Note: Descriptions are shown in the official language in which they were submitted.
272g3-6
~298016
The invention relates to a process for increasing the
proportion of components which are non-volatile under processing
conditions, in basecoat compositions containing predominantly
organic diluents or solvents, for the production of multicoat
finishes, preferably metallic finishes.
In the area of automotive finishing in particular, but
also in other areas, considerable interest centers on basecoat
compositions for the production of multicoat finishes.
Multicoat finishes of the basecoat-clearcoat type have
gained wide acceptance in automotive finishing, in particular for
metallic finishes.
Basecoat-clearcoat finishes are produced in such a way
that a pigmented basecoat is applied first, and after a short
flash-off period without baking ~the wet-on-wet process), a clear-
coat is applied over the basecoat and susbsequently the basecoat
and clearcoat are baked together.
The paints for the production of these basecoats must
be capable of being processed by the now customary economical
wet-on-wet process, ie. they must be capable of being over-coated
with a more or less transparent topcoat after a predrying period
which is as short as possible, without baking, and without mani-
festing interfering dissolution and strike-in phenomena.
In addition, still further problems must be solved in
the development of paints for metallic finish basecoats. The
metallic effect depends crucially on the orientation of the
metallic pigment particles in the paint film. A metallic finish
,
~298016
27293-6
basecoat suitable for the wet-on-wet process must therefore pro-
duce paint films in which the metallic pigments are present r after
application, in a favorable spatial orientation and in which this
orientation is rapidly fixed in such a way that it cannot be dis-
turbed in the course of the coating process.
A whole range of basecoat compositions containing pre-
dominantly organic diluents or solvents for the production of
multicoat finishes, in particular metallic finishes, is known
which is suitable for producing multicoat finishes with excellent
1 0 properties.
However, these known basecoat compositions have the
disadvantage of containing a relatively low proportion of compo-
nents which are non-volatile under the processing conditions.
It is a declared aim of paint manufacturers to reduce
the proportion of components which are volatile under processing
conditions in basecoat compositions containing predominantly
organic diluents or solvents, for the production of multicoat
finishes, preferably metallic finishes.
There has been no shortage of experiments aiming at
increasing the proportion of non-volatile components at the
expense of the volatile components.
Thus attempts have been made, for example, to reduce
the mean molecular weight of the binders contained in the basecoat
compositions and/or to add microgels and/or solid fillers to the
basecoat compositions.
All these measures, however, have disadvantages.
-- 2
27293-6
i2980~6
If, for example, the mean molecular weight of the
binder components in established, optimally balanced basecoat
compositions containing metallic pigments is reduced, it is true
that a part of the organic diluents or solvents which are volatile
under processing conditions can be dispensed with, but against
that one must balance a poorer metallic effect, redissolution
problems, deterioration of color retention, and loss of reliabi-
lity in application.
The addition of microgels usually affects the rheologi-
cal properties of the paint systems; in addition, compatibilityproblems can occur.
Microgels cannot be added to established, optimally
balanced basecoat compositions, in particular basecoat composi-
tions containing metallic pigments, without creating further
problems. They require an expensive adaptation of the total paint
system to the amounts and type of the microgels to be added.
The addition of solid fillers to the basecoat composi-
tions, in particular to basecoat compositions containing metallic
pigments, has a negative effect on the appearance of the resultant
finishes and usually does not permit any reduction of the absolute
amount of components contained in the basecoat compositions which
are volatile under processing conditions.
The present invention seeks to provide a process for
increasing the proportion of the components which are non-volatile
under processing conditions, in basecoat compositions containing
predominantly organic diluents or solvents for the production of
i298016 27293-6
multicoat finishesr preferably metallic finishes.
The process is believed to be applicable to many known
and used optimally balanced basecoat compositions, in particular
to basecoat compositions containing metallic pigments, without
any large technical outlay, and it should not affect negatively
the quality (for example redissolution behavior, color retention,
reliability in application and achievable metallic effect) of the
known, optimally balanced basecoat compositions.
Surprisingly, these objects can be achieved by replacing
up to 10% by weight of the components which are volatile under
processing conditions by an aliphatic polyether, or by mixtures
of aliphatic polyethers the aliphatic polyethers having a mean
molecular weight of not less than 300, containing not less than
one, preferably not less than two, hydroxyl groups per molecule
and being liquid under normnal conditions.
The invention also relates to the use of aliphatic
polyethers, which are liquid under normal conditions, or of mix-
tures of aliphatic polyethers, preferably polypropylene oxides,
having a mean molecular weight of not less than 300 and containing
not less than one, preferably not less than two, hydroxyl groups
per molecule, for increasing the proportion of components which
are non-volatile under processing conditions, in basecoat compo-
`~ sitions containing predominantly organic diluents or solvents, for
;~ the production of multicoat finishes, preferably metallic finishes.
; The process according to the invention can be employed
for all basecoat compositions containing predominantly organic
- 4 -
' ~
~6 27293-6
diluents or solvents and which may also contain microgels, for
the production of multicoat finishes, and is suitable for base-
coat compositions which may also contain metallic pigments.
The process according to the invention is preferably
used for basecoat compositions containing predominantly organic
diluents or solvents, which are suitable for the production of
metallic finishes of the basecoat-clearcoat type. Many such
basecoat compositions are described in the literature. There are
for example the compositions discussed in U.S. Patents 3,639,147;
4,576,868; 4,220,679; and 4,477,536. Paints containing metallic
pigments and based on cellulose acetobutyrate/polyester, cellulose
acetobutyrate/acrylate resin, polyurethane/polyester, microgel/
acrylate resin or microgel/polyurethane/polyester binder systems
are particularly preferred.
The basecoat compositions under discussion are basecoat
compositions which contain non-aqueous organic diluents or solvents.
These basecoat compositions are supplied to the paint finisher
with a viscosity which is higher than that required for the appli-
cation. There the paint is processed by the user in such a way
that
(1) it is brought to the viscosity required for the applica-
tion, by the addition of suitable organic solvents or diluents,
(2) it is applied to the substrate by means of generally
known application methods (in particular by air spraying or by
electrostatic high-speed rotary atomization),
(3) it is overcoated with a clearcoat after a flash-off
27293-6
i29~0i6
period generally lasting 30 to 500 seconds, and finally
(4) it is baked in general from about 120 to 140C for
about 20 minutes.
The term "components non-volatile under processing
conditions" is in this context understood to mean paint components
which do not lose more than 5% of their weight by volatilization,
ie. by evaporation, under conditions prevailing in the processing
stages (1) to (4).
The term "aliphatic polyethers" is understood to mean
substances containing several strucural units of the general
formula R-O, in which R represents an alkylene radical of 2 to 6
carbon atoms.
The aliphatic polyethers which can be used according
to the invention, must possess a mean molecular weight of not
less than 300. Furthermore, they must contain not less than one,
preferably not less than two, hydroxyl groups per molecule and
they must be liquid under normal conditions (ie. at about 20C
and 1 atmosphere pressure).
Provided that these limitations are observed, any
aliphatic polyether which is soluble or dispersible in the organic
solvents or diluents can be used for increasing the proportion of
components which are non-volatile under processing conditions.
Examples of such aliphatic polyethers are polyalkylene oxide
~; polyols, such as for example polyethylene oxide polyols, poly-
propylene oxide polyols as well as ethoxylation and/or propoxy-
lation products of suitable di- to hexavalent starter molecules,
-- 6
~2~0~6 27293-6
such as for example glycerol, trimethylolpropane, hexanetriol,
pentaerythritol, sorbitol, sucrose, ammonia, ethylenediamine,
aniline etc. Mixtures of aliphatic polyethers can also be used.
Polypropylene oxide polyols are preferably used. A particularly
preferred embodiment employs a polypropylene oxide polyol or a
mixture of polypropylene oxide polyols having a molecular weight
of 300 to 900.
The addition of the aliphatic polyethers according to
the invention is limited by two factors: on the one hand the
aliphatic polyethers according to the invention behave in the
coatings produced from the basecoat compositions as plasticizers,
and on the other hand the aliphatic polyethers according to the
invention increase the hydrophilicity of the coatings produced
from the basecoat compositions. The extent of the two effects
depends as much on the composition of the basecoat compositions as
on the nature of the aliphatic polyethers used. The average
person skilled in the art can rapidly determine by simple means in
what amount a particular aliphatic polyether can be incorporated
in a basecoat composition without the coatings produced from it
being too soft or too hydrophilic.
Surprisingly, up to 10~ by weight of the components
which are volatile under processing conditions can be replaced in
established, optimally balanced basecoat compositions preferably
containing metallic pigments, by the aliphatic polyethers
according to the invention without negatively affecting
- 7 -
12980i6 27293-6
redissolution behavior, color retention, reliability in
application or metallic effect of the coatings produced from the
basecoat compositions.
The aliphatic polyethers according to the invention
probably act as reactive diluents or solvents. They do not have
- 7a -
12980~6 27293-6
a negative effect on the good properties of optimally balanced
basecoat compositions, they are non-volatile under processing
conclitions and probably react in the baking process via their
hydroxyl groups with suitable binder components, for example
melamine-formaldehyde resins.
Surprisingly, it has been further found that the addi-
tion according to the invention of such aliphatic polyethers also
improves the spray mist pick-up and facilitates the electrostatic
application.
By the process according to the invention a process has
been made available which permits an increase, by very simple
means, of the proportion of components which are non-volatile
under processing conditions, in the basecoat compositions under
discussion or to adjust it to a given value.
The invention is explained in further detail in the
examplesbelow. All parts and percentages are by
-- 8 --
i29~0~6
weight, unless exDressly stated otherwise.
Example A 1
741 9 of a polyester prepared from adipic acid
and neopentyl glycol with a hydroxyl value of 113 and
26.5 9 of diethylene glycol are weighed into a four-necked
flask provided with a stirrer, thermometer and reflux
condenser, and heated to 100C. The flask is then con-
nected to a vacuum for half an hour in order to remove
any moisture present. 1,850 9 of butyl acetate, 393 9 of
4,4'-dicyclohexylmethane diisocyanate and 0.3 9 of dibutyl
tin dilaurate are added at 5 minute intervals and the
temperature is kept at 10QC for 1.5 hours. The NC0 con-
tent is then determined. It is 1.36%.
A dilution vessel is initially charged with a
mixture of 1,840 9 of butyl acetate, 1,230 9 of n-butanol
and 70 9 of hexamethylenediamine. The intermediate con-
taining the NC0 groups is added in the course of 15-20
minutes with stirring. An almost colorless viscous solu-
tion is obtained with a solids content of 20%.
Example A 2
1,300 9 of a caprolactone polyester with a hy-
droxyl value of 112 are dehydrated with 73 9 of neopentyl
glycol in vacuo as in Example A 1. After the addition of
1,850 9 of butyl acetate, 688 9 of 3-isocyanatomethyl-
3,5,5-trimethylcyclohexyl isocyanate are added first.
After about 5 minutes 0.3 9 of dibutyl tin dilaurate are
added. After a reaction time of 2 hours at 100C, the NC0
content of the solution is 2.27%.
A dilution vessel is initially charged with a
12980~6
- 10 --
miYture of 1,490 9 of butyl acetate, l,b71 9 of n-butanol
and 88 9 of 1,3-diaminopropane. The intermediate contain-
ing the NC0 groups is added in the course of 15-20 minutes
with stirring. An almost colorless v;scous solution is
obtained with a sol;ds content of 30%.
Example A 3
1,500 9 of a polyester prepared from 1,6-hexane-
diol, neopentyl glycol and adipic acid with a hydroxyl
value of 75 are dehydrated in vacuo as in Example A 1.
After the addition of 2,200 9 of butyl acetate, 393 9 of
4,4'-dicyclohexylmethane diisocyanate are first added,
followed by the addition, after about S minutes, of 0.3 9
of dibutyl tin dilaurate. After a reaction time of 2
hours at 100C the NC0 content of the solution is 0.98%.
A dilution vessel is initially charged with a mix-
ture of 2,280 9 of butyl acetate, 1,490 9 of butanol and
98 9 of 1-amino-3-aminomethylcyclohexane. The inter-
mediate containing the NC0 groups is added in the course
of 15-20 minutes with stirring. A faintly yellowish v;s-
cose solution with a solids content of 25~ is obtained.
Example B 1
111.3 9 of 1,3-propanediol, 329.9 9 of 2,2-dime-
thyl-1,3-propanediol, 163.5 9 of 1,1,1-trimethylolpropane,
216.7 9 of phthalic anhydride, 243.0 9 of isophthalic
acid, 245.0 9 of adipic acid, 30.0 9 of xylene and 2 9
of dibutyl tin oxide are weighed into a 2 liter four-necked
flask provided with a stirrer, electric resistance heat-
ing, a thermometer, a column packed with Pall rings,
equipped with a head thermometer, a distillation bridge,
1298016
-- 1 1 --
3 condenser and a receiver The reaction mixture is
rapidly heated to 160C with stirring. rhe temperature is
raised from 160C to 220C in the course of 5 hours at such
a rate that the temperature at the head of the column
does not exceed 103C. The temperature is maintained at
220C and esterification is continued until an acid number
(according to DIN) of 15 is reached. The reaction mixture
is then cooled to 140C, and the polyester is dissolved in
8ûO g of a 1:1 mixture of xylene and ethylglycol acetate
with further cooling. A 60% solution, based on the solid
polyester, of a polyester of a molecular weight of 93a and
a hydroxyl value (DIN) of 160 is obtained.
Example 3 2
60.4 9 of 1,2-ethanediol, 74.0 g of 1,2-propane-
diol, 227.9 9 of 2,2-dimethyl-1,3-propanediol, 229.9 9 of
1,6-hexanediol, 485.1 9 of isophthalic acid, 40.0 9 of a
mixture of aromatic solvents with a boiling range from
180 to 205C and 3.0 9 of dibutyl tin oxide are weighed
out, using the apparatus described in Example ~ 1. The
mixture is heated in the same manner as in Example 1 and
esterified to an acid value of 20. It is then cooled to
160C, 213.3 9 of adipic acid and 93.5 9 of trimellitic
anhydride are added and the temperature is aga;n brought
to 200C. It is kept at 200C and esterification is
~ 25 allowed to proceed to an acid number of 25. The mixture
;~ is then cooled and dissolved as in Example B 1. A 60%
solution, based on the solid polyester, of a polyester
with a molecular weight of 960 and a hydroxyl value of
: :
115 is obtained.
~: :
12980~6
- 12 -
~xamp~e B 3
Using the apparatus and procedure described in
Example 8 l, the following are ~eighed out and esterified
at not more than 220-C: 113.4 9 of 1,2-ethanediol,
S 142.6 9 of 2,2-dimethyl-1,3-propanediol, 279.8 9 of hy-
droxypivalic acid neopentyl glycol ester, 91.9 9 of 1,1,1-
trimethylolpropane, 303.5 9 of isophthalic acid, 208.5 9
of hexahydrophthalic anhydride, 200.2 9 of adipic acid,
30 9 of xylene and 2 9 of dibutyl tin oxide.
Esterification is carried out at 220C to an acid
number ¢f S. A 60% solution, based on the solid polyester,
of a polyester with a molecular weight of 1,520 and a
hydroxyl value of 100 is obtained.
Example B 4
Using the apparatus and procedure described in
Example B 1, the following are weighed out and ester;fied
at not more than 220C: 102.2 9 of 1,2-propanediol,
102.2 9 of 1,3-propanediol, 372.8 9 of 2,2-dimethyl-1,3-
propanediol, 60.0 9 of 1,1,1-trimethylolpropane, 331.6 9
of phthalic anhydride, 172.0 9 of trimellitic anhydride,
196.3 9 of adipic acid and 40 9 of a mixture of aromatic
solvents of a boiling range of 180-205C.
Heating is carried out as in Example B 1, paying
special attention to the temperature at the head of the
column, and esterification is allowed to proceed at 200C
to an acid number of 10. The reaction mixture is cooled
and dissolved as described in Example 8 1. A 60% solution,
based on the solid polyester, of a polyester with a
molecular weight of 780 and a hydroxyl value of 198 is
1298016
- 13 -
obtained.
Example C Melamine resin
The following are weighed into a Z liter four-
necked flask provided with electrical resistance heat-
ing, a stirrer, a thermometer and a distillation ap-
paratus for the continuous removal of ~ater with 3 water
separator: 560 9 of isobutanol, 250 9 of a 37% aqueous
formaldehyde solution, 30 9 of toluene and O.OS g of 85%
phosphoric acid. The reaction mixture is heated to 40C
and 95.3 9 of melamine are added. The mixture is heated
to 85C and the temperature is slowly raised to 100C, so
that the reaction mixture continuously distills, water
being separated off. The mixture is kept at 100C until
one part of it is compatible with 5 parts of a petroleum
ether of boiling range 135-180C. The reflux part of the
distillation apparatus is then closed off and 300 9 of
solvent are distilled off; the temperature thereby rises
to 115C. The temperature is then reduced to 80C and the
reaction mixture is diluted with 65 9 of isobutanol. A
solution of a melamine resin with a solids content (60 min
100C) of 55~ and a viscosity of 250 sec (DIN 53 211) is
obtained.
Example D Copolymer dispersion
200 9 of xylene and 100 9 of an ethylene/vinyl
acetate copolymer with a vinyl acetate content of 12~ are
weighed into a mixer which can be heated and is provided
with a high-speed stirrer, the mixture is heated to 100C
and stirred until a homogeneous solution is obtained. The
temperature is then reduced to 80C and the solution is
1298016
- 14 -
precipitated with 700 9 or a mixture of xylene and butyl
acetate, the temperature thereby dropping to 50~C. A
10% dispersion of the copolymer is obtained.
Example E 1 Preparation of a microgel concentrate
.
2,510 9 of demineralized water are heated to 80C
with 34 9 of 35% sodium lauryl sulfate solution in 3
polymerization vessel provided with a stirrer, re~lux
condenser and two inlet vessels.
A pre-emulsion, consisting of 1,267 9 of deminera-
lized water, 65 9 of 35% sodium lauryl sulfate solution,
490 9 of butanediol diacrylate, 478 9 of methyl methacry-
late and 140 9 of hydroxypropyl methacrylate is prepared,
with stirring, in a seperate vessel provided with a stirrer.
One of the inlet vessels is charged with the ini-
tiator solution, consisting of 14 g of ammonium per-sul-
fate and 660 g of demineralized water. The pre-emulsion
and the initiator solution are then metered in simul-
taneously at such a rate that the addition of the pre-
emulsion takes 2 hours and that of the initiator solu-
tion 3 hours. The temperature is kept at 80C by cool-
ing. At the end of the addition, the temperature is kept
at 80C for a further 1 hour.
; A 20% dispersion of crosslinked particles insolu-
ble in any organic solvent, is obtained.
2,000 g of this aqueous dispersion are vigorously
shaken in a separating funnel with 620 9 of n-butanol for
10 minutes. After a waiting period of 30 minutes, 2
phases are obtained. The lower aqueous phase is discarded.
The butanol phase containing the microgel is
' ~
. .
12980~6
_ 15 _
transferrei into a distillation flask equipped with a
water separator and a stirrer. a33 9 Ot the polyester
described in Example B 2 and S00 9 of ethylglycol acetate
are added. The remaining water is then distilled off
azeotropically in vacuo at a temperature not higher than
60C. A microgel concentrate with a solids content of 32~o
is obtained.
Example E 2
2,000 9 of the aqueous dispersion described in
Example E 1 are vigorously shaken in a separating funnel
with 800 9 of butyl acetate for 15 minutes. After a
waiting period of 1.5 hours, 2 phases are obtained. The
aqueous phase is discarded. The organic phase is trans-
ferred into a distillation flask equipped with a water
separator and a stirrer. 400 9 of a polyester prepared
from adipic acid and neopentyl glycol with a hydroxyl
value of 123 are added. Any water still present is then
distilled azeotropically in vacuo at a temperature not
higher than 60C. A microgel concentrate with a solids
content of 60~ is obtained. 280 9 of 4,4'-dicyclohexyl-
- methane diisocyanate and 0.3 9 of dibutyl tin dilaurate
are added to 1,500 9 of this concentrate as in Example
A 1. After a 2 hours' reaction, the NC0 content is 2.66~.
-;~ A dilution vessel is charged with a mixture of
Z5 1,090 9 of butyl acetate, 218 9 of n-butanol and 95 9 of
1-amino-3-aminomethylcyclohexane. The intermediate con-
~- taining the NC0 groups and the microgel is added with
stirring in the course of 15-20 minutes. A turbid paste-
like mass with a bluish glitter with a solids content of
16
- l6
40~ is obtained.
~xamples ~asecoats l to 10
The polyurethane/polyurea elastomer solutions
described in Examples A 1 to A 3 are mixed, with stlrring,
with the polyester solutions described in Examples 8 1 to
8 4, the melamine-formaldehyde resin described in Exam-
ple C and, if appropriate, the copolymer dispersion des-
cribed in Example D and/or the microgel dispersion des-
cribed in Examples E 1 and E 2 in a vessel provided with
a stirrer in such a manner that a homogeneous mixture is
produced having the composition, based on 100 parts by
weight of the solid, corresponding to the data in Table
1. Subsequently an amount of a non-leafing aluminum
bronze indicated in the Table, in the form of a 65% paste
with aliphatic hydrocarbons, is cautiously mixed to a
dough with 1.5 times the amount of butyl acetate, based
on the solid aluminum bronze, added to the previously
described mixtures of polyurethane/polyurea elastomer
solutions, polyester, melamine-formaldehyde resin solu-
tions and, if appropriate, copolymer dispersion or micro-
~ gel, and dispersed. The resultant mixtures are adjusted
; to a solids content of 25~ by weight using a mixture of
50 parts by weight of butyl acetate, 25 parts by weight
of butylglycol acetate and 25 parts by weight of butanol.
Z5 Subsequently 6 to 7 parts by weight (based on the totalpaint system) of polypropylene oxide diol which is liquid
under normal conditions and has a mean molecular weight
of about 900, are added to the basecoats formulated in
this manner.
.
1298016
- 17 -
N I I U~ I ~ I I I N
~D CO ~ ~
u~ 0 N
~, ,
a~ O _ N ~ N
n
O
L ~O N I I U~ I I I ~ I I I
Q
c
.,
~n O ~
.,
O _ o ,n N O N
aJ ~
11
J N 10 ~J
O C C" I I ~r II C~J I ~ I I ~.1
aJ
C C
al o
C O O ~U ~ C~J
o ~n ~ 1 1 1 1'~I I
V~ _
~ O
~ V~
o _ _l O O ~ ~ ~
:~ O
~ C
: ~ ~ : ~ O
O
.~
~1 ~ U) E
m n
~-; " ~ ~ ~: m ~ m m
~ ' ~
::
~298016
Examole K 1, Cle3rcoat-acrylate
941 g of a mixture of aromatic solvents with a
boiling range of 156-170C are weighed into a 3 liter
reaction vessel provided with a thermometer, a stirrer,
electric resistance heating, a reflux condenser and an
inlet vessel, and heated to 140C with stirring. A mix-
ture of 223 9 of styrene, 223 9 of methyl methacrylate,
208 9 of 1,4-butanediol monoacrylate, 30 9 of acrylic
acid, 803 9 of n-butyl acrylate and 18 g of di-tert-butyl
peroxide is added to the reaction vessel from the inlet
vessel in a regular stream in the course of 3 hours and
the temperature is kept at 140C. The reaction mixture is
kept at 140C for a further 30 minutes and then a soLution
of 4 9 of di-tert-butyl peroxide in S0 9 of the mixture
of aromatic solvents with a boiling range between 156 and
172C is added.
After a further 2 hours at 140C, an acryLate
resin solution with a solidscontent of 60% is obtained.
The acrylate resin has an acid number of 14, a hydroxyl
number of 109 and a viscosity of 250 mPa.s (determined
as a 50% solution in xylene using the ICI viscometer).
Example K 2, CLearcoat
300 9 of the solution of the melamine-formaldehyde
resin described in Example C, 150 9 of xylene and 50 9 of
butylglycol acetate are added with stirring to 550 9 of
the 60% acryLate resin solution described in ExampLe K 1
and cautiously mixed. A clearcoat with 3 sol ids content
of 46.5% is obtained.
12980~6
~ - 19 -
?roduct~on of ~he coatings
To produce the coatings, sections of body panels
used in automotive mass Droduction finishing which have
been passivated by iron phosphating and have received a
coating of paint by cathodic electrodeposition and a baking
filler, are coated ~ith the basecoats described in Examples
1 to 13 and the clearcoat described in Example K 2.
For this purpose, the viscosity of the basecoats
described in Examples 1 to 10 iâ adjusted to a value
of 16 sec according to DIN 53 211 using a solvent mixture
of xylene and butyl acetate (70:30), and that of the clear-
coat described in Example K 2 to a viscosity of 28 sec ac-
cording to DIN 53 211 using this solvent mixture.
The pre-treated body panel sections, described
above, are spray-coated with the adjusted basecoats using
a flow-cup spray gun with a nozzle 1.2 mm wide and a spray
pressure of 4 bar in such a manner that a basecoat dry
film thickness of 12 to 17 ~m is obtained. The sprayed-
on basecoat is spray-coated after 5 minutes with the ad-
justed clearcoat, using the spraying conditions indicated
above, in such a manner that a clearcoat dry film thick-
~ ness of 35 to 40 ~m is obtained. After a 15 minutes'
;~ flash-off period at room temperature the panels are baked
in a circulating air oven at 130C for 30 minutes.
The coatings prepared in this manner exhibit a
metallic effect considered to be outstanding by an exPert,
they meet the requirements of the tests listed in the tech-
nical delivery conditions of automotive mass production
finishing and they are indistinguishable from coatings
~ .
1298016
- 2~ -
prepared from po~ye~her-free systems under the same con-
ditions.
Systems which are free from polyethers require
for the adjustment of spray viscosity a greater amount
S of diluting solvent mixture than the systems according
to the invention containing polyethers.
.
