DE2753595A1 - GALVANIC COATING APPLICATION - Google Patents

Description

PatentanwSfttf ÜP.-lng. Walter Abitz Dr. Dieter F. IVi ο rf Dipl.-Piiys. M. Lritschneder 8 Uflnchen 86, Pienzenauerstt. 2 &

December 1, 1977 PP 7421 B

EI DU PONT DE NEMORS AND COMPANY Wilmington> Delaware _f V.St.A.

Galvanic overlay

809823/0781

The invention relates to a method for the cathodic application of polymer coatings. In particular concerns the Invention a method of applying coatings Acrylic polymers containing amino groups »which provides coatings with a minimal amount of retained water and retained acid.

As is well known, organic coatings can be galvanized either on a conductive substrate connected as an anode or be deposited on a substrate connected as a cathode. Although most conventional electroplating methods follow the anodic route, »this method has certain shortcomings. The anodic coating is generally applied with the aid of an alkaline coating bath. The pH increases at the coating surface and creates conditions »which, together with the electrolyte effect of the coating bath can lead to the dissolution of metal ions from the substrate and subsequent deposition of these ions within the resulting coatings. This can result in contamination and reduced corrosion resistance. There is also a tendency that the previously produced phosphate coatings are attacked by the electrolysis. Furthermore, the oxygen that is developed on the substrate to be coated, which is connected as an anode, can cause various problems such as oxidative destruction of the coatings.

The slectroendoosmosis has the tendency to »the water of to keep away the resulting anodized coatings »so that coatings with a low retained water content and a solids content of around 85 to 95 pounds result.

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PP 7421 B ς

This is an advantage over cathodic coverings represents »for which it cannot be assumed» that the mentioned phenomenon will prove to be useful (parts and percentages here relate to the weight, unless otherwise stated and the designation of a range with "X to Y" or "X-Y", where X and Y each represent a number, is to be understood to include both X and Y).

The cathodic coating application has - in part due to the for. the bath needed acidic pH - developed more slowly. With this method there is also the There is a tendency »that water is sucked into the outer layers and retained there together with acid residues from the bath. The quality of the upper parts can of course be impaired as a result. In contrast to the Anodic electroplating at the anode produces oxygen at the cathode in the cathodic method. Although this hydrogen is in the Coatings can cause pores or cracks »of course it does not lead to the oxidative destruction of the film or the film. Upper pull.

Before applying organic protective coatings to metal surfaces (e.g. iron or steel), these are Surfaces normally subjected to a pretreatment (such as phosphating). U.S. Patent 870,937 describes one Method of treating iron or steel surfaces with Phosphoric acid solutions »which can contain iron powder or elsenic phosphates. In the context of the development of phosphate coatings for metals (especially ferrous metals), some chemical modifications of the phosphate coatings have proven to be beneficial, for example the incorporation of Calcium and molybdenum in the coating and the rinsing with chromatic solutions.

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Processes and compositions of matter for the cathodic Coating applications are described, for example, in U.S. Pat. No. 2,345,544-3 (which uses a cationic melainin-formaldehyde resin) and U.S. Pat. No. 3,922,212. The latter patent specification relates to a process in which the Bad incorporates a freshener mix "which-one." Ion-forming acid contains »which is not used up as quickly as the resin. OIe acid is in the refreshing mixture in a lower concentration than in the bath the acid does not accumulate in the bath. According to the patent, special amino alcohol esters of polycarboxylic acids are used, and the acrylic polymers can be mixed with zinc phosphate at low pH values (such as from 2 to 7) using phosphoric acid as the ion-forming acid deposited from a solution onto a cathodic substrate.

They U.S. Patents 3,455,806 and 3,458,420 deal with nitrogen-based copolymers and their cathodic deposition. Cathodic sulfonium systems are described by Wesaling et al. in "Electrodeposition of Coatings" , edited by EF Brewer "American Chemical Society (1973)" pages 110 to 127 "described.

One deals with the galvanic deposition methods extensive literature. Two interesting papers "dealing with this technology" are "Electro-painting Principles and Process Variables "» Brower »Metal Piniehing, (September 1976)» Page 58 »and" Coatings Update: Electrocoating "Americus" Pigment and Besin Technology (August 1976) »page 17 · However, none of these articles and none of the aforementioned patents gives any suggestion for a method» with the help of which cathodically applied resin coatings with an optimally low

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Water and acid retention and high corrosion resistance can be achieved.

The invention provides a method for the galvanic application of a top coating to a negatively charged one Substrate that is immersed in a coating bath containing an aqueous dispersion of the coating agent, which has a cathode area containing the substrate and an anode area containing a current-carrying anode »wherein the substrate and the anode represent electrodes with opposite sense of charge» which are via the bath in electrical contact with each other are kept »and wherein the bath is a cationic, film-forming polymer» a includes acidic ionizing agent and a crosslinking agent characterized by »that one

a) as an acidic ionizing agent, phosphoric acid »

b) as a cationic film-forming polymer, a graft copolymer with a backbone having secondary and / or tertiary amine functionality, which graft copolymer is stabilized in the aqueous dispersion by a phosphate salt of the amine functionality, the backbone with a hydrophobic copolymer derived from epoxy esters being graft-polymerized hydrophobic copolymers are present in the graft polymer in a sufficiently high proportion that the coating applied to the substrate has a pesticide content of at least about 83 Ί » and the phosphoric acid concentration in the coating agent applied is not more than about 17» 5 f> the phosphoric acid concentration in the bath »and

c) as a crosslinking agent, a substance that is non-reactive in the bath »at elevated temperatures, however, compared to the film-forming polymer is reactive »

used.

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The invention also relates to acrylic resins which are particularly suitable for the coating agents used in the methods according to the invention and which contain both a resin suitable for priming agents and a resin / which is suitable for top coating agents which either as a single coating or cathodically over an electrically conductive one Primer (primer) can be applied. ■ - '■

The primer resin is a graft copolymer of one on an acrylic backbone grafted on Spoxid »which essentially consists of the following components (proportions by weight» based on the graft copolymer):

a) in the acrylic framework: about 15 to 25 pounds of one Polymers or copolymers of at least one monomer from the group of the alkyl »aminoalkyl and hydroxyalkyl acrylates and methacrylates» where the copolymer 0 »02 up to 0.1 (- preferably 0.02 to 0.06) equivalent of secondary and / or tertiary amine functionality and optionally 0.01 to 0.05 (preferably 0.01 to 0 * 02) Has equivalent of quaternary ammonium functionality; and

b) in the graft percentage: about 75 to 85 1 * of a copolymer "that approximately 3 to 7 Ί" of a glycidyl ester of a tertiary carboxylic acid having 7 to 9 carbon atoms and from about 72 to 80 i "of a mixture of about 55 to 60 Jl of a condensation polymer of Epichlorhydrln and Bisphenol-A with about 15 to 20 % tall oil fatty acids, contributed

("Equivalents" here means "equivalent functionality or functional β groups per 100 g of graft copolymers ***).

Preferred is a graft polymer * that is essentially consists of the following components (weight components, based on the graft copolymer):

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a) about 17 to 21 £ (preferably about 19 SO of a copolymer "which contains about 3 to 5 1" (preferably about 4%) of methyl methacrylate, about 4 to 6 Ί "(preferably about 5 £) butyl acrylate, about 1 to 4 i> (preferably about

3 %) Hydroxyäthylmethacrylat, about 1 to 3 £ (preferably about 2 H) Simethylaminoäthylmethacrylat and about

4 to 6 f> (preferably about 5 1>) tert-butylaminoethyl methacrylate is contributed and is graft polymerized with

b) about 79 to 83 % (preferably about 81%) of a mixture of about 5% of at least one compound of the general formula

R ₁ -

ι ι η f \ E ₂ -C - CO-CH ₂ -CH-CH ₂

^fi 3

in which R ₁ »R ₂ and R, each mean a saturated aliphatic radical with a total of 7 to 9 carbon atoms» where at least one of the radicals R ₁ »R ₂ and R, is a methyl group» and

about 74 to 78 £ (preferably about 76 £) of a mixture of about 57 to 60 i "(preferably about 58" 5 £) a condensation polymer of about 27 to 31 Ί "(preferably 29" 25 £) of epichlorohydrin and about 27 to 31 £ (preferably 29 »25 %) bisphenol-A with about £ 16 to £ 19 (preferably £ 17» 5) tall oil fatty acids.

The top coat resin is a one-on-one copolymer Acrylic basic structure grafted on epoxy, which essentially consists of the following components (parts by weight, based on the graft copolymer):

a) in the acrylic backbone content: about 80 to 92 % of a polymer or copolymer of at least one monomer from the group of the alkyl, aminoalkyl and hydroxyalkyl acrylates and methacrylates, the copolymer 0.02 to 0.1

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Λ "

(preferably 0.02 to 0.08) equivalent of secondary and / or tertiary amine functionality and optionally Has 0.01 to 0.05 (preferably 0.01 to 0.03) equivalent of quaternary ammonium functionality; and

b) in the graft fraction: about 8 to 20 Jt of a comonomer in Form of a glycidyl ester of a tertiary carboxylic acid with 7 to 9 carbon atoms.

Preference is given to a graft polymer that is essentially consists of the following components (parts by weight, related on the graft copolymer):

a) about 85 to 91 pounds (preferably about 89 pounds) of a copolymer comprising about 9 to 11 pounds (preferably about 10 pounds) of methyl methacrylate, about 42 to 46 pounds (preferably about 44 pounds) of 2-ethylhexyl acrylate, about 6.5 to B ₉ $ Jt (preferably about 7.5 #) tert. -Butylaminoethyl methacrylate, about 2 to 3 i "(preferably about 2.5 Jt) dimethylaminoethyl methacrylate and about 23 to 27% (preferably, about 25 H) Hydrozyäthylmethacrylat and contributes pfropfpolymerislert with 1st

b) about £ 9 to £ 15 (preferably about 11 Jt) at least a compound of the following general formula:

R ₁ 0 J \ H ₂ -C - CO-CH ₂ -CH-CH ₂ Ε,

in which E ₁ , H ₂ and H, each denote a saturated aliphatic radical with a total of 7 to 9 carbon atoms, at least one of the radicals R ₁ * H ₂ and R 1 being a methyl group.

The invention creates an expedient method according to which first a passivating phosphate salt coating (preferably

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in the form of at least one monolayer) applied cathodically and then a protective resin coating with low water and acid retention on the phosphate coating as well high durability and corrosion resistance is electrodeposited. The method of the invention can be calibrated on pretreated metals (such as phosphated steel) or bare metals (like cleaned »but not phosphated ten steel). Furthermore, the method according to the invention is suitable for other metal substrates with a zinc content such as galvanized (galvanized) steel as well as for aluminum and various alloys. Since in the process according to the invention a phosphate coating is applied »on which the polymer coating is subsequently deposited» is the process less sensitive to changes on the part of the substrate and its pretreatment than other galvanic methods. If the inventive method on an already Using phosphated material, the phosphate coating can be improved because of this versatility of the invention. However, pre-phosphating is not necessary.

The bath used according to the invention preferably contains a water-soluble dihydrogen phosphate M (H _{2 PCh) 2} * where M is Pe »Zn» Ca »Mg or Al. In the cathodic application of the coating according to the invention, the pH value at the cathode rises »whereby an approximately 0.1 to 0.1 cm thick layer is produced» in which the soluble phosphate is converted into an insoluble phosphate M (HPO ^) or M ₅ (PCh ) ₂ is transferred »which is deposited on the substrate surface. The driving force for salt deposition is thus a change in pH and precipitation on the substrate surface. Such a phenomenon caused by a change in pH also leads, according to the invention, to the deposition of dense polymer coatings. More dense coatings are formed than with the electrophoresis of quaternary ammonium salts, in which the main driving force is a concentration gradient.

8 0 9 8 2 3/0 7 8 ~ 1

Al

In a special embodiment of the invention "in which a ferrous metal substrate is immersed in the coating bath", the phosphoric acid contained in the bath dissolves small amounts of iron (II) ions from the substrate when the voltage is applied to form the coating. The Pe (H ₂ PCK) ₂ formed in this way is soluble in the bath at pH values of 3 »0 or below. However, a boundary layer with an increased pH value quickly forms on the substrate, which means that the insoluble salts Pe (HPO.) And Pe ₅ (PCK) ₂ are formed and deposited on the substrate. These salts provide effective protection against corrosion »which is increased» because the salts on the substrate generally form a coherent layer »usually at least one monolayer» instead of being completely distributed in the subsequently created »overlying resin coating. According to a preferred embodiment of the invention, water-soluble zinc salts are added to the bath, which likewise deposit on the substrate in the form of insoluble phosphates. Zinc dihydrogen pheophate [Zn (H ₂ PCL) ₂ ] is stable in the bath at pH values from 2.5 to 3.5. The invention can be implemented at pH values in the range from 2.0 to 4 »0 (preferably 2.5 to 3» 0). At pH values below about 3 »0, the free phosphoric acid present in the bath reacts with the iron metal substrates to form soluble iron dihydrogen phosphate [Pe (H ₂ PO ₄ J ₂ J. Since the solubility of the metal dihydrogen phosphates decreases with increasing temperature, the process according to the invention can be used best performed at bath temperatures of 20 to 25 ^° C. If zinc salts dissolve in the bath, the phosphate coating formed on the steel can also have two minerals as main components, namely phosphophyllite [Zn ₂ Pe (PO ^) _{2 .4H 2} OJ and hopeite [Zn ^ (POj) ₂ .4H ₂ O],

The practical failure of some conventional cathodic isolators Overlay application methods relies, at least in part, on

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the high water retained in the resin coating narrow and In this »water that is not easily removed from the coating dissolved acids and salts. The water can make the coating unusable by various mechanisms » while the acid residues either directly or by providing a hygroscopic material in the coating » which promotes the penetration of water and other corrosive substances »which can promote corrosion.

In contrast to the beneficial effects of electroendoosmosis » which takes place during the application of the anodic coating to the anode and has a tendency to repel water from the anodic coating the electrical forces can even be sucked into the coating. However, water retained in a cathodic coating can be particularly detrimental. To these effects To eliminate as far as possible »the invention provides resins» which are so hydrophobic and coatings with such a hardness or density »that provide a total water repellency from the coating as it is formed is achieved.

The erf indungsgemässen beneficial effects are achieved by using certain hydrophobic Pfropfeopolymerer _f which in their ßrundgerüst secondary and / or tertiary amine functionality or amino groups. These groups promote the adhesion of the resin coating to the substrate, which is still present after the coatings have been heated for the purpose of crosslinking. This is an advantage over cathodic sulfonium systems in which the hydrophobicity is only developed after thermal decomposition of the sulfonium groups. Thermal decomposition of the sulfonium groups during crosslinking of the film would cause »

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Λ *

that the groups mentioned are no longer available for increasing the adhesion of the resin coating to the substrate. Although quaternary ammonium salts in the inventive may contain film-forming polymers, these salts can also contain the secondary or tertiary amino groups do not replace. When the pilm was heated, the quaternary ammonium salts became biö for crosslinking purposes decompose to a certain degree and thereby lose their adhesion to the substrate promoting effect. The polymer compositions according to the invention are described in more detail below.

Although advantages due to the inventive method Entry can be achieved while the system is running (live entry) by applying the coating voltage »while the objects to be coated are immersed in the bath» you can use a reduced tension for certain special effects during the introduction. You for bringing in however, additional electrical equipment required under reduced voltage is usually not necessary or desired. It is convenient »the coated substrate to be taken from the bath when the coating voltage is still applied or soon after it has been switched off. .

Ser for the galvanic baths used according to the invention The container used can be lined with an organic coating that is resistant to the acidic pH of the bath. In order to eliminate corrosion as much as possible » you can use pipes and pump parts made of corrosion-resistant steel or plastic. Often, however, carbon steel parts can be used »and made by gradual Iron (II) ions that get into the bath when the device materials are dissolved are more useful than harmful to the coating process. Due to their self-paseivation, we

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ι »7421 β

As a result, phosphoric acid is less corrosive to steel than some at the pH values used other mineral acids * so that more expensive materials are often superfluous.

It has been found that the usual bacteria do not thrive in the aqueous coating compositions according to the invention. Therefore, ordinary circulating ultrafiltration can be used for the bath components to remove contaminants from the coated parts. In addition, membranes and ordinary purged anodes may be useful, although such devices are not necessary. As an alternative to the use of rinsed anodes, the excess »phosphoric acid enriched in the bath can be used up by adding zinc» ZnO »Zn (OH) ₂ or other metals or compounds which form the metal dihydrogen phosphates in solution.

Although an uncoated container can be used as an anode, anodes made of corrosion-resistant steel, the surface of which is smaller than that of the one to be coated, are normally used as the cathode for technical purposes switched substrate is. In this way, a favorable current density distribution is achieved.

In the galvanic coating process according to the invention, the metal part provided as the substrate to be coated is immersed in a bath of a galvanic cell. The bath is an aqueous dispersion of about 2 to 35 Gknr.-1C of a cationic film-forming polymer »which is at least partially neutralized with an acidic substance. Is used for this purpose preferably phosphoric acid in an amount "of from 60 i" that amount "which for a stöchlometrische reaction of the first hydrogen atoms of the

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Αϊ

three-basic satire with all available amino group bonds in the polymer is required, up to an excess of 120% of the stuchiometric amount. The use of less than about 60 % of the stoichiometric amount of phosphoric acid can lead to instability of the bath. A phosphoric acid content higher than 120 μl (even 270 % or more) can sometimes be tolerated »although a lower pH limit of 2.2 to 2» 5 is reached »if more free phosphoric acid is present. In the presence of the acid, the film-forming polymer forms cations in the bath.

The metal object to be coated is connected to the negative pole of a direct current source in order to act as the cathode of the cell. During the entire residence time of the object in the bath (approx. 0.01 to 5 min.), Current is passed through the cell at a voltage of approx. 1 to 500 T, with a coating of the cationic polymer being deposited on the substrate. When the cover has reached the desired thickness »the object is removed from the bath. The object is then preferably rinsed with water or with piltrate removed from the process to remove excess coating agent. Subsequently, the object tree in temperature is dried or 5 to 40 min. Fired at 100 to 300 ⁰ C "with a top coat having a thickness of about 0" 00254 to 0.127 is obtained at the (5 mils to about 0.1). Typical efficiency is about 30 mg deposited film solids per coulomb of electricity

The current density used in the galvanic cell generally does not exceed 1.85 l / cm ² (0.3 A / in ² ) of the anode surface immersed in the bath. It is preferable to work at lower current densities. During the deposition of the cationic film-forming polymer, voltages of 5 to 400 V are preferably used for 0.25 to 2 minutes.

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applied »so that a high-quality top coat is achieved.

The coating agents according to the invention can contain pigments. These are generally incorporated into the agent in a conventional manner by first producing a pigment paste (mill base) or pigment dispersion which contains the pigment and the aforementioned cationic film-forming polymer or another water-dispersible polymer or surfactant. The pigment paste is then mixed with other film-forming ingredients and the organic solvent. If the pigment paste is then acidified and dispersed in water, the polymers tend to envelop the pigments. This effect prevents the de-stabilization of the dispersion or other undesirable effects that could be caused by the use of a basic pigment (such as TiO ₂ ) in an acidic dispersion. Pigments that are stable in acidic media can be used »for example the surface-treated TiOp pigments from US Pat Surface treatment, eg with titanium dioxide and sues), chromates, such as lead chromates, sulfates »carbon black» silicon dioxide »talc» aluminum silicates, such as kaolin (china clay) and finely divided kaolin »organic pigments and soluble organic dyes.

Except for the cathodic coating application, the coating agents according to the invention also by any conventional methods »such as by spraying» electrostatic Spray on »Spread on or brush on» Plied coating or by the immersion method ». The reaction of the amino groups of the polymer with phosphoric acid is generally not necessary »if the coating agent is intended for purposes other than electroplating

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FF 7421 B

is seen. Thermally decomposable organic acids, such as formic acid, can be used in such applications to achieve water solubility. The coating should be about 5 to 40 min. Are baked at about 175-200 ⁰ C, so that coating can be achieved with a bead of about 0 * 00254-0 * 127 mm (about 0.1 to 5 mils). When used for cathodic coating application, the coating agents according to the invention are preferably used in such a way that thicknesses (after drying) of about 0.0203 to 0.0305 mm (about 0.8 to 1.2 mils) are achieved.

The inventive coating agent contains a crosslinking agent, which together with the film-forming component in Water can be dispersed. Based on the solid content in the bathroom »which is roughly the same as the pesticide content in the Film, there will be about 60 to 95 pounds (preferably about 70 pounds) of the cationic film-forming polymer combined with about 5 to 40 j6 (preferably about 30 Jt) crosslinking agent used.

Typical examples of crosslinking agents which can be used according to the invention are melamine / formaldehyde resins, alkylated Melamine-formaldehyde resins »such as hexakis (methoxymethyl) melamine and partially methylated melamine-formaldehyde resins, butylated Helamln-formaldehyde resins »methylated urea-formaldehyde resins» urea-formaldehyde resins and phenol-formaldehyde resins. Benzoguanamine-formaldehyde resins are particularly useful crosslinking agents which deliver high-quality products with the cationic polymers. A preferred benzoguanamine formaldehyde resin is XM 1125 (American Cyanamid Co.) "an acidic" self-catalyzed Crosslinking agents with an acid number of 25 to 32.

When inventive coating compositions as a primer for

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PP 7421 B 2.0

Metals (such as treated and untreated steel or aluminum) »you can use conventional acrylic enamels» acrylic dispersion enamels and other coating agents directly onto the primers as top coats. Acrylic paints (acrylic lacquers) »Acrylic emulsion paints or acrylic powder coatings can be applied to those made from the new compositions formed base coats are applied; however, a suitable intermediate coating, such as a Pore sealer »use to improve the adhesion of the paint or powder top coat on the primer.

The glycidyl ester used both in the primer and in the topcoat and the optional epoxy-fatty acid components of the primer give the polymer sufficient hydrophobicity so that the electrodeposited film contains at least about 83 % (preferably 85 to 95%) pesticides. Although such high levels of pesticides are not uncommon for anodically applied coatings, they are not easy to achieve with cathodic deposition because of the amount of water that is usually trapped. The phosphoric acid concentration in the electrodeposited PiIm is 10 to 15 # of the phosphoric acid concentration in the bath. This corresponds to a value of about 0.05 1 »of the applied film itself. The figures mentioned apply to the electrodeposited PiIm or coating before it is dried and stoved. The amino groups present in the PiIm lead to a low phosphate concentration in the Pilm »the retained water, however, increases the phosphoric acid content to a harmful extent. Empirical tests have shown »that it is disadvantageous» if 20 to 25 1> of the phosphoric acid concentration of the bath remains in the pilm; such values lead to a reduced

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ten corrosion resistance »the appearance of bubbles and other undesirable effects.

In the process according to the invention, the critical phosphoric acid concentration in the dry PiIm is given as a percentage of the phosphoric acid concentration in the bath; the term "phosphoric acid" also includes phosphoric acid derivatives with a corresponding effect in the form of phosphates and metal phosphates reacted with amino groups of the polymer. In relation to the total electroplated coating, the metal phosphate layer directly on the substrate only contributes negligible amounts of phosphate * The main amount of phosphoric acid derivatives is in the form of free phosphoric acid or amine salts within the water enclosed in the PiIm. The ionically bound phosphate content in the polymer depends on the amine content in the polymer. Higher proportions of amine result in higher proportions of the bonded phosphate reacted with them. Most of the phosphate is released from the polymer in the form of phosphate ions due to the change in pH and electrical phenomena when the polymer is applied to the substrate. However, a different proportion of phosphate remains in the PiIm. The amount of phosphate applied is most reliably determined as the proportion of the phosphate concentration in the bath. The bath concentration is a dynamic value that depends on the speed of the coating as well as the extent to which the substance is dragged out and rinsing, and is best averaged over a period of time during which phosphoric acid is incorporated into the bath and partially removed with the outer layers.

Although phosphoric acid according to the invention for several reasons is used (the most important reason is to ensure the formation of the phosphate coating on the substrate in the same

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FP 7421 B 22

Process »which also supplies the top coat), can except In addition to phosphoric acid, other acids can be used with the same results. Acids »which at low pH, Water-soluble salts of the desired metals (in particular zinc, elsenic, calcium, magnesium or aluminum salts) form »which are then converted into insoluble salts in the boundary layer when the pH value is increased» can be used. Oxalic, chromic, sulfamic, benzoic and boric acids can show such behavior. However, it can happen that the salts of such acids deposited in the absence of phosphates are not the passivating ones or have the corrosion-inhibiting effects of phosphates.

The coating compositions according to the invention can contain further auxiliaries which do not significantly change the basic and new features of the invention and therefore do not change them by the phrase "consisting essentially of" are intended to be included. Examples of such auxiliaries are Thickeners »Foam inhibitors» Pigments »Microgels» Pigment dispersants »Polymer powders» Microbiota and coalescing solvents. Typical suitable coalescing solvents »which are in a concentration of About 0.5 # of the total bath volume can be used »are ethylene glycol monobutyl ether, ethylene glycol monobutyl ether and cyclohexanol.

The graft polymers according to the invention can have basic structures of various types »provided that they have the required amine functionality and, when grafted with epoxy copolymers, assume a suitable hydrophobicity. They preferred backbone parts are acrylic compounds »like Alkyl acrylates »methacrylic compounds and of acrylic or Polymers derived from methacrylic compounds. Further examples of suitable backbone fractions are polyamines of

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PP 7421 B 23

maleated oils »polyester» maleated polybutadiene and epoxidized UIe.

Secondary imines in the backbone of the graft copolymer can have a similar puncture as tertiary imines. Man can produce secondary imines, for example, by combining glycidyl methacrylate with ammonia to form a primary amine converts »which is then converted into a secondary amine by grafting with suitable epoxy components. You to Graft copolymerization used in the preparation of the compositions according to the invention converts secondary imines in the reaction components in tertiary imines and accordingly primary imines into secondary amines and tertiary imines into quaternary ammonium salts.

The deposition of quaternary ammonium salts on the substrates occurs mainly due to a concentration gradient instead of due to the pH changes in the narrow Border zone »which lead to the deposition of secondary and tertiary amines. The concentration gradient has an effect slower than the border zone effect and, in the absence of secondary and tertiary amino groups, leads to softer, less dense outer layers. Such softer coatings are bulkier and more porous and therefore have a higher thickness Conductivity on. The consequence of this is that the thickness of the coatings increases with continued electrodeposition is enlarged. In contrast, the self-limiting effect of pilms with lower conductivity provides More uniform thickness coatings. Except that they are the Improve the adhesion of the pilm to the substrate after baking, Secondary and tertiary amines in the basic structure also increase the resistance of the polymer in aqueous dispersions.

To improve the adhesion to the substrates and the

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809823/0781

PP 7421 B 2f

The film-forming polymer according to the invention preferably contains 0.04 to 0.8 equivalent of tertiary amine functionality (or amino groups) for stability of the aqueous dispersion. The primer preferably contains about 0.04 equivalent and the topcoat preferably contains about 0.05 equivalent of tertiary amino groups. The preferred secondary amine (before grafting) is tert-butylaminoethyl methacrylate, the preferred tertiary amine is dimethylaminoethyl methacrylate.

Contained in the acrylic framework before the graft polymerisation tertiary amines, which are converted into quaternary ammonium salts during grafting, promote graft copolymerization. The graft polymers according to the invention therefore preferably contain about 0.01 to 0.05 (especially about 0.01 to 0.02) equivalent of quaternary ammonium functional itate or ammonium groups. However, these do not need to be built into the basic structure, but can can be used as an external catalyst to promote graft polymerization. That way you avoid the somewhat deleterious effects of quaternary ammonium groups in the basic structure of the electrodeposited coatings.

Although it is difficult to give meaningful quantitative information on the softness or hardness of the resin, certain resins according to the invention have a degree of hardness which, in combination with the hydrophobicity of the resins, keeps the water away from the mushrooms or coatings, so that the specified water- and acid retention values can be achieved.

The molecular weights of the polymers according to the invention are generally not critical. Typical average molecular weights determined by gel permeation chromatography, however, are: for the backbone portion 12,000, for the graft copolymer of the primer 11,000 to 12,000 and for the

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PP 7421 B

Graft copolymers of the topcoat 15,000. These values show that typically 80 to 85 pounds of the epoxy the basic structure are grafted on.

Although attempts have been made to explain the way in which the advantages according to the invention are achieved and their causes, there is no restriction in any way to any Theories intended.

The following examples are intended to describe the preparation of the graft polymers according to the invention and their use in explain cathodic deposition methods according to the invention.

example

A black primer is made and applied as follows:

Section I and Section II describe the two resin components, which are graft polymerized and with the Pigment dispersions from Section III are used in the paint or coating material from Section IV.

Section I;

-It will be producing one for graft copolymerization suitable epoxy ester described.

The following components are placed in a equipped with a stirrer »thermometer» reflux condenser and heating jacket Reaction vessel given to form an epoxy ether resin solution:

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FF 7421 B

Share 1

Parts by weight

Epoxy resin (Epon 1001) 1677t00

(Epon 1001 is an epoxy resin of the formula

CH ₂ -CH-CH ₂ - -

0-CH ₂ -CH-CH ₂

in the η a sufficiently large integer "that a Gardner-Holdt viscosity of DG (measured in a Xthylenglykolmonobutylätherlösung the polymer with a solids content of 40 weight Jt at 25 ⁰ C) is obtained, and the resin is an epoxy equivalent of 450 to 550 has.

Share 2

Tall oil fatty acids Benzyltrimethylammonium hydroxide

Share 3

Ethylene glycol monoethyl ether

Parts by weight 503.10 1 * 70

419 »30

Part 1 is placed in the reaction vessel, placed under nitrogen and heated ^{to about 128 to 140 ° C. to melt the resin. Part 2 is then added and the mixture is heated to about 150 to 160 °} C. for about 3 hours, with constant stirring, until the reaction mixture has an acid number of 0.01. Bann sets portion 3 bu, cools down and filtered.

The obtained epoxy ester resin solution has a solid content holds about 84 # »an acid number of at most 0.01

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PP 7421 B

Epoxy equivalent from 1300 to 1900 and a Gardner-Holdt-Vi Bko si did of DP (measured on an ethyl glycol monoethyl ether solution of the polymer with a petroleum content of 40 at 25 ⁰ C).

Section II:

The production of an acrylic resin and the grafting of the aforementioned epoxy ester onto this resin are described.

Part 1 Ieopropanol

Share 2

Parts by weight 400.00

Methyl methacrylate 100.00 Butyl acrylate 125.00 tert. -Butylaminoethyl methacrylate 140.00 Simethylaminoethyl methacrylate 40.00 Hydroxyethyl methacrylate 75.00 Share 3 Isopropanol 100.00 Methyl ethyl ketone 25.00 Azo-bis-isobutyronitrile 10.00 Share 4 Methyl ethyl ketone 8.00 Azo-bis-isobutyronitrile 1.00

Share 5

Ethylene glycol monoethyl ether

350.00

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PP 7421 B 23

Proportion 6 parts by weight

Epoxy ester (manufactured according to Section I) 2300 »00

Ethylene glycol monoethyl ether 350.00

Cardura E-10 125.00 (glycidyl ester of epichlorohydrin, implemented with Versatic acid 911 *, commercial product from Shell Oil Co.)

deionized water 50.00

* "Versatic Acids" = highly branched, saturated aliphatic monocarboxylic acid with C _Q , C _1Q and side chains and tertiary carboxyl groups.

Part 1 is placed in a reaction vessel, which is equipped like the aforementioned reaction vessel, and heated to the reflux temperature. The reaction mixture is kept under nitrogen throughout the reaction. The portions and 3 are premixed separately and slowly added simultaneously over the course of 90 minutes, the reaction mixture being kept at the reflux temperature. The reaction is allowed to proceed for a further 60 minutes, portion 4 is added and the reaction mixture is refluxed for a further 30 minutes. The reaction solvent is stripped off simultaneously with the addition of portion 5 »which replaces the solvent. After 533 parts of solvent have been stripped off and the entire portion 5 has been added to the reaction vessel, portion 6 is added, the temperature is increased to 115 to 117 ^° C. and kept at this value for 4 hours with constant stirring. The epoxy equivalent is then determined. When this is zero or less than 1 epoxy unit / 500,000 g, the reaction is complete. The solids content is 70% and the Gardner-Holdt viscosity with a 25% reduction in the pesticide content with ethylene glycol monoethyl ether U to X.

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Section III

A black pigment dispersion is made from the following components:

Parts by weight

Solution polymer (prepared according to Section II) 318.00

Ethylene glycol monoethyl ether 84.00 Buss as pigment 31.80

The ingredients are premixed and put in a conventional sand mill at a rate of 113 * 55 l / hin. (30 gall./min) ground, keeping the temperature of the mixture below 70 ⁰ C. Russ dispersion has a Peststoffgehalt of about 58 f>.

An extender pigment dispersion that contains aluminum silicate as an extender pigment is produced from the following components:

Solution polymer (prepared according to Section II)

Ethylene glycol monoethyl ether aluminum silicate

The components are premixed and in a conventional sand mill at a speed of 113 »55 l / min. Ground (30 gall./min) "while maintaining the temperature of the mixture below 70 ⁰ C. The aluminum silicate dispersion obtained has a pesticide content of about $ 63.

A water-soluble zinc phosphate (zinc dihydrogen phosphate), which is added to the coating material containing the aforementioned polymer

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Weight Parts 193 , 00 142 , 00 206 , 00

PP 7421 B 30

tel to improve the corrosion resistance of the cathodic deposited coating is to be incorporated is made of the following components:

ZnO (zinc oxide) 85 # phosphoric acid deionized water

The ingredients are mixed for 5 to 8 hours at room temperature, until the zinc oxide has completely dissolved. The pH of the solution obtained is 2.6 to 3.0.

Section IV

Weight Parts 4 » 00 14th 00 500, 00

A galvanic coating agent for the production of a black coating (flated black paint) is made from the following components:

Share 1 part by weight

Resin solution from Section II 320.00

black pigment dispersion from Section III 97.00

Aluminum silicate pigment dispersion from Section III 440.00

85 # benzoguanamine-formaldehyde resin solution

in ethylene glycol monobutyl ether (XM 1125 from

American Cyanamid Co.) 190.00

Share 2

deionized water 632.00

85% phosphoric acid 22.00

Share 3

Zinc dihydrogen phosphate 510.00

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PP 7421 B

Part 1 is placed in a Miechgefäee » ^{heated to 65» 6 0} C (130 ⁰ F) and mixed for 3 hours at this temperature. Part 2 is added to another mixing vessel, mixed for 10 minutes and part 1 is added with constant stirring. The pigment-containing aqueous dispersion is mixed for 2 hours and diluted to a solids content of 15 l » with deionized water and portion 3» so that the concentration of zinc dihydrogen phosphate in the coating dispersion is 450 ppm (based on the total weight of the electroplating coating agent).

The galvanic coating agent », which has a pH value of 2» 7 and a conductivity of 1700 microsiemens, is placed in a galvanizing tank made of corrosion-resistant steel. An untreated "cold-rolled steel sheet or a phosphated steel sheet is then inserted into the middle of the container and connected to the negative pole of a direct current source" so that it forms the cathode of the galvanic cell. The container is connected to the positive pole of the direct current source and forms the anode of the cell. Then allowed a direct current for 2 minutes at 150 volts. Flow at room temperature (20 to 25 ⁰ C) through the cell "wherein an about 0.0154 mm (about 0.6 mil) thick is deposited paint film on the metal sheet. The coated metal sheet is removed from the cell, washed and ^{baked at about 160 °} C. for 30 minutes. The primer film obtained adheres very well to the metal substrate »is hard and has very good corrosion and soap resistance in comparison to mere» cold-rolled steel and phosphated steel. A acrylic enamel adheres to the primer film, and conventional acrylic lacquers can be applied to the primer using conventional pore closers to give a high quality top coat.

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FF 7421 B

Typical deposited films have a solids content of 90 to 95% and contain 10 to 12 % of the phosphoric acid present in the bath.

The coating agent described is particularly suitable for priming automobile or truck bodies by galvanic means, with optimal corrosion protection over all body parts including such areas where a poor phosphate pretreatment or no pretreatment at all has taken place.

example

Weight Parts 314 , 00 137 , 00 549 , 00

A white pigment dispersion is made from the following Components:

Solution polymer of Section II of Example 1

Ethylene glycol monoethyl ether titanium dioxide

The components are premixed and in a conventional sand mill at a speed of 113.55 l / min. (30 gall./min) ground, keeping the temperature of the mixture below 70 ⁰ C. The titanium dioxide dispersion obtained has a solids content of about 76 % .

A white coating agent is made from the following components from:

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Share 1 part by weight Resin solution from Section II of Example 1560, 00

85 pound benzoguanamine formaldehyde resin

Dissolution in ethylene glycol monobutyl ether 245.00 Titanium Dioxide Pigment Dispersion 700.00

Share 2

85% phosphoric acid 30.00

deionized water 1,400.00

A galvanic coating agent with a pesticide content of £ 15 and one is made from parts 1 and 2 pH of 2.8 and uses it according to the method described in Example 1.

The coating agent is suitable for primers or individual coatings that are applied directly to metal parts of equipment or technical systems are applied. It has good corrosion resistance and detergent resistance Compared to bare, cold-rolled steel or phosphatieΓι em steel.

Coatings made according to Example 1 give similar ones Results.

example Proportion 1 part by weight Isopropanol 1,200.00

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Portion 2 methyl methacrylate, 2-ithylhexyl acrylate, tert-butylaminomethyl methacrylate, dimethylaminoethyl methacrylate, hydroxyethyl methacrylate, azo-bis-isobutyronitrile

Parts by weight

500.00

1000.00

180.00

60.00

600.00

40.00

Portion 3 azo-bis-isobutyronitrile acetone

2.00 15.00

Share of 4 ethylene glycol monoethyl ether

900.00

Share 5

Cardura E-10 (commercial product of Shell Oil Co ·) 260.00

Part 1 is placed in a reaction vessel that is in the aforementioned Way is equipped and heated to reflux temperature. The reaction mixture is used throughout Implementation kept under nitrogen.

Part 2 is premixed separately and at the same time slowly added over the course of 90 minutes, the reaction mixture being kept at the reflux temperature. The implementation is continued for another 60 minutes. Part 3 is then added and the reaction mixture is refluxed for a further 30 minutes. The reaction solvent is stripped off at the same time as the addition of portion 4, which is intended to replace the solvent. 1200 parts of solvent are stripped off and the entire portion 4 is added to the reaction vessel. Part 5 is then added, the temperature is increased to 115 to 117 ^° C. and the batch is kept for 4 hours.

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ter constant stirring at these temperatures. The epoxy equivalent is then determined. When this is zero or less than 1 epoxy unit / 500,000 g, the reaction is complete. The solids content is £ 70 and the product has a Gardner-Holdt viscosity of Z ₂ -Z.

Coatings are produced according to Example 1; these typically have a pesticide content of 85 to 90 % and contain 15 Ί » of the phosphoric acid present in the bathroom.

example

A white pigment dispersion is made from the following Components:

Parts by weight

Resin solution of Example 3 320.00 Ethylene glycol monoethyl ether HO, 00 Titanium dioxide 550.00

The components are premixed and in a conventional sand mill at a speed of 113.55 l / min. (30 gall./min) ground, keeping the temperature of the mixture below 70 ⁰ C. They obtained titanium dioxide pigment dispersion has a plague st off content of about 76 i 'on.

A white coating is made from the following components:

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PP 7421 B

Share 1 part by weight

Resin solution from Example 3 560, OO

85 # Benzoguanamine Formaldehyde Resin

solution in ethylene glycol monobutyl ether 250 »OO

Titanium dioxide pigment dispersion 700 »00

Share 2

85% phosphoric acid 30, OO

deionized water 1 400 00

Share 3

Tin dihydrogen phosphate 510-00

A galvanic coating agent with a pesticide content of 15 » and a pH of 2.7 is prepared from portions 1, 2 and 3, and it is used according to the method described in Example 1 to apply the coating.

The coating material is particularly suitable for direct application individual coatings on metal parts that have a high gloss and gloss retention after UV exposure as well as good corrosion resistance regardless of the type and quality of the pretreatment. Furthermore, with the help of the coating agent achieve a white top coat that does not have the typical discoloration of conventional galvanic Has top coatings.

Coatings produced analogously to Example 1 give similar results.

End of description

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Claims (1)

S. I. SU PONT DS NSHOUBS AND COMPANY 7421 B PATENT CLAIMS Process for the galvanic application of a coating agent to a negatively charged substrate in a a coating bath containing an aqueous dispersion of the coating agent is immersed »which has a cathode area containing the substrate and an anode area containing a current-carrying anode» where the substrate and the anode represent electrodes with opposite sense of charge »those over the bath in electrical contact with each other »and wherein the bath contains a cationic» f-forming polymer »an acidic ionizing agent and a crosslinking agent» characterized »that one a) as an acidic ionizing agent, phosphoric acid » b) a graft copolymer with a secondary and / or tertiary polymer as the cationic film-forming polymer Amine functional skeleton »which graft copolymer in the aqueous dispersion a phosphate salt of the amine functionality is stabilized - 1 -809823/0781 PP 7421 B Z is "wherein the backbone is graft-polymerized with one derived from epoxy esters hydrophobic copolymers" wherein the hydrophobic copolymer in the graft copolymer in a sufficiently high proportion exists that the pressure applied to the substrate top pull content a Peststoff of at least about 83 i "and the phosphoric acid concentration in the applied Oberzugsmittel the phosphoric acid concentration in the bath is no more than about 17 »5» and c) as a crosslinking agent a substance »which is non-reactive in the bath» at elevated temperatures, however is reactive with the film-forming polymer, used . Graft copolymer »containing an epoxide grafted onto an acrylic backbone» characterized in that it consists essentially of the following components (in parts by weight, based on the graft copolymer): a) in the acrylic basic structure: about 15 to 25 % of a polymer or copolymer of at least one monomer from the group of alkyl, aminoalkyl and hydroxyalkyl acrylates and methacrylates »where the copolymer is 0.02 to 0.1 equivalent of secondary and / or tertiary amine functionality | and b) in the graft percentage: about 75 to 85 f> a copolymer comprising about 3 to 7% of a Glyoidylesters a tertiary carboxylic acid having 7 to 9 carbon atoms and about 72 to 80% of a mixture of about 55 to 60 £ of a condensation polymer of epichlorohydrin and Bisphenol-A contributes about 15 to 20 pounds of fatty acids. 809823/0781 3. Graft copolymer containing an acrylic backbone grafted-on epoxy »characterized» in that it essentially consists of the following components (in parts by weight, based on the graft copolymer) consists of: a) in the acrylic backbone content: about 80 to 92- £ of a polymer or copolymer of at least one monomer from the group of alkyl- »aminoalkyl- and hydrozyalkyl acrylates and methacrylates» where the copolymer 0.02 to 0 »1 equivalent of secondary and / or has tertiary amine functionality; and b) in the plug portion t about 8 to 20 Jt of a plug comonomer in the form of a glycidyl ester of a tertiary carboxylic acid having 7 to 9 carbon atoms. 809823/0781