Heat-sensitive stencil, method of preparing stencil printing master and stencil printer

1. A heat-sensitive stencil comprising:

a thermoplastic resin film,

a porous resin layer provided on said thermoplastic resin film, and

one or more porous reinforcing layers having a tensile strength of at least 385 N/m,

wherein the one or more porous reinforcing layers are provided on a side of said porous resin layer which is opposite to the thermoplastic resin film, and

wherein at least one of said porous reinforcing layers is a fibrous layer formed from fibers having a diameter at least 21 μm.

2. A heat-sensitive stencil as set forth in claim 1 , wherein at least one of said porous reinforcing layers is a layer of a mesh screen.

3. A heat-sensitive stencil as set forth in claim 1 , wherein at least one of said porous reinforcing layers is a resin layer obtained by printing or coating.

4. A heat-sensitive stencil as set forth in claim 2 , wherein said only one porous reinforcing layer is present.

5. A heat-sensitive stencil as set forth in claim 3 , wherein said only one porous reinforcing layer is present.

6. A heat-sensitive stencil as set forth in claim 1 , further comprising at least one fibrous porous layer provided between said porous resin layer and said porous reinforcing layers.

7. A heat-sensitive stencil as set forth in claim 6 , wherein at least one of said porous reinforcing layers is a fibrous layer formed from a fiber having a diameter greater than the fiber of said fibrous porous layer.

8. A heat-sensitive stencil as set forth in claim 1 , wherein said porous resin layer has pores exposed to a surface thereof to form a multiplicity of openings, and wherein the total area of said openings having an equivalent diameter of at least 5 μm is 4-80% of the area of said surface of said porous resin layer, said equivalent diameter being defined as a diameter of a circle having the same area as that of the corresponding opening.

9. A heat-sensitive stencil as set forth in claim 1 , wherein said porous resin layer has pores exposed to a surface thereof to form a multiplicity of openings, wherein the total area of said openings having an equivalent diameter of at least 5 μm is at least 50% of a total area of said openings, said equivalent diameter being defined as a diameter of a circle having the same area as that of the corresponding opening.

10. A heat-sensitive stencil as set forth in claim 1 , and providing air permeability of 1.0 cm 3 /cm 2 ·sec to 157 cm 3 /cm 2 ·sec, when perforated to have an open ratio of at least 20%.

11. A heat-sensitive stencil as set forth in claim 1 , and provided with imagewise perforations each having an area of at least D μm, wherein said porous resin layer has pores exposed to a surface thereof to form a multiplicity of openings, wherein the total area of said openings is Y % of a total area of said surface, and wherein D and Y have the following relationship:

D =(61 −Y )/0.0063.

12. A method of preparing a printing master, comprising perforating a heat-sensitive stencil as set forth in claim 1 with part of said porous resin layer in each perforation remaining unremoved and covering the perforation.

13. A heat-sensitive stencil as set forth in claim 6 , wherein said porous resin layer has pores exposed to a surface thereof to form a multiplicity of openings, and wherein the total area of said openings having an equivalent diameter of at least 5 μm is 4-80% of the area of said surface of said porous resin layer, said equivalent diameter being defined as a diameter of a circle having the same as that of the corresponding openings.

14. A heat-sensitive stencil as set forth in claim 6 , wherein said porous resin layer has pores exposed to a surface thereof to form a multiplicity of openings, wherein the total area of said openings having an equivalent diameter of at least 5 μm is at least 50% of a total area of said openings, said equivalent diameter being defined as a diameter of a circle having the same area as that of the corresponding opening.

15. A heat-sensitive stencil as set forth in claim 6 , and providing air permeability of 1.0 cm 3 /cm 2 ·sec to 157 cm 3 /cm 2 ·sec, when perforated to have an open ratio of at least 20%.

16. A heat-sensitive stencil as set forth in claim 6 , and provided with imagewise perforations each having an area of at least D μm, wherein said porous resin layer has pores exposed to a surface thereof to form a multiplicity of openings, wherein the total area of said openings is Y % of a total area of said surface, and wherein D and Y have the following relationship:

D =(61 −Y )/0.0063.

17. A method of preparing a printing master, comprising perforating a heat-sensitive stencil as set forth in claim 6 with part of said porous resin layer in each perforation remaining unremoved and covering the perforation.

18. A stencil printer having a stencil as set forth in claim 1 .

19. A stencil printer having a stencil as set forth in claim 6 .