DE1098813B - Process for preventing the scumming of photographic gelatin planographic printing plates - Google Patents

Description

GERMAN

In flat printing, which in principle is based on the different behavior of image areas and planum Based on water and fat color, it is common to use weakly acidic, mostly phosphoric acid-containing dampening agents and To use »fixages«. This applies [especially to printing with offset reproduction machines. The processing of printing forms, the surface of which is made of a hydrophilic but water-insoluble coating material exists, sets - if you change the dampening system or the dampening agents on the Machine wants to avoid - therefore advance that of such layers in the weakly acidic pn range mentioned (4 to 7) can be printed continuously without sound.

Of the numerous organic colloids that give hydrophilic and water layers, but meet just these requirements, so this gelatin is very suitable, since on the one hand near the isoelectric point, which is just in the mentioned p _H range of 4 to 7, shows the slightest swelling and thus only little water flow during printing and, on the other hand, due to the hardening of such gelatin layers necessary to achieve a certain mechanical strength, the gelatin is always hydrophobicized to a greater or lesser extent. Compared to other hydrophilic colloids, such as. B. Carboxymethylcellulose hardened with heavy metal salts, but gelatin layers have the advantage of being alkali-resistant and are therefore suitable for carrying out photographic processes which are bound to an alkaline development. In the case of printing films whose color-decreasing images are produced by photographic means, a coating with gelatin as the hydrophilic water-bearing colloid is therefore preferred. Such printing forms are z. B. in the German patent 1011280 and the patent applications A 27030 IVa / 57d from 25.4.1957, and A 27721 IVa / 57d from 16.8.1957 and A 29778 IVa / 57d from 27.6.1958 have been proposed. When printing with these printing plates, it has proven difficult with Feuchtungsmitteln of said p _H -region 4-7 completely achromatic deductions to obtain, especially if the machine u or by paper dust. Like. Contaminated.

It has now been found that gelatin layers for lithographic printing are used, give even at extremely high curing and using Feuchtungsmitteln with p _H values 4-7 completely achromatic prints, by treating the gelatin with a substantially neutralized aqueous fluosilicic .

You can use the partially neutralized fluosilicic acid add to the gelatine before pouring or by means of an aftertreatment bath in the already introduce gelatin layer on a carrier.

Method of preventing scumming

of photographic gelatin planographic printing plates

Applicant:

Agfa Aktiengesellschaft,

Leverkusen-Bayerwerk,

Kaiser Wilhelm Allee

Dr. Eberhard Günther, Leverkusen,

and Dr. Wolfgang Lässig, Cologne-Stammheim,

have been named as inventors

In the latter case, a treatment of the gelatin layer with other baths, such as B. hardening baths, solutions, the development nuclei - possibly also silver halide solvents - Contained for the production of silver images by the silver salt diffusion process, among other things precede or follow.

The degree of neutralization of the fluosilicic acid is of decisive importance for the effectiveness of the process. A satisfactory hydrophilization of the gelatin is only obtained if the fluosilicic acid down to the p ^ range from 5.0 to 6.5, but preferably from 5.5 to 5.8, is neutralized. Since to neutralize the fluosilicic acid to the mentioned pn range of 5.0 to 6.5 significantly more base is consumed than the formula

H ₂ SiF ₆ + 2 MeOH -> ■ Me ₂ SiF ₆ + H ₂ O

corresponds, it must be assumed that at the same time or subsequent to the neutralization of the dibasic fluosilicic acid, hydrolysis of the [SiF ₆ ] anion to form silica sols of unknown constitution which may still contain fluoride ions takes place.

Apparently only those divide in this pn area occurring silica sols when introducing or applying to the gelatin layers are finely dispersed insoluble silica particles to which the observed hydrophilizing effect can be attributed. This theoretical

However, considerations in no way represent a restriction of the claimed method.

For the neutralization of fluosilicic acid, basic compounds are suitable, such as. B. the hydroxides and Carbonates of lithium, sodium and ammonium.

109 508/353

The fluosilicic acid neutralized to pH 5 to 6.5 is used as a 0.5 to 10%, preferably U to 5%, aqueous solution.

Depending on the concentration of the fluosilicic acid used and the type of cation precipitation can occur with partial neutralization to the mentioned pn range of 5 to 6.5, which are filtered off before using the solution.

example 1

In a first step, a paper carrier is made with a gelatin solution of the following composition doused:

I. 170 parts aqueous gelatin solution (30%),

170 parts of a 7% fluosilicic acid (filtered) neutralized with soda to pH 5.5 to 5.8, 30 parts aqueous sodium thiosulphate solution (50%), 10 parts aqueous saponin solution (7.5%).

The pH of the total solution is 5.5.

This solution is diluted with a 3.5% fluosilicic acid (filtered), also neutralized with soda to pH 5.5 to 5.8, to such an extent that the gelatin application is 2 to 4 g / m ² under the given casting conditions. The molding is dried at 70 to 80 ⁰ C.

In a second step, the gelatin layer is then applied treated with the following aqueous solution:

II. 350 teüe of water,

50 parts of an aqueous 1% solution of colloidal sulfur over,

2 parts aqueous sodium thiosulphate solution (50%), 12 parts aqueous caustic soda solution (10%),
6 parts aqueous formalin solution (about 30%),
10 parts aqueous saponin solution (7.5%).

The cast is dried at 70 to 80 ^° C. and the paper coated in this way is deposited for 8 days. The layer is then sufficiently hard to withstand prolonged mechanical stress in a planographic printing machine.

Since the foils of the paper coated in this way are alkali-resistant and contain fusing soda and germs (colloidal sulfur over) for the build-up according to the salt diffusion process can be used on them are generated according to the salt diffusion process. These Süberbüder can then continue, z. B. according to the method of German patent 1 011 280 and patent applications A 27030 IVa / 57 d and A 27721 IVa / 57 d, can be converted into a book that takes on a fat color.

When printing with these paper foils in a device that works according to the offset process, shows in such foHen using dampening agents of the pn range from 4 to 7 and themselves very bold printing inks no toning, regardless of whether it is a question of foHing with smiths or converted, Bold color-taking on either or not. Analog paper foHing, with those in the first cast no fluosilicic acid neutralized to pH 5.5 to 5.8 was used, however, show more or less heavy toning, depending on the pn value, the amount of dampening solution and the type of printing ink used (fat or lean).

Example 2

A paper support as described under 1 is coated with a gelatin solution in a first step watered with the following composition:

I. 170 parts aqueous gelatin solution (15%),

15 parts aqueous sodium thiosulphate solution (50%), 5 parts aqueous saponin solution (7.5%).

This solution is diluted with water to such an extent that an amount of gelatin of 2 to 4 g / m ² is obtained under the given casting conditions. The molding is dried at 120 ⁰ C.

In a second step, the gelatin layer is poured over with an aqueous solution of the following Composition:

II. 370 parts of water,

12 parts aqueous caustic soda solution (10%),

2 parts aqueous formalin solution (about 30%),
¹ ^ 10 teüe aqueous saponin solution (7.5%).

The molding is dried at 12O ⁰ C.

In a third step, the layer is with

watered the following aqueous solution:
20th

III. 170 Teüe one with soda to pn 5.5 to 5.8 neutral

Hsed 1.5% fluosilicic acid (filtered),
5 teas of saponin solution (7.5%).

The molding is dried at 120 ⁰ C.
In a fourth step, the SchHeß-Hch layer is doused with the following aqueous solution:

IV. 280 parts of water,

20 parts of an aqueous 1% solution of colloidal sulfur,

60 parts of aqueous sodium thiosulphate solution (50%), 10 parts of aqueous saponin solution (7.5%).

The casting is dried at 120.degree.

The paper coated in this way is deposited for 8 days to harden the gelatin layer.

If one compares such paper foils with those which the third cast with the partly neutralized one Fluosilicic acid is absent, when printing with acidic dampening agents (pn 4 to 7), only the former show no trace of toning, regardless of the printing inks used. As already under 1 stated, both on foHen with after the Sübersalzdiffusionverfahren angry siblings and their transformed brothers who have taken on fat color as well as on non-photographically treated prints.

Example 3

A paper support as described under 1 is followed in a first step with a gelatin solution Composition poured:

^: I. 170 parts of aqueous gelatin solution (15%),

25 pts. Aqueous, 1% solution of koUoidalem

Sulfur over,

50 parts aqueous sodium thiosulphate solution (50%), 5 parts aqueous saponin solution (7.5%).

The solution is diluted with water to such an extent that a gelatin application of 2 to 4 g / m ² is obtained under the given casting conditions. The molding is dried at 120 ⁰ C.

In a second step, the gelatin layer is poured with the following aqueous solution:

JI. 370 teaspoons of water,

12 parts aqueous caustic soda solution (10%),

3 parts aqueous formalin solution (about 30%),
10 parts aqueous saponin solution (7.5%).

The molding is dried at 120 ⁰ C.

In a third step, the following aqueous solution is poured over the layer:

III. 170 parts of a 1.5% fluosilicic acid (nitrated) neutralized with soda to 5.5 to 5.8 pn,
5 parts of aqueous saponin solution (7.5%).

The casting is ^{dried at 120 °} C. and the paper coated in this way is deposited for 8 days.

A comparison of foils of the paper coated in this way with those that lack the third cast, in the case of the under 1 mentioned experimental conditions shows that only the treated with the partially neutralized fluosilicic acid Foil does not show any scumming.

Example 4

A paper support as described under 1 is made in a first step with the following gelatin solution doused:

I. 170 parts of aqueous gelatin solution (15%),

5 parts of aqueous saponin solution (7.5%).

The solution is diluted with water to such an extent that a layer application of about 4 to 6 g / m ² is obtained. The molding is dried at 70 to 8O ⁰ C.

In a second step, the gelatin layer is poured with the following aqueous solution:

II. 370 parts of water,

12 parts of aqueous caustic soda solution (10%),

6 parts of aqueous formalin solution (about 30%), 10 parts of aqueous saponin solution (7.5%).

The molding is dried at 70 to 8O ⁰ C.
In a third step, the following aqueous solution is poured over the layer:

III. 370 parts of a with ammonium carbonate to pn 5.5 up to 5.8 neutralized 1% fluosilicic acid, 10 parts aqueous saponin solution (7.5%).

The casting is dried at 70 to 80 ° C.

In a fourth step, the following aqueous solution is poured over the layer:

IV. 280 parts of water,

20 parts of an aqueous 1% solution of colloidal silver sulfur,

15 parts of aqueous sodium thiosulfate solution (50%), 10 parts of aqueous saponin solution (7.5%).

The molding is dried at 70 to 8O ⁰ C and the thus-coated paper deposited 8 days.

Here, too, a tone-free print can be achieved from foils of the paper coated in this way under the test conditions mentioned under 1, in contrast to a blank sample in which the third casting (III) was omitted.

Example 5

A paper carrier as described under 1 is treated in four operations as under 4, except that one to partially neutralize the fluosilicic acid of the third step (III) lithium carbonate instead used by ammonium carbonate. The results are analogous to those listed under 4.

Claims (4)

Patent claims: 1. A method for the prevention of toning produced photographically gelatin lithographic printing plates suitable for printing with greasy ink, characterized in that the gelatin used in the manufacture of the printing form is treated with an aqueous Fluokieselsäurelösung that a _pH value from about 5 to 6.5, preferably 5.5 to 5.8, is neutralized. 2. The method according to claim 2, characterized in that the aqueous fluosilicic acid solution of the Gelatin is added before pouring. 3. The method according to claim 1, characterized in that one with the aqueous fluosilicic acid solution treated the gelatin layer already cast on a support as a post-bath. 4. The method according to claim 1 to 3, characterized in that a 0.5 to 10% strength, preferably 1-5% aqueous fluosilicic acid solution is used.