Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
  • B05D7/142—Auto-deposited coatings, i.e. autophoretic coatings
  • B05D7/144—After-treatment of auto-deposited coatings

Definitions

• the present invention relates to a method for coating a metal surface, for example a metal such as iron, zinc, iron alloys and zinc alloys, and the like, by autodeposition to form a predominantly organic coating on the surface of the metal, more particularly a coating which, besides having outstanding corrosion resistance and adhesion, also has a good appearance without any unevenness in gloss.
• a metal surface for example a metal such as iron, zinc, iron alloys and zinc alloys, and the like
• Coating compositions which enable the formation of a resin coating on a metal surface by bringing said metal surface into contact with an acidic composi ⁇ tion which includes an organic film-forming resin are known as "autodepositing" or “autodeposition” compositions and are usually water-based.
• autodepositing or “autodeposition” compositions and are usually water-based.
• Such composi ⁇ tions are disclosed in Japanese Patent S47-17630, Japanese Examined Patent S52-21006, Japanese Examined Patent S54-13435 and Japanese Unexamined Laid-Open Patent Application S61 -168673.
• the defining characteristic of autodepositing water-based coating compo ⁇ sitions is that by contacting a suitable metal material having a clean surface with the coating composition, a resin coating film which increases in thickness or weight as immersion time increases forms spontaneously as a result of chemical reaction between the metal and the coating composition. (Metal ions dissolved from the metal surface are believe to interact with the resin particles and to be deposited together with them onto the metal surface.) Thus, a resin coating film can be beneficially formed on said metal surface without the need for external electromotive force, as is required in electrodeposition.
• the corrosion resistance and adhesion of an autodeposited resin coating film is not entirely satisfactory, and various means have been disclosed for improving these properties. Such means include chemical treatments of wet autodeposited coating films before they are dried.
• Japanese Unexamined Laid-Open Patent Application S51 -30245 a method is disclosed for preventing poor appearance, such as blistering and cracking and the like, of autodeposited resin coating films after hot drying, by bringing the said resin coating film before drying into contact with an aqueous so- lution containing from 10 - 100 grams per liter (hereinafter usually abbreviated as " g/L") of a water-soluble solvent such as an alcohol, ketone, alcohol ester, ke ⁇ tone ester, ketone ether, or ester ether.
• a water-soluble solvent such as an alcohol, ketone, alcohol ester, ke ⁇ tone ester, ketone ether, or ester ether.
• Japanese Unexamined Laid-Open Patent Application S52-68240 a method is disclosed for raising the corrosion resistance of an autodeposited resin coating film formed on a coated object after hot drying by bringing said resin coating film before drying into contact with an aqueous solution or aqueous dis ⁇ persion containing from 5 - 100 g/L in total of one or more substances selected from the group consisting of nitrogen-containing organic compounds such as amines, carboxylic acid amine salts, amino acids, melamine and amides, for ex- ample.
• nitrogen-containing organic compounds such as amines, carboxylic acid amine salts, amino acids, melamine and amides
• Japanese Unexamined Laid-Open Patent Application H5- 186889 discloses a method for raising the post-drying adhesion and corrosion resistance of an autodeposited resin coating film formed on a coated object by bringing the said resin coating film before hot drying into contact with an aqueous solution with a pH from 7 to 11 containing from 0.05 to 5 percent by weight (here ⁇ inafter usually abbreviated as "wt%") of anions derived from an acid selected from 1 ,1 -diphosphonic acid, citric acid, succinic acid and oxalic acid.
• wt% percent by weight
• coating by autodeposition is generally performed by immersion, in many cases the coating liquid is prone to being initially retained in, and later to sag or run in the vicinity of, specific structural features, such as bolt holes when the coated material is to be bolted in place. In such instances, a consistent coating film appearance is not usually obtained, because there is a variation in gloss between the portions where sagging occurs and other portions.
• an autodeposited resin coating film is the last or only coating employed on the coat ⁇ ed object, this variation in gloss considerably affects the quality of the appear ⁇ ance ofthe coated object.
• the pre-drying modifying rinses of autodeposited res- in coating films known from the art described previously are beneficial for raising the corrosion resistance of said resin films and for preventing blistering and cracking of the resin film, but have not been found to have any benefit when it comes to preventing variation in gloss.
• the painting of metal sur ⁇ faces is being required to give greater added value, so that high corrosion resist- ance, high adhesion and also a uniform appearance are required, and an im ⁇ provement in this appearance would be desirable. Disclosure of the Invention
• the object of the present invention is to provide a method for coating a metal surface which enables the formation of an autodeposited resin coating film which has outstanding corrosion resistance and adhesion, and also has a good appearance without any variation in gloss.
• a method for coating a metal surface which comprises forming a resin coating film on the metal surface by maintaining said metal surface in contact with an autodepositing type water-based coating composition comprising a coat-forming resin emulsion, an acid and an oxidizing agent, and, optionally, additional metal ions for a sufficient time to form a wet aut ⁇ odeposited film thereon, discontinuing contact between the wet autodeposited film and any part of the autodepositing type water-based coating composition, ex ⁇ cept that which is physically incorporated into the autodeposited film, bringing said wet autodeposited film into contact with an aqueous solution which has a pH value from 6 to 11 and which, in addition to water, comprises, preferably consists essentially of, or more preferably consists of from 0.2 - 10.0 g/L of dissolved, dis ⁇ persed, or both dissolved and dispersed polymer(s) selected from the group con ⁇ sisting of polymers of carboxylic acid monomers having an ethylenic double bond and
• Figure 1 is a drawing of the largest area surface of the test panels used in the examples and comparison examples, showing the positions at which gloss values were determined and the relation of these positions and their size to the position and size of a hole through the test panels.
• the resin in the film-forming resin emulsion employed in the present invention can be any resin which is capable of satisfactory use in an autodepositing water-based coating composi- tion.
• examples include resins made from (meth)acrylic acid type monomers, which include homopolymers of (meth)acrylic acid ester monomers such as methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-hydroxyethyl acrylate, 2-hy- droxypropyl acrylate, 2-ethylhexyl acrylate, methyl acrylate, ethyl methacrylate, n-butyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacryl- ate, glycidyl acrylate and glycidyl methacrylate, and the like and also acrylamide, methacrylamide, acrylonitrile, acrylic acid and methacrylic acid.
• suitable monomers include styrene, ethylene, vinyl chloride, vinylidene chloride, vinyl ace ⁇ tate, and the like.
• suitable resins may be copolymers from any two or more of these previously recited monomer, urethane resins, epoxy resins, and polyester resins.
• the resin employed in the present invention can also be any mixture of the resins above.
• the molecular weight of the coat- forming resin preferably is from 50,000 to 1,000,000, and more preferably is from 100,000 to 1,000,000.
• the film-forming resin emulsion employed in the present invention can be any resin emulsion ordinarily used in preparing autodepositing water-based coat ⁇ ing compositions; in most cases it will be a resin emulsion obtained by ordinary emulsion polymerization, but it can also be a resin emulsion formed by emulsify ⁇ ing in water a resin obtained by another method of polymerization.
• a film-forming resin emulsion can be obtained by subjecting a mixture comprising at least water, an anionic surfactant and/or nonionic surfactant, resin constituent monomers as noted above, and a polymerization initiator to conditions which will activate the polymerization initiator to produce a polymerization reaction.
• An autodepositing water-based coating composition employed in the pres ⁇ ent invention can be obtained by mixing a film-forming resin emulsion obtained as described above with an acid and an oxidizing agent, and if desired a com- pound which can supply a metal ion, and adding water if necessary.
• hydrofluoric acid is preferred.
• the oxidizing agent hydrogen peroxide, potassium perman- ganate and sodium nitrite, and the like, can be used; but hydrogen peroxide is preferred.
• compounds which can supply metal ions provided that they are stable in said coating composition; examples include ferric fluoride, ferric nitrate, ferrous phosphate and cobaltous nitrate, and the like, and ferric fluoride is preferred.
• the content of resin in an autodepositing water-based coating composition employed in the present invention is preferably from 5 to 550 g/L, and more preferably from 50 to 100 g/L.
• the concentration of acid is preferably from 0.1 to 5.0 g/L, and more preferably from 0.5 to 3.0 g/L; and the concentration of oxidizing agent is preferably from 0.01 to 3.0 g/L, and more preferably from 0.03 to 1.0 g/L.
• a compound which can sup ⁇ ply metal ions does not have to be used, but is preferably used; when used, the concentration should be ⁇ 50 g/L, and is preferably from 1.0 to 5.0 g/L.
• An autodepositing water-based coating composition employed in the pres ⁇ ent invention may also contain as optional components a film-forming aid such as trialkylpentanediol isobutyrate or alkylcarbitol, and the like, for example, in order to lower the film-forming temperature and facilitate the coalescence of the deposited resin particles, and/or a pigment such as a carbon black, phthalocyan ⁇ ine blue, phthalocyanine green, quinacridone red, hansa yellow, and/or benzidine yellow pigment, and the like.
• a film-forming aid such as trialkylpentanediol isobutyrate or alkylcarbitol, and the like, for example, in order to lower the film-forming temperature and facilitate the coalescence of the deposited resin particles
• a pigment such as a carbon black, phthalocyan ⁇ ine blue, phthalocyanine green, quinacridone red, hansa yellow, and/or benzidine yellow pigment, and the like
• Autodepositing coating compositions employed in the present invention can be used for treating surfaces of iron, zinc, iron alloy and zinc alloy, and par- ticularly steel portions of various components such as automobile sheet compon ⁇ ents and automobile components such as shock absorbers, jacks, leaf springs, suspension components and brackets, and the like, and components of furniture such as drawer rails, and the like.
• the film thickness after drying is preferably from 5 to 40 micrometers (hereinafter usually abbreviated as " ⁇ m"), and more preferably is from 20 to 30 ⁇ m.
• a metal surface preferably is degreased and rinsed with water before applying said coating composition.
• the rinsing with water can be performed by ex- posure to running water, but will ordinarily by performed by immersion for from 10 to 120 seconds, or preferably from 20 to 60 seconds, in water at ordinary am ⁇ bient temperature.
• a modifying rinse process of the present inven ⁇ tion is performed by bringing the resin coating film produced as above into con- tact with an aqueous solution (modifying rinse solution) having a pH from 6 to 11 and containing a total of from 0.2 to 10.0 g/L of at least one polymer selected from polymers of carboxylic acid monomers having an ethylenic double bond and salts thereof.
• the total concentration of such polymers and salts thereof is pref ⁇ erably from 0.5 to 4.5 g/L, and more preferably from 1.0 to 3.0 g/L.
• Polymers of carboxylic acid monomers having an ethylenic double bond and salts thereof include copolymers of (meth)acrylic acid with acrylate, methac ⁇ rylate, and maleate ester monomers, which can be the same (meth)acrylic acid esters listed in connection with the resin in the aforementioned film-forming resin emulsion, and or copolymers of styrene with a carboxylic acid monomer having an ethylenic double bond (acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, and the like), and sodium salts and ammonium salts of these, and the like.
• the weight ratio of (meth)acrylic acid ester monomer(s) and/or styrene to carboxylic acid monomer(s) having an ethylenic double bond is preferably from 1 :99 to 50:50, and more preferably from 3:97 to 30:70.
• the molecular weight of the polymers of carboxylic acid monomers having an ethylenic double bond is preferably from 2000 to 200,000, and more preferably from 10,000 to 50,000.
• the polymer of a carboxylic acid monomer having an ethylenic double bond can be obtained by any method of polymerization; it is also possible to use a polymer purified from a polymerization Iiquor when making said modifying rinse solution, or the polymerization liquor itself can be used provided that it will not in ⁇ terfere with the purpose of the present invention.
• the pH of said modifying rinse solutions needs to be from 6 to 11.
• a pH of 6.5 to 8.5 is preferred. With a pH less than 6.0, there is usually no benefit of preventing variation in gloss after drying, and corrosion resistance and adhesion are not usually adequate; on the other hand, when the pH exceeds 11 , adhesion becomes inadequate and/or there is an undesirable etching of the metal surface coated.
• a known substance disclosed in Japanese Unexamined Laid-Open Patent Appli ⁇ cation H3-505841 or Japanese Unexamined Laid-Open Patent Application H5- 186889 preferably is used.
• Examples include ammonium bicarbonate, ammoni ⁇ um hydroxide and hydroxides of alkali metals such as sodium, potassium and lithium.
• ammonium bicarbonate, ammonium hydroxide and sodium hydroxide is/are used.
• Ammonium bicarbonate and/or ammonium hydroxide are more preferred.
• a modifying rinse process according to the invention can suitably be performed by immersion at a temperature from 5 to 60 °C, and preferably at ordinary ambient temperature, with a contact time of from 30 to 120 seconds, or more preferably from 60 to 90 seconds.
• moisture on the coating film is evaporated and the coalescence of the resin part ⁇ icles preferably is accelerated by subjecting the coated object to a drying treat ⁇ ment.
• this drying in general it can preferably be performed at 60 to 200 °C, or more preferably at 100 to 180 °C, for a time from 5 to 30 minutes, or preferably from 10 to 20 minutes.
• An autodepositing water-based coating composition prepared as noted below was held at a bath temperature of 20 to 22 °C, and a pre-cleaned cold- rolled steel sheet (size 70 x 150 x 1 mm) test panel having a bolt hole 1 as shown in Figure 1 was painted by immersion in this composition for 180 seconds, rinsed by immersion in deionized water for 60 seconds, immersed for 60 seconds in Modifying Rinse Solution A below at ordinary ambient temperature, and dried for 20 minutes in a hot air oven at 110 °C, and was then submitted to the tests of coating film performance described hereinafter.
• Test autodepositing water-based coating composition was held at a bath temperature of 20 to 22 °C, and a pre-cleaned cold- rolled steel sheet (size 70 x 150 x 1 mm) test panel having a bolt hole 1 as shown in Figure 1 was painted by immersion in this composition for 180 seconds, rinsed by immersion in deionized water for 60 seconds, immersed for 60 seconds in Modifying Rinse Solution A below at ordinary ambient temperature, and
• SaranTM SL-143 Latex is an emulsion containing a vinylidene chloride co ⁇ polymer resin, which becomes a coat-forming resin when combined with the other ingredients listed.
• Modifying Rinse Solution A An aqueous solution of polyacrylic acid (solids 25 %) (Toagosei product) diluted with deionized water to give a polyacrylic acid concentration of 2.0 g/L, and adjusted to pH 6.5 with ammonium bicarbonate, was used. Examples 2 to 8
• Example 1 The procedure of Example 1 was repeated, except for using Modifying Rinse Solutions B - H, with the compositions shown in Table 1 , which were pre ⁇ pared in the same way as Modifying Rinse Solution A, except for the different substances and/or amounts thereof used as ingredients. Table 1
• Carboxylic acid polymers and salts g/L of Polyacrylic acid 1 2.0 1.5 1.0 g/L of Ammonium 1.5 1.0 polyacrylate 2 g/L of Sodium polyacrylate 3 0.5 0.5 g/L of Acrylic acid/ethyl 0.5 acrylate copolymer 4 g/L of Polymaleic acid 5 1.0
• Carboxylic acid polymers and salts g/L of Polyacrylic acid 1 2.0 0.1 g/L of Ammonium 3.0 4.5 5.0 polyacrylate 2 g/L of Sodium polyacrylate 3 10.0 g/L of Acrylic acid/ethyl acrylate copolymer 4 g/L of Polymaleic acid 5
• Footnotes for Tahle 1 continued 6 Product of Toray; water soluble, with a molecular weight of about 20,000.
• ⁇ Peel width value is for 192 hours instead of 500 hours.
• Carboxylic acid polymers and salts g/L of Polyacrylic acid 1 2.0 2.0 g/L of Ammonium polyacrylate 2 g L of Sodium polyacrylate 3 g/L of Acrylic acid/ethyl acrylate copolymer 4 g/L of Polymaleic acid 5
• Example 9 The procedure of Example 1 was repeated, except for using Modifying Rinse Solutions I - P with the compositions shown in Table 1 , prepared in the same way as Modifying Rinse Solution A, except for the different substances and/or amounts thereof used as ingredients.
• Example 9 The procedure of Example 1 was repeated, except for using Modifying Rinse Solutions I - P with the compositions shown in Table 1 , prepared in the same way as Modifying Rinse Solution A, except for the different substances and/or amounts thereof used as ingredients.
• Film-forming aid A from below 4.00
• Film-forming aid A was trialkylpentanedioi isobutyrate; its addition gave a minimum film-forming temperature in the vicinity of 20 °C.
• the film-forming emulsion was made as follows: A monomer mixture comprising methacrylic acid 2 parts (which are parts by weight, here and herein- after), methyl methacrylate 28 parts, acrylonitrile 30 parts, ethyl acrylate 20 parts, and butyl acrylate 20 parts was mixed with 1.0 part of an acrylic acid ester type reactive surfactant in an amount of 1.0 wt% of the total weight of the previous five monomers, 0.3 part of ammonium persulfate and 399.6 parts of deionized water, and emulsion polymerized by a conventional method at 75 °C for 4 hours to make a dispersion including 20 % of polymer resin solids.
• This dispersion was then cooled to 40 °C, mixed with additional deionized water and the other ingred ⁇ ients noted above and adjusted to pH 5 to 8, then finally adjusted with additional deionized water so as to produce a volume that gave the concentrations speci ⁇ fied above for the various active ingredients, to give the coat-forming resin dis ⁇ persion.
• Comparison Example 9 The autodepositing water-based coating composition used in Example 9 was held at a bath temperature of 20 to 22 °C, and a pre-cleaned cold-rolled steel sheet (size 70 x 150 x 1 mm) having a bolt hole as shown in Figure 1 was painted by immersion in this for 180 seconds as a test panel, rinsed by immer ⁇ sion in deionized water for 90 seconds and dried for 20 minutes in a hot air oven o at 180 °C, and was then submitted to the tests of coating film performance de ⁇ scribed hereinafter.
• the gloss values ofthe coating film were determined at three points at the top, in the middle and at the bottom of each of Zone A, the surface inside dotted line 2, and Zone B, the surface inside solid line 3, both as shown in Figure 1 , using a digital variable- angle gloss meter (Suga Test Instruments Model UGV-5K), and the mean values for the two zones were calculated and reported, along with the difference be- 5 tween the mean values for the two zones.
• the coating film on the test sheet was cross-cut down to the bare metal, and then submitted to salt spray test (JIS Z-2371 ) for 500 hours. After the test it was peeled with a tape, and the maximum width on either side that peeled from the cross-cut part was determined and reported in millimeters ("mm").
• Comparison Examples 4 and 5 in which the pH of the modifying rinse solution was less than 6, the corrosion resistance of the coating film and its adhesion after immersion in warm water were inferior, and the coating film had a variable gloss.
• Comparison Examples 6 and 7 in which an organic resin other than a polymer of a carboxylic acid monomer having an ethyl ⁇ enic double bond or a salt thereof was used, and in Comparison Example 8 in which ammonium bicarbonate was used on its own as a modifying rinse solution, variations in gloss were produced in the coating film. Variations in the gloss of the coating film were also produced in Comparison Example 9, in which no modi ⁇ fying rinse solution was employed. Benefits of the Invention
• an autodeposited resin coating film can be obtained which has outstanding corro- sion resistance and adhesion and in addition also has a better appearance than coating films obtained by prior methods, without any substantial variation in gloss.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Paints Or Removers (AREA)

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• 1995
  • 1995-07-25 JP JP7209215A patent/JPH0938573A/ja active Pending
• 1996
  • 1996-07-24 WO PCT/US1996/011833 patent/WO1997004880A1/en not_active Application Discontinuation
  • 1996-07-24 CA CA002227587A patent/CA2227587A1/en not_active Abandoned
  • 1996-07-24 EP EP96925341A patent/EP0871549A1/de not_active Withdrawn
  • 1996-07-24 TR TR1998/00113T patent/TR199800113T1/xx unknown
  • 1996-07-24 BR BR9609702A patent/BR9609702A/pt not_active Application Discontinuation
  • 1996-07-24 MX MX9800584A patent/MX9800584A/es unknown
  • 1996-07-24 ZA ZA9606294A patent/ZA966294B/xx unknown

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