Printing plate forming method and cylindrical forming apparatus for printing plate

1. A method of forming a printing plate to be mounted on an outer periphery of a cylindrical plate cylinder, the method comprising:

a notch forming step of forming a positioning notch in a rectangular elastic material sheet having a resin layer serving as a plate section formed on one surface of the elastic material sheet;

a cylindrical material forming step of rolling the elastic material sheet in which the positioning notch is formed with the positioning notch configured to engage with a positioning stepped portion extending from an end stopper of a cylinder member having the same shape as the plate cylinder and joining both end portions of the elastic material sheet in an overlapped state to form a cylindrical shape; and

a plate section engraving step of engraving a printing pattern at the plate section of the elastic material sheet formed into a cylinder shape by mounting the elastic material sheet on the plate cylinder.

2. The method of forming a printing plate as recited in claim 1 , wherein the positioning notch is provided at a position other than a joint portion in which both the end portions of the elastic material sheet are joined in an overlapped manner.

3. The method of forming a printing plate as recited in claim 1 ,

wherein the cylindrical material forming step includes:

first processing of rounding the elastic material sheet to plastically deform until a predetermined processing degree is reached; and

second processing of further rounding the elastic material sheet to overlap both end portions of the elastic material sheet into a cylindrical shape.

4. The method of forming a printing plate as recited in claim 3 , wherein in the first processing, the elastic material sheet is plastically deformed until a diameter of the elastic material sheet, after the joining, becomes about 1.2 times or more and about 3 times or less.

5. The method of forming a printing plate as recited in claim 3 , wherein the first processing is performed such that a processing degree is set to be different between one end portion side and the other end portion side of the elastic material sheet.

6. The method of forming a printing plate as recited in claim 1 ,

wherein at both side portions of a joint portion where both end portions of the cylindrically shaped elastic material sheet are overlapped and joined, bent portions are provided at a distance approximately equal to a width dimension of a flat portion formed by removing a part of an outer periphery of the plate cylinder along an axial direction, and

wherein the printing plate and the plate cylinder are positioned by the bent portions and the flat portion.

7. The method of forming a printing plate as recited in claim 6 , wherein the positioning notch is provided at a portion other than a portion between the bent portions including the joint portion.

8. The method of forming a printing plate as recited in claim 1 , further comprising a fixing step of fixing the elastic sheet material to the plate cylinder by pressing a vicinity of the positioning notch of the elastic sheet material to engage with a positioning protrusion.

9. The method of forming a printing plate as recited in claim 1 , wherein the notch forming step occurs before the joining of the end portions of the elastic material sheet in an overlapped state.