CA1084357A

CA1084357A - Coating metal surfaces

Info

Publication number: CA1084357A
Application number: CA253,441A
Authority: CA
Inventors: Hideaki Kaneko; Kiyoichi Yamazaki; Yasunobu Matsushima
Original assignee: Oxy Metal Industries Corp
Current assignee: Oxy Metal Industries Corp
Priority date: 1975-05-28
Filing date: 1976-05-27
Publication date: 1980-08-26
Also published as: DE2621970A1; FR2312302A1; GB1547873A; SE7606041L; IT1060706B; NL7605664A; JPS51138733A; MX142935A; JPS5410014B2; AU1390776A; BE842167A; AU502391B2; FR2312302B1

Abstract

COATING METAL SURFACES

ABSTRACT OF THE DISCLOSURE
Disclosed is a process for obtaining an adherent protective coating on a metal surface. The surface is contacted with an aqueous composition containing an organic film-forming resin, a free radically polymerizable monomer and a free radical initiator.

Description

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i BACKGROUND OF THE INVENTION
The present invention relates to a composition and pro-cess for coating the surface of a metal such as iron, zinc, galvanized steel plate, aluminum, copper and the like with an organic polymer. It provides a process for coating a metal sur-face which can be carried out inexpensively with good results such as improved corrosion resistance and favorable appearance.
The present process for coating metal surface with an organic polymer resin by employing a solution, emulsion or suspension of a polymer resin is different markedly from conventional proce-dure and aims at depositing an organic polymer film by contact-ing the metal surface to be treated with an aqueous solution of suspension containing a film-forming composition by immers-ing, pouring or coating with rollers and provides a coating process for depositing a polymer film-coating material on the metal surface.
It has been known to apply a film by immersing a metal surface in an aqueous emulsion, dispersion or solution contain-ing a film-forming polymer resin. ~he thickness of film thus ' 20 obtained depends on the total solids concentration, specific gravity, bath temperature, ambient temperature, ambient hu~idity ~-~ and other factors. A metal surface having such a film thereon cannot generally be washed or rinsed with water before drying or curing causing partial or total removal of the film-forming material. Also, excess film-forming material flows by gravity , - to the lower part of the coated article to form drips which give an undesirable appearance upon drying. To avoid such problems, the electrostatic coating process w'nich does not form such drips and does not require a water rinse has been em-ployed. However, equipment required for electrostatic coating is expensive. In addition, the film cannot readily be applied .. ' ~ .

35~7 uniformly is, because of the shape of the object, non-uniform current densi-ties are obtained~
,~ SUMM~RY ~ T~E INVENTION
It has now been founcl that the fore~oing problems may be overcome by a composition arld process for coating an organic polymer resin on a metal surfac:e by contacting the metal with an aqueous solution or dispersion containing an organic polymer resin, one or more monomers or oligomers polymerizable to poly-mer resin and a polymerization initiator.
In accordance with the invention, there is provided a proc~s for coating a metal surface comprising contacting the surface with an aqueous acidic composition c~mprising an organic film-forming resin, a monomer polymerizable by free radical mechanism and a free radical polymerization initiator.
DETAILED DESCRIPTION OF THE INVENTIOM
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The film-forming polymer resins usable in the present invention include almost all or~anic polymer resins which have employed, e.g., an aqueous solution, emulsion, or suspension consisting of one or more polymer resins such as vinyl polymers -and copolymers of vinyl acetate, vinyl chloride, vinylidenechloride and the like; acrylic polymers and copolymers of acryl-ic acid, methacrylic acid, acrylic esters, methacrylic esters, '~
hydroxyacrylic acid, hydroxymethacrylic acid, alkyd resins, ` epoxy resins, fluorocarbon resins; urethane resins, polyester resins, styrene resins, olefine polymers and copolymers, syn-thetic rubbers such as butadiene rubber as well as natural - polymers. ;~
me monomers polymerizable to the polymers and usable ~-- in the present invention include all monomers polymerizable by free radical mechanism such as acrylic acid, methacrylic acid;

methyl-, ethyl-, butyl-, and 2-ethylhexylhydroxy-acrylate es-ters .. -' '.' .

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~` ~1)8~3~7 or methacrylate esters, vinyl acetate, vinyl propionate, vinyl caproate, s-tyrene, itaconic ac:id, crotonic acid, methylvinyl ether, vinylidene chloride, acrylonitrile, acrylamide, methecryl-amide, 2-aminomethylvinyl ether, glycidyl ether, glycidyl me-th-acrylate, hydro,xyalkyl acrylates and the like as well as , t~` - 2a -. ~ .
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8~7 , various organic compounds within the category of so-called oli-gomers which are included in the definition of monomers for purposes of this invention. See, for example, Textbook of Polymer Science, Bill Meyer, editor, ~ohn Wiley & Sons, Inc., 1965, page 292 for monomers polymerizable by the free radical mechanism.
The polymerization initiators usable in the present in-~- vention may be selected from any known free radical initiators but should be chosen from those which are relatively stable in an aqueous medium at ambient temperature. Such initiators include any stable organic peroxides such as ketone peroxides, peroxyketals, cumene hydroperoxide, t-butylcumyl peroxide, ' acetyl peroxide, benzoyl peroxide, t-butylperoxyisobutylate, t-butylperoxyphthalate, lauroyl peroxide, as well as persulfates, percarbonates, perborates, hydrogen peroxide and the like.
The present invention comprises an aqueous solution ' !~ or suspension containing:
(1) an aqueous solution or dispersion containing at least one film-forming polymer resin in a concentration ranging from 0.5 to 50% by weight,

(2) at least one free radically polymerizable mono-mer or oligomer in a concentration from 0.1 to 10% by weight, and : .
,- t3) a free-radical polymerization initiator in an i amount ranging from 0.02 to 5% by weight, ~-, :
~- and the process of coating therewith. An aqueous solution or F ~ dispersion containing the film-forming polymer resin in an amount of less than 0.5% by weight will deposit the film in a thickness too thin to be effective for practical uses. If the ` 30 film-forming polymer resin concentraticn is increased to an ,, .

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amount of more than 50% by weig1ht, it will be economically disadvanta~eous because an increase in the viscosity of the ; solution or dispersion will increase the amount of dray-out.
. The monomer or oligomer polymerizable to the polymer may be present in an amount sufficient for bonding the film-forming polymer resin particles to each other. When used in an amount of less than 0.1% by weight, the quantity of film-forming polymer resin formed will be small and have poor deposition ' properties. In an amount of higher than 10% by weight, it will tend to gelate ~ith the film-forming polymer resin which is detrimental to the stability of the solution or dispersion.
At a concentration of lower than 0.02% by weight of the polymerization initiator, the deposition rate on the metal surface will be retarded, while at a concentration of higher than 5% by weight, the deposition will tend to occur prematurely and affect the stability of solution or dispersion adversely.
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~ In order to enhance the film-forming ability of the ; polymer resin and to improve the dissolution or dispersion cf polymerization initiator, the solution or dispersion may include ~;
~ 20 a plasticizer such as phthalate ester, dibasic fatty acid es-,~ ters, glycol esters, fatty acid esters, phosphate esters, epoxy plasticizers, trioctyl trimellitate, butylphthalylbutyl glyco-late, tributyl acetylcitrate, chlorinated paraffin, polypropy-lene adipate, polypropylene sebacate and their known equiva-lents--and a high boiling solvent, for example, ketones, esters - or glycols such as cellosolve, butyl glycol.
For the purpose of coloration and improvement in the corrosion resistance, the solution or dispersion according to the present invention may include an inorganic pigment such as carbon, iron oxide, titanium dioxide and the like or an organic pigment such as-Phthlocyanine Blue, Phthalocyanine Green, : . , .

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Benzydine Yellow, Naphtol YelloW and the like. However, the pigment should be selected from -those which don't decompose the polymerization initiator at ambient temperature and should be stable in the compounded preparation of the present invention.
In addition, if desired, the preparation may include a dispersing agent, wetting agent, antifungal agent, antiseptic agent or antifoaming agent.
The preparation of the present invention must be aci-dic in order to etch the metal to be treated. The pH depends on the type of metals to be treated but is, in general, prefer-ably adjusted wlthin the range from 1.2 to ~Ø In order to adjust the p~ in such a preparation, either an inorganic acid such as a phosphoric acid, nitric acid, sulfuric acid, hydro-fluoric acid, hydrochloric acid or salts thereof, or an organic acid such as oxalic acid, citric acid, malic acid, maleic acid, acetic acid, lactic acid, phthalic acid, tartaric acid, chloro-acetic acid, acrylic acid or the like or salts thereof may be employed.
In order to promote the deposition of the film-forming ~-polymer resin, the preparation may additionally include an - oxidizing agent as employed in the conventional phosphating and -chromating processes such as NaN03, NaClO3, H202, NaN02, HN02, hydroxylamine or the like.
After the deposition of film-forming polymer resin on the metal surface by the pretreatment of the present invention, the treated metal articles are removed from the bath and can be rinsed with water without any loss in the deposition on the surface prior to baking or drying. For this reason, non-- uniformities due to drips tend not to occur.

me present invention will be further illustrated by way of the following examples.
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. . , E~MPLE 1 250g of a 40 wt. % sollds aqueous emulsion of poly-acrylic ester (commercially available under the trademark of Tocryl N-142 from Toyo Ink Co.) was dlluted with water (about 500ml). To this was added a so:Lution containing 1.25g t-butyl-~ peroxyphthalate as a polymerization inhibitor ~available under S the trademark of Perbutyl MA from Nippon Yushi Co.) and 20 g 2-hydroxyethyl-methacrylic acid monomer. The mixture was ayitated ~; and water added to make up the preparation to 1 liter.
To this preparation, a steel plate (SPCCD, JIS-G 3145, ~;~ manufactured by Shin Nippon Seitetsu Co.) having a size of 0.8mmx 50mm x lOOmm and cleaned with an alkali cleaner was immersed t. at a bath temperature of 25C for 3 minutes, followed by rinsing; with water. The treated plate was then dried at 120C for 3 minutes to form a transparent polymer resin film having a thick-ness of about 8 microns.
The film was tested and showed good properties and no ~ -peeling-off in accordance with the Checker and Impact Test des-cribed below.
As a control, when the cleaned steel plate was treated similarly with the above-mentioned preparation except containing neither 2-hydroxyethyl-methacrylic acid monomer nor the radical -polymerization initiator of t-butylperoxyphthalate, there was no formation of polymer resin film.
-~ By way of reference, the Checker Test is one for testing ~~ the adhesion of paints in which two orthogonal sets of parallel lines are scratched through the paint film from the surface to - the base metal at intervals of about lmm in each direction to form 100 checkers each lmm square. Then Scotch tape is applied -~ 30 and removed and the % paint removal from the checkered area is - recorded.
The Impact Test was carried out using an impact rod weighing 500 g and having a diameter of 1/2 dropped from a .

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distance of 30cm by means of a Du Pont impact tester. Impact was made on the panel back an~ paint adhesion on the front was measured by the application and removal of Scotch tape.
EX~MPLE 2 lb the same preparatic,n as in Example 1, a copper plate, cleaned by polishing with steel wool, was immersed at a bath temperature of 25C for 3 minutes, rinsed with water and dried at 120C for 3 minutes to form a transparent polymer re-sin film having a thickness of about 10 microns.

250g of a 40 wt. % solids butadiene-methylmethacrylate latex having a pH of 9.0-9.5 (commercially available under the trademark of Lacstar KS-l) was diluted with an aqueous solution containing 8g of 85% phosphoric acid, 0,75g of the t-butyl-peroxyphthalate of EXAMPLE 1 and 15g of 2-hydroxyethylmetha-crylic acid monomer. The mixture was agitated and water added to make up the preparation to 1 liter.
To this preparation, a steel plate which had been treated with a conventional alkali cleaner (Finecleaner 4306, an -alXaline composition commercially available under that trade mark ;
from ~ihon Parkerizing Co.) was immersed at 30C for about 2 mi-nutes, rinsed with water and dried at 120C for 5 minutes to form a transparent film having a thickness of 10 microns.
The dried film showed good results in the Checker and Impact Tests.
As a control, a steel plate cleaned as above was im-mersed in a preparation as above but containing no 2-hydroxy-` ethyl monomer, at 30C for about 2 minutes, rinsed with water and dried in a dryer at 120C for 5 minutes, but substantially no deposition of polymer film was obtained.EXAMPLE 4 ~ A clean hot galvanized steel plate was immersed in an :` :
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s ' . aqueous dispersion containinq the components of EXAMPLE 3 at . the indicated concentrations at 25C for about 3 minutes, rinsed s. with water and dried to form a deposited polymer resin film having a thickness of about 8 microns.
Component Concentration - q~l t Butadiene-methylmethac:rylate latex 250g s 2-hydroxymethacrylic acid monomer lOg t-butylperoxyphthalate 0.5g 85% phosphoric acid ~g Water to 1 liter r A clean aluminium panel ~63S) which had been washed by etching with a conventional alkali cleaner (commercial available from Nihon Parkerizing Co. under the Trademark of Percoalum-etch 391) at 60C for one minute, desmutted with 20% nitric acid and rinsed with water was immersed in an aqueous dispersion contain-i: :
i ing the components of EXAMPLE 3 and acetonitrite at the indicat-ed concentrations at 25C for about 3 minutes, dragged out from the bath, rinsed with water and dried to form a transparent film ~- 20 having a thickness of about 7 microns.
~: Component Concentration - q~l -. Butadiene-methylmethacrylate latex 250g 2-hydroxymethacrylic acid monomer 15g t-butylperoxyphthalate 0.75g Acetonitrile 5g -. 85% phosphoric acid 8g -`.: Water to 1 liter As a control when an aluminum panel (63S) was treated - similarly with a preparation of the above-mentioned composition without the 2-hydroxymethacrylic acid monomer, no film was deposited.
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: -8-~ P-10~33 1~3~7 E~lPLE 6 A clean steel plate was immersed in a dispersion containing the components o EX~PLE 1 and an iron oxide pigment at a bath temperature of 25C for about 5 minutes and .; 5 dried at 120C for about 5 minutes to form a reddish brown deposited organic polymer film having a thickness of about 10 microns.
Component Concentration - g/l Polyacrylate ester emulsion 250g 2-hydroxyethylmethacrylic acid monomer 20g t~butylperoxyphthalate 1~25g Iron oxide pigment (non-volatile -~: . matter: 64.0~; commercially available .
under the Registered Trademark of , EM Red Y-3 from Toyo Ink Co.) 30g Water to 1 liter .
~EXAMPLE 7 ; .
' A clean steel plate was immersed into a preparation of . the following composition at 25C for about 3 minutes, rinsed with.
: 20 water and dried at 120C for about 3 minutes to form a transparent organic polymer film of a thickness of about 7 microns. . `
Component Concentration _ Butadiene-methylmethacrylate latex ` (Lacstar XS-l) 250g t-butylperoxyphthalate ~Perbutyl MA) l.Og Acrylonitrile monomer 15g 85% phosphoric acid 8g .- Water to 1 liter : EXAMPLE 8 . . ~
~- 3~0 A clean steel plate was immersed into a bath of the following composition at 30C for about 3 minutes, rinsed with ' _g_ .: . - !
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P-105~3 wa-ter and dried ~.t 120C for about 3 minutes to form a transparent organic polymer film OI a thic]cness of about 5 microns.
Component_ Concentration- g/l sutadiene-methylmethacrylat:e latex (Lacstar KS-l) 250g Benzoyl peroxide (purity: 'iO~;
commercially available from Nippon Yushi Co. under the trademark of Nayper BO) 2g 2-hydroxyethylmethacrylate monomer 20g 85~ phosphoric acid 6g Water to 1 liter ' '' ~

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Claims

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A process for coating a metal surface comprising contacting the surface with an aqueous acidic composition com-prising 0.5 to 50 wt. % of an organic film-forming resin, 0.1 to 10 wt. % of a monomer polymerizable by free radical mechanism and 0.02 to 5 wt. % of a free radical polymerization initiator.

2. The process of claim 1 wherein the resin is select-ed from the group consisting of vinyl polymers and copolymers of vinyl acetate, vinyl chloride, vinylidene chloride; acrylic polymers and copolymers of acrylic acid, methacrylic acid, acry-lic esters, methacrylic esters, hydroxyacrylic acid, hydroxy-methacrylic acid; alkyd resins; epoxy resins, fluorocarbon resins; urethane resins, polyester resins; styrene resins; olefin polymers and copolymers; synthetic rubbers such as butadiene rubber as well as natural polymers.

3. The process of claim 1 wherein the monomer is se-lected from the group consisting of acrylic acid, methacrylic acid; methyl-, ethyl-, butyl-, and 2-ethylhexylhydroxy-acrylate esters or methacrylate esters; vinyl acetate, vinyl propionate, vinyl caproate, styrene, itaconic acid, crotonic acid, methyl-vinyl ether, vinylidene chloride acrylonitrile, acrylamide, me-thacrylamide, 2-aminoethylvinyl ether, glycidyl ether, glycidyl methacrylate, and hydroxyalkyl acrylates.

4. The process of claim 1 wherein the initiator is selected from the group consisting of ketone peroxides, peroxy-ketals, cumene hydroperoxide, t-butylcumyl peroxide, acetyl peroxide, benzoyl peroxide, t-butylperoxyisobutylate, t-butylperoxyphthalate, lauroyl peroxide, as well as persulfa-tes, percarbonates, perborates, and hydrogen peroxide.

5. The process of claim 1 wherein the coated surface is water rinsed before the coating is dried.

6. The process of claim 1 wherein the contacting is accomplished by immersion, spray or roll-on techniques.