JPH01501488A - Cationic electrodeposition coating method using a dissolution-resistant anode - Google Patents

Abstract

Cationic electrodeposition of an aqueous cationic resinous composition with an anode comprising a self-supporting substrate to which is adhered a coating of a conductive material selected from the group consisting of platium, palladium, rhodium, ruthenium, osmium, iridium, gold, oxides thereof, and mixtures thereof. The anode is more resistant to dissolution than stainless steel anodes which are conventionally used in cationic electrodeposition.

Description

[Detailed description of the invention] Blood stoppage 11 King peeled cation ``1 work Gakiou Kokutai The present invention relates to electrodeposition coating, and in particular to cationic coating using an aqueous suspension of a cationic resin composition. Regarding electrodeposition coating.

Yi Wuji jade Cationic electrodeposition coatings have been used industrially since 1972.

Early cationic electrodeposition compositions incorporated quaternary ammonium base-containing resins into aminoplasts. It was contained in combination with a hardening agent. In 1976, amine base-containing resin Cationic compositions containing in combination with blocked isocyanate curing agents automatically It was introduced for undercoating car bodies. Today, more than 90% of automobile bodies is primed by cationic electrodeposition coating, but in particular all cationic The composition uses an amine salt-blocked isocyanate resin.

In cationic electrodeposition coating, the part to be coated is, of course, the cathode. Most mosquitoes Because thione electrodeposition baths are acidic in nature.

The counter electrode or anode is typically made from a corrosion resistant material such as stainless steel.

The electrochemical reaction that occurs at the anode allows stainless steel electrodes to be cationically deposited. It will gradually dissolve over time. As a general rule, the dissolution rate depends on the current density and the voltage to which the anode is exposed. Depends on the bathing temperature; the greater the current density and the higher the temperature, the more On-dissolution rate becomes faster. The composition to which the electrode is exposed also affects the rate of dissolution. I can get it. The presence of chloride ions greatly promotes dissolution and inhibits other unknown components of the electrodeposition bath. can also affect dissolution. For example, in the area where the electrodeposition bath is located, stainless steel Another part of the electrodeposition bath that is relatively inert to the poles, but uses the same cationic paint. has been found to be highly corrosive to stainless steel prepared anodes. There is. When the anode dissolves, the formation of the coating decreases and the appearance becomes poor. In the end, it melted If the solution is large enough, this anode must be replaced, which takes 9 hours. This would result in the termination of the five uneconomical electrodeposition steps.

The purpose of the present invention is to overcome the above-mentioned problems and to avoid deterioration in any cationic electrodeposition environment. An object of the present invention is to provide a cationic electrodeposition coating method using an anode that is resistant to melting and dissolution.

Carrying out cationic electrodeposition in this way guarantees consistent results regarding the quality of the coating. Significant labor savings as there is no need to replace the anode for testing and melting. bring.

Matasato Hadajo According to the present invention, a cathode and an anode immersed in an aqueous suspension of a cationic resin composition are provided. A method is provided for electrocoating a conductive surface that acts as a cathode in an electrical circuit containing It will be done. This method involves passing an electric current between the cathode and the anode to deposit paint onto the cathode. It includes making things happen. The anode is made of platinum, palladium, rhodium, ruthenium, or The group consisting of smium, iridium, gold, their oxides, and mixtures thereof self-suppo formed with a coating of conductive material selected from rting) material.

The electrode of the present invention did not dissolve or deteriorate in a cationic electrodeposition environment, and its quality remained constant. Gives a coating. Also, the need to replace melted stainless steel electrodes There is no need for maintenance work, which greatly reduces maintenance work.

In the cationic electrodeposition process, an aqueous electrodeposition bath containing the electrodeposition paint has a conductive anode and a conductive cathode. while the anode and cathode are immersed in the electrodeposition bath. current between the electrodes.

A coherent film of paint is deposited on the cathode, usually by passing a direct current. paint Electrodeposition is carried out at a constant voltage, typically between 50V and 500V, and at a current density. degrees occur at about 0.5 to 10 amps per square foot. During the initial stages of electrodeposition, A high current density is used and as the coating being deposited insulates the cathode the current density increases. It gradually decreases.

Typically, the cathode 1, for example a series of car bodies, is continuously exposed to an electrodeposition bath or bath. introduced continuously. The cathode is passed through an acid bath, throughout which a series of Cross the anode. - the first anode in the row, i.e. the anode facing the inlet end of the bath; receives the largest current flow and, in the case of stainless steel electrodes, melts the fastest. do. It is these anodes that are preferably replaced by the anodes of the invention. Ste All stainless steel anodes can be replaced with electrodes of the invention, but not necessarily at the outlet end of the bath. There is no need to replace the stainless steel anode located closer to the The electrodes are not subjected to large current flows (due to the insulating effect of the deposited coating) and are This is because it does not dissolve significantly. Therefore, in the bath opposite the inlet end of the bath The electrode should be one according to the invention, but the other electrode closer to the outlet end of the bath , can be of conventional stainless steel type.

The anode may be exposed directly to the electrodeposition paint or, as is the most common case, in an electrodeposition bath. may be part of an electrodialysis cell located in the For example, this anode is Separated from electrodeposition paint. Semi-permeable membranes are suitable for ionic substances such as acid anions and chlorine ions. Although it can pass water-soluble anionic impurities such as on.

It does not allow paint resins or pigments to pass through. Ionics attracted to the anode and passed through this membrane The material can then be removed from the bath by periodically flushing the anode area with water. Ru. In an electrodialysis tank.

The anode region is commonly referred to as the anolyte bath and is the liquid with which the anode contacts the anolyte solution. this Using an anode as such may result in excess acid being formed from the cationic electrodeposition resin. Highly desirable, especially in problematic cases.

The electrodeposition paint used in the electrodeposition process is a cationic resin and R material.

crosslinking agents, and auxiliary materials (e.g., flow control agents, inhibitors, organic cosolvents), and Of course, it contains water as a dispersion medium.

A specific example of a cationic electrodeposition composition includes a cationic electrodeposition composition containing active hydrogen and having an amine base. Resin 1 For example, an epoxy resin and a primary or secondary amine capped isocyanate. compositions based on acid solubilized reaction products in combination with nate hardeners. these No. 4,031,050. An example of a specially modified cationic resin If the polyepoxide is a diketoimine having at least one secondary amine group (e.g. For example, reacting with diethylenetriamine (methylisobutyldiketoimine) Cationic resins with primary amine groups formed by are also well-known electrodeposition resins. and cationic paints using these resin components.

As described in Jerabek et al., US Pat. No. 4.017.438. changed The chain of cationic resin 9, such as polyepoxide, is extended.

Cationic resins obtained by increasing the molecular weight can also be used in the method of the invention. Ru. Such resins are described in U.S. Pat. No. 4,148,772 to Jerabek et al. (the polyepoxide chains are extended with a polyester polyol), and W No. 4,468,307 to Ismer et al. (where the polyepoxide chains are (elongated with polyester polyol). Also, Canadian special Chain extension as described in US Pat. No. 1,179,443 may also be used.

The cationic electrodeposition coating may preferably contain a capped isocyanate curing agent. . These curing agents provide curing at low temperatures and develop optimal properties of the cured coating. It is from. However, based on epoxy resins and capped polyisocyanates, Cationic electrodeposition paints are often contaminated with chloride ions. This chlorine On is a by-product in the preparation of epoxy resins and capped polyisocyanates. It is a thing. Many epoxy resins are made from shrimp chlorohydrin, and some Polyisocyanates are produced from phosgene. Chlorine is a traditional stainless steel It has a very detrimental effect on the dissolution of the electrode. Therefore, the present invention is particularly useful. The solution is to use a cationic paint containing chloride ions. This kind of paint .

Typically at least 10 ppm, usually based on the total weight of the aqueous suspension. It has a chloride ion concentration of 10-200 ppm.

Anodes useful in the method of the invention are chemically resistant materials with the characteristics described below. a self-retaining material substrate on which a coating of certain metals and metal oxides is formed; . The substrate may be metal, preferably valve metal. ).

“°The term “valve metal paste” refers to an oxidation reaction under anionic conditions that results in a chemically resistant surface. Defines a metal that forms a high-quality oxide and is resistant to the passage of electric current.

Chemical resistance makes the substrate resistant to the surrounding electrolyte, i.e. electrocoat or anodic solution. resistant to corrosion, deterioration or electrolyte attack to a significant extent. It means that there is no.

Examples of suitable valve metals are titanium, tantalum, and niobium.

and alloys of these metals 2 e.g. titanium containing 1 to 15% by weight of molybdenum Included. Excellent corrosion resistance, price and effectiveness.

Titanium is preferred because of its adhesion to metal or metal oxide coatings. metal.

It is not essential that the entire substrate be valve metal. Rather, copper The metal core, such as aluminum, is wrapped or coated with valve metal. You can stay there.

The self-shape-retaining substrate is coated with a material that has electrical conductivity and functions as an anode in an electric circuit. Or a layer is formed. Additionally, the material exhibits a high resistance to the surrounding electrolyte under anionic conditions. Should be chemical resistant. Examples of suitable materials include platinum, palladium, and rhodium. metals such as aluminum, ruthenium, osmium, iridium, and gold.

and alloys of two or more of these metals. Also.

Oxides of these metals, such as ruthenium oxide and iridium oxide, and Mixtures of oxides and larger oxides may also be used.

Also, mixtures of metals and metal oxides may be used. price, and in an electrodeposition environment. Ruthenium oxide and iridium oxide are preferable because of their performance, and ruthenium oxide is most preferred.

The thickness of the substrate and the thickness of the metal or metal oxide top layer are not critical. of the base material The thickness provides a self-retaining structure, and the metal or metal oxide layer acts as an anode. function. In other words, it exists in a sufficient amount to satisfy both the required current density and corrosion resistance. All that is required is that there be.

Typically, the substrate thickness is about 50-500 mils and is made of metal or metal oxide. The layer thickness is between 0.01 and 10 mils. The coating of metal or metal oxide layer is applied to the substrate This can be done on both sides or on one side, ie, the side facing the cathode. Preferably, the substrate is The whole is coated with a metal or metal oxide layer.

The placement of the anode is not particularly important, but when used in an electrodeposition bath it is usually square or square. is a rectangle. Typically, when used in industrial electrocoat baths, about 10 to 5 An electrode with an area of 0 square feet is used, and as mentioned above, two usually a series of electrodes are used. The poles are placed in the cell so that they extend from the inlet to the outlet end of the cell.

The method of manufacturing the electrodes is generally proprietary to the manufacturer. In general , metal or metal oxide, evaporation method.

by pyrolysis of suitable metals or metal oxides in organic media, and electroplating. Can be coated. Most coating methods involve first etching the valve metal9. It is then coated with metal in liquid phase. If an oxide is desired, this oxide can be .

Deposited by thermal or electrical means. Oxides of the metal groups mentioned above also apply. The coating can be applied directly to the valve metal support in an oxide melt bath.

People's development In the examples below, typical cationic electrocoat stainless steel anodes and Corrosion of titanium anodes coated with ruthenium oxide and titanium anodes coated with iridium oxide The effectiveness was evaluated.

On the other hand, cationic electrodeposition paint is acid-solubilized shrimp chlorohydrin-bisphenol. Type A epoxy resin-amine reaction product.

and based on capped isocyanate curing agents. The epoxy resin is shrimp It was chlorohydrin-bisphenol A type. This paint is PPG Indust It was available from Leeds, Inc. under the trade name UNI-PRIME. second The paint is a cationic acrylic resin prepared from glycidyl methacrylate. It contained a capped polyisocyanate curing agent. This paint is PPG It was available as HD-4000 from Japan. Anolyte solution samples of these paints were taken. A sample was taken and used for the test.

The anodes tested were 6 x 1 inch in size and had two 6 x 1 inch steel negatives. It formed part of an electrical circuit inserted between the poles. The electrode spacing is approximately 2 inches. The electrodes were then immersed in the anolyte solution to a depth of 2 inches. Electrode weight reduction The effects of temperature, amperage, and time on

The results are shown in Table ■ below.

(Margin below) Submission of translation of written amendment (Article 184-7, Paragraph 1 of the Patent Act) November 2, 1988

Claims (7)

[Claims] 1. Electrical circuit including a cathode and an anode immersed in an aqueous suspension of a cationic resin composition A method of electrocoating a conductive surface serving as a cathode, comprising: passing an electric current between the anodes and depositing paint on the cathode; The anode is made of platinum or palladium. rhodium, ruthenium, osmium, iridium , gold, oxides thereof, and mixtures thereof. comprising a self-shape-retaining substrate formed with a coating of material; Electrodeposition painting method. 2. The amount of chloride ions in the aqueous suspension is small based on the weight of the aqueous suspension. 2. A method according to claim 1, wherein the compound is present in an amount of at least 10 ppm. 3. 2. The method of claim 1, wherein the self-shape-retaining substrate is a valve metal. 4. 4. The method of claim 3, wherein the valve metal is titanium. 5. The coating material may be ruthenium oxide, iridium oxide, or a mixture thereof. The method according to claim 1, wherein the method is selected from the group consisting of: 6. 6. The method of claim 5, wherein the material is ruthenium oxide. 7. The valve metal is titanium, and the material is ruthenium oxide, ruthenium oxide, Claim 3 selected from the group consisting of iridium, and mixtures thereof. The method described in.