JPH02273298A - Printing plate correction agent - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (A) Industrial Application Field The present invention improves ink receptivity in offset printing plates by converting unnecessary portions of images formed on the printing plates into hydrophilic ones. It relates to an image correcting agent for offset printing plates that erases, and more specifically, it is used to appropriately identify unnecessary parts of images on offset printing plates formed by photographic or physical methods at any stage in the printing process. The present invention relates to treating the surface with a treatment agent to completely make it hydrophilic and eliminate ink receptivity without causing any problems in printing properties, substrates, etc. Since such processing is usually called "correction" in the printing field, the present inventors will follow this term hereinafter.

Furthermore, the processing agent used in the correction operation will be referred to as a "correction agent."

CB) Prior art and its problems In general, areas that require correction that occur in printing master plates manufactured by photolithography include those that already exist in the copy original, those that occur during exposure, and other irregularities. There are some that occur during the development process.

This means, for example, if there are unwanted images in the reproduced original, if there are dust and dirt particles, fingerprints or other stains, or if the original is made by pasting together various originals, Shadows may appear during exposure.

In order to obtain good printed matter, all of these points must be corrected during the plate-making and printing stages.

- Correction operations are essential in boat fishing, and it is desirable to be able to make necessary corrections at any stage of the plate-making and printing processes.

Many attempts have been made to correct unwanted images in offset printing plates that utilize the silver image for ink receptivity.

For example, JP-A-48-92101% JP-A-51-21901
Compounds having a mercapto or thione group and a hydrophilic group described in ``Sho 54-53002, ``Sho 59-9661, etc.'' can reliably and almost instantaneously make silver images hydrophilic. However, it has drawbacks such as having a bad odor, having an adverse effect on the human body due to its strong acidity, and lacking in storage stability, so improvements are desired.

In addition, the correction agent containing red blood salt or EDTA metal salt and thiocyanate described in JP-A No. 48-41808 has problems with pollution and gradually loses ink acceptance after printing after correction. It has drawbacks such as smudging after the recovery of its properties and lack of storage stability.

(C) Object of the Invention The object of the present invention is to provide an offset printing plate that can be corrected quickly and reliably, can maintain hydrophilicity for a long period of time after correction, and has excellent storage stability of the correction agent solution. The purpose is to provide a corrective agent.

CD) Structure of the Invention The present invention is a correction agent for offset printing plates, characterized by comprising a solution containing nitrocellulose.

Nitrocellulose is used as a solution in an organic solvent such as alcohols such as methyl alcohol, ethyl alcohol, and inpropyl alcohol, acetone, ketones such as methyl ethyl ketone, and selonols such as methyl cellosolve. The concentration of nitrocellulose used is preferably in the range of 0.1 to 5% by weight.

Modifiers of the present invention can include hydrophilic binders. A preferred hydrophilic binder is gelatin. In addition to regular gelatin, gelatin is a so-called graft material obtained by dispersing gelatin modified with organic acids such as acetic acid, maleic acid, and salicylic acid in an organic solvent and grafting monomer onto gelatin in the presence of a polymerization initiator. gelatin, low molecular weight gelatin described in Modifier of JP-A-63-207645, and the like. Ze 5! It is preferable to use f-n in an amount of 1 to 20% by weight.

Other water-based binders such as hydroxyethyl cellulose, carboxymethyl cellulose can be used.

In addition, dyes, organic or inorganic pigments, and the like can be included as elements for coloring the liquid.

Furthermore, fine particle powder as described in JP-A-51-21901 may also be included.

The modifier of the present invention is stable and odorless. In addition, it can be quickly and completely corrected, and even if it is rubbed strongly after correction, the inner part will not get on the correction part.

Therefore, a larger number of sheets can be printed.

Offset printing plates include Japanese Patent Publication No. 48-30562, Japanese Patent Application Laid-open No. 53-21602, and U.S. Patent No. 3゜721.5.
In addition to No. 59 and No. 3,490,905, offset printing plates having silver halide images that are ink-receptive such as those disclosed in U.S. Patent No. 3,454,398 and Japanese Patent Application Laid-open No. 53-9603 are preferred. , 28 edition, or an electrophotographic offset printing plate.

(E) Examples Example 1 Hydroquinone x, oy/W? A lithographic printing material was produced in the same manner except that it was contained.

After the lithographic printing HIJ material was imagewise exposed, it was immersed in a transfer developer having the following formulation at 30°C for 30 seconds to carry out transfer development, and subsequently, it was immersed in a stop solution having the following formulation for 30 seconds.
The material was immersed for seconds (25° C.), squeezed to remove excess liquid, and dried under atmospheric conditions.

The following correction liquid was prepared as a correction agent, and the portion of the lithographic printing plate to be corrected was wiped with the correction liquid soaked in absorbent cotton.

[Transfer developer]

[Correcting agent] [Stopping liquid] The printing plate thus obtained was subjected to an offset printing machine N.B. Dick 350CD (A, B, Dick 350CD
After wiping the plate surface with a liquid called Prescription (E), printing was performed. The printing room was at 22° C. and 60% humidity.

[E] Swell gelatin 20F with 40 cc of water. Add 50 f of glacial acetic acid and 90 units of methyl alcohol to this and heat to dissolve. Maintaining the temperature at 40° C., add 0.452 f hydrogen peroxide and 0.9 f ascorbic acid while stirring vigorously. A mixture of ethyl acrylate (15F) and STEREF 51 was charged into this. The reaction is completed in about 1 hour.

Even after printing 3,000 sheets, ink did not get on the corrected area, and good correction was possible.

Example 2 When the following formulation was used as the correcting agent in Example 1, good results similar to those in Example 1 were obtained.

[Correcting agent]

Claims (1)

[Claims] 1. A correction agent for offset printing plates, characterized by comprising a solution containing nitrocellulose.