrusion process. In Figure 2, a substrate comes in on the left, a primer is applied and cured, and another material is applied over that from the extruder.
The primer is treated with ozone before extrusion coating.
Extrusion coating is used to protect printing. It puts a layer of material over the printed surface to prevent any scuffing or smearing. It can also be used to bond materials that can't be coextruded, materials with very different melting points, or materials that can't be extruded like paper, foil, metallized films or oriented films.
The process of thermal lamination uses heat, pressure and thermoplastic material to combine substrates without an in-line adhesive application. Webs of paper, paperboard, etc. are bonded with BON film using polyolefin thermoplastics as the bonding medium. Sufficient heat and pressure are momentarily introduced to nearly melt the thermoplastic surface at the laminating nip and create a mechanical bond. Such a coating material should also be able to make a very good bond with printed substrate, also. Thus, bonding is as much chemical as it is mechanical.

The laminating section of the roll fed thermal laminator consists of large diameter heated rolls, nip rolls, preheat rolls, idlers, spreader roll and chill rolls. The heated steel rolls are driven, and have a double-wall design, and are teflon coated. This allows for a controlled, balanced flow of large volumes of heating media for uniform temperature and dwell time on the heated rolls. Electrical heating system is also available which is controlled by thermocouple inserted in to the rolls.
Films used in thermal lamination are run over web-driven, fixed-bow rolls, which keep them wrinkle free and flat as they enter the lamination nip. After the lamination is complete, the web is transported over two or three driven, double wall, flow-through, chrome-plated-steel chill rolls. The web is cooled to room temperature to solidify the thermoplastic layer and complete the bonding process.
It has been discovered unexpectedly that a laminatable multilayered BON film may be provided which exhibits excellent thermal lamination properties on a variety of paper based printed substrates including newer ink substrates obtained by more modern digital printing methods. The new and improved thermal laminating film comprises a base layer of a BON film having modified surfaces. A thermal laminating layer is disposed on the surface, which comprises 100% by weight of an ethylene vinyl acetate copolymer containing from about 10 to about 20% by weight of vinyl acetate units.
Thermal lamination is a process, where an extrusion coated biaxially oriented nylon (BON) film, is laminated to printed paper by the application of heat & pressure, present unique thermal lamination film is made by extrusion coating of EVA or a blend with modified EVA. Thermal lamination process is an effective alternative to the conventional wet lamination, where printed paper & plastic web are laminated together with the help of water based adhesive.
Total thickness of the thermal laminating film is from about 20 micron to about 40 micron. Similarly thickness of the base layer which is made of biaxially oriented nylon film is from about 10 micron to 20 micron and the thermal layer has the thickness from about 10 to 20 micron.

However, the most important aspect of this innovation is the low melting thermoplastic that is extrusion coated on BON film. This thermoplastic has got to have excellent optics, very good flowability, low melting point.
Characteristics of the present thermal lamination film.
• A process for laminating paper & film with out water based adhesive
• A process to increase productivity
• Elimination of post lamination defects
• Clean shop floor
• No solvent emission
• Immediate post-lamination operations
In order to meet & exceed these demands, the product was conceived to have the following characteristics. They are,
• Lamination process will use heat & pressure
• Since high temperature will deform BON film itself, lamination temperature has
to be lower or typically in the range of 80 to 140 deg. C depending on the machine
speed
• This means, surface of BON film should melt at low temperature and flow
easily. Also, it needs be polar enough to give a certain degree of chemical bond
with printed paper.
Unexpectedly, in view of the foregoing, it has now been discovered that a thermally laminatable multilayered BON film may be provided which exhibits excellent thermal lamination properties on a variety of paper based printed substrates including newer ink substrates obtained by more modern digital printing methods. The new and improved thermal laminating film comprises a base layer of a BON film. A thermal laminating layer is disposed on the surface, which comprises 100% by weight of an

ethylene vinyl acetate copolymer containing from about 10 to about 20% by weight of vinyl acetate units.
In an embodiment, a new and improved method for making a thermal laminating film is provided comprising the steps of: providing a biaxially oriented nylon base layer having modified with primer for the excellent adhesion with EVA and its copolymers. The thermal laminating layer comprises 100% by weight of an ethylene vinyl acetate copolymer containing from about 10 to about 20% by weight vinyl acetate unit.
The primer is based on polyethyleneimine resin disposed in water of solid content of about 5 to 15% requiring less ozone bombardment.
In an embodiment of the method, the thermal laminating layer is applied onto the surface of the BON base layer by extrusion process.
In an embodiment, a new and improved method for making the thermal lamination films is performed at lower temperatures than commercially employed such that unwanted thermal history defects in the thermal lamination films can be dramatically reduced or eliminated.
The new and improved thermal laminating films provided in accordance with an embodiment of the invention, may be employed in thermal lamination equipment to provide new and improved thermal laminate assemblies. In accordance with this aspect of the invention, new and improved thermal laminate assemblies are provided comprising: a printed substrate, including a surface with printed ink disposed imagewise on the surface. A protective thermoplastic polymer layer is thermally laminated to the printed surface with a thermal laminating layer disposed between the protective layer and the surface. The thermal laminating layer comprises 100% by weight of an ethylene vinyl acetate, copolymer containing from about 10% to about 20% by weight of vinyl acetate and has the melt flow index between 18 to 30.

In an embodiment, a new and improved method for making a thermal laminate assembly is provided comprising the steps of preparing a printed substrate to be laminated comprising a substrate having a surface with printed ink disposed image wise on the surface. A thermal laminating film is prepared comprising a protective thermoplastic polymer planar base layer having a surface and a thermal laminating layer disposed on the surface. The thermal laminating layer comprises 100% by weight of ethylene vinyl acetate copolymer containing form about 10 to about 20% by weight of vinyl acetate. The printed substrate and thermal laminating film are moved relative to each other so that the printed substrate and thermal laminating film are disposed in a registering overlying relationship so that the thermal laminating layer is disposed on the printed surface of the substrate to form a pre-assembly. Thereafter, the pre-assembly is exposed to conditions of elevated temperature and pressure to effectively bond the thermal laminating film to the surface of the printed substrate to provide the finished thermal laminate assembly product.
R & D Center planned a production trial with production, Quality Control and Slitting Department. Various apprehensions were discussed in detail and necessary steps were decided. The important factors discussed were,
• Gel-free melt of low melting thermoplastic
• Thickness variation of coating across the width
• Defect free winding
• Good bond strength in excess of 1500g/ inch
• At maximum possible out put
• Lamination trials, etc.
Since extrusion coating of such low melting & high flowing thermoplastic is tricky, we needed to take extra precautions. On starting the trial, we faced following problems,
• Gelling: Countered by optimizing the temperature profile
• Low bond strength between base film & extrudate: Optimization of nip roll
pressure, height of the extruder head was done

• Breaks during in line trimming: Changed the position of trimming & design of
suction pipes
• Improper winding: winding tension, web path & pressure were altered &
optimized to effect proper winding.
• Productivity: Initial mismatch of web speed & extrusion speed resulted in
excessive gauge variation & improper coating. This took us lot of time of
optimize & synchronize the speeds of web & extrusion.
Example 1 (Glossy film)
(Table Remove)

"THERMAL LAMIANTION FILM"
Properties of Glossy thermal laminaiton film (Table Remove)
Surface 1 in unique BON thermal laminating film comprises with the layer of 100% by weight of an ethylene vinyl acetate copolymer containing from about 10 to about 20% by weight of vinyl acetate units and melt index of 18 to 30.
In accordance with the preferred embodiment, depicted in Fig. 1, surface 2 is the base layer of BON film before extrusion coating. Surface 2 is modified with primer before extrusion coating and thus it provides excellent bonding with ethylene vinyl acetate.
As depicted in Fig. 1, the base layer of BON film which has got excellent optics and thermal laminating layer of EVA may have a thickness of from about 10 to 20 micron.
Extrusion coating line from Fonki
Fig. 2 shows the schematic diagram and Fig. 2 shows the picture of Extrusion coating line.
As depicted in Fig. 2 & 3 there are four basic states in the extrusion coating process:
1. Resin handling and conditioning
2. Substrate handling and surface preparation
3. Extrusion coating
4. Coated substrate takeoff
Resin handling and conditioning:
The production of high quality extrusion coated substrates requires particularly close
attention to preventing resin contamination during production, storage, loading and
shipment. Since polyolefin resins are non-hygroscopic, they don't require drying prior
to being melted in the extruder. Following steps used in our process to eliminate
contamination:
• Cleaning all filters in the transfer system periodically
• Ensuring that the suction line is not lying on the ground when the system is
started. This prevents debris or gravel from entering the system.
• Placing air filters over hopper car hatches and bottom valves during unloading to
prevent debris or moisture from contaminating the resin.
• Initially purging the lines with air and then with a small amount of product prior
to filling storage silos or bins. Allow the blowers run several minutes after
unloading to clean the lines. This reduces the chance of cross-contamination of
product.
Substrate handling and surface preparation:
The extrusion coating process starts with feeding the substrate to the coating rolls from pay-off roll or unwind roll. As the substrate comes off the pay-roll, the diameter of this roll decreases. Without some compensating force, usually web tension, the decreasing diameter of the pull-off roll would manifest itself in non-uniform tension in the unrolling substrate. Without uniform tension, the coating is inconsistent. Automatic web tension control provided for the unrolling substrate and unwinder roll designs include single roll, non-indexing dual roll, roll frame, dual width turret rollstand, phantom shaft and cantilevered rollstand.
Primer coating is required for good adhesion of coating material (i.e., ethylene vinyl acetate) on BON film surface.
Extrusion coating:
To coat a substrate with polyolefin, the resin is first subjected to heat and pressure inside the barrel, or cylinder, of an extruder. Now the molten resin is then forced by the extruder screw through the narrow slit of the extrusion coating die. The slit is straight, and thus, melt emerges as thin film.
This molten film is drawn down from the die into the nip between two rolls below the die - the driven, water cooled chill roll and a rubber covered pressure roll. Here while coming into contact with the faster moving substrate on the rubber-covered pressure
roll, hot film is drawn out to the desired thickness, or gauge. The hot film is then forced onto the substrate as both layers are pressed together between the two rolls. The pressure is nearly between 50 to 100 Ibs/linear inches. The combination of substrate and polyolefin coating is then rapidly cooled by the chill roll.
The extrusion coating machine consists of the following components:
Hopper - Volumetric feeders refill the hopper on a schedule based on the extruder system's output
Extruder - The extruder is the single screw type, mounted on top of a carriage consists of:
• A gear box
• A drive motor
• A barrel that encloses a constantly turning, flighted auger screw and several
heaters (induction or resistance)
• A cooling system on the outside of the barrel
• Many thermocouples to measure and control zone temperatures via a control
instrument
• A valve adapter with a screen pack through which the melt is directed into a flat
die.
• A melt thermocouple and back pressure transducer for indicating process
conditions.
• Chill roll - The chill roll has three functions:
• In less than one revolution, it solidifies the coating and cools it to a temperature
low enough to permit the coated substrate to be rewound.
• It's speed controls the coating thickness or coating weight by drawing the melt
film form the die. Speed also controls the economy of the extrusion coating
process.
• The chill roll surface determines, to a large degree, the surface smoothness of the
coating. We have a matte finish roll to give a dull coating surface.
• The chill roll is chrome-plated, twin-shell steel drum with an outer shell and inner body containing spiral grooves for cooling water. Chill roll water temperature is maintained at 17 to 27 deg. C.
Coated substrate take-off:
After coming off the chill roll, the coated substrate passes through a series of feed rollers before it wound up by the take-off equipment. As the EVA coating melt leaves the extrusion coating slot die and is drawn down in thickness from 15 to 20 micron. With neck-in, a bead usually forms at the edge of the web, thicker than the average coating thickness across the web. The amount of beading depends upon the coating thickness relative to the thickness of the substrate. Here the beading must be trimmed off before the web is rewound. Here the trim portion is carried out by specially designed air suction. The edge trim from the extrusion coating operation is conveyed from coater through pneumatic trim disposal tubes and it is sold as scrap.
Nuclear sensor device is used to measure the coating weights. The sensor reading is used to adjust the die opening Automatically.
Corona treatment on the coated surface is done immediately after trimming. The dyne level is maintained at around 40 to 52 dynes/cm.
The extrusion coated substrate is wound tightly onto a cardboard tube, called a core. The core is turned by a winder. The winders are characterized by
• The type of take-up roll drive: centre assist
• The type of roll changing: fully automatic
Thermal lamination process
The picture of thermal lamination m/c is shown in fig. 4 and the schematic diagram is shown in Fig. 5.
In the fig. 4 and 5, the thermal film and substrate laminated each other with the application of heat (90 to 130 deg. C) and pressure.

Advantage of the Invention
Excellent optics
Clear film gives excellent optics after lamination.
Eco-friendly
As solvent is not involved either for priming or for lamination, use of dry film eliminates environmental pollution. This also eliminates the laborious task of cleaning the laminator and the work place. Thermal lamination is very safe and waste free process. It does not emi harmful volatile and other substances into atmosphere.
Enhanced Productivity:
Dry film can be laminated on high speed lines as it gives good bond strength at as low
as 95°C.
As dry lamination eliminates the stages like adhesive application & subsequent
drying, speed of lamination can be tremendously increased.
Time-saving:
Owing to immediate bond strength achieved with dry lamination film, there will be no delay in subsequent processing stages such as embossing, grooving, etc. Two side in-line laminating, in line embossing are trouble free with dry film. This saves the time lapses between lamination and subsequent operations.
Low Capital Investment:
Most conventional laminators can be converted at low cost for operating with our dry film. Now a days, such laminators are available that could be used for both solvent and dry lamination.
Above all, hassle-free film handling reduces the set up times thereby makes even short production runs economically possible.
What kinds of things can be laminated?
Lamination is for preserving, protecting, enhancing, presenting and displaying. Listed below are the applications for Thermal biaxially oriented nylon film.
Applications:
• Flexible packaging
• Retort packaging
• Book cover
• Liquid bag in a box
• Multiwall bulk bags/Large pouches
• Modern digitally printed substrates

WE CLAIM:-
1. A thermal laminating film comprising: a base layer of biaxially oriented nylon
film having a primer coating, and a thermal laminating layer disposed on the surface,
wherein the thermal laminating layer comprises 100% by weight of an ethylene vinyl
acetate copolymer containing from about 10% to 20% by weight of vinyl acetate units,
and having melt flow index of 18 to 30.
2. A thermal laminating film as claimed in claim 1, wherein the base layer
comprises a thermoplastic bi-axially oriented nylon (BON) film which is coated with
primer and then treated with ozone before extrusion coating with EVA material.
3. A thermal laminating film as claimed in claim 1, wherein the primer is
polyethyleneimine resin dispersed in water of solid content of 5 to 15% requiring less
ozone bombardment.
4. A thermal laminating film as claimed in claim 1, wherein said base layer of
biaxially oriented nylon film has a thickness about 10 micron to 20 micron.
5. A thermal laminating film as claimed in claim 1, wherein nylon is nylon 6.
6. A thermal laminating film as claimed in claim 1 wherein said thermal
laminating layer has a thickness varying from about 10 to 20 micron and a total film
thickness varying from about 20 micron to about 40 microns.
7. A process for preparing a thermal laminating film as claimed in claim 1,
comprising the following steps:
(a) feeding the biaxially oriented nylon (BON) base film to the coating roll from
payoff roll or unwind roll;
(b) coating the BON base film with a thin hot film of ethylene vinyl acetate
copolymer resin;

(c) passing the said thin hot film and BON base film between the two rolls under
suitable pressure and temperature ranging from about 80°C to 140°C for proper
bonding;
(d) rapid cooling the combined film of (BON) base film and polyolefin resin film
by chill rolls.

8. The process as claimed in claim 7, wherein automatic web tension controlling
is being provided for the pay off roll or unwind roll.
9. The process as claimed in claim 7, wherein said chill roll is maintained at a
temperature between 17 to 27°C to get rapid cooling and proper bonding of the film.
10. The process as claimed in claim 7, wherein the pressure about 50 to 100 Ibs
linear inch is maintained between the two rolls.
11. A thermal laminate assembly comprising: a printed paper based substrate
including a surface with printed ink disposed imagewise on the surface of the
substrate; and a protective thermoplastic polymer layer thermally laminated to the
surface with a thermal laminating layer disposed between the protective layer and the
surface, said thermal laminating layer comprising 100% by weight of an ethylene
vinyl acetate copolymer containing from about 10% to about 20% by weight of vinyl
acetate units and melt index is ranging from 18 to 30.
12. The method of claim 11, wherein said laminate gives good scuff resistance
when used in print lamination applications
13. A thermal laminating film as defined in claim 1 improves the oxygen and
aroma barrier properties when used in packaging applications
14. A thermal laminating film, substantially as hereinbefore described with the
accompanying drawings.

15. A process for preparing a thermal laminating film, substantially as hereinbefore described with the accompanying drawings.