1. Field of the invention
The present invention relates to a support for a lithographic printing plate and a presensitized plate, particularly to a positive working presensitized plate having a photosensitive layer that can become alkali-soluble by photothermal conversion with laser beams and a support for a lithographic printing plate used for the positive working presensitized plate.
2. Description of the Related Arts
Lithographic printing is a printing method using the property that water and oil are immiscible. On the printing surface of the lithographic printing plate used for the method, areas (hereunder referred to as non-image areas) that accept water and repel oil ink and areas (hereunder referred to as image areas) that repel water and accept oil ink are formed.
The support for a lithographic printing plate, which is used so as to carry the non-image areas of the surface, requires various properties such as water wettability and water receptivity, and further good adhesion to a photosensitive layer provided thereon, which are incompatible.
When the water wettability of the support is too low, ink attaches on the non-image areas during printing and a stain is generated on a blanket cylinder, then a so-called scum develops on a print. When the water receptivity of the support is too low, a significant amount of fountain solution is needed to prevent clogging on shadow areas during printing. Therefore, a so-called water range becomes narrow.
Recent years, accompanied with development of image formation technology, it has come to be possible to make a printing plate directly by scanning narrow focused laser beams on the printing plate and by forming a manuscript of letters, images and the like directly on the plate without using a film manuscript.
For example, in the case of a so-called thermal positive working type presensitized plate in which a positive image is formed by making a photosensitive layer alkali-soluble by photothermal conversion in the photo sensitive layer, heat generated from photothermal conversion materials in the photosensitive layer by applying laser beams induces image forming reaction.
Here, when a deep pit generated by graining treatment exists on the surface of support treated for graining, thickness of the portion of the photosensitive layer becomes thicker, and image forming reaction on the bottom of the pit becomes inadequate. As a result, local residual layers (hereunder referred to also as dot residual layers) are generated on the non-image areas, causing a problem of scum developing on the non-image areas during printing.
Moreover, the amount of the fountain solution is decided based on a water gloss on the plate in the event of controlling fine adjustment of water scale during printing operation. Accordingly, in the case where the pit is shallow after graining treatment, a gloss of the non-image areas increases, thus resulting in difficulty in fine adjustment of the amount of the fountain solution during printing.
In order to solve the problems described above, specifying of a surface shape of the support has been proposed before.
For example, a rough surface shape having a pit, in which the slope of a straight line by the first order regression analysis of a pit diameter and the maximum depth in a direction perpendicular to the diameter is 0.300 or less under 1.5 xcexcm or less of the pit diameter, has been proposed in JP-A-9-86068 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). Here, it is described that the rough surface shape prevents scum developing on the non-image areas during printing and provides excellent ballpoint pen characteristics. However, though the method shown in the above gazette could solve the problem with dot residual layers, the method was not sufficient for fine control of water volume and a water range during printing.
The brush graining process in which at least two kinds of brushes are used for graining to prevent scum and clogging on the shadow areas has been proposed in JP-A-6-135175. However, though the method shown in the foregoing gazette was sufficient for fine control of water volume and water width during printing, the method could not solve the problem with the dot residual layers sufficiently.
Moreover, a support comprising a double structure of small and large pits, in which an average opening diameter of a larger pit with uniformity is 3 m or more and 6 m or less, an average opening diameter of a small pit is 0.2 xcexcm or more and 0.8 xcexcm or less, and a ratio of depth to the opening diameter of the small pit is not more than 0.2 xcexcm, has been proposed in JP-A-11-184074. Here, it is described that the support could improve dot gain with high definition, resistance to stain developing on a blanket, scum resistance under small water volume and printability on YUPO paper. Although the method described in the foregoing gazette could provide better fine control of water volume, further improvements in restraining the dot residual layers are desired.
In the presensitized plate using an aluminum support which has been treated for graining and having an anodized layer formed thereon, since thermal conductivity of the support is much higher than that of the photosensitive layer, heat generated around an interface of the photosensitive layer and the support moves into the support before image forming reaction (alkali-soluble reaction) occurs sufficiently. As a result, solubility of the photosensitive layer to plate developer becomes inadequate around the interface of the photosensitive layer and the support, and the residual layers are easily generated on the areas which must be non-image areas originally. Therefore, high sensitive developer must be used, but by using it, non-image portions are easily generated on the area to be the image area. That is, slight variation of sensitivity of the developer indicated by electronic conductivity during developing easily causes development failure, and the intrinsic problem remains, in which development latitude is much narrower than the conventional PS plate system that has been used before. In order to solve the problem, various methods for improving development performance of the photosensitive layer around the interface of the photosensitive layer and the support in the presensitized plate of a thermal positive working type have been studied, but the result has not reached a satisfactory level.
When the photosensitive layer that can become alkali-soluble by heating sustains damage by some causes, the area to be an image area also becomes easily soluble in developer. That is, the printing plate sustains damage easily in practical use. For this reason, scratch-like non-image portions is generated by tiny contact to the plate surface such as bumping in handling the printing plate, tiny abrasion in interleaving sheets and contact to the plate surface by fingers. Accordingly, handling of the printing plate is very difficult under the present circumstance.
In particular, in the presensitized plate of a thermal positive working type, when the alkali-soluble level of the photosensitive layer by exposure of laser is not that high, sometimes a slightly soluble layer is formed as the top layer of the photosensitive layer to obtain clear discrimination of an image on development. In this case, since other parts than the slightly soluble layer are soluble in alkali, the foregoing narrowness of development latitude and the generating of the scratch-like non-image portion are especially problematic.
It is also indispensable for a recording layer of such a thermal type to contain infrared absorbent having a photothermal conversion function. Since solubility of the absorbent is low due to high-molecular weight of the absorbent and further the absorbent adsorbed in micro openings on the anodized layer of the support can not be removed easily, there has been the problem that the residual layers are easily generated on a development process with alkali developer.
In order to solve this problem, various under-coatings have been studied to improve the development performance of the photosensitive layer on the interface of the photosensitive layer and the support in the positive working presensitized plate. But, the result has not reached a satisfactory level.
In particular, as recent market movements, a request of shortening exposure time for increasing the productivity and a request of using laser at lower output for a longer life of the laser are strong. Therefore, a presensitized plate has been requested, in which a printing plate is directly made by laser beams, generated heat is effectively utilized for image forming reaction, good solubility to alkali developer is provided to the non-image areas, and scum on the non-image areas caused by high sensitivity and the residual layers are restrained.
A first object of the present invention is to provide a positive working presensitized plate of a thermal type, which has wide development latitude in order not to cause development failure easily by variation of sensitivity of developer, and which does not generate scratch-like non-image portions easily and is handled easily in the conventional operation.
A second object of the present invention is to provide a presensitized plate that can be processed to such a lithographic printing plate that a blanket cylinder is not stained easily, no local residual layer is generated on non-image areas, fine adjustment of the amount of the fountain solution is easily controlled during printing and ink spreading does not occur easily under small volume of water, and to provide a support for a lithographic printing plate that can be used suitably for the presensitized plate.
A third object of the present invention is to provide a presensitized plate that can be processed to such a lithographic printing plate that a blanket cylinder is not stained easily, no local residual layer is generated on non-image areas, fine adjustment of the amount of the fountain solution is easily controlled during printing and ink spreading does not occur easily under small volume of water, and to provide a support for a lithographic printing plate that can be used suitably for the presensitized plate and a preparing method thereof.
A fourth object of the present invention is to provide a presensitized plate of a thermal type that can be processed to such a lithographic printing plate that no local residual layer is generated on non-image areas, fine adjustment of the amount of the fountain solution is easily controlled during printing, and to provide a support for a lithographic printing plate that can be used suitably for the presensitized plate of a thermal type.
A fifth object of the present invention is to provide a positive working presensitized plate of a thermal type, which can utilize heat generated with infrared absorbent effectively for image forming, in which there is no residual layer caused by penetration of a photosensitive layer into a micropore formed on an anodized layer, which has high sensitivity, that can be processed to a lithographic printing plate with excellent scum resistance on non-image areas and in which high quality image can be formed, and to provide a support for a lithographic printing plate that can be used suitably for the positive working presensitized plate of a thermal type.
The inventors of the present invention completed the present invention as a result of conducting extensive study to attain the first object described above.
A first aspect of the present invention is a presensitized plate comprising: an intermediate layer readily soluble in alkali; and a photosensitive layer that can become alkali-soluble by heating, said layers being sequentially provided on a support for a lithographic printing plate, provided by subjecting an aluminum plate to graining treatment, alkali etching treatment and anodizing treatment, wherein an amount of alkali etching is set in a range of 0.5 to 4 g/m2 for said alkali etching treatment, and an average thickness of thinnest 10% of said photosensitive layer on convex portions of a surface of the support is set in a range of 0.2 to 2 xcexcm.
In the first aspect of the presensitized plate, it is conceivable that convex portions on the surface of the support are rounded and smoothed by alkali etching with the foregoing quantity after graining treatment, thus resulting in improvement in development performance by eliminating residual layers, and that stress to pressure from the upper side of the photosensitive layer is dispersed to prevent breaks of the photosensitive layer by setting the thickness of a thinnest portion of the photosensitive layer on the convex portions of the surface of the support in the above-described range when forming the photosensitive layer on the support.
In the case where amount of alkali etching is less than 0.5 g/m2, or the average thickness of thinnest 10% of the foregoing photosensitive layer on the convex portions of the surface of the support is less than 0.2 xcexcm, the thickness may decrease easily and inadequate inking may occur when the developer has high sensitivity, and also scratch resistance may highly decrease.
On the other hand, in the case where amount of alkali etching is more than 4 g/m2, asperities on the support decrease largely, thus causing decrease of anchor effects of the photosensitive layer, easy falling off of the photosensitive layer, inferior development performance in the high sensitive developer and also inferior scratch resistance. In the case where the average thickness of thinnest 10% of the photosensitive layer on the convex portions of the surface of the support is more than 2 xcexcm, energy required for making the whole photosensitive layer alkali-soluble becomes large, causing generating of the residual layers very easily during development, which results in narrow development latitude.
As described above, development latitude can be expanded and better damage resistance can be provided by using the presensitized plate according to the first aspect of the present invention.
The inventors of the present invention, as a result of conducting extensive study to attain the second object described above, completed a support for a lithographic printing plate according to the second aspect of the present invention, in which, with regard to the support before coating the photosensitive layer, (1) for a surface of the support, arithmetic average roughness (Ra) measured in compliance with JIS B0601-1994 is set in a range of 0.3 to 0.5 xcexcm, (2) for the surface of the support, 10-point average roughness (Rz) measured in compliance with JIS B0601-1994 is set in a range of 3.0 to 6.0 xcexcm, and (3) for the surface of the support, the number PC of roughness curve peaks is 15 or more per 1 mm, when a set value is 0.3-0.3 xcexcm. It was found out that in the support, there is no local residual layer on non-image areas and fine adjustment of the amount of the fountain solution can be easily controlled, ink spreading hardly occurs under small volume of water.
Specifically, the second aspect of the present invention is a support for a lithographic printing plate, provided by a treatment process including at least two or more steps of subjecting an aluminum plate to graining and any one of etching and desmutting steps between said graining steps, wherein for a surface of said support, arithmetic average roughness (Ra) measured in compliance with JIS B0601-1994 is set in a range of 0.3 to 0.5 xcexcm, for the surface of said support, 10-point average roughness (Rz) measured in compliance with JIS B0601-1994 is set in a range of 3.0 to 6.0 xcexcm, and for the surface of said support, the number Pc of roughness curve peaks is 15 or more per 1 mm, when a set value is 0.3-0.3 xcexcm.
Preferably, for the surface of said support, an 85-degree surface gloss regulated by JIS Z8741-1997 is set equal to 30 or lower.
In one of the preferable embodiments, said treatment process lastly includes a step of anodizing.
In another of the preferable embodiments, said treatment process lastly includes a step of anodizing, and then a step of water wettability treatment.
The second aspect of the present invention also provides a presensitized plate comprising said support for a lithographic printing plate and a photosensitive layer thereof. In this case, further interlayer comprising organic materials may be formed between the support for the lithographic printing plate according to the second aspect and the photosensitive layer.
The inventors of the present invention, as a result of conducting extensive study to attain the third object described above, completed a support for a lithographic printing plate according to the third aspect of the present invention, in which, with regard to the aluminum support before coating the photosensitive layer, (1) for a surface of the support, in a filtered waviness curve measured at a cut-off value of 0.8 mm and an evaluation length of 6 mm in compliance with JIS B0610-1987, the number of waves having a depth of 0.3 xcexcm or deeper is set in a range of 35 to 60, and the number of waves having a depth of 1.0 xcexcm or deeper is 5 or less, (2) for the surface of the foregoing support, arithmetic average roughness measured at the cut-off value of 0.8 mm and the evaluation length of 6 mm in compliance with JIS B0601-1994 is set in a range of 0.35 to 0.5 xcexcm, and (3) a uniform honeycomb pit having a diameter set in a range of 0.5 to 2 xcexcm is provided on a full surface of the surface of the foregoing support. It was found out that in the support, the stain hardly develops on a blanket cylinder, there is no residual layer on non-image areas, fine adjustment of the amount of the fountain solution can be easily controlled during printing and ink spreading hardly occurs under small volume of water.
Specifically, the third aspect of the present invention is a support for a lithographic printing plate, provided by a treatment process including at least two or more steps of subjecting an aluminum plate to electrochemical graining and any one of etching and desmutting steps between said electrochemical graining steps, wherein for a surface of said support, in a filtered waviness curve measured at a cut-off value of 0.8 mm and an evaluation length of 6 mm in compliance with JIS B0610-1987, the number of waves having a depth of 0.3 xcexcm or deeper is set in a range of 35 to 60, and the number of waves having a depth of 1.0 xcexcm or deeper is 5 or less, for the surface of said support, arithmetic average roughness measured at the cut-off value of 0.8 mm and the evaluation length of 6 mm in compliance with JIS B0601-1994 is set in a range of 0.35 to 0.5 xcexcm, and uniform honeycomb pits having a diameter set in a range of 0.5 to 2 xcexcm are provided on a full surface of said support.
Preferably, for the surface of said support, an 85-degree surface gloss regulated by JIS Z8741-1997 is set equal to 30 or lower.
In one of the preferable embodiments, said treatment process lastly includes a step of water wettability treatment.
The inventors of the present invention completed a preparing method of a support for a lithographic printing plate according to the present invention, the preparing method comprising the steps of: performing an electrochemical graining to form a surface having the number of waves of a depth 0.3 xcexcm or deeper set in a range of 35 to 60, and the number of waves of a depth 1.0 xcexcm or deeper set equal to 5 or less, in a filtered waviness curve measured at a cut-off value of 0.8 mm and an evaluation length of 6 mm in compliance with JIS B0610-1987; and performing further electrochemical graining. It was found out that the method described above is suitable to obtain a support in which stain hardly develops on a blanket cylinder, there is no local residual layer on non-image areas, fine adjustment of the amount of the fountain solution can be easily controlled, and ink spreading hardly occurs under small volume of water.
Specifically, the third aspect of the present invention also provides a method for preparing a support for a lithographic printing plate, having a treatment process including at least two or more steps of subjecting an aluminum plate to electrochemical graining and any one of etching and desmutting steps between said electrochemical graining steps, comprising the steps of: performing one electrochemical graining to form a surface having the number of waves of a depth 0.3 xcexcm or deeper set in a range of 35 to 60, and the number of waves of a depth 1.0 xcexcm or deeper set equal to 5 or less, in a filtered waviness curve measured at a cut-off value of 0.8 mm and an evaluation length of 6 mm in compliance with JIS B0610-1987; and performing another electrochemical graining.
The third aspect of the present invention also provides a presensitized plate comprising said support for a lithographic printing plate and a photosensitive layer thereof. In this case, further interlayer comprising organic materials may be formed between the support for the lithographic printing plate according to the second aspect and the photosensitive layer.
The inventors of the present invention, as a result of extensive study to attain the fourth object, also completed a support for a lithographic printing plate according to the fourth aspect of the present invention by regulating size and number of concave portions formed on the surface of the support and by keeping the gloss of the surface in some scope. It was found out that when the support is processed into a lithographic printing plate, there is no local residual layer on non-image areas and fine adjustment of the amount of the fountain solution is easily controlled during printing.
The fourth aspect of the present invention provides a support for a lithographic printing plate, provided by subjecting an aluminum plate to graining treatment, wherein for a surface of said support, the number of concave portions within 1 mm is ten or less, each of said concave portions having a width of 8 xcexcm or wider, alternatively a maximum depth of 1.7 xcexcm or deeper in a direction perpendicular to the width, and for the surface of said support, an 85-degree surface gloss regulated by JIS Z8741-1997 is 30 or lower.
Here, the width and maximum depth of the concave portions on the surface of the support for the lithographic printing plate are measured by observing a cross sectional shape with a scanning electron microscope. When a cross section of the support for the lithographic printing plate according to the fourth aspect of the present invention is measured at an optional place, the number of concave portions having 8 xcexcm or more in the width, or 1.7 xcexcm or more in the maximum depth perpendicular to the width is 10 pieces or less in 1 mm of the cross section.
The fourth aspect of the present invention also provides a presensitized plate comprising said support for a lithographic printing plate and a recording layer thereof, said recording layer containing infrared absorbent and a high-molecular compound insoluble in water and soluble in an alkali aqueous solution, wherein solubility to an alkali developer is increased by infrared laser exposure.
It is presumable that in the fourth aspect of the present invention, the possibility that the photosensitive layer existing on deep concave portions remains during development can be reduced by controlling the number of concave portions exceeding the set dimensions in width and depth within a certain range on the support for the lithographic printing plate prepared by performing graining treatment on an aluminum plate. However, when the surface becomes too smooth by controlling the number of wider or deeper concave portions, problems such as decrease of adhesion to photosensitive layers, difficulty in fine control of water volume due to gloss increase during printing, come up easily. Therefore, in the fourth aspect of the present invention, the 85-degree surface gloss is controlled under 30 to satisfy all of restraining of the residual layers, adhesion to the photosensitive layer and controlling of fine water volume during printing.
The inventors of the present invention, as a result of extensive study to attain the fifth object of the present invention, completed a support for lithographic printing plate according to the fifth aspect of the present invention, on which an anodized layer with a specified opening area is formed. It was found out that the residual layers are not generated during printing by using the support, the support has high sensitivity, a lithographic printing plate processed from the support has better scum resistance on non-image areas and high quality image can be formed.
Specifically, the fifth aspect of the present invention provides a support for a lithographic printing plate, provided by subjecting an aluminum plate to graining treatment and anodizing treatment, wherein when a diameter and a density of a micropore present in an anodized layer are respectively d(m) andxcfx81 (number of micropores/m2), both satisfy an expression (i) below:
0.5 less than xcfx80(d/2)2xc3x97xcfx81 less than 2.0xe2x80x83xe2x80x83(i) 
The fifth aspect of the present invention also provides a presensitized plate comprising said support for a lithographic printing plate and a recording layer thereof, said recording layer containing infrared absorbent and a high-molecular compound insoluble in water and soluble in an alkali aqueous solution, wherein solubility to an alkali developer is increased by infrared laser exposure.
In the fifth aspect of the present invention, the diameter of micropores d (referred to also as pore diameter hereunder) is determined by an average diameter of at least 30 pieces which are read by visual observation on SEM (scanning electron microscope) pictures. The SEM pictures are prepared by observing on the surface of the presensitized plate with a scanning electron microscope of electrical field emission type and without vapor deposition, after gum on the non-image areas of the plate after recording an image is washed off and air-dried. Density of microporesxcfx81 (referred to as pore density hereunder) is determined by counting and averaging micropores observed in at least 10 fields of view with 400 nm square in the SEM pictures taken by 150,000 times in the same way.
Aluminum oxide which is main substance composing the anodized layer has lower thermal conductivity compared with metal aluminum and has advantage over metal aluminum in point of restraining diffusion of heat generated in the photosensitive layer. Since the anodized layer, in particular, has many fine cells called micropores (referred to also as pore hereunder) in the thickness direction of the anodized layer, thermal conductivity of the layer becomes further lower than the conventional aluminum oxide layer, thus resulting in advantage in restraining heat diffusion.
In the fifth aspect of the present invention, characteristics of the micropores existing on the anodized layer are determined in the expression (i) described above. The expression (i) determines a ratio of an opening area of the micropores when the micropores on the surface are observed from the surface of the layer.
In the fifth aspect of the present invention, improvement in sensitivity and restraining residual layer generation are attained by combination of an anodized layer having the specified opening area ratio and the positive working photosensitive layer of a thermal type. This is because adhesion to the photosensitive layer, void holding property and thermal insulation property can be well balanced by keeping the ratio of opening area in the set range determined by the expression (i) described above.
As a result that the opening area ratio indicated in the expression (i) is kept in the range more than 0.5 and less than 2.0, preferably not more than 1.0, more preferably not more than 0.9, decrease of the thermal insulation property caused by deep penetration of the photosensitive layer into the micropores and clogging of the pores can be prevented, and the phenomena that the penetrated photosensitive layer can not be removed easily by developer can be prevented, thus attaining the restraining of the residual layer generation. Further, since the pore diameter of the micropores and the pore density on the anodized layer are controlled within a specified range and the thickness and void ratio of the anodized layer effective for restraining the heat diffusion are secured, thermal insulation effect of the anodized layer can be kept effectively, and sensitivity can be improved.
The diameter and density of the micropores can be adjusted by controlling conditions for forming the anodized layer and conditions for post-treatment such as acid/alkali treatment, treatment for clogging the pore and the like after forming the anodized layer, as well known before.
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