JPH0558076A - Method for forming surface shape of blanket for offset printing - Google Patents

Abstract

PURPOSE:To produce a printing blanket capable of reconciling paper releasability and dot reproducibility in a high level and excellent in washability. CONSTITUTION:A printing blanket is produced from a projection forming process forming independent projections wherein the area ratio thereof is 4-below 20%, the height thereof is 15mum or less and the average surface area of the upper part of them is 2000-50000mum<2> by a printing system using a photosensitive elastomer, drying process evaporating the solvent of the projections and a curing process using the irradiation with ultraviolet rays. As the printing system, an arbitrary system such as a planographic printing system, a gravure printing system, a screen printing system or a letterpress printing system can be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a surface shape of a printing blanket used in an offset printing machine.

[0002]

2. Description of the Related Art A printing unit of an offset printing machine will be described. First, a printing plate is supplied with dampening water from a water supply device, then ink is supplied from an inking device, and an ink image on the plate is mounted on a blanket cylinder. The image is transferred to a blanket, and the image is printed on the printing paper passing between the impression cylinder and the blanket. In such offset printing, the blanket has a great influence on the print quality, and in particular, the unevenness of the blanket surface affects the quality of the printed image. The quality of the outline of the halftone dots forming the printed image and the amount of ink deposited on the halftone dots is influenced by the surface shape of the blanket. Furthermore, the surface shape of the blanket influences the ease of separation of the printing paper from the blanket when the printing paper passes between the blanket cylinder and the impression cylinder, that is, the so-called paper separation property. Problems such as deformation of the upper ink image occur. If the paper separation property is further deteriorated, the printing paper may not be separated from the surface of the blanket, and the printing paper may be cut to make printing impossible.

The blanket surface is formed by applying a powder of talc or the like to the surface rubber, vulcanizing and molding the powder, and then removing the powder by a powder coating method. There are a polishing method of polishing the surface, and an elution method of thinly applying rubber mixed with soluble particles on the surface, vulcanizing and molding, and then removing the soluble particles with a solvent to form irregularities on the surface. Then, in any of the forming methods, the Journal of the Printing Society of Japan, Vol. 19, No. 4, No. 25, No. 5, and No. 26, Vol.
The smoother the surface of the blanket, the better the reproducibility of the contours of halftone dots, etc., as reported in No. Issued by the Japan Institute of Printing. May cut the printing paper. On the other hand, in order to improve the paper releasability, the blanket surface may be roughened, but conversely, the dot reproducibility decreases. Therefore, conventionally, the balance between the image quality and the paper-releasing property has been balanced, and the surface shape of the blanket has to be controlled by sacrificing either one or the other to some extent.

Although the shape of the blanket surface varies depending on the forming method, in each case, the convex portions are continuous, and the convex portions have a constant shape such as large or small portions, or thick or thin portions. is not. As described above, in the conventional forming method, the blanket surface shape could be formed only on the irregular uneven surface.

On the other hand, Japanese Patent Application Laid-Open No. 64-22595 discloses that the composition is "a density of 20 to 70% on the surface of the surface layer" for the purpose of good paper discharge property and halftone dot reproducibility. The present invention discloses a printing blanket and a method for producing the same, in which a cylindrical or truncated cone-shaped projection is provided, and the top surface dimension of the projection is 5 to 50 μm and the height is 2.5 to 25 μm. The surface of the protrusion of the present invention is formed in a fixed shape, and is different from the conventional blanket in that it is independent.

[0006]

However, as a result of various studies by the inventor, it was found that the invention described in the above publication has the following problems. That is, the protrusions are formed by stacking a photosensitive resin on the surface layer, exposing it with a mask having a halftone dot pattern, and etching away the non-exposed portions. ~
It is extremely difficult to form a film having a density of 50 μm and a density of 20 to 70% with the current manufacturing technology, and it cannot be put to practical use. For example, the top dimension is 5 μm and the density is 70
% Pattern must use a film (mask) of 5000 DPI (dot per inch), and a pattern with a top surface dimension of 5 μm and a density of 20% must also use a 2500 DPI film. become. The size of the blanket used for the most common small-sized printing machine (Kikuhan size) currently used is 6
The size is 80 mm × 600 mm, but a halftone dot film with a maximum of 500 DPI is usually the limit for this size. Therefore, it is extremely difficult to manufacture a halftone dot film of 2500 to 5000 DPI by the current manufacturing technology.

Further, the surface of the printing blanket is cleaned by dirt or when the plate is replaced, and such cleaning is frequently performed. Then, the ink adhering to the surface of the blanket must be completely removed by washing, but if the protrusion density exceeds 20%, the gap between the protrusions becomes narrow, and the ink in the gap becomes difficult to wash, resulting in poor cleaning performance. It was found to be significantly reduced. Therefore, not only the cleaning time becomes long, but also the blanket is damaged by the cleaning liquid.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a printing blanket which is capable of achieving a high level of both paper releasability and halftone dot reproducibility and is excellent in cleaning property. It is a thing.

[0009]

In order to achieve the above object, the present invention has the following constitution. That is, an independent protrusion having an area ratio of 4% or more and less than 20%, a height of 15 μm or less, and an average surface area of 2000 to 50000 μm ² on the upper portion of the protrusion is formed on the surface of the surface layer to be a printed surface. The method is characterized by comprising a step of forming protrusions by a printing method using a photosensitive elastomer, a drying step of evaporating the solvent of the protrusions, and a curing step by irradiation of ultraviolet rays. As the printing method, a lithographic printing method, a gravure printing method, a screen printing method, a letterpress printing method, or the like can be used.

1 and 2 show an example of a blanket manufactured according to the present invention. FIG. 1 is a longitudinal sectional view, and FIG. 2 is an enlarged perspective view for explaining a surface shape traced by a micrograph. .. The blanket 10 is provided with fine independent protrusions 13 on the upper surface of the surface printing layer 11, and on the lower surface side of the surface printing layer 11, an intermediate layer 15 which is a fiber layer and a compressible layer 17 which is a foam layer are woven. Cloth support 19
Are laminated.

An oil-resistant polymer is used for the surface printing layer 11 in consideration of printing ink, ink cleaning solvent, etc., and examples thereof include polychloroprene rubber (CR), polysulfide rubber (T), polyacrylonitrile-butadiene rubber (NB).
R) or the like. Such an oil resistant polymer may be a polymer to which one or more kinds of vulcanizing agents, vulcanization accelerators, reinforcing agents, antioxidants, etc. are added.

The upper surface shape of the protrusion 13 may be any shape, and the surface shape is not particularly limited as long as it is an independent protrusion such as a circle, an ellipse, a polygon or a star. The higher the height of the protrusions 13, the better the paper-releasing property, but the reproducibility of halftone dots decreases. Therefore, the protrusion 13
The height is less than 15 μm. This is because if it exceeds 15 μm, the contour of the halftone dot is disturbed.

The average surface area of each protrusion 13 is 2000 to 50000 μm ² . Area of protrusion is 2
If it is less than 000 μm ² , good paper release property cannot be obtained,
This is because the halftone dot reproducibility deteriorates when it is 50,000 μm ² or more. Further, the effect is weakened if the number of protrusions 13 is too small or too large. That is, when the total surface area of the protrusions 13 is smaller than the total area of the surface printing layer, there is no action of the protrusions and the paper separation property deteriorates. Becomes smaller, the effect of the projection disappears, and the paper separating property and the cleaning property decrease. Therefore, in order to maintain excellent halftone dot reproducibility without impairing the paper releasability, the total surface area of the upper portions of the protrusions 13 is set to 4% or more and less than 20% with respect to the total area of the surface printing layer 11.

The protrusion 13 having the above structure can be formed by printing a photosensitive elastomer on the surface printing layer by a printing method. First, after stacking an unvulcanized surface layer by a known manufacturing method, this is vulcanized and the upper surface of the surface layer is polished smoothly with an abrasive. Then, the protrusion 13 is formed by printing a photosensitive elastomer on the surface of the surface layer formed by smooth polishing using an arbitrary printing method. As the photosensitive elastomer, an oil-resistant elastomer such as NBR mixed with a photosensitizer can be used. This is transferred as fine halftone dots to the surface of the surface printing layer by a printing method to form the protrusions having the above-mentioned configuration. Therefore, the surface shape of the projection becomes the same as the halftone dot of the plate, and the projection having an arbitrary surface shape can be formed by changing the halftone dot shape of the plate.

The printing method is not particularly limited, and a known method can be used. Therefore, the projections of the photosensitive elastomer can be printed on the blanket surface layer by a method such as gravure printing, screen printing, or letterpress printing, in addition to lithographic printing which is a general printing method. Prior to the printing process, a primer may be applied to the surface layer in order to increase the adhesion between the surface layer of the blanket and the photosensitive elastomer.

In the lithographic printing method, as shown in FIG. 4, an offset lithographic plate having a predetermined pattern is mounted on the plate cylinder 20, dampening water is supplied to the plate cylinder 20 from a water supply device 21, and a rubber solution is used. The photosensitive rubber solution is supplied from the supply device 23. Therefore, by passing the blanket 25 with the surface printing layer on the plate cylinder 20 side in the nip between the plate cylinder 20 and the impression cylinder 24, the halftone dot pattern 26 of the photosensitive rubber solution on the plate cylinder 20 can be transferred.

In the gravure printing method, first, a gravure plate cylinder 27 in which a predetermined pattern is formed on the plate cylinder by, for example, engraving or etching, as in the case of ordinary gravure plate making, is manufactured. A part of the cylinder 27 is filled in a concave portion of the cylinder 27 by rotating while being immersed in a photosensitive rubber solution 29 prepared by dissolving a photosensitive rubber composition in a solvent (toluene), and a scraper 30 is used to remove the excess. Scrap the rubber solution. The surface printing layer is provided between the gravure cylinder 27 and the impression cylinder 31 having the above-described structure.
When the blanket 33 is passed to the 7 side, the halftone dot pattern 35 of the photosensitive rubber solution in the cylinder 27 is transferred (see FIG. 5).

In the screen printing method, a gauze screen 37 having a predetermined pattern is stretched between the frames 39 and 39, and a blanket 40 is installed below the screen 37 at a constant interval. And the screen 3
Place the photosensitive rubber solution 41 on one end side of the squeegee 4
If the photosensitive rubber solution 41 is moved while being pushed while pressing 3 on the blanket 40, the halftone dot pattern 45 of the screen 37 can be printed on the surface printing layer of the blanket 40 (see FIG. 6). ..

In the relief printing method, as shown in FIG. 7, a fountain roll 4 partially immersed in a photosensitive rubber solution 47 is used.
An arbitrary pattern 57 can be printed on the surface printing layer by passing the blanket 55 between the relief cylinder 50 and the impression cylinder 53 with the transfer roll 51 interposed therebetween. The halftone dot pattern on the surface of the relief cylinder 50 may be formed by a known means, and the photosensitive rubber solution 47 attached to the surface of the fountain roll 49 is received on the surface of the relief cylinder 50 via the transfer roll 51. Therefore, when the surface printing layer is made to face the relief cylinder 50 and is passed between the impression cylinder 53, the halftone dot pattern 57 of the relief cylinder 50 is printed on the surface printing layer of the blanket.

After a predetermined halftone dot pattern is printed on the surface printing layer by the above printing method, a drying process is performed to evaporate the solvent of the photosensitive rubber solution forming the protrusions. Drying can be performed by any method such as blowing hot air on the protrusions or irradiating infrared rays, and the method is not particularly limited. When the drying process of evaporating the solvent is completed, the process of curing the protrusion is started. Curing of the protrusions is performed by irradiating energy rays such as ultraviolet rays. In this way, protrusions having a predetermined halftone dot pattern can be formed on the surface printing layer of the blanket (see FIG. 3).

The cotton cloth constituting the support 19 can be formed by a commonly used woven cloth such as cotton cloth, rayon cloth and polyester cloth. The woven fabric may have one layer, but may have two or three layers. As described above, when the support is formed of a woven cloth, a large tensile strength is obtained, and the support is excellent in durability and easy to mount on a printing machine. Further, instead of the woven fabric, a paper sheet which is strong and has high tensile strength can be used as the support. As the paper sheet, one or more kinds of rubber-impregnated paper, kraft paper, chimpan paper, and the like can be used, and a high tensile strength plastic sheet may be laminated. When the support is formed of a paper sheet, it is possible to obtain a uniform thickness and a smooth surface layer.

Further, since the present invention does not limit the structure of the blanket, a compressible blanket having a compressible layer between the support and the surface printing layer does not have a compressible layer. It does not matter whether it is a blanket. Which blanket to use can be appropriately selected depending on printing conditions. Furthermore, although the case where the surface-printed layer is vulcanized and then polished to a rough surface has been described, a halftone dot pattern can be printed after vulcanization without polishing.

[0023]

The independent fine protrusions formed by the predetermined halftone dot pattern formed by the printing method work to improve the halftone dot reproducibility and the paper separation property.

[0024]

According to the present invention, the projections can be formed by the printing method, and the dot pattern can be easily controlled. Further, the projections have an area ratio of 4% or more and less than 20%, a height of 15 μm or less, and an average surface area of the upper portion of 2000 to 50000 μm ^2. Therefore, good paper can be obtained without impairing dot reproducibility. A separation property can be obtained.

[0025]

The following is a comparison between the case where the blanket surface shape is formed by the present invention and the case where the blanket surface shape is formed by the conventional polishing method.

First, as shown in FIG. 1, a blanket is made of cotton woven fabric as the lowermost support, and the rubber composition is laminated in three layers as an adhesive layer by a known production method, and then foamed. The compressible layer and the intermediate layer were sequentially laminated, and a surface printing layer made of a rubber composition having the following composition was formed on the uppermost layer (hereinafter, simply referred to as a laminate).

Rubber composition (parts by weight) Acrylonitrile / butadiene copolymer rubber (NBR) 80 Polysulfide rubber 20 Zinc oxide 5 Stearic acid 1 Hydrous silica 30 DOP 20 Vulcanization accelerator TMTM 1 Vulcanization accelerator MBTS 1 Sulfur 3

After the rubber was vulcanized and molded, it was ground with polishing paper No. 320 and then No. 600 so that the surface became smooth,
A base surface printing layer was prepared. 1 by this polishing
The 0-point average roughness became 2.5 μm. A gravure cylinder 27 having a dot pattern of 100 lines / inch and 10% was manufactured. The pattern was formed by engraving as in the usual gravure plate making. A photosensitive rubber composition 29 was prepared by dissolving the photosensitive rubber composition in a solvent (toluene). The photosensitive rubber solution 29 was applied to the concave portion of the gravure plate cylinder, and the scraper 30 scraped off the excess rubber solution. Next, the laminated body was passed between the impression cylinder 31 and the plate cylinder 27, and the protrusion pattern 35 of the rubber solution was printed on the surface printing layer. The solvent of the protrusion pattern was evaporated in a hot air oven, and ultraviolet rays were irradiated for 20 seconds with an ultraviolet lamp having a main wavelength of 350 nm to crosslink the protrusion pattern on the surface printing layer. Furthermore, in order to increase the strength of this rubber protrusion,
The rubber was heat treated at 160 ° C. for 20 minutes to increase the degree of crosslinking of the rubber. In order to improve the adhesion between the protrusions and the surface print layer, a primer treatment was performed before forming the pattern.

Photosensitive rubber composition (parts by weight) Acrylonitrile / butadiene copolymer rubber (NBR) 100 Benzophenone (photosensitizer) 3 Zinc oxide 5 Stearic acid 1 Hydrous silica 20 DOP 10 Vulcanization accelerator TMTD 3

The height of the protrusion formed on the surface printing layer was controlled by the depth of the pattern (recess) of the gravure plate cylinder 27. Table 1 shows the heights of the obtained protrusions.

[0031]

[Table 1]

In the same manner as in the above example, a cotton woven cloth was used as the lowermost support by the known manufacturing method, the rubber composition was laminated as three adhesive layers, and the compressibility by foaming was further used. The layer and the intermediate layer were sequentially laminated, and a surface printing layer made of the rubber composition having the above composition was formed on the uppermost layer. This was vulcanized and molded, and then polished with No. 280 abrasive paper as Comparative Example 1. Further, Comparative Example 2 was prepared by polishing the surface printing layer with No. 320 polishing paper and then with No. 600 polishing paper, and the surface roughness was made equal to that of the surface printing layer serving as the base of the embodiment.

The blanket thus prepared was applied to an offset printing machine (manufactured by Komori Corporation, Lithrone 2).
6) attached to the art paper (7
A halftone image was printed on 0.5 kg). The disorder of the contour of the circular halftone dot at 50% of 150 lines / inch was evaluated as a circularity coefficient by using an image analyzer (LA-500 manufactured by Pierce). The calculation method of the circularity coefficient is obtained by the following mathematical formula 1. The closer this coefficient is to 1, the closer the halftone dots are to the circle, and the less the disturbance of the contour.

[0034]

[Equation 1]

When a solid image (ink is adhered to the entire surface) is printed, the rearmost portion of the paper after printing (referred to as the mulch end side) is rolled up. This winding height (called curl height) correlates with paper releasability, and the higher the curl height, the worse the paper releasability. Therefore, the solid image was printed in the same manner and the curl height was measured. The measurement results are shown in Table 1.

Comparing Comparative Example 1 and Comparative Example 2, when the surface is apparently smooth, the circularity coefficient is close to 1 and the halftone dot contour is improved, but the curl height is increased and the paper releasability is deteriorated. Comparing Examples 1 to 4 and Comparative Example 2, the circularity coefficients were almost the same and the dot contours were good. The surface roughness of Comparative Example 2 was similar to the surface roughness of the base excluding the protrusions of Examples 1 to 4, but the curl height was clearly lower in Examples 1 to 4 than in Table 1, and the paper separation It has good reproducibility, and by providing independent fine protrusions, the reproducibility of halftone dots and paper releasability can be achieved at a high level. The circularity coefficient of Examples 1 to 4 and Example 5 is illustrated in FIG. 8, and it was found that the circularity coefficient greatly decreases when the height of the protrusion exceeds 15 μm. Therefore, it is desirable that the height of the protrusion is 15 μm or less.

240, 220, 150, 60, 45, 4
A gravure cylinder 27 having a 15% halftone dot pattern of 0 lines / inch was manufactured. A photosensitive rubber composition 29 was prepared by dissolving the photosensitive rubber composition in a solvent (toluene). The laminate was passed between the impression cylinder 31 and the gravure plate cylinder 27 in the same manner as in Examples 1 to 5 to form the protrusion pattern 35 of the rubber solution on the surface printing layer. The solvent in the rubber solution was evaporated in a hot air oven, and ultraviolet rays were irradiated for 20 seconds by an ultraviolet lamp having a main wavelength of 350 nm to crosslink the protrusion pattern on the surface printing layer. Further, in order to increase the strength of the rubber protrusions, heat treatment was performed at 160 ° C. for 20 minutes to increase the degree of crosslinking of the rubber. In order to improve the adhesion between the protrusions and the surface print layer, a primer treatment was performed before forming the pattern.

240 lines / inch in Examples 6 and 22
0 line / inch of Example 7 and 150 line / inch of Example 8 and 60 line / inch of Example 9 and 45
The line / inch was used as Example 10 and the 40 line / inch was used as Example 11. The upper average surface area per protrusion formed on each surface printing layer was measured by the above-described image analysis device. In addition, printing was performed under the same conditions as in Examples 1 to 4, and the circularity coefficient of the 50% halftone dot portion of the printed image and the curl height during solid image printing were measured. Table 2 shows the measurement results.

[0039]

[Table 2]

As is apparent from FIG. 9, the circularity coefficient of halftone dots was almost the same and good in all of Examples 6 to 10, but the average surface area of the upper part per protrusion was 5
When it exceeded 0000 μm ² , the halftone dot shape was rapidly deteriorated as in Example 11. On the other hand, the curl height is shown in FIG.
As is clear from the above, when the average surface area of the upper part per protrusion is smaller than 2000 μm ² , the paper releasability is remarkably reduced. Therefore, it is desirable that the average surface area of the upper part of each protrusion is in the range of 2000 to 50000 μm ² .

22%, 18%, 16 at 100 lines / inch
%, 10%, 5%, 3% and 2% halftone dot patterns were respectively formed to produce a multilayer lithographic plate. The plate-making technology in ordinary lithographic printing was adopted for the production of the multilayer lithographic plate. The photosensitive rubber composition was dissolved in a solvent (toluene) to prepare a photosensitive rubber solution. The multi-layer lithographic plate is mounted on the plate cylinder 20, water is supplied to the non-image part from the water supply part 21, and then the photosensitive rubber solution is supplied to the image part from the rubber solution supply device 23 to apply the photosensitive rubber solution onto the plate. A protrusion pattern was formed, and the laminate was passed between the plate cylinder 20 and the impression cylinder 24 to form a protrusion pattern 26 of the rubber solution on the surface printing layer. The solvent in this projection pattern was evaporated in a hot air oven, and ultraviolet rays were irradiated for 20 seconds with an ultraviolet lamp having a main wavelength of 350 nm to crosslink the projection pattern on the surface printing layer. Further, in order to increase the strength of the rubber protrusions, heat treatment was performed at 160 ° C. for 20 minutes to increase the degree of crosslinking of the rubber. In order to improve the adhesion between the protrusions and the surface print layer, a primer treatment was performed before forming the pattern.

The halftone dot% of the multilayer lithographic plate used to form the protrusions is 2
2% in Example 12 and 18% in Example 13,
16% in Example 14 and 10% in Example 1
5% to 5% of Example 16 and 3% of Example 1
Example 7 was the one with 7% and 2%. The ratio of the total surface area of the upper portions of the protrusions formed on each surface-printed layer to the total surface-printed layer was measured by the above-described image analyzer. In addition, printing was performed under the same conditions as in Examples 1 to 4, and the circularity coefficient of the 50% halftone dot portion of the printed image and the curl height during solid image printing were measured. Table 3 shows the measurement results.

[0043]

[Table 3]

As is clear from FIG. 11, the circularity coefficient of halftone dots was almost the same and good in all of Examples 13 to 18, but when the area ratio of protrusions exceeded 20%, Example 12 was used. The halftone dot shape deteriorated rapidly as shown in. On the other hand, regarding the curl height, as is apparent from FIG. 12, when the area ratio of the protrusions is less than 4% or exceeds 20%, the paper releasability is remarkably deteriorated. In order to prevent plate replacement and deterioration of printed images, cleaning is generally performed by dropping ink or the like on the blanket surface. Then, as a result of evaluating the ink washability of the blanket, as is clear from Table 3, when the projection area ratio exceeds 20%, it markedly decreases. Therefore, in order to maintain excellent halftone dot reproducibility without impairing the paper releasability, the total surface area of the projections is controlled to be 4% or more and less than 20% with respect to the total area of the surface printing layer. It is desirable to do.

A 10% halftone dot pattern was formed at 60 lines / inch on a 380 mesh gauze screen used for screen printing. As the forming method, a gauze pattern forming method in screen printing was adopted. That is, a pattern was formed by applying a photosensitive solution on a gauze, drying it, exposing it to a halftone dot film, exposing it, and developing it. This screen 37 is a frame 39
And the laminate was placed under the frame. further,
Place the photosensitive rubber solution 41 on the screen on one frame side,
The rubber solution 41, which was scraped up by the squeegee 43 and passed through the halftone dot pattern portion of the screen, was transferred onto the laminate,
The protrusions of the rubber solution were formed on the laminate.

The solvent in the protrusion pattern was evaporated in a hot air oven and irradiated with ultraviolet rays for 20 seconds with an ultraviolet lamp having a main wavelength of 350 nm to crosslink the protrusion pattern on the surface printing layer. Furthermore, in order to increase the strength of this rubber protrusion,
The rubber was heat treated at 160 ° C. for 20 minutes to increase the degree of crosslinking of the rubber. In order to improve the adhesion between the protrusions and the surface print layer, a primer treatment was performed before forming the pattern. A blanket on which projections were formed in this manner was set as Example 19. The shape of the formed protrusion and 15 when printing is performed using this
Table 4 shows the circularity coefficient and the curl height of a circular halftone dot of 0 line / inch, 50%. Due to the effect of the protrusions formed on the printing surface layer, a blanket having good dot reproducibility and paper release properties was obtained.

[0047]

[Table 4]

A 10% convex halftone dot pattern was formed on a copper plate at 100 lines / inch. As a forming method, a plate making technique in letterpress printing was adopted. That is, a copper plate was coated with a photosensitive solution, dried, and overlaid with a halftone dot film for exposure, and the unexposed portion was removed with a solvent to form a convex pattern. The halftone dot pattern thus formed was attached to the plate cylinder 50. Photosensitive rubber solution 4
7 was supplied from the fountain roll 49 through the transfer roll 51 to the convex pattern of the plate cylinder 50. Impression cylinder 53 and plate cylinder 5
The photosensitive rubber solution 47 on the convex pattern of the plate cylinder 50 was transferred to the above-mentioned laminated body by passing the laminated body between 0 and 0, and the protrusion 57 of the photosensitive rubber solution was formed.

The solvent in the projection pattern was evaporated in a hot air oven and irradiated with ultraviolet rays for 20 seconds with an ultraviolet lamp having a main wavelength of 350 nm to crosslink the projection pattern on the surface printing layer. Furthermore, in order to increase the strength of this rubber protrusion,
The rubber was heat treated at 160 ° C. for 20 minutes to increase the degree of crosslinking of the rubber. In order to improve the adhesion between the protrusions and the surface print layer, a primer treatment was performed before forming the pattern. A blanket having projections formed in this manner was used as Example 20. The shape of the formed protrusion and 15 when printing is performed using this
Table 4 shows the circularity coefficient and the curl height of a circular halftone dot of 0 line / inch, 50%. Due to the effect of the protrusions formed on the printing surface, a blanket having good dot reproducibility and paper release properties was obtained.

[Brief description of drawings]

FIG. 1 is an explanatory sectional view showing an example of the structure of a blanket according to the present invention.

FIG. 2 is an enlarged perspective view for explanation in which the surface shape is traced by a micrograph.

FIG. 3 is a schematic process drawing for explaining the manufacturing method of the present invention.

FIG. 4 is an explanatory side view showing a method of forming a halftone dot pattern by a lithographic printing method.

FIG. 5 is an explanatory side view showing a method of forming a halftone dot pattern by a gravure printing method.

FIG. 6 is an explanatory side view showing a method of forming a halftone dot pattern by a screen printing method.

FIG. 7 is an explanatory side view showing a method of forming a halftone dot pattern by a relief printing method.

FIG. 8 is a graph showing the relationship between the protrusion height and the circularity coefficient.

FIG. 9 is a graph showing the relationship between the average surface area of each protrusion and the circularity coefficient.

FIG. 10 is a graph showing the relationship between the average surface area of the upper part of each protrusion and the curl height.

FIG. 11 is a graph showing the relationship between the protrusion area ratio and the circularity coefficient.

FIG. 12 is a graph showing the relationship between the protrusion area ratio and the curl height.

[Explanation of symbols]

 10 Printing Blanket 11 Surface Printing Layer 13 Protrusion 15 Intermediate Layer 17 Compressible Layer 19 Support

Claims (5)

[Claims] 1. An area ratio of 4% or more and less than 20%, a height of 15 μm or less on the surface of a surface layer to be a printing surface, and an average surface area of upper portions of the protrusions of 2000 to 5000.
An offset printing blanket, comprising: a protrusion forming step of forming independent protrusions of 0 μm ² by a printing method using a photosensitive elastomer; a drying step of evaporating a solvent of the protrusions; and a curing step by ultraviolet irradiation. Method of forming surface shape. 2. The method for forming the surface shape of an offset printing blanket according to claim 1, wherein the printing method is a lithographic printing method. 3. The method of forming a surface shape of a blanket for offset printing according to claim 1, wherein the printing method is a gravure printing method. 4. The method for forming a surface shape of an offset printing blanket according to claim 1, wherein the printing method is a screen printing method. 5. The method for forming a surface shape of a blanket for offset printing according to claim 1, wherein the printing method is a relief printing method.