US2320442A - Electroplating equipment - Google Patents

Description

June 1, 1943. A. E. MAIBAUER ELECTROPLATING EQUIPMENT Filed July 28, 1939 INVENTOR ALBERT E. MAIBAUER BY Z ATTORN EY 'ctented June 1, 1943 UNITED STATES PATENT OFFICE:

2,320,442 nnac'mormrnvc. EQUIPMENT Albert E. Maibauer. Travis, Staten N. I,

assignor, by mesne" assignments. to Union Carbide and Carbon Corporation. New York, N. Y., a corporation oi New York Application July as, 1939, Serial Nb. 287,054

6 Claims. (01.204-297) This invention relates to the art of electroplating and electroplating equipment and insulation practice, however, electroplating is a procedure which requires extremely close attention and fine regulation to produce an acceptable plated' deposit in view of the complicated chemical reactions taking place within the electrolyte as well as at-the electrodes; for example the composition of the electrolyte must be maintained within close limits and variations in the temperature, current density, etc. change the character of the deposit.

In commercial electroplating a number of the objects to be plated are frequently afilxed to a rack of a conducting metal,and the entire rack is immersed in the plating bath. It is a practical necessity that the racks be insulated else the plating process cannot satisfactorily be controlled and will be uneconomical as the plating metal will deposit on the rack which wastes the plating metal and current used to deposit it, shortly renders the rack unserviceable and renders it difflcult for the plater to determine how much of a deposit has occurred on the articles which it was intended to plate. Among other difllculties, the metal of an uninsulated rack may dissolve in the plating bath and ruin it.

Various insulating media for racks have been tried and described in the literature. These include lacquers and it would seem relatively simpie to insulate a rack merely by dipping it into an insulating lacquer or varnish or spraying or painting the lacquer on the rack and then permitting the coating to harden. In practice, however, lacquers leave much to be desired from the standpoint of economical application to the racks and operation of the racks after the lacquer is applied. Lacquers and varnishes usually contain volatile solvents for the gums or resins which deposit when the solvent evaporates, but the evaporation of the solvents may leave pin holes in the coating and thus numerous applications or the lacquer are frequently required and between each application it is often necessary to process the rack very carefully by air-drying and baking (see the United States patent to. Herzog No. 2,072,170, March 2, 1937), as any solvent remaining thecoating will expand andiorniblisters which eventually disrupt the coating. Even with this care the coated rack is not as satisiac-I tory as is desired'since the coating may beuneven; it is diilicult to apply an even coating by spraying or painting and'when a dipped'rack is hung up to. drain the coating is always thinner on the upper parts 0! the rack and on the upper surfaces 01 the rack bars than on the lower. Thus a lacquer coated rack is not the ultimate in such devices.

With regard to thematerials used for coatingthe racks there are numerous desid'erata among which are that'the coating material must not contaminate the bath and-11; must be as tough as possible, be substantially unafiected by acids or alkalis. have suitable electricalinsulating properties and must maintain these characteristics at relatively high temperatures as well as at low temperatures. One of the most suitable bases for coatings is a copolymer 0! vinyl chloride or vinyl benzene and vinyl acetate containingfrom 50% to of vinyl chloride or vinyl benzene and from 50% .to 5% of vinyl acetate. Other vinyl halogen esters or vinyl aryl esters and vinyl esters or the lower aliphatic acids, that is acids containing from two up to five or six carbon atoms may be used. But even these basic materials require modification for the most satisi'ao tory stop-offs. In practical electroplating the racks are subjected toa great deal or rough han-' dling and temperature change and the insulation has to withstand all of these. For instance, the racks are subjected to abrasion when they are handled after insulating and during use and they are subjected to hot electrolyte and hot cleaning solutions and cold water washes, yet the insulation must-not break through nor loosen from the rack during'the handling nor may it crack when it is subjected to cold water-while the metal of the rack is hot and in an expanded condition nor may it loosen from the rack when it is sub- Jected to hot electrolyte while the rack is still cold and in a contracted condition. Another dif-- flculty with using an unmodified vinyl copolymer is that the baked, unmodified copolymer is in a harder, more brittle and stiffer condition and the coated rack is less satisfactory for practical use.

The accompanying drawing shows a plating rack embodying my invention. In the drawing,

Fig. 1 is an elevation of a partially insulated rack;

Fig. 2 is a section on line 2-2 oi. Fig. 1, viewed in the direction of the arrows;

with an insulating tape I2, the composition of which is important and includes the modified copolymers of vinyl compounds. The tape contains no readily volatile solvents and is not porous nor do pin holes develop in it; thus the electrolyte does not contact the rack. The tape is elastic and has elastic recovery so that when wrapped around the rack under tension, it contracts and presses against the parts of the rack with such pressure that the electrolyte cannot seep between the insulation and the metal of the rack. The tape also has such flexibility and yield that when it contracts onto the parts of the rack any irregularities the rack, for instance nodules or tool marks are covered or filled in, thus permittingthe use of a rack which is merely a rough casting or'a'roughly machined part. The tape isa decided improvement over a lacquer which would produce an extremely thin coating, if any, on the point of a nodule or on'the ridge or burr left by rough machining. Furthermore, the preferred tape has the characteristic that one edge can stretch withoutstretching the other edge or can stretch more than the other edge and this, in conjunction with the elastic recovery, permits the tape to be wound around angles H in the rack and give a smooth non-puckering edge IS on the short side of the turn. The elastic recovery of the tape also obviates the necessity of using primer coatings on the rack which have heretofore been required to make lacquers of the vinyl copolymers adhere to the metal of the rack, as the tape contracts around the rack bars and remains in place on the bars even though there is no primer. does not lose its elasticity and elastic recovery even though heated and cooled and this is of distinct advantage when the racks are submitted to alternate heating and cooling as the tape will hug the metal of the rack and remain sealed against it when the rack is transferred between a hot electrolyte or cleaning bath and a cold wash water. A further advantage of a contractible tape is that at certain parts [9 of a rack, for instancewhere the article to be plated (or its support) makes electrical contact with the rack, it

' insulation and rack. In addition to the foregoing features a rack may be insulated more thoroughly, easily and quickly with tape than with lacquer. With a tape it is necessary only to wrap the rack with the tape, preferably with the edges of successive convolutions of the tape overlapping. This may be done very quickly and easily and all surfaces of the rack may be insulated equally and thoroughly whereas with a ,lacquer the tops of the rack bars and the points of the nodules as well as other parts where the lacquer runs off. have extremely thin insulating coverings. The tape may be and preferably is sufficiently thick, say from 5 to 15 mils. that a single wrapping on the majority of the rack is Another feature of the tape is that it all that is necessary but a further advantage of tape as compared to lacquers is that several tape layers may expeditiously be applied where desirable, for instance where the breaks I8 in the insulation are necessary for contact purposes and at the corners 22 of the racks where abrasion and other mechanical injury may occur. An electroplating rack has been used to illustrate this phase of the invention but the tapes may also be used with other articles of electroplating equipment which are in the form of bars or tubes so that they may be wrapped and advantage taken of tapes as distinguished from lacquers and large sheets used to cover fiat surfaces; in fact the characteristics of the'tapes, previously referred to, which give them a decided advantage over lacquers on surfaces which can be wrapped are somewhat of a disadvantage or are of no benefit if large sheets are applied to flat surfaces as the sheets, if applied under tension would draw away from the edges'of flat surfaces leaving the edges exposed to the electrolyte, and also the elastic recovery of the material is of no advantage in holding a sheet against a plane surface to prevent electrolyte or cleaning solution from working in between the surface and the sheet.

With regard to the composition of the tapes, they are, aspreviously stated, based on the vinyl copolymers, but these require modification for the most satisfactory stop-offs to obtain the maxi mum desirable physical and chemical characteristics noted herein and a minimum sealing temperature. crease in molecular weight due to polymerization, thinfilms thereof become increasingly brittle and fragile and the unmodified copolymers also become increasingly hard, stiif and unworkable at ordinary temperatures, and their solubility decreases. If unmodified and in the state of polymerization where they are soluble they may be strong and non-brittle in thick molded pieces somewhat as glass is, but in thin films such as are deposited from lacquer they are quite fragile and easily break and shatterundcr a blow. Thus racks covered with lacquer films of the unmodified polymers cannot long endure the handling they receive in practical factory use. It is obviously desirable for the best stop-offs to retainthe vinyl copolymers in their best operable condition for as long a. time as possible. But it is necessary in modifying the vinyl copolymers that the modifying agents be such that they do not contaminate the electrolyte nor substantially affect the plating operation.

I have found that the group of modifiers suit able for admixture with the copolymers to give the composition the desired characteristics is rather limited. In general they should contain an aryl group or lead which contribute to inertness in an electroplating bath, or the phosphate radical which appears to do no particular harm to electroplating baths, or a radical which partakes of the nature of the copolymers. ifiers should also be insoluble in water. Thus a modifier may be triphenyl phosphate (including thereby homologs) which combines aryl groups with the phosphate radical and is characterized by water insolubility, or an organic phthalate ester for instance a butyl, amyl, etc. phthalate or dibutoxy ethyl phthalate which contain an aryl group, or a lead salt or oxide, for instance lead stearate, lead oxide or lead abietate, which arequite inert, or cyclohexanol acetate which partakes of the nature of the acetate in the copolymer or chlorhydrin phthalate which partakes of As the unmodified copolymers in- The modthe nature of the chloride of the copolymer and also contains an aryl group.

It has also been found desirable to use a low molecular weight copolymer to modify a high molecular weight polymer. The low molecular weight polymers, when thoroughly incorporated with the high molecular weight polymers, do not render the high molecular weight polymers fragile as would ordinarily be expected but they do enable the overlapping edges of the tapes to seal against one another, this action being assisted by such modifiers as tricresyl phosphate which imparts a certain amount of adhesiveness to the tape particularly at elevated temperatures although leaving the surface substantially nontacky at room temperatures. Thus the tape is characterized by such a dry surface at room temperature that it does not adhere to a person's hands and can easily be wrapped on a rack yet at elevated temperatures, say from 100 C. to 140 C.

or when wet with an adhesive or a solvent for the low molecular weight polymer one surface of the tape will seal against an overlapping tape surface effectively to prevent leakage of the electrolyte between the surfaces. The mechanical contraction of one layer of tape on the other at room temperatures combined with the adhesiveness of the tape surfaces toward each other (even though substantially dry to a person's hands) is sufficient to seal against the electrolyte even at room temperatures but a substantially impervious seal is obtained under the influence of heat, adhesive or solvent as previously described.

Of the modifiers which may be used with the high molecular weight polymers, the low molecular weight polymers plastify the high molecular weight polymers and enable the tapes to seal without substantially aifecting other properties, the tricresyl phosphate plastifies while increasing the tackiness of the surface as previously described, the lead compounds stabilize the mixture and the phthalates plastify while leaving the surface dry.

The foregoing and other objects and features of the invention will in part be obvious and in part will be pointed out in the following claims and description of a manner in which the tapes may be made and applied to electroplating racks. It is to be understood, however, that the description is for illustrative purposes only and that the invention is not to be limited strictly thereto.

In making the tape from 90 to 180 parts (by weight) of a copolymer containing 95% vinyl chloride and vinyl acetate and a molecular weight from approximately 22,000 to 24,000, and from 350 to 630 parts of a copolymer containing 80% vinyl chloride and vinyl acetate and a molecular weight of approximately 9,000 (molecular weights being calculated according to the Staudinger formula from dilute solutions of the resins) are thoroughly incorporated with from 140 to 266 parts of tricresyl phosphate, about parts of lead abietate and from 32 to 61 parts of diamyl phthalate, the larger amounts of plastifying modifier being used with the larger parts of the high molecular weight vinyl copolymers to give tapes having such characteristics of elasticity, adhesiveness, softening temperature, etc. as are desired. After thorough incorporation, tapes may be formed from the mass either by extrusion, casting or milling. The tapes from 5 to 15 mils. in thickness and from to 1 inches in width have been found satisfactory in practical electroplating use but other thicknesses and widths may be used if desired.

more on one edge than on the other and to stretch more at the center than at the edges, a

smooth and non-puckered covering may be had on the corners and where side bars join the main stem of the rack, even in the angles of the junctures the freedom from puckers permits a tight seal. sired, be subjected to heat which softens the tape somewhat although it does not destroy the contraction of the tape on the rack bars. The softening of the tape combined with its contraction causes the overlapping edges to seal against each other. The heat may be applied in any suitable manner for instance by immersing the rack in hot oil or inserting in an oven for a few moments for instance 15 minutes at 245 F. or by fanning with a blow torch. The heat is preferably merely a flash heat sufficientto soften the tape and no prolonged air drying or baking to remove solvent is necessary or desirable and the covering is not porous after the heat treatment. The tapes offer a practical advantage in effecting repairs if the covering becomes broken; for instance a patch of the tape may easily be applied by pressing one end of a section of new repair tape on the old tape which is already on the rack, somewhat be-. yond the break. The new tape and the old may be united firmly by fanning with a blow torch. The patching tape may then be stretched tightly over the break or wound over the break and while held in position may be sealed in place with the blow torch. Repairs are thus effected very easilyand quickly.

As the electroplating racks are almost invariably of metal which absorbs heat quite readily and the tapes do not conduct heat very readily, it will be seen that when a taped rack is subjected to heat, the highest tape temperature will be obtained at the overlapping edges of the tape where there are two thicknesses of tape and where sealing of the tape is desired.

If desired, the taped rack may be given a superficial treatment with a solvent for the low molecular weight component of the tape, for instance acetone or methyl ethyl ketone, or with a lacquer comprising a copolymer and a solvent. The solvent or lacquer softens the exposed overlapping edge and effects a seal but does not affect the tape to any appreciable depth. Thus the main body or interior portion of the tape is not affected and draws the overlapping edges together and any porosity resulting from the evaporation of the solvent is merely on the surface. The solvent or lacquer may be applied in any of the usual ways, for example by spraying, painting or dipping but dipping in a pure solvent or very thin lacquer is preferred and the rack should merely be plunged into the liquid and immediately withdrawn to wet the surface of but not soak the tape, and the solvent should be quickly evaporable as those mentioned above. It may here be remarked that if, for any reason, it is desirable to use a lacquer to coat parts of electroplating equipment, a solution of a soluble copolymer including the previously dis- In using the tape, the plating rack is merely After the rack is wrapped it may, if de-' closed modifiers has been found to be better than the mere solution of the copolymer.

I claim z,

1. Electroplating equipment to be subjected to 'halides and vinyl benzene, said tape being wrapped under tension on the part with the turns overlapping, the insulation on said part being substantially impervious to said electrolyte.

2. Electroplating equipment to be subjected to electrolyte including a part insulated from said electrolyte with a stretched elastic tape consisting essentially of a plasticized copolymer of vinyl chloride and vinyl acetate, said tape being wrapped under tension on the part with the turns overlapping, the insulation on said part being substantially impervious to said electrolyte.

3. Electroplating equipment to be subjected to electrolyte including a part insulated from said electrolyte with a stretched elastic tape consisting-essentially of a plasticized copolymer formed from a vinyl ester of an aliphatic carboxylic acid having from two to six carbon atoms with a member of the group consisting of vinyl halides and vinyl benzene, said tape being impervious to the electrolyte and wrapped under tension on the part.

4. Electropl'ating equipment to be subjected to electrolyte including a pluralityyof parts in angular relation to each other and wrapped stretched elastic tape insulation on said parts, said tape consisting essentially of a plasticized copolymer formed from a vinyl ester of an altph'atic carboxylic acid having from two to six carbon atoms with a member of the group consisting of vinyl halides and vinyl benzene, said tape being wrapped on said parts under tension, and the insulation including the copolymer being substantially impervious to said electrolyte and insulating said parts from said electrolyte.

5. Electroplating equipment to be subjected to electrolyte including a part insulated from said electrolyte with a stretched elastic tape consisting essentially of a mixture of high and low molecular weight copolymers formed from a vinyl ester of an aliphatic carboxylic acid having from two to six carbon atoms witha member of the group consisting of vinyl halides and vinyl benzene, said high molecular weight copolymer having a molecular weight between approximately 22,000 and 24,000, said low molecular weight copolymer having a molecular weight of approximately 9.000, said tape being wrapped on said part under tension, and the insulation including said copolymers being substantially impervious to said electrolyte.

6. Electroplating equipment to be subjected to electrolyte including a part insulated from said electrolyte with wrappings of a stretched elas-.

tic tape consisting essentially of a plasticized copolymer formed from a vinyl ester of an aliphatic carboxylic acid having from two to six carbon atoms with a member of the group consisting of vinyl halides and vinyl benzene, a substantially water insoluble plastifier for the said copolymers and a stabilizer for the said copolymers, said plastifier and stabilizer being substantially free from deleterious effect on the electrolyte, said tape being wrapped on said part under tension.

ALBERT E. MAIBAUER.

Images