CA2227587A1 - Composition and process for autodeposition with modifying rinse of wet autodeposited coating film - Google Patents
Composition and process for autodeposition with modifying rinse of wet autodeposited coating film Download PDFInfo
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- 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
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Abstract
The uniformity of gloss of a dried autodeposited resin film on a metal surface can be increased by rinsing the wet autodeposited film initially formed with an aqueous modifying rinse having a pH from 6 to 11 and comprising from 0.2 to 10.0 g/L in total of polymers of carboxylic acid monomers having an ethylenic double bond and salts thereof.
Description
CA 02227~87 1998-01-22 W O 97/04880 PCTrUS96/11833 ~escription COMPOSITION AND PROCESS FOR AUTODEPOSITION WITH MODIFYING
RINSE OF WET AUTODEPOSITED COATING FILM
Technical Field The pr~ser,l invention relates to a " ,elhod for coating a metal surface, for exa",ple a metal such as iron, zinc, iron alloys and zinc alloys, and the like, by autodeposition to form a predor"in2ntly organic coating on the surface of the metal, more particularly a coating which, besides having outstanding corrosion r~sislance and adhesion, also has a good appearance without any unevenness in gloss.
Background Art Coating ~lll~ ~siLions which enable the ror"~alion of a resin coating on a ~0 metal surface by bringing said metal surface into co"ta~l with an acidic composi-tion which includes an organic film-forming resin are known as "autodepositing"
or "~ ocleposilio,1" compositions and are usually water-based. Such composi-tions are ~ losed in Japanese Patent S47-17630, Japanese Examined Patent S52-21006, Japanese Examined Patent S54-13435 and Japanese Unexamined Laid-Open PatentApplication S61-168673.
The defining cl ,ard.;ieri~lic of ~utodeposili"g water-based coating compo-sitions is that by conla.ling a sl ~iPh'e metal material having a clean surface with the coating cGr"posil,or" a resin coating film which increases in thickness or weight as i,r" "e, :,ion time increases forms spo"laneously as a result of chemical reaclion 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 deposiled 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 elec~r~".,oli~/e force, as is required in ele~L.odeposiliol-. However, in some cases the co"usion resisla"ce and adhesion of an autodeposited resin coating film is not entirely satisfactory, and various means have been disclosed for improving these ~rupe, lies. Such means include che,nical l,~dl,nel ,ls of wet autodeposited coating films before they are dried. (Such chemical treatments are known by various names in the art; the most col.,mon such name is probably "final rinse", CA 02227~87 1998-01-22 which is wcll cs~ hli'jl ,ed but often a l "is"o" ,er, ber~use there may be other sub-sequent water rinses. Other names are "after-treatment", "post-treatment", "re-action rinse", "cher"ical rinse", and the one preferred herein, "modifying rinse".) The following citations exemplify such treatments. t s In Japanese Examined Patent S53-15093 and US Patent 3,795,546 it is disclosed that by bringing a coated object into contact with an aqueous solutioncontaining a hexavalent chromium compound and polyacrylate after immersion in an autodepositing aqueous coating composition and before hot drying the coated resin film, the corrosion resistance of the coating film after drying is ~o raised.
In 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, bybringing the said resin coating film before drying into co"lacl with an ~queous so-lution containing from 10 - 100 grams per liter (hereinafter usually abbreviatedas " glL") of a water-soluble solvent such as an alcohol, ketone, alcohol ester, ke-tone ester, ketone ether, or ester ether.
In Japanese Unexamined Laid-Open Patent Application S52~8240 a "l~lhod is ~lis-,lQsed for raising the cc,lusion resi~ldr,ce of an ~ulo.le~osiled resin coating film formed on a coated object after hot drying by bringing said resin cûdling film before drying into contact with an aqueous solution or aqueous dis-per~iGn 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, c~, L,oxylic acid amine salts, amino acids, melamine and amides, for ex-ample.
In Japanese Unexamined Laid-Open Patent Application H3-505841 a method is ~Ecclosed for raising the post-drying adhesion and cor, usion resislance of an ~ulodeposiled resin coating film formed on a coated object by bringing said resin coali. ,g film, before hot drying, into co"lacl with an aqueous solution of an alkaline substance.
Similarly, Japanese Unexamined Laid-Open Patent Application H5-186889 discloses a method for raising the post-drying adhesion and corrosion W O 97/04880 PCT~US96/11833 resislance of an ~utodeposited resin coating film formed on a coated object by bringing the said resin coali"g film before hot drying into CGI ,la~ with an ~q"esus solution with a pH from 7 to 11 COI)ldil lil l!3 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.
Rec~use coaling by ~u(ndeposilion 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 l l Idlel ial is to be bolted in place. In such instances, a consistent .0 coali"g fiim appear~,)ce is not usually obtained, because there is a variation in gloss between the portions where sagy;~ ~9 occurs and other portions. When an ~ llodeposiled resin coaling film is the last or only codlil ,9 employed on the coat-ed object, this variation in gloss considerably affects the quality of the appear-ance of the coated object. The pre-drying modifying rinses of autodeposited res-in codlil ,9 fiims known from the art cies~ ibed previously are beneficial for raisingthe 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 Vdl idLiol I in gloss. In recent years the painting of metal sur-faces is being required to give yl ealer added value, so that high corrosion resist-ance, high adhesion and also a uniform appearance are required, and an im-provement in this appeara"ce would be desirable.
Disclosure of the Invention Problems to Be Solved by the Invention The object of the present invention is to provide a method for coating a metal surface which enables the formation of an ~ llodel~osiled resin coating film which has o~ ,la,)d;ng co"usion resislar,ce and adhesion, and also has a good appeara,)ce without any variation in gloss.
~ummary of the Invention The problem above is solved by a method for coating a metal surface which co""~, ises forming a resin co~li"y film on the metal surface by maintaining said metal surface in contact with an autodepositing type water-based coating co",posiLion cor"p, ising a coat-forming resin emulsion, an acid and an oxidizing CA 02227~87 1998-01-22 .
agent, and, oplio, lally, addiliG,)al metal ions for a su~ficient time to form a wet aut-odeposited film thereon, discGnlinuing contact between the wet autodeposited film and any part of the ~utocleposiling type water-based coating composition, ex-cept that which is physically incorporated into the autodeposited film, bringingsaid wet ~ odeposiLed film into con~ with an ~queous solution which has a pH
value from 6 to 11 and which, in addition to water, co" ,,u, ises, preferably consists esse"lially of, or more ~rerel dbly CGI ,sisls of from 0.2 - 10.0 g/L of dissoived, dis-persed, or both dissolved and dispersed polymer(s) selected from the group con-sisting of polymers of carboxylic acid ,no"o,ners having an ethylenic double bond ~o and salts thereof.
Brief Description of the Drawing Figure 1 is a drawing of the largest area surface of the test panels used in the examples and col"parisol1 examples, showing the positions at which gloss values were deter",ined and the relation of these positions and their size to the position and size of a hole through the test panels.
Details of the Invention, Including Preferred Embodiments There are no narrow restrictions as to the resin in the film-forming resin emulsion employed in the present invention, which can be any resin which is capal~l~ of sali:jraclor~/ 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 ",~ll,ac,ylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacryl-ate, glycidyl acrylate and glycidyl " ,ell ,a~ ylate, and the like and also acrylamide,methacrylamide, acrylonitrile, acrylic acid and methacrylic acid. Other suitable ~u~ IGr"e,:, include styrene, ethylene, vinyl chlo, ide, vinylidene chloride, vinyl ace-tate, and the like. Other 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.
There are no narrow restrictions as to the molecular weight of the coat-CA 02227~87 1998-01-22 forming resin, but, for example, the mo'Qc~ r weight as measured by gel perme-ation cluo" ,aloy~ apl ,y in tetrahydrofuran, using polystyrene or a poly(acrylic acid ester) as a reference, 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 prese, ll invention can be any resin emulsion or~lina, ily used in ,~,repa, ing Al ~to~ leposili~ ,9 water-based coat-ing coll~posiliv, ,s, in most cases it will be a resin emulsion obtained by ordi,)a,y emulsion polymeri~aliot), but it can also be a resin emulsion formed by emulsify-ing in water a resin obtained by another method of polymerization.
~0 There are also no narrow r~sl, ictio"s as to the conditions for polymeriza-tion to give a polymer emulsion by emulsion polymeri~aliol " and this can be per-formed by an ordinary method; however, as an example a film-forming resin emulsion can be obtained by subjecting a mixture co" ,prising at least water, ananionic surfactant and/or nonionic su~raclanl, resin constituent monomers as noted above, and a pol~"nel i~dlion initiator to conditions which will activate the polymeri~dlion initiator to produce a polymerization reaction.
An ~ulorleposili~ ~y water-based coating c~" "~osilion 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 necess~ry.
As the acid, for e~d" ,ple, any one or more selected from hydrofluo i, co"ic acid, hydrofluolilan,c acid, hydrofluosilicic acid, hydrofluoboric acid, hydrofluoric acid".,hospho(ic acid, nitric acid, and the like, can be employed, but hydrofluoric acid is p,efe"ed. As the oxidi~in~ agent h~,-l,o~Jen peroxide, potassium perman-ganate and sodium nitrite, and the like, can be used; but hydrogen peroxide is pl-~fer~ed. There are no narrow restrictions as to compounds which can supply metal ions, provided that they are stable in said coating composition; examples include ferric fluoride, ferric nitrate, ferrous p hosphdle and cobaltous nitrate, and the like, and ferric fluoride is preferred.
The co,-te, ll of resin in an aulocleposili"g water-based coating co" Iposilio,,employed in the presenl invention, measured as the COI ~cenll dlion of resin solids, is preferably from 5 to 550 g/L, and more preferably from 50 to 100 g/L. The CA 02227~87 1998-01-22 W O 97104880 PCT~US96/11833 concer,l, dliOII of acid is prerer~1bly from 0.1 to 5.0 g/L, and more preferably from 0.5 to 3.0 g/L; and the conce"l,dlion of oxidi~il)g agent is preferably from 0.01 to 3.0 g/L, and more prererably 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 r s conce"l,alion should be s 50 g/L, and is preferably from 1.0 to 5.0 g/L.
An ~ ~todeposili, lg 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 deposiled resin particles, andtor a pigment such as a carbon black, phthalocyan-ine blue, phthalocyanine green, quinac, ido"e 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 pGI L;GI IS of various cornpone,)ls such as automobile sheet compon-ents and aulo",obile compGnents such as shock absorbers, jacks, leaf springs, suspel Isiol, co" ,pol~enls and brackets, and the like, and components of furniture such as drawer rails, and the like.
There are no narrow restrictions as to the method for contacting a metal surface using an autodeposili,-g ccdlillg co",posilion employed in the present in-vention, and any method generally applicable to surface treatment, such as im-r"ersion, spraying or roll coali"g, and the like, can be adopted; however, immer-sion is usuaily pr~fe" ed. There are also no narrow restrictions as to the temper-ature of treatment or the duration of treatment; however, in the case of immer-z5 sion treatment, i"""e,~io" at o,di"aly ambient temperature, e.g. 18 to 25 ~C, for from 30 to 300 seconds, and prererably from 90 to 240 seconds, is generally suit-able.
There are no narrow lil"ildlions as to the quantity of said coali"g composi-tion applied to the metal; however, the film thickness after drying is prererably from 5 to 40 micrometers (hereinafter usually abbreviated as ",um"), and more preferal,ly is from 20 to 30 l~m.
01 dil Idl ily a metal surface prerer~bly is degreased and rinsed with water CA 02227~87 1998-01-22 W O 97/04880 PCT~US96/11833 before applying said coating composition.
After applying said cGcllil ,9 cor, l~osilion to a metal, it is prererdbly subject-ed to or~ ,aly rinsing with water; then the modifying rinse that characterizes the pr~senl invention is pe~ ru~ med. 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 ~ r~:rerably from 20 to 60 seco"ds, in water at ordinary am-bient te",peralure.
As menlio"ed previously, a modifying rinse process of the present inven-tion is pe, ro""ed by bringing the resin coating film produced as above into con-tact with an Zl~ll leO US 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 ,l ,onor"er~ having an ethylenic double bond and salts ll ,ereor. The total conce, Ill~lion 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. With a con-centration less than 0.2 g/L, no benefits can normally be expected in terms of preventing va, i~tiGn in the gloss of the coaLi,)g film after drying, and on the other hand when the total co"ce~ lll dliOII exceeds 10.0 g/L, the drying properties of the oule""osl surface of the resin coating film become uneven and this in itself tends to produce variations in gloss.
Polymers of carboxylic acid monomers having an ethylenic double bond and salts ll ,ereor 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 co"nection with the resin in the droren,enlioned 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, ilaco" ~ acid, crolo"ic acid, and the like), and sodium salts and ammoniumsalts of these, and the like. Of these, polyacrylic acid and the ammonium salts ll ,erec r are ~ferer, ed. In the case of copolymers, the weight ratio of (meth)acrylic acid ester m~"o",er(s) and/or styrene to carboxylic acid monomer(s) having an ethylenic double bond is p,-erer~bly from 1:99 to 50:50, and more preferably from 3:97 to 30:70. There are no narrow resl, iotio"s as to the molecular weight of the polymers of carboxylic acid ")onc r"er~ having an ethylenic double bond; howev-CA 02227~87 1998-01-22 W O 97/04880 PCT~US96/11833 er, the molec~ weight is prererably from 2000 to 200,000, and more preferably from 1 0,000 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 uses a polymer purified from a pol~" ,eri,dlion liquor when making said modifying rinse solution, or the polymeri~alion 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 pr~re"ed. With a pH less than 6.0, there is usually no benefit of preventing variation in gloss after drying, and cc " usio~ ~ resistance and adhesion are not usually adequate; on the other hand, when the pH exceeds 11, adhesion becomes in~dequ~te and/or there is an undesirable etching of the metal surface coated.
As the substance used to adjust the pH of said modifying rinse solution a known substance disclosed in Japanese Unexamined Laid-Open Patent Appli-cation H3-505841 or Japanese Unexami,)ed Laid-Open Patent Application H5-186889 ~r~re, dbly is used. EXdl I Iples include ammonium bicarbonate, dl "n ,o"i-um hydroxide and hydroxides of alkali metals such as sodium, potassium and lithium. Pl ererably at least one of dl l ll l lGI ,ium biCdl uonale, ammonium hydroxide and sodium hydroxide is/are used. Ammonium bicarbonate andlor ammonium hydroxide are more preferred.
There is no narrow re~l, i.:(iu" as to the modifying rinse process conditions of the present invention; a modifying rinse process according to the invention can suitably be performed by immersion at a temperature from 5 to 60 ~C, and prererably at Gldi~)aly ambient temperature, with a conlaul time of from 30 to 120 seconds, or more p,ererdbly from 60 to 90 seconds. After said modifying rinse, moisture on the cGali"g film is evapordled and the coalescence of the resin part-icles ,u~ ~re, ably is accelerated by subjecting the coated object to a drying treat-ment. There is no narrow restriction as to this drying; in general it can preferably be performed at 60 to 200 ~C, or more ~u,eferably at 100 to 180 ~C, for a time from 5 to 30 minutes, or pr~rerauly from 10 to 20 minutes.
The present invention is ex~,lained in more detailed terms below by means CA 02227~87 1998-01-22 W O 97/04880 PCTrUS96/11833 of examples and comparison examples.
FY~mPIeS and Comparison Examples EYample 1 An ~l Itodepositing water-based coating composition prepared as noted below was held at a bath te~l~peralLIre 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 i~ "ner~iol H n this composition for 180 seconds rinsed by i" " "er~iGn in deior,i~ed water for 60 secc ,)~ls i,n,oer:,ed for 60 seconds in Modifying Rinse Solution A below at ordinary ambient teml~erdl-lre and dried .0 for 20 minutes in a hot air oven at 110 ~C, and was then submitted to the tests of coali"~ film pe, r~,r"~dnce described hereinafter.
Test autodepositing water-based coating composition Inaredient COI Icenll dlion (g/L) SaranTM SL-143 Latex (solids 55%) 95.00 ~s (a W. R. Grace product) Hydrofluoric acid 0.70 Ferric fluoride 3.00 HycJ,oyen peroxide 0.10 The above ing, ~d,e. Ils were combined with deionized water only to produce the autodepositing coating composition.
SaranTM SL-143 Latex is an emulsion co, ll~il ,;"g a vinylidene chloride co-polymer resin which becomes a coat-forming resin when combined with the other ingredients listed Modifying Rinse Solution A
An ~ eous solution of polyacrylic acid (solids 25 %) (Toagosei product) diluted with deionized water to give a polyacrylic acid concel ,l,alion of 2.0 g/L
and adjusted to pH 6.5 with a,n",o,1ium bicarbonate was used.
FYzlrnoles 2 to 8 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 sub-~lances and/or amounts thereof used as ingredients.
Table 1 COMPOSITIONS AND TEST RESULTS FOR THE EXAMPLES AND COMPARISON
E)CAMPLES
F~mp'e N-~.. .be Modir~;.. g Rinse 1~ Letter: A B C D E F
Carboxylic acid polymers and salts:
g/L of Polyacrylic acidl2.0 1.5 1.0 g/L of ~ - ~ 1.5 1.0 polyacrylate2 g/L of Sodium polyacrylate3 0.5 0.5 g/L of Acrylic acidtethyl 0.5 acrylate copolymer4 g/L of Polymaleic acid5 1.0 Pûl,~ ~dE resin6 Urethane resin' Suhs~r-e(s) Used to Adjust pH:
~~ bicarbonate Yes Yes Yes - hydro~ide Yes Yes Yes Sodium hyd~u~ide Yes pH 6.5 7.0 7.6 8.2 9.0 9.5 Dry Film ~h;rknpss~ ~m 22 20 23 23 20 22 Gloss Values:
Position A 36.2 34.9 36.1 35.5 33.8 35.7 Position B 36.5 35.2 36.5 36.0 36.0 36.5 Dil~.~ -e, B - A 0.3 0.3 0.4 0.5 2.2 0.8 500Hour corrosionpeel, mm 5 5 5 6 5 6 Footnotes for Table I
~ProductofToagosei Chrmir~ du~l~i.,5. 2ProductofToagosei(: h~mir,~lTn~ tri~.s 3Product of Toagosei C~h~mir~l T~ 4Product of Rohm & Haas.
5Product of Nippon !Sh- ~lh~i .. Table I and its footnotes are continued on the next page. ..
W O 97/04880 PCT~US96111833 Table1 continued F. - . 'e Nl ~~ . Comparison F.Y5 N~ P~-ModifyingRinseId~ ;fiP~ Letter: G H A I J K
CarL.GA~lic acid pol~,..e. ~ and salts:
g/L of Polyacrylic acidl 2.0 0.1 g/L of ~ ~ .m 3.0 4.5 5.0 polyacrylate2 &/L of Sodium polyacrylate3 10.0 g/L of Acrylic acid/ethyl ae. ylate copolymer4 ~/L of Polymaleic acid5 Polyamide resin6 Urethane resin' Jt ~ e (s) Used to Adjust pH:
~r~ t~ Yes Yes -- hydroside Yes Yes Yes Sodium l.~d~ ~idL Yes pH 10.0 10.6 6.5 8.5 12.9 11.8 Dry Film lh rL~-P~ m 23 22 22 22 20 22 Gloss Values:
Pc -~ A 35.1 36.0 35.1 27.9 35.5 34.0 Pos;li.,n B 35.9 36.5 35.6 35.7 36 0 36.5 D;l~. ~nce, B - A 0.8 0.5 0.5 7.8 0.5 2.5 SOO Hour corrosion peel, mrn 6 6 4* 5 6 6 Footnotes for Table 1 continued 6Product of Toray, water soluble, with a mrle l~r weight of about 20,000.
7Product of Dai-ichi Kogyo Seiya~u; a self-c.,~lsirying anionic resin.
*Peel width value is for 192 hours instead of 500 hours.
.. Table I and its notes are continued on the next page. ..
W O 97/04880 PCT~US96/11833 Table 1 concluded Comparison FY~m, ' e N, ' _-:
Mod;~ Rinse Id. . ~;1;. ~ Letter: L M N O P
Carbo~ylic acid pol~...e.~ and salts:
g/L of Pol~uc, ylic acidl 2.0 2.0 g/L of ~ -polyacrylatel g/L of Sodium polyacrylate3 g/L of Acrylic acid/ethyl ac. yl~le copol~ ~
g/L of Poly ~ ir acidS
Polyamide resin6 2.0 Ur~ '' ~~~ resin' 5.0 _ - e (s) Used to Adjust pH:
bicarbonate Yes Yes Yes Yes ~ L~ o,ide Sodium l.~d. .,,ide pH 2.8 5.6 7.5 8.6 7.3 Dry Film ~ m 20 23 20 22 23 20 Gloss Values:
Position A 25.5 26.0 22.2 21.8 25.0 27.9 Position B 36.0 36.2 34.6 32.5 36.0 35.7 Diff~ence, B - A 10.5 10.2 12.4 10.7 11.0 7.8 500 Hour corrosion peel, mm 8 7 6 7 5 5*
General Note for Table 1 All test panels had 100 % ratings for ~ ;o.~ on both tests a and b. However, in Co"r~)~iso" F.x~mrl~s 2 - 5, there was etching of the test sarnples revealed by test b; no such etching was a~J~alt;ll~ on any of the other s~mrles CA 02227~87 1998-01-22 Com~arison Examples 1 - 8 The procedure of Example 1 was repeated, except for using Modifying Rinse Solutions î - 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 An ~ deposi~ water-based coating composition prepared accordins~
to the formula 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) having a bolt hole as ~0 shown in Figure 1 was painted by immersion in this for 180 seconds as a test panel, rinsed by i",n,ersion in deionized water for 90 seconds immersed for 60 seconds in Modifying Rinse Solution A at o, .ii. ,ary ambient temperature and dried for 20 minutes in a hot air oven at 180 ~C and was then submitted to the tests of coating film pe, ru""ance desc, i~cl hereinafter.
~s Autode~ositing water-based coating composition for Example 9 Ingredient Co"ce,llldlion (g/L) Film-forming resin emulsion from below 250.00 Film-forming aid A from below 4.00 Hydrofluoric acid 0.70 Hydrogen peroxide 0.10 Film-fûr,,,ing aid A was trialkylpentanediol isobutyrate; its addition gave a minimum film-forming te""~erdlure in the vicinity of 20 ~C.
The film-forming emulsion was made as follows: A monomer mixture co,~ ,,urisi"g metl ,a~ylic acid 2 parts (which are parts by weight here and herein-after), methyl " l~li ,acr~/late 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 s-~ rdclal ll in an amount of 1.0 wt% of the total weight of the previous five ,~onol"ers, 0.3 part of a""~onium persulfate and 399.6 parts of deionized ~ water, and emulsion poly",eri~ed by a conventional method at 75 ~C for 4 hours 30 to make a dispe, ~,on including 20 % of polymer resin solids. This clisper~ion was then cooled to 40 ~C, mixed with a.ldilional deionized water and the other ingred-ients noted above and adjusted to pH 5 to 8 then finally adjusted with additional CA 02227~87 1998-01-22 W O 97/04880 PCT~US96/11833 deiot ,i~ed water so as to produce a volume that gave the concenlralions speci-fied above for the various active ingredients, to give the coat-forming resin dis-persion.
Comparison Example 9 The ~lodepo.si~ing 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 deior,i~ed water for 90 seconds and dried for 20 minutes in a hot air oven at 180 ~C, and was then submitted to the tests of coating film pe,ror"lance de-scribed hereinafter.
The methods for testing the performance of the coating films were as follows:
(1) Film thickness The thickness of the coalil ,9 film was cle~el " ,i. ,ed at 3 points at the top, in the middle and at the bottom of the test sheet, and the mean value of these three measurements was calcul~ted and repo~ led.
(2) Gloss values of the coatin~ film The gloss values of the co~li"y film, specirically 60~ mirror surface reflec-tion values, were deler",i,)ed 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 calc~ te l and reported, along with the difference be-tween the mean values for the two zones.
RINSE OF WET AUTODEPOSITED COATING FILM
Technical Field The pr~ser,l invention relates to a " ,elhod for coating a metal surface, for exa",ple a metal such as iron, zinc, iron alloys and zinc alloys, and the like, by autodeposition to form a predor"in2ntly organic coating on the surface of the metal, more particularly a coating which, besides having outstanding corrosion r~sislance and adhesion, also has a good appearance without any unevenness in gloss.
Background Art Coating ~lll~ ~siLions which enable the ror"~alion of a resin coating on a ~0 metal surface by bringing said metal surface into co"ta~l with an acidic composi-tion which includes an organic film-forming resin are known as "autodepositing"
or "~ ocleposilio,1" compositions and are usually water-based. Such composi-tions are ~ losed in Japanese Patent S47-17630, Japanese Examined Patent S52-21006, Japanese Examined Patent S54-13435 and Japanese Unexamined Laid-Open PatentApplication S61-168673.
The defining cl ,ard.;ieri~lic of ~utodeposili"g water-based coating compo-sitions is that by conla.ling a sl ~iPh'e metal material having a clean surface with the coating cGr"posil,or" a resin coating film which increases in thickness or weight as i,r" "e, :,ion time increases forms spo"laneously as a result of chemical reaclion 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 deposiled 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 elec~r~".,oli~/e force, as is required in ele~L.odeposiliol-. However, in some cases the co"usion resisla"ce and adhesion of an autodeposited resin coating film is not entirely satisfactory, and various means have been disclosed for improving these ~rupe, lies. Such means include che,nical l,~dl,nel ,ls of wet autodeposited coating films before they are dried. (Such chemical treatments are known by various names in the art; the most col.,mon such name is probably "final rinse", CA 02227~87 1998-01-22 which is wcll cs~ hli'jl ,ed but often a l "is"o" ,er, ber~use there may be other sub-sequent water rinses. Other names are "after-treatment", "post-treatment", "re-action rinse", "cher"ical rinse", and the one preferred herein, "modifying rinse".) The following citations exemplify such treatments. t s In Japanese Examined Patent S53-15093 and US Patent 3,795,546 it is disclosed that by bringing a coated object into contact with an aqueous solutioncontaining a hexavalent chromium compound and polyacrylate after immersion in an autodepositing aqueous coating composition and before hot drying the coated resin film, the corrosion resistance of the coating film after drying is ~o raised.
In 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, bybringing the said resin coating film before drying into co"lacl with an ~queous so-lution containing from 10 - 100 grams per liter (hereinafter usually abbreviatedas " glL") of a water-soluble solvent such as an alcohol, ketone, alcohol ester, ke-tone ester, ketone ether, or ester ether.
In Japanese Unexamined Laid-Open Patent Application S52~8240 a "l~lhod is ~lis-,lQsed for raising the cc,lusion resi~ldr,ce of an ~ulo.le~osiled resin coating film formed on a coated object after hot drying by bringing said resin cûdling film before drying into contact with an aqueous solution or aqueous dis-per~iGn 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, c~, L,oxylic acid amine salts, amino acids, melamine and amides, for ex-ample.
In Japanese Unexamined Laid-Open Patent Application H3-505841 a method is ~Ecclosed for raising the post-drying adhesion and cor, usion resislance of an ~ulodeposiled resin coating film formed on a coated object by bringing said resin coali. ,g film, before hot drying, into co"lacl with an aqueous solution of an alkaline substance.
Similarly, Japanese Unexamined Laid-Open Patent Application H5-186889 discloses a method for raising the post-drying adhesion and corrosion W O 97/04880 PCT~US96/11833 resislance of an ~utodeposited resin coating film formed on a coated object by bringing the said resin coali"g film before hot drying into CGI ,la~ with an ~q"esus solution with a pH from 7 to 11 COI)ldil lil l!3 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.
Rec~use coaling by ~u(ndeposilion 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 l l Idlel ial is to be bolted in place. In such instances, a consistent .0 coali"g fiim appear~,)ce is not usually obtained, because there is a variation in gloss between the portions where sagy;~ ~9 occurs and other portions. When an ~ llodeposiled resin coaling film is the last or only codlil ,9 employed on the coat-ed object, this variation in gloss considerably affects the quality of the appear-ance of the coated object. The pre-drying modifying rinses of autodeposited res-in codlil ,9 fiims known from the art cies~ ibed previously are beneficial for raisingthe 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 Vdl idLiol I in gloss. In recent years the painting of metal sur-faces is being required to give yl ealer added value, so that high corrosion resist-ance, high adhesion and also a uniform appearance are required, and an im-provement in this appeara"ce would be desirable.
Disclosure of the Invention Problems to Be Solved by the Invention The object of the present invention is to provide a method for coating a metal surface which enables the formation of an ~ llodel~osiled resin coating film which has o~ ,la,)d;ng co"usion resislar,ce and adhesion, and also has a good appeara,)ce without any variation in gloss.
~ummary of the Invention The problem above is solved by a method for coating a metal surface which co""~, ises forming a resin co~li"y film on the metal surface by maintaining said metal surface in contact with an autodepositing type water-based coating co",posiLion cor"p, ising a coat-forming resin emulsion, an acid and an oxidizing CA 02227~87 1998-01-22 .
agent, and, oplio, lally, addiliG,)al metal ions for a su~ficient time to form a wet aut-odeposited film thereon, discGnlinuing contact between the wet autodeposited film and any part of the ~utocleposiling type water-based coating composition, ex-cept that which is physically incorporated into the autodeposited film, bringingsaid wet ~ odeposiLed film into con~ with an ~queous solution which has a pH
value from 6 to 11 and which, in addition to water, co" ,,u, ises, preferably consists esse"lially of, or more ~rerel dbly CGI ,sisls of from 0.2 - 10.0 g/L of dissoived, dis-persed, or both dissolved and dispersed polymer(s) selected from the group con-sisting of polymers of carboxylic acid ,no"o,ners having an ethylenic double bond ~o and salts thereof.
Brief Description of the Drawing Figure 1 is a drawing of the largest area surface of the test panels used in the examples and col"parisol1 examples, showing the positions at which gloss values were deter",ined and the relation of these positions and their size to the position and size of a hole through the test panels.
Details of the Invention, Including Preferred Embodiments There are no narrow restrictions as to the resin in the film-forming resin emulsion employed in the present invention, which can be any resin which is capal~l~ of sali:jraclor~/ 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 ",~ll,ac,ylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacryl-ate, glycidyl acrylate and glycidyl " ,ell ,a~ ylate, and the like and also acrylamide,methacrylamide, acrylonitrile, acrylic acid and methacrylic acid. Other suitable ~u~ IGr"e,:, include styrene, ethylene, vinyl chlo, ide, vinylidene chloride, vinyl ace-tate, and the like. Other 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.
There are no narrow restrictions as to the molecular weight of the coat-CA 02227~87 1998-01-22 forming resin, but, for example, the mo'Qc~ r weight as measured by gel perme-ation cluo" ,aloy~ apl ,y in tetrahydrofuran, using polystyrene or a poly(acrylic acid ester) as a reference, 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 prese, ll invention can be any resin emulsion or~lina, ily used in ,~,repa, ing Al ~to~ leposili~ ,9 water-based coat-ing coll~posiliv, ,s, in most cases it will be a resin emulsion obtained by ordi,)a,y emulsion polymeri~aliot), but it can also be a resin emulsion formed by emulsify-ing in water a resin obtained by another method of polymerization.
~0 There are also no narrow r~sl, ictio"s as to the conditions for polymeriza-tion to give a polymer emulsion by emulsion polymeri~aliol " and this can be per-formed by an ordinary method; however, as an example a film-forming resin emulsion can be obtained by subjecting a mixture co" ,prising at least water, ananionic surfactant and/or nonionic su~raclanl, resin constituent monomers as noted above, and a pol~"nel i~dlion initiator to conditions which will activate the polymeri~dlion initiator to produce a polymerization reaction.
An ~ulorleposili~ ~y water-based coating c~" "~osilion 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 necess~ry.
As the acid, for e~d" ,ple, any one or more selected from hydrofluo i, co"ic acid, hydrofluolilan,c acid, hydrofluosilicic acid, hydrofluoboric acid, hydrofluoric acid".,hospho(ic acid, nitric acid, and the like, can be employed, but hydrofluoric acid is p,efe"ed. As the oxidi~in~ agent h~,-l,o~Jen peroxide, potassium perman-ganate and sodium nitrite, and the like, can be used; but hydrogen peroxide is pl-~fer~ed. There are no narrow restrictions as to compounds which can supply metal ions, provided that they are stable in said coating composition; examples include ferric fluoride, ferric nitrate, ferrous p hosphdle and cobaltous nitrate, and the like, and ferric fluoride is preferred.
The co,-te, ll of resin in an aulocleposili"g water-based coating co" Iposilio,,employed in the presenl invention, measured as the COI ~cenll dlion of resin solids, is preferably from 5 to 550 g/L, and more preferably from 50 to 100 g/L. The CA 02227~87 1998-01-22 W O 97104880 PCT~US96/11833 concer,l, dliOII of acid is prerer~1bly from 0.1 to 5.0 g/L, and more preferably from 0.5 to 3.0 g/L; and the conce"l,dlion of oxidi~il)g agent is preferably from 0.01 to 3.0 g/L, and more prererably 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 r s conce"l,alion should be s 50 g/L, and is preferably from 1.0 to 5.0 g/L.
An ~ ~todeposili, lg 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 deposiled resin particles, andtor a pigment such as a carbon black, phthalocyan-ine blue, phthalocyanine green, quinac, ido"e 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 pGI L;GI IS of various cornpone,)ls such as automobile sheet compon-ents and aulo",obile compGnents such as shock absorbers, jacks, leaf springs, suspel Isiol, co" ,pol~enls and brackets, and the like, and components of furniture such as drawer rails, and the like.
There are no narrow restrictions as to the method for contacting a metal surface using an autodeposili,-g ccdlillg co",posilion employed in the present in-vention, and any method generally applicable to surface treatment, such as im-r"ersion, spraying or roll coali"g, and the like, can be adopted; however, immer-sion is usuaily pr~fe" ed. There are also no narrow restrictions as to the temper-ature of treatment or the duration of treatment; however, in the case of immer-z5 sion treatment, i"""e,~io" at o,di"aly ambient temperature, e.g. 18 to 25 ~C, for from 30 to 300 seconds, and prererably from 90 to 240 seconds, is generally suit-able.
There are no narrow lil"ildlions as to the quantity of said coali"g composi-tion applied to the metal; however, the film thickness after drying is prererably from 5 to 40 micrometers (hereinafter usually abbreviated as ",um"), and more preferal,ly is from 20 to 30 l~m.
01 dil Idl ily a metal surface prerer~bly is degreased and rinsed with water CA 02227~87 1998-01-22 W O 97/04880 PCT~US96/11833 before applying said coating composition.
After applying said cGcllil ,9 cor, l~osilion to a metal, it is prererdbly subject-ed to or~ ,aly rinsing with water; then the modifying rinse that characterizes the pr~senl invention is pe~ ru~ med. 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 ~ r~:rerably from 20 to 60 seco"ds, in water at ordinary am-bient te",peralure.
As menlio"ed previously, a modifying rinse process of the present inven-tion is pe, ro""ed by bringing the resin coating film produced as above into con-tact with an Zl~ll leO US 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 ,l ,onor"er~ having an ethylenic double bond and salts ll ,ereor. The total conce, Ill~lion 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. With a con-centration less than 0.2 g/L, no benefits can normally be expected in terms of preventing va, i~tiGn in the gloss of the coaLi,)g film after drying, and on the other hand when the total co"ce~ lll dliOII exceeds 10.0 g/L, the drying properties of the oule""osl surface of the resin coating film become uneven and this in itself tends to produce variations in gloss.
Polymers of carboxylic acid monomers having an ethylenic double bond and salts ll ,ereor 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 co"nection with the resin in the droren,enlioned 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, ilaco" ~ acid, crolo"ic acid, and the like), and sodium salts and ammoniumsalts of these, and the like. Of these, polyacrylic acid and the ammonium salts ll ,erec r are ~ferer, ed. In the case of copolymers, the weight ratio of (meth)acrylic acid ester m~"o",er(s) and/or styrene to carboxylic acid monomer(s) having an ethylenic double bond is p,-erer~bly from 1:99 to 50:50, and more preferably from 3:97 to 30:70. There are no narrow resl, iotio"s as to the molecular weight of the polymers of carboxylic acid ")onc r"er~ having an ethylenic double bond; howev-CA 02227~87 1998-01-22 W O 97/04880 PCT~US96/11833 er, the molec~ weight is prererably from 2000 to 200,000, and more preferably from 1 0,000 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 uses a polymer purified from a pol~" ,eri,dlion liquor when making said modifying rinse solution, or the polymeri~alion 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 pr~re"ed. With a pH less than 6.0, there is usually no benefit of preventing variation in gloss after drying, and cc " usio~ ~ resistance and adhesion are not usually adequate; on the other hand, when the pH exceeds 11, adhesion becomes in~dequ~te and/or there is an undesirable etching of the metal surface coated.
As the substance used to adjust the pH of said modifying rinse solution a known substance disclosed in Japanese Unexamined Laid-Open Patent Appli-cation H3-505841 or Japanese Unexami,)ed Laid-Open Patent Application H5-186889 ~r~re, dbly is used. EXdl I Iples include ammonium bicarbonate, dl "n ,o"i-um hydroxide and hydroxides of alkali metals such as sodium, potassium and lithium. Pl ererably at least one of dl l ll l lGI ,ium biCdl uonale, ammonium hydroxide and sodium hydroxide is/are used. Ammonium bicarbonate andlor ammonium hydroxide are more preferred.
There is no narrow re~l, i.:(iu" as to the modifying rinse process conditions of the present invention; a modifying rinse process according to the invention can suitably be performed by immersion at a temperature from 5 to 60 ~C, and prererably at Gldi~)aly ambient temperature, with a conlaul time of from 30 to 120 seconds, or more p,ererdbly from 60 to 90 seconds. After said modifying rinse, moisture on the cGali"g film is evapordled and the coalescence of the resin part-icles ,u~ ~re, ably is accelerated by subjecting the coated object to a drying treat-ment. There is no narrow restriction as to this drying; in general it can preferably be performed at 60 to 200 ~C, or more ~u,eferably at 100 to 180 ~C, for a time from 5 to 30 minutes, or pr~rerauly from 10 to 20 minutes.
The present invention is ex~,lained in more detailed terms below by means CA 02227~87 1998-01-22 W O 97/04880 PCTrUS96/11833 of examples and comparison examples.
FY~mPIeS and Comparison Examples EYample 1 An ~l Itodepositing water-based coating composition prepared as noted below was held at a bath te~l~peralLIre 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 i~ "ner~iol H n this composition for 180 seconds rinsed by i" " "er~iGn in deior,i~ed water for 60 secc ,)~ls i,n,oer:,ed for 60 seconds in Modifying Rinse Solution A below at ordinary ambient teml~erdl-lre and dried .0 for 20 minutes in a hot air oven at 110 ~C, and was then submitted to the tests of coali"~ film pe, r~,r"~dnce described hereinafter.
Test autodepositing water-based coating composition Inaredient COI Icenll dlion (g/L) SaranTM SL-143 Latex (solids 55%) 95.00 ~s (a W. R. Grace product) Hydrofluoric acid 0.70 Ferric fluoride 3.00 HycJ,oyen peroxide 0.10 The above ing, ~d,e. Ils were combined with deionized water only to produce the autodepositing coating composition.
SaranTM SL-143 Latex is an emulsion co, ll~il ,;"g a vinylidene chloride co-polymer resin which becomes a coat-forming resin when combined with the other ingredients listed Modifying Rinse Solution A
An ~ eous solution of polyacrylic acid (solids 25 %) (Toagosei product) diluted with deionized water to give a polyacrylic acid concel ,l,alion of 2.0 g/L
and adjusted to pH 6.5 with a,n",o,1ium bicarbonate was used.
FYzlrnoles 2 to 8 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 sub-~lances and/or amounts thereof used as ingredients.
Table 1 COMPOSITIONS AND TEST RESULTS FOR THE EXAMPLES AND COMPARISON
E)CAMPLES
F~mp'e N-~.. .be Modir~;.. g Rinse 1~ Letter: A B C D E F
Carboxylic acid polymers and salts:
g/L of Polyacrylic acidl2.0 1.5 1.0 g/L of ~ - ~ 1.5 1.0 polyacrylate2 g/L of Sodium polyacrylate3 0.5 0.5 g/L of Acrylic acidtethyl 0.5 acrylate copolymer4 g/L of Polymaleic acid5 1.0 Pûl,~ ~dE resin6 Urethane resin' Suhs~r-e(s) Used to Adjust pH:
~~ bicarbonate Yes Yes Yes - hydro~ide Yes Yes Yes Sodium hyd~u~ide Yes pH 6.5 7.0 7.6 8.2 9.0 9.5 Dry Film ~h;rknpss~ ~m 22 20 23 23 20 22 Gloss Values:
Position A 36.2 34.9 36.1 35.5 33.8 35.7 Position B 36.5 35.2 36.5 36.0 36.0 36.5 Dil~.~ -e, B - A 0.3 0.3 0.4 0.5 2.2 0.8 500Hour corrosionpeel, mm 5 5 5 6 5 6 Footnotes for Table I
~ProductofToagosei Chrmir~ du~l~i.,5. 2ProductofToagosei(: h~mir,~lTn~ tri~.s 3Product of Toagosei C~h~mir~l T~ 4Product of Rohm & Haas.
5Product of Nippon !Sh- ~lh~i .. Table I and its footnotes are continued on the next page. ..
W O 97/04880 PCT~US96111833 Table1 continued F. - . 'e Nl ~~ . Comparison F.Y5 N~ P~-ModifyingRinseId~ ;fiP~ Letter: G H A I J K
CarL.GA~lic acid pol~,..e. ~ and salts:
g/L of Polyacrylic acidl 2.0 0.1 g/L of ~ ~ .m 3.0 4.5 5.0 polyacrylate2 &/L of Sodium polyacrylate3 10.0 g/L of Acrylic acid/ethyl ae. ylate copolymer4 ~/L of Polymaleic acid5 Polyamide resin6 Urethane resin' Jt ~ e (s) Used to Adjust pH:
~r~ t~ Yes Yes -- hydroside Yes Yes Yes Sodium l.~d~ ~idL Yes pH 10.0 10.6 6.5 8.5 12.9 11.8 Dry Film lh rL~-P~ m 23 22 22 22 20 22 Gloss Values:
Pc -~ A 35.1 36.0 35.1 27.9 35.5 34.0 Pos;li.,n B 35.9 36.5 35.6 35.7 36 0 36.5 D;l~. ~nce, B - A 0.8 0.5 0.5 7.8 0.5 2.5 SOO Hour corrosion peel, mrn 6 6 4* 5 6 6 Footnotes for Table 1 continued 6Product of Toray, water soluble, with a mrle l~r weight of about 20,000.
7Product of Dai-ichi Kogyo Seiya~u; a self-c.,~lsirying anionic resin.
*Peel width value is for 192 hours instead of 500 hours.
.. Table I and its notes are continued on the next page. ..
W O 97/04880 PCT~US96/11833 Table 1 concluded Comparison FY~m, ' e N, ' _-:
Mod;~ Rinse Id. . ~;1;. ~ Letter: L M N O P
Carbo~ylic acid pol~...e.~ and salts:
g/L of Pol~uc, ylic acidl 2.0 2.0 g/L of ~ -polyacrylatel g/L of Sodium polyacrylate3 g/L of Acrylic acid/ethyl ac. yl~le copol~ ~
g/L of Poly ~ ir acidS
Polyamide resin6 2.0 Ur~ '' ~~~ resin' 5.0 _ - e (s) Used to Adjust pH:
bicarbonate Yes Yes Yes Yes ~ L~ o,ide Sodium l.~d. .,,ide pH 2.8 5.6 7.5 8.6 7.3 Dry Film ~ m 20 23 20 22 23 20 Gloss Values:
Position A 25.5 26.0 22.2 21.8 25.0 27.9 Position B 36.0 36.2 34.6 32.5 36.0 35.7 Diff~ence, B - A 10.5 10.2 12.4 10.7 11.0 7.8 500 Hour corrosion peel, mm 8 7 6 7 5 5*
General Note for Table 1 All test panels had 100 % ratings for ~ ;o.~ on both tests a and b. However, in Co"r~)~iso" F.x~mrl~s 2 - 5, there was etching of the test sarnples revealed by test b; no such etching was a~J~alt;ll~ on any of the other s~mrles CA 02227~87 1998-01-22 Com~arison Examples 1 - 8 The procedure of Example 1 was repeated, except for using Modifying Rinse Solutions î - 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 An ~ deposi~ water-based coating composition prepared accordins~
to the formula 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) having a bolt hole as ~0 shown in Figure 1 was painted by immersion in this for 180 seconds as a test panel, rinsed by i",n,ersion in deionized water for 90 seconds immersed for 60 seconds in Modifying Rinse Solution A at o, .ii. ,ary ambient temperature and dried for 20 minutes in a hot air oven at 180 ~C and was then submitted to the tests of coating film pe, ru""ance desc, i~cl hereinafter.
~s Autode~ositing water-based coating composition for Example 9 Ingredient Co"ce,llldlion (g/L) Film-forming resin emulsion from below 250.00 Film-forming aid A from below 4.00 Hydrofluoric acid 0.70 Hydrogen peroxide 0.10 Film-fûr,,,ing aid A was trialkylpentanediol isobutyrate; its addition gave a minimum film-forming te""~erdlure in the vicinity of 20 ~C.
The film-forming emulsion was made as follows: A monomer mixture co,~ ,,urisi"g metl ,a~ylic acid 2 parts (which are parts by weight here and herein-after), methyl " l~li ,acr~/late 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 s-~ rdclal ll in an amount of 1.0 wt% of the total weight of the previous five ,~onol"ers, 0.3 part of a""~onium persulfate and 399.6 parts of deionized ~ water, and emulsion poly",eri~ed by a conventional method at 75 ~C for 4 hours 30 to make a dispe, ~,on including 20 % of polymer resin solids. This clisper~ion was then cooled to 40 ~C, mixed with a.ldilional deionized water and the other ingred-ients noted above and adjusted to pH 5 to 8 then finally adjusted with additional CA 02227~87 1998-01-22 W O 97/04880 PCT~US96/11833 deiot ,i~ed water so as to produce a volume that gave the concenlralions speci-fied above for the various active ingredients, to give the coat-forming resin dis-persion.
Comparison Example 9 The ~lodepo.si~ing 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 deior,i~ed water for 90 seconds and dried for 20 minutes in a hot air oven at 180 ~C, and was then submitted to the tests of coating film pe,ror"lance de-scribed hereinafter.
The methods for testing the performance of the coating films were as follows:
(1) Film thickness The thickness of the coalil ,9 film was cle~el " ,i. ,ed at 3 points at the top, in the middle and at the bottom of the test sheet, and the mean value of these three measurements was calcul~ted and repo~ led.
(2) Gloss values of the coatin~ film The gloss values of the co~li"y film, specirically 60~ mirror surface reflec-tion values, were deler",i,)ed 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 calc~ te l and reported, along with the difference be-tween the mean values for the two zones.
(3) Coating film adhesion (cross-hatch tape peel test) Before and after immersion in warm water at 40 ~C for 240 hours, one hundred 1-mm squares were cut in the test sheet, and the number of squares of paint film remaining after peeling with a tape were determined.
~o (4) Corrosion resistance The coaling 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 CA 02227~87 1998-01-22 W O 97/04880 PCT~US96/11833 it was peeled with a tape, and the maximum width on either side that peeled fromthe cross-cut part was determined and reported in millimeters ("mm").
Results of all of the coali"g film performance tests are shown in Table 1, from which it is clearly evident that in Examples 1 through 9 in which the coali"y ",elhod of the prt:senl invention was used, the coating film after drying had out-standing corrosion resistance, adhesion, and little or no variation in gloss. Bycont, d:~l, there was a large va, ialio" in gloss in Comparison Example 1 in which the polyacrylate conce"l,dlion of the modifying rinse solution was low; and, al-though the appearance of the coating film was good in Comparison Examples 2 10 and 3, in which the pH of the modifying rinse solution exceeded 11, undesirable etching of the metal was revealed by the test of the adhesion of the coating film after i",llle,~io,l in warm water. In Comparison Examples 4 and 5, in which the pH of the modifying rinse solution was less than 6, the corrosion resisla"ce of the codling film and its adl ,esion after immersion in warm water were inferior, and the t5 coalilly film had a variable gloss. In Com,ua~ ison Examples 6 and 7, in which an organic resin other than a polymer of a carboxylic acid " ,ono" ,er having an ethyl-enic double bond or a salt thereof was used, and in Comparison Example 8 in which an""o";um bicalbonala was used on its own as a modifying rinse solution, va, ialions in gloss were produced in the coating film. Variations in the gloss of the coaliny film were also pro~ Gerl in Comparison Example 9, in which no modi-fying rinse solution was employed.
Benefits of the Invention By using the ,netl ,od of the prese,)l invention for coating a metal surface, an aulodelJosiled resin coating film can be obtained which has oul~la,)di"g corro-sion resislance and adhesion and in addition also has a better appearance thancoating films obtained by prior methods, without any substantial variation in gloss.
~o (4) Corrosion resistance The coaling 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 CA 02227~87 1998-01-22 W O 97/04880 PCT~US96/11833 it was peeled with a tape, and the maximum width on either side that peeled fromthe cross-cut part was determined and reported in millimeters ("mm").
Results of all of the coali"g film performance tests are shown in Table 1, from which it is clearly evident that in Examples 1 through 9 in which the coali"y ",elhod of the prt:senl invention was used, the coating film after drying had out-standing corrosion resistance, adhesion, and little or no variation in gloss. Bycont, d:~l, there was a large va, ialio" in gloss in Comparison Example 1 in which the polyacrylate conce"l,dlion of the modifying rinse solution was low; and, al-though the appearance of the coating film was good in Comparison Examples 2 10 and 3, in which the pH of the modifying rinse solution exceeded 11, undesirable etching of the metal was revealed by the test of the adhesion of the coating film after i",llle,~io,l in warm water. In Comparison Examples 4 and 5, in which the pH of the modifying rinse solution was less than 6, the corrosion resisla"ce of the codling film and its adl ,esion after immersion in warm water were inferior, and the t5 coalilly film had a variable gloss. In Com,ua~ ison Examples 6 and 7, in which an organic resin other than a polymer of a carboxylic acid " ,ono" ,er having an ethyl-enic double bond or a salt thereof was used, and in Comparison Example 8 in which an""o";um bicalbonala was used on its own as a modifying rinse solution, va, ialions in gloss were produced in the coating film. Variations in the gloss of the coaliny film were also pro~ Gerl in Comparison Example 9, in which no modi-fying rinse solution was employed.
Benefits of the Invention By using the ,netl ,od of the prese,)l invention for coating a metal surface, an aulodelJosiled resin coating film can be obtained which has oul~la,)di"g corro-sion resislance and adhesion and in addition also has a better appearance thancoating films obtained by prior methods, without any substantial variation in gloss.
Claims (13)
1. A process for coating a metal surface, said process comprising steps of:
(I) bringing said metal surface into contact with an autodepositing type water-based coating composition comprising water and (A) a coat-forming resin dispersed in the composition, (B) an acid, and (C) an oxidizing agent, and, optionally, (D) metal ions and maintaining contact between said coating composition and said metal surface for a sufficient time that a wet autodeposited film forms on said metal surface;
(II) discontinuing contact between said wet autodeposited film and any of said coating composition that is not physically incorporated into said wet auto-deposited film;
(III) contacting the wet autodeposited film formed in steps (I) and (II), while it is still wet, with an aqueous modifying rinse composition having a pH
value from 6 to 11 and comprising a total of from 0.2 to 10.0 g/L of polymer molecules selected from the group consisting of (i) homopolymer molecules and copolymer molecules of carboxylic acid monomers having an ethylenic double bond and (ii) salts of the polymer molecules as recited in part (i), so as to produce a modified wet autodsposited film;
(IV) discontinuing contact between said modifed wet autodeposited film and any of said aqueous modifying rinse composition that is not physically incorporated into said modified wet autodeposited film; and (V) hot drying the modified wet autodeposited film formed in steps (III) and (IV), so as to convert the modified wet autodeposited film into an adherent dry autodeposited coating on the metal surface.
(I) bringing said metal surface into contact with an autodepositing type water-based coating composition comprising water and (A) a coat-forming resin dispersed in the composition, (B) an acid, and (C) an oxidizing agent, and, optionally, (D) metal ions and maintaining contact between said coating composition and said metal surface for a sufficient time that a wet autodeposited film forms on said metal surface;
(II) discontinuing contact between said wet autodeposited film and any of said coating composition that is not physically incorporated into said wet auto-deposited film;
(III) contacting the wet autodeposited film formed in steps (I) and (II), while it is still wet, with an aqueous modifying rinse composition having a pH
value from 6 to 11 and comprising a total of from 0.2 to 10.0 g/L of polymer molecules selected from the group consisting of (i) homopolymer molecules and copolymer molecules of carboxylic acid monomers having an ethylenic double bond and (ii) salts of the polymer molecules as recited in part (i), so as to produce a modified wet autodsposited film;
(IV) discontinuing contact between said modifed wet autodeposited film and any of said aqueous modifying rinse composition that is not physically incorporated into said modified wet autodeposited film; and (V) hot drying the modified wet autodeposited film formed in steps (III) and (IV), so as to convert the modified wet autodeposited film into an adherent dry autodeposited coating on the metal surface.
2. A process according to claim 1, also comprising a step (II) of rinsing the wet autodeposited resin film formed in step (II) with water before performing step (III).
3. A process according to claim 2, wherein, the autodepositing type water-based coating composition used in step (I), the coat-forming resin has a molecular weight in a range from 100,000 to 1,000,000 and is present in a concentration from 50 to 100 g/L.
4. A process according to claim 1 wherein in the autodepositing type water-based coating composition used in step (I) the coat-forming resin has a molecular weight in a range from 50,000 to 1,000,000 and is present in a concentration from 5 to 550 g/L.
5. A process according to claim 4, wherein, in the autodepositing type water-based coating composition used in step (I) acid is present in a concentration from 0.1 to 5.0 g/L and oxidizing agent is present in a concentration from 0.01 to 3.0 g/L.
6. A process according to claim 3, wherein, in the autodepositing type water-based coating composition used in step (I), acid is present in a concentration from 0.5 to 3.0 g/L and oxidizing agent is present in a concentration from 0.03 to 1.0 g/L.
7. A process according to claim 2, wherein, in the autodepositing type water-based coating composition used in step (I), acid is present in a concentration from 0.5 to 3.0 g/L and oxidizing agent is present in a concentration from 0.03 to 1.0 g/L.
8. A process according to claim 1, wherein, in the autodepositing type water-based coating composition used in step (I), acid is present in a concentration from 0.1 to 5.0 g/L and oxidizing agent is present in a concentration from 0.01 to 3.0 g/L.
9. A process according to any one of claims 1 to 8, wherein, in the modifying rinse solution, polymer molecules selected from the group consisting of polymer molecules of acrylic acid and ammonium salts thereof are present in a total concentration from 0.5 to 4.5 g/L.
10. A process according to claim 9, wherein, in the modifying rinse solution, polymer molecules selected from the group consisting of polymer molecules of acrylic acid and ammonium salts thereof are present in a total concentration from 1.0 to 3.0 g/L and have a molecular weight from 10,000 to 50,000.
11. A process according to claim 10, wherein, in the autodepositing type water-based coating composition used in step (I), the acid is hydrofluoric acid and the oxidizing agent is hydrogen peroxide.
12. A process according to claim 9, wherein, in the autodepositing type water-based coating composition used in step (I), the acid is hydrofluoric acid and the oxidizing agent is hydrogen peroxide.
13. A process according to any one of claims 1 to 8, wherein, in the autode-positing type water-based coating composition used in step (I), the acid is hydro-fluoric acid and the oxidizing agent is hydrogen peroxide.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP7209215A JPH0938573A (en) | 1995-07-25 | 1995-07-25 | Coating method for metal surface |
| JP7/209215 | 1995-07-25 | ||
| PCT/US1996/011833 WO1997004880A1 (en) | 1995-07-25 | 1996-07-24 | Composition and process for autodeposition with modifying rinse of wet autodeposited coating film |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2227587A1 true CA2227587A1 (en) | 1997-02-13 |
Family
ID=16569263
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002227587A Abandoned CA2227587A1 (en) | 1995-07-25 | 1996-07-24 | Composition and process for autodeposition with modifying rinse of wet autodeposited coating film |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0871549A1 (en) |
| JP (1) | JPH0938573A (en) |
| BR (1) | BR9609702A (en) |
| CA (1) | CA2227587A1 (en) |
| MX (1) | MX9800584A (en) |
| TR (1) | TR199800113T1 (en) |
| WO (1) | WO1997004880A1 (en) |
| ZA (1) | ZA966294B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3860693B2 (en) * | 1999-12-17 | 2006-12-20 | 日本パーカライジング株式会社 | Self-depositing type coating composition, method for coating metal surface, and coated metal material |
| FR3019477B1 (en) * | 2014-04-03 | 2023-03-17 | Commissariat Energie Atomique | SURFACE FUNCTIONALIZATION PROCESS |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5248525A (en) * | 1991-01-24 | 1993-09-28 | Henkel Corporation | Treating an autodeposited coating with an alkaline solution containing anions of multifunctional organic acids |
-
1995
- 1995-07-25 JP JP7209215A patent/JPH0938573A/en active Pending
-
1996
- 1996-07-24 WO PCT/US1996/011833 patent/WO1997004880A1/en not_active Application Discontinuation
- 1996-07-24 ZA ZA9606294A patent/ZA966294B/en unknown
- 1996-07-24 CA CA002227587A patent/CA2227587A1/en not_active Abandoned
- 1996-07-24 MX MX9800584A patent/MX9800584A/en unknown
- 1996-07-24 TR TR1998/00113T patent/TR199800113T1/en unknown
- 1996-07-24 EP EP96925341A patent/EP0871549A1/en not_active Withdrawn
- 1996-07-24 BR BR9609702A patent/BR9609702A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| WO1997004880A1 (en) | 1997-02-13 |
| JPH0938573A (en) | 1997-02-10 |
| TR199800113T1 (en) | 1998-05-21 |
| EP0871549A1 (en) | 1998-10-21 |
| ZA966294B (en) | 1997-02-11 |
| MX9800584A (en) | 1998-04-30 |
| BR9609702A (en) | 1999-03-23 |
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