US3516829A - Photographic activator solution - Google Patents

Description

United States Patent 3,516,829 PHOTOGRAPHIC ACTIVATOR SOLUTION Robert George Clarke, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Mar. 16, 1966, Ser. No. 534,648

Int. Cl. G03c 5/26 US. C]. 96-50 3 Claims ABSTRACT OF THE DISCLOSURE This invention concerns activators for use with unhardened photographic emulsions to obtain copies by the colloid transfer process.

In the colloid transfer process, an image in soft adhesive organic colloid is formed photographically and a discrete stratum of the image is transferred to a receiving sheet to provide a reproduction of the subject. This process is described in Yutzy et al., US. Pats 2,596,756, issued May 3, 1952, and 2,716,059, issued Aug. 26, 1955, and embodies the exposure to a subject of a substantially unhardened gelatino-silver halide emulsion layer, which may contain a gelatin tanning silver halide developing agent as well as a nontanning silver halide developing agent.

Upon activation of the exposed gelatino-silver halide emulsion with an alkaline solution in the presence of the developing agent or agents, tanning development of the most exposed regions of the emulsion corresponding to the highlights of the subject proceeds, although some development of the less exposed regions also takes place to provide visual density for the transferred image as explained in U.S. Pat. 2,716,059 above. Thereafter, the developed emulsion is pressed into contact with an absorbent receiving sheet to cause the less exposed regions and less developed regions, of the emulsion to adhere to the receiving sheet. Subsequently, when the emulsion and receiving sheet are separated, a stratum of the less exposed regions of the emulsion remains on the sheet and appears as a positive silver image of the original subject.

In the preparation of lithographic printing plates, an unhardened emulsion of the type described above can be used to provide an image on a support which can then be used for offset printing purposes. Typical processes of this type are described in detail in Clark et al., US. Pat. 2,763,553, issued Sept. 18, 1956, and Lake et al., US. Pat. 2,794,388, issued June 4, 1957.

In carrying out the colloid transfer process, the exposed unhardened emulsion is immersed in an alkaline activator solution which causes development of the most exposed regions and tanning in these areas. The mechanism of the colloid transfer depends upon the unhardened areas of the emulsion transferring to the receiver sheet when the emulsion is pressed in contact therewith. However, the transferred image areas are of unhardened gelatin and relatively soft in nature so that in some instances too much unhardened gelatin is transferred to the support for satisfactory use. With some activators, image bleeding also occurs. Accordingly, it has been desirable to find an activator solution which would provide satisfactory activation of the emulsion so that a regulated amount of the unhardened areas of the unexposed emulsion would be made to adhere to a Patented June 23, 1970 receiving sheet, and image bleeding and background transfer are reduced.

Moreover, the alkaline activator solutions which are commonly used have a temperature latitude of 8183 F. to obtain satisfactory lithographic plates or copies. Athigher temperatures, image bleeding may increase. At temperatures, image bleeding may increase. This means that a controlled environment is desirable in order to obtain the optimum results.

Accordingly, it has been desirable to find an activator which would be useful for colloid transfer emulsions which would provide a transferred image suitable for lithographic use having good definition, smoothness with proper contrast, good inking rate, satisfactory offset quality and long press life without emulsion picking. Moreover, the activator should have greater temperature latitude, preferably operating ranges as high as 93-96 F.

We have found an activator and a method of improving conventional activators which provide improved lithographic plates from colloid transfer materials as well as improving the operating temperature range of activators for use in making lithographic plates.

One subject of this invention is to provide an alkaline activator solution which will provide satisfactory lithographic plates from colloid transfer emulsions. Another object is to provide an activator for colloid transfer systems having an operating working temperature up to about 96 F. and as low as 65 F. A further object is to provide an improved lithographic plate from a colloid transfer process having uniform photographic characteristics. An additional object is to provide a method of processing colloid transfer materials which results in an image having a good inking rate and good oifset quality.

A still further object is to provide a method of regulating the amount of unhardened gelatin transferred in the colloid transfer process to improve resistance to copy bleeding and transfer of background.

The above objects are obtained by employing a conventional activator solution to which has been added an amphoteric metal salt. There may also be added formaldehyde or a formaldehyde donor. When this activator solution is used for development of a colloid transfer emulsion in the presence of a tanning silver halide developer, the addition of a hydrolysis product of the formaldehyde donor may also be desirable.

In one embodiment of my invention, the aluminum is used as the amphoteric metal. The range of concentration of alumniate ion with respect to formaldehyde donor (e. g., 3-fi-hydroxyethyl oxazolidene) varies. When using 1 g./l. (0.1%) oxazolidene and 2 g./l. (0.2%) 2,2'-iminodiethanol, the range of salt supplying the aluminate ion is from 50 mg. (0.005%) per liter to 3 g./l. (0.3%); when using 5 gm. (0.5%) per liter of formaldehyde donor, (e.g., oxazolidene) and 10 g./l. (1%) of 2,2-iminodiethanol, the range may be from a low of 25 mg. (0.0025%) per liter to a high of 1 gm. (0.1%) per liter.

Any form of aluminum can be used to form the aluminate ion needed. Aluminum metal can be dissolved in a strong base such as sodium or potassium hydroxide. Water soluble salts of aluminum such as aluminum sulfate, aluminum nitrate, and aluminum chloride can be used as long as the final product in which they are used is maintained at a pH above the point where the precipitation of insoluble aluminum hydroxide occurs. Aluminum hydroxide, alumina (hydrated or dehydrated aluminum oxide), alum or other double salts of aluminum such as sodium aluminum sulfate can all be used.

The aluminate ion has been used herein to illustrate my invention but it will be understood that the other amphoteric metals can be added to activator solutions ICC amount of -40 grams per liter. Sodium salicylate may be incorporated in an amount of 012.5 grams per liter. It is also useful to use a sequestering agent such as a sodium salt of ethylenediamine tetraacetic acid in an amount of about 0-5 grams per liter. This is especially helpful where hard waters are used.

A particularly useful amount of the amphoteric metal salt may be 50 mg. to 3 g./l. of the activator solution. Salts of various amphoteric metals may be used including, for example, those supplying ions of aluminate, zincate, plumbate, chromate, molybdate, stannate, etc. The activator solution must be alkaline and is particularly useful at a pH of or above.

Activators containing formaldehyde in trace quantities of about 30-250 mg./liter of the free formaldehyde are also useful, the use of a formaldehyde donor rather than formaldehyde itself provides an activator solution in which the amount of free formaldehyde can be maintained at the desired level.

It is also advantageous to incorporate in the activator, gelatin softeners, such as, for example, potassium isophthalate, potassium para toluene sulfonate, sodium benzoate, potassium nitrate, cinnamic acid, sodium salicylate, etc.

Inorganic bases, such as the carbonates, can be used as well as phosphates and the like in an amount of 0-40% by weight. Additional variations can be made by substituting alkali salts such as sodium or potassium carbonate, trisodium phosphate, sodium or potassium hydroxide, etc. If desired, the activators can be made up as concentrates. A useful two-package concentrate comprises one package containing the salt of the amphoteric metal in an amount of 0.01% to 1.5% by weight, hydrolysis product of the formaldehyde donor, sodium bicarbonate, sodium salicylate, ethylenediamine tetraacetic acid and (if desired) a small amount of water. This can be mixed with the second packages contents comprising 0.40% to 0.20% by weight of the formaldehyde donor. As an alternative, all of the components may be included in the same package or same mixture and sold as a concentrate.

Since a concentrated activator may contain little or no water, the relationship between the components will be on a different basis. For instance, the salt of the amphoteric metal would usefully constitute 0.01% to 1.5%. In the event that the formaldehyde donor is also used, it may be present in an amount of about 0.4% to 2.0%. Other components may also be used, including those which are conveniently used in activator solutions. For instance, an alkali metal hydroxide such as sodium hydroxide could be present in an amount of about 60% and acids could be added to provide other desirable ions. Typical acids include phosphoric acid and cinnamic acid. It is also useful to incorporate a sequestering agent, such as ethylenediamine tetraacetic acid. The packaging of the concentrate will depend somewhat on the amount of water present. For some purposes, the concentrate could be in paste or powder form whereas for other purposes, it might be in a concentrated solution. In any event, it could be prepared with all the components in one package or one or more of the components could be packaged separately for ease in shipment, stability, or the like.

It will be appreciated that while these activator solutions containing a salt of an amphoteric metal are useful in providing improved lithographic printing plates, the activator can also be used for making copies according to the colloid transfer process in the customary manner. These activators have a relatively long tank life of 4 to 6 months and can be replenished merely by adding more of the same activator.

It will be understood that a large number of formaldehyde donors may be used in the activator to provide the desired level of free formaldehyde. Among those which may be used are, for example:

( 1 2- (hydroxymethyl)-2-nitro-l,3-propanediol (2) 2-methyl-2-nitro- 1 3-propanediol (3 2-ethyl-2-nitro-l-propanediol (4) Z-methyl-Z-nitro-l-propanol (5) sodium formaldehyde bisulfite (6) 3 -/8-hydroxyethyloxazolidine (7) 3-phenyloxazolidine (8) oxazolidine (9) 3-methyloxazolidine l0) methylenebisoxazolidine 11) 3-ethyloxazolidine The instances where it is desirable to increase the total quantity of formaldehyde donor without increasing the level of formaldehyde in the activator, can be accomplished by including in the activator a reaction product of the formaldehyde yielding compounds. These materials act by mass action to suppress the formation of formaldehyde from the parent compounds. Thus, iminodiethanol added to an activator containing 3-B-hydroxyethyl oxazolidine serves to increase the tolerance of the activator for this formaldehyde donor. An activator containing 20 g./ 1. of iminodiethanol will tolerate 10 g./l. of axazolidine while the same activator without iminodiethanol will fail to work at 2 g./l. level of 3-,B-hydroxyethyl axozolidine.

Other variations can be made in the activator to achieve desired effects. By decreasing phosphate level and/or increasing the salicylate level, relatively more of the formaldehyde donors can be tolerated.

It will be appreciated that although a particularly useful method of using my invention involves incorporation of trace amounts of formaldehyde in the activator, in certain instances, the formaldehyde donor may be in corporated in the colloid process silver halide emulsion as well as the donor hydrolysis product. A very small amount of formaldehyde donor and donor hydrolysis product incorporated in the substantially unhardened silver halide emulsion unexpectedly improves the number of copies obtained in certain instances employing document copy methods.

The following examples are intended to illustrate our invention but not to limit it in any way.

EXAMPLE 1 An activator for the colloid transfer process was prepared by mixing the following components:

Components: Grams per liter Z-diethyqlaminoethanol 40 NaHCO 7.5 Ethylenediarnine tetraacetic acid (disodium salt) Z-hydroxymethyl-Z-nitro-1,3-propanediol 0.33 Sodium salicylate 5.0 Sodium aluminate 0.5

1 Sufiicient water was added to bring the volume to one iter.

The activator as prepared above was used in a colloid transfer process of the type described in Yutzy et al., U.S. Pat. 2,596,756. When the exposed silver halide emulsion containing a tanning developer and a nontanning developer was immersed for 6 seconds and while still wet, pressed in contact with a receiving sheet, a good quality print was obtained by transfer of the unexposed areas. The temperature of the activator was 83 F. The transferred 5 image was then immersed in an image conditioner to improve the wetting properties of the paper base and the inking properties of the image.

The image conditioner had the following composition:

Components: Grams per liter Condensate of .4 mole of 2-furaldehyde with 1 mole of resorcinol 100 Tannic acid 12.5 1,3-diethyl-2-thiourea 5 Glycerol 50 Ethanol 95% 5'0 Glacial acetic acid 5 Water 277.5

The printing plate was a good photographic reproduction and when used directly in a lithographic printing press was found to be satisfactory for offset use. The image readily accepted greasy printing ink and had good reproducing characteristics. A thousand copies were prepared, indicating good press life.

EXAMPLE 2 An activator solution containing the following components:

Components: Grams per liter K CO 40 Ethylenediamine tetraacetic acid (disodium salt) 5 p-Toluenesulfonic acid (sodium salt) 60 K 80 20 Iminodiethanol 2.5 2-hydroxymethyl-2-nitro-1,3-propanediol 1.0 Potassium aluminate 3.0

was prepared with suflicient water added to make 1 liter of solution and used as in Example 1. Good results were obtained. It was also used to make copies by the colloid transfer process with good results.

EXAMPLE 3 Activator solutions were prepared with suflicient water to make one liter of solution having the following compositions:

Components A B C 2-diethylaminoethanol (g./l.) 60 40 40 Sodium salieylate 5. 5. 0 2-(hydroxymethyl)-2-nitro-1, 3-p1'opanedial 1. 0 25 0.33 Sodium bicarbonate 40 7. 5 Ethylenediamine tetra-acetic acid (disodium salt) 1.0 1.0 1.0 Sodium aluminate 3. 0 1. 0 005 These activators, used to activate silver halide emulsions of the type described in U.S. Pat. 2,763,553 and 2,794,388 containing a tanning developer, were found to have good offset printing characteristics at temperatures from 80-96 F.

EXAMPLE 4 Concentrated activators are prepared having the following compositions:

These concentrated activators are mixed with sufficient water to provide a liquid activator and used as in Example 2. Good copies are obtained.

A typical activator when the concentrate is mixed with water has the following composition:

G./l. Potassium phosphate (tribasic) 67.5 Potassium cinnamate 60 Sequestrene (tetrasodium salt) 1 2,2-iminodiethanol 5 3-,8-hydroxyethyloxozolidine 2 Potassium aluminate 0.2

Water to make 1 liter.

EXAMPLE 5 An activator having wide temperature latitude was prepared as follows:

110 grams K CO grams cinnamic acid 63 grams of 45% KOH 0.005 g. potassium aluminate 4 gm. ethylenediamine tetra acetic acid tetrasodium salt 4 gm. 3- 3-hydroxyethyloxazolidine Water to 2 liters.

This activator when used as in Example 3 was found to provide satisfactory copies at temperatures from 81-96 F.

It will be appreciated that the tanning developers and/ or nontanning developers may also be incorporated in the developer or activator solution as well as in the emulsion providing the unhardened silver halide emulsion is developed in the presence of at least one tanning silver halide developer.

By an unhardened silver halide emulsion is intended one that is not harder than a gelatin layer containing 0.7 gram of formaldehyde per pound of gelatin freshly coated.

The silver halide sensitized sheet may be exposed by projection or contact printing methods under a two-tone subject such as a line or half-tone transparency or printed matter. If desired, reflex exposure methods may be used for making the exposure. The support, to which the unhardened stratum is transferred, is preferably a paper stock which has thereon a gelatin overcoat. However, other surfaces may be used to receive the transferred image, including metal plates, polymeric plates and the like. Additional useful printing plates are described in US Pats. 2,763,553 and 2,794,388.

While development in the above activator solutions is proceeding, light should be excluded to the extent required by the particular silver halide present in the emulsion. With daylight working emulsions, limited exposure to roomlights may be given during the exposure and development steps. Other emulsions may require the use of the usual safelights during the exposure and processing steps. When the proper amount of exposure has been given, gelatin tanning silver halide development occurs principally in the more highly exposed areas of the emulsion and little or no tanning development in the other areas.

When the development is complete as determined by trial with the particular emulsion in conditions of operations and use, the sensitive element is pressed into contact with the receiving material such as paper "by means of a squeegee blade or rollers. Immediately thereafter, the sensitive element and receiving support are separated, leaving a stratum of the less exposed and thus less hardened regions of the emulsions adhering to the receiving sheet.

In a preferred embodiment of the invention, the developing agent or agents are present in the emulsion. However, the developing agent or agents may be present in the alkaline activator solution or both in the emulsion. A very useful combination of developing agents is 4-phenylcatechol with 4-methoxy-alpha-naphthol. Since the latter is self-coupling, it forms a colored compound 7 during developing which contributes density to the print. Other useful tanning and nontanning silver halide developing agents are disclosed in the above patents.

A useful image conditioner which can be used for treating the transferred image on the printing plate comprises a mixture of a condensate of .2 to .6 mole of Z-furaldehyde with 1 mole of resorcinol, tannic acid, 1,3-diethyl- 2-thiourea, glycerol, ethyl alcohol, glacial acetic acid, and water. At least 10 percent of the concentrate is used. Other useful proportionate ranges are as follows:

Grams per 500 grams Component: of final solution Condensate 10-200 Tannic acid n 2.512.5 1,3-diethyl-2-thiourea 5-25 Glycerol 10-100 Ethyl alcohol 95% 10-100 Glacial acetic acid 1-10 Water to make 500 grams of final solution.

The image conditioner may be applied by any convenient method such as swabbing the image, immersing in a conditioner bath or the like. The 2-furaldehyde and resorcinol condensate can be prepared by dissolving the resorcinol in warm water, cooling to room temperature and adding the 2-furaldehyde. A small amount of sodium hydroxide is added and the reaction permitted to continue until the condensate is formed. The remaining components of the image conditioner can then be added to the reaction solution without separating the condensate.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. An aqueous alkaline activator solution for use in developing a substantially unhardened gelatino-silver halide emulsion in the presence of a tanning developer, said solution containing:

(a) water;

(-b) ions selected from the class consisting of aluminate, zincate, plumbate, chromate, molybdate, and stannate ions, at a concentration equivalent to that which would be provided by about 3 g. to about 50 mg. of sodium aluminate per liter of solution;

() at least some gelatin softener comprising moieties selected from the group consisting of isophthalate, p-toluenesulfonate, 'benzoate, cinnamate, and salicylate;

(d) sufficient alkali to maintain solution; and

(e) formaldehyde at a concentration of about 30 mg.

to about 250 mg. per liter.

2. The invention according to claim 1 and wherein 20 aluminate is the selected ion.

3. The invention according to claim 1 and wherein the aluminate is provided as an alkali metal aluminate.

References Cited UNITED STATES PATENTS 2,199,904 5/19'40 Alburger 9*6-66.3 3,189,449 6/1965 Yost 96--28 NORMAN G. TORCHIN, Primary Examiner M. F. KELLEY, Assistant Examiner US. Cl. X.R.