The present invention relates to a biaxially oriented polypropylene (BOPP) film, which is useful as wrap around labels possessing high stiffness and excellent antistatic properties.
Further more, this invention depicts an opaque, cavitated biaxially oriented polypropylene film with very high yield & stiffness that helps easy die-punch and dispensing.
In normal practice, white opaque films are made with the help of Calcium carbonate masterbatch and titanium di-oxide, in masterbatch form. These inorganic components, when added in Polymer matrix, like polypropylene or polyethylene or any other polyolefins, they form voids thanks to their incompatibility with polymer matrix.
However, such voided films lack properties like gloss & stiffness. Lack of gloss hampers aesthetics & low stiffness hampers runnability & dispensing.
Prior Art
US patent # 4377616 teaches use of nylon as void initiating particles an opaque, biaxially oriented polymeric film structure of lustrous satin appearance comprises, a core thermoplastic polymer matrix material within which is located a strata of voids; positioned at least substantially within at least a substantial number of each of said voids, is at least one spherical void-initiating solid particle which is phase distinct and incompatible with said matrix material, the void-space occupied by said particle being substantially less than the volume of said void, with one generally cross-sectional dimension of said particle at least approximating a corresponding cross-sectional dimension of said void; void-free, transparent, thermoplastic skin layers adhering to the surfaces of said core layer, said skin layers being of a thickness such that the outer surfaces Thereof do not at least substantially, manifest the surface irregularities of said

of less than 70% light transmission: said structure having a 45 degree gloss measurement greater than 100%. However, nylon being a hygroscopic material absorbs moisture that causes bubble during film formation.
Summary of the Invention
This present invention relates to a biaxially oriented film with improved gloss & stiffness. It is a further objective of this invention to facilitate easy dispensing of labels.
The film structure of the present invention is an opaque, biaxially oriented polymeric film structure comprising:
a thermoplastic material, for example. Polypropylene, voided with an incompatible polymer. This incompatible polymer is polybutylene terephthalate in spherical form and around which formed are voids, owing to incompatibility. Such a voided matrix results in reduction in density of polymer matrix, depending upon the extent of void formation.
In a preferred embodiment of this invention, the aforementioned film structure is having on at least one surface thereof a void-free thermoplastic skin layer of a thickness such that the outer surface thereof does not, at least substantially, manifest any surface irregularities of said core layer.
The invention is also directed to a resin combination comprising a thermoplastic polymer matrix and dispersed therein, as a distinct phase, a multiplicity of small spherical solid particles of polybutylene terephthalate.
The other embodiments resides in the invention is also directed to a process for preparing the composition resin combination comprising:

heating at least to a flowable condition a thermoplastic polymeric matrix material having a melting point lower than that of polybutylene terephthalate;
adding to the molten polymer polybutylene terephthalate and heating the combination to above the melting point of the polybutylene terephthalate;
subdividing and uniformly dispersing the molten polybutylene terephthalate into discrete spherical particles throughout said matrix material; and while so subdivided decreasing the temperature to solidify the polybutylene terephthalate, further decreasing the temperature to solidify said polymer matrix material.
Statement of Invention:
The present invention relates to a biaxially oriented film with improved gloss and stiffness comprising a core layer of 50-95% of the total thickness and made up of a resin combination and sandwiched between two skin layers each of 5 to 25% of the total thickness said skin layers made up of polypropylene compounded with antiblocking agents; wherein the resin combination comprises a thermoplastic polymer matrix and dispersed therein, as a distinct phase, a multiplicity of small spherical particles of incompatible organic polymers.
The present invention also relates to a process for preparing a biaxially oriented film with improved
gloss and stiffness as claimed in claim 1 comprising the following steps:
(i) extruding three melt streams from three separate extrudes namely core layer through the main
extruder, satellite I and satellite II for skin layer I and II;
(ii) pressing extruded layers in a slit die which are extruded as a single layer;
(iii) quenching the said single layer on a chill roll and/or water bath and/or combination of both;
(iv) stretching at least mono axially, preferably biaxially, longitudinally at a temperature of 110 to
150°C;and
(v) reheating and stretching in cross-section or transverse direction at a temperature range of 130 to 190C0, heat setting or annealed or thermally fixed at a temperature 1 to 35oC below transverse stretching temperature, thus obtaining the final film.

DESCRIPTION OF THE INVENTION
The invention is further directed to a process for preparing a biaxially oriented opaque film by forming an extruded film of the above described resin combination and thereafter biaxially orienting the film either simultaneously or sequentially.
In the preferred embodiment, the film is a multi layer, precisely three layered, opaque consisting of polypropylene polymer. Out of the three layers, core layer accounts for 50-95 % of the total thickness, preferably 75-90%. Minor layers are called skin layers, namely skin I, comprising 2.5 to 25% of the total thickness, preferably 5-12.5% of total film thickness and skin II. comprising 2.5 to 25% of the total thickness, preferably 5-12.5% of total film thickness.
In a further preferred embodiment, core layer consists of polypropylene polymer with melt flow index of 0.2 to 7 g/ 10 min., preferably 1 to 6 g/ 10 min and more preferably 2.5 to 4.5 g/10 min. The selected polypropylene polymer for core layer has a crystallinity of more than 60% and isotactic index of more than 80%, preferably more than 90%. Melting point of the subject polypropylene is not less than 160 C. Polypropylene selected

for core layer is a commonly available commercial grade such as PD 382 from Montell for an example.
In a further embodiment of this invention, core layer also contains incompatible organic polymers like Nylon, Potybutylene terephthalate (PBT), Polyethylene terephthalate, etc. More preferably, core layer contains Polybutylene terephthalate (PBT) to the tune of 2 to 30%, preferably between 4 and 10%.
When a master batch precursor composition is made for ultimate dilution with more matrix polymer for a final film, the master batch can contain as much PBT as can practically be dispersed in the thermoplastic matrix polymer in spherical subdivided particles of a size ranging from about 0.1 to about 10 microns. With little difficulty up to about 30% by weight of the PBT can be dispersed, in this size range, in the matrix resin. It is preferred that the degree of opacity of the oriented film be less than 70% light transmission. The opacity of the film can be enhanced by the inclusion in the film of from about 1 to 3% by weight of a pigment, such as TiO.sub.2, colored oxides and the like. The pigment should be in a particle size such that it does not contribute in any material sense to void initiation in the matrix resin.
The polybutylene terephthalate (PBT), is a highly crystalline polymer characterized by good mechanical, chemical, electrical properties and a rapid crystallization rate. It has a melting point of 226.degree. C. and a glass transition temperature of approximately 40.degree. C. Typical processing conditions for PBT range from 235.degree.- 260.degree. C. However, temperatures above 270 deg. C are to be avoided.
The thermoplastic matrix resin for the PBT resin can be any thermoplastic resin material which is incompatible with the PBT and which can be oriented in film form. Incompatibility means existence of two distinct phases. Particularly preferred as the matrix resin for the PBT is polypropylene.

In a preferred embodiment of this invention, PBT is added as a compound during film formation as it helps better dispersion.
In order to improve slip properties of the film slip agents such as, erucamide, Oleamide, glycerol mono stearate (GMS), waxes and metallic greases are added at a concentration between 10 and lOOOppm, preferably 20-500 ppm and more preferably. 50-150ppm. In addition, polymers from the polysiloxane group are used.
To minimize static charge anti static agents comprising alkali alkanesulphonates, polyether-modified i.e., ethoxylated and/or propoxylated polysiloxanes and/or straight chain, saturated aliphatic tertiary amines, which contain an aliphatic radical with 10 to 20 carbon atoms and which contain two hydroxyalkyl (C1-C4 groups as substituents, among which N, N-bis(2-hydroxyethyl)-alkylamines with C10-C20, preferably C12-C18, as the alkyl groups are particularly suitable. The effective amount of antistatic agent falls within the range of 0.05 to 3.0% by weight with respect to the concerned.
Skin I, comprising 2.5 to 25% of the total thickness, preferably 5-12.5% of total film thickness, predominantly of polypropylene polymer with melt flow index of 0.2 to 7 g/ 10 min., preferably 1 to 6 g/ 10 min and more preferably 2.5 to 4.5 g/ 10 min. Skin I also contains anti blocking agents that are spherical, organic compounds such as polymethyl methacrylate, Nylon, Polyisobutyl methacrylate, Polydimethyl siloxanes or simply silicones to name a few. These organic antiblocks may be used separately or in combination and in the range of 0.01 to 2.0%,, preferably 0.02 to 1.0%.
Skin II, comprising 2.5 to 25% of the total thickness, preferably 5-12.5% of total film thickness, predominantly of polypropylene polymer with melt flow index of 0.2 to 7 g/10 min., preferably ) ro 6 g/ 10 min and more preferably 2.5 to 4.5 g/ 10 min. Skin II also contains anti blocking agents that are spherical, organic compounds such as polymethyl
methacrylate. Nylon. polyi-obutyl mathacrylate. Polydimethyl silexanes or simply

silicones to name a few. These organic antiblocks may be used separately or in combination and in the range of 0.01 to 2.0%, preferably 0.02 to 1.0%.
The films according to the invention may be produced by monoaxial orientation or preferably biaxial orientation both by double bubble process and sequential stretching on a tenter frame followed by melt extrusion. Three melt streams from three extruders, namely main extruder giving the core layer, satellite I for skin I and satellite II for skin II, are pressed together in the slit die and are extruded as a single sheet. This is quenched on a chill roll and/or water bath and/or a combination of both and is stretched at least mono axially, preferably biaxially. In the course, the film is stretched in the machine direction or longitudinally at a ratio of 4:1 to 7:1, preferably 5:1 to 6:1. at a temperature of 110 to 150°C, preferably 120 to 145°C. This monoaxially oriented polymeric film is reheated and stretched in the cross direction or transverse direction with a stretch ratio of 8:1 to 12:1, preferably 9:1 to 11:1. This is effected at a temperature range of 130 to 190°C, preferably 145 to 170 C. So produced biaxially oriented polypropylene film is heat set or annealed or thermally fixed at a temperature 1 to 35 C below transverse stretching temperature.
At the end of this operation, final film thickness is 20 to 80µ preferably 25 to 70p. Before taking the film on winder, edges of the film carried by the clips of transverse direction orienter is trimmed and recycled.
Generally, the polyolefinic single layer or multi layer films, as found out in the invention are considerably non-polar, which makes the spreading of inks, adhesives, etc., exempli gratia, on the film surface difficult or impossible. In order to increase the surface energy or wettability of the film by known processes such corona treatment, flame treatment, plasma treatment and fluorine pretreatment. In this invention film surface is exposed to corona discharge or a beam of electrons, which in effect deposits the atmospheric oxygen on the surface in the form of carbonyl, epoxide, ether and/cr alcohol groups. These

groups increase the surface energy of film and hence the affinity for printing inks or adhesives. Treatment intensities fall in the range of 36 to 42 dynes/cm.
Film thus produced can be printed, die-punched and used for PS label application or can be used for wrap around label application in roll form..
Accordingly the present invention relates to a biaxially oriented film with improved gloss and stiffness comprising a core layer accounting for 50-95% of the total thickness made up of a resin combination and sandwiched between twfo skin layers each accounting for 5 to 25% of the total thickness made up of polypropylene compounded with antiblocking agents.
The present invention also relates to a process for preparing a biaxially oriented film with improved
gloss and stiffness as claimed in claim 1 comprising the following steps:
extruding three melt streams from three separate extrudes namely core layer through the main
extruder, satellite I and satellite II for skin layer I and II;
pressing extruded layers in a slit die and are extruded as a single layer;
quenching the said single layer on a chill roll and/or water bath and/or combination of both;
stretching at least mono axially, preferably biaxially, longitudinally at a temperature of 110 to 150°C;
and reheating and stretching in cross-section or transverse direction at a temperature range of 130 to
190C0, heat setting or annealed or thermally fixed at a temperature 1 to 35°C below transverse
stretching temperature, thus obtaining the final film.

Example 1
A biaxially oriented polypropylene multi layer film was produced by means of the coextrusion process as described elsewhere, with the preferred stretching ratios (machine direction 5:1 and transverse direction 9.5:1) at an average machine direction stretching temperature of 135 C and at an average transverse direction stretching temperature of 165 C. The external surfaces of the skin layers are corona treated to 44 dyne/cm. The entire film thickness is 38µ or 152 gauge and its composition is as under
(Table Removed)

Example 2
A three layer film with a total thickness of 38µ was produced by the process depicted in example I, but the raw material composition was altered as follows
(Table Removed)
Comparison 1
A three layer film with a total thickness of 38µ was produced by the process depicted in example I, but the raw material composition was altered as follows
(Table Removed)
The properties of the three layered biaxially oriented polypropylene films of examples and comparison have been compared and summarized in a table A.

The superiority of the three layer, biaxially oriented film produced according to the invention corresponding to" examples 1 - 2 is exhibited in high stiffness & consequent ease of dispensing.
Table A
(Table Removed)
Opacity
Opacity is the tendency of film to block light rays and therefore transmission is reduced to drastic low.
45° Gloss
Gloss is a measure of specular reflection of light from the surface and the successive layers of the film at a specified angle. The gloss measurement was performed following ASTM D 2457. The gloss is in units GE, which are based on Wood's glass standard. The value of the surface gloss should be as high as possible.
Stiffness
It is nothing but Secant Modulus, i.e., Stress/Strain at 1% elongation.
Friction
Frictional properties of the film were studied according to ASTM D 1894. This basically
throws light on the sliding behavior of the film with another layer of the same film and
with metal surface.
Friction under weight is an indication of the ease with which a laminate can slide in a
stack. This was also measured the same way as mentioned afore. The values have been
tabulated in table A. Lower the value of coefficient of friction; lower the tendency to
lock.
The subject application is a mere statement of invention where alterations and modifications are possible without deviating from the scope of the invention. Hence, the same should not be construed to restrict the scope of the invention.

We claim:
1. A biaxially oriented film with improved gloss and stiffness comprising a core layer of 50-95% of the total thickness and made up of a resin combination and sandwiched between two skin layers each of 5 to 25% of the total thickness said skin layers made up of polypropylene compounded with antiblocking agents; wherein the resin combination comprises a thermoplastic polymer matrix and dispersed therein, as a distinct phase, a multiplicity of small spherical particles of incompatible organic polymers.
2. The biaxially oriented film with improved gloss and stiffness as claimed in claim 1, wherein the incompatible polymer in the said resin combination is nylon, polybutylene terephthalate (PBT) or polyethylene or a combination thereof.
3. The biaxially oriented film with improved gloss and stiffness as claimed in claim 1, wherein the
incompatible polymer in the said resin combination is polybutylene terephthalate (PBT).
4. The biaxially oriented film with improved gloss and stiffness as claimed in claim 1, wherein the incompatible polymer in the said resin combination is 2 - 30% of the total volume of core layer.
5. The biaxially oriented film with improved gloss and stiffness as claimed in any of the preceding claims, wherein the polypropylene polymer has a melt flow index of 0.2 to 7g/10 min the crystallanity of more than 60% and isotactic index of more than 80% with the melting point of atleast 100%.
6. The biaxially oriented film with improved gloss and stiffness as claimed in claim 1, wherein the resin combination is prepared by the following process:

(a) heating at least to a flowable condition a thermoplastic polymeric matrix material having a melting point lower than that of polybutylene terephthalate;
(b) adding polybutylene terephthalate to the heated thermoplastic polymer and heating the combination to above the melting point of the polybutylene terephthalate; and
(c) subdividing and uniformly dispersing the molten polybutylene terephthalate into discrete spherical particles throughout said matrix material; and while so subdivided decreasing the temperature to solidify the polybutylene terephthalate, further decreasing the temperature to solidify said polymer matrix material.

7. A process for preparing a biaxially oriented film with improved gloss and stiffness as claimed in
claim 1 comprising the following steps:
(i) extruding three melt streams from three separate extrudes namely core layer through the main
extruder, satellite I and satellite II for skin layer I and II;
(ii) pressing extruded layers in a slit die which are extruded as a single layer;
(iii) quenching the said single layer on a chill roll and/or water bath and/or combination of both;
(iv) stretching at least mono axially, preferably biaxially, longitudinally at a temperature of 110 to
150°C;and
(v) reheating and stretching in cross-section or transverse direction at a temperature range of 130 to
190C°, heat setting or annealed or thermally fixed at a temperature 1 to 35°C below transverse
stretching temperature, thus obtaining the final film.
8. The process for preparing a biaxially oriented film with improved gloss and stiffness as claimed in claim 7, wherein the film is reheated and stretched with stretch ratio of 8:1 to 12:1.
9. The process for preparing a biaxially oriented film with improved gloss and stiffness as claimed in claim 7, wherein the film is produced by monoxial orientation or biaxially orientation both by double bubble process and sequential stretching on a tenter frame followed by melt extrusion.
10. The process for preparing a biaxially oriented film with improved gloss and stiffness as claimed in
claim 7, wherein the said film is produced is used for wrap around label application in roll form.
11. A biaxially oriented film with improved gloss and stiffness, substantially as hereinbefore described
with reference to the foregoing examples.
12. A process for preparing a biaxially oriented film, substantially as hereinbefore described with reference to the foregoing examples.