JPS63256439A - Method for making lithography - Google Patents

Abstract

PURPOSE:To make a lithography having no instability but having superior etching properties, a high resolving power, and a high plate wear, by a method wherein a lithographic original plate provided with a non-photosensitive layer surface-roughened with fine particles on a conductive substrate is disposed opposedly to a photosensitive body provided with a conductive layer, and a positive electrostatic latent image is formed on the non-photosensitive layer of the original plate, thereafter being developed and fixed. CONSTITUTION:A non-photosensitive layer having a surface roughened with fine particles forms a uniform gap from a photosensitive body opposed thereto when being exposed to light and also has advantages in uniformizing an applied voltage and enhancing repeated reproducibility. The fine particles are dispersed in the non-photosensitive layer which is dielectric and soluble in alkali. A lithographic original plate having this non-photosensitive layer on a conductive substrate and the photosensitive body having a conductive layer are disposed opposedly to each other and an image is exposed to light while an appropriate voltage is applied between both layers. A positive electrostatic latent image is formed on the non-photosensitive layer, and this image is developed using a developer with a polarity reversed to this latent image and fixed. In this manner, a process superior in reproducibility and stability in addition to etching properties and plate wear is obtained, and the uniformity and high picture quality in a laser scanner process, and economical profits, such as the reduction of cost of the original plate and repeated use, are obtained.

Description

[Detailed description of the invention] (A> Industrial application field The present invention relates to a method for making a printing plate.

(B) Prior art and its problems Many printing plates have been developed and put into practical use to date.

Photosensitive lithographic printing plates, in which the printing plate itself has photosensitivity, are manufactured using presensitized (presensitized) materials using diazonium compounds, etc.
PS) plates, silver salt printing plates using silver halide, electrophotographic printing plates using zinc oxide or organic leading compounds, etc. are known.

As a printing plate with high sensitivity and high printing durability, a printing plate coated with an organic leading compound on an aluminum plate, for example,
7-17162@, No. 38-6961, No. 41-24
No. 26, No. 46-39405, Japanese Unexamined Patent Publication No. 50-1950
No. 9, No. 50-19510, No. 54-145538, No. 54-89801, No. 54-134632, No. 54-19803@, No. 55-105254@, No. 57
-161863, 58-76843, 58-7
No. 6844, 58-118658@, 60-244
No. 959, etc., and these printing plates undergo corona charging, camera exposure or laser exposure, wet or dry development, fixing, and elution of non-image areas with alkaline solution (
The plate is made by sequentially going through the steps (etching).

However, although the method of creating a printing plate using the electrophotographic process as described above has many advantages, it also has several disadvantages and drawbacks. , one of which originates from the use of corona charging. That is, the charging mechanism due to corona discharge has not been completely elucidated, and corona charging changes greatly due to changes in temperature and humidity, resulting in instability in that the photographic characteristics and printing characteristics differ each time the plate is made.

Roughly speaking, corona charging occurs when a large printing plate, such as for newspaper printing, is exposed with a scanner using a laser such as argon, helium-neon, or semiconductor. There is a problem in that it is difficult to form a toner image. Furthermore, another drawback of the conventional method stems from the high sensitivity.

That is, for example, JP-A-58-118658 and JP-A-60
- Like the printing version described in No. 244959 etc.
Not only can you use a so-called functionally separated type in which a charge generation layer and a charge transfer layer are laminated to increase sensitivity, but also in a single layer type.
Inevitably, the film thickness becomes thicker, and a large amount of organic photoconductive compound is used, which reduces the etching power of the alkaline solution, impairs resolution, and makes it difficult to form a resist with excellent printing durability. There's a problem.

Furthermore, the disadvantage of the conventional method from an economic point of view is that the printing plate itself uses an expensive photoreceptor, so it is generally expensive. It is practically difficult to reuse it.

The inventors of the present invention have made extensive studies taking into consideration the various drawbacks and disadvantages of current electrophotographic lithographic printing plates as described above, and as a result, it has become possible to create a lithographic printing plate that solves these drawbacks and disadvantages. I found a way.

(C) Purpose of the Invention The purpose of the present invention is to eliminate the instability of the conventional plate-making method using the corona charging method, provide excellent etching performance, high resolution,
An object of the present invention is to provide a method for creating a lithographic printing plate with high printing durability.

Another object of the present invention is to provide a method for making a lithographic printing plate without the image non-uniformity found in conventional plate making methods using corona charging and laser light.

Still another object of the present invention is to provide a method for preparing a lithographic printing plate which is inexpensive compared to conventional plate making methods, allows printing original plates to be easily re-prepared and used as desired, and has great economic benefits. There is something to do.

Other objects and advantages of the present invention will be understood from the following description of the specification.

(D) Structure of the Invention The above object of the present invention is to place a lithographic printing original plate having a dielectric, alkali-soluble, non-photosensitive layer roughened with fine particles on a conductive support and a photoconductor having a conductive layer facing each other. Then, with a DC voltage applied between both conductive layers from a DC power source, exposure is performed from either side of the transparent plate to form a positive static N latent image on the non-photosensitive layer of the original plate. This was achieved by a method for creating a lithographic printing plate, which is characterized by gelling, developing and fixing.

The present invention forms, develops, and fixes an electrostatic latent image on the non-photosensitive layer without performing corona charging, so it is stable against changes in the plate-making environment. It is possible to obtain a uniform printed image even when making a large-sized plate like this. In addition, since the printing original plate does not use a photoconductor as a photoreceptor, the non-photosensitive layer, that is, the printing layer, can be made as thin as possible, and the non-photosensitive layer contains fine particles and has a rough surface. Therefore, it is possible to improve the resistivity and etching speed when etching (eluting) non-image areas with an alkaline solution, and it is possible to obtain a printing plate with high resolution and high printing durability.

During exposure, the non-photosensitive layer is roughened with fine particles.
It also has the advantage of forming a uniform gap between the opposing photoreceptors, making the applied voltage uniform, and improving repeatability.

The fine particles used in the present invention have an average particle size of about 1 to about 20
tm, preferably about 3 to about 15IIIt8! It is a degree of organic or inorganic compound.

These fine particles are dispersed in a dielectric, alkali-soluble, non-photosensitive layer, and must not be dissolved or melted and mixed with the alkali-soluble resin from the coating solution to the time of coating film formation.

The fine particles used in the present invention include polystyrene, a copolymer of styrene and an unsaturated carboxylic acid such as acrylic acid, a copolymer of styrene and a lower alkyl (meth)acrylic acid, or a copolymer of styrene and an unsaturated carboxylic acid such as acrylic acid. Organic fine particles such as copolymers, polymethyl methacrylate, copolymers of methyl methacrylate and (meth)acrylic acid lower alkyl esters or unsaturated carboxylic acids such as acrylic acid, silicon dioxide, titanium dioxide,
Examples include inorganic fine particles such as zinc oxide and calcium carbonate, fine particles composed of a composite of organic and inorganic substances, and crosslinked organic fine particles.

It is preferable that one or more of these fine particles be contained in the non-photosensitive layer in an amount of about 0.1 to about 5% by weight, but the amount may be other than this. Further, the height of the roughened peaks is preferably about 0.5 to about 10 IIft, but the height may be other than this.

The present invention uses a photoreceptor separated from the printing original plate, and not only can the photoreceptor be used repeatedly, but the printing layer of the printing plate used for printing can be removed, and the dielectric non-photosensitive layer described above can be removed. By simply coating the support, it can be used again as a printing original plate, which is extremely economically advantageous.

In the present invention, a lithographic printing original plate having a dielectric non-photosensitive layer roughened with fine particles on a conductive support and a photoreceptor having a conductive layer are placed facing each other, and the conductive support of the printing original plate and the photoreceptor are made to face each other. With a DC voltage applied between the conductive layers of the body by a DC power source, image-wise exposure is performed from one side of the light-transmitting body, usually the side of the light-transmitting photoreceptor, onto the non-photosensitive layer. A positive electrostatic latent image is formed and developed with a developer of opposite polarity to this latent image.
It is here to stay.

Regarding the formation line groove of this positive electrostatic latent image, although it cannot be said that it is necessarily clear, it can be considered that there are 2 to 3 Ia sides. In other words, in the area irradiated with light, Original printing plate~
A mechanism in which an electrostatic latent image is formed by internal discharge occurring in the range where the partial pressure between the photoconductors exceeds the dielectric strength voltage in the air gap between them, and charges are accumulated on the non-photosensitive layer, or by light irradiation. Mobile carriers generated in the receiving area are injected and transferred to the dielectric surface by the action of an external electric field, or charges are injected into that area from the electrode surface and move to the dielectric surface, forming an electrostatic latent image. , etc.

The present invention is not limited to any particular mechanism, but forms a positive electrostatic latent image in the exposed area by laser exposure or exposure of a negative original through the process described above.

The method of forming an image without performing such corona charging is known, for example, "Charge tanster electroph".
otography” (R.

L, JepSen and G,F,Day,”
Electrophotography-2ndlnt
International Conference”, D
,R,Whiteed, ,p28 (SPSE, 19
74): H, Feinleib and S, Ru
therford, Appl, Photogr,
Eng., 4.9 (1976)), etc.

However, these known documents contain information on not only its use as a lithographic printing plate but also its excellent etching properties, high printing durability, high reproducibility, stable plate making, and uniformity in laser scanner plate making. - Economic benefits such as high image quality, lower cost of original printing plates, and repeated reuse are not shown.

The conductive support used in the printing original plate of the present invention is preferably a metal plate such as an aluminum plate, a zinc plate, an iron plate, a copper plate, etc., but metal vapor-deposited, metal foil laminated, or conductively treated films can also be used.

In particular, in the case of metal plates, it is preferable to use surface treatments such as graining or anodizing, so that during exposure, the support functions as an electrode and at the same time becomes a printing plate by elution of non-image areas. The non-photosensitive layer provided on the support is a resin that can capture charges transferred from the photoreceptor as a dielectric or insulator, and can be hydrophilic. Apply a resin that can be used to create a C. Examples of such resins include resins in which at least one component of the copolymer is a heptamer containing an acidic group such as acrylic acid, methacrylic acid, and crotonic acid, such as styrene maleic anhydride copolymers, maleic acid ester resins, Acetic acid and nyl crotonic acid covalent combination, vinyl acetate-maleic anhydride copolymer, (meth)acrylic acid ester-(meth)
Examples include acrylic acid copolymers, acrylic acid halfesters, and phenol resins.

These resin layers can be made into thin films, for example, 5 II ft or less, sometimes even 2-Ift or less, so that even if a strong film required for a printing plate is formed, it can be easily eluted.

On the other hand, the photoreceptor used in the present invention may be a photoreceptor used in ordinary electrophotography, but since the original printing plate is often non-transparent, as a support for the photoreceptor,
A translucent material such as film or glass is used, and since it is necessary to form an electrode with the printing original plate, it must be electrically conductive. The photosensitive component is preferably a photoconductive compound sensitive to laser light as described above. Organic photoconductors such as azo pigments, copper-phthalocyanine, and PVK-TNF, or inorganic photoconductors such as amorphous selenium and cadmium sulfide can be used, and a functionally separated type may be used.

In the method of the present invention, a printing original plate and a photoreceptor are opposed to each other, and image exposure is performed while applying an appropriate voltage (generally 200 V or more is good) between the two.

The toner used for image formation may be either a so-called dry toner or a wet toner, but in order to obtain printed matter with excellent resolution, a wet toner using a liquid development method is far more preferable. Furthermore, in order to be used as a printing plate, the toner must be hydrophobic, ink receptive, and have sufficient adhesion to the printing plate to withstand printing. Furthermore, when etching (elution) with an alkali and/or alcohol solution, resistivity is required.

Examples of the alkali used in the etching solution include sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium phosphate, potassium phosphate, alkanolamine, and ammonia.

Examples of the alcohol include lower alcohols such as methanol, ethanol, propatool, and benzyl alcohol, aromatic alcohols, and ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and cellosolves. Etching treatment can also be performed using an alkaline aqueous solution alone.

The following etching solution can be used as an example.

[Example of etching solution]

The invention will now be explained by some examples.

Example 1 A photoreceptor was manufactured by applying a solution in which copper-phthalocyanine was dispersed using an acrylic resin onto a transparent conductive film (Mitsubishi Kasei, IP-001) and drying it.

On the other hand, a printing original plate was produced by coating a phenol resin at 2 g/rd on an anodized aluminum plate and drying it (reference printing original plate a).

The coated surfaces of the above-mentioned photoreceptor and printing original plate were overlapped, and while applying a voltage of 400 V from a DC power source between the photoreceptor and printing original plate from the outside, image exposure was performed from the back of the photoreceptor through a transparent negative original.

When the voltage was removed and this printing original plate was developed with liquid toner and fixed, a positive image with a maximum image density of 1.5 and no fog was obtained, but some image unevenness occurred due to local uneven adhesion.

On the other hand, a printing original plate of the present invention was produced in the same manner as in reference printing plate a, except that 0.04 g/m of monodisperse polystyrene fine particles having an average particle size of 4II11 was contained in 2 g/Td of the phenolic resin. Thereafter, exposure, development, and fixing were carried out in the same manner as for reference printing original plate a, and a good positive image was obtained without any poor adhesion.

Next, when these image-formed printing plates were eluted with the etching solution described above, the non-image areas of the reference printing plate A were removed in 15 seconds, whereas the non-image areas of the printing plate A of the present invention were removed in 9 seconds. .

All of these printing plates were capable of printing 50,000 sheets or more.

Example 2 Instead of the phenolic resin used in the original plate of Example 1, styrene/butyl methacrylate/acrylic RTI (weight ratio: 60:20:20> 5 g/min of joint,
Example 1 except that 0.1 g/Td of polymethyl acrylate with an average particle size of 10 tan was used instead of the polystyrene fine particles.
repeated. The photoreceptor used in Example 1 was reused.

Similar results were obtained.

Claims (1)

[Claims] (1) Dielectric surface roughened with fine particles on a conductive support,
A lithographic printing original plate having an alkali-soluble non-photosensitive layer and a photoreceptor having a conductive layer are placed facing each other, and while a DC voltage is applied between both conductive layers from a DC power source, one side of the light-transmitting plate is placed. A method for preparing a lithographic printing plate, which comprises exposing the original plate to light to form a positive electrostatic latent image on the non-photosensitive layer of the original plate, and then developing and fixing the image.