DE3219986A1 - METHOD FOR PROCESSING AN EXPOSED AND DEVELOPED LITHOGRAPHIC PLATE - Google Patents

Description

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The invention relates to lithographic printing plates and, more particularly, to a method of making plates developed during to protect the melting of the image from contamination of the exposed hydrophilic substrate surfaces, without making the images blind or matting. This is supposed to be done by treating the developed plate done with a special finishing agent before the melting process.

The difficulties and unpredictability of making lithographic plates that are too qualitative quality printing is detailed in an article, "Science on the Surface," British Printer, March 1980, described. The problems are also described in GB-PS 1 513 368, in which it is proposed that a developed lithographic plate to be treated with a water-soluble salt to give a water-soluble layer result, which prevents contamination of the exposed substrate during the melting of the printing ink touch the receiving printing surfaces.

Examples of specific water-soluble salts that are described in the aforementioned GB-PS are sodium dodecylphenoxybenzene disulfonate, a sodium salt of alkylated naphthalenesulfonic acid, a disodium salt of methylenedinaphthalenesulfonic acid, a sodium dodecylbenzenesulfonate, a sodium salt of sulfonated alkyl diphenyl oxide or Lithium nitrate. These materials are hereinafter referred to as finishing agents or fusible rubber according to accepted nomenclature.

The difficulty with the means of completion proposed so far is that the use application is not only time consuming, but that these finishing means won't work properly if the

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Instructions are strictly followed. In addition, there are certain known finishing means too lead to a blinding or matting of the image areas.

In GB-PS 1 513 368 the following process steps for heating a substrate that is coated with a radiation-sensitive layer, proposed:

1. Image-wise exposure of the layer to irradiation] q lung or so that the layer includes exposing the radiation struck areas and not from the radiation struck areas of differing solubility;

2. Development of the imagewise exposed layer to selectively remove the more soluble areas and to expose the substrate underlying these areas;

3 · Treatment of the element to obtain a water soluble salt on the exposed substrate in order to to prevent contaminants from coming into contact with the exposed substrate; .

4. Heat cLcj »less soluble area that is on remains on the substrate after development; and

5. Removal of the water-soluble layer. 30th

The invention is based on the object of an improved A method of processing lithographic printing plates to provide an impurity the plates before printing is avoided. 35

Furthermore, an improved method for treating lithographic printing plates using a

special finishing means are made available, the latter not having the disadvantages of the known Completion funds should have.

Furthermore, a finishing treatment is to be made available which can be applied to wet or dry panels and for specific purposes, such as fabric offset machines, can be applied and which requires a minimum of follow-up treatments.

According to the present invention, it has been found that an improved processing method for a lithographic plate can be obtained if you use a special finishing agent, i.e. a compound of the general formula:

SO ₃ M SO ₃ M

wherein R ₁ and R _{2 are the} same or different and each represent a hydrogen atom or a linear alkyl group having 14 to 18 carbon atoms with the proviso that both groups R ₁ and R _{2 are not} hydrogen atoms and M represents an alkali metal cation, or a Mixture of these used.

According to a preferred embodiment, R _{1 is} a III- ³ ^ linear alkyl group with 16 carbon atoms, R ₂ is a hydrogen atom or R ₁ and M are sodium. Mixtures thereof are also preferably used.

The number of carbon atoms in the alkyl groups (R) ³ ^ is important, as is the use of a linear alkyl group. For example, when using lower alkyl chains, such as linear C _{1 n} - or branched ones

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C ^ groups, the treated plate shows a pronounced poorer receptivity for the printing ink.

In general, lithographic plates suitable for practicing the invention contain a sheet of metal or a metal plate, of which at least one The surface is coated with a radiation-sensitive layer containing a radiation-sensitive component, their solubility in developing agents before and after exposure to said radiation differ is.

Conventional support members can be used in the practice of this invention. The preferred carriers can be any standard metal plates or standard plates with a metallic surface, which are usually can be used in lithographic printing. Aluminum and zinc are two of the most preferred Plates. Naturally, the panels can be specially treated or with an intermediate coating or with backing layers as is well known in the art. For example, it is in the case of aluminum It is often advantageous to anodize the surface chemically or electrolytically. The metal surface can can also be silicatized.

Radiation-sensitive materials known as photopolymer materials are used after exposure to radiation less soluble and therefore negative transparency is used during exposure. In this case it is dis by the radiation not hit, which are removed by the development, and those of the Areas struck by radiation remain on the substrate to form the image. Other materials that behave similarly, are well known, such as the diazo resins, chromium-sensitized colloids, diazonium or acid-sensitized resins or polymers containing such

Groups wear. Elements with a radiation-sensitive layer based on such materials are known as negative working elements.

Radiation-sensitive materials, such as those based on orthoquinone lactides, are removed after exposure more soluble in the radiation and a positive transparency or stencil is therefore used during exposure. In this case it is the areas hit by the radiation that are removed by development, and the areas not struck by the radiation remain on the substrate to form the image. elements with such radiation-sensitive layers are known to be positive working.

The radiation-sensitive component in the form of a dispersion or solution can pass onto the carrier element Dipping, spraying, roller coating, brushing or other conventional techniques can be applied. If so desired said protective coating can be applied over said radiation-sensitive component, to protect their photosensitivity. Conventional procedures can be used for this purpose will.

In general, the printing plates used in the present invention are of the subtractive type and can be mixed with water or developed with aqueous solutions in which the constituents other than water are harmless and / or light Are biodegradable or are present in extremely small quantities. The developed image quickly takes the ink away on. The background is hydrophilic and oleophobic.

In general, the developing agents should have a pH of less than 9 for rapid development. The higher the pH is above 9, the slower the development. If the pH is too low, then the substrate can be attacked.

After the development has been carried out, the plaxte is rinsed, squeezed off and, if desired, dried. If necessary the plate can be corrected after the initial rinse stage and rinsed again before it is squeezed and is dried. All of these stages are conventional in nature and do not include any critical ones and / or essential features of the present invention.

After developing the exposed plate, the plate according to the invention Completion treatment carried out. Thus, the finishing means described above becomes the Formula I on the plate, which can be wet or dry, as an aqueous solution with a solids content of about 5 applied to about 20% by weight and excess solution removed to leave a thin layer of finishing agent on the developed plate. Using For a solution with a lower solids content, the plate must be predried before this step.

The thus treated plate is then heated to about 180 to about 24O ⁰ C for about 5 to 10 minutes to melt the dru colorant-receiving areas of the plate.

After melting, a plate feeder can be used

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ration machine, z.L. a Roland Favorit B machine, Test prints are made. After a few turns, the copies are clean. In most cases, however, it will the plate rinsed after cooling to the finishing agent to remove, squeezed and covered with a normal gum, such as dextrin, gum arabic, polyvinyl alcohol or the like. The plate can now be brought into the printing machine.

The invention is illustrated in the examples. 35

-ιοί examplei

20% strength by weight aqueous solutions of compounds of the formula I were applied to freshly developed printing plates (18 × 60 cm), the image areas of which are a fixed area and comprised several halftone areas (screen area 60 lines per cm and 20 and 80% stain area).

The thus treated panels were then heated in a furnace for 5 minutes at 24O ⁰ C and air cooled. These plates were then used without further treatment, such as a

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Wash, used on a Roland Favorit printing machine. The effectiveness of the finishing agent for Protection of the developed plate during melting is measured by the number of copies that pass through must before a decent copy is made. Table I shows the results of these experiments using of the above solutions.

Table I.

Compound of formula I, M = Na number of copies R

C ^ p branches 26

C ₁₀ linear 18

C ₁ ^ linear (according to the present

Invention) 11

The above values show that the greater the chain length

^{Ou of} the linear alkyl groups, the better the ink absorption and that compounds with branched alkyl groups show a considerably poorer ink absorption capacity.

Example2

Another test of ink receptivity

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was carried out using the finishing agents according to the invention with two commercially available finishing agents RC ™ 99 (Kalle) and Thermoc ™ (Howson Algraphy) were compared.

The compound of the formula I according to the invention was used according to Example 1, while the other products according to manufacturer's instructions were used, with plate rinsing after melting and before printing or has been washed. Using a positive

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ven lithographic plate (GP II, Polychrome Corp.) The results obtained are shown in columns 4 and 5 of Table II below. "Dry" and "wet" refer to the printing of the molten plate in absurdity or the presence of an aqueous ink for fountain pens.

It can thus be seen that both "wet" and Also, "dry" procedures involve a reduction in the number of copies that must be made before a clean copy is obtained will be around a third compared to after that Prior art finished plates is achieved when the developed plate according to the present invention is treated.

Table II

Attempt completion % solid number of copies medium materials up to the first clean copy GP II GP II

(dry wet)

1 according to the invention

Finishing materials used 20 20 17

2 RC 99 20th 28 27 3 Thermotec 20th 28 30th

The above results show that the invention produces results that are superior to competing products are. In addition, the compositions used according to the invention are 100% biodegradable and that the Disadvantages of the known fusible rubbers, such as the blindness of the image areas and the need for time-consuming Following instructions to get the results you want can be avoided.

Claims (11)

FATE NATIONAL LAWYERS AND APPROVED REPRESENTATIVES BEFORE THE EUROPEAN PATENT OFFICE DR. WALTER KRAUS D IPLO M CH EM I KER · D R.-l N G. AN N EKÄTE WEISERT DIPL.-ING. SPECIALIZATION CHEMISTRY IRMGARDSTRASSE 15 D-8000 MUNICH 71. TELEPHONE Ο8Θ / 7 9 7O 77-79 7O78 · TELEX O5-21215 6 kpat d TELEGRAM CRAUS PATENT 3326 WK / rm POLYCHROME CORPORATION New York / USA Process for processing an exposed and developed lithographic plate Claims '1 \ method for processing an exposed and developed lithographic plate by treatment of the developed lithographic plate before heating to form a melt of the image with an aqueous solution of a water-soluble substance, characterized in that as water-soluble substance is a compound of the general formula: SO ₃ M SO ₃ M wherein fL and Rp, which are the same or different, each represent a hydrogen atom or a linear alkyl group having 14 to 18 carbon atoms, with the proviso that both groups R 1 and R _{2 are not} hydrogen atoms, and M represents an alkali metal cation, or a mixture of such compounds is used. 2. The method according to claim 1, characterized in that R ^ is a linear C.g-alkyl group IQ is and that Rp has the same meaning as R ^ or a Is hydrogen atom. 3. Process according to Claim 2, characterized in that M stands for sodium. 4. The method according to claim 2, characterized in that g e k e η η, that the aqueous solution has a solids content of about 5 to 20 wt .-%. 5 · The method according to claim 1, characterized in that the molten lithographic Plate being used directly in a fabric offset machine. 6. The method according to claim 1, characterized in that the molten lithographic Plate cools, rinsed with water, squeezed and then with a normal gum from the group of gum arabic, Polyvinyl alcohol and dextrin are preserved and then used in a printing machine. 7. The method according to claim 1, characterized in that the water-soluble coating to a temperature of about 180 to 240 C above, a sufficient Period of time for a coalescence to be effected, heated. _ HL _ ] 8. Lithographic plate with a 3ines surface metallic carrier element, on which surface a Layer of a positive or negative acting, radiation-reactive mass is, the lithographic Plate has been exposed imagewise to a radiation source and then developed is, characterized in that exposed to the exposed surface or the radiation Surface of the lithographic plate before melting the areas insoluble in the developer an aqueous solution has been applied which contains about 5 to 20% by weight of a compound of the general formula: SO ₃ M. wherein R ₁ , R ₂ and M have the definitions given in claim 1, contains. 9. A lithographic plate according to claim 8, characterized in that R _{1 stands} for nC, jgH ", that R _{2 has} the same meaning as R ₁ or stands for ¥ hydrogen and that M is Na ⁺ . 10. Lithographic plate according to claim 8, characterized in that the Fe material content of the aqueous solution is 20 wt .- #. 11. A lithographic plate according to claim 8, characterized in that the plate is heated after application of the aqueous solution to a temperature of about 180 to 24O ⁰ C. .