Polyester film and lithographic plate

Abstract

A lithographic plate includes a substrate made of a polyester film having a light transmittance of 50% or less, a bending angle in the range of 30 DEG to 90 DEG , and a rupture strength after being bent of 8 kg/mm2 or more. Alternatively, a lithographic plate includes a substrate made of a polymer film containing a polyester and a thermoplastic resin incompatible with the polyester, wherein the polymer film is oriented along at least one axis and has minute cavities formed by the orientation, and the density of the film is in the range of 1.05 g/cm3 to 1.3 g/cm3.

What is claimed is: 
     
       1. A lithographic plate comprising a substrate made of a polyester film having a light transmittance of 50% or less, a bending angle in the range of 30° to 90°, and a rupture strength after being bent of 8 kg/mm 2  or more. 
     
     
       2. A lithographic plate according to claim 1, which has a hydrophilic layer subjected to corona treatment and a photosensitive layer formed on the substrate in this order. 
     
     
       3. A lithographic plate according to claim 2, wherein the hydrophilic layer is made of a composition containing a water-soluble or water-dispersible binder and zinc oxide dispersed in the binder, and the composition becomes a water-insoluble hydrophilic substance by the reaction between a component in an etchant for the lithographic plate and the zinc oxide. 
     
     
       4. A lithographic plate according to claim 1, which has a conductive intermediate layer and a photoconductive layer formed on the surface of the substrate in this order, and has at least one of a conductive back coat layer and a dielectric back coat layer formed on the reverse surface of the substrate. 
     
     
       5. A lithographic plate according to claim 4, wherein the surface resistivity of the conductive intermediate layer is in the range of 10 2  Ω/cm 2  to 10 8  Ω/cm 2 . 
     
     
       6. A lithographic plate according to claim 4, wherein the surface resistivity of the conductive back coat layer is in the range of 10 2  Ω/cm 2  to 10 12  Ω/cm 2 . 
     
     
       7. A lithographic plate according to claim 4, wherein the dielectric constant of the dielectric back coat layer is 5 or more. 
     
     
       8. A lithographic plate according to claim 1, which has a conductive intermediate layer and a hydrophilic layer formed on the substrate in this order, or has a hydrophilic layer having a surface resistivity in the range of 10 8  Ω/cm 2  to 10 13  Ω/cm 2  directly formed on the substrate. 
     
     
       9. A lithographic plate comprising a substrate made of a polymer film containing a polyester and a thermoplastic resin incompatible with the polyester, wherein the polymer film is oriented along at least one axis and has minute cavities formed by the orientation, and the density of the film is in the range of 1.05 g/cm 3  to 1.3 g/cm 3 .   
     
     
       10. A lithographic plate according to claim 9, which has a hydrophilic layer subjected to corona treatment and a photosensitive layer formed on the substrate in this order. 
     
     
       11. A lithographic plate according to claim 10, wherein the hydrophilic layer is made of a composition containing a water-soluble or water-dispersible binder and zinc oxide dispersed in the binder, and the composition becomes a water-insoluble hydrophilic substance by the reaction between a component in an etchant for the lithographic plate and the zinc oxide. 
     
     
       12. A lithographic plate according to claim 9, which has a conductive intermediate layer and a photoconductive layer formed on the surface of the substrate in this order, and has a conductive or dielectric back coat layer formed on the reverse surface of the substrate. 
     
     
       13. A lithographic plate according to claim 12, wherein the surface resistivity of the conductive intermediate layer is in the range of 10 2  Ω/cm 2  to 10 8  Ω/cm 2 . 
     
     
       14. A lithographic plate according to claim 12, wherein the surface resistivity of the conductive back coat layer is in the range of 10 2  Ω/cm 2  to 10 12  Ω/cm 2 . 
     
     
       15. A lithographic plate according to claim 12, wherein the dielectric constant of the dielectric back coat layer is 5 or more. 
     
     
       16. A lithographic plate according to claim 9, which has a conductive intermediate layer and a hydrophilic layer formed on the substrate in this order, or has a hydrophilic layer having a surface resistivity in the range of 10 8  Ω/cm 2  to 10 13  Ω/cm 2  directly formed on the substrate. 
     
     
       17. A lithographic plate comprising a substrate made of a polymer film containing a polyester and a thermoplastic resin incompatible with the polyester, wherein the polymer film is oriented along at least one axis and has minute cavities formed by the orientation, and the density of the film is in the range of 1.05 g/cm 3  to 1.3 g/cm 3 , the polymer film having a light transmittance of 50% or less, a bending angle in the range of 30° to 90°, and rupture strength after being bent of 8 kg/mm 2  or more.   
     
     
       18. A lithographic plate according to claim 17, which has a hydrophilic layer subjected to corona treatment and a photosensitive layer formed on the substrate in this order. 
     
     
       19. A lithographic plate according to claim 18, which has a hydrophilic layer is made of a composition containing a water-soluble or water-dispersible binder and zinc oxide dispersed in the binder, and the composition becomes a water-insoluble hydrophilic substance by the reaction between a component in an etchant for the lithographic plate and the zinc oxide. 
     
     
       20. A lithographic plate according to claim 17, which has a conductive intermediate layer and a photoconductive layer formed on the surface of the substrate in this order, and has a conductive or dielectric back coat layer formed on the reverse surface of the substrate. 
     
     
       21. A lithographic plate according to claim 20, wherein the surface resistivity of the conductive intermediate layer is in the range of 10 2  Ω/cm 2  to 10 8  Ω/cm 2 . 
     
     
       22. A lithographic plate according to claim 20, wherein the surface resistivity of the conductive back coat layer is in the range of 10 2  Ω/cm 2  to 10 12  Ω/cm 2 . 
     
     
       23. A lithographic plate according to claim 20, wherein the dielectric constant of the dielectric back coat layer is 5 or more. 
     
     
       24. A lithographic plate according to claim 17, which has a conductive intermediate layer and a hydrophilic layer formed on the substrate in this order, or has a hydrophilic layer having a surface resistivity in the range of 10 8  Ω/cm 2  to 10 13  Ω/cm 2  directly formed on the substrate. .Iadd. 
     
     
       25.  A polyester film having a light transmittance of 50% or less, a bending angle in the range of 30° to 90°, and a rupture strength after being bent of 8 kg/mm 2  or more. .Iaddend..Iadd.26. The polyester film according to claim 25, which is a multilayer film having a cavity inclusion rate gradually increasing from the front layer towards the back layer along the thickness direction of the film. .Iaddend..Iadd.27. A polymer film comprising a polyester and a thermoplastic resin incompatible with the polyester, wherein the polymer film is oriented along at least one axis and has minute cavities formed by the orientation, and the density of the film is in the range of 1.05 g/cm 3  to 1.3 g/cm 3 . .Iaddend..Iadd.28. A polymer film comprising a polyester and a thermoplastic resin incompatible with the polyester,   wherein the polymer film is oriented along at least one axis and has minute cavities formed by the orientation, and the density of the film is in the range of 1.05 g/cm 3  to 1.3 g/cm 3 , the polymer film having a light transmittance of 50% or less, a bending angle in the range of 30° to 90°, and rupture strength after being bent of 8 kg/mm 2  or more. .Iaddend.