Note: Descriptions are shown in the official language in which they were submitted.
5`TATE OF THE ART ~ ~ 3 3 ~ a3 0
Water-dilutable coating agents based on a~ueous polyur-
ethane dispersions for the prepara-tion o~ surfacers are known from
EP-OS No. 27~,3~. Polyether polyols haviny a functionality of at
least 3 are used therein as longer-chain polyols for preparing the
polyure-thane resin and the resulting dispersions are preferably
used for improving the use properties of polyester/melamine resin
mix-tures.
In contrast, German O~fenlegungsschrift No. 3,545r618 relates
to water-dilutable coating agents based on aqueous polyurethane
dispersions for producing the base coat of a multilayer topcoat.
To prepare the polyurethane resin, iOlliC prepolymers containing
NCO groups are reacted with polyols containing at least three
hydroxyl groups resulting in chain-lengthening and possibly chain
branching. Mention of other areas of application than those for
base coats is not made in this publication.
OBJECTS OF THE INVENTION
It is an object o~ the invention to provide aqueous coating
compositions for primers and primer surfacers having good interlayer
adhesion and improved stone chlp resistance and the process ~or
their preparation~
It is another object o~ the invention to provide coated sub-
strates, especially auto body par-ts, having improved corrosion
protection and stone chip resistance.
These and other objects and advantages of the invention will
become obvious from the following detailed description.
~ E~-IN-vr~-Nll~IoN 2 ~ 3 3 ~ ~ ~
'l'he novel aqueous coating composi-tions of the invention ~or
preparing primers or prilner surfacers contain at least one wa-ter-
clispersible ~lnder resin, and crosslinking agents and optionally
conventional additives, wherein at least some of the water-
dispersible binder resin is a polyure-thane resin containing struc-
tural un:its derived from
(~) polyisocyallates,
(B) polyols haviny an average molecular weiyht Mn ~ at least ~00,
(C) optionally low-molecular weiyht polyols,
~D) compounds havillg at least two yroups which are reactive toward
isocyanato groups and a-t least one group which is capable of
anion formation,
(~) polyols carrying no o-ther groups which are reactive with iso-
cyanato ~roups, these structural units (E) being in
each case at the chain end of the polyurethane xesin,
(F) optionally compounds which are monoEunctional or contain active h~drogen
of varying reactivity and are dif~erent from (E), these s-truc-
tural units (~) likewise being at the chain end o~
the polyurethane resin and,
(G) optionally ccmpounds which are diEferen-t:Er~m (B), (C), (D), (E) and ~F)
and conkain at least -two groups which are reacti.ve with NCO
group~
SurEacer or pr:imer surEacer la~ver is intended to mean the
layer between the primer and topcoat, particularly in automotive
bodies or parts tllereof, whicll serve Eor .ieveling out uneven places
in the primer, whicll has the function of ensuring ~lawless
appearance o~ the topcoat and Eor improving the stone chip resist-
ance o~ the entire coating. By virtue of its plastic behavior,
tl l~yer is intellded to prevent stone chip5 and the ~l~e;~ su~ch as
are thrown agaillst the coating by other cars or even the car
itself, from penetrating the coating. Moreover, the surfacer com-
positions must produce relatively hard films to permit wet grinding
of the coating without giving rise to glazing of the gri~ paper.
The polyurethane resin of the invention ha~ generally an
average molecular weight Mn (calculated from the stoichiometry of
the startiny material) o~ 1,600 to 50,000, preferably 1,600 to
10,000 and most preferably 2,000 to 6,000, an acid number of 10 to
80, pre~erably 25 to 60, and a hydroxyl number of 30 to 200, pre-
ferably 50 to 100. It is water-dispersible at least in an alkaline
medium and at low molecular weights frequently even water-soluble
under these conditions. In general, the structure of the molecule
chains of this polyurethane resin is pxedominantly linear, although
in some cases a slight degree oE branching o~ preferably up to
30%, more preferably up to 10~, may be present. The gel content is
generally less than 5~ by weight, preferably less than 1~ by
weight. On statistical average, each polymer chain preferably con-
tains at least two, preferably 4 to 6, groups having active hydro-
gen such as amino and/or OH groups.
The polyisocyanates, pre~erably diisocyanates, (A) are com-
pounds known in the area oE polyurekhanes or coatings such as
aliphatic, cycloaliphatic or aromcltic diisocyanates. They pre-
~erably have the Eormula Q(NCO)z, in which Q is a hydrocarbon of
to ~0 carbon atoms, preerably ~ to 20 carbon atoms, and is more
preEerably an aliphatic hydrocarbon of ~ to 12 carbon atoms, a cyclo-
~liphatic hydrocarboll o~ 6 to 15 carbon atoms,an aromatic hydrocarbon
of 6 to 15 carbon atoms, or an araliphatic hydrocarbon of 7 to 15 carbon
atoms~ Examples o~ diisocyanates of this type to be used are
preferably tetramethylene diisocyana-te, hexamethylene diisocyana-te,
dodeca~ethylene diisocyana-te, 1~4-diisocyanatocyclohexane,
2 ~ ~ 3 ' ~1~
3~ ocyanat~m~t:hyl-3,5,5-tr.i~ ttly.Lcyclohexyl.
:isocyanate (isophorone diisocyanate), ~,~t-diisocyanato dicyclo-
hexylmethane, 2,2-(4,4'-diisocyanatodicyclohexyl)-propane, 1,4-dii~
socyanatobenzene, 2,~- or 2,G ~iisocyana-totoluene or mixtures of
these isomers, 4,~'- or 2,~'-diisocyanatodiphenylmethane, 2,2-
(4,~'-diisocyanatodiphenyl)-propane, p-xylylene diisocyanate and
a,a,a',a'-tetramethyl-m- or ~xylylene diis~cyanate and mixtures oE
these compounds.
Apart from these simple polyisocyanates, those containing
hetero atoms in the group linking the isocyana~o yroups are also
suitable. Examples of these are polyisocyanates having car-
bodiimido groups, allophonato groups, isocyanurato groups, urekhane
groups, acylated urea groups or biuret groups. As regards further
suitable polyisocyanates, see for example, German Offenlegungs-
schrift No. 2,928,552.
The polyisocyanate (~) content in the polyurethane resin is
usually about 10 to 50~ by weight, preferably 25 to 35~ by weight,
relative to the polyurethane resin.
The polyols o~ (B) preferably have an average molecular weight
~n oE 400 to 5,000, more preferably 800 to 2,000. Their hydroxyl
number is genera].ly 30 to 2~0, pre~erably 50 to 200 and more pre-
Eerably ~0 to 160, my o~ K0H/g.
~ xamples oP polyols o:E this type which are the compounds known
Prom polyureth~ne chem:istry are polyather polyols, polyester
polyol.¢, polycarbonate polyo:ls, polyesteramido polyols, polyamido
polyols, epoxy resin polyols and their reaction products with COz,
polyacrylate polyols and the like. Polyols of khis type which can
also be used in a mixture are described, for example, in German
Ol ...leyunysscil:riften No. 2,020,905; No. 2,314,51~ ~'a ~ ~ .
3,12~,7~4 and ~uropean Of~enlegunysschrift No. 120,466.
of these polyols, the polyether and polyester polyols are pre-
ferred, preferably those having only terminal OFI groups and a
functionality o less than 3, preferably 2.~ to 2 and most pre-
ferably 2.
Examples of suitable polysther polyols are polyoxyethylene
polyols, polyoxypropylene polyols, polyoxybutylene polyols and
preEerably polytetrahydrofuran having terminal OH groups.
The polyester polyols which are particularly preEerred in khe
invention are known polycondensation products of di- and, if appro-
priate, poly(tri-, tetra)ols with di- and, if appropriate, poly
(tri-, tetra)carboxylic acids, or hydroxycarboxylic acids or
lactones. It is also possible to use the corresponding polycar-
boxylic acid anhydrides or the corresponding polycarboxylic acid
esters of lower alcohols, instead of the ~ree polycarbox~vlic acids,
for preparing the polyesters. Examples of suitable diols are
ethylene glycol, butylene glycol, diethylene glycol, triethylene
glycol, polyalkylene glycols such as polyethylene glycol, further-
more propanediol, 1,4-butanediol, 1,6-hexanediol, neopentylglycol
or neopentylglycol hydroxypivalate, the three last-mentioned compounds bein~
preE~r:red~ Example~ o~ suitable polyols which optionally can also be
used are krimethy:Lolpropalle, glycerol, erythrl~ol, pentaerythritol,
krimekhylolbenzene or tris(hydroxyethyl.)isocyanurate.
Examples o~ suitable dicarboxylic acid~ are phthalia acid,
isophthalic acid, kerephthalic acid, tetrahydrophthalic acid,
hexahydrophthalic acid, cyclohexane-dicarboxylic acid, adipic acid,
azelaic acid, sebacic acid, glutaric acid, "chlorendic acid'l,
tet~ hlorophth~lic acicl, maleic acid, fumaric acid, itaconlc ac
malonic acid, suberic acid, 2-methylsuccinic acid, 3,3-diethyl-
glutaric acid and 2,2-dimethylsuccinic acid. Anhydrides of these
acids are also useful insofar as they exist. Consequently, the
anhydrides are also covered by the term "acid". It is also
possible to use monocarboxylic acids such as benzoie acid and
hexanecarboxylic acid, provided the average functionality of the
polyol is higher than 2. Saturated aliphatie or aromatie aeids are
preferred such as adipic acid or isophthalic aeid. A polycar-
boxylic aeid which optionally may additiona:lly be used in
relatively small amounts is trimellitie aeid.
Examples of hydroxycarboxylie acids which ean be used as
reactants in the preparation of a polyestsr polyol having terminal
hydroxyl include hydroxycaproic acid, hydroxybutyrie aeid,
hydroxydecanoie acid, hydroxystearie acid and the like. Useful
lactones ineluds eaprolaetone, butyrolaetone and the lika.
The amount of eomponent ~B~ in the polyurethane resin is
usually between 15 and 80% by weight, preferably 40 to 60% by
weight, relative to the polyurethane resin.
The low-moleeular-weight polyols (C) whieh optionally, may be
used ~or synthesiziny the polyurethane resins usually have the
e~Eect o~ stifEening the polymer ehain. In general, they hav~ a
moleeular weight oE about 60 to ~00, preferably 60 to 200, and
hydroxyl numbers oE, for example, 200 to 1,500. They ean eontain
aliphatie, al:ieyclie or aromatie yroup~ and the amount thereof is
generally 0 to 20, pre~erably 1 to ~0% by weight, relative to polyol
eomponents (B) tu (D). ~xamples are the low-moleeular-weight
polyols having up to about 20 carhon atoms per moleeule, for
example ethylene glyeol, diethylene glyeol, 1,2-propanediol, 1-3-
2~3~4~B
.~panecliol, ~ but~nediQl, l,3-butylene glycol cyclohexanediol,
l,~-cyclohexanediDl~thallol, l,6-hexanediol, bisphenol A (2,2~bis(4
I-lydroxyphenyl)-prop~ne), hydrogenated bisphenol A (2,2-bis(4-
hydroxycyclollexyl)-propane) and mix-tures thereof, and as triol
trimethylolpropane.
Examples of compounds suitable ~or ~tru~-tural unit(D) are
described in U.S. Patents No. 3,~12,054 and No. 3,640,924 and in
German Offenlegungsschriften No. 2,624,442 and No. 2,744,544
incorporated herein by reference. In particular, khose polyols are
suitable, pre~erably diols, which contain at least one carboxyl
group, generally l to 3 carboxyl groups per molecule. Sulfo groups
are also suitable as groups capable of anion formation. Examples
of these are: dihydroxycarboxylic acids such as Nr ~-dialkylol
alkanoic acids like ~, a-dimethylolalkanoic acids ~uch as 2,2-
dimethylolacetic acid, 2,2-dimethylolpropionic acid, 2,2-
dimethylolbutyric acid, 2,2-dimethylolpentanoic acid, dihydroxy-
succinic acid and polyhydroxy acids such as gluconic acid. Of
these, 2,2-dimethylolpropionic acid is particularly pre~erred.
Examples of amino-containing compounds (D) are ~ diaminovaleric
acid, 2,4-diaminotoluene-5-sul~onic acid and the like. Mixtures of
the compounds (D) can also be used and the amount o~ component ~D)
in the polyurethane resin is generally 2 to 20, preEerably 4 to 10%
by weiyht, relative to the polyurethane resin.
The polyurethane resins used in the invention also contain
struc~ural uni~ ) which are predominantly, pre~erably to the
extent o~ 70 to 90%, each present at the chain ends and terminate
them ~chain termina-tors). Suitable polyols llere are those having
at least three, pre~erably 3 or ~, hyroxyl yroups. Examples are
ylycerol, hexanetriol, pentaerythritol and trimethylolpropane, the
latter beiny preferred. 'rhe amount o~ ~E) is usually between 2 and
15, pre~erably 5 to 15% by weiyht, relative to the polyurethane
2~3~
1 .in. If desl.red, these ~tructur~l units(E) are present in the
polyurethane resin in a mixture with structural units (F) .
The structural units(~'J are derived ~rom mono~unctional com-
pounds whi.ch are reactive with NCO groups such as monoamines,
particularly seco~dary monoamines or monoalcohols. Examples are
methylamine, ethylamine, propylamine, butylamine, octylamine,
laurylamine, stearylamine, isononyloxypropylamine, dimethylamine,
diethylamine, dipropylamine, dibutylamine, N-methylaminopropyl-
amine, diethyl(methyl~aminopropylamine, morpholine, piperidine, or
suitably substituted derivatives thereof, amidoamines from primary
diamines and monocarboxylic acids, monoketimines of primary
dia~nes, primary/tertiary amines such as N,N-dimethylaminopropyl-
amine and the like.
Preferably, suitable compounds for (F) are those containing
active hydrogen of varying reactivity toward NCO groups such as
compounds having, apart ~rom a primary amino group, also secondary
amino groups, or, apart from an OH group, also COOH groups, or,
apart from a primary or secondary amino group, also OH groups, the
latter being preferred. Examples o~ these are: primary/secondary
amines such as 3-amino-1-methylaminopropane, 3-amino-1-ethylamino-
propane, 3-amino-1-cyclohexylaminopropane, 3-amino-1-methylamino-
butane; monohydroxycarboxylic acids such as hydroxyacetic acid,
lactic acid or malic acid, and al]canolamines such as N-aminoethyl-
ethanolamine, ethanolamine, 3-aminopropanol, neoperltanolamine ancl
particularly preEe.rably diethanolamine.
In this manner, functional groups are additionally incorpo-
rated in the final polymer product which is thus made more reactive
toward materials such as curing ayents. The amount oE (F) in the
polyurethane resin is usually between 2 and 20, preferably
2~33~ ~
3 a~cl 10% by weight, rel~tive -to the polyurethane resin.
In addition -to the structuraL ~uts according to (E) and (F),
-the polyuret~lane resi~ of the invention can op-tionally also contain
structural units (G) which are derived from so-called chai.n-
lellgthening agen-ts, although thi~ variation is less preferred.
Compounds which are suitable for this are the known compounds which
are reactive toward NCO groups and are preferab:ly clifunc- .
tional compounds no-t .identical with (B~, (C), (D), (E) and (F) and
in most cases having average molecular weights of up to 400.
Examples are water, hydrazine, poly(di)amines such as ethylene-
cliamine, diaminopropane and hexamethylenediamine which can also
~arry substituents such as OH groups. Polyamines of this type are
described, for example, in German Offenlegungsschri~t No.
3,644,371. The amount of (G) in the polyuretllane resin is usually
between 1 and 10, preferably 2 and 5% by weight, relative to the
polyurethane resin.
~ he polyurethane resin of the invention is preferably pre-
pared in such a manner that first a polyurethane prepolymer is pre~
pared ~rom the polyisocyanates of (A), the polyols of (B) and
optionally the low-molecular-weight polyols of (C) and the com-
pounds o~ (D), which prepolymer contains on average at least 1.7,
preferably 2 to 2.5, ~ree isocyanato groups per molecule, the pre-
polymer is then reactecl with a stoichiometric excess of the com-
pounds of (~ desired in a mixture with (F) and/or (G), in a
non-aqueous system, and the completely reacted polyurethane resin
is then preferably neutralized ancl transferrd into an aqueous
system. If desired, the reaction with tG) can also take place
after transfer into the aqueous system.
2~ ~3 ~ ~
The preparation oE the polyurethane prepolymer is carried out
by known processes in whicl1 the polyisocyanate is used in excess,
relative to polyols (B) to (V), resulting in a product having ~ree
isocyanato groups. These isocyanato groups are terminal and/or
pendant, pre~erably -terminal. A~vantageously, the amount o~ poly-
isocyanate is such that the equivalent ratio of isocyanato groups
to the overall number o~ O~l groups in polyols (B) to (D) is l.05 to
l.4, preferably l.l to l.3.
The reaction for preparing the prepolymer is usually carried
out at temperatures of 60 to s5c, preferably 6~ ~o 75C, depending
on the reactivity of the isocyanate used, as a rule., in the absence
of a catalyst, but preferably in t.he prasence of solvents inert to-
ward isocyanate. In particular, those solvents are suitable for
this which are water-compatihle such as the ethers, ketones and
esters mentioned below and N-methylpyrrolidone. The amount o~ this
solvent advantageously ~oes not exceed 20~ by weight, and is pre-
ferably in the range of 5 to 15% by weight, in each case relative
to the sum of polyurethane resin and solvent. Advantageously, the
polyisocyanate is slowly added to the solution of the other com-
ponellts .
The prepolymer or its solution is then reacted w:Lth the com-
pound o~ (~), if desired in a mixture with (~) and/or ~G), the
temperatur~ being advantageously in the range o~ 50 to 100C, pre-
~erably between 60 and ~0C, un-til t~le NC0 content in the pre-
polymer has virtually dropped to zero. For thi~ purpose, com-
pound (E), i:e desired together with ~F) and/or (G)is used in excess.
The amount oE (El is advantageously such that the equivalent ratio
of NCO groups of the prepolymer, which previously may already have
been reacted with compounds according to (F) and/or (G), to reac-tive
groups o~ (E~ is 1~1.1-to 1:5, preferably 1:1.5 -to 1:3. The amount
11
3~3~
of (F) and/or ~G) can be 0 t~ 90 %, preferably 0 to 20 ~,
relative to (1:~.
A portion of the ~unneutralized) COOI-I groups, pre~erably 5 to
30% can, if desired, be reacted with difunctional compounds which
are reac-tive w:ith COOH groups such as diepoxides.
For neutraliziny the result:ing product preferably containing
COOH groups, in par-ticular tertiary amines are suitable. Examples
are trialkylamines having 1 to 12, preferably l to 6 carbon atoms
in each alkyl. Examples of these are trimethylamine, trie~hyl-
amine, methyldiethylamine, tripropylamine. The alkyls can also
carry, for example, hydroxyl groups as in the case of dialkyl-
monoalkanolamines, alkyldialkanolamines and trialkanolamines. Anexample o~ these is dimethylethanolamine which preferably serves as
neutralizing agent. Neutralizing agents which may also be used are
inorganic bases such as ammonia or sodium hydroxide and potassiuim
hydroxide.
In most cases, the neutralizing agent is used in a molar ratio
o~ about 0.3:1 to 1.3:1, preferably about 0.5:1 to 1:1, relative to
the COOH yroups of the prepolymer. The neutralization, which, as
a rule, i5 carried out between room temperatures and 80C, pre-
Eerably ~0 to ~0C can be carried out in any desired manner, Eorexample by adding the water-conta:Lning neutraliziny ayent to the
polyurethane resin or vice versa. ~lowever, it :Ls also possible
~irst to add to the polyurethane resin the neutralizing agent and
only then the water. In yeneral, this gives solids contents of 20
to 70%, preEerably 30 to 50%.
The polyurethane resin content in the aqueous coating composi-
tion is generally 5 to 40, pre~erably 15 to 30% by weight, relative
to the entire coating composition.
12
2 ~ ? 3 "~
~ part from the polyurethane r~sinr the aclueous coating
CO~lpOSitiOIl can also contain, as binder, up to 60, preferably up-to
30% by weight, relative to the polyurethane resin, Oe other oligo-
meric or polymeric materials such as crosslinkable, water-soluble
or water-dispersible phenolic resins, polyester resins, epoxy
resins or acrylic resins and the like as described in European
Offenlegungsschrift No. 89,497.
Fur-thermore, excess polyol Oe t~) is usually present in the
coating composition of the invention, in most cases in amounts of
1 to 10~, preferably 2 -to 5% by weight, relative to the
polyurethane resin.
Suitable crosslinking agents are the curing agents customary
for polyol resins as long as they are water-compatihle. Examples
are water-compatible (water-soluble or water-dispersible~ amino
resins, particularly commer~ially available etherifiad melamine/
formaldehyde condensation products such as hexamethoxymethyl-
melamine, phenolic resinsor capped polyisocyanates as described in
German Offenlegungsschrift No. 3,6~4,372. The amount of cross-
linking agent is usually 10 to 35~ by weight, preferably 15 to 25%
by weight, relative to the sum of binder to be crosslinked ancl
crosslinking agen-t.
~ he aqueous coa-ting compositions oE the invention, whose pH is
in most cases in the range o~ about 6.0 to 10.0, pre~erably 6.8 to
~.5, aan additionally contain conventional paint additives such as
piyments and Eillers, and paint additives, Por example anti-settl-
ing agents, antieoams and/or wetting agents, flow-improving agents,
raac-tlve thinners, plasticizers, catalysts, dissolution aids,
thickeners and the like. At least part oE these additives do not
have to be added to the coating composition until immediately
13
~3~
b~ ~re processint). Tlle s~lection alld dosage of these substances
W}liCh can be added to -the individual components and/or the entire
m.ixture are known ko one skilled in the art.
Examples o~ sui.table piyments are iron oxides, lead oxides,
lead silicates, titanium dioxide, barium sulfate, zinc oxide, zinc
sulfide, phthalocyanine complexes and the like, and suitable
fillers are mica, kaolin, chalk, quartz powder, asbestos powder,
slate powder, various silicas, silicates and -talc, including so-
callecl micro-talc having a maximum particle size of 10 ~um (cf.
European Offenlegungsschrift No. 2~9,727). These pigments and/or
fillers are usually used in amounts of 10 to 70, preferably 30 to
50% by weight,relative-to the overall solids content of ~he coating
composition.
Suitable catalysts are the convenkion~l acid curing catalysts
such as p-toluenesulfonic acid, dodecylhenzenesul~onic acicl and the
like.
The dissolution aids, for example ethers such as dimethyl
~diethyl)glycol, dimethyl(diethyl)diglycol or tetrahydro~uran,
ketones such as methyl ethyl ketone, acetone or cyclohexanone,
esters such as butyl acetate, ethylglycol acetate or methylglycol
acetate, methoxypropyl acetate, alcohols such as ethanol, propanol
or butanol are used, i.~ ak all, only in very low amounts for
reason~ oE environmental protection, usually not exceeding 10, pre-
Perably 1 to 5~ by weight re].ative to water (a~ the main diluent).
The amount o~ water in the aqueous coating composition is in most
cases 15 to 80~ by weiyht, prePerably 30 to 60% by wei~ht, relative
to the entire coatiny composition.
14
2 ~ 3z~J~
~ he a~ueous coating compositions are prepared using conven-
tional methods oE p~int production as can be seen from the standard
recipe given below.
The aqueous coatiny composition which is infinitely dilutablP
with water and whose overall solids content (125C/2 hours) is
generally 35 to 75, preferably 40 to 60~ by weight, is applied in
a Xnown manner, for example by spraying using the compressed air
process or by airless or electrostatic sprayiny processes. To cure
the layers applied, temperatures o~ 120 to 200~C, preferably 150 to
170C, are generally applied. The curing time is generally 15 to
30 minutes, preferably 18 to 20 minutes.
The crosslinked coatings thus obtained are distinguishecl in
particular by improved stone chip resistance at low temperatures
(0C to -30C) and by good interlayer adhesion. Moreover, they have
good elongation at break and excellent impact resistance. The
resistance to atmospheric humidity and so~vents is also very good
In the following examples, there are described several pre-
ferred embodiments to illustrate the invention. However, it should
be understood that the invention is not intended to be limited to
the specific embodiments.
E~A~
~ mixkure was prepared ~rom 235 g of a polyester of molecular
weiyllt 8~0 prepared from adipic acid, 1,6-hexanediol, neopentyl
glycol and ~2.9 g of dimethylolpropionic acid and 75 g of N-mekhyl-
pyrrolidone and the mixture was heated to 100C. The clear solu-
tion was cooled to about 60C, and then 1~1.8 g of a mixture of
2/4~ and 2,6-toluylene diisocyanate were added dropwise at this
2033~?0
tel _rature ~t such a rate that the temperature did not exceed 65C
to 70c. S-tirr:ing ~t this temperature was then continued until the
isocyanate value had reached 1.6% (=2 isocyanato groups per
moleculQ). 29.5 g of trimethylolpropane were than ~dded, during
which the system rernained readily stirrable. After neutralization
with 22.4 CJ of dimethyle-thanolamine, the finished polyurethane
resin was dispersed by addiny 590 g of deionized water to obtain
a clear, approximately 40~ strength dispersion having a viscosity
oE 1500 mPas.
EXAMPLE 2
235.6 g of a polyester with a molecular weightoE 1020 prepared
from adipic acid, l,6-hexanediol and neopentyglycol were mixed
with 56.0 g of polytetrahydrofuran (M = 1000), 42.9 g of dimethy-
lolpropionic acid and 75 g of N-me-thylpyrrolidone and the mixture
was reacted as described in Example 1 with toluylene diisocyanate
(mixture of isomers). After reaction of the prepolymer with
glycerol, the mixture was neutralized with 22.8 g of dimethyl-
ethanolamine, and the resin was dispersed in 620 g of deionized
water.
EXAMPLE 3
317.1 g of a polyester with a molecular weight of 1130 prepared
~rom aclipic acid, hexanediol, neopentyglycol and terephthalic acid
were mlxed with 42.9 g o~ dimethylolpropionic acid and 90 g of
N--methylpyrrolidone and the mixture was heated to 100C. After
cooling to 65C, 1~3.7 g oE ~,4'~diisocyanatodicylcohexylmethane
(Desmodur W) were added dropwise and the reaction batch was then
maintainecl at 80C until the calculated isocyanate value of 1.33
(=2 isocyanato groups per molecule) had been reached. 80.4 g of
16
2 ~ 3 ~
t~ .ethylo~propane and then 22.8 y of dimethylethanolamine were
added arlcl stirring of tile mixture was continued for 20 minutes.
The polyurethane resin was then d:isper~ed by adding 700 g of
deionized water.
STANDAl~D RECIPE FOR SURFACER_ORMULATION
58.0 par-ts of the binder from Example 1 to 3 were dispersed
with 4.0 parts of a commercially available melamine/ormaldehyde
condensation product, 13.3 parts o~ titanium dioxide, 13.2 par-ts of
barium sulfate (Blanc ~ix micro), 0.1 part of carbon black, 11.1
parts of deionized water and 0.3 parts of conventional paint addi-
tives in a pearl mill for 20 minutes at ~000 rpm to form the sur-
facer composition which was applied to a zinc-phosphat~d steel
sheet coa-ted -to about 30 ~m with a cathodically deposited electro-
primer with a compressed air gun. The curing o~ the surfacer wascarried out in a through-circulation oven at 80C for 10 minutes
and then at 160C for 20 minutes toobtain a dry ~ilm thickness of
35 -~ 2 ~m. A commercially available alkyd/melamine automotive
paint was applied on top o~ the surfacer coat and baked at 130C
for 30 minutes for dry film thickness of about 30+ 5 ~m. The test
results are summarized in Table I below and the stabilities of the
films (resistance to solvents and water) are those required in
commercial practice.
~PPL~.~R~!CE OF '~E~TOPCOAT
Gloss and surEace oE the topcoat on various .surEacer materials
were rated subjectively b~v a scale ~rom l = very yood to 5 = very
poor.
STONE CHIP_RE~S~ CE
Tested by the stone chip testing apparatus o~ VD~ (from
Erichsen, type 508). For this test, the test specimens were
~33~3~
bomb,~d~d in eacll case with 1 kg of steel shot (angular~ 4 5 mm)
acc~lerated by compressed air ~2 bar). ~y comparison with control
spec:imens, t:opcoa~ aclllesior~ (o = no chippi~g off Erom surfacer, 10 =
comple-te delamination) and penetratiolls down to the metal (o - no
penetration, lO = a large number o~ penetrations) were rated.
T~BLE: 1
~3xalllp1e 1 2 3
l~ppearallce Or t:ho
I:opcoel 1;2 - 3 2 2
. .
Topcoat adllesion
-~ 20C 1 - 2 1 2 - 3
- 20 C 1 - 2 1 - 2 2 - 3
. _ . ~ . . _ . _ . . .
Pene l:rations
~ 20~C 1 1 2
- 20 C 1 2 3
.. . . _ . . _ _ . _ _ .. _
Cros ~ha l:ch
(accordlng t:o
DIN 53151) ch 0 ch 0 ch 0
_ _ _ .. ..
Various modifications o~ the compositions and process of the
invention may be made without departing from the spirit or scope
thereof and it is to be understood that the invention is intended
to be limited only as defined in the appended claims.
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