Note: Descriptions are shown in the official language in which they were submitted.
39'~
RD-9679
IMPROVED MELAMIN~ COATINGS
Background of the Invention
Polymeric ultraviolet light absorbers are especially
desirable in thin films of between about 0.05 mils and about
0.5 mils since monomeric absorbers are readily lost by diffu-
sion, and solvent leaching because of the high surface area in
relation to the volume of material employed. The preparation
of polymeric UV-absorbers usually involves the vinyl polymeriza-
tion of substituted UV-screeners such as (2-hydroxy-4-methacryl-
oxybenzophenone) or the condensation polymerization of properly
substituted UV-screeners such as 2-hydroxybenzophenone-4,4'-
dicarboxylic acid with glycols or 2-hydroxy-4,4'-bishydroxy-
methyl benzophenone with diacids.
It has now been discovered that improved polymeric
films can be formed from a melamine nucleus compound, a benzo-
phenone and preferably a polyol. Moreover, the benzophenone
appears to be incorporated in the polymer as indicated by long
term thermal aging tests, which renders the transparent coating
ideally suited for protecting transparent polycarbonates, and
other UV degradable materials.
Brief Description of the Invention
Ultraviolet resistant surface coatings are provided
of a transparent copolymer of (A) a melamine nucleus compound
of the formula,
R ~ N ~ / R
N-C C-N
R/ l ll R
N N
~ C/
N
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wherein the R groups are independently selected from H, -CH2O~I,
and -CH2O(CH2)XH, wherein x is an integer of from 1 to 4; and
a stabilizing amount (B) of a benzophenone of the formula,
D-C~
R'
wherein R' is selected from -OH and -NH2 groups in the 3,4 or
5 positions of the ring, and D is an aromatic radical of less
than 4 six membered rings which can be substituted with -OH and
-NH2 groups; and preferably (C) a polyfunctional compound con-
taining at least two hydroxyl groups. The coatings are particu-
larly well suited for protecting polycarbonate resins and otherUV light degradable materials.
Detailed Description of the Invention
Melamine nucleus compounds which can be employed in
the invention are those of the above formula wherein the R
groups can be methoxymethyl, ethoxymethyl, propoxymethyl, or
butoxymethyl and hydrogen. Preferably the R groups are all
the same and are alkoxymethyl.
The polyfunctional compound containing at least two
hydroxyl groups can be aromatic or aliphatic. Representative
aromatic compounds are phenols which include resorcinol, 2,2'-
methylenediphenol, 2,4-methylenediphenol, 4,4'-isopropylidene-
diphenol, 4,4'-(cyclohexylidene)diphenol, and 4,4'-dihydroxydi-
phenol, and 4,4'-dihydroxydiphenylsulfone. Representative
aliphatic compounds are alcohols which include ethylene glycol,
diethylene glycol, triethylene glycol, tetraethylene glycol,
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propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentane-
diol, 1,2,3-propanetriol, pentaerythritol and sorbitol. In
acldition, the polyfunctional hydroxyl compound can be an alkyd
resin, such as a hydroxyl containing epoxy resin, a soluble
cellulose derivative, a vinyl polymer having free hydroxyl
groups, such as poly(vinyl alcohol) or partial saponified poly
(vinyl acetate). The polyfunctional hydroxyl compound (e.g.
polyol) can also contain carboxyl and amine groups but should
contain at least two hydroxyl groups.
Among the dihydroxybenzophenones of the above formula
which can be employed are the following:
2,3-dihydroxybenzophenone,
2,4-dihydroxybenzophenone,
2,5-dihydroxybenzophenone,
2,3'-dihydroxybenzophenone,
2,4'-dihydroxybenzophenone,
2-hydroxy-5-aminobenzophenone,
2-hydroxy-4'-aminobenzophenone,
2,2',4,4'-tetrahydroxybenzophenone,
2,2',3,3'-tetrahydroxybenzophenone,
2,2',5,5'-tetrahydroxybenzophenone,
dihydroxynaphthophenones,
dihydroxyanthrophenones,
dihydroxydinaphthoketones,
dihydroxyanthrones, etc.
The preferred compounds are where D is a substituted
or unsubstituted benzene ring.
The benzophenone should be used in an amount suffic-
ient to reduce the UV light degradation. Generally, from about
one to about five percent by weight of the composition is
sufficient.
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The benzophenone can be reacted solely with the mel-
amine nucleus compound but preferably a polyol is employed such
as described in the specification. Generally, the melamine
nucleus compound will constitute from about 20 to about 80 per-
cent of the mixture and the polyol the remainder, exclusive ofthe benzophenone.
In order to form the UV light resistant composition
and apply it to a suitable substrate, the reactants can be
dissolved or suspended in a suitable solvent such as n-butanol,
ethanol and the like, preferably with a suitable acid catalyst
which is activated at elevated temperature such as benzene sul-
fonic acid and sulfamic acid and preferably with a surface
active agent to aid in forming a film of the composition. A
variety of catalysts and surface active agents can be employed
and are commercially available.
The coating composition can be applied to a suitable
substrate by conventional means such as spraying, dipping and
the like. The thickness of the coating is not critical but will
generally be between about 0.05 mil and about 0.5 mil for a sub-
strate of between about 1 mil and about 0.5 inches. After appli-
cation, the reaction can be accomplished at a temperature between
about 100 and about 150C in a period of from 15 minutes to
about four hours in an air oven. The resultant article is then
resistant to UV degradation and it is found that the benzophenone
does not leach out as it is reacted within the composition.
Among the materials which can be protected by the
compositions of the invention are those which are readily
degraded by UV light such as, for example, polycarbonates, poly-
carbonate-polysiloxane copolymers, polystyrene, polyvinyl
chloride, ABS polymers~ poly(2,6-dimethylphenylene oxide) alone
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or copolymerized with high impact polystyrene, or even wood.
The following examples will serve to illustrate the
invention, but are not meant to be limiting. All parts and
percentages in said examples and elsewhere in the specification
and claims are by weight unless otherwise indicated.
A coating blend of 750 parts of hexamethoxymethyl-
melamine and a like amount of caprolactone polyol (Nyax Polyol
PCP-0300) was mixed with 7.5 parts surface active agent (Mall-
inckrodt BYK-300) and catalyzed with 1.5% of p-toluene sulfonic
acid. The reaction mixture was then diluted with 1500 parts
N-butanol to 50% solids and a 10 mil Lexan polycarbonate sheet
cleaned with isopropanol dipped into this coating blend, with-
drawn slowly and allowed to drain for 5 minutes at room temper-
ature to permit the solvent to evaporate. The coated sheet was
cured for an hour at 125C in a circulating air oven.
The above procedure was repeated several times but
for the exception that to 600 parts of the above mixture was
added one of the following W-stabilizers in the amount indicated.
Examples 1-7
20Example 1: 15 parts (5% on solids) 2,4-dihydroxy-
benzophenone (DHBP)
Example 2: 15 parts (5% on solids) Resorcinol
mono benzoate
Example 3: 15 parts (5~ on solids) 2(2'-hydroxy-
255'-octylphenyl)benzotriazole (Cyasorb 5411)
Example 4: 9 parts (3% on solids) 2,4-dihydroxybenzo-
phenone (DHBP)
Example 5: 9 parts (3% on solids) 2-hydroxy-4-n-
octoxybenzophenone (Cyasorb UV 531)
30Example 6: 9 parts (3% on solids) ethyl-2-cyano-
-3,3-diphenyl acrylate (Uvinul N-35)
Example 7: 9 parts (3% on solids) 2-cyano-3,3-
diphenyl acrylic acid
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Lexan polycarbonate panels coated with the various
blends of samples 1, 2 and 3 were exposed to UV light from
RS sunlamps. The protection afforded by the various screeners
is most easily seen by the change in yellowness index (~ YI) of
the various samples. The sample number 1 had the lowest A YI
of 1.66 while sample number 2 had a ~YI of 13.63 compared to
13.68 for an unprotected control and sample number 3 had a ~YI
of 3.74. The change in yellowness was determined by the method
of ASTM D-1925-70 for samples tested for 1000 hours.
Ten mil Lexan polycarbonate film samples were then
coated on one side with one of the coating blends of Examples 4,
5, 6 and 7 and allowed to air dry for 30 minutes at room
temperature (25-30C). The UV absorbances of these uncured
coatings were measured with a UV-spectrometer before and after
curing for 1 hours at 125C. The coated films were then baked
for 50 hours at 125C while UV-absorbance measurements were
taken at intervals.
Absorbance
Cured Baked Baked Baked Baked
Sample Peak~ Uncured 1 hr 3 hrs 13 hrs 20 hrs 50 hrs
4 328 nm 2.391 2.184 2.090 2.184 2.223 2.226
293 nm 2.283 1.468 1.086 0.650 0.557 0.539
6 305 nm 2.592 0.253 0.041 0.053 0.059 0.070
7 304 nm 2.568 2.700 2.625 1.905 1.276 0.275
From an examination of the data it can be seen that
the composition of the invention, sample 4, is considerably
more resistant to thermal degradation after an extended period
of 50 hours.
In repeating the examples, similar results are
achieved with other benzophenones of the invention, such as
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RD-9679
2,3-dihydroxybenophenone, 2,5-dihydroxybenzophenone, 2-
hydroxy-5-aminobenzophenone, 2-hydroxy-4'-aminobenzo-
phenone, 2,2',4,4'-tetrahydroxybenzophenone and 2,4-
dihydroxynaphthophenone; and with polyols such as
polyvinyl alochol, ethylene glycol, and propylene glycol;
melamine compounds such as hexa(ethoxymethyl)-melamine and
polymers such as a copolymer of Lexan polycarbonate and
polydimethylsiloxane.
