Thermoplastic films having asymmetric properties

1. A thermoplastic film, comprising:

a biaxially-oriented polyethylene terephthalate (PET) layer;

an acrylic primer layer on at least one side of the film, wherein the acrylic primer layer comprises cross-linking agents;

a tensile strength in the longitudinal direction of about 2000 kg/cm 2 or more;

a tensile strength in the transverse direction of about 3000 kg/cm 2 or more;

a crystallinity in the transverse direction that is reduced as compared to a crystallinity in the longitudinal direction; and

a tear force in the longitudinal direction that is about 1.5 times as large as a tear force in the transverse direction;

wherein the polyethylene terephthalate layer comprises a polyethylene terephthalate homopolymer.

2. The film of claim 1 , wherein the polyethylene terephthalate layer further comprises a polyethylene terephthalate copolymer.

3. The film of claim 1 , further comprising a coating on at least one side of the film, the coating selected from the group consisting of an acrylic coating, a polyurethane coating, a polysulphonester coating, and a quaternary ammonium-based coating.

4. The film of claim 1 , wherein the film comprises two or more layers.

5. The film of claim 4 , wherein the film consists essentially of three layers.

6. The film of claim 4 , wherein one or more of the layers includes silica.

7. The film of claim 6 , wherein the one or more layers that include silica have a dynamic coefficient of friction to steel of about 0.45 or less.

8. The film of claim 6 , wherein the layer that includes silica is comprised of polyethylene terephthalate.

9. The film of claim 6 , wherein the layer that includes silica is interposed between layers that do not include silica.

10. The film of claim 6 , wherein the film comprises, from top to bottom, a first polyethylene terephthalate layer, a polyethylene terephthalate-silica layer, and a second polyethylene terephthalate layer.

11. The film of claim 1 , wherein the one or more layers that include silica have a dynamic coefficient of friction to steel of about 0.45 or less when heated to 150° C.

12. The film of claim 1 , wherein the film has a total thickness of about 50 μm or less.

13. The film of claim 1 , wherein the film has a total thickness of about 30 μm or less.

14. The film of claim 1 , wherein the film has a total thickness of about 5 μm to about 15 μm.

15. A process for producing the thermoplastic film of claim 6 , comprising:

producing a biaxially-oriented polyethylene terephthalate (PET) layer which comprises a polyethylene terephthalate homopolymer;

producing a biaxially-oriented polyethylene terephthalate layer that includes silica (PET-silica);

laminating the polyethylene terephthalate layer on one or both sides of the polyethylene terephthalate-silica layer to produce a multilayer film;

applying an acrylic primer layer on at least one side of the film;

stretching the multilayer film in a longitudinal direction; and

stretching the multilayer film in a transverse direction.

16. The process of claim 15 , wherein the step of stretching the multilayer film in the longitudinal direction includes stretching the multilayer film by a factor of about 2 to about 4.

17. The process of claim 15 , wherein the step of stretching the multilayer film in the transverse direction includes stretching the multilayer film by a factor of about 3 to about 4.5.

18. The process of claim 15 , wherein the step of stretching the multilayer film in the transverse direction is performed at a temperature of about 80° C. to about 140° C.

19. The process of claim 15 , further comprising coating at least one side of the multilayer film after the step of stretching the multilayer film in a longitudinal direction and prior to the step of stretching the multilayer film in the transverse direction.

20. The process of claim 19 , wherein coating the multilayer film comprises inline coating the multilayer film.

21. A thermoplastic film produced by the process according to claim 15 .