FR2467706A1 - WHITE LITHOGRAPHIC SUPPORT - Google Patents

Abstract

Disclosed is an aluminum foil suitable as a white lithographic support for printing. The support sheet according to the invention is produced by a process comprising the following steps: graining of said sheet then immersing said sheet in an aqueous bath of trisodium phosphate at a concentration ranging up to 30% by weight for a period of up to 'at 5 min at a temperature between room temperature and the boiling point.

Description

The present invention relates to the preparation of support bases for

lithographic printing plates and more

  in particular, new bases supporting a lithographic plate

aluminum phique having a substantially whiter surface than those produced previously. It is well recognized that the almost majority of lithographic photosensitive printing plates currently produced

are made of aluminum foil. This aluminum foil

  minium has been shown over the years to present certain

  venenets which pocket the direct application of photo-

  sensitive on the aluminum base sheet. It has been found that, by direct application of the photosensitive composition to the sheet

  aluminum base and subsequent exposure to light and

Mining areas not impressed by the image for the preparation of a lithographic printing plate, the resulting printing plate has many annoying characteristics which make it unacceptable for commercial use in the printing industry. Among the disadvantages of these plates, we can cite

the fact that the eliminated areas which do not form the image do not have

  tooth not sufficient hydrophilic and oleophobic characteristics ei, when printing, they therefore take the flaws of the background found on the final copy. Furthermore, as aluminum is

a rather soft metal, it does not have the necessary resistance properties

  grips to withstand long press runs when more

  approximately 100,000 copies are required. In addition, the characteristics

  aluminum surface ticks are such that one encounters a

  problem to achieve a strong bond between the photo-

  sensitive and aluminum base sheet, which therefore causes the image area to detach from the plate surface and makes

the imperfect printing plate.

Until now, in the production of litho-

  metallic presensitized printing graphics, it has been found advantageous to carry out various surface treatments on the aluminum surface to give it any one of many advantageous characteristics. These treatments include surface graining, etching, anodizing and coating with inter-layer adhesive materials before applying a photosensitive coating. U.S. Patent No. 4,090,880

  describes the chemical attack in trisodium phosphate with anodi-

Subsequent sation in sulfuric acid and application of an intermediate layer. U.S. Patent No. 3,891,516 describes graining with an aqueous pumice slurry with

  subsequent anodizing to form a dark surface plate.

The prior art indicates that it is desirable to treat the surface of the metal foil support receiving the photosensitive coating material, which, after exposure to light and development, becomes the printing surface of the printing plate, with a underlying coating substance which forms a strong bond with the metal foil support

and with the photosensitive coating material.

  Numerous coating treatments of this type are known in the art for manufacturing lithographic plates with a longer service life and can be used on the sheets according to the invention. U.S. Patents Nos. 3,160,506, Nos. 3,136,636, Nos. 2,946,683 and No. 2,922,715 describe various products suitable for depositing underlying coatings

of adhesive material on plates and methods of applying them.

  Alkali metal silicates, silicic acid, alkali metal fluozirconates and fluozirconic acid solutions are

  currently the most important commercial adhesive substances.

  The technique indicates several treatments in two stages of attack and graining which are distinct from the invention and have aberrant surface characteristics. As previously mentioned, U.S. Patent No. 4,090,880, particularly in Examples 1-4, indicates a process for degreasing aluminum and etching in trisodium phosphate followed by '' a mechanical graining step, however this

  process produces a dark surface plate. The United States patent

  United States of America No. 3,891,516 indicates degreasing and cleaning in sodium hydroxide, graining with a pumice porridge and anodizing to voluntarily produce a surface of

hard dark plate.

24 67 70 6

  The invention relates to a method for preparing an aluminum sheet with an extremely white surface which improves the visibility of an exposed and developed photosensitive coating placed on this surface. The invention includes the steps of embossing the aluminum surface, for example with a wire brush or by abrading with a porridge of pumice stone followed by a subsequent attack in trisodium phosphate. Typically, the reverse order gives a plate with a dark surface, while the order of steps according to the invention gives a plate with a substantially white surface. It is important to note that the surface topography

of this aluminum is such that a litho- plate can be produced

  excellent graphics when coated with a photographic composition. Also, the shelf life and the duration of

  press service of such a plate are excellent.

  The subject of the invention is also a new lithographic plate having image clarity, visibility and

improved whiteness of plaque.

  The invention also relates to an improved lithographic printing plate which has a shelf life and a

  excellent press service.

These and other objects will appear on reading

the following description of a preferred embodiment.

  In the first step of the process of the invention, a metallic support sheet, preferably aluminum and its alloys,

  in particular the aluminum compositions suitable for the manufacture

  cation of lithographic printing plates, such as Alcoa 3003 and Alcoa 1100, which may or may not have been pretreated by conventional graining, cleaning, degreasing and / or etching techniques well known in the art, is grained, preferably by brushing, for example with a wire brush or rubbing with a mass

  moist with graining, such as an aqueous pumice porridge.

  This grained leaf is then immersed in an aqueous solution of trisodium phosphate. Preferred parameters of the solution include a trisodium phosphate concentration of up to about 307, although this is not essential. The solution is preferably kept between room temperature and

2467706.

  boiling point, with immersion times up to approximately 5 min. It has been found that, by increasing the immersion time and / or the temperature of the solution, the whiteness of the plate increases. For a given solution temperature and immersion time, a variation in the concentration of the solution does not appreciably modify the whiteness of the plate. According to a preferred embodiment, a

5% solution of trisodium phosphate at 85 C for 45 s.

The following table indicates the optical density of the plates produced first by degreasing an aluminum sheet, graining with an aqueous suspension of pumice stone and immersion

  in a solution of trisodium phosphate under the conditions indicated.

  All measurements are made with a Macbeth surface reflection densitometer, model RD 514. The concentration is in percent by weight of trisodium phosphate in water. The temperature is in degrees centigrade. The duration is in seconds. The optical density is in arbitrary units, the whiteness increasing when the value of

optical density increases.

BOARD

  Concentration Temperature Duration Optical density% 55 C 15 s 0.60 57% 55 C 30 s 0.65% 55 C 45 s 0.66% 70 C 15 s 0.52 5% 70 C 30 s 0.48% 70 C 45 s 0.34% 85 C 15 s 0.38% 85 C 30 s 0.25% 85 C 45 s 0.19 10% 55 C 15 s 0.60% 55 C 30 s 0.65% 7. 55 C 45 s 0.56% 70 C 15 s 0.48% -70 C 30 s 0.45 10% 7. 70 0C 45 s 0.37 Concentration Temperature Duration Optical density% 85 C 15 s 0.36% 85 C 30 s 0.26% 85 C 45 s 0.23 20% 55 C 15 s 0.61% 55 C 30 s 0.67% 55 C 45 s 0.49% 700C 15 s 0.45% 70 0C 30 s 0.45! 0 20% 70 C 45 s 0.35% 85 C 15 s 0.33% 85 C 30 s 0.25% 85 C 45 s 0.21% 55 C 15 s 0.56 30% 55 C 30 s 0.47% 55 C 45 s 0.42% 70 C 15 s 0.48% 70 C 30 s 0 , 34% 70 C 45 s 0.28 30% 85 C 15 s 0.35% 85 0C 30 s 0.25% 85 C 45 s 0.22 The pickled sheet can then be optionally anodized by a well known technique, by example in an aqueous solution of sulfuric acid: chromic or phosphoric having a

  concentration of about 0.5 to 25% by weight of acid in water.

Anodizing takes place preferably in a bath maintained at a temperature of about 15 to 35 C for 1 to about 20 min at a voltage of about 5 to 20 V and at a current density of about 1.07

at 7.5 A / dm2.

  The pickled sheet may optionally be coated by spraying, brushing, immersion or by other means with

  a composition suitable for use as interlayers

  media for lithographic plates. The coating compositions which can be used in the practice of the invention include aqueous solutions of alkali metal silicates, silicic acid,

  Group IV-B metal fluorides, polyacrylic acid, fluo-

  zirconates of alkali metals, such as potassium fluozirconate or fluozirconic acid in concentrations of 0.5 to 20% by volume. A preferred concentration range is 3 to 8%, more

particularly from 4 to 5%.

  The pickled sheet can optionally be anodized and treated with an intermediate layer composition or treated with an intermediate layer composition and then anodized

  with an optional second treatment for intermediate layer.

  It is understood that the above parameters are necessarily interdependent and that various combinations and modifications of these parameters can be used, in the context of the invention. The previously mentioned parameters

  are not intended to limit the scope of the invention.

  The resulting backing sheet can then be coated with a photosensitive composition suitable for lithographic applications. The photosensitive compositions which

  can be used with satisfaction in the practice of information

vention are those which are suitable for lithography and which are reactive to actinic and ultraviolet light. The photosensitive compositions which can be used in the practice of the invention are those which function by giving negative or positive images and include photosensitive agents, such as diazoaromatic compositions, such as those containing diazonium salts or diazides and photosensitive compositions containing products which can be polymerized,

  crosslinked or hardened by exposure to light.

The following examples illustrate the invention without

however limit its scope.

EXAMPLE 1

  We degrease two sheets of Alcoa 3003 aluminum

  lithographic quality in a 5% solution of trisodium phosphate.

  Sheet A, according to the prior art, is then grained with a suspension of pumice stone and anodized in an electrolyte with 18% sulfuric acid for 60 s at 14 A. The optical density is measured at 0.75 by the apparatus described previously. The sheet B according to the invention is again immersed in a bath containing 5% of trisodium phosphate after the step of graining with pumice stone

  for 45 s at 85 C. The optical density is 0.19.

EXAMPLE 2

  Example 1 is repeated, except that the graining is carried out by wear with a wire brush. Similar results are obtained.

EXAMPLE 3

We degrease three Alcoa 3003 aluminum sheets

of lithographic quality in a 5% 7 solution of triso- phosphate

  die and they are subjected to graining with a pumice porridge.

  Plate A according to the invention is again immersed in a bath containing 5% of trisodium phosphate for 45 s at 85 C. Plate B is attacked

  in an attack bath with 25% sodium hydroxide for 5 s at 50 C.

  Plate C is immersed in an aqueous attack bath with 30% phosphoric acid for 40 s at 80 C. Each plate is then anodized in an electrolyte of 18% aqueous sulfuric acid for 60 s at 14 A, subjected a sodium silicate treatment for an intermediate layer and coated with a photosensitive composition comprising

  a paradiazodiphenylamine-paraformal- condensate reaction product

dehyde with 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid. A sample of each sheet is subjected to an accelerated shelf life test. Plate A retains its ability as an acceptable lithographic printing plate for 18 months, while

  plates B and C are only useful for 12 months. Another exchange

  tillon of each plate is exposed to ultraviolet radiation at

through a mask, developed and placed on a printing press.

  Plate A gives 70,000 acceptable reproductions, while plates B and C each produce only 42,000 reproductions

acceptable.

  It is understood that the invention is not limited to the preferred embodiments described above by way of illustration and that those skilled in the art may make modifications to them without

depart from the scope of the invention.

2467706.

REVE N D I CA T I 0 N S

  1. Aluminum foil suitable as lithographic support

phique, characterized in that it is produced by a process comprising the following steps: graining said sheet and then immersing said sheet in an aqueous bath of trisodium phosphate at a concentration of up to 30% by weight for a period of up to '' at 5 min at a temperature between room temperature

and the boiling point.

2. Sheet according to claim 1, characterized in that the first graining step is carried out by wear with

  an aqueous pumice brush or porridge.

  3. Sheet according to claim 2, characterized in that the concentration of the solution is up to 10% by weight, the temperature is 70 C at the boiling point and the duration of immersion

is 30 to 90 s.

4. Sheet according to claim 1, characterized in that

that it was later anodized.

  5. Sheet according to claim 1, characterized in that it has been subsequently treated with an intermediate layer composition chosen from aqueous solutions of alkali metal silicates, silicic acid, Group IV-B metal fluorides, l polyacrylic acid, alkali metal fluozirconates

and fluozirconic acid.

6. Sheet according to claim 5, characterized in that

that it was later anodized.

  7. Sheet according to claim 4, characterized in that it has been subsequently treated with a composition for an intermediate layer chosen from aqueous solutions of alkali metal silicates, silicic acid, Group IV-B metal fluorides, polyacrylic acid, metal fluozirconates

alkaline and fluozirconic acid.

  8. Sheet according to claim 1, 2, 3, 4, 5, 6 or 7 characterized in that it was subsequently coated with a

photosensitive composition.

9. Element produced by the process comprising the following steps: a) degreasing of an aluminum sheet; b) graining the surface of said sheet by wear with a brush or with an aqueous pumice slurry; c) immersion of the sheet in an aqueous bath of

trisodium phosphate in which the concentration of trisodium phosphate

  dique goes up to 30% by weight, the bath temperature is between room temperature and the boiling point for a period of up to 5 min; d) anodizing said sheet; e) treating said sheet with a composition for an intermediate layer chosen from aqueous solutions of alkali metal silicates, silicic acid, Group IV-B metal fluorides, polyacrylic acid, alkali metal fluozirconates and fluozirconic acid; and f) coating at least one face of said sheet.

with a photosensitive composition.

  10. Element according to claim 9, characterized in that said graining step b) is carried out with an aqueous pumice boil; said step c) is carried out with a bath concentration of up to 10% at a bath temperature of 70 C at the boiling point for 30-90 s; and said anodizing step d) is

  performed with sulfuric acid or phosphoric acid.

11. Element according to claim 10, characterized in that said photosensitive composition comprises the product of the reaction of the condensation product of paradiazodiphenylamine

  with paraformaldehyde with 2-hydroxy-4-methoxybenzophenone acid-

-sulfonic.