JPH0362268B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a printing original plate, and more particularly to a printing original plate that has excellent printing durability and improved dissolution properties in non-image areas. Conventional technology Conventionally, printing original plates using the principles of electrophotographic technology include, for example, Japanese Patent Publications No. 47-47610 and No. 48-48.
No. 40002, No. 48-18325, No. 51-15766, No. 51
A zinc oxide-resin dispersion type offset printing original plate described in No. 25761 is known, and in such an offset printing original plate, a toner image is formed using an electrophotographic method, and then the toner image is formed using an electrophotographic method. It is used as a printing plate by desensitizing the non-image areas other than the image areas. However, in this type of printing plate, since the image area is formed only from toner particles, printing durability is poor, and the number of prints using this original plate is limited to approximately 5,000 to 10,000 sheets, and many more sheets can be printed. It is unsuitable for printing. Furthermore, since it is necessary to use an acidic solution such as ferrocyan alkali metal salt to carry out the desensitizing treatment, there is a problem that the use of the above treatment liquid is undesirable from the viewpoint of pollution control or occupational health. It also has In addition, Special Publications No. 37-17163, No. 38-7758,
46-39405, JP-A No. 52-2437, etc., the organic photoconductor-resin printing original plate is a photoconductive material in which oxazole or oxadiazole is bonded with a styrene-maleic anhydride copolymer. The body layer is mounted on a grained aluminum plate. In this printing plate, a toner image is formed on a photoconductor layer using electrophotographic technology, and then a non-image area is removed using an alkaline organic solvent to create a printing plate. In this printing plate, the image area is not formed only from toner particles but from a resin containing an organic photoconductive substance and toner particles, so it has excellent printing durability, but it is difficult to remove the non-image area. This requires organic solvents such as ethylene glycol, glycerin, methanol, and ethanol, which also pose undesirable problems from the standpoint of pollution control and occupational health. On the other hand, JP-A No. 56-20543, JP-A No. 55-105254
No. 55-153948, No. 55-161250, No. 55-
No. 105380 and the like describes a printing original plate in which a photoconductor layer using a phenolic resin, which is an alkali-soluble resin, and an organic pigment-based photoconductive substance is provided on a grained aluminum plate. In this original printing plate, a toner image is created on a photoconductor layer using an electrophotographic method, and then a non-image area is eluted with an alkaline aqueous solution to create a printing plate. "Elution" here refers to the form of image formation in which the non-image area is dissolved in an alkaline aqueous solution, and simply immersing the non-image area in an alkaline aqueous solution results in slight swelling. Most of it is not removed and can be removed by rubbing the plate with a sponge, brush, etc. after immersion in an aqueous alkaline solution, during or after rinsing with water, or by applying a strong shower of water. The non-image area is completely removed only by using mechanical force, such as by blowing it onto the printing plate, and the non-image area is wiped or scraped off adjacent to the support. It means form. In the printing original plate described in the above-mentioned Japanese Patent Publication No. 56-20543, etc., the image area is formed from a photoconductive resin layer and toner particles, and it is not possible to use an organic solvent for elution of the non-image area. However, in these printing master plates, printing durability, which is an important function for printing plates, and the above-mentioned elution property have a contradictory relationship, and for example, non-image areas may elute under relatively mild alkaline elution conditions. Plate materials, that is, plate materials with excellent elution properties, have poor printing durability, and conversely, plate materials with excellent printing durability cannot elute non-image areas unless under strong alkaline elution conditions. It is in. In such strong alkaline elution conditions, the alkaline aqueous solution used for elution is highly concentrated, used at high temperature, or the immersion time is long, or even mechanical scraping after immersion. Regardless of whether the conditions are strong or not, undesirable problems such as operational risks, longer processing times, and larger elution machines may occur, as well as strong alkaline elution. Under these conditions, the toner image itself may become unstable, and the toner image may leak out during immersion in an alkaline aqueous solution or during rubbing after immersion, resulting in problems such as not being able to obtain a good printed image. . Therefore, the present inventor has made repeated studies in order to obtain an excellent printing original plate by improving the contradictory properties of printing durability and dissolution properties as described above. Purpose of the Invention The objective of the present invention is to provide a printing original plate with excellent printing durability, and another objective is to use an alkali-soluble resin and a pigment-based photoconductive substance in an image forming process. An object of the present invention is to provide a printing original plate in which the image forming layer in areas other than the toner image is eluted with an alkaline aqueous solution, in which the non-image area can be eluted under mild alkali elution conditions, and which has high printing durability. Yet another object is to provide a printing original plate that has appropriate electrophotographic sensitivity, dark decay characteristics, residual potential, and other electrophotographic properties, and forms images using electrophotographic principles. Structure of the Invention It is an object of the present invention to provide a printing original plate having an image forming layer containing a photoconductive substance and an alkali-soluble resin on a conductive support, in which the image forming layer is composed of a plurality of layers, and the image forming layer is composed of a plurality of layers. This can be achieved by using a printing original plate in which the alkali elubility of the layer provided closest to the conductive support is greater than the alkali elution property of at least one other layer. The invention will now be described in more detail. First, in the present invention, the meaning of the words "high or low alkali elubility" and the method for measuring the same will be explained. First, in the present invention, a layer whose image forming layer can be eluted under milder alkali elution conditions is referred to as having a high or excellent alkali elution property, and the opposite is referred to as having a low or poor alkali elution property. Next, a method for measuring alkali dissolution will be described. (Measurement method) (1) The sample is immersed in an alkaline aqueous solution at a constant concentration and temperature, and the shortest immersion time is required to elute the image forming layer. (2) The lowest alkaline aqueous solution temperature at which the image forming layer can be eluted when immersed in an alkaline aqueous solution of a certain concentration for a certain period of time. (3) The lowest concentration of alkaline aqueous solution at which the image forming layer can be eluted when immersed in alkaline aqueous solution at a constant temperature for a certain period of time. (4) The minimum rubbing pressure or rubbing density at which the image forming layer can be eluted during rubbing of a print after immersion in an alkaline aqueous solution under certain conditions. The quality of dissolution is determined by comparing the results of the above-mentioned measurement methods, and methods for detecting the end point of elution include visual discrimination as well as the following methods. (a) Drop a certain amount of the dye containing it onto the non-image area after it has been eluted, and compare the size of the spread (diameter or area) with the size of the spread after dropping the same solution on a blank sample. (b) Drop a certain amount of water onto the non-image area after elution,
The contact angle with the plate surface is measured and compared with the contact angle with the plate surface of the same liquid on a blank sample. As mentioned above, the printing original plate of the present invention has a structure having a plurality of image forming layers on a conductive support, and the method for measuring the alkali elution property of the constituent layers having such a multilayer structure is as follows. , separately prepare a sample in which a single layer with the same composition as the layer to be measured is provided on the same support, and perform the measurement method described above.
Measure and compare according to (1) to (4). Next, in the present invention, as a means for forming a layer with relatively high alkali elution property, (1) 1. A resin with high alkali solubility is used as a binder. (2)1 Lowering the content of alkali-insoluble or poorly soluble substances; (3)1 Not using reinforcing agents such as coupling agents or reducing their amount; A layer with low alkali elution property can be formed by this method. Next, a typical layer structure of the present invention will be described based on whether or not a pigment-based photoconductive substance is contained. When the printing original plate of the present invention has two image forming layers on a conductive support, as an embodiment in which these image forming layers contain a pigment-based photoconductive substance as described below as a photoconductive substance. There are three forms as follows. (Part 1) Both the upper and lower layers contain a pigment-based photoconductive substance. (Part 2) The upper layer does not contain a pigment-based photoconductive substance, and only the lower layer near the support contains a pigment-based photoconductive substance. (Part 3) Only the upper layer contains a pigment-based photoconductive substance, and the lower layer does not contain a pigment-based photoconductive substance. If we functionally divide the image forming layer consisting of the above two-layer structure, in the structure (Part 1) above, both of the two layers are photoconductor layers, and in the case of the structure (Part 2), the following It can be further divided into two functionally. (Part 2-1) The upper layer is a protective layer, and the lower layer is a photoconductor layer. (Part 2-2) The upper layer contains a charge transfer substance and is a charge transfer layer, and the lower layer is a charge generation layer. Furthermore, regarding the configuration (part 3), it can be further divided into the following two functionally. (Part 3-1) The upper layer is a photoconductor layer, and the lower layer is an adhesive layer. (Part 3-2) The upper layer is a charge generation layer, and the lower layer contains a charge transfer substance and is a charge transfer layer. In the present invention, when the image forming layer has a two-layer structure as described above, the effects of the present invention can be obtained by making the alkali elubility of the lower layer, that is, the layer closer to the support greater than that of the upper layer. The above layer structure is an embodiment of the present invention in which the image forming layer is composed of two layers, but in the present invention, for example, three or more image forming layers may be provided on the conductive support. In this case as well, at least one of the layers contains a pigment-based photoconductive substance, and as mentioned above, the alkali elubility of the layer closest to the support is made greater than that of at least one other layer. The object of the invention is thereby achieved. In the present invention, pigment-based photoconductive substances that can be used as photoconductive substances or charge-generating substances contained in the image forming layer include phthalocyanine pigments, azo pigments, disazo pigments, quinacridone pigments, perylene pigments, and indigo pigments. , quinone pigment,
Aromatic polycondensed ring pigments, bisbezimidazole pigments, zinc oxide, etc. can be used, and they can be used in combination with conventionally known sensitizers such as rose bengal, bromophenol blue, piacyanol, oxazole, oxadiazole, etc. I can do it. Further, as the charge transfer substance that can be used in the present invention, organic substances conventionally known as charge transfer substances such as diphenylmethane type, triarylmethane type, hydrazone type, polymethine type, fluorenone type, and oxazole type can be used. can. Further, binder resins that can be used in the present invention include phenol resins, urea resins, melamine resins, furan resins, epoxy resins, silicone resins,
Use resins with insulating properties such as polyurethane resin, xylene resin, toluene resin, vinyl chloride-vinyl acetate copolymer, vinyl acetate-methacrylic copolymer, acrylic resin, polycarbonate, and cellulose derivatives with a volume resistivity of 107 Ωcm or more. However, in order to form a layer with high alkali elution property, it is particularly desirable to use a phenolic resin. The conductive support used in the present invention includes a conductive film, an aluminum plate, a zinc plate, an iron plate surface-treated with chrome plating, a copper-aluminum plate, a copper-stainless steel plate, a chrome-plated plate, etc.
A substrate with a hydrophilic surface such as a bimetallic plate such as a copper plate, or a trimetallic plate such as a chromium-copper-aluminum plate, a chromium-lead-iron plate, or a chromium-copper-stainless steel plate is used, but in particular, the surface may be grained. An aluminum plate which is then subjected to a hydrophilic treatment such as anodization, and further immersed in an aqueous solution of a silicate, a phosphate, or a fluorinated zirconate to seal the holes can be suitably used. In the present invention, the alkaline solution used for elution of the image forming layer includes, for example, caustic soda,
Examples include aqueous solutions of caustic potassium, soda carbonate, ammonium carbonate, sodium phosphate, potassium phosphate, ammonium phosphate, sodium metasilicate, and sodium silicate. The present invention will be described in more detail below with reference to Examples, but the present invention is not limited thereto. Example 1 First, phenolic resin SDP-1 (manufactured by Konishiroku Photo Industry Co., Ltd.,
When the solubility of PS plate developer (alkaline aqueous solution containing sodium metasilicate as the main component) in a 7-fold dilution with water was measured, the solubility of the phenolic resin shown in [] and [] was 0.005 g/
ml, and 0.001 g/ml. Next, after dissolving 5.0 g of the resin shown in [] with 50 g of ethyl cellosolve, 1.0 g of β-type copper phthalocyanine (Ciba Geigy, Chromophthal Blue 4GN) was added, and the mixture was homogenized using glass beads dispersion. I got it.
In exactly the same manner, a dispersion B containing the phenolic resin shown in [ ] and the above β-type copper phthalocyanine in a ratio of 5:1 was obtained. The above dispersion A was applied to a 0.3 mm thick aluminum plate whose surface had been grained, anodized, and sealed to a dry film thickness of 3 μm, and after drying, dispersion B was applied on top of it. A printing original plate (1) according to the present invention having a photoconductor layer having a total film thickness of 6 μm was obtained by applying the photoconductor layer to a dry film thickness of 3 μm. Next, the above-mentioned dispersion A was coated onto an aluminum plate whose surface had been grained, anodized, and sealed to give a dry film thickness of 6 μm to obtain a printing original plate (1) for comparison. Furthermore, instead of the dispersion A, the dispersion B
A comparative printing original plate (2) having a photoconductor layer with a dry film thickness of 6 μm was obtained in exactly the same manner as the above method except that . A toner image was formed on the image forming layer of the printing original plate (1) of the present invention and the comparative originals (1) and (2) obtained as described above by a normal electrophotographic method.
After immersing it in a 7-fold dilution of SDP-1 in water, the image surface was wiped with a sponge to remove the non-image area. After washing with water and drying, it was put on a printing machine to test the number of prints. Table 1 below shows the results obtained regarding the immersion time in the 7-fold water dilution of SDP-1 necessary for removing the non-image area and the number of printed sheets.

[Table] As shown in Table 1 above, the printing original plate of the present invention has excellent alkali elution properties and has a longer printing life than the comparative printing original plate with the same immersion time for alkali elution. It turned out that the number was dramatically higher. Example 2 6.0g of phenolic resin having the following structure []
was dissolved in 50 g of ethyl cellosolve, 1.0 g of ε-type copper phthalocyanine was added, and the mixture was homogenized using glass beads to obtain a dispersion liquid C. Next, after dissolving 6.0 g of the above phenol resin in 50 g of ethyl cellosolve, 3.0 g of ε-type copper phthalocyanine
was added and homogenized using glass bead dispersion to obtain a dispersion liquid C. The above dispersion C was applied to a 0.3 mm thick aluminum plate whose surface had been grained, anodized, and sealed to a dry film thickness of 3 μm. After drying, apply the above dispersion D on the coated surface to a dry film thickness.
It was coated to a thickness of 3μ and dried to obtain a printing original plate (2) according to the present invention having a photoconductor layer with a total thickness of 6μ. The above-mentioned dispersion liquid C was applied onto the above-mentioned aluminum plate so that the dry film thickness was 6 μm, and dried to obtain a printing original plate (3) for comparison. Further, the above dispersion D was applied onto the above aluminum plate so that the dry film thickness was 6 μm, and dried to obtain a printing original plate (4) for comparison. Original printing plate according to the present invention obtained as above (2)
The original plates for comparison (3) and (4) were processed according to the usual electrophotographic method to form a toner image on the image forming layer, and after being immersed in a 7-fold diluted solution of SDP-1 in water,
The non-image area was removed by wiping the image surface with a sponge. After washing with water and drying, the paper was put on a printing machine to test the number of prints it would last. The results of the immersion time in the 7-fold water dilution of SDP-1 necessary for removing the non-image area and the number of printed sheets are shown in Table 2 below.

[Table] As is clear from the results in Table 2 above, the printing original plate of the present invention has excellent alkali elution properties,
Moreover, it was found that the number of printed sheets was significantly greater than that of a comparative printing original plate having the same immersion time for alkali elution. Effects of the Invention The present invention has a plurality of image forming layers on a conductive support, and the alkali elution property of the layer provided closest to the support is greater than the elution property of at least one other layer. The original printing plate not only has excellent alkali elution properties but also can significantly improve printing durability.

Claims (1)

[Claims] 1. In a printing original plate having an image forming layer containing a photoconductive substance and an alkali-soluble resin on a conductive support, the image forming layer is composed of a plurality of layers, and among the plurality of layers, the conductive support A printing original plate characterized in that the alkali elubility of a layer provided closest to the layer is greater than that of at least one other layer.