JPS61160296A - Desensitizing treatment solution for neutral paper offset printing - Google Patents

Abstract

PURPOSE:To prevent printing background staining when neutral paper was used as offset printing paper, by using a desensitizing treatment solution containing an org. compound having a specific acid dissociation degree. CONSTITUTION:A desensitizing treatment solution for neutral paper offset printing containing an org. compound with an acid dissociation degree (pKa) of 4-6 is obtained and neutral paper is selected as printing paper to perform printing by using the desensitizing treatment solution containing the org. compound with pKa of 4-6 or dampening water. As a buffer, an org. compound with an acid disiociation degree (pKa) of 4-6 developing sufficient buffering capacity at pH 4-6 is pref. used. As the org. compound, there are an org. acid such as acetic acid, thioacetic acid, succinic acid, maleic acid, malonic acid or an aromatic acid such as phthalic acid, trimellitic acid or trimesic acid and water-soluble salts thereof and the concn. thereof in the desensitizing treatment solution is properly 1-200g/l.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Industrial Application The present invention relates to a desensitizing liquid and a method thereof for preventing staining of the printing surface when neutral paper is used for offset printing paper.

(2) Prior art Conventionally, acidic paper containing sulfuric acid has been widely used as printing paper, but in recent years acid-free paper containing fillers such as calcium carbonate has suddenly come into the spotlight due to problems such as paper deterioration. , and came to be used for various printing papers.

By the way, there are two types of printing: systems that do not use water during printing, such as gravure, letterpress, intaglio, and stencil printing, and so-called offset lithography that uses water during printing, which is the mainstream of printing. Such offset printing plates include 28 plates, silver substrates, direct printing plates, and electrophotographic plates, and desensitizing agents for offset printing plates include those that simply use a desensitizing agent and those that include a desensitizing agent. be. Among these, in the zinc oxide master (electrophotographic plate) that uses non-coated paper such as high-quality paper for printing, the desensitization treatment liquid is mainly composed of cyanide containing iron hexacyanosalt, phytic acid, guanidine derivatives, etc. It is broadly classified into cyan-free type. However, although there are differences in the level of desensitizing ability of these processing liquids when printing on acidic paper, there is no singular point within the range of printing conditions for printing paper, that is, acidic paper. In addition, there is something else that must be considered in order to perform optimal offset printing. That is, there are problems with the characteristics of the paper used for printing and the printing characteristics caused by the characteristics of this paper. Generally, it is thought that 5% to 20% of the moisture in the dampening liquid that the plate material can have is transferred to the printing paper during printing, and although the absolute amount of this water is small, Printing properties depend on various aspects.

Therefore, Qr H'14 whose cold water extraction pH exceeds 6.5
In the case of acid-free paper, if the conventional desensitization treatment tL is used, the basic compounds present in the acid-neutral paper will dissolve in the dampening water over time during printing, raising its pH to over 7, and causing extremely strong ink. Emulsification occurs completely, causing problems during continuous printing. This phenomenon is
This is a common problem regardless of type M of offset printing plates.

In addition, it should be noted that the desensitization treatment of zinc oxide master, which is currently the mainstream in light inlays, is due to the chemical interaction between iron hexacyano salt, phosphoric acid (ester) salt, and zinc oxide. However, since this is strong on the acidic side, when the acidity of the dampening water decreases, these salts that have acted on the master surface are washed away by the neutral dampening water. This results in the loss of desensitization treatment and also causes background stains from the master side.

(3) Object of the Invention The object of the present invention is to provide a desensitizing treatment liquid which solves the printing incompatibility caused by the conventional treatment liquid peculiar to neutral paper. In other words, when preparing the dampening solution, the dampening solution must be fully buffered to ensure sufficient buffering capacity for the medium, and when the printing paper comes into contact with the dampening solution, the reduction in acidity due to the dissolution of basic compounds can be prevented by reducing the buffering capacity and the dampening solution. There is a way to prevent this by replenishing water.

(4) Structure of the Invention The buffering agent for achieving the above object is preferably an organic compound having a degree of dissociation (pKa) of 4 to 6 and exhibits sufficient buffering ability at pH 4 to 6. This is because the compound exhibits a protective effect near the dissociation point, but this is especially true for polybasic acids whose molecular structure allows two or more carboxyl groups to have chemical interactions such as hydrogen bonds. More desirable for stabilizing anions.

Organic compounds that meet this condition include acetic acid, thioacetic acid,
Monobasic and polybasic acids such as succinic acid, maleic acid, malonic acid, glutaric acid, β-ethylglutaric acid, citric acid, butyric acid, malic acid, pimelic acid, cyclobutanedicarboxylic acid, cyclopentanedicarboxylic acid, tartaric acid, adipic acid, etc. Water-soluble salts of basic fatty acids, organic acids such as phthalic acid, tylephthalic acid, isophthalic acid, aromatic acids such as trimellitic acid, and trimesic acid, and their respective compounds are present, and the concentration during desensitization treatment is 12 /l to 200 t/l, preferably 10 f/l
A range of 1.about.100 f/l is suitable. The above compounds may be used alone or in combination of two or more. Further, these may be in the form of acids or salts, but the treatment liquid should be prepared to have a pH of 4 to 5.

When preparing a desensitizing treatment using the compound of the present invention, a desensitizing agent such as a hexacyanoferrous salt such as potassium ferrocyanide, or a non-cyanide compound such as inkt hexaphosphoric acid is contained as a desensitizing agent. However, in addition, various additives such as metal salts such as cupric chloride and ferric chloride, chelating agents such as EDTA and hexanecine cobalt salt, wetting agents such as 2-gropanol, ethylene glycol, and sodium alginate, and phosphoric acid. Phosphates and ammonium salts such as potassium, ammonium phosphate, and ammonium nitrate can be added, but are not limited to these. Furthermore, the treatment solution of the present invention can be diluted 2 to 10 times with water and used as a dampening solution. It's okay.

EXAMPLES The present invention will be specifically explained below using examples, but the present invention is not limited by these examples.

Example 1 A desensitizing treatment liquid for neutral paper offset masters was prepared according to the following recipe.

Potassium ferrocyanide 6.02 Aluminum hydrogen phosphate 6,02 Amber
5.022-Glopanol 4.
02 While adding distilled water to this, adjust the pH with sodium hydroxide.
4.5, and the total amount was k100 r. It was also diluted with gold water to 80% and used as a dampening solution.

On the other hand, a commercially available electrophotographic offset master plate making machine EP-
11 (manufactured by Mitsubishi Steel Corporation) was etched with a desensitizing treatment liquid of the above formulation, and then etched with a small offset Into-shin (manufactured by Mitsubishi Steel Corporation).
Talk-81O1 (manufactured by Tokyo Aircraft Keiki) was used to print 9,300 sheets (each print was 9,300 sheets) continuously using neutral paper, and the quality was stable with no background stains from the beginning to the end of printing. A print was obtained. At this time, the ink on the roll was no different from when acid paper was used, and the pH of the dampening water increased by about 0.4.

Comparative example 1 In Example 1, succinic acid (pKa, 4.21).

pKa, 5.64) instead of milk (l[(pKa
3.86), the entire desensitization treatment solution was prepared.

When a dampening solution was prepared by diluting this treatment f and the same test as in Example 1 was carried out, it was found that after 12,000 sheets, scumming began to appear and the ink had become severely emulsified. Also, the pH of the dampening water at that time increased by 1.6 to 6.3.
Met.

Example 2 A desensitizing treatment was carried out according to the following recipe.

Sodium ferrocyanide 4.01 Magnesium dihydrogen phosphate 5.02 EDTA-4Na
O, 5? Acetic acid 4.02 was diluted with distilled water while adding an aqueous sodium hydroxide solution to prepare a solution 1002 with a pH of 4.5. When this was printed in the same manner as in Example 1, no scumming occurred until 18,000 sheets were printed. pI of dampening water
The l increase was 0.6.

Comparative Example 2 When a similar test was conducted using pyruvic acid (pKa 2.49)'e instead of acetic acid (pKa 4.76) in Example 2Vc, scumming occurred after 10,000 sheets were printed. I started to see intertwined lines. At this time, the pH of the dampening water increased by 1.7 to 6.3.

Claims (2)

[Claims] (1) A desensitizing treatment liquid for neutral paper offset printing containing an organic compound having an acid dissociation degree (pKa) of 4 to 6. (2) A printing method comprising printing on neutral paper using a desensitizing liquid or dampening solution containing an organic compound having a pKa of 4 to 6.