DE2119353A1 - Composition for an electrodeposition bath and electrodeposition process - Google Patents

Description

Dr. A. Manizel April 16, 1971

DlpUng.W. Dahlke Da.-w / ho

Patent attorneys

Refraih near Cologne
Celestial 137

CANADA WIRE AND GABLE COMPANY LIMITED City of East York, Ontario, Canada

"Composition for an electrodeposition bath and electrodeposition method ¹¹

The invention relates to a composition for a. Electro-plating bath and an electrocoating process.

The electrical servicing is about a. Procedure, in which an observation film is applied to all surfaces of an object is applied by using an electric current to flow between is brought to the object and another electrode,

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while being immersed in a liquid bath containing the coating composition. Usually it acts the liquid bath is an aqueous reading or suspension the coating film components, although non-aqueous liquid suspensions are sometimes used can. The process of electrocoating is now the common way of applying paint to metal objects, such as automobile bodies. Usually the object to be coated is used as the anode, while the bath structure itself is the cathode. Between direct current flows.

In the case of electro-coating processes, the Objects immersed in the dispersion of the coating composition, coated by flowing the electric current and taken out of the bathroom. Excessive coating adhered to the object merely as a result of immersion, remains, is removed, and then, the coated. Objects heated to permanently bond the coating to the object. The coating usually consists of one thermosetting. Resin that turns into a permanent film by firing is cured after it has been applied to the object. An electrocoating process can easily be used for a continuous. Operation to be set up, for example by transporting the to be coated. Objects continuously through the bath and into an oven.

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While the electrocoating process has many advantageous Properties compared to other coating and painting processes brings with it, particularly in terms of the ease of developing continuous work processes and an effective use of the coating composition, there are also problems associated with it. One of the problems is that the finished cured coating of the object tends to be unevenly thick. In particular, the sharp edges and corners of the object generally have a much thinner finish than the remainder of the surface of the article.

The normal way of proceeding to increase the thickness of the coating on the item during electrocoating increase is to increase the amount of current that flows between the electrodes. However, it has been found that which does not result in a thicker final coating of resin on the sharp edges and corners of the item, only the type coating thickness on the other parts of the surface increases. Providing a top coat more adequate Thickness on all surfaces is a goal that is especially important when the coating is an electrical insulation of the object should form.

Ordinarily one might expect the coating thickness at the sharp edges and corners of an object that passes through

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an electrocoating process is actually being coated stronger than the coating on the. smooth surfaces would be. The coating composition preferably accumulates. from the parts of the surface of the object electrode which the highest electrical. Have charge densities, i.e. the sharp ones Edges and corners.

It has been found that the root of the difficulty of adequate edge and corner coverage is not in the real. Electro-coating process lies, but in the subsequent Behavior of the coating before its final. Curing. An adequate coating. the sharp ligaments and Corners are apparently reached in the bathroom, but the film tends to wander away from these bands and corners in time which elapses when the coated object is taken out of the bath becomes and is eventually hardened. This migration can possibly come with the removal of water from the coating film go hand in hand, possibly also with a certain heating stage of the coating film, possibly even with a certain hardening stage of the resin.

According to the invention is a composition for an electrocoating bath provided, consisting of a dilute aqueous Dispersion of 10 parts by weight of a thermosetting resin and 0.001 to 1.5 parts by weight of an essentially insoluble. Silicon dioxide with a surface area of 150 to

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450 m per gram and an average particle diameter of. 0.007 microns to 0.015 microns.

The optimal. Quantities, at. Silicon dioxide that worked with in the bathroom will depend on. the type of thermosetting resin that is used. If so, a water soluble epoxy ester resin is used, the share is due. Silica preferably between about 0.001 and about 0.8 parts by weight per 10 parts by weight. Resin. If you are working with an acrylic resin, that is The proportion of silicon dioxide is preferably about 0.75 to 1.3 parts by weight per 10 parts by weight of resin, the preferred range being between. 0.9 and 1.2 parts by weight. Silicon dioxide lies.

The shares of. Silicon dioxide, which is best in conjunction with an alkyd resin or a styrene-butadiene resin are between about 0.2 and 1.2 parts by weight per 10 parts by weight Resin, the preferred range being between. 0.3 and 1.0 parts by weight. In the case of a tung oil paint, it is best to suitable amounts, between about 0.4 and 0.7 parts by weight. Silicon dioxide per 10 parts by weight of resin.

The most suitable silicon dioxides are due to a very small particle size and featured a very large surface area. As previously defined, they are essentially in the aqueous coating bath insoluble, rather they form colloidal dispersions. Suitable silicon dioxide, which has the required par-

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The particle size and surface area are, as well as "damped" silica formed by vapor deposition, of which commercial examples are ^M Gab-O-Sile "(a trademark of Oabot Corporation).

Furthermore, according to the invention, there is an electrical exposure process for the coating of metal strip, as it consists in that the tape is immersed in. an eye-sight composition 'which also comes into contact with an electrode, a. Direct current is caused to flow through the composition between the electrode and the tape, the tape is removed from the bath and the tape is heated to cure the coating thereon, causing the coating to wet out a dilute aqueous dispersion, of 10 parts by weight of a thermosetting resin and from 0.001 to 1.5 parts by weight of a substantially insoluble silica which

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a surface of 150 to 450 m per gram and one, average. Has particle diameters of from 0.007 "to 0.015 microns.

The preferred thermosetting resins for use in connection with the invention are epoxy resins. Other suitable resins include acrylic resins, alkyd resins, styrene-butadiene resins, and tung oils. In general, acrylic resins are only effective at high levels. Temperatures thermosetting so that there is a risk that the resin will be decomposed when ea is heated instead of hardening.

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When using acrylic resins in the process according to the invention is therefore preferably a small proportion of a suitable one Cross linking agent used. The chosen cross-linking agent must of course be such that the desired electrical characteristics of the electrodeposition bath as Whole does not interfere and that has the right level of water solubility in order for proper walking in the electroplating bath except that it is an effective cross-linking agent for the acrylic resin chosen under the given conditions is. Suitable crosslinking agents include amines of the Hexaki type, which are preferred, but can also Epoxy compounds and urea-formaldehyde condensates can be used. The proportion of a cross-linking agent can be between 5 and 3096 of the total amount of acrylic resin and crosslinking agent and preferably it is $ 15 to $ 20 thereof. The cross-linking agent can be added to the resin prior to adding it to the electrocoating bath, or it can be in the polymerization medium are dispersed therein after the formation of the resin.

It is also desirable to have a crosslinking agent together to provide with an alkyd resin within the scope of the invention. In general can use the same cross-linking agents in the same Relative proportions are used, as they are with the acrylic resins be used.

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A. particularly advantageous application of the invention. Process consists in. The electrocoating of aluminum strip, to make an electrical insulating coating of epoxy ester resin thereon. to make the tape for use in. large. To make transformer windings suitable. In one such process, an aluminum belt is continuously passed through a bath composition performed as described and containing the epoxy ester resin. In "the bath is the tape with the resin coated to provide insulation for the aluminum, and thereafter the tape is continuously passed through an oven in which the coating is fired and cured. With the help of this process, aluminum strips are continuously coated with a sufficiently high insulating capacity provided over the entire surface of the tape to allow use of the tape in transformer windings to enable. Known attempts to produce such a coated aluminum strip with the aid of an electro-coating process resulted in a tape that had insufficient insulating properties on its sharp edges and coatings Had corners, so that a use for such an application was not possible.

Epoxy ester resins are due for use in this process their beneficial electrical and chemical properties chosen to provide a permanent, flexible, inert, heat-resistant and electrically insulating coating on aluminum

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niummetall to "form. The chosen epoxy ester resin is said to be a. resin with a high. Carboxylic acid content. Which is made soluble by partial neutralization, so that the coating bath at least partially consists of a solution of resin in water. Epoxy ester resins can, according to one of the "known methods, be prepared., "for example by esterifying a Epoxy resin with one or more. Fatty acids to one. Obtain resin with a low acid value. In this procedure the resulting epoxy ester resin can then react with a other amount of an organic acid can be brought in order to increase the acid number of the resin and convert it into a suitable. Condition for the subsequent preparation of the aqueous. Coating bath bring to. To 3? preferred epoxy ester resins include, those made by esterification, an epoxy resin in the solid. Physical state, that from. Ep ic hl or hy drin, and bisphenol-A is derived, with dehydrated. Castor oil fatty acids are created around a. Epoxy ester with an acid value (milligrams of potassium hydroxide that is required is to neutralize one gram of resin.) of. make about 8 to 10. Then the resin is made with succinic anhydride heated until the acid number reaches about 50. Another preferred epoxy ester resin is that made by that the same epoxy resin is esterified in the solid state with linseed oil fatty acids and then the resin with phthalic anhydride is heated. In both. The resin solutions are then suitably treated with organic hydroxyl solvents diluted, for example ethylglycol monobutyl ether and butyl

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alcohol until one. Solids content of about $ 76 arises. In this State, storage and further use takes place.

A composition for an electrocoating bath using an epoxy ester resin for this. Case contains about 5 parts by weight to about 15 parts by weight resin in 100 parts by weight. Water.

The proportion of. Silica gel thickener that worked with is conveniently expressed as a percentage of the proportion of Epoxidesterharζ that is present. The suitable one Range with this resin is between about 0.001 and about 0.8 parts by weight resin, the preferred range being absent of additives, to increase the effectiveness of the silicon dioxide between about 0.2 and 0.8 parts by weight. Silicon dioxide per 10 Parts by weight of resin, and about 0.5 parts is best.

"Steamed" silicas are known as thickeners, to increase the viscosity of various liquids. They are examples of a large number of substances available on the market, which act as "thixotropic" agents. A. th_ixotropic agent dispersed in a fluid vehicle to its own to form a stable network of coelloidal particles. The presence Such a network prevents the flow of the liquid and thus increases its viscosity. The effect on the upper

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surface consists in a thickening of the liquid, and therefore the term "thickener" is used for these substances. Various from a large number and range Types of known thixotropic agents are the subdued silicas, as previously described, however, considered the most appropriate to use in conjunction with resins such as solubilized epoxy ester resins. has been determined for this application.

In preparing these electro-bleaching substances, it is necessary to ensure thorough dispersion of the silica in the aqueous bath. This can be done by first preparing a dispersion of, for example, 10% of the silicon dioxide in deionized water under conditions of high shear agitation. If a thorough # OK strength dispersion has been reached, the concentration of silica is reduced to the target value, ³¹ Uem, a further dilution with deionized water.

The effectiveness of the thixotropic agent "steamed" silica in improving the coating of the sharp bands and corners can be further increased by adding small proportions of suitable foam generators, for example isooctylphenyl polyepoxyethanol. The use of this additive in a ratio of 0.003 to about 0.015 parts by weight of the Foam generator per 10 parts by weight of epoxy ester resin allows

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the desired improvement in the coating of. Edges and corners with slightly smaller amounts of the thixotropic silica agent. If this additive is present in the specified. Amounts can be between about 0.1 and about 0.5 parts by weight of "attenuated" silica per 10 parts by weight of resin in can be used effectively. Both in the selection and in the type of use of. Foam generators must, however care must be taken as they can lead to instability in the plating bath.

According to the invention, the composition can be used for the electrocoating bath in addition to an epoxy ester resin or a styrene-butadiene resin, a water-soluble phenol-formaldehyde resin that hardens itself quickly at room temperatures. The use of such a resin allows working with smaller proportions of silicon dioxide while the required Edge coating properties are maintained. The phenolic resin appears to be the coating's resistance to one Wandering from the edges, to favor if the tape is from the bathroom is transported into the furnace. The presence of the phenolic resin also appears to have other beneficial effects on the coating exerted, for example, an increased chemical resistance of the finished cured film and a more uniform Dispersion of the silicon dioxide. However, it appears that the phenolic resin is only used satisfactorily can be if the coating resin is an epoxy ester or

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Is styrene butadiene resin. The most suitable proportion of. Ph.enolh.arz depends on the alkalinity of the resin system, it lies generally, but within the range of about 0.05 to about 0.5 parts by weight per 10 parts by weight of coating resin. For an epoxy ester resin with an alkalinity of 45 milliequivalents per 100 grams of epoxy ester resin solids is, for example a. Share of 0.2 parts. Phenolic resin per 10 parts of epoxy ester resin is suitable. When the alkalinity is 72 milliequivalents is, can. man work with a proportion of 0.075 parts phenolic resin. When working with eriem such phenolic resin can be a Range from about 0.001 to about 0.6, preferably from about 0.01 to about 0.6 parts of silica per 10 parts by weight of coating resin be used.

A particularly well-suited phenolic resin for this purpose is that sold under the trademark ¹¹ BEIY 12i5 "by Union Carbide Corporation. It is believed to be made by mixing phenol with an excess of formaldehyde in an aqueous solution in" a "solution. alkaline medium is reacted until a water-soluble resin is formed in its resol state of about $ 56 pesticides.

Further, the electrocoating composition can contain both Foam generator as well as the phenolic resin contain as described. In such a case, a suitable bath composition can be used 10 parts by weight of the epoxy ester resin or styrene butadiene resin,

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between, about 0.002 and about 0.01 parts by weight of isooctylphenyl polyepoxide ethanol and between about 0.1 and 0.25 parts by weight of the water soluble. Have phenol-formaldehyde resin.

When working with an epoxy ester resin it will be in front of it. Clogging, in the coating bath 50% of the acidity by adding the required amounts, of an amine, for example one Triethylamine, a dimethylethanolamine or a mixture

P neutralized therefrom under high shear conditions. That Amin is about 76 ^ -igen. Resin solution added, which was already mentioned has been. The partially neutralized resin solution that results in this way is then diluted with water, and again under conditions of high shear agitation, and then a. Mix with the watery. Dispersion of silicon dioxide, which has been produced is, as already described has been. The bath is then kept to the desired solids level diluted with deionized water, and optionally the phenolic resin is added. The plating bath is located is now in a usable condition for an electrical coating system »

The electrocoating compositions according to the invention are in accordance with normal electrocoating technology. all, usual aspects, designed to make desirable electrical Maintain characteristics and electrocoating characteristics. So you will be on relatively low total fixed

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Maintained substance content, expediently 5 to 25 $ and preferably 12 "to 20%. Furthermore, they become essentially free of ionizable salts and such substances. that the continued operation of the pool over long periods of time disturb, for example by excessive accumulation in it.

The procedure is in the following. Examples shown:

EXAMPLE 1

An epoxy ester resin having good electrical insulating properties was prepared and made water-soluble, and an aqueous electrocoating composition was prepared from this resin. The bath composition was used to electrically coat aluminum tape with the epoxy ester resin. The epoxy ester resin was made as follows. 1435 grams (1-0H-A'equivalents) of the commercially available epoxy resin Epon 1001 (derived from epichlorohydrin and bisphenol-A and sold by Shell Chemical Company Limited) were, with 1085 grams (0.4 equivalents) of dehydrated castor oil fatty acids and 0.22 grams (0.425 milliequivalents) anhydrous sodium carbonate ^{mixed at a temperature of 100 0} C under a nitrogen atmosphere. The mixture was then heated. After the temperature had reached 16O ⁰ C, was added dropwise started with the addition of xylene to facilitate the removal of water of esterification, which was created during the reaction. That

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Mixture was brought to a temperature of. Heated to 220 C and held at this temperature for 2 to 5 hours until the resulting resin had an acid number of 8 to 10 milligrams of KOH per gram of resin. The reaction mixture was then cooled to HO ⁰ C.

The epoxy ester resin formed in this way was then heated with further acid in order to increase the carboxyl content of the resin. For this purpose 199 grams (0.2 mole) of succinic anhydride were added to the resin, namely at 140 ° C., and this reaction temperature was maintained for about 2 hours until the resin had an acid number of. Had 4-50 milligrams of KOH per gram of resin. Then, the reaction mixture was cooled to 11O ⁰ C.

The resulting resin was reduced to 80% solids diluted by adding 674 grams of ethylene glycol monobutyl ether became. It was on one. $ 76 solids further diluted, by adding 170 grams of butanol. In this condition the solubilized epoxy ester resin can be stored for subsequent use.

The silica used as the thixotropic agent in this example was that available as "Cab-O-Sil M-5 ^M and sold by Cabot Corporation. It has a surface area of 200-25 m each Grams, an average particle diameter of 0.012 microns

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and a maximum density of 36.84 kg per cubic meter. The silicon dioxide was prepared for use in the electrocoating composition by making a 10 ^ dispersion, of silica was formed in deionized water under high shear agitation conditions. After in. This way a good dispersion has arisen, another one can be used Achieve dilution as needed by adding more deionized water. In this example, the concentration was of silicon dioxide lowered to $ 1.

The composition for the electrodeposition bath was then from these components. All of the mixing of the various solutions and dispersions were effected under high shear agitation "conditions. A portion of the diluted 76% owned. Epoxy resin solution containing 1 31 grams of resin, was made as described and was neutralized by adding 4 grams (45 milliequivalents per 100 Grams of resin) were added to thylethanolamine. Di e ^ jfar ti eil neutralized resin solution were then. 500 grams of the $ 1 aqueous dispersion, fumed silica added. 361.25 Grams of deionized water, then, were added to the solid to lower the content of the composition to $ 10. In the end were 3 »75 grams of the aqueous solution of phenolic resin with $ 56 Solid particles added, making a total of 1000 grams of solution revealed.

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So the bath composition contained $ 10 epoxy ester resin, Q »5 $ fumed silica and 0.2 $ of the water-soluble Phertol resin. The composition had a. milky appearance .. it had a conductivity of about 1000 / umho and one. PH value from. about 7.5.

This bath composition was used to wrap a piece of aluminum tape in a discontinuous. Experiment on a small scale. Dimensional bar w electrically to coat. The aluminum * ■ "" ack, which is 0.25 mm thick and has a surface (on one side) of.

ρ
19.55 cm was immersed in the bath composition and used as the anode in a. Electric circuit switched on.

The cathode of the circuit was formed by a steel plate.

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det that has a surface of. 25.8 cm on one side and immersed in the bath composition at a distance of about 13 mm from the alumina anode. A direct current of 100 YoIt voltage and an amperage of about 0.1 amperes was caused to flow between the anode and the cathode for a period of 15 minutes, causing the deposit of a translucent white. Coating on the aluminum anode caused. The aluminum piece was then taken out of the bath composition, washed with water, 30 minutes, dried at 15O ⁰ O and 5 minutes fired at 25O ⁰ C for. The resulting cured resin coating was yellow and 0.025 to 0.038 mm thick.

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The insulating ability of the applied coating was thereby increased checked that a voltage difference between the aluminum (under the coating) and a movable electrical probe. By putting the electrical probe over all parts of the surface of the aluminum piece have been moved, including the sharp edges and corners thereof found that the coating had an insulating capacity of more than 1100 volts in all places, which was a good surface edge and corner coverage.

While in this example the composition for the electroplating bath used in a discontinuous laboratory element on a small scale to show its effect, it will be understood that for large scale operations the same composition is used in a continuous system wherein the composition is contained in a metal bath containing cathodes for operation, and wherein the aluminum strip anode has a great length and is continuously passed through. This is the preferred one commercial process. After emerging from the bath, the tape is continuously passed through an air shower and passed an oven where drying and curing takes place.

EXAMPLE 2

In this example, a composition for an electrical

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"Coating bath was prepared and used to coat a piece of aluminum tape essentially as described in Example 1, except that a different epoxy ester resin was used. The epoxy ester resin for this example was prepared as follows? 1435 grams of Epon 1001 epoxy resin were 1075 grams Linseed oil fatty acids and 0.22 grams of anhydrous sodium carbonate are mixed at a temperature of 100 ^° C. under a nitrogen atmosphere.

The production then went on, just like that for the resin according to Example 1 has been described.

The epoxy ester resin thus prepared became the reaction brought to increase its carboxyl content by adding 311 Grams of phthalic anhydride were added. The reaction proceeded as described in Example 1 to a To produce resin with an acid number of 50 milligrams KOH per gram of resin. After cooling, the resin was solubilized to a solids content of. 80% diluted by 705 grams Ethylene glycol monobutyl ether was added, and then a further dilution was carried out to a solids content of $ 76 Adding 176 grams of butanol

The composition for the electrodeposition bath was turned off made of this resin in exactly the same way, as described in Example 1, being the same

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Ingredients have been used in the same proportions. at electrocoating an equal piece of aluminum tape in in the same manner using this bath composition, a coating having an insulating ability of more than 1000 volts produced at all points on the belt including the sharp edges and corners.

EXAMPLE 5

This example illustrates the use of an acrylic resin in an electrocoating bath according to the invention containing thickening agents as in the previous example, and it illustrates the electrocoating of an aluminum strip using such a bath composition. The acrylic resin used was that made by American Cyanamid Co. under the designation XO-4010. A. Cross-linking agent was the resin added, in a stake of $ 18 cross-links based on the total weight of resin and crosslinking agent. The specially used means of cross-connection the amino cross-linking agent was XM 1116 from American Cyanamid, which is a Hexakistype, namely a modified hexamethylmethoxymethylmelamine. The resin was first solubilized by neutralization in the usual manner, and then it became brought into an aqueous solution dispersion. Two different

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Electro-plating baths were made as before has been described by placing the components under conditions high shear agitation. The first aqueous coating bath contained 10% of solubilized acrylic resin and 196 Qab-0-Sil M5 · The second bath contained $ 10 resin and $ 1.2 Cab-0-Sil M5.

Aluminum strips with a thickness of. 0.25 mm and an upper

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^w area (on one side) of. 19 »35 cm were immersed in these baths as in Example 1 and coated by passing direct current with a voltage of 100 YoIt through the bath for 20 seconds. On each strip, there was one. Film deposited to a thickness of 0.025 mm. The coated. Tapes were taken out of the bath, washed, dried, and fired. The insulating capacity of the coating was tested characterized in that a voltage difference between the aluminum, was k also placed under the coating, and a movable electrical probe. The probe was moved over all parts of the tape, including the tapes and corners.

The coating on the tape from the first bath had one Insulation ability of more than 1100 volts at all. Make, both on. the. levels. Surfaces as well. the. Ribbons .. that is called classified very well. The coating on the tape from the second bath had an insulation capacity of more than 1100 volts and on more than 60% of all positions on the levels. Surfaces and ribbons. This coating is classified as acceptable.

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In contrast, a tape that was coated in a bath became, which the same concentration, the same, soluble made acrylic resin contained, but not silica, and which was coated and tested in the same way as very poor in terms of the insulating properties of its' coatings on the ribbons, classified.

EXAMPLE 4

This example illustrates the use of the same thixotropic attenuated. Silica agent in a composition for an electrocoating bath containing an alkyd resin.

The alkyd resin that was used was the water-soluble alkyd resin, that is known as Arol-on 369 (Trademark) and that manufactured by Archer, Daniels, Midland Company. This resin was given the same cross-linking agent as in the example 3 added, in a proportion around 20 percent by weight of the cross-linking agent based on the total weight of resin and cross-linking agent to supply. Three different electrocoating baths were made like this has already been described, each 10 percent by weight contained this resin. Enough Gab-O-Sil M5 was added to the first bath to give a concentration of $ 0.3. Sufficient Cab-O-Sil M5 was added to the second bathroom.

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sets to a concentration of. Get $ 0.5. The third. Sufficient Cab-O-Sil M5 was added to the bath to achieve a concentration from $ 0.8.

The Cab-O-Sil was added in the manner described above, and all mixing was under high shear agitation conditions take place.

P An aluminum strip was electrically coated in the respective bath, as described, where the electrocoating lasted 20 seconds and with a current of. 100 volts gearbeilFVurde. The film thickness on the first tape was 0.0275 mm. On the second and on the third tape there was a. Film with a thickness of. 0.025 mm deposited. After washing, drying and Burning, the insulating ability of the coatings on the. respective bands, measured by a movable electrical Probe was used as described. Under the

. same. The measuring conditions were the coating at the edges of bands 1 and 3 are classified as acceptable. The coating on the edges and on the. Corner of the tape from the second bathroom was rated as good.

Again, a control experiment was carried out using the same resin. the same concentration, being carried out in the bathroom, however no silica was used. With the same. Coating method was a 0.0275 mm thick resin coating

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deposited on an aluminum tape in the control bath. However, the insulation ability at the edge of this tape was very poor,

EXAMPLE 5

This example illustrates the use of styrene butadiene resins in bath compositions. according to the invention.

The styrene butadiene resin chosen was a. such that under the ' Name QX-3531 (Trademark.) Of. from The Dow Chemical Company is manufactured. Aqueous compositions for the electrocoating bath have been solubilized therefrom. Styrene butadiene resin made that $ 10 of the resin in. Water contained. Four different baths were made, the first $ 0.1 Cab-O-Sil M5, the second $ 0.3 Cab-O-Sil M5 and the third included $ 0.5 Cab-0-Sil M5. The fourth bath was called Control bath used to which no silica was added.

As already described, aluminum strips were coated by they were immersed in the bath and adding a. Electricity at 100 volts was passed through the bath for 15 seconds. The coated Tapes were then taken out of the bath, washed, dried and fired. In. the first and fourth bath the resulting film thickness was 0.0275 mm. In the second and in the third bath, the film thickness was 0.025 mm.

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The insulating ability of those deposited in this way. Coating was then. measured in the manner previously described using a movable electrical probe and a Voltage difference of 1100 volts was applied. The second and the third bath had coated tapes that had good dielectric strength around the edges. The ones from the first, and tapes removed from the fourth bath were found in the insulating ability the coating on the edges, classified as poor.

EXAMPLE 6

This example illustrates the use of a tung oil varnish as the resin in. a composition for electroplating bath according to the invention »

A composition for an electrocoating bath was thereby obtained produced that a tung oil varnish was dispersed under the designation B-516 in. Water, which of. the company Abrex Specialty Coatings Limited, in a proportion of. $ 10 resin. This bath was in. A share of $ 0.5 Cab-O-Sil M5 was added as described above. A second bathroom was made in the same manner except that the Cab-O-Sil were omitted to act as a control bath.

In. the respective bathroom was a. Aluminum tape immersed and electrically coated by a voltage difference of 100

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Volt was applied for 20 seconds. The coated tapes were taken out from the respective baths, washed, dried and baked, and the insulating ability of the respective Coatings were measured in the manner already described. The tape that was coated in. The bath, which containing silicon dioxide had good insulating properties on both their flat surfaces and their sharp edges and corners. The tape from the control bath had a coating with poor insulating properties on the sharp ones Edges and corners.

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Claims (9)

Claims . Composition for a. Electro-plating bath consisting of from a dilute, aqueous. Dispersion, a thermosetting. Resin, characterized by the Presence, an essentially insoluble one. Silicon dioxide therein, with a surface area of about 150 to about »2
m per gram and an average. Particle diameters from about 0.007 micromillimeters to about 0.015 micromillimeters, the silicon dioxide being in a proportion of. about 0.001 to about 1.3 parts by weight per 10 parts by weight of resin is present. 2. Composition according to claim 2, characterized in that - k e η. η. ζ e i c h n, e t that the thermosetting resin is releasable made epoxy ester resin and that the proportion of silicon. dioxide between about 0.001 and about 0.8 parts by weight per 10 parts by weight of resin. 3 · Composition according to claim 2, g ek e η. η. ζ e i c h n. e t by the presence of. about 0.003 to about 0.015 Parts by weight of a suitable foam generator per 10 parts by weight Resin. - 29 109845/1853 4. Composition according to claim. 2, marked by the presence of from about 0.05 "to about 0.5 parts by weight per 10 parts by weight of resin of a water-soluble Phenol-formaldehyde resin, which is quickly self-curing at room temperature. 5. Composition according to claim 1, characterized in that shows that the thermosetting resin is a solubilized one Is acrylic resin and that the silica is present in an amount of about 0.75 "to 1.3 parts by weight per 10 parts by weight of resin. 6. Composition according to claim 1, characterized in that draws that the heat hard bare resin. soluble Is alkyd resin and that the silica in. A proportion of about 0.2 to about 1.0 parts by weight per 10 parts by weight Resin is present. 7. Composition according to claim 1, characterized in that that the thermosetting resin is a soluble styrene butadiene resin and that the silicon dioxide in one Proportion from about 0.2 to about 1.2 parts by weight per 10 parts by weight Resin is present. 8. Composition according to claim 7, characterized by the additional presence of about 0.05 to - 30 - 1 09845/1 853 about 0.5 part by weight per 10 parts by weight of resin one water-soluble phenol-formaldehyde resin, which is quickly self-curing at room temperatures. 9. Composition according to claim 1, characterized in that that the thermosetting resin is a tung oil; and that the silicon dioxide is in a proportion of. about 0.4 to about 0.7 parts by weight per 10 parts by weight of tung oil. ^ia ' ^t 10, electrocoating process for coating metal strip, in which the tape is immersed in a coating composition which is also in contact with an electrode, When electric current is made to flow through the bath of the electrode and the tape, the tape is removed from the bath and the tape for curing the coating on it is heated, characterized in that that the coating composition by a dilute aqueous dispersion of 10 parts by weight of a thermosetting Resin and about 0.001 to about 1.3 parts by weight of a substantially insoluble one. Silicon dioxide is formed, that has a surface area of about 150 to 450 m per gram and an average. Has particle diameters of from about 0.007 micromillimeters to about 0.015 micromillimeters. 109845/1 853