DE2002562C3 - - Google Patents

Description

The invention relates to printing plates for the offset process, in particular with paper as the Tiägennate rial, on which there is a coating with a surface that is insoluble in water, absorbs water

mend, but printing ink is repellent during offset Processes are oleophilic in the image areas and therefore accept oily printing ink, whereas those free from printing Parts are hydrophilic and therefore wettable with water. This printing plate provided with printing ink

can now in the usual way directly or via a rubber blanket to produce a number of prints products are applied.

Such layers have been built up from a hy drophilic binder or colloid, such as

Starch, casein, polyvinyl alcohol, alginates, carboxy methyl cellulose, polyacrylates and the like, the un Solubilized with an acid or salt and pigmented with a fine, inorganic see substance such as kaolinite, barium sulfate, colloidal

Silica, zinc oxide or titanium dioxide.

If paper is used as the carrier material in the production of an offset printing plate, then it is important to know fig this generally first provided with a coating to protect it against the ingress of water

seal the wet strength of the paper and the haf to improve the printing layer. The development is now that the number of layers to be applied to the paper is as low as possible will. The present inventor also goes in this direction because it brings a printing plate for the offset Printing process with only 2 layers, namely a top layer with that of the printing process effective area and an underlayer on the paper carrier. The printing plates according to the invention

are characterized by particularly great usability, good shelf life and particularly balanced hy drophobic and hydrophilic properties, the oily or greasy printing ink is very firmly bound to it so a large number of prints are more excellent Quality are produced. For printing even the most varied of products can be used as printing ink and wiping medium], so that a universally applicable reproduction material is obtained. The invention Printing plates can be presensitized with sensitizers in order to print on an image accepting printing ink by exposure. The invention relates to In addition, a process for the production of these new printing plates for the offset process ren.

The printing plate according to the invention (see figure) is composed of a 2-layer system, with the printing topsheet 14 made of a binder such as

Polyvinyl alcohol or hydroxyethylated starch as The bottom layer 12 between the paper layer 10 and the top layer 14 contains the only hydrophilic colloid with customary pigments or fillers as an essential component in the binder, especially polyvinyl alcohol, together with pigments or Fillers salts of polyvalent metals, which serve the printing area of the top layer from below to make her insoluble, without the need for acidic, catalyzing salts in or on the printing area itself.

This principle is exactly the opposite of the previous structure of offset printing plates using paper carriers, with salts being multivalent Metals are usually either in situ in the top layer or by an extra surface treatment with a salt solution, optionally with Binder to be applied to this surface.

Another essential feature of the invention According to printing plates lies in the presence of phosphates of ammonium or monovalent Me talle in the upper layer, which serve to produce anions for the reaction with the polyvalent metal ions of the sublayer available to provide a pore-closing deposit in the sublayer as well as at the interface of the lower layer with the upper layer.

By not converting the salts of the polyvalent metal into the effective area, but can be provided at a distance from this area pH value with regard to the drying of an oleophilic or lacquer-like printing ink can be adjusted to the most favorable value without the advantages pigmented printing layers containing salts of polyvalent metals are lost.

About the mode of action of these salts of polyvalent metals, US Pat. No. 2,534,650 shows that a water-soluble and water-stable, divalent metal-containing salt in penetrate the pores and cavities of the layer and clog them, so the capillaries seals in or around the fine mineral particles within the colloid of the layer present, especially if a mopping water is used which is mixed with the salt of the bivalent metal tails is able to react with the formation of a voluminous precipitate. A component of in large Wiping solutions widely used is a monovalent metal phosphate, particularly sodium dihydrogen phosphate. It exists! Cause for the assumption that this substance of the wiper water reacts with the zinc ions and creates a curly precipitate, as mentioned in this patent specification, forms.

In the reverse arrangement according to the invention, aluminum and zinc salts or other their polyvalent metals in the lower layer, whereas a soluble phosphate is in the upper layer. The reaction mechanism of this The arrangement is easy if one considers that there is a fluffy, mixed Impact of both aluminum and zinc salts forms at the interface between the lower and upper layers when the upper layer is in the frame their application comes into contact with the underlayer. This flaky material will probably fill completely the pores of the sublayer, increasing its effectiveness and its ability to prevent excessive migration of free aluminum. Zinc and / or To delay chloride up through the top layer, whereby the printing surface can be sensitive to fingerprints or a higher one Acidity is maintained, as it is beneficial for the normal drying of finished or oily printing inks, especially in the production of intermediate originals, such as for forms, checks or the like can be used.

The main aspects of the printing plates according to the invention lie in the following points:

1. Contrary to common practice, the salts of the polyvalent metals are in the lower layer

2. There are no polyvalent salts in the top layer and thus in the printing surface Metals and

3. In the upper layer there is a water-soluble phosphate which, with some of the polyvalent metal salts in the lower layer are able to react and obviously for every compatible, hydio phile, colloidal binders can be selected. For example, instead of polyvinyl alcohol, you can use hy Use hydroxyethylated starch.

It has been said that polyphosphates, such as Na trium hydrogen pyrophosphate and hexametaphosphate, give the best results, however one can basically use any soluble phosphate according to the invention, which anions are available sets up those with the aluminum and zinc ions forming one of the pores in the underlayer as well the intermediate surface between the lower and upper layers of the precipitation filling is able to react, especially the ammonium and alkali phosphates.

In principle, any colloidal binder can be used, provided that it contains the salts of polyvalent metals to the application of the layer on the paper and removal of the water capable of being preserved in solution during drying without coagulating. The binder for the The top layer should also be compatible with these metal salts and should work perfectly with the bottom layer associate. Sodium alginate is not suitable for this because it coagulates with metal ions and becomes one poor connection with the underlayer results in the formation of a weak interlayer of Zinc and / or aluminum alginate.

The pigments for the top layer are selected in the customary manner in order to obtain a printing surface that accepts all customary printing inks and cosmetic agents as far as possible. Is preferred According to the invention, an aluminum-modified silica as filler or pigment for the top layer, whereby a better adhesion of the greasy paint is achieved, as it is in common ribbons from Typewriters or ballpoint pens is used. Such a ratio is particularly preferred from kaolinite to silica that the porosity and the anchoring effect for firmly adhering images or Writing made of wax material, as is the case with lettering on carbon paper or plastic strips, is guaranteed. It is desirable in that Introducing the top layer of silica in order to improve the absorption and adhesion of graphic and written characters due to its slightly rubbing effect, how they can be applied with copier and drawing pens. However, other commonly used fillers and pigments can also be used.

The printing plates according to the invention are the first real "all-purpose plates" and are suitable for for example the following areas of application:

1. Direct lettering: the plate directly receives and holds images or writing from any lettering device such as is commonly used the image fixed, due to the above properties as well as the fact that the image or Characters also on places where you have erased with an eraser and thus smoothed the surface keep it safe, because by erasing surface areas are somewhat more active from a chemical point of view than the original surface. This support in chemical terms, which is known to be the salts for cause the fixation of the image or the characters, compensates for the partial loss of anchoring possibility and porosity due to the erasing and smoothing action of the eraser.

2. Xerographical copying:

The thermosetting undercoat, containing the metal salt, enables both the topcoat as well as the backing layer does not need to contain any hygroscopic or unstable substances and therefore allows wrinkle-free and generally high quality xerographic transfer.

3. As the surface is generally neutral and does not contain any substances that cause a delay or hinder the drying of oily or varnish-like printing inks, the new one is suitable Material especially for preprints.

Briefly summarized, the printing plate or master copy according to the invention is so constructed that the printing surface of the top layer contains polyvinyl alcohol as the only hydrophilic colloid and with one or more fillers in the form of kaolinite or colloidal silica is pigmented, but may also contain other pigments and fillers, such as titanium dioxide or zinc oxide. In this upper class the printing surface therefore does not contain a salt of polyvalent metals in order to modify their hydrophobic-hydrophilic properties. Likewise are no wiping fluids required for the printing surface, which contain polyvalent metal salts in solution to make the colloid insoluble and the to modify hydrophobic-hydrophilic properties. This also causes an overlaying of the printing surface with excess water-soluble Avoided metal salts, which could have a detrimental effect on the firm bond of the printing inks to the surface and / or lead to an uneven surface Insolubilization reaction could result. All of this is known to affect the drying of the Printing ink for templates or intermediate originals for the production of e.g. forms or checks.

Generally speaking, the underlayer is composed of an adhesive binder system, in which polyvinyl alcohol is an essential component and, according to a preferred embodiment of the invention, also melamine-formaldehyde resins and melamine are included. The sub-layer can also be kaolin or clay or others mentioned above, contain commonly used fillers. In addition, however, it also contains a water-soluble salt of a polyvalent metal, whereby the Adhesion of the symbols on the printing surface is influenced.

According to the invention, polyvinyl alcohol is preferred as the binder, but the overall structure of the inventive printing plate regardless of the binder system used, so that any colloidal, hydrophilic, adhesive product can be used which does not irreversibly coagulate by adding salts of polyvalent metals ί or does so when it comes into contact with a polyvalent surface Contains metal salt. These binders can therefore be used both in the upper and in the lower layer instead of polyvinyl alcohol

ίο be. An example of this is hydroxyethylated starch.

Small proportions of substances, such as surface-active substances, can be introduced into both layers Agents, antifoams, fungicides and the like that only serve to stabilize and preserve the layers and affect the printing properties and such as have no influence.

The invention is explained in more detail using the following examples:

example 1

The lower layer was built up from the following material:

kg

7.7 polyvinyl alcohol

1.5 melamine (recrystallized)

5.8 Resin emulsion

so 29.4 clay slurry, 68% solids

salary

1.8 milamin formaldehyde resin 40% solids

1.0 equal parts tributyl phosphate and Butanol as an anti-foaming agent

0.5 40% solids in the antifoam 123.7 water

1.4 50% aluminum chloride solution

6.5 Zinc acetate solution 25% 20.7 water

The resin emulsion mentioned above is a plastic emulsion with a solid content of 44%, which is about 63 percent by weight ethyl acrylate, 35% acrylonitrile and 2% methacrylic acid contains.

The polyvinyl alcohol is dispersed in the 1st portion of water and heated to about 90 ° C solved. Then the other ingredients are using

Except for the metal salts and the 2nd water quantity

placed in a mixer and finally the

Salts and the remaining amount of water to form the Application mass added A paper, about 81, SgZm ^{2 was used} from the carrier; the

Application takes place in the usual way, for example with the aid of an application roller or by pouring on, an application rate of about 130 g / m ^{2 being} used. Excessively applied mass was removed with the help of a blade. The layer was then left in the air dried in an oven at a temperature of about 100 to 200 ° C for 1 to 30 minutes. It is also possible to apply a layer without resin.

The following recipe was used for the top layer:

kg

5.4 polyvinyl alcohol 36.0 clay slurry, 68% solids 43.2 Colloidal silica, 30% solids

kg
3.3

Melamine formaldehyde resin emulsion 40% solids

0.6 tributyl phosphate and butanol equal parts

0.2 surface active agent 75% solids in water (dioctyl ester of Sodium sulfosuccinate)

8.9 acid sodium pyrophosphate 75%

solution
102.4 water

The polyvinyl alcohol was again first dispersed in cold water and heated to υ about 90 ° C dissolved. Then the remaining ingredients were mixed in.

The application was carried out in such a way that a dry weight of 59 g / m ^{2 was} obtained, again with the aid of an application roller or by pouring on, the excess amount being drawn off with the aid of a doctor blade or a blade. The surface was then smoothed and the whole thing was air-dried at an oven temperature of about 100 to 250 ° C. in 0.5 to 15 minutes.

The binder in the two layers can contain a small amount of polyvinyl alcohol Polyvinyl acetate contain, for example, 2 to 10 percent by weight, as is the case with the above-mentioned commercial products the case is. For the backsheet, the polyvinyl alcohol can be 7 to 35 weight percent, preferably 15 to 29 percent by weight - calculated on the solid polyvinyl alcohol in the application mass - make up, for the top layer 4 to 20 percent by weight, preferably 8 to 16 percent by weight.

The melamine-formaldehyde resins of the lower layer can be various commercially available Trade products. However, other aminoplasts such as dimethylolurea or urea can also be used Formaldehyde resins are used. The proportion of these resins in the underlayer makes 0.4 to 4 percent by weight, preferably 1.3 to 2.6 weight percent solids. Melamine-formaldehyde resins can be used in the top layer in an amount of 0.5 to 5 percent by weight, preferably 2 to 4 percent by weight. in the application mass, are used.

Generally speaking, a resin can be used for the resin emulsion mentioned above, which is 85 up to 55 parts by weight of ethyl acrylate, 20 to 45 parts by weight of acrylonitrile and 0.5 to 4 parts by weight of methacrylic acid units contains. The proportion of this resin in the underlayer is 3 to 15 percent by weight, preferably 5 to 10 weight percent calculated on dry solids. "

Instead of clay or kaolin, other pigments, such as barium sulfate, can be used in the two layers. Use titanium dioxide or colloidal silica, the amount of filler is 1 to 3 parts by weight Pigment or filler in the sub-layer per part by weight of binder or based on pigment or Fillers in the application mass 40 to 80 percent by weight, preferably 50 to 70 percent by weight. The topsheet can have 1 to 8 parts of filler per part Polyvinyl alcohol, preferably 6 to 7 times the 6J Contained by weight, i.e. 75 to 90 percent by weight, preferably 81 in the application mass up to 86 percent solids by weight.

The colloidal silica used for the top layer is preferably one those in which at least part of the silicon is replaced by aluminum. Such a product is called colloidal system in aqueous medium with a solids content of 30% on the market, but you can also use other commercially available colloidal silicic acid preparations. The amount of colloidal silica in the upper layer can be between 8 and 40 percent by weight, preferably 10 to 35 percent by weight - calculated on the silica solids in the coating mass - contribute.

The antifoams and surface-active agents serve to stabilize the coating composition and their application to the paper carrier. Of course, other common substances than antifoam agents, surfactant or wetting agent can be applied.

Instead of the aluminum chloride and zinc acetate in the underlayer, other water-soluble ones can be used Salts of polyvalent metals, such as the chlorides, nitrates, formates, acetates or propionates of finished metals, such as zinc, calcium, nickel, copper, cobalt, barium, strontium and trivalent metals such as aluminum use. A combination of 2 and 3 valent metal salts such as zinc chloride is preferred or zinc acetate and aluminum chloride, in a ratio of 1 to 4 parts by weight of divalent Metal salt to 1 part by weight of trivalent metal salt. In the lower layer, the amount of multivalent Metal salts make up 2 to 15 percent by weight, preferably 5 to 8 percent by weight, of the coating composition.

Example 2

A composition of the following composition was used for the lower layer.

123.7 water

1.5 melamine (recrystallized)

7.7 polyvinyl alcohol

29.4 clay slurry 68% solids

5.8 Resin emulsion 44% solids (85 to
55 parts by weight of ethyl acrylate, 20 to 45
Parts by weight of acrylonitrile and 0.5 to 4
Parts by weight methacrylic acid)

1.8 Meiamine formaldehyde resin 40% solids

1.0 antifoam
0.5 antifoam agent

., 4 aluminum chloride 50% solution

6.5 Zinc chloride 25% solution
10.7 water

A mass of the following composition was applied to this lower layer as an upper layer.

kg
104.0

5.5
31.5

9.4
36.5

3.4

water

Polyvinyl alcohol

colloidal silica 30% solids

colloidal silica 40% solids

Clay slurry 68% solids Melamine formaldehyde resin emulsion

40% solids

kg
1.1
0.6
0.2
9.0

melamine

Antifoam

Wetting agents

Sodium hydrogen pyrophosphate

solution

7%

The printing plate obtained in this way is distinguished by its particularly long working life.

Example 3

For a medium-time sheet, the following can be used Lower layer can be applied.

kg

123.7 water

1.5 melamine (recrystallized)

7.7 polyvinyl alcohol

29.4 clay slurry 68% solids

5.8 Resin emulsion 44% solids

1.8 melamine formaldehyde resin 40% solids

., 0 antifoam
0.5 antifoam agent

3.1 Aluminum chloride 50% solution

13.5 zinc acetate, 25% solution

25.6 water, ₀

Instead of the zinc acetate solution used here, you can also use an equivalent amount of cobalt acetate or use nickel acetate.

By combining resin emulsion, polyvinyl alcohol, melamine formaldehyde resin and melamine in the mass for the lower layer is a self-hardening system, which a good bond of the mineral pigments and perfect adhesion to the paper backing. This Layer has certain hydrophilic properties and is impermeable to water. The one present in the lower class The amount of polyvalent metal salts is sufficient to achieve the desired balance between the Maintain hydrophilic and hydrophobic properties and the top layer lastingly for that Desired ratio to provide required amount of polyvalent metal salt available, in spite of the Amounts that are used as part of the application of the plate by pre-etching and wiping solutions with which the The plate surface is continuously moistened during printing, must be removed. The lower class can keep it functioning for a long time since

40

45 it is protected from the action of solutions by the top layer, but the optimal printing properties can still be used. This is where the printing plate or template according to the invention differs quite significantly from the known ones.

Another advantage of the arrangement according to the invention, which is practically opposite to the previous arrangement is, lies in the simplification of the regulation of making the layers insoluble at the same time Guarantee of optimal printing properties. The polyvalent metal salts have been customary up to now applied to the printing surface of the layer in the form of a solution, the amount of salt being particularly had to be adjusted carefully, as excessive salt content was caused by brushing or the like had to be removed. Nevertheless, there are wide fluctuations in the salt concentration; in any case a layer of metal salt remains as a coating and impairs adhesion and anchoring the greasy ink in the printing areas.

Another advantage of the invention is that corrections to the image-bearing printing plate by erasing or removing image parts are possible and the surface properties for a new one Lent lettering is sufficient. In the previous processes with coating solutions containing polyvalent Metal salts, the removal of parts of the image by erasing not only removes the printing ink, but also also this essential component in the layer important for offset printing, so that such a Material cannot be re-labeled or typed over after correction.

Example 4

A top layer was produced from a composition from Example 1, but without the melamine-formaldehyde component. In this case, the metal salts of the sub-layer of the previous examples do this Insolubilizing the binder and clogging the pores.

From the above it can be seen that the offset printing plate or original according to the invention is a permanent one Adjustment of optimal printing properties in terms of image adhesion and the production of a large number Good quality copies are permitted. The principle according to the invention can be applied to a large number of materials. Corrections can be made without any disadvantages on the already provided with font or bud Plate to be made.

1 sheet of drawings

Claims (15)

Patent claims: 1. Offset printing plate consisting of a carrier material and 2 layers containing hydrophilic binders and polyvalent metal salts, characterized in that the underlayer resting on the paper carrier material is the polyvalent metal salts and the top layer with the printing area contains a soluble phosphate, which uses the polyvalent metal ions to react with the formation of a voluminous precipitate in the pores of the lower layer and at the interface between the lower and upper layers able to 2. Offset printing plate according to claim 1, characterized in that the lower layer contains 2 to 15 percent by weight of polyvalent metal salts 3. Offset printing plate according to claim 1 or 2, characterized in that the polyvalent metal salts are 1 to 4 parts by weight of divalent and 1 part by weight of trivalent metal salt. 4. Offset printing plate according to claim 1 to 3, characterized in that the polyvalent metal salts are the chlorides, nitrates, formates, acetates or proprionates of zinc, calcium, nickel, copper, cobalt, barium or strontium and the trivalent metal salts chloride, nitrate, formate or acetate of aluminum. 5. Offset printing plate according to claim 1 to 4, characterized in that - that the soluble phosphate of the top layer is sodium dihydrogen phosphate, Disodium hydrogen phosphate, tetrasodium pyrophosphate, sodium hydrogen pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate or is the corresponding ammonium or potassium phosphates 6. Offset printing plate according to claim 1 to 5, characterized in that the hydrophilic, colloidal binder of the two layers is polyvinyl alcohol or hydroxyethylated starch. 7. offset printing plate according to claim 1 to 5, characterized in that the binder is a or both layers contain an amidaldehyde resin 8. offset Druckpiütte according to claim 7, characterized in that the lower layer 0.4 to 4 percent by weight and the top layer 0.5 to 5 parts by weight of a melamine-formaldehyde resin contains 9. offset printing plate according to claim 1 to 8, characterized in that the binder of the The lower layer also has a resin containing ethyl acrylate, acrylonitrile and methacrylic acid. 10. Offset printing plate according to claim 9, characterized in that the binder 3 to 15 percent by weight of the resin. 11. Offset printing plate according to claim 1 to 10, characterized in that the top layer and / or the sub-layer contains fillers or pigments. 12. Offset printing plate according to claim 11, characterized in that the fillers or pigments kaolin and colloidal, optionally with Alumina modified, silica are. 13. Offset printing plate according to claim 11 or 12, characterized in that the proportion of Fillers in the top layer makes up 5 to 8 parts by weight to 1 part by weight of polyvinyl alcohol 14. Offset Drockplatte according to claim 13, characterized in that the top layer 50 to Contains 60 percent by weight clay or kaolin and 5 to 40 percent by weight colloidal silica 15. Offset printing plate according to claim II or 12, characterized in that the proportion of fillers in the lower layer 1 to 4 parts per 1 part by weight of polyvinyl alcohol.