FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
THE PATENTS RULES, 2003
As amended by the Patents (Amendment) Rules, 2006
PROVISIONAL SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
Polypropylene film based sheets
APPLICANTS
Reliance Industries Limited, 5 Floor, Maker Chamber IV, Nariman Point, Mumbai 400 021, Maharashtra, India, an Indian Company
PREAMBLE TO THE DESCRIPTION
The following specification describes the invention. :

Field of Invention
The invention relates to oriented polypropylene film based sheets and to a process for
preparing them from biaxially oriented polypropylene films.
Background
Conventionally, polypropylene sheets are prepared by extrusion process wherein
polypropylene is melted and forced through an extruder. Polypropylene sheets so
prepared are usually used for low end thermoforming applications like manufacture of
disposable containers. To increase the durability of the sheets and to extend the scope of
their applications, it is required that they possess good combination of mechanical
properties like tensile strength, stiffness and impact strength. Also, in order to improve
the aesthetic appeal of the articles prepared from polypropylene sheets, it is desirable that
the sheets have good translucence and can be incorporated with decorative materials
during their manufacture.
Detailed description of the invention
The invention provides a process for preparing oriented polypropylene sheets with good combination of mechanical properties like tensile strength, stiffness and impact strength and with good translucence. The polypropylene film based sheets of the invention have the potential of being used for high end engineering applications and for applications requiring good aesthetic appeal. The invention also provides a process for preparing oriented polypropylene film based sheets, the process comprising stacking a plurality of
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polypropylene substrates one above another, heat sealing the substrates under pressure and cooling the sheet formed in the pressed condition, the substrates each comprising a biaxially oriented polypropylene film and a layer of sealant material having melting point lower than the film, stretch ratio of the film in the transverse direction being greater than that in the longitudinal direction. Stacking of the films is carried out in such a manner that the orientations of adjacent films are aligned or distributed or staggered as to obtain sheets having their mechanical properties correspondingly oriented or distributed or staggered. In one embodiment, the stacking is done in such a manner that the stretching orientations in adjacent films are staggered so as to allow distribution of molecular orientation between adjacent films resulting in overall reinforcement of mechanical properties among films forming the sheet. In another embodiment, the stacking is done in such a manner that stretching orientations along any of the directions in a given film aligns with the stretching orientation along the same direction in the adjacent film so as to allow preferential distribution of molecular orientation along a particular direction among adjacent films resulting in preferential reinforcement of mechanical properties along a particular direction among films forming the sheet. In a preferred embodiment, the stacking is done in such a manner that longitudinal stretching orientation in a given film aligns with the transverse stretching orientation of the adjacent film so as to allow even distribution of molecular orientation along both transverse and longitudinal directions resulting in reinforcement of mechanical properties along both transverse and longitudinal directions among films forming the sheet.
The invention also involves a process for preparing polypropylene sheets of varied translucence and mechanical properties by interposing the polypropylene films with
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materials other than biaxially oriented polypropylene film. The materials that are interposed between the polypropylene films include metal foils, metallic meshes, decorative materials and polyolefin fabrics. Such materials are often coated by a sealant material having melting point lower than the biaxially oriented polypropylene film. By interposing polypropylene films with materials of varied transparency, polypropylene sheets that are translucent or opaque are prepared. By interposing the polypropylene films with meshes and of opaque sheets with interstitial spaces, partly opaque polypropylene sheets with intermittent translucent regions are prepared. Polypropylene sheets having decorative appeal are prepared by interposing polypropylene films with decorative materials.
The process of the invention results in fusion bonding of films of polypropylene to form oriented sheets with orientation of the sheets being distributed, oriented (aligned) or staggered in such a manner as to obtain mechanical properties of the sheets in the desired manner. The method is suitable to prepare polypropylene sheets of high thickness and good translucence.
In a typical process of the invention, around 14 to 400 biaxially oriented films of polypropylene coated with a polyolefin based sealant layers are fused at a temperature of 120 -155°C and pressure of 10 - 75 bars in a multi daylight hydraulic press to produce sheets having thickness in the range of 0.5 mm to 15 mm. The sheets are then cooled under pressed condition. During the process of the invention, materials like metal foils, metallic meshes, papers or decorative materials are optionally interposed between the
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substrates forming the sheet. The thickness of each polypropylene film is around 40 micron with the thickness of the sealant layer in the range of 1- 2 microns. Oriented polypropylene sheets are prepared at an output rate of 200 kg/hr to 400 kg/hr.
The process of the invention provides oriented polypropylene sheets with desired reinforcement of mechanical properties like tensile strength, stiffness and impact strength. Oriented polyopropylene sheets with reinforcement of mechanical properties along both transverse and longitudinal directions to oriented polypropylene sheets with preferrential reinforcement of mechanical properties along a particular direction could be obtained by the process of the invention.
Due to good combination of mechanical properties, the film based polypropylene sheets of the invention can be used in reduced thickness in applications where thick conventional polypropylene sheets are used. This helps in reducing the weight as well as to provide cost competitiveness of articles produced from the sheet. The polypropylene sheets of the invention are durable and have good translucence and can be used in high end engineering applications like manufacture of automotive components. The unique combination of mechanical properties and lower cost make them a potential substitute to polycarbonate, which is a widely used thermoplastic material in engineering applications. By preparing polypropylene sheets incorporated with decorative materials, the scope of applications of polypropylene film based sheets of the invention is extended to those
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requiring good aesthetic appeal. The polypropylene sheets of the invention can be formed into shapes suitable for various high end engineering applications.

Dated this the 29th day of May 2007