Note: Descriptions are shown in the official language in which they were submitted.
~37~83
This invention relates to the use of specially blocked
polyisocyanates having a latent isocyanate (NCO) content as a
hardener of polyols.
Blocked polyisocyanates axe used in the production of
thermosetting l-K-PUR baking systems which are stable in storage
at room temperature. A mixture of a polyisocyanate and a polyol
is only stable in storage at room temperature and is only workable
at a higher temperature with pigments and other additives if the
reactive NCO groups are blocked and, hence, are unable to react.
In the hardening stage, the blocking agents must, of course, be
able to split off.
The masking or blocking of polyisocyanates is a
procedure which has long been known for the temporary protection
of NCO groups. The production of such masked isocyanates, is
described, for example, in Houben Weyl, "Methods of Organic
Chemistry"~ XIV/2, pages 61-70. The literature cites various
blocking agents, for example, tertiary alcohols, phenols, aceto-
~cetic ester, ethyl malonate, acetyl acetone, phthalimide,
imidazole, hydrochloric acidr and hydrocyanic acid. Also
described are ~-caprolactam and phenol, which have achieved
technical importance. Such isocyanates blocked with -caprolactam
and phenol are described in DE-OS 21 66 423. The masked
isocyanates have the property of reacting like isocyanates at an
elevated temperature. The greater the acidity of the hydrogen
atom of the masking group, the easier the blocking agent will
split o~f.
However, a serious disadvantage in the use of phenols
`;~
37~13
or ~-caprolactam as blocking agents is, for a number of applica-
tions, the relatively high temperature required for spl.itting
off. Fox most polyisocyanates, the splitting temperature required
when using these two blocking agents is at least 140C or more.
There is great interes~ in polyisocyanates which deblock at lower
temperatures.
It is an object of the present invention to provide a
polyurethane one-component heat-curing coating material made of
a polyol and a blocked polyisocyanate, which is stable in storage,
but which may be hardened at temperature above 120 C.
Accordingly the present invention provides a poly-
urethane heat-curing coating material which is stable in storage
and is hardened above a temperature of about 120C, which
comprises a polyol compound having a low glass transi-tion
temperature, and a blocked polyisocyanate compound, wherein said
blocked polyisocyanate compound is the reaction product o:E a
polyisocyanate compound and a secondary amine compound having
the formula:
CR3
H~
CR13
wherein R is selected from the group consisting of hydrogen
atom, C3-Cg alkyl radical, unsubstituted cycloalkyl radical,
cycloalkyl radical substituted by Cl-C4 alkyl radicals, heteroatom-
containing cycloalkyl radical, unsubstituted aralkyl radical,
aralkyl radical substituted by Cl-C4 alkyl radicals, or
heteroatom-containing aralkyl radical, wherein each R is identical
-- 2 --
~8~7~83
to or different from each other; Rl is selected from the group
consisting of alkyl radical, cycloalkyl radical, or aralkyl
radical, wherein each Rl is identical to or different from each
other; or R and Rl are chemically bonded therebetween, thereby
forming a ring structure.
The coating material can be applied as one component.
Surprisingly, it has now been discovered that it is
possible to produce r in a simple manner, blocked polyisocyanates
that may be deblocked at considerably lower temperatures than
the isocyanates masked with the customary blocking agents, if
certain secondary amines are used for the production of the
blocked polyisocyanates. The polyurethane one-component heat-
curing coating material of the present invention is made of a
polyol and a blocked polyisocyanate, wherein the blocked
polyisocyanate is a reaction product of a polyisocyanate and a
secondary amine having the formula:
HN /
\ CR3
wherein R may be a hydrogen atom, C3-Cg alkyl, unsubstituted
cycloalkyl, cycloalkyl substltuted by Cl-C4 alkyl, heteroatom-
containing cycloalkyl, unsubstituted aralkyl, aralkyl substitutedby Cl-C4 alkyl or heteroatom-containing aralkyl radicals, wherein
each R may be identical to or different from each other; Rl is an
alkyl, cycloalkyl, or aralkyl radical, wherein each Rl may be
identical to or different from each other; and R and Rl may form
a common ring structure. In forming the blocked polyisocyanates
-- 3 --
~8'7d~83
of the present invention, 0.5 to 1 mole of secondary amine may
be used for one isocyanate group; however, it is preferable to
use 0.8 to 1 mole of secondary amine for one isocyanate group.
It is surprising that amines, secondary as well as
primary, have not been described as blocking agents for
polyisocyanates in the literature. There are a n~ber of United
States patents wherein ureas derived from mono- and diisocyanates
and primary or secondary amines are described as epoxy resin
hardeners, for example United States Patents 3,227,679, 3,317,612;
3,321,549; 3,789,071; 3,407,175; and 3,956,237. In this process,
the hardening takes place for the most part through a reaction
of the urea group with the epoxide group, with an oxaæolidinone
ring being formed. However, there are no references in the
literature, at splitting temperatures below 200C, pertaining to
ureas derived from polyisocyanates and secondary amines as heat-
curing hardeners or polyols. It must be stressed that not all
secondary amines are suitable for the production of the compounds
appropriate to the invention. The amines that may be used
according to the invention must provide steric hindrance; thus,
for example, di-n-propylamine, in contrast to di-isopropylamine,
is not suitable as a blocking agent because -the polyurethanes
produced with di-n-propylamine are too stable. The greater the
steric hindrance of the secondary amine -- more precisely, the
steric shielding of the H atom bound to the N -- the lower the
splitting temperature of the polyisocyanate blocked therewith.
The following are suitable as initial compounds ~hich
may be blocked with the secondary amines according to the present
~B7~83
in~ention: polyisocyanates, especially diisocyanates such as
aliphatic, cycloaliphatic, araliphatic, aryl-substituted
aliphatic and/or aromatic diisocyanates, as they are described,
~or example, in Houben-Weyl~ "Methods of Organic Chemistry",
Volume XIV/2, pages 61-70, and in the article o~ W. Sie~ken in
"Justus Liebigs Annalen der Chemie" 562, pages 75-136, including
such compounds such as 1,2-ethylene diisocyanate, 1,4-tetra-
methylene diisocyanate, 1,6-hexamethylene diisocyanate, ~,2,4- or
2,4,4-trimethyl-1,6-hexamethylene diisocyanate (TMDI), 1,12-
dodecane diisocyanate, W,Wl-diisocyanate dipropylether,
cyclobutane-l, 3-diisocyanate, cyclohexane-1,3- and 1,4-
diisocyanate, 3-isocyanate methyl-3,5,5-trimethylcyclohexyl
isocyanate, which is also called isophorone diisocyanate and is
also abbreviated as IPDI, decahydro-8-methyl-(1,4-me-thano-
naphthalene-2 (or 3) 5-ylene dimethylene diisocyanate, decahydro-
4,7-metha-no-inda 1 (or 2) 5 (or 6)-ylene dimethylene diiso-
cyanate, hexahydro-4-7-methane indan-l (or 2) 5 (or 6)-ylene
diisocyanate, hexahydro-1,3- or 1,4-phenylene diisocyanate, 2,4-
and 2,6-hexahydrotoluene diisocyanate, perhydro-2,4l-and/or-4,4'-
diphenyl methane diisocyanate, W,~l-diisocyanate-1,4-diethyl
benzene, 1,4-phenylene diisocyanate, 4,4'-diisocyanate diphenyl,
4,4'-diisocyana-te-3,3'-dichlorodiphenyl, 4,4'-diisocyanate-3,3'-
dimethoxyd-phenyl, 4,4'-diisocyanate-3,3'-dimethyldiphenyl,
4,4' diisocyanate-3,3'-diphenyldiphenyl, 4,4'-diisocyanate-
diphenylmethane, naphthylene-1,5-diisocyanate, toluene
diisocyanate, toluylene-2,4- or 2,6-diisocyanate, N,N'-(4,4'-
dimethyl-3,3'-diisocyanate diphenyl)-uretdione, m-xylylene
-- 5 --
~87i~83
diisocyanate, but also the triisocyanates such as 2,4,4-tri-
isocyanate diphenylether, 4,4',~"-triisocyanatetriphenylmethane,
tris(4-isocyanate phenyl~-thi.ophosphate. Additional suitable
isocyanates are described in the above-mentioned article in the
"Annalen" on page 122 ff.
Particularly preferred are the commercially a~ailable
aliphatic, cycloaliphatic and aromatic diisocyanates and
especiall~ 3-isocyanatomethyl-3,5,5-trimeth~lcyclohexylisocyanate
and toluene diisocyanate and their isomer mixturesO
In addition to the monomer polyisocyanates, the dimer
and trimer forms of the polyisocyanates, such as uretdiones and
isocyanurates can, o~ course/ also be used. The latter two can
be produced according to well-known methods.
The polyisocyanates which may be used according to
this invention also include those which prior to blocking with
the secondary amines are subjected to a reaction to increase the
size of the molecule with so-called chain extending agents
customary in isocyanate chemistry, such as, for example, polyols,
whereby the bi- or trifunctional chain extending agents, that is,
those with groups capable of reacting with isocyanate groups,
such as, for example, hydroxyl-group-bearing compounds, are used
in such quantities that the resulting new isocyanate carries at
least two isocyanate groups.
Suitable polyols which may be used as chain extending
agents, are, for example, diols and triols, such as ethylene
glycol, propylene glycol, 1,2- and 1,3-propane diol and 2,2-
dimethy].propane diol-(1,3); butanediols, such as butanediol-(1,4~;
-- 6 --
~8~33
hexanediols, such as hexanediol-(1,6), 2,2,4-trimethylhexanedio-
(1,6), 2,4,4-trimethylhexanediol-(1,6); and heptanediol-(1,7),
octadecene-9, 10-diol-(1,12), thiodiglycol, octadecanediol-(1,18),
2,4-dimethyl-2-propylheptanediol~ ), butene- or butinediol-
(1,~), diethylene glycol, triethylene glycol, trans- and cis-1,4-
cyclohexanedimethanol, l,~-cyclohexanediols, glycerin,
hexanetriol-1,2,6), l,l,l-trimethylolpropane, and l,l,l-trimethyl-
olethane. Mixtures of the above-mentioned compounds may also be
used.
The reaction of the polyisocyanates, prior to blocking,
with the mentioned chain extending agents in the cited proportions
can be carried out at temperatures ranging from 0 to 150C,
preferably at 80-120C.
Suitable secondary amines which may be used according
to this invention which are in accordance with the formula
described earlier are, for example, diisopropylamine, isopropyl--
tert.-butylamine,-dicyclohexylamine, di~(3,5,5-trimethylcyclo-
hexyl) amine, 2,6-dimethylpiperidine, 2,5-dime-thylpyrrolidine,
2,2,6~6-tetramethylpiperidine, 2,2,4,6-tetramethylpiperidine,
isopropylcyclohexylamine, and others. Mixtures of the secondary
amines appropriate to the invention may also be used.
The reaction of the polyisocyanates with secondary
amines may be performed with solvents as well as by melting. If
a solvent is used, the amount of the secondary amine added to the
polyisocyanate heated to 70-120C is such that the temperature
of the reaction mixture does not exceed 130C. After all of the
blocking agent has been added, the reaction mixture continues to
7~83
be heated for about another hour at about 100-120C to complete
the reaction.
While the blocking may be carried out using solvents,
the solvents must not react with polyisocyanates. Examples of
such solvents are ketones, such as acetone, methylethylketone,
methylisobutyl~etone~ cyclopentanone, cyclohexanone; aromatics,
such as benzene, toluol, cyclols, chlorobenzene, nitrobenzene;
cyclic ethers, such as tetrahydrofuran, dioxane; chlorinated
hydrocarbons, such as chloroform, carbon tetrachloride; and
aprotic solvents, such as dimethylformamide, dimethylacetamide,
and dimethylsulfoxide.
The adducts thus obtained, in general, are compounds
having a molecular weight of 300-2500~ preferably 300-1000. The
process products have a melting temperature range of 30-220C,
preferably 80-160C. The polyisocyanates blocked with the
secondary amines are further characterized by containing
isocyanate groups in final blocked form (calculated as NCO) of
4-25~ by weight, preferably 10 21% by weight~
The process products are especially suitable as
hardeners for higher functional compounds having Zerewitinoff-
active hydrogen atoms~ In combination with compounds having
Zerewi-tinoff-active hydrogen atoms, the process products form,
above 120C, preferably 130-200C, systems hardenable into high-
~rade plastics.
The most important field of application for the
compounds according to this invention is their use as a bonding
agent for solvent-containing l-K-PUR coating.
- 8 -
7~83
Suitable reactants with the process products for the
production of such heat~hardenable systems are compounds contain-
in~ at least two hydroxyl or amino groups. The use of
polyhydroxyl compounds, especially those with a molecular weight
o~ 400-2000, is preferred. These O~-containing compounds are
polyesters, polyethers, polyacetals, polyesteramides, and
polyepoxides, preferably containing 2-6 hydroxyl groups.
The hydroxyl-containing polyesters according to the
invention must have a low glass transition temperature; it should
be below 20C and above -25C. Significant component polyesters
are:
1~ Cyclic polycarboxylic acids and their esters and
anhydrides, for example, phthalic acid, isophthalic acid,
terephthalic acid, benzene, 1,2,4-tricarboxylic acid, trimellitic
acid anhydride, dimethylterephthalate (DMT) and their hydrogena-
tion products.
2) Diols, for example, ethylene glycol, 1,2-propanediol,
1,2- or 1,3- or 1,4-bu-tanediol, 2,2-dimethylpropanediol, 3-methyl-
pentanediol-1,5, hydroxypivalic acid neopentyl glycol ester,
hexanediol-1,6, cyclohexane diol, 4~4-dihydroxydicyclohexyl
propane-2,2, 1,4-dihydroxymethylcyclohexane, diethelene ~1YCQ1,
and triethylene glycol.
3) Polyols, such as glycerin, hexanetriol, penta-
erythrite, trimethylolpropane, and trimethylolethane.
Proportionately, the polyesters may also contain
monofunctional carboxylic acids, for example, benzoic acid, as
well as acyclic polycarboxylic acids such as adipic acid, 2,2,4-
(2,4,4) trimethyladipic acid, sebacic acid or dodecane
9 _
,~.,
~37~83
dicarboxylic acid. The polyesters are produced in the well-
known manner by esterification or interchange of ester radicals
possibly in the presence o~ the usual catalysts. Through the
appropriate choice of the COOH/OH ratio~ end products are
attained whose hydroxyl number is between 40 and 240, but
preferably between 70 and 150.
Solvents whose lower boiling point is approximately
100C are suitable for use with the one-component heat-curing
coating material according to the present invention. The upper
limit of the boiling point o~ the solvent intended for use depends
on the prevailing baking conditions. If the baking is done at
higher temperatures, then the boiling points of the solvents to
be used must lie at higher temperatures. The following compounds,
~mony others, may be used as solvents: hydrocarbons, such as
toluol, xylol, solvesso 150 la Shell solvent mixture), tetralin,
cumene; ketones, such as methyl isobutyl ketone, diisobutyl
ketone, isophorone; and esters, such as acetic acid-n-hexylester,
acetic acid butylester, ethylene glycol acetate (EGA), and butyl
glycol acetate. The above-mentioned compounds may also be used
in mixtures. The concentration of the resin (oxyester)/hardener
mixture in the mentioned solvents lies between ~0 and 70% by
weight.
The one-component heat-curing coating material according
to this invention may be produced in suitable mixing aggregates,
for example in vessels having a stirrer, by simply mixing the
three lacquer components (high-boiling-point solvent, polyester,
and blocked polyisocyanate~ at 80-100 C.
-- 10 --
`:
~8~7~83
Further customary additives, such as pigments, flow
improvers, gloss improvers, antioxidants and heat stabilizers
may also be added to the coating solution. The one-component
coating materials are especially suitable for application to
metal surfaces; however, they can also be applied to objects
made of other materials~ such as glass or plastics. The coating
materials according to this invention are primarily applicable
to the coil-coating industry for outdoors weather-resisting
one-and-two-layer coatings.
The hardening of the coating material according to
this invention occurs, depending on applica~ion, in a temperature
range of 1~0-350C t preferably between 130 and 300C during a
period from 30 minutes to 30 seconds. The hardened coatings
have excellent coating properties.
It is known that the hardening of PUR coatings in the
presence of amines ~eads to yellowing. Therefore, it is
surprising that no ~iscolouration occurs during the hardening
of the heat-curing coating of the present invention.
The present invention will be further illustrated by
certain examples and references which are provided for purposes
of illustration only and are not intended to limit the present
invention.
I. Production of Bloc~ed Polyisocyanates
-
Example 1
724 parts by weight of dicyclohexylamine were added
drop-by-drop to 444 parts by weight of isophorone diisocyanate
(IPDI) at 120C, so that the temperature of the reaction mixture
-- 11 --
1~7~83
did not exceed 140C. After the dicyclohexylamine had been
added, heating at 130C was continued for about one hour to
complete the reaction.
~ he reaction product had a melting point of 105-110 C
and a 14.38% content of blocked NCO; free amine was no longer
detectable.
Example 2
In a manner similar to the process described in
Example 1, 226 parts by weight of 2,6-dimethylpiperidine were
added to 222 parts by weight IPDI at 130C. After the 2,6-
dimethylpiperidine had been added, hea~ing at 130C was continued
for about another hour to complete the reaction.
The reaction product had a melting point of 99-103C
and an 18.7% content of blocked NCO; free amine was no longer
detectable.
Example 3
101 parts by weight of diisopropylamine were added
drop-by-drop at room temperature over approximately 2 hours to
111 parts by weight of IPDI that had been dissolved in 500 parts
by weight of anhydrous acetone. After the diisopropylamine had
been added, heating at 50C was continued for 2 hours. There-
after, the acetone was removed by distillation; the last traces
of acetone ~ere removed in the vacuum drier at 60C and 1 torr.
The reaction product had a melting point of 65-74C and a 19.8%
content of blocked NCO.
Example 4
530 parts by weight of di-(3,5,5-trimethyl~-cyclohexyl-
amine were added drop-by-drop over a period of about 2 hours to
- 12 -
. ~
:
~3~8'7~83
222 parts by weight of IPDI. After all the amine had been added,heatin~ of the reaction mixture was continued at 130C for
another 2 hours. The reaction product had a melting point of
84-91C and an 11.1% content of blocked NCO.
Example 5
2S2 parts by weight o~ 2,2,4,6-tetramethylpiperidine
were added drop-by-drop over a period of approximately 2 hours
to 222 parts by weight of IPDI at 130 C. After the 2,2,4,6-
tetramethylpiperidine had been added, heating of thQ reaction
mixture at 130C was continued for approximately 1 hour.
The reaction product had a melting point of 120-125C
and a 16.6% content of b~ocked NCO. In contrast to the compounds
in Examples 1-4, the amine used for blocking was quantitat.ively
detected within about 2 hours, by titration with aqueous ~Cl.
Thus the IPDI hlocked with 2,2,4,6-tetramethylpiperidine is
not hydrolysis resistant.
Example 6
202 parts by weight of diisopropylamine were added
drop-by-drop within 2 hours to 168 parts by weight of hexamethyl-
ene diisocyanate at 130C. After all the diisopropylamine hadbeen added, heating of the reaction mixture at 130C was
continued for about 1 hour~ The reaction product had a melting
point o~ 130-140C and a 22.7% content of blocked NCO.
Example _
41.~ parts by weight of diisopropylamine were added
at 100C over about 3 hours to 100 parts ~y weight of IPDI-T
1890 (trimer IPDI; product of the Chemische Werke Huels~ with a
17.2% NCO content that had been dissolved in 100 parts by weight
of xylol/ethyl glycol acetate (weight ratio: 2:1). Thereafter,
heating was continued for 2 hours. The solution thus obtained
had a viscosi~y of 261 mPas at room temperature. The content
of blocked NCO was 7.1%.
II. Reactivity of the Compounds
To examine the reactivity of a polyisocyanate, blocked
with an amine, with a polyol, the polyisocyanate was kneaded in
a kneading chamber with a polyol at a ratio of (NCOblock:OH = 1:1)
at various temperatures and the resistance to kneading was
followed as a function of time. The resistance to kneading
increased to the same extent as the reaction occurred. When
cross-linking occurred, the resistance to kneading rose sharply
followed by an abrupt drop. The cross-linked product was finely
ground and then offered only slight resistance. The polyiso-
cyanate used was a diisocyanate. The results are shown in
Table 1.
- 14 -
.
~8~7~3
Table J
Hardeners _neading Behaviour of Hardenrs/Oxyester
P 1137 (NCO : OH = 1 : 1) at
120 C 160 C 1~0 C
IPDI blocked with
piperidine - no cross- -
linking
IPDI blocked with
2,6 dimethylpiperidine cross-linked cross-linked
after 10 after 4
minutes minutes
IPDI blocked with
2,2,4,6-tetramethyl-
piperidine immediately
cross-linked
IPDI blocked with
caprolactam cross-linked
after 18
minutes
P 1137: Oxyester with an OH number of 106-114 and a melting
range of from 70-90C (product of the Chemische Werke Huels)
III. Appllcation Examples
Application Example 1
A) Polyester containing hydroxyl groups (production)
7 moles of isophthalic acid (1.163 g~/ 6 moles of
hexanediol-1,6 (709 g) and 2 moles of l,l,l-trimethylolpropane
(268 g) were esterified in a 4-liter glass flask with the
admixture of 0.1% by weight of n-dibutyltin oxide. With rising
temperature, a homogenous batch developed. At about 195C, the
first separation of water occurred. Within 8 hours, -the tempera-
ture was raised to 220C and at this temperature the
ester;fication was completed during the subsequent 6 hours. The
:~8'7~83
acid number was smaller than 1 mg KOH/g. After the polyester
batch had been cooled down to 200C, the volatile components
were removed in a vacuum of 20-30 mm Hg during 30-45 minutes.
During the entire reaction, a weak N2-flow was
directed through the xeaction systemO
Chemical and physical characteristics data of the
polyester:
OH number 105 mg KOH/g
Acid number <1 mg KOH/g
Mole weight 2400
Glass transition
temperature -12C to +5C
B) Blocked isocyanate components
The polyisocyanate described in production Example 3
was used.
C) PUR heat-curing coating
-
100 g of the polyester obtained in part A of this
application example are mixed and dissolved with 398 g of the
blocked polyisocyanate of production Example 3, in 466 g
n-butylacetate and 446 g xylol solvents at 40-50C to form a
resin solution. In the customary fashion, a heat-hardening
white coating was formulated according to the following composi-
tion
65% by weight of the above-described resin solution;
3% by weight of n-butyl glycol acetate;
2% by weight of iosphorone;
2808% by weight of a white pigment (Tio2);
2% by weight of a 10% solution of a soluble flow
- 16 -
~87~83
improver in ethylglycol acetate; on the basis of an organo-
functional silicone oil, and
0.2% by weight dibutyltin dilaurate.
An aluminum sheet was coated with the described coating
and hardening was undertaken under varying conditions.
The test results are presented in Table 2.
Table 2
.
E~ardening
Condition Coating Testing
.
_ PE~ ET GS G20 G45 G60 MEK Test Yellowing
min 110C 40 153 0.5 1 90 60 96 60 none
min 120C 30 179 7.8 0 87 56 96 >200 none
min 1400C 35 181 6.5 0 90 55 94 >200 none
0.75 min 300 C 25 174 8.5 0 69 56 92 >200 none
Explanation of symbols:
SD: coating thickness in llm
PH: Koenig pendulum hardness, DIN 53 157
ET: Erichsen cupping, DIN 53 156
GS: Cross-cut adhesion test, DIN 53 151
G: gloss according to Gardner ASTMD 523
The test data shown in Table 2 illustrate that
quantitative cross-linking/hardening is possible with the above-
described coating material starting from about 120C.
Surprisingly, no yellowing occurs d~spite the aminic blocking agent.
-- 17 --
1~8~
Application Example 2
A) Polyester containing hydroxyl groups
(production)
Analogously to the process described in application
Example lA, a polyester containing hydroxyl groups was produced.
The following raw materials were used:
moles isophthalic acid (1661 g)
5~5 moles hexanediol-1,6 (650 g)
2.0 moles diethylene glycol (212 g)
4.0 moles trimethylolpropane (537 g)
Characteristic values of the polyester:
OH number 132 mg KOH/g
Acid number 2 mg KOH/g
The polyester was dissolved in n-butylacetate/xylol solvent (1:1).
The solid substance content of the solution was 60% by weight.
B) Blocked isocyanate components
-
The blocked polyisocyanate described in production
Example 7 was used.
G) PUR heat-curing coating
A clear coating was formulated according to the
following composition:
49.3~ solution of the polyester obtained in part A
of this application example;
41.5~ solution of the blocked polyisocyanate produced
in production example 7;
3.0% butylglycol acetate;
2.0~ isophorone;
- 18 -
~17~1~3
1.0~ of a 10~ solution of a flo~ improver in
ethylglycol acetate on the basis of an organofunctional
silicone oil;
0.2~ dibutyl tin dilaurate.
An aluminum sheet was coated with the above-described
coating material and was hardened under various conditions.
The test results are shown in Table 3.
Table 3
Hardening
10Condition COATING TESTING
SD P~I ET GS MEK-Test Yellowing
25 min 1300C 35 186 7.0 0 >200 none
7 min 160 C 40 193 7.8 0 >200 none
4 min 180C 40 186 8.1 0 >200 none
~ . .
Explanation of symbols:
SD: coating thickness in ~m
PH: Koen.Lg pendulum hardness, DIN 53 157
ET: Erichsen cupping, DIN 53 156
GS Cross-cut adhesion test, DIN 53 151
G: gloss according to Gardner ASTMD 523
The test data shown in Table 3 illustrates that cross-
linking/hardening of the above-described coating yields results
at a temperature of 130C which are comparable to those ob-tained
at a temperature of 180C.
- - 19 -
8~33
Having now fully described this invention, it will
be apparent to one of ordinary skill in the art that many changes
and modifications can be made thereto without departing from
the spirit or scope of the invention as set forth herein.
- 20 -
