US3922229A

US3922229A - Powderless etching bath for magnesium printing plates

Info

Publication number: US3922229A
Application number: US415052A
Authority: US
Inventors: Marvin H Fishaber; Philip C White
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1973-11-12
Filing date: 1973-11-12
Publication date: 1975-11-25
Anticipated expiration: 1992-11-25

Abstract

An etching bath for printing plates of magnesium or alloys thereof comprising: aqueous nitric acid; a sulfated fatty acid ester; a first saturated or olefinically unsaturated carboxylic acid which comprises a hydroxy-unsubstituted monocarboxylic acid of from 2 to 6 carbon atoms, or a polycarboxylic or hydroxy substituted monocarboxylic acid of from 2 to 8 carbon atoms; a polyhydric alcohol of from 2 to 10 carbon atoms or an ether derivative thereof; a second saturated or olefinically unsaturated carboxylic acid which comprises at least one hydroxyunsubstituted monocarboxylic acid of from 8 to 24 carbon atoms; and an alkylarylsulfonate. A concentrated additive comprising all of the foregoing bath ingredients except the aqueous nitric acid, to which water and nitric acid are added to provide a powderless etching bath. A method for etching printing plates of magnesium or alloys thereof using the foregoing bath formulation.

Description

Fishaber et al.

'United States Patent [1 1 1 Nov. 25, 1975 POWDERLESS ETCHING BATH FOR MAGNESIUM PRINTING PLATES Assignee:

Filed:

inventors: Marvin H. Fishaber, Saginaw; Philip C. White, Midland, both of Mich.

The Dow Chemical Company,

Midland, Mich.

Nov. 12, 1973 Appl. No.: 415,052

US. Cl. 252/794; 156/14; 156/18 Int. Cl. C09K 13/06 Field of Search 156/14, 18, 8; 252/794;

References Cited UNITED STATES PATENTS Patsko et al. 156/14 Sherer Messerschmidt et al.. v Messerschmidt et a1.

'Messerschmidt et al. 156/14 Primary ExaminerChar1es E. Van Horn Assistant Examiner-Jerome W. Massie Attorney, Agent, or FirmGlenn H. Korfl1age; Edward E. Schilling ABSTRACT tuted monocarboxylic acid of from 2 to 8 carbon atoms; a polyhydric alcohol of from 2.to'l0 carbon atoms or an ether derivative thereof; a second saturated or olefinically unsaturated carboxylic acid which comprises at least one hydroxy-unsubstituted monocarboxylic acid of from 8 to 24 carbon atoms; and an alkylarylsulfonate. A concentrated additive comprising all of the foregoing bath ingredients except the aqueous nitric acid, to which water and nitric acid are added to provide a powderless etching bath. A method for etching printing plates of magnesium or alloys thereof using the foregoing bath formulation.

37 Claims, No Drawings POWDERLESS ETCHING BATH FOR MAGNESIUM PRINTING PLATES BACKGROUND OF THE INVENTION This invention relates to a novel powderless etching bath composition for etching plates of magnesium or alloys thereof, an additive for use with nitric acid and water to form an etching bath formulation, and a method for etching plates of magnesium or magnesium alloy. (Hereinafter the term magnesium includes alloys thereof containing at least about 70 weight percent magnesium.)

In the preparation of metal printing plates, a plate of an acid soluble metal such as magnesium is coated in the plate making plant with a light sensitive coating or enamel which is applied to the metal surface which is usually flat but may be curved. Alternatively, photoresist coated (presensitized) flat plates are now available commercially which enable one practicing the art to avoid the time consuming coating step immediately prior to exposing the plate. The coated surface is exposed to light through a negative having an image thereon so as to cause or initiate cross-linking in the polymeric coating material to produce a corresponding image in the coating. The exposed coated surface is developed, and a pattern of an acid resistant coating is thereby formed on the plate in the form of the image produced by the exposure and is known as the photoresist image, or simply resist image. Depending on the type of coating employed, an additional heating step may be required to further harden and affix the acid resistant coating to the metal surface. Subsequently, the image bearing surface of the plate is etched by contacting it with an acid, thereby dissolving metal from those portions of the plate which are not protected by the photoresist. In the absence of any means of sidewall protection, the acid also tends to etch laterally and undercut the resist as the etching proceeds, thus distorting or destroying the image.

Originally, this undercutting was controlled by the time consuming and difficult method known as powdering of the plate, whereby the sides of the relief were manually covered with an acid resistant powder several times during the etching process.

Approximately 20 years ago, powderless etching baths usable in etching machines were introduced as taught in U.S. Pat. Nos. 2,640,763-767 which were so formulated as to eliminate the need for powdering. Though at the time they represented a revolutionary advance over the prior art, these early formulations were deficient in many respects.

The art of powderless etching has continued to be refined and advanced in recent years, and is now a wellknown, widely practiced technique. Subsequent formulations, such as that taught in US. Pat. No. 2,979,387, for example, employed large quantities of a water immiscible organic liquid which is substantially unreac tive with the aqueous acid bath. However, the modern formulations employing such organic liquid are undesirable in that they pose a substantial waste disposal problem. Since the water immiscible organic liquid, which is generally a petroleum solvent, is a serious pollutant, it is ecologically unsound to dispose of the used bath by merely draining it in a conventional drain. Very recently, a series of five patents have issued (U.S. Pat. Nos. 3,725,158; 3,725,159; 3,728,180; 3,730,899; and 3,736,197), which teach new formulations whereby the 2 water immiscible organic liquid can be eliminated or at least reduced. The etching bath of each of these recent patents employs a sulfonated carboxylic acid.

It is an important object of this invention to provide a novel bath for etching at high speeds without sacrificing the quality of the etch produced, shaped articles of magnesium or magnesium alloys such as photoengraving plates.

It is another object of this invention to provide an improved, high speed etching bath having a markedly improved filming capacity for better side wall protection.

Other objectives of this invention include providing a novel high speed etching bath capable of producing desired depths of etch in all kinds of image areas of combination plates, including solid areas, half tones, and large open areas; providing a high speed etching bath of capable of forming a stable protective film to prevent or retard lateral etching and chipping of relief side walls; and providing a high speed etching bath which eliminates or minimizes the so-called pimpling in large open areas.

Two additional objectives of this invention are to provide a novel additive for use in connection with water and nitric acid in making up etching baths and to provide a novel method for high speed etching.

Finally, it is a primary objective to accomplish all of the above as well as arriving at a stable composition for enhanced bath life without employing an unreactive water immiscible organic liquid.

Other and additional objects will become apparent from a consideration of this entire specification, including the claims.

SUMMARY OF THE INVENTION It has been discovered that by employing an etching bath formulation described as follows, each of the above objectives is accomplished. The formulation comprises, per liter of bath:

a. from about grams to about 360 grams of 42 Baume nitric acid;

b. from about 0.25 gram to about 5 grams of a sulfated fatty acid ester wherein the acid moiety contains from 10 to 24 carbon atoms and the alcohol moiety contains from I to 12 carbon atoms;

c. from about 0.25 gram to about 6 grams of a first saturated or olefinically unsaturated carboxylic acid which comprises a hydroxy-unsubstituted monocarboxylic acid of from 2 to 6 carbon atoms, or a polycarboxylic or hydroxy-substituted monocarboxylic acid of from 2 to 8 carbon atoms;

cl. from about 2 grams to about 25 grams of a polyhydric alcohol of from 2 to 10 carbon atoms or an ether derivative thereof;

e. from about 2 grams to about 15 grams of a second saturated or olefinically unsaturated carboxylic acid which comprises at least one monobasic fatty acid having from 8 to 24 carbon atoms;

f. from about 0.25 gram to about 4 grams of an alkylarylsulfonate selected from the group consisting of the alkylbenzenesulfonates wherein the alkyl portions contains from 8 to 18 carbon atoms and the alkylnapthalenesulfonates wherein the alkyl portion contains from 3 to 18 carbon atoms, as exemplified in the formula RA-SO X wherein R is an alkyl radical having from 3 to 18 carbon atoms inclusive, A is an aromatic nucleus, such as, for example, phenyl or naphthyl, and X is hydrogen or a salt forming cation, e.g., an alkali metal or alkaline earth metal; and

g. water to volume.

Since the quantities of nitric acid and water far ex ceed that of the other components of the bath, it is commercially advantageous to mix in advance the remaining components, along with a quantity of water sufficient to maintain the mix in a single phase and to yield a desired predetermined dilution level, and to ship and/or store the resulting mixture separately for subsequent use as an additive with an aqueous solution of nitric acid. Accordingly, such an additive is within the scope of this invention apart from the bath itself.

Also within the scope of this invention is a method for etching plates of magnesium employing a bath such as is described herein, maintaining the bath at a substantially uniform preselected temperature and contacting the plate surface to be etched with the bath.

FURTHER DESCRIPTION OF THE INVENTION In the practice of this invention, use of a polyvinyl cinnamate based photoresist is much preferred. While a polyvinyl alcohol based photoresist which has been very thoroughly hardened is satisfactory for very shallow depths of etch, it has been discovered that such a photoresist often fails in the etching bath of this invention before a commercially acceptable depth of etch has been attained. Distorted side walls also often result when plates having a polyvinyl alcohol based photoresist are contacted with a bath as contemplated herein.

Nitric Acid. The nitric acid component of the bath is well-known. Generally, the rate of etch increases with increasing concentration of nitric acid. An insufficient concentration will result in a slower rate of etch. An excess of nitric acid, however, is undesirable for several reasons. Since the etching reaction is exothermic, more heat is generated per unit area in relatively open areas of the plate than in those areas covered with the photoresist in more dense patterns, thus causing substantial temperature differences between the open and the image containing portions of the plate. Moreover, the gradation is augmented as the etching continues since the higher temperature of the open areas of the plate in turn results in a more rapid rate of etch. As a consequence, an excess of nitric acid can cause the open areas to be etched completely through the plate while the image containing areas are attaining the proper relief. Additionally, portions of the image adjacent to the open areas may be lost. Furthermore, excessive fuming occurs at higher concentrations of nitric acid.

Generally, a suitable range is from about 70 grams to about 360 grams of 42 Baume HNO per liter of bath, while from about 140 grams to about 285 grams per liter is preferred. Herein, the amount of nitric acid is expressed in terms of 42 Baume HNO merely for convenience: an equivalent amount of nitric acid introduced in other concentrations is also within the scope of the invention, and the teachings and claims which follow are to be interpreted accordingly.

While the amounts of the ingredients in the bath other than nitric acid remain essentially unchanged during use ofthe bath, the nitric acid is consumed as etching proceeds. To etch the maximum number of plates with a particular bath, therefore, it is desirable to fortify the bath periodically with additional nitric acid. In the usual practice of this invention, for example, after each etch run, i.e., wherein a single plate is etched or a plurality of plates are etched simultaneously, the partially depleted bath is fortified with from about 4 to about 9 grams of 42 Baume nitric acid per gram of magnesium dissolved in the bath during that particular run.

Sulfated Fatty Acid Ester The sulfated fatty acid ester component is comprised of at least one sulfated ester of a fatty acid, and is selected from those esters which are mutually soluble or dispersible with the remaining bath ingredients when employed at concentrations and conditions suggested as preferred.

The fatty acid moiety of the ester,

is derived from fatty acids of from 10 to 24 carbon atoms which are unsaturated, or, which are saturated but have at least one hydroxyl group on their respective hydrocarbon chains at which position sulfation can occur. The term sulfated is used herein in the technically correct sense, i.e., denoting that the sulfur is not bonded directly to the carbon atom, but rather is bonded to an oxygen atom which is bonded to the carbon. Examples of suitable fatty acids which, when esterified and sulfated, are suitable for use in this invention include oleic, ricinoleic, linoleic, palmitoleic, petroselinic, and vaccenic acids.

In the alcohol moiety of the ester, OR' in R contains from 1 to 12 carbon atoms, and R can be alkyl, cycloalkyl, saturated heterocyclyl having a preponderance of carbon atoms in the basic ring structure, or aryl, though alcohol moieties wherein R is alkyl are preferred. The terms cycloalkyl and saturated heterocyclyl as used herein are together intended to embrace not only the usual saturated carbocyclic radicals such as cyclobutyl, cyclopentyl, or cyclohexyl, but also saturated heterocyclic radicals such as, for example, pyrrolidinyl and tetrahydrofurfuryl.

Mixtures of a plurality of sulfated fatty acid esters having the characteristics just described are also beneficially employed. Examples of commercial grade mixtures of such esters which have been found to be particularly useful include, for example, those marketed under the trademarks Emkafol OT brand of sulfated fatty esters and Surfax W0 brand of sulfated propyl oleate, and particularly Calsolene Oil I-ISA brand of sulfated fatty acid ester.

While the sulfated fatty acid esters may be employed in concentrations ranging from about 0.25 gram to about 5 grams per liter of bath, the most satisfactory results have been obtained over a range from about 1 gram to about 3.5 grams per liter. These ranges are in terms of activity; where a commercial product containing such an ester or a mixture of such esters containing a lesser percentage of the active ingredient is employed, those skilled in the art will of course compensate accordingly.

First Carboxylic Acid The first carboxylic acid component is at least one saturated or olefinically unsaturated hydroxy-unsubstituted (i.e., non-hydroxylated) monocarboxylic acid of from 2 to 6 carbon atoms, or at least one polycarboxylic or hydroxy-substituted monocarboxylic acid of from 2 to 8 carbon atoms, or a mixture thereof. Acid meeting the requirements of the preceding sentence acids; saturated dicarboxylic acids whether or not hydroxy substituted, e.g., adipic, malic, and tartaric acids; and saturated hydroxy tricarboxylic acids, e.g., citric acid, are preferable in that smaller quantities of such acids are required to achieve comparable results to those achieved with greater amounts of other acids. The saturated hydroxy diand tricarboxylic acids are the most preferred, especially tartaric, malic, and citric acids.

While the specific optimum amount is readily determinable by those skilled in the art, within the range set forth of from about 0.25 gram to about 6 grams per liter of bath, depending on the particular application and also on the quantities of the remaining ingredients employed, it is generally preferred to include from about 0.5 gram to about 2 grams of the first carboxylic acid per liter of bath.

Polyhydric Alcohol or Ether Derivative The polyhydric alcohols or ether derivatives thereof may be saturated or olefmically unsaturated, and should be selected from those which are at least slightly soluble or dispersible in water, i.e., at least about 0.05 gram per liter of water. Although those which tend to be only slightly soluble are operable, those which are highly soluble are generally found to be preferable. Moreover, the hydrophobic portions preferably should be selected so as not to decrease substantially the water solubility or dispersibility of the molecule to such an extent that it would no longer be soluble in the bath at the concentrations and conditions set forth herein as preferred.

The polyhydric alcohols usable herein are preferably dior trihydric but may contain more OH groups (as in sorbitol). Alcohols of from 2 to 10 carbon atoms are preferred, particularly those having from 2 to 6 carbon atoms, and also those alcohols which are oxyalkylene or polyoxyalkylene glycols whose carbon chain is internot etherified, are in fact preferred for use herein, relative to the, alcohols per se, and most preferred are ether derivatives in which the total number of carbon atoms per alkoxy group is from ,1 to 4 for every internal oxygen atom interrupting the carbon chain of the alcohol. Thus, for example, a mono-ether derivative of diethylene glycol, the carbon chain of which is interrupted by one internal oxygen atom, preferably contains up to 4 carbon atoms in the alkoxy group:

R-O-CCOCCOH as in, e.g., diethylene glycol ethyl ether or diethylene glycol n-butyl ether. Diethylene glycol n-butyl ether has been found to give a particularly superior product.

The R group in the OR moiety of the ether derivatives of the polyhydric alcohols contemplated herein may be alkyl, cycloalkyl, saturated heterocyclyl having I a preponderance of carbon atoms in the basic ring rupted by one or more oxygen atoms, as in certain socalled ether glycols. Illustrative of operative alcohols under this invention are ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, hexylene glycol, diand tripropylene glycol, glycerine, and the like.

rated heterocyclyl ethers, and alkylene glycol aryl ethers described in the next paragraphQGlycol ethers,

'as used herein denoting the ether derivatives of the polyhydric alcohols hereinbefore described in which at least one OH function is etherified and at least one is include not only those wherein the R group of the OR moiety is phenyl (as in, e.g., ethylene glycol phenyl ether) or naphthyl, but also those wherein the R group is a substituted aryl radical. Substituents on the aryl ring may be alkyl, alkoxy, halo, nitro, cyano, sulfo, and the like. The cycloalkyl and saturated heterocyclyl moieties contemplated herein may, of course, be similarly substituted with the substituents envisioned for the aryl moieties. Thus, compounds such as the monocyclobutyl ethers of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and butylene glycol are embraced herein. Generally, those etherswherein the alkoxy, cycloalkoxy, or aryloxy moiety is relatively bulky are preferably ethers of polyoxyalkylene glycols, as opposed to ethers of polyhydric alcohols having no internal oxygen atom.

Generally, the amount of the polyhydric alcohol or ether in the final bath compositions will range from about 2 to about 25 grams per liter. While quantities of from about 3 grams to about 23 grams per liter are generally preferred, quantities from about 3 grams to about 10 grams per liter have been found to give superior results in the most preferred embodimentsof this invention. It can readily be appreciated that optimum.

,in plates etched with a bath containing an insufficient quantity of the component, while an excess results in undercutting of the relief image.

Second Carboxylic Acid The second saturated or olefinically unsaturated carboxylic acid comprises at least one hydroxy-unsubstituted monocarboxylic acid of from 8 to 24 carbon atoms. Generally, however, it is very much preferable to employ a blend of such acids, the preponderance of which comprises one or more acids having 18 carbon atoms, such as, for example, oleic acid. Furthermore, it has surprisingly been discovered that the use of saturated acids, rather than unsaturated acids or a mixture of saturated and unsaturated acids, results in a significantly more stable bath which will not deteriorate appreciably even if left standing for periods in excess of one week. For example, very stable baths producing ex- 7 cellent etch results have been obtained when isostearic acid comprises the preponderance of the second carboxylic acid.

When employing a preponderance of acids having 18 carbon atoms, it is particularly advantageous to include, per liter of bath, at least about 0.05 gram per liter of bath of one or more saturated hydroxy-unsubstituted monocarboxylic acids having from 8 to 12 carbon atoms, such as caprylic or capric acids, not to exceed a total of about one gram per liter of bath. A most preferred embodiment employs a blend of such shorter chain acids, wherein two or more of such acids each comprise at least about 20 weight percent of the blend, and together comprise at least about 85 weight percent of the blend. Emery 658 brand blend of 56% caprylic acid, 40% capric acid, 2% caproic acid and 2% lauric acid, as well as those blends of capric and caprylic acids sold under the trademarks Neo-Fat 360 and Hydrofol Acids 0856 have been found to be quite suitable for use in the invention contemplated herein.

The second carboxylic acid should be employed in quantities ranging from about 2 grams to about l grams per liter of bath, and preferably from about 5 grams to about grams per liter of bath. A most preferred embodiment employs from about 5 grams to about 10 grams per liter of bath of an 18 -carbon acid and from about 0.12 gram to about 0.15 gram per liter of bath of an 8- to l2-carbon fatty acid or blend thereof. As with each of the other ingredients, however, the above quantities are only approximations and may vary depending upon, for example, the nature and quantity of the other bath ingredients selected by one practicing the invention. While the longer chain fatty acids in combination with other bath components are employed to provide heavy filming protection against lateral etching, the shorter chain acids are particularly useful in selectively controlling the loss of the ends of lines in open areas such as are formed, for example, on plates prepared for printing business forms. Accordingly, one skilled in the art can readily arrive at an optimum quantity of the acid for the particular application.

Alkylarylsulfonate The suitable alkylaryl-sulfonates, i.e., salts of the corresponding alkylaryl-sulfonic acid, are selected from the group consisting of the alkylbenzenesulfonates wherein the alkyl portion contains from 8 to [8 carbon atoms and the alkylnapthalenesulfonates wherein the alkyl portion contains from 3 to 18 carbon atoms, as exemplified in the formula RA SO X in which R is an alkyl radical having from 3 to 18 carbon atoms inclusive, A is an aromatic nucleus, such as phenyl or naphthyl, and X is hydrogen or a salt forming cation, e.g., an alkali metal or alkaline earth metal.

Typical of the alkylarylsulfonates that may be employed are sodium decylbenzenesulfonate, sodium dodecylbenzenesulfonate, sodium tetradecylbenzenesulfonate, sodium propylnaphthalenesulfonate, sodium amylnaphthalenesulfonate, sodium diamylnaphthalenesulfonate and sodium dodecylnaphthalenesulfonate. in the above illustrations, it will be understood that sodium can be replaced by, e.g., an amine to provide amine salts. The alkyl substituent or substituents are preferably such that the total number of carbon atoms in all the alkyl radicals taken together does not exceed about 14. The particular position of the alkyl radical on the aryl ring can also be varied. Thus, ortho alkylarylsulfonates, para alkylarylsulfonates, and meta alkylarylsulfonates are contemplated.

Examples of commercially available alkylarylsulfonates suitable for use in this invention include those marketed under the following trademarks: Bio Soft D-35, Bio Soft D-60, and Bio Soft D-62 brand of dodecylbenzenesulfonates; Emkal BNS butylnaphthalenesulfonate, Emkal NNS nonylnaphthalenesulfonate; Rueterg No. 40T, Rueterg No. 40U, and Rueterg No. 97S brand of alkylarylsulfonates; Sorbit P mixture of the sodium salts of monoand di-butylnaphthalenesulfonates; and Wixol TC and Wixol BD brand of alkylarylsulfonates. While quantities ranging from about 0.25 gram to about 4 grams of the active alkylarylsulfonate ingredient per liter of bath have been found to be satisfactory, the best results have been obtained when using from about 0.5 to about 2 grams per liter of bath.

Additive As was suggested above, it is convenient to prepare in advance an additive formulation, often referred to in the art as an etch concentrate or mix, to which nitric acid and additional water are added to make up the hereinbefore described bath compositions. Such additive compositions can be transported per se as articles of commerce and constitute an embodiment of this invention separate from the ultimate etching bath composition.

It will be understood by those skilled in the art that it is advantageous to neutralize the acids in the additive formulation with an alkaline material such as sodium hydroxide so as to reduce the corrosiveness of the additive during shipment and storage. It will also be understood that additional minor ingredients such as foam suppressants may desirably be incorporated into either the additive or the ultimate bath composition in order to minimize foaming during the formulation, shipping, and handling of the additive composition and also during the actual etching process and eventual disposal of the spent bath.

Anadditive composition which has been found to be optimal has approximately the following composition of active components, based on the total weight of the additive:

Caustic soda to neutralize to pH about 8, and water Balance to I00 Satisfactory baths can also be prepared using additive formulations which contain the above components in proportions within about 10 percent of the weight percents set forth above. Thus, a useful additive may be comprised of from about 4.9 to about 6 weight percent sulfated fatty acid ester; from about 1.95 to about 2.45 weight percent first carboxylic acid; from about 16 to about 20 weight percent polyhydric alcohol or ether; from about 12 to about 14.6 weight percent second carboxylic acid; and from about 2.4 to about 3 weight percent alkylarylsulfonate. Similarly, the second carboxylic acid component preferably comprises an 18- chine of the type disclosed in US. Pat. No. 2,669,048, issued Feb. 16, 1954. In this machine, elongated paddles dipping into the bath composition intermittently throw, by splashing, the etching bath composition in sheets upwardly against the image bearing side of the object being etched. Other etching machines designed for powderless etching are also applicable.

The following examples are given to further illustrate the present invention; they should be considered merely as being representative and not as limitations on the overall scope of the invention.

EXAMPLE 1 An etching bath consisting of the following imgredients was prepared in a l30-liter paddle-type powderless carbon acid, such as, for example, isostearic acid, in an amount of from about 97.25 to about 98.25 weight'percent, and an 8- to 12- carbon saturated acid, such as, for example, capric acid or caprylic acid, or a mixture thereof as hereinbefore described, in an amount of from about 1.75 to about 2.75 weight percent, based on the total weight of the second carboxylic acid component.

When a bath is made up from an additive mix, from about 30 grams to about 50 grams of the additive can be employed per liter of bath, but generally from about 35 grams to about 45 grams per liter is preferred. Of course, it will be recognized that the quantity of mix required will vary somewhat depending on the actual amount of water in the particular mix. The appropriate quantity of nitric acid to be used is set forth above in the description of the actual etching bath, and water is etching machine, and the temperature of the bath maintained in the range of from 108 F. to 110 F.:

Water, to volume (1.2 g. active) added to make up the desired volume of bath.

Process for Etching In practicing the high speed etching of plates according to the present invention, a bath as hereinbefore described is prepared and maintained at a preselected temperature of preferably from about 100 F. to about 1 15 F. For purposes of the claims, about 100 F. shall be construed as including temperatures at least as low as 98 F. The bath is operable at temperatures outside this range, but in doing so, either etch speed or safe working conditions must be compromised to some extent. Lower temperatures result in progressively slower etch rates. While faster etch rates can be obtained at somewhat higher temperatures, excessive fuming of the nitric acid component results, thereby rendering undesirable operation at temperatures much above the range indicated. It will be understood, of course, that the bath need not be maintained in the above temperature range during periods when it is not actually being used.

When mixed and adjusted to the preselected operat- An image presensitized plate bearing a polyvinyl cin namate based photoresist was descummed by scrubbing with a 5 percent aqueous nitric acid solution containing gum arabic. The plate was positioned in the etching machine. The machine was closed and the paddles adjusted to operate at a speed of 520 revolutions per minute (RPM). After four minutes of etching at such conditions, the machine was stopped and the plate removed and washed with an aqueous solution of ordinary household detergent and rinsed. The plate was etched to a depth of 0.032 inch. The quality of the etch was excellent, with no chipping or lateral etching being observed and with closed portions of letters such as A, a, B, b, etc. being etched to a desirable depth.

EXAMPLES 2 THROUGH 9 Following procedures essentially similar to that described in Example 1, additional plates were etched using various bath compositions and etching conditions. The results obtained using a representative sample of these baths under the conditions stated are summarized in Table I. In each instance, the particular plate described in each of Examples 2 through 9 was the first plate etched in the particular bath.

The various ingredients in Table I are identified as follows:

glycol ethyl ether -continued Key Trademark Description EB Emkal BNS EN Emkal NNS EP Dowanol EPh butylnaphthalenesulfonate (33%) nonylnaphthalenesulfonate (33%) ethylene glycol phenyl ether triethylene glycol butyl ether containing highers alkylnaphthalenesulfonate (30%) TB DowanolTBH WT Wixol TC TABLE I COMPOSlTlON AND PERFORMANCE OF BATHS FOR EXAMPLES 2 THROUGH 9 All quantities are in grams per liter. Where components are identified by a tradename, correction has been made where the commercial product is less than 100% active; thus, all quantities shown are in terms of active ingredients.

65 Line Polyhydric Screen First Alcohol(s) Second Alkylaryl- Halftone 42 Sulfated Carboxylic or Carboxylic Sulfonate- Run Bath Paddle Hi-lite Line Ex. Be. Ester(s) Acid Ether(s) Acid(s) (s) Time, Temp. Speed Depth, Depth No. HNO; Key Quan. Key Quan. Key Quan. Key Quan. Key Quan. Min. "F. RPM lnch Inch Comments Fair to 2 169 CO 3.3 LA 4.8 DB 5.6 1A 5.8 B4 0.97 3.0 110 500 0.009 0.022 good plate (PVA resist) Fair to good; clean 3 282 CO 135 CA 1.0 TB 5.0 1A 8.5 SP 1.4 3.5 110 550 0.0075 0.028 someshoulderirreg. 4 282 CO 1.35 AA 2.0 TB 5.0 IA 8.5 WT 1.35 3.5 110 550 0.009 0.031 Goodetch 5 282 CO 1.35 MA 1.0 EP 8.0 IA 8.5 WT 1.35 3.5 110 550 0.0085 0.030 Goodetch Fair to 6 240 CO 2.2 MA 0.81 TB 4.9 lA 3.21 RU 0.71 4.0 110 520 0.006 0.030 good.

usable TB 4.6 7 232 SW 3.9 MA 1.85 DE 11.5 0A 6.9 EN 2.8 5.0 98 415 0.005 0.028 Good plate Fair but TB 4.6 usable; 8 240 SW 3.4 MA 1.38 0A 7.7 EB 1.27 5.0 110 420 0.006 0.030 someshoul- DE 17.5 derirreg.

Good 9 282 SW 29 TA DB 74 IA 5.9 B6 1.2 4.0 104 500 0.008 0.028 plate; clean EXAMPLE 10 A bath composition was formulated as follows in a l30-liter machine:

Ingredient Grams Per Liter 42 Baume HNO, 268 Calsolene Oil HSA brand of sulfated 4.9

fatty acid ester (45% activity) (2.2 g active) Tartaric acid 0.893 Diethylene glycol n-butyl ether 7.35 lsostearic acid 5.3 Emery 658 brand blend of short chain 0.122

saturated acids Bio Soft D-60 brand of dodecylbenzene- 1.84

sulfonate (60% activity) (1.1 g active) Water. to volume rate of 0.0015 inch per minute was obtained. Additional plates could have been etched using the same bath upon further fortification with an appropriate amount of additional nitric acid.

EXAMPLE 1 1 At the same temperature and paddle speed as in Example 10, an etch rate of 0.0025 inch per minute was realized using a bath containing about 5471 grams of magnesium and replenished with 7.0 grams of 42 Baume HNO per gram of dissolved magnesium. The bath used in this Example was initially formulated as follows:

Ingredient Grams per liter 42 Baume HNO, 268 Calsolene oil HSA brand of sulfated 6.13

fatty acid ester (45% activity) (2.76 g. active] Tartaric acid 1.12

Diethylene glycol n-butyl ether 9.2 lsostearic acid 6.64 Emery 658 brand blend of short chain saturated acids 0.153 Bio Soft D-60 brand of dodecylbenzene- 2.3

Sulfonate (60% activity) (1.38 g. active) Water, to volume What is claimed is: v Y

l. A bath composition for etching photoengraving plates of magnesium or alloys thereof whichcomprises water and, per liter of bath:

a. from about 70 grams to about 360 grams of 42 Baume nitric acid;

b. from about 0.25 gram to about 5 grams of a sulfated fatty acid ester having from to 24 carbon atoms in the acid moiety and from 1 to 12 carbon atoms in the alcohol moiety.

c. from about 0.25 gram to about 6 grams'of a first saturated or olefinically unsaturated carboxylic acid which comprises a hydroxy-unsubstituted monocarboxylic acid of from 2 to 6 carbon atoms, or a polycarboxylic or hydroxy-substituted monocarboxylic acid of from 2 to 8 carbon atoms;

d. from about 2 grams to about 25 grams of a polyhydric alcohol of from 2 to 10 carbon atoms or an ether derivative thereof;

e. from about 2 grams to about grams of a second saturated or olefinically unsaturated carboxylic acid which comprises at least one hydroxy-unsubstituted monocarboxylic acid having-from 8 to 24 carbon atoms; and

f. from about 0.25 gram to about 4 grams of an alkylarylsulfonate selected from the group consisting of the alkylbenzenesulfonates wherein the alkyl portion contains from 8 to 18 carbon atoms and the alkylnaphthalenesulfonates wherein the alkyl portion contains from 3 to 18 carbon atoms.

2. The etching bath of claim 1 wherein the first saturated or olefinically unsaturated carboxylic acid is selected from the group consisting of saturated hydroxy monocarboxylic acids, saturated dicarboxylic acids, and saturated hydroxy tricarboxylic acids.

3. The etching bath of claim 1 wherein the first saturated or olefinically unsaturated carboxylic acid is selected from the group consisting of glycolic, lactic, adipic, malic, tartaric, and citric acids.

4. The etching bath of claim 1 wherein the polyhydric alcohol or ether derivative is a glycol ether.

5. The etching bath of claim 1 wherein the polyhydric alcohol or ether derivative thereof is selected from the group consisting of diethylene glycol n-butyl ether, diethylene glycol ethyl ether; ethylene glycol n-butyl ether, ethylene glycol phenyl ether, triethylene glycol methyl ether, and triethylene glycol butyl ether.

6. The etching bath of claim 1 wherein the second saturated or" olefinically unsaturated carboxylic acid consists of, per liter-of bath, from about 2 grams to about 15 grams of at least one saturated or olefinically unsaturated hydroxy-unsubstituted monocarboxylic acid having 18 carbon atoms and from about 0.05 gram to about 1 gram of at least one saturated hydroxyunsubstituted monocarboxylic acid of from 8 to 12 carbon atoms.

7. The etching bath of claim 1 wherein the second saturated olefinically unsaturated carboxylic acid is oleic acid.

8. The etching bath of claim 1 wherein the second saturated or olefinically unsaturated carboxylic acid consists of one or more saturated acids.

9. The etching bath of claim 1 wherein the second 14 11. The etching bath of claim 1 whereinthe alkylarylare employed per liter of bath.

13. The etching bath of claim 1 wherein from about 1 gram to about 3.5 gramsof the sulfated fatty acid ester are employed per. liter of bath.

14. The etching bathofclaim 1 wherein from about 0.5 gram to about 2 grams of the first saturated or olefinically unsaturated carboxylic acid are employed per liter of bath.

, 15. The etching bath of claim 1 wherein from about 3 grams to about 10 grams of the polyhydric alcohol or ether derivative thereof are employed per liter of bath.

16. The etching bath of claim 1 wherein from about 5 grams to about 10 grams of the second saturated or olefinically unsaturated carboxylic acid are employed per liter of bath.

17. The etching bath of claim 1 wherein from about 0.5 gram to about 2 grams of the alkylarylsulfonate are employed per liter of bath.

18. The etching bath of claim 6 wherein from about 5 grams to about 10 grams of the monocarboxylic acid having 18 carbon atoms and from about 0.12 gram to about 0.15 gram of a saturated monocarboxylic acid of from 8 to 12 carbon atoms or a mixture thereof are employed per liter of bath.

19. The etching bath of claim 6 wherein the acid having 18 carbon atoms is oleic acid.

20. The etching bath of claim 6 wherein the acid hav ing 18 "carbon atomsconsists of a saturated acid.

21. The etching bath'of claim 6 wherein the acid having 18 carbon atoms is isostearic acid.

22. The etching bath of claim 6 wherein the saturated monocarboxylic acid of from 8 to 18 carbon atoms is comprised of a blend of capric and caprylic acids.

23. The etching bath of claim 22 wherein the acid having 18 carbon atoms is oleic acid.

24. The etching bath of claim 22 wherein the acid having 18 carbon atoms is isostearic acid.

25. The etching bath of claim 22 wherein the first saturated or olefinically unsaturated carboxylic acid is selected from the group consisting of hydroxy monocarboxylic acids, dicarboxylic acids, and hydroxy tricarboxylic acids.

26. The etching bath of claim 25 wherein the polyhydric'alcohol or ether derivative thereof is a glycol ether.

27. The etching bath of claim 22 wherein the acid having 18 carbon atoms consists of a saturated acid.

28. The etching bath of claim 27 wherein the first saturated or olefinically unsaturated carboxylic acid is selected from the group consisting of hydroxy monocarboxylic acids, dicarboxylic acids, and hydroxy tricarboxylic acids.

29. The etching bath of claim 28 wherein the polyhydric alcohol or ether derivative thereof is a glycol ether.

30. The etching bath composition of claim 22 which comprises water and, per liter of bath:

a. from about grams to about 285 grams of 42 Baume nitric acid;

b. from about 1 to about 3.5 grams of a sulfated fatty acid ester having from 10 to 24 carbon atoms in the acid moiety and from 1 to 12 carbon atoms in the alcohol moiety;

c. from about 0.5 to about 2 grams of tartaric acid;

(I. from about 3 grams to about 10 grams of diethylene glycol n-butyl ether;

e. from about 5 grams to about grams of isostearic acid;

f. from about 0.12 gram to about 0.15 gram of a blend of caprylic and capric acids; and

g. from about 0.5 grams to about 2 grams of a dodecylbenzenesulfonate salt.

31. An additive composition adapted for use in admixture with aqueous nitric acid as a bath for the powderless etching of printing plates of magnesium or magnesium alloys, which bath is essentially free from organic water immiscible liquids which are substantially unreactive with the aqueous acid bath, said additive composition comprising, based on the total weight of said additive composition:

a. from about 4.9 to about 6 weight percent of a sulfated fatty acid ester having from 10 to 24 carbon atoms in the acid moiety and from 1 to 12 carbon atoms in the alcohol moiety;

b. from about 1.95 to about 2.45 weight percent of a first saturated or olefinically unsaturated carboxylic acid which comprises a hydroxy-unsubstituted monocarboxylic acid of from 2 to 6 carbon atoms, or a polycarboxylic or hydroxy-substituted monocarboxylic acid of from 2 to 8 carbon atoms;

0. from about 16 to about 20 weight percent of a polyhydric alcohol of from 2 to 10 carbon atoms of an ether derivative thereof;

(1. from about l2 to about 14.6 weight percent of a second saturated or olefinically unsaturated carboxylic acid which comprises at least one hydroxyunsubstituted monocarboxylic acid having from 8 to 24 carbon atoms; and

. from about 2.4 to about 3 weight percent of an alkylarylsulfonate selected from the group consisting of the alkylbenzenesulfonates wherein the alkyl portion contains from 8 to 18 carbon atoms and the alkylnaphthalenesulfonates wherein the alkyl portion contains from- 3 to 18 carbon atoms; and

f. the balance to 100 weight percent, substantially water.

.32. The additive composition of claim 31 wherein the second saturated or olefinically unsaturated carboxylic acid component comprises, based on the total weight of said second carboxylic acid component, from about 97.25 to about 98.25 weight percent of an hydroxyunsubstituted monocarboxylic acid having 18 carbon atoms and from about 1.75 weight percent to about 2.75 weight percent of a saturated hydroxy-unsubstituted monocarboxylic acid having from 8 to 12 carbon atoms or a mixture thereof.

33. The additive composition of claim 31 wherein the second saturated or olefinically unsaturated carboxylic acid component consists of from about 97.25 to about 98.25 weight percent of a saturated hydroxy-unsubstituted monocarboxylic acid having 18 carbon atoms and from about 1.75 weight percent to about 2.75 weight percent of a saturated hydroxy-unsubstituted monocarboxylic acid having from 8 to 12 carbon atoms or a mixture thereof.

34. The additive composition of claim 32 wherein the first saturated or olefinically unsaturated carboxylic acid is selected from the group consisting of saturated hydroxy monocarboxylic acids, saturated dicarboxylic acids, and saturated hydroxy tricarboxylic acids, and, wherein the polyhydric alcohol or ether derivative thereof is a glycol ether.

35. The additive composition of claim 33 wherein the first saturated or olefinically unsaturated carboxylic acid is selected from the group consisting of saturated hydroxy monocarboxylic acids, saturated dicarboxylic acids, and saturated hydroxy tricarboxylic acids, and, wherein the polyhydric alcohol or ether derivative thereof is a glycol ether.

36. The additive composition of claim 34 wherein the additive is comprised of:

a. about 5.4 weight percent of the sulfated fatty acid ester;

b. about 2.2 weight percent of the first saturated or olefinically unsaturated carboxylic acid;

0. about 18 weight percent of the glycol ether;

d. about 13 weight percent of the saturated or olefinically unsaturated hydroxy-unsubstituted monocarboxylic acid having 18 carbon atoms;

e. about 0.3 weight percent of the saturated hydroxyunsubstituted monocarboxylic acid having 8 to 12 carbon atoms or the mixture thereof;

f. about 2.7 weight percent of the alkylarylsulfonate;

and

g. the balance to weight percent, substantially water.

37. The additive composition of claim 36 wherein the first saturated or olefinically unsaturated carboxylic acid is tartaric acid, the glycol ether is diethylene glycol n-bu'tyl ether, and the second saturated or olefinically unsaturated carboxylic acid consists of about 97.75 weight percent isostearic acid and about 2.25 weight percent of a mixture of 8- to l2-carbon unsaturated hydroxy-unsubstituted monocarboxylic acids comprised of capric acid and caprylic acid.

UNITED STATES PATENT AND TRADEMARK OFFICE EETIFICATE OF CORRECTIUN PATENT NO. 2 3,922,229

DATED November 25, 1975 INVENTO 1 Marvin H. Fishaber et al.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: Q

In column 2, line 16, delete "of" at the end of the liner,

Column 6, line 19, insert the word -asbefore 9 the word "contemplated"o Column 10, in the table beginning at the bottom of the column, in line 2, column 2 of said table, change 9 "Bio soft" to --Bio Soft.

Column 13, Claim 1, line 10, after the word "moiety" delete the period and insert a semicolon Q Signed and Scaled this second Day Of March 1976 9 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Q Arresting Officer (mnmissiuner nj'Parents and Trademarks

Claims

1. A BATH COMPOSITION FOR ETCHING PHOTOENGRAVING PLATES OF MAGNESIUM OR ALLOYS THEREOF WHICH COMPRISES WATER AND, PER LITER OF BATH: A. FROM ABOUT 70 GRAM TO ABOUT 360 GRAMS OF 42* BAUME NITRIC ACID, B. FROM ABOUT 0.25 GRAM TO ABOUT 5 GRAMS OF A SULFATED FATTY ACID ESTER HAVING FROM 10 TO 24 CARBON ATOMSS IN THE ACID MOIETY AND FROM 1 TO 12 CARBON ATOMS IN THE ALCOHOL MOIETY. C. FROM ABOUT 0.25 GRAM TO ABOUT 6 GRAMS OF A FIRST STRUCTED OR OLEFINICALLY UNSATURATED CARBOXYLIC ACID WHICH COMPRISES A HYDROXY-UNSUBSTITUTED MONOCARBOXYLIC ACID OF FROM 2 TO 6 CARBON ATOMS, OR A POLYCARBOXYLIC OR HYDROXYSUBSTITUTED MONOCARBOXYLIC ACID OF FROM 2 TO 8 CARBON ATOMS, D. FROM ABOUT 2 GRAMS TO ABOUT 25 GRAMS OF A POLYHYDRIC ALCOHOL OF FROM 2 TO 10 CARBON ATOMS OR AN ETHER DERIVATIVE THEREOF, E. FROM ABOUT 2 GRAMS TO ABOUT 15 GRAMS OF A SECOND SATURATED OR OLEFINICALLY UNSATURATED CARBOXYLIC ACID WHICH COMPRISES AT LEAST ONE HYDROXY-UNSUBSTITUTED MONOCARBOXYLIC ACID HAVING FROM 8 TO 24 CARBON ATOMS, AND F. FROM ABOUT 025 GRAM TO ABOUT 4 GRAMS OF AN ALKYLARYLSULFONATE SELECTED FROM THE GROUP CONSISTING OF THE ALKYLBENZENESULFONATES WHEREIN THE ALKYL PORTION CONTAINS FROM 8 TO 18 CARBON ATOMS AND THE ALKYLNAPHTHALENESULFONATES WHEREIN THE ALKYL PORTION CONTAINS FROM 3 TO 18 CARBON ATOMS.

5. The etching bath of claim 1 wherein the polyhydric alcohol or ether derivative thereof is selected from the group consisting of diethylene glycol n-butyl ether, diethylene glycol ethyl ether, ethylene glycol n-butyl ether, ethylene glycol phenyl ether, triethylene glycol methyl ether, and triethylene glycol butyl ether.

6. The etching bath of claim 1 wherein the second saturated or olefinically unsaturated carboxylic acid consists of, per liter of bath, from about 2 grams to about 15 grams of at least one saturated or olefinically unsaturated hydroxy-unsubstituted monocarboxylic acid having 18 carbon atoms and from about 0.05 gram to about 1 gram of at least one saturated hydroxy-unsubstituted monocarboxylic acid of from 8 to 12 carbon atoms.

9. The etching bAth of claim 1 wherein the second saturated or olefinically unsaturated carboxylic acid is isostearic acid.

10. The etching bath of claim 1 wherein the alkylarylsulfonate is an alkylbenzenesulfonate wherein the alkyl portion contains from 8 to 18 carbon atoms.

11. The etching bath of claim 1 wherein the alkylarylsulfonate is an alkylnaphthalenesulfonate wherein the alkyl portion contains from 3 to 18 carbon atoms.

12. The etching bath of claim 1 wherein from about 140 grams to about 285 grams of 42* Baume nitric acid are employed per liter of bath.

13. The etching bath of claim 1 wherein from about 1 gram to about 3.5 grams of the sulfated fatty acid ester are employed per liter of bath.

14. The etching bath of claim 1 wherein from about 0.5 gram to about 2 grams of the first saturated or olefinically unsaturated carboxylic acid are employed per liter of bath.

15. The etching bath of claim 1 wherein from about 3 grams to about 10 grams of the polyhydric alcohol or ether derivative thereof are employed per liter of bath.

20. The etching bath of claim 6 wherein the acid having 18 carbon atoms consists of a saturated acid.

21. The etching bath of claim 6 wherein the acid having 18 carbon atoms is isostearic acid.

26. The etching bath of claim 25 wherein the polyhydric alcohol or ether derivative thereof is a glycol ether.

30. The etching bath composition of claim 22 which comprises water and, per liter of bath: a. from about 140 grams to about 285 grams of 42* Baume nitric acid; b. from about 1 to about 3.5 grams of a sulfated fatty acid ester having from 10 to 24 carbon atoms in the acid moiety and from 1 to 12 carbon atoms in the alcohol moiety; c. from about 0.5 to about 2 grams of tartaric acid; d. from about 3 grams to about 10 grams of diethylene glycol n-butyl ether; e. from about 5 grams to about 10 grams of isostearic acid; f. from about 0.12 gram to about 0.15 gram of a blend of caprylic and capric acids; and g. from about 0.5 grams to about 2 grams of a dodecylbenzenesulfonate salt.

31. An additive composition adapted for use in admixture with aqueous nitric acid as a bath for the powderless etching of printing plates of magnesium or magnesium alloys, which bath is essentially free from organic water immiscible liquids which are substantially unreactive with the aqueous acid bath, said additive composition comprising, based on the total weight of said additive composition: a. from about 4.9 to about 6 weight percent of a sulfated fatty acid ester having from 10 to 24 carbon atoms in the acid moiety and from 1 to 12 carbon atoms in the alcohol moiety; b. from about 1.95 to about 2.45 weight percent of a first saturated or olefinically unsaturated carboxylic acid which comprises a hydroxy-unsubstituted monocarboxylic acid of from 2 to 6 carbon atoms, or a polycarboxylic or hydroxy-substituted monocarboxylic acid of from 2 to 8 carbon atoms; c. from about 16 to about 20 weight percent of a polyhydric alcohol of from 2 to 10 carbon atoms of an ether derivative thereof; d. from about 12 to about 14.6 weight percent of a second saturated or olefinically unsaturated carboxylic acid which comprises at least one hydroxy-unsubstituted monocarboxylic acid having from 8 to 24 carbon atoms; and e. from about 2.4 to about 3 weight percent of an alkylarylsulfonate selected from the group consisting of the alkylbenzenesulfonates wherein the alkyl portion contains from 8 to 18 carbon atoms and the alkylnaphthalenesulfonates wherein the alkyl portion contains from 3 to 18 carbon atoms; and f. the balance to 100 weight percent, substantially water.

32. The additive composition of claim 31 wherein the second saturated or olefinically unsaturated carboxylic acid component comprises, based on the total weight of said second carboxylic acid component, from about 97.25 to about 98.25 weight percent of an hydroxy-unsubstituted monocarboxylic acid having 18 carbon atoms and from about 1.75 weight percent to about 2.75 weight percent of a saturated hydroxy-unsubstituted monocarboxylic acid having from 8 to 12 carbon atoms or a mixture thereof.

36. The additive composition of claim 34 wherein the additive is comprised of: a. about 5.4 weight percent of the sulfated fatty acid ester; b. about 2.2 weight percent of the first saturated or olefinically unsaturated carboxylic acid; c. about 18 weight percent of the glycol ether; d. about 13 weight percent of the saturated or olefinically unsaturated hydroxy-unsubstituted monocarboxylic acid having 18 carbon atoms; e. about 0.3 weight percent of the saturated hydroxy-unsubstituted monocarboxylic acid having 8 to 12 carbon atoms or the mixture thereof; f. about 2.7 weight percent of the alkylarylsulfonate; and g. the balance to 100 weight percent, substantially water.

37. The additive composition of claim 36 wherein the first saturated or olefinically unsaturated carboxylic acid is tartaric acid, the glycol ether is diethylene glycol n-butyl ether, and the second saturated or olefinically unsaturated carboxylic acid consists of about 97.75 weight percent isostearic acid and about 2.25 weight percent of a mixture of 8- to 12-carbon unsaturated hydroxy-unsubstituted monocarboxylic acids comprised of capric acid and caprylic acid.