US3423214A - Magnetic cobalt and cobalt alloy plating bath and process - Google Patents

Description

Jan. 21, 1969 H. KORETZKY MAGNETIC COBALT AND COBALT ALLOY PLATING BATH AND PROCESS Filed June 30, 1965 J 4| 0. 0 O 0 86420 D :TN 0 ITA 2 0G 0 CL C P 0 l 2 S H mw [LE 8 Mm G MM ll M F I m J 0 0 0 0 0 0 0 0 0 0 0 0 0O 6 4 2 1 C H S B H c H CH2 (000H)2 (gm/9.)

. All 9. 5:25;:

FIG.3

INVENTOR HERMAN KORETZKY ATTORNEY United States Patent Claims ABSTRACT OF THE DISCLOSURE Magnetic cobalt and cobalt-base alloy films having controlled coercivity in the range of from 20 to 200 oersteds are obtained by contacting a catalytic surface with an aqueous solution comprising cobalt ions, hypophosphite ions and a ligand which comprises a saturated unsubstituted short chain aliphatic dicarboxylic anion. The molar ratio of cobalt ion to ligand anions is essentially one, and the molar ratio of cobalt ions to hypophosphite ions is between 0.15 to 2.0. The pH of the solution is adjusted to be at least 8 by the addition of ammonia molecules and hydroxyl ions. The solution is heated to a temperature between 70 C. to 80 C. to permit electroless deposition to proceed upon the catalytic surface.

This invention relates to the electroless deposition of ferromagnetic metals and, more particularly, to the method and bath for electrolessly forming ferromagnetic metals such as cobalt and cobalt-base alloys that are characterized by a unique combination of magnetic properties.

Ever since A. Brenner and G. E. Riddell reported the electroless plating of nickel on steel by chemical reduction in The Journal of Research, Nat. Bureau of Standards, volume .37, p. 1 (1946), both the academic community and industry have expended consideable effort in the study and development of the technique. While a variety of other techniques are available for forming ferromagnetic metals, electroless plating has several inherent advantages: electroless solutions have nearly perfect throwing power and yield uniform deposits on com plex geometries; the resulting deposits are more pore-free than electrodeposits; and, thirdly, non-conductive substrates are more readily prepared for the reception of electroless deposits than for electrodeposits.

The term electroleess plating, coined by the original inventors of the process, has been Widely accepted as designating that process wherein a metal or alloy is deposited by autocatalytic chemical reaction. The process entails, briefly, dissolving one or more salts of the constituents desired in the deposit in an aqueous solution containing a reductant; thereafter a catalytic surface is immersed in the aqueous solution. The reaction begins spontaneously at the catalytic surface and the dissolved salts yield a metal deposit thereon. The deposited metal catalyzes the reaction, causing it to continue autocatalytically. Thus, in addition to the heretofore mentioned inherent features of the process, electroless plating dispenses with the need of an electric current such as that required in electrodeposition.

One area of technology where electroless plating would appear to offer both the scientific and commercial advantages over other known techniques is that of forming magnetic materials. With the advent of the electronic computer and micro-electronic circuit networks, industry has been seeking a means for producing ferromagnetic deposits that exhibit a unique combination of squareness and coercivity characteristics, with the further requirement that the process yield such a product with a high degree of reliability and reproducibility. While some success has been realized with ferromagnetic deposits having high squareness and preselected coercivities, particularly where the coercivities are less than 10 oersteds or greater than 200 oersteds, much remains wanting in the production of ferromagnetic electroless deposits having high squareness and coercivities in the range between 20 and 200 oersteds. Since ferromagnetic materials having these characteristics find large usage in switching networks and hysteresis motors, it has been an object of considerable research, therefore, to provide ferromagnetic cobalt and cobalt-base alloys from an electroless process offering device predictability and reproducibility in the magnetic properties.

It is therefore a primary object of this invention to provide an improved electroless plating process for forming ferromagnetic deposits of cobalt and cobalt-base alloys characterized by a unique combination of magnetic parameters.

It is still a further object of this invention to provide an aqueous electroless plating solution, which plating solution yields cobalt and cobalt-base alloys characterized by a unique combination of magnetic properties.

It is still a further object of this invention to provide an improved process for electrolessly depositing ferromagnetic cobalt and cobalt-base alloy deposits having high squareness and predetermined magnitudes of coercivity.

It is yet another object of this invention to provide an electrolessly deposited cobalt and cobalt-base alloy characterized by a unique combination of magnetic properties.

It is still a further object of this invention to provide an economical and commercially feasible process for electrolessly forming ferromagnetic deposits of cobalt and cobalt-base alloys exhibiting predetermined magnetic properties.

These and other objects are realized with an improved electroless plating solution that contains an alkaline aqueous solution of cobalt ions, a ligand, which is a saturated unsubstituted short chain aliphatic dicarboxylic anion, hypophosphite ions and ammonia molecules, wherein in said solution the molar ratio of cobalt ions to ligand is essentially 1, and, further wherein the molar ratio of cobalt ions to hypophosphite ions is between 0.15 to 2.0 but preferably between 0.30 to 1.0 and desirably is 0.63 and the initial pH is at least 8 and preferably at about 9. The solution once formed to conform to the above is then heated to a temperature between 70 C. to 80 C. and preferably .to a temperature of about C. A catalytic surface which is selected from the group consisting of titanium, iron, nickel, palladium, platinum, and the like, is immersed in the solution. Of course it will be recognized by those versed in the art that non-catalytic surfaces such as non-catalytic metals and non-metallics may undergo the beneficial treatment as heretofore defined provided the surface of the non-catalytic material is first sensitized by producing a film of one of the catalytic materials on its surface. A variety of techniques are available and are well known to those skilled in the art.

The catalytic nature of the surface causes the reaction to begin spontaneously thereby depositing metal on the surface. That metal that is deposited now acts as a catalyst and maintains the autocatalytic nature of the reaction. At the solid-liquid interface, the cations, which are cobalt ions, receive electrons from the reductant which, in the instant case, is the hypophosphite (ions) and thereafter adhere as metal atoms onto the surface of the catalytic material. With the electroless solution and with the electroless process as described, cobalt coatings and films are deposited on the catalytic surface that are characterized by a coercivity in the order of 110 to 135 oersteds accompanied by a squareness ratio of about 1.

When electrolessly plating cobalt from an alkaline solution, the presence of a compound-forming water soluble cobalt complex is necessary in order to inhibit the precipitation of the cobalt as a hydroxide or hyp'ophosphite: the addition of selected concentrations of ammonia or ammonium salts, which may form a cobalt hexammine complex ion, arrests the precipitation of the cobalt cation as a hydroxide or phosphorus compound. Furthermore, the ammonia or ammonium salts act as a buffer, assist in regulation of pH and provide a ready reservoir for the ammonium ions required in the electroless plating reactions. Similarly, the activity of the hypophosphite ions is regulated by the adjustment of the free alkali content as measured by the hydroxyl ion concentration of the solution, which is accomplished, in the present case, with the addition of ammonium hydroxide, sodium hydroxide, or the like. Also, any water soluble salt which is not antagonistic to the plating process and may furnish the cobalt cations such as in the form of sulfates, acetates, chlorides, sulfamates, or mixtures thereof, may be used.

But while the cobalt cations, hydroxide anions, and ammonium salts may be derived from a variety of water soluble salts, the selection of the complexing agents, pH, and plating temperature, is severely limited if the objects, in accordance with the present invention, are to be realized. While prior art cobalt electroless plating solutions use any of a number of complexing agents such as organic complex forming agents containing one or more of the following functional groups: primary amino group (NI-I second amino group NH), tertiary amino group N-), imino group (=NH), carboxy group (COOH) and hydroxy group (OH), it is both a necessary and essential condition in the practice of the present invention that the complexing agent is a soluble salt of a simple short chain aliphatic dicarboxylic acid, and, preferably comprising the malonate or succinate ion. Of course, in conjunction therewith, the initial pH of the solution is regulated to lie above 8 while the plating temperature is maintained in the range between 70 C. to 80 C.

The prior art electroless solutions, as indicated heretofore, have, in the past, employed complexing agents which comprise saturated soluble salts of unsubstituted short chain aliphatic carboxylic anions; the activity of the complexing agent was regulated by controlling the number of carboxyl groups introduced into the solution. Thus, free substitution of monocarboxylic acid salts was made with dicarboxylic acid salts by using one-half the molar concentration of the latter to replace the former. Where the substitution was made with a carboxylic acid salt containing three or more carboxylic groups, the concentration of the higher order carboxylic acid salts was maintained to provide the same number of carboxylic groups as that obtained with the monocarboxylic acid salts. Now it is surprisingly discovered that where magnetic properties are sought, it is critical that the complexing agent comprise a dicarboxylic acid salt, replacement of that complexing agent with a monocar'ooxylic acid salt, or a higher order carboxylic acid salt containing more than two carboxylic groups as previously taught in the art even where the molar ratio of the carboxyl groups is maintained constant, does not result in the magnetic properties obtained with the dicarboxylic acid salts.

While it is not fully understood as to why the saturated unsubstittued short chain aliphatic dicarboxylic acid anions are important, a working hypothesis has been formulated: it is believed that electroless plating reaction comprises a series of three competing reactions which include hydrogen evolution, metal deposition, and phosphorus deposition, and that of the three reactions, the evolution of hydrogen and deposition of phosphorus remains consant. Thus, the addition of the ligand, the complexing agent containing the carboxyl groups, is effective only in changing the rate of deposition of the cobalt and is essentially ineffective as to the other two reactions. Further, it is found from experimental and analytical consideration that where the ligand contains higher order carboxyl groups, that is, more than two, the rate of deposition of metal on a catalytic surface is impeded, resulting in a high phosphorus containing film and high coercivities. On the other hand, it is found that where the ligand is a monocarboxylic acid anion, that essentially spontaneous decomposition of the electroless solution takes place providing little if any control over the ultimate magnetic properties. But, where the ligand is selected from saturated unsubstituted short-chain aliphatic dicarboxylic anions, such as those that comprise the malonate and succinate ions, the octahedral structure that the cobalt cation forms during the plating reaction is just sutficiently distorted such that the cobalt is deposited under precisely those conditions that result in square loop properties accompanied by coercivities in the range between and oersteds. Accordingly, the present invention provides electroless cobalt deposits heretofore not available in the art.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a graphical representation of the hystersis characteristics of e ectrolessly deposited cobalt in accordance with the invention wherein the absicssa of said graph is the driving field (H) in oersteds and the ordinate is magnetic flux density (B) in gauss.

FIGURE 2 is a graphical representation of the effect Of the aliphatic dicarboxylic anion on coercivity (H and phosphorus (P) content wherein the abscissa of said graph is the anion in grams per liter and the ordinate is coercivity (H in oersteds.

FIGURE 3 is a graphical representation of the effect of temperature on the pH of the solution wherein the abscissa of said graph is the pH and the ordinate is the temperature in degrees centigrade C.).

Now, more particularly as to the formation of an electrolessly deposited cobalt or cobalt-base alloy, in accordance with the present invention, reference is made to FIG- URE 1 to facilitate the description of the magnetic roperties sought. Squareness is defined as the ratio of the remanent magnetic flux density point B on the graph to the saturation magnetic flux density B on the graph: that ratio is, for convenience, designated B /B For many computer and micro-electronic applications, it is desirable, and, in many instances, essential, to have a B /B ratio of 1 or thereabout. In practical effect, a magnetic deposit having a hysteresis loop With such a squareness ratio indicates that the material has high magnetic remanence or retentivity. What this means is when the material is magnetized in one direction by an applied magnetizing force, the material remains magnetized in that direction, even after the magnetizing force is removed, i.e., it remembers the flux direction. Similarly, when a magnetizing force is applied in the opposite direction and then removed, the material similarly remains magnetized in the opposite direction. Note that there is an abrupt transition between flux in one magnetic state and the flux in the opposite state. The material has the unique property of remembering which of the two states it was driven into. In each state the remanent flux is nearly equal to the saturation flux of the material and is accordingly characterized as a square loop material.

A second magnetic property which is of interest in evaluating materials for computer and micro-electronic applications, is that of coercive force, the value of the H parameter along the abscissa of the graph when the magnetic flux (B) is equal to 0. That parameter, coercive force, designated H is an indication of the resistance of the magnetic dipoles to realign themselves under the action of an applied field. The magnetic parameters of remanent magnetic flux density B (the value of the magnetic flux density when H is equal to 0), the saturation magnetic flux density B the squareness ratio B /B and coercivity H are significant parameters by which to evaluate the suitability of the magnetic material for many applications.

In carrying out the electroless plating process, the article that is to receive the electroless deposit, that is, the catalytic substrate, is properly prepared prior to electroless deposition by mechanical means and degreasing techniques according to the standard practice of the industry. Now, where the material that is to receive the electrolessly deposited cobalt is copper or copper alloy, the substrate is then further prepared by dipping the same in a bydrochloric acid solution for about 30 seconds which is maintained at room temperature. Then the substrate is activated by dipping it in a 0.1 gram per liter palladium chloride solution for about seconds which is also maintained at room temperature.- The substrate is then ready for receipt of the electroless cobalt deposit.

Non-metallic substrates such as plastic, ceramics and glass, are generally hydrophobic, that is, they have a surface which generally repels water, and accordingly it is necessary to activate the surface to render it hydrophilic, that is, a surface that tends to absorb water. The technique for performing this is well known in the art. Generally, the technique entails mechanically roughening the material with an abrasive or the like. Thereafter chemical etching is used to further condition the surface and activate nucleation sites over the surface. In the case of a polyethylene terephthalate web, for example, a conditioning treatment such as that described in US. Patent 3,142,- 582 to Koretzky et al., or that described in Us. Patent 3,142,581 to B. Leland, are employed in the pretreatment of the surface for electroless plating.

The surface roughness and etching treatments are then followed by sensitizing treatments. This entails immersing the substrate in stannous chloride; the stannous ion is absorbed onto the surface of the substrate during the immersion and the absorbed stannous ion is readily oxidized. The substrate is then dipped into a second solution containing a noble metal such as palladium, and the palladium is reduced and absorbed onto the surface of the substrate. Thereafter the palladium acts as a catalytic site for electroless deposit that is subsequently plated onto the substrate.

The phrase catalytic surface is hereafter used to denote and connote a surface or substrate which is inherently catalytic when immersed in the electroless solution or one that is treated to act as such, as heretofore discussed.

The substrate is then ready to undergo electroless plating. The electroless plating solution contains an alkaline aqueous solution of cobalt ions, which cobalt ions are derived from any suitable soluble salt such as cobalt chloride, cobalt sulfate, cobalt acetate, or cobalt sulfamate. To this is added ammonium sulfate, (or other ammonium salts whose anion corresponds to the anion carrying the cobalt) which, as indicated heretofore, functions as a buffer, assists in the regulation of the pH of the bath, and further provides a ready source of ammonia molecules which are required for the plating reactions. Thereafter, a ligand is added, which ligand is a saturated unsubstituted short chain aliphatic dicarboxylic anion and comprises malonate or succinate ions or combinations thereof, with the molar concentration of the cobalt ions to the ligand ions being maintained at essentially 1. Then hypophosphite ions are added to the solution and are introduced :into solution as an alkaline hypophosphite. It is important that the molar ratio of cobalt ions to hypophosphite ions lie between 0.15 to 2.0 but preferably between 0.30 to 1.0 and desirably at about 0.63. The initial pH of the solution is then adjusted to lie above 8, and, preferably above 9, by adding ammonium hydroxide or the like to the solution which acts as a source of hydroxyl anions. The solution is then heated to a temperature between 70 C. to 80 C. and preferably to a temperature of about 75 C.

to effectuate the electroless deposition of the cobalt onto the catalytic substrate.

As heretofore indicated, it is important that the ratio of cobalt ions to ligand ions is essentially l and that the ratio of cobalt ions to hypophosphite ions is in the range between 0.15 to 2.0 if the desired squareness and coercivity are to be realized. The significance and import of maintaining the molar ratio of the cobalt ions to the ligand ions at essentially l and the molar ratio of cobalt ions to hypophosphite ions in the range between 0.15 to 2.0 is brought out by FIGURE 2 above. There, it is noted, a graphical representation is presented, wherein the abscissa has plotted thereon the concentration of ligand in grams per liter while the ordinate thereof is a plot of coercivity in oersteds. The upper curve, which is shown as a continuous line, is a plot of coercivity against ligand concentration and that curve has a valley at essentially that concentration where the molar ratio of cobalt ions to ligand ions is about 1. Note that where the ratio of cobalt ions to ligand ions changes from one, the magnitude of the coercive force rapidly increases. Thus coercivities in the range between to 135 oersteds are only available when the molar concentration of the cobalt ions to the ligand anions is maintained at essentially 1.

Also plotted in FIGURE 2 is phosphorus content against ligand concentration. The abscissa is again the concentration of ligand, in grams per liter, but now the ordinate (which is brought out by the scale at the right side of the plot) is phosphorus content of the resulting film in weight percent. That curve is shown in phantom; it is to be noted that a similar minimum occurs for phosphorus content as occurred for coercivity.

To further illustrate the import of the molar concentration of the cobalt ions to the ligand ions, and the molar concentration of the cobalt ions to the hypophosphite ions, typical electroless plating solutions are given below in Examples I through IV. The resulting variance of coercivity and phosphorus content with ligand concentration for each of the examples is presented in Tables I through IV, each of the tables corresponding to the specific example depicted directly above the table.

EXAMPLE I CoSO -7H O 34.5 gm./l.+(281.10)E0.12 M (NH4)2SO4 66.0 gm./l.:-(l32.l4) 50.50 M NaH PO -H O 20.0 gm./l.:-(105.99)E0.19 M crrgcoorn 0-30.0 gm./l.+(104.06)500.29 M

TABLE I Column N o.

EXAMPLE II TABLE II Column No.

EXAMPLE III TABLE III Column No.

EXAMPLE IV Co (NH SO 30.6 gm./l.:- (250.93 50.12 M NH ,(NH SO 39.5 gm./l.+(114.12) 20.34 M NaH PO H O 20.0 gm./l.-:-(105.99) 50.19 M CH (COOH) 0-300 gm./l.-:(104.06) -029 M TABLE IV Column No.

In the tables presented, the first column of each gives the amount of cobalt salt added, in grams, and the second column presents the amount of cobalt salt added in terms of the number of mols of the cobalt cation made available to the plating reaction. The third column gives the weight of ligand added to the bath while the fourth column presents this, in terms of the number of mols of ligand anions released to the solution. The fifth column of the Table presents the ratio of the molar concentration of the cobalt cations to the molar concentration of the ligand anions. In the sixth column, coercivity, in oersteds, of the resulting electroless deposit is presented, while in the seventh column is found the weight percent of phosphorus observed in the resulting electrolessly deposited films. It is readily apparent that coercivity is a minimum only when the ratio of the molar concentration of cobalt cations to the molar concentration of ligand anions is maintained at about 1. In the examples given, the initial pH of the solution was 9 and was adjusted to this level by adding NH OH to the solution. Thereafter, the electroless solution was heated to a temperature in the range between C. to 80 C. and the electroless plating of the catalytic surface permitted to take place. During the plating process, the solution was maintained in a quiescent state (no agitation) and the catalytic surface immersed in the electroless solution for a period between 30 seconds to about 5 minutes. But, for optimum conditions, it has been found from experience that it is preferable to maintain the electroless solution at a temperature of about C. and immerse the catalytic surface therein for a period of about 1 minute.

Under the conditions heretofore given, it is to be noted that along with the desired coercivity that the electroless deposit exhibits a squareness ratio B /B of about 1. Acceptable thicknesses of electroless deposit vary from 250 to 3750 Angstroms while the remanent magnetic flux density 13,. at the desired coercivity is about 11 kilogauss and the saturation flux density B is also about 11 kilogauss:

That these magnetic characteristics are obtainable with an electroless solution containing a ligand which is a saturated unsubstituted short chain aliphatic dicarboxylic anion is shown above wherein the anion utilized was the malonate ion. It will be readily recognized to those versed in the art that similar results are obtainable with the succinate ion. For example, with an electroless solution containing 34.5 grams per liter (0.12 mol) of cobalt sulfate, 66 grams per liter (0.50 mol) ammonium sulfate, 20 grams per liter (0.19 mol) sodium hypophosphite, and 14.2 grams per liter (0.12 mol) succinic acid, provided an electroless deposit on a catalytic surface having a squareness ratio B /B of essentially 1 and a coercivity of about 130 oersteds; plating was conducted under the conditions as heretofore described.

In FIGURE 3 above, the variance of pH with temperature is shown. The abscissa of the graph is pH while the ordinate is temperature in degrees centigrade C.). What the plot indicates is that the pH of the solution decreases with increasing temperature. It is found that it is most advantageous to maintain'the pH at about 9 and electrolessly plate at a temperature of about 75 C. but satisfactory results are obtained when the pH is above 8 and the plating temperature is maintained in the range between 70 C. to C. However, it is found that where the temperature of plating exceeds C. that excessive volatilization of the ammonia takes place, thus depleting the bath and upsetting the required chemical reactions.

What has been described is a method and electroless solution for electrolessly depositing cobalt and cobaltbase alloys on a catalytic substrate such that the resulting electroless deposit exhibits a squareness ratio (B /B of about 1 and which squareness is accompanied by coercivity (H in the range between to oersteds. That to obtain these results it is both a necessary and an essential condition of the electroless plating solution or process that the electroless solution contain a ligand, which ligand is derived from a saturated unsubstituted short chain aliphatic dicarboxylic anion wherein the molar ratio of the cobalt cation to ligand anion is essentially 1. Further, it is shown that the electroless solution in order to yield these desired results must contain hypophosphite ions so that the molar ratio of the cobalt cations to hypophosphite anions is preferably at about 0.63 although satisfactory results are obtained when that ratio is maintained in the range between 0.15 to 2.0. This is accomplished with a plating rate which varies from about 1500 A./min. to about 400 A./min. and with a plating time that spans a range from about 30 seconds to about 5 minutes. It should be noted, however, that as the hypophosphite ion concentration increases the peaking rate increases, the percent of phosphorus obtained in the resulting electroless deposit increases, but that solution stability decreases. Accordingly, the molar ratio of cobalt to hypopl1osphite ions is important. Further it is shown that the desired electroless deposit which contains 0.15 to 3.0 weight percent phosphorus with the balance cobalt and with the preferred composition containing 0.2 percent by weight phosphorus with the balance cobalt is obtained only when the electroless plating parameters are regulated as heretofore described.

While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other advantages in form and detail may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A process for electrolessly depositing magnetic cobalt and cobalt-base alloy films on a catalytic surface, said films having a coercivity in the range of from about 110 to about 135 oersteds and a squareness ratio B /B of essentially 1 comprising contacting said surface with an aqueous solution consisting essentially of cobalt ions, hypophosphite ions and a ligand wherein said ligand is selected from the group consisting of malonate and succinate ions, further wherein the molar ratio of cobalt ions to ligand anions is essentially 1 and further wherein the molar ratio of said cobalt ions to hypophosphite ions is between 0.15 to 2.0; and,

adjusting the initial pH of said solution to lie at at least 8 with the addition of ammonia molecules and hydroxyl ions, and, thereafter heating the solution to a temperature between 70 C. and 80 C. to permit the electroless deposition to proceed upon the catalytic surface.

2. A solution for electrolessly depositing magnetic cobalt and cobalt-base alloy films on a catalytic surface wherein the electroless deposit is characterized by a squareness ratio B /B of essentially 1, and a coercivity which lies in the range between 110 to 135 oresteds, wherein said solution consists essentially of:

an aqueous solution of cobalt ions, hypophosphite ions,

hydroxyl anions, ammonia molecules and ligand, where said ligand is a saturated unsubstituted aliphatic dicarboxyl anion which is selected from the group consisting of malonate and succinate ions, wherein the molar ratio of said cobalt ions to said ligand ions is essentially 1 and further wherein the molar ratio of said cobalt ions to hypophosphite ions lies between 0.15 to 2.0 and further wherein the pH of said solution is at least 8. 3. The process of claim 1 wherein said aqueous solution contains ammonia molecules and hydroxyl anions. 4. The process of claim 1 wherein said molar ratio of said cobalt ions to hypophosphite ions is maintained at about 0.63 and said solution is heated to about 75 C.

5. The solution of claim 2 wherein said molar ratio of cobalt ions to hypophosphite ions is about 0.63.

References Cited UNITED STATES PATENTS 2,942,990 6/1960 Sullivan 106-1 3,138,479 6/1964 Foley 106-1 XR 3,238,061 3/1966 Koretzky et a1 106l XR 3,245,826 4/1966 Luce et al. 1l7130 3,269,854 8/1966 Hei 11771 XR JULIUS F ROME, Primary Examiner. L. HAYES, Assistant Examiner.

U.C. Cl. X.R.

Images