US3320171A - Powderless etching bath and method for etching curved segments - Google Patents

Description

United States Patent Delaware No Drawing. Filed Aug. 27, 1964, Ser. No. 392,589

Claims. (Cl. 252-794) This invention relates to etching metal. More particularly it relates to a new and novel bath composition and method concerning the powderless etching of curved magnesium base metal work pieces such as curved etchable photoengraving plates and the like.

The art of etching flat plates or work pieces by powderless etching processes has been developed so as to be acceptable to most users. In general, most of the conventional powderless etching bath compositions comprise a mineral acid; a filming agent; and a water-immiscible organic fluid. U.S. Patent 3,023,138 is illustrative of such a bath, employing particular filming agents, specifically usable for fiat plate etching and comprises: nitric acid with the optional inclusion therewith of small amounts of sulfuric acid, hydrochloric acid, acetic acid and the like; an organic water-immiscible solvent stable in the presene of dilute acids, and a substituted halogenated diaryloxide sulfonate wherein the substituents on halogenated diaryloxide sulfonates are hydrophobic groups containing up to 30 carbon atoms; the balance being essentially water including, for example, various by-products generated from the bath components.

In addition, so-called film controlling agents have been added to the above bath formulations in an attempt to improve their performance. One such group of film controlling agents comprises, for example, a single organic dicarboxylic acid or a blend of such compounds which individually consist of only hydrogen, carbon, and oxygen and have from 4 to 10 carbon atoms with up to 3 carbon to carbon double bonds, the latter referring to aromatic unsaturation as well as that which may occur in aliphatic chains. Such additaments may be aromatic, cycloaliphatic or aliphatic in character or a combination thereof such as alkylaromatics. By their use in the above described etching baths, it is possible to increase the depths of etch obtainable in small areas of penetration in combination of photoengraving plates, such as halftone areas where proper or adequate depths of etch are usually difiicult to obtain by bath modulation without, at the same time, adversely weakening the protection achieved in open line areas of the same plate. In addition, the film-controlling agents have a beneficial stabilizing effect on the protective film in open line areas of the plate thereby minimizing lateral etching and chipped or rough image sidewalls.

Notwithstanding the aforesaid improved bath compositions, however, when they are applied to etching curved plates, particularly those exceeding about 5 inches in diameter, severe non-uniform image shoulders commonly result causing in many cases loss of the image due, for example, to chipping along the edges. In addition, excessively wide or elongated image shoulders or tails (this affect being termed herein as tailing) are usually encountered in the direction of curvature. Conversely, the transverse shoulders are frequently exteremely tight, i.e., essentially vertical, and in severe cases undercutting of the image itself may occur. Furthermore, engraved curved plates which are dirty, i.e., having pimple-like projections in the non-image areas, are common. This requires an additional step in the overall operation, which may be aggravated if the number of such pimples ice is excessive, of removing them to obtain a clear plate. These undesirable results, either in combination or alone, cause poor quality in the reproduced image, and when severe, frequently results ultimately in the entire plate being scrapped.

Though various etching machines have been developed in an attempt to improve etching of curved segments, an example of such a machine being described in U.S. Patent 3,122,150, these machines do not significantly nor routinely avoid the heretofore mentioned problems, nor has any satisfactory bath composition yet been devised for use with these machines for specifically etching curved plates which consistently avoids these diificulties.

Accordingly, a bath composition specifically designed for etching curved work pieces which essentially avoids the foregoing difficulties is needed in the art.

An object of the present invention, therefore, is to provide a new and novel etching bath composition and method specifically for powderless etching of magnesium and magnesium base alloy curved segments, which significantly minimizes the disadvantages herein before mentioned with respect to etching such work pieces.

Another object of the invention is to provide a novel bath solution primarily for etching curved magnesium and magnesium base alloy photoengraving plates of large diameter which substantially avoids chipping, tailing of the image shoulder and dirty, pimply plates, and which improves the uniformity, quality and cleanliness of the plate and relief images in general.

Still another object is to provide a novel method of powderless etching curved work pieces.

It has now been found that by substituting a particular three component organic solvent system for the waterirnmiscible organic fluids used in the here-inbefore described flat plate baths, a new and novel bath formulation is obtained in accordance with the present invention which when used to etch curved segments substantially avoids the aforesaid difficulties of tailing, bleed off, chipping and undercutting of the image. Moreover, a clean photo engraved plate is obtained wherein the number of pimplelike projections in the non image areas have been markedly reduced, if not substantially eliminated.

This three component organic solvent system comprises three groups of organic liquids, each group being identified by a certain range of Kauri Butanol values (termed herein as KB values). The first group is called the low KB solvent having a KB range of from about 25 to about 75, the second group being called the intermediate KB solvent having a KB range of fro-m about to about 100, and the third group called the high KB solvent having a KB value in excess of 100. The term KB value as used herein refers to a known and used standard test for determining the solvent power value of a given organic liquid as the amount of a solvent which can be added to a standard kauri gum solution in butanol to produce a definite turbidity, as compared with the amount of pure benzene used as a standard in a similar titration and arbitrarily taken as percent standard.

Required properties of the low KB solvent are that it have a KB value within the range of from about 25 to about 75, be substantially stable in the presence of dilute nitric acid at bath temperatures, have some solvency for the filming agent employed and that it be substantially water-immiscible. Substantially stable is defined as the non-occurrence of deterioration, within a reasonable time period, in contact with dilute nitric acid which deterioration significantly alters the function of the organic waterimmiscible component within the bath in an unfavorable manner. Also, it is essential that this additive be a liquid at bath temperatures. Suitable organic materials which can be used individually, or in combination with other such solvents within the total amount of such solvent as specified below, are aromatics, aliphatics, napht'henes, ethers, and esters having a KB value Within the range of from 25 to 75. Such low KB solvents include, for example, dodecylbenzenes, (an alkylbenzene, wherein the average of the alkyl chains contains 12 carbon atoms), mineral seal oils, other alkylbenzenes, napthenes with alkyl carbon atoms with the inclusive range of from about 8 to 10, and the like. Generally, it may be said that water-immiscible esters, ketones, terpenes, ethers, aliphatic, naphthenic, and aromatic hydrocarbons which have a KB in the range of 25 to 75 are operable.

The total amount of the low KB solvent employed may range from about 0.5 to about 2 volume percent of the bath and preferably from about 0.75 to about 1.25 volume percent. A particularly desirable amount to use has been found to be about 1.0 percent.

The intermediate KB solvent constituent is present in the present novel bath formulation for the purpose and function, among other things, of aiding in the control of the transverse shoulder width, in general, and more specifically to avoid tightening and under-cutting of the shoulder in the transverse direction of the curve of the plate. This organic liquid is a solvent having with respect to the other organic solvents in the bath as intermediate KB value, for example, from 75 to 100. Examples of such organic liquids suitable for use in the present invention are: Solvesso 150 (a trade name for a mixture of approximately 90 percent alkylbenzenes, 2 percent napthalene and 8 percent napthenes); diethylbenzenes, such as, for example, Penola H.A.N. (a trade name for an aromatic solvent containing 84 percent of such aromatics having a flash point of 140 F. and initial boiling point of about 340 F.) and other aromatic and alkyl-aromatic hydrocarbons having a KB value within the above range of 75 to 100. The amount of such organic liquid to be used individually or in mixture thereof will be within the range of from about 0.8 to about 2.8 percent by volume of the composite bath. Preferably, the amount Will be within the range of from about 1.0 to about 1.8 volume percent, said Solvesso 150 being preferred as the organic liquid to be used.

The high KB, low viscosity, solvents are characterized by their immiscibility with water and a relatively high KB value, preferably within the range, for example, of from about 100 to about 130, but also including those having a KB value in excess of 130, such as, for example, hexylacetate which has a KB value of about 203. In addition they are substantially unreactive with the mineral acid component (dilute as used in the bath) and contain no terminal functional groups but rather a preponderance of carbon and hydrogen atoms. These solvents may be used separately or in mixture within the total amount of said high KB solvent to be used, as specified below and have the primary function in the present bath of aiding in clean liness of etch, i.e., avoidance of pimples on the etched plate without causing tailing on the image shoulders of half-tone dots, or bleed off as it is called herein since it concerns more particularly the shoulders of half-tone highlight dot type images. The total amount of this high KB solvent to be used in the bath ranges from about 0.25 to about 1.5 volume percent and preferably from about 0.4 to about 0.6 volume percent. A particularly suitable amount has been found to be about 0.5 volume percent. Examples of such high KB solvents include hexyl acetate, dibutyl phthalate, trichloroethylene and the like. A very desirable high KB solvent preferred for use herein is a group of high boiling aromatic naphtha solvents known under the trade name of Panasol AN petroleum solvents, having high flash points (190230 F.), particularly those designated as AN-l made and identified as such by the Amoco Chemicals Corporation which are a group of relatively non-toxic, low volatile, aromatic napthas of wide boiling range, having a KB value of about 108 and containing typically 99 percent of said high boiling aromatics.

In practicing the invention the novel three component, water-immiscible, organic solvent is admixed with the dilute nitric acid, a filming agent and a film controlling agent, all as previously described, the balance being essentially water, to form an etching bath. This novel bath is then impinged upon the surface to be etched, such impingement being accomplished as by spraying, splashing, bubbling agitated immersion, or the like. Etching is continued until the desired depth, which may be, for example, from about 25 to about 40 thousandths of an inch in large, open, non-image areas, is achieved.

The average bath temperature may be within a range from 40 to 120 F. but a preferred range is from to 90 F., and more preferably from to 85 F.

In formulating the etching bath, it is a general rule that as the concentration of the nitric acid is increased within the aforementioned limits, it is usually desirable to also increase the proportion of filming agent employed. Also, as will be manifest to those skilled in the art, it may become desirable during the use of the bath to replenish the acid that has been used up and possibly to add other agents such as bath extenders for special purposes.

The metals which may be etched by the process of this invention include primary magnesium, and magnesium base alloys, which are substantially homogeneous and suitable for photoengraving. A magnesium base alloy is defined as having percent of the base component. The bath while selectively forming an acid-resistant film on the plate to protect the resist .and relief side walls or shoulders from lateral etching, substantially avoids formation of excessively elongated shoulders as heretofore discussed, thus producing a quality etched curved photoengraving plate to a degree heretofore unobtainable.

A preferred bath composition of the present invention for use particularly in an etching machine adapted to etching curved plates comprises from about 88 to about 107 grams per liter of nitric acid; from about 1.0 to about 1.8 volume percent of Solvesso .150 (defined hereinbefore) as the intermediate KB solvent; from about 3.2 to about 3.6 grams per liter of bath volume percent of a filming agent comprising a mixture primarily of the sodium salts of mono and disulfonated monochlorododecyl, mostly C12, diphenyloxide with a preponderance of monosulfonated oxide (termed herein as diphenyloxide mixture); from about 1.2 grams per liter of bath to about 1.8 grams per liter of bath of adipic acid as a film controlling agent; from about 0.75 to about 1.25 percent by volume of the low KB solvent dodecylbenzene; and from about 0.4 to about 0.6 percent by volume of Panasol AN-l as the high KB solvent.

Though from 88 to 107 grams per liter of nitric acid is preferred in the bath composition as stated above, it is to be understood that from about 78 to about 116 grams per liter of bath of said acid may also operably be employed. Similarly, it is to be understood that from about 2.5 to about 4.0 grams per liter of bath of the filrn'ng agent may also be operably employed. A particularly desirable group of filming agents to use comprise a mixture of primarily the sodium salts of mono and disulfonated monochlorododecyl, mostly 1-2 carbons, diphenyloxide with a preponderance of monosulfonated oxide, both the pure compounds and mixtures thereby being termed herein as diphenyloxide filming agents. Operable amounts of the film controlling agents which may be 7 used include from about 0. 3 to about 2.5 grams per liter of bath of said agent. The film controlling agents may be, for example, single organic dicarboxylic acid or a blend of such compounds which individually consist of only hydrogen, carbon and oxygen and have 4 to 10 carbon atoms with up to 3 carbon to carbon double bonds, the latter referring to aromatic unsaturation as well as that which may occur in aliphatic chains. Such additaments may be aromatic, cycloaliphatic or aliphatic in character or a combination thereof such as alkylaromatic. Adipic acid is a preferred film controlling agent.

The following examples further illustrate the present invention but are not intended to limit thereof:

Example I A powderles-s etching bath of 77 liters was prepared for use in etching curved photoengraving plates in a M-32 master etching machine by admixing; 9.93 grams per liter of HNO 0.335 grams per liter of bath of the aforesaid diphenyloxide mixture (both defined hereinbefore); 1.34 percent by volume of Solvesso 150; 1 percent by volume of dodecylbenzene; and 0.5 volume percent of Panasol AN-l, and 1.5 grams per liter .of adipic acid. The balance of the bath was made up with water. The bath temperature was then adjusted .to 80 F. A 11 inch diameter by 18 inch long curved segment 0.064 inch thick of an etchable magnesium base alloy phot-oengraving plate exhibiting a polyvinyl alcohol type etch resist coating as the image pattern and bare metal in the non-image areas (the areas to be etched) was then placed in position for etching in the machine by clamping it onto a mandrel. The machine was then operated whereupon, the paddles were turned and the prepared bath compositions splashed on the segment as it turned. The mandrel speed was about 40 rpm, and the direction of rotation was reversed each 20 seconds. Etching was continued for about minutes to a depth of about .030 inch. The depth of the etch in the high-light dot areas of the 65 line screen halt-tone areas was about 0.005 inch.

An examination of the etched segment showed an absence of excessive tailing and bleed off. All the image shoulders were observed to be significantly more uniform, and chip free, and at an overall angle of approximately 45 to the horizontal. This plate was suitable for direct printing purposes.

Example [I To illustrate the present invention on a comparative basis, an 8 inch diameter curved segment was etched in a powderless etching bath in the same machine and under the same conditions as used in Example I, except that a lower bath temperature of about 70-71 F. was employed, and the etching time was increased to give the same open area depth of about 0.030 of an inch. This standard bath contained 94 grams per liter of HNO 3.3 grams per liter of a diphenyloxide filming agent, 1.5 grams per liter of adipic acid, and 45 volume percent of Solvesso 150. Subsequently, an examination of the plate segment showed severe tailing and bleed oif (bleed off being a form of tailing as related to half-tone highlight dots) of the image shoulders in the direction of the curvature. The transverse shoulders, that is, those at 90 angles to the shoulders in the direction of curvature, were extremely tight, that is, essentially vertical, and in some cases undercutting of the image itself was evident. In order to determine more objectively the severity of the tailing of the image shoulders, the distance from the top edge of the image shoulder to where the shoulder meets the relief surface was measured and the figure so obtained divided by the depth of the total etch on the plate, to give a quotient which was the tangent of the shoulder angle. By reference to trigonometry tables the shoulder angle Was then determined. The procedure was then repeated but with respect to the transverse shoulder. The angle obtained from this latter transverse shoulder measurement was'then subtracted from the former to obtain an angle of difference which indicates generally the quality of the overall shoulder profile. In so doing an angle of difference of about 59 was obtained indicating that the image shoulder was excessively elongated in the direction of curvature. In addition several pimples in the nonimage areas were present.

The foregoing etching and examination procedure was repeated using the same curved plate size, equipment, and etching conditions except that in this case the new and novel bath composition of the present invention for etching curved plates was employed at a bath temperature of about F. The angle of difference obtained was 34, indicating that significantly more uniform image shoulders were produced, thus a markedly higher quality plate was made. Moreover, the plate was generally cleaner and exhibited no pimples in the non-image areas, thus was suitable for direct printing purposes.

Combinations of bath additives with the present invention other than those hereinbefore specified may also be used to constitute other novel bath composition formulations within the present invention with the same good results in etching curved plates, with respect to significantly reducing tailing and bleed-01f aflects. Examples of such other combination include:

(a) The same composition as in Example I except that 2 percent Solvesso 150 and 2 percent dodecylbenzene was used including 0.5 percent of Panasol AN-2 instead of AN-l.

(b) The same composition as in Example I except that 1 percent Solvesso 150 was used and also a mixture of 1 percent diisodecylphthalate and 0.5 percent Panasol AN-l as the high KB solvent.

(0) The same composition as in Example I except that /2 percent of Solvesso 150 was used and also a mixture of A percent diisodecylphthalate and 1 percent Panasol AN-l as the high KB solvent.

It is manifest that various modifications can be made in the process of the present invention without departing from the spirit or scope thereof and it is understood that I limit myself only as defined by the appended claims.

What is claimed is:

1. In an etching bath composition comprising substantially nitric acid, a sulfonated dodecyl diphenyl oxide filming agent, a film controlling agent and an organic water-immiscible fluid substantially stable in the presence of dilute nitric acid, the balance being essentially water; the improvement consisting essentially of employing a three-component organic solvent system as the waterimmisci-ble fluid, said system comprising as a first component from about 0.5 to about 2.0 volume percent of the bath of at least one organic liquid having a kauributanol value within the range of from about 25 to about 75, as a second component from about 0.8 to about 2.8 volume percent of the bath of an organic liquid having a kauri-butanol value within the range of from about 75 to about 100, and as a third component from about 0.25 to about 1.5 volume percent of the bath of an organic liquid having a kauri-butanol value in excess of 100.

2. The improved bath of claim 1 wherein the third component organic liquid has a kauri-butanol value within the range of from about 100 to about 130.

3. The improved bath of claim 1 wherein the first component organic liquid is an alkyl benzene.

4. The improved bath of claim 3 wherein the alkyl benzene is dodecylbenzene.

5. The improved bath of claim 1 wherein the second component organic liquid is a mixture of approximately percent alkylbenzenes with about 2 percent of naphthalene and 8 percent naphthenes.

6. The improved bath of claim 1 wherein the third component organic liquid is a high boiling, substantially non toxic, aromatic naphtha solvent having a high flash point.

7. The improved bath of claim 6 wherein, the aromatic, high boiling, naphtha has a kauri-butanol value of about 108.

8. The improved bath of claim 1 wherein the mineral acid is nitric acid.

9. An aqueous bath composition for etching etchable curved photoengraving plates consisting essentially of from about 88 to about 107 grams per liter of nitric acid; from about 3.0 to about 3.6 grams per liter of bath of a sodium salts of mono and disulfonated monochlorododecyl diphenyl oxide filming agent; from about 0.75 to about 1.25 volume percent of the bath of dodecyl benzene; from about 1.0 to about 1.8 volume percent of the bath of a mixture of approximately 90 percent alkyl benzenes, 2 percent naphthalene and 8 percent naphthenes; from about 0.4 to about 0.6 volume percent of the bath of a high boiling aromatic naphtha solvent having a kauri-butanol value of about 108; from about 1.2 to about 1.8 grams per liter of bath of adipic acid as a film controlling agent; the balance being essentially water.

10. A method of etching etchable curved photoengraving plates of magnesium base metal having an acid resistant image on the surfaces thereof to be etched comprising; (a) establishing an aqueous powderless etching bath composition comprising from about 88 to about 107 grams per liter of nitric acid, from about 2.5 to about 4.0 grams per liter of bath of a sodium salts of mono and disulfonated monochlorododecyl diphenyl oxide filming agent; from about 0.5 to about 2 volume percent of the bath of at least one organic liquid having a kauri-butanol value within the range of from about 25 to about 75; from about 0.8 to about 2.8 volume percent of the bath of at least one organic solvent having a kauri-butanol value within the range of from about 75 to about 100; from about 0.25 to about 1.0 volume percent of the bath of at least one organic solvent having a kauri-butanol value in excess of 100; from about 1.2 to about 1.8 grams per liter of at least one film controlling agent, the balance being essentially water; and (b) impinging said bath composition upon the surfaces to be etched of said photoengraving, said bath composition being at a temperature of from about 65 to 85 F. until the desired depth of relief is obtained.

References Cited by the Examiner UNITED STATES PATENTS 2,318,559 5/1943 Percival 252l42 X 3,023,138 2/1962 Easley et a1. 25279.4 X 3,152,083 10/1964 Croisant et a1. 25279.4

LEON D. ROSDOL, Primary Examiner.

ALBERT T. MEYERS, Examiner.

SUSAN E. DARDEN, M. WEINBLATT,

Assistant Examiners.

Claims (1)

1. IN AN ETCHING BATH COMPOSITION COMPRISING SUBSTANTIALLY NITRIC ACID, A SULFONATED DODECYL DIPHENYL OXIDE FILMING AGENT, A FILM CONTROLLING AGENT AND AN ORGANIC WATER-IMMISCIBLE FLUID SUBSTANTIALLY STABLE IN THE PRESENCE OF DILUTE NITRIC ACID, THE BALANCE BEING ESSENTIALLY WATER; THE IMPROVMENT CONSISTING ESSENTIALLY OF EMPLOYING A THREE-COMPONENT ORGANIC SOLVENT SYSTEM AS THE WATERIMMISCIBLE FLUID, SAID SYSTEM COMPRISING AS A FIRST COMPONENT FROM ABOUT 0.5 TO ABOUT 2.0 VOLUME PERCENT OF THE BATH OF AT LEAST ONE ORGANIC LIQUID HAVING A KAURIBUTANOL VALUE WITHIN THE RANGE OF FROM ABOUT 25 TO ABOUT 75, AS A SECOND JCOMPONENT FROM ABOUT 0.8 TO ABOUT 2.8 VOLUME PERCENT OF THE BATH OF AN ORGANIC LIQUID HAVING A KAURI-BUTANOL VALUE WITHIN THE RANGE OF FROM ABOUT 75 TO ABOUT 100, AND AS A THIRD COMPONENT FROM ABOUT 0.25 TO ABOUT 1.5 VOLUME PERCNET OF THE BATH OF AN ORGANIC LIQUID HAVING A KAURI-BUTANOL VALUE IN EXCESS OF 100.