DE2656649C2 - Hydrophilic bath for offset printing plates produced by electrophotography - Google Patents

Description

R ₁

CH, =

(1)

-COO (C H

where mean:

R, a hydrogen atom or a methyl radical and Ri a remainder of the formulas:

- CONH ₂ -CONHRj -CON (Rj) ₂ -CONHCH ₂ OH

where R3 is an alkyl radical with 1 to 8 carbon atoms) stands;

or at least one copolymer of different monomers of the general formula I or at least one copolymer of monomers of the general formula I with monomers the general formula:

R ₄ R ₅

I i

C = C i! I)

i ι
R ₁ R ₅

where mean:

R ₄ and R ₄ - a hydrogen atom or a methyl radical or a radical of the formulas -COOH, -COOR ₆ or -COOMe;

R ₅ and Ry represent a hydrogen atom or a methyl radical or a radical of the formulas: -COOH, -COOR ₆ , -COOMe or -CH ₂ COOH (where R ₆ each represents a methyl or ethyl radical and Me, Mg, Ba, Ca, Co, Mn, Fe, Ni or Zn), where the following applies if R ₄ = R ₄ , R _S * R _V and if R ₄ ^ R ₄ . R ₅ = Ry or R ₅ Φ R ₅ contains.

2. Hydrophilizing bath according to claim 1, characterized in that it is a hydrophilic Hp.iz. Acrylic acid / acrylamide mixed polymer contains.

3. Hydrophilizing bath according to claim!, Characterized marked that it. based on its total

weight, 0.1 to 10% by weight of the hydrophilic resin

4. Hydrophilization bath according to claim 1, characterized in that there is also an organic Contains acid and has a pH below 6

5. hydrophilizing bath according to claim 4, characterized in that it is used as an organic acid Contains malonic acid

6. Use of a hydrophilizing bath according to claim 1 after dilution in the ratio one part in 2 to 10 parts as cleaning water.

The invention relates to a hydrophilizing bath for electrophotographic means. , - !! te offset printing forms containing a hexacyanoferrate (II), a water-soluble phosphate and a hydrophilic resin.

An offset printing form is usually obtained electrophotographically with the aid of an electrophotographic one Recording material with a photoconductive layer in the finely divided zinc oxide powder, an insulating resin as a binder and, if necessary, a sensitizing dye are evenly mixed and dispersed with each other, by charging, exposing and developing as well Treating the image obtained with its hydrophilizing bath.

A hydrophilizing bath suitable for this purpose must give the offset printing form a suitable offset printing capacity confer, it must also bring about a sufficient hydrophilization and finally that Allow or facilitate the adhesion of the printing ink to the image areas.

Hydrophilic baths have already been developed for offset printing forms that meet the requirements outlined above to some extent suffice and which are also in practical use. For example, there is a Hydrophilization bath known, which is essentially a hexacyanoferrate (II), a water-soluble phosphate and Contains polyacrylic acid as a hydrophilic resin (cf. BE-PS 5 91935). These ingredients probably make that Non-image areas of the offset printing form become hydrophilic more quickly and reinforce the hydrophilic film-like formed on the non-image areas of the photoconductive layer Coating.

However, it has not yet been possible to use the conventional hydrophilization baths described above Type to produce fully satisfactory offset printing forms.

In order to produce prints with the aid of an offset printing form produced in the manner described can, the offset printing form is placed around the printing cylinder of an offset printing press, whereupon the Surface of the offset printing form clamped in this way with a 1: 6 to ΙΟ solution of the hydrophilizing bath, d. H. is wetted with water. Then the offset printing font is colored with printing ink in such a way that the printing ink selectively only adheres to the image areas of the printing form. That kind of Applied printing ink is applied to a printing blanket and from there to a receiving material made of conventional paper transfer. Since an offset printing press is designed such that the printing cylinder or the Blanket cylinder by means of a gear mechanism

is actuated, there is an abrupt external force when the teeth of the gears mesh, e.g. a frictional force on the contact surface between the ones around the printing cylinder Offset-Druckiorm and the blanket cylinder. In this way, a spot or a spot of the the contact surface exposed to the action of external force is somewhat more likely to smear the printing ink than the normal inking process takes place (this smearing of printing ink is called "gear stripes"). In fact, the appearance of such "gear stripes" can be observed with the usual, well-known hydrophilizing baths do not avoid.

The invention is based on the object of creating a hydrophilizing bath for offset printing forms, which makes an offset printing form hydrophilic very quickly, a hydrophilic film-like top layer is more excellent Provides water-holding properties, prevents the occurrence of "gear stripes", the durability the printing form when printing is significantly longer compared to conventional, known hydrophilization baths and finally, after suitable dilution, can be used as mopping water.

The subject of the invention is thus a hydrophilizing bath of the type characterized in claim 1

Among copolymers of various monomers of the general formula I S'.nd, for example Copolymers from the monomers

H
CH ₂ = C

CONH ₂
and the monomer

CH ₃
CH ₂ = C

CONHCH ₂ OH

to understand.

A hydrophilizing bath according to the invention is obtained by adding one of the homopolymers mentioned and / or copolymers to which the essential constituents of conventional hydrophilic baths form Hexacyanoferrate (II) and water-soluble phosphate. As hexacyanoferrates (II) are suitable for hydrophilic baths according to the invention in aqueous solutions stable hexacyanoferrate (II), for. B. sodium hexacyanoferrate (II) and Potassium hexacyanoferrate (II). These Hexacyanoferrate (II) can either individually or in Mixture of two or more are used. Based on the total weight of the hydrophilizing bath the amount of hexacyanoferrate (II) should be greater than 0.2% by weight. As water soluble Phosphates are suitable in hydrophilizing baths according to the invention, primary ammonium phosphate, secondary Ammonium phosphate, primary sodium phosphate or secondary sodium phosphate. These phosphates can be used either alone or in combination of two or more. Based on the Total weight of the hydrophilizing bath, the amount of water-soluble phosphate should be 0.1 to 12 % By weight.

The water-soluble phosphate forms a hydrophilic film by reaction with the zinc oxide forming the photoconductor in the photoconductive layer. The film-like coating thus formed has good hydrophilic properties, but is insufficient in strength so that it is occasionally peeled off during printing. However, if the hexacyanoferrate (II) is mixed with the water-soluble phosphate, the strength of the hydrophilic film-like ίο coating and thus its durability during printing increases. In hydrophilizing baths with such water-soluble phosphates and hexacyanoferrates (II), however, it is on the one hand impossible to store the two constituents in a stable manner next to one another over a long period of time, and on the other hand the advantages sought according to the invention cannot be achieved either. However, all of these questions can be resolved by adding one of the hydrophilic homopolymers and / or copolymers mentioned to the two constituents mentioned.
As already mentioned, these hydrophilic polymers to be added to the hexacyanoferrate (II) and the water-soluble phosphate consist of monopolymers of monomers of the general formula I, copolymers of different monomers of the general formula I and copolymers of monomers of the general formula I with monomers of the general formula II. Examples of such polymers are
Polyacrylamide,
Acrylamide / N-dimethyl acrylamide

Mixed polymers,
Acrylamide / N-methyl acrylamide

Copolymers,

Acrylamide / acrylic acid copolymers,
Dimethyiaminoethyl methacrylate /

Maleic acid / e copolymers,
N.N'-dioctylacrylamide / fumaric acid

Copolymers and
N-ethylaminomethacrylate / itaconic acid

Copolymers.

These polymers can be used either alone or in combination of two or more. Tests have shown that of the homopolymers and copolymers mentioned, acrylic acid / acrylamide copolymers give the best results. This is presumably due to the fact that acrylic acid / acrylamide copolymers are substances which are able to form chelate compounds. Based on the total weight of the hydrophilizing vi bath, the amount of the said homopolymers or copolymers 0.1 to 10, are preferably 0.5 to 5 wt .-%. If less than 0.1% by weight of homo- and / or mixed polymer is used, the printing form cannot be given sufficient pressure resistance. If more than 10% by weight of homo- and / or mixed polymer is used, the formation of a hydrophilic film-like coating is impaired.

In the preparation of a hydrophilic bath according to the invention, firstly a hexacyanoferrate (II), secondly a water-soluble phosphate and thirdly at least one homo- and / or mixed polymer of the type described dissolved in water. According to a preferred embodiment, one of these ". term hydrophilization bath or an organic acid, z. B. tartaric acid, fumaric acid or malonic acid, added, to adjust its pH to a value below 6. Particularly good results are achieved

with addition of malonic acid.

With a waterproofing bath for offset printing forms of the type described, all the advantages sought in accordance with the invention can be achieved. By adding very special hydrophilic resins, the water retention properties of the Improved hydrophilic film-like coating formed in non-image areas of the offset printing form, so that avoid the occurrence of >> gear stripes «and at the same time increase the durability of the printing form Let printing improve. In conventional offset printing forms, attempts were made to improve the durability of the printing form during the printing process by increasing the strength of the on the surface of the printing form Applying the hydrophilizing bath to be formed film-like hydrophilic coating and / or an elevation the rate of formation of the film-like coating. Let according to the invention In addition to the improvements outlined, the water-holding properties of the hydrophilic film-like one also show Improve the coating, so that overall the advantages mentioned above can be achieved.

If a hydrophilizing bath according to the invention is diluted in a ratio of one part to 2 to 10 parts, the diluted hydrophilizing bath can be applied to the surface of the printing form as wiping water.

example 1

On a waterproof paper as a support is made by applying a mixture of photoconductive zinc oxide with an acrylic resin binder using the dispersion obtained, a photoconductive layer is applied and the whole is then dried, whereby an electrophotographic recording material is obtained.

Furthermore, hydrophilization baths 1 to 11 according to the invention and comparative hydrophilization baths become 12 to 16 prepared. The individual hydrophilization baths have the following composition:

Hydrophilic bath 1:

Sodium hexacyanoferrate (ll)

Polyacrylamide

(NiU) ₂ HPO ₄

citric acid

water

Hydrophilization bath 2:

K.a ' ^: umhexacyanofcrrat (ll)
Acrylamide / acrylic acid copolymer (molar ratio:
Na ₂ HPO ₄
citric acid
water

Hydrophilizing bath 3:

3: 1)

20 g
20 g
60 g
24 g
1000 m!

30 g

10g

40 g

40 g

1000 ml

Sodium hexaecyanene ferrate (II) 25 g
Dimiethylaminoethyl methacrylate /

Maleic acid copolymer

(Molar ratio: 5: 5) 40 g

secondary sodium phosphate 50 g

Citric acid 30 g

ίο

water

1000 ml hydrophilizing bath 4:

Potassium hexacyanoferrate (II) 15 g N.N'-dioctylacrylamide / fumaric acid copolymer

(Molar ratio: 3: 7) 5 g

Tertiary sodium phosphate 20 g

Tartaric acid 10 g

Water 1000 ml

Hydrophilic bath 5:

Potassium hexacyanoferrate (II) 45 g

Methacrylic acid N-ethylaminoethyl ester / itaconic acid

Mixed polymer

(Molar ratio: 7: 3) 20 g

Secondary ammonium phosphate 30 g

Malonic acid 10 g

Water 1000 ml

Hydrophilic bath 6:

Sodium hexacyanoferrate (Ii) 30 g methacrylamide / methacrylic acid copolymer

(Molar ratio: 5: 5) 10 g

Pyrophosphoric acid 20 g

Diammonium hydrogen phosphate 40 g

Malic acid 10 g

Water 1000 m «

Hydrophilic bath 7:

Potassium hexacyanoferrate (II) 30 g acrylic acid / acrylamide / methacrylic acid copolymer

(Molar ratio: 2: 3: 5) 5 g

Diammonium hydrogen phosphate 60 g

Malonic acid 30 g

Water 1000 ml

Hydrophilic bath 8:

Sodium hexacyanoferrate (II) 30 g methyl methacrylate /

N -Methyl methacrylamide / maleic acid mixed polymer

(Molar ratio: 1: 1: 8) 5 g

Carboxymethyl cellulose 1 g

Ammonium hydrogen phosphate 40 g

Diammonium hydrogen phosphate 20 g

Malonic acid 30 g

Water 1000 ml

Hydrophilic bath 9:

Potassium hexacyanoferrate (II) 30 g of N.N'-dimethylacrylamide / fumaric acid copolymer

(Molar ratio: 5: 5) 10 g

Sodium phosphate 60 g

Citric acid 30 g

Alginic acid 0.5 g

Water 1000 ml

Hydrophilizing bath 10:

Sodium hexacyanoferrate (II) 50 g

Cobalt acrylate / acrylic acid /

N-methyl acrylamide copolymer

(Molar ratio: 1: 5: 4) 5 g

Disodium phosphate 100 g

Sodium glutamate

Tartaric acid

water

Hydrophilization bath 11:

Potassium hexacyanoferrate (ll)

Ν, Ν'-dimethyl methacrylamide / calcium acrylate / acrylic acid copolymer
(Molar ratio: 3: 2: 5)

Triammonium phosphate

Malonic acid

water

Comparative hydrophilizing bath 12:

Sodium hexacyanoferrate (II)
Secondary sodium phosphate citric acid
water

Comparative hydrophilizing bath 13:

Sodium hexacyanoferrate (ll)

Vinyl pyrrolidone

Secondary ammonium phosphate citric acid

water

Comparative hydrophilic bath 14:

Primary sodium phosphate

Polyvinyl pyrrolidone

citric acid

water

Comparative hydrophilizing bath 15:

Sodium hexacyanoferrate (l I)
Secondary ammonium phosphate maleic anhydride / vinyl acetate copolymer

(Molar ratio: 5: 5)
citric acid
water

Comparative hydrophilization bath 16 (according to BE-PS 5 91 935):

Sodium hexacyanoferrate!)

Secondary ammonium phosphate polyacrylic acid

citric acid

water

10g

30 g 1000 ml

45 g

20 g

60 g

30 g

1000 ml

20 g

60 g

40 g

1000 ml

20 g 20 g 60 g 24 g 1000 ml

20 g

20 g

10g

1000 ml

20 g 20 g

20 g

24 g

1000 ml

20 g 20 g 20 g 24 g 1000 ml are used in a standard device with the different hydrophilic baths or comparative hydrophilic baths treated, whereby various offset printing forms are obtained.

The individual offset printing forms are in a commercial offset printing press clamped and treated with the 1: 6 diluted hydrophilizing baths or Comparative hydrophilization baths treated as cleaning water. Then 5000 Prints made. After the 5000 prints have been made, the condition of each printing form and the Condition of prints examined. The following results are obtained:

The electrophotographic recording material produced in the manner described is now carried out Corona discharge charged and then exposed by developing with a commercially available dry developer and fixing the toner image by heating, an image copy is obtained. Numerous such image copies

I lyclrriphilioriingshiul
Ivw. Comparative Seal No.

Printing form

pressure

XX

XX

XX

9
10
11
12th
13th
14th
15th
16

Footnotes:

The symbol G stands for "gear stripes do not occur":

the + symbol stands for "minor occurrence of gear stripes";

the symbol x stands for "noticeable appearance of gear stripes";

The symbol xx stands for »noticeable appearance of gear stripes and clear formation of spots the background «.

Example 2

Example 1 is repeated using this as a binder in the photoconductive layer of the electrophotographic The recording material used by a silicone resin, a styrene / acrylic resin or a binder Acrylic / alkyd resin, a styrene / butadiene mixed polymer is replaced. Practically the same results as in Example 1 are obtained.

Example 3

In the hydrophilizing bath 8, the malonic acid is replaced by citric acid. Otherwise, example 1 is used repeatedly It is shown that the occurrence of "gear stripes" can be reduced by 30%

Claims (1)

Patent claims: 1. Hydrophilizing bath for offset printing plates produced by electrophotography with a content of a hexacyanoferrate (II), a water-soluble phosphate and a hydrophilic Resin, characterized in that there is at least one homopolymer as the hydrophilic resin of monomers of the general formula: