Note: Descriptions are shown in the official language in which they were submitted.
BACKGROIIND OF THE INVENTION
The present invention relates to a thermosetting
paint composition and a method of forming a coated layer (film)
5 from such a thermosetting paint composition, and more
particularly to a thermosetting paint composition capable of
providing a coated layer having excellent acid resistance and
scuff (mar) resistance as well as good appearance, which is
suitable for automotive topcoats, coats of building exteriors, etc.,
10 and a method of forming a coated layer (film) from such a
thermosetting paint composition.
Recently, the deterioration of surfaces of
automobiles, buildings, etc. by acid rain has becorne a serious
problem. For instance, automotive topcoats conventionally
15 formed from acrylic resin-type paints, polyester resin-type
paints, etc. are stained with spots, discoloration, etc. when
brought into contact with the acid rain, and in extreme cases the
topcoats themselves are destroyed.
Coatings having high resistance to acid rain can be
2 0 obtained from silicone resin paints, fluorine resin paints,
polyurethane resin paints, etc. However, these resins are
generally very expensive and poor in paintability. Thus, various
rneasures have been taken for conventional coatings formed
from acrylic resin-type paints or polyester resin-type paints to
2 5 prevent their cleterioration by acid rain.
F;or instance, Japanese Patent Laid-Open No. 3-
172368 discloses a coatirlg composition having a high resistance
to ~cid rain, which comprises an acrylic resin and a particular
- 1 -
amount of a polyfunctional blocked polyisocyanate of non-
yellowing type.
However, automotive topcoat is required to have a
good scuff (mar) resistance in addition to a good acid rain
5 resistance. For instance, if there is dust on the coat surfaces of
automobiles at the time of cleaning by car washing machines,
small scut`fs may be produced on the coat surfaces, thereby
deteriorating their appearance. Thus, attempts have been made
to improve the scuff (mar) resis~ance of the topcoats. For
instance, Japanese Patent Laid-Open No. 2-142867 discloses a
method of improving the scuff (mar) resistance of a film formed
from a melamine resin and an acid catalyst for increasing a
cross-linlcing density in the coated film to make the surface
h ard er .
However, to meet the requirements of an acid rain
resistance and a scuff (mar) resistance simultaneously, it would
not be satisfactory to simply conduct the above two methods at
the same time, because the resulting coated film would show
extreme yellowing and wrinkle, and the paints are poor in
2 0 storage stability. In view of these problems, such paints eannot
practically be used for automotive topcoats.
Development has been conducted to provide paint
compositions capable of satisfying both acid rain resistanee and
seuff (mar) resistance. For instance, Japanese Patent Laid-Open
2 5 No. 1-158079 cliscloses a composition comprising a particular
acrylic copolymer, an alkyl ether-substitutecl melamine resin,
and if necessary a blockecl polyisocyanate. This reference has a
deseription to the effeet that the bloeked polyisoeyanate may be
- 2 -
h ~3i ~ ~ 3
a polyisocya~ e ~locked with oxirne or alcohol In Examples of
this reference, polyisocyanntes blocked with oxime are used. In
the composition of Japanese Patent Laid-Open No. 1-158079, an
acid catalyst such as paratoluene sulfonic acid, etc. is used.
Japanese Patent Laid-Open No. 2-86671 discloses a
composition cornprising a hydroxyl group containing acrylic
copolymer, a polyisocyanate and an alkyl ether-substituted
melamine resin. The hydroxyl group containing acrylic
copolymer contains a vinyl monomer having a sulfonic acid
group which acts to accelerate the hardening of the rnelamine
resin .
Coatings formed from the above two compositions
show relatively good acid resistance and scuff (mar) resistance,
but fail to maintain good appearance for a long period of time as
15 required on luxurious automobiles.
Further, Japanese Patent Laid-Open No. 2-242867
discloses a thermosetting paint composition consisting essentially
of (A) a hydroxyl group containing resin, (B) an amino resin, and
(C) a blocked polyisocyanate, a temperature at which the
20 reaction of (A) and (C) starts to take place being within the range
of between -20C and -~50C relative to a temperature at which
the reaction of (A) and (B) starts to take place. The specification
of this reference describes: The paint composition is
characterized by adding a blocked polyisocyanate (component
2 5 (C)) as a supplemental cross-linking agent to an organic solvent-
type paint containing the components (A) and (~) as vehicle
cornponents. As a reslllt, hydroxyl groups remaining in the
cornponent (A) after reaction with the component (B) are reacted
- 3 -
2 ~ 7 ~ ~3 ~ ~
wi~h the compol-ent (C) isol~ltecl from a blocking agen~, thereby
reducing the amOUrlt of the hydroxyl groups, which leads to
improvement of water resistance ancl acid resistance. Since
urethane bonds formed by the reaction between the hydroxyl
groups and the blocked polyisocyanate are chemically stable7 the
resulting coated layer shows excellent chemical resis~ance, water
resistance, as well as excellent mechanical strength and surface
conditions (sagging, flowing, etc.). Incidentally, Japanese Patent
Laid-Open No. 2-242867 has Example in which an isocyanate
blocked with ethyl acetoacetate is used. However, the isocyanate
blocked with ethyl acetoacetate is subjected to dissociation
under a baking condition of about 120 160C for 30 minutes"
and ~he dissociated isocyanate is reacted with the componen~ (A)
(hydroxyl group containing resin) ~o form urethane bonds.
Acco-rding to the inventors' research, however, it has
been found that many of the blocked polyisocyanates which are
dissociated at a relatively low temperature such as a baking
temperature (specifically about 120-160C) cause the
deterioration of significant coating properties such as extreme
- 2 0 yellowing, wrinkling, etc. of the topcoat film, and make paints
containing them less stable in storage. Therefore, the
thermosetting paint composition of Japanese Patent Laid-Open
No. 2-242867 fails to provide a coated layer (film) c,apable of
maintaining good appearance as required for the automotive
topcoats for a long periocl of time.
O~JEC'l' AND SIJM~lAR~ OlF THI~ INVENTION
s~pJ~
Accorclingly, all object of the present irlvention is to
provide a thermosetting paint composition capable of satisfying
the requirements of excellent acid rain resistance and scuff
(mar) resistance and good film appearance simultaneously.
Another object of the present invention is to provide
a method of forming a coated layer (film) satisfying the above
requirements from the above thermosetting paint composition.
As a result of intense research in view of the above
objects, the inventors have found that by adding, to a
thermosetting paint composition comprising a hydroxyl group
containing resin and a highly alkyl-etherified melarnine resin~ a
blocked polyisocyanate having active hydrogen remaining even
at a baking temperature of the coated layer (film) and an acid
catalyst, the resulting coated layer (film) can show good coating
appearance without yellowing. They also have found that a
substitution reaction of active hydrogen proceeds between the
blocked polyisocyanate and the remaining functional groups of
the highly alkyl-etherified melamine resin which have not
participated in a reaction with the hydroxyl group containing
2 0 resin in the process of baking, whereby a self-condensation
reaction of the remaining melamine resin in the coated layer
(film) is prevented to provide the hardened coated layer with
excellent acid rain resistance and scuff (mar) resistance. The
present invention has been completed based on these findings.
2 5 Thus, the thermosetting paint composition according to
thc present invention comprises:
(a) a hyclroxyl grollp containing resin;
(b) an acicl catalyst;
- 5 -
2 ~ rd~
(c) a highly allcyl-etherified melamine resin capable of
forming carbonium ions in the presence of the acid catalyst;
and
(d) a blocked polyisocyanate having active hydrogen at a
baking temperature of a wet film, the active hydrogen being
substitutable with the carbonium ions formed from the highly
alkyl-etherified melamine resin,
the amount of the acid catalyst being, on a solid basis, 0.3-5 weight
% based on the total amount of the resin components.
The method of forming a coated film comprising the
steps of;
( 1~ coating, onto a substrate, a thermosetting paint composition
comprlslng;
(a) a hydroxyl group containing resin;
( b) an acid catalyst;
(c) a highly alkyl-etherified melamine resin capable of
forming carbonium ions in the presence of the acid catalys~;
and
(d) a blocked polyisocyanate having active hydrogen at a
2 0 baking temperature of a wet coated layer, the active hydrogen
being substitutable with the carbonium ions formed from the
highly alkyl-etherified melamine resin,
the amount of the acid catalyst being, on a solid basis, 0.3-5
weight % based on the total amount of the resin components;
2 5 and
(2) baking the wet coated layer to cause (i) a cross-tinking
reaction between the hydroxyl group containing resin ancl the
highly nlkyl etherified melnmine resin, (ii) the formation of
- 6 -
~ ~ 7 ~
carbonillrrl ions from tlle remaining functional groups of the
highly alkyl-e~herified melamine resin in the presence of the acid
catalyst, and (iii) the rcaction between the carbonium ions and the
blocked polyisocyanate.
DETAII,ED DESCRIPTION OF THE INVENTION
The present invention will be explained in detail
below .
[A] Reaction of Thermosetting Paint Composition
As described above, the thermosetting paint
composition of the present invention comprises a hydroxyl group
containing resin, an acid catalyst, a highly alkyl-etherified
melamine resin, and a blocked polyisocyanate having active
hydrogen remaining at a baking temperature of the wet coated
15 layer. In the process of hardening of the wet coated layer formed
from the above thermosetting paint composition, the hydroxyl
group containing resin is subjected to a cross-linking reaction with
the highly alkyl-etherified melamine resin.
Along with the reaction, the following reaction proceeds.
2 0 First, the remaining functional groups of the highly alkyl-etherified
melamine resin which have not participated in the above cross-
linking reaction with the hydroxyl group containing resin are
subjected to an active hydrogen substitution reaction with the
blocked polyisocyanate. By this reaction, the self-condensation of
2 5 the remaining highly alkyl-etllerified melamine resin can be
prevented. The above active hyckogen substitution reaction is
represented by the following formulae (1) ancl (2):
~s~
,COR, C -t
N~C~ N,C~N
Il l + 1~ C C ~ RlOH (1)
~C~N~C~ ~ ~
C-~ ,C-N-C-OR2
N`'~ I ~ O
,C~ "C~ + --N-C-OR~ _ IN ~N + H+ . . . ~2)
whereill Rl-represents an alkyl group having 1-4 carbon atorlls,
S and R2 represents a hydrocarbon group derived from the
blocking agent.
In the reaction (1) the melamine resin generates
carbonium ions in the presence of the acid catalyst, and in the
reaction (2) the carbonium ions are reacted with the blocked
10 polyisocyanate, whereby the active hydrogen atoms of the blocked
polyisocyanate are substituted with the carbonium ions.
The degree of the above reaction can be assessed by
measuring the infrared spectroscopic absorption of imino groups in
the reaction product of the melamine resin and the polyisocyanate.
The thermosetting paint composition of the present
invention is characterized by containing the acid catalyst, the highly
alkyl-etherified melamine resin generating the carbonium ions in
the presence of the acid catalyst, the blocked polyisocyanate having
active hydrogen substitutable with the carbonium ions at a baking
2 0 temperature of the wet coated layer, such that the active hydrogen
substitlltion reaction proceeds along with the reaction of the paint
composition. Accordingly, the reactiorl mechanisrn of the
I'~'J ~ L7 i~ ~
therrnosettil)g paint composition of the present invention is
apparently clifferent t`rom the reaction mechanism of the
conventional thermosetting paint cornposition containing a
melamine resin and a blocked polyisocyanate, in which the blocked
5 polyisocyanate acts as a supplemental cross-linking agent, reacting
with the hydroxyl groups of the hydroxyl group containing resin to
form urethane bonds.
[B] Components of Thermosetting Paint Composition
(a) Hydroxyl group containing resin
The hydroxyl group containing resin usable in the
present invention is a resin having at least 2 hydroxyl groups
acting as reaction sites with the highly alkyl-etherified
melamine resin in one molecule. Specific examples of such
- hydroxyl group containing resins include hydroxyl group
15 containing acrylic resins, hydroxyl group containing polyester
resins, hydroxyl group containing fluorine resins, hydroxyl group
containing amido resins, etc. Among them, the hydroxyl group
containing acrylic resins and the hydroxyl group containing
polyester resins are particularly preferable.
2 0 ( I ) Hydroxy I group containing acrylic resin
The hydroxyl group containing acrylic resins usable in
the present invention are those having a number-average
molecular weight of 1,200-12,000, a hydroxyl value of 50-200 and
an acid value of 0-50. Such hyc'roxyl group containing acrylic
2 5 resins can be procluced by a usual method from at least one of the
rnonomcrs (i) ancl at least one selected fronn the group consisting of
the monomers (ii) and (iii):
(i) Ethylenic monomers corltailling hydroxyl group~s ~s~cQ~as
hydroxymethyl acrylatc, hyclroxymethyl methacrylate,
hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl
acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate,
hydroxybutyl methacrylate, N-methylol acrylarnine, etc.;
(ii) Ethylenic monomers containing carboxyl groups such as
acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric
acid, maleic acid, etc.; and
(iii) Ethylenic monomers copolymerizable with the above
monomers (i) and (ii) such as alkyl acrylates and alkyl
methacrylates including methyl acrylate, methyl methacrylate,
ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl
methacrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl
acrylate, n-octyl acrylate, n-dodecyl acrylate, etc., acrylonitrile,
methacrylonitrile, styrene, etc.
When the number-average molecular weight of the
hydroxyl group containing acrylic resin is less than 1,200, sufficient
cross-linking does not take place in the resulting coated layer, so
that the coated layer shows poor properties. On the other hand,
2 0 when it exceeds 12,000, the paint composition shows an
undesirably increased viscosity, and a coated layer having enough
surface smoothness and evenness cannot be obtained. The
number-average molecular weight of the hydroxyl group containing
acrylic resin is preferably 1,500-10,000, and more preferably
2 5 3,000-6,000.
With respect to the hyclroxyl value, when it is less th~n
50, the resulting coate(l layer suffers from a poor adhesion and a
decreased hardness. On the other hand, when it exceeds 200, the
- ~0 -
~7~
resulting coated layer suffers frorn a decrease in a water resistance
and an acid resist.lnce due to the hydroxyl groups remaining in the
coated layer. The hydroxyl value of the hydroxyl group containing
acrylic resin is preferably 70-16û, and more preferably 80-120.
With respect to the acid value, when it exceeds 50, the
thermosetting paint composition has low storage stability and
shows too high a reaction speed due to too many functional groups
remaining in the coated layer, so that the resulting coated layer
shows a poor acid resistance, lacking in surface smoothness. The
preferred acid value of the hydroxyl group containing acrylic resin
is ()-30.
(2) Hydroxyl group containing polyester resin
The hydroxyl group containing polyester resins usable
in the present invention are those having a number-average
molecular weight of 200-10,000, a hydroxyl value of 50-350, and
an acid value of 3-50. Since the hydroxyl group containing
polyester resins are produced by an esterification reaction of
polyvalent alcohols and polybasic acids or their anhydrides, they
contain hydroxyl groups in their molecules.
2 0 The polyvalent alcohols which may be used in the
production of the hydroxyl group containing polyester resins
according to the present invention include ethylene glycol,
propylene glycol, butylene glycol, 1,6-hexanediol, diethylene glycol,
dipropylene glycol, neopentyl glycol, triethylene glycol, glycerin,
Z 5 trimethylol ethane, trimethylol propnne, pentaerithritol,
dipentaerithritol, etc.
The polybasic acids or their anhydrides which may be
used in the present invention inclucle phthalic acicl, phthalic
- 11 -
~7~
anhydride, isophthalic .Icid, terephthalic acid, succinic acid, succinic
anhydricle, adipic acill, azelaic acid, sebacic acid, tetrahydrophthalic
anhydride~ hexahydrophthalic anhyclride, maleic anhydlide,
fumaric acid, itaconic acid, trimellitic anhydride, etc~
The hydroxyl group containing polyester resin usable in
the present invention is produced by a reaction in which a molar
ratio of ~he hydroxyl groups of the above polyvalent alcohol to the
carboxyl groups of the above polybasic acid or its anhydride is 1.2-
1.8, so that the polyester has residùal hydroxyl groups in the
1 0 rnolecule.
When the number-average molecular weight of the
hydroxyl group containing polyester resin is less than 200,
sufficient cross-linking does not take place in the coated layer, and
the resulting coated layer does not have suf-ficient properties. On
the other hand, when it exceeds 1,000, the viscosity of the paint
composition is undesirably increased, and the resulting coated layer
does not have a good appearance such as surface evenness, etc. The
number-average molecular weight of the hydroxyl group containing
polyester is preferably 300-6,000, and more preferably 300-3,000.
2 0 With respect to the hydroxyl value, when it is less than
50, the resulting coated layer has poor adhesion and decreased
hardness. When it exceeds 350, the resulting coated layer suffers
from a decrease in a water resistance and an acid resistance due to
the remaining hydroxyl groups. The preferred hydroxyl value of
2 5 the hydroxyl group containing polyester resin is 70-280.
With respect to the acicl value, when it is less than 3,
the resulting coated film has poor hardness. On the other hand,
when it exeeeds 50, the thermosetting paint composition has low
- 12 -
~ J~
storage stability ancl shows too high a reactiorl speed due to too
many functional groups remaining in the coated layer, so that the
resulting coated layer (film) shows poor acid resistance and surface
smoothness (appearance). The preferred acid value of the hydroxyl
group containing polyester resin is 5-20.
(b) Acid catalyst
The acid catalysts used to accelerate the reaction in the
present invention mean those acids functioning to activate the
highly alkyl-etherified melamine resin so that the highly alkyl-
etherified mélamine resin can generate carbonium ions. Typical
examples of the acid catalysts include carboxylic acids such as
acetic acid, lactic acid, succinic acid, oxalic acid, maleic acid,
decanedicarboxylic acid, (meth)acrylic acid, e~c.; sulfonic acids such
as paratoluene sulfonic acid, dodecylbenzene sulfonic acid,
dinonylnaphthalene (di)sulfonic acid, etc.; esters of organic ~lkyl
phosphates such as dimethyl phosphate, dibutyl phosphate,
dimethyl pyrophosphate, dibutyl pyrophosphate, etc. Among these
organic acids, sulfonic acids, particularly dodecylbenzene sulfonic
acid, paratoluene sulfonic acid and dinonylnaphthalene (di)sulfonic
2 0 acid are preferable to achieve a high cross-linking density.
The acid ca~alyst is preferably blocked with a blocking
agent which can be dissociated at a baking temperature of a usual
coated layer. If an unblocked acid catalys~ is used, the
~hermosetting paint cornposition shows poor storage stability.
2 5 As the blocking agent, an arnine is preferable. The
amines usable in the present invention include prima~y, secondary
or tertiary ,alkyl.lrnines, alkanolamines, alicyclic amines, N-
heterocyclic amines~ etc., each having 40 or less carbon atoms.
- 13 -
3 a ~
'I`heir specific c~amp1es are ethylamine, diethylamine,
triethylamine, ethanol.lmine, diethanolamine, triethanolamine, n-,
iso-, sec-, or tert- butylamine, N,N-dimethyl stearylamine, tri-
isopropanolamine, etc.
Commercially available acid catalysts are PTSA (Nacure
2500X manufactured by King), DDBSA (Nacure 522S7;'lmanufactured
~,t
by King), DNNSA (Nacure 1015 manufactured by King), DNNDSA
(Macure 155 manufactured by King), phosphate-type (Nacure 4054
manufactured by King), etc.
(G) Highly alkyl-etllerified melamine resin
The highly alkyl-etherified melamine resins usable
in the present invention are melamine resins whose amino
groups are completely or at least 50% bonded wi~h alkyl ether
groups. The amount of the alkyl ether groups is expressed as an
average percentage of the alkyl ether groups actually bonded to
the triazine ring, assuming that it is 100% when all of the
hydrogen atoms of the amino groups in the melamine resin are
substituted by alkoxy groups. Since there are three amino
groups per each triazine ring, "50% or more of the alkyl ether
2 0 groups" means that 3 or more alkyl ether groups are bonded to
one triazine ring on average. When the amount of the alkyl
ether is less than S0% in the highly alkyl-etherified melamine
resin, the resulting coated layer (film) shows poor acid
resistance .
Specific examples of such highly alkyl-etherified
melamine resins include those having amino groups bonded with
methylol groups whose H atoms are substitwtecl with alkyl
5 ~ ~
groups such as a me~hyi glOLlp, an ethyl group, arl n-butyl group,
an isobutyl group, etc.
Such highly alkyl-etherified melamine resin can be
produced by an addition reaction or an addition-condensa~ion
reaction between the melamine resin and an aldehyde such as
formaldehyde, paraformaldehyde, etc. and then ~y etherification
with a monovalent alcohol having 1-4 carbon atoms.
The highly alkyl-etherified melam;ne resin preferably
has a number-aver.lge molecwlar weight of 2,000 or less. When the
number-average molecular weight exceeds 2,000, ~he viscosity of
the paint composition is unclesirably increased, resulting in a coated
layer (film) having a poor appearance such as poor surface
smoothness, etc. The preferred number-average molecular weigh~
of the highly alkyi-etherified melamine resin is 450-1,200.
As described above, the highly alkyl-etherified
melamine resin generates carbonium ions in the presence of the
acid catalyst, and the carbonium ions are subjected to an active
hydrogen substitution reaction with the blocked polyisocyanate.
(d) Blocked polyisocyanate
2 0 If reaction is caused by the above hydroxyl group
containing resin and the highly alkyl-etherified melamine resin
having 50% or more of alkyl ether groups per one triazine ring,
the resulting coated klyer (film) would not have desired acid
resistance. Thus, the blockecl polyisocyanate having active
hydrogen cap.lble of reacting with the carbonium ions generated
from the highly alkyl-etherified melamine resin is added in the
present inven~ion.
- 15 -
The blocked polyisocyanate used in ~he present
invention has active hydrogen remaining at a baking
temperature of the coated layer (film). Accordingly, the blocked
polyisocyanate is substantially reacted not with the hydroxyl
groups of the hydroxyl group containing resin, but with the
highly alkyl-etherified melamine resin. Thus, the active
hydrogen (hydrogen atoms in amino groups) of the blocked
polyisocyanate is substituted witll carbonium ions generated
from the highly alkyl-etherified melamine resin (refer to the
formulae ( 1 ) and (2)).
The blocked polyisocyanates usable in the present
invention include aliphatic polyfunctional isocyanates such as
non-yellowing type hexamethylene diisocyanate (HMDI)?
alicyclic polyfunctional isocyanates such as isophorone
diisocyanate (IPDI), other isocyanates such as diphenylmethane-
4,4'-diisocyanate (MDI), hydrogenated MDI, etc. The functional
groups (NCO) of these polyisocyanate are partially or totally
blocked with blocking agents which are not thermally
dissociated.
2 0 The blocking agent should be chemically stable in the
process of forming a wet film, and retain active hydrogen even
at a baking temperature. The preferred blocking agents are
alcohols, -caprolactam, phenols, etc. and alcohols are
particularly preferable. Alcohols usable as blocking agents are
2 5 methanol, ethanol, isopropyl alcohol, butanol, 2-ethylhexanol,
cyclohexanol, etc.
The polyisocyanate blocked with alcohols are
generally dissociated at about 1 80-200C, though this
- 16 -
dissoci~ltion tenlper.lture may change slightly depending on the
types of alcollols. Since usllal baking conditions applicable to the
thermosetting paint composition of this type are 120-160C and
15-30 minutes, the active hydrogen can remain in the
5 polyisocyanate under such baking conditions.
Particularly preferable as blocked polyisocyanate are
HMDI and IPDI both blocked with Z ethylhexanol or methanol.
[C] Proportions of Components in Therrnosetting Paint
Composition
1 0 ( 1 ) Weight ratio of (a) to (c)
The weight ratio of component (a)/component (c) on
a solid basis is preferably within the range of 40/60-90l10.
When it is less than 40/60 (a melamine resin exists too much),
the resulting cs~ateci layer (film) shows drastically decreased acid
15 resistance and poor strength. On the other hand, when the
weight ra~io of (a)/(c) exceeds 90/10, the coated layer (film) is
not sufficiently hardened. The weight ratio of (a)/(c~ is more
preferably within the range of 50/50-85/15, further preferably
55/45-80/20, and most preferably 60/40-75/25.
20 (2) Weight ratio of (d) to [(a)+(c)]
The weight ratio of component (d) to [component
(a)+component (c)] on a solid basis is preferably within the range
of 1.5/100-50/100. When it is less than 1.5/100, the
substitution reaction of the active hydrogen of the blocked
2 5 polyisocyanate cloes not proceed sufficiently, resulting in a
coated klyer (film) with poor acid resistance and scuff (mar)
resist.lnce. On the other hand, when the weight ratio of
(d)/~(a)+(c)l exceeds 50/100, the coatecl layer (film~ is not
17 -
sut`ficiently harclellecl, also resulting in a coated layer (film) with
poor acid resistance and scut`f (mat) resistance. The weight ratio
of (d)/[(a)+(c)l is more preferably within the range of 5/100-
30/100, and further preferably 10/100-20/100.
(3) Weight ratio of (b) to [(a)-~(c)+(d)l
The amount of the acid catalyst (component (b))
expressed by a weight ratio of (b) to [(a)~(c)+(d)] on a solid basis
is preferably within the range of 0.3/100-5/100. In other
words, the amount of the acid catalyst is 0.3-5 weight % based
on the total amount of the resin components. When it is less
than 0 3 weight %, the above-described active hydrogen
substitution reaction does not proceed sufficiently, resulting in a
poor hardness oiF a coated layer (film). On the other hand, when
it exceeds 5 weight %, the resulting coated layer (film) is too
hard and brittle. The amount of component (b) is more
preferably within the range of 0.5-3 weight %, and further
preferably 0.5-2 weight %.
(4) Hydroxyl group containing resin
When both of the hydroxyl group containing acrylic
2 0 resin ancl the hyclroxyl group containing polyester resin are
used, a weight ratio of the hydroxyl group containing acrylic
resin to the hydroxyl group containing polyester resin is
preferably 100/0-60/40.
~D] Other Components
2 5 In aclclition to the above components, the
thermosetting paint cornposition of the present invention may
contain metallic pigments, inorgallic pigments, organic pigments,
etc.
- 18 -
(a~ Metallic pigments
The metallic pigments usable in the present
invention include mica, finely divided metal flakes such as
aluminum flakes, bronze flakes, tin flakes, gold flakes, silver
5 flakes, copper flakes, titanium flakes, stainless steel flakes,
nickel flakes, chromium flakes, flakes of alloys of these metals,
metal compound powders such as cobalt sulfide, manganese
sulfide, titanium sulfide, etc., finely divided metal flakes coated
with plastics, etc. These flakes preferably have an average
10 diameter of 1 0-45 ,um.
(b) Inorganic pigments
The inorganic pigments usable in the presen~
inYention include transparent iron oxide such as Sicotrans red
L2915D, Sicotrans yellow L1915 and 1916 available from BASF,
15 carbon black, titanium dioxide, yellow iron oxide, red iron oxide~
etc.
(c) Organic pigments
The organic pigments usable in the present invention
include Chromophthal red A213 available from Ciba GeigyT~
2 0 transparent pigments having dark color of red, blue, purple,
brown, black, etc. such as Chromophthal violet ~and Irgazin
yellow 3R available from Ciba Geigy, phthalocyanine blue,
phthalocyanine green, quinacridoné, indanthrone, isoindolenone,
perylene, anthrapyrimicline, benzimidazolone, etc.
2 5 (d) Organic solvents
The organic solvents aclded to the thermosetting
paint composition of the present invention to adjust its viscosity
rnay be organic liquids or their mixtures commonly available as
- 19 -
., ,
~7~ ,? ~
paint reducers. Org.lnic solvents having high boiling points are,
for instance, alcohols such as ethylene glycol monobutyl ether,
ethylene glycol rnonobutyl ether acetate, etc.; aromatic
hydrocarbons such as solvesso 100, solvesso 150, etc.; ethers
S such as carbitol acetate, butyl carbitol, etc. Organic solvents
having low boiling points are, for instance, esters such as ethyl
acetate, butyl acetate, etc.; aromatic hydrocarbons such as
toluene, xylene, etc.; ketones such as methyl ethyl ketone,
methyl isobutyl ketone, acetone, etc.; alcohols such as methanol,
butanol, isopropanol, ethylene glycol monomethyl ether, etc.
[E] l~lethod of F'orming Coated Layer (Film) from
Thermosetting Paint Composition
The thermosetting paint composition of the present
invention may be coated in the same manner as in usual
automotive painting. First, a substrate is subjected to a chemical
treatment tG form a chemical layer. After coating an
electrodeposition layer and an intermediate layer successively
on the chemical layer, the thermosetting paint composition of the
present invention is coated as a topcoat paint. Alternatively, the
2 0 thermosetting paint composition may be applied as a clear
topcoat onto a usual non-metallic or metallic basecoat to
maintain a high durability. In this case, either or both of the
electrodeposition layer and an intermediate layer may be
omitted.
2 5 With respect to application conditions, they may be
the same as conventional ones used for the automotive coating.
In a case where the paint composition of the present invention is
applied as a non-metallic topcoat or a clear coat onto the
- 20 -
~76~
basecoat, an air spray method or an electrostatic coating method
is preferable. In this case, the viscosity of ~ne paint is
preferably 20-30 seconds/#4 Ford Cup (hereinafter referred to
as #4FC) at 20C~
Baking conditions of the wet coated layer may be
substantially the same as in a case where usual melamine resin
or polyisocyanate is used alone as a cross-linking agent; 120-
1 60C for about 15-30 minutes.
As described above, since the thermosetting paint
composition of the present invention contains the component (d)
in addition to the components (a) and (c), the following special
reaction takes place in the process of forming a film. First, when
the wet film formed from the thermosetting paint composition of
the present invention is baked, a cross-linking reaction between
the hydroxyl groups of the hydroxyl group containing resin and
the melamine resin proceeds, but substantially no reaction takes
place between the blocked polyisocyanate and the hydroxyl
group containing resin because the blocked polyisocyanate
retains active hydrogen in the baking process of the coated layer
2 0 (film) (namely, the blocking agent is kept bonded to the
polyisocyanate). However, since the blocked polyisocyanate is
reactive to the melamine resin, the remaining functional groups
of the melamine resin which have not participated in a reaction
with the hydroxyl group containing resin (component (a)) are
2 5 reacted with the blocked polyisocyanate. In other words, the
above-described active hydrogen substitution reaction proceeds.
By this reaction, the self-condensation of the component (c) can
be prevented, thereby providing a coated layer (film) with
- 21 -
e;ccellent acicl resistance arld scuff (mar) resistance. Incidentally,
if the self-conclens.ltion of the cornponent (c) takes place, tne
resulting coated layer (film) would show a drastically decreased
acid resistance.
The presen~ invention will be explained in further
detain by the following Examples.
Examplese_l-13~ Compar2tive Exarnples_ 1 6
A dull steel plate having a th;ckness of 0.8 mm treated
with a zinc phosphate chernical was subjected to electrodeposition
coating using a cationic electrodeposition paint [POWERTOP U-50
manufactured by Nippon Paint Co., Ltd.] at a dry film thickness of
about 25 llm.
Next, the resulting electrodeposition-coated layer was
coated with an inteTmedia~e coating paint [ORGA S-90 SEALER7~
manufactured by Nippon Paint Co., Ltd.l at a dry film thickness of
about 40 !lm by an air-spraying method and baked at 140QC for 30
minutes. Thereafter, an acrylic resin basecoat paint [SIJPERLUCK,
manufactured by Nippon Paint Co. Ltd.] was applieel at a dry film
thickness of about 20 ,um, and subjected to setting for 3 minutes.
Next, each of the resulting clear paint compositions shown in Table
1 was adjusted so that it had a viscosity of 2S seconds by FORDCUP
~4, and applied at a dry film thickness of about 40 ~m under
spraying pressure of 5 kg/cm2 by means of an electrostatic spray
2 5 machine (AUTO REA, manufactured by Ransberg Gemma). hfter
setting t`or 7 minutes, it was baked at 1~()C for 30 minutes.
For comparison, a thermosetting paint composition
eontaining no polyisocyanate (Connparative Examples 1, 5 and 6), a
- 22 -
thermosetting pairlt colllposition containing a polyisocyanate
blocked with MEK oxime (Comparative Example 2), a thermosesting
paint composition containing no acid catalyst (Comparative
Examples 3 and 4) were prepared, and coated and baked in the
5 same manner as in Example 1.
Incidentally, in Example 11, a 2-coat, 2-bake system
was used. In Example 8 and Comparative E~xample 5, a topcoat
paint shown in Table l was coated at a dry film thiclcness of about
40 ~lm directly on the above intermediate coat, and set for about 7
mirlutes and then baked at 140C for 30 minutes.
- 23 -
3 $~ ~
Table l - I
Example No. 1 2 3 4 5
Component (a)
Acrylic Resin-l(l) 60 60 40 81 60
Acrylic Resin-2(2)
Acrylic Resin-3(3) - - - - -
Polyester Resin- 1(4)
Polyester Resin-2(5)
Component (b)
Acid Catalyst-1(6) 1 1 0 S 3
Acid Catalyst-2(7)
Component (c)
Melamine Resin-1(8)3 2 - 5 4 1 4 14
Melamine Resin-2(9) - - - -
Melamine Resin-3(1) - 2 4
_omponent (d)
IC-1(1l) 8 16 6 5
IC-2(12) - - - 16
IC-3(l3)
IC-4(14)
IC-5(15)
Pigment(l6)
Wel ~h t R atio
(a)/(c) 65/35 71/29 43/57 85/lS 71/29
(d)(17) 8.7/10019/100 6.4/100 5/10019/100
(b)(t8~ I/lO0 1/100 0.5/lO0 3/100 1/100
- 2~ -
.
~7~50~
Table 1-2
~ç~, 6 7 8 9 1 0
Come~nent (a~
Acrylic Resin- 1(1) - 6 0 - 4 6
Acrylic Resin-2(2) 4 7
Acrylic Resin-3(3) - - - - 5 5
Polyester Resin-1(4) - - 7 0
Polyester Resin-2(5) 8
Component ~b)
Acid Catalyst- 1(6) 1 1 1 2 2
Acid Catalyst-2(7)
Component ~c)
Melamine Resin- I (8) 3 6 - 2 4 31 3 6
Melamine Resin-2(9) - 2 4
Melamine Resin-3(10)
Component (d)
IC-1(1l) 9 16 6 23 9
IC-2(l2) - - - - - :
IC-3(13)
Ic-4t l 4)
IC-5(15)
Pigment(16) - - 3 - - ;
Wei~ht Ratio ~ :
(a)/(c) 60/40 71/29 74/26 60/40 :~60/40
(d)(17) 9.:9/100 19/1006.4/100 30/100 9.91100
b)(l8) 1/100 1/100 1/100 2/100 : 2/100
- 25 -
,
..
:
~7~
~ ble 1 -3
No. Ex. I I Ex. 12 Ex. 13 (Com. Ex I Com. Ex. 2
Component (a~
Acrylic Resin- 1(1) 6 0 6 0 6 0 6 0 6 0
Acrylic Resin-2(2) - - - ~ -
Acrylic Resin-3(3) - - - - -
Polyester Resin- 1(4)
Polyester Resin-2(s)
Component (b~
Acid Catalyst- 1(6) - 2 2
Acid Catalyst-~(7)
Component (c)
Melamine Resin- 1(8) 3 2 2 8 2 8 4 0 3 2
Melamine Resin~2(9)
Melamine Resin-3(10)
Component (d)
IC-1(1l) 8
IC 2(l2)
IC-3(13) - 8
IC-4(l 4) 1 4 - .
Ic-S(ls) - - 16
Pigment(16)
Weight Ratio
(a)/(c) 65/35 68/32 68132 60/4065/35
(d)(17) 8.7/100 16/100 18/100 0/1008.7/100
(b)(l8) 1/lO0 2/100 2/100 l/lO01/100
- 26 -
Ç~
'I'.able 1-4
Comparative Exam,ple No. 3 4 5 6
Component (a~
Acrylic Resin-l(l) 60 60 - -
Acrylic Resin-2(0 - - - 4 7
Acrylic Resin-3(3) - - - -
Polyester Resin-1(4) - - 7 0
Polyester Resin-2(5) - - - g
Component (b)
Acid Catalyst- 1(6) _ -
Acid Catalyst-2(7) - - - -
Component (c)
Melamine Resin-1(8) - - - 4 5
Melamine Resin-2(9) - 2 4 3 0
Melamine Resin-3(10)3 2 - - -
Component (d)
IC-1(1l) 8 16
IC-2(l2)
IC-3(13)
IC-4(l4)
IC-5(1s)
Pigment(16) - - 3
,Wei~ht_Ratio
(a)/(c) 65/35 71/29 70/3055/45
(d)(17) 8.7/100 19/100 0/1000/100
(b)(18) 0/100 0/100 l/lO01/100
- 27 -
Note:
(1): Acrylic resin (copolymer of styrene, ethylhexyl methacrylate,
n-butyl methacrylate and hydroxyethyl methacrylate, and
having a number-average molecular weight of 47000, a
hydroxyl value of 95 and an acid value of 22).
(2): Acrylic resin (copolymer of styrene, ethylhexyl methacrylate,
ethylhexyl acrylate and hydroxyethyl methacrylate, and
having a number-average molecular weight of 2,000, a
hydroxyl value of 100 and an acid value of 20).
(3): Acrylic resin (copolymer of styrene, lauryl methacrylate,
hydroxybutyl methacrylate and isobutyl methacrylate, and
having a number-average molecular weight of 4,000, a
hydroxyl value of 95 and an acid value of 0).
(4): Polyester resin (copolymer of phthalic anhydride,
isophthalic aGid, trimethylol ethane and neopentyl glycol and
having a number-average molecular weight of 3,000, a
hydroxyl value of 80, and an acid value of 5).
(5~: Polyester resin (copolymer of hexahydrophthalic anhydride
and neopentyl glycol and having a number-average
molecular weight of 500, a hydroxyl value of 270, and an
acid value of 10).
(6): Dodecylbenzene sulfonic acid (Nacure 5225 available from
King) blocked with diethanol amine.
(7): Dodecylbenzene sulfonic acid (Nacure 5225 available from
2 5 King).
(8): Methylbutyl-substituted methylol-type melamine resin
(C~MEL 267, m~lnuf'actured by American Cyanamide, alkyl
etller group content: about 80~/o).
- 28 -
(9): Methylbutyl-substitlltecl melamine resin (CYMEL 232,
manuf,lctured by American Cyanamide, alkyl ether group
content: 90% or more).
(10): Methylbutyl-substituted imino-type melamine resin (CYMEL
253, manufactured by American Cyanamide, alkyl ether
group content: about 30%).
( 11 ): 2-ethylhexanol-blocked polyisocyanate (nurate-type HMDI).
(12): Methanol-blocked polyisocyanate (nurate-type HMDI).
(13): MEK oxime-blocked polyisocyanate (nurate-type HMDI)
(SUMlDUR-BL4165,'rmanufactured by Sumitomo Bayer~.
(14): Polyisocyanate (CORONATE HX7~anufactured by Nippon
Polyurethane Co. (nurate-type HMDI), 2/3 of NCO groups of
which are blocked with cyclohexanol).
(15): Polyisocyanate (the above partially blocked polyisocyanate
(14), the remaining NCO groups of which are completely
blocked with -caprolactam).
(16): MA-10~manufactured by Mitsubishi Carbon Co.).
~17): Weight ratio on a solid basis: (d)/[(a)+(c)].
(18): Weight ratio on a solid basis: (b)/[(a)+(c)~(d)].
Each coated layer (film) thus produced was evaluated
with respect to film appearance, yellowing, pencil hardness, acid
resistance and scuff (mar) resistance according to the following
standards: The results are shown in Table 2.
2 5 ( 1 ) Film appearance
Each test piece produced by the above method was
observed by the bare eye with respect to defects such as roughness,
- 29 -
gloss, blistering, dent, uneven color, cracking, wrinkling, etc., and
evalu,lte(l according to tlle following standards:
O: No defects.
x: There was at least one of the above defects.
5 (2) Yellowing
A tinplate was coated with a non-yellowing type7 high
solid type, white topcoat paint based on a polyester resin and a
melamine resin in a thickness of 40 llm, and baked at 140C for 25
minutes to obtain a reference plate. The reference plate was coated
with each paint composition of Examples 1-7 and 9-13 and
Comparative Examples 1-4 and 6 in a thickness of 40 llm with one
side masked, and baked at 1 40C for 30 minutes. The difference in
color between the reference surface (masked surface) and the
coated surface was measured by an SM color computer (SM-37
15 available from Suga Shikenki K. K.).
(3) Pencil hardness
Measured according to JIS K5400 8, 4.2.
(4) Acid resistance
0.6 ml of a 10~weight-% sulfalric acid solution was
2 0 dropped onto each test piece kept horizontal at 70C, and the test
piece was kept at 70C for 15 minutes without air flow. After
drying, defects such as discoloration, etching and blistering were
observed with the naked eye. The evaluation of acid resistance was
conducted according to the following standards:
2 5 ~): No traces (defects).
O: Slight traces, but they could be erased by
polishing the test piece surface with an ultrafine
powder compound (Unicon FMC-81J available
- 30 -
from Ishihara Yakuhin K. K.).
X: Substantial traces, wlhich could not be erased by
polishing with the above compound.
(5) Scuff (mar) resistance
About 1 cm3 of a cleanser liquid [mixture of a foamable-~
type cleanser available from Kaneyo K. K. ~a~rasive: 93%, and~;linear~;
alkylbenzene surfactant: 4%) and water at a ratio of 1/3] was
dropped onto two plies of flannel, and the knit was fixed to a
vibration head of a ~wear resistance tester. Under a load~ of ~500 g,
the vibration head was moved reciprocally 1 0 times. Thereafter,
the 20 gloss of a tested poriion of the flannel was mensured; to~
determine the gloss ;retent1on. The evaluation of scuff (mar)
resistance was conducted according to the following standards.
Gloss Retention
~): 90 or more.
0: 70: or~ more and less than 90.
40 or~ more and less than 70.
X: ~less ~than ~0.~
:~ :
~. ~ : : :
,
: :
- 31
; . . .
~ .
2~rl~0~
I`able 2
Film Pencil Acid Scuff (Mar)
~L ~L~ Yellowing Hardne~ss B~s~ Resistance
Exam
O 0.5 F
2 0 1) . 6 F (~ ~)
3 O 0.5 F ~
4 0 0.~ ) O
O 0.6 F
6 O 0.6 ~ O O
7 O 0.3 F ~ ~
8 0 - HB O o
9 0 0.7 F ~) O
0 7 H (~
1 1 O 0.8 H O
12 O 0.6 H O O
13 O 0.8 H O O
Comparative Exam~e
0 0.5 F x O
2Yellowed 6.4 F X O
3 0 0.4 ~IB X X
4 -- --
O - ~' x O
6 0 0.6 F X O
Note *: The paint composition was not hardened well.
As describecl above in cletail, the coatecl layer obtained
5 by using the thermosetting p~lint composition of the present
invention h.acl excellent scuff (mar) resistance and acid resistance,
as well as goocl film appe.lrance without suffering from yellowing.
The thermosetting paint composition of the present invention was
suitable for an automotive topcoat and a coat for buildings, o~ltdoor
5 constructions, etc. It may also be used for clear coats to be formed
on the topcoats made of high-solid paints, metallic paints, etc
