CA2022234A1

CA2022234A1 - Preprimed metal substrates for formed metal application

Info

Publication number: CA2022234A1
Application number: CA002022234A
Authority: CA
Inventors: Etienne G. Maze; Christine M. J. S. Tournillon
Original assignee: Etienne G. Maze; Christine M. J. S. Tournillon; Akzo N.V.
Current assignee: Akzo NV
Priority date: 1989-07-31
Filing date: 1990-07-30
Publication date: 1991-02-01
Also published as: DE69015280T2; US5229214A; JPH0369352A; ATE115976T1; ES2066958T3; GR3015478T3; EP0411690B1; BR9003710A; EP0411690A1; DK0411690T3; DE69015280D1

Abstract

PREPRIMED METAL SUBSTRATES FOR FORMED METAL APPLICATIONS

ABSTRACT OF THE DISCLOSURE

The present invention relates to preprimed metal substrates suitable for use in formed metal applications. The preprimed metal substrate is coated with, as primer layer, a first coating layer applied onto the metal substrate, the first coating layer being based upon a particular hydroxyl groups-containing block copolymer, and at least one flexible subsequent coating layer applied onto the first coating layer. The preprimed metal substrates are especially useful in automotive applications.
* * * * *

Description

2~4~

PREPRIM D METAL SUBSTRATES FOR FORMED METAL_APP~ICATIONS

BACKGROUND OF THE INVENTION

The present invention relates generally to preprimed metal substrates, such as sheets, which are suitable for formed metal applications, for exampIe, the manufacture of automotive body parts for repair and~or on-line assembly.
In the usual formed metal applications, a metal sheet is first formed by well-Xnown methods tdrawing, dye cutting, etc.) into the desirad shape then subsequent:ly coated with a primer (postpriming). The primer serves a number of well-known functions, including provlding a barrier layer and~or corrosion protection layer for the underlying metal substrate.
Typical examples o~ primers ~or metal applications, such as automotive applications, include the following.
U.S. 4,602,053 describes epoxyester linsar block ~ligomers made with ~-1 moles of fatty acid groups and n moles of epoxy oligomer, which are said to bQ particularly suit~d for chip-resistant coating compositions (preferably containing small pi~nent ~olume concentrations). See also EP-A-0179281D
W0 85/00375 discloses thermosettlng coating compositlons based upon an epoxy-polyester graft copolymer and a polyisocyanate crosslinker, which is said to be useful as a chip resistant primer ~or the automotive industry.
EP-A-0070008 describes zinc rich coatings having binders comprised of thermoplastic polyhydroxyethers, epoxy resins, epoxy ester resins, alkyl silicates, etc., which are useful for corrosion protection in the automotive industry. Theæe coatings particularly contain aluminum trihydrate for improved combined spot welding/corrosion resistance properties on automotive components.
In automotive applications where the formed metals may take a number of odd or complex shapes, postpriming by normal on-line paintiny methods may result in a signi~icant portion o~ the underlying metlal substrate being unprimed or underprimed, as in the normal on-line palnting methods it is ~Q~2~3~

difficult to adequately apply the primer in the varlous corners and other odd-shaped areas of the formed metal, parti-cularly on both sides. In many instances, the various body parts are not primed until after assembly, thereby exacerbating the problem o~ unprimed or underprimed base metal. A common result is the early rusting and d~creased life of the part.
It is, therefore, an object of the present invention to overcome this shortcoming by providin~ a preprimed metal substrate which may subsequently be formed into a shape suitable for use in automotive applications.
The general concept of preprimed ~etal substrates for formed metal applications is, of course, not new. Most primers suitable for use in automotive applications, however, ara not suitable for preprimed formed metal applications, ~or example, because of either insufficient adhesion to the me.tal substrate or insufficient flexibility. In forming the preprimed matal subs~raté, particularly in the manner and degree necessary for automotive applications, insufficient adhesion can cause the primer to separate from the substrate, while insufficient flexibility can cause tha primer to crack.
Both can result, as indicated above, in the early rusting and decrease life of the part.

SUMMARY OF THE INVENTION

The present invention, therefore, provides a preprimed metal substrate comprising a metal substrate coated with a primer layer, wherein that the primer layer comprises, in its overall concept:
(1) a first coating layer applied onto the metal substrate, the first coating layer comprising a coating composition based upon, as a binder, an hydroxyl groups-containing block copolymer built up from (A) one or more blocks of a carboxyl-term~nated polyester ~esin and (B) one or more blocks of an epoxy resin; and 2 3 ~

(2) at least one flexible suhsequent coating layer applied onto the first coating layer.
The ~irst coating layer should provide good adhesion to the substrate, be sufficiently flexible to be formed, and exhibit sufficient solvent resistance so that a second coating layer applied over the surface of the first coating layer will adhere to, but not substantially dissolve, the first coatlng layer.
It has been found that, to obtain good adhesion of the first coating layer to the substxate, the dry thickness of the first layer should not exceed about 15 ~m. It has also been -found that the overall coatlng thickness naeds to be in the range of about 15 ~m to about 45 ~m to provide the desired final appearance for aut~motive applications and other applications where a glossy finish is dQsired, 80 it iS
necessary to apply at least a second coating layer~
The at least one~subsequent coating layer should, in general, be a flexible material which exhibits stone chip resistance. It has bsen discovered that polye~t~r polyols crosslinked with polyisocyanates and/or melamines adhere well to the first coating layer, provid0 good flexibillty and possess excellent stone chip resistance.
The present invention also provide~ a method of prepriming a metal substrate, the method comprising the steps of:
(1~ applying the aforementioned first coating layer onto a metal ~ubstrate, and (2) applying the aforementioned at least one ~lexible subsequent coating layer onto the ~irst coating layer.
The resulting preprimed metal substrates find particular use in formed metal applications which reguire deep draw capability during forming, such as the deep draw required in the automotive industry, and which require excellent stona chip resistance of the finished metal part.
These and other features and advantages of the present invention will be mo~e readily understood by those skilled in the art ~rom a reading of the following detailed description.
I

~223~

DET LED DES_ PTION OF THE PREFERRED _MBODIMENTS

As indicate~ previously, the present invention ifi related to preprimed metal substrates and, more particularly, to those suitable for us~ in applications wherein the prPpri~ed substrate is subsequently formed into a shape.
Suitable metal substrates lncl~de a wide variety of pretreated or non-pretreated metals, including alloy~, composites and the like comprising ~uch metals. Particularly preferred are those normally utilized in the automobile industry, such a~ iron, galvanized iron, 6teel, galvanized steel and aluminum. For formed metal applications, of courss, the metal substrate to b~ preprimed should substantially be in the physical form of a sheet.
These metal substrates ar~ rendered suitable for ~ormed metal applications by application of a particular primer layer prior to forming of ~he metal, hence the name ~Ipreprimed~l metal. In accordance with the present in~ention, this primer layer comprises:
(1) a first coating layer applied onto the metal substrate, the first coating layer com~rising a aoati~g composition based upon, as a binder, an hydroxyl groups-containing block copolymer built up from (A) one or more blocks of a aarboxyl-te~ninated polyester resin and (B~ one or more blocks of a epoxy resin; and (2) at least one flexible subsequent coating layer applied onto the ~irst coating layer.
As suitable hydroxyl groups-containing block copolymers may be mentioned those described in EP-B-0111986 (United States Patent Application Serial No. 07/334,747) and European Patent Application No. 8~201350.9 (United States Patent ~pplicatlon Serial No~ 07/525,~11), both of which are incorporated by reference herein ~or all purposes.
BrieEly, the carboxyl-terminated polyester block (~) preferably compriseslthe polycondensation product of one or 2 3~

more carboxylic diacids and one or more difunctlonal hydroxy compounds.
As suitable carboxylic diacids may be mentloned aromatic carboxylic diacids (EP-B-01119~6), aliphatic carhoxylic diacids (European Patent Application No. 89201350.g) and mixtures thereof.
As examples of suitable aromatic carboxylic diaclds may be mentioned terephthalic acid and isophthalic acid.
As examples of suitable aliphatic carboxylic diacids may be mentioned compounds of the gen~ral formula (I) HOOC-R-COOH ~I) wherein R is an aliphatic hydrocarbon group, preferably a (cyclo)aliphatic hydrocarbon group, and more preferably a linear alkyl group, having ~rom 1 to 34 carbon atoms and preferably 1 to 12 carbon atoms. As specific examples o~` such may be mentioned malonic acid, sucainic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acld, sebacic acid, dodecane dioic acid, dimeric fatty acids, trimethyl adipic acid, maleic acid and cyclohexane dicarboxylic aclds.
Especially preferred are adipic acid and sebacic acld~
At the time of application of the subsequent coating layer~s) over the first coating layer of the prepriming coating, it is desirable to have the second coating layer adhere tol but not substantially dissolve, the first coating layer. It has been found that use of the aromatic carboxylic diacids is preferred for formation of the carboxyl terminated polyester block, since the sol~ent resistance of the ~irst coating layer is thereby increased making poss~ble the use of a wider variety o~ second coating layer materials.
Suitable difunctional hydroxy compounds may be branched or unbranched, and may contain ether and/or ester linkages in their structures. As examples of such may be mentioned 1,2-propylene glycol, 1,3-propylene glycol, neopentyl glycol, 1,2-butane diol, 1,3-but~ane diol, 1,4-butane~diol, 1,5-pentane diol, 1,6-hexane diol, polyalkylene glycols such as diethylene ~`2:~23~

glycol, triethylene glycol and dipropylene glycol, trimethyl hexane diol, polycAprolactone diolsl, l.l'-isopropylidene-~is-(p-phenylene-oxy)-di~ -ethanol and l.l~-isopropylidene-bls-( phenylene-oxy~-di~ ~ethanol. Particularly preferred o~ these are the diols and polyalkylene glycols, especially those having from 2 to 8 carbons atoms.
Optionally, one or more hydroxy acid and/or lactone compounds may also be utilized ln the production of the carboxyl-terminated polyester blocks ~A).
As suitable hydroxy acids may be mentioned those of the general formula (II) HO-Rl-COOH (II) wherein R is preferably a hydrocarbon group, more preferably a (cyclo)aliphatic hydrocarbon group, having from 1 to 17 carbon atoms and espapially from 7 to 17 carbon atoms. A5 specific examples may be mentioned hydroxycaproic acid and hydroxystearic acid.
As suitable laatone compounds may be msntioned those of thP ~eneral formula (III) R -COO (III) wherein R2 is a hydrocarbon group, more preferably an aliphatic hydrocarbon group, having from 2 to 10, more preferably 5 to 9, carbon atoms. As a speci~ic example may be mentioned ~-caprolactone.
In the preparation of the carboxyl-terminated polyester blocks (A), use may also be made of derivatives of the aforementioned components such as epoxy compounds, acid chlorides, acid anhydrides and methyl diesters.
The polycondensation xeaction of the above componen~s is generally carried out at a temperature of from about 14~ C to about 30~ C, preferably from about 18~ C to about 26~ C, and in an inert atmospher;e of, for example, nitrogen and/or carbon dioxide. The water evolved in the polycondensation reaction ~22~

7 ~CO 2201 may be remo~ed in a normal manner, e.g., by di~tillation under reduced pressure or by azeotropic d1still~tion with the aid oE
an organic solvent such as toluene, xylene or mlxed aromatic solvents. After termination of the polycondensation, these solvents may optionally be removed from the polye~ter resin by distillation.
The polycondensation mixture may optionally contain an esterification catalyst, for example, sulfuric acid, p-toluene sulfonic acidl benzene sul~onic acid, naphthalene ~ulfonic acid, a sulfonlc acid cation exchanyer or a metal compound such as dibutyltin dilaurate or lead acetate.
The polycondensation reaction is oontinued until the polyester resin has the desired acid number, pre~erably ~rom about 10 to about 140, and more pra~erably ~ro~ about 20 to about 110. The hydroxyl number of the resulting polyeste:r resin preferably should al80 not be highe.x than about 2, and more preferably fromj0 to about 0.8. The acid number and hydroxyl number are expréssad in mg KOH per g o~ polyester resin. Further, the polyester resin should have a number average molecular weight (M~) o~ from about 800 to about 10000, more pre~erably from about 1000 to about 6000O
Epoxy resins suit~ble ~or use in the present block copolymers may be ~olid or ~iguid, with an epoxy funationality o~ from about 1.5 to about 2~5 and an epoxy e~uivalent weight of from about 100 to about 2~00.
Examples of ~uch suitable epoxy resins are detailed ~n the previously incorporated r~ferences, and include glycidyl groups-containing resins such as polyaarylic resins, polyesters, polyethers or polyurethanes which all contain one or more glycidyl groups per molecule. Use may also be made of mixtures o~ these epoxy resins. Optionally, the epoxy resin may be used as a solution in a suitable solvent.
Preferred epoxy resins are those of the general ~ormula (IV) H2C - CH-CH2-(o-R3-o-CH2-CHoH-CH2)n-o-R3-o-cH~-Hc - CH2 (IV) o ,i ~:~

~2~3~

~ AC0 2201 wherein R3 represents an aliphaticd cycloaliphatlc or aromatic group, preferably containing from :2 to about 18 carbon atoms, and n is a number from 0 to 50, preferably 0 to about 10.
Adducts of these epoxy resins with (cyclo3aliphatic or heterocyclic diamines, preferably a dl-secondary amine such a~
piperazine, are also suitable.
Examples of these preferred epoxy resins include the ~lycidyl ethers o, ~or example, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,5-pentane diol, bis-(4-hydroxycyclohexyl)-2,2-propane, 4,4'-dihydxoxyben20phenone, bis--(4-hydroxyphenyl)methane, bis-(4-hydroxyphanyl)~ ethane, bis-(4-hydroxyphenyl)-1,1-isobutane and 1,5-dihydroxynaphthalene.
In more preferred aspects, ~he epoxy resin has an epoxy functionality of from about 1.~ to about 2.2, an epoxy equivalent weight of ~xom about 100 to about 700, most praferably ~rom about 150 to about 500, and an Mn of from about 150 to about 1250.
The block copolymer may be prepared in any convenient manner by reaction of ~he car~oxyl-terminated polyester resin with the epoxy resin. ThP block copolymer may optionally be prepared by using two or mora carboxylic polyester and/or epoxy resins.
A suitable procedure for producing the block copolymers comprises the stepwise addition of the epoxy resin~s) to a solution of the polyester resin(s) and heating the mixtur~ to a temperature generally in the range of from about 8~ C to about 19~ C, preferably from about 10~ C to about 18~ C. The reaction mixture may, if required, be made to contain a cataly t known in itself, for instance, triphenyl phosphine, benzyl triphenyl phosphonium chloride, benzyl trimethyl ammonium methoxide, a tertiary amine such as benzyl dimethylamine, or a metal compound such as zirconium octoate.
A preferred solvent for the polyester resin and resulting block copolymer is an aromatic hydrocarbon such as toluene, xylene or a mixture olf aromatic hydrocarbons having a boiling point of, for example, about 14~ C to about 18~ C. To the i ~:~2223~
g AC0 2Z01 resulting block copolymer obtained cn the conclusion o~ the reaction may be added a polar solvent such a~ isophoron, methylethyl ketone, diacetone alcohol, the ethyl ether of ethylene glycol and the ethyl ether of ethylene glycol acetate.
The weight ratio of ~he carboxyl-terminated polyester resin (A) to the epoxy resin (B) i~ generally chosen ~o that, at the start of the reaction to form the block copolymer, the reaction mixture contains from 0.5 to 2.0, preferably from 0.7 to 1.3, moles of epoxy of the epoxy resin per mole of carboxyl of th~ polyester rssin. In this manner, a block copoly~er having carboxyl and/or epoxy end groups ls obtained.
The most preferred block copol~mer is built up of from 3 to 11 blocks (A) and 2 to 10 blocks (~), or from 2 to 10 blocks (A) and 3 to 11 blocks (B).
The number average molecular weight of the resulting block copolymer i~ preferably from about 3000 to about 80000, and more preferably from about 5000 to about 30000. The acid number of the block copolymer i5 preferably not higher than about 23, and more preferably in the range o~ from 0 to about 15.
Further details o~ the block copolymer can be had by reference to previously incorporated EP-B-011198~ and European Patent ~pplication No. ~9201350.9.
The coating composition of the ~irst coating layer typically contains (~ut need not contain) a curing agent for the hydroxyl groups of the block copolymer, which are the result of the reaction between the carboxyl of the polyester and the epoxy group. Suitable curing agents are blocked or non-blocked isocyanurate compounds or blocked or non-blocked aliphatic, cycloaliphatic or aromatic di-, tri- or polyvalent isocyanates, specific examples of which are listed in previously incorporated EP-B-0111986 (see page 3, lines 39 52). For blocking the isocyanate or isocyanurate compound, use may be made of any well-known blocking agent.
In~tead of or in~ addition to the isocyanate and isocyanurate curing agents, other suitable blocked and 2022~3l~

unblocXed curing agents such as thP N-methyloyl groups- and/or N-methyloyl ether groups-containing aminoplasts and phenol resins, as mentioned in previously incorporated EP~B-0111986 (see page 3, lines 53-65), may also be utilized.
The curing agent should be present in the coating composition in an amount such that the molar ratlo of the reactive groups of tha curing agent to that o~ the hydroxyl groups of the block copolymer is in the range of from 0.1 to about 1~7, preferably from about 0.2 to about 1.5.
Optionally, the coating composition of the ~irst coating layer may contain solid powdered polymers and pigments such as mentioned in previously incorporated EP-B-0111986 (see page 4, lines 4-28), and also the usual adjuvan~s and additives, fox example, pigment dispersing agents, antisag agent~, rheology control agents~ corrosion inhibiting compounds (e.y., metallic zinc or metallic aluminum), plasticizers, gloss agents and accelerators such as p-toluene sulfonic acid and blocked products of such accelerators.
As examples of suitable pigments may be mentioned thQ
usual types of acid, neutral or baæic pigments which may be organic or inorganic. The plgments may be optiona~ly treated to modify their propertias. As speci~ic examples may be mentioned titanium dioxide, red iron oxide~ lead chrom~te, carbon black and phthalocyanine pigments. The term pigments as used herein also refers to metallic pigments Ruch as aluminum and stainless steel. The weight ratio of pigment to block copolymer and curing agent is generally in the range o~
about 0.05 to 19, the higher ratios being used for generally metal-rich compositions, which are weldable if they contain metal as pigment or corrosion inhibiting compound.
The coating composition of the first coating layer may be applied to a substrate in any convenient manner, such as by roller coating or (electrostatic) spraying, and may be cured or baked in the usual manner. For example, in a coil coating process baking i5 to be carried out at an applied final temperature of the st~tbstrate o~ about 20~ C to about 28~ C, i 2 ~ l~

which temperature is normally reached hy contacting the coated substrate for a short time ~e.g., 10 to 90 seconds) with air or combustion gases at a temperature of about 25~ C to about 40~ C. Applica~ion and baking conditions during coil coating are known to one skilled in the art and need not be ~urther described here. Suitable baking temperatures for other fields of application may, for example, range from about 12~ C to about 21~ C.
The at least one flexible subsequent coating layer to be applied over the first coating layer is characterized by performance characterîstics such as high flexibility as measured by the T-hend test and the Eriahsen impact test, a glass transition temperature in the range o~ about 3~ C to about 7~ C, adhesion capability relative to the first coatlng layer, stone chipping resistanca and leveling properties. Ona skilled in the art can select a coating material which wi:Ll perform well in combination with the above-described first coating layer. Coating materials known to perform well a~ the second cvating layer include polyurethane coatings based upon polyester polyols crosslinked using a polyisocyanate (such as commercially available under the trade designation PZ 2000 from Akzo Coatings) and polyester polyols, having a relatively low Mn ~e.g., about 2,000 to about 10,000) and a functionality of about 2, crosslinked using a mslamine.
The ~lexible subsequent coating layer material may also contain adjuvants and additives of the type previously discussed for use in the first soating }ayer.
The coating composition of the at least one flexible subsequent coating layer may be appliecl, as with the coating composition of the ~irst coating layer, in any convenient manner, such as by roller coating or (electrostatic) spraying, and cured or baked ln the usual manner such as, for example, as described above.
It is pre~erred that the ~irst coating layer be applied to a dry layer thickness of up to about 15 ~m, more preferably from about 3 ~m to abJout 10 ~m/ and the a~ least one flexible su~sequent coating layer to a dry layer thickness up to about 2 3 '~

30 ~m, more preferably from about 12 ~m to about 25 ~m. The total primer dry layer thickness should preferably range from about 15 ~m to about 45 ~m, more pre~erably from about Z0 ~m to about 30 ~m.
The resulting preprimed metal substrate can then be utilized in formed metal applications. The forming of the preprimed metal substrate may be accomplished by any well-known means, such as by bending, stamplng, profiling and drawing.
The preprimed metal substrate prepared according to the present invention finds use in metalllc construckion such as buildings, appliances, metallic furniture and particularly in the automotive field, where properties such as high corrosion protection, excellent ston~ chipping resistance, and ease of deep draw shape formation are especially important.
The foregoing general discussion of this lnvention will be further exemplified by the following specific examples offered by way of illustration and not llmitation o~ the above-described invention.

EXAMPLES 1-1~ 3nd COMPARATIVE EX~M_LES Cll and C12 Preparation of Polyester/Epoxy Block Copolymer ~or ~xamples 1-10 .

In Examples 1-10 use was made of caxboxyl-terminated polyeRter resins (A-G~ obtained by the polycondensation o~ the components in the amounts (paxts hy we.ight) as listed below in Table I.
The polycond~nsation was carxied out at a temperature o~
about 24~ C to about 26~ C in the presence o~ 3% by weight o~
xyl~ne (based upon the total polycondensation mixture). The polycondPnsation was continued until the polyester had the desired acid number. Esterlfication catalysts used were dibutyltin oxide (polyesters A, B, D and F~ and tributylt.in oxide (polyesters C and E). No esterification catalyst was used in the preparation of polyester G~
The resulting polyester resins all had an hydroxyl number of O and showed no crystallinity~ Table I al~o llsts other characteristics of the so~produced polyester resins.

2~2~

14 ~C0 2201 T_~h~

Polyestex Resin Components A _ B C ~ _ E F G _ 1,2-propane diol 26.83 ~ 9.03 1~5-pentane diol - - 37.60 35.25 33.28 - 10.30 1,6-hexane diol - 39.53 - - ~ 28.08 30.73 l,l,l-trimethylol propane - - - 0.46 2.25 isophthalic acid 73.07 - 31.15 64.29 64~47 62.59 terephthalic acid - 60.37 31.15 trimellitic anhydride - - - - 0.21 adipic acid - - - - ~ ~ 5~-97 Pr~perties _ _ __ Acid Number il2 37 19 56 56 29 57 Carboxyl Functionality ~.0 2.0 2.0 2.08 2.482.05 2.0 Number Average MW 10003000 6000 2081 24754000 1358 The polyester/epoxy block copolymers, BCl-BC10, used in Examples 1-10 were prepared by addiny one or more epoxy resins, of the types and in the amounts as set forth below in Table II, to solutions of the above polyester resins. All amounts for the epoxy resins and polyesters in Table II are expressed as parts by weight (solids).
Epoxy resin A was a diglycidyl ether of Bisphenol A with an epoxide equivalent of 170 (commercially available under the trade designation Epikote 828 ~rom Shell Chemical). Epoxy resin B was a diglycidyl ether o~ Bisphenol A with an epoxide equivalent o~ 454 (commercially available under the trade designation Epikote 1001 and Epon 1001 from Shell Chemical).
Epoxy resin C was a ~iglycidyl ether of ~,4-butane diol with ~2~3~

an epoxlde equivalent of 101. Epoxy resin D was an adduct of 2 molas of Epoxy resin A and 1 mo].e of piperazine.
The solutions of polyester resins A-F were prepared by dissolving each in 51.5 parts by weight of an aromatic hydrocarbon sol~ent (commercially ~vailable under the trade designation Solvesso 100 from Shell Chemical). The ~olution of the polyester resin G was pr~pared by dissolving in 40 parts by weight of this aroma~ic hydrocarbon ~olvent.
Subsequent to the addition of the epoxy resin to the polyester resin solutions, 0.1 parts by weight of benzyl diethylamine for polyester resins A~F, and 0.3 paxts by weight triphenyl phosphine for pvlyester resin Ç, were added and the reaction mixtures kept at a temperature of about 15~ C untll the block copolymer fo~med had the acid number as set ~orth in Table II. Also set forth in Table II are other character-istics of the so-prepared polyester~epoxy block copolymer~.

~22~3~

16 ACO ~201 TABTJE Il .
Polye~ter/Epoxy ~lock Copolymers BCl BC2 BC3 C4_ _~C5 BC6 BC7 BC8 BC9 _C10 PE Type A A B B G C D E F G
~mount 71.67 77.05 79.83 76.37 85.64 92.74 51~60 ~8.74 75.75 60.~0 Epoxy A 28.23 8.68 - - - 2.96 Epoxy B - 3.86 20.07 - 14.26 4.21 38O30 41.16 24.16 39.80 Epoxy C - 10.31 Epoxy D - - - 33.53 Properties Acid No. 3.0 4.5 7.i0 1 a 0 2 ~ 0 4 ~ O O ~ 5 0 ~ 5 0 ~ 4 0 ~ 4Carboxyl 0.32 0.68 1.5~ 0.34 0.71 1.43 0.11 0.11 0~13 o.0 Func.
OH No. 108.5 104.0 52.0 ~9.-o 39.0 ~2.0 90.0 93.0 57.0 84.4 OH Func. 11.60 15.75 11.08 9.68 13.85 7.76 19.36 19.91 17.80 12.63 Mn 6000 8500 12000 19000 20000 20000 12000 12000 17500 8400 To the solutions of the poIyester/epoxy block copolymers thus prepared were added ethyl ether of ethylene glycol (BCl-BC9)~ methoxy propanol (BC10) and the pxeviously used aromatic hydrocarbon solvent in amounts such that ~olutions were obtained having a soli~s content of about 40% by weight of the block copolymer in a mixture of equal parts by weight of the two sol~ents.

Comparative Resin 11 for Comparative Example Cll Comparative Exa~ple Cll was based upon an epoxy resin (CRll) which was the diglycidyl ether of ~isphenol A with an ~`2223~
17 AC0 2~01 epoxide equivalent of about 240~ o 4000 (commercially a~ailable under the trade deslgnation Epon 1009 rom 5hell Che~ical). A 40~ solutlon of the epoxy resi~ was prepared by dissolving, at 10~ C, 40 parts by weight of the epoxy resin into a solvent mixture compri~ing 36 parts by weight of the aforementioned aromakic ~olvent and 24 part~ by weight methoxypropanol.

First Coating Layer Compo~itions (Primer First Coating Lay r) for Examples 1-10 and Comparative Examples Cll and C12.

To obtain the first coating layer compositions used in Examples 1-10 and Comparative Example 11, the corrP6pondingly numbered polyester/epoxy block copolymers and aomparatlve resin, in the amounts as s~t forth in Table III ~in parts by weight solids), and in the ~orm o~ the prevlously de~cribed solutions, were homo,geneously mixed with the other components in the amount~ (in parts by weight) as listed in Table III.
The crosslinking agent was the adduct of hexamethylene diisocyanate and 1 mole of water (commercially available under the trade designation De~modur N from Bayer AG), blocked with methylethylXetoxime, in methoxypropanol acetate (NV~ 75%).

223~

1~ ~CO 2201 TABLE III
__ _ First Coating Resin Resin Titan. Stront. Cross. Meth. Arom.
yQ~ Type_ Amount _iox~ Chrom, Silica A~ent ~rop. ~1Y~
Pl BCl 42.7 15.9 2.0 2.5 3.7 13.3 19.9 P2 BC2 42.7 15.9 2.0 2.5 3.7 13.3 19.9 P3 BC3 42.7 15.9 2.0 2.5 3.7 13.3 19.9 P4 BC4 42.7 15.9 2.0 2.5 3.7 13.3 19.9 P5 BC5 42.7 15.9 2.0 2.5 3.7 13.3 19.9 P6 BC6 42.7 15.9 2.0 2.5 3.7 13.3 19.9 P7 BC7 42.7 15.9 2.0 2.5 3.7 13.3 19.9 R8 BC8 42.7 15.9 2.0 2.5 3.7 13.3 19.9 P9 BC9 42.7 15.9 2.0 ~.5 3.7 13.3 19.9 P10 BC10 43.9 19.2 2.4 3.0 3.4 11.3 16.9 CPll CRll 42.7 15.9 2.0 2.5 3.7 13.3 19.9 The first coating layer composition for Comparative Example 12 ~CP12) was a standard coil coating currently used in the precoating industry as a primer for steel or zinc coated stael. This primer is based upon an urea ~ormol epoxy precondensate, whlch is commerGially available under the trade designation 7E1328 fxom Akzo Coatings France.
The ten primer first coating layers (Pl-P10) based upon the polyester/~poxy block copolymers and two comparative primers (CPll and CP12) were applied as the ~irst coating layer onto a hot dip galvanized steel substrate (commercially available under the trade designation Extragal Z100 from Sollac). After cleaning and sur~ace treatment of the metal substrate using alkaline degreasing chromotation (Granodine 93CF from CFPI chromic zinc), the primers were applied by roller coating, then cured at a Pic Maximum Temperature of 24~ C with a dwell time of 30". Each dry film thickness was about 5 ~m.
Over this primer first coating layer was applied a primer second coating layer of a polyurethane based coating ~a polyester polyol cros~inked used an isocyanate) commercially available under the trade designation RZ2000 Prom Akzo 2 3 '~

19 ~Co 2201 polyester polyol crossllnked used an isocyanate) commerclally available under the trade designation PZ2000 from Akzo Coatings. This primer second coating layer was applied by roller coating over the dried primer first coating layer, then curing at a Pic Maximum Temperature of 24~ C with a dwell time of 35". The dry ~ilm thickness of the second primer layer was about 20 ~m.
The resulting coated metal panels were evaluated ~or the performance level of the flexibility and capability of deep draw, as exempli~ied by the following tests:
(1) the Erichsen indentation test - DIN 53 156;
(2) the reverse impact test - ASTM D 2794-1982 texpressed in in-lb);
(3) the double-draw test - RNUR (Regie Nationale das Unines Renault) D.lll 700:
(4) the T-Bend test - European Coil Coating ABSOCiatiOn (expressed in ratings T0, Tl, T2, etc. - a value of 0 denotes excellent flexibility and a value of 4 acceptable flexibility~; and 15) tha stone chipping resistance - RNU~ D.Z4 1702.
Corrosion resistance was evaluated by the salt spray test in accordance with ASTM B 117, with results reported in mm delamination on the scribe. Corrosion re~istance after deformation was also evaluated by the following procedure: the coated panels were submitted to a 20% uniaxial stretching, then a 25mm diameter hole punched in the ~iddle. The resulting panels were then exposed according to the 3-C test of RNUR
D.17 1686. The results are expressed in mm delamination obtained on th~ edges of the hole after 5 cycles.
The results of the testing are presented in Table IV
below.

3~

. TABLE .5V

First Coating Erich. Rever. Doub. Stone Corr. Corr.Res.
EX Layer Inden Impact Draw_ T-Bend Chip Res. A~ter Deform.
1 Pl 9.0 160 Pass 0.5 2 2 2 P2 9.2 160 Pass 0.5 2 1.5 1.5 3 P3 9.6 160 P~ss 0.5 2 2 2 4 P4 9.4 160 Pass 0.5 1.5 P5 9.8 160 Pass 0.~ 2 2 2.5 6 P6 10.0 160 Pass 0.5 2 1 2 7 P7 9.9 160 Pass 0.5 2 8 PB 9.2 160 Pass 0.5 2 1.5 1.5 9 P9 9.5 160 Pass 0.5 2 2 2 P1010.0 160 Pass 0 2 ~1 <1 Cll CPll~.7 160 Fail 1.5 3.5 7 4 C12 CP128.7 140 ~ail 1.5 305 8 5 ~. _ _ _ ~ _ . ... _ _ . .

The results oE testing, as shown in Table IV, demonstrate that preprimed metal surfaces prepared using the coating materials of the present invention ~and particularly having a first coating layer composition of the type disalosed herein) can be double drawn ~formed~ in a manner not possible using the present commonly used metal primers. In addition, the corxosion resistance ~hows an unexpected improvement when the preprimed metal sur~aces of the present invention are compared with conventional preprimed surfaces. After deformation, the preprimed metal surfaces of the present invention also showed substantially better corrosion resistance than the metal surEaces preprimed with conventional primers~ The flexib:llity and ætone chip resistance of the preprimed metal surfaces of the present invention are signiflcantly better than the flexibility and stone chip resistance of conventionally primed metal surfaces.

20~223~

EX_M LE 13 and COMPARATIVE EXAMP E C14 Example 7 and Comparative Exclmple C12 were repeatecl in their Pntirety, except that a particular polyester based coating, as described below, was applied as the second primer layer in place of the polyurethane based coating described above.
The polyester resin for the polyester based coating was prepared by charging, to a suitable vessel ~aintalned under nitrogen atmosphere, 24.8 parts by weight polypropylene glycol, 12.4 parts by weight neopentyl glycol and 0.05 parts by weight dibutyltin oxide a~ cataly~t. The temp~rature of the contents of the vessel was raised to 11~ C, then 22.1 parts by weight adlpic acid, 39 . 8 paxts hy weight isophthalic acid and ~ 9 9 parts by weight trimellitic acid were ~urther charged. The temperature was then raised to 22~ C and maintained until thejacid value ~all below 30.
The reaction wa~er was then removed by azeotropic distillation with an aromatic hydrocarbon solvent (co~nercially available under the trade designation Solvesso 100 ~rom Shell) until the acid ~alue fell below 3, at which point the mixture was cooled to about 15~ C. Finally, 33.4 parts by welght aromatic hydrocarbon solvent ~commercially available under the trade des.ignation Solvesso 150 fro~ Shell) and 22.9 parts by weight methoxypropanol acetate were acld~ed to bring the solids content of the resulting solution to 60.1%~
A grey polyester based coating was prepared from the above polyester resin solution by mixing the following components in the amounts as set forth below in ~able V
(nu~bers are in parts by weight):

22 ~CO ~201 T_BLE ~i1 Components Parts Components Parts ~. . .. _ Polyester resin (solids) 46.0 Carbon black 1.0 Crosslinker 6~4 Titanium diox:Lde 32.7 Catalyst 1.0 Solvent ~.o Flow agent 0.1 Methoxy propanol acetate 2.5 Butyl acetate 6.3 . _ . _ The crosslinker was a melamine resin co~Lmex~ially available under the trade designation Cymel 303 from ~m~rican Cyanamid. The catalyst was a blocked acid catalyst commercially available under the trade designation Cycat 405 from American Cyanamid. The flow agent was a silioone additive commercially available under the trade designation Silicone L.75 from U~ion Carblde Corp. The sol~ent w~ a mixed aromatic ~olvent commercially available under the trade designation Solvesso 200 from Shell Chemical.
The resulting coated metal panels were evaluated in the manner of Examples 1-10 and Compa.rative Examples C11 and C12.
The results are presented below in Table VI.

2~2~
2~ AC0 2201 TABLE ~I

... . _ . .
Erich Rever. Doub. Stone Corr. Corr.Res.
EX Primer Indent. Impact _raw T-Bend Chip_ Res. After Deform.
13 P7 10.~ 120 Pass- 1.5 1.5 0 C14 CP12 ~.0 ~o Fa~l 2.5 4 4 4 _ ~

Again, the results of testing, as shown in Table VI, demonstrate that the preprimed metal surface prepared using the coating materials and method of the present invention permitted ~ormation ~dou~le draw) not possible using a conventional priming material as a prepriming coating. In addition, corrosion resistance ls substantially improved, as is stone chip resistance, by use of the present invention.
.

Example 15 Example 7 was r0peated in its entirety except that, as the metal substrate, was utilized an electrogalvanized steel (70/70 g/m2l commercially available from Sollac). The results of the testing are presented below in Table VII.

3'~`
24 ACO ~201 TA~LE VII

Erich. R~ver. Doub. Stone Corr. Corr.Res.
EX Primer Indent. Impact Draw T-Bend Chip Re~ After Deform.
P7 10 . 0 160 Pass 0 . 5 1. 5 .. . . . . .
The results shown in Table VII indicate that the prepriming composition and m~thod of the present invention provided the improved performance previou~ly discu~sed whether the metal ~urfare being preprimed i3 hot dipped galvanized steel or electrogalvallized steel.
Many modifications and variations may ba made to th~
embodiments specifically mentioned here without substantially departing from the concept of the pres~nt invention.
Accordingly, it should bs clearly understood that the preferred embodiments of the invention described herein are exemplary only, and not intended as a limitation on the ~cope of the invention as de~ined in the followlng alaims.

Claims

1. A preprimed metal substrate comprising a metal substrate coated with a primer, wherein the primer comprises:
(1) a first coating layer applied onto the metal substrate, the first coating layer comprising a coating composition based upon, as a binder, a hydroxyl groups-containing block copolymer built up from (A) one or more blocks of a carboxyl-terminated polyester resin, and (B) one or more blocks of an epoxy resin; and (2) at least one flexible subsequent coating layer applied onto the first coating layer.

2. The preprimed metal substrate of claim 1, wherein the carboxyl-terminated polyester resin comprises the polycondensation product of one or more carboxylic diacids and one or more difunctional hydroxy compounds, wherein the carboxylic diacid is selected from aromatic carboxylic diacids, aliphatic carboxylic diacids and mixtures thereof.

3. The preprimed metal substrate of claim 2, wherein the carboxylic diacid is selected from aromatic carboxylic diacids.

4. The preprimed metal substrate of claim 3, wherein the aromatic carboxylic diacid is selected from terephthalic acid and isophthalic acid.

5. The preprimed metal substrate of claim 1, wherein the carboxyl-terminated polyester resin comprises an acid number of from about 10 to about 140, an hydroxyl number not higher than about 2 and a number average molecular weight of from about 800 to about 10000.

6. The preprimed metal substrate of claim 1, wherein the epoxy resin has an epoxy functionality ranging from about 1.5 to about 2.5, and an epoxy equivalent weight of from about 100 to about 2000.

7. The preprimed metal substrate of claim 6, wherein the epoxy resin has an epoxy functionality of from about 1.8 to about 2.2, an epoxy equivalent weight of from about 100 to about 700, and a number average molecular weight of from about 150 to about 1250.

8. The preprimed metal substrate of claim 1, wherein the hydroxyl groups-containing block copolymer is built up from 3 to 11 blocks (A) and 2 to 10 blocks (B), or from 2 to 10 blocks (A) and 3 to 11 blocks (B).

9. The preprimed metal substrate of claim 1, wherein the hydroxyl groups-containing block copolymer has a number average molecular weight of from about 3000 to about 80000, and an acid number not higher than about 23.

10. The preprimed metal substrate of claim 9, wherein the hydroxyl groups-containing block copolymer has a number average molecular weight of from about 5000 to about 30000, and an acid number in the range of from 0 to about 15.

11. The preprimed metal substrate of claim 1, wherein the first coating layer further contains a crosslinking agent for the hydroxyl groups of the hydroxyl groups-containing block copolymer.

12. The preprimed metal substrate of claim 1, wherein the first coating layer is pigmented.

13. The preprimed metal substrate of claim 1, wherein the at least one flexible subsequent coating layer has a glass transition temperature ranging from about 30°C to about 70°C.

14. The preprimed metal substrate of claim 5, wherein the at least one flexible subsequent coating layer comprises a coating selected from a polyester polyol crosslinked using a polyisocyanate and a polyester polyol crosslinked using a melamine.

15. The preprimed metal substrate of claim 1, wherein the metal substrate comprises a metal sheet.

16. The preprimed metal substrate of claim 1, wherein the first coating layer comprises a dry layer thickness up to about 15 µm, the at least one flexible subsequent coating layer comprises a dry layer thickness up to about 30 µm, and the total primer dry layer thickness ranges from about 15 µm to about 45 µm.

17. The preprimed metal substrate of claim 16, wherein the first coating layer comprises a dry layer thickness of from about 3 µm to about 10 µm, the at least one flexible subsequent coating layer comprises a dry layer thickness of from about 12 µm to about 25 µm, and the total primer dry layer thickness ranges from about 20 µm to about 30 µm.

18. A method of prepriming a metal substrate by applying a primer layer thereon, characterized in that the primer layer comprises:
(1) a first coating layer applied onto the metal substrate, the first coating layer comprising a coating composition based upon, as a binder, a hydroxyl groups-containing block copolymer built up from (A) one or more blocks of a carboxyl-terminated polyester resin, and (B) one or more blocks of an epoxy resin; and (2 at least one flexible subsequent coating layer applied onto the first coating layer.

19. The method of claim 18, wherein the carboxyl-terminated polyester resin comprises the polycondensation product of one or more carboxylic diacids and one ox more difunctional hydroxy compounds, wherein the carboxylic diacid is selected from aromatic carboxylic diacids, aliphatic carboxylic diacids and mixtures thereof.

20. The method of claim 18, wherein the carboxyl-terminated polyester resin comprises an acid number of from about 10 to about 140, an hydroxyl number not higher than about 2 and a number average molecular weight of from about 800 to about 10000.

21. The method of claim 18, wherein the epoxy resin has an epoxy functionality ranging from about 1.5 to about 2.5, and an epoxy equivalent weight of from about 100 to about 2000.

22. The method of claim 18, wherein the hydroxyl groups-containing block copolymer is built up from 3 to 11 blocks (A) and 2 to 10 blocks (B), or from 2 to 10 blocks (A) and 3 to 11 blocks (B).

23. The method of claim 18, wherein the hydroxyl groups-containing block copolymer has a number average molecular weight of from about 3000 to about 80000, and an acid number not higher than about 23.

24. The method of claim 18, wherein the first coating layer further contains a crosslinking agent for the hydroxyl groups of the hydroxyl groups-containing block copolymer.

25. The method of claim 18, wherein the first coating layer is pigmented.

26. The method of claim 18, wherein the at least one flexible subsequent coating layer has a glass transition temperature ranging from about 30°C to about 70°C.

27. The method of claim 26, wherein the at least one flexible subsequent coating layer comprises a coating selected from a polyester polyol crosslinked using a polyisocyanate and a polyester polyol crosslinked using a melamine.

28. The method of claim 18, wherein the metal substrate comprises a metal sheet.

29.The method of claim 18, wherein the first coating layer comprises a dry layer thickness up to about 15 µm, the at least one flexible subsequent coating layer comprises a dry layer thickness up to about 30 µm, and the total primer dry layer thickness ranges from about 15 µm to about 45 µm.

30. The method of claim 29, wherein the first coating layer comprises a dry layer thickness of from about 3 µm to about 10 µm, the at least one flexible subsequent coating layer comprises a dry layer thickness of from about 12 µm to about 25 µm, and the total primer dry layer thickness ranges from about 20 µm to about 30 µm.

31. The method of claim 18, wherein the so-preprimed metal substrate is subsequently formed.