DE2061185C3 - Process for retouching an offset printing form produced by electrophotography - Google Patents

Description

The invention relates to a method for retouching an electrophotographic Ways produced offset printing form, which by imagewise exposing an electrophotographic Recording material with photoconductive zinc oxide in its photoconductive layer, by developing with a resinous toner of this recording material, by fixing the toner image and making it hydrophilic with an aqueous solution, containing a water-soluble metal hexacyanide salt and / or ammonium phosphate will.

The production of offset printing forms by electrophotographic means is in this way known. The photoconductive layer made of photoconductive zinc oxide is generated, for example, by corona discharge electrically charged and then kept in the dark until imagewise exposed. Through the exposure causes the charge to flow in the areas of the photoconductive layer struck by the light while it remains in the areas not struck by light, so that a latent electrostatic Image is created. This lantern electrostatic image is developed by sputtering a colored powder carrying a charge or by immersion in an insulating liquid, in which the color powder is dispersed. made visible. After this development, the fixing is carried out Heat only the resinous toner.

Since the colored powder is covered with a jar /, the developed part (! - .. ·, picture poliophü. For. Use ai> Otfsot-l) n> kforrn mub der niclii ilarzusteiienck · lii.teieii of Hikk · ^ can be made hydrophilic. Ihis. uoscliieb * fli'-vi Henetzunj: mi 'Kniumiferrocyanid, Sodiumferrocyanid, Kaliumferricyanid, Ammoniuniphosphat etc. in solution, whereby a coating of water-insoluble precipitate arises when hydrophilizing, z. B. K ₂ Zn ₃ [Fe (CN) ₆ ] O, ZnNH ₄ PO ₄ etc. Wetting with the solution can be carried out by simply wiping the surface with absorbent cotton or a gauze impregnated with the solution.

The production of an offset printing form is on

ίο this way very easy. However, it is with offset printing forms In addition, it also required retouching in a similar manner to one To make a process for which special manual skills are not required.

The object of the invention is therefore to provide a method for retouching offset printing forms to create, through which only those areas of the offset printing form can be removed that are not printed become so, or even veiled areas or spots.

According to the invention, this object is achieved in that prior to the treatment with the hydrophilizing solution An aqueous retouching solution is applied to areas that should not be printed will that be a water-soluble metal sal? contains, which with the water-soluble metal hexacyanide salt and or the ammonium phosphate forms a water-insoluble precipitate and a cation thereof of the following chemical elements Be, Mg, Zn, Hg,

In, Cu? Ag, Al, Tl, Th, Sn, Pb, Bi, Zr, Cr, Cd, Co. Ni, Fe, Mn or Ga is assigned.

One can thus in a simple manner a water-insoluble and hydrophilic precipitate on the Reach areas of the offset printing form or printing plate to be retouched before the printing plate is made hydrophilic with metal hexacyanide salt and / or ammonium phosphate. It can be that simple be retouched. There can also be veils and any stains on the plate completely removed. Special handicrafts Skills are no longer required for this. Simple retouching is therefore effective adapted to the simple work with such offset printing forms.

In the drawing, the invention is explained by way of example, namely shows

F i g. 1 shows a cross section through an electrophotographic Paper with a toner image,

Fi g. 2 a cross section through a hydraulic

Make 5 "phil from the electrophotographic paper manufactured offset printing plate,

Fig. 3 shows a cross section through the printing plate, the printing pattern surface of which according to the invention with is provided with the retouching agent. and

F i g. 4 shows a cross-section through the by making the plate according to FIG. 3 received Printing plate.

Fit. 'shows a layer carrier I made of paper with a pliotoconductive insulating layer 2 with zinc oxide and a resin binder and a colored powder layer 3 glued to the printing surface. a hydrophilic and water-insoluble precipitate, e.g. B. KjZnJFe (CN) ₀ J.,. ZnNH., PO, etc. Although: A surface was cleaned off with the solution, so it is not; ■> reich hvdrophii to be printed, during: ¹ viii der ObfMache des

In the area to be printed there are no substances that react with this solution and form a hydrophilic and water-insoluble precipitate. This is illustrated in Fig. 2, is provided with de ^r a zinc compound 4, which is hydrophilic and water-insoluble due to their reaction with the treatment solution.

The hydrophilicizing solution contains water-insoluble metal hexacyanide salts for retouching. z. B. alkali metal salts of hexacyan cobalt acid (II) and (III), ferrocyanide and ferricyanide or ammonium phosphate [(NHJ ₂ HPO ₄ ], and in the retouching solution is a compound of a metallic element from the group Be, Mg, Zn, Hg, Cu, Ag , AS, Tl, Th, Sn, Pb, Bi, Zr, Co, Cr, Cd, Ni, Fe, Mn and Ga. The solvent of the retouching solution is, for example, water, methanol or water-methanol The retouching solution is applied to the area to be retouched so that layer 5 is obtained in FIG or gauze impregnated with a hydrophilizing solution, so that the layer 5 in Fig. reacts with this solution and forms a hydrophilic and water-insoluble precipitate, as shown in Fig. 4 is shown at 6, and the zinc oxide of the non-pressing areas forms a hydrophilic and water-insoluble precipitate. Areas 4 and 6 in FIG. 4 are hydrophilic yetnaclit and do not take color nn. In this way you get a retouched printing plate.

The above-mentioned metallic elements are; generally in the form of chlorides or nitrates, in order to form aqueous or alcoholic solutions. Such compounds can, for example, BeCl. ,, MgCl.,. ZnCl.,. ' He (ClO ₃ ), CuC !, · 2 H ₀ O, AgNO. ,, AICL ₁ . TICK Th (NO.,) ₄ ■ 4 H ₁ O, SnCl. ,, PbCl.,. Pb (CH ₁ COO).,. BiCL ₁ . ZrCl., Con ,, - (KH ₂ O, CrCl ,, CdCl ,,, Ni (NO,), '- 6H ₂ O, FcC., MnCl ,, GaCL, etc.

The concentration of these compounds in the RiMuschieriösung is preferably in the range of I to 30 percent by weight, based on the metallic Element.

When using a hydrophilizing solution. The metal hexacyanide salt and / or ammonium phosphate contains, compounds of alkali metals and some alkaline earth metals, such as Ca, Sr, Ba, do not produce a water-insoluble precipitate, which forms a compound with this solution, and are therefore not usable as retouching agents. For example, Ca and Kuliumferrocyanid form a connection to CaJFe (CN) ₀ ] · 12 H ₂ O. which is water soluble. Furthermore, the Ca combines with ammonium phosphate to form CaHPO ₄ , which is insoluble in water in a neutral solution, but soluble in water in an acidic medium. In connection with; as RelusL never; medium usable metal compounds dagCL '-..-: i. such as B. Zn. Fe and Co, with this solution a connection to K., Zn, Fe (CN),.],. ZnVi. ' ¹ C ,. FeJFc (CN) J.,. FcPO _4. "Cc-JFe (CN) Ji un. CoNH ₁ PO .. cm. Thus all static water-free: · Precipitation.

The process according to the invention cannot only an electrostatically developed image obtained by particularly wet development, independently can be completely retouched from the original as desired, but veils can also be used and any stains present on the plate can be completely and easily removed.

example 1

_{10 g of Zn (NO 3} ), - 6H.O were dissolved in a mixture of 50 g of water and 40 g of methanol and the resulting solution was used as a retouching agent. The image area to be removed in a plate obtained by liquid electrophotographic development was provided with retouching agent and dried. The entire surface was then treated with a hydrophilizing solution, which was obtained by dissolving 120 a K ₄ Fe (CN) ₆ ■ 3, Ο, 370 g NH ₄ H ₂ PO ₄ , 130 g (NH ₄ ), HPO ₄ and 50 g H ₃ PO ₄ SO ⁰ ZoJg prepared in water and a total of 10! has been replenished. Offset printing was then carried out using this treated plate.

The area to be removed was not printed at all and no stains were seen.

Example 2

30 g of Zn (NO _s ), 6H ₂ O were dissolved in 70 g of methanol, and the resulting solution was used as a retouching agent. The treatment described in Example 3 was repeated and an offset print was carried out. The area to be removed was not imprinted at all and no stains were seen. Even after the drying process had taken place after wearing the retouching agent by self-drying at room temperature, the plate had excellent print resistance and after printing about 1000 sheets, there were no defects whatsoever.

Example L ">

The procedure of Example 2 was repeated with the exception that ZnCL was used in place of Zn (NO.,), - 6Η, Ο was used; the result ?: were equally good.

Example 4

The procedure of Example 2 was repeated, with the exception that the Ζ.η (ΝΟ ₃ ), · 6H ₂ O was replaced by Zn (CH ₁ COO) ₀ ; the results were equally good.

B e i s ρ i e 1 5

The procedure of Example 2 was repeated, with the exception that the retouching agent used was a solution obtained by dissolving 3 g of FeCl ₁ -6 H ₂ O in 4 g of water and 18 g of methanol; the results corresponded to those according to Examples 2 to 4.

This retouching medium was colored and the reverse-inert area was immediately recognizable.

Example 6

The procedure of Example 2 was repeated with the exception that as a retouching agent 6- a Lö * -U! Iv was used, which was created by solving rig SnC ';., · .; Ιί., Ο in a mixture of 5 g of water and 20p Niethanoi was obtained; the results were clciv.ii nut.

Example 7

The procedure of Example 2 was repeated, with the exception that the retouching agent used was a solution obtained by dissolving 3 g of AgNo ₃ in a mixture of 5 g of water and 20 g of methanol; the results were equally good.

Example 8

The procedure of Example 2 was repeated, with the exception that as a retouching agent a solution was used that was obtained by dissolving

3 g of AlCl _{3 was obtained} in a mixture of 5 g of water and 20 g of methanol; the results were equally good.

Example 9

There was repeated the procedure of Example 2, except that a solution was used as Retii ^c chiermittel that -sen by L "of

4 g of MgCl _{2 was obtained} in a mixture of 5 g of water and 20 g of methanol; the results were equally good.

Example 10

The procedure of Example 2 was repeated, with the exception that the retouching agent used was a solution obtained by dissolving 4 g of MnCl ₂ in a mixture of 5 g of water and 20 g of methanol; the results were equally good.

_s example 11

1.0 g of a 2% solution of vinyl acetate resin in xylene toluene was added to a mixture containing 0.2 g of H ₃ PO _{4 at} a concentration of 85%, 50 g of H _{2 O and 30% methanol.} 3.0 g of ZnCl _{2 were} dissolved in it, and the solution obtained was used as a retouching agent! used.

After performing dry electrophotographic development, the retouching agent adhered flawlessly on the image surface, which was heat-set. Through this treatment were obtained the same good results as in the preceding examples.

Example 12

0.2 g of aniline blue were dissolved in the retouching agents according to Examples 2, 3 and 4 in order to color them. These were used as retouching agents. The area to be retouched became colored blue and could be seen at first glance. the Results were equally good.

In the examples described above, (by means of hot air with the help of a hair dryer or at Raum temperature dried.

1 sheet of drawings

Claims (2)

2 061 claims: 1. Process for retouching an offset printing form produced by electrophotography, by imagewise exposing an electrophotographic recording material with photoconductive zinc oxide in its photoconductive layer, by developing this recording material with a resin-containing toner, by fixing the toner image and making it hydrophilic with an aqueous solution containing a water-soluble metal hexacyanide salt and / or contains ammonium phosphate, characterized in that that before the treatment with the hydrophilizing solution on areas which should not print, an aqueous retouching solution is applied, which contains a water-soluble metal salt, which with the water-soluble Metal hexacyanide salt and / or the ammonium phosphate a water-insoluble precipitate and whose cation forms one of the following chemical elements Be, Mg, Zn, Hg, In, Cu, Ag, Al, Tl, Th, Sn, Pb, Bi, Zr, Co, Cr, Cd, Ni, Fe, Mn or Ga is assigned. 2. The method according to claim 1, characterized in that that the metal salt of the retouching solution is a chloride or a nitrate.